Novel Lithium-Sulfur Polymer Battery Operating at Moderate Temperature

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 degrees 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 degrees 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 degrees 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.