A coated separator and a method for preparing and using the same

Abstract

This invention discloses a coated separator, its preparation method, and its application, belonging to the field of battery materials technology. The coated separator includes a base film and a composite coating; the composite coating includes a porous resin layer and a discontinuous polymer adhesive layer; the discontinuous polymer adhesive layer contains multiple randomly distributed acrylate copolymer particles with a core-shell structure; the average pore size of the porous resin layer is d, where d is 0.1 μm to 0.8 μm; the average particle size of the acrylate copolymer particles is D, where 0.25 ≤ K = d / D ≤ 0.75; the coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer is η1, where 5% ≤ η1 ≤ 18%. The above-mentioned coated separator exhibits high adhesion, air permeability, ion conductivity, and safety performance, which is beneficial for improving the hardness and cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a coated separator, its preparation method, and its application. Background Technology

[0002] As the requirements for thermal safety levels of power batteries continue to upgrade, organic heat-resistant materials (such as aramid or polyimide) stand out due to their advantages such as strong molecular chain rigidity, dense intermolecular hydrogen bonds, high thermal decomposition temperature, and low high-temperature thermal shrinkage rate. Coating them onto existing polyolefin separators can effectively improve the problems of high-temperature melting shrinkage and thermal runaway perforation risks of traditional polyolefin separators, making them the preferred high-end coated separator solution for high-safety systems such as high-nickel ternary batteries and energy storage batteries. However, organic heat-resistant materials themselves have significant application shortcomings: the molecules of organic heat-resistant materials are regularly packed, have strong surface chemical inertness, and lack flexible bonding segments, so they have almost no bonding properties. When coated onto polyolefin separators, they are difficult to form interfacial adhesion with the positive and negative electrode sheets, and cannot meet the strict requirements of separator-electrode interface adhesion in the winding and packaging process of soft-pack batteries. Problems such as interface slippage and increased internal resistance are prone to occur during cycling.

[0003] Existing technologies often employ the following solutions to address the lack of adhesion in organic heat-resistant material coated diaphragms: One approach is to introduce polyvinylidene fluoride (PVDF) as a binder component into the organic heat-resistant material system for blending and modification. The polar fluorine chain structure of PVDF imparts adhesion to the coated diaphragm. However, the highly polar organic heat-resistant material system has poor thermodynamic compatibility with the fluorine-containing segments of PVDF. The high interfacial energy and weak intermolecular forces between the two make direct blending prone to phase separation and component agglomeration. This not only results in loose bonding and powder shedding within the coating but also damages the original microporous structure of the coating layer and impairs the integrity of the pores, leading to poor air permeability consistency and hindered electrolyte conduction, thereby affecting the performance of the battery cell. Secondly, an organic heat-resistant material coating is first applied, followed by an oil-based PVDF layer. This is to improve the adhesion between the organic heat-resistant material layer and the electrode. However, since the oil-based PVDF layer also involves an extraction pore-forming process, the PVDF easily penetrates into the pores of the organic heat-resistant material layer during the extraction process. The PVDF then plasticizes within these pores, obstructing the pores and increasing the overall permeability of the coated separator. This worsens the cell's internal resistance and affects the battery's cycle performance. Thirdly, a first coating... An organic heat-resistant material coating is applied, followed by a water-based polyvinylidene fluoride (PVDF) layer. This is done to improve the adhesion between the organic heat-resistant material layer and the electrode. However, since PVDF is a hydrophobic polymer, a higher proportion of membrane bonding polymer is required when applying the water-based PVDF layer. During the membrane drying process, the membrane bonding polymer can easily clog the pores of the organic heat-resistant material layer, resulting in excessive air permeability of the membrane. This deteriorates the overall internal resistance of the cell, affects the cycle performance of the battery, and may even lead to localized lithium plating.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a coated diaphragm, its preparation method, and its application, so as to solve or improve the above-mentioned technical problems.

[0006] This invention can be implemented as follows: In a first aspect, the present invention provides a coated diaphragm, comprising a base film and a composite coating disposed on at least one surface of the base film; The composite coating includes a porous resin layer disposed on the surface of a base film and a discontinuous polymer adhesive layer disposed on the surface of the porous resin layer; the discontinuous polymer adhesive layer comprises a plurality of randomly distributed polymer particles; the polymer particles include acrylate copolymer particles with a core-shell structure; The average pore size of the porous resin layer is d, which is 0.1 μm to 0.8 μm; the average particle size of the acrylate copolymer particles is D, where K = d / D, and 0.25 ≤ K ≤ 0.75. The coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer is η1, where 5% ≤ η1 ≤ 18%.

[0007] In an optional embodiment, the porous resin layer includes at least one of the following features: Feature 1: The thickness of the porous resin layer is 0.5μm~3.0μm; Feature 2: The high-temperature resistant resin in the porous resin layer includes at least one of aromatic polyamide, polyamide-imide, poly-N-vinylacetamide, polyether block amide, polyimide, polyetherimide, polyethersulfone, polysulfone, polyether ketone and polyketone; optionally, the high-temperature resistant resin includes poly(m-phenylene isophthalamide).

[0008] In an optional embodiment, the coating basis weight of the discontinuous polymer adhesive layer is 0.05 g / m². 2 ~0.18g / m 2 .

[0009] In an optional embodiment, the powder shedding rate of the discontinuous polymer adhesive layer is no higher than 6.5%.

[0010] In an optional embodiment, the acrylate copolymer particles include at least one of the following characteristics: Feature 3: The particle size D of the acrylate copolymer particles is 0.4μm~1.0μm; Feature 4: The swelling rate of the acrylate copolymer particles is 60%~100%; Feature 5: The acrylate copolymer particles include a core layer and a shell layer covering the core layer. The glass transition temperature of the core layer is Tg1, and the glass transition temperature of the shell layer is Tg2. 40℃≤Tg1≤60℃, -30℃≤Tg2≤-10℃.

[0011] In an optional embodiment, the shell layer in the acrylate copolymer particles has a mass percentage of 10% to 20%.

[0012] In an optional embodiment, the core layer comprises a first polymer formed by polymerizing at least two monomers selected from ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, n-butyl acrylate, butyl methacrylate, methacrylonitrile, styrene, and acrylonitrile.

[0013] In an optional embodiment, the shell layer comprises a second polymer formed by polymerization of at least two monomers selected from ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, n-butyl acrylate, butyl methacrylate, methacrylonitrile, styrene, and acrylonitrile.

[0014] In an optional embodiment, the composite coating further includes a wetting agent, which includes at least one of alkyl sulfate, polyoxyethylene alkylphenol ether, alkylphenol polyoxyethylene ether, and fatty alcohol polyoxyethylene ether.

[0015] In an optional embodiment, the base film includes at least one of PE base film and PP base film; And / or, the thickness of the base film is 4μm~16μm; And / or, a ceramic layer may also be included between the base film and the porous resin layer.

[0016] In an optional embodiment, the coated diaphragm also has at least one of the following characteristics: Feature 6: After the discontinuous polymer adhesive layer is hot-pressed at 1MPa and 60℃ for 1min, the coverage of the porous resin layer on the surface is η2, 10%≤η2≤30%, and η2>η1; Feature 7: The hot-pressing bonding force between the coated diaphragm and the positive electrode sheet at 85℃ is F, 5N / m≤F≤10N / m; Feature 8: The air permeability growth rate of the coated diaphragm does not exceed 19%; Feature 9: The membrane rupture temperature of the coated diaphragm is not lower than 170℃; Feature 10: The ionic conductivity of the coated diaphragm is not less than 0.8 mS / cm; Feature 11: The thermal shrinkage rate of the coated diaphragm at 130°C does not exceed 9.7% in the MD direction and 8.3% in the TD direction; Feature 12: The thermal shrinkage rate of the coated diaphragm in the MD direction at 150°C does not exceed 44.5%, and the thermal shrinkage rate in the TD direction does not exceed 38%.

[0017] In a second aspect, the present invention provides a method for preparing a coated diaphragm as described in any of the foregoing embodiments, comprising the following steps: preparing a porous resin layer on the surface of a base membrane, and then preparing a discontinuous polymer adhesive layer on the surface of the porous resin layer.

[0018] Thirdly, the present invention provides a battery comprising a coated separator according to any of the foregoing embodiments.

[0019] The beneficial effects of this invention include: This invention enables the coated separator to simultaneously possess superior heat resistance, adhesion, air permeability, and ion conduction properties by simultaneously controlling d to be 0.1μm~0.8μm, K to be 0.25~0.75, and η1 to be 5%~18%. After the coated separator is prepared into a cell or battery, the hardness, safety performance, and cycle performance of the cell or battery can be further improved. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The image shows a SEM image of the coated diaphragm prepared in Example 1 before hot pressing. Figure 2 The image shows the SEM image of the coated diaphragm prepared in Example 1 after hot pressing. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The coated diaphragm, its preparation method, and its application provided by the present invention will be described in detail below.

[0024] In this article, pore size and particle size are both results of the material in a dry state.

[0025] The present invention provides a coated diaphragm, the coated diaphragm comprising a base membrane and a composite coating disposed on at least one surface of the base membrane; the composite coating comprising a porous resin layer disposed on the surface of the base membrane and a discontinuous polymer adhesive layer disposed on the surface of the porous resin layer; the discontinuous polymer adhesive layer comprising a plurality of randomly distributed polymer particles; the polymer particles comprising acrylate copolymer particles having a core-shell structure; The average pore size of the porous resin layer is d, the average particle size of the acrylate copolymer particles is D, K=d / D, 0.25≤K≤0.75.

[0026] In some alternative implementations, K can be 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, or 0.75, or other values ​​within the range of 0.25 to 0.75. In some more typical implementations, K can be 0.27 to 0.75.

[0027] When the K-value of the coated separator is large, polymer particles easily enter the pores of the porous resin layer, not only blocking the conductivity of the pores but also failing to provide effective adhesion between the separator and the electrode. This easily deteriorates the adhesion of the polymer particles, leading to lithium plating problems after battery cycling, thus affecting the battery's cycle performance and safety. When the K-value of the coated separator is small, fewer polymer particles enter the porous resin layer, and the contact between the polymer particles and the porous resin layer is mainly point contact. This reduces the adhesion of the polymer particles in the porous resin layer, making them prone to detachment. This results in severe powder shedding from the discontinuous polymer adhesive layer. After the polymer particles detach, the number of polymer particles in the coated separator used for bonding with the electrode is reduced, which also leads to a decrease in the adhesion between the coated separator and the electrode. When the coated separator and the positive and negative electrodes are used to prepare the battery cell, the adhesion is insufficient, and the battery is prone to softening and swelling after cycling, thus affecting the battery's cycle performance and safety.

[0028] This invention controls the value of K between 0.25 and 0.75. On the one hand, it can prevent acrylate copolymer particles from penetrating into the pores of the porous resin layer, thereby preventing them from deteriorating the gas permeability of the separator and its adhesion to the electrode. On the other hand, it can also improve the adhesion of acrylate copolymer particles to the porous resin layer, prevent the acrylate copolymer particles from falling off, and give the coated separator high adhesion and ion conduction performance, which is beneficial to improving the hardness and cycle performance of the battery.

[0029] In some alternative embodiments, the thickness of the porous resin layer can be 0.5μm to 3.0μm, such as 0.5μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm or 3.0μm, or other values ​​within the range of 0.5μm to 3.0μm.

[0030] In some optional embodiments, the average pore size d of the porous resin layer can be 0.1 μm to 0.8 μm, such as 0.1 μm, 0.2 μm, 0.5 μm, or 0.8 μm, or other values ​​within the range of 0.1 μm to 0.8 μm. In some more typical embodiments, the average pore size d of the porous resin layer can be 0.12 μm to 0.75 μm.

[0031] When the pore size of the porous resin layer is too small, the coating of a discontinuous polymer adhesive layer can easily lead to an increase in overall air permeability. After the coated separator is used to prepare the battery, the effective ion conduction channels are limited, increasing the internal resistance of the battery and easily leading to lithium plating problems. This deteriorates the overall cycle performance and safety performance of the battery. When the pore size of the porous resin layer is too large, the heat resistance provided by the porous resin layer is insufficient, the membrane rupture temperature of the coated separator is reduced, and the particle size of the polymer particles used needs to be larger, thereby reducing the polymer bonding sites and affecting the adhesion performance between the coated separator and the electrode sheet. After the coated separator is used to prepare the battery, it can easily lead to a deterioration in cycle performance and safety performance.

[0032] In some alternative embodiments, the high-temperature resistant resin in the porous resin layer may exemplary include at least one selected from aromatic polyamide, polyamide-imide, poly-N-vinylacetamide, polyether-block-Amide (PEBA), polyimide, polyetherimide, polyethersulfone, polysulfone, polyetherketone, and polyketone. In some more typical embodiments, the high-temperature resistant resin includes poly(m-phenylene isophthalamide).

[0033] In some optional embodiments, the high-temperature resistant resin in the porous resin layer accounts for 84wt% to 96wt% of the composite coating, such as 84wt%, 85wt%, 88wt%, 90wt%, 92wt%, 95wt%, or 96wt%, or other values ​​within the range of 84wt% to 96wt%.

[0034] In some optional embodiments, the coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer is η1, where 5% ≤ η1 ≤ 18%. η1 can be 5%, 8%, 10%, 12%, 15%, or 18%, or other values ​​within the range of 5% to 18%. In some more typical embodiments, η1 can be 5.6% to 17.5%.

[0035] In some optional embodiments, after the discontinuous polymer adhesive layer is hot-pressed at 1 MPa and 60°C for 1 min, the coverage of the porous resin layer surface is η2, where 10% ≤ η2 ≤ 30%, and η2 > η1. η2 can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, or 30%, or other values ​​within the range of 10% to 30%. In some more typical embodiments, η2 can be 10.2% to 29.6%.

[0036] When the coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer is low, the polymer particles can provide fewer bonding sites, resulting in weak adhesion between the coated separator and the electrode sheets. When the coated separator and the positive and negative electrodes are used to prepare a battery, the insufficient adhesion makes the battery prone to softening and swelling after cycling, thus affecting the battery's cycle performance and safety performance. When the coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer is high, on the one hand, the greater the coverage, the greater the impact on the overall air permeability of the coated separator, which can easily block the ion shuttle channels, affecting ion conduction and leading to lithium plating problems. On the other hand, the greater the coverage, the more bonding sites the polymer particles can provide, resulting in stronger adhesion between the coated separator and the electrode sheets. When the coated separator and the positive and negative electrodes are used to prepare a battery, the excessive adhesion makes it impossible to effectively dissipate heat when the battery releases heat, deteriorating the battery's safety performance. Therefore, excessive coverage will lead to a deterioration in battery cycle performance and safety performance.

[0037] By setting the coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer and the coverage after hot pressing within the above-mentioned range, the present invention can achieve high adhesion between the coated separator and the electrode, while the coated separator has reduced air permeability, and can improve the battery hardness without worsening the battery internal resistance, thereby effectively improving the overall cycle performance of the battery.

[0038] In some alternative embodiments, the coating basis weight of the discontinuous polymer adhesive layer can be 0.05 g / m². 2 ~0.18g / m 2 For example, 0.05g / m 2 0.08g / m 2 0.1g / m 2 0.12g / m 2 0.15g / m 2 Or 0.18g / m 2 etc., can also be 0.05g / m 2 ~0.18g / m 2 Other values ​​within the range. In some typical embodiments, the coating basis weight of the discontinuous polymer adhesive layer can be 0.05 g / m². 2 ~0.17g / m 2 .

[0039] In some alternative embodiments, the powder shedding rate of the discontinuous polymer adhesive layer is not higher than 6.5%, such as 2.3% to 6.4%.

[0040] In some alternative embodiments, the particle size D of the acrylate copolymer particles can be 0.4 μm to 1.0 μm, such as 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1.0 μm, or other values ​​in the range of 0.4 μm to 1.0 μm.

[0041] In some alternative embodiments, the swelling ratio of the acrylate copolymer particles can be 60% to 100%, such as 60%, 70%, 80%, 90%, or 100%, or other values ​​within the range of 60% to 100%. In some more typical embodiments, the swelling ratio of the acrylate copolymer particles can be 62% to 95%.

[0042] In some alternative embodiments, the acrylate copolymer particles may account for 3.5wt% to 15wt% of the composite coating, such as 3.5wt%, 5wt%, 8wt%, 10wt%, 12wt%, or 15wt%, or other values ​​within the range of 3.5wt% to 15wt%.

[0043] In some alternative embodiments, the acrylate copolymer particles include a core layer and a shell layer covering the core layer, the glass transition temperature of the core layer is Tg1, the glass transition temperature of the shell layer is Tg2, 40℃≤Tg1≤60℃, and -30℃≤Tg2≤-10℃.

[0044] Tg1 can be 40℃, 45℃, 50℃, 55℃ or 60℃, or other values ​​within the range of 40℃ to 60℃.

[0045] Tg2 can be -30℃, -25℃, -20℃, -15℃ or -10℃, or other values ​​within the range of -30℃ to -10℃.

[0046] In some alternative embodiments, the core layer may exemplary comprise a first polymer formed by polymerizing at least two monomers selected from ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, n-butyl acrylate, butyl methacrylate, methacrylonitrile, styrene, and acrylonitrile.

[0047] The shell may, by way of example, comprise a second polymer formed by polymerization of at least two monomers selected from ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, n-butyl acrylate, butyl methacrylate, methacrylonitrile, styrene, and acrylonitrile.

[0048] In some alternative embodiments, the mass percentage of the shell layer in the acrylate copolymer particles can be 10% to 20%, such as 10%, 12%, 15%, 18% or 20%, or other values ​​within the range of 10% to 20%.

[0049] In the design of polymer particles, this invention adopts polymer particles that are soft on the outside and hard on the inside with low swelling. When coating the polymer particle layer, it can avoid the impact of traditional separator adhesive polymers on the air permeability of the porous heat-resistant resin layer. At the same time, the acrylate copolymer particles are not easy to fall off. The low swelling acrylate copolymer particle design effectively avoids the acrylate copolymer particles swelling after the cell is filled with electrolyte, which would cause the coated separator to block the pores. After the battery is made with the coated separator, the battery hardness is improved and the cycle performance is improved.

[0050] In some optional embodiments, the composite coating further includes a wetting agent, which may account for 0.1wt% to 2wt% of the composite coating, such as 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, or 2wt%, or other values ​​within the range of 0.1wt% to 2wt%. The wetting agent may, by way of example but not limitation, include at least one of alkyl sulfates, polyoxyethylene alkylphenol ethers, alkylphenol polyoxyethylene ethers, and fatty alcohol polyoxyethylene ethers.

[0051] In some optional embodiments, the base film may include at least one of a PE base film and a PP base film. The thickness of the base film may be 4μm to 16μm, such as 4μm, 8μm, 10μm, 12μm, or 16μm, or other values ​​within the range of 4μm to 16μm. In some optional embodiments, a ceramic layer may also be included between the base film and the porous resin layer.

[0052] In addition, by coating the base film with the aforementioned porous resin layer, the present invention can improve the heat resistance of the base film, thereby improving the safety performance of the battery; by coating the porous resin layer with the aforementioned discontinuous polymer adhesive layer, the adhesion between the coated separator and the electrode can be increased, thereby improving the overall hardness of the battery and the cycle performance of the cell.

[0053] In some optional embodiments, the hot-pressing bonding force between the coated diaphragm and the positive electrode sheet at 85°C is F, where 5 N / m ≤ F ≤ 10 N / m, such as 5.8 N / m to 8.8 N / m.

[0054] In some alternative implementations, the coating permeability growth rate of the diaphragm does not exceed 19%, such as 5.2% to 18.6%.

[0055] In some optional embodiments, the membrane breaking temperature of the coated diaphragm is not lower than 170°C, such as 170.4°C to 236.7°C.

[0056] In some alternative embodiments, the ionic conductivity of the coated membrane is not less than 0.8 mS / cm, such as 0.803 mS / cm to 0.935 Ms / cm.

[0057] In some alternative embodiments, the heat shrinkage rate of the coated diaphragm in the MD direction at 130°C does not exceed 9.7%, such as 0.5% to 9.7%; and the heat shrinkage rate in the TD direction does not exceed 8.3%, such as 0.4% to 8.3%.

[0058] In some alternative embodiments, the heat shrinkage rate of the coated diaphragm in the MD direction at 150°C does not exceed 44.5%, such as 2.5% to 44.1%; and the heat shrinkage rate in the TD direction does not exceed 38%, such as 1.6% to 37.7%.

[0059] Accordingly, the present invention also provides a method for preparing the above-mentioned coated diaphragm, comprising the following steps: preparing a porous resin layer on the surface of a base membrane, and then preparing a discontinuous polymer adhesive layer on the surface of the porous resin layer.

[0060] In some alternative embodiments, the preparation of the porous resin layer may include: mixing a high-temperature resistant resin with a solvent to obtain a slurry; coating the slurry onto the surface of a base film using a microgravure coating method; subsequently performing phase separation to form pores and drying to obtain a porous high-temperature resistant resin coating.

[0061] In some alternative embodiments, the preparation of the discontinuous polymer adhesive layer may include: using an emulsion polymerization method, thermally initiating the polymerization of monomers for preparing the core layer to obtain the core layer of acrylate copolymer particles; subsequently adding monomers for preparing the shell layer and an initiator, and continuing polymerization to form a shell layer on the surface of the core layer. The acrylate copolymer particles are then made into a slurry, which is subsequently coated onto the surface of the porous resin layer and dried.

[0062] Furthermore, the present invention also provides a battery comprising the aforementioned coated separator. This battery exhibits superior hardness and cycle performance.

[0063] In some alternative implementations, the battery hardness degradation rate after cycling does not exceed 4.5%, such as 2.8% to 4.5%.

[0064] In some alternative implementations, the battery's capacity retention rate after cycling is not less than 95.5%, such as 95.6% to 97.0%.

[0065] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0066] Example 1 This embodiment provides a coated diaphragm, the preparation method of which includes: S1: Coated with a porous resin layer.

[0067] Forty parts of a mixture of N,N-dimethylacetamide and poly(m-phenylene isophthalamide) with a solid content of 15%, 58 parts of N,N-dimethylacetamide, and 2.0 parts of isopropanol were mixed and stirred in a sealed container for 4 hours to obtain a first slurry. The first slurry was coated onto a 7 μm thick PE substrate membrane using microgravure coating technology. The coated membrane was then sequentially passed through extraction tanks containing 30 wt%, 10 wt%, and 0 wt% N,N-dimethylacetamide, and then dried to obtain an areal density of 0.75 g / m³. 2 The porous resin layer.

[0068] The thickness of the porous resin layer is 1.51 μm, and the average pore size d is 0.25 μm.

[0069] S2: Coating a discontinuous polymer adhesive layer.

[0070] S2-1: Core layer for synthesizing acrylate copolymer particles. 1.70 parts sodium dodecyl sulfate and 400 parts deionized water were placed in a reactor. Nitrogen gas was introduced to purge the air from the reactor. 21.25 parts 2-ethylhexyl acrylate and 63.75 parts styrene were added, and the pH was adjusted to approximately 8.0. The reactor was then heated and pressurized, with the temperature controlled at 75℃ and the pressure at 2.6 MPa. After the temperature and pressure stabilized, the stirring speed was adjusted, and 1.28 parts sodium persulfate were added. The polymerization reaction was carried out at a constant temperature and pressure for 8 hours. S2-2: The shell layer of the synthesized acrylate copolymer particles. Continuing to add 13.50 parts of 2-ethylhexyl acrylate and 1.50 parts of styrene to the reactor in S2-1, maintaining the original synthesis temperature and pressure, 0.15 parts of sodium persulfate were added again, and the polymerization reaction was carried out at a constant temperature and pressure for 5 hours. Then, the temperature and pressure were reduced to room temperature and pressure, and deionized water was added for dilution to obtain an acrylate copolymer particle emulsion with a solid content of 15%. The average particle size D of the acrylate copolymer particles in this emulsion is 0.55 μm, Tg1 is 50℃, Tg2 is -20℃, and the swelling ratio is 78%. The K value = d / D = 0.25 / 0.55, approximately 0.45.

[0071] In the above-mentioned acrylate copolymer particles, the shell layer accounts for 14.7% of the total mass.

[0072] S2-3: Take 30 parts of the acrylate copolymer particle emulsion obtained in S2-2, 70 parts of deionized water, and 0.45 parts of wetting agent (alkylphenol polyoxyethylene ether), mix and stir evenly to obtain a second slurry. Apply the second slurry to the surface of the porous resin layer using microgravure coating technology, and dry to obtain an areal density of 0.12 g / m³. 2 A discontinuous polymer adhesive layer is used to obtain a coated diaphragm.

[0073] Example 2 The difference between this embodiment and Embodiment 1 is that the average pore size of the porous resin layer is d=0.40μm, and the K value is d / D=0.4 / 0.55, which is approximately 0.73.

[0074] The average pore size of the aforementioned porous resin layer was achieved by reducing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 27 wt%.

[0075] Example 3 The difference between this embodiment and Embodiment 1 is that the average pore size of the porous resin layer is d=0.15μm, and the K value is d / D=0.15 / 0.55, which is approximately 0.27.

[0076] The average pore size of the aforementioned porous resin layer was achieved by increasing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 36 wt%.

[0077] Example 4 The difference between this embodiment and Embodiment 1 is that the coating basis weight of the discontinuous polymer adhesive layer is 0.17 g / m². 2 η1=17.5%, η2=29.6%.

[0078] Example 5 The difference between this embodiment and Embodiment 1 is that the coating basis weight of the discontinuous polymer adhesive layer is 0.05 g / m². 2 η1=5.6%, η2=10.2%.

[0079] Example 6 The difference between this embodiment and Embodiment 1 is that acrylonitrile is used instead of styrene when synthesizing the shell, and the glass transition temperature of the shell is Tg2 = -10℃.

[0080] Example 7 The difference between this embodiment and Example 1 is that isooctyl acrylate is used instead of 2-ethylhexyl acrylate when synthesizing the shell, and the glass transition temperature of the shell is Tg2 = -30℃.

[0081] Example 8 The difference between this embodiment and Example 1 is that the average particle size D of the acrylate copolymer particles is 1.00 μm, the average pore size d of the porous resin layer is 0.75 μm, the K value is d / D = 0.75 / 1 = 0.75, η1 = 8.9%, and η2 = 13.7%.

[0082] The average pore size of the aforementioned porous resin layer was achieved by reducing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 22 wt%.

[0083] The average particle size of the above-mentioned acrylate copolymer particles was achieved by reducing the polymerization temperature from 75°C to 72°C.

[0084] Example 9 The difference between this embodiment and Example 1 is that the average particle size D of the acrylate copolymer particles is 0.40 μm, the average pore size d of the porous resin layer is 0.12 μm, the K value is d / D = 0.12 / 0.4 = 0.30, η1 = 14.4%, and η2 = 25.8%.

[0085] The average pore size of the aforementioned porous resin layer was achieved by increasing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 39 wt%.

[0086] The average particle size of the above-mentioned acrylate copolymer particles was achieved by increasing the polymerization temperature from 75°C to 77°C.

[0087] Example 10 The difference between this embodiment and Embodiment 1 is that an inorganic heat-resistant ceramic layer with a thickness of 1 μm is coated between the porous resin layer and the base film. (The inorganic heat-resistant ceramic layer is composed of 93.5 parts of alumina with a particle size of 0.5 μm, 5 parts of polyacrylate, 1 part of sodium polymethyl cellulose, and 0.5 parts of alkylphenol polyoxyethylene ether.)

[0088] Example 11 The difference between this embodiment and embodiment 10 is that the coated diaphragm adopts a symmetrical design, and an inorganic heat-resistant ceramic layer, a porous resin layer, and a discontinuous polymer adhesive layer are coated on both sides of the base membrane. The coating specifications are the same as those in embodiment 10.

[0089] Comparative Example 1 The difference between this comparative example and Example 1 is that the average pore size of the porous resin layer is d=0.55μm, and the K value is d / D=0.55 / 0.55=1.00.

[0090] The average pore size of the aforementioned porous resin layer was achieved by reducing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 25 wt%.

[0091] Comparative Example 2 The difference between this comparative example and Example 1 is that the average pore size of the porous resin layer is d=0.10μm, and the K value is d / D=0.1 / 0.55, which is approximately 0.18.

[0092] The average pore size of the aforementioned porous resin layer was achieved by increasing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 40 wt%.

[0093] Comparative Example 3 The difference between this comparative example and Example 1 is that the particle size D of the acrylate copolymer particles is 1.00 μm, and the coating weight of the discontinuous polymer adhesive layer is 0.05 g / m². 2 The average pore size of the porous resin layer is d=0.75μm, K value=d / D=0.75 / 1=0.75, η1=3.5%, η2=8.6%.

[0094] The average pore size of the aforementioned porous resin layer was achieved by reducing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 22 wt%.

[0095] The particle size of the above-mentioned acrylate copolymer particles was achieved by reducing the polymerization temperature from 75°C to 72°C.

[0096] Comparative Example 4 The difference between this comparative example and Example 1 is that the particle size D of the acrylate copolymer particles is 0.40 μm, and the coating weight of the discontinuous polymer adhesive layer is 0.18 g / m². 2 The average pore size of the porous resin layer is d=0.12μm, K value=d / D=0.12 / 0.4=0.30, η1=28.5%, η2=43.6%.

[0097] The average pore size of the aforementioned porous resin layer was achieved by increasing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 39 wt%.

[0098] The particle size of the above-mentioned acrylate copolymer particles was achieved by increasing the polymerization temperature from 75°C to 77°C.

[0099] Comparative Example 5 The difference between this comparative example and Example 1 is that the particle size of the acrylate copolymer particles is 0.30 μm, the average pore size of the porous resin layer is d=0.08 μm, the K value is d / D=0.08 / 0.3, which is about 0.27, η1=16.4%, and η2=28.1%.

[0100] The average pore size of the aforementioned porous resin layer was achieved by increasing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 45 wt%.

[0101] The particle size of the above-mentioned acrylate copolymer particles was achieved by increasing the polymerization temperature from 75°C to 79°C.

[0102] Comparative Example 6 The difference between this comparative example and Example 1 is that the particle size of the acrylate copolymer particles is 1.40 μm, the average pore size of the porous resin layer is d=1.00 μm, the K value is d / D=1 / 1.4, which is about 0.71, η1=6.2%, and η2=12.7%.

[0103] The average pore size of the aforementioned porous resin layer was achieved by reducing the concentration of N,N-dimethylacetamide in the first extraction tank from 30 wt% to 15 wt%. The particle size of the above-mentioned acrylate copolymer particles was achieved by reducing the polymerization temperature from 75°C to 70°C.

[0104] Test case The following tests were performed on Examples 1 to 11 and Comparative Examples 1 to 6, and the results are shown in Tables 1 to 3.

[0105] (1) Tg1 and Tg2: Take the core polymer emulsion obtained in S2-1 and the acrylate copolymer particle emulsion obtained in S2-2, dry them, weigh 6mg of each sample, and test the Tg by differential scanning calorimetry. Test equipment: METTLERDSC3, test temperature range: -80℃ to 150℃, heating rate: 5℃ / min. During the test, the first heating and cooling is used to eliminate the thermal history, and then the Tg of the polymer is tested. After the test, the test curve is integrated to obtain the Tg1 of the core polymer emulsion and the Tg of the acrylate copolymer particle emulsion. There are two Tg values ​​for the acrylate copolymer particle emulsion, one of which is the core Tg1 and the other is the shell Tg2.

[0106] (2) Particle size test of acrylate copolymer particles: Take the coated membrane and take pictures using a scanning electron microscope. Adjust the magnification of the scanning electron microscope to 10,000x and count the particle sizes D1, D2...Dn of all polymer particles at this magnification. Then take the average value, i.e., D=(D1+D2+...+Dn) / n. Test 10 samples in parallel using the same method and take the final average value as the average particle size D of the acrylate copolymer particles.

[0107] (3) Swelling rate test of acrylate copolymer particles: The acrylate copolymer particle emulsion was dried to obtain a film. About 1g of the film was weighed as m1. The film was placed in a sealable container and an electrolyte (EC:EMC:DEC=3:5:3, 1.5mol / L LiPF6) was added to cover the film. The container was then sealed and placed in an oven at 60℃ for 24h. The container was then removed and allowed to cool naturally. The film was removed from the container and the surface electrolyte was wiped off with a lint-free paper. The film weight was weighed again as m2. The swelling rate of the acrylate copolymer particles = [(m2-m1) / m1]×100%.

[0108] (4) Thickness h of porous resin layer: Take the coated membrane, cut the cross section of the coated membrane using an argon ion section polisher (CP), and then use SEM to test the thickness of the porous resin layer. Test 10 samples in the same way and take the final average value, which is the thickness h of the porous resin layer.

[0109] (5) Average pore diameter d of the porous resin layer: Take the coated membrane and take pictures using a scanning electron microscope. Adjust the magnification of the scanning electron microscope to 40,000 times (field of view area 3.2μm×2.4μm). Mark the maximum diameters d1, d2...dn of all the pores in the porous resin layer at this magnification. Then calculate the average value d, i.e. d=(d1+d2+...+dn) / n. Test 10 samples in parallel using the same method. The final average value is the average pore diameter of the porous resin layer.

[0110] (6) Test of the coverage η1 of the discontinuous polymer adhesive layer on the surface of the porous resin layer: Take the coated diaphragm and take pictures using a scanning electron microscope. Adjust the magnification of the scanning electron microscope to 10000x (field of view area 12.8μm×9.6μm) to count the number of polymer particles n in the field of view. Measure the diameters L1, L2...Ln of all polymer particles in the field of view. Then the average diameter L of all polymer particles in the field of view is L=(L1+L2+...+Ln) / n, and η1=(n×π×L 2 (4×12.8×9.6), and 10 samples were tested in parallel using the same method. The final average value was taken as the coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer. The SEM image of the coated diaphragm prepared in Example 1 in this test is shown below. Figure 1 As shown.

[0111] (7) Test of the coverage η2 of the discontinuous polymer adhesive layer on the surface of the porous resin layer after hot pressing: Take the coated diaphragm and PET diaphragm, cut them into 3cm×3cm pieces respectively, stack the coated surface of the cut coated diaphragm with the PET diaphragm, and then put them into a hot press. Adjust the pressure and temperature of the hot press to 1MPa and 60℃, and hot press for 1min. Take out the coated diaphragm and take a scanning electron microscope. The imaging method and calculation method are the same as those for the test η1. The coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer after hot pressing can be obtained. The SEM image of the coated diaphragm prepared in Example 1 in this test is shown below. Figure 2 As shown.

[0112] (8) Powder shedding test of discontinuous polymer adhesive layer: Take the same sample coated with a diaphragm and divide it into two parts. One part is photographed using a scanning electron microscope. Adjust the magnification of the scanning electron microscope to 10,000x (field of view area 12.8μm×9.6μm). Count the number of polymer particles in this field of view. Test 5 points in parallel and take the average of these 5 points as the number of polymer particles in this field of view, which is N1. Take the other part coated with a diaphragm and test it using a dyeing fastness tester RT-300S. Take the coated diaphragm... Cut the coated diaphragm into strips of 30cm × 2cm, with the coated side facing up, fix the strips, cover the friction element with a friction cloth, and place it on the diaphragm. Turn on the power, and rub the friction element back and forth on the diaphragm once. Remove the diaphragm after friction and take pictures with a scanning electron microscope. According to the test method of N1, the number of polymer particles N2 at the same magnification after friction can be obtained. Then, the powder loss of the discontinuous polymer adhesive layer = [(N1-N2) / N1] × 100%. Perform the same test 5 times in parallel and take the arithmetic mean.

[0113] (9) Permeability growth rate of coated diaphragm: Permeability refers to the time required for 100 mL of gas to pass through a fixed area diaphragm. Permeability growth rate = [(permeability time of coated diaphragm - permeability time of base membrane) / permeability time of base membrane] × 100%.

[0114] (10) K-value test of coated diaphragm: The K-value of coated diaphragm is the ratio of the average pore size d of the porous resin layer to the average particle size D of the acrylate copolymer particles, i.e., K=d / D.

[0115] (11) Adhesion test between coated separator and positive electrode: The coated separator and positive electrode are cut into 3cm×5cm specifications, the coated surface of the electrode is aligned with and overlapped with the coated surface of the separator, the hot press parameters (1MPa, 1min, 85℃) are adjusted and then dry pressed, and the adhesion between the separator and the positive electrode is tested by peeling at 180° with a peeling speed of 60mm / min. Finally, the adhesion between the coated separator and the electrode is obtained. The same sample is tested in parallel 5 times and the arithmetic mean is taken.

[0116] (12) Ionic conductivity test of coated membrane: In an argon-filled glove box, the membrane was made into a 2016 button cell. An appropriate amount of electrolyte (EC:EP:DEC=1:1:3, 1.0 mol / L LiPF6) was added. The AC impedance was measured using an electrochemical workstation. The result is σ=L / (Rb×A), where σ is the ionic conductivity (mS / cm); L is the thickness of the membrane (cm); Rb is the intrinsic resistance of the membrane (Ω); and A is the effective area (cm²). 2 The arithmetic mean of five parallel tests on the same sample is taken.

[0117] (13) Coated diaphragm heat shrinkage test: Take the coated diaphragm and cut it into 10cm×10cm squares along the MD and TD directions respectively. Mark the MD and TD directions. Place the diaphragm between two A4 sheets of paper and clamp it. Then transfer it to an oven at 130℃ and 150℃ and bake for 1 hour. Take it out and test the length of MD and TD after baking. The shrinkage rate of MD = [(length of MD before baking - length of MD after baking) / length of MD before baking] × 100%. Similarly, the shrinkage rate of TD can be obtained. Perform the same test 5 times in parallel and take the final average value.

[0118] (14) Test of membrane breakage temperature of coated diaphragm: Take the coated diaphragm, cut it into diaphragm samples with a width of 5 mm and an effective clamping length of 10 mm, clamp it in the TMA film fixture, apply a constant tensile force of 20 mN, and heat it from room temperature to 270 °C at a rate of 5 °C / min. Record the curve of sample deformation with temperature throughout the process. The temperature at which the curve shows a sudden displacement and the sample melts and breaks is the membrane breakage temperature of the coated diaphragm. The same sample is tested in parallel 5 times and the arithmetic mean is taken.

[0119] (15) Hardness decay test of the cell before and after cycling: The coated separator, lithium iron phosphate positive electrode, and graphite negative electrode are stacked to form a bare cell. The bare cell is charged at a constant current of 3.0C to 3.6V, and then charged at a constant voltage of 3.6V to a current of 0.02C. The charging is then terminated and the cell is left to stand for 30 minutes. The cell is discharged at a constant current of 2.0C to 2.0V. The discharge is then terminated and the cell is left to stand for 30 minutes. The hardness R1 of the bare cell is then tested. The cell is charged and discharged for 300 cycles according to the parameters of the first cycle. The hardness R2 of the bare cell after the 600th cycle is recorded. The hardness decay rate of the cell before and after cycling is calculated as (R1-R2) / R1.

[0120] (16) Lithium plating and capacity retention rate test after cell cycling: The coated separator, lithium iron phosphate positive electrode, and graphite negative electrode are wound to form the cell. The battery is charged at a constant current of 3.0C to 3.6V, and then charged at a constant voltage of 3.6V to a current of 0.02C. The charging is then stopped and the battery is left to stand for 20 minutes. The battery is discharged at a constant current of 3.0C to 2.0V, and the discharge is stopped. The battery is left to stand for 20 minutes and the first discharge capacity is recorded. The battery is cycled 600 times according to the parameters of the first cycle and the discharge capacity of the 600th cycle is recorded. The discharge capacity of the 600 cycles is compared with the discharge capacity of the first cycle to obtain the capacity retention rate of the cell after 600 cycles. The cell is then disassembled and the lithium plating of the electrode is observed. Slight lithium plating: sporadic, dotted grayish-white or light gold spots appear on the surface of the negative electrode, without obvious dendritic protrusions; Severe lithium plating: a large area of ​​continuous silvery-white metallic luster appears on the surface of the negative electrode, or moss-like or dendritic protrusions are visible.

[0121] (17) Cell safety performance test: The coated separator and ternary NCM811 positive electrode and graphite negative electrode are stacked to form the cell. After being fully charged, the cell is placed in an oven and heated to 140°C at 5°C / min and kept at a constant temperature for 30min. If the cell smokes, explodes or catches fire, the battery safety performance is deemed to have failed. The safety performance of 10 cells is tested in parallel using the same method. Then the cell safety test pass rate is calculated as [(number of cells that pass / 10)] × 100%.

[0122] The reason why different types of positive electrode sheets were used in the above capacity retention and safety performance tests is that lithium iron phosphate has a strong cycle stability benchmark, which can better reflect the effect of different separators; ternary positive electrode materials are more sensitive to safety, which can better reflect the differences between different separators.

[0123] Table 1 Polymer Particle Properties

[0124] Table 2 Properties of Composite Membrane

[0125] Table 3 Battery cell performance after composite film is used to prepare the battery cell

[0126] As can be seen from Tables 1 to 3, the coated separators prepared in the embodiments of the present invention, when combined with the positive and negative electrodes to form a battery, result in a battery with superior overall performance. In Examples 10 and 11, coating an inorganic heat-resistant ceramic layer between the porous resin layer and the base membrane further enhances the overall heat resistance and rupture temperature of the coated separator, thereby better ensuring the safety performance of the battery.

[0127] As can be seen from Comparative Examples 1 and 2, when the K value of the coated separator is large, polymer particles easily enter the pores of the porous resin layer, not only blocking the conductivity of the pores but also failing to provide effective adhesion between the separator and the electrode, thus easily deteriorating the adhesion of the polymer particles. This can easily lead to lithium plating problems after battery cycling, thereby affecting the cycle performance and safety performance of the battery. When the K value of the coated separator is small, fewer polymer particles enter the porous resin layer, and the contact between the polymer particles and the porous resin layer is mainly point contact, which reduces the adhesion of the polymer particles in the porous resin layer. The polymer particles are easy to fall off, causing severe powder shedding of the discontinuous polymer adhesive layer. After the polymer particles fall off, the number of polymer particles in the coated separator used for bonding with the electrode is reduced, which also leads to a decrease in the adhesion between the coated separator and the electrode. When the coated separator and the positive and negative electrodes are used to prepare the battery cell, the adhesion is insufficient, and the battery is prone to softening and swelling after cycling, thus affecting the cycle performance and safety performance of the battery.

[0128] As can be seen from Comparative Examples 3 and 4: When the coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer is low, the polymer particles can provide fewer bonding sites, resulting in weak adhesion between the coated separator and the electrode sheets. When the coated separator and the positive and negative electrode sheets are used to prepare a battery, the insufficient adhesion makes the battery prone to softening and swelling after cycling, thus affecting the battery's cycle performance and safety performance. When the coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer is high, on the one hand, the larger the coverage, the greater the impact on the overall air permeability of the coated separator, which can easily block the ion shuttle channels, affecting ion conduction and leading to lithium plating problems. On the other hand, the larger the coverage, the more bonding sites the polymer particles can provide, resulting in stronger adhesion between the coated separator and the electrode sheets. When the coated separator and the positive and negative electrode sheets are used to prepare a battery, the excessive adhesion makes it impossible to effectively dissipate heat when the battery releases heat, deteriorating the battery's safety performance. Therefore, excessive coverage will lead to a deterioration in battery cycle performance and safety performance.

[0129] As can be seen from Comparative Examples 5 and 6, when the pore size of the porous resin layer is too small, the coating of the discontinuous polymer adhesive layer easily leads to an increase in overall air permeability. After the coated separator is used to prepare the battery, the effective ion conduction channels are limited, increasing the internal resistance of the battery and easily leading to lithium plating problems. The overall cycle performance and safety performance of the battery deteriorate. When the pore size of the porous resin layer is too large, the heat resistance provided by the porous resin layer is insufficient, the membrane rupture temperature of the coated separator is reduced, and the particle size of the polymer particles used needs to be larger, thereby reducing the bonding sites of the polymer and affecting the adhesion performance between the coated separator and the electrode sheet. After the coated separator is used to prepare the battery, the cycle performance and safety performance deteriorate.

[0130] In summary, the coated separator provided by this invention has high adhesion, air permeability, ion conduction and safety performance, which is beneficial for further improving the hardness and cycle performance of the battery.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coated diaphragm, characterized in that, Includes a base film and a composite coating disposed on at least one surface of the base film; The composite coating includes a porous resin layer disposed on the surface of the base film and a discontinuous polymer adhesive layer disposed on the surface of the porous resin layer; the discontinuous polymer adhesive layer comprises a plurality of randomly distributed polymer particles; the polymer particles include acrylate copolymer particles with a core-shell structure; The average pore size of the porous resin layer is d, which is 0.1 μm to 0.8 μm; the average particle size of the acrylate copolymer particles is D, where K = d / D, and 0.25 ≤ K ≤ 0.

75. The coverage of the discontinuous polymer adhesive layer on the surface of the porous resin layer is η1, where 5% ≤ η1 ≤ 18%.

2. The coated diaphragm according to claim 1, characterized in that, The porous resin layer includes at least one of the following characteristics: Feature 1: The thickness of the porous resin layer is 0.5μm~3.0μm; Feature 2: The high-temperature resistant resin in the porous resin layer includes at least one of aromatic polyamide, polyamide-imide, poly-N-vinylacetamide, polyether block amide, polyimide, polyetherimide, polyethersulfone, polysulfone, polyether ketone and polyketone.

3. The coated diaphragm according to claim 1, characterized in that, The coating weight of the discontinuous polymer adhesive layer is 0.05 g / m³. 2 ~0.18g / m 2 ; And / or, the powder shedding rate of the discontinuous polymer adhesive layer is not higher than 6.5%.

4. The coated diaphragm according to claim 1, characterized in that, The acrylate copolymer particles include at least one of the following characteristics: Feature 3: The particle size D of the acrylate copolymer particles is 0.4 μm to 1.0 μm; Feature 4: The swelling rate of the acrylate copolymer particles is 60%~100%; Feature 5: The acrylate copolymer particles include a core layer and a shell layer covering the core layer. The glass transition temperature of the core layer is Tg1, and the glass transition temperature of the shell layer is Tg2. 40℃≤Tg1≤60℃, -30℃≤Tg2≤-10℃.

5. The coated diaphragm according to claim 4, characterized in that, In the acrylate copolymer particles, the mass percentage of the shell layer is 10% to 20%.

6. The coated diaphragm according to claim 4, characterized in that, The core layer comprises a first polymer formed by polymerizing at least two monomers selected from ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, n-butyl acrylate, butyl methacrylate, methacrylonitrile, styrene, and acrylonitrile.

7. The coated diaphragm according to claim 4, characterized in that, The shell comprises a second polymer formed by polymerizing at least two monomers selected from ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, n-butyl acrylate, butyl methacrylate, methacrylonitrile, styrene, and acrylonitrile.

8. The coated diaphragm according to claim 1, characterized in that, The composite coating also includes a wetting agent, which includes at least one of alkyl sulfate, polyoxyethylene alkylphenol ether, alkylphenol polyoxyethylene ether, and fatty alcohol polyoxyethylene ether.

9. The coated diaphragm according to claim 1, characterized in that, The base film includes at least one of PE base film and PP base film; And / or, the thickness of the base film is 4μm~16μm; And / or, a ceramic layer may be further included between the base film and the porous resin layer.

10. The coated diaphragm according to any one of claims 1 to 9, characterized in that, The coated diaphragm also has at least one of the following characteristics: Feature 6: After the discontinuous polymer adhesive layer is hot-pressed at 1MPa and 60℃ for 1 min, the coverage of the porous resin layer on the surface is η2, 10%≤η2≤30%, and η2>η1; Feature 7: The hot-pressing bonding force between the coated diaphragm and the positive electrode sheet at 85°C is F, where 5N / m≤F≤10N / m; Feature 8: The air permeability growth rate of the coating on the diaphragm does not exceed 19%; Feature 9: The rupture temperature of the coated diaphragm is not lower than 170°C; Feature 10: The ionic conductivity of the coated diaphragm is not less than 0.8 mS / cm; Feature 11: The thermal shrinkage rate of the coated diaphragm at 130°C does not exceed 9.7% in the MD direction and does not exceed 8.3% in the TD direction; Feature 12: The thermal shrinkage rate of the coated diaphragm in the MD direction at 150°C does not exceed 44.5%, and the thermal shrinkage rate in the TD direction does not exceed 38%.

11. A method for preparing a coated diaphragm as described in any one of claims 1 to 10, characterized in that, Includes the following steps: The porous resin layer is prepared on the surface of the base film, and then the discontinuous polymer adhesive layer is prepared on the surface of the porous resin layer.

12. A battery, characterized in that, Includes the coated diaphragm as described in any one of claims 1 to 10.

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