A conductive paste of oligomeric wall tubes composite graphene for a positive electrode sheet and a preparation method thereof

Abstract

The present invention provides a conductive paste of oligomeric walled nanotubes composite graphene and a preparation method thereof, comprising raw materials in the following mass ratios: 1-4% of oligomeric walled carbon nanotubes, 0.1-0.5% of graphite, 0.5-2% of a dispersion aid, 0.5-1% of a viscosity reducer, 0.1-0.5% of a conductive aid, and the balance being NMP; the dispersion aid includes a polyvinylpyrrolidone with a small molecular weight, a polyvinylpyrrolidone with a large molecular weight, and a polyaniline composite material. By adding graphene, the present invention makes use of the softer characteristics of graphene to enable the oligomeric walled carbon nanotubes to fit more closely with the cathode active material and have a wider contact area, thereby improving the conductivity of the material and the cycle performance, rate performance, etc. of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and particularly relates to a conductive paste of oligomeric wall nanotube composite graphene for a positive electrode sheet and a preparation method thereof. Background Art

[0002] Due to the structural limitations of active substances such as lithium iron phosphate, ternary, and lithium cobaltate used in the positive electrode sheet of lithium-ion batteries, their conductivity has reached a bottleneck. To break through the structural bottleneck of the active substances, it is necessary to add other materials to improve their conductivity. The conductive agent additives include graphene, carbon black, carbon nanotubes, nano silver, etc. Among them, carbon nanotubes are widely used as conductive additives in the field of lithium-ion batteries due to their excellent conductive performance, and their conductivity is much higher than that of traditional conductive agents such as conductive carbon black. When carbon nanotubes are applied to the positive electrode material, as the addition amount increases, the carbon nanotubes come into contact with each other, and the carbon nanotubes come into contact with the positive electrode active substances, forming a line-point type conductive network on the surface of the positive electrode material, increasing the conductivity of the positive electrode, and improving the battery cycle performance, rate performance, etc. The currently used carbon nanotubes are mostly multi-walled carbon nanotubes, and the diameter of the multi-walled carbon nanotubes is generally 5-20 nanometers, and the number of tube wall layers is greater than 5 layers. Compared with multi-walled carbon nanotubes, oligomeric wall carbon nanotubes are a nano-tubular structure composed of carbon atoms, with a diameter between 2-5 nanometers. However, the strength of oligomeric wall carbon nanotubes is stronger than that of multi-walled carbon nanotubes, the conductive ability is stronger, and the stability is better, and they can withstand high temperature and high pressure environments. Therefore, using oligomeric wall carbon nanotubes in lithium-ion batteries is more conducive to improving the conductive performance. However, the aspect ratio of oligomeric wall carbon nanotubes is relatively large, and they are extremely prone to agglomeration, which in turn affects their conductive performance. Moreover, the oligomeric wall carbon nanotubes and the positive electrode material are in line-point contact, with fewer contact surfaces and contact points, making it difficult to comprehensively improve the conductivity of the positive electrode activity, and it will also cause it to be difficult to effectively wrap on the surface of the electrode material to form a conductive network, thereby leading to a decrease in the conductive performance of the electrode paste. It can be seen that how to avoid the agglomeration of oligomeric wall carbon nanotubes in the positive electrode conductive paste to improve its conductive performance is a problem that needs to be solved at the present stage. Summary of the Invention

[0003] In order to solve the problem of the conductivity of the positive electrode sheet in the prior art, the present invention provides a conductive paste of oligomeric wall nanotube composite graphene for a positive electrode sheet and a preparation method thereof, which improve the conductivity of the positive electrode sheet by forming a point-line-plane structure with the positive electrode active substances.

[0004] The present invention solves its technical problems by adopting the following technical solutions:

[0005] The first object of the present invention is to provide a conductive paste of oligomeric walled carbon nanotube composite graphene for a positive electrode sheet, which comprises raw materials in the following mass ratios: 1-4% of oligomeric walled carbon nanotubes, 0.1-0.5% of graphite, 0.5-2% of a dispersion aid, 0.5-1% of a viscosity reducer, 0.1-0.5% of a conductive aid, and the balance is NMP; the dispersion aid includes polyvinylpyrrolidone with a small molecular weight, polyvinylpyrrolidone with a large molecular weight, and a polyaniline composite material.

[0006] Further, the mass ratio of the polyvinylpyrrolidone with a small molecular weight, the polyvinylpyrrolidone with a large molecular weight, and the polyaniline composite material is 40-60:25-35:15-25.

[0007] Further, the mass ratio of the polyvinylpyrrolidone with a small molecular weight, the polyvinylpyrrolidone with a large molecular weight, and the polyaniline composite material is 45-55:28-32:18-23.

[0008] Further, the mass ratio of the polyvinylpyrrolidone with a small molecular weight, the polyvinylpyrrolidone with a large molecular weight, and the polyaniline composite material is 50:30:20.

[0009] Further, the polyvinylpyrrolidone with a small molecular weight is selected from PVP-K15 and PVP-K30.

[0010] Further, the polyvinylpyrrolidone with a large molecular weight is selected from PVP-K60 and PVP-K90.

[0011] Further, the polyvinylpyrrolidone with a small molecular weight is selected from PVP-K30, and the polyvinylpyrrolidone with a large molecular weight is selected from PVP-K90.

[0012] Further, the diameter of the oligomeric walled carbon nanotubes is 3-9 nm; the number of layers is 3-5 layers.

[0013] Further, the oligomeric walled carbon nanotubes are coiled tubes or array tubes.

[0014] Further, the oligomeric walled carbon nanotubes are iron-based, cobalt-based or nickel-based carbon nanotubes.

[0015] Further, the graphite is multi-layered reduced graphene oxide.

[0016] Further, the viscosity reducer is selected as anhydrous piperazine.

[0017] Further, the conductive aid is a lithium supplementing agent.

[0018] Further, the lithium supplementing agent is selected from any one of lithium-rich oxides, nano-composites, and binary lithium compounds.

[0019] The second object of the present invention is to provide a method for preparing a conductive paste of multi-walled carbon nanotube composite graphene for a positive electrode plate, comprising the following steps: weighing NMP, a dispersion aid, and a viscosity reducer, mixing them and stirring to prepare a pre-solution, then adding graphite, adding the mixed pre-solution into a homogenizer for high-pressure homogenization to exfoliate the graphite flakes to form graphene with 3 to 5 layers; after high-pressure homogenization until the viscosity is less than 3000 cp and D50 is less than 5 μm, adding multi-walled carbon nanotubes, and continuing homogenization until the viscosity is less than 2000 cp and D50 is less than 3 μm; finally, adding a conductive aid and continuing homogenization until the viscosity is less than 1000 cp and D50 is less than 3 μm to obtain the conductive paste.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] See the appendix Figure 1 , in the present invention, by adding graphene and utilizing the softer characteristics of graphene, the multi-walled carbon nanotubes are more closely attached to the positive electrode active material, with a wider contact area, thereby improving the conductivity of the material and the cycle performance, rate performance, etc. of the battery. In the present invention, a composite dispersion aid formed by a small molecular weight polyvinylpyrrolidone, a large molecular weight polyvinylpyrrolidone, and a polyaniline composite material is used. The small molecular weight polyvinylpyrrolidone is used to disperse graphite, the large molecular weight polyvinylpyrrolidone is used to disperse multi-walled carbon nanotubes, and the adsorption of the polyaniline composite fixes the carbon nanotubes on the surface of the composite material, generating mutual repulsion through the electrostatic effect, thereby preventing the collision and aggregation of nanoparticles; at the same time, the branches of the multi-branched polyaniline rely on the large number of benzene ring and quinone ring structures contained therein to form a large π system with the surface of the carbon nanotubes, and the carbon nanotubes are adsorbed between the layers of the polyvinylpyrrolidone PVP-K30 / polyvinylpyrrolidone PVP-K90 / polyaniline composite material through π-π interaction, thereby destroying the self-aggregation force of the carbon nanotubes and not damaging the original structure and performance of the carbon nanotubes during the dispersion process. After enhancing the dispersion of the multi-walled carbon nanotubes in the present invention, graphene is used to increase the contact between the active substance and the multi-walled carbon nanotubes, significantly enhancing the conductivity of the multi-walled carbon nanotube conductive paste.

[0022] In the present invention, a polyvinylpyrrolidone PVP-K30 / polyvinylpyrrolidone PVP-K90 / polyaniline composite material is used as a dispersion aid to disperse graphite and multi-walled carbon nanotubes respectively, and the adsorption of the polyaniline composite is used to form a multi-walled carbon nanotube-graphene composite, increasing the contact area with the positive electrode active material.

[0023] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other objects, features, and advantages of the present invention more obvious and understandable, the following specifically illustrates the specific embodiments of the present invention. Description of the Drawings

[0024] Figure 1 This is the conductive principle diagram of the conductive paste of the present invention.

[0025] Figure 2 This is the scanning diagram of the electrode sheet obtained in Example 1 of the conductive paste of a multi-walled tube composite graphene and its preparation method of the present invention.

[0026] Figure 3 This is the scanning diagram of the electrode sheet obtained in Comparative Example 1 of the conductive paste of a multi-walled tube composite graphene and its preparation method of the present invention.

[0027] Figure 4 This is the perspective view of the multi-walled carbon nanotubes of the present invention.

[0028] Figure 5 This is the perspective view of the graphene of the present invention.

[0029] Figure 6 This is the resistivity diagram of the electrode sheets obtained in Example 1 and Comparative Example 2 of the conductive paste of a multi-walled tube composite graphene and its preparation method of the present invention.

[0030] Figure 7 This is the charge-discharge 1C cycle diagram of the electrode sheets obtained in Example 1 and Comparative Example 2 of the conductive paste of a multi-walled tube composite graphene and its preparation method of the present invention.

[0031] Figure 8 This is the charge-discharge 0.5C specific capacity-voltage diagram of the electrode sheets obtained in Example 1 and Comparative Example 2 of the conductive paste of a multi-walled tube composite graphene and its preparation method of the present invention. Detailed Embodiments

[0032] The technical solution of the present invention will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the following embodiments are only illustrative of and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0033] In addition, unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or prepared by existing methods.

[0034] Example 1

[0035] A preparation method of a conductive paste of multi-walled tube composite graphene for a positive electrode sheet includes the following steps:

[0036] Mix 96.5 parts of NMP, 0.25 parts of PVP-K30, 0.15 parts of PVP-K90, 0.1 part of polyaniline composite material, and 0.5 part of anhydrous piperazine, and stir to prepare a pre-solution. Then add 0.3 part of redox graphite, and add the mixed pre-solution to a homogenizer for high-pressure homogenization to exfoliate the graphite layers, forming graphene with 3 to 5 layers; after high-pressure homogenization until the viscosity is less than 3000 cp and D50 is less than 5 μm, add 2 parts of oligomeric wall carbon nanotubes, and continue to homogenize until the viscosity is less than 2000 cp and D50 is less than 3 μm; finally, add 0.2 part of lithium oxide lithium supplement and continue to homogenize until the viscosity is less than 1000 cp and D50 is less than 3 μm to obtain a conductive paste.

[0037] Example 2

[0038] A method for preparing a conductive paste of oligomeric wall tube composite graphene for a positive electrode plate, comprising the following steps:

[0039] Mix 94.6 parts of NMP, 0.5 parts of PVP-K30, 0.3 parts of PVP-K90, 0.2 part of polyaniline composite material, and 0.7 part of anhydrous piperazine, and stir to prepare a pre-solution. Then add 0.1 part of redox graphite, and add the mixed pre-solution to a homogenizer for high-pressure homogenization to exfoliate the graphite layers, forming graphene with 3 to 5 layers; after high-pressure homogenization until the viscosity is less than 3000 cp and D50 is less than 5 μm, add 3.5 parts of oligomeric wall carbon nanotubes, and continue to homogenize until the viscosity is less than 2000 cp and D50 is less than 3 μm; finally, add 0.1 part of lithium oxide lithium supplement and continue to homogenize until the viscosity is less than 1000 cp and D50 is less than 3 μm to obtain a conductive paste.

[0040] Example 3

[0041] A method for preparing a conductive paste of oligomeric wall tube composite graphene for a positive electrode plate, comprising the following steps:

[0042] Mix 95.1 parts of NMP, 0.6 parts of PVP-K30, 0.36 parts of PVP-K90, 0.24 part of polyaniline composite material, and 0.8 part of anhydrous piperazine, and stir to prepare a pre-solution. Then add 0.5 part of redox graphite, and add the mixed pre-solution to a homogenizer for high-pressure homogenization to exfoliate the graphite layers, forming graphene with 3 to 5 layers; after high-pressure homogenization until the viscosity is less than 3000 cp and D50 is less than 5 μm, add 2 parts of oligomeric wall carbon nanotubes, and continue to homogenize until the viscosity is less than 2000 cp and D50 is less than 3 μm; finally, add 0.4 part of lithium oxide lithium supplement and continue to homogenize until the viscosity is less than 1000 cp and D50 is less than 3 μm to obtain a conductive paste.

[0043] Comparative Example 1

[0044] The difference from Example 1 is that oligomeric carbon nanotubes are used instead of reduced graphene oxide.

[0045] Comparative Example 2

[0046] The difference from Example 1 is that multi-walled carbon nanotubes are used instead of oligomeric carbon nanotubes.

[0047] Prepare the conductive pastes obtained in the above examples and comparative examples into electrode sheets:

[0048] Stir and mix the conductive pastes obtained in the examples and comparative examples with PVDF and LFP, coat the mixed mixture on the foil, and bake at 120 °C for 15 min; cut the dried electrode sheets into circular pieces and press them under 1 Mpa for 1 min to obtain electrode sheets.

[0049] See Appendix Figure 2 and Appendix Figure 3 As shown in Appendix

[0050] See Appendix Figure 4 As shown in the transmission image of oligomeric carbon nanotubes, the diameter of oligomeric carbon nanotubes is much smaller than that of multi-walled carbon nanotubes, and the aspect ratio is higher than that of multi-walled carbon nanotubes, and the conductivity is better than that of multi-walled carbon nanotubes. See Appendix Figure 5 As shown in the perspective view of graphene, it can be seen that graphite is exfoliated under high pressure in a high-pressure homogenizer to form graphene with fewer layers, which improves the specific surface area and softness of graphene, thus facilitating the contact between graphene and the active material, and enabling graphene to better increase the contact area between oligomeric carbon nanotubes and the active material, thereby improving the conductivity.

[0051] See Appendix Figure 6 As shown in Appendix

[0052] See AppendixFigure 7 , which is the 1C discharge cycle diagram of the coin cell of the electrode sheet obtained in Example 1 of the present invention and Comparative Example 2. It can be seen that the electrochemical cycling performance of the electrode sheet with multi-walled carbon nanotubes added is significantly lower than that of the electrode sheet with few-walled carbon nanotubes added, and the discharge cycling performance is stable.

[0053] See the appendix Figure 8 , which is the discharge specific capacity-voltage diagram of the coin cell of the electrode sheet obtained in Example 1 of the present invention and Comparative Example 2. It can be seen that the battery rate of the electrode sheet with multi-walled carbon nanotubes added is significantly lower than that of the electrode sheet with few-walled carbon nanotubes added.

[0054] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages and disadvantages of the embodiments.

[0055] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the claims of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A conductive slurry of oligo-walled tube composite graphene for positive electrode plates, characterized in that: The invention comprises the following raw materials in mass ratio: 1-4% of oligo-walled carbon nanotubes, 0.1-0.5% of graphite, 0.5-2% of dispersing aid, 0.5-1% of viscosity reducer, 0.1-0.5% of conductive aid, and the balance is NMP; the dispersing aid comprises a composite material of low molecular weight polyvinyl pyrrolidone, high molecular weight polyvinyl pyrrolidone and polyaniline in a mass ratio of 40-60:25-35:15-25; the low molecular weight polyvinyl pyrrolidone is selected from PVP-K15 and PVP-K30, and the high molecular weight polyvinyl pyrrolidone is selected from PVP-K60 and PVP-K90; The preparation method of the conductive paste comprises the following steps: weighing NMP, a dispersing agent and a viscosity reducer, mixing and stirring to prepare a pre-solution, then adding graphite, adding the mixed pre-solution into a homogenizer for high-pressure homogenization to peel off graphite sheets to form 3 to 5 layers of graphene; high-pressure homogenization until the viscosity is less than 3000cp and D50 is less than 5um, adding oligo-walled carbon nanotubes, and continuing to homogenize until the viscosity is less than 2000cp and D50 is less than 3um; finally, adding a conductive agent and continuing to homogenize until the viscosity is less than 1000cp and D50 is less than 3um to obtain a conductive paste.

2. A conductive slurry of oligo-walled tube composite graphene for positive electrode plates as claimed in claim 1, characterized in that: The diameter of the oligo-walled carbon nanotube is 3-9 nm, and the number of layers is 3-5.

3. The conductive slurry of oligo-walled tube composite graphene for positive electrode sheet according to claim 1, characterized in that: The graphite is multi-layer redox graphite.

4. The conductive slurry of oligo-walled tube composite graphene for positive electrode sheet according to claim 1, characterized in that: The viscosity reducing agent is anhydrous piperazine.

5. A method for preparing a conductive slurry of oligo-walled tube composite graphene for positive electrode sheets according to any one of claims 1 to 4, characterized in that: The following steps are involved: The weighed NMP, dispersing agent and viscosity reducer are mixed and stirred to prepare a pre-solution, and then graphite is added. The mixed pre-solution is added into a homogenizer for high-pressure homogenization to peel off the graphite flakes to form 3-5 layers of graphene; after high-pressure homogenization until the viscosity is less than 3000cp and D50 is less than 5um, oligo-walled carbon nanotubes are added and homogenization is continued until the viscosity is less than 2000cp and D50 is less than 3um; finally, a conductive agent is added and homogenization is continued until the viscosity is less than 1000cp and D50 is less than 3um to obtain a conductive slurry.

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