Polymer particles, preparation method therefor, polymer particles emulsion, separator membrane, secondary

Abstract

The invention provides a polymer particle and a preparation method thereof, a polymer particle emulsion, an isolating membrane, a secondary battery monomer, a battery device and a power utilization device, the polymer particle comprises a first structure unit and a second structure unit, the first structure unit comprises a vinyl structure unit, and the second structure unit comprises a vinyl structure unit. The second structural unit comprises maleimide or a maleimide derivative structural unit. The polymer particles are used in the isolating membrane, so that the secondary battery monomer has high mass energy density and high reliability.

Description

Technical Field

[0001] This disclosure relates to a polymer particle and its preparation method, a polymer particle emulsion, a separator, a secondary battery cell, a battery device, and an electrical device. Background Technology

[0002] As the application range of rechargeable battery cells becomes increasingly widespread, the demands on them are also growing, with higher requirements for energy density and reliability. Therefore, how to achieve higher energy density in rechargeable battery cells while maintaining high reliability is a pressing technical problem that needs to be solved. Summary of the Invention

[0003] This disclosure provides a polymer particle and its preparation method, a polymer particle emulsion, a separator, a secondary battery cell, a battery device, and an electrical device. The polymer particles are used in the separator, which enables the secondary battery cell to have both high energy density and high reliability.

[0004] In a first aspect, this disclosure provides a polymer particle comprising a first structural unit and a second structural unit, wherein the first structural unit comprises a vinyl structural unit and the second structural unit comprises a maleimide or a derivative structural unit of maleimide.

[0005] The polymer particles have a low density, allowing secondary battery cells to achieve higher gravimetric energy density. The polymer particles disclosed herein possess both vinyl structural units and maleimide or maleimide derivative structural units. The high rigidity of the maleimide or maleimide derivative structural units enhances the heat resistance of the polymer particles. Using these polymer particles in a separator improves the overall thermal shrinkage of the separator, enhances its heat resistance, and improves the reliability of the secondary battery cell. Furthermore, the strong polarity of the maleimide or maleimide derivative structural units allows for stronger interactions between the polymer particles and the binder in the porous coating of the separator. This results in stronger adhesion between the porous coating and the porous base film, while also improving the overall structural integrity of the separator. Therefore, using the polymer particles disclosed herein in a separator enables secondary battery cells to achieve both high gravimetric energy density and high reliability.

[0006] In some embodiments, the first structural unit includes one or more of styrene or styrene derivative structural units, acrylate structural units, acrylonitrile structural units, vinyl ether structural units, alkyl vinyl ester structural units, N-vinylpyrrolidone or N-vinylpyrrolidone derivative structural units.

[0007] In some embodiments, the styrene or styrene derivative structural unit includes one or more of the following: styrene structural unit, 1-methyl-1-styrene structural unit, 4-methylstyrene structural unit, 2-methylstyrene structural unit, 2,4-dimethylstyrene structural unit, and 2,5-dimethylstyrene structural unit.

[0008] In some embodiments, the acrylate structural units include one or more of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0009] In some embodiments, the acrylonitrile structural unit includes one or both of acrylonitrile structural units and methacrylonitrile structural units.

[0010] In some embodiments, the vinyl ether structural unit includes one or more of the following: methyl vinyl ether structural unit, ethyl vinyl ether structural unit, propyl vinyl ether structural unit, butyl vinyl ether structural unit, cyclopropyl vinyl ether structural unit, cyclobutyl vinyl ether structural unit, cyclopentyl vinyl ether structural unit, and cyclohexyl vinyl ether structural unit.

[0011] In some embodiments, the alkyl vinyl ester structural unit includes one or more of vinyl acetate structural units, vinyl propionate structural units, vinyl butyrate structural units, and vinyl valerate structural units.

[0012] In some embodiments, the N-vinylpyrrolidone or N-vinylpyrrolidone derivative structural unit includes one or more of the following: N-vinylpyrrolidone structural unit, 4-methyl-1-vinyl-2-pyrrolidone structural unit, and 1-vinyl-3-methyl-2-pyrrolidone structural unit.

[0013] In some embodiments, the second structural unit includes one or more of maleimide structural units, N-substituted maleimide structural units, and bismaleimide structural units.

[0014] In some embodiments, the N-substituted maleimide structural unit includes one or more of N-alkyl maleimide structural units, N-cycloalkyl maleimide structural units, and N-aromatic maleimide structural units.

[0015] In some embodiments, the bismaleimide structural unit is formed by bonding the nitrogen atoms of two maleimide structural units together via organic groups.

[0016] In some embodiments, the organic groups connecting the nitrogen atoms of the two maleimide structural units in the bismaleimide structural unit include substituted or unsubstituted C1-C12 alkylene groups, substituted or unsubstituted bicyclohexyl groups, substituted or unsubstituted alkylene dicyclohexyl groups, substituted or unsubstituted phenyl groups, substituted or unsubstituted biphenyl groups, substituted or unsubstituted alkylene diphenyl groups, substituted or unsubstituted diphenyl ether groups, substituted or unsubstituted diphenyl sulfide groups, and substituted or unsubstituted diphenyl sulfone groups. The substituted substituents include one or more combinations of C1-C3 alkyl groups, -O-, -S-, -OO-, and -SS-.

[0017] In some embodiments, the polymer particles further include crosslinking structural units, which include one or more of the following: divinylbenzene structural units, ethylene glycol dimethacrylate structural units, pentaerythritol tetraacrylate structural units, 1,4-butanediol diacrylate structural units, 1,6-hexanediol diacrylate structural units, 1,8-octanediol diacrylate structural units, trimethylolpropane triacrylate structural units, pentaerythritol trimethacrylate structural units, tetraethylene glycol dimethacrylate structural units, tripropylene glycol diacrylate structural units, N,N-methylenebisacrylamide structural units, N,N'-vinylbisacrylamide structural units, 1,3,5-triacryloylhexahydro-1,3,5-triazine structural units, and triallyl isocyanurate structural units.

[0018] In some embodiments, the glass transition temperature T of the polymer particles g The glass transition temperature (T) of the polymer particles ranges from 150℃ to 275℃. g With a temperature range of 150℃-275℃, it has high thermal stability, which can better resist the thermal shrinkage of the separator, improve the heat resistance of the separator, and improve the reliability of the secondary battery cells.

[0019] In some embodiments, the polymer particles have no melting point. The absence of a melting point indicates good heat resistance and thermal stability, which better resists thermal shrinkage of the separator, improves the heat resistance of the separator, and enhances the reliability of the secondary battery cells.

[0020] In some embodiments, the initial thermogravimetric temperature T of the polymer particles3d The initial thermogravimetric temperature (T) of the polymer particles is 350℃-430℃. 3d The high value indicates good thermal stability, which can better resist the thermal shrinkage of the separator, improve the heat resistance of the separator, and enhance the reliability of the secondary battery cells.

[0021] In some embodiments, the cyclic voltammetry curve of the polymer particles in the first cycle does not exhibit an oxidation peak within a voltage range of 2.5V to 4.45V. The absence of an oxidation peak in the cyclic voltammetry curve of the polymer particles in the first cycle within this voltage range indicates that the polymer particles are stable within this range, exhibiting good electrochemical stability. This allows them to be applied in high-voltage secondary battery cells, improving the operating voltage and energy density of the secondary battery cells.

[0022] In some embodiments, the swelling degree of the polymer particles after being immersed in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 at 60°C for 7 days is less than or equal to 2.5%. The low swelling degree of the polymer particles in organic solvents results in high structural stability of the secondary battery cell during long-term use, thereby improving the problem of decreased air permeability of the separator during use.

[0023] In some embodiments, the dissolution rate of the polymer particles after being immersed in a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7 at 60°C for 7 days is less than or equal to 2%. The low dissolution rate of the polymer particles in organic solvents indicates high structural stability during long-term use of the secondary battery cell and high chemical stability in the electrolyte, thereby enabling the secondary battery cell to exhibit long-cycle stability.

[0024] In some embodiments, the volume distribution particle size Dv50 of the polymer particles is 110 nm-700 nm. A volume distribution particle size Dv50 within this range is beneficial for the separator to have good heat resistance and air permeability.

[0025] In a second aspect, this disclosure provides a method for preparing polymer particles, comprising the following steps: providing a pre-emulsion, the pre-emulsion comprising a monomer, an emulsifier, an initiator, and water, the monomer comprising a first monomer and a second monomer, the first monomer comprising a vinyl monomer, and the second monomer comprising maleimide and its derivative monomers; subjecting the pre-emulsion to an emulsion polymerization reaction under heating, inert gas protection, and stirring conditions to obtain polymer particles.

[0026] In some embodiments, the second monomer includes one or more of monomaleimide monomers and bismaleimide monomers.

[0027] In some embodiments, the second monomer comprises a bismaleimide monomer.

[0028] Optionally, the mass fraction of the second monomer is 5%-35% based on the total mass of the monomers being 100%.

[0029] Optionally, the monomer further includes a crosslinking agent monomer, wherein the mass fraction of the crosslinking agent monomer is 1%-20% based on the total mass of the monomer (100%).

[0030] In some embodiments, the second monomer includes a monomaleimide monomer and a bismaleimide monomer.

[0031] Optionally, based on the total mass of the monomers, the mass fraction of the monomaleimide monomer is 1%-50%, and the mass fraction of the bismaleimide monomer is 5%-30%.

[0032] Optionally, the monomer further includes a crosslinking agent monomer, wherein the mass fraction of the crosslinking agent monomer is 1%-10% based on the total mass of the monomers (100%).

[0033] In some embodiments, the second monomer comprises a monomaleimide monomer, and the monomer further comprises a crosslinking agent monomer.

[0034] Optionally, based on the total mass of the monomers as 100%, the mass fraction of the crosslinking agent monomer is 5%-40%, and the mass fraction of the second monomer is 5%-55%.

[0035] In some embodiments, the crosslinking agent monomer includes one or more of the following: divinylbenzene, ethylene glycol dimethacrylate, pentaerythritol tetraacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,8-octanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol trimethacrylate, tetraethylene glycol dimethacrylate, tripropylene glycol diacrylate, N,N-methylenebisacrylamide, N,N'-vinylbisacrylamide, 1,3,5-triacryloylhexahydro-1,3,5-triazine, and triallyl isocyanurate.

[0036] In some embodiments, the monomaleimide monomer includes one or more of maleimide, N-alkylmaleimide, N-cycloalkylmaleimide, N-aromatic maleimide, and their respective derivatives.

[0037] Optionally, the monomaleimide monomer includes one or more of the following: maleimide, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, N-n-butylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide, N-n-pentylmaleimide, N-n-octylmaleimide, N-cyclobutylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, N-cycloheptylmaleimide, N-phenylmaleimide, N-benzylmaleimide, N-(p-methylphenyl)maleimide, N-(o-methylphenyl)maleimide, N-(m-methylphenyl)maleimide, N-(2,4-dimethylphenyl)maleimide, and N-(2,3-dimethylphenyl)maleimide.

[0038] In some embodiments, the bismaleimide monomer comprises one or more compounds of Formula 1, wherein R1 is selected from substituted or unsubstituted C1-C12 alkylene, substituted or unsubstituted bicyclohexyl, substituted or unsubstituted alkylene dicyclohexyl, substituted or unsubstituted phenyl, substituted or unsubstituted biphenyl, substituted or unsubstituted alkylene diphenyl, substituted or unsubstituted diphenyl ether, substituted or unsubstituted diphenyl sulfide, substituted or unsubstituted diphenyl sulfone, wherein the substituted substituents include one or more combinations of C1-C3 alkyl, -O-, -S-, -OO-, -SS-.

[0039]

[0040] Optionally, R1 is selected from any of the following, where # indicates the connection position.

[0041]

[0042]

[0043] In some embodiments, the mass fraction of the first monomer is greater than or equal to 40% when the total mass of the monomer is 100%.

[0044] In some embodiments, the first monomer includes one or more of styrene and its derivative monomers, acrylate monomers, acrylonitrile monomers, vinyl ether monomers, alkyl vinyl ester monomers, N-vinylpyrrolidone or N-vinylpyrrolidone derivative monomers.

[0045] In some embodiments, the styrene and its derivative monomers include one or more of styrene, 1-methyl-1-styrene, 4-methylstyrene, 2-methylstyrene, 2,4-dimethylstyrene, and 2,5-dimethylstyrene.

[0046] In some embodiments, the acrylate monomers include one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0047] In some embodiments, the acrylonitrile monomer includes one or both of acrylonitrile and methacrylonitrile.

[0048] In some embodiments, the vinyl ether monomers include one or more of methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, cyclopropyl vinyl ether, cyclobutyl vinyl ether, cyclopentyl vinyl ether, and cyclohexyl vinyl ether.

[0049] In some embodiments, the alkyl vinyl ester monomer includes one or more of vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl valerate.

[0050] In some embodiments, the N-vinylpyrrolidone or N-vinylpyrrolidone derivative monomer includes one or more of N-vinylpyrrolidone, 4-methyl-1-vinyl-2-pyrrolidone, and 1-vinyl-3-methyl-2-pyrrolidone.

[0051] In some embodiments, the emulsion polymerization reaction includes the following steps: under a first temperature, inert gas protection and stirring conditions, the pre-emulsion is dropwise added to a reactor containing water; after the dropwise addition is completed, the reaction continues at the first temperature for a first time; then the temperature is raised to a second temperature to mature the reaction for a second time to obtain polymer particles.

[0052] In some embodiments, the first temperature is 55°C-80°C.

[0053] In some embodiments, the first time is 2h-8h.

[0054] In some embodiments, the second temperature is 70°C-92°C.

[0055] In some embodiments, the second time is 1 hour to 6 hours.

[0056] Thirdly, this disclosure provides a polymer particle emulsion comprising the polymer particles of the first aspect, or obtained by the method of the second aspect.

[0057] Fourthly, this disclosure provides an isolation membrane comprising a porous base membrane and a porous coating located on at least one side of the porous base membrane, the porous coating comprising polymer particles of the first aspect, or polymer particles prepared by the method of the second aspect.

[0058] In some embodiments, the polymer particle content in the porous coating is 50%-99% based on the total mass of the porous coating.

[0059] In some embodiments, the thickness of the porous coating is 0.5 μm-5 μm.

[0060] In some embodiments, the separation film is heated at a constant temperature of 140°C for 1 hour, and the longitudinal thermal shrinkage rate is less than or equal to 30%.

[0061] In some embodiments, the separator is heated at a constant temperature of 140°C for 1 hour, and the transverse thermal shrinkage rate is less than or equal to 30%.

[0062] Fifthly, this disclosure provides a secondary battery cell that includes the separator membrane of the fourth aspect of this disclosure.

[0063] In a sixth aspect, this disclosure provides a battery device comprising a plurality of secondary battery cells according to the fifth aspect of this disclosure.

[0064] In a seventh aspect, this disclosure provides an electrical device that includes a secondary battery cell according to the fifth aspect of this disclosure or a battery device according to the sixth aspect. Attached Figure Description

[0065] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments of this disclosure will be briefly described below. Obviously, the drawings described below are merely some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0066] Figure 1 A schematic diagram of a secondary battery cell provided in some embodiments of this disclosure is shown.

[0067] Figure 2 A schematic diagram of an electrical device provided in some embodiments of this disclosure is shown. Detailed Implementation

[0068] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the polymer particles, their preparation methods, polymer particle emulsions, separators, secondary battery cells, battery devices, and electrical devices of this disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter of the claims.

[0069] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] Unless otherwise specified, all embodiments and optional embodiments of this disclosure may be combined with each other to form new technical solutions, and such technical solutions should be considered as included in the disclosure of this disclosure.

[0071] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions, and such technical solutions should be considered as included in the disclosure of this disclosure.

[0072] Unless otherwise specified, all steps in this disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0073] Unless otherwise specified, in this disclosure, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0074] In this disclosure, the terms "multiple" or "a variety" refer to two or more kinds.

[0075] In the description of the embodiments of this disclosure, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0076] Unless otherwise stated, the test temperature for all parameters mentioned in this disclosure is 25°C.

[0077] The secondary battery cell mentioned in the embodiments of this disclosure can independently perform charge and discharge functions. After discharge, it can be reactivated by charging to allow for continued use. The secondary battery cell can be cylindrical, cuboid, or other shapes, and the embodiments of this disclosure are not limited in this regard. Figure 1 The example is a cuboid-structured secondary battery cell 5.

[0078] The secondary battery cells provided in the embodiments of this disclosure may include, but are not limited to, lithium battery cells and sodium battery cells, such as lithium-ion battery cells, sodium-ion battery cells, lithium metal battery cells, sodium metal battery cells, etc.

[0079] The secondary battery cell provided in the embodiments of this disclosure includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this disclosure are not limited in this regard. The secondary battery cell also includes an outer packaging, which can be used to encapsulate the electrode assembly. The outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, such as one or more of aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0080] The battery apparatus mentioned in the embodiments of this disclosure may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple secondary battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0081] In some embodiments, a battery cell assembly is typically formed by arranging multiple secondary battery cells.

[0082] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple secondary battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple secondary battery cells together with cable ties.

[0083] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0084] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0085] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple secondary battery cells to the housing.

[0086] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0087] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0088] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0089] The technical solutions described in this disclosure are applicable to various electrical devices that use secondary battery cells or battery devices, such as, but not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. Secondary battery cells and battery devices are used to store or provide electrical energy.

[0090] Figure 2 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0091] In the context of this disclosure, the "polymer particles" in the porous coating of the separator primarily serve to improve heat resistance and have almost no adhesive properties.

[0092] The separator is a crucial component supporting the electrochemical processes of charging and discharging in a secondary battery cell. Commonly used separators are often made of polyolefins; however, polyolefins have poor heat resistance and are prone to softening or melting at high temperatures, which can lead to short circuits in the secondary battery cells. To improve the heat resistance of the separator, a porous coating is typically applied. Boehmite, alumina, and other inorganic particles are commonly used heat-resistant fillers; however, these fillers have high density and a large mass for the same bulk volume, thus affecting the energy density of the secondary battery cells.

[0093] Based on this, embodiments of the present disclosure provide polymer particles that, when used in a separator, enable secondary battery cells to possess both high energy density and high reliability.

[0094] The polymer particles disclosed herein include a first structural unit and a second structural unit, the first structural unit including a vinyl structural unit and the second structural unit including a maleimide or a derivative structural unit of maleimide.

[0095] Polymer particles have a low density, allowing secondary battery cells to have a higher mass energy density.

[0096] Vinyl polymer particles possess good electrochemical stability, but their heat resistance is not excellent. The polymer particles disclosed herein possess both vinyl structural units and maleimide or maleimide derivative structural units. The maleimide or maleimide derivative structural units have high rigidity, which can improve the heat resistance of the polymer particles. By using these polymer particles in a separator, the overall thermal shrinkage of the separator can be improved, enhancing its heat resistance and the reliability of the secondary battery cell. Furthermore, the maleimide or maleimide derivative structural units have strong polarity. Therefore, by using these polymer particles in the porous coating of the separator, the polymer particles can also generate stronger interactions with the binder in the porous coating, resulting in stronger adhesion between the porous coating and the porous base film, while also improving the overall structural integrity of the separator.

[0097] Therefore, the polymer particles disclosed herein, when used in a separator membrane, enable secondary battery cells to possess both high energy density and high reliability.

[0098] In some embodiments, the first structural unit may include one or more of the following: styrene or styrene derivative structural units, acrylate structural units, acrylonitrile structural units, vinyl ether structural units, alkyl vinyl ester structural units, N-vinylpyrrolidone or N-vinylpyrrolidone derivative structural units.

[0099] Optionally, the first structural unit may include one or more of styrene or styrene derivative structural units and acrylate structural units.

[0100] In some embodiments, the styrene or styrene derivative structural unit may include one or more of the following: styrene structural unit, 1-methyl-1-styrene structural unit, 4-methylstyrene structural unit, 2-methylstyrene structural unit, 2,4-dimethylstyrene structural unit, and 2,5-dimethylstyrene structural unit.

[0101] In some embodiments, the acrylate structural unit may include one or more of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0102] In some embodiments, the acrylonitrile structural unit may include one or both of the acrylonitrile structural unit and the methacrylonitrile structural unit.

[0103] In some embodiments, the vinyl ether structural unit may include one or more of the following: methyl vinyl ether structural unit, ethyl vinyl ether structural unit, propyl vinyl ether structural unit, butyl vinyl ether structural unit, cyclopropyl vinyl ether structural unit, cyclobutyl vinyl ether structural unit, cyclopentyl vinyl ether structural unit, and cyclohexyl vinyl ether structural unit.

[0104] In some embodiments, the alkyl vinyl ester structural unit may include one or more of the following: vinyl acetate structural unit, vinyl propionate structural unit, vinyl butyrate structural unit, and vinyl valerate structural unit.

[0105] In some embodiments, the N-vinylpyrrolidone or N-vinylpyrrolidone derivative structural unit may include one or more of the following: N-vinylpyrrolidone structural unit, 4-methyl-1-vinyl-2-pyrrolidone structural unit, and 1-vinyl-3-methyl-2-pyrrolidone structural unit.

[0106] In some embodiments, the second structural unit may include one or more of maleimide structural units, N-substituted maleimide structural units, and bismaleimide structural units.

[0107] In some embodiments, the N-substituted maleimide structural unit may include one or more of the following: N-alkyl maleimide structural unit, N-cycloalkyl maleimide structural unit, and N-aromatic maleimide structural unit.

[0108] In some embodiments, the bismaleimide structural unit is formed by the nitrogen atoms of two maleimide structural units being bonded to each other via organic groups.

[0109] Optionally, the organic group connecting the nitrogen atoms of the two maleimide structural units in the bismaleimide structural unit may include substituted or unsubstituted C1-C12 alkylene, substituted or unsubstituted bicyclohexyl, substituted or unsubstituted alkylene dicyclohexyl, substituted or unsubstituted phenyl, substituted or unsubstituted biphenyl, substituted or unsubstituted alkylene diphenyl, substituted or unsubstituted diphenyl ether, substituted or unsubstituted diphenyl sulfide, or substituted or unsubstituted diphenyl sulfone.

[0110] Optionally, the substituents include one or more combinations of C1-C3 alkyl, -O-, -S-, -OO-, and -SS- groups.

[0111] Alternatively, the organic group connecting the nitrogen atoms of the two maleimide structural units in the bismaleimide structural unit may include any of the following, where # indicates the connection position.

[0112]

[0113]

[0114] In some embodiments, the polymer particles may further include cross-linked structural units.

[0115] Optionally, the crosslinking structural unit may include one or more of the following: divinylbenzene structural unit, ethylene glycol dimethacrylate structural unit, pentaerythritol tetraacrylate structural unit, 1,4-butanediol diacrylate structural unit, 1,6-hexanediol diacrylate structural unit, 1,8-octanediol diacrylate structural unit, trimethylolpropane triacrylate structural unit, pentaerythritol trimethacrylate structural unit, tetraethylene glycol dimethacrylate structural unit, tripropylene glycol diacrylate structural unit, N,N-methylenebisacrylamide structural unit, N,N'-vinylbisacrylamide structural unit, 1,3,5-triacryloylhexahydro-1,3,5-triazine structural unit, and triallyl isocyanurate structural unit.

[0116] The polymer particles disclosed herein are poorly soluble in both water and organic solvents, such as tetrahydrofuran (THF), dichloromethane (DCM), dimethylformamide (DMF), trichlorobenzene (TCB), and chloroform, at 25°C. They are also insoluble in the mobile phase used in gel permeation chromatography and the molecular weight of the polymer particles cannot be determined by gel permeation chromatography.

[0117] In some embodiments, the glass transition temperature T of the polymer particles g The temperature range is 150℃-275℃.

[0118] The glass transition temperature T of the polymer particles disclosed herein g With a temperature range of 150℃-275℃, it has high thermal stability, which can better resist the thermal shrinkage of the separator, improve the heat resistance of the separator, and improve the reliability of the secondary battery cells.

[0119] Glass transition temperature T of polymer particles gThe temperature range is 150℃ to 275℃, for example, it can be 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, 265℃, 270℃, 275℃, or any combination of the above values.

[0120] Optionally, the glass transition temperature T of the polymer particles g The temperature ranges are 155℃-275℃, 165℃-275℃, 180℃-275℃, 190℃-275℃, 195℃-275℃, 200℃-275℃, 205℃-275℃, and 210℃-275℃.

[0121] Glass transition temperature T of polymer particles g The test can be performed as follows: Take an appropriate amount of sample (e.g., 5mg-15mg) and place it in the crucible of the differential scanning calorimeter (DSC), level it, and cover the crucible. Parameter settings: nitrogen atmosphere, purge gas 60mL / min, protective gas 20mL / min; program settings: heat from 25℃ to 200℃ at a heating rate of 10℃ / min, hold for 5min to eliminate thermal history, then cool from 200℃ to -40℃ at a cooling rate of 10℃ / min, and then heat to 300℃ at a heating rate of 10℃ / min. The glass transition temperature T is obtained from the DSC curve. g .

[0122] In some embodiments, the polymer particles have no melting point.

[0123] The polymer particles disclosed herein have no melting point, indicating that they have good heat resistance and thermal stability. This allows them to better resist the thermal shrinkage of the separator, improve the heat resistance of the separator, and enhance the reliability of the secondary battery cells.

[0124] Melting point can be tested as follows: Take an appropriate amount of sample (e.g., 5mg-15mg) and place it in the crucible of a differential scanning calorimeter (DSC), level it, and cover the crucible. Parameter settings: nitrogen atmosphere, purge gas 60mL / min, protective gas 20mL / min; program settings: heat from 25℃ to 200℃ at a heating rate of 10℃ / min, hold for 5min to eliminate thermal history, then cool from 200℃ to -40℃ at a cooling rate of 10℃ / min, and then heat to 300℃ at a heating rate of 10℃ / min. The DSC curve is used to determine whether the polymer particles have a melting point below 300℃. Polymer particles without a melting point mean that the DSC curve of the polymer particles does not show a melting peak.

[0125] In some embodiments, the initial thermogravimetric temperature T of the polymer particles 3d The temperature range is 350℃-430℃. Initial thermogravimetric temperature T 3d This refers to the temperature at which the mass of a thermogravimetric analysis test sample is reduced by 3% relative to its initial mass.

[0126] The initial thermogravimetric temperature T of polymer particles 3d The high value indicates good thermal stability, which can better resist the thermal shrinkage of the separator, improve the heat resistance of the separator, and enhance the reliability of the secondary battery cells.

[0127] The initial thermogravimetric temperature T of polymer particles 3d The test can be performed as follows: Take an appropriate amount of sample (e.g., 5mg-15mg) and place it in the alumina crucible of the thermogravimetric analyzer (TGA), level it, and cover the crucible with the lid; Parameter settings: nitrogen atmosphere, purge gas 60mL / min, protective gas 20mL / min; Temperature rise program: heating rate 10℃ / min, temperature range 35℃-600℃; Obtain the temperature corresponding to a 3% loss of sample mass relative to the initial mass (i.e., 97% of the initial mass) from the test curve, which is the initial thermogravimetric temperature T. 3d .

[0128] In some embodiments, the cyclic voltammetry curve of the polymer particles during the first cycle does not have an oxidation peak in the voltage range of 2.5V to 4.45V.

[0129] The cyclic voltammetry curve of the polymer particles in the first cycle shows no oxidation peak in the voltage range of 2.5V to 4.45V, indicating that the polymer particles are stable in this voltage range and have good electrochemical stability. Therefore, they can be applied to high-voltage secondary battery cells to improve the working voltage and energy density of the secondary battery cells.

[0130] The oxidation peak potential of the cyclic voltammetry curve of polymer particles can be tested as follows: Polymer particles, binder polyacrylate, and conductive agent conductive carbon black are dissolved in water at a solid content mass ratio of 64:7:29 to prepare a slurry. The slurry is coated onto aluminum foil as the positive electrode, and lithium foil is used as the negative electrode to assemble a coin cell. Cyclic voltammetry (CV) is performed on the coin cell at a scan rate of 0.10 mV / s, a voltage range of 2.5V-5.0V, and 3 cycles. The voltage corresponding to the peak point of the first cyclic voltammetry curve is taken as the oxidation peak potential. The electrolyte used in the test is LiPF6 with a concentration of 1 mol / L. The solvent of the electrolyte is obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:7.

[0131] In some embodiments, the swelling degree of polymer particles immersed in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 at 60°C for 7 days can be less than or equal to 2.5%.

[0132] The polymer particles have low swelling in organic solvents and high structural stability during long-term use of secondary battery cells, thereby improving the problem of decreased air permeability of the separator during use.

[0133] The swelling degree of polymer particles can be tested as follows: Take an appropriate amount of sample (e.g., about 1g), denoted as m1, and place it in a semi-permeable membrane sample bag. Seal the bag; the sample bag should be permeable to the solvent but not to the sample. Immerse the sample bag in an appropriate amount of solvent (e.g., about 50g) at 60°C for 7 days. After immersion, remove the sample bag and the sample from the bag. Wipe away excess solvent and weigh the sample again, m2. Swelling degree = (m2-m1) / m1 × 100%. The solvent is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0134] In some embodiments, the dissolution rate of polymer particles soaked in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 at 60°C for 7 days can be less than or equal to 2%.

[0135] The polymer particles have a low dissolution rate in organic solvents, high structural stability during long-term use of secondary battery cells, and high chemical stability in electrolytes, which enables secondary battery cells to have long-cycle stability.

[0136] The dissolution rate of polymer particles can be tested as follows: Take an appropriate amount of sample (e.g., about 1g), and record its mass as m1. Place it in a semi-permeable membrane sample bag, seal it, and record the total mass of the sample bag as m2. The sample bag is permeable to the solvent but not to the sample. Immerse the sample bag in an appropriate amount of solvent (e.g., about 50g) at 60°C for 7 days. After that, remove the sample bag, drain it, dry it, and weigh the total mass of the sample bag again as m3. Dissolution rate = (m2-m3) / m1 × 100%. The solvent is a mixed solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0137] In some embodiments, the volume distribution particle size Dv50 of the polymer particles can be 110nm-700nm, for example, it can be 110nm, 130nm, 150nm, 170nm, 200nm, 240nm, 280nm, 320nm, 360nm, 400nm, 440nm, 480nm, 520nm, 560nm, 600nm, 640nm, 700nm, or any range of the above values.

[0138] The volume distribution particle size Dv50 of the polymer particles is within the above range, which is beneficial for the separator to have good heat resistance and air permeability.

[0139] Dv50 represents the particle size corresponding to a cumulative volumetric distribution percentage of 50% for the material. It can be measured using a laser particle size analyzer, referring to GB / T19077-2016. During testing, add 1g of the sample to a clean small beaker, along with 20ml of deionized water. Sonicate at 53kHz / 120W for 5 minutes to ensure complete dispersion. Turn on the laser particle size analyzer, clean the optical path system, and automatically test the background. Stir the sonicated solution to ensure uniform dispersion, then place it in the sample cell as required and begin measuring the particle size. A MasterSizer 3000 laser particle size analyzer can be used as the testing instrument.

[0140] This disclosure also provides a method for preparing polymer particles, which can prepare the polymer particles of this disclosure.

[0141] The method for preparing polymer particles includes the following steps: providing a pre-emulsion, the pre-emulsion comprising monomers, emulsifiers, initiators and water, the monomers comprising a first monomer and a second monomer, the first monomer comprising a vinyl monomer and the second monomer comprising maleimide and its derivative monomers; subjecting the pre-emulsion to emulsion polymerization under heating, inert gas protection and stirring conditions to obtain polymer particles.

[0142] The preemulsion includes maleimide and its derivative monomers, which possess high polarity and rigid imide rings, and their molecular structure also contains double bonds capable of free radical polymerization. Therefore, by including maleimide and its derivative monomers in the preemulsion, maleimide or maleimide derivative structural units can be introduced into the molecular structure of polymer particles through copolymerization with vinyl monomers, thereby improving the heat resistance of the polymer particles.

[0143] In some embodiments, the emulsion polymerization reaction may include the following steps: adding a pre-emulsion dropwise to a reactor containing water under a first temperature, an inert gas protection and stirring conditions; continuing the reaction at the first temperature for a first time after the dropwise addition is completed; and then raising the temperature to a second temperature to mature the reaction for a second time to obtain polymer particles.

[0144] In some embodiments, the first temperature can be 55℃-80℃, for example, it can be 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, or any range of the above values.

[0145] In some embodiments, the first time can be 2h-8h, for example, it can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, or any range of the above values.

[0146] In some embodiments, the second temperature can be 70℃-92℃, for example, it can be 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, or any range of the above values.

[0147] In some embodiments, the second time can be 1h-6h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any range of the above values.

[0148] In some embodiments, the mass fraction of the first monomer may be greater than or equal to 40% when the total mass of the monomers is 100%.

[0149] In some embodiments, the first monomer may include one or more of styrene and its derivative monomers, acrylate monomers, acrylonitrile monomers, vinyl ether monomers, alkyl vinyl ester monomers, N-vinylpyrrolidone or N-vinylpyrrolidone derivative monomers.

[0150] In some embodiments, styrene and its derivative monomers may include one or more of styrene, 1-methyl-1-styrene, 4-methylstyrene, 2-methylstyrene, 2,4-dimethylstyrene, and 2,5-dimethylstyrene.

[0151] In some embodiments, acrylate monomers may include one or more of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0152] In some embodiments, acrylonitrile monomers may include one or both of acrylonitrile and methacrylonitrile.

[0153] In some embodiments, vinyl ether monomers may include one or more of methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, cyclopropyl vinyl ether, cyclobutyl vinyl ether, cyclopentyl vinyl ether, and cyclohexyl vinyl ether.

[0154] In some embodiments, the alkyl vinyl ester monomer may include one or more of vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl valerate.

[0155] In some embodiments, N-vinylpyrrolidone or N-vinylpyrrolidone derivative monomers may include one or more of N-vinylpyrrolidone, 4-methyl-1-vinyl-2-pyrrolidone, and 1-vinyl-3-methyl-2-pyrrolidone.

[0156] In some embodiments, the second monomer may include one or more of monomaleimide monomers and bismaleimide monomers.

[0157] In some embodiments, the second monomer may include a bismaleimide monomer.

[0158] Optionally, based on the total mass of the monomers as 100%, the mass fraction of the second monomer can be 5%-35%, for example, it can be 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 35%, or any range of the above values.

[0159] Optionally, the monomer may also include a crosslinking agent monomer, and the mass fraction of the crosslinking agent monomer may be 1%-20% based on the total mass of the monomer, for example, it may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, or any range of the above values.

[0160] In other embodiments, the second monomer may include a monomaleimide monomer and a bismaleimide monomer.

[0161] Optionally, based on the total mass of monomers as 100%, the mass fraction of the monomaleimide monomer can be 1%-50%, for example, it can be 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or any range of the above values.

[0162] Optionally, based on the total mass of monomers of 100%, the mass fraction of bismaleimide monomers can be 5%-30%, for example, 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or any combination of the above values.

[0163] Optionally, the monomer may also include a crosslinking agent monomer, and the mass fraction of the crosslinking agent monomer may be 1%-10% based on the total mass of the monomer, for example, it may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range of the above values.

[0164] In some other embodiments, the second monomer includes a monomaleimide monomer, and the monomer also includes a crosslinking agent monomer.

[0165] Optionally, based on the total mass of monomers as 100%, the mass fraction of crosslinking agent monomers can be 5%-40%, for example, it can be 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, or any range of the above values.

[0166] Optionally, based on the total mass of the monomers as 100%, the mass fraction of the second monomer can be 5%-55%, for example, it can be 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 55%, or any range of the above values.

[0167] In some embodiments, the crosslinking agent may include one or more of divinylbenzene, ethylene glycol dimethacrylate, pentaerythritol tetraacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,8-octanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol trimethacrylate, tetraethylene glycol dimethacrylate, tripropylene glycol diacrylate, N,N-methylenebisacrylamide, N,N'-vinylbisacrylamide, 1,3,5-triacryloylhexahydro-1,3,5-triazine, and triallyl isocyanurate.

[0168] In some embodiments, monomaleimide monomers may include one or more of maleimide, N-alkylmaleimide, N-cycloalkylmaleimide, N-aromatic maleimide, and their respective derivatives.

[0169] Optionally, the monomaleimide monomer may include one or more of the following: maleimide, N-methylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, N-n-butylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide, N-n-pentylmaleimide, N-n-octylmaleimide, N-cyclobutylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, N-cycloheptylmaleimide, N-phenylmaleimide, N-benzylmaleimide, N-(p-methylphenyl)maleimide, N-(o-methylphenyl)maleimide, N-(m-methylphenyl)maleimide, N-(2,4-dimethylphenyl)maleimide, and N-(2,3-dimethylphenyl)maleimide.

[0170] In some embodiments, bismaleimide monomers may include one or more of the compounds shown in Formula 1.

[0171]

[0172] R1 may be selected from substituted or unsubstituted C1-C12 alkylene groups, substituted or unsubstituted bicyclohexyl groups, substituted or unsubstituted alkylene dicyclohexyl groups, substituted or unsubstituted phenyl groups, substituted or unsubstituted biphenyl groups, substituted or unsubstituted alkylene diphenyl groups, substituted or unsubstituted diphenyl ether groups, substituted or unsubstituted diphenyl sulfide groups, and substituted or unsubstituted diphenyl sulfone groups. The substituted substituents include one or more combinations of C1-C3 alkyl groups, -O-, -S-, -OO-, and -SS-.

[0173] Optionally, R1 can be selected from any of the following, where # indicates the connection position.

[0174]

[0175]

[0176] In some embodiments, the emulsifier may include one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, fatty acid sorbitan, polysorbate, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl alcohol, polyoxyethylene ether emulsifier, cellulose and its derivatives. Optionally, the polyoxyethylene ether emulsifier may include OP-type emulsifiers, such as OP-4, OP-7, OP-10, OP-15, OP-20, etc.

[0177] In some embodiments, the mass fraction of the emulsifier may be 0.2%-5% based on the total mass of the monomers (100%).

[0178] In some embodiments, the initiator may be one or more of sodium persulfate, potassium persulfate, ammonium persulfate, sodium sulfite, sodium bisulfite, azobisisobutyramidine hydrochloride, azobisisobutyramidine hydrochloride, and azobisisopropylimidazoline.

[0179] This disclosure also provides a polymer particle emulsion, which includes the polymer particles of this disclosure, or can be obtained by the above-described method for preparing polymer particles.

[0180] This disclosure also provides a separator membrane. The separator membrane includes a porous base membrane and a porous coating located on at least one side of the porous base membrane. The porous coating includes an adhesive and polymer particles of this disclosure, or polymer particles prepared by the methods of this disclosure.

[0181] Both the porous base membrane and the porous coating have a porous structure, which gives the separator good air permeability and facilitates ion passage. In the porous coating, the polymer particles are interconnected and fixed by a binder, and the gaps between the polymer particles can form a porous structure.

[0182] In some embodiments, the polymer particle content in the porous coating may be 50%-99% based on the total mass of the porous coating.

[0183] Optionally, the mass content of polymer particles in the porous coating can be 60%-99%, 70%-99%, 80%-99%, 85%-99%, 88%-99%, 80%-97%, 85%-97%, 88%-97%, 80%-95%, 85%-95%, or 88%-95%.

[0184] In some embodiments, the binder in the porous coating may be one or more of the following: polyacrylate binders, nitrile rubber binders, polyacrylic acid, polymethacrylic acid, sodium polyacrylate, polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0185] In some embodiments, the porous coating may further include a dispersant, such as one or more of alkylphenol polyoxyethylene ethers, polyacrylic acid dispersants, and cellulose dispersants, including but not limited to. As an example, the dispersant may include, but is not limited to, one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and ammonium polyacrylate.

[0186] In some embodiments, the separator may also include polymer binder particles.

[0187] The "polymer binder particles" in the porous coating of the separator membrane play a role in improving the adhesion between the separator membrane and the electrode, but they have virtually no heat resistance.

[0188] In some embodiments, polymer binder particles may be embedded in polymer particles and form protrusions on the porous coating surface.

[0189] In other embodiments, the porous coating of the separator includes a heat-resistant layer and an adhesive layer. The heat-resistant layer is disposed on the porous base membrane, and the adhesive layer is disposed on at least a portion of the surface of the heat-resistant layer on the side away from the porous base membrane. Polymer particles are disposed in the heat-resistant layer, and polymer adhesive particles are disposed in the adhesive layer.

[0190] In some other embodiments, the porous coating of the separator includes a heat-resistant layer and an adhesive layer. The heat-resistant layer is disposed on one side of the porous base membrane, and the adhesive layer is disposed on at least a portion of the surface of the other side of the porous base membrane. Polymer particles are disposed in the heat-resistant layer, and polymer adhesive particles are disposed in the adhesive layer.

[0191] In some embodiments, the average particle size of the polymer binder particles can be 6 μm-18 μm.

[0192] In some embodiments, the polymer binder particles may include vinylidene fluoride polymer particles, such as polyvinylidene fluoride (PVDF) particles and / or copolymer particles of vinylidene fluoride monomer and comonomer.

[0193] Comonomers may include at least one of olefin monomers, fluorinated olefin monomers, chlorinated olefin monomers, acrylate monomers, acrylic monomers, and fluoroether monomers.

[0194] Optionally, the comonomer may include at least one of the following: trifluoroethylene, trifluorochloroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro(alkyl vinyl) ether (e.g., perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether), perfluoro(1,3-m-dioxacyclopentene), and perfluoro(2,2-dimethyl-1,3-m-dioxacyclopentene).

[0195] In some embodiments, the thickness of the porous coating can be 0.5 μm-5 μm. The thickness of the porous coating refers to the thickness of the porous coating located on one side of the porous base film. Optionally, the thickness of the porous coating can be 0.5 μm-4 μm, 0.5 μm-3 μm, 0.5 μm-2 μm, 0.8 μm-4 μm, 0.8 μm-3 μm, or 0.8 μm-2 μm.

[0196] In some embodiments, the porous base membrane may comprise a membrane or nonwoven web selected from any one or at least two of the following: polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymer, polyphenylene sulfide, and polyvinylnaphthalene.

[0197] Porous base membranes can be single-layer thin films or multi-layer composite thin films. When a porous base membrane is a multi-layer composite thin film, the materials of each layer can be the same or different.

[0198] In some embodiments, the thickness of the porous base film can be 4μm-12μm, and optionally 4μm-9μm.

[0199] In some embodiments, the porosity of the porous base membrane can be 25%-60%, optionally 28%-50%.

[0200] In some embodiments, the thickness of the separator can be 5μm-14μm, optionally 5μm-12μm or 6μm-12μm. This is beneficial for improving the energy density of the secondary battery cell.

[0201] In some embodiments, the longitudinal (MD) heat shrinkage rate of the separator film can be less than or equal to 30% when heated at a constant temperature of 140°C for 1 hour.

[0202] In some embodiments, the transverse (TD) heat shrinkage rate of the separator film can be less than or equal to 30% when heated at a constant temperature of 140°C for 1 hour.

[0203] It should be noted that the porous coating parameters of the above-mentioned separator are all the porous coating parameters of one side of the porous base membrane. When the porous coating is disposed on both sides of the porous base membrane, if the porous coating parameters of either side meet the requirements of this disclosure, it is considered to fall within the protection scope of this disclosure.

[0204] The separator membrane can be prepared according to methods known in the art.

[0205] In some embodiments, a slurry comprising polymer particles and a binder can be coated on at least one side of a porous base membrane, and after drying, a separation membrane is obtained.

[0206] In some embodiments, the slurry may further include polymer binder particles, which, after drying, are embedded in the polymer particles and form protrusions on the porous coating surface.

[0207] In some embodiments, the method for preparing the separator membrane may include: applying a heat-resistant layer slurry comprising polymer particles and an adhesive to at least one side of a porous base membrane, and drying it to form a heat-resistant layer; and applying an adhesive layer slurry comprising polymer adhesive particles and an adhesive to at least a portion of the surface of the heat-resistant layer, and drying it to obtain the separator membrane.

[0208] In some embodiments, the method for preparing the separator membrane may include: coating a heat-resistant slurry comprising polymer particles and an adhesive onto one side of a porous base membrane, and coating an adhesive layer slurry comprising polymer adhesive particles and an adhesive onto at least a portion of the surface of the other side of the porous base membrane, and drying the slurry to obtain the separator membrane.

[0209] In some embodiments, the solvent for the slurry may be water, such as deionized water.

[0210] In some embodiments, the slurry may also include other components, such as dispersants and / or wetting agents.

[0211] This disclosure also provides a secondary battery cell. The secondary battery cell includes the separator provided in this disclosure. This allows the secondary battery cell to possess both high energy density and high reliability.

[0212] A secondary battery cell also includes a positive electrode, a negative electrode, and an electrolyte, with a separator disposed between the positive and negative electrodes. The positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process.

[0213] The secondary battery cells disclosed herein may include, but are not limited to, lithium secondary battery cells, sodium battery cells, etc. The composition of the positive electrode, negative electrode and electrolyte may differ depending on the type of secondary battery cell.

[0214] [Positive electrode plate]

[0215] In some embodiments, the positive electrode may include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0216] Taking a lithium-ion secondary battery cell as an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. In some embodiments, to further improve the energy density of the secondary battery cell, the positive electrode active material may include materials of the general formula Li a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes but is not limited to one or more of N, F, S and Cl.

[0217] As an example, the positive electrode active material may include, but is not limited to, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.1 Al 0.05 One or more of O2, LiFePO4, and LiMnPO4.

[0218] During the charging and discharging process, Li undergoes insertion / extraction and consumption in a single secondary battery cell, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this disclosure, the molar Li content represents the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to a secondary battery cell, the molar Li content changes after charge-discharge cycles. Similarly, in the examples of positive electrode active materials in this disclosure, the molar O content is only a theoretical value. Lattice oxygen release causes changes in the molar O content, and the actual molar O content will also fluctuate.

[0219] Taking sodium-ion battery cells as an example, the positive electrode active material can be one or more of the following, including but not limited to sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials. For example, the positive electrode active material can be, but is not limited to, NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials, with the general formula X p M' q (PO4) r O x Y 3-x One or more of the materials. In general formula X p M' q (PO4) r O x Y 3-x In this case, 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X includes, but is not limited to, H. + Li + Na + K + and NH4 + One or more of the following, M' is a transition metal cation, optionally including but not limited to one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, optionally one or more of F, Cl and Br.

[0220] The modified compounds for the positive electrode active materials of the aforementioned lithium secondary battery cells and sodium battery cells can be obtained by doping and / or surface coating modifications of the positive electrode active materials.

[0221] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0222] In some embodiments, the positive electrode film layer may further include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0223] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0224] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing positive electrode active materials, positive electrode conductive agents, positive electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0225] [Negative electrode plate]

[0226] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0227] The negative electrode active material may be any material known in the art for use in secondary battery cells. As an example, the negative electrode active material may include, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include, but are not limited to, one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include, but are not limited to, one or more of elemental tin, tin oxide, and tin alloys.

[0228] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0229] In some embodiments, the negative electrode film layer may further include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0230] In some embodiments, the negative electrode film layer may also include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0231] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0232] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, negative electrode conductive agent, negative electrode binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0233] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet also includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector.

[0234] In some embodiments, the negative electrode sheet can be made of foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not contain a negative electrode active material.

[0235] [Electrolytes]

[0236] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0237] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and an organic solvent.

[0238] Taking a lithium secondary battery cell as an example, the electrolyte salt may include, but is not limited to, one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0239] Taking sodium battery cells as an example, the electrolyte salt may include, but is not limited to, one or more of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium difluorosulfonyl imide (NaFSI), sodium difluoromethanesulfonyl imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0240] In some embodiments, the organic solvent may include, but is not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ether.

[0241] In some embodiments, the electrolyte may also include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the secondary battery cell, such as additives that improve overcharge performance, additives that improve high-temperature performance, additives that improve low-temperature performance, etc.

[0242] Optionally, the additive may include one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), and ethylene sulfate (DTD).

[0243] Methods for preparing secondary battery cells are well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with the aforementioned electrolyte. After vacuum sealing, settling, and formation processes, a secondary battery cell is obtained.

[0244] Example

[0245] The following examples describe the contents of this disclosure in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0246] Example 1

[0247] A pre-emulsion was prepared by emulsifying 0.25g sodium dodecyl sulfate, 0.1g sodium persulfate, 25ml deionized water, 37.5g styrene, 7.5g divinylbenzene, and 5g N-phenylmaleimide. 175g deionized water was added to a reactor, and the temperature was raised to 70℃. Under nitrogen protection and stirring, the prepared pre-emulsion was added dropwise. After reacting for 4 hours, the temperature was raised to 85℃ and the reaction was allowed to mature for 1.5 hours to obtain polymer particle emulsion #1.

[0248]

[0249] The above emulsion, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were added to deionized water and stirred until homogeneous to obtain a porous coating slurry. The solid content mass ratio of the polymer particles, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 90:2:8.

[0250] A commercially available 7μm thick polyethylene film was used as the porous base membrane. The porous coating slurry was coated onto the two surfaces of the porous base membrane using a microgravure method, and then the membrane was obtained through drying and slitting processes.

[0251] Example 2

[0252] A pre-emulsion was prepared by emulsifying 0.25 g sodium dodecyl sulfate, 0.1 g sodium persulfate, 25 ml deionized water, 37.5 g styrene, and 12.5 g N,N'-(4,4'-methylenediphenyl)bismaleimide. 175 g of deionized water was added to a reactor, and the temperature was raised to 70 °C. Under nitrogen protection and stirring, the prepared pre-emulsion was added dropwise. After reacting for 4 hours, the temperature was raised to 85 °C and the reaction was allowed to mature for 1.5 hours to obtain polymer particle emulsion #2.

[0253]

[0254] The above emulsion, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were added to deionized water and stirred until homogeneous to obtain a porous coating slurry. The solid content mass ratio of the polymer particles, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 90:2:8.

[0255] A commercially available 7μm thick polyethylene film was used as the porous base membrane. The porous coating slurry was coated onto the two surfaces of the porous base membrane using a microgravure method, and then the membrane was obtained through drying and slitting processes.

[0256] Example 3

[0257] A pre-emulsion was prepared by emulsifying 0.25g sodium dodecyl sulfate, 0.1g sodium persulfate, 25ml deionized water, 37.5g styrene, 7.5g divinylbenzene, and 5g N,N-1,3-phenylenebismaleimide. 175g deionized water was added to a reactor, and the temperature was raised to 70℃. Under nitrogen protection and stirring, the prepared pre-emulsion was added dropwise. After reacting for 4 hours, the temperature was raised to 85℃ and the reaction was allowed to mature for 1.5 hours to obtain polymer particle emulsion #3.

[0258]

[0259] The above emulsion, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were added to deionized water and stirred until homogeneous to obtain a porous coating slurry. The solid content mass ratio of the polymer particles, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 90:2:8.

[0260] A commercially available 7μm thick polyethylene film was used as the porous base membrane. The porous coating slurry was coated onto the two surfaces of the porous base membrane using a microgravure method, and then the membrane was obtained through drying and slitting processes.

[0261] Example 4

[0262] A pre-emulsion was prepared by emulsifying 0.25g sodium dodecyl sulfate, 0.1g sodium persulfate, 25ml deionized water, 27.5g styrene, 5g ethyl acrylate, 7.5g divinylbenzene, and 10g N-phenylmaleimide. 175g deionized water was added to a reactor, and the temperature was raised to 70℃. Under nitrogen protection and stirring, the prepared pre-emulsion was added dropwise. After reacting for 4 hours, the temperature was raised to 85℃ and the reaction was allowed to mature for 1.5 hours to obtain polymer particle emulsion #4.

[0263]

[0264] The above emulsion, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were added to deionized water and stirred until homogeneous to obtain a porous coating slurry. The solid content mass ratio of the polymer particles, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 90:2:8.

[0265] A commercially available 7μm thick polyethylene film was used as the porous base membrane. The porous coating slurry was coated onto the two surfaces of the porous base membrane using a microgravure method, and then the membrane was obtained through drying and slitting processes.

[0266] Example 5

[0267] 0.25g sodium dodecyl sulfate, 0.1g sodium persulfate, 25ml deionized water, 25g styrene, 10g N,N'-(4,4'-methylenediphenyl)bismaleimide, and 15g N-phenylmaleimide were emulsified to obtain a pre-emulsion for later use. 175g deionized water was added to a reactor, and the temperature was raised to 70℃. Under nitrogen protection and stirring, the prepared pre-emulsion was added dropwise. After reacting for 4 hours, the temperature was raised to 85℃ and the reaction was allowed to mature for 1.5 hours to obtain polymer particle emulsion #5.

[0268] The above emulsion, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were added to deionized water and stirred until homogeneous to obtain a porous coating slurry. The solid content mass ratio of the polymer particles, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 90:2:8.

[0269] A commercially available 7μm thick polyethylene film was used as the porous base membrane. The porous coating slurry was coated onto the two surfaces of the porous base membrane using a microgravure method, and then the membrane was obtained through drying and slitting processes.

[0270] Example 6

[0271] 0.25g sodium dodecyl sulfate, 0.1g sodium persulfate, 25ml deionized water, 32.5g ethyl acrylate, 5g N,N-1,3-phenylenebismaleimide, and 12.5g N-phenylmaleimide were emulsified to obtain a pre-emulsion for later use. 175g deionized water was added to a reactor, and the temperature was raised to 70℃. Under nitrogen protection and stirring, the prepared pre-emulsion was added dropwise. After reacting for 4 hours, the temperature was raised to 85℃ and the reaction was allowed to mature for 1.5 hours to obtain polymer particle emulsion #6.

[0272] The above emulsion, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were added to deionized water and stirred until homogeneous to obtain a porous coating slurry. The solid content mass ratio of the polymer particles, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 90:2:8.

[0273] A commercially available 7μm thick polyethylene film was used as the porous base membrane. The porous coating slurry was coated onto the two surfaces of the porous base membrane using a microgravure method, and then the membrane was obtained through drying and slitting processes.

[0274] Comparative Example 1

[0275] 0.25 g sodium dodecyl sulfate, 0.1 g sodium persulfate, 25 ml deionized water, 49.4 g styrene, and 0.6 g divinylbenzene were emulsified to obtain a pre-emulsion for later use. 175 g deionized water was added to a reactor, and the temperature was raised to 70 °C. Under nitrogen protection and stirring, the prepared pre-emulsion was added dropwise. After reacting for 4 hours, the temperature was raised to 85 °C and the reaction was allowed to mature for 1.5 hours to obtain polymer particle D1# emulsion.

[0276] The above emulsion, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were added to deionized water and stirred until homogeneous to obtain a porous coating slurry. The solid content mass ratio of the polymer particles, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 90:2:8.

[0277] A commercially available 7μm thick polyethylene film was used as the porous base membrane. The porous coating slurry was coated onto the two surfaces of the porous base membrane using a microgravure method, and then the membrane was obtained through drying and slitting processes.

[0278] Performance testing

[0279] (1) Thermal shrinkage rate test of the separator film

[0280] The heat shrinkage rate test of the release liner can be referenced in GB / T 36363-2018.

[0281] Cut the release film into samples with a width of 50mm and a length of 100mm using a punching machine. Take 5 parallel samples and place them on A4 paper. Then place the A4 paper containing the samples on corrugated paper with a thickness of 1mm to 5mm.

[0282] Set the temperature of the forced-air drying oven to 140℃. After the temperature reaches the set temperature and stabilizes for 60 minutes, place the A4 paper placed on the corrugated paper into the forced-air drying oven and start timing. After the set time (1 hour in this disclosure) is reached, measure the length and width of the isolation film, and mark the values ​​as a and b respectively.

[0283] Calculation of heat shrinkage rate: Longitudinal (MD) heat shrinkage rate = [(100-a) / 100]×100%, Transverse (TD) heat shrinkage rate = [(50-b) / 50]×100%, take the average value of 3 parallel samples as the test result.

[0284] (2) Peel force test between the porous coating of the separator and the porous base film

[0285] Cut the release liner into three 2.5cm x 15cm strips. Attach the strips to a test steel plate. Use 2cm wide test tape to adhere to the side of the release liner to be tested. Using a tensile testing machine, clamp the steel plate on one side and the tape on the other, perform a 180° peel test. Take the average peel force of the three strips as the peel force between the porous coating and the porous base film. The tensile rate is 50mm / min.

[0286] Table 1

[0287]

[0288] The test results above show that the polymer particles disclosed herein have a high glass transition temperature T0. g and high initial thermogravimetric temperature T 3d When used in separators, it can improve the heat resistance of the separator and the peel force between the porous coating and the porous base film.

[0289] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. Polymer particles, characterized in that, The polymer particles include a first structural unit and a second structural unit, the first structural unit includes a vinyl structural unit, and the second structural unit includes a maleimide or a derivative structural unit of maleimide.

2. The polymeric particles according to claim 1, characterized in that, The first structural unit includes one or more of a styrene or a derivative structural unit of styrene, an acrylate structural unit, an acrylonitrile structural unit, a vinyl ether structural unit, an alkyl acid vinyl ester structural unit, an N-vinyl pyrrolidone or a derivative structural unit of N-vinyl pyrrolidone.

3. The polymer particles according to claim 2, wherein The styrene or the derivative structural unit of styrene includes one or more of a styrene structural unit, a 1-methyl-1-styrene structural unit, a 4-methylstyrene structural unit, a 2-methylstyrene structural unit, a 2,4-dimethylstyrene structural unit, and a 2,5-dimethylstyrene structural unit; and / or, The acrylate structural unit includes one or more of a methyl acrylate structural unit, an ethyl acrylate structural unit, a n-propyl acrylate structural unit, a n-butyl acrylate structural unit, an isobutyl acrylate structural unit, a sec-butyl acrylate structural unit, a t-butyl acrylate structural unit, a cyclohexyl acrylate structural unit, a lauryl acrylate structural unit, a 2-ethylhexyl acrylate structural unit, a 2-hydroxyethyl acrylate structural unit, a 2-hydroxypropyl acrylate structural unit, a methyl methacrylate structural unit, an ethyl methacrylate structural unit, a n-butyl methacrylate structural unit, a 2-ethylhexyl methacrylate structural unit, an isobornyl methacrylate structural unit, a lauryl methacrylate structural unit, a 2-hydroxyethyl methacrylate structural unit, and a 2-hydroxypropyl methacrylate structural unit; and / or, The acrylonitrile structural unit includes one or both of an acrylonitrile structural unit and a methacrylonitrile structural unit; and / or, The vinyl ether structural unit includes one or more of a methyl vinyl ether structural unit, an ethyl vinyl ether structural unit, a propyl vinyl ether structural unit, a butyl vinyl ether structural unit, a cyclopropyl vinyl ether structural unit, a cyclobutyl vinyl ether structural unit, a cyclopentyl vinyl ether structural unit, and a cyclohexyl vinyl ether structural unit; and / or, The alkyl acid vinyl ester structural unit includes one or more of a vinyl acetate structural unit, a vinyl propionate structural unit, a vinyl n-butyrate structural unit, and a vinyl pentanoate structural unit; and / or, The N-vinyl pyrrolidone or the derivative structural unit of N-vinyl pyrrolidone includes one or more of an N-vinyl pyrrolidone structural unit, a 4-methyl-1-vinyl-2-pyrrolidone structural unit, and a 1-vinyl-3-methyl-2-pyrrolidone structural unit.

4. The polymeric particles according to any one of claims 1 to 3, characterized in that, The second structural unit includes one or more of a maleimide structural unit, an N-substituted maleimide structural unit, and a bismaleimide structural unit.

5. The polymer particles according to claim 4, wherein The N-substituted maleimide structural unit includes one or more of an N-alkyl maleimide structural unit, an N-cycloalkyl maleimide structural unit, and an N-aromatic hydrocarbon maleimide structural unit; and / or, The bismaleimide structural unit is bonded to each other via nitrogen atoms of two maleimide structural units via an organic group.

6. The polymeric particles according to claim 5, characterized in that, The organic group connecting the nitrogen atoms of the two maleimide structural units in the bismaleimide structural unit includes one or more of a substituted or unsubstituted C1-C12 alkylene group, a substituted or unsubstituted bicyclohexyl group, a substituted or unsubstituted alkylene bicyclohexyl group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenyl group, a substituted or unsubstituted alkylene biphenyl group, a substituted or unsubstituted diphenyl ether group, a substituted or unsubstituted diphenyl sulfide group, and a substituted or unsubstituted diphenyl sulfone group. The substituted substituent includes one or more of a combination of a C1-C3 alkyl group, -O-, -S-, -O-O-, and -S-S-.

7. The polymeric particles according to any of claims 1 to 6, characterized in that, The polymer particles further include a crosslinking structural unit, which includes one or more of a divinyl benzene structural unit, a dimethyl glycol acrylate structural unit, a pentaerythritol tetraacrylate structural unit, a 1,4-butanediol diacrylate structural unit, a 1,6-hexanediol diacrylate structural unit, a 1,8-octanediol diacrylate structural unit, a trimethylolpropane triacrylate structural unit, a pentaerythritol trimethacrylate structural unit, a tetraethylene glycol dimethacrylate structural unit, a tripropylene glycol diacrylate structural unit, an N,N-methylene bisacrylamide structural unit, an N,N'-vinyl bisacrylamide structural unit, a 1,3,5-triacryloyl hexahydro-1,3,5-triazine structural unit, and a trimeric isocyanuric acid triallyl ester structural unit.

8. The polymeric particles according to any one of claims 1 to 7, characterized in that, The glass transition temperature T g is 150°C to 275°C.

9. The polymer particles according to any one of claims 1-8, wherein, The polymer particles have no melting point; and / or, The initial thermal weight loss temperature T of the polymer particles 3d is 350°C to 430°C.

10. The polymeric particles according to any one of claims 1 to 9, characterized in that, The polymer particles have no oxidation peak in a cyclic voltammetry curve of a first cycle in a voltage range of 2.5 V to 4.45 V.

11. The polymer particles according to any one of claims 1-10, wherein, The polymer particles have a swelling degree of less than or equal to 2.5% when immersed in a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7 at 60°C for 7 days; and / or, The polymer particles have a dissolution rate of less than or equal to 2% when immersed in a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7 at 60°C for 7 days.

12. The polymeric particles according to any one of claims 1 to 11, characterized in that, The polymer particles have a volume distribution particle size Dv50 of 110 nm-700 nm.

13. A method for preparing polymer particles, comprising the following steps: providing a pre-emulsion, the pre-emulsion including monomers, an emulsifier, an initiator, and water, the monomers including a first monomer and a second monomer, the first monomer including a vinyl monomer, and the second monomer including a maleimide and derivatives thereof; and performing emulsion polymerization of the pre-emulsion under heating, inert gas protection, and stirring to obtain the polymer particles.

14. The method of claim 13, wherein, The second monomer includes one or more of a monomaleimide monomer, a bismaleimide monomer.

15. The method of claim 14, wherein, The second monomer includes a bismaleimide monomer.

16. The method of claim 15, wherein, The mass fraction of the second monomer is 5%-35% based on the total mass of the monomers.

17. The method according to any of claims 15-16, characterized by, The monomers further include a crosslinker monomer, and the mass fraction of the crosslinker monomer is 1%-20% based on the total mass of the monomers.

18. The method of claim 14, wherein, The second monomer includes a monomaleimide monomer and a bismaleimide monomer.

19. The method of claim 18, wherein, The mass fraction of the monomaleimide monomer is 1%-50% and the mass fraction of the bismaleimide monomer is 5%-30% based on the total mass of the monomers.

20. The method of any one of claims 18-19, wherein, The monomers further include a crosslinker monomer, and the mass fraction of the crosslinker monomer is 1%-10% based on the total mass of the monomers.

21. The method of claim 14, wherein, The second monomer includes a monomaleimide monomer, and the monomers further include a crosslinker monomer.

22. The method of claim 21, wherein, The mass fraction of the crosslinker monomer is 5%-40% and the mass fraction of the second monomer is 5%-55% based on the total mass of the monomers.

23. The method of any one of claims 17, 20-22, wherein, The crosslinker monomer includes one or more of divinylbenzene, ethylene glycol dimethacrylate, pentaerythritol tetraacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,8-octanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol trimethacrylate, tetraethylene glycol dimethacrylate, tripropylene glycol diacrylate, N,N-methylenebisacrylamide, N,N'-vinylbisacrylamide, 1,3,5-triacryloylhexahydro-1,3,5-triazine, and triallyl isocyanurate.

24. The method of any one of claims 14-23, wherein: The monomaleimide monomer includes one or more of a maleimide, an N-alkyl maleimide, an N-cycloalkyl maleimide, an N-aromatic hydrocarbon maleimide, and respective derivatives thereof; and / or The bismaleimide monomer includes one or more of a compound represented by Formula 1, R1is selected from a substituted or unsubstituted C1-C12 alkylene, a substituted or unsubstituted bicyclohexyl, a substituted or unsubstituted alkylenebicyclohexyl, a substituted or unsubstituted phenyl, a substituted or unsubstituted biphenyl, a substituted or unsubstituted alkylenebiphenyl, a substituted or unsubstituted diphenyl ether, a substituted or unsubstituted diphenyl sulfide, and a substituted or unsubstituted diphenyl sulfone, wherein the substituents include one or more of a combination of C1-C3 alkyl, -O-, -S-, -O-O-, and -S-S-.

25. The method of claim 24, wherein: The monomaleimide monomer includes one or more of maleimide, N-methyl maleimide, N-ethyl maleimide, N-isopropyl maleimide, N-n-butyl maleimide, N-isobutyl maleimide, N-tert-butyl maleimide, N-n-pentyl maleimide, N-n-octyl maleimide, N-cyclobutyl maleimide, N-cyclopentyl maleimide, N-cyclohexyl maleimide, N-cycloheptyl maleimide, N-phenyl maleimide, N-benzyl maleimide, N-(p-methylphenyl) maleimide, N-(o-methylphenyl) maleimide, N-(m-methylphenyl) maleimide, N-(2,4-dimethylphenyl) maleimide, N-(2,3-dimethylphenyl) maleimide; and / or, R1is selected from any one of the following, # indicates a connection position, 26. The method of any one of claims 13-25, wherein, The mass fraction of the first monomer is greater than or equal to 40% based on the total mass of the monomers being 100%.

27. The method of any one of claims 13-26, wherein, The first monomer includes one or more of a styrene and derivative monomer, an acrylic ester monomer, an acrylonitrile monomer, a vinyl ether monomer, an alkyl acid vinyl ester monomer, N-vinyl pyrrolidone or an N-vinyl pyrrolidone derivative monomer.

28. The method of claim 27, wherein, The styrene and derivative monomer includes one or more of styrene, 1-methyl-1-styrene, 4-methylstyrene, 2-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene; and / or, The acrylic ester monomer includes one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, t-butyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate; and / or, The acrylonitrile monomer includes one or both of acrylonitrile and methacrylonitrile; and / or, The vinyl ether monomer includes one or more of methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, cyclopropyl vinyl ether, cyclobutyl vinyl ether, cyclopentyl vinyl ether, cyclohexyl vinyl ether; and / or, The alkyl acid vinyl ester monomer includes one or more of vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl valerate; and / or, The N-vinyl pyrrolidone or N-vinyl pyrrolidone derivative monomer includes one or more of N-vinyl pyrrolidone, 4-methyl-1-vinyl-2-pyrrolidone, 1-vinyl-3-methyl-2-pyrrolidone.

29. The method of any one of claims 13-28, wherein, The emulsion polymerization reaction comprises the following steps: under the conditions of a first temperature, inert gas protection and stirring, the pre-emulsion is added dropwise into a reactor containing water, after the dropwise addition is completed, the reaction is continued at the first temperature for a first time, then the temperature is raised to a second temperature for a second time for maturation, to obtain polymer particles.

30. The method of claim 29, wherein, the first temperature is 55-80℃; and / or, the first time is 2-8h; and / or, the second temperature is 70-92℃; and / or, the second time is 1-6h.

31. An emulsion of polymer particles, characterized in that, The polymer particles of any one of claims 1-12, or obtained by the method of any one of claims 13-30.

32. A separator membrane comprising a porous base membrane and a porous coating on at least one side of the porous base membrane, characterized in that, The porous coating layer comprises the polymer particles of any one of claims 1-12, or the polymer particles prepared by the method of any one of claims 13-30.

33. The separator film of claim 32, wherein, the mass content of the polymer particles in the porous coating layer is 50-99% based on the total mass of the porous coating layer; and / or, the thickness of the porous coating layer is 0.5-5μm.

34. The separator film of any one of claims 32-33, wherein, the longitudinal heat shrinkage of the separator film is less than or equal to 30% when heated at 140℃ for 1h; and / or, the transverse heat shrinkage of the separator film is less than or equal to 30% when heated at 140℃ for 1h.

35. A secondary battery cell characterized by The separator film of any one of claims 32-34.

36. A battery device, characterized by The secondary battery cell of claim 35.

37. An electrical device, comprising: The secondary battery cell of claim 35 or the battery device of claim 36.

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