Improved lithium-ion batteries are essential for renewable energy and alternatives to fossil fuels. Current production batteries incorporate a liquid electrolyte solution that is flammable and prone to dendritic damage. Solid polymer electrolytes hold potential for addressing those issues though these polymers often suffer from lower conductivity due to coupling to polymer segmental motion. Previous research has suggested there may be increased decoupling of ion motion from segmental motion for polymers with bulky and rigid backbones. Our goal is to synthesize a polymer with an optimal ionic conductivity while balancing Tg and decoupling segmental motion. The novel polymer studied in this work has a bulky oxanorbornene dicarboxide backbone with an ethylene oxide side chain (17 units) and has been synthesized using ring opening metathesis polymerization. Electrochemical impedance spectroscopy was performed to measure ion conductivity for this polymer with lithium trifluoromethane sulfonimide salt at concentrations up to 50% (w/w). Subsequently, the samples with the highest conductivity were characterized using pulse field gradient NMR to measure diffusion coefficients for both the cation and anion. From these two methods of characterization, inverse haven ratio and transference numbers were calculated. The data appears to suggest that correlated ion jumps may be enhancing ion conductivity. These results are additionally compared to previous data from our group for the same system except using a shorter oligomeric ethylene oxide sidechain of 12 units.

Synthesis and characterization of a solid polymer electrolyte using electrochemical impedance spectroscopy and pulse field gradient NMR diffusion spectroscopy

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