Abstract
Lithium-ion batteries (LIBs) are widely used in power tools, digital products, aerospace and military fields due to their light weight, high energy density, and no memory effects. Although LIBs are widely used, they have potential safety hazards. The most important problem is the combustion and explosion caused by the thermal runaway (TR) of the battery, especially during charge and discharge processes. In order to analyse the thermal behaviour of the cylindrical lithium-ion batteries from charge/discharge processes to TR, eight electrochemical-thermal models (ECT) with different levels of fidelity and dimensionality (from one-dimensional (1D) to three-dimensional (3D) electrochemical and thermal models) are firstly established for a Li[Ni8Co1Mn1]O2/graphite 18650 type cylindrical LIB. The effect of different levels of model simplification on the predicted LIB thermal and electrochemical characteristics are compared under different discharge and cooling rates. The accuracy and computation time of different models are compared, and the applicable scope of different models is discussed comprehensively. Then, a 3D TR model is developed to predict the battery TR behaviours under different SOCs. Through the method of combining experiments and simulations, we obtained the chemical reaction sequence of the battery during TR and the proportion of reaction heat of different reactions of the battery. Finally, through coupling the established ECT model and the TR model, we established an ECT-TR model for a commercial 18650 type 2.6 Ah NCM523/graphite battery to analyse the TR characteristics of the battery under different environment temperature, heat transfer coefficient and C-rates during charge and discharge processes. The results show that the TR risk of the battery is in the cycle process >charge process >discharge process, but the risk of accelerated battery aging due to chemical reactions in the discharge process is greater than that in the charge process.