Mesoporous Li4Ti5O12−x/C submicrospheres with comprehensively improved electrochemical performances for high-power lithium-ion batteries

Abstract

To comprehensively improve the performance of Li₄Ti₅O₁₂ (LTO), a synergistic method combining compositing, crystal structure modification and hierarchical particle structuring is employed in this work. Monodispersed/multidispersed mesoporous Li₄Ti₅O_12−x/C submicrospheres were fabricated using monodispersed/multidispersed TiO₂ submicrospheres, lithium hydroxide and sucrose as precursors. The Li₄Ti₅O_12−x/C submicrospheres have a well-crystallized spinel structure, no blockages of Li⁺ ion transport pathways, 2.69–3.03% O²⁻ vacancy contents (vs. all 32e sites in the spinel structure), and 12.9–14.6% Ti³⁺ ion contents (vs. all titanium ions). Thus, the electronic conductivity and Li⁺ ion diffusion coefficient of particles can be significantly improved, and the working potential is 4.4–4.7 mV lower than that of LTO. Furthermore, these submicrospheres contain 1.06–1.44 wt% carbon as carbon coatings (2–3 nm in thickness) and carbon nanoparticles (∼20 nm in size), resulting in smaller primary particle sizes (<100 nm), large specific surface areas (12–15 m² g⁻¹), proper pore sizes (∼4 nm) and enhanced electrical conduction between particles. In addition, the submicrospherical morphology allows large tap densities (1.41–1.71 g cm⁻³). As a result of this desirable structure, these mesoporous Li₄Ti₅O_12−x/C submicrospheres exhibit comprehensively improved electrochemical performances. The optimized sample, with an ideally graded sphere-size distribution ranging from 100 nm to 600 nm, shows the largest tap density of 1.71 g cm⁻³, high first cycle Coulombic efficiency of 95.0% and 4.5 mV lower working potential. At 10 C, its capacity is as high as 119 mA h g⁻¹ with capacity retention of 95.9% over 100 cycles.