Solubility and dissolution kinetics of sulfur and sulfides in electrolyte solvents for lithium-sulfur and sodium-sulfur batteries

Hakeem A Adeoye; Matthew Dent; John F Watts; Stephen Tennison; Constantina Lekakou

doi:10.1063/5.0132068

Solubility and dissolution kinetics of sulfur and sulfides in electrolyte solvents for lithium-sulfur and sodium-sulfur batteries

J Chem Phys. 2023 Feb 14;158(6):064702. doi: 10.1063/5.0132068.

Authors

Hakeem A Adeoye¹, Matthew Dent¹, John F Watts¹, Stephen Tennison¹, Constantina Lekakou¹

Affiliation

¹ Centre of Engineering Materials, School of Mechanical Engineering Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom.

PMID: 36792496
DOI: 10.1063/5.0132068

Abstract

In this study, we monitor the dissolution of sulfur and sulfides in electrolyte solvents for lithium-sulfur (Li-S) and sodium-sulfur (Na-S) batteries. The first aim of this research is to assemble a comprehensive set of data on solubilities and dissolution kinetics that may be used in the simulation of battery cycling. The investigation also offers important insights to address key bottlenecks in the development and commercialization of metal-sulfur batteries, including the incomplete dissolution of sulfur in discharge and insoluble low-order sulfides in charge, the probability of shuttling of soluble polysulfides, and the pausing of the redox reactions in precipitated low order sulfides depending on their degree of solid state. The tested materials include sulfur, lithium sulfides Li₂S_x, x = 1, 2, 4, 6, and 8, and sodium sulfides Na₂S_x, x = 1, 2, 3, 4, 6, and 8, dissolved in two alternative electrolyte solvents: DOL:DME 1:1 v/v and TEGDME. The determined properties of the solute dissolution in the solvent include saturation concentration, mass transfer coefficient, and diffusion coefficient of the solvent in the solid solute. In general, the DOL:DME system offers high solubility in Li-S batteries and TEGDME offers the highest solubility in Na-S batteries. Low solubility sulfides are Li₂S₂ and Li₂S for the Li-S batteries, and Na₂S₃, Na₂S₂, and Na₂S for the Na-S batteries. However, it is noted that Na₂S₃ dissolves fast in TEGDME and also TEGDME diffuses fast into Na₂S₃, offering the possibility of a swollen Na₂S₃ structure in which Na⁺ ions might diffuse and continue the redox reactions in a semisolid state.