Thermal Modelling

Heat sources in batteries (ohmic, reaction, entropic), lumped vs distributed thermal models, and thermal runaway risk.

When a battery operates, not all energy goes into powering devices—some is inevitably lost as heat due to internal resistance and electrochemical processes. Managing this heat is essential for performance, lifespan, and safety, especially in large-format cells used in electric vehicles or grid storage.

Heat Generation in Batteries

Every battery generates heat during operation. The main sources include:

Source	Description
Ohmic losses	Resistive heating from current flow
Reaction overpotentials	Energy lost at electrode interfaces
Concentration gradients	Entropic effects from lithium redistribution

In small cells or at low currents, the generated heat may dissipate naturally. However, in high-power or large-capacity applications, heat can accumulate, leading to temperature rises that affect battery performance and accelerate degradation.

In extreme cases, excessive heat can trigger thermal runaway—a dangerous, self-reinforcing cycle of overheating.

Thermal Model Types

Thermal models are coupled with electrochemical models (such as the Doyle-Fuller-Newman model): the electrochemical processes dictate how much heat is generated, while the battery temperature affects transport properties inside the cell.

Lumped Thermal Models

These treat the entire battery as having a uniform temperature.

Advantages:

• Simpler and computationally efficient
• Suitable for real-time battery management systems (BMS)

Best for:

• Systems where temperature gradients are minimal
• Applications requiring fast calculations

Spatially Distributed Models

These account for temperature variations within the battery.

Depending on the desired level of resolution, these models can capture:

• Temperature differences across the current collector or cell thickness
• Detailed variations within each battery layer

Best for:

• Large-format cells
• High-power applications where internal temperature gradients significantly impact performance and safety

Choosing the Right Model

Model Type	Complexity	Accuracy	Use Case
Lumped	Low	Moderate	Real-time BMS control
Spatially distributed	High	High	Design and analysis

In practice, many battery management systems use simplified models for real-time control, while more detailed models are employed for design and analysis.

Impact on Battery Aging

Temperature control isn’t just about efficiency—it directly influences battery aging. Elevated temperatures accelerate chemical degradation processes, leading to:

• Capacity fade
• Increased internal resistance

This brings us to the topic of State of Health (SoH) and battery degradation.

Related Topics

• Internal Resistance—the primary source of heat generation
• State of Health—how temperature affects battery aging
• Degradation Overview—mechanisms accelerated by high temperature
• Lithium Plating—a degradation mechanism affected by low temperature
• Battery Packs—thermal management at the pack level