Conductive carbon material dispersing agent and high-conductivity slurry for lithium battery

Abstract

The invention relates to the technical field of lithium battery slurry materials, in particular to a conductive carbon material dispersing agent which comprises one of modified polyvinyl alcohol, alkyl ammonium salt copolymer, olefin block maleic anhydride copolymer and pyrrolidone copolymer, or mixtures thereof, and can effectively disperse carbon nanotube, graphene and other conductive carbon materials in a solvent to obtain uniform conductive slurry; further disclosed is a high-conductivity slurry for the lithium battery, which comprises 0.5-15.0% by weight of a conductive carbon material and 0.1-3.0% by weight of a dispersing agent, and can remarkably reduce the bulk resistivity of a positive electrode system of the lithium battery and improve the conductivity of a pole piece.

Claims

1. A conductive carbon material dispersing agent, comprising modified polyvinyl alcohol, alkylammonium salt copolymer and acrylic acid-maleic anhydride copolymer, wherein the modified polyvinyl alcohol is polyvinyl alcohol-maleic anhydride crosslinked polymer.

2. The conductive carbon material dispersing agent according to claim 1, further comprising one selected from a group consisting of polyethylene glycol, polyvinylpyrrolidone, polyvinylidene fluoride, and mixtures thereof.

3. The conductive carbon material dispersing agent according to claim 1, wherein the alkylammonium salt copolymer is selected from a group consisting of BYK-9076 and BYK-9077 of BYK Chemie, MOK®-5022 of Merck, German, and analogous alkylammonium salt copolymer thereof in the market.

4. A high-conductivity slurry for a lithium battery, comprising the conductive carbon material dispersing agent according to claim 1, and further comprising a conductive carbon material and a solvent, wherein a proportion of the conductive carbon material in the high-conductive slurry is 0.5-15.0% by weight, a proportion of the conductive carbon material dispersing agent in the high-conductive slurry is 0.1-3.0% by weight, and the rest is the solvent.

5. The high-conductivity slurry for a lithium battery according to claim 4, wherein the conductive carbon material comprises one selected from a group consisting of single-walled carbon nanotube, multi-walled carbon nanotube, graphene, carbon black-based conductive material, and mixtures thereof.

6. The high-conductivity slurry for a lithium battery according to claim 4, wherein the solvent is one selected from a group consisting of N-methylpyrrolidone, methanol, ethanol, isopropanol, water, and mixtures thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the morphology of the conductive slurry in Example 2 through SEM;

(2) FIG. 2 shows the morphology of the conductive slurry in Example 6 through SEM;

(3) FIG. 3 shows the morphology of the conductive slurry in Example 9 through SEM.

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention will now be described in detail with reference to the accompanying drawings and examples.

EXAMPLE 1

(5) In this example, 12 g carbon nanotube was taken as the conductive carbon material, 6 g styrene-maleic anhydride copolymer was taken, whose synthesis method can be learned with reference to Document 3 (Li Xiaohua, Qiang Xihuai, Hong Xinqiu. Styrene-maleic Anhydride Copolymer and Application [J]. Leather Science and Engineering, 2009, 19(2):42-46), and 384 g N-methylpyrrolidone was taken as the solvent. Firstly, the styrene maleic anhydride copolymer was pre-dissloved in the N-methyl pyrrolidone, then the carbon nanotube was added, mechanical stirring and pre-dispersing were carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube conductive slurry A1.

EXAMPLE 2

(6) In this example, 14 g of carbon nanotube was taken as the conductive carbon material, 7 g polyvinyl formal was taken, and 379 g N-methyl pyrrolidone (NMP) was taken as the solvent. The dispersing agent was pre-dissolved in NMP, then the conductive carbon material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube conductive slurry A2.

EXAMPLE 3

(7) In this example, 2.0 g carbon nanotube material was taken as the conductive carbon material, 0.4 g BYK Chemie BYK-9076 was taken, and 397.6 g pure water was taken as the solvent. The dispersing agent was pre-dissolved in pure water, then the conductive carbon material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube conductive slurry A3.

EXAMPLE 4

(8) In this example, 14 g carbon nanotube was taken as the conductive carbon material, 3.0 g polyvinyl butyral was taken, 4.0 g German Merck MOK®-502 was taken, and 379 g NMP was taken as the solvent. The dispersing agents were pre-dissolved in NMP, then the conductive carbon material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube conductive slurry A4.

EXAMPLE 5

(9) In this example, 14 g carbon nanotube was taken as the conductive carbon material, 3.0 g polyvinyl acetal was taken, 4.0 g polyvinyl pyrrolidone was taken, and 379 g ethanol was taken as the solvent. The dispersing agents were firstly pre-dissolved in ethanol, then the conductive carbon material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and ultrasonic dispersing was carried out further for 1.5 h to obtain a carbon nanotube conductive slurry A5.

EXAMPLE 6

(10) In this example, 2 g graphene material was taken as the conductive carbon material, 2.4 g polyvinylidene fluoride was taken, 1.6 g alkyl vinyl ether-maleic anhydride copolymer was taken, whose preparation method can be learned with reference to Document 4 (Tianjun, Research on Vinyl Ether-Maleic Anhydride Copolymer [D]. Graduate University of Chinese Academy of Sciences (Institute of Physical and Chemical Technology), 2008), and 380 g NMP was taken as the solvent. The dispersing agents were pre-dissolved in NMP, then the conductive carbon material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a graphene conductive slurry B 1.

EXAMPLE 7

(11) In this example, 20 g of graphene material was taken as the conductive carbon material, 5.0 g polyvinyl butyral was taken, and 375 g isopropyl alcohol was taken as the solvent.

(12) The dispersing agent d was pre-dissolved in isopropanol, then the conductive carbon material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a graphene conductive slurry B2.

EXAMPLE 8

(13) In this example, 16 g graphene material was taken as the conductive carbon material, 2.0 g polyvinylidene fluoride was taken, 0.5 g polyethylene glycol was taken, 1.5 g carboxyl modified polyvinyl alcohol was taken, and 380 g NMP was taken as the solvent. The dispersing agents were pre-dissolved in NMP, then the conductive carbon material was added, material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and ultrasonic dispersing were carried out further for 1.0 h to obtain a graphene conductive slurry B3.

EXAMPLE 9

(14) In this example, 8 g carbon nanotube and 8 g graphene material were taken as the conductive carbon material, 2.0 g olefin block maleic anhydride was taken, whose preparation method can be learned with reference to Document 5 (ADUR ASHOK M; TARANEKAR PRASAD. Olefin-Maleic Anhydride Copolymer Compositions and Uses Thereof: CN 104736643 A [P]. 2015), 2.0 g polyvinylidene fluoride was taken, and 380 g NMP was taken as the solvent. The dispersing agents were pre-dissolved in NMP, then the conductive carbon material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube/graphene composite conductive slurry C1.

EXAMPLE 10

(15) In this example, 8 g carbon nanotube and 8 g graphene material were taken as the conductive carbon materials, 0.8 g polyvinylpyrrolidone was taken, 1.2 g epoxy-modified polyvinyl alcohol was taken, 2.0 g polyvinylidene fluoride was taken, and 380 g NMP was taken as the solvent. The dispersing agents were pre-dissolved in NMP, then the conductive carbon materials were added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube/graphene composite conductive slurry C2.

EXAMPLE 11

(16) In this example, 6.0 g carbon nanotube and 54.0 g conductive carbon black were taken as the conductive carbon materials, 6.0 g polyvinylpyrrolidone was taken, 6.0 g polyvinyl alcohol-maleic anhydride crosslinked polymer was taken, and 328 g NMP was taken as the solvent. The dispersing agents were pre-dissolved in NMP, then the conductive carbon materials were added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube/conductive carbon black composite conductive slurry Dl.

COMPARATIVE EXAMPLE 1

(17) In this example, 12 g carbon nanotube was taken as the conductive carbon material, 8 g dispersing agent was taken, and 380 g NMP was taken as the solvent. Polyvinylpyrrolidone was taken as the dispersing agent and pre-dissolved in NMP, then the conductive carbon material was added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube conductive slurry A0.

COMPARATIVE EXAMPLE 2

(18) In this example, 16 g graphene material was taken as the conductive carbon material, 4 g dispersing agent was taken, and 380 g NMP was taken as the solvent. Polyvinylidene fluoride was taken as the dispersing agent and pre-dissolved in NMP, then the conductive carbon materials were added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a graphene conductive slurry B0.

COMPARATIVE EXAMPLE 3

(19) In this example, 8 g carbon nanotube and 8 g graphene material were taken as the conductive carbon materials, 4 g dispersing agent was taken, and 380 g NMP was taken as the solvent. 2.0 g polyvinylpyrrolidone and 2.0 g polyvinylidene fluoride were taken as the dispersing agents and were pre-dissolved in NMP, the conductive carbon materials were added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube/graphene composite conductive slurry C0.

COMPARATIVE EXAMPLE 4

(20) In this example, 6.0 g carbon nanotube and 54.0 g of conductive carbon black were taken as the conductive carbon materials, 12.0 g polyvinylpyrrolidone was taken, and 328 g NMP was taken as the solvent. The dispersing agent was pre-dissolved in NMP, then the conductive carbon materials were added, mechanical stirring and pre-dispersing was carried out for 10 min, and sanding and dispersing were carried out further for 1.5 h to obtain a carbon nanotube/conductive carbon black composite conductive slurry D0.

(21) In order to further verify the application situation of the conductive slurry in the lithium battery, the positive electrode mixed slurry of the lithium ion battery with different positive electrode main material systems was prepared and coated on a PET film, after being dried at high temperature, the bulk resistivity of the pole piece was tested by a four-probe method, and the difference of the conductivity of the pole piece under different formulas was obtained. The process specifically includes:

(22) 1) dissolving a typical lithium battery adhesive in a solvent, adding an appropriate amount of the conductive slurry in the above-mentioned Examples 1-10 and Comparative Examples 1-4 according to a conventional formula, and stirring and mixing at a low speed to obtain a mixed slurry;

(23) 2) adding a positive electrode active material (taking a nickel-cobalt-manganese ternary material NCM or a lithium iron phosphate material LFP as an example) into the mixed slurry, and uniformly dispersing at a high speed to obtain a positive electrode slurry;

(24) 3) coating the obtained positive electrode slurry on a polyethylene terephthalate (PET) film by using an automatic film coating machine with a 200 um scraper, and then drying at high temperature to obtain a positive electrode pole piece; and 4) cutting the pole piece by using a wafer punching machine, compacting by using a pressing machine, testing the bulk resistivity of the pole piece by using a four-probe tester, testing two pieces to obtain of six groups of data, and averaging.

(25) The exemplary NCM and LFP positive electrode system formulas in bulk resistivity testing are recommended formulas in downstream market applications, specifically as follows in Table 1:

(26) TABLE-US-00001 TABLE 1 Conductive PVDF Slurries of the carbon (Polyvinylidene Examples are LFP material fluoride) applicable 95.25% 1.00% 3.50% All the slurries NCM Conductive PVDF Slurries of all the carbon (Polyvinylidene Examples of the material fluoride) present invention are applicable 98.50% 0.40% 1.00% A0-A5 98.06% 0.75% 1.00% B0-B3, C0-C2, D0-D1

(27) The bulk resistivities of the above Examples 1-11 were as follows in Table 2 and Table 3:

(28) TABLE-US-00002 TABLE 2 Positive Graphene (GRN) electrode Carbon nanotube (CNT) conductive slurry conductive slurry material Types A1 A2 A3 A4 A5 B1 B2 B3 LFP Dosage 1.0% 1.0% 1.0% 1.0% 1.0%  1.0%  1.0%  1.0% Bulk 14.84 7.42 13.24 11.56 10.25 20.75 17.68 20.54 resistivity NCM Dosage 0.4% 0.4% 0.4% 0.4% 0.4% 0.75% 0.75% 0.75% Bulk 16.64 13.21 15.48 10.18 15.28 25.62 19.72 23.22 resistivity

(29) TABLE-US-00003 TABLE 3 Carbon Positive nanotube/ CNT/GRN compound carbon black electrode slurry compound slurry material Types C1 C2 D1 LFP Dosage 1.0% 1.0% 1.0% Bulk 13.52 8.85 54.72 resistivity NCM Dosage 0.75% 0.75% 0.75% Bulk 13.28 12.42 164.56 resistivity

(30) The bulk resistivities of the corresponding Comparative Examples 1-4 were shown in Table 4 below:

(31) TABLE-US-00004 TABLE 4 Positive electrode material Types A0 B0 C0 D0 LFP Dosage 1.0% 1.0% 1.0% 1.0% Bulk resistivity 22.62 30.82 21.26 80.34 NCM Dosage 0.4% 0.75% 0.75% 0.75% Bulk resistivity 22.75 32.48 20.71 216.4

(32) It can be learned from the data in the above tables that:

(33) compared with the carbon nanotube conductive slurry AO in Comparative Example 1, the bulk resistivities of Al-A4 in Examples 1-4 were reduced by 34.39%, 67.20%, 41.47% and 48.90% in the LFP system and by 26.86%, 41.93%, 31.96% and 55.25% in the NCM system, respectively. The conductivity data proved that: with the same carbon nanotube material, the dispersing agent provided by the present invention plays a key role in the performance of the conductive slurry prepared by sanding; when the product is used for a lithium battery positive electrode system, the positive electrode pole piece prepared by using the dispersing agent provided by the present invention has superior conductivity. As for the slurry A5 prepared in Example 5 by ultrasonic sanding, the bulk resistivity was also reduced by 54.69% and 22.08% in the NCM and LFP systems, respectively, which indicates that the dispersing agent of the present invention also has an excellent effect on the ultrasonic dispersion slurry preparation process.

(34) Compared with the graphene conductive slurry BO in Comparative Example 2, the bulk resistivities of B 1-B2 in Examples 5-7 were reduced by 32.67%, 42.63% and 33.35% in the LFP system and by 21.12% and 39.29% in the NCM system, respectively. The conductivity data proved that: with the same graphene material, the dispersing agent disclosed by the present invention plays a key role in the performance of the conductive slurry prepared by sanding; when the product is used for a lithium battery positive electrode system, the positive electrode pole piece prepared by using the dispersing agent disclosed by the invention has superior conductivity. As for the slurry B3 prepared in Example 8 by ultrasonic sanding, the bulk resistivity was also reduced by 30.15% and 36.76% in the NCM and LFP systems, respectively, which indicates that the novel dispersing agent also had excellent effect on the ultrasonic dispersion slurry preparation process.

(35) Compared with the carbon nanotube and graphene composite conductive slurry CO in Comparative Example 3, the bulk resistivities of C1-C2 in Examples 9-10 were reduced by 36.41% and 58.37% in the LFP system and by 35.88% and 40.03% in the NCM system, respectively. The conductivity data proved that: with the same carbon material, the dispersing agent of the present invention plays a key role in the performance of the conductive slurry prepared by sanding; when the product is used for a lithium battery positive electrode system, the positive electrode pole piece prepared by using the dispersing agent of the present invention has superior conductivity.

(36) Compared with the carbon nanotube and graphene compounded conductive slurry DO in Comparative Example 4, the bulk resistivity of the slurry D1 in Example 11 was reduced by 31.89% and 31.50% in the LFP and NCM systems respectively. The conductivity data proved that: with the same carbon material, the dispersing agent of the present invention plays a key role in the performance of the conductive slurry prepared by sanding; when the product is used for a lithium battery positive electrode system, the positive pole piece prepared by using the dispersing agent disclosed by the present invention has superior conductivity.

(37) In summary of the above Examples, the application of the novel conductive slurry as a conductive additive in a positive electrode system of a lithium battery shows a remarkable gain effect on reducing the pole piece bulk resistivity, and also proves the superiority of the high-conductivity conductive slurry prepared according to the dispersing agent formula in the Examples.

(38) As can be seen from the scanning electron micrographs (SEM) of FIGS. 1-3, the conductive slurry prepared in the above Examples was well dispersed and the conductive carbon materials were well dispersed from each other without significant agglomeration. When applied to a positive electrode system, the conductive carbon material can be uniformly coated on the surface of the positive electrode main material, an advance three-dimensional conductive network can be effectively constructed after the pole piece is compacted, so that the conductive performance of the positive electrode main material originally with poor conductivity can be remarkably enhanced, and the overall performance of the lithium battery is improved. In addition, it is noteworthy that the internal resistance of the lithium battery, which is caused by different factors including but not limited to the conductivity of the positive pole piece, cannot be equal to the resistivity of the positive pole piece, but an improved conductivity of the positive pole piece is beneficial to reducing the internal resistance of the lithium battery.

(39) It is to be noted that the above-mentioned Examples are only those mentioned, the dispersing agent still has a gain effect on carbon material conductive slurry prepared separately or in combination with other carbon materials such as carbon black, and the excellent effect exhibited by the conductive slurry is not limited to the application in the above-mentioned NCM/LFP positive electrode system, but should include the lithium cobaltate (LCO) system and other positive electrode systems.

(40) The above-mentioned examples are merely preferred embodiments of the present invention, and the scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions falling within the spirit of the present invention fall within the scope of the present invention. It should be noted that those skilled in the art will appreciate that various modifications and adaptations can be made without departing from the spirit and scope of the present invention.