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Green Wheels

Battery doubts hamper EV sales

Published April 26, 2013

How long will an Electric Vehicle (EV) battery last?

Mikhael Cugnet, of France’s Atomic Energy Commission, has an answer: It depends, he says, “on many factors.”

Cugnet’s analysis, presented at a recent meeting of the American Chemical Society, seems both good and bad news for the EV industry.

Batteries are the big stumbling block to mass acceptance of EVs. At $10,000 or more apiece, they’re expensive. They provide limited range and slow refuelling.

Most important for Cugnet’s work, potential buyers also fear having to replace this expensive component after just a few years.

Cugnet defines battery death as the loss of 20 per cent of capacity, at which time — and this is considered good news — it can be used as a stationary backup power source, or recycled.

He says his tests — extrapolations of 8 kilometres of real-world driving — show a battery pack, properly cared for, could operate for 15 years; possibly 20.

However, abuse it and it might have too little energy-storage capacity to run a car after just five years.

What are those “factors” it depends on?

Lithium-ion batteries dislike hot weather. Although they always deteriorate with use, capacity decreases when the thermometer climbs above 30C, and the damage is permanent if the heat persists.

“Batteries . . . exposed to high mean temperatures tend to degrade significantly faster than those in colder climates,” Cugnet told the DesignNews website.

“If you’re living in Abu Dhabi, the battery life will be much shorter than if you’re in a place that has colder winters. And if you have your car parked under the sun in Atlanta or Louisiana (or Toronto) three months of every year, the battery won’t last 20 years.”

Cugnet also concluded EV batteries are happiest when charged to only 50 per cent of capacity. They should rarely go above 80 per cent or below 20. Which means if they’re to reach a ripe old age, drivers must be willing to accept greatly reduced range.

How they’re recharged counts, too, Cugnet says. Batteries deteriorate faster if they’re refilled on DC fast chargers that promise 80 per cent of capacity in 30 minutes or less.

“A fast charging procedure involves high currents with strong mechanical stress on the electrode active materials,” he explained by email.

“If you’re really in a hurry, it’s okay to do it a few times,” he told DesignNews. “But most of the time, you should charge your car overnight.”

On the positive side, he says lithium-ion batteries should last longer than official ratings, which are based on laboratory tests usually conducted in warm conditions and at an unrealistic, accelerated pace.

All this, he concludes, is “good news when you consider that some estimates put the average life expectancy of a new car at about eight years.”

Or not so good, given that North Americans typically keep their cars for 12 to 15 years.

Cugnet’s results suggest there’s potential for long battery life, but at the cost of reducing already limited usefulness.

Some manufacturers are attacking this problem by offering leased batteries: Smart in the U.S., Nissan in Britain, and Renault throughout Europe.

As well, Nissan promises to replace a purchased Leaf battery if it loses more than 30 per cent of its capacity within five years — with another pack that has at least 30 per cent remaining. Not great, but at least it’s a start.

Cugnet’s conclusions have limitations. Most important, he tested just one of several forms of lithium-ion technology.

“Therefore the results we obtained with the technology cannot be applicable to other technologies” and there’s “no consensus” among manufacturers on the one to be used.

“The way they decide to charge the battery pack is also very often confidential,” he adds.

As well, he says, we won’t know for 20 years whether batteries will, in fact, last that long.

Which means, in a nutshell, that electric vehicles will either be much improved by then or parked beside Stanley Steamers in car museums.

wheels@thestar.ca

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