Chloride Electrolytes Promote the Formation of a Stable Inorganic-Rich SEI in PEO-Based ASSLMBs

Composite polymer electrolytes (CPEs)─which comprise organic polymer electrolyte matrices and inorganic electrolyte particles─are promising materials for all-solid-state lithium–metal batteries (ASSLMBs) due to their unique mechanical properties and scalable production. Herein, addition of a small amount of Li₃InCl₆ (LIC) into the poly(ethylene oxide) (PEO) electrolyte promoted a stable interface on the lithium metal surface and enabled long-term battery cycling. The addition of LIC reduced the crystallinity of the polymer electrolyte and increased the proportion of the amorphous region to promote lithium ion transport. Incorporating 1% of LIC increased the lithium-ion conductivity by nearly 50% at 45 °C and improved the elastic modulus of the electrolyte. Fourier transform infrared and Raman spectroscopy showed the presence of Lewis acid–base interactions between LIC and PEO, which may result in the anions of lithium salts being more easily reduced by lithium metal. The CPE-1% LIC demonstrated prolonged cycling capability, sustaining lithium plating/stripping for over 7000 h in lithium–lithium symmetric cells. The X-ray photoelectron spectroscopy measurements revealed LiF, Li₃N, Li₂O, Li₂S, and LiCl on the Li metal surface, which originated from the decomposition reaction of lithium bis(trifluoromethane)sulfonylimide (LiTFSI) and LIC. These inorganic decomposition products that act as electronic insulators can effectively prevent electron tunneling, ensure rapid transport of lithium ions, promote uniform lithium deposition, avoid the formation of lithium dendrites, and prevent adverse reactions between lithium metal and polymers. When matched with the LiFePO₄ cathode and Li anode, the full cell exhibited a capacity retention rate of 92.4% after 500 cycles at 0.2C and 45 °C. This work highlights a promising path for designing ASSLMBs using chloride electrolytes.