In‐Built Quasi‐Solid‐State Poly‐Ether Electrolytes Enabling Stable Cycling of High‐Voltage and Wide‐Temperature Li Metal Batteries

Abstract Developing solid‐state electrolytes with good compatibility for high‐voltage cathodes and reliable operation of batteries over a wide‐temperature‐range are two bottleneck requirements for practical applications of solid‐state metal batteries (SSMBs). Here, an in situ quasi solid‐state poly‐ether electrolyte (SPEE) with a nano‐hierarchical design is reported. A solid‐eutectic electrolyte is employed on the cathode surface to achieve highly‐stable performance in thermodynamic and electrochemical aspects. This performance is mainly due to an improved compatibility in the electrode/electrolyte interface by nano‐hierarchical SPEE and a reinforced interface stability, resulting in superb‐cyclic stability in Li || Li symmetric batteries ( > 4000 h at 1 mA cm −2 /1 mAh cm −2 ; > 2000 h at 1 mA cm −2 /4 mAh cm −2 ), which are the same for Na, K, and Zn batteries. The SPEE enables outstanding cycle‐stability for wide‐temperature operation (15–100 ° C) and 4 V‐above batteries (Li || LiCoO 2 and Li || LiNi 0.8 Co 0.1 Mn 0.1 O 2 ). The work paves the way for development of practical SSMBs that meet the demands for wide‐temperature applicability, high‐energy density, long lifespan, and mass production.