Using cryo-electron microscopy to observe battery materials and interface atomic structure technology revealed

　　[Background introduction]

　　Cryo-EM (Cryo-EM) is an ultra-low temperature freezing sample preparation and transmission technology used for scanning electron microscopy. It can realize direct observation of liquid, semi-liquid and samples sensitive to electron beams, such as biology, polymer materials, etc. After the sample has been processed by ultra-low temperature freezing, fracture, and coating sample preparation (gold spraying/carbon spraying), it can be observed by placing it into the cold stage of the electron microscope (temperature can reach -185°C) through the freezing transport system. Among them, rapid freezing technology can make water in a glassy state at low temperatures, reducing the generation of dendrites without affecting the structure of the sample itself. The freezing transmission system ensures electron microscopy observation of samples at low temperatures. The more classic lithium-ion battery consists of a negative electrode (anode), a positive electrode (cathode), a polymer separator and an organic liquid electrolyte. Although in reality each battery component is macroscopic, many times it is necessary to study it at the micro, nano and atomic scales to explore more properties of the battery. Although transmission electron microscopy (TEM) can be used to study battery materials, imaging is limited to samples that are stable under the electron beam. Moreover, transmission electron microscopy studies cannot maintain the original state of the beam-sensitive cell material after operation, and the material only retains its original state under low temperature conditions.

　　【Achievements Introduction】

　　On October 27, 2017, Beijing time, Science published online an article titled "Atomic structure of sensitive battery materials and interfaces revealed by cryo-electron microscopy" by the team of Cui Yi (corresponding author) of Stanford University in the United States. After cryo-electron microscopy won the Nobel Prize, it is another masterpiece in the application of cryo-electron microscopy. In theory, individual lithium metal atoms and their interfaces can be broken down at the atomic scale. Cui Yi's team realized the use of cryo-electron microscopy to observe the atomic structure of battery materials and interfaces, and observed that dendrites in carbonate-based electrolytes grow into single-crystal nanowires along the <111> (preferred), <110> or <211> directions. . These growth directions may change, but no crystal defects were observed. In addition, the team also revealed different SEI nanostructures formed in different electrolytes. This work provides a simple method to preserve and image the pristine state of beam-sensitive cell materials at the atomic scale, revealing their detailed nanostructure. The relevant data observed from these experiments can enable a complete understanding of battery failure mechanisms. Although this work uses Li metal as an example to demonstrate the utility of cryo-EM, this approach may also be extended to other studies involving beam-sensitive materials such as lithiated silicon or sulfur.

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