Empowering higher energy sodium‐ion battery cathode by oxygen chemistry

Abstract Sodium (Na) ion batteries (SIBs) promise low‐cost energy storage systems but are still restricted by insufficient energy density. Introducing oxygen (O) redox into the design of the Na‐storage cathode is presently considered an effective avenue to generate extra capacity in solving the energy density bottleneck. The succeeding issues are how to overcome the irreversible electrochemical behavior accompanied by O release. Meanwhile, the O redox chemistry and subsequent structural evolution remain ambiguous so far. Here, we deliberate on the O redox mechanism in Na‐storage transition metal oxides. Challenges associated with the reaction irreversibility and structural collapse are summarized by virtue of the advanced characterization techniques. Beyond that, strategies that potentially enhance the electrochemical properties of O redox and future research perspectives on exploring useable O redox cathode materials are outlined.