Investigation of Polysulfide Adsorption on FeS2 Additive in Sulfur Cathode of Li–S Battery by Ex situ UV–Visible Spectroscopy

The performance of lithium–sulfur (Li–S) rechargeable batteries is strongly dependent on the entrapment of the higher-order intermediate polysulfides at the sulfur cathode. An attracting way of preventing the polysulfide shuttle is by introducing a polar host which can form a Lewis acid–base complex with polysulfides. Herein, the Li–S battery by incorporating iron sulfides (FeS₂) as a polar Lewis acid to entrap higher-order polysulfides at the cathode center is investigated. FeS₂/S cathode demonstrates largely improved retention of capacity compared to C/S cathode (capacity fading per cycle of 0.12% and 0.80% for FeS₂/S and C/S respectively) and good rate performance in Li–S batteries compared to conventional carbon–sulfur (C/S) cathode. This is attributed to the decrease in polysulfide dissolution and better retention of active sulfur in the cathode during battery cycling which is due to the polar FeS₂ additive that well anchors polysulfides. The effect of FeS₂ in preventing the shuttle mechanism is demonstrated by ex situ UV–vis spectroscopy and ex situ Raman spectroscopy studies.