C56-12a-272379 As transportation systems rely more on electrical power, the energy density of batteries must increase and cost must decrease. Moreover, current state-of-the-art battery technology heavily relies on critical minerals (e.g., nickel, manganese, and cobalt) and cell production from foreign countries, especially China. Lithium-sulfur batteries are a promising cell chemistry that reduce the rare earth metals supply chain issues and offer a low-cost chemistry. They have a theoretical specific energy of 2600 Wh/kg, with demonstrated specific capacity between 300-500 Wh/kg. However, sulfur batteries suffer from rapid capacity fade due to polysulfide shuttle and irreversible deposition of solid lithium sulfide. Incorporation and/or infusion of sulfur into high surface area carbons helps suppress these adverse effects but bring additional limitations including high porosity (>60%) and low material loadings (typically <5 mg/cm2). Functionalizing sulfur to polymers such as sulfurized polyacrylonitrile has been shown to increase cycle life to several hundred cycles by binding polysulfides and forming reversible lithium sulfides. While these polymers have high sulfur utilization (>1000 mAh/g), they have low overall sulfur concentration (typically 20-40%), which drops the specific energy, typically <250 Wh/kg. A recent discovery in 2013 demonstrated that organic crosslinkers are able to stabilize and polymerize molten sulfur chains via inverse vulcanization, also known as copolymerization. These sulfur polymers utilize a sulfur backbone which is bound together via an organic crosslinker; therefore, the sulfur concentration is extremely high (e.g., 95%). Lithium-sulfur cells utilizing sulfur polymers can have extremely high gravimetric energy density (>400 Wh/g) and long-term cycling (>500 cycles). However, sulfur polymers are still in their infancy and the knowledge of their types, structure, charge/discharge mechanism, and properties are still deficient. Additionally, this technology has not be scaled and requires additional support to transition into commercial use. The proposed project will develop a lithium sulfur cell chemistry which will have higher energy density and lower cost compared to current high nickel cells. Moreover, utilizing sulfur as the cathode active material, which is an under-utilized byproduct of gas and petroleum refineries, will help reduce the United States dependency on critical minerals from China. The lithium sulfur cell technology will leverage a novel inverse volcanized sulfur cathode active material developed. In Phase I, the sulfur polymer chemistry will be refined in double layer pouch cells to improve performance. In Phase II, the technology will be scaled to full size pouch cells. Additionally, a transition path will be developed to scale production using semi-automated pilot production equipment, including a 1000 ft2 dry room.
