Search

For years, NASA and the battery industry have been improving passive propagation resistant (PPR) Li-ion battery cell technology by enhancing their material and design choices. These efforts help ensure that a single cell’s TR event does not overheat adjacent cells or the entire battery pack ultimately causing fire or explosion. To improve cell integrity, single cells within battery packs are triggered into TR so that the battery pack can be analyzed for its TR resistance. ThermoArc operates by initiating a plasma arc, capable of delivering thermal energy up to 100W, to a very small (1mm diameter) section of the cell. The extremely localized high heat flux rapidly degrades a small section of the internal cell separator, resulting in a short circuit that leads to TR. This technology comprises several components: a high-turn-ratio step-up transformer capable of producing a minimum of 1,000 V upon the secondary winding, an H-bridge electronic circuit to drive the transformer on the primary side, two tungsten electrodes to deliver the plasma arc, and a power supply unit. ThermoArc applications may exist in any Li-ion battery cell/pack testing application where TR must be induced in an individual cell. Such applications could include testing of PPR battery packs to ensure single cell runaway does not cause catastrophic damage, more general battery destructive testing designed to better understand battery failure states, or other experimental testing. Companies interested in licensing this innovation may include those that manufacture internal short-circuit (ISC) cells or other devices used to induce TR at the individual cell level, battery testing firms, and Li-ion battery manufacturers with a focus on Li-ion battery packs for critical applications. ThermoArc is at a technology readiness level (TRL) 5 (component and/or breadboard validation in laboratory environment) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.

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.