EV batteries may last up to 40% longer than expected – Stanford

Actual driving and charging habits may make EV batteries last longer than researchers previously thought, finds a new Stanford-SLAC study.

New research from the SLAC-Stanford Battery Center published on December 9 at Natural Power suggests that real-world driving habits — such as stop-and-go traffic, freeway driving, fast city commutes, and lots of time spent parking — can make EV batteries last about a third longer than previously thought. This means that the average EV owner may not need to replace their battery pack or upgrade to a new vehicle for several more years, saving money and extending the life of their trip.

Battery scientists often test new designs in labs by cycling them through a constant rate of discharge and charge, speeding up the process to quickly see how long they will last and how well they work. However, according to a new study published on December 9 at Natural Powerthat approach does not reflect how EV batteries are used in the real world.

For everyday EV riders, this is big news. Although battery prices have fallen by nearly 90% in the past 15 years, they still make up about a third of the cost of a new EV. Research suggests that current and future EV drivers can enjoy more miles before needing a replacement.

“We weren't testing EV batteries properly,” said Simona Onori, senior author and associate professor of energy science and engineering at the Stanford Doerr School of Sustainability. “To our surprise, real fast driving, braking that charges the batteries slowly, stopping to pull into a shop, and letting the batteries rest for hours at a time helps the batteries last longer than we thought based on an industry-standard lab. exams.”

The researchers created four different EV emission profiles, ranging from standard emissions to extremes based on real-world driving data. Over two years, they tested 92 lithium-ion batteries using these profiles. The results were clear: The closer the profiles are to actual driving behavior, the longer the batteries last.

So, what accounts for this amazing longevity? A machine learning algorithm trained on a mountain of collected data helped reveal how dynamic discharge patterns reduce battery degradation. It turns out that the way people drive may actually be easier on batteries than scientists expected.

For example, short, sharp acceleration in EVs actually reduces battery wear. That flips the script on what researchers – including the team behind this study – had assumed for years: that acceleration spikes were the battery's worst enemy.

Alexis Geslin, one of the three lead authors of the study and a PhD student in materials science and engineering and computer science at Stanford's School of Engineering, explained:

We battery engineers think that cyclic wear is more important than wear caused by time. That's especially true for commercial EVs like buses and delivery vans that are almost always being used or recharged.

For consumers who use their EVs to get to work, pick up their kids, go to the grocery store, but often don't use them or charge them, time becomes the main cause of wear and tear on cycling.

The study points to a sweet spot for discharge rates that measure time wear and cycle wear – at least for the commercial batteries they tested. That list is consistent with how most people drive their EVs. Automakers can use this insight to adjust battery management software, to help extend battery life and improve real-world driving performance.

Moving forward, energy science and engineering postdoctoral scholar Le Xu notes, “Researchers can now revisit the aging mechanisms assumed at the chemistry, materials, and cellular levels to deepen their understanding. This will facilitate the development of advanced control algorithms that optimize the use of existing commercial battery structures. “

Read more: Researchers have developed an EV battery that charges 0-80% in 15 minutes

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