Electrolyte swelling-resistant polymer microsphere as well as preparation method and application thereof

Abstract

The invention relates to an electrolyte swelling resistant polymer microsphere and a preparation method and application thereof, and belongs to the technical field of microspheres, the preparation method comprises the following steps: carrying out emulsion polymerization on a monomer A, a monomer B, a monomer C and a monomer D to obtain a polymer microsphere dispersion liquid; adding a high-temperature-resistant solvent and a dispersing aid into the polymer microsphere dispersion liquid or microsphere powder obtained by filtering the polymer microsphere dispersion liquid to obtain a mixed solution; and heating the mixed solution to 100-240 DEG C or above, heating and refluxing for 5-48 hours, cooling to room temperature, and carrying out suction filtration, washing and drying to obtain the electrolyte swelling resistant polymer microspheres. Compared with the prior art, the microspheres prepared by the preparation method disclosed by the invention have the advantages that on the basis of maintaining the original morphology, the electrolyte swelling resistance is obviously enhanced, and the swelling degree ((swelled volume-original volume) / original volume) is not more than 20% after the microspheres are soaked in an electrolyte at 80 DEG C for 24 hours.

Description

Technical Field

[0001] The invention relates to the technical field of microspheres, and in particular to electrolyte swelling-resistant polymer microspheres and a preparation method and application thereof. Background Art

[0002] Lithium batteries are widely used in electronic communications, energy storage, power supply and other fields. They are mainly composed of positive electrode, negative electrode, electrolyte and battery separator, among which the separator is one of the key inner components. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the battery's capacity, cycle and safety performance. Excellent performance separators play an important role in improving the comprehensive performance of batteries. The melting point of commercial porous polyolefin (PE) separators is only between 135 and 165 ° C. When the battery is heated, the separator will shrink or break, resulting in internal short circuit, thermal runaway and even explosion, which seriously threatens the safety of the battery. In addition, the low porosity of polyolefin separators and poor affinity for liquid electrolytes, and the easy obstruction of ion migration are also important reasons that hinder the development of high-performance lithium batteries.

[0003] Nowadays, lithium battery separators are usually modified with inorganic coatings or organic polymers. Inorganic coatings have excellent heat resistance and can improve the thermal stability of the separator. The most widely used inorganic ceramics include SiO2, Al2O3, ZrO2, NaY zeolite, TiO2, etc. However, inorganic nano-coatings are not only prone to pore blocking, resulting in excessive air permeability of the coating, increased conductive resistance of lithium ions, affecting the migration of lithium ions during charging and discharging, and reducing battery capacity, but also have fewer gaps in the dense coating and cannot accommodate more electrolyte, which is prone to lithium precipitation in the later stages of battery cycles, causing the battery performance to fail drastically. Organic polymer coating materials such as PVDF and aramid have the problem of insufficient temperature resistance. Currently, polymer microspheres are commonly used to optimize lithium battery separators.

[0004] Emulsion polymerization is a classic method for preparing polymer microspheres. It can prepare submicron polymer microspheres of uniform size in large quantities, and industrial production of some products has been achieved. However, due to the inherent properties of organic matter, most polymer microspheres swell or dissolve to varying degrees in organic solvents, which limits their application in specific fields. For example, when battery cells or diaphragm materials work in an electrolyte environment, the microspheres need to have a certain ability to resist solvent swelling to prevent pore blockage caused by dissolved substances, thereby affecting the cyclability and safety of the battery.

[0005] At present, the common method to enhance the solvent resistance of polymer microspheres is to increase the crosslinking degree of polymer microspheres by introducing a crosslinking agent during the polymerization process. For example, by crosslinking the polymer microspheres with a silane coupling agent, a polymer microsphere with a gelation rate higher than 90% can be obtained, thereby greatly inhibiting its swelling in organic solvents; or by compounding with inorganic substances, such as coating or depositing inorganic substances on the surface or inside of microspheres containing specific functional groups, to obtain organic-inorganic composite microspheres, thereby reducing the proportion of polymer in the microspheres and thus reducing their swelling. However, the introduction of crosslinking agents or inorganic sources will increase production costs and the complexity of the production process on the one hand; on the other hand, the scope of applicable monomers is often limited, and the current price of swelling-resistant polymer microspheres is generally high. Summary of the invention

[0006] The purpose of the present invention is to provide an electrolyte swelling-resistant polymer microsphere and its preparation method and application in order to overcome at least one of the defects of the above-mentioned prior art. The microspheres provided by the present invention have significantly enhanced resistance to electrolyte swelling while maintaining the original morphology. The swelling degree ((volume after swelling-original volume) / original volume) after immersion in 80°C electrolyte for 24 hours does not exceed 20%.

[0007] From the chemical essence, the polymer microspheres in the present invention are a kind of agglomerates composed of multiple long polymer chains. Small molecule solvents can easily enter between the long chain molecules, so that the chains are filled with solvents, the distance between the polymer chains is increased, and the entanglement between the chains is untied, which is manifested as swelling or even dissolution of the microspheres on a macro scale. Although a certain amount of polyvinyl monomers for crosslinking, such as divinylbenzene, etc., are added to the formula, during the reaction process, when one of the vinyl groups in the molecule is reacted into the polymer main chain, due to the influence of steric hindrance and the traction of the macromolecular main chain, the momentum of the monomer molecule is reduced, so the reactivity of another vinyl group in the monomer molecule is greatly reduced relative to the free monomer. Therefore, even after all the monomers are consumed, only a part of the polyvinyl monomers are still involved in the crosslinking between the macromolecules, so the degree of crosslinking is also limited, and it is easy to be swollen or even dissolved by the solvent. However, in the emulsion polymerization process, especially in the preparation of high-solid products, excessive addition of polyvinyl monomers almost inevitably leads to adhesion and agglomeration between the balls. In the present invention, when a small amount of crosslinking agent is added, after all free monomers are consumed, the kinetic energy of unreacted vinyl monomers existing in the microspheres is transferred by high temperature, so that the vinyl monomers can collide with other vinyl monomers and react, thereby completing crosslinking.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] One of the purposes of the present invention is to provide a method for preparing polymer microspheres resistant to swelling by electrolyte, comprising the following steps:

[0010] emulsion polymerizing monomer A, monomer B, monomer C and monomer D to obtain a polymer microsphere dispersion;

[0011] Then, a high temperature resistant solvent and a dispersing aid are added to the polymer microsphere dispersion or the microsphere powder obtained by filtering the polymer microsphere dispersion to obtain a mixed solution;

[0012] The mixed solution is heated to above 100 to 240° C., heated under reflux for 5 to 48 hours, cooled to room temperature, filtered, washed, and dried to obtain electrolyte swelling-resistant polymer microspheres;

[0013] Wherein, the mass ratio of monomer A, monomer B, monomer C and monomer D is (10-70):(15-65):(10-65):(1-65);

[0014] Wherein, the mass ratio of the microsphere powder to the mixed liquid is 1:1000 to 1:3;

[0015] Wherein, the mass ratio of the high temperature resistant solvent to the mixed liquid is 1:10 to 4:5;

[0016] Wherein, the mass ratio of the dispersing aid to the mixed liquid is 0:1 to 1:10.

[0017] Preferably, the mass ratio of monomer A, monomer B, monomer C and monomer D is 4.5:4.3:4.5:1.

[0018] Furthermore, the emulsion polymerization comprises the following steps:

[0019] After monomer A, monomer B, monomer C and monomer D are mixed, surfactant and deionized water are added, and emulsification is performed by high-speed shearing to obtain an emulsion;

[0020] Add part of the emulsion into the autoclave reactor, add saturated potassium sulfate solution to initiate the addition, and start adding the remaining emulsion at the same time. After the addition is completed, react for at least 16 hours.

[0021] Preferably, the sum of the masses of the monomer A, monomer B, monomer C and monomer D is recorded as the total monomer mass, and the mass ratio of the total monomer mass, surfactant and deionized water is 14.3:0.14:80.

[0022] Furthermore, the surfactant includes but is not limited to Tween 20, Tween 21, Tween 40, Tween 60, Tween 61, Tween 80, Tween 81, Tween 85, AEO3, AEO4, AEO5, AEO7, AEO9, AEO11, AEO12, AEO13, AEO14, AEO15, AEO20, AEO23, Sban 20, Sban 40, Sban 60, and Sban 80.

[0023] Preferably, the surfactant is a mixture of Tween 80 and Span 80, and the mass ratio of the two is 3:11.

[0024] Furthermore, the initiator includes but is not limited to potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, tert-butyl hydroperoxide, benzoyl peroxide, azobisisobutyronitrile or cumene hydroperoxide.

[0025] Furthermore, the monomer A is one or more of styrene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, chloromethylstyrene, itaconic acid, maleic acid, maleic anhydride, and fumaric acid.

[0026] Further, the monomer B is one or more of acrylamide, acrylonitrile, 2-methyl-5-vinylpyridine, sodium p-vinylbenzenesulfonate, N-vinylformamide, N-vinylpyrrolidone, aniline, adipic dihydrazide, carbonate dihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, N-aminoacrylamide, methylenebisacrylamide, N-hydroxymethylacrylamide, N-methoxymethylacrylamide, N-isopropyloxymethylacrylamide, N-butoxymethylacrylamide, N-isobutoxymethylacrylamide, N-octyloxymethylacrylamide, and N-carboxymethoxymethylacrylamide.

[0027] Further, the monomer C is one or more of acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, dodecyl acrylate, glycidyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate, and allyl glycidyl ether.

[0028] Further, the monomer D is one or more of divinylbenzene, butadiene, 1,3-pentadiene, isoprene, 2,3-dimethylbutadiene, chloroprene, ethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropyl triacrylate, ethoxytrimethylolpropane triacrylate, diallyl maleate, allyl methacrylate, pentaerythritol triallyl ester, pentaerythritol triallyl ether, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and diallyl terephthalate.

[0029] Preferably, the monomer A is styrene; the monomer B is acrylonitrile; the monomer C is methyl methacrylate; and the monomer D is one or more of divinylbenzene, dipentaerythritol pentaacrylate or dipentaerythritol hexaacrylate.

[0030] Furthermore, the high temperature resistant solvent includes, but is not limited to, one or more of water, ethylene glycol, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, butanol, and acetic acid.

[0031] Furthermore, the dispersing aid is a high molecular polymer that can be dispersed in a high temperature resistant solvent, including but not limited to one or more of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, polystyrene maleic anhydride, polyethylene oxide or polyacrylic acid.

[0032] Furthermore, the mixed solution is preferably heated to 100-240° C. and heated to reflux for 4-16 hours.

[0033] The second object of the present invention is to provide a polymer microsphere resistant to swelling in electrolyte, which is obtained by the preparation method as described above, and the size of the microsphere is 100nm-10μm.

[0034] The third object of the present invention is to use the above-mentioned electrolyte swelling-resistant polymer microspheres in battery separators.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) The present invention provides a method for preparing polymer microspheres resistant to electrolyte swelling. When a small amount of crosslinking agent is added, after all free monomers are consumed, the kinetic energy of the unreacted vinyl monomers already present in the microspheres is transferred by high temperature, so that the kinetic energy can collide with other vinyl monomers and react, thereby completing crosslinking.

[0037] (2) The present invention provides a method for preparing polymer microspheres resistant to swelling by electrolytes. The method is simple, efficient, and has a wide range of monomer applicability.

[0038] (3) The present invention provides a polymer microsphere resistant to swelling in electrolyte. The microsphere has significantly enhanced resistance to swelling in electrolyte while maintaining its original morphology. The swelling degree ((volume after swelling-original volume) / original volume) after immersion in an electrolyte at 80°C for 24 hours does not exceed 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The scanning electron micrographs of the polymer microspheres used in Examples 2, 3, 4, 5, 6, and 7;

[0040] Figure 2 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 2;

[0041] Figure 3 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 3;

[0042] Figure 4 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 4;

[0043] Figure 5 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 5;

[0044] Figure 6 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 6;

[0045] Figure 7 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 7;

[0046] Figure 8 This is a scanning electron microscope image of the polymer microspheres after swelling in the electrolyte;

[0047] Fig. 9 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 2 after swelling in the electrolyte;

[0048] Fig.10 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 4 after swelling in the electrolyte;

[0049] Fig.11 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 6 after swelling in the electrolyte;

[0050] Fig.12 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in Example 7 after swelling in the electrolyte;

[0051] Fig.13 This is a schematic diagram of the processing of the swelling-resistant microspheres of the present invention. DETAILED DESCRIPTION

[0052] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented under the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. If specific conditions are not specified, proceed according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0053] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0054] The polymer microspheres in the present invention are a kind of agglomerates composed of multiple long polymer chains. Small molecule solvents can easily enter between the long chain molecules, so that the solvent is filled between the chains, the distance between the polymer chains is increased, and the entanglement between the chains is untied, which is manifested macroscopically as the microspheres swelling or even dissolving.

[0055] Compared with the prior art, the amount of polyvinyl monomers added to the formula of the present invention for crosslinking is not very large. During the reaction, when one of the vinyl groups in the molecule is reacted into the polymer main chain, due to the influence of steric hindrance and the traction of the macromolecular main chain, the momentum of the monomer molecule is reduced, so the reaction activity of another vinyl group in the monomer molecule is greatly reduced relative to the free monomer. Therefore, even after all the monomers are consumed, only a part of the polyvinyl monomers are still involved in the crosslinking between the macromolecules, so the degree of crosslinking is also limited, and it is easy to be swollen or even dissolved by the solvent.

[0056] During the emulsion polymerization process, especially during the preparation of high solid content products, excessive addition of multi-vinyl monomers will almost inevitably lead to adhesion and agglomeration between the microspheres. Therefore, in the present invention, after all free monomers are consumed, the high temperature is used to transfer the kinetic energy of the unreacted vinyl monomers in the microspheres, so that they can collide with other vinyl monomers and react, thereby completing crosslinking.

[0057] A method for preparing polymer microspheres resistant to electrolyte swelling comprises the following steps:

[0058] emulsion polymerizing monomer A, monomer B, monomer C and monomer D to obtain a polymer microsphere dispersion;

[0059] Adding a high temperature resistant solvent and a dispersing aid into a polymer microsphere dispersion or microsphere powder obtained by filtering the polymer microsphere dispersion to obtain a mixed solution;

[0060] The mixed solution is heated to above 100 to 240° C., heated under reflux for 5 to 48 hours, cooled to room temperature, filtered, washed, and dried to obtain electrolyte swelling-resistant polymer microspheres;

[0061] Wherein, the mass ratio of monomer A, monomer B, monomer C and monomer D is (10-70):(15-65):(10-65):(1-65);

[0062] The mass ratio of the microsphere powder to the mixed liquid is 1:1000 to 1:3;

[0063] The mass ratio of the high temperature resistant solvent to the mixed liquid is 1:10 to 4:5;

[0064] The mass ratio of the dispersing aid to the mixed liquid is 0:1 to 1:10.

[0065] Preferably, the mass ratio of monomer A, monomer B, monomer C and monomer D is 4.5:4.3:4.5:1.

[0066] Wherein, the emulsion polymerization comprises the following steps:

[0067] After monomer A, monomer B, monomer C and monomer D are mixed, surfactant and deionized water are added, and emulsification is performed by high-speed shearing to obtain an emulsion;

[0068] Add part of the emulsion into the autoclave reactor, add saturated potassium sulfate solution to initiate the addition, and start adding the remaining emulsion at the same time. After the addition is completed, react for at least 16 hours.

[0069] Preferably, the sum of the masses of the monomer A, monomer B, monomer C and monomer D is recorded as the total monomer mass, and the mass ratio of the total monomer mass, surfactant and deionized water is 14.3:0.14:80.

[0070] In some embodiments of the present invention, the surfactant includes but is not limited to Tween 20, Tween 21, Tween 40, Tween 60, Tween 61, Tween 80, Tween 81, Tween 85, AEO3, AEO4, AEO5, AEO7, AEO9, AEO11, AEO12, AEO13, AEO14, AEO15, AEO20, AEO23, Span 20, Span 40, Span 60, and Span 80.

[0071] Preferably, the surfactant is a mixture of Tween 80 and Span 80, and the mass ratio of the two is 3:11.

[0072] In some embodiments of the present invention, the initiator includes but is not limited to potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, tert-butyl hydroperoxide, benzoyl peroxide, azobisisobutyronitrile or cumene hydroperoxide.

[0073] In some embodiments of the present invention, the monomer A is one or more of styrene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, chloromethylstyrene, itaconic acid, maleic acid, maleic anhydride, and fumaric acid.

[0074] In some embodiments of the present invention, the monomer B is one or more of acrylamide, acrylonitrile, 2-methyl-5-vinylpyridine, sodium p-vinylbenzenesulfonate, N-vinylformamide, N-vinylpyrrolidone, aniline, adipic dihydrazide, carbonate dihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, N-aminoacrylamide, methylenebisacrylamide, N-hydroxymethylacrylamide, N-methoxymethylacrylamide, N-isopropyloxymethylacrylamide, N-butoxymethylacrylamide, N-isobutyloxymethylacrylamide, N-octyloxymethylacrylamide, and N-carboxymethoxymethylacrylamide.

[0075] In some embodiments of the present invention, the monomer C is one or more of acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, dodecyl acrylate, glycidyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate, and allyl glycidyl ether.

[0076] In some embodiments of the present invention, the monomer D is one or more of divinylbenzene, butadiene, 1,3-pentadiene, isoprene, 2,3-dimethylbutadiene, chloroprene, ethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropyl triacrylate, ethoxytrimethylolpropane triacrylate, diallyl maleate, allyl methacrylate, pentaerythritol triallyl ester, pentaerythritol triallyl ether, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and diallyl terephthalate.

[0077] Preferably, the monomer A is styrene; the monomer B is acrylonitrile; the monomer C is methyl methacrylate; and the monomer D is one or more of divinylbenzene, dipentaerythritol pentaacrylate or dipentaerythritol hexaacrylate.

[0078] In some embodiments of the present invention, the high temperature resistant solvent includes but is not limited to one or more of water, ethylene glycol, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, butanol, and acetic acid.

[0079] In some embodiments of the present invention, the dispersing aid is a high molecular polymer that can be dispersed in a high temperature resistant solvent, including but not limited to one or more of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, polystyrene maleic anhydride, polyethylene oxide or polyacrylic acid.

[0080] Example 1

[0081] In this example, four types of polymer microspheres were prepared, which were named microsphere 1, microsphere 2, microsphere 3 and microsphere 4, respectively.

[0082] Among them, the prepared microsphere 2 does not add monomer B, the microsphere 3 does not add monomer C, and the microsphere 4 does not add monomer D; the scanning electron microscope image of microsphere 1 is shown in Figure 1 .

[0083] The formula is shown in the following table:

[0084]

[0085] 1. Preparation of polymer microspheres: monomers A, B, C, and D were mixed, and surfactants (Span 80 and Tween 80) and deionized water were added. The mixture was emulsified by high-speed shearing. 30 wt% of the emulsion was directly added to a 250 ml conical flask and heated to 80° C. A saturated potassium persulfate solution was added dropwise to initiate the addition, and the remaining 70 wt% of the emulsion was added dropwise at the same time. After the addition was completed, the reaction was continued for 16 hours to obtain a polymer microsphere dispersion.

[0086] 2. Add 60 g of ethylene glycol, a high temperature resistant solvent, and 2 g of PVP-K90, a dispersing aid, to 20 ml of the polymer microsphere dispersion after the polymerization is completed to obtain a mixed solution of polymer microspheres.

[0087] 3. Heat the polymer microsphere mixture, evaporate 15g of water, raise the temperature to 140℃ and start refluxing for 5h.

[0088] 4. Add ethanol and water to the obtained microspheres, centrifuge them three times each, and obtain the finished product.

[0089] During the polymerization process, a large amount of precipitation was generated in the microspheres 3, and a large amount of attachments were present on the stirring blade and the bottle wall.

[0090] Thermal decomposition temperature test :

[0091] The temperature at which the mass of the microspheres loses 5 wt% after being dried at 80°C in a nitrogen atmosphere at a heating rate of 20°C / min.

[0092] Microsphere 1 is 353°C, which meets the application requirements, while microsphere 2 is 303°C, which does not meet the application requirements, indicating that monomer B is very important for increasing the thermal decomposition temperature of the microspheres.

[0093] Solvent resistance test :

[0094] 1 g of the swelling-resistant microspheres was weighed and dispersed in 10 mL of solvent (3 mL of ethylene carbonate + 7 mL of ethyl methyl carbonate) and placed in an oil bath at 85°C for 24 h. Microsphere 4 was directly dissolved in the electrolyte, indicating that monomer D is very important for improving the swelling resistance of the microspheres.

[0095] In addition, 1 g of microsphere 1 was dispersed in 10 mL of solvent (3 mL of ethylene carbonate + 7 mL of ethyl methyl carbonate) and placed in an oil bath at 85 °C for 24 h. Figure 8 The scanning electron microscope image of the original microsphere 1 after swelling in the electrolyte. Figure 8 It can be seen that microsphere 1 has undergone severe swelling.

[0096] Example 2

[0097] The average size of the microspheres prepared in this embodiment is about 300 nm, and the average size of the microspheres after swelling is 310 nm. After being soaked in the electrolyte, the boundaries between the microspheres are unclear and they are already adhered. Figure 2 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example. Fig. 9 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example after swelling in the electrolyte. Figure 2 It can be seen that the particle size of microspheres prepared by emulsion polymerization is very uniform; Fig. 9 It can be seen that after heating and refluxing in a high-boiling-point dispersant, the swelling degree of the microspheres is significantly reduced. In this embodiment, when a small amount of crosslinking agent is added, after all free monomers are consumed, the kinetic energy of the unreacted vinyl monomers already present in the microspheres is transferred by high temperature, so that the vinyl monomers collide with other vinyl monomers and react, thereby completing crosslinking.

[0098] The polymer microspheres of this embodiment are microspheres 1 prepared in Example 1.

[0099] The steps of this embodiment are basically the same as those of Embodiment 1, except that the parameters shown in the following table are changed in this embodiment:

[0100]

[0101] Feeding :

[0102] 50 g of ethylene glycol was weighed into a round-bottom flask, and then 50 g of polymer microspheres (15% aqueous dispersion) were added. The mixture was mechanically stirred for 30 min, and 2 g of PVP-K90 additive was added to disperse the mixture evenly. The stirring rate was 170 rpm.

[0103] Heating reflux :

[0104] The temperature was raised to 120°C, the condensation reflux device was turned on, and mechanical stirring was continued for 16 h.

[0105] Discharging :

[0106] Cool naturally to room temperature, discharge the material, filter and recover the dispersant, wash and dry.

[0107] Solvent resistance test :

[0108] Weigh 1 g of the swelling-resistant microspheres, disperse them in 10 mL of solvent (3 mL of ethylene carbonate + 7 mL of ethyl methyl carbonate), and place them in an oil bath at 85°C for 24 h.

[0109] Example 3

[0110] The average size of the microspheres prepared in this embodiment is about 300 nm, and the average size of the microspheres after swelling is 310 nm. After being soaked in the electrolyte, the microspheres are still adhered to each other. Figure 3 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example.

[0111] The polymer microspheres of this embodiment are microspheres 1 prepared in Example 1.

[0112] The steps of this embodiment are basically the same as those of Embodiment 1, except that the parameters shown in the following table are changed in this embodiment:

[0113]

[0114] Feeding :

[0115] 50 g of ethylene glycol was weighed into a round-bottom flask, and then 50 g of polymer microspheres (15% aqueous dispersion) were added. The mixture was mechanically stirred for 30 min, and 2 g of PVP-K90 additive was added to disperse the mixture evenly. The stirring rate was 170 rpm.

[0116] Heating reflux :

[0117] The temperature was raised to 130°C, the condensation reflux device was turned on, and mechanical stirring was continued for 16 h.

[0118] Discharging :

[0119] Cool naturally to room temperature, discharge the material, filter and recover the dispersant, wash and dry.

[0120] Solvent resistance test :

[0121] Weigh 1 g of the swelling-resistant microspheres, disperse them in 10 mL of solvent (3 mL of ethylene carbonate + 7 mL of ethyl methyl carbonate), and place them in an oil bath at 85°C for 24 h.

[0122] Example 4

[0123] The average size of the microspheres prepared in this embodiment is about 300 nm, and the average size of the microspheres after swelling is 310 nm. The boundaries between the microspheres are clear and there is no fusion phenomenon, which allows the electrolyte to pass through the gaps.

[0124] Figure 4 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example. Fig.10 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example after swelling in the electrolyte. Fig. 9 , 10 It can be seen that with the increase of treatment temperature, the swelling resistance of the microspheres gradually improves.

[0125] The polymer microspheres of this embodiment are microspheres 1 prepared in Example 1.

[0126] The steps of this embodiment are basically the same as those of Embodiment 1, except that the parameters shown in the following table are changed in this embodiment:

[0127]

[0128] Feeding :

[0129] 50 g of ethylene glycol was weighed into a round-bottom flask, and then 50 g of polymer microspheres (15% aqueous dispersion) were added. The mixture was mechanically stirred for 30 min, and 2 g of PVP-K90 additive was added to disperse the mixture evenly. The stirring rate was 170 rpm.

[0130] Heating reflux :

[0131] The temperature was raised to 140°C, the condensation reflux device was turned on, and mechanical stirring was continued for 16 h.

[0132] Discharging :

[0133] Cool naturally to room temperature, discharge the material, filter and recover the dispersant, wash and dry.

[0134] Solvent resistance test :

[0135] Weigh 1 g of the swelling-resistant microspheres, disperse them in 10 mL of solvent (3 mL of ethylene carbonate + 7 mL of ethyl methyl carbonate), and place them in an oil bath at 85°C for 24 h.

[0136] Example 5

[0137] No additives were added during the preparation process of this embodiment, resulting in severe agglomeration. Figure 5 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example.

[0138] The polymer microspheres of this embodiment are microspheres 1 prepared in Example 1.

[0139] The steps of this embodiment are basically the same as those of Embodiment 1, except that the parameters shown in the following table are changed in this embodiment:

[0140]

[0141] Feeding :

[0142] 50 g of ethylene glycol was weighed into a round-bottom flask, and then 50 g of polymer microspheres (15% aqueous dispersion) were added, and mechanical stirring was performed for 30 minutes at a stirring rate of 170 rpm.

[0143] Heating reflux :

[0144] The temperature was raised to 140°C, the condensation reflux device was turned on, and mechanical stirring was continued for 16 h.

[0145] Discharging :

[0146] Cool naturally to room temperature, discharge the material, filter and recover the dispersant, wash and dry.

[0147] Example 6

[0148] In the preparation process of this example, the ratio of high boiling point dispersant ethylene glycol to polymer microsphere dispersion was 1:3, and bumping occurred in the late stage of the reaction. Figure 6 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example. Fig.11 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example after swelling in an electrolyte.

[0149] The polymer microspheres of this embodiment are microspheres 1 prepared in Example 1.

[0150] The steps of this embodiment are basically the same as those of Embodiment 1, except that the parameters shown in the following table are changed in this embodiment:

[0151]

[0152]

[0153] Feeding :

[0154] 25 g of ethylene glycol was weighed into a round-bottom flask, and then 75 g of polymer microspheres (15% aqueous dispersion) were added. The mixture was mechanically stirred for 30 min, and 2 g of PVP-K90 additive was added to disperse the mixture evenly. The stirring rate was 170 rpm.

[0155] Heating reflux :

[0156] The temperature was raised to 140°C, the condensation reflux device was turned on, and mechanical stirring was continued for 16 h.

[0157] Discharging :

[0158] Cool naturally to room temperature, discharge the material, filter and recover the dispersant, wash and dry.

[0159] Solvent resistance test :

[0160] Weigh 1 g of the swelling-resistant microspheres, disperse them in 10 mL of solvent (3 mL of ethylene carbonate + 7 mL of ethyl methyl carbonate), and place them in an oil bath at 85°C for 24 h.

[0161] Example 7

[0162] In the preparation process of this embodiment, the ratio of high boiling point dispersant ethylene glycol to polymer microsphere dispersion is 3:1.

[0163] Figure 7 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example. Fig.12 This is a scanning electron microscope image of the swelling-resistant microspheres prepared in this example after swelling in the electrolyte.

[0164] The polymer microspheres of this embodiment are microspheres 1 prepared in Example 1.

[0165] The steps of this embodiment are basically the same as those of Embodiment 1, except that the parameters shown in the following table are changed in this embodiment.

[0166]

[0167] Feeding :

[0168] 75 g of ethylene glycol was weighed into a round-bottom flask, and then 25 g of polymer microspheres (15% aqueous dispersion) were added. The mixture was mechanically stirred for 30 min, and 2 g of PVP-K90 additive was added to disperse the mixture evenly. The stirring rate was 170 rpm.

[0169] Heating reflux :

[0170] The temperature was raised to 140°C, the condensation reflux device was turned on, and mechanical stirring was continued for 16 h.

[0171] Discharging :

[0172] Cool naturally to room temperature, discharge the material, filter and recover the dispersant, wash and dry.

[0173] Solvent resistance test :

[0174] Weigh 1 g of the swelling-resistant microspheres, disperse them in 10 mL of solvent (3 mL of ethylene carbonate + 7 mL of ethyl methyl carbonate), and place them in an oil bath at 85°C for 24 h.

[0175] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing polymer microspheres resistant to electrolyte swelling, characterized in that: The steps include: emulsion polymerizing monomer A, monomer B, monomer C and monomer D to obtain a polymer microsphere dispersion; Adding a high temperature resistant solvent and a dispersing aid into a polymer microsphere dispersion or microsphere powder obtained by filtering the polymer microsphere dispersion to obtain a mixed solution; The mixed solution is heated to above 100 to 240° C., heated under reflux for 5 to 48 hours, cooled to room temperature, filtered, washed, and dried to obtain electrolyte swelling-resistant polymer microspheres; Wherein, the mass ratio of monomer A, monomer B, monomer C and monomer D is (10-70):(15-65):(10-65):(1-65); The mass ratio of the microsphere powder to the mixed liquid is 1:1000 to 1:3; The mass ratio of the high temperature resistant solvent to the mixed liquid is 1:10 to 4:5; The mass ratio of the dispersing aid to the mixed liquid is 0:1 to 1:

10.

2. The method for preparing electrolyte swelling-resistant polymer microspheres according to claim 1, characterized in that: The emulsion polymerization comprises the following steps: After monomer A, monomer B, monomer C and monomer D are mixed, surfactant and deionized water are added, and emulsification is performed by high-speed shearing to obtain an emulsion; Add part of the emulsion into a tank reactor, add saturated potassium sulfate solution to initiate, and add the remaining emulsion at the same time. After the addition is completed, react for at least 16 hours.

3. The method for preparing electrolyte swelling-resistant polymer microspheres according to claim 2, characterized in that: The surfactant includes but is not limited to Tween 20, Tween 21, Tween 40, Tween 60, Tween 61, Tween 80, Tween 81, Tween 85, AEO3, AEO4, AEO5, AEO7, AEO9, AEO11, AEO12, AEO13, AEO14, AEO15, AEO20, AEO23, Span 20, Span 40, Span 60, and Span 80.

4. The method for preparing electrolyte swelling-resistant polymer microspheres according to claim 2, characterized in that: The initiator includes, but is not limited to, potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, tert-butyl hydroperoxide, benzoyl peroxide, azobisisobutyronitrile or cumene hydroperoxide.

5. The method for preparing electrolyte swelling-resistant polymer microspheres according to claim 1, characterized in that: The monomer A is one or more of styrene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, chloromethylstyrene, itaconic acid, maleic acid, maleic anhydride, and fumaric acid; The monomer B is one or more of acrylamide, acrylonitrile, 2-methyl-5-vinylpyridine, sodium p-vinylbenzenesulfonate, N-vinylformamide, N-vinylpyrrolidone, aniline, adipic dihydrazide, carbonate dihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, N-aminoacrylamide, methylenebisacrylamide, N-hydroxymethylacrylamide, N-methoxymethylacrylamide, N-isopropyloxymethylacrylamide, N-butoxymethylacrylamide, N-isobutyloxymethylacrylamide, N-octyloxymethylacrylamide, and N-carboxymethoxymethylacrylamide; The monomer C is one or more of acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, dodecyl acrylate, glycidyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate, and allyl glycidyl ether; The monomer D is one or more of divinylbenzene, butadiene, 1,3-pentadiene, isoprene, 2,3-dimethylbutadiene, chloroprene, ethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropyl triacrylate, ethoxytrimethylolpropane triacrylate, diallyl maleate, allyl methacrylate, pentaerythritol triallyl ester, pentaerythritol triallyl ether, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and diallyl terephthalate.

6. The method for preparing electrolyte swelling-resistant polymer microspheres according to claim 1 or 5, characterized in that: The monomer A is styrene; The monomer B is acrylonitrile; The monomer C is methyl methacrylate; The monomer D is one or more of divinylbenzene, dipentaerythritol pentaacrylate or dipentaerythritol hexaacrylate.

7. The method for preparing electrolyte swelling-resistant polymer microspheres according to claim 1, characterized in that: The high temperature resistant solvent is not limited to one or more of water, ethylene glycol, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, butanol, and acetic acid; The dispersing aid is a high molecular polymer that can be dispersed in a high temperature resistant solvent, including but not limited to one or more of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, polystyrene maleic anhydride, polyethylene oxide or polyacrylic acid.

8. The method for preparing electrolyte swelling-resistant polymer microspheres according to claim 1, characterized in that: The mixed solution is preferably heated to 100-240° C. and heated under reflux for 4-16 hours.

9. A polymer microsphere resistant to swelling by electrolyte, characterized in that: The microspheres are obtained by the preparation method according to any one of claims 1 to 8, and the size of the microspheres is 100 nm to 10 μm.

10. Use of the electrolyte swelling-resistant polymer microspheres as claimed in claim 9 in battery separators.

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