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Lithium anodes are known as the holy grail of battery design manufacturing because they enable batteries to have extremely high energy densities. For decades, they have always been the goal pursued by scientists. A few days ago, a group of researchers at Stanford University in the United States claimed that they have manufactured a stable metal lithium anode battery, and took a big step toward this goal. The researchers said that the new research is expected to make ultra-light, ultra-small, ultra-large capacity batteries become a reality, wearable devices, mobile phones and electric vehicles will all benefit. The related papers were published in the latest issue of Nature Nanotechnology magazine.
Professor Cui Yi, a professor of materials and engineering at Stanford University who led the study, said that lithium has the greatest potential in all materials that can be used to make battery anodes. It is very light and has a very high energy density. Lighter, smaller batteries have more capacity. However, the manufacture of lithium anodes is a very difficult matter, so many scientists have to give up after persisting for many years.
At present, lithium anodes need to face at least two challenges: First, the phenomenon of lithium expansion occurs when charging. When charging, lithium ions will condense and expand. All anode materials, including graphite and silicon, swell, but not as much as lithium. Lithium's expansion is "almost infinite" relative to other materials. Not only that, this expansion is still uneven, causing pits and cracks. These cracks will allow precious lithium ions to escape from it, forming hair or mossy growth. This can cause the battery to short circuit, severely reducing its service life.
The second is that the lithium anode has a high activity after contact with the electrolyte. This consumes electrolytes and shortens battery life. An additional problem that this creates is that they heat up when they come into contact. Overheating will cause burning and even explosions. Therefore, this is a serious safety issue.
"Although it is so difficult, we still find a solution to the problem," said Dr. Zheng Guangyuan who is working in Cui Yi's lab. He is the first author of the dissertation. The physicist's organization network reported on July 28th that in order to solve these problems, researchers used carbon as a lithium anode to create a nano-protective layer called "nanosphere." These nanosphere protective layers look like honeycombs in appearance, are flexible and chemically stable, and have a single thickness of only 20 nanometers.
Cui Yi said that the nanospheres are made of invisible carbon, which not only has good chemical stability, but also has good strength and flexibility. It can not only prevent the lithium from contacting with the electrolyte, but also has a certain mechanical strength, and can withstand the expansion phenomenon of the lithium anode during the charging process.
In terms of technology, nanoballs can greatly increase the coulombic efficiency of the battery (also called charge and discharge efficiency), that is, the charge discharged during discharge under a certain charge and discharge condition and the charge percentage charged during charging. Under normal circumstances, in order to meet the daily use needs, the battery should be able to achieve more than 99.9% charge and discharge efficiency.
Experiments have shown that an unprotected lithium anode can achieve a 96% charge and discharge efficiency, which can only reach 50% after 100 cycles of charge and discharge, apparently not enough. The Stanford team's new lithium electrode after charging and discharging 150 times, the charge and discharge efficiency can be maintained at 99%. The difference between 99% and 96% for battery charge and discharge efficiency is huge.
Cui Yi said: "Although we have not yet achieved the goal of 99.9%, we are slowly approaching and compared with the previous technology, the new design has achieved a great leap forward. With further research and the adoption of new electrolytes We believe that success is in sight."
We have been pursuing powerful batteries and have placed our hopes on the most promising lithium. While scientists around the world are trying to break through the limitations of the development of lithium batteries, Stanford's research team puts on it a “clothing†of nanomaterials. This innovative new attempt not only makes up for the shortcomings of traditional lithium batteries, but also makes an outstanding contribution to improving the efficiency of battery charging and discharging. With the increasing number of miniaturized devices, we expect this new technology will help metal lithium anode batteries become more popular, so that future batteries are not only safe to use, but also lighter, smaller, and lasting longer. (Reporter Wang Xiaolong)
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