Perfluoro Polyether Coated Chloride Solid Electrolytes Enable Stable All-Solid-State Batteries with Ultrahigh-Nickel Cathodes

All-solid-state lithium batteries (ASSLBs) with ultrahigh-nickel cathodes offer high energy density and safety yet face challenges from poor interface compatibility under high voltage. This work reports a versatile strategy using perfluoro polyether (PFPE-COOH) to coat chloride solid electrolytes Li_0.9NbO_0.9Cl_4.1 (LNOC). Through simple ball milling, a uniform 1.2 nm coating is formed on LNOC, which maintains high ionic conductivity of 5.82 mS cm^-1 while effectively suppressing oxidative decomposition. Furthermore, PFPE-COOH significantly reduces the Young's modulus of LNOC from 3.78 to 1.53 GPa, enhancing mechanical flexibility to mitigate physical contact loss during cycling. ASSLBs using single-crystal LiNi_0.92Co_0.05Mn_0.03O₂ cathodes and the modified LNOC exhibit exceptional stability, retaining 80.6% capacity after 400 cycles at a 4.6 V cutoff voltage. This study provides an effective interfacial engineering route for developing high-energy-density and long-cycling ASSLBs.