Achieving reversible Mn2+/Mn4+ double redox couple through anionic substitution in a P2-type layered oxide cathode

P2-type Mn-based layered oxides have emerged as promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical capacity. However, the incorporation of Mn 3+ cations induce severe Jahn-Teller (J-T) effect, which seriously distorts the localized lattice structure and results in insufficient battery performance. Herein, we successfully introduce reversible Mn 2+ /Mn 4+ double redox couple into P2-type Na 0.6 Mg 0.3 Mn 0.7 O 2 cathode with suppressed J-T effect through F anion doping strategy. The comprehensive results clearly suggest that F-substitution with an appropriate amount enlarges the interlayer spacing and reduces the band gap, resulting in accelerated charge transfer kinetics. In addition, the strong interaction between Mn and F suppresses the Mn 2+ dissolution at discharged states and promotes the reversible conversion from Mn 2+ to Mn 4+ at charged states, leading to ameliorated J-T effect and enhanced electrochemical performance. Moreover, the oxygen redox reaction is also enhanced through F anion doping strategy. Our present study provides an effective avenue to address the J-T effect by introducing reversible Mn 2+ /Mn 4+ double redox couple in Mn-based oxides, which is expected to revive this cathode family toward practical applications of SIBs. Reversible Mn 2+ /Mn 4+ double redox couple and enhanced oxygen redox reaction in Mn-based cathodes of sodium-ion batteries are achieved through F anion doping strategy, leading to the ameliorated J-T effect and enhanced electrochemical performance. • Reversible Mn 2+ /Mn 4+ double redox couple in Mn-based layered oxides is achieved through F anion doping. • Appropriate amount of F doping improves the specific capacity and rate capability of cathode material. • The strong bonding between Mn and F suppresses the dissolution of Mn 2+ and ameliorate Jahn-Teller effect. • The redox reaction of oxygen is enhanced because the robust Mn-F bond whittles the interaction between Mn and O.