Lithium ion battery single-layer pole piece volume change detection device and application thereof

Abstract

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

Description

Technical Field

[0001] The present invention relates to a device for detecting volume changes of a single-layer pole piece of a lithium-ion battery, and in particular to a device for detecting volume changes of a single-layer pole piece of a lithium-ion battery based on image feature extraction technology. Background Art

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

[0003] It can be said that studying the uneven expansion of lithium-ion battery electrode materials at the level of single-layer pole pieces is of great significance for improving the energy density of lithium-ion batteries and reducing safety hazards. However, existing detection methods for measuring the volume expansion of single-layer pole pieces, such as the electrochemical dilatometer measurement method, can only detect the overall volume change behavior of lithium-ion battery pole pieces during the charging and discharging process, and do not have spatial resolution capabilities; at the same time, the sensors required for its measurement are expensive and difficult to promote.

[0004] When the volume expansion of a single-layer electrode of a lithium-ion battery is spatially heterogeneous, the measurement of its heterogeneity is transformed into the measurement of the overall thickness and surface morphology of the material. As an important technical means to characterize the surface morphology of materials, atomic force microscopy has atomic-level measurement accuracy. However, when the electrode has a highly uneven surface morphology, is wetted by electrolyte in the working environment, and a solid electrolyte interface is generated on the surface, the scanning rate and scanning accuracy of the atomic force microscope will be limited. At the same time, the atomic force microscope cannot measure the overall volume change of the material. When the system works at a higher charge and discharge rate, the volume expansion of the material will also affect its scanning process. It can be said that imaging the uneven volume expansion of a single-layer electrode faces huge challenges. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a device for detecting volume changes of a single-layer pole piece of a lithium-ion battery and its application, so as to solve the imaging problem of uneven volume expansion of a single-layer pole piece.

[0006] Technical solution: A device for detecting volume change of a single-layer electrode of a lithium-ion battery of the present invention comprises:

[0007] An image acquisition module, including an optical imaging system and an image acquisition device, for real-time optical imaging and image collection of samples;

[0008] A button-type lithium-ion battery, used to load a test sample and provide anhydrous and oxygen-free conditions required for the normal operation of the button-type lithium-ion battery, wherein the button-type lithium-ion battery is provided with a window for optical imaging;

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

[0010] Temperature and humidity test module, used to measure changes in test environment temperature and humidity during battery testing;

[0011] The sample moving module is used to test the quantitative movement of the battery in the vertical sample direction and complete the quantitative movement process during the volume measurement of the single-layer pole piece of the lithium-ion battery;

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

[0013] Furthermore, the optical imaging system includes a light source, an objective lens and an objective lens adapter component, and adopts a reflective light path. After the illumination light is incident from the light source, it is reflected and scattered on the sample surface, and the outgoing light enters the image acquisition device through the objective lens and the objective lens adapter component to achieve reflective imaging of the sample surface.

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

[0015] Furthermore, the button-type lithium-ion battery includes a sample electrode piece and a counter electrode piece for testing volume change, a detachably connected test battery upper cover, a test battery cell body and a test battery lower cover, wherein a test battery conductive column and a conductive spring are arranged between the test battery cell body and the test battery lower cover; the test electrode upper cover is provided with a through hole, a glass window piece and a fixing ring are arranged on one side of the through hole, the counter electrode piece is placed between the glass window piece and the through hole, a perforated diaphragm is arranged on the other side of the through hole, and the sample electrode piece is placed between the diaphragm and the test battery conductive column.

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

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

[0018] The present invention provides an application of the above device in detecting the volume change of a single-layer pole piece of a lithium-ion battery, including the measurement of the overall volume change behavior of the pole piece and the imaging of the volume change process of the pole piece in space.

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

[0020] Step 1): Loading the test sample into the button lithium-ion battery to complete the initialization of the detection device;

[0021] Step 2): Setting the scanning range and working image features in the vertical sample direction required for volume measurement;

[0022] Step 3): Obtaining a scanning working curve: The measuring cell is moved to different positions corresponding to different system focal lengths by the sample moving module to obtain different image features, and an image feature-system focal length curve is drawn, 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 perpendicular to the sample surface. The computer host calculates the image features during the scanning process in real time, moves the sample through the sample moving module, makes the acquired image features constant at the working image features, records the movement path of the sample, and combines the scanning working curve to realize the detection of the volume change of the single-layer electrode of the lithium-ion battery.

[0024] Furthermore, in the step 1), after the button-type lithium-ion battery is assembled, an initialization operation is performed, including standing, forming, and exhausting; the initialization of the detection device includes: turning on the device light source and turning on each module in the device; thereafter, communicating with the image acquisition device, the sample moving module, the temperature and humidity test module, and the battery test module in sequence through the computer host; finally, manually adjusting the sample position so that the image acquisition device can capture a clear image of the test sample surface.

[0025] Furthermore, the operation steps also include that while acquiring the image features, the temperature and humidity testing module reads the temperature value in real time to obtain the temperature-time curve; before the volume test, the test battery system where the sample is located 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 the image features on the temperature fluctuations of the measurement environment.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: This method realizes the online measurement and imaging of the overall volume change of a single-layer electrode sheet of a lithium-ion battery through real-time acquisition and subsequent analysis of scanned images, so that the volume change detection of the lithium-ion battery electrode sheet has spatial resolution. This method has the characteristics of non-destructive detection, high temporal resolution, and strong universality. After obtaining the uneven volume change of a single-layer electrode sheet during charging and discharging, combined with the charge state and health state of the lithium-ion battery for analysis, it is expected to answer the relationship between the degree of uneven volume change and the degree of material aging, and provide more methods and ways to reduce the safety hazards of lithium-ion batteries and achieve hazard warnings, thereby promoting the healthy development of the lithium-ion battery industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of a volume change detection device for a single-layer pole piece of a lithium-ion battery based on optical imaging according to the present invention;

[0028] Figure 2 A schematic diagram of the structure of a button-type lithium-ion battery for optical imaging;

[0029] Figure 3 It is a structural schematic diagram of the test battery upper cover, the test battery cell body and the test battery lower cover;

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

[0031] Figure 5 Image features of the surface of the lithium iron phosphate material obtained according to the image feature extraction technology provided in the embodiment of the present invention;

[0032] Figure 6 An example scanning curve for the volume measurement process of a lithium iron phosphate positive electrode sheet provided in an embodiment of the present invention;

[0033] Figure 7 An image feature evolution curve is obtained during the measurement of the volume change of the battery pole piece provided in the embodiment of the present invention;

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

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

[0036] Fig.10 Schematic diagram of the surface morphology of the battery electrode when the lithium iron phosphate SOC = 100%.

[0037] In the figure, 1-light source; 2-objective lens; 3-image acquisition device; 4-button lithium-ion battery; 5-sample moving module; 6-temperature and humidity test module; 7-battery test module; 8-monitor; 9-computer host; 10-test battery upper cover; 11-test battery cell body; 12-test battery lower cover; 13-fixing ring; 14-glass window; 15-counter electrode plate; 16-diaphragm; 17-sample plate; 18-test battery conductive column; 19-conductive spring. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0039] Example 1

[0040] This embodiment provides a button-type lithium-ion battery for optical imaging and an assembly method thereof. The button-type lithium-ion battery provides the water-free, oxygen-free, sufficient electrolyte, and battery conductive path required by lithium-ion batteries, and its special structural design allows the use of optical methods to image and measure it.

[0041] like Figure 2-3 As shown, the button-type lithium-ion battery for optical imaging of this embodiment includes a sample electrode 17 (battery positive electrode) for testing volume change, a counter electrode 15 (battery negative electrode), a metal lithium sheet or a lithium titanate electrode, a diaphragm 16, a test battery upper cover 10, a glass window 14 and a fixing ring 13, a test battery cell body 11, a test battery lower cover 12, a test battery conductive column 18 and a conductive spring 19;

[0042] The test electrode cover 10 is a cylindrical stainless steel product with a depression inside and a through hole in the center. There are depressions on both sides of the through hole for placing a sealing gasket and a glass window 14. The thread of the fixing ring 13 matches and is pressed against the thread of the test electrode cover 10 to form the introduction and sealing of the glass window 14.

[0043] In order to isolate the volume change of the test sample counter electrode (mainly metal lithium sheet), the sample 17 and the counter electrode sheet 15 are placed without contact and fixed separately; the counter electrode sheet 15 is placed between the glass window sheet 14 and the through hole of the test electrode upper cover 10, the perforated diaphragm 16 is placed on the other side of the through hole of the test electrode upper cover 10, and the sample electrode sheet 17 is placed between the diaphragm 16 and the test battery conductive column 18. The test electrode upper cover 10 and the test battery lower cover 12 are both provided with countersunk screw holes for connection and fixation with the corresponding nuts in the test battery cell body 11.

[0044] When assembling the button-type lithium-ion battery, it is necessary to assemble it from the top cover to the bottom cover in a glove box with a protective gas atmosphere as shown in the figure;

[0045] When assembling the test battery cover 10, first place the counter electrode plate 15 on the glass window 14 side of the cover. When using a material plate, the collector side of the plate 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 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. Then introduce a sealing rubber gasket into the recess on one side of the test battery cell body 11, opposite to the test battery cover 10, connect it with countersunk screws, assemble and fix it, and the assembly of the test battery cover 10 and the test battery cell body 11 is completed.

[0046] After the above assembly steps are completed, a small amount of lithium-ion battery electrolyte is injected into the test battery cell body 11 to achieve negative electrode infiltration and cell body leakage detection; after the electrolyte fully infiltrates and submerges the M-shaped through hole of the test battery upper cover 10, a lithium-ion battery separator 16 with a hole punched in the center that has been fully infiltrated in advance is added to the test battery cell body 11, and its hole is aligned with the center of the M-shaped through hole. At the same time, the hole of the separator 16 should be slightly smaller than the M-shaped through hole to avoid contact between the positive and negative electrodes of the battery and cause a battery short circuit; after eliminating the bubbles that may be caused by the introduction of the separator 16, the The material surface of the sample electrode 17 for volume change detection should face downward during assembly, and its status should be observed at the upper glass window 14 to ensure that it is located in the center and is fully soaked by the lithium-ion battery electrolyte; after adding a proper amount of electrolyte, adding the test electrode conductive column 18 and the conductive spring 19, the electrolyte is added until the entire cavity is filled, and finally the lower cover 12 of the test battery is pressed, and the overall packaging is completed by countersunk screws; after assembly is completed, turn over the test battery to observe whether there are bubbles introduced by the packaging on the upper cover side and whether the position of the test sample is correct.

[0047] Example 2

[0048] like Figure 1 As shown, this embodiment provides a lithium-ion battery single-layer pole piece volume change detection device based on image feature extraction, including: an image acquisition module, a button-type lithium-ion battery 4 for optical imaging, a battery testing module 7, a temperature and humidity testing module 6, a sample moving 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 central wavelength of 810 nanometers, the objective lens 2 uses an objective lens with a magnification of 20 times and a numerical aperture of 0.45, and the image acquisition device 3 uses an electronic coupling element as an image acquisition device. The image acquisition module adopts a reflective light path. After the illumination light is incident from the light source 1, it is reflected and scattered on the sample surface. The outgoing light enters the image acquisition device 3 through the objective lens 2 and the objective lens adapter component to realize the reflective imaging of the sample surface; by communicating with the computer host 9 in the real-time monitoring and communication module, the image acquired by the image acquisition device 3 will enter the memory and be reserved for subsequent calculations.

[0050] The button-type lithium-ion battery 4 used for optical imaging adopts the measuring device and assembly method described in Example 1. Before performing the single-layer pole piece volume change detection, it needs to be subjected to battery initialization operations such as static, formation, and exhaust.

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

[0052] The temperature and humidity test 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 to communicate 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 moving module 5 is used to quantitatively move the sample in the vertical sample direction. 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 driving 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 moving 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] When initializing the detection device, the device light source 1 should be turned on first to turn on all modules in the device; thereafter, the computer host 9 is used to communicate with the image acquisition device 3, the sample moving module 5, the temperature and humidity test module 6, and the battery test module 7; finally, the sample position is manually adjusted so that the image acquisition device 3 can capture a clearer image of the test sample surface. At this point, the initialization of the single-layer pole piece volume change detection device based on optical imaging is completed.

[0056] Example 3

[0057] This embodiment respectively demonstrates the principles of the feature acquisition method, feature description method, and feature noise reduction technology of the image feature extraction technology, and demonstrates a method for expanding the image feature extraction technology into a spatial image feature extraction technology.

[0058] Feature acquisition method

[0059] The feature acquisition method can obtain image features by calculating the image. Since the image is essentially a matrix, the image feature is actually a matrix of the same size as the original image. In the image acquisition module (a specific optical system) described in the present invention, the image feature is specifically manifested as the convolution of the point spread function of the optical system and the average morphological features of the particles on the surface of the pole piece. Since the point spread function is related to the focal length of the optical system, the image feature will be able to reflect the focal length change of the measurement system and can be used for volume change detection of battery pole pieces; since the average morphological features of the surface particles are related to the average particle size of the particles, the unit of the image feature can be expressed in length units. The volume change detection device provided by the present invention generally uses micrometers as units.

[0060] The image-based calculation formula used by the feature acquisition method is:

[0061]

[0062] like Figure 4 As shown, the image is composed of pixels arranged in a certain way. Each pixel has its own intensity, which is represented by i and its position in the image coordinates. For example, the intensity of the pixel corresponding to the 1st row and 1st column of an image is represented by i(1,1); taking the pixel at a specific position as the reference, the correlation between the intensity of the remaining pixels and the intensity of the pixel is calculated in turn, and the correlation value of the pixel will be obtained; the above operation is performed on each pixel in the image range in turn, as shown in the above formula, and finally the original image feature of the same size as the image will be obtained for subsequent calculations.

[0063] Feature Description Method

[0064] The feature description method can simplify and describe the image features. Since the above feature acquisition method only obtains a matrix of image features, it is necessary to simplify it to achieve the description of image features.

[0065] The image features can be understood as the convolution of the real morphological features of the sample and the point spread function of the imaging system. The real morphological features of the sample can be understood as the average particle size of the particles, so it should have a length unit.

[0066] In the optical system described in the present invention, when the numerical aperture of the system light source and the objective lens remains unchanged, its point spread function will only be affected by the focal length of the system. Because the point spread function of the optical system is subject to the diffraction limit and is related to the wavelength of the light source (such as the central bright spot diameter of the Airy disk d = 2.44*λ, λ is the wavelength of the light source), it also has a length feature. Therefore, the image feature should have a length unit, and micrometers are used as the unit in the present invention.

[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 part of the center in the original image feature matrix is ​​selected for feature description.

[0068] In the present invention, two-dimensional Gaussian fitting (normal distribution) is used to describe image features, and the formula is:

[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 standard deviation in the x direction, C represents standard deviation in the y direction, and D represents 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 Noise Reduction Technology

[0073] Feature noise reduction technology will be mainly used to optimize optical systems and improve measurement sensitivity. Because both feature acquisition methods and feature description methods start from the image itself, their performance is affected by the quality of the acquired image itself.

[0074] When the image acquisition device is working, it will be affected by electronic interference and ambient light interference, which will affect the quality of the acquired image. The interference of such random noise on image features can be reduced by improving the average image level. At the same time, the appropriate exposure time and camera gain level will further improve the quality of the acquired image.

[0075] Since the image characteristics are affected by the point spread function of the optical system, the optical elements in the optical system will also affect the sensitivity of the volume measurement system. The measurement sensitivity of a long-wave light source will be better than that of a short-wave light source; at the same magnification, the measurement sensitivity of an objective lens with a larger numerical aperture is better than that of an objective lens with a smaller numerical aperture.

[0076] Spatial Image Feature Extraction Technology

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

[0078] By setting the window size and window step, the original input image can be divided using the convolution idea, and the feature acquisition technology, feature description technology, and feature denoising technology can be used in sequence to obtain a spatial image feature distribution map.

[0079] For a specific part of the material, there is a specific image feature; by recording the changes in the image features of this part and combining it with the scanning working curve of the area, the spatial image feature extraction technology allows us to perform real-time imaging of the volume changes 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; at the same time, because the pole piece is composed of many particles stacked (typical thickness is 40 microns), the thickness of the pole piece will also change. When the position of the objective lens and the light source in the optical system remains unchanged, the changing thickness will cause a change in the degree of focus, causing a change in the point spread function, and thus affecting the image characteristics.

[0082] Therefore, for a lithium-ion battery electrode material system, the image characteristics of its surface image will be affected by both the surface particle size and the system focal length. However, the impact of the system focal length on the image characteristics is far greater than the impact of the change in particle size. It can be considered that the change in surface particle size under different charge states will not affect the image characteristics.

[0083] Therefore, by moving the measurement 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] In order to keep the image features of the acquired image at the working image features, it is necessary to scan perpendicular to the sample surface: move the measuring cell to different positions (corresponding to different system focal lengths) to obtain different image features, draw the image feature-system focal length curve, and define it as the scanning working curve.

[0085] By obtaining the scanning working curve, calculating the sample position corresponding to the working image feature, and moving the test battery to this position, the image feature can be maintained.

[0086] Scanning measurement parameter optimization and measurement feedback algorithm

[0087] Due to the operation of the sample moving module and the introduction of the average image level, the acquisition of a scanning working 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 time resolution of the volume measurement. To this end, it is necessary to adjust the scanning measurement parameters.

[0088] According to the results of in-situ X-ray crystal diffraction, the volume of graphite anode material changes by about 10% during the cycle, which corresponds to a volume change of about 4 microns. Therefore, the scale of the scanning working curve should be controlled within an appropriate range, generally about 5 microns.

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

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

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

[0092] Example 5

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

[0094] The principle of this method is that the volume change of the electrode material during the charging and discharging process will affect the focal length of the optical system. Select a working image feature with higher sensitivity, continuously scan and move the sample in the vertical direction of the sample, so that the image feature position of the test battery system is constant, and the volume change of the electrode material can be monitored. The method includes the following steps:

[0095] Step 1) assembling button-type lithium-ion batteries for optical imaging, and completing the static, formation, and exhaust battery initialization operations after the assembly is completed;

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

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

[0098] Step 4) Setting the vertical sample direction scanning range and working image features required for volume measurement, the image features will be obtained according to the image feature extraction technology; the image features of the image obtained during the measurement process will fluctuate around the working image features; setting the scanning interval required for volume measurement;

[0099] Step 5) Setting the battery measurement conditions of the battery test module;

[0100] Step 6) Start volume measurement and perform real-time calculation on the acquired image to maintain the constant image features; acquire image features - vertical position curve, temperature curve, real-time volume change curve of the pole piece and display them on the monitor; also include static and temperature calibration process, battery charge and discharge test process;

[0101] Step 7) using the temperature calibration curve obtained during the static process, combined with the calibration temperature curve obtained during the battery charge and discharge process, to correct the volume test curve, and obtain a single-layer electrode volume change measurement curve that eliminates the effect of temperature on the method;

[0102] Step 8) Using the spatial image feature extraction technology, the working image feature image obtained during the measurement process is calculated, and combined with the scanning working curve, the imaging of the volume change process of the single-layer pole piece is realized.

[0103] Test example

[0104] Taking a button-type lithium-ion battery with a lithium plate as the negative electrode and a lithium iron phosphate plate as the positive electrode as an example, according to the method described in Example 5, an accurate volume change curve of the lithium iron phosphate plate and an image of the surface morphology change of the plate can be obtained.

[0105] Specifically, Figure 4 The surface image of the lithium iron phosphate positive electrode sheet obtained by the optical microscopic imaging module of the present invention is shown; Figure 5 The image features of the surface of lithium iron phosphate material obtained by the present invention according to the image feature extraction technology are shown; Figure 6 A scanning working curve during the measurement process is shown, and its image feature value is equal to the vertical sample direction position corresponding to the working image feature, that is, the material surface height measured in this scan.

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

[0107] Figure 8It reflects the volume change of the lithium iron phosphate electrode and the change of the button lithium-ion battery voltage; during the charging process, the lithium iron phosphate voltage increases and the volume decreases; during the discharging process, the lithium iron phosphate voltage decreases and the volume increases.

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

[0109] The uneven volume change at the pole piece level may be caused by rough production processes and uniform electrode coatings; the uneven degree of pole piece volume change can be used as an indicator to evaluate material production and coating processes, and reduce safety hazards of lithium-ion batteries at the pole piece level. At the same time, when the volume detection method has spatial resolution, it will also be more suitable for evaluating the unevenness 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 changes of a single-layer electrode of a lithium-ion battery, characterized in that: include: An 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 button-type lithium-ion battery, used to load the test sample and provide the anhydrous and oxygen-free conditions required for the normal operation of the button-type lithium-ion battery, wherein the button-type lithium-ion battery is provided with a window for optical imaging; Battery testing module, used to set battery testing conditions, perform charge and discharge cycles on the battery, and obtain real-time electrochemical parameters; Temperature and humidity test module, used to measure changes in test environment temperature and humidity during battery testing; The sample movement module is used to test the quantitative movement of the battery in the vertical sample direction and complete the quantitative movement process during the volume measurement of the single-layer electrode of the lithium-ion battery; The real-time monitoring and communication module includes a monitor and a computer host. The computer host controls each module in the device and reads data by communicating with the image acquisition device, sample movement module, temperature and humidity test module, and battery test module. The monitor is used to output the volume change curve of the lithium-ion battery under test conditions.

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

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

4. The device for detecting volume change of a single-layer electrode of a lithium-ion battery according to claim 1, wherein: The button-type lithium-ion battery includes a sample electrode and a counter electrode for testing volume changes, a detachably connected test battery upper cover, a test battery cell body, and a test battery lower cover. A test battery conductive column and a conductive spring are arranged between the test battery cell body and the test battery lower cover; the test electrode upper 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 column.

5. The device for detecting volume change of a single-layer electrode of a lithium-ion battery according to claim 4, characterized in that: The fixing ring and the test battery upper cover are provided with matching threads, and the fixing ring is used to press the glass window and seal it.

6. The device for detecting volume change of a single-layer electrode of a lithium-ion battery according to claim 4, characterized in that: The test electrode upper cover, the test battery lower cover and the test battery body are all connected by threads.

7. An application of the device according to any one of claims 1 to 6 in detecting volume changes of a single-layer electrode of a lithium-ion battery, characterized in that: It includes the measurement of the overall volume change behavior of the pole piece and the imaging of the pole piece volume change process in space.

8. The use according to claim 7, characterized in that The steps are as follows: Step 1): loading the test sample into the button lithium-ion battery to complete the initialization of the detection device; Step 2): Set the scanning range and working image features in the vertical sample direction required for volume measurement; Step 3): Obtaining a scanning working curve: The sample moving module moves the measurement cell to different positions corresponding to different system focal lengths to obtain different image features, and draws an 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 perpendicular to the sample surface. The computer host calculates the image features during the scanning process in real time, moves the sample through the sample movement module, makes the acquired image features constant at the working image features, records the movement path of the sample, and combines the scanning working curve to realize the detection of the volume change of the single-layer electrode of the lithium-ion battery.

9. The use according to claim 8, characterized in that After the button-type lithium-ion battery is assembled in step 1), an initialization operation is performed, including resting, forming, and exhausting. The initialization of the detection device includes: turning on the device light source and enabling each module in the device; thereafter, sequentially communicating with the image acquisition device, the sample movement module, the temperature and humidity test module, and the battery test module through the computer host; finally, manually adjusting the sample position so that the image acquisition device can capture a clear image of the test sample surface.

10. The use according to claim 8, characterized in that The operation steps also include that while acquiring image features, the temperature and humidity test module continuously reads the temperature value in real time to obtain a temperature-time curve; before volume testing, the test battery system where the sample is located is allowed 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 the image features on the temperature fluctuation of the measurement environment.

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