(Invited) High-Capacity Lithium-Sulfur Batteries at Low Electrolyte/Sulfur Ratios

Abstract

Lithium-sulfur ((Li-S) batteries have a high theoretical specific energy of 2600Wh/kg, which makes it promising as a next generation electrochemical energy storage system. Li-S system operates by electrochemical conversion of sulfur through a multi-step redox reaction, forming different lithium sulfide products. The formation of soluble polysulfide and insoluble, insulating Li2S contributes to poor sulfur utilization and cycling efficiency, and capacity fading. As one important component in Li-S batteries, the electrolyte plays a key role in the electrochemical performance of lithium-sulfur batteries. The excess of electrolyte is still required for adequate Li-S cell performance and resultant drawdown in the energy density. The presentation will discuss development of Li-S batteries with emphases on applications of new functional electrolyte which enables an alternate electrochemical reaction pathway for sulfur cathodes by the formation of dimethyl polysulfides and lithium organosulfides as intermediates and reduction products.1 This new pathway not only provides high capacity but also enables excellent capacity retention. Furthermore, we demonstrate a stable capacity of around 1000 mAh g-1 at a low electrolyte/sulfur ratio of 5 mL g-1 using high-sulfur-loading (4 mg cm-2) cathodes, which almost doubles the capacity obtained with conventional electrolytes under the same conditions. These results highlight the practical potential of this electrolyte system to enable high-energy-density Li-S batteries.