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The CFRP sleeve was originally intended for crewed space flight lithium-ion 18650 battery packs rated over 80 Watt-hours (Wh), which are required to be passively propagation-resistant for increased safety. Previous battery designs have addressed SWR propagation by using aluminum or steel interstitial materials to prevent SWRs from directly impacting neighboring cells, but these materials were underperforming. During testing of 18650 battery cells, it was discovered that cells over 2.6Ah in capacity can have an undesirable failure mode in which the cell wall will rupture or breach during a thermal runaway (TR) event sending heat and ejecta into an undesirable direction. TR is typically triggered when heat produced by the battery cell’s exothermic reaction leads to increased and escalating internal cell temperature, pressure, and boiling of the electrolytes. When internal cell pressure exceeds the cell’s safety relief mechanism, rupture or bursting can occur, initiating a cell-to-cell propagation that in turn results in a battery pack fire. By adding a carbon fiber reinforced polymer (CFRP) sleeve to cylindrical battery cells, a sidewall rupture (SWR) can be prevented from occurring or propagating. In initial testing, there were no SWRs of a battery cell using a CFRP sleeve. This result is believed to be due in part to a unique characteristic of CFRP sleeves compared to other materials. Carbon fiber material has a negative coefficient of expansion and accordingly shrinks when heated, while steel and aluminum expand. The shrinking of the CFRP sleeve when heated compresses the cell located within it, significantly aiding in the prevention of SWR. This technology can be implemented into other multi-physics battery safety models to guide the design of the next generation of battery cells and battery packs. This thermal runaway propagation resistant technology has a technology readiness level (TRL) of 6 (System/sub-system model or prototype demonstration in an operational environment) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.

The Thermal Ejecta Shielding System comprises strategically layered materials that fasten to the top of a Li-ion cylindrical battery pack casing. It can protect individual battery cells in a battery pack by shielding them from a neighboring cell’s hot thermal ejecta during a TR event while providing primary functions of connecting, insulating, grounding, and distributing power. In laboratory testing, this technology improved the resistance to TR collateral damage of a PPR battery pack by overcoming two primary drawbacks of its design. Modern Li-ion cylindrical battery cell packs comprise a nickel bus plate that aligns with and connects the positive buttons along the battery tops to distribute power. Insulating G10 composite layers sandwich the bus plate atop the cells, however, these are rendered vulnerable to burn-through during a TR event due to their thinness, and they can allow escaping thermal ejecta to penetrate the button cavities of neighboring battery cells within the battery pack. Additionally, the nickel and composite bussing layering is prone to separation, or "tenting", when subjected to extreme heat, as it relies solely on an adhesive bond to prevent delamination. The hot ejecta spray stemming from a battery cell undergoing a TR event can weaken this adhesive bond. These issues can lead to adjacent battery cell damage resulting in their reduced performance, zero-voltage, or susceptibility to a larger TR event. The Thermal Ejecta Shielding System for Li-ion Battery Packs was developed from a multi-pronged strategy to improve upon the drawbacks by introducing these novel components and accompanying features: • Capture Plate Cell “Chimney” - Redirects ablative ejecta away from adjacent cells and creates a volume for liquid “sealer” protection; • Adhesively Backed Mica Cell Donut - Provides an insulative layer to protect the positive bus plate from creating a short circuit to the negative cell can during TR; • Adhesive Transfer Tape - Provides an adhesive layer for a more uniform/reproducible bond between the nickel bussing, mica, the G10/FR4 insulating layer, and the aluminum layers; • Continuous Mica Cell Cover Sheet - Replaces individually installed mica covers (upper layer of G10/FR4) with a single sheet of perforated mica; • Rupture Sheet Cover Plate - Introduces a thin aluminum fastener plate above the Continuous Mica Cell Cover Sheet to prevent delamination of bussing sandwich layers; • Narrowed Bus Plate Tab - Introduces a narrowed tab to allow for unrestricted header expansion and severing/separation during TR; • Steel Ring - Protects cell from spin groove ruptures and redirects ablative ejecta away from adjacent cells; and • Liquid Cell Covers - Introduces a high temperature liquid “sealer” to fill the void between cell button and mica cover to prevent ejecta burn-through from compromising the seal.