Effects of TiO_2 Starting Materials on the Solid-State Formation of Li_4Ti_5O_(12)

摘要

This study examined the formation mechanism of Li_4Ti_5O_(12) by a solid-state reaction between Li_2CO_3 and TiO_2 for applications in lithium ion batteries. To explain the intermittent existence of rutile TiO_2 in the final Li_4Ti_5O_(12), five types of TiO_2 which had different anatase/rutile ratios were used as starting materials. Anatase to rutile-phase transformation occurred from 600℃, which is significantly lower than the typical TiO_2 transition temperature, when a pure anatase TiO_2 and Li_2CO_3 mixture were heat-treated. Moreover, this rutile TiO_2 transformed from pure anatase TiO_2 was found to be more rigid in the solid-state reaction than an intact rutile or anatase-rutile mixture, existing in the final Li_4Ti_5O_(12), even after heat treatment at 900℃ for 15 h. This difference is explained by the anatase/rutile-phase boundaries where an amorphous Li-precursor was located, enhancing the solid-state reaction due to the decreased diffusion path. Based on the observations, different formation mechanisms of Li_4Ti_5O_(12) depending on the types of TiO_2 starting materials were proposed.