Evaluation method and measurement system equipment for electrode assembly arc region pole piece gap

Abstract

The invention belongs to the technical field of batteries, and provides an evaluation method and measurement system equipment for a pole piece gap in an arc region of an electrode assembly, and the method comprises the steps: obtaining a current collector winding image of a cross section of a ring layer of the electrode assembly where a target point Dab is located through a detector; the distance Sab between the current collector of the target point Dab and the current collector of the same pole piece of the previous circle layer is directly measured, and the pole piece thickness Hab at the position of the target point Dab, the pole piece thickness at the intersection point between the radius where the target point is located and each inner pole piece and the pole piece thickness at the intersection point between the radius where the target point is located and each outer pole piece are determined; according to the type and the number of the pole pieces included in the distance Sab and the number and the thickness of the diaphragms included in the distance Sab, the gap value Pab between the target point Dab and the same pole piece of the previous circle layer can be obtained through a specific calculation formula, and the gap value Qab between the target point and the other pole piece of the previous circle layer can be further calculated.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a method for evaluating the gap between electrode sheets in the arc region of an electrode assembly and a measurement system device. Background Art

[0002] The winding process is an important means widely used in the manufacture of lithium-ion battery electrode assemblies. By means of a winding needle mechanism of a winding device, the positive and negative electrode sheets and the separator are wound in multiple turns in a specific order to form an electrode assembly. The winding process is applicable to various types of battery structures, especially for the production of square batteries and cylindrical batteries.

[0003] According to the different types of target batteries, the shape of the winding needle mechanism for winding and the shape of the obtained electrode assembly are different. Generally, in a view of the plane side where the layer structure is exposed in the electrode assembly, the outer contour of the cylindrical battery electrode assembly is generally circular as a whole, while the outer contour of the square battery electrode assembly is a kind of rounded rectangle, which has a straight long side of a rectangle and arc sides connected at both ends of the long side. The use of a smooth transition of the arc instead of a sharp right angle helps to disperse stress, avoids the risk of rupture or leakage that may occur under extreme conditions, and can also improve the distribution uniformity of the electrolyte in the electrode assembly to a certain extent, which is beneficial to improving the overall performance of the battery.

[0004] However, in actual winding production, the electrode sheets and the separator do not always form an ideal tight contact. After multiple turns of winding, there are often gaps between the electrode sheets and the separator and / or between the electrode sheets. Especially in the rounded rectangle electrode assembly, the junction of the long side and the arc side and the R-corner region (i.e., the arc side region) are more likely to have gaps due to the need for bending deformation. Such gaps will affect the transmission path of lithium ions, cause insufficient infiltration of the electrolyte, and abnormal problems such as abnormal black spots, lithium deposition, and insufficient lithium intercalation are likely to occur in places with larger gaps, seriously affecting the performance, stability, and safety of the battery, resulting in irreparable losses.

[0005] However, there is currently no effective monitoring solution for the gaps in the electrode assembly in the industry, and it is impossible to identify risks in advance. Therefore, there is an urgent need to develop a method for measuring and evaluating the gaps in the electrode assembly in advance to improve the product consistency and production quality. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for evaluating the gap between electrode sheets in the arc region of an electrode assembly and a measurement system device. The evaluation method includes assigning an a value according to the positional relationship between the arc region and the plane region where the target point is located, and assigning a b value according to the number of winding layers of the electrode sheet at the position where the target point D ab is located; obtaining the target point D by using a detector abThe current collector winding image of the cross-section of the electrode assembly layer where it is located, and the target point D is directly measured in the current collector winding image ab The distance S between the current collector of the current collector of the target point D and the current collector of the same pole piece in the previous layer ab , after determining the target point D ab The pole piece thickness H at the position ab And the target point D ab The pole piece thickness at the intersection of the radius where it is located and each inner pole piece, the target point D ab After the pole piece thickness at the intersection of the radius where it is located and each outer pole piece, according to the distance S ab The types and quantities of pole pieces contained between them, as well as the quantity and thickness of the contained separator, the gap value P between the target point D ab And the same pole piece in the previous layer can be obtained through a specific calculation formula ab , and the gap value Q between the target point D ab And the other pole piece in the previous layer can be further deduced ab .

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a method for evaluating the pole piece gap in the arc area of the electrode assembly, including the following steps:

[0009] For any target point on the pole piece in the arc area, according to the positional relationship between the arc area where the target point is located and the plane area, assign a value to a, and according to the number of winding layers of the pole piece at the position where the target point is located, assign a value to b, and record the target point as D ab ; In the cross-section of the electrode assembly layer where the target point D ab is located, along the width direction of the electrode assembly, the two end points of the winding needle mechanism are respectively used as the center points of the corresponding arc areas, and both arc areas are regarded as semi-circles; determine the pole piece thickness at the position of the target point D ab , denoted as H ab , and determine the pole piece thickness at the intersection of the radius where the target point D ab is located and each inner pole piece, denoted as H 1 ab , and the pole piece thickness at the intersection with each outer pole piece, denoted as H 2 ab ;

[0010] Use a detector to scan the cross-section of the electrode assembly layer where the target point D ab is located, obtain the current collector winding image where the target point D ab is located, and calculate the gap in the following manner:

[0011] Along the target point D abThe radius where it is located is directly measured in the obtained current collector winding image to obtain the target point D ab The distance between the current collector of the current electrode tab and the current collector of the same electrode tab in the previous layer is denoted as S ab ; The target point D ab The gap between the current electrode tab and the same electrode tab in the previous layer is denoted as P ab , The target point D ab The gap between the current electrode tab and the other electrode tab in the previous layer is denoted as Q ab , Then when the electrode tab where the target point D ab is located is the inner electrode tab, P ab =S ab -0.5(H ab +H 1 a(b-1) )-2m-H 2 a(b-1) , Q ab =0.5P ab ; When the electrode tab where the target point D ab is located is the outer electrode tab, P ab =S ab -0.5(H ab +H 2 a(b-1) )-2m-H 1 a(b-1) , Q ab =0.5P ab ; Wherein, m represents that the diaphragm thickness is a constant value; when b - 1 is 0, the values of H 1 a(b-1) and H 2 a(b-1) are both 0.

[0012] It should be noted that in this field, the electrode assembly usually includes an inner diaphragm, an inner electrode tab, an outer diaphragm and an outer electrode tab. After winding to form the electrode assembly, the central axis direction of the electrode assembly is the height direction of the electrode assembly; and in the thickness direction of the electrode assembly are two opposite planar regions, and in the width direction of the electrode assembly are two arc regions provided at both ends of the planar region. The method for evaluating the tab gap in the arc region of the electrode assembly according to the present invention is for an electrode assembly having such a structure.

[0013] In the evaluation method of the present invention, the wound electrode assembly is scanned across the cross-section of a certain electrode assembly layer, and a winding image of the metal current collector of the same pole piece (taking the negative pole piece as the inner pole piece as an example) in the cross-section of this electrode assembly layer is obtained. Thus, in the arc region, the radial distance S between the negative pole piece's metal current collectors of two adjacent layers can be obtained. The radial distance S includes half of the respective thicknesses of the negative pole pieces of two adjacent layers, as well as the thickness of a complete other pole piece (i.e., the positive pole piece as the outer pole piece), the thicknesses of two separator layers, and the thickness of the gap P. Therefore, after subtracting the remaining thicknesses from the distance S, the gap P between two adjacent layers in the negative pole piece is obtained, and half of its value is used to represent the gap Q between the negative pole piece and the positive pole piece of the adjacent layer.

[0014] Therefore, the calculation of the gap is specifically divided into the following two cases:

[0015] When the target point D ab is on the inner pole piece, along the radius where the target point D ab is located, direct measurement is performed in the obtained current collector winding image to obtain the distance between the current collector of the inner pole piece where the target point D ab is located and the current collector of the inner pole piece of the previous layer, denoted as S ab ; the gap between the inner pole piece where the target point D ab is located and the inner pole piece of the previous layer is denoted as P ab , the gap between the inner pole piece where the target point D ab is located and the outer pole piece of the previous layer is denoted as Q ab , then P ab =S ab -0.5(H ab +H 1 a(b-1) )-2m-H 2 a(b-1) , Q ab =0.5P ab ;

[0016] When the target point D ab is on the outer pole piece, along the radius where the target point D ab is located, direct measurement is performed in the obtained current collector winding image to obtain the distance between the current collector of the outer pole piece where the target point D ab is located and the current collector of the outer pole piece of the previous layer, denoted as S ab ; the gap between the outer pole piece where the target point D ab is located and the outer pole piece of the previous layer is denoted as P ab , the gap between the outer pole piece where the target point D ab is located and the inner pole piece of the previous layer is denoted as Q ab , then Pab =S ab -0.5(H ab +H 2 a(b-1) )-2m-H 1 a(b-1) , Q ab =0.5P ab ;

[0017] Among them, when b-1 is 0, H 1 a(b-1) and H 2 a(b-1) The value of is 0. The thickness of the inner diaphragm and the outer diaphragm is a constant value m.

[0018] As can be seen from the above, after directly measuring the distance S from the wound image of the current collector, the key point is to determine the thickness of each electrode contained in the distance S. The electrode thickness corresponding to the target points at different positions is different. The reason is that in the industrial production of the winding process, the electrode and the separator are both used in rolls, and the separator thickness can be regarded as a constant value. However, the electrode is composed of the current collector and the coating layer. The thickness of the electrode is the sum of the thickness of the current collector and the thickness of the coating layer. The coating layer is obtained by coating the slurry on the current collector, rolling it, and drying it. The slurry coating process may cause the thickness of the coating layer to be uneven due to factors such as die head vibration. The electrode and separator are wound by the winding needle mechanism of the winding equipment to form an electrode assembly. The thickness of the electrode at a certain position in the electrode assembly will vary due to the uneven thickness of the coating layer. After winding multiple times, the thickness of the coating layer will accumulate. Obviously, a constant value cannot be used to measure the thickness of the electrode at all positions in the electrode assembly.

[0019] Therefore, the present invention assigns a value and b value to the target point to obtain the corresponding electrode thickness according to the different target point positions. It can be understood that, in addition to the target point, any point on the electrode selected in the arc area of the electrode assembly has a corresponding a value and b value.

[0020] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0021] As a preferred technical solution of the present invention, the inner electrode sheet in the electrode assembly is a negative electrode sheet.

[0022] Preferably, starting from the starting end of the pole piece, along the winding direction, the first arc area reached is the first arc area, having the first center point, and the second arc area reached is the second arc area, having the second center point; when the target point D ab In the first arc zone, a=1, and in the second arc zone, a=2.

[0023] Preferably, along the width direction of the electrode assembly, the intersection points of the radius passing through the second center point and each pole piece in the second arc region are used as the layer boundary points of the corresponding pole pieces; along the winding direction, the target point D is determined ab The number g of layer boundary points contained between the starting end of the pole piece where the target point D ab is located and the target point D is b = g + 1.

[0024] As a preferred technical solution of the present invention, the method for determining the thickness of the pole piece at the position of the target point D ab includes:

[0025] (1) Before the pole piece is wound to form the electrode assembly, a thickness gauge is used to continuously measure the unwound pole piece. Taking a point on the starting end of the pole piece as the coordinate origin, a right-angled first coordinate system is established on the pole piece, with the length direction of the pole piece as the horizontal axis direction and the coordinate value as x, and the width direction of the pole piece as the vertical axis direction and the coordinate value as y; the thickness values of the pole piece at each test point are measured and recorded as H. At the same time, the coordinate information (x, y) of each test point is recorded, and a database is established with the data [(x, y), H]; the thickness of the separator is measured with a thickness gauge and recorded as m and regarded as constant;

[0026] (2) In the electrode assembly, a second coordinate system is established with the coordinate origin and the height direction of the electrode assembly, and the coordinate value of the target point D ab is recorded as z;

[0027] On the pole piece in the cross-section of the electrode assembly layer where the target point is located, according to the a value and b value of the target point D ab , measure and estimate the winding length value of the pole piece from the starting end to the target point D ab along the winding direction, and record it as L ab . Take L ab as the simulated coordinate value of the target point D ab , and form the coordinate information (L ab , z) of the target point D ab with the coordinate value z;

[0028] (3) Substitute (L ab , z) into the database established with the data [(x, y), H], establish a numerical correspondence between L ab and x, establish a numerical correspondence between z and y, match the (x, y) corresponding to (L ab , z), and output the H value in the data [(x, y), H] where (x, y) is located as the thickness H of the pole piece at the position of the target point D ab ; ab .

[0029] In this field, a thickness gauge can be used to perform single-point measurement on the thickness of the unrolled electrode sheet. For example, for a double-sided coated electrode sheet, the obtained thickness is the sum of the current collector thickness at the test point and the coating layer thicknesses on both sides thereof. However, the thickness gauge can only measure the thickness of the electrode sheet before winding, and cannot directly measure the thickness of the electrode sheet at a certain position in the electrode assembly without disassembling the electrode assembly. At the same time, during the process of winding the electrode sheet to form an electrode assembly, the arc area of the electrode assembly of the square battery is more likely to have gaps due to the required bending deformation. Therefore, before winding the electrode sheet to form an electrode assembly, continuously testing the thickness of each position on the unwound electrode sheet with a thickness gauge does not represent the thickness of the electrode sheet at a certain position after winding to form the electrode assembly. Even if the problem that the arc area is more likely to have gaps due to the required bending deformation is not considered, due to the different shapes and size specifications of the electrode assemblies, it is also impossible to know the specific position of a specific test point targeted by the thickness gauge in the electrode assembly. In other words, when obtaining the thickness of the electrode sheet at a certain position in the electrode assembly, it is not known which specific test point it corresponds to among the numerous data obtained by the thickness gauge. Because the thickness gauge is often set up and used as an independent device, it does not contain the determination rules or calculation logic of this mapping relationship, and there is no corresponding module inside it to implement this function, and there is also no solution in this field to integrate the thickness gauge to obtain the thickness of the electrode sheet at a certain position in the electrode assembly.

[0030] In this field, the unwound electrode sheet and separator enter the winding process in the stacking order of the inner separator - inner electrode sheet - outer separator - outer electrode sheet. Both the electrode sheet and the separator have a long side that conforms to the unwinding direction starting from the starting end, and a short side perpendicular to the unwinding direction. When winding through the winding needle mechanism of the winding device, the short sides of the electrode sheet and the separator form the height direction (central axis direction) of the electrode assembly, and the long sides of the electrode sheet and the separator form a specific outer contour shape in a plane perpendicular to the height direction (i.e., on the cross-section of the electrode assembly layer of the electrode assembly). On this basis, in the method for determining the thickness of the electrode sheet at the target point D ab in the position, the main purpose of step (1) is to, before winding, use a thickness gauge to test the thickness of the electrode sheet (including the inner electrode sheet and the outer electrode sheet), while recording the thickness value of the test point, match the length position information (i.e., coordinate value x) and width position information (i.e., coordinate value y) of the corresponding test point on the electrode sheet, and establish a database; the main purpose of step (2) is to, considering that the short side (width direction of the electrode sheet) of the electrode sheet forms the height direction of the electrode assembly after winding, a second coordinate system (a one-dimensional coordinate system when only including the height direction) is established in the electrode assembly, so as to correspond the height position information (i.e., coordinate value z) of the target point D ab in the electrode assembly with the coordinate value y, and at the same time measure and estimate the winding length value L ab of the electrode sheet at the target point Dab to facilitate correspondence with the coordinate value x. Therefore, the main purpose of step (3) is to substitute the coordinate information of the target point D ab into the database to find the test point corresponding to the coordinate information, and then the thickness value of the test point can be output to represent the thickness value of the pole piece at the target point D ab .

[0031] According to the above, it can be seen that the present invention only needs to use a thickness gauge to perform tests before winding to form the electrode assembly. Further, an inspection instrument can be used to obtain the winding image of the current collector on the cross-section of the electrode assembly layer, without the need for more test equipment, which is convenient for implementation. It can be understood that, further, a host and / or modules such as calculation processing and data storage can be added to incorporate the calculation formula and calculation process into the program to achieve automatic operation.

[0032] As a preferred technical solution of the present invention, in step (1), the coordinate origin is set at a vertex at the starting end of the pole piece. After winding, the vertex is located at the bottom of the electrode assembly.

[0033] Preferably, in the thickness direction of the electrode assembly, the positive projections of the coordinate origins of the inner pole piece and the outer pole piece coincide.

[0034] As a preferred technical solution of the present invention, in step (2), the pole piece winding length value L ab is measured and estimated on the inner circle side of the pole piece close to the winding needle mechanism.

[0035] As a preferred technical solution of the present invention, the length of the radius where the target point D ab is located in the arc area is denoted as R ab , then there is:[[]]

[0036] When the target point is on the inner pole piece, R ab =(2b - 1)m + ∑H 1 a(b-1) + ∑H 2 a(b-1) ;

[0037] When the target point is on the outer pole piece, R ab = 2bm + ∑H 2 a(b-1) + ∑H 1 ab ;

[0038] Among them, when b - 1 is 0, the values of H 1 a(b-1) and H 2 a(b-1) are both 0.

[0039] It should be noted that ∑H1 a(b-1) representing H 1 a0 、H 1 a1 、H 1 a2 、H 1 a3 up to H 1 a(b-1) the summation of ∑H 2 a(b-1) representing H 2 a0 、H 2 a1 、H 2 a2 、H 2 a3 up to H 2 a(b-1) the summation of ∑H 1 ab representing H 1 a0 、H 1 a1 、H 1 a2 、H 1 a3 up to H 1 a(b-1) and H 1 ab the summation of.

[0040] In the present invention, the calculation formula of the radius R ab represents the sum of the thicknesses of the respective inner diaphragms, inner electrode tabs, outer diaphragms, and outer electrode tabs from the target point to the corresponding center point in the arc region.

[0041] As a preferred technical solution of the present invention, in the cross-section of the electrode assembly layer where the target point D ab is located, the starting end of the electrode tab coincides with the second center point.

[0042] Preferably, the winding length of the electrode tab in the electrode assembly in each planar region is regarded as equal to half of the surface circumference c of the winding needle mechanism.

[0043] The present invention provides a method for measuring the thickness of an electrode tab in the arc region of an electrode assembly, which is particularly suitable for measuring and estimating the thickness and gap of the electrode tab at the target point in the arc region of a rounded rectangular electrode assembly. For the convenience of the winding length value L of the electrode tab abFor the measurement and estimation, the present invention delimits the boundary between the arc region and the planar region in the rounded rectangular electrode assembly. The present invention takes the part outside both ends of the corresponding coiling needle mechanism as the arc region, and regards the arc region as a semi - circle to facilitate the calculation of the length of the arc edge of each layer in the arc region. When the pole piece is wound on the planar region between the first center point and the second center point, the winding length on one planar region each time is regarded as half of the surface circumference c of the coiling needle mechanism, and one winding requires passing through two opposite planar regions, so it is equal to the surface circumference c of the coiling needle mechanism.

[0044] It can be understood that, for the convenience of measuring the length between the starting end of the inner pole piece and the first center point in the first layer at the beginning of winding, it is preferably specified that the starting end of the pole piece coincides with the second center point, that is, the winding starting point is at the second center point. Then, the winding length between the starting end of the inner pole piece and the first center point in the first layer is the length of passing through one planar region, that is, half of the surface circumference c of the coiling needle mechanism; if the winding starting point is set in the planar region between the second center point and the first center point, the winding length between the starting end of the pole piece and the first center point in the first layer can still be directly measured on the coiling needle mechanism, that is, the surface length from the winding starting point to the first center point on the coiling needle mechanism along the winding direction.

[0045] Preferably, in the same layer with the same b value, along the winding direction, the target point D ab passes through a central angle of θ1 in the first arc region and a radian of θ2 in the second arc region. Then, in step (2), for the target point D ab the pole piece winding length value L ab is calculated in the following way:

[0046] When a = 1, then L ab =(2(b - 1)+a)×0.5c+π(∑R 1(b-1) +∑R 2(b-1) +R 1b (θ1 / 180°);

[0047] When a = 2, then L ab =(2(b - 1)+a)×0.5c+π(∑R 1b +∑R 2(b-1) +R 2b (θ2 / 180°);

[0048] Among them, when b - 1 is 0, the values of R 1(b-1) and R 2(b-1) are both 0; c is the surface circumference of the coiling needle mechanism.

[0049] As a preferred technical solution of the present invention, when the target point is on the inner pole piece, R 11 and R 21All are regarded as equal to 0.

[0050] It should be noted that ∑R 1(b-1) represents the sum of R 10 , R 11 , R 12 , R 13 up to R 1(b-1) ; ∑R 2(b-1) represents the sum of R 20 , R 21 , R 22 , R 23 up to R 2(b-1) ; ∑R 1b represents the sum of R 10 , R 11 , R 12 , R 13 up to R 1(b-1) and R 1b .

[0051] In the present invention, the winding length of the pole piece in the planar region is related to the surface circumference of the winding needle mechanism, and the winding length of the pole piece in the arc region is related to the semi-circular arc length (i.e., the radius). Thus, the measured and estimated value of the winding length of the pole piece L ab is the sum of the lengths of all the planar regions and the arc regions passed from the starting end of the pole piece along the winding direction to the target point. From the relevant calculation formula of the radius R ab of the D ab at the target point, although it involves using the pole piece thickness at the intersection of the radius where the target point is located and each inner pole piece and each outer pole piece, but when the pole piece thickness (i.e., the inner pole piece thickness of the innermost circle of the electrode assembly) H 1 11 at the intersection of the inner pole pieces in the first layer is determined, as well as H 2 11 , the remaining H 1 ab and H 2 ab can all be obtained successively through calculation. And precisely, in the present invention, the surface circumference c of the winding needle mechanism and the separator thickness m are obtained and determined by pre-measurement as initial conditions, which means that when the target point is at these two intersections of the inner pole pieces, i.e., D 11 and D 21 , R 11 =R 21 =m, then L 11 =0.5c + πm(θ1 / 180°), L 21= c + π(m + m(θ2 / 180°)), all of which can be calculated. Further, considering that compared with the thickness of the electrode tab, the thickness m of the separator is very small, and there is only one layer of separator inside the inner electrode tab in the first layer, so it can be regarded as R 11 = R 21 = 0, at this time, L 11 = 0.5c, L 21 = c.

[0052] In a second aspect, the present invention provides a measurement system device for the gap between electrode tabs in the arc area of an electrode assembly. The evaluation method described in the first aspect is implemented through the measurement system device. The measurement system device includes:

[0053] A thickness gauge, arranged between the electrode tab unwinding device and the winding device, for continuously measuring the unwound electrode tab to obtain the electrode tab thickness value H of each target point D ab ;

[0054] An inspection device, arranged after the hot pressing and shaping device, for inspecting the cross-section of the electrode assembly layer where the target point Dab is located in the electrode assembly to obtain the current collector winding image;

[0055] A host computer, electrically connected to the thickness gauge and the inspection device, for automatically controlling the thickness gauge and the inspection device, as well as processing and storing data.

[0056] Preferably, the thickness gauge includes a laser thickness gauge.

[0057] Preferably, the inspection device includes a CT scanning device.

[0058] It should be noted that the measurement system device can be integrated into an existing unwinding-winding process production line, which should have unwinding devices for positive electrode tabs, negative electrode tabs and separators, roller passing devices, conveying and grasping devices, winding devices (including winding needle mechanisms), and hot pressing and shaping devices after winding, etc.

[0059] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0060] Through the method for evaluating the gap between pole pieces in the arc region of the electrode assembly according to the present invention, early identification of the risks of the electrode assembly can be achieved, abnormal electrode assemblies can be selected, and safety accidents caused by the outflow of risks can be prevented; it can be further used to adjust the process in advance, reduce lithium deposition or black spots at the gap position caused by too large a gap between pole pieces, reduce the scrapping of electrode assemblies, improve the product quality consistency of electrode assemblies, and increase the cycle life of electrode assemblies; the lithium deposition risk of the designed NP ratio in the arc region during the design of the electrode assembly can be further calculated through the gap value, and design risks can be avoided in advance; it can also be further used to predict whether the fluctuation of the winding tension is reasonable, monitor the fluctuation of the tension in reverse, improve the monitoring ability of product parameters, and prevent the increase in the binding force of the electrode assembly caused by the tension fluctuation from affecting the performance of the electrode assembly.

[0061] The evaluation method according to the present invention only needs to use a thickness gauge and a detector for testing, and more testing equipment is not required, and the gap between adjacent two-layer pole pieces can be estimated, which is convenient for implementation and automated operation. Brief Description of the Drawings

[0062] Figure 1 It is a schematic diagram of the unrolled negative pole piece, showing a situation where a right-angled first coordinate system is set on the pole piece.

[0063] Figure 2 It is a schematic diagram of the unrolled positive pole piece, showing another situation where a right-angled first coordinate system is set on the pole piece.

[0064] Figure 3 It is a three-dimensional schematic diagram of one side of the electrode assembly facing the top, showing a situation where a second coordinate system is set in the electrode assembly.

[0065] Figure 4 It is a schematic diagram of the cross-section of the electrode assembly layer where the target point is located, showing another situation where a second coordinate system is set in the electrode assembly.

[0066] Figure 5 For Figure 4 It is a schematic diagram of the method for evaluating the gap between pole pieces in the arc region of the electrode assembly for the target point in

[0067] Figures 1 to 5Among them, 110 - negative electrode sheet, 120 - positive electrode sheet, 130 - starting end of the electrode sheet, 140 - coordinate origin, 210 - planar region, 220 - arc region, 221 - first arc region, 222 - second arc region, 231 - first center point, 232 - second center point, 300 - target point, 301 - first layer boundary point, 302 - second layer boundary point, 303 - third layer boundary point, 310 - first intersection point of the negative electrode sheet, 320 - second intersection point of the negative electrode sheet, 330 - third intersection point of the negative electrode sheet, 410 - first intersection point of the positive electrode sheet, 420 - second intersection point of the positive electrode sheet, 430 - third intersection point of the positive electrode sheet.

[0068] Figure 6 It is the current collector winding image obtained by the detector detecting the electrode assembly.

[0069] Figure 7 It is a schematic diagram of the winding measurement system device for implementing the evaluation method of the pole piece gap in the arc region of the electrode assembly.

[0070] Figure 7 Among them, 1a - positive electrode film roll, 1b - negative electrode film roll, 1 - positive electrode sheet, 2 - negative electrode sheet, 3 - electrode assembly, 5 - first idler roller, 6 - second idler roller, 7 - thickness gauge, 8 - third idler roller, 9 - fourth idler roller, 10 - separator film roll, 10a - separator, 11 - winding needle mechanism, 12 - transfer fixture, 13 - conveyor belt, 14 - hot pressing and shaping station, 15 - detector. Specific embodiments

[0071] The technical solution of the present invention will be further described below through specific embodiments.

[0072] Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0073] Embodiment 1

[0074] This embodiment provides an evaluation method for the pole piece gap in the arc region of the electrode assembly. The evaluation method includes the following steps:

[0075] (1) During the unwinding process of the negative electrode sheet, positive electrode sheet and separator, before winding to form the electrode assembly, use a thickness gauge to continuously measure the unwound pole piece. Take a point on the starting end of the pole piece as the coordinate origin, establish a right - angled first coordinate system on the pole piece, with the length direction of the pole piece as the horizontal axis direction (X - direction) and the coordinate value as x, and the width direction of the pole piece as the vertical axis direction (Y - direction) and the coordinate value as y; measure the pole piece thickness value of each test point, denoted as H, and record the coordinate information (x, y) of each test point at the same time, and establish a database with the data [(x, y), H]; use a thickness gauge to measure the separator thickness, denoted as m and regarded as constant.

[0076] For clarity of explanation, Figure 1 Fig. Figure 1 shows a case where a rectangular first coordinate system is set on the unwound negative electrode sheet 110, and the coordinate origin 140 can be set at the middle of the starting end 130 of the electrode sheet. Figure 2 Fig. Figure 2 shows another case where a rectangular first coordinate system is set on the unwound positive electrode sheet 120. The coordinate origin 140 can be set at a vertex of the starting end 130 of the electrode sheet, and after winding, the vertex is located at the bottom of the electrode assembly. It can be understood that the coordinate origin 140 can also be set at the other vertex of the starting end 130 of the electrode sheet, and after winding, the vertex is located at the top of the electrode assembly.

[0077] In this embodiment, databases are respectively established for the negative electrode sheet and the positive electrode sheet. The coordinate origins of the negative electrode sheet and the positive electrode sheet are both selected at a vertex on the same side position of the electrode sheet, and after winding, the vertex is located at the bottom of the electrode assembly.

[0078] (2) Taking the negative electrode sheet as the inner electrode sheet and the positive electrode sheet as the outer electrode sheet, winding is performed in the stacking form of inner separator - inner electrode sheet - outer separator - outer electrode sheet. The winding starting point on the winding needle mechanism is set at one end of the winding needle mechanism. After the starting ends of the electrode sheet and the separator are set at the winding starting point on the winding needle mechanism, an electrode assembly is obtained through winding; the surface circumference c of the winding needle mechanism is obtained;

[0079] The central axis direction of the obtained electrode assembly is the height direction; the electrode assembly is divided into two opposite planar regions arranged in the thickness direction, and two arc regions respectively arranged at both ends of the planar regions in the width direction; at this time, in the thickness direction of the electrode assembly, the positive projections of the coordinate origins of the inner electrode sheet and the outer electrode sheet coincide;

[0080] For any target point on the electrode sheet in the arc region, an a value is assigned according to the positional relationship between the arc region where the target point is located and the planar region, and a b value is assigned according to the number of winding layers of the electrode sheet where the target point is located. The target point is denoted as D ab ; at the target point D ab In the cross-section of the electrode assembly layer where the target point D is located, along the width direction of the electrode assembly, the two end points of the winding needle mechanism are respectively used as the center points of the corresponding arc regions, and both arc regions are respectively regarded as semi-circles;

[0081] In the electrode assembly, a second coordinate system is established with the coordinate origin and the height direction of the electrode assembly, and the coordinate value of the target point D ab is recorded as z.

[0082] For clarity of explanation, Figure 3Shows a situation where a second coordinate system is set in the electrode assembly. The origin of the coordinate system is set at a vertex at the starting end of the pole piece. After winding, this vertex is located at the top of the electrode assembly, that is, the side with the tab. At this time, in the electrode assembly composed of the planar region 210 and the arc regions 220 at both ends, the origin of the coordinate 140 is on the top surface of the electrode assembly, and the vertical axis Z direction is parallel to the central axis direction of the electrode assembly. At this time, if a right-angled three-dimensional coordinate system is established with the origin of the coordinate 140 and the vertical axis Z direction, such as Figure 3 the additional A direction and B direction set in

[0083] Among them, at the target point D ab in the cross-section of the electrode assembly layer where it is located, starting from the starting end of the pole piece and along the winding direction, the first arc region reached is the first arc region, which has a first center point, and the second arc region reached is the second arc region, which has a second center point. When the target point D ab is in the first arc region, a = 1, and when it is in the second arc region, a = 2; along the width direction of the electrode assembly, the intersection points of the radius passing through the second center point and each pole piece in the second arc region are used as the layer boundary points of the corresponding pole pieces; along the winding direction, determine the starting end of the pole piece where the target point D ab is located to the target point D ab The number g of layer boundary points contained between them, b = g + 1.

[0084] To explain clearly, Figure 4 shows another situation where a second coordinate system is set in the electrode assembly, that is, the method adopted in this embodiment, that is, the origin of the coordinate is set at another vertex of the starting end 130 of the pole piece. After winding, this vertex is located at the bottom of the electrode assembly, that is, the side without the tab. At this time, the origin of the coordinate 140 is on the bottom surface of the electrode assembly, and the vertical axis Z direction is parallel to the central axis direction of the electrode assembly; starting from the starting end 130 of the pole piece and along the clockwise winding direction, the first arc region reached is the first arc region 221, which has a first center point 231, and the second arc region reached is the second arc region 222, which has a second center point 232; the intersection points of the radial line passing through the second center point 232 in the width direction of the electrode assembly and each pole piece in the second arc region 222 are used as the layer boundary points of the corresponding pole pieces. Among them, the pole piece where the target point 300 is located is the negative pole piece as the inner pole piece. Along the winding direction, from the starting end of the extreme to the target point 300, the corresponding layer boundary points included are the first layer boundary point 301, the second layer boundary point 302, and the third layer boundary point 303. At this time, a = 1, b = 1 + 3 = 4, z = 0 for the target point 300. Then the target point 300 is denoted as D 14 .

[0085] On the pole piece in the cross-section of the electrode assembly layer where the target point D ab is located, according to the target point Dab The a and b values are measured and estimated along the winding direction from the beginning of the pole piece to the target point D. ab The winding length of the pole piece between the pole pieces is recorded as L ab ; L ab As the target point D ab The simulated coordinate value of the target point D is formed with the coordinate value z ab Coordinate information (L ab ,z);

[0086] Specifically, the pole piece winding length L ab Measure and estimate the inner circle side of the pole piece close to the winding needle mechanism. ab The radius of the location is recorded as R ab , the target point D ab The thickness of the pole piece at the intersection of the radius and each inner pole piece is recorded as H 1 ab The thickness of the pole piece at the intersection with each outer pole piece is recorded as H 2 ab ,but:

[0087] When the target point is on the inner pole piece, R ab =(2b-1)m+∑H 1 a(b-1) +∑H 2 a(b-1) ;

[0088] When the target point is on the outer pole piece, R ab =2bm+∑H 2 a(b-1) +∑H 1 ab ;

[0089] Among them, when b-1 is 0, H 1 a(b-1) and H 2 a(b-1) The value of is 0;

[0090] Since at the target point D ab In the cross section of the electrode assembly coil layer, the starting end of the electrode piece coincides with the second circle center point; the winding length of the electrode piece in the electrode assembly in a plane area each time is considered to be equal to half of the surface circumference c of the winding needle mechanism; in the same coil layer with the same b value, along the winding direction, the target point D ab The center angle of the circle passing through the first arc area is θ1, and the center angle of the circle passing through the second arc area is θ2, so the target point D in step ab The pole piece winding length L ab It is calculated as follows:

[0091] When a = 1, then L ab = (2(b - 1) + a)×0.5c + π(∑R 1(b-1) + ∑R 2(b-1) + R 1b (θ1 / 180°);

[0092] When a = 2, then L ab = (2(b - 1) + a)×0.5c + π(∑R 1b + ∑R 2(b-1) + R 2b (θ2 / 180°);

[0093] Wherein, when b - 1 is 0, the values of R 1(b-1) and R 2(b-1) are both 0; c is the surface perimeter of the coiling needle mechanism; R 11 and R 21 are both considered to be equal to 0.

[0094] For the sake of clarity, taking Figure 5 as an example, the process of relevant calculations for the measurement method of the thickness of the electrode tab in the arc area of the electrode assembly in the cross-section of the electrode assembly layer where the target point 300 is located is described as follows:

[0095] As obtained in step (2), a = 1 and b = 4 for the target point 300. Then the radius of the target point is denoted as R 14 . The radial direction between the target point 300 and the first center point 231 forms intersections with each of the other electrode tabs, including: the third positive electrode tab intersection 430 formed with the positive electrode tab in the third layer, and the thickness of the positive electrode tab at this point is denoted as H 2 13 ; the third negative electrode tab intersection 330 formed with the negative electrode tab in the third layer, and the thickness of the negative electrode tab at this point is denoted as H 1 13 ; the second positive electrode tab intersection 420 formed with the positive electrode tab in the second layer, and the thickness of the positive electrode tab at this point is denoted as H 2 12 ; the second negative electrode tab intersection 320 formed with the negative electrode tab in the second layer, and the thickness of the negative electrode tab at this point is denoted as H 1 12 ; the first positive electrode tab intersection 410 formed with the positive electrode tab in the first layer, and the thickness of the positive electrode tab at this point is denoted as H 2 11 ; the first negative electrode tab intersection 310 formed with the negative electrode tab in the first layer, and the thickness of the negative electrode tab at this point is denoted as H 1 11 ; Along the winding direction, starting from the third layer boundary point 303 to the target point 300, the central angle passed through in the second arc area 222 is θ2 = 90°, and the central angle passed through in the first arc area 221 is θ1 = 135°.

[0096] Then the radius R at the target point 300 14 =(2×4 - 1)×m + H 2 13 +H 2 12 +H 2 11 +H 1 13 +H 1 12 +H 1 11 。To obtain the specific value of R 14 , it is necessary to know the specific values of H 2 13 、H 2 12 、H 2 11 、H 1 13 、H 1 12 and H 1 11 。

[0097] Among them, to obtain H 1 11 , it is necessary to use the first intersection point 310 of the negative electrode sheet as a new target point to obtain the winding length value of this point and then match the thickness value in the database. When the first intersection point 310 of the negative electrode sheet is used as a new target point, it is on the inner electrode sheet, and a = 1, b = 1, and the winding length value L 11 =(2×(1 - 1)+1)×0.5c + π×R 11 ×(θ1 / 180°). In this embodiment, since the first intersection point 310 of the negative electrode sheet is on the inner electrode sheet when used as a new target point, so R 11 and R 21 are both regarded as equal to 0, and θ1 is also regarded as equal to 0. Therefore, L 11 =0.5c. Substitute the coordinate information (L 11 , z) of the first intersection point 310 of the negative electrode sheet, that is, (0.5c, 0) into the database to obtain the thickness H 1 11 of the first intersection point 310 of the negative electrode sheet.

[0098] To obtain H 2 11 , it is necessary to use the first intersection point 410 of the positive electrode sheet as a new target point to obtain the winding length value of this point and then match the thickness value in the database. When the first intersection point 410 of the positive electrode sheet is used as a new target point, it is on the outer electrode sheet, and a = 1, b = 1, and the winding length value L 11=(2×(1 - 1)+1)×0.5c + π×R 11 ×(θ1 / 180°). When the target point is on the outer pole piece, R 11 =2×1×m + H 1 11 , θ1 is 135°. H 1 11 was obtained in the previous step, so L 11 value can be determined. Substitute the coordinate information (L 11 , z) of the first intersection point 410 of the positive pole piece into the database to obtain the thickness H 2 11 .

[0099] To obtain H 1 12 , the second intersection point 320 of the negative pole piece needs to be used as a new target point to obtain the winding length value of this point so as to match the thickness value in the database. When the second intersection point 320 of the negative pole piece is used as a new target point, it is on the inner pole piece, and a = 1, b = 2, and the winding length value L 12 =(2×(2 - 1)+1)×0.5c + π(R 11 +R 21 +R 12 ×(θ1 / 180°)). In this embodiment, since the second intersection point 320 of the negative pole piece is used as a new target point and it is on the inner pole piece, R 12 =(2×2 - 1)×m + H 1 11 +H 2 11 , θ1 is 135°. H 1 11 and H 2 11 have been obtained in the previous steps, and R 11 and R 21 are both considered to be equal to 0, so L 12 value can be determined. Substitute the coordinate information (L 12 , z) of the second intersection point 320 of the negative pole piece into the database to obtain the thickness H 2 11 .

[0100] And so on. Starting from the center point and radially outward, after calculating the thickness values of the pole pieces at all intersection points in turn according to the measurement method of the pole piece thickness in the arc area of the electrode assembly, the radius R at the target point 300 can be obtained 14, during this calculation process, the corresponding radii at each intersection point, the radii at each layer boundary point, and the pole piece thickness have been obtained. Since the target point 300 is on the inner pole piece, its pole piece winding length L can be determined. 14 =(2×(4 - 1)+1)×0.5c+π(R 11 +R 12 +R 13 +R 21 +R 22 +R 23 +R 14 ×(θ1 / 180°)).

[0101] It can be seen that the above calculation process can be automatically calculated by writing a calculation program. As long as the surface circumference c of the winding needle mechanism and the separator thickness m are measured and determined, the central angles θ1 and / or θ2 passed by the target point along the winding direction in the arc region are measured and / or determined as needed, and the position values a and b of the target point where you want to be input are input. Taking these as the initial input conditions, the pole piece thickness at the position of the target point in the electrode assembly can be deduced.

[0102] (3) Substitute the coordinate information (L 14 , z) of the target point 300 into the database, and output the pole piece thickness H at the position of the target point 300 14 .

[0103] (4) Use a detector to scan the cross-section of the electrode assembly layer where the target point D ab is located, and obtain the winding image of the current collector where the target point D ab is located. As shown in Figure 6 , it is an actual winding image of the current collector of an electrode assembly. Obtain the pole piece thickness H at the position of the target point D ab according to the above steps, and obtain the pole piece thickness at the intersection of the radius where the target point D ab is located and each inner pole piece, denoted as H ab 1 ab , and the pole piece thickness at the intersection of the radius where the target point D 2 ab is located and each outer pole piece is denoted as H;

[0104] When the pole piece where the target point D ab is located is the inner pole piece, directly measure along the radius where the target point D ab is located in the obtained current collector winding image, and obtain the distance between the current collector of the inner pole piece where the target point D ab is located and the current collector of the inner pole piece of the previous layer, denoted as S ab ; Denote the gap between the inner pole piece where the target point D ab is located and the inner pole piece of the previous layer as P ab, the gap between the inner pole piece where the target point D is located and the outer pole piece of the previous layer is denoted as Q ab ab , then P ab = S ab - 0.5(H ab + H 1 a(b-1) ) - 2m - H 2 a(b-1) , Q ab = 0.5P ab ab ;

[0105] When the pole piece where the target point D is located is an outer pole piece, directly measure along the radius where the target point D is located in the obtained current collector winding image to obtain the distance between the current collectors of the outer pole piece where the target point D is located and the outer pole piece of the previous layer, denoted as S ab ab ab ; Denote the gap between the outer pole piece where the target point D is located and the outer pole piece of the previous layer as P ab ab , denote the gap between the outer pole piece where the target point D is located and the inner pole piece of the previous layer as Q ab ab ab , then P = S ab - 0.5(H ab + H 2 a(b-1) ) - 2m - H 1 a(b-1) , Q ab = 0.5P ab 1 ;

[0106] Among them, when b - 1 is 0, the values of H a(b-1) 2 and H a(b-1) are both 0.

[0107] For clarity of explanation, take the Figure 5 situation to illustrate the process of the relevant calculation of the target point 300:

[0108] Through Example 1, the pole piece thickness H at the position of the target point 300 can be obtained 14 , the pole piece thickness H at the position of the third intersection point 430 of the positive pole piece can be obtained 2 13 , and the pole piece thickness H at the position of the third intersection point 330 of the negative pole piece can be obtained 1 13 ​​​​​​;By using a detector to scan the cross-section of the electrode assembly layer where the target point 300 is located in the electrode assembly, the distance S between the current collector of the negative electrode sheet where the target point 300 is located and the current collector of the negative electrode sheet at the third intersection point 330 of the negative electrode sheet in the adjacent layer can be directly measured in the radial direction. 14 Then, the gap P between the inner electrode sheet where the target point 300 is located and the negative electrode sheet at the third intersection point 330 of the negative electrode sheet in the adjacent layer can be calculated. 14 =S 14 -0.5(H 14 +H 1 13 )-2m-H 2 13 ;Thus, the electrode sheet gap between the inner electrode sheet where the target point 300 is located and the positive electrode sheet at the third intersection point 430 of the positive electrode sheet in the adjacent layer can be represented by Q. 14 =0.5P 14 .

[0109] A method for evaluating the electrode sheet gap in the arc area of the electrode assembly provided in Embodiment 1 can be carried out in a winding measurement system device as shown in Figure 7 . The positive electrode film roll 1a is unwound, and the positive electrode sheet 1 is conveyed through the first roller 5 and the second roller 6. A thickness gauge 7 is provided between the first roller 5 and the second roller 6 for testing the thickness of the positive electrode sheet before winding. At the same time, the negative electrode film roll 1b is unwound, and the negative electrode sheet 2 is conveyed through the third roller 8 and the fourth roller 9. A thickness gauge 7 is provided between the third roller 8 and the fourth roller 9 for testing the thickness of the negative electrode sheet before winding; at the same time, two rolls of separator film rolls 10 are unwound, and the separator 10a is conveyed through the roller; winding is carried out on the winding needle mechanism 11 in the order of separator 10a, inner electrode sheet is negative electrode sheet 2, separator 10a, and outer electrode sheet is positive electrode sheet 1 to obtain the electrode assembly 3. The electrode assembly 3 is transferred to the conveyor belt 13 through the transfer fixture 12, conveyed to the hot pressing and shaping station 14 for hot pressing and shaping, and then conveyed to the detector 15 to detect the cross-section of the electrode assembly layer where the target point is located to obtain an image. The detector 15 includes a CT scanning device. The winding measurement system device further includes a host, which is electrically connected to the thickness gauge and the detector for automatically controlling the thickness gauge and the detector, as well as processing and storing data, including establishing a [(x, y), H] database, input initial conditions, and automatically obtaining the data of the required thickness, winding length, and gap according to the above calculation formula based on the initial conditions.

[0110] The present invention uses a thickness gauge to test the thickness H of each test point on the electrode sheet before winding, and takes the corresponding electrode sheet length position value x and electrode sheet width position value y as coordinate information to establish a database; then measures and estimates the electrode sheet winding length value L from the starting end of the electrode sheet along the winding direction to the target point in the obtained electrode assembly.ab As the analog coordinate value, combined with the height value z in the electrode assembly where the target point is located, as the coordinate information, substitute the coordinate information of the target point into the database established with the test points, find the data of the test point corresponding to the target point, and output the thickness value of the test point as the thickness value of the target point. With this measurement method, only a thickness gauge is needed to obtain the thickness of the electrode sheets at various positions in the arc area of the wound electrode assembly. On this basis, by combining the distance between the current collectors of two adjacent layers of the same electrode sheet obtained through the detector test, subtracting the separator thickness and the electrode sheet thickness contained therein, the gap between the electrode sheets of two adjacent layers can be estimated.

[0111] As can be seen from the above, the method for measuring the thickness of the electrode sheet in the arc area of the electrode assembly of the present invention only requires testing with a thickness gauge before winding, without the need for more testing equipment, which is convenient for implementation; on this basis, by combining the distance between two adjacent layers of the same electrode sheet obtained by the detector, the inner ring gap between the electrode sheets of two adjacent layers can be estimated.

[0112] Through the method for evaluating the gap of the electrode assembly in the arc area of the present invention, the risk of the electrode assembly can be identified in advance, abnormal electrode assemblies can be selected, and safety accidents caused by the outflow of risks can be eliminated; it can be further used to adjust the process in advance, reduce the lithium deposition or black spots at the gap position caused by too large a gap between the electrode sheets, reduce the scrapping of the electrode assembly, improve the product quality consistency of the electrode assembly, and increase the cycle life of the electrode assembly; it can further calculate the lithium deposition risk of the designed NP ratio in the arc area during the design of the electrode assembly through the gap value, and avoid the design risk in advance; it can also be further used to predict whether the fluctuation of the winding tension is reasonable, monitor the fluctuation of the tension in reverse, improve the monitoring ability of product parameters, and prevent the increase of the binding force of the electrode assembly caused by the tension fluctuation from affecting the performance of the electrode assembly.

[0113] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0114] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0115] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. An evaluation method for the gap between electrode sheets in the arc region of an electrode assembly, characterized in that, The steps include the following: According to the positional relationship between the arc area and the planar area where the target point is located, assign a value to a, and according to the number of winding layers of the pole piece where the target point is located, assign a value to b, and record the target point as D ab ; In the cross-section of the electrode assembly layer where D ab is located, along the width direction of the electrode assembly, the two end points of the coiling needle mechanism are respectively used as the center points of the corresponding arc areas, and both arc areas are respectively regarded as semi-circles; determine D ab the thickness H of the pole piece at the position ab , and determine D ab the thickness H of the pole piece at the intersection of the radius where it is located and each inner pole piece 1 ab , and the thickness H of the pole piece at the intersection with each outer pole piece 2 ab ; Use a detector to scan the cross-section of the electrode assembly layer where D is located to obtain the winding image of the current collector where D is located, and calculate the gap in the following manner: ab ab ​​ Along D ab The radius where it is located is directly measured in the obtained current collector winding image to obtain D ab The distance S between the current collectors of the current collector of the electrode sheet where it is located and the current collector of the same electrode sheet in the previous layer ab ; Regarding D ab The gap P between the electrode sheet where it is located and the same electrode sheet in the previous layer ab ; Regarding D ab The gap Q between the electrode sheet where it is located and the other electrode sheet in the previous layer ab ; Then when the electrode sheet where D ab is located is the inner electrode sheet, P ab = S ab - 0.5(H ab + H 1 a(b-1) ) - 2m - H 2 a(b-1) , Q ab = 0.5P ab ; When the electrode sheet where D ab is located is the outer electrode sheet, P ab = S ab - 0.5(H ab + H 2 a(b-1) ) - 2m - H 1 a(b-1) , Q ab = 0.5P ab ; Among them, m represents that the diaphragm thickness is a constant value; when b - 1 is 0, the values of H 1 a(b-1) and H 2 a(b-1) are both 0.

2. The method for evaluating the pole piece gap in the arc region of the electrode assembly according to claim 1, wherein The inner pole piece is a negative electrode piece.

3. The method for evaluating the pole piece gap in the arc region of the electrode assembly according to claim 1 or 2, characterized in that, Starting from the starting end of the electrode tab and along the winding direction, the first arc area reached is the first arc area, which has a first center point, and the second arc area reached is the second arc area, which has a second center point; when D ab When in the first arc area, a = 1, and when in the second arc area, a = 2; Preferably, along the width direction of the electrode assembly, the intersection points of the radius passing through the second center point and each pole piece in the second arc region are used as the layer boundary points of the corresponding pole pieces; along the winding direction, determine the number g of layer boundary points contained between the starting end of the pole piece where D ab is located and D ab , and b = g + 1.

4. The method for evaluating the pole piece gap in the arc region of the electrode assembly according to claim 3, wherein Determine D ab The method for determining the thickness of the pole piece at the position includes: (1) Before the pole pieces are wound to form an electrode assembly, a thickness gauge is used to continuously measure the unwound pole pieces. Taking a point on the starting end of the pole piece as the coordinate origin, a right-angled first coordinate system is established on the pole piece. The length direction of the pole piece is the horizontal axis direction with the coordinate value being x, and the width direction of the pole piece is the vertical axis direction with the coordinate value being y. The thickness values of the pole piece at each test point are measured and denoted as H. At the same time, the coordinate information (x, y) of each test point is recorded, and a database is established with the data [(x, y), H]. The thickness of the separator is measured with a thickness gauge and denoted as m, which is regarded as constant. (2) In the electrode assembly, a second coordinate system is established with the origin of coordinates and the height direction of the electrode assembly, and the coordinate value of D ab is recorded as z; At D ab On the pole piece in the cross-section of the electrode assembly layer where D ab is located, according to the a value and b value of D ab , measure and estimate the pole piece winding length value from the starting end of the pole piece to D ab , denoted as L ab ; Take L ab as the simulated coordinate value of D ab , and form the coordinate information (L ab , z) of D with the coordinate value z; (3) Substitute (L ab , z) into the database established with data [(x, y), H], establish a numerical correspondence between L ab and x, establish a numerical correspondence between z and y, match (x, y) corresponding to (L ab , z), and output the H value in the data [(x, y), H] where (x, y) is located as the pole piece thickness H ab at position D ab .

5. The method for evaluating the pole piece gap in the arc region of the electrode assembly according to claim 4, wherein In step (1), the coordinate origin is set at a vertex on the starting end of the pole piece. After winding, the vertex is located at the bottom of the electrode assembly. Preferably, in the thickness direction of the electrode assembly, the positive projections of the coordinate origins of the inner pole piece and the outer pole piece coincide.

6. The method for evaluating the pole piece gap in the arc region of the electrode assembly according to claim 4 or 5, characterized in that In step (2), the pole piece winding length value L ab is measured and estimated on the inner ring side of the pole piece close to the winding needle mechanism.

7. The evaluation method of the pole piece gap in the arc area of the electrode assembly according to claim 6, characterized in that, Let the length of the radius where D is located in the arc region be denoted as R ab ab , then we have:​ When the target point is on the inner pole piece, R ab =(2b - 1)m + ∑H 1 a(b-1) + ∑H 2 a(b-1) ; When the target point is on the outer pole piece, R ab = 2bm + ∑H 2 a(b-1) + ∑H 1 ab ; Wherein, when b - 1 is 0, H 1 a(b-1) and H 2 a(b-1) are both valued at 0.

8. The method for evaluating the pole piece gap in the arc region of the electrode assembly according to claim 7, wherein At D ab In the cross-section of the electrode assembly layer where it is located, the starting end of the electrode tab coincides with the second center point; Preferably, the winding length of the pole pieces in the electrode assembly in each planar area is regarded as equal to half of the surface circumference c of the winding needle mechanism. Preferably, in the same layer with the same b value, along the winding direction, D ab The central angle passed through in the first arc region is θ1, and the central angle passed through in the second arc region is θ2. Then, in step (2), D ab The winding length value L of the pole piece ab is calculated in the following manner: When a = 1, then L ab = (2(b - 1)+a)×0.5c + π(∑R 1(b-1) + ∑R 2(b-1) + R 1b (θ1 / 180°); When a = 2, then L ab =(2(b - 1)+a)×0.5c + π(∑R 1b +∑R 2(b-1) +R 2b (θ2 / 180°); Wherein, when b - 1 is 0, the values of R 1(b-1) and R 2(b-1) are both 0; c is the surface perimeter of the bobbin winding mechanism.

9. The method for evaluating the pole piece gap in the arc region of the electrode assembly according to claim 8, wherein When the target point is on the inner pole piece, R 11 and R 21 are both considered to be equal to 0.

10. A measuring system device for the pole piece gap in the arc region of an electrode assembly, characterized in that, The evaluation method according to any one of claims 1-9 is implemented by the measurement system device, and the measurement system device includes: A thickness gauge is arranged between the pole piece unwinding device and the winding device, and is used for continuously measuring the unwound pole piece to obtain the pole piece thickness value H of each D ab ; A detector, which is arranged after the hot pressing and shaping equipment, is used to detect the cross-section of the electrode assembly layer where D in the electrode assembly is located and obtain the winding image of the current collector. ab ​ A mainframe, electrically connected to the thickness gauge and the detector, for automatically controlling the thickness gauge and the detector, as well as processing and storing data.

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