Bifunctional Membrane for High Energy, Long Shelf Life Li-S Batteries

The adoption of high energy lithium sulfur batteries hinges on significant improvements in charge/recharge cycle life. Cycle life is limited by migration of dissolved polysulfide species which creates an electrochemical short circuit. In this NASA SBIR, Navitas Systems will demonstrate and scale up a bifunctional membrane separator that impedes polysulfide transport. Bifunctionality will combine pore structure engineered for high capacity and selectivity to polysulfides with metal-like electronic conductivity to support electrochemical regeneration. The proposed membranes will be fabricated using slurry cast methods that readily scale to continuous roll-to-roll production. The slurry will combine a nanoporous conductive ceramic powder with a binder and solvent. Slurries will be castable onto conventional porous polyolefin battery separators. In Phase I, membrane separators will be produced at bench scale and evaluated to assure good adhesion and uniform dispersion at the target weight loading, with minimal added impedance to lithium ion transport. Membrane separators will be incorporated into prototype lithium sulfur batteries and subjected to commercially relevant performance and life testing.

High energy lithium sulfur batteries can safely provide 500+ Wh/kg and potentially reduce the mass of energy storage systems by up to 50%. Through improving cycle life, the proposed separator advance will address the key limitation for space applications. With improved cycle life, lithium sulfur batteries will meet multi-use or cross platform space energy storage applications. Successfully deployed safe lithium-sulfur batteries would result in significant mass and volume savings and operational flexibility. Potential NASA applications include EVA space suits and tools, human example, lunar and martian landers, construction equipment, rovers, science platforms and surface solar arrays.

If successful, the proposed technology is expected to improve lithium sulfur battery cycle life by >2X which will help enable adoption of lithium sulfur batteries that double the energy of commercial lithium ion batteries. Initial commercial adoption is expected to be commercial electronics, drones, and soldier portable power, with the ultimate target of meeting performance, life and cost goals for Electric Vehicle batteries.

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