High Energy Density, Long-Life Li-S Batteries for Aerospace Applications

Lithium-ion batteries have been successfully employed in several Mars surface missions, e.g., Mars Exploration Rovers (Spirit and Opportunity), Mars Phoenix Lander, and more recently in the Mars Science Laboratory rover (Curiosity).¹   With distinct benefits in gravimetric and volumetric densities combined with good low temperature performance relative to the aqueous battery systems, Li-ion batteries contribute to reduced launch costs, increased payload and science capabilities in the space missions.  NASA’s upcoming missions however need energy storage systems with enhanced performance capability, especially higher specific energies and  energy densities.  One such application involves astronaut Extra Vehicular Activity (EVA), wherein the astronaut’s Portable Life Support System (PLSS) is expected to support 8 hours of EVA. The state of art batteries with ~200 Wh/kg at the cell level can support only four hours of EVA. 

            To address these needs, we are developing high-energy and long-life lithium-sulfur cells, with the following performance targets: cell specific energy of 400 Wh/kg ii) cycle life exceeding 200 cycles and iii) ability to operate safely over a wide temperature of -10 to +30 °C.  We have been developing improved cell components for Li-S cells, e.g., protected Li anode, dense sulfur cathode and compatible electrolytes, mainly addressing the key technological hurdlesof poor utilization at high cathode loading (necessary for a practical high energy cell) and limited cycle life.^2-5 We have developed new sulfur cathodes that show high specific capacities of ≥800 mAh/g at C/5 rate with practical material loadings, ii) Li anode protected with a polymer electrolyte that displays efficient Li cycling and durability in laboratory Li-S cells, and iii) Electrolytes and new proprietary coatings of polysulfide blocking layers which inhibit the deleterious effects of sulfur redistribution and contribute to a good cycle life.  We have also developed suitable cell designs and fabricated pouch cells that displayed specific energies of ~300 Wh/kg, moderate cycle and safety towards thermal and electrical abuse.  In this paper, we will describe some of these material developments and their performance in laboratory cells and later in prototype cells.

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6. S. S. Zhang, Front. Energy Res. 1, 1 (2013).