Stabilized Conductive Agent/Sulfide Solid Electrolyte Interface via a Halide Solid Electrolyte Coating for All‐Solid‐State Batteries

ABSTRACT All‐solid‐state batteries (ASSBs) have garnered significant interest as the next‐generation in battery technology, praised for their superior safety and high energy density. However, a conductive agent accelerates the undesirable side reactions of sulfide‐based solid electrolytes, resulting in poor electrochemical properties with increased interfacial resistance. Here, we propose a wet chemical method rationally designed to achieve a conformal coating of lithium–indium chloride (Li₃InCl₆) onto vapor‐grown carbon fibers (VGCFs) as conductive agents. First, with the advantage of the Li₃InCl₆ protective layer, use of VGCF@Li₃InCl₆ leads to enhanced interfacial stability and improved electrochemical properties, including stable cycle performance. These results indicate that the Li₃InCl₆ protective layer suppresses the unwanted reaction between Li₆PS₅Cl and VGCF. Second, VGCF@Li₃InCl₆ effectively promotes polytetrafluoroethylene fibrillization, leading to a homogeneous electrode microstructure. The uniform distribution of the cathode active material in the electrode results in reduced charge‐transfer resistance and enhanced Li‐ion kinetics. As a result, a full cell with the LiNi_xMn_yCo_zO₂/VGCF@Li₃InCl₆ electrode shows an areal capacity of 7.7 mAh cm⁻² at 0.05 C and long‐term cycle stability of 77.9% over 400 cycles at 0.2 C. This study offers a strategy for utilizing stable carbon‐based conductive agents in sulfide‐based ASSBs to enhance their electrochemical performance.