Abstract

Neglection of nominal operating conditions in Li-ion batteries can lead to internal damage and failure of the cells. This usually triggers chemical reactions that produce a large volume of hot gas. As a safety feature, 18650 battery cells are equipped with a safety vent. Once an internal pressure threshold is exceeded, the vent opens and the gas escapes the cell at a high velocity to prevent uncontrolled structural failure. Within a battery pack the hot gas needs to be guided to exit the pack while at the same time keeping neighbouring battery cells cool enough to stay within the nominal operating range. CFD simulation offers the capabilities to explore the mechanism of battery cell venting and flow guidance. This paper describes how such a simulation can be set up and run. Several steps are necessary to achieve this. First, Simcenter Battery Design Studio is used to model the 18650 battery cells. However, it is also described how this step can be avoided if certain prior knowledge about the process is available. Simcenter STAR-CCM+ is used for that and all subsequent steps. The cells are then arranged to a battery module and placed within a simplified battery pack housing. Then, the module is discharged with a constant current while one battery cell is heated by a constant volumetric heat source to model non-nominal behavior. Once this cell reaches a pre-defined average temperature, it is considered to fall in the regime of venting. Thus, in the next step hot gas is inserted into the pack domain through the vent at a high velocity. The gas flows through the pack and escapes through an outlet on the opposing side, passing the neighbouring cells. During this process, the average temperatures of these cells are constantly monitored to evaluate the chance of thermal runaway propagation.