Coating slurry, separator, preparation method for separator, and battery

Abstract

A coating slurry, a separator, a preparation method for a separator, and a battery. The separator comprises a substrate and a coating layer provided on at least one surface of the substrate. The coating layer comprises non-fluoropolymer microspheres and a fluorine-free binder. The mass ratio of the non-fluoropolymer microspheres to the fluorine-free binder is (1-18):1. The melting point of the non-fluoropolymer microspheres is denoted as T, the glass transition temperature of the fluorine-free binder is denoted as T(g), and T and T(g) satisfy the following relationship: 30≤|T+T(g)|≤190. The described separator can achieve low-temperature cold pressing with positive and negative electrode sheets. In addition, the bonding force between the separator and the positive and negative electrode sheets is high, interface bonding performance is excellent, and the separator has good air permeability, thermal stability, and anti-liquid wrinkling performance.

Description

A coating slurry, a separator, a method for preparing the separator, and a battery. Technical Field

[0001] This application relates to the field of lithium-ion battery technology, such as a coating slurry, a separator, a method for preparing the separator, and a battery. Background Technology

[0002] The separator, a polymer material used to separate the positive and negative electrodes in a lithium-ion battery, is one of the key components. The performance of the separator significantly impacts battery safety, charge / discharge performance, and cycle life. Therefore, using high-performance separators is one way to improve the performance of lithium-ion batteries.

[0003] To improve the adhesion between the separator and the positive and negative electrodes, an adhesive coating is usually applied to the surface of the base film. Commonly used adhesive coatings are mainly fluoropolymer coatings, such as polyvinylidene fluoride (PVDF). However, PVDF has a high melting point, is expensive, and is environmentally unfriendly due to its fluorine content. Furthermore, even after hot-pressing the separator to the positive and negative electrodes under high temperature and pressure during battery production, problems such as low adhesion and incomplete compaction still exist.

[0004] Therefore, developing a separator that can be pressed together with the positive and negative electrodes at a lower temperature and has high adhesion to the positive and negative electrodes is an urgent problem to be solved in this field. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0006] This application provides a coating slurry, a separator, a method for preparing the separator, and a battery. The separator can be cold-pressed with positive and negative electrodes at low temperatures, and the separator has high adhesion to the positive and negative electrodes, exhibiting excellent interfacial bonding performance.

[0007] In a first aspect, this application provides a diaphragm, comprising a substrate and a coating layer disposed on at least one surface of the substrate, the coating layer comprising non-fluoropolymer microspheres and a non-fluoro binder; the mass ratio of the non-fluoropolymer microspheres to the non-fluoro binder is (1-18):1; the melting point of the non-fluoropolymer microspheres is denoted as T, the glass transition temperature of the non-fluoro binder is denoted as Tg, and T and Tg satisfy the following relationship: 30≤|T+Tg|≤190.

[0008] In this application, the coating layer comprises non-fluorinated polymer microspheres and non-fluorinated binder in a specific mass ratio, and the melting point of the non-fluorinated polymer microspheres and the glass transition temperature of the non-fluorinated binder are controlled to satisfy a specific relationship, enabling the separator to bond with the positive and negative electrode sheets at a lower temperature. Through low-temperature bonding, not only is the air permeability of the inner and outer layers of the battery separator better uniform, making it less likely for the separator to experience pore blockage during hot pressing, but it also avoids the problem of uneven heat distribution during hot pressing, which causes the core to be relatively soft and the battery performance to be inconsistent. Moreover, low-temperature bonding has low energy consumption and low cost. Furthermore, during pressing, the non-fluoropolymer microspheres soften and deform, riveting with the positive and negative electrode interfaces. After pressing, the microspheres harden to become an intermediate connecting the separator and the positive and negative electrode materials. The mechanical riveting effect and van der Waals forces at the interface between the microspheres and the electrode sheets together provide good interfacial adhesion. Therefore, by compounding the non-fluoropolymer microspheres with non-fluoro binders, the cold pressing adhesion between the separator and the positive and negative electrode sheets can be improved, and the separator has good air permeability, thermal stability, and anti-liquid wrinkling properties.

[0009] In this application, the mass ratio of the non-fluorinated polymer microspheres to the non-fluorinated binder is (1-18):1, wherein the specific values ​​of (1-18) can be, for example, 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, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, etc.

[0010] In this application, the specific value of |T+Tg| can be, for example, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, etc., and can be selected as 30≤|T+Tg|≤130.

[0011] In this application, controlling T and Tg to satisfy a specific relationship is beneficial to obtaining batteries with better performance and reducing production energy consumption and costs.

[0012] In one embodiment, the melting point of the non-fluoropolymer microspheres is 100–124°C, for example, it can be 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 120°C, 121°C, 122°C, 123°C, 124°C, etc.; it can be optionally 105–120°C.

[0013] During the partial wetting of the separator by the electrolyte, capillary action causes the separator to bulge at the liquid flow front, resulting in gaps between the separator and the electrode. The electrolyte diffuses into the internal pores of the separator and the electrode, and the discharged gas accumulates at the interface between the electrode and the separator to form bubbles, causing local deformation and wrinkles in the separator. In this application, controlling the melting point of the non-fluorinated polymer microspheres and the glass transition temperature of the non-fluorinated binder to satisfy a specific relationship is beneficial to improving the adhesion between the separator and the positive and negative electrodes, while also achieving better anti-wrinkling performance during cell assembly.

[0014] In one embodiment, the non-fluoropolymer microspheres comprise polyethylene wax microspheres and / or modified polyethylene wax microspheres.

[0015] In one embodiment, the modified polyethylene wax microspheres comprise alkyl acrylate-grafted modified polyethylene wax microspheres and / or alkyl methacrylate-grafted modified polyethylene wax microspheres.

[0016] In one embodiment, in the modified polyethylene wax microspheres, the number of alkyl backbone carbon atoms of the alkyl acrylate and alkyl methacrylate is independently ≥1, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.; optionally, the number of alkyl backbone carbon atoms is independently ≥3.

[0017] In one embodiment, the alkyl acrylate in the modified polyethylene wax microspheres includes n-alkyl acrylate; the alkyl methacrylate includes n-alkyl methacrylate.

[0018] In this application, alkyl methacrylate grafted and modified polyethylene wax microspheres can be selected. By using alkyl methacrylate to graft and modify polyethylene wax microspheres, the melting point of polyethylene wax microspheres can be controlled, resulting in a membrane with better adhesion performance. Alkyl methacrylate with long molecular chain and low steric hindrance can be selected.

[0019] In one embodiment, the glass transition temperature of the non-fluorinated adhesive is -70 to 70°C, for example, it can be -70°C, -68°C, -66°C, -64°C, -62°C, -60°C, -58°C, -56°C, -54°C, -52°C, -50°C, -48°C, -46°C, -44°C, -42°C, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, etc.; it can be optionally -70 to -4°C.

[0020] In this application, the glass transition temperature of the non-fluorinated binder is within the aforementioned range, which is beneficial for improving the adhesion between the separator and the positive and negative electrodes, while also achieving better anti-wrinkling performance during cell assembly. Furthermore, when the glass transition temperature is lower, the separator is more likely to undergo molecular chain movement between the separator and the electrode under cold pressing conditions, forming van der Waals forces, thereby improving the electrode adhesion and battery performance. However, the glass transition temperature should not be too low, otherwise the separator's heat shrinkage resistance will be poor due to the low melting point of the binder.

[0021] In one embodiment, the non-fluorinated adhesive includes alkyl acrylate adhesives and their modifications, and / or alkyl methacrylate adhesives and their modifications.

[0022] In this application, the alkyl acrylate binder and alkyl methacrylate binder refer to alkyl acrylate polymers and alkyl methacrylate polymers, which can be homopolymers or copolymers; the phrase "and its modified products" refers to (meth)acrylate alkyl acrylate binders and / or their modified products; the modified product refers to grafting modification of (meth)acrylate alkyl acrylate binders, grafting side chains into their molecular structure to increase the length of the molecular chain side chains, such as grafting long-chain groups such as butyl and octyl.

[0023] In one embodiment, the alkyl acrylate includes at least one of acrylates such as ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-ethylhexyl acrylate; the alkyl methacrylate includes hexyl methacrylate.

[0024] In one embodiment, in the alkyl acrylate binder or alkyl methacrylate binder, the number of carbon atoms in the main chain of the alkyl group is ≥5.

[0025] In this application, the (meth)acrylate and (meth)acrylate binder in the modified polyethylene wax microspheres are not limited to the acrylate compounds mentioned above.

[0026] In this application, the (meth)acrylate alkyl ester binder can be obtained commercially or prepared by oneself.

[0027] In this application, when the (meth)acrylate alkyl ester binder is prepared, its Tg is related to the molecular chain length of the monomer, the steric hindrance of the molecules, the preparation method, and the type of emulsifier. To obtain a (meth)acrylate alkyl ester binder with a low Tg, monomers with high molecular chain flexibility, long molecular chains, and low steric hindrance can be selected. The preparation method can be carried out by dropwise addition of mixed monomers. If a pre-emulsification method is used, the high polydispersity of the emulsion system, i.e., the increased number of droplets and decreased diameter, greatly increases the surface area. The influence of the emulsifier on the intermolecular forces and steric hindrance is greatly enhanced, leading to an increase in Tg. The type of emulsifier can be a nonionic emulsifier. Anionic emulsifiers are used because they have ionizable polar groups, such as sulfate, benzenesulfonate, phosphate, and maleate, which can form hydrogen bonds with water, increasing the internal rotational activation energy of the molecules and the electrostatic repulsion between molecules, thereby causing an increase in the Tg of the polymer.

[0028] In one embodiment, the coating layer further includes inorganic materials.

[0029] In one embodiment, the mass ratio of the inorganic material to the non-fluorinated binder is (0-9):1, wherein the specific values ​​of (0-9) can be, for example, 0.01, 0.02, 0.05, 0.08, 0.1, 0.5, 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, etc.

[0030] In one embodiment, the inorganic material includes at least one of alumina, boehmite, barium sulfate, calcium oxide, silicon carbide, or silicon dioxide.

[0031] In one embodiment, the thickness of the coating layer is 1.0 to 3 μm, for example, it can be 1.0 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, etc.

[0032] In one embodiment, the thickness of the substrate is 3 to 16 μm, for example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, etc.

[0033] In one embodiment, the substrate includes at least one of a polypropylene substrate, a polyethylene substrate, and a multilayer composite substrate of polypropylene and polyethylene.

[0034] Secondly, this application provides a coating slurry, which, by mass percentage, comprises 30-70% non-fluoropolymer microspheres (e.g., 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.) and 2-10% non-fluoro binder (e.g., 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%, etc.), with the balance being solvent; the melting point of the non-fluoropolymer microspheres is denoted as T, and the glass transition temperature of the non-fluoro binder is denoted as Tg, wherein T and Tg satisfy the following relationship: 30≤|T+Tg|≤190.

[0035] In one embodiment, the non-fluoropolymer microspheres satisfy at least one of the following conditions: (1) the melting point of the non-fluoropolymer microspheres is 100–124°C, for example, it can be 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 119°C, 110 ... 8℃, 119℃, 120℃, 121℃, 122℃, 124℃, etc.; (2) The non-fluoropolymer microspheres include at least one of polyethylene wax microspheres, alkyl acrylate grafted modified polyethylene wax microspheres or alkyl methacrylate grafted modified polyethylene wax microspheres; in the alkyl acrylate or alkyl methacrylate, the number of carbon atoms in the alkyl main chain is ≥1, for example, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0036] In one embodiment, the non-fluorinated adhesive satisfies at least one of the following conditions: (1) the glass transition temperature of the non-fluorinated adhesive is -70 to 70°C, for example, it can be -70°C, -68°C, -66°C, -64°C, -62°C, -60°C, -58°C, -56°C, -54°C, -52°C, -50°C, -48°C, -46°C, -44°C, -42°C, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, etc.; (2) The non-fluorinated adhesive includes alkyl acrylate adhesives and their modified forms, and / or alkyl methacrylate adhesives and their modified forms; the alkyl acrylate includes at least one of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-ethylhexyl acrylate; the alkyl methacrylate includes hexyl methacrylate.

[0037] In one embodiment, the solvent includes at least one of water, acetone, ethanol, and N-methylpyrrolidone (NMP).

[0038] In one embodiment, the coating slurry further comprises, by weight percentage, 0-67% inorganic materials (e.g., 0.1%, 0.2%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc.) and / or 0-12% additives (e.g., 0.06%, 0.08%, 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, etc.).

[0039] In this application, the inorganic material in the coating slurry includes at least one of alumina, boehmite, barium sulfate, calcium oxide, silicon carbide, or silicon dioxide.

[0040] In one embodiment, the additives include dispersants and / or wetting agents.

[0041] In this application, the coating slurry comprises, by weight percentage, 0-10% dispersant (e.g., 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 5%, 10%, etc.) and 0-2% wetting agent (e.g., 0.06%, 0.08%, 0.1%, 0.5%, 1%, 2%, etc.).

[0042] In this application, leveling agents, thickeners, or suspending agents may be added to the coating slurry as needed.

[0043] Thirdly, this application provides a method for preparing a diaphragm according to the first aspect, the method comprising: S1: providing a substrate; S2: preparing a coating slurry as described in the second aspect and coating it on at least one surface of the substrate; S3: drying the slurry at a temperature of 50 to 80°C to obtain a diaphragm.

[0044] In this application, the method for preparing the coating slurry includes: mixing non-fluoropolymer microspheres, non-fluoro binder and solvent, as well as optional inorganic materials and additives uniformly to obtain the coating slurry.

[0045] Fourthly, this application provides a battery comprising at least one of the following: (1) the separator described in the first aspect; (2) the separator prepared by the preparation method described in the third aspect; and (3) the coating layer prepared by the coating slurry described in the second aspect.

[0046] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0047] Compared with related technologies, the beneficial effects of this application are as follows:

[0048] The separator provided in this application has a coating layer comprising non-fluorinated polymer microspheres and a non-fluorinated binder in a specific mass ratio. The melting point of the non-fluorinated polymer microspheres and the glass transition temperature of the non-fluorinated binder are controlled to satisfy a specific relationship, enabling the separator to bond with the positive and negative electrode sheets at a relatively low temperature (25–60°C). Simultaneously, it improves the adhesion between the separator and the positive and negative electrode sheets, ensures better anti-wrinkling performance during cell assembly, and provides good air permeability and thermal stability. Furthermore, it is low-cost, the material is fluorine-free, and it is environmentally friendly.

[0049] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0050] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0051] Figure 1 is a schematic diagram showing the interaction between the polymer microspheres and the surface of the positive or negative electrode when the separator provided in this application is cold-pressed with the positive or negative electrode.

[0052] Wherein, 1-positive or negative electrode sheet; 2-powder particles on the surface of the positive or negative electrode sheet; 3-polymer microspheres in the coating layer; 4-substrate. Detailed Implementation

[0053] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0054] All materials used in this application are commercially available or prepared using conventional methods. Unless otherwise specified, the materials used in this application are as follows:

[0055] Non-fluoropolymer microspheres

[0056] Polyethylene wax microspheres 1 (PE wax-1): melting point 110℃, Guangzhou Zhuhai Carbon Language New Material Co., Ltd.

[0057] Polyethylene wax microspheres 2 (PE wax-2): melting point 105℃, KAR-02 from Guangzhou Zhuhai Carbon Language New Material Co., Ltd.

[0058] Polyethylene wax microspheres 3 (PE wax-3): melting point 118℃, KAR-01 from Guangzhou Zhuhai Carbon Language New Material Co., Ltd.

[0059] Polyethylene wax microspheres 4 (PE wax-4): melting point 95℃, Guangzhou Zhuhai Carbon Language New Material Co., Ltd.

[0060] Polyethylene wax microspheres 5 (PE wax-5): melting point 125℃, Guangzhou Zhuhai Carbon Language New Material Co., Ltd.

[0061] Non-fluorinated adhesives

[0062] The n-butyl acrylate adhesive, with a glass transition temperature of -56°C, was purchased from Merck Life Sciences.

[0063] Isobutyl acrylate adhesive, with a glass transition temperature of -4°C, was purchased from Maclean Chemicals.

[0064] n-Butyl methacrylate adhesive, with a glass transition temperature of 20°C, was purchased from Merck Life Sciences.

[0065] 2-Ethylhexyl acrylate adhesive, with a glass transition temperature of -70°C, was purchased from Merck Life Sciences.

[0066] Ethyl acrylate adhesive, with a glass transition temperature of -22°C, was purchased from Merck Life Sciences.

[0067] In this application, Tg and T can be tested by differential scanning calorimetry (DSC).

[0068] Example 1

[0069] This embodiment provides a diaphragm, which includes a substrate (a 7μm thick polyethylene substrate, Shenzhen Xingyuan Material Technology Co., Ltd.) and a coating layer (2μm thick) disposed on one surface of the substrate. The coating layer includes polyethylene wax microspheres 1 (Guangzhou Zhuhai Carbon Language New Material Co., Ltd., T is 110℃), n-butyl acrylate binder, and boehmite (Anhui Yishitong Material Technology Co., Ltd. BG-601). The mass ratio of polyethylene wax microspheres 1 to n-butyl acrylate binder is 5:1; the mass ratio of boehmite to n-butyl acrylate binder is 5:1.

[0070] This embodiment provides a method for preparing a diaphragm, specifically including the following steps:

[0071] By weight percentage, 35% polyethylene wax microspheres, 35% boehmite, 7% n-butyl acrylate binder, 0.05% wetting agent (SY-190 from Guangdong Fangding New Materials Co., Ltd.), 0.05% dispersant (8823 from Shenzhen Yanyi New Materials Co., Ltd.) and 22.9% deionized water are mixed evenly to obtain a coating slurry; the coating slurry is coated onto one surface of a substrate and dried at 60°C to obtain the diaphragm.

[0072] In this application, the interaction between the polymer microspheres in the coating layer and the powder particles on the surface of the positive or negative electrode sheet before and after the diaphragm is cold-pressed is shown in Figure 1. As can be seen from Figure 1, under cold-pressing conditions, the polymer microspheres soften and deform, and the microspheres are riveted to the positive (negative) electrode interface. After cold pressing, the microspheres harden and become an intermediate connecting the diaphragm and the positive (negative) electrode material. The mechanical riveting effect of the microspheres and the electrode interface and the van der Waals force together give good interfacial adhesion performance.

[0073] Examples 2-8, Comparative Examples 1-3

[0074] Examples 2-8 and Comparative Examples 1-3 each provide a separator and a battery, which differ from Example 1 only in that the coating layer of the separator is different. The thickness of the coating layer, the type of material, the mass ratio of non-fluoropolymer microspheres to non-fluoro binder in the coating layer, the mass ratio of inorganic materials to non-fluoro binder, and the absolute value of T+Tg are shown in Tables 1-2. In the table, " / " indicates that the component is not in the formulation, and "Δ" indicates that the component is in the formulation. In the preparation method of the separator, the composition of the coating slurry is adjusted according to the different coating layers (ensuring that the contents of solvent, dispersant, and wetting agent remain unchanged, and adjusting the contents of non-fluoropolymer microspheres, acrylate binder, and inorganic materials to meet the mass ratio in the table). Everything else is the same as in Example 1.

[0075] Table 1

[0076] Table 2

[0077] Performance testing

[0078] (1) Cold pressing adhesion: The separator and the negative electrode sheet are cut to the same size, and then the separator and the negative electrode sheet are bonded together. They are cold pressed for 60s at 25℃ and 6.5MPa, and then stretched at a speed of 200mm / min using a stretching machine to test the cold pressing adhesion between the separator and the negative electrode sheet.

[0079] (2) Hot-pressing adhesion: The diaphragm and the negative electrode sheet are cut to the same size, and then the diaphragm and the negative electrode sheet are bonded together. They are hot-pressed for 60s at 90℃ and 6.5MPa, and then stretched at a speed of 200mm / min using a stretching machine to test the hot-pressing adhesion between the diaphragm and the negative electrode sheet.

[0080] The negative electrode sheet was purchased from Guangdong Candlelight New Energy Technology Co., Ltd.

[0081] (3) Air permeability increment: The air permeability of the diaphragms and substrates provided in Examples 1-8 and Comparative Examples 1-3 was tested using an air permeability instrument. The air permeability increment was obtained by subtracting the air permeability of the substrate from the air permeability of the diaphragm.

[0082] (4) Heat shrinkage rate: The diaphragms provided in Examples 1 to 8 and Comparative Examples 1 to 3 were cut into 160×130mm sizes. A 100×100mm square was drawn in the middle of each diaphragm. Five sheets of paper were placed on the top and bottom of the diaphragm. After placing them in an oven at 130°C for 1 hour, the shrinkage rate of the diaphragm in the MD direction was tested.

[0083] (5) Anti-wrinkling performance of liquid injection: The diaphragms provided in Examples 1-8 and Comparative Examples 1-3 were used to simulate cell assembly (positive and negative electrode sheets were purchased from Guangdong Zhuguang New Energy Technology Co., Ltd.), and then propylene carbonate was injected. After being placed at room temperature for 5 days, the diaphragms were disassembled, and the number of wrinkles per square meter on the surface of the diaphragm coating was observed and recorded. Ten parallel tests were conducted, and the average value was taken. Among them, a wrinkle with a length greater than 1 cm was counted as 1 wrinkle, and a wrinkle less than or equal to 1 cm was considered as no wrinkle.

[0084] The specific test results are shown in Table 3:

[0085] Table 3

[0086] As shown in Table 3, the diaphragm provided in this application has a coating layer comprising non-fluorinated polymer microspheres and non-fluorinated binder in a specific mass ratio. Furthermore, controlling the melting point of the non-fluorinated polymer microspheres and the glass transition temperature of the non-fluorinated binder to satisfy a specific relationship enables the diaphragm to bond with the positive and negative electrode sheets at a lower temperature. Simultaneously, it improves the adhesion between the diaphragm and the positive and negative electrode sheets, ensures better anti-wrinkling performance during cell assembly, and guarantees good air permeability and thermal stability of the diaphragm. The cold-pressing adhesion of the diaphragm is 4–13 N / m, and can even reach 8–13 N / m; the hot-pressing adhesion of the diaphragm is 11–20 N / m, and can even reach 17–20 N / m; the air permeability increment is 7–50 s, the thermal shrinkage rate is 0.25–3.5%, and the number of wrinkles per square meter is 0–2.

[0087] As shown in Comparative Example 1, replacing non-fluoropolymer microspheres with fluoropolymers results in diaphragms with low cold-pressing and hot-pressing adhesion, which differs significantly from the target adhesion; and poor resistance to injection-induced wrinkling. As shown in Comparative Examples 2 and 3, the Tg of the non-fluoropolymer microspheres and the Tg of the non-fluoropolymer binder do not satisfy a specific relationship, or the mass ratio of the non-fluoropolymer microspheres to the non-fluoropolymer binder is outside the range, resulting in diaphragms with high thermal shrinkage rates.

[0088] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A diaphragm, comprising a substrate and a coating layer disposed on at least one surface of the substrate, wherein, The coating layer comprises non-fluoropolymer microspheres and a non-fluoro binder; The mass ratio of the non-fluorinated polymer microspheres to the non-fluorinated binder is (1-18):1; The melting point of the non-fluoropolymer microspheres is denoted as T, and the glass transition temperature of the non-fluoro binder is denoted as Tg. T and Tg satisfy the following relationship: 30≤|T+Tg|≤190.

2. The diaphragm according to claim 1, wherein, The melting point of the non-fluoropolymer microspheres is 100–124°C, and can be selected as 105–120°C.

3. The diaphragm according to claim 1 or 2, wherein, The non-fluoropolymer microspheres include polyethylene wax microspheres and / or modified polyethylene wax microspheres.

4. The diaphragm according to claim 3, wherein, The modified polyethylene wax microspheres include alkyl acrylate grafted modified polyethylene wax microspheres and / or alkyl methacrylate grafted modified polyethylene wax microspheres.

5. The diaphragm according to claim 4, wherein, In the modified polyethylene wax microspheres, the number of alkyl backbone carbon atoms in the alkyl acrylate and alkyl methacrylate is ≥1, and can be selected as ≥3.

6. The diaphragm according to any one of claims 1-5, wherein, The glass transition temperature of the non-fluorinated adhesive is -70 to 70°C, and can be selected as -70 to -4°C.

7. The diaphragm according to any one of claims 1-6, wherein, The non-fluorinated adhesives include alkyl acrylate adhesives and their modified forms, and / or alkyl methacrylate adhesives and their modified forms; Optionally, the alkyl acrylate includes at least one selected from ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-ethylhexyl acrylate; the alkyl methacrylate includes hexyl methacrylate. Optionally, in the alkyl acrylate binder or alkyl methacrylate binder, the number of carbon atoms in the main chain of the alkyl group is ≥5.

8. The diaphragm according to any one of claims 1-7, wherein, The coating layer also includes inorganic materials; Optionally, the mass ratio of the inorganic material to the non-fluorinated binder is (0-9):1; Optionally, the inorganic material includes at least one of alumina, boehmite, barium sulfate, calcium oxide, silicon carbide, or silicon dioxide.

9. The diaphragm according to any one of claims 1-8, wherein, The thickness of the coating layer is 1.0–3 μm; Optionally, the thickness of the substrate is 3–16 μm; Optionally, the substrate includes at least one of a polypropylene substrate, a polyethylene substrate, and a multilayer composite substrate of polypropylene and polyethylene.

10. A coating slurry, wherein, The coating slurry comprises 30-70% non-fluorinated polymer microspheres and 2-10% non-fluorinated binder by weight percentage, with the remainder being solvent. The melting point of the non-fluoropolymer microspheres is denoted as T, and the glass transition temperature of the non-fluoro binder is denoted as Tg. T and Tg satisfy the following relationship: 30≤|T+Tg|≤190.

11. The coating slurry according to claim 10, wherein, The non-fluoropolymer microspheres satisfy at least one of the following conditions: (1) The melting point of the non-fluoropolymer microspheres is 100-124℃; (2) The non-fluoropolymer microspheres include at least one of polyethylene wax microspheres, alkyl acrylate grafted modified polyethylene wax microspheres, or alkyl methacrylate grafted modified polyethylene wax microspheres.

12. The coating slurry according to claim 10, wherein, The non-fluorinated binder satisfies at least one of the following conditions: (1) The glass transition temperature of the non-fluorinated adhesive is -70 to 70°C; (2) The non-fluorinated adhesive includes alkyl acrylate adhesives and their modified forms, and / or alkyl methacrylate adhesives and their modified forms; The alkyl acrylates include at least one of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-ethylhexyl acrylate; the alkyl methacrylates include hexyl methacrylate.

13. The coating slurry according to claim 10, wherein, The solvent includes at least one of water, acetone, ethanol, and N-methylpyrrolidone; Optionally, the coating slurry further includes 0-67% inorganic materials and / or 0-12% additives by weight percentage; Optionally, the additives include dispersants and / or wetting agents.

14. A method for preparing a diaphragm according to any one of claims 1-9, comprising: S1: Provide substrate; S2: Prepare the coating slurry as described in any one of claims 10-13 and coat it on at least one surface of the substrate; S3: Dry the slurry at a temperature of 50-80°C to obtain a diaphragm.

15. A battery comprising at least one of the following: (1) The diaphragm according to any one of claims 1-9; (2) The diaphragm prepared by the method of claim 14; (3) The coating layer obtained by the coating slurry according to any one of claims 10-13.

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