Sumyeong Choi

The mainstream of high‐energy cathode development is focused on increasing the Ni‐ratio in layered structured cathode materials. The increment of the Ni portion in the layered cathode material escalates not only the deliverable capacity but also the structural degradation. High‐Ni layered cathodes are highly vulnerable to exposure to air that contains CO₂ and H₂O, forming problematic residual lithium compounds at the surface. In this work, a novel air‐ and moisture robust surface modification is reported for LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) via the sol‐gel coating method that selectively coats the internal surface area of the polycrystalline morphology secondary particles. Bare‐, Li₂SnO₃‐coated and LiCoO₂‐coated NCM811 are exposed to different ambient environments (air, hot‐air, and moisture‐air) to systematically investigate the correlation between the internal/external coating morphology and performance degradations. The LiCoO₂‐coated NCM811s exhibit high‐capacity retention after exposure to all environments, due to the internal surface coating that prevents the penetration of harmful compounds into the polycrystalline NCM811. On the other hand, the Li₂SnO₃‐coated NCM811s exposed to the ambient environments show gradual capacity fading, implying the occurrence of internal degradation. This paper highlights the impact of the internal degradation of polycrystalline NCM811 after environmental exposure and the correct coating mechanisms required to successfully prevent it.