Initialization of Thermal Runaway in Lithium-Ion Batteries and Measures to Prevent Thermal Propagation

摘要

Different methods are proposed for the initialization of the thermal runaway (TR) in a Li-ion cell such as nail penetration, heat injection, overcharge and short circuit. The TR might spread by thermal propagation (TP) to neighbouring cells in Li-ion-battery-modules and - packs and might evoke hazardous situations if the TP is not confined. Thus, the United Nations global technical regulation on electrical vehicle safety (GTR EVS) requires that after TR detection the passengers have a few minutes to leave safely the car before a hazardous situation in the passenger compartment occurs. There are two approaches to stop or at least delay the TP. The first option is based on thermal barrier materials with very low thermal conductivity coefficients between the Li-ion cells. The second option, which has been investigated in our work, applies phase change or endothermic materials that partially absorb the TR energy of a cell and thus, limits the temperature at the interface between the cells. In this work we focus on the thermal characterization of different phase change and endothermic materials. A fundamental evaluation of thermal material properties has been carried out by differential scanning calorimetry to investigate the temperature ranges of reaction and the respective endothermic enthalpies of different material classes. Based on this experimental data set and further parameters like density, chemical reactivity and availability, materials have been selected to be investigated under TP conditions of PHEV 2 cells. In this investigation, the TR has been induced by nail penetration tests to observe how phase change and endothermic materials limit the TP in Li-ion modules and packs. Literature: Draft Global Technical Regulation on Electric Vehicle Safety, 2017. ECE/TRANS/WP.29/GRSP/2017/2, section Ⅰ. E. 7 c 112, Ⅱ. 5.3.3 and Ⅱ. 7.2.3.