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

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.