Mikael Cugnet of the French Atomic Energy Commission said current estimates of an eight-year lithium-ion life have been based on accelerated tests that don’t necessarily provide an accurate picture of how long the batteries will really last in electric cars and hybrids. He believes that if managed properly, EV battery packs could operate reliably for 15 years, and possibly as long as 20 years.
”The accelerated testing that’s performed in labs is not exactly representative of what will happen during real road use,” Cugnet told Design News. “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.”
Cugnet contends that accelerated testing often takes place at temperatures as high as 40C (104F), which is higher than the mean temperature at most locations around the world. “That’s the way we do it because there’s not enough time to do a real field test,” he told us. “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," Cugnet said. But he argues that packs made with those materials tend to use less consistent manufacturing processes.
”Lithium-ion batteries should perform better because they have fewer impurities,” he said. “So the degradation will not be as fast.” He added that electronic battery management is simpler and more reliable if material quality is more consistent from cell to cell.
Other factors also play into the life expectancy of lithium-ion batteries. The first of those factors -- temperature -- is the most important. Batteries that are exposed to high mean temperatures tend to degrade significantly faster than those in colder climates. “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,” Cugnet told us. “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.”
The wrong charging techniques can also shorten a battery’s life. Lithium-ion battery packs need to stay as close as possible to a 50 percent charge, he said, usually going no higher than 80 percent and no lower than 20 percent. Moreover, electric car owners should refrain from doing too many “fast charges,” in which an EV battery can be recharged in under an hour. ”At high power, there is deformation of the material on a particle scale,” Cugnet said. “If you’re really in a hurry, it’s OK to do it a few times,” he said. “But most of the time, you should charge your car overnight.”
If managed properly, and if the car’s manufacturer incorporates a good, active cooling system, lithium-ion EV batteries should operate much more than eight years before finally losing more than 20 percent of their original power. The truth won’t be known, however, until lithium cells have been on the road for a couple decades, Cugnet said.
“The extrapolation we’ve made from our own tests shows that lithium-ion packs can last 15 or even 20 years,” he said. “It mostly depends on how you charge it and what temperature it operates at.”