Preparation method of carbon-coated aluminum foil for battery

Abstract

The invention belongs to the technical field of lithium batteries, and provides a preparation method of a carbon-coated aluminum foil for a battery, which can realize real-time monitoring of the annealing process of the aluminum foil by acquiring a stress distribution diagram of an aluminum foil material in an annealing period, marking a concentration area and a dispersion area in the same period and calculating a phase change coefficient of the aluminum foil between adjacent periods. Annealing parameters are adjusted according to the real-time condition of aluminum foil annealing, resource utilization maximization is achieved, the aluminum foil production process is accelerated, meanwhile, by obtaining the three-dimensional model of the aluminum foil after annealing is completed and conducting fine adjustment on the surface structure, the influence of diffusion induced stress caused by material surface flatness on the service life of the aluminum foil is eliminated, and the service life of the aluminum foil is prolonged. The battery service life is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a preparation method of carbon-coated aluminum foil for batteries. Background Art

[0002] When an aluminum plate is annealed at high temperature and then undergoes 2 to 3 passes of cold rolling, the grains are severely broken and appear fibrous or strip-shaped. At the same time, the dislocation density in the aluminum plate is relatively high, the lattice distortion is severe, the plasticity is poor, and the work hardening rate is relatively high. It is no longer suitable for further processing. Intermediate annealing can eliminate most dislocations by heating the cold-rolled alloy above the recrystallization temperature, improve the alloy properties, increase the plasticity of the material, and restore the alloy to its initial state for further processing. Recrystallization annealing is a process of reorganizing and changing the microstructure, which plays a crucial role in improving the properties of aluminum alloys, increasing production efficiency, and ensuring the quality of aluminum foil. However, most of the current intermediate annealing parameters are set manually based on experience, and it is impossible to adjust the annealing parameters in real time, resulting in waste of resources. At the same time, it is impossible to monitor the product quality during the annealing process, which affects the service life of the battery using this aluminum foil. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of carbon-coated aluminum foil for batteries to solve one or more technical problems existing in the prior art, and at least provide a beneficial choice or create conditions.

[0004] To achieve the above purpose, according to one aspect of the present invention, there is provided a preparation method of carbon-coated aluminum foil for batteries, and the preparation method of the carbon-coated aluminum foil for batteries includes the following steps:

[0005] S100, weighing each raw material by weight percentage and mixing, first melting to obtain a melt, and then subjecting the melt to continuous casting and rolling to form a continuous casting and rolling blank;

[0006] S200, performing homogenization annealing on the continuous casting and rolling blank formed by continuous casting and rolling;

[0007] S300, cold-rolling the above continuous casting and rolling blank to obtain a cold-rolled blank;

[0008] S400, performing intermediate annealing on the cold-rolled blank;

[0009] S500, rolling the annealed aluminum alloy strip into aluminum foil;

[0010] S600, slitting the aluminum foil obtained in step S500 to obtain a finished aluminum foil product;

[0011] Further, in S400, during the intermediate annealing process, a stress image sequence is obtained to finely adjust the step control, and the specific method is as follows:

[0012] S410, perform an intermediate annealing operation on the cold-rolled blank to obtain a stress map sequence;

[0013] S420, obtain a stress change sequence based on the stress map sequence;

[0014] S430, calculate the phase transformation coefficient based on the stress change sequence;

[0015] S440, fine-tune the intermediate annealing parameters according to the phase transformation coefficient.

[0016] Furthermore, in S100, the specific contents and percentages of each raw material are as follows: AL: 96.785 - 97.085%, Si: 0.23 - 0.27%, Fe: 0.44 - 0.50%, Cu: 0.185 - 0.205%, Mn: 0.86 - 0.90%, Mg: 1.19 - 1.24%, Cr ≤ 0.04%, Zn ≤ 0.06%, Ti: 0.01 - 0.025%.

[0017] Furthermore, in S500, rolling the annealed aluminum alloy strip into aluminum foil includes the following steps:

[0018] S510, roll the intermediate annealed aluminum alloy strip into an aluminum alloy strip with a thickness of 0.4 mm;

[0019] S520, roll the 0.4 mm aluminum alloy strip into aluminum foil.

[0020] Furthermore, in S600, use the Wanying Machinery WYSL-1300M microcomputer-controlled double middle-axis aluminum foil slitter to slit the aluminum foil to obtain the finished aluminum foil product.

[0021] Furthermore, in S600, the slitting speed is 200 - 300 m / min.

[0022] Furthermore, in S200, the specific method for performing homogenization annealing on the continuously cast and rolled blank is: subject the aluminum alloy strip to homogenization annealing at 580°C for 4.5 hours and 550°C for 20 hours, and the thickness of the aluminum alloy strip during homogenization annealing is 3.5 mm.

[0023] Furthermore, in S400, the specific method for performing intermediate annealing on the cold-rolled blank is: subject the aluminum alloy strip to intermediate annealing at 250°C for 2 hours and 195°C for 4 hours, and the thickness of the aluminum alloy strip during intermediate annealing is 0.9 mm.

[0024] Further, in S520, the specific method of rolling an aluminum alloy strip with a thickness of 0.4 mm into aluminum foil is as follows: in the first pass, it is pressed from 0.4 mm to 0.18 mm; in the second pass, it is pressed from 0.18 mm to 0.042 mm; in the third pass, it is pressed from 0.042 mm to 0.019 mm; and in the fourth pass, it is pressed from 0.019 mm to 0.012 mm.

[0025] Since, during the casting and rolling stage, the grain structure at the center of the aluminum plate advances forward along with the crystallization direction, the heat transfer rate of the melt decreases, the degree of supercooling also decreases, and the dendrites have sufficient time to grow fully under the condition of a relatively low crystallization rate, resulting in a relatively coarse grain structure. This causes the grains at the longitudinal section of the cold-rolled plate to be in a streamline-shaped fibrous structure. As the deformation amount gradually increases, the grains are further elongated, and the grain structure at the cross-section shows uneven distribution in the thickness direction. At the same time, during the rolling process of the aluminum plate, the degree of deformation gradually decreases from the edge to the center, and the grains are more obviously fibrous, making it more difficult to change their morphology, resulting in an increase in the strength and a decrease in the ductility of the formed cold-rolled material, which has an adverse effect on the subsequent plastic operation of slitting. See the reference: Research on the Optimization Process of One-Time Intermediate Annealing of AA8079 Double-Zero Aluminum Foil.

[0026] Further, in S410, the specific method of obtaining a stress map sequence by performing an intermediate annealing operation on a cold-rolled blank is as follows: starting from the execution of the intermediate annealing operation, obtain the stress distribution map of the cold-rolled blank at a preset time t interval, perform edge detection on the stress distribution map, and divide the stress distribution map into multiple excitation regions according to the results of the edge detection. Each excitation region corresponds to a part of the stress image. Let i be the serial number of the stress image, and Tsen i represents the stress image of the i-th excitation region. The stress images obtained in the current interval are used to form a stress map sequence.

[0027] Further, in S420, the specific method of obtaining a stress change sequence according to the stress map sequence is as follows: calculate the stress mean value of each point in all the stress images in the stress image sequence obtained in the current interval, and form a mean value image (there is only one mean value image) with the stress mean values of each point. Subtract each stress image from the mean value image respectively to obtain a differential stress image sequence, which forms the stress change sequence. Traverse the magnitudes of the stress values in the excitation regions of all the differential stress images, and mark all the excitation regions with stress values greater than zero as stress dispersion regions, and mark all the excitation regions with stress values less than zero as stress concentration regions.

[0028] The stress dispersion zone and stress concentration zone in the above steps represent the phase transformation behavior that occurs during the intermediate annealing of the blank. Solid-state phase transformation phenomena occur during the intermediate annealing of metal materials. This is because under specific temperature and time conditions, the crystal structure of the material changes, resulting in obvious changes in the stress distribution map. The stress dispersion zone indicates the gradual decrease in stress values within this zone, indicating that the shape and distribution of grains in the current zone are gradually becoming finer and more uniform. The stress concentration zone indicates the gradual increase in stress values within this zone, indicating that the shape and distribution of grains in the current zone are gradually becoming coarser and more uneven. The distribution of the stress dispersion zone and stress concentration zone can help understand the annealing process of the current blank.

[0029] Since phase transformation behavior occurs constantly during the annealing process of aluminum foil materials, the types, sizes, and shapes of the precipitated second-phase microstructures change with the variation of each process parameter. Under large cold rolling deformation, fine-sized αc(AlFeSi) phases and fibrous FeAl6 phases will be generated within the material. After annealing, more irregular long needle-like θ(FeAl3) phases and larger-sized blocky βp(AlFeSi) phases will be produced in the ingot. The types, morphologies, and quantities of the second phases have a profound impact on the processing performance and metal properties of the material. For example, the needle-like θ(FeAl3) phase is relatively hard and brittle, and it is prone to causing stress concentration in the aluminum foil processing, which is more harmful to the alloy. Currently, the annealing operation still controls the annealing parameters based on the initial state of the blank before annealing and artificial experience, unable to dynamically control the annealing parameters, lacking flexibility, and at the same time increasing resource waste. To solve the above problems, the present invention proposes the following method to fine-tune the annealing parameters by calculating the phase transformation coefficient of the excitation zone in the stress distribution map of the blank during annealing:

[0030] Further, in S430, the specific method for calculating the phase transformation coefficient according to the stress change sequence is as follows:

[0031] Within the value range of t, mark the projection area of each stress dispersion zone obtained in the previous cycle in the differential stress image obtained in the next cycle as Parea t , mark the projection area of each stress concentration zone of the blank obtained in the previous cycle in the corresponding differential stress image obtained in the next cycle as Qarea t , and at the same time obtain the stress dispersion zone and stress concentration zone of the next cycle, and simultaneously mark the differential stress areas of the stress dispersion zone and stress concentration zone of the next cycle as Parea t+1 and Qarea t+1 ;

[0032] Denote the maximum stress in Parea t as sp_max t , and the maximum stress is in the area Parea tThe corresponding point in it is p_max t , denote Qarea t The maximum stress in it is sq_max t , and the maximum stress is at the point q_max corresponding to it in the area Qarea t ; t ;

[0033] Denote Parea t The minimum stress in it is p_min t , and the minimum stress is at the point p_min corresponding to it in the area Parea t ; t , denote Qarea t The minimum stress in it is sq_min t , and the minimum stress is at the point q_min corresponding to it in the area Qarea t ; t ;

[0034] Denote Parea t+1 The maximum stress in it is sp_max t+1 , and the maximum stress is at the point p_max corresponding to it in the area Parea t+1 ; t+1 , denote Qarea t+1 The maximum stress in it is sq_max t+1 , and the maximum stress is at the point q_max corresponding to it in the area Qarea t+1 ; t+1 ;

[0035] Denote Parea t+1 The minimum stress in it is sp_min t+1 , and the minimum stress is at the point p_min corresponding to it in the area Parea t+1 ; t+1 , denote Qarea t+1 The minimum stress in it is sq_min t+1 , and the minimum stress is at the point q_min corresponding to it in the area Qarea t+1 ; t+1 ;

[0036] Denote the quadrilateral area formed by the points p_max t , p_min t , q_max t , q_min t as the pre-phase transition area, and denote the quadrilateral area formed by the points p_max t+1 , p_min t+1 , q_max t+1 , q_min t+1The formed quadrilateral region is used as the post-phase transition region. The common region of the pre-phase transition region and the post-phase transition region is denoted as the phase transformation region, and the logarithm of the ratio of the total area of the phase transformation region to the total area of the pre-phase transition region and the post-phase transition region is denoted as the transformation ratio;

[0037] Denote sp_max t and sq_max t+1 The absolute difference is M1. Denote sq_max t and sq_max t+1 The absolute difference is M2. The average of M1 and M2 is denoted as the transformation amplitude;

[0038] Take the product of the transformation ratio and the transformation amplitude as the phase change coefficient between the previous cycle and the next cycle.

[0039] Furthermore, in S440, the specific method for fine-tuning the intermediate annealing parameters according to the phase change coefficient is as follows:

[0040] When the phase change coefficient is less than zero, the specific method for adjusting the annealing parameters is as follows:

[0041] Increase the annealing temperature by 5°C every 1 minute until the annealing temperature reaches 215°C, and maintain 215°C until the end of the current cycle;

[0042] When the phase change coefficient is greater than zero, the specific method for adjusting the annealing parameters is as follows:

[0043] Reduce the annealing temperature by 5°C every 1 minute until the annealing temperature reaches 175°C, and maintain 175°C until the end of the current cycle.

[0044] Since the purpose of intermediate annealing is to eliminate the coarse grains that appear in the blank after rolling, these coarse grains will cause uneven stress distribution. If the second-phase (grain) distribution is uneven, the deformation dislocation during crystal slip will also be uneven, the work-hardening rate of the material will increase, and the second-phase particles located at the grain boundaries will cut the grains, having a certain impact on their continuity and integrity, thus weakening the bonding strength between grains, affecting the ductility of the blank and the ion storage capacity, and further affecting the service life of the battery. The dispersion zone in the above method is represented as the area where the stress distribution in the blank is not concentrated, that is, the grains contained in the dispersion zone do not have coarse grains. The concentration zone is represented as the area where the stress distribution is relatively concentrated, that is, there are more coarse grains in the grains contained in the concentration zone. Therefore, the stress in the concentration zone will also be concentrated. During the intermediate annealing process, these coarse grains will undergo recrystallization and gradually transition into uniform and fine grains. On the stress distribution map, it is shown that the concentration area in the latter cycle will gradually spread compared with the concentration area in the previous cycle, but the stress magnitude will continuously tend to be uniform. After the annealing work is completed, there are no longer coarse grains inside the blank, which are completely replaced by uniform and fine grains. The conversion ratio represents the conversion range of the grains in the blank in the latter cycle compared with the previous cycle, and the conversion amplitude represents the conversion degree of the grains. The product of the two can represent the conversion and distribution of the grains formed by recrystallization in the current blank (that is, the size of the phase transformation coefficient reflects the recrystallization situation of the blank during the current intermediate annealing process. Adjusting the annealing parameters according to the recrystallization situation can timely master the processing process of the aluminum foil).

[0045] The above method can monitor the grain transformation and distribution inside the blank in real time, ensure the uniform distribution of grains inside the blank to ensure the ductility and plasticity of the blank. However, during the use of lithium batteries, due to the frequent charging and discharging operations of the battery, ions are repeatedly embedded and extracted in the structure composed of the electrode material, resulting in the formation of concentration gradients and diffusion-induced stress. Excessive diffusion-induced stress will damage the structure composed of the electrode material, thereby greatly reducing the service life of the battery. To solve the above problems, the current method is to control the charge and discharge rate and cycle to control the ion movement rate and then control the concentration change of the electrode material particles. However, this method can only be used for finished batteries and cannot be well applied in the manufacturing process. Current relevant research shows that diffusion-induced stress is not only related to the charge and discharge rate, but also closely related to the structure of the electrode material. In a finite element analysis reference entitled "The influence of graphite material microstructure of lithium-ion batteries on diffusion-induced stress", it is mentioned that the surface area of ​​the electrode affects the diffusion-induced stress. A lot of research has been done on the concave-convex structure of the electrode surface and the diffusion-induced stress. The results show that the number of convex particles on the electrode surface is positively correlated with the diffusion-induced stress. Therefore, although the above method can monitor the size and uniformity of the grains in the blank in real time, it cannot reflect the number and distribution of concave-convex particles on the blank surface, so it is impossible to monitor the size of the diffusion-induced stress caused by the blank structure. In order to solve the above problem, the present invention proposes to mark the area where the electrode generates diffusion-induced stress by the induced risk area, and then offset the generated diffusion-induced stress by constructing a coarsening area to eliminate the influence of the corresponding battery life:

[0046] Obtain a three-dimensional structural model of the blank, analyze the stress state of the electrode material particles based on the equivalent stress of the failure criterion of the three-dimensional structural model of the blank, and generate a risk stress map according to the stress value in the three-dimensional structural model, detect multiple areas of the risk stress map through the Sobel edge, mark the area where the average stress value in the area is greater than the average stress value of all areas as a convex area, record the points corresponding to the maximum stress values ​​in all convex areas as convex points, and form all convex points into a convex point set;

[0047] Furthermore, the method for obtaining the equivalent stress based on the failure criterion comes from the method for obtaining the equivalent stress in the finite element analysis of the influence of the microstructure of graphite materials of lithium-ion batteries on the diffusion-induced stress in the reference.

[0048] Further, the convex point sets are divided into multiple groups of relative convex point sets according to the acquisition positions on the blank (each group of convex point sets is obtained from the risk stress map of the relative surface of the blank model). The projection points of the convex points in any one of the convex point sets in each group of relative convex point sets on the opposite side of the blank (the opposite side refers to the area where the surface of the blank where the current convex point is located is vertically projected onto the other surface of the blank, and the area and shape of the opposite side are the same as those of the surface of the blank where the current convex point is located) are denoted as projection convex points. At the same time, in the convex point set on the current opposite side, calculate the distances between all convex points and the projection convex points, and mark the convex point with the closest distance as the accompanying convex point of the projection convex point, and each accompanying convex point corresponds to only one convex point;

[0049] Among them, the convex points represent the locally existing maximum internal stress caused by the convex particles of the electrode material. The internal stress reflects the diffusion-induced stress generated at the current position due to the changes in ion concentration and transport speed (since the convex particles increase the surface area of the material, the ion concentration here is higher than that in other regions, resulting in a concentration difference and thus diffusion-induced stress here). It is shown in the reference literature that the diffusion-induced stress brought by symmetrically distributed convex particles is much greater than that brought by asymmetrically distributed convex particles during charge and discharge. Therefore, by marking the accompanying convex points, the electrode materials that do not form a symmetric structure can be intuitively screened out.

[0050] After the marking is completed, mark the convex regions corresponding to the unmarked convex points as induced risk regions, and denote the projection region of the risk region on the opposite side of the electrode as the roughened region;

[0051] Calculate the distances from the point corresponding to the maximum stress value to each point in the induced risk region and denote it as the ascending path P_im, calculate the distances from the point corresponding to the minimum stress value to each point in the induced risk region and denote it as the descending path P_in. Denote the average value of all ascending paths as P_mm, and the average value of all descending paths as P_mn. Traverse each point in the induced risk region. If the ascending path of the current point is greater than the descending path, set the height of the current point as |P_mm - P_mn| + |P_im - P_in|; if the ascending path of the current point is less than the descending path, set the height of the current point as |P_mm - P_mn| - |P_im - P_in|; if the ascending path of the current point is equal to the descending path, set the height at the current point as |P_mm - P_mn|. Map the heights corresponding to each point in the induced risk region directly to the heights corresponding to each point in the roughened region.

[0052] Further, use a double-sided blade circular saw to continue precision cut the slit aluminum foil to the finished narrow width specification, and use corona treatment 1 - 2 times, with a corona power of 12 - 19 kw, a linear speed of 150 - 250 m / min, and a unwind reel tension of 12 - 28 N / mm 2, the rubber roller of the rewinder needs to be cleaned once with a clean dust-free cloth for each roll to ensure no aluminum chips, no dust, and no oil stains. The surface dyne value of the aluminum foil after corona treatment should not be lower than 32 Dyn.

[0053] Furthermore, the processed aluminum foil is treated through three steps: soaking in surface acid-base solution, water washing, and drying. The acid-base solution is a solution of acids or alkaline substances such as NaOH and HCl. The acid-base washing needs to be soaked and infiltrated for 5 - 10S, and it is based on completely removing the surface oxygen grease and powder residues under microscopic observation.

[0054] Furthermore, in the roughened area, according to the specific height values corresponding to each point as the protrusion height, a laser texturing machine is used to texture the surface of the roll and texture the double-sided bright aluminum foil.

[0055] The roughened area in the above method is used to eliminate the diffusion-induced stress generated by the asymmetric parts on the surface of the current electrode material. The construction of the roughened area can change the electrode material from an asymmetric structure to a symmetric structure. According to the magnitude of the diffusion-induced force generated at each point in the induced risk area on the surface of the raw material (i.e., the magnitude of the ascending diameter and descending diameter corresponding to each point in the induced risk area), it is directly mapped to the height of each point in the roughened area, enabling the diffusion-induced stress generated at each point in the constructed roughened area to cancel out the diffusion-induced force generated at each point of the asymmetric part, thereby greatly reducing the diffusion-induced force generated by the overall electrode and prolonging the service life of the battery.

[0056] The beneficial effects of the present invention are as follows: The present invention provides a preparation method for carbon-coated aluminum foil for batteries, which can obtain the phase change degree of the aluminum foil during annealing to monitor the annealing process, achieve precise control of annealing parameters, and reduce resource waste; at the same time, by constructing a roughened area, it eliminates the diffusion-induced stress caused by the incomplete symmetric structure on the surface of the aluminum foil after annealing, greatly prolonging the service life of the battery. Description of the Drawings

[0057] Figure 1 Shown is a flowchart of a preparation method for carbon-coated aluminum foil for batteries. Detailed Embodiments

[0058] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as a limitation of the present invention.

[0059] Embodiment 1

[0060] Figure 1 Shown is a flowchart of a preparation method for carbon-coated aluminum foil for batteries.

[0061] S100, Weigh each raw material by weight percentage and mix them. First, melt them to obtain a melt, and then subject the melt to continuous casting and rolling to form a continuous casting and rolling blank;

[0062] S200, Perform homogenization annealing on the continuous casting and rolling blank formed by continuous casting and rolling;

[0063] S300, Cold-roll the above continuous casting and rolling blank to obtain a cold-rolled blank;

[0064] S400, Perform intermediate annealing on the cold-rolled blank;

[0065] S500, Roll the annealed aluminum alloy strip into aluminum foil;

[0066] S600, Slit the aluminum foil obtained in step S500 to obtain the finished aluminum foil product;

[0067] Furthermore, in S400, during the intermediate annealing process, obtain a stress image sequence to finely adjust the step control. The specific method is as follows:

[0068] S410, Perform intermediate annealing on the cold-rolled blank to obtain a stress map sequence;

[0069] S420, Obtain a stress change sequence based on the stress map sequence;

[0070] S430, Calculate the phase transformation coefficient based on the stress change sequence;

[0071] S440, Fine-tune the intermediate annealing parameters according to the phase transformation coefficient.

[0072] Furthermore, in S100, the specific content and percentage of each raw material are as follows: AL: 96.882%, Si: 0.25%, Fe: 0.47%, Cu: 0.195%, Mn: 0.88%, Mg: 1.21%, Cr: 0.04%, Zn: 0.06%, Ti: 0.013%.

[0073] Furthermore, in S500, rolling the annealed aluminum alloy strip into aluminum foil includes the following steps:

[0074] S510, Roll the aluminum alloy strip after intermediate annealing into an aluminum alloy strip with a thickness of 0.4 mm;

[0075] S520, Roll the 0.4 mm aluminum alloy strip into aluminum foil.

[0076] Furthermore, in S600, use the Wanying Machinery WYSL-1300M microcomputer-controlled double middle-axis aluminum foil slitter to slit the aluminum foil to obtain the finished aluminum foil product.

[0077] Furthermore, in S600, the slitting speed is 250 m / min.

[0078] Further, in S200, the specific method for homogenizing annealing the continuously cast and rolled blank is as follows: The aluminum alloy strip is subjected to homogenizing annealing at 580°C for 4.5 hours and then at 550°C for 20 hours, and the thickness of the aluminum alloy strip during homogenizing annealing is 3.5 mm.

[0079] Further, in S400, the specific method for intermediate annealing of the cold-rolled blank is as follows: The aluminum alloy strip is subjected to intermediate annealing at 250°C for 2 hours and then at 195°C for 4 hours, and the thickness of the aluminum alloy strip during intermediate annealing is 0.9 mm.

[0080] Further, in S520, the specific method for rolling a 0.4-mm aluminum alloy strip into aluminum foil is as follows: In the first pass, it is pressed from 0.4 mm to 0.18 mm, in the second pass from 0.18 mm to 0.042 mm, in the third pass from 0.042 mm to 0.019 mm, and in the fourth pass from 0.019 mm to 0.012 mm.

[0081] Further, in S410, the specific method for obtaining a stress map sequence by performing intermediate annealing on the cold-rolled blank is as follows: Starting from the execution of the intermediate annealing operation, a stress distribution map of the cold-rolled blank is obtained with a 1-hour acquisition period, and edge detection is performed on the stress distribution map. According to the results of the edge detection, the stress distribution map is divided into multiple excitation regions, where each excitation region corresponds to a part of the stress image. Using i as the serial number of the stress image, Tsen i represents the stress image of the i-th excitation region, and all the stress images obtained in the current period form a stress map sequence.

[0082] Further, in S420, the specific method for obtaining a stress change sequence based on the stress map sequence is as follows: Calculate the stress mean value of each point in all the stress images in the stress image sequence obtained in the current period, and form a mean value image (there is only one mean value image) with the stress mean values of each point. Subtract each stress image from the mean value image respectively to obtain a difference stress image sequence to form a stress change sequence. Traverse the magnitudes of the stress values in the excitation regions in all the difference stress images, and mark the excitation regions where all the stress values are greater than zero as stress dispersion regions, and mark the excitation regions where all the stress values are less than zero as stress concentration regions.

[0083] Further, in S430, the specific method for calculating the phase change coefficient based on the stress change sequence is as follows:

[0084] Within the value range of t, mark the projection area in the difference stress image obtained in the next period for each stress dispersion region obtained in the previous period as Parea t, mark the projection area of each stress concentration area of the blank obtained in the previous cycle in the corresponding differential stress image obtained in the next cycle as Qarea t , and simultaneously obtain the stress dispersion area and the stress concentration area in the next cycle, and simultaneously mark the differential stress area of the stress dispersion area and the stress concentration area in the next cycle as Parea t+1 and Qarea t+1 ;

[0085] Record the maximum stress in Parea t as sp_max t , and the point corresponding to the maximum stress in the area Parea t is p_max t , record the maximum stress in Qarea t as sq_max t , and the point corresponding to the maximum stress in the area Qarea t is q_max t ;

[0086] Record the minimum stress in Parea t as p_min t , and the point corresponding to the minimum stress in the area Parea t is p_min t , record the minimum stress in Qarea t as sq_min t , and the point corresponding to the minimum stress in the area Qarea t is q_min t ;

[0087] Record the maximum stress in Parea t+1 as sp_max t+1 , and the point corresponding to the maximum stress in the area Parea t+1 is p_max t+1 , record the maximum stress in Qarea t+1 as sq_max t+1 , and the point corresponding to the maximum stress in the area Qarea t+1 is q_max t+1 ;

[0088] Record the minimum stress in Parea t+1 as sp_min t+1 , and the point corresponding to the minimum stress in the area Parea t+1 is p_min t+1 , record the minimum stress in Qarea t+1 as sq_min t+1 , and the point corresponding to the minimum stress in the area Qareat+1 The corresponding point is q_min t+1 ;

[0089] Denote the quadrilateral region formed by the points p_max t , p_min t , q_max t , and q_min t as the pre-phase transition region. Denote the quadrilateral region formed by the points p_max t+1 , p_min t+1 , q_max t+1 , and q_min t+1 as the post-phase transition region. Denote the common region of the pre-phase transition region and the post-phase transition region as the phase conversion region, and denote the logarithm of the ratio of the total area of the phase conversion region to the total area of the pre-phase transition region and the post-phase transition region as the conversion ratio;

[0090] Denote the absolute difference between sp_max t and sq_max t+1 as M1, and denote the absolute difference between sq_max t and sq_max t+1 as M2. Denote the average of M1 and M2 as the conversion amplitude;

[0091] Take the product of the conversion ratio and the conversion amplitude as the phase change coefficient between the previous cycle and the next cycle.

[0092] Furthermore, in S440, the specific method for fine-tuning the intermediate annealing parameters according to the phase change coefficient is as follows:

[0093] When the phase change coefficient is less than zero, the specific method for adjusting the annealing parameters is as follows:

[0094] Increase the annealing temperature by 5°C every 1 minute until the annealing temperature reaches 215°C, and maintain 215°C until the end of the current cycle;

[0095] When the phase change coefficient is greater than zero, the specific method for adjusting the annealing parameters is as follows:

[0096] Reduce the annealing temperature by 5°C every 1 minute until the annealing temperature reaches 175°C, and maintain 175°C until the end of the current cycle.

[0097] Example 2

[0098] Although the above method can monitor the size and distribution uniformity of grains in the blank in real time, it cannot reflect the number and distribution of concave and convex particles on the surface of the blank. Therefore, it is impossible to monitor the magnitude of the diffusion-induced stress caused by the blank structure. To solve the above problems, the present invention provides the following Embodiment 2. By marking the induced risk area, which represents the area where the electrode generates diffusion-induced stress, and then constructing a roughened area to offset the generated diffusion-induced stress to eliminate the impact on the corresponding battery life, specifically:

[0099] Obtain the three-dimensional structure model of the blank, analyze the stress state of the electrode material particles based on the equivalent stress of the failure criterion for the three-dimensional structure model of the blank, and generate a risk stress map according to the magnitude of the stress values in the three-dimensional structure model. Detect multiple regions from the risk stress map through Sobel edge detection. Mark the region where the average stress value within the region is greater than the average stress value of all regions as the convex region. Denote the point corresponding to the maximum stress value among all convex regions as the convex point, and form a convex point set with all convex points;

[0100] Furthermore, the method for obtaining the equivalent stress based on the failure criterion is from the method for obtaining in the finite element analysis of the influence of the microstructure of graphite materials in lithium-ion batteries on diffusion-induced stress in the reference literature.

[0101] Furthermore, divide the convex point set into multiple groups of relative convex point sets according to the acquisition positions on the blank (each group of convex point sets is obtained from the risk stress map of the relative surfaces of the blank model). Denote the projection point of any convex point in each group of relative convex point sets on the opposite side of the blank (the opposite side refers to the area where the surface of the blank where the current convex point is located is vertically projected onto the other surface of the blank, and the area and shape of the opposite side are the same as those of the surface of the blank where the current convex point is located) as the projection convex point. At the same time, in the convex point set on the current opposite side, calculate the distance between all convex points and the projection convex point, and mark the convex point with the closest distance as the companion convex point of the projection convex point, and each companion convex point corresponds to only one convex point;

[0102] After the marking is completed, mark the convex region corresponding to the convex points that have not been marked as the induced risk area, and denote the projection area of the risk area on the opposite side of the electrode as the roughened area;

[0103] The distance from the point corresponding to the maximum calculated stress to each point in the induced risk area is denoted as the ascending diameter \(P_{im}\), and the distance from the point corresponding to the minimum value to each point in the induced risk area is denoted as the descending diameter \(P_{in}\). The average value of all ascending diameters is denoted as \(P_{mm}\), and the average value of all descending diameters is denoted as \(P_{mn}\). Traverse each point in the induced risk area. If the ascending diameter of the current point is greater than the descending diameter, then set the height of the current point as \(|P_{mm}-P_{mn}|+|P_{im}-P_{in}|\); if the ascending diameter of the current point is less than the descending diameter, then set the height of the current point as \(|P_{mm}-P_{mn}|-|P_{im}-P_{in}|\); if the ascending diameter of the current point is less than the descending diameter, and if the ascending diameter of the current edge point is equal to the descending diameter, then set the height at the current point as \(|P_{mm}-P_{mn}|\). Map the height corresponding to each point in the induced risk area directly to the height corresponding to each point in the roughened area.

[0104] Further, use a double-edged disc cutter to further precisely cut the slit aluminum foil to the finished narrow width specification, use corona treatment twice, with a corona power of 15 kw, a linear speed of 200 m / min, and an unwinding reel tension of 20 N / mm. 2 The rubber roller of the rewinder needs to be cleaned once with a clean dust-free cloth for each roll to ensure no aluminum chips, no dust, and no oil stains. The surface dyne value of the aluminum foil after corona treatment is required to be not less than 32 Dyn.

[0105] Further, the processed aluminum foil is treated through three steps: soaking in a surface acid-base solution, water washing, and drying. The acid-base solution is a solution of acids or alkaline substances such as NaOH and HCl. The acid-base washing needs to be soaked and infiltrated for 8S, and it is based on completely removing the surface oxygen grease and powder residues under a microscope.

[0106] Further, in the roughened area, according to the specific value of the height corresponding to each point as the protrusion height, use a laser texturing machine to perform surface texturing on the roll and perform texturing rolling on the double-sided bright aluminum foil.

[0107] Comparative Example 1

[0108] The aluminum foil production method in the embodiment of the Chinese invention patent named "A production process of aluminum foil for power batteries" applied on August 20, 2021, with the publication number CN113652579B.

[0109] The aluminum foils produced by the methods in Example 1, Example 2, and Comparative Example 1 of the present invention are assembled into No. 1 lithium battery, No. 2 lithium battery, and No. 3 lithium battery according to the same existing assembly method.

[0110] Charge the No. 1 lithium battery, No. 2 lithium battery, and No. 3 lithium battery to 1.5V at a rate of 0.33C respectively, and then discharge them to 3V at 0.33C for cycle testing. When the number of cycles reaches 100 times, 500 times, 1000 times, and 3000 times respectively, detect the capacitance of the battery. The results are shown in Table 1:

[0111] Further, the charge-discharge experiment was tested using an Arbin BT-2043 supercapacitor charge-discharge tester from the United States;

[0112] Further, the battery capacitance test experiment was tested using a ZENNIUM XC electrochemical workstation from ZAHNER Company in Germany;

[0113] Table 1 Capacitance and the proportion of battery capacity decline at the end of the cycle under different charge-discharge cycle numbers

[0114]

[0115] Analysis: Before the cyclic charge and discharge of the three lithium batteries, the battery capacitance of the three batteries was tested respectively. The observation results showed that the capacitance content of the No. 1 and No. 2 lithium batteries was higher than that of the No. 3 lithium battery, indicating that the method provided by the present invention can increase the battery capacitance content. This is because in the process of intermediate annealing, the method of Example 1 of the present invention can monitor the annealing process in real time, achieve precise control of the annealing parameters, and make the billet show uniform refinement in structure. Compared with the traditional production method in Comparative Example 1, the finished battery produced by the aluminum foil produced by Example 1 of the present invention can accommodate more lithium ions. In Example 2 of the present invention, the volume of the electrode sheet is slightly increased by constructing a coarsening region after annealing, so the initial capacitance content of the No. 2 battery is larger than that of the No. 1 battery, and the capacitance content of the No. 1 and No. 2 lithium batteries is higher than that of the No. 3 lithium battery;

[0116] After the cyclic charge and discharge of the three lithium batteries, the battery capacitance of the three batteries was tested respectively. The observation results showed that the battery capacitance decline ratios of the No. 1 battery, No. 2 battery and No. 3 battery were 11.89%, 6.90% and 17.62% respectively. The capacitance decline ratios of the three batteries were all less than 20%, meeting the GB / T 36276-2023 standard. Among them, the capacitance decline ratio of the No. 2 battery was much smaller than that of the No. 1 and No. 3 batteries. This is because in Example 2 of the present invention, by constructing a coarsening region on the electrode sheet, the diffusion-induced stress generated in the material during the charging process is greatly reduced, the internal structure of the electrode sheet is protected to the greatest extent from damage, the aging of the battery is delayed, and the service life of the battery is extended.

[0117] The beneficial effects of the present invention are as follows: The present invention provides a preparation method of carbon-coated aluminum foil for batteries, which can obtain the phase change degree of aluminum foil during annealing to monitor the annealing process, achieve precise control of annealing parameters, and reduce resource waste; at the same time, by constructing a coarsening region, the diffusion-induced stress caused by the incomplete symmetric structure on the surface of the aluminum foil after annealing is eliminated, and the service life of the battery is greatly extended.

[0118] Although the description of the present invention has been quite detailed and has particularly described several of the described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, so as to effectively cover the intended scope of the present invention. In addition, the present invention has been described above in terms of embodiments foreseeable by the inventors for the purpose of providing a useful description, and non-substantive modifications to the present invention that are not currently foreseeable may still represent equivalent modifications of the present invention.

Claims

1. A preparation method of carbon-coated aluminum foil for batteries, characterized in that, The method includes the following steps: S100, Weigh each raw material by weight percentage and mix them. First, melt them to obtain a melt, and then cast-roll the melt to form a cast-rolled blank; S200, Perform homogenization annealing on the cast-rolled blank formed by casting and rolling; S300, Cold-roll the above cast-rolled blank to obtain a cold-rolled blank; S400, Perform intermediate annealing on the cold-rolled blank; S500, Roll the annealed aluminum alloy strip into aluminum foil; S600, Slit the aluminum foil obtained in step S500 to obtain the finished aluminum foil; In S400, during the intermediate annealing process, obtain a stress image sequence for fine-tuning step control. The specific method is as follows: S410, Perform intermediate annealing operation on the cold-rolled blank to obtain a stress map sequence; S420, Obtain a stress change sequence according to the stress map sequence; S430, Calculate the phase transformation coefficient according to the stress change sequence; S440, Fine-tune the intermediate annealing parameters according to the phase transformation coefficient.

2. The preparation method of a carbon-coated aluminum foil for a battery according to claim 1, characterized in that, In S100, the specific content and percentage of each raw material are as follows: Si: 0.23 - 0.27%, Fe: 0.44 - 0.50%, Cu: 0.185 - 0.205%, Mn: 0.86 - 0.90%, Mg: 1.19 - 1.24%, Cr ≤ 0.04%, Zn ≤ 0.06%, Ti: 0.01 - 0.025%.

3. The preparation method of a carbon-coated aluminum foil for a battery according to claim 2, wherein, In S200, the specific method for performing homogenization annealing on the cast-rolled blank formed by casting and rolling is as follows: Perform homogenization annealing on the aluminum alloy strip at 580°C for 4.5 hours and at 550°C for 20 hours.

4. The preparation method of a carbon-coated aluminum foil for a battery according to claim 3, characterized in that In S400, the specific method for performing intermediate annealing on the cold-rolled blank is as follows: Perform intermediate annealing on the aluminum alloy strip at 250°C for 2 hours and at 195°C for 4 hours.

5. The preparation method of a carbon-coated aluminum foil for a battery according to claim 1, characterized in that, In S410, the specific method for obtaining a stress map sequence by performing an intermediate annealing operation on a cold-rolled blank is as follows: starting from the execution of the intermediate annealing operation, obtain the stress distribution map of the cold-rolled blank at preset time intervals of t, perform edge detection on the stress distribution map, and divide the stress distribution map into multiple excitation regions according to the results of the edge detection. Each excitation region corresponds to a part of the stress image. Let i be the serial number of the stress image, and Tsen i represents the stress image of the i-th excitation region. The stress images obtained in the current cycle are used to form a stress map sequence.

6. The preparation method of a carbon-coated aluminum foil for a battery according to claim 1, characterized in that In S420, the specific method for obtaining a stress change sequence according to the stress map sequence is as follows: Calculate the stress mean value of each point in all stress images in the stress image sequence obtained in the current cycle. Form a mean value image with the stress mean values of each point. Subtract each stress image from the mean value image respectively to obtain a differential stress image to form a stress change sequence. Traverse the magnitudes of the stress values in the excitation regions in all differential stress images. Mark the excitation regions where all stress values are greater than zero as stress dispersion regions, and mark the excitation regions where all stress values are less than zero as stress concentration regions.

7. The preparation method of a carbon-coated aluminum foil for a battery according to claim 1, characterized in that, In S430, the specific method for calculating the phase transformation coefficient according to the stress change sequence is as follows: Within the value range of t, mark the projection area of each stress dispersion area obtained in the previous cycle in the differential stress image obtained in the next cycle as Parea t , mark the projection area of each stress concentration area of the blank obtained in the previous cycle in the corresponding differential stress image obtained in the next cycle as Qarea t , simultaneously obtain the stress dispersion area and stress concentration area in the next cycle, and simultaneously obtain the differential stress areas of the stress dispersion area and stress concentration area in the next cycle as Parea t+1 and Qarea t+1 ; Denote Parea t The maximum stress in it is sp_max t , and the point corresponding to the maximum stress in the region Parea t is p_max t , denote Qarea t The maximum stress in it is sq_max t , and the point corresponding to the maximum stress in the region Qarea t is q_max t ; Denote Parea t The minimum stress in it is p_min t , and the point corresponding to the minimum stress in the region Parea t is p_min t . Denote Qarea t The minimum stress in it is sq_min t , and the point corresponding to the minimum stress in the region Qarea t is q_min t ; Denote Parea t+1 The maximum stress in it is sp_max t+1 , and the point corresponding to the maximum stress in the area Parea t+1 is p_max t+1 , Denote Qarea t+1 The maximum stress in it is sq_max t+1 , and the point corresponding to the maximum stress in the area Qarea t+1 is q_max t+1 ; Denote Parea t+1 The minimum stress in it is sp_min t+1 , and the point corresponding to the minimum stress in the area Parea t+1 is p_min t+1 , Denote Qarea t+1 The minimum stress in it is sq_min t+1 , and the point corresponding to the minimum stress in the area Qarea t+1 is q_min t+1 ; Denote the point p_max t , as p_min t , q_max t , q_min t The quadrilateral region formed is regarded as the front phase change region. Denote the point p_max t+1 , as p_min t+1 , q_max t+1 , q_min t+1 The quadrilateral region formed is regarded as the rear phase change region. Denote the common region of the front phase change region and the rear phase change region as the phase conversion region, and denote the logarithm of the ratio of the total area of the phase conversion region to the total area of the front phase change region and the rear phase change region as the conversion ratio; Denote sp_max t The absolute difference from sq_max t+1 is M1. Denote sq_max t The absolute difference from sq_max t+1 is M2. Denote the average of M1 and M2 as the conversion amplitude; Take the product of the transformation ratio and the transformation amplitude as the phase transformation coefficient between the previous cycle and the next cycle.

8. The preparation method of a carbon-coated aluminum foil for a battery according to claim 1, characterized in that, In S440, the specific method for fine-tuning the intermediate annealing parameters according to the phase transformation coefficient is as follows: When the phase transformation coefficient is less than zero, the specific method for adjusting the annealing parameters is as follows: Increase the annealing temperature by 5°C every 1 minute until the annealing temperature reaches 215°C, and maintain 215°C until the end of the current cycle; When the phase transformation coefficient is greater than zero, the specific method for adjusting the annealing parameters is as follows: Decrease the annealing temperature by 5°C every 1 minute until the annealing temperature reaches 175°C, and maintain 175°C until the end of the current cycle.

9. The preparation method of a carbon-coated aluminum foil for a battery according to claim 1, characterized in that, In S440, in S500, rolling the annealed aluminum alloy strip into aluminum foil includes the following steps: S510, roll the aluminum alloy strip after intermediate annealing into a thickness of 0.4 mm; S520, roll the 0.4-mm aluminum alloy strip into a finished aluminum foil.

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