High-entropy substitution: A strategy for advanced sodium-ion cathodes with high structural stability and superior mechanical properties

O3-type sodium layered oxides are promising energy storage materials because of their high initial Na content and 2D diffusion channels. However, the undesired structural degradations during the repeated charging/discharging process and the severe performance fade following the brief exposure to the humid air, have greatly limited their practical application. Herein, by introducing high-entropy components into the crystal structure of O3-NaNi0.5Mn0.5O2, these concerns are significantly alleviated. To do this, eight metal species sharing the same site are introduced into the transition metal slabs, thus achieving an in-plane high-entropy configuration, which exhibits a postponed phase evolution, an enhanced humid-air stability, and a soothing evolution of interlayer distance. In addition, the stronger mechanical properties of micro-scale particles are also achieved in this multi-component substituted cathode, which keeps the particle integrity even after a long-term cycle. Our work provides an important guidance for the study of high-entropy substitution strategies in the sodium-ion layered cathodes.