Temperature and state-of-charge management key to EV battery life

Published:  04 June, 2021

Parking up an EV that is on a 70%-80% state of charge, (SoC) causes the greatest damage to the Lithium-ion (Li-ion) and temperature plays a vital role as well, according to new research.

The study by the technical team at EV battery warranty provider Altelium investigated calendar degradation of Li-ion batteries which is caused by chemical deterioration of batteries when they are not in use, especially when parked.

The research suggests that parking a car at a 70%-80% state of charge, (SoC) causes the greatest calendar ageing. Meanwhile, reducing the battery temperature, through the use of a thermal management system within an EV, from 40°C to 25°C could double the overall lifetime of the battery.

Dr. Alana Zülke, the lead research author and a member of the battery research team at Altelium, said: “Calendar ageing dominates electric vehicle battery degradation when parked. In the UK, a car will spend on average more than 95% of its time parked. To improve the lifecycle of batteries, it is vital to define the optimal conditions to reduce such degradation. Our research is another important step in quantifying the impact of working and environmental conditions on battery state-of-health. By doing so, we are able to predict battery life cycles and develop strategies to prolong their usefulness more accurately.

“Ultimately this data will not only inform EV battery and battery management systems (BMS) design, but also has further applications for the industry. Information about battery degradation will inform risk calculations for EV battery-related insurance and warranty products and further still, help to consider the value of second-hand cars and second-life batteries.”

The experiments showed that batteries stored at 70%-80% could lose up to 4% - 8% of their capacity to hold charge at the end of one year.Dr. Zülke continued: “Although 4% - 8% may not sound that much, you have to remember that current Li-ion batteries on the market used in EVs are deemed to need replacing when their ability to hold charge drops by as little as twenty or thirty per cent. In this scenario, 8% becomes a pivotal margin”.

“When batteries reduce their capacity by 20 or 30%, they can be repurposed to second-life applications such as battery energy storage system (BESS). The previous history of these batteries, including calendar ageing, will impact their second-life performance.”

On the temperature impact, Dr. Zülke said: “The consumer has the option to pay more to have an EV which is able to control its battery pack temperature even when the car is parked and switched off. In the UK, high temperatures are not an overt concern but based on long parking times, state of charge is an important metric that should be considered by owners when both choosing their vehicle and looking after it.”

The full research paper is available via https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/batt.202100046

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