High capacity of lithium-sulfur batteries at low electrolyte/sulfur ratio enabled by an organosulfide containing electrolyte

Lithium-sulfur (Li-S) battery is a promising energy storage technology to replace lithium ion batteries for higher energy density and lower cost. Dissolution of lithium polysulfide intermediates in conventional Li-S electrolytes is known as one of the key technical barriers to the development of Li-S, because it promotes redistribution and irreversible deposition of Li₂S, and also forces large amounts of electrolyte to be used, shortening cycling life and driving down cell energy density. Recently, dimethyl disulfide as a functional co-solvent has been demonstrated to show an alternate electrochemical reaction pathway for sulfur cathodes by the formation of dimethyl polysulfides and lithium organosulfides as intermediates and reduction products. In this work, comprehensive studies show that this new pathway not only provides high capacity but also enables excellent capacity retention through a built-in automatic discharge shutoff mechanism by tuning carbon/sulfur ratio in sulfur cathodes to reduce unfavorable Li₂S formation. Furthermore, this new electrolyte system is also found to enable high capacity of high-sulfur-loading cathodes with low electrolyte/sulfur (E/S) ratios, such as a stable specific capacity of around 1000 mAh g⁻¹ using a low electrolyte amount (i.e, E/S ratio of 5 mL g⁻¹) and high-sulfur-loading (4 mg cm⁻²) cathodes. This electrolyte system almost doubles the capacity obtained with conventional electrolytes under the same harsh conditions. These results highlight the practical potential of this electrolyte system to enable high-energy-density Li-S batteries.