Tech Talk: Fast charging tech is moving up a gear

Emerging technologies are often flawed in a way that makes it impossible to imagine them improving beyond that stage. Such is the case with BEVs and the still-thorny issue of how long it takes to charge one on longer journeys.

Leaving charger availability aside, 45 minutes to bring a 400V car from 10 or 20 percent charge back up to 80 percent and, say, 30 minutes to do the same for an 800V car is still unacceptable to many drivers.

In 2021, we reported on how StoreDot had developed a silicon-dominant lithium-ion battery anode technology, which it called XFC (‘extreme fast charge’). The technology was still at the laboratory stage at the time, but the firm expected it would cut charge times by 50 percent with no extra cost.

Recently, it was proven that the technology works not only at the laboratory level but also in a full-size battery pack fitted in a current, driveable car. The test was carried out by StoreDot’s technology partner, Polestar, using a prototype Polestar 5. Polestar’s engineers set up a test to charge the battery from 10 percent state of charge (SOC) to 80 percent within 10 minutes, but the technology actually exceeded expectations by a slight margin, reaching 82 percent in the allotted time.

A 77kWh battery pack was specially commissioned to fit the car, and Polestar said it has the potential for capacity to be tweaked to 100kWh. As it stands, the 10-minute charge time would be equivalent to a range increase of 200 miles.

The reality of operating EVs on longer trips, though, and what numbers like these add up to in real-world convenience terms, often won’t tell the whole story. One key point to emerge from the test relates to a marked improvement in the charge curve. Normally, fast charging rates can drop significantly as the battery’s SOC increases during charging, so by the time a battery reaches 80 percent, it may be charging at a much slower rate than it was at 10 percent or 20 percent.

In this test, the opposite happened. Polestar engineers saw the charge rate increase from 310kW at 10 percent SOC to more than 370kW at 80 percent. This makes it far more worthwhile to grab a ‘splash and dash’ charge while stopping on a trip for some other reason when the battery isn’t that depleted. A driver plugging in at 50 percent SOC could be away again at 80 percent in just five minutes.

Those 10- and five-minute timescales are much closer to that of refuelling an ICE car with petrol or diesel, especially given that there’s no need to stand there holding the pump, and then maybe queuing to pay.

Apart from the obvious convenience to the driver, ultrafast charge speeds will also free up chargers more quickly. Polestar believes this to be a world-first. It said nothing was added outside the battery pack, and the 5 still had its standard cooling pump and fan. It also said the battery technology could appear in its production cars in the next two to three years.