Temperature-Driven Anisotropic Mg 2+ Doping for a Pillared LiCoO 2 Interlayer Surface in High-Voltage Applications.

High-voltage lithium cobalt oxide (LiCoO) has the highest volumetric energy density among commercial cathode materials in lithium-ion batteries due to its high working voltage and compacted density. However, under high voltage (4.6 V), the capacity of LiCoO fades rapidly due to parasitic reactions of high-valent cobalt with the electrolyte and the loss of lattice oxygen at the interface. In this study, we report a temperature-driven anisotropic doping phenomenon of Mg that results in surface-populated Mg doping to the side of the (003) plane of LiCoO. Mg dopants enter the Li sites, lower the valence state of Co ions with less hybridization between the O 2p and Co 3d orbitals, promote the formation of surface Li/Co anti-sites, and suppress lattice oxygen loss on the surface. As a result, the modified LiCoO demonstrates excellent cycling performance under 4.6 V, reaching an energy density of 911.2 Wh/kg at 0.1C and retaining 92.7% (184.3 mAh g) of its capacity after 100 cycles at 1C. Our results highlight a promising avenue for enhancing the electrochemical performance of LiCoO by anisotropic surface doping with Mg.