Modified polyacrylic acid, water-based edge coating slurry, preparation method of water-based edge coating slurry and current collector

Abstract

The invention provides modified polyacrylic acid, water-based edge coating slurry, a preparation method of the water-based edge coating slurry and a current collector. The modified polyacrylic acid comprises a polymer matrix and boron nitride nanosheets dispersed in the polymer matrix, the polymer matrix includes an acrylic acid derived structural unit and an acrylate derived structural unit. The modified polyacrylic acid has excellent thermal viscosity and insulativity, and when the modified polyacrylic acid is applied to current collector slurry, a water-based edge coating scheme with co-thermal viscosity and high insulativity can be realized.

Description

Technical Field

[0001] This invention relates to the field of current collector technology, and more particularly to a modified polyacrylic acid, an aqueous edge coating slurry, a preparation method thereof, and a current collector. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, transportation, power tools, and energy storage. Aluminum foil current collectors are composite materials formed by combining aluminum foil with other materials such as paper, plastic film, and coatings.

[0003] To improve lithium battery performance, the lithium battery industry employs a carbon-coated current collector strategy to increase the rate of operation and overall performance. However, to enhance the safety of the current collector, a ceramic edge-coating technique is used to coat the edges of the carbon-coated current collector. This edge-coating involves applying a ceramic slurry to the edges of the carbon-coated current collector, and this technique has the following significant implications for lithium battery manufacturing:

[0004] (1) Safety: Directly reduces the risk of battery short circuit and thermal runaway, meeting the high safety standards of power batteries (such as electric vehicles).

[0005] (2) Lifetime improvement: Reduce edge side reactions (such as lithium plating and corrosion) and extend cycle life.

[0006] (3) High energy density design: By edge protection, electrode thickness or material system can be optimized more aggressively.

[0007] Therefore, the core purpose of carbon coating the edge of the current collector is to "eliminate edge risks and improve battery reliability and performance". It is one of the key steps in the detailed optimization of battery manufacturing, especially important in high-end applications such as power batteries and high-nickel systems.

[0008] Conventional edge coating slurries often consider factors such as coating thickness, insulation, and miscibility, neglecting the adhesion between the edge coating and the electrode. This adhesion is no less than that of the positive electrode active material, referring to the thermal adhesion of the dry electrode sheet. The dry electrode sheet and the carbon-coated current collector are typically bonded together using a hot press. The carbon-coated current collector of the dry electrode has thermal adhesion, and after hot pressing, it adheres to the electrode sheet. If the edge coating does not have thermal adhesion, the electrode is highly susceptible to detachment at the edge coating after hot pressing, which could lead to battery safety issues.

[0009] Furthermore, when selecting the adhesive solution for dry electrodes in the edge coating slurry, the particle size of boehmite in the adhesive solution is smaller than that of carbon black, making the slurry prone to dispersion difficulties. Even if the dispersion problem is solved by dispersant, the dry electrode adhesive solution will still result in weak adhesion between the edge coating and the substrate, and may even cause powdering.

[0010] Therefore, developing a new water-based edge coating slurry is of great significance. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention provides a modified polyacrylic acid, a water-based edge coating slurry, its preparation method, and a current collector. By modifying the acrylic acid monomer with flexible monomers and boron nitride nanosheets, a water-based edge coating slurry that combines thermal adhesion and high insulation is achieved, with broad application prospects.

[0012] To achieve this objective, the present invention adopts the following technical solution:

[0013] In a first aspect, the present invention provides a modified polyacrylic acid comprising a polymer matrix and boron nitride nanosheets dispersed in the polymer matrix. The polymer matrix comprises acrylic acid-derived structural units and acrylate-derived structural units.

[0014] The modified polyacrylic acid provided by this invention introduces flexible monomers of acrylate into polyacrylic acid, disrupting the rigidity of the polyacrylic acid molecular chain, lowering the glass transition temperature, and causing it to soften upon heating and exhibit thermal bonding properties. Simultaneously, nano-boron nitride (BN) is uniformly dispersed in the polyacrylic acid, utilizing the high insulation and low dielectric constant of BN to construct a charge-blocking layer, suppressing conductivity loss and improving the insulation of the modified polyacrylic acid, resulting in an adhesive that combines insulating and thermal bonding properties.

[0015] The modified polyacrylic acid obtained by this invention is used as a binder in edge coating slurry. The resulting coating can achieve strong adhesion under heating and pressure conditions, and also has excellent insulation properties, providing a feasible material for water-based edge coating schemes for dry electrodes.

[0016] Specifically, the principle of BN modification is as follows:

[0017] (1) BN has a graphene-like layered structure, but the strong polarity of BN bonds (the ionic bond content is about 30%) makes its band gap as wide as ~6eV, which is much higher than that of graphite (0eV), and it is almost non-conductive.

[0018] (2) After the boron nitride nanosheets are uniformly dispersed in the PAA matrix, they form a continuous insulating network, which forces the charge migration path to become tortuous and significantly increases the resistance.

[0019] (3) The low dielectric constant of BN (ε≈4) can neutralize the high ε (~5-6) of the polar carboxyl group of PAA, so that the overall ε of the composite material is reduced to 3.5~4.5, reducing the dielectric loss at high frequencies.

[0020] Preferably, the molar ratio of acrylate-derived structural units to acrylic acid-derived structural units in the polymer matrix is ​​(0.6~1.5):1, for example, it can be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] The present invention preferably controls the molar ratio of acrylate-derived structural units to acrylic acid-derived structural units within the range of (0.6~1.5):1, thereby better improving the thermal bonding performance of modified polyacrylic acid.

[0022] Preferably, the boron nitride nanosheets in the modified polyacrylic acid have a mass percentage content of 5-15 wt%, for example, 5 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] The present invention preferably controls the content of boron nitride nanosheets within the above-mentioned range, which can better improve the insulation of modified polyacrylic acid, while also taking into account the thermal bonding performance of modified polyacrylic acid.

[0024] Preferably, the acrylate-derived structural unit includes any one or a combination of at least two of butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, or hydroxyethyl acrylate, wherein typical but non-limiting combinations are combinations of butyl acrylate and ethyl acrylate, combinations of 2-ethylhexyl acrylate and ethyl acrylate, combinations of butyl acrylate and 2-ethylhexyl acrylate, and combinations of hydroxyethyl acrylate and ethyl acrylate.

[0025] Generally, the molecular chains of pure polyacrylic acid form a rigid structure due to the strong hydrogen bonding between carboxyl groups (-COOH) and the close arrangement of the polar backbone, with a glass transition temperature above 100°C. The present invention preferably uses the above-mentioned acrylate, which can provide alkyl side chains. The alkyl side chains can hinder the close packing of the PAA backbone, weaken the hydrogen bond network, and at the same time, the non-polar alkyl chains reduce the interaction forces between molecular chains and increase the free volume of chain segments. When the temperature rises to the glass transition temperature of the copolymer, the units of butyl acrylate promote molecular chain slip, and the material changes from a glassy state to a highly elastic / viscous flow state. The softened copolymer chains can penetrate into the micropores on the surface of the bonded materials to form a mechanical interlock.

[0026] Preferably, the boron nitride nanosheets are boron nitride nanosheets modified with silane coupling agents.

[0027] This invention uses boron nitride nanosheets modified with silane coupling agent. The improved interfacial compatibility between BN and PAA reduces interfacial defects and prevents charge accumulation at the interface, thereby further improving insulation performance.

[0028] Preferably, the lateral dimension of the boron nitride nanosheet is 0.5~2μm, for example, it can be 0.5μm, 0.7μm, 0.9μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.7μm, 1.9μm or 2μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] The present invention preferably has boron nitride nanosheets with lateral dimensions within the above-mentioned range. When the size of the boron nitride nanosheets is too small, there are problems such as difficulty in dispersion and easy agglomeration. When the size of the boron nitride nanosheets is too large, the coating surface is rough and the flatness is relatively low. Large-sized sheets are prone to protruding from the surface in thin coatings, forming microscopic protrusions and scratches, which affect the appearance and density of the coating.

[0030] Preferably, the thickness of the boron nitride nanosheet is 10~50nm, for example, it can be 10nm, 15nm, 19nm, 24nm, 28nm, 33nm, 37nm, 42nm, 46nm or 50nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] In a second aspect, the present invention provides a method for preparing the modified polyacrylic acid described in the first aspect, the method comprising the following steps:

[0032] (1) Mix acrylic acid, acrylate monomer and emulsifier to obtain a pre-emulsion.

[0033] (2) Mix the pre-emulsion and the initiator to carry out the polymerization reaction and obtain the polymer matrix.

[0034] (3) Mix the boron nitride nanosheet dispersion and the polymer matrix described in step (2), and then modify the mixture to obtain the modified polyacrylic acid.

[0035] The preparation method provided by the second aspect of the present invention can produce the modified polyacrylic acid described in the first aspect. The modified polyacrylic acid can take into account both thermal bonding performance and insulation performance, and its application in dry electrodes can effectively improve the safety and stability of batteries.

[0036] Preferably, the mixing in step (1) includes mixing water, acrylic monomer, acrylate monomer and emulsifier, and then subjecting the mixture to a first ultrasonic treatment to obtain a pre-emulsion.

[0037] Preferably, the power of the first ultrasound is 200~500W, for example, it can be 200W, 230W, 260W, 300W, 330W, 360W, 400W, 430W, 460W or 500W, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the duration of the first ultrasound is 5 to 15 minutes, for example, it can be 5 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, the mass ratio of the acrylate monomer to the polyacrylic acid is (0.6~1.5):1, for example, it can be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the mass ratio of the emulsifier to polyacrylic acid is (0.05~0.1):1, for example, it can be 0.05:1, 0.056:1, 0.062:1, 0.067:1, 0.073:1, 0.078:1, 0.084:1, 0.089:1, 0.095:1 or 0.1:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] Preferably, the emulsifier comprises any one or a combination of at least two of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, sodium fatty alcohol polyoxyethylene ether sulfate, or sodium allyloxyhydroxypropyl sulfonate, wherein typical but non-limiting combinations are the combination of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate, the combination of octylphenol polyoxyethylene ether and sodium dodecylbenzene sulfonate, the combination of sodium dodecyl sulfate and octylphenol polyoxyethylene ether, and the combination of sodium fatty alcohol polyoxyethylene ether sulfate and sodium allyloxyhydroxypropyl sulfonate.

[0042] Preferably, the mass ratio of water to acrylic monomer in step (1) is (3~15):1, for example, it can be 3:1, 5:1, 6:1, 7:1, 9:1, 10:1, 11:1, 13:1, 14:1 or 15:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the mixing and polymerization reaction in step (2) includes: mixing water and the first part of the pre-emulsion, heating to the first reaction temperature, adding an initiator, adding the second part of the pre-emulsion, heating to the second reaction temperature after the addition is complete, terminating the polymerization reaction, and then precipitating and purifying to obtain the polymer matrix.

[0044] Preferably, the mass ratio of the first part of the preemulsion to the second part of the preemulsion is (0.8~1):1, for example, it can be 0.8:1, 0.83:1, 0.85:1, 0.87:1, 0.89:1, 0.92:1, 0.94:1, 0.96:1, 0.98:1 or 1:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the range of the first reaction temperature is 60~80℃, for example, it can be 60℃, 63℃, 65℃, 67℃, 69℃, 72℃, 74℃, 76℃, 78℃ or 80℃, etc., but is not limited to the listed values, and other unlisted values ​​in this range are also applicable.

[0046] Preferably, the initiator comprises any one or a combination of at least two of ammonium persulfate, potassium persulfate, sodium persulfate, or azobisisobutyronitrile, wherein typical but non-limiting combinations are a combination of ammonium persulfate and potassium persulfate, a combination of sodium persulfate and potassium persulfate, a combination of ammonium persulfate and sodium persulfate, or a combination of azobisisobutyronitrile and potassium persulfate.

[0047] Preferably, the amount of the initiator added accounts for 0.2 to 0.5 wt% of the pre-emulsion, for example, it can be 0.2 wt%, 0.24 wt%, 0.27 wt%, 0.3 wt%, 0.34 wt%, 0.37 wt%, 0.4 wt%, 0.44 wt%, 0.47 wt%, or 0.5 wt%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the second reaction temperature ranges from 60 to 80°C, for example, it can be 60°C, 63°C, 65°C, 67°C, 69°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, the dripping time of the second part of the pre-emulsion is 2 to 3 hours, for example, it can be 2 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, nitrogen gas is introduced into both the mixing and polymerization reactions in step (2) to remove oxygen.

[0051] Preferably, the polymerization reaction lasts for 3 to 5 hours, for example, 3 hours, 3.3 hours, 3.5 hours, 3.7 hours, 3.9 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, or 5 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] Preferably, the mixing of water and the first pre-emulsion comprises: first adding water to the reactor and then introducing nitrogen to remove oxygen, and then adding the first pre-emulsion.

[0053] Preferably, hydroquinone is used as the terminating agent for the polymerization reaction.

[0054] Preferably, the precipitation purification includes placing the reaction solution after the polymerization reaction in an organic solvent to precipitate a precipitate, and then washing and drying the precipitate to obtain a polymer matrix.

[0055] Preferably, the organic solvent includes ethanol.

[0056] Preferably, the washing process uses ethanol.

[0057] Preferably, the washing is performed at least twice.

[0058] Preferably, the drying is vacuum drying.

[0059] Preferably, the drying temperature is 50~60℃, for example, it can be 50℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃ or 60℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0060] Preferably, the drying time is 18 to 30 hours, for example, it can be 18 hours, 20 hours, 21 hours, 22 hours, 24 hours, 25 hours, 26 hours, 28 hours, 29 hours or 30 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0061] Preferably, the vacuum degree of the drying process is 50 kPa to 200 kPa, for example, it can be 50 kPa, 60 kPa, 80 kPa, 100 kPa, 110 kPa, 130 kPa, 150 kPa, 160 kPa, 180 kPa or 200 kPa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0062] Preferably, the boron nitride nanosheets in the boron nitride nanosheet dispersion in step (3) have a mass percentage content of 3 to 5 wt%, for example, 3 wt%, 3.3 wt%, 3.5 wt%, 3.7 wt%, 3.9 wt%, 4.2 wt%, 4.4 wt%, 4.6 wt%, 4.8 wt%, or 5 wt%, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0063] Preferably, the preparation of the boron nitride nanosheet dispersion includes:

[0064] (3.1) Boron nitride nanosheets were dispersed in a silane coupling agent solution and dried to obtain silane coupling agent modified boron nitride nanosheets.

[0065] (3.2) Disperse the silane coupling agent modified boron nitride nanosheets obtained in step (3.1) in water to obtain a boron nitride nanosheet dispersion.

[0066] Preferably, the solvent of the silane coupling agent solution in step (3.1) includes ethanol and water.

[0067] Preferably, the mass ratio of ethanol to water in the solvent of the silane coupling agent solution is (7.5~9):1, for example, it can be 7.5:1, 7.7:1, 7.9:1, 8:1, 8.2:1, 8.4:1, 8.5:1, 8.7:1, 8.9:1 or 9:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0068] Preferably, the pH of the silane coupling agent solution is 4 to 5, for example, it can be 4, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0069] Preferably, the mass fraction of the silane coupling agent in the silane coupling agent solution is 0.5-2.0%, for example, it can be 0.5%, 0.7%, 0.9%, 1%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9% or 2.0%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0070] Preferably, the mass ratio of the boron nitride nanosheets to the silane coupling agent is (9~10):1, for example, it can be 9:1, 9.2:1, 9.3:1, 9.4:1, 9.5:1, 9.6:1, 9.7:1, 9.8:1, 9.9:1 or 10:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0071] Preferably, the dispersion in step (3.1) includes ultrasonic dispersion.

[0072] Preferably, the power of ultrasonic dispersion in step (3.1) is 250~320W, for example, it can be 250W, 258W, 266W, 274W, 282W, 289W, 297W, 305W, 313W or 320W, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0073] Preferably, the ultrasonic dispersion time in step (3.1) is 0.8~1.2h, for example, it can be 0.8h, 0.85h, 0.89h, 0.94h, 0.98h, 1.03h, 1.07h, 1.12h, 1.16h or 1.2h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0074] Preferably, the dispersion in step (3.2) includes ultrasonic dispersion.

[0075] Preferably, the power of ultrasonic dispersion in step (3.2) is 250~320W, for example, it can be 250W, 258W, 266W, 274W, 282W, 289W, 297W, 305W, 313W or 320W, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0076] Preferably, the ultrasonic dispersion time in step (3.2) is 0.8~1.2h, for example, it can be 0.8h, 0.85h, 0.89h, 0.94h, 0.98h, 1.03h, 1.07h, 1.12h, 1.16h or 1.2h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0077] Preferably, the modification process in step (3) includes mechanical stirring, ultrasonic treatment, and then casting the mixture into a mold for drying to obtain modified polyacrylic acid.

[0078] Preferably, the mechanical stirring speed is 500~600 rpm, for example, it can be 500 rpm, 510 rpm, 520 rpm, 530 rpm, 540 rpm, 550 rpm, 560 rpm, 570 rpm, 580 rpm or 600 rpm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0079] Preferably, the mechanical stirring treatment time is 1.8 to 2.5 hours, for example, it can be 1.8 hours, 1.9 hours, 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours or 2.5 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0080] Preferably, the power of the ultrasonic treatment in the modification process is 250~320W, for example, it can be 250W, 258W, 266W, 274W, 282W, 289W, 297W, 305W, 313W or 320W, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0081] Preferably, the ultrasonic treatment time in the modification process is 0.8 to 1 hour, for example, it can be 0.8 hours, 0.83 hours, 0.85 hours, 0.87 hours, 0.89 hours, 0.92 hours, 0.94 hours, 0.96 hours, 0.98 hours or 1 hour, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0082] Preferably, the drying temperature in the modification treatment is 50~60℃, for example, it can be 50℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃ or 60℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0083] Preferably, the drying time in the modification treatment is 18 to 30 hours, for example, it can be 18 hours, 20 hours, 21 hours, 22 hours, 24 hours, 25 hours, 26 hours, 28 hours, 29 hours or 30 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0084] As a preferred embodiment of the present invention, the preparation method of the modified polyacrylic acid includes the following steps:

[0085] (1) First, the acrylic monomer is subjected to vacuum distillation at 70~90℃ and 0.005~0.02 bar to remove the polymerization inhibitor. Then, water, acrylic monomer, acrylate monomer and emulsifier are mixed in a mass ratio of (3~15):1:(0.6~1.5):(0.05~0.1), and then subjected to a first ultrasonic treatment at 200~500W for 5~15min to obtain a pre-emulsion.

[0086] The emulsifier includes any one or a combination of at least two of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, sodium fatty alcohol polyoxyethylene ether sulfate, or sodium allyloxyhydroxypropyl sulfonate.

[0087] (2) First, purge the container with nitrogen for 25-40 minutes to remove oxygen from the container. Then, mix water and the first part of the pre-emulsion and heat to the first reaction temperature of 60-80°C. Add the initiator dropwise at a ratio of 0.2-0.5 wt% of the initiator to the pre-emulsion. Then, slowly add the second part of the pre-emulsion dropwise over 2-3 hours. The mass ratio of the first part of the pre-emulsion to the second part of the pre-emulsion is (0.8-1):1. Continue to purge with nitrogen. After the addition is complete, heat to the second reaction temperature of 60-80°C and carry out the polymerization reaction for 3-5 hours. Add hydroquinone as a terminator to terminate the polymerization reaction. Place the reaction solution after the polymerization reaction in ethanol to precipitate the precipitate. Wash the precipitate with ethanol at least twice and vacuum dry it at 50-60°C and 50-200 kPa for 18-30 hours to obtain the polymer matrix.

[0088] (3) Mix ethanol and water in a mass ratio of 7.5 to 9:1, adjust the pH to 4 to 5 with acetic acid, and then add silane coupling agent to the above solution to obtain a silane coupling agent solution with a mass fraction of 0.5 to 2.0%; vacuum dry boron nitride nanosheets at 100 to 130°C for 1 to 4 hours to remove surface adsorbed water; then disperse boron nitride nanosheets in the silane coupling agent solution in a mass ratio of 9 to 10:1, using ultrasonic dispersion at 250 to 320 W for 0.8 to 1.2 hours, and dry to obtain silane coupling agent modified boron nitride nanosheets.

[0089] The obtained silane coupling agent-modified boron nitride nanosheets were dispersed in water by ultrasonic dispersion at 250-320 W for 0.8-1.2 h to obtain a boron nitride nanosheet dispersion. The polymer matrix was added to water, and the pH was adjusted to 7-8 with sodium hydroxide to obtain a polymer matrix solution with a polymer matrix content of 5-15 wt%.

[0090] The boron nitride nanosheet dispersion and the polymer matrix solution are mixed and mechanically stirred at 500-600 rpm for 1.8-2.5 h, then ultrasonically treated at 250-320 W for 0.8-1 h. The mixture is then cast into a polytetrafluoroethylene mold and dried at 50-60°C for 18-30 h to obtain the modified polyacrylic acid.

[0091] Thirdly, the present invention provides an aqueous edge coating slurry, wherein the aqueous edge coating slurry comprises the modified polyacrylic acid described in the first aspect.

[0092] The water-based edge coating slurry provided in the third aspect of the present invention includes the modified polyacrylic acid described in the first aspect, thereby improving the safety and stability of the battery when applied in a dry electrode, and has broad application prospects.

[0093] Preferably, the aqueous edge coating slurry further includes a dispersant, an insulating material, and a wetting agent. The dispersant includes any one or a combination of at least two of ethylenediaminetetraacetic acid (EDTA), polyvinyl chloride (PVP), fatty alcohol polyoxyethylene ether (FAE), sodium polyacrylate, or oxalic acid. Typical but non-limiting combinations include EDTA and PVP, fatty alcohol FAE and PVP, EDTA and fatty alcohol FAE, sodium polyacrylate and PVP, and EDTA and oxalic acid.

[0094] Preferably, the insulating material comprises any one or a combination of at least two of boehmite, alumina, magnesium oxide, barium sulfate, or PET, wherein typical but non-limiting combinations are combinations of boehmite and alumina, magnesium oxide and alumina, boehmite and barium sulfate, PET and alumina, and boehmite and PET.

[0095] Preferably, the wetting agent comprises any one or a combination of at least two of polyether siloxanes, modified polyether siloxanes, or alcohols, wherein typical but non-limiting combinations are combinations of polyether siloxanes and modified polyether siloxanes, combinations of alcohols and modified polyether siloxanes, and combinations of polyether siloxanes and alcohols.

[0096] Preferably, the dispersant accounts for 1 to 3 wt% of the mass of the insulating material, for example, it can be 1 wt%, 1.3 wt%, 1.5 wt%, 1.7 wt%, 1.9 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, or 3 wt%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0097] The present invention preferably uses a dispersant with a mass percentage content within the above-mentioned range, which can better improve the dispersion effect of the insulating material, thereby improving the adhesion stability of the current collector coating and the electrochemical stability of the battery.

[0098] Preferably, the content of insulating material in the water-based edge coating slurry is 60~80wt%, for example, it can be 60wt%, 62wt%, 63wt%, 65wt%, 67wt%, 68wt%, 70wt%, 72wt%, 75wt%, 78wt%, or 80wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0099] Preferably, the content of wetting agent in the water-based edge coating slurry is 5~15wt%, for example, it can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0100] Preferably, the modified polyacrylic acid content in the water-based edge coating slurry is 7~25wt%, for example, it can be 7wt%, 8wt%, 9wt%, 10wt%, 12wt%, 14wt%, 15wt%, 18wt%, 19wt%, 20wt%, 22wt%, or 25wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0101] Fourthly, the present invention provides a method for preparing the water-based edge coating slurry described in the third aspect, the method comprising: mixing modified polyacrylic acid, water, dispersant and insulating material, adjusting the pH, adding a wetting agent, and then homogenizing to obtain the water-based edge coating slurry.

[0102] Preferably, the mixed modified polyacrylic acid, water, dispersant, and insulating material comprises:

[0103] S1, mix water and modified polyacrylic acid to obtain the first mixture.

[0104] S2. Mix the first mixture and the dispersant, and then disperse them to obtain the second mixture.

[0105] S3. Mix the second mixture and the first part of the insulating material, and then disperse them in the second way to obtain the third mixture.

[0106] S4. The third mixture and the second insulating material are mixed and dispersed in the third stage to obtain the fourth mixture.

[0107] S5, mix water and the fourth mixture, and then disperse it in the fourth stage to obtain the fifth mixture.

[0108] Preferably, the solid content in the first mixture in step S1 is 15~25wt%, for example, it can be 15wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt% or 25wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0109] Preferably, the viscosity of the first mixture in step S1 is 800~3000 mPa·s, for example, it can be 800 mPa·s, 1040 mPa·s, 1280 mPa·s, 1530 mPa·s, 1770 mPa·s, 2020 mPa·s, 2260 mPa·s, 2510 mPa·s, 2750 mPa·s or 3000 mPa·s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0110] The present invention preferably has a viscosity of the first mixture within the above-mentioned range, which can balance the adhesive performance and the coating uniformity.

[0111] Preferably, the first dispersion includes dispersion using a double-star stirred tank.

[0112] Preferably, the rotational speed of the first dispersion is 200~600 rpm, for example, it can be 200 rpm, 245 rpm, 280 rpm, 330 rpm, 370 rpm, 420 rpm, 460 rpm, 510 rpm, 550 rpm or 600 rpm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0113] Preferably, the first dispersion time is 20 to 40 minutes, for example, it can be 20 minutes, 23 minutes, 25 minutes, 27 minutes, 29 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes or 40 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0114] Preferably, the mass ratio of the first part of the insulating material to the second part of the insulating material is (1~1.2):1, for example, it can be 1.0:1, 1.03:1, 1.05:1, 1.07:1, 1.09:1, 1.12:1, 1.14:1, 1.16:1, 1.18:1 or 1.2:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0115] Preferably, the second dispersion includes dispersion using a twin-star stirred tank.

[0116] Preferably, the second dispersion speed is 2000~2600 rpm, for example, it can be 2000 rpm, 2060 rpm, 2100 rpm, 2200 rpm, 2260 rpm, 2330 rpm, 2400 rpm, 2460 rpm, 2530 rpm or 2600 rpm, but is not limited to the listed values, other unlisted values ​​in this range are also applicable.

[0117] Preferably, the second dispersion time is 30 to 40 minutes, for example, it can be 30 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes or 40 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0118] Preferably, the third dispersion includes dispersion using a double-star stirred tank.

[0119] Preferably, the rotational speed of the third dispersion is 2000~2600 rpm, for example, it can be 2000 rpm, 2060 rpm, 2100 rpm, 2200 rpm, 2260 rpm, 2330 rpm, 2400 rpm, 2460 rpm, 2530 rpm or 2600 rpm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0120] Preferably, the third dispersion time is 20 to 40 minutes, for example, it can be 20 minutes, 23 minutes, 25 minutes, 27 minutes, 29 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes or 40 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0121] Preferably, the fourth dispersion includes dispersion using a double-star stirred tank.

[0122] Preferably, the rotational speed of the fourth dispersion is 2000~2600 rpm, for example, it can be 2000 rpm, 2060 rpm, 2100 rpm, 2200 rpm, 2260 rpm, 2330 rpm, 2400 rpm, 2460 rpm, 2530 rpm or 2600 rpm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0123] Preferably, the fourth dispersion time is 30 to 45 minutes, for example, it can be 30 minutes, 32 minutes, 34 minutes, 35 minutes, 37 minutes, 39 minutes, 40 minutes, 42 minutes, 44 minutes or 45 minutes, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0124] Preferably, the pH adjuster is a sodium hydroxide solution.

[0125] Preferably, the pH adjustment is to 8-9, for example, 8, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0126] Preferably, the fifth dispersion is carried out after the addition of the wetting agent.

[0127] Preferably, the fifth dispersion includes dispersion using a double-star stirred tank.

[0128] Preferably, the rotational speed of the fifth dispersion is 10~15 rpm, for example, it can be 10 rpm, 11 rpm, 12 rpm, 13 rpm, 14 rpm or 15 rpm, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0129] Preferably, the fifth dispersion time is 30 to 45 minutes, for example, it can be 30 minutes, 32 minutes, 34 minutes, 35 minutes, 37 minutes, 39 minutes, 40 minutes, 42 minutes, 44 minutes or 45 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0130] Preferably, the homogenization pressure is 600~800 bar, for example, it can be 600 bar, 620 bar, 645 bar, 660 bar, 680 bar, 710 bar, 730 bar, 750 bar, 770 bar or 800 bar, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0131] Preferably, the homogenization process is performed at least twice, for example, twice, three times, four times, five times, six times, seven times, eight times, nine times, or ten times.

[0132] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0133] S1, mixed with water and modified polyacrylic acid, yields a first mixture with a solid content of 15-25 wt% and a viscosity of 800-3000 mPa·s.

[0134] S2. Mix the first mixture and the dispersant, and disperse them in a double-star mixing tank at 200-600 rpm for 20-40 minutes to obtain the second mixture.

[0135] S3. Mix the second mixture and the first part of the insulating material, and disperse them in a double-star mixing tank at 2000~2600rpm for 30~40min to obtain the third mixture.

[0136] S4. Mix the third mixture and the second insulating material, and disperse them in a double-star mixing tank at 2000~2600 rpm for 20~40 min to obtain the fourth mixture. The mass ratio of the first insulating material to the second insulating material is 1~1.2:1.

[0137] S5, mix water and the fourth mixture, and disperse in a double-star mixing tank at 2000~2600rpm for 30~45min to obtain the fifth mixture.

[0138] S6. Adjust the pH of the fifth mixture to 8-9 with sodium hydroxide solution, add wetting agent, and then disperse the fifth mixture in a double-star mixing tank at 10-15 rpm for 30-45 min. Then, perform homogenization treatment at 600-800 bar for at least 2 times to obtain water-based edge coating slurry.

[0139] Fifthly, the present invention provides a current collector, which is formed by coating the current collector substrate with the water-based edge coating slurry described in the third aspect.

[0140] Compared with the prior art, the present invention has at least the following beneficial effects:

[0141] (1) The modified polyacrylic acid provided by the present invention can have both thermal bonding performance and insulation properties through molecular structure regulation and nano-boron nitride composite.

[0142] (2) When the water-based edge coating slurry provided by the present invention is applied to the edge of the current collector substrate to form a coating, it can achieve a firm bond under heating and pressurization conditions, and at the same time has excellent insulation properties. The current collector prepared by the present invention can improve the adhesion between the coating and the substrate, reduce powder shedding, and improve the safety and stability of the electrode when applied in dry electrode, and has broad application prospects. Detailed Implementation

[0143] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0144] It should be understood that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0145] The silane coupling agent used in the following examples and comparative examples is available from Sinopharm Group, model KH550 (Shanghai Test), ≥98.0%, Sinopharm code 30213867. Boehmite is available from Sinopharm Group, model 3.4µm (Wokai), Sinopharm code XW01131823601.

[0146] Example 1

[0147] This embodiment provides a modified polyacrylic acid, which includes a polymer matrix and boron nitride nanosheets dispersed in the polymer matrix.

[0148] The polymer matrix comprises acrylic acid-derived structural units and butyl acrylate-derived structural units. The molar ratio of butyl acrylate-derived structural units to acrylic acid-derived structural units in the polymer matrix is ​​1:1.

[0149] The modified polyacrylic acid contains 10 wt% boron nitride nanosheets; the boron nitride nanosheets are silane coupling agent modified boron nitride nanosheets; the lateral dimensions of the boron nitride nanosheets are 0.6~0.8 μm, and the thickness is 12~18 nm.

[0150] This embodiment also provides a method for preparing the above-mentioned modified polyacrylic acid, the preparation method comprising the following steps:

[0151] (1) First, the acrylic monomer is subjected to vacuum distillation at 85°C and 0.01 bar to remove the polymerization inhibitor. Then, water, acrylic monomer, butyl acrylate monomer and emulsifier (sodium dodecyl sulfate) are mixed in a mass ratio of 10:1:1.0:0.08, and then subjected to a first ultrasonic treatment at 300W for 10 min to obtain a pre-emulsion.

[0152] (2) First, purge the container with nitrogen for 30 minutes to remove oxygen from the container. Then, mix water and the first part of the pre-emulsion and heat to the first reaction temperature of 70°C. Add the initiator (azobisisobutyronitrile) dropwise at 0.3wt% of the initiator in the pre-emulsion. Then, slowly add the second part of the pre-emulsion dropwise over 2.5 hours. The mass ratio of the first part of the pre-emulsion to the second part of the pre-emulsion is 0.9:1. Continue to purge with nitrogen. After the addition is complete, heat to the second reaction temperature of 70°C and carry out the polymerization reaction for 4 hours. Add hydroquinone as a terminator to terminate the polymerization reaction. Then, place the reaction solution after the polymerization reaction in ethanol to precipitate the precipitate. Wash the precipitate three times with ethanol and dry it under vacuum at 55°C and 100kPa for 20 hours to obtain the polymer matrix.

[0153] (3) Ethanol and water were mixed in a mass ratio of 8.5:1, and the pH was adjusted to 4.5 with acetic acid. Then, silane coupling agent (KH550) was added to the above solution to obtain a silane coupling agent solution with a mass fraction of 1.5%. Boron nitride nanosheets were vacuum dried at 120°C for 2 hours to remove surface adsorbed water. Boron nitride nanosheets were then dispersed in the silane coupling agent solution in a mass ratio of 9.5:1 to the silane coupling agent by ultrasonic dispersion at 300W for 1.0 hour and dried to obtain silane coupling agent modified boron nitride nanosheets.

[0154] The obtained silane coupling agent-modified boron nitride nanosheets were dispersed in water by ultrasonic dispersion at 300W for 1.0 h to obtain a boron nitride nanosheet dispersion. The polymer matrix was added to water, and the pH was adjusted to 7.5 with sodium hydroxide to obtain a polymer matrix solution with a polymer matrix content of 10 wt%.

[0155] The boron nitride nanosheet dispersion and the polymer matrix solution were mixed and mechanically stirred at 550 rpm for 2.2 h, then ultrasonically treated at 300 W for 0.9 h. The mixture was then cast into a polytetrafluoroethylene mold and dried at 55 °C for 20 h to obtain the modified polyacrylic acid.

[0156] Example 2

[0157] This embodiment provides a modified polyacrylic acid, which includes a polymer matrix and boron nitride nanosheets dispersed in the polymer matrix.

[0158] The polymer matrix comprises acrylic acid-derived structural units and amyl acrylate-derived structural units. The molar ratio of amyl acrylate-derived structural units to acrylic acid-derived structural units in the polymer matrix is ​​1.5:1 amyl acrylate.

[0159] The modified polyacrylic acid contains 5 wt% boron nitride nanosheets; the boron nitride nanosheets are silane coupling agent modified boron nitride nanosheets; the lateral dimensions of the boron nitride nanosheets are 0.5~1.0 μm, and the thickness is 10~15 nm.

[0160] This embodiment also provides a method for preparing the above-mentioned modified polyacrylic acid, the preparation method comprising the following steps:

[0161] (1) First, the acrylic monomer is subjected to vacuum distillation at 70°C and 0.02 bar to remove the polymerization inhibitor. Then, water, acrylic monomer, amyl acrylate monomer and emulsifier (sodium dodecylbenzene sulfonate) are mixed in a mass ratio of 15:1:1.5:0.1, and then subjected to a first ultrasonic treatment at 500W for 5 minutes to obtain a pre-emulsion.

[0162] (2) First, purge the container with nitrogen for 25 minutes to remove oxygen from the container. Then, mix water and the first part of the pre-emulsion and heat to the first reaction temperature of 60°C. Add the initiator (ammonium persulfate) dropwise at a ratio of 0.2 wt% of the initiator to the pre-emulsion. Then, slowly add the second part of the pre-emulsion dropwise over 2 hours. The mass ratio of the first part of the pre-emulsion to the second part of the pre-emulsion is 0.8:1. Continue to purge with nitrogen. After the addition is complete, heat to the second reaction temperature of 60°C and carry out the polymerization reaction for 5 hours. Add hydroquinone as a terminator to terminate the polymerization reaction. Then, place the reaction solution after the polymerization reaction in ethanol to precipitate the precipitate. Wash the precipitate twice with ethanol and dry it under vacuum at 50°C and 50 kPa for 30 hours to obtain the polymer matrix.

[0163] (3) Ethanol and water were mixed in a mass ratio of 7.5:1, and the pH was adjusted to 4 with acetic acid. Then, silane coupling agent (KH550) was added to the above solution to obtain a silane coupling agent solution with a mass fraction of 0.5%. Boron nitride nanosheets were vacuum dried at 100°C for 4 hours to remove surface adsorbed water. Boron nitride nanosheets were then dispersed in the silane coupling agent solution in a mass ratio of 10:1 to the silane coupling agent by ultrasonic dispersion at 320W for 0.8 hours and dried to obtain silane coupling agent modified boron nitride nanosheets.

[0164] The obtained silane coupling agent-modified boron nitride nanosheets were dispersed in water by ultrasonic dispersion at 320W for 0.8h to obtain a boron nitride nanosheet dispersion. The polymer matrix was added to water, and the pH was adjusted to 7 with sodium hydroxide to obtain a polymer matrix solution with a polymer matrix content of 15wt%.

[0165] The boron nitride nanosheet dispersion and the polymer matrix solution were mixed and mechanically stirred at 500 rpm for 2.5 h, then ultrasonically treated at 320 W for 0.8 h. The mixture was then cast into a polytetrafluoroethylene mold and dried at 50 °C for 30 h to obtain the modified polyacrylic acid.

[0166] Example 3

[0167] This embodiment provides a modified polyacrylic acid, which includes a polymer matrix and boron nitride nanosheets dispersed in the polymer matrix.

[0168] The polymer matrix comprises acrylic acid-derived structural units and butyl acrylate-derived structural units. The molar ratio of butyl acrylate-derived structural units to acrylic acid-derived structural units in the polymer matrix is ​​0.6:1 butyl acrylate.

[0169] The modified polyacrylic acid contains 15 wt% boron nitride nanosheets; the boron nitride nanosheets are silane coupling agent modified boron nitride nanosheets; the lateral dimensions of the boron nitride nanosheets are 1.5~2 μm, and the thickness is 30~50 nm.

[0170] This embodiment also provides a method for preparing the above-mentioned modified polyacrylic acid, the preparation method comprising the following steps:

[0171] (1) First, the acrylic monomer is subjected to vacuum distillation at 90℃ and 0.005 bar to remove the polymerization inhibitor. Then, water, acrylic monomer, butyl acrylate monomer and emulsifier (sodium allyl hydroxypropyl sulfonate) are mixed in a mass ratio of 3:1:0.6:0.05, and then subjected to sonication at 200W for 15 minutes to obtain a pre-emulsion.

[0172] (2) First, purge the container with nitrogen for 40 minutes to remove oxygen from the container. Then, mix water and the first part of the pre-emulsion and heat to the first reaction temperature of 80°C. Add the initiator (sodium persulfate) dropwise at a ratio of 0.5 wt% of the initiator to the pre-emulsion. Then, slowly add the second part of the pre-emulsion dropwise over 3 hours. The mass ratio of the first part of the pre-emulsion to the second part of the pre-emulsion is 1:1. Continue to purge with nitrogen. After the addition is complete, heat to the second reaction temperature of 80°C and carry out the polymerization reaction for 3 hours. Add hydroquinone as a terminator to terminate the polymerization reaction. Then, place the reaction solution after the polymerization reaction in ethanol to precipitate the precipitate. Wash the precipitate three times with ethanol and dry it under vacuum at 60°C and 200 kPa for 18 hours to obtain the polymer matrix.

[0173] (3) Ethanol and water were mixed at a mass ratio of 9:1, and the pH was adjusted to 5 with acetic acid. Then, silane coupling agent (KH550) was added to the above solution to obtain a silane coupling agent solution with a mass fraction of 2.0%. Boron nitride nanosheets were vacuum dried at 130°C for 1 h to remove surface adsorbed water. Then, boron nitride nanosheets were dispersed in the silane coupling agent solution at a mass ratio of 9:1 to boron nitride nanosheets. The dispersion method was ultrasonic dispersion at 250 W for 1.2 h, and then dried to obtain silane coupling agent modified boron nitride nanosheets.

[0174] The obtained silane coupling agent-modified boron nitride nanosheets were dispersed in water by ultrasonic dispersion at 250W for 1.2h to obtain a boron nitride nanosheet dispersion. The polymer matrix was added to water, and the pH was adjusted to 8 with sodium hydroxide to obtain a polymer matrix solution with a polymer matrix content of 5wt%.

[0175] The boron nitride nanosheet dispersion and the polymer matrix solution were mixed and mechanically stirred at 600 rpm for 1.8 h, then ultrasonically treated at 250 W for 1 h. The mixture was then cast into a polytetrafluoroethylene mold and dried at 60 °C for 18 h to obtain the modified polyacrylic acid.

[0176] Example 4

[0177] This embodiment provides a modified polyacrylic acid. Except for the molar ratio of butyl acrylate-derived structural units to acrylic acid-derived structural units in the polymer matrix being 2:1, the modified polyacrylic acid is the same as that in Example 1, and will not be repeated here.

[0178] Example 5

[0179] This embodiment provides a modified polyacrylic acid. Except for the molar ratio of butyl acrylate-derived structural units to acrylic acid-derived structural units in the polymer matrix being 0.5:1, the modified polyacrylic acid is the same as that in Example 1, and will not be repeated here.

[0180] Example 6

[0181] This embodiment provides a modified polyacrylic acid. Except for the boron nitride nanosheets in the modified polyacrylic acid having a mass percentage content of 1 wt%, the modified polyacrylic acid is the same as that in Example 1, and will not be repeated here.

[0182] Example 7

[0183] This embodiment provides a modified polyacrylic acid. Except for the boron nitride nanosheets in the modified polyacrylic acid having a mass percentage content of 20 wt%, the modified polyacrylic acid is the same as in Example 1, and will not be repeated here.

[0184] Example 8

[0185] This embodiment provides a modified polyacrylic acid. Except for replacing butyl acrylate with methyl acrylate, the modified polyacrylic acid is the same as in Example 1, and will not be repeated here.

[0186] Comparative Example 1

[0187] This comparative example provides a modified polyacrylic acid, which is the same as that in Example 1 except that boron nitride nanosheets are not added, and will not be described again here.

[0188] Comparative Example 2

[0189] This comparative example provides a modified polyacrylic acid, which is the same as that in Example 1 except that butyl acrylate is not added, and will not be described again here.

[0190] Comparative Example 3

[0191] This comparative example provides a polyacrylic acid. Except for the unmodified acrylic monomer, the rest is the same as in Example 1, and will not be repeated here.

[0192] Application Example 1

[0193] This application example provides an aqueous edge coating slurry, which includes modified polyacrylic acid, dispersant (EDTA), insulating material (boehmite powder), and wetting agent (isopropanol) provided in Example 1. The aqueous edge coating slurry contains 70 wt% insulating material, 10 wt% wetting agent, and 18.6 wt% modified polyacrylic acid. The dispersant accounts for 2 wt% of the mass of the insulating material.

[0194] This application example also provides a method for preparing the above-mentioned water-based edge coating slurry, the preparation method comprising the following steps:

[0195] S1, mixed with water and modified polyacrylic acid, yielded a first mixture with a solid content of 20 wt% and a viscosity of 2000 mPa·s.

[0196] S2. Mix the first mixture and the dispersant, and disperse them in a double-star mixing tank at 400 rpm for 30 min to obtain the second mixture.

[0197] S3. Mix the second mixture and the first part of the insulating material, and disperse them in a double-star mixing tank at 2200 rpm for 35 minutes to obtain the third mixture.

[0198] S4. The third mixture and the second insulating material are mixed and dispersed at 2200 rpm for 30 minutes in a double-star mixing tank to obtain the fourth mixture. The mass ratio of the first insulating material to the second insulating material is 1.1:1.

[0199] S5, mix water and the fourth mixture, and disperse in a double-star mixing tank at 2200 rpm for 35 min to obtain the fifth mixture.

[0200] S6. The fifth mixture is adjusted to pH 8.5 with sodium hydroxide solution, a wetting agent is added, and then the mixture is dispersed at 12 rpm for 35 min in a double-star mixing tank. Then it is homogenized at 700 bar for 3 times to obtain water-based edge coating slurry.

[0201] Application Example 2

[0202] This application example provides an aqueous edge coating slurry, which includes modified polyacrylic acid, dispersant (EDTA), insulating material (boehmite powder), and wetting agent (isopropanol) provided in Example 2. The aqueous edge coating slurry contains 60 wt% insulating material, 15 wt% wetting agent, and 23.2 wt% modified polyacrylic acid. The dispersant accounts for 3 wt% of the mass of the insulating material.

[0203] This application example also provides a method for preparing the above-mentioned water-based edge coating slurry, the preparation method comprising the following steps:

[0204] S1, mixed with water and modified polyacrylic acid, yielded a first mixture with a solid content of 25 wt% and a viscosity of 3000 mPa·s.

[0205] S2. Mix the first mixture and the dispersant, and disperse them in a double-star mixing tank at 600 rpm for 20 min to obtain the second mixture.

[0206] S3. Mix the second mixture and the first part of the insulating material, and disperse them in a double-star mixing tank at 2600 rpm for 30 minutes to obtain the third mixture.

[0207] S4. The third mixture and the second insulating material are mixed and dispersed at 2000 rpm for 40 minutes in a double-star mixing tank to obtain the fourth mixture. The mass ratio of the first insulating material to the second insulating material is 1.2:1.

[0208] S5, mix water and the fourth mixture, and disperse in a double-star mixing tank at 2600 rpm for 30 min to obtain the fifth mixture.

[0209] S6. The fifth mixture is adjusted to pH 8.0 with sodium hydroxide solution, a wetting agent is added, and then the mixture is dispersed at 15 rpm for 30 min in a double-star mixing tank. Then it is homogenized at 600 bar for 4 times to obtain the water-based edge coating slurry.

[0210] Application Example 3

[0211] This application example provides an aqueous edge coating slurry, which includes modified polyacrylic acid, dispersant (EDTA), insulating material (boehmite powder), and wetting agent (isopropanol) provided in Example 3. The aqueous edge coating slurry contains 80 wt% insulating material, 5 wt% wetting agent, and 14.2 wt% modified polyacrylic acid. The dispersant accounts for 1 wt% of the mass of the insulating material.

[0212] This application example also provides a method for preparing the above-mentioned water-based edge coating slurry, the preparation method comprising the following steps:

[0213] S1, mixed with water and modified polyacrylic acid, yielded a first mixture with a solid content of 15 wt% and a viscosity of 800 mPa·s.

[0214] S2. Mix the first mixture and the dispersant, and disperse them in a double-star mixing tank at 200 rpm for 40 min to obtain the second mixture.

[0215] S3. Mix the second mixture and the first part of the insulating material, and disperse them in a double-star mixing tank at 2000 rpm for 40 minutes to obtain the third mixture.

[0216] S4. The third mixture and the second insulating material are mixed and dispersed at 2600 rpm for 20 minutes in a double-star mixing tank to obtain the fourth mixture. The mass ratio of the first insulating material to the second insulating material is 1:1.

[0217] S5, mix water and the fourth mixture, and disperse in a double-star mixing tank at 2000 rpm for 45 minutes to obtain the fifth mixture.

[0218] S6. Adjust the pH of the fifth mixture to 9.0 with sodium hydroxide solution, add wetting agent, and then disperse the fifth mixture at 10 rpm for 45 min in a double-star mixing tank. Then, homogenize it at 800 bar twice to obtain water-based edge coating slurry.

[0219] Application Examples 4-8 and Comparative Examples 1-3

[0220] Application Examples 4-8 and Comparative Examples 1-3 provide an aqueous edge coating slurry. Except for the use of modified polyacrylic acid in Examples 4-8 and Comparative Examples 1-3, the aqueous edge coating slurry is the same as that in Application Example 1, and will not be described again here.

[0221] Application Example 9

[0222] This application example provides an aqueous edge coating slurry, which is the same as that in Application Example 1 except that the modified polyacrylic acid content is 30 wt%. It will not be described again here.

[0223] Application Example 10

[0224] This application example provides a water-based edge coating slurry. Except for the modified polyacrylic acid content of 5 wt%, the water-based edge coating slurry is the same as that in Application Example 1, and will not be described again here.

[0225] Application Example 11

[0226] This application example provides an aqueous edge coating slurry. Except for the dispersant accounting for 0.5 wt% of the mass of the insulating material, the aqueous edge coating slurry is the same as that in Application Example 1, and will not be described again here.

[0227] Application Example 12

[0228] This application example provides a water-based edge coating slurry. Except that the content of insulating material in the water-based edge coating slurry is 50 wt%, and the content of other substances is adjusted according to the proportion, the rest is the same as in application example 1, and will not be repeated here.

[0229] In the above application examples and comparative examples, the thickness of the single-sided insulating layer is 2μm and the coating width is 300mm. To test the sheet resistance and transmission resistance of the samples, several strips with a length and width of 20×5cm were taken, and the surface sheet resistance of the samples was tested using a four-probe sheet resistance meter. Then, the new strips were cut into small samples of 5×5cm, and the transmission resistance was tested under a film resistance meter, and the test data were recorded.

[0230] Hot-pressed electrode peel force: Take a 12×12cm current collector with edge coating and an identical 12×12cm electrode. Place the current collector and electrode under a hot press and hot press at 80℃. Then cut the hot-pressed electrode into 12×2cm samples. Attach the prepared samples to the test plate with 3M double-sided tape to separate the active material on the electrode from the edge coating. Attach the sample to the carbon-coated aluminum foil with adhesive tape and test the 180° electrode peel force on a tensile testing machine.

[0231] The test results of the above application examples and application comparison examples are shown in Table 1.

[0232] Table 1

[0233]

[0234] The following points can be observed from Table 1:

[0235] (1) As can be seen from the comprehensive application examples 1 to 3, when the modified polyacrylic acid provided by the present invention is applied to the water-based edge coating slurry, the sheet resistance and penetration resistance of the obtained electrode sheet are completely insulated, and the peel force is above 23 N / m, thus obtaining an electrode sheet with both insulation performance and high peel force.

[0236] (2) Comparing Application Example 1 and Application Examples 4-5, it can be seen that in Application Example 1, the molar ratio of butyl acrylate-derived structural units to acrylic acid-derived structural units is 1:1. Compared with the molar ratios of butyl acrylate-derived structural units to acrylic acid-derived structural units in Application Examples 4-5, which are 2:1 and 0.5:1 respectively, the sheet resistance and penetration resistance of the electrode sheet obtained in Application Example 1 are completely insulated, and the peel force is 25 N / m. The insulation performance of Application Examples 4-5 is reduced, and the peel forces are only 22 N / m and 10 N / m respectively. This shows that the present invention preferably controls the molar ratio of acrylate-derived structural units to acrylic acid-derived structural units within a reasonable range, which can better improve the thermal bonding performance and insulation performance.

[0237] (3) Comparing Application Example 1 and Application Examples 6-7, it can be seen that the mass percentage of boron nitride nanosheets in the modified polyacrylic acid in Application Example 1 is 10 wt%. Compared with the mass percentages of boron nitride nanosheets in the modified polyacrylic acid in Application Examples 4-5, which are 1 wt% and 20 wt% respectively, the sheet resistance and penetration resistance of the electrode sheet obtained in Application Example 1 are completely insulated, and the peel force is 25 N / m. The insulation performance of Application Examples 6-7 is significantly reduced, and the peel forces are only 21 N / m and 13 N / m respectively. This shows that the present invention preferably controls the mass percentage of boron nitride nanosheets within a reasonable range, which can better improve the thermal bonding performance and insulation performance.

[0238] (4) Comparing Application Example 1 and Application Example 8, it can be seen that in Application Example 8, butyl acrylate is replaced with methyl acrylate, which makes it difficult for the long-chain alkyl side chain to play its role in hindering the tight stacking of the PAA main chain. The insulation of the electrode sheet obtained in Application Example 8 is reduced, and the peeling force is also significantly reduced.

[0239] (5) Comparing Application Example 1 and Application Examples 9-10, it can be seen that the modified polyacrylic acid content in Application Example 1 is 18.6 wt%, compared with the modified polyacrylic acid content of 30 wt% and 5 wt% in Application Examples 9-10. The sheet resistance and penetration resistance of the electrode sheet obtained in Application Example 1 are completely insulated, and the peel force is 25 N / m. The insulation performance of Application Examples 9-10 is significantly reduced, and the peel force is only 16 N / m and 12 N / m respectively. This shows that the present invention preferably controls the content of modified polyacrylic acid in the water-based edge coating slurry within a reasonable range, which can better improve the thermal bonding performance and insulation performance.

[0240] (6) Comparing Application Example 1 and Application Examples 11-12, it can be seen that the present invention preferably controls the content of each component in the water-based edge coating slurry within a reasonable range, which can better improve the thermal bonding performance and insulation performance.

[0241] (7) In Comparative Example 1, the absence of boron nitride nanosheets resulted in a significant decrease in insulation performance and a drop in peel strength to 20 N / m after coating. In Comparative Example 2, the absence of butyl acrylate modification did not affect insulation performance, but the peel strength dropped significantly to 5 N / m. In Comparative Example 3, the unmodified polyacrylic acid was used directly, resulting in a significant decrease in both peel strength and insulation performance. This indicates that the polyacrylic acid modified with acrylate monomers and nano-boron nitride in this invention can significantly improve the insulation and thermal adhesion performance of water-based edge coating slurry.

[0242] In summary, when the water-based edge coating slurry provided by the present invention is applied to the edge of the current collector substrate to form a coating, it can achieve strong adhesion under heating and pressurization conditions, while also possessing excellent insulation properties; specifically, under preferred conditions, the sheet resistance and penetration resistance of the electrode sheet are completely insulated, and the peel force is above 20 N / m.

[0243] The present invention has been illustrated with the above embodiments to illustrate its detailed features, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected technical features, additions of auxiliary technical features, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A modified polyacrylic acid, characterized in that, The modified polyacrylic acid comprises a polymer matrix and boron nitride nanosheets dispersed in the polymer matrix; The polymer matrix comprises acrylic acid-derived structural units and acrylate-derived structural units.

2. The modified polyacrylic acid according to claim 1, characterized in that, The modified polyacrylic acid satisfies at least one of the following conditions: A1. The molar ratio of acrylate-derived structural units to acrylic acid-derived structural units in the polymer matrix is ​​(0.6~1.5):1; A2. The modified polyacrylic acid contains boron nitride nanosheets at a mass percentage of 5-15 wt%. A3. The acrylate-derived structural unit includes any one or a combination of at least two of butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, or hydroxyethyl acrylate. A4. The boron nitride nanosheets are silane coupling agent modified boron nitride nanosheets; A5. The lateral dimension of the boron nitride nanosheets is 0.5~2μm; A6. The thickness of the boron nitride nanosheets is 10~50 nm.

3. A method for preparing the modified polyacrylic acid according to claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) Mix acrylic monomers, acrylate monomers and emulsifiers to obtain a pre-emulsion; (2) Mix the pre-emulsion and the initiator, and carry out the polymerization reaction to obtain the polymer matrix; (3) Mix the boron nitride nanosheet dispersion and the polymer matrix described in step (2), and then modify the mixture to obtain the modified polyacrylic acid.

4. The preparation method according to claim 3, characterized in that, The mixing in step (1) includes: mixing water, acrylic monomers, acrylate monomers, and emulsifiers, and subjecting the mixture to a first ultrasonic treatment to obtain a pre-emulsion; wherein the mixing satisfies at least one of the following conditions: B1. The mass ratio of the acrylate monomer to the acrylic monomer is (0.6~1.5):1; B2. The mass ratio of the emulsifier to the acrylic monomer is (0.05~0.1):1; B3. The emulsifier includes any one or a combination of at least two of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, sodium fatty alcohol polyoxyethylene ether sulfate, or sodium allyloxyhydroxypropyl sulfonate. B4. The mass ratio of water to acrylic monomer in step (1) is (3~15):1; And / or, the mixing and polymerization reaction in step (2) includes: mixing water and the first part of the preemulsion, heating to the first reaction temperature, adding an initiator dropwise, then adding the second part of the preemulsion dropwise, and after the addition is complete, heating to the second reaction temperature to carry out the polymerization reaction, terminating the polymerization reaction, and then purifying by precipitation to obtain the polymer matrix; wherein, the mixing and polymerization reaction in step (2) satisfies at least one of the following conditions: C1. The mass ratio of the first part of the preemulsion to the second part of the preemulsion is (0.8~1):1; C2. The range of the first reaction temperature is 60~80℃; C3. The initiator includes any one or a combination of at least two of ammonium persulfate, potassium persulfate, sodium persulfate, or azobisisobutyronitrile. C4. The amount of the initiator added is 0.2~0.5 wt% of the preemulsion; C5. The range of the second reaction temperature is 60~80℃; C6. The dripping time of the second part of the pre-emulsion is 2~3 hours; C7. Nitrogen gas is introduced into both the mixing and polymerization reactions described in step (2) to remove oxygen; C8. The polymerization reaction lasts for 3 to 5 hours. C9. The mixing of water and the first part of the pre-emulsion includes: first adding water to the reactor and then introducing nitrogen to remove oxygen, and then adding the first part of the pre-emulsion. C10. Hydroquinone is used as a terminator to terminate the polymerization reaction. C11. The precipitation purification includes placing the reaction solution after the polymerization reaction in an organic solvent to precipitate the precipitate, and washing and drying the precipitate to obtain the polymer matrix.

5. The preparation method according to claim 3 or 4, characterized in that, The boron nitride nanosheets in the boron nitride nanosheet dispersion in step (3) have a mass percentage content of 3-5 wt%; And / or, the preparation of the boron nitride nanosheet dispersion includes: (3.1) Boron nitride nanosheets were dispersed in a silane coupling agent solution and dried to obtain silane coupling agent modified boron nitride nanosheets; (3.2) Disperse the silane coupling agent modified boron nitride nanosheets obtained in step (3.1) in water to obtain a boron nitride nanosheet dispersion; And / or, the modification process described in step (3) includes mechanical stirring, ultrasonic treatment, and then casting the mixture into a mold for drying to obtain modified polyacrylic acid.

6. A water-based edge coating slurry, characterized in that, The water-based edge coating slurry includes the modified polyacrylic acid as described in claim 1 or 2.

7. The water-based edge coating slurry according to claim 6, characterized in that, The water-based edge coating slurry further includes a dispersant, an insulating material, and a wetting agent; wherein the water-based edge coating slurry satisfies at least one of the following conditions: D1. The dispersant comprises any one or a combination of at least two of the following: ethylenediaminetetraacetic acid, PVP, fatty alcohol polyoxyethylene ether, sodium polyacrylate, or oxalic acid. D2. The insulating material includes any one or a combination of at least two of boehmite, alumina, magnesium oxide, barium sulfate, or PET; D3. The wetting agent includes any one or a combination of at least two of polyether siloxane, modified polyether siloxane, or alcohol. D4. The dispersant accounts for 1-3 wt% of the mass of the insulating material; D5. The content of insulating material in the water-based edge coating slurry is 60~80wt%; D6. The wetting agent content in the water-based edge coating slurry is 5~15wt%; D7. The modified polyacrylic acid content in the water-based edge coating slurry is 7~25wt%.

8. A method for preparing the water-based edge coating slurry according to claim 6 or 7, characterized in that, The preparation method includes: Modified polyacrylic acid, water, dispersant and insulating material are mixed, and after pH adjustment, wetting agent is added and then homogenized to obtain water-based edge coating slurry.

9. The preparation method according to claim 8, characterized in that, The mixed modified polyacrylic acid, water, dispersant, and insulating material comprise: S1, mix water and modified polyacrylic acid to obtain the first mixture; S2. Mix the first mixture and the dispersant, and then disperse them to obtain the second mixture; S3. Mix the second mixture and the first portion of the insulating material, and then disperse them in the second stage to obtain the third mixture; S4. The third mixture and the second insulating material are mixed and dispersed in the third stage to obtain the fourth mixture; S5, mix water and the fourth mixture, and then disperse it in the fourth stage to obtain the fifth mixture; Wherein, in step S1, the solid content of the first mixture is 15~25wt%; and / or, the viscosity of the first mixture in step S1 is 800~3000mPa·s.

10. A current collector, characterized in that, The current collector is formed by coating the edge of the current collector substrate with the water-based edge coating slurry as described in claim 6 or 7.

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