The mechanical degradation of cathodes during charge–discharge cycling poses a critical limitation to the cycle life of aqueous zinc‐ion batteries (AZIBs). Although the degradation of MnO 2 cathodes has been extensively investigated, the underlying reaction mechanisms have long remained a subject of debate, and the associated mechanical evolution during cycling is still poorly understood. In this work, a comprehensive investigation of electrochemical phase transitions and chemical strain evolution in δ‐MnO 2 cathode is presented using a custom‐built in situ strain testing system based on digital image correlation. The results reveal that the discharge–charge mechanism of δ‐MnO 2 proceeds through initial cointercalation of H + and Zn 2+ causing elastic deformation, followed by phase transformation to ZnMn 2 O 4 . During charging, this phase transformation coupled with ZnMn 3 O 7 formation induces irreversible plastic deformation, generating substantial residual strain and cathode volume expansion. Increasing current density can effectively reduce residual strain by suppressing phase transformation, thereby enhancing electrode cycling stability.
Chen et al. (Thu,) studied this question.