High-Energy-Density Lithium-Sulfur Battery Based on a Lithium Polysulfide Catholyte and Carbon Nanofiber Cathode

Li-S batteries are promising large-scale energy storage systems but currently suffer from performance issues; a major reason is the dissolution of polysulfides in electrolytes. To this end, we report a high-energy-density Lithium-Sulfur (Li-S) battery that combines a catholyte and a sulfur-free carbon nanofiber (CNF) cathode. The cathode was synthesized by carbonizing binder-free polyacrylonitrile (PAN) nanofibers, affording a high surface area. In the catholyte, added polysulfides acted as both conductive Li salts and active materials. Investigating the electrochemical performance of this concept in both Swagelok- and pouch-type cells afforded energy densities exceeding 3 mAh cm-2 at a discharge rate of 0.1 C. This combination could also be utilized in high-capacity pouch cells with capacities of up to 250 mAh g-1. Both cell types exhibited good cycle performance. Adding LiNO3 to the electrolyte suppressed the redox shuttle reactions. Moreover, the cathode being binder-free increased the energy density and simplified cathode fabrication. Characterizing the cathode before and after cycling revealed that deposition was reversible, and that cell reactions at least partially formed sulfur as the end product, resulting in high sulfur amounts in the cell. We expect our concept to greatly aid in the development of practically applicable Li-S cells.