A novel ultra-thin copper foil and a method for manufacturing the same

Abstract

The present application relates to the technical field of lithium battery current collector, in particular to a novel extremely thin copper foil and a preparation method thereof, which adopts a mixed copper foil layer, realizes atomic level deposition through pulse electron beam sputtering, can quickly diffuse to form a dense film, and can control the molar ratio of amorphous copper and nanocrystalline copper of the mixed copper foil layer to be 6-6.5:3.5-4, and the thickness of the mixed copper foil layer is 1.8-2.5 μm. The amorphous copper has high strength due to no grain boundary defects, the nanocrystalline copper improves the strength through grain boundary strengthening effect and meanwhile retains certain ductility, realizes the balance of strength and plasticity, makes the elongation rate reach 8%-12% and the tensile strength reach 290-320 MPa, is superior to the traditional 6 μm copper foil, the thickness is reduced by 60%-70%, the copper consumption is significantly reduced, the copper material cost is reduced, the battery volume energy density can be increased by about 3%-5% per 1 μm reduction of the copper foil thickness. The thickness of 1.8-2.5 μm can make the energy density increase by 12%-18%, and meet the high endurance requirement.

Description

Technical Field

[0001] This invention relates to the field of lithium battery current collector technology, specifically to a novel ultrathin copper foil and its preparation method. Background Technology

[0002] Current collectors are the core components in a battery system that carry the active materials of the electrodes and collect current. In lithium-ion batteries, aluminum foil is used as the positive electrode and copper foil as the negative electrode, both traditionally used as current collector materials.

[0003] Traditional negative electrode copper foil has a thickness of 6-12μm in order to maintain good tensile strength and elongation. Although existing technology can reduce the thickness of copper foil to 4.5μm, it is grown layer by layer by electroplating. However, its tensile strength and elongation are weakened to varying degrees. In addition, there are still problems such as high copper consumption and cost, and low volumetric energy density. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide a novel ultrathin copper foil.

[0005] Another objective of this invention is to provide a novel method for preparing ultrathin copper foil, which is simple to operate, easy to control, has high production efficiency, low production cost, and can be used for large-scale production.

[0006] The objective of this invention is achieved through the following technical solution: a novel ultrathin copper foil, comprising a mixed copper foil layer, wherein the mixed copper foil layer comprises amorphous copper and nanocrystalline copper, and the thickness of the mixed copper foil layer is 1.8~2.5μm.

[0007] This invention discloses a novel ultra-thin copper foil, whose hybrid copper foil layer is a mixture of amorphous copper and nanocrystalline copper. Amorphous copper, lacking grain boundary defects, possesses high strength, while nanocrystalline copper enhances strength through grain boundary strengthening effects, while retaining a certain degree of ductility, achieving a balance between strength and plasticity. Amorphous copper serves as the continuous matrix, and nanocrystalline copper as the dispersed phase, suppressing crack propagation through a "soft matrix + hard particles" structure. When the amorphous copper content is 60%-65%, the grain boundary slip of nanocrystalline copper can absorb energy, resulting in an elongation of 8%-12% and a tensile strength of 290-320 MPa, superior to traditional 6μm copper foil, meeting the processing requirements after ultra-thinning. Simultaneously, compared to traditional 6μm copper foil, the thickness is reduced by 60%-70%, significantly decreasing copper usage and lowering copper material costs. For every 1μm reduction in copper foil thickness, the volumetric energy density of the battery can be increased by approximately 3%-5%. A thickness of 1.8-2.5μm can increase energy density by 12%-18%, meeting the demand for long battery life.

[0008] Preferably, in the mixed copper foil layer, the molar ratio of amorphous copper to nanocrystalline copper is 6~6.5:3.5~4. Using this specific ratio of mixed copper foil layer, amorphous copper, lacking grain boundary defects, exhibits high strength, while nanocrystalline copper enhances strength through grain boundary strengthening effects, retaining a certain degree of ductility. The grain boundary slip of nanocrystalline copper can absorb energy, resulting in an elongation of 8%-12% and a tensile strength of 290~320MPa, superior to traditional 6μm copper foil, meeting the processing requirements after ultra-thinning.

[0009] Preferably, the tensile strength of the mixed copper foil layer is 290~320MPa; the elongation of the mixed copper foil layer is 8%~12%.

[0010] Another objective of this invention is achieved through the following technical solution: the above-mentioned method for preparing the novel ultrathin copper foil includes the following steps: (S1) Take a substrate with release agent attached to its surface, use a copper target as the target material, and use pulsed electron beam sputtering to form a mixed copper foil layer on the substrate. The mixed copper foil layer consists of amorphous copper and nanocrystalline copper, and its thickness is 1.8~2.5μm. (S2) Peel the mixed copper foil layer from the substrate to obtain a novel ultrathin copper foil.

[0011] The novel method for preparing ultrathin copper foil of the present invention achieves atomic-level deposition through pulsed electron beam sputtering, which can rapidly diffuse to form a dense film without relying on hot pressing and stretching in the thickness direction, thus avoiding the problem of easy breakage of ultrathin copper foil in traditional rolling processes and breaking through the 4.5μm thickness limit of traditional rolling processes.

[0012] Preferably, in step (S1), the pulsed electron beam sputtering parameters are as follows: vacuum level of 10⁻⁴ to 10⁻⁶ Pa, pulse energy of 0.1 to 2 J / cm², pulse frequency of 1 kHz to 40 kHz, substrate temperature of 100 to 150 °C, target temperature of 25 to 100 °C, bias voltage of -1 kV to -10 kV, and working pulse width of 10 ns to 1000 ns. The electron beam sputtering spot size is a circular spot with a diameter of 1.0 to 4.5 mm. Controlling the vacuum level helps reduce the scattering of sputtered atoms by gas molecules, improving the deposition rate and film purity; controlling the pulse energy at 0.1 to 2 J / cm² promotes amorphous formation and induces nanocrystalline growth; controlling the substrate temperature at 100 to 150 °C promotes atomic surface diffusion, forming a dense film, while avoiding excessively high temperatures that could lead to amorphous crystallization. Setting the above bias voltage and operating pulse width is beneficial for attracting positively charged copper ions to the substrate and accelerating their movement, thereby increasing the deposition rate. At the same time, the negative bias voltage can introduce compressive stress and suppress crack propagation.

[0013] Preferably, the release agent is dimethyl silicone oil or PTFE, and the substrate is a silicon substrate, a copper substrate, or a stainless steel substrate. Using the above-mentioned release agent can reduce the adhesion between the mixed copper foil layer and the substrate, reduce the chemical bonding between the copper foil and the substrate, and achieve non-destructive peeling.

[0014] The beneficial effects of this invention are as follows: The novel ultra-thin copper foil of this invention uses a mixture of amorphous copper and nanocrystalline copper in its hybrid copper foil layer. Amorphous copper has high strength due to the absence of grain boundary defects, while nanocrystalline copper enhances strength through grain boundary strengthening effect, while retaining a certain degree of ductility, achieving a balance between strength and plasticity. Amorphous copper serves as a continuous matrix, and nanocrystalline copper serves as a dispersed phase, suppressing crack propagation through a "soft matrix + hard particles" structure. When the proportion of amorphous copper is 60%-65%, the grain boundary slip of nanocrystalline copper can absorb energy, resulting in an elongation of 8%-12% and a tensile strength of 290-320 MPa, which is superior to traditional 6μm copper foil and meets the processing requirements after ultra-thinning. At the same time, compared with traditional 6μm copper foil, the thickness is reduced by 60%-70%, the amount of copper used is significantly reduced, and the cost of copper materials is lowered. For every 1μm reduction in copper foil thickness, the volumetric energy density of the battery can be increased by about 3%-5%. A thickness of 1.8-2.5μm can increase energy density by 12%-18%, meeting the demand for long battery life.

[0015] The preparation method of the present invention is simple to operate, easy to control, has high production efficiency, low production cost, and can be used for large-scale production. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention; The attached figure is labeled as: 1. Mixed copper foil layer. Detailed Implementation

[0017] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0018] Example 1 like Figure 1 As shown, a novel ultrathin copper foil includes a mixed copper foil layer 1, wherein the mixed copper foil layer 1 comprises amorphous copper and nanocrystalline copper, and the thickness of the mixed copper foil layer is 2.0 μm.

[0019] In the mixed copper foil layer 1, the molar ratio of amorphous copper to nanocrystalline copper is 6.2:3.8.

[0020] The method for preparing the novel ultrathin copper foil includes the following steps: (S1) Take a substrate with release agent attached to its surface, use a copper target as the target material, and use pulsed electron beam sputtering to form a mixed copper foil layer 1 on the substrate. The mixed copper foil layer 1 consists of amorphous copper and nanocrystalline copper, and its thickness is 2.0 μm. (S2) Peel the mixed copper foil layer 1 from the substrate to obtain a novel ultrathin copper foil.

[0021] In step (S1), the operating parameters for pulsed electron beam sputtering are as follows: vacuum degree of 10⁻⁵ Pa, pulse energy of 1 J / cm², pulse frequency of 10 kHz, substrate temperature of 120 °C, target temperature of 50 °C, bias voltage of -5 KV, working pulse width of 100 ns, and electron beam sputtering spot size of a circular spot with a diameter of 2.5 mm.

[0022] The release agent is dimethyl silicone oil, and the substrate is a stainless steel substrate.

[0023] Example 2 A novel ultrathin copper foil includes a mixed copper foil layer, the mixed copper foil layer comprising amorphous copper and nanocrystalline copper, the mixed copper foil layer having a thickness of 1.8 μm.

[0024] In the mixed copper foil layer, the molar ratio of amorphous copper to nanocrystalline copper is 6:4.

[0025] The method for preparing the novel ultrathin copper foil includes the following steps: (S1) Take a substrate with release agent attached to its surface, use a copper target as the target material, and use pulsed electron beam sputtering to form a mixed copper foil layer on the substrate. The mixed copper foil layer consists of amorphous copper and nanocrystalline copper, and its thickness is 1.8 μm. (S2) Peel the mixed copper foil layer from the substrate to obtain a novel ultrathin copper foil.

[0026] In step (S1), the operating parameters for pulsed electron beam sputtering are as follows: vacuum level of 10⁻⁶ Pa, pulse energy of 1.5 J / cm², pulse frequency of 10 kHz, substrate temperature of 150 °C, target temperature of 80 °C, bias voltage of -9 KV, and working pulse width of 800 ns. The electron beam sputtering spot size is a circular spot with a diameter of 2.0 mm.

[0027] The release agent is dimethyl silicone oil, and the substrate is a stainless steel substrate.

[0028] Example 3 A novel ultrathin copper foil includes a mixed copper foil layer, wherein the mixed copper foil layer comprises amorphous copper and nanocrystalline copper, and the thickness of the mixed copper foil layer is 2.3 μm.

[0029] In the mixed copper foil layer, the molar ratio of amorphous copper to nanocrystalline copper is 6.5:3.5.

[0030] The method for preparing the novel ultrathin copper foil includes the following steps: (S1) Take a substrate with release agent attached to its surface, use a copper target as the target material, and use pulsed electron beam sputtering to form a mixed copper foil layer on the substrate. The mixed copper foil layer consists of amorphous copper and nanocrystalline copper, and its thickness is 2.3 μm. (S2) Peel the mixed copper foil layer from the substrate to obtain a novel ultrathin copper foil.

[0031] In step (S1), the operating parameters for pulsed electron beam sputtering are as follows: vacuum degree of 10⁻⁴ Pa, pulse energy of 0.5 J / cm², pulse frequency of 30 kHz, substrate temperature of 100 °C, target temperature of 40 °C, bias voltage of -2 kV, working pulse width of 80 ns, and electron beam sputtering spot size of a circular spot with a diameter of 3.5 mm.

[0032] The release agent is PTFE, and the substrate is a stainless steel substrate.

[0033] Comparative Example 1 A lithium battery negative electrode copper foil, selected from Qian Dingli's 6μm double photoelectrolytic copper foil, with core material 77 and temperature resistance of 200℃.

[0034] Example 4 The copper foils from Examples 1-3 and Comparative Example 1 were used to test their tensile strength, elongation, and energy density of the battery volume, respectively. The test methods are as follows: Tensile strength: According to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test at room temperature", copper foil is cut into standard specimens, both ends of the specimen are clamped in the fixture of the testing machine, and tensile force is applied to the specimen at a constant tensile speed until the specimen breaks. The maximum tensile force at the time of breakage is recorded.

[0035] Elongation: According to GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test at room temperature," during the tensile test in a universal testing machine, the elongation at fracture is measured, and the elongation is calculated based on the original gauge length. The formula for calculating the elongation is: Elongation = [(Gazelle length at fracture - Original gauge length) / Original gauge length] × 100%.

[0036] Battery volume energy density test Battery fabrication: Copper foil is used as the negative electrode current collector, and the battery is assembled according to the conventional ternary lithium battery fabrication process.

[0037] Battery energy: According to the industry standard YD / T 998-1999 "Lithium-ion batteries for mobile communication", the assembled battery is charged and discharged using a battery charge and discharge tester. Data such as the battery's charge and discharge capacity and voltage are recorded. The battery energy is calculated from the capacity and voltage obtained from the charge and discharge test.

[0038] Volume measurement: Use tools such as vernier calipers to measure the length, width, and height of the battery and calculate the battery volume.

[0039] The formula for calculating volumetric energy density is: Volumetric energy density = Battery energy ÷ Battery volume.

[0040] The test results are shown in Table 1 below:

[0041] As shown in Table 1 above, the tensile strength of the novel ultra-thin copper foils prepared in Examples 1-3 is higher than that of the lithium battery negative electrode copper foil in Comparative Example 1. This is attributed to the use of pulsed electron beam sputtering to prepare the novel ultra-thin copper foils. The special structure of amorphous copper and nanocrystalline copper in the mixed copper foil layer, along with the precisely controlled preparation parameters, results in a denser internal structure and finer grains, effectively improving the tensile strength. The elongation of Examples 1-3 is also superior to that of Comparative Example 1. The present invention endows the copper foil with good plastic deformation ability through the mixed structure of amorphous copper and nanocrystalline copper, which can better coordinate deformation under external force, thereby improving the elongation. When the copper foils prepared in Examples 1-3 are applied to batteries, the volumetric energy density of the batteries is significantly higher than that of Comparative Example 1. Because the novel ultra-thin copper foil is thinner, it can provide more space for active materials within the same battery volume, thereby improving the energy density of the battery.

[0042] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A novel ultrathin copper foil, characterized in that: It includes a mixed copper foil layer, the mixed copper foil layer being composed of amorphous copper and nanocrystalline copper, and the thickness of the mixed copper foil layer being 1.8~2.5μm.

2. The novel ultra-thin copper foil according to claim 1, characterized in that: In the mixed copper foil layer, the molar ratio of amorphous copper to nanocrystalline copper is 6~6.5:3.5~4.

3. The novel ultra-thin copper foil according to claim 1, characterized in that: The tensile strength of the mixed copper foil layer is 290~320MPa; the elongation of the mixed copper foil layer is 8%~12%.

4. A method for preparing a novel ultrathin copper foil as described in any one of claims 1-3, characterized in that, Includes the following steps: (S1) Take a substrate with release agent attached to its surface, use a copper target as the target material, and use pulsed electron beam sputtering to form a mixed copper foil layer on the substrate. The mixed copper foil layer consists of amorphous copper and nanocrystalline copper, and its thickness is 1.8~2.5μm. (S2) Peel the mixed copper foil layer from the substrate to obtain a novel ultrathin copper foil.

5. The method for preparing a novel ultrathin copper foil according to claim 4, characterized in that: In step (S1), the operating parameters for pulsed electron beam sputtering are as follows: vacuum level of 10⁻⁴ to 10⁻⁶ Pa, pulse energy of 0.1 to 2 J / cm², pulse frequency of 1K to 40KHz, substrate temperature of 100 to 150℃, target temperature of 25 to 100℃, bias voltage of -1KV to -10KV, and working pulse width of 10ns to 1000ns. The size of the electron beam sputtering spot is a circular spot with a diameter of 1.0 to 4.5 mm.

6. The method for preparing a novel ultrathin copper foil according to claim 4, characterized in that: The release agent is dimethyl silicone oil or PTFE, and the substrate is a silicon substrate, a copper substrate, or a stainless steel substrate.

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