Electric vehicles (EVs) continue to gain in global popularity even though, says John Williams, the VP of Technical Services at Aspen Aerogels, "Inside each of these vehicles are hundreds, if not thousands of lithium ion cells — one of the densest ways that we know to store electrical energy in a battery, but they come with tradeoffs."
One of those tradeoffs is that every now and again, a lithium ion cell catches fire and, if allowed to burn, could ignites those around it.
That's why the Department of Energy recently provided Aspen Aerogels with a $670.6 million loan to build a new factory in Georgia. The federal government is hoping the technology that the company is developing will help contain EV fires.
An ethereal, almost magical, material
When a battery in an EV gets too hot, it can lead to something called thermal runaway. "In the case of some kind of defect, under the right kinds of circumstances, the temperature goes up and up and up until eventually the battery catches on fire," says Williams.
A lithium ion battery in a car is way less likely to ignite than an internal combustion engine, says Williams, but it burns hotter and is harder to put out. "So the goal for a vehicle designer is to give a passenger enough time to exit the vehicle, get off of the road, get clear of the vehicle if the worst should come to happen," he explains.
This is where an aerogel can help. Williams calls it the world's best thermal insulation. It's a substance akin to a very light, yet firm piece of gelatin. It's not new but the technology continues to improve.
"This is a very ethereal material," says Aspen Aerogels Chief Technology Officer George Gould. "It's very delicate. They are a little bit translucent, you might say. There is a smoky appearance to the material."
At the company's research lab in Northborough, Mass., some 35 miles west of Boston, Gould holds up a chunk of aerogel roughly the shape of a hockey puck. "That piece is probably 99% air," says Gould. The rest is an extremely porous material made mostly of silicon and oxygen.
Irene Melnikova, a chemist at the company, walks through the process of making the material. She takes two liquids (reprocessed silicone materials and an alcohol), combines them, and then pours the mixture onto a patch of fibrous material that absorbs the liquid. Within a minute, it solidifies.
"It's amazing," she says. "You have a fluid and it's liquid. And after that, you have a solid." This solid has a rather useful property: "It can survive at high temperature and protect materials from heat," says Melnikova.
"And that combination together makes a flexible insulation material," says Gould, "which is extremely good at preventing heat from transferring from one side to another of a layer of insulation."
Engineer Matt Gwin demonstrates this high temperature resilience. In the lab, a piece of aerogel material a couple millimeters thick is held taut inside a metal frame. This is what's placed between the lithium ion cells of EV batteries currently inside certain vehicles made by GM, Toyota, Honda, and others.
Gwin turns a couple knobs to get the propane flowing and ignites it. A jet of fire some 2000 degrees Fahrenheit erupts outwards.
No flame comes out the other side. There's no evidence that anything is burning. "The secret of our material is that it's passing the energy on very slowly," says Gould.
After a minute or two, Gwin kills the flame and Gould touches the aerogel material immediately. It's completely intact and only feels warm—as if it had not just been scalded. "It's like magic," Gould says with a chuckle.
The limits of the technology
An aerogel does not prevent a fire in the first place, but if a lithium ion cell wrapped with this material ignites, the aerogel keeps the fire from spreading too far. "Think of it as a firewall," says Williams.
Aspen Aerogels' products go beyond EVs. Gould says by varying how the aerogel is prepared, the material can be used for insulating the pipes associated with liquified natural gas transport, refineries, and subsea oil exploration and extraction. "We have products in outer space and particle physics detectors," says Gould. "Separating hot and cold in the most challenging environments is our strength."
Amar Pradhan is with Mobility Impact Partners, a venture capital firm that invests in emerging transportation technologies. He says aerogels are just one kind of safety measure under development.
"There's different ways to stop the fire depending on the timeline of battery fires," says Pradhan. "You can solve it before it happens, you can solve it while it happens, you can solve it after it's already on fire."
A range of approaches is necessary, especially given the life cycle of a lithium ion cell inside an EV and afterwards in a landfill. "You could prevent the problem years before by picking a better chemistry," says Pradhan. "You could prevent it hours before by predicting it using data."
Ultimately, he says it will take a variety of interventions to ensure that EVs are as powerful and safe as possible.
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