Researchers at Stanford University’s Precourt Institute for Energy and SLAC National Laboratory have shown that an average electric vehicle (EV) battery could last 40% longer than what standard laboratory tests forecast.

This means EV owners may not have to buy a new battery pack or replace their car for an additional few years, delivering a higher return on their decision to go electric. 

To end tail-pipe emissions, countries are promoting the adoption and use of EVs. The 965km ranges for EVs today have addressed range anxiety among potential owners. Still, worries about the health of the battery packs remain. 

Battery costs may have reduced to a 10th of what they were over a decade ago, but they still account for a third of the price of a new EV. In such a scenario, EV owners dread when their battery pack may end its life cycle and there emerges a need for complete replacement. 

The joint study by Stanford and SLAC researchers shows that the day will arrive much later than EV manufacturers forecast, which applies even to the roughest EV owners. 

Testing the EV batteries in the wrong way

Standard laboratory tests for batteries check new battery designs by discharging them constantly and recharging them fully. They repeat this exercise over multiple cycles to determine if the battery design is reliable and has an acceptable life expectancy. 

In the real world, though, this does not happen. A battery pack on an EV runs to power the car in the high traffic of the cities, on the highways, at frequent traffic lights, or staying parked for long hours at home or office parking, none of which are factored for in battery tests. 

“We’ve not been testing EV batteries the right way,’ said Simona Onori, an associate professor of energy science and engineering at the Stanford Doerr School of Sustainability who was involved in this work. 

“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.” 

What did the team study? 

To represent battery usage scenarios more accurately, the research team designed four types of EV discharge profiles, including a consistent and dynamic discharge setup using real-world driving data. 

Over two years, the team tested 92 commercially available lithium-ion batteries and found that the battery life climbed as the profiles reflected more real-world driving behaviour. 

For instance, the study showed that short and sharp EV acceleration slowed the degradation of batteries, and pressing the pedal hard slows down the battery’s ageing instead of hastening it, the press release added.

The researchers also investigated if batteries aged faster when going through charge-discharge cycles continuously, like delivery vehicles or when they were sitting idle for longer durations. They found that the sweet spot for ageing was between the two, which is more realistic for EV consumers.

Tweaks to battery management systems from EV manufacturers could help deploy their research in real-world conditions immediately. 

The applications of their research extend beyond EV batteries into energy storage and even powering implants in the human body.  

The research findings were published in the journal Nature Energy