The synergy mechanism of CsSnI3 and LiTFSI enhancing the electrochemical performance of PEO‐based solid‐state batteries

Abstract Lithium metal solid‐state battery is the first choice of batteries for electromobiles and consumer electronic products because of the specific capacity of 3860 mAh g−1 and high electrochemical potential (−3.04 V) of Li metal. Flexible polymer solid electrolytes have become the optimal solution to produce high energy density lithium batteries with arbitrary size and shape. In this work, we introduce a halide perovskite, CsSnI3, into the polyethylene oxide/lithium bis‐(trifluoromethanesuphone)imide (PEO–LiTFSI) polymer matrix. The CsSnI3 could form a LixSn alloy with Li, leading to homogenization of the electric field and Li+‐flux at the interface, Sn atom also bonds with the TFSI− anion to provide more dissociated Li+. Besides that, the I atom could interact with Li to form an electronic insulation with a strong blocking effect on electron tunneling. As a proof of concept, the synergy mechanism of the PEO–LiTFSI–CsSnI3 electrolyte improves the stable cycle life of the symmetric battery to more than 500 h, and the Li+ conductivity raised to 6.1 × 10−4 S cm−1 at 60°C. The application of the “zwitter ions analog” halide perovskite in PEO–LiTFSI provides a new choice among various methods to improve the electrochemical performance of polymer solid‐state batteries.