EV batteries might last a lot longer than we thought

Researchers in America have found that the way we have been testing the lifespan of electric vehicle batteries is flawed and most may last around 40% longer than previously thought.

The traditional way to test how long a battery is likely to remain effective has been to repeatedly charge and discharge it. Almost always the battery is discharged at a constant rate, something that is very unlikely to happen in a real-world scenario. 

As such, a team from the SLAC-Stanford Battery Center has been discharging batteries under a variety of different conditions and found that, counter-intuitively, a more realistic scenario in which a car might make long and short journeys and, of course, be frequently stuck in traffic adds to a battery’s longevity rather than reduces it.

Simona Onori, senior author and an associate professor of energy science and engineering in the Stanford Doerr School of Sustainability said: ‘We’ve not been testing EV batteries the right way. 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 team spent two years testing 92 commercial lithium­ ion batteries under different discharge conditions, one involving constant discharging as traditionally used in such research. The other batteries were discharged to test their performance under more realistic conditions.

It was found that short, sharp EV accelerations were associated with slower battery degradation, contrary to the widely accepted idea that that acceleration peaks are bad for EV batteries.

Alexis Geslin, one of three lead authors of the study and a PhD student in materials science and engineering said: ‘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. 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.’

Energy science and engineering postdoctoral scholar Le Xu said: ‘Going forward, evaluating new battery chemistries and designs with realistic demand profiles will be really important. 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 optimise the use of existing commercial battery architectures.’

The full research can be read here.