Is fast-charging the boost EVs need?

Fast-charging stations recharge a battery to 80 per cent capacity in half an hour.

  • FastCharger

Fast charging is expected to give electric vehicles a big boost, especially with the next generation of EVs, starting with Chevrolet’s Bolt — promising a range of up to 320 kilometres.

But will it?

Fast-charging stations recharge a battery to 80 per cent capacity in half an hour.

That performance, coupled with the increased range, would seem to propel EVs from their “city car” niche into the ranks of all-purpose vehicles, capable of long-distance trips.

With a 320-kilometre range, the 80 per cent recharge would provide another 256 kilometres of travel. Which means, at the highway speed limit, EV drivers would need to stop every two-and-a-half hours or so for a 30-minute “fill.”

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That doesn’t match the range and refill speed of gasoline-powered cars, but it would offer a manageable, albeit relaxed, pace for a road trip. And it seems a quicker, cheaper way to make EVs more useful than waiting for the next leap in battery development.

Tesla has acknowledged the significance of fast charging by installing an extensive, and expanding, network of stations, including a few in Canada. The Ontario government recently announced plans to support investments in the service.

The trouble is, fast charging is hard on batteries. It damages them, reducing their ability to store and discharge energy.


That’s why, when Chevrolet unveiled its Bolt EV, with a range of up to 320 kilometres, it included some disappointing news: A half-hour fast charge, it said, would add, at most, only 150 kilometres of travel. So, instead of stopping every two-and-a-half hours for a recharge, it’s every 90 minutes.

Basically, the more rapidly a battery is recharged, and the more often, the faster it degrades. A simple measure of charging speed is based on the battery’s C-rate — the rate at which it can discharge its energy. If the charging rate is the same as the discharge rate, it’s known as 1C. Double the discharge rate is 2C. Lithium-ion batteries prefer to be charged at just under 1C.

The C-rate has a big impact on battery life, says Cadex Electronics Inc., a battery-analysis company based in Richmond, B.C. After 500 charge and discharge cycles, a battery charged at 1C drops to 84 per cent of its original capacity. At 2C, it declines to 49 per cent. At 3C, it’s just 30 per cent.

Cold or hot temperatures hasten the decline.

Degradation can be slowed if the fast-charger can “talk” to the hundreds of cells in each battery pack, ensuring they’re all near their preferred temperature and recharged to the same extent.

But most fast-chargers assume every cell is in good condition. As batteries age, some cells decline faster than others. The battery-management system might not recognize the differences, making things worse.

And, as always with batteries, when you improve one aspect of performance, another suffers. Batteries with thin negative electrodes, or anodes, coated with small graphite particles, handle fast charging better than those with thicker electrodes and larger particles. But they hold much less energy.

Of course, if, as expected, EV drivers do most recharging on slower chargers, at home or work, declines wouldn’t be so precipitous.

Still, as the Bolt announcement shows, the impact of fast charging is another roadblock on EVs’ move to the mainstream.

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