Novel Lithium‐Sulfur Polymer Battery Operating at Moderate Temperature

Abstract A safe lithium‐sulfur (Li−S) battery employs a composite polymer electrolyte based on a poly(ethylene glycol) dimethyl ether (PEGDME) solid at room temperature. The electrolyte membrane enables a stable and reversible Li−S electrochemical process already at 50 °C, with low resistance at the electrode/electrolyte interphase and fast Li + transport. The relatively low molecular weight of the PEGDME and the optimal membrane composition in terms of salts and ceramic allow a liquid‐like Li−S conversion reaction by heating at moderately high temperature, still holding the solid‐like polymer state of the cell. Therefore, the electrochemical reaction of the polymer Li−S cell is characterized by the typical dissolution of lithium polysulfides into the electrolyte medium during discharge and the subsequent deposition of sulfur at the electrode/electrolyte interphase during charge. On the other hand, the remarkable thermal stability of the composite polymer electrolyte (up to 300 °C) suggests a lithium‐metal battery with safety content significantly higher than that using the common, flammable liquid solutions. Hence, the Li−S polymer battery delivers at 50 °C and 2 V a stable capacity approaching 700 mAh g S −1 , with a steady‐state coulombic efficiency of 98 %. These results suggest a novel, alternative approach to achieve safe, high‐energy batteries with solid polymer configuration.