Graphene carbon nanotube positive electrode sheet and preparation method thereof

Abstract

The application provides a graphene carbon nanotube positive electrode sheet. The positive electrode sheet comprises a current collector and a conductive coating layer coated on the current collector. The conductive coating layer is obtained by coating and curing a conductive slurry. The conductive slurry is composed of the following components: active material: organic bentonite: polyacrylic acid: carboxymethyl cellulose: conductive agent, with a mass ratio of 70-97.5%: 0.1-5%: 0.5-15%: 0.5-10%: 1-5%; wherein the conductive agent is composed of carbon nanotubes: graphene: super-conductive carbon black, with a mass ratio of 0.5-1.5: 0.5-1.5: 1-2. The particle size of the graphene is 50-400 nm, and the carbon nanotube diameter is 5-10 nm. The active material is composed of LiNi 0.8 Co 0.15 Al 0.05 O2 and LiMn2O4, with a mass ratio of 1.7-8: 1. The thickness of the conductive coating layer is 0.1-4 microns. The application provides an electrode material with good conductivity, corrosion resistance, heat dissipation and adhesion.

Description

Technical Field

[0001] This invention relates to the field of electrode materials, specifically to a graphene carbon nanotube positive electrode and a method for preparing the graphene carbon nanotube positive electrode. Background Technology

[0002] Existing lithium-ion batteries generally use carbon-coated aluminum foil as the carrier of positive electrode material. However, carbon-coated aluminum foil has some defects, such as poor adhesion of the carbon coating layer, which makes it easy to peel off. In order to improve the adhesion, the binder of carbon conductive paste is added, which will reduce the conductivity of the carbon coating layer. In addition, there is an aluminum oxide film on the surface of the aluminum foil, which affects the conductivity of the carbon-coated aluminum foil.

[0003] Therefore, developing a positive electrode with good conductivity, corrosion resistance, heat dissipation, and adhesion, which can effectively improve the discharge capacity and extend the cycle life of lithium batteries, is of great significance for promoting the further development of the lithium battery field. Summary of the Invention

[0004] The inventors discovered through analysis that existing methods for bonding carbon-coated aluminum foil to the current collector involve adding a dispersant to ensure the carbon coating adheres firmly. However, this requires a relatively large amount of dispersant to guarantee adhesion between the carbon coating and the current collector. Furthermore, because the dispersant is a poor conductor of electrons, it limits the electron conductivity of the conductive coating, thereby limiting the overall electron conductivity of the electrode and hindering the rate performance of the electrochemical system. This invention, through the compounding of active materials, three composite conductive agents, and a dispersant, prepares a graphene carbon nanotube positive electrode sheet that not only suppresses battery polarization and reduces thermal effects, but also improves the conductivity of the positive electrode sheet without affecting the bonding force between the conductive coating and the current collector.

[0005] This invention provides a graphene carbon nanotube positive electrode sheet, comprising: a current collector and a conductive coating coated on the current collector; the conductive coating is obtained by coating and curing a conductive slurry. The conductive slurry is composed of the following components: active material: organic bentonite: polyacrylic acid: carboxymethyl cellulose: conductive agent in a mass ratio of 70-97.5%: 0.1-5%: 0.5-15%: 0.5-10%: 1-5%; wherein the conductive agent is composed of carbon nanotubes: graphene: super conductive carbon black in a mass ratio of 0.5-1.5: 0.5-1.5: 1-2. The graphene has a particle size of 50-400 nm, and the carbon nanotubes have a diameter of 5-10 nm. The active material is composed of LiNi... 0.8 Co 0.15 Al 0.05 O2 and LiMn2O4 are composed in a mass ratio of 1.7 to 8:1. The thickness of the conductive coating is 0.1 to 4 μm.

[0006] Another aspect of the present invention provides a method for preparing a graphene carbon nanotube positive electrode sheet, the method comprising the following steps:

[0007] The conductive paste is coated onto the current collector, dried, and then pressed to obtain the graphene carbon nanotube positive electrode sheet.

[0008] The beneficial effects achieved by this invention include at least one of the following:

[0009] 1. The graphene carbon nanotube cathode of the present invention improves the conductivity of the cathode without affecting the bonding force between the conductive coating and the current collector. For example, at room temperature, the conductivity does not exceed 3 × 10⁻⁶. -8 Ω·m, electrode peel strength not less than 90 N / m.

[0010] 2. The graphene carbon nanotube cathode prepared by this invention provides an electrode material with good conductivity, corrosion resistance, heat dissipation, and adhesion through the coating of conductive paste and current collector. Furthermore, the graphene carbon nanotube cathode prepared by this invention through the compounding of active material, three composite conductive agents, and dispersant can suppress battery polarization and reduce thermal effects. Detailed Implementation

[0011] In an exemplary embodiment of the present invention, the graphene carbon nanotube positive electrode includes: a current collector and a conductive coating coated on the current collector; the conductive coating is obtained by coating and curing a conductive paste; the current collector may be an aluminum foil, however, the present invention is not limited thereto.

[0012] The conductive paste is composed of the following components: active material: organic bentonite: polyacrylic acid: carboxymethyl cellulose: conductive agent in a mass ratio of 70-97.5%: 0.1-5%: 0.5-15%: 0.5-10%: 1-5%; wherein the conductive agent is composed of carbon nanotubes: graphene: super conductive carbon black in a mass ratio of 0.5-1.5: 0.5-1.5: 1-2. The graphene has a particle size of 50-400 nm, and the carbon nanotubes have a diameter of 5-10 nm. The active material is composed of LiNi 0.8 Co 0.15 Al 0.05 O2 and LiMn2O4 are composed in a mass ratio of 1.7 to 8:1. The thickness of the conductive coating is 0.1 to 4 μm.

[0013] In an exemplary embodiment of the present invention, the thickness of the conductive coating can be 2.5–3.5 μm. Insufficient thickness of the conductive coating will make the current collector susceptible to corrosion by the electrode active material, while excessive thickness of the conductive coating on the current collector will affect the electrochemical performance of the electrochemical system.

[0014] In an exemplary embodiment of the present invention, the mass ratio of the active material: organobentonite: polyacrylic acid: carboxymethyl cellulose: conductive agent is 75-90%: 1.5-4%: 3-10%: 2-8%: 2-4%. Further, the mass ratio of the active material: organobentonite: polyacrylic acid: carboxymethyl cellulose: conductive agent is 80-85%: 2-3%: 5-8%: 4-6%: 2.5-3%.

[0015] In an exemplary embodiment of the present invention, the mass ratio of carbon nanotubes:graphene:superconducting carbon black is 0.8–1.2:0.8–1.2:1.2–1.6. The graphene has a particle size of 100–300 nm, and the carbon nanotubes have a diameter of 7–9 nm.

[0016] In an exemplary embodiment of the present invention, the solvent for the conductive paste is at least one selected from deionized water, anhydrous ethanol, and an alkaline solution. The pH of the alkaline solution is 9 to 10.

[0017] In an exemplary embodiment of the present invention, organobentonite, polyacrylic acid, and carboxymethyl cellulose are mixed and dissolved thoroughly in deionized water to obtain a first mixture. A conductive agent is added to the first mixture and stirred until homogeneous to obtain a second mixture. An active material is added to the second mixture and stirred further until homogeneous to obtain the graphene-carbon nanotube composite conductive slurry. The conductive slurry is uniformly coated onto a current collector, dried, and then pressed into a sheet to obtain a graphene-carbon nanotube positive electrode sheet. For example, after coating, the sheet is dried in a vacuum drying oven at 90–130°C for 7–12 hours before pressing. However, the present invention is not limited thereto.

[0018] In this invention, organobentonite, polyacrylic acid, and carboxymethyl cellulose are used as dispersants; carbon nanotubes, graphene, and superconducting carbon black are used as conductive agents. Dissolving the dispersants first ensures that the prepared slurry has a high viscosity in a static state, effectively preventing sedimentation and agglomeration. For example, when forming the slurry, the mass ratio of conductive agent:dispersant:solvent can be 2–5:0.1–5:90–97.9; however, this invention is not limited to this.

[0019] The preparation method of the graphene carbon nanotube positive electrode sheet of the present invention includes the following steps:

[0020] A conductive paste is coated onto the current collector, dried, and then pressed to obtain the graphene carbon nanotube positive electrode sheet. The pressing process can be performed using a roller press. The following examples illustrate the specific operating steps:

[0021] Example 1

[0022] The required active material, carbon nanotubes, graphene, and superconducting carbon black were ground. The raw materials were prepared in a mass ratio of organic bentonite: polyacrylic acid: carboxymethyl cellulose of 2%:3%:3%. Deionized water was added dropwise, and the mixture was magnetically stirred at a constant temperature until fully dissolved. Then, a conductive agent was added and stirred until homogeneous. The mass ratio of carbon nanotubes: graphene: superconducting carbon black was 0.8:0.8:1, with graphene particle size of 100 nm and carbon nanotube diameter of 6 nm. Finally, the active material, LiNi, was added and stirred further. 0.8 Co 0.15 Al 0.05 The graphene carbon nanotube composite conductive paste was obtained by mixing O2 and LiMn2O4 in a mass ratio of 2:1. The conductive paste was coated onto aluminum foil using a coating machine spatula to ensure even coating. After coating, the foil was placed in a vacuum drying oven and dried at 100°C for 8 hours. The resulting material was then pressed into sheets to obtain the graphene carbon nanotube cathode material, which was then cut into graphene carbon nanotube cathode sheets.

[0023] Example 2

[0024] The required active materials, carbon nanotubes, graphene, and superconducting carbon black were ground in a mortar. The raw materials were prepared in a mass ratio of organic bentonite: polyacrylic acid: carboxymethyl cellulose of 3%:5%:5%. Deionized water was added dropwise, and the mixture was magnetically stirred at a constant temperature until fully dissolved. Then, a ternary conductive agent was added and stirred until homogeneous. The mass ratio of carbon nanotubes: graphene: superconducting carbon black was 1:0.8:1.5, with graphene particle size of 80 nm and carbon nanotube diameter of 9 nm. Finally, the active material was added and stirred further. The active material was LiNi. 0.8 Co 0.15 Al 0.05 The graphene carbon nanotube composite conductive paste was obtained by mixing O2 and LiMn2O4 in a mass ratio of 5:1. The conductive paste was coated onto aluminum foil using a coating machine spatula to ensure even coating. After coating, the foil was placed in a vacuum drying oven and dried at 80°C for 12 hours. The resulting sheet was then pressed and cut to obtain the graphene carbon nanotube positive electrode sheet.

[0025] Example 3

[0026] The required active materials, carbon nanotubes, graphene, and superconducting carbon black were ground in a mortar. The raw materials were prepared at a mass ratio of organic bentonite: polyacrylic acid: carboxymethyl cellulose of 2%:10%:6%. Deionized water was added dropwise, and the mixture was magnetically stirred at a constant temperature until fully dissolved. Then, a ternary conductive agent was added and stirred until homogeneous. The mass ratio of carbon nanotubes: graphene: superconducting carbon black was 0.8:1:1.5, with graphene particle size of 200 nm and carbon nanotube diameter of 6 nm. Finally, the active material, LiNi, was added and stirred further. 0.8 Co0.15 Al 0.05 The graphene carbon nanotube composite conductive paste was obtained by mixing O2 and LiMn2O4 in a mass ratio of 3:1. The conductive paste was coated onto aluminum foil using a coating machine spatula to ensure even coating. After coating, the foil was placed in a vacuum drying oven and dried at 120°C for 10 hours. The resulting sheet was then pressed and cut to obtain the graphene carbon nanotube positive electrode sheet.

[0027] Comparative Example 1

[0028] Based on Example 1, the difference is that organic bentonite is not added to the conductive slurry.

[0029] Comparative Example 2

[0030] Based on Example 1, the difference is that polyacrylic acid is not added to the conductive paste.

[0031] Comparative Example 3

[0032] Based on Example 1, the difference is that carboxymethyl cellulose is not added to the conductive paste.

[0033] Comparative Example 4

[0034] The difference from Example 1 is that the thickness of the conductive coating is 15 μm.

[0035] Comparative Example 5

[0036] The difference from Example 1 is that the thickness of the conductive coating is 30 μm.

[0037] Under the same conditions, the graphene carbon nanotube positive electrode sheets provided in Examples 1 to 3 and Comparative Examples 1 to 5 were subjected to electrode resistivity tests at different temperatures. The volume resistivity test results are listed in Table 1. At room temperature, the mechanical properties of the electrode sheets were tested, and the peel strength of the electrode sheets of the present invention was tested using a tensile testing machine. The test results are listed in Table 2.

[0038] Table 1. Volume resistivity test results

[0039]

[0040]

[0041] Table 2 Results of Electrode Peel Strength Test

[0042] Peel strength (N / m) Example 1 95 Example 2 94 Example 3 97 Comparative Example 1 50 Comparative Example 2 45 Comparative Example 3 54 Comparative Example 4 55 Comparative Example 5 50

[0043] Referring to Table 1, the volume resistivity test results of Examples 1, 2, and 3 show that the resistivity of the graphene carbon nanotube cathode prepared by this invention does not exceed 3 × 10⁻⁶ at 25°C. -8Ω·m. At higher temperatures, such as 75°C, the resistivity does not exceed 10 × 10⁻⁶ Ω·m. -8 Ω·m.

[0044] Referring to Table 1, compared with Example 1, Comparative Examples 1, 2, and 3 respectively show that reducing the use of dispersants organic bentonite, polyacrylic acid, and carboxymethyl cellulose will increase the resistivity of the graphene carbon nanotube positive electrode of the present invention. However, as shown in Table 2, the electrode peel strength decreases by about 50%.

[0045] As shown in Table 1, compared with Example 1, Comparative Examples 4 and 5 have excessively thick conductive coatings, which is detrimental to the electrochemical performance of the electrode. Meanwhile, as shown in Table 2, the peel strength of the electrode is also reduced due to excessively thick electrode.

[0046] In summary, the graphene-carbon nanotube cathode of the present invention improves the conductivity of the cathode without affecting the bonding force between the conductive coating and the current collector. For example, at room temperature, the conductivity does not exceed 3 × 10⁻⁶. -8 The electrode peel strength is not less than 90 N / m (Ω·m). Furthermore, the graphene carbon nanotube positive electrode of this invention exhibits good corrosion resistance and heat dissipation, which contributes to improving the electrochemical performance of the battery.

[0047] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A graphene-carbon nanotube positive electrode, characterized in that, The graphene carbon nanotube positive electrode includes: a current collector and a conductive coating coated on the current collector; the conductive coating is obtained by coating and curing a conductive slurry; the conductive slurry is composed of the following components: active material: organic bentonite: polyacrylic acid: carboxymethyl cellulose: conductive agent in a mass ratio of 70-97.5%: 0.1-5%: 0.5-15%: 0.5-10%: 1-5%; wherein the conductive agent is composed of carbon nanotubes: graphene: super conductive carbon black in a mass ratio of 0.5-1.5: 0.5-1.5: 1-2; the graphene particle size is 50-400 nm, and the carbon nanotube diameter is 5-10 nm; the active material is LiNi 0.8 Co 0.15 Al 0.05 O2 and LiMn2O4 are composed in a mass ratio of 1.7 to 8:1; the thickness of the conductive coating is 0.1 to 4 μm; The current collector is aluminum foil; The solvent for the conductive paste is at least one of deionized water, anhydrous ethanol, and an alkaline solution.

2. The graphene carbon nanotube positive electrode sheet according to claim 1, characterized in that, The thickness of the conductive coating is 2.5–3.5 μm.

3. The graphene carbon nanotube positive electrode sheet according to claim 1, characterized in that, The active material, organic bentonite, polyacrylic acid, carboxymethyl cellulose, and conductive agent are present in a mass ratio of 75-90% : 1.5-4% : 3-10% : 2-8% : 2-4%.

4. The graphene carbon nanotube positive electrode sheet according to claim 1, characterized in that, The active material, organic bentonite, polyacrylic acid, carboxymethyl cellulose, and conductive agent are present in a mass ratio of 80-85% : 2-3% : 5-8% : 4-6% : 2.5-3%.

5. The graphene carbon nanotube positive electrode sheet according to claim 1, characterized in that, The mass ratio of carbon nanotubes:graphene:super conductive carbon black is 0.8-1.2:0.8-1.2:1.2-1.

6.

6. The graphene carbon nanotube positive electrode sheet according to claim 1, characterized in that, The graphene has a particle size of 100–300 nm, and the carbon nanotubes have a diameter of 7–9 nm.

7. A method for preparing a graphene carbon nanotube positive electrode sheet as described in any one of claims 1 to 6, characterized in that, The process includes the following steps: coating the current collector with a conductive paste, drying it, and then pressing it into a sheet to obtain the graphene carbon nanotube positive electrode sheet.

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