Composite copper foil and preparation method and application thereof

Abstract

The present application relates to a kind of composite copper foil and its preparation method and application, the preparation method of the composite copper foil includes the following steps: (1) using magnetron sputtering is deposited on polymer substrate copper layer, then through liquid phase immersion treatment or gas deposition treatment, self-assembled molecular transition layer is coated on the polymer substrate of deposition copper layer, and composite structure layer is obtained;(2) the composite structure layer obtained in step (1) is sequentially subjected to water electroplating treatment and post-processing, and the composite copper foil is obtained.The present application is modified with chemical molecules having strong binding force with copper as transition layer on the surface of magnetron sputtering metal layer, which enhances the adhesion of magnetron sputtering metal layer and water electroplating layer, and improves the mechanical properties and electrical properties of the composite copper foil by combining the optimization of water electroplating process and formula.

Description

Technical Field

[0001] This invention relates to the field of energy materials technology, specifically to a composite copper foil and its preparation method and application. Background Technology

[0002] In recent years, with the rapid development of electric vehicles and portable rechargeable devices, the demand for and performance requirements of lithium-ion batteries have gradually increased. Anode-free lithium metal batteries have received widespread attention due to their advantages such as high energy density, low cost, and ease of production, and are currently an ideal alternative to lithium-ion batteries. However, copper current collectors account for more than 25% of the total weight of anode-free batteries, significantly reducing energy and power density. Composite copper foil, as a new type of negative electrode current collector for lithium-ion batteries, has significant advantages in terms of low cost, high safety, and lightweight, and is highly effective in reducing production costs and improving battery energy density.

[0003] Typically, composite copper foil has a sandwich structure, with a polymer as the substrate, such as polypropylene, polyethylene terephthalate, or polyimide, and copper layers as conductive layers on both sides prepared using magnetron sputtering, vacuum evaporation, electroless plating, or electroplating processes. However, the interaction forces between the polymer substrate and the copper layer, and between the copper layer and the electroplated layers, are weak, resulting in a high sheet resistance and poor structural stability of the composite current collector, which severely restricts the performance improvement of electrodeless batteries. Therefore, how to enhance the bonding force of each interfacial layer to obtain a stable and efficient composite copper foil is an urgent problem to be solved.

[0004] Sun Hao's team (Adv. Mater. 2024, 36, 2407648) endowed the composite current collector with excellent interfacial stability by controlling the molecular structure of the substrate polyamide urea and utilizing the strong coordination between the NH and C=O groups and the copper layer. In addition, Pan Jun'an's team (Adv. Funct. Mater. 2024, 2310925) enhanced the metal / polymer interfacial strength by introducing a chromium layer into polyethylene terephthalate. These strategies all aim to improve the bonding force between the polymer and the metal layer in a one-step preparation process; however, the one-step method for preparing composite copper foil has high production costs and low efficiency.

[0005] The two-step method combining magnetron sputtering and electroplating offers advantages in terms of high production efficiency and low cost. However, its main problem lies in the poor adhesion between the electroplated layer and the magnetron sputtering or chemical plating substrate. After thickening with electroplating, the coating is prone to breakage or complete detachment. Even if it can bond with the substrate during subsequent processing and battery cycling, the electroplated layer is extremely easy to detach. In addition, the surface of the electroplated layer in traditional processes is too smooth and flat, resulting in extreme unevenness during lithium deposition. This easily leads to the formation of lithium dendrites, resulting in low coulombic efficiency and the potential to puncture the separator, thus shortening battery life. CN115700295A discloses a continuous preparation process for PET composite copper foil rolls, which uses a pulse electroplating strategy to prepare composite copper foil with a thickness of 6.5-7.5 micrometers after magnetron sputtering on the PET surface. Fang Huiming et al. (Electroplating & Finishing, 2024, 43, 25-31) modified the electroplating solution formulation by screening accelerators, inhibitors, and leveling agents for copper electroplating in a sulfate system, achieving copper deposition on both sides of ultrathin organic polymer films with a thickness of 1-2 micrometers. However, the above research only changed the electroplating process and formulation and did not fundamentally enhance the adhesion between the magnetron sputtered layer and the electroplated layer. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a composite copper foil, its preparation method and application, which can enhance the adhesion performance of electroplating and magnetron sputtering substrates, and improve the mechanical and electrical properties of the composite copper foil.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing composite copper foil, the method comprising the following steps:

[0009] (1) A copper layer is deposited on a polymer substrate by magnetron sputtering, and then a self-assembled molecular transition layer is coated on the polymer substrate with the deposited copper layer by liquid phase immersion treatment or vapor phase deposition treatment to obtain a composite structure layer.

[0010] (2) The composite structure layer obtained in step (1) is subjected to electroplating and post-treatment in sequence to obtain the composite copper foil.

[0011] The method for preparing composite copper foil provided by this invention employs a molecular self-assembly strategy. A chemical molecule with strong affinity for metallic copper is modified onto the surface of a magnetron sputtered metal layer as a transition layer, thereby enhancing the adhesion to the electroplated layer. Encapsulating the self-assembled molecular transition layer through liquid-phase immersion or vapor-phase deposition offers advantages such as low cost and suitability for large-area production. The constructed nanoscale molecular transition layer does not increase weight or thickness, and the chemical bonding forces significantly improve the adhesion between the magnetron sputtered layer and the electroplated layer, preventing coating detachment.

[0012] Preferably, the polymer substrate in step (1) comprises PET.

[0013] Preferably, the thickness of the polymer substrate in step (1) is 3-5 μm, for example, it can be 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] Preferably, the copper layer deposition thickness in step (1) is 0.5-1.2 μm, for example, it can be 0.5, 0.6, 0.7, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm or 1.2 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] The copper layer deposition on the polymer substrate described in this invention refers to the deposition of copper layers on both sides of the polymer substrate by magnetron sputtering.

[0016] Preferably, step (1) includes cleaning and drying the polymer substrate with the deposited copper layer before coating the self-assembled molecular transition layer.

[0017] Preferably, the cleaning includes sequential cleaning with dilute hydrochloric acid and cleaning with acetone.

[0018] Preferably, the drying process is performed using high-purity nitrogen gas.

[0019] The term "high-purity nitrogen" refers to nitrogen with a purity of ≥99.99%.

[0020] Preferably, the reagents used in the liquid phase immersion treatment and the vapor phase deposition treatment in step (1) are both organic solutions of copper-loving self-assembling molecules.

[0021] Preferably, the concentration of the calciphilic self-assembly molecules in the organic solution of the calciphilic self-assembly molecules is 2.5-15 mmol / L, for example, it can be 2.5 mmol / L, 4 mmol / L, 5 mmol / L, 8 mmol / L, 10 mmol / L, 12 mmol / L or 15 mmol / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0022] Preferably, the calciphilic self-assembly molecules in the organic solution of the calciphilic self-assembly molecules include any one or a combination of at least two of cyanuric acid, melamine, cyanuric acid, benzotriazole, or 2-mercaptobenzothiazole. Typical but non-limiting combinations include a combination of cyanuric acid and melamine, a combination of cyanuric acid, benzotriazole, and 2-mercaptobenzothiazole, a combination of cyanuric acid, melamine, cyanuric acid, and benzotriazole, or a combination of cyanuric acid, melamine, cyanuric acid, benzotriazole, and 2-mercaptobenzothiazole.

[0023] The copper-affinity self-assembled molecule described in this invention is a conductive molecule that has a binding force with copper metal, which can enhance the adhesion performance of electroplating and magnetron sputtering substrates. The self-assembled molecular transition layer formed has multiple copper-affinity molecular groups, such as S, N, O and other anchoring groups. Moreover, the transition layer is thin and light, uniform and dense, with a size of 5-10 nm, and has good conductivity and a relatively light mass ratio.

[0024] Preferably, the solvent in the organic solution of the copper-loving self-assembling molecule includes any one or a combination of at least two of N-methylpyrrolidone, ethanol, N,N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, or acetone. Typical but non-limiting combinations include the combination of N-methylpyrrolidone and ethanol, the combination of N,N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, and acetone, or the combination of N-methylpyrrolidone, ethanol, N,N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, and acetone.

[0025] The solvent in the organic solution of the basophilic self-assembly molecule can also be other liquids capable of dissolving the basophilic self-assembly molecule.

[0026] Preferably, the specific steps of the liquid phase immersion treatment in step (1) include: immersing the polymer substrate with deposited copper layer in an organic solution of copper-loving self-assembling molecules, and then cleaning it with ethanol and drying it with high-purity nitrogen.

[0027] Preferably, the temperature of the organic solution containing the copper-loving self-assembling molecules is 45-65°C, for example, 45°C, 50°C, 55°C, 60°C or 65°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the soaking time is 3-60 minutes, for example, it can be 3 minutes, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes or 60 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the specific steps of the vapor deposition process in step (1) include: placing a container containing an organic solution of copper-loving self-assembling molecules in an oven, and suspending a polymer substrate with a deposited copper layer on top of the container for vapor deposition.

[0030] Preferably, the temperature of the vapor deposition is 45-120°C and the time is 55-65 min.

[0031] The temperature for vapor deposition is 45-120°C, for example, 45°C, 50°C, 80°C, 100°C or 120°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] The vapor deposition time is 55-65 min, for example, 55 min, 58 min, 60 min, 62 min or 65 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the electrolyte used in the electroplating process in step (2) comprises: 0.02-0.04 mol / L copper sulfate, 0.1-0.4 mol / L sodium hypophosphite, 0.0015-0.005 mol / L nickel sulfate, 0.03-0.07 mol / L trisodium citrate, 0.3-1 mol / L boric acid, and 1-15 g / L polyethylene glycol, with the pH of the electrolyte adjusted to 7-9 using a 4 mol / L sodium hydroxide solution.

[0034] The concentration of copper sulfate in the electrolyte is 0.02-0.04 mol / L, for example, it can be 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.035 mol / L or 0.04 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] The concentration of sodium hypophosphite in the electrolyte is 0.1-0.4 mol / L, for example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.3 mol / L or 0.4 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] The concentration of nickel sulfate in the electrolyte is 0.0015-0.005 mol / L, for example, it can be 0.0015 mol / L, 0.002 mol / L, 0.003 mol / L, 0.004 mol / L or 0.005 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] The concentration of trisodium citrate in the electrolyte is 0.03-0.07 mol / L, for example, it can be 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L or 0.07 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] The concentration of boric acid in the electrolyte is 0.3-1 mol / L, for example, it can be 0.3 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L or 1 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] The concentration of polyethylene glycol in the electrolyte is 1-15 g / L, for example, it can be 1 g / L, 3 g / L, 5 g / L, 8 g / L, 10 g / L, 12 g / L or 15 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] The pH value of the electrolyte is 7-9, for example, it can be 7, 7.5, 8, 8.5 or 9, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] The electrolyte used in the electroplating process can also be a copper pyrophosphate system.

[0042] Preferably, the temperature of the electrolyte used in the electroplating process in step (2) is 60-80℃, for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, in the electroplating process described in step (2), the composite structure layer is used as the working electrode, and a copper sheet of the same area is polished and used as the counter electrode, with an electrode spacing of 2-5 cm.

[0044] The electrode spacing is 2-5cm, for example, it can be 2cm, 2.5cm, 3cm, 4cm or 5cm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] The electroplating process can also be a three-electrode system.

[0046] Preferably, a magnetic stirrer is added during the electroplating process in step (2).

[0047] Preferably, the current density of the electroplating process in step (2) is 1-4 mA / cm². 2 The deposition time is 5-30 minutes.

[0048] The current density of the electroplating process is 1-4 mA / cm². 2 For example, it could be 1mA / cm 2 2.3mA / cm 2 3mA / cm 2 3.5mA / cm 2 or 4mA / cm 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0049] The deposition time for the electroplating process is 5-30 minutes, for example, 5 minutes, 10 minutes, 15 minutes, 20 minutes or 30 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] This invention optimizes the electroplating process and formulation to develop a micro / nano array structure with tunable surface morphology, thereby improving the mechanical and electrical properties of composite copper foil. The prepared electroplated layer consists of a flat substrate layer and a copper-nickel alloy micro / nano array layer. The substrate layer enhances mechanical properties and provides structural support. The copper-nickel alloy micro / nano array layer slows down the formation of lithium dendrites, forming a flat and uniform lithium plating layer during cycling. Furthermore, the mechanical interlocking between the micro / nano cavities and the initially nucleated lithium enhances the affinity of lithium deposition. The micro / nano structure cavities also effectively reduce the stress caused by volume expansion during lithium cycling.

[0051] Preferably, the post-processing in step (2) includes sequential deionized water cleaning, high-purity nitrogen blowing, stamping and forming, and vacuum drying.

[0052] Secondly, the present invention provides a composite copper foil, which is prepared by the method for preparing composite copper foil described in the first aspect.

[0053] The composite copper foil provided by this invention enhances the adhesion between the magnetron sputtered metal layer and the electroplated layer by modifying the surface of the magnetron sputtered metal layer with a self-assembled molecular transition layer, thus preventing the coating from peeling off. At the same time, the self-assembled molecular transition layer is a nanoscale transition layer, which does not cause changes in weight and volume, and the composite copper foil has a low areal density.

[0054] Thirdly, the present invention provides an application of the composite copper foil as described in the second aspect, wherein the composite copper foil is used as an electrode material for lithium-ion batteries and an electronic component material.

[0055] The composite copper foil provided by this invention, when used as a current collector to assemble a half-cell, has a lower interfacial transport impedance. In addition, it has a micro-nano array structure with adjustable surface morphology, which helps to uniformly deposit lithium metal, reduce lithium dendrite formation, and improve battery cycle performance.

[0056] Preferably, when the composite copper foil is used as an electrode material for a lithium-ion battery, the steps for preparing a coin cell include:

[0057] A coin cell is assembled using a composite copper foil as the positive electrode, a lithium metal sheet as the negative electrode, and an ether electrolyte. The resulting half-cell is then encapsulated. Lithium metal is electrodeposited on the surface of the composite copper foil in the half-cell, and the resulting lithium-plated composite copper foil is used as the negative electrode. A ternary nickel-cobalt-manganese electrode or a lithium iron phosphate electrode is used as the positive electrode. The coin cell is then assembled using an ester or ether electrolyte.

[0058] Preferably, during the assembly of the button cell, a 25μm thick polypropylene separator is used to separate the positive and negative electrodes.

[0059] Preferably, the composition of the ether electrolyte includes: 1M LiTFSI, DOL and DME in a volume ratio of 1:1, and 2wt% LiNO3.

[0060] Preferably, the specific steps of electrodepositing lithium metal include: clamping the half-cell in an electrical testing cabinet, and applying 0.5-1.5 mA / cm². 2 Discharge at current density of 0.5-5 mAh / cm² was applied to the surface of the composite copper foil. 2 Lithium metal.

[0061] The current density is 0.5-1.5 mA / cm². 2 For example, it could be 0.5 mA / cm 2 0.8mA / cm 2 1mA / cm 2 1.2mA / cm 2 Or 1.5mA / cm 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0062] The energy density of the electrodeposited lithium metal is 0.5-5 mAh / cm³. 2 For example, it could be 0.5mAh / cm³. 2 1mAh / cm 2 2mAh / cm 2 3mAh / cm 2 or 5mAh / cm 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0063] The lithium-plated composite copper foil obtained after electrodeposition of lithium metal is used as a negative electrode after being washed and dried by DME.

[0064] Preferably, during the assembly of the button cell, a 25μm thick polypropylene separator is used to separate the positive and negative electrodes.

[0065] Preferably, when the composite copper foil is used as an electrode material for a lithium-ion battery, in the step of preparing a soft-pack full battery, copper sheets are used to weld the two sides of the composite copper foil together, and after stamping, it serves as the negative electrode.

[0066] Because the polymer substrate in the middle of the composite copper foil has poor conductivity, copper sheets are usually welded to connect the two sides of the composite copper foil. After preparation, it is stamped and formed, and used as the negative electrode. Ternary nickel-cobalt-manganese electrode or lithium iron phosphate electrode is used as the positive electrode. A suitable basic electrolyte is added to assemble a full cell for testing.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] (1) The method for preparing composite copper foil provided by the present invention adopts a molecular self-assembly strategy, modifying the surface of the magnetron sputtered metal layer with a chemical molecule that has a strong binding force with metallic copper as a transition layer, thereby enhancing the adhesion to the electroplated layer. Encapsulating the self-assembled molecular transition layer through liquid phase immersion treatment or vapor phase deposition treatment has the advantages of low cost and suitability for large-area production; the constructed nanoscale molecular transition layer does not increase weight or thickness, and can significantly improve the adhesion between the magnetron sputtered layer and the electroplated layer by utilizing chemical bond forces, thus avoiding the peeling off of the plating layer.

[0069] (2) By optimizing the electroplating process and formula, this invention develops a micro-nano array structure with adjustable surface morphology, which improves the mechanical and electrical properties of the composite copper foil. Attached Figure Description

[0070] Figure 1 This is an optical image of the polymer substrate surface after a copper layer has been deposited by magnetron sputtering, as provided in Embodiment 1 of the present invention.

[0071] Figure 2 This is an optical image of the magnetron sputtering layer surface coated with trithiocyanate provided in Embodiment 1 of the present invention;

[0072] Figure 3 This is an optical image of the surface of the composite copper foil provided in Embodiment 1 of the present invention;

[0073] Figure 4 This is the Fourier transform infrared spectrum of the magnetron sputtering layer surface coated with trithiocyanate provided in Embodiment 1 of the present invention;

[0074] Figure 5 This is a diagram showing the interface transmission impedance variation of a half-cell provided in Embodiment 1 of the present invention;

[0075] Figure 6 This is a scanning electron microscope cross-sectional image of the composite copper foil after lithium plating provided in Embodiment 1 of the present invention;

[0076] Figure 7 This is a SEM image of the polymer substrate surface after a copper layer has been deposited by magnetron sputtering, as provided in Example 4 of this invention.

[0077] Figure 8 This is a SEM image of the composite copper foil provided in Embodiment 4 of the present invention;

[0078] Figure 9 This is a SEM image of the composite copper foil provided in Embodiment 5 of the present invention;

[0079] Figure 10 This is an optical image of the composite copper foil provided in Comparative Example 1 of the present invention;

[0080] Figure 11 This is a scanning electron microscope cross-sectional image of the composite copper foil after lithium plating provided in Comparative Example 1 of this invention. Detailed Implementation

[0081] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0082] Example 1

[0083] This embodiment provides a composite copper foil, the preparation method of which includes the following steps:

[0084] (1) A 1 μm copper layer was deposited on both sides of a 4 μm thick PET substrate by magnetron sputtering. The substrate was then cleaned with dilute hydrochloric acid, acetone, and high-purity nitrogen. The polymer substrate with the deposited copper layer was then immersed in an ethanol solution of trithiocyanate at 50°C and 5 mmol / L for 5 min. A self-assembled molecular transition layer was then coated on the polymer substrate with the deposited copper layer. After removal, the substrate was cleaned with ethanol and dried with high-purity nitrogen to obtain a composite structure layer.

[0085] (2) The composite structure layer obtained in step (1) is used as the working electrode, and a copper sheet of the same area is polished and used as the counter electrode. The electrode spacing is 3 cm. The temperature of the electrolyte is 75℃. The electrolyte composition includes: 0.03 mol / L copper sulfate, 0.24 mol / L sodium hypophosphite, 0.0024 mol / L nickel sulfate, 0.05 mol / L trisodium citrate, 0.5 mol / L boric acid and 6 g / L polyethylene glycol. The pH of the electrolyte is adjusted to 8 using 4 mol / L sodium hydroxide solution. A magnetic stirrer is added for stirring, and the current density is 2.3 mA / cm². 2 The composite copper foil is subjected to electroplating treatment for 20 minutes, followed by deionized water cleaning, high-purity nitrogen drying, stamping and forming, and vacuum drying to obtain the composite copper foil.

[0086] In this embodiment, the optical image after a copper layer is deposited on the polymer substrate surface by magnetron sputtering is shown below. Figure 1 As shown, the optical pattern of the magnetron sputtered layer after coating the surface with trithiocyanate is as follows. Figure 2 As shown, the optical pattern of the composite copper foil surface is as follows: Figure 3 As shown, the polymer substrate with deposited copper layer turns yellow after being modified with trithiocyanate. After further electroplating, the electroplated layer on the surface does not peel off and the color is relatively uniform.

[0087] The Fourier transform infrared spectrum of the magnetron sputtered layer coated with trithiocyanate is shown below. Figure 4 As shown, at 1440cm -2 The characteristic features of tridentate thio compounds appeared at 1238 cm⁻¹. -2 The characteristic peaks confirm the formation of thiols with covalent metal-sulfur bonds. These characteristic peaks of trithiocyanate combined with copper further illustrate that the self-assembled molecules achieved uniform coating on the magnetron sputtered metal layer.

[0088] The areal density of the composite copper foil was tested to be 4.63 mg / cm³. 2 This indicates that the self-assembled molecular transition layer is a nanoscale transition layer and does not cause changes in weight or volume. The final prepared composite copper foil has a lower areal density compared to an areal density of 8.55 mg / cm³. 2 The commercially available composite copper foil has a reduced areal density of approximately 45.8%.

[0089] Using the composite copper foil as the positive electrode and the lithium metal sheet as the negative electrode, an ether electrolyte with a formulation of 1M LiTFSI, a 1:1 volume ratio of DOL and DME, and 2wt% LiNO3 was employed. A 25μm thick polypropylene separator was used to separate the positive and negative electrodes, resulting in a sandwich-structured 2032 coin cell. The casing was then hydraulically sealed to obtain a half-cell. The interface transport impedance variation is shown in the figure. Figure 5 As shown in the figure, the composite copper foil provided in this embodiment, when used as a current collector to assemble a half-cell, has a lower interface transmission impedance compared to commercially available composite copper foil-assembled half-cells.

[0090] Place the half-cell clamp in the electrical testing cabinet and apply 1.5 mA / cm². 2 The current density for lithium deposition is 2.5 mAh / cm³. 2 After disassembly, the composite copper foil was cleaned and dried using DME, and observed using a scanning electron microscope. The cross-sectional image of the composite copper foil after lithium plating prepared in this embodiment is shown in the following figure. Figure 6 As shown, the magnetron sputtering layer and the electroplated layer are tightly bonded. Furthermore, since the micro-nano cavities of the electroplated layer can mechanically interlock with the initially deposited lithium, the bonding force between the electroplated layer and the lithium deposition layer is strong. In addition, the high specific surface area also inhibits dendrite growth, resulting in dense and uniform deposited lithium.

[0091] Tensile mechanical properties were tested using a tensile testing machine. The results showed that the composite copper foil prepared in this embodiment had a tensile strength that was approximately 45% higher than that of untreated commercial composite copper foil. This was mainly due to the π-π interactions and hydrogen bonds between trithiocyanate molecules, as well as the coordination bonds between the self-assembled molecules and copper. Further testing of the half-cell performance assembled with lithium sheets showed that the composite copper foil prepared in this embodiment could operate stably for over 300 cycles without capacity decay. Using the obtained lithium-plated composite copper foil as the negative electrode and lithium iron phosphate as the positive electrode, a coin cell assembled with these electrodes could operate stably for 500 cycles without capacity decay, which was superior to that of the untreated composite copper foil.

[0092] Example 2

[0093] This embodiment provides a composite copper foil, the preparation method of which includes the following steps:

[0094] (1) A 0.5 μm copper layer was deposited on both sides of a 3 μm thick PET substrate by magnetron sputtering. The substrate was then cleaned with dilute hydrochloric acid, acetone, and high-purity nitrogen. The polymer substrate with the deposited copper layer was then immersed in an acetone solution of melamine at 45°C and 2.5 mmol / L for 60 min. A self-assembled molecular transition layer was then coated on the polymer substrate with the deposited copper layer. After removal, the substrate was cleaned with ethanol and dried with high-purity nitrogen to obtain a composite structure layer.

[0095] (2) The composite structure layer obtained in step (1) is used as the working electrode, and a copper sheet of the same area is polished and used as the counter electrode. The electrode spacing is 2 cm. The temperature of the electrolyte is 60℃. The electrolyte composition includes: 0.02 mol / L copper sulfate, 0.1 mol / L sodium hypophosphite, 0.0015 mol / L nickel sulfate, 0.03 mol / L trisodium citrate, 0.3 mol / L boric acid and 1 g / L polyethylene glycol. The pH of the electrolyte is adjusted to 7 using 4 mol / L sodium hydroxide solution. A magnetic stirrer is added and the current density is 1 mA / cm². 2 The composite copper foil is subjected to electroplating treatment for 30 minutes, followed by deionized water cleaning, high-purity nitrogen drying, stamping and forming, and vacuum drying to obtain the composite copper foil.

[0096] In this embodiment, the polymer substrate with deposited copper layer was coated with a self-assembled molecular transition layer and then further electroplated. Tests showed that the electroplated layer on the surface did not peel off and the color was relatively uniform. Copper sheets were welded to connect the two sides of the composite copper foil, and after stamping, it was used as the negative electrode to prepare a soft-pack full battery. Tests showed that the soft-pack battery using lithium iron phosphate as the positive electrode and using an ether-based electrolyte with the following composition: 1M LiTFSI, DOL / DME = 1:1 v / v%, 2wt% LiNO3, 10wt% FEC, 0.05% PPS, had a capacity retention of 85% after 50 cycles.

[0097] Example 3

[0098] This embodiment provides a composite copper foil, the preparation method of which includes the following steps:

[0099] (1) A 1.2 μm copper layer was deposited on both sides of a 5 μm thick PET substrate by magnetron sputtering. The substrate was then cleaned with dilute hydrochloric acid, acetone, and high-purity nitrogen. The polymer substrate with the deposited copper layer was then immersed in a tetrahydrofuran solution of benzotriazole at 65 °C and 15 mmol / L for 3 min. A self-assembled molecular transition layer was then coated on the polymer substrate with the deposited copper layer. After removal, the substrate was cleaned with ethanol and dried with high-purity nitrogen to obtain a composite structure layer.

[0100] (2) The composite structure layer obtained in step (1) is used as the working electrode, and a copper sheet of the same area is polished and used as the counter electrode. The electrode spacing is 5 cm. The temperature of the electrolyte is 80℃. The electrolyte composition includes: 0.04 mol / L copper sulfate, 0.4 mol / L sodium hypophosphite, 0.005 mol / L nickel sulfate, 0.07 mol / L trisodium citrate, 1 mol / L boric acid and 15 g / L polyethylene glycol. The pH of the electrolyte is adjusted to 9 using 4 mol / L sodium hydroxide solution. A magnetic stirrer is added and the current density is 4 mA / cm. 2 The copper foil is subjected to electroplating treatment for 5 minutes, followed by deionized water cleaning, high-purity nitrogen drying, stamping and forming, and vacuum drying to obtain the composite copper foil.

[0101] In this embodiment, the polymer substrate with deposited copper layer was coated with a self-assembled molecular transition layer and then subjected to electroplating. Tests showed that the electroplated layer on the surface did not peel off and the color was relatively uniform. Tests also showed that the lithium-ion half-cell assembled with the lithium-ion foil could run stably for 250 cycles, which was better than commercial composite copper foil without any treatment.

[0102] Example 4

[0103] This embodiment provides a composite copper foil. The difference between the preparation method of the composite copper foil and that of Embodiment 1 is that in step (1), a container containing an ethanol solution of 5 mmol / L trithiocyanate is placed in an oven, and the polymer substrate of the deposited copper layer is suspended on top of the container for vapor deposition at a temperature of 50°C for 60 min. The rest is the same as in Embodiment 1.

[0104] In this embodiment, the SEM image of the polymer substrate surface after magnetron sputtering deposition of a copper layer is shown below. Figure 7 As shown in the figure, its surface is too smooth, which easily leads to dendrite growth during lithium deposition. The SEM image of the composite copper foil obtained in this embodiment is shown below. Figure 8As shown in the figure, the surface of the composite copper foil is a copper-nickel alloy micro-nano array structure, which can reduce the lithium nucleation overpotential and local current density in lithium battery applications, and has a significant effect on improving the reversibility and kinetics of the lithium metal deposition-stripping process.

[0105] In this embodiment, the polymer substrate with deposited copper layer was coated with a self-assembled molecular transition layer and then subjected to electroplating. Tests showed that the electroplated layer on the surface did not peel off and the color was relatively uniform. Tests also showed that its electrochemical performance was almost identical to that of the product prepared by liquid-phase coating of trithiocyanate, both of which could run stably for more than 300 cycles, and its impedance was much lower than that of untreated commercial copper foil.

[0106] Example 5

[0107] This embodiment provides a composite copper foil. The difference between the preparation method of the composite copper foil and that of Embodiment 1 is that the electrolyte in step (2) does not contain nickel sulfate, while the rest are the same as in Embodiment 1.

[0108] The SEM image of the composite copper foil obtained in this embodiment is as follows: Figure 9 As shown in the figure, the surface of the composite copper foil has a micro-nano protrusion structure, which greatly improves the smoothness of the polymer substrate surface after magnetron sputtering deposited copper layer.

[0109] In this embodiment, the polymer substrate with deposited copper layer was coated with a self-assembled molecular transition layer and then subjected to electroplating. Tests showed that the electroplated layer did not peel off and the color was relatively uniform. Tests also showed that the battery could run stably for 220 cycles during half-cell cycling. This indicates that, compared with electroplating using an electrolyte containing nickel sulfate, the surface morphology of the electroplated layer did not form an array structure, resulting in a slight decrease in battery performance.

[0110] Example 6

[0111] This embodiment provides a composite copper foil. The difference between the preparation method of the composite copper foil and that of Embodiment 1 is that the current density of the electroplating process in step (2) is adjusted to 0.5 mA / cm². 2 Except for the above, everything else is the same as in Example 1.

[0112] In this embodiment, the polymer substrate with deposited copper layer is coated with a self-assembled molecular transition layer and then subjected to electroplating. Tests show that the surface electroplated layer cannot grow into a coarse array structure, but rather a particle film. Tests show that the lithium-ion assembled half-cell can run stably for 200 cycles. This indicates that the current density of the electroplating treatment is too low, which is not conducive to the formation of a surface array structure and results in a decrease in the performance of the battery.

[0113] Example 7

[0114] This embodiment provides a composite copper foil. The difference between the preparation method of the composite copper foil and that of Embodiment 1 is that the current density of the electroplating process in step (2) is adjusted to 4.5 mA / cm². 2 Except for the above, everything else is the same as in Example 1.

[0115] In this embodiment, the polymer substrate with deposited copper layer was coated with a self-assembled molecular transition layer and then subjected to electroplating. Tests showed that the surface electroplated layer was relatively coarse and the array structure was very sparse, with many areas not having grown an array structure. Tests showed that it could run stably for 200 cycles in a lithium half-cell, indicating that the current density of the electroplating process was too high, which was not conducive to the formation of the surface array structure and resulted in a decrease in the performance of the battery.

[0116] Comparative Example 1

[0117] This comparative example provides a composite copper foil. The difference between the preparation method of the composite copper foil and that of Example 1 is that the polymer substrate on which the copper layer is deposited in step (1) is not covered with a self-assembled molecular transition layer, and is directly used as a working electrode for electroplating. The rest is the same as that of Example 1.

[0118] The optical pattern of the composite copper foil obtained in this comparative example is as follows: Figure 10 As shown in the figure, the electroplating layer has poor adhesion, exhibiting either overall detachment or localized breakage. (1.5 mA / cm) 2 The current density for lithium deposition on a polymer substrate with only a magnetron sputtered copper layer is 2.5 mAh / cm². 2 After disassembly, the composite copper foil was cleaned and dried using DME, and observed using a scanning electron microscope (SEM). The SEM cross-sectional image of the lithium-plated composite copper foil provided in this comparative example is shown below. Figure 11 As shown, the lithium layer is relatively easy to detach from the substrate. Tests revealed that the lithium layer began to degrade after approximately 150 cycles in a half-cell containing the lithium sheet.

[0119] In summary, the method for preparing composite copper foil provided by this invention employs a molecular self-assembly strategy. A chemical molecule with strong affinity for metallic copper is modified onto the surface of a magnetron sputtered metal layer as a transition layer, thereby enhancing the adhesion to the electroplated layer. Encapsulating the self-assembled molecular transition layer through liquid-phase immersion or vapor-phase deposition offers advantages such as low cost and suitability for large-area production. The constructed nanoscale molecular transition layer does not increase weight or thickness, and the chemical bonding forces significantly improve the adhesion between the magnetron sputtered layer and the electroplated layer, preventing coating detachment.

[0120] This invention develops a micro-nano array structure with adjustable surface morphology through optimization of electroplating process and formula, thereby improving the mechanical and electrical properties of composite copper foil.

[0121] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing composite copper foil, characterized in that, The preparation method includes the following steps: (1) A copper layer is deposited on a polymer substrate by magnetron sputtering, and then a self-assembled molecular transition layer is coated on the polymer substrate with the deposited copper layer by liquid phase immersion treatment or vapor phase deposition treatment to obtain a composite structure layer. (2) The composite structure layer obtained in step (1) is subjected to electroplating and post-treatment in sequence to obtain the composite copper foil; The reagents used in step (1) for liquid phase immersion treatment and vapor phase deposition treatment are both organic solutions of copper-loving self-assembling molecules; The chalcophilic self-assembly molecules in the organic solution of the chalcophilic self-assembly molecules include any one or a combination of at least two of the following: cyanuric acid, benzotriazole, or 2-mercaptobenzothiazole. The electrolyte used in step (2) for electroplating comprises: 0.02-0.04 mol / L copper sulfate, 0.1-0.4 mol / L sodium hypophosphite, 0.0015-0.005 mol / L nickel sulfate, 0.03-0.07 mol / L trisodium citrate, 0.3-1 mol / L boric acid, and 1-15 g / L polyethylene glycol. The pH of the electrolyte is adjusted to 7-9 using a 4 mol / L sodium hydroxide solution. The temperature of the electrolyte used in the electroplating process in step (2) is 60-80℃; In step (2), the composite structure layer is used as the working electrode and a copper sheet of the same area is used as the counter electrode in the electroplating process. The electrode spacing is 2-5 cm. The current density of the electroplating process in step (2) is 1-4 mA / cm². 2 The deposition time is 5-30 minutes.

2. The preparation method according to claim 1, characterized in that, The polymer substrate in step (1) includes PET.

3. The preparation method according to claim 1, characterized in that, The thickness of the polymer substrate in step (1) is 3-5 μm.

4. The preparation method according to claim 1, characterized in that, The thickness of the copper layer in step (1) is 0.5-1.2 μm.

5. The preparation method according to claim 1, characterized in that, Step (1) includes cleaning and drying the polymer substrate with the deposited copper layer before the coating of the self-assembled molecular transition layer.

6. The preparation method according to claim 5, characterized in that, The cleaning process includes sequential cleaning with dilute hydrochloric acid and cleaning with acetone.

7. The preparation method according to claim 5, characterized in that, The drying process involves using high-purity nitrogen gas.

8. The preparation method according to claim 1, characterized in that, The concentration of the chalcophilic self-assembly molecules in the organic solution is 2.5-15 mmol / L.

9. The preparation method according to claim 1, characterized in that, The solvent in the organic solution of the copper-loving self-assembling molecule includes any one or a combination of at least two of N-methylpyrrolidone, ethanol, N,N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, or acetone.

10. The preparation method according to claim 5, characterized in that, The specific steps of the liquid phase immersion treatment in step (1) include: immersing the polymer substrate with deposited copper layer in an organic solution of copper-loving self-assembling molecules, and then cleaning it with ethanol and drying it with high-purity nitrogen.

11. The preparation method according to claim 10, characterized in that, The temperature of the organic solution containing the copper-loving self-assembling molecules is 45-65℃.

12. The preparation method according to claim 10, characterized in that, The soaking time is 3-60 minutes.

13. The preparation method according to claim 1, characterized in that, The specific steps of the vapor deposition process in step (1) include: placing a container containing an organic solution of copper-loving self-assembled molecules in an oven, and suspending a polymer substrate with a deposited copper layer on top of the container for vapor deposition.

14. The preparation method according to claim 13, characterized in that, The vapor deposition temperature is 45-120℃ and the time is 55-65 min.

15. The preparation method according to claim 1, characterized in that, In step (2), a magnetic stirrer is added during the electroplating process.

16. The preparation method according to claim 1, characterized in that, The post-processing in step (2) includes sequential deionized water cleaning, high-purity nitrogen blowing, stamping and forming, and vacuum drying.

17. A composite copper foil, characterized in that, The composite copper foil is prepared by the method described in any one of claims 1-16.

18. An application of the composite copper foil as described in claim 17, characterized in that, The composite copper foil is used as an electrode material for lithium-ion batteries and as a material for electronic components.

19. The application according to claim 18, characterized in that, When the composite copper foil is used as an electrode material for lithium-ion batteries, the steps for preparing a coin cell include: A coin cell is assembled using a composite copper foil as the positive electrode, a lithium metal sheet as the negative electrode, and an ether electrolyte. The resulting half-cell is then encapsulated. Lithium metal is electrodeposited on the surface of the composite copper foil in the half-cell, and the resulting lithium-plated composite copper foil is used as the negative electrode. A ternary nickel-cobalt-manganese electrode or a lithium iron phosphate electrode is used as the positive electrode. The coin cell is then assembled using an ester or ether electrolyte.

20. The application according to claim 18, characterized in that, When the composite copper foil is used as an electrode material for lithium-ion batteries, in the step of preparing a soft-pack full battery, copper sheets are welded to connect the two sides of the composite copper foil, and after stamping, it serves as the negative electrode.

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