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Graphic representing batteries, data, and an electric vehicle. Credit: Cube3D
A new study from the SLAC-Stanford Battery Center indicates that electric vehicle (EV) batteries may last significantly longer in real-world conditions than previously anticipated.
By testing batteries with dynamic discharge profiles that mimic actual driving scenarios, researchers found that these conditions could extend battery life, debunking some long-standing assumptions about EV battery degradation.
EV Battery Longevity
Electric vehicle (EV) batteries used under typical driving conditions — such as navigating heavy traffic, taking long highway trips, making short city drives, and spending long periods parked — may last about 30% longer than previously estimated. This finding comes from a new study conducted by researchers at the SLAC-Stanford Battery Center, a collaboration between Stanford University’s Precourt Institute for Energy and SLAC National Accelerator Laboratory. The results suggest that EV owners might not need to replace their costly battery packs or purchase new vehicles as soon as they thought.
Flaws in Standard Battery Testing
Traditionally, battery scientists and engineers have tested new battery designs in laboratories by cycling them through repeated charge and discharge processes at a constant rate. This approach allows researchers to quickly assess battery life and other performance characteristics. However, these tests may not accurately reflect real-world driving conditions, leading to overly conservative lifespan estimates.
This is not a good way to predict the life expectancy of EV batteries, especially for people who own EVs for everyday commuting, according to the study published on December 9 in Nature Energy. While battery prices have plummeted about 90% over the past 15 years, batteries still account for almost a third of the price of a new EV. So, current and future EV commuters may be happy to
Real-World Benefits for EV Owners
“We’ve not been testing EV batteries the right way;’ said Simona Onori, senior author and an associate professor of energy science and engineering in the Stanford Doerr School of Sustainability. “To our surprise, real driving with frequent acceleration, braking that charges the batteries a bit, stopping to pop into a store, and letting the batteries rest for hours at a time, helps batteries last longer than we had thought based on industry-standard lab tests.”
From left, Simona Onori, Devi Ganapathi, Alexis Geslin, Le Xu, and William Chueh in the SLAC-Stanford Battery Center. Credit: Jim Gensheimer / SLAC National Accelerator Laboratory
A Pleasant Surprise
The researchers designed four types of EV discharge profiles, from the standard constant discharge to dynamic discharging based on real driving data. The research team tested 92 commercial lithium ion batteries for more than two years across the discharge profiles. In the end, the more realistically the profiles reflected actual driving behavior, the higher EV life expectancy climbed.
Several factors contribute to the unexpected longevity, the study finds. A machine learning algorithm trained on all the data the team collected helped tease out the impacts of dynamic discharge profiles on battery degradation.
For example, the study showed a correlation between sharp, short EV accelerations and slower degradation. This was contrary to long-held assumptions of battery researchers, including this study’s team, that acceleration peaks are bad for EV batteries.
Pressing the pedal with your foot hard does not speed up aging. If anything, it slows it down, explained Alexis Geslin, one of three lead authors of the study and a PhD student in materials science and engineering and in computer science in Stanford’s School of Engineering.
Aging Factors in EV Batteries
The research team also looked for differences in battery aging due to many charge-discharge cycles versus battery aging that just comes with time. Your batteries at home that have been sitting unused in a drawer for years will not operate as well as when you bought them, if they work at all.
“We battery engineers have assumed that cycle aging is much more important than time-induced aging. That’s mostly true for commercial EVs like buses and delivery vans that are almost always either in use or being recharged,” said Geslin. “For consumers using their EVs to get to work, pick up their kids, go to the grocery store, but mostly not using them or even charging them, time becomes the predominant cause of aging over cycling.”
The study identifies an average discharge rate sweet spot for balancing time aging and cycle aging, at least for the commercial battery they tested. Luckily, that window is in the range of realistic consumer EV driving. Carmakers could update their EV battery management software to take advantage of the new findings and to maximize battery longevity under real-world conditions.
Future Directions in Battery Research
“Going forward, evaluating new battery chemistries and designs with realistic demand profiles will be really important,” said energy science and engineering postdoctoral scholar Le Xu. “Researchers can now revisit presumed aging mechanisms at the chemistry, materials, and cell levels to deepen their understanding. This will facilitate the development of advanced control algorithms that optimize the use of existing commercial battery architectures.”
The implications extend beyond batteries, the study suggests. Scientists and engineers could apply the principles to other energy storage applications, as well as to other materials and devices in physical sciences in which aging is crucial, like plastics, glasses, solar cells, and some biomaterials used in implants.
“This work highlights the power of integrating multiple areas of expertise – from materials science, control, and modeling to machine learning- to advance innovation,” Onori said.
Reference: “Dynamic cycling enhances battery lifetime” by Alexis Geslin, Le Xu, Devi Ganapathi, Kevin Moy, William C. Chueh and Simona Onori, 9 December 2024, Nature Energy.
DOI: 10.1038/s41560-024-01675-8
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