Stanford study predicts 40% longer EV battery life
Scientists at the SLAC-Stanford Battery Centre have published a study on this topic in the journal Nature Energy. The centre, which is located in the USA, is made up of the Precourt Institute for Energy at Stanford University and the SLAC National Accelerator Laboratory. Their thesis, which has now been substantiated, is that the real-life stop-and-go operation of electric vehicles by drivers is better for the batteries than the uniform wear and tear simulated in almost all laboratory tests.
By “normal use of real-world drivers”, the researchers refer to heavy traffic, a mix of long and short journeys and predominantly parking. Used in this way, batteries could last up to 40 per cent longer than previously assumed, according to the study organisers. They argue that the frequently used laboratory tests on service life are not adequate for predicting the life expectancy of electric car batteries. Simona Onori, lead author and Associate Professor of Energy Science and Engineering at the Stanford Doerr School of Sustainability, comments: “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.”
The researchers outline their own test setup as follows: They first designed four types of discharge profiles for electric vehicles, from laboratory-like constant discharge to dynamic discharge based on real driving data. The team then tested 92 commercially available lithium-ion batteries for more than two years with different discharge profiles. “In the end, the more realistically the profiles reflected actual driving behaviour, the higher EV life expectancy climbed.”
The research team also investigated the differences between battery ageing, which results from high usage and a correspondingly large number of charging and discharging cycles, and battery ageing purely over time without usage. “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,” says Alexis Geslin, one of the three lead authors of the study and a PhD student in materials science and engineering and computer science at the Stanford School of Engineering. “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 researchers believe that the results are particularly relevant for car manufacturers, who could use the new findings to update their battery management software in order to maximise the service life of the battery under real-life conditions. “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. In the next step, the researchers themselves are endeavouring to verify the assumed ageing mechanisms at the level of chemistry, materials and cells in order to deepen their understanding. This should facilitate the development of advanced control algorithms that optimise the use of existing commercial battery architectures.
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