Activating sulfur oxidation reaction six-electron redox mesocrystal NiS for sulfur-based aqueous batteries.

Sulfur-based aqueous batteries (SABs) are deemed promising candidates for safe, low-cost, and high-capacity energy storage. However, despite their high theoretical capacity, achieving high reversible value remains a great challenge due to the thermodynamic and kinetics problems of elemental sulfur. Here, the reversible six-electron redox electrochemistry is constructed by activating the sulfur oxidation reaction (SOR) process of the elaborate mesocrystal NiS (M-NiS). Through the unique 6e solid-to-solid conversion mechanism, SOR efficiency can reach an unprecedented degree of 96.0%. The SOR efficiency is further revealed to be closely associated with the kinetics feasibility and thermodynamic stability of the M-NiS intermedium in the formation of elemental sulfur. Benefiting from the boosted SOR, compared with the bulk electrode, the M-NiS electrode exhibits a high reversible capacity (1258 mAh g), ultrafast reaction kinetics (932 mAh g at 12 A g), and long-term cyclability (2000 cycles at 20 A g). As a proof of concept, a new M-NiS‖Zn hybrid aqueous battery exhibits an output voltage of 1.60 V and an energy density of 722.4 Wh kg, which opens a new opportunity for the development of high-energy aqueous batteries.