Strengthened π-type interaction in layered oxide cathodes with reversible anionic redox for sodium-ion batteries.

Activating anionic redox activity in P2-type layered oxide cathodes is a promising pathway to enhance the specific capacity for sodium-ion batteries (SIBs). However, the highly active anionic redox process arising from the non-bonding O 2p orbitals frequently leads to irreversible oxygen release and surface degradation, which severely limit the long-term cycling stability. Herein, we propose a strategy of strengthening transition metal-oxygen (TM-O) π-type interaction with a regulated local oxygen coordination environment by incorporating the Ru/Ru redox couple into P2-type NaLiMnO (NLMO) to achieve a reversible anionic redox reaction.