A Good Thermal Active Management System, Like The One Found In The Chevrolet Volt, Should Extend Useful Life Past 8 Years Of Service

Most end of life calculations for electric vehicles are based on an assumption of achieving 8 years of useful operation before falling below 80% of original capacity.  However, a battery expert has told the American Chemical Society in a speech last week that we can reasonably expect a much longer life.

How much longer?

French Battery Expert Expects Longer Than Expected Results From Today's Lithium-Ion Battery Technology (Focus Electric Shown)

How does 15 or even 20 years sound?

That kind of longevity would certainly tip the cost of ownership scales in the favor of plug-in cars over their contemporary gas siblings.

And that extended longevity expectation is just what Mikael Cugnet, of the French Atomic Energy Commission, has said could be a reality.

He noted that current benchmarks are a product of accelerated tests that may not be providing an accurate preview of how long the batteries could actually last. Over time, Mr. Cugnet believes that if the battery packs inside EVs are maintained properly, plug-in vehicles could "reliably" last 15, maybe 20 years.

In a interview with Design News, Cugnet said:

”The accelerated testing that’s performed in labs is not exactly representative of what will happen during real road use.  Accelerated testing is usually performed at much higher temperatures and in a much shorter time period than you’d see in real-life use. That’s why people are getting such low values.”

Last Year In Arizona We Learned First Hand What Happens To Lithium Batteries Operating Well Outside The Norms (picture via MyNissanLeaf)

The expert says that these accelerated battery tests take place at temperatures as high as 104F, and that is a much greater average temperature than can be expected in the real world, at least in the majority of situations.

“That’s the way we do it because there’s not enough time to do a real field test,” he said to Design News, “But it’s not accurate. It doesn't represent what the battery will really see in the field. 

Up to now, researchers have also based their estimates for lithium batteries on prior experience with lead-acid and nickel-metal hydride...Lithium-ion batteries should perform better because they have fewer impurities, so the degradation will not be as fast.”

Factors that affect battery life according to Mr. Cugnet are:

  • temperature - the higher the average temperature a battery is subjected to, will translate into less life.   The expert explains, “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 three months of every year, the battery won’t last 20 years.”
  • charging techniques - too many "fast charges" can damage the ability of a lithium battery to hold a charge over time
  • state of charge - although wildly impractical for obvious reasons, lithium packs that are only charged to 50% will last the longest.  Ideally, a charge should stay between 20% and 80% of total pack capacity
  • management system - an on board active cooling system, whether that be air or liquid, is a big assist to battery life.
The researcher from the French Atomic Energy Commission concludes that by optimizing the above factors, electric vehicle owners should achieve a lot more than eight years of use before losing more than 20% of the battery's original capacity.

Design News

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