Recent Progress in High Donor Electrolytes for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries continue to be considered promising post-lithium-ion batteries owing to their high theoretical energy density. In pursuit of a Li-S cell with long-term cyclability, most studies thus far have relied on using ether-based electrolytes. However, their limited ability to dissolve polysulfides requires a high electrolyte-to-sulfur ratio, which impairs the achievable specific energy. Recently, the battery community found high donor electrolytes to be a potential solution to this shortcoming because their high solubility toward polysulfides enables a cell to operate under lean electrolyte conditions. Despite the increasing number of promising outcomes with high donor electrolytes, a critical hurdle related to stability of the lithium-metal counter electrode needs to be overcome. This review provides an overview of recent efforts pertaining to high donor electrolytes in Li-S batteries and is intended to raise interest from within the community. Furthermore, based on analogous efforts in the lithium-air battery field, strategies for protecting the lithium metal electrode are proposed. It is predicted that high donor electrolytes will be elevated to a higher status in the field of Li-S batteries, with the hope that either existing or upcoming strategies will, to a fair extent, mitigate the degradation of the lithium-metal interface.