Electrolytic rolled copper foil with high bending resistance and preparation method thereof

Abstract

The invention relates to the technical field of copper foils, and provides a high-bending-resistance electrolytic rolled copper foil and a preparation method thereof. According to the method, the electrolytic copper foil serves as a base material, residual stress is eliminated through first annealing, a grain boundary structure is stabilized, then thinning is conducted through short-process asymmetrical rolling, and finally recrystallization strengthening is conducted through two-stage annealing, so that the electrolytic rolled copper foil is obtained. The preparation method provided by the invention is simple in step, low in cost and high in yield, the bending resistance of the obtained electrolytic rolled copper foil is good, and the advantages of the electrolytic copper foil and the rolled copper foil are combined. The result of the embodiment shows that the prepared bare copper foil with the thickness of 20 microns is bent for 400-460 times, which is 2.5-2.9 times of the bending times of the conventional rolled copper foil at present.

Description

Technical Field

[0001] The present invention relates to the technical field of copper foil, and in particular to an electrolytically rolled copper foil with high bending resistance and a preparation method thereof. Background Art

[0002] Copper foil is a vital material widely used in the electronics industry. Due to its high strength, high conductivity, and good ductility, it is widely used in flexible printed circuit boards (FPCs), new energy batteries, 5G communications equipment, and consumer electronics. Bending resistance is a crucial property of copper foil, especially in flexible electronic products such as foldable phones and wearable devices. Its bending resistance directly determines the reliability and service life of the product under repeated bending conditions. Inadequate bending resistance can lead to circuit breakage or signal degradation.

[0003] Currently, copper foil is categorized as rolled copper foil and electrolytic copper foil based on different production methods. The core production process for rolled copper foil includes smelting and casting, hot rolling to create blanks, multiple cold rolling passes, intermediate annealing, and surface treatment. High-purity copper raw material is smelted and continuously cast into ingots. This ingot is then initially thinned by hot rolling, followed by multiple cold rolling passes combined with annealing to control the grain structure, ultimately resulting in a high-performance foil with micron-level thickness accuracy. Electrolytic copper foil is produced by electrodepositing copper ions from a copper sulfate electrolyte onto the surface of a titanium cathode roller. Under the influence of an electric field, the copper ions are reduced on the titanium substrate to form an initial deposit. As the cathode roller rotates continuously, the copper ions accumulate layer by layer to the target thickness before being peeled off and rolled. Currently, rolled copper foil is the primary copper foil used in flexible electronic devices. However, the production of rolled copper foil requires more than 20 rolling-annealing cycles, with energy consumption accounting for over 40% of the production cost. The complex production process and yield rate are less than 70%, resulting in high costs.

[0004] Compared to rolled copper foil, electrolytic copper foil offers lower manufacturing costs, controllable surface roughness, and better thickness uniformity. However, the grain structure of electrolytic copper foil is typically coarser and anisotropic, resulting in weaker bending resistance. Repeated bending can easily lead to microcracks or even breakage, potentially affecting the long-term reliability of flexible circuits.

[0005] In summary, there is an urgent need to provide a copper foil with a simple preparation method, low cost, and high bending resistance. Summary of the Invention

[0006] In view of this, the present invention provides a highly resistant electrolytic rolled copper foil and a method for preparing the same. The method for preparing the electrolytic rolled copper foil provided by the present invention is simple, low-cost, and has good resistant bending properties, combining the advantages of electrolytic copper foil and rolled copper foil.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] A method for preparing an electrolytically rolled copper foil with high bending resistance comprises the following steps:

[0009] The electrolytic copper foil is subjected to a first annealing, a rolling and a second annealing in sequence to obtain an electrolytic rolled copper foil with high bending resistance; the temperature of the first annealing is 200-250°C; the rolling is asynchronous rolling, and the number of rolling passes is 7-10; the second annealing includes a low-temperature annealing and a medium-temperature annealing performed in sequence; the temperature of the low-temperature annealing is 120-150°C, and the temperature of the medium-temperature annealing is 300-320°C.

[0010] Preferably, the electrolytic copper foil has a width of 50 to 200 mm and a thickness of 50 to 110 μm.

[0011] Preferably, the first annealing time is 40 to 80 minutes.

[0012] Preferably, the roller speed difference of the asynchronous rolling is 5-10%.

[0013] Preferably, the target thickness of the rolling is 6 to 20 μm, and the reduction rate of a single pass of the rolling is 3% to 20%.

[0014] Preferably, the rolling passes are 8 passes.

[0015] Preferably, in the rolling, the first rolling pass has a reduction ratio of 7% to 14%, a rolling force of 18 to 23 kN, and a rolling speed of 10 to 15 m / min;

[0016] The second rolling pass has a reduction rate of 5% to 6%, a rolling force of 18 to 23 kN, and a rolling speed of 10 to 15 m / min;

[0017] The third rolling pass has a reduction rate of 5% to 7%, a rolling force of 18 to 23 kN, and a rolling speed of 10 to 15 m / min;

[0018] The fourth rolling pass has a reduction rate of 7% to 10%, a rolling force of 28 to 32 kN, and a rolling speed of 15 to 17 m / min;

[0019] The fifth rolling pass has a reduction rate of 8% to 12%, a rolling force of 28 to 32 kN, and a rolling speed of 15 to 17 m / min;

[0020] The sixth rolling pass has a reduction rate of 3% to 5%, a rolling force of 33 to 38 kN, and a rolling speed of 16 to 20 m / min;

[0021] The seventh rolling pass has a reduction ratio of 15% to 20%, a rolling force of 33 to 38 kN, and a rolling speed of 16 to 20 m / min;

[0022] The eighth rolling pass has a reduction ratio of 10% to 15%, a rolling force of 33 to 38 kN, and a rolling speed of 16 to 20 m / min.

[0023] Preferably, the low-temperature annealing time is 5 to 10 minutes; the medium-temperature annealing time is 3 to 5 minutes.

[0024] The present invention also provides a highly bend-resistant electrolytically rolled copper foil prepared by the preparation method described in the above scheme, characterized in that the surface layer of the electrolytically rolled copper foil is fine-grained and the core layer is coarse-grained; the grain size of the fine crystals is 3.8 to 4.5 μm, and the grain size of the coarse crystals is 11.4 to 18.8 μm.

[0025] Preferably, the chemical composition of the electrolytically rolled copper foil includes, by mass fraction, Cr≤0.000015%, Pb≤0.00001%, S≤0.00001%, Ni≤0.00001%, and the balance is copper.

[0026] The present invention provides a method for preparing an electrolytically rolled copper foil with high bending resistance, comprising the following steps: sequentially subjecting the electrolytic copper foil to a first annealing, rolling, and a second annealing to obtain the electrolytically rolled copper foil with high bending resistance; the temperature of the first annealing is 200-250°C; the rolling is asynchronous rolling, with 7-10 passes; the second annealing comprises a low-temperature annealing and a medium-temperature annealing performed sequentially; the temperature of the low-temperature annealing is 120-150°C, and the temperature of the medium-temperature annealing is 300-320°C. The present invention uses the electrolytic copper foil as the base material, first eliminating residual stress and stabilizing the grain boundary structure through the first annealing, then thinning the foil through asynchronous rolling in a short process, and finally recrystallizing and strengthening the foil through a two-stage annealing (i.e., the second annealing) to form a gradient structure of fine surface grains and coarse core grains, thereby improving the bending resistance of the copper foil. Compared with the traditional copper foil preparation method, the present invention has the following advantages: the present invention uses electrolytic copper foil as the base material, and can obtain electrolytic rolled copper foil through a short process rolling, which can circumvent the defects of the traditional rolling process with more steps, reduce energy consumption and thickness deviation, and improve the yield; and the present invention combines the high purity of electrolytic copper foil with the dynamic recrystallization effect of rolling processing, which can achieve the compatibility improvement of bending resistance and surface roughness. In summary, the preparation method provided by the present invention has simple steps and low cost, and the obtained electrolytic rolled copper foil has good bending resistance, combining the advantages of electrolytic copper foil and rolled copper foil. The results of the embodiment show that the bare copper foil with a thickness of 20μm prepared by the present invention has a bending number of 400 to 460 times, which is 2.5 to 2.9 times the bending number of conventional rolled copper foil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a morphology image of the electrolytically rolled copper foil prepared in Example 1;

[0028] Figure 2 This is the stress-strain curve of the electrolytically rolled copper foil prepared in Example 1;

[0029] Figure 3 This is an EBSD photograph of the electrolytically rolled copper foil prepared in Example 1, wherein the left side is the orientation distribution map of the electrolytically rolled copper foil, and the right side is the grain boundary distribution map;

[0030] Figure 4 These are the test results of the number of bending times of the electrolytically rolled copper foils prepared in Examples 1 to 3 and the rolled copper foil in Comparative Example 1. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing an electrolytically rolled copper foil with high bending resistance, comprising the following steps:

[0032] The electrolytic copper foil is subjected to a first annealing, a rolling and a second annealing in sequence to obtain an electrolytic rolled copper foil with high bending resistance.

[0033] In the present invention, the electrolytic copper foil specifically refers to a copper foil prepared by electrochemical deposition; the width of the electrolytic copper foil is preferably 50 to 200 mm, specifically 50 mm, 80 mm, 100 mm, 150 mm or 200 mm, and the thickness of the electrolytic copper foil is preferably 50 to 110 μm, specifically 50 μm, 60 μm, 80 μm, 100 μm or 110 μm. The present invention has no special requirements for the source of the electrolytic copper foil, and can be prepared using commercially available electrolytic copper foil or by methods well known to those skilled in the art. Traditional rolled copper foil uses copper ingots as the base material during preparation, and requires more than 20 rolling-annealing cycles. The present invention uses electrolytic copper foil as the rolled base material, does not require multiple complex preparation processes, and greatly reduces the number of rolling passes, thereby reducing production costs and being environmentally friendly.

[0034] The present invention performs a first annealing on the electrolytic copper foil. In the present invention, the first annealing temperature is 200-250°C, specifically 200°C, 220°C, 230°C, 240°C, or 250°C; the first annealing time is preferably 40-80 minutes, specifically 40 minutes, 50 minutes, 60 minutes, 70 minutes, or 80 minutes. The present invention eliminates residual stress in the electrolytic copper foil and stabilizes the grain boundary structure through the first annealing.

[0035] After the first annealing is completed, the present invention rolls the copper foil after the first annealing. In the present invention, the rolling is asynchronous rolling, and the roller speed difference of the asynchronous rolling is preferably 5-10%, specifically 5%, 6%, 8%, or 10%. The roller speed difference specifically refers to the linear speed difference between the upper and lower work rolls. In a specific embodiment of the present invention, the specific roller speeds of the upper and lower work rolls in the asynchronous rolling can be determined according to the rolling speed. Through asynchronous rolling, the present invention can make the deformation of the copper foil more uniform during the rolling process, improve the surface roughness and microstructure of the copper foil, and enhance the surface quality. It also helps to control the grain size and texture within the copper foil, thereby improving the mechanical properties.

[0036] In the present invention, the target thickness of the rolling is preferably 6 to 20 μm, specifically 6 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, and the single-pass reduction rate of the rolling is preferably 3% to 20%, specifically 3%, 5%, 10%, 15% or 20%.

[0037] In the present invention, the number of rolling passes is preferably 7 to 10, more preferably 8; specifically, when the number of rolling passes is 8, the reduction rate of the first rolling pass is preferably 7% to 14%, specifically 7%, 8%, 10%, 12% or 14%, the rolling force is preferably 18 to 23 kN, specifically 18 kN, 20 kN or 22 kN, and the rolling speed is preferably 10 to 15 m / min, specifically 10 m / min, 12 m / min or 15 m / min; the reduction rate of the second rolling pass is preferably 5% to 6%, specifically 5%, 5.5% or 6%, the rolling force is preferably 18 to 23 kN, specifically 20 kN or 22 kN, and the rolling speed is preferably 10 to The rolling reduction rate of the third pass is preferably 5% to 7%, specifically 5%, 6% or 7%, the rolling force is preferably 18 to 23 kN, specifically 20 kN or 22 kN, and the rolling speed is preferably 10 to 15 m / min, specifically 10 m / min, 12 m / min or 15 m / min; the rolling reduction rate of the fourth pass is preferably 7% to 10%, specifically 7%, 8%, 9% or 10%, the rolling force is preferably 28 to 32 kN, specifically 28 kN, 30 kN or 32 kN, and the rolling speed is preferably 15 to 17 m / min, specifically 15 m / min. in, 16m / min or 17m / min; the reduction rate of the fifth rolling pass is preferably 8% to 12%, specifically 8%, 10% or 12%, the rolling force is preferably 28 to 32kN, specifically 28kN, 30kN or 32kN, and the rolling speed is preferably 15 to 17m / min, specifically 15m / min, 16m / min or 17m / min; the reduction rate of the sixth rolling pass is preferably 3% to 5%, specifically 3%, 4% or 5%, the rolling force is preferably 33 to 38kN, specifically 33kN, 35kN or 38kN, and the rolling speed is preferably 16 to 20m / min, specifically 16m / min, 18m / min or 20m / min; the reduction rate of the seventh rolling pass is preferably 15% to 20%, specifically 15%, 16%, 18% or 20%, the rolling force is preferably 33 to 38 kN, specifically 33 kN, 35 kN or 38 kN, and the rolling speed is preferably 16 to 20 m / min, specifically 16 m / min, 18 m / min or 20 m / min; the reduction rate of the eighth rolling pass is preferably 10% to 15%, specifically 10%, 12%, 13% or 15%, the rolling force is preferably 33 to 38 kN, specifically 35 kN or 38 kN, and the rolling speed is preferably 16 to 20 m / min, specifically 16 m / min, 18 m / min or 20 m / min.

[0038] In the present invention, when the number of rolling passes is 7, the eighth rolling pass can be omitted; when the number of rolling passes is 9 or 10, the range of rolling force and rolling speed of the ninth and tenth passes is preferably consistent with that of the eighth pass.

[0039] After rolling is completed, the present invention performs a second annealing on the rolled copper foil. In the present invention, the second annealing includes low-temperature annealing and medium-temperature annealing performed sequentially; the temperature of the low-temperature annealing is 120-150°C, specifically 120°C, 130°C, 140°C or 150°C, and the time of the low-temperature annealing is preferably 5-10 minutes, specifically 5 minutes, 8 minutes or 10 minutes; the temperature of the medium-temperature annealing is 300-320°C, specifically 300°C, 310°C or 320°C, and the time of the medium-temperature annealing is preferably 3-5 minutes, specifically 3 minutes, 4 minutes or 5 minutes. In the second annealing process of the present invention, the work hardening is first released by low-temperature annealing, and then dynamic recrystallization is promoted by medium-temperature annealing to form a gradient structure of fine crystals on the surface and coarse crystals in the core.

[0040] The present invention also provides a highly bend-resistant electrolytically rolled copper foil prepared by the preparation method described in the above scheme, wherein the surface layer of the electrolytically rolled copper foil is fine-grained and the core layer is coarse-grained; the grain size of the fine crystals is preferably 3.8 to 4.5 μm, and the grain size of the coarse crystals is preferably 11.4 to 18.8 μm.

[0041] In the present invention, the chemical composition of the electrolytically rolled copper foil preferably includes, by mass fraction, Cr≤0.000015%, Pb≤0.00001%, S≤0.00001%, Ni≤0.00001%, and the balance is copper.

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] Example 1

[0044] A method for preparing an electrolytically rolled copper foil with high bending resistance, the specific implementation steps are as follows:

[0045] (1) Pretreatment of electrolytic copper foil:

[0046] The electrolytic copper foil with a thickness of 50 μm and a width of 200 mm was annealed at a temperature of 200 ° C for 60 min to eliminate residual stress and stabilize the grain boundary structure.

[0047] (2) Rolling:

[0048] The annealed electrolytic copper foil was rolled from an initial thickness of 50 μm to a target thickness of 20 μm in 8 passes using asynchronous rolling (with a 10% speed difference between the upper and lower work rolls). The specific rolling conditions are as follows:

[0049] The first rolling process: the reduction rate is 14%, the rolling force is 20kN, and the rolling speed is 10m / min;

[0050] The second rolling process: the reduction rate is 5%, the rolling force is 20kN, and the rolling speed is 10m / min;

[0051] The third rolling process: the reduction rate is 7%, the rolling force is 20kN, and the rolling speed is 15m / min;

[0052] The fourth rolling process: the reduction rate is 10%, the rolling force is 30kN, and the rolling speed is 15m / min;

[0053] The fifth rolling process: the reduction rate is 12%, the rolling force is 30kN, and the rolling speed is 15m / min;

[0054] The sixth rolling process: the reduction rate is 3%, the rolling force is 35kN, and the rolling speed is 18m / min;

[0055] The seventh rolling process: the reduction rate is 20%, the rolling force is 35kN, and the rolling speed is 18m / min;

[0056] The eighth rolling process: the reduction rate is 13%, the rolling force is 35 kN, and the rolling speed is 20 m / min.

[0057] (3) Gradient annealing strengthening:

[0058] The rolled copper foil is annealed in two stages: first, low-temperature annealing at 150°C for 5 minutes to release work hardening, and then medium-temperature annealing at 300°C for 3 minutes to promote dynamic recrystallization and form a gradient structure of fine grains on the surface and coarse grains in the core to obtain electrolytically rolled copper foil.

[0059] Example 2

[0060] (1) Pretreatment of electrolytic copper foil:

[0061] The electrolytic copper foil with a thickness of 70 μm and a width of 100 mm was annealed at a temperature of 220°C for 60 min to eliminate residual stress and stabilize the grain boundary structure.

[0062] (2) Rolling:

[0063] The annealed electrolytic copper foil was rolled from an initial thickness of 70 μm to a target thickness of 20 μm in 9 passes using asynchronous rolling (with a 10% speed difference between the upper and lower work rolls). The specific rolling conditions are as follows:

[0064] The first rolling process: the reduction rate is 12%, the rolling force is 18kN, and the rolling speed is 10m / min;

[0065] The second rolling process: the reduction rate is 5%, the rolling force is 22kN, and the rolling speed is 10m / min;

[0066] The third rolling process: the reduction rate is 7%, the rolling force is 20kN, and the rolling speed is 15m / min;

[0067] The fourth rolling process: the reduction rate is 8%, the rolling force is 28kN, and the rolling speed is 15m / min;

[0068] The fifth rolling process: the reduction rate is 10%, the rolling force is 28kN, and the rolling speed is 15m / min;

[0069] The sixth rolling process: the reduction rate is 4%, the rolling force is 38kN, and the rolling speed is 18m / min;

[0070] The seventh rolling process: the reduction rate is 15%, the rolling force is 33kN, and the rolling speed is 18m / min;

[0071] The eighth rolling process: the reduction rate is 15%, the rolling force is 38kN, and the rolling speed is 20m / min.

[0072] (3) Gradient annealing strengthening:

[0073] The rolled copper foil is annealed in two stages: first, low-temperature annealing at 120°C for 10 minutes to release work hardening, and then medium-temperature annealing at 300°C for 5 minutes to promote dynamic recrystallization and form a gradient structure of fine grains on the surface and coarse grains in the core to obtain electrolytically rolled copper foil.

[0074] Example 3

[0075] A method for preparing an electrolytically rolled copper foil with high bending resistance, the specific implementation steps are as follows:

[0076] (1) Pretreatment of electrolytic copper foil:

[0077] The electrolytic copper foil with a thickness of 70 μm and a width of 100 mm was annealed at a temperature of 250°C for 40 min to eliminate residual stress and stabilize the grain boundary structure.

[0078] (2) Rolling:

[0079] The annealed electrolytic copper foil was rolled from an initial thickness of 70 μm to a target thickness of 20 μm in 8 passes using asynchronous rolling (with a 10% speed difference between the upper and lower work rolls). The specific rolling conditions are as follows:

[0080] The first rolling process: the reduction rate is 12%, the rolling force is 22kN, and the rolling speed is 12m / min;

[0081] The second rolling process: the reduction rate is 5%, the rolling force is 22kN, and the rolling speed is 12m / min;

[0082] The third rolling process: the reduction rate is 7%, the rolling force is 22kN, and the rolling speed is 15m / min;

[0083] The fourth rolling process: the reduction rate is 8%, the rolling force is 32kN, and the rolling speed is 17m / min;

[0084] The fifth rolling process: the reduction rate is 12%, the rolling force is 32kN, and the rolling speed is 15m / min;

[0085] The sixth rolling process: the reduction rate is 3%, the rolling force is 33kN, and the rolling speed is 20m / min;

[0086] The seventh rolling process: the reduction rate is 20%, the rolling force is 35kN, and the rolling speed is 20m / min;

[0087] The eighth rolling process: the reduction rate is 13%, the rolling force is 35 kN, and the rolling speed is 20 m / min.

[0088] (3) Gradient annealing strengthening:

[0089] The rolled copper foil is annealed in two stages: first, low-temperature annealing at 120°C for 10 minutes to release work hardening, and then medium-temperature annealing at 310°C for 5 minutes to promote dynamic recrystallization and form a gradient structure of fine grains on the surface and coarse grains in the core to obtain electrolytically rolled copper foil.

[0090] Performance test results:

[0091] 1. Surface morphology

[0092] Figure 1 is a morphology diagram of the electrolytically rolled copper foil prepared in Example 1; Figure 1 It can be seen that the surface of the electrolytically rolled copper foil prepared by the present invention is smooth and has no holes or cracks.

[0093] 2. Tensile properties

[0094] Figure 2 The stress-strain curve of the electrolytically rolled copper foil prepared in Example 1; Figure 2 It can be seen that the final tensile strength of the electrolytically rolled copper foil prepared by the present invention is 318 MPa, and the elongation at break is 1.10%.

[0095] 3. EBSD test

[0096] Figure 3 The EBSD photos of the electrolytically rolled copper foil prepared in Example 1, where the left side is the orientation distribution map of the electrolytically rolled copper foil, and the right side is the grain boundary distribution map. Figure 3 It can be seen that the electrolytically rolled copper foil has a typical deformation structure. The equiaxed crystals are flattened and broken, and ultrafine grains are formed in some areas with an average grain size of 3.9 μm.

[0097] 4. Surface roughness test

[0098] The surface roughness of the original electrolytic copper foil in Example 1 and the electrolytic rolled copper foil obtained after rolling were tested. The results showed that the roughness of the original electrolytic copper foil was 2.84 μm on the matte surface and 0.22 μm on the glossy surface, while the roughness of the electrolytic rolled copper foil was 0.14 μm on the matte surface and 0.12 μm on the glossy surface.

[0099] 5. Bending resistance test

[0100] The electrolytically rolled copper foils prepared in Examples 1 to 3 were tested for their bending resistance. The specific testing method is as follows:

[0101] Cut the copper foil sample to be tested into strips of 12.7×152mm using a mold, clamp the sample in the fixture of the bending tester, and ensure that the axis of the sample is perpendicular to the axis of the bending shaft; set the bending angle to 90° and the force to 500g, start the tester, and start counting. When the sample breaks or shows other damage, the tester automatically stops counting. The counted value is the number of times the copper foil is bent.

[0102] At the same time, the same bending resistance test was carried out on a commercially available rolled copper foil with a thickness of 20 μm as comparative example 1. Figure 4 shown.

[0103] according to Figure 4 It can be seen that the electrolytic rolled copper foil of the present invention can withstand 400 to 460 bending times, while the commercially available rolled copper foil of the same thickness can withstand only 160 bending times. Compared with traditional rolled copper foil, the electrolytic rolled copper foil of the present invention has greatly improved bending resistance.

[0104] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing an electrolytically rolled copper foil with high bending resistance, characterized in that: The following steps are involved: The electrolytic copper foil is subjected to a first annealing, a rolling and a second annealing in sequence to obtain an electrolytic rolled copper foil with high bending resistance; the temperature of the first annealing is 200-250°C; the rolling is asynchronous rolling, and the number of rolling passes is 7-10; the second annealing includes a low-temperature annealing and a medium-temperature annealing performed in sequence; the temperature of the low-temperature annealing is 120-150°C, and the temperature of the medium-temperature annealing is 300-320°C.

2. The preparation method according to claim 1, characterized in that The electrolytic copper foil has a width of 50 to 200 mm and a thickness of 50 to 110 μm.

3. The preparation method according to claim 1, characterized in that The first annealing time is 40 to 80 minutes.

4. The preparation method according to claim 1, characterized in that The roller speed difference of the asynchronous rolling is 5-10%.

5. The preparation method according to claim 1, characterized in that The target thickness of the rolling is 6 to 20 μm, and the reduction rate of a single pass of the rolling is 3% to 20%.

6. The preparation method according to claim 1, characterized in that The number of rolling passes is 8.

7. The preparation method according to claim 6, characterized in that In the rolling, the first rolling pass has a reduction ratio of 7% to 14%, a rolling force of 18 to 23 kN, and a rolling speed of 10 to 15 m / min; The second rolling pass has a reduction rate of 5% to 6%, a rolling force of 18 to 23 kN, and a rolling speed of 10 to 15 m / min; The third rolling pass has a reduction rate of 5% to 7%, a rolling force of 18 to 23 kN, and a rolling speed of 10 to 15 m / min; The fourth rolling pass has a reduction rate of 7% to 10%, a rolling force of 28 to 32 kN, and a rolling speed of 15 to 17 m / min; The fifth rolling pass has a reduction rate of 8% to 12%, a rolling force of 28 to 32 kN, and a rolling speed of 15 to 17 m / min; The sixth rolling pass has a reduction rate of 3% to 5%, a rolling force of 33 to 38 kN, and a rolling speed of 16 to 20 m / min; The seventh rolling pass has a reduction ratio of 15% to 20%, a rolling force of 33 to 38 kN, and a rolling speed of 16 to 20 m / min; The eighth rolling pass has a reduction ratio of 10% to 15%, a rolling force of 33 to 38 kN, and a rolling speed of 16 to 20 m / min.

8. The preparation method according to claim 1, characterized in that The low-temperature annealing time is 5 to 10 minutes; the medium-temperature annealing time is 3 to 5 minutes.

9. The electrolytically rolled copper foil with high bending resistance prepared by the method according to any one of claims 1 to 8, characterized in that: The surface layer of the electrolytically rolled copper foil is fine-crystalline, and the core layer is coarse-crystalline; the grain size of the fine crystals is 3.8 to 4.5 μm, and the grain size of the coarse crystals is 11.4 to 18.8 μm.

10. The electrolytically rolled copper foil with high bending resistance according to claim 9, characterized in that: Calculated by mass fraction, the chemical composition of the electrolytic rolled copper foil includes: Cr≤0.000015%, Pb≤0.00001%, S≤0.00001%, Ni≤0.00001%, and the balance is copper.

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