> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ionworks.com/llms.txt
> Use this file to discover all available pages before exploring further.

# 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](/guide/batteries-101/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.

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

## 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)](/guide/batteries-101/state-of-health) and battery degradation.

## Related Topics

* [Internal Resistance](/guide/batteries-101/internal-resistance)—the primary source of heat generation
* [State of Health](/guide/batteries-101/state-of-health)—how temperature affects battery aging
* [Degradation Overview](/guide/batteries-101/degradation)—mechanisms accelerated by high temperature
* [Lithium Plating](/guide/batteries-101/lithium-plating)—a degradation mechanism affected by low temperature
* [Battery Packs](/guide/batteries-101/battery-packs)—thermal management at the pack level