A lithium ion battery single-layer electrode sheet volume change detection device and application thereof

Abstract

The application discloses a kind of lithium ion battery single-layer pole piece volume change detection device and its application, the device includes image acquisition module, for optical imaging button type lithium ion battery, battery test module, temperature and humidity test module, real-time monitoring and communication module.The application proposes and develops the image feature extraction technique for lithium ion battery electrode material, and realizes the monitoring of single-layer pole piece volume change by scanning measurement method and corresponding feedback algorithm based on image feature extraction technique;By using spatial image feature extraction technology, the surface topography image of pole piece is obtained, which is combined with the volume change curve of single-layer pole piece, and the spatial resolution is given to the volume measurement method.

Description

Technical Field

[0001] This invention relates to a device for detecting volume change of a single-layer electrode in a lithium-ion battery, and more particularly to a device for detecting volume change of a single-layer electrode in a lithium-ion battery based on image feature extraction technology. Background Technology

[0002] As an important type of rechargeable battery, lithium-ion batteries have brought great convenience to production and daily life, and have also greatly promoted the development of clean energy. However, the lifespan degradation and safety issues of lithium-ion batteries have restricted their development: during the charge and discharge cycle of the battery, as the degree of irreversible side reactions increases, the unevenness of the volume expansion of the lithium-ion battery electrode materials increases, increasing the probability of battery short circuits or even explosions; at the same time, the rough manufacturing process of the battery electrodes and the uneven electrode coatings are also very likely to cause battery short circuits.

[0003] Studying the non-uniform expansion of lithium-ion battery electrode materials at the level of single-layer electrodes is of great significance for improving the energy density of lithium-ion batteries and reducing safety hazards. However, existing methods for measuring the volume expansion of single-layer electrodes, such as electrochemical dilatometers, can only detect the overall volume change behavior of lithium-ion battery electrodes during charging and discharging, and lack spatial resolution. At the same time, the sensors required for such measurements are expensive and difficult to promote.

[0004] When the volume expansion of a single-layer electrode in a lithium-ion battery exhibits spatial heterogeneity, measuring this heterogeneity transforms into measuring the overall thickness and surface morphology of the material. Atomic force microscopy (AFM), as an important technique for characterizing material surface morphology, possesses atomic-level measurement precision. However, when the electrode has a highly uneven surface morphology, is wetted by electrolyte in the operating environment, or has a solid electrolyte interface formed on the surface, the scanning rate and precision of AFM are limited. Furthermore, AFM cannot measure the overall volume change of the material; when the system operates at high charge-discharge rates, the volume expansion of the material also affects the scanning process. Therefore, imaging the non-uniform volume expansion of a single-layer electrode faces significant challenges. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a device for detecting volume changes of a single-layer electrode in a lithium-ion battery and its application, thereby solving the imaging problem of uneven volume expansion of the single-layer electrode.

[0006] Technical solution: The present invention provides a lithium-ion battery single-layer electrode volume change detection device, comprising:

[0007] The image acquisition module, including an optical imaging system and an image acquisition device, is used for real-time optical imaging and image collection of samples.

[0008] A button cell lithium-ion battery is used to load test samples and provide the anhydrous and oxygen-free conditions required for the normal operation of the button cell lithium-ion battery. The button cell lithium-ion battery is provided with a window for optical imaging.

[0009] The battery testing module is used to set battery testing conditions, perform charge-discharge cycles on the battery, and acquire real-time electrochemical parameters.

[0010] The temperature and humidity testing module is used to measure changes in the temperature and humidity of the test environment during battery testing.

[0011] The sample movement module is used to test the quantitative movement of the battery in the direction perpendicular to the sample, and to complete the quantitative movement process in the process of measuring the volume of a single-layer electrode of a lithium-ion battery.

[0012] The real-time monitoring and communication module includes a monitor and a computer host; the computer host communicates with the image acquisition device, sample movement module, temperature and humidity testing module, and battery testing module to control and read data from each module in the device; the monitor is used to output the volume change curve of the lithium-ion battery under test conditions.

[0013] Furthermore, the optical imaging system includes a light source, an objective lens, and an objective lens adapter. It adopts a reflected light path. After the illumination light is incident from the light source, it is reflected and scattered on the sample surface. The outgoing light then enters the image acquisition device through the objective lens and the objective lens adapter, thereby realizing the reflection imaging of the sample surface.

[0014] Furthermore, the sample moving module includes a drive motor and a transmission device to realize quantitative movement of the sample relative to the image acquisition device.

[0015] Furthermore, the button-type lithium-ion battery includes a sample electrode and its counter electrode for testing volume change, a detachably connected test battery top cover, a test battery cell body, and a test battery bottom cover. A test battery conductive post and a conductive spring are disposed between the test battery cell body and the test battery bottom cover. The test electrode top cover is provided with a through hole, a glass window and a fixing ring are provided on one side of the through hole, the counter electrode is placed between the glass window and the through hole, a perforated diaphragm is provided on the other side of the through hole, and the sample electrode is placed between the diaphragm and the test battery conductive post.

[0016] Furthermore, the retaining ring and the test battery cover are provided with matching threads, and the retaining ring is used to press the glass window and seal it.

[0017] Furthermore, the test electrode cover, the test battery cover, and the test battery body are all connected by threads.

[0018] The present invention provides an application of the above-mentioned device in detecting volume changes of a single-layer electrode in a lithium-ion battery, including measuring the overall volume change behavior of the electrode and imaging the spatial volume change process of the electrode.

[0019] Furthermore, the application includes the following operational steps:

[0020] Step 1): Load the test sample into the coin cell lithium-ion battery to complete the initialization of the testing device;

[0021] Step 2): Set the scanning range and working image features perpendicular to the sample direction required for volume measurement;

[0022] Step 3): Obtain the scanning working curve: Move the measuring battery to different positions corresponding to different system focal lengths using the sample moving module to obtain different image features, and plot the image feature-system focal length curve, which is the scanning working curve;

[0023] Step 4): Start volume measurement: Set the battery charge and discharge measurement conditions through the battery test module, set the scanning interval required for volume measurement, and then scan along the perpendicular to the sample surface. The computer host calculates the image features in real time during the scanning process, moves the sample through the sample moving module to keep the acquired image features constant at the working image features, records the sample movement path, and combines it with the scanning working curve to realize the detection of the volume change of the single-layer electrode of the lithium-ion battery.

[0024] Further, after the coin cell lithium-ion battery is assembled in step 1), an initialization operation is performed, including standing, formation, and venting; the initialization of the detection device includes: turning on the device light source and turning on each module in the device; thereafter, communication with the image acquisition device, sample movement module, temperature and humidity testing module, and battery testing module is realized sequentially through the computer host; finally, the sample position is manually adjusted so that the image acquisition device can acquire a clear image of the test sample surface.

[0025] Furthermore, the operation steps also include, while acquiring image features, the temperature and humidity testing module reads the temperature value in real time to obtain a temperature-time curve; before the volume test, the test battery system containing the sample is left to stand for no less than 6 hours to obtain the image feature-temperature relationship, and temperature calibration is performed through the temperature-time curve and the image feature-temperature relationship to eliminate the influence of temperature fluctuations in the measurement environment on the image features.

[0026] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This method achieves online measurement and imaging of the overall volume change of a single-layer electrode sheet in lithium-ion batteries through real-time acquisition and subsequent analysis of scanned images, enabling spatial resolution in the detection of volume changes in lithium-ion battery electrode sheets. This method features non-destructive testing, high temporal resolution, and strong universality. After acquiring the non-uniform volume change of the single-layer electrode sheet during charging and discharging, analysis combined with the state of charge and health status of the lithium-ion battery is expected to answer the relationship between the degree of volume non-uniformity and the degree of material aging, providing more methods and approaches to reduce safety hazards in lithium-ion batteries and achieve hazard warning, thus promoting the healthy development of the lithium-ion battery industry. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the lithium-ion battery single-layer electrode volume change detection device based on optical imaging according to the present invention.

[0028] Figure 2 This is a schematic diagram of the structure of a coin cell lithium-ion battery used for optical imaging.

[0029] Figure 3 A schematic diagram of the structure of the test battery top cover, test battery cell body and test battery bottom cover;

[0030] Figure 4 A surface image of a lithium iron phosphate positive electrode sheet acquired by an optical imaging system provided in an embodiment of the present invention;

[0031] Figure 5 The image features of the lithium iron phosphate material surface obtained by image feature extraction technology are provided in the embodiments of the present invention.

[0032] Figure 6 This is an example scan curve provided in an embodiment of the present invention for the process of measuring the volume of a lithium iron phosphate cathode sheet;

[0033] Figure 7 This invention provides an embodiment of the image feature evolution curve obtained during the measurement of battery electrode volume change.

[0034] Figure 8 The battery electrode volume change evolution curve and voltage curve provided in the embodiments of the present invention;

[0035] Figure 9 Schematic diagram of the surface morphology of the battery electrode when the SOC of lithium iron phosphate is 0%.

[0036] Figure 10 This is a schematic diagram of the surface morphology of the battery electrode under the condition of lithium iron phosphate SOC=100%.

[0037] In the diagram, 1-light source; 2-objective lens; 3-image acquisition device; 4-button lithium-ion battery; 5-sample moving module; 6-temperature and humidity testing module; 7-battery testing module; 8-monitor; 9-computer host; 10-test battery top cover; 11-test battery cell; 12-test battery bottom cover; 13-fixing ring; 14-glass window; 15-counter electrode; 16-separator; 17-sample electrode; 18-test battery conductive post; 19-conductive spring. Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0039] Example 1

[0040] This embodiment provides a coin cell lithium-ion battery for optical imaging and its assembly method. While providing the necessary anhydrous, oxygen-free, and sufficient electrolyte and conductive pathways required for lithium-ion batteries, the coin cell lithium-ion battery's unique structural design allows for imaging and measurement using optical methods.

[0041] like Figures 2-3 As shown, the coin cell lithium-ion battery for optical imaging in this embodiment includes a sample electrode 17 (positive electrode of the battery) for testing volume change, a counter electrode 15 (negative electrode of the battery), and uses a lithium metal sheet or lithium titanate electrode, a separator 16, a test battery top cover 10, a glass window 14 and a fixing ring 13, a test battery cell body 11, a test battery bottom cover 12, a test battery conductive post 18 and a conductive spring 19.

[0042] The test electrode cover 10 is a cylindrical stainless steel product with an internal recess and a cross-shaped through hole in the center. There are recesses on both sides of the cross-shaped through hole to place the sealing gasket and the glass window 14. The thread of the fixing ring 13 matches and is pressed with the thread of the test electrode cover 10 to form the introduction and sealing of the glass window 14.

[0043] To isolate the volume change of the counter electrode (mainly lithium metal sheet) of the test sample, the sample 17 and the counter electrode 15 are placed and fixed separately without contact. The counter electrode 15 is placed between the glass window 14 and the star-shaped through hole of the test electrode cover 10. The perforated separator 16 is placed on the other side of the star-shaped through hole of the test electrode cover 10. The sample electrode 17 is placed between the separator 16 and the conductive post 18 of the test battery. Both the test electrode cover 10 and the test battery cover 12 have countersunk screw holes for connection and fixation with the corresponding nuts inside the test battery body 11.

[0044] When assembling this button lithium-ion battery, it must be assembled from top to bottom in a glove box with a protective atmosphere, as shown in the diagram.

[0045] When assembling the test battery cover 10, first place the counter electrode 15 on the glass window 14 side of the cover. When using material electrodes, the current collector side of the electrode should be in contact with the glass window 14. Then, place a sealing rubber gasket in the recess of the test battery cover 10, and place the glass window 14 on top of it. Pay attention to the compression state of the rubber gasket to avoid misalignment. Finally, tighten the fixing ring 13. When the fixing ring 13 is in a good fixed position, its height should be flush with the top height of the test battery cover 10. After that, introduce a sealing rubber gasket into the recess on one side of the test battery cell 11, opposite to the test battery cover 10, and connect it with countersunk screws to assemble and fix it. This completes the assembly of the test battery cover 10 and the test battery cell 11.

[0046] After the above assembly steps are completed, a small amount of lithium-ion battery electrolyte is injected into the test battery cell 11 to achieve negative electrode wetting and cell leakage detection. After the electrolyte has fully wetted and submerged the star-shaped through hole of the test battery cover 10, a pre-wetted lithium-ion battery separator 16 with a central hole is added into the test battery cell 11, aligning its hole with the center of the star-shaped through hole. The hole in the separator 16 should be slightly smaller than the star-shaped through hole to avoid short circuit caused by contact between the positive and negative electrodes. After eliminating any air bubbles introduced by the separator 16, the battery is then filled with electrolyte. For the sample electrode 17 used for volume change detection, its material side should face down during assembly. Observe its state through the upper glass window 14, ensuring it is centered and fully wetted by the lithium-ion battery electrolyte. After adding an appropriate amount of electrolyte, the test electrode conductive pillar 18, and the conductive spring 19, add more electrolyte until the entire cavity is filled. Finally, press the lower cover 12 of the test battery and complete the overall encapsulation using countersunk screws. After assembly, flip the test battery over and observe whether there are any air bubbles introduced by the encapsulation on the upper cover side and whether the test sample is in the correct position.

[0047] Example 2

[0048] like Figure 1 As shown, this embodiment provides a lithium-ion battery single-layer electrode volume change detection device based on image feature extraction, including: an image acquisition module, a coin-type lithium-ion battery 4 for optical imaging, a battery testing module 7, a temperature and humidity testing module 6, a sample movement module 5, and a real-time monitoring and communication module.

[0049] The image acquisition module includes a light source 1, an objective lens 2, and an image acquisition device 3. In this embodiment, the light source 1 is a light-emitting diode with a center wavelength of 810 nanometers, the objective lens 2 is a 20x magnification objective lens with a numerical aperture of 0.45, and the image acquisition device 3 uses an electronic coupling element as the image acquisition device. The image acquisition module adopts a reflected light path. After the illumination light enters from the light source 1, it is reflected and scattered on the sample surface. The outgoing light then enters the image acquisition device 3 through the objective lens 2 and the objective lens adapter, realizing the reflection imaging of the sample surface. Through communication with the computer host 9 in the real-time monitoring and communication module, the image acquired by the image acquisition device 3 will be stored in memory for subsequent calculations.

[0050] The coin cell lithium-ion battery 4 used for optical imaging employs the measuring device and assembly method described in Example 1. Before performing single-layer electrode volume change detection, it is necessary to perform battery initialization operations such as settling, formation, and venting.

[0051] Battery testing module 7 is used to set battery test conditions, perform charge-discharge cycles on the battery, and acquire the electrochemical response of the test battery in real time. In this embodiment, battery testing module 7 uses an electrochemical workstation manufactured by Shanghai Chenhua, model CHI760e.

[0052] The temperature and humidity testing module 6 is used to measure the micro-area temperature and ambient humidity of the sample. In this embodiment, a temperature and humidity sensor chip is used, which communicates with the computer host 9 in the real-time monitoring and communication module to realize on-demand reading of temperature and humidity.

[0053] The sample movement module 5 is used to quantitatively move the sample in the direction perpendicular to the sample. It communicates with the computer host 9 in the real-time monitoring and communication module to achieve the purpose of moving the sample and recording the real-time position of the sample. It includes a drive motor and a transmission device, which can quantitatively move the sample and realize scanning.

[0054] The real-time monitoring and communication module includes a monitor 8 and a computer host 9. Through communication with the image acquisition device 3, the sample movement module 5, the temperature and humidity testing module 6, and the battery testing module 7, the computer host 9 is used to control and read data from each module in the device. The monitor 8 is used to display the real-time volume change measurement curve.

[0055] During the initialization of the detection device, the light source 1 should be turned on first to ensure all modules within the device are in the active state. Then, communication should be established sequentially with the image acquisition device 3, sample movement module 5, temperature and humidity testing module 6, and battery testing module 7 via the computer host 9. Finally, the sample position should be manually adjusted so that the image acquisition device 3 can acquire a relatively clear image of the test sample surface. At this point, the initialization of the single-layer electrode volume change detection device based on optical imaging is complete.

[0056] Example 3

[0057] This embodiment demonstrates the principles of feature acquisition, feature description, and feature denoising techniques in image feature extraction technology, as well as a method for extending image feature extraction technology to spatial image feature extraction technology.

[0058] Feature acquisition methods

[0059] The feature acquisition method can obtain image features through image calculation. Since an image is essentially a matrix, the image feature is actually a matrix of the same size as the original image. Within the image acquisition module (a specific optical system) described in this invention, the image feature is specifically represented as the convolution of the optical system's point spread function and the average morphology features of the electrode surface particles. Because the point spread function is related to the focal length of the optical system, the image feature can reflect changes in the focal length of the measurement system and can be used for detecting volume changes in battery electrodes. Because the average morphology features of the surface particles are related to the average particle size, the unit of the image feature can be expressed in length units. The volume change detection device provided in this invention generally uses micrometers as the unit.

[0060] The image-based calculation formula used in the feature extraction method is as follows:

[0061]

[0062] like Figure 4 As shown, an image is composed of pixels arranged in a certain way. Each pixel has its own intensity, represented by i and its position in the image coordinates. For example, the intensity of the pixel corresponding to the first row and first column of an image is represented by i(1,1). Taking a pixel at a specific position as a reference, the correlation between the intensity of the remaining pixels and the intensity of that pixel is calculated in turn to obtain the correlation value of that pixel. The above operation is performed on each pixel in turn within the image range, as shown in the above formula. Finally, the original image features of the same size as the image are obtained for subsequent calculations.

[0063] Feature description methods

[0064] Feature description methods can simplify and describe image features. Since the feature acquisition methods described above only obtain a matrix of image features, it is necessary to simplify them to achieve a proper description of the image features.

[0065] Image features can be understood as the convolution of the sample's true morphological features and the imaging system's point spread function. The sample's true morphological features can be understood as the average particle size, and therefore should have a unit of length.

[0066] In the optical system described in this invention, when the numerical apertures of the system's light source and objective lens remain constant, its point spread function will only be affected by the system's focal length. Because the point spread function of the optical system is constrained by the diffraction limit and is related to the wavelength of the light source (e.g., the diameter of the central bright spot of the Airy disk d = 2.44 * λ, where λ is the wavelength of the light source), it also has length characteristics. Therefore, image features should have a unit of length; in this invention, the unit is micrometer.

[0067] Since most of the energy of the optical system is concentrated in a small part of the center of the point spread function, a portion of the center of the original image feature matrix is ​​selected for feature description.

[0068] This invention uses two-dimensional Gaussian fitting (normal distribution) to describe image features, as shown in the formula:

[0069] G(x,y)=A*exp{-0.5*[(x / B)^2+(y / C)^2]}+D

[0070] In the above formula, A represents Gaussian intensity, B represents the standard deviation in the x-direction, C represents the standard deviation in the y-direction, and D represents the baseline height.

[0071] The C-value of the two-dimensional Gaussian fitting result is used as the image feature; when the sample is in different vertical positions (corresponding to different focal lengths of the system), the image acquired by the image acquisition device will have different image features, and the image features can be described.

[0072] Feature-based noise reduction technology

[0073] Feature-based noise reduction techniques will primarily be used for optimizing optical systems and improving measurement sensitivity. Since both feature acquisition and feature description methods originate from the image itself, their performance is influenced by the quality of the acquired image.

[0074] Image acquisition equipment is susceptible to electronic and ambient light interference during operation, which can affect the quality of acquired images. Improving the average image quality can reduce the impact of such random noise on image features. Furthermore, appropriate exposure time and camera gain levels will further enhance the quality of the acquired images.

[0075] Because image features are affected by the point spread function of the optical system, the optical components within the optical system will also affect the sensitivity of the volume measurement system. Longer-wavelength light sources will have better measurement sensitivity than shorter-wavelength light sources; at the same magnification, larger numerical aperture objectives have better measurement sensitivity than smaller numerical aperture objectives.

[0076] Spatial image feature extraction technology

[0077] When a feature extraction method is applied to an image (called the input image), a matrix of the same size as the input image is obtained, seemingly indicating that only one image feature can be extracted from the input image; however, since an image is composed of many pixels, it can be divided at a smaller scale.

[0078] By setting the window size and window step, and utilizing the concept of convolution, the original input image can be divided into segments. Then, by sequentially applying feature acquisition, feature description, and feature denoising techniques, a spatial image feature distribution map can be obtained.

[0079] A specific part of a material has a specific image feature; by recording the changes in the image feature of that part and combining it with the scanning curve of that area, spatial image feature extraction technology allows us to perform real-time imaging of the volume change of a single-layer electrode.

[0080] Example 4

[0081] This embodiment demonstrates a scanning measurement method based on image feature extraction and a corresponding measurement feedback algorithm. When the volume of the lithium-ion battery electrode material changes, its particle size will change accordingly; simultaneously, since the electrode sheet is composed of many stacked particles (typically 40 micrometers thick), the thickness of the electrode sheet will also change. When the positions of the objective lens and the light source within the optical system remain unchanged, the changing thickness will cause a change in the degree of focusing, leading to a change in the point spread function, and thus affecting the image features.

[0082] Therefore, for a lithium-ion battery electrode material system, the image features of its surface image will be affected by both the surface particle size and the system focal length. However, the influence of the system focal length on image features is far greater than the influence of particle size variation; it can be assumed that changes in surface particle size under different charging states will not affect image features.

[0083] Therefore, by moving the measuring battery, keeping the image features of the acquired image constant, and recording the movement path of the battery, the volume change of the single-layer electrode of the lithium-ion battery can be detected. This image feature that needs to be kept constant is called the working image feature.

[0084] To preserve the image features of the acquired image in the working image features, a scan perpendicular to the sample surface is required: the measurement cell is moved to different positions (corresponding to different system focal lengths) to acquire different image features, and the image feature-system focal length curve is plotted and defined as the scanning working curve.

[0085] By obtaining the scanning working curve, the sample position corresponding to the working image feature is calculated, and the test battery is moved to that position to maintain the image feature.

[0086] Scan measurement parameter optimization and measurement feedback algorithm

[0087] Due to the operation of the sample movement module and the introduction of image leveling, the acquisition of a single scanning curve cannot be completed in a short time; when the duration of a single scan is long, the volume change of the sample cannot be ignored; in order to make the volume measurement more accurate, it is necessary to improve the temporal resolution of the volume measurement. Therefore, it is necessary to adjust the scanning measurement parameters.

[0088] According to in-situ X-ray crystallography results, the graphite anode material undergoes a volume change of approximately 10% during cycling, corresponding to a volume change of about 4 micrometers. Therefore, the scale of the scanning working curve should be controlled within an appropriate range, generally about 5 micrometers.

[0089] To improve temporal resolution, the recommended scan range is divided into approximately 25 scan steps; a typical scan curve acquisition takes about 60 seconds.

[0090] By fitting the scanning curve, the accurate sample position corresponding to the features of the working image can be calculated, rather than the sample position corresponding to a specific scanning step, which further improves the measurement sensitivity. When the sample movement module uses a servo motor, the actual position of the sample is returned after each scanning step, which makes the scanning curve more accurate.

[0091] The sample is moved to the target location using the sample moving module 5. At this time, the image acquisition device 3 will acquire and save an image at the target location for spatial image feature extraction.

[0092] Example 5

[0093] This embodiment further provides an application method of the apparatus of Embodiment 2 in detecting volume changes of a single-layer electrode in a lithium-ion battery.

[0094] The principle of this method is that the volume change of the electrode material during charging and discharging will affect the focal length of the optical system. By selecting a highly sensitive working image feature and continuously scanning and moving the sample in the direction perpendicular to the sample, the image feature position of the test battery system is kept constant, thereby realizing the monitoring of the volume change of the electrode material. The method includes the following steps:

[0095] Step 1) Assemble the coin cell lithium-ion battery for optical imaging, and complete the static, formation, and venting battery initialization operations after assembly;

[0096] Step 2) Turn on the light source, connect the image acquisition device, and adjust the objective lens position to obtain a clear test electrode surface pattern;

[0097] Step 3) Establish communication with the image acquisition module and temperature and humidity testing module through the real-time monitoring module, set the scanning mode to drive the sample movement module to move, and take a set number of pictures and measure the temperature after each scanning step;

[0098] Step 4) Set the vertical sample direction scanning range and working image features required for volume measurement. The image features will be obtained using image feature extraction technology. The image features of the images acquired during the measurement process will fluctuate around the working image features. Set the scanning interval required for volume measurement.

[0099] Step 5) Set the battery measurement conditions for the battery test module;

[0100] Step 6) Begin volume measurement and maintain constant image features by performing real-time calculations on the acquired images; acquire image features - vertical position curve, temperature curve, and real-time volume change curve of the electrode and display them on the monitor; also includes static and temperature calibration process, and battery charge and discharge test process;

[0101] Step 7) Use the temperature calibration curve obtained during the resting process, combined with the calibration temperature curve obtained during the battery charging and discharging process, to correct the volume test curve and obtain a single-layer electrode volume change measurement curve that eliminates the influence of temperature on the method.

[0102] Step 8) Using spatial image feature extraction technology, the feature images of the working images obtained during the measurement process are calculated and combined with the scanning working curve to realize the imaging of the volume change process of the single-layer electrode.

[0103] Test case

[0104] Taking a coin cell lithium-ion battery with a lithium electrode as the negative electrode and a lithium iron phosphate electrode as the positive electrode as an example, the method described in Example 5 can yield accurate volume change curves and surface morphology change images of the lithium iron phosphate electrode.

[0105] Specifically, Figure 4 The image shows a surface image of a lithium iron phosphate cathode obtained by the optical microscopy imaging module of the present invention. Figure 5 This invention demonstrates the image features of the lithium iron phosphate material surface obtained using image feature extraction technology. Figure 6 The image shows a scanning curve during the measurement process. The image feature value is equal to the position of the vertical sample direction corresponding to the working image feature, which is the material surface height measured in this scan.

[0106] By extracting image features from the acquired images, the operational status of the detection device can be determined. Generally, due to the influence of system fluctuations and limitations in the accuracy of the sample movement module, the image features of the acquired images will fluctuate around the characteristics of the working image; for example... Figure 7 The image feature-time curve obtained during the measurement process shown indicates that the system is in good working condition.

[0107] Figure 8This reflects the changes in the volume of the lithium iron phosphate electrode and the voltage of the coin cell lithium-ion battery; during charging, the lithium iron phosphate voltage increases and the volume decreases; during discharging, the lithium iron phosphate voltage decreases and the volume increases.

[0108] Figure 9 and Figure 10 The surface morphology of the electrode obtained by spatial image feature extraction method is shown when the SOC of lithium iron phosphate is 0% and 100%. By comparing the surface morphology images of the electrode at different charging states, it is found that the surface morphology changes during charging and discharging, that is, the volume change of the electrode is spatially non-uniform.

[0109] Non-uniform volume changes at the electrode level may be caused by rough manufacturing processes or uneven electrode coatings. The degree of non-uniformity in electrode volume changes can serve as an indicator for evaluating material production and coating processes, reducing safety hazards in lithium-ion batteries at the electrode level. Furthermore, when volume detection methods have spatial resolution, they will be more suitable for assessing the non-uniformity of material doping, which is of great significance for improving the energy density of lithium-ion batteries and reducing their safety hazards.

Claims

1. A device for detecting volume change of a single-layer electrode in a lithium-ion battery, characterized in that, include: The image acquisition module, including an optical imaging system and an image acquisition device, is used for real-time optical imaging and image collection of samples. A coin cell lithium-ion battery is used to load test samples and provide the anhydrous and oxygen-free conditions required for the normal operation of the coin cell lithium-ion battery. The coin cell lithium-ion battery is provided with a window for optical imaging. The coin cell lithium-ion battery includes a sample electrode and its counter electrode for testing volume change, a detachably connected test battery top cover, a test battery cell body, and a test battery bottom cover. A test battery conductive post and a conductive spring are provided between the test battery cell body and the test battery bottom cover. The test electrode top cover is provided with a through hole. A glass window and a fixing ring are provided on one side of the through hole. The counter electrode is placed between the glass window and the through hole. A perforated separator is provided on the other side of the through hole. The sample electrode is placed between the separator and the test battery conductive post. The battery testing module is used to set battery testing conditions, perform charge-discharge cycles on the battery, and acquire real-time electrochemical parameters. The temperature and humidity testing module is used to measure changes in the temperature and humidity of the test environment during battery testing. The sample movement module is used to test the quantitative movement of the battery in the direction perpendicular to the sample, and to complete the quantitative movement process in the process of measuring the volume of a single-layer electrode of a lithium-ion battery. The real-time monitoring and communication module includes a monitor and a computer host; the computer host communicates with the image acquisition device, sample movement module, temperature and humidity testing module, and battery testing module to control and read data from each module in the device; the monitor is used to output the volume change curve of the lithium-ion battery under test conditions.

2. The lithium-ion battery single-layer electrode volume change detection device according to claim 1, characterized in that, The optical imaging system includes a light source, an objective lens, and an objective lens adapter. It adopts a reflected light path. After the illumination light is incident from the light source, it is reflected and scattered on the sample surface. The outgoing light then enters the image acquisition device through the objective lens and the objective lens adapter, thereby realizing the reflection imaging of the sample surface.

3. The lithium-ion battery single-layer electrode volume change detection device according to claim 1, characterized in that, The sample moving module includes a drive motor and a transmission device, which enables quantitative movement of the sample relative to the image acquisition device.

4. The lithium-ion battery single-layer electrode volume change detection device according to claim 1, characterized in that, The retaining ring and the test battery cover are provided with matching threads, and the retaining ring is used to press the glass window and seal it.

5. The lithium-ion battery single-layer electrode volume change detection device according to claim 1, characterized in that, The test electrode cover, the test battery cover, and the test battery body are all connected by threads.

6. The application of the apparatus according to any one of claims 1-5 in detecting volume changes of a single-layer electrode in a lithium-ion battery, characterized in that, This includes measuring the overall volume change behavior of the electrode and imaging the spatial volume change process of the electrode.

7. The application according to claim 6, characterized in that, The following steps are included: Step 1): Load the test sample into the coin cell lithium-ion battery to complete the initialization of the testing device; Step 2): Set the scanning range and working image features perpendicular to the sample direction required for volume measurement; Step 3): Obtain the scanning working curve: Move the measuring battery to different positions corresponding to different system focal lengths using the sample moving module to obtain different image features, and plot the image feature-system focal length curve, which is the scanning working curve; Step 4): Start volume measurement: Set the battery charge and discharge measurement conditions through the battery test module, set the scanning interval required for volume measurement, and then scan along the perpendicular to the sample surface. The computer host calculates the image features in real time during the scanning process, moves the sample through the sample moving module to keep the acquired image features constant at the working image features, records the sample movement path, and combines it with the scanning working curve to realize the detection of the volume change of the single-layer electrode of the lithium-ion battery.

8. The application according to claim 7, characterized in that, After the coin cell lithium-ion battery is assembled in step 1), an initialization operation is performed, including settling, formation, and venting. The initialization of the detection device includes turning on the device light source and turning on all modules in the device. Then, communication with the image acquisition device, sample movement module, temperature and humidity test module, and battery test module is realized sequentially through the computer host. Finally, the sample position is manually adjusted so that the image acquisition device can acquire a clear image of the test sample surface.

9. The application according to claim 7, characterized in that, The operation steps also include, while acquiring image features, the temperature and humidity testing module continuously reads temperature values ​​in real time to obtain a temperature-time curve; before the volume test, the test battery system containing the sample is left to stand for no less than 6 hours to obtain the image feature-temperature relationship, and temperature calibration is performed through the temperature-time curve and the image feature-temperature relationship to eliminate the influence of temperature fluctuations in the measurement environment on the image features.

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