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

In 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 (C-r) 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.

Automated summary

In the literature, Zn-Mn aqueous batteries (ZMABs) exhibit abnormal capacity behavior and various charge/discharge behaviors due to electrolyte additive-induced complexes. However, the current performance assessment for ZMABs remains unregulated and lacks a comprehensive and impartial evaluation protocol. This hinders further research and commercialization. Therefore, a pH clue (proton-coupled reaction) is proposed to understand different mechanisms, and performance metrics including rated capacity (C-r) and electrolyte contribution ratio from Mn2+ (CfM) are discussed. Moreover, the relationship between Mn (II) <-> Mn (III) <-> Mn (IV) conversion chemistry and protons consumption/production is established, and the design concepts of a tunable H+/Zn2+/Mn2+ storage system for customized application scenarios are proposed, paving the way for the next-generation high-safety and reliable energy storage system.