SAE ARP7131

This SAE Aerospace Recommended Practice (ARP) is an industrial collaboration with regulatory bodies like the European Aviation Safety Agency (EASA) and the Federal Aviation Administration (FAA) to determine the worst-case credible thermal runaway (TR) condition (energy released and maximum temperature) for the design of an aviation large propulsion battery system to quantitatively verify TR in lieu of battery level RTCA DO-311A testing with protections disabled. The ARP considers the three stages of TR within a cell and defines the two critical temperatures for a specific cell design. These temperatures are key to understanding the layers of monitoring necessary to determine the severity of a TR event. Different trigger methods can be used to quantify the heating characteristics and resultant energy profile releases as a function of time. Results show three general phases of the event critical temperature (see 1.5) corresponding with the reaction between the cell’s solid electrolyte interphase (SEI) for graphite anodes and the electrolyte, resulting in heat generated by the cell rather than heat supplied from the accelerating rate calorimeter (ARC). The temperature of the cell continues to rise until the separator begins to melt. Critical Temperature 2 occurs after the separator melts and electrodes are shorted together to generate large amounts of heat, raising the cell temperature quickly to 377 °C. These temperatures are key precursors of TR, regarding the length and severity of an event. Understanding this key bit of information is vital to the approach presented herein. A Lithium-Ion battery thermal runaway event cannot be reliably prevented, but the effects can be limited to improve aviation safety. RTCA DO-311A is currently used as guidance for the design, performance, characterization, and installation of permanently installed rechargeable Lithium aircraft batteries. However, certain electric aircraft propulsion initiatives necessitate more comprehensive design and implementation guidance beyond the valid methodologies addressed within the DO-311A standard. This recommended practice complements the standard with practical cell to system considerations that better resolve the context of a layered set of preventative failure mitigations necessary for these much larger and more energy-dense battery powertrain systems.