Energy Dense Batteries Based on Highly Conductive Solid Electrolyte and Cathode Materials

Statement of the Problem or Situation that is being addressed Lithium-ion batteries are considered candidates for large-scale energy storage mainly because of their high energy density and flexibility. However, current lithium-ion battery technology does not meet the critical requirements in terms of safety, ultra-long cycle life and shelf life, low cost, and improved energy density. Element Sulfur, an earth abundant element, is a promising cathode material because of its high theoretical specific energy of 2600 Wh/kg, about 4 times higher than the 585 Wh/kg for the current commercial cathodes. Still, several formidable challenges remain, including low electrical and ionic conductivity of sulfur, dissolution of intermediate discharge products into the liquid electrolyte, and unsafe metallic lithium anodes. Mainstream Li-S battery research inherits the conventional design of Li-ion batteries, i.e., a liquid electrolyte contained in a porous separator sandwiched between a solid cathode and a solid anode. The corrosive liquid electrolyte greatly limits the long-term cycle life of batteries while inherently presenting safety concerns. General Statement of How This Problem is being Addressed In the proposed project, a solid-state lithium-sulfide battery will be developed for large-scale energy storage. A high conduction, highly stable solid electrolyte will replace the conventional liquid electrolyte and separators. The new solid electrolyte can be prepared as free standing thin membranes with a thickness of less than 20 m or as thin coatings on the electrodes through a proprietary solution coating process. Lithium ion-conducting polysulfide compounds and composites of metal sulfides will be cycled at the solid state as the cathode. The anode will be pure lithium metal. The battery will be cycled at elevated temperature up to the melting point of lithium (180C) in order to achieve desirable power density; therefore, sulfides can be used to replace sulfur to avoid the volatility problems of elemental sulfur. Commercial Applications and Other Benefits The to-be-developed solid-state lithium-sulfide batteries are of great interest for large-scale energy storage. The low cost and relatively low operating temperature of the new batteries enable its wide application for smart electric grids, energy storage media for renewable energy sources such as solar cells and wind electricity generators, as well as electric vehicles. Keywords lithium-ion battery, sulfur, solid electrolyte, lithium anode, low cost Summary for Members of Congress The advanced solid-state lithium-sulfide battery has the potential as energy storage medium for smart grids, solar/wind generators, and electric vehicles. It will provide more than two times the energy density compared with commercial lithium-ion batteries with half of the cost.