Engineers have been searching for ways to mitigate the risk of fire with Li-ion batteries since the technology was first commercialized. Chemists are creating new cell formulations that are less prone to problems, electronics experts are designing fail-safe battery management systems, and mechanical engineers are building complex cooling and fire suppression systems.
A common rule of thumb for any new technology is that it typically needs to be significantly better than existing solutions to gain real traction. And that is true for the safety of large Li-ion-powered systems.
By and large, the technology is very safe, particularly when compared to the risk of fire with liquid or gas hydrocarbon fuels. However, advanced Li-ion technology is fairly new, so even rare problems make big headlines and have a real impact on consumer perception.
PyroPhobic Systems has been focused on the science of fire prevention for 15 years. The Ontario-based company’s claim to fame is its intumescent fire-resistant thermoplastic technology. The company designed a resin that can be added to just about any type of thermoplastic (though it primarily works with HDPE and PVC) and swells when exposed to heat, increasing in volume by about 20 times.
“We figured out how to injection-mold intumescent thermoplastics without having them react in the injection tool – which would be a really bad thing,” PyroPhobic’s head of international business development Timothy Riley told Charged. “And we can use standard injection molding equipment. The material can also be extruded into shapes or sheets and CNC machined into precise specifications.”
Today, PyroPhobic’s material is primarily used in the commercial construction industry for barrier applications. For example, if you have a fire-rated concrete slab that you want to pass a conduit through, you would use the intumescent plastic inside of the conduit. If a fire occurs, the material swells and fills the opening, preventing the transfer of heat or flame through the conduit. The company says that it produces millions of parts a year for the construction industry.
“About five years ago, we started to track lithium battery applications,” said Riley. “In that time we’ve developed a lot of data, and created a specific product for batteries.”
Snuffing out battery problems
Using the same intumescent fire-resistant thermoplastic technology, PyroPhobic says it can help ease safety concerns for large battery packs in applications like EVs, electrified marine vessels and stationary energy storage systems.
Battery fires are classified as Class D fires because they involve combustible metal, and can go from ambient temperature to about 1,000° C in a matter of seconds. In order to stop a chain reaction that spreads to every cell in a pack, you need to be able to react very quickly to contain a problem.
To target the growing industry for advanced batteries, PyroPhobic developed a new product line that it calls Lithium Prevent – described as an airbag for batteries. “If you have a lithium cell fire, the material absorbs the heat and expands to provide good separation between the cells so you don’t have a cascading event,” explained Riley. “It’s considered to be a phase-change material. If it were sitting on your desk it would just look like regular plastic. But when a fire happens it causes an endothermic reaction in the material, so it absorbs the heat, which causes it to change into a high-volume char-like ash. When the pack is properly designed with Lithium Prevent, the problem cell is entombed in the material and separated from an oxygen-rich environment. It breaks the fire triangle and also can control the flow of vented electrolyte from the damaged battery to prevent it from pouring over into adjacent cells.”
“The temperature that causes Li-ion runaway is usually about 200 to 225° C,” Riley continued. “After that the cells can get up to 1,000° C pretty quickly. We’ve done tests that show our material can separate the energy so that an adjacent cell, right next to the runaway cell, is about 110 to 120°. That’s half the temperature required for runaway. The thermal separation between cells is excellent. I’ve seen this achieved with as little as 2.5 mm of our material between large prismatic cells. In fact, NASA did some tests with our material and published a public report which confirms the prevention of thermal runaway propagation. We’ve also done a lot of other studies with clients, but that data is private for now.”
PyroPhobic’s magical material is the result of a range of proprietary methods and materials that are included in its resin. The company formulates and pre-mixes it into the plastic. So when you order a batch of its special blend, you receive a plastic-resin mix that is ready to go into the injection molding machine. The company also has the capacity to produce and deliver molded parts. “We make millions of parts a year for the commercial construction industry, and we can do the same for the battery industry,” said Riley. “Our typical design process is to first find out what the client wishes to accomplish, and review their specifications and current designs they are using. Then we modify the design to include the Lithium Prevent as a component in their system, and work with them to test and evaluate the system to achieve the required goals.”
Lithium Prevent products have about the same mechanical properties as the host thermoplastic, for example HDPE or PVC. PyroPhobic says the material can also be used to simply replace other parts within a pack, with the added benefit of enhanced fire suppression capabilities beyond the typical plastics.
The market for safety
The company’s pitch to battery pack designers is simple: This is the most effective fire protection system you can build. “There are no other solutions in the marketplace that can react this quickly,” said Riley. “There are others that are designed for petrochemical fires or commercial construction applications, but those aren’t nearly as severe as a lithium battery fire. If you look at a time/temperature curve, you see that our material reacts in seconds and begins to cool the pack within that short period of time.”
NASA prototype testing – nine 18650 Li-ion cells in a pack, center cell thermal event did not cascade to adjacent cells
Having a prevention system that can stop a problem in its tracks is valuable in many applications, from cars to boats to buildings. However, one could argue that in applications with a large number of people in a dense area, like battery packs aboard ships at sea or in basements of buildings, these advanced fire suppression systems are even more critical.
“If you have a Li-ion energy storage system in a hospital, or on a cruise ship with thousands of people onboard, you’d better have a robust fire protection system,” said Riley. “And even with an EV in the garage, I think you would sleep better with the type of protection that Lithium Prevent can provide. There are some active systems that manufacturers are using in some applications, like using a water mist, halon, or CO2 systems. And they are all effective at suppressing fires, however our products can greatly reduce the amount of damage that is done and stop a thermal runaway before active systems need to be discharged. Many people in the fire science industry are saying that it will be best to have multiple lines of defense wherever possible – active systems combined with passive suppression products like Lithium Prevent. However, in a lot of consumer electronics and transportation cases like e-scooters or bikes, using our product may be the only feasible solution.”
There is also a range of less elegant fire safety solutions. For example, in some high-risk applications like airplanes, engineers have basically sealed the battery pack in a stainless steel box that’s inside of another stainless steel box. “The weight of that is considerable,” said Riley. “Also, with that kind of solution, when one cell runs away, they’re all going to run away, so you’re going to have a much larger event with greater risk. With our materials you can design it to stop the fire at a single cell, so it doesn’t cascade through the entire pack. So we offer a considerable weight advantage and a much higher degree of responsiveness.”
There are currently no regulations for fire protection in passenger vehicle battery packs, but Riley believes it’s just a matter of time. For marine and commercial building batteries, regulators appear to be acting more quickly. Also, when you’re dealing with multi-million-dollar pieces of equipment like ships or large commercial buildings, the insurance companies get involved, and that helps to drive things more quickly. “There are many code committees that are meeting right now to develop those industry specs for fire protection,” said Riley. “Then the standards will be reviewed and eventually adopted by code authorities around the world. There are different philosophies about what people think is necessary in regulations, so the battery industry has to work its way through that.”
PyroPhobic says that it’s currently working on development projects with several companies “that we would know,” but it can’t disclose them at this time. With the market for large battery packs continuing to grow significantly, the company is optimistic about the advantages its unique technology offers.
“The beauty of our product is that you can injection-mold it with a high degree of specificity,” said Riley. “With that precision you can design a system to control events at a single point and stop major fires before they happen.”