Electrolyte engineering for thermally stable Li–S batteries operating from –20 °C to 100 °C

Abstract

Lithium–sulfur (Li–S) batteries are deemed one of the most promising high-energy density battery technologies. However, their operation under thermal extremes, e.g., subzero and above 60 °C, remains largely underexplored. Especially, high temperatures (HT) accelerate sulfur dissolution and undesired side reactions, presenting significant challenges for electrolyte design. In this work, contrary to traditional understanding, we discovered that even (localized) high-concentration electrolytes (HCEs), which have shown promise within moderate temperature ranges (0–60 °C), fail at temperatures above 80 °C. Detailed investigations revealed that Li-anion aggregates in HCE trigger uncontrolled reductive decomposition at the Li anode side once the temperature exceeds a threshold of 80 °C. The resultant parasitic byproducts caused serious crosstalk and cathode oxidation in HT Li–S batteries. To counter this issue, we developed a localized medium-concentration electrolyte that features a well-mediated solvation structure and energy level, demonstrating excellent thermodynamic stability at high temperatures with superb kinetics at low temperatures. Consequently, high-performance and safely operating Li–S pouch cells are achieved over an unprecedented range of −20 to 100 °C. These findings link electrolyte microstructure, temperature, SEI structure, and degradation mechanism, offering a design protocol for the reliable function of batteries in extreme environments.