Method and system for testing internal stress distribution and change of battery

Abstract

The invention provides a battery internal stress distribution and change test method and system, and relates to the technical field of battery detection, and the method comprises the steps: S1, replacing an original diaphragm with an ionic membrane in a lithium ion battery manufacturing process, testing a plurality of lithium ion batteries under different test pressures, and disassembling and taking out all the ionic membranes after the test is completed; and S2, acquiring membrane images of all ionic membranes, and comparing the membrane images to obtain stress distribution and change results. The method has the beneficial effects that the stress distribution of each position of the pole piece can be globally reflected, abnormal points can be accurately positioned, the method is sensitive to tiny stress difference, key risk areas such as poor pole piece fitting and local overpressure can be detected, the stress distribution of an arc-shaped surface can be completely analyzed, white stripes or spots caused by uneven left and right tension can be identified, and the detection comprehensiveness is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery detection, and in particular to a test method and system for internal stress distribution and change of a battery. BACKGROUND

[0002] Lithium ion batteries have become the core energy storage devices in the fields of mobile electronic devices, electric tools and new energy vehicles, etc. due to their high specific capacity, small self-discharge, wide operating temperature range, long cycle life and other advantages. However, the performance degradation of lithium ion batteries is closely related to the internal stress change: the increase of internal stress will lead to problems such as closure of the separator and rupture of the SEI film, thereby causing capacity attenuation, lithium and salt precipitation and other safety hazards, and even causing the risk of thermal runaway. Especially in the wound battery, the left and right tension of the electrode sheet is uneven due to the winding process, which leads to uneven stress distribution and further aggravates the performance degradation. At present, there is still a lack of effective means for precise monitoring of the internal stress distribution and dynamic change of lithium ion batteries, which seriously restricts the optimization of battery design and the improvement of reliability.

[0003] In the prior art, the internal stress of the battery is mainly evaluated by the following two methods: one is to use an internal or external pressure sensor, but this method can only measure the pressure value at a single point and cannot reflect the stress distribution characteristics at each position of the electrode sheet of the battery; the other is to use pressure-sensitive paper to test the surface stress of the battery, but this method requires a large pressure to be applied, which masks the difference in internal stress of the battery, and there is a blind area in the detection of the surface stress distribution of the curved electrode sheet of the wound battery, which cannot accurately identify the uneven left and right tension problem. In addition, the pressure-sensitive paper has insufficient sensitivity to small pressure changes, and it is difficult to capture the poor adhesion of the electrode sheet in the low stress area (which is prone to lithium / salt precipitation) and the critical point of safety risk in the high stress area. The above defects make the existing method unable to meet the high-precision analysis requirements of the dynamic distribution of internal stress in the development of new batteries and the optimization of production line process. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a test method for internal stress distribution and change of a battery, comprising:

[0005] Step S1: replacing the original separator with an ion film during the process of a lithium ion battery, testing a plurality of lithium ion batteries under different test pressures, and disassembling and removing all the ion films after the test is completed;

[0006] Step S2: collecting the film images of all the ion films, and obtaining the stress distribution and change results by comparing each film image.

[0007] Preferably, the step S2 comprises:

[0008] Step S21, the ion membrane obtained by disassembling is placed in a standard light box with constant temperature and humidity, and a multi-spectral imaging system is used to collect the membrane image;

[0009] Step S22, for each of the membrane images, the stress distribution uneven area and the stress distribution uniform area existing in the membrane image are identified, and the gray scale of the stress distribution uneven area and the gray scale of the stress distribution uniform area are matched with the pre-constructed standard stress-gray scale database respectively to obtain the corresponding stress.

[0010] Step S23, for each of the membrane images, the pressure difference between each of the stress distribution uneven area and the stress distribution uniform area is calculated respectively.

[0011] Step S24, the membrane images are sequentially sorted according to the test pressure, the stress distribution uneven area with an overlapping part between adjacent membrane images is associated, and the area growth rate ratio of the associated stress distribution uneven area is calculated.

[0012] Step S25, for each of the stress distribution uneven area in each of the membrane images, the stress distribution uniform area which does not overlap with any stress distribution uneven area in the adjacent membrane image is marked as a newly appeared stress uneven area.

[0013] Step S26, all the newly appeared stress distribution uneven areas and the area growth rate ratios of all the stress distribution uneven areas are taken as the stress distribution and change results.

[0014] Preferably, the establishment process of the standard stress-gray scale database comprises:

[0015] A pressure calibration device is arranged in a glove box, and then the standard ion membrane is tested by gradually adjusting the pressure through the pressure calibration device for multiple times of static pressure testing, a plurality of pressure points with different gray scales are formed on the standard ion membrane, and a standard pressure-gray scale database is established.

[0016] Preferably, edge feature points are arranged in advance at the four corners of the ion membrane; and after the membrane image is collected in step S21, the image correction process further comprises:

[0017] The adjacent edge feature points are sequentially connected to form an image collection area, an initial image in the image collection area is collected, then one of the vertices of the initial image is taken as a reference point, the reference point is overlapped with the reference point of the pre-saved standard membrane image, then the remaining vertices of the initial image are sequentially overlapped with the remaining vertices of the standard membrane image in the order of adjacent first and then relative, and the stretching correction of the initial image is completed to obtain the corrected membrane image.

[0018] Preferably, the surface of the ion membrane is coated with an LATP coating corresponding to the negative electrode of the lithium ion battery.

[0019] Preferably, the standard light box is provided with an ion membrane stretching device, and the ion membrane is pressed and reversely stretched at both ends by the ion membrane stretching device.

[0020] Preferably, the bottom surface of the standard light box is provided with a vacuum adsorption platform.

[0021] The application also provides a test system for internal stress distribution and change of a battery, which applies the test method, and comprises:

[0022] A result detection module is configured to replace the original separator with the ion membrane during the process of the lithium ion battery, test a plurality of lithium ion batteries under different test pressures, disassemble and take out all the ion membranes after the test is completed, then collect the membrane images of all the ion membranes, and obtain the stress distribution and change results by comparing the membrane images.

[0023] Preferably, the result detection module comprises:

[0024] An image collection unit is configured to place the disassembled ion membrane into a standard light box with constant temperature and humidity, and collect the membrane images by using a multi-spectral imaging system;

[0025] A stress detection unit is connected to the image collection unit and is configured to, for each of the membrane images, identify the stress distribution uneven area and the stress distribution uniform area existing in the membrane image, and match the gray scale in the stress distribution uneven area and the gray scale of the stress distribution uniform area with a pre-constructed standard stress-gray scale database respectively to obtain the corresponding stress.

[0026] A pressure difference calculation unit is connected to the stress detection unit and is configured to, for each of the membrane images, calculate the pressure difference between each of the stress distribution uneven areas and the stress distribution uniform area respectively.

[0027] A speed increase calculation unit is connected to the stress detection unit and is configured to sort the membrane images in order according to the test pressure, associate the stress distribution uneven areas with overlapping parts between adjacent membrane images, and calculate the area speed increase ratio between the associated stress distribution uneven areas.

[0028] A new area marking unit is connected to the stress detection unit and is configured to, for each of the stress distribution uneven areas in each of the membrane images, mark the stress distribution uniform area which does not overlap with any stress distribution uneven area in adjacent membrane images as a newly appeared stress uneven area.

[0029] The result output unit is connected with the new area marking unit, the speed increasing calculating unit and the pressure difference calculating unit, and is used for taking all the area speed increasing ratios of the new stress distribution uneven areas and all the stress distribution uneven areas as stress distribution and change results.

[0030] Preferably, the method comprises a standard stress-gray database establishing module, which is used for setting a pressure calibration device in a glove box, then gradually adjusting the pressure on the standard ion membrane through the pressure calibration device for multiple times of static pressure testing, forming multiple pressure points with different gray scales on the standard ion membrane, and establishing a standard pressure-gray database.

[0031] The above technical scheme has the following advantages or beneficial effects:

[0032] 1. Solving the limitation of single-point measurement: the traditional pressure sensor can only obtain single-point pressure data, while the image formed by the color change of the ion membrane can globally reflect the stress distribution of each position of the pole piece, and accurately locate the abnormal points.

[0033] 2. Breaking through the insufficient sensitivity of pressure-sensitive paper: the pressure-sensitive paper needs to be applied with a large pressure to develop color, while the ion membrane can produce color change due to lithium ion migration during normal charging and discharging of the battery, without the need for additional pressure, and is sensitive to small stress differences, and can detect key risk areas such as poor adhesion of the pole piece (low stress) and local overpressure (high stress).

[0034] 3. Covering the detection blind area of the winding type battery: the traditional pressure-sensitive paper cannot detect the arc-shaped pole piece of the winding type battery, while the present scheme can analyze the stress distribution of the arc-shaped surface by image acquisition after disassembly, and can identify the white stripes or spots caused by uneven left and right tension, thereby significantly improving the detection comprehensiveness. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 In a preferred embodiment of the present application, a flowchart of a battery internal stress distribution and change testing method is shown;

[0036] Figure 2 In a preferred embodiment of the present application, a sub-flowchart of step S2 is shown;

[0037] Figure 3 In a preferred embodiment of the present application, a schematic diagram of an ion membrane is shown;

[0038] Figure 4 In a preferred embodiment of the present application, a structural diagram of a battery internal stress distribution and change testing system is shown. DETAILED DESCRIPTION

[0039] The application will be described in detail below with reference to the drawings and specific embodiments. The application is not limited to this embodiment, and other embodiments can also fall within the scope of the application as long as they meet the main idea of the application.

[0040] In a preferred embodiment of the application, based on the above-mentioned problems existing in the prior art, a test method for the stress distribution and change in the battery is provided, as shown in Figure 1 The test method comprises the following steps:

[0041] Step S1, replacing the original separator with an ion membrane during the process of the lithium ion battery, testing a plurality of lithium ion batteries under different test pressures, and disassembling and taking out all ion membranes after the test is completed;

[0042] Step S2, collecting the membrane images of all ion membranes, and comparing the membrane images to obtain the stress distribution and change results.

[0043] Specifically, in the embodiment, the test method has the following beneficial effects:

[0044] 1. Full-area stress visualization detection: by replacing the original separator with an ion membrane, and using the color change characteristics (white→black) during the charging and discharging process, the stress distribution of the battery internal electrode sheet can be intuitively and completely presented, overcoming the limitations of single-point measurement of traditional pressure sensors, and realizing the visualization analysis of the stress state of the whole electrode sheet.

[0045] 2. High sensitivity and low pressure detection capability: the color change of the ion membrane is sensitive to small stress differences, and can accurately capture the poor adhesion of the electrode sheet in the low pressure area (such as the lithium / salt precipitation risk area) and the stress concentration point in the high pressure area, solving the problem that the pressure-sensitive paper covers the subtle stress difference due to the need to apply large pressure.

[0046] 3. Adapt to complex structure battery detection: especially suitable for the detection of arc-shaped electrode sheets of wound batteries. After disassembly, the membrane image analysis can clearly identify the left and right stress distribution differences caused by uneven tension during winding, breaking through the technical bottleneck that traditional pressure-sensitive paper cannot cover the arc surface.

[0047] 4. Dynamic stress change tracking capability: through multi-pressure gradient testing and membrane image comparison, the area growth rate ratio of the uneven stress distribution area under different pressures can be associated, and the stress change trend can be dynamically tracked, providing data support for battery process optimization.

[0048] 5. Non-invasive in-situ monitoring: the ion membrane directly participates in the charging and discharging process as an internal component of the battery, without the need for external sensors, and the ion membrane obtained after disassembly is closer to the stress state representation under real working conditions.

[0049] The stress-color response mechanism of the LATP ion membrane is used to innovatively convert the internal stress distribution of the battery into visual image information, and the advantages of high sensitivity, global coverage and dynamic tracking are combined, so that the defects of the traditional method in the detection range, precision and applicability are fundamentally solved, and an efficient tool is provided for process optimization and reliability improvement of the lithium ion battery.

[0050] In the preferred embodiment of the present application, as shown in Figure 2 The step S2 includes:

[0051] In step S21, the disassembled ion membrane is placed in a constant temperature and humidity standard light box, and a multispectral imaging system is used to collect membrane images.

[0052] In step S22, for each membrane image, the stress distribution uneven area and the stress distribution uniform area existing in the membrane image are identified, and the gray scale of the stress distribution uneven area and the gray scale of the stress distribution uniform area are matched with the pre-constructed standard stress-gray database to obtain the corresponding stress.

[0053] In step S23, for each membrane image, the pressure difference between each stress distribution uneven area and the stress distribution uniform area is calculated.

[0054] In step S24, the membrane images are sequentially sorted according to the test pressure, the stress distribution uneven areas with overlapping parts between adjacent membrane images are associated, and the area growth rate ratio of the associated stress distribution uneven areas is calculated.

[0055] In step S25, for each stress distribution uneven area in each membrane image, the stress distribution uniform area that does not overlap with any stress distribution uneven area in the adjacent membrane image is marked as a newly appeared stress uneven area.

[0056] In step S26, all newly appeared stress distribution uneven areas and the area growth rate ratio of all stress distribution uneven areas are used as the stress distribution and change result.

[0057] Specifically, in the present embodiment, step S21 realizes standardized image acquisition

[0058] 1. The constant temperature (such as 25℃) and constant humidity (such as 50% RH) standard light box can avoid color distortion of the membrane image caused by changes in temperature and humidity, ensure consistent imaging conditions of different test samples, and eliminate environmental interference.

[0059] 2. By multi-band imaging (such as 400-1000nm range) of visible light, infrared and the like, the subtle spectral reflection differences of the LATP coating under different stresses can be captured, and the identification sensitivity of the low gray scale area is enhanced.

[0060] 3. Unified light intensity and angle (e.g. D65 standard light source) to avoid analysis errors caused by external light differences and provide a reference for subsequent image matching.

[0061] Overcome the problem of color instability caused by environmental temperature and humidity sensitivity of pressure-sensitive paper, and improve the reliability of small stress difference detection.

[0062] Step S22 realizes stress area identification and matching

[0063] 1. Identify the stress distribution uneven area (white area) and uniform area (black area) by image segmentation algorithm (such as edge detection, threshold segmentation), such as Figure 3 As shown, for example, define the area with gray value > 200 as high stress area.

[0064] 2. Match the gray scale with the standard database (such as pre-calibrated 0.1 MPa corresponding gray scale 150, 0.5 MPa corresponding gray scale 50), realize the digital conversion from color to stress, for example, the gray scale 180 of a certain area corresponds to 0.8 MPa.

[0065] 3. Combined with the reference gray value of the uniform area (such as gray value 50 under normal stress), real-time correction of database offset caused by film batch difference or aging.

[0066] Instead of traditional single-point sensor discrete data, realize quantitative and visual analysis of the stress distribution of the whole piece of pole piece.

[0067] Step S23 realizes pressure difference calculation

[0068] 1. Calculate the pressure difference between the uneven area and the uniform area (such as 0.3 MPa in a certain area vs. 0.8 MPa in the uniform area, difference 0.5 MPa), quickly identify the risk points exceeding the safety threshold (such as ΔP> 0.4 MPa).

[0069] 2. Show the stress mutation of each position of the pole piece through the difference distribution diagram (such as heat map), and assist in judging the risk of lithium analysis or structural deformation area.

[0070] Quantify the degree of local overpressure / underpressure, and make up for the deficiency of pressure-sensitive paper that cannot provide numerical pressure difference.

[0071] Step S24 realizes correlation analysis and acceleration ratio calculation

[0072] 1. Sort the images according to the pressure gradient (such as 5 MPa, 10 MPa, 15 MPa test group), correlate the overlapping stress area (such as a white spot with an area of 2 mm 2 at 5 MPa, expanded to 5 mm 2 at 10 MPa), calculate the area acceleration ratio ((5-2) / 5=60%), and predict the stress expansion trend.

[0073] 2. If the area growth rate increases sharply in the 10-15 MPa range (e.g. from 30% to 120%), it can be determined that this pressure range is the critical point for battery safety design.

[0074] The nonlinear relationship between stress and pressure is disclosed, providing data support for process parameter optimization (such as winding tension setting).

[0075] Step S25: New stress area marking

[0076] 1. Mark the new stress area that does not overlap with the historical image (such as the white crack area first appearing in the 15 MPa test), indicating process defects or material fatigue.

[0077] 2. Distinguish between real new stress areas and image noise by overlapping verification (such as spatial coordinate matching algorithm), improve detection accuracy.

[0078] Capture the new defects generated by dynamic tension fluctuations in winding batteries, avoid the problem that traditional methods can only detect static stress.

[0079] Step S26 realizes the output of the integrated results

[0080] 1. Integrate the parameters such as new stress area position, area growth rate, and pressure difference into a comprehensive report (such as a heat map superimposed with a growth vector diagram), and intuitively display the stress evolution law.

[0081] 2. For example, a certain type of battery has a new stress area concentrated on the right side of the pole piece at 10 MPa, indicating that the tension mechanism on the right side of the winding equipment needs to be calibrated.

[0082] Provide global and dynamic stress analysis conclusions to support battery design iteration and production line debugging.

[0083] The following provides an example to illustrate the winding battery stress test process of step S2:

[0084] I. Test object

[0085] Power battery winding cell (model NCM811, winding tension setting value 20N)

[0086] II. Implementation process and effect

[0087] Image acquisition (S21):

[0088] Method: After disassembly, the ion membrane is placed in a standard light box (25℃ / 50%RH), and a multispectral camera (wavelength 400-900nm) is used to take pictures.

[0089] Effect: Eliminate environmental light interference, reduce image gray scale standard deviation from ±15 to ±3, and clearly show the stress concentration on the edge of the curved pole piece.

[0090] Stress matching (S22):

[0091] Means: Image segmentation and matching database to identify high stress area gray scale 210 (corresponding to 0.85 MPa).

[0092] Effect: Quantitative discovery of the right side of the pole piece stress (0.85 MPa) is significantly higher than the left side (0.35 MPa), and the winding tension imbalance is located.

[0093] Pressure difference calculation (S23):

[0094] Means: Calculate the right side ΔP = 0.5 MPa (threshold value 0.4 MPa).

[0095] Effect: Mark the right side as a high risk area for lithium precipitation, and guide to strengthen the electrolyte infiltration process in this area.

[0096] Acceleration ratio analysis (S24):

[0097] Means: Correlate 10 MPa and 15 MPa images, and calculate the area acceleration ratio of a certain area from 50% to 130%.

[0098] Effect: Determine that 15 MPa is the upper limit of the safety pressure of the battery cell, and suggest that the battery module design pressure be ≤12 MPa.

[0099] New area marking (S25):

[0100] Means: In the 15 MPa group, 0.6 mm 2 New stress area is found that does not overlap.

[0101] Effect: Trace back to the No. 3 roller wear of the winding machine, and after replacement, the new defect rate is reduced by 70%.

[0102] Result output (S26):

[0103] Means: Generate a comprehensive report, mark the high stress area on the right side, the 15 MPa critical point and the new defect coordinates.

[0104] Effect: After optimizing the winding tension parameters, the cycle life of the battery cell is improved from 800 times to 1200 times.

[0105] Implementation results

[0106] Through the scheme, the stress distribution of the winding type battery arc-shaped pole piece is detected for the first time, the process debugging period is shortened from 3 months to 2 weeks, and the accuracy of the safety pressure threshold value of the battery module is improved by 40%.

[0107] In a preferred embodiment of the present application, the establishment process of the standard stress-gray scale database comprises:

[0108] The pressure calibration device is set in a glove box, and then the standard ion film is tested by gradually adjusting the pressure through the pressure calibration device, thereby forming multiple pressure points with different gray scales on the standard ion film, and establishing a standard pressure-gray scale database.

[0109] Specifically, in the embodiment, the calibration is performed in an inert gas environment glove box (such as an argon atmosphere, humidity <1% RH) to avoid performance drift caused by ion film oxidation or moisture absorption.

[0110] Then, the standard ion film is tested by a pressure calibration device (such as a high-precision servo press, resolution 0.01 MPa) in a step-by-step static pressure (for example, 0.1 MPa, 0.5 MPa, 1.0 MPa…10.0 MPa).

[0111] After the pressure at each pressure point is stabilized (for example, 30 seconds), the same type of multi-spectral imaging system is used to record the gray scale value of the coating, and pressure-gray scale mapping data is generated.

[0112] The advantages over the prior art are:

[0113] 1. Solving the problem of insufficient sensitivity of pressure-sensitive paper:

[0114] The traditional pressure-sensitive paper can only develop color under a pressure of >0.5 MPa, while the present database extends the lower limit of detection to 0.05 MPa through intensive calibration in the low-pressure region, and can identify micron-level defects of the electrode sheet (such as the lithium precipitation germination zone).

[0115] 2. Overcoming the single-point limitation of the sensor:

[0116] The pressure sensor needs to be measured point by point, while the present database supports single imaging to obtain the stress distribution of the entire electrode sheet (such as 10 cm x 5 cm electrode sheet detection at one time) through full-film calibration.

[0117] 3. Improving the applicability of the detection of the wound battery:

[0118] In view of the stress gradient characteristics of the arc-shaped electrode sheet of the wound battery, the arc-shaped pressure is simulated (such as a curved pressure head) during calibration, so that the database contains arc compensation parameters (such as a gray scale correction coefficient of 1.2 for the edge area), and the problem of underestimation of edge stress caused by plane calibration is solved.

[0119] In one specific embodiment, the database is established and verified:

[0120] I. Calibration process:

[0121] In the glove box, the standard ion film (LATP coating thickness 10 μm) is pressurized from 0.1 MPa to 10 MPa in 50 steps, each step is pressurized for 30 seconds, and the multi-spectral image (wavelength 550 nm as the main waveband) is recorded.

[0122] Output: Generate pressure-gray curve (P-G) Figure 1 ), the fitting formula is G = 255-18P 1.5 (R 2 = 0.998).

[0123] II. Verification test:

[0124] The gray scale matching is carried out on the unknown pressure sample (the measured pressure is 1.2 MPa), the database backstepping pressure value is 1.18 MPa, the error is 1.7%, which meets the industrial detection requirement (±5%).

[0125] III. Application effect:

[0126] In the winding type battery detection, after the arc compensation parameter correction, the stress detection error of the arc region of the pole piece is reduced from 12% to 3%.

[0127] Through high-precision pressure calibration and multi-pressure point data acquisition in the glove box, the database establishment process realizes:

[0128] Full range coverage: high-resolution mapping of 0.05-10 MPa stress range;

[0129] Environmental interference isolation: the error caused by humidity / temperature fluctuation is reduced by more than 90%;

[0130] Process adaptability: support for arc stress correction of winding type batteries.

[0131] The database provides a reliable reference for ion membrane stress detection, and fundamentally solves the defects of low sensitivity and narrow application range of traditional methods.

[0132] In the preferred embodiment of the application, edge feature points are pre-set at the four corners of the ion membrane; after the membrane image is collected in step S21, the image correction process further includes:

[0133] The adjacent edge feature points are sequentially connected to form an image collection area, an initial image in the image collection area is collected, then one of the vertices of the initial image is taken as a reference point, the reference point is overlapped with the reference point of the pre-stored standard membrane image, then the remaining vertices of the initial image are sequentially overlapped with the remaining vertices of the standard membrane image in the order of adjacent first and then relative, and the stretching correction of the initial image is completed to obtain the corrected membrane image.

[0134] Specifically, in the embodiment, the image correction is realized according to the following process:

[0135] 1. Edge feature point pre-setting: high-contrast marks (such as Figure 3Middle cross or round feature points (diameter 1mm) are printed by laser etching or fluorescent material, ensuring that the marks are complete after mechanical disassembly.

[0136] 2. Image acquisition area division: Form a rectangular / trapezoidal acquisition area by connecting adjacent feature points (such as left top-right top-right bottom-left bottom), excluding background interference.

[0137] 3. Reference point alignment and stretching correction:

[0138] 3.1 Initial alignment: Align the left top feature point of the collected image with the left top point of the standard film image (coordinates (0, 0)).

[0139] 3.2 Sequential matching: Align adjacent points (right top→ standard image (Width, 0)), opposite points (right bottom→ (Width, Height)) in turn, and finally adjust the left bottom point to (0, Height).

[0140] 3.3 Geometric transformation: Adopt perspective transformation (Perspective Transformation) algorithm to complete stretching correction by solving homography matrix.

[0141] Achievable beneficial effects:

[0142] After disassembly, the ion exchange membrane may be wrinkled or locally stretched due to mechanical stress (such as the deformation rate of the arc-shaped coiled membrane after flattening is >5%). Through feature point positioning and perspective transformation, the deformed membrane image is restored to the standard geometric shape.

[0143] Under different test pressures, the membrane image may be misjudged due to the angle offset caused by the placement angle (such as 5° inclination causing a 3mm coordinate deviation). Align the standard membrane coordinate system to eliminate rotation / translation differences.

[0144] After disassembly, the membrane of the coiled battery is curved in an arc shape, and traditional plane correction fails. Four feature points support trapezoidal / curved surface area correction (such as flattening the arc-shaped membrane).

[0145] In a preferred embodiment of the present application, the surface of the ion exchange membrane is coated with a LATP coating, and the LATP coating corresponds to the negative electrode of the lithium ion battery.

[0146] Specifically, the core mechanism in the present embodiment is that the LATP (Lithium Titanate Phosphate) coating has lithium ion conduction characteristics. During the charging and discharging process, lithium ion intercalation / deintercalation will cause changes in the crystal structure of the coating, resulting in changes in optical reflectivity (white→black). Areas with uneven stress distribution are hindered by lithium ion migration, resulting in reduced color change of the coating (remaining white), thereby forming an intuitive stress distribution map.

[0147] Implementation logic:

[0148] Ion membrane functional design: the LATP coating is faced to the negative electrode, and the ion interaction between the LATP coating and the negative electrode active material is utilized to amplify the influence of stress difference on lithium ion migration and enhance the color contrast.

[0149] Image quantitative analysis: the gray difference of the film surface is captured by a multispectral imaging system, and the color characteristics are converted into quantitative stress values by combining a standard stress-gray database, so as to realize digital characterization of the stress distribution.

[0150] Dynamic correlation analysis: the area growth rate of the stress uneven area under different test pressures is calculated, and the critical pressure threshold of stress evolution is identified, so as to provide a key parameter for battery safety design.

[0151] In a preferred embodiment of the present application, an ion membrane stretching device is arranged in the standard light box, and the ion membrane is tightly pressed and reversely stretched at both ends by the ion membrane stretching device.

[0152] Specifically, a bidirectional stretching device (such as a clamp driven by a servo motor) is arranged in the standard light box, the ion membrane is tightly pressed at both ends and a reverse tension (such as 0-50 N adjustable) is applied, so that the membrane sheet maintains a constant tension.

[0153] After disassembly, the ion membrane is prone to wrinkles (such as the wrinkle height of the flat arc-shaped wound membrane is greater than 1 mm) due to the release of winding stress or mechanical damage, resulting in abnormal image gray. By applying a pre-tightening force of 5-10 N to stretch the membrane sheet, the wrinkles are eliminated (the flatness is improved to ±0.05 mm).

[0154] The difference in the free state of the membrane sheet under different test pressures leads to a decrease in the comparability of the stress distribution (such as the gray fluctuation of the relaxed membrane sheet is ±20%). By fixing the stretching tension (such as 10 N), all the membrane sheets are in the same initial stress state, and the test reference is unified.

[0155] After disassembly, the membrane sheet edge of the wound battery is warped (such as the curvature radius of the arc-shaped area is 50 mm), and the traditional planar imaging is distorted. By dynamically adjusting the tension difference between the two sides (such as 12 N on the left side and 10 N on the right side), the asymmetric deformation is compensated, and the complex deformation is adapted.

[0156] In a preferred embodiment of the present application, a vacuum suction platform is arranged on the bottom surface of the standard light box.

[0157] Specifically, in this embodiment, a multi-hole vacuum suction platform (such as a hole diameter of 0.5 mm and a negative pressure of-80 kPa) is arranged on the bottom surface of the light box, and the ion membrane is tightly attached to the platform surface by air suction.

[0158] The membrane sheet is micron-level displaced (such as 50 μm offset leading to coordinate registration failure) due to vibration of the stretching device or air flow disturbance. The membrane sheet is fixed by vacuum suction (the attachment force is greater than 1 N / cm2 ), combined with the platform surface micro-texture (Ra = 0.1 μm) to enhance friction and suppress micro-displacement errors.

[0159] Partial overhang of the diaphragm can cause image defocus (e.g., blur in the center, grayscale error ±15%). Negative pressure is used to keep the gap between the diaphragm and the platform less than 10 μm, ensuring consistent optical focal plane across the entire area.

[0160] The present invention also provides a battery internal stress distribution and change test system, the application of the test method, such as Figure 4 Shown, including:

[0161] A test module is used to replace the original diaphragm with an ion membrane during the lithium-ion battery manufacturing process and test multiple lithium-ion batteries at different test pressures;

[0162] The result detection module is used to dismantle and remove all the ion membranes after the test is completed, then collect membrane images of all the ion membranes, and compare the membrane images to obtain stress distribution and change results.

[0163] In a preferred embodiment of the present invention, Figure 4 As shown, the result detection module 2 includes:

[0164] An image acquisition unit 21 is used to place the disassembled ion membrane into a standard light box with constant temperature and humidity, and to acquire membrane images using a multispectral imaging system;

[0165] The stress detection unit 22 is connected to the image acquisition unit 21 and is used to identify the stress uneven distribution area and the stress uniform distribution area in each membrane image, and match the grayscale of the stress uneven distribution area and the grayscale of the stress uniform distribution area with a pre-built standard stress-grayscale database to obtain the corresponding stress;

[0166] The pressure difference calculation unit 23 is connected to the stress detection unit 22 and is used to calculate the pressure difference between each stress uneven distribution area and each stress uniform distribution area for each film image;

[0167] The growth rate calculation unit 14 is connected to the stress detection unit 12 and is used to sort the membrane images in order according to the test pressure, associate the stress distribution uneven areas with overlapping parts between adjacent membrane images, and calculate the area growth rate ratio between the associated stress distribution uneven areas;

[0168] A new region marking unit 25 is connected to the stress detection unit 22 and is used to mark, for each stress uneven distribution region in each film image, a stress uniform distribution region that does not overlap with any stress uneven distribution region in an adjacent film image as a newly appeared stress uneven region;

[0169] The result output unit 26 is connected to the new area marking unit 25, the speed increasing calculating unit 24 and the pressure difference calculating unit 23, and is used for outputting the area speed increasing ratio of all the newly appeared stress distribution uneven areas and all the stress distribution uneven areas as the stress distribution and change result.

[0170] In the preferred embodiment of the present application, the establishing module of the standard stress-gray database is used for setting a pressure calibration device in a glove box, then gradually adjusting the pressure through the pressure calibration device to perform multiple static pressure tests on the standard ion membrane, forming multiple pressure points with different gray scales on the standard ion membrane, and establishing the standard pressure-gray database.

[0171] The above merely describes the preferred embodiments of the present application, but does not limit the implementation manners and the protection scope of the present application. It should be realized by those skilled in the art that any equivalent replacement and obvious change made according to the present application and the drawings should be included in the protection scope of the present application.

Claims

1. A method for testing the internal stress distribution and changes of a battery, characterized in that: include: Step S1, replacing the original diaphragm with an ion membrane during the manufacturing process of the lithium-ion battery, testing multiple lithium-ion batteries under different test pressures, and disassembling and removing all the ion membranes after the test is completed; Step S2: collecting membrane images of all the ion membranes, and comparing the membrane images to obtain stress distribution and change results.

2. The testing method according to claim 1, wherein: The step S2 includes: Step S21, placing the disassembled ion membrane into a standard light box with constant temperature and humidity, and collecting the membrane image using a multispectral imaging system; Step S22: for each of the membrane images, identifying the stress uneven distribution area and the stress uniform distribution area in the membrane image, and matching the grayscale in the stress uneven distribution area and the grayscale in the stress uniform distribution area with a pre-built standard stress-grayscale database to obtain the corresponding stress; Step S23, for each of the film images, respectively calculating the pressure difference between each of the stress uneven distribution areas and the stress uniform distribution area; Step S24, sorting the membrane images in order according to the test pressure, associating the stress uneven distribution areas with overlapping portions between adjacent membrane images, and calculating the area growth rate ratio between the associated stress uneven distribution areas; Step S25, for each of the stress uneven distribution areas in each of the film images, marking a stress uniform distribution area that does not overlap with any stress uneven distribution area in an adjacent film image as a newly appeared stress uneven area; Step S26: taking all the newly appeared stress uneven distribution areas and the area growth rate ratios associated with all the stress uneven distribution areas as stress distribution and change results.

3. The testing method according to claim 2, wherein: The process of establishing the standard stress-grayscale database includes: A pressure calibration device is set up in the glove box, and then the pressure is gradually adjusted by the pressure calibration device to perform multiple static pressure tests on the standard ion membrane, forming multiple pressure points with different grayscales on the standard ion membrane, and establishing a standard pressure-grayscale database.

4. The testing method according to claim 1, wherein: Edge feature points are pre-set at the four corners of the ion membrane; then, after acquiring the membrane image in step S21, an image correction process is also included, including: Adjacent edge feature points are connected in sequence to form an image acquisition area, an initial image in the image acquisition area is acquired, and then one of the vertices of the initial image is used as a reference point, and the reference point is aligned with the reference point of a pre-saved standard membrane image. Subsequently, the remaining vertices of the initial image are aligned with the remaining vertices of the standard membrane image in the order of adjacent first and relative later, completing the stretch correction of the initial image to obtain the corrected membrane image.

5. The testing method according to claim 1, wherein: The surface of the ion membrane is coated with a LATP coating, and the LATP coating corresponds to the negative electrode of the lithium ion battery.

6. The testing method according to claim 2, wherein: The standard illumination box is provided with an ion membrane stretching device, and both ends of the ion membrane are pressed and stretched in opposite directions by the ion membrane stretching device.

7. The testing method according to claim 2, characterized in that: The bottom surface of the standard light box is provided with a vacuum adsorption platform.

8. A battery internal stress distribution and change testing system, characterized in that: Applying the test method according to any one of claims 1 to 7, comprising: A test module is used to replace the original diaphragm with an ion membrane during the lithium-ion battery manufacturing process and test multiple lithium-ion batteries at different test pressures; The result detection module is used to dismantle and remove all the ion membranes after the test is completed, then collect membrane images of all the ion membranes, and compare the membrane images to obtain stress distribution and change results.

9. The test system according to claim 8, characterized in that: The result detection module includes: An image acquisition unit is used to place the disassembled ion membrane into a standard light box with constant temperature and humidity, and to acquire an image of the membrane using a multispectral imaging system; a stress detection unit connected to the image acquisition unit, configured to identify, for each of the membrane images, an area with uneven stress distribution and an area with uniform stress distribution in the membrane image, and match the grayscale in the area with uneven stress distribution and the grayscale in the area with uniform stress distribution with a pre-established standard stress-grayscale database to obtain corresponding stresses; a pressure difference calculation unit, connected to the stress detection unit, for calculating, for each of the film images, the pressure difference between each of the stress uneven distribution areas and the stress uniform distribution area; an increase rate calculation unit, connected to the stress detection unit, for sequentially sorting the membrane images according to the magnitude of the test pressure, associating the stress uneven distribution areas with overlapping portions between adjacent membrane images, and calculating the area increase rate ratio between the associated stress uneven distribution areas; a new region marking unit connected to the stress detection unit, configured to mark, for each of the stress uneven distribution regions in each of the film images, a stress uniform distribution region that does not overlap with any stress uneven distribution region in an adjacent film image as a newly appeared stress uneven region; A result output unit is connected to the new area marking unit, the growth rate calculation unit and the pressure difference calculation unit, and is used to take all the newly appeared stress distribution uneven areas and the area growth rate ratios associated with all the stress distribution uneven areas as stress distribution and change results.

10. The test system according to claim 9, characterized in that: It includes a module for establishing the standard stress-grayscale-crystal phase characteristic database, which is used to set a pressure calibration device in the glove box, and then gradually adjust the pressure through the pressure calibration device to perform multiple static pressure tests on the standard ion membrane, forming multiple pressure points with different grayscales on the standard ion membrane, and establishing a standard pressure-grayscale database.

Images