Thermal runaway in batteries – requirements for insulation materials

The safety of lithium-ion batteries is a central issue in electromobility, stationary energy storage, and power electronics. A particularly critical scenario is thermal runaway in batteries – an uncontrolled chain reaction within a cell that can lead to extreme temperatures, gas emissions, and, in the worst case, fires.

To minimize this risk, insulation materials for batteries play a crucial role. They help to prevent or at least significantly delay the spread of a thermal runaway.

What is thermal runaway in batteries?

The term thermal runaway in batteries describes a condition in which a battery cell continues to heat up due to internal faults. Triggers can include, among others:

• mechanical damage
• Overcharging or deep discharging
• internal short circuits
• thermal overload

Once a critical temperature is exceeded, exothermic reactions begin. These generate additional heat, which intensifies the process itself – a classic “runaway” effect.

The greatest danger is that thermal runaway in batteries spreads from a single cell to neighboring cells (thermal propagation).

Challenges for battery design

Modern battery systems consist of densely packed cells with high energy density. This significantly increases the demands on safety and material selection.

Key challenges include:

• Prevention of cell-to-cell spread
• Thermal management at high power densities
• Electrical insulation under simultaneous high heat load
• Mechanical stability under extreme conditions

This is where specialized insulation materials for batteries are used, which must fulfill several functions simultaneously.

Requirements for insulation materials for batteries

Insulation materials for batteries must perform significantly better than conventional electrical insulators. They are an integral part of the safety concept of modern battery systems.

1. High temperature resistance

In the event of a thermal runaway, temperatures exceeding 600–1000 °C can occur. Materials must:

• withstand extreme temperatures in the short term
• preserve their structural integrity
• do not represent an additional fire load

2. Low thermal conductivity (targeted barrier effect)

To slow the propagation of thermal runaway in batteries, low thermal conductivity is crucial. The goal is to minimize heat transfer to neighboring cells.

3. Electric Isolation

In addition to thermal protection, insulation materials for batteries must also ensure reliable electrical insulation, even under extreme conditions.

4. Flame retardancy and fire protection

Materials should:

• be flame-resistant
• do not release toxic gases
• Ideally, they should be self-extinguishing.

5. Mechanical stability

During a thermal runaway, pressure and mechanical stresses occur. Materials must:

• retain their shape
• show no cracks or delamination
• act as a physical barrier

Typical material solutions

Different material classes are used to meet these requirements, often in combination:

• High-temperature resistant films (e.g. polyimide)
• Mica-based insulation materials
• Ceramic-filled composites
• Special foams with insulating properties
• Multilayer systems (multilayer solutions)

These materials are used as cell separators, intermediate layers, housing insulation, or protective barriers.

Role of insulation materials in thermal management

In addition to pure insulation, materials are increasingly taking on functions in thermal management. While some materials act as a barrier, others are specifically used to dissipate heat.

The interplay of:

• thermal insulation
• targeted heat conduction
• structural protection

is crucial for the safety and performance of modern battery systems.

Significance for electromobility and energy storage

With the growth of electromobility and stationary energy storage, the importance of safe battery systems is increasing. Regulations and standards are becoming increasingly stringent, particularly with regard to:

• Thermal Propagation Tests
• fire protection requirements
• Safety certifications

This brings insulation materials for batteries even more into focus in development and design.

Perspective of Dr. Dietrich Müller GmbH

Dr. Dietrich Müller GmbH has extensive experience in the processing and application of technical insulation materials, films, laminates and composite materials.

In the context of thermal runaway in batteries, tailored material solutions play a crucial role in meeting safety requirements while enabling high-performance battery systems.

By combining materials expertise and application-specific manufacturing, solutions can be developed that:

• Optimize thermal barriers
• Ensure electrical safety
• Increase mechanical stability

Conclusion

Thermal runaway in batteries represents one of the biggest challenges for modern energy storage systems. Without appropriate protective measures, it can lead to critical safety risks.

Insulation materials for batteries are therefore a key component of any safety concept. They prevent heat dissipation, ensure electrical insulation, and contribute significantly to the stability of the system.

With increasing energy density and rising safety requirements, the importance of these materials will continue to grow.