Experts in a government lab are taking an extremely close look at pouch battery cells — using advanced imaging tech — with the goal to better understand how they age.
The analysis method is now available to battery researchers and producers as they work to make cheaper, safer, and better-performing packs, according to a news release from the U.S. Department of Energy's Argonne National Laboratory.
The battery snoops are getting an atomic-level view thanks to nuclear magnetic resonance, or NMR, images.
It works by using a "noninvasive technique that relies on magnetic properties of atomic nuclei to study the chemical environments in a sample. A radio-frequency field is applied to a sample immersed in a strong magnetic field, causing the sample to absorb energy.
"Then, the radio-frequency field is removed, and a probe measures the energy released when the nuclei return to their lower energy state. The measurements provide insights about the atomic and molecular structures and reactions, including those in battery materials," according to Argonne's description.
The summary added that the NMR technique is similar to MRIs commonly used to take images of the human body.
The lengthy description is a mouthful. But study author Argonne chemist Baris Key said that he hopes it becomes a "bread-and-butter" process for battery makers.
It's for those "who want to probe the long-term evolution of their batteries without opening them up," Key said in the summary.
Of particular note are emerging silicon anodes being developed by Panasonic and others as a better alternative to costly graphite. One hitch with the anode tech has been expansion and contraction that happens when the battery charges and discharges. When batteries operate, ions move between the electrodes, the anode and cathode, in a substance called electrolyte. Silicon anodes can expand by 400%, causing cracks that impair performance, according to the Argonne release.
As part of the study, the team took NMR scans of silicon anodes as the battery cycled, watching how lithium atoms acted once inside. The cells were then left idle for seven months.
"What we did in our study was like taking MRIs of operating battery cells, except that we didn't produce images of the cells," study main author Evelyna Wang said in the release. "Instead, the output was information on how the lithium chemical environment in the cells changed due to charging, discharging, resting, and aging."
The researchers learned how lithium atoms congregate with other atoms inside the packs, providing useful information about how the interactions cause batteries to degrade. The team observed that some lithium ions were trapped in the anode, instead of continuing the journey between electrodes.
Better batteries can boost performance for energy storage units, and for packs that power electric vehicles, expanding their use. Each EV that replaces a gas-guzzler prevents thousands of pounds of heat-trapping exhaust from hitting the atmosphere, as cited by the U.S. Energy Department. The pollution is flagged by medical experts as a detriment to lung health.
Switching to an EV can save you thousands of dollars in fuel costs and has tax breaks, as well.
At Argonne, findings include the hack that magnesium salt can limit the amount of trapped lithium. It's an example of breakthroughs that experts hope will be developed with help from NMR. They said a variety of battery types and components can be scanned.
"We hope industry and battery consortia will be interested in this method and in working with us," Key said in the summary.
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