Dynamic Proton Activity Regulation via Brønsted Bases Enables Durable and High‐Energy‐Density Zn||MnO 2 Batteries

ABSTRACT Acidic Zn||MnO 2 batteries offer exceptional promise for grid‐scale storage due to high theoretical energy and power densities, yet their practical deployment is fundamentally limited by conflicting proton activity requirements at the electrodes: the MnO 2 cathode demands high H + concentration to drive reversible two‐electron Mn 2+ /MnO 2 conversion, while the Zn anode suffers severe hydrogen evolution corrosion (HEC) under these conditions. We resolve this incompatibility by designing a dynamically regulated weak‐acid electrolyte using strategically introduced Brønsted bases. The tuned proton affinity kinetically suppresses acid dissociation at the Zn/electrolyte interface to mitigate HEC, while sustaining high‐voltage Mn 2+ /MnO 2 conversion at the MnO 2 cathode. This intrinsic kinetic regulation achieved without electrolyte decoupling, protective interphases, or uncontrolled pH drift enables designed Zn||MnO 2 cells to achieve an ultrahigh energy density of 951 Wh kg −1 (based on MnO 2 cathode mass) and exceptional cycling stability (80% capacity retention after 200 cycles at 0.5 A g −1 ). This work establishes a practical, scalable electrolyte platform for durable high‐performance Zn||MnO 2 batteries.