Method for producing conductive material slurry

Abstract

To provide a manufacturing method of a conductive material slurry which facilitates pre-dispersion by reducing a particle size of a conductive material by introduction of a dry process, produces a high-concentration dispersion, and has excellent dispersion characteristics by introduction of a post-process, as compared with a conventional manufacturing method of a conductive material slurry.SOLUTION: A method of preparing a conductive material dispersed slurry includes: dry-grinding a conductive material; pre-dispersing the conductive material by mixing the conductive material with a solvent and a dispersant; main-dispersing the pre-dispersed conductive material; and post-dispersing the main-dispersed mixture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a carbon nanotube slurry, and more particularly to a method for producing a carbon nanotube slurry in which the concentration of carbon nanotubes is increased by introducing a dry process and the carbon nanotube slurry is further homogenized by introducing a post-dispersion process. [Background technology]

[0002] Secondary batteries have been continuously developed and researched since their introduction in the 1990s. Research and development is being conducted not only on the key components of secondary batteries—positive and negative electrode active materials, electrolytes, and separators—but also on various auxiliary elements that complement and enhance their properties. In recent years, as the application of secondary batteries has expanded to medium- to large-scale battery applications such as electric vehicles and energy storage systems (ESS), the importance of conductive materials has increased. Increasing the theoretical capacity of secondary batteries requires increasing the amount of positive or negative electrode active material. However, as the amount of active material increases in the same electrode, the amount of conductive material decreases. Therefore, conductive materials that can demonstrate excellent performance even in small amounts are needed. In this regard, carbon nanotubes (CNTs) have attracted attention as a new conductive material. CNTs have a cylindrical structure with a nanometer-sized diameter, and carbon atoms are arranged in a helical pattern with an sp2 bond structure. These CNTs exhibit excellent physical properties in various aspects, including excellent electrical properties, strength, resilience, and thermal conductivity. As a conductive material for secondary battery electrodes, CNTs are expected to increase energy density and extend battery life, while also reducing battery size, compared to existing powder-type carbon materials. These advantages are particularly advantageous for electric vehicle batteries, which require high capacity and fast charging. Summary of the Invention [Problem to be solved by the invention]

[0003] Compared with conventional methods for manufacturing conductive slurry, the present invention aims to provide a method for manufacturing conductive slurry with excellent dispersion characteristics by introducing a dry process to reduce the particle size of the conductive material, thereby facilitating pre-dispersion and producing a highly concentrated dispersion, and by introducing a post-process. [Means for solving the problem]

[0004] A method for preparing a conductive material slurry according to an embodiment of the present invention may include dry-grinding a conductive material, pre-dispersing the conductive material by mixing it with a solvent and a dispersant, main-dispersing the pre-dispersed dispersion, and post-dispersing the main-dispersed mixture.

[0005] The conductive material may be at least one selected from the group consisting of multi-wall carbon nanotubes, single-wall carbon nanotubes, carbon fibers, graphene, and carbon black.

[0006] The multi-walled carbon nanotubes may have a particle size of 10 μm to 50 μm (D50).

[0007] The single-walled carbon nanotubes may have a particle size of 100 μm to 200 μm (D50).

[0008] The dispersant may be one or more selected from polyvinylpyrrolidone, polyvinylidene fluoride, HNBR (Hydrogenated Nitrile Rubber), polyacrylic acid, carboxymethyl cellulose, and tannic acid. In addition to the above substances, the dispersant may be selected from a copolymer solution having a pigmented affine group.

[0009] The solvent may be one or more selected from NMP or distilled water (H2O).

[0010] The step of completely dispersing the conductive material may be a step of performing dispersion three to ten times at a pressure of 1000 bar to 2000 bar using a cell of 100 μm to 200 μm. [Effects of the Invention]

[0011] According to one embodiment of the present invention, a method can be provided in which a highly concentrated conductive material dispersion is produced by reducing the particle size of the conductive material through the introduction of a dry process, and a conductive material dispersion slurry with excellent dispersion properties is produced through the introduction of a post-process. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a flowchart illustrating a method for manufacturing a conductive material slurry according to an embodiment of the present invention. [Figure 2] 1 is a graph showing the particle size of a dispersion (Comparative Example 1). [Figure 3] 1 is a graph showing the particle size of a dispersion (Comparative Example 2). [Figure 4] 1 is a graph showing particle size of a dispersion (Example 1) prepared according to an embodiment of the present invention. [Figure 5] 1 is a graph showing particle size of a dispersion (Example 2) prepared according to an embodiment of the present invention. [Figure 6] 1 is a graph showing the particle size of a dispersion (Comparative Example 3). [Figure 7] 1 is a graph showing the particle size of a dispersion (Comparative Example 4). [Figure 8] 1 is a graph showing particle size of a dispersion (Example 3) prepared according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The terms and phrases used in the following specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept that is consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the terms in order to best describe his or her invention.

[0014] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that at the time of this application, there may be various equivalents and modifications that can replace them.

[0015] Throughout this specification, when a part "comprises" one component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified. Furthermore, when a part is "coupled" to another part, this includes not only "directly coupled" but also "electrically coupled" via another element therebetween.

[0016] The terms used in this specification are for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in this specification, singular terms can include plural terms unless the context clearly dictates otherwise. Furthermore, as used in this specification, the terms "comprise" and / or "comprising" specify the presence of a stated shape, step, number, operation, member, element, and / or group thereof, but do not exclude the presence or addition of one or more other shapes, steps, numbers, operations, members, elements, and / or group thereof.

[0017] Furthermore, the term "connected" as used in this specification does not only mean that each component is directly connected, but also includes the concept of indirectly connecting each component by the presence of another component between them.

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily understand the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. In the drawings, parts that are not relevant to the description are omitted in order to clearly explain the present invention, and similar parts are designated by similar reference numerals throughout the specification.

[0019] A method for preparing a conductive material slurry according to an embodiment of the present invention may include dry-grinding a conductive material, pre-dispersing the conductive material by mixing it with a solvent and a dispersant, main-dispersing the pre-dispersed dispersion, and post-dispersing the main-dispersed mixture.

[0020] The step of dry-milling the conductive material is a step for reducing the particle size of the conductive material. By including the step of dry-milling the conductive material in the present invention, the total dispersion time required in the method for preparing a conductive material slurry can be reduced. Another advantage is that the content of the conductive material relative to the total dispersion in the pre-dispersion step can be maintained at 5% to 10% for MWCNTs and 0.4% to 1.5% for SWCNTs.

[0021] The step of pre-dispersing the conductive material by mixing it with a solvent and a dispersant may be performed after the dry-grinding step, or the steps of pre-dispersion, main dispersion, and post-dispersion may be performed sequentially after the dry-grinding step.

[0022] Specifically, the steps of pre-dispersing the conductive material by mixing it with a solvent and a dispersant, main-dispersing the pre-dispersed dispersion, and post-dispersing the main-dispersed mixture are sequentially performed, thereby providing an effect of reducing the viscosity of the finally prepared conductive material slurry.

[0023] The conductive material may be at least one selected from the group consisting of carbon nanotubes, carbon fibers, graphene, and carbon black.

[0024] The carbon nanotubes can include single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs).

[0025] The multi-walled carbon nanotubes may have a particle size of 10 μm to 50 μm (D50). Specifically, the multi-walled carbon nanotubes may have a particle size of 10 μm to 50 μm (D50) after the dry-milling step. The dry-milling step has the effect of reducing the process time required for the subsequent pre-dispersion, main dispersion, and post-dispersion steps. In addition, by using the conductive material whose particle size has been reduced in the dry-milling step for pre-dispersion, the viscosity of the conductive material slurry produced can be reduced.

[0026] The single-walled carbon nanotubes may have a particle size of 100 μm to 200 μm (D50). Specifically, the single-walled carbon nanotubes may have a particle size of 100 μm to 200 μm (D50) after the dry-milling step. The dry-milling step has the effect of reducing the process time required for the subsequent pre-dispersion, main dispersion, and post-dispersion steps. In addition, by using the conductive material whose particle size has been reduced in the dry-milling step for pre-dispersion, the viscosity of the conductive material slurry produced can be reduced.

[0027] The dispersant may be one or more selected from polyvinylpyrrolidone, polyvinylidene fluoride, HNBR (Hydrogenated Nitrile Rubber), polyacrylic acid, carboxymethyl cellulose, and tannic acid. In addition to the above substances, the dispersant may also be selected from a copolymer solution having a pigmented affine group.

[0028] Specifically, the dispersant may be a dispersant for a positive electrode or a dispersant for a negative electrode.

[0029] The dispersant for the positive electrode may be one or more selected from polyvinylpyrrolidone, polyvinylidene fluoride, and HNBR (Hydrogenated Nitrile Rubber).

[0030] The dispersant for the negative electrode may be one or more selected from polyvinylpyrrolidone, polyacrylic acid, carboxymethyl cellulose, and tannic acid.

[0031] The solvent may be one or more selected from NMP or distilled water (H2O).

[0032] Specifically, the solvent may be a positive electrode solvent or a negative electrode solvent.

[0033] As the positive electrode solvent, NMP may be used.

[0034] The negative electrode solvent may be H2O.

[0035] In a specific example, when preparing a conductive material slurry for a positive electrode, in the step of pre-dispersing the conductive material by mixing it with a solvent and a dispersant, the proportions of the conductive material, the solvent, and the dispersant may be 40 wt% to 100 wt%, 880 wt% to 95.20 wt%, and 0.80 wt% to 2.0 wt%, respectively, based on the total weight of the conductive material slurry.

[0036] The ratio of the conductive material to the dispersant in the conductive material slurry may be 20-50:4-10. Within this range, the particle size of the produced conductive material slurry is small, resulting in excellent dispersibility and low viscosity of the conductive material slurry.

[0037] In a specific example, when preparing a conductive material slurry for a negative electrode, in the step of pre-dispersing the conductive material by mixing it with a solvent and a dispersant, the ratio of the conductive material, the solvent, and the dispersant may be 0.4 to 2.0:95.0 to 99.0:0.6 to 3.0 wt %, respectively, based on the total weight of the conductive material slurry.

[0038] The ratio of the conductive material to the dispersant in the conductive material slurry may be 2:10 to 3:15. Within this range, the particle size of the produced conductive material slurry is small, which can result in excellent dispersibility and low viscosity of the conductive material slurry.

[0039] The slurry prepared according to an embodiment of the present invention may have a particle size of 0.01 μm to 20 μm (D50). For example, the particle size of the slurry may be 0.03 μm to 18 μm, or 0.06 μm to 16 μm. Within this range, the prepared slurry may have excellent dispersibility.

[0040] The positive electrode conductive material slurry prepared according to one embodiment may have a particle size of 0.01 μm to 0.82 μm (D50). The negative electrode conductive material slurry prepared according to another embodiment may have a particle size of 6.5 μm to 14.5 μm (D50).

[0041] The slurry prepared according to an embodiment of the present invention may have a particle size of 0.01 μm to 60 μm (D90). For example, the particle size of the slurry may be 0.07 μm to 50 μm or 0.1 μm to 40 μm. Within this range, the prepared slurry may have excellent dispersibility.

[0042] The positive electrode conductive material slurry prepared according to one embodiment may have a particle size of 0.078 μm to 3.4 μm (D90). The negative electrode conductive material slurry prepared according to another embodiment may have a particle size of 6.5 μm to 14.5 μm (D50).

[0043] The slurry prepared according to one embodiment of the present invention may have a viscosity of 100 cPs to 30,000 cPs. Specifically, the viscosity of the slurry measured at a shear rate of 10 / s using a TA HR-1 rheometer may be 100 cPs to 30,000 cPs. For example, the viscosity of the prepared slurry may be 120 cPs to 29,000 cPs, and preferably 160 cPs to 28,500 cPs. Within this range, the prepared slurry may have excellent dispersibility.

[0044] The step of dry-pulverizing the conductive material may be a step of filling a vessel of a dry mill with zirconia beads of 1φ to 5φ so that the volume of the vessel occupies 20% to 80% of the total volume of the vessel, and then continuously pulverizing the material at 500 rpm to 1500 rpm.

[0045] The step of pre-dispersing the conductive material by mixing it with the solvent and the dispersant may be performed using a disperser having two or more impellers.

[0046] The step of pre-dispersing the conductive material may be performed in an atmosphere at a temperature of 15° C. to 30° C., for example, 16° C. to 28° C. or room temperature. By pre-dispersing the conductive material in this range, a separate high-temperature treatment is not required, thereby saving energy and time.

[0047] The step of pre-dispersing the conductive material may be carried out at a pressure of 0.35 bar to 1.85 bar.

[0048] The step of pre-dispersing the conductive material may be performed under a nitrogen atmosphere.

[0049] The step of completely dispersing the conductive material may be a step of performing dispersion three to ten times at a pressure of 1000 bar to 2000 bar using a cell of 100 μm to 200 μm.

[0050] The step of dispersing the conductive material may be carried out in an atmosphere at a temperature of 15°C to 30°C, for example, 16°C to 28°C, or at room temperature.

[0051] The step of dispersing the conductive material may be carried out at a pressure of 1,000 bar to 2,000 bar.

[0052] The step of dispersing the conductive material may be performed by passing the conductive material through a cell of 100 μm to 200 μm three to ten times.

[0053] The post-dispersion step of the dispersed mixture may be a step of disintegrating the mixture using a basket-type impeller at 3000 rpm to 8000 rpm. The post-dispersion step has the effect of ensuring uniformity of the final dispersion of the slurry and optimizing its viscosity and physical properties.

[0054] Comparative Example 1: Method for producing carbon nanotube slurry for positive electrode

[0055] 94g of NMP solvent, 1g of dispersant (HNBR), and 5g of multi-walled carbon nanotubes (MWCNT) were mixed using a Dyno-mill wet bead mill and then dispersed. The dispersion method was circulation for 12 hours, followed by pre-dispersion using the wet bead mill.

[0056] The pre-dispersed material was then subjected to main dispersion using a high-pressure disperser, which was repeated eight times in a 200 μm cell under a pressure of 1,000 bar.

[0057] Comparative Example 2: Method for producing carbon nanotube slurry for positive electrode

[0058] The multi-walled carbon nanotube powder was dry-milled using a dry bead mill developed by our company.

[0059] Then, 94 g of NMP (solvent), 1 g of HNBR (dispersant), and 5 g of the dry-milled multi-walled carbon nanotube powder were mixed and pre-dispersed using a multi-impeller mixer under conditions of jog 80 rpm / impeller 9,000 rpm for 4 hours.

[0060] Thereafter, the dispersion that had undergone the pre-dispersion step was subjected to main dispersion using a high-pressure disperser, which was repeated four times in a 200 μm cell under a pressure of 1,000 bar.

[0061] Example 1. Method for producing carbon nanotube slurry for positive electrode

[0062] The multi-walled carbon nanotube powder was dry-milled using a dry bead mill developed by our company.

[0063] Then, 94 g of NMP (solvent), 1 g of HNBR (dispersant), and 5 g of the dry-milled multi-walled carbon nanotube powder were mixed and pre-dispersed using a multi-impeller mixer under conditions of jog 80 rpm / impeller 9,000 rpm for 4 hours.

[0064] Thereafter, the dispersion that had undergone the pre-dispersion step was subjected to main dispersion using a high-pressure disperser, which was repeated four times in a 200 μm cell under a pressure of 1,000 bar.

[0065] The dispersion that had undergone this dispersion stage was then subjected to a post-dispersion stage, which was carried out under a nitrogen atmosphere at 5,000 rpm for 2 hours.

[0066] Example 2. Method for producing carbon nanotube slurry for positive electrode

[0067] The multi-walled carbon nanotube powder was dry-milled using a dry bead mill developed by our company.

[0068] Then, 90.4 g of NMP solvent, 1.6 g of dispersant (HNBR), and 8 g of the dry-milled multi-walled carbon nanotube powder were mixed and pre-dispersed using a multi-impeller mixer under conditions of jog 80 rpm / impeller 9,000 rpm for 4 hours.

[0069] Thereafter, the dispersion that had undergone the pre-dispersion step was subjected to main dispersion using a high-pressure disperser, which was repeated four times in a 200 μm cell under a pressure of 1,000 bar.

[0070] The dispersion that had undergone this dispersion stage was then subjected to a post-dispersion stage, which was carried out under a nitrogen atmosphere at 5,000 rpm for 2 hours.

[0071] Example 3: Method for producing aqueous conductive material slurry for negative electrodes

[0072] The single-walled carbon nanotubes were dry-milled using a dry bead mill developed by our company.

[0073] Next, 97g of solvent (DI water) and 1.8g of dispersant (carboxymethyl cellulose) were mixed and stirred to dissolve the dispersant. 1.2g of single-walled carbon nanotubes (SWCNTs) dry-milled using our proprietary dry bead mill equipment was added to the solution, and the mixture was pre-dispersed using a mixer with multiple impellers. After the pre-dispersion step, the dispersion was then subjected to main dispersion using a high-pressure disperser. This main dispersion was repeated four times under an atmosphere of 200μm cells and 1,000 bar pressure.

[0074] The dispersion that had undergone this dispersion stage was then subjected to a post-dispersion stage, which was carried out under a nitrogen atmosphere at 5,000 rpm for 2 hours.

[0075] Comparative Example 3: Method for producing aqueous conductive material slurry for negative electrodes

[0076] 99 g of solvent (DI water) and 0.6 g of dispersant (carboxymethyl cellulose) were stirred to dissolve the dispersant. 0.4 g of single-walled carbon nanotubes (SWCNTs) were added to the solution, and the mixture was circulated for 12 hours using a Dyno Mill, a wet dispersion bead mill, to perform pre-dispersion. The pre-dispersed dispersion was then subjected to main dispersion using a high-pressure disperser. This main dispersion was repeated eight times using a 200 μm cell at a pressure of 1,000 bar.

[0077] Comparative Example 4: Method for producing aqueous conductive material slurry for negative electrodes

[0078] The single-walled carbon nanotube powder was dry-milled using a dry bead mill developed by our company.

[0079] Next, 97g of solvent (DI water) and 1.8g of dispersant (carboxymethyl cellulose) were mixed together to dissolve the dispersant. 1.2g of single-walled carbon nanotubes (SWCNTs) dry-milled using our proprietary dry bead mill were added to the solution, and the mixture was pre-dispersed using a mixer with multiple impellers. The resulting dispersion was then subjected to main dispersion using a high-pressure disperser. This main dispersion was repeated four times under an atmosphere of 200μm cells and 1,000 bar pressure.

[0080] Experimental Example 1. Measurement of particle size and viscosity of prepared carbon nanotube slurry for cathode

[0081] The particle sizes of the conductive material slurries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured using a particle size analyzer, Mastersizer 3000+ manufactured by Marburn.

[0082] In addition, the viscosity of the conductive material slurries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was measured using a TA HR-1 rheometer and a Brookfield LVT, respectively.

[0083] Table 1 below shows the particle size and viscosity of the conductive material slurries prepared in Examples 1 and 2 and Comparative Examples 1 and 2.

[0084] [Table 1]

[0085] Referring to Table 1 below and FIGS. 2 to 5, it can be seen that Comparative Example 1 was subjected to strong shear stress, resulting in very uneven peaks in the graph.

[0086] On the other hand, in the case of Comparative Example 2, as a result of the dry grinding process, it was subjected to a lower shear stress than in Comparative Example 1, and it can be confirmed that two uniform peaks were observed.

[0087] In the case of Examples 1 and 2, it can be seen that as a result of the post-dispersion process, the shear stress is relieved and one uniform peak is observed.

[0088] Experimental Example 2. Measurement of particle size and viscosity of the prepared carbon nanotube slurry for negative electrode

[0089] The particle size of the conductive material slurries prepared in Example 3, Comparative Example 3, and Comparative Example 4 was measured using a particle size analyzer, Marburn Mastersizer 3000+.

[0090] In addition, the viscosity of the conductive material slurries prepared in Example 3, Comparative Example 3, and Comparative Example 4 was measured using a TA HR-1 rheometer and a Brookfield LVT, respectively.

[0091] Table 2 below shows the particle size and viscosity of the conductive material slurries prepared in Example 3, Comparative Example 3, and Comparative Example 4.

[0092] [Table 2]

[0093] Referring to Table 2 below and FIGS. 6 to 8, it can be seen that Comparative Example 3 was subjected to strong shear stress and exhibited very uneven peaks in the graph.

[0094] On the other hand, in the case of Comparative Example 4, as a result of the dry grinding process, it was found that the sample was subjected to a lower shear stress than that of Comparative Example 3, and showed two uniform peaks.

[0095] In the case of Example 3, it can be seen that as a result of the post-dispersion process, the shear stress is relieved and one uniform peak is observed.

Claims

1. dry-milling the conductive material; pre-dispersing the conductive material by mixing it with a solvent and a dispersant; a step of dispersing the pre-dispersed dispersion; and post-dispersing the dispersed mixture; A method for producing a conductive material dispersed slurry comprising the steps of:

2. 2. The method for producing a conductive material dispersion slurry according to claim 1, wherein the conductive material is at least one selected from the group consisting of multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon fibers, graphene, and carbon black.

3. 3. The method for producing a conductive material dispersion slurry according to claim 2, wherein the multi-walled carbon nanotubes have a particle size of 10 μm to 50 μm (D50).

4. 3. The method for producing a conductive material dispersion slurry according to claim 2, wherein the single-walled carbon nanotubes have a particle size of 100 μm to 200 μm (D50).

5. 2. The method for producing a conductive material dispersion slurry according to claim 1, wherein the dispersant is one or more selected from the group consisting of polyvinylpyrrolidone, polyvinylidene fluoride, HNBR (Hydrogenated Nitrile Rubber), polyacrylic acid, carboxymethyl cellulose, and tannic acid.

6. The solvent is NMP or distilled water (H ２ 2. The method for producing a conductive material-dispersed slurry according to claim 1, wherein the conductive material-dispersed slurry is one or more selected from the group consisting of:

7. 2. The method for producing a conductive material-dispersed slurry according to claim 1, wherein in the step of dry-pulverizing the conductive material, zirconia beads having a diameter of 1φ to 5φ are filled into a vessel of a dry pulverizer so that the volume of the vessel occupies 20% to 80% of the total volume of the vessel, and then the pulverization is performed continuously at a speed of 500 rpm to 1500 rpm.

8. 2. The method of claim 1, wherein the step of pre-dispersing the conductive material with the solvent and the dispersant is performed using a disperser having two or more impellers.

9. 2. The method of claim 1, wherein the step of dispersing the conductive material comprises performing dispersion 3 to 10 times using a cell of 100 μm to 200 μm at a pressure of 1000 bar to 2000 bar.

10. 2. The method of claim 1, wherein the post-dispersion of the dispersed mixture is performed by crushing the dispersed mixture at 3,000 to 8,000 rpm using a basket-type impeller.

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