Interplay between Cation and Anion Redox in Ni-Based Disordered Rocksalt Cathodes.

The reversibility of the redox processes plays a crucial role in the electrochemical performance of lithium-excess cation-disordered rocksalt (DRX) cathodes. Here, we report a comprehensive analysis of the redox reactions in a representative Ni-based DRX cathode. The aim of this work is to elucidate the roles of multiple cations and anions in the charge compensation mechanism that is ultimately linked to the electrochemical performance of Ni-based DRX cathode. The low-voltage reduction reaction results in the low energy efficiency and strong voltage hysteresis. Our data reveal that the Mo migration between octahedral and tetrahedral sites enhances the O reduction potential, thus offering a potential strategy to improve energy efficiency. This work highlights the important role that the high-valence transition metal plays in the redox chemistry and provides useful insights into the potential pathway to further address the challenges in Ni-based DRX systems.