A core-shell microsphere-containing adhesive emulsion and a method for preparing the same

Abstract

The application discloses a kind of core-shell microspheres-containing bonding emulsion and preparation method thereof, and the bonding emulsion includes, by mass parts, core-shell microspheres 100-150 parts, emulsifier 0.1-5 parts, deionized water 150-2000 parts, the particle size D50 of core-shell microspheres is 0.02-5 μm, and the core-shell microspheres have polyolefin inner core and outer shell chemically bonded with polyolefin inner core, and the mass ratio of inner core and outer shell is (50-150):(1-150);The core-shell microspheres are prepared by the following steps: modified polyolefin resin is reacted with active group-containing vinyl monomer to obtain vinyl-containing polyolefin inner core;And then, acrylic polymer and / or acrylate polymer-containing outer shell are prepared by reaction.The bonding emulsion of the application considers electrochemical stability and ultra-low elution swelling rate, high temperature resistance, high peel force and other multi-dimensional synergistic properties under the premise of fluorine-free environmental protection, effectively solves the bottleneck problems such as high-silicon negative electrode expansion, high-temperature cycle and high-voltage stability.

Description

Technical Field

[0001] This invention relates to the field of water-based adhesives, and more particularly to an adhesive emulsion containing core-shell microspheres and its preparation method. Background Technology

[0002] Currently, there are many types of waterborne adhesives on the market, mainly including waterborne polyester, waterborne polyurethane, waterborne epoxy, waterborne EVA, waterborne styrene-butadiene latex (SBR), waterborne polyacrylate, and waterborne PVDF. Among them, waterborne polyacrylate latex, waterborne styrene-butadiene latex (SBR), and waterborne PVDF are widely used in the lithium-ion battery field due to their good film-forming properties, adhesion, and process adaptability, especially in negative electrode adhesive emulsions and separator coating adhesive emulsions.

[0003] With the continuous iteration of lithium battery technology and the rapid increase in performance requirements, the limitations of traditional aqueous binding emulsions in high-performance battery systems are becoming increasingly apparent, mainly in the following three aspects:

[0004] 1. The Expansion Challenge of High-Silicon-Content Anodes: Silicon-carbon anodes have become the preferred material for next-generation high-energy-density anodes due to their high theoretical specific capacity (up to 4200 mAh / g). However, silicon expands by more than 300% during charge and discharge, leading to a surge in stress on the electrode structure and placing extreme demands on the high peel strength and dynamic adaptability of the bonding emulsion. Although existing aqueous polyacrylate and SBR bonding emulsions have a certain degree of flexibility, they are prone to bonding failure in high-silicon-loaded systems (Si content > 10%), resulting in active material detachment and accelerated capacity decay.

[0005] 2. Ion transport and structural stability under high-temperature cycling: In pursuit of higher energy density, the battery operating temperature window is constantly widening (often reaching above 60℃), while fast charging technology demands higher Li... + Diffusion rate. This requires the diaphragm coating binder emulsion to not clog micropores and maintain stable air permeability during long-term high-temperature cycling; simultaneously, the negative electrode binder emulsion must have low swelling ratio and non-softening properties at high temperatures to avoid colloidal dissolution or excessive expansion hindering Li. + Insertion / extraction channels. Although traditional PVDF is resistant to electrolytes, it contains fluorine and is prone to swelling at high temperatures; water-based polyacrylates are prone to ester bond hydrolysis in high-temperature electrolytes, resulting in leaching products that contaminate the electrolyte and trigger side reactions.

[0006] 3. Electrochemical stability requirements for high-voltage cathodes: With the increasing use of high-voltage cathodes such as lithium cobalt oxide (LiCoO2) and high-nickel ternary cathodes (NCM811 / NCA) (>4.3V vs. Li / Li), the electrochemical stability requirements for high-voltage cathodes are becoming more stringent. +With the increasing prevalence of [unclear - possibly referring to a specific technology or process], binding emulsions need to withstand stronger oxidative environments. The ester and hydroxyl functional groups in traditional aqueous binding emulsions are prone to oxidative decomposition under high voltage, producing gases or deposits that threaten battery safety and cycle life. Narrow electrochemical windows and insufficient oxidative stability have become key bottlenecks restricting the application of aqueous systems in high-end batteries.

[0007] Furthermore, increasingly stringent environmental regulations are driving the trend towards fluorine-free production. While PVDF, as a representative of fluorinated adhesive emulsions, boasts excellent performance, its production and disposal processes pose a risk of fluorine pollution, leading to gradual restrictions. Although aqueous systems are fluorine-free, existing products struggle to simultaneously achieve multiple performance characteristics such as high-temperature resistance, low dissolution, low swelling, and high adhesion, making it difficult to meet the comprehensive requirements of next-generation solid-state / semi-solid-state batteries and high-safety power batteries.

[0008] Patent application CN120865819A discloses a flexible waterborne adhesive prepared by graft copolymerization of vinyl-terminated waterborne polyurethane prepolymer and acrylic monomer, used to improve the brittleness problem of polyacrylic acid adhesives. This patent achieves point-to-point / point-to-line bonding by introducing long-chain polybutadiene flexible segments, with a peel force of 12–15 N / m, a swelling rate of 18%–25%, and a precipitation rate of 0.8%–1.2%, exhibiting significantly better flexibility than traditional polyacrylic acid adhesives. Similarly, patent CN118853027B discloses a network crosslinked polyacrylic acid adhesive prepared by free radical polymerization of acrylic acid / amide / nitrile / ester + bisphenol compounds, used as a replacement for CMC+SBR in lithium battery anodes. This patent utilizes bisphenol polyphenol crosslinking and hydrogen bonding to achieve high thickening, high elastic modulus, and excellent adhesion, with a volume expansion rate of 5.3%–12.3% and a capacity retention rate of 92.3%–94.5% in graphite anodes, significantly better than traditional CMC+SBR.

[0009] However, the above-mentioned solutions still use polyacrylic acid as the main structure, containing a large number of active groups such as -COOH, -CONH2, and phenol-OH. Under the intense expansion of the high-silicon anode, the rigidity is too high, making it prone to brittleness and unable to adapt dynamically. Under high-temperature cycling, ester / hydrogen bonds hydrolyze, resulting in a high rate of change in permeability, which cannot meet the requirements of fast charging. Under high-voltage conditions, phenol / nitrile groups oxidize and decompose, leading to poor electrochemical stability. Invention patent application CN121086725A discloses a modified acrylate emulsion adhesive, its preparation method, and its application. This modified acrylate emulsion adhesive is prepared by a semi-continuous emulsion polymerization method, using an aqueous polyolefin as the core structure of the emulsion and an acrylate polymer as the shell structure. This application aims to overcome the technical problem of poor compatibility between acrylate emulsion films and polyolefin separators, and through this modified acrylate emulsion adhesive, improves its compatibility with polyolefin separators and electrolytes, thereby improving the electrochemical performance of lithium-ion batteries. However, the core-shell structure of the emulsion particles in this emulsion adhesive neglects the bonding ability between its polyolefin core layer and acrylate copolymer shell layer, which easily leads to core-shell separation. This requires a larger shell mass to fully cover the core layer, amplifying the defects of the shell layer in application.

[0010] Therefore, how to optimize the structure of waterborne adhesive emulsions to achieve comprehensive performance such as low dissolution, low swelling, high temperature resistance, and high peel strength while ensuring electrochemical safety is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0011] To address the shortcomings of the existing technologies, this invention provides a core-shell microsphere adhesive emulsion and its preparation method. The emulsion uses polyolefin resin as a temperature-resistant inert core, introduces carbon-carbon double bonds as seeds through vinyl monomers containing active groups, and initiates the polymerization of acrylic monomers and / or acrylate monomers to form a core-shell microsphere adhesive emulsion that chemically bonds the core and shell. Under the premise of being fluorine-free and environmentally friendly, it achieves a comprehensive performance across multiple dimensions, including electrochemical stability, ultra-low dissolution, low swelling, high temperature resistance, and high peel strength, thus solving the comprehensive bottlenecks of high-silicon anode expansion, high-temperature cycling, and high voltage stability.

[0012] In a first aspect, the present invention provides an adhesive emulsion containing core-shell microspheres, wherein, by weight, the adhesive emulsion comprises:

[0013] 100-150 parts of core-shell microspheres;

[0014] Emulsifier 0.1 to 5 parts;

[0015] 150-2000 parts of deionized water;

[0016] The particle size D50 of the core-shell microspheres is 0.02–5 μm;

[0017] The core-shell microspheres have a polyolefin core and a shell chemically bonded to the polyolefin core, wherein the mass ratio of the polyolefin core to the shell is (50-150):(1-150).

[0018] The core-shell microspheres are prepared by the following steps:

[0019] The modified polyolefin resin is reacted with a vinyl monomer containing an active group to obtain a vinyl-containing polyolefin core;

[0020] Acrylic monomers and / or acrylate monomers are mixed with the vinyl-containing polyolefin core and reacted to obtain the outer shell containing acrylic polymers and / or acrylate polymers.

[0021] This invention obtains a polyolefin core with a vinyl-activated layer through a pre-reaction of vinyl monomers containing active groups with modified polyolefin resin. This pre-reaction significantly enhances the polarity of the polyolefin core, better matching its polarity with acrylic polymers and / or acrylate polymers, thus strengthening core-shell compatibility. The chemical bonds formed through the reaction further firmly bond the core and shell together, resulting in a three-layer core-shell integrated structure: a modified polyolefin resin inner layer, a vinyl-activated layer, and an outer shell. Furthermore, the mass and thickness of the polyolefin core and shell offer greater design flexibility. For example, if the mass percentage of the polyolefin core is designed to be above 40 wt%, it is difficult to form a complete and stable core-shell structure using other mixing or coating methods. It also achieves comprehensive properties such as low dissolution, low swelling, high temperature resistance, and high peel strength.

[0022] Preferably, the particle size D50 of the core-shell microspheres is 0.2–3 μm.

[0023] Preferably, the solid content of the core-shell microsphere-containing adhesive emulsion is 10% to 50%.

[0024] This invention utilizes a high water-to-oil ratio emulsion system and the synergistic effect of selected emulsifiers and co-emulsifiers to form fine and stable oil droplets under high shear dispersion by controlling the solid content of the adhesive emulsion and the particle size of the core-shell microspheres. By combining the timing control of the polymerization inhibitor and the dual initiation system, it ensures that the grafting of vinyl monomers occurs only on the surface of the polyolefin resin and the polymerization of the shell monomers occurs only oriented on the surface of the oil droplets, avoiding particle coarsening or agglomeration. Finally, after solvent removal, the emulsion yields a core-shell particle dispersion with moderate solid content and uniform particle size.

[0025] The above-mentioned preferred solid content and particle size range can effectively improve the storage stability and coating processability of the emulsion, ensuring that the bonding emulsion is evenly dispersed and forms a dense film in the negative electrode slurry or separator coating; the fine particle size increases the contact area between the core-shell particles and the active material or ceramic particles, strengthens the interfacial adhesion and structural buffering capacity, and further synergistically improves the comprehensive performance of the fluorine-free core-shell bonding emulsion in terms of ultra-low dissolution, low swelling, high temperature resistance and high peel strength.

[0026] Preferably, the modified polyolefin resin includes one or more of maleic anhydride-grafted polyolefin, (meth)acrylic acid-grafted polyolefin, and (meth)acrylic acid-ethylene copolymer;

[0027] The active groups in the vinyl monomer containing active groups include one or more of hydroxyl, epoxy, and amino groups.

[0028] More preferably, the maleic anhydride-grafted polyolefin has a grafting rate of 0.2% to 10%, a melting point range of 60 to 150°C, preferably 70 to 130°C, and a weight-average molecular weight (Mw) range of 5000 Da to 200,000 Da, preferably 40,000 Da to 120,000 Da.

[0029] The grafting rate of the (meth)acrylic acid grafted polyolefin is 0.2% to 10%, the melting point range is 60 to 150°C, preferably 70 to 130°C, and the weight-average molecular weight (Mw) ranges from 5000 Da to 200,000 Da, preferably 40,000 Da to 120,000 Da.

[0030] The (meth)acrylic acid-ethylene copolymer, preferably a methacrylic acid-ethylene copolymer, has a MI (190℃ / 2.16kg) ≥ 20 g / 10min and a melting point range of 60~130℃.

[0031] This invention selects the aforementioned specific modified polyolefin resins as core materials and utilizes the active carboxyl or anhydride groups provided by the maleic anhydride, acrylic acid, or ethylene acrylate structural units grafted into their molecular chains to directly react chemically with vinyl monomers containing active groups, further improving the generation density and distribution uniformity of carbon-carbon double bond seed sites on the polyolefin surface. Specifically, the anhydride or carboxyl groups of maleic anhydride-grafted polyolefins, acrylic acid-grafted polyolefins, and ethylene acrylate copolymers can undergo condensation reactions with the amino, hydroxyl, and epoxy groups of the vinyl monomers to form stable amide or ester bonds. All three types of modified polyolefins possess high melt indexes and suitable melting points, ensuring that the oil phase exhibits low viscosity flow dynamics at emulsification temperatures, facilitating high-shear dispersion into fine, stable oil droplets, while maintaining the inherent chemical inertness and high-temperature stability of the core material. The above-mentioned modified polyolefin resin significantly improves the grafting efficiency and seed point density of vinyl monomers on the core surface, further strengthens the chemical bonding strength of the core-shell interface, and enhances the structure's anti-peeling ability under the severe expansion and high-temperature cycling of the high-silicon anode. At the same time, the polar groups introduced by the grafted side chains moderately improve the hydrophilicity of the core surface, optimize the emulsification stability of the water-oil two-phase system, inhibit emulsion demulsification and particle size coarsening, and ensure the regularity of the core-shell morphology and the uniformity of film formation. Finally, in the fluorine-free system, it further synergistically improves the comprehensive performance of low dissolution, low swelling, high temperature resistance and high peeling force.

[0032] More preferably, the vinyl monomer containing the active group includes one or more of the following: hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, 1,2,5-pentanetriol acrylate, 1,2,5-pentanetriol methacrylate, 4-hydroxybutyl acrylate, glycidyl methacrylate, glycidyl acrylate, epoxy polyethylene glycol acrylate, 3,4-epoxycyclohexylmethyl methacrylate, and acrylamide monomer.

[0033] This invention selects the aforementioned vinyl monomers containing active groups, utilizing the chemical reactions of hydroxyl, epoxy, or amino groups in their molecular structure with carboxyl and anhydride groups on the surface of polyolefin resins to form stable covalent bonds, thereby efficiently generating carbon-carbon double bond seed sites on the polyolefin surface. Specifically, hydroxyl groups (such as hydroxyethyl acrylate and hydroxypropyl methacrylate) form ester bonds through condensation with acidic groups; epoxy groups (such as glycidyl methacrylate) form ether bonds with carboxyl or anhydride groups through ring-opening reactions; and amino groups can react with anhydride or carboxyl groups to form amide bonds. These reactions, under the action of an initiator, further promote double bond exposure and free radical initiation, enhancing the density and uniformity of seed sites and ensuring the directional polymerization of the shell monomer on the core surface. The selection of these active groups significantly improves the affinity and grafting efficiency between the vinyl monomer and the polyolefin core, strengthens the covalent bond strength at the core-shell interface, and effectively prevents phase separation or peeling under high-temperature electrolyte conditions.

[0034] Preferably, the emulsifier comprises anionic emulsifier or a combination of anionic emulsifier and nonionic emulsifier;

[0035] Optionally, it may include 0 to 120 parts of a co-emulsifier, wherein the co-emulsifier includes at least one of ethanol, isopropanol, and butanol.

[0036] The anionic emulsifier includes one or more of the following: higher fatty acid salt emulsifiers, alkyl sulfate emulsifiers, alkyl sulfonate emulsifiers, and phosphate ester emulsifiers.

[0037] The nonionic emulsifier includes one or more of polyethylene glycol emulsifiers, polyether emulsifiers, and polyol emulsifiers.

[0038] Furthermore, the anionic emulsifier includes higher fatty acid salt emulsifiers such as R-COONa or R-COOK, wherein R is C8 to C90. 18 ;

[0039] Alkyl sulfate emulsifiers include R-SO4Na, where R is C8 to C4. 18 ;

[0040] Alkyl sulfonate emulsifiers include R-SO3Na, where R is C8 to C96. 18 alkyl or alkylbenzene fused ring structure;

[0041] Phosphate emulsifiers include alkyl polyoxyethylene ether phosphate salts and / or alkyl phosphate salts, with the following structural formulas:

[0042] ,

[0043] Where R is: C8~C 18 Polyoxyethylene ether or pure alkyl; M is Na + or K + ;

[0044] The polyethylene glycol emulsifier includes at least one of the following substances:

[0045] (1) Fatty alcohol polyoxyethylene ether (AEO), with the structural formula: RO(CH2CH2O) n H, n≤20;

[0046] (2) Alkylphenol polyoxyethylene ether, with the following structural formula:

[0047] ;

[0048] (3) Fatty acid polyoxyethylene ester, with the structural formula: RCOO(CH2CH2O) n H, n≤20.

[0049] The polyether emulsifier has the following structural formula:

[0050] ,

[0051] Where a+b+c=20~80.

[0052] The polyol emulsifiers include at least one of glycerol fatty acid esters, pentaerythritol fatty acid esters, sorbitol fatty acid esters, and glycosyl fatty acid esters.

[0053] This invention utilizes a preferred combination of anionic and nonionic emulsifiers. The anionic emulsifier's strong charge repulsion creates a high-density negatively charged layer on the oil droplet surface, significantly improving the emulsion's electrostatic stability and preventing droplet aggregation under high temperature or high shear. The nonionic emulsifier further reduces the oil-water interfacial tension through steric hindrance and hydrophilic segment extension, enhancing emulsification and dispersion efficiency and suppressing demulsification in the electrolyte environment. The combination of these two agents synergistically constructs a dual stabilization mechanism under high aqueous and oil phase ratios, ensuring that polyolefin oil droplets maintain a fine and uniform particle size throughout the shell polymerization process, providing a stable microenvironment for uniform shell coating.

[0054] Secondly, the present invention also provides a method for preparing the adhesive emulsion containing core-shell microspheres, comprising the following steps:

[0055] S1 preparation of the core of core-shell microspheres:

[0056] Polyolefin resin is dissolved in a solvent, and a catalyst and vinyl monomers containing active groups are added to react and obtain a vinyl-containing polyolefin core.

[0057] S2 Preparation of Seed Emulsion:

[0058] The vinyl-containing polyolefin core obtained in step S1 is mixed with an emulsifier and deionized water, and then emulsified by high-speed shearing to form an intermediate emulsion.

[0059] The intermediate emulsion was distilled to remove the solvent, yielding the seed emulsion;

[0060] S3 preparation of the outer shell of core-shell microspheres:

[0061] In an inert atmosphere, an initiator is added to the seed emulsion and the temperature is raised. Then, acrylic monomers and / or acrylate monomers are added to carry out a polymerization reaction to obtain a shell bonded to the core.

[0062] Unreacted monomers were removed by negative pressure distillation to obtain the adhesive emulsion containing core-shell microspheres.

[0063] Preferably, step S1 satisfies at least one of the following:

[0064] (1) The solvent includes one or more of the following: alcohol solvents, ketone solvents, ether solvents, ester solvents, olefin solvents, aromatic solvents, and halogen solvents;

[0065] (2) The catalyst includes at least one of esterification catalyst, epoxy-maleic anhydride catalyst and amidation reaction catalyst;

[0066] (3) The reaction temperature is 80-150℃ and the reaction time is 2-24h.

[0067] Furthermore, the alcohol solvents include at least one selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, sec-pentanol, tert-pentanol, 1-ethyl-1-propanol, 2-methyl-1-butanol, n-hexanol, and cyclohexanol; the ketone solvents include at least one selected from methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone, and cyclohexanone; the ether solvents include at least one selected from tetrahydrofuran, dioxane, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monomethyl ether; and the ester solvents include ethyl acetate and acetic acid. The solvent comprises at least one of the following: n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, 3-methoxybutyl acetate, methyl propionate, ethyl propionate, and diethyl carbonate; the olefin solvent comprises at least one of the following: n-pentane, n-hexane, n-heptane, cycloheptane, cyclohexane, methylcyclohexane, and petroleum ether; the aromatic solvent comprises at least one of the following: benzene, toluene, and xylene; and the halogen solvent comprises at least one of the following: carbon tetrachloride, chloroform, 1,2-dichloroethane, 1,1-dichloroethylene, trichloroethylene, and 1,1,1-trichloromethane.

[0068] This invention utilizes the preferred solvents described above, leveraging their differentiated solubility and volatility characteristics in polyolefin resins, to achieve full expansion and viscosity control of polyolefin molecular chains in the oil phase. This results in a low-viscosity flow dynamic at the emulsification temperature, facilitating high-shear dispersion into fine, uniform oil droplets. Simultaneously, the appropriate miscibility between the solvent molecules and the aqueous phase precisely controls the oil-water interfacial tension, synergistically constructing a highly stable emulsion system with the emulsifier, providing an ideal micro-reaction environment for the directional polymerization of the shell monomers. After polymerization, the solvent is completely removed through vacuum distillation or gradient heating processes, avoiding residues that could trigger electrochemical side reactions or affect the purity of the adhesive emulsion.

[0069] Furthermore, the esterification catalyst includes one of p-toluenesulfonic acid, sulfuric acid, hydrochloric acid, and solid acid catalysts (such as A15 ion exchange resin).

[0070] Epoxy-maleic anhydride catalysts include at least one of the following: tertiary amine epoxy-maleic anhydride catalysts, quaternary ammonium salt epoxy-maleic anhydride catalysts, imidazole and its derivatives epoxy-maleic anhydride catalysts, organophosphorus epoxy-maleic anhydride catalysts, and metal complex epoxy-maleic anhydride catalysts.

[0071] The tertiary amine epoxy-maleic anhydride catalyst includes at least one of benzyl dimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, triethanolamine, and bis(2-morpholinodiethyl) ether; the quaternary ammonium salt epoxy-maleic anhydride catalyst includes at least one of benzyl triethylammonium chloride, tetramethylchloroethylamine, and tetrabutylammonium bromide; the imidazole and its derivative epoxy-maleic anhydride catalyst includes at least one of methylimidazolium, 2-ethyl-4-methylimidazolium, 1,2-dimethylimidazolium, and 2-phenylimidazolium; the organophosphorus epoxy-maleic anhydride catalyst includes triphenylphosphine; and the metal complex epoxy-maleic anhydride catalyst includes at least one of zinc acetylacetonate, cobalt acetylacetonate, stannous octoate, and zinc naphthenate.

[0072] The amidation reaction catalysts include carbodiimide amidation reaction catalysts, acylurea amidation reaction catalysts, carbocation amidation reaction catalysts, and organophosphorus amidation reaction catalysts;

[0073] The carbodiimide amidation catalyst includes at least one of DCC dicyclohexylcarbodiimide, DIC diisopropylcarbodiimide, and EDC 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; the acylurea amidation catalyst includes at least one of HOBt 1-hydroxybenzotriazole and HOAt 1-hydroxy-7-azabenzotriazole; the carbocation amidation catalyst includes BOP benzotriazole-1-yl-oxo-tris(dimethylamino)phosphine hexafluorophosphate; and the organophosphorus amidation catalyst includes at least one of DPPA diphenylphosphine azide and bis(2-oxo-3-oxazolidinyl)phosphonyl chloride.

[0074] More preferably, step S1 further includes a polymerization inhibitor, and step S2 further includes a co-emulsifier and an alkaline substance.

[0075] The polymerization inhibitor includes at least one of hydroquinone, p-hydroxyanisole, oxygen, and phenothiazine, preferably two of which are used in combination.

[0076] The co-emulsifier includes at least one of ethanol, isopropanol, and butanol;

[0077] The alkaline substances include organic bases and / or inorganic bases.

[0078] The organic base includes at least one of ammonia, triethylamine, N,N-dimethylethanolamine, isopropylamine, aminoethanol, dimethylaminoethanol, diethylaminoethanol, ethylamine, diethylamine, isobutylamine, dipropylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, n-butylamine, 2-methoxyethylamine, 3-methoxypropylamine, 2,2-dimethoxyethylamine, monoethanolamine, morpholine, N-methylmorpholine, pyrrole, and pyridine; the inorganic base includes at least one of sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0079] This invention utilizes the preferred introduction of catalysts, co-emulsifiers, and alkaline substances. The catalysts efficiently promote the chemical grafting reaction between the active groups of vinyl monomers and the carboxyl and anhydride groups on the surface of polyolefins. For example, esterification catalysts accelerate the dehydration of hydroxyl and carboxyl groups to form esters, epoxy-maleic anhydride catalysts promote the ring-opening addition of epoxy groups, and amidation catalysts drive the dehydration of amino and carboxyl groups to form amides, thereby significantly improving the seed point generation rate and grafting density. The co-emulsifiers further optimize emulsification dispersion efficiency and oil droplet stability by reducing oil-water interfacial tension and co-solizing with solvents to regulate oil phase viscosity. The addition of alkaline substances during the emulsification stage can improve the hydrophilicity of the vinyl-containing polyolefin core, neutralize acidic groups, and adjust the emulsion pH, promoting emulsification and maintaining emulsion stability, ensuring smooth subsequent polymerization reactions and uniform shell growth.

[0080] Preferably, in step S2, the mass ratio of the aqueous phase to the oil phase is ≥1.2, the shear rate is ≥5000 rpm, and the emulsification time is 10–60 min.

[0081] Preferably, in step S3, the initiator is an oil-based initiator and / or an aqueous initiator. The initiator is added and the temperature is raised to the polymerization temperature of 50-90°C. Acrylic monomers and / or acrylate monomers are slowly added dropwise, and the polymerization reaction time is 1-6 hours.

[0082] More preferably, the oily initiator is azobisisobutyronitrile, and the aqueous initiator is ammonium persulfate, sodium persulfate, and potassium persulfate.

[0083] This invention utilizes a preferred combination of oil-based and water-based initiators. Azobisisobutyronitrile (AIBN) decomposes in the oil phase to generate free radicals, which preferentially initiate the grafting reaction of residual double bonds or vinyl monomers on the surface of polyolefins, ensuring efficient seed point generation. The water-based initiators ammonium persulfate and potassium persulfate decompose in the aqueous phase, continuously delivering free radicals to the surface of the oil droplets, precisely driving the directional polymerization and epitaxial growth of the shell monomers at the seed points. The synergistic effect of the dual initiation system achieves stepwise controlled release, inhibits free polymerization, and strengthens interfacial chemical bonding.

[0084] The adhesive emulsion containing core-shell microspheres and its preparation method provided by this invention have at least the following beneficial effects:

[0085] (1) This invention uses polyolefin resin to form a high-temperature resistant inert core, introduces high-density carbon-carbon double bond seed points by in-situ grafting of vinyl monomers containing active groups, and initiates the directional polymerization of acrylic (ester) shell monomers to form a chemically bonded core-shell structure. Under the premise of fluorine-free and environmentally friendly, it achieves multi-dimensional performance synergy of ultra-low dissolution, low swelling, high temperature resistance and high peel strength, and completely solves the key bottlenecks such as adhesion failure caused by the severe expansion of high silicon anode, ion transport hindrance and structural softening under high temperature cycling and electrochemical oxidation decomposition in high voltage environment.

[0086] (2) By selecting modified polyolefin resin and specific active group vinyl monomer, the present invention improves the interfacial chemical grafting efficiency and seed point density, strengthens the core-shell covalent bonding strength and morphological regularity, further enhances the dynamic buffering capacity and anti-peeling performance of the structure against high silicon volume changes, and optimizes oil-water emulsification stability to ensure film uniformity and electrochemical inertness.

[0087] (3) By optimizing the anionic-nonionic compound emulsifier, the differentiated solvent and auxiliary component system, the present invention synergistically constructs a highly stable emulsion and precisely controls the polymerization sequence, ensuring small and uniform particle size and complete shell coating, significantly improving the emulsion storage processability and electrolyte tolerance, comprehensively reducing the risk of dissolution and swelling, and achieving comprehensive optimization of high temperature resistance, low residue and high adhesion in a fluorine-free system. Attached Figure Description

[0088] Figure 1 This is a schematic diagram illustrating the reaction principle of the core-shell microspheres of the present invention.

[0089] Figure 2 The images show SEM images of the adhesive emulsion samples of Example 1 and Comparative Example 1 before and after aging at 110°C for 12 hours. In the images, A is the SEM image of the sample of Example 1 before aging, B is the SEM image of the sample of Example 1 after aging, C is the SEM image of the sample of Comparative Example 1 before aging, and D is the SEM image of the sample of Comparative Example 1 after aging. Detailed Implementation

[0090] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0091] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0092] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0093] This invention provides an adhesive emulsion containing core-shell microspheres and its preparation method. The raw materials for preparing the adhesive emulsion containing core-shell microspheres, by weight, specifically include:

[0094] (1) Modified polyolefin resin, 50-150 parts, preferably 80-120 parts, wherein the modified polyolefin comprises one or more of maleic anhydride grafted polyolefin, (meth)acrylic acid grafted polyolefin, and (meth)acrylic acid-ethylene copolymer;

[0095] The maleic anhydride-grafted polyolefin has a grafting rate of 0.2% to 10%, a melting point range of 60 to 150°C, preferably 70 to 130°C, and a weight-average molecular weight (Mw) range of 5000 Da to 200,000 Da, preferably 40,000 Da to 120,000 Da. Exemplary examples of maleic anhydride-grafted polyolefins include:

[0096] 1) Maleic anhydride-grafted polypropylene, with the following molecular structure:

[0097] ;

[0098] 2) Maleic anhydride grafted with APAO, the molecular structure is as follows:

[0099] ;

[0100] 3) Maleic anhydride grafted with POE, the molecular structure is as follows:

[0101] ;

[0102] The grafting rate of the (meth)acrylic acid grafted polyolefin is 0.2% to 10%, the melting point ranges from 60 to 150°C, preferably from 70 to 130°C, and the weight-average molecular weight (Mw) ranges from 5000 Da to 200,000 Da, preferably from 40,000 Da to 120,000 Da. Exemplary examples of the (meth)acrylic acid grafted polyolefin include:

[0103] 1) Acrylic acid grafted polypropylene, with the following molecular structure:

[0104] ;

[0105] 2) Acrylic acid grafted with APAO, molecular structure as follows:

[0106] ;

[0107] 3) Acrylic acid grafted with POE, the molecular structure is as follows:

[0108] ;

[0109] The (meth)acrylic acid-ethylene copolymer, preferably a methacrylic acid-ethylene copolymer, has a melting point (MI) (190℃ / 2.16kg) ≥ 20 g / 10min and a melting point range of 60–130℃. Its chemical structure is as follows (R1 is methyl or H; R2 is H):

[0110] .

[0111] (2) Vinyl monomer, 1.5 to 15 parts, preferably 3 to 12 parts, is a vinyl monomer containing an active group, wherein the active group includes one or more of hydroxyl, epoxy, and amino groups;

[0112] Specifically, vinyl monomers containing active groups may include one or more of the following: hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, 1,2,5-pentanetriol acrylate, 1,2,5-pentanetriol methacrylate, 4-hydroxybutyl acrylate, glycidyl methacrylate, glycidyl acrylate, epoxy-based polyethylene glycol acrylate, 3,4-epoxycyclohexylmethyl methacrylate, and acrylamide monomers.

[0113] (3) Shell monomer, 1-150 parts, preferably 3-100 parts, comprising acrylic monomers and / or acrylate monomers, including but not limited to (meth)acrylic acid, (meth)acrylate ... Cinnamyl ester, tridecyl methacrylate, stearyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, diethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-aminoethyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, 2-hydroxyethyl methacrylate phosphate, dipropylene glycol diacrylate, trimethylolpropane triacrylate, etc.

[0114] (4) Initiator, 0.01 to 5 parts, including oily initiator and / or aqueous initiator; more preferably, the oily initiator is azobisisobutyronitrile, and the aqueous initiator is ammonium persulfate, sodium persulfate and potassium persulfate.

[0115] (5) Emulsifier, 0.1 to 5 parts, preferably 0.5 to 3 parts, including anionic emulsifier or a combination of anionic emulsifier and nonionic emulsifier;

[0116] The anionic emulsifier includes one or more of the following: higher fatty acid salt emulsifiers, alkyl sulfate emulsifiers, alkyl sulfonate emulsifiers, and phosphate ester emulsifiers.

[0117] The nonionic emulsifier includes one or more of polyethylene glycol emulsifiers, polyether emulsifiers, and polyol emulsifiers.

[0118] Furthermore, the anionic emulsifier includes higher fatty acid salt emulsifiers such as R-COONa or R-COOK, wherein R is C8 to C90. 18 ;

[0119] Alkyl sulfate emulsifiers include R-SO4Na, where R is C8 to C4. 18 ;

[0120] Alkyl sulfonate emulsifiers include R-SO3Na, where R is C8 to C96. 18 alkyl or alkylbenzene fused ring structure;

[0121] Phosphate emulsifiers include alkyl polyoxyethylene ether phosphate salts and / or alkyl phosphate salts, with the following structural formulas:

[0122] ,

[0123] Where R is: C8~C 18 Polyoxyethylene ether or pure alkyl; M is Na + or K + ;

[0124] The polyethylene glycol emulsifier includes at least one of the following substances:

[0125] 1) The structural formula of fatty alcohol polyoxyethylene ether (AEO) is: RO(CH2CH2O) n H, n≤20;

[0126] 2) Alkylphenol polyoxyethylene ether, with the following structural formula:

[0127] ;

[0128] 3) The structural formula of fatty acid polyoxyethylene ester is RCOO(CH2CH2O). n H, n≤20.

[0129] The polyether emulsifier has the following structural formula:

[0130] ,

[0131] Where a+b+c=20~80.

[0132] The polyol emulsifiers include at least one of glycerol fatty acid esters, pentaerythritol fatty acid esters, sorbitol fatty acid esters, and glycosyl fatty acid esters.

[0133] (6) Solvent, 100 to 1000 parts, preferably 150 to 900 parts, including one or more of alcohol solvents, ketone solvents, ether solvents, ester solvents, olefin solvents, aromatic solvents, and halogen solvents;

[0134] Among them, alcohol solvents include at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, sec-pentanol, tert-pentanol, 1-ethyl-1-propanol, 2-methyl-1-butanol, n-hexanol, and cyclohexanol; ketone solvents include at least one of methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone, and cyclohexanone; ether solvents include at least one of tetrahydrofuran, dioxane, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monomethyl ether; ester solvents include ethyl acetate, n-propyl acetate, and ethyl acetate. At least one of the following: esters, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, 3-methoxybutyl acetate, methyl propionate, ethyl propionate, and diethyl carbonate; olefin solvents including at least one of n-pentane, n-hexane, n-heptane, cycloheptane, cyclohexane, methylcyclohexane, and petroleum ether; aromatic solvents including at least one of benzene, toluene, and xylene; and halogen solvents including at least one of carbon tetrachloride, chloroform, 1,2-dichloroethane, 1,1-dichloroethylene, trichloroethylene, and 1,1,1-trichloromethane.

[0135] (7) Deionized water, 100-2000 parts, preferably 200-1800 parts;

[0136] (8) Catalyst, 0.01 to 5 parts, wherein the catalyst is used for the vinylation reaction of polyolefin resin, including at least one of esterification catalyst, epoxy-maleic anhydride catalyst and amidation reaction catalyst;

[0137] The esterification catalyst includes one of p-toluenesulfonic acid, sulfuric acid, hydrochloric acid, and solid acid catalysts (such as A15 ion exchange resin);

[0138] Epoxy-maleic anhydride catalysts include at least one of the following: tertiary amine epoxy-maleic anhydride catalysts, quaternary ammonium salt epoxy-maleic anhydride catalysts, imidazole and its derivatives epoxy-maleic anhydride catalysts, organophosphorus epoxy-maleic anhydride catalysts, and metal complex epoxy-maleic anhydride catalysts.

[0139] The tertiary amine epoxy-maleic anhydride catalyst includes at least one of benzyl dimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, triethanolamine, and bis(2-morpholinodiethyl) ether; the quaternary ammonium salt epoxy-maleic anhydride catalyst includes at least one of benzyl triethylammonium chloride, tetramethylchloroethylamine, and tetrabutylammonium bromide; the imidazole and its derivative epoxy-maleic anhydride catalyst includes at least one of methylimidazolium, 2-ethyl-4-methylimidazolium, 1,2-dimethylimidazolium, and 2-phenylimidazolium; the organophosphorus epoxy-maleic anhydride catalyst includes triphenylphosphine; and the metal complex epoxy-maleic anhydride catalyst includes at least one of zinc acetylacetonate, cobalt acetylacetonate, stannous octoate, and zinc naphthenate.

[0140] The amidation reaction catalysts include carbodiimide amidation reaction catalysts, acylurea amidation reaction catalysts, carbocation amidation reaction catalysts, and organophosphorus amidation reaction catalysts;

[0141] The carbodiimide amidation catalyst includes at least one of DCC dicyclohexylcarbodiimide, DIC diisopropylcarbodiimide, and EDC 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; the acylurea amidation catalyst includes at least one of HOBt 1-hydroxybenzotriazole and HOAt 1-hydroxy-7-azabenzotriazole; the carbocation amidation catalyst includes BOP benzotriazole-1-yl-oxo-tris(dimethylamino)phosphine hexafluorophosphate; and the organophosphorus amidation catalyst includes at least one of DPPA diphenylphosphine azide and bis(2-oxo-3-oxazolidinyl)phosphonyl chloride.

[0142] Optional (9) co-emulsifier, 0.5 to 120 parts, preferably 40 to 100 parts, including at least one of ethanol, isopropanol and butanol.

[0143] Optional (10) alkaline substance, 0.1 to 10 parts, preferably 0.5 to 5 parts, including organic base and / or inorganic base; wherein, the organic base includes at least one of ammonia, triethylamine, N,N-dimethylethanolamine, isopropylamine, aminoethanol, dimethylaminoethanol, diethylaminoethanol, ethylamine, diethylamine, isobutylamine, dipropylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, n-butylamine, 2-methoxyethylamine, 3-methoxypropylamine, 2,2-dimethoxyethylamine, monoethanolamine, morpholine, N-methylmorpholine, pyrrole and pyridine; the inorganic base includes at least one of sodium hydroxide, lithium hydroxide and potassium hydroxide.

[0144] Optional (10) polymerization inhibitor, used in amounts of less than 0.1 parts, includes at least one of hydroquinone, p-hydroxyanisole, oxygen, and phenothiazine, preferably two of which are used in combination.

[0145] The above-mentioned polyolefin resin and solvent are used as the oil phase, and the emulsifier, co-emulsifier and deionized water are used as the aqueous phase, with a mass ratio of aqueous phase to oil phase ≥ 1.2.

[0146] The present invention provides a method for preparing the above-mentioned adhesive emulsion containing core-shell microspheres, comprising the following steps:

[0147] S1. Preparation of the core-shell microsphere core: Vinylating polyolefin resin through esterification, ring-opening, and amidation reactions to obtain a vinyl-containing polyolefin core, including:

[0148] 1) Esterification reaction: Grafting polyolefin resin with hydroxyl-containing acrylic acid (ester).

[0149] A suitable solvent is selected based on the resin's solubility for dissolution. After dissolution, a catalyst, hydroxyl-containing acrylic acid (ester), and a polymerization inhibitor are added to initiate the reaction. A water separator is used during the reaction to remove water and promote the forward reaction. Examples of some of the reaction processes are as follows:

[0150] ①The esterification reaction of maleic anhydride-grafted polyolefins with hydroxyethyl acrylate is as follows:

[0151] ;

[0152] ②The esterification reaction of acrylic acid-grafted polyolefins with hydroxyethyl acrylate is as follows:

[0153] ;

[0154] ③ The esterification reaction of ethylene-acrylic acid copolymer with hydroxyethyl acrylate is as follows:

[0155] ;

[0156] 2) Epoxy-maleic anhydride or carboxylic acid reaction

[0157] A suitable solvent is selected based on the resin's solubility for dissolution. After dissolution, a catalyst, epoxy acrylate monomer, and polymerization inhibitor are added to initiate the reaction. Examples of some of the reaction processes are as follows:

[0158] ①The reaction process of triethylamine-catalyzed maleic anhydride-grafted polyolefin with GMA is as follows:

[0159] ;

[0160] ②The reaction process of triphenylphosphine-catalyzed acrylic acid-grafted polyolefin with GMA is as follows:

[0161] ;

[0162] ③The reaction process of triphenylphosphine-catalyzed ethylene-acrylic acid copolymer with GMA is as follows:

[0163] ;

[0164] 3) Amide reaction

[0165] A suitable solvent is selected based on the resin's solubility for dissolution. After dissolution, a catalyst (or dehydrating agent), acrylamide monomer, and polymerization inhibitor are added to initiate the reaction. Examples of some of the reaction processes are as follows:

[0166] ①The reaction process of maleic anhydride-grafted polyolefin with acrylamide is as follows:

[0167] ;

[0168] ②The reaction process of acrylic acid grafted polyolefin with acrylamide is as follows:

[0169] ;

[0170] ③The reaction process of ethylene-acrylic acid copolymer with acrylamide is as follows:

[0171] ;

[0172] S2. Seed emulsion preparation: The vinyl-containing polyolefin core is emulsified.

[0173] S2.1 Prepare oil phase and aqueous phase solutions according to the specified ratios;

[0174] S2.2 Mix the aqueous phase and the oil phase, with a mass ratio of aqueous phase to oil phase ≥1.2, and emulsify them at a high speed of shearing rate ≥5000rpm to obtain an intermediate emulsion. The emulsification time is 10 to 60 min.

[0175] S2.3 The solvent molecules are removed by heating and negative pressure processes (such as using a distillation reactor) to obtain a seed emulsion, with a desolventizing vacuum of -0.08 to -0.1 MPa.

[0176] S3. Preparation of the outer shell of core-shell microspheres:

[0177] S3.0 Optionally, the acrylic monomers and / or acrylate monomers with poor water solubility are pre-emulsified to obtain a monomer emulsion; the acrylic monomers and / or acrylate monomers with good water solubility can be directly added to the seed emulsion subsequently.

[0178] S3.1 After purging oxygen by introducing an inert gas (such as Ar, N2, etc.) into the reactor, add the initiator to the seed emulsion, stir and heat to the polymerization temperature of 50-90℃;

[0179] S3.2 Slowly add acrylic (ester) monomers or monomer emulsions to carry out a polymerization reaction for 1-6 hours to obtain a shell bonded to the core. The above polymerization process is as follows: Figure 1 As shown;

[0180] S3.3 Unreacted monomers are distilled off under negative pressure to obtain the finished adhesive emulsion containing core-shell microspheres.

[0181] Analysis of the adhesive emulsion containing core-shell microspheres obtained by the aforementioned preparation method revealed that, by mass, the adhesive emulsion containing core-shell microspheres comprises:

[0182] 100-150 parts of core-shell microspheres;

[0183] Emulsifier 0.1 to 5 parts;

[0184] 150-2000 parts of deionized water;

[0185] The solid content of the adhesive emulsion is 5% to 70%, preferably 10% to 50%;

[0186] The core-shell microspheres have a polyolefin core and a shell containing acrylic polymers and / or acrylate polymers, with a particle size D50 of 0.02 to 5 μm, preferably 0.2 to 3 μm, and the mass ratio of the polyolefin core to the shell is (50 to 150): (1 to 150).

[0187] After sufficient reaction and negative pressure distillation, the core-shell microsphere-containing adhesive emulsion of this invention has virtually no monomer residues. Under the premise of ensuring electrochemical safety, it has excellent properties such as low dissolution, low swelling, high temperature resistance, high adhesion and fluorine-free properties.

[0188] Example 1

[0189] The core-shell microsphere-containing adhesive emulsion of this embodiment is prepared by the following steps:

[0190] S1. Preparation of the core-shell microspheres

[0191] S1.1 Take 100g of self-made maleic anhydride-grafted polypropylene (maleic anhydride grafting rate 2.8%, melting point 98℃, weight average molecular weight Mw 80,000 Da) and 400g of solvent methylcyclohexane.

[0192] S1.2 Put the above materials into a four-necked flask, place it in a 130°C oil bath, and stir with a paddle at 150 rpm for 1 hour while removing water using a water separator.

[0193] S1.3 Add 0.074 g of p-toluenesulfonic acid catalyst and stir for 30 min to mix evenly;

[0194] S1.4 Using a peristaltic pump, 3.71 g of hydroxyethyl acrylate was slowly added dropwise at a rate of 17.5 rpm. The reaction was carried out for 12 h to complete the grafting reaction and obtain a vinyl-containing polyolefin core.

[0195] S2. Preparation of seed emulsion

[0196] S2.1 Weigh 0.5g of Tween 40 emulsifier, 1.5g of sodium dodecylbenzenesulfonate and 760g of deionized water, and mix them evenly to prepare an aqueous phase;

[0197] S2.2 The prepared aqueous phase and oil phase are mixed and emulsified under high-speed shear at 12000 rpm for 30 min until a stable intermediate emulsion is formed;

[0198] S2.3 Pour the intermediate emulsion into a four-necked flask, stir at 140 rpm, and place it in a 130°C oil bath to remove the solvent by -0.1 MPa negative pressure distillation to obtain the seed emulsion;

[0199] S3. Preparation of the outer shell of core-shell microspheres

[0200] S3.1 Purge the seed emulsion with nitrogen gas for 20 min in a four-necked flask, then add 0.019 g of ammonium persulfate to the seed emulsion, stir well, and heat the emulsion to 70 °C.

[0201] S3.2 Using a peristaltic pump, 6 g of methacrylic acid was slowly added dropwise at a rate of 17.5 rpm, and the reaction was carried out for 4 h to obtain a shell bonded to the core.

[0202] S3.3 The reacted emulsion is subjected to negative pressure distillation to remove unreacted monomers, resulting in the final adhesive emulsion product containing core-shell microspheres.

[0203] Examples 2-8

[0204] Examples 2-8 are prepared using the same methods as Example 1, except for the different raw material composition and proportions, as detailed in Table 1:

[0205] Table 1. Raw material composition and proportions in the preparation of adhesive emulsions in Examples 1-8 and Comparative Example 1.

[0206]

[0207] The information regarding the aforementioned raw materials is as follows:

[0208] Homemade MA-PP-01: melting point 98℃, weight-average molecular weight Mw 80,000 Da, maleic anhydride grafting rate 2.8%;

[0209] Homemade MA-PP-02: Melting point 80℃, weight-average molecular weight Mw 75,000 Da; acrylic acid grafting rate 1.5%;

[0210] 002PP-NW: Purchased from Kayabrid, with a weight-average molecular weight (Mw) of 65,000 Da and a maleic anhydride grafting rate of 2%;

[0211] Fusabond N216: Purchased from Dow Chemical, maleic anhydride grafting rate of 0.2-0.5%;

[0212] MH7510: Purchased from Mitsui Chemicals, maleic anhydride grafting rate 1%;

[0213] NUCREL EMAA 599: Purchased from DuPont, methacrylic acid content is 10%;

[0214] A15: Solid acid, catalyst for esterification reaction;

[0215] K54: 2,4,6-Tris(dimethylaminomethyl)phenol, catalyst for epoxy curing reaction;

[0216] ANTRAROX BL-240 / W: Fatty alcohol ethoxylated polypropylene ether copolymer;

[0217] RHODAFAC RS-610: Phosphate ester anionic emulsifier;

[0218] ABEX DBR Z: Anionic emulsifier.

[0219] Comparative Example 1

[0220] The difference between Comparative Example 1 and Example 1 is that the adhesive emulsion contains modified polyolefin microspheres, but not a core-shell structure.

[0221] The preparation of an aqueous adhesive emulsion containing maleic anhydride-grafted polypropylene microspheres includes the following steps:

[0222] Step 1: Prepare the oil phase: Take 100g of self-made maleic anhydride-grafted polypropylene (maleic anhydride grafting rate 2.8%, melting point 98℃, weight average molecular weight Mw is 80,000Da), 248g of toluene and 85g of acetone as solvents.

[0223] The above materials were put into a four-necked flask, placed in an oil bath at 130°C, and stirred with a paddle at 150 rpm for 1 hour while removing water using a water separator.

[0224] Step 2: Prepare the aqueous phase: Weigh 0.5g of Tween 40 emulsifier, 1.5g of sodium dodecylbenzenesulfonate and 640g of deionized water, and mix them evenly to prepare the aqueous phase;

[0225] Step 3: Prepare the adhesive emulsion:

[0226] The prepared aqueous phase and oil phase were mixed and emulsified under high-speed shearing conditions of 12,000 rpm for 30 min until a stable intermediate emulsion was formed.

[0227] The intermediate emulsion was poured into a four-necked flask and stirred at 140 rpm. The solvent was removed by distillation under a negative pressure of -0.1 MPa in a 130°C oil bath to obtain the adhesive emulsion containing modified polyolefin microspheres of Comparative Example 1.

[0228] Comparative Example 2

[0229] This comparative example uses Voltabond 082 waterborne styrene-butadiene emulsion (SBR) as the adhesive emulsion.

[0230] Comparative Example 3

[0231] This comparative example uses Reynolds Nipol LX874 polyacrylate as the adhesive emulsion.

[0232] Test methods

[0233] 1. Emulsion particle size test

[0234] 1.1 The parameters for using the Topsizer laser particle size analyzer are set as follows:

[0235] Sample material: polypropylene; refractive index: 1.491; absorptivity: 0.01; refractive index (blue light): 1.491; absorptivity (blue light): 0.01; dispersion medium: water; refractive index of dispersion medium: 1.33; particle type: spherical;

[0236] 1.2 The emulsion sample was dropped into a Topsizer laser particle size analyzer to test the particle size.

[0237] 2. Air permeability increment test

[0238] Apply an emulsion to the BOPP separator, controlling the coating weight to be 0.5–1.0 g / m³. 2 The membrane coated with emulsion was placed in a 50℃ oven and baked for 3 minutes to dry the moisture. The air permeability value of the membrane before aging (P1) was tested. The membrane coated with emulsion was placed in a 110℃ oven and aged for 12 hours. The air permeability value of the membrane after aging (P2) was tested. The increase in air permeability before and after aging was calculated as P2-P1, with the unit being s / 100ml.

[0239] 3. Dissolution rate and swelling rate test

[0240] Take 60g of emulsion sample with 20% solid content; pour the emulsion sample into a 16cm×16cm×1cm Teflon mold; place the mold in a 50℃ oven and bake for 24 hours;

[0241] 3.1 Dissolution rate test: Take 1.4g (M1) of the baked sample and put it into a 10ml vial, and add 7g (M2) of electrolyte (by mass ratio, ethylene carbonate EC: propylene carbonate PC: diethyl carbonate DEC: ethyl propionate EP = 3:1:3:3), seal the vial and bake it in an 85℃ oven for 24h; use a 1ml syringe to extract the electrolyte from the vial while it is still hot and put it into a TGA (thermogravimetric analyzer) crucible; nitrogen gas at a flow rate of 20ml / min is used for protection throughout the experiment, the temperature program is set to 30℃-350℃, the heating rate is 10℃ / min, and the percentage A is obtained; calculate the dissolution rate: M1×100% / (M2×A);

[0242] 3.2 Test swelling rate: Take 2g (M1) of the baked sample and put it into a 100mL container, add 20g of electrolyte (as above), seal it and bake it in a 60℃ oven for 24h; take out the glue block, wipe the surface of the glue block with lint-free paper and measure its weight M2; calculate the swelling rate: (M2-M1)×100% / M1.

[0243] 4. Pre-immersion peel strength and liquid-resistant peel strength test

[0244] 4.1 Peel strength test before immersion: The substrate consists of a diaphragm and a positive electrode (ternary nickel-cobalt-manganese single-sided electrode). The emulsion is coated onto the diaphragm using a wire rod. The diaphragm is then baked in a 50℃ oven for 3 minutes to dry the moisture, and the coating thickness is measured to be 2μm. The diaphragm is cut into strips 20mm wide and 100mm long, and the side coated with the emulsion is attached to the positive electrode. The attached sample is then hot-pressed at 85℃ and 1MPa for 1 hour. The peel strength at 180° is then measured at a speed of 50mm / min, which is the peel strength before immersion, expressed in N / m.

[0245] 4.2 Liquid peel strength test: The sample preparation process is the same as in 4.1. After bonding, the sample is hot-pressed at 85℃ and 1MPa for 1h and then completely immersed in the electrolyte (as above) and baked at 85℃ for 4h. After taking out the sample and drying it, the peel strength at 180° is measured at a speed of 50mm / min. This is the liquid peel strength, and the unit is N / m.

[0246] Test Results

[0247] The test results of Examples 1-8 and Comparative Examples 1-3 are shown in Table 2:

[0248] Table 2 Performance test results of the adhesive emulsions prepared in Examples 1-8 and Comparative Examples 1-3

[0249]

[0250] In Examples 1-8, the particle size D50 of the core-shell microspheres was significantly larger than that of Comparative Examples 2 and 3, with D50 concentrated in the range of 0.5–1.5 μm. This reduced the risk of the emulsion clogging the membrane pores during high-temperature processes. The dissolution rate in the electrolyte was below 2.0%, far lower than the 5.62% and 8.39% of Comparative Examples 2 and 3, significantly reducing the negative impact of emulsion dissolution on battery electrochemistry and demonstrating excellent electrolyte chemical stability. The swelling rate in the electrolyte was controlled below 80%, preferably below 60%, far lower than the 187% and 228% of Comparative Examples 2 and 3, significantly suppressing battery swelling. Although the pre-immersion peel strength of Examples 1-8 and Comparative Examples 1-3 was higher than 100 N / m, the post-immersion peel strength of Examples 1-8 remained between 69 and 162 N / m, higher than the 24 N / m and 18 N / m of Comparative Examples 2 and 3, respectively. This significant improvement in peel strength greatly enhanced battery safety.

[0251] The particle size of the emulsion microspheres in Comparative Example 1 is similar to that in Example 1. Although the non-core-shell polyolefin microspheres are slightly better than those in Example 1 in terms of liquid peel resistance, the increase in aging air permeability is significantly higher than that in Examples 1-8. Furthermore, compared with examples with similar particle sizes (such as Example 1), the swelling rate and dissolution rate of Comparative Example 1 are both higher.

[0252] The emulsions from Example 1 and Comparative Example 1 were coated and aged at 110°C for 12 hours. SEM characterization tests were performed on the emulsions before and after aging. The results are as follows: Figure 2 As shown, A is the SEM image of the sample from Example 1 before aging, B is the SEM image of the sample from Example 1 after aging, C is the SEM image of the sample from Comparative Example 1 before aging, and D is the SEM image of the sample from Comparative Example 1 after aging. The comparison shows that before aging, the microspheres in Example 1 and Comparative Example 1 have clear morphologies. However, the non-core-shell polyolefin microspheres in Comparative Example 1 have weaker shape retention and temperature resistance, and are prone to deformation and collapse after aging. In contrast, the core-shell microspheres in Example 1 basically maintain their original morphology after aging.

[0253] The above data fully verify the synergistic optimization effect of the core-shell structure of the present invention in terms of ultra-low dissolution, low swelling, high temperature resistance and high peel strength, and completely solve the comprehensive failure problem of traditional water-based adhesive emulsions under high silicon anode, high temperature fast charging and high voltage system.

[0254] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A bonding emulsion containing core-shell microspheres, characterized in that, The adhesive emulsion comprises, by weight, parts of: 100-150 parts of core-shell microspheres; Emulsifier 0.1 to 5 parts; 150-2000 parts of deionized water; The particle size D50 of the core-shell microspheres is 0.02–5 μm; The solid content of the adhesive emulsion is 5%–70%; The emulsifier includes anionic emulsifiers, or a combination of anionic emulsifiers and nonionic emulsifiers; The core-shell microspheres have a polyolefin core and a shell chemically bonded to the polyolefin core, wherein the mass ratio of the polyolefin core to the shell is (50-150):(1-150). The core-shell microspheres are prepared by the following steps: A modified polyolefin resin is reacted with a vinyl monomer containing an active group to obtain a vinyl-containing polyolefin core; wherein the active group in the vinyl monomer containing the active group includes one or more of hydroxyl, epoxy, and amino groups; Acrylic monomers and / or acrylate monomers are mixed with the vinyl-containing polyolefin core and reacted to obtain the outer shell containing acrylic polymers and / or acrylate polymers.

2. The adhesive emulsion as described in claim 1, characterized in that, The particle size D50 of the core-shell microspheres is 0.2–3 μm.

3. The adhesive emulsion as described in claim 1 or 2, characterized in that, The modified polyolefin resin includes one or more of maleic anhydride-grafted polyolefin, (meth)acrylic acid-grafted polyolefin, and (meth)acrylic acid-ethylene copolymer.

4. The adhesive emulsion as described in claim 3, characterized in that, The modified polyolefin resin satisfies at least one of the following: (1) The modified polyolefin resin includes maleic anhydride-grafted polyolefin with a grafting rate of 0.2% to 10%, a melting point of 60 to 150°C, and a weight-average molecular weight Mw of 5,000 Da to 200,000 Da. (2) The modified polyolefin resin includes (meth)acrylic acid grafted polyolefin with a grafting rate of 0.2% to 10%, a melting point of 60 to 150°C, and a weight-average molecular weight Mw of 5,000 Da to 200,000 Da. (3) The modified polyolefin resin includes (meth)acrylic acid-ethylene copolymer, with an MI of more than 20 g / 10 min at 190°C and 2.16 kg, and a melting point of 60 to 130°C.

5. The adhesive emulsion as described in claim 3, characterized in that, Vinyl monomers containing active groups include one or more of the following: hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, 1,2,5-pentanetriol acrylate, 1,2,5-pentanetriol methacrylate, 4-hydroxybutyl acrylate, glycidyl methacrylate, glycidyl acrylate, epoxy-based polyethylene glycol acrylate, 3,4-epoxycyclohexylmethyl methacrylate, and acrylamide monomers.

6. A method for preparing an adhesive emulsion containing core-shell microspheres as described in any one of claims 1-5, characterized in that, Includes the following steps: S1 preparation of the core of core-shell microspheres: The modified polyolefin resin is dissolved in a solvent, and a catalyst and vinyl monomers containing active groups are added to react and obtain a vinyl-containing polyolefin core. S2 Preparation of Seed Emulsion: The vinyl-containing polyolefin core obtained in step S1 is mixed with an emulsifier and deionized water, and then emulsified by high-speed shearing to form an intermediate emulsion. The intermediate emulsion was distilled to remove the solvent, yielding the seed emulsion; S3 preparation of the outer shell of core-shell microspheres: In an inert atmosphere, an initiator is added to the seed emulsion and the temperature is raised. Then, acrylic monomers and / or acrylate monomers are added to carry out a polymerization reaction to obtain a shell bonded to the core. Unreacted monomers were removed by negative pressure distillation to obtain the adhesive emulsion containing core-shell microspheres.

7. The preparation method according to claim 6, characterized in that, Step S1 satisfies at least one of the following: (1) The solvent includes one or more of the following: alcohol solvents, ketone solvents, ether solvents, ester solvents, olefin solvents, aromatic solvents, and halogen solvents; (2) The catalyst includes at least one of esterification catalyst, epoxy-maleic anhydride catalyst and amidation reaction catalyst; (3) The reaction temperature is 80-150℃ and the reaction time is 2-24h.

8. The preparation method according to claim 6, characterized in that, In step S2, the mass ratio of the aqueous phase to the oil phase is ≥1.2, the shear rate is ≥5000 rpm, and the emulsification time is 10–60 min.

9. The preparation method according to any one of claims 6-8, characterized in that, In step S3, the initiator is an oil-based initiator and / or an aqueous initiator. The initiator is added and the temperature is raised to the polymerization temperature of 50-90°C. Acrylic monomers and / or acrylate monomers are slowly added dropwise, and the polymerization reaction time is 1-6 hours.

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