A thin and high-strength composite polymer solid-state electrolyte with a highly efficient and uniform ion-transport network

Solid polymer electrolytes for solid-state lithium metal batteries face the challenges of low ionic conductivity, poor mechanical properties, and large thickness. Herein, a thin and high-strength composite polymer electrolyte (CPE) is developed via infusing a polyethylene oxide (PEO)/(CF3SO2)2NLi (LiTFSI) electrolyte into a polyacrylonitrile (PAN) network, where highly efficient and uniform interfacial ion-transport channels are constructed through micro-wetting using trace electrolyte vapor. The trace electrolyte vapor creates fast-ion-transport channels at both the external CPE/electrode interface and the internal PAN/PEO interface in the CPE, and its LiPO2F2 product is favorable for the cycling stability. The rigid PAN network can not only enhance the mechanical strength and promote Li-ion conductivity, but it also strongly adsorbs Li-salt anions and improves the lithium-ion transference number (0.49) of the CPE, inducing the uniform stripping and deposition of Li metal and suppressing Li dendrite growth. The LiFePO4 (LFP)/CPE/Li solid-state battery achieves a specific capacity of 141.1 mA h g−1 with a capacity retention rate of 85.6% and Coulombic efficiency of 100.0% after 360 cycles at 25 °C. This work provides a facile strategy for constructing thin and high strength CPEs with high performance at room temperature.