A Flexible Sandwich‐Type Hybrid Solid Polymer Electrolyte Enables High‐Temperature of 80 °C Resistant Lithium Metal Solid‐State Batteries

The solid‐state electrolyte is a promising candidate for advancing the dual goals of high energy density and high safety for batteries. However, it is difficult for current solid electrolyte systems to balance the high ion transport, mechanical strength, thermal safety, and electrochemical stability simultaneously, which will greatly restrict their scale‐up and practical applications in batteries. Herein, a sandwich‐type hybrid solid polymer electrolytes (SHSPEs) is prepared via a simple coating method, the gel polymer filled in the middle porous polyethylene (PE) separator endows SHSPEs fast ion transport (7.13 × 10 −4 S cm −1 , 25 °C) and good mechanical properties (205.67 MPa), while the solid composite polymer layers on both sides ensure adequate lithium‐ion transfer number (0.42), electrochemical and thermal safety stability. The Li//Li symmetric battery with optimized solid electrolyte can circulate steadily for more than 1800 h, especially at 80 °C. For further illustration, the solid‐state LiFePO 4 //Li cells provide ideal cyclic stability and rate capability, as well as extreme temperature endurance till 80 °C. Thus, this work provides an auspicious strategy to design a safe, high‐strength, high‐energy density battery for high‐temperature special needs.