Surface-Engineered Li₄Ti₅O₁₂ Nanostructures for High-Power Li-Ion Batteries

Materials with high-power charge-discharge capabilities are of interest to overcome the power limitations of conventional Li-ion batteries. In this study, a unique solvothermal synthesis of Li₄Ti₅O₁₂ nanoparticles is proposed by using an off-stoichiometric precursor ratio. A Li-deficient off-stoichiometry leads to the coexistence of phase-separated crystalline nanoparticles of Li₄Ti₅O₁₂ and TiO₂ exhibiting reasonable high-rate performances. However, after the solvothermal process, an extended aging of the hydrolyzed solution leads to the formation of a Li₄Ti₅O₁₂ nanoplate-like structure with a self-assembled disordered surface layer without crystalline TiO₂. The Li₄Ti₅O₁₂ nanoplates with the disordered surface layer deliver ultrahigh-rate performances for both charging and discharging in the range of 50-300C and reversible capacities of 156 and 113 mAh g^-1 at these two rates, respectively. Furthermore, the electrode exhibits an ultrahigh-charging-rate capability up to 1200C (60 mAh g^-1; discharge limited to 100C). Unlike previously reported high-rate half cells, we demonstrate a high-power Li-ion battery by coupling Li₄Ti₅O₁₂ with a high-rate LiMn₂O₄ cathode. The full cell exhibits ultrafast charging/discharging for 140 and 12 s while retaining 97 and 66% of the anode theoretical capacity, respectively. Room- (25 °C), low- (- 10 °C), and high- (55 °C) temperature cycling data show the wide temperature operation range of the cell at a high rate of 100C.