Tuning Surface Rock-Salt Layer as Effective O Capture for Enhanced Structure Durability of LiCoO2 at 4.65 V

Recently, the rock-salt (RS) phases are utilized to enhance the surface stability of LiCoO2 (LCO), however, the optimization mechanism still remains vague. Herein, the structure stability of LCO is successfully enhanced via constructing a tough surface RS layer (approximate to 5 nm), namely, the RS-LCO. This surface RS layer plays a significant role on capturing the migrated lattice O ions upon charging, leading to the progressive phase transition from an inert RS phase to an ionic conductive spinel phase in the surface, and suppresses the bulk H1-3 separation beyond 4.6 V. As a result, not only the oxygen redox induced side reactions are greatly reduced, but also the Li+-ion's transport is significantly promoted. The RS-LCO/Li cells show a remarkable cycle stability with 89.7% capacity retention after 1000 cycles in 3-4.6 V at current of 1 C (1 C = 200 mA g(-1)), and 81.2% capacity retention after 400 cycles in 3-4.65 V at 1 C. Besides, the RS-LCO/graphite cells show nearly no capacity decay in 600 cycles in 3-4.55 V at 1 C. This work provides a new insight to understand the role of surface RS phase layer on developing the advanced LCO.