Carbon-coated aluminum foil conductive paste, preparation method, carbon-coated aluminum foil and positive pole piece

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to carbon-coated aluminum foil conductive paste, a preparation method, a carbon-coated aluminum foil and a positive pole piece. The carbon-coated aluminum foil conductive slurry is prepared from a conductive carbon material, a binder, a dispersant, a solvent, a leveling agent and a defoaming agent. The binder is a copolymer binder prepared by carrying out polymerization reaction on a polar monomer, a non-polar monomer and a conductive ion monomer in water under the action of an initiator and a cross-linking agent, through innovation of a bonding system and construction of a multi-dimensional conductive network, the prepared conductive paste is applied to coating of a positive electrode aluminum foil, and a formed carbon layer is high in adhesive force with the aluminum foil, good in conductivity and high in stripping force with a positive electrode active material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a carbon-coated aluminum foil conductive paste, its preparation method, the carbon-coated aluminum foil, and the positive electrode sheet. Background Technology

[0002] Lithium-ion batteries are a new type of green chemical power source. Compared with traditional nickel-cadmium and nickel-metal hydride batteries, they have advantages such as high energy density, wide voltage window, and long lifespan, and are widely used in high-value-added consumer electronics and power battery fields. Current collectors play a crucial role in lithium-ion batteries; they not only carry the active material but also collect the current generated by the battery's active material and output it externally. Therefore, the current collector should have sufficient contact with the active material, and the lower the contact resistance, the better the current conduction. Aluminum foil is a commonly used material for the positive electrode current collector in lithium-ion batteries. However, the poor adhesion between the positive electrode binder PVDF and the aluminum foil surface, and the high contact resistance between the positive electrode particles and the aluminum foil, can lead to problems such as low battery capacity and shortened lifespan.

[0003] To address the aforementioned issues, existing technologies have developed carbon-coated aluminum foil. This process involves coating a conductive paste onto the surface of aluminum foil, drying it to form a specific conductive carbon layer, and then coating the carbon-coated aluminum foil with a positive electrode paste, followed by drying to obtain the positive electrode. This conductive carbon layer acts as a transition layer between current conduction and lithium-ion transport, reducing the contact resistance between the positive electrode active material and the aluminum foil, and improving the adhesion between the active material and the aluminum foil. This results in suppressing battery polarization, reducing thermal effects, and improving the battery's rate performance. Therefore, conductive aluminum foil has attracted widespread attention in the power battery industry, becoming an effective method for improving the overall performance of current collectors and optimizing battery manufacturing processes. However, with the continuous upgrading of battery performance requirements, the conductivity of the conductive carbon layer and the adhesion between the conductive carbon layer and the aluminum foil and positive electrode coating face challenges and require further improvement. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a carbon-coated aluminum foil conductive paste, a preparation method, a carbon-coated aluminum foil, and a positive electrode sheet. By innovating the bonding system in the conductive carbon layer, a multi-dimensional conductive network is constructed. The prepared conductive paste is applied to the coating of the positive electrode aluminum foil, resulting in a conductive carbon layer with strong adhesion to the aluminum foil, good conductivity, and high peel strength from the positive electrode active material.

[0005] The present invention is specifically implemented through the following technical solutions.

[0006] This invention provides a conductive paste for carbon-coated aluminum foil, which is made of conductive carbon material, copolymer binder, dispersant, solvent, leveling agent and defoamer; wherein, in the conductive paste, the mass fraction of conductive carbon material is 2%~10%, the mass fraction of copolymer binder is 2%~5%, the mass percentage of dispersant is 0.5%~1%, the mass percentage of solvent is 85%~90%, the mass percentage of leveling agent is 0.05%~0.1%, and the mass percentage of defoamer is 0.05%~0.1%, totaling 100%.

[0007] The copolymer binder is prepared by polymerization of polar monomers, nonpolar monomers and ion-conducting monomers in water under the action of an initiator and a crosslinking agent. The copolymer binder has a viscosity of 2000 mPa·s to 10000 mPa·s, a solid content of 20 wt.% to 30 wt.%, and a weight-average molecular weight of 8 × 10⁻⁶. 4 g·mol -1 ~2.5×10 5 g·mol -1 .

[0008] Preferably, the polar monomer is at least one selected from acrylic acid, acrylamide, vinylpyrrolidone, methacrylic acid, 2-hydroxyethyl acrylate, and acrylonitrile.

[0009] The nonpolar monomer is at least one of methyl acrylate, ethyl acrylate, butyl acrylate, hydroxypropyl acrylate, isooctyl acrylate, and methyl methacrylate.

[0010] The ion-conducting monomer is at least one of sodium p-styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and sodium 3-allyloxy-2-hydroxy-1-propanesulfonate.

[0011] The crosslinking agent is at least one of divinylbenzene, N-hydroxymethylacrylamide, diacetone acrylamide, and N'N-methylenebisacrylamide.

[0012] The initiator is at least one of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, azobisisovalerate, potassium persulfate, ammonium persulfate, sodium dithionite, and sodium persulfate.

[0013] Preferably, the mass ratio of polar monomer, nonpolar monomer, ion-conducting monomer, and crosslinking agent is (69~90):(5~15):(5~10):(0.5~1).

[0014] The initiator has a mass of 0.01% to 0.15% of the sum of the masses of all monomers; the total mass concentration of all monomers in water is 8% to 20%, preferably 15% to 20%.

[0015] Preferably, the polymerization reaction temperature is 60℃~80℃, and the holding time is 4h~6h.

[0016] Preferably, the conductive carbon material is one or more of acetylene black, furnace black, graphite, graphene, carbon nanotubes, and carbon nanofibers.

[0017] Preferably, in the conductive paste, the solvent is at least one selected from water, ethanol, propanol, isopropanol, and n-butanol.

[0018] The dispersant is at least one of sodium carboxymethyl cellulose (CMC), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and Tween 80.

[0019] The leveling agents are polyether-modified polysiloxane (BYK-331), polyester-modified polysiloxane (Tego Glide 410), and fluorinated polymer (Dyneon). TM At least one of TF).

[0020] The defoamer is at least one of the following: silicone-based BYK-019 and TEGO Foamex 810, and non-silicone polymer-based TEGO Foamex 805 and BYK-011.

[0021] Preferably, the viscosity of the conductive paste is 50 mpa·s to 200 mpa·s; the mass percentage of solids in the conductive paste is 15% to 25%.

[0022] Preferably, the particle size of the conductive paste is D50 of 1 µm to 5 µm and D90 of 5 µm to 10 µm.

[0023] This invention provides a method for preparing the above-mentioned carbon-coated aluminum foil conductive paste, comprising the following steps: Conductive carbon material, copolymer binder, dispersant and solvent are mixed and dispersed evenly, wet nano-grinding and homogenization are performed, and leveling agent and defoamer are added and dispersed evenly to obtain conductive slurry.

[0024] Preferably, the above preparation method specifically includes the following steps: Step 1, Preparation of copolymer binder: Polar monomers, non-polar monomers, ion-conducting monomers, and crosslinking agents are added to deionized water and mixed to form a mixture.

[0025] Step 2: Add an initiator to the mixture to form a reaction system.

[0026] Step 3: The reaction system is heated in a gradient to carry out the polymerization reaction and form a copolymer binder solution; Step 4: Disperse the pre-prepared copolymer binder solution with strong adhesion and dispersant into the solvent and stir until the dispersion is uniform.

[0027] Step 5: Add conductive carbon material and disperse for 3-6 hours at a speed of 200-300 rpm until the surface of the conductive particles is completely wetted to obtain a dispersion.

[0028] Step 6: Wet nano-grinding and homogenization of the dispersion is carried out at a speed of 1500 rpm to 3000 rpm for 12 to 15 hours. Then, leveling agent and defoamer are added and dispersed evenly to obtain conductive slurry.

[0029] This invention provides a carbon-coated aluminum foil, comprising an aluminum foil and a conductive carbon layer. The conductive carbon layer is formed by coating the aluminum foil surface with the aforementioned conductive paste and then drying it. The thickness of the conductive carbon layer is 1 μm to 2 μm. During the coating process, the oven drying temperature is 110℃ to 120℃.

[0030] The present invention also provides a positive electrode sheet, comprising the above-mentioned carbon-coated aluminum foil and a positive electrode coating, wherein the positive electrode coating is formed by coating the surface of the carbon-coated aluminum foil with a positive electrode slurry and drying it; the positive electrode slurry is made of an active material, a conductive agent and a positive electrode binder.

[0031] Compared with the prior art, the present invention has the following beneficial effects: This invention innovatively improves the bonding system in conductive pastes, constructing a multi-dimensional conductive network. The prepared conductive paste, when applied to positive electrode aluminum foil coating, forms a carbon layer with good conductivity, strong adhesion to the aluminum foil, and high peel strength from the positive electrode active material. Specifically: (1) This invention optimizes the binder in the conductive slurry. By introducing polar functional groups into the binder system, not only is the bonding force between conductive particles and between conductive particles and aluminum foil improved, but the peeling force between the current collector and the positive electrode active material is also improved. Non-polar groups improve the film-forming properties and flexibility of the copolymer. The introduction of ion-conducting monomers further increases the dispersion effect of conductive particles. The polymer is uniformly coated on the surface of conductive particles, and the particle dispersion ability is improved through electrostatic repulsion, preventing the conductive slurry from agglomerating and settling. The conductive slurry prepared by this invention can build a stable conductive network in the current collector coating, which can effectively reduce the contact resistance of the positive electrode material particles on the surface of the current collector, improve the battery rate performance, and improve the battery cycle life, etc.

[0032] (2) The conductive slurry of the present invention is coated on aluminum foil to form a conductive carbon layer. Then, a positive electrode slurry is coated on the conductive carbon layer to prepare a positive electrode sheet. The conductive carbon layer can not only form a stronger mechanical interlocking effect with the positive electrode particles, but also the large number of polar groups such as carboxyl, carbonyl, and amino groups in the conductive carbon layer binder can form hydrogen bonds with the positive electrode slurry binder PVDF, further enhancing the peel force between the positive electrode coating and the carbon current collector, thereby extending the battery's service life.

[0033] Therefore, the binder prepared by this invention not only has strong adhesion to aluminum foil, but also effectively improves the bonding force between the current collector and the positive electrode coating. Applied to the positive electrode current collector of lithium-ion batteries, the conductive carbon layer, as a transition layer between current conduction and lithium-ion transport, can not only reduce contact resistance, but also improve the adhesion between the active material and the aluminum foil, thereby achieving effects such as suppressing battery polarization, reducing thermal effects, and improving the rate performance of the battery. Furthermore, the preparation method provided by this invention is simple, easy to operate, and suitable for large-scale production.

[0034] By adopting the above technical solution, the conductive paste has good chemical corrosion resistance and can remain stable in the working environment of lithium batteries, thereby improving the electrolyte resistance of the cathode material, enhancing the rate performance of the battery, and extending the service life of the lithium battery. Attached Figure Description

[0035] Figure 1 The figure shows the peel force test results of the positive electrode sheets prepared using the conductive pastes of Example 1, Comparative Example 1, and Comparative Example 3.

[0036] Figure 2 The graph shows the rate performance test results of the batteries prepared using the conductive pastes of Example 1 and Comparative Example 4. Detailed Implementation

[0037] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention. Unless otherwise specified, the experimental methods and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials described are commercially available.

[0038] This invention provides a conductive paste for carbon-coated aluminum foil, which is made of conductive carbon material, copolymer binder, dispersant, solvent, leveling agent and defoamer; wherein, in the conductive paste, the mass fraction of conductive carbon material is 2%~10%, the mass fraction of copolymer binder is 2%~5%, the mass percentage of dispersant is 0.5%~1%, the mass percentage of solvent is 85%~90%, the mass percentage of leveling agent is 0.05%~0.1%, and the mass percentage of defoamer is 0.05%~0.1%, totaling 100%.

[0039] The copolymer binder is prepared by polymerization of polar monomers, nonpolar monomers, and ion-conducting monomers in water under the action of an initiator and a crosslinking agent. The copolymer binder has a viscosity of 2000 mPa·s to 10000 mPa·s, a solid content of 20 wt.% to 30 wt.%, and a weight-average molecular weight of 8 × 10⁻⁶. 4 g·mol-1 ~2.5×10 5 g·mol -1 .

[0040] This invention provides a method for preparing a conductive paste for carbon-coated aluminum foil, comprising the following steps: Step 1: Under a protective inert gas atmosphere, the polar monomer, non-polar monomer, ion-conducting monomer, crosslinking agent, deionized water and initiator are mixed and polymerized to obtain a copolymer solution.

[0041] Step 2: Use the copolymer solution prepared in Step 1 as a binder, disperse it with the dispersant in the solvent, stir evenly, then add the conductive carbon material and disperse it until the surface of the conductive carbon material is completely wetted to obtain a dispersion.

[0042] Step 3: Wet nano-milling of the dispersion, then adding leveling agent and defoamer, and dispersing evenly to prepare conductive slurry.

[0043] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known to those skilled in the art.

[0044] This invention involves mixing polar monomers, nonpolar monomers, ion-conducting monomers, water, and an initiator to perform a polymerization reaction, thereby obtaining a copolymer binder solution. In this invention, the preferred mass ratio of the polar monomers, nonpolar monomers, ion-conducting monomers, and crosslinking agent is (69~90):(5~15):(5~10):(0.5~1); more preferably, it is (81.2~85.5):(8~10):(6~8):(0.5~0.8); the preferred water is deionized water, and the preferred total mass concentration of all monomers in the water is 15%~20%, more preferably 20%.

[0045] The polar monomer is at least one of acrylic acid, acrylamide, vinylpyrrolidone, methacrylic acid, 2-hydroxyethyl acrylate, and acrylonitrile; the nonpolar monomer is at least one of methyl acrylate, ethyl acrylate, butyl acrylate, hydroxypropyl acrylate, isooctyl acrylate, and methyl methacrylate; the ion-conducting monomer is at least one of sodium p-styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and sodium 3-allyloxy-2-hydroxy-1-propanesulfonate; and the crosslinking agent is at least one of divinylbenzene, N-hydroxymethylacrylamide, diacetone acrylamide, and N'N-methylenebisacrylamide.

[0046] In this invention, the initiator comprises one or more of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, azobisisovalerate, potassium persulfate, ammonium persulfate, sodium dithionite, and sodium persulfate. More preferably, it is a mixture of sodium bisulfite and potassium persulfate, or a mixture of azobisisobutyramidine hydrochloride and potassium persulfate. In the mixture of sodium bisulfite and potassium persulfate, the mass ratio of sodium bisulfite to potassium persulfate is preferably 1:2; in the mixture of azobisisobutyramidine hydrochloride and potassium persulfate, the mass ratio of azobisisobutyramidine hydrochloride to potassium persulfate is preferably 2:1. The mass of the initiator is preferably 0.01% to 0.15% of the sum of the masses of all monomers, more preferably 0.08% to 0.1%.

[0047] In this invention, the preferred method for mixing the polar monomer, nonpolar monomer, ion-conducting monomer, crosslinking agent, water, and initiator is as follows: dispersing the polar monomer, nonpolar monomer, ion-conducting monomer, and crosslinking agent in water to obtain a mixture; adding an initiator to the mixture; and then introducing a protective gas into the resulting mixture. In this invention, the protective gas is preferably argon or nitrogen, and the introduction time of the protective gas is preferably 60 min. This invention removes oxygen from the reaction system by introducing a protective gas, preventing oxygen from inhibiting the polymerization reaction.

[0048] In this invention, the polymerization reaction temperature is preferably 60℃~80℃, more preferably 65℃~70℃; the polymerization reaction holding time is preferably 4 h~6 h, more preferably 4.5 h~5.5 h. In this invention, no further processing is required after the polymerization reaction.

[0049] The prepared copolymer binder has a viscosity of 2000 mPa·s to 10000 mPa·s, a solid content of 20 wt.% to 30 wt.%, and a weight-average molecular weight of 8 × 10⁻⁶. 4 g·mol -1 ~2.5×10 5 g·mol -1 .

[0050] This invention involves dispersing the prepared copolymer binder and dispersant in a solvent, stirring until homogeneous, then adding conductive carbon material and dispersing until the surface of the conductive carbon material is completely wetted to obtain a dispersion. The dispersion is then subjected to wet nano-grinding and homogenization. After grinding, a leveling agent and an antifoaming agent are added to obtain the conductive slurry. In this invention, the conductive carbon material comprises one or more of acetylene black, furnace black, graphite, graphene, carbon nanotubes, and carbon nanofibers, more preferably acetylene black, graphite, and carbon nanotubes, wherein the mass ratio of acetylene black, graphite, and carbon nanotubes is 2:1:1. The preferred mass ratio of the conductive carbon material, copolymer binder, dispersant, solvent, leveling agent, and defoamer is (2~10):(2~5):(0.5~1):(85~90):(0.05~0.1):(0.05~0.1). The solvent is a mixture of at least one of water, ethanol, n-propanol, isopropanol, and n-butanol, more preferably water and isopropanol, with a mass ratio of water to isopropanol of (90~80):(10~20).

[0051] The dispersant is at least one of sodium carboxymethyl cellulose (CMC), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and Tween 80. The leveling agent is polyether-modified polysiloxane (BYK-331), polyester-modified polysiloxane (Tego Glide 410), or fluorinated polymer (Dyneon). TM At least one of the following: TF. The defoamer is at least one of the following: silicone-based BYK-019 and TEGO Foamex 810, and non-silicone polymer-based TEGO Foamex 805 and BYK-011.

[0052] The viscosity of the conductive paste is 50 mPa·s to 200 mPa·s; the mass percentage of solids in the conductive paste is 15% to 25%. The particle size of the conductive paste is D50 of 1 µm to 5 µm and D90 of 5 µm to 10 µm.

[0053] This invention also provides a carbon-coated aluminum foil, comprising an aluminum foil and a conductive carbon layer. The conductive carbon layer is formed by coating the aluminum foil surface with the aforementioned conductive paste and then drying it. The thickness of the conductive carbon layer is 1 μm to 2 μm. During the coating process, the oven temperature is 110℃ to 120℃. The conductive carbon layer prepared by this invention exhibits high adhesion and high conductivity.

[0054] The present invention utilizes the above-mentioned carbon-coated aluminum foil to prepare a positive electrode sheet, including a carbon-coated aluminum foil and a positive electrode coating. The positive electrode coating is formed by coating the carbon-coated aluminum foil with a positive electrode slurry and drying it. The positive electrode slurry is made of active material, conductive agent and positive electrode binder.

[0055] The present invention will be specifically described below through the following embodiments and comparative examples.

[0056] Example 1 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 86 g of polar monomer acrylic acid, 8 g of non-polar monomer methyl acrylate, 6 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent N'N-methylenebisacrylamide crosslinking agent, add them to 400 g of deionized water, and stir until fully mixed.

[0057] (2) Add 0.2 g sodium persulfate and 0.1 g sodium dithionite to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it at that temperature for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0058] (3) Take 150 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of PVP dispersant and stir until uniformly dispersed, add 10 g of acetylene black, 10 g of graphene and 10 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0059] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive slurry with particle sizes of D50: 3.1 µm and D90: 6.9 µm.

[0060] The conductive paste is denoted as N1.

[0061] Example 2 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 80 g of polar monomer acrylic acid, 10 g of non-polar monomer methyl acrylate, 10 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent N'N-methylenebisacrylamide crosslinking agent, add them to 400 g of deionized water, and stir until fully mixed.

[0062] (2) Add 0.1 g of potassium persulfate to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it warm for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0063] (3) Take 150 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of PVP dispersant and stir until uniformly dispersed, add 20 g of acetylene black, 10 g of graphene and 10 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0064] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive paste with particle sizes of D50: 3.0 µm and D90: 5.4 µm.

[0065] The conductive paste is denoted as N2.

[0066] Example 3 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 90 g of polar monomer acrylic acid, 5 g of non-polar monomer methyl acrylate, 5 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent N'N-methylenebisacrylamide crosslinking agent, add them to 400 g of deionized water, and stir until fully mixed.

[0067] (2) Add 0.1 g of potassium persulfate to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it warm for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0068] (3) Take 50 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of PVP dispersant and stir until uniformly dispersed, add 2 g of acetylene black, 1 g of graphene and 1 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0069] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 h. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive paste with particle size D50: 3.0 µm and D90: 5.7 µm.

[0070] The conductive paste is designated as N3.

[0071] Example 4 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 70 g of polar monomer acrylic acid, 5 g of non-polar monomer methyl acrylate, 25 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent N'N-methylenebisacrylamide crosslinking agent, add them to 400 g of deionized water, and stir until fully mixed.

[0072] (2) Add 0.1 g of ammonium persulfate to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it at that temperature for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0073] (3) Take 50 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of PVP dispersant and stir until uniformly dispersed, add 2 g of acetylene black, 1 g of graphene and 1 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0074] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive slurry with particle sizes of D50: 3.2 µm and D90: 6.4 µm.

[0075] The conductive paste is designated as N4.

[0076] Example 5 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 75 g of polar monomer acrylic acid, 6 g of non-polar monomer methyl acrylate, 19 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent diacetone acrylamide, add them to 400 g of deionized water, and stir until fully mixed.

[0077] (2) Add 0.2 g sodium persulfate and 0.1 g sodium dithionite to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it at that temperature for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0078] (3) Take 50 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of dispersant and stir until uniformly dispersed, add 10 g of acetylene black, 10 g of graphene and 10 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0079] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive paste with particle sizes of D50: 2.9 µm and D90: 5.7 µm.

[0080] The conductive paste is designated as N5.

[0081] Example 6 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 86 g of polar monomer acrylic acid, 8 g of non-polar monomer methyl acrylate, 6 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent diacetone acrylamide, add them to 400 g of deionized water, and stir until fully mixed.

[0082] (2) Add 0.2 g sodium persulfate and 0.1 g sodium dithionite to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it at that temperature for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0083] (3) Take 120 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of PVP dispersant and stir until uniformly dispersed, add 10 g of acetylene black, 10 g of graphene and 10 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0084] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive slurry with particle sizes of D50: 3.0 µm and D90: 5.5 µm.

[0085] The conductive paste is designated as N6.

[0086] Example 7 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 80 g of polar monomer acrylic acid, 10 g of non-polar monomer methyl acrylate, 10 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent diacetone acrylamide, add them to 400 g of deionized water, and stir until fully mixed.

[0087] (2) Add 0.1 g of potassium persulfate to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it warm for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0088] (3) Take 120 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of dispersant and stir until uniformly dispersed, add 10 g of acetylene black, 10 g of graphene and 10 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0089] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive slurry with particle sizes of D50: 3.3 µm and D90: 5.6 µm.

[0090] The conductive paste is designated as N7.

[0091] Example 8 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 90 g of polar monomer acrylic acid, 5 g of non-polar monomer methyl acrylate, 5 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent diacetone acrylamide, add them to 400 g of deionized water, and stir until fully mixed.

[0092] (2) Add 0.1 g of potassium persulfate to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it warm for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0093] (3) Take 150 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of PVP dispersant and stir until the dispersion is uniform, add 15 g of acetylene black, 10 g of graphene and 5 g of carbon nanotube powder, stir and disperse for 1 h, the speed of the disperser is 1500 RPM, until the surface of the conductive material is completely wetted, and the dispersion is obtained. (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive slurry with particle sizes of D50: 3.3 µm and D90: 6.3 µm.

[0094] The conductive paste is designated as N8.

[0095] Example 9 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 70 g of polar monomer acrylic acid, 5 g of non-polar monomer methyl acrylate, 25 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent diacetone acrylamide, add them to 400 g of deionized water, and stir until fully mixed.

[0096] (2) Add 0.1 g of ammonium persulfate to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it at that temperature for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0097] (3) Take 150 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of PVP dispersant and stir until uniformly dispersed, add 10 g of acetylene black, 10 g of graphene and 10 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0098] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive paste with particle sizes of D50: 3.0 µm and D90: 6.4 µm.

[0099] The conductive paste is designated as N9.

[0100] Example 10 A carbon-coated conductive paste for aluminum foil coating in lithium-ion batteries is prepared through the following steps: (1) Take 75 g of polar monomer acrylic acid, 6 g of non-polar monomer methyl acrylate, 19 g of ion-conducting monomer sodium p-benzenesulfonate, and 0.5 g of crosslinking agent diacetone acrylamide, add them to 400 g of deionized water, and stir until fully mixed.

[0101] (2) Add 0.2 g sodium persulfate and 0.1 g sodium dithionite to the above mixture and purge with nitrogen for 60 min to remove oxygen from the system; heat the resulting solution system to 60°C and keep it at that temperature for 6 h to obtain a copolymer binder solution with a solid content of 20 wt%.

[0102] (3) Take 150 g of the strong adhesion copolymer adhesive solution with a solid content of 20 wt% prepared in step (2), disperse it in a mixed solution of 180 g of deionized water and 50 g of isopropanol, add 3 g of dispersant and stir until uniformly dispersed, add 10 g of acetylene black, 10 g of graphene and 10 g of carbon nanotube powder, stir and disperse for 1 h, with the disperser speed at 1500 RPM, until the surface of the conductive material is completely wetted, and obtain the dispersion.

[0103] (4) The dispersion was subjected to wet nano-grinding and homogenization at a speed of 2000 RPM for 10 hours. Then, 0.2 g of leveling agent BYK-333 and 0.2 g of defoamer BYK-019 were added and dispersed evenly to obtain the conductive paste with particle sizes of D50: 3.4 µm and D90: 6.5 µm.

[0104] The conductive paste is designated as N10.

[0105] Comparative Example 1 The method for preparing carbon-coated conductive paste provided in this comparative example is similar to that in Example 1, except that commercially available CMC / SBR (i.e., sodium carboxymethyl cellulose / styrene-butadiene rubber, with a mass ratio of CMC to SBR of 2:3) is used as a binder in this conductive paste.

[0106] Comparative Example 2 The method for preparing carbon foil conductive paste provided in this comparative example is similar to that in Example 1, except that the conductive materials in this conductive paste are acetylene black and graphene, and the mass ratio of acetylene black to graphene is 1:1.

[0107] Comparative Example 3 The method for preparing the carbon foil conductive paste provided in this comparative example is similar to that in Example 1, except that the conductive paste uses a polyacrylic acid binder with a solid content of 20 wt%, and no non-polar monomers are added compared to Example 1.

[0108] Comparative Example 4 The method for preparing the carbon foil conductive paste provided in this comparative example is similar to that in Example 1, except that a polyacrylic acid copolymer binder with a solid content of 20 wt% is used in this conductive paste, and no ion-conducting monomer is added compared to Example 1.

[0109] The conductive pastes prepared in Examples 1-10 and Comparative Examples 1-4 were respectively coated onto the surface of aluminum foil and dried in an oven at 110°C for 30 seconds, resulting in a coating thickness of 1.5 μm, thus obtaining carbon-coated aluminum foil. A 180° peel strength test was performed on the carbon coating layer of the aluminum foil using 3M tape (1.9 cm wide) at a speed of 1 mm / s. The carbon-coated aluminum foil was tested three times using a film resistance meter, and the average value was taken.

[0110] The positive electrode peel strength verification test process is as follows: A positive electrode slurry is prepared by mixing lithium iron phosphate (LPF), conductive agent, and binder PVDF at a mass ratio of 97:1:2, with the solid content of the slurry controlled at 60 wt%. The positive electrode slurry is coated onto the surface of carbon-coated aluminum foil, with a coating thickness controlled at 250 μm. After drying and rolling, a positive electrode sheet is obtained. Then, a peel strength test is performed using the same method as above: a 180° peel strength test is conducted on the positive electrode coating of the positive electrode sheet using 3M tape (1.9 cm wide) at a test speed of 1 mm / s.

[0111] The positive electrode sheet prepared by the above method was assembled with a commercial graphite negative electrode to form a soft-pack full-electric battery. The rate performance was tested at 0.5C full charge and 0.2C / 1C / 2C / 3C / 5C / 7C discharge in a voltage range of 2.0~4.0 V at room temperature.

[0112] The results are shown in Table 1.

[0113] Table 1 Performance data of each embodiment and comparative sample As can be seen from Table 1, compared with Comparative Examples 1 to 4, the conductive carbon layer formed after the slurry is coated on the surface of aluminum foil and dried in Examples 1 to 10 of the present invention has improved conductivity and improved adhesion between the conductive carbon layer and the aluminum foil and the positive electrode. Figure 1The figures show the peel force test results of the positive electrode sheets prepared using the conductive pastes of Example 1, Comparative Example 1, and Comparative Example 3. In Comparative Example 2, compared with Example 1, the conductive materials in the conductive paste are acetylene black and graphene, with a mass ratio of acetylene black to graphene of 1:1. The reason for the increased film resistance is that the addition of conductive nanotubes constructs a two-dimensional electron transport channel, which helps to improve the conductivity of the coating. Compared with Example 1, Comparative Example 3 reduces the number of nonpolar monomers and ion-conducting monomers, resulting in a decrease in peel force and an increase in resistance. This is because the nonpolar monomers can interact with the nonpolar functional diagrams on the conductive particles and the positive electrode binder, which helps to improve the peel force. Figure 2 The figures show the rate performance test results of batteries prepared using the conductive slurries of Example 1 and Comparative Example 4. Comparative Example 4 reduced the number of ion-conducting monomers compared to Example 1, because the addition of ion-conducting monomers facilitates lithium-ion transport and improves battery rate performance.

[0114] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the spirit and scope of the invention. Therefore, it is intended to include any modifications and variations of this invention that fall within the scope of the claims and their equivalents.

Claims

1. A carbon-coated aluminum foil conductive paste, characterized by, The conductive paste is prepared from conductive carbon material, copolymer binder, dispersant, solvent, leveling agent and defoaming agent; wherein, in the conductive paste, the mass fraction of the conductive carbon material is 2%~10%, and the mass fraction of the copolymer binder is 2%~5%. The copolymer binder is prepared by polymerization reaction in water under the action of initiator and crosslinking agent, and is prepared from polar monomer, non-polar monomer and ion-conducting monomer. The viscosity of the copolymer binder is 2000 mPa-s ~ 10000 mPa-s, the solid content is 20 wt.% ~ 30 wt.%, the weight average molecular weight of the copolymer is 8 x 10 4 g / mol -1 ~ 2.5 x 10 5 g / mol -1 .

2. The carbon-coated aluminum foil conductive paste according to claim 1, wherein, The polar monomer is at least one of acrylic acid, acrylamide, vinyl pyrrolidone, methacrylic acid, 2-hydroxyethyl acrylate and acrylonitrile. The non-polar monomer is at least one of methyl acrylate, ethyl acrylate, butyl acrylate, hydroxypropyl acrylate, isooctyl acrylate and methyl methacrylate. The ion-conducting monomer is at least one of sodium p-styrenesulfonate, 2-acrylamido-2-methylpropane sulfonic acid and 3-allyloxy-2-hydroxy-1-propane sulfonic acid sodium. The crosslinking agent is at least one of divinylbenzene, N-hydroxymethyl acrylamide, diacetone acrylamide and N’N-methylene bisacrylamide. The initiator is at least one of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, azobisisovaleronitrile, potassium persulfate, ammonium persulfate, sodium hyposulfite and sodium persulfate.

3. The carbon-coated aluminum foil conductive paste of claim 1, wherein, The mass ratio of the polar monomer, non-polar monomer, ion-conducting monomer and crosslinking agent is 69~90:5~15:5~10:0.5~1. The mass of the initiator is 0.01%~0.15% of the sum of the mass of all monomers; the total mass concentration of all monomers in water is 8%~20%.

4. The carbon-coated aluminum foil conductive paste of claim 1, wherein, The temperature of the polymerization reaction is 60℃~80℃, and the holding time is 4h~6h.

5. The carbon-coated aluminum foil conductive paste of claim 1, wherein, The conductive carbon material is one or more of acetylene black, furnace black, graphite, graphene, carbon nanotube and carbon nanofiber.

6. The carbon-coated aluminum foil conductive paste of claim 1, wherein, The viscosity of the conductive paste is 50 mPa·s~200 mPa·s; the mass percentage of solids in the conductive paste is 15%~25%.

7. The carbon-coated aluminum foil conductive paste of claim 1, wherein, The particle size of the conductive paste is D50 of 1 µm~5 µm, and D90 of 5 µm~10 µm.

8. A method of preparing the carbon-coated aluminum foil conductive paste according to any one of claims 1 to 7, characterized by, The method comprises the following steps: The conductive carbon material, copolymer binder, dispersant and solvent are mixed and uniformly dispersed, wet nanogrinding and homogenization are performed, the leveling agent and defoaming agent are added and uniformly dispersed, and the conductive paste is prepared.

9. A carbon-coated aluminum foil, characterized by, The conductive carbon layer is formed by coating the conductive paste on the surface of the aluminum foil and then drying; the thickness of the conductive carbon layer is 1 μm~2 μm.

10. A positive electrode sheet characterized by comprising: The positive electrode coating is formed by coating positive electrode paste on the surface of the carbon-coated aluminum foil and then drying; the positive electrode paste is prepared from active material, conductive agent and positive electrode binder.

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