12V27A battery.In-situ characterization technology of multi-scale structures of lithium-ion batteries

　　With the development of human society, global environmental and energy problems have become increasingly severe, and the development of clean, safe, and efficient new energy storage technologies has become the focus of researchers. Among all energy storage methods, lithium-ion batteries have the advantages of high energy density, low self-discharge, long cycle life, and environmental friendliness. They have been widely used in portable electronic devices such as mobile phones and tablet computers, and have achieved great commercial success. However, in recent years, with the rapid development of the new energy automobile industry, currently commercialized lithium-ion batteries are no longer able to meet the hard demand of the market. Compared with traditional fuel vehicles, there is still a big gap between pure electric vehicles and traditional fuel vehicles in terms of performance, safety, battery life and other issues. Therefore, it is urgent to develop high-performance lithium-ion batteries with high specific capacity, long cycle life and stable structure.

　　The electrochemical performance of lithium-ion batteries depends on the dynamic coupling of internal micro and macro structural changes. The structural stability of positive and negative electrode materials during the process of lithium ion insertion and extraction has always been the key to restricting further upgrades of lithium-ion batteries. Therefore, achieving structural characterization of electrode materials during charge and discharge is crucial to the development and design of high-performance lithium-ion batteries. However, it has been difficult to characterize the structure of battery materials in their working state. On the one hand, electrochemical reaction is a non-equilibrium process, in which there are various complex physical and chemical changes, which greatly increases the difficulty of material structure characterization and analysis; on the other hand, these structural changes occur at different length scales Within the battery, many microscopic and macroscopic structural changes are coupled with each other, such as lattice distortion and pole piece cracks, phase structure transformations and side reactions, etc., which together determine the final performance of the battery. Over the past few decades, various time-resolved in situ characterization techniques have been developed and applied in battery research. Among them, high-energy synchrotron radiation X-rays and high-flux pulsed neutrons have gradually developed into powerful tools for characterizing multi-scale structural changes in recent years due to their complementary scattering, spectral and imaging capabilities, and have promoted the development of lithium-ion battery research and industry. Rapid development.

　　Recently, Liu Qi's team from the Department of Physics, City University of Hong Kong, based on the interaction mechanism between X-rays/neutrons and materials, systematically introduced various synchrotron radiation and neutron in-situ characterization methods, in-situ equipment and battery design, and their Applications in the field of lithium-ion battery research (Figure 1). Neutrons are neutral subatomic particles that interact directly with atomic nuclei; in contrast, X-rays are electromagnetic waves that interact with electrons outside the nucleus of atoms by generating an electromagnetic field. Although the mechanisms of action are different, elastic scattering and inelastic scattering occur when X-rays and neutrons pass through matter. In addition, photons with specific energy will also excite various electronic states, achieving transitions between occupied and non-occupied states by absorbing and emitting photons. The coupling of these interactions with the intrinsic properties of materials has gradually opened the door to the world of material microstructures.

　　For example, elastic scattering of X-rays and neutrons can produce small-angle scattering (SAS), diffraction (XRD or neutrondiffraction) and total scattering (PDF) patterns, which can be used to analyze structural changes in different scale ranges; on the other hand, hard X-ray X-ray and soft X-ray absorption (XAS), emission spectroscopy (XES), and their corresponding imaging techniques (TXM, etc.) can be used to characterize the electronic and bonding states around specific elements. After introducing the above characterization mechanism in detail, the author systematically elaborated on the design of in-situ batteries and in-situ devices and corresponding research examples. Finally, the author gives a technical outlook for the application of synchrotron radiation and neutron in-situ characterization technology in the battery field.

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