Surface Passivation of LiCoO₂ by Solid Electrolyte Nanoshell for High Interfacial Stability and Conductivity

The practical application of lithium cobalt oxide (LiCoO₂ ) cathodes at high voltages is hindered by the instability of the surface structure and side reactions with the electrolyte. Herein, we prepared a multifunctional hierarchical core@double-shell structured LiCoO₂ (MS-LCO) cathode material using a scalable sol-gel method. The MS-LCO cathode material comprised an outer shell with fast lithium-ion conductivity, a La/Zr co-doped inner shell, and a bulk LiCoO₂ core. The outermost shell prevented direct contact between the electrolyte and LiCoO₂ core, which alleviated the electrolyte decomposition and loss of active cobalt, while the La/Zr co-doped shell improved the structural stability at higher voltages in a half-cell with a liquid electrolyte. The MS-LCO cathode exhibited a stable capacity of 163.1 mAh g^-1 after 500 cycles at 0.5 C, and a high specific capacity of 166.8 mAh g^-1 at 2 C. In addition, a solid lithium battery with the surface-passivated MS-LCO cathode and a polyethylene oxide (PEO)-based inorganic/organic composite electrolyte retained 85.8 % of its initial discharge capacity after 150 cycles at a charging cutoff voltage of 4.3 V. Thus, the introduction of a surface-passivating shell can effectively suppress the decomposition of PEO caused by highly reactive oxygen species in LiCoO₂ at high voltages.