Strategies to Enable Lean Electrolytes for High Loading & Stable Li-S Pouch Cells

Lithium-sulfur (Li-S) batteries offer the potential for higher energy densities owing to the high theoretical capacities of the sulfur cathodes (1675 mAh g-1). Moreover, elemental sulfur is an abundant low-cost material making it more economical than conventional lithium-lithium battery cathodes. Sulfur-based cathodes also offer improved safety factors owing to their conversion-based reaction mechanisms which reduce the risks of thermal runaway typical of host-type materials. However, the commercialization of Li-S still faces several technical barriers that impede its commercialization: 1) Inability to enable lean electrolyte conditions necessary for high energy densities and 2) Polysulfide dissolution resulting in sulfur inventory loss & continuous electrolyte consumption. To achieve targets of 500 Wh/kg under realistic sulfur cathode loadings (≥80 wt%), lean electrolyte conditions of <2 g/Ah are needed. The highly porous nature of low-density carbon-sulfur (C-S) composite cathodes makes it difficult to prepare compact electrodes with high sulfur loading, often resulting in cracking during the fabrication process. Continuous electrolyte consumption originating from polysulfide shuttling also results in the need for a large excess of liquid electrolytes to achieve reasonable sulfur utilization and cycle life. There is an urgent need to develop compact electrodes with high sulfur loading and low porosity, with a focus on balancing high tap density and sufficient intrinsic porosity to allow wettability as well as efficient polysulfide adsorption. In this project, we seek to deliver full Li-S multilayer pouch-type cells of >1 Ah with cell level energy densities of up to >500 Wh/kg using high sulfur loadings of >15 mg cm-2 and electrolyte excess of ~2 g/Ah. Additionally, scalable fabrication processes will demonstrate feasible costs of <65 $/kWh (cell level). The pathways to achieve goals include:

1. Demonstration of a highly dense redox-active conjugated polymer in Li-S batteries to achieve low porosity (<40% before calendaring) and reduce electrolyte excess (<2.5 g/Ah). 

2. Identify key bottlenecks in capacity fade using advanced characterization tools and develop strategies to further reduce electrolyte (<2 g/Ah) with high S loading (>15 mg cm^-2).

3. Scalable synthesis of electrode materials (>1 kg) to achieve cost goals (<65 $/kWh and fabrication of >1 Ah pouch-type full cells that meet 500 Wh/kg with optimized electrode and electrolyte formulations.

Commercial Value: Ampcera developed a scaled processing method for a polymer/carbon nanotube composite binder designed for carbon-sulfur composite cathodes. The composite binder enables low porosity electrodes - lean electrolytes in Li-S batteries. The binder can be manufactured at scale and is commercially available.