Polyimide-reinforced solid polymer electrolyte with outstanding lithium transferability for durable Li metal batteries

Abstract

Solid polymer electrolytes drastically enhance the operational safety of Li metal battery by eliminating the flammable liquid electrolyte, but still suffer from low ionic conductivity and inferior thermostability. Herein, we tack this issue by strengthening the polyvinylidene fluoride matrix with lithiophilic polyimide. The actively conjugated carbonyl groups in polyimide polymer backbone with Li+-conductivity feature accelerate the ion conduction, accordingly improving the ionic conductivity up to 4.1 × 10−4 S cm−1. With the polyimide solid electrolyte, lithium symmetrical battery shows a stable operation without obvious dendrite growth over 300 h at 0.17 mA cm−2, effectively uniformizing the Li+ deposition at the electrolyte/anode interface. The LiFePO4 cell based on the polyimide electrolyte delivers a high discharge capacity of 126 mAh g−1 at 25 °C with a capacity retention of 86% after 500 cycles at 0.15 mA cm−2. In addition, polyimide chain with high thermostability owns affinity to polyvinylidene fluoride with an adsorption energy of 0.1 eV, giving rise to 35% enhancement in mechanical strength and 68% reduction in thermal shrinkage at 300 °C as compared with pure polyvinylidene fluoride electrolyte. This design allows a promising route for enhancing the safety operation of polymer electrolyte and promoting ionic transfer by reconstructing the polymer architecture.