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

Zhou, Yin, Lyu, Zhiyang, Liu, Zhenjie, Dai, Wenrui, Guo, Rui, Yang, Jinlin, Cui, Xinhang, Zhao, Yong, Lin, Ming, Lai, Min, Peng, Zhangquan, Chen, Wei
Journal of materials chemistry A 2019 v.7 no.15 pp. 8777-8784
batteries, cathodes, electrochemistry, electrolytes, electrons, lithium, oxidation, oxygen, solvents, sulfur, thiosulfates
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 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–O₂ batteries by altering the discharge products.