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

Abstract The rechargeable aqueous Zn||MnO 2 batteries have been extensively explored, but the electrochemical reaction mechanisms, especially in terms of Mn 2+ /MnO 2 dissolution/deposition and Zn 2+ /H + intercalation chemistry, are still not fully understood. Herein, a Zn||MnO 2 ‐based battery system is constructed and the variation of the battery composition is skillfully regulated by the separation of variables. The possibility of Zn 2+ /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 MnO 2 dissolution dominated by the surplus H + in the electrolyte, while Discharge Plateau II is the smooth discharge plateau resulting from the hydrolysis of Zn 2+ 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||MnO 2 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.