Compact Solid Electrolyte Interface Realization Employing Surface‐Modified Fillers for Long‐Lasting, High‐Performance All‐Solid‐State Li‐Metal Batteries

Abstract The implementation of polymer‐based Li‐metal batteries is hindered by their low coulombic efficiency and poor cycling stability attributed to continuous electrolyte decomposition. Enhancement of the solid electrolyte interface (SEI) stability is key to mitigating electrolyte decomposition. This study proposes surface‐functionalized silica mesoball fillers to fabricate a composite polymer electrolyte (MSBM‐CPE). As a result of surface modification, the polyethylene oxide matrix benefits from the uniform distribution of the filler, which provides a large surface area and Lewis acid sites. Molecular dynamics simulations reveal that the dissociation energy of lithium bis(trifluoromethanesulfonyl)imide in the filler is fourfold higher (−1.95 eV) than that of the filler‐free electrolyte. Consequently, the MSMB‐CPE diffusivity is 30 times higher than its filler‐free counterpart. The MSMB‐CPE of ionic conductivity of 1.16 × 10 −2 S cm −1 @60 °C and a venerable Li‐ion transference number of 0.81. The excellent compatibility of MSMB‐CPE with the Li anode is demonstrated by its stable symmetric cell performance under high current density (200 µA cm −2 @60 °C) for over 5000 h. Approximately 85.60% retention capacity of the [Li/MSMB‐CPE/LiFePO 4 ] full cell after 700 cycles. Furthermore, compositional analysis reveals that the SEI layer in MSMB‐CPE is smooth with fewer by‐products at the electrolyte/Li interface.