Preparation method and application of graphene in-situ growth CNT composite conductive paste

Abstract

The invention provides a preparation method and application of graphene in-situ growth CNT composite conductive slurry. The preparation method comprises the following steps: adding a sodium hydroxide solution into a graphene oxide composite salt solution for reaction, and performing suction filtration after the reaction is completed to obtain a graphene oxide composite catalyst; repeatedly cleaning with deionized water, drying, firing at high temperature, and crushing to obtain a catalyst; the preparation method comprises the following steps: putting a catalyst into a CVD (Chemical Vapor Deposition) tubular furnace, carrying out high-temperature reaction under the protection of inert gas in the whole process, sequentially introducing reducing gas and carbon source gas to obtain coarse carbon nanotube powder, and then carrying out high-temperature oxidation purification in air to obtain high-purity CNT powder; the preparation method comprises the following steps: fully dissolving a dispersant in a solvent, adding high-purity CNT powder, stirring, and carrying out high-pressure homogeneous dispersion. The graphene oxide is selected as a carrier of the carbon nanotube catalyst, so that the activity of the catalyst and the growth multiple of the carbon nanotube are improved, and the carbon nanotube powder with good conductivity is prepared on the surface of the graphene.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and particularly relates to a preparation method and application of a graphene in-situ growth CNT composite conductive paste. Background Art

[0002] At present, the conductive agents for lithium or sodium batteries are mainly carbon materials, including carbon black, conductive graphite, carbon nanofibers, carbon nanotubes, and graphene, etc. From the development process of conductive agents, a single conductive agent can no longer well meet the use of existing lithium-ion batteries due to the differences in conductivity, dispersion, and liquid absorption performance. The composite conductive agent combines the advantages and disadvantages of various conductive agents. Under the full play of their respective synergistic effects, it can greatly improve the performance of lithium-ion batteries and has become the development trend of conductive agents at present and in the future.

[0003] Carbon nanotubes and graphene are new types of conductive agents developed in recent years. Both have excellent electronic conductivity, can significantly reduce the addition amount of conductive agents, and then increase the proportion of the positive electrode material in the electrode material, improving the battery energy density. At present, the carbon nanotube composite graphene conductive paste is a type widely used by current customers. However, most of the graphene in such composite conductive pastes is obtained by high-pressure homogenization dispersion of low-fold expanded graphite. The graphene sheets prepared by this physical and mechanical method are relatively thick, and the high conductivity and extreme flexibility of graphene cannot be fully utilized. If graphene with a thin sheet diameter and good conductivity is desired, it is often prepared by chemical methods. When used in combination with carbon nanotubes, it has good conductivity and consistency. However, the graphene prepared by chemical methods has a high cost and is not easy to be popularized on a large scale. Summary of the Invention

[0004] In order to solve the problems such as the high cost of preparing graphene by chemical methods in the prior art, the present invention provides a preparation method and application of a graphene in-situ growth CNT composite conductive paste. Using graphene oxide as the carrier of the carbon nanotube catalyst, based on the characteristics of graphene oxide such as high specific surface area, large layered pore structure, and good hydrophilicity, the activity and growth multiple of the catalyst can be improved, thus obtaining excellent carbon nanotube powder. At the same time, during the growth of carbon nanotubes on graphene, graphene oxide is reduced, reducing the content of functional groups such as carboxyl and hydroxyl groups on its surface, effectively solving the energy consumption caused by the separate high-temperature reduction of graphene oxide, and further reducing the cost problem.

[0005] The present invention realizes the solution of its technical problems by adopting the following technical solutions:

[0006] The first object of the present invention is to provide a preparation method of a graphene in-situ growth CNT composite conductive paste, including the following steps:

[0007] 1) Add sodium hydroxide solution to the graphene oxide composite salt solution and react. After the reaction is completed, perform suction filtration to obtain the graphene oxide composite catalyst;

[0008] 2) Wash the graphene oxide composite catalyst obtained in step 1) repeatedly with deionized water and then dry it. After high-temperature calcination and pulverization, obtain the catalyst;

[0009] 3) Place the catalyst obtained in step 2) into a CVD tube furnace and carry out a high-temperature reaction under the protection of an inert gas. Sequentially introduce a reducing gas and a carbon source gas to obtain a crude carbon nanotube powder, and then perform high-temperature oxidation purification in the air to obtain a high-purity CNT powder;

[0010] 4) Dissolve the dispersant fully in the solvent, add the high-purity CNT powder obtained in step 3), and obtain the composite conductive paste after stirring and high-pressure homogenization dispersion.

[0011] Further, the graphene oxide composite salt solution is obtained by mixing and reacting graphene oxide powder with a metal salt solution.

[0012] Further, the metal salt solution is selected from an aqueous solution of one or more of cobalt nitrate, iron nitrate, aluminum nitrate, manganese nitrate, magnesium nitrate, molybdenum nitrate, and aluminum nitrate.

[0013] Further, the mass concentration of the graphene oxide composite salt in the graphene oxide composite salt solution is 0.5-2%.

[0014] Further, the carbon content in the graphene oxide powder is 40%-70%, the oxygen content is 30%-60%, the specific surface area is ≥400m 2 / g, and its D50 is 1-3μm.

[0015] When the carbon content in the graphene oxide powder is 40%-70%, if the carbon content of the graphene oxide <40%, the oxidation degree is higher, and the content of functional groups carried on its surface is high, which is not conducive to subsequent high-temperature sintering and reduction; when the carbon content of the graphene oxide >70%, the oxidation degree is low, the thickness of the graphene oxide sheets contained is relatively thick, and the content of hydrophilic oxygen-containing groups is small, resulting in poor conductivity and dispersion effect after the reduction of graphene oxide.

[0016] Further, after adding sodium hydroxide in step 1), the pH value of the solution is detected in real time, and the reaction is stopped when the pH value reaches 10-11.

[0017] Further, the temperature during the reaction in step 1) is controlled at 35-40°C, and the temperature is controlled by water bath heating.

[0018] Further, the concentration of the sodium hydroxide solution is 25%.

[0019] Further, the number of times of washing with deionized water in step 2) is ≥ 3 times.

[0020] Further, the drying temperature in step 2) is 100 - 120 °C, and the drying time is 12 - 24 h.

[0021] Further, the high-temperature calcination temperature in step 2) is 350 - 450 °C, and the calcination time is 3 - 6 h.

[0022] Further, the particle size of the catalyst after pulverization in step 2) is 80 - 100 mesh.

[0023] Further, the inert gas refers to argon, the reducing gas refers to hydrogen, and the carbon source gas is selected from ethylene, propylene, natural gas or other small-molecule organic gases.

[0024] Further, the high-temperature reaction temperature in step 3) is 600 - 700 °C, the heating rate is 5 - 15 °C / min, and the reaction time is 1 - 2 h.

[0025] Further, the high-temperature oxidation purification reaction temperature in step 3) is 300 - 400 °C, and the reaction time is 2 - 4 h.

[0026] Further, the dispersant is selected from PVP, PVDF, HNBR, CMC or PAA.

[0027] Further, the mass ratio of the dispersant, CNT powder and solvent added in step 4) is 0.5 - 2:2 - 5:93 - 97.5.

[0028] Further, the solvent is pure water or NMP.

[0029] Further, the rotation speed during stirring in step 4) is 600 - 2000 rpm, and the stirring time is 1 - 2 h.

[0030] Further, the high-pressure homogenization conditions are a pressure ≥ 800 bar and a cycle number ≥ 3 times.

[0031] The second object of the present invention is to provide an application of a graphene in-situ growth CNT composite conductive paste in a new energy battery.

[0032] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0033] The present invention selects graphene oxide as the carrier of the carbon nanotube catalyst. This is mainly because graphene oxide has a high specific surface area, a relatively large layered pore structure, and a large number of carboxyl and hydroxyl functional groups on its surface, showing good hydrophilicity and other characteristics. This allows the active components of the CNT catalyst to be evenly dispersed on the surface and within the layered pores of graphene oxide, which is beneficial for improving the activity of the catalyst and the growth multiple of carbon nanotubes, and thus obtaining carbon nanotube powder with good conductivity on the surface of graphene.

[0034] In the present invention, the reduction of graphene oxide can be fully achieved during the growth of carbon nanotubes, reducing the content of functional groups such as carboxyl and hydroxyl on its surface and improving its conductivity. Therefore, it can effectively solve the energy consumption caused by the separate high-temperature reduction of graphene oxide, thereby further reducing the cost.

[0035] The carbon nanotubes grown on graphene in the present invention have a high specific surface area, and the growth of CNTs between the graphene sheets can prevent their aggregation, which is beneficial for the dispersion of the powder. It can fully utilize the linear CNT and planar graphene conductive network structures to help build a sufficient continuous-phase conductive network for the electrode, thereby improving the performance of the battery.

[0036] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the content of the specification. And in order to make the above and other purposes, 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

[0037] Figure 1 It is the SEM electron microscope scanning image of the graphene in-situ growth carbon nanotube powder in Example 1 of the present invention. Detailed Description of the Invention

[0038] The following further details the technical solution of the present invention in conjunction with the drawings and specific embodiments. It should be understood that the following embodiments are only for illustrative explanation of the present invention and should not be construed as limiting the protection scope 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.

[0039] 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.

[0040] A preparation method of a graphene in-situ growth CNT composite conductive paste includes the following steps:

[0041] 1) Add a sodium hydroxide solution to the graphene oxide composite salt solution for reaction. After the reaction is completed, perform suction filtration to obtain the graphene oxide composite catalyst;

[0042] 2) The graphene oxide composite catalyst obtained in step 1) is repeatedly washed with deionized water and then dried, calcined at high temperature and pulverized to obtain a catalyst.

[0043] 3) The catalyst obtained in step 2) is placed in a CVD tube furnace and subjected to a high-temperature reaction under the protection of an inert gas throughout the process. A reducing gas and a carbon source gas are sequentially introduced to obtain a crude carbon nanotube powder, and then high-temperature oxidation purification is carried out in the air to obtain a high-purity CNT powder.

[0044] 4) The dispersant is fully dissolved in a solvent, and the high-purity CNT powder obtained in step 3) is added. After stirring and high-pressure homogenization dispersion, the composite conductive paste is obtained.

[0045] Example 1

[0046] A preparation method of a graphene in-situ growth CNT composite conductive paste includes the following steps:

[0047] 1) Preparation of graphene oxide composite catalyst

[0048] In a reaction kettle, 2000 g of a 1% concentration graphene oxide composite salt solution is added, where graphene oxide: cobalt nitrate: magnesium nitrate: aluminum nitrate = 7:2:0.5:0.5; then 25% concentration sodium hydroxide is slowly added through a peristaltic pump. The water bath temperature of the whole reaction is controlled at 35°C, and the reaction ends when the pH value is controlled at 10.5. Then it is vacuum filtered to obtain a graphene oxide composite catalyst.

[0049] 2) Preparation of catalyst

[0050] The graphene oxide composite catalyst obtained in step 1) is washed 3 times with pure water, and then the filter cake is collected and dried in a blast drying oven at 110°C for 12 h, then transferred to a muffle furnace and calcined at 400°C for 4 h, and then mechanically pulverized and passed through an 80-mesh sieve to obtain a catalyst for carbon nanotube growth.

[0051] 3) CNT powder preparation

[0052] The catalyst obtained in step 2) is placed in a quartz crucible, placed in a CVD tube furnace, argon is introduced for protection, the heating rate is 8°C / min, the temperature is raised to 650°C for constant temperature control, and then hydrogen is introduced, hydrogen: argon = 50:150 sccm, the catalyst is reduced for 15 min, and then a carbon source gas is introduced, and the hydrogen: carbon source gas: argon flow rate is adjusted to 30:200:200 sccm, and the temperature is kept for 60 min and all gas sources are closed to obtain a crude carbon nanotube powder; finally, after the reaction temperature is lowered to 350°C, the grown carbon nanotube powder is oxidized in the air for 3 h through air to obtain a high-purity graphene in-situ growth carbon nanotube powder.

[0053] 4) Preparation of Composite Conductive Paste

[0054] At room temperature, 190 g of N-methylpyrrolidone, 2 g of polyvinylpyrrolidone, and 20 g of graphene in-situ grown carbon nanotube powder were added in sequence according to a mass ratio of 95:1:4. A composite conductive paste with a concentration of 5% was prepared through mechanical stirring and high-pressure homogenization. The mechanical stirring speed was 1000 rpm; the pressure used in the homogenization equipment was 900 - 1000 bar, and the cyclic homogenization was carried out 5 times.

[0055] See Appendix Figure 1 , which is the SEM electron microscope scanning image of the graphene in-situ grown carbon nanotube powder obtained in step 3) of this example. It can be seen that the graphene layer remains relatively intact, and there are slight warps or deformations in some areas due to the growth of carbon nanotubes; the carbon nanotubes extend from the surface of graphene. Restricted by the interlayer space of graphene, they mostly show a curved shape, but there is no agglomeration phenomenon among them.

[0056] Example 2

[0057] Compared with Example 1, the difference in this example is that the mass ratio of graphene oxide: cobalt nitrate: magnesium nitrate: aluminum nitrate in step 1) is mixed according to a ratio of 6:2.7:0.65:0.65, and the rest of the process is the same as that in Example 1.

[0058] Example 3

[0059] Compared with Example 1, in this example, the CVD temperature in step 3) is adjusted to 700 °C, and the rest of the process is the same as that in Example 1.

[0060] Comparative Example 1

[0061] Step 1) in Example 1 was adjusted to:[[]]

[0062] In a reaction kettle, 2000 g of a composite salt solution with a concentration of 1% was added, where cobalt nitrate: magnesium nitrate: aluminum nitrate = 2:0.5:0.5; then 25% concentration of sodium hydroxide was slowly added through a peristaltic pump. The water bath temperature of the whole reaction was controlled at 35 °C, and the reaction ended when the pH value was controlled at 10.5. Then it was vacuum filtered to obtain a composite catalyst.

[0063] The rest of the process is the same as that in Example 1.

[0064] Comparative Example 2

[0065] Compared with Example 1, when reducing the reaction under argon protection in step 3), the CVD temperature was adjusted to 500 °C, and the rest of the process was the same as that in Example 1.

[0066] Experimental Example

[0067] The conductive pastes obtained in Examples 1-3 and Comparative Examples 1-2 were respectively formulated into pastes with lithium iron phosphate cathode material for lithium-ion batteries and PVDF in a mass ratio of 95:2.5:2.5 in NMP solvent, and the mass of NMP was 1.2-1.5 times the mass of the solid. The obtained pastes were coated on an aluminum foil with a thickness of 16 μm and a PET film with a thickness of 60 μm using a 300-μm doctor blade, and then dried, rolled, and punched into button-shaped discs with a diameter of 12 mm.

[0068] Among them, the resistivity of the PEI film discs was measured using a four-probe resistivity tester. Using a sodium foil as the counter electrode, a button 2032 battery was assembled with the above-prepared aluminum foil button discs. The main components of the battery electrolyte were as follows: the lithium salt was lithium hexafluorophosphate with a concentration of 1.0 mol / L; the solvents were ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate with a mass ratio of 1:1:1. The separator thickness was 20 μm, a polyethylene microporous separator.

[0069] The first charge-discharge capacity of the battery was tested at a 0.1C rate and its first charge-discharge efficiency was calculated. The cycling performance was tested at a 1C rate for 100 cycles (Note: The specific capacity of the lithium iron phosphate cathode material was calculated as 150 mAh / g). The charge-discharge cut-off voltage for battery testing was 2.0-4.2 V. The test results are shown in Table 1.

[0070] Table 1 First discharge and cycling test results of Examples 1-3 and Comparative Examples 1-2

[0071]

[0072] As can be seen from Table 1 above, when the graphene in-situ grown CNT conductive paste of the present invention was used on the lithium iron phosphate cathode material for lithium-ion batteries, the resistivity of the electrode sheet decreased significantly, from 28.93 Ω·cm of the pure carbon nanotube conductive paste in Comparative Example 1 to 8.85 Ω·cm in Example 1, indicating that the paste had good conductivity. The capacity of the button batteries in each example of the present invention did not decay after 100 cycles at a 1C rate, while the capacity retention rate in Comparative Example 1 decayed to 58.6%. It can be seen that...

[0073] Table 2 Rate performance test results of Examples 1-3 and Comparative Examples 1-2

[0074]

[0075] As can be seen from Table 2 above, the graphene in-situ growth CNT conductive paste of the present invention also performs excellently in rate performance. When discharging at a high rate of 3C, there is still nearly 60% of the capacity compared to 0.1C. For Comparative Example 1, only a very small amount of capacity is discharged, which is 12.9% of the 0.1C capacity. If the temperature is too low during the reduction of graphene oxide, the reduction is incomplete, and the functional groups and defects carried will affect its electronic conductivity, increase the internal resistance of the battery, and thus the rate performance is not ideal either.

[0076] Both graphene and CNT have excellent electronic conductivity, good electrochemical and thermal stability, and small charge transfer impedance. Graphene has a two-dimensional sheet structure with strong intermolecular forces, and it is difficult to achieve uniform and stable dispersion in conventional dispersion equipment, which will affect the actual application effect. CNT has a one-dimensional linear structure, and together with graphene, it creates a wire-plane conductive network structure. At the same time, its strong interaction with the electrode active material is of great help in buffering the expansion stress of the electrode material and the battery cycle. At the same time, considering that the current chemical method graphene is expensive and not easy to scale up, the present invention uses graphene oxide as the carrier of the CNT catalyst, which can reduce the graphene oxide while growing CNT. At the same time, the growth of CNT further exfoliates the graphene oxide, which is beneficial to the dispersion and processing of the powder.

[0077] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0078] 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 only 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 present invention and the claims. All of these are within the protection scope of the present invention.

Claims

1. A preparation method of a graphene in-situ grown CNT composite conductive paste, characterized in that, It includes the following steps: 1) Add a sodium hydroxide solution to the graphene oxide composite salt solution for reaction. After the reaction is completed, perform suction filtration to obtain the graphene oxide composite catalyst; 2) Wash the graphene oxide composite catalyst obtained in step 1) repeatedly with deionized water, then dry it, calcine it at high temperature, and crush it to obtain the catalyst; 3) Place the catalyst obtained in step 2) into a CVD tube furnace and carry out a high-temperature reaction under the protection of an inert gas. Sequentially introduce a reducing gas and a carbon source gas to obtain a crude carbon nanotube powder, and then perform high-temperature oxidation purification in the air to obtain a high-purity CNT powder; 4) Fully dissolve the dispersant in the solvent, add the high-purity CNT powder obtained in step 3), and obtain the composite conductive paste after stirring and high-pressure homogenization dispersion.

2. The preparation method of a graphene in-situ growth CNT composite conductive paste as described in claim 1, characterized in that: The graphene oxide composite salt solution is obtained by mixing a graphene oxide powder with a metal salt solution for reaction.

3. The preparation method of a graphene in-situ growth CNT composite conductive paste as described in claim 2, characterized in that: The metal salt solution is selected from an aqueous solution of one or more of cobalt nitrate, iron nitrate, aluminum nitrate, manganese nitrate, magnesium nitrate, molybdenum nitrate, and aluminum nitrate.

4. The preparation method of a graphene in-situ growth CNT composite conductive paste as described in claim 1, wherein: The carbon content in the graphene oxide powder is 40%-70%, the oxygen content is 30%-60%, the specific surface area is ≥400m 2 / g, and its D50 is 1-3μm.

5. The preparation method of a graphene in-situ growth CNT composite conductive paste according to claim 1, characterized in that: During the reaction in step 1), the temperature is controlled at 35-40°C, and the temperature is controlled by water bath heating.

6. The preparation method of a graphene in-situ growth CNT composite conductive paste as described in claim 1, characterized in that: The inert gas refers to argon, the reducing gas refers to hydrogen, and the carbon source gas is selected from ethylene, propylene, natural gas, or other small-molecule organic gases.

7. The preparation method of a graphene in-situ growth CNT composite conductive paste as described in claim 1, characterized in that: In step 3), the high-temperature reaction temperature is 600-700°C, the heating rate is 5-15°C / min, and the reaction time is 1-2 h.

8. The preparation method of a graphene in-situ growth CNT composite conductive paste according to claim 1, characterized in that: The dispersant is selected from PVP, PVDF, HNBR, CMC, or PAA.

9. The preparation method of a graphene in-situ growth CNT composite conductive paste as described in claim 1, characterized in that: In step 4), the mass ratio of the added dispersant, CNT powder, and solvent is 0.5-2:2-5:93-97.

5.

10. Application of the graphene in-situ growth CNT composite conductive paste obtained by the method according to any one of claims 1-9 in a new energy battery.

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