Protocol in Evaluating Capacity of Zn–Mn Aqueous Batteries: A Clue of pH

Abstract

AbstractIn the literature, Zn–Mn aqueous batteries (ZMABs) confront abnormal capacity behavior, such as capacity fluctuation and diverse “unprecedented performances.” Because of the electrolyte additive‐induced complexes, various charge/discharge behaviors associated with different mechanisms are being reported. However, the current performance assessment remains unregulated, and only the electrode or the electrolyte is considered. The lack of a comprehensive and impartial performance evaluation protocol for ZMABs hinders forward research and commercialization. Here, a pH clue (proton‐coupled reaction) to understand different mechanisms is proposed and the capacity contribution is normalized. Then, a series of performance metrics, including rated capacity (Cr) and electrolyte contribution ratio from Mn2+ (CfM), are systematically discussed based on diverse energy storage mechanisms. The relationship between Mn (II) ↔ Mn (III) ↔ Mn (IV) conversion chemistry and protons consumption/production is well‐established. Finally, the concrete design concepts of a tunable H+/Zn2+/Mn2+ storage system for customized application scenarios, opening the door for the next‐generation high‐safety and reliable energy storage system, are proposed.