UBC Theses and Dissertations
Lithium intercalation in titanium based oxides and sulfides Colbow, Kevin Michael
The Li-Ti-S ternary system was investigated. The elements and/or compounds, such as lithium sulfide, titanium disulfide and titanium trisulfide, were combined at high temperature (typically 500-900°C). The synthesized compounds containing one or more phases were structurally characterized using x-ray powder diffraction. When Lix TiS₂, (0 ≤ x ≤ 1) was synthesized at elevated temperature, a new polytype, 3R-LixTiS₂, was found for some values of x. The regions of stability of the 3R polytype and the well known 1T polytype are presented. Lithium can be intercalated or de-intercalated from both polytypes at room temperature. Ambient temperature Li/3R-LixTiS₂ cells have higher average voltages than Li/1T-Li TiS₂, cells. The lithium spinel oxides are another class of materials receiving attention as cathode materials in lithium secondary batteries. LiTi₂0₄ is metallic, has the cubic spinel structure and reacts with one further lithium atom to form Li₂Ti₂0₄. The related spinel Li₄/₃Ti₅/₃⁰₄͵ which is electrically insulating, also reacts reversibly with one lithium atom. Both Li₂Ti₂0₄ and Li₄/₃Ti₅/₃⁰₄͵ cells cycle reversibly, but have subtle differences in their voltage profiles. The difference in cell behaviour was interpreted based on the band structure of Li₁˖xTi₂₋x⁰₄. The mixed spinels LiMnyTi₂₋y⁰₄ (0 ≤ y ≤ 2) were also investigated. These compounds were synthesized at high temperature but their performance as cathodes in lithium batteries was not encouraging.
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