Composition‐Controlled Cathode Protective Layer via Powder‐Atomic Layer Deposition for All‐Solid‐State Batteries

Abstract Controlling the ionic and electronic conductivities of the protective layers on cathode active materials (CAMs) is critical for interface stabilization with sulfide‐based solid electrolytes in all‐solid‐state batteries (ASSBs). In this study, lithium zirconium oxide layers with varying compositions are grown on LiNi _0.8 Co _0.1 Mn _0.1 O ₂ using an O ₃ ‐based atomic layer deposition process. The ionic conductivity reaches 2.20 × 10 ⁻⁷ S cm ⁻¹ at 25 °C, and the electronic conductivity ranges from 10 ⁻¹⁰ to 10 ⁻⁷ S cm ⁻¹ depending on composition. These composition‐dependent transport properties directly affect electrochemical performance, leading to a 4.5% difference in initial Coulombic efficiency and a 37% difference in long‐term retention. Compared to their uncoated counterparts, the coated CAMs exhibited 6.7% and 43% increases in initial efficiency and capacity retention of the cells, respectively. This study establishes a quantitative correlation between the protective layer's composition and battery performance, emphasizing that composition control is a key strategy for interfacial engineering in sulfide‐based ASSBs.