Electrocatalyst Modulation toward Bidirectional Sulfur Redox in Li–S Batteries: From Strategic Probing to Mechanistic Understanding

Abstract Electrocatalyst design has stimulated considerable attention and strenuous effort to tackle a multitude of detrimental issues in lithium–sulfur (Li–S) systems, mainly pertaining to the severe polysulfide shuttle effect and sluggish sulfur redox kinetics. In this context related advances in expediting bidirectional sulfur reactions have lately surged. Nonetheless, the structure–activity correlation and electrocatalytic mechanism remain rather elusive, as a result of elusory active sites, complicated aprotic environments, and multistep conversion pathways. This review summarizes burgeoning strategies in the modulation of heterogeneous and homogeneous electrocatalysts, wherein the advanced electrokinetic measurements, operando instrumental probing, and theoretical simulations are elucidated with an emphasis on deciphering bidirectional sulfur electrochemistry. Notably, a “3s” electrocatalysis model is proposed to deepen the mechanistic understanding in this realm. Finally, a development roadmap is sketched and future research layouts are discussed, aiming in essence, to realize favorable bidirectional redox kinetics and ultimately bridge the gap between reality and ideal systems in working Li–S batteries.