A synergetic promotion of surface stability for high-voltage LiCoO₂ by multi-element surface doping: a...

The utilization of high-voltage LiCoO₂ is an effective approach to break through the bottleneck of practical energy density in lithium ion batteries. However, the structural and interfacial degradations at the deeply delithiated state as well as the associated safety concerns impede the application of high-voltage LiCoO₂. Herein, we present a synergetic strategy for promoting the surface stability of LiCoO₂ at high voltage by Ti-Mg-Al co-doping and systematically study the effects of the dopants on the surface stability, electronic structure and Li⁺ diffusion properties of the LiCoO₂ (104) surface using first-principles calculations. It is found that Ti, Mg and Al dopants can be facilely introduced into the Co sites of the LiCoO₂ (104) surface. Furthermore, the co-doping could significantly stabilize the surface oxygen of LiCoO₂ at a high delithiation state. Particularly, by aggregating Ti-Mg-Al co-dopant distribution in the surface layer, surface oxygen loss is dramatically suppressed. In addition, analysis of the electronic structure indicates that Ti-Mg-Al co-doping can enhance the electronic conductivity of the LiCoO₂ (104) surface and greatly inhibit the charge deficiency of the superficial lattice O atoms at a highly delithiated state. In spite of a negligible improvement in the surface Li⁺ diffusion kinetics, the Ti-Mg-Al surface-modified LiCoO₂ is expected to exhibit improved electrochemical performance at high voltage due to its superior surface stability. Our results suggest that aggregating Ti, Mg and Al co-dopant distribution in the surface layer is a promising modulation strategy to synergistically promote the surface oxygen stability of LiCoO₂ at high voltages.