Ammonium Additives to Dissolve Lithium Sulfide through Hydrogen Binding for High-Energy Lithium-Sulfur Batteries

In rechargeable Li-S batteries, the uncontrollable passivation of electrodes by highly insulating Li₂S limits sulfur utilization, increases polarization, and decreases cycling stability. Dissolving Li₂S in organic electrolyte is a facile solution to maintain the active reaction interface between electrolyte and sulfur cathode, and thus address the above issues. Herein, ammonium salts are demonstrated as effective additives to promote the dissolution of Li₂S to 1.25 M in DMSO solvent at room temperature. NMR measurements show that the strong hydrogen binding effect of N-H groups plays a critical role in dissolving Li₂S by forming complex ligands with S^2- anions coupled with the solvent's solvating surrounding. Ammonium additives in electrolyte can also significantly improve the oxidation kinetics of Li₂S, and therefore enable the direct use of Li₂S as cathode material in Li-S battery system in the future. This provides a new approach to manage the solubility of lithium sulfides through cation coordination with sulfide anion.