A Mn²⁺-S redox electrochemistry for energetic aqueous manganese ion battery

Aqueous manganese ion batteries (AMIBs) have recently garnered attention due to the abundance of manganese and their intrinsic safety. However, the development of current AMIBs remains plagued by restrictive actual capacities. Herein, we propose an energetic Mn²⁺-S redox electrochemistry with a solid-liquid-solid redox pathway. Operando X-ray absorption fine spectroscopy and synchrotron X-ray diffraction unveil the Mn²⁺ storage mechanism of S₈ ↔ MnS₄ ↔ MnS₂ ↔ MnS. A capacity of 1,242 mAh g⁻¹ with a high sulfur utilization of 74.3 wt % can be achieved, surpassing the capacity limitations of previously reported AMIBs. As a proof of concept, a system intergrating the S/MnS and MnO₂/Mn²⁺ redox couples delivers an energy density of 396 Wh kg_S+MnO2⁻¹ and cycles for 800 cycles stably at 4 A g⁻¹. We have elucidated the mechanism underlying the redox of Mn²⁺-S and may open an avenue for the next high-energy AMIBs.