What are intumescent thermoplastics, and how are they used in EVs?
Both “polymer” and “thermoplastic” are terms frequently used in materials science and engineering, especially in the context of plastics. All thermoplastics are polymers, but not all polymers are thermoplastics. The term “polymer” is a broad term that encompasses a wide variety of materials, both natural and synthetic. “Thermoplastic,” on the other hand, specifically refers to a subset of synthetic polymers that can be melted and reshaped multiple times without undergoing a significant chemical change.
A thermoplastic is a type of polymer that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. This process is reversible, which means you can reheat a thermoplastic material, reshape it, and then cool it back down to solidify multiple times.
Thermoplastics tend to have high molecular weights and lack cross-linking between polymer chains. This absence of cross-linking allows the chains to slide past one another when heated, making the material soft and moldable. Polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) are examples of thermoplastic materials.
Intumescent thermoplastics share many of the same characteristics as intumescent polymers, with the added benefit of being moldable. Intumescent thermoplastics are not a specific type of plastic but rather thermoplastics that have been formulated or combined with intumescent additives. These additives allow the thermoplastic to exhibit intumescent properties, such as expanding when exposed to heat. Intumescent thermoplastics offer several properties desirable in EV applications, including thermal management, fire safety, lightweighting, design flexibility, and compatibility with manufacturing.
LithiumPrevent, a unique thermoplastic safety material for BESS applications
LithiumPrevent is an intumescent thermoplastic composite. The thermoplastic polymer base is also a phase change material that melts and absorbs heat when exposed to heat, which is the fusion enthalpy. The composite includes a high loading of Pyrophobic’s proprietary intumescent additive that, during the phase change process, decomposes, causing the release of water vapor to dilute the flammable gases in and around battery packs.
Containment of Flames and Gases:
The dehydration reaction is endothermic, absorbing energy from the event, which lessens the severity. The intumescent reaction of the materials is also endothermic, and the associated volume expansion provides remarkable heat absorption.
- During thermal runaway, the cell electrolytes of Li-ion batteries decompose into flammable gases. Dilution of these flammable gases with non-flammable ones can significantly reduce the fire and/or explosion risk. In addition, the expansion effect of LithiumPrevent can fill any free space around the heat/fire source to cut off the oxygen supply, breaking the fire triangle so that the fire can be extinguished through a smothering effect. LithiumPrevent 200, for example, can expand 2-3x the original part size if the material is exposed to a thermal event for a long enough period of time.
- The intumescent reaction results in porous fire-resistant char, which is highly thermally insulative. The porous char can effectively prevent the heat generated in typical battery runaway events from transferring to the adjacent batteries; thus, it can prevent fire propagation in multiple-cell battery packs.
This multi-phase, fire-resistant process makes the material particularly effective at combating short and violent events such as thermal runaway. The material has an activation temperature of approximately 200°C, which aligns with typical thermal runaway temperatures of many cell types. Of importance, the material reacts instantaneously to combat thermal runaway, which is necessary given the rapid, violent nature of the event.
In addition to its remarkable fire-resistant properties, LithiumPrevent is electrically insulative, possessing a high dielectric strength of 9.5 kV/mm.
- This characteristic is particularly unique amongst intumescent materials as most are graphitic, causing them to be electrically conductive.
- This attribute makes LithiumPrevent particularly effective for insulating busbar components with the added benefit of enhanced fire safety performance.
- If the surface material needs to eliminate a heat or energy event (arcing for example), it may micro intumesce, leaving a reserve of insulative material underneath that continues to provide protection against short circuits.
To summarize, given its aforementioned characteristics, LithiumPrevent uniquely combines features of several passive fire safety materials into one platform, which allows engineers to simplify their design and unlock efficiencies:
- Manufacturing scalability of a thermoplastic
- Dielectric strength of traditional insulative materials
- Fire resistance of an inorganic material
Take the Next Step Towards Enhanced Fire Safety with Pyrophobic
Are you ready to enhance your fire safety measures with the leader in passive fire safety solutions? At Pyrophobic Systems, we specialize in bringing proprietary intumescent polymer technologies to various industries, including building construction, energy storage, and electric vehicles. Our cutting-edge products are designed to contain lithium-ion battery fires, prevent thermal runaway propagation, and mitigate external short circuits. With over 25 years of experience in the market, we’ve mastered the art of manufacturing our material in complex shapes at scale, unlocking new fire safety possibilities for OEMs.
Our team of experts is ready to help engineer your fire safety solution. We offer custom-designed systems that integrate seamlessly with your operations while adhering to the highest fire safety standards. From design suggestions, prototyping, and testing to full-scale production, we’re with you every step of the way. Don’t compromise on safety. Contact us today to learn more about our passive fire-barrier solutions and start your journey toward a safer future.