CN-121721080-B - Method and system for testing thermal shrinkage rate of battery diaphragm

CN121721080BCN 121721080 BCN121721080 BCN 121721080BCN-121721080-B

Abstract

A testing method and system for thermal shrinkage rate of battery diaphragm relates to the field of testing or analyzing materials by measuring chemical or physical properties of the materials, the method comprises collecting backlight image of diaphragm sample before heating, extracting contour coordinates and calculating area before heating; the method comprises the steps of obtaining a backlight image, a top light image and a side light image of a heated sample, respectively determining an edge point set, identifying a fold region and obtaining three-dimensional depth characteristics, dividing the edge points into a flat edge section and a fold edge section based on gray variance of the top light image, accumulating Euclidean distances of adjacent points on the flat edge section to obtain a flat measurement length, calculating fold correction lengths of the fold edge section according to the three-dimensional depth characteristics and a flattening correction coefficient, splicing the lengths of the sections according to a space sequence to obtain real side lengths after heating, calculating a heated area, and calculating a heat shrinkage rate according to the areas before and after heating. By implementing the method, the calculation deviation of the thermal shrinkage rate of the battery diaphragm can be reduced.

Inventors

Ou Huihuang
YANG XIAOLU
CHEN JIXIN

Assignees

元能科技（厦门）有限公司

Dates

Publication Date: 20260505
Application Date: 20260225

Claims (10)

1. A method for testing thermal shrinkage rate of a battery separator, which is applied to a system for testing thermal shrinkage rate of a battery separator, the method comprising: collecting a backlight image of a diaphragm sample to be measured before heating, extracting initial contour coordinates through a high-contrast edge in the backlight image, and calculating the area before heating based on the initial contour coordinates; Sequentially acquiring a backlight image, a top light image and a side light image for the heated diaphragm sample, wherein the backlight image is used for determining an edge point set of the heated whole outline, the top light image is used for identifying a fold region in the edge point set, and the side light image is used for acquiring three-dimensional depth characteristics of the fold region; Dividing the edge point set into a flat edge section and a fold edge section based on the local gray variance of the top light image, wherein the gray variance of the flat edge section is lower than a preset threshold value and the edge trend is continuous, and the gray variance of the fold edge section is higher than the preset threshold value and has periodical light and shade variation; Calculating Euclidean distances between adjacent edge points of the flat edge section, accumulating to obtain a flat measurement length, calculating a fold height parameter of the fold edge section according to the three-dimensional depth characteristic, and calculating a fold correction length according to the projection measurement length of the fold edge section and a flattening correction coefficient based on the fold height parameter; Splicing the leveling measurement length of each leveling edge section and the fold correction length of each fold edge section according to the spatial position sequence in the whole outline to obtain the real side lengths of the four heated sides, and calculating the heated area based on the real side lengths; And calculating the heat shrinkage rate according to the area before heating and the area after heating.
2. The method according to claim 1, wherein the step of dividing the edge point set into a flattened edge segment and a wrinkled edge segment based on the local gray variance of the top-light image, in particular comprises: Extracting gray values in a preset window range taking the edge point as a center from the top light image for each edge point in the edge point set, and calculating gray variance of all pixel points in the preset window range to be used as a local gray variance characteristic value; Comparing the local gray variance characteristic value with a preset gray threshold value, and merging edge point sequences with the local gray variance characteristic value lower than the preset gray threshold value and continuous space positions into the flat edge section; and carrying out frequency domain transformation on a gray value sequence in an area corresponding to the edge point with the local gray variance eigenvalue not lower than the preset gray threshold value, identifying an edge point sequence with periodical light and shade variation, and merging the edge point sequence into the fold edge section.
3. The method according to claim 1, wherein the step of calculating a pleat height parameter for the pleat edge segments from the three-dimensional depth feature comprises: Extracting a side view contour line corresponding to the fold edge section from the side view image, detecting wave crests and wave troughs of the side view contour line, and identifying a local highest point as a fold wave crest point and a local lowest point as a fold wave trough point; Calculating the vertical distance between each fold crest point and the adjacent fold trough point as the height value of a single fold; and counting the height values of all folds in the fold edge section, calculating the average value and the maximum value of the height values, and combining the average value and the maximum value to obtain the fold height parameter.
4. The method according to claim 1, wherein the step of calculating a pleat modification length from the projected measured length of the pleat edge segments and a flattening modification factor based on the pleat height parameter, specifically comprises: Accumulating Euclidean distances between adjacent edge points in the fold edge sections to obtain the projection measurement length of the fold edge sections; Calculating a wrinkle fluctuation amplitude index according to the average value and the maximum value in the wrinkle height parameter, and determining the flattening correction coefficient based on the wrinkle fluctuation amplitude index; multiplying the projection measurement length by the flattening correction coefficient to obtain the fold correction length of the fold edge section.
5. The method according to claim 1, wherein the step of sequentially splicing the measured flat length of each flat edge section and the corrected pleat length of each pleat edge section in spatial position in the overall profile to obtain the real side lengths of the four heated sides specifically comprises: identifying four corner points of the diaphragm sample based on the integral outline in the backlight image, and dividing the edge point set into edge point subsets corresponding to four sides according to the four corner points; sequentially extracting the leveling measurement length of the leveling edge section and the fold correction length of the fold edge section from the edge point subset corresponding to each edge according to the spatial position sequence of the edge points; and summing all the leveling measurement lengths and the fold correction lengths in the edge point subsets corresponding to each side to obtain the real side length of each side in the four sides after heating.
6. The method of claim 1, wherein after the step of calculating a heat shrinkage rate from the pre-heating area and the post-heating area, the method further comprises: Acquiring real-time temperature data of the diaphragm sample in the heating process and an intermediate state image at a corresponding moment, wherein the intermediate state image is used for recording the deformation evolution process of the diaphragm sample from the heating start to the heating end; performing contour extraction and area calculation on the intermediate state image to obtain intermediate area values corresponding to a plurality of moments, and associating the intermediate area values with the corresponding real-time temperature data; And calculating the stage shrinkage rate of the diaphragm sample in different temperature intervals according to the area before heating, the intermediate area value and the area after heating, wherein the stage shrinkage rate represents the thermal shrinkage characteristic of the diaphragm sample in a specific temperature range.
7. The method of claim 6, wherein after the step of calculating the stage shrinkage of the diaphragm sample at different temperature intervals based on the pre-heating area, the intermediate area value, and the post-heating area, the method further comprises: Carrying out overall fold distribution analysis on the top light image of the heated diaphragm sample, and counting the proportion of the total length of the fold edge section to the total circumference of the whole outline to obtain the fold ratio; Judging the thermal shrinkage uniformity of the diaphragm sample according to the fold ratio and the thermal shrinkage rate, judging uniform shrinkage when the fold ratio is lower than a preset duty ratio threshold value, and judging non-uniform shrinkage when the fold ratio is higher than the preset duty ratio threshold value; And generating a quality evaluation result of the diaphragm sample based on the determination result of the thermal shrinkage uniformity and the thermal shrinkage rate.
8. A battery separator thermal shrinkage testing system comprising one or more processors and memory coupled to the one or more processors, the memory for storing computer program code comprising computer instructions that the one or more processors invoke to cause the battery separator thermal shrinkage testing system to perform the method of any of claims 1-7.
9. A computer readable storage medium comprising instructions that, when run on a battery separator thermal shrinkage test system, cause the battery separator thermal shrinkage test system to perform the method of any of claims 1-7.
10. A computer program product, characterized in that the computer program product, when run on a battery separator thermal shrinkage test system, causes the battery separator thermal shrinkage test system to perform the method of any one of claims 1-7.

Description

Method and system for testing thermal shrinkage rate of battery diaphragm Technical Field The application relates to the field of testing or analyzing materials by means of measuring chemical or physical properties of the materials, in particular to a testing method and a testing system for the thermal shrinkage rate of a battery diaphragm. Background The lithium ion battery diaphragm is arranged between the anode and the cathode to play a physical isolation role, so that the battery is prevented from being short-circuited. The thickness of the diaphragm is generally less than 10 micrometers, heat shrinkage can be generated in a high-temperature environment, and the excessive heat shrinkage can cause short circuit caused by contact of positive and negative electrodes, so that safety accidents are caused. Therefore, accurately testing the thermal shrinkage rate of the battery diaphragm at different temperatures has important significance for guaranteeing the safety performance of the battery. At present, a mode of combining oven heating with size measurement is adopted for the thermal shrinkage rate test of the battery diaphragm. Measuring the length and width of a diaphragm sample to calculate an initial area, clamping and fixing the diaphragm by using a glass plate, putting the diaphragm into an oven for heating for a plurality of hours, taking out and cooling after heating, measuring the size again to calculate the heated area, and finally calculating the heat shrinkage rate according to the area change. However, irregular folds and warpage can be generated on the edge of the diaphragm after the diaphragm is heated at high temperature, a unified reference is difficult to determine during measurement, and the repeatability of repeated measurement of the same sample is poor. The actual unfolding length of the fold area is different from the plane projection length, and the conventional measurement can only acquire the projection length, so that the thermal shrinkage rate calculation deviation is caused. Disclosure of Invention The application provides a method and a system for testing the thermal shrinkage rate of a battery diaphragm, which are used for reducing the calculation deviation of the thermal shrinkage rate of the battery diaphragm. The application provides a method for testing the thermal shrinkage rate of a battery diaphragm, which is applied to a battery diaphragm thermal shrinkage rate testing system, and comprises the steps of collecting a backlight image before heating a diaphragm sample to be tested, extracting initial contour coordinates through a high-contrast edge in the backlight image, and calculating the area before heating based on the initial contour coordinates; sequentially acquiring a backlight image, a top light image and a side light image for a heated diaphragm sample, wherein the backlight image is used for determining an edge point set of a heated overall contour, the top light image is used for identifying a fold region in the edge point set, the side light image is used for acquiring three-dimensional depth characteristics of the fold region, the edge point set is divided into flat edge sections and fold edge sections based on local gray variance of the top light image, gray variance of the flat edge sections is lower than a preset threshold value and edge trend is continuous, gray variance of the fold edge sections is higher than the preset threshold value and periodical light and shade change exists, euclidean distance between adjacent edge points is calculated for the flat edge sections and accumulated to obtain flat measured lengths, fold edge sections are calculated to obtain fold corrected lengths according to three-dimensional depth characteristics, the flat measured lengths of the fold edge sections and the fold corrected lengths of the fold edge sections are sequentially spliced according to spatial positions in the overall contour to obtain real side lengths of the four sides after heating, the heated area is calculated based on the real side lengths, and the heat shrinkage rate is calculated according to the heated area. In the above embodiment, the system acquires the complete morphology information of the diaphragm sample by a multi-light source collaborative imaging mode, the backlight image provides a clear outline border, the top light image reveals surface fold texture features, and the side light image supplements depth dimension data. Based on the local gray variance characteristic value, the flattening area and the fold area are automatically identified, a three-dimensional depth correction coefficient is introduced to the fold edge section to compensate projection measurement errors, and the lengths of the corrected edge sections are spliced and calculated according to a space sequence to calculate the real side length, so that the actual area after heating is accurately obtained, and the measurement accuracy of the heat shrinkage rate is improved. In