Conductive agent, an electrode for a lithium battery and a method for producing the conductive agent

Abstract

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 dried, preferably freeze-dried, mixture of a carbon nanostructure and a carbon black.

Description

Technical area

[0001] The present invention relates to a conductive agent, an electrode for a lithium battery and a method for producing the conductive agent, in particular to a conductive agent comprising a dried, preferably freeze-dried, mixture of a carbon nanostructure and a carbon black, an electrode for a lithium battery comprising the conductive agent, and a method for producing the conductive agent. background

[0002] Carbon nanotubes exhibit excellent conductivity and a high aspect ratio. By adding carbon nanotubes to an electrode material, such as the positive electrode material of a lithium-ion battery, a conductive network can be effectively formed, electrode conductivity can be improved, and the lithium-ion battery can be provided with excellent performance, making it suitable for high-end digital batteries and batteries for new energy vehicles.

[0003] However, dispersing carbon nanotubes is extremely difficult. In the current technology, the manufactured carbon nanotubes are dispersed in a solvent to form a slurry for sale. Thus, the carbon nanotube content in the conductive carbon nanotube slurry is only 3% to 8%, and the solvent content exceeds 90%, which limits the scope and application of carbon nanotubes. The large amount of solvent has also led to transportation difficulties and higher usage costs for customers.

[0004] Chinese Patent Application CN110894068A discloses a method for producing easily dispersible carbon nanotube powder, comprising the following steps: (1) preparing a dispersion slurry containing carbon nanotubes by bead milling; and (2) drying the dispersion slurry prepared in step (1) to obtain the solid powder. The application discloses that the specific resistance of the electrode foil of the carbon nanotube powder of this invention is superior to or equivalent to 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 the problem that when used as a conductive agent in a lithium battery, the battery performance, especially the low-temperature discharge capacity, is significantly reduced compared to the original carbon nanotube dispersion slurry. Therefore, while the freeze-dried carbon nanotube solves the problem of easy transportation, the properties of the resulting lithium battery are degraded, which significantly hinders the practical application of the freeze-dried carbon nanotube in lithium batteries. Summary of the invention

[0006] Therefore, there is a need for carbon nanotube powder to be easily dispersible when used in a lithium battery, but the performance and low-temperature discharge performance of the battery are not significantly reduced compared to the original dispersion slurry.

[0007] In view of the disadvantages of the prior art, the object of the present invention is to provide a conductive agent comprising carbon nanotube powder that improves the dispersibility of the carbon nanotube powder and, at the same time, when the conductive agent comprising the carbon nanotube powder is used in a lithium battery, does not significantly reduce the performance and low-temperature discharge performance of the battery compared to the original dispersion slurry.

[0008] In one aspect, the present invention provides a conductive agent comprising a dried, preferably freeze-dried, mixture of a carbon nanostructure and a carbon black.

[0009] 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 selected from single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes.

[0010] In X-ray diffraction analysis, the carbon nanotube exhibits a peak at a diffraction angle of 20 = 25° ± 2°, and the half-width of the peak is 1° to 6°.

[0011] The carbon nanotube has an average outer diameter in the range of 1 to 40 nm, preferably 2 to 35 nm, more preferably 5 to 30 nm, especially 10 to 20 nm and even more especially 10 to 15 nm.

[0012] The carbon nanotube has a BET surface area in the range of 100 to 1200 m 2 / g, preferably 120 to 1000 m 2 / g, more preferably 150 to 800 m 2 / g, especially 180 to 500 m 2 / g and especially 200 to 300 m 2 / G.

[0013] The carbon nanostructure comprises a first carbon nanotube and a second carbon nanotube, wherein in particular the first carbon nanotube has a BET surface area in the range of 100 to 240 m 2 / g, preferably 150 to 230 m 2 / g, and more preferably 200 to 220 m 2 / g, and the second carbon nanotube has a BET surface area in a range of 250 to 1200 m 2 / g, preferably 260 to 500 m 2 / g, and more preferably 270 to 300 m 2 / g, wherein in particular the weight ratio of the first carbon nanotube to the second carbon nanotube is 1:9 to 9:1, preferably 2:8 to 8:2, more preferably 5:5 to 8:2 and in particular 7:3 to 8:2.

[0014] The soot is at least one from the group consisting of furnace black, channel black and thermal black, preferably furnace black.

[0015] The soot has a BET surface area in the range of 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 and especially 1000 to 1200 m 2 / G.

[0016] The carbon black has a DBP oil absorption value 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, especially 230 to 280 ml / 100 g and even more especially 240 to 260 ml / 100 g.

[0017] 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 especially 3:7 to 4:6.

[0018] According to a further aspect, the present invention provides an electrode, preferably a positive electrode, for a lithium battery comprising the conductive agent.

[0019] According to another aspect, the present invention provides a method for producing the conductive agent, comprising: mixing and dispersing a carbon nanostructure and a carbon black in a solvent to obtain a dispersion slurry; and drying, preferably freeze-drying, the obtained dispersion slurry.

[0020] The dispersion slurry further comprises a dispersant, wherein the dispersant is preferably at least one of the following: polyvinylpyrrolidone, polyacrylamide, polycarboxylic acid, polyacrylic acid, polycarboxylate, polyacrylate, polyvinyl alcohol, ethoxylated alcohol, montanin wax, polyvinyl butyral, nitrile rubber; carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol, polyvinyl acetate, polystyrenesulfonate, polymethacrylate, polyethyleneimine, polyethyleneamine, polypropylenamine, poly(2-vinylpyridine), block copolyether, cellulose acetate, a copolymer of polystyrene and maleic anhydride, and copolymers and derivatives containing monomers of the above-mentioned polymers, preferably polyvinylpyrrolidone.

[0021] Freeze-drying is carried out at a temperature range of -40°C to -70°C.

[0022] 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, preferably water.

[0023] By using the conductive agent of the present invention, it is possible to easily disperse the carbon nanotube powder. When the conductive agent is used in a lithium battery, the battery's performance and discharge performance at low temperatures are not significantly reduced compared to the original dispersion slurry. Short description of the figures Fig. is a scanning electron microscope (SEM) image of a freeze-dried mixture of carbon nanotubes and carbon black prepared in Example 6. Fig.is an SEM image of a carbon nanotube and carbon black dispersion slurry prepared in Reference Example 6. Fig. is an SEM image of freeze-dried carbon nanotubes prepared in Comparative Example 3. Fig. is an SEM image of a carbon nanotube dispersion slurry prepared in Reference Example 9. Fig. is an SEM image of freeze-dried carbon nanotubes prepared in Comparative Example 1. Fig. is an SEM image of a carbon nanotube dispersion slurry prepared in Reference Example 7. Detailed embodiments

[0024] As mentioned above, it is extremely difficult to disperse carbon nanotubes in the prior art, so the carbon nanotubes are generally dispersed in a solvent to produce a slurry for sale, which is then used by battery manufacturers to manufacture lithium batteries. However, the conductive carbon nanotube slurry produced in this way has a low carbon nanotube content and contains a large amount of solvent, resulting in transportation difficulties and increased usage costs for the customer.

[0025] To solve this problem, a method for producing easily dispersible carbon nanotube powder has been proposed, which involves preparing a dispersion slurry containing carbon nanotubes and drying the dispersion slurry to obtain the solid powder. However, such a method may compromise the performance of the carbon nanotubes because they are subjected to drying, especially freeze-drying.

[0026] The inventors have found that the carbon nanotube powder obtained by such a production method has the problem that when used as a conductive agent in a lithium battery, the battery performance, especially the power and discharge performance at low temperatures, 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 carbon species.

[0027] Through extensive research, the inventors surprisingly found that when a certain type of carbon (soot) is added to a carbon nanotube dispersion slurry and then dried, a dried mixture of carbon nanotubes and soot is obtained that is easily well dispersed, and at the same time, the performance rates and low-temperature discharge performance of the lithium battery prepared using the mixture as a conductive agent are not significantly reduced.

[0028] Therefore, in one embodiment, the present invention provides a conductive agent (powder) comprising a dried mixture of carbon nanostructures and carbon black.

[0029] In one embodiment, the conductive agent can be prepared by mixing the carbon nanostructures and the carbon black with a solvent to prepare a dispersion slurry and then drying the dispersion slurry.

[0030] Preferably, the mixture of the carbon nanostructure and the carbon black is freeze-dried (lyophilized). The mixture of the carbon nanostructures and the carbon black prepared by freeze-drying is easier to disperse and, when used to manufacture a lithium battery, retains properties such as power and low-temperature discharge performance comparable to those of the original dispersion slurry.

[0031] In one embodiment, the carbon nanostructure may have an aspect ratio of at least 20:1, preferably at least 100:1, and more preferably at least 500:1.

[0032] In one embodiment, the carbon nanostructure is not particularly limited and can be selected from at least one of the group consisting of carbon nanotubes, carbon nanofibers, and carbon nanobundles (CNS). The carbon nanobundle (CNS) exhibits lateral interconnection properties.

[0033] In one embodiment, the carbon nanostructure may be a carbon nanotube, preferably at least one of single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes, especially multi-walled carbon nanotubes. For example, the carbon nanotube structure may be one or more carbon nanotubes, such as multi-walled carbon nanotubes. The carbon nanotube may be fabricated by a method known in the art, such as a chemical vapor deposition (CVD) method, an arc discharge method, or a laser deposition method. In particular, the carbon nanotube may be fabricated by a CVD method, such as the powder catalyst CVD method or the floating catalyst CVD method, and preferably by the powder catalyst CVD method.

[0034] In one embodiment, the carbon nanotube exhibits a peak at a diffraction angle of 2θ = 25° ± 2° in an X-ray diffraction analysis, and the half-width of the peak is 1° to 6°, for example, 2° to 5°, 2° to 4°, or 2° to 3°. The X-ray diffraction analysis can be performed using Cu-Kα rays.

[0035] In one embodiment, the carbon nanotube may have an average outer diameter in the range of 1 to 40 nm, preferably 2 to 35 nm, more preferably 5 to 30 nm, in particular 10 to 20 nm and even more particularly 10 to 15 nm.

[0036] In one embodiment, the carbon nanotube may have a BET surface area in a range of 100 to 1200 m 2 / g, preferably 120 to 1000 m 2 / g, more preferably 150 to 800 m 2 / g, especially 180 to 500 m 2 / g and especially 200 to 300 m 2 / g.

[0037] In one embodiment, the powder resistance of the carbon nanotube under a pressure of 5 to 120 MPa may be not more than 0.2 Ω·cm, preferably not more than 0.1 Ω·cm, more preferably not more than 0.08 Ω·cm, in particular not more than 0.06 Ω·cm, and even more particularly not more than 0.05 Ω·cm.

[0038] In one embodiment, the carbon nanostructure may comprise a first carbon nanotube and a second carbon nanotube. In particular, the first carbon nanotube may have a BET surface area in a range of 100 to 240 m 2 / g, preferably 150 to 230 m 2 / g and more preferably 200 to 220 m 2 / g, and the second carbon nanotube may have a BET surface area in a range of 250 to 1200 m 2 / g, preferably 260 to 500 m 2 / g and more preferably 270 to 300 m 2 / g. The weight ratio of the first carbon nanotube to the second carbon nanotube can be 1:9 to 9:1, preferably 2:8 to 8:2, more preferably 5:5 to 8:2, and especially 7:3 to 8:2.

[0039] 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, preferably furnace black.

[0040] Soot is amorphous carbon, which is a light, fluffy, and extremely fine black powder. Soot is generally a product obtained by incomplete combustion or thermal decomposition of a carbon-containing substance (such as coal, natural gas, heavy oil, fuel oil, etc.) under inadequate air conditions.

[0041] The soot may contain hard soot and soft soot, with the hard soot having a particle size of less than 40 nm and the soft soot having a particle size of 40 nm or more.

[0042] In one embodiment, the carbon black may have a BET surface area in a range of 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 and especially 1000 to 1200 m 2 / g. Within the range, if the carbon black has a BET surface area in the range of 800 to 1250 m 2 / g, preferably 1000 to 1200 m 2 / g, the lithium battery made from the conductive agent can have better performance and better discharge performance at low temperatures.

[0043] In one embodiment, the carbon black may have a DBP oil absorption value in a range of 180 to 360 ml / 100 g, preferably 200 to 320 ml / 100 g, more preferably 220 to 300 ml / 100 g, especially 230 to 280 ml / 100 g, and especially 240 to 260 ml / 100 g. Within this range, the lithium battery made from the conductive agent can have a better performance rate and discharge performance at low temperatures when the carbon black has a DBP oil absorption value in the range of 230 to 280 ml / 100 g, preferably 240 to 260 ml / 100 g.

[0044] In one embodiment, 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 especially 3:7 to 4:6.

[0045] In one embodiment, the conductive agent may further comprise a dispersant. The dispersant is not particularly limited and may include at least one of polyvinylpyrrolidone, polyacrylamide, polycarboxylic acid, polyacrylic acid, polycarboxylate, polyacrylate, polyvinyl alcohol, ethoxylated alcohol, montanin wax, polyvinyl butyral, nitrile rubber, carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol, polyvinyl acetate, polystyrenesulfonate, polymethacrylate, polyethyleneimine, polyethyleneamine, polypropylenamine, poly(2-vinylpyridine), block copolyether, cellulose acetate, a copolymer of polystyrene and maleic anhydride, and copolymers and derivatives containing monomers of the above-mentioned polymers, preferably polyvinylpyrrolidone.

[0046] In one embodiment, the conductive agent (powder) consists of a dried mixture of carbon nanostructure, carbon black and optionally the dispersant.

[0047] In one embodiment, the conductive means may have a porosity in a range of about 70% to about 86%, for example, about 75% to about 85%, for example, about 80% to about 84%.

[0048] In one embodiment, the conductive agent may have a BET specific surface area in a range of about 50 m 2 / g up to about 120 m 2 / g, for example about 70 m 2 / g up to about 115 m 2 / g, for example about 90 m 2 / g up to about 110 m 2 / g.

[0049] In one embodiment, the conductive agent may have a true density in a range of about 1.86 g / cm 3 up to about 2.00 g / cm 3 , for example about 1.87 g / cm 3 up to about 1.95 g / cm 3 , for example about 1.88 g / cm 3 up to about 1.90 g / cm 3 , have.

[0050] In one embodiment, the conductive agent may have an average particle size (D50) in a range of about 2.2 to about 5 µm, for example, about 2.2 to about 4 µm, for example, about 2.21 to about 3 µm, for example, about 2.22 to about 2.5 µm. D50 is a particle size based on 50% of the particle size distribution.

[0051] The present invention relates to an electrode for a lithium battery comprising the conductive agent. The electrode is preferably a positive electrode.

[0052] In one embodiment, the electrode may be prepared by mixing an electrode active material, the conductive agent, a binder, and a solvent to prepare a composition, which is then applied to an electrode collector and dried.

[0053] The present invention relates to a lithium battery comprising the electrode.

[0054] In one embodiment, the lithium battery can be manufactured as follows. The conductive agent, an active material, a binder, a solvent, and the like are mixed to prepare a positive / negative electrode slurry, and the slurry is applied to a current collector to obtain a positive / negative electrode foil. A separator is inserted between the positive and negative electrode foils to prepare an electrode assembly, the electrode assembly is inserted into a casing, and an electrolyte is injected into the casing to prepare the lithium battery.

[0055] In one embodiment, the conductive agent is used in the positive electrode of a lithium battery.

[0056] The present invention relates to a method for producing a conductive agent, comprising: mixing and dispersing the carbon nanostructure and the carbon black in a solvent to obtain a dispersion slurry; and drying the resulting dispersion slurry.

[0057] In one embodiment, dispersion can be carried out by a dispersing device at room temperature. The dispersion time is not particularly limited and can be from 5 minutes to 5 hours, for example, from 10 minutes to 3 hours, and especially from 30 minutes to 2 hours. The dispersing device can be a bead mill or a homogenizer. By dispersing with the dispersing device for the above-mentioned time, a uniform dispersion slurry can be prepared.

[0058] In one embodiment, drying can be performed by freeze-drying. Freeze-drying can be carried out at a temperature in the range of -40°C to -70°C. Specifically, the dispersion slurry can be dried by a vacuum freeze-dryer at a temperature in the range of -40°C to -70°C for 24 to 48 hours, thereby removing the solvent and obtaining the freeze-dried powder.

[0059] 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, preferably water.

[0060] In one embodiment, the dispersion slurry may further comprise a dispersant. In this case, the carbon nanostructure, the carbon black, and the dispersant may be mixed and dispersed in the solvent to obtain the dispersion slurry.

[0061] The dispersant is not particularly limited and may be at least one of the following: polyvinylpyrrolidone, polyacrylamide, polycarboxylic acid, polyacrylic acid, polycarboxylate, polyacrylate, polyvinyl alcohol, ethoxylated alcohol, montanin wax, polyvinyl butyral, nitrile rubber; carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol, polyvinyl acetate, polystyrenesulfonate, polymethacrylate, polyethyleneimine, polyethyleneamine, polypropylenamine, poly(2-vinylpyridine), block copolyether, cellulose acetate, a copolymer of polystyrene and maleic anhydride, and copolymers and derivatives containing monomers of the above-mentioned polymers, preferably polyvinylpyrrolidone.

[0062] In the conductive agent (powder) of the present invention, the carbon black and the carbon nanostructure are processed together into a dispersion slurry and then dried, whereby the advantage of easy dispersibility of the carbon nanostructure is retained while the following disadvantages caused by the carbon nanostructure alone can be overcome: The performance and low-temperature discharge performance of the battery are significantly reduced compared with the original dispersion slurry.That is, by using the conductive agent of the present invention, the carbon nanostructure powders are easily dispersed, and the performance rate and low-temperature discharge performance of the battery are not significantly reduced when the conductive agent containing the carbon nanostructure powder is used in the lithium battery, compared with the original dispersion slurry.

[0063] The conductive agent according to the present invention will be described in detail below using examples. However, the present invention is not limited to the following examples. Examples

[0064] Materials used in the examples: Carbon nanotube: H4 (ENERMAX61, Cabot) H10 (ENERMAX31, Cabot) type Multi-walled carbon nanotube Multi-walled carbon nanotube Half-width of the peak at a diffraction angle of 2θ = 25° ± 2° in XRD 2,697 2,736 Powder resistance 0.005-0.03 Ω·cm 0.007-0.046 Ω·cm mean outer diameter 10-11 nm 10-13 nm BET specific surface area 276,15 m 2 / g 216,30 m 2 / g Soot: CSX1005 (Cabot) LITX93R (Cabot) type black furnace soot black furnace soot BET specific surface area 1100 m 2 / g 70 m 2 / g DBP oil absorption value 252 ml / 100 g 210 ml / 100 g Dispersant: Polyvinylpyrrolidone (PVP) Solvent: N-methylpyrrolidone (NMP) Example 1: (H4 + LITX93R) freeze-dried powder

[0065] H4 as carbon nanotube, LITX93R as carbon black, the dispersant, and the solvent were mixed in a weight ratio of 4:6.7:1:88.3 and dispersed with a homogenizer at room temperature for 1 hour to prepare a uniform dispersion slurry.

[0066] The dispersion slurry was then frozen in a vacuum freeze dryer at -45 °C for 4 hours and vacuum dried for 48 hours to remove the solvent and obtain the freeze-dried powder. Example 2: (H4 + CSX1005) freeze-dried powder

[0067] The freeze-dried powder was prepared in the same manner as in Example 1, except that CSX1005 was used as carbon black instead of LITX93R. Example 3: (H10 + LITX93R) freeze-dried powder

[0068] The freeze-dried powder was prepared in the same manner as in Example 1, except that H10 was used as the carbon nanotube instead of H4. Example 4: (H10 + CSX1005) freeze-dried powder

[0069] The freeze-dried powder was prepared in the same manner as in Example 2, except that H10 was used as the carbon nanotube instead of H4. Example 5: (H4 + H10 + LITX93R) freeze-dried powder

[0070] The freeze-dried powder was prepared in the same manner as in Example 1, except that a mixture of H4 and H10 was used instead of H4 as the carbon nanotube and the weight ratio of H4 to H10 was 0.8:3.2. Example 6: (H4 + H10 + CSX1005) freeze-dried powder

[0071] The freeze-dried powder was prepared in the same manner as in Example 5, except that CSX1005 was used as carbon black instead of LITX93R. Example 7: (H4 + CSX1005) freeze-dried powder

[0072] The freeze-dried powder was prepared in the same manner as in Example 2, except that the ratio of H4 to CSX1005 was changed to 9.5:0.5, that is, H4, CSX1005, the dispersant, and the solvent were mixed in a weight ratio of 10.165:0.535:1:88.3. Example 8: (H4 + CSX1005) freeze-dried powder

[0073] The freeze-dried powder was prepared in the same manner as in Example 2, except that the ratio of H4 to CSX1005 was changed to 0.5:9.5, that is, H4, CSX1005, the dispersant and the solvent were mixed in a weight ratio of 0.535:10.165:1:88.3. Comparative example 1: H4 freeze-dried powder

[0074] The freeze-dried powder was prepared in the same manner as in Example 1, except that no carbon black was used, i.e., H4 as the carbon nanotube, the dispersant and the solvent were mixed in a weight ratio of 4:1:95. Comparative example 2: H10 freeze-dried powder

[0075] The freeze-dried powder was prepared in the same manner as in Comparative Example 1, except that H10 was used as the carbon nanotube instead of H4. Comparative example 3: (H4 + H10) freeze-dried powder

[0076] The freeze-dried powder was prepared in the same manner as in Comparative Example 1, except that a mixture of H4 and H10 was used instead of H4 as the carbon nanotube and the weight ratio of H4 to H10 was 0.8:3.2. Comparative Example 4: H4 freeze-dried powder + LITX93R

[0077] First, the freeze-dried H4 powder was prepared in the same manner as in Comparative Example 1. Then, the freeze-dried H4 powder and LITX93R were mixed in a weight ratio of 4:6.7 to obtain the mixture of the freeze-dried H4 powder and LITX93R. Comparative Example 5: H4 freeze-dried powder + CSX1005

[0078] First, the freeze-dried H4 powder was prepared in the same manner as in Comparative Example 1. Then, the freeze-dried H4 powder and CSX1005 were mixed in a weight ratio of 4:6.7 to obtain the mixture of freeze-dried H4 powder + CSX1005. Reference Example 1: (H4 + LITX93R) Dispersion Slurry

[0079] H4 as carbon nanotube, LITX93R as carbon black, the dispersant and the solvent were mixed in a weight ratio of 4:6.7:1:88.3 and dispersed with the homogenizer at room temperature for 1 hour to prepare a uniform dispersion slurry. Reference Example 2: (H4 + CSX1005) Dispersion Slurry

[0080] The dispersion slurry was prepared in the same manner as in Reference Example 1 except that CSX1005 was used as carbon black instead of LITX93R. Reference Example 3: (H10 + LITX93R) Dispersion Slurry

[0081] The dispersion slurry was prepared in the same manner as in Reference Example 1, except that H10 was used instead of H4 as the carbon nanotube. Reference Example 4: (H10 + CSX1005) Dispersion Slurry

[0082] The dispersion slurry was prepared in the same manner as in Reference Example 2, except that H10 was used as the carbon nanotube instead of H4. Reference Example 5: (H4 + H10 + LITX93R) Dispersion Slurry

[0083] The dispersion slurry powder was prepared in the same manner as in Reference Example 1, except that a mixture of H4 and H10 was used instead of H4 as the carbon nanotube and the weight ratio of H4 to H10 was 0.8:3.2. Reference Example 6: (H4 + H10 + CSX1005) Dispersion Slurry

[0084] The dispersion slurry was prepared in the same manner as in Reference Example 5 except that CSX1005 was used as carbon black instead of LITX93R. Reference Example 7: H4 Dispersion Slurry

[0085] The dispersion slurry was prepared in the same manner as in Reference Example 1, except that no carbon black was used, that is, H4 as the carbon nanotube, the dispersant and the solvent were mixed in a weight ratio of 4:1:95. Reference Example 8: H10 Dispersion Slurry

[0086] The dispersion slurry was prepared in the same manner as in Reference Example 7, except that H10 was used as the carbon nanotube instead of H4. Reference Example 9: (H4 + H10) Dispersion Slurry

[0087] The dispersion slurry was prepared in the same manner as in Reference Example 7, except that a mixture of H4 and H10 was used instead of H4 as the carbon nanotube and the weight ratio of H4 to H10 was 0.8:3.2. Reference Example 10: (H4 + CSX1005) Dispersion slurry

[0088] The dispersion slurry was prepared 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, the dispersant, and the solvent were mixed in a weight ratio of 10.165:0.535:1:88.3. Reference Example 11: (H4 + CSX1005) Dispersion slurry

[0089] The dispersion slurry was prepared 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, the dispersant, and the solvent were mixed in a weight ratio of 0.535:10.165:1:88.3. Evaluation example 1: Dispersibility

[0090] The freeze-dried powders and dispersed slurries prepared in the Examples, Comparative Examples, and Reference Examples were analyzed using a scanning electron microscope (SEM). The SEM images obtained are shown in the Fig. shown.

[0091] Fig. is a scanning electron microscope (SEM) image of the freeze-dried powder prepared in Example 6, Fig. is an SEM image of the dispersion slurry prepared in Reference Example 6, Fig. is an SEM image of the freeze-dried powder prepared in Comparative Example 3, Fig. is an SEM image of the dispersion slurry prepared in Reference Example 9, Fig. is an SEM image of the freeze-dried powder prepared in Comparative Example 1 and Fig. is an SEM image of the dispersion slurry prepared in Reference Example 7.

[0092] From the Fig.It can be seen that the carbon nanotubes were slightly well dispersed in both the freeze-dried powder and the dispersion slurry. Evaluation example 2: physical properties

[0093] The freeze-dried powders and dispersed slurries prepared 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.

[0094] Porosity: A mercury porosimeter was used to measure porosity.

[0095] BET specific surface area: The BET specific surface area was calculated from the nitrogen adsorption amount at the temperature of liquid nitrogen using a physical adsorption device.

[0096] True density: A fully automated true density analyzer was used to measure the true density using the gas expansion method.

[0097] D50: The particle size was measured by measuring the scattered light intensity with a particle size analyzer using the laser diffraction method. D50 is a particle size based on 50% of the particle size distribution of the dispersion. Table 1 Example 6 (H4+H10+CSX1005 freeze-dried powder) Reference Example 6 (H4+H10+CSX1005 slurry) Comparative Example 3 (H4+H10 freeze-dried powder) Reference Example 9 (H4+H10 dispersion slurry) Comparative Example 1 (H4 freeze-dried powder) Reference Example 7 (H4 Dispersion Slurry) porosity 83,7% 87,98% 87,37% 90,59% 92,88% 87,50% BET specific surface area (m 2 / G) 109,6 129,41 140,24 235,57 137,86 276,15 True density (g / cm 3 ) 1,89 1,8576 2,1411 2,3257 1,9368 2,3904 D50 (µm) 2,243 0,157 1,850 3,582 2,195 0,818

[0098] From Table 1, it can be seen that the porosity and BET surface area of ​​the freeze-dried powders are reduced compared to the original dispersion slurries. Evaluation example 3: Performance rate (5C / 0.5C)

[0099] A lithium battery was manufactured as follows.

[0100] Preparation of the positive electrode: The conductive agent prepared in the examples, comparative examples or reference examples, a positive electrode active material (ternary material of LiNi 0,6 Co 0,2 Mn 0,2 O2) and a binder (polyvinylidene fluoride, PVDF) were mixed in a weight ratio of 1.2:97.8:1 in an N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, which was then coated onto an aluminum foil as a positive electron collector. The weight of the conductive agent was the dry weight of the conductive agent.

[0101] Preparation of the negative electrode: A conductive agent (carbon black), an active material (graphite), a binder (styrene-butadiene rubber, SBR), and a thickener (carboxymethyl cellulose, CMC) were mixed in a weight ratio of 1.2:95.8:1.6:1.4 in a solvent of NMP to prepare a negative electrode slurry, which was then coated on a copper foil as a negative electrode collector.

[0102] Lithium battery manufacturing: A separator was inserted between the positive and negative electrodes prepared above to form an electrode assembly. The electrode assembly was inserted into a casing, and an electrolyte containing lithium hexafluorophosphate (Lithium-ion Battery Electrolyte Type 5101A, Shandong Tianrun New Energy Co., Ltd.) was injected into the casing to form the lithium battery.

[0103] The performance of the manufactured lithium batteries was evaluated as follows. At 25°C, the lithium batteries were charged to 4.25V at a current of 0.5C, then charged at a voltage of 4.25V until the cutoff current reached 0.05C, and then discharged to 3.0V at a current of 0.5C and 5C, respectively. The discharge capacities of the lithium batteries at currents of 0.5C and 5C were measured, and the ratio of the discharge capacity at 5C to the discharge capacity at 0.5C (5C / 0.5C) was calculated to evaluate the performance. The results are shown in Table 2 below. Table 2 Conductive agent in the positive electrode of a lithium battery Power rate 5C / 0.5C (25 (°)C ) Difference between freeze-dried powder and dispersion slurry Reference Example 7 (H4 Dispersion Slurry) 65,72% -5,54% Comparative Example 1 (H4 freeze-dried powder) 60,18% Reference Example 1 (H4 + LITX93R dispersion slurry) 71,92% -2,94% Example 1 (H4 + LITX93R freeze-dried powder) 68,98% Reference Example 2 (H4 + CSX1005 dispersion slurry) 79,27% -1,46% Example 2 (H4 + CSX1005 freeze-dried powder) 77,81% Reference Example 10 (H4 + CSX1005 dispersion slurry) 65,87% -4,79% Example 7 (H4 + CSX1005 freeze-dried powder) 61,08% Reference Example 11 (H4 + CSX1005 dispersion slurry) 73,53% -2,70% Example 8 (H4 + CSX1005 freeze-dried powder) 70,83% Reference Example 8 (H10 Dispersion Slurry) 63,61% -3,5% Comparative Example 2 (H10 freeze-dried powder) 60,11% Reference Example 3 (H10 + LITX93R dispersion slurry) 69,79% -2,42% Example 3 (H10 + LITX93R freeze-dried powder) 67,37% Reference Example 4 (H10 + CSX1005 dispersion slurry) 77,78% -1,23% Example 4 (H10 + CSX1005 freeze-dried powder) 76,55% Reference Example 9 (H4 + H10 dispersion slurry) 64,74% -4,13% Comparative Example 3 (H4 + H10 freeze-dried powder) 60,61% Reference Example 5 (H4 + H10 + LITX93R dispersion slurry) 70,27% -2,19% Example 5 (H4 + H10 + LITX93R freeze-dried powder) 68,08% Reference Example 6 (H4 + H10 + CSX1005 dispersion slurry) 79,21% -1,56% Example 6 (H4 + H10 + CSX1005 freeze-dried powder) 77,65% Reference Example 1 (H4 + LITX93R dispersion slurry) 71,92% -11,36% Comparative Example 4 (H4 freeze-dried powder + LITX93R) 60,56% Reference Example 2 (H4 + CSX1005 dispersion slurry) 79,27% -18,94% Comparative Example 5 (H4 freeze-dried powder + CSX1005) 60,33%

[0104] From Table 2, it can be seen that in the case of the freeze-dried carbon nanotube powder alone in the comparative examples, the decrease in the performance rate of the lithium batteries was very significant compared to the original dispersion slurries (-5.54% in the case of H4, -3.5% in the case of H10, and -4.13% in the case of H4+H10). In contrast, in the case of the freeze-dried mixed powder of carbon nanotubes and carbon black in the examples, the decrease in the performance rate of the lithium batteries was significantly smaller (less than 5% in the case of H4, less than 2.5% in the case of H10, and less than 2.5% in the case of H4+H10) compared to the original dispersed slurries.

[0105] In particular, from Examples 2, 7 and 8, it can be seen that the lithium batteries could have a better performance rate when the weight ratio of carbon nanostructures to carbon black is in a range of 3:7 to 4:6.

[0106] Furthermore, Comparative Examples 4 and 5 show that when carbon black was mixed with freeze-dried carbon nanotube powder, the degradation of lithium battery performance was not less pronounced, but even greater. This means that mixing carbon black with freeze-dried carbon nanotube powder could not solve the problem of the very sharp degradation of lithium battery performance.

[0107] Evaluation example 4: Discharge performance at low temperatures (-25°C / 25 °C).

[0108] The lithium battery was manufactured as described in Evaluation Example 3.

[0109] The low-temperature discharge performance of the manufactured 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 a voltage of 4.25V until the cutoff current reached 0.05C. After 2 hours at the test temperature, the lithium batteries were discharged to 3.0V at a current of 0.5C, and the discharge capacities at -25°C were measured. The discharge capacities at 25°C were measured similarly. The low-temperature discharge performance was evaluated by calculating the ratio of the discharge capacity at -25°C to that at 25°C (-25°C / 25°C). The results are shown in Table 3 below. Table 3 Conductive agent in the positive electrode of a lithium battery Low temperature discharge power -25°C / 25°C (0.5C) Differences between freeze-dried powder and dispersion slurry Reference Example 7 (H4 Dispersion Slurry) 75,36% -2,14% Comparative Example 1 (H4 freeze-dried powder) 73,22% Reference Example 1 (H4 + LITX93R dispersion slurry) 87,43% -1,61% Example 1 (H4 + LITX93R freeze-dried powder) 85,82% Reference Example 2 (H4 + CSX1005 dispersion slurry) 93,43% -1,61% Example 2 (H4 + CSX1005 freeze-dried powder) 91,82% Reference Example 11 (H4 + CSX1005 dispersion slurry) 85,48% +1,38% Example 8 (H4 + CSX1005 freeze-dried powder) 86,86% Reference Example 8 (H10 Dispersion Slurry) 70,67% -1,96% Comparative Example 2 (H10 freeze-dried powder) 68,71% Reference Example 3 (H10 + LITX93R dispersion slurry) 85,76% -1,47% Example 3 (H10 + LITX93R freeze-dried powder) 84,29% Reference Example 4(H10 + CSX1005 90,68% -1,2% Example 4 (H10 + CSX1005 freeze-dried powder) 89,48% Reference Example 9 (H4 + H10 dispersion slurry) 73,33% -1,85% Comparative Example 3 (H4 + H10 freeze-dried powder) 71,48% Reference Example 5 (H4 + H10 + LITX93R dispersion slurry) 86,23% -0,47% Example 5 (H4 + H10 + LITX93R freeze-dried powder) 85,76% Reference Example 6 (H4 + H10 + CSX1005 dispersion slurry) 92,87% -1,54% Example 6 (H4 + H10 + CSX1005 freeze-dried powder) 91,33% Reference Example 1 (H4 + LITX93R dispersion slurry) 87,43% -20,37% Comparative Example 4 (H4 freeze-dried powder + LITX93R) 67,06% Reference Example 2 (H4 + CSX1005 dispersion slurry) 93,43% -25,99% Comparative Example 5 (H4 freeze-dried powder + CSX1005) 67,44%

[0110] From Table 3, it can be seen that in the case of the freeze-dried carbon nanotube powder alone in the comparative examples, the decrease in the low-temperature discharge performance of the lithium batteries was about 2% or more compared to the original dispersion slurries. In contrast, in the case of the freeze-dried mixed powder of carbon nanotubes and carbon black in the examples, the decrease in the low-temperature discharge performance of the lithium batteries was about 1.6% or less compared to the original dispersed slurries.

[0111] Particularly, in Example 5, which included the two types of carbon nanotubes and low surface area carbon black, the discharge efficiency of the lithium battery at low temperatures further decreased to less than 0.5%.

[0112] Furthermore, in Example 8, when the weight ratio of the carbon nanostructures to the carbon black was in a range of 0.5:9.5 to 1:9, the low-temperature discharge performance of the lithium batteries was even improved.

[0113] Furthermore, Comparative Examples 4 and 5 show that when carbon black was mixed with freeze-dried carbon nanotube powder, the decrease in the performance rate of the lithium batteries was not less, but even greater. This means that the mixture of carbon black with freeze-dried carbon nanotube powder could not solve the problem of the very sharp decrease in the performance rate of the lithium batteries. Evaluation example 5: Specific resistance of the electrode foil

[0114] The resistivity of the electrode foil was evaluated as follows.

[0115] The conductive agent in the examples, comparative examples or reference examples, an active material (ternary material of LiNi 0,6 Co 0,2 Mn 0,2 O2) and a binder (PVDF) were mixed in a weight ratio of 1.2:97.8:1 in an NMP solvent to prepare a positive electrode slurry, which was then evenly coated onto a PET membrane with a 200 µm doctor blade and dried to obtain the electrode film. The weight of the conductive agent was the dry weight of the conductive agent.

[0116] The resistivity of the electrode foil was tested using a four-terminal electrode foil resistance meter. The results are shown in Table 4 below. Table 4 Conductive agent in the electrode foil Specific resistance of the electrode foil (Ω cm) Reference Example 7 (H4 Dispersion Slurry) 10 Comparative Example 1 (H4 freeze-dried powder) 51 Reference Example 1 (H4 + LITX93R dispersion slurry) 97 Example 1 (H4 + LITX93R freeze-dried powder) 209 Comparative Example 4 (H4 freeze-dried powder + LITX93R) 426 Reference Example 2 (H4 + CSX1005 dispersion slurry) 62 Example 2 (H4 + CSX1005 freeze-dried powder) 135 Comparative Example 5 (H4 freeze-dried powder + CSX1005) 389 Reference Example 10 (H4 + CSX1005 dispersion slurry) 13 Example 7 (H4 + CSX1005 freeze-dried powder) 49 Reference Example 11 (H4 + CSX1005 dispersion slurry) 695 Example 8 (H4 + CSX1005 freeze-dried powder) 698 Reference Example 8 (H10 Dispersion Slurry) 53 Comparative Example 2 (H10 freeze-dried powder) 103 Reference Example 3 (H10 + LITX93R dispersion slurry) 353 Example 3 (H10 + LITX93R freeze-dried powder) 355 Reference Example 4 (H10 + CSX1005 dispersion slurry) 285 Example 4 (H10 + CSX1005 freeze-dried powder) 288 Reference Example 9 (H4 + H10 dispersion slurry) 39 Comparative Example 3 (H4 + H10 freeze-dried powder) 74 Reference Example 5 (H4 + H10 + LITX93R dispersion slurry) 263 Example 5 (H4 + H10 + LITX93R freeze-dried powder) 265 Reference Example 6 (H4 + H10 + CSX1005 dispersion slurry) 257 Example 6 (H4 + H10 + CSX1005 freeze-dried powder) 224

[0117] From Table 4, it can be seen that the resistivity of the electrode foils may be higher, lower, or comparable between the freeze-dried powders and the original dispersion slurries. However, as mentioned above, compared with the lithium batteries using the original dispersion slurries, the decrease in both the performance and low-temperature discharge performance of the batteries using the conductive agents prepared in Examples of the present invention was significantly smaller, that is, there was no significant decrease regardless of the resistivities of the electrode foils. Therefore, the resistivity of the electrode foil in the present invention had no relationship with the performance and low-temperature discharge performance of the battery.

[0118] Since the conductive agent of the present invention uses the dried, preferably freeze-dried, mixed powder of the carbon nanostructure and the carbon black, such a mixed powder could be easily well dispersed, and at the same time, the discharge rate and the low-temperature discharge performance of the battery prepared using the mixture as the conductive agent were not significantly reduced.

[0119] It is understood that the embodiments described herein are to be considered in a descriptive sense only and are not to be used for limiting purposes. The description of features or aspects in each embodiment should typically be considered applicable to other similar features or aspects in other embodiments. Those skilled in the art will understand that various changes in form and detail may be made without departing from the spirit and scope of the appended claims. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] CN 110894068A

[0004]

Claims

[1] Conductive agent comprising a dried, preferably freeze-dried mixture of a carbon nanostructure and a carbon black. [2] The conductive agent according to claim 1, wherein 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, or multi-walled carbon nanotubes, in particular, wherein in the X-ray diffraction analysis the carbon nanotube has a peak at a diffraction angle 2θ = 25° ± 2° and the half-width of the peak is 1° to 6°; and / or in particular, wherein the carbon nanotube has an average outer diameter in the range of 1 to 40 nm, preferably 2 to 35 nm, more preferably 5 to 30 nm, in particular 10 to 20 nm and even more particularly 10 to 15 nm; and / or in particular, wherein the carbon nanotube has a BET surface area in a range of 100 to 1200 m 2 / g, preferably 120 to 1000 m 2 / g, more preferably 150 to 800 m 2 / g, especially 180 to 500 m 2 / g and especially 200 to 300 m 2 / g. [3] Conductive agent according to claim 1, wherein the carbon nanostructure comprises a first carbon nanotube and a second carbon nanotube, in particular wherein the first carbon nanotube has a BET surface area in the range of 100 to 240 m 2 / g, preferably 150 to 230 m 2 / g and more preferably 200 to 220 m 2 / g, and the second carbon nanotube has a BET surface area in a range of 250 to 1200 m 2 / g, preferably 260 to 500 m 2 / g and more preferably 270 to 300 m 2 / g, wherein in particular the weight ratio of the first carbon nanotube to the second carbon nanotube is 1:9 to 9:1, preferably 2:8 to 8:2, preferably 5:5 to 8:2 and in particular 7:3 to 8:

2. [4] A conductive agent according to claim 1, wherein the carbon black is at least one selected from the group consisting of furnace black, channel black and thermal black, preferably furnace black, in particular, wherein the carbon black has a BET surface area in a range of 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 and especially 1000 to 1200 m 2 / g; and / or in particular, wherein the carbon black has a DBP oil absorption value in a range of 180 to 360 ml / 100 g, preferably 200 to 320 ml / 100 g, more preferably 220 to 300 ml / 100 g, in particular 230 to 280 ml / 100 g and still more preferably 240 to 260 ml / 100 g. [5] A 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, and especially 3:7 to 4:

6. [6] An electrode, preferably a positive electrode, for a lithium battery, containing 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 nanostructure and the carbon black in a solvent to obtain a dispersion slurry; and Drying, preferably freeze-drying, the resulting dispersion slurry. [8] The method according to claim 7, wherein the dispersion slurry further comprises a dispersant, wherein the dispersant is preferably at least one of polyvinylpyrrolidone, polyacrylamide, polycarboxylic acid, polyacrylic acid, polycarboxylate, polyacrylate, polyvinyl alcohol, ethoxylated alcohol, montanin wax, polyvinyl butyral, nitrile rubber; carboxymethylcellulose, hydroxyethylcellulose, polyethylene glycol, polyvinyl acetate, polystyrenesulfonate, polymethacrylate, polyethyleneimine, polyethyleneamine, polypropylenamine, poly(2-vinylpyridine), block copolyether, cellulose acetate, a copolymer of polystyrene and maleic anhydride, and copolymers and derivatives containing monomers of the above-mentioned polymers, preferably polyvinylpyrrolidone. [9] The process according to claim 7, wherein the freeze-drying is carried out at a temperature in the range of -40°C to -70°C. [10] The process 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, preferably water.

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