Atomistic Structure and Ab Initio Electrochemical Properties of Li₄Ti₅O₁₂Defect Spinel for Li Ion Batteries

The Li 4 Ti 5 O 12 defect spinel is a promising anode material for lithium ion batteries because it transforms to/from Li 7 Ti 5 O 12 with a negligible volume change during charging/discharging. Ab initio calculation is a powerful approach for modern materials design and mechanistic studies. However, the atomistic models of the stoichiometric Li 4 Ti 5 O 12 and Li 7 Ti 5 O 12 defect spinel have not been optimized due to the requirements of large unit cells and numerous atomistic arrangements of Li and Ti ions at the 16d sites of the defect spinel. In this study, ab initio calculations were systematically performed and the most energetically favorable full supercell models were constructed for both Li 4 Ti 5 O 12 and Li 7 Ti 5 O 12 defect spinel. The equilibrium lattice parameter of Li 4 Ti 5 O 12 was 8.4257 Å, while a slight lattice shrinkage of 0.77% and an average intercalation voltage of 1.41 V during charging/discharging were obtained. Moreover, the Li 4 Ti 5 O 12 phase shows insulating property with a wide bandgap of around 2.3 eV, while the Li 7 Ti 5 O 12 phase exhibits metallic property. All the calculated structural and electrochemical properties agree closely with the experimental findings in literature. Further theoretical studies on the Li 4 Ti 5 O 12 defect spinel or other defect spinel in general can be realized according to the full supercell models proposed in this study.