Polysulfide-driven low charge overpotential for aprotic lithium-oxygen batteries

Developing Li-O-2 batteries with high-rate and long-cycle performance remains a major challenge due to the high charge overpotential induced by the insulating discharge products of Li2O2. Herein, we develop a strategy to achieve high-rate and excellent cycle performance Li-O-2 batteries by introducing sacrificial lithium polysulfide in aprotic electrolyte to realize ultralow charge overpotential, where the discharge products of Li2O2 have been replaced with lithium thiosulfate. In a demonstration study using Li2S6 during the discharge process, O-2 receives electrons and reacts with Li2S6 to form thiosulfate intermediates, which further accept electrons and convert Li2S6 to Li2S2 and Li2S4O6. The charge process is divided into three stages: the oxidation of low-order lithium polysulfide to high-order polysulfide, Li2S2O3 to Li2S4O6, and high-order polysulfide to sulfur, respectively, resulting in low charge overpotential. Despite gradual consumption of Li2S6 by the solvent, the electrochemical performance significantly increases. At a high current density of 0.5 A g(-1), the battery with CNTs as the cathode and Li2S6 as the electrolyte additive demonstrates an excellent cycle performance of 147 cycles with a low initial charge overpotential of 0.19 V at a fixed capacity of 500 mA h g(-1). This study provides a promising strategy to design high-rate and long-cycle performance of Li-O-2 batteries by altering the discharge products.