Mitigating Negative Effects of Polysulfide Dissolution in 18650 Lithium Sulfur Battery

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Trusted AI and Autonomy; Microelectronics; Space Technology; Renewable Energy Generation and Storage; Advanced Materials OBJECTIVE: The objective of this topic is to improve cycle life and capacity retention of Lithium-Sulfur battery chemistry by addressing and resolving negative effects of parasitic polysulfide reactions. DESCRIPTION: The current state-of-practice specific energy in 18650 Li-ion cells used in space missions is as low as 150 W-h/kg. Lithium-Sulfur, with its 2600 W-h/kg theoretical specific energy, has been identified as a promising chemistry to achieve for the U.S. Space Force's (USSF) short-term 18650 rechargeable battery target of 450 W-h/kg. A higher energy rechargeable power source would have impacts across all areas of the USSF mission to enable spacecraft resilience and survivability. Most practical issues with Lithium-Sulfur chemistry can be attributed to polysulfide shuttling , the dissolution of Lithium Polysulfide in liquid electrolyte which results in parasitic reactions and its relatively low volumetric energy density, especially when in a small form factor battery cell such as an 18650. These reactions cause low Sulfur utilization and capacity fade, resulting in poor cycling efficiency. Recent efforts have been focused on either (1) suppressing diffusion of the dissolved polysulfides out of the cathode, or (2) protecting the lithium anode from reacting with the dissolved polysulfides. Li-S modelling is necessary to understand the technology development way-forward. This topic proposes the investigation of these or other methods to mitigate the inhibiting effects of polysulfide dissolution and improve its volumetric energy density. Findings will be incorporated into materials and 18650 cell design that can improve cycle life performance while maintaining a high specific energy intrinsic to the chemistry. PHASE I: Investigate the feasibility of practical solutions to the polysulfide dissolution problem affecting the lithium-sulfur chemistry while maintaining a high 18650 specific energy and energy density. Using the results of this investigation, synthesize and characterize proof-of-concept anode, cathode, separator, and/or electrolyte materials that will provide a potential for improved cycle life and capacity retention to be used in the 18650 cell form factor. Model proposed Li-S cell-level performance. A small quantity of material and the cell-level model are encouraged Phase I deliverables. PHASE II: Continue the research efforts initiated in Phase I. Optimize materials and test the impact on the cyclability of resultant Lithium-Sulfur cells using coin cell, pouch cell, and/or other cell methodology. Optimize Li-S cell model. Utilizing the materials developed during Phase I and optimized during Phase II, construct 18650 cells and provide an appropriate number of cell samples to conduct electrochemical performance testing to AIAA S-144-202X. Performance targets for deliverables include specific energy of 450 W-h/kg at the 18650 cell level and 500 cycles of at least 80% capacity retention at 20% DOD. PHASE III DUAL USE APPLICATIONS: Transition technology to the USSF supply chain by completing AIAA S-144-202X qualification. Lithium-Sulfur battery chemistry is the USSF's most near-term high specific energy storage solution. Successful Phase I and II development provides opportunities for transition to the USSF's supply chain into programs of record. REFERENCES: Li, et al. "Status and prospects in sulfur-carbon composites as cathode materials for rechargeable lithium-sulfur batteries." Carbon, 92. 2015; Zhang, Sheng S. "Liquid electrolyte lithium/sulfur battery: Fundamental chemistry, problems, and solutions." Journal of Power Sources, 231. 2013; Cheon, et al. "Rechargeable Lithium Sulfur Battery: Structural Change of Sulfur Cathode During Discharge and Charge." Journal of The Electrochemical Society, 150(6). 2003; Cheon, et al. "Rechargeable Lithium Sulfur Battery: Rate Capability and Cycle Characteristics." Journal of The Electrochemical Society, 150(6). 2003; KEYWORDS: Rechargeable Battery; Lithium-Sulfur; High Specific Energy; Polysulfide Shuttling