Method for preparing aluminum foil for lithium ion battery and carbon-coated aluminum foil

Abstract

The application belongs to the technical field of lithium batteries, and provides a preparation method of aluminum foil for lithium ion batteries and carbon-coated aluminum foil. By obtaining a finite element model of a rolling mill and aluminum foil in a rolling process, a risk deformation area on the model is marked, a deformation coefficient of the risk deformation area is calculated, and the working parameters of the rolling mill are adjusted in real time according to the deformation coefficient, so that dynamic monitoring of the rolling quality can be realized, the shortcoming that the rolling process cannot be dynamically adjusted at present is made up, and the problem that aluminum foil products are inconsistent due to the rebound phenomenon in the rolling process caused by differences in aluminum foil materials can be eliminated, the quality of aluminum foil products is improved, and the service life of the battery is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a preparation method of an aluminum foil for a lithium ion battery and a carbon-coated aluminum foil. BACKGROUND

[0002] At present, in the production process of battery aluminum foil, the active material slurry is generally directly coated on the current collector. Since the active particles and the current collector or the conductive layer do not contact sufficiently, the internal resistance of the battery is increased. To solve the above problems, a kind of carbon-coated aluminum foil and its preparation method are disclosed in Chinese Invention Patent No. CN114142041B, which is published on March 4, 2022, and the patent name is a kind of carbon-coated aluminum foil and its preparation method. The preparation method can solve the problems of poor coating effect and easy peeling of the coating without affecting the conductive contact between the positive active material and the aluminum foil and the conductive layer, and the cost is low without the need for high-cost equipment. The original adhesive is replaced by a rolling process to enhance the adhesion of the coating and the aluminum foil, thereby realizing the effects of firm coating and not easy to peel. However, in the above method, all the aluminum foils are only subjected to one rolling treatment in the rolling process, which cannot guarantee the uniformity of the aluminum foils. Because the force points of the rolling machine are not uniform, the active material on the surface of the aluminum foil is easily partially broken and powdered, which affects the storage effect of lithium ions in the use process and further affects the service life of the lithium battery. SUMMARY

[0003] The purpose of the present application is to provide a preparation method of an aluminum foil for a lithium ion battery to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0004] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a preparation method of an aluminum foil for a lithium ion battery is provided, which comprises the following steps:

[0005] S100, surface treatment is performed on the surface of the aluminum foil;

[0006] S200, a solvent is sprayed on the surface of the aluminum foil;

[0007] S300, carbon powder is uniformly sprayed on the surface of the aluminum foil, and first baking and drying are performed, and the amount of the carbon powder is 0.1-5g / m2;

[0008] S400, the aluminum foil is subjected to rolling treatment;

[0009] S500, the aluminum foil is subjected to second baking and drying, i.e., a carbon-coated aluminum foil is prepared.

[0010] Further, in S400, a finite element analysis fine adjustment step control is performed on the aluminum foil during the rolling treatment, and the specific method is as follows:

[0011] S410, obtaining a three-dimensional model of the rolling machine and the aluminum foil in the rolling process;

[0012] S420, loading the three-dimensional model into finite element software, and obtaining a finite element model using a meshing algorithm;

[0013] S430, dividing the rolling finite element model and the aluminum foil finite element model according to the obtained finite element model;

[0014] S440, performing stress analysis on the obtained finite element model to obtain a risk deformation area;

[0015] S450, calculating a deformation coefficient of the risk deformation area;

[0016] S460, fine-tuning the rolling parameters according to the deformation coefficient.

[0017] Further, in S100, the surface treatment includes physical roughening or chemical etching treatment.

[0018] Preferably, the method of physical roughening is specifically: using a gas carrying aluminum powder to blow the surface of the aluminum foil or directly performing wire drawing treatment on the surface of the aluminum foil, then washing clean with deionized water and drying; the method of chemical etching treatment is specifically: using 0.2-2mol / L HCL and 0.05-0.5mol / L Al2(SO4)3 aqueous solution for etching for 1-20min, then washing clean with deionized water and drying.

[0019] Further, in S100, the gas used to carry the aluminum powder is carbon dioxide or nitrogen.

[0020] Further, in S200, the solvent is at least one of heptane, hexane, cyclohexane, carbon disulfide, carbon tetrachloride, benzene, toluene, chloropropane, bromoethane, chloroform, dichloromethane, dichloroethane, isopropyl ether, diethyl ether, and tetrahydrofuran.

[0021] Further, in S300, the temperature of the first baking and drying is 30-100℃, and the time is 1-10min, and the carbon powder is at least one of carbon black, carbon nanotube, vapor phase grown carbon fiber, graphene, natural graphite, and artificial graphite.

[0022] Further, in S300, the temperature of the first baking and drying is 30-100℃, and the time is 1-10min.

[0023] Further, in S400, the rolling pressure is 10-30T, and the rolling speed is 10m / min, and T represents a unit ton.

[0024] Further, in S500, the temperature of the second baking and drying is 60-150℃, and the time is 0.5-10min.

[0025] The rolling process is that after the aluminum foil passes through the coating and drying processes, the thickness consistency of the aluminum foil surface is poor and the coating density is low, which cannot meet the use requirements, so the aluminum foil is passed through a rolling machine, so that the coating material is densified and the thickness of the aluminum foil is thinned under the pressure of the rolling mill of the rolling machine, thereby meeting the use requirements. Since the aluminum foil is a three-layer composite structure of coating-current collector-coating, the rolling of the aluminum foil is very different from the rolling of the metal plate. The density of the metal plate does not change during the rolling process, while the rolling of the aluminum foil is mainly the compaction of the coating material, and the density of the coating material changes during the rolling process, while the current collector hardly deforms. However, the existing method cannot guarantee the uniformity of the aluminum foil by concentrating all the aluminum foil for one-time rolling treatment, which easily leads to partial crushing and pulverization of the active substances on the surface of the aluminum foil, causing the storage effect of lithium ions in the use process, thereby affecting the service life of the lithium battery. To solve the above problems, the present application proposes the following method: by obtaining the finite element model of the rolling mill in the rolling process, marking the risk deformation zone of the model to calculate the deformation coefficient, and realizing dynamic monitoring of the rolling process:

[0026] Further, in S410, the specific method for obtaining the three-dimensional model of the rolling mill and the aluminum foil in the rolling process is to use 3D scanning to generate the three-dimensional model of the rolling mill and the aluminum foil.

[0027] Further, in S420, the three-dimensional model is loaded into the Elmer finite element software, and the specific method for obtaining the finite element model using the mesh division algorithm is as follows: the current rolling mill working parameters (including radius, pressure, speed, material) and aluminum foil material parameters are loaded into the finite element software, the contact part of the rolling mill and the aluminum foil is made of an elastomer, the mesh division of the elastomer part of the rolling mill is made in the mesh division mode, the mesh is divided by quadrilateral solid elements, the mesh in the dense part is divided by neutral axis mesh division mode, and the advanced algorithm is used in the transition part, and the mesh is all divided by hexahedral solid elements to generate the finite element model;

[0028] Further, the advanced algorithm is the Advancing Front algorithm.

[0029] Preferably, since the elastic deformation of the lithium ion battery aluminum foil during the rolling process is mainly concentrated in the contact part of the rolling mill and the aluminum foil, the mesh of the contact part of the rolling mill and the aluminum foil is dense, and the densest mesh size is 15um; since the size of the aluminum foil will deform greatly during the rolling process, the mesh type is selected as CPE4R linear reduced integration element, the use of linear reduced integration element can effectively prevent overfitting problem, can ensure that the model operation avoids the shear self-locking phenomenon of the unit, and can ensure the accuracy of the model calculation result;

[0030] The contact between the roller and the aluminum foil adopts surface-to-surface contact. Since there is a primary surface and a secondary surface in each pair of contact surfaces when surface-to-surface contact is adopted by Elmer, the primary surface should be selected from surfaces with relatively rigid material properties, relatively large grid sizes, and relatively small deformations. In the finite element model for rolling of the lithium ion battery aluminum foil, the material properties of the roller are relatively rigid and the deformation is relatively small compared with the aluminum foil. Therefore, the outer surface of the roller is selected as the primary surface, and the upper and lower surfaces of the aluminum foil are set as the secondary surfaces. The tangential behavior in the contact attribute is constrained by the penalty function method, the normal behavior is set as hard contact, and the size of the finite element model is consistent with the actual rolling process.

[0031] Further, in S430, the specific method for dividing the rolling mill finite element model and the aluminum foil finite element model according to the obtained finite element model is: using feature extraction method and classification algorithm to distinguish the rolling mill region and the aluminum foil region of the obtained finite element model, drawing a boundary around the rolling mill region identified by the three-dimensional model, and separating the rolling mill region from the entire three-dimensional model to obtain the rolling mill finite element model, drawing a boundary around the aluminum foil region identified by the three-dimensional model, and separating the aluminum foil region from the entire three-dimensional model to obtain the aluminum foil finite element model.

[0032] Further, in S440, the specific method for obtaining the risk deformation region by stress analysis of the obtained finite element model is: importing the rolling mill finite element model into the finite element analysis software, calculating the pressure received by each grid in the rolling mill finite element model through the pressure analysis in the finite element analysis software, recording the pressure of the i-th grid as Str(i), i = 1 ， 2,…,M, M is the number of all grids in the rolling mill finite element model, M numbers Str(1), Str(2), …, Str(M) are combined to form a stress sequence recorded as stress, the element with the maximum value and the element with the minimum value in the stress sequence are recorded as STR1 and STR2 respectively, the grid corresponding to STR1 is recorded as anchor grid, and the grid corresponding to STR2 is recorded as target grid;

[0033] The distance between the center point of the anchor grid and the center point of the target grid is recorded as the dispersion distance, and the direction from the center point of the anchor grid to the center point of the target grid is recorded as the reference direction; all the pressure sizes in the stress sequence are traversed, the absolute difference between Str(i) and STR1 is recorded as M1, the absolute difference between Str(i) and STR2 is recorded as M2, and the grid corresponding to all M1 smaller than M2 is marked as column grid;

[0034] The direction vector formed by the center point of each column mesh is denoted as the main force vector. The projection of the main force vector onto the reference direction of the anchor mesh center point is denoted as the main force projection. The direction vector formed by the center point of each column mesh to the center point of the target mesh is denoted as the secondary force vector. The projection of the secondary force vector onto the reference direction is denoted as the secondary force projection. The main force projection and the secondary force projection are added together, and the magnitude of the result is denoted as the force value of the current mesh.

[0035] The column grid with a stress value greater than the average stress value is marked as a risk grid. All adjacent risk grids are combined into a risk stress grid group. The edges of the risk stress grid group are traversed and the traversal result is recorded as the risk stress zone.

[0036] Traverse all risk stress zones, and denote the geometric center of all risk stress zones as P. k , will P K Forming line segment L1 with the center point of the anchor grid, P K The center point of the anchor mesh forms line segment L2 with the center point of the target mesh, and the center point of the anchor mesh forms line segment L3 with the center point of the target mesh. All meshes in the triangular region formed by L1, L2 and L3 on the finite element model are denoted as the risk deformation zone.

[0037] The above method obtains a finite element model of the rolling mill and uses finite element software to perform stress analysis and mark the risk deformation zone. During the rolling process, the rolling quality of aluminum foil is greatly affected by the rolling mill. If the rolling mill experiences uneven pressure, some material particles will break, thus affecting the quality of the aluminum foil and reducing the battery's lifespan. The risk deformation zone in the above method can well reflect the places where the pressure applied on the rolling mill is uneven. That is, the risk deformation zone represents the area where material breakage may occur. By accurately marking these risk areas using the above method, dynamic monitoring and real-time adjustment of the rolling quality can be achieved.

[0038] Furthermore, in S450, the specific method for calculating the deformation coefficient of the risk deformation zone is as follows:

[0039] Traverse all pressure values ​​in the risk deformation zone and denote them as D(k,j). D(k,j) represents the pressure value corresponding to the j-th grid in the k-th risk deformation zone. Calculate the average pressure of all values ​​in the risk deformation zone.

[0040] The deformation coefficient of any grid in the risk deformation area is calculated, and the calculation method is as follows: if the pressure value corresponding to the current grid is greater than the pressure average value, the absolute difference between the pressure value corresponding to the current grid and the maximum pressure value in the risk deformation area is calculated as N1, the distance between the center point of the current grid and the center point of the anchor grid is recorded as R1, the absolute difference between the pressure value corresponding to the current grid and the minimum pressure value in the risk deformation area is calculated as N2, and the distance between the center point of the current grid and the center point of the target grid is recorded as R2, according to the formula the deformation coefficient of the current grid is calculated, otherwise according to the formula The deformation coefficient of the current grid is calculated, wherein the Ln() function is the logarithmic function with e as the base, and the sum of the deformation coefficients of all grids in the risk deformation area is taken as the deformation coefficient of the current risk deformation area.

[0041] The above method can judge whether the current area will appear risk deformation, that is, material crushing problem, by calculating the deformation coefficient in each risk deformation area. The scaling principle of the logarithmic function can eliminate unnecessary interference of the small pressure difference on the result, and avoid the small difference in the result caused by the material difference of the rolling mill, so that the working parameters of the current rolling mill can be adjusted more accurately.

[0042] Further, in S460, the specific method of fine-tuning the rolling parameters according to the deformation coefficient is as follows: if the deformation coefficient of the current risk deformation area is less than zero, the current rolling mill speed is kept unchanged, and the rolling mill pressure is adjusted to 20-50T;

[0043] If the deformation coefficient of the current risk deformation area is greater than zero, the current rolling mill speed is kept unchanged, and the rolling mill pressure is adjusted to 30-60T.

[0044] However, the lithium ion battery aluminum foil may have a rebound phenomenon during the rolling process, because although the thickness of the aluminum foil will be thinned when it is subjected to the rolling pressure during the rolling process, the aluminum foil will have a certain degree of elastic recovery after the rolling pressure is removed. The rebound phenomenon of the lithium ion battery aluminum foil during the rolling process will affect the thickness consistency of the aluminum foil, leading to the decline of the performance of the lithium ion battery and the generation of safety hazards during the use of the battery, and other adverse effects. In order to solve the above problems, the present application provides the following method to judge whether the rebound phenomenon will occur according to the stress condition of the aluminum foil, so as to adjust the rolling mill parameters:

[0045] A three-dimensional model of the aluminum foil in the current production process is obtained at a preset period t, and a finite element model of the aluminum foil is generated according to the current production parameters, the finite element model of the aluminum foil is imported into a finite element analysis software, and the pressure analysis in the finite element analysis software is used to calculate the pressure of each grid in the finite element model of the aluminum foil,

[0046] The pressure value of the rth grid is Pie(r), r = 1 ， 2,…,K, K is the number of all grids in the finite element model of the rolling mill, and the K numbers Pie(1), Pie(2), …, Pie(M) form a sequence piezo. The average value of the sequence piezo is calculated, and all grids greater than the average value of the pressure are marked as stress grids on the aluminum foil finite element model;

[0047] All adjacent stress grids are marked as stress regions, and the pressure values corresponding to the adjacent grids of all stress regions are obtained. The grids with pressure values greater than the pressure values obtained in the previous period are marked as the pan grids of the stress region;

[0048] The acquisition period in which the average value of the stress region in the current period is greater than the average value of the stress region in the previous period is recorded as the pressing period. The acquisition period in which the average value of the stress region in the current period is less than the average value of the stress region in the previous period is recorded as the rebound period. All stress regions marked in the aluminum foil finite element model in the pressing period and the rebound period are arranged in sequence according to the acquisition time to form a sequence list;

[0049] Since the lithium ion battery aluminum foil will rebound during the rolling process, which is a small amplitude thickness change after the pressure is removed. This small amplitude change depends on the elastic deformation of the aluminum foil material. After the pressure is applied, the elastic deformation can be partially recovered. Even if the aluminum foil material has received a strong enough pressure to produce a relative density structure, the elastic deformation of the material particles may still cause the rebound phenomenon. Moreover, this rebound phenomenon is not easy to detect and has a short duration. Therefore, the above method can timely capture the rebound time.

[0050] The difference between the pan grid of the most recently acquired stress region in the sequence list and the maximum stress in the stress region is calculated. The number of grids with a difference greater than zero is recorded as K1, and the average value of all differences greater than zero is calculated as Q1. The difference between the pan grid of the stress region in the sequence list and the minimum stress in the stress region is calculated. The number of grids with a difference greater than zero is recorded as K2, and the average value of all differences greater than zero is calculated as Q2. According to the formula The rebound modulus of the current stress region is calculated.

[0051] The rolling parameters are fine-tuned according to the rebound modulus of the current stress region. The specific method is:

[0052] If the rebound modulus of the current stress region is greater than zero, the current rolling mill pressure is kept unchanged, and the rolling mill speed is adjusted to 20 m / min until the rolling ends;

[0053] If the rebound modulus of the current stress area is less than zero, the current rolling mill pressure is kept unchanged, and the rolling mill speed is adjusted to 30 m / min until the rolling ends.

[0054] The present application has the advantages that: the present application provides a preparation method of aluminum foil for lithium ion batteries, by obtaining a three-dimensional model of the rolling mill and the aluminum foil during rolling, and performing stress analysis on the model through finite element software, the area where local force application abnormity occurs is accurately marked on the rolling mill, so that the working parameters of the rolling mill are dynamically adjusted, the phenomenon that the aluminum foil material is partially pulverized due to uneven stress is avoided, and the stress condition of the aluminum foil during rolling can be monitored in real time, the rebound phenomenon caused by inconsistent materials is avoided to affect the quality of the aluminum foil product, and the service life of the lithium ion battery is greatly prolonged. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 The present application provides a preparation method of aluminum foil for lithium ion batteries, as shown in the flowchart. DETAILED DESCRIPTION

[0056] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0057] Embodiment 1

[0058] Figure 1 The present application provides a preparation method of aluminum foil for lithium ion batteries, as shown in the flowchart.

[0059] Referring to Figure 1 , the present application provides a preparation method of aluminum foil for lithium ion batteries, which comprises the following steps:

[0060] S100, surface treatment is performed on the surface of the aluminum foil;

[0061] S200, the surface of the aluminum foil is sprayed with a solvent;

[0062] S300, carbon powder is uniformly sprayed on the surface of the aluminum foil, and first baking and drying are performed, the amount of the carbon powder is 2.5 g / m 2 ;

[0063] S400, the aluminum foil is subjected to rolling treatment;

[0064] S500, the aluminum foil is subjected to second baking and drying, i.e. a carbon-coated aluminum foil is prepared.

[0065] Further, in S400, a finite element analysis fine adjustment step control is performed on the aluminum foil during the rolling treatment, and the specific method is that:

[0066] S410, obtaining a three-dimensional model of the rolling machine and the aluminum foil during the rolling process;

[0067] S420, loading the three-dimensional model into finite element software and obtaining a finite element model using a meshing algorithm;

[0068] S430, dividing the rolling finite element model and the aluminum foil finite element model according to the obtained finite element model;

[0069] S440, performing stress analysis on the obtained finite element model to obtain a risk deformation area;

[0070] S450, calculating a deformation coefficient of the risk deformation area;

[0071] S460, fine-tuning the rolling parameters according to the deformation coefficient.

[0072] Further, in S100, the surface treatment includes physical roughening or chemical etching treatment.

[0073] Preferably, the method of physical roughening is specifically: blowing the surface of the aluminum foil with gas carrying aluminum powder or directly drawing the surface of the aluminum foil, then washing it with deionized water and drying it; the method of chemical etching treatment is specifically: using 1.5 mol / L HCL and 0.25 mol / L Al2(SO4)3 aqueous solution for etching for 15 min, then washing it with deionized water and drying it.

[0074] Further, in S200, the solvent is heptane.

[0075] Further, in S300, the temperature of the first baking and drying is 60°C, the time is 5 min, and the carbon powder is graphene.

[0076] Further, in S400, the rolling pressure is 20T, and the rolling speed is 10 m / min.

[0077] Further, in S410, the specific method of obtaining a three-dimensional model of the rolling machine and the aluminum foil during the rolling process is: using 3D scanning to generate a three-dimensional model of the rolling machine and the aluminum foil.

[0078] Further, in S420, the three-dimensional model is loaded into the Elmer finite element software, and the specific method for obtaining the finite element model using the mesh division algorithm is as follows: the current rolling mill working parameters (including radius, pressure, speed, and material) and the aluminum foil material parameters are loaded into the finite element software, the roller contact part with the aluminum foil is an elastic body, the mesh division of the roller elastic body part is performed using the mesh division method, the mesh is divided using quadrilateral solid elements, the mesh in the dense part is divided using the neutral axis mesh division method, and the advanced algorithm is used in the transition part, and the mesh is entirely divided using hexahedral solid elements.

[0079] Further, the advanced algorithm is the Advancing Front algorithm.

[0080] Preferably, since the elastic deformation in the lithium ion battery aluminum foil rolling process is mainly concentrated in the contact part of the roller and the aluminum foil, the mesh of the contact part of the roller and the aluminum foil is dense, and the densest mesh size is set to 15 um; since the size of the aluminum foil will be deformed greatly during the rolling process, the mesh type is selected as CPE4R linear reduced integration element, the use of linear reduced integration element can effectively prevent overfitting problem, can ensure that the model running avoids the shear locking phenomenon of the unit, and can ensure the accuracy of the model calculation result;

[0081] The contact between the roller and the aluminum foil adopts surface-to-surface contact, because when Elmer adopts surface-to-surface contact, there is a main surface and a slave surface in each pair of contact surfaces, the main surface should be selected to have a material property of being relatively hard, a mesh size of being relatively large, and a deformation of being relatively small, in the lithium ion battery aluminum foil rolling finite element model, compared with the aluminum foil, the material property of the roller is relatively hard and the deformation is relatively small, therefore, the outer surface of the roller is selected as the main surface, and the upper and lower surfaces of the aluminum foil are set as the slave surface, the tangential behavior in the contact attribute is constrained using the penalty function method, the normal behavior is set as hard contact, and the size of the finite element model is consistent with the actual rolling process.

[0082] Further, in S430, the specific method for dividing the rolling mill finite element model and the aluminum foil finite element model according to the obtained finite element model is as follows: the feature extraction method and the classification algorithm are used to distinguish the rolling mill region and the aluminum foil region of the obtained finite element model, the boundary around the rolling mill region of the three-dimensional model is drawn, and the rolling mill region is separated from the entire three-dimensional model to obtain the rolling mill finite element model, the boundary around the aluminum foil region of the three-dimensional model is drawn, and the aluminum foil region is separated from the entire three-dimensional model to obtain the aluminum foil finite element model.

[0083] Further, in S440, the specific method for stress analysis of the obtained finite element model to obtain the risk deformation area is: importing the roll press finite element model into the finite element analysis software, calculating the pressure of each grid in the roll press finite element model through the pressure analysis in the finite element analysis software, recording the pressure of the i-th grid as Str(i), i=1, 2, …, M, M is the number of all grids in the roll press finite element model, forming a stress sequence with M numbers Str(1), Str(2), …, Str(M) as stress, recording the element with the maximum value and the minimum value in the stress sequence as STR1 and STR2 respectively, recording the grid corresponding to STR1 as the anchor grid, and recording the grid corresponding to STR2 as the target grid;

[0084] Recording the distance between the center point of the anchor grid and the center point of the target grid as the dispersion distance, and recording the direction from the center point of the anchor grid to the center point of the target grid as the reference direction; traversing all the pressure values in the stress sequence, calculating the absolute difference value between Str(i) and STR1 as M1, and calculating the absolute difference value between Str(i) and STR2 as M2, marking the grid corresponding to all M1 smaller than M2 as the column grid;

[0085] Traversing all the column grids, recording the direction vector formed by the center point of the anchor grid to the center point of the column grid as the main force vector, and recording the projection of the main force vector in the reference direction as the main force projection; traversing all the column grids in the main force sequence, recording the direction vector formed by the center point of the column grid to the center point of the target grid as the auxiliary force vector, and recording the projection of the auxiliary force vector in the reference direction as the auxiliary force projection; performing addition operation on the main force projection and the auxiliary force projection, and recording the modulus of the operation result as the stress value of the current grid;

[0086] Marking the column grid with a stress value greater than the average stress value as a risk grid, and forming a risk stress grid group with all adjacent risk grids, traversing the edges of the risk stress grid group, and recording the traversal result as a risk stress area;

[0087] After traversing all the risk stress areas, recording the geometric center of all the risk stress areas as P k , recording the line segment L1 formed by P K and the center point of the anchor grid, recording the line segment L2 formed by P K and the center point of the target grid, recording the line segment L3 formed by the center point of the anchor grid and the center point of the target grid, and recording all the grids in the triangular area formed by L1, L2 and L3 in the finite element model as the risk deformation area;

[0088] Further, in S450, the specific method for calculating the deformation coefficient of the risk deformation area is:

[0089] Traverse all the pressure value sizes in the risk deformation zone and record them as D(k, j), D(k, j) represents the pressure value size corresponding to the jth grid in the kth risk deformation zone, and the pressure average in the risk deformation zone is calculated;

[0090] In the value range of j, the deformation coefficient of any grid in the risk deformation zone is calculated. If the pressure value corresponding to the current grid is greater than the pressure average, the absolute difference between the pressure value corresponding to the current grid and the maximum pressure value in the risk deformation zone is calculated as N1, the distance between the center point of the current grid and the center point of the anchor grid is recorded as R1, the absolute difference between the pressure value corresponding to the current grid and the minimum pressure value in the risk deformation zone is calculated as N2, and the distance between the center point of the current grid and the center point of the target grid is recorded as R2. According to the formula the deformation coefficient of the current grid is calculated, otherwise according to the formula the deformation coefficient of the current grid is calculated, wherein the Ln() function is the logarithmic function with e as the base, and the sum of the deformation coefficients of all the grids in the risk deformation zone is taken as the deformation coefficient of the current risk deformation zone.

[0091] Further, in S460, the specific method of fine-tuning the roll pressure parameter according to the deformation coefficient is: if the deformation coefficient of the current risk deformation zone is less than zero, the current roll speed is kept unchanged, and the roll pressure is adjusted to 35T;

[0092] If the deformation coefficient of the current risk deformation zone is greater than zero, the current roll speed is kept unchanged, and the roll pressure is adjusted to 45T;

[0093] Embodiment 2

[0094] Since the lithium ion battery aluminum foil may rebound during the rolling process, although the thickness of the aluminum foil will be thinned after being subjected to the rolling pressure during the rolling process, the aluminum foil will have a certain degree of elastic recovery after the rolling pressure is removed. The rebound phenomenon of the lithium ion battery aluminum foil during the rolling process will affect the thickness consistency of the aluminum foil, leading to the decline of the performance of the lithium ion battery and the generation of safety hazards during the use of the battery, and other adverse effects. In order to solve the above problems, the following embodiment 2 is provided, which adjusts the roll parameters according to whether the aluminum foil will rebound according to the stress condition of the aluminum foil, and the specific method is as follows:

[0095] A three-dimensional model of the aluminum foil in the current production process is obtained with 1 min as the collection period, and an aluminum foil finite element model is generated according to the current production parameters. The aluminum foil finite element model is imported into a finite element analysis software, and the pressure analysis in the finite element analysis software is used to calculate the pressure size of each grid in the aluminum foil finite element model,

[0096] The pressure of the rth grid is denoted as Pie(r), r = 1, 2, …, K, K is the number of all grids in the finite element model of the roller press, and K numbers Pie(1), Pie(2), …, Pie(M) form a sequence piezo. The average value of the sequence piezo is calculated, and all grids greater than the average value of the pressure are marked as stress grids on the aluminum foil finite element model;

[0097] All adjacent stress grids are marked as stress regions, and the pressure values of the adjacent grids of all stress regions are obtained. The grids with pressure values greater than the pressure values obtained in the previous period are marked as the spread grids of the stress regions;

[0098] The acquisition period in which the average value of the stress in the stress region in the current period is greater than the average value of the stress in the previous period is recorded as the pressing period. The acquisition period in which the average value of the stress in the stress region in the current period is less than the average value of the stress in the previous period is recorded as the rebound period. All stress regions marked in the aluminum foil finite element model obtained in the pressing period and the rebound period are arranged in sequence list according to the acquisition time;

[0099] The difference between the spread grids of the stress region and the maximum stress in the stress region in the sequence list is calculated, the number of grids with a difference greater than zero is recorded as K1, the average value of all differences greater than zero is calculated as Q1, the difference between the spread grids of the stress region and the minimum stress in the stress region in the sequence list is calculated, the number of grids with a difference greater than zero is recorded as K2, and the average value of all differences greater than zero is calculated as Q2. According to the formula The rebound modulus of the current stress region is calculated.

[0100] The rolling parameters are fine-tuned according to the rebound modulus of the current stress region. The specific method is as follows:

[0101] If the rebound modulus of the current stress region is greater than zero, the current roller press pressure is kept unchanged, and the roller press speed is adjusted to 20 m / min until the rolling ends;

[0102] If the rebound modulus of the current stress region is less than zero, the current roller press pressure is kept unchanged, and the roller press speed is adjusted to 30 m / min until the rolling ends.

[0103] Comparative Example 1

[0104] The aluminum foil production method in Example 4 of the Chinese invention patent named A Carbon Coated Aluminum Foil and a Preparation Method thereof, with the publication number CN 114142041B, applied on November 26, 2021.

[0105] The aluminum foils produced according to the method in Example 1, Example 2 and Comparative Example 1 in the present application were assembled into No. 1 lithium battery, No. 2 lithium battery and No. 3 lithium battery according to the same existing assembly method.

[0106] The No. 1 lithium battery, No. 2 lithium battery and No. 3 lithium battery were first charged at room temperature in a standard charge-discharge mode, the initial capacity was calculated by standard discharge to 2.75V, and the cell was charged to 4.1V at a constant current and constant voltage of 0.5C current, then placed in a 85℃ constant temperature oven for storage for 1000h, and then the retention capacity was calculated by standard discharge, 10 cells were randomly selected for testing, and the average value of the results was taken, as shown in Table 1.

[0107] Further, the charge-discharge experiment was tested using a super capacitor charge-discharge tester BT-2043 of Arbin, USA;

[0108] Further, the battery capacity test experiment was tested using a ZENNIUM XC electrochemical workstation of ZAHNER, Germany;

[0109] Table 1 Initial capacity and 85℃ constant temperature capacity of three kinds of lithium batteries

[0110]

[0111] Analysis: From the results of Table 1, it was found that there was no great difference in the capacity content of the battery before the No. 1 lithium battery, No. 2 lithium battery and No. 3 lithium battery were stored at high temperature, but after the capacity content of the three batteries was detected again after high temperature storage, the capacity content of the No. 1 lithium battery and No. 2 lithium battery was obviously higher than that of the No. 3 lithium battery, which was because the aluminum foil in the No. 2 lithium battery was subjected to a one-time concentration rolling process, and due to the uneven stress on the aluminum foil, part of the material was broken, which led to the continuous consumption of lithium ions in the high temperature environment, thereby greatly reducing the storage amount of lithium ions. The aluminum foil in the No. 1 lithium battery and No. 2 lithium battery used the dynamic control method in the present application to flexibly control the working parameters of the rolling mill according to the stress condition of the aluminum foil, so there was no problem of material breakage, so the capacity content of the No. 1 lithium battery and No. 2 lithium battery was obviously higher than that of the No. 3 lithium battery.

[0112] The lithium iron phosphate positive electrode slurry was coated on the aluminum foil materials prepared in Example 1, Example 2 and Comparative Example 1 above, respectively, to form three lithium iron phosphate positive electrode aluminum foils, namely No. 1 aluminum foil, No. 2 aluminum foil and No. 3 aluminum foil. The peel strength of the three aluminum foils was tested on a universal testing machine, and the test results are shown in Table 2.

[0113] Table 2 Peel strength test results of three kinds of aluminum foils

[0114] Peeling strength (mN / mm) No. 1 aluminum foil 900 No. 2 aluminum foil 1200 No. 3 aluminum foil 890

[0115] Analysis: observing the results in table 2, it is found that there is no great difference in the peeling strength between the No. 1 aluminum foil and the No. 3 aluminum foil, and the peeling strength of the No. 2 aluminum foil is significantly greater than that of the No. 1 aluminum foil and the No. 3 aluminum foil, indicating that the method in the embodiment 2 in the present application can effectively avoid the rebound phenomenon in the aluminum foil rolling process, thereby ensuring the quality of the aluminum foil.

[0116] The present application has the beneficial effects that: the present application provides a preparation method of aluminum foil for lithium ion battery, by obtaining the three-dimensional model of the rolling mill and the aluminum foil in the rolling process, and performing stress analysis on the model through finite element software, the local force abnormal area on the rolling mill is accurately marked, thereby dynamically adjusting the working parameters of the rolling mill, avoiding the phenomenon that the aluminum foil material is partially pulverized due to uneven stress, and at the same time, the stress condition of the aluminum foil in the rolling process can be monitored in real time, avoiding the rebound phenomenon due to inconsistent materials affecting the quality of the aluminum foil finished product, greatly prolonging the service life of the lithium ion battery.

[0117] Although the description of the present application has been quite detailed and particularly described with respect to several described embodiments, it is not intended to be limited to any of these details or embodiments or any special embodiment, thereby effectively covering the intended scope of the present application. In addition, the present application is described above in the embodiments that the inventors can foresee, the purpose is to provide a useful description, and those non-essential modifications to the present application that have not yet been foreseen can still represent equivalent modifications of the present application.

Claims

1. A method for producing an aluminum foil for a lithium-ion battery, characterized by, The method comprises the following steps: S100, surface treatment is performed on the surface of the aluminum foil; S200, a solvent is sprayed on the surface of the aluminum foil; S300, carbon powder is uniformly sprayed on the surface of the aluminum foil, first baking and drying are performed, and the amount of the carbon powder is 0.1-5 g / m2; S400, the aluminum foil is subjected to roll pressing treatment; S500, the aluminum foil is subjected to second baking and drying, and the carbon-coated aluminum foil is obtained; In S400, the finite element analysis fine adjustment step control is performed on the aluminum foil during the roll pressing treatment, and the specific method is as follows: S410, a three-dimensional model of the roll press and the aluminum foil during the roll pressing treatment is obtained; S420, the three-dimensional model is loaded into finite element software, and a finite element model is obtained by using a mesh division algorithm; S430, the roll pressing finite element model and the aluminum foil finite element model are divided according to the obtained finite element model; S440, stress analysis is performed on the obtained finite element model to obtain a risk deformation zone; S450, a deformation coefficient of the risk deformation zone is calculated; S460, the roll pressing parameters are fine adjusted according to the deformation coefficient.

2. The method of claim 1, wherein the aluminum foil is prepared by the steps of: In S410, the three-dimensional model of the roll press and the aluminum foil during the roll pressing treatment is obtained by using 3D scanning to generate the three-dimensional model of the roll press and the aluminum foil. ​ 3. The method of claim 1, wherein the aluminum foil is prepared by the steps of: In S420, the three-dimensional model is loaded into finite element software, and the finite element model is obtained by using a mesh division algorithm, and the specific method is as follows: the current roll press working parameters and the aluminum foil material parameters are loaded into the finite element software, the contact part of the roll and the aluminum foil is an elastic body, the mesh division of the roll elastic body part is performed by using a mesh division method, the mesh is divided by using a quadrilateral solid unit, the mesh in a dense part is divided by using a neutral axis mesh division method, an advanced algorithm is used in a transition part, and the mesh is entirely divided by using a hexahedral solid unit to generate the finite element model. ​ 4. The method of claim 1, wherein the aluminum foil is prepared by the steps of: In S430, the roll pressing finite element model and the aluminum foil finite element model are divided according to the obtained finite element model, and the specific method is as follows: ​ A feature extraction method and a classification algorithm are used to distinguish the roll press region and the aluminum foil region of the obtained finite element model, a boundary is drawn around the roll press region identified by the three-dimensional model, the roll press region is separated from the entire three-dimensional model to obtain the roll press finite element model, a boundary is drawn around the aluminum foil region identified by the three-dimensional model, the aluminum foil region is separated from the entire three-dimensional model to obtain the aluminum foil finite element model.

5. The method of claim 1, wherein the aluminum foil is prepared by the steps of: In S440, the risk deformation zone is obtained by performing stress analysis on the obtained finite element model, and the specific method is as follows: ​ The roll press finite element model is imported into the finite element analysis software, the stress of each mesh in the roll press finite element model is calculated by using the pressure analysis in the finite element analysis software, the stress of the i-th mesh is recorded as Str(i), i=1, 2, …, M, M is the number of all meshes in the roll press finite element model, M numbers Str(1), Str(2), …, Str(M) are combined to form a stress sequence recorded as stress, the element with the maximum value and the element with the minimum value in the stress sequence are recorded as STR1 and STR2 respectively, the mesh corresponding to STR1 is recorded as an anchor mesh, and the mesh corresponding to STR2 is recorded as a target mesh; The distance between the center point of the anchor grid and the center point of the target grid is recorded as the dispersion distance, and the direction from the center point of the anchor grid to the center point of the target grid is recorded as the reference direction; all pressure values in the stress sequence are traversed, the absolute difference between Str(i) and STR1 is recorded as M1, and the absolute difference between Str(i) and STR2 is recorded as M2, and the grid corresponding to the pressure value with all M1 less than M2 is marked as a column grid; The direction vector formed by the center point of the anchor grid to the center point of the column grid is recorded as the main force vector, and the projection of the main force vector in the reference direction is recorded as the main force projection; all column grids in the main force sequence are traversed, the direction vector formed by the center point of the column grid to the center point of the target grid is recorded as the secondary force vector, and the projection of the secondary force vector in the reference direction is recorded as the secondary force projection; The main force projection and the secondary force projection are added, and the modulus of the operation result is recorded as the stress value of the current grid; The column grid with a stress value greater than the average stress value is marked as a risk grid, all adjacent risk grids form a risk stress grid group, and the edge of the risk stress grid group is traversed, and the traversal result is recorded as a risk stress area; After traversing all risk stress zones, let P be the geometric center of all risk stress zones. k , will P K Forming line segment L1 with the center point of the anchor grid, P K The center point of the anchor mesh forms line segment L2 with the center point of the target mesh, and the center point of the anchor mesh forms line segment L3 with the center point of the target mesh. All meshes contained in the triangular region formed by L1, L2 and L3 on the finite element model are denoted as the risk deformation zone.

6. The method of claim 1, wherein the aluminum foil is prepared by the steps of: In S450, the specific method for calculating the deformation coefficient of the risk deformation area is: ​ All pressure values in the risk deformation area are traversed and recorded as D(k, j), D(k, j) represents the pressure value corresponding to the jth grid in the kth risk deformation area, and the average of all pressure values in the risk deformation area is calculated; The deformation coefficient of any grid in the risk deformation area is calculated, and the calculation method is as follows: if the pressure value corresponding to the current grid is greater than the pressure average, the absolute difference between the pressure value corresponding to the current grid and the maximum pressure in the risk deformation area is calculated as N1, the distance between the center point of the current grid and the center point of the anchor grid is recorded as R1, the absolute difference between the pressure value corresponding to the current grid and the minimum pressure in the risk deformation area is calculated as N2, the distance between the center point of the current grid and the center point of the target grid is recorded as R2, and the deformation coefficient of the current grid is calculated according to the formula The deformation coefficient of the current grid is calculated, otherwise the deformation coefficient of the current grid is calculated according to the formula The deformation coefficient of the current grid is calculated, otherwise the deformation coefficient of the current grid is calculated according to the formula The sum of the deformation coefficients of all grids in the risk deformation area is taken as the deformation coefficient of the current risk deformation area.

7. The method of claim 1, wherein the aluminum foil is prepared by the steps of: In S460, the specific method for fine-tuning the rolling parameter according to the deformation coefficient is: ​ If the deformation coefficient of the current risk deformation area is less than zero, the current rolling mill speed is kept unchanged, and the rolling press pressure is adjusted to 20-50T; If the deformation coefficient of the current risk deformation area is greater than zero, the current rolling mill speed is kept unchanged, and the rolling press pressure is adjusted to 30-60T.

8. An aluminum foil prepared by the method of claim 1-7.

Images