In the development process of lithium-ion batteries, we hope to obtain a large amount of useful information to help us conduct data analysis on materials and devices to understand their various aspects of performance. At present, the commonly used research methods for lithium-ion battery materials and devices mainly include characterization methods and electrochemical measurements. The electrochemical test is mainly divided into three parts: (1) charge and discharge test, which mainly looks at the battery's charge and discharge performance and rate; (2) cyclic voltammetry, which mainly looks at the battery's charge and discharge reversibility, peak current, and peak position. ; (3) EIS AC impedance, looking at the resistance and polarization of the battery, etc. The following is a brief introduction to the characterization methods used in comprehensive research on lithium batteries, which are roughly divided into eight parts: composition characterization, morphology characterization, crystal structure characterization, material functional group characterization, observation of material ion transport, and material micromechanics Properties, material surface work functions and other experimental techniques. 1. Composition characterization (1) Inductively coupled plasma (ICP) is used to analyze the constituent elements of substances and the content of various elements. ICP-AES can well meet the needs of routine analysis of primary, secondary and trace elements in laboratories. Compared with ICP-AES, ICP-MS is a newly developed technology in recent years. The instrument is more expensive and the detection limit is lower. Mainly used for trace/ultra-trace analysis. When Aurbac et al. studied the interface problem between the cathode material and the electrolyte, they used ICP to study the solubility of LiCOO2 and LiFePO4 in the electrolyte. By changing parameters such as temperature and the type of lithium salt in the electrolyte, ICP is used to measure the changes in the Co and Fe content in the electrolyte when the parameters are changed, thereby finding the key to reducing the dissolution of the cathode material in the electrolyte [1]. It is worth noting that if the element content is high (for example, higher than 20%), the error will be large when using ICP detection, and other methods should be used in this case. (2) Secondary ion mass spectrometry (SIMS) characterizes the sample composition by emitting hot electrons to ionize argon or oxygen plasma to bombard the surface of the sample and detect the charged ions or ion clusters overflowing from the sample surface. It can image the isotope distribution and characterize the sample composition; detect the longitudinal distribution of the sample composition. Ota et al. used TOF-SIMS technology to study the composition of the SEI film formed on the surface of the graphite negative electrode and LiC0O2 positive electrode after vinyl sulfite was added as an additive to the standard electrolyte. [2]. Castle et al. used SIMS to detect the distribution of Li+ from the electrode surface to the interior of V2O5 after lithium insertion to study the diffusion process of Li+ in V2O5 [3]. (3) X-ray photon spectroscopy (XPS) was gradually developed and perfected in the 1950s and 1960s by Professor KaiSiegbahn and his group at the Institute of Physics, Uppsala University, Sweden. X-ray photoelectron spectroscopy can not only measure the constituent elements on the surface, but also provide information on the chemical state of each element. It has high energy resolution, a certain spatial resolution (currently at the micron scale), and a time resolution (minute level). . It is used to measure the constituent elements of the surface and give information on the chemical state of each element. Hu Yongsheng et al. used XPS to study the composition of SEI generated by VEC on the graphite surface under high voltage. It is mainly composed of C, O, and Li. Combined with FTIR, it was found that the main component is alkoxylithium salt [4]. (4) Electron energy loss spectroscopy (EELS) uses the energy lost by inelastic scattering such as electronic excitation and ionization on the material surface caused by incident electrons. The composition of the element can be obtained by analyzing the location of energy loss. EELS has better resolution of light elements than EDX. The energy resolution is 1 to 2 orders of magnitude higher. Due to the transmission electron microscope technology, the spatial resolution can also reach the order of 10?10m. It can also be used for Test the film thickness and have a certain time resolution. By fitting the EELS spectrum with density functional function (DFT), we can further obtain accurate information on the valence states and even electronic states of elements. AI. When studying nanocomposite electrode materials of iron fluoride and carbon, Sharab et al. used STEM-EELS combined technology to study the chemical element distribution, structural distribution and valence state of iron in nanocomposites of iron fluoride and carbon under different charge and discharge states. distribution[5]. (5) Scanning transmission X-ray microscopy (STXM) is a new spectroscopy microscopy technology based on the third-generation synchrotron radiation light source, high-power laboratory X-ray source, and X-ray focusing technology. Using the principle of transmission X-ray absorption imaging, STXM can achieve three-dimensional imaging with high spatial resolution of tens of nanometers, while also providing certain chemical information. STXM can achieve non-destructive three-dimensional imaging, which can provide key information for understanding complex electrode materials, solid electrolyte materials, separator materials, electrodes and batteries, and these technologies can realize in-situ testing functions. Sun et al. studied that carbon-coated Li4Ti5O12 has better rate performance and cycle performance than before without coating. The author used STXM-XANES and high-resolution TEM to determine that the amorphous carbon layer was uniformly coated on the surface of LTO particles, with a coating thickness of approximately 5nm. Among them, the author obtained the C, Ti, and O distribution of a single LTO particle through STXM, in which C is coated on the particle surface [6]. (6) X-ray absorption near-edge spectroscopy (XANES) is a technique for calibrating elements and their valence states. The same element in the same valence state in different compounds has high absorption of X-rays of specific energy, which we call near-edge absorption spectrum. In the field of lithium batteries, XAS is mainly used for charge transfer research, such as the price change problem of transition metals in cathode materials. Kobayashi et al. used XANES to study LiNi0.80Co0.15Al0.05O2 cathode material. XANES detected Li2Co3 and other additional cubic phase impurities on the particle surface [7]. (7) X-ray fluorescence spectroscopy (XRF) is a method that uses primary X-ray photons or other microscopic ions to excite atoms in the substance to be measured, causing them to produce fluorescence (secondary X-rays) to conduct material composition analysis and chemical state research. According to different excitation, dispersion and detection methods, it is divided into X-ray spectroscopy (wavelength dispersion) and X-ray energy spectroscopy (energy dispersion). According to different dispersion modes, X-ray fluorescence analyzers are divided into X-ray fluorescence spectrometers (wavelength dispersion) and X-ray fluorescence spectrometers (energy dispersion). XRF is widely used in the industry to analyze the main components and impurity elements of lithium-ion battery materials. The detection limit for some elements can reach the order of 10-9. 2. Morphology characterization (1) Scanning electron microscope (SEM) collects secondary electron information on the surface of the sample to reflect the surface morphology and roughness of the sample. SEM with EDS accessories can further analyze element types, distribution and semi-quantitative analysis. Elemental content. Although the resolution of SEM is much smaller than that of TEM, it is still the most basic tool for characterizing the particle size and surface morphology of battery materials. Li Wenjun et al. used a sealed transfer box to transfer samples and redesigned a scanning electron microscope for metallic lithium electrodes. The sample holder was used to study the formation process of surface pores and dendrites during the intercalation and extraction process of Li in the metallic lithium electrode [8]. (2) The morphology and characteristics of the surface and interface of transmission electron microscopy (TEM) materials are often introduced in literature on surface coating and surface SEI. TEM can also be equipped with energy spectrum accessories to analyze the type and distribution of elements. Compared with SEM, TEM can observe smaller particles, and high-resolution transmission electron microscopy can observe the crystal lattice. The function of in-situ TEM is more powerful. In-situ cells are assembled in the TEM electron microscope cavity, and at the same time, with the help of TEM's high Resolution characteristics, real-time measurement and analysis of the morphology and structural evolution of battery materials during cycling. Huang Jianyu and others used an in-situ sample rod to conduct an in-situ study on the morphology and structural evolution of SnO2 during the process of inserting and removing lithium in ionic liquids. representation. Subsequently, they improved the device for the TEM in-situ battery experiment and used lithium oxide naturally produced on metal Li as the electrolyte to replace the originally used ionic liquid, which improved the stability of the experiment and better protected the electron microscope cavity. body[9,10]. Extended reading: Academic dry stuff│The role of in-situ transmission electron microscopy in the study of gas-liquid phase chemical reactions of materials. (3) Atomic force microscopy (AFM) observation of nanoscale flat surfaces is often used in the characterization of carbon materials. 3. Crystal structure characterization (1) X-ray diffraction technology (XRD) Through XRD, the crystal structure, crystallinity, stress, crystal orientation, superstructure and other information of the material can be obtained. It can also reflect the average crystal structure properties of the bulk material, and the average The unit cell structure parameters change, and the atomic occupancy information can be obtained after fitting. Thurston et al. applied in-situ XRD technology to lithium-ion batteries for the first time. By using hard X-rays from synchrotron radiation sources to detect bulk electrode materials in in-situ battery devices, the results of lattice expansion and contraction, phase changes, and multiphase formation can be intuitively observed. (2) Extended X-ray absorption fine spectroscopy (EXAFS) is a technology that reflects the differences and changes in the local structure of the material by absorbing some incident photons of specific energy through the interaction between X-rays and the sample's electrons. It has certain energy and time resolution capabilities. It mainly obtains information such as radial distribution, bond length, order, coordination number and other information in the crystal structure; usually a strong light source of a synchrotron radiation light source is required to implement EXAFS experiments. Jung et al. studied the SnOx/CuOx-embedded carbon nanonegative electrode by using EXAFS analysis. The electrochemical properties of the material indicate that the carbon nanofibers embedded with SnOx/CuOx have a disordered structure, forming a special distribution of SnOx particles, which leads to improved electrochemical performance [12]. (3) Neutron Diffraction (ND) When there are larger atoms in the lithium-ion battery material, X-rays will be difficult to accurately detect the lithium ion occupation. Neutrons are sensitive to lithium in lithium-ion battery materials, so neutron diffraction plays an important role in the research of lithium-ion battery materials. Arbi et al. determined the Li+ occupancy in LATP, the solid electrolyte material for lithium ion batteries, through neutron diffraction [13]. (4) Nuclear Magnetic Resonance (NMR) NMR has high energy resolution and spatial resolution. It can detect chemical information in materials and image them, detect dendrite reactions, measure lithium ion self-diffusion coefficients, and study phase transformation reactions inside particles. Gray et al. have conducted a large amount of research work on NMR in lithium-ion battery cathode materials. It shows that rich chemical information and local charge order and disorder information can be obtained from the NMR spectrum of the cathode material, and paramagnetic or metallic materials can be detected, and the weak changes in the electronic structure caused by doping can also be detected to reflect Element chemical state information. In addition, combined with isotope tracing, side reactions in the battery can also be studied [14]. (5) Purpose of spherical aberration corrected scanning transmission electron microscope (STEM): used to observe the arrangement of atoms, atomic-level real-space imaging, and can clearly see the crystal lattice and atomic occupation; it has high requirements on samples; it can realize in-situ experiments Oshima et al. used a spherical aberration-corrected scanning transmission microscope (ABF-STEM) with annular brightfield imaging to observe the atomic arrangement of Li, V, and O in Li2VO4 in real space [15]. (6) Raman used Raman spectroscopy to study the crystal structure of LiC0O2 in the early days. There are two Raman active modes in LiC0O2, the peak of Co-O stretching vibration Alg and the peak of O-Co-O bending vibration Eg [16]. It is also often used to characterize the degree of graphitization of carbon materials in lithium-ion batteries. 4. Characterization of functional groups Functional groups, also known as functional groups and functional groups, are atoms and atomic groups that determine the chemical properties of organic compounds. Common functional groups include hydrocarbon groups, halogen-containing substituents, oxygen-containing functional groups, nitrogen-containing functional groups, and phosphorus- and sulfur-containing functional groups. (1) Raman spectroscopy (RS) was discovered by the Indian physicist Raman in an experiment in which monochromatic light irradiated liquid benzene and scattered spectral lines with different frequencies from the incident light. From Raman spectrum, molecular vibration and rotation can be obtained Information. Raman spectroscopy is suitable for molecules with less polar symmetric structures. For example, for molecules with fully symmetric vibration modes, under the action of excitation photons, molecular polarization will occur, resulting in Raman activity, which is very strong. When characterizing lithium-ion battery electrode materials, due to the disassembly and transfer process, it is inevitable that human or atmospheric factors will cause interference to the electrode materials. Therefore, in-situ technology is used together with Raman spectroscopy for the characterization of electrode materials. Raman spectroscopy is very sensitive to material structural symmetry, coordination and oxidation state, and can be used to measure transition metal oxides. For cases where the sensitivity of the Raman spectrum is not enough, some metals such as Au and Ag can be used to treat the sample surface. Due to the enhancement of the electromagnetic field close to the sample surface on the conductor surface or sol of these special metals, the Raman spectrum signal of the adsorbed molecules is enhanced. , called surface-enhanced Raman scattering (SERS). Peng et al. used SERS to confirm that the intermediate product LiO2 does exist during the charge and discharge process of lithium-air batteries, but LiO2 was not observed during the charging process, indicating that the discharge process of lithium-air batteries is a two-step reaction process, with LiO2 As an intermediate product, and the charging process is an asymmetric one-step reaction, the direct decomposition of Li2O2 is difficult due to the poor conductivity of Li2O2, which is also the reason why the charging polarization is greater than the discharge polarization [17]. (2) Fourier transform infrared spectroscopy (FT-IS) uses a similar band to Raman. Many molecules with weak Raman activity can be characterized using infrared spectroscopy. Infrared spectroscopy can also be used as a supplement to Raman spectroscopy. , infrared spectrum is also called molecular vibration spectrum, which belongs to molecular absorption spectrum. The infrared light area can be divided into three areas according to the different wavelengths of the infrared light area: ① The near-infrared area, that is, the over-frequency area, refers to the area with a wave number above 4000cm?1, which mainly measures O—H, C—H, and N. —Frequency doubling absorption of H bonds; ② The mid-infrared region, that is, the basic vibration region, with a wave number ranging from 400 to 4000 cm?1, is also the area with the most research and application, mainly measuring molecular vibrations and accompanying vibrations; ③ The far-infrared region, that is, molecules The vibration area refers to the area where the wave number is below 400cm?1. The main measurement is the rotation information of the molecules. Since water is a very polar molecule and its infrared absorption is very strong, the infrared spectrum cannot be measured directly from aqueous solutions. Usually, infrared spectrum samples need to be ground into KBr pellets. Usually infrared spectrum data needs to be processed by Fourier transform, so the infrared spectrometer and Fourier change processor are used together, which is called Fourier transform infrared spectroscopy (FITR). In the research of lithium-ion battery electrolyte, there is a lot of work using infrared spectroscopy. Mozhzhukhina et al. used infrared spectroscopy to study the stability of dimethyl sulfoxide, a commonly used solvent for lithium-air battery electrolytes, and found that the failure of DMSO in lithium-air batteries was mainly due to the attack of superoxide ions (O2-). The signal of SO2 is observed in the infrared spectrum. This reaction is unavoidable. Even at a potential as low as 3.5V, DMSO cannot be stable [18]. (3) Deep ultraviolet spectroscopy (UV) is mainly used for the analysis of characteristic functional groups in solutions. 5. The phenomenon of ion transport in materials (1) Neutron diffraction (ND) combined with the maximum entropy simulation analysis method can obtain information about the Li+ diffusion channel in the electrode material [19] (2) Nuclear Magnetic Resonance (NMR) measured the changes in the nuclear magnetic resonance spectra of some elements with the heat treatment temperature, The self-diffusion coefficient of Li+ was measured. Gobet et al. used pulsed gradient field NMR technology to characterize the changes in 1H, 6.7Li, and 31P nuclear magnetic resonance spectra in β-Li3PS4 solids with the heat treatment temperature. The self-diffusion coefficient of Li+ was measured, which is consistent with the previously reported Li+ conductivity is of the same order of magnitude [20]. (3) Atomic force microscope series technology (AFM) uses the van der Waals force between the tip atoms and the sample surface atoms to feedback the sample surface morphology information. AFM has high spatial resolution (about 0.1?) and time resolution. Since it does not detect energy, it does not have energy resolution. It was first used in lithium-ion battery research in 1996. Zhu et al. used solid electrolytes to pass magnetic control. A full battery was prepared by sputtering, and then the changes in the surface morphology of the Ti02 negative electrode with the loaded triangular waveform voltage were detected by insituAFM [21]. 6. Material micromechanical properties Battery materials are generally polycrystalline, and there is stress inside the particles. During the charging and discharging process, the intercalation and extraction of lithium will cause lattice expansion and contraction, resulting in local stress changes, which will further cause volume changes of particles and electrodes, stress release, lattice stacking changes, and cracks in particles and electrode layers. (1) Atomic force microscope series technology (AFM) and nanoimprint technology, as well as combined testing with nanoprobes and STM probes in TEM to observe morphological characteristics, can measure in-situ mechanical properties and stress when using solid-state batteries Jeong used AFM to observe in situ the thickness of the surface film formed on the HOPG basal surface during the cyclic voltammetry process [22]. (2) SPM probe purpose: to study the mechanical properties of the SEI film in contact mode, using constant force to probe When a needle is inserted into the membrane, the response curve of the penetration depth with force can be obtained, and further information such as Young's modulus can be obtained [23]. 7. Material surface work function (1) Kelvin Probe Force Microscopy (KPFM) obtains the potential distribution on the sample surface by detecting the force exerted by the surface potential on the probe. Agpure et al. used Kelvin Probe Microscopy (KPFM) to measure the aging process. The surface potential of lithium-ion batteries, the aged battery has a lower surface potential, which can be attributed to the influence of particle size, phase change of the surface layer, and the physical and chemical properties of the new deposits [24]. (2) Electronic holography measured the changes in electric potential during the charging and discharging process of all-solid-state lithium-ion batteries, and obtained the distribution of electric potential at the interface under different systems. The Yamamoto group directly observed the electric potential during the charging and discharging process of all-solid-state lithium-ion batteries through electronic holography. The changes in the potential distribution at the interface under different systems were successfully obtained, verifying the conclusion that the potential is mainly distributed at the cathode/electrolyte interface [25]. (3) Optical emission electron microscopy (PEEM) is used to obtain the distribution of surface potential: In addition to the above characterization methods, some other characterization techniques will also be used in actual experiments, such as: (1) Angle-resolved photoelectron spectroscopy ( ARPES), purpose: to directly measure the energy band structure of materials; (2) DFT calculation, purpose: to obtain the electronic structure of the material; (3) Electron flooding technology (PAT), purpose: to measure defect structure and electronic structure; (4) Luther Backscattering (RBS), use: can measure the composition of thin films; (5) Resonant inelastic X-ray scattering (RIXS), use: study the magnetic interaction between atoms; (6) Auger electron imaging technology (AES), use: Directly detect the spatial distribution of lithium elements on the surface of particles and electrodes, and conduct elemental depth analysis through Ar ion ablation. Of course, electrochemical characterization is also very important when studying lithium batteries.1) Neutron diffraction (ND) combined with the maximum entropy simulation analysis method can obtain information about the Li+ diffusion channel in the electrode material [19] (2) Nuclear Magnetic Resonance (NMR) measured the changes in the nuclear magnetic resonance spectra of some elements with the heat treatment temperature, The self-diffusion coefficient of Li+ was measured. Gobet et al. used pulsed gradient field NMR technology to characterize the changes in 1H, 6.7Li, and 31P nuclear magnetic resonance spectra in β-Li3PS4 solids with the heat treatment temperature. The self-diffusion coefficient of Li+ was measured, which is consistent with the previously reported Li+ conductivity is of the same order of magnitude [20]. (3) Atomic force microscope series technology (AFM) uses the van der Waals force between the tip atoms and the sample surface atoms to feedback the sample surface morphology information. AFM has high spatial resolution (about 0.1?) and time resolution. Since it does not detect energy, it does not have energy resolution. It was first used in lithium-ion battery research in 1996. Zhu et al. used solid electrolytes to pass magnetic control. A full battery was prepared by sputtering, and then the changes in the surface morphology of the Ti02 negative electrode with the loaded triangular waveform voltage were detected by insituAFM [21]. 6. Material micromechanical properties Battery materials are generally polycrystalline, and there is stress inside the particles. During the charging and discharging process, the intercalation and extraction of lithium will cause lattice expansion and contraction, resulting in local stress changes, which will further cause volume changes of particles and electrodes, stress release, lattice stacking changes, and cracks in particles and electrode layers. (1) Atomic force microscope series technology (AFM) and nanoimprint technology, as well as combined testing with nanoprobes and STM probes in TEM to observe morphological characteristics, can measure in-situ mechanical properties and stress when using solid-state batteries Jeong used AFM to observe in situ the thickness of the surface film formed on the HOPG basal surface during the cyclic voltammetry process [22]. (2) SPM probe purpose: to study the mechanical properties of the SEI film in contact mode, using constant force to probe When a needle is inserted into the membrane, the response curve of the penetration depth with force can be obtained, and further information such as Young's modulus can be obtained [23]. 7. Material surface work function (1) Kelvin Probe Force Microscopy (KPFM) obtains the potential distribution on the sample surface by detecting the force exerted by the surface potential on the probe. Agpure et al. used Kelvin Probe Microscopy (KPFM) to measure the aging process. The surface potential of lithium-ion batteries, the aged battery has a lower surface potential, which can be attributed to the influence of particle size, phase change of the surface layer, and the physical and chemical properties of the new deposits [24]. (2) Electronic holography measured the changes in electric potential during the charging and discharging process of all-solid-state lithium-ion batteries, and obtained the distribution of electric potential at the interface under different systems. The Yamamoto group directly observed the electric potential during the charging and discharging process of all-solid-state lithium-ion batteries through electronic holography. The changes in the potential distribution at the interface under different systems were successfully obtained, verifying the conclusion that the potential is mainly distributed at the cathode/electrolyte interface [25]. (3) Optical emission electron microscopy (PEEM) is used to obtain the distribution of surface potential: In addition to the above characterization methods, some other characterization techniques will also be used in actual experiments, such as: (1) Angle-resolved photoelectron spectroscopy ( ARPES), purpose: to directly measure the energy band structure of materials; (2) DFT calculation, purpose: to obtain the electronic structure of the material; (3) Electron flooding technology (PAT), purpose: to measure defect structure and electronic structure; (4) Luther Backscattering (RBS), use: can measure the composition of thin films; (5) Resonant inelastic X-ray scattering (RIXS), use: study the magnetic interaction between atoms; (6) Auger electron imaging technology (AES), use: Directly detect the spatial distribution of lithium elements on the surface of particles and electrodes, and conduct elemental depth analysis through Ar ion ablation. Of course, electrochemical characterization is also very important when studying lithium batteries.

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