UBC Theses and Dissertations
Nuclear magnetic resonance characterization of solid polymer electrolyte materials Michan, Alison Louise
Solid polymer electrolytes have the potential to improve manufacturability, performance, and safety characteristics of lithium-ion batteries by replacing conventional liquid electrolytes. Two different solid polymer electrolyte materials were characterized using Nuclear Magnetic Resonance (NMR) techniques. The first material is a result of research efforts on single-ion conducting polymers. The material is intended to combine the high conductivity properties of ionic liquids with lithium cation single-ion conduction. The goal of the synthesis was to produce a polymerized ionic liquid, where crosslinking an anionic monomer (AMLi) with poly(ethylene glycol) dimethacrylate (PEGDM) immobilizes the fluorinated anionic species. Pulsed-field gradient NMR diffusion measurements of the AMLi/PEGDM samples have demonstrated that both the lithium cations and fluorinated anions are mobile and contributing toward conductivity. Therefore, further work is required to successfully immobilize the fluorinated anion in a crosslinked network. The ⁷Li and ¹⁹F diffusion coefficients of the AMLi/PEGDM 40/60 sample were 3.4x10⁻⁸ cm²/s and 2.2x10⁻⁸ cm²/s at 100°C. The second material incorporates a poly(ethylene oxide) (PEO) conductive block and polyethylene (PE) reinforcement block. The PEO/PEO-b-PE/LiClO₄ samples were not intended to be single-ion conducting and materials synthesis aimed to maximize conductivity and mechanical properties. A ⁷Li diffusion coefficient of ~4x10⁻⁸ cm²/s at 60°C was observed. It is expected that the anion would also be mobile and therefore the polymer electrolyte would be a bi-ionic conductor. These samples demonstrated higher ⁷Li diffusion coefficients at a given temperature and superior mechanical properties for a flexible polymer electrolyte compared to the AMLi/PEGDM samples. Practically, the diffusion measurements of the solid polymer samples are extremely challenging, as the spin-spin (T₂) relaxation times are very short, necessitating the development of specialized pulsed-field gradient apparatus. These results provide valuable insight into the conduction mechanisms in these materials, and will drive further optimization of solid polymer electrolytes.
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