An energetic K+-S aqueous battery with 96% sulfur redox utilization

Potassium-sulfur electrochemistry represents a compelling energy storage technology due to its cost-efficient chemicals and unparalleled capacity. However, achieving high sulfur redox utilization (SRU) remains a great challenge during K+ storage due to K2Sn kinetics inertia. Here, for the first time, we unveil an aqueous K+-S electrochemistry, leveraging boosted K2Sn conversion kinetics in water. A stable two-electron charge transfer process is achieved via tuning K2S solubility. Spectroscopic evaluation and molecular dynamics simulations reveal a unique solid-liquid-solid conversion pathway (S ↔ K2S4 ↔ K2S), which effectively avoids soluble K2S shuttling. Consequently, an unprecedented K+ storage capacity of 1,619 mAh g−1 (ca. 96% SRU) can be achieved with 95% initial Coulombic efficiency, appealing cyclability over 500 times, and a high-energy density of 392 Wh kgS+Zn−1. These findings signify a paradigm shift and introduce transformative opportunities for the design of safe and high-energy aqueous batteries.