Short Circuit-Driven Thermal Effects in Automotive Batteries

Simulia

Mentors: Christian Linder (Stanford), Yitao Qiu (Stanford), Victor Oancea (SIMULIA), Yunfei Shi (SIMULIA), and Youngwon Hahn (SIMULIA)

Students: Ege Acaroglu (not all students are listed)

Goal:

To create a computationally inexpensive model for a sub-module of an automotive battery pack, and to run simulations of discharging, charging, and abusive loading scenarios (short circuiting).

Problem:

Performing physical tests on battery modules and packs for electric vehicles is expensive and hazardous. Thus, computationally simulating abusive loading and failure accurately is of great interest to vehicle manufacturers. A battery cell contains dozens of individual parts, and meshing of all the separate parts results in models of a single cells which contain millions of finite elements. A battery pack contains thousands of these cells, and as a result, current battery models are computationally very expensive to run. In order to produce accurate simulation results for use in safer battery pack design, a simplified model that can appropriately predict the effects of charging, discharging, and short-circuiting is needed.

What did the team do?

To begin with, the team calculated the overall thermal properties of a single cell using a detailed model provided by Dassault Systems, and applied them to a model of a solid single part cell with much fewer elements than the expensive model. That model turned out not to be accurate enough, so the team split the cell into three parts and separately recalculated the properties for the three different parts of the cell. The new coefficients were applied to a solid three-part cell, greatly increasing the accuracy of the simulations. Thus, a simplified cell geometry was achieved with comparable performance under simulations to that of the detailed model.

The single cell was then used for making a 20-cell sub-module model. The team built the model inspired by a Tesla battery pack, and included similar parts in the assembly as can be found in those packs. The parts in the model are the cells, polycarbonate casings, busbars, wires, a cooling channel, and thermally conductive silicone sheets. The team researched materials, and assembly methods to define the various features of the model.

When the sub-module model was ready, the team ran multiple simulations on it, and drew conclusions from the simulations. The simulations included discharging at different rates, charging at different rates without cooling, short circuits, and a 31 hour discharge-and-charge cycle based on estimated use of an electric vehicle.