Thermal Simulation and Safety Design of Electric Vehicle Battery Modules

Ensuring Battery Safety in Electric Vehicles: A Critical Focus on Thermal Management

In electric vehicle (EV) applications, ensuring the safety of batteries and battery modules is paramount to protecting the lives and property of vehicle occupants. The design and manufacturing of battery modules prioritize heat management to maintain safety. Even if a battery module passes safety standard tests, connecting cells in series within the module can reduce the heat dissipation area, introducing risks. Misuse or unexpected conditions can lead to thermal runaway within the internal battery, posing severe safety concerns. Effective risk control (Failsafe) is essential to prevent comprehensive burnout and protect lives and property.

Understanding Battery Thermal Energy and Heat Management

Thermal Energy Generation in Li-ion Batteries
The thermal state of a lithium-ion battery arises from the energy consumed by electric current passing through the battery's impedance during operation. This process generates heat, causing the battery's temperature to rise.

In experiments, such as the discharge testing of 18650 Li-ion batteries in an open environment, critical insights were observed:

• Temperature Rise with Increased C-Rates: The battery temperature rises rapidly with higher C-rates. However, within the average operating voltage range, the temperature increase is gradual.
• Thermal Runaway at Lower Capacities: When battery capacity drops to approximately 1.5 Ah, voltage decreases, and the temperature rises rapidly, signaling increased thermal risks.

Heat Dissipation Challenges in Battery Modules
Battery modules, composed of multiple cells connected in series and parallel, face unique heat management challenges:

• Non-Uniform Heat Dissipation: Internal batteries experience higher temperatures due to limited heat dissipation compared to outer batteries. This creates non-uniform heat distribution.
• Impact on Battery Life: Higher temperatures accelerate the decay rate of batteries. Temperature uniformity and control are critical to minimizing these effects.

Key Strategies for Optimal Battery Safety

To enhance battery module performance and safety, the following measures are essential:

1. Temperature Difference Control: Maintain temperature differences within the module to less than 5˚C to ensure uniform heat distribution.
2. Maximum Temperature Regulation: Implement mechanisms to control peak battery temperatures, improving safety and extending battery life.
3. Thermal Management Solutions: Utilize advanced materials and designs to optimize heat dissipation and enhance safety margins in EV applications.

Conclusion

Effective thermal management is critical for ensuring battery safety in EVs. By addressing heat dissipation challenges and maintaining uniform temperatures, manufacturers can significantly enhance battery performance and reliability while safeguarding lives and property.

 

Author

Professor Wei-Keng Lin

Education｜Ph.D., University of Maryland

Occupation｜Professor, National Tsing Hua University 

Specialty｜Electronic package heat dissipation, Heat pipe, Loop heat pipes(CPL，LHP，PHP), Energy-saving design, Solar heat storage and cooling, Heat flow system, Cooling of electronic components, Two-phase flow, Heat transfer elements of artificial satellite and high-altitude flying object