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 robust Mn-F bond whittles the interaction between Mn and O, giving rise to more oxygen participating in the charge compensation process. 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.