Conductive agent, electrode for lithium battery, and method for producing conductive agent

Abstract

FIELD OF THE INVENTION The present invention relates to a conductive agent, an electrode for a lithium battery, and a method for producing the conductive agent. The conductive agent comprises a dry mixture, preferably a freeze-dried mixture, of carbon nanostructures and carbon black.

Description

[Technical Field]

[0001] The present invention relates to a conductive agent, an electrode for a lithium battery, and a method for producing the conductive agent, and more particularly to a conductive agent containing a dry mixture, preferably a freeze-dried mixture, of a carbon nanostructure and carbon black, a lithium battery electrode containing the conductive agent, and a method for producing the conductive agent. [Background technology]

[0002] Carbon nanotubes have excellent electrical conductivity and a high aspect ratio. Adding carbon nanotubes to electrode materials, such as the cathode material of lithium-ion batteries, can effectively form a conductive network, improving the conductivity of the electrode and making lithium-ion batteries superior in performance, suitable for use in high-end digital batteries and new energy vehicles.

[0003] However, dispersing carbon nanotubes is extremely difficult. In conventional technology, manufactured carbon nanotubes are dispersed in a solvent to form a slurry for sale. As such, the carbon nanotube content in the conductive carbon nanotube slurry is only 3% to 8%, while the solvent content exceeds 90%, limiting the range and fields of application of carbon nanotubes. The large amount of solvent also causes transportation problems and increases customer usage costs.

[0004] Patent Document 1 discloses a method for producing easily dispersible carbon nanotube powder, which includes step (1) of producing a dispersion slurry containing carbon nanotubes by bead polishing, and step (2) of drying the dispersion slurry produced in step (1) to obtain a solid powder. Patent Document 1 also discloses that the electrode sheet resistivity of the carbon nanotube powder is equal to or greater than that of the carbon nanotube slurry.

[0005] However, it has been found that the carbon nanotube powder obtained by the above-mentioned production method has a problem in that when the carbon nanotube powder is used as a conductive agent in a lithium battery, the battery performance, particularly the rate performance and low-temperature discharge performance, is significantly reduced compared to the original carbon nanotube dispersion slurry. Therefore, although freeze-dried carbon nanotubes solve the problem of ease of transportation, the performance of lithium batteries produced from the carbon nanotubes is reduced, which significantly hinders the practical use of freeze-dried carbon nanotubes in lithium batteries. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Chinese Patent Application Publication No. 110894068 Summary of the Invention

[0007] Therefore, when using carbon nanotube powder in a lithium battery, it is required to make it easy to disperse the carbon nanotube powder while preventing a significant decrease in the rate performance and low-temperature discharge performance of the lithium battery compared to the original dispersion slurry.

[0008] In view of the shortcomings of the prior art, the present invention aims to provide a conductive agent containing carbon nanotube powder, which makes it easy to disperse the carbon nanotube powder, and at the same time, when the conductive agent containing carbon nanotube powder is used in a lithium battery, the rate performance and low-temperature discharge performance of the lithium battery do not decrease significantly compared to the original dispersed slurry.

[0009] According to one aspect, the present invention provides a conductive agent comprising a dry mixture, preferably a freeze-dried mixture, of carbon nanostructures and carbon black.

[0010] The carbon nanostructure is at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and carbon nanobundles, preferably carbon nanotubes, and more preferably at least one of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0011] In X-ray diffraction analysis, carbon nanotubes have a peak at a diffraction angle 2θ=25°±2°, and the full width at half maximum of the peak is 1° to 6°.

[0012] The average outer diameter of the carbon nanotubes is in the range of 1 to 40 nm, preferably 2 to 35 nm, more preferably 5 to 30 nm, particularly 10 to 20 nm, and further particularly 10 to 15 nm.

[0013] The BET surface area of ​​carbon nanotubes is 100-1200 m 2 / g, preferably 120 to 1000m 2 / g, more preferably 150 to 800m 2 / g, especially 180-500m 2 / g, and especially 200-300m 2 / g range.

[0014] The carbon nanostructure includes a first carbon nanotube and a second carbon nanotube, and the first carbon nanotube has a BET surface area of ​​100 to 240 m 2 / g, preferably 150 to 230 m 2 / g, more preferably 200 to 220 m 2 / g, and the BET surface area of ​​the second carbon nanotubes is in the range of 250-1200 m 2 / g, preferably 260 to 500m 2 / g, more preferably 270 to 300m 2 / g, and more particularly the weight ratio of the first carbon nanotubes to the second carbon nanotubes is 1:9 to 9:1, preferably 2:8 to 8:2, more preferably 5:5 to 8:2, especially 7:3 to 8:2.

[0015] The carbon black is at least one selected from the group consisting of furnace black, channel black and thermal black, with furnace black being preferred.

[0016] The BET surface area of ​​carbon black is 70 to 1500 m 2 / g, preferably 200 to 1400m 2 / g, more preferably 500 to 1300m 2 / g, especially 800-1250m 2 / g, and especially 1000-1200m 2 / g range.

[0017] The DBP oil absorption of carbon black is in the range of 180 to 360 ml / 100 g, preferably 200 to 320 ml / 100 g, more preferably 220 to 300 ml / 100 g, particularly 230 to 280 ml / 100 g, and further particularly 240 to 260 ml / 100 g.

[0018] The weight ratio of the carbon nanostructure to the carbon black is 0.5:9.5 to 9.5:0.5, preferably 1:9 to 9:1, more preferably 2:8 to 8:2, and particularly 3:7 to 4:6.

[0019] According to another aspect, the present invention provides an electrode for a lithium battery, preferably a positive electrode for a lithium battery, containing a conductive agent.

[0020] According to yet another aspect, the present invention provides a method for producing a conductive agent, the method comprising: mixing and dispersing carbon nanostructures and carbon black in a solvent to obtain a dispersion slurry; and drying, preferably freeze-drying, the obtained dispersion slurry.

[0021] The dispersed slurry further contains a dispersant, and the dispersant is preferably at least one of polyvinylpyrrolidone, polyacrylamide, polycarboxylic acid, polyacrylic acid, polycarboxylate, polyacrylate, polyvinyl alcohol, ethoxylated alcohol, montan wax, polyvinyl butyral, nitrile rubber; carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, polyvinyl acetate, polystyrene sulfonate, polymethacrylate, polyethyleneimine, polyethyleneamine, polypropyleneamine, poly(2-vinylpyridine), block copolyether, cellulose acetate, copolymer of polystyrene and maleic anhydride, and copolymers and derivatives containing monomers of the above polymers, and polyvinylpyrrolidone is preferred.

[0022] Freeze-drying is carried out at temperatures between -40°C and -70°C.

[0023] The solvent is at least one of water, methanol, ethanol, n-propanol, isopropanol, acetone, NMP, butanol, butanediol, pentane, n-hexane, cyclohexane, trichloroethane, carbon tetrachloride, ethyl acetate, methyl ethyl ketone, dimethylformamide, dimethylacetamide, benzene, and xylene, and water is preferred.

[0024] The conductive agent of the present invention can facilitate dispersion of carbon nanotube powder, while when used in a lithium battery, the rate performance and low-temperature discharge performance of the lithium battery are not significantly reduced compared to the original dispersion slurry. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a scanning electron microscope (SEM) photograph of the freeze-dried mixture of carbon nanotubes and carbon black produced in Example 6. [Figure 2] FIG. 2 is an SEM photograph of the dispersed slurry of carbon nanotubes and carbon black produced in Reference Example 6. [Figure 3] FIG. 3 is an SEM photograph of the freeze-dried carbon nanotubes produced in Comparative Example 3. [Figure 4] FIG. 4 is an SEM photograph of the carbon nanotube dispersion slurry produced in Reference Example 9. [Figure 5] FIG. 5 is an SEM photograph of the freeze-dried carbon nanotubes produced in Comparative Example 1. [Figure 6] FIG. 6 is an SEM photograph of the carbon nanotube dispersion slurry produced in Reference Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0026] As mentioned above, it is very difficult to disperse carbon nanotubes in conventional technologies, so carbon nanotubes are typically dispersed in a solvent to form a commercial slurry, which battery manufacturers use to manufacture lithium batteries. However, such conductive carbon nanotube slurries have a low carbon nanotube content and a high solvent content, which causes transportation problems and increases customer usage costs.

[0027] To address this issue, methods have been proposed for producing easily dispersible carbon nanotube powders, including preparing a dispersion slurry containing carbon nanotubes and drying the dispersion slurry to obtain a solid powder. However, these methods involve drying, particularly freeze-drying, the carbon nanotubes, which can affect their performance.

[0028] The inventors have discovered that the carbon nanotube powder obtained by this production method has a problem in that when the carbon nanotube powder is used as a conductive agent in a lithium battery, the battery performance, particularly the rate performance and low-temperature discharge performance, is significantly reduced compared to the original carbon nanotube dispersion slurry. This problem cannot be solved by simply mixing the freeze-dried carbon nanotube powder with other types of carbon.

[0029] Surprisingly, after extensive investigation, the inventors have discovered that when a specific type of carbon (carbon black) is added to a dispersion slurry of carbon nanotubes and then dried, a dry mixture of carbon nanotubes and carbon black is obtained, which can be easily and well dispersed, and at the same time, the rate performance and low-temperature discharge performance of lithium batteries manufactured using this mixture as a conductive agent do not significantly deteriorate.

[0030] Thus, in one embodiment, the present invention provides a conductive agent (powder) comprising a dry mixture of carbon nanostructures and carbon black.

[0031] In one embodiment, the conductive agent can be produced by mixing carbon nanostructures and carbon black with a solvent to produce a dispersion slurry, and then drying the dispersion slurry.

[0032] The mixture of carbon nanostructures and carbon black is preferably freeze-dried (lyophilized). The mixture of carbon nanostructures and carbon black produced by freeze-drying is more easily dispersible, and when used in the manufacture of lithium batteries, it can maintain performance such as rate performance and low-temperature discharge performance equivalent to that of the original dispersed slurry.

[0033] In one embodiment, the aspect ratio of the carbon nanostructures may be at least 20:1, preferably at least 100:1, and more preferably at least 500:1.

[0034] In one embodiment, the carbon nanostructure is not particularly limited and may be at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and carbon nanobundles (CNS), which have short-side connectivity.

[0035] In one embodiment, the carbon nanostructures may be carbon nanotubes, more preferably at least one of single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes, and particularly multi-walled carbon nanotubes. For example, the carbon nanotube structures may be one or more carbon nanotubes, such as multi-walled carbon nanotubes. The carbon nanotubes may be produced by methods known in the art, such as chemical vapor deposition (CVD), arc discharge, or laser deposition. In particular, the carbon nanotubes may be produced by CVD methods, such as powdered catalytic CVD or floating catalytic CVD, preferably powdered catalytic CVD.

[0036] In one embodiment, in an X-ray diffraction analysis, the carbon nanotubes have a peak at a diffraction angle 2θ=25°±2°, and the full width at half maximum of the peak is 1° to 6°, for example, 2° to 5°, 2° to 4°, or 2° to 3°. The X-ray diffraction analysis may be performed using CuKα radiation.

[0037] In one embodiment, the average outer diameter of the carbon nanotubes may be in the range of 1 to 40 nm, preferably 2 to 35 nm, more preferably 5 to 30 nm, particularly 10 to 20 nm, and even more particularly 10 to 15 nm.

[0038] In one embodiment, the BET surface area of ​​the carbon nanotubes is between 100 and 1200 m 2 / g, preferably 120 to 1000m 2 / g, more preferably 150 to 800m 2 / g, especially 180-500m 2 / g, and especially 200-300m 2 / g.

[0039] In one embodiment, the resistivity of the carbon nanotube powder at a pressure of 5 to 120 MPa may be 0.2 Ω·cm or less, preferably 0.1 Ω·cm or less, more preferably 0.08 Ω·cm or less, particularly 0.06 Ω·cm or less, and even more particularly 0.05 Ω·cm or less.

[0040] In one embodiment, the carbon nanostructure may include a first carbon nanotube and a second carbon nanotube. In particular, the first carbon nanotube has a BET surface area of ​​100 to 240 m 2 / g, preferably 150 to 230 m 2 / g, more preferably 200 to 220 m 2 / g, and the BET surface area of ​​the second carbon nanotubes is in the range of 250-1200 m 2 / g, preferably 260 to 500m 2 / g, more preferably 270 to 300m 2 The weight ratio of the first carbon nanotubes to the second carbon nanotubes may be in the range of 1:9 to 9:1, preferably 2:8 to 8:2, more preferably 5:5 to 8:2, and particularly 7:3 to 8:2.

[0041] In one embodiment, the carbon black is not particularly limited and may be at least one selected from the group consisting of furnace black, channel black, and thermal black, and may be preferably furnace black.

[0042] Carbon black is amorphous carbon, which is a lightweight, brittle, fine black powder. Generally, carbon black is a product of the incomplete combustion or pyrolysis of carbon-containing substances (e.g., coal, natural gas, heavy oil, fuel oil, etc.) in the absence of air.

[0043] The carbon black may include hard carbon black and soft carbon black, where the hard carbon black has a particle size of less than 40 nm and the soft carbon black has a particle size of 40 nm or more.

[0044] In one embodiment, the carbon black has a BET surface area of ​​70 to 1500 m 2 / g, preferably 200 to 1400m 2 / g, more preferably 500 to 1300m 2 / g, especially 800-1250m 2 / g, and especially 1000-1200m 2 Within this range, the BET surface area of ​​the carbon black may be in the range of 800 to 1250 m / g. 2 / g, preferably 1000 to 1200m 2 / g, lithium batteries fabricated from the conductive agent may have better rate capability and low temperature discharge performance.

[0045] In one embodiment, the DBP oil absorption of the carbon black may be in the range of 180 to 360 ml / 100 g, preferably 200 to 320 ml / 100 g, more preferably 220 to 300 ml / 100 g, particularly 230 to 280 ml / 100 g, and even more particularly 240 to 260 ml / 100 g. When the DBP oil absorption of the carbon black is in the range of 230 to 280 ml / 100 g, preferably 240 to 260 ml / 100 g, lithium batteries manufactured from the conductive agent may have better rate performance and low-temperature discharge performance.

[0046] In one embodiment, the weight ratio of carbon nanostructures to carbon black is 0.5:9.5 to 9.5:0.5, preferably 1:9 to 9:1, more preferably 2:8 to 8:2, especially 3:7 to 4:6.

[0047] In one embodiment, the conductive agent may further contain a dispersant. The dispersant is not particularly limited and may be at least one of polyvinylpyrrolidone, polyacrylamide, polycarboxylic acid, polyacrylic acid, polycarboxylate, polyacrylate, polyvinyl alcohol, ethoxylated alcohol, montan wax, polyvinyl butyral, nitrile rubber, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, polyvinyl acetate, polystyrene sulfonate, polymethacrylate, polyethyleneimine, polyethyleneamine, polypropyleneamine, poly(2-vinylpyridine), block copolyether, cellulose acetate, copolymer of polystyrene and maleic anhydride, and copolymers and derivatives containing monomers of the above polymers, preferably polyvinylpyrrolidone.

[0048] In one embodiment, the conductive agent (powder) is comprised of a dry mixture of carbon nanostructures, carbon black, and optionally a dispersant.

[0049] In one embodiment, the porosity of the conductive agent may be in the range of about 70% to about 86%, for example, about 75% to about 85%, for example, about 80% to about 84%.

[0050] In one embodiment, the BET specific surface area of ​​the conductive agent is about 50 m 2 / g ~ approx. 120m 2 / g, for example, about 70m 2 / g ~ approx. 115m 2 / g, for example, about 90m 2 / g ~ approx. 110m 2 / g.

[0051] In one embodiment, the true density of the conductive agent is about 1.86 g / cm 3 ~Approx. 2.00g / cm 3 , for example, about 1.87 g / cm 3 ~Approx. 1.95g / cm 3 , for example, about 1.88 g / cm 3 ~Approx. 1.90g / cm 3 may be in the range of

[0052] In one embodiment, the average particle size (D50) of the conductive agent may be in the range of about 2.2 to about 5 μm, for example, about 2.2 to about 4 μm, for example, about 2.21 μm to about 3 μm, for example, about 2.22 μm to about 2.5 μm. D50 is the particle size based on 50% of the particle size distribution.

[0053] The present invention provides an electrode for a lithium battery, preferably a positive electrode, containing a conductive agent.

[0054] In one embodiment, the electrode may be fabricated by mixing an electrode active material, a conductive agent, a binder, and a solvent to form a composition, applying the composition to an electrode current collector, and drying the composition.

[0055] The present invention provides a lithium battery containing the electrode.

[0056] In one embodiment, a lithium battery may be manufactured as follows: A conductive agent, an active material, a binder, a solvent, etc. are mixed to prepare a cathode / anode slurry, which is then applied to a current collector to obtain a cathode / anode sheet. A separator is inserted between the cathode sheet and the anode sheet to prepare an electrode assembly. The electrode assembly is then placed in a case and an electrolyte is injected to manufacture a lithium battery.

[0057] In one embodiment, the conductive agent is used in the positive electrode of a lithium battery.

[0058] The present invention provides a method for producing a conductive agent, which includes mixing and dispersing carbon nanostructures and carbon black in a solvent to obtain a dispersion slurry, and drying the obtained dispersion slurry.

[0059] In one embodiment, dispersion may be carried out at room temperature using a disperser. The dispersion time is not particularly limited and may be 5 minutes to 5 hours, for example, 10 minutes to 3 hours, and particularly 30 minutes to 2 hours. The disperser may be a bead mill or a homogenizer. When dispersion is carried out for the above time using a disperser, a uniformly dispersed slurry can be produced.

[0060] In one embodiment, the drying may be freeze-drying. The freeze-drying may be carried out at a temperature of −40° C. to −70° C. In particular, the solvent may be removed by drying the dispersion slurry at a temperature of −40° C. to −70° C. for 24 to 48 hours using a vacuum freeze dryer to obtain a freeze-dried powder.

[0061] In one embodiment, the solvent is not particularly limited and may be at least one of water, methanol, ethanol, n-propanol, isopropanol, acetone, NMP, butanol, butanediol, pentane, n-hexane, cyclohexane, trichloroethane, carbon tetrachloride, ethyl acetate, methyl ethyl ketone, dimethylformamide, dimethylacetamide, benzene, and xylene, and preferably water.

[0062] In one embodiment, the dispersed slurry may further contain a dispersant. In this case, the dispersed slurry may be obtained by mixing and dispersing the carbon nanostructures, carbon black, and the dispersant in a solvent.

[0063] The dispersant is not particularly limited, and may be at least one of polyvinylpyrrolidone, polyacrylamide, polycarboxylic acid, polyacrylic acid, polycarboxylate, polyacrylate, polyvinyl alcohol, ethoxylated alcohol, montan wax, polyvinyl butyral, nitrile rubber; carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, polyvinyl acetate, polystyrene sulfonate, polymethacrylate, polyethyleneimine, polyethyleneamine, polypropyleneamine, poly(2-vinylpyridine), block copolyether, cellulose acetate, copolymer of polystyrene and maleic anhydride, and copolymers and derivatives containing monomers of the above polymers, and preferably polyvinylpyrrolidone.

[0064] In the conductive agent (powder) of the present invention, both carbon black and carbon nanostructures are dispersed into a slurry and then dried, thereby maintaining the advantage of easy dispersion of the carbon nanostructures while overcoming the drawback caused by the carbon nanostructures alone, namely, a significant decrease in the rate performance and low-temperature discharge performance of the lithium battery compared to the original dispersed slurry. In other words, when a conductive agent containing carbon nanostructure powder is used in a lithium battery, by using the conductive agent of the present invention, the carbon nanostructure powder is easily dispersed without a significant decrease in the rate performance and low-temperature discharge performance of the lithium battery compared to the original dispersed slurry.

[0065] The conductive agent according to the present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples. [Example]

[0066] [Table A] [Table B]

[0067] Example 1: (H4+LITX93R) Lyophilized Powder Carbon nanotubes H4, carbon black LITX93R, dispersant and solvent were mixed in a weight ratio of 4:6.7:1:88.3 and dispersed at room temperature for 1 hour using a homogenizer to prepare a uniformly dispersed slurry.

[0068] Next, the dispersion slurry was frozen at −45° C. for 4 hours using a vacuum freeze dryer, and then vacuum dried for 48 hours, thereby removing the solvent and obtaining a freeze-dried powder.

[0069] Example 2: (H4+CSX1005) Lyophilized Powder A freeze-dried powder was produced in the same manner as in Example 1, except that CSX1005 was used as the carbon black instead of LITX93R.

[0070] Example 3: (H10+LITX93R) Lyophilized Powder A freeze-dried powder was produced in the same manner as in Example 1, except that H10 was used instead of H4 as the carbon nanotubes.

[0071] Example 4: (H10 + CSX1005) Lyophilized Powder A freeze-dried powder was produced in the same manner as in Example 2, except that H10 was used instead of H4 as the carbon nanotubes.

[0072] Example 5: (H4+H10+LITX93R) Lyophilized Powder A freeze-dried powder was produced in the same manner as in Example 1, except that a mixture of H4 and H10 was used as the carbon nanotubes instead of H4, and the weight ratio of H4 to H10 was 0.8:3.2.

[0073] Example 6: (H4 + H10 + CSX1005) Lyophilized Powder A freeze-dried powder was produced in the same manner as in Example 5, except that CSX1005 was used as the carbon black instead of LITX93R.

[0074] Example 7: (H4+CSX1005) Lyophilized Powder A freeze-dried powder was produced in the same manner as in Example 2, except that the ratio of H4 to CSX1005 was changed to 9.5:0.5, i.e., H4, CSX1005, dispersant and solvent were mixed in a weight ratio of 10.165:0.535:1:88.3.

[0075] Example 8: (H4+CSX1005) Lyophilized Powder A freeze-dried powder was produced in the same manner as in Example 2, except that the ratio of H4 to CSX1005 was changed to 0.5:9.5, i.e., H4, CSX1005, dispersant and solvent were mixed in a weight ratio of 0.535:10.165:1:88.3.

[0076] Comparative example 1: H4 freeze-dried powder A freeze-dried powder was produced in the same manner as in Example 1, except that carbon black was not used, that is, H4 was used as the carbon nanotubes, and the dispersant and solvent were mixed in a weight ratio of 4:1:95.

[0077] Comparative example 2: H10 freeze-dried powder A freeze-dried powder was produced in the same manner as in Comparative Example 1, except that H10 was used instead of H4 as the carbon nanotubes.

[0078] Comparative example 3: (H4+H10) freeze-dried powder A freeze-dried powder was produced in the same manner as in Comparative Example 1, except that a mixture of H4 and H10 was used as the carbon nanotubes instead of H4, and the weight ratio of H4 to H10 was 0.8:3.2.

[0079] Comparative example 4: H4 freeze-dried powder + LITX93R First, freeze-dried powder of H4 was produced in the same manner as in Comparative Example 1. Next, the freeze-dried powder of H4 and LITX93R were mixed in a weight ratio of 4:6.7 to obtain a mixture of freeze-dried powder of H4 and LITX93R.

[0080] Comparative example 5: H4 freeze-dried powder + CSX1005 First, freeze-dried powder of H4 was produced in the same manner as in Comparative Example 1. Next, the freeze-dried powder of H4 and CSX1005 were mixed in a weight ratio of 4:6.7 to obtain a mixture of freeze-dried powder of H4 and CSX1005.

[0081] Reference Example 1: (H4 + LITX93R) Dispersed Slurry Carbon nanotubes H4, carbon black LITX93R, dispersant and solvent were mixed in a weight ratio of 4:6.7:1:88.3 and dispersed at room temperature for 1 hour using a homogenizer to prepare a uniformly dispersed slurry.

[0082] Reference Example 2: (H4 + CSX1005) Dispersed Slurry A dispersed slurry was prepared in the same manner as in Reference Example 1, except that CSX1005 was used as the carbon black instead of LITX93R.

[0083] Reference Example 3: (H10 + LITX93R) Dispersed Slurry A dispersion slurry was produced in the same manner as in Reference Example 1, except that H10 was used instead of H4 as the carbon nanotubes.

[0084] Reference Example 4: (H10 + CSX1005) Dispersed Slurry A dispersion slurry was produced in the same manner as in Reference Example 2, except that H10 was used instead of H4 as the carbon nanotubes.

[0085] Reference Example 5: (H4 + H10 + LITX93R) Dispersed Slurry A dispersed slurry powder was produced in the same manner as in Reference Example 1, except that a mixture of H4 and H10 was used as the carbon nanotubes instead of H4, and the weight ratio of H4 to H10 was 0.8:3.2.

[0086] Reference Example 6: (H4 + H10 + CSX1005) Dispersed Slurry A dispersed slurry was prepared in the same manner as in Reference Example 5, except that CSX1005 was used as the carbon black instead of LITX93R.

[0087] Reference Example 7: H4 Dispersed Slurry A dispersion slurry was produced in the same manner as in Reference Example 1, except that no carbon black was used, that is, H4 was used as the carbon nanotubes, the dispersant and the solvent were mixed in a weight ratio of 4:1:95.

[0088] Reference Example 8: H10 Dispersed Slurry A dispersion slurry was produced in the same manner as in Reference Example 7, except that H10 was used instead of H4 as the carbon nanotubes.

[0089] Reference Example 9: (H4+H10) Dispersed Slurry A dispersion slurry was produced in the same manner as in Reference Example 7, except that a mixture of H4 and H10 was used as the carbon nanotubes instead of H4, and the weight ratio of H4 to H10 was 0.8:3.2.

[0090] Reference Example 10: (H4 + CSX1005) Dispersed Slurry A dispersion slurry was produced in the same manner as in Reference Example 2, except that the ratio of H4 to CSX1005 was changed to 9.5:0.5, that is, H4, CSX1005, dispersant and solvent were mixed in a weight ratio of 10.165:0.535:1:88.3.

[0091] Reference Example 11: (H4 + CSX1005) Dispersed Slurry A dispersion slurry was produced in the same manner as in Reference Example 2, except that the ratio of H4 to CSX1005 was changed to 0.5:9.5, that is, H4, CSX1005, dispersant and solvent were mixed in a weight ratio of 0.535:10.165:1:88.3.

[0092] Evaluation example 1: Dispersibility The freeze-dried powders and dispersion slurries produced in the Examples, Comparative Examples, and Reference Examples were analyzed using a scanning electron microscope (SEM). The obtained SEM photographs are shown in FIGS.

[0093] Figure 1 is a scanning electron microscope (SEM) photograph of the freeze-dried powder produced in Example 6, Figure 2 is an SEM photograph of the dispersion slurry produced in Reference Example 6, Figure 3 is an SEM photograph of the freeze-dried powder produced in Comparative Example 3, Figure 4 is an SEM photograph of the dispersion slurry produced in Reference Example 9, Figure 5 is an SEM photograph of the freeze-dried powder produced in Comparative Example 1, and Figure 6 is an SEM photograph of the dispersion slurry produced in Reference Example 7.

[0094] It can be seen from FIGS. 1 to 6 that the carbon nanotubes were easily and well dispersed in both the freeze-dried powder and the dispersed slurry.

[0095] Evaluation example 2: Physical properties The freeze-dried powders and dispersion slurries produced in the Examples, Comparative Examples, and Reference Examples were measured for porosity, BET surface area, true density, and D50. The measurement results are shown in Table 1 below.

[0096] Porosity: The porosity was measured using a mercury porosimeter.

[0097] BET specific surface area: The BET specific surface area was calculated from the amount of nitrogen adsorbed at the temperature of liquid nitrogen using a physical adsorption machine.

[0098] True density: The true density was measured by the gas expansion method using a fully automatic true density analyzer.

[0099] D50: The particle size was measured by measuring the intensity of scattered light by a laser diffraction method using a particle size analyzer. D50 is the particle size based on 50% of the particle size distribution of the dispersion. [Table 1]

[0100] Table 1 shows that the porosity and BET surface area of ​​the freeze-dried powder are reduced compared to the original dispersion slurry.

[0101] Evaluation example 3: Rate performance (5C / 0.5C) A lithium battery was fabricated as follows.

[0102] Preparation of positive electrode: Conductive agent and positive electrode active material (LiNi 0.6 Co 0.2 Mn 0.2 A positive electrode slurry was prepared by mixing the ternary material (O2) and a binder (polyvinylidene fluoride, PVDF) in a weight ratio of 1.2:97.8:1, and then coated onto an aluminum foil positive electrode current collector. The weight of the conductive agent was the dry weight of the conductive agent.

[0103] Preparation of negative electrode: Conductive agent (carbon black), active material (graphite), binder (styrene butadiene rubber, SBR), and thickener (carboxymethyl cellulose, CMC) were mixed in a solvent of NMP in a weight ratio of 1.2:95.8:1.6:1.4 to prepare negative electrode slurry, which was then applied to a copper foil as a negative electrode current collector.

[0104] Manufacture of lithium battery: A separator was inserted between the positive electrode and negative electrode manufactured as above to manufacture an electrode assembly, which was then placed in a case. An electrolyte containing lithium hexafluorophosphate (5101A-type lithium-ion battery electrolyte, Shandong Tianrun New Energy Co., Ltd.) was then poured into the case to manufacture a lithium battery.

[0105] The rate performance of the fabricated lithium batteries was evaluated as follows. At 25°C, the lithium batteries were charged to 4.25 V at a current of 0.5 C, charged at 4.25 V until the cutoff current reached 0.05 C, and then discharged to 3.0 V at currents of 0.5 C and 5 C, respectively. The discharge capacities of the lithium batteries at currents of 0.5 C and 5 C were measured, and the ratio of the 5 C discharge capacity to the 0.5 C discharge capacity (5 C / 0.5 C) was calculated to evaluate the rate performance. The results are shown in Table 2 below. [Table 2-1] [Table 2-2]

[0106] Table 2 shows that the freeze-dried powder of carbon nanotubes alone in the comparative example showed a significantly larger decrease in lithium battery rate performance (-5.54% for H4, -3.5% for H10, and -4.13% for H4 + H10) compared to the original dispersion slurry. In contrast, the freeze-dried powder of carbon nanotubes and carbon black in the examples showed a significantly smaller decrease in lithium battery rate performance (less than 5% for H4, less than 2.5% for H10, and less than 2.5% for H4 + H10) compared to the original dispersion slurry.

[0107] In particular, Examples 2, 7 and 8 show that when the weight ratio of carbon nanostructure to carbon black is in the range of 3:7 to 4:6, the lithium battery may have good rate performance.

[0108] Furthermore, it can be seen from Comparative Examples 4 and 5 that when carbon black was mixed with freeze-dried carbon nanotube powder, the rate performance of the lithium battery was significantly decreased rather than slightly decreased, i.e., mixing carbon black with freeze-dried carbon nanotube powder did not solve the problem of the extremely large decrease in rate performance of the lithium battery.

[0109] Evaluation example 4: Low temperature discharge performance (-25℃ / 25℃) A lithium battery was fabricated as described in Evaluation Example 3.

[0110] The low-temperature discharge performance of the fabricated lithium batteries was evaluated as follows. At 25°C, the lithium batteries were charged to 4.25V at a current of 0.5C, and then charged at 4.25V until the cutoff current reached 0.05C. After leaving the batteries at the test temperature for 2 hours, they were discharged to 3.0V at a current of 0.5C, and the discharge capacity at -25°C was measured. The discharge capacity at 25°C was also measured in the same manner. The low-temperature discharge performance was evaluated by calculating the ratio of the discharge capacity at -25°C to the discharge capacity at 25°C (-25°C / 25°C). The results are shown in Table 3 below. [Table 3-1] [Table 3-2]

[0111] From Table 3, it can be seen that in the case of the freeze-dried powder of carbon nanotubes alone in the comparative example, the decrease in low-temperature discharge performance of the lithium battery was about 2% or more compared to the original dispersion slurry. In contrast, in the case of the powder of the freeze-dried mixture of carbon nanotubes and carbon black in the example, the decrease in low-temperature discharge performance of the lithium battery was about 1.6% or less compared to the original dispersion slurry.

[0112] In particular, in Example 5, when two types of carbon nanotubes and carbon black with a small surface area were contained, the decrease in low-temperature discharge performance of the lithium battery was further reduced to less than 0.5%.

[0113] Furthermore, in Example 8, when the weight ratio of the carbon nanostructure to the carbon black was in the range of 0.5:9.5 to 1:9, the low-temperature discharge performance of the lithium battery was further improved.

[0114] Furthermore, it can be seen from Comparative Examples 4 and 5 that when carbon black was mixed with freeze-dried carbon nanotube powder, the decrease in rate performance of the lithium battery was not small but rather large. In other words, mixing carbon black with freeze-dried carbon nanotube powder did not solve the problem of the extremely large decrease in rate performance of the lithium battery.

[0115] Evaluation Example 5: Electrode sheet resistivity The electrode sheet resistivity was evaluated as follows.

[0116] The conductive agent and active material (LiNi 0.6 Co 0.2 Mn 0.2 The positive electrode slurry was prepared by mixing the conductive agent (a ternary material of O2) and the binder (PVDF) in a weight ratio of 1.2:97.8:1. The conductive agent was then uniformly applied to a PET film using a 200 μm doctor blade and dried to obtain an electrode sheet. The weight of the conductive agent was the dry weight of the conductive agent.

[0117] The electrode sheet resistivity was tested using a four-terminal electrode sheet resistance tester, and the results are shown in Table 4 below. [Table 4-1] [Table 4-2]

[0118] Table 4 shows that the electrode sheet resistivity of the freeze-dried powder and the original dispersion slurry may be higher, lower, or remain the same. However, as described above, the deterioration in both the rate performance and low-temperature discharge performance of the batteries using the conductive agents manufactured in the examples of the present invention was significantly smaller than that of the lithium batteries using the original dispersion slurry. That is, no significant deterioration was observed regardless of the electrode sheet resistivity. Therefore, the electrode sheet resistivity was not related to the rate performance and low-temperature discharge performance of the batteries of the present invention.

[0119] The conductive agent of the present invention uses a powder of a dry mixture of carbon nanostructures and carbon black, preferably a freeze-dried mixture, and therefore, such a powder of the mixture can be easily and well dispersed. At the same time, the rate performance and low-temperature discharge performance of the battery manufactured using the mixture as the conductive agent are not significantly reduced.

[0120] It is understood that the embodiments described herein are intended to be illustrative and not restrictive. The description of a feature or aspect in each embodiment should generally be considered applicable to other similar features or aspects in other embodiments. Those skilled in the art will appreciate that various changes in form and detail can be made without departing from the spirit and scope defined in the appended claims.

Claims

1. A conductive agent comprising a dry mixture, preferably a freeze-dried mixture, of carbon nanostructures and carbon black.

2. The carbon nanostructure is at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and carbon nanobundles, preferably carbon nanotubes, and more preferably at least one of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes, and in particular, in X-ray diffraction analysis, the carbon nanotubes have a peak at a diffraction angle 2θ=25°±2°, and the full width at half maximum of the peak is 1° to 6°; and / or, in particular, the average outer diameter of the carbon nanotubes is in the range of 1 to 40 nm, preferably 2 to 35 nm, more preferably 5 to 30 nm, particularly 10 to 20 nm, and further particularly 10 to 15 nm; and / or, in particular, the BET surface area of ​​the carbon black is in the range of 100 to 1200 m ２ / g, preferably 120 to 1000m ２ / g, more preferably 150 to 800 m ２ / g, especially 180 to 500m ２ / g, more particularly 200 to 300 m ２ The conductive agent according to claim 1, wherein the range is 1 / g.

3. The carbon nanostructure includes a first carbon nanotube and a second carbon nanotube, and the BET surface of the first carbon nanotube is 100 to 240 m. ２ / g, preferably 150 to 230 m ２ / g, more preferably 200 to 220 m ２ / g, and the BET surface area of ​​the second carbon nanotubes is in the range of 250 to 1200 m ２ / g, preferably 260 to 500m ２ / g, more preferably 270 to 300 m ２ / g, more particularly a weight ratio of the first carbon nanotubes to the second carbon nanotubes is 1:9 to 9:1, preferably 2:8 to 8:2, more preferably 5:5 to 8:2, particularly 7:3 to 8:

2.

4. The carbon black is at least one selected from the group consisting of furnace black, channel black, and thermal black, and is preferably furnace black. In particular, the BET surface area of ​​the carbon black is 70 to 1500 m ２ / g, preferably 200 to 1400 m ２ / g, more preferably 500 to 1300 m ２ / g, especially 800 to 1250 m ２ / g, more particularly 1000 to 1200 m ２ / g, and in particular, the DBP oil absorption of the carbon black is in the range of 180 to 360 ml / 100 g, preferably 200 to 320 ml / 100 g, more preferably 220 to 300 ml / 100 g, particularly 230 to 280 ml / 100 g, and further particularly 240 to 260 ml / 100 g.

5. The conductive agent according to claim 1, wherein the weight ratio of the carbon nanostructure to the carbon black is 0.5:9.5 to 9.5:0.5, preferably 1:9 to 9:1, more preferably 2:8 to 8:2, particularly 3:7 to 4:

6.

6. An electrode for a lithium battery, preferably a positive electrode for a lithium battery, comprising the conductive agent according to any one of claims 1 to 5.

7. A method for producing the conductive agent according to any one of claims 1 to 5, comprising: mixing and dispersing the carbon nanostructures and the carbon black in a solvent to obtain a dispersion slurry; and drying, preferably freeze-drying, the obtained dispersion slurry.

8. 8. The method according to claim 7, wherein the dispersed slurry further contains a dispersant, and the dispersant is preferably at least one of polyvinylpyrrolidone, polyacrylamide, polycarboxylic acid, polyacrylic acid, polycarboxylate, polyacrylate, polyvinyl alcohol, ethoxylated alcohol, montan wax, polyvinyl butyral, nitrile rubber, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, polyvinyl acetate, polystyrene sulfonate, polymethacrylate, polyethyleneimine, polyethyleneamine, polypropyleneamine, poly(2-vinylpyridine), block copolyether, cellulose acetate, copolymer of polystyrene and maleic anhydride, and copolymers and derivatives containing monomers of the above polymers, and is preferably polyvinylpyrrolidone.

9. The method according to claim 7, wherein the freeze-drying is carried out at a temperature of -40°C to -70°C.

10. 8. The method according to claim 7, wherein the solvent is at least one of water, methanol, ethanol, n-propanol, isopropanol, acetone, NMP, butanol, butanediol, pentane, n-hexane, cyclohexane, trichloroethane, carbon tetrachloride, ethyl acetate, methyl ethyl ketone, dimethylformamide, dimethylacetamide, benzene, and xylene, and is preferably water.

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