Electron Localization in Cation-Disordered Rock Salt Electrodes

In Li-ion battery cathode materials, the degree of electron localization and the resulting electron transport schemes fundamentally determine the redox behavior. How these fundamental properties exist in cation disordered rock salts (DRXs), an emerging class of Li-ion battery cathodes, and the roles of these properties in the electrochemistry of DRXs are intriguing questions yet to be answered. In this work, we report a strong electron localization effect in a series of Ni-based DRXs via a systematic array of electrochemical, computational, and spectroscopic analyses, and we determine the effect is due to the unique structure of the DRXs. By applying the same set of analyses to the well-known Ni-based layered cathode, we find that the strong electron localization effect is a decisive factor in the electrochemical performance of the rock salts. This work reveals an important property of DRXs, which has not been sufficiently emphasized by the community and also suggests a few opportunities regarding the development of all-new DRX cathodes.