A battery separator coating slurry and its preparation method and application

Abstract

The present invention discloses a battery separator coating slurry, a preparation method, and an application thereof. The battery separator coating slurry comprises, by weight, 3-15 parts of a polymer microsphere binder, 1-20 parts of an inorganic filler, 1-5 parts of an aqueous auxiliary binder, 0.5-3 parts of a thickener, 0.5-2 parts of a dispersant, 0.2-0.5 parts of a wetting agent, 0.3-1 parts of a defoamer, 0.5-3 parts of an adhesion promoter, and 30-80 parts of water. The raw materials of the polymer microsphere binder comprise, 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 auxiliary agent. The battery separator coating slurry is simple to use in preparing a coated separator. A single application on the battery separator can achieve adhesion requirements. The prepared coated separator has strong adhesion, good durability, and low air permeability.

Description

Technical Field

[0001] The present invention relates to the technical field of battery coating membranes, and in particular to a battery membrane coating slurry, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, driven by the growing market share of new energy vehicles, demand for lithium batteries, a key component, has also been growing. As one of the four main components of lithium batteries, the performance of the separator largely determines the performance of the battery itself. High-performance separators play a crucial role in improving the overall performance of batteries. Existing separators are primarily coated, with polyvinylidene fluoride (PVDF) secondary coating currently dominating the market. Alternatively, a single coating process involving mixing PVDF with a ceramic slurry is also available. However, due to the high price of PVDF, its use requires the use of the toxic solvent N-methylpyrrolidone (NMP), which is inconsistent with the green and environmentally friendly philosophy of new energy vehicles.

[0003] Some studies have used polymer microspheres instead of PVDF to mix with ceramic slurry for lithium battery separator coating. For example, CN113410576A discloses a battery separator and a preparation method thereof. The battery separator includes a base film and a coating covering the surface of the base film; the coating contains core-shell spheres; the coating includes the following components in parts by weight: 5-80 parts of inorganic matter, 0.625 parts to 10 parts of thickener, and 0.4 parts to 7.2 parts of aqueous adhesive; the mass ratio of the inorganic matter to the core-shell spheres is (5-80): (5-30); optionally, the inorganic matter includes aluminum oxide, boehmite, silicon dioxide, At least one of titanium, barium sulfate, calcium carbonate and calcium oxide; the addition of core-shell polymer microspheres is beneficial to increasing the bonding strength of the coating without affecting the heat resistance of the battery separator (small thermal shrinkage). However, actual studies have found that the coating bonding stability is not good, especially in long-term high-rate discharge working environments (the battery will have more obvious heat generation during high-rate discharge. When the discharge rate increases to a certain level (such as 3C or above), the surface temperature of the battery may exceed 40°C or even reach 60°C). High temperature will reduce the adhesion of the coating and easily cause partial peeling of the coating, resulting in uneven coating and affecting battery performance.

[0004] As new energy vehicles place increasing demands on battery safety, higher performance requirements are also being placed on separators. Existing coated separators are no longer able to meet the demands of high-rate, high-capacity lithium batteries. The development of separator coating slurries to achieve high-performance separators has become a key research focus in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a battery diaphragm coating slurry and its preparation method and application; the battery diaphragm coating slurry of the present invention can realize the preparation of high-performance coated diaphragms, and the coated diaphragms have excellent bonding properties (high bonding force and good bonding stability) and good air permeability, meeting the use requirements of high-rate and high-capacity lithium batteries.

[0006] The technical solutions of the present invention are as follows:

[0007] The present invention provides a battery separator coating slurry. The formula of the battery separator coating slurry includes, by weight, 3-15 parts of a polymer microsphere binder, 1-20 parts of an inorganic filler, 1-5 parts of an aqueous auxiliary binder, 0.5-3 parts of a thickener, 0.5-2 parts of a dispersant, 0.2-0.5 parts of a wetting agent, 0.3-1 parts of a defoaming agent, 0.5-3 parts of an adhesion promoter, and 30-80 parts of water.

[0008] The raw materials of the polymer microsphere adhesive include, by weight, 20-40 parts of basic monomer, 5-10 parts of functional monomer, 1-5 parts of initiator I, 3-10 parts of cross-linking agent, 50-90 parts of solvent I and 2-8 parts of reactive auxiliary agent;

[0009] Among them, the basic monomers include hard monomers and soft monomers; the hard monomers are monomers with a glass transition temperature Tg1 of 50°C ≤ Tg1 ≤ 120°C and a double bond structure that can undergo free radical polymerization; the soft monomers are monomers with a glass transition temperature Tg2 of -80°C ≤ Tg2 < 50°C and a double bond structure that can undergo free radical polymerization (the glass transition temperature is measured by differential thermal analysis (DSC): the sample is tested using a differential scanning calorimeter (DSC) in a nitrogen atmosphere with a test temperature range of -80°C to 150°C and a heating rate of 10°C / min);

[0010] The functional monomer is selected from monomers containing at least one of carboxyl, amido, hydroxyl and epoxy groups;

[0011] The reactive auxiliary agent is selected from one or more of acrylate-trithiocarbonate copolymer and acrylic acid-trithiocarbonate copolymer.

[0012] Furthermore, the inorganic filler is selected from one or more of boehmite, alumina and zirconia;

[0013] More preferably, the particle size D50 of the inorganic filler is 0.1-0.5 μm.

[0014] Furthermore, the water-based auxiliary adhesive is selected from one or more of polyacrylate adhesives, water-based epoxy resin adhesives, water-based polyurethane adhesives, butadiene-styrene copolymer adhesives, styrene-acrylate copolymer adhesives, polyvinyl acetate adhesives, and ethylene-vinyl acetate copolymer adhesives;

[0015] Furthermore, the thickener is selected from cellulose thickeners;

[0016] More 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.

[0017] Furthermore, the dispersant is a polymeric dispersant with an affinity for inorganic fillers. The main function of the dispersant is to better disperse the inorganic fillers and prevent agglomeration or flocculation. It also shortens the dispersion time of the slurry, allowing for a more uniformly dispersed slurry to be obtained more quickly, making the entire mixing process more efficient. The dispersant used in the present invention is preferably a highly polar, water-soluble dispersant, and more preferably a polymeric copolymer dispersant with an affinity for inorganic fillers.

[0018] The wetting agent has a non-volatile matter content of at least 40% at 150°C for 10 minutes and can improve the wetting of solids.

[0019] 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 copolymer wetting agents, and styrene-maleic anhydride copolymer wetting agents.

[0020] Furthermore, the defoaming agent is a silicone defoaming agent; the main function of the defoaming agent is to eliminate bubbles in the slurry, improve the coating aesthetics of the slurry coating, prevent bubbles from interfering with the slurry film formation, and improve the uniformity of the slurry filling on the diaphragm.

[0021] 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 acidic group-containing hydroxyl-functional copolymer adhesion promoters. The adhesion promoter primarily functions to enhance the polymer microspheres' ability to wet the battery separator under high temperature and high pressure, improve the mechanical interlocking of the polymer microspheres with the separator under hot pressing, and thus assist in enhancing the bonding of the polymer microspheres.

[0022] Furthermore, the polymer microsphere binder is a polymer microsphere emulsion having a solid content of 10-30%;

[0023] The reactive auxiliary agent added to the raw material of the polymer microsphere adhesive of the present invention has polar and non-polar groups and can serve as a stabilizer. At the same time, it can participate in the polymerization reaction, regulate the reaction process, reduce by-products in the polymerization process, and improve the yield.

[0024] The participation of reactive additives in the reaction is mainly divided into five stages:

[0025] (1) Chain initiation stage: At the beginning of the polymerization reaction, initiator I added to the system first generates free radicals through thermal decomposition, and then reacts with the monomer to form chain-growing free radicals;

[0026] (2) Chain transfer and chain growth stage: Chain growth free radicals react with reactive additives to produce intermediate free radicals, which then rapidly undergo β-breakage at a certain side arm to form leaving radicals and dormant species;

[0027] (3) Re-initiation stage: the newly formed leaving radical continues to initiate the remaining monomers to form new chain-growing radicals;

[0028] (4) Chain equilibrium stage: The newly generated chain growth free radicals react with dormant species to produce new intermediate free radicals, which then break to form new chain growth free radicals and dormant species. The chain transfer process between dormant species and chain growth free radicals forms the main equilibrium of "initiation-inactivation". This process is accompanied by the rapid establishment of exchange equilibrium between dormant species and active growth chains. Therefore, polymer chains with similar chain lengths can be formed in the reaction system, thereby forming polymers with a narrow molecular weight distribution. At the same time, the chain growth rate of the reaction system is always lower than the addition-fragmentation equilibrium reaction rate, so that the number of dormant species is much larger than that of active free radicals, thereby reducing the chance of chain termination.

[0029] (5) Chain termination stage: When the polymerization process reaches a certain extent, the diradical termination reaction accelerates, and the free radicals are quenched due to disproportionation termination or coupling termination.

[0030] The relative molecular weight of the reactive auxiliary agent has a certain influence on the size of the synthesized microspheres and the adhesive force of the coated diaphragm. The polymerization degree of the reactive auxiliary agent is preferably between 200-1000.

[0031] Furthermore, the polymerization degree of the reactive auxiliary agent is preferably 200-400.

[0032] Furthermore, the trithiocarbonate in the reactive auxiliary agent is preferably 2-(dodecyl trithiocarbonate)-2-methylpropionic acid;

[0033] Furthermore, the acrylate in the reactive auxiliary agent is preferably one or more selected from methyl acrylate, butyl acrylate, isooctyl acrylate, ethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl acrylate;

[0034] The reactive auxiliary agent of the present invention can be obtained commercially or by self-production. The present invention provides a method for synthesizing the reactive auxiliary agent, comprising the following steps:

[0035] (1) By weight, 20-50 parts 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 are mixed;

[0036] (2) React at 70-80°C under protective atmosphere for 2-10 hours;

[0037] (3) Purify and dry to obtain the reactive auxiliary agent.

[0038] Furthermore, the initiator II is preferably azobisisobutyronitrile;

[0039] Furthermore, the solvent II is preferably selected from 1,4-dioxane, ethanol, and methanol.

[0040] Furthermore, the reaction time is preferably 4-6 h.

[0041] The polymer microsphere binder of the present invention incorporates both hard and soft monomers. The hard monomer provides the microspheres with a certain degree of rigidity and thermal stability, while ensuring a certain degree of cohesion under hot pressing. The soft monomer, on the other hand, provides the microspheres with a certain degree of flowability under hot pressing, promoting wetting between the microspheres and the interface, thereby improving adhesion. The synergistic effect of the two allows the microspheres to be used as a binder in the diaphragm ceramic coating slurry, effectively improving the adhesion between the diaphragm and the electrode.

[0042] Furthermore, the weight ratio of the hard monomer to the soft monomer in the basic monomer is preferably 30-70:70-30.

[0043] Furthermore, the hard monomer is selected from one or more of acrylonitrile, styrene, methyl methacrylate, ethyl methacrylate, methacrylic acid, hydroxyethyl methacrylate, tert-butyl methacrylate, and isopropyl methacrylate.

[0044] Furthermore, 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.

[0045] The functional monomers of the present invention are preferably selected from one or more of methacrylic acid, diacetone acrylamide, hydroxyethyl acrylate, N-methylol acrylamide, hydroxypropyl methacrylate, and hydroxypropyl acrylate. By adding a certain amount of the functional monomers, their functional groups can form chemical bonds with the electrode interface groups, further improving the bonding ability between the microspheres and the interface.

[0046] The initiator I of the present invention is preferably an azo initiator; its main function is to generate free radicals under heating to initiate polymerization reaction.

[0047] Furthermore, the initiator I is selected from one or more of azobisisobutyronitrile and azobisisoheptanenitrile;

[0048] Furthermore, the crosslinking agent of the present invention is a monomer having two or three double bonds and having a crosslinking function. The addition of the crosslinking agent can promote polymerization to produce a crosslinked structure, which is beneficial to improving the stability of the microspheres in the electrolyte.

[0049] Furthermore, the crosslinking agent is preferably selected from one or more of N,N-methylenebisacrylamide, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, divinylbenzene, and allyl methacrylate;

[0050] Furthermore, the solvent I is selected from one or more combinations of methanol, ethanol, isopropanol and water, and is mainly used as a dispersion medium.

[0051] Furthermore, the particle size D50 of the polymer microspheres is 1-7 μm;

[0052] The amount of polymer microsphere binder added is limited to the range of 3-15 parts mainly because too low an amount of microspheres added cannot ensure good adhesion, and a higher amount of addition will cause the polymer microspheres to form a film in the diaphragm after hot pressing, resulting in pore blockage, which is not conducive to the transmission of lithium ions.

[0053] More preferably, the amount of the polymer microsphere binder added is 4-12 parts.

[0054] Furthermore, the preparation method of the polymer microsphere binder comprises the following steps:

[0055] The basic monomer, functional monomer, initiator I, crosslinking agent, reactive auxiliary agent and solvent I are mixed and reacted at 60-70° C. for 8-15 hours under a protective atmosphere to obtain a polymer microsphere adhesive.

[0056] Further preferably, the preparation method of the polymer microsphere binder comprises the following steps:

[0057] (1) Place the weighed monomers (including basic monomers, functional monomers, and cross-linking agents) into the reactor, add 1 / 2-3 / 4 of solvent I, control the temperature at 50-60°C, and maintain the speed at 150-200 rpm;

[0058] (2) Then add the reactive additive, keep the temperature constant, and increase the speed to 200-300 rpm;

[0059] (3) Vacuum for 0.5-1 hour to remove internal oxygen and then pass nitrogen through. The reaction is carried out under a nitrogen atmosphere to increase the polymerization rate and reduce the residue rate;

[0060] (4) Add initiator I to the remaining 1 / 4-1 / 2 of solvent I, stir until homogeneous, and then add dropwise to the reactor;

[0061] (5) After all initiator I is added, the temperature is raised to 60-70°C and the reaction is carried out at this temperature for 8-15 hours to obtain the target polymer microsphere emulsion;

[0062] (6) The emulsion is then filtered through a 200-mesh sieve, the filtrate is centrifuged, and then redispersed with a reaction solvent. This process is repeated 2-5 times, and finally dispersed with water to obtain a polymer microsphere binder.

[0063] The method for preparing the above-mentioned battery separator coating slurry comprises the following steps:

[0064] (1) Mix the inorganic filler, thickener and water, maintain the speed at 400-700 rpm, and stir for 1-2 hours;

[0065] (2) Increase the speed to 600-900 rpm, add the dispersant dropwise, and stir for 0.5-1 hour after addition;

[0066] (3) Add polymer microsphere binder and wetting agent, increase the speed to 1000-1200 rpm, and maintain high-speed stirring for 0.5-1 hour;

[0067] (4) Reduce the rotation speed to 150-300 rpm, add defoaming agent, water-based auxiliary binder and adhesion promoter drop by drop, and keep stirring at low speed for 0.5-1 hour after adding to eliminate the bubbles inside the slurry, and then obtain the battery separator coating slurry.

[0068] A coated separator comprises a battery separator and the above-mentioned battery separator coating slurry, wherein the battery separator coating slurry is coated on the surface of the battery separator.

[0069] The method for preparing the coated diaphragm comprises the following steps:

[0070] The battery separator coating slurry is coated on the battery separator, and then dried 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.

[0071] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0072] (1) The battery separator coating slurry of the present invention is added with a polymer microsphere binder and an adhesion promoter. The prepared coated separator has low air permeability increment, strong adhesion to the electrode, good durability, and an air permeability increment of only within 20 seconds. The adhesion to the electrode at room temperature after hot pressing is more than 2 N / m. The adhesion of the hot-pressed sample after being kept at 50°C for 30 minutes and after being immersed in the electrolyte for 3 days is more than 2 N / m. Compared with the existing battery separator coating slurry, it has stronger advantages.

[0073] (2) The preparation method of the battery separator of the present invention does not require complicated operation steps. The bonding requirements can be achieved by coating the battery separator coating slurry on the separator once. Compared with the conventional secondary coating, one step is omitted and it has higher convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a SEM photo of the coated diaphragm prepared in Example 1. DETAILED DESCRIPTION

[0075] In order to make the purpose, technical solutions and advantages of the present invention more clear, several examples will be cited to further illustrate the present invention in detail. The technical solutions listed are only used to explain the present invention and do not limit the scope of protection of the present invention. If the concept remains unchanged, any replacement or substitution of the technical solution should be within the technical protection scope of the present invention. Unless otherwise specified, all chemical reagents were purchased from Aladdin Chemical Reagents.

[0076] In order to characterize the advantages of the battery separator coating slurry of the present invention, the prepared coated separator was tested using commonly used testing methods. The tested properties included air permeability and average adhesion to the electrode.

[0077] (1) Air permeability test: According to the Gurley method (the instrument applies a pressure of 1.21 kPa, 100 mL of air passes through an area of 6.45 cm 2 The test was carried out using the equipment manufactured by Guangzhou Runhu Instrument Co., Ltd. The equipment model was RH-TQG645. Each group of coated diaphragms was tested three times, and the average value was taken and rounded to an integer as the final result.

[0078] (2) Adhesion test with the electrode: Cut the coated diaphragm into 6 The slurry coating surface was overlapped with the battery negative electrode graphite plate of the same size, and then a hot press (Shenzhen Xinyi Hydraulic Equipment Co., Ltd., model XY-Z2118-3T) was used to press the sample at 80 ° C for 1 minute under 3 MPa. After the sample cooled, the separator was cut into pieces with a width of 2 12 cm specimens were then tested for adhesion using an electronic tensile testing machine (Guangzhou Runhu Instrument Co., Ltd., model RH-L600). Each group of samples was tested 3 times, and the average value was taken and rounded to 1 decimal place as the final result. In order to highlight the adhesion advantage of the battery separator coating slurry in the present invention, the hot-pressed samples were kept at 50 ° C for 30 minutes and immersed in the electrolyte (wherein the mass ratio of ethylene carbonate: dimethyl carbonate: diethyl carbonate = 3:5:2) for 3 days before being tested for adhesion using a tensile testing machine. Each group of samples was tested 3 times, and the average value was taken and rounded to 1 decimal place as the final result.

[0079] (3) Microsphere size: Take a small amount of the aqueous dispersion of microspheres, dilute it with water to an appropriate concentration, and then ultrasonically disperse it for 5 minutes. Use a Malvern 3000 particle size analyzer to measure the size of the microspheres and measure the particle size D50 of the microspheres.

[0080] The "parts" in the examples are all parts by weight.

[0081] Example 1

[0082] This example proposes 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 aluminum oxide (A500, Zhongyan Nano New Materials), 1 part of water-based polyacrylate auxiliary binder (LA136D, Sichuan Yindile Materials Technology Co., Ltd.), 0.5 parts of carboxymethyl cellulose thickener (Aladdin Chemical Reagent, C501052), 1 part of dispersant (Tech-6074, Tiger Additive), 0.2 parts of polyacrylate wetting agent (BYK-ET-3030, BYK Chemical), 0.3 parts of defoaming agent (Tech-38101, Tiger Additive), 1 part of adhesion promoter (BYK-4500, BYK Chemical), and 80 parts of water (laboratory purified water).

[0083] The preparation method of polymer microsphere binder is as follows:

[0084] (1) A mixture of 33 parts of styrene and n-octyl methacrylate (mass ratio 5:5), 5 parts of methacrylic acid, and 7 parts of ethylene glycol dimethacrylate were weighed and placed in a reactor. 3 / 4 of the 50 parts of methanol was added. The temperature was controlled at 55°C and the rotation speed was maintained at 150 rpm.

[0085] (2) Then, 3 parts of PMA400 were added, the temperature was kept constant, and the rotation speed was increased to 200 rpm;

[0086] (3) Vacuum for 1 hour to remove internal oxygen and then pass nitrogen through. The reaction is carried out under a nitrogen atmosphere to increase the polymerization rate and reduce the residue rate;

[0087] (4) Add 2 parts of azobisisobutyronitrile to the remaining 1 / 4 of methanol, stir until homogeneous, and then add dropwise to the reactor;

[0088] (5) After all the initiators are added, the temperature is raised to 65°C and the reaction is carried out at this temperature for 10 hours to obtain the target microsphere emulsion;

[0089] (6) The emulsion is then filtered through a 200-mesh sieve, the filtrate is centrifuged, and then redispersed with a reaction solvent. This process is repeated twice, and finally dispersed with water to a solid content of 20% to obtain a polymer microsphere binder.

[0090] The preparation method of additive PMA400 is as follows:

[0091] (a) 30 parts of methyl acrylate, 0.3 parts of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, 1 part of azobisisobutyronitrile, and 68.7 parts of 1,4-dioxane were placed in a round-bottom flask preheated at 70°C;

[0092] (b) nitrogen was passed through for 30 minutes to remove the internal air, followed by reaction at 70°C for 4 hours;

[0093] (c) The sample was recrystallized from n-hexane and then dissolved in 1,4-dioxane, and this process was repeated three times;

[0094] (d) The sample was vacuum dried in a vacuum oven at 40°C for 20-25 hours to obtain the desired reactive stabilizer PMA400.

[0095] The coating process of battery separator coating slurry is as follows:

[0096] (1) Mix the weighed inorganic filler, thickener and water and stir at a speed of 500 rpm for 1 hour;

[0097] (2) Increase the speed to 700 rpm, add the dispersant dropwise, and stir for 0.5 hours after addition;

[0098] (3) Add polymer microsphere binder and wetting agent, increase the speed to 1200 rpm, and maintain high-speed stirring for 0.5 hours;

[0099] (4) Reduce the rotation speed to 200 rpm, add defoamer, water-based auxiliary binder and adhesion promoter drop by drop, and keep stirring at low speed for 0.5 hours after adding to eliminate the bubbles inside the slurry, and the battery separator coating slurry required for the battery separator can be obtained;

[0100] (5) The battery separator coating slurry is coated on the battery separator, and then dried at 60°C. The coating thickness after drying is controlled to be 2 microns, and a coated separator can be prepared.

[0101] Example 2

[0102] This example proposes 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 aluminum oxide (A500, Zhongyan Nano New Materials), 1 part of water-based ethylene-vinyl acetate copolymer auxiliary binder (558ED, Wacker Chemie), 0.5 parts of thickener methyl cellulose (Aladdin Chemical Reagent, M112867), 1 part of dispersant (Tech-6320, Tiger Additive), 0.2 parts of wetting agent (BYK-ET-3032, BYK Chemical), 0.3 parts of defoaming agent (Tech-371W, Tiger Additive), 1 part of adhesion promoter (BYK-4509, BYK Chemical), and 80 parts of water (laboratory purified water).

[0103] Wherein, the preparation method of polymer microsphere binder is:

[0104] (1) 20 parts of a mixture of methyl methacrylate, butyl methacrylate and hydroxypropyl methacrylate (mass ratio of 3:2:5), 6 parts of diacetone acrylamide and 5 parts of ethylene glycol dimethacrylate were weighed and placed in a reactor. 63 parts of a mixed solvent of 3 / 4 methanol and water (mass ratio of 8:2) were added. The temperature was controlled at 55°C and the rotation speed was maintained at 150 rpm.

[0105] (2) Then, 3 parts of PEA300 were added, the temperature was kept constant, and the rotation speed was increased to 200 rpm;

[0106] (3) Vacuum for 1 hour to remove internal oxygen and then pass nitrogen through. The reaction is carried out under a nitrogen atmosphere to increase the polymerization rate and reduce the residue rate;

[0107] (4) Add 3 parts of azobisisobutyronitrile to the remaining 1 / 4 of the mixed solvent of methanol and water, stir until homogeneous, and then add dropwise to the reactor;

[0108] (5) After all the initiators are added, the temperature is raised to 65°C and the reaction is carried out at this temperature for 10 hours to obtain the target microsphere emulsion;

[0109] (6) The emulsion is then filtered through a 200-mesh sieve, the filtrate is centrifuged, and then redispersed with a reaction solvent. This process is repeated twice, and finally dispersed with water to a solid content of 20% to obtain a polymer microsphere binder.

[0110] The preparation method of additive PEA300 is as follows:

[0111] (a) 30 parts of ethyl acrylate, 0.3 parts of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, 1 part of azobisisobutyronitrile, and 68.7 parts of 1,4-dioxane were placed in a round-bottom flask preheated at 70°C;

[0112] (b) nitrogen was passed through for 30 minutes to remove the internal air, followed by reaction for 6 hours;

[0113] (c) The sample was recrystallized from n-hexane and then dissolved in 1,4-dioxane, and this process was repeated three times;

[0114] (d) The sample was dried in a vacuum oven at 40°C for 20-25 hours to obtain the desired reactive stabilizer PEA300.

[0115] The coating process of the battery separator coating slurry is the same as that in Example 1.

[0116] Example 3

[0117] This example proposes 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 aluminum oxide (A500, Zhongyan Nano New Materials), 1 part of water-based polyacrylate auxiliary binder (LA136D, Sichuan Yindile Materials Technology Co., Ltd.), 0.5 parts of thickener hydroxypropyl cellulose (Aladdin Chemical Reagent, H742522), 1 part of dispersant (Tech-6076, Tiger Additive), 0.2 parts of wetting agent (BYK-ET-3034, BYK Chemical), 0.3 parts of defoaming agent (Tech-3362, Tiger Additive), 1 part of adhesion promoter (BYK-4510, BYK Chemical), and 80 parts of water (laboratory purified water).

[0118] The preparation method of polymer microsphere binder is as follows:

[0119] (1) A mixture of 37 parts of styrene, acrylonitrile and butyl methacrylate (mass ratio of 2:2:6), 5 parts of hydroxypropyl methacrylate and 3 parts of allyl methacrylate were weighed and placed in a reactor. 3 / 4 of the 50 parts of ethanol was added. The temperature was controlled at 55°C and the rotation speed was maintained at 150 rpm.

[0120] (2) Then, 3 parts of PEHA400 were added, the temperature was kept constant, and the rotation speed was increased to 200 rpm;

[0121] (3) Vacuum for 1 hour to remove internal oxygen and then pass nitrogen through. The reaction is carried out under a nitrogen atmosphere to increase the polymerization rate and reduce the residue rate;

[0122] (4) Add 2 parts of azobisisobutyronitrile to the remaining 1 / 4 of ethanol, stir until homogeneous, and then add dropwise to the reactor;

[0123] (5) After all the initiators are added, the temperature is raised to 65°C and the reaction is carried out at this temperature for 10 hours to obtain the target microsphere emulsion;

[0124] (6) The emulsion is then filtered through a 200-mesh sieve, the filtrate is centrifuged, and then redispersed with a reaction solvent. This process is repeated twice, and finally dispersed with water to a solid content of 20% to obtain a polymer microsphere binder.

[0125] The synthesis method of additive PEHA400 is:

[0126] (a) Place 20 parts of isooctyl acrylate, 0.1 parts of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, 0.9 parts of azobisisobutyronitrile, and 79 parts of ethanol in a round-bottom flask preheated at 70°C;

[0127] (b) nitrogen was passed through for 30 minutes to remove the internal air, followed by reaction at 70°C for 4 hours;

[0128] (c) The sample was recrystallized from n-hexane and then dissolved in ethanol, and this process was repeated three times;

[0129] (d) The sample was dried in a vacuum oven at 40°C for 20-25 hours to obtain the desired reactive stabilizer PEHA400.

[0130] The coating process of the battery separator coating slurry is the same as that in Example 1.

[0131] Example 4

[0132] This example proposes 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 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, 2 wt% aqueous solution at 20°C, Aladdin Chemical Reagent), 1 part of dispersant (Tech-6270, Tiger Additives), 0.2 parts of wetting agent (BYK-ET-3033, BYK Chemicals), 0.3 parts of defoaming agent (Tech-3901, Tiger Additives), 0.5 parts of adhesion promoter (Tech-7720, Tiger Additives), and 79 parts of water.

[0133] The preparation method of the polymer microsphere binder is the same as that in Example 1.

[0134] The preparation method of the additive PMA400 is the same as that in Example 1.

[0135] The coating process of the battery separator coating slurry is the same as that in Example 1.

[0136] Example 5

[0137] This example proposes a battery separator coating slurry, its preparation method, and application. The formula of the separator 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 (150-400 mPa·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.

[0138] The preparation method of the polymer microsphere binder is the same as that in Example 1.

[0139] The preparation method of the additive PMA400 is the same as that in Example 1.

[0140] The coating process of the battery separator coating slurry is the same as that in Example 1.

[0141] Example 6

[0142] In Example 1, the coating thickness of the membrane coating slurry after drying is controlled to be 3 μm, and the other raw materials and processes remain the same.

[0143] Example 7

[0144] The addition amount of the polymer microsphere binder in Example 1 was changed to 15 parts, and the other raw materials and processes remained the same.

[0145] Example 8

[0146] 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.

[0147] Example 9

[0148] The amount of adhesion promoter added in Example 1 was changed from 1 part to 3 parts, and the other raw materials and processes remained the same.

[0149] Example 10

[0150] The amount of adhesion promoter added in Example 1 was changed from 1 part to 0.5 parts, and the other raw materials and processes remained the same.

[0151] In order to more clearly highlight the advantages of the present invention, Example 1 is used as a reference benchmark, and a ceramic slurry prepared by not adding a polymer microsphere binder to the ceramic slurry is used as Comparative Example 1; Example 1 is used as a reference benchmark, and the amount of the polymer microsphere binder added to the ceramic slurry is modified to 18 parts as Comparative Example 2; Example 1 is used as a reference benchmark, and the adhesion promoter in the ceramic slurry is removed, and the other raw materials and processes remain the same as Comparative Example 3; the polymer microsphere binder in Example 1 is replaced with PSt microspheres of the same size as Comparative Example 4; the auxiliary agent in the original Example 1 is changed from the original PMA400 to PMA50 to prepare polymer microspheres as Comparative Example 5; the functional monomer (methacrylic acid) in the original Example 1 is removed from the preparation raw materials to prepare polymer microspheres as Comparative Example 6;

[0152] The synthesis method of the auxiliary agent PMA50 in the comparative example is:

[0153] (1) By weight, 4 parts of methyl acrylate, 0.3 parts of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, 1 part of azobisisobutyronitrile, and 68.7 parts of 1,4-dioxane were placed in a round-bottom flask preheated at 70°C;

[0154] (2) Nitrogen was passed through for 30 minutes to remove the internal air, followed by reaction at 70°C for 4 hours;

[0155] (3) The sample was recrystallized with n-hexane and then dissolved with 1,4-dioxane, and this process was repeated three times;

[0156] (4) The sample is vacuum dried in a vacuum oven at 40°C for 20-25 hours to obtain the desired reactive stabilizer PMA50.

[0157] The above examples and comparative examples were tested for air permeability, average adhesion to the electrode under different conditions, etc. The detailed test results are summarized in Table 1:

[0158] Table 1

[0159]

[0160] Data Analysis:

[0161] It can be seen from the examples in Table 1 that the coated diaphragms prepared by the present invention have good adhesion under different environments. At the same time, the air permeability increase of the diaphragm after coating is within 20s. The lower air permeability increase indicates that the battery diaphragm coating slurry prepared by the present invention has little effect on the air permeability of the diaphragm itself, and can ensure the smooth transmission of lithium ions between the diaphragms.

[0162] It can also be seen from Comparative Example 1 that without the addition of the polymer microsphere binder of the present invention, the adhesion between the diaphragm and the electrode is almost untestable, making it difficult to meet the requirements for use; in Comparative Example 2, due to the high amount of microspheres added, the adhesion is greater, but at the same time it causes a large increase in the air permeability of the diaphragm, hindering the transmission of lithium ions. Therefore, the microspheres should be within a reasonable range, not the more the better; after the adhesion promoter is removed in Comparative Example 3, the air permeability increase is slightly smaller than that in Example 1, mainly because the adhesion is significantly reduced, 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 instead of the polymer microspheres prepared in the present invention, and the adhesion is very low. In Comparative Example 5, PMA50 is used as a reactive auxiliary agent in the raw materials for preparing the polymer microsphere binder, and the adhesion of the coated diaphragm 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 diaphragm is low.

Claims

1. A battery separator coating slurry, characterized in that: The composition comprises, by weight, 3-15 parts of a polymer microsphere binder, 1-20 parts of an inorganic filler, 1-5 parts of an aqueous auxiliary binder, 0.5-3 parts of a thickener, 0.5-2 parts of a dispersant, 0.2-0.5 parts of a wetting agent, 0.3-1 parts of a defoaming agent, 0.5-3 parts of an adhesion promoter, and 30-80 parts of water; The raw materials of the polymer microsphere adhesive include, by weight, 20-40 parts of basic monomer, 5-10 parts of functional monomer, 1-5 parts of initiator I, 3-10 parts of cross-linking agent, 50-90 parts of solvent I and 2-8 parts of reactive auxiliary agent; the polymerization degree of the reactive auxiliary agent is 200-1000; The basic monomers include hard monomers and soft monomers; the hard monomers are monomers with a glass transition temperature Tg1 of 50°C ≤ Tg1 ≤ 120°C and a double bond structure capable of free radical polymerization; the soft monomers are monomers with a glass transition temperature Tg2 of -80°C ≤ Tg2 < 50°C and a double bond structure capable of free radical polymerization; The functional monomer is selected from monomers containing at least one of carboxyl, amido, hydroxyl and epoxy groups; The reactive auxiliary agent is selected from one or more of acrylate-trithiocarbonate copolymer and acrylic acid-trithiocarbonate copolymer; wherein, by weight, the acrylic acid or acrylate monomer is 20-50 parts, and the trithiocarbonate is 0.1-2 parts.

2. The battery separator coating slurry according to claim 1, characterized in that: The inorganic filler is selected from one or more of boehmite, alumina and zirconia; The water-based auxiliary adhesive is selected from one or more of polyacrylate adhesives, water-based epoxy resin adhesives, water-based polyurethane adhesives, butadiene-styrene copolymer adhesives, styrene-acrylate copolymer adhesives, polyvinyl acetate adhesives, and ethylene-vinyl acetate copolymer adhesives; The thickener is selected from one or more of carboxymethyl cellulose thickeners, hydroxymethyl cellulose thickeners, hydroxyethyl cellulose thickeners, hydroxypropyl cellulose thickeners and methyl cellulose thickeners; The dispersant is a polymeric 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 copolymer wetting agents, and styrene-maleic anhydride copolymer wetting agents; The defoaming agent is a silicone defoaming agent; 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 acidic group-containing hydroxyl functional copolymer adhesion promoters.

3. The battery separator coating slurry according to claim 1, characterized in that: The polymer microsphere adhesive is a polymer microsphere emulsion with a solid content of 10-30%; 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, characterized in that: The hard monomer is selected from one or more of acrylonitrile, styrene, methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, tert-butyl methacrylate, and 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-methylol acrylamide, hydroxypropyl methacrylate, and hydroxypropyl acrylate; Initiator I is selected from one or more of azobisisobutyronitrile and azobisisoheptanenitrile; The crosslinking agent is selected from one or more of N,N-methylenebisacrylamide, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, divinylbenzene, and allyl methacrylate; Solvent I is selected from one or more combinations of methanol, ethanol, isopropanol and water; The trithiocarbonate in the reactive auxiliary agent is 2-(dodecyl trithiocarbonate)-2-methylpropionic acid; The acrylic acid ester in the reactive auxiliary agent 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 agent comprises the following steps: (1) By weight, 20-50 parts 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 are mixed; (2) React at 70-80°C under protective atmosphere for 2-10 hours; (3) Purify and dry to obtain the reactive auxiliary agent.

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

7. The battery separator coating slurry according to claim 1, characterized in that: The particle size D50 of the polymer microspheres is 1-7 μm; The preparation method of the polymer microsphere binder comprises the following steps: The basic monomer, functional monomer, initiator I, crosslinking agent, reactive auxiliary agent and solvent I are mixed and reacted at 60-70° C. for 8-15 hours under a protective atmosphere to obtain a polymer microsphere adhesive.

8. The method for preparing the battery separator coating slurry according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Mix the inorganic filler, thickener and water, maintain the speed at 400-700 rpm, and stir for 1-2 hours; (2) Increase the speed to 600-900 rpm, add the dispersant dropwise, and stir for 0.5-1 hour after addition; (3) Add polymer microsphere binder and wetting agent, increase the speed to 1000-1200 rpm, and maintain high-speed stirring for 0.5-1 hour; (4) Reduce the rotation speed to 150-300 rpm, add defoaming agent, water-based auxiliary binder and adhesion promoter drop by drop, and keep stirring at low speed for 0.5-1 hour after adding to eliminate the bubbles inside the slurry, and then obtain the battery separator coating slurry.

9. A coated diaphragm, characterized in that: The invention comprises a battery separator and the battery separator coating slurry according to any one of claims 1 to 7, wherein the battery separator coating slurry is coated on the surface of the battery separator.

10. The method for preparing the coated diaphragm according to claim 9, characterized in that: The following steps are involved: The battery separator coating slurry is coated on the battery separator, and then dried 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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