A performance analysis and detection method for carbon negative electrode materials of lithium batteries for new energy vehicles

Abstract

The present invention relates to the field of battery detection technology, and in particular to a performance analysis and detection method for a carbon negative electrode material of a lithium battery for a new energy vehicle. The method obtains a scanning electron microscope image of the carbon negative electrode material, performs edge detection on material particles in the scanning electron microscope image, obtains complete particle edge lines and incomplete particle edge lines, and obtains a particle size corresponding to each complete particle edge line; for any incomplete particle edge line, the incomplete particle edge line is divided into two edge curves, and the particle size corresponding to the incomplete particle edge line is obtained according to the endpoint distance and the curvature of each edge curve; according to the particle sizes corresponding to each complete particle edge line and each incomplete particle edge line, the degree of uniformity of the particle size is obtained, and the material performance of the carbon negative electrode material is detected according to the degree of uniformity of the particle size, so as to reduce the influence of material particle overlap on the judgment of particle size uniformity, and improve the evaluation accuracy of the performance of the carbon negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery detection, and in particular to a performance analysis and detection method for a carbon negative electrode material of a lithium battery for a new energy vehicle. Background Art

[0002] The performance of carbon negative electrode materials for lithium batteries of new energy vehicles usually needs to be analyzed and tested during production and trial to ensure the effectiveness and safety of carbon negative electrode materials for lithium batteries in practical applications. The uniformity of the particle size of carbon negative electrode materials is an important factor affecting the electrochemical performance of lithium batteries, and will directly affect the charge and discharge performance of the battery. The smaller the particle size of the carbon negative electrode material and the more uniform the particle size distribution, the smaller the van der Waals force that needs to be overcome when lithium ions are embedded, and the easier the embedding is. In addition, the smaller the particle size, the shorter the channel for lithium ion embedding and extraction, which is more conducive to quickly reaching a fully embedded lithium state, thereby having better charge and discharge performance; in addition, when the particle size distribution of carbon negative electrode materials is wider and more uniform, small particles can effectively fill the gaps in large particles, which helps to increase the compaction density of the pole piece and improve the volume energy density of the lithium battery.

[0003] In the prior art, the particle size uniformity of carbon negative electrode materials is mainly detected by observation. The detection method is relatively complicated and time-consuming, and is easily affected by the subjective influence of the operator during the detection process. For example, during manual observation, the mutual occlusion between material particles will interfere with the judgment of the particle size, resulting in inaccurate evaluation results of the particle size uniformity of the carbon negative electrode material, thereby affecting the charge and discharge performance of the lithium battery.

[0004] Therefore, how to improve the evaluation efficiency and accuracy of the particle size uniformity of carbon negative electrode materials has become an urgent problem to be solved. Summary of the invention

[0005] In view of this, an embodiment of the present invention provides a performance analysis and detection method for carbon negative electrode materials of lithium batteries for new energy vehicles to solve the problem of how to improve the evaluation efficiency and accuracy of the particle size uniformity of carbon negative electrode materials.

[0006] The present invention provides a method for analyzing and detecting the performance of a carbon negative electrode material for a lithium battery of a new energy vehicle. The method comprises the following steps:

[0007] Acquire a scanning electron microscope image of a carbon negative electrode material, and perform edge detection on material particles in the scanning electron microscope image to obtain at least one material particle edge line;

[0008] According to the change of the position slope of each pixel point on each material particle edge line, all material particle edge lines are divided to obtain complete particle edge lines and incomplete particle edge lines, and the particle size corresponding to each complete particle edge line is obtained;

[0009] For any incomplete particle edge line, the incomplete particle edge line is divided into at least two edge curves, the endpoint distance corresponding to each edge curve is obtained, the curvature of the corresponding edge curve is obtained according to the change rate of each edge curve, and the particle size corresponding to the incomplete particle edge line is obtained according to the endpoint distance and curvature of each edge curve;

[0010] According to the particle size corresponding to each complete particle edge line and the particle size corresponding to each incomplete particle edge line, the particle size uniformity of the carbon negative electrode material is obtained, and the material properties of the carbon negative electrode material are detected according to the particle size uniformity.

[0011] Preferably, the step of dividing all material particle edge lines according to the change in the position slope of each pixel point on each material particle edge line to obtain complete particle edge lines and incomplete particle edge lines includes:

[0012] For any pixel point on the edge line of all material particles, obtain the left adjacent pixel point and the right adjacent pixel point on the edge line of the material particle where the pixel point is located, calculate the position slope between the pixel point and the left adjacent pixel point and the right adjacent pixel point respectively, and obtain the position slope difference, which is recorded as the position slope change rate of the pixel point;

[0013] According to the difference in the position slope change rate between the pixel point and each pixel point on the material particle edge line where the pixel point is located, a possibility index of the pixel point belonging to the material particle edge intersection point is obtained; if the possibility index of the pixel point belonging to the material particle edge intersection point is greater than a preset possibility threshold, the pixel point is determined to be a suspected material particle edge intersection point;

[0014] For any material particle edge line, if the number of suspected material particle edge intersections on the material particle edge line does not meet a preset number threshold, the material particle edge line is taken as a complete particle edge line; if the number of suspected material particle edge intersections on the material particle edge line meets a preset number threshold, the material particle edge line is taken as a target edge line;

[0015] According to the suspected material particle edge intersection point on each of the target edge lines, all target edge lines are divided into a plurality of incomplete particle edge lines.

[0016] Preferably, obtaining the possibility index of the pixel point belonging to the intersection point of the edge of the material particle according to the difference in the position slope change rate between the pixel point and each pixel point on the edge line of the material particle where the pixel point is located includes:

[0017] The absolute value of the difference between the position slope change rate of the pixel point and each pixel point on the edge line of the material particle where it is located is calculated to obtain the sum of the absolute values ​​of the differences, and the sum of the absolute values ​​of the differences is normalized to obtain a possibility index that the pixel point belongs to the intersection of the edge of the material particle.

[0018] Preferably, the method of dividing all target edge lines into a plurality of incomplete particle edge lines according to the suspected material particle edge intersection points on each target edge line comprises:

[0019] For any target edge line, according to the possibility index corresponding to each suspected material particle edge intersection point on the target edge line, obtain the suspected material particle edge intersection point corresponding to the maximum possibility index as the first target point; among all the suspected material particle edge intersection points on the target edge line, obtain the suspected material particle edge intersection point closest to the first target point, and form a group of matching pixel points with the first target point;

[0020] Among the unmatched suspected material particle edge intersections, obtain the suspected material particle edge intersection corresponding to the maximum likelihood index as the second target point, and among the unmatched suspected material particle edge intersections, obtain the suspected material particle edge intersection closest to the second target point, and form a group of matching pixel points with the second target point; and so on, obtain multiple groups of matching pixel points, use the connecting lines between each group of matching pixel points as cutting lines, and divide the target edge line into multiple incomplete particle edge lines based on all cutting lines.

[0021] Preferably, obtaining the particle size corresponding to each complete particle edge line includes:

[0022] For any complete particle edge line, the distance between every two pixel points on the complete particle edge line is calculated, and the maximum distance is used as the particle diameter corresponding to the complete particle edge line.

[0023] Preferably, dividing the incomplete particle edge line into at least two edge curves comprises:

[0024] If the number of endpoints on the incomplete particle edge line exceeds 2, each sub-curve in the incomplete particle edge line is used as an edge curve;

[0025] If there are only two endpoints on the incomplete particle edge line, for any endpoint, the pixel point farthest from the endpoint is obtained on the incomplete particle edge line as the first pixel point, and the curve between the first pixel point and the endpoint is taken as the edge curve.

[0026] Preferably, obtaining the curvature of the corresponding edge curve according to the rate of change of each edge curve includes:

[0027] For any edge curve, obtain the chain code of the edge curve, count the number of occurrences of each chain code value of the edge curve in the chain code, obtain the maximum number of occurrences, and use the inverse of the maximum number of occurrences as the change rate of the edge curve;

[0028] Obtaining the absolute value of the difference between the starting chain code value and the ending chain code value of the edge curve, obtaining the absolute value of the difference between the maximum chain code difference and the absolute value of the difference, and performing negative mapping on the absolute value of the difference using an exponential function with a natural constant as the base to obtain the credibility of the change rate of the edge curve;

[0029] The curvature of the edge curve is obtained according to the product of the change rate of the edge curve and the change rate credibility.

[0030] Preferably, obtaining the particle size corresponding to the incomplete particle edge line according to the endpoint distance and curvature of each edge curve includes:

[0031] For any edge curve, obtain the addition result between the curvature of the edge curve and a constant 1, and use the product of the addition result and the end point distance of the edge curve as the correction distance corresponding to the edge curve;

[0032] The change rate credibility corresponding to each edge curve is used as a weight, and the corrected distance corresponding to each edge curve is weighted and summed up and then averaged to obtain the particle size corresponding to the incomplete particle edge line.

[0033] Preferably, obtaining the particle size uniformity of the carbon negative electrode material according to the particle size corresponding to each of the complete particle edge lines and the particle size corresponding to each of the incomplete particle edge lines comprises:

[0034] The particle size standard deviation of the particle size corresponding to all complete particle edge lines and the particle size corresponding to all incomplete particle edge lines is calculated, and the particle size uniformity of the carbon negative electrode material is obtained according to the reciprocal of the sum of the particle size standard deviation and the constant 1.

[0035] Preferably, the detecting the material properties of the carbon negative electrode material according to the degree of uniformity of the particle size comprises:

[0036] A preset particle size uniformity threshold is obtained. If the particle size uniformity degree is greater than or equal to the particle size uniformity threshold, it is determined that the material performance of the carbon negative electrode material meets the requirements; if the particle size uniformity degree is less than the particle size uniformity threshold, it is determined that the material performance of the carbon negative electrode material does not meet the requirements.

[0037] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0038] The present invention obtains a scanning electron microscope image of a carbon negative electrode material, performs edge detection on material particles in the scanning electron microscope image, and obtains at least one material particle edge line; divides all material particle edge lines according to the change in the position slope of each pixel point on each material particle edge line, obtains complete particle edge lines and incomplete particle edge lines, and obtains the particle size corresponding to each complete particle edge line; for any incomplete particle edge line, divides the incomplete particle edge line into two edge curves, obtains the endpoint distance corresponding to each edge curve, obtains the curvature of the corresponding edge curve according to the rate of change of each edge curve, and obtains the particle size corresponding to the incomplete particle edge line according to the endpoint distance and curvature of each edge curve; obtains the particle size uniformity of the carbon negative electrode material according to the particle size corresponding to each complete particle edge line and the particle size corresponding to each incomplete particle edge line, and detects the material performance of the carbon negative electrode material according to the particle size uniformity. Among them, by dividing the edge lines of material particles in the scanning electron microscope image, incomplete particle edge lines corresponding to partially overlapping particles are obtained, and then the edges of carbon negative electrode material particles (incomplete particle edge lines) that are incomplete in the image due to overlap are divided into two edge curves whose end points are close to the maximum diameter of the particles. The particle size of the corresponding particles is reflected according to the rate of change and curvature of each edge curve, so as to obtain the true particle size of each incomplete particle edge line, which effectively reduces the influence of the irregular shape of material particles on the accuracy of the particle size calculation results, so that the particle size uniformity of the carbon negative electrode material obtained according to the particle size of all particles is more in line with reality, thereby improving the efficiency and accuracy of the performance analysis of the carbon negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0040] Figure 1 This is a method flow chart of a performance analysis and detection method for a carbon negative electrode material of a lithium battery for a new energy vehicle provided in Example 1 of the present invention;

[0041] Figure 2 A schematic diagram of an edge line of a material particle including two material particles provided by an embodiment of the present invention;

[0042] Figure 3 A schematic diagram of an intersection point of edge lines corresponding to two material particles provided by an embodiment of the present invention;

[0043] Figure 4 A schematic diagram of target edge line division provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0044] Embodiments of the present disclosure are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present disclosure, but should not be understood as limiting the present disclosure.

[0045] It should be noted that the terms "first", "second", etc. in the specification of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present disclosure described herein can be implemented in an order other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the present disclosure.

[0046] In order to illustrate the technical solution of the present invention, specific embodiments are provided below for illustration.

[0047] See also Figure 1 , is a method flow chart of a performance analysis and detection method for a carbon negative electrode material of a lithium battery for a new energy vehicle provided in Example 1 of the present invention, such as Figure 1 As shown, the method may include:

[0048] Step S101, obtaining a scanning electron microscope image of a carbon negative electrode material, performing edge detection on material particles in the scanning electron microscope image, and obtaining at least one material particle edge line.

[0049] For the carbon negative electrode material of lithium batteries, the surface contaminants or impurities of the carbon negative electrode material sample are removed as much as possible before testing, and then the carbon negative electrode material sample is cut into small pieces suitable for mounting on the microscope sample stage, ensuring that the surface is flat and in the correct scanning position. Specifically, a conductive glue (such as silver glue) is used to fix the small piece on the sample stage, and the carbon negative electrode material is scanned using a scanning electron microscope to obtain the corresponding scanning electron microscope image.

[0050] Since overlapping material particles may cause errors in the evaluation of the particle size of a single material particle when detecting the particle size of material particles in a scanning electron microscope image, it is necessary to evaluate the particle size of the corresponding material particle by analyzing the curvature of the edge of each material particle to ensure the detection accuracy. In the embodiment of the present invention, the gradient value of each pixel point in the scanning electron microscope image is first obtained by using the Sobel algorithm. However, since the material contains different components, some edges similar to noise points will appear, and these noise edge pixels have different gradients due to different components. Therefore, according to the gradient value of each pixel point, the absolute value of the gradient value difference between adjacent pixels is obtained, which is recorded as the gradient value difference between the corresponding two adjacent pixels. Continuous pixels whose gradient value difference is within the gradient difference threshold of 3 are regarded as the same edge line. At the same time, the edge lines whose number of pixels in the edge lines is less than the preset number of 5 are removed, and the remaining edge lines are used as material particle edge lines, that is, the real material particle edges.

[0051] It is worth noting that the Sobel algorithm belongs to the prior art and will not be described in detail here. There is no limit on the gradient difference threshold and the preset number, and they can be set according to the implementation scenario.

[0052] Step S102, according to the position slope change of each pixel point on each material particle edge line, all material particle edge lines are divided to obtain complete particle edge lines and incomplete particle edge lines, and the particle size corresponding to each complete particle edge line is obtained.

[0053] Due to the overlap of material particles, the edge line of a material particle does not contain a material particle, such as Figure 2 As shown, this material particle edge line contains two material particles. Since the material particles have similar colors, the overlapping part has no obvious edge. Therefore, the material particle edge line needs to be further divided to divide it into edge lines corresponding to single material particles.

[0054] Considering that the material particles are circular in shape as a whole, the slope changes between adjacent pixels on their edge lines are basically the same, while the edge intersection of the overlapping parts of the material particles will have a large difference from the slope changes of the edges at other positions due to the different slopes of the edges of the two material particles. Therefore, according to the position slope change of each pixel point on each material particle edge line, all material particle edge lines are divided to obtain complete particle edge lines and incomplete particle edge lines. One complete particle edge line corresponds to one material particle, and one incomplete particle edge line corresponds to one material particle. The specific process of division is as follows:

[0055] (1) For any pixel point on the edge line of all material particles, obtain the left adjacent pixel point and the right adjacent pixel point on the edge line of the material particle where the pixel point is located, calculate the position slope between the pixel point and the left adjacent pixel point and the right adjacent pixel point respectively, and obtain the position slope difference, which is recorded as the position slope change rate of the pixel point.

[0056] In one embodiment, a two-dimensional coordinate system is constructed with the lower left corner of the scanning electron microscope image as the origin, and the coordinates (x, y) of each pixel point on the edge line of all material particles can be obtained according to the two-dimensional coordinate system. For the i-th pixel point on the edge line of all material particles, the position slope change rate of the i-th pixel point is obtained according to the coordinates of the i-th pixel point and the coordinates of the adjacent pixel points on the edge line of the material particle to which it belongs, and the calculation expression of the position slope change rate is:

[0057]

[0058] in, represents the rate of change of the position slope of the i-th pixel, Represents the coordinates of the i+1th pixel point on the edge line of the material particle to which the i-th pixel point belongs. Represents the coordinates of the i-1th pixel point on the edge line of the material particle to which the i-th pixel point belongs. Represents the coordinates of the i-th pixel.

[0059] (2) A possibility index of whether the pixel point belongs to an edge intersection of a material particle is obtained based on the difference in the rate of change of the position slope between the pixel point and each pixel point on the edge line of the material particle where it is located. If the possibility index of whether the pixel point belongs to an edge intersection of a material particle is greater than a preset possibility threshold, the pixel point is determined to be a suspected edge intersection of a material particle.

[0060] The absolute value of the difference between the position slope change rate of the pixel point and each pixel point on the edge line of the material particle where it is located is calculated to obtain the sum of the absolute values ​​of the differences, and the sum of the absolute values ​​of the differences is normalized to obtain a possibility index that the pixel point belongs to the intersection of the edge of the material particle.

[0061] In one embodiment, assuming that the i-th pixel point belongs to the d-th material particle edge line, the possibility index of the i-th pixel point belonging to the material particle edge intersection is obtained according to the difference in the position slope change rate between the i-th pixel point and each pixel point on the d-th material particle edge line:

[0062]

[0063] in, It indicates the possibility index that the i-th pixel belongs to the intersection of the edge of the material particle, norm() indicates the normalization function, Indicates the number of pixels on the edge line of the d-th material particle to which the ith pixel belongs. represents the rate of change of the position slope of the i-th pixel, It represents the rate of change of the position slope of the j-th pixel point on the edge line of the d-th material particle to which the ith pixel point belongs, and || represents the absolute value sign.

[0064] It should be noted that the material particle edge intersection point refers to the intersection point of the edge lines corresponding to two material particles. The difference between the position slope change rates of each pixel point within the edge line of the same material particle is small, so The larger the value of , the greater the possibility that the i-th pixel point is the intersection point of the edge lines corresponding to two material particles, and the greater the possibility index that the i-th pixel point belongs to the intersection point of the edge of the material particles.

[0065] The possibility threshold is set to 0.8. There is no limit here. It can be set according to the implementation scenario. If the i-th pixel point belongs to the possibility index of the intersection of the edge of the material particle , then the i-th pixel point is determined to be a suspected material particle edge intersection point. Similarly, the possibility index of each pixel point on each material particle edge line belonging to the material particle edge intersection point is obtained, and then the suspected material particle edge intersection point on each material particle edge line is obtained.

[0066] (3) For any material particle edge line, if the number of suspected material particle edge intersections on the material particle edge line does not meet the preset number threshold, the material particle edge line is regarded as a complete particle edge line; if the number of suspected material particle edge intersections on the material particle edge line meets the preset number threshold, the material particle edge line is regarded as a target edge line.

[0067] In one embodiment, considering that the material particles are circular, when they overlap, there will be at least two intersections, therefore, the preset number threshold is set to 2, if the number of suspected material particle edge intersections on any material particle edge line is less than 2, it is considered that the material particle edge line corresponds to a complete material particle, there is no particle overlap, and then the material particle edge line is used as a complete particle edge line. On the contrary, if the number of suspected material particle edge intersections on any material particle edge line exceeds 2, it is considered that the material particle edge line corresponds to an overlapping material particle, including at least two material particles, and then the material particle edge line is used as the target edge line.

[0068] (4) According to the suspected material particle edge intersection point on each of the target edge lines, all target edge lines are divided into a plurality of incomplete particle edge lines.

[0069] Specifically, for any target edge line, according to the possibility index corresponding to each suspected material particle edge intersection point on the target edge line, the suspected material particle edge intersection point corresponding to the maximum possibility index is obtained as the first target point; among all the suspected material particle edge intersection points on the target edge line, the suspected material particle edge intersection point closest to the first target point is obtained, and a group of matching pixel points is formed with the first target point;

[0070] Among the unmatched suspected material particle edge intersections, obtain the suspected material particle edge intersection corresponding to the maximum likelihood index as the second target point, and among the unmatched suspected material particle edge intersections, obtain the suspected material particle edge intersection closest to the second target point, and form a group of matching pixel points with the second target point; and so on, obtain multiple groups of matching pixel points, use the connecting lines between each group of matching pixel points as cutting lines, and divide the target edge line into multiple incomplete particle edge lines based on all cutting lines.

[0071] In one embodiment, since the material particle edge intersections generated by the overlap of material particles are matched in pairs, all target edge lines are divided into multiple incomplete particle edge lines by matching the suspected material particle edge intersections on each target edge line. Taking a target edge line as an example, among the possibility indicators that each suspected particle edge intersection on the target edge line belongs to a material particle edge intersection, the maximum possibility indicator is obtained. The corresponding suspected particle edge intersection is recorded as the first target point, and the distance between the first target point and each suspected particle edge intersection on the target edge line is calculated. The two points corresponding to the minimum distance are obtained as a set of matched pixel points. Then, the maximum possibility index is also obtained in the unmatched suspected material particle edge intersection on the target edge line. The corresponding suspected particle edge intersection is recorded as the second target point. According to the matching method of the first target point, a group of matching pixel points corresponding to the second target point is obtained, and so on, until all the suspected material particle edge intersections on the target edge line are matched, and multiple groups of matching pixel points are obtained. It should be noted that each group of matching pixel points is as follows Figure 3 The intersection of the edge lines corresponding to the two material particles shown ( Figure 3 black circle in the figure).

[0072] Further, see Figure 4 , which is a schematic diagram of the target edge line division, Figure 4 In the example, each set of matched pixels is connected to obtain the corresponding connection line, which is Figure 4 The dotted line in is used as the cutting line to divide the target edge line into multiple incomplete particle edge lines, and one incomplete particle edge line corresponds to one material particle.

[0073] At this point, all material particle edge lines are divided into complete particle edge lines and incomplete particle edge lines. Since a complete particle edge line is a complete material particle, there is no particle overlap. Therefore, for any complete particle edge line, the distance between every two pixel points on the complete particle edge line is calculated, and the maximum distance is used as the particle size corresponding to the complete particle edge line. For incomplete particle edge lines, due to the existence of particle overlap, the accurate particle size cannot be detected. Therefore, it is necessary to evaluate the particle size of the corresponding material particle according to the curvature of the incomplete particle edge line. See below for details.

[0074] Step S103, for any incomplete particle edge line, divide the incomplete particle edge line into at least two edge curves, obtain the endpoint distance corresponding to each edge curve, obtain the curvature of the corresponding edge curve according to the rate of change of each edge curve, and obtain the particle size corresponding to the incomplete particle edge line according to the endpoint distance and curvature of each edge curve.

[0075] Since the shape of the carbon negative electrode material is close to a circle, the slope change of each pixel point on the edge line corresponding to a complete material particle is basically the same, and the sum of the slopes of all pixel points on the closed circular edge line is 0. Therefore, in the embodiment of the present invention, for any incomplete particle edge line, the incomplete particle edge line is first divided into at least two edge curves, and then the particle size corresponding to the incomplete particle edge line is obtained according to the curvature of each edge curve.

[0076] The method of dividing the incomplete particle edge line into at least two edge curves is as follows:

[0077] If the number of endpoints on the incomplete particle edge line exceeds 2, each sub-curve in the incomplete particle edge line is used as an edge curve;

[0078] If there are only two endpoints on the incomplete particle edge line, for any endpoint, the pixel point farthest from the endpoint is obtained on the incomplete particle edge line as the first pixel point, and the curve between the first pixel point and the endpoint is taken as the edge curve.

[0079] The method for obtaining the curvature of each edge curve is as follows:

[0080] For any edge curve, obtain the chain code of the edge curve, count the number of occurrences of each chain code value of the edge curve in the chain code, obtain the maximum number of occurrences, and use the inverse of the maximum number of occurrences as the change rate of the edge curve;

[0081] Obtaining the absolute value of the difference between the starting chain code value and the ending chain code value of the edge curve, obtaining the absolute value of the difference between the maximum chain code difference and the absolute value of the difference, and performing negative mapping on the absolute value of the difference using an exponential function with a natural constant as the base to obtain the credibility of the change rate of the edge curve;

[0082] The curvature of the edge curve is obtained according to the product of the change rate of the edge curve and the change rate credibility.

[0083] In one embodiment, an edge curve is taken as an example, and the end point of the edge curve is taken as the starting point, and the chain code of the edge curve is obtained using an 8-connected chain code, wherein the chain code belongs to the prior art and will not be described here. If the rate of change of the edge curve, that is, the faster the change of its chain code, the smaller the corresponding material particles, for example: when the edge curve is a semicircular arc, the chain code corresponding to the pixel points at both ends of the curve should be the numbers on the diagonal of the 8-connected chain code, and the smaller material particles have fewer edge pixel points, in order to form a semicircular arc curve, the number of repetitions of the chain code value of the edge pixel point is less, and the corresponding chain code changes faster, so according to the number of repetitions of the chain code value of the edge curve, the rate of change of the edge curve is calculated:

[0084]

[0085] Among them, b represents the rate of change of the edge curve, max() represents the maximum value function, Indicates the number of occurrences of the ath chain code value on the edge curve, where the chain code value is 0-7 and 1 represents a constant.

[0086] After obtaining the rate of change of the edge curve, considering that the more complete the edge line of the material particle is, the closer the corresponding edge curve should be to a semicircular arc, the rate of change of the edge curve can better reflect the actual curvature of the material edge; if the edge line of the material particle is blocked to a high degree by other material particles, the obtained edge curve is a smaller arc, and the reliability of its rate of change in reflecting the curvature of the edge line of the material particle is low. Since the two ends of the chain code corresponding to the semicircular arc should be diagonal lines, that is, the maximum difference of the chain code value is 4, that is, the maximum difference value is set to 4 in the embodiment of the present invention, therefore, it is necessary to calculate the credibility of the rate of change of the edge curve:

[0087]

[0088] in, Indicates the credibility of the rate of change of the edge curve, exp() represents an exponential function with a natural constant as the base, 4 represents the maximum difference, Indicates the first chain code value (starting chain code value) on the edge curve. Represents the last chain code value (end chain code value) on the edge curve, and || represents the absolute value symbol.

[0089] Combining the rate of change of the edge curve and the credibility of the rate of change, the curvature of the edge curve is obtained:

[0090]

[0091] in, It represents the curvature of the edge curve, b represents the rate of change of the edge curve, and the credibility of the rate of change of the edge curve.

[0092] Similarly, the curvature of each edge curve can be obtained, and then according to the curvature of each edge curve, the particle size corresponding to the corresponding incomplete particle edge line can be obtained. Specifically, the distance d between the two end points of each edge curve is first obtained, and then, considering that the material particles are blocked by other material particles, the distance between the two end points of the edge curve is less than the maximum diameter of the material particles (that is, the actual particle size). Therefore, the curvature of the edge curve is used to correct the distance between the two end points of the edge curve to obtain the material particle size reflected by the material curve (that is, the corrected distance). The greater the curvature, the larger the particle size of the material particles. The distance correction method is:

[0093] For any edge curve, the addition result between the curvature of the edge curve and a constant 1 is obtained, and the product of the addition result and the end point distance of the edge curve is used as the correction distance corresponding to the edge curve.

[0094] In one embodiment, the calculation expression of the corrected distance is:

[0095]

[0096] in, represents the correction distance, d represents the distance between the two end points of the edge curve, 1 represents a constant, Indicates the curvature of the edge curve.

[0097] Similarly, obtain the material particle size reflected by each edge curve , combined with the degree to which each edge curve reflects the actual particle size of the material particles, that is, the credibility of the change rate corresponding to the edge curve, calculate the particle size corresponding to the edge line of the incomplete particle. Specifically, the credibility of the change rate corresponding to each edge curve is used as a weight, and the weighted sum of the corrected distances corresponding to each edge curve is calculated to obtain the particle size corresponding to the edge line of the incomplete particle.

[0098] In one embodiment, the calculation expression of the particle size corresponding to the incomplete particle edge line is:

[0099]

[0100] in, Indicates the particle size corresponding to the edge line of the incomplete particle, represents the corrected distance corresponding to the i-th edge curve, represents the credibility of the change rate corresponding to the ith edge curve, and m represents the number of edge curves corresponding to the incomplete particle edge line.

[0101] At this point, the particle size corresponding to each incomplete particle edge line can be obtained.

[0102] Step S104, obtaining the particle size uniformity of the carbon negative electrode material according to the particle size corresponding to each complete particle edge line and the particle size corresponding to each incomplete particle edge line, and detecting the material properties of the carbon negative electrode material according to the particle size uniformity.

[0103] Through the above steps S102 and S103, the particle size corresponding to each complete particle edge line and the particle size corresponding to each incomplete particle edge line can be obtained, that is, the particle size of each material particle in the scanning electron microscope image is obtained. Then, the particle size standard deviation of the particle size corresponding to all complete particle edge lines and the particle size corresponding to all incomplete particle edge lines is calculated, and the particle size uniformity of the carbon negative electrode material is obtained according to the reciprocal of the sum between the particle size standard deviation and the constant 1.

[0104] Among them, the calculation expression of particle size uniformity is:

[0105]

[0106] Wherein, h represents the uniformity of the particle size of the carbon negative electrode material. represents the standard deviation of particle size, and 1 represents a constant.

[0107] It should be noted that the smaller the standard deviation of the particle size, the smaller the difference in particle size between the material particles in the carbon negative electrode material, the higher the consistency of the corresponding particle size, and the better the charge and discharge performance of the carbon negative electrode material.

[0108] Furthermore, the preset particle size uniformity threshold is set to 0.5, which is not limited here and can be set according to the implementation scenario. If the particle size uniformity degree is greater than or equal to the particle size uniformity threshold, it is determined that the material performance of the carbon negative electrode material meets the requirements; if the particle size uniformity degree is less than the particle size uniformity threshold, it is determined that the material performance of the carbon negative electrode material does not meet the requirements.

[0109] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A performance analysis and detection method for carbon negative electrode materials of lithium batteries for new energy vehicles, characterized in that: The method comprises: Acquire a scanning electron microscope image of a carbon negative electrode material, and perform edge detection on material particles in the scanning electron microscope image to obtain at least one material particle edge line; According to the change of the position slope of each pixel point on each material particle edge line, all material particle edge lines are divided to obtain complete particle edge lines and incomplete particle edge lines, and the particle size corresponding to each complete particle edge line is obtained; For any incomplete particle edge line, the incomplete particle edge line is divided into at least two edge curves, the endpoint distance corresponding to each edge curve is obtained, the curvature of the corresponding edge curve is obtained according to the change rate of each edge curve, and the particle size corresponding to the incomplete particle edge line is obtained according to the endpoint distance and curvature of each edge curve; According to the particle size corresponding to each of the complete particle edge lines and the particle size corresponding to each of the incomplete particle edge lines, the particle size uniformity of the carbon negative electrode material is obtained, and the material performance of the carbon negative electrode material is detected according to the particle size uniformity; According to the change of the position slope of each pixel point on each material particle edge line, all material particle edge lines are divided to obtain complete particle edge lines and incomplete particle edge lines, including: For any pixel point on the edge line of all material particles, obtain the left adjacent pixel point and the right adjacent pixel point on the edge line of the material particle where the pixel point is located, calculate the position slope between the pixel point and the left adjacent pixel point and the right adjacent pixel point respectively, and obtain the position slope difference, which is recorded as the position slope change rate of the pixel point; Calculate the absolute value of the difference between the position slope change rate of the pixel point and each pixel point on the edge line of the material particle where it is located, obtain the sum of the absolute values ​​of the differences, perform normalization on the sum of the absolute values ​​of the differences, and obtain a possibility index that the pixel point belongs to the edge intersection of the material particle; if the possibility index that the pixel point belongs to the edge intersection of the material particle is greater than a preset possibility threshold, determine that the pixel point is a suspected edge intersection of the material particle; For any material particle edge line, if the number of suspected material particle edge intersections on the material particle edge line does not meet a preset number threshold, the material particle edge line is taken as a complete particle edge line; if the number of suspected material particle edge intersections on the material particle edge line meets a preset number threshold, the material particle edge line is taken as a target edge line; For any target edge line, according to the possibility index corresponding to each suspected material particle edge intersection point on the target edge line, obtain the suspected material particle edge intersection point corresponding to the maximum possibility index as the first target point; among all the suspected material particle edge intersection points on the target edge line, obtain the suspected material particle edge intersection point closest to the first target point, and form a group of matching pixel points with the first target point; Among the unmatched suspected material particle edge intersection points, the suspected material particle edge intersection point corresponding to the maximum likelihood index is obtained as the second target point, and among the unmatched suspected material particle edge intersection points, the suspected material particle edge intersection point closest to the second target point is obtained, and a group of matching pixel points is formed with the second target point; and so on, multiple groups of matching pixel points are obtained, and the connecting line between each group of matching pixel points is used as a cutting line, and the target edge line is divided into multiple incomplete particle edge lines based on all the cutting lines; The step of obtaining the particle size corresponding to each complete particle edge line includes: For any complete particle edge line, calculate the distance between every two pixel points on the complete particle edge line, and use the maximum distance as the particle size corresponding to the complete particle edge line; The step of obtaining the curvature of the corresponding edge curve according to the change rate of each edge curve includes: For any edge curve, obtain the chain code of the edge curve, count the number of occurrences of each chain code value of the edge curve in the chain code, obtain the maximum number of occurrences, and use the inverse of the maximum number of occurrences as the change rate of the edge curve; Obtaining the absolute value of the difference between the starting chain code value and the ending chain code value of the edge curve, obtaining the absolute value of the difference between the maximum chain code difference and the absolute value of the difference, and performing negative mapping on the absolute value of the difference using an exponential function with a natural constant as the base to obtain the credibility of the change rate of the edge curve; Obtaining the curvature of the edge curve according to the product of the change rate of the edge curve and the change rate credibility; The step of obtaining the particle size corresponding to the incomplete particle edge line according to the endpoint distance and curvature of each edge curve comprises: For any edge curve, obtain the addition result between the curvature of the edge curve and a constant 1, and use the product of the addition result and the end point distance of the edge curve as the correction distance corresponding to the edge curve; The change rate credibility corresponding to each edge curve is used as a weight, and the corrected distance corresponding to each edge curve is weighted and summed up and then averaged to obtain the particle size corresponding to the incomplete particle edge line.

2. The performance analysis and detection method of a carbon negative electrode material for a new energy vehicle lithium battery according to claim 1, characterized in that: The step of dividing the incomplete particle edge line into at least two edge curves comprises: If the number of endpoints on the incomplete particle edge line exceeds 2, each sub-curve in the incomplete particle edge line is used as an edge curve; If there are only two endpoints on the incomplete particle edge line, for any endpoint, the pixel point farthest from the endpoint is obtained on the incomplete particle edge line as the first pixel point, and the curve between the first pixel point and the endpoint is taken as the edge curve.

3. The performance analysis and detection method of a carbon negative electrode material for a new energy vehicle lithium battery according to claim 1, characterized in that: The step of obtaining the particle size uniformity of the carbon negative electrode material according to the particle size corresponding to each of the complete particle edge lines and the particle size corresponding to each of the incomplete particle edge lines comprises: The particle size standard deviation of the particle size corresponding to all complete particle edge lines and the particle size corresponding to all incomplete particle edge lines is calculated, and the particle size uniformity of the carbon negative electrode material is obtained according to the reciprocal of the sum of the particle size standard deviation and the constant 1.

4. The performance analysis and detection method of a carbon negative electrode material for a new energy vehicle lithium battery according to claim 1, characterized in that: The detecting the material properties of the carbon negative electrode material according to the degree of uniformity of the particle size comprises: A preset particle size uniformity threshold is obtained. If the particle size uniformity degree is greater than or equal to the particle size uniformity threshold, it is determined that the material performance of the carbon negative electrode material meets the requirements; if the particle size uniformity degree is less than the particle size uniformity threshold, it is determined that the material performance of the carbon negative electrode material does not meet the requirements.

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