Battery diaphragm coating slurry as well as preparation method and application thereof

Abstract

The invention discloses battery diaphragm coating slurry as well as a preparation method and application thereof. The battery diaphragm coating slurry is prepared from the following components in parts by weight: 3 to 15 parts of polymer microsphere binder, 1 to 20 parts of inorganic filler, 1 to 5 parts of water-based auxiliary binder, 0.5 to 3 parts of thickening agent, 0.5 to 2 parts of dispersing agent, 0.2 to 0.5 part of wetting agent, 0.3 to 1 part of defoaming agent, 0.5 to 3 parts of adhesion promoter and 30 to 80 parts of water, the polymer microsphere binder comprises the following raw materials in parts by weight: 20-40 parts of a basic monomer, 5-10 parts of a functional monomer, 1-5 parts of an initiator I, 3-10 parts of a cross-linking agent, 50-90 parts of a solvent I and 2-8 parts of a reactive aid. The battery diaphragm coating slurry is used for preparing a coating diaphragm, the operation is simple and convenient, the bonding requirement can be met by coating the battery diaphragm on the coating slurry once, and the prepared coating diaphragm is strong in bonding force, good in durability and low in breathable increment.

Description

Technical Field

[0001] The present invention relates to the technical field of battery coating diaphragms, and particularly relates to a battery diaphragm coating slurry, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, due to the continuous increase in the market share of new energy vehicles, the demand for lithium batteries, which are key components thereof, has also been increasing day by day. As one of the four major components of lithium batteries, the performance of the diaphragm largely determines the performance of the battery itself. A diaphragm with excellent performance plays a crucial role in improving the comprehensive performance of the battery. Among the existing diaphragms, coated diaphragms are mainly dominant. Among them, the secondary coating of polyvinylidene fluoride (PVDF) is the current market leader, and there is also a process of one-time coating after mixing PVDF with ceramic slurry. Given the high price of PVDF and the need to use a toxic solvent, N-methylpyrrolidone (NMP), during use, it does not conform to the green and environmental protection concept of new energy itself.

[0003] Some studies have used polymer microspheres instead of PVDF to be mixed with ceramic slurry for lithium battery diaphragm coating. For example, CN113410576A discloses a battery diaphragm and a preparation method thereof. The battery diaphragm includes a base film and a coating covering the surface of the base film; the coating contains core-shell type spheres; the coating includes the following components in parts by weight: 5-80 parts of inorganic substances, 0.625 parts - 10 parts of a thickener, 0.4 parts - 7.2 parts of an aqueous binder; the mass ratio of the inorganic substances to the core-shell type spheres is (5-80):(5-30); optionally, the inorganic substances include at least one of aluminum oxide, boehmite, silicon dioxide, titanium dioxide, barium sulfate, calcium carbonate, and calcium oxide. By adding core-shell type polymer microspheres, it is beneficial to increase the bonding strength of the coating and does not affect the heat resistance of the battery diaphragm (the thermal shrinkage rate is small). However, actual research has found that the bonding stability of its coating is not good, especially in a long-term high-rate discharge working environment (when the battery discharges at a high rate, there will be an obvious heating situation. When the discharge rate increases to a certain extent (such as 3C or above), the surface temperature of the battery may exceed 40°C or even reach 60°C). High temperature will cause the bonding force of the coating to decrease, and partial peeling of the coating layer is likely to occur, resulting in uneven coating and affecting the battery performance.

[0004] With the continuous improvement of the requirements for battery safety in new energy vehicles, higher requirements are also put forward for the performance of diaphragms. The existing coated diaphragms are difficult to meet the usage requirements of high-rate and high-capacity lithium batteries. The development of diaphragm coating slurries to achieve high-performance diaphragms has become one of the research focuses in this field. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a battery separator coating slurry, its preparation method and application; the battery separator coating slurry of the present invention can realize the preparation of high-performance coated separators, the coated separators have excellent bonding properties (high bonding strength and good bonding stability), and good air permeability, meeting the use requirements of high-rate and high-capacity lithium batteries.

[0006] The technical solution of the present invention is as follows: The present invention provides a battery separator coating slurry. By weight, the formula of the battery separator coating slurry includes 3-15 parts of polymer microsphere binder, 1-20 parts of inorganic filler, 1-5 parts of water-based auxiliary binder, 0.5-3 parts of thickener, 0.5-2 parts of dispersant, 0.2-0.5 parts of wetting agent, 0.3-1 part of defoaming agent, 0.5-3 parts of adhesion promoter and 30-80 parts of water; By weight, the raw materials of the polymer microsphere binder include 20-40 parts of basic monomer, 5-10 parts of functional monomer, 1-5 parts of initiator I, 3-10 parts of crosslinking agent, 50-90 parts of solvent I and 2-8 parts of reactive auxiliary agent; Among them, the basic monomer includes a hard monomer and a soft monomer; the hard monomer is a monomer with a glass transition temperature Tg1 of 50°C ≤ Tg1 ≤ 120°C and having a double bond structure that can undergo free radical polymerization itself; the soft monomer is a monomer with a glass transition temperature Tg2 of -80°C ≤ Tg2 < 50°C and having a double bond structure that can undergo free radical polymerization itself (the glass transition temperature is measured by differential scanning calorimetry (DSC): using a differential scanning calorimeter (DSC) in a nitrogen atmosphere, the test temperature range is -80°C to 150°C, and the heating rate is 10°C / min to test the sample); The functional monomer is selected from monomers containing at least one group of carboxyl, amide, hydroxyl, epoxy groups; The reactive auxiliary agent is selected from one or more of acrylate-trithiocarbonate copolymer, acrylic acid-trithiocarbonate copolymer.

[0007] Furthermore, the inorganic filler is selected from one or more of boehmite, alumina and zirconia; More preferably, the particle size D50 of the inorganic filler is 0.1-0.5 microns.

[0008] Furthermore, the water-based auxiliary binder is selected from one or more of polyacrylate binders, water-based epoxy resin binders, water-based polyurethane binders, butadiene-styrene copolymer binders, styrene-acrylate copolymer binders, polyvinyl acetate binders, ethylene-vinyl acetate copolymer binders; Furthermore, the thickener is selected from cellulose thickeners; Further preferably, the cellulose thickener is selected from one or more of carboxymethyl cellulose thickeners, hydroxymethyl cellulose thickeners, hydroxyethyl cellulose thickeners, hydroxypropyl cellulose thickeners, and methyl cellulose thickeners.

[0009] Furthermore, the dispersant is a polymer-type dispersant with an inorganic filler-affinity group; the main function of the dispersant is to enable better dispersion of the inorganic filler, prevent agglomeration or flocculation, and at the same time shorten the dispersion time of the slurry, obtain a more uniformly dispersed slurry faster, and make the entire mixing process more efficient. The dispersant used in the present invention is preferably a highly polar water-soluble dispersant, and further preferably a polymer copolymer dispersant with an inorganic filler-affinity group.

[0010] The non-volatile content of the wetting agent at 150 °C for 10 minutes is at least 40%; it can improve the wetting of solids.

[0011] Furthermore, the wetting agent is selected from one or more of polyacrylate wetting agents, styrene-modified polyacrylate wetting agents, styrene-acrylate copolymer wetting agents, styrene-maleic acid copolymer wetting agents, styrene-maleic anhydride ester copolymer wetting agents, and styrene-maleic anhydride copolymer wetting agents.

[0012] Furthermore, the defoaming agent is a silicone defoaming agent; the main function of the defoaming agent is to eliminate the bubbles in the slurry, improve the coating appearance of the slurry coating, prevent bubbles from interfering with the film formation of the slurry, and improve the uniformity of the slurry filling on the separator.

[0013] Furthermore, the adhesion promoter is selected from one or more of epoxy-silane copolymer adhesion promoters, modified alkylene copolymer adhesion promoters, polyester alkyl ammonium salt adhesion promoters, and hydroxy-functional copolymers with acidic groups adhesion promoters. The main function of the adhesion promoter is to improve the wetting ability of the polymer microspheres on the battery separator under high temperature and high pressure, improve the mechanical interlocking of the polymer microspheres on the separator under hot pressing, and play an auxiliary role in enhancing the adhesion of the polymer microspheres.

[0014] Furthermore, the polymer microsphere binder is a polymer microsphere emulsion with a solid content of 10-30%; In the raw materials of the polymer microsphere binder of the present invention, a reactive auxiliary is added. It has polar and non-polar groups, can act as a stabilizer, and can also participate in the polymerization reaction to regulate the reaction process, reduce by-products in the polymerization process, and improve the yield.

[0015] The participation of the reactive auxiliary in the reaction is mainly divided into 5 stages: (1) Chain initiation stage: In the initial stage of the polymerization reaction, initiator I added to the system first generates free radicals through thermal cracking, and then reacts with the monomer to form chain growth free radicals; (2) Chain transfer and chain growth stage: The chain growth free radicals undergo an addition reaction with the reactive additive to generate intermediate free radicals, and then β-scission rapidly occurs on one of the side arms to form leaving group free radicals and dormant species; (3) Re-initiation stage: The newly formed leaving group free radicals continue to initiate the remaining monomers to form new chain growth free radicals; (4) Chain equilibrium stage: The newly generated chain growth free radicals react with the dormant species to generate new intermediate free radicals, and then break to form new chain growth free radicals and dormant species. Through the chain transfer process between the dormant species and the chain growth free radicals, a main equilibrium of "initiation-inactivation" is formed. This process is accompanied by a rapid establishment of an exchange equilibrium between the dormant species and the active growing chains. Therefore, polymer chains with similar chain lengths can be formed in the reaction system, thereby forming a polymer with a narrow molecular weight distribution. At the same time, the chain growth rate of the reaction system is always less than the addition-fragmentation equilibrium reaction rate, making the number of dormant species much larger than the number of active free radicals, thus reducing the chance of chain termination; (5) Chain termination stage: When the polymerization reaction reaches a certain extent, the bimolecular termination reaction accelerates, and the free radicals are quenched due to disproportionation termination or coupling termination.

[0016] The relative molecular weight of the reactive additive has a certain influence on the size of the synthesized microspheres and the adhesion of the coated separator. The polymerization degree of the reactive additive is preferably between 200 and 1000.

[0017] Furthermore, the polymerization degree of the reactive additive is preferably 200 - 400.

[0018] Further, the trithiocarbonate in the reactive additive is preferably 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid; Further, the acrylate in the reactive additive is preferably one or more of methyl acrylate, butyl acrylate, isooctyl acrylate, ethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl acrylate; The reactive additive of the present invention can be obtained commercially or by self-preparation. The present invention provides a method for synthesizing a reactive additive, including the following steps: (1) Mix 20 - 50 parts by weight of acrylic acid or acrylate monomer, 0.1 - 2 parts of trithiocarbonate, 1 - 5 parts of initiator II, and 50 - 70 parts of solvent II; (2) React at 70 - 80 °C for 2 - 10 hours under a protective atmosphere; (3) Purify and dry to obtain the reactive additive.

[0019] Further, the initiator II is preferably azobisisobutyronitrile; Further, the solvent II is preferably selected from one of 1,4-dioxane, ethanol, and methanol.

[0020] Further, the reaction time is preferably 4 - 6 h.

[0021] In the raw materials of the polymer microsphere binder of the present invention, both a hard monomer and a soft monomer are added. The hard monomer provides a certain rigidity and thermal stability to the microspheres, and at the same time ensures that the microspheres have a certain cohesive force under the hot pressing state; while the soft monomer can provide a certain flow ability to the microspheres under the hot pressing conditions, promoting the infiltration of the microspheres and the interface, thereby improving the adhesiveness. The two work together, enabling the microspheres to be used as a binder in the diaphragm ceramic coating slurry, effectively improving the adhesion between the diaphragm and the electrode sheet.

[0022] Further, the weight ratio of the hard monomer to the soft monomer in the basic monomer is preferably 30 - 70:70 - 30.

[0023] Further, the hard monomer is selected from one or more of acrylonitrile, styrene, methyl methacrylate, ethyl methacrylate, methacrylic acid, 2-hydroxyethyl methacrylate, tert-butyl methacrylate, and isopropyl methacrylate.

[0024] Further, the soft monomer is selected from one or more of glycidyl methacrylate, butyl methacrylate, n-pentyl methacrylate, propyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, and 2-hydroxypropyl methacrylate.

[0025] The functional monomer of the present invention is preferably selected from one or more of methacrylic acid, diacetone acrylamide, 2-hydroxyethyl acrylate, N-hydroxymethyl acrylamide, 2-hydroxypropyl methacrylate, and 2-hydroxypropyl acrylate. By adding a certain amount of the functional monomer, its functional groups can form chemical bonds with the interfacial groups of the electrode sheet, further improving the adhesion ability between the microspheres and the interface.

[0026] The initiator I of the present invention is preferably an azo initiator; its main function is to generate free radicals under heating conditions to initiate the polymerization reaction.

[0027] Further, the initiator I is selected from one or more of azobisisobutyronitrile and azodiisobutyronitrile; Further, the crosslinking agent of the present invention is a monomer with crosslinking function containing two or three double bonds. The addition of the crosslinking agent can promote the formation of a crosslinked structure during polymerization, which is beneficial to improving the stability of the microspheres in the electrolyte.

[0028] Furthermore, the crosslinking agent is preferably selected from one or more of N,N-methylenebisacrylamide, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, divinylbenzene, and allyl methacrylate; Furthermore, Solvent I is selected from one or more combinations of methanol, ethanol, isopropanol, and water. It mainly serves as a dispersion medium.

[0029] Furthermore, the particle size D50 of the polymer microspheres is 1 - 7 microns; The addition amount of the polymer microsphere binder is limited to the range of 3 - 15 parts mainly because too low an addition amount of microspheres cannot ensure good adhesion, and too high an addition amount will cause the polymer microspheres to form a film after hot pressing of the separator, resulting in pore blockage and being unfavorable for the transmission of lithium ions.

[0030] More preferably, the addition amount of the polymer microsphere binder is 4 - 12 parts.

[0031] Furthermore, the preparation method of the polymer microsphere binder includes the following steps: Mix the basic monomer, functional monomer, initiator I, crosslinking agent, reactive auxiliary agent, and Solvent I, and react at 60 - 70 °C for 8 - 15 hours under a protective atmosphere to obtain the polymer microsphere binder.

[0032] More preferably, the preparation method of the polymer microsphere binder includes the following steps: (1) Put the weighed monomers (including the basic monomer, functional monomer, and crosslinking agent) into the reaction kettle, and add 1 / 2 - 3 / 4 of Solvent I. Control the temperature at 50 - 60 °C and maintain the rotation speed at 150 - 200 rpm; (2) Subsequently, add the reactive auxiliary agent, keep the temperature unchanged, and increase the rotation speed to 200 - 300 rpm; (3) Evacuate for 0.5 - 1 hour to remove the internal oxygen and then introduce nitrogen. React under a nitrogen atmosphere to increase the polymerization rate and reduce the residue rate at the same time; (4) Add Initiator I to the remaining 1 / 4 - 1 / 2 of Solvent I, stir until it is in a homogeneous state, and then drop it into the reaction kettle; (5) After all of Initiator I is added, raise the temperature to 60 - 70 °C and react at this temperature for 8 - 15 hours to obtain the target polymer microsphere emulsion; (6) Subsequently, filter the emulsion through a 200 - mesh sieve, centrifuge the filtrate, and then redisperse it with the reaction solvent. Repeat this 2 - 5 times, and finally disperse it with water to obtain the polymer microsphere binder.

[0033] The above - mentioned preparation method of the battery separator coating slurry includes the following steps: (1) Mix and stir the inorganic filler, thickener and water, maintaining a rotation speed of 400 - 700 rpm and a stirring time of 1 - 2 hours; (2) Increase the rotation speed to 600 - 900 rpm, add the dispersant drop by drop, and stir for 0.5 - 1 hour after adding; (3) Add the polymer microsphere binder and wetting agent, increase the rotation speed to 1000 - 1200 rpm, and maintain at high - speed stirring for 0.5 - 1 hour; (4) Decrease the rotation speed to 150 - 300 rpm, add the defoamer, water - based auxiliary binder and adhesion promoter drop by drop, and maintain low - speed stirring for 0.5 - 1 hour after adding to remove the air bubbles inside the slurry, then the battery separator coating slurry can be obtained.

[0034] A coated separator includes a battery separator and the above - mentioned battery separator coating slurry, and the battery separator coating slurry is coated on the surface of the battery separator.

[0035] The preparation method of the above - mentioned coated separator includes the following steps: Coat the battery separator coating slurry on the battery separator, and then dry it at 50 - 70 °C to prepare the coated separator; the thickness of the coating after drying is 1 / 3 to 2 / 3 of the diameter of the polymer microspheres.

[0036] The advantages and beneficial effects of the present invention compared with the prior art: (1) In the battery separator coating slurry of the present invention, a polymer microsphere binder and an adhesion promoter are added. The prepared coated separator has a low increase in air permeability, strong adhesion to the electrode sheet and good durability. The increase in air permeability is only within 20 s, the adhesion force with the electrode sheet after hot pressing at room temperature is more than 2 N / m, and the adhesion forces of the hot - pressed samples after maintaining at 50 °C for 30 minutes and after soaking in the electrolyte for 3 days are both more than 2 N / m; it has stronger advantages compared with the existing battery separator coating slurries.

[0037] (2) The preparation method of the battery separator of the present invention does not require cumbersome operation steps. Coating the battery separator coating slurry on the separator once can meet the adhesion requirements, saving one step of operation compared with the conventional secondary coating, and has high convenience. Description of the Drawings

[0038] Figure 1 SEM photograph of the coated separator prepared in Example 1. Detailed Embodiments

[0039] To make the objectives, technical solutions and advantages of the present invention clearer, several examples will be cited to further elaborate on the present invention. The cited technical solutions are only used to explain the present invention and do not limit the protection scope of the present invention. Without changing the idea, any replacement or substitution of this technical solution shall fall within the technical protection scope of the present invention. All chemical reagents are purchased from Aladdin Chemical Reagents unless otherwise specified.

[0040] To characterize the advantages of the battery separator coating slurry in the present invention, combined with the commonly used testing methods currently, the prepared coated separators are tested. The tested properties include air permeability and average adhesion to the electrode.

[0041] (1) Air permeability test: It is detected according to the Gurley method (the time required for 100 mL of air to pass through a separator with an area of 6.45 cm 2 under a pressure of 1.21 kPa applied by the instrument). The equipment manufacturer is Guangzhou Runhu Instrument Co., Ltd., and the equipment model is RH-TQG645. Each group of coated separators is tested 3 times, and the average value is taken and rounded to an integer as the final result.

[0042] (2) Adhesion test with the electrode: The coated separator is cut into a rectangle of 6 × 12 cm. The side with the coating slurry is overlapped with the graphite electrode of the negative electrode of the battery of the same size. Subsequently, a hot press (Shenzhen Xinyi Hydraulic Equipment Co., Ltd., model XY-Z2118-3T) is used to hot press at 3 MPa and 80 °C for 1 minute. After the sample cools down, the separator is cut into strips with a width of 2 × 12 cm. Subsequently, an electronic tensile machine (Guangzhou Runhu Instrument Co., Ltd., model RH-L600) is used for the adhesion test. Each group of samples is tested 3 times, and the average value is taken and rounded to 1 decimal place as the final result; to highlight the adhesion advantage of the battery separator coating slurry in the present invention, the samples after hot pressing are additionally kept at 50 °C for 30 minutes and then immersed in the electrolyte (where the mass ratio of ethylene carbonate: dimethyl carbonate: diethyl carbonate = 3:5:2) for 3 days, and then the tensile machine is used for the adhesion test. Each group of samples is tested 3 times, and the average value is taken and rounded to 1 decimal place as the final result.

[0043] (3) Microsphere size: Take a small amount of the aqueous dispersion of microspheres, dilute it with water to a suitable concentration, and then ultrasonically disperse it for 5 minutes. The Malvern 3000 particle size analyzer is used to statistically analyze the size of the microspheres, and the particle size D50 of the microspheres is measured.

[0044] "Parts" in the examples all refer to parts by weight.

[0045] Example 1 This example presents a battery separator coating slurry, its preparation method and application. The formulation of the battery separator coating slurry includes 6 parts of polymer microsphere binder, 10 parts of inorganic filler alumina (A500, Zhongyan Nano New Materials), 1 part of waterborne polyacrylate auxiliary binder (LA136D, Sichuan Yindi Le Material Technology Co., Ltd.), 0.5 part of carboxymethyl cellulose thickener (Aladdin Chemical Reagent, C501052), 1 part of dispersant (Tech-6074, Tiger Auxiliaries), 0.2 part of polyacrylate wetting agent (BYK-ET-3030, BYK Chemie), 0.3 part of defoamer (Tech-38101, Tiger Auxiliaries), 1 part of adhesion promoter (BYK-4500, BYK Chemie), and 80 parts of water (laboratory purified water).

[0046] The preparation method of the polymer microsphere binder is as follows: (1) Put 33 parts of a mixture of styrene and n-octyl methacrylate (mass ratio 5:5), 5 parts of methacrylic acid, and 7 parts of ethylene glycol dimethacrylate into a reaction kettle, and add 3 / 4 of 50 parts of methanol. Control the temperature at 55 °C and maintain the rotation speed at 150 rpm; (2) Subsequently, add 3 parts of PMA400, keep the temperature unchanged, and increase the rotation speed to 200 rpm; (3) Evacuate for 1 hour to remove internal oxygen and then introduce nitrogen. React under a nitrogen atmosphere to increase the polymerization rate while reducing the residue rate; (4) Add 2 parts of azobisisobutyronitrile to the remaining 1 / 4 of methanol, stir until homogeneous, and then drop it into the reaction kettle; (5) After all the initiator is added, raise the temperature to 65 °C and react at this temperature for 10 hours to obtain the target microsphere emulsion; (6) Subsequently, filter the emulsion through a 200-mesh sieve, centrifuge the filtrate, and then redisperse it with the reaction solvent. Repeat this process 2 times, and finally disperse it with water to a solid content of 20% to obtain the polymer microsphere binder.

[0047] The preparation method of the auxiliary PMA400 is as follows: (a) Place 30 parts of methyl acrylate, 0.3 part of 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, 1 part of azobisisobutyronitrile, and 68.7 parts of 1,4-dioxane in a round-bottom flask that has been preheated to 70 °C; (b) Pass nitrogen for 30 minutes to remove internal air, and then react at 70 °C for 4 hours; (c) Recrystallize the sample with n-hexane, and then dissolve it with 1,4-dioxane. Repeat this process 3 times; (d) Vacuum dry the sample in a vacuum oven at 40 °C for 20 - 25 hours to obtain the required reactive stabilizer PMA400.

[0048] The coating process of the battery separator coating slurry is as follows: (1) Mix and stir the weighed inorganic filler, thickener and water, keep the rotation speed at 500 rpm, and stir for 1 hour; (2) Increase the rotation speed to 700 rpm, add the dispersant drop by drop, and stir for 0.5 hour after adding; (3) Add the polymer microsphere binder and wetting agent, increase the rotation speed to 1200 rpm, and keep stirring at high speed for 0.5 hour; (4) Reduce the rotation speed to 200 rpm, add the defoamer, waterborne auxiliary binder and adhesion promoter drop by drop, and keep stirring at low speed for 0.5 hour after adding to remove the bubbles inside the slurry, then the battery separator coating slurry required for the battery separator can be obtained; (5) Coat the battery separator coating slurry on the battery separator, and then dry it at 60 °C, control the thickness of the dried coating to be 2 microns, and then the coated separator can be prepared.

[0049] Example 2 This example presents a battery separator coating slurry, its preparation method and application. The formula of the battery separator coating slurry includes 6 parts of polymer microsphere binder, 10 parts of inorganic filler alumina (A500, Zhongyan Nano New Materials), 1 part of waterborne ethylene-vinyl acetate copolymer auxiliary binder (558ED, Wacker Chemical), 0.5 part of thickener methyl cellulose (Aladdin Chemical Reagent, M112867), 1 part of dispersant (Tech-6320, Tiger Auxiliaries), 0.2 part of wetting agent (BYK-ET-3032, BYK Chemical), 0.3 part of defoamer (Tech-371W, Tiger Auxiliaries), 1 part of adhesion promoter (BYK-4509, BYK Chemical), and 80 parts of water (laboratory pure water).

[0050] Among them, the preparation method of the polymer microsphere binder is as follows: (1) Put the weighed mixture of 20 parts of methyl methacrylate, butyl methacrylate and hydroxypropyl methacrylate (mass ratio 3:2:5), 6 parts of diacetone acrylamide, and 5 parts of ethylene glycol dimethacrylate into the reaction kettle, and add 63 parts of 3 / 4 of the mixed solvent of methanol and water (mass ratio 8:2), control the temperature at 55 °C, and maintain the rotation speed at 150 rpm; (2) Then add 3 parts of PEA300, keep the temperature unchanged, and increase the rotation speed to 200 rpm; (3) Evacuate the air for 1 hour to remove internal oxygen, then introduce nitrogen gas, and carry out the reaction under a nitrogen atmosphere to increase the polymerization rate while reducing the residue rate; (4) Add 3 parts of azobisisobutyronitrile to the remaining 1 / 4 of the mixed solvent of methanol and water, stir until homogeneous, and then drop it into the reaction kettle; (5) After all the initiator is added, raise the temperature to 65 °C and react at this temperature for 10 hours to obtain the target microsphere emulsion; (6) Then filter the emulsion through a 200-mesh sieve, centrifuge the filtrate, and then redisperse it with the reaction solvent. Repeat this process 2 times. Finally, disperse it with water until the solid content is 20% to obtain the polymer microsphere binder.

[0051] The preparation method of the auxiliary agent PEA300 is as follows: (a) Place 30 parts of ethyl acrylate, 0.3 parts of 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, 1 part of azobisisobutyronitrile, and 68.7 parts of 1,4-dioxane in a round-bottom flask that has been preheated to 70 °C; (b) Pass nitrogen gas for 30 minutes to remove internal air, and then react for 6 hours; (c) Recrystallize the sample with n-hexane, and then dissolve it with 1,4-dioxane. Repeat this process 3 times; (d) Vacuum-dry the sample in a vacuum oven at 40 °C for 20 - 25 hours to obtain the required reactive stabilizer PEA300.

[0052] The coating process of the battery separator coating slurry is the same as that in Example 1.

[0053] Example 3 This example presents a battery separator coating slurry, its preparation method and application. The formula of the battery separator coating slurry includes 6 parts of polymer microsphere binder, 10 parts of inorganic filler alumina (A500, Zhongyan Nano New Materials), 1 part of water-based polyacrylate auxiliary binder (LA136D, Sichuan Yindi Le Material Technology Co., Ltd.), 0.5 part of thickener hydroxypropyl cellulose (Aladdin Chemical Reagent, H742522), 1 part of dispersant (Tech-6076, Tiger Auxiliaries), 0.2 part of wetting agent (BYK-ET-3034, BYK Chemie), 0.3 part of defoamer (Tech-3362, Tiger Auxiliaries), 1 part of adhesion promoter (BYK-4510, BYK Chemie), and 80 parts of water (laboratory pure water).

[0054] The preparation method of the polymer microsphere binder is as follows: (1) Put 37 parts of the mixture of styrene, acrylonitrile and butyl methacrylate (mass ratio 2:2:6), 5 parts of hydroxypropyl methacrylate, and 3 parts of allyl methacrylate into a reaction kettle, and add 3 / 4 of 50 parts of ethanol. Control the temperature at 55 °C and maintain the rotation speed at 150 rpm; (2) Subsequently, add 3 parts of PEHA400, keep the temperature unchanged, and increase the rotation speed to 200 rpm; (3) Evacuate for 1 hour to remove internal oxygen and then introduce nitrogen. React under a nitrogen atmosphere to increase the polymerization rate while reducing the residue rate; (4) Add 2 parts of azobisisobutyronitrile to the remaining 1 / 4 of ethanol, stir until homogeneous, and then drop it into the reaction kettle; (5) After all the initiator is added, raise the temperature to 65 °C and react at this temperature for 10 hours to obtain the target microsphere emulsion; (6) Subsequently, filter the emulsion through a 200-mesh sieve, centrifuge the filtrate, and then redisperse it with the reaction solvent. Repeat this 2 times, and finally disperse it with water until the solid content is 20% to obtain the polymer microsphere binder.

[0055] The synthesis method of the auxiliary agent PEHA400 is as follows: (a) Put 20 parts of isooctyl acrylate, 0.1 part of 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, 0.9 part of azobisisobutyronitrile, and 79 parts of ethanol into a round-bottom flask preheated at 70 °C; (b) Pass nitrogen for 30 minutes to remove internal air, and then react at 70 °C for 4 hours; (c) Recrystallize the sample with n-hexane, and then dissolve it with ethanol. Repeat this 3 times; (d) Vacuum dry the sample in a vacuum oven at 40 °C for 20 - 25 hours to obtain the required reactive stabilizer PEHA400.

[0056] The coating process of the battery separator coating slurry is the same as that in Example 1.

[0057] Example 4 This example proposes a battery diaphragm coating slurry and its preparation method and application, wherein the formula of the battery diaphragm coating slurry includes 6 parts of polymer microsphere binder, 10 parts of inorganic filler zirconium oxide (500 nanometers, Lijia Metal Materials), 2 parts of water-based polyurethane auxiliary binder (8401E, Jiasheng Engineering Plastics), 1 part of thickener hydroxyethyl cellulose (800-1,500 mPa·s, 2wt% aqueous solution at 20°C, Aladdin Chemical Reagent), 1 part of dispersant (Tech-6270, Tiger Additive), 0.2 parts of wetting agent (BYK-ET-3033, BYK Chemical), 0.3 parts of defoaming agent (Tech-3901, Tiger Additive), 0.5 parts of adhesion promoter (Tech-7720, Tiger Additive), and 79 parts of water.

[0058] The preparation method of the polymer microsphere binder is the same as that of Example 1.

[0059] The preparation method of the additive PMA400 is the same as that in Example 1.

[0060] The coating process of the battery separator coating slurry is the same as that in Example 1.

[0061] Example 5 This example proposes a battery diaphragm coating slurry and its preparation method and application, wherein the formula of the diaphragm ceramic coating slurry includes 10 parts of polymer microsphere binder, 8 parts of inorganic filler zirconium oxide (500 nanometers, Lijia Metal Materials), 3 parts of water-based styrene acrylic emulsion auxiliary binder (BC-01, Luyuan Chemical), 1 part of thickener hydroxypropyl cellulose (150-400mPa·s, 2% aqueous solution at 20°C, Aladdin Chemical Reagent), 1 part of dispersant (Tech-6078, Tiger Additive), 0.5 part of wetting agent (BYK-ET-3033, BYK Chemical), 0.5 part of defoaming agent (Tech-3904, Tiger Additive), 0.5 part of adhesion promoter (BYK-ET-4510, BYK Chemical), and 75.5 parts of water.

[0062] The preparation method of the polymer microsphere binder is the same as that of Example 1.

[0063] The preparation method of the additive PMA400 is the same as that in Example 1.

[0064] The coating process of the battery separator coating slurry is the same as that in Example 1.

[0065] Example 6 In Example 1, the coating thickness of the diaphragm coating slurry after drying is controlled to be 3 microns, and the other raw materials and processes remain the same.

[0066] Example 7 The amount of the polymer microsphere binder added in Example 1 was changed to 15 parts, and the other raw materials and processes remained the same.

[0067] Example 8 The addition amount of the polymer microsphere binder in Example 1 was changed to 3 parts, and the other raw materials and processes remained the same.

[0068] Example 9 The addition amount of the adhesion promoter in Example 1 was modified from 1 part to 3 parts, and the other raw materials and processes remained the same.

[0069] Example 10 The addition amount of the adhesion promoter in Example 1 was modified from 1 part to 0.5 part, and the other raw materials and processes remained the same.

[0070] To more clearly highlight the advantages of the present invention, Example 1 was used as a reference benchmark, and the ceramic slurry prepared without adding the polymer microsphere binder in the ceramic slurry was used as Comparative Example 1; taking Example 1 as a reference benchmark, the addition amount of the polymer microsphere binder in the ceramic slurry was modified to 18 parts as Comparative Example 2; taking Example 1 as a reference benchmark, the adhesion promoter in the ceramic slurry was removed, and the other raw materials and processes remained the same as Comparative Example 3; the polymer microsphere binder in Example 1 was replaced with PSt microspheres of the same size, and this was used as Comparative Example 4; the original auxiliary agent in Example 1 was changed from the original PMA400 to PMA50 to prepare polymer microspheres, and this was used as Comparative Example 5; the original functional monomer (methacrylic acid) in Example 1 was removed from the preparation raw materials to prepare polymer microspheres, and this was used as Comparative Example 6; The synthesis method of the auxiliary agent PMA50 in the comparative example is as follows: (1) By weight, 4 parts of methyl acrylate, 0.3 part of 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid, 1 part of azobisisobutyronitrile, and 68.7 parts of 1,4-dioxane were placed in a round-bottomed flask preheated at 70 °C; (2) Nitrogen was passed for 30 minutes to remove the internal air, and then the reaction was carried out at 70 °C for 4 hours; (3) The sample was recrystallized with n-hexane and then dissolved with 1,4-dioxane, and this was repeated 3 times; (4) The sample was vacuum dried in a vacuum oven at 40 °C for 20 - 25 hours to obtain the required reactive stabilizer PMA50.

[0071] The above examples and comparative examples were tested for air permeability, average adhesion force under different conditions of the electrode sheet, etc., and the detailed test results are summarized in Table 1: Table 1

[0072] Data analysis: As can be seen from the examples in Table 1, the coated separator prepared by the present invention has good adhesion in different environments. At the same time, the increase in air permeability of the separator after coating is within 20 s. The lower increase in air permeability indicates that the coating slurry for the battery separator prepared by the present invention has little effect on the air permeability of the separator itself, and can ensure the smooth transmission of lithium ions between the separators. It can also be seen from Comparative Example 1 that without adding the polymer microsphere binder in the present invention, the adhesion between the separator and the electrode sheet can hardly be measured, and it is difficult to meet the use requirements. In Comparative Example 2, due to the high addition amount of the microspheres, the adhesion is greater, but at the same time, the increase in air permeability of the separator is large, which hinders the transmission of lithium ions. Therefore, the microspheres should be within a reasonable range, not the more the better. In Comparative Example 3, after removing the adhesion promoter, the increase in air permeability is slightly smaller compared with Example 1, mainly because the adhesion decreases significantly, indicating that the synergistic effect of the polymer microsphere binder and the adhesion promoter can bring greater adhesion. In Comparative Example 4, conventional PSt microspheres are used to replace the polymer microspheres prepared in the present invention, and the adhesion is very low. In Comparative Example 5, PMA50 is used as the reactive auxiliary in the raw materials for preparing the polymer microsphere binder, and the adhesion of the coated separator is low. In Comparative Example 6, no functional monomer is added to the raw materials for preparing the polymer microsphere binder, and the adhesion of the coated separator is low.

Claims

1. A battery separator coating slurry, characterized in that, By weight parts, it includes 3 - 15 parts of polymer microsphere binder, 1 - 20 parts of inorganic filler, 1 - 5 parts of aqueous auxiliary binder, 0.5 - 3 parts of thickener, 0.5 - 2 parts of dispersant, 0.2 - 0.5 parts of wetting agent, 0.3 - 1 part of defoamer, 0.5 - 3 parts of adhesion promoter and 30 - 80 parts of water; The raw materials of the polymer microsphere binder, by weight parts, include 20 - 40 parts of basic monomer, 5 - 10 parts of functional monomer, 1 - 5 parts of initiator Ⅰ, 3 - 10 parts of crosslinking agent, 50 - 90 parts of solvent Ⅰ and 2 - 8 parts of reactive auxiliary agent; Among them, the basic monomer includes a hard monomer and a soft monomer; the hard monomer is a monomer with a glass transition temperature Tg1 of 50℃ ≤ Tg1 ≤ 120℃ and having a double - bond structure that can undergo free - radical polymerization by itself; the soft monomer is a monomer with a glass transition temperature Tg2 of - 80℃ ≤ Tg2 < 50℃ and having a double - bond structure that can undergo free - radical polymerization by itself; The functional monomer is selected from monomers containing at least one group among carboxyl group, acylamino group, hydroxyl group, and epoxy group; The reactive auxiliary agent is selected from one or more of acrylate - trithiocarbonate copolymer and acrylic acid - trithiocarbonate copolymer.

2. The battery separator coating slurry according to claim 1, wherein, The inorganic filler is selected from one or more of boehmite, alumina, and zirconia; The aqueous auxiliary binder is selected from one or more of polyacrylate binders, aqueous epoxy resin binders, aqueous polyurethane binders, butadiene - styrene copolymer binders, styrene - acrylate copolymer binders, polyvinyl acetate binders, ethylene - vinyl acetate copolymer binders; The thickener is selected from cellulose - type thickeners; The cellulose - type thickeners are selected from one or more of carboxymethyl cellulose - type thickeners, hydroxymethyl cellulose - type thickeners, hydroxyethyl cellulose - type thickeners, hydroxypropyl cellulose - type thickeners, and methyl cellulose - type thickeners; The dispersant is a polymer - type dispersant with an inorganic - filler - affinity group; The wetting agent is selected from one or more of polyacrylate wetting agents, styrene - modified polyacrylate wetting agents, styrene - acrylate copolymer wetting agents, styrene - maleic acid copolymer wetting agents, styrene - maleic anhydride ester copolymer wetting agents, styrene - maleic anhydride copolymer wetting agents; The defoamer is a silicone - type defoamer; The adhesion promoter is selected from one or more of epoxy - silane copolymer - type adhesion promoters, modified alkylene copolymer - type adhesion promoters, polyester alkyl ammonium salt - type adhesion promoters, and hydroxyl - functional copolymer - type adhesion promoters containing acidic groups.

3. The battery separator coating slurry according to claim 1, wherein The polymer microsphere binder is a polymer microsphere emulsion with a solid content of 10 - 30%; The degree of polymerization of the reactive auxiliary agent is 200 - 1000; The weight ratio of the hard monomer to the soft monomer in the basic monomer is 30 - 70:70 - 30.

4. The battery separator coating slurry according to claim 1, wherein The hard monomer is selected from one or more of acrylonitrile, styrene, methyl methacrylate, methyl acrylate, methacrylic acid, 2 - hydroxyethyl methacrylate, tert - butyl methacrylate, isopropyl methacrylate; The soft monomer is selected from one or more of glycidyl methacrylate, butyl methacrylate, n-pentyl methacrylate, propyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, and hydroxypropyl methacrylate; The functional monomer is selected from one or more of methacrylic acid, diacetone acrylamide, hydroxyethyl acrylate, N-hydroxymethyl acrylamide, hydroxypropyl methacrylate, and hydroxypropyl acrylate; The initiator I is an azo initiator; the initiator I is selected from one or more of azobisisobutyronitrile and azodiisopentanenitrile; The crosslinking agent is a monomer with crosslinking function containing two or three double bonds; the crosslinking agent is selected from one or more of N,N-methylenebisacrylamide, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, divinylbenzene, and allyl methacrylate; The solvent I is selected from one or more combinations of methanol, ethanol, isopropanol, and water; The trithiocarbonate in the reactive auxiliary is 2-(dodecyltrithiocarbonate)-2-methylpropanoic acid; The acrylate in the reactive auxiliary is selected from one or more of methyl acrylate, butyl acrylate, isooctyl acrylate, ethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl acrylate.

5. The battery separator coating slurry according to claim 1, characterized in that, The synthesis method of the reactive auxiliary includes the following steps: (1) Mix 20-50 parts by weight of acrylic acid or acrylate monomer, 0.1-2 parts of trithiocarbonate, 1-5 parts of initiator II, and 50-70 parts of solvent II; (2) React at 70-80 °C for 2-10 hours under a protective atmosphere; (3) Purify and dry to obtain the reactive auxiliary.

6. The battery separator coating slurry according to claim 5, characterized in that, The initiator II is azobisisobutyronitrile; The solvent II is selected from one of 1,4-dioxane, ethanol, and methanol.

7. The battery separator coating slurry according to claim 1, wherein The particle size D50 of the polymer microspheres is 1-7 microns; The preparation method of the polymer microsphere binder includes the following steps: Mix the basic monomer, functional monomer, initiator I, crosslinking agent, reactive auxiliary, and solvent I, and react at 60-70 °C for 8-15 hours under a protective atmosphere to obtain the polymer microsphere binder.

8. The preparation method of the battery separator coating slurry according to any one of claims 1-7, characterized in that, Include the following steps: (1) Mix the inorganic filler, thickener, and water and stir, maintaining the rotation speed at 400-700 rpm for 1-2 hours; (2) Increase the rotation speed to 600-900 rpm, dropwise add the dispersant, and stir for 0.5-1 hour after adding; (3) Add the polymer microsphere binder and wetting agent, increase the rotation speed to 1000-1200 rpm, and maintain at high speed for 0.5-1 hour; (4) Decrease the rotation speed to 150-300 rpm, dropwise add the defoamer, water-based auxiliary binder, and adhesion promoter, and maintain low-speed stirring for 0.5-1 hour after adding to remove the bubbles inside the slurry, and the battery separator coating slurry can be obtained.

9. A coated separator, characterized in that, It includes a battery separator and the battery separator coating slurry according to any one of claims 1-7, and the battery separator coating slurry is coated on the surface of the battery separator.

10. The method for preparing the coated separator according to claim 9, characterized in that, Include the following steps: Coat the battery separator coating slurry on the battery separator, and then dry it at 50-70 °C to prepare a coated separator; the coating thickness after drying is 1 / 3 to 2 / 3 of the diameter of the polymer microspheres.

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