Tuning of electrolyte solvation structure for low-temperature operation of lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) can be good candidates for low-temperature batteries owing to the use of solvents with low freezing points. However, the clustering of lithium polysulfides (LiPSs) and inhomogeneous lithium deposition hinder the successful operation of LSBs at low temperatures. Herein, we demonstrate that changing the solvation state of solvents and polysulfides (PSs) in an electrolyte via a high-donor number (DN) salt anion (NO3−) enables operation at low temperatures; NO3− relieves LiPS clustering by strongly coordinating to lithium ions, thereby improving the kinetics and diffusion process of LiPSs at −20 °C. Furthermore, the NO3−-coordinated lithium ion solvation structure facilitates the desolvation process of lithium ions and mitigates solvent decomposition at the lithium metal electrode, which results in excellent cycling stability at −20 °C. A pouch cell with a LiNO3-rich electrolyte provides 76% of its room-temperature discharge capacity and operates stably for 100 cycles at −20 °C. The results of this study broaden our knowledge about the factors determining the low-temperature performance of LSBs. Moreover, they imply that controlling the electrolyte solvation structure can result in high-performance LSBs for operation at low temperatures.