Many of the concerns and challenges around EVs come down to the battery: how expensive it is to make them, the environmental impacts of mining critical raw materials for them, how well they hold a charge––and crucially, how much they degrade over time.
That last consideration is the subject of a new paper published in Nature this month by researchers at Stanford University’s SLAC National Accelerator Laboratory.
The report, titled “Dynamic cycling enhances battery lifetime,” reaches a conclusion that was surprising to its authors: Contrary to popular belief, the ways that batteries discharge power in real-world driving conditions can actually improve the lifetime of lithium-ion EV batteries by as much as 38%.
“We cycled batteries in ways that are representative of real EV driving, and tried to compare that to how batteries are regularly cycled—meaning, charged and discharged—traditionally in the lab,” Alexis Geslin, a lead co-author of the paper and a PhD candidate at Stanford, told Tech Brew. “Usually in the lab, they are charged and discharged with a constant current, just because it’s easy to implement. But in real life, you don’t drive your vehicle at a constant pace.”
The findings, he said, have implications for the way researchers conduct experiments on battery cells––and for the ways that battery management systems are designed. And it’s good news for EV buyers because it suggests that their vehicles’ batteries might hold up longer than they expected.
“Instead of having to change your battery every 10 years,” Geslin said, “you may just be able to keep your battery for 15 years.”
Let’s research: To conduct the study, researchers cycled 92 commercial EV lithium-ion cells over the course of two years. They tested four different “discharge profiles.”
The research also involved using machine learning to help unravel some of the complexities of real-world driving conditions, Geslin said.
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In the report, the authors explained that lithium-ion batteries’ performance depends on how, exactly, the batteries are used. “Understanding how degradation occurs across realistic use cases is essential to accelerate material design and improve battery management systems,” they wrote.
Historically, researchers have conducted testing on lithium-ion batteries in labs using constant-current discharge profiles. In real life, however, drivers are often stopping and starting––meaning, the battery is discharging in more dynamic ways.
“This work illustrates the importance of testing batteries under realistic conditions of use and challenges the broadly adopted convention of constant current discharge in the laboratory,” the researchers concluded. “Evaluating batteries with realistic cycling profiles is necessary to properly understand aging mechanisms at the chemistry, material, and cell levels.”
Geslin said that while the findings may not have direct bearing on the costs of manufacturing batteries, they suggest that EV batteries may last longer than previously thought.
The findings could help alleviate concerns about how battery degradation influences EVs’ resale value. Reuters recently reported that there are growing efforts in the EV battery sector to validate battery performance and health in used EVs, prices of which also influence the new-vehicle market.
Battery degradation is a common concern for prospective EV buyers. But there may be growing awareness that EV batteries hold up pretty well.
“We have a lot of good science that explains how batteries age and what accelerates their degradation,” Liz Najman, director of market insights for EV startup Recurrent, told CleanTechnica. “That data comes from laboratory testing on battery cells, so the way it translates to EV battery packs…is still a bit of an open question. But from everything we’re seeing, EV packs are holding up a lot better than these test cells.”