Electrolyte Solvation Chemistry for the Solution of High-Donor-Number Solvent for Stable Li-S Batteries

Passivation of the sulfur electrode by insulating lithium sulfide (Li2S) restricts the reversibility and sulfur utilization of lithium-sulfur (Li-S) batteries. Although electrolytes with high donor number (DN) solvents induce tri-sulfur radical intermediate thus 3D nucleation of Li2S with fast kinetics can be achieved, their catastrophic reactivities with Li metal hinder practical applications. Here, the use of high DN solvent as an additive instead of as co-solvent to solve their incompatibility between cathode and anode is proposed, by adopting N-methyl-2-pyrrolidone (NMP) as a proof-of-concept. Such a strategy is accomplished by the unique solvation structure of the NMP added electrolyte, where the preference of NMP-Li+ coordination squeezes out partial 1,2-dimethoxyethane (DME) molecules while enriching 1,3-dioxolane (DOL) molecules in the first solvation sheath of Li+ ions. It affords the robust SEI on Li metal from corrosion either by NMP or the dissolved polysulfides. Spectral analyses (Raman and UV-vis) also verify that the coordinated NMP additive preserves its S-3(center dot-) radicals stabilization ability as it does as a co-solvent, which effectively improves the sulfur conversion kinetics and reversibility. This approach enables competitive capacity retention and a stable cycling performance of 340 cycles, which is one of the longest lifespans known for the high DN solvent involved Li-S batteries.

Automated summary

This study proposes the use of high donor number (DN) solvents as additives to improve the reversibility and sulfur utilization of lithium-sulfur batteries. By adopting N-methyl-2-pyrrolidone (NMP) as a proof-of-concept, the researchers achieved a solvation structure that prevents unwanted reactions between Li metal and the cathode, leading to a robust solid electrolyte interphase (SEI) and improved sulfur conversion kinetics and reversibility. This approach demonstrated competitive capacity retention and stable cycling performance.