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Identification of the Mo₃S₄ intercalation system in lithium batteries made with natural MoS₂ Mulhern, Peter John 1982

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IDENTIFICATION OF THE Mo0S, INTERCALATION SYSTEM IN LITHIUM BATTERIES MADE WITH NATURAL MoS by PETER JOHN MULHERN B.Sc, Simon Fraser University, 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF PHYSICS We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1982 © Peter John Muihern, 1982 October 7 ,1982 To whom i t may concern: Peter Mulhern has used diagrams i n his thesis that have been previously published either by myself or by other members of my research group. I hearby give my permission for the use of these diagrams for this purpose. Dr. R.R. Haering In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Physics The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date September 24, 1982 DE-6 (3/81) 11 IDENTIFICATION OF THE Mo 3S« INTERCALATION SYSTEM IN LITHIUM BATTERIES MADE WITH NATURAL MoS2 ABSTRACT Investigations of the lithium/molybdenum d i s u l f i d e i n t e r c a l a t i o n battery showed that naturally occurring molybdenite, MoS2, from the Endako mines had a type of capacity not found in synthetic MoS2. The behaviour of thi s extra capacity was examined and attempts were made to find i t s source. Materials were synthesized that could i n d i r e c t l y produce the same electrochemical behaviour, and i n - s i t u X-ray d i f f r a c t i o n determined M O 3 S 4 to be the c r y s t a l responsible for this capacity. The lithium/Mo 3Si, system was found to be an inte r c a l a t i o n battery with an energy density of about 275 watt-hours per kilogram of cathode material. Over half of the capacity was at 2.09V in a f i r s t order phase t r a n s i t i o n which did not greatly a l t e r the host l a t t i c e . Most of the remaining capacity was divided evenly between regions of continuous l a t t i c e expansion near 2.46V and 2.05V. i i i TABLE OF CONTENTS Page Abstract i i L i s t of Figures v Acknowledgements v i i 1 Introduction 1.1 Motivation for Research 1 1.2 The Intercalation Battery . 2 1.3 Intercalation Materials 4 1.4 Lithium Intercalated M0S2 8 2 Experimental Techniques 2.1 Preparation of Cathode Material 11 2.2 Cathode Preparation and C e l l Construction 13 2.3 Constant Current Cycling 17 2.4 Linear Sweep Voltammetry . 20 2.5 Constant Current Voltammetry 22 3 Capacity in a-Phase M0S2 3.1 I n i t i a l Discovery of High Voltage Capacity in Endako M0S2 26 3.2 Cycling the Extra Capacity 32 3.3 Ef f e c t of Sample Preparation 38 4 Electrochemical Examinations 4.1 Attempts to Find an Impurity i n M0S2 42 4.2 Attempts to Dope M0S2 with Copper 46 4.3 Attempts to Dope MoS2 with Other Elements 50 4.4 Examinations of X-Phase 52 4.5 Other Electrochemical Studies 58 i v TABLE OF CONTENTS (CONTINUED) Page 5 X-Ray Examinations 5.1 X-Ray D i f f r a c t i o n 60 5.2 Preliminary Examinations 61 5.3 Attempts to Dope MoS2 62 5.4 Determination of La t t i c e Parameters 66 5.5 Intercalation i n Mo^S^ 70 6 Results and Discussion 6.1 Interpretation of Results 78 6.2 Suggestions for Future Work 83 6.3 Summary 88 Bibliography 90 Appendix 1 93 Appendix II 94 LIST OF FIGURES v Figure Page 1 The Electrochemical C e l l 3 2 Structure of Layered Transition Metal Dichalcogenides . .7 3 Typical M0S2 Behaviour 9 4 Flange C e l l 16 5 X-Ray C e l l 18 6 Endako M0S2 a to 3 Phase Transition 27 7 Endako MoS2 -- 6 Phase Cycling 28 8 De t a i l of High Voltage a Phase Endako Capacity 30 9 P a r t i c l e Size Dependence of the Extra Endako Capacity . 31 10 Cycling 10-20 ym Endako MoS9 Powder Between 2.0 and 2.7 Volts Z 33 11 Cycling <38 ym Endako MoS0 Powder Between 2.0 and 2.7 Volts z : 34 12 Cycling 10-20 ym Endako MoS~ Powder Between 1.5 and 2.7 Volts Z 36 13 Cycling <38 ym Endako MoS0 Powder Between 1.5 and 2.7 Volts 37 14 Cycling a-Phase Endako Powder 39 15 Unheated Endako MoS2 41 16 Cycling Cu^ gS and Cu2S 43 17 Cycling CuS and PbS . . 44 18 Cycling CuFeS 2 and ZnS 45 19 Cycle of MoS2~Copper Mixture Between 1.5 and 2.6 Volts. 48 20 Cycling the MoS2~Copper Mixture . . 49 21 F i r s t Discharge of MoS2~Iron Material 51 22 Cycling the MoS 2-Iron Material 53 23 F i r s t Discharge of "X-Phase" 55 24 Cycling "X-Phase" 56 v i Figure Page 25 (101) D i f f r a c t i o n Line Between 2.04 and 2.2V 71 26 (104) and (212) D i f f r a c t i o n Lines Between 2.04 and 2.2V 72 27 (104) and (212) D i f f r a c t i o n Lines Between 2.4 and 2.6V 74 28 (223) D i f f r a c t i o n Line Between 2.5 and 2.1V 75 29 (104) and (212) D i f f r a c t i o n Lines Between 1.84 and 2.08V 76 30 X-Ray Scan of C e l l PMX-11 at 2.700V 99 31 X-Ray Scan of C e l l PMX-11 at 2.100V 100 32 X-Ray Scan of C e l l PMX-11 at 2.050V 101 33 X-Ray Scan of C e l l PMX-11 at 1.800V 102 v i i Acknowledgments I would l i k e to thank rny supervisor, Rudi Haering, for his many suggestions and his advice during the course of work on this thesis. Credit must also be given to the many other members of the lab, Jeff Dahn in p a r t i c u l a r , who contributed many ideas and helped me c l a r i f y several concepts. The data for Figure 18 was col l e c t e d by Rod McMi1lan. F i n a l l y , I would l i k e to thank the Natural Sciences and Engineering Research Council for f i n a n c i a l support. 1 CHAPTER 1 INTRODUCTION 1.1 M o t i v a t i o n f o r R e s e a r c h A good b a t t e r y s y s t e m i s t h e key t o t h e d e v e l o p m e n t o f e l e c t r i c c a r s f o r t h e g e n e r a l p u b l i c . The b a t t e r i e s must g i v e t h e v e h i c l e t h e r a n g e , s p e e d , and a c c e l e r a t i o n t h a t p e o p l e demand i n d a y - t o - d a y d r i v i n g . The c e l l s must a l s o be c a p a b l e of b e i n g q u i c k l y c h a r g e d , and have a c o n v e n i e n t l y l o n g l i f e b e f o r e t h e y must be r e p l a c e d . These r e q u i r e m e n t s have prompted much r e s e a r c h i n t o h i g h e n e r g y d e n s i t y b a t t e r y s y s t e m s . I n v e s t i g a t i o n s o f l i t h i u m i n t e r c a l a t i o n r e v e a l e d a sy s t e m t h a t a p p e a r s u s e f u l f o r e n e r g y s t o r a g e -- t h e l i t h i u m / m o l y b d e n u m d i s u l f i d e i n t e r c a l a t i o n b a t t e r y (U.S. P a t e n t 4224390). I t has a v o l t a g e t h a t r a n g e s from 2.6 t o 1.7 v o l t s , d e p e n d i n g on t h e s t a t e o f c h a r g e , and has an e n e r g y d e n s i t y of a b o u t 8.4X10 6 j o u l e s p e r k i l o g r a m of c a t h o d e m a t e r i a l (~250 w a t t - h o u r s p e r k i l o g r a m ) i n t h i s v o l t a g e r a n g e . The MoS 2 s y s t e m i s s t i l l n o t f u l l y u n d e r s t o o d , and r e s e a r c h i s underway t o i n v e s t i g a t e i t s p r o p e r t i e s . T h e r e a r e s e v e r a l d i f f e r e n t MoS 2 p h a s e s , e a c h w i t h i t s own d i s t i n c t e l e c t r o c h e m i c a l b e h a v i o u r . A p r a c t i c a l b a t t e r y must be r u n i n a - phase w i t h a l a r g e amount o f r e v e r s i b l e c a p a c i t y . E x a m i n a t i o n s of n a t u r a l l y o c c u r r i n g MoS 2, m o l y b d e n i t e , 2 from near Endako, B r i t i s h Columbia uncovered extra capacity which was not present in synthetic MoS2. This discovery was interesting for two reasons. F i r s t , i f the capacity was from something other than MoS2 then i t might lead to a po t e n t i a l l y useful battery material. And second, i f i t were due to some modification of the MoS2 i t s e l f , then the capacity might be linked with some of the basic properties of i n t e r c a l a t i o n systems and serve as a tool for studying them. This thesis discusses the e f f o r t s made to identif y the source of the extra capacity in Endako MoS2. 1.2 The Intercalation Battery Intercalation is the process by which an atom or molecule can be reversibly inserted into a host l a t t i c e without major structural changes in the host. The electrochemical method of int e r c a l a t i o n i s of interest for batteries. Lithium metal can be used as one electrode, the anode, and the other electrode, the cathode, is a host material such as MoS2. A lithium salt e l e c t r o l y t e connects the two electrodes i o n i c a l l y , but no direc t electronic contact is allowed (Figure 1). The chemical potential of a lithium atom in a metal, •, at the anode is higher than the chemical potential of an intercalated C atom, , at the cathode. This results in a potential difference, V, between the anode and cathode. where e i s the electron charge. 3 anion f rom -Li salt Li metal • anode o —>• External load O o N L. Li + o o o o o 1M Li salt in PC / Li ;+ cation L i x M X 2 cathode Figure 1 -- The Electrochemical C e l l (from Johnson 1982) LiAsF-g was the s a l t used in a l l experiments for- this thesis-. 4 The c e l l can be d i s c h a r g e d by p r o v i d i n g an e l e c t r i c a l pathway t h r o u g h an e x t e r n a l c i r c u i t . A l i t h i u m atom i n t h e m e t a l c a n i o n i z e and go i n t o s o l u t i o n w h i l e a n o t h e r i o n l e a v e s t h e s o l u t i o n and e n t e r s t h e h o s t . C h a r g e n e u t r a l i t y i s p r e s e r v e d i n t h e anode, e l e c t r o l y t e , and c a t h o d e when t h e e l e c t r o n t h a t came from t h e i o n i z a t i o n of t h e l i t h i u m p a s s e s i n t o t h e c i r c u i t t o go t o t h e c a t h o d e . The anode d i s o l v e s a s t h e c e l l d i s c h a r g e s , and t h e l i t h i u m c o n t e n t o f t h e h o s t i n c r e a s e s . The h o s t m a t e r i a l i s d e i n t e r c a l a t e d by r e c h a r g i n g t h e c e l l w i t h an a p p l i e d e x t e r n a l p o t e n t i a l t h a t c an d r i v e e l e c t r o n s from t h e h o s t t o t h e l i t h i u m m e t a l . As a r e s u l t , t h e l i t h i u m c o n t e n t of t h e h o s t w i l l d r o p and m e t a l w i l l r e p l a t e a t t h e anode as t h e l i t h i u m i o n s move t o p r e s e r v e c h a r g e n e u t r a l i t y . 1.3 I n t e r c a l a t i o n M a t e r i a l s A h o s t m a t e r i a l must not be g r e a t l y a l t e r e d d u r i n g t h e p r o c e s s of i n t e r c a l a t i o n , and t h i s r e s t r i c t s t h e h o s t s t o c e r t a i n c l a s s e s o f m a t e r i a l s . An e l e c t r o c h e m i c a l i n t e r c a l a t i o n b a t t e r y has t h e f u r t h e r r e q u i r e m e n t t h a t t h e r e must be a c h e m i c a l p o t e n t i a l d i f f e r e n c e between an atom i n t h e h o s t and one o u t s i d e . T h e r e must be a way f o r t h e g u e s t t o r e a c h t h e s e s i t e s , so t h e r e must be pathways t h r o u g h t h e h o s t t h a t a r e l a r g e enough f o r t h e g u e s t t o p a s s t h r o u g h . L i t h i u m was u s e d as t h e g u e s t s p e c i e s i n t h e s e e l e c t r o c h e m i c a l s t u d i e s . L i t h i u m atoms a r e s m a l l and can p a s s t h r o u g h narrow o p e n i n g s i n ' t h e h o s t l a t t i c e , and t h e 5 m e t a l i s l i g h t , w h i c h i m p r o v e s t h e e n e r g y d e n s i t y of a p r a c t i c a l c e l l . N o r m a l l y , t h e l i t h i u m c o n t e n t o f an i n t e r c a l a t i o n h o s t can be v a r i e d c o n t i n u o u s l y t h r o u g h o u t t h e c r y s t a l w h i l e t h e h o s t l a t t i c e s l o w l y expands or c o n t r a c t s . T h i s i s i m p o r t a n t f o r p r a c t i c a l a p p l i c a t i o n s b e c a u s e l i t t l e damage i s t h e n done t o t h e h o s t as t h e c e l l i s c h a r g e d and d i s c h a r g e d . A c h e m i c a l r e a c t i o n between t h e h o s t and t h e g u e s t atoms can o f t e n e i t h e r a l t e r t h e h o s t s t r u c t u r e a n d / o r not be r e v e r s i b l e , and i n e i t h e r c a s e would n o t be an i n t e r c a l a t i o n s y s t e m . The l o c a l a t o m i c e n v i r o n m e n t i n t h e h o s t c r e a t e s s i t e s i n t h e s t r u c t u r e i n t o w h i c h t h e l i t h i u m c a n be i n s e r t e d . T y p i c a l l y , t h e d i s c h a r g e of an e l e c t r o c h e m i c a l i n t e r c a l a t i o n c e l l w i l l move l i t h i u m i n t o s i t e s where t h e atoms have a l o w e r c h e m i c a l p o t e n t i a l t h a n i n t h e l i t h i u m m e t a l . I f l i t h i u m i n i t i a l l y s i t s i n s i t e s w i t h a h i g h e r c h e m i c a l p o t e n t i a l t h a n t h e m e t a l , t h e n t h e h o s t m a t e r i a l would be t h e anode and i t would be d e i n t e r c a l a t e d as t h e - c e l l i s d i s c h a r g e d . The l i t h i u m c o n t e n t of a h o s t can be c h a n g e d by mechanisms o t h e r t h a n i n t e r c a l a t i o n . O f t e n a c a t h o d e m a t e r i a l w i l l u ndergo a f i r s t o r d e r phase t r a n s i t i o n as t h e c e l l i s d i s c h a r g e d . In t h i s t y p e of r e a c t i o n , a phase f r o n t , r e p r e s e n t i n g a d i s c o n t i n u i t y i n t h e l i t h i u m c o n c e n t r a t i o n , moves t h r o u g h t h e c r y s t a l . The p h a s e s on e i t h e r s i d e of t h e f r o n t can have r a d i c a l l y d i f f e r e n t s t r u c t u r e s a n d / o r l i t h i u m c o n t e n t , as i s u s u a l l y t h e c a s e i f t h e h o s t and t h e l i t h i u m u n d e r g o a c h e m i c a l r e a c t i o n (sometimes c a l l e d a d i s p l a c e m e n t 6 r e a c t i o n ) . I t i s p o s s i b l e t o have b o t h i n t e r c a l a t i o n and a f i r s t o r d e r phase t r a n s i t i o n o c c u r r i n g s i m u l t a n e o u s l y i f i t i s t h e g u e s t atoms w h i c h u n d e r g o t h e t r a n s i t i o n w h i l e t h e h o s t l a t t i c e i s not g r e a t l y a l t e r e d . The l a y e r e d t r a n s i t i o n m e t a l d i c h a l c o g e n i d e s , MoS 2 i n c l u d e d , s a t i s f y t h e c o n d i t i o n s f o r i n t e r c a l a t i o n (McKinnon 1980), a l t h o u g h t h e s e s y stems can a l s o be c o m p l i c a t e d by n o n - i n t e r c a l a t i o n phase t r a n s i t i o n s . T h e s e m a t e r i a l s form i n t o s a n d w i c h - l i k e l a y e r s w i t h t h e c h a l c o g e n atoms ( s u l p h u r , s e l e n i u m , or t e l l u r i u m ) on t h e o u t s i d e and t h e m e t a l ( f r o m G r o u p s IVB, VB, o r VIB) on t h e i n s i d e . T h e s e l a y e r s a r e t h e n s t a c k e d one on t o p of a n o t h e r , and a r e h e l d t o g e t h e r by weak Van d e r Waals f o r c e s . F i g u r e 2a shows two s a n d w i c h e s , ' w h e r e M . r e p r e s e n t s a l a y e r of m e t a l s and X a l a y e r of c h a l c o g e n s . D i f f e r e n t l a y e r e d d i c h a l c o g e n i d e s have d i f f e r e n t c r y s t a l s t r u c t u r e s b e c a u s e of s l i g h t v a r i a t i o n s i n t h e a t o m i c a r r a n g e m e n t s . The two b a s i c s t r u c t u r e s of t h e s a n d w i c h e s t h e m s e l v e s a r e shown i n F i g u r e 2b. The s u l p h u r s f o r m i n t o p l a n e s on a t r i a n g u l a r l a t t i c e , and t h e m e t a l atoms can be c o o r d i n a t e d e i t h e r t r i g o n a l p r i s m a t i c a l l y o r o c t a h e d r a l l y between two o f t h e s e p l a n e s . The s a n d w i c h e s can t h e n be s t a c k e d i n d i f f e r e n t o r i e n t a t i o n s as shown i n F i g u r e 2c. The l i t h i u m can move t h r o u g h t h e Van d e r Waals gap, and t h e t h r e e common p o l y t y p e s shown a l l have b o t h t e t r a h e d r a l and o c t a h e d r a l s i t e s i n t h e gap i n w h i c h t h e l i t h i u m atoms can s i t . I n t e r c a l a t i o n o c c u r s i n more t h a n j u s t l a y e r e d 7 (a) 7 General form X M van der Waals gap X z X (b) Coordination units for MX2 layer structures AbA trigonal prism AbC octahedron (c) 2H-MoS-•1120 2H-NbS-1120 l T - T i S . -*II20 AbA BaB AbA CbC AbC AbC Figure 2 -• Structure of Layered Transition Metal Dichalcogenides (from McKinnon 1980) 8 s t r u c t u r e s . R u t i l e s , w h i c h have t u n n e l s f o r t h e l i t h i u m t o p a s s t h r o u g h , and s p i n e l s , w h i c h a r e s i m i l a r t o l a y e r e d compounds, have a l s o been u s e d a s i n t e r c a l a t i o n h o s t s (Murphy 1978, E i s e n b e r g 1980). F u r t h e r a d d i t i o n s t o t h e l i s t of h o s t s a r e b o t h p o s s i b l e and p r o b a b l e . 1.4 L i t h i u m I n t e r c a l a t e d Mos 2 MoS 2 i s a s u i t a b l e , but c o m p l i c a t e d , h o s t f o r l i t h i u m i n t e r c a l a t i o n . The 2H-MoS 2 p o l y t y p e i s t h e most common, and f o r e l e c t r o c h e m i c a l p u r p o s e s i t was d e s i g n a t e d as t h e a-phase s t r u c t u r e . The o-phase has v e r y l i t t l e c a p a c i t y above a b o u t 1.15 v o l t s ( F i g u r e 3a) and i s a poor p r a c t i c a l b a t t e r y mater i a l . When t h e a-phase i s d i s c h a r g e d below a b o u t 1.15 v o l t s , i t goes t h r o u g h a f i r s t o r d e r p h a s e t r a n s i t i o n and forms t h e 1T p o l y t y p e d e s i g n a t e d as p-phase (Py 1982). I t i s t h e p-phase t h a t shows p r o m i s e as a c o m m e r c i a l b a t t e r y . T h i s phase i s m e t a s t a b l e o v e r t h e v o l t a g e range of ~0.6V t o ~2.6V, w h i c h c o r r e s p o n d s a p p r o x i m a t e l y t o g o i n g from L i M o S 2 t o L i 0 > 1 M o S 2 . T h e r e i s some slow phase c o n v e r s i o n from p-phase t o a-phase a t h i g h v o l t a g e s , but t h i s seems t o be sample d e p e n d e n t and i s not y e t f u l l y u n d e r s t o o d . The v o l t a g e p r o f i l e of a p-phase c e l l b e i n g c y c l e d a t c o n s t a n t c u r r e n t i s shown i n F i g u r e 3b. MoS 2 can a l s o be d r i v e n i n t o r - p h a s e by g o i n g t h r o u g h a n o t h e r phase t r a n s i t i o n a t a b o u t 0.6 v o l t s . The s t r u c t u r e of t h i s phase i s unknown, and i t s p r o p e r t i e s have not been 0 1 2 3 4 5 6 Time (hours) 3 b) Time (hours) 3 c) 0 10 20 Time (hours) Figure 3 -- Typical M0S2 Behaviour a) a-Phase b) 3-Phase c) y-Phase Constant Current Cycling of C e l l PM-94 100 uA current 3.86 mg cathode of Atomergic MoS0 10 f u l l y investigated. Except for noting i t s existence, Figure 3c, 7-phase w i l l not be discussed. 1 1 CHAPTER 2 EXPERIMENTAL TECHNIQUES 2.1 P r e p a r a t i o n of C a t h o d e M a t e r i a l B o t h s y n t h e t i c a l l y p r e p a r e d and n a t u r a l l y o c c u r r i n g MoS 2 powders were u s e d as c a t h o d e m a t e r i a l s . The s y n t h e t i c MoS 2 was o b t a i n e d from t h e A t o m e r g i c C h e m i c a l s C o r p o r a t i o n . A m i c r o s c o p i c e x a m i n a t i o n r e v e a l e d t h a t t h e powder c o n s i s t e d of i r r e g u l a r l y s h a p e d p l a t e l e t s t h a t a v e r a g e d about f i v e m i c r o n s i n d i a m e t e r . A l l p a r t i c l e s were s m a l l e r t h a n f i f t e e n m i c r o n s . T h i s powder r e q u i r e d no g r i n d i n g or c l e a n i n g b e f o r e i t was made i n t o c a t h o d e s . The n a t u r a l l y o c c u r r i n g MoS 2, m o l y b d e n i t e , was o b t a i n e d from Canex P l a c e r L i m i t e d , Endako mines d i v i s i o n . The Endako c o n c e n t r a t e was c o n t a m i n a t e d w i t h c h e m i c a l r e s i d u e s from t h e r e f i n i n g p r o c e s s and was an u n s u i t a b l e c a t h o d e m a t e r i a l u n t i l i t was c l e a n e d . About two h u n d r e d grams of MoS 2 was t h o r o u g h l y mixed w i t h a s o l v e n t and t h e n t h e s u s p e n s i o n was a l l o w e d t o s e t t l e o v e r n i g h t b e f o r e t h e l i q u i d was d e c a n t e d . The p r o c e s s was r e p e a t e d u n t i l t h e s u p e r n a t a n t f l u i d r a n c l e a r . The powder was a l t e r n a t e l y washed i n t h r e e o r g a n i c s o l v e n t s : S o l v e x , w h i c h i s p r i m a r i l y b e n z e n e ; c h l o r o f o r m ; and t r i c h l o r o e t h y l e n e . Some of t h e powder l e s s t h a n one m i c r o n i n d i a m e t e r was l o s t b e c a u s e i t r e m a i n e d i n s u s p e n s i o n when the l i q u i d was p o u r e d o f f . The powder was d r i e d by h e a t i n g i t t o 750°C under a f l o w o f a r g o n . The c l e a n Endako powder was s i e v e d i n t o t h e f o l l o w i n g 12 size fra c t i o n s : greater than 105 microns; 105 to 75 microns; 75 to 38 microns; and less than 38 microns. The smallest size fraction was further divided by using a Stokes' s e t t l i n g technique (Allman and Lawrence 1972). A Stokes' s e t t l i n g separation uses the p r i n c i p l e that large p a r t i c l e s f a l l faster than small ones when they are in a viscous medium. About half a gram ,of MoS2 was put into a graduate cylinder and then methanol was added to a 20cm depth in the tube (~l90ml). Methanol was used rather than water to maintain sample purity--the p a r t i c l e s would not separate in water without also adding a dispersant. The cylinder was covered and then vigorously shaken to mix the powder and alcohol. The tube was l e f t to s i t for a given time, after which only p a r t i c l e s less than a certain size were l e f t in suspension, and these p a r t i c l e s were siphoned out. Repeating this procedure three or four times removed a l l the smaller p a r t i c l e s from the larger ones. This technique was so e f f e c t i v e that a d i s t i n c t murky/clear boundary was often seen during the last s e t t l i n g . The s e t t l i n g times were estimated by using formulas which asumed spherical p a r t i c l e s , but the MoS2 p l a t e l e t s were always within a micron or two of the predicted size. A 20 to 38 micron size fr a c t i o n settled to the bottom of the tube after five minutes, and a 10 micron boundary required siphoning after twenty minutes. Any p a r t i c l e s t i l l in suspension after an hour and a half was smaller than five microns. The powders in a l l Stokes' settled fractions had no p a r t i c l e s any larger than the upper size l i m i t , and very 13 l i t t l e , p r o b a b l y l e s s t h a n one p e r c e n t by w e i g h t , was s m a l l e r t h a n t h e l o w e r s i z e l i m i t . 2.2 C a t h o d e P r e p a r a t i o n and C e l l C o n s t r u c t i o n The p r e p a r e d powder was made i n t o c a t h o d e s by b a k i n g i t o n t o m e t a l s u b s t r a t e s . The s u b s t r a t e s e r v e d t o p r o v i d e b o t h p h y s i c a l s u p p o r t and e l e c t r i c a l c o n t a c t f o r t h e c a t h o d e powder. The most commonly u s e d c a t h o d e s u b s t r a t e s were made from 0.125mm t h i c k n i c k e l f o i l c u t i n t o rough s q u a r e s 1.2cmX1.2cm and e t c h e d w i t h n i t r i c a c i d . I n c h s q u a r e 0.25mm b e r y l l i u m s h e e t s were u s e d as t h e b a c k i n g i n X - r a y c e l l s , and aluminum f o i l was o c c a s i o n a l l y u s e d f o r heavy c a t h o d e s . U s u a l l y a b o u t 1Omg of d r y powder was weighed o n t o t h e s u b s t r a t e , and t h e n two d r o p s of p r o p y l e n e g l y c o l were added. The l i q u i d and powder were mixed i n t o a s l u r r y w hich was d i s t r i b u t e d e v e n l y o v e r an a r e a of t h e s u b s t r a t e . The c a t h o d e was t h e n baked a t 200°C under an a r g o n f l o w u n t i l t h e l i q u i d e v a p o r a t e d . P a r t i c l e s s m a l l e r t h a n a b o u t t h i r t y e i g h t m i c r o n s a d h e r e d w e l l t o t h e m e t a l and u s u a l l y would not be j a r r e d l o o s e by t h e s m a l l bumps t h a t o c c u r d u r i n g h a n d l i n g and w e i g h i n g . Powder l a r g e r t h a n t h i r t y e i g h t m i c r o n s i n d i a m e t e r t e n d e d t o f l a k e o f f t h e m e t a l u n l e s s t h e s u b s t r a t e was h a n d l e d v e r y c a r e f u l l y . The e x a c t w e i g h t of th e c a t h o d e m a t e r i a l was d e t e r m i n e d by w e i g h i n g t h e s u b s t r a t e w i t h and w i t h o u t t h e powder. The f i n i s h e d c a t h o d e had t o be a s s e m b l e d i n t o a c e l l u nder an i n e r t a t m o s p h e r e t o p r e v e n t water and oxygen from, r e a c t i n g w i t h t h e o t h e r c e l l components. A Vacuum 14 A t m o s p h e r e s Company d r y box was u s e d f o r c e l l c o n s t r u c t i o n . P r e - p u r i f i e d a r g o n from Matheson of Canada L i m i t e d f i l l e d t h e box, and was k e p t c l e a n by c i r c u l a t i n g t h e gas t h r o u g h a Matheson Model 8301 Hydrox P u r i f i e r t o remove t h e oxygen and w a t e r . The t u n g s t e n f i l a m e n t of a 3 watt b u l b a l s o a c t e d a s a g e t t e r , and t h e l i f e t i m e o f t h e b u l b s e r v e d as an i n d i c a t i o n o f t h e q u a l i t y of t h e a t m o s p h e r e . T h e s e p r o c e d u r e s u s u a l l y k ept t h e water and oxygen c o n t e n t s of t h e box below 0.1ppm. L i t h i u m f o i l , 0.010 i n c h e s t h i c k , f r o m F o o t e M i n e r a l Company was made i n t o t h e c e l l anode by c u t t i n g t h e f o i l t o a s i z e s l i g h t l y l a r g e r t h a n t h e c a t h o d e . The l i t h i u m s u r f a c e s were s c r a p e d c l e a n j u s t b e f o r e t h e c e l l was a s s e m b l e d t o p r e v e n t any s u r f a c e c o a t i n g from a f f e c t i n g t h e c e l l p e r f o r m a n c e . The s a l t f o r t h e one m o l a r e l e c t r o l y t e was L i A s F 6 , and the s o l v e n t was p r o p y l e n e c a r b o n a t e w h i c h had been d i s t i l l e d t o l e s s t h a n 20ppm of p r o p y l e n e g l y c o l and w a t e r . A p o r o u s p l a s t i c f i l m from C e l g a r d M i c r o p o r o u s F i l m P r o d u c t s , wet w i t h e l e c t r o l y t e , was used as a s e p a r a t o r t o p r e v e n t i n t e r n a l s h o r t s between t h e anode and c a t h o d e . The s e p a r a t o r s were made from e i t h e r C e l g a r d #3501, w h i c h had s u r f a c t a n t , or C e l g a r d #2500, w h i c h d i d n o t . E l e c t r o l y t e would o n l y e n t e r t h e p o r e s o f t h e s e p a r a t o r s w i t h o u t s u r f a c t a n t i f t h e p r e s s u r e e x c e e d e d about t h r e e a t m o s p h e r e s , but t h e o t h e r ones c o u l d be w e t t e d a t a t m o s p h e r i c p r e s s u r e . The c e l l s were u s u a l l y a s s e m b l e d i n one of two c o n f i g u r a t i o n s . 15 Most commonly, t h e f l a n g e c e l l ( F i g u r e 4) was u s e d . The c a t h o d e would be a t t a c h e d t o t h e base of t h e c e l l w i t h a t i n y dab of vacuum g r e a s e , and t h e n t h e c e l l a s s e m b l y would be b r o u g h t i n t o t h e g l o v e box. A d r o p or two o f e l e c t r o l y t e was p ut on t h e c a t h o d e , and t h e l o o s e l y p a c k e d powder would q u i c k l y soak up t h e l i q u i d . A wet s e p a r a t o r would t h e n be c a r e f u l l y p l a c e d on t o p o f t h e c a t h o d e . F i n a l l y , t h e s c r a p e d l i t h i u m w ould be p l a c e d on t h e s e p a r a t o r , and t h e t o p f l a n g e would be s l i p p e d i n t o p l a c e and b o l t e d on. The p r e - g r e a s e d O - r i n g s e a l e d out t h e water and oxygen t h a t c o u l d r e a c t w i t h t h e l i t h i u m and e l e c t r o l y t e a f t e r t h e c e l l was removed from t h e g l o v e box. B o l t i n g t h e c e l l t o g e t h e r not o n l y h o l d s t h e p i e c e s i n p l a c e , but a l s o a p p l i e s p r e s s u r e t o e n s u r e t h e c a t h o d e powder w i l l be i n good e l e c t r i c c o n t a c t w i t h t h e s u b s t r a t e . Two t y p e s of f l a n g e c e l l were u s e d . The s t a i n l e s s s t e e l one p i c t u r e d i n F i g u r e 4 had t h e d i s a d v a n t a g e s o f r e q u i r i n g a n o n - c o n d u c t i n g v i t o n O - r i n g w h i c h would a b s o r b t h e p r o p y l e n e c a r b o n a t e s o l v e n t , and a l s o r e q u i r e d c a r e f u l a s s e m b l y t o p r e v e n t s h o r t c i r c u i t s . The p o l y p r o p y l e n e f l a n g e c e l l s were n o n - c o n d u c t i n g so t h e r e was no d a n g e r o f a s h o r t , and a s l i g h t l y c o n d u c t i n g n e o p r e n e O - r i n g c o u l d be u s e d . E l e c t r i c a l c o n t a c t was made t o t h e a c t i v e c e l l components w i t h n i c k e l p l a t e d b r a s s b o l t s w h i c h p a s s t h r o u g h t h e c e n t r e of t h e p l a s t i c f l a n g e s . S i x b o l t s , not t h r e e as shown i n F i g u r e 4 were r e q u i r e d t o e n s u r e a p r o p e r s e a l w i t h t h e s o f t e r p o l y p r o p y l e n e . A s p e c i a l t y p e of c e l l _,.was._ us e d t o c o l l e c t X - r a y Figure 4 -- Flange C e l l (from Von Sacken 1980) 17 d i f f r a c t i o n patterns of the cathode material while the battery was in use (Dahn, Py, and Haering 1982). The special feature of i t s construction was a beryllium window which allowed copper K n X-rays (k-1 .54178A) to pass into the working c e l l (Figure 5). This c e l l was designed to f i t into a modified PW 1050/80 goniometer of a P h i l i p s PW 1730 X-ray powder diffractometer. Construction of the X-ray c e l l was almost i d e n t i c a l to that for the flange c e l l s , except for using beryllium as the cathode substrate and a polypropylene gasket instead of an O-ring. 2.3 Constant Current Cycling The basic information on operating voltages, capacity, and r e v e r s i b i l i t y of a battery was obtained by continuously charging and discharging a c e l l between set voltage l i m i t s . Cyclers made by the U.B.C. Physics department electronics shop supplied an e s s e n t i a l l y constant current that could be varied from a few microamperes to 100 milliamperes. High and low t r i p voltages could be chosen and the c e l l automatically changed from charge to discharge, and vice versa, when the c e l l potential reached these l i m i t s . The cycler also had an analog output of the c e l l voltage. The c e l l voltage as a function of time was recorded by feeding the cycler output into a s t r i p chart recorder with a b u i l t - i n time base, and the most commonly used recorder was the Soltec S-4201. The t y p i c a l MoS2 behaviour that was shown in Figure 3 was obtained in t h i s way. The main disadvantage of t h i s technique of recording data i s that i t i s often 7» ANGLE NYLON SCREW ^ CELLTQP CELL VOLTAGE CONTACT CELL CATHODE ON .010" THICK BERYLLIUM WINDOW POLYPROPYLENE GASKET LITHIUM ANODE GLASS SPACER FLUID INLET  THERMISTOR  CELL VOLTAGE CONTACT  FLUID OUTI  CELL BASE Figure 5 -- X-Ray C e l l (from Dahn, Py, and Haering 1982) 00 19 d i f f i c u l t t o see s u b t l e f e a t u r e s i n t h e v o l t a g e c u r v e s . . An a d v a n t a g e of c o n s t a n t c u r r e n t c y c l i n g i s t h a t t h e v o l t a g e v e r s u s t i m e c u r v e s a r e d i r e c t l y r e l a t e d t o t h e t h e r m o d y n a m i c s of t h e c e l l . The d i f f e r e n t i a l c h ange i n t h e G i b b s f r e e e n e r g y o f a c a t h o d e m a t e r i a l i s dG = y dN - S dT + v dp (2) where v i s the c h e m i c a l p o t e n t i a l of t h e l i t h i u m atoms i n t h e h o s t , N i s t h e number of i n t e r c a l a t e d atoms, S i s t h e e n t r o p y , T i s t h e a b s o l u t e t e m p e r a t u r e , v i s t h e volume, and p i s t h e p r e s s u r e . U s u a l l y t h e l a s t term c a n be o m i t t e d b e c a u s e t h e p r e s s u r e i s e s s e n t i a l l y a c o n s t a n t . The c h e m i c a l p o t e n t i a l i s r e l a t e d t o t h e c e l l p o t e n t i a l t h r o u g h E q u a t i o n 1 of t h e p r e v i o u s c h a p t e r , and t h e number o f i n t e r c a l a t e d atoms, N, can be r e l a t e d t o t h e l e n g t h of t i m e a c e l l i s c h a r g i n g or d i s c h a r g i n g a t c o n s t a n t c u r r e n t . At c o n s t a n t t e m p e r a t u r e , t h e v o l t a g e v e r s u s t i m e c u r v e s r e f l e c t an e q u a t i o n of s t a t e of t h e c e l l . I d e a l l y , t h e amount of l i t h i u m t r a n s f e r r e d i n t o or o u t of a c a t h o d e i s t h e p r o d u c t of t h e c u r r e n t and t h e t i m e d u r i n g w h i c h th e c u r r e n t f l o w e d . The n e t number o f e l e c t r o n s t h a t have been p a s s e d from t h e anode t o t h e c a t h o d e i s e q u a l t o t h e number of l i t h i u m atoms i n t h e h o s t . The l i t h i u m c o n t e n t of a c a t h o d e i s o f t e n w r i t t e n as a c h e m i c a l f o r m u l a l i k e L i MoS 2 where x i s t h e mole f r a c t i o n o f l i t h i u m . The amount of c h a r g e t h a t f l o w s w h i l e t h e c e l l p o t e n t i a l c h a n g e s between two v a l u e s i s d e f i n e d as t h e c a p a c i t y of t h e c e l l i n t h a t v o l t a g e r a n g e . 20 T h e r e a r e two major p r o b l e m s i n d e t e r m i n i n g t h e t r u e v a l u e o f x. F i r s t , n o t a l l t h e c a t h o d e m a t e r i a l may be e l e c t r i c a l l y c o n n e c t e d t o t h e s u b s t r a t e , and as a r e s u l t t h e mole f r a c t i o n w i l l be computed u s i n g t h e wrong amount of h o s t m a t e r i a l . Second, not a l l t h e c h a r g e t h a t f l o w s i s a s s o c i a t e d w i t h th e i n t e r c a l a t i o n s y s t e m i f a s i d e r e a c t i o n i s p r e s e n t . The p r e s e n c e of a p a r a s i t i c s i d e r e a c t i o n can o c c a s i o n a l l y be d e t e c t e d i f a r e v e r s i b l e r e a c t i o n t a k e s d i f f e r e n t amounts o f t i m e t o c h a r g e and d i s c h a r g e a t t h e same c u r r e n t . 2.4 L i n e a r Sweep V o l t a m m e t r y L i n e a r sweep v o l t a m m e t r y i s a method o f e x a m i n i n g b a t t e r y c a p a c i t y i n a way t h a t p e r m i t s d i r e c t e x a m i n a t i o n of some of t h e thermodynamic p r o p e r t i e s of t h e c e l l . The d i f f e r e n t i a l change i n c a p a c i t y w i t h r e s p e c t t o v o l t a g e , dQ/dV, r e f l e c t s t h e b e h a v i o u r of t h e e q u a t i o n of s t a t e o f a c e l l . The r e l a t i o n between dQ/dV and dx/dV i s dQ _ F m dx dV M dV U ; where F i s t h e F a r a d a y c o n s t a n t , M i s t h e m o l e c u l a r w e i g h t of t h e a c t i v e m a t e r i a l , and m i s i t s mass. The v a l u e of dQ/dV t e l l s how much c h a r g e w i l l f l o w i f t h e v o l t a g e i s c h a n g e d , and t h e number t e n d s t o i n f i n i t y a t a f i r s t o r d e r p hase t r a n s i t i o n . T h i s i s c o m p l e t e l y a n a l o g o u s t o t h e 1 d"V i s o t h e r m a l c o m p r e s s i b i l i t y o f a g a s , - ^ 8p^T ' w h i c h e x p r e s s e s t h e .volume change of a gas as t h e p r e s s u r e i s a l t e r e d , and a l s o becomes i n f i n i t e a t a phase t r a n s i t i o n . 21 O t h e r s o u r c e s o f c a p a c i t y , s u c h as t h a t a s s o c i a t e d w i t h t h e l a t t i c e gas model o f i n t e r c a l a t i o n , w i l l have a c e r t a i n shape of voltammogram f e a t u r e , and so e x a m i n a t i o n s of dQ/dV v e r s u s v o l t a g e o r dQ/dV v e r s u s x can o c c a s i o n a l l y be u s e d t o d e t e r m i n e t h e p h y s i c a l mechanism w h i c h i s r e s p o n s i b l e f o r c a p a c i t y i n a c e l l . The l i n e a r sweep v o l t a m m e t r y t e c h n i q u e measures t h e c u r r e n t t h r o u g h t h e c e l l as t h e v o l t a g e i s s l o w l y swept between two p o t e n t i a l s . The c u r r e n t , I , i s r e l a t e d t o t h e d i f f e r e n t i a l c a p a c i t y t h r o u g h i - v $ UJ where v" i s t h e r a t e a t w h i c h t h e v o l t a g e c h a n g e s (Dahn and Haer i n g ) . A PAR 175 U n i v e r s a l Programmer and a PAR 173 P o t e n t i o s t a t / G a l v a n o s t a t were u s e d t o p r o d u c e a l i n e a r ramp t h a t c o u l d change a v o l t a g e a p p l i e d t o a c e l l by as l i t t l e a s a few m i c r o v o l t s p e r s e c o n d . A PAR 179 D i g i t a l C o u l o m e t e r p l u g - i n f o r t h e 173 u n i t measured the c u r r e n t and t o t a l c h a r g e t h a t f l o w e d . C u r r e n t v e r s u s v o l t a g e or c u r r e n t v e r s u s c h a r g e were p l o t t e d on X-Y r e c o r d e r s . D i f f u s i o n i s a major p r o b l e m i n l i n e a r sweep v o l t a m m e t r y . C u r r e n t f l o w s t o e q u a l i z e t h e c e l l p o t e n t i a l and t h e p o t e n t i a l of t h e v o l t a g e ramp, but t h e c e l l v o l t a g e i s d e t e r m i n e d by t h e l i t h i u m c o n c e n t r a t i o n a t t h e s u r f a c e of t h e p a r t i c l e s i n t h e c a t h o d e . I t t a k e s t i m e f o r t h e l i t h i u m t o d i f f u s e t h r o u g h t h e c r y s t a l , and so t h e s u r f a c e of t h e p a r t i c l e s may be a t a d i f f e r e n t p o t e n t i a l t h a n t h e i n s i d e s 22 of t h e g r a i n s . L i t h i u m w i l l d i f f u s e t h r o u g h t h e h o s t t o e q u a l i z e t h e c h e m i c a l p o t e n t i a l t h r o u g h o u t t h e c r y s t a l , but t h e n c u r r e n t must f l o w t o m a i n t a i n t h e s u r f a c e c o n c e n t r a t i o n o f l i t h i u m . As a r e s u l t , t h e c u r r e n t measured a t a c e r t a i n ramp v o l t a g e i s due t o b o t h t h e amount of c a p a c i t y a t t h a t p o t e n t i a l and some o f t h e c a p a c i t y a t p o t e n t i a l s p r e v i o u s l y swept t h r o u g h . D i f f u s i o n s m e a r i n g o b s c u r e s t h e a c t u a l w i d t h s of t h e r e g i o n s of c a p a c i t y , and t h e c e l l v o l t a g e had t o be swept v e r y s l o w l y t o m i n i m i z e t h e p r o b l e m . 2.5 C o n s t a n t C u r r e n t V o l t a m m e t r y C o n s t a n t c u r r e n t v o l t a m m e t r y i s a n o t h e r method o f m e a s u r i n g dQ/dV. T h i s t e c h n i q u e d e t e r m i n e s t h e d i f f e r e n t i a l c a p a c i t y from where At was t h e t i m e i t to o k f o r t h e c e l l t o change i t s p o t e n t i a l by some s m a l l amount AV w h i l e a c u r r e n t I was f l o w i n g . U s i n g c o n s t a n t c u r r e n t v o l t a m m e t r y was u s u a l l y p r e f e r a b l e t o u s i n g l i n e a r sweep v o l t a m m e t r y . R u n n i n g a c e l l on l i n e a r sweep s l o w l y enough so d i f f u s i o n p r o b l e m s d i d not b l u r t h e shape of t h e f e a t u r e s o f t e n took a p r o h i b i t i v e l y l o n g t i m e . C o n s t a n t c u r r e n t c y c l i n g had t h e a d v a n t a g e t h a t t h e p o t e n t i a l would q u i c k l y p a s s t h r o u g h low c a p a c i t y r e g i o n s , y e t t h e r a t e of v o l t a g e change i n a h i g h c a p a c i t y r e g i o n c o u l d be much s m a l l e r t h a n c o u l d be a t t a i n e d w i t h t h e s l o w e s t l i n e a r sweep ramp. (5) 23 The d i f f e r e n c e between c o n s t a n t c u r r e n t and l i n e a r sweep v o l t a m m e t r y was most n o t i c e a b l e w i t h f i r s t o r d e r phase t r a n s i t i o n s where, i f t h e r e were no k i n e t i c p r o b l e m s , t h e r e s h o u l d be an i n f i n i t e s p i k e i n t h e g r a p h of dQ/dV v e r s u s v o l t a g e . The c o n s t a n t c u r r e n t t e c h n i q u e would show t h i s as a sudden, s h a r p r i s e i n c a p a c i t y f o l l o w e d by a d i f f u s i o n t a i l . O f t e n a l i n e a r sweep t e s t w ould skew t h e f i r s t o r d e r peak so much t h a t i t would bear l i t t l e r e s e m b l a n c e t o a ' s p i k e ' o f c a p a c i t y . In p r i n c i p l e , b o t h t h e s e methods o f m e a s u r i n g dQ/dV a r e i d e n t i c a l i f t h e c e l l p o t e n t i a l i s c h a n g e d s l o w l y enough, however i n p r a c t i c e t h e c o n s t a n t c u r r e n t t e c h n i q u e i s b e t t e r b e c a u s e i t can o f t e n be b o t h f a s t e r and more a c c u r a t e t h a n l i n e a r sweep. A c o r r e c t i o n f o r an .IR s h i f t , where R was t h e c e l l impedance, had t o be i n c l u d e d i n - o r d e r t o f i n d t h e c o r r e c t v o l t a g e p o s i t i o n of a f e a t u r e . I f t h e f e a t u r e was f u l l y r e v e r s i b l e , t h e n t h e measured p o s i t i o n s on c h a r g e and d i s c h a r g e w o u l d e a c h be s h i f t e d by IR, and t h e c o r r e c t p o s i t i o n was i n t h e m i d d l e of t h e two o b s e r v a t i o n s . I f t h e r e were h y s t e r e s i s , as i s t h e c a s e w i t h t h e MoS 2 p-phase, t h e n r e a d i n g s a t s e v e r a l c u r r e n t s had t o be made, f o l l o w e d by a z e r o c u r r e n t e x t r a p o l a t i o n . A d e t a i l e d a n a l y s i s of c o n s t a n t c u r r e n t v o l t a m m e t r y i s g i v e n by J o h n s o n (1982). I n i t i a l l y , t h e c o n s t a n t c u r r e n t v o l t a m m e t r y e x p e r i m e n t s u s e d s e v e r a l p i e c e s of equipment under t h e c o n t r o l of a T e k t r o n i x 4052 m i c r o c o m p u t e r . The c y c l e r d e s c r i b e d i n s e c t i o n 2.3 r a n t h e c e l l , and t h e o u t p u t was f e d i n t o a 24 H e w l e t t P a c k a r d 3455A D i g i t a l V o l t m e t e r . The computer would r e a d b o t h t h e v o l t m e t e r and a H e w l e t t P a c k a r d 59309A HP-IB D i g i t a l C l o c k and r e c o r d t h e numbers as r e f e r e n c e v a l u e s . The v o l t m e t e r would be r e a d c o n t i n u o u s l y u n t i l t h e v o l t a g e d i f f e r e d from t h e r e f e r e n c e by more t h a n 2.5 m i l l i v o l t s i n a r e g i o n of low c a p a c i t y , o r 1.0 m i l l i v o l t s i n a h i g h c a p a c i t y r e g i o n . The c l o c k was t h e n r e a d a g a i n , and dQ/dV was computed from E q u a t i o n 5. The most r e c e n t t i m e and v o l t a g e measurements were t h e n r e c o r d e d as new r e f e r e n c e v a l u e s . The r e a d i n g c y c l e would t h e n r e p e a t . E v e n t u a l l y , t h e d a t a was p r i n t e d on a t e l e t y p e and p l o t t e d by hand. T h i s s y s t e m debugged t h e s o f t w a r e and p o i n t e d out t h e need f o r t e m p e r a t u r e c o n t r o l of t h e c e l l s . In one e x p e r i m e n t , th e d a y - t o - n i g h t t e m p e r a t u r e v a r i a t i o n i n t h e l a b made t h e c e l l v o l t a g e change two h u n d r e d t h s of a v o l t - - a m a s s i v e change compared t o t h e r e s o l u t i o n o f t h e a p p a r a t u s . A f t e r w a r d s , c e l l s were run a t 20°C i n a Haake K c o n s t a n t t e m p e r a t u r e b a t h f i l l e d w i t h t r a n s f o r m e r o i l and under t h e c o n t r o l of a Haake F3 c i r c u l a t o r . A p i e c e of equipment f o r m o n i t o r i n g t h e c y c l e r o u t p u t was d e s i g n e d by t h e U.B.C. P h y s i c s d e p a r t m e n t e l e c t r o n i c s shop t o be d e d i c a t e d t o c o n s t a n t c u r r e n t v o l t a m m e t r y . T h i s s y s t e m p r o v e d t o be s u p e r i o r t o t h e one d e s c r i b e d i n t h e p r e v i o u s p a r a g r a p h . The d e v i c e l o o k e d f o r v o l t a g e c h a n g e s o f 500 nV w i t h a r e s o l u t i o n of 45 j*V. I t a l s o a v e r a g e d s e t s of v o l t a g e measurements t o remove any j i t t e r c a u s e d by e i t h e r n o i s e o r minor f l u c t u a t i o n s i n t h e s y s t e m . The o u t p u t of t h i s d e v i c e was a n a l o g o n l y , and was f e d i n t o an X-Y 25 recorder. 26 CHAPTER 3 CAPACITY IN c -PHASE ENDAKO MoS 2 S e r e n d i p i t y - - a n assumed g i f t f o r f i n d i n g v a l u a b l e o r a g r e e a b l e t h i n g s n o t s o u g h t f o r - W e b s t e r ' s T h i r d New I n t e r n a t i o n a l D i c t i o n a r y 3.1 I n i t i a l D i s c o v e r y o f H i g h V o l t a g e C a p a c i t y i n Endako MoS 2 A s e t of e x p e r i m e n t s t o i n v e s t i g a t e t h e d i f f u s i o n e f f e c t s i n i n t e r c a l a t i o n b a t t e r i e s compared c e l l s w h i c h had c a t h o d e s made w i t h d i f f e r e n t s i z e d p a r t i c l e s . The c a t h o d e m a t e r i a l was n a t u r a l l y o c c u r r i n g m o l y b d e n i t e from t h e Endako mines w h i c h had been c l e a n e d and d i v i d e d i n t o f i v e s i z e f r a c t i o n s by s i e v i n g and S t o k e s ' s e t t l i n g . The s i m p l e c o n s t a n t c u r r e n t c y c l i n g of s e c t i o n 2.3 had shown no a p p a r e n t d i f f e r e n c e s when t h e p a r t i c l e s i z e was v a r i e d , so th e c e l l s were examined by l i n e a r sweep v o l t a m m e t r y ( s e c t i o n 2 . 4 ) . A f e a t u r e was d i s c o v e r e d a t ab o u t 2.1 v o l t s w h i c h was n o t p r e s e n t i n t h e s y n t h e t i c MoS 2 from A t o m e r g i c . F i g u r e 6 shows an Endako MoS 2 c e l l d i s c h a r g i n g t h r o u g h t h e o t o p p h a s e t r a n s i t i o n , and t h e e x t r a f e a t u r e i s i n d i c a t e d . The e x t r a c a p a c i t y seemed t o r e m a i n even i n t h e p-phase, as shown i n F i g u r e 7. Most o f t h e c e l l s made w i t h t h e n a t u r a l l y o c c u r r i n g powder showed, i n d i f f e r i n g amounts, what w i l l be r e f e r r e d t o as t h e " e x t r a Endako c a p a c i t y " . A s e t of c o n s t a n t c u r r e n t v o l t a m m e t r y e x p e r i m e n t s were p e r f o r m e d t o examine t h e MoS 2 o t o p phase t r a n s i t i o n i n 27 0 .8 1.0 1.2 1.4 1.6 1.8 2 .0 Vol tage (V) Figure 6 -- Endako M0S2 a to 3 Phase Transition Linear Sweep Voltammogram of C e l l PM-19 15 yV/sec Voltage Ramp 9.35 mg cathode of 10-20 ym Endako powder The arrow indicates the extra capacity usually found i n Endako powders. 100 < 3. c CD 3 o 80 h 60 \ -40 h 20 0 0 . 8 1.0 1.2 1.4 1.6 1.8 2 .0 Vol tage (V) Figure 7 -- Endako MoS, 3 Phase Cycling Linear Sweep Voltammogram of C e l l PM-19 15 yV/sec Voltage Ramp 9.35 mg cathode of 10-20 ym Endako powder The two small arrows indicate the extra capacity usually found i n Endako powders. 29 c e l l s made w i t h d i f f e r e n t , s i z e d c a t h o d e p a r t i c l e s . T h e s e measurements a l l o w e d c r u d e e s t i m a t e s o f t h e m a g n i t u d e o f t h e e x t r a c a p a c i t y . The s i z e o f t h e new f e a t u r e was e x p r e s s e d a s t h e r a t i o of i t s c a p a c i t y t o t h e t o t a l c a p a c i t y o f t h e c e l l . A t o m e r g i c MoS 2 i n a-phase has no a p p r e c i a b l e c a p a c i t y above two v o l t s , so t h e c a p a c i t y between 2.0 a n d 2.1 v o l t s was a measure of t h e s i z e of t h e new f e a t u r e ( F i g u r e 8 ) . A l m o s t a l l t h e c a p a c i t y o f t h e c e l l on t h e f i r s t d i s c h a r g e was i n t h e a t o p phase t r a n s i t i o n between 1.0 and 1.2 v o l t s . The amount of e x t r a Endako c a p a c i t y a s a f u n c t i o n of p a r t i c l e s i z e i s shown i n F i g u r e 9. The c a p a c i t y of t h e s m a l l e r t h a n f i v e m i c r o n powder was not a c c u r a t e l y d e t e r m i n e d , and so was not p l o t t e d . The d a s h e d l i n e on t h i s g r a p h r e p r e s e n t s t h e c a p a c i t y of t h e s m a l l e r t h a n t h i r t y e i g h t m i c r o n powder, and s i n c e t h e r e was v e r y l i t t l e m a t e r i a l b i g g e r t h a n t h i s , i t i s a l s o a good i n d i c a t i o n of the amount of e x t r a c a p a c i t y t h a t would be f o u n d i n t h e u n s i z e d powder. The r a t i o s f o r b o t h t h e t e n t o twenty and th e s m a l l e r t h a n t h i r t y e i g h t m i c r o n powders were d e t e r m i n e d by making a heavy c a t h o d e (~60mg of a c t i v e m a t e r i a l ) w h i c h a l l o w e d more a c c u r a t e measurements than d i d t h e e a r l i e r e x p e r i m e n t s . E v e n t u a l l y , t h e i n v e s t i g a t i o n s o f t h e d i f f u s i o n p r o b l e m s were s u s p e n d e d i n f a v o u r of s t u d i e s of t h e newly d i s c o v e r e d c a p a c i t y . 30 0.70 o > C L CO _Q E _o Z3 O o > O 0.00 1.8 2 .0 Voltage (V) F i g u r e 8 -- D e t a i l o f Hi g h V o l t a g e a Phase Endako C a p a c i t y Constant C u r r e n t Voltammogram o f the F i r s t D i s c h a r g e of C e l l PM-30 25 yA c u r r e n t -- microcomputer c o n t r o l l e d a p p a r a t u s 8.8 7 mg cathode of 5-10 ym Endako Powder 0.6 0.5 0.4 0.3 0.2 0.1 \-0.0 ' ' 1 u u 5 10 20 40 80 Par t i c le S i ze ( m i c r o n s ) gure 9 -- P a r t i c l e Size Dependence of the Extra Endako Capacity 32 3.2 G y c l i n g t h e E x t r a C a p a c i t y The e x t r a Endako c a p a c i t y was f o u n d t o have two d i f f e r e n t t y p e s of b e h a v i o u r : one t y p e i f t h e c e l l was a l w a y s kept above a b o u t 1.8 v o l t s , w h i c h was t h e t y p e d i s c u s s e d i n t h e p r e v i o u s s e c t i o n ; and a n o t h e r t y p e i f t h e c e l l was e v e r d i s c h a r g e d below t h i s p o t e n t i a l . F i g u r e 10 shows a c o n s t a n t c u r r e n t voltammogram of t h e f i r s t few c y c l e s between 2.0 and 2.7V o f an Endako MoS 2 c e l l w i t h a c a t h o d e of t e n t o twenty m i c r o n p a r t i c l e s . The l a r g e s t c a p a c i t y , seen as a peak i n t h e voltammogram, was l o c a t e d a t 2.070+0.005V on t h e f i r s t d i s c h a r g e , but on t h e l a t e r d i s c h a r g e s i t was a t 2.078±0.005V. The c o r r e s p o n d i n g peak on r e c h a r g e was a t 2.093V. C o r r e c t i n g f o r t h e IR s h i f t , t h e peak was c e n t r e d a t 2.085V. A n o t h e r c e l l was made from s m a l l e r t h a n t h i r t y e i g h t m i c r o n p a r t i c l e s ( F i g u r e 11). T h i s c e l l a l s o had i t s major c a p a c i t y c e n t r e d a t 2.085±0.005V, and t h e peak on t h e f i r s t d i s c h a r g e was f o u r m i l l i v o l t s l o w e r t h a n t h e p o t e n t i a l of t h e s u b s e q u e n t d i s c h a r g e p e a k s . Most c e l l s showed e v i d e n c e of some c a p a c i t y near 2.45V. T h i s c a p a c i t y was so s m a l l t h a t i t was not c l e a r l y seen ( F i g u r e 11) u n t i l a c e l l was made w i t h t e n t i m e s t h e no r m a l amount of c a t h o d e m a t e r i a l . The f i r s t d i s c h a r g e s shown i n F i g u r e s 10 and 11 were d i f f e r e n t from t h e l a t e r d i s c h a r g e s b e c a u s e , i n p a r t , of t h e s m a l l , i r r e v e r s i b l e c a p a c i t y o f a f r e s h s u b s t r a t e . N o r m a l l y , t h e c a p a c i t y of t h e s u b s t r a t e i s not seen b e c a u s e i t i s t i n y compared t o t h e c a p a c i t y of most c e l l s . The e x t r a c a p a c i t y i n t h e Endako powder was so s m a l l t h a t t h e s u b s t r a t e 33 > CD C L CO -Q E O O > TJ 2.20 1.10 h 0.00 1.10 - 2 . 2 0 | -2.00 2 .15 2.30 2 .45 Voltage (V) 2.60 Figure 10 -- Cycling 10-20 ym Endako MoS? Powder Between 2.0 and 2.7 Volts' Constant Current Voltammogram of C e l l PM-85 10 yA current . 58.80 mg cathode of 10-20 ym Endako MoS2 Powder The arrows indicate the f i r s t discharge of the c e l l . 34 2 .00 2 . 1 5 2 .30 2 . 4 5 2 .60 Vol tage (V) Figure 11 -- Cycling <38 ym Endako MoS~ Powder Between 2.0 and 2.7 Volts Constant Current Voltammogram of C e l l PM-96 5 yA current 100 mg cathode of <38 ym Endako M0S2 powder The arrows indicate the f i r s t discharge of the c e l l . 35 c a p a c i t y was a c o m p a r a b l e s i z e . The e l e c t r o c h e m i c a l b e h a v i o u r of t h e e x t r a Endako c a p a c i t y c h a n g e s as a r e s u l t o f d i s c h a r g i n g t h e c e l l below a b o u t 1.8 v o l t s . A c o n s t a n t c u r r e n t voltammogram of t h e f i r s t d i s c h a r g e o f an A t o m e r g i c MoS 2 c e l l would show an e s s e n t i a l l y smooth, m o n o t o n i c r i s e i n c a p a c i t y between 2.0 and 1.5V. The Endako powder showed e v i d e n c e o f a c a p a c i t y between a b o u t 1.8V and 1.84V w h i c h was not p r e s e n t i n t h e A t o m e r g i c m a t e r i a l , as i n d i c a t e d i n F i g u r e s 12 and 13. The amount of c a p a c i t y between 2.0 and 2.7 v o l t s was r o u g h l y d o u b l e d as a r e s u l t of d i s c h a r g i n g t h e c e l l below 1.8V. About t h r e e q u a r t e r s of t h e s e c o n d t y p e of Endako c a p a c i t y was c e n t r e d a r o u n d 2.088V, and most of t h e r e m a i n d e r was n e a r 2.460V. The above c o m p a r i s o n of t h e t e n t o t w e n t y m i c r o n powder and t h e s m a l l e r t h a n t h i r t y e i g h t m i c r o n powder i n d i c a t e d t h a t t h e e l e c t r o c h e m i c a l b e h a v i o u r of t h e e x t r a Endako c a p a c i t y was i n d e p e n d e n t of p a r t i c l e s i z e . The e x t r a Endako c a p a c i t y was e x t r e m e l y r e v e r s i b l e . In one t e s t , a c c u r a t e t o o n l y f i v e p e r c e n t , t h e r e was no o b s e r v e d l o s s of c a p a c i t y a f t e r more t h a n 100 c y c l e s between 1.9 and 2.2 v o l t s o v e r a f o u r day p e r i o d . A more a c c u r a t e t e s t d e t e c t e d a s e v e n p e r c e n t l o s s of c a p a c i t y between 1.5 and 3.1 v o l t s a f t e r 100 c y c l e s o f a c e l l w i t h a heavy c a t h o d e . T h i s s e c o n d t e s t l a s t e d o v e r two months, and t h e l o s s of c a p a c i t y may have been due t o a d e g r a d a t i o n of t h e c a t h o d e m a t e r i a l , c a t h o d e m a t e r i a l becoming e l e c t r i c a l l y d i s c o n n e c t e d , o r damage t o t h e l i t h i u m or e l e c t r o l y t e due t o 36 1.5 1.7 1.9 2 .1 2 . 3 2 . 5 2 . 7 Vo l tage (V) Figure 12 -- Cycling 10-20 ym Endako MoS0 Powder Between 1.5 and 2.7 Volts Constant Current Voltammogram of C e l l PM-85 10 yA current 58.80 mg cathode of 10-20 :m Endako MoS2 Powder The arrow indicates the extra capacity not normally seen on the f i r s t discharge of an Atomergic M0S2 c e l l . The graph shows the f i r s t discharge from 2.05 to 1.5V, and then one cycle between 1.5 and 2.7V. 37 1.6 1.8 2 . 0 2 . 2 2 . 4 2 . 6 Vo l tage (V) Figure 13 -- Cycling <38 ym Endako MoS9 Powder Between 1.5 and 2.7 Volts Constant Current Voltammogram of C e l l PM-96 5 yA current 100 mg cathode of <38 ym Endako M0S2 Powder The arrow indicates the extra capacity not normally seen on the f i r s t discharge of an Atomergic M0S2 c e l l . The graph shows the f i r s t discharge from 2.05V to 1.5V, and then one cycle between 1.5 and 2.7V. - 38 slow leakage of water and oxygen through the O-ring seal. A loss of capacity of more than ten percent over a two month period is not uncommon because the flange c e l l s are not designed for long term experiments. Figure 14 shows a voltammogram taken after a c e l l made with smaller than t h i r t y eight micron Endako MoS2 had been cycled more than one hundred times. The capacity near 2.087V appears to be a f i r s t order phase t r a n s i t i o n , as indicated by the very sharp spike of capacity, and there is some single phase capacity on both sides of the t r a n s i t i o n . The feature at 2.463V is symmetric on charge and discharge, which is suggestive of a single phase int e r c a l a t i o n of lithium into the host. A very small amount of capacity was detected at ~1.83V, but i t was not clear i f a f i r s t order phase t r a n s i t i o n was responsible for this capacity. The second type of behaviour for the extra Endako capacity seemed to be superior to the f i r s t type because both the t o t a l c e l l capacity above 2.0V and the average voltage were greater. This spurred e f f o r t s to try and identif y the source of the second type of capacity. 3.3 Effect of Sample Preparation The sample preparation procedure was examined to see i f i t was related to the extra observed capacity. Atomergic MoS2 was cleaned in Solvex, chloroform, and trichloroethylene and then baked at 750°C. There was no observed a-phase capacity between 2.0 and 2.1 volts after t h i s treatment. 1 1 1 1 1 1 1 1 1 Discharge _ A . " — r Y -Charge 1 1 1 1 1 1 1 1 .6 1.8 2 . 0 2 . 2 2 . 4 Vol tage (V) Cycling a-Phase Endako Powder Constant Current Voltammogram of C e l l PM-60 25 yA current vL50 mg of <38 ym Endako MoS2 Powder 40 An Endako MoS 2 sample was c l e a n e d i n t h e s o l v e n t s , but not b a k e d . T h i s sample had a v e r y s m a l l amount o f c a p a c i t y • a t 2.75V and 2.35V, p o t e n t i a l s where o t h e r s amples had shown no c a p a c t i t y , but t h e r e was no s i g n i f i c a n t c a p a c i t y between 2.0 and 2.1 v o l t s or a r o u n d 1.83V ( F i g u r e 1 5 ) . In b r i e f , t h e e x t r a c a p a c i t y was not p r e s e n t i n t h e Endako powder u n t i l i t was baked a t h i g h t e m p e r a t u r e . The s o u r c e of t h e e x t r a c a p a c i t y does not o c c u r n a t u r a l l y i n t h e Endako MoS 2. I t was p r o d u c e d i n some r e a c t i o n t h a t i n v o l v e d some c o m b i n a t i o n o f t h e MoS 2 and/or t h e i m p u r i t i e s i n t h e powder. 41 O > 0) C L co _Q E _o D O O > O I 3.00 2.50 2.00 1.50 1.00 0.50 0.00 First Discharge Below Two Volts First Discharge 1.6 1.8 2.0 2 . 2 2 . 4 2 . 6 2 . 8 3 .0 Voltage (V) Figure 15 -- Unheated Endako MoS2 Constant Current Voltammogram of C e l l PM-83 5 yA current on f i r s t discharge, 10 yA current on l a t e r discharge 77.07 mg cathode of unsized Endako M0S2 P ° w c ^ e r The f i r s t discharge of the c e l l from 3.0V to 2.0V at 5 yA i s shown in the graph. The c e l l was then cycled between 2.0 and 2.7V at 10 yA, but the featureless cycles are not shown. The t r i p voltage was then lowered and the f i r s t discharge below two vo l t s i s also included i n the graph. 42 CHAPTER 4 ELECTROCHEMICAL EXAMINATIONS 4.1 A t t e m p t s t o F i n d an I m p u r i t y i n MoS 2 T h e r e were two p o s s i b l e e x p l a n a t i o n s of t h e e x t r a c a p a c i t y i n t h e Endako MoS 2. T h e r e m i g h t have been some m a t e r i a l o r m a t e r i a l s s e p a r a t e and d i s t i n c t from t h e MoS 2 w h i c h c o n t r i b u t e d t h e o b s e r v e d c a p a c i t y , o r t h e MoS 2 i t s e l f may have been m o d i f i e d i n some way as t o change i t s e l e c t r o c h e m i c a l b e h a v i o u r . T e s t s were made on s e v e r a l of t h e m i n e r a l s w h i c h may have been p r e s e n t i n t h e Endako powder. C e l l s were made from q u a r t z ( S i 0 2 ) , g a l e n a ( P b S ) , s p h a l e r i t e ( Z n S ) , c h a l c o p y r i t e ( C u F e S 2 ) , c h a l c o c i t e ( C u 2 S ) , ' d i g e n i t e ( C u u 8 S ) , and c o v e l i t e ( C u S ) . Most of t h e c y c l i n g c u r v e s a r e shown i n F i g u r e s 16 t h r o u g h 18. Q u a r t z i s not shown b e c a u s e i t had no o b s e r v e d c a p a c i t y . None of t h e s e m i n e r a l s e x p l a i n e d t h e e x t r a c a p a c i t y of Endako MoS 2. E f f o r t s were t h e n d i r e c t e d t o see i f t h e MoS 2, a s e m i c o n d u c t o r , c o u l d be a l t e r e d i n a way t o g i v e i t e x t r a c a p a c i t y . I t was p o s t u l a t e d b o t h t h a t t h e Endako MoS 2 c o u l d be doped p - t y p e , and t h a t l i t h i u m was an n - t y p e i m p u r i t y . D i s c h a r g i n g t h e c e l l would r e d u c e t h e measured v o l t a g e and i n c r e a s e t h e c h e m i c a l p o t e n t i a l i n t h e c r y s t a l , but t h e c h e m i c a l p o t e n t i a l of a s e m i c o n d u c t o r i s r e l a t e d t o t h e number and t y p e of i m p u r i t i e s p r e s e n t . N - t y pe l i t h i u m would have t o be added t o t h e c r y s t a l t o make t h e c h e m i c a l b) Figure 16 20 40 Time (hours) Time (hours) Cycling Cu-^  gS and C^S a) Constant Current Cycling of Ce l l PM-84 50 yA current 9.80 mg cathode of Digenite, Cu-^  gS b) Constant Current Cycling of C e l l PM-100 25 yA current 7.52 mg cathode of Chalcocite, C^S 60 a ) b) a) cn o o > cn o o > 3 2 1 0 l-Ax=.2-l J 1 1 I I I I I J L 0 4 6 8 Time (hours) 10 12 3 2 1 0 — y — — r-Ax= 3H — I i i i 1 1 I 5 10 15 20 Figure 17 Time (hours) •- Cycling CuS and PbS a) Constant Current Cycling of C e l l PM-77 500 yA current 10.26 mg cathode of Covelite, CuS • ' b) Constant Current Cycling of C e l l PM-33 The arrow indicates an increase in current from 20 yA to 200 yA. The time scale of the part of the graph showing the 20 yA discharge was divided by ten to allow the horizontal scale to be proportional to Ax. 24.85 mg cathode of Galena, PbS • a ) b) r j i D O > Time (hours) 0 0 50 100 Figure 18 -- Cycling CuFeS 2 and ZnS Time (hours) a) Constant Current Cycling of C e l l RSM-7 100 yA current %10 mg cathode of Chalcopyrite, CuFeS 2 b) Constant Current Cycling of C e l l RSM-3 The arrow indicates an increase i n current from 0.2mA to 1.0mA. The time scale of the part of the graph showing the 0.2mA discharge was divided by f i v e to allow the horizontal scale to be proportional to Ax. 67 mg cathode of Sphalerite, ZnS 4> 46 p o t e n t i a l r i s e , and most o f t h e c a p a c i t y would be c e n t r e d a r o u n d t h e p o t e n t i a l s a t w h i c h t h e a c c e p t o r i m p u r i t i e s i o n i z e and l i t h i u m c o u l d c h a r g e compensate them. C a n t e s t L i m i t e d o f V a n c o u v e r p r e p a r e d a l i s t o f i m p u r i t i e s f o u n d i n t h e Endako MoS 2 powder, and a t t e m p t s were made t o dope A t o m e r g i c MoS 2 w i t h v a r i o u s m e t a l s f o u n d on t h i s l i s t . The MoS 2 was mixed w i t h t h e do p a n t i n an a p p r o x i m a t e two t o one a t o m i c r a t i o . The m a t e r i a l was put i n t o a q u a r t z t u b e , e v a c u a t e d t o 10"" t o r r , and s e a l e d . The tube was t h e n h e a t e d t o a b o u t 1100°C f o r u s u a l l y two d a y s , and t h e n c o o l e d t o room t e m p e r a t u r e o v e r a s e v e n hour p e r i o d . I t was hoped t h a t t h e r e would be v a p o u r t r a n s p o r t of the m e t a l i n t o t h e MoS 2, but i t was l a t e r l e a r n e d t h a t MoS 2 was not s t a b l e above 610°C ( T s i g d i n o s 1978, Moh 1978) and i t c o u l d r e a c t c h e m i c a l l y w i t h t h e m e t a l . 4.2 A t t e m p t s t o Dope MoS 2 w i t h Copper The m e t a l u s e d i n t h e f i r s t a t t e m p t t o dope A t o m e r g i c MoS 2 was A l f a P r o d u c t s two n i n e s p u r e c o p p e r t u r n i n g s . A f t e r b a k i n g , t h e powder had t h e same g r e y - b l a c k l u s t r e a s s o c i a t e d w i t h MoS 2. The c o p p e r t u r n i n g s were s t i l l p r e s e n t , t h o u g h t h e y were b l a c k e n e d and b r i t t l e , i n d i c a t i n g t h a t t h e tub e had p r o b a b l y n e v e r r e a c h e d t h e 1063°C m e l t i n g t e m p e r a t u r e of c o p p e r . The f i r s t d i s c h a r g e o f t h e M o S 2 ~ c o p p e r m i x t u r e had no c a p a c i t y a t 2.46V, and o n l y a s m a l l amount (Ax of a b o u t 0.02 a s s u m i n g t h e c a t h o d e was e s s e n t i a l l y MoS 2) a t ab o u t 2.02±0.02V. T h e r e was a f i r s t o r d e r phase t r a n s i t i o n a t 47 ""1.86V (AX = 0.1) w h i c h c h a n g e d t h e b e h a v i o u r o f t h e c e l l . F i g u r e 19 i s a l i n e a r sweep voltammogram made of a c y c l e between 1.5 and 2.6 v o l t s a f t e r t h e c e l l had gone t h r o u g h t h e phase t r a n s i t i o n . T h e r e were f e a t u r e s a t a b o u t 2.45, 2.08 and 1.83V t h a t had t h e same shape and r e l a t i v e s i z e as t h e f e a t u r e s o b s e r v e d i n t h e Endako powder. T h e r e were o t h e r r e g i o n s of c a p a c i t y w h i c h d i d not a p p e a r i n t h e Endako m a t e r i a l , but t h e b r o a d c a p a c i t y a t 1.6V on d i s c h a r g e and t h e 1.85 and 2.36V f e a t u r e s on c h a r g e a p p e a r t o be t h e e l e c t r o c h e m i c a l s i g n a t u r e of c h a l c o c i t e , C u 2 S . F i g u r e 20 shows a c o n s t a n t c u r r e n t voltammogram of t h e same c e l l c y c l e d between 1.7 and 2.7 v o l t s . The c h a l c o c i t e f e a t u r e s were e l i m i n a t e d by k e e p i n g t h e c e l l p o t e n t i a l above 1.7 v o l t s . The l a r g e s t c a p a c i t y a p p e a r e d t o be a f i r s t o r d e r phase t r a n s i t i o n c e n t r e d a t 2.089±0.005V. T h e r e was a s y m metric peak c e n t r e d a t 2.461V, a s m a l l e r amount of c a p a c i t y a t ~1.83V, and w h a t • a p p e a r e d t o be s i n g l e phase c a p a c i t y i n t h e t e n t h of a v o l t below the t r a n s i t i o n . A l l t h e s e o b s e r v a t i o n s were w i t h i n e x p e r i m e n t a l e r r o r of t h e measurements of t h e e x t r a Endako c a p a c i t y as shown i n F i g u r e 14. The c a p a c i t y n e a r 1.83V i n t h e M o S 2 - c o p p e r m i x t u r e was r e s o l v e d i n t o two f e a t u r e s , one c e n t r e d a t 1.836V and t h e o t h e r a t 1.808V. Measurements of t h e 1.83V c a p a c i t y i n t h e Endako powder were s u g g e s t i v e of a two peak s t r u c t u r e , but l a c k e d t h e c l a r i t y t o make a q u a n t i t a t i v e e s t i m a t e o f t h e i r p o s i t i o n . A n o t h e r b a t c h of A t o m e r g i c MoS 2 and c o p p e r was p r e p a r e d 48 I. 5 1.7 1.9 2.1 2.3 2.5 Vol tage (V) Figure 19 -- Cycle of MoS~-Copper Mixture Between 1.5 and 2,6 Volts Linear Sweep Voltammogram of C e l l PM-65 5 yV/sec Voltage Ramp II. 49 mg cathode of 1100 C MoS2-Copper material The s o l i d l i n e corresponds to the discharge and the broken l i n e to the charge. The c e l l was not f u l l y equilibrated at 2.6V before the discharge began. Lithium was d i f f u s i n g out of the host, so the current was i n i t i a l l y negative. The charge cycle had been properly equilibrated. 49 O > CD C L CO _o D O O > X5 O 30 20 10 0 -10 -20 1 1 1 1 i i i i r - 1 Discharge - . J A — R Y Charge 1 1 1 1 1 1 1 1 I 1 .6 1.8 2 . 4 Figure 20 -• 2 . 0 ' 2 . 2 Vol tage (V) Cycling the Mc^-Copper Mixture Constant Current Voltammogram of C e l l PM-65 25 yA current 11.49 mg cathode of 1100 C Atomergic MoS2~Copper material 50 i n t h e same way as t h e m a t e r i a l d e s c r i b e d above, e x c e p t t h a t t h e q u a r t z t u b e was o n l y h e a t e d t o t h e 750°C t e m p e r a t u r e a t wh i c h t h e Endako powder was baked t o remove t h e c l e a n i n g s o l v e n t s . The c o n s t a n t c u r r e n t c y c l i n g o f t h e r e s u l t i n g m a t e r i a l between 1.8V and 2.7V p r o d u c e d t h e e x a c t same e l e c t r o c h e m i c a l b e h a v i o u r as t h e m a t e r i a l w h i c h had been baked a t 1100°C. 4.3 A t t e m p t s t o Dope MoS 2 w i t h O t h e r E l e m e n t s Two a t t e m p t s were made t o dope A t o m e r g i c MoS 2 w i t h i r o n . The f i r s t sample u s e d i r o n powder from A t l a n t i c E quipment E n g i n e e r s as a d o p a n t , but t h i s powder was l a t e r f o u n d t o be s l i g h t l y c o n t a m i n a t e d w i t h FeO. The r e s u l t i n g b a t c h was a d u l l g r e y powder u n l i k e MoS 2. A l a t e r a t t e m p t was made t o l i g h t l y dope t h e MoS 2, so o n l y t e n a t o m i c p e r c e n t i r o n powder from Spex I n d u s t r i e s I n c o r p o r a t e d was mixed w i t h t h e MoS 2. T h i s - b a t c h r e s u l t e d i n a powder t h a t l o o k e d i d e n t i c a l t o MoS 2. The f i r s t d i s c h a r g e of a c e l l p r e p a r e d w i t h t h e f i r s t b a t c h of t h e M o S 2 - i r o n m a t e r i a l had a s m a l l amount of c a p a c i t y a t 2.02V (Ax=0.04 a s s u m i n g t h a t MoS 2 i s t h e o n l y a c t i v e m a t e r i a l ) , and a phase t r a n s i t i o n a t 1.86V (Ax=0.2) as shown i n F i g u r e 21. In l a t e r c y c l e s between 1.5 and 2.7 v o l t s t h e main c a p a c i t y was c e n t r e d a t 2.089V and i t r e s e m b l e d a f i r s t o r d e r phase t r a n s i t i o n . T h e r e was a symm e t r i c peak a t 2.461V, and some c a p a c i t y was near 1.82V. T h e r e was some s i n g l e phase c a p a c i t y j u s t below t h e phase t r a n s i t i o n , but none between 2.1 and 2.3 v o l t s . The o b s e r v e d 51 O > C L CO JD E _o D O o > O 40 h 20 h 0 h 1 .6 1.8 2 . 0 2 . 2 Vo l tage (V) 2 . 4 2 . 6 Figure 21 -- F i r s t Discharge of Mc^-Iron Material Constant Current Voltammogram of C e l l PM-95 10 yA current 6.62 mg cathode of Atomergic MoS2~Iron material The arrow indicates a voltage r i s e during discharge. This i s analogous to supercooling, 52 p o s i t i o n s and shapes of t h e major f e a t u r e s o f t h e M o S 2 - i r o n sample ( F i g u r e 22) were w i t h i n e r r o r of t h e measurements made on t h e Endako powder ( F i g u r e 14) and t h e M o S 2 - c o p p e r sample a f t e r i t had gone t h r o u g h i t s phase t r a n s i t i o n ( F i g u r e 2 0 ) . The s e c o n d b a t c h o f M o S 2 - i r o n had a r a d i c a l l y d i f f e r e n t b e h a v i o u r . T h e r e was no s i g n i f i c a n t c a p a c i t y above 1.5 v o l t s , and t h e c e l l went t h r o u g h a f i r s t o r d e r phase t r a n s i t i o n a t about 1.35V. On r e c h a r g e , t h e r e was a n o t h e r f i r s t o r d e r t r a n s i t i o n a r o u n d 1.75V. No o t h e r c a p a c i t y was p r e s e n t when t h e c e l l was c y c l e d between 1.3 and 2.7 v o l t s . A t o m e r g i c MoS 2 was h e a t e d t o 750°C w i t h magnesium and w i t h s u l p h u r i n o t h e r a t t e m p t s t o p r o d u c e t h e e x t r a Endako c a p a c i t y . N e i t h e r of t h e s e m a t e r i a l s showed any e v i d e n c e of h a v i n g any s i g n i f i c a n t c a p a c i t y i n a-phase above two v o l t s . 4.4 E x a m i n a t i o n s of X-Phase R e a c t i n g A t o m e r g i c MoS 2 and c o p p e r y i e l d e d s e v e r a l m a t e r i a l s i n c l u d i n g : MoS 2; t h e c o p p e r - m o l y b d e n u m - s u l p h u r X-pha s e ; and o t h e r u n i d e n t i f i e d c r y s t a l s ( as d e s c r i b e d i n C h a p t e r 5 ) . I t was assumed t h a t a m a t e r i a l o t h e r t h a n MoS 2 might be t h e s o u r c e of t h e e x t r a Endako c a p a c i t y , so an a t t e m p t was made t o p r o d u c e some p u r e X -phase. A g r o u p o f s i m i l a r m a t e r i a l s w h i c h c an form i n n o n - s t o i c h i o m e t r i c r a t i o s have been d e s c r i b e d as X-phase, and t h e r e a r e a v a r i e t y of f o r m u l a s u s e d t o d e s c r i b e them ( G r o v e r 1965, Wang and Moh 1976, Moh 1978). The X - r a y p a t t e r n of t h e s u b s t a n c e f o u n d i n t h e M o S 2 - c o p p e r m i x t u r e l e d t o Cu 1 > 3 8 M o 3 S „ - - a 53 O > CD C L 00 _Q _o 3 O U > "D O 10 0 -10 1 1 1 1 1 1 1 1 1 J Discharge X r v ~ Charge 1 1 1 1 1 1 1 1 1 1.6 1.8 2 .0 2 . 2 Vol tage (V) 2 . 4 2 . 6 Figure 22 -- Cycling the MoS2~Iron Material Constant Current Voltammogram of C e l l PM-95 10 yA current 6.62 mg cathode of Atomergic MoS2~Iron material 54 m a t e r i a l w h i c h i s c o p p e r i n s e r t e d i n a M o 3 S „ s t r u c t u r e . A l f a c o p p e r t u r n i n g s , f o u r n i n e s p u r e molybdenum from Spex I n d u s t r i e s I n c o r p o r a t e d , and s i x n i n e s p u r e s u l p h u r a l s o f r o m Spex were mixed i n a r a t i o t o make Cu 1 f 3Mo 3S t t. The m i x t u r e was h e a t e d f o r two d a y s a t 1100°C, but a f t e r c o o l i n g , t h e powder had two d i s t i n c t l y d i f f e r e n t c o l o u r s i n d i f f e r e n t p a r t s o f t h e t u b e . The powders were shaken t o g e t h e r and t h e t u b e was r e h e a t e d f o r a n o t h e r two d a y s . The r e s u l t was a m i x t u r e of X-phase and a s m a l l amount of MoS 2. The b a t t e r y b e h a v i o u r of t h e X-phase a c c o u n t e d f o r many of t h e f e a t u r e s , t h a t were seen when c y c l i n g t h e A t o m e r g i c M o S 2 - c o p p e r m a t e r i a l . The f i r s t d i s c h a r g e , F i g u r e 23, had a r e g i o n of c a p a c i t y n e a r 2.00V and a f i r s t o r d e r p hase t r a n s i t i o n a t 1.856±0.005V. T h r e e q u a r t e r s of t h e c a p a c i t y on t h e f i r s t d i s c h a r g e was a s s o c i a t e d w i t h t h e phase t r a n s i t i o n . The f i r s t d i s c h a r g e of t h e M o S 2 - c o p p e r m a t e r i a l a l s o showed t h e s e two f e a t u r e s p l u s some o t h e r c a p a c i t y n e a r •1.6V a t t r i b u t e d t o C u 2 S . L a t e r c y c l e s of t h e X-phase m a t e r i a l ( F i g u r e 24) were a l m o s t i d e n t i c a l t o t h e b e h a v i o u r of t h e e x t r a Endako c a p a c i t y . T h e r e was a s y mmetric pe"ak a t 2.457±0.005V, a f i r s t o r d e r phase t r a n s i t i o n a t 2.087V, and a s m a l l e r amount of c a p a c i t y n e a r 1.84V. A s m a l l amount of MoS 2 was known t o be p r e s e n t w i t h t h e X-phase, but i n a d i s c h a r g e from 2.7 t o 0.8V t h e MoS 2 o t o p t r a n s i t i o n a c c o u n t e d f o r l e s s t h a n f i v e p e r c e n t of t h e t o t a l c a p a c i t y of t h e c e l l . The r e s t of t h e c a p a c i t y (Ax=~1.5 i n L i x C u 1 > 3 M o 3 S „ ) was t h e " e x t r a Endako c a p a c i t y " . 55 O > C L 00 XI E O O > O 1.5 1.7 1.9 2.1 2.3 Vol tage (V) Figure 23 2.5 2.7 F i r s t Discharge of "X-Phase" Constant Current Voltammogram of C e l l PM-91 10 yA current 12.02 mg cathode of M:u, ,Mo0S,--"X-Phase" ° 1 . 4 3 4 The arrow indicates a voltage r i s e during discharge. This i s analogous to supercooling 56 1 I I 1 1 1 1 1 [ 1.6 1.8 2 .0 2 . 2 2 . 4 2 . 6 Vol tage (V) Figure 24 -- Cycling "X-Phase" Constant Current Voltammogram of C e l l PM-91 15 yA current 12.02 mg cathode of %Cu-L 4Mo 3S 4 -- "X-Phase" 57 T h i s h i g h l y c o n c e n t r a t e d s o u r c e of t h e e x t r a Endako c a p a c i t y a l l o w e d d e t a i l e d measurements t o be made w i t h o u t o t h e r s o u r c e s of c a p a c i t y o b s c u r i n g t h e r e s u l t s . The e x t r a Endako c a p a c i t y d i d not a p p e a r u n t i l t h e X-phase ( o r t h e M o S 2 _ i r o n m i x t u r e ) was d r i v e n t h r o u g h a f i r s t o r d e r phase t r a n s i t i o n . About n i n e t y p e r c e n t of t h e l i t h i u m t h a t was t r a n s f e r r e d i n t o t h e c e l l as i t was b r o u g h t t h r o u g h t h e t r a n s i t i o n c o u l d be l a t e r removed by c h a r g i n g t h e b a t t e r y . The m a t e r i a l w h i c h p r o d u c e d t h e e x t r a Endako c a p a c i t y p r o b a b l y had l i t t l e o r no l i t h i u m i n i t when i t was f u l l y c h a r g e d . About twenty p e r c e n t of t h e e x t r a c a p a c i t y was c e n t r e d a r o u n d 2.46 v o l t s . Between 2.3 and 2.7V t h e r e was, t o w i t h i n e x p e r i m e n t a l e r r o r , an e q u a l amount of l i t h i u m t r a n s f e r r e d i n t o t h e c e l l on d i s c h a r g e as was removed when the c e l l was c h a r g e d . C o n s t a n t c u r r e n t v o l t a m m e t r y showed t h a t t h e w i d t h of t h e f e a t u r e on c h a r g e was about 20mV and t h e d i s c h a r g e peak was 1OmV wide ( F i g u r e s 22 and 2 4 ) , w h i c h i n d i c a t e d h y s t e r e s i s i n t h e c e l l . The f e a t u r e s were n o t p e r f e c t l y s y m m e t r i c , but were s l i g h t l y skewed by d i f f u s i o n . . J u s t o v e r h a l f of t h e c a p a c i t y between 1.5 and 2.7V was i n what a p p e a r e d t o be a f i r s t o r d e r phase t r a n s i t i o n c e n t r e d a t 2.088V. The s h a r p r i s e f o l l o w e d by a d i f f u s i o n t a i l e x p e c t e d i n s u c h t r a n s i t i o n s was c l e a r l y shown i n many voltammograms, i n c l u d i n g F i g u r e s 22 and 24. The w i d t h of t h i s f e a t u r e i n c r e a s e d p r o p o r t i o n a t e l y w i t h t h e c u r r e n t , as e x p e c t e d . The Endako powder had what a p p e a r e d t o be s i n g l e phase 58 c a p a c i t y b o t h above and below t h e phase t r a n s i t i o n , as d i d t h e M o S 2 - c o p p e r m a t e r i a l . The M o S 2 - i r o n sample had c a p a c i t y below t h e t r a n s i t i o n but n o t above i t . The X-phase m a t e r i a l o r i g i n a l l y had c a p a c i t y i n t h e 2.1 t o 2.2V r a n g e , but i t d i s a p p e a r e d a f t e r l e s s t h a n one dozen c y c l e s . I t i s r e a s o n a b l e t o assume t h a t t h e s i n g l e phase c a p a c i t y above t h e t r a n s i t i o n i s not d i r e c t l y a s s o c i a t e d w i t h t h e major f e a t u r e s o f t h e e x t r a Endako c a p a c i t y . The s i n g l e phase r e g i o n below t h e f i r s t o r d e r t r a n s i t i o n a c c o u n t e d f o r a b o u t t w e n t y p e r c e n t of t h e c a p a c i t y i n an X-phase c e l l w h i c h had been c y c l e d many t i m e s . The c ombined c a p a c i t y of t h e f i r s t o r d e r t r a n s i t i o n and t h e s i n g l e phase r e g i o n was t h e same on b o t h c h a r g e and d i s c h a r g e . The f e a t u r e s n e a r 1.83 v o l t s a c c o u n t e d f o r about f i v e p e r c e n t of the c a p a c i t y . T h e r e was v e r y l i t t l e h y s t e r e s i s i n t h e c y c l e s of t h e e x t r a Endako c a p a c i t y . Many voltammograms showed about n i n e t y e i g h t p e r c e n t of t h e e n e r g y r e q u i r e d t o c h a r g e t h e c e l l b e i n g r e c o v e r e d on d i s c h a r g e . T h i s i s much b e t t e r t h a n t h e a p p r o x i m a t e l y n i n e t y p e r c e n t e f f i c i e n t 0-phase MoS 2. 4.5 O t h e r E l e c t r o c h e m i c a l S t u d i e s The e x t r a Endako c a p a c i t y was p r o d u c e d from a c o m b i n a t i o n of c o p p e r , molybdenum, and s u l p h u r as w e l l as a c o m b i n a t i o n of iron,molybdenum, and s u l p h u r . B o t h t h e s e were t e r n a r y compounds i n i t i a l l y , but t h e y had t o go t h r o u g h a f i r s t o r d e r , n o n - r e v e r s i b l e phase t r a n s i t i o n b e f o r e t h e e x t r a c a p a c i t y a p p e a r e d . The n e a r l y i d e n t i c a l e l e c t r o c h e m i c a l b e h a v i o u r o f t h e two m a t e r i a l s i n d i c a t e d 59 t h a t t h e e x t r a Endako c a p a c i t y was p r o b a b l y r e l a t e d t o t h e molyb d e n u m - s u l p h u r e n v i r o n m e n t and not t o t h e o t h e r m e t a l . The f i r s t o r d e r t r a n s i t i o n t h e s e m a t e r i a l s had t o go t h r o u g h c o u l d have been a d i s p l a c e m e n t r e a c t i o n w h i c h p r o d u c e d a molybdenum s u l f i d e and some o t h e r s u b s t a n c e . Molybdenum s e q u i s u l f i d e , M o 2 S 3 , w h i c h i s t h e s t a b l e s u l f i d e above 610°C, was made from t h e e l e m e n t s . Even t h o u g h t h i s m a t e r i a l i s e s s e n t i a l l y a l a y e r e d compound ( J e l l n i k 1961, de Jonge e t . a l . 1970), i t had no s i g n i f i c a n t c a p a c i t y above 1.3V. A t t e m p t s t o make M o 3 S 4 by e t c h i n g some X-phase w i t h HC1 and w i t h HN0 3 ( C h e v r e l 1974) f a i l e d t o p r o d u c e a p u r e sample. 60 CHAPTER 5 X-RAY EXAMINATIONS 5.1 X - r a y D i f f r a c t i o n X - r a y d i f f r a c t i o n i s one of t h e most i m p o r t a n t t e c h n i q u e s f o r d e t e r m i n i n g t h e s t r u c t u r e of a c r y s t a l . I n c i d e n t X - r a y s a r e s c a t t e r e d by t h e m a t e r i a l i n d i r e c t i o n s d e t e r m i n e d by t h e s p a c i n g between p l a n e s of atoms. The i n t e n s i t y of t h e s c a t t e r e d X - r a y s depends on t h e shape and s i z e of t h e u n i t c e l l of t h e c r y s t a l and t h e t y p e and p o s i t i o n s o f t h e atoms i n i t . I f t h e e m p i r i c a l f o r m u l a of t h e c r y s t a l i s known, t h e n t h e i n t e n s i t y d a t a c an be u s e d t o d e t e r m i n e t h e a t o m i c p o s i t i o n s . The X - r a y d i f f r a c t i o n p a t t e r n can a l s o be u s e d t o " f i n g e r p r i n t " an unknown s u b s t a n c e f o r c o m p a r i s o n w i t h known m a t e r i a l s . The a n g l e s a t w h i c h i n t e n s e X - r a y beams a r e d e t e c t e d c a n be r e l a t e d t o t h e u n i t c e l l of t h e c r y s t a l . The r e l a t i o n between t h e s c a t t e r i n g a n g l e and t h e s p a c i n g between p l a n e s o f atoms, d, i s X = 2 d s i n 9 (6) where 29 i s t h e a n g l e between t h e i n c i d e n t and s c a t t e r e d X-r a y s , and X. i s t h e w a v e l e n g t h of t h e r a d i a t i o n . M i l l e r i n d i c e s , ( h k l ) , c an t h e n be u s e d t o e x p r e s s t h e d s p a c i n g s i n t e r m s o f t h e t h r e e l a t t i c e v e c t o r s of t h e u n i t c e l l . T h e s e i n d i c i e s a r e d e f i n e d by C u l l i t y (1959) as " t h e r e c i p r o c a l s o f t h e f r a c t i o n a l i n t e r c e p t s w h i c h t h e p l a n e 61 makes w i t h t h e c r y s t a l l o g r a p h i c a x e s . " S e v e r a l p a t t e r n s were i n d e x e d as p a r t of t h e d a t a a n a l y s i s , b ut t h e t e x t of t h i s t h e s i s w i l l o n l y use t h e i n d i c e s as a way of r e f e r r i n g t o a p a r t i c u l a r d i f f r a c t i o n l i n e . 5.2 P r e l i m i n a r y E x a m i n a t i o n s The c l e a n e d Endako powder was t h e s u b j e c t of t h e f i r s t X - r a y e x a m i n a t i o n s . Q u a r t z was t h e major i m p u r i t y i n t h e sample, b u t t h e r e were many o t h e r d i f f r a c t i o n l i n e s p r e s e n t . U n f o r t u n a t e l y , t h e MoS 2 and q u a r t z s i g n a l s would have masked any s m a l l e r l i n e s w h i c h may have been p r e s e n t a t t h e same a n g l e s . U s i n g t h e J o i n t Committee on Powder D i f f r a c t i o n S t a n d a r d s ' Powder D i f f r a c t i o n F i l e S e a r c h Manual p r o v e d t o be n e a r l y u s e l e s s i n i d e n t i f y i n g t h e e x t r a l i n e s s t i l l v i s i b l e . I n s t e a d , t h e Endako d i f f r a c t i o n p a t t e r n was examined t o t r y and f i n d e x p e c t e d i m p u r i t i e s . The g a l e n a , PbS, c o v e l i t e , CuS, c h a l c o c i t e , C u 2 S , and 3R p o l y t y p e of MoS 2 p a t t e r n s were a l l c h e c k e d , but none o f t h e s e m a t e r i a l s were p r e s e n t i n any d e t e c t a b l e amount. X - r a y i n v e s t i g a t i o n s of t h e Endako powder were s t o p p e d when i t l o o k e d as i f t h e y would be f r u i t l e s s . 62 5.3 A t t e m p t s t o Dope MoS 2 The f i r s t a t t e m p t t o dope A t o m e r g i c MoS 2 i n v o l v e d h e a t i n g i t t o g e t h e r w i t h c o p p e r t o 1100°C. T h i s f a i l e d b e c a u s e MoS 2 i s u n s t a b l e a t h i g h t e m p e r a t u r e s and r e a c t s w i t h t h e c o p p e r t o form new compounds. Many of t h e l i n e s i n t h e X - r a y d i f f r a c t i o n p a t t e r n were a t t r i b u t e d t o MoS 2, and th e Powder D i f f r a c t i o n F i l e S e a r c h Manual and A l p h a b e t i c a l Index were u s e d t o t r y and i d e n t i f y t h e o t h e r s . T h e r e was e x c e l l e n t c o r r e s p o n d e n c e between s e v e r a l o f t h e e x t r a l i n e s and t h e p a t t e r n f o r Cu 1 > 3 8 M o 3 S „ , and t h e s e r e s u l t s prompted t h e a t t e m p t t o s y n t h e s i z e t h i s compound from t h e e l e m e n t s . O t h e r r e f e r e n c e s a t t r i b u t e d t h e s e same X - r a y l i n e s t o a c l a s s of m a t e r i a l s c a l l e d X - p h a s e . The phase d i a g r a m of t h e c o p p e r - m o l y b d e n u m - s u l p h u r s y s t e m p r e p a r e d by Moh (1978) showed t h a t when c o p p e r and MoS 2 a r e h e a t e d t o g e t h e r t h e e x p e c t e d p r o d u c t s a r e MoS 2, X-phase, and C u 2 S . The d i f f r a c t i o n l i n e s of MoS 2 and X-phase were f o u n d i n t h e t h e M o S 2 - c o p p e r p a t t e r n , but t h e o t h e r l i n e s d i d not c o r r e s p o n d t o C u 2 S . However, C u 2 S had been f o u n d e l e c t r o c h e m i c a l l y i n t h e M o S 2 - c o p p e r m a t e r i a l . A m a t e r i a l may be p r e s e n t i n a sample, but may n o t be e v i d e n t i n a d i f f r a c t i o n p a t t e r n i f t h e m a t e r i a l i s e i t h e r p o o r l y c r y s t a l l i n e or i f t h e p a r t i c l e s a r e t o o s m a l l t o be an e f f e c t i v e d i f f r a c t i o n g r a t i n g f o r t h e X - r a y s . The s o u r c e o f one dozen l i n e s t h a t were d e t e c t e d i n a s c a n from 10 t o 90 d e g r e e s o f 2e c o u l d n ot be i d e n t i f i e d , a l t h o u g h c o m p a r i s o n s were made w i t h t h e known p a t t e r n s of C u 2 S , C u 1 < 8 S , CuS, Cu, S, Mo, M o 2 S 3 and M o 3 S „ . 63 The l a t e r m i x t u r e o f MoS 2 and c o p p e r w h i c h was h e a t e d t o 750°C showed o n l y MoS 2 and X-phase l i n e s , even t h o u g h t h i s m a t e r i a l a l s o behaved as i f t h e r e were some C u 2 S p r e s e n t . T h e r e a r e a v a r i e t y o f r e p o r t s i n t h e l i t e r a t u r e w h i c h c a n be u s e d t o i d e n t i f y t h e X - p h a s e . The t e r m "X-phase" was u s e d by G r o v e r ( 1 9 6 5 ) , Wang and Moh (1976) and Moh (1978) t o d e s c r i b e a t e r n a r y s y s t e m of c o p p e r , molybdenum, and s u l p h u r . O t h e r r e s e a r c h e r s d e s c r i b e d s i m i l a r l y p r e p a r e d compounds. C o m p a r i s o n s were t h e n made between t h e p u b l i s h e d i n f o r m a t i o n and t h e d a t a c o l l e c t e d d u r i n g t h e c o u r s e of t h e i n v e s t i g a t i o n s of t h e e x t r a Endako c a p a c i t y . A summary of a l l t h e l a t t i c e p a r a m e t e r s u s e d i n t h e t e x t of t h i s t h e s i s i s p r e s e n t e d i n A p p e n d i x I . Wang and Moh i n d e x e d t h e X-phase on a h e x a g o n a l l a t t i c e w i t h p a r a m e t e r s a=9.73A and C=10.22A. They a l s o c l a i m e d t h e c o m p o s i t i o n of t h i s m a t e r i a l t o be CuMo 2"S 3, but i n d i c a t e d t h a t t h e s t o i c h i o m e t r y was not i n p e r f e c t agreement w i t h t h i s f o r m u l a . O t h e r work was p e r f o r m e d by C h e v r e l e t . a l . (1971) on C u x M o n S n + ^ , where n was t h r e e or f o u r . C h e v r e l g r a p h e d t h e l a t t i c e p a r a m e t e r s as x v a r i e d from one t o two, and t h e g r a p h showed C u 2 M o „ S 5 was h e x a g o n a l w i t h a=9.73A and C=10.2A. Yvon e t . a l . (1977) d e s c r i b e d Cu 1 < 3 8Mo 3 S ^  a s h e x a g o n a l w i t h a = 9.713A and C=10.213A, and C u 1 > 4 7 M o 3 S „ w i t h t h e p a r a m e t e r s a=9.735A and C=10.221A. The l i n e s of t h e X-phase f o u n d i n t h e M o S 2 - c o p p e r m i x t u r e were i n d e x e d , and l e d t o t h e d e t e r m i n a t i o n o f a h e x a g o n a l u n i t c e l l w i t h a=9.73& and C=10.22A. A l a r g e number of m a t e r i a l s a l l have 64 a p p r o x i m a t e l y t h e same l a t t i c e p a r a m e t e r s , making i t d i f f i c u l t f o r X - r a y d i f f r a c t i o n a l o n e t o i d e n t i f y t h e m a t e r i a l i n t h e M o S 2 - c o p p e r m i x t u r e . The b e s t c h a r a c t e r i z e d o f t h e above m a t e r i a l s were t h e C u 9 _ M o 3 S 4 compounds w h i c h Yvon had n o t o n l y i n d e x e d , but he had a l s o d e t e r m i n e d t h e atom p o s i t i o n s . The q u a l i t y of t h e o t h e r d a t a i s unknown. I t i s p o s s i b l e t h a t e r r o r s i n t h e measurement o f t h e c o m p o s i t i o n o f a sample may have l e d t o d i f f e r e n t c h e m i c a l f o r m u l a s b e i n g a t t r i b u t e d t o t h e same m a t e r i a l , and t h e v a r i e t y o f l a t t i c e p a r a m e t e r s c o u l d be due t o a s l i g h t d i f f e r e n c e i n t h e s t o i c h i o m e t r y of t h e s a m p l e s . U s u a l l y , t h e l a t t i c e p a r a m e t e r s of a m a t e r i a l a r e p u b l i s h e d , but not t h e d i f f r a c t i o n p a t t e r n s or c h e m i c a l a n a l y s i s . The a t t e m p t t o make Cu,. 3 8Mo 3S f l, w h i c h was ' t h e i n i t i a l i d e n t i f i c a t i o n made of t h e X-phase, p r o d u c e d a m a t e r i a l w h i c h had an X - r a y d i f f r a c t i o n p a t t e r n t h a t was v e r y c l o s e t o t h a t of t h e e x p e c t e d m a t e r i a l . The h e x a g o n a l l a t t i c e p a r a m e t e r s were a= 9 . 7 2 9 A and C = 1 0 . 2 1 8 A, w h i c h c o r r e s p o n d e d t o a p p r o x i m a t e l y C u 1 > a M o 3 S « ( C h e v r e l 1 9 7 1 ) . T h e r e was a l s o a v e r y s m a l l amount of MoS 2 p r e s e n t , and t h e r e were o n l y two o t h e r weak, u n i d e n t i f i e d l i n e s i n t h e s c a n from 10 t o 9 0 ° of 2 6 . Two a t t e m p t s were made t o dope MoS 2 w i t h i r o n . The f i r s t a t t e m p t , w h i c h p r o d u c e d a m a t e r i a l w h i c h showed t h e e x t r a Endako c a p a c i t y , r e s u l t e d i n a p a t t e r n w h i c h showed no e v i d e n c e of e i t h e r MoS 2 or i r o n . The m a t e r i a l made i n t h e s e c o n d a t t e m p t , w h i c h d i d not show t h e e x t r a c a p a c i t y , o n l y had l i n e s i n i t s d i f f r a c t i o n p a t t e r n t h a t c o r r e s p o n d e d t o 65 e i t h e r MoS 2 o r t h e s t r o n g l i n e s s een i n t h e s c a n of t h e f i r s t m a t e r i a l . However, t h e s e c o n d s c a n showed no e v i d e n c e of f o u r s t r o n g l i n e s w h i c h had been seen i n t h e f i r s t p a t t e r n . The f o u r l i n e s c o u l d be i n d e x e d on a h e x a g o n a l c e l l w i t h a=9.5lA and C = 1 0 . 3 7 £ . These p a r a m e t e r s a r e w i t h i n one p e r c e n t of a m a t e r i a l t h a t Moh (1978) c a l l e d t h e i r o n -m o l ybdenum-sulphur Y-phase (a=9.52&, C=10.27A) b e c a u s e i t was a n a l o g o u s t o t h e X- p h a s e . A l s o , C h e v r e l (1971) a t t r i b u t e d a=9.564A and C=10.273A t o F e M o 5 S 6 , G u i l l e v i c e t . a l . (1976) u s e d t h e s e same p a r a m e t e r s t o d e s c r i b e Fe 0.66Mc>3S«, and S c h o l l h o r n (1977) s a i d F e M o 3 S 4 had a = 9.55A and C=10.30A. I t i s l i k e l y t h a t t h e m a t e r i a l w h i c h p r o d u c e d t h e f o u r e x t r a d i f f r a c t i o n l i n e s a l s o p r o d u c e d t h e e x t r a Endako c a p a c i t y i n t h e same way t h a t X-phase l e d t o t h i s c a p a c i t y . X - r a y d i f f r a c t i o n d i d not a l l o w a p o s i t i v e i d e n t i f i c a t i o n of t h e s o u r c e of t h e f o u r d i f f r a c t i o n l i n e s b e c a u s e a v a r i e t y o f m a t e r i a l s have l a t t i c e p a r a m e t e r s v e r y s i m i l a r t o t h e p a r a m e t e r s d e t e r m i n e d from t h e l i n e s . T r o i l i t e , FeS, was t h e o n l y o t h e r m a t e r i a l i d e n t i f i e d f rom t h e s c a n of t h e M o S 2 - i r o n m i x t u r e . P u b l i s h e d p a t t e r n s f o r FeS p y r i t e , FeS m a r c a s i t e , c u b i c FeS, F e 7 S 8 , F e 3 S 4 , FeMo ( W i l s o n 1963), F e 3 M o 2 ( G r o v e r e t . a l 1975), F e M o 2 S „ ( G u i l l e v i c 1974), M o 2 S 3 , and M o 3 S « f a i l e d t o i d e n t i f y t h e e x t r a l i n e s . E x c e p t where i n d i c a t e d , a l l t h e i r o n p a t t e r n s a r e from t h e JCPDS Powder F i l e . 66 5.4 D e t e r m i n a t i o n of L a t t i c e P a r a m e t e r s N e i t h e r t h e X-phase o r t h e M o S 2 _ i r o n m i x t u r e showed t h e b e h a v i o u r of t h e e x t r a Endako c a p a c i t y u n t i l i t had gone t h r o u g h a f i r s t o r d e r phase t r a n s i t i o n . I n v e s t i g a t i o n s of the m a t e r i a l formed i n t h i s t r a n s i t i o n were made u s i n g t h e X - r a y c e l l d e s c r i b e d i n C h a p t e r 2. The i n - s i t u X - r a y d i f f r a c t i o n t e c h n i q u e made i t p o s s i b l e t o o b t a i n t h e d i f f r a c t i o n p a t t e r n a t v a r i o u s s t a t e s o f c h a r g e , and p r o v i d e d a way o f d i s t i n g u i s h i n g between a f i r s t o r d e r phase t r a n s i t i o n and a c o n t i n u o u s e x p a n s i o n of t h e l a t t i c e . The c e l l was c y c l e d a few t i m e s t h r o u g h t h e 1.86V phase t r a n s i t i o n t o i n s u r e f u l l p h ase c o n v e r s i o n t o t h e m a t e r i a l w h i c h p r o d u c e d t h e e x t r a Endako c a p a c i t y . A f t e r w a r d s , t h e c e l l was a t t a c h e d t o a PAR 173 P o t e n t i o s t a t / G a l v a n o s t a t and was a l l o w e d t o e q u i l i b r a t e t o t h e p o t e n t i a l s e t on t h e PAR. The c e l l was c o n s i d e r e d t o be e q u i l i b r a t e d when t h e c u r r e n t f l o w i n g t h r o u g h i t r e d u c e d t o t h e o r d e r of one mic r o a m p e r e , and t h e s c a n of t h e d i f f r a c t i o n p a t t e r n was t h e n made. A t t e m p t s were made t o g u e s s t h e M i l l e r i n d i c i e s of t h e l i n e s by a s s u m i n g t h e c r y s t a l t o be h e x a g o n a l and u s i n g t h e p a t t e r n s f o r C u 2 _ x M o 3 S a and M o 3 S „ as g u i d e s . A l e a s t s q u a r e s e s t i m a t e o f t h e a and c p a r a m e t e r s of t h e c r y s t a l was made from t h e a n g l e s of t h e l i n e s and t h e i r assumed i n d i c e s . A c a l c u l a t e d d i f f r a c t i o n p a t t e r n was t h e n g e n e r a t e d u s i n g t h e s e p a r a m e t e r s , w h i c h i n t u r n was us e d t o h e l p g u e s s t h e i n d i c e s of more l i n e s . T h i s p r o c e d u r e was r e p e a t e d u n t i l t h e p a t t e r n was f u l l y i n d e x e d . The agreement between t h e o b s e r v e d and c a l c u l a t e d d s p a c i n g s was e s t i m a t e d by 67 c o m p u t i n g t h e sum o f t h e s q u a r e s o f the d i f f e r e n c e s of t h e s e two v a l u e s . I t was t h e n p o s s i b l e t o make a c o m p a r i s o n o f t h e f i t t o a x 2 d i s t r i b u t i o n by d i v i d i n g t h e sum o f s q u a r e s by t h e number of i n d e x e d l i n e s . A c o r r e c t i o n had t o be made t o t h e o b s e r v e d l i n e p o s i t i o n s b e f o r e t h e l a t t i c e p a r a m e t e r s c o u l d be e s t i m a t e d . The powder d i f f T a c t o m e t e r was a l i g n e d t o measure a n g l e s r e l a t i v e t o t h e a x i s of t h e g o n i o m e t e r . The c o n s t r u c t i o n o f t h e X - r a y c e l l f o r c e s t h e a c t i v e m a t e r i a l out o f t h e m e a s u r i n g p l a n e by a d i s t a n c e 6 g i v e n by 6 = R { s i n 0 - t a n 9^  cos 6 } (7) m B m where R i s t h e d i s t a n c e f r o m t h e sample t o t h e d e t e c t o r - -173mm, 9 m i s t h e measured a n g l e , and G-g i s t h e t r u e B r a g g a n g l e . The out of p l a n e c o r r e c t i o n was d e t e r m i n e d by u s i n g t h e known and measured p o s i t i o n s of the MoS 2 l i n e s . A summary of t h e p o s i t i o n s of- t h e d i f f r a c t i o n l i n e s and t h e i r M i l l e r i n d i c i e s a r e g i v e n i n A p p e n d i x I I . L a t t i c e p a r a m e t e r s of a=9.l96A and C=10.891A were o b t a i n e d when t h e m a t e r i a l w h i c h p r o d u c e d t h e e x t r a Endako c a p a c i t y was f u l l y c h a r g e d t o 2.700V. The x 2 v a l u e of 0.00978 showed e x c e l l e n t agreement between t h e o b s e r v e d and c a l c u l a t e d p a t t e r n s . The l a t t i c e p a r a m e t e r s f o r Mo 3Si,, as r e p o r t e d by Yvon, were a=9.202A and C=10.877A. T h e s e numbers f o r M o 3 S „ a r e o n l y a b o u t 0.1 p e r c e n t d i f f e r e n t from t h e l a t t i c e p a r a m e t e r s c a l c u l a t e d f r o m t h e phase . c o n v e r t e d X-phase m a t e r i a l . C h e v r e l (1974) a l s o p u b l i s h e d t h e i n t e n s i t y d a t a f o r a M o 3 S „ s c a n , and t h e X - r a y c e l l d a t a i s i n 68 q u a l i t a t i v e agreement w i t h t h a t . The o n l y d i f f e r e n c e s i n t h e i n t e n s i t y d a t a were s m a l l enough t o be a t t r i b u t e d t o p r e f e r e n t i a l o r i e n t a t i o n of powder i n t h e c e l l . The l a t t i c e p a r a m e t e r s were a l s o computed above and o below t h e phase t r a n s i t i o n . At 2.100V t h e a a x i s was 9.358A and t h e c a x i s was 10.725A. The x 2 v a l u e was 0.020, i n d i c a t i n g a f a i r f i t . The c e l l p o t e n t i a l was below t h e p hase t r a n s i t i o n and i n t h e r e g i o n of s i n g l e p h a s e c a p a c i t y a t 2.050V. Here a was 9.754A and c was 10.589A w i t h a x 2 o f 0.00955. The e x t r a Endako c a p a c i t y was f u l l y d i s c h a r g e d a t 1.800V and a was c a l c u l a t e d t o be 9.795A and c was 10.553A w i t h a x 2 of 0.0398. T h i s was a r a t h e r p o o r f i t of t h e l a t t i c e p a r a m e t e r s t o t h e o b s e r v e d d a t a , and i t a r o s e b e c a u s e many of t h e d i f f r a c t i o n l i n e s were e i t h e r b r o a d and p o o r l y d e f i n e d , o r t h e y c o i n c i d e d w i t h l i n e s from t h e c e l l c a s e . O b s e r v e d and p r e d i c t e d l i n e p o s i t i o n s d i f f e r e d by a l m o s t as much as two t e n t h s of a d e g r e e a t 60° of 26. The l a t t i c e p a r a m e t e r s o b t a i n e d were w i t h i n h a l f a p e r c e n t o f t h o s e r e p o r t e d by C h e v r e l e t . a l . (1971) f o r L i 2 M o 2 S 3 --a=9.728A and C=10.525A, however o n l y t h e s i z e of t h e l a t t i c e was l i s t e d , and no d a t a was p u b l i s h e d on t h e i n t e n s i t y of t h e d i f f r a c t i o n l i n e s . I t would be u n l i k e l y t h a t t h e 1.800V m a t e r i a l would be L i 2 M o 2 S 3 b e c a u s e M o 2 S 3 was d i s c o v e r e d t o have no c a p a c i t y . I t was p o s s i b l e t h a t L i 2 M o 3 S ( , c o r r e s p o n d e d t o t h e d i s c h a r g e d m a t e r i a l and t h a t i t had a u n i t c e l l o f a p p r o x i m a t e l y t h e same s i z e as d i d L i 2Mo 2 S 3 . 69 T h e r e was a t r e n d f o r t h e u n i t c e l l of t h e c r y s t a l t o expand as t h e c e l l was d i s c h a r g e d . I t was 797.5A 3 a t 2.700V and i t grew t o 813.4& 3 a t 2.100V. T h e r e was a l a r g e i n c r e a s e i n t h e c r y s t a l volume as t h e b a t t e r y went t h r o u g h t h e f i r s t o r d e r t r a n s i t i o n and some of i t s s i n g l e p h a s e c a p a c i t y . At 2.050V t h e u n i t c e l l was 872. 4A"3. The f u l l y d i s c h a r g e d m a t e r i a l a t 1.800V had a volume o f 876.97A3. Even t h o u g h t h e l e a s t s q u a r e s f i t s t o t h e l a t t i c e p a r a m e t e r s were not as p r e c i s e as was hoped, t h e d a t a does i n d i c a t e t h a t t h e u n i t c e l l volume i n c r e a s e s as more l i t h i u m i s a d d e d . Many m a t e r i a l s of t h e t y p e MMOnSn+i' where M i s a m e t a l and n i s an i n t e g e r from two t o s i x , have a p p r o x i m a t e l y t h e same s i z e d l a t t i c e s , w h i c h makes i t d i f f i c u l t t o i d e n t i f y one of t h e s e m a t e r i a l s s o l e l y on t h e b a s i s of t h e l a t t i c e p a r a m e t e r s . However, b o t h t h e l a t t i c e p a r a m e t e r s and t h e i n t e n s i t y d a t a f o r t h e Mo 3Si, showed e x c e l l e n t agreement w i t h t h e d a t a f o r t h e f u l l y c h a r g e d m a t e r i a l w h i c h p r o d u c e s th e e x t r a Endako c a p a c i t y . The e x t r a Endako c a p a c i t y can a l s o be e x p l a i n e d i n terms of i n t e r c a l a t i o n i n t h e M o 3 S « s t r u c t u r e by a n a l o g y w i t h Yvon's work on Cu„ M o 3 S „ . E v e n t u a l l y , d a t a on t h e e l e c t r o c h e m i c a l b e h a v i o u r of M o 3 S „ was "found i n a p a p e r by S c h o l l h o r n (1977). T h e r e were p r o b l e m s w i t h S c h o l l h o r n ' s d a t a c o l l e c t i o n t e c h n i q u e s , as w i l l be d i s c u s s e d i n C h a p t e r 6, but h i s i n f o r m a t i o n a l s o i n d i c a t e d t h e same c o n c l u s i o n : t h e s o u r c e o f t h e e x t r a Endako c a p a c i t y was M o 3 S „ . 70 5.5 I n t e r c a l a t i o n i n M o 3 S „ F u r t h e r X - r a y e x a m i n a t i o n s e x p l o r e d o t h e r p r o p e r t i e s o f t h e e x t r a Endako c a p a c i t y . The e l e c t r o c h e m i c a l b e h a v i o u r o f t h e M o 3 S „ i n d i c a t e d t h a t t h e 2.45V c a p a c i t y was i n t e r c a l a t i o n and t h e c a p a c i t y n e a r 2.09V was a phase t r a n s i t i o n i n v o l v i n g e i t h e r a d i s p l a c e m e n t r e a c t i o n o r an i n t e r c a l a t i o n . T h e s e p r e d i c t i o n s were c o n f i r m e d i n an e x p e r i m e n t where an X - r a y c e l l was c h a r g e d from 1,800V t o 2.700V o v e r a s i x hour p e r i o d and e v e r y t e n m i n u t e s s c a n s were t a k e n of two r a n g e s of a n g l e s . F i g u r e 25 shows t h e b e h a v i o u r of t h e (101) l i n e a s t h e c e l l v o l t a g e c h a n ges from 2.04V t o 2.20V, and F i g u r e 26 shows t h e (212) and (104) l i n e s o v e r t h e same v o l t a g e r a n g e . As t h e v o l t a g e r o s e , a l i n e a p p e a r e d a t 13.92° w h i l e t h e i n t e n s i t y of t h e beam a t 13.67° d r o p p e d . S i m i l a r l y , t h e (104) l i n e moved d i s c o n t i n u o u s l y from 35.72° t o 35.43° and t h e (212) l i n e d i s a p p e a r e d from 33.01° t o r e a p p e a r a t 3 3 . 9 0 ° . As would be e x p e c t e d i n a f i r s t o r d e r t r a n s i t i o n , t h e r e a r e two d i f f e r e n t l a t t i c e s w i t h d i f f e r e n t p a r a m e t e r s and as t h e l i t h i u m c o n t e n t i s a l t e r e d t h e c r y s t a l c h a n g e s from one o f t h e s e s t r u c t u r e s t o t h e o t h e r . Y e t , even t h o u g h t h e r e i s a f i r s t o r d e r t r a n s i t i o n , t h e l i n e s on e i t h e r s i d e of t h e t r a n s i t i o n c an be i n d e x e d w i t h t h e same M i l l e r i n d i c e s , and t h e c o r r e s p o n d i n g l i n e s have a p p r o x i m a t e l y t h e same i n t e n s i t i e s . T h i s means t h a t t h e h o s t l a t t i c e i s not b e i n g g r e a t l y a l t e r e d as t h e l i t h i u m i s i n s e r t e d , and a s s u c h t h e r e v e r s i b l e i n s e r t i o n i s an i n t e r c a l a t i o n . F i g u r e 26 a l s o shows a s m a l l l i n e a t 33.30° w h i c h i s c a u s e d by t h e I I I I I I I 1 I I 1 I 1 I I I I I I I I I I I I I 13.0 14.0 13.0 14.0 13.0 14.0 13.0 14.0 13.0 14.0 20(°) 20(°) 20(°) 20(°) 20(°) Figure 25 -- (101) D i f f r a c t i o n Line Between 2.04 and 2.2V C e l l PMX-11 ^10 mg cathode of "X-Phase" material The diagrams correspond to 2.04V, 2.103V, 2.109V, 2.128V, and 2.20V respectively. to c D -•-» D 0) C Figure 26 -- (104) and (212) D i f f r a c t i o n Lines Between 2.04 and 2.2V Cel l PMX-11 ^10 mg cathode of "X-Phase" material The diagrams correspond to 2.08V, 2.108V, and 2.20V respectively, N 3 73 c e l l c a s e and i s not p a r t of t h e i n t e r c a l a t i o n s y s t e m . F i g u r e 27 shows t h e p o s i t i o n s of t h e (104) and (212) l i n e s a s t h e c e l l i s c h a r g e d from 2.3V t o 2.6V. F i g u r e 28 shows t h e (223) l i n e on a d i s c h a r g e c y c l e between 2.5V and 2.1V. T h e s e l i n e s s l o w l y c h a n g e d t h e i r p o s i t i o n s by a b o u t h a l f a d e g r e e of 29 as t h e amount o f l i t h i u m was v a r i e d . The p o s i t i o n change i s p r e s e n t i n a l l l i n e s , but i n some, s u c h as t h e ( 1 0 1 ) , i t i s a s u b t l e e f f e c t and h a r d t o s e e . The l i t h i u m / M o 3 S 4 s y s t e m does not have two d i f f e r e n t c r y s t a l s t r u c t u r e s n e a r 2.46 v o l t s , and i n s t e a d t h e l a t t i c e c a n c o n t i n u o u s l y v a r y i t s s i z e as t h e c o n c e n t r a t i o n of l i t h i u m i s c h a n g e d . T h i s i s t h e b e h a v i o u r n o r m a l l y a s s o c i a t e d w i t h i n t e r c a l a t i o n . The s i n g l e p hase c a p a c i t y below t h e phase t r a n s i t i o n was a l s o i n t e r c a l a t i o n . F i g u r e 29 shows t h e c o n t i n u o u s movement of t h e (104) and (212) l i n e s a s t h e c e l l p o t e n t i a l was swept t h r o u g h t h i s r e g i o n . The p o s i t i o n s of t h e l i n e s s h i f t e d by a b o u t 0.05 d e g r e e s of 20, w h i c h i s d i f f i c u l t t o d e t e c t from t h e f i g u r e . The d i f f r a c t i o n l i n e s a r e b r o a d e n e d w h i l e c u r r e n t i s f l o w i n g b e c a u s e of d i f f u s i o n e f f e c t s . D i f f e r e n t p a r t s of t h e c r y s t a l have d i f f e r e n t l i t h i u m c o n t e n t s , and t h u s d i f f e r e n t l a t t i c e p a r a m e t e r s . E a c h p a r t of t h e c r y s t a l t h e n d i f f r a c t s X - r a y s a t s l i g h t l y d i f f e r e n t a n g l e s . S i n c e t h e l a t t i c e i s not g r e a t l y d i s t o r t e d , even i n t h e f i r s t o r d e r phase- t r a n s i t i o n , and s i n c e as many coulombs f l o w on c h a r g e as on d i s c h a r g e , t h e l i t h i u m / M o 3 S „ s y s t e m can be c l a s s i f i e d as an i n t e r c a l a t i o n b a t t e r y . CO o *JQ D CO C CD 1 1 1 I I I _ _ (212) "/Ay (104) -LA; I I I I I I 33 34 35 20(°) 36 Figure 27 -- (104) and (212) D i f f r a c t i o n Lines Between 2.4 and 2.6V Cell PMX-11 ^10 mg cathode of "X-Phase" material The diagrams correspond to 2.4V, 2.44V, and 2.6V respectively, CO o o CO c I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 46 48 46 47 20(°) 48 47 48 46 47 48 46 47 20(°) 20(°) 20(°) Figure 28 -- (223) D i f f r a c t i o n Line Between 2.5 and 2.1V Cell PMX-11 ^10 mg cathode of "X-Phase" material The diagrams correspond to 2.507V, 2.44V, 2,41V, and 2.12V respectively, 111111111111111 1 1 1 1 1 1 1 1 1 1 1 1 1 11 III 1111111 33 34 35 36 33 34 35 36 33 34 35 36 20(°) 20(°) 20(°) Figure 29 -- (104) and (212) D i f f r a c t i o n Lines Between 1.84 and 2.08V Cel l PMX-11 ^10 mg cathode of "X-Phase material The diagrams correspond to 1.84V, 2.04V, and 2.08V respectively. 77 The M o S 2 _ i r o n m i x t u r e was a l s o X - r a y e d a f t e r i t had been d r i v e n t h r o u g h t h e phase t r a n s i t i o n w h i c h p r o d u c e d t h e e x t r a Endako c a p a c i t y , and t h e l i n e s t h a t a p p e a r e d a f t e r t h e phase c o n v e r s i o n c o r r e s p o n d e d t o t h e l i t h i u m i n t e r c a l a t e d M o 3 S „ . However, v e r y few o f t h e l i n e s from t h e M o 3 S „ s y s t e m c o u l d be d e t e c t e d b e c a u s e o f t h e l a r g e number o f o t h e r l i n e s i n t h e p a t t e r n , and so i t was d i f f i c u l t t o g e t a good e s t i m a t e o f t h e l a t t i c e p a r a m e t e r s . The l i n e s t h a t were o b s e r v e d were w i t h i n e x p e r i m e n t a l e r r o r of t h o s e seen i n t h e p a t t e r n s from t h e c e l l s made w i t h t h e X-phase m a t e r i a l . 78 CHAPTER 6 RESULTS AND DISCUSSION 6.1 I n t e r p r e t a t i o n of R e s u l t s The d i s c o v e r y of t h e e x t r a Endako c a p a c i t y m o t i v a t e d e x p e r i m e n t s d e s i g n e d t o t r y and i d e n t i f y and r e p r o d u c e i t s s o u r c e . I t was l e a r n e d t h a t t h i s c a p a c i t y c o u l d be p r o d u c e d from m a t e r i a l s made d u r i n g t h e h e a t i n g o f MoS 2 w i t h e i t h e r i r o n or c o p p e r , or from t h e c o p p e r - m o l y b d e n u m - s u l p h u r X-p h a s e . T h e s e powders a l l p r o d u c e d e s s e n t i a l l y t h e same e l e c t r o c h e m i c a l b e h a v i o u r a f t e r t h e y were b r o u g h t t h r o u g h a f i r s t o r d e r phase t r a n s i t i o n a r o u n d 1.8 v o l t s , i n d i c a t i n g t h a t t h e m a t e r i a l w h i c h p r o d u c e d t h e e x t r a Endako c a p a c i t y was p r o b a b l y t h e p r e f e r r e d c r y s t a l s t r u c t u r e when l i t h i u m was p r e s e n t . The e x t r a Endako c a p a c i t y p r o d u c e d as a r e s u l t of r e a c t i n g MoS 2 w i t h c o p p e r or i r o n seemed t o be t h e same i r r e s p e c t i v e of t h e m e t a l . I t was o b v i o u s t h a t i t was t h e l o c a l m o lybdenum-sulphur e n v i r o n m e n t t h a t gave r i s e t o t h i s c a p a c i t y . T h i s e n v i r o n m e n t c o u l d have been p r o d u c e d i n two ways. F i r s t , a b i n a r y m o l y b d e n u m - s u l p h u r phase c o u l d have been formed as a r e s u l t of t h e f i r s t o r d e r phase t r a n s i t i o n t h a t was seen w i t h b o t h t h e m a t e r i a l s . S e cond, t h e t r a n s i t i o n c o u l d have been a n a l o g o u s t o t h e MoS 2 a t o p phase t r a n s i t i o n where t h e s t r u c t u r e i s a l t e r e d a l t h o u g h t h e c o m p o s i t i o n r e m a i n s e s s e n t i a l l y t h e same. I t was p o s s i b l e t h a t t h e molybdenum-sulphur e n v i r o n m e n t n eeded f o r t h e e x t r a 79 Endako c a p a c i t y c o u l d o n l y e x i s t i f a n o t h e r m e t a l s t a b i l i z e d t h e c r y s t a l . X - r a y d i f f r a c t i o n e x p e r i m e n t s p e r m i t t e d a b e t t e r u n d e r s t a n d i n g of t h e e x t r a Endako c a p a c i t y . The c a p a c i t y was f o u n d t o be a complex i n t e r c a l a t i o n s y s t e m where not o n l y were t h e r e r e g i o n s o f c o n t i n u o u s l a t t i c e e x p a n s i o n , but t h e r e was a l s o a f i r s t o r d e r t r a n s i t i o n w h i c h d i d n o t g r e a t l y a l t e r t h e h o s t l a t t i c e . The l a t t i c e p a r a m e t e r s of t h e f u l l y c h a r g e d m a t e r i a l were w i t h i n 0.1 p e r c e n t of t h o s e p u b l i s h e d f o r M o 3 S „ , however t h i s was i n s u f f i c i e n t t o u n a m b i g u o u s l y i d e n t i f y t h e s o u r c e of t h e c a p a c i t y . Many o f t h e m e t a l - M o n S n +-^ compounds had v e r y s i m i l a r l a t t i c e s i z e s , and t h e r e was a p o s s i b i l i t y t h a t t h e s o u r c e of t h e e x t r a Endako c a p a c i t y was one of t h e s e . T h e r e was a l s o e x c e l l e n t agreement between t h e measured i n t e n s i t y d a t a and t h a t p u b l i s h e d by C h e v r e l (1974) f o r M o 3 S „ and i t was u n l i k e l y t h a t one o f t h e o t h e r m a t e r i a l s c o u l d be a b e t t e r f i t t o t h e d a t a . The l i t e r a t u r e c o n t a i n e d r e f e r e n c e s t o metal-Mo S ,., n n+1 m a t e r i a l s w h i c h were c l a i m e d t o be M o 3 S « compounds. S c h o l l h o r n ' s p a r t i a l l y s u c c e s s f u l work on a l k a l i m e t a l s i n M o 3 S „ (1977) was o f p a r t i c u l a r i n t e r e s t . C o n f i r m a t i o n t h a t M o 3 S „ was t h e h o s t came from l a t e r work o f S c h o l l h o r n ' s (1979) i n w h i c h s i m i l a r l y p r e p a r e d samples were u s e d . Yvon e t . a l . (1977) had been s u c c e s s f u l i n e s t a b l i s h i n g t h e p r o p e r t i e s of s e v e r a l M o 3 S „ compounds, and S c h o l l h o r n ' s 1979 work on c o p p e r i n M o 3 S „ was i n r e a s o n a b l e agreement w i t h d a t a from Yvon's Cu M o 3 S „ c r y s t a l s . 80 The q u a l i t y o f S c h o l l h o r n ' s d a t a was q u i t e p o o r , p r i m a r i l y b e c a u s e o f s e v e r e d i f f u s i o n p r o b l e m s . U s u a l l y , c l e a r d a t a c an o n l y be o b t a i n e d from a l i n e a r sweep voltammogram i f one c y c l e o f t h e c e l l l a s t s s e v e r a l d a y s , y e t t e n m i n u t e s was a t y p i c a l c y c l e t i m e i n S c h o l l h o r n ' s work. The d a t a from c o n s t a n t c u r r e n t c y c l i n g was b e t t e r , a l t h o u g h t h e r e was some d i f f u s i o n b l u r r i n g of t h e f e a t u r e s . I t was p o s s i b l e t o d e t e r m i n e some o f t h e g e n e r a l c h a r a c t e r i s t i c s of t h e l i t h i u m / M o 3 S i , c e l l from t h e d a t a , but two g r a p h s t h a t were s u p p o s e d t o show a s i m i l a r d i s c h a r g e were c o n s i d e r a b l y d i f f e r e n t . T h e r e was a r e g i o n of c a p a c i t y f o l l o w e d by a d r o p of a few t e n t h s o f a v o l t , and t h e n t h e r e was a s e c o n d r e g i o n of c a p a c i t y r o u g h l y two t o t h r e e t i m e s as l a r g e a s t h e f i r s t . T h i s i s i n q u a l i t a t i v e agreement w i t h t h e b e h a v i o u r of t h e e x t r a Endako c a p a c i t y . The c o m b i n a t i o n of e l e c t r o c h e m i c a l and X - r a y a n a l y s e s e s t a b l i s h e d the s o u r c e of t h e e x t r a Endako c a p a c i t y t o be M o 3 S a . F u r t h e r e v i d e n c e i n s u p p o r t of t h i s c o n c l u s i o n came w i t h t h e d i s c o v e r y of S c h o l l h o r n ' s s i m i l a r d a t a . A q u a l i t a t i v e e x p l a n a t i o n o f t h e b e h a v i o u r of t h e e x t r a Endako c a p a c i t y c an be b a s e d on Yvon's d e s c r i p t i o n of C u 9 M o 3 S a . These c r y s t a l s c o n s i s t of g r o u p s o f M o 6 S 8 b u i l d i n g b l o c k s w i t h t h e s u l p h u r s f o r m i n g a rhomboid i n s i d e t h e b l o c k s , and t h e molybdenum atoms f o r m i n g an o c t a h e d r o n by s i t t i n g n e a r t h e rhomboid f a c e s . E a c h u n i t c e l l of t h e c r y s t a l had two s e t s of s i x e q u i v a l e n t s i t e s , c a l l e d t h e t y p e one and t y p e two s i t e s , i n w h i c h t h e c o p p e r c o u l d s i t . 81 The t y p e one s i t e s were p r e f e r e n t i a l l y f i l l e d a t low c o p p e r c o n c e n t r a t i o n s . The o c c u p a n c y o f t h e t y p e two s i t e s r o s e as t h e amount c o p p e r was i n c r e a s e d , and some o f t h e c o p p e r was f o r c e d o u t o f t h e f i r s t p o s i t i o n s . The b e h a v i o u r of t h e l i t h i u m / M o 3 S i , s y s t e m may be e x p l a i n e d by a n a l o g y w i t h t h e c o p p e r s y s t e m . The 2.46V c a p a c i t y m i g h t r e p r e s e n t t h e i n t e r c a l a t i o n o f l i t h i u m i n t o t h e t y p e one s i t e s . Yvon c l a i m e d t h a t t h e i n t e r c a l a t e d atoms a r e i o n i z e d , so e l e c t r o s t a t i c r e p u l s i o n c o u l d p r e v e n t f i l l i n g a l l s i x of t h e f i r s t s i t e s . One q u a r t e r of t h e o f t h e t o t a l c a p a c i t y c o u l d be a s s o c i a t e d w i t h f i l l i n g one of t h e s i x t y p e one s i t e s i n e a c h u n i t c e l l . The c e l l p o t e n t i a l w i l l d r o p when as many as p o s s i b l e of t h e t y p e one s i t e s a r e o c c u p i e d , and i t w i l l c o n t i n u e t o d r o p u n t i l t h e t y p e two s i t e s can f i l l . The e l e c t r o s t a t i c r e p u l s i o n between i o n s i n a t y p e one and a t y p e two s i t e m i ght be g r e a t e r t h a n t h e r e p u l s i o n between two i o n s i n t y p e two s i t e s . This' r e p u l s i o n might be s u f f i c i e n t t o move i o n s i n t y p e one s i t e s i n t o t y p e two p o s i t i o n s i f l i t h i u m i s put i n t o a t y p e two s i t e . I f a d d i n g more l i t h i u m c a u s e s t h i s major r e d i s t r i b u t i o n o f t h e i o n s a l r e a d y p r e s e n t , t h e n t h i s would be a f i r s t o r d e r phase t r a n s i t i o n of t h e g u e s t atoms, and i t need not g r e a t l y a l t e r t h e h o s t s t r u c t u r e . About h a l f t h e c a p a c i t y i s a s s o c i a t e d w i t h t h e phase t r a n s i t i o n , and t h i s would c o r r e s p o n d t o a d d i n g two l i t h i u m s t o e a c h M o 6 S 8 u n i t c e l l . I t may be t h a t i t i s e n e r g e t i c a l l y f a v o u r a b l e t o add a l i t h i u m t o a u n i t c e l l w h i c h has two l i t h i u m s i n t y p e two p o s i t i o n s r a t h e r t h a n add t h e i o n t o a c e l l w h i c h has a t y p e one s i t e 82 o c c u p i e d . The s i n g l e p h a s e c a p a c i t y below t h e phase t r a n s i t i o n would t h e n r e p r e s e n t t h e f i l l i n g of t h e u n i t c e l l t o t h e l i m i t , p r o b a b l y L i f t M o 6 S 8 . The s m a l l f e a t u r e s n e a r 1.83V may r e p r e s e n t i n t e r a c t i o n s between d i f f e r e n t u n i t c e l l s i m p o s i n g some s o r t o f o r d e r on t h e l i t h i u m g u e s t s , but t h e r e i s no e v i d e n c e a v a i l a b l e t o s u p p o r t t h i s l a s t s u p p o s i t i o n . C e l l s made w i t h t h e Endako powder, t h e X-phase, or t h e M o S 2 - i r o n m a t e r i a l d i d not show t h e M o 3 S „ b e h a v i o u r u n t i l t h e b a t t e r y was d i s c h a r g e d below a b o u t 1.8V. C h a p t e r 3 p o i n t e d out t h a t t h e main d i f f e r e n c e s between Endako c e l l s a l w a y s kept above 1.8V and t h o s e t h a t had been d i s c h a r g e d below t h i s p o t e n t i a l were t h a t t h e c e l l s b r o u g h t t h r o u g h t h e 1.8V t r a n s i t i o n had c a p a c i t y n e a r 2.46V and t h e t o t a l c a p a c i t y above two v o l t s i n c r e a s e d . T h i s can be e x p l a i n e d i n t e r m s of t h e same model of g u e s t atoms f i l l i n g s i t e s i n t h e M o 3 S a . The M o 3 S „ can not be formed u n l e s s t h e r e i s a n o t h e r m e t a l p r e s e n t t o s t a b i l i z e t h e s t r u c t u r e . I f t h i s m e t a l s a t i n a t y p e one s i t e , t h e n t h e l i t h i u m would be p r e v e n t e d from e n t e r i n g t h e s e p o s i t i o n s . T h i s would e l i m i n a t e t h e 2.46V c a p a c i t y . B o t h t h e f i r s t and s e c o n d t y p e s of t h e e x t r a Endako c a p a c i t y have c a p a c i t y between 2.0 and 2.1 v o l t s . T h i s would c o r r e s p o n d t o the l i t h i u m e n t e r i n g t h e v a c a n t t y p e two s i t e s . I f a t some v o l t a g e i t i s e n e r g e t i c a l l y f a v o u r a b l e f o r l i t h i u m t o d i s p l a c e t h e i m p u r i t y m e t a l , t h e n t h i s would c a u s e t h e t r a n s i t i o n from t h e f i r s t t y p e of b e h a v i o u r t o t h e t o t h e s e c o n d t y p e . The maximum l i t h i u m c o n t e n t p e r u n i t c e l l i s not 83 d e t e r m i n e d by t h e t o t a l number o f s i t e s . Yvon (1977) s t a t e d t h a t " t h e M o 6 S 8 c l u s t e r s h o u l d be r e g a r d e d as a pseudo-atom a c t i n g a s an e l e c t r o n a c c e p t o r . O n l y f o u r e l e c t r o n s a r e n e c e s s a r y t o f i l l t h e Mo-Mo bond o r b i t a l s c o m p l e t e l y . . . " . T h i s c an be modeled by c o n s i d e r i n g t h e t h i r t y a t o m i c molybdenum d - o r b i t a l s i n e a c h u n i t c e l l and s e e i n g how t h e bands a r e s p l i t by t h e s u l p h u r i o n s . E a c h of t h e molybdenums has f i v e s u l p h u r s as n e a r e s t n e i g h b o u r s : f o u r f o r m t h e c o r n e r s of t h e rhomboid f a c e n e a r w h i c h t h e molybdenum s i t s ; and one o t h e r i s i n t h e a d j a c e n t u n i t c e l l . A l l f i v e i o n s a r e a p p r o x i m a t e l y e q u i d i s t a n t from t h e molybdenum. The d e g e n e r a c y of t h e molybdenum's d - o r b i t a l s would be l i f t e d by t h e p r e s e n c e of t h e s u l p h u r atoms. I t i s l i k e l y t h a t one of t h e s e o r b i t a l s has a lower e n e r g y t h a n t h e o t h e r s , and i t can accomodate two e l e c t r o n s p e r molybdenum. S i x t e e n of t h e t w e n t y - f o u r molybdenum d - e l e c t r o n s i n e a c h c e l l a r e u s e d t o i o n i z e t h e s u l p h u r and t h e o t h e r e i g h t e n t e r t h e l o w e s t e n e r g y d-band. T h i s l e a v e s f o u r u n o c c u p i e d s t a t e s i n t h i s band w h i c h can be f i l l e d w i t h e l e c t r o n s from i o n i z e d l i t h i u m . The c o m p o s i t i o n L i 2 M o 3 S u would r e p r e s e n t t h e f i l l i n g of t h e l o w e s t e n e r g y d-band of t h e M o 6 S 8 . 6.2 S u g g e s t i o n s f o r F u t u r e Work Many of t h e q u e s t i o n s r a i s e d by t h e d i s c o v e r y o f M o 3 S „ t o be an i n t e r c a l a t i o n h o s t c a n o n l y be answered i f a s o u r c e of e s s e n t i a l l y p u r e m a t e r i a l i s o b t a i n e d . M o 3 S „ c a n n o t be p r o d u c e d d i r e c t l y from t h e e l e m e n t s , but i t i s p o s s i b l e t o make m e t a l - M o 3 S „ compounds. T h e s e t e r n a r y compounds c a n t h e n • 84 be e i t h e r a c i d e t c h e d ( C h e v r e l 1974) or d e i n t e r c a l a t e d ( S c h o l l h o r n 1977,1979) t o remove t h e e x t r a m e t a l . Work s h o u l d be done t o f i n d w h i c h of t h e s e two methods i s t h e most c o n v e n i e n t t o p r o d u c e M03Sfl f r e e from m e t a l c o n t a m i n a t i o n . S c h o l l h o r n ' s work on t h e e l e c t r o c h e m i c a l p r o p e r t i e s o f M o 3 S a s h o u l d be r e p e a t e d u s i n g a c c u r a t e v o l t a m m e t r y and X-r a y s t u d i e s . Much o f h i s work on c o p p e r i n t e r c a l a t e d Mo 3S f l i s i n c o n s i s t e n t ( 1 9 7 9 ) , p r o b a b l y b e c a u s e of t h e l a r g e d i f f u s i o n p r o b l e m s i n d u c e d by h i s methods. S i m i l a r p r o b l e m s e x i s t i n h i s e a r l i e r work (1977) w i t h l i t h i u m and o t h e r m e t a l s . S c h o l l h o r n a l s o c l a i m e d t h a t x c a n n o t e x c e e d 1.8 i n L i x M o 3 S a , and Yvon i m p l i c i t l y p r e d i c t e d x would e q u a l two. T h i s s h o u l d be r e l a t i v e l y e a s y t o d e t e r m i n e w i t h a p u r e M o 3 S „ sample. A n o t h e r , and more d i f f i c u l t , q u e s t i o n r e g a r d s how t h e l i t h i u m o c c u p i e s t h e s i t e s . I t was s u g g e s t e d - t h a t t h e l i t h i u m f i r s t f i l l e d one t y p e of s i t e p r e f e r e n t i a l l y and t h e n underwent a phase t r a n s i t i o n t o a d i f f e r e n t s i t e as t h e c o n c e n t r a t i o n i n c r e a s e d . T h i s must be e xamined. I n t e n s i t y d a t a from X - r a y d i f f r a c t i o n would not be v e r y e f f e c t i v e i n f i n d i n g t h e p o s i t i o n s of t h e l i t h i u m b e c a u s e t h e s e atoms o n l y weakly s c a t t e r X - r a y s . L i t h i u m i s an e f f e c t i v e n e u t r o n s c a t t e r e r , so i t may be p o s s i b l e t o f i n d t h e atom p o s i t i o n s from n e u t r o n d i f f r a c t i o n . O t h e r m e t a l s i n t e r c a l a t e d i n M o 3 S « m i g h t a l s o show b e h a v i o u r s i m i l a r t o t h a t a s s o c i a t e d w i t h l i t h i u m / M o ^ n , i . e . two r e g i o n s ' of c a p a c i t y w i t h c o n t i n u o u s l a t t i c e 85 e x p a n s i o n and an i n t e r c a l a t i o n f i r s t o r d e r phase t r a n s i t i o n . I f t h e m e t a l i s a good X - r a y s c a t t e r e r , t h e n t h e p o s i t i o n s of t h e atoms c o u l d be d e t e r m i n e d from t h e i n t e n s i t i e s of t h e s c a t t e r e d beams. I f c o n s i s t e n t r e s u l t s a r e o b t a i n e d w i t h s e v e r a l s i n g l y i o n i z e d m e t a l s , t h e n i t c o u l d be a r g u e d t h a t l i t h i u m would p r o b a b l y behave i n t h e same way. A n o t h e r a p p r o a c h t o f i n d i n g t h e b e h a v i o u r of l i t h i u m i n M o 3 S „ would be t o use NMR b e c a u s e l i t h i u m and molybdenum have good NMR s i g n a l s , b u t , u n f o r t u n a t e l y , s u l p h u r does n o t . An a l t e r n a t e l i n e of s t u d y might p r o v e t o be more c o n v e n i e n t f o r u n d e r s t a n d i n g t h e l i t h i u m / M o ^ , , s y s t e m . M o 3 S e „ has t h e same s t r u c t u r e as M o 3 S „ , and i t can be p r e p a r e d d i r e c t l y f rom t h e e l e m e n t s . T h i s m a t e r i a l s h o u l d be examined t o see i f i t s e l e c t r o c h e m i c a l b e h a v i o u r i s t h e same as t h a t of M o 3 S a . S e l e n i u m has a good NMR s i g n a l , so i t might be p o s s i b l e t o use l i t h i u m i n t e r c a l a t e d M o 3 S e « i n NMR s t u d i e s . O t h e r work s h o u l d a l s o be done on t h e a p p l i c a t i o n s of M o 3 S „ f o r a c o m m e r c i a l b a t t e r y m a t e r i a l . M o 3 S „ i s not a n a t u r a l l y o c c u r r i n g m i n e r a l , so a method must be f o u n d of s y n t h e s i z i n g t h i s m a t e r i a l i n a way t h a t would be e c o n o m i c a l on an i n d u s t r i a l s c a l e . F o r example, i t may be p o s s i b l e t o d i r e c t l y make L i 2 M o 3 S / , b e c a u s e t h i s m a t e r i a l would have a m e t a l t o s t a b i l i z e t h e M o 3 S „ s t r u c t u r e a t h i g h t e m p e r a t u r e s . The phase t r a n s i t i o n s seen i n t h e e l e c t r o c h e m i c a l work done on t h e X-phase and t h e M o S 2 - i r o n m i x t u r e seems t o i n d i c a t e t h a t L i 2 M o 3 S u i s more l i k e l y t o form t h a n e i t h e r o f . t h e o t h e r two m a t e r i a l s . The L i 2 M o 3 S 4 c o u l d be a s s e m b l e d d i r e c t l y i n t o a c e l l , and i t would p r o d u c e t h e M o 3 S „ as i t 86 was c h a r g e d . T h e r e would be a p r o b l e m i f M o 3 S a can o n l y be made i.n t h e p r e s e n c e o f o t h e r t r a n s i t i o n m e t a l s , b e c a u s e p r o c e s s i n g t h e m a t e r i a l t o remove t h e o t h e r m e t a l s c o u l d be e x p e n s i v e . I f t h e l i t h i u m / M o 3 S a s y s t e m i s d e v e l o p e d as a c o m m e r c i a l c e l l , t h e n i t s main c o m p e t i t i o n would l i k e l y come from t h e l i t h i u m / M o S 2 s y s t e m . B o t h t h e s e b a t t e r i e s have a p p r o x i m a t e l y t h e same e n e r g y d e n s i t y (~250 w a t t - h o u r s p e r k i l o g r a m ) i n a p r a c t i c a l v o l t a g e range of 2.7 t o 1.3V, but t h e M o 3 S „ s y s t e m might be s u p e r i o r i n c e r t a i n a p p l i c a t i o n s . The M o 3 S „ c e l l s have a h i g h e r v o l t a g e t h a n do t h e MoS 2 ones, and t h e s m a l l e r h y s t e r e s i s makes them more e f f i c i e n t t h a n m o l y b d e n i t e . MoS 2 can go t h r o u g h a 0 t o a t r a n s i t i o n when i t i s f u l l y c h a r g e d , and so l o s e a l l of i t s h i g h v o l t a g e c a p a c i t y u n t i l i t i s b r o u g h t back i n t o p - p h a s e . M o 3 S „ i s b e l i e v e d t o be s t a b l e a t room t e m p e r a t u r e and w i l l not phase c o n v e r t t o a n o t h e r m a t e r i a l . However, i t i s not known i f L i 2 M o 3 S a can decompose i n t o o t h e r m a t e r i a l s , and t h i s must be s t u d i e d . Many p r a c t i c a l d e v i c e s a r e d e s i g n e d t o be o p e r a t e d a t a c o n s t a n t v o l t a g e . The M o 3 S „ s y s t e m has ab o u t t h r e e q u a r t e r s of i t s c a p a c i t y i n a one t e n t h of a v o l t r a n g e , but d r a w i n g t h r e e q u a r t e r s of t h e c a p a c i t y of a p-phase MoS 2 c e l l would change t h e p o t e n t i a l by a t l e a s t h a l f a v o l t . Y e t , t h e MoS 2 c e l l m i g h t p r o v e t o be s u p e r i o r f o r g e n e r a l - p u r p o s e a p p l i c a t i o n s i n s p i t e of t h e many a d v a n t a g e s of t h e M o 3 S „ s y s t e m . MoS 2 i s n a t u r a l l y o c c u r r i n g , but M o 3 S „ must be s y n t h e s i z e d . I f Mo 3S f l c a n not be e c o n o m i c a l l y p r o d u c e d , t h e n i t i s u n l i k e l y t h a t i t w i l l have many ' 8 7 c o m m e r c i a l a p p l i c a t i o n s . The c o e f f i c i e n t o f l i t h i u m d i f f u s i o n i n b o t h MoS 2 and M o 3 S „ s h o u l d be d e t e r m i n e d . T h i s number w i l l i n d i c a t e w h i c h of t h e s e two m a t e r i a l s would l i k e l y be a b e t t e r b a t t e r y i n a h i g h c u r r e n t d r a i n a p p l i c a t i o n . Many o t h e r i n v e s t i g a t i o n s c o u l d be b a s e d on o t h e r m e t a l s i n t h e s t r u c t u r e . F o r example, G u i l l e v i c e t . a l . (1976,1976) have shown t h a t l e a d i n M o 3 S a forms a s l i g h t l y d i f f e r e n t s t r u c t u r e t h a n i f n i c k e l , i r o n , or c o b a l t i s i n s e r t e d . T hese C h e v r e l p h a s e s a r e o f t e n s u p e r c o n d u c t o r s and t h e c r i t i c a l t e m p e r a t u r e v a r i e s w i t h d i f f e r i n g amounts of m e t a l i n t h e h o s t . I n t e r c a l a t i o n c a n s e r v e as a c o n v e n i e n t way of c h a n g i n g t h e amount of m e t a l i n t h e sample. A n o t h e r b r a n c h of e x p e r i m e n t s c o u l d i n v e s t i g a t e t h e m e t a l - m o l y b d e n u m - o x i d e s r a t h e r t h a n t h e metal-molybdenum-s u l f i d e s . Work has a l r e a d y been done on the- l i t h i u m i n t e r c a l a t i o n of Mo0 2 (VonSacken 1980) and v a r i o u s o t h e r o x i d e s ( J a c o b s o n 1979, and C h r i s t i a n 1980). As was m e n t i o n e d e a r l i e r , t h e molybdenum s e l e n i d e s a r e a l s o p o t e n t i a l l y u s e f u l . The i n v e s t i g a t i o n of t h e v a r i o u s m i n e r a l s w h i c h may have been i n t h e Endako MoS 2 h i g h - l i g h t e d a n o t h e r i m p o r t a n t use f o r i n t e r c a l a t i o n . E l e c t r o c h e m i c a l s i g n a t u r e s of m a t e r i a l s a r e o f t e n d i s t i n c t i v e , and so a v o l t a g e p r o f i l e c a n be u s e d t o i d e n t i f y i t s s o u r c e . The major a d v a n t a g e of t h i s t e c h n i q u e i s t h e s e n s i t i v i t y t o d e t e c t s m a l l i m p u r i t i e s . The e x t r a Endako c a p a c i t y was o n l y one t h i r d of 88 one p e r c e n t of t h e t o t a l c a p a c i t y Of t h e Endako powder. E l e c t r o c h e m i c a l s t u d i e s c a n a l s o d e t e c t m a t e r i a l s w h i c h can not be i d e n t i f i e d w i t h X - r a y d i f f r a c t i o n , a s was t h e c a s e w i t h t h e c h a l c o c i t e w h i c h d i d n o t a p p e a r i n t h e d i f f r a c t i o n p a t t e r n o f t h e M o S 2 - c o p p e r m i x t u r e . L i t h i u m i n t e r c a l a t i o n shows g r e a t p r o m i s e as a method f o r t h e i d e n t i f i c a t i o n o f unknown m a t e r i a l s . The b i g g e s t s i n g l e p r o b l e m i n t h e d e v e l o p m e n t of t h i s t e c h n i q u e i s t h e need t o p r o d u c e a l i b r a r y of d a t a t h a t c h a r a c t e r i z e s known sam p l e s by t h e i r e l e c t r o c h e m i c a l b e h a v i o u r . 6.3 Summary I n v e s t i g a t i o n s of t h e e x t r a Endako c a p a c i t y l e d t o t h e d i s c o v e r y of M o 3 S „ t o be a p o t e n t i a l l y . u s e f u l b a t t e r y m a t e r i a l . About h a l f of t h e c a p a c i t y i s a s s o c i a t e d w i t h a f i r s t o r d e r phase t r a n s i t i o n a t 2.088V, and a n o t h e r twenty p e r c e n t of t h e c a p a c i t y i s i n a s i n g l e phase r e g i o n s l i g h t l y below t h i s p o t e n t i a l . A f u r t h e r t w enty p e r c e n t of t h e c a p a c i t y i s c e n t r e d n e a r 2.46V, and t h e r e i s a n o t h e r f i v e p e r c e n t o f t h e c a p a c i t y n e a r 1.83V. The l i t h i u m / M o 3 S a b a t t e r y i s an i n t e r c a l a t i o n s y s t e m w i t h an e n e r g y d e n s i t y o f a r o u n d 275 w a t t - h o u r s p e r k i l o g r a m of c a t h o d e m a t e r i a l . The c e l l s c y c l e d w e l l , l o s i n g t h e i r c a p a c i t y no f a s t e r t h a n d i d MoS 2 p-phase c e l l s o p e r a t i n g u nder s i m i l a r c o n d i t i o n s . M O 3 S K c a n n o t be made d i r e c t l y from t h e e l e m e n t s , but i t was d i s c o v e r e d t h a t c o p p e r or i r o n i n t e r c a l a t e d M o 3 S „ c o u l d be u s e d t o make i t i n d i r e c t l y . I f t h e c a t h o d e of a l i t h i u m b a t t e r y i s made w i t h one of t h e s e m a t e r i a l s , t h e n t h e m e t a l 89 would be d i s p l a c e d as t h e c e l l was d i s c h a r g e d . L a t e r c y c l e s would show t h e e l e c t r o c h e m i c a l b e h a v i o u r of l i t h i u m i n M o 3 S a . The l i t h i u m / M o 3 S 4 s y s t e m i s i n t e r e s t i n g b e c a u s e i t o f f e r s a c h a n c e t o i n v e s t i g a t e a m a t e r i a l i n w h i c h a f i r s t o r d e r phase t r a n s i t i o n i s a l s o an i n t e r c a l a t i o n . T h i s l e a d s t o t h e p r o b l e m of u n d e r s t a n d i n g t h e p h y s i c s of s u c h a p r o c e s s . However, one of t h e p r i m e m o t i v a t i o n s f o r i n t e r c a l a t i o n r e s e a r c h was t h e d e v e l o p m e n t of a p r a c t i c a l b a t t e r y . The m a t e r i a l w h i c h g i v e s t h e e x t r a - E n d a k o c a p a c i t y m i g h t p r o v e t o be u s e f u l f o r s u c h a p u r p o s e . 90 B i b l i o g r a p h y A l l m a n , M., and Lawrence, D.F. (1972) G e o l o g i c a l L a b o r a t o r y  T e c h n i q u e s , B l a n d f o r d P r e s s , London C h e v r e l , R., S e r g e n t , M. , and P r i g e n t , J . (1971) J . S o l i d S t a t e Chem 3, 515 C h e v r e l , R., S e r g e n t , M., and P r i g e n t , J . (1974) Mat. Res. B u l l . 9,1487 C h r i s t i a n , P.A., C a r i d e s , J.N., D i S a l v o , F . J . , and Waszczak, J.V. (1980) J . E l e c . S o c. 127 , 231 5 C u l l i t y , B.D. (1956) E l e m e n t s o f X-Ray D i f f r a c t i o n , A d d i s o n -W e s l e y , London Dahn, J.R., and H a e r i n g , R.R. (1981) S. S t a t e I o n i c s 2,19 Dahn, J.R., Py, M.A., and H a e r i n g , R.R. (1982) Can. J . Phys. 60,307 De Jonge, R., Popma, T.J.A., W i e g e r s , G.A., J e l l i n e k , F. (1970) J . S o l i d S t a t e Chem. 2,188 E i s e n b e r g , M. (1980) J . E l e c . S o c. 127,2382 G r o v e r , B. (1965) N. J b . M i n e r . Mh., 219 G r o v e r , B., K u l l e r u d , G., and Moh, G.H. (1975) N. J b . M i n e r . Abh. 124,246 G u i l l e v i c , P . J . , l e M a r o u i l l e , J . , G r a n d j e a n , D. (1974) A c t a C r y s t . B 3_0, 1 1 1 G u i l l e v i c , P . J . , B a r s , 0., and G r a n d j e a n , D. (1976) A c t a C r y s t . B 3_2, 1 338 G u i l l e v i c , P . J . , L e s t r a t , H., and G r a n d j e a n , D. (1976) A c t a C r y s t . B 32,1342 91 H a e r i n g , R.R., S t i l e s , J.A.R., and B r a n d t , K. (.1980) U n i t e d S t a t e s P a t e n t 4,224,390 J a c o b s o n , A . J . , C h i a n e l l i , R.R., R i c h , S.M., W h i t t i n g h a m , M.S. ( 1 979 ) Mat. Res. B u l l . J_4, 1437 J e l l i n e k , F. (1961) N a t u r e 192,1065 J o h n s o n , G.W. (1982) M.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h C o l u m b i a , V a n c o u v e r y - - J o i n t Committee on Powder D i f f r a c t i o n S t a n d a r d s * Powder  D i f f r a c t i o n F i l e A l p h a b e t i c a l Index (1981) Swarthmore, P e n n s y l v a n i a - - J o i n t Committee on Powder D i f f r a c t i o n S t a n d a r d s ' Powder  P i f f r a c t i o n F i l e S e a r c h Manual (1981) Swarthmore, P e n n s y l v a n i a M cKinnon, W.R. (1980) Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a Moh, G.H. (1978) i n T o p i c s i n C u r r e n t C h e m i s t r y 7 6 ( e d . F.L. B o s c h k e ) S p r i n g e r - V e r l a g , New York Murphy, D.W., D i S a l v o , F . J . , C a r i d e s , J.M., and Waszczak, J.V. (1978) Mat. Res. B u l l . 21,1395 Py, M.A., H a e r i n g , R.R. (1982) Can. J . P h y s . ( t o be p u b l i s h e d ) S c h o l l h o r n , R. , and Kumpers, M. ( 1 977 ) Mat. Res. B u l l . J_2, 781 S c h o l l h o r n , R., and Kumpers, M. (1979) Mat. Res. B u l l . 14, 1039 T s i g d i n o s , G.A. (1978) i n T o p i c s i n C u r r e n t C h e m i s t r y 76 ( e d . F.L. B o s c h k e ) S p r i n g e r - V e r l a g , New York 92 Von S a c k e n , U.G., (1980) M.Sc.. T h e s i s , U n i v e r s i t y of B r i t i s h C o l u m b i a , V a n c o u v e r Wang, N., and Moh, G.H. (1976) N. J b . M i n e r . Mh., 36 W i l s o n , C.G., and S p o o n e r , F . J . (1963) A c t a C r y s t . j_6,230 Yvon, K., P a o l i , A., F l u k i g e r , R., and C h e v r e l , R. (1977) A c t a C r y s t . B 3_3,3066 APPENDIX I 93 Summary of Lat t i c e Parameters Hexagonal Formula Parameters a c . 9. 73 10. 22 CuMo 2S 3 9. 73 10. 2 Cu 2Mo 4S 5 9. 713 10. 213 C u1.38 M o3 S4 9. 735 10. 221 C u1.47 M o3 S4 9. 73 10. 22 9. 729 10. 218 9. .52 10. .27 Y-phase 9. .564 10. ,273 FeMo 5S 6 9. .564 10. ,273 F e 0 . 6 6 M o 3 S 4 9. .55 10. .30 FeMo 3S 4 9, .51 10, .37 9 .202 10 .877 Mo 3S 4 9 .728 10 .525 L i 2 M o 2 S 3 9 . 196 10 .891 9 .358 10 . 725 9 . 754 10 .589 9 .795 10 .553 ed in this Thesis Source Wang and Moh 1976 Chevrel e t . a l . 1971 Yvon e t . a l . 1977 Yvon e t . a l . 1977 1100°C MoS 2~copper material "X-phase" material Moh 1978 Chevrel e t . a l . 1971 G u i l l e v i c e t . a l . 19 76 Schollhorn 1977 F i r s t Batch MoS 2~iron material Yvon e t . a l . 1977 Chevrel e t . a l . 1971 Extra Endako Capacity at 2.700V Extra Endako Capacity at 2.100V Extra Endako Capacity at 2.050V Extra Endako Capacity at 1.800V A p p e n d i x II 94 The f o l l o w i n g i s a summary of t h e X - r a y d a t a c o l l e c t e d a t f o u r d i f f e r e n t v o l t a g e s o f PMX-11, a c e l l w i t h ~1(3mg c a t h o d e o f "X-phase" m a t e r i a l . T h e r e a r e two t a b l e s w h i c h summarize t h e l i n e p o s i t i o n s and i n t e n s i t i e s and f o u r f i g u r e s w h i c h show t h e d i f f r a c t i o n p a t t e r n s . The d a t a was c o l l e c t e d a t : 2.700V, t h e f u l l y c h a r g e d c e l l ; 2.100V, t h e c e l l p o t e n t i a l j u s t above t h e phase t r a n s i t i o n ; 2.050V, where t h e c e l l i s d i s c h a r g e d t h r o u g h t h e phase t r a n s i t i o n and p a r t of t h e s i n g l e phase c a p a c i t y below i t ; and 1.800V, t h e f u l l y d i s c h a r g e d c e l l . The f i r s t t a b l e i s a c o m p a r i s o n of t h e l i n e p o s i t i o n s a t t h e f o u r s t a t e s o f c h a r g e . The numbers marked w i t h an a s t e r i s k (*) had c l e a r l y d e f i n e d p o s i t i o n s and were us e d i n t h e d e t e r m i n a t i o n of t h e l a t t i c e p a r a m e t e r s of t h e m a t e r i a l . L i n e s t h a t were o b s c u r e d by d i f f r a c t i o n from o t h e r s o u r c e s a r e marked w i t h a q u e s t i o n mark ( ? } . The s e c o n d t a b l e i s a l i s t of t h e d i f f r a c t i o n l i n e s c a u s e d by t h e MoS 2 c o n t a m i n a t i o n , t h e c e l l components ( s u c h as l i t h i u m ) , and t h e c e l l c a s e . The i n t e n s i t i e s a r e q u o t e d r e l a t i v e t o t h e (101) d i f f r a c t i o n l i n e of t h e M o 3 S „ m a t e r i a l . T h e s e l i n e s were p r e s e n t i n a l l t h e s c a n s and r e m a i n e d c o n s t a n t . The l i n e p o s i t i o n and i n t e n s i t y i n f o r m a t i o n was o b t a i n e d by c o l l e c t i n g d a t a a t 0.01 d e g r e e i n t e r v a l s o f 2 e . The number o f X - r a y s d e t e c t e d i n t e n s e c o n d s a t e a c h a n g u l a r p o s i t i o n was r e c o r d e d . The i n t e n s i t i e s q u o t e d i n t h e t a b l e s 95 were d e t e r m i n e d . by s u b t r a c t i n g t h e number o f b a c k g r o u n d c o u n t s f r o m t h e d a t a , and t h e n n o r m a l i z i n g t h e d a t a t o t h e s t r o n g e s t d i f f r a c t i o n l i n e . The i n t e n s i t y d a t a was e x p r e s s e d i n two ways: as a r a t i o , o f maximum i n t e n s i t i e s i n two l i n e s (I / I ); and a s t h e r a t i o o f t o t a l a r e a s under t h e p o -d i f f r a c t i o n l i n e s ( / I / I 0 ) . Peak p o s i t i o n s below ~ 4 3 ° r e f e r t o t h e a v e r a g e c o p p e r K„ r a d i a t i o n (k=1.54178A) and p o s i t i o n s above t h i s a n g l e r e f e r t o c o p p e r K ^ j r a d i a t i o n U=1 .54433A) . The q u o t e d peak p o s i t i o n s a r e a t s l i g h t l y h i g h e r a n g l e s t h a n t h e t r u e peak p o s i t i o n s b e c a u s e t h e powder was 325 m i c r o n s above t h e m e a s u r i n g p l a n e o f t h e d i f f T a c t o m e t e r . The c o r r e c t i o n needed i s d e s c r i b e d i n E q u a t i o n 7. T h r e e of t h e f i g u r e s were p l o t t e d from t h e d a t a t h a t was u s e d t o o b t a i n t h e peak p o s i t i o n s and i n t e n s i t i e s . The d a t a f o r t h e 2.700V m a t e r i a l was n o t s t o r e d i n a machine r e a d a b l e form, so t h e g r a p h was p l o t t e d by d i g i t i z i n g a slow c o n t i n u o u s s c a n of t h e c e l l . SUMMARY OF PEAK POSITIONS AND INTENSITIES 2 .700V 2 .100V 2 .050V 1 .800V LINE POSITION (29) / I / I 0 P o POSITION (20) nn o I /I P o POSITION (26) / I / I o I 11 P o POSITION (20) nn o I 11 P < (101) 14.00* 100 100 13.91* 100 100 13.63* 100 100 13.61* 100 100 (110) 19.52 <1 <1 19.17* <1 <1 '18.40* 6 6 18.30* 5 5 (201) 24.01 • ' <1 1 23.70 <1 <1 - - - - - -(003) 24.73* 3 4 25.08 4 4 25.44* 6 4 25.51* 6 4 (202) 27.95* 6 4 27.81* 5 6 27.21 3 3 27.19* 3 4 (211) 31.02* 17 16 30.55* 16 13 29.41* 15 13 29.44 4 6 (212) 34.23* 41 29 33.88 39 29 32.95* 25 21 33.01 26 11 (104) 35.02* 15 14 35.43 21 13 35.73* 15 12 35.79* 14 10 (220) 39.37* 16 11 38.71* 15 9 37.04* 18 12 36.83 10 5 (204) 40.30* 3 2 40.28 3 2 - - - - -(311) 41.90* 37 26 41.26* 37 25 39.57* 47 29 39.46* 17 12 (303) 42.34* 42 24 42.08* 17 15 1 ? ? 1 SUMMARY OF PEAK POSITIONS AND INTENSITIES (CONTINUED) 2 .700V 2 . 100V 2 • 050V 1 ,800V LINE POSITION (20) SI/I o I / I - p o POSITION (20) fl/lo 1 P o POSITION (20) / I / I o I / I p o POSITION (20) fill o I / I P o (105) 43.22* 17? 18? 43.85* 1 7 ? 7 7 7 7 7 (312) ? 1 1 ? 1 ? 42.35* 33 26 42.20* 26 13 (214) 45.05* 28 21 45.09* 21 18 ? 7 7 44 .'7 9* 33? 20? (223) 46.93* 83 53 46.55* 72 50 45.36* 68 47 45.47 55 20 (402) 48.88 <1 <1 48.08* 1 ? 7 ? ? 7 7 7 (321) ? 7 ? 49.99 24 15 47.85 21 13 47.49 14 7 (322) ? ? ? ? ? ? 50.28* 51 33 50.13* 25 18 (314) 53.54 4 3 ? ? ? 7 ? 7 ? ? (116) 54.48* 2 2 55.06 3 2 - - - - - -(324) 61.20 17 12 60.72 18 14 59.20* 21 14 59.25 5 6 (413) _ _ — - - - 56.44* 8 6 56.25 13 3 DIFFRACTION LINES PRESENT IN ALL SCANS POSITION (2 6) INTEGRATED COMMENTS INTENSITY 14.62 103 MoS2 (002) 17.19 5 18.72 1 20.49 <1 25.79 3 28.76 2 29.22 9 MoS2 (004) 33.29 5 36.18 29 L i (110) 37.00 3 39.77 12 MoS2 (103) 41.50 47 43.51 25 44.34 66 45.90 13 50.50 to 52.50 612 Several Peaks 53.00 14 60.28 71 MoS2 (008) 66 100 ro CM s^unoQ ro CM s j u n o o > o o CNJ P4 0) u M-l o c o CO I X n a) }-< • H fe 1 0 1 r o CM s j u n o Q 11111111 I I I 1 I 1 1 1 o o o o o o o o o o o o o o o o o o o o o CM CO o CO CO m CO m CM o o 'SS' m CM c o c o CM O ^ * 00 t o K) CM s j u n o Q > o m o C N 4 J CO fe CU C_> m o c cd a c n cd Pi i X i i CNl O O CD u faO • H fe 102 I I I I I I I I I t o CN ? s s^unoQ I 1 I I I I 1 I o o o o m o o o o o o o o o o o o to CM o o o o CM CD O CO CO m CO m ^ * m CM m o <^  io CM 00 CO CM o CO O t o s ^ u n o o > o o oo 4 - J Cd fe CD c cd o CO cd Pd i X! i co CO CD bO •rl fe 

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