Atomic‐Resolution Electron Microscopy of Cathode–Electrolyte Interfacial Degradation: Zr‐Based Oxide‐Coated Regions Preserve Layered LiCoO ₂

Layered metal oxides are used as cathode materials in lithium‐ion batteries due to their high energy density. However, these materials undergo degradation due to structural changes at high charging voltages (>4.2 V vs. Li/Li + ). One approach to addressing this issue involves coating the cathode with metal oxides, but understanding the effects of such a coating remains limited. In this study, we investigated the effect of a Zr‐based oxide coating on an epitaxial LiCoO 2 (LCO) model cathode using atomic‐resolution scanning transmission electron microscopy (STEM), focusing on the cathode–electrolyte interfacial structure under partially coated conditions. Electrochemical measurements showed that LCO with Zr‐based oxide coating exhibited reduced discharge voltage decay during 4.5 V cycling under our conditions. STEM observations indicated that the Zr‐based oxide coating is spatially non‐uniform, enabling a direct comparison between adjacent coated and uncoated regions. The layered LCO cathode is preserved at the coated regions, while a spinel Co 3 O 4 ‐like structure approximately 2 nm thick forms at the adjacent uncoated regions. These observations provide direct structural evidence of a spatial correspondence between local coating presence and preservation of layered LCO at the interface.