Protective Coating of Single-Crystalline Ni-Rich Cathode Enables Fast Charging in All-Solid-State Batteries

Improving interfacial stability between cathode active material (CAM) and solid electrolyte (SE) is vital for developing high-performance all-solid-state batteries (ASSBs), with compatibility issues among the cell components representing a major challenge. CAM surface coating with a chemically inert ion conductor is a promising approach to suppress side reactions occurring at the cathode interfaces. Another strategy to mitigate mechanical degradation involves utilizing single-crystalline particle morphologies. Their more robust bulk structure and lower tortuosity for charge transport, compared to polycrystalline (PC) CAMs, can significantly enhance cyclability in ASSBs. Herein, we coated a LiNbO₃ protective layer onto the free surface of quasi single-crystalline LiNi_0.83Co_0.12Mn_0.05O₂ (SC83) particles. Pellet-stack ASSB cells using the LiNbO₃@SC83 CAM and argyrodite Li₆PS₅Cl as SE showed a capacity retention of 88% after 1000 cycles at the 1 C rate, compared to only 71% for the uncoated counterpart and far superior to that of LiNbO₃@PC83 (30%). The effectiveness of LiNbO₃ coating and the SC-NCM nature in mitigating electro-chemo-mechanical degradation was studied by combining modeling and physical/electrochemical characterizations. We demonstrate that the capacity decay at fast charge is due primarily to the mechanical degradation of CAM particles, while it is strongly determined by CAM|SE interfacial reactions under slow-charging conditions.