Tuning Low Concentration Electrolytes for High Rate Performance in Lithium-Sulfur Batteries

While lithium-sulfur (Li-S) batteries promise very high gravimetric energy densities, they typically suffer from short cycle life and low power densities, particularly at high electrode loadings. Highly concentrated electrolytes (2M-5M) may demonstrate improved capacity retention, but at the expense of added weight and cost of electrolyte salts and reduced rate performance. Here we report our counter-intuitive findings on very promising performance of electrolyte compositions with salt concentrations below 0.3M. Such a low concentration enables effective use of unconventional salts and electrolyte additives which do not dissolve in the ether-based solvents at higher concentrations typically used in experimental and commercial batteries, thus substantially increasing cell design freedom. The significantly lower viscosity of the low concentration electrolytes also allows for faster electrolyte permeation. This report opens a new and promising field of studying low concentration electrolytes for Li-S and likely other chemistries.