Activating Aqueous Multivalent Metal–Sulfur Electrochemistry via Kinetic Promoter

Abstract Sulfur-based aqueous batteries for sustainable energy storage have the advantages of material abundance, low cost, and high theoretical capacity. While aqueous multivalent metal–sulfur electrochemistry is effective in suppressing sulfide dissolution due to its low solubility product constant, it is intrinsically limited by sluggish conversion kinetics. Here, we decouple sulfur-conversion kinetics from sulfur-species stabilization by introducing a kinetic promoter. Operando spectroscopy, electrochemical quartz crystal microbalance analysis, and density functional theory simulations reveal that the Li+ promoter preferentially targets long-chain sulfur species and lowers the redox barrier, while Mn2+ anchors sulfur species and immobilizes short-chain intermediates, steering the reaction from a dissolution route to a rapid, solid-state-dominated pathway. This cooperative mechanism induces the formation of a highly reversible ternary solid phase with an apparent average composition close to Li4Mn6S8, suppressing the accumulation of soluble polysulfide intermediates and enabling deep discharge at ultrahigh rates. Consequently, the SABs with kinetic promoter exhibit highly reversible sulfur redox chemistry with a capacity of 1012 mAh g–1 at 15 A g–1. We also demonstrate the strategy in Zn2+-S and Ni2+-S systems, illustrating its effectiveness in various multivalent aqueous sulfur batteries.