EV batteries age differently than thought - thankfully

A study by Stanford University in California examined the longevity of 92 lithium-ion batteries, like those found in electric vehicles. Over more than two years, various charging and discharging profiles were rapidly simulated to analyse differences in battery cell ageing.

Some of the batteries underwent rapid discharging at high power and constant charge cycles, whilst others were subject to realistic charge and discharge profiles for comparison. These particular batteries had to cope with fast discharge (experienced during acceleration) and low power usage (seen during stop-and-go driving, longer stops, or parking overnight). Irregular charging at various current intensities also came into play.

To the researchers’ surprise, battery health deteriorated much slower when batteries were discharged dynamically. The data collected helped researchers identify numerous factors contributing to longer life expectancy.

In particular, one such factor is the short and sharp discharge seen during typical acceleration, for example when pulling away from a traffic light. But here’s the problem: until now, the architecture of battery cells has been designed to facilitate as many smooth charging cycles as possible.

Rethinking cell structure and test procedures

As it turns out, this approach is not just out of touch with reality but also counterproductive, considering we underestimated the positive effects of using EV batteries as we normally do in real life. To understand how significant these effects are, we can look at the data concerning the number of charge cycles required for battery capacity to decrease to 85% (typically after 10 to 15 years of use). An evenly discharged battery achieved around 900 charge cycles, whereas a dynamically discharged battery (a more realistic scenario) managed to survive 1,200 charge cycles before reaching the stated limit.

According to the study, focusing on such discharge profiles could help us achieve even better results without having to modify the fundamental architecture or structure of batteries. Nonetheless, even with a conservatively estimated range of 250 km per charge, 1,200 cycles would translate to an overall mileage of 300,000 km. There’s still more room for improvement.