Screening Na-Excess Cation-Disordered Rocksalt Cathodes with High Performance.

The practical application of Na-ion cathode materials is currently restricted by their low energy density and sluggish dynamics, while the cation-disordered rocksalt (DRX) structures offer a possible solution to the challenge. In this study, among the 24 candidates containing elements, we use mixing temperature as a descriptor to screen the synthesizable Na-excess DRX, and we have identified NaMnMoO as the most promising candidate that exhibits a Na percolating fraction of 53%, which is higher than that of LiMnTiO (35%) proposed in the previous study due to the larger lattice constant in Na-excess DRX cathodes. More importantly, NaMnMoO is predicted to have a capacity of 228 mAh/g with an energy density of 552 Wh/kg derived from percolation theory and cluster-expansion Monte Carlo simulations, which is higher than that of NaNbMnO and NaMnTiO synthesized recently. For a better understanding, the redox mechanism is explored, which involves Mo/Mo, Mn/Mn, and O/O (0 < < 2), indicating the participation of anionic redox. Meanwhile, the Na diffusion prefers a divacancy mechanism via an o-t-o diffusion channel with a low diffusion barrier of 0.29 eV. This study expands the family of DRX for the cathode of Na-ion batteries with enhanced performance.