Effects of Metal Composition and Preparation Process on Negative Electrode Properties and Crystal Structure of Ga-Substituted TiNb<sub>2</sub>O<sub>7</sub>

In this paper, we investigated the effects of Ga substitution and preparation process on the negative-electrode properties of Wadsley–Roth phase TiNb2O7. We also investigated the crystal structures of the samples with different Ga compositions via the Rietveld refinements and then discussed the relationship between the electrode properties and the structure. We demonstrated that the Ga substitution to TiNb2O7 was successful based on the diffraction patterns and X-ray absorption near-edge structure (XANES) spectra. The investigation of the electrode properties showed that the capacities associated with the insertion and deinsertion of Li+ were improved by the Ga substitution, and that excellent electrode properties could be achieved by optimizing the preparation process. Furthermore, by performing Rietveld analysis using both neutron and synchrotron X-ray diffraction data, it was revealed that the distortion of the crystal structure was suppressed by the Ga substitution. Such a structural change by the Ga substitution was considered to be one of the factors for improving the electrode properties.