Effect of transition metal cations on the local structure and lithium transport in disordered rock-salt oxides.

Lithium-excess oxides LiTiMnO and LiNbMnO with a disordered rock-salt structure and Mn/Mn as a redox couple were compared to analyze the effect of different d metal ions on the local structure and Li ion migration. These cathode materials were obtained by mechanochemically assisted solid-state synthesis. Using XRD, Li NMR and EPR spectroscopy and transmission electron microscopy it was shown that the Mn ions are prone to form clusters, while d metal ions are evenly distributed in the crystal lattice. The presence of Nb ions contributes to the formation of noticeably larger Mn clusters and larger gaps in the Li migration maps as compared to Ti. These results were confirmed by the geometrical-topological method, BVSE simulation and DFT calculations, and are in good agreement with the Li diffusion coefficient determined by GITT, which is 1.5 orders of magnitude higher in LiTiMnO than that in LiNbMnO.