Cross-linked ionic copolymer solid electrolytes with loose Coordination-assisted lithium transport for lithium batteries

PEO-based solid electrolytes have attracted great attentions and made rapid development in the fields of lithium ion batteries, however its low ionic conductivity and low lithium ion transference number at ambient temperature prevent its practical applications. Herein we report a novel freestanding crosslinked ionic copolymer solid electrolytes fabricated via cross-linking polytetramethylene ether glycol with 1-vinyl-3-butylimidazole bis(trifluoromethylsulfonyl)imide ionic liquid. Polytetramethylene ether glycol is chosen to build polymer matrix owing to their loose coordination with lithium ions and vinyl imidazolium ionic liquids provide ionic species. As expected, the novel electrolytes exhibit lithium-ion transference number (tLi+) up to 0.47 at ambient temperature, good electrochemical stability up to 5.1 V and stable interface compatibility. Furthermore, the lithium ion batteries assembled with lithium anodes and LiFePO4 cathodes exhibit good cycling performance and rate performance, delivering a good discharge capacity of 154.3 mAh g−1 after 100 cycles at 0.1C and an initial discharge capacity of 137.6 mAh g−1 at 0.5C with capacity retention of 92% after 100 cycles at ambient temperature.