Separator and preparation method therefor, secondary battery cell, battery device, and electric device

Abstract

A separator and a preparation method therefor, a secondary battery cell, a battery device, and an electric device. The separator comprises a porous base film and a porous coating located on at least one side of the porous base film; the porous coating comprises cross-linked styrene organic particles and fibrous materials, and at least part of the cross-linked styrene organic particles is located between the fibrous materials. The separator is used in the secondary battery cell, such that the secondary battery cell has both high quality energy density and high reliability.

Description

Separator and method for manufacturing the same, secondary battery cell, battery device, and power using device

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411388915.4, filed on September 30, 2024, entitled “Separator and method for manufacturing the same, secondary battery cell, battery device, and power using device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to a separator and method for manufacturing the same, secondary battery cell, battery device, and power using device. BACKGROUND

[0004] With the increasingly wide range of applications of secondary battery cells, people’s demand for the use of secondary battery cells is also increasing, such as the increasingly high requirements for the energy density and reliability of secondary battery cells. Therefore, how to make the secondary battery cell have higher energy density under the premise of high reliability is a technical problem to be solved at present. SUMMARY

[0005] The present disclosure provides a separator and method for manufacturing the same, secondary battery cell, battery device, and power using device, which is used in a secondary battery cell and can make the secondary battery cell have high mass energy density and high reliability.

[0006] In a first aspect, the present disclosure provides a separator, comprising a porous base film and a porous coating layer located on at least one side of the porous base film, the porous coating layer comprising cross-linked styrene-based organic particles and fibrous material, and at least part of the cross-linked styrene-based organic particles being located between the fibrous material.

[0007] The cross-linked styrene-based organic particles and the fibrous material have small density, so that the secondary battery cell using them can have higher mass energy density. The separator of the present disclosure comprises a mixture of cross-linked styrene-based organic particles and fibrous material in the porous coating layer, and after the introduction of the fibrous material, the cross-linked styrene-based organic particles can be connected in series, improving the structural properties and heat resistance of the whole porous coating layer, reducing the thermal shrinkage of the whole separator, and improving the reliability of the secondary battery cell. Therefore, the separator of the present disclosure can make the secondary battery cell have high mass energy density and high reliability.

[0008] In some embodiments, the glass transition temperature T g is 110°C-165°C. By using cross-linked styrene-based organic particles with high glass transition temperature T gThe cross-linked styrene-based organic particles can be used in the isolation film, which can improve the overall thermal shrinkage of the isolation film, improve the heat resistance of the isolation film, improve the reliability of the secondary battery cell, and reduce the risk of thermal runaway of the secondary battery cell.

[0009] In some embodiments, the cross-linked styrene-based organic particles have no melting point. The cross-linked styrene-based organic particles have no melting point, which means that they have good heat resistance and thermal stability, and thus can better resist the thermal shrinkage of the isolation film, improve the heat resistance of the isolation film, and improve the reliability of the secondary battery cell.

[0010] In some embodiments, the cross-linked styrene-based organic particles have no oxidation peak in the cyclic voltammetry curve of the first cycle in the voltage range of 2.5V to 4.4V. The cross-linked styrene-based organic particles have no oxidation peak in the cyclic voltammetry curve of the first cycle in the voltage range of 2.5V to 4.4V, indicating that the cross-linked styrene-based organic particles are stable in the voltage range of 2.5V to 4.4V and have good electrochemical stability, which can be applied to high-voltage secondary battery cells to improve the operating voltage and energy density of the secondary battery cell.

[0011] In some embodiments, the cross-linked styrene-based organic particles have a swelling degree of less than or equal to 3% when immersed in a mixed solvent composed of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7 at 60°C for 7 days. The cross-linked styrene-based organic particles have a low swelling degree in organic solvents, which has high structural stability during long-term use of the secondary battery cell, thereby improving the problem of reduced air permeability of the isolation film during use.

[0012] In some embodiments, the cross-linked styrene-based organic particles have a dissolution rate of less than or equal to 3% when immersed in a mixed solvent composed of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7 at 60°C for 7 days. The cross-linked styrene-based organic particles have a low dissolution rate in organic solvents, which has 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 have long cycle stability.

[0013] In some embodiments, the cross-linked styrene-based organic particles include styrene or styrene derivative structural units and cross-linked structural units.

[0014] Optionally, the styrene or styrene derivative structural units include one or more of styrene structural units, 1-methyl-1-styrene structural units, 4-methylstyrene structural units, 2-methylstyrene structural units, 2,4-dimethylstyrene structural units, and 2,5-dimethylstyrene structural units.

[0015] Optionally, the cross-linking structure unit comprises one or more of a divinylbenzene structure unit, a ethylene glycol dimethacrylate structure unit, a pentaerythritol tetraacrylate structure unit, a 1,4-butanediol diacrylate structure unit, a 1,6-hexanediol diacrylate structure unit, a 1,8-octanediol diacrylate structure unit, a trimethylolpropane triacrylate structure unit, a pentaerythritol trimethacrylate structure unit, a tetraethylene glycol dimethacrylate structure unit, a tripropylene glycol diacrylate structure unit, a N,N-methylenebisacrylamide structure unit, a N,N'-vinylbisacrylamide structure unit, a 1,3,5-triacryloylhexahydro-1,3,5-triazine structure unit, a trisallyl isocyanurate structure unit.

[0016] In some embodiments, the cross-linked styrene-based organic particles have a volume distribution particle size Dv50 of 88 nm-300 nm. The volume distribution particle size Dv50 of the cross-linked styrene-based organic particles within the above range is beneficial for the porous coating of the separator membrane to have good heat resistance and air permeability.

[0017] In some embodiments, the cross-linked styrene-based organic particles have a true density of 1.0 g / cm3-1.4 g / cm3. 3 -1.4 g / cm3. 3 .

[0018] In some embodiments, the cross-linked styrene-based organic particles have a first polar group.

[0019] Optionally, the first polar group comprises one or more of an ester group, a carboxyl group, a carboxylate group, a hydroxyl group, a cyano group, an amide group.

[0020] The cross-linked styrene-based organic particles having a first polar group are applied to the porous coating of the separator membrane, which can produce stronger interaction with the binder in the porous coating, such as forming hydrogen bonds or ionic bonds, etc., so that the adhesion between the porous coating and the porous base film is stronger, thereby improving the overall structural integrity of the separator membrane, and further improving the heat resistance of the separator membrane. In addition, these first polar groups have good electrolyte affinity, which can reduce the surface tension of the cross-linked styrene-based organic particles and improve the electrolyte wettability of the cross-linked styrene-based organic particles, thereby also reducing the internal resistance of the secondary battery cell and improving the cycle performance of the secondary battery cell.

[0021] In some embodiments, the fibrous material has a diameter in the range of 10 nm-200 nm.

[0022] In some embodiments, the fibrous material has a length in the range of 0.15 μm-30 μm.

[0023] In some embodiments, the fibrous material comprises one or more of sugar-based fibers, protein-based fibers, synthetic polymer fibers, inorganic fibers.

[0024] In some embodiments, the fibrous material comprises one or more of alginic acid and its derivative fibers, nanocellulose and its derivative fibers, chitosan and its derivative fibers, chitin and its derivative fibers, plant cellulose, silk fibroin fibers, spider silk protein fibers, corn protein fibers, soy protein fibers, keratin fibers, wool fibers, cashmere fibers, aramid fibers, polyester fibers, polyamide fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, polyethylene fibers, ultra-high molecular weight polyethylene fibers, polypropylene fibers, polytetrafluoroethylene fibers, polyvinylidene fluoride fibers, polyurethane fibers, acetate fibers, polycaprolactone fibers, polylactic acid fibers, polyether sulfone fibers, acrylic fibers, acrylic polymer fibers, polymethyl methacrylate fibers, poly-2-hydroxyethyl methacrylate fibers, polyethylene terephthalate fibers, polyethylene terephthalate fibers, para-phenylenediamine terephthalic acid fibers, glass fibers, asbestos fibers, silica fibers.

[0025] In some embodiments, the fibrous material has a second polar group.

[0026] Optionally, the second polar group comprises one or more of a hydroxyl group, a carboxyl group, an ester group, an amide group, a cyano group, an amine group, an aldehyde group, a sulfonic acid group, a boronic acid group, a phosphoric acid group.

[0027] The fibrous material having a second polar group applied to the porous coating layer of the separator film can form stronger interactions, such as hydrogen bonds or ionic bonds, with the binder in the porous coating layer, resulting in stronger adhesion between the porous coating layer and the porous base film, thereby improving the overall structural integrity of the separator film and further enhancing the heat resistance of the separator film.

[0028] In some embodiments, the mass content of the cross-linked styrene-based organic particles in the porous coating layer is greater than or equal to 55% based on the total mass of the porous coating layer.

[0029] In some embodiments, the mass content of the fibrous material in the porous coating layer is 0.5%-30% based on the total mass of the porous coating layer. The mass content of the fibrous material in the above range can enable the separator film to have both good heat resistance and air permeability, thereby enabling the secondary battery cell to have high reliability and good cycle performance.

[0030] In some embodiments, the porous coating layer further comprises a binder.

[0031] In some embodiments, the thickness of the porous coating layer is 0.4 μm-5 μm.

[0032] In a second aspect, the present disclosure provides a method for preparing the separation membrane of the first aspect, comprising the following steps: providing a porous base membrane; providing a slurry comprising crosslinked styrene-based organic particles, a fibrous material, a binder; coating the slurry on at least one side of the porous base membrane, and drying to obtain the separation membrane.

[0033] In some embodiments, the method for providing crosslinked styrene-based organic particles comprises the following steps: providing a pre-emulsion comprising monomers, a crosslinking agent, an emulsifier, an initiator, and water, the monomers comprising one or more of styrene and derivatives thereof; subjecting the pre-emulsion to emulsion polymerization under conditions of heating, inert gas protection, and stirring to obtain crosslinked styrene-based organic particles.

[0034] In some embodiments, the monomers comprise one or more of styrene, 1-methyl-1-styrene, 4-methylstyrene, 2-methylstyrene, 2,4-dimethylstyrene, and 2,5-dimethylstyrene.

[0035] In some embodiments, the crosslinking agent comprises 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.

[0036] In some embodiments, the emulsifier comprises one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, fatty acid sorbitan, polysorbate, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl alcohol, and polyoxyethylene ether emulsifier.

[0037] In some embodiments, the mass fraction of the crosslinking agent is 5%-40%, based on the total mass of the monomers and the crosslinking agent being 100%.

[0038] In some embodiments, the mass fraction of the emulsifier is 0.25%-5%, based on the total mass of the monomers and the crosslinking agent being 100%.

[0039] In some embodiments, the pre-emulsion further comprises a functional monomer, the functional monomer having a first polar group.

[0040] Optionally, the first polar group comprises one or more of an ester group, a carboxyl group, a carboxylate salt, a hydroxyl group, a cyano group, and an amide group.

[0041] In some embodiments, the emulsion polymerization reaction comprises the steps of: dropping the pre-emulsion into a reactor containing water under the conditions of a first temperature, inert gas protection and stirring, and after a first time, heating to a second temperature for a second time to obtain cross-linked styrene-based organic particles.

[0042] In some embodiments, the first temperature is 55-70℃.

[0043] In some embodiments, the first time is 3-6h.

[0044] In some embodiments, the second temperature is 72-92℃.

[0045] In some embodiments, the second time is 1-6h.

[0046] In a third aspect, the present disclosure provides a secondary battery cell comprising a positive electrode sheet, a negative electrode sheet, and the separator film of the first aspect of the present disclosure, the separator film being disposed between the positive electrode sheet and the negative electrode sheet.

[0047] In a fourth aspect, the present disclosure provides a battery device comprising a plurality of the secondary battery cell of the third aspect of the present disclosure.

[0048] In a fifth aspect, the present disclosure provides an electric device comprising the secondary battery cell of the third aspect of the present disclosure or the battery device of the fourth aspect of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings needed to be used in the embodiments of the present disclosure will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0050] FIG. 1 shows a schematic diagram of a secondary battery cell according to some embodiments of the present disclosure.

[0051] FIG. 2 shows a schematic diagram of an electric device according to some embodiments of the present disclosure.

[0052] FIG. 3 shows a scanning electron microscope (SEM) image of a separator film according to the present disclosure. DETAILED DESCRIPTION

[0053] Hereinafter, embodiments of the separator film and the method for manufacturing the same, the secondary battery cell, the battery device, and the power using device of the present disclosure are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0054] The ranges disclosed by the present disclosure are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present disclosure, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing the arbitrary real number combinations between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present disclosure.

[0056] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present disclosure.

[0057] If not otherwise specified, all steps of the present disclosure can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0058] If not otherwise specified, in the present disclosure, the terms "first", "second", etc. are used to distinguish different objects, rather than to describe a specific sequence or primary and secondary relationship.

[0059] In the present disclosure, the terms "a plurality of" and "a plurality of" refer to two or more.

[0060] In the description of the embodiments of the present disclosure, if not otherwise specified, the first feature is "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature can be "above", "over" and "on" the second feature, which can be that the first feature is directly above or obliquely above the second feature, or only means that the horizontal height of the first feature is higher than that of the second feature. The first feature can be "below", "under" and "under" the second feature, which can be that the first feature is directly below or obliquely below the second feature, or only means that the horizontal height of the first feature is less than that of the second feature.

[0061] Unless otherwise specified, the test temperature of each parameter mentioned in the present disclosure is 25℃.

[0062] The secondary battery cell mentioned in the embodiments of the present disclosure can realize the function of charging and discharging independently, and can continue to be used by activating the active material through charging after discharging. The secondary battery cell can be in the shape of a cylinder, a cuboid or other shapes, which are not limited in the embodiments of the present disclosure. As shown in FIG. 1, the secondary battery cell 5 is a cuboid structure as an example.

[0063] The secondary battery cell provided by the embodiments of the present disclosure can include but is not limited to lithium battery cells, sodium battery cells, such as lithium ion battery cells, sodium ion battery cells, lithium metal battery cells, sodium metal battery cells, etc.

[0064] Embodiments of the present disclosure provide a secondary battery cell including an electrode assembly. The electrode assembly can be in a jelly-roll structure or in a stacked structure, and the present disclosure is not limited in this regard. The secondary battery cell further includes an outer package that can be used to encapsulate the electrode assembly. The outer package can be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The outer package can also be a soft package, such as a pouch-type soft package. The soft package can be made of plastic, such as one or more of an aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0065] A battery apparatus as referred to in embodiments of the present disclosure can include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly can include a plurality of secondary battery cells connected in series, in parallel, or in a mixed connection through a busbar component.

[0066] In some embodiments, a battery cell assembly is generally formed by arranging a plurality of secondary battery cells.

[0067] As an example, a battery cell assembly can be a battery module formed by arranging and fixing a plurality of secondary battery cells into one independent module. As an example, a battery module can be formed by bundling a plurality of secondary battery cells with a cable tie.

[0068] In some embodiments, a battery apparatus can be a battery pack including a case and one or more battery cell assemblies housed in the case.

[0069] As an example, a battery cell assembly can be a battery module, and the battery cell assembly can be housed in the case by fixing the battery module in the case.

[0070] As an example, a battery cell assembly can also be housed in the case by directly fixing a plurality of secondary battery cells in the case.

[0071] As an example, the case can include a first case and a second case. The first case and the second case are coupled so that an enclosed space is formed inside the case to receive the battery cell assembly. Here, enclosed means covered or closed, and can be sealed or unsealed. The first case can be a top cover or a bottom plate.

[0072] As an example, the case can include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively coupled to the frame so that an enclosed space is formed inside the case to receive the battery cell assembly.

[0073] In some embodiments, the box can be part of a chassis structure of a vehicle. For example, portions of the box can become at least part of a floor of the vehicle, or portions of the box can become at least part of cross members and longitudinal members of the vehicle.

[0074] The technical solutions described in the embodiments of the present disclosure are applicable to various electric devices using secondary battery cells and battery devices, such as, but not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as 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. The secondary battery cells and battery devices are used to store or provide electric energy.

[0075] FIG. 2 is a schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0076] In the context of the present disclosure, the cross-linked styrene-based organic particles mainly play a role in improving the heat resistance of the porous coating of the separator film, and almost have no adhesion.

[0077] The separator film is an important component for supporting the secondary battery cell to complete the electrochemical process of charging and discharging. Commonly used separator films are mostly polyolefin films, but the heat resistance of the polyolefin film is poor, which is easy to soften or melt at high temperature, thereby causing a short circuit of the secondary battery cell. In order to improve the heat resistance of the separator film, a porous coating layer is usually coated on the separator film to improve the heat resistance of the separator film. Inorganic particles such as boehmite and aluminum oxide are commonly used heat-resistant fillers, but the density of such heat-resistant fillers is large, and the mass is large under the same packing volume, thereby affecting the energy density of the secondary battery cell.

[0078] Based on this, the embodiments of the present disclosure provide a separator film used in a secondary battery cell, which can make the secondary battery cell have high mass energy density and high reliability.

[0079] The separator film of the present disclosure comprises a porous base film and a porous coating layer located on at least one side of the porous base film, the porous coating layer comprises cross-linked styrene-based organic particles and fibrous material, and at least part of the cross-linked styrene-based organic particles are located between the fibrous material.

[0080] The porous base film and the porous coating layer both have a pore structure, so that the separator film has good air permeability and facilitates the passage of ions.

[0081] The cross-linked styrene-based organic particles and the fibrous material have small density, so that the secondary battery cell using them has higher mass energy density.

[0082] The crosslinked styrene-based organic particles alone do not have excellent heat resistance at high temperatures; the fibrous material has the characteristics of high strength, high heat resistance, and low heat shrinkage, but has a small diameter, and when used alone and in a separator film, there can be a problem of reducing the gas permeability of the separator film. The porous coating of the separator film of the present disclosure includes a mixture of crosslinked styrene-based organic particles and a fibrous material, and after the introduction of the fibrous material, the crosslinked styrene-based organic particles can be connected in series, improving the structural properties and heat resistance of the entire porous coating, reducing the heat shrinkage of the entire separator film, and improving the reliability of the secondary battery cell. In addition, the porous coating of the separator film of the present disclosure includes a mixture of crosslinked styrene-based organic particles and a fibrous material, and thus can also reduce the problem of clogging the pores and the problem of significantly reducing the gas permeability of the separator film that can occur when the fibrous material is used alone.

[0083] Therefore, the separator film of the present disclosure can allow the secondary battery cell to have both high mass energy density and high reliability.

[0084] The crosslinked styrene-based organic particles of the present disclosure are difficult to dissolve in water and organic solvents such as tetrahydrofuran (THF), dichloromethane (DCM), dimethylformamide (DMF), trichlorobenzene (TCB), chloroform at 25°C, i.e., are insoluble in the mobile phase for gel permeation chromatography testing, and the molecular weight of the crosslinked styrene-based organic particles cannot be tested by gel permeation chromatography.

[0085] In some embodiments, the true density of the crosslinked styrene-based organic particles can be 1.0 g / cm 3 -1.4 g / cm 3 .

[0086] Currently, the true density of inorganic particles such as boehmite and alumina is generally 2.5 g / cm 3 -3.5 g / cm 3 The true density of the crosslinked styrene-based organic particles of the present disclosure is small, and thus the secondary battery cell using the separator film of the present disclosure can have a higher mass energy density.

[0087] In some embodiments, the glass transition temperature T g110℃-165℃, for example, it can be 110℃, 111℃, 112℃, 113℃, 114℃, 115℃, 116℃, 117℃, 118℃, 119℃, 120℃, 121℃, 122℃, 123℃, 124℃, 125℃, 126℃, 127℃, 128℃, 129℃, 130℃, 131℃, 132℃, 133℃, 134℃, 135℃, 136℃, 137℃, 138℃, 139℃, 140℃, 141℃, 142℃, 143℃, 144℃, 145℃, 146℃, 147℃, 148℃, 149℃, 150℃, 151℃, 152℃, 153℃, 154℃, 155℃, 156℃, 157℃, 158℃, 159℃, 160℃, 161℃, 162℃, 163℃, 164℃, 165℃, or a range consisting of any of the above values.

[0088] At present, the glass transition temperature T g of the non-crosslinked styrene-based organic particles and the commercially available crosslinked styrene-based organic particles is relatively small, usually below 100℃. The glass transition temperature T g of the crosslinked styrene-based organic particles of the present disclosure is 110℃-165℃, which has relatively high thermal stability. By using crosslinked styrene-based organic particles with high glass transition temperature T g in the isolation film, the overall thermal shrinkage of the isolation film can be improved, the heat resistance of the isolation film can be improved, and the reliability of the secondary battery cell can be improved.

[0089] In addition, during the charging and discharging process of the secondary battery cell, due to abnormal environmental factors, internal factors, etc., the temperature of the secondary battery cell abnormally rises to the glass transition temperature T g of the crosslinked styrene-based organic particles, the crosslinked styrene-based organic particles become soft at this time, at this time, under the dual action of the electrode assembly expansion force and high temperature, the crosslinked styrene-based organic particles in the porous coating will be deformed and flattened, which can to some extent hinder the ion transmission between the positive and negative electrodes, thereby reducing the risk of thermal runaway of the secondary battery cell.

[0090] Optionally, the glass transition temperature T g of the crosslinked styrene-based organic particles can be 117℃-165℃, 119℃-165℃, 120℃-165℃, 124℃-165℃, 126℃-165℃, 130℃-165℃, 134℃-165℃, 140℃-165℃, 144℃-165℃.

[0091] The glass transition temperature T gThe test can be performed as follows: take an appropriate amount of sample (for example, 5 mg-15 mg) and place it in a differential scanning calorimeter (DSC) crucible, shake it flat, and cover it with a crucible cover; parameter settings: nitrogen atmosphere, purge gas 60 mL / min, protective gas 20 mL / min; program settings: temperature increase from 25°C to 200°C at a rate of 10°C / min, hold for 5 min to eliminate thermal history, temperature decrease from 200°C to -40°C at a rate of 10°C / min, and temperature increase from -40°C to 300°C at a rate of 10°C / min. The glass transition temperature Tg of the organic particles can be obtained from the DSC curve. g .

[0092] In some embodiments, the crosslinked styrene-based organic particles have no melting point.

[0093] The crosslinked styrene-based organic particles of the present disclosure have no melting point, indicating that they have good heat resistance and thermal stability, and thus can better resist thermal shrinkage of the isolation film, improve the heat resistance of the isolation film, and improve the reliability of the secondary battery cell.

[0094] The melting point can be tested as follows: take an appropriate amount of sample (for example, 5 mg-15 mg) and place it in a differential scanning calorimeter (DSC) crucible, shake it flat, and cover it with a crucible cover; parameter settings: nitrogen atmosphere, purge gas 60 mL / min, protective gas 20 mL / min; program settings: temperature increase from 25°C to 200°C at a rate of 10°C / min, hold for 5 min to eliminate thermal history, temperature decrease from 200°C to -40°C at a rate of 10°C / min, and temperature increase from -40°C to 300°C at a rate of 10°C / min. Whether the organic particles have a melting point below 300°C can be determined from the DSC curve. The crosslinked styrene-based organic particles have no melting point, meaning that the DSC curve of the crosslinked styrene-based organic particles has no melting peak.

[0095] In some embodiments, the crosslinked styrene-based organic particles have no oxidation peak in the cyclic voltammetry curve of the first cycle in the voltage range of 2.5V to 4.4V.

[0096] The crosslinked styrene-based organic particles have no oxidation peak in the cyclic voltammetry curve of the first cycle in the voltage range of 2.5V to 4.4V, indicating that the crosslinked styrene-based organic particles are stable in the voltage range of 2.5V to 4.4V and have good electrochemical stability, and can be applied in high-voltage secondary battery cells to improve the working voltage and energy density of the secondary battery cells.

[0097] The oxidation peak potential of the crosslinked styrene-based organic particles can be tested by the following method: the organic particles, the binder polymethyl methacrylate, and the conductive agent conductive carbon black are dissolved in water to form a slurry at a solid content mass ratio of 64:7:29, the slurry is coated on an aluminum foil as a positive electrode, a lithium foil is used as a negative electrode, and a button cell is assembled; the button cell is subjected to cyclic voltammetry (CV) test at a scanning rate of 0.10 mV / s, a voltage range of 2.50 V-5.00 V, and 3 cycles, and the voltage corresponding to the peak point of the first cycle of the cyclic voltammetry curve is taken as the oxidation peak potential. The electrolyte salt of the electrolyte used for testing is LiPF6, and the concentration is 1 mol / L. The solvent of the electrolyte is obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (EMC) at a volume ratio of 3:7.

[0098] In some embodiments, the swelling degree of the crosslinked styrene-based organic particles in a mixed solvent composed of ethylene carbonate and methyl ethyl carbonate at a volume ratio of 3:7 and soaked at 60°C for 7 days can be less than or equal to 3%.

[0099] The crosslinked styrene-based organic particles have a small swelling degree in an organic solvent, and have high structural stability during long-term use of the secondary battery monomer, thereby improving the problem of the decrease in the air permeability of the separator during use.

[0100] The swelling degree of the crosslinked styrene-based organic particles can be tested by the following method: an appropriate amount of sample (for example, about 1 g) is weighed as m1, placed in a semi-permeable membrane sample bag, sealed, and the sample bag can permeate the solvent but cannot permeate the sample; the sample bag is soaked in an appropriate amount of solvent (for example, about 50 g) at 60°C for 7 days, then the sample bag is taken out, the sample is taken out from the sample bag, the excess solvent is wiped off, and the mass of the sample is weighed again as m2; the swelling degree is (m2-m1) / m1x100%. The solvent is a mixed solvent obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (EMC) at a volume ratio of 3:7.

[0101] In some embodiments, the dissolution rate of the crosslinked styrene-based organic particles in a mixed solvent composed of ethylene carbonate and methyl ethyl carbonate at a volume ratio of 3:7 and soaked at 60°C for 7 days can be less than or equal to 3%.

[0102] The crosslinked styrene-based organic particles have a small dissolution rate in an organic solvent, and have high structural stability during long-term use of the secondary battery monomer, and have high chemical stability in the electrolyte, thereby enabling the secondary battery monomer to have long cycle stability.

[0103] The dissolution rate of the crosslinked styrene-based organic particles can be tested according to the following method: take an appropriate amount of sample (for example, about 1 g), and record the mass as m1, place it in a semi-permeable membrane sample bag, seal it, record the total mass of the sample bag m2, the sample bag can permeate the solvent, but cannot permeate the sample; immerse the sample bag in an appropriate amount of solvent (for example, about 50 g) at 60°C for 7 days, then take out the sample bag, drain, dry, and weigh the total mass of the sample bag again m3; dissolution rate = (m2-m3) / m1x100%. The solvent is a mixed solvent obtained by mixing ethylene carbonate (EC) and methyl ethyl carbonate (EMC) at a volume ratio of 3:7.

[0104] In some embodiments, the crosslinked styrene-based organic particles can have first polar groups.

[0105] Optionally, the first polar groups can include one or more of ester groups, carboxyl groups, carboxylate groups, hydroxyl groups, cyano groups, amide groups.

[0106] The crosslinked styrene-based organic particles having the first polar groups, when applied to the porous coating layer of the separator film, can form stronger interactions with the binder in the porous coating layer, such as hydrogen bonds or ionic bonds, etc., so that the adhesion between the porous coating layer and the porous base film is stronger, thereby improving the overall structural integrity of the separator film, and further improving the heat resistance of the separator film. In addition, these first polar groups have good electrolyte affinity, which can reduce the surface tension of the crosslinked styrene-based organic particles and improve the electrolyte wettability of the crosslinked styrene-based organic particles, thereby also reducing the internal resistance of the secondary battery cell and improving the cycle performance of the secondary battery cell.

[0107] In some embodiments, the crosslinked styrene-based organic particles include styrene or styrene derivative structural units and crosslinking structural units.

[0108] The crosslinking structural units of the crosslinked styrene-based organic particles refer to structural units used to connect the styrene or styrene derivative structural units.

[0109] Optionally, the styrene or styrene derivative structural units can include one or more of styrene structural units, 1-methyl-1-styrene structural units, 4-methylstyrene structural units, 2-methylstyrene structural units, 2,4-dimethylstyrene structural units, 2,5-dimethylstyrene structural units.

[0110] Optionally, the cross-linking structural unit can include one or more of a divinylbenzene structural unit, an ethylene glycol dimethacrylate 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-methylenebisacrylamide structural unit, an N,N'-vinylbisacrylamide structural unit, a 1,3,5-triacryloylhexahydro-1,3,5-triazine structural unit, a trisallyl isocyanurate structural unit.

[0111] In some embodiments, the volume distribution particle size Dv50 of the cross-linked styrene-based organic particles can be 88 nm-300 nm, for example, can be 88 nm, 95 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, or a range consisting of any of the above values.

[0112] The volume distribution particle size Dv50 of the cross-linked styrene-based organic particles in the above range is conducive to the porous coating of the isolation film having good heat resistance and air permeability.

[0113] Dv50 represents the particle size corresponding to the cumulative volume distribution percentage reaching 50%, which can be tested by a laser particle size analyzer according to GB / T 19077-2016. During the test, 1 g of the sample to be tested is added to a clean small beaker, 20 ml of deionized water is added, and ultrasonic treatment is performed at 53 KHz / 120 W for 5 min to ensure that the sample is completely dispersed. After the light path system is cleaned, the background is automatically tested. The solution to be tested after ultrasonic treatment is stirred to make it uniformly dispersed, and then placed in the sample cell as required, and the particle size is measured. The testing instrument can be a MasterSizer 3000 laser particle size analyzer.

[0114] In some embodiments, the diameter of the fibrous material can range from 10 nm to 200 nm.

[0115] Optionally, the diameter of the fibrous material can range from 10 nm to 160 nm, 12 nm to 160 nm, 14 nm to 160 nm, 16 nm to 160 nm, 18 nm to 160 nm, 20 nm to 160 nm, 10 nm to 120 nm, 12 nm to 120 nm, 14 nm to 120 nm, 16 nm to 120 nm, 18 nm to 120 nm, 20 nm to 120 nm, 10 nm to 100 nm, 12 nm to 100 nm, 14 nm to 100 nm, 16 nm to 100 nm, 18 nm to 100 nm, 20 nm to 100 nm, 10 nm to 80 nm, 12 nm to 80 nm, 14 nm to 80 nm, 16 nm to 80 nm, 18 nm to 80 nm, 20 nm to 80 nm, 14 nm to 50 nm, 16 nm to 50 nm, 18 nm to 50 nm, 20 nm to 50 nm.

[0116] In some embodiments, the length of the fibrous material can range from 0.15 pm to 30 pm.

[0117] Optionally, the length of the fibrous material can range from 0.3 pm to 20 pm, 0.4 pm to 20 pm, 0.5 pm to 20 pm, 0.6 pm to 20 pm, 0.8 pm to 20 pm, 0.3 pm to 15 pm, 0.4 pm to 15 pm, 0.5 pm to 15 pm, 0.6 pm to 15 pm, 0.8 pm to 15 pm, 0.3 pm to 10 pm, 0.4 pm to 10 pm, 0.5 pm to 10 pm, 0.6 pm to 10 pm, 0.8 pm to 10 pm, 0.3 pm to 8 pm, 0.4 pm to 8 pm, 0.5 pm to 8 pm, 0.6 pm to 8 pm, 0.8 pm to 8 pm, 0.3 pm to 5 pm, 0.4 pm to 5 pm, 0.5 pm to 5 pm, 0.6 pm to 5 pm, 0.8 pm to 5 pm, 0.3 pm to 4 pm, 0.4 pm to 4 pm, 0.5 pm to 4 pm, 0.6 pm to 4 pm, 0.8 pm to 4 pm.

[0118] The length of the fibrous material can range from 0.3 pm to 20 pm, 0.4 pm to 20 pm, 0.5 pm to 20 pm, 0.6 pm to 20 pm, 0.8 pm to 20 pm, 0.3 pm to 15 pm, 0.4 pm to 15 pm, 0.5 pm to 15 pm, 0.6 pm to 15 pm, 0.8 pm to 15 pm, 0.3 pm to 10 pm, 0.4 pm to 10 pm, 0.5 pm to 10 pm, 0.6 pm to 10 pm, 0.8 pm to 10 pm, 0.3 pm to 8 pm, 0.4 pm to 8 pm, 0.5 pm to 8 pm, 0.6 pm to 8 pm, 0.8 pm to 8 pm, 0.3 pm to 5 pm, 0.4 pm to 5 pm, 0.5 pm to 5 pm, 0.6 pm to 5 pm, 0.8 pm to 5 pm, 0.3 pm to 4 pm, 0.4 pm to 4 pm, 0.5 pm to 4 pm, 0.6 pm to 4 pm, 0.8 pm to 4 pm.

[0119] In some embodiments, the fibrous material can include one or more of sugar-based fibers, protein-based fibers, polymeric fibers, inorganic fibers.

[0120] In some embodiments, the fibrous material can include one or more of alginic acid and its derivative fibers, nanocellulose and its derivative fibers, chitosan and its derivative fibers, chitin and its derivative fibers, plant cellulose, silk fibroin fibers, spider silk fibroin fibers, corn protein fibers, soy protein fibers, keratin fibers, wool fibers, cashmere fibers, aramid fibers, polyester fibers, polyamide fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, polyethylene fibers, ultra-high molecular weight polyethylene fibers, polypropylene fibers, polytetrafluoroethylene fibers, polyvinylidene fluoride fibers, polyurethane fibers, acetate fibers, polycaprolactone fibers, polylactic acid fibers, polyethersulfone fibers, acrylic fibers, acrylic polymer fibers, polymethyl methacrylate fibers, poly-2-hydroxyethyl methacrylate fibers, polyethylene terephthalate fibers, polyethylene terephthalate fibers, para-phenylenediamine terephthalic acid fibers, glass fibers, asbestos fibers, silica fibers.

[0121] Optionally, the alginic acid and its derivative fibers can include one or more of alginic acid fibers, alginate fibers, and other chemically modified alginic acid derivative fibers.

[0122] Optionally, the nanocellulose and its derivative fibers can include one or more of nanocellulose fibers, carboxymethyl cellulose fibers, carboxyethyl cellulose fibers, sulfonated cellulose fibers, hydroxymethyl cellulose fibers, hydroxyethyl cellulose fibers, hydroxypropyl cellulose fibers, oxidized cellulose fibers, and other chemically modified cellulose derivative fibers.

[0123] Optionally, the chitosan and its derivative fibers can include one or more of chitosan fibers, carboxymethyl chitosan fibers, carboxyethyl chitosan fibers, hydroxypropyl chitosan fibers, hydroxyethyl chitosan fibers, sulfonated chitosan fibers, succinyl chitosan fibers, acetylated chitosan fibers, propionyl chitosan fibers, butyryl chitosan fibers, chitin fibers, and other chemically modified chitosan derivative fibers.

[0124] Optionally, the chitin and its derivative fibers can include one or more of chitin fibers, carboxymethyl chitin fibers, carboxyethyl chitin fibers, sulfonated chitin fibers, acetylated chitin fibers, and other chemically modified chitin derivative fibers.

[0125] Plant cellulose refers to cellulose made from plants that are rich in cellulose. Optionally, the plant cellulose can include one or more of bamboo cellulose, cotton cellulose, lignocellulose, herbaceous plant cellulose, sugar cane bagasse cellulose, flax cellulose.

[0126] In some embodiments, the fibrous material can have a second polar group.

[0127] Optionally, the second polar group can include one or more of a hydroxyl group, a carboxyl group, an ester group, an amide group, a cyano group, an amine group, an aldehyde group, a sulfonic acid group, a boronic acid group, a phosphoric acid group.

[0128] The fibrous material has the second polar group, which can form stronger interactions with the binder in the porous coating layer of the separator film, such as hydrogen bonds or ionic bonds, etc., so that the adhesion between the porous coating layer and the porous base film is stronger, thereby improving the overall structural integrity of the separator film, and further improving the heat resistance of the separator film.

[0129] In some embodiments, the mass content of the cross-linked styrene-based organic particles in the porous coating layer can be greater than or equal to 55% based on the total mass of the porous coating layer. Optionally, the mass content of the cross-linked styrene-based organic particles in the porous coating layer can be greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75%, greater than or equal to 80%.

[0130] In some embodiments, the mass content of the fibrous material in the porous coating layer can be 0.5%-30%, such as 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or a range consisting of any of the above values, based on the total mass of the porous coating layer.

[0131] Optionally, the mass content of the fibrous material in the porous coating layer can be 0.5%-20%, 0.5%-15%, 0.5%-10%, 0.5%-8%, 0.5%-6%, 0.8%-20%, 0.8%-15%, 0.8%-10%, 0.8%-8%, 0.8%-6%, 1%-20%, 1%-15%, 1%-10%, 1%-8%, 1%-6%.

[0132] The mass content of the fibrous material in the above range can make the separator film have both good heat resistance and air permeability, thereby making the secondary battery cell have high reliability and good cycle performance.

[0133] In some embodiments, the porous coating layer includes a binder, which can include but is not limited to one or more of a polyacrylate binder, a nitrile rubber binder, polyacrylic acid, polymethacrylic acid, sodium polyacrylate, polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0134] In some embodiments, the mass content of the binder in the porous coating can be 0.5% to 10%, for example, can be 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a range consisting of any of the aforementioned values, based on the total mass of the porous coating. Alternatively, the mass content of the binder in the porous coating can be 1% to 8%.

[0135] In some embodiments, the porous coating can further include a dispersant, for example, can include but is not limited to one or more of alkylphenol polyoxyethylene ether and the like, polyacrylic dispersant, cellulose dispersant. As an example, the dispersant can include but is not limited to one or more of sodium carboxymethyl cellulose, sodium polyacrylate, ammonium polyacrylate.

[0136] In some embodiments, the separator film can further include polymer binder particles.

[0137] The "polymer binder particles" play a role in improving the adhesion of the separator film to the pole piece in the porous coating of the separator film, and have substantially no high-temperature resistance.

[0138] In some embodiments, the polymer binder particles can be embedded in the crosslinked styrene-based organic particles and the fibrous material and form protrusions on the surface of the porous coating.

[0139] In other embodiments, the porous coating of the separator film includes a heat-resistant layer disposed on the porous base film and a bonding layer disposed on at least a portion of the surface of the heat-resistant layer away from the porous base film, the crosslinked styrene-based organic particles are disposed in the heat-resistant layer, and the polymer binder particles are disposed in the bonding layer.

[0140] In yet other embodiments, the porous coating of the separator film includes a heat-resistant layer disposed on one side of the porous base film and a bonding layer disposed on at least a portion of the surface of the other side of the porous base film, the crosslinked styrene-based organic particles are disposed in the heat-resistant layer, and the polymer binder particles are disposed in the bonding layer.

[0141] In some embodiments, the average particle size of the polymer binder particles can be 6 μm to 18 μm.

[0142] In some embodiments, the polymer binder particles can include a vinylidene fluoride-based polymer particle, for example, a polyvinylidene fluoride (PVDF) particle and / or a copolymer particle of a vinylidene fluoride monomer and a comonomer.

[0143] The comonomer can include at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate monomer, an acrylic monomer, and a fluorine ether monomer.

[0144] Optionally, the comonomer can include at least one of 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-dioxolane), and perfluoro(2,2-dimethyl-1,3-dioxolane).

[0145] In some embodiments, the thickness of the porous coating layer can be 0.4 μm-5 μm. The thickness of the porous coating layer refers to the thickness of the porous coating layer on one side of the porous base film. Optionally, the thickness of the porous coating layer 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, 0.8 μm-2 μm.

[0146] In some embodiments, the porous base film can include a film or nonwoven web selected from any one or at least two of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyether sulfone, polyphenylene ether, cyclic olefin copolymer, polyphenylene sulfide, polyvinyl naphthalene.

[0147] The porous base film can be a single-layer film or a multi-layer composite film. When the porous base film is a multi-layer composite film, the materials of the layers can be the same or different.

[0148] In some embodiments, the thickness of the porous base film can be 4 μm-12 μm, optionally 4 μm-9 μm.

[0149] In some embodiments, the porosity of the porous base film can be 25%-60%, optionally 28%-50%.

[0150] In some embodiments, the thickness of the separator film can be 5 μm-14 μm, optionally 5 μm-12 μm, 6 μm-12 μm. This is conducive to improving the energy density of the secondary battery cell.

[0151] It should be noted that the above-mentioned parameters of the porous coating layer of the separator film are the parameters of the porous coating layer on one side of the porous base film. When the porous coating layer is arranged on both sides of the porous base film, the parameters of the porous coating layer on any one side meet the present disclosure, and are considered to fall within the protection scope of the present disclosure.

[0152] The present disclosure also provides a method for preparing a separator film, which can prepare the separator film provided by the present disclosure.

[0153] The method for preparing the separation film includes the following steps: providing a porous base film; providing a slurry including cross-linked styrene-based organic particles, fibrous material, and binder; and coating the slurry on at least one side of the porous base film to obtain the separation film after drying.

[0154] In some embodiments, the slurry can further include polymer binder particles, and the polymer binder particles are embedded in the cross-linked styrene-based organic particles and the fibrous material and form protrusions on the surface of the porous coating after drying of the slurry.

[0155] In some embodiments, the method for preparing the separation film can include the following steps: coating a heat-resistant layer slurry including cross-linked styrene-based organic particles and binder on at least one side of the porous base film to form a heat-resistant layer after drying; and coating a bonding layer slurry including polymer binder particles and binder on at least a part of the surface of the heat-resistant layer to obtain the separation film after drying.

[0156] In some embodiments, the method for preparing the separation film can include the following steps: coating a heat-resistant slurry including cross-linked styrene-based organic particles and binder on one side of the porous base film, and coating a bonding layer slurry including polymer binder particles and binder on at least a part of the surface of the other side of the porous base film to obtain the separation film after drying.

[0157] In some embodiments, the solvent of the slurry can be water, for example, deionized water.

[0158] In some embodiments, the slurry can further include other components, for example, can further include dispersants and / or wetting agents, etc.

[0159] In some embodiments, the method for providing the cross-linked styrene-based organic particles can include the following steps: providing a pre-emulsion including monomers, cross-linking agent, emulsifier, initiator, and water, the monomers including one or more of styrene and derivatives thereof; and performing emulsion polymerization of the pre-emulsion under the conditions of heating, inert gas protection, and stirring to obtain the cross-linked styrene-based organic particles.

[0160] In some embodiments, the monomers can include one or more of styrene, 1-methyl-1-styrene, 4-methylstyrene, 2-methylstyrene, 2,4-dimethylstyrene, and 2,5-dimethylstyrene.

[0161] The cross-linking agent forms cross-linking structural units of the cross-linked styrene-based organic particles after polymerization with the monomers.

[0162] In some embodiments, the crosslinking agent can 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, trisallyl isocyanurate.

[0163] In some embodiments, the mass fraction of the crosslinking agent can be 5%-40%, for example, can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or a range consisting of any of the above values, based on the total mass of the monomer and the crosslinking agent being 100%.

[0164] A high content of the crosslinking agent can make the obtained crosslinked styrene-based organic particles have better heat resistance.

[0165] Alternatively, the mass fraction of the crosslinking agent can be 7%-40%, 9%-40%, 11%-40%, 13%-40%, 15%-40%, 7%-35%, 9%-35%, 11%-35%, 13%-35%, 15%-35%, 7%-31%, 9%-31%, 11%-31%, 13%-31%, 15%-31%.

[0166] In some embodiments, the emulsifier can include one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl alcohol, polyoxyethylene ether emulsifier.

[0167] Alternatively, the polyoxyethylene ether emulsifier can include OP-type emulsifiers, such as OP-4, OP-7, OP-10, OP-15, OP-20, and the like.

[0168] In some embodiments, the mass fraction of the emulsifier can be 0.25%-5%, based on the total mass of the monomer and the crosslinking agent being 100%.

[0169] In some embodiments, the initiator can include, but is not limited to, one or more of sodium persulfate, potassium persulfate, ammonium persulfate, sodium sulfite, sodium bisulfite, azobisdimethylaminoformamide hydrochloride, azobisdimethylaminoimidazole hydrochloride, azobisdiisopropylimidazole.

[0170] In some embodiments, the pre-emulsion can further include a functional monomer, the functional monomer having a first polar group.

[0171] Optionally, the first polar group can include one or more of an ester group, a carboxyl group, a carboxylate salt, a hydroxyl group, a cyano group, an amide group.

[0172] In some embodiments, the functional monomer can include one or more of an organic small molecule monomer having an unsaturated bond, a polymer, at least one of the organic small molecule monomer having an unsaturated bond and the polymer having the first polar group.

[0173] Optionally, the organic small molecule monomer having an unsaturated bond can include one or more of a (meth)acrylic acid and derivatives thereof, a (meth)acrylate and derivatives thereof, a (meth)acrylate salt and derivatives thereof, an acrylamide and derivatives thereof, an acrylonitrile and derivatives thereof, a maleic anhydride and derivatives thereof.

[0174] Optionally, the polymer can include one or more of a polyvinyl alcohol, a polyvinylpyrrolidone, a poly(meth)acrylic acid and alkali metal salts thereof, a methoxypolyethylene glycol acrylate, a polyethylene glycol acrylate, a polypropylene glycol acrylate, a polyethylene glycol diacrylate, a polyethylene glycol methyl ether acrylate, a polyethylene glycol ethyl ether acrylate, a methoxypolyethylene glycol methacrylate, a polyethylene glycol methacrylate, a polypropylene glycol methacrylate, a polyethylene glycol dimethacrylate, a polyethylene glycol methyl ether methacrylate, and respective derivatives thereof.

[0175] Optionally, the molecular weight of the polymer can be 5000 or less.

[0176] In some embodiments, the mass fraction of the functional monomer can be 0.01%-10%, based on 100% of the total mass of the monomer and the crosslinking agent.

[0177] In some embodiments, the emulsion polymerization reaction can include the following steps: dropping the pre-emulsion into a reactor containing water under the conditions of a first temperature, inert gas protection and stirring, and after a first time, warming to a second temperature for a second time to obtain crosslinked styrene-based organic particles.

[0178] In some embodiments, the first temperature can be 55°C-70°C.

[0179] In some embodiments, the first time can be 3h-6h.

[0180] In some embodiments, the second temperature can be 72-92℃, for example, can be 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, or a range consisting of any of the aforementioned values.

[0181] In some embodiments, the second time can be 1-6h, for example, can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h or a range consisting of any of the aforementioned values.

[0182] The emulsion polymerization reaction is carried out under the protection of inert gas. In some embodiments, the inert gas can include one or more of nitrogen, argon, helium.

[0183] The embodiments of the present disclosure also provide a secondary battery cell. The secondary battery cell includes the separator film provided by the present disclosure, or the separator film prepared by the method of the present disclosure. Thus, the secondary battery cell can have both high quality energy density and high reliability.

[0184] The secondary battery cell also includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, and the separator film is arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet, the separator film, and the negative electrode sheet can form an electrode assembly through a rolling process and / or a stacking process.

[0185] The secondary battery cell provided by the present disclosure can include, but is not limited to, a lithium battery cell, a sodium battery cell, etc. The composition of the positive electrode sheet, the negative electrode sheet, and the electrolyte will vary depending on the type of the secondary battery cell.

[0186] [Positive electrode sheet]

[0187] In some embodiments, the positive electrode sheet can include a positive current collector and a positive film layer arranged on at least one surface of the positive current collector and including a positive active material. For example, the positive current collector has two surfaces opposite in the thickness direction of itself, and the positive film layer is arranged on any one or both of the two opposite surfaces of the positive current collector.

[0188] LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi0.8Co0.2O2, LiNi0.8Mn0.2O2, LiNi0.5Co0.2Mn0.3O2, LiNi0.6Co0.2Mn0.2O2, LiNi0.5Co0.3Mn0.2O2, LiNi0.8Al0.2O2, LiFePO4, LiMnPO4, and modified compounds of each of the foregoing, and the like. In some embodiments, to further enhance the energy density of the secondary battery cell, the positive active material can include one or more of lithium transition metal oxides of the general formula Li a Ni b Co c M d O e A f 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes one or more of N, F, S, and Cl.

[0189] LiCoO2, LiNiO2, LiMnO2, LiMn2O4, 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 O2, LiFePO4, LiMnPO4, and modified compounds of each of the foregoing, and the like.

[0190] The secondary battery cell will be accompanied by Li deintercalation and consumption during charging and discharging, and the molar content of Li is different when the secondary battery cell is discharged to different states. In the enumeration of the positive electrode active material in the present disclosure, the molar content of Li is the initial state of the material, i.e. the state before feeding, and the positive electrode active material is applied to the secondary battery cell. After charging and discharging cycle, the molar content of Li will change. In the enumeration of the positive electrode active material in the present disclosure, the molar content of O is only the theoretical state value, and the lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will also appear to float.

[0191] Taking a sodium battery cell as an example, the positive electrode active material can include but is not limited to one or more of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), prussian blue type materials. As an example, the positive electrode active material can include but is not limited to one or more of NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 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 type materials, and materials of the general formula X p M’ q (PO4) r O x Y 3-x . In the general formula X p M’ q (PO4) r O x Y 3-x , 0 < p < 4, 0 < q < 2, 1 < r < 3, 0 < x < 2, X includes but is not limited to one or more of H + , Li + , Na + , K + and NH4 + , M' is a transition metal cation, which can optionally include but is not limited to one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, which can optionally be one or more of F, Cl and Br.

[0192] The modified compounds of the positive electrode active materials of the above lithium battery cells and sodium battery cells can be doping modification and / or surface coating modification of the positive electrode active materials.

[0193] In some embodiments, the positive electrode film layer can further include a positive electrode conductive agent. As an example, the positive electrode conductive agent can include, but is not limited to, one or more of super-P, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0194] In some embodiments, the positive electrode film layer can further include a positive electrode binder. As an example, the positive electrode binder can include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic resin.

[0195] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. As an example of the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can include, but is not limited to, one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer can include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0196] The positive electrode film layer is generally formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold-pressing. The positive electrode slurry is generally formed by dispersing and uniformly stirring a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and any other components in a solvent. The solvent can be N-methyl pyrrolidone (NMP), but is not limited thereto.

[0197] [Negative electrode tab]

[0198] In some embodiments, the negative electrode tab can include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite in the thickness direction of itself, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0199] The negative electrode active material can employ a material known in the art that can be used for a secondary battery cell. As an example, the negative electrode active material can include, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate. The silicon-based material can include, but is not limited to, one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material can include, but is not limited to, one or more of elemental tin, tin oxide, and tin alloy material.

[0200] In some embodiments, the negative electrode film layer can further include a negative electrode conductive agent. As an example, the negative electrode conductive agent can include, but is not limited to, one or more of super P, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0201] In some embodiments, the negative electrode film layer can further include a negative electrode binder. As an example, the negative electrode binder can include, but is not limited to, one or more of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethylacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0202] In some embodiments, the negative electrode film layer can further include other auxiliary agents. As an example, the other auxiliary agents can include thickening agents, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0203] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0204] The negative electrode film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is generally formed by dispersing and uniformly stirring a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and other optional auxiliary agents in a solvent. The solvent can be N-methyl pyrrolidone (NMP) or deionized water, but is not limited thereto.

[0205] The negative electrode tab does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode tab further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) interposed between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector.

[0206] In some embodiments, the negative electrode tab can use a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, foamed carbon, or the like. When the foamed metal is used as the negative electrode tab, the surface of the foamed metal can not be provided with a negative electrode active material, and of course, can be provided with a negative electrode active material.

[0207] [Electrolyte]

[0208] The electrolyte functions to conduct ions between the positive electrode and the negative electrode.

[0209] In some embodiments, the electrolyte employs an electrolyte solution that includes an electrolyte salt and an organic solvent.

[0210] Taking a lithium battery cell as an example, the electrolyte salt can include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalato borate (LiDFOB), lithium bisoxalato borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalato phosphate (LiDFOP), and lithium tetrafluorooxalato phosphate (LiTFOP).

[0211] Taking a sodium battery cell as an example, the electrolyte salt can include, but is not limited to, one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bisfluorosulfonylimide (NaFSI), sodium bis-trifluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalato borate (NaDFOB), sodium bisoxalato borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalato phosphate (NaDFOP), and sodium tetrafluorooxalato phosphate (NaTFOP).

[0212] In some embodiments, the organic solvent can include, but is not limited to, one or more of 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), butylene 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, crown ether.

[0213] In some embodiments, the electrolyte can further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and an additive capable of improving certain performance of the secondary battery cell, such as an additive capable of improving overcharge performance, an additive capable of improving high-temperature performance, an additive capable of improving low-temperature performance, and the like.

[0214] Optionally, the additive can include one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), and vinyl sulfate (DTD).

[0215] Methods for preparing secondary battery cells are known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery cell. As an example, a positive electrode sheet, a separator, and a negative electrode sheet can be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly can be placed in an outer package, the electrolyte described above can be injected after drying, and the secondary battery cell can be obtained through processes such as vacuum packaging, standing, and formation.

[0216] Embodiments

[0217] The following examples further illustrate the present disclosure, which is not limited to the examples, as various modifications and equivalents will be apparent to one skilled in the art. Unless otherwise stated, all proportions, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used as received without further purification, and the instruments used in the examples are commercially available.

[0218] Example 1

[0219] A pre-emulsion was prepared by emulsifying 0.8 g of sodium dodecyl sulfate, 80 mg of sodium persulfate, 20 ml of deionized water, 34 g of styrene, and 6 g of divinylbenzene. 140 g of deionized water and 15 mg of sodium polyacrylate were added to a reactor, which was heated to 70°C. The pre-emulsion was added dropwise under nitrogen protection and stirring, and the reaction was carried out for 4 h. The temperature was then increased to 85°C for 1.5 h to complete the reaction, and a cross-linked styrene-based organic particle emulsion was obtained.

[0220] The above emulsion, nanocellulose fibers, a binder polymethyl methacrylate, and a dispersant sodium carboxymethyl cellulose were uniformly stirred in deionized water to obtain a porous coating slurry. The nanocellulose fibers had a length in the range of 0.2 μm-5 μm and a diameter in the range of 20 nm-50 nm. The solid content mass ratio of the cross-linked styrene-based organic particles, nanocellulose fibers, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 88:2:2:8.

[0221] A commercially available polyethylene microporous film having a thickness of 7 μm was used as the porous base film. The porous coating slurry was applied to both surfaces of the porous base film by microgravure coating, and then dried and slit to obtain the separator.

[0222] Example 2

[0223] A pre-emulsion was prepared by emulsifying 0.8 g of sodium dodecyl sulfate, 80 mg of sodium persulfate, 20 ml of deionized water, 34 g of styrene, and 6 g of divinylbenzene. 140 g of deionized water and 15 mg of sodium polyacrylate were added to a reactor, which was heated to 70°C. The pre-emulsion was added dropwise under nitrogen protection and stirring, and the reaction was carried out for 4 h. The temperature was then increased to 85°C for 1.5 h to obtain a cross-linked styrene-based organic particle emulsion.

[0224] The above emulsion, nanocellulose fibers, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were uniformly stirred in deionized water to obtain a porous coating slurry. The length of the nanocellulose fibers ranged from 0.2 μm to 5 μm, and the diameter ranged from 20 nm to 50 nm. The solid content mass ratio of the cross-linked styrene-based organic particles, nanocellulose fibers, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 86:4:2:8.

[0225] A commercially available polyethylene microporous film having a thickness of 7 μm was used as the porous base film. The porous coating slurry was applied to both surfaces of the porous base film by microgravure coating, and then dried and slit to obtain the separator.

[0226] Example 3

[0227] A pre-emulsion was prepared by emulsifying 0.8 g of sodium dodecyl sulfate, 80 mg of sodium persulfate, 20 ml of deionized water, 34 g of styrene, and 6 g of divinylbenzene. 140 g of deionized water and 15 mg of sodium polyacrylate were added to a reactor, which was heated to 70°C. The pre-emulsion was added dropwise under nitrogen protection and stirring, and the reaction was carried out for 4 h. The temperature was then increased to 85°C for 1.5 h to obtain a cross-linked styrene-based organic particle emulsion.

[0228] The above emulsion, nanocellulose fibers, binder polymethyl methacrylate, and dispersant sodium carboxymethyl cellulose were uniformly stirred in deionized water to obtain a porous coating slurry. The length of the nanocellulose fibers ranged from 0.2 μm to 5 μm, and the diameter ranged from 20 nm to 50 nm. The solid content mass ratio of the cross-linked styrene-based organic particles, nanocellulose fibers, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 86:4:2:8.

[0229] A commercially available polyethylene microporous film with a thickness of 7 μm was used as the porous base film. The porous coating slurry was coated on both surfaces of the porous base film by microgravure coating, and then dried and slit to obtain the separator.

[0230] Comparative Example 1

[0231] A pre-emulsion was prepared by emulsifying 0.8 g of sodium dodecyl sulfate, 80 mg of sodium persulfate, 20 ml of deionized water, 39.6 g of styrene, and 0.4 g of divinylbenzene. 140 g of deionized water and 15 mg of sodium polyacrylate were added to a reactor, which was heated to 70°C. The pre-emulsion was added dropwise under nitrogen protection and stirring conditions. After 4 h of reaction, the temperature was increased to 85°C for 1.5 h of curing reaction to obtain a cross-linked styrene-based organic particle emulsion.

[0232] The above emulsion, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate were uniformly mixed in deionized water to obtain a porous coating slurry. The solid content mass ratio of cross-linked styrene-based organic particles, dispersant sodium carboxymethyl cellulose, and binder polymethyl methacrylate in the porous coating slurry was 90:2:8.

[0233] A commercially available polyethylene microporous film with a thickness of 7 μm was used as the porous base film. The porous coating slurry was coated on both surfaces of the porous base film by microgravure coating, and then dried and slit to obtain the separator.

[0234] Performance Test

[0235] The heat shrinkage rate of the separator can be tested according to GB / T 36363-2018.

[0236] The separator was cut into samples with a width of 50 mm and a length of 100 mm by a punch press. Five parallel samples were placed on an A4 paper, and the A4 paper with the samples was placed on corrugated paper with a thickness of 1 mm to 5 mm.

[0237] The temperature of the air-blast oven was set to 140°C. After the temperature reached the set temperature and stabilized for 60 min, the A4 paper placed on the corrugated paper was placed in the air-blast oven, and the timing started. After the set time (1 h in the present disclosure) was reached, the length and width of the separator were measured, and the values were marked as a and b, respectively.

[0238] Heat shrinkage rate calculation: longitudinal (MD) heat shrinkage rate = [(100-a) / 100] x 100%, and transverse (TD) heat shrinkage rate = [(50-b) / 50] x 100%. The average value of three parallel samples was taken as the test result.

[0239] Table 1

[0240] FIG. 3 shows a scanning electron microscope (SEM) image of the isolation film of the present disclosure.

[0241] From the above test results, it can be seen that the isolation film of the present disclosure has better heat resistance.

[0242] It should be noted that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and exerting the same effects as the technical idea within the scope of the technical solutions of the present disclosure are all included in the technical scope of the present disclosure. Furthermore, within the scope of the main idea of the present disclosure, various modifications that can be thought of by those skilled in the art are applied to the embodiments, and other modes constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

An isolation membrane comprising a porous base film and a porous coating layer on at least one side of the porous base film, wherein, The porous coating includes crosslinked styrene-based organic particles and fibrous materials, and at least part of the crosslinked styrene-based organic particles are located between the fibrous materials. The separator film according to claim 1, wherein The glass transition temperature T of the crosslinked styrenic organic particles is g 110 °C to 165 °C. The separator film according to any one of claims 1-2, wherein, The crosslinked styrene-based organic particles satisfy at least one of the following conditions (1) to (4): (1) The crosslinked styrene-based organic particles have no melting point; (2) The crosslinked styrene-based organic particles have no oxidation peak in a cyclic voltammogram of the first cycle in a voltage range of 2.5V to 4.4V; (3) The crosslinked styrene-based organic particles have a swelling degree of 3% or less 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; (4) The crosslinked styrene-based organic particles have a dissolution rate of 3% or less 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. The separator film according to any one of claims 1 to 3, wherein The crosslinked styrene-based organic particles include styrene or styrene derivative structural units and crosslinking structural units; Optionally, the styrene or styrene derivative structural units include one or more of styrene structural units, 1-methyl-1-styrene structural units, 4-methylstyrene structural units, 2-methylstyrene structural units, 2,4-dimethylstyrene structural units, and 2,5-dimethylstyrene structural units; Optionally, the crosslinking structural units include one or more of 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 trisallyl isocyanurate structural units. The separator film according to any one of claims 1-4, wherein, The crosslinked styrene-based organic particles have a volume distribution particle size Dv50 of 88nm-300nm; and / or, The crosslinked styrenic organic particles have a true density of 1.0 g / cm 3 -1.4 g / cm 3 . The separator film according to any one of claims 1 to 5, wherein The crosslinked styrene-based organic particles have a first polar group, Optionally, the first polar group includes one or more of ester groups, carboxyl groups, carboxylate groups, hydroxyl groups, cyano groups, and amide groups. The separator film according to any one of claims 1-6, wherein, The fibrous materials have a diameter ranging from 10nm to 200nm; and / or, The fibrous materials have a length ranging from 0.15μm to 30μm. The separator film according to any one of claims 1 to 7, wherein The fibrous materials include one or more of sugar-based fibers, protein-based fibers, polymeric fibers, and inorganic fibers. Optionally, the fibrous material comprises one or more of alginic acid and its derivative fibers, nanocellulose and its derivative fibers, chitosan and its derivative fibers, chitin and its derivative fibers, plant cellulose, silk fibroin fibers, spider silk protein fibers, corn protein fibers, soy protein fibers, keratin fibers, wool fibers, cashmere fibers, aramid fibers, polyester fibers, polyamide fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, polyethylene fibers, ultra-high molecular weight polyethylene fibers, polypropylene fibers, polytetrafluoroethylene fibers, polyvinylidene fluoride fibers, polyurethane fibers, acetate fibers, polycaprolactone fibers, polylactic acid fibers, polyether sulfone fibers, acrylic fibers, acrylic polymer fibers, polymethyl methacrylate fibers, poly-2-hydroxyethyl methacrylate fibers, polyethylene phthalate fibers, polyethylene terephthalate fibers, poly-p-phenylene terephthalamide fibers, glass fibers, asbestos fibers, silica fibers. The separator film according to any one of claims 1 to 8, wherein The fibrous material has a second polar group, Optionally, the second polar group comprises one or more of a hydroxyl group, a carboxyl group, an ester group, an amide group, a cyano group, an amine group, an aldehyde group, a sulfonic acid group, a boronic acid group, a phosphoric acid group. The separator membrane according to any one of claims 1-9, wherein, The mass content of the crosslinked styrene-based organic particles in the porous coating is greater than or equal to 55% based on the total mass of the porous coating; and / or, The mass content of the fibrous material in the porous coating is 0.5%-30% based on the total mass of the porous coating. The separator membrane according to any one of claims 1-10, wherein, The porous coating further comprises a binder; and / or, The thickness of the porous coating is 0.4-5 μm. A method for preparing the separator membrane according to any one of claims 1-11, comprising the steps of: providing a porous base film; providing a slurry comprising crosslinked styrene-based organic particles, fibrous material, and a binder; coating the slurry on at least one side of the porous base film to obtain the separator membrane after drying. The method of claim 12, wherein, A method for providing crosslinked styrene-based organic particles, comprising the steps of: providing a pre-emulsion comprising monomers, a crosslinking agent, an emulsifier, an initiator, and water, the monomers comprising one or more of styrene and its derivatives; and performing emulsion polymerization of the pre-emulsion under heating, inert gas protection, and stirring to obtain the crosslinked styrene-based organic particles. The method according to claim 13, wherein, The monomers comprise one or more of styrene, 1-methyl-1-styrene, 4-methylstyrene, 2-methylstyrene, 2,4-dimethylstyrene, and 2,5-dimethylstyrene; and / or, the crosslinking agent comprises 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, triallyl isocyanurate; and / or, the emulsifier comprises one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, fatty acid sorbitan, polysorbate, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl alcohol, polyoxyethylene ether emulsifier. The method of any one of claims 13-14, wherein, a mass fraction of the crosslinking agent is 5%-40% based on a total mass of the monomer and the crosslinking agent being 100%; and / or, a mass fraction of the emulsifier is 0.25%-5% based on the total mass of the monomer and the crosslinking agent being 100%. The method according to any one of claims 13-15, wherein the pre-emulsion further comprises a functional monomer, the functional monomer having a first polar group; Optionally, the first polar group comprises one or more of an ester group, a carboxyl group, a carboxylate salt, a hydroxyl group, a cyano group, an amide group. The method according to any one of claims 13-16, wherein The emulsion polymerization reaction comprises the following steps: dropping the pre-emulsion into a reactor containing water under a first temperature, inert gas protection, and stirring, and after a first time, warming up to a second temperature for a second time to obtain crosslinked styrene-based organic particles. The method of claim 17, wherein, the first temperature is 55-70℃; and / or, the first time is 3-6h; and / or, the second temperature is 72-92℃; and / or, the second time is 1-6h. A secondary battery monomer comprising a positive electrode sheet, a negative electrode sheet, and the separator film of any one of claims 1-11, the separator film being disposed between the positive electrode sheet and the negative electrode sheet. A battery device comprising a plurality of the secondary battery monomers of claim 19. An electric device comprising the secondary battery monomer of claim 19 or the battery device of claim 20.

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