Oily conductive paste and preparation method thereof, carbon-coated aluminum foil and positive plate

Abstract

The invention provides oily conductive paste and a preparation method thereof, a carbon-coated aluminum foil and a positive plate, and belongs to the technical field of secondary batteries. Based on the total mass of the oily conductive paste being 100%, the oily conductive paste comprises the following components: 6.5-7% of a conductive agent, 2.5-3% of an oily binder, 1-3% of a dispersant and 87-90% of a solvent, the conductive agent comprises a first conductive agent and a second conductive agent, the first conductive agent is at least one of acetylene black, graphite microchips and expanded graphite, and the second conductive agent is at least one of acetylene black, graphite microchips and expanded graphite. The second conductive agent is at least one of crystalline flake graphite, graphite microchips and expanded graphite, the oily binder is at least one of solvent-type polyacrylic acid, solvent-type polyimide, solvent-type polyvinyl alcohol, solvent-type polypropylene and solvent-type butadiene styrene rubber, and the dispersing agent is a modified polyether compound. The solvent is N-methyl pyrrolidone. The oily conductive paste can effectively solve the problem of oil stain on the surface of an aluminum foil, and in addition, the oily conductive paste can coexist with positive electrode paste.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to an oily conductive paste, a preparation method thereof, a carbon-coated aluminum foil, and a positive electrode sheet. Background Art

[0002] The prevailing carbon-coated aluminum foil paste system in the current industry is aqueous-based, and the formula includes: a conductive agent (one or more in combination), a binder (mostly acrylic polymers), a dispersant, and a solvent (deionized water). The conductive paste under this system has high requirements for the substrate (aluminum foil). Especially the rolling oil on the surface of the aluminum foil will directly affect the coating effect of the aqueous conductive paste on its surface, resulting in missed coating, thereby increasing the ohmic resistance of the battery and ultimately affecting the service life of the battery. In the prior art, generally, a corona machine is used to perform surface treatment on the aluminum foil and then coat the aqueous conductive paste. On the one hand, it will increase the production cost of the carbon-coated aluminum foil due to the increase in processes. On the other hand, ozone will be emitted during the corona process.

[0003] Secondly, since the positive electrode paste has extremely high requirements for moisture, the aqueous conductive paste and the positive electrode paste cannot coexist. The production method of the aqueous carbon-coated aluminum foil can only be distributed (the base coating factory and the battery cell factory are established independently), and the construction cost of the base coating factory is relatively high, which will undoubtedly increase the production cost of the carbon-coated aluminum foil and the battery. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to some extent. To this end, an embodiment of the present invention provides an oily conductive paste, a preparation method thereof, a carbon-coated aluminum foil, and a positive electrode sheet. The oily conductive paste can effectively solve the problem of missed coating caused by oil stains on the surface of the aluminum foil. In addition, the oily conductive paste and the positive electrode paste can coexist, and there is no need to establish a separate base coating factory.

[0005] In a first aspect, an embodiment of the present invention provides an oily conductive paste. Based on the total mass of the oily conductive paste being 100%, the oily conductive paste includes the following components: 6.5 - 7% of a conductive agent, 2.5 - 3% of an oily binder, 1 - 3% of a dispersant, and 87 - 90% of a solvent. The conductive agent includes a first conductive agent and a second conductive agent. The first conductive agent is at least one of acetylene black, graphite microparticles, and expanded graphite. The second conductive agent is at least one of flake graphite, graphite microparticles, and expanded graphite. The oily binder is at least one of solvent-based polyacrylic acid, solvent-based polyimide, solvent-based polyvinyl alcohol, solvent-based polypropylene, and solvent-based styrene-butadiene rubber. The dispersant is a modified polyether compound. The solvent is N-methylpyrrolidone.

[0006] The advantages and technical effects brought by the oily conductive paste of the embodiment of the present invention are as follows:

[0007] (1) The oil-based conductive paste of the embodiment of the present invention uses the solvent NMP, which improves the dispersibility of the conductive agent in the oil-based system, makes the surface coating of the aluminum foil more uniform, and has a better appearance. Moreover, NMP is compatible with the rolling oil remaining on the aluminum foil. Therefore, the oil-based conductive paste of the embodiment of the present invention can effectively solve the problem of oil stains on the surface of the aluminum foil.

[0008] (2) The oil-based conductive paste of the embodiment of the present invention uses an oil-based binder, which can be evenly dispersed in NMP, facilitating the improvement of the adhesiveness of the oil-based conductive paste.

[0009] (3) The oil-based conductive paste of the embodiment of the present invention can coexist with the positive electrode paste, which means that the undercoat factory and the battery cell factory can be integrated into an undercoat battery cell factory, greatly reducing the construction and production costs.

[0010] In some embodiments, the solid content of the oil-based conductive paste is 10-12%.

[0011] In some embodiments, the solid content of the oil-based binder is 20-40%.

[0012] In some embodiments, the types of the first conductive agent and the second conductive agent are different.

[0013] In some embodiments, based on the total mass of the oil-based conductive paste being 100%, the content of the first conductive agent is 6-6.5%, and the content of the second conductive agent is 0.4-0.6%.

[0014] In some embodiments, the Dv50 of the solid particles in the oil-based conductive paste is 8.8-9.6 μm.

[0015] Second, the embodiment of the present invention also provides a preparation method of an oil-based conductive paste, including the following steps:

[0016] S1. Add the oil-based binder and the dispersant to part of the solvent, stir and disperse for at least 10 min to obtain a mixture;

[0017] S2. Add the second conductive agent to the mixture, stir and disperse for at least 15 min to obtain a first intermediate;

[0018] S3. Add the first conductive agent to the first intermediate in at least two portions, stir and disperse for at least 140 min to obtain a second intermediate;

[0019] S4. Add the remaining solvent to the second intermediate, stir and disperse for at least 140 min to obtain a conductive paste before grinding;

[0020] S5. Grind and stir the conductive paste before grinding to obtain the oil-based conductive paste.

[0021] The advantages and technical effects brought by the preparation method of the oil-based conductive paste in the embodiments of the present invention are as follows:

[0022] The preparation method in the embodiments of the present invention is simple to operate and suitable for industrial promotion.

[0023] In a third aspect, the embodiments of the present invention provide a carbon-coated aluminum foil, which includes an aluminum foil and a carbon-coated layer provided on the surface of the aluminum foil, and the carbon-coated layer is formed by coating with the oil-based conductive paste of the first aspect.

[0024] The advantages and technical effects brought by the carbon-coated aluminum foil in the embodiments of the present invention are as follows:

[0025] Due to the adoption of the oil-based conductive paste in the embodiments of the present invention, the problem of missed coating caused by oil stains on the surface of the aluminum foil is solved, and there is no need to separately build a primer coating factory and a battery cell factory. Therefore, the production cost of the carbon-coated aluminum foil in the embodiments of the present invention is reduced.

[0026] In a fourth aspect, the embodiments of the present invention provide a positive electrode sheet, which includes the carbon-coated aluminum foil of the third aspect and a positive electrode active layer located on at least one surface of the carbon-coated aluminum foil.

[0027] The advantages and technical effects brought by the positive electrode sheet in the embodiments of the present invention are as follows:

[0028] Due to the adoption of the carbon-coated aluminum foil in the embodiments of the present invention, the production cost of the positive electrode sheet in the embodiments of the present invention is also reduced accordingly. Description of the Drawings

[0029] Figure 1 is a flowchart of the preparation method of the oil-based conductive paste of the present invention.

[0030] Figure 2 is a coating device for the carbon-coated aluminum foil of the present invention. Detailed Embodiments

[0031] The following describes in detail the embodiments of the present invention, and the examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0032] In a first aspect, an embodiment of the present invention provides an oil-based conductive paste. Based on 100% of the total mass of the oil-based conductive paste, the oil-based conductive paste comprises the following components: 6.5-7% of a conductive agent, 2.5-3% of an oil-based binder, 1-3% of a dispersant, and 87-90% of a solvent. The conductive agent includes a first conductive agent and a second conductive agent. The first conductive agent is at least one of acetylene black, graphite microflakes, and expanded graphite. The second conductive agent is at least one of flake graphite, graphite microflakes, and expanded graphite. The oil-based binder is at least one of solvent-based polyacrylic acid (PAA), solvent-based polyimide (PI), solvent-based polyvinyl alcohol (PVA), solvent-based polypropylene (PP), and solvent-based styrene-butadiene rubber (SBR). The dispersant is a modified polyether compound. The solvent is N-methylpyrrolidone (NMP).

[0033] The embodiment of the present invention has developed a new type of oil-based conductive paste, which can replace the corona machine to solve the problem of oil stains on the surface of aluminum foil. While reducing the production cost of the negative electrode sheet, it also reduces the emission of ozone. The oil-based conductive paste of the embodiment of the present invention uses the solvent NMP, which improves the dispersibility of the conductive agent in the oil-based system, makes the surface coating of the aluminum foil more uniform, and has a better appearance. Moreover, NMP is compatible with the rolling oil residue on the aluminum foil. Therefore, the oil-based conductive paste of the embodiment of the present invention can effectively solve the problem of oil stains on the surface of aluminum foil. In addition, the oil-based conductive paste of the embodiment of the present invention can coexist with the positive electrode paste, which means that the undercoat factory and the battery cell factory can be integrated into an undercoat battery cell factory, which can greatly reduce the construction and production costs.

[0034] In the oil-based conductive paste of the embodiment of the present invention, based on 100% of the total mass of the oil-based conductive paste, the content of the conductive agent is 6.5-7%, such as 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7%, etc. The conductive agent with the above content can make the oil-based conductive paste have good conductivity.

[0035] In some embodiments, based on 100% of the total mass of the oil-based conductive paste, the content of the first conductive agent is 6-6.5%, and the content of the second conductive agent is 0.4-0.6%. The compounding of the two conductive agents with the above content is beneficial to improving the conductivity.

[0036] In the oil-based conductive paste of the embodiment of the present invention, based on 100% of the total mass of the oil-based conductive paste, the content of the oil-based binder is 2.5-3%, such as 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc. The binder with the above content helps to improve the adhesion between the carbon-coated layer and the aluminum foil.

[0037] In some embodiments, the solid content of the oily conductive paste is 10-12%, such as 10%, 10.2%, 10.4%, 10.6%, 10.8%, 11%, 11.2%, 11.4%, 11.6%, 11.8%, 12%, etc. Maintaining the above solid content helps the oily conductive paste to be evenly gravure-coated on the aluminum foil, so that the bonding performance distribution is more uniform, which is beneficial to the subsequent coating of the carbon coating. In addition, maintaining the above solid content can improve the effective bonding between the binder and the aluminum foil and enhance the peel strength of the carbon coating.

[0038] In some embodiments, the solid content of the oily binder is 20-40%, such as 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, etc. Keeping the solid content of the oily binder within the above range helps to improve the conductivity and adhesiveness of the carbon coating.

[0039] In some embodiments, the types of the first conductive agent and the second conductive agent are different. The compounding of the two conductive agents is beneficial to improving the conductivity.

[0040] In the oily conductive paste of the embodiment of the present invention, based on the total mass of the oily conductive paste being 100%, the content of the dispersant is 1-3%, such as 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, etc. The dispersant with the above content helps to improve the dispersibility of the conductive agent.

[0041] In the oily conductive paste of the embodiment of the present invention, based on the total mass of the oily conductive paste being 100%, the content of the solvent is 87-90%, such as 87%, 87.5%, 88%, 88.5%, 89%, 89.5%, 90%, etc. The solvent with the above content can make the oily conductive paste maintain a suitable solid content and viscosity, which is beneficial to uniform coating.

[0042] In some embodiments, the Dv50 of the solid particles in the oily conductive paste is 8.8-9.6 μm, such as 8.8 μm, 9.0 μm, 9.2 μm, 9.4 μm, 9.6 μm, etc. When the Dv50 of the solid particles in the oily conductive paste is within the above range, it helps to improve the conductivity and stability of the oily conductive paste. It should be understood that Dv50 refers to the particle size corresponding to the cumulative volume distribution percentage reaching 50%, that is, the volume content of the particles less than or equal to this particle size accounts for 50% of the total volume of all particles.

[0043] Second, the embodiment of the present invention provides a preparation method of an oily conductive paste, as Figure 1 shown, including the following steps:

[0044] S1. adding the oily binder and the dispersant to part of the solvent, stirring and dispersing for at least 10 min to obtain a mixture;

[0045] S2. Adding the second conductive agent to the mixture, stirring and dispersing for at least 15 minutes to obtain a first intermediate;

[0046] S3. Add the first conductive agent to the first intermediate at least twice, and stir and disperse for at least 140 minutes to obtain a second intermediate;

[0047] S4. Add the remaining solvent to the second intermediate, stir and disperse for at least 140 min to obtain a conductive slurry before grinding;

[0048] S5. Grind and stir the pre-grinding conductive paste to obtain the oily conductive paste.

[0049] In the preparation method of the embodiment of the present invention, the oily binder and dispersant can be uniformly dispersed in part of the solvent in step S1, and then the second conductive agent can be uniformly dispersed in the solvent in step S2, and then the first conductive agent can be uniformly dispersed in the solvent in step S3, and then the remaining solvent is added in step S4 to adjust the solid content and viscosity of the slurry, and finally the final oily conductive slurry is obtained by grinding and stirring. Among them, step S3 needs to add the first conductive agent at least twice because the loose density of graphite is very small, that is, the volume per unit weight is very large, so adding it all at once will cause the problem that the mixing tank cannot be loaded, and it must be added in batches.

[0050] In a third aspect, an embodiment of the present invention provides a carbon-coated aluminum foil, comprising an aluminum foil and a carbon coating layer disposed on a surface of the aluminum foil, wherein the carbon coating layer is formed by coating the oily conductive slurry of the first aspect.

[0051] Since the oily conductive slurry of the embodiment of the present invention is used, the problem of missing coating caused by oil stains on the surface of the aluminum foil is solved, and there is no need to build a primer factory and a battery cell factory separately, so the production cost of the carbon-coated aluminum foil of the embodiment of the present invention is reduced.

[0052] In a fourth aspect, an embodiment of the present invention provides a positive electrode sheet, comprising the carbon-coated aluminum foil of the third aspect and a positive electrode active layer located on at least one side surface of the carbon-coated aluminum foil.

[0053] Since the carbon-coated aluminum foil of the embodiment of the present invention is adopted, the production cost of the positive electrode sheet of the embodiment of the present invention is also reduced.

[0054] The present invention is described in detail below with reference to the embodiments and the accompanying drawings.

[0055] Example 1

[0056] (1) Add 2.5% oily polyacrylic acid (PAA, with a solid content of PAA being 27.5% ± 2%) and 1% of a modified polyether compound to 50% of NMP, and stir and disperse at a speed of 800 rmp for 10 min to obtain a mixture;

[0057] (2) Add 0.5% of the second conductive agent, flake graphite, to the mixture, and stir and disperse at a speed of 2000 rmp for 15 min to obtain a first intermediate;

[0058] (3) Add the first conductive agent, acetylene black, to the first intermediate in two portions, with a total content of the first conductive agent being 6.0%, and stir and disperse at a speed of 3600 rmp for 140 min to obtain a second intermediate;

[0059] (4) Add 40% of NMP to the second intermediate and stir for 140 min to obtain the conductive paste before grinding;

[0060] (5) Grind while stirring to obtain the final oily conductive paste as shown in Table 1.

[0061] Double-sidedly coat the above-mentioned oily conductive paste on the surface of the aluminum foil to obtain a carbon-coated layer with a thickness of 1 μm on one side and 2 μm on both sides.

[0062] The coating device used is as Figure 2 shown, including: ① aluminum foil unwinding device, ② preheating oven, ③ gravure coater (side A), ④ extrusion coater (side A), ⑤ double-layer oven, ⑥ gravure coater (side B), ⑦ extrusion coater (side B), ⑧ winding device.

[0063] The working flow chart of this coating device is as Figure 2 shown: (1) Unwind the aluminum foil using the aluminum foil unwinding device ①, (2) Dry the aluminum foil using the preheating oven ② to remove the rolling oil on the surface of the aluminum foil, (3) Coat the oily conductive paste of this embodiment on side A of the aluminum foil using the micro gravure coater ③ to obtain a carbon-coated layer A, and coat the positive electrode paste on the surface of the carbon-coated layer A using the extrusion coater ④ to obtain a semi-finished positive electrode sheet, (5) Dry the above-mentioned semi-finished positive electrode sheet using the double-layer oven ⑤, with the oven length being 160 m and steam heating being adopted, (6) Coat the oily conductive paste of this embodiment on side B of the aluminum foil, where side B is opposite to side A, to obtain a carbon-coated layer B, (7) Coat the positive electrode paste on the surface of the carbon-coated layer B using the extrusion coater ⑦ to obtain a positive electrode sheet, (8) Wind up the positive electrode sheet using the winding device ⑧.

[0064] Example 2

[0065] (1) Add 3% oily polyacrylic acid (PAA, PAA solid content is 27.5% ± 2%) and 1% modified polyether compound into 50% NMP, stir and disperse at 800 rmp for 10 min to obtain a mixture;

[0066] (2) Add 0.5% second conductive agent flake graphite into the mixture, stir and disperse at 2000 rmp for 15 min to obtain a first intermediate;

[0067] (3) Add the first conductive agent acetylene black into the first intermediate in two portions, with a total content of the first conductive agent being 6.5%, stir and disperse at 3600 rmp for 140 min to obtain a second intermediate;

[0068] (4) Add 39% NMP into the second intermediate, stir for 140 min to obtain a conductive paste before grinding;

[0069] (5) Grind and stir simultaneously to obtain the final oily conductive paste as shown in Table 1.

[0070] Double-side coat the above-mentioned oily conductive paste on the surface of aluminum foil to obtain a carbon-coated layer with a single-side thickness of 1 μm and a double-side thickness of 2 μm.

[0071] Example 3

[0072] (1) Add 2.5% oily polyacrylic acid (PAA, PAA solid content is 27.5% ± 2%) and 3% modified polyether compound into 50% NMP, stir and disperse at 800 rmp for 10 min to obtain a mixture;

[0073] (2) Add 0.5% second conductive agent flake graphite into the mixture, stir and disperse at 2000 rmp for 15 min to obtain a first intermediate;

[0074] (3) Add the first conductive agent acetylene black into the first intermediate in two portions, with a total content of the first conductive agent being 6.0%, stir and disperse at 3600 rmp for 140 min to obtain a second intermediate;

[0075] (4) Add 38% NMP into the second intermediate, stir for 140 min to obtain a conductive paste before grinding;

[0076] (5) Grind and stir simultaneously to obtain the final oily conductive paste as shown in Table 1.

[0077] Double-side coat the above-mentioned oily conductive paste on the surface of aluminum foil to obtain a carbon-coated layer with a single-side thickness of 1 μm and a double-side thickness of 2 μm.

[0078] Example 4

[0079] The preparation method of this example is the same as that of Example 1, except that the first conductive agent is graphite microflakes.

[0080] The above-mentioned oily conductive paste was coated on both sides of the aluminum foil surface to obtain a carbon-coated layer with a thickness of 1 μm on one side and 2 μm on both sides.

[0081] Example 5

[0082] The preparation method of this example is the same as that of Example 1, except that the second conductive agent is expanded graphite.

[0083] The above-mentioned oily conductive paste was coated on both sides of the aluminum foil surface to obtain a carbon-coated layer with a thickness of 1 μm on one side and 2 μm on both sides.

[0084] Example 6

[0085] The preparation method of this example is the same as that of Example 1, except that the binder is oily polyimide (PI, the solid content of PI is 27.5% ± 2%).

[0086] The above-mentioned oily conductive paste was coated on both sides of the aluminum foil surface to obtain a carbon-coated layer with a thickness of 1 μm on one side and 2 μm on both sides.

[0087] Example 7

[0088] The preparation method of this example is the same as that of Example 1, except that the binder is oily styrene-butadiene rubber (SBR, the solid content of SBR is 40.0% ± 2%).

[0089] The above-mentioned oily conductive paste was coated on the aluminum foil surface to obtain a carbon-coated layer with a thickness of 1 μm on one side and 2 μm on both sides.

[0090] Comparative Example 1

[0091] (1) 2.5% of oily PVDF (the solid content of PVDF is 7%) and 1% of modified polyether compound were added to 50% NMP, and stirred and dispersed at 800 rmp for 120 min to prepare a PVDF adhesive solution;

[0092] (2) 0.5% of the second conductive agent, flake graphite, was added to the PVDF adhesive solution, and stirred and dispersed at 2000 rmp for 15 min to obtain a first intermediate;

[0093] (3) The first conductive agent, acetylene black, was added to the first intermediate in two portions, and the total content of the first conductive agent was 6.0%. It was stirred and dispersed at 3600 rmp for 140 min to obtain a second intermediate;

[0094] (4) 40% of NMP was added to the second intermediate, and stirred and dispersed for 140 min to obtain the conductive paste before grinding;

[0095] (5) Grind and stir simultaneously to obtain the final oily conductive paste as shown in Table 1.

[0096] The above-mentioned oily conductive paste has a high viscosity and cannot be coated.

[0097] Comparative Example 2

[0098] (1) Add 2.5% of oily polyacrylic acid (PAA, the solid content of PAA is 27.5% ± 2%) and 1% of modified polyether compound into 50% of NMP, and stir and disperse at a speed of 800 rmp for 10 min to obtain a mixture.

[0099] (2) Add 6.5% of the second conductive agent, flake graphite, into the mixture, and stir and disperse at a speed of 2000 rmp for 140 min to obtain the first intermediate.

[0100] (3) Add 40% of NMP into the second intermediate and stir for 140 min to obtain the conductive paste before grinding.

[0101] (4) Grind and stir simultaneously to obtain the final oily conductive paste as shown in Table 1.

[0102] Double-side coat the above-mentioned oily conductive paste on the surface of aluminum foil to obtain a carbon-coated layer with a single-side thickness of 1 μm and a double-side thickness of 2 μm.

[0103] Comparative Example 3

[0104] (1) Add 2.5% of aqueous polyacrylic acid (PAA, the solid content of PAA is 27.5% ± 2%) and 1% of modified polyether compound into 50% of deionized water, and stir and disperse at a speed of 800 rmp for 120 min to obtain a mixture.

[0105] (2) Add 0.5% of the second conductive agent, flake graphite, into the mixture, and stir and disperse at a speed of 2000 rmp for 15 min to obtain the first intermediate.

[0106] (3) Add the first conductive agent, acetylene black, into the first intermediate in two portions, the content of the first conductive agent is 6.0%, and stir and disperse at a speed of 3600 rmp for 140 min to obtain the second intermediate.

[0107] (4) Add 40% of deionized water into the second intermediate and stir and disperse for 140 min to obtain the conductive paste before grinding.

[0108] (5) Grind and stir simultaneously to obtain the final aqueous conductive paste as shown in Table 1.

[0109] Double-side coat the above-mentioned aqueous conductive paste on the surface of aluminum foil to obtain a carbon-coated layer with a single-side thickness of 1 μm and a double-side thickness of 2 μm.

[0110] Performance Test:

[0111] (1) Adhesion:

[0112] ① Prepare samples: Wear rubber gloves to take samples. Take a carbon-coated aluminum foil sample with a length of 30 cm and a flat surface;

[0113] ② Preparation before testing: Prepare 3 strips of 3M tape, each 10 cm long;

[0114] ③ Start testing: Stick the 3M tape to the carbon-coated aluminum foil, roll it back and forth 3 times with a manual roller press, then tear the 3M tape at a 180° angle from the coating, connect the tensile machine, and test the garbage;

[0115] ④ Read and record data: Conduct the test 3 times, read the data of the three tests, and take the average value (if the data of the three tests vary greatly, retesting is required).

[0116] (2) Membrane Resistance:

[0117] ① Prepare samples: Wear rubber gloves to take samples and cut them into circular samples with a diameter of 19 mm;

[0118] ② Turn on the machine: Turn on the power of the device and the computer;

[0119] ③ Set parameters: Set the parameters of the samples to be tested, such as specifications, thickness dimensions, resistance range, required air pressure, pressure holding time, etc.;

[0120] ④ Preparation before testing: Wipe the electrode posts with alcohol and lint-free cloth;

[0121] ⑤ Start testing: Click to connect the instrument to the computer and start the test;

[0122] ⑥ Place the sample and start: Place the taken sample in the center of the metal probe and click the start button to test;

[0123] ⑦ Read and record data: Read and record the resistance data of the sample;

[0124] ⑧ After the measurement is completed, turn off the power.

[0125] Table 1. Physical properties of the conductive pastes in the above examples and comparative examples, as well as the adhesion and membrane resistance of the carbon-coated layer

[0126]

[0127]

[0128] In the present invention, terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0129] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. An oily conductive paste, characterized in that: Taking the total mass of the oily conductive paste as 100%, the oily conductive paste includes the following components: 6.5-7% of a conductive agent, 2.5-3% of an oily binder, 1-3% of a dispersant and 87-90% of a solvent, the conductive agent includes a first conductive agent and a second conductive agent, the first conductive agent is at least one of acetylene black, graphite microsheets and expanded graphite, the second conductive agent is at least one of flake graphite, graphite microsheets and expanded graphite, the oily binder is at least one of solvent-based polyacrylic acid, solvent-based polyimide, solvent-based polyvinyl alcohol, solvent-based polypropylene and solvent-based styrene-butadiene rubber, the dispersant is a modified polyether compound, and the solvent is N-methylpyrrolidone.

2. The oily conductive paste according to claim 1, characterized in that: The solid content of the oily conductive paste is 10-12%.

3. The oily conductive paste according to claim 1 or 2, characterized in that: The solid content of the oily binder is 20-40%.

4. The oily conductive paste according to claim 1 or 2, characterized in that: The first conductive agent and the second conductive agent are of different types.

5. The oily conductive paste according to claim 1 or 2, characterized in that: Based on the total mass of the oily conductive paste being 100%, the content of the first conductive agent is 6-6.5%, and the content of the second conductive agent is 0.4-0.6%.

6. The oily conductive paste according to claim 1 or 2, characterized in that: The Dv50 of the solid particles in the oily conductive slurry is 8.8-9.6 μm.

7. The method for preparing the oily conductive paste according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. adding the oily binder and the dispersant to part of the solvent, stirring and dispersing for at least 10 min to obtain a mixture; S2. Adding the second conductive agent to the mixture, stirring and dispersing for at least 15 minutes to obtain a first intermediate; S3. Add the first conductive agent to the first intermediate at least twice, and stir and disperse for at least 140 minutes to obtain a second intermediate; S4. Add the remaining solvent to the second intermediate, stir and disperse for at least 140 min to obtain a conductive slurry before grinding; S5. Grind and stir the pre-grinding conductive paste to obtain the oily conductive paste.

8. A carbon-coated aluminum foil, characterized in that: It comprises an aluminum foil and a carbon coating layer arranged on the surface of the aluminum foil, wherein the carbon coating layer is formed by coating the oily conductive paste according to any one of claims 1 to 6.

9. A positive electrode sheet, characterized in that: It comprises the carbon-coated aluminum foil as claimed in claim 8 and a positive electrode active layer located on at least one side surface of the carbon-coated aluminum foil.

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