Researchers in the United States have discovered a simple method of extending the lifespan of lithium-ion batteries by as much as 50 per cent.
In a study published in late August in the journal Joule, researchers from the SLAC-Stanford Battery Center in the United States discovered that charging lithium-ion batteries at high currents just before they leave the factory can increase their average lifespan by 50 per cent.
Using scientific machine learning, a type of artificial intelligence (AI), the researchers were able to determine the why behind the discovery.
The study, ‘Data-driven analysis of battery formation reveals the role of electrode utilization in extending cycle life’, was also described in an article published by the SLAC-Stanford Battery Center, which outlined the discovery and the ways in which it may help to optimise battery manufacturing.
When a battery first leaves the factory, the positive electrode of a newly minted battery is 100% full of lithium, but every time a battery goes through a charge-discharge cycle, some of the lithium is deactivated.
According to one of the researchers, Xiao Cui, minimising the lithium deactivation losses is key in prolonging the battery’s working lifespan.
The first charge a lithium-ion goes through causes the creation of a layer called the solid electrolyte interphase (SEI) that forms on the surface of the negative electrode during the first charge. Subsequently, the SEI layer protects the negative electrode from side reactions that would otherwise accelerate the lithium loss and accelerate the battery’s degradation.
Getting this SEI layer just right is therefore vitally important and is known as the ‘formation charge’.
“Formation is the final step in the manufacturing process, so if it fails, all the value and effort invested in the battery up to that point are wasted,” Cui said.
Traditionally, battery manufacturers generally give lithium-ion batteries their first charge with low currents, working on the theory that a lower current would create a more robust SEI layer. However, charging at these low currents means longer and more costly charging times, without yielding optimal results.
The SLAC-Stanford Battery Center researchers, led by Professor Will Chueh in collaboration with researchers from the Toyota Research Institute (TRI), the Massachusetts Institute of Technology and the University of Washington, wanted to understand the alternative of an initial charge at higher currents.
Utilising machine learning to test all the possible combinations that go into forming the SEI layer during the first charge, the researchers found that only two factors stood out – the temperature and the current.
“Brute force optimization by trial-and-error is routine in manufacturing– how should we perform the first charge, and what is the winning combination of factors?” said Chueh.
“Here, we didn’t just want to identify the best recipe for making a good battery; we wanted to understand how and why it works. This understanding is crucial for finding the best balance between battery performance and manufacturing efficiency.”
Their experiments subsequently confirmed that charging at high currents is not only beneficial compared to low currents, but in fact has a huge impact, increasing the lifespan by up to 70 per cent, but with an average of 50 per cent.
“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. In similar fashion, deactivating more lithium ions during formation frees up headspace in the positive electrode and allows the electrode to cycle in a more efficient way, improving subsequent performance.”
The research could have significant long-term benefits, given that the results were gained by only modifying the final step in the whole manufacturing process.
“The cool thing is that we didn’t change any chemistry of the battery,” William Chueh told NewScientist.
“We just changed that last step in manufacturing to form the battery a little differently.”
Steven Torrisi, a senior research scientist at TRI who collaborated on the research, added that the results of the research “demonstrate a generalizable approach for understanding and optimizing this crucial step in battery manufacturing. Further, we may be able to transfer what we have learned to new processes, facilities, equipment and battery chemistries in the future.”
