Activation of anionic redox reactions with vacancies in layered potassium manganese oxide

Layered manganese-based oxides are promising cathode materials for potassium-ion batteries (PIBs) owing to the abundant K resources. However, their energy density is limited to the accessible redox centers. Herein, P'2-type K_0.51Mn_0.93Mn_□0.07O₂ (Mn_□ = Mn vacancy) is synthesized to activate anionic redox reactions (ARRs) by introducing native Mn vacancies into the transition-metal slabs. The vacant Mn sites facilitate the formation of non-bonding O 2p orbitals to trigger ARRs, owing to their high orbital energy close to the Fermi level, and provide additional capacity. The presence of ARRs suppresses phase transition and results in formation of O-O dimers for stable oxygen networks to mitigate oxygen loss. High specific capacity of 116 mAh g^-1 with long cycle stability can be obtained based on the successive redox of Mn^3.75+/Mn^3.88+ and O^2-/O^n- (n < 2). This work provides a new pathway to activate ARRs with vacancies for high specific capacities and stable cycling for PIBs.