Electrochemical Phase Evolution of Metal‐Based Pre‐Catalysts for High‐Rate Polysulfide Conversion

Abstract In situ evolution of electrocatalysts is of paramount importance in defining catalytic reactions. Catalysts for aprotic electrochemistry such as lithium–sulfur (Li‐S) batteries are the cornerstone to enhance intrinsically sluggish reaction kinetics but the true active phases are often controversial. Herein, we reveal the electrochemical phase evolution of metal‐based pre‐catalysts (Co 4 N) in working Li‐S batteries that renders highly active electrocatalysts (CoS x ). Electrochemical cycling induces the transformation from single‐crystalline Co 4 N to polycrystalline CoS x that are rich in active sites. This transformation propels all‐phase polysulfide‐involving reactions. Consequently, Co 4 N enables stable operation of high‐rate (10 C, 16.7 mA cm −2 ) and electrolyte‐starved (4.7 μL mg S −1 ) Li‐S batteries. The general concept of electrochemically induced sulfurization is verified by thermodynamic energetics for most of low‐valence metal compounds.