Info Current and Verified · Updated 03/2026
Short Description
The Thermal Management Design stage is dedicated to designing systems that effectively control the temperature of the battery cells within the module during operation (charge, discharge, storage). Proper thermal management is critical for battery performance (cells operate best within a specific temperature window), safety (preventing overheating and thermal runaway), and lifespan (extreme temperatures accelerate degradation). It involves selecting appropriate thermal runaway (TR) propagation resistant materials, defining a cell venting strategy, developing a module cooling/heating concept, and designing efficient thermal interfaces.
Relevant Material Streams
4.1Module Cooling/Heating
- Determining the module's heat generation rate under various operating conditions (charge/discharge C-rates, ambient temperatures).
- Selecting a cooling/heating method:
- Air Cooling (Passive/Forced): Simple, but limited effectiveness for high-power modules.
- Liquid Cooling (Direct/Indirect): Using coolant (e.g., water-glycol) flowing through cold plates or channels in direct contact or close proximity to cells. Highly effective but more complex.
- Phase Change Materials (PCMs): Absorb latent heat during temperature excursions.
- Refrigerant Cooling (Direct Expansion - DX): Similar to air conditioning systems.
- Designing coolant flow paths, manifolds, and connections for liquid cooling systems.
- Sizing pumps, fans, radiators (if applicable).
- Considering heating requirements for cold-weather operation.
4.2Thermal Runaway & Cell Venting
Thermal runaway propagation and cell venting focus on preventing a failure in one battery cell from spreading to adjacent cells and on safely managing the gases, heat, and pressure released during a cell failure. This includes
- understanding how cells behave under abuse conditions
- designing venting and degassing pathways
- selecting suitable thermal protection materials, and
- validating the safety concept through testing and simulation.
Because thermal runaway is the most severe failure mode in lithium-ion batteries, engineers must combine testing, modelling, material selection, and safety design to reduce the risk of propagation and protect users, surrounding systems, and first responders.
A robust thermal runaway mitigation strategy combines testing, engineering judgement, and design integration. The goal is not only to meet standards, but to ensure that a cell failure does not escalate into a larger safety event.
1. Understanding thermal runaway behavior
Thermal runaway is an uncontrollable, self-sustaining exothermic reaction triggered by mechanical, electrical, or thermal abuse. As cell energy density increases, preventing propagation from one cell to neighboring cells becomes a central engineering challenge.
To understand failure behavior, engineers carry out abuse testing such as nail penetration, overcharge, impact, drop, vibration, and shock testing. These tests help determine whether a cell enters thermal runaway, how it vents, how much heat is released, and whether the failure remains contained or propagates further.
2. Calorimeter testing and cell characterization
Calorimeter testing is used to determine key failure characteristics of a cell, including:
- Venting temperature
- Thermal runaway onset temperature
- Heat release
- Gas volume
- Gas composition
This information is essential for parameterizing thermal runaway models at module and pack level and for developing propagation resistance strategies.
3. Venting and degassing strategy
When a cell vents, hot gases and particles must be directed safely away from sensitive components and, where relevant, away from passengers. The venting and exhaust design must also prevent dangerous pressure buildup inside the module or pack that could lead to deflagration or explosion.
A venting strategy typically considers pressure relief elements, gas flow paths, housing design, and the interaction between vent gases and surrounding materials.
4. Passive propagation resistance design
Passive propagation resistance aims to keep the heat transfer from a failing cell to neighboring cells below their trigger threshold. This is typically achieved by integrating thermal barrier materials between cells or around cell groups.
Material selection depends on several factors, including:
- Thermal conductivity
- Heat capacity
- Flame retardancy
- Mechanical stability
- Manufacturability
- Ease of integration into the module design
Common thermal barrier materials include aerogels, mica, ceramic papers, ceramic fibers, intumescent materials, and phase change materials.
5. Modelling and simulation
Computational fluid dynamics (CFD) and thermal modelling are used to simulate hot gas flow, conductive heat transfer, and the interaction of failure events with busbars, housing structures, and neighboring modules. These models support design decisions before full-scale testing and help identify weak points in the safety concept.
6. Safety assessment and engineering responsibility
EUCAR hazard levels are often used to define acceptable failure outcomes, ranging from Level 1 (no effect) to Level 7 (explosion). For many automotive and battery energy storage applications, a single-cell failure is typically expected to remain within Level 4 (venting).
At the same time, engineers should not rely on compliance alone. Safety must be treated as a continuous design responsibility throughout development. Cost, timeline, and resource constraints are important, but they should never outweigh user safety or system integrity. In practice, exceeding minimum requirements can reduce long-term risk, liability, and redesign effort.
Additional process considerations
Thermal runaway mitigation is not based on a single material or component, but on the interaction of multiple design features working together.
Thermal barrier materials such as aerogels, mica, ceramic papers, and ceramic fibers are widely used to slow heat transfer between cells. The right choice depends on the application, required performance, packaging constraints, and manufacturing approach.
Thermal runaway bonding materials can play an important role in keeping thermal barrier materials in place during a failure event while also contributing to propagation resistance.
Vent discs and breathable membranes are used to release pressure when internal gas generation occurs, while maintaining sealing performance during normal operation.
Intumescent materials expand when exposed to heat or flame, creating a temporary insulating barrier that can slow heat transfer and shield adjacent components.
The overall design is usually a compromise between cost, safety performance, integration complexity, manufacturability, and space constraints.
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4.3Cell Venting
- Understanding the venting mechanism of the selected cells (e.g., score lines on cylindrical cells, specific vent ports on prismatic cells, pouch seam bursting).
- Designing the module enclosure and internal layout to safely channel and direct hot gases and ejecta away from sensitive components and out of the module/pack in a controlled manner during a cell venting event.
- Ensuring vent paths are not obstructed and can handle the expected volume and pressure of vented gases.
- Considering the impact of vented materials on surrounding components.
This is one stage of the full battery module development workflow
See how Thermal Management fits into the end-to-end Battery Module Development journey.
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