(298a) Development of Rechargeable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery is a highly desirable technology featuring high energy density and low-cost materials. However, the challenges with the technology are also well documented. In organic electrolytes, the redox of sulfur goes through a soluble polysulfide mechanism, which greatly impacts the cycle life and practical energy density. In the past few years, we have focused on developing sulfurized polyacrylonitrile, SPAN, as a stable alternative to elemental sulfur-based cathodes. The SPAN reaction does not involve the soluble polysulfide mechanism, which delivers exceptionally long life. Electrolyte engineering, however, remains the key to enable stable lithium metal anode while preserving the stability of SPAN. We show that localized high concentration electrolytes are the optimum choice which form stable interphases on both the Li anode and the SPAN cathode.

SPAN’s limitation lies in its limited sulfur content (~ 43 wt%) and specific capacity (< 700 mAh/g). To further raise cell energy density, it is necessary to revisit elemental sulfur. In this regard, we focus on batteries with sulfide-based solid electrolytes. In order to overcome the poor conductivity and large volume change of sulfur cathodes, we discovered a new sulfur-iodine material that features a semiconductor level electronic conductivity and a melting point of 65^oC. These features have enabled a solid state Li-S battery with high power density that is also healable. Degradation due to the volume change can be reversed by remelting the cathode, thus restoring performance. We will concluded by discussing remaining challenges for Li-S battery technologies and potential pathways to bring them closer to commercial reality.