Water-based composite conductive paste, carbon-coated aluminum foil, and preparation method and application of carbon-coated aluminum foil

Abstract

The invention discloses a water-based composite conductive paste, which comprises a graphene dispersion paste, a thickening agent, a conductive agent and a binder, in the graphene dispersed slurry, the content of graphene is 3-4wt%; the thickening agent accounts for 40-60 wt% of the graphene content; the conductive agent accounts for 40-70wt% of the content of the graphene; the binder accounts for 50-75 wt% of the content of the graphene. Compared with dispersion slurry such as carbon black or graphite, the water-based composite conductive slurry and the graphene dispersion slurry have stronger adhesive force with aluminum foil and smaller impedance, and polarization of the battery in the charge-discharge cycle process can be effectively slowed down. In addition, the graphene, the carbon nanotubes and the conductive carbon black in the composite conductive slurry form a multi-dimensional conductive network, so that the contact resistance between the current collector and the active material is reduced, and the electron transmission efficiency is improved; compared with reduced graphene oxide, the water-based graphene dispersion slurry prepared by adopting an electrochemical stripping method has the advantages that the process is simpler, and the dispersity is better.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of positive electrode current collector, in particular to a water-based composite conductive paste, a preparation method of the water-based composite conductive paste, a carbon-coated aluminum foil, a preparation method of the carbon-coated aluminum foil and an application of the water-based composite conductive paste. BACKGROUND

[0002] The carbon-coated aluminum foil is widely used as a commercialized positive electrode current collector, because the carbon coating layer increases the contact area between the electrode material and the current collector, improves the adhesion between the electrode material and the current collector to a certain extent, and reduces the internal resistance. At the same time, the carbon coating layer can also protect the surface of the aluminum foil, prevent the corrosion of the aluminum foil, and improve the cycle life of the battery. However, the material of the carbon coating layer is generally carbon black or graphite, and such coating layer has problems such as low adhesion, large impedance, and serious polarization in the charging and discharging cycle process. In addition, the thickness of the carbon coating layer is generally thick, and the thick carbon coating layer will cause the problem of low electrical conductivity.

[0003] Therefore, it is necessary to provide a carbon-coated aluminum foil with strong adhesion, small impedance and thin coating thickness. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a water-based composite conductive paste, a carbon-coated aluminum foil and a preparation method and application thereof, so as to solve the problems of low adhesion, large impedance, serious polarization in the charging and discharging cycle process and the like of the coating layer.

[0005] In one aspect, the present application provides a water-based composite conductive paste, which comprises a graphene dispersion paste, a thickening agent, a conductive agent and a binder. In the graphene dispersion paste, the content of graphene is 3-4 wt%; the thickening agent is 40-60 wt% of the content of graphene; the conductive agent is 40-70 wt% of the content of graphene; and the binder is 50-75 wt% of the content of graphene.

[0006] Optionally, the graphene dispersion paste is prepared by an electrochemical exfoliation method.

[0007] Optionally, the thickening agent is at least one of sodium carboxymethyl cellulose and polyacrylamide.

[0008] Optionally, the conductive agent is at least one of conductive carbon black (SP), Ketjen black (KB) and acetylene carbon black (AB).

[0009] Optionally, the binder is at least one of styrene-butadiene rubber, polyurethane and acrylic acid.

[0010] Secondly, this application provides a method for preparing the above-mentioned aqueous composite conductive slurry, wherein a graphene dispersion slurry is weighed, a thickener is added to it, and the mixture is stirred and dispersed for 120 min, a conductive agent is added, and the mixture is stirred and dispersed for 30 min, and finally a binder is added and stirred and dispersed for 60 min to obtain the aqueous composite conductive slurry.

[0011] Thirdly, this application provides a carbon-coated aluminum foil, including the aqueous composite conductive paste described above.

[0012] Optionally, the aluminum foil has a thickness of 12 μm; the aqueous composite conductive paste has a thickness of 1~2 μm.

[0013] Fourthly, this application provides a method for preparing the above-mentioned carbon-coated aluminum foil, wherein the aqueous composite conductive paste described above is coated onto the aluminum foil using a wet coating method, and the aluminum foil is obtained by drying at 75°C and rolling.

[0014] Fifthly, this application provides the application of the above-mentioned aqueous composite conductive paste in the field of positive electrode current collectors.

[0015] In summary, the present invention has at least one of the following beneficial technical effects: 1. Compared to dispersions made of carbon black or graphite, graphene dispersions exhibit stronger adhesion to aluminum foil and lower impedance, effectively mitigating polarization during battery charge-discharge cycles. Furthermore, the graphene, carbon nanotubes, and conductive carbon black in the composite conductive slurry form a multidimensional conductive network, reducing the contact resistance between the current collector and the active material and improving electron transport efficiency. 2. The electrochemical exfoliation method used in this invention to prepare aqueous graphene dispersion slurry is simpler and produces better dispersibility compared to reduced graphene oxide. Detailed Implementation

[0016] The present application will be further described in detail below with reference to the embodiments.

[0017] Unless otherwise specified, the main components involved in the following embodiments of this application are all purchased from commercially available products.

[0018] Graphene dispersion slurry: preferably prepared by electrochemical exfoliation method.

[0019] Conductive agent: SP conductive agent (carbon black conductive agent) is preferred.

[0020] Thickener: Sodium carboxymethyl cellulose is preferred as a thickener.

[0021] Adhesive: Styrene-butadiene rubber adhesive is preferred. Specific Implementation Preparation Example 1 In this preparation example, the aqueous composite conductive paste is prepared as follows: Weigh 1000g of graphene dispersion slurry with a solid content of 3%, add 12g of sodium carboxymethyl cellulose thickener, stir and disperse for 120min, then add 12g of SP carbon black conductive agent, stir and disperse for 30min, and finally add 15g of styrene-butadiene rubber binder, stir and disperse for 60min to prepare water-based composite conductive slurry.

[0023] Preparation Example 2 In this preparation example, the method for preparing the aqueous composite conductive paste differs from that in Preparation Example 1 in that the amount of SP carbon black conductive agent added is different, as detailed below: Weigh 1000g of graphene dispersion slurry with a solid content of 3%, add 12g of sodium carboxymethyl cellulose thickener, stir and disperse for 120min, then add 15g of SP carbon black conductive agent, stir and disperse for 30min, and finally add 15g of styrene-butadiene rubber binder, stir and disperse for 60min to prepare an aqueous composite conductive slurry.

[0024] Preparation Example 3 In this preparation example, the method for preparing the aqueous composite conductive paste differs from that in Preparation Example 1 in that the amount of SP carbon black conductive agent added is different, as detailed below: Weigh 1000g of graphene dispersion slurry with a solid content of 3%, add 12g of sodium carboxymethyl cellulose thickener, stir and disperse for 120min, then add 21g of SP carbon black conductive agent, stir and disperse for 30min, and finally add 15g of styrene-butadiene rubber binder, stir and disperse for 60min to prepare water-based composite conductive slurry.

[0025] Preparation Example 4 In this preparation example, the method for preparing the aqueous composite conductive paste differs from that in Preparation Example 1 in that SP carbon black conductive agent is not added in this preparation example, as detailed below: Weigh 1000g of graphene dispersion slurry with a solid content of 3%, add 12g of sodium carboxymethyl cellulose thickener, stir and disperse for 120min, and finally add 15g of styrene-butadiene rubber binder, stir and disperse for 60min to prepare water-based composite conductive slurry.

[0026] Example 1 In this embodiment, the aqueous composite conductive paste prepared in Preparation Example 1 is used to prepare carbon-coated aluminum foil, as follows: The aqueous composite conductive paste prepared in Preparation Example 1 was coated onto an aluminum foil with a thickness of 12 μm using a wet coating method. After drying at 75°C and rolling, a carbon-coated aluminum foil was obtained, with a carbon coating layer thickness of 1 μm.

[0027] Example 2 In this embodiment, the aqueous composite conductive paste prepared in Preparation Example 2 is used to prepare carbon-coated aluminum foil, as follows: The aqueous composite conductive paste prepared in Preparation Example 2 was coated onto an aluminum foil with a thickness of 12 μm using a wet coating method. After drying at 75°C and rolling, a carbon-coated aluminum foil was obtained, with a carbon coating layer thickness of 1 μm.

[0028] Example 3 In this embodiment, the aqueous composite conductive paste prepared in Preparation Example 3 is used to prepare carbon-coated aluminum foil, as follows: The aqueous composite conductive paste prepared in Preparation Example 3 was coated onto an aluminum foil with a thickness of 12 μm using a wet coating method. After drying at 75°C and rolling, a carbon-coated aluminum foil was obtained, with a carbon coating layer thickness of 1 μm.

[0029] Comparative Example 1 This comparative example uses the aqueous composite conductive paste prepared in Preparation Example 4 to prepare carbon-coated aluminum foil, as follows: The aqueous composite conductive paste prepared in Preparation Example 4 was coated onto an aluminum foil with a thickness of 12 μm using a wet coating method. After drying at 75°C and rolling, a carbon-coated aluminum foil was obtained, with a carbon coating layer thickness of 1 μm.

[0030] Application Example 1 Lithium-ion batteries were prepared using the carbon-coated aluminum foil prepared in Example 1, as detailed below: A positive electrode was obtained by coating lithium iron phosphate slurry onto carbon-coated aluminum foil prepared in Example 1, and a negative electrode was obtained by coating graphite slurry onto copper foil. After stacking, encapsulation, baking, and formation processes, a lithium-ion battery was obtained. The electrolyte salt was lithium hexafluorophosphate, with an electrolyte concentration of 1 mol / L. The solvents were ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with a solvent mass ratio of 1:2:1.

[0031] Application Example 2 Lithium-ion batteries were prepared using the carbon-coated aluminum foil prepared in Example 2, as detailed below: A positive electrode was obtained by coating lithium iron phosphate slurry onto carbon-coated aluminum foil prepared in Example 2, and a negative electrode was obtained by coating graphite slurry onto copper foil. After stacking, encapsulation, baking, and formation processes, a lithium-ion battery was obtained. The electrolyte salt was lithium hexafluorophosphate, with an electrolyte concentration of 1 mol / L. The solvents were ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with a solvent mass ratio of 1:2:1.

[0032] Application Example 3 Lithium-ion batteries were prepared using the carbon-coated aluminum foil prepared in Example 3, as detailed below: A positive electrode was obtained by coating lithium iron phosphate slurry onto carbon-coated aluminum foil prepared in Example 3, and a negative electrode was obtained by coating graphite slurry onto copper foil. After stacking, encapsulation, baking, and formation processes, a lithium-ion battery was obtained. The electrolyte salt was lithium hexafluorophosphate, with an electrolyte concentration of 1 mol / L. The solvents were ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with a solvent mass ratio of 1:2:1.

[0033] Application Example 4 Lithium-ion batteries were prepared using the carbon-coated aluminum foil prepared in Comparative Example 1, as detailed below: A positive electrode was obtained by coating lithium iron phosphate slurry onto carbon-coated aluminum foil prepared in Comparative Example 1, and a negative electrode was obtained by coating graphite slurry onto copper foil. After stacking, encapsulation, baking, and formation processes, a lithium-ion battery was obtained. The electrolyte salt was lithium hexafluorophosphate, with an electrolyte concentration of 1 mol / L. The solvents were ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with a solvent mass ratio of 1:2:1.

[0034] The lithium-ion batteries prepared in Application Examples 1-4 above were subjected to performance testing, and the testing methods are as follows: I. Conductivity Testing Methods 1) Sampling: Cut out a 2cm×2cm square sample from the evenly coated electrode area.

[0035] 2) Testing: Turn on the four-probe tester and press the four probes vertically and steadily onto the sample surface. Ensure that the four probes are in good contact with the sample and that their orientation is parallel to the sample edge.

[0036] 3) Data recording: Measure at multiple points on different locations on the sample surface, record the test data and calculate the average value.

[0037] II. Adhesion 1) Sampling: Samples are taken along the coating direction (MD) and transverse direction (TD). Standard size: 50mm wide × 150mm long.

[0038] 2) Tape application and pressing: Use a tape cutter to cut tape to a length of 75mm and a width of 25mm. Apply the tape to the middle of the electrode and let it stand for 60±5 seconds after application.

[0039] 3) Testing: Use a tensile testing machine to perform a 180° tensile test.

[0040] 4) Data recording: No less than 3 test samples in each direction, record the test values ​​and calculate the average value.

[0041] III. 5C discharge capacity retention rate At an ambient temperature of (25±3)℃, the battery cell is charged to 3.65V using a 1C constant current and constant voltage method, with a cutoff current of 0.05C. It is then discharged to 2.0V using 1C and 50C constant current methods. Calculate the ratio of the 5C discharge capacity to the 1C discharge capacity.

[0042] IV. Capacity retention rate after 500 cycles At (25±3)℃, 1C standard charge and discharge, 100% DOD 500 cycles.

[0043] The test results are shown in Table 1.

[0044] Table 1 Performance parameters of lithium-ion batteries prepared in Application Examples 1-4 Lithium ion battery Electrical conductivity (S / cm) Adhesion (N) 5C discharge capacity retention rate (%) 500-cycle capacity retention rate (%) Application Example 1 39.67 8.2 98.75 93.42 Application Example 2 50.16 9.3 99.24 93.57 Application Example 3 35.39 7.6 98.68 93.06 Application Example 4 31.62 7.1 97.62 92.10 The cathode material prepared by using the carbon-coated aluminum foil prepared with the aqueous composite conductive slurry prepared in this application has high conductivity and strong adhesion; and the lithium-ion battery prepared by this method has high 5C discharge capacity retention and high capacity retention after 500 cycles.

[0045] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A water-based composite conductive paste, characterized in that, Includes graphene dispersions, thickeners, conductive agents, and binders; The graphene dispersion slurry contains 3-4 wt% graphene; the thickener contains 40-60 wt% graphene; the conductive agent contains 40-70 wt% graphene; and the binder contains 50-75 wt% graphene.

2. The water-based composite conductive paste according to claim 1, characterized in that, The graphene dispersion slurry was prepared by electrochemical exfoliation.

3. The water-based composite conductive paste according to claim 1, characterized in that, The thickener is at least one of sodium carboxymethyl cellulose and polyacrylamide.

4. The water-based composite conductive paste according to claim 1, characterized in that, The conductive agent is at least one of conductive carbon black, Ketjen black, and acetylene black.

5. The water-based composite conductive paste according to claim 1, characterized in that, The adhesive is at least one of styrene-butadiene rubber, polyurethane, and acrylic acid.

6. A method for preparing the aqueous composite conductive paste according to claim 1, characterized in that, Weigh out the graphene dispersion slurry, add a thickener, stir and disperse for 120 minutes, add a conductive agent, stir and disperse for 30 minutes, and finally add a binder, stir and disperse for 60 minutes to obtain an aqueous composite conductive slurry.

7. A carbon-coated aluminum foil, characterized in that, Includes the water-based composite conductive paste as described in claim 1.

8. The carbon-coated aluminum foil according to claim 7, characterized in that, The aluminum foil has a thickness of 12 μm; the water-based composite conductive paste has a thickness of 1~2 μm.

9. A method for preparing carbon-coated aluminum foil according to claim 7, characterized in that, The aqueous composite conductive paste described in claim 1 is coated onto aluminum foil using a wet coating method, and then dried at 75°C and rolled to obtain carbon-coated aluminum foil.

10. The application of the aqueous composite conductive paste according to claim 1 in the field of positive electrode current collectors.