A Partner for the Automotive Industry:
How WACKER and CFP Composites Are Revolutionizing Fire Protection for Battery Packs

Briehn: Here we draw a distinction between protection that provides thermal insulation for individual battery cells, for battery modules, which contain multiple cells, and for the entire battery pack, which in turn contains the modules. Given the component geometry in standard battery designs, manufacturers have preferred to use heat-resistant materials in the form of thin sheets or mats, that, while thin, can meet the temperature requirements. Mica sheets are one example of an established system used widely for thermal and electrical insulation, both in various technical applications, as well as in everyday appliances like hair dryers and microwaves. While mica sheets are cost-effective and lightweight, their brittleness greatly limits their use in three-dimensional molding processes. Brittleness is especially a problem when batteries undergo runaway, exposing the brittle mica sheet to a powerful jet of abrasive particles.

Price: Demand and interest are growing for high-performance material solutions that are lightweight and thin enough for use in the tight spaces found in battery packs. There aren’t very many materials that are at all suitable in the temperature range we’re talking about. Our newly developed composite material has come at the right time, in other words. The number of inquiries we’ve received from battery manufacturers and the automotive industry has grown for a good two-and-a-half years now, and there are two reasons for that: increasing energy density is making thermal runaway in lithium-ion batteries more and more relevant, and battery safety is considered one of the most important development issues for automakers and their suppliers right now.

Price: One thing you need to know is that the battery pack is the heaviest component of the car. The last thing manufacturers want is to add even more weight for fire protection. More weight ultimately cuts into range. Plus, a few millimeters between individual battery components are all we have to work with for thermal insulation. But despite those design constraints, we’ve managed to develop an incredibly powerful material: our new FR.10 composite is made of carbon fibers and silicone resins. It can be produced in a thickness of down to 1 mm, and it’s very lightweight at just 1.5 kg/m² for the thinnest product. Another advantage is that our product doesn’t get brittle and doesn’t expand when exposed to heat. We don’t see any structural change across a very broad range of temperatures. Our production process also opens the door to making more than just flat plates – we can also create 3D geometries, which has many advantages in batteries. Our internal tests clearly demonstrated the fire resistance of the laminates: over a period of 7 hours, a 1,500 °C burner flame could not burn through a 2-mm-thick FR.10 sheet.

Briehn: We were especially pleased that the composite material performed very well in a challenging fire safety test conducted by UL Solutions – the world’s leading independent testing laboratory. At the company’s US electromobility lab in Illinois, scientists subjected our material to the UL2596 test, a method developed in-house for testing battery safety. This involved exposing the 2-mm-thick composite to the hot particle stream produced by thermal runaway. Our material withstood those conditions, with the laminate remaining intact.

Price: We assume that the carbon fibers dissipate the heat to the sides, preventing it from quickly burning through the laminate. We’re also seeing evidence that the composite reflects the heat, at least in part.

Briehn: Our composite makes clever use of what carbon fibers and silicone resins do naturally: carbon fibers are very lightweight and provide excellent mechanical strength. Because they adhere well to the fibers, silicone resins produce a strong bond. Also, the resins we use have a high silicon dioxide content with very little fire load. They ceramify at high temperatures and when exposed to fire which additionally reinforces the fire protective properties of the material. Comparable composite materials containing organic binders can’t do that.