A robust strategy for crafting monodisperse Li₄Ti₅O₁₂ nanospheres as superior rate anode for lithium ion batteries

The ability to synthesizing monodisperse Li₄Ti₅O₁₂ (LTO) nanospheres is the key to reducing the irreversible capacity of LTO materials, and thus improving their power performance. However, it remains a grand challenge to achieve uniform precursors of LTO nanospheres and maintain their spherical structures after annealing. Herein, we develop a robust strategy for the synthesis of monodisperse LTO nanospheres with an average diameter of 120nm via the use of titanium nitride (TiN) as a titanium source for lithium ion batteries (LIBs). The precursors composed of uniform TiO₂/Li⁺ nanospheres were formed in a stable alkaline environment during the course of heating of the solution of peroxo-titanium complex as a result of the dissolution of TiN, while TiO₂/Li⁺ microspheres were easily yielded with the decrease in pH value of the precursor solution. The OH^- anion was found to effectively retard the hydrolysis of peroxo-titanium complex as well as the aggregation of TiO₂/Li⁺ nanoparticles. Intriguingly, a uniform polyvinyl pyrrolidone (PVP) layer formed in-situ on the surface of TiO₂/Li⁺ nanospheres rendered LTO to retain the monodisperse spherical morphology after annealing. Notably, the as-prepared monodisperse LTO nanospheres comprised of the interconnected LTO nanograins with an average size of ~15nm uniformly coated by a carbon layer derived from the carbonization of PVP exhibited a high tap density (1.1gcm^-3) and an outstanding rate-cycling capability. The charge specific capacities at 1, 10, 50 and 80C were 159.5, 151.1, 128.8 and 108.9mAh g^-1, respectively. More importantly, the capacity retention after 500 cycles at 10C was as high as 92.6%. This work opens up an avenue to craft the uniform precursors of LTO and thus monodisperse LTO nanospheres that possess superior rate performance with high volumetric energy densities and long-term cyclic stability.