Polymer microsphere material, and preparation method therefor and use thereof

Abstract

The present disclosure relates to the technical field of core-shell polymer materials, and provides a polymer microsphere material, and a preparation method therefor and the use thereof. Specifically, the polymer microsphere material comprises a core layer, a transition layer and a shell layer from the inside to the outside, wherein the core layer comprises a first modified acrylate copolymer, the glass transition temperature of which is less than or equal to 35ºC; the transition layer is obtained by polymerizing at least one functional monomer; and the shell layer comprises a second modified acrylate copolymer, the glass transition temperature of which is 60ºC to 250ºC. In the present disclosure, by introducing the functional transition layer, the bonding between the soft core layer and the hard shell layer can be effectively enhanced, thereby making the whole core-shell structure more compact and firmer; moreover, the structural defects of excessive swelling of polymer microspheres and proneness to breakage due to long-term pressure can be effectively overcome, and the polymer microsphere material is widely applicable to the field of separators of secondary batteries, and has good application prospects.

Description

Polymer microsphere material, preparation method and application thereof

[0001] Cross-reference to related applications

[0002] The present disclosure claims priority to the application No. 2024111109815, filed on August 14, 2024, with the China Patent Office, and entitled "Polymer microsphere material, preparation method and application thereof", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of core-shell polymer materials, in particular, to a polymer microsphere material, a preparation method and application thereof. BACKGROUND

[0004] In recent years, in the field of battery separators, polymer microspheres as separator coating materials have been increasingly concerned. For example, polymer microspheres are coated on the surface of the separator to realize the bonding function between the separator and the electrode, or to adjust the mechanical properties of the separator; for another example, polymer microspheres are used as separator modification materials to improve the thermal response performance, ionic conductivity, stability performance, etc. of the separator, thereby realizing the improvement of the safety performance or electrical performance of the battery.

[0005] CN 202110675299.0 discloses a battery separator, comprising a base film and a coating layer, wherein the coating layer comprises core-shell type spheres, inorganic substances, thickening agents and water-based adhesives; the core-shell type spheres comprise an inner core and an outer shell coated on the outer surface of the inner core, the glass transition temperature of the inner core is 10℃, the glass transition temperature of the outer shell is 60℃, and the materials of the inner core and the outer shell are both polymethyl methacrylate. The prior art uses inorganic-organic composite separator coating layer to effectively enhance the bonding capacity of the separator, and at the same time realizes the transformation of the outer shell and the inner core into high-elastic state during hot pressing, thereby avoiding the separation of the coating layer and the base film. However, the prior art still includes a high content of ceramic or ceramic-like inorganic components, which has the defect of insufficient thermal stability, and still causes cracks in the coating layer itself during hot pressing or drying and winding. In addition, the core-shell type spheres are two-layer polymethyl methacrylate, and other structures or functional groups are not introduced, so that the functionality of the core-shell type spheres is relatively single, and the performance in other aspects except the bonding capacity with the base film is general, and there is still a large space for improvement in mechanical strength, electrolyte resistance or electrolyte affinity performance, etc.

[0006] CN202211325940.9 discloses a large-particle-size core-shell polymer particle and a preparation method and application thereof; the designed core-shell polymer particle has a particle size D50 of 1-50 μm, and its structure includes a water-insoluble soft substance layer and a hard substance layer, the weight ratio of the soft substance layer to the hard substance layer is 1:0.1-10, and the hard substance layer is located at the outer layer of the soft substance layer. The polymer particle of the prior art can improve the hardness of the battery cell and inhibit the deformation of the battery cell without affecting the air permeability; compared with general micron-level homogeneous polymer particles, the soft core and hard shell structure thereof is also beneficial to improving the performance of the separator, the hard substance layer located at the outer layer of the particle ensures that the separator coating is not sticky after drying, so that the separators are not adhered to each other after being wound; and the soft substance layer located at the inner layer of the particle can provide strong adhesion, so that the separator and the pole piece have higher peeling strength. However, through in-depth research, it is found that although the prior art can meet the adhesion requirements of the secondary battery separator and the pole piece and improve the rigidity of the battery cell, further test results show that the swelling rate of the polymer microspheres provided by the prior art in the electrolyte is high; when used for a long time, the excessive swelling of the polymer microspheres can cause adhesion failure, block the ion transmission channel, cause the separator to wrinkle or the battery cell to deform, and other serious technical defects. In addition, after the emulsion containing the polymer microspheres is coated on the separator and dried and wound, during storage, the microspheres can be broken due to extrusion caused by the winding tension for a long time, causing the separator to adhere, and the product to fail.

[0007] Therefore, the present disclosure is proposed.

[0008] DISCLOSURE

[0009] A first object of the present disclosure is to provide a polymer microsphere material, in particular a micron-level three-layer core-shell structure polymer microsphere material; mainly used to solve the technical defects of high swelling rate, insufficient structural stability, uneven particle size distribution, etc. of the existing polymer coating material for secondary battery separators.

[0010] A second object of the present disclosure is to provide a preparation method of the polymer microsphere material, which is simple and easy to implement, and can meet the batch production requirements.

[0011] A third object of the present disclosure is to provide a separator for a secondary battery, which can improve the rigidity of the battery cell without affecting the adhesion performance with the electrode, so that the battery cell is not prone to wrinkling, opening or deformation.

[0012] A fourth object of the present disclosure is to provide a secondary battery, which uses a polymer microsphere coated modified separator to effectively enhance the mechanical and safety performance of the battery as a whole.

[0013] In order to achieve the above objects of the present disclosure, the following technical solutions are adopted:

[0014] In a first aspect, the present disclosure provides a polymer microsphere material, comprising a core layer, a transition layer and a shell layer from inside to outside;

[0015] The core layer comprises a first modified acrylate copolymer, and the glass transition temperature of the first modified acrylate copolymer is ≤ 35℃; the transition layer is polymerized from at least one functional monomer; and the shell layer comprises a second modified acrylate copolymer, and the glass transition temperature of the second modified acrylate copolymer is 60℃-250℃.

[0016] The raw material of the transition layer comprises a functional monomer, and the functional monomer comprises at least one of a front-end crosslinking monomer, a strong polar monomer or a long side chain monomer; the front-end crosslinking monomer contains at least 2 polymerizable alkenyl functional groups; the functional groups of the strong polar monomer comprise at least one of a hydroxyl group, a carbonyl group, an acyloxy group, an ether bond, an epoxy group, an amine group, a sulfonic acid group and a substituted aromatic ring; and the side groups of the long side chain monomer comprise at least one carbon chain or carbon-oxygen chain with a carbon number ≥ 4.

[0017] Preferably, the mass of the transition layer is 5wt.%-85wt.% of the core layer, and the mass of the shell layer is 5wt.%-200wt.% of the sum of the core layer and the transition layer.

[0018] Preferably, the first modified acrylate copolymer is prepared from the following components by weight fraction: 45-85 parts of a non-water-soluble soft monomer, 15-35 parts of a non-water-soluble hard monomer, 5-20 parts of a water-soluble organic acid monomer, 0.001-5 parts of a non-ionic surfactant, 0.065-5 parts of a water-soluble initiator and a certain amount of deionized water.

[0019] Preferably, the second modified acrylate copolymer is prepared from the following components by weight fraction: 50-95 parts of a non-water-soluble hard monomer, 0.1-15 parts of a front-end crosslinking monomer, 0.056-3.9 parts of a water-soluble initiator and a certain amount of deionized water.

[0020] Preferably, the diameter of the polymer microsphere material is 1-50μm.

[0021] In a second aspect, the present disclosure also provides a preparation method of the polymer microsphere material, comprising the following steps:

[0022] (1) mixing the raw material components of the core layer sufficiently and performing a polymerization reaction to obtain a core layer emulsion;

[0023] (2) adding the raw material components of the transition layer to the core layer emulsion and performing a second polymerization reaction to obtain a core emulsion coated with a transition layer;

[0024] (3) adding the shell layer raw material components to the core emulsion of the coated transition layer, and performing a third polymerization reaction to obtain an emulsion containing the polymer microsphere material.

[0025] Preferably, the temperature of the polymerization reaction is 55-75℃, and the holding time of the polymerization reaction is 12-15h.

[0026] Preferably, the temperature of the second polymerization reaction is 70-90℃, and the holding time of the second polymerization reaction is 0.5-3h.

[0027] Preferably, the temperature of the third polymerization reaction is 70-90℃, and the holding time of the third polymerization reaction is 1-3h.

[0028] In a third aspect, the present disclosure further provides a separator for a secondary battery, comprising the polymer microsphere material in any of the above embodiments or prepared by the preparation method in any of the above embodiments.

[0029] In a fourth aspect, the present disclosure further provides a secondary battery comprising the separator for a secondary battery in the above embodiments.

[0030] Compared with the prior art, the present disclosure has the following beneficial effects:

[0031] The present disclosure provides a micron-level, three-layer core-shell structure polymer microsphere material for the field of secondary battery separator coating, comprising a core layer at the innermost, a shell layer at the outermost, and a functional transition layer between the two. The polymer microsphere material of the present disclosure has good particle size uniformity, good adhesion with the separator, and good anti-sticking during winding. By introducing a functional transition layer, the present disclosure can effectively enhance the connectivity of the soft core layer and the hard shell layer, making the overall core-shell structure more compact and firm; it can also effectively solve the structural defects of the polymer microsphere swelling too much and easily breaking under long-term pressure.

[0032] The present disclosure provides a separator and a secondary battery comprising the polymer microsphere material; specifically, a separator coated with a polymer microsphere material is assembled with a positive and negative electrode sheet to obtain a battery cell, and after the battery cell is treated under a certain temperature and pressure, the separator and the electrode sheet are fixedly connected through the adhesive effect of the polymer microsphere material, and the rigidity of the battery cell is improved, and the swelling rate is low under long-term electrolyte immersion environment; thus, a secondary battery with good mechanical properties and safety performance is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the specific embodiments of the present disclosure or the prior art, the drawings needed to be used in the specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0034] Figure 1 provides a particle size distribution diagram of the embodiment 5 of the present disclosure;

[0035] Figure 2 provides a SEM diagram of the embodiment 5 of the present disclosure. DETAILED DESCRIPTION

[0036] The technical solutions of the present disclosure will be described clearly and completely in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present disclosure, not all the embodiments, and are only used to illustrate the present disclosure, and should not be regarded as limiting the scope of the present disclosure. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without any creative effort are within the scope of protection of the present disclosure. The specific conditions are not indicated in the embodiments, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not indicated by the manufacturer, and are conventional products that can be purchased on the market. In addition, the terms "one", "two", "1", "2" are only used for description purposes, and cannot be understood as indicating or implying relative importance.

[0037] The first aspect of the present disclosure is to provide a polymer microsphere material, which comprises a core layer, a transition layer and a shell layer from inside to outside; wherein the core layer comprises a first modified acrylate copolymer, and the glass transition temperature of the first modified acrylate copolymer is ≤ 35℃; the transition layer is obtained by polymerization of at least one functional monomer; and the shell layer comprises a second modified acrylate copolymer, and the glass transition temperature of the second modified acrylate copolymer is 60℃-250℃.

[0038] As a preferred embodiment, in the polymer microsphere material, the diameter of the microspheres is 1 μm-50 μm, in some more preferred embodiments, the diameter is 1.5 μm-25 μm, and in further preferred embodiments, the diameter is 2 μm-10 μm.

[0039] As a preferred embodiment, the mass of the transition layer is 5wt.% to 85wt.% of the core layer; in some more preferred embodiments, the ratio is taken from 10wt.% to 20wt.% or 55wt.% to 70wt.%; in some optional embodiments, the mass ratio of the transition layer to the core layer includes but is not limited to any one of 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85% or a numerical interval composed of any two of them.

[0040] As a preferred embodiment, the mass of the shell layer is 5wt.% to 200wt.% of the sum of the core layer and the transition layer; in some more preferred embodiments, the ratio is taken from 10wt.% to 20wt.% or 100wt.% to 120wt.%; in some optional embodiments, the mass ratio of the shell layer to the sum of the mass of the core layer and the transition layer includes but is not limited to any one of 5%, 10%, 20%, 40%, 50%, 60%, 80%, 100%, 120%, 140%, 150%, 160%, 180%, 200% or a numerical interval composed of any two of them.

[0041] As a preferred embodiment, the glass transition temperature of the first modified acrylic ester copolymer includes but is not limited to any one of 35, 30, 25, 20, 15, 10, 5, 1, 0(℃) or a numerical interval composed of any two of them; in some more preferred embodiments, the glass transition temperature of the first modified acrylic ester copolymer is calculated by the following formula:

[0042] wherein, T g is the glass transition temperature of the first modified acrylic ester copolymer, i is the monomer number (i.e. the i-th monomer), w i is the mass fraction of the i-th monomer in the total monomers, T gi is the glass transition temperature of the i-th monomer.

[0043] In the present disclosure, the core layer mainly plays a bonding role; as a preferred embodiment, the first modified acrylic ester copolymer is prepared by including the following components: non-water-soluble soft monomer, non-water-soluble hard monomer, water-soluble organic acid monomer, non-ionic surfactant, water-soluble initiator and deionized water; in some more preferred embodiments, the first modified acrylic ester copolymer is prepared by including the following components by weight fraction: non-water-soluble soft monomer 45 to 85 parts, non-water-soluble hard monomer 15 to 35 parts, water-soluble organic acid monomer 5 to 20 parts, non-ionic surfactant 0.001 to 2.8 parts, water-soluble initiator 0.065 to 2.8 parts and deionized water.

[0044] In some more preferred embodiments, the non-water soluble soft monomer is used to provide the core layer with initial tack, and the non-water soluble soft monomer includes an acrylic ester compound having one alkenyl functional group; the solubility of the non-water soluble soft monomer (25°C, aqueous environment) is ≤ 30 g / L, the solubility of the homopolymer of the non-water soluble soft monomer (25°C, aqueous environment) is ≤ 1 g / L, and the glass transition temperature of the homopolymer of the non-water soluble soft monomer is ≤ 0°C; in further preferred embodiments, the non-water soluble soft monomer includes, but is not limited to, at least one of n-butyl acrylate, n-octadecyl acrylate, isooctyl acrylate, lauryl acrylate, or vinyl neodecanoate.

[0045] In some more preferred embodiments, the non-water soluble hard monomer is used to provide the core layer with permanent tack; the glass transition temperature of the homopolymer of the non-water soluble hard monomer is ≥ 60°C, and in further preferred embodiments, the glass transition temperature of the homopolymer of the non-water soluble hard monomer is 70°C to 200°C; the solubility of the homopolymer of the non-water soluble hard monomer is ≤ 1 g / L; the solubility of the non-water soluble hard monomer is 10 g / L to 90 g / L or 0 to 5 g / L, and the non-water soluble hard monomer is divided into a first non-water soluble hard monomer and a second non-water soluble hard monomer according to the two solubility ranges; in further preferred embodiments, the first non-water soluble hard monomer includes at least one of methyl methacrylate or acrylonitrile, and the second non-water soluble hard monomer includes at least one of styrene or tert-butyl methacrylate; in optional embodiments, the mass ratio of the first non-water soluble hard monomer to the second non-water soluble hard monomer is 9:1 to 1:9, and it can be understood that the mass ratio of the two non-water soluble hard monomers can be used to obtain core layer polymers with different particle sizes and distributions; the higher the amount of the first non-water soluble hard monomer, the higher the particle size and the wider the distribution of the core layer polymer, and vice versa.

[0046] In some more preferred embodiments, the water-soluble organic acid monomer mainly serves to improve the adhesion and electrolyte resistance of the core layer; the solubility of the water-soluble organic acid monomer and its homopolymer (the degree of polymerization of the homopolymer is <1000) in water (25°C, water environment) is ≥50 g / L; the water-soluble organic acid monomer used in the present disclosure ionizes at least one hydrogen ion in water, and is divided into a first water-soluble organic acid monomer (pKa≥3.0) and a second water-soluble organic acid monomer (pKa<3.0) according to the ionization ability; in further preferred embodiments, the first water-soluble organic acid monomer includes but is not limited to at least one of acrylic acid, maleic acid, itaconic acid, or p-vinylphenol; the second water-soluble organic acid monomer includes but is not limited to at least one of p-styrene sulfonic acid, 2-acrylamide-2-methylpropane sulfonic acid, or allyl sulfonic acid; in optional embodiments, the mass ratio of the first water-soluble organic acid monomer to the second water-soluble organic acid monomer is 1:1-10:1, and it can be understood that different particle sizes and distributions of the core layer polymer can be obtained by adjusting the mass ratio of the two water-soluble organic acid monomers; the higher the amount of the first non-water-soluble hard monomer, the higher the particle size and the wider the distribution of the core layer polymer, and vice versa.

[0047] In some more preferred embodiments, the non-ionic surfactant serves to prevent the core layer product particles from agglomerating and precipitating, maintain the stability of the emulsion, and assist in regulating the particle size; the non-ionic surfactant used in the present disclosure belongs to a water-soluble polymer and does not ionize after being dissolved in water; in further preferred embodiments, the non-ionic surfactant includes but is not limited to at least one of polyvinyl alcohol, polyoxyethylene ether, polyvinylpyrrolidone, or hydroxyethyl cellulose; it can be understood that the higher the mass ratio of the non-ionic surfactant in the core layer raw materials, the smaller the particle size of the core layer polymer, and the higher the stability of the prepared core layer.

[0048] In some more preferred embodiments, the water-soluble initiator serves to promote the polymerization reaction of the core layer raw materials; the water-soluble initiator is selected from a persulfate compound, including but not limited to at least one of ammonium persulfate, potassium persulfate, or sodium persulfate.

[0049] In some more preferred embodiments, by adjusting the amount of the deionized water, the solid content of the core layer is 10%-35%, and is further preferably 15%-25%.

[0050] In some more preferred embodiments, the raw material components of the first modified acrylate copolymer further include: a water-soluble neutralizing agent, including but not limited to at least one of alkali metal hydroxides (such as lithium hydroxide, sodium hydroxide, etc.), ammonia water or monovalent saturated organic amine; in further preferred embodiments, the amount of the water-soluble neutralizing agent is 70% to 120% of the molar amount of hydrogen ions produced by ionization of the water-soluble organic acid monomer.

[0051] In some more preferred embodiments, the raw material components of the first modified acrylate copolymer further include: 1 to 10 parts of a water-soluble non-electrolyte monomer, which is water-soluble and does not ionize after dissolution based on its name, and its role is to assist in controlling the particle size of the core layer polymer, and by adding a water-soluble non-electrolyte monomer, a core layer product with a narrower particle size distribution is obtained; the water-soluble non-electrolyte monomer and its homopolymer (homopolymer ≤1000) are ≥50 g / L; in further preferred embodiments, the water-soluble non-electrolyte monomer includes but is not limited to at least one of acrylamide or hydroxyethyl acrylate.

[0052] In some more preferred embodiments, the raw material components of the first modified acrylate copolymer further include: 0.01 to 10 parts of a front-end crosslinking monomer, which is not limited in water solubility, but at least contains 2 polymerizable alkenyl functional groups and completes crosslinking in the polymerization reaction of the core layer, and its role is to improve the adhesion strength and electrolyte resistance of the core layer; in further preferred embodiments, the first modified acrylate copolymer includes but is not limited to at least one of ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate or pentaerythritol tetramethacrylate.

[0053] In some more preferred embodiments, the raw material components of the first modified acrylate copolymer further include: an anionic surfactant, which plays a role in assisting to improve the stability of the core layer, including but not limited to at least one of sodium dodecyl sulfate or sodium octyl sulfonate; in further preferred embodiments, the mass ratio of the anionic surfactant to the non-ionic surfactant is 20% to 80%.

[0054] In the present disclosure, the transition layer is a homopolymer or copolymer synthesized based on several functional monomers, which can be water-soluble or non-water-soluble, and generally has no effect on the particle size of the polymer microsphere material, but can significantly improve the adhesion, electrolyte swelling resistance and other key properties of the microsphere material. Further, when its amount is limited within certain preferred ranges, specific related properties can be achieved; as a preferred embodiment, the raw material (functional monomer) of the transition layer includes at least one of a front-end crosslinking monomer, a strong polar monomer or a long side chain monomer.

[0055] In some more preferred embodiments, the front-end cross-linking monomer contains at least 2 polymerizable alkenyl-containing (meth)acrylate compounds to complete cross-linking during polymerization and form a dense cross-linked layer on the surface of the core layer to improve the electrolyte resistance of the polymer microsphere material; in further preferred embodiments, the front-end cross-linking monomer includes, but is not limited to, at least one of ethylene glycol dimethacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, 1,6-hexanediol diacrylate, or 1,4-butanediol diacrylate.

[0056] In some more preferred embodiments, the side groups of the strong polarity monomer include at least 1 strong polarity functional group, which includes, but is not limited to, a hydroxyl group, a carbonyl group, an acyloxy group, an ether bond, an epoxy group, an amine group, a sulfonic acid group, a substituted aromatic ring, etc., the side group refers to a group on the non-main chain structure, which functions to promote the interaction between the molecular chain and the positive and negative active materials, thereby improving the adhesion to the electrode; in further preferred embodiments, the strong polarity monomer includes, but is not limited to, at least one of tetrahydrofurfuryl acrylate, carboxyethyl acrylate, hydroxyethyl acrylate, dimethylaminoethyl acrylate, 2-phenoxyethyl acrylate, ethoxyethoxyethyl acrylate, diacetone acrylamide, or cyclotrimethylolpropane formal acrylate.

[0057] In some more preferred embodiments, the side groups of the long side chain monomer include at least 1 carbon chain or carbon-oxygen chain with a carbon number ≥ 4, which functions to improve the flexibility of the polymer microsphere material, change its mechanical properties after being pressed, and better conform to the electrode; in further preferred embodiments, the long side chain monomer includes, but is not limited to, at least one of hydroxybutyl methacrylate, lauryl acrylate, PEG350MA, or APEG2400.

[0058] In some more preferred embodiments, in addition to the functional monomers, the raw materials of the transition layer also include a transition layer initiator, which functions to promote the polymerization reaction of the functional monomers in the transition layer; the transition layer initiator is selected from a persulfate compound, which includes, but is not limited to, at least one of ammonium persulfate, potassium persulfate, or sodium persulfate; in further preferred embodiments, the amount of the transition layer initiator is 0.1% to 2% of the total amount of the functional monomers in terms of mass.

[0059] In some optional embodiments, in addition to the functional monomers, the raw materials of the transition layer also include a water-soluble surfactant, which includes a non-ionic surfactant and an anionic surfactant, and the specific component selection is the same as the component selection range of the corresponding surfactant in the core layer described above, but it is not necessary to select the same surfactant as the core layer; in further preferred embodiments, the amount of the water-soluble surfactant is 0.002% to 2% of the total amount of the functional monomers in terms of mass.

[0060] In some more preferred embodiments, in addition to the functional monomer, the raw materials of the transition layer also include solvent deionized water, and the amount of the deionized water is 1-5 times the mass of the total raw materials of the transition layer.

[0061] In the present disclosure, the shell layer mainly plays a supporting and shielding role, and softens or breaks when the shell layer is pressed, thereby releasing the adhesive components of the core layer (and the transition layer); as a preferred embodiment, the second modified acrylate copolymer is prepared by using the following components: non-water-soluble hard monomer, front crosslinking monomer, water-soluble initiator, and deionized water; in some more preferred embodiments, the second modified acrylate copolymer is prepared by using the following components in parts by weight: non-water-soluble hard monomer 50-95 parts, front crosslinking monomer 0.1-15 parts, water-soluble initiator 0.056-3.9 parts, and deionized water.

[0062] As a more preferred embodiment, the non-water-soluble hard monomer in the shell layer mainly functions to constitute the shell layer skeleton; the properties or components of the non-water-soluble hard monomer are consistent with those in the core layer, which are not repeated here; but it can be understood that the property parameters of the non-water-soluble hard monomers in the core layer and the shell layer are not necessarily the same, and the specific components selected are not necessarily the same, and those skilled in the art can make the same or different selection within the preferred range in the specification.

[0063] As a more preferred embodiment, the front crosslinking monomer in the shell layer mainly functions to crosslink and obtain a dense shell structure during the polymerization of the shell layer, improve the supporting role of the shell layer, and improve the electrolyte resistance of the polymer microsphere material; the properties or components of the front crosslinking monomer are consistent with those in the transition layer, which are not repeated here; but it can be understood that the property parameters of the front crosslinking monomers in the core layer and the transition layer are not necessarily the same, and the specific components selected are not necessarily the same, and those skilled in the art can make the same or different selection within the preferred range in the specification.

[0064] As a more preferred embodiment, the water-soluble initiator functions to promote the polymerization reaction of the shell layer raw materials; the water-soluble initiator is selected from a persulfate compound, including but not limited to at least one of ammonium persulfate, potassium persulfate, or sodium persulfate.

[0065] As an optional embodiment, the raw material components of the second modified acrylate copolymer further comprise 0.1-25 parts of a back-end crosslinking monomer; the back-end crosslinking monomer comprises 1 polymerizable alkenyl functional group and at least 1 back-end crosslinking group, wherein the back-end crosslinking group refers to a group that does not react during polymerization but reacts and forms crosslinking during storage or use of the polymer microsphere material; the back-end crosslinking monomer functions to, on the one hand, enable the shell to become more compact, improve the support of the shell, and at the same time improve the electrolyte resistance of the polymer microsphere, and on the other hand, through back-end crosslinking, promote the formation of chemical bonds between the polymer microsphere and the adherend, and improve the adhesion of the polymer microsphere; in a further preferred embodiment, the back-end crosslinking group comprises but is not limited to an epoxy group, a siloxane group, a methylol group, a hydroxyethyl group, or an activated hydrogen atom, etc. (wherein, for the case of an activated hydrogen atom, an example is given as follows: when a methylene group is connected to a carbon-carbon double bond or a carbon-oxygen double bond on both sides through a single bond, such as O=C-CH2-C=O, the hydrogen atom on the methylene group is activated under the conjugation of the two double bonds and is easy to form a free radical under oxidative delocalization; those skilled in the art can determine whether the hydrogen atom is activated according to the actual situation of the hydrogen atom); in a further optional embodiment, the back-end crosslinking monomer comprises but is not limited to at least one of N-methylol acrylamide, γ-methacryloyloxypropyltrimethoxysilane, carboxybutyl acrylate, acetoacetoxyethyl methacrylate, or glycidyl methacrylate.

[0066] As a further optional embodiment, when the raw material components of the second modified acrylate copolymer comprise the back-end crosslinking monomer, the second modified acrylate copolymer further comprises a water-soluble external crosslinking agent for promoting crosslinking during storage or use of the polymer microsphere, and the water-soluble external crosslinking agent needs to be added to the product after the end of the polymerization reaction and stirred uniformly; in some optional embodiments, the back-end crosslinking monomer comprises but is not limited to at least one of a polyamine, a polybasic anhydride, or a protic acid, and the molar ratio of the back-end crosslinking monomer to the back-end crosslinking monomer is 25%-100%.

[0067] As an optional embodiment, the raw material components of the second modified acrylate copolymer further include 1-15 parts of strong polar monomer, which functions to give the shell layer stronger polarity and promote the interaction between the molecular chains of the polymer microspheres and the positive and negative active materials, thereby improving the bonding capacity of the polymer microsphere material; the properties or components of the strong polar monomer are selected to be consistent with those of the strong polar monomer in the transition layer, which will not be repeated here; but it can be understood that the property parameters of the strong polar monomers in the shell layer and the transition layer are not necessarily the same, and the specific components selected are not necessarily the same, and those skilled in the art can make the same or different selection within the preferred range of the specification.

[0068] As an optional embodiment, the raw material components of the second modified acrylate copolymer further include 5-45 parts of non-water-soluble soft monomer, which mainly functions to reduce the rigidity of the shell layer, so that it is easier to soften or break under pressure; the solubility of the non-water-soluble soft monomer (25℃, water environment) is ≤30g / L, the solubility of the homopolymer of the non-water-soluble soft monomer (25℃, water environment) is ≤1g / L, and the glass transition temperature of the homopolymer of the non-water-soluble soft monomer is ≤35℃; the components of the non-water-soluble soft monomer are selected to be consistent with those of the non-water-soluble soft monomer in the core layer, which will not be repeated here; but it can be understood that the specific selected components of the non-water-soluble soft monomers in the shell layer and the core layer are not necessarily the same, and those skilled in the art can make the same or different selection within the preferred range of the specification.

[0069] As an optional embodiment, the raw material components of the second modified acrylate copolymer further include 0.001-3.9 parts of water-soluble surface active agent, which functions to improve the stability of the outer shell layer of the polymer microspheres; the properties or components of the water-soluble surface active agent are selected to be consistent with those of the water-soluble surface active agent in the transition layer, which will not be repeated here; but it can be understood that the property parameters of the water-soluble surface active agents in the shell layer and the transition layer are not necessarily the same, and the specific components selected are not necessarily the same, and those skilled in the art can make the same or different selection within the preferred range of the specification.

[0070] As a further preferred embodiment, the mass of the deionized water is 1-5 times the total mass of the raw material components (excluding the deionized water itself) of the second modified acrylate copolymer.

[0071] The second aspect of the present disclosure is to provide a preparation method of the polymer microsphere material according to the first aspect, comprising the following steps (1)-(3):

[0072] (1) Preparation of the core layer: fully mix the raw material components of the core layer, and perform a polymerization reaction to obtain a core layer emulsion.

[0073] As a preferred embodiment, the temperature of the polymerization reaction is 55-75°C, and the holding time of the polymerization reaction is 12-15h.

[0074] As a preferred embodiment, the polymerization reaction is carried out by a batch process. In particular, the batch process refers to the process of mixing the raw material components of the core layer except the initiator, heating to the temperature of the polymerization reaction, adding the initiator, and then initiating the monomer to carry out the polymerization reaction to obtain the core layer emulsion.

[0075] (2) Preparation of core layer-transition layer: adding the raw material components of the transition layer to the core layer emulsion, carrying out the second polymerization reaction, and obtaining the core emulsion coated with the transition layer.

[0076] As a preferred embodiment, the temperature of the second polymerization reaction is 70-90°C, and the holding time of the second polymerization reaction is 0.5-3h.

[0077] As a preferred embodiment, the second polymerization reaction is carried out by a batch process or a semi-continuous process. In particular, the semi-continuous process refers to the process of mixing the raw material components, gradually adding them to the core layer emulsion at a slow speed, continuously initiating and carrying out the second polymerization reaction, and obtaining the core emulsion coated with the transition layer.

[0078] (3) Preparation of core layer-transition layer-shell layer: adding the raw material components of the shell layer to the core emulsion coated with the transition layer, carrying out the third polymerization reaction, and obtaining the emulsion containing the polymer microsphere material.

[0079] As a preferred embodiment, the temperature of the third polymerization reaction is 70-90°C, and the holding time of the third polymerization reaction is 1-3h.

[0080] As a preferred embodiment, the entire preparation process is carried out in a protective gas atmosphere.

[0081] The third aspect of the present disclosure provides a separator for a secondary battery, comprising the polymer microsphere material according to the first aspect.

[0082] The fourth aspect of the present disclosure provides a secondary battery, comprising the separator for a secondary battery according to the third aspect.

[0083] As a preferred embodiment, the preparation method of the secondary battery comprises: coating the emulsion containing the polymer microsphere material to at least one side of the base film, then assembling it with the positive electrode and the negative electrode, carrying out pressure treatment, and obtaining the battery cell.

[0084] As a more preferred embodiment, the pressure of the pressurized treatment is 4±0.5 MPa, and the temperature of the pressurized treatment is 23±2℃.

[0085] Examples 1-6

[0086] S1: Preparation of the core layer: the raw material components of the core layer were thoroughly mixed and stirred, and after stirring for 30 min, a polymerization reaction was carried out at 60℃ for 14 h under a nitrogen atmosphere to obtain a core layer emulsion. The core layer raw materials of each example are provided in Tables 1 and 2 below, where the numbers after the components refer to the weight fraction of each raw material; the neutralization degree of 100% in Table 1 refers to the amount of M1-3-a being equivalent to the molar amount of hydrogen ions produced by ionization of M1-3. It is also worth noting that the materials used in Tables 1 and 2 are all conventional commercially available products.

[0087] S2: Preparation of the core layer-transition layer: 100 parts of the core layer emulsion of each example S1 (since the designed solid content is 21%±1%, the total non-volatile substance is calculated as 21 parts) were added to a reaction vessel under a nitrogen atmosphere, and then the raw material components of each transition layer were added to the reaction vessel, which was thoroughly stirred for 30 min, and then the temperature in the reaction vessel was raised to 80℃, and then the temperature was maintained for 2 h to obtain an intermediate emulsion (transition layer-core layer emulsion). The transition layer raw material components of each example are provided in Table 3 below, where the numbers after the components refer to the weight fraction of each raw material.

[0088] S3: Preparation of the core layer-transition layer-shell layer: 400 parts of the emulsion prepared in S2 (since the designed solid content is 21%±1%, the total non-volatile substance is calculated as 84 parts) were maintained at 80℃ and under stirring; the raw material components of the shell layer, excluding the external crosslinking agent (M3-3-a), were added to each example, and the addition was completed uniformly within 4 h; then the reaction was continued for 2 h, and after cooling to room temperature, the external crosslinking agent (M3-3-a) was added, and after uniform stirring, the material was collected to obtain the microsphere material of each example. The shell layer raw material components of each example are provided in Table 4 below, where the numbers after the components refer to the weight fraction of each raw material. In addition, the mass concentration of ammonia in Table 4 is 25%.

[0089] Table 1

[0090] Table 2

[0091] Table 3

[0092] Table 4

[0093] Comparative Example 1

[0094] A water-based suspension with solid content of 21%±1%, particle size (D50) of 3.1 μm and microsphere glass transition temperature of 40±2℃ was prepared by micro-suspension polymerization method using methyl methacrylate 10 parts, styrene 10 parts, butyl acrylate 8 parts and ethylene glycol dimethacrylate 0.14 parts as monomers, deionized water as dispersion system, azobisisobutyronitrile as initiator and sodium dodecyl sulfate and polyvinyl alcohol as surfactants.

[0095] The micro-suspension polymerization method in the present comparative example refers to dissolving the initiator in the non-water-soluble monomers, then adding the dispersion system and the surfactants successively, obtaining the micro-suspension of monomer droplets by high-speed shearing homogenization, and then initiating polymerization by heating to obtain the polymer microspheres of the present comparative example.

[0096] Comparative Example 2

[0097] A water-based suspension with solid content of 21%±1%, particle size (D50) of 5.5 μm and microsphere glass transition temperature of 75±2℃ was prepared by dispersion polymerization method using styrene 27 parts, butyl acrylate 3 parts and p-divinylbenzene 0.15 parts as monomers, deionized water-ethanol mixed solution as dispersion system, potassium persulfate as initiator and polyvinylpyrrolidone as surfactant.

[0098] The dispersion polymerization method in the present comparative example refers to dissolving the monomers, the initiator and the surfactants in the dispersion system, then initiating polymerization by heating, and continuously precipitating the generated polymers due to insolubility and uniformly dispersing into spherical shape under the action of the surfactants to obtain the polymer microspheres of the present comparative example.

[0099] Comparative Example 3

[0100] A water-based suspension with solid content of 21%±1%, particle size (D50) of 4.5 μm and microsphere glass transition temperature of ≥130℃ was prepared by micro-suspension polymerization method using methyl methacrylate 15 parts, isobornyl methacrylate 15 parts and ethylene glycol dimethacrylate 0.15 parts as monomers, azobisisobutyronitrile as initiator and sodium dodecyl sulfate and polyvinyl alcohol as surfactants. The implementation of the micro-suspension polymerization method is the same as that of Comparative Example 1.

[0101] Subsequently, a soft shell layer having a glass transition temperature of about -10°C was coated on the surface of the aforementioned microspheres by a semi-continuous method using sodium acrylate 10 parts, butyl acrylate 40 parts, methyl methacrylate 10 parts, and 1,6-hexanediol diacrylate 0.3 parts as monomers, sodium dodecyl sulfate as an emulsifier, and potassium persulfate as an initiator, thereby obtaining a core-shell structure microspheres aqueous suspension having a solid content of 21% ± 1% and a particle size (D50) of 4.8 μm. In the semi-continuous method of the present comparative example, all the raw material components were mixed thoroughly and then gradually added to the aforementioned aqueous suspension at a slow speed to continuously initiate and perform a polymerization reaction, thereby obtaining the core-shell structure microspheres material of the present comparative example.

[0102] Comparative Example 4

[0103] A commercially available aqueous PVDF microspheres of a certain brand had a nominal particle size (D50) of 7 ± 1 μm and an actual measured particle size of 7.2 μm.

[0104] Comparative Example 5

[0105] The same as Example 1 except that Step S2 was omitted.

[0106] Comparative Example 6

[0107] The same as Example 1 except that Step S3 was omitted.

[0108] Comparative Example 7

[0109] The same as Example 1 except that Steps S2 and S3 were omitted.

[0110] Test Example 1

[0111] The materials of Examples 1 to 6 and Comparative Examples were subjected to the following tests of key properties.

[0112] (1) Particle size: D50 was measured by a laser particle size analyzer.

[0113] (2) Adhesion I: Each microspheres material was uniformly coated onto the surface of a polyethylene-polypropylene three-layer composite wet porous separator having a thickness of 9 μm and dried, and the coating amount was 0.3 g / m 2 . Subsequently, the coated surface of the separator was attached to a graphite negative electrode sheet, and pressure was applied at 25°C and 1 MPa for 10 s to form an adhesion between the separator and the negative electrode sheet. The 180° peeling strength (counted as peeling strength I in Table 5) was measured by an electronic tensile testing machine.

[0114] (3) Adhesion II: Each microspherical material, ceramic powder, and other additives were mixed in a dry weight ratio of 10 wt. %: 85 wt. %: 5 wt. %, to form an aqueous slurry, which was coated onto the surface of the composite wet-process porous separator of step (2) to obtain a separator with a ceramic-polymer microsphere composite coating on the surface; wherein the other additives include a binder (aqueous polyacrylate, commercially available product, 3.75 wt. %), a dispersant (polyacrylate, commercially available product, 0.75 wt. %), and a wetting agent (lauryl polyoxyethylene ether, commercially available product, 0.5 wt. %). The dry weight ratio of the microspherical material in the coating was 10 wt. %, and the areal density of the coating was 3 g / m2. 2 The composite-coated separator was attached to a graphite negative electrode sheet, and pressure was applied at 25 °C and 7 MPa for 120 s to form an adhesion between the separator and the negative electrode sheet; and the 180° peeling strength was tested by an electronic tensile testing machine (counted as peeling strength II in Table 5).

[0115] (4) Anti-winding adhesion: used to test the degree of adhesion of the microspherical material of the present disclosure to the separator after coating, caused by winding tension, storage temperature, and the like. Each microspherical material was uniformly coated onto the surface of a polyethylene-polypropylene three-layer composite wet-process porous separator with a thickness of 9 μm and dried, and the coating amount was 0.3 g / m2. 2 The coated separator was attached to another uncoated separator, pressure was applied at 40 °C and 1 MPa for 120 s, and the 180° peeling strength was then tested by an electronic tensile testing machine (counted as peeling strength III in Table 5).

[0116] According to the test results, the microspherical material prepared in the present disclosure did not have the negative defect of separator winding adhesion when it was used for single coating; wherein single coating refers to directly coating the microspherical material prepared in the present disclosure onto the separator; and mixed coating refers to coating the microspherical material mixed with ceramic powder (such as alumina, boehmite, etc.).

[0117] (5) Air permeability: the single-coated and mixed-coated separators prepared in steps (2) and (3) were respectively tested for air permeability by a Gurley air permeability tester, and the air permeability value of the uncoated base film was subtracted to obtain air permeability increase value I and air permeability increase value II, respectively.

[0118] (6) Resistance to electrolyte swelling: the microspherical material prepared in each example and comparative example was baked to obtain a film; the film was immersed in an electrolyte at 70 °C for 7 days, and the weight change difference (equivalent to the swelling rate) of the film before and after immersion was tested. The electrolyte composition was: EC: DEC: DMC = 3: 5: 2 by mass.

[0119] The test results of Test Example 1 are provided in Table 5. In addition, FIG. 1 provides the particle size distribution test information and particle size diagram of Example 5, and FIG. 2 provides the SEM diagram of Example 5.

[0120] Table 5

[0121] Examples 7-19: To investigate the influence of the proportion of the core layer, the transition layer and the shell layer on the performance of the polymer microsphere material. In Example 1, it is calculated that the proportion of the weight fraction of the solid content in the three-layer structure is 21:17.1:59.26; that is, the amount of the transition layer in Example 1 is about equal to 81wt.% of the core layer, and the amount of the shell layer is about equal to 155wt.% of the sum of the core layer and the transition layer. Thus, in this part of the examples, it is basically consistent with Example 1, and the only difference is that the total solid content of the transition layer or the shell layer is changed separately.

[0122] In Examples 7-11: the amount of the transition layer is equal to 72wt%, 54wt%, 36wt%, 18wt%, 5wt% of the core layer, respectively, in terms of solid content. In addition, in Comparative Example 8: the amount of the transition layer is equal to 100wt% of the core layer, respectively, in terms of solid content.

[0123] In Examples 12-19: the amount of the shell layer is about equal to 200wt.%, 175wt%, 135wt%, 100wt%, 75wt%, 55wt%, 25wt%, 5wt% of the sum of the core layer and the transition layer, respectively, in terms of solid content. In addition, in Comparative Example 9: the amount of the shell layer is equal to 220wt% of the sum of the core layer and the transition layer, respectively, in terms of solid content.

[0124] Test Example 2: The same test items as Test Example 1 are used, and only the test object is changed; the test results of Test Example 2 are provided by Tables 6 and 7.

[0125] Table 6

[0126] As can be seen from the above Table 6, the amount of the transition layer has little effect on the particle size, and has little effect on the air permeability and the swelling rate. The transition layer mainly affects the adhesion, and has a greater effect on the electrode adhesion (mixed coating) and the mutual adhesion of the separator. When the amount of the transition layer is too high, the electrode adhesion (mixed coating) of the product is better; when the amount of the transition layer is too low, the product has a better electrode adhesion (single coating) while also having a lower mutual adhesion of the separator, that is, the product has a better effect of preventing the adhesion of the separator. However, when the amount of the transition layer is too much (as shown in Comparative Example 8), although it is beneficial to improve the electrode adhesion, it also leads to a significant increase in the mutual adhesion of the separator, which means that the effect of preventing the adhesion of the separator is significantly worse.

[0127] Table 7

[0128] As can be seen from Table 7, in general, the thinner the shell layer, the stronger the adhesion, but the indicators such as air permeability and swelling rate are deteriorated to varying degrees. Among them, when the shell layer is in a relatively high amount, especially in Examples 12-15 (the amount of the shell layer is more than 100 wt.%), the pole piece adhesion (single coating) has a large increase, and at the same time, the indicators such as the mutual adhesion of the separator, the air permeability, and the swelling rate are not significantly deteriorated, but when the amount of the shell layer is too high (such as Comparative Example 9), the pole piece adhesion is obviously deteriorated; and when the amount of the shell layer is relatively low, especially in Examples 18-19 (the amount of the shell layer is not more than 25 wt.%), the pole piece adhesion (mixed coating) has a large increase, and at the same time, the indicators such as the air permeability (mixed coating) and the swelling rate are not significantly deteriorated.

[0129] In summary, from Tables 6 and 7, it can be seen that under the premise of ensuring that the performance indicators are in good condition, the present disclosure can strengthen a certain performance indicator by adjusting the amount of each level; and a person skilled in the art can adjust the amount and thickness of the level according to the actual performance requirements.

[0130] Examples 20-48: To investigate the influence of the proportion of each raw material component in the core layer on the performance of the polymer microsphere material. In Example 2, it is calculated that: the mass proportion of M1-1 is 56 wt.% in terms of solid content, the mass proportion of M1-2 (including M1-2-1 and M1-2-2) is 28 wt.%, the mass proportion of M1-3 (including M1-3-1 and M1-3-2) is 9.5 wt.%, the mass proportion of M1-4 is 2.8 wt.%, the mass proportion of M1-5 is 1.9 wt.%, and the mass proportion of M1-6 is 0.05 wt.%.

[0131] Therefore, in this part of the examples, it is basically consistent with Example 2, and the only difference is that the solid content of a certain raw material component or a certain type of raw material component is changed alone. It should be noted that after changing the solid content of a certain raw material component, other raw material components are increased or decreased according to the proportion of Example 2; when the solid content of a certain type of raw material component is changed, for example, M1-2, M1-2-1 and M1-2-2 are also increased or decreased simultaneously according to the proportion of Example 2.

[0132] Examples 20-23: The amount of M1-1 is 45 wt.%, 67 wt.%, 78 wt.%, and 85 wt.% in terms of solid content, respectively.

[0133] Examples 24-26: The amount of M1-2 is 34 wt.%, 22 wt.%, and 16 wt.% in terms of solid content, respectively.

[0134] Examples 27-31: The amount of M1-3 is 7.5 wt.%, 5.5 wt.%, 11.5 wt.%, 15.5 wt.%, and 19.5 wt.% in terms of solid content, respectively.

[0135] Examples 32-36: The amount of M1-4 is 1.4 wt.%, 4.2 wt.%, 5.6 wt.%, 7.7 wt.%, 9.6 wt.% by solid content, respectively.

[0136] Examples 37-43: The amount of M1-5 is 0.9 wt.%, 0.09 wt.%, 0.01 wt.%, 3.8 wt.%, 5.7 wt.%, 7.6 wt.%, 9.5 wt.% by solid content, respectively.

[0137] Examples 44-48: The amount of M1-6 is 0.01 wt.%, 0.001 wt.%, 0.1 wt.%, 1 wt.%, 2 wt.% by solid content, respectively.

[0138] Test Example 3: The same test items as Test Example 1 are adopted, and only the change of the test object exists; the test results of Test Example 3 are provided by Table 8.

[0139] Table 8

[0140] Examples 49-60: For investigating the influence of the proportion of each raw material component in the transition layer on the performance of the polymer microsphere material. In Example 3, it is calculated that: the mass proportion of M2-1 is 24.83 wt.% by solid content, the mass proportion of M2-2 is 55.86 wt.%, and the mass proportion of M2-3 is 18.62 wt.%.

[0141] Thus in this part of the examples, it is basically consistent with Example 3, and the only difference is that the solid content of a certain raw material component or a certain type of raw material component is changed alone. It should be noted that after changing a certain solid content, other raw material components are increased or decreased according to the proportion of Example 3.

[0142] Examples 49-53: The amount of M2-1 is 15 wt.%, 5 wt.%, 35 wt.%, 45 wt.%, 55 wt.% by solid content, respectively.

[0143] Examples 54-57: The amount of M2-2 is 28 wt.%, 14 wt.%, 7 wt.%, 70 wt.% by solid content, respectively.

[0144] Examples 58-60: The amount of M2-3 is 9 wt.%, 3 wt.%, 27 wt.% by solid content, respectively.

[0145] Test Example 4: The same test items as Test Example 1 are adopted, and only the change of the test object exists; the test results of Test Example 4 are provided by Table 9.

[0146] Table 9

[0147] Examples 61-79: To investigate the influence of the proportion of each raw material component in the shell layer on the performance of the polymer microsphere material. In Example 5, it is calculated that the mass proportion of M3-1 is 67.83wt.%, the mass proportion of M3-2 is 9.69wt.%, the mass proportion of M3-3 (including M3-3 and M3-3-a) is 4.8wt.%, the mass proportion of M3-4 is 7.75wt.%, and the mass proportion of M3-5 is 6.78wt.%.

[0148] Thus in this part of the examples, it is basically consistent with Example 5, and the only difference is that the solid content of a certain raw material component or a certain type of raw material component is changed alone. It should be noted that after changing a certain solid content, other raw material components are increased or decreased according to the proportions of Example 5.

[0149] Examples 61-64: The amount of M3-1 is 60wt.%, 50wt.%, 85wt.%, and 95wt.% respectively based on the solid content.

[0150] Examples 65-68: The amount of M3-2 is 15wt.%, 5wt.%, 1wt.%, and 0.1wt.% respectively based on the solid content.

[0151] Examples 69-72: The amount of M3-3 is 1wt.%, 0.1wt.%, 15wt.%, and 25wt.% respectively based on the solid content.

[0152] Examples 73-76: The amount of M3-4 is 4wt.%, 1wt.%, 12wt.%, and 15wt.% respectively based on the solid content.

[0153] Examples 77-79: The amount of M3-5 is 14wt.%, 28wt.%, and 42wt.% respectively based on the solid content.

[0154] Test Example 5: The same test items as Test Example 1 are used, and only the test object is changed; the test results of Test Example 5 are provided in Table 10.

[0155] Table 10

[0156] Examples 80-83: To investigate the influence of the polymerization temperature of the core layer on the performance of the polymer microsphere material. Examples 80-83 are basically the same as Example 4, and the only difference is that the temperature of the polymerization reaction in step S1 is 55°C, 65°C, 70°C, and 75°C respectively. In addition, Comparative Examples 10-11 are basically the same as Example 4, and the only difference is that the temperature of the polymerization reaction in step S1 is 45°C and 85°C respectively.

[0157] The results show that:

[0158] (1) The expected products were obtained in Example 4 and Examples 80-83, and the relevant test results are shown in Table 11.

[0159] (2) The expected product was not obtained in Comparative Example 10, and the reaction was not effectively initiated due to the excessively low polymerization reaction temperature in Step S1, and a large amount of lumps and unreacted residual monomers were observed in the reaction system.

[0160] (3) The expected product was not obtained in Comparative Example 11, and the initiator was consumed too quickly due to the excessively high polymerization reaction temperature in Step S1, resulting in a large amount of monomers remaining in the reaction system without being initiated.

[0161] Test Example 6: The same test items as in Test Example 1 were used, except for the change in the test object; the test results of Test Example 6 are provided in Table 11. It can be understood that since Comparative Examples 10 and 11 cannot provide the expected microsphere material product, no relevant data of Comparative Examples 10 and 11 are provided in Table 11.

[0162] Table 11

[0163] As can be seen from Table 11, when in the appropriate polymerization temperature range, the temperature has a relatively significant effect on the particle size of the core layer product, and has almost no effect on other properties. When the core layer polymerization reaction temperature is too low (such as Comparative Example 10), the monomers are difficult to initiate and the reaction is difficult to proceed; when the core layer polymerization reaction temperature is too high (such as Comparative Example 11), the initiator is consumed too quickly, and the product has too much residual monomer. Both too low and too high core layer polymerization reaction temperatures will adversely affect the performance of the microsphere material.

[0164] Although the present disclosure has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present disclosure, and not to limit them; those skilled in the art should understand that the technical solutions described in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents, without departing from the spirit and scope of the present disclosure; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure; therefore, this means that all these replacements and modifications within the scope of the present disclosure are included in the appended claims. Industrial applicability

[0165] The polymeric microsphere material provided by the present disclosure has good particle size uniformity, good adhesion with the separator, and good anti-sticking during winding. By introducing a functional transition layer, the connectivity of the soft core layer and the hard shell layer can be effectively enhanced, making the overall core-shell structure more compact and firm. Meanwhile, the structural defects of the polymeric microsphere, such as swelling too large and easy to break under long-term pressure, can be effectively solved. The separator and secondary battery containing the polymeric microsphere material of the present disclosure, the separator coated with the polymeric microsphere material is assembled with the positive and negative electrode sheets to obtain a battery cell. After the battery cell is treated under a certain temperature and pressure, the separator and the electrode sheet are fixedly connected through the adhesion of the polymeric microsphere material, and the rigidity of the battery cell is improved, and the swelling rate is low in a long-term electrolyte immersion environment. Thus, a secondary battery with good mechanical properties and safety performance is obtained, which has very good industrial applicability.

Claims

1. A polymeric microsphere material, characterized in that, The polymer microsphere material comprises a core layer, a transition layer and a shell layer from inside to outside; The core layer comprises a first modified acrylate copolymer, and the glass transition temperature of the first modified acrylate copolymer is ≤35℃; the transition layer is polymerized from at least one functional monomer; and the shell layer comprises a second modified acrylate copolymer, and the glass transition temperature of the second modified acrylate copolymer is 60℃-250℃; The raw material of the transition layer comprises a functional monomer, and the functional monomer comprises at least one of a front-end crosslinking monomer, a strong polar monomer or a long side chain monomer; the front-end crosslinking monomer contains at least 2 polymerizable alkenyl functional groups; the functional groups of the strong polar monomer comprise at least one of a hydroxyl group, a carbonyl group, an acyloxy group, an ether bond, an epoxy group, an amine group, a sulfonic acid group and a substituted aromatic ring; and the side groups of the long side chain monomer comprise at least one carbon chain or carbon-oxygen chain with a carbon number ≥4; The first modified acrylate copolymer is prepared from the following components by weight fraction: non-water-soluble soft monomer 45-85 parts, non-water-soluble hard monomer 15-35 parts, water-soluble organic acid monomer 5-20 parts, non-ionic surfactant 0.001-5 parts, water-soluble initiator 0.065-5 parts and deionized water. The second modified acrylate copolymer is prepared from the following components by weight fraction: non-water-soluble hard monomer 50-95 parts, front-end crosslinking monomer 0.1-15 parts, water-soluble initiator 0.056-3.9 parts and deionized water.

2. The polymeric microsphere material of claim 1, wherein, The mass of the transition layer is 5wt.%-85wt.% of the core layer, and the mass of the shell layer is 5wt.%-200wt.% of the sum of the core layer and the transition layer.

3. The polymeric microsphere material of claim 1 or 2, wherein, The diameter of the polymer microsphere material is 1μm-50μm.

4. The method of claim 1 to 3, wherein The preparation method of the polymer microsphere material comprises the following steps: (1) fully mixing the raw material components of the core layer, and performing a polymerization reaction to obtain a core layer emulsion; (2) adding the raw material components of the transition layer to the core layer emulsion, and performing a second polymerization reaction to obtain a core emulsion coated with a transition layer; (3) adding the raw material components of the shell layer to the core emulsion coated with a transition layer, and performing a third polymerization reaction to obtain an emulsion containing a polymer microsphere material.

5. The method of claim 4, wherein the polymer microsphere material is prepared by a process comprising: At least one of the following features (a)-(c) is included: (a) the temperature of the polymerization reaction is 55℃-75℃, and the holding time of the polymerization reaction is 12h-15h; (b) the temperature of the second polymerization reaction is 70℃-90℃, and the holding time of the second polymerization reaction is 0.5h-3h; (c) the temperature of the third polymerization reaction is 70℃-90℃, and the holding time of the third polymerization reaction is 1h-3h.

6. A separator for a secondary battery, characterized by, The diaphragm comprises the polymer microsphere material according to any one of claims 1-3 or prepared by the preparation method of any one of claims 4-5.

7. A secondary battery characterized by comprising: The secondary battery comprises the diaphragm according to claim 6.

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