High-adhesion carbon-coated copper foil, preparation method thereof, negative electrode sheet and battery

Abstract

This invention discloses a high-adhesion carbon-coated copper foil, its preparation method, a negative electrode sheet, and a battery, belonging to the field of lithium-ion battery technology. The carbon-coated copper foil includes a copper foil substrate and a carbon coating layer on its surface. The carbon coating layer is composed of anionic polymer, cationic polymer, SBR, wetting agent, and carbon conductive agent, and is prepared by a two-step pre-coating-crosslinking method. The mass ratio of the total mass of the anionic polymer and SBR to the mass of the carbon conductive agent is 1:1 to 5, and the mass concentration of the cationic polymer solution is 0.5% to 3%. This invention utilizes the aforementioned high-adhesion carbon-coated copper foil, its preparation method, a negative electrode sheet, and a battery. Through anionic-cationic charge crosslinking, a three-dimensional network is constructed within the coating, significantly improving the adhesion strength between the carbon coating layer and the copper foil, exhibiting high peel strength and resistance to electrolyte / water swelling. The carbon-coated copper foil can be used to prepare negative electrode sheets and batteries, especially suitable for lithium-ion battery systems with high adhesion requirements.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a highly adhesive carbon-coated copper foil and its preparation method, a negative electrode sheet, and a battery. Background Technology

[0002] As a core component of the negative electrode current collector in lithium-ion batteries, copper foil's performance directly affects the battery's energy density and cycle life. With the increasing demand for high energy density driving the shift from graphite to silicon-carbon composite materials for negative electrodes, the 100%–300% volume expansion during charge-discharge of silicon-carbon materials poses a more severe challenge to interfacial adhesion. Traditional copper foil, with its smooth surface, struggles to resist the expansion shear force, easily leading to coating peeling. Carbon-coated copper foil, by constructing a composite layer of carbon-containing materials and binders on the copper foil surface, effectively improves surface roughness and has become the mainstream solution.

[0003] Currently, most industrial carbon-coated copper foils use epoxy / acrylic resin systems. While this enhances interfacial forces through physical interlocking, it suffers from three limitations: the interface between the carbon-coated copper foil and the silicon-carbon anode relies solely on weak van der Waals forces, lacking chemical cross-linking and interlocking, leading to easy shedding of the silicon-carbon anode during long cycles; the resin has weak resistance to polar solvents (such as water) (swelling rate >10%), hindering the coating of water-based anode slurries; and curing releases VOCs or leaves residual toxic monomers, contradicting environmental trends. Tests show that when this type of copper foil is paired with a silicon-carbon anode, the peel strength decreases by 60% after 2000 cycles, hindering its application in long-cycle-life batteries and highlighting the bottleneck of the "physical reinforcement" approach.

[0004] Therefore, there is an urgent need for a three-dimensional cross-linkable carbon-coated copper foil manufacturing method to solve the problems of weak interfacial bonding and poor electrolyte tolerance of existing carbon-coated copper foils. Through the synergistic effect of three-dimensional cross-linking inside the carbon coating layer and secondary cross-linking between the carbon coating layer and the negative electrode binder, the interfacial peel strength, solvent resistance and environmental friendliness can be improved simultaneously, and the active control of the current collector interface engineering of lithium-ion batteries can be achieved. Summary of the Invention

[0005] The purpose of this invention is to provide a high-adhesion carbon-coated copper foil and its preparation method, as well as a negative electrode and a battery, to solve the problems of poor resistance to electrolyte / water swelling and low peel strength of existing carbon-coated copper foils.

[0006] This invention provides a highly adhesive carbon-coated copper foil, comprising a copper foil substrate and a carbon coating layer disposed on the surface of the copper foil substrate; The carbon coating layer includes anionic polymers, cationic polymers, SBR, wetting agents, and carbon conductive agents; The ratio of the total mass of the anionic polymer and SBR to the mass of the carbon conductive agent is 1:(1-5). The mass ratio of the anionic polymer to the wetting agent is 1:(0.3-1).

[0007] Preferably, the anionic polymer is one of polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), or sodium alginate; the cationic polymer is one of polydimethyldiallylammonium chloride (PDADMAC), chitosan quaternary ammonium salt, or polyethyleneimine (PEI).

[0008] Preferably, the wetting agent is one or a combination of PVP, PEO, and PVA.

[0009] Preferably, the carbon conductive agent is one or a combination of graphene, carbon nanotubes, conductive carbon black, and Ketjen black.

[0010] A method for preparing a high-adhesion carbon-coated copper foil as described above is provided, comprising the following steps: Step 1: Prepare coating material. First, add wetting agent to water and stir to dissolve to obtain an aqueous solution of wetting agent. Add carbon conductive agent to the aqueous solution of wetting agent and disperse by sand milling to obtain carbon conductive agent dispersion. Prepare anionic polymer adhesive and add it to the carbon conductive agent dispersion to obtain carbon adhesive. Add SBR emulsion to carbon adhesive to obtain carbon slurry. Step 2: Pre-coating, applying carbon paste to copper foil and drying to form a pre-coated carbon layer; Step 3: Crosslinking. Prepare a cationic polymer solution, coat it onto the pre-coated carbon layer, and carry out a crosslinking reaction. A three-dimensional network carbon coating layer is formed through the interaction of anionic and cationic charges, resulting in carbon-coated copper foil.

[0011] Preferably, in step 1, the wetting agent in the aqueous solution accounts for 0.05% to 0.5% of the water by mass; and in the anionic polymer solution, the anionic polymer accounts for 0.5% to 5% of the water by mass.

[0012] Preferably, the drying conditions in step 2 are 60–90°C and the drying time is 30–60 min.

[0013] Preferably, the solid content of the cationic polymer solution in step 3, based on the total mass of the solution, is 0.5% to 3%; the temperature of the crosslinking reaction is 25 to 90°C, preferably 60 to 90°C, and the time is 10 to 60 minutes, preferably 15 to 30 minutes.

[0014] A negative electrode sheet is provided, comprising the aforementioned silicon-carbon negative electrode sheet with high adhesion carbon-coated copper foil.

[0015] A battery is provided, comprising the aforementioned negative electrode sheet, which is a lithium-ion battery.

[0016] The lithium-ion battery, apart from the negative electrode sheet described in this invention, may use materials, battery structures, and components that are known in the industry; for example, the positive electrode may be at least one of lithium iron phosphate or ternary lithium.

[0017] Therefore, the present invention, employing the above-mentioned high-adhesion carbon-coated copper foil and its preparation method, negative electrode sheet, and battery, has the following beneficial effects: (1) High bonding performance is achieved through the synergistic effect of dual cross-linking. First, the internal cross-linking of the carbon coating layer forms a stable three-dimensional network. Second, during battery assembly, the cationic polymer can undergo secondary cross-linking with the CMC and PAA anionic binders in the silicon-carbon material of the negative electrode, thereby strengthening the interface anchoring effect. This solves the problem of negative electrode material loss during charging and discharging.

[0018] (2) The three-dimensional cross-linked network structure greatly restricts the movement of polymer molecular chains, significantly reducing the swelling rate of the carbon coating layer in carbonate electrolytes and aqueous systems. Tests show that after immersing in room temperature electrolyte or water for 24 hours, the swelling rate of the carbon-coated copper foil of this invention is less than 1.5% in electrolyte and less than 3% in water, and the battery capacity retention rate after 300 cycles is ≥70%, which is far superior to traditional copper foil. The excellent solvent resistance ensures the structural integrity of the carbon coating layer during long-term battery cycling and effectively suppresses the growth of interfacial impedance.

[0019] (3) The preparation process adopts conventional coating and drying processes, without the need for additional special equipment. It is directly compatible with existing carbon-coated copper foil production lines, the process parameters are easy to control, the product yield is high, and it is suitable for large-scale industrial production.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 Comparative images of Example 1 and Comparative Examples 1 and 2 after peeling and kneading of the electrode tape in the present invention, which describes a high-adhesion carbon-coated copper foil and its preparation method, as well as the negative electrode sheet and battery. Figure 2 This is a front-side SEM image of the carbon-coated copper foil in Example 1 of the present invention, which describes a highly adhesive carbon-coated copper foil, its preparation method, negative electrode sheet, and battery. Figure 3 This is a side SEM image of the carbon-coated copper foil in Example 1 of the present invention, which describes a high-adhesion carbon-coated copper foil, its preparation method, negative electrode sheet, and battery. Figure 4 The cycling performance curves of lithium-ion batteries prepared in Example 1 and Comparative Example 1 are shown for the high-adhesion carbon-coated copper foil and its preparation method, negative electrode sheet and battery of the present invention. Detailed Implementation

[0022] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0024] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0025] A method for preparing highly adhesive carbon-coated copper foil, using polyethyleneimine as an example of a cationic polymer, includes the following specific steps: Step (1): Add the wetting agent to the water and stir to dissolve it; the wetting agent is any one or a combination of PVP, PEO, and PVA; the mass fraction of the wetting agent in the water is 0.05% to 0.5%.

[0026] Step (2): Add carbon conductive agent to the aqueous solution of wetting agent and disperse by sand milling to obtain carbon conductive agent dispersion. The carbon conductive agent is selected from at least one of graphene, carbon nanotubes, conductive carbon black, Ketjen black or any combination thereof, and is used to improve the conductivity of the coating and reduce the interfacial impedance.

[0027] Step (3): Prepare an anionic polymer solution and add it to the carbon conductive agent dispersion in step (2) to obtain a carbon solution. The anionic polymer is CMC, PAA or sodium alginate, which contains carboxyl groups and can provide negative charge sites. The mass fraction of anionic polymer in the anionic polymer solution is 0.5% to 5% of water. The mass ratio of anionic polymer to wetting agent is 1: (0.3 to 1).

[0028] Step (4): Add SBR emulsion to the carbon slurry in step (3) to obtain carbon slurry. The mass fraction of SBR in water is 0.2% to 2%. The ratio of the total mass of the anionic polymer and SBR to the mass of the carbon conductive agent is 1:1 to 5. This ratio can ensure the balance between the network skeleton and the conductive pathway. Step (5): The carbon paste from step (4) is coated onto the surface of the copper foil substrate using a comma scraper or a micro-gravure coating machine, dried at 60-90°C for 30-60 minutes to remove the solvent and form a pre-coated carbon layer of binder-carbon conductive agent composite network. Step (6): Prepare a cationic polymer solution with a solid content of 0.5% to 3%, ensuring sufficient cross-linking. Coat the solution onto the pre-coated carbon copper foil prepared in step (5), and dry it at 25 to 90°C for 10 to 60 minutes to achieve cross-linking. A three-dimensional network structure is formed through the interaction of anionic and cationic charges, resulting in the carbon-coated copper foil. The cationic polymer is selected from polydiallyl ammonium chloride, chitosan quaternary ammonium salt, or polyethyleneimine, containing amino / quaternary ammonium groups, which can provide positive charge sites.

[0029] Carbon-coated copper foil improves battery cycle performance by enhancing electrode peeling force; at the same time, it has the advantages of low raw material cost, simple and environmentally friendly process, and easy mass production.

[0030] To provide a clearer and more detailed description of the high-adhesion carbon-coated copper foil, its preparation method, negative electrode sheet, and battery provided by the embodiments of the present invention, specific embodiments will be described below.

[0031] Example 1 1g of PEO was added to 500g of water and stirred for 20 minutes until completely dissolved. 12.5g of SP was added to the PEO aqueous solution and dispersed by sand milling for 2 hours to obtain a carbon conductive agent dispersion. 75g of 2% CMC adhesive was prepared and added to the carbon conductive agent dispersion, stirred for 30 minutes to obtain a carbon adhesive. 13g of 48% SBR adhesive was then added and stirred for 30 minutes to obtain a carbon paste. The carbon paste was gravure-coated onto a copper foil substrate and dried at 90℃ for 45 minutes to obtain a pre-coated carbon copper foil with a coating thickness of 1μm. A 0.5% PEI solution was prepared and coated onto the pre-coated carbon copper foil. It was dried at 90℃ for 30 minutes to obtain a carbon-coated copper foil.

[0032] The capacity is 4.5mAh / cm². -2 The 811 ternary cathode sheet, using prepared carbon-coated copper foil, has an areal capacity of 5.4 mAh / cm². -2 A silicon-carbon anode sheet was used. The positive electrode sheet, anode sheet, PP separator, and electrolyte were assembled to obtain the CR2025 coin cell lithium-ion full battery.

[0033] The effect of peeling and kneading the silicon-carbon negative electrode tape in this embodiment is as follows: Figure 1 As shown, the SEM image of the carbon-coated copper foil prepared in this embodiment is as follows. Figure 2 and Figure 3 In this embodiment, the capacity retention rate of the full cell assembled with electrode plates after 300 cycles at 1C is significantly improved, and the cycling performance is as follows: Figure 4 As shown.

[0034] Example 2 Compared with Example 1, the only difference is that the solid content of the PEI solution is 0.2%, while all other operations and parameters are the same as in Example 1.

[0035] Example 3 Compared with Example 1, the only difference is that the solid content of the PEI solution is 1%, while all other operations and parameters are the same as in Example 1.

[0036] Example 4 Compared with Example 1, the only difference is that the solid content of the PEI solution is 1.5%, and all other operations and parameters are the same as in Example 1.

[0037] Example 5 Compared with Example 1, the only difference is that the wetting agent is PVP, and all other operations and parameters are the same as in Example 1.

[0038] Example 6 Compared with Example 1, the only difference is that the wetting agent is PVA, and all other operations and parameters are the same as in Example 1.

[0039] Comparative Example 1 Compared to Example 1, the difference lies in the fact that the copper foil used is ordinary mass-produced copper foil without carbon coating. The silicon-carbon electrode tape prepared using this copper foil exposes the substrate after peeling or kneading. Figure 1 The capacity retention of the assembled full battery after 300 cycles at 1C was significantly lower than that of Example 1, see [link to example]. Figure 4 .

[0040] Comparative Example 2 Compared to Example 1, the difference lies in that the copper foil used is commercially available carbon-coated copper foil. The silicon-carbon electrode tape prepared using this copper foil partially exposes the substrate after peeling or kneading. (See...) Figure 1 .

[0041] Performance testing: The lithium-ion battery negative electrode sheets prepared in Examples 1-6 and Comparative Examples 1 and 2 were tested for peel strength using adhesive tape. The electrode sheets were immersed in electrolyte or water at room temperature (25°C) for 24 h, then dried at 60°C for 5 h, and the swelling rate of the electrode sheets before and after immersion was tested. Electrodes prepared in the above examples and comparative examples were then assembled into full cells, and 1C cycle performance tests were performed. The test results are shown in Table 1.

[0042] Table 1 Test Results Data

[0043] Therefore, this invention employs the aforementioned highly adhesive carbon-coated copper foil and its preparation method, along with a negative electrode and a battery. The three-dimensional cross-linked network structure formed between the binder molecules within the carbon coating layer significantly restricts the movement of polymer molecular chains, substantially reducing the swelling rate of the carbon coating layer in carbonate electrolytes and aqueous systems. Tests show that after immersion in room-temperature electrolyte or water for 24 hours, the swelling rate of the carbon-coated copper foil in the electrolyte is less than 1.5%, and the swelling rate in water is less than 3%. Excellent solvent resistance ensures the structural integrity of the carbon coating layer during long-term battery cycling, effectively suppressing the growth of interfacial impedance. Furthermore, thanks to the secondary cross-linking of the cationic polymer in the carbon coating layer with CMC and PAA-type anionic binders in the silicon-carbon negative electrode material, the assembled battery retains ≥70% of its capacity after 300 cycles, far superior to traditional copper foil.

[0044] The preparation process uses conventional coating and drying procedures, requiring no additional special equipment. It is directly compatible with existing carbon-coated copper foil production lines, the process parameters are easy to control, the product yield is high, and it is suitable for large-scale industrial production.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-adhesion coated copper foil, characterized by, Includes a copper foil substrate and a carbon coating layer disposed on the surface of the copper foil substrate; The carbon coating layer includes anionic polymers, cationic polymers, SBR, wetting agents, and carbon conductive agents; The ratio of the total mass of the anionic polymer and SBR to the mass of the carbon conductive agent is 1:(1-5). The mass ratio of the anionic polymer to the wetting agent is 1:(0.3-1).

2. The high-adhesion coated copper foil according to claim 1, wherein The anionic polymer is one of polyacrylic acid, sodium carboxymethyl cellulose, or sodium alginate; the cationic polymer is one of polydimethyldiallylammonium chloride, chitosan quaternary ammonium salt, or polyethyleneimine.

3. The high adhesion coated copper foil according to claim 1, wherein, The wetting agent is one or a combination of PVP, PEO, and PVA.

4. The high adhesion coated copper foil according to claim 1, wherein, The carbon conductive agent is one or more of graphene, carbon nanotubes, conductive carbon black, and Ketjen black.

5. A method for preparing a high-adhesion carbon-coated copper foil as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Prepare coating material. First, add wetting agent to water and stir to dissolve to obtain an aqueous solution of wetting agent. Add carbon conductive agent to the aqueous solution of wetting agent and disperse by sand milling to obtain carbon conductive agent dispersion. Prepare anionic polymer adhesive and add it to the carbon conductive agent dispersion to obtain carbon adhesive. Add SBR emulsion to carbon adhesive to obtain carbon slurry. Step 2: Pre-coating, applying carbon paste to copper foil and drying to form a pre-coated carbon layer; Step 3: Crosslinking. Prepare a cationic polymer solution, coat it onto the pre-coated carbon layer, and carry out a crosslinking reaction. A three-dimensional network carbon coating layer is formed through the interaction of anionic and cationic charges, resulting in carbon-coated copper foil.

6. The method for preparing a high-adhesion carbon-coated copper foil according to claim 5, characterized in that, In step 1, the wetting agent in the aqueous solution accounts for 0.05% to 0.5% of the water by mass; and in the anionic polymer solution, the anionic polymer accounts for 0.5% to 5% of the water by mass.

7. The method for preparing a high-adhesion carbon-coated copper foil according to claim 5, characterized in that, In step 2, the drying conditions are 60–90°C and the drying time is 30–60 min.

8. The method for preparing a high-adhesion carbon-coated copper foil according to claim 5, characterized in that, The solid content of the cationic polymer solution in step 3, based on the total mass of the solution, is 0.5% to 3%; the temperature of the crosslinking reaction is 25 to 90°C, and the time is 10 to 60 minutes.

9. A negative electrode sheet characterized by comprising: Including the high-adhesion carbon-coated copper foil as described in any one of claims 1-4.

10. A battery, characterized by Includes the negative electrode sheet as described in claim 9.

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