To Make a Painstaking Investigation: Revealing the Electrochemical Reactions in Aqueous Zn‐Mn Batteries

Abstract: The rechargeable aqueous Zn||MnO2 batteries have been extensively explored, but the electrochemical reaction mechanisms, especially in terms of Mn2+/MnO2 dissolution/deposition and Zn2+/H+ intercalation chemistry, are still not fully understood. Herein, a Zn||MnO2‐based battery system is constructed and the variation of the battery composition is skillfully regulated by the separation of variables. The possibility of Zn2+/H+ intercalation chemistry is ruled out and the dominance of the dissolution/deposition mechanism is strongly demonstrated. This study confirms that the chemistry of the controversial double‐discharge platform is a dissolution reaction, determined by different proton concentrations and zinc ions hydrolysis. Discharge Plateau I is the MnO2 dissolution dominated by the surplus H+ in the electrolyte, while Discharge Plateau II is the smooth discharge plateau resulting from the hydrolysis of Zn2+ releasing protons when the proton concentration decreases to the point of Zn(OH)2 generation. This work provides a better understanding of the dissolution/deposition mechanism of Zn||MnO2 and paves the way for the practical application of manganese‐based aqueous batteries. It also provides a comprehensive method to study the mechanism of electrochemical reactions.