Further Understanding and Modeling of the Thermal Runaway of High Energy Density Lithium-Ion Batteries

Abstract

Since the commercialization of Lithium-Ion Battery (LIB) by Sony Inc. in 1991 until today, recurrent incidents involving LIBs have been reported worldwide. During these incidents, the most energetic catastrophic failure of a LIB system is a cascading thermal runaway event. It is characterized by a deficit of energy dissipation versus energy accumulation in the cells leading to uncontrollable overheating of the battery system [1,2]. This complex event involves multi-scale phenomena ranging from internal parallel or cascading physico-chemical to battery components reactions (electrodes, electrolytes & separator) and further to the thermal propagation of cell core & safety features. Complexity of the comprehensive understanding of the thermal runaway hazard also lies in the fact that both normal operation (through aging and relating medium/long term degradation effects) and abuse conditions can contribute to a thermal runaway event, as recently discussed by [2] or [3].Battery safety is becoming even more critical with the emergence of highly reactive Ni-rich LIBs in the market. These batteries are commercialized to meet novel energy- or power-demanding applications and are expected to dominate the market in the coming years, likely until the occurrence of a new technological breakthrough. Therefore, these newly introduced LIBs presenting such high energy density characteristics and integrating more intrinsically reactive materials could possibly lead to more catastrophic events subsequent to the thermal runaway. Therefore, there is a clear need to better understand the underlying specific electrochemical and thermal behaviors of these technologies in both normal and abuse conditions across their lifetime. Inspired by the former collaborative IFPEN/INERIS research works on the thermal runaway of LIBs (essentially focused on LFP/Graphite and relating batteries) [2], this work aims to go deeper into the understanding & modeling of this complex phenomenon at cell scale, taking into account the influence of novel highly reactive technologies and the influence of aging with 2 target degradation mechanisms: SEI growth and Li Plating, in order to understand what the keys are towards inherently safer design and operation of highly reactive LIBs. It is a matter of establishing the link between the materials used (electrodes, electrolytes) in high energy density & intrinsically reactive LIB technologies, the degradation products during cell calendar and cycling aging (mainly analyzed through SEI evolution during cell lifetime and Li deposition during cold recharges) as well as the thermal runaway kinetics.The selected technologies studied in this research are two commercial 18650 Ni-rich LIBs, namely a Panasonic NCR GA and a LG HG2, which were based on Li(Ni0.8Co0.15Al0.05)O2 (NCA) and Li(Ni0.8Mn0.1Co0.1)O2 (NMC811), respectively, for positive electrodes, in combination with graphite-SiOx composite negative electrodes.With the goal of finding the keys factors that can improve the safety of these highly reactive LIBs during usage, the research strategy relies on the achievements of the previous projects and on the synergism offered by combined experimental and modeling studies as illustrated in Figure 1.The experimental study includes the 3 interconnected experimental processes here after specified: a complete multi-scale cell analysis in order to analyze the pristine, aged and thermally abused cells;a safety-focused aging campaign in order to artificially age battery samples, focusing on each target mechanism (SEI growth, Lithium plating) in a controlled and measurable way;accelerating rate calorimetry (ARC)thermal abuse tests in quasi-adiabatic conditions at cell level in order to qualifying the thermal runaway phenomenon as well as calibrating the thermal runaway model. The modeling study leads to the development of an extended thermal runaway model in order to predict the behaviors of different LIBs nearby and during thermal runaway under field conditions. This coupled multi-physics model will improve and extend the initial thermal runaway model built by [2] by integrating the impact of Li plating & SEI-driven cycling aging.The final result will be a multi-dimensional multiphysical model of LIB capable of accounting for the triggering of runaway under different thermal and electrical conditions and as a function of the state of aging. The predictions of the models will be validated based on other thermal abuse tests. This model will further be implemented to understand the electrical or thermal initiation of the phenomenon of thermal runaway and its propagation within a battery pack regarding its design. They will eventually be transposed into tools enabling the best design of the packs and avoidance of this undesirable phenomenon.