Testing of Thermal Runaway Tolerant Battery Designs Utilizing High Energy Density 18650 Lithium Ion Cells

Abstract

ABSL builds batteries using commercial off the shelf (COTS) lithium-ion cells of the 18650 form factor. The commercial applications of 18650 lithium-ion cells have grown tremendously over the last 20 years, and cell manufacturers continue to improve the state-of-the-art by increasing energy density (Wh/L) and specific energy (Wh/kg) of their products. The increasing mass efficiency of these cells has facilitated more widespread and cost-effective adoption of lithium-ion as a power source in portable applications, which in turn has inspired investment in the development of new cells with ever increasing energy density. For space applications, the benefits of using cells with the highest possible mass efficiency are well established. But for a variety of reasons - the most significant being the increased amount of stored electrochemical potential energy - high energy density cells pose additional challenges to safely integrate into a battery solution. This is particularly true for the risk of catastrophic failure related to a thermal runaway event, and specific requirements are typically levied against battery designs in human spaceflight applications through JSC 20793, “Crewed Space Vehicle Battery Safety Requirements”. In order to characterize the thermal runaway behavior of a high energy density cell selected for a human spaceflight program, ABSL carried out a progressive development testing campaign. Starting from loose single cells, the test campaign incrementally included flight-like design features intended to mitigate the observed thermal runaway behavior. The results of the testing were subsequently incorporated into the flight design and the next level of development testing. The test campaign culminated in summer 2019 with successful verification of the JSC 20793 requirements on the CDR battery design.