Balanced Interfacial Ion Concentration and Migration Steric Hindrance Promoting High‐Efficiency Deposition/Dissolution Battery Chemistry

The solid–liquid transition reaction lays the foundation of electrochemical energy storage systems with high capacity, but realizing high efficiency remains a challenge. Herein, in terms of thermodynamics and dynamics, this work demonstrates the significant role of both interfacial H+ concentration and Mn2+ migration steric hindrance for the high‐efficiency deposition/dissolution chemistry of zinc–manganese batteries. Specially, the introduction of formate anions can buffer the generated interfacial H+ to stabilize interfacial potential according to the Nernst equation, which stimulates high capacity. Compared with acetate and propionate anions, the formate anion also provides high adsorption density on the cathode surface to shield the electrostatic repulsion due to the small spatial hindrance. Particularly for the solvated Mn2+, the formate‐anion‐induced lower energy barrier of the rate‐determining step during the step‐by‐step desolvation process results in lower polarization and higher electrochemical reversibility. In situ tests and theoretical calculations verify that the electrolyte with formate anions achieve a good balance between ion concentration and ion‐migration steric hindrance. It exhibits both the high energy density of 531.26 W h kg‐1 and long cycle life of more than 300 cycles without obvious decay. The important influence of interfacial ion effect on aqueous zinc–manganese batteries is proposed. The interfacial ion concentration and steric hindrance in the electric double layer are comprehensively balanced from the perspective of thermodynamics and kinetics, respectively, to achieve both high specific capacity and long cycle stability simultaneously.