International audienceSafety issues pertaining to Li-ion batteries justify intensive testing all along their value chain. However, progress in scientific knowledge regarding lithium based battery failure modes, as well as remarkable technologic breakthroughs in computing science, now allow for development and use of prediction tools to assist designers in developing safer batteries. Subsequently, this paper offers a review of significant modeling works performed in the area with a focus on the characterization of the thermal runaway hazard and their relating triggering events. Progress made in models aiming at integrating battery ageing effect and related physics is also discussed, as well as the strong interaction with modeling-focused use of testing, and the main achievements obtained towards marketing safer systems. Current limitations and new challenges or opportunities that are expected to shape future modeling activity are also put in perspective. According to market trends, it is anticipated that safety may still act as a restraint in the search for acceptable compromise with overall performance and cost of lithium-ion based and post lithium-ion rechargeable batteries of the future. In that context, high-throughput prediction tools capable of screening adequate new components properties allowing access to both functional and safety related aspects are highly desirable

Li-ion secondary rechargeable batteries are becoming the preferred solution to store energy on board of new generation electric and hybrid vehicles or manage renewable energy in stationary applications. However, Li-ion batteries (LIBs) are still suffering limited lifetime, high cost and significant safety issues increasing their time to mass market. Thermal runaway is still nowadays considered as a major hazard of LIBs. This multiscale and multistep phenomenon originating at the microscale level potentially leads to uncontrolled fire and explosion of the battery. This work is focused on the development and validation of a 3D physical model of the LIB electro-thermal behavior nearby thermal runaway conditions. A combined modeling and experimental investigation provides a better understanding of the mechanisms leading to thermal runaway of LIBs, and of the ageing influence on this process. One major outcome of this work is also the proven fact that calendar ageing leads to a delayed onset of the cell self-heating temperature with a thermal runaway starting at a lower temperature. This is supported by computer simulations showing that the thickening of the solid electrolyte interface (SEI) hinders the diffusion of Li ions, which delays the degradation of the negative electrode and the occurrence of thermal runaway. HIGHLIGHTS  Development of an original 3D thermal runaway model including calendar ageing.  Model includes 3D thermal, 3D chemical reaction, and 0D calendar ageing sub-models. Calibration of the model for cylindrical 26650 LFP/C cells using a BTC. Validation of the model for fresh as well as 10% and 30% aged cells in oven tests.  Fresh and aged cells are compared in terms of critical temperatures under overheating 2

The main safety issue pertaining to operating lithium-ion batteries (LIBs) relates to their sensitivity to thermal runaway. This complex multiphysics phenomenon was observed in two commercial 18650 Ni-rich LIBs, namely a Panasonic NCR GA and a LG HG2, which were based on L i ( N i 0.8 C o 0.15 A l 0.05 ) O 2 (NCA) and L i ( N i 0.8 M n 0.1 C o 0.1 ) O 2 (NMC811), respectively, for positive electrodes, in combination with graphite-SiOx composite negative electrodes. At pristine state, the batteries were charged to different levels of state of charge (SOC) (100% and 50%) and were investigated through thermal abuse tests in quasi-adiabatic conditions of accelerating rate calorimetry (ARC). The results confirmed the proposed complete thermal runaway of exothermic chain reactions. The different factors impacting the thermal runaway kinetics were also studied by considering the intertwined impacts of SOC and the related properties of these highly reactive Ni-rich technologies. All tested cells started their accelerated thermal runaway stage at the same self-heating temperature rate of ~48 °C/min. Regardless of technology, cells at reduced SOC are less reactive. Regardless of SOC levels, the Panasonic NCR GA battery technology had a wider safe region than that of the LG HG2 battery. This technology also delayed the hard internal short circuit and shifted the final venting to a higher temperature. However, above this critical temperature, it exhibited the most severe irreversible self-heating stage, with the highest self-heating temperature rate over the longest duration.