Anion‐Regulated Deposition–Dissolution Chemistry in Acidic Aqueous Indium─MnO 2 Batteries

Abstract Acidic aqueous metal─MnO 2 rechargeable batteries enable high‐capacity energy storage via a two‐electron MnO 2 /Mn 2+ redox chemistry but suffer from severe anode corrosion and poor reversibility in acidic environments. Here, we report an acidic In─MnO 2 battery (IMB) system that employs anion‐regulated interfacial chemistry to enable reversible deposition–dissolution reactions at both electrodes. The In 3+ /In redox couple offers a favorable potential that mitigates acidic corrosion while matching the MnO 2 two‐electron redox. Systematic investigation of anion effects reveals that concentrated Cl − anions restructure the In 3+ solvation, forming stable chloro‐complexes that lower dissociation energy and promote uniform Indium (In) deposition. Conversely, SO 4 2− ‐rich electrolytes impede In plating but enhance MnO 2 crystallization and MnO 2 /Mn 2+ reversibility. Through tailored Cl − /SO 4 2− ratios and an anion‐decoupled dual‐electrolyte configuration, the battery operates at ∼1.7 V with 72.3% energy efficiency (EE) and over 1500 cycles at 5 mA cm −2 . Furthermore, we demonstrate an electrode‐less IMB using a Bi substrate at the anode, where in situ alloying‐driven In deposition enables over 2000 stable cycles at 4 mA cm −2 (2 mAh cm −2 ), delivering a compelling energy density of 484.5 Wh kg −1 and a high cumulative areal capacity of 4120 mAh cm −2 . This work establishes a design paradigm coupling anion‐regulated interfacial chemistry with substrate engineering for high‐performance acidic IMB.