Optimized Solid-State Reaction Process of Synthesizing Li4Ti5O12 with Improved Rate Capability for Li-Ion Batteries

Abstract

Spinel Li4Ti5O12 (LTO) has been actively studied due to its predominant properties in safety issue. LTO can be synthesized by different synthesis techniques including solid-state reaction, sol-gel, high energy ball milling, hydrothermal method, spray pyrolysis, etc. Among these synthesizing methods, the solid-state reaction method is the most commercially available process. It is very important to reduce calcination temperature and time in mass production using solid-state reaction. We prepared several sets of LTOs using commercially available precursors (TiO2) which have various particle sizes. We also varied calcination temperature in each fixed TiO2 particle size. We found the optimum process condition that has the best electrochemical properties. The sizes of the TiO2 precursors are 15 nm, 25 nm, 32 nm, and 40 nm. The calcination temperatures are 700 °C, 750 °C, 800 °C, and 850 °C. The calcination time (36 hr) is too long to prepare single phase LTO at 700 °C. The single phase LTOs are obtained in all the size of the used TiO2 particle at 800 °C and 850 °C, but the LTO particles are 1 ~ 2 um, which is too large. The pure LTOs are synthesized in all the TiO2 particle size except for 15 nm at 750 °C. The calcination time was varied from 36 hr to 1hr. The rate performance is conducted in all the fabricated samples. When the calcination time is 36hr, the best capacity is obtained in the sample, which 32 nm TiO2 particle is used. At 50 C, the capacity of the sample was 88 mAh/g when the 32 nm TiO2 precursor is used. The synthesized LTO at 750 °C shows best capacity of 122 mAh/g when the calcination time is 1 hr. The best electrochemical performance was due to small particle size, resulting in fast Li-ion diffusion and larger contact area between particles. We also fabricated Li-ion capacitor using the LTO and investigated the electrochemical behaviors.