Breakthrough: ‘High current first charge can boost battery lifespan by 70%’

Researchers from the SLAC-Stanford Battery Center, linked to Californian Stanford University, have found that using high currents for the first charging after the battery’s production can improve its lifespan by 50 to 70%.

At first glance, this might contradict the general belief that charging EV batteries frequently at ‘superchargers’ shortens their lifespan. However, it could be a significant breakthrough in battery manufacturing because it can reduce costs by saving valuable time, making batteries cheaper and lasting fully at least 12 to 15 years, compared to the eight years generally guaranteed now.

Managing the ‘formation’ process

The study published in the scientific paper Joule shows that the process called ‘formation,’ dramatically determines how long the battery will work from then on and how many cycles of charging and discharging it can handle before deteriorating.

When recent studies suggested that faster charging with higher currents does not degrade battery performance, the researchers at SLAC/Stanford wanted to dig deeper. Using scientific machine learning, they managed to pin down the most critical of many factors in the ‘formation’ process to just two—the temperature and current at which the battery is charged—standing out from the rest.

The study was carried out by a SLAC/Stanford team led by Professor Will Chueh in collaboration with researchers from the Toyota Research Institute (TRI), the Massachusetts Institute of Technology (MIT), and the University of Washington. They elaborately tested 186 Li-ion batteries cycled across 62 different ‘formation’ protocols but with the same aging test.

Critical last step

The formation is a critical last step in battery manufacturing. “So if it fails, all the value and effort invested in the battery up to that point are wasted,” says Xiao Cui, the lead researcher for the battery informatics team.

Typically, battery makers use low currents at the first charge to stabilize the battery materials inside. However, slow charging takes hours and is one of the costly bottlenecks in battery cell manufacturing.

The researchers at SLAC explain that in that process, the electrode of a newly made battery is 100% complete of lithium at the start and loses up to 9% of its lithium. When using high currents over short fast-charging cycles of 20 minutes instead, the lithium loss is much higher, up to 30%.

Lithium losses not in vain

However, somewhat to their surprise, this showed that it helped boost the overall life span of the battery 50 to 70% later. That lost lithium is not in vain, as it becomes part of a protective layer called the solid electrolyte interphase, or SEI, that forms on the surface of the negative electrode.

SEI protects the negative electrode from side reactions that accelerate lithium loss and degrade the battery faster over time. Some of the lithium is deactivated every time the battery goes through a charge-discharge cycle during its lifespan.

Minimizing those losses prolongs the battery’s working lifetime. Oddly enough, losing more lithium in the initial formation process decreases the later losses significantly, making the battery less prone to deterioration.

“Under fast charging conditions, lithium ions are also consumed during side reactions at the negative electrode. This creates additional headspace in both electrodes and helps improve battery performance and lifespan.”

“Removing more lithium ions up front is a bit like scooping water out of a full bucket before carrying it,” Cui said. “The extra headspace in the bucket decreases the amount of water splashing out along the way. Similarly, deactivating more lithium ions during formation frees up headspace in the positive electrode and allows the electrode to cycle more efficiently, improving subsequent performance.”