Revisiting Membrane-Free Zn–Mn Redox Flow Batteries: An Innovative Universal Aspartic Acid Additive for Superior Stability

Abstract

An all-aqueous membrane-free Zn–Mn redox flow battery utilizing deposition chemistry can be an excellent alternative to conventional aqueous redox flow batteries for reducing costs and improving stability. In the neutral/mildly acidic electrolyte environment of aqueous Zn–Mn redox flow batteries, the anode still suffers from issues such as zinc dendrite growth and corrosion, while the cathode struggles with poor reversibility. The same issues arise in membrane-free Zn–Mn redox flow batteries that use a combined electrolyte, where both anolyte and catholyte are combined. Therefore, it is possible to simultaneously address the issues of both the anode and cathode by using a single additive in the combined electrolyte. Here, aspartic acid is introduced as a universal additive for an all-aqueous membrane-free Zn–Mn redox flow battery. In the combined electrolyte, aspartic acid bonded to the Zn anode surface, Zn²⁺ ions, and Mn²⁺ ions, resolving almost all the side reactions. Impressively, membrane-free Zn–Mn redox flow battery with aspartic acid demonstrated remarkable cycling stability of 300 cycles at an areal capacity of 10 mAh cm⁻². A new efficient strategy is proposed for controlling overall side reactions by the simple addition of a single additive in the integrated electrolyte with this report.