10-Minute Fast Charging Could Be Just Three Years from Production for Polestar

Swedish EV specialist Polestar partnered with fast-charging battery pioneer StoreDot to charge a Polestar 5 prototype from a 10 percent state of charge to 80 percent in just 10 minutes.

They did this with the battery installed in a drivable verification prototype rather than a battery test lab stand and saw a consistent charge rate that started at 310 kilowatts and peaked at 370 kW. For comparison, the Kia EV9 I recently charged on an Electrify America 350-kW charging station started at 170 kW and peaked at 209 kW.

The Polestar test vehicle, in contrast, blasted power into the battery at a consistently high level without overheating the cells. “We got there and got it within the margin,” crowed Polestar Battery System Chief Engineer Jens Groot after the test. “We got to 82 percent [state of charge] and we had plenty of margin in cell voltage and in cell temperature.”

Polestar did this by using StoreDot’s XFC silicon-dominant battery cells in a 77-kWh battery pack. This technology could support a 100-kWh pack, in which case the demonstrated charge rate would supply 200 miles of driving range to the Polestar 5 in that 10-minute charging time, according to the company. This capability could be in customers’ cars within three years, Groot stated. “We typically have a development cycle of two to three years, so I'd say we could put this into production within that time period.”

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StoreDot’s XFC technology uses silicon-dominant battery cells that have an energy density equivalent to the latest Nickel-Manganese-Cobalt (NMC) lithium-ion cells. The key to the test’s success was incorporating improved cooling capacity into the battery modules. This was done without increasing the modules’ weight and while retaining serviceability and recyclability of the battery pack, Polestar said.

The company acknowledges that fast-charging batteries is common but points out that such tests are typically done under lab conditions rather than this demonstration using a complete battery pack that is installed in a car. “This is proof that we can now charge at these speeds in a standard car,” Groot said.

Polestar's prototype battery module employing StoreDot cell technology and improved cooling. POLESTAR

“We tried now to prove that we can do this just by better integration and better cooling inside the battery pack, focusing on the battery pack with a good cooling interface,” he said. “We didn't add anything new outside the battery pack. It still had the original cooling pump and fan.”

Another characteristic of the StoreDot technology is the ability to plow through the charging speed limit that strikes other lithium batteries when they exceed an 80 percent state of charge. Normally, EV battery charging rates plunge when they reach 80 percent, making it impractical to use the last 20 percent of capacity when fast charging.

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Polestar engineers did the charging test with the battery installed in this real car rather than on a test bench in a lab. POLESTAR

“With this battery, it almost doesn't matter when you stop to charge your car,” said Groot. “In this sense, the experience is more like filling up your car at the petrol station. Because of that, this test really feels like a major step towards alleviating both range and charging concerns in customers,” he said. “It definitely has the potential to be transformative.”

The hardest part of the test? “It wasn’t easy to find a cable that can handle this current, I’ll tell you that,” Groot noted.