Elucidating the Catalytic Activity of Oxygen Deficiency in the Polysulfide Conversion Reactions of Lithium–Sulfur Batteries

Abstract The accelerated conversion of soluble lithium polysulfides (the intermediate products in the charging and discharging of lithium–sulfur batteries) to insoluble sulfur and lithium sulfide is an effective method to suppress the “polysulfide shuttle” that is detrimental to the battery performance. The results of this study show that oxygen‐deficient tungsten oxide (WO 3− x ) nanoplate is an effective bidirectional electrocatalyst for the polysulfide conversion reactions. Two different designs of asymmetric cells are used to elucidate the catalysis of the polysulfide conversion reactions and to confirm the role of oxygen deficiency on the conversion kinetics. The fast polysulfide conversion prevents the accumulation of polysulfides in the sulfur cathode and their ensuing loss to the electrolyte. Consequently, a sulfur cathode with WO 3− x nanoplates is able to improve the cycle stability from a fade rate of 0.49% per cycle (over 100 cycles) to 0.13% per cycle (over 300 cycles) at the 0.5 C rate. In addition, the WO 3− x nanoplates also improve the high rate performance of the sulfur cathode (at the 4 C rate) from a capacity of 444.1 to 693.2 mAh g −1 . The results of this study provide the first direct experimental proof of the beneficial effects of oxygen deficiency in polysulfide conversion reactions.