Gel electrolytes based on an ether-abundant polymeric framework for high-rate and long-cycle-life lithium ion batteries

This study reports a gel polymer electrolyte (GPE) that is synthesized using a poly(ethylene oxide)-co-poly(propylene oxide) copolymer blending diglycidyl ether of bisphenol-A (i.e., P(EO-co-PO)) as a host swelled by a liquid electrolyte (LE) of 1 M LiPF₆ in carbonate solvents. The P(EO-co-PO) copolymer in the GPE contains a high concentration of ether groups to coordinate solvent molecules and solvated Li⁺ ions for achieving high ionic conductivity (3.8 × 10^-3 S cm^-1 at 30 °C), and exhibits an excellent Li⁺ transference number of 0.7. The GPE is assembled in a full-cell lithium ion battery (LIB) consisting of an LiFePO₄ cathode and a graphite anode, and the copolymer network facilitates ion motion to reduce the equivalent series resistance by 50% and increase the specific power by two times relative to the performance of an LIB assembled using the LE. This GPE-based LIB exhibits a capacity of 125 mA h g^-1 at 0.1 C and is able to deliver 22 mA h g^-1 of electricity at 15 C. This LIB exhibits superior stability; it presents negligible capacity decay after 200 charge-discharge cycles at 1 C and exhibits 77% capacity retention after 450 cycles. The distinctive merit of the GPE film is its mechanical integrity, which ensures that the roll-to-roll assembly of GPE-based LIBs is readily scalable to industrial levels.