High-Rate Solid Polymer Electrolyte Based Flexible All-Solid-State Lithium Metal Batteries

A flexible poly(vinylidene fluoride)-polyetherimide@poly(ethylene glycol) (PVDF-PEI@PEG) solid composite polymer electrolyte is prepared by an in situ thermal curing approach. The homogeneous PVDF-PEI composite porous membrane with an optimized PVDF and PEI weight ratio increases the amorphous phase, while the fast lithium ion transport channels are formed through the filled PEG electrolytes. The optimized polymer electrolyte exhibits high ionic conductivity of 2.36 × 10^-4 S cm^-1 at 60 °C and lithium ion transference number of 0.578 as well as excellent electrochemical stability window of 5.5 V. Moreover, the superior stability toward lithium metal anode enables over 3600 h cycling of the Li//Li symmetric cell at 0.1 mA cm^-2. In particular, the LiFePO₄//Li battery delivers high specific capacities of 132.4 and 111.5 mAh g^-1 with a retention of 86.6% and 85.9% after 200 cycles at 2 C and 100 cycles at 3 C rate under 60 °C, respectively, demonstrating the feasibility as an energy storage device with high rate capability.