Oligowall carbon nanotube aqueous conductive slurry, preparation method and application thereof

Abstract

The application provides an oligowall carbon nanotube water-based conductive slurry as well as a preparation method and application thereof, and the preparation method comprises the following steps: mixing a dispersing agent and water, adding carbon nanotubes for dispersion to obtain a premix, and then grinding the obtained premix by using a grinding medium. By using a first grinding medium with a particle size of 0.8-1.2 mm and a second grinding medium with a particle size of 0.3-0.7 mm for compounding, the grinding efficiency is improved, and at the same time, multi-dimensional impact on the product is realized, so that the carbon nanotubes in the obtained oligowall carbon nanotube water-based conductive slurry have high dispersion uniformity, and meanwhile, the carbon nanotubes also maintain high aspect ratios and lengths, and further have higher conductivity and are more easily coated on the surface of a negative electrode material to form a conductive network, so that the rate performance and cycle performance of a battery prepared by using the negative electrode material can be effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of conductive paste, and particularly relates to an oligowall carbon nanotube aqueous conductive paste and a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the increasing influence of petrochemical energy on the environment, clean energy is being widely used as a substitute. As a major component of clean energy, new energy batteries are gradually becoming the first choice for storing electric energy in the fields of passenger cars, buses and energy storage.

[0003] In the field of lithium batteries, carbon nanotubes, with their superior conductivity, are widely used by lithium battery manufacturers as a new type of conductive agent to improve the energy density and cycle life of lithium batteries. However, with the rapid development of new energy vehicles and the improvement of the energy density of power lithium batteries, the replacement of traditional conductive agents will accelerate, which will drive the high-speed growth of the demand for carbon nanotube conductive paste products. After being dispersed into paste, the larger the aspect ratio of carbon nanotubes, the more excellent the conductive performance. Meanwhile, the longer the carbon nanotubes, the easier it is to form a more optimal conductive network, which is conducive to the improvement of the large rate and cycle performance of the battery. Moreover, due to the large size of the negative electrode material, carbon nanotubes with a large aspect ratio are particularly important for improving the performance of the negative electrode material. The dispersion of carbon nanotubes in the lithium battery electrode, only when the carbon nanotubes are uniformly dispersed in the electrode, can a good conductive effect be achieved.

[0004] Therefore, the development of carbon nanotube conductive paste with a higher aspect ratio and more excellent dispersion uniformity is still a hot research topic. CN107579208A discloses a high-purity high-conductive carbon nanotube paste for high-end lithium ion secondary batteries. The paste is composed of the following components by mass fraction: 3-8% of high-purity high-conductive carbon nanotubes, 0.1-2.0% of a dispersion stabilizer, and the balance of N-methyl pyrrolidone. The high-purity high-conductive carbon nanotubes used in the invention have a typical distribution of 410 nm in tube diameter, an average tube diameter of 7 nm, an aspect ratio of 200-2000, and a metal content of less than 100 ppm. The carbon nanotubes are well dispersed in the paste, meeting the requirements of high-end lithium ion secondary batteries. However, carbon nanotubes with a large aspect ratio are prone to agglomeration, and usually need to be pre-dispersed with a suitable dispersant and dispersing equipment. However, the aspect ratio of the carbon nanotubes in the carbon nanotube conductive paste obtained after pre-dispersion will be significantly smaller, which will affect its conductive performance, and also make it difficult to effectively wrap the surface of the negative electrode material to form a conductive network, thereby causing the conductive performance of the negative electrode paste to decrease, affecting the rate and cycle performance of the battery.

[0005] Therefore, the development of a preparation method for an oligowall carbon nanotube aqueous conductive paste that can maintain a high aspect ratio of carbon nanotubes and has high dispersion uniformity is a technical problem that needs to be solved in the field. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application aims to provide an oligowall carbon nanotube aqueous conductive slurry, a preparation method and application thereof, wherein the preparation method is to compound two specific particle sizes of grinding media, so that the carbon nanotubes in the prepared oligowall carbon nanotube aqueous slurry have a high aspect ratio and excellent dispersion uniformity, and further have high conductivity, which is more likely to form a conductive network on the surface of the negative electrode material, thereby further improving the rate performance and cycle performance of the battery.

[0007] To achieve the object of the present application, the following technical solutions are adopted:

[0008] In a first aspect, the present application provides a preparation method of an oligowall carbon nanotube aqueous conductive slurry, which comprises the following steps:

[0009] (1) mixing a dispersant and water, adding carbon nanotubes for dispersion to obtain a premix;

[0010] (2) grinding the premix obtained in step (1) using compound grinding media to obtain the oligowall carbon nanotube aqueous conductive slurry;

[0011] The compound grinding media comprises first grinding media with a particle size of 0.8-1.2 mm (for example, 0.85 mm, 0.9 mm, 0.95 mm, 1 mm, 1.05 mm, 1.1 mm or 1.15 mm, etc.) and second grinding media with a particle size of 0.3-0.7 mm (for example, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm or 0.65 mm, etc.).

[0012] The preparation method of the oligomeric carbon nanotube water-based conductive slurry provided by the application first mixes a dispersant and water, adds carbon nanotubes for dispersion, obtains a premix, and grinds the obtained premix to obtain the carbon nanotube water-based conductive slurry; the application takes the aspect ratio and tube length of most existing carbon nanotubes as a starting point, controls and compounding the particle size of the grinding medium, and finds the best grinding point of the carbon nanotube water-based slurry; specifically, the first grinding medium with a particle size of 0.8-1.2 mm and the second grinding medium with a particle size of 0.3-0.7 mm are compounded, the second grinding medium with a smaller particle size can fill the gap position of the first particle size with a larger particle size, increase the contact points of the ground material and the grinding medium, not only improve the grinding efficiency, but also realize multi-dimensional impact on the ground material, ensure that the carbon nanotubes in the obtained carbon nanotube water-based slurry still have a high aspect ratio and tube length, improve the dispersion uniformity of the carbon nanotubes, make the carbon nanotubes have high conductivity, and more easily form a conductive network on the surface of the negative electrode material, so that the obtained negative electrode slurry has better dispersion and limitation, and when further applied to a battery, the rate performance and cycle performance of the battery can be effectively improved.

[0013] Preferably, the content of the dispersant in the premix is 2-10 parts by weight, for example, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, or 9 parts by weight, etc.

[0014] Preferably, the dispersant includes polyvinylpyrrolidone and / or sodium carboxymethyl cellulose.

[0015] Preferably, the content of water in the premix is 400-750 parts by weight, for example, 450 parts by weight, 500 parts by weight, 550 parts by weight, 600 parts by weight, 650 parts by weight, or 700 parts by weight, etc.

[0016] Preferably, the content of the carbon nanotubes in the premix is 10-30 parts by weight, for example, 12 parts by weight, 14 parts by weight, 16 parts by weight, 18 parts by weight, 20 parts by weight, 22 parts by weight, 24 parts by weight, 26 parts by weight, or 28 parts by weight, etc.

[0017] Preferably, the aspect ratio of the carbon nanotubes is 6000-10000, for example, 6500, 7000, 7500, 8000, 8500, 9000, or 9500, etc.

[0018] Preferably, the length of the carbon nanotubes is 30-50 μm, for example, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm, 42 μm, 44 μm, 46 μm, or 48 μm, etc.

[0019] Preferably, the mixing time is 10-30 min, such as 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min or 28 min, etc.

[0020] Preferably, the mixing is carried out under stirring, further preferably under stirring at a rotation speed of 800-1200 rpm, such as 840 rpm, 880 rpm, 920 rpm, 960 rpm, 1000 rpm, 1040 rpm, 1080 rpm, 1120 rpm or 1160 rpm, etc.

[0021] Preferably, the dispersing time is 30-75 min, such as 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min or 70 min, etc.

[0022] Preferably, the rotation speed for the dispersing is 800-1200 rpm, such as 840 rpm, 880 rpm, 920 rpm, 960 rpm, 1000 rpm, 1040 rpm, 1080 rpm, 1120 rpm or 1160 rpm, etc.

[0023] Preferably, the first and second grinding media each independently comprises any one or a combination of at least two of zirconium balls, aluminum balls or steel balls.

[0024] Preferably, the particle size ratio of the first and second grinding media is 1:(0.3-0.7), such as 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6 or 1:0.65, etc.

[0025] As a preferred technical solution of the present application, the particle size ratio of the first and second grinding media is limited to 1:(0.3-0.7), which can make the aspect ratio and length of the carbon nanotubes in the final carbon nanotube aqueous slurry longer, and further make the conductive performance of most carbon nanotube aqueous slurries more excellent.

[0026] Preferably, the mass ratio of the first and second grinding media is 1:(0.1-9), such as 1:0.3, 1:0.6, 1:0.9, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7 or 1:1.8, etc.

[0027] Preferably, the grinding is carried out in a grinding machine.

[0028] Preferably, the grinding time is 0.5-5 h, such as 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h or 4.5 h, etc.

[0029] Preferably, the rotation speed of the grinder is 600-800 rpm, such as 620 rpm, 640 rpm, 660 rpm, 680 rpm, 700 rpm, 720 rpm, 740 rpm, 760 rpm or 780 rpm, etc.

[0030] As a preferred technical solution, the preparation method comprises the following steps:

[0031] (1) 2-10 parts by weight of dispersant and 400-750 parts by weight of water are mixed under stirring conditions at a rotation speed of 800-1200 rpm for 10-30 min, 10-30 parts by weight of carbon nanotubes are added and dispersed under the condition of rotation speed of 800-1200 rpm for 30-75 min to obtain a premix;

[0032] (2) the premix obtained in step (1) is ground in a grinder with a rotation speed of 600-800 rpm using a compound grinding medium for 0.5-5 h to obtain the oligowall carbon nanotube aqueous conductive slurry;

[0033] The compound grinding medium comprises first grinding medium with a particle size of 0.8-1.2 mm and second grinding medium with a particle size of 0.3-0.7 mm.

[0034] In a second aspect, the present application provides an oligowall carbon nanotube aqueous conductive slurry, which is prepared by the preparation method of the first aspect.

[0035] Preferably, the aspect ratio of the carbon nanotubes in the oligowall carbon nanotube aqueous conductive slurry is 1000-5000, such as 1500, 2000, 2500, 3000, 3500, 4000 or 4500, etc.

[0036] Preferably, the length of the carbon nanotubes in the oligowall carbon nanotube aqueous conductive slurry is 5-25 μm, such as 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm or 23 μm, etc.

[0037] In a third aspect, the present application provides a negative electrode slurry, which comprises the oligowall nanotube aqueous conductive slurry of the second aspect, a negative electrode active material and a binder.

[0038] Preferably, the negative electrode active material comprises any one or a combination of at least two of graphite, carbon or silicon-carbon.

[0039] In a fourth aspect, the present application provides a lithium ion battery, which comprises the negative electrode slurry of the third aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The method for preparing oligowalled carbon nanotube aqueous conductive slurry provided by the present invention includes mixing a dispersant and water, adding carbon nanotubes for dispersion to obtain a premix, and then grinding the obtained premix using a grinding media. By using a first grinding media with a particle size of 0.8-1.2 mm and a second grinding media with a particle size of 0.3-0.7 mm for compounding, not only is the grinding efficiency improved, but also multi-dimensional impact on the product is achieved. This results in the carbon nanotubes in the obtained oligowalled carbon nanotube aqueous conductive slurry having high dispersion uniformity, while maintaining a high aspect ratio and length. Consequently, it has higher conductivity and is easier to coat onto the surface of the negative electrode material to form a conductive network, which can effectively improve the rate performance and cycle performance of the battery prepared using the negative electrode material. Attached Figure Description

[0042] Figure 1 This is a scanning electron microscope image of the aqueous conductive slurry containing oligowalled carbon nanotubes obtained in Example 1.

[0043] Figure 2 The image shows a scanning electron microscope (SEM) image of the aqueous conductive slurry containing oligowalled carbon nanotubes obtained in Comparative Example 1.

[0044] Figure 3 The image shows a scanning electron microscope (SEM) image of the aqueous conductive slurry containing oligowalled carbon nanotubes obtained in Comparative Example 2.

[0045] Figure 4 The image shows a scanning electron microscope (SEM) image of the negative electrode slurry obtained in Application Example 1.

[0046] Figure 5 For comparison, see the scanning electron microscope image of the negative electrode slurry obtained in Application Example 1;

[0047] Figure 6 The scanning electron microscope image of the negative electrode slurry obtained in Application Example 2 is shown for comparison. Detailed Implementation

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0049] Example 1

[0050] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes includes the following steps:

[0051] (1) Mix 5 parts by weight of polyvinylpyrrolidone (BASF, K30) and 750 parts by weight of water under stirring at 100 rpm for 20 min, add 24 parts by weight of carbon nanotubes (aspect ratio between 6000 and 10000, length between 30 and 50 μm) and disperse at 1000 rpm for 75 min to obtain a premix.

[0052] (2) The premix obtained in step (1) is ground in a mill with a speed of 700 rpm using a compound grinding medium for 2 hours to obtain the oligowalled carbon nanotube aqueous conductive slurry;

[0053] The compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 1 mm and 0.5 kg of zirconium balls with a particle size of 0.5 mm.

[0054] Example 2

[0055] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes includes the following steps:

[0056] (1) Mix 4 parts by weight of polyvinylpyrrolidone (BASF, K30), 2 parts by weight of sodium carboxymethyl cellulose and 730 parts by weight of deionized water at a stirring speed of 1000 rpm for 26 min, add 27 parts by weight of carbon nanotubes (aspect ratio between 6000 and 10000, length between 30 and 50 μm) and disperse at a stirring speed of 1000 rpm for 65 min to obtain a premix.

[0057] (2) The premix obtained in step (1) is ground in a mill with a speed of 700 rpm using a compound grinding medium for 5 hours to obtain the oligowalled carbon nanotube aqueous conductive slurry;

[0058] The compound grinding media consists of 0.3 kg of zirconium balls with a particle size of 1 mm and 0.7 kg of zirconium balls with a particle size of 0.6 mm.

[0059] Example 3

[0060] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes includes the following steps:

[0061] (1) Mix 5 parts by weight of polyvinylpyrrolidone (BASF, K30), 5 parts by weight of sodium carboxymethyl cellulose and 680 parts by weight of deionized water at a stirring speed of 1000 rpm for 24 min, add 30 parts by weight of carbon nanotubes (aspect ratio between 6000 and 10000, length between 30 and 50 μm) and disperse at a stirring speed of 1000 rpm for 65 min to obtain a premix.

[0062] (2) The premix obtained in step (1) is ground in a mill with a speed of 700 rpm using a compound grinding medium for 4 hours to obtain the oligowalled carbon nanotube aqueous conductive slurry.

[0063] The compound grinding media consists of 0.2 kg of zirconium balls with a particle size of 1 mm and 0.8 kg of zirconium balls with a particle size of 0.5 mm.

[0064] Example 4

[0065] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes includes the following steps:

[0066] (1) Mix 3 parts by weight of polyvinylpyrrolidone (BASF, K30), 3 parts by weight of sodium carboxymethyl cellulose and 650 parts by weight of deionized water at a stirring speed of 1000 rpm for 22 min, add 21 parts by weight of carbon nanotubes (aspect ratio between 6000 and 10000, length between 30 and 50 μm) and disperse at a stirring speed of 1000 rpm for 55 min to obtain a premix.

[0067] (2) The premix obtained in step (1) is ground in a mill with a speed of 700 rpm using a compound grinding medium for 3 hours to obtain the oligowalled carbon nanotube aqueous conductive slurry;

[0068] The compound grinding media consists of 0.1 kg of zirconium balls with a particle size of 1 mm and 0.9 kg of zirconium balls with a particle size of 0.6 mm.

[0069] Example 5

[0070] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes includes the following steps:

[0071] (1) Mix 4 parts by weight of polyvinylpyrrolidone (BASF, K30), 4 parts by weight of sodium carboxymethyl cellulose and 600 parts by weight of deionized water at a stirring speed of 1000 rpm for 20 min, add 18 parts by weight of carbon nanotubes (aspect ratio between 6000 and 10000, length between 30 and 50 μm) and disperse at a stirring speed of 1000 rpm for 50 min to obtain a premix.

[0072] (2) The premix obtained in step (1) is ground in a mill with a speed of 700 rpm using a compound grinding medium for 2.5 h to obtain the oligowalled carbon nanotube aqueous conductive slurry;

[0073] The compound grinding media consists of 0.6 kg of zirconium balls with a particle size of 1 mm and 0.4 kg of zirconium balls with a particle size of 0.4 mm.

[0074] Example 6

[0075] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes includes the following steps:

[0076] (1) Mix 4 parts by weight of polyvinylpyrrolidone (BASF, K30), 2 parts by weight of sodium carboxymethyl cellulose and 550 parts by weight of deionized water at a stirring speed of 1000 rpm for 18 min, add 15 parts by weight of carbon nanotubes (aspect ratio between 6000 and 10000, length between 30 and 50 μm) and disperse at a stirring speed of 1000 rpm for 45 min to obtain a premix.

[0077] (2) The premix obtained in step (1) is ground in a mill with a speed of 700 rpm using a compound grinding medium for 1.5 h to obtain the oligowalled carbon nanotube aqueous conductive slurry;

[0078] The compound grinding media consists of 0.7 kg of zirconium balls with a particle size of 1 mm and 0.3 kg of zirconium balls with a particle size of 0.5 mm.

[0079] Example 7

[0080] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes includes the following steps:

[0081] (1) Mix 1.5 parts by weight of polyvinylpyrrolidone (BASF, K30), 2.5 parts by weight of sodium carboxymethyl cellulose and 500 parts by weight of deionized water at a stirring speed of 1000 rpm for 14 min, add 12 parts by weight of carbon nanotubes (aspect ratio between 6000 and 10000, length between 30 and 50 μm) and disperse at a stirring speed of 1000 rpm for 40 min to obtain a premix.

[0082] (2) The premix obtained in step (1) is ground in a mill with a speed of 700 rpm using a compound grinding medium for 1 h to obtain the oligowalled carbon nanotube aqueous conductive slurry;

[0083] The compound grinding media consists of 0.8 kg of zirconium balls with a particle size of 1 mm and 0.2 kg of zirconium balls with a particle size of 0.5 mm.

[0084] Example 8

[0085] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes includes the following steps:

[0086] (1) Mix 1 part by weight of polyvinylpyrrolidone (BASF, K30), 1 part by weight of sodium carboxymethyl cellulose and 400 parts by weight of deionized water at a stirring speed of 1000 rpm for 10 min, add 10 parts by weight of carbon nanotubes (aspect ratio between 6000 and 10000, length between 30 and 50 μm) and disperse at a stirring speed of 1000 rpm for 30 min to obtain a premix.

[0087] (2) The premix obtained in step (1) is ground in a mill with a speed of 700 rpm using a compound grinding medium for 0.5 h to obtain the oligowalled carbon nanotube aqueous conductive slurry;

[0088] The compound grinding media consists of 0.9 kg of zirconium balls with a particle size of 1 mm and 0.1 kg of zirconium balls with a particle size of 0.5 mm.

[0089] Example 9

[0090] A method for preparing an aqueous conductive paste of oligowalled carbon nanotubes is disclosed, which differs from the example only in that the compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 1 mm and 0.5 kg of zirconium balls with a particle size of 0.3 mm. All other conditions and parameters are the same as in Example 1.

[0091] Example 10

[0092] A method for preparing an aqueous conductive paste of oligowalled carbon nanotubes is disclosed, the only difference from the example being that the compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 1 mm and 0.5 kg of zirconium balls with a particle size of 0.7 mm, while all other conditions and parameters are the same as in Example 1.

[0093] Example 11

[0094] A method for preparing an aqueous conductive paste of oligowalled carbon nanotubes is disclosed, which differs from the example only in that the compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 0.8 mm and 0.5 kg of zirconium balls with a particle size of 0.7 mm. All other conditions and parameters are the same as in Example 1.

[0095] Example 12

[0096] A method for preparing an aqueous conductive paste of oligowalled carbon nanotubes is disclosed, which differs from the example only in that the compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 1.2 mm and 0.5 kg of zirconium balls with a particle size of 0.3 mm. All other conditions and parameters are the same as in Example 1.

[0097] Comparative Example 1

[0098] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes is disclosed, which differs from the example only in that the grinding medium consists of 1 kg of zirconium balls with a particle size of 1 mm, while all other conditions and parameters are the same as in Example 1.

[0099] Comparative Example 2

[0100] A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes is disclosed, which differs from the example only in that the grinding medium consists of 1 kg of zirconium balls with a particle size of 0.5 mm. All other conditions and parameters are the same as in Example 1.

[0101] Comparative Example 3

[0102] A method for preparing an aqueous conductive paste of oligowalled carbon nanotubes is disclosed, which differs from the example only in that the compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 1 mm and 0.5 kg of zirconium balls with a particle size of 0.8 mm. All other conditions and parameters are the same as in Example 1.

[0103] Comparative Example 4

[0104] A method for preparing an aqueous conductive paste of oligowalled carbon nanotubes is disclosed, which differs from Example 1 only in that the compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 1 mm and 0.5 kg of zirconium balls with a particle size of 0.2 mm. All other conditions and parameters are the same as in Example 1.

[0105] Comparative Example 5

[0106] A method for preparing an aqueous conductive paste of oligowalled carbon nanotubes is disclosed, which differs from Example 1 only in that the compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 0.7 mm and 0.5 kg of zirconium balls with a particle size of 0.5 mm. All other conditions and parameters are the same as in Example 1.

[0107] Comparative Example 6

[0108] A method for preparing an aqueous conductive paste of oligowalled carbon nanotubes is disclosed, which differs from the example only in that the compound grinding media consists of 0.5 kg of zirconium balls with a particle size of 1.3 mm and 0.5 kg of zirconium balls with a particle size of 0.5 mm. All other conditions and parameters are the same as in Example 1.

[0109] Application Example 1

[0110] A negative electrode slurry with a solid content of 45% is composed of a water-based conductive slurry of graphite, SBR, CMC and oligowalled carbon nanotubes in a mass ratio of 95.5:2.5:1.2:0.8 (Example 1).

[0111] The method for preparing the negative electrode slurry includes: stirring graphite, SBR (Japan Ayuron, SN-307R), CMC (Japan Paper, MAC500LC) and oligowalled carbon nanotube aqueous conductive slurry evenly in water to obtain the negative electrode slurry.

[0112] Application Examples 2-12

[0113] A negative electrode slurry differs from Application Example 1 only in that the aqueous conductive slurry of oligowalled carbon nanotubes obtained in Examples 2 to 12 is used instead of the aqueous conductive slurry of oligowalled carbon nanotubes obtained in Example 1. All other structures and parameters are the same as in Application Example 1.

[0114] Application Example 13

[0115] A button-type lithium-ion half-cell, the preparation process of which includes the following steps:

[0116] (1) The negative electrode slurry obtained in Application Example 1 is coated on copper foil to obtain a negative electrode sheet; a lithium sheet is used as the positive electrode.

[0117] (2) Assemble the negative electrode shell, negative electrode sheet, separator, electrolyte, lithium sheet, gasket, spring sheet and positive electrode shell in the order from bottom to top, and then seal them to obtain a button half battery. The battery is tested after standing for 24 hours; the battery model is CR2025.

[0118] Application Examples 14-24

[0119] A lithium-ion battery differs from Application Example 13 only in that the negative electrode slurry obtained in Application Examples 2 to 12 is used to replace the negative electrode slurry obtained in Application Example 1, while the other structures and parameters are the same as in Application Example 13.

[0120] Comparative Application Examples 1-6

[0121] A negative electrode paste, which differs from Application Example 1 only in that the carbon nanotube aqueous conductive paste obtained in Comparative Examples 1 to 6 is used instead of the carbon nanotube aqueous conductive paste obtained in Example 1, while the other structures and parameters are the same as in Application Example 1.

[0122] Compare and contrast examples 7-12

[0123] A lithium-ion battery differs from Application Example 13 only in that the negative electrode slurry obtained in Comparative Application Examples 1 to 6 is used instead of the negative electrode slurry obtained in Application Example 1. All other structures and parameters are the same as in Application Example 13.

[0124] Performance testing:

[0125] (1) Morphological observation of aqueous conductive carbon nanotube slurry: The aqueous conductive oligomeric carbon nanotube slurries obtained in Example 1 and Comparative Examples 1-2 were tested using a scanning electron microscope (Regulus 8100). The scanning electron microscope images of the aqueous conductive oligomeric carbon nanotube slurries provided in Example 1 and Comparative Examples 1-2 are shown below. Figures 1-3 As shown, from Figure 1 As can be seen, the carbon nanotubes in the aqueous conductive slurry of oligowalled carbon nanotubes obtained in Example 1 have a large aspect ratio, and the carbon nanotubes are less entangled and easier to coat, indicating that the aqueous conductive slurry of oligowalled carbon nanotubes prepared by the preparation method provided in Example 1 can maintain the aspect ratio of carbon nanotubes while having good dispersibility; from Figure 2 and Figure 3 It can be seen that the carbon nanotubes in the aqueous conductive slurry prepared by Comparative Example 1 and Comparative Example 2 have a lower aspect ratio than those in Example 1, and the dispersion is also worse.

[0126] (2) Morphology observation of negative electrode slurry: The negative electrode slurries obtained in Application Example 1 and Comparative Application Examples 1-2 were tested using a scanning electron microscope (Regulus 8100). The scanning electron microscope images of the negative electrode slurries provided in Application Example 1 and Comparative Application Examples 1-2 are shown below. Figures 4-6 As shown, from Figure 4 It can be seen that the coating of the negative electrode slurry provided in Example 1 is complete, indicating that the carbon nanotube aqueous conductive slurry obtained by the preparation method provided in Example 1 is easily coated on the surface of the negative electrode material; while from Figure 5 and Figure 6 It can be seen that carbon nanotubes in some areas of the negative electrode slurry obtained in Comparative Application Example 1 and Comparative Application Example 2 agglomerate, indicating that the dispersion is uneven and the coating of the negative electrode material is not ideal.

[0127] (3) Aspect Ratio Test Method: The oligomeric aqueous carbon nanotube slurries obtained in each embodiment and comparative example were diluted with distilled water, and sodium dodecyl sulfate was added. After dilution, the mass percentage of carbon nanotubes was 1.0 × 10⁻⁶. -4 The mass percentage of sodium dodecyl sulfate is 1.0 × 10⁻⁶ wt.%. -4 wt.%; The diluted and dispersed slurry was deposited onto the substrate and dried at 120℃ for 5 hours. The length and diameter of carbon nanotubes in the aqueous carbon nanotube slurry were measured using scanning electron microscopy (SEM). 120 samples were taken from different regions, and the 10 shortest and 10 longest carbon nanotubes were removed. The length and diameter of 100 carbon nanotubes were statistically analyzed, and the average value of the 100 sets of aspect ratio data was taken.

[0128] (4) Electrode resistivity test method: A water-based conductive slurry system of graphite:SBR:CMC:oligowalled carbon nanotubes = 95.5:2.5:1.2:0.8 with a solid content of 45% was used. The slurry was homogenized at 2000 rpm for 15 min. Then, the homogenized slurry was coated on the PI film with a coating thickness of 200 μm and dried at 140℃ for 1 h. Finally, the resistivity of the electrode was tested using a four-probe resistivity tester (model: RTS-8).

[0129] The oligowalled carbon nanotube aqueous conductive pastes provided in Examples 1-12 and Comparative Examples 1-6 were tested according to the above test methods. The test results are shown in Table 1.

[0130] Table 1

[0131]

[0132]

[0133] According to the data in Table 1:

[0134] (1) By using a first grinding medium with a particle size of 0.8 to 1.2 mm and a second grinding medium with a particle size of 0.3 to 0.7 mm to produce an oligowalled carbon nanotube aqueous conductive slurry, the aspect ratio of the carbon nanotubes is greater than that of the oligowalled carbon nanotube aqueous conductive slurry obtained by using a single medium (Comparative Examples 1 to 2) under the same conditions and by using the first and second grinding compound media (Comparative Examples 3 to 6) outside the above particle size range.

[0135] (2) By using a first grinding medium with a particle size of 0.8 to 1.2 mm and a second grinding medium with a particle size of 0.3 to 0.7 mm to produce a composite, the carbon nanotube dispersion uniformity in the produced oligowalled carbon nanotube aqueous conductive slurry is better than that of the carbon nanotube dispersion of the oligowalled carbon nanotube aqueous conductive slurry obtained by using a single medium (Comparative Examples 1 to 2) under the same conditions and by using a first and second grinding composite medium (Comparative Examples 3 to 6) outside the above particle size range. Specifically, the electrode resistivity is better. In particular, the resistivity of the electrode prepared by using the oligowalled carbon nanotube aqueous conductive slurry obtained in Examples 1 to 8 is 100.4 to 131.1 Ω·cm.

[0136] (3) Cyclic performance: The Xinwei test system (CT-4008-5V50mA) was used. The test conditions were: constant current and constant voltage charging at 0.3C, constant current discharging at 0.5C, and capacity retention rate after 100 cycles.

[0137] (4) Rate performance: The test system (CT-4008-5V50mA) was used. The test conditions were constant current and constant voltage charging at 0.3C, and constant current discharging at 0.3C, 0.5C, 1C, 2C, 3C and 5C respectively. The rate performance was expressed as the capacity retention rate under the conditions from 0.3C to 5C.

[0138] The button lithium-ion half-cells obtained according to the above test methods and corresponding test cases 13-24 and comparative application examples 7-12 were tested. The test results are shown in Table 2.

[0139] Table 2

[0140]

[0141]

[0142] According to the data in Table 2:

[0143] The button lithium-ion half-cells prepared by compounding a first grinding medium with a particle size of 0.8–1.2 mm and a second grinding medium with a particle size of 0.3–0.7 mm, and further preparing the aqueous conductive slurry of oligowalled carbon nanotubes, exhibit excellent rate performance and cycle performance. Furthermore, by further limiting the particle size ratio and mass ratio of the first and second grinding media, the cycle performance and rate performance of the prepared button lithium-ion half-cells can be further improved. Specifically, the button lithium-ion half-cells obtained in Examples 1–20 exhibit a capacity retention rate of 90.4–95.3% after 100 cycles in the cycle performance test, and a capacity retention rate of 70.2–78.6% under the rate performance test conditions from 0.3C to 5C.

[0144] Comparing Application Example 13 with Comparative Application Examples 7-12, it can be seen that the cycle performance and rate performance of the button lithium-ion half-cells prepared by combining the oligowalled carbon nanotube aqueous conductive slurry prepared with a single particle size grinding medium (Comparative Application Examples 7-8) and two grinding media with particle sizes other than those specified in this invention (Comparative Application Examples 9-12) are both reduced.

[0145] The applicant declares that this invention illustrates the advantages and applications of a carbon nanotube aqueous conductive paste and its preparation method through the above embodiments. However, this invention is not limited to the above process steps, meaning that this invention does not necessarily rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials used in this invention, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. A method for preparing an aqueous conductive paste using oligowalled carbon nanotubes, characterized in that, The preparation method includes the following steps: (1) Mix the dispersant and water, add carbon nanotubes for dispersion, and obtain a premix; (2) The premix obtained in step (1) is ground using a compound grinding medium to obtain the oligowalled carbon nanotube aqueous conductive slurry; The compound grinding media consists of a first grinding media with a particle size of 0.8~1.2 mm and a second grinding media with a particle size of 0.3~0.7 mm; The particle size ratio of the first grinding media and the second grinding media is 1:(0.4~0.6); The mass ratio of the first grinding medium to the second grinding medium is 1:(0.1~9).

2. The preparation method according to claim 1, characterized in that, The content of dispersant in the premix is ​​2 to 10 parts by weight.

3. The preparation method according to claim 1, characterized in that, The dispersant includes polyvinylpyrrolidone and / or sodium carboxymethyl cellulose.

4. The preparation method according to claim 1, characterized in that, The water content in the premix is ​​400-750 parts by weight.

5. The preparation method according to claim 1, characterized in that, The premix contains 10 to 30 parts by weight of carbon nanotubes.

6. The preparation method according to claim 1, characterized in that, The aspect ratio of the carbon nanotubes is 6000~10000.

7. The preparation method according to claim 1, characterized in that, The length of the carbon nanotubes is 30~50 µm.

8. The preparation method according to claim 1, characterized in that, The mixing time is 10-30 minutes.

9. The preparation method according to claim 1, characterized in that, The mixing is carried out under stirring conditions.

10. The preparation method according to claim 1, characterized in that, The mixing is carried out under stirring conditions at a speed of 800~1200 rpm.

11. The preparation method according to claim 1, characterized in that, The dispersion time is 30~75 min.

12. The preparation method according to claim 1, characterized in that, The dispersion speed is 800~1200 rpm.

13. The preparation method according to claim 1, characterized in that, The first and second grinding media each independently comprise any one or a combination of at least two of zirconium balls, aluminum balls, or steel balls.

14. The preparation method according to claim 1, characterized in that, The grinding is carried out in a grinding machine.

15. The preparation method according to claim 1, characterized in that, The grinding time is 0.5 to 5 hours.

16. The preparation method according to claim 14, characterized in that, The grinding mill rotates at a speed of 600-800 rpm.

17. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix 2-10 parts by weight of dispersant and 400-750 parts by weight of water at a stirring speed of 800-1200 rpm for 10-30 min, add 10-30 parts by weight of carbon nanotubes and disperse at a stirring speed of 800-1200 rpm for 30-75 min to obtain a premix. (2) The premix obtained in step (1) is ground in a mill with a speed of 600~800 rpm using a compound grinding medium for 0.5~5 h to obtain the oligowalled carbon nanotube aqueous conductive slurry; The compound grinding media includes a first grinding media with a particle size of 0.8~1.2 mm and a second grinding media with a particle size of 0.3~0.7 mm; The particle size ratio of the first grinding media and the second grinding media is 1:(0.4~0.6); The mass ratio of the first grinding medium to the second grinding medium is 1:(0.1~9).

18. A water-based conductive paste containing oligowalled carbon nanotubes, characterized in that, The oligowalled carbon nanotube aqueous conductive paste is prepared by the preparation method described in any one of claims 1 to 17.

19. The aqueous conductive paste for oligowalled carbon nanotubes according to claim 18, characterized in that, The aspect ratio of the carbon nanotubes in the oligowalled carbon nanotube aqueous conductive slurry is 1000~5000.

20. The aqueous conductive paste for oligowalled carbon nanotubes according to claim 18, characterized in that, The length of the carbon nanotubes in the oligowalled carbon nanotube aqueous conductive slurry is 5~25 µm.

21. A negative electrode slurry, characterized in that, The negative electrode slurry includes the oligowalled carbon nanotube aqueous conductive slurry as described in any one of claims 18 to 20, the negative electrode active material, and the binder.

22. The negative electrode slurry according to claim 21, characterized in that, The negative electrode active material includes any one or a combination of at least two of graphite, carbon, or silicon-carbon.

23. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode slurry as described in claim 21 or 22.

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