Room-Temperature Potassium–Sulfur Batteries Enabled by Microporous Carbon Stabilized Small-Molecule Sulfur Cathodes

Potassium–sulfur (K–S) batteries are a promising alternative to lithium ion batteries for large-area energy storage applications, owing to their high capacity and inexpensiveness, but they have been seldom investigated. Here we report room-temperature K–S batteries utilizing a microporous carbon-confined small-molecule sulfur composite cathode. The synergetic effects of the strong confinement of microporous carbon matrix and the small-molecule sulfur structure can effectually eliminate the formation of soluble polysulfides and ensure a reversible capacity of 1198.3 mA h g–1 and retain 72.5% after 150 cycles with a Coulombic efficiency of ∼97%. The potassium-storage mechanism was investigated by X-ray photoelectron spectroscopy analysis and theoretical calculations. The results suggest that K2S is the final potassiation product along with the reaction of 2K + S ↔ K2S, giving a theoretical capacity of 1675 mA h g–1. Our findings not only provide an effective strategy to fabricate high-performance room-temperature K–S batteries but also offer a basic comprehension of the potassium storage mechanism of sulfur cathode materials.