Electric vehicle (EV) batteries may have a significantly longer lifespan than previously thought, according to a new study by scientists at the SLAC-Stanford Battery Center—a collaboration between Stanford University’s Precourt Institute for Energy and SLAC National Accelerator Laboratory.
The research, published in Nature Energy (Dynamic cycling enhances battery lifetime), indicates that real-world driving conditions, characterized by stop-and-go traffic, varied trip lengths, and extended periods when vehicles are parked, actually benefit battery longevity. This contrasts with the industry-standard laboratory tests, which typically use constant rates of discharge and recharge to evaluate battery life quickly.
Surprising Findings from Realistic Driving Simulations
The study involved designing four types of EV discharge profiles, ranging from standard constant discharge to dynamic discharging based on actual driving data. Over more than two years, the research team tested 92 commercial lithium-ion batteries across these profiles. The results revealed that batteries subjected to simulations reflecting real driving behaviors exhibited up to 33% longer life expectancy.
“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.”
A machine learning algorithm analyzed the extensive data collected, uncovering that sharp, short accelerations and regenerative braking contribute to slower battery degradation. Contrary to long-held assumptions, aggressive acceleration does not speed up aging; it may actually slow it down.
Balancing Time-Induced and Cycle-Induced Aging
The research also differentiated between battery aging due to charge-discharge cycles and aging that occurs over time regardless of use. For typical EV owners who use their vehicles for daily commuting and errands, time-induced aging becomes a significant factor since vehicles spend a considerable amount of time parked.
“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 team identified an optimal average discharge rate that balances both aging processes, aligning with realistic consumer driving patterns. This insight suggests that automakers could update battery management software to enhance battery longevity under real-world conditions.
Implications for Future Battery Design and Beyond
“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 study’s implications extend beyond EV batteries, potentially influencing other energy storage applications and materials where aging is critical.
“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.
Source: StanfordReport
