Axial Compressive Strain Stabilized High Spin State of Mn 3+ Enables High‐Performance Aqueous Zinc‐Ion Battery

ABSTRACT Aqueous zinc‐ion batteries (AZIBs) are promising candidates for grid‐scale energy storage owing to their intrinsic safety, low‐cost, and environmental benignity. Manganese dioxide (MnO 2 ) cathodes, in particular, offer high theoretical capacity and natural abundance but suffer from irreversible Jahn–Teller distortion induced by Mn 3+ species and subsequent manganese dissolution, leading to severe capacity degradation. Herein, we propose an innovative axial compressive strain engineering strategy to tackle this challenge via the substitution of O 2− with highly electronegative F − anions in the MnO 2 lattice. This deliberate anion doping effectively shortens the axial Mn‐O bond, thereby directly suppressing the Jahn–Teller distortion. More profoundly, the incorporation of F − ions disrupts the lone electron occupancy in the e g orbital. During the battery discharge process, the electron configuration transitions from the high‐spin t 2g 3 e g 1 state to the more stable t 2g 3 e g 2 configuration, which stabilizes the Mn 3+ state and drastically inhibits Mn dissolution. As a result, the F‐doped MnO 2 (F‐MnO 2 ) cathode delivers exceptional cycling stability, retaining 81% of its initial capacity after 1000 cycles at 2 A g −1 . This work not only demonstrates an effective cathode material but also provides fundamental insights into stabilizing crystal structures of manganese oxides for advanced energy storage technologies.