A Phosphoramide-Based electrolyte with high affinity towards Li+ and low polysulfide solubility enables high-performance lithium-sulfur batteries

Abstract

The polysulfide shuttle effect and the growth of Li dendrites are detrimental to the practical use of lithium–sulfur (LiS) batteries. Here, we show that these challenges can be eliminated with hexamethylphosphoramide (HMPA) as a co-solvent. HMPA shows strong coordination interaction with Li⁺ and thus preferentially remains in the inner sheath of the Li⁺ solvation structure. The solvation structure not only minimizes the solubility of polysulfides but also generates a LiF-rich solid-electrolyte interphase, which are responsible to the suppression of polysulfide shuttle effect and the elimination of Li dendrites, respectively. As a result, HMPA-based electrolytes enable Li//Li symmetric cells to exhibit long cycling lifetimes of up to 600 h at 5 mA cm⁻² along with significantly reduced polarization. Moreover, LiS cells containing the HMPA-based electrolyte also display marked enhancement in cycling stability (e.g., 619.6 mAh g⁻¹ after 300 cycles at 0.2C). These results are superior to those measured for control cells that contain a conventional electrolyte. The concepts and method described herein may be extended to benefit other types of energy storage devices that use active metals as anodes.