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

Abstract

Developing Li–O₂ 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–O₂ 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, O₂ 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 Li₂S₄O_6, 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–O₂ batteries by altering the discharge products.