A research team from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have measured the slow process of energy loss in lithium-ion batteries resulting from escaping oxygen atoms and reported their findings in Nature Energy on June 14.
“We were able to measure a very tiny degree of oxygen trickling out, ever so slowly, over hundreds of cycles,” said Peter Csernica, a Stanford PhD student who worked on the experiments with Associate Professor Will Chueh. “The fact that it’s so slow is also what made it hard to correct.”
Researchers have long known that oxygen atoms leak out of the particles as lithium moves back and forth two electrodes in batteries that temporarily store charge, but the process was too slow to measure directly.
“The total amount of oxygen leakage, over 500 cycles of battery charging and discharging, is 6%,” Csernica said. “That’s not such a small number, but if you try to measure the amount of oxygen that comes out during each cycle, it's about one one-hundredth of a percent.”
So, in this study, the researchers measured the oxygen leakage indirectly, observing how oxygen loss modifies the chemistry and structure of the particles—ranging from the tiniest nanoparticles to clumps of nanoparticles to the full thickness of an electrode.
The team cycled batteries for variable amounts of time, took them apart, and sliced electrode nanoparticles for high-res chemical analysis with an X-ray microscope at Lawrence Berkeley National Laboratory’s Advanced Light Source. The data was combined with ptychography to reveal details in billionths of a meter.
At SLAC’s Stanford Synchrotron Light Source, the team shot X-rays through electrodes to confirm that what they were seeing in nanoscale level was also true at a larger scale.
The team concluded that an initial burst of oxygen emerges from the surfaces of particles, followed by a slow trickle from the interior. Within nanoparticle clumps, it was found that they lost less oxygen at the center, in comparison to the outer surface.
Researcher Chueh described the degradation of the battery: “When oxygen leaves, surrounding manganese, nickel and cobalt atoms migrate. All the atoms are dancing out of their ideal positions. This rearrangement of metal ions, along with chemical changes caused by the missing oxygen, degrades the voltage and efficiency of the battery over time. People have known aspects of this phenomenon for a long time, but the mechanism was unclear.” Chueh said that his team’s findings could lead to new ways of mitigating oxygen loss in lithium batteries.
https://www6.slac.stanford.edu/news/2021-06-11-scientists-discover-how-oxygen-loss-saps-lithium-ion-batterys-voltage.asp
