Dissociation–Precipitation Chemistry of Lithium Polysulfides and Its Correlation to Dynamic Evolution of Cathode–Electrolyte Interphase in Highly Solvating Electrolyte

Abstract Lithium–sulfur (Li−S) batteries has been regarded as one of the most promising next‐generation energy storage systems due to their high theoretical energy density. However, the practical application of Li−S batteries is still hindered by the unstable cathode‐electrolyte interphase and the early passivation of charge product (Li2S), leading to poor cycling stability and low S utilization. Herein, we propose an electrolyte engineering strategy using highly solvating hexamethylphosphoramide (HMPA) as a co‐solvent to elucidate the dissociation–precipitation chemistry of lithium polysulfides (LiPSs). The multimode optical spectroscopies confirm that this electrolyte engineering is able to effectively regulate the solvation of LiPSs to initiate a radical‐assisted conversion pathway and control three‐dimensional (3D) Li2S electrodeposition to boost sulfur utilization. More importantly, the dynamic evolution of cathode–electrolyte interphase, featuring with S‐/P‐containing species, is also assessed by both distribution of relaxation times technology and X‐ray photoelectron spectroscopy, which can suppress the passivation of Li2S to enhance conversion reversibility. As a proof‐of‐concept, a Li−S cell with high S loading mass of 7.75 mg cm−2 demonstrates an extremely high area capacity of 7.86 mAh cm−2 at a current density of 1.30 mA cm−2, representing a significant advancement in promoting the development of practical high‐energy‐density Li−S batteries.