Towards stable lithium-sulfur batteries: Mechanistic insights into electrolyte decomposition on lithium metal anode

Lithium (Li) metal battery is strongly considered as one of the potential candidates for next-generation energy storage devices due to its ultrahigh energy density. However, gas evolution induced by spontaneous decomposition of organic electrolytes during cell cycling leads to the capacity decay and safety issues of Li metal batteries (LMBs). Herein, the gas evolution behavior in a working Li-sulfur (Li-S) battery based on the most widely used 1,3-dioxolane (DOL)/1,2-dimethoxyethane (DME) electrolyte was probed through gas phase chromatography, mass spectrum of as-produced gas in pouch cells, as well as the first-principles calculations and ab initio molecular dynamics. An adsorption-to-reaction mechanism that DOL/DME firstly adsorbed lithium and then decomposed was proposed and verified. DOL with a small decomposition barrier was found to be easily decomposed into ethylene. When the DME: DOL ratio in the organic of Li-S cell was increased, a high and long discharge plateau as well as a large discharge capacity were observed. We also protected Li metal anode to avoid the direct contact between electrolyte and fresh Li metal through the polysulfide additives. The as obtained cell afforded few gas evolution and consequently a long cycling life. This understanding sheds fresh light of ultra-long cycling life of Li-S pouch cell from the viewpoint of stable electrolyte based on theoretical predictions and experimental verifications, which can be extended to other LMBs based on multi-electron redox reactions.