US scientists uncover battery aging with groundbreaking NMR tool

The study resembled MRIs of battery cells, providing data on lithium’s chemical changes during charging, discharging, resting, and aging.

Jijo Malayil

The NMR probe (the metal cylinder) alongside a small-scale battery pouch cell (the rectangular device atop the probe) utilized in the Argonne study.

ANL

Researchers developed a new method to assess long-term aging in real-world battery cells.The US Department of Energy’s (DOE) Argonne National Laboratory (ANL) team’s approach relies on nuclear magnetic resonance (NMR), a technique often used in medical imaging.

NMR spectroscopy is a noninvasive technique that uses the magnetic properties of atomic nuclei to analyze chemical environments, providing insights into atomic structures and reactions in battery materials.According to researchers, this marks the first application of NMR spectroscopy capable of precisely monitoring the chemical changes in commercial pouch battery cells over extended operational periods.“The application of NMR to batteries has been limited to date. But with our powerful new capability, I hope that it will become ‘bread and butter’ for researchers and manufacturers who want to probe the long-term evolution of their batteries without opening them up,” said Baris Key, an ANL chemist and one of the study’s authors, in a statement.

In order to transform stored energy into electrical power, electrolytes move lithium ions between two electrodes in today’s lithium-ion batteries. The anodes, or negative electrodes, of the majority of lithium-ion batteries found in EVs are composed of graphite. Longer driving ranges, however, require new electrode materials with higher energy densities, like silicon.A number of technical issues need to be resolved before silicon can be used in the anode to its full potential. Lithium ions combine with silicon during the charging process of a silicon-anode battery cell to create substances called lithium silicides.According to researchers, this results in the anode’s volume increasing by up to 400 percent. Lithium leaves the anode when the cell discharges, which causes it to contract.The silicon anode may crack due to expansion and contraction. Lithium silicides are also extremely reactive, making their interaction with the cell’s electrolyte considerably less stable.

The NMR spectroscopy technique was created and used in the ANL study to track the fate of lithium atoms in silicon-anode cells during their charging and discharging processes, followed by a seven-month rest period. It is comparable to magnetic resonance imaging (MRI), which is used in medicine to provide fine-grained images of the body.The team’s study resembled taking MRIs of battery cells in action, but instead of images, it provided data on lithium’s chemical environment changes during charging, discharging, resting, and aging.“This information allowed us to determine where the lithium atoms go, how they interact with other atoms, how many lithium atoms are involved in those interactions and whether there is any associated degradation. Our goal was to understand why the silicon anodes degrade over time,” said Evelyna Wang, a postdoctoral appointee at ANL and the study’s main author, in a statement.

Argonne researchers applied NMR to observe real-time aging in commercial-grade pouch battery cells, marking a first for this “operando” technique.This approach allows for continuous monitoring of structural and electronic changes during operation, in contrast to standard methods that evaluate cells after disassembly. To improve durability for extended cycling, Argonne’s researchers produced cells that closely resembled commercial products.According to their research, charging reduced the amount of lithium that was available and decreased the anode’s potential to store energy by causing lithium atoms to build up as lithium silicides.

The confined lithium’s reaction with the electrolyte accelerated degradation. By adding magnesium salt to the electrolyte, they proposed new ways to prolong battery life by reducing the formation of these trapped lithium silicides.According to researchers, the flexible NMR technique, which is sensitive to elements like silicon and lithium, can be applied to different battery technologies, such as solid-state and sodium-ion, and may pave the way for cooperation between battery research organizations and industry.

The details of the team’s research were published in the Journal of Power Sources.

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Jijo Malayil Jijo is an automotive and business journalist based in India. Armed with a BA in History (Honors) from St. Stephen's College, Delhi University, and a PG diploma in Journalism from the Indian Institute of Mass Communication, Delhi, he has worked for news agencies, national newspapers, and automotive magazines. In his spare time, he likes to go off-roading, engage in political discourse, travel, and teach languages.

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