Thermal Modeling
Thermal modeling of Lithium-ion batteries is a critical aspect of battery system design, especially in applications such as electric vehicles (EVs), energy storage systems (ESS), and portable electronics. Thermal modeling helps in predicting the temperature distribution within the battery under various operating conditions, which is vital for safety, performance, and longevity.
There are various types of models listed below:
- Lumped thermal model assumes uniform temperature throughout the battery. Single thermal node per cell or module.
- Distributed thermal model spatially resolves temperature variation. It is based on finite element methods and requires more computation power
- Coupled electrochemical – thermal model integrates electrochemical behavior with thermal dynamics and captures feedback between temperature and battery performance.
Following are the key parameters needed:
- Geometry of battery cells (cylindrical, prismatic, pouch)
- Material properties: thermal conductivity, specific heat capacity, density of electrodes, separator and electrolyte
- Internal resistance and electrochemical co-efficient
- Boundary conditions like ambient temperature, cooling method etc.
- Operating profile like current, voltage, duty cycle etc.
The major applications of thermal models are:
- Battery thermal management system (BTMS) design
- Predicting and preventing thermal runaway
- Optimizing charge/discharge cycles
- Battery pack layout and cooling system integration
- State of health (SOH) monitoring and state of charge (SOC) estimation
Example test:
Here is an example of a simple thermal model of a battery pack of 5S x 5P design (Cylindrical 18650) where, trigger cell in the center heats up from 20 deg C to 150 deg C in 20 minutes. Then let it heat and go over 400 deg C. Surrounding cells heat up due to heat transfer from the trigger cell. Thermal runaway reactions have been suppressed.
Simulation model to replicate Thermal Runaway Propagation Testing
Modeling sample result
FAQ:
1. Why is Thermal Modeling important?
Batteries are sensitive to temperature. High heat can accelerate aging or trigger thermal runaway, while low temperatures reduce performance. Thermal models improve battery safety, performance, reduce aging and help in design optimization.
- Safety: Excessive heat can lead to thermal runaway — a dangerous chain reaction that can result in fire or explosion.
- Performance: Battery performance (capacity, power output, efficiency) is temperature dependent.
- Aging: Elevated temperatures accelerate degradation, reducing battery life.
- Design Optimization: Helps in designing efficient thermal management systems (cooling/heating).
2. Who needs thermal modeling?
- Battery pack designer
- Thermal management system designer
- Cell designer
- Material developers
- Battery pack charge/discharge cycle optimizer
3. What are the main sources of heat in a battery?
- Joule heating from internal resistance (I²R losses).
- Reversible (entropic) heating during charge/discharge.
- Side-reaction heat during aging or failure.
- Decomposition heat during abuse or thermal runaway
4. How are thermal models validated?
Models are validated through experiments such as calorimetry, thermocouple measurements, thermal imaging, and pulse current tests. Comparing measured vs. predicted temperatures ensures accuracy.