Sulfur‐Assisted Surface Modification of Lithium‐Rich Manganese‐Based Oxide toward High Anionic Redox Reversibility

Energy storage via anionic redox provides extra capacity for lithium‐rich manganese‐based oxide cathodes at high voltage but causes gradual structural collapse and irreversible capacity loss with generation of On− (0 ≤ n < 2) species upon deep oxidation. Herein, the stability and reversibility of anionic redox reactions are enhanced by a simple sulfur‐assisted surface modification method, which not only modulates the material's energy band allowing feasible electron release from both bonding and antibonding bands, but also traps the escaping On− via an as‐constructed SnS2−x−σOy coating layer and return them to the host lattice upon discharge. The regulation of anionic redox inhibits the irreversible structural transformation and parasitic reactions, maintaining the specific capacity retention of as‐modified cathode up to 94% after 200 cycles at 100 mA g−1, along with outstanding voltage stability. The reported strategy incorporating energy band modulation and oxygen trapping is promising for the design and advancement of other cathodes storing energy through anion redox. Sulfur‐assisted modification is introduced for the construction of SnS2−x−σOy coating and sulfur atoms substituting lattice oxygen. The sulfur anions in the lattice enhance the reversibility of the anionic redox by modulating the band of the redox‐active center. The additional coating effectively traps the escaping active oxygen, and the trapped oxygen and coating return to the pristine upon discharge.