A method and system for measuring strain distribution of a battery anode material

Abstract

The present application relates to the technical field of battery internal microstructure measurement, and particularly relates to a kind of battery negative electrode material strain distribution measurement method and system, method includes: sample preparation, thin slice sample is prepared by FIB;Data acquisition, four-dimensional diffraction data set is obtained using 4D-STEM;Data analysis, local lattice vector is calculated and compared with reference lattice, and strain tensor is obtained;Result output, strain distribution diagram of nanoscale spatial resolution is drawn.The system includes corresponding module.The present application solves the problems of insufficient spatial resolution, inadaptation to complex negative electrode system and lack of adaptive micro-nano processing method in the prior art, and realizes high-precision quantitative measurement of graphite and silicon-based battery negative electrode strain distribution.

Description

Technical Field

[0001] This invention relates to the field of battery internal microstructure measurement technology, and in particular to a method and system for measuring the strain distribution of battery negative electrode materials. Background Technology

[0002] Lithium-ion batteries are crucial power batteries in new energy vehicles, consumer electronics, and energy storage systems. The volume expansion of their internal active materials is a key issue affecting battery performance, safety, and cycle life. Currently, lithium-ion batteries widely use carbon-based and silicon-based materials for lithium storage in their negative electrodes. During charging and discharging, lithium-ion insertion, extraction, or alloying reactions occur in the negative electrode material, leading to microstructural changes such as changes in interlayer spacing and volume expansion. This accumulated and transmitted expansion stress deteriorates with each charge-discharge cycle, directly impacting key indicators such as capacity retention, cycle life, and power performance.

[0003] Currently, strain testing is conducted at two levels. First, at the macroscopic level, strain manifests as changes in length and curvature in a specific direction. Common methods include resistance strain gauges, fiber optic strain sensors, and laser interferometry to detect macroscopic deformation and overall strain of an object. For example, the literature Xie.HM, Yang.W, Kang.YL, et al., In-situ Strain Field Measurement and Mechano-electro-chemical Analysis of Graphite Electrodes Via Fluorescence Digital Image Correlation [J]. Experimental Mechanics, 2021, 61:1249-1260, reports the use of fluorescence digital imaging to detect the strain field of a graphite electrode, obtaining the macroscopic deformation of the electrode caused by the expansion due to lithium ion embedding in the graphite layer. The electrode sheet size was 8 mm. Second, at the microscopic level, strain manifests as changes in the material's crystal structure, including widening or narrowing of the lattice spacing, band axis tilting, and bending and slippage of crystal planes. Currently, the main approach is to utilize high-throughput, high-energy X-ray beams to provide lattice structure information of samples through reciprocal space diffraction patterns. This can be used to study the lattice spacing variations and volume expansion behavior of various material systems, including graphite. For example, the literature TJ Marrow, D. Liu, SM Barhli, L. Saucedo Mora, Ye. Vertyagina, DM Collins, C. Reinhard, S. Kabra, PEJ Flewitt, DJ Smith, In situ measurement of the strains within a mechanically loaded polygranular graphite [J], 2016, 96:285-302, reports the use of neutron diffraction and X-ray diffraction (XRD) methods to study the strain response of graphite under tensile and bending loads. Transmission electron microscopy based on spherical aberration correction has atomic resolution, and geometrical phase analysis (GPA) directly probes the atomic images of the sample, locates atomic positions in real space, and analyzes lattice variations to obtain the strain distribution.For example, the literature Li.YH, Han.B, Yang.X., et al., Single-Dislocation Phonons: Atomic-Scale Measurement and Their Thermal Properties [J]. Chinese Physical Society and IOP Publishing Ltd, 2025, 42, 6, reports the strain distribution in the region surrounding a single dislocation nucleus at the silicon-germanium interface.

[0004] Research on existing strain detection methods reveals that macroscopic methods detect macroscopic deformation of objects, i.e., the overall expansion rate and bending amount, which is not the same concept as the structural changes of materials inside the battery negative electrode at the lattice level. Furthermore, macroscopic methods typically use single objects larger than millimeters, making it impossible to detect micron-sized particles. Diffraction methods, such as XRD, lack sufficient spatial resolution, providing only information on the overall structural changes of the sample and lacking results on the strain distribution in specific regions. This limits the detection of specific expansion or bending behavior inside the battery, particularly the correlation between its internal composition and structure, thus hindering the understanding of its volume expansion mechanism. High spatial resolution transmission electron microscopy (GPA) methods are based on atomic imaging, therefore only suitable for small-scale analysis (within tens of nanometers). Atomic resolution imaging also has stringent requirements for samples, requiring the entire sample to be a single phase and a positive band axis, making this method unsuitable for material systems with complex crystal phases. In summary, existing technologies cannot measure the internal expansion, amorphization, and lattice changes of the battery anode caused by charging and discharging. This is because although the process occurs at the nanoscale inside the anode, the entire micron-sized particle undergoes corresponding transformations. Existing measurement and analysis methods either lack sufficient spatial resolution, are difficult to study anode systems with numerous crystal phases and complex structures, or lack a micro / nano fabrication method that is compatible with the measurement methods and effectively exposes the internal structure of the sample. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a method and system for measuring the strain distribution of battery anode materials, so as to solve the problems of insufficient spatial resolution, incompatibility with anode systems with numerous crystal phases and complex structures, and lack of suitable micro-nano fabrication methods for effectively exposing the internal structure of samples in existing measurement technologies.

[0006] To achieve the above objectives, the present invention provides a method for measuring the strain distribution of a battery negative electrode material, comprising the following steps: Sample preparation involves disassembling the battery after state parameter testing to obtain the negative electrode sheet. The negative electrode sheet is then extracted and etched using a focused ion beam to obtain a thin sheet sample. Data acquisition involves performing 4D-STEM scanning on the thin-film sample to obtain a complete electron diffraction pattern for each scanning point, resulting in a four-dimensional dataset. Data analysis involves calculating local lattice vectors in the electron diffraction patterns of the four-dimensional dataset, and comparing the calculation results with the unstrained lattice vectors to obtain the strain tensor of the scanning point. The results are output, and based on the strain tensor, a strain distribution map in the strain space is plotted to obtain a strain distribution map with nanometer-level spatial resolution.

[0007] The present invention also provides a measurement system for implementing the measurement method, comprising: A sample preparation module is used to prepare the aforementioned thin-film sample; The data acquisition module is used to perform 4D-STEM scanning on the thin-film sample to obtain a four-dimensional dataset; The data analysis module is used to analyze the crystal structure information of the four-dimensional dataset, compare and calculate the crystal structure information, and obtain the strain tensor. The results output module plots the strain distribution map of the strain tensor and outputs a strain distribution map with nanometer-level spatial resolution.

[0008] The beneficial effects of this invention are as follows: By disassembling the tested battery, a negative electrode sheet containing negative electrode particles is obtained. Then, the negative electrode material is cut into thin slices suitable for transmission electron microscopy in a scanning electron beam focused ion beam microscope (SEM-FIB). A two-dimensional spatial region is then scanned using four-dimensional scanning transmission electron microscopy (4D-STEM) to obtain an electron diffraction pattern dataset with nanometer-level spatial resolution. Finally, by strain analysis of the electron diffraction pattern corresponding to each scanning point, the phase distribution and strain distribution of the region with nanometer-level spatial resolution are obtained.

[0009] This invention provides a quantitative method for detecting strain distribution, enabling quantitative comparison of strain detection results from different batteries. This allows for the determination of the irreversible expansion and bending behavior of negative electrode particles during cycling. The process can be performed on batteries from the same batch with the same number of cycles but different states of charge (SOC), and the magnitude of strain can be quantitatively compared to detect the graphite expansion and bending behavior during a single charge-discharge cycle. Similarly, the process can be performed on batteries from the same batch with different cycle counts (all with a uniform SOC of zero) to quantitatively compare the magnitude of strain, thus enabling the detection of how the number of charge-discharge cycles affects the structure of the negative electrode particles after volume expansion, thus influencing the structure of the negative electrode and the electrode structure. Not only can the strain distribution be obtained, but crystal orientation distribution maps can also be acquired simultaneously. More importantly, this method can directly correlate quantitative strain information at the nanoscale with macroscopic electrochemical parameters of the battery (such as cycle count, SOC, SOH, and cutoff voltage), providing a powerful experimental tool for establishing the structure-property relationship between "electrochemical history, micromechanical response, and macroscopic performance degradation." Attached Figure Description

[0010] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a flowchart of the measurement method according to an embodiment of the present invention; Figure 2 This is a block diagram of the measurement system according to an embodiment of the present invention; Figure 3 This is a 4D-STEM scan of the real space inside a graphite crystal according to Embodiment 1 of the present invention; Figure 4 This is a crystal orientation distribution diagram of the graphite crystal in Embodiment 1 of the present invention; Figure 5 This is a stress distribution diagram of graphite crystals after cycling in Embodiment 1 of the present invention; Figure 6 This is a 4D-STEM scan of the real space inside a silicon crystal according to Embodiment 2 of the present invention; Figure 7 Crystal orientation distribution diagram of silicon crystal in Embodiment 2 of the present invention; Figure 8 This is a stress distribution diagram of the silicon crystal after cycling in Embodiment 2 of the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0013] Terminology Explanation (Parameters, Industry-Common Terms) 4D-STEM: Four-Dimensional Scanning Transmission Electron Microscopy (4D-STEM) is a materials science technique that uses pixelated electron detectors to capture the complete electron diffraction pattern at each location as the electron beam scans the sample in a transmission electron microscope. This creates a four-dimensional dataset (two dimensions in real space are used for scanning, and two dimensions in the diffraction pattern are used for the diffraction pattern itself). This allows for advanced analysis of atomic structure, including visualizing atoms, mapping crystal orientation and strain distribution, and identifying electric and magnetic fields.

[0014] FIB (Focused Ion Beam) technology is an advanced technique that uses a focused, high-intensity ion beam (usually gallium or xenon ions) to precisely process, deposit, cut, and analyze materials. FIB technology is often integrated with scanning electron microscopy (SEM) in a dual-beam system for high-precision transmission electron microscopy sample preparation, fault analysis, and integrated circuit modification at the nanoscale, and has wide applications in semiconductors, materials science, and biology.

[0015] SOC: State of Charge (SOC) refers to the percentage of usable charge remaining in a battery relative to its nominal capacity. It is an important monitoring metric for the battery management system (BMS), which uses the SOC value to control the battery's operating state. The remaining charge of a battery reflects its state of charge.

[0016] SOH: State of Health (SOH) can be understood as the percentage of the battery's current capacity relative to its factory-set capacity.

[0017] Spatial resolution refers to the minimum distance between two adjacent features that can be distinguished in an image. The smaller the spatial resolution value, the clearer the details that can be identified, and the stronger the ability to identify objects. In the field of scanning electron imaging, when the scanning pixels are sufficiently dense, the spatial resolution is determined by the electron beam spot size.

[0018] Cut-off voltage: The lowest / highest voltage that the battery is allowed to rise / fall to during charging and discharging.

[0019] To address the problem of measuring strain at the nanoscale microstructure of battery internal structures in existing technologies, this invention provides a method for measuring the strain distribution of battery negative electrode materials, comprising the following steps: Sample preparation involves disassembling the battery after state parameter testing to obtain the negative electrode sheet. The negative electrode sheet is then extracted and etched using a focused ion beam to obtain a thin sheet sample. Data acquisition involves performing 4D-STEM scanning on the thin-film sample to obtain a complete electron diffraction pattern for each scanning point, resulting in a four-dimensional dataset. Data analysis involves calculating local lattice vectors in the electron diffraction patterns of the four-dimensional dataset, and comparing the calculation results with the unstrained lattice vectors to obtain the strain tensor of the scanning point. The results are output, and based on the strain tensor, a strain distribution map in the strain space is plotted to obtain a strain distribution map with nanometer-level spatial resolution.

[0020] As one possible implementation, the extraction and etching of the target sample on the negative electrode sheet using a focused ion beam includes the following steps: A sampling area is selected on the negative electrode sheet of the battery. After the sampling area is protected by a deposition layer using a focused ion beam, it is then cut and sampled to obtain a small sample. The small sample was rigidly connected to the support structure of the TEM, and then the small sample was etched with a focused ion beam to a thickness of less than 50 nm.

[0021] In one possible implementation, the voltage of the focused ion beam is 10~30kV. In another possible implementation, performing 4D-STEM scanning on the thin-film sample to obtain a complete electron diffraction pattern for each scanning point includes the following steps: Multiple target particle regions are selected in the thin-film sample, and 4D-STEM scanning is performed on the target particle regions to obtain a complete electron diffraction pattern for each scanning point. The electron diffraction pattern contains real space two-dimensional position information and reciprocal space two-dimensional diffraction information.

[0022] As one possible implementation, the electron beam convergence angle of the 4D-STEM scan is 1~5mrad, and the scanning step size is ≤1nm.

[0023] As one possible implementation method, the data analysis includes the following steps: Identify the electron diffraction pattern of each scanning point and locate the position of the Bragg diffraction disk; Based on the location, the average reciprocal lattice vector of the scanning point is determined, and the crystal orientation corresponding to the scanning point is determined to obtain crystal structure information. Based on the crystal structure information, the unstrained reference lattice is determined. The strain tensor of each scan point is calculated by comparing the deviation of the local lattice vector of each scan point with the reference lattice. The strain tensor contains at least two normal strain components and one tangential strain component.

[0024] As one possible implementation, the state parameters include at least one of cycle number, state of charge, health state, and charge / discharge cutoff voltage.

[0025] As one possible implementation, the negative electrode material of the battery is graphite or silicon-based material.

[0026] Meanwhile, this embodiment of the invention also provides a measurement system for implementing the measurement method, comprising: A sample preparation module is used to prepare the aforementioned thin-film sample; The data acquisition module is used to perform 4D-STEM scanning on the thin-film sample to obtain a four-dimensional dataset; The data analysis module is used to analyze the crystal structure information of the four-dimensional dataset, compare and calculate the crystal structure information, and obtain the strain tensor. The results output module plots the strain distribution map of the strain tensor and outputs a strain distribution map with nanometer-level spatial resolution.

[0027] As one possible implementation, the result output module further includes a visualization unit for simultaneously displaying the strain distribution map and the 4D-STEM scan image.

[0028] The principle of this invention is to process the negative electrode of the battery to a thickness of about 50 nm. By utilizing the nanoscale electron probe and electron diffraction capabilities of a scanning transmission electron microscope, an electron diffraction pattern corresponding to each pixel is acquired by scanning a series of graphite regions at the hundred-nanometer scale. Based on the inverse relationship between the spacing of the Bragg diffraction disks in the diffraction pattern and the interatomic spacing in real space, the local strain is calculated and a visualized strain field distribution map is obtained, thereby determining the deformation state such as expansion and bending at various locations and analyzing the relationship between microstructure and strain.

[0029] Utilizing 4D-STEM technology, a full-field, scanning measurement of hundreds of nanometer regions within micron-sized anode particles was achieved. By analyzing diffraction information, the strain tensor was directly calculated, yielding a quantitative strain distribution map with a spatial resolution of 1–2 nanometers, overcoming the limitations of insufficient spatial resolution in XRD and the limited applicability of GPA. The method is applicable to various anode material systems, including graphite and silicon. Even for partially amorphous silicon anodes, local strain can still be analyzed using residual lattice diffraction information, demonstrating broad applicability.

[0030] As a specific embodiment 1, the present invention provides a method for measuring the strain distribution of a battery negative electrode material, such as... Figure 1 The process includes the following steps: 101 Sample preparation: The battery that has undergone state parameter testing is disassembled to obtain the negative electrode sheet. The negative electrode sheet is then extracted and etched using a focused ion beam to obtain a thin sheet sample.

[0031] Specifically, the battery that has undergone state parameter testing is disassembled to obtain the battery negative electrode sheet containing negative electrode particles. A sampling area is selected on the battery negative electrode sheet, and a focused ion beam is used to deposit a protective layer on the sampling area before cutting and sampling to obtain small samples.

[0032] More specifically, taking graphite anode material as an example, the tested battery is disassembled to obtain the battery anode sheet containing graphite particles. The battery should have a complete test report, including the battery's SOC and SOH parameters, so that the battery parameter information can be correlated with strain information in subsequent analysis. The entire battery disassembly process is carried out in a glove box filled with argon as a protective gas to maintain the battery's original state as much as possible and prevent chemical reactions between the battery components and oxygen or water vapor in the air. The disassembled battery anode sheet is cut into small samples of 0.5mm × 0.5mm, glued to the sample stage of the SEM-FIB with conductive adhesive, and transferred from the glove box to the SEM-FIB microscope chamber using a sample transfer rod with an isolation chamber, again without contact with air during the process.

[0033] On the negative electrode sheet of the battery with graphite particles attached to its surface, a sampling area with a feature size of 30µm × 5µm is selected. A Pt protective layer is then deposited using focused ion beam (FIP) induction deposition. The voltage of the FIP is 10–30 kV; 30 kV is used in this embodiment. The thickness of the protective layer is not less than 2µm. Above and below the sampling area, pits with a depth exceeding 15µm are etched using the FIP. The vertical width of both etched areas is approximately 20µm, and the horizontal width exceeds the width of the sampling area. The FIP etching is used to smooth the upper and lower sides of the sampling area. A 5×5µm pit is etched on the left side of the sampling area to facilitate the insertion of a probe for sample extraction in the next step. The bottom and left and right sides of the sampling area are then cut using the FIP until, except for a small section on the right, the remaining sampling area is separated from the electrode sheet.

[0034] Insert a probe, with the probe tip contacting the left side of the sampling area. Deposit Pt at the probe tip to weld the probe to the sampling area. Cut the right connection of the sampling area with the focused ion beam to completely separate the sampling area from the electrode. Use the probe to extract a small sample from the sampling area. The small sample has the characteristic dimensions of 30 μm in length, 15 μm in width, and 5 μm in thickness.

[0035] The probe moves a small sample onto a TEM copper plate with V-shaped pillars and welds it to the ends of the V-shaped pillars. Specifically, the left and right ends of the small sample are welded to the left and right sides of the grooves in the V-shaped pillars, severing the connection between the probe tip and the sample in the sampling area. This two-sided fixed welding method rigidly connects the small sample to the TEM copper plate, maximizing the limitation on the sample's size. The sample will not deform or change size (unless the V-shaped pillars deform or are damaged), helping to maintain the original strain distribution of the sample.

[0036] A 20 μm wide region in the middle of the small sample was selected as the thinning area. The upper and lower surfaces of this thinning area were etched using the focused ion beam with a grazing incidence angle of 1°~2°. When the thickness of the thinned area reached below 100 nm, a low-voltage ion beam was used to continue scanning and etching the upper and lower surfaces. The voltage of the low-voltage ion beam was 5~10 kV; in this embodiment, 8 kV was used. The amorphous damage layer caused by the focused ion beam was removed, and the thickness of the thin area was further reduced to below 50 nm, making it suitable for STEM observation conditions, resulting in a thin-film sample.

[0037] The focused ion beam uses a FIB equipped with xenon ions, which helps to prevent gallium ions from entering the sample, especially the lithium-containing part, thereby preventing sample contamination and preserving the original state of the prepared sample to the greatest extent.

[0038] When thinning the sample, using a FIB equipped with a frozen sample stage helps to avoid damage to the sensitive components of the sample by high-energy ion beam irradiation, and allows the prepared sample to maintain its original state to the greatest extent.

[0039] 102 Data acquisition: Perform 4D-STEM scanning on the thin-film sample to obtain a complete electron diffraction pattern for each scanning point, thus obtaining a four-dimensional dataset.

[0040] Specifically, multiple target particle regions are selected in the thin-film sample, and 4D-STEM scanning is performed on the target particle regions to obtain a complete electron diffraction pattern for each scanning point. The electron diffraction pattern includes real space two-dimensional position information and reciprocal space two-dimensional diffraction information.

[0041] More specifically, the thinned areas of the sample, i.e. thin sheet samples, are found under transmission electron microscopy. Thin regions containing graphite particles are located in the thin sheet samples, and multiple 300nm×300nm regions are selected from the surface to the inside of the thin region to make the results statistically significant.

[0042] Each selected region was scanned using 4D-STEM to obtain a series of 4D-STEM datasets. Each dataset is represented as a four-dimensional matrix, with the four dimensions being the two spatial dimensions of the scan and the two momentum dimensions of the diffraction pattern. Each scan point corresponds to the electron diffraction pattern obtained at the electron beam spot.

[0043] 4D-STEM scanning employed a Talos transmission electron microscope based on an Arinal camera. The parameters were set to maximize the electron beam convergence angle to increase spatial resolution while ensuring the resolution of the electron diffraction pattern. The accelerating voltage was set to 200 kV, but those skilled in the art could select a suitable accelerating voltage within the range of 80 kV-300 kV based on sample characteristics (such as sensitivity to electron beam irradiation). The convergence angle was 2.1 mrad, resulting in a minimum spot size of 0.73 nm. Considering aberrations, the expected spot size was 1 nm. The spatial scan image had a pixel count of 400 × 400, and the scanned area size was 268 × 268 nm. Each pixel corresponded to a 0.67 nm interval between adjacent scanned beam spots, with an overlap rate of approximately 33%. The camera constant was 160 mm, and the electron diffraction pattern had a pixel count of 196 × 196 pixels.

[0044] 103. Data analysis: Local lattice vector calculation is performed on the electron diffraction pattern in the four-dimensional dataset, and the calculation results are compared with the unstrained lattice vector to obtain the strain tensor of the scanning point.

[0045] Specifically, the electron diffraction pattern of each scanning point is identified and the position of the Bragg diffraction disk is located; Based on the location, the average reciprocal lattice vector of the scanning point is determined, and the crystal orientation corresponding to the scanning point is determined to obtain crystal structure information. Based on the crystal structure information, the unstrained reference lattice is determined. The strain tensor of each scan point is calculated by comparing the deviation of the local lattice vector of each scan point with the reference lattice. The strain tensor contains at least two normal strain components and one tangential strain component.

[0046] More specifically, use the open-source Python library py4DSTEM or other software / algorithms with equivalent functionality for data processing and analysis. Configure the Python environment, install and import necessary libraries, including py4DSTEM, numpy, and matplotlib. Use the functions provided by the Python-based library py4DSTEM to read 4D-STEM data and perform data preprocessing, including noise removal and background correction.

[0047] For each scanned pixel, the position of the Bragg diffraction disk is extracted, the average reciprocal lattice vector is determined, the crystal orientation at that pixel is determined, and a crystal orientation distribution map is plotted. For example... Figure 3 The image shown is a real-space image of the interior of a graphite crystal acquired by 4D-STEM at 0.1C, with a discharge cutoff voltage of 0.01V and a charge cutoff voltage of 1.5V, after 500 cycles of the battery.

[0048] 104 Results are output. Based on the strain tensor, a strain distribution map in the strain space is plotted to obtain a strain distribution map with nanometer-level spatial resolution.

[0049] Specifically, an unstrained reference lattice is determined using the material's CIF and crystal orientation. The strain tensor at each scan location is calculated by comparing the deviation of the local lattice vector from the reference lattice. The components of the strain field, namely the normal strain distribution and the tangential strain distribution, are visualized and plotted, as shown below. Figure 4 As shown, this diagram illustrates the crystal orientation distribution of graphite crystals by comparing the collected diffraction information with the standard CIF information of the graphite crystal material. The diagram is described using an axial coordinate system, where blue represents (1 0 -1 0), green represents (1 -1 0 0), and red represents (0 0 0 1). The scale bar is consistent with... Figure 4 The same. Images of graphite at scales below 1 μm are obtained, showing layered structures, crystal orientations, or strain distributions. For example... Figure 5 As shown, red represents tensile strain (maximum +150%), blue represents compressive strain (-150%), and gray-white represents the same as the standard lattice (zero strain). εxx represents the strain distribution in the horizontal direction, εyy represents the strain distribution in the vertical direction, and εxy represents the shear strain. After 500 cycles at 0.1C, the graphite crystal surface is subjected to tensile strain in both the horizontal and vertical directions. The shear strain indicates that crystal rotation or angular distortion has occurred compared to the standard lattice. This suggests that after 500 cycles, the stress caused by lithium ions being extracted and embedded in the crystal leads to lattice distortion. The higher lattice shear strain mechanically explains the correlation between the unstable state of the particles and the slippage of the graphite interlayers induced by internal shear strain.

[0050] By performing 4D-STEM measurements on long-cycle graphite crystals, the internal strain of the particles was quantified. The horizontal, vertical, and shear stress distribution levels were used to demonstrate the impact of multiple lithium-ion insertion / extraction processes on the graphite crystals during the electrochemical reaction.

[0051] As a specific embodiment 2, the present invention provides a method for measuring the strain distribution of a battery negative electrode material, which is the same as embodiment 1, except that the battery negative electrode material is silicon.

[0052] like Figure 6The images are real-space images of the silicon anode crystal after three cycles of 4D-STEM acquisition at 0.1C, with 50% SOC, a discharge cutoff voltage of 0.17V, and a charge cutoff voltage of 1.5V.

[0053] Figure 7 To obtain the crystal orientation distribution of silicon crystals by comparing the standard CIF information of silicon crystal materials with the collected diffraction information, the following coordinate system is used: blue represents (111), green represents (011), and red represents (0 0 1). The scale of the blank area is [not specified]. Figure 6 Similarly, after three cycles, the silicon anode surface locally exhibited an amorphous state, indicating that lithium-ion insertion and extraction during the electrochemical reaction induces particle amorphization. By controlling the cutoff voltage to 0.1V, crystal information can be preserved, and the mechanical effects of local lithium insertion / extraction on the internal crystal can be reflected.

[0054] Figure 8 In the diagram, red represents tensile strain (maximum +3%), blue represents compressive strain (maximum -3%), and gray-white represents the same as the standard lattice (zero strain). εxx represents the strain distribution in the horizontal direction, εyy represents the strain distribution in the vertical direction, and εxy represents the shear strain. On the silicon crystal surface, after three cycles at 0.1C, the material experiences tensile strain in both the horizontal and vertical directions. The shear strain indicates that crystal rotation or angular distortion has occurred compared to the standard lattice. By controlling the cutoff voltage to 0.1V, crystal information can be preserved, and the mechanical effects on the internal crystal after local lithium insertion / extraction can be reflected.

[0055] 4D-STEM measurements were performed on silicon anode particles subjected to a 3-cycle, limited cutoff voltage of 0.1V. 4D-STEM qualitatively described the effect of lithium-ion insertion / extraction on the crystal (amorphous and crystalline regions) through crystal orientation distribution. Furthermore, the stress changes within the crystal due to localized lithium insertion / extraction were determined through strain distribution.

[0056] The strain distribution map corresponds to the scanning transmission electron microscopy (STEM) image of the region, quantitatively revealing the strain of the negative electrode particles in this region. The strain distribution map includes the normal strain distribution map in the x and y directions within the scanning plane, and the tangential strain distribution map within the scanning plane. The strain unit is percentage. The spatial resolution of the strain distribution map is determined by the scanning electron beam spot size and can reach 1 nm. The values ​​in the strain distribution map are not only comparable within this dataset but also across different datasets, and can be used to compare the strain magnitude of negative electrode particles in different batteries.

[0057] By comparing the magnitude and type of graphite strain in batteries at different states of charge (SOC), we can determine how the amount of lithium intercalation affects the degree of graphite strain. By comparing the magnitude and type of graphite strain in batteries with different cycle counts, we can determine how cycling induces irreversible changes in graphite. Finally, by comparing the magnitude and type of graphite strain in batteries with different cycle counts, we can determine how cycling causes irreversible structural changes in graphite, and correlate this information with the battery's state of health (SOH).

[0058] By comparing the magnitude and type of strain in the silicon anode of the battery under different cutoff potentials, it was found that different cutoff potentials lead to different proportions of amorphous and crystalline components within the silicon anode. By meticulously limiting the battery's cutoff voltage, the study investigated how different cutoff voltages induce irreversible changes in the silicon anode and correlated this information with battery health.

[0059] As an implementable comparative example 1, this comparative example 1 uses the macroscopic strain gauge method to process the same battery sample of Example 1.

[0060] Results: Because the sample consists of micron-sized particles, it is impossible to mount the strain gauge onto a single particle, and the measured signal reflects the overall deformation of the electrode, making it impossible to obtain the signal shown in the attached figure. Figure 5 The nanoscale strain distribution shown cannot reveal the shear strain concentration region inside the grain.

[0061] As an implementable comparative example, this comparative example 2 uses XRD diffraction to process the same battery sample from Example 1.

[0062] Results: Although the average lattice expansion of the sample could be measured, its micrometer-level spatial resolution prevented the determination of details such as those shown in the attached figure. Figure 4 The crystal orientation variations shown, and as attached Figure 5 The gradient distribution of strain in the hundreds of nanometers region obscures the failure mechanism caused by local stress concentration.

[0063] As a feasible comparative example, this comparative example 3 uses atomic resolution GPA to process the same battery sample from Example 1.

[0064] Results: Due to the disordered band axis and complex crystal phase of graphite particles after cycling, it is difficult to obtain high-quality atomic images with large area and uniform band axis. Only a few tens of nanometer regions that occasionally meet the imaging conditions can be analyzed, which lacks statistical representativeness and is completely unable to process silicon anode samples that have been partially amorphized, such as in Example 2.

[0065] This invention successfully overcomes all the above limitations by combining adapted FIB sample preparation technology (such as rigid connection to maintain strain) with 4D-STEM full-field diffraction analysis technology, and realizes quantitative, high-resolution, full-field visualization measurement of nanoscale strain field of real and complex battery anode materials under working conditions.

[0066] The present invention also provides a measurement system for implementing the measurement method, as shown in the module diagram below. Figure 2 As shown, it includes: 201 Sample preparation module, used to prepare the thin-film sample.

[0067] Specifically, the battery that has undergone state parameter testing is disassembled to obtain the negative electrode sheet. The negative electrode sheet is then used to extract and etch the target sample using a focused ion beam to obtain a thin sheet sample.

[0068] 202 Data acquisition module, used to perform 4D-STEM scanning on the thin-film sample to obtain a four-dimensional dataset.

[0069] Specifically, multiple target particle regions are selected in the thin-film sample, and 4D-STEM scanning is performed on the target particle regions to obtain a complete electron diffraction pattern for each scanning point. The electron diffraction pattern includes real space two-dimensional position information and reciprocal space two-dimensional diffraction information.

[0070] The 203 data analysis module is used to analyze the crystal structure information of the four-dimensional dataset, compare and calculate the crystal structure information, and obtain the strain tensor.

[0071] Specifically, the electron diffraction pattern of each scanning point is identified and the position of the Bragg diffraction disk is located; Based on the location, the average reciprocal lattice vector of the scanning point is determined, and the crystal orientation corresponding to the scanning point is determined to obtain crystal structure information. Based on the crystal structure information, the unstrained reference lattice is determined. The strain tensor of each scan point is calculated by comparing the deviation of the local lattice vector of each scan point with the reference lattice. The strain tensor contains at least two normal strain components and one tangential strain component.

[0072] The 204 Result Output Module plots the strain distribution map of the strain tensor and outputs a strain distribution map with nanometer-level spatial resolution.

[0073] Specifically, the result output module also includes a visualization unit for simultaneously displaying the strain distribution map and the 4D-STEM scan image.

[0074] An unstrained reference lattice is determined using the material's CIF and crystal orientation. The strain tensor at each scan location is calculated by comparing the deviation of the local lattice vector from the reference lattice. The components of the strain field, namely the normal strain distribution and the tangential strain distribution, are visualized and plotted.

[0075] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in the details for the sake of brevity.

[0076] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for measuring the strain distribution of a battery negative electrode material, characterized in that, Includes the following steps: Sample preparation involves disassembling the battery after state parameter testing to obtain the negative electrode sheet. The negative electrode sheet is then extracted and etched using a focused ion beam to obtain a thin sheet sample. Data acquisition involves performing 4D-STEM scanning on the thin-film sample to obtain a complete electron diffraction pattern for each scanning point, resulting in a four-dimensional dataset. Data analysis involves calculating local lattice vectors in the electron diffraction patterns of the four-dimensional dataset, and comparing the calculation results with the unstrained lattice vectors to obtain the strain tensor of the scanning point. The results are output, and based on the strain tensor, a strain distribution map in the strain space is plotted to obtain a strain distribution map with nanometer-level spatial resolution.

2. The measurement method according to claim 1, characterized in that, The extraction and etching of the target sample on the negative electrode sheet using a focused ion beam includes the following steps: A sampling area is selected on the negative electrode sheet of the battery. After the sampling area is protected by a deposition layer using a focused ion beam, it is then cut and sampled to obtain a small sample. The small sample was rigidly connected to the support structure of the TEM, and then the small sample was etched with a focused ion beam to a thickness of less than 50 nm.

3. The measurement method according to claim 2, characterized in that, The voltage of the focused ion beam is 10~30kV.

4. The measurement method according to claim 1, characterized in that, The step of performing 4D-STEM scanning on the thin-film sample to obtain a complete electron diffraction pattern for each scanning point includes the following steps: Multiple target particle regions are selected in the thin-film sample, and 4D-STEM scanning is performed on the target particle regions to obtain a complete electron diffraction pattern for each scanning point. The electron diffraction pattern contains real space two-dimensional position information and reciprocal space two-dimensional diffraction information.

5. The measurement method according to claim 4, characterized in that, The electron beam convergence angle of the 4D-STEM scan is 1~5mrad, and the scanning step size is ≤1nm.

6. The measurement method according to claim 1, characterized in that, The data analysis includes the following steps: Identify the electron diffraction pattern of each scanning point and locate the position of the Bragg diffraction disk; Based on the location, the average reciprocal lattice vector of the scanning point is determined, and the crystal orientation corresponding to the scanning point is determined to obtain crystal structure information. Based on the crystal structure information, the unstrained reference lattice is determined. The strain tensor of each scan point is calculated by comparing the deviation of the local lattice vector of each scan point with the reference lattice. The strain tensor contains at least two normal strain components and one tangential strain component.

7. The measurement method according to claim 1, characterized in that, The state parameters include at least one of the following: number of cycles, state of charge, health state, and charge / discharge cutoff voltage.

8. The measurement method according to claim 1, characterized in that, The negative electrode material of the battery is graphite or silicon-based material.

9. A measurement system for implementing the measurement method according to any one of claims 1 to 8, characterized in that, include: A sample preparation module is used to prepare the aforementioned thin-film sample; The data acquisition module is used to perform 4D-STEM scanning on the thin-film sample to obtain a four-dimensional dataset; The data analysis module is used to analyze the crystal structure information of the four-dimensional dataset, compare and calculate the crystal structure information, and obtain the strain tensor. The results output module plots the strain distribution map of the strain tensor and outputs a strain distribution map with nanometer-level spatial resolution.

10. The measurement system according to claim 9, characterized in that, The result output module also includes a visualization unit for simultaneously displaying the strain distribution map and the 4D-STEM scan image.

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