Lithium-ion Battery CFD Simulation: ANSYS Tutorial

Lithium-ion batteries power everything from mobile phones to modern electric cars. When a battery discharges power, complex chemical reactions happen inside the solid casing. These chemical reactions create electricity, but they also generate dangerous physical heat. If this heat stays trapped inside the cell, the battery will age very quickly and can even catch fire.

CFD Engineers use simulation software to look inside the battery before manufacturing it. Our objective in this CFD project is to analyze a single lithium-ion cell during a steady discharge cycle. We want to see how the electrical current flows and observe where the physical heat builds up. To build our virtual model correctly, we use a respected academic paper by Kim et al. as a helpful guide for the physical dimensions. By understanding internal thermal stress, designers can build safer and cheaper cooling systems for large energy packs.

• Reference [1]: Kim, Ui Seong, et al. “Modeling the dependence of the discharge behavior of a lithium-ion battery on the environmental temperature.” Journal of The Electrochemical Society5 (2011): A611.

Figure 1: The reference geometry of the lithium-ion cell detailing the physical sizes based on our guide paper. [1].

Simulation Process: The Coupled MSMD and NTGK Models

We build a test space for the battery cell using the dimensions provided in our guide paper. We divide this space into 1264 structured hexahedral cells. This mesh size is small, but it is highly efficient. It allows the solver to calculate the thermal behavior accurately without needing a supercomputer. To capture the physics, we activate the MSMD (Multi-Scale Multi-Domain) battery model inside ANSYS Fluent. We pair it directly with the NTGK electrochemistry model. This powerful combination solves the electrical field and the chemical reactions at the same time. We force the battery to discharge its energy at a continuous 1C rate. To ensure realistic behavior, we limit the operating voltage to a safe window between 3 V and 4.3 V. You can find more about this topic in our fuel cell and battery CFD tutorials.

Figure 2: The battery model built to calculate fluid flow, electricity, and internal temperature.

Post-processing: Electrical Bottlenecks and Physical Heat

The data tells a clear story about how electrical stress creates physical danger. First, we look at how the power leaves the battery. The voltage graph tracks the electrical output over 300 s. The battery starts strong at 4.12 V. It drops very quickly in the first few moments. This fast drop happens because the battery needs to spend extra energy just to activate the internal chemical reactions. After this initial shock, the voltage falls slowly and smoothly to a final operating level of 4.015 V. This smooth decline proves the battery is draining its lithium concentration normally.

While the voltage drops, the battery generates continuous heat. The temperature graph shows a perfectly straight, upward line. The maximum heat in the cell rises from a starting baseline of 300 K to a final peak of 300.62 K. This small 0.62 K increase is important. Because the line is straight, it proves that a steady 1C discharge rate produces thermal energy at a highly predictable, constant speed.

Figure 3: The temperature history proving that a steady electrical discharge creates a constant thermal rise.

Figure 4: The electrical performance curve showing the natural chemical voltage loss during the power cycle.

However, this heat does not spread evenly across the battery. The thermal contour shows a dangerous hot spot forming right at the top of the cell. The peak heat generation reaches an extreme 4655 W/m³ directly at the base of the small metal tabs.

To understand why this hot spot forms, we must look at the current magnitude contour. The massive main body of the battery handles the electrical flow easily and stays cool. But all that electrical power must squeeze out through the tiny connection tabs to power the device. This creates a severe physical bottleneck. The current density spikes to a massive 102,785 A/m² in this narrow area. This extreme electrical traffic jam creates high resistance. The battery must fight this resistance, and that electrical fight burns directly as intense physical heat.

Figure 5: The spatial heat distribution proving that thermal energy is concentrated heavily at the top.

Figure 6: The electrical flow paths demonstrating the extreme current stress placed on the small metal tabs.

FAQ About Lithium-ion Battery Simulation

• Why does the battery voltage drop so fast at the very beginning? Before a battery can provide steady power, it has to jumpstart its own internal chemistry. This is called activation polarization. The battery spends a burst of its own energy to get the chemical reactions moving, which causes a quick initial drop in voltage.
• Why do the small metal tabs get so hot? The main body of the battery is large, but the tabs are very small. All the electrical current must squeeze through these tiny metal tabs to exit the battery. This creates a massive electrical bottleneck, and that high resistance turns directly into heat.
• How is the academic paper used in this CFD project? We use the academic paper purely as a guide. It helps us set up the proper physical dimensions and provides a reliable baseline to understand how the battery should behave during the simulation.