Local Structures in Disordered Rocksalt-Type Li3NbO4-Based Positive Electrode Materials for a Lithium-Ion Battery

Li-rich transition-metal oxides with a disordered rocksalt structure have drawn much attention as promising candidates for a positive electrode material of a lithium-ion battery. Among the oxides, this study focuses on Li1.3Nb0.3Fe0.4O2 and Li1.3Nb0.43Ni0.27O2, and investigates local distortions around the cations and local cation ordering in the materials by means of a reverse Monte Carlo modeling using neutron and synchrotron X-ray total scattering data. It is found from the simulated atomic configurations that a local distortion around Nb is larger than those around the other cations in both the materials. The large distortion is supposed to be induced by a smaller ionic radius of Nb than the others and/or a mismatch of electronic state of Nb in the disordered rocksalt structure. Furthermore, a coordination-number analysis on the materials demonstrates that Li tends to be surrounded by Nb significantly in the disordered rocksalt structure. From these results, it can be considered that Li diffusion is disturbed by a cation with a higher valence in the disordered rocksalt structure.