High-pressure study of Li[Li1/3Ti5/3]O4 spinel

Abstract

Crystal structures and electrochemical reactivities of high-pressure forms of the lithium titanium spinel Li[Li_1/3Ti_5/3]O₄ (LTO) were investigated under a pressure of 12 GPa to elucidate its structural phase transition from spinel to post-spinel and to obtain a wide variety of electrode materials for lithium-ion batteries. LTO is recognized as a “zero-strain” lithium insertion material, because the change in the lattice parameter is negligibly small during charge and discharge reactions. As the heating temperature increased, the initially spinel-structured LTO decomposed into an amorphous phase at 400 °C and then changed into a mixture of columbite-type TiO₂ (C-TiO₂) and Li₂O phases at temperatures above 600 °C. According to selected-area electron diffraction analyses, the amorphous phase at 400 °C was a mixture of two different phases, one of which was C-TiO₂. Electrochemical investigations of the sample heated to 1000 °C exhibited stable charge and discharge curves with a rechargeable capacity of ∼40 mA h g⁻¹, as was previously reported for C-TiO₂. Details of the structural change from the spinel to columbite structure are also discussed in this report.