Cr ₂ O ₃ Induces Uniform Deposition of MnO ₂ for Enhancing the Long‐Cycle Stability of Aqueous Zn‐MnO ₂ Batteries

Aqueous zinc‐manganese batteries (AZMBs) are promising grid‐scale energy‐storage devices due to their high theoretical capacity, safety, and low cost. However, their practical deployment is limited by the formation of electrochemically inactive “dead MnO 2 ”‐resulting from disordered deposition and inevitable detachment of MnO 2 ‐as well as sluggish Mn 2+ /MnO 2 reaction kinetics. Herein, we report an in situ synthesis of Cr 2 O 3 nanoparticles on carbon cloth (Cr 2 O 3 @CC) via rapid reactive Joule heating. The modified substrate exhibits a negatively charged surface in the electrolyte, which enhances Mn 2+ adsorption and promotes uniform MnO 2 deposition through regulated nucleation. This approach effectively suppresses cracking and structural degradation of the MnO 2 layer. Moreover, the deposited MnO 2 possesses a high concentration of oxygen vacancies, accelerating the redox kinetics. Consequently, the fabricated AZMBs demonstrate robust cycling stability, sustaining 2500 cycles at 1 mAh cm −2 , 610 cycles at 2.5 mAh cm −2 , and maintaining 120 cycles even under an ultrahigh areal capacity of 20 mAh cm −2 . Remarkably, when scaled to a flow‐cell configuration, the system achieves an exceptional lifetime of nearly 9500 cycles at 20 mA cm −2 while retaining 1 mAh cm −2 , underscoring its outstanding practical potential for grid‐scale energy storage.