Al 2 S 3 Cathode for Rechargeable Aluminum‐Sulfur Batteries with Improved Cycling Reversibility

Rechargeable aluminum‐sulfur (Al−S) batteries are regarded as the potential choice for next‐generation energy storage system with advantages of high theoretical energy density (1340 Wh kg −1 ), the earth abundance of the constituent electrode materials, and safe operation. Whereas the electrochemical performance of Al−S batteries is beset by its poor reversibility. In this article, we demonstrate a highly reversible Al−S battery with Al 2 S 3 as the cathode. Mechanistic studies with electrochemical and spectroscopic methodologies identified that the enhancement in reversibility by Al 2 S 3 cathode is attributed to the circumvention of the sluggish conversion of polysulfides to sulfur. Al 2 S 3 cathode undergoes a faster solid to liquid conversion reaction (Al 2 S 3 ↔polysulfide) than that of the sulfur cathode that suffers from slow kinetic process of solid‐to‐solid conversion (S↔Al 2 S 3 ). Thus, Al−S battery composed of Al 2 S 3 cathode delivers a highly reversible electrochemical reaction with the average Coulombic efficiency >95 % for 100 cycles.