E. Benner, S. Byrne, C. Call
GridFlow, Inc.,
United States
Keywords: lithium, sulfur, hybrid flow battery, energy storage
Summary:
Standard lithium batteries are prone to catastrophic failure by thermal runaway from dendrite formation-caused battery shorting. Furthermore, Li-ion technologies are limited by poor energy density in current cathode materials. GridFlow Inc. is commercializing lithium-sulfur hybrid redox flow battery technology licensed from Sandia National Laboratories. This technology relies on high energy density Li metal anodes coupled to flowing Li2S catholyte and represents vast improvements in safety, capacity, and cost compared to available long-duration energy storage battery technologies. This renders the technology competitive to multiple industry sectors including grid-scale energy storage, residential, and automotive. Lithium-sulfur has much greater energy density than other Li-ion technologies while flowing the catholyte minimizes the risk of thermal runaway and negates sulfur conductivity constraints. Additionally, there is abundant domestic supply of sulfur and the lithium supply chain is already well-developed. We are advancing the technology from single-cell toward 4 kW battery modules designed to store daytime charge cycles and provide long-duration capability of up to 20 hours or more. GridFlow has developed battery stacks and is working toward achieving 20 mA cm-2 discharge currents. We anticipate an initial cost per module below $60 kWh-1 at this discharge rate. Our hybrid flow cell recirculates catholyte through a carbon felt where sulfur is reacted. Lithium metal is plated on a Ni-foam anode which is separated from the sulfurous catholyte by a specialized membrane. The foam architecture reduces the risk of dendrite formation and increases charge and discharge rates while improving energy efficiency. The catholyte is pumped through an external reservoir where insoluble sulfides accumulate, isolating most of the sulfur from the lithium at any given time. Stacks are constructed from individual cells connected by built-in fluidic manifolds that simplify the hybrid-flow design. We are currently demonstrating increasing cycle life toward long-term storage, battery charge and capacity toward resilient power requirements leading to technology readiness at the prototype level.