When it comes to predicting battery performance and degradation, more and more engineers are seeing the benefit of utilizing simulation tools like GT-AutoLion, the leading Li-ion battery simulation software. With simulation, engineers can predict battery performance and aging outside the standard capabilities of physical testing and because models run much faster than real-time, the simulated models expedite the process of testing lithium ion-batteries.
However, some engineers face a challenge that prevents them from utilizing simulation to its full potential, and at times from even attempting simulation. When engineers start with limited knowledge of the Li-ion cell, for example with nothing but a cell specifications sheet that contains only the very basics of the cell (i.e. chemistry and geometry), they struggle to build models that are an accurate reflection of the actual cell.
Because we noticed this struggle, GT created a process to calibrate cell models, then we developed a “cookbook” that walks through this process of going from a cell specification sheet to a predictive model. While I won’t cover the entire process of calibrating a battery model, in this blog, I’ll introduce some of the early steps using the GT “cookbook”, also known as the GT-AutoLion Application Manual and Calibration Process.
What type of cell are we working with?
The first step in calibrating a model is to determine the type of cell you have. Cells can range from having low-energy density and high-power density to having high-energy density and low-power density. Power-dense cells are used in applications such as power tools and mild and full hybrid electric vehicles (HEVs), where the battery is able to take high-power discharges and charges for starting the engine and regenerative braking. On the other hand, energy-dense cells are used in consumer electronics and battery-electric vehicles (BEV) in order to maximize the duration of the product.
If you don’t know which type of cell you are working with, start by looking at the voltage discharge curve, which you will find on your cell specification sheets. The figure below shows example discharge curves for batteries that use the same active material and electrolyte, but are designed for power-density or energy-density. If you have a high-power density cell, the voltage discharge curve on your cell specification sheet will look like the curve shown below on the left. These power-dense cells are capable of providing high C-rates continuously. If you have an energy-dense cell, the curve will look closer to the one shown below on the right. The deliverable capacity of these energy-dense cells goes down with increasing C-rates much faster than that of high-power cells.