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 regulated local oxygen coordination environment by incorporating Ru4+/Ru5+ redox couple into P2-type Na0.6Li0.2Mn0.8O2 (NLMO) to achieve reversible anionic redox reaction. Upon high-voltage charging, the formed Ru5+ state with a half-filled t2g 4d3 electronic configuration establishes a strengthened π-type interaction with non-bonding O 2p orbitals within the Na-O-Li configuration compared to the inherently weaker Mn-O π-type interaction in NLMO. Such a strengthened π-type interaction effectively enhances anionic redox reversibility, suppresses irreversible oxygen release and realizes a complete solid-solution behavior with stable TMO6 octahedra throughout cycling. This preserved structural integrity also prevents crack formation and minimizes transition metal dissolution, thereby mitigating surface degradation. The resulting Na0.6Li0.2Mn0.7Ru0.1O2 (NLMRO) thus exhibits a reversible anionic redox with markedly improved cycling stability. Our work highlights that dynamically engineering potent π-interaction during electrochemical cycling is a promising avenue for developing high-performance SIBs with cumulative cationic and anionic redox reactions.
