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 proposes to develop an atomically precise and bifunctional membrane separator for lithium sulfur batteries 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. Phase I results showed that the proposed separator significantly improves the energy density and cycle life of lithium sulfur batteries. The Phase I proof of concept effort focused on validating the membrane materials property advantages in lab prototype cells. Phase II will scale up production of separator using high volume roll-to-roll (R2R) coating. Phase II will demonstrate separator robustness to automated high-speed cell assembly operations and to variation in the porous polymer substrate. Membrane performance, cycle life, and abuse tolerance advantages will be validated in commercially relevant prototype pouch cells with at least 2Ah capacity. Phase II technical objectives are to reduce coating thickness to <5 µm, continuously coat at least 20m of separator, demonstrate a 400 Wh/kg lithium sulfur battery cell with 200% improvement in cycle life, and show immunity to thermal runaway under NASA mission-relevant abuse testing protocols..

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 LSB cycle life by >2X which will help enable adoption of batteries that double the specific energy of commercial lithium ion batteries. Initial target markets include consumer 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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