High-Valent Thiosulfate Redox Electrochemistry for Advanced Sulfur-Based Aqueous Batteries.

Sulfur-based aqueous batteries (SABs) are promising for safe, low-cost, and high-capacity energy storage. However, the low output voltage of sulfur cannot meet the demands of high-energy cathode applications due to its intrinsic negative potential (E 0 = -0.51 V vs SHE) of low-valent polysulfide redox (S 2- /S 0 ). Here, instead of relying on traditional aqueous polysulfide redox, for the first time, we demonstrate a high-valent thiosulfate redox (S 2 O 3 2- /S 4 O 6 2- ) electrochemistry, exhibiting positive redox potential (E 0 > 0 V vs SHE) and reversible cation storage in aqueous environment. Operando X-ray absorption fine structure spectroscopy, in situ Raman spectroscopy, and density functional theory calculations reveal the high reversibility and dynamic charge transfer process of high-valent thiosulfate redox. Significantly, the aqueous thiosulfate redox exhibits a high operating voltage of approximately 1.4 V, a reversible capacity of 193 Ah L -1 , and a long cycling life of over 1000 cycles (99.6% capacity retention). This work provides new insights into the high-valent S-based electrochemistry and opens a new pathway to achieve energetic aqueous batteries.