Scientists found that the cause of the lithium battery frequently explose.

With the rapid development of portable electronic devices and electric vehicles, in addition to the pursuit of people,The lithium battery The capacity of the larger, charge and discharge faster, more concern is how to protect lithium The battery The safety of use. Because every now and then Lithium electricity Pool events such as explosion, MianBuDe make people nervous .Is the premise of how to solve the problem of lithium battery safety, scientists as in-depth and comprehensive understanding of the lithium battery as the cause of the explosion.

The scientific level of explanation is that the lithium electrode surface deposition can form "dendritic" (dendrites), and it will continue to grow, resulting in battery internal short circuit caused by fault or may cause a fire. But how to know and study from the atomic structure level, and then to find the solution to the problem, the lack of effective technical means in the past.

This month has just won the Nobel Prize in chemistry 2017 frozen electron microscope (journal - EM) technology, it provides powerful technical support. At Stanford university, directly under the department of energy (doe) SLAC national accelerator laboratory of professor yi cui, Steven chu, a Nobel laureate in physics in 1997, such as people's team, just by freezing electron microscope (journal - EM) captured images of the first atomic lithium metal dendrite. The results of the study was published on October 27 local time in the international academic periodicals of the journal Science.

Each lithium dendrite is a long strip, and molding perfect six-sided crystals. Previously observed by electron microscope lens is irregular shape of the crystal. Yi cui said, "the results of the study are very exciting, as well as related research opened a new situation!"

Frozen electron microscope, just as its name implies is the application of frozen fixation, using transmission electron microscopy (TEM) at low temperature (Transmission Electron Microscope, TEM) to observe the microstructure of the sample. Frozen electron microscope are important structural biology research methods, and is important means to obtain biological macromolecular structure.

Because the image is the key to understand the mechanism, scientific breakthroughs are often based on using the naked eye on the target successfully get its visual structure. For a long time, people think that TEM is not suitable for observation of biological molecules, because strong electron beam will destroy the biological materials. However, the production of frozen electron microscopy (sem), allow researchers to biological molecules are "frozen", an unprecedented movement process analysis, the characterization of the development of the understanding of the chemistry and pharmacology has a decisive influence. Because of this, the frozen electron will also will in this year's Nobel Prize in chemistry.

Left: in the TEM images at room temperature, lithium dendrite was exposed to air and corrode, electron beam also melt out on a large number of holes; Right: then EM image, under freezing environment keep its original state, shows that the crystalline nano wires with a clear interface.

For materials such as lithium, too, can't use the projection electron microscope to view the dendrite atomic other results. Similar to biological materials, when using TEM at room temperature by electron beam collision, dendrite edge will curl even melting. Took part in the work of Stanford university doctoral YanbinLi says, "tem sample preparation is in the air, but lithium metal corrosion will soon be in the air", "every time we try to use lithium electron microscopy at high magnification, the electrons will 'drill holes in the dendrite, even put it completely melt."

Involved in the study at Stanford university doctoral YanbinLi says, "it's like in the sun with a magnifying glass according to the leaves. But, if you can put the leaf cooling, this problem will be solved: you put the light focusing on leaves, heat is also lost, the leaves will not be damaged. This is what we use electron microscope can achieve the effect of frozen, use imaging on battery materials, difference is very apparent."

So, frozen electron microscope enables the biochemistry into a new era, but also make for the first time, scientists at atomic don't see the complete structure of lithium dendrite. The researchers also found that in carbonate electrolyte in the dendrite along a specific direction for single crystal growth of nanowires. Some of them will appear in the process of "growing" knot, but their crystal structure is still complete.

Another person involved in the study, said Stanford university doctoral yuzhangli also can see the solid electrolyte interface (SEI) membrane, but also reveals the different SEI formed in different electrolytes nanostructures. Because when battery charging and discharging, the same coating will be formed on the metal electrode, so the control of its production and the stability is vital for the efficient use of battery.

Use then EM, scientists were able to observe how electrons from the atoms in the dendrite pop-up, which demonstrates the position of individual atoms (left).Scientists even able to measure the distance between the atoms (YouShangTu), and atomic spacing just to show that they are lithium atoms (upper).

SLAC, according to a press release under the microscope, the researchers use different techniques to observe electrons from the atoms dendrite pop up in a way, revealing the crystal and its film coating the position of individual atoms in the solid electrolyte interface. When they add chemicals is often used to improve battery performance, film coating the atomic structure of solid electrolyte interface becomes more orderly, and it will help to explain why additives may play a role.

"We are very excited, this is the first time that we can get such detailed images of the dendrite, also is the first time we see the solid electrolyte interface membrane layer of nanometer structure."YanbinLi said, "this tool can help us to understand the different electrolyte, respectively, have what kind of role, and why certain electrolyte effect is better than that of the other."

The observed data from these experiments can realize further understanding of the mechanism for the battery failure. Although this work is lithium metal as an example to prove then EM is practical, but this method may also be extended to involve light sensitive materials (such as lithium silicon or sulfur) to other studies. The team also said that they plan to focus on to know more about the chemical properties and structure of the solid electrolyte interface membrane layer.

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