In situ study of solid-state synthesis of Li4Ti5O12-Li2TiO3 and Li4Ti5O12-TiO2 composites

Lithium titanate Li4Ti5O12 (LTO) with a spinel structure has been actively studied as a potential candidate for the negative electrode material in lithium ion batteries. In this work, LTO-Li2TiO3 (LTC) and LTO-TiO2 (LTT) composites were investigated. The use of powder X-ray diffraction (PXRD) with synchrotron radiation (SR) made it possible to trace the process of formation of the composites in situ and obtain information on changes in the phase composition of reaction products depending on the temperature and the ratio of the initial reagents, Li2CO3 and TiO2. It was found that irrespective of the initial ratio of reagents (lack of Li2CO3, stoichiometric ratio or excess of Li2CO3 for LTC, LTO and LTT samples, respectively), the synthesis proceeds in three stages, including formation of nanocrystalline Li2TiO3 as intermediate phase. LTC composites consist of microparticles of Li4Ti5O12phase covered by a layer of Li2TiO3phase, whereas in LTT composites large particles of TiO2 phase are surrounded by microparticles of LTO phase. Electrochemical studies showed that LTT composites have relatively low capacity as expected assuming that TiO2 is electrochemically inactive phase in the composites. In contrast, LTC composites have a specific capacity of 187 mAh/g that exceeds the theoretically expected capacity values. According to highresolution electron microscopy data (HREM), LTC composites have a large number of Li4Ti5O12/Li2TiO3 interfaces, which are diffuse and seem to be coherent due to similarity of crystal structures LTO and Li2TiO3.