Modelling Venting and Pressure Build-up in a 18650 LCO Cell during Thermal Runaway (ABSTRACT)

Li-ion batteries are a very popular type of electric storage devices that possess high energy density when compared to the other battery chemistries. Due to this property, when operating under abusive conditions such as high ambient temperature, the batteries can experience thermal runaway, which may lead to fires and explosions. To prevent this, it is therefore important to model thermal runaway considering different events such as venting and the pressure development inside the battery cell, which makes the main purpose of this
paper.
A model consisting of the different decomposition reactions in the anode, cathode and SEI, but also in electrochemical reactions and boiling of the electrolyte is developed for a cylindrical 18650 LCO cell (Lithium Cobalt Oxide). For determining the pressure and the temperature after venting, the isentropic flow equations are included in the model. By fitting the activation energies, and measuring experimentally the mass of the ejecta during thermal runaway, the model is compared and validated against an extensive experiment performed
by Golukbov et al. [1] during oven heating.
When analysing the results, it is found that by including the venting of ejecta and the isentropic flow equations, the model provides a better accuracy in evaluating the temperature of the cell. After the experimental validation of the model, the total energy, the reactions fractions and the pressure are evaluated numerically. By analysing the pressure, the results show that the volume occupied by the electrolyte affects the pressure build-up considerably. As a result, the venting triggering time is also affected, which means that the model can assist in predicting the venting event.