Liquid electrolyte lithium/sulfur battery: Fundamental chemistry, problems, and solutions

Lithium/sulfur (Li/S) battery has a 3–5 fold higher theoretical energy density than state-of-art lithium-ion batteries, and research has been ongoing for more than three decades. However, the commercialization of Li/S battery still cannot be realized due to many problematic issues, including short cycle life, low cycling efficiency, poor safety and a high self-discharge rate. All these issues are related to the dissolution of lithium polysulfide (PS), the series of sulfur reduction intermediates, in liquid electrolyte and to resulting parasitic reactions with the lithium anode and electrolyte components. On the other hand, the dissolution of PS is essential for the performance of a Li/S cell. Without dissolution of PS, the Li/S cell cannot operate progressively due to the non-conductive nature of elemental sulfur and its reduction products. In this review article, we start with the fundamental chemistry of elemental sulfur in order to discuss the problems and solutions of liquid electrolyte Li/S battery.