A bend-resistant extremely thin copper foil and a method for manufacturing the same

Abstract

The present application relates to a kind of bend-resistant ultra-thin copper foil and its preparation method, the copper foil includes core layer, intermediate layer and outer layer;The core layer is fine-grained ultra-thin copper layer, the intermediate layer is coarse-grained ultra-thin copper layer, and the outer layer is passivation layer.The present application improves the bend-resistant performance of copper foil while ensuring high tensile strength by redesigning the crystal structure.

Description

Technical Field

[0001] This invention belongs to the field of electrolytic copper foil technology, and specifically relates to a bend-resistant, ultra-thin copper foil and its preparation method. Background Technology

[0002] The winding process is currently the most efficient method for lithium-ion battery production and is widely used in lithium-ion battery manufacturing practices. Taking square aluminum-cased batteries as an example, the stress at the corners of the wound core is significantly increased, posing a risk of breakage due to localized stress concentration during the cell winding process and battery charging and discharging. The current collector is a crucial mechanical process material in the cell; excellent bending resistance is essential for improving the safety and lifespan of the cell and battery. Conventional lithium-ion battery copper foil is mostly formed through a single electrochemical deposition, resulting in almost identical crystal structures in the thickness direction. Uneven stress on the inner and outer sides of the copper foil, acting as the current collector, poses a risk of breakage leading to cell failure. Furthermore, with increasingly higher energy density requirements downstream, the penetration rate of high-specific-capacity anode materials, represented by silicon-carbon materials, is gradually increasing. Although silicon-carbon anodes have a much higher specific capacity than traditional graphite anodes, their relatively high volume expansion rate poses a significant challenge to battery cycle life and safety. The stress generated on the silicon-carbon anode material during charging and discharging needs to be buffered by the copper foil current collector. Therefore, high-tensile-strength copper foil is an ideal choice for high-capacity silicon-carbon anodes. Conventional copper foil achieves increased tensile strength by reducing grain size through the Hall-Petch effect. However, grain refinement increases the difficulty of dislocation slip, resulting in relatively low elongation and poor bending resistance of the copper foil. Consequently, conventional copper foil with a uniform crystal structure struggles to simultaneously achieve both high tensile strength and excellent bending resistance. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a bend-resistant ultrathin copper foil and its preparation method. By redesigning the crystal structure, the bend resistance of the copper foil is improved while ensuring high tensile strength.

[0004] The present invention provides a bend-resistant ultrathin copper foil, the copper foil comprising a core layer, an intermediate layer and an outer layer; the core layer is a fine-grained ultrathin copper layer, the intermediate layer is a coarse-grained ultrathin copper layer, and the outer layer is a passivation layer.

[0005] Furthermore, the average grain size of the fine-grained ultrathin copper layer is <1.0μm, and the relatively small grain size is used to improve the tensile strength of the copper foil.

[0006] Furthermore, the average grain size of the coarse-grained ultrathin copper layer is >1.0μm, and the coarse grains with relatively large grain size are used to improve the bending resistance of the copper foil.

[0007] Furthermore, the coarse-grained ultrathin copper layer includes a first coarse-grained ultrathin copper layer and a second coarse-grained ultrathin copper layer.

[0008] Furthermore, the thickness ratio of the first coarse-grained ultrathin copper layer, the fine-grained ultrathin copper layer, and the second coarse-grained ultrathin copper layer is 1-2:1-4:1-2.

[0009] This invention also provides a method for preparing a bend-resistant, ultra-thin copper foil, comprising the following steps: S1. A carrier copper foil with a release layer is produced by magnetron sputtering or electrochemical deposition. The carrier copper foil provides a substrate and support for the electrochemical deposition of an extremely thin copper layer. The release layer can prevent the extremely thin copper layer from sticking together with the carrier copper foil due to mutual diffusion. S2. A first coarse-grained ultrathin copper layer is deposited on the surface of a carrier copper foil by electrochemical deposition assisted by additives. S3. A fine-grained ultrathin copper layer is deposited on the surface of the first ultrathin copper layer by electrochemical deposition assisted by additives. S4. A second coarse-grained ultrathin copper layer is deposited on the surface of the fine-grained ultrathin copper layer by electrochemical deposition assisted by additives. S5. The carrier copper foil and the ultra-thin copper layer (including the first coarse-grained ultra-thin copper layer, the fine-grained ultra-thin copper layer and the second coarse-grained ultra-thin copper layer) are peeled off. The carrier copper foil is wound up and reused. The ultra-thin copper layer is washed with water and then subjected to double-sided passivation treatment to obtain a passivation layer. After the passivation treatment, the copper foil is baked to remove the residual moisture on the surface and then collected into a roll to obtain a bend-resistant ultra-thin copper foil.

[0010] Preferably, the additives in steps S2 and S4 include a leveling agent with a concentration of 10-20 mg / L.

[0011] Preferably, the additives in step S3 include a brightener at a concentration of 5-10 mg / L, a positioning agent at a concentration of 10-20 mg / L, and a leveling agent at a concentration of 5-10 mg / L.

[0012] Beneficial effects (1) By redesigning the crystal structure, the present invention improves the bending resistance of copper foil while ensuring high tensile strength.

[0013] (2) The present invention can control the tensile strength and elongation of copper foil within a wide range by adjusting the ratio of coarse and fine grains.

[0014] (3) The symmetrical structure of the present invention can effectively counteract the internal stress of the copper foil and effectively suppress the copper foil warping caused by residual internal stress due to excessively fast electrochemical deposition rate. Attached Figure Description

[0015] Figure 1This is a schematic diagram of the structure of the bend-resistant ultrathin copper foil of the present invention; wherein, L01-coarse-grained ultrathin copper layer, L02-fine-grained ultrathin copper layer, L03-passivation layer.

[0016] Figure 2 This is a schematic diagram of the preparation process of the bend-resistant ultrathin copper foil of the present invention. Detailed Implementation

[0017] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0018] Example 1 This embodiment relates to a method for producing a bend-resistant, ultra-thin copper foil. The specific process is as follows: S1. Deposition of Release Layer on Copper Foil: A release layer with a thickness not exceeding 100 nm is deposited on the smooth surface of the copper foil carrier using physical vapor deposition. The parameters during the release layer deposition process are as follows: Target material: Mo (purity ≥ 99.95%); Working gas: Ar (99.99%); Sputtering power: 25 kW; Working air pressure: 1.0 Pa; Sputtering time: 20 min.

[0019] S2. Additive-assisted deposition of the first coarse-grained ultrathin copper layer: A coarse-grained ultrathin copper layer with a thickness of 1.0 μm is deposited on one side of the carrier copper foil via electrochemical deposition. The process parameters for the electrochemical deposition of the coarse-grained ultrathin copper layer are as follows: Copper ion concentration: 90 g / L; Sulfuric acid concentration: 150 g / L; Leveling agent (collagen) concentration: 10 mg / L; Chloride ion: 20.0 mg / L; Electrolyte temperature: 50℃; Electrolyte flow rate: 10 m³ 3 / h; Current density: 3000 A / m 2 .

[0020] S3. Additive-assisted deposition of a fine-grained ultrathin copper layer: A fine-grained ultrathin copper layer with a thickness of 4.0 μm is deposited on the surface of the first coarse-grained ultrathin copper layer via electrochemical deposition. The process parameters for the electrochemical deposition of the fine-grained ultrathin copper layer are as follows: Copper ion concentration: 100 g / L; Sulfuric acid concentration: 120 g / L; Brightener concentration (SPS): 5 mg / L; Leveling agent (PEG-2000) concentration: 10 mg / L; Leveling agent (collagen) concentration: 5 mg / L; Chloride ion: 20 mg / L; Electrolyte temperature: 50℃; Electrolyte flow rate: 10 m³ 3 / h; Current density: 6000 A / m 2 .

[0021] S4. Additive-assisted deposition of a second coarse-grained ultrathin copper layer: A coarse-grained ultrathin copper layer with a thickness of 1.0 μm is deposited on the surface of the fine-grained ultrathin copper layer by electrochemical deposition. The process parameters for the electrochemical deposition of the coarse-grained ultrathin copper layer are the same as those in S2.

[0022] S5. Ultra-thin copper layer stripping and surface anti-oxidation treatment to form a passivation layer. The process parameters for the anti-oxidation treatment are as follows: Chromium (VI) concentration: 1 g / L; Electrolyte temperature: 30 ℃; Electrolyte flow rate: 5 m 3 / h; Current density: 50 A / m 2 .

[0023] Example 2 The difference between this embodiment and Embodiment 1 lies in the composition and preparation method of the release layer. The Mo-containing release layer deposited by physical vapor deposition is replaced with an electrochemically deposited Ni-Mo alloy release layer, while the process parameters for other steps remain unchanged. The process parameters for the electrochemical deposition of the Ni-Mo alloy are as follows: Ni ion concentration: 10 g / L; Mo ion concentration: 1 g / L; Potassium pyrophosphate concentration: 150 g / L; Electrolyte pH: 10.0; Electrolyte flow rate: 5 m 3 / h; Electrolyte temperature: 40 ℃; Current density: 80 A / m 2+； Electrodeposition: 30s.

[0024] Example 3 The difference between this embodiment and Embodiment 1 is that the thickness ratio of coarse grains to fine grains is adjusted. The copper foil with a total thickness of 6 μm is changed from a coarse grain:fine grain:coarse grain = 1:4:1 structure to a 2:2:2 structure, while the process parameters of other steps remain unchanged.

[0025] Example 4 The difference between this embodiment and Embodiment 1 is that the thickness ratio of coarse grains to fine grains has been adjusted. The structure of the copper foil with a total thickness of 6 μm has been changed from coarse grains:fine grains:coarse grains = 1:4:1 to 1.5:3.0:1.5. The process parameters of other steps remain unchanged.

[0026] Example 5 The difference between this embodiment and Embodiment 1 is that the total thickness of the ultrathin copper foil is reduced from 6.0 μm to 4.0 μm, and the coarse grain: fine grain: coarse grain = 1:4:1 structure is adjusted to a 1:2:1 structure. The process parameters of other steps remain unchanged.

[0027] Example 6 The difference between this embodiment and Embodiment 1 is that the total thickness of the ultrathin copper foil is reduced from 6.0 μm to 4.0 μm, and the structure of coarse grain: fine grain: coarse grain = 1:4:1 is adjusted to 1.3:1.4:1.3. The process parameters of other steps remain unchanged.

[0028] Comparative Example 1 The difference between this comparative example and Example 1 is that an electrolytic foil-making machine was used to produce high-tensile copper foil with uniform crystal structure for performance comparison testing.

[0029] Comparative Example 2 The difference between this comparative example and Example 1 is that an electrolytic foil-making machine was used to produce high-elongation copper foil with uniform crystal structure for performance comparison testing.

[0030] The criteria for judging tensile strength are as follows: Typical tensile strength: 300-400 MPa; Medium tensile strength: 400-500 MPa; High tensile strength: >500 MPa.

[0031] The criteria for judging elongation are as follows: Standard elongation rate: 3%-6%; Medium elongation: 6%-9%; High elongation: >9%.

[0032] The criteria for judging the number of bending cycles are as follows: Low bending resistance: <10 times; Medium bending resistance: 10-20 times; High bending resistance: >20 times.

[0033] Table 1 Performance Tests of Copper Foil Samples Comparison reveals that homogeneous composition high-tensile-strength copper foil exhibits relatively high tensile strength but low elongation and unsatisfactory bending resistance. Homogeneous composition high-elongation copper foil demonstrates excellent bending resistance, but its relatively low tensile strength cannot meet the stress requirements of high-capacity anode materials during charging and discharging. Compared to conventional homogeneous composition electrolytic copper foil, the multilayer copper foil in this example exhibits relatively high tensile strength / elongation and bending resistance; furthermore, with the same total thickness, a higher proportion of coarse grains results in better elongation and bending resistance.

Claims

1. A bend-resistant, ultra-thin copper foil, characterized in that, The copper foil comprises a core layer, an intermediate layer, and an outer layer; the core layer is a fine-grained ultra-thin copper layer, the intermediate layer is a coarse-grained ultra-thin copper layer, and the outer layer is a passivation layer.

2. The bend-resistant ultrathin copper foil according to claim 1, characterized in that, The average grain size of the fine-grained ultrathin copper layer is <1.0 μm.

3. The bend-resistant ultrathin copper foil according to claim 1, characterized in that, The average grain size of the coarse-grained ultrathin copper layer is >1.0 μm.

4. The bend-resistant ultrathin copper foil according to claim 1, characterized in that, The coarse-grained ultrathin copper layer includes a first coarse-grained ultrathin copper layer and a second coarse-grained ultrathin copper layer.

5. The bend-resistant ultrathin copper foil according to claim 4, characterized in that, The thickness ratio of the first coarse-grained ultrathin copper layer, the fine-grained ultrathin copper layer, and the second coarse-grained ultrathin copper layer is 1-2:1-4:1-2.

6. A method for preparing an extremely thin, bend-resistant copper foil, characterized in that, Includes the following steps: S1. Producing carrier copper foil with a release layer by magnetron sputtering or electrochemical deposition; S2. A first coarse-grained ultrathin copper layer is deposited on the surface of a carrier copper foil by electrochemical deposition assisted by additives. S3. A fine-grained ultrathin copper layer is deposited on the surface of the first ultrathin copper layer by electrochemical deposition assisted by additives. S4. A second coarse-grained ultrathin copper layer is deposited on the surface of the fine-grained ultrathin copper layer by electrochemical deposition assisted by additives. S5. The carrier copper foil and the ultra-thin copper layer are peeled off. The carrier copper foil is rolled up and reused. The ultra-thin copper layer is washed with water and then subjected to double-sided passivation treatment to obtain a passivation layer. After the passivation treatment, the copper foil is baked to remove the residual moisture on the surface and then collected into a roll to obtain a bend-resistant ultra-thin copper foil.

7. The preparation method according to claim 6, characterized in that, The additives in steps S2 and S4 include a leveling agent with a concentration of 10-20 mg / L.

8. The preparation method according to claim 6, characterized in that, The additives in step S3 include a brightener at a concentration of 5-10 mg / L, a positioning agent at a concentration of 10-20 mg / L, and a leveling agent at a concentration of 5-10 mg / L.

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