Solvothermal synthesis and electrochemical behavior of nanocrystalline cubic Li-Ti-O oxides with cationic disorder

Electrochemically active Li-Ti-O oxides of approximate composition LiTi2O4 + δ were prepared by solvothermal reaction between TiO2 and lithium hydroxide in water or ethanol at temperatures below 200 °C. This reaction proceeds via dissolution-precipitation mechanism and its course is not sensitive to crystal structure of TiO2 used in synthesis. The product of the hydrothermal process has cubic structure derived from that of spinel (Fd3m), with O atoms in 32e sites, Li in 8a sites and Ti atoms randomly distributed between 16c and 16d positions. The materials prepared in ethanol contain Ti in the 16d position only; on the other hand, Li is distributed between both types of available tetrahedral sites 8a and 8b. All prepared materials are active for Li insertion. Li entering the material during reduction process is preferentially located in 8b position. The presence of Li tetrahedrally coordinated positions indicates that Li insertion leads to a formation of a metastable structure stabilized probably by the nanocrystalline character of the material.