Ratnakumar Bugga^*, Simon Jones, John-Paul Jones, Jasmina Pasalic, Frederick C. Krause, Mary Hendrickson^** and Edward Plichta^**

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109

^**US Army RDECOM CERDEC, 5100 Magazine Rd., Aberdeen Proving Ground, MD 21005

^* rvbugga@jpl.nasa.gov

Li-ion batteries, being compact, lightweight, and durable, have contributed to a significant enhancement or even enablement of several planetary and space missions. However, NASA’s future missions, e.g., Astronaut’s Portable Life Support System (PLSS) for Extra-Vehicular Activities (EVA), small planetary rovers, planetary probes, CubeSats etc., require battery technologies with higher specific energies and energy densities, for short cyclic lifetimes. Similarly, DoD is interested in the development of a high energy rechargeable battery system for soldier applications. The lithium/sulfur system is deemed the most viable future technology, because of its high theoretical specific energy (3-4x vs Li-ion). Despite several years of development, this system hasn’t matured yet, mainly due to the challenges from the soluble polysulfides, which results in a ‘redox shuttle’ and a deposition of lihium sulfides and impedance growth at the lithium anode. Several attempts were reported in the literature with novel cathode designs, e.g., hierarchical porous carbon structures to sequester sulfur and its reduction products, and also with electrolyte solutions to minimize their solubility. ^1-3 Good cycle life was achieved in some of these cases with nanostructured sulfur cathodes in both organic electrolytes containing suitable additives (LiNO₃) and in ionic liquids, but the sulfur loadings in the cathodes are much lower (below 4 mg/cm²) than desired. For example, to realize high specific energy from a Li/S cell, sulfur loading will need to be high, i.e., > 12 mg/cm² per side or >6 mAh/cm² areal capacity. Recently, our group^4,5 and several others^6-8 have been developing new sulfur composite cathodes blended with transition metal sulfides (e.g., titanium and molybdenum disulfide), which not only provide good electronic and ionic conductivity, but assist in the trapping of polysulfides within the cathode. We have demonstrated that MoS₂ doesn’t undergo a redox transition, unlike TiS₂, and yet provides similar benefits. In addition, we have demonstrated similar improvement in the cycle life of sulfur cathodes with a thin coating of a metal sulfide. In this paper, we will describe our studies with high-areal-capacity sulfur cathodes blended or coated with new metal sulfides, demonstrating their performance and understanding their mechanism.

Acknowledgements

The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) and supported by US Army-CERDEC.

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