Impact of Mg-Doping Site Control in the Performance of Li₄Ti₅O₁₂ Li-Ion Battery Anode: First-Principles Predictions and Experimental Verifications

Li₄Ti₅O₁₂ (LTO) has attracted tremendous attention as a stationary Li-ion battery anode material due to its excellent stability. However, the poor rate capability caused by the low electrical conductivity limits its practical use. Previously, Mg-doping in LTO has been used to improve the electrical conductivity and electrochemical properties, but the Mg-doped LTO system generally exhibits large anomalies in the electrical properties and capacities, which limits the reliable mass-production of engineered LTO. In this study, on the basis of first-principles calculations and related experiments, we systematically study the effects of charge-compensating point defects of the Mg-doped LTO on the electrical properties. A combination of first-principles calculations with thermodynamic modeling shows that high-temperature annealing under reducing conditions could effectively alter the Mg-doping site from a Ti⁴⁺ to Li⁺ site and increase the electrical conductivity significantly due to reduced electron effective mass and increased carrier concentration. Mg-doped LTO annealed under reducing condition exhibits a significantly improved rate capability compared with that of LTO annealed under air condition. The theoretical-analysis-associated experimental results provide more general design guidelines for the preparation of doped LTO with the promise of further improvements in performance. (Graph Presented).