Single-walled carbon nanotube composite conductive paste, preparation method and stability evaluation method of paste

Abstract

The invention discloses a single-walled carbon nanotube composite conductive paste, a preparation method and a stability evaluation method of the paste. The paste comprises the following raw materials in percentage by weight: 0.4%-8% of a dispersing agent, 0.2%-1% of a single-walled carbon nanotube, 0.2%-1% of graphene oxide, 0.01%-0.2% of fluorescein and 89.8%-99.19% of a solvent. According to the technical scheme, the method has the advantages that the single-walled carbon nanotubes can be efficiently dispersed, and the stability of the conductive paste can be rapidly evaluated.

Description

Technical Field

[0001] The present application relates to the field of nanomaterials, and in particular to a single-walled carbon nanotube composite conductive slurry, a preparation method, and a slurry stability evaluation method. Background Art

[0002] Single-walled carbon nanotubes are ideal materials for preparing silicon-carbon negative electrode conductive agents due to their high aspect ratio, high mechanical strength and excellent electrical conductivity. They can reduce the expansion ratio of silicon-carbon negative electrodes, improve electrical conductivity and enhance the cycle performance of lithium-ion batteries. However, single-walled carbon nanotubes have a large specific surface area, which makes them easy to agglomerate. Poorly dispersed single-walled carbon nanotubes may agglomerate in the negative electrode slurry, resulting in obstructed electron transport, thereby reducing the conductivity of the battery; on the other hand, good dispersion of single-walled carbon nanotubes in the negative electrode material helps to alleviate the volume expansion of the silicon-carbon negative electrode during the charge and discharge process, reduce particle crushing, and thus improve the cycle stability of the battery, while poorly dispersed single-walled carbon nanotubes will affect the cycle life of the battery. Poor dispersion prevents single-walled carbon nanotubes from exerting their performance advantages and also increases the application cost of single-walled carbon nanotubes. Therefore, how to efficiently disperse single-walled carbon nanotubes is the key to achieving their large-scale application. Graphene oxide (GO) can be easily mass-produced from cheap graphite materials using the Hummer method at a low cost. Its edge is an ionizable carboxylic acid group, and its center is an unoxidized sp2 structure, which can be considered as a polyelectrolyte with surfactant properties. The carboxylic acid groups on its edge give it good hydrophilicity, while the benzene ring structure in its central region allows it to have strong π-π interactions with other sp2 conjugated structures. Therefore, GO can be used as a good dispersant to disperse carbon-based nanomaterials. In addition, compared with other organic surfactants, GO itself is also a carbon-based nanomaterial. Using GO to disperse single-walled carbon nanotubes is beneficial to further improve the conductivity of the system.

[0003] On the other hand, the stability of the slurry is very important in the application. In the preparation process of the battery slurry, the conductive slurry with poor stability will experience sedimentation, flocculation and other phenomena, resulting in large particles. This will not only have a great impact on subsequent coating and other processes, but will also greatly affect the conductivity of the battery slurry, resulting in an increase in the internal resistance of the battery, affecting the coulombic efficiency, specific capacity and cycle performance of the battery. Therefore, how to quickly evaluate the stability of the conductive slurry is also very important. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present application provides a single-walled carbon nanotube composite conductive paste that can efficiently disperse single-walled carbon nanotubes and can also quickly evaluate the stability of the conductive paste.

[0005] To solve the above technical problems, the technical solution adopted in this application is as follows: a single-walled carbon nanotube composite conductive paste, and the raw materials and their corresponding weight percentage contents of the paste include: 0.4%-8% of a dispersant, 0.2%-1% of single-walled carbon nanotubes, 0.2%-1% of graphene oxide, 0.01%-0.2% of fluorescein, and 89.8%-99.19% of a solvent.

[0006] Further, the particle size range of the graphene oxide is 300-500 nm (0.3-0.5 μm), wherein the oxygen mass fraction is 36%-53%, and the carbon mass fraction is 45%-62%.

[0007] Furthermore, the graphene oxide is graphene oxide after centrifugation treatment, and the specific steps of the centrifugation treatment include: dispersing the graphene oxide in water, centrifuging at a rotation speed of 3500-4500 rpm, standing for 0.5-2 h after centrifugation, and taking the supernatant; collecting the supernatant in a container, performing freeze-drying, and grinding after drying to obtain graphene oxide powder with a particle size distribution of 300-500 nm.

[0008] Furthermore, before the centrifugation treatment of the graphene oxide, the number of layers is less than 5 layers, and the particle size is less than 3 μm; the graphene oxide obtained after the centrifugation treatment has a particle size not greater than 500 nm and 2-3 layers.

[0009] Further, the dispersant is at least one of sodium carboxymethyl cellulose, polyethylene glycol, and sodium dodecyl sulfate.

[0010] Furthermore, the degree of substitution of the sodium carboxymethyl cellulose is 0.7-1.1, and the molecular weight is 500.

[0011] Further, the diameter of the single-walled carbon nanotubes is 0.8-1.5 nm, the length is 2-10 μm, and the purity is greater than 98.5%.

[0012] Further, the fluorescein can be at least one of methoxypolyethylene glycol fluorescein (mPEG-FITC), fluorescein isothiocyanate (FITC), hydroxy polyethylene glycol-fluorescein isothiocyanate (OH-PEG-FITC, fluorescein isothiocyanate ester-polyethylene glycol-hydroxy), methoxy e-coelenterazine (Me-Oe-CTZ), tetraethyl rhodamine (RIB200), and tetramethyl rhodamine isothiocyanate (TRITC, tetramethyl rhodamine isothiocyanate).

[0013] Furthermore, the fluorescein can be methoxypolyethylene glycol fluorescein (mPEG-FITC), and its structure is shown in the following formula (1), and the weight-average molecular weight of the PEG part in the structure is 2000.

[0014]

[0015]

[0016] Further, the solvent is deionized water.

[0017] This application also provides a method for preparing the above-mentioned single-walled carbon nanotube composite conductive paste, including:

[0018] (1) Weigh various raw materials of the conductive paste according to the formula ratio, then perform ultrasonic mixing treatment on each raw material component, disperse it through a mechanical stirrer, and then transfer the mixed solution to a high-pressure homogenizer for dispersion;

[0019] (2) After dispersion, a uniform paste is obtained, and it is subjected to suction filtration;

[0020] (3) After suction filtration, a filter cake is obtained. Transfer the filter cake to a container, add deionized water, and then perform ultrasonic dispersion for 0.5 - 2 h; repeat the above suction filtration - ultrasonic dispersion steps 2 - 3 times to wash away the fluorescein not adsorbed on the surface of the carbon nanotubes, and obtain the conductive paste.

[0021] Further, the rotation speed range of the mechanical stirring in step (1) is 6000 - 10000 rpm, the dispersion time is 30 - 60 min, and the number of times is 2 - 3 times.

[0022] Further, the operating pressure of the homogenizer in step (1) is set to 600 - 1000 bar, and continuous dispersion is performed 5 - 15 times.

[0023] Further, the ultrasonic mixing time in step (1) is 5 - 15 min.

[0024] Further, the suction filtration in step (2) is performed using a nylon filter membrane with a pore size of 500 nm.

[0025] This application also provides a method for evaluating the stability of the above-prepared single-walled carbon nanotube composite conductive paste, including: (S1) testing the fluorescence photometry of the conductive paste before and after standing; (S2) judging the stability of the conductive paste according to the change in fluorescence photometry.

[0026] Further, in the step (S1), specifically: Take a sample from the prepared conductive paste, dilute the paste 10,000 times, denote it as sample 1, and test the fluorescence intensity of sample 1; Let the paste stand, take samples at fixed time intervals, denote them as sample 2, sample 3,..., sample n, and test the fluorescence intensity of the taken samples.

[0027] Further, for the step (S2), specifically: compare the fluorescence intensities of Sample 1, Sample 2, …, Sample n. If the change in fluorescence intensity is small, it is considered that the slurry has good stability.

[0028] Furthermore, the method for testing the fluorescence intensity of the sample is as follows: use the F-4600 fluorescence spectrometer produced by Hitachi Corporation, with a 150W xenon lamp as the light source, the light source spectral range is 200~750m, and the scanning speed is 2400nm·min -1 , the excitation slit is 5nm, the emission slit is 5nm, the photomultiplier tube voltage is 400V, the wavelength interval is 10nm, and the scanning wavelength interval is 1nm.

[0029] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0030] 1. For the conductive slurry of the present application, each component used, the benzene ring structure in the central region of graphene oxide enables it to have a strong π-π interaction with single-walled carbon nanotubes, adsorb on the surface of single-walled carbon nanotubes, and wrap the single-walled carbon nanotubes. The hydroxyl and carboxyl groups on the surface of graphene oxide are ionized in the solution, resulting in an electrostatic repulsion between graphene oxides. Therefore, graphene oxide can be used to disperse single-walled carbon nanotubes; in addition, graphene oxide itself is also a carbon-based material. Using graphene oxide to disperse single-walled carbon nanotubes is beneficial to further improve the conductivity of the system; the fluorescein used in the present application is an organic compound with strong fluorescence characteristics, and its structure usually contains conjugated double bonds, and energy absorption and emission are realized through the conjugated double bond system; fluorescein isothiocyanate (FITC), hydroxy polyethylene glycol-fluorescein isothiocyanate (HO-PEG-FITC), methoxy e-coelenterazine (Me-Oe-CTZ), tetraethyl rhodamine (RIB200), and tetramethyl rhodamine isothiocyanate (TRITC) are common water-soluble organic small molecule fluoresceins, and their structural formulas contain conjugated benzene rings, which have π-π interactions with the benzene rings in the single-walled carbon nanotube wall and the middle region of graphene oxide, and can simultaneously disperse and modify the two; for example, the benzene ring part in the structure of methoxy polyethylene glycol fluorescein (mPEG-FITC) can have π-π interactions with single-walled carbon nanotubes and graphene oxide, and the PEG branch chain in the structure can penetrate into the solvent, improving its hydrophilicity and increasing steric hindrance; therefore, the use of fluorescein in the present application can indirectly monitor the stability of the dispersion liquid by monitoring the change in the fluorescence intensity of the fluorescein adsorbed on the surfaces of single-walled carbon nanotubes and graphene oxide; therefore, the fluorescein in the present application is adsorbed on the surfaces of graphene oxide and single-walled carbon nanotubes through π-π interactions, further improving the hydrophilicity of graphene oxide and single-walled carbon nanotubes; at the same time, through steric hindrance, graphene oxide and single-walled carbon nanotubes are dispersed; the synergistic effect of fluorescein and graphene oxide greatly improves the dispersion of single-walled carbon nanotubes in the slurry.

[0031] 2. This application centrifuges the commercially available graphene oxide. Since the size distribution range of the commercially available graphene oxide is relatively large, the graphene oxide nanosheets that are too large or too small have a weak wrapping effect on single-walled carbon nanotubes, which is not conducive to the efficient dispersion of single-walled carbon nanotubes at a low dispersant concentration. Therefore, the purchased graphene oxide is centrifuged and separated to screen for graphene oxide with appropriate sizes, which can effectively improve its wrapping effect on single-walled carbon nanotubes and is more conducive to dispersion.

[0032] 3. This application uses graphene oxide for the efficient dispersion of single-walled carbon nanotubes. Compared with using surfactants to disperse single-walled carbon nanotubes, using graphene oxide to disperse single-walled carbon nanotubes not only achieves efficient dispersion but also increases the conductivity of the system.

[0033] 4. This application can determine the stability of the conductive paste by measuring the fluorescence intensity of the conductive paste before and after standing. The stability of the conductive paste can be judged according to the change in fluorescence intensity, and the stability of the paste can be continuously observed through a simple method. At the same time, the fluorescein structure has a large π bond, and the delocalized electron cloud is conducive to electron transmission. Compared with surfactants, it is beneficial to increase the conductivity of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the stability test result of Example 1 of this application;

[0035] Figure 2 It is the stability test result of Example 2 of this application;

[0036] Figure 3 It is the stability test result of Comparative Example 2 of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0038] In the following embodiments, the judgment basis for the stability of the conductive paste is the change in the fluorescence intensity of the paste.

[0039] Specifically, since the conductive paste contains fluorescein, this material can adsorb on the surfaces of single-walled carbon nanotubes and graphene oxide. If the conductive paste is unstable, that is, the conductive agents single-walled carbon nanotubes and graphene oxide sink, then the fluorescein will sink with the carbon-based conductive agents, and the fluorescence intensity of the upper-layer conductive paste measured will become weaker; on the contrary, the fluorescence intensity of the lower-layer conductive paste will become stronger. By observing the change in the fluorescence intensity of the conductive paste, the stability of the conductive paste can be judged.

[0040] The specific steps include taking a sample from the prepared conductive paste, denoted as Sample 1, and performing a fluorescence photometric test on the Sample 1. The prepared conductive paste is placed in a container and left to stand. Samples are taken every time interval t, denoted as Sample 2, Sample 3, ……, Sample n respectively, and fluorescence photometric tests are performed on the taken samples.

[0041] The method for testing the fluorescence intensity of the sample is as follows:

[0042] An F-4600 fluorescence spectrometer produced by Hitachi is used. The light source is a 150W xenon lamp, the spectral range of the light source is 200 - 750m, the scanning speed is 2400nm·min-1, the excitation slit is 5nm, the emission slit is 5nm, the voltage of the photomultiplier tube is 400V, the wavelength interval is 10nm, and the scanning wavelength interval is 1nm. The excitation wavelength corresponding to fluorescein is 494nm.

[0043] Among them, the standing observation time of the conductive paste can be 24h, 48h, 72h, etc. Here, there is no limit on the sampling interval time and the stability observation time, which can be set according to actual needs. For the convenience of testing, the longer the observation time of the conductive paste, the sampling interval time can be appropriately enlarged; the shorter the observation time, the sampling interval time can be shortened. It should be noted that the paste should be covered and tightened during the standing process, and sealed with raw material tape and sealing film to prevent solvent evaporation; to ensure the accuracy of the test, the same area of the sample should be selected each time for sampling. For example, each time the sample is taken from the upper layer area of the paste, or the lower layer area of the paste is selected; and the fluorescence test should be carried out immediately after sampling to prevent changes in the sample during the placement process and affect the test results. The fluorescence test uses a fluorometer and can be tested according to the conventional fluorescence test method.

[0044] Taking time as the abscissa and fluorescence intensity as the ordinate, a relationship curve of time-fluorescence intensity is plotted. If the fluorescence intensity remains unchanged or fluctuates slightly (maintaining a horizontal state overall) with the change of time, it is considered that the stability of the paste is good; if the fluorescence intensity fluctuates greatly with the change of time (for example, if the sample is taken from the upper layer area of the paste, the fluorescence intensity shows a downward trend; if the sample is taken from the lower layer area of the paste, the fluorescence intensity shows an upward trend), it is considered that the stability of the paste is poor.

[0045] Example 1

[0046] A preparation method of a conductive paste for efficiently dispersing single-walled carbon nanotubes and quickly evaluating stability, comprising the following steps:

[0047] Weigh 95.1% deionized water and 3.2% sodium carboxymethylcellulose according to the weight ratio and put them into a clean and dry dispersion tank, and mechanically stir for 1 h until completely dissolved. Weigh 0.8% single-walled carbon nanotubes, 0.8% graphene oxide, and 0.1% fluorescein (methoxypolyethylene glycol fluorescein (mPEG-FITC)) into the cellulose solution and perform ultrasonic mixing treatment for 0.5 h to preliminarily disperse the additives. Then disperse for 8 h through a mechanical stirrer. Finally, transfer the mixed solution to a high-pressure homogenizer, with an operating pressure of 800 bar, and continuously disperse 5 times to prepare the conductive paste.

[0048] Place the prepared conductive paste in a container, take 5 mL of the upper-layer paste into a test tube, and perform fluorescence testing on it; then take the upper-layer paste every 6 h, and immediately perform fluorescence testing each time a sample is taken until the paste stands still for 48 h. Take a sample again after 168 h for fluorescence intensity testing, and then take samples for fluorescence intensity testing every 168 h and repeat 3 times.

[0049] After the test, draw a time-fluorescence intensity relationship curve according to the test results, as Figure 1 shown: As the standing time prolongs, although the fluorescence photometry fluctuates, the change is not significant, and it basically remains at a level state, indicating that the conductive paste of this example has good stability.

[0050] Example 2

[0051] A method for preparing a conductive paste for efficiently dispersing single-walled carbon nanotubes and quickly evaluating stability, comprising the following steps:

[0052] Weigh 95.0% deionized water and 3.2% sodium carboxymethylcellulose according to the weight ratio and put them into a clean and dry dispersion tank, and mechanically stir for 1 h until completely dissolved. Weigh 0.8% single-walled carbon nanotubes, 0.8% graphene oxide, and 0.2% fluorescein (methoxypolyethylene glycol fluorescein (mPEG-FITC)) into the cellulose solution and perform ultrasonic mixing treatment for 0.5 h to preliminarily disperse the additives. Then disperse for 8 h through a mechanical stirrer. Finally, transfer the mixed solution to a high-pressure homogenizer, with an operating pressure of 800 bar, and continuously disperse 5 times to prepare the conductive paste.

[0053] Place the prepared conductive paste in a container, take 5 mL of the upper-layer paste into a test tube, and perform fluorescence testing on it; then take the upper-layer paste every 6 h, and immediately perform fluorescence testing each time a sample is taken until the paste stands still for 48 h. Take a sample again after 168 h for fluorescence intensity testing, and then take samples for fluorescence intensity testing every 168 h and repeat 3 times.

[0054] After the test, draw a time-fluorescence intensity relationship curve according to the test results, as Figure 2As shown in the figure, with the extension of the standing time, although the fluorescence photometry fluctuates, the change is not significant and it basically maintains a horizontal state, indicating that the conductive paste in this embodiment has good stability.

[0055] Example 3

[0056] A method for preparing a conductive paste that can efficiently disperse single-walled carbon nanotubes and quickly evaluate stability includes the following steps:

[0057] Weigh 95.1% deionized water and 3.2% sodium carboxymethylcellulose according to the weight ratio and add them to a clean and dry dispersion tank, and mechanically stir for 1 h until completely dissolved. Weigh 0.64% single-walled carbon nanotubes, 0.96% graphene oxide, and 0.1% fluorescein (fluorescein isothiocyanate (FITC)) and add them to the cellulose solution for ultrasonic mixing treatment for 0.5 h to preliminarily disperse the additives. Then disperse them through a mechanical stirrer for 8 h. Finally, transfer the mixed solution to a high-pressure homogenizer, with an operating pressure of 800 bar, and continuously disperse it 5 times to obtain the conductive paste.

[0058] Example 4

[0059] A method for preparing a conductive paste that can efficiently disperse single-walled carbon nanotubes and quickly evaluate stability includes the following steps:

[0060] Weigh 95.1% deionized water and 3.2% sodium carboxymethylcellulose according to the weight ratio and add them to a clean and dry dispersion tank, and mechanically stir for 1 h until completely dissolved. Weigh 0.96% single-walled carbon nanotubes, 0.64% graphene oxide, and 0.1% fluorescein (tetramethyl rhodamine isothiocyanate) and add them to the cellulose solution for ultrasonic mixing treatment for 0.5 h to preliminarily disperse the additives. Then disperse them through a mechanical stirrer for 8 h. Finally, transfer the mixed solution to a high-pressure homogenizer, with an operating pressure of 800 bar, and continuously disperse it 5 times to obtain the conductive paste.

[0061] Comparative Example 1 (without fluorescein)

[0062] Weigh 95.2% deionized water and 3.2% sodium carboxymethylcellulose according to the weight ratio and add them to a clean and dry dispersion tank, and mechanically stir for 1 h until completely dissolved. Weigh 0.8% single-walled carbon nanotubes and 0.8% graphene oxide and add them to the cellulose solution for ultrasonic mixing treatment for 0.5 h to preliminarily disperse the additives. Then disperse them through a mechanical stirrer for 8 h. Finally, transfer the mixed solution to a high-pressure homogenizer, with an operating pressure of 800 bar, and continuously disperse it 5 times to obtain the conductive paste.

[0063] Comparative Example 2 (without graphene oxide)

[0064] Weigh 95.9% deionized water and 3.2% sodium carboxymethylcellulose according to the weight ratio and add them to a clean and dry dispersion tank. Stir mechanically for 1 h until completely dissolved. Weigh 0.8% single-walled carbon nanotubes and 0.1% fluorescein (same as in Example 1) and add them to the cellulose solution. Perform ultrasonic mixing treatment for 0.5 h to preliminarily disperse the additives. Then disperse for 8 h through a mechanical stirrer. Finally, transfer the mixed solution to a high-pressure homogenizer, with an operating pressure of 800 bar, and continuously disperse 5 times to prepare the conductive paste.

[0065] After the test, draw a time-fluorescence intensity relationship curve according to the test results, as Figure 3 shown: As the standing time prolongs, the fluorescence of the paste is relatively stable in the first 48 h, and the fluorescence intensity decreases significantly after 48 h. This indicates that the paste of Comparative Example 2 has poor stability, the single-walled carbon nanotubes agglomerate, and then precipitate at the bottom, resulting in a decrease in the detectable concentration of fluorescein in the supernatant.

[0066] Test the resistivity of the conductive pastes of the above comparative examples and examples, and the data results are shown in Table 1.

[0067] Table 1 Experimental results of resistivity tests of examples and comparative examples

[0068]

[0069] Referring to Table 1, comparing Comparative Example 1 with Example 1, it can be seen that the addition of fluorescein in the conductive paste composition of the present application has a beneficial effect on the conductivity of the paste.

[0070] Referring to Table 1, comparing Comparative Example 2 with Example 1, it can be seen that the addition of graphene oxide in the conductive paste composition of the present application has a significant effect on the conductivity of the paste.

[0071] Referring to Table 1, comparing Example 3 with Example 4, it can be seen that the influence of carbon nanotubes on the conductivity of the conductive paste of the present application is greater than that of graphene oxide.

[0072] From the above comparative examples and examples, it can be learned that for the conductive paste of the present application, by adding graphene oxide with a specific specification and specific fluorite, the stability of the overall paste can be effectively improved. And the addition of fluorescein can not only achieve the following technical effects: by testing the fluorescence intensity of the conductive paste before and after standing, the stability of the conductive paste can be judged according to the change of fluorescence intensity, and the stability of the paste can be continuously observed by a simple method; at the same time, the fluorescein structure has a large π bond, and the delocalized electron cloud is beneficial to electron transport. Compared with surfactants, it is beneficial to improve the conductivity of the system.

Claims

1. A single-walled carbon nanotube composite conductive paste, characterized in that: The raw materials of the slurry and their corresponding weight percentage contents include: 0.4%-8% of a dispersant, 0.2%-1% of single-walled carbon nanotubes, 0.2%-1% of graphene oxide, 0.01%-0.2% of fluorescein, and 89.8%-99.19% of a solvent.

2. The single-walled carbon nanotube composite conductive paste according to claim 1, wherein: The particle size range of the graphene oxide is 300-500 nm, where the oxygen mass fraction is 36%-53%, and the carbon mass fraction is 45%-62%.

3. The single-walled carbon nanotube composite conductive paste according to claim 2, wherein: The graphene oxide is the graphene oxide after centrifugation treatment.

4. The single-walled carbon nanotube composite conductive paste according to claim 3, wherein: For the centrifugation treatment of the graphene oxide, specifically: disperse the graphene oxide in water, centrifuge at a speed of 3500-4500 rpm, let it stand for 0.5-2 h after centrifugation, and take the supernatant; collect the supernatant in a container, perform freeze-drying, and after drying is completed, grind it to obtain graphene oxide powder with a particle size distribution of 300-500 nm.

5. The single-walled carbon nanotube composite conductive paste according to claim 4, wherein: Before the centrifugation treatment of the graphene oxide, its number of layers is less than 5 layers, and the particle size is less than 3 μm; the graphene oxide obtained after centrifugation treatment has a particle size less than 500 nm and 2-3 layers.

6. The single-walled carbon nanotube composite conductive paste according to claim 1, wherein: The dispersant is at least one of sodium carboxymethyl cellulose, polyethylene glycol, and sodium dodecyl sulfate.

7. The single-walled carbon nanotube composite conductive paste according to claim 6, wherein: The degree of substitution of the sodium carboxymethyl cellulose is 0.7-1.1, and the molecular weight is 500.

8. The single-walled carbon nanotube composite conductive paste according to claim 1, wherein: The diameter of the single-walled carbon nanotubes is 0.8-1.5 nm, the length is 2-10 μm, and the purity is greater than 98.5%.

9. The single-walled carbon nanotube composite conductive paste according to claim 1, wherein: The fluorescein is at least one of methoxypolyethylene glycol fluorescein, fluorescein isothiocyanate, hydroxy polyethylene glycol-fluorescein isothiocyanate, methoxy e-coelenterazine, tetramethylrhodamine, and tetramethyl isothiocyanate rhodamine.

10. The single-walled carbon nanotube composite conductive paste according to claim 1, wherein: The solvent is deionized water.

11. A method for preparing a single-walled carbon nanotube composite conductive paste according to any one of claims 1-10, characterized in that: It includes: (1) Weigh various raw materials of the conductive slurry according to the formula ratio, then perform ultrasonic mixing treatment on each raw material component, then disperse it through a mechanical stirrer, and then transfer the mixed solution to a high-pressure homogenizer for dispersion; (2) After dispersion, a uniform slurry is obtained, and it is subjected to suction filtration; (3) After suction filtration, a filter cake is obtained, transfer the filter cake to a container, add deionized water, and then perform ultrasonic dispersion for 0.5-2 h; repeat the above steps of suction filtration-ultrasonic dispersion 2-3 times to wash away the fluorescein that has not adsorbed on the surface of the carbon nanotubes to obtain the conductive slurry.

12. The preparation method of the single-walled carbon nanotube composite conductive paste according to claim 11, characterized in that: The rotation speed range of the mechanical stirring in step (1) is 6000-10000 rpm, the dispersion time is 30-60 min, and the number of times is 2-3 times; the operating pressure of the homogenizer in step (1) is set to 600-1000 bar, and continuous dispersion is carried out 5-15 times; the ultrasonic time in step (1) is 5-15 min.

13. An evaluation method for the stability of a single-walled carbon nanotube composite conductive paste according to any one of claims 1 to 10, characterized in that: It includes: (S1) Test the fluorescence intensity of the conductive slurry before and after standing; (S2) Judge the stability of the conductive slurry according to the change in the fluorescence intensity.

14. The evaluation method for the stability of the single-walled carbon nanotube composite conductive paste according to claim 13, characterized in that: For step (S1), specifically: take a sample from the prepared conductive slurry, dilute the slurry 10,000 times, record it as sample 1, and test the fluorescence intensity of sample 1; let the slurry stand, take samples at fixed intervals, record them as sample 2, sample 3,..., sample n, and test the fluorescence intensity of the samples taken.

15. The evaluation method for the stability of the single-walled carbon nanotube composite conductive paste according to claim 13, wherein: For the said step (S2), specifically: compare the fluorescence intensities of sample 1, sample 2, ……, sample n. If the change in fluorescence intensity is small, it is considered that the slurry stability is good.

16. The evaluation method for the stability of the single-walled carbon nanotube composite conductive paste according to claim 14, characterized in that: The method for testing the fluorescence intensity of the sample is as follows: Use an F-4600 fluorescence spectrometer produced by Hitachi. The light source is a 150W xenon lamp, the spectral range of the light source is 200 - 750m, and the scanning speed is 2400nm·min -1 , the excitation slit is 5nm, the emission slit is 5nm, the voltage of the photomultiplier tube is 400V, the wavelength interval is 10nm, and the scanning wavelength interval is 1nm.

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