||Potassium−sulfur (K−S) batteries offer low cost and high specific energy density. Previous work pioneered a K−S battery system operating at room temperature based on the conversion reaction S8 ⇆ K2S3. However, no major follow-up work has been reported beyond this, mainly because of the difficulties associated with the high reactivity of the potassium metal anode and the slow reaction kinetics of solid sulfur. we propose a novel K−S cell consisting of a solution phase potassium polysulfide catholyte and a 3-dimensional freestanding carbon nanotube film electrode. (as a reservoir for the polysulfide catholyte). Based on the reversible conversion reactions, K2Sx (5 ≤ x ≤ 6) →K2S3 (discharge) → K2S5 (charge), the proposed K−S battery delivered a high discharge capacity with stable cycle retention and good rate capability. In addition, instead of an explosive and highly reactive potassium metal electrode, a full cell consisting of an electrochemically potassium-impregnated hard carbon and the K2Sx (5 ≤ x ≤ 6) catholyte was constructed to demonstrate the feasibility of a safe K−S battery system free of metallic potassium.