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.