Carbon-foil-coated conductive paste and preparation method thereof, carbon-coated foil and lithium ion battery positive electrode

Abstract

The invention belongs to the technical field of lithium ion battery positive electrodes, and particularly relates to carbon-foil-coated conductive paste and a preparation method thereof, a carbon-coated foil and a lithium ion battery positive electrode. The carbon foil-coated conductive paste is prepared from the following components in percentage by mass: 6%-10% of a mixture of graphite and graphene, 6%-20% of a polyacrylic acid binder, 0.5%-5.0% of a dispersant, 1.0%-4.0% of sodium hydroxide, 5%-10% of an alcohol solvent and the balance of deionized water, totaling 100%. The dispersing agent is formed by blending one or more of polystyrene, polyvinylidene fluoride, polymethacrylate, polyoxyethylene ether, polymethylacrylic acid, polyacrylonitrile and polyvinyl alcohol; according to the preparation method, the surface of the graphene is modified by introducing the multi-component blending type polymeric dispersant, so that uniform and stable dispersion of the graphene in the slurry is realized.

Description

Technical Field

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

[0002] Lithium-ion batteries, due to their advantages such as high operating voltage, high energy density, low self-discharge rate, stability, and environmental friendliness, are now widely used in the power supplies of various smart electronic products. In recent years, with the rapid rise of new energy vehicles, higher demands have been placed on the energy density, charge-discharge life, and production cost of lithium-ion batteries. This has led to the continuous expansion of the carbon foil coating market; currently, nearly 90% of power batteries utilize carbon foil coating technology. Carbon foil coating technology involves uniformly coating a well-dispersed conductive agent onto aluminum foil to improve the conductivity and thermal conductivity of the foil. Carbon foil coating can reduce the contact resistance between the positive electrode material and the current collector, increase the adhesion between them, and reduce the amount of binder used during slurry preparation, thereby significantly improving the battery's specific capacity, cycle stability, rate performance, and safety performance.

[0003] The carbon material currently used in carbon foil coating technology is mainly carbon black (SP), which has the characteristics of large specific area and small particle size. However, carbon black is prone to agglomeration and forming large particles during slurry preparation. This can lead to uneven distribution when applied to the aluminum foil surface, and the particles are easy to fall off, thus affecting the overall conductivity of the carbon foil.

[0004] To enhance the processing performance and conductivity of carbon-coated foil, graphite is typically added to improve the stability of the slurry. Compared to graphite, graphene possesses higher electrical conductivity, mechanical strength, and chemical stability. The sheet-like structure of graphene increases the effective filling between active materials, significantly reducing the contact resistance between the cathode material and the current collector, thus increasing the conductivity of the carbon-coated foil. Furthermore, graphene, as a carbon-coated foil processing technology for cathode current collectors, exhibits superior conductivity and adhesion compared to traditional carbon black-coated foils. However, strong van der Waals forces and π-π interactions exist between graphene sheets, making them prone to aggregation and stacking, forming large aggregates. Moreover, graphene's high hydrophobicity affects its wettability in certain solvent systems, leading to a decrease in slurry stability (sedimentation, stratification). With prolonged slurry settling time, graphene sheets agglomerate and precipitate under the influence of gravity and van der Waals forces, affecting not only the construction of the conductive network but also hindering subsequent coating processes. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a carbon-coated conductive slurry and its preparation method, as well as a carbon-coated foil and a lithium-ion battery cathode. This solves the problems of easy stratification and sedimentation in current graphene-based conductive slurries. By introducing a multi-component blended polymeric dispersant to modify the graphene surface, the hydrophobic groups in the dispersant form π-π bonds with the six-membered ring structure of graphene or stably bind to it in a non-covalent manner and adsorb onto the graphene surface. Meanwhile, the long molecular chains of the hydrophilic groups in the components create a steric hindrance effect in the solution, effectively inhibiting the aggregation of graphene, thus achieving uniform and stable dispersion of graphene in the slurry.

[0006] The present invention is specifically implemented through the following technical solutions.

[0007] The first objective of this invention is to provide a carbon foil-coated conductive paste, comprising the following components by mass fraction: a mixture of graphite and graphene: 6%–10%, a polyacrylic acid binder: 6%–20%, a dispersant: 0.5%–5.0%, sodium hydroxide: 1.0%–4.0%, an alcohol solvent: 5%–10%, and the balance being deionized water, totaling 100%. The dispersant is composed of one or more of polystyrene, polyvinylidene fluoride, polymethyl methacrylate, polyoxyethylene ether, polymethyl methacrylate, polyacrylonitrile, and polyvinyl alcohol. The mass ratio of graphite to graphene is 5–6:1.5–3.

[0008] Preferably, the amount of graphite and graphene mixture added is 7%, the mass ratio of graphite to graphene is 5:2, and the amount of polyacrylic acid binder added is 8%. The alcohol solvent is n-propanol and / or isopropanol.

[0009] A second objective of this invention is to provide a method for preparing the above-mentioned carbon foil-coated conductive paste, comprising the following steps: A pre-dispersed slurry was prepared by mixing graphite and graphene, polyacrylic acid binder, dispersant, sodium hydroxide solution, isopropanol and deionized water; The pre-dispersed slurry was ground to control the fineness of the slurry to within 1 μm, and then filtered through a 220-mesh sieve.

[0010] A third objective of this invention is to provide a carbon-coated foil, comprising an aluminum foil substrate and a conductive coating, wherein the conductive coating is obtained by coating the aluminum foil substrate surface with the aforementioned carbon-coated foil conductive paste and then drying it.

[0011] Preferably, the solid content of the carbon foil conductive paste is 13wt%~18wt%, and the viscosity is controlled between 100mPa·s and 300mPa·s.

[0012] Preferably, the thickness of the conductive coating is 1 μm to 1.2 μm, and the load per unit area is 0.02 mg / cm². 2 ~0.04mg / cm 2The carbon-coated foil provided by this invention has a uniform surface coating and good conductivity, which improves the processing performance and conductivity of the positive electrode current collector, thereby improving the cycle life of the lithium-ion battery.

[0013] The fourth objective of this invention is to provide a lithium-ion battery positive electrode, comprising the aforementioned carbon-coated foil and a positive electrode coating, wherein the positive electrode coating is obtained by coating a positive electrode slurry onto the conductive coating surface of the carbon-coated foil and then drying it.

[0014] Preferably, the positive electrode slurry is made of the following components by mass percentage: 90%~95% active material, 3%~5% conductive agent, 2%~5% binder, and the balance being solvent, totaling 100%.

[0015] Preferably, the active material is one or more of lithium iron phosphate, lithium cobalt oxide, and lithium nickel oxide. The conductive agent, binder, and solvent are all commonly used materials in the art; carbon black is preferred as the conductive agent, PVDF as the binder, and NMP as the solvent.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention uses a mixture of graphite and graphene in a specific ratio as the carbon material for the carbon foil coated with the positive electrode current collector. Since both graphite and graphene have sheet-like structures, with the graphene sheet diameter ranging from 10 to 15 μm, a multi-component blended polymeric dispersant is employed. By introducing benzene rings and polyether segments into the molecular structure of the dispersant, the long hydrophobic segments on the main chain of the component achieve multi-point adsorption with the graphene surface through hydrophobic forces. Meanwhile, the benzene ring structure on the side chain forms π-π bonds with the six-membered ring structure of graphene or stably binds to it in a non-covalent form and adsorbs onto the graphene surface. Furthermore, the long molecular chains of the hydrophilic groups in the component create a steric hindrance effect in the solution, effectively inhibiting graphene aggregation. Through steric repulsion / or electrostatic repulsion, the strong attractive forces between particles are overcome, achieving uniform and stable dispersion of graphite and graphene in the slurry.

[0017] The two-dimensional sheet structure of graphene can increase the effective filling between active materials and provide a large number of contact sites, enhancing the conductive medium between the active material and particles of the electrode and increasing the conductivity of the carbon-coated foil. The carbon coating slurry uses graphene with a sheet thickness of 5 nm, which has a small thickness and almost no deformation. When coated on the surface of the substrate foil, it can completely adhere to the foil and has a higher conductivity than graphite and carbon black conductive agents. The coating adhesive of this invention uses polyacrylic acid binder, which contains a large number of -COOH and -OH functional groups, which can improve the structural stability of the slurry and enhance the adhesion between the substrate and the slurry.

[0018] The positive electrode current collector using the carbon-coated foil of this invention has good conductivity, which effectively improves the rate capability and cycle life of lithium-ion batteries. Attached Figure Description

[0019] Figure 1 This is a SEM image of the graphene used in Example 1.

[0020] Figure 2 The image shows a SEM image of a carbon-coated foil prepared using the slurry obtained in Example 1. Detailed Implementation

[0021] 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.

[0022] The polymers used in this invention can be within the following molecular weight ranges: polystyrene M w =500,000 to 500,000, polymethyl methacrylate M w =100,000~200,000, polyoxyethylene ether Mw=50,000~200,000, polyacrylonitrile M w =80,000 to 200,000, Polyvinyl alcohol M w =80,000 to 500,000, polymethyl methacrylate M w =50,000 to 500,000, polyvinylidene fluoride M w =120,000 to 300,000, polyacrylic acid M w =100,000 to 200,000.

[0023] Preparation Example 1 A ternary copolymer polymeric dispersant, composed of polystyrene (M w =100,000), polymethyl methacrylate (M w =150,000) and polyoxyethylene ether (M w =100,000) are blended at a weight ratio of 1:1:2.

[0024] Preparation Example 2 A ternary copolymer polymeric dispersant, composed of polystyrene (M w =100,000), polyacrylonitrile (M) w =100,000) and polyoxyethylene ether (M w =100,000) are blended at a weight ratio of 1:1:2.

[0025] Preparation Example 3 A ternary copolymer polymeric dispersant, composed of polystyrene (M w =100,000), polyvinyl alcohol (M w =200,000) and polyoxyethylene ether (M w =100,000) are blended at a weight ratio of 1:1:1.

[0026] Preparation Example 4 A ternary copolymer polymeric dispersant, composed of polystyrene (M w =100,000), polymethyl methacrylate (M w =200,000), polyvinylidene fluoride (M w =150,000) are blended at a weight ratio of 1:1:1.

[0027] Preparation Example 5 A ternary copolymer polymeric dispersant, composed of polymethyl methacrylate (M... w =200,000), polyoxyethylene ether (M w =100,000), polyvinylidene fluoride (M w =150,000) are blended at a weight ratio of 1:1:1.

[0028] Example 1 A carbon foil-coated conductive paste is prepared from the following components in the indicated mass fractions: Graphite: 5%; Graphene: 2%; Polyacrylic acid (M w =150,000): 8%; Dispersant: 1%, Sodium hydroxide (added as a 30% aqueous solution, the main function of sodium hydroxide is to adjust the pH of the slurry to improve its leveling properties): 1%; Isopropanol 10%; the balance is deionized water, total 100%. The dispersant in this example is the dispersant in Preparation Example 1. The SEM image of graphene is shown below. Figure 1 As shown, graphene with an average sheet thickness of 5 nm and a sheet diameter between 10 and 15 μm was used.

[0029] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 1 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining deionized water to prepare a dispersion. Subsequently, add the polyacrylic acid binder and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add graphite and graphene to the mixed solution. Finally, add the remaining isopropanol to the premix and control the stirring speed to 300 rpm for 30 min. After stirring, a predispersed slurry is obtained.

[0030] The pre-dispersed slurry was then ground for 1 hour at 2200 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated conductive slurry.

[0031] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The aluminum foil thickness was 10 μm, and the carbon coating layer thickness was 1 μm. The resulting carbon-coated foil was then dried in an oven at 100°C for 5 hours. The SEM image of the resulting carbon-coated foil is shown below. Figure 2 As shown.

[0032] Example 2 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 5%; Graphene: 2%; Polyacrylic acid: 10%; Dispersant: 1.0%; Sodium hydroxide (added as a 30% aqueous solution): 1%; Isopropanol: 10%; Balance: Deionized water, total 100%. The dispersant used in this example is the dispersant used in Preparation Example 2.

[0033] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 2 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining deionized water to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add graphite and graphene to the mixed solution. Finally, add the remaining isopropanol to the premix and control the stirring speed to 280 rpm for 30 min. After stirring, a predispersed slurry is obtained.

[0034] The pre-dispersed slurry was then ground for 1.5 hours at a speed of 2200 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0035] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 120°C for 6 hours.

[0036] Example 3 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 5%; Graphene: 1.5%; Polyacrylic acid: 8%; Dispersant: 2%; Sodium hydroxide (added as a 30% aqueous solution): 1.5%; Isopropanol 10%; Balance: deionized water, total 100%. The dispersant used in this example is the same as that in Preparation Example 3.

[0037] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 3 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining deionized water and isopropanol mixed solution to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add graphite and graphene to the mixed solution, control the stirring speed at 320 rpm, and stir for 45 min. After stirring, a pre-dispersed slurry is obtained.

[0038] The pre-dispersed slurry was then ground for 2.0 h at a speed of 2500 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0039] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 150°C for 5 hours.

[0040] Example 4 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 6%; Graphene: 2%; Polyacrylic acid: 12%; Dispersant: 1%; Sodium hydroxide (added as a 30% aqueous solution): 1.5%; Isopropanol 10%; Balance: deionized water, total 100%. The dispersant used in this example is the same as that in Preparation Example 4.

[0041] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 4 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining mixed solution of deionized water and isopropanol to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add graphite and graphene to the mixed solution, control the stirring speed at 350 rpm, and stir for 1 hour. After stirring, a pre-dispersed slurry is obtained.

[0042] The pre-dispersed slurry was then ground for 2.0 h at a speed of 2200 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0043] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 130°C for 6 hours.

[0044] Example 5 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 6%; Graphene: 3%; Polyacrylic acid: 12%; Dispersant: 1%; Sodium hydroxide (added as a 30% aqueous solution): 1.0%; Isopropanol 10%; Balance: deionized water, total 100%. The dispersant used in this example is the same as that in Preparation Example 5.

[0045] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 5 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining deionized water and isopropanol mixed solution to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add graphite and graphene to the mixed solution, control the stirring speed at 300 rpm, and stir for 1 h. After stirring, a pre-dispersed slurry is obtained.

[0046] The pre-dispersed slurry was then ground for 1.5 hours at a speed of 2500 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0047] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 150°C for 5 hours.

[0048] The graphene-based conductive pastes from Examples 1 to 5 were allowed to stand for 7 and 14 days, respectively, and then diluted by centrifugation. The UV spectra of all conductive pastes were then measured. Since the six-membered ring of graphene exhibits a UV absorption peak near 270 nm, its absorption intensity satisfies the Lambert-Beer law with respect to the concentration of graphene in the solution. The higher the UV absorbance of the slurry, the higher the concentration of graphene dispersion, which confirms that the steric hindrance of the slurry is stronger, thus effectively inhibiting graphene agglomeration. Therefore, it is beneficial for graphene to be uniformly dispersed in the carbon-coated foil to form an effective conductive network.

[0049] Table 1 records the light absorption intensity of the slurry after 7 and 14 days of standing. As can be seen from Table 1, the UV absorption intensity of the slurry at around 270 nm decreased slightly with the extension of the standing time. This is because the dispersant modifies the surface of graphene, allowing it to be stably dispersed in the slurry for a longer time, which can generate a strong steric hindrance effect and thus inhibit the aggregation of graphene.

[0050] Comparative Example 1 A carbon foil-coated conductive paste is prepared from the following components in the indicated mass fractions: Graphite: 5%; conductive carbon black: 2%; polyacrylic acid: 8%; dispersant: 1%; sodium hydroxide (added as a 30% aqueous solution): 1%; isopropanol 10%; balance: deionized water, total 100%.

[0051] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 1 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining deionized water to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add conductive carbon black and graphite to the mixed solution. Finally, add the remaining isopropanol to the premix and control the stirring speed at 300 rpm for 30 min. After stirring, a predispersed slurry is obtained.

[0052] The pre-dispersed slurry was then ground for 1 hour at 2200 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0053] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 100°C for 5 hours.

[0054] Comparative Example 2 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 5%; conductive carbon black: 2%; polyacrylic acid: 10%; dispersant: 1.0%; sodium hydroxide (added as a 30% aqueous solution): 1%; isopropanol 10%; balance: deionized water, total 100%.

[0055] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 2 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining deionized water to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add conductive carbon black and graphite to the mixed solution. Finally, add the remaining isopropanol to the premix and control the stirring speed to 280 rpm for 30 min. After stirring, a predispersed slurry is obtained.

[0056] The pre-dispersed slurry was then ground for 1.5 hours at a speed of 2200 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0057] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 120°C for 6 hours.

[0058] Comparative Example 3 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 5%; Conductive carbon black: 1.5%; Polyacrylic acid: 8%; Dispersant: 2%; Sodium hydroxide (added as a 30% aqueous solution): 1.5%; Isopropanol 10%; Balance: deionized water, total 100%.

[0059] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 3 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining mixed solution of deionized water and isopropanol to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add graphite and conductive carbon black to the mixed solution, control the stirring speed at 320 rpm, and stir for 45 min. After stirring, a pre-dispersed slurry is obtained.

[0060] The pre-dispersed slurry was then ground for 2.0 h at a speed of 2500 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0061] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 150°C for 5 hours.

[0062] Comparative Example 4 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 6%; Conductive carbon black: 2%; Polyacrylic acid: 12%; Dispersant: 1%; Sodium hydroxide (added as a 30% aqueous solution): 1.5%; Isopropanol 10%; Balance: deionized water, total 100%.

[0063] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 4 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining mixed solution of deionized water and isopropanol to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add conductive carbon black and graphite to the mixed solution, control the stirring speed at 350 rpm, and stir for 1 h. After stirring, a pre-dispersed slurry is obtained.

[0064] The pre-dispersed slurry was then ground for 2.0 h at a speed of 2200 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0065] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 130°C for 6 hours.

[0066] Comparative Example 5 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 6%; Conductive carbon black: 3%; Polyacrylic acid: 12%; Dispersant: 1%; Sodium hydroxide (added as a 30% aqueous solution): 1.0%; Isopropanol 10%; Balance: deionized water, total 100%.

[0067] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve the dispersant of Preparation Example 5 in a portion of the isopropanol / water (volume ratio 1:1) solvent and stir at room temperature to obtain a mixed system. Then, dissolve the mixed system in the remaining mixed solution of deionized water and isopropanol to prepare a dispersion. Subsequently, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. Then, add conductive carbon black and graphite to the mixed solution, control the stirring speed at 300 rpm, and stir for 1 h. After stirring, a pre-dispersed slurry is obtained.

[0068] The pre-dispersed slurry was then ground for 1.5 hours at a speed of 2500 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0069] The method for preparing carbon foil is as follows: The prepared conductive paste was coated onto the surface of aluminum foil using a coating device. The thickness of the aluminum foil was 10 μm, and the thickness of the carbon coating layer was 1 μm. The resulting carbon-coated foil was then placed in an oven and dried at 150°C for 5 hours.

[0070] Comparative Example 6 A conductive paste for carbon foil coating is prepared from the following components by mass fraction: Graphite: 6%; Graphene: 3%; Polyacrylic acid: 12%; Polyvinylpyrrolidone dispersant: 1%; Sodium hydroxide (added as a 30% aqueous solution): 1.0%; Isopropanol 10%; Balance: deionized water, total 100%.

[0071] The preparation method of the above conductive paste: According to the mass fraction of each component mentioned above, weigh each raw material. First, dissolve polyvinylpyrrolidone (PVP) in a mixed solution of deionized water and isopropanol to prepare a dispersion. Then, add polyacrylic acid and sodium hydroxide solution to the above dispersion and mix and dissolve. After that, add conductive carbon black and graphite to the mixed solution. Control the stirring speed to 300 rpm and the stirring time to 1 h. After stirring, a pre-dispersed slurry is obtained.

[0072] The pre-dispersed slurry was then ground for 1.5 hours at a speed of 2500 rpm using a grinder to control the fineness of the slurry to within 1 μm. Finally, the slurry was filtered through a 220-mesh sieve to obtain the final carbon-coated slurry.

[0073] The carbon-coated foils obtained in Examples 1 to 5 and Comparative Examples 1 to 6 of the present invention were subjected to relevant physical property tests, including measuring the resistance of the carbon-coated foil (four-probe method test) and the peel force of the carbon-coated foil.

[0074] Positive electrode slurry was coated onto the carbon-coated foil obtained in Examples 1-5 and Comparative Examples 1-6, respectively, and dried to obtain a positive electrode coating. The composition ratio of the positive electrode slurry was as follows: lithium iron phosphate (LFP) 90%, conductive agent carbon black 3%, binder PVDF 2%, and solvent NMP as the balance, totaling 100%.

[0075] The above positive electrodes were assembled into lithium batteries with the same rated capacity using the same parameters, and cycle performance tests were conducted (charge and discharge at 1.0 C, voltage window of 2.5~3.6 V). The capacity retention rate of the prepared batteries after 500 cycles was recorded. The results are shown in Table 2.

[0076] Table 2 Performance test data of Examples 1-5 and Comparative Examples 1-6 As shown in Table 2, compared with Example 1, Example 2 had a higher amount of polyacrylic acid added, resulting in greater peel strength of the carbon-coated foil, but also higher resistance and reduced cycling performance. Therefore, it is necessary to control the amount of polyacrylic acid binder added within a suitable range to balance the peel strength and resistance of the carbon-coated foil.

[0077] Compared to Example 1, Example 3 had less graphene, more dispersant, higher carbon foil resistance, reduced carbon foil peel strength, and lower cycle performance. This is because, compared to graphite, graphene has higher electrical conductivity, mechanical strength, adhesion, and chemical stability. The sheet-like structure of graphene increases the effective filling between active materials, significantly reducing the contact resistance between the cathode material and the current collector, and increasing the conductivity of the carbon foil. Therefore, reducing the amount of graphene increases the resistance and reduces the peel strength of the carbon foil. Furthermore, the increased amount of dispersant, being a polymer that is not conductive, further increases the resistance.

[0078] Compared to Example 1, Example 4 contained more graphite, more polyacrylic acid, and more dispersant, resulting in increased peel strength of the carbon-coated foil, but also increased resistance and decreased cycle performance. This is because graphite itself has lower conductivity than graphene, and the dispersant, being a polymer compound, also has poor conductivity; increasing its amount leads to increased resistance and decreased cycle performance. Polyacrylic acid provides adhesion to the carbon-coated foil, and increasing its amount will increase the peel strength of the foil.

[0079] Compared to Example 1, Example 5 contains more graphite, graphene, and resin, resulting in greater peel strength of the carbon-coated foil. However, the carbon-coated foil also exhibits higher resistance and reduced cycle performance. This is because polyacrylic acid provides the adhesive properties for the carbon-coated foil, and increasing its amount leads to increased peel strength. Furthermore, as a polymer compound, polyacrylic acid has poor conductivity, and increasing its amount results in increased resistance and decreased cycle performance.

[0080] In Comparative Examples 1-5, the use of conductive carbon black and graphite increased the resistance of the carbon-coated foil and reduced its cycling performance. Furthermore, the conductive carbon black easily agglomerated, forming larger particles, which reduced the overall peel strength of the carbon-coated foil. Although Comparative Example 6 used graphite and graphene as the main conductive materials and conventional polyvinylpyrrolidone (PVP) as the dispersant, the resistance of the prepared carbon-coated foil was close to that of Examples 1-5. However, because PVP had a poorer dispersion effect on graphite and graphene than in Examples 1-5, it easily caused agglomeration of the two materials, resulting in a decrease in the peel strength of the carbon-coated foil.

[0081] 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 foil-coated conductive paste, characterized in that, Made from the following components by mass fraction: Graphite and graphene mixture: 6%~10%, polyacrylic acid binder: 6%~20%, dispersant: 0.5%~5.0%, sodium hydroxide: 1.0%~4.0%, alcohol solvent: 5%~10%, balance: water, total 100%; The dispersant is composed of one or more of the following: polystyrene, polyvinylidene fluoride, polymethacrylate, polyoxyethylene ether, polymethacrylic acid, polyacrylonitrile, and polyvinyl alcohol. The mass ratio of graphite to graphene is 5~6:1.5~3.

2. The carbon foil-coated conductive paste according to claim 1, characterized in that, The alcohol solvent is n-propanol and / or isopropanol.

3. A method for preparing a carbon foil-coated conductive paste according to claim 1, characterized in that, Includes the following steps: A pre-dispersed slurry was prepared by mixing graphite and graphene, polyacrylic acid binder, dispersant, sodium hydroxide, isopropanol and water; The pre-dispersed slurry was ground to control the fineness of the slurry to within 1 μm, and then filtered through a 220-mesh sieve.

4. A carbon-coated foil, characterized in that, It includes an aluminum foil substrate and a conductive coating, wherein the conductive coating is obtained by coating the aluminum foil substrate surface with the carbon foil conductive paste as described in claim 1 and then drying it.

5. The carbon-coated foil according to claim 4, characterized in that, The solid content of the carbon foil conductive paste is 13wt%~18wt%, and the viscosity is controlled between 100mPa·s and 300mPa·s.

6. The carbon-coated foil according to claim 4, characterized in that, The conductive coating has a thickness of 1μm to 1.2μm and a surface loading of 0.02mg / cm². 2 ~0.04mg / cm 2 .

7. A lithium-ion battery positive electrode, characterized in that, It includes the carbon-coated foil and positive electrode coating as described in claim 4, wherein the positive electrode coating is obtained by coating the conductive coating surface of the carbon-coated foil with a positive electrode slurry and then drying it.

8. The lithium-ion battery positive electrode according to claim 7, characterized in that, The positive electrode slurry is made of the following components by mass percentage: 90%~95% active material, 3%~5% conductive agent, 2%~5% binder, and the balance being solvent, totaling 100%.

9. The lithium-ion battery positive electrode according to claim 8, characterized in that, The active material is one or more of lithium iron phosphate, lithium cobalt oxide, and lithium nickel oxide.

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