High elongation aluminum foil and method of making same

Abstract

The application discloses a high-elongation aluminum foil and a preparation method thereof, wherein the preparation method comprises the following steps: step S1, preparing a continuous casting and rolling roll with a thickness of 6.600-6.800 mm by adopting a double-roller continuous casting and rolling mode; step S2, performing first cold rolling on the continuous casting and rolling roll to obtain a first cold rolling roll with a thickness of 2.300-2.600 mm; step S3, performing incomplete annealing on the first cold rolling roll; step S4, performing second cold rolling on the first cold rolling roll after the incomplete annealing to obtain a second cold rolling roll with a thickness of 0.200-0.220 mm; and step S5, performing foil rolling on the second cold rolling roll to obtain the high-elongation aluminum foil with a thickness less than or equal to 0.013 mm. The high-elongation aluminum foil prepared by the preparation method has a tensile strength greater than or equal to 220 MPa and an elongation after fracture greater than or equal to 6.5%.

Description

Technical Field

[0001] This invention relates to the field of aluminum processing technology, and in particular to a high-elongation aluminum foil and its preparation method. Background Technology

[0002] Battery aluminum foil is a type of aluminum foil used as a current collector in lithium-ion batteries. As lithium-ion batteries develop towards higher energy density and longer cycle life, this aluminum foil needs to be improved to be more durable.

[0003] If the aluminum foil used in lithium-ion batteries has insufficient elongation after breakage, it will cause micro-cracks or strip breakage during high-speed slitting and rolling processes, which will seriously affect the qualification rate of its application in lithium-ion batteries and also pose hidden dangers to the safety and reliability of the batteries in the long term.

[0004] When the elongation after fracture of aluminum foil used in lithium-ion batteries is low, its defects are mainly reflected in the following two aspects: First, in the tab welding and subsequent processes, the microscopic damage caused by the low elongation after fracture will significantly increase the risk of internal short circuit in the battery; Second, in the long-term charge and discharge cycle, the repeated changes in the volume of the active material will constantly test the plasticity of the current collector, and the low elongation after fracture will accelerate the fatigue of the aluminum foil, causing the active material to fall off and the capacity to decay more rapidly.

[0005] Therefore, the elongation at break of aluminum foil used in lithium-ion batteries is crucial for ensuring battery manufacturing efficiency, safety, and cycle life. However, in related technologies, the elongation at break of aluminum foil used in lithium-ion batteries is generally between 1.5% and 3%. Figure 2 As shown in Figure (b), it cannot meet the needs of the ongoing development of lithium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a high-elongation aluminum foil and its preparation method, so as to solve the problem that the elongation after break of aluminum foil used in lithium-ion batteries in related technologies is 1.5~3%, which cannot meet the needs of the continuous development of lithium-ion batteries.

[0007] In a first aspect, embodiments of the present invention provide a method for preparing high-elongation aluminum foil, comprising the following steps: Step S1: Prepare cast-rolled coils with a thickness of 6.600~6.800mm using a twin-roll continuous casting and rolling method based on the raw material formula; Step S2: Perform a first cold rolling on the cast-rolled coil to obtain a first cold-rolled coil with a thickness of 2.300~2.600mm; Step S3: Perform incomplete annealing on the first cold-rolled coil; Step S4: Perform a second cold rolling on the first cold-rolled coil after incomplete annealing to obtain a second cold-rolled coil with a thickness of 0.200~0.220mm; Step S5: Perform foil rolling on the second cold-rolled coil to obtain the high-elongation aluminum foil with a thickness of less than or equal to 0.013 mm; The high-elongation aluminum foil is obtained by four foil rolling passes. The control modes for the first, second, and third foil rolling passes are tension control, while the control mode for the fourth foil rolling pass is speed control. The entry tension for the first, second, and third foil rolling passes is greater than or equal to 50 N / mm. 2 The inlet tension of the fourth foil rolling pass is 60 N / mm. 2 The exit tension of the first foil rolling pass, the exit tension of the second foil rolling pass, and the exit tension of the third foil rolling pass are all 35~40 N / mm. 2 The exit tension of the fourth foil rolling pass is 40~45 N / mm. 2 The rolling speed of the first foil rolling pass is less than or equal to 800 m / min, the rolling speed of the second and third foil rolling passes is less than or equal to 900 m / min, and the rolling speed of the fourth foil rolling pass is 850 ± 25 m / min.

[0008] Preferably, in step S5, the rolling thickness of the four foil rolling passes is as follows: 0.200~0.220mm → 0.100~0.110mm → 0.040~0.050mm → 0.019~0.022mm → less than or equal to 0.013mm; the rolling force of the first foil rolling pass, the second foil rolling pass, and the third foil rolling pass are all 320±20t, and the rolling force of the fourth foil rolling pass is 280±20t; the sheet shape curve of the foil coil obtained from the first foil rolling pass and the foil coil obtained from the second foil rolling pass are both -5 to -7, the sheet shape curve of the foil coil obtained from the third foil rolling pass is -7 to -8, and the sheet shape curve of the foil coil obtained from the fourth foil rolling pass is -12 to -13.

[0009] Preferably, in step S5, the roughness of the rolls used in the first foil rolling pass and the second foil rolling pass are both 0.15~0.17μm, the roughness of the rolls used in the third foil rolling pass is both 0.11~0.13μm, and the roughness of the rolls used in the fourth foil rolling pass is both 0.09~0.10μm; the convexity of the rolls used in the first foil rolling pass and the second foil rolling pass is both 0.045mm, and the convexity of the rolls used in the third foil rolling pass and the fourth foil rolling pass is both 0.065mm.

[0010] Preferably, in step S5, the rolling oil used for foil rolling has an acid value of 0.1~0.2 mgKOH / g, an alcohol content of 6.0~9.0%, and an ester content of less than or equal to 1.5%.

[0011] Preferably, the oil temperature of the rolling oil used in the first foil rolling pass and the second foil rolling pass is 30±2℃, the oil temperature of the rolling oil used in the third foil rolling pass is 38±2℃, and the oil temperature of the rolling oil used in the fourth foil rolling pass is 42±2℃; the oil pressure of the rolling oil used in the first foil rolling pass, the second foil rolling pass, the third foil rolling pass, and the fourth foil rolling pass is 5~6MPa; and the oil flow rate of the rolling oil used in the first foil rolling pass, the third foil rolling pass, and the fourth foil rolling pass is 50±2%.

[0012] Preferably, in step S1, the components and mass percentages of the raw material formula are: Si=0.40~0.50%, Fe=0.60~0.70%, Cu=0.02~0.04%, Ti≤0.06%, and the balance is Al.

[0013] Preferably, in step S1, the twin-roll continuous casting and rolling method is carried out using a casting and rolling mill; the front box temperature of the casting and rolling mill is 700±2℃, the nozzle opening of the casting and rolling mill is 13±1mm, and the length of the casting and rolling zone of the casting and rolling mill is 55±5mm; when the casting and rolling mill is rolling, the discharge speed of the cast and rolled billet is 780±50mm / min; and the temperature of the coolant used in the casting and rolling mill is 40±2℃.

[0014] Preferably, in step S2, the first cold rolling is performed by two cold rolling passes to obtain the first cold-rolled coil; the rolling thickness of the two cold rolling passes in the first cold rolling is as follows: 6.600~6.800mm → 3.900~4.100mm → 2.300~2.600mm. In step S3, before performing incomplete annealing on the first cold-rolled coil, the step of trimming the first cold-rolled coil is also included. In step S4, the second cold-rolled coil is obtained by five cold-rolling passes; the rolling thickness of the five cold-rolling passes of the second cold rolling is as follows: 2.300~2.600mm → 1.400~1.500mm → 0.800~0.900mm → 0.500~0.600mm → 0.300~0.350mm → 0.200~0.220mm; In step S5, before foil rolling the second cold-rolled coil, the step of trimming the second cold-rolled coil is also included.

[0015] Preferably, in step S3, the temperature used for incomplete annealing is 240±40℃.

[0016] Secondly, embodiments of the present invention provide a high-elongation aluminum foil, which is made by the above-described method for preparing high-elongation aluminum foil; the average size of cracks on the surface of the high-elongation aluminum foil perpendicular to its rolling direction is less than or equal to 25 μm, the volume fraction of crack surface perpendicular to its rolling direction on the surface of the high-elongation aluminum foil is less than or equal to 35%, and the crack depth on the surface of the high-elongation aluminum foil perpendicular to its rolling direction is less than or equal to 1 μm.

[0017] Compared with related technologies, the high-elongation aluminum foil preparation method of the present invention sequentially prepares high-elongation aluminum foil by adopting a twin-roll continuous casting and rolling process, a first cold rolling, incomplete annealing, a second cold rolling, and foil rolling. The control mode, inlet tension, outlet tension, and rolling speed of the four foil rolling passes are limited, so that the tensile strength of the prepared high-elongation aluminum foil is greater than or equal to 220 MPa and the elongation after fracture is greater than or equal to 6.5%, so as to meet the needs of the new development of lithium-ion batteries. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 A flowchart illustrating the steps of a method for preparing high-elongation aluminum foil according to an embodiment of the present invention; Figure 2This is a comparison diagram of the elongation after fracture of the high-elongation aluminum foil prepared by the high-elongation aluminum foil preparation method of the present invention and the high-elongation aluminum foil in the related art; wherein, (a) is the high-elongation aluminum foil prepared by the high-elongation aluminum foil preparation method of the present invention, with an elongation after fracture of 8.2%, and (b) is the high-elongation aluminum foil in the related art, with an elongation after fracture of 3.0%. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 This invention provides a method for preparing high-elongation aluminum foil, combined with... Figure 1 As shown, it includes the following steps: Step S1: Prepare cast-rolled coils with a thickness of 6.600~6.800mm using a twin-roll continuous casting and rolling method based on the raw material formula.

[0021] The raw material formula contains the following components and mass percentages: Si = 0.40~0.50%, Fe = 0.60~0.70%, Cu = 0.02~0.04%, Ti ≤ 0.06%, with the balance being Al.

[0022] The twin-roll continuous casting and rolling process is carried out using a casting and rolling mill. The mill's front box temperature is 700±2℃, the casting nozzle opening is 13±1mm, and the casting zone length is 55±5mm. During rolling, the billet discharge speed is 780±50mm / min. The coolant temperature used in the mill is 40±2℃. By defining these casting and rolling parameters, the cooling intensity of the cast coil can be improved, preventing high alloying levels that could lead to center segregation.

[0023] Step S2: Perform a first cold rolling on the cast-rolled coil to obtain a first cold-rolled coil with a thickness of 2.300~2.600mm.

[0024] The first cold rolling is performed by rolling the first cold-rolled coil through two cold rolling passes; the rolling thickness of the two cold rolling passes in the first cold rolling is as follows: 6.600~6.800mm → 3.900~4.100mm → 2.300~2.600mm.

[0025] Step S3: Perform incomplete annealing on the first cold-rolled coil.

[0026] Before performing incomplete annealing on the first cold-rolled coil, the process further includes the step of trimming the edges of the first cold-rolled coil.

[0027] Incomplete annealing is performed in an annealing furnace at a temperature of 240±40℃. If the temperature in the annealing furnace is too high or too low, the elongation at break of the final high-elongation aluminum foil will decrease.

[0028] Step S4: Perform a second cold rolling on the first cold-rolled coil after incomplete annealing to obtain a second cold-rolled coil with a thickness of 0.200~0.220mm.

[0029] The first and second cold rolling processes are both performed using a cold rolling mill; the second cold rolling is carried out by five cold rolling passes to obtain the second cold-rolled coil; the rolling thickness of the five cold rolling passes in the second cold rolling is as follows: 2.300~2.600mm → 1.400~1.500mm → 0.800~0.900mm → 0.500~0.600mm → 0.300~0.350mm → 0.200~0.220mm.

[0030] Step S5: Perform foil rolling on the second cold-rolled coil to obtain the high-elongation aluminum foil with a thickness of less than or equal to 0.013 mm.

[0031] Before foil rolling the second cold-rolled coil, the process further includes the step of trimming the edges of the second cold-rolled coil.

[0032] The foil rolling is performed by a foil rolling mill; the foil rolling is performed through four foil rolling passes to obtain the high-elongation aluminum foil; the rolling thickness of the four foil rolling passes is as follows: 0.200~0.220mm → 0.100~0.110mm → 0.040~0.050mm → 0.019~0.022mm → less than or equal to 0.013mm.

[0033] The control modes for the first, second, and third foil rolling passes are all tension control, while the control mode for the fourth foil rolling pass is speed control. Limiting the control mode for the fourth foil rolling pass to speed control improves the shape of the obtained high-elongation aluminum foil by reducing parameter fluctuations.

[0034] The inlet tension for the first foil rolling pass, the inlet tension for the second foil rolling pass, and the inlet tension for the third foil rolling pass are all greater than or equal to 50 N / mm. 2 The inlet tension of the fourth foil rolling pass is 60 N / mm. 2 .

[0035] The exit tension for the first foil rolling pass, the second foil rolling pass, and the third foil rolling pass are all 35~40 N / mm. 2 The exit tension of the fourth foil rolling pass is 40~45 N / mm. 2 .

[0036] The rolling speed of the first foil rolling pass is less than or equal to 800 m / min, the rolling speed of the second foil rolling pass and the rolling speed of the third foil rolling pass are both less than or equal to 900 m / min, and the rolling speed of the fourth foil rolling pass is 850 ± 25 m / min.

[0037] By controlling the inlet tension, outlet tension, and rolling speed of the foil, the obtained high-elongation aluminum foil can reach a critical lubrication state, thereby reducing cracks on its surface perpendicular to its rolling direction and improving the elongation at break of the high-elongation aluminum foil.

[0038] The rolling force for the first foil rolling pass, the second foil rolling pass, and the third foil rolling pass are all 320±20t, and the rolling force for the fourth foil rolling pass is 280±20t.

[0039] The sheet shape curves of the foil coils obtained from the first foil rolling pass and the second foil rolling pass are both -5 to -7. The sheet shape curves of the foil coils obtained from the third foil rolling pass are -7 to -8. The sheet shape curves of the foil coils obtained from the fourth foil rolling pass are -12 to -13.

[0040] The surface roughness of the rolls used in the first and second foil rolling passes is 0.15–0.17 μm, the surface roughness of the rolls used in the third pass is 0.11–0.13 μm, and the surface roughness of the rolls used in the fourth pass is 0.09–0.10 μm. The roll roughness needs to be adapted to the rolling speed. At the same speed, a lower roll roughness can reduce surface cracks perpendicular to the rolling direction on the resulting high-elongation aluminum foil, thereby improving the elongation at break of the high-elongation aluminum foil.

[0041] The convexity of the rolls used in the first foil rolling pass and the second foil rolling pass is 0.045 mm. The convexity of the rolls used in the third foil rolling pass and the fourth foil rolling pass is 0.065 mm.

[0042] The rolling oil used in foil rolling has an acid value of 0.1~0.2 mgKOH / g, an alcohol content of 6.0~9.0%, and an ester content of less than or equal to 1.5%.

[0043] The rolling oil temperature used in the first foil rolling pass and the second foil rolling pass is 30±2℃, the rolling oil temperature used in the third foil rolling pass is 38±2℃, and the rolling oil temperature used in the fourth foil rolling pass is 42±2℃.

[0044] The oil pressure of the rolling oil used in the first foil rolling pass, the second foil rolling pass, the third foil rolling pass, and the fourth foil rolling pass is all 5~6MPa.

[0045] The oil flow rate of the rolling oil used in the first foil rolling pass, the third foil rolling pass, and the fourth foil rolling pass is 50±2%.

[0046] To better understand the limiting parameters for the four foil rolling passes in this embodiment, the following will be defined using Tables 1 and 2: Table 1. Partial Limiting Parameters for Four Foil Rolling Passes in Foil Rolling

[0047] Table 1 contains the control modes, entry tension, rolling speed, and rolling force for the four foil rolling passes.

[0048] Table 2. Additional Limiting Parameters for Four Foil Rolling Passes

[0049] Table 2 includes the plate shape curves of the four foil rolling passes, the oil temperature of the rolling oil, the roughness of the rolls, the crown of the rolls, the oil pressure of the rolling oil, the oil flow rate of the rolling oil, the acid value of the rolling oil, the alcohol content of the rolling oil, and the grease content of the rolling oil.

[0050] The following are examples illustrating certain technical characteristics: Si=0.491%, Fe=0.680%, Cu=0.024%, Ti=0.019%, with the balance being Al; the limiting parameters for the first and second cold rolling passes are shown in Table 3 below. The thickness of the first cold-rolled coil obtained from the second cold rolling is 0.22mm, the tensile strength is 218MPa, and the elongation after fracture is 4%; the limitation of the incomplete annealing process is that the temperature in the annealing furnace needs to be raised to 240℃ in about 1 hour, and after reaching 240℃, it is held for 18.5 hours. During the 18.5 hours of holding, the first cold-rolled coil is limited to being raised to 240℃ in about 16 hours, and then held at 240℃ for about 2.5 hours. Finally, the first cold-rolled coil is removed from the annealing furnace and air-cooled, which is done by cooling the first cold-rolled coil with air as the medium.

[0051] Table 1. Limiting parameters for the first and second cold rolling passes.

[0052] Among them, processing passes 1 and 2 are the processing passes for the first cold rolling, and processing passes 3 to 7 are the processing passes for the second cold rolling.

[0053] Based on the limitations illustrated above and the high-elongation aluminum foil prepared according to the method described in this embodiment, the high-elongation aluminum foil has a tensile strength of 225 MPa and an elongation after fracture of 8.2%. Figure 2 As shown in Figure (a), this allows it to meet the evolving needs of lithium-ion batteries.

[0054] Compared with related technologies, the high-elongation aluminum foil preparation method in this embodiment sequentially employs a twin-roll continuous casting and rolling process, a first cold rolling, incomplete annealing, a second cold rolling, and foil rolling to prepare high-elongation aluminum foil. The control mode, inlet tension, outlet tension, and rolling speed of the four foil rolling passes are limited, thereby enabling the prepared high-elongation aluminum foil to have a tensile strength greater than or equal to 220 MPa and an elongation after fracture greater than or equal to 6.5%, so as to meet the needs of the continuous development of lithium-ion batteries.

[0055] Example 2 This invention provides a high-elongation aluminum foil for the preparation of battery current collectors. The high-elongation aluminum foil is prepared using the method described in Example 1.

[0056] Wherein, the average size of the cracks on the surface of the high-elongation aluminum foil perpendicular to its rolling direction is less than or equal to 25 μm, the volume fraction of the crack surface perpendicular to its rolling direction on the surface of the high-elongation aluminum foil is less than or equal to 35%, and the crack depth on the surface of the high-elongation aluminum foil perpendicular to its rolling direction is less than or equal to 1 μm.

[0057] Since the high-elongation aluminum foil in this embodiment is made by the preparation method of the high-elongation aluminum foil in Example 1, it can also achieve the technical effect achieved by the preparation method of the high-elongation aluminum foil in Example 1, which will not be elaborated here.

[0058] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing high-elongation aluminum foil, characterized in that, The method for preparing the high-elongation aluminum foil includes the following steps: Step S1: Prepare cast-rolled coils with a thickness of 6.600~6.800mm using a twin-roll continuous casting and rolling method based on the raw material formula; Step S2: Perform a first cold rolling on the cast-rolled coil to obtain a first cold-rolled coil with a thickness of 2.300~2.600mm; Step S3: Perform incomplete annealing on the first cold-rolled coil; Step S4: Perform a second cold rolling on the first cold-rolled coil after incomplete annealing to obtain a second cold-rolled coil with a thickness of 0.200~0.220mm; Step S5: Perform foil rolling on the second cold-rolled coil to obtain the high-elongation aluminum foil with a thickness less than or equal to 0.013 mm; The high-elongation aluminum foil is obtained by four foil rolling passes. The control modes for the first, second, and third foil rolling passes are tension control, while the control mode for the fourth foil rolling pass is speed control. The entry tension for the first, second, and third foil rolling passes is greater than or equal to 50 N / mm. 2 The inlet tension of the fourth foil rolling pass is 60 N / mm. 2 The exit tension of the first foil rolling pass, the exit tension of the second foil rolling pass, and the exit tension of the third foil rolling pass are all 35~40 N / mm. 2 The exit tension of the fourth foil rolling pass is 40~45 N / mm. 2 The rolling speed of the first foil rolling pass is less than or equal to 800 m / min, the rolling speed of the second foil rolling pass and the rolling speed of the third foil rolling pass are both less than or equal to 900 m / min, and the rolling speed of the fourth foil rolling pass is 850 ± 25 m / min. In step S5, the rolling thickness of the four foil rolling passes is as follows: 0.200~0.220mm → 0.100~0.110mm → 0.040~0.050mm → 0.019~0.022mm → less than or equal to 0.013mm; the rolling force of the first foil rolling pass, the second foil rolling pass, and the third foil rolling pass are all 320±20t, and the rolling force of the fourth foil rolling pass is 280±20t; the sheet shape curve of the foil coil obtained from the first foil rolling pass and the foil coil obtained from the second foil rolling pass are both -5 to -7, the sheet shape curve of the foil coil obtained from the third foil rolling pass is -7 to -8, and the sheet shape curve of the foil coil obtained from the fourth foil rolling pass is -12 to -13; In step S5, the roughness of the rolls used in the first foil rolling pass and the second foil rolling pass are both 0.15~0.17μm, the roughness of the rolls used in the third foil rolling pass is both 0.11~0.13μm, and the roughness of the rolls used in the fourth foil rolling pass is both 0.09~0.10μm; the convexity of the rolls used in the first foil rolling pass and the second foil rolling pass is both 0.045mm, and the convexity of the rolls used in the third foil rolling pass and the fourth foil rolling pass is both 0.065mm.

2. The method for preparing high-elongation aluminum foil as described in claim 1, characterized in that, In step S5, the rolling oil used for foil rolling has an acid value of 0.1~0.2 mgKOH / g, an alcohol content of 6.0~9.0%, and an ester content of less than or equal to 1.5%.

3. The method for preparing high-elongation aluminum foil as described in claim 2, characterized in that, The oil temperature of the rolling oil used in the first foil rolling pass and the second foil rolling pass is 30±2℃, the oil temperature of the rolling oil used in the third foil rolling pass is 38±2℃, and the oil temperature of the rolling oil used in the fourth foil rolling pass is 42±2℃; the oil pressure of the rolling oil used in the first foil rolling pass, the second foil rolling pass, the third foil rolling pass, and the fourth foil rolling pass is 5~6MPa.

4. The method for preparing high-elongation aluminum foil as described in claim 1, characterized in that, In step S1, the components and mass percentages of the raw material formula are: Si = 0.40~0.50%, Fe = 0.60~0.70%, Cu = 0.02~0.04%, Ti ≤ 0.06%, and the balance is Al.

5. The method for preparing high-elongation aluminum foil as described in claim 1, characterized in that, In step S1, the twin-roll continuous casting and rolling method is carried out using a casting and rolling mill; the temperature of the front box of the casting and rolling mill is 700±2℃, the opening degree of the casting nozzle of the casting and rolling mill is 13±1mm, and the length of the casting and rolling zone of the casting and rolling mill is 55±5mm; when the casting and rolling mill is rolling, the discharge speed of the cast and rolled billet is 780±50mm / min; and the temperature of the coolant used in the casting and rolling mill is 40±2℃.

6. The method for preparing high-elongation aluminum foil as described in claim 1, characterized in that, In step S2, the first cold rolling is performed by rolling the first cold-rolled coil through two cold rolling passes; the rolling thickness of the two cold rolling passes in the first cold rolling is as follows: 6.600~6.800mm → 3.900~4.100mm → 2.300~2.600mm. In step S3, before performing incomplete annealing on the first cold-rolled coil, the step of trimming the first cold-rolled coil is also included. In step S4, the second cold-rolled coil is obtained by five cold-rolling passes; the rolling thickness of the five cold-rolling passes of the second cold rolling is as follows: 2.300~2.600mm → 1.400~1.500mm → 0.800~0.900mm → 0.500~0.600mm → 0.300~0.350mm → 0.200~0.220mm. In step S5, before foil rolling the second cold-rolled coil, the step of trimming the second cold-rolled coil is also included.

7. The method for preparing high-elongation aluminum foil as described in claim 1, characterized in that, In step S3, the temperature used for incomplete annealing is 240±40℃.

8. A high-elongation aluminum foil, characterized in that, The high-elongation aluminum foil is made by the preparation method of the high-elongation aluminum foil according to any one of claims 1 to 7; the average size of the cracks on the surface of the high-elongation aluminum foil perpendicular to its rolling direction is less than or equal to 25 μm, the volume fraction of the crack surface perpendicular to its rolling direction on the surface of the high-elongation aluminum foil is less than or equal to 35%, and the crack depth on the surface of the high-elongation aluminum foil perpendicular to its rolling direction is less than or equal to 1 μm.

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