Composition Dependencies of Positive Electrode Properties and Local Structures of Li_1+xNb_xFe_1–2xO₂ with a Disordered Rocksalt Structure

In this study, Li_1+xNb_xFe_1–2xO₂ (x = 0.05~0.25) with the disordered rocksalt structure were synthesized and the electrode properties and atomic arrangement were investigated. The local structures were examined by X-ray total scattering measurements and reverse Monte Carlo modeling using the data. It is found that the lattice parameter increases with increasing the Li (Nb) content, but the M−O distance in the first coordination shell decreases due to the contribution of the Nb−O correlation. This structural change could increase the space for lithium-ion diffusion. On the other hand, Nb with high valence tends to be localized around Li, suggesting that Nb inhibits ion diffusion during charge and discharge processes. Based on these results, it is necessary to consider not only the size of the constituent cations but also their valence to design new materials.