Scientists X-ray Li-ion batteries for deeper insight

The research provided quantitative proof of the hypothesis that electrode performance depends on carbon coating and not ion diffusion.
Ameya Paleja
Better understanding of batteries can lead to more efficient solutions
Better understanding of batteries can lead to more efficient solutions


A research collaboration between scientists of some of the top institutions in the US has led to significant discoveries about reactivity inside lithium iron phosphate batteries, a press release said. Scientists mined X-ray images of the battery to learn about phenomena previously unseen by the human eye.

Lithium iron phosphate (LFP) offers multiple advantages, such as lower cost, better safety, and higher life cycle over conventional Li-ion batteries, making them attractive options for use in electric vehicles (EVs) and energy storage solutions.

An electrode of the battery is made of many tiny particles, each about a micron (1/1,000th of a millimeter) in diameter and about 100 nanometers in thickness. The electrode is in contact with the electrolyte solution. When the battery discharges, lithium ions flow from the electrolyte into the LFP electrode in a process known as intercalation.

Modeling the reaction

LFP as a material has two preferences: to be full of lithium ions or empty. Known as phase separation, scientists have been working on mathematical modeling for distinctive patterns of lithium-ion flow.

Back in 2015, Martin Bazant, a professor at MIT, teamed up with William Chueh, an associate professor of materials science at Stanford, to work on this problem. The duo used scanning X-ray microscopy to obtain images of LFP particles. The work led to detailed images of the electrode that revealed the concentration of lithium ions.

By taking multiple images of electrodes at different times of charge and discharge cycle, the researchers were able to create movies of the lithium-ion flow. In 2017, the team furthered their research by taking X-ray images of 63 LFP particles as they charged and discharged. Using 180,000 pixels, the researchers were able to train computational models to produce equations to describe the nonequilibrium thermodynamics and reaction kinetics of the material.

Relation to the carbon coating

Scientists X-ray Li-ion batteries for deeper insight
Improving coating of the electrode can deliver more efficient battery

"Every little pixel in there is jumping from full to empty, full to empty. And we’re mapping that whole process, using our equations to understand how that’s happening," said Bazant in the press release. "It was a real surprise to us that we could learn the variations in surface reaction rate simply by looking at the images. There are regions that seem to be fast and others that seem to be slow."

The team found that the differences in reaction rates could be correlated with the thickness of the carbon coating on the LFP particles. LFP by itself is slow to conduct, so carbon coating is applied to aid in conducting electricity faster.

"We discovered at the nanoscale that variation of the carbon coating thickness directly controls the rate, which is something you could never figure out if you didn't have all of this modeling and image analysis," Bazant added.

These findings also tell us that the performance of the electrodes in an LFP battery depends on the coupled ion-electron transfer at the interface between solid particles and carbon coating and not the rate of ion diffusion into the solid. This will help future research to be directed toward optimizing the thickness of the carbon layer to make more efficient batteries.