A methodology for reliable thermal runaway propagation mitigation in battery systems with large-format prismatic NMC-811 and LFP battery cells

Thermal runaway propagation mitigation is a crucial aspect of battery safety, ensuring the vehicle occupants’ safety. For this reason, it is a major part of legal requirements and must be proven in tests for homologation. The test results are usually subject to significant statistical variance. However, these uncertainties are often neglected in thermal runaway propagation simulations used in the safety-related design of battery systems, leaving the confidence level of the simulation results unclear. This article presents a methodology for reliable thermal runaway propagation mitigation. The focus is on modeling thermal runaway propagation in battery systems with prismatic NMC-811 and LFP battery cells, identifying safe system configurations, evaluating their reliability, and comparing different system configurations at a similar safety level. A thermal runaway propagation risk assessment revealed that an aerogel thickness of 4 mm is sufficient to prevent thermal runaway propagation in the NMC-811 cell stack. Meanwhile, an aerogel thickness smaller than 1 mm is necessary to prevent thermal runaway propagation in an identical LFP cell stack, allowing for discussion of smaller aerogel thicknesses or the elimination of the intermediate material. However, only an aerogel thickness of 5 mm in the NMC-811 cell stack offers a comparable level of safety to the LFP cell stack with 1 mm aerogel thickness, considering the reliability of the thermal runaway propagation prevention. Thus, the method enables a more reliable safety design concerning thermal runaway propagation and a time- and cost-efficient safety assessment of different system configurations in the early phase of battery development.