Preparation of a spinel Li_4Ti_5O_(12) (111) surface from a rutile TiO_2 single crystal

摘要

Spinel Li_4Ti_5O_(12) is a very promising material for electrodes in a wide range of Li-ion battery applications because of its unique Li-insertion/extraction properties. Although the bulk properties of Li_4Ti_5O_(12) have been studied intensively, there have been few reports about the structure and properties of Li_4Ti_5O_(12) surfaces in spite of the importance of solid/electrolyte interfaces. This is because of the difficulty in preparing Li_4Ti_5O_(12) samples with accessible flat surfaces suitable for scanning probe microscopy study. To address this, we have successfully prepared a flat Li_4Ti_5O_(12) crystal surface by solid state reaction from a rutile TiO_2 (111) wafer with LiOHH_2O powder. Out-of-plane X-ray diffraction (XRD) and transmission electron microscopy revealed that a highly oriented and crystallized Li_4Ti_5O_(12) (111) film was formed on the TiO_2 (111) wafer. Atomic force microscopy observations revealed that an atomically flat Li_4Ti_5O_(12) (111) surface was formed on the film with terraces of 200-300 nm width and steps of a {111} inter-planar height. The formed thin films were also investigated by cyclic voltammetry and galvanostatic experiments, revealing that the films have electrochemical activity as battery electrodes.