Reversible Mn3+/Mn2+ redox chemistry for high-rate aqueous manganese-ion batteries

Abstract

The Mn³⁺/Mn²⁺ redox couple is a promising candidate for high-rate energy storage scenarios owing to its high theoretical voltage and rapid redox kinetics. However, critical challenges such as Mn³⁺ disproportionation and shuttle effects in aqueous electrolytes significantly limit practical implementation. Herein, we propose a synergistic strategy integrating coordination optimization and interfacial confinement to achieve highly reversible Mn³⁺/Mn²⁺ redox chemistry in a mild aqueous electrolyte. Ethylenediaminetetraacetic coordinating anions are utilized to reshape the first solvation shell of Mn²⁺, stabilizing hydrated Mn³⁺ intermediates and enabling a single-electron-dominated redox pathway. A sucrose-derived molecular adsorption layer is engineered on the cathode surface through electrostatic polarity interactions, effectively suppressing Mn³⁺ migration into the bulk electrolyte. The well-designed Mn³⁺/Mn²⁺ cathode delivers an areal capacity of 0.36 mAh cm⁻² at 4 mA cm⁻² with 81 % capacity retention over 3000 cycles. As proof of concept, a high-rate aqueous Mn-ion battery is assembled by pairing the Mn³⁺/Mn²⁺ cathode with a polyimide anode, achieving a specific capacity of 104 mAh g⁻¹ at 0.5 A g⁻¹, exceptional rate capability, and 73.2 % capacity retention after 1000 cycles. This work unveils the directional regulation of manganese redox chemistry by a solvation-interfacial coupling mechanism, offering a design blueprint for next-generation grid-scale energy storage technologies.