Energy storage mechanisms and manganese deposition effects in zinc-manganese batteries with various anion salt electrolytes

Aqueous zinc-manganese secondary batteries have garnered significant interest because of their safety, low cost and high theoretical specific capacity. Nevertheless, the underlying energy storage mechanism is currently unclear, hindering advancements in their capacity and stability. Herein, the charge-discharge mechanisms of layered δ-MnO 2 in Zn(OAc) 2 , ZnSO 4 , Zn(OTf) 2 electrolytes, as well as in electrolytes with added manganese salts , are investigated through various electrochemical and structural analyses. The results indicate that in acetate electrolytes, the primary mechanism involves manganese dissolution and deposition, whereas in sulfate and sulfonate electrolytes, the energy storage process is predominantly governed by the intercalation and deintercalation of Zn 2+ /H + , with manganese dissolution and deposition contributing partially to the overall capacity. Additionally, the study further confirms that the dissolution degree of δ-MnO 2 during discharge varies across different anion salt electrolytes, following the order of acetate > sulfate > sulfonate . The primary function of the manganese salt additive is to facilitate the formation of amorphous MnO 2 during the charging process, thereby contributing additional capacity to the system. This research offers a novel perspective on the formulation of electrolytes and the design of battery devices for zinc-manganese secondary batteries. • The charge storage mechanisms of δ-MnO. • The order of dissolution degree of δ-MnO 2 is acetate > sulfate > sulfonate. • Manganese salt additives facilitate the formation of amorphous MnO 2 .