An acrylic copolymer, composition thereof and use thereof

Abstract

The present application relates to an acrylic copolymer, a composition and application thereof, the copolymer is prepared by polymerization of monomers; the monomers include carboxylic acid containing carbon-carbon double bond, acrylonitrile, styrene, acrylamide, acrylic ester, itaconic acid diester and amphiphilic monomer containing carbon-carbon double bond; the amphiphilic monomer containing carbon-carbon double bond includes one or more of acrylic polyether phosphate, diisooctyl maleate, allyloxy nonylphenol polyoxyethylene ether, 2-acrylamido-2-methylpropane sulfonic acid.The acrylic copolymer of one embodiment of the present application can be used as a dispersant for single-walled carbon nanotubes, and can make the single-walled carbon nanotubes have a good dispersion state in water.

Description

Technical Field

[0001] This invention relates to acrylic copolymers, and more particularly to an acrylic copolymer capable of improving the dispersibility of single-walled carbon nanotubes. Background Technology

[0002] Lithium-ion batteries are widely used in smartphones, tablets, automobiles, and other fields. A lithium-ion battery consists of a positive electrode, a negative electrode, a separator, an electrolyte, and a casing. The negative electrode material is developing towards higher energy density, upgrading from graphite to silicon-based negative electrodes. The theoretical capacity of silicon-based negative electrodes is approximately 3758 mAh / g, 10 times that of commercially available graphite. Because the lithium storage mechanism of elemental silicon is a typical alloying / dealloying mechanism in lithium-ion batteries, the huge lithium insertion / extraction capacity and the complex phase transition of LixSi cause severe volume expansion (nearly 300%) and structural changes in silicon negative electrode materials during lithium insertion / extraction. This volume expansion can cause cracks and even pulverization in silicon-based negative electrode materials, disrupting the electrical contact between active materials, electrode materials, and current collectors, increasing internal resistance, and causing rapid capacity decay.

[0003] Single-walled carbon nanotubes (SWNTs) are a novel nanomaterial with excellent electrical conductivity and mechanical properties. Structurally, their high aspect ratio allows for the formation of a good three-dimensional conductive network with minimal addition, while also suppressing the expansion of silicon anodes. However, as a highly kinetic conductive additive, SWNTs face two major challenges when applied to silicon anodes: firstly, their strong hydrophobicity makes them difficult to disperse in water; secondly, their poor compatibility with binders poses a risk of precipitation in the slurry. Current research largely focuses on dispersing SWNTs in water by grafting modified hydrophilic functional groups, but this method easily disrupts the conductive network of SWNTs. Dispersants prepared through physical interactions, when highly hydrophilic, readily exist in the aqueous phase due to the strong van der Waals forces between carbon nanotubes, leading to re-agglomeration; conversely, when highly hydrophobic, they exist within the carbon nanotube aggregates, failing to achieve stable existence. Therefore, balancing the hydrophilicity and hydrophobicity of dispersants and developing SWNT dispersants is crucial for the large-scale application of SWNTs in anodes. Summary of the Invention

[0004] To overcome at least one of the defects of the prior art, in a first aspect, one embodiment of the present invention provides an acrylic copolymer, which is obtained by polymerization of a polymerizable monomer; the polymerizable monomer includes carboxylic acids containing carbon-carbon double bonds, acrylonitrile, styrene, acrylamide, acrylates, itaconic acid diesters, and amphiphilic monomers containing carbon-carbon double bonds;

[0005] The amphiphilic monomer containing carbon-carbon double bonds includes one or more of polyether phosphate acrylate, diisooctyl maleate, allyloxynonylphenol polyoxyethylene ether, and 2-acrylamido-2-methylpropanesulfonic acid.

[0006] In a second aspect, one embodiment of the present invention provides a composition of an acrylic copolymer comprising the above-described acrylic copolymer and a crosslinking agent, wherein the crosslinking agent comprises a bifunctional diacylpropidine compound.

[0007] Thirdly, one embodiment of the present invention provides the application of the above-mentioned acrylic copolymer or a composition of the above-mentioned acrylic copolymer as a dispersant for single-walled carbon nanotubes or in the preparation of lithium battery anodes.

[0008] Fourthly, one embodiment of the present invention provides a single-walled carbon nanotube dispersion comprising the above-mentioned acrylic copolymer or a composition of the above-mentioned acrylic copolymer and single-walled carbon nanotubes.

[0009] Fifthly, one embodiment of the present invention provides a negative electrode slurry comprising the above-described acrylic copolymer composition or the above-described single-walled carbon nanotube dispersion.

[0010] Sixthly, one embodiment of the present invention provides a negative electrode sheet, the raw materials for which include the above-mentioned negative electrode slurry.

[0011] In a seventh aspect, one embodiment of the present invention provides a lithium battery including the negative electrode sheet described above.

[0012] An acrylic copolymer of one embodiment of the present invention can be used as a dispersant for single-walled carbon nanotubes, enabling single-walled carbon nanotubes to have a good dispersion state in water. Detailed Implementation

[0013] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the description herein is for illustrative purposes only and not intended to limit the present invention.

[0014] One embodiment of the present invention provides an acrylic copolymer, which is obtained by polymerization of polymerizable monomers; wherein the polymerizable monomers include carboxylic acids containing carbon-carbon double bonds, acrylonitrile, styrene, acrylamide, acrylates, itaconic acid diesters, and amphiphilic monomers containing carbon-carbon double bonds;

[0015] Amphiphilic monomers containing carbon-carbon double bonds include one or more of polyether acrylate, diisooctyl maleate, allyloxynonylphenol polyoxyethylene ether, and 2-acrylamido-2-methylpropanesulfonic acid.

[0016] In one embodiment, the mass content of carboxylic acid containing carbon-carbon double bonds is 30-40% based on the total mass of the polymerized monomers, for example, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, or 39%.

[0017] In one embodiment, the acrylonitrile content is 20-35% based on the total mass of the polymerizable monomers, for example, 21%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, or 34%.

[0018] In one embodiment, the styrene content is 5-10% by mass, for example, 6%, 7%, 8%, or 9%, based on the total mass of the polymerized monomers.

[0019] In one embodiment, the acrylamide content is 8-12% by mass, based on the total mass of the polymerizing monomers, for example, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, or 11.5%.

[0020] In one embodiment, the mass content of acrylate is 15-20% based on the total mass of the polymerized monomers, for example, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, or 19.5%.

[0021] In one embodiment, the itaconic acid diester content is 4-8% based on the total mass of the polymerized monomers, for example, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, or 7.5%.

[0022] In one embodiment, the mass content of the amphiphilic monomer containing carbon-carbon double bonds is 2-6% based on the total mass of the polymerizable monomers, for example, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, and 5.5%.

[0023] In one embodiment, the amphiphilic monomer containing a carbon-carbon double bond can be one or more of polyether acrylate, diisooctyl maleate, allyloxynonphenol polyoxyethylene ether, and 2-acrylamido-2-methylpropanesulfonic acid. Further, the weight-average molecular weight of the polyether acrylate can be 200–3000, for example, 300, 500, 600, 800, 1000, 1500, 2000, or 2500; the weight-average molecular weight of the allyloxynonphenol polyoxyethylene ether can be 200–3000, for example, 300, 500, 600, 800, 1000, 1500, 2000, or 2500.

[0024] In one embodiment, the carboxylic acid containing a carbon-carbon double bond comprises 3 to 6 carbon atoms (e.g., 4 carbon atoms, 5 carbon atoms), and further, the carboxylic acid containing a carbon-carbon double bond comprises one carbon-carbon double bond and one or two carboxyl groups.

[0025] In one embodiment, the carboxylic acid containing a carbon-carbon double bond includes one or more of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid.

[0026] In one embodiment, the acrylate includes one or more of ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, hexyl acrylate, hexyl methacrylate, isooctyl acrylate, and isooctyl methacrylate.

[0027] In one embodiment, itaconic acid diester may be itaconic acid dibutyl ester.

[0028] One embodiment of the present invention provides a composition of an acrylic copolymer comprising the above-described acrylic copolymer and a crosslinking agent, wherein the crosslinking agent comprises a bifunctional diacylpropidine compound.

[0029] In one embodiment, the crosslinking agent is present in the composition at a mass content of 0.2% to 0.5%, for example, 0.3% or 0.4%, based on the total mass of the polymerized monomers of the acrylic copolymer.

[0030] In one embodiment, the bifunctional bisacrylidine compound comprises two nitrogen heterocyclic structures and at least two trifluoromethyl groups. For example, the bifunctional bisacrylidine compound may be 3,3'-((perfluoropropane-2,2-diyl)bis(4,1-phenylene)-3H-diazacyclobutane) as shown in Formula 1 and / or bis(2-((4-(3-(trifluoromethyl)-3H-diazacyclo-3-yl)benzyl)oxy)ethyl)amine as shown in Formula 2.

[0031]

[0032] In one embodiment, the acrylic copolymer composition includes an acrylic copolymer, a crosslinking agent, and water; that is, the acrylic copolymer composition is a solution or dispersion containing an acrylic copolymer and a crosslinking agent.

[0033] In one embodiment, the composition of the acrylic copolymer is an aqueous solution or aqueous dispersion containing the acrylic copolymer and a crosslinking agent, wherein the nonvolatile matter content or solute content can be 2 to 6 wt%, for example 3 wt%, 4 wt%, or 5 wt%; and the pH value can be 7 to 9, for example 8.

[0034] One embodiment of the present invention provides a single-walled carbon nanotube dispersion comprising the above-mentioned acrylic copolymer and single-walled carbon nanotubes.

[0035] In one embodiment, the single-walled carbon nanotube dispersion comprises the above-described acrylic copolymer composition and single-walled carbon nanotubes.

[0036] In one embodiment, the single-walled carbon nanotube dispersion can be used to prepare the negative electrode sheet of a lithium battery.

[0037] In one embodiment, the mass content of single-walled carbon nanotubes in the single-walled carbon nanotube dispersion can be 0.2-0.4%, for example, 0.3%; the mass content of acrylic copolymers can be 0.4-0.8%, for example, 0.5%, 0.6%, or 0.7%.

[0038] One embodiment of the present invention provides the application of the above-mentioned acrylic copolymers or compositions thereof as dispersants for single-walled carbon nanotubes or in the preparation of lithium battery anode slurries.

[0039] In one embodiment of the acrylic copolymer, the carboxylic acid structure containing a carbon-carbon double bond provides strong hydrophilicity, the acrylate structure forms a strong adsorption with single-walled carbon nanotubes, and the amphiphilic structure containing a carbon-carbon double bond acts as a thickener to improve the stability of the dispersion. Simultaneously, during the preparation of the acrylic copolymer, the amphiphilic monomer containing a carbon-carbon double bond also acts as an emulsifier in the early stages of the reaction. Specifically, the carboxylic acid structure containing a carbon-carbon double bond is formed after the polymerization of a carboxylic acid containing a carbon-carbon double bond, the acrylate structure is formed after the polymerization of an acrylate, and the amphiphilic structure containing a carbon-carbon double bond is formed after the polymerization of an amphiphilic monomer containing a carbon-carbon double bond.

[0040] One embodiment of the present invention provides a method for preparing the above-mentioned acrylic copolymer, comprising: mixing a pre-emulsion with an initiator to carry out a polymerization reaction; wherein the pre-emulsion comprises a polymeric monomer.

[0041] One embodiment of the present invention provides a method for preparing the above-mentioned acrylic copolymer composition, comprising: mixing a pre-emulsion with an initiator to carry out a polymerization reaction; wherein the pre-emulsion comprises a bifunctional bisacrylidine compound comprising a polymerizing monomer and a crosslinking agent.

[0042] In one embodiment, the bifunctional diazinon-propidine crosslinking agent does not participate in the polymerization reaction of the monomer. It is added to the pre-emulsion for convenient subsequent use, or the crosslinking agent can be added after the polymerization reaction is completed.

[0043] In one embodiment, the method for preparing the acrylic copolymer includes the following steps:

[0044] S1: Mix the polymer monomer with water (e.g., deionized water) to prepare a preemulsion;

[0045] S2: Dissolve the initiator in water (e.g., deionized water) to obtain an initiator solution;

[0046] S3: Take a portion of the pre-emulsion and a portion of the initiator solution and add them to the reactor for bottom polymerization;

[0047] S4: Add the remaining preemulsion and the remaining initiator solution dropwise into the reactor for dropwise polymerization;

[0048] S5: Keep the solution obtained in step S4 at a warm temperature to eliminate residual monomers;

[0049] S6: Add alkali solution to the system in step S5 for neutralization to obtain a composition of dispersant acrylic copolymer.

[0050] In one embodiment, the reaction temperature in step S3 can be 80-90°C, for example 82°C, 84°C, 85°C, 86°C, or 88°C; and the reaction time can be 15-30 min, for example 18 min, 20 min, 22 min, or 25 min.

[0051] In one embodiment, the reaction temperature in step S4 can be 82-88°C, for example 82°C, 84°C, 85°C, or 86°C; and the reaction time can be 150-240 min, for example 160 min, 170 min, 180 min, 190 min, 200 min, or 220 min.

[0052] In one embodiment, the initiator is selected from one or more of potassium persulfate, sodium persulfate, and ammonium persulfate.

[0053] In one embodiment, the initiator content is 0.2-0.5% based on the total mass of the polymerizing monomers.

[0054] In one embodiment, the method for preparing the acrylic copolymer includes the following steps:

[0055] S1: Add the amphiphilic monomer containing carbon-carbon double bonds and deionized water to a pre-emulsification tank and dissolve them thoroughly. Add other polymerizable monomers while stirring for 10-30 minutes to obtain a pre-emulsion.

[0056] S2: Dissolve the initiator in water to prepare an initiator solution; wherein the mass ratio of initiator to water is 1:10-20, and 30-40% is used as the bottom initiator;

[0057] S3: Take 2-6% of the preemulsion obtained in step S1 and add it to the reactor. Heat the reactor to 80-90°C and simultaneously add the bottom initiator mentioned above. Keep the temperature for 15-30 minutes to carry out bottom polymerization.

[0058] S4: Control the reaction temperature of the reactor to 82-88℃, and add the remaining initiator and pre-emulsion dropwise into the reactor for dropwise polymerization. The dropwise addition time is 150-240 min.

[0059] S5: After the addition is complete, keep the system in the reactor at a constant temperature for 1-2 hours, filter and wash 2-3 times, and retain the filtered solid in the reactor.

[0060] S6: Add deionized water and lithium hydroxide monohydrate to the system in the reactor for neutralization, and adjust the non-volatile content to 2-6 wt% and the pH to 7-9.

[0061] One embodiment of the present invention provides a negative electrode slurry comprising the above-mentioned acrylic copolymer or a combination thereof or the above-mentioned single-walled carbon nanotube dispersion.

[0062] In one embodiment, the negative electrode slurry includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes silicon carbide and graphite, and the conductive agent includes a single-walled carbon nanotube dispersion.

[0063] In one embodiment, the binder may be a linear polyacrylic acid-based negative electrode binder, and the conductive agent may be a single-walled carbon nanotube dispersion or a mixture of a single-walled carbon nanotube dispersion and conductive carbon black.

[0064] One embodiment of the present invention provides a negative electrode sheet, the raw materials for which include the above-mentioned negative electrode slurry.

[0065] In one embodiment, a negative electrode sheet is prepared by coating a negative electrode slurry onto a current collector and then drying it. Further, the dried negative electrode sheet can be activated by passing an electric current through it. Under the influence of the current, a crosslinking agent inserts into adjacent CH structures in the acrylic copolymer, causing molecular crosslinking and generating carbene radicals to initiate curing. This leads to bonding with the current collector, thereby increasing the interaction force between the negative electrode current collector (e.g., copper foil) and the negative electrode active material.

[0066] In one embodiment, the current collector can be either copper foil or carbon-coated copper foil.

[0067] One embodiment of the present invention provides a lithium battery including the negative electrode sheet described above.

[0068] An acrylic copolymer or composition thereof, according to one embodiment of the present invention, can be used as a dispersant for single-walled carbon nanotubes (SUVs), enabling SUVs to exhibit good dispersion (e.g., uniform dispersion) in water. Specifically, the carbon chain structure of the itaconic acid diester in the acrylic copolymer exhibits a strong interaction with the SUVs, allowing the carbon chain to enter the SUV clusters and weakening the van der Waals interactions between carbon nanotubes under the influence of hydrophilic groups. Therefore, the itaconic acid diester structure can compensate for the insufficient adhesion between other structures of the acrylic copolymer and SUVs, achieving strong adhesion and thus enabling uniform dispersion and good stability of SUVs in the aqueous phase.

[0069] Existing dispersants used in electrode slurries are mostly small molecule dispersants, which are easily oxidized and reduced in lithium batteries, leading to a decline in electrical performance. An acrylic copolymer dispersant of one embodiment of the present invention has a strong hydrophilic and single-walled carbon nanotube-friendly structure, which enables the single-walled carbon nanotubes to have a good dispersion state in water, thereby improving the performance of the prepared negative electrode sheet.

[0070] An embodiment of the present invention provides an acrylic copolymer composition in which the acrylic copolymer exhibits good water solubility; the bifunctional bisacrylidine compound generates carbene radicals under electro-excitation, which not only interact with adjacent CH structures to form strong cohesion, but also bond with the current collector of the electrode to form good adhesion. Therefore, the single-walled carbon nanotube dispersion containing this composition has good dispersion effect, and after preparing the electrode sheet using this dispersion, the adhesion between the cured electrode slurry layer and the current collector can be significantly improved by electro-activation.

[0071] The negative electrode slurry of one embodiment of the present invention can improve the performance of the prepared negative electrode and the overall performance of the lithium battery by using a single-walled carbon nanotube dispersion.

[0072] An acrylic copolymer according to one embodiment of the present invention, when applied to the preparation of lithium-ion battery silicon-based negative electrode sheets, can uniformly disperse single-walled carbon nanotubes, thereby giving the negative electrode sheet a better state and stronger peeling force.

[0073] The preparation and application of an acrylic copolymer composition according to one embodiment of the present invention will be further described below with reference to examples. The raw materials and testing methods involved in each example and comparative example are as follows.

[0074] raw material

[0075]

[0076]

[0077] Test methods

[0078] 1. Test of non-volatile content in single-walled carbon nanotube dispersions

[0079] Prepare a weighing dish with an aluminum foil diameter of 5 cm and a height of approximately 3 cm. Maintain constant weight in an oven, cool to room temperature in a desiccator, and record its mass as m0, accurate to 0.1 mg. Weigh (2 ± 0.05) g of the test sample into the weighing dish with the same precision, recording it as m1 (the sample mass is generally (1 ± 0.05) g). Distribute the sample evenly on the bottom of the weighing dish. Then place the weighing dish containing the sample into a preheated oven at 150°C. Start timing after the temperature recovers and dry for 40 minutes. Remove the sample, cool it to room temperature in a desiccator, and record its mass as m2.

[0080] The content of nonvolatile matter X in the upper or lower liquid of the dispersion is:

[0081] X = (m2 - m0) / m1 × 100%.

[0082] X represents the mass fraction (%) of non-volatile matter in the sample;

[0083] m0 is the mass of the weighing dish, in grams;

[0084] m1 is the mass of the sample weighed, in grams;

[0085] m2 is the mass of the sample and weighing dish after heating, in grams.

[0086] 2. Test of 180° peel force of negative electrode sheet

[0087] The negative electrode sheet obtained after coating and drying is cut into strips of 1.5cm × 20cm. Using rollers, it is then coated at a speed of 1×10... 5 The load of N / m was applied twice, and the electrode was attached to a 2mm thick steel plate with double-sided tape. The coated side of the slurry after curing was attached to the steel plate. The coating was peeled off in the 180° direction using a tensile testing machine at a speed of 50mm / min to obtain the peel force before electro-activation.

[0088] After coating and drying, the negative electrode sheet is activated by a 2V voltage for 2 minutes, and the peel force is tested using the above method to obtain the peel force after electro-activation.

[0089] Example

[0090] Preparation of compositions (dispersants) of acrylic copolymers

[0091] S1: At room temperature and pressure, add Ag amphiphilic monomer containing carbon-carbon double bonds and 150g deionized water to a pre-emulsification vessel and mix thoroughly to dissolve. While stirring, add Bg acrylate, Cg dibutyl itaconic acid, Dg acrylamide, Eg acrylonitrile, Fg styrene, Gg carboxylic acid containing carbon-carbon double bonds, and Hg crosslinking agent in sequence. Stir at 350rpm for 15min to obtain a pre-emulsion.

[0092] S2: Dissolve 1g of potassium persulfate in 19g of deionized water. After stirring and dissolving, take 8g as the bottom initiator for bottom polymerization and 12g as the dropwise polymerization initiator.

[0093] S3: At room temperature and pressure, add 40g of deionized water to the reactor, heat to 85℃, add 5% of the total mass of the pre-emulsion obtained in step S1 to the reactor, and quickly add the 8g of initiator solution prepared in step S2. Keep the reactor warm for 20min.

[0094] S4: Control the reaction temperature to 85℃, and simultaneously add the remaining pre-emulsion and the initiator prepared in step S2 to the reaction vessel. The total addition time is 180 minutes.

[0095] S5: After the addition is complete, keep the reactor at 85℃ for 1 hour, filter and wash 2-3 times, and retain the filtered solid in the reactor.

[0096] S6: When the temperature of the reactor system drops to 75℃, add lithium hydroxide monohydrate solution to adjust the pH of the system to 7-9, add deionized water to adjust the content of non-volatile substances in the system to 4%, and stir for 30 minutes to obtain acrylic copolymer dispersant.

[0097] Preparation of single-walled carbon nanotube dispersions

[0098] Single-walled carbon nanotubes, the aforementioned acrylic copolymer dispersant, and deionized water were mixed to obtain a carbon nanotube dispersion slurry with a non-volatile content of 1 wt%. The mass percentages of carbon nanotubes and dispersant solids in the slurry were 0.4 wt% and 0.6 wt%, respectively. After stirring, the dispersion slurry was subjected to ultrasonic treatment at a frequency of 20 Hz using a cell disruptor. After 4 hours, the mixture was filtered to obtain a single-walled carbon nanotube dispersion.

[0099] Preparation of negative electrode sheet

[0100] (1) Based on solid mass, 0.5 parts by mass of conductive carbon black, 9 parts by mass of SiC, 88 parts by mass of graphite, 100 parts by mass of deionized water, 0.5 parts by mass of single-walled carbon nanotube dispersion and 2 parts by mass of polyacrylic acid solution binder are mixed and stirred at a high speed of 2000 r for 30 min to obtain negative electrode slurry.

[0101] (2) The filtered negative electrode slurry is uniformly coated on the surface of the copper foil current collector with a coating thickness of 300 micrometers; then, the current collector coated with negative electrode slurry is placed in a 90°C oven and dried for 5 minutes to obtain the negative electrode sheet.

[0102] Examples 1-17 all used the above process to prepare dispersants (composed of acrylic copolymers), single-walled carbon nanotube dispersions and negative electrode sheets. The difference lies in the types and amounts of raw materials used, as detailed in Table 1.

[0103] Comparative Examples 1-4

[0104] Comparative Examples 1-4 used the same raw materials and processes as the above examples to prepare dispersants, single-walled carbon nanotube dispersions and negative electrode sheets. The difference was that the types and amounts of raw materials used were different, as detailed in Table 2.

[0105] The single-walled carbon nanotube dispersions prepared in each example and comparative example were diluted 500 times with deionized water. The presence of obvious particles in the water was observed; the presence of obvious particles indicated poor dispersibility, while the absence of obvious particles indicated good dispersion. Specific results are shown in Table 3. The single-walled carbon nanotube dispersions prepared in each example and comparative example were allowed to stand at room temperature for 14 days (14d), and then diluted 500 times with deionized water. The presence of obvious particles in the water was observed again. The results are shown in Table 3.

[0106] After the single-walled carbon nanotube dispersions prepared in each embodiment and comparative example were allowed to stand at room temperature for 14 days, the non-volatile content in the upper and lower parts of the dispersions was measured according to the aforementioned method. The results are shown in Table 3.

[0107] The negative electrode sheets prepared in each embodiment and comparative example were tested for peel strength according to the aforementioned method, and the results are shown in Table 3.

[0108] Table 1. Raw materials and amounts (g) used in each embodiment.

[0109]

[0110]

[0111] Table 2. Raw materials and amounts (g) used in each comparative example.

[0112]

[0113] Table 3. Stability, peeling force, and electrode plate test results of single-walled carbon nanotube dispersions.

[0114]

[0115]

[0116] As shown in Table 3, after 14 days of standing, the non-volatile matter content of the upper and lower liquids of the single-walled carbon nanotube dispersions prepared in Examples 1-17 was not significantly different, indicating that the dispersions did not exhibit significant floating or settling and had good storage stability. Furthermore, the dilution states (good permeability, no particles) of the dispersions after 0 days and 14 days of standing in Table 3 indicate that the single-walled carbon nanotube dispersions have good dispersibility and long-term storage stability; the surface state of the negative electrode sheet indicates that the negative electrode slurry has good dispersibility.

[0117] Furthermore, according to the peel force data before and after electro-activation in Table 3, the peel force of the negative electrode sheets in Examples 1 to 17 is significantly improved after electro-activation.

[0118] As shown in Tables 1 and 2, compared to Example 2, Comparative Example 1 used propylene carbonate instead of dibutyl itaconic acid. Table 3 shows that the dispersion of Comparative Example 1 contained a large number of insoluble particles after standing for 14 days, indicating poor stability. Therefore, the acrylic copolymer using dibutyl itaconic acid monomer has a better dispersing effect on single-walled carbon nanotubes than the acrylic copolymer using propylene carbonate monomer under the same conditions.

[0119] Furthermore, the amount of dibutyl itaconic acid in Comparative Example 2 was relatively low, accounting for only 2.4% of the polymeric monomer mass. According to the results in Table 3, after standing for 14 days, the non-volatile matter content in the upper and lower parts of the dispersion in Comparative Example 2 differed significantly, and a large number of insoluble particles appeared, indicating poor dispersibility and stability. Therefore, the amount of dibutyl itaconic acid significantly affects the dispersibility and stability of the dispersion. Preferably, based on the total mass of the polymeric monomers, the mass content of dibutyl itaconic acid is 4–8%.

[0120] As shown in Tables 1 and 2, Comparative Example 3 did not use an amphiphilic monomer containing carbon-carbon double bonds, unlike Example 2. Table 3 shows that after standing for 14 days, the non-volatile matter content in the upper and lower parts of the dispersion in Comparative Example 3 differed significantly, and a large number of insoluble particles appeared, indicating poor dispersibility and stability. Therefore, the use of amphiphilic monomers containing carbon-carbon double bonds has a significant impact on the dispersibility and stability of the dispersion.

[0121] As shown in Tables 1 and 2, compared with Example 15, Comparative Example 4 used N,N-methylenebisacrylamide instead of bisacrylamide as the crosslinking agent. According to the results in Table 3, the peel force of the negative electrode sheets of Example 15 and Comparative Example 4 was similar before electroactivation. However, after electroactivation, the peel force of the electrode sheet of Example 15 increased significantly, while the peel force of the electrode sheet of Comparative Example 4 changed less. This indicates that the bisacrylamide compound in Example 15 underwent crosslinking under electroactivation, providing stronger adhesion to the electrode sheet.

[0122] In summary, the acrylic copolymer composition of the present invention can achieve uniform dispersion of single-walled carbon nanotubes in an aqueous phase, and the dispersion has excellent long-term storage stability. At the same time, it has strong interaction with both the current collector and the active material under electrical action, thereby improving the peeling force of the prepared electrode sheet.

[0123] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0124] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. A composition of an acrylic copolymer, comprising an acrylic copolymer and a crosslinking agent; wherein, The crosslinking agent includes a difunctional bisacrylidine compound; the acrylic copolymer is obtained by polymerization of a monomer; the monomer includes carboxylic acids containing carbon-carbon double bonds, acrylonitrile, styrene, acrylamide, acrylates, itaconic acid diesters, and amphiphilic monomers containing carbon-carbon double bonds; The amphiphilic monomer containing a carbon-carbon double bond includes one or more of polyether acrylate and allyloxynonylphenol polyoxyethylene ether; the carboxylic acid containing a carbon-carbon double bond comprises 3 to 4 carbon atoms, one carbon-carbon double bond and one carboxyl group; Based on the total mass of the polymerizable monomers, the mass content of the carboxylic acid containing carbon-carbon double bonds is 30-40%, the mass content of the acrylonitrile is 20-35%, the mass content of the styrene is 5-10%, the mass content of the acrylamide is 8-12%, the mass content of the acrylate is 15-20%, the mass content of the itaconic acid diester is 4-8%, and the mass content of the amphiphilic monomer containing carbon-carbon double bonds is 2-6%. Based on the total mass of the polymeric monomers, the crosslinking agent in the composition has a mass content of 0.2% to 0.5%.

2. The composition according to claim 1, wherein, The carboxylic acids containing carbon-carbon double bonds include one or more of acrylic acid, methacrylic acid, and crotonic acid; and / or, The acrylates include one or more of ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, hexyl acrylate, hexyl methacrylate, isooctyl acrylate, and isooctyl methacrylate; and / or, The itaconic acid diester includes itaconic acid dibutyl ester.

3. The composition according to claim 1, wherein, The composition comprises the acrylic copolymer, the crosslinking agent, and water; and / or, The bifunctional diazinoniden compounds include one or two of the following compounds: 、 。 4. The composition of the acrylic copolymer according to any one of claims 1 to 3, used as a dispersant for single-walled carbon nanotubes or for the preparation of lithium battery anodes.

5. A single-walled carbon nanotube dispersion comprising the composition of the acrylic copolymer according to any one of claims 1 to 3 and single-walled carbon nanotubes.

6. A negative electrode slurry comprising a composition of an acrylic copolymer according to any one of claims 1 to 3 or a single-walled carbon nanotube dispersion according to claim 5.

7. A negative electrode sheet, wherein the raw materials for its preparation include the negative electrode slurry as described in claim 6.

8. A lithium battery comprising the negative electrode sheet as described in claim 7.

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