Insight into the formation mechanism of Li4Ti5O12 microspheres obtained by a CTAB-assisted synthetic method and their electrochemical performances

Abstract

Porous Li₄Ti₅O₁₂ (LTO) microspheres consisting of a stack of primary nano-crystalline grains were prepared by adding dropwise LiOH solution into tetrabutyl titanate (TBT)/cetyltrimethylammonium bromide (CTAB) glycol solution, followed by hydrothermal synthesis and further calcination. In order to understand the formation mechanism of LTO microspheres, the effects of cationic species and pH of solution on the hydrolysis of TBT in TBT/CTAB/LiOH solution were studied first by using NaOH, KOH and LiCl as substitutes for LiOH solution. Furthermore, in order to study the effect of CTAB, the morphology and microstructure of hydrothermal products and calcined products from TBT/CTAB/LiOH and TBT/LiOH solution were characterized by scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. The results indicate that strong basicity of solution and existence of CTAB in TBT/CTAB/LiOH solution are two necessary factors for the formation of LTO microspheres. The spinel LTO microspheres obtained are porous because of the loose stacking of primary nano-crystalline grains. The structure is beneficial for the improvement of the contact surface area between the electrode and electrolyte, and the quick diffusion of electrons and ions. Therefore, LTO microspheres exhibit excellent electrochemical performance. The specific capacities at 10C, 20C, 30C, 40C, 50C and 60C are up to 177, 175, 170, 165, 158 and 157 mA h g⁻¹, respectively. When the current density returns to 10C, the discharge capacity of LTO microspheres returns to the capacity at 10C; moreover, the capacity retention reaches 93% after 500 cycles.