A new study from the SLAC-Stanford University Battery Center shows that electric vehicle (EV) batteries may last much longer under real-world conditions than previously thought. By testing the batteries through dynamic discharge profiles that simulated actual driving scenarios, the researchers found that these conditions can extend battery life, overturning some long-held assumptions about EV battery degradation.
Electric vehicle (EV) batteries used under typical driving conditions, such as driving through heavy traffic, long trips on the highway, short trips in the city, and long periods of parking, may last up to 30% longer than previously estimated. The discovery comes from a new study by researchers at the SLAC-Stanford Battery Center, a collaboration between Stanford University's Precourt Institute for Energy Research and the SLAC National Accelerator Laboratory. The findings suggest electric vehicle owners may not need to replace expensive battery packs or buy new vehicles as quickly as they think.
Traditionally, when battery scientists and engineers test new battery designs in the lab, they cycle charge and discharge repeatedly at a constant rate. This approach allows researchers to quickly evaluate battery life and other performance characteristics. However, these tests may not accurately reflect real-world driving conditions, resulting in overly conservative estimates of battery life.
According to research published Dec. 9 in Nature Energy, that's not a good way to predict the life of an electric vehicle's battery, especially for those who own electric vehicles for daily commuting. Although battery prices have plummeted by about 90% over the past 15 years, batteries still account for nearly a third of the price of new electric vehicles. So current and future EV passengers may be happy to hear this news.
"We didn't test EV batteries the right way," said senior author Simona Onori, an associate professor in the Department of Energy Science and Engineering at Stanford's Dole School of Sustainability. "To our surprise, during actual driving, frequent acceleration, braking to recharge the battery, stopping to shop in stores, and letting the battery rest for a few hours all helped extend the battery's life, not what we thought based on industry standard laboratory testing."
The researchers designed four electric vehicle discharge curves, ranging from standard continuous discharge to dynamic discharge based on real driving data. The research team conducted discharge curve tests on 92 commercial lithium-ion batteries for more than two years. Ultimately, the more closely the discharge curve reflects actual driving behavior, the longer the expected life of the electric vehicle.
The study found that several factors contribute to the unexpectedly long lifespan. Machine learning algorithms trained on all the data collected by the research team help figure out the impact of dynamic discharge curves on battery degradation.
For example, research shows a correlation between sharp, brief EV acceleration and slower decay. This goes against a long-held assumption by battery researchers, including our team, that peak acceleration is bad for EV batteries.
Pressing the pedal harder will not speed up aging. Alexis Geslin, one of the study's three lead authors and a doctoral student in materials science and engineering and computer science at Stanford's School of Engineering, explains.
The team also studied the difference between battery aging due to multiple charge and discharge cycles and battery aging over time. If a battery at home sits unused in a drawer for many years, even if it works, it won't work as well as when you bought it.
"Our battery engineers believe that cyclic aging is much more important than time-induced aging. This mainly applies to commercial electric vehicles, such as buses and delivery vans, which are almost always in use or charging," Geslin said. "For consumers who use EVs to get to work, pick up their kids, go to the grocery store, but mostly don't use them or even leave their cars and batteries completely idle, time becomes a more dominant cause of aging than circulation."
This study identified an average discharge rate sweet spot that balances time aging and cycle aging, at least for the commercial cells they tested. Fortunately, this window falls within the range of consumers actually driving electric vehicles. Automakers can update their electric vehicle battery management software to take advantage of new research to maximize battery life under real-world conditions.
"Going forward, it will be important to evaluate novel battery chemistries and designs with realistic demand curves," said LeXu, a postdoctoral scholar in energy science and engineering. "Researchers can now revisit putative aging mechanisms at the chemical, materials, and battery levels to gain a deeper understanding. This will facilitate the development of advanced control algorithms to optimize the use of existing commercial battery architectures." "
This study shows that the implications are not limited to batteries. Scientists and engineers can apply these principles to other energy storage applications, as well as to other materials and devices in areas of physical science where aging is critical, such as plastics, glass, solar cells and some biomaterials used in implants.
"This work highlights the power of integrating multiple fields of expertise, from materials science to controls and modeling to machine learning, to drive innovation," Onori said.
Compiled from /ScitechDaily