Role of Oxide Ions in Thermally Activated Lithium Diffusion of Li[Li1/3Ti5/3]O4: X-ray Diffraction Measurements and Raman Spectroscopy

Abstract

Although Li[Li1/3Ti5/3]O4 (LTO) has been considered as an ideal electrode material for lithium-ion batteries (LIBs) because of its “zero-strain” character, initial LTO exhibits high Li conductivity (σLi) at high temperatures (T). In this paper, to clarify the inter-relation between LTO’s Li-diffusive nature and structural environment, we performed a systematic structural study on LTO using X-ray diffraction (XRD) measurements and Raman spectroscopy. The average and static information obtained by XRD measurements suggested that the bottleneck radius for Li conduction is limited to ∼0.41 even at 873 K, which is too small to explain the high σLi values in LTO. However, Raman spectroscopy demonstrated the dynamic structural changes of the LiO6 octahedron with T; the bond interaction between Li and O atoms decreases with T because of its anharmonic potential energy. Because the Raman-active modes in LTO correspond to changes in oxide ion position, oxide ions are determined to play a crucial role in obtaining h...