Researchers find the cause of shortening the life of lithium metal batteries
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Lithium ion batteries (lithium ion secondary batteries) are used in electronic devices such as PCs and smartphones, but researchers are working on new batteries such as lithium metal batteries to further improve battery performance. The A research team led by researchers at the University of California, San Diego , has identified the cause of the weaknesses of lithium metal batteries that deteriorate with each charge and discharge by developing new analytical methods.
Quantifying inactive lithium in lithium metal batteries | Nature
https://doi.org/10.1038/s41586-019-1481-z
Study identifies main culprit behind lithium metal battery failure
https://jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=2850
Ordinary lithium-ion batteries use graphite for the anode of the battery, but lithium metal batteries have improved performance by using lithium metal for the anode. Lithium metal batteries have twice the energy density of conventional lithium ion batteries, and if they are put to practical use, it is expected that the battery life will be longer and the weight of the battery can be reduced.
However, lithium metal batteries have the disadvantage that their rechargeable battery life is shorter than lithium-ion batteries because of their low “Coulomb efficiency”, which indicates how much of the charged capacity can be discharged.
Researchers believe that the low Coulomb efficiency of lithium metal batteries is caused by the growth of a layer called the solid electrolyte interphase interface (SEI) formed between the anode and the electrolyte. I have been struggling with stabilization. However, Y. Shirley Meng of the University of California, San Diego pointed out that the low coulomb efficiency of lithium metal batteries overlooked not only the formation of the SEI layer, but also other important aspects.
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Meng et al.'S research team thinks that lithium is separated from the anode while the lithium metal battery is discharged and is trapped in the SEI layer, deactivating it and reducing coulomb efficiency. It was.
To confirm this hypothesis, the research team developed a method to accurately measure how much unreacted lithium is contained in the inert lithium on the anode. The technique is to put the sample in a sealed flask and add water to scientifically react with lithium to generate hydrogen gas. By measuring the amount of hydrogen gas, it is possible to know the lithium content in inert lithium.
In addition to lithium, there are lithium ions that are components of the SEI layer, and the amount of lithium ions can be determined by subtracting the lithium content in the inert lithium. According to the results of the research team, it was found that the main component in the inert lithium was lithium that was peeled off from the anode, and lithium ions were not the main component. In other words, the decrease in coulomb efficiency and the amount of lithium ions, which are the main components of the SEI layer, are not related, and it can be said that lithium separated from the anode is related to the decrease in coulomb efficiency.
According to the research team, the accumulation of lithium at the anode during charging of the lithium metal battery is related to the decrease in coulomb efficiency. If lithium accumulates on the anode at a high density, the rate at which lithium is taken into the SEI layer during discharge can be reduced, and the Coulomb efficiency can be prevented from decreasing. “I hope our insights will stimulate lithium metal battery research to the next level,” Meng said.
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