Diaphragm adhesive composition, diaphragm and lithium ion battery

Abstract

The invention provides a diaphragm adhesive composition, a diaphragm and a lithium ion battery, the solid content of the diaphragm adhesive composition is 10-40wt%, and when the solid content of the diaphragm adhesive composition is diluted to 5wt%, the surface tension of a diluent is not less than 28mN / m; the diaphragm adhesive composition comprises polymer particles A and a polymer adhesive B, wherein the solid mass ratio of the polymer particles A to the polymer adhesive B is 100: (3-30); the particle size of the polymer particles A is 0.2-10 [mu] m, and the glass transition temperature of the polymer particles A is 30-90 DEG C; and the polymer adhesive B is a water-based emulsion type adhesive, the particle size of polymer particles contained in the polymer adhesive B is 0.1-1 mu m, and the glass transition temperature of the polymer adhesive B is-50-20 DEG C. The diaphragm adhesive composition disclosed by the invention is not easy to spread on a base material, can prevent an adhesive glue solution from being quickly diffused on the surface of a diaphragm, forms controllable, uniform-size and uniformly-distributed adhesive coating points on the surface of the base material, and has small influence on the air permeability of the diaphragm.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a diaphragm adhesive composition, a diaphragm and a lithium ion battery. Background Art

[0002] As a rechargeable battery with broad application prospects, lithium-ion batteries have gained widespread favor across various industries due to their high energy density, long lifespan, compact size, maintenance-free operation, and environmental friendliness. They have expanded from mobile phones and laptops to electric bicycles, electric vehicles, energy storage systems, and various portable devices, becoming an ideal mobile power source.

[0003] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. The separator is a key internal component, separating the positive and negative electrodes of the battery to prevent contact and short circuits. Currently, polyolefin porous membranes are commonly used as separator materials in lithium-ion batteries. However, this material has a low melting point. When the battery temperature rises due to internal or external factors, the polyolefin porous membrane may shrink or melt, causing direct contact between the positive and negative electrodes, resulting in a short circuit, which can lead to safety accidents such as battery combustion or explosion.

[0004] To address this issue, inorganic particles are typically coated onto the surface of a separator substrate using a polymer binder to create a composite separator. For example, ceramic particles are coated onto the separator substrate to form a ceramic / polymer composite separator. The heat resistance of the ceramic particles is utilized to reduce the separator's thermal shrinkage. Furthermore, a layer of polymer binder, such as polyvinylidene fluoride (PVDF), is applied to the separator surface to enhance adhesion to the positive and negative electrodes, ensuring the stability of the battery structure.

[0005] At present, the commonly used coating methods are mainly roller coating, spray coating and spot coating. In the glue-coated diaphragm prepared by roller coating, the adhesive particles are evenly distributed on the entire diaphragm and have good adhesion, but the flat adhesive glue will have a significant negative impact on the air permeability of the diaphragm. In the glue-coated diaphragm prepared by spraying, the adhesive is distributed on the diaphragm in the form of small droplets. Due to the uneven size and distribution of the droplets, it may cause unstable adhesion and also affect the air permeability of the diaphragm. In the glue-coated diaphragm prepared by spot coating, the adhesive is evenly distributed on the surface of the diaphragm in the form of dots, the adhesion is stable, and the effect on the added value of the diaphragm air permeability is small. However, the existing battery diaphragm coating process has the problem that the adhesive coating points are easy to spread. The size of the coating points also affects the air permeability of the battery diaphragm and its adhesion to the electrode, and ultimately affects the stability of the battery service life.

[0006] The adhesive dot coating needs to minimize diffusion to ensure that the dot size is controllable. Therefore, a separator adhesive composition has been developed. The adhesive composition can be used for dot coating, achieving controllable dot size without diffusion, and resulting in a separator with excellent adhesion and air permeability. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides a separator adhesive composition, a separator and a lithium ion battery.

[0008] In a first aspect, the present invention provides a diaphragm adhesive composition, wherein the solid content of the diaphragm adhesive composition is 10wt%~40wt%, and when the solid content of the diaphragm adhesive composition is diluted to 5wt%, the surface tension of the diluted liquid of the diaphragm adhesive composition is not less than 28mN / m; the diaphragm adhesive composition includes polymer particles A and polymer adhesive B, and the solid mass ratio of the polymer particles A to the polymer adhesive B is 100:(3~30); the particle size of the polymer particles A is 0.2~10μm, and the glass transition temperature of the polymer particles A is 30~90°C; the polymer adhesive B is an aqueous emulsion-type binder, the particle size of the polymer microparticles contained therein is 0.1~1μm, and the glass transition temperature of the polymer adhesive B is -50~20°C.

[0009] The surface tension of a 5% diluted solution of the separator adhesive composition is no less than 28 mN / m, making it difficult for the separator adhesive composition to spread on the substrate. This prevents the adhesive from spreading too quickly on the separator surface, forming controllable, uniformly sized, and evenly distributed coating spots on the substrate surface, minimizing the impact on the separator's air permeability. Furthermore, appropriate surface tension promotes interaction between the separator substrate and the separator adhesive composition, resulting in stronger physical adsorption, thereby improving the bond strength between the separator and the electrode material and enhancing the stability of the battery assembly. Higher surface tension also helps reduce defects such as bubbles and pinholes during the coating process, ensuring the smoothness and flatness of the separator surface, which is crucial for improving battery performance and reliability.

[0010] The solid content of the diaphragm adhesive composition is 10 wt % to 40 wt %, indicating that the diaphragm adhesive has good fluidity and is easy to dilute to a lower solid content so as to control the surface density of the diaphragm adhesive coating.

[0011] Preferably, when the solid content of the separator adhesive composition is diluted to 5 wt %, the surface tension of the diluted solution of the separator adhesive composition is 28-60 mN / m. The surface tension of the diluted solution of the separator adhesive composition includes but is not limited to 28-40 mN / m, 40-50 mN / m, or 50-60 mN / m.

[0012] The diaphragm adhesive composition includes polymer particles A and polymer binder B, wherein the solid mass ratio of polymer particles A to polymer binder B is 100:(3-30). In this application, the solid mass of polymer particles A refers to the mass of the polymer contained in polymer particles A, and the solid mass of polymer binder B refers to the mass of the polymer contained in polymer binder B.

[0013] The particle size of the polymer particles A is 0.2~10μm; the glass transition temperature of the polymer particles A is 30~90℃. By controlling the particle size and glass transition temperature of the polymer particles A, when applied to the diaphragm, the diaphragm has both lower air permeability value-added and better peel strength. If the particle size of the polymer particles A is too small, it is easy to clog the diaphragm pores, resulting in increased air permeability value-added, and the peel strength is also weak. If the particle size of the polymer particles A is too large, the polymer particles A are easy to fall off after coating, and the peel strength is reduced. If the glass transition temperature of the polymer particles A is too high, it cannot be softened during hot pressing, and the peel strength is low; if the glass transition temperature is too low, it is easy to form a film, resulting in increased air permeability value-added of the diaphragm.

[0014] The polymer adhesive B is a water-based emulsion adhesive, and the particle size of the polymer particles contained therein is 0.1-1 μm; the glass transition temperature of the polymer adhesive B is -50-20°C.

[0015] Since the glass transition temperature of polymer binder B is lower than that of polymer particles A and the particle size of polymer binder B is small, polymer particles A and non-conductive particles and other materials can be effectively bonded to the diaphragm substrate, thereby improving the bonding effect.

[0016] By controlling the solid mass ratio of the polymer particles A and the polymer binder B, it is possible to ensure good adhesion and good ion conductivity of the diaphragm. If the proportion of polymer binder B is too high, it is easy to cause pore blockage in the diaphragm and affect the conduction of ions. If the proportion of polymer particles A is too high, it will cause insufficient adhesion between the diaphragm and the electrode sheet.

[0017] In the present invention, both the polymer particles A and the polymer binder B can be obtained by polymerization of monomers containing polymerizable double bonds.

[0018] Preferably, the polymer binder B is selected from at least one of styrene-butadiene latex and polyacrylate emulsion. The polyacrylate is obtained by polymerizing at least one acrylate or methacrylate monomer, while the styrene-butadiene latex is obtained by copolymerizing at least butadiene and styrene. The monomers used to prepare the polymer binder B can also be used to copolymerize the monomers used to prepare the polymer particles A.

[0019] In the present invention, materials such as styrene-butadiene latex and polyacrylate emulsion possess excellent inherent bonding capabilities, effectively and tightly bonding the separator to polymer particles A, ensuring that polymer particles A are unlikely to fall off the separator, thus maintaining stability between battery components and improving overall battery performance. Furthermore, these materials exhibit good compatibility with electrolyte components and are less susceptible to chemical reactions, ensuring long-term battery reliability. The selected materials also exhibit excellent thermal stability, maintaining stable performance even under the high temperatures generated during battery charging and discharging, reducing performance degradation caused by temperature increases and improving battery safety and service life. These materials are mostly aqueous emulsions or solutions, making them easier to handle than traditional organic solvent-based adhesives, with lower volatile organic compound (VOC) emissions, making them more environmentally friendly and in line with the trend toward green production.

[0020] Preferably, the polymerizable double bond monomer is selected from at least one of vinyl monomers, maleate monomers, itaconate monomers, maleimide monomers, (meth)acrylamide monomers, and (meth)acrylate monomers.

[0021] The (meth)acrylamide monomers include acrylamide monomers and methacrylamide monomers, and the (meth)acrylate monomers include acrylate monomers and methacrylate monomers.

[0022] Preferably, the vinyl monomer is selected from vinyl esters, vinyl (thio) ethers, vinyl ketones, vinyl sulfones, acrylonitrile, methacrylonitrile, cyanostyrene, 4-vinylpyridine, 2-vinylpyridine, vinylimidazole, N-vinylpyrrole, N-vinylthiopyrrolidone, ethylene, propylene, butylene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, butadiene, isoprene, 1,4-pentadiene, 1,6-hexadiene and 1, At least one of 7-octadiene, cyclohexene, vinylcyclohexene, ethylidene bicycloheptene, cyclopentadiene, cycloheptadiene, dicyclopentadiene, dicycloheptadiene, limonene and indene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, crotylstyrene, divinylbenzene, divinyltoluene, divinylxylene, trivinylbenzene, vinylnaphthalene, and p-tert-butylstyrene.

[0023] The maleate monomer is selected from at least one of C1-C12 monoalkyl maleate and C1-C12 dialkyl maleate.

[0024] The itaconate ester monomer is selected from one of itaconate C1-C12 monoester and itaconate C1-C12 diester;

[0025] The (meth)acrylamide monomer is selected from at least one of (meth)acrylamide, N-methyl(meth)acrylamide, N-butylacrylamide, acetylacetonate acrylamide, N-hydroxymethyl(meth)acrylamide, N,N'-methylenebis[(meth)acrylamide], cinnamamide, N,N-dimethylacrylamide, N,N-dibenzylacrylamide, methacryloylformamide, N-methyl N-vinylacetamide, and N-vinylpyrrolidone.

[0026] Preferably, the (meth)acrylate monomer is selected from acrylic acid, methacrylic acid, methacrylates and acrylates, and exemplarily includes but is not limited to: acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, isobornyl acrylate, phenoxyethyl acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, benzyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, carboxyethyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, methacrylic acid At least one of isobornyl methacrylate, phenoxyethyl methacrylate, dicyclopentenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, polyethylene glycol mono[(meth)acrylate] ester, aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, tert-butylaminoethyl methacrylate, glycidyl (meth)acrylate, tetrahydrofuran (meth)acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, ethoxylated ethylene glycol diacrylate, ethoxylated ethylene glycol dimethacrylate, allyl methacrylate, diallyl phthalate, diallyl adipate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol diacrylate, pentaerythritol dimethacrylate, pentaerythritol triacrylate, and pentaerythritol trimethacrylate.

[0027] In a second aspect, the present invention provides a diaphragm, comprising the diaphragm adhesive composition as described in the first aspect and a substrate, wherein the substrate may be a diaphragm base film and / or a coated diaphragm with non-conductive particles coated on the base film, and the diaphragm adhesive composition is coated on the substrate by dot matrix coating.

[0028] Preferably, after the diaphragm adhesive composition is applied, the diameter change rate of the adhesive coating point is less than 30%, so as to form coating points that are consistent in size, controllable, and evenly distributed. At the same time, it can prevent the adhesive glue from spreading too quickly on the diaphragm surface, which is beneficial to improving the bonding force between the diaphragm and the electrode.

[0029] Preferably, the diaphragm base film is selected from one of a polyethylene base film, a polypropylene base film, a polypropylene-polyethylene-polypropylene laminated base film, and a non-woven fabric base film.

[0030] When the solid content of the diaphragm adhesive composition is diluted to 5wt%, the contact angle between the diaphragm adhesive composition and the diaphragm base film is greater than 30°, making it difficult for the diaphragm adhesive composition to spread on the substrate, preventing the adhesive liquid from spreading too quickly on the diaphragm surface, and forming controllable, uniformly sized, and evenly distributed coating points on the substrate surface, which has little effect on the air permeability of the diaphragm and helps to improve the bonding force between the diaphragm and the electrode.

[0031] Preferably, when the solid content of the separator adhesive composition is diluted to 5 wt %, the contact angle between the separator adhesive composition and the separator base film is 30° to 70°. The contact angle between the separator adhesive composition and the separator base film includes but is not limited to 30° to 45°, 45° to 60°, or 60° to 70°.

[0032] Preferably, the non-conductive particles in the non-conductive particle diaphragm layer are selected from at least one of hydrated alumina, aluminum oxide, boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, and heat-resistant organic polymer particles.

[0033] The application of dot matrix coating technology enables the diaphragm adhesive composition to form a coating of uniform size and uniform distribution on the substrate, avoiding the problem of uneven thickness that may be caused by traditional coating methods, and helping to improve the battery's charge and discharge efficiency and cycle stability. It can not only reduce the use and emissions of harmful substances, but also reduce energy consumption, meeting the requirements of sustainable development.

[0034] In a third aspect, the present invention provides a lithium-ion battery, comprising the separator adhesive composition according to the second aspect or the separator according to the second aspect.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The surface tension of a 5% diluted solution of the separator adhesive composition of the present invention is no less than 28 mN / m, making it difficult for the separator adhesive composition to spread on the substrate, preventing the adhesive solution from spreading too quickly on the separator surface. This forms controllable, uniformly sized, and evenly distributed adhesive spots on the substrate surface, minimizing the impact on the separator's air permeability while also helping to improve the adhesion between the separator and the electrode. Furthermore, appropriate surface tension can promote interaction between the separator substrate and the separator adhesive composition, forming stronger physical adsorption, thereby improving the bonding strength between the separator and the electrode material and enhancing the stability of the battery assembly. High surface tension also helps reduce defects such as bubbles and pinholes that appear during the coating process, ensuring the smoothness and flatness of the separator surface, which is very important for improving battery performance and reliability. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions of the present invention in conjunction with specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment provides a method for preparing a diaphragm adhesive composition, comprising the following steps:

[0040] Polymer particles A: Weigh 1 part of sodium lauryl sulfate and 225 parts of deionized water into a stirring container, then add 98 parts of methyl methacrylate, 51 parts of butyl acrylate, and 1 part of divinylbenzene. Control the stirring speed to 150±50 rpm, stir and heat to 74±1°C, then add 0.8 parts of initiator, maintain stirring at 74±1°C for 6 hours, then raise the temperature to 79±1°C, and continue the reaction for 3 hours to obtain an emulsion of polymer particles A with a solid content of 40 wt%, an average particle size of 0.2 μm, and a glass transition temperature of 30°C.

[0041] Polymer adhesive B: Weigh 1.5 parts of sodium lauryl sulfate and 225 parts of deionized water into a stirring vessel, add 88 parts of styrene and 62 parts of butadiene, control the stirring speed to 150±50 rpm, stir and heat to 74±1°C, then add 0.8 parts of initiator, maintain stirring at 74±1°C for 6 hours, then raise the temperature to 79±1°C and continue the reaction for 3 hours to obtain a polymer adhesive B emulsion with a solid content of 40 wt%, an average particle size of 0.1 μm, and a glass transition temperature of 18°C.

[0042] An emulsion of polymer particles A and an emulsion of polymer binder B were mixed at a solids mass ratio of 100:3 to produce a separator adhesive composition with a solids content of 40 wt%. The surface tension of the 5 wt% dilution was 29.24 mN / m, and the 5 wt% dilution was a separator adhesive composition diluted to a solids content of 5 wt%.

[0043] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0044] Example 2

[0045] This embodiment provides a method for preparing a diaphragm adhesive composition, comprising the following steps:

[0046] Step 1: Mix 10 parts of monomer with 0.5 parts of dilauroyl peroxide, stir and dissolve evenly to form a mixed monomer; the monomers used in this embodiment are a mixture of styrene, butyl acrylate, isooctyl acrylate, and divinylbenzene, with a mass ratio of 90:6:3:1;

[0047] Step 2: Dissolve polyvinyl alcohol 1788 in 90 parts of deionized water to prepare a dispersant aqueous solution with a dispersant concentration of 0.5wt%;

[0048] Step 3: Pour the mixed solution from the first step into the dispersant aqueous solution from the second step, and homogenize into an oil-water dispersion using a high-speed homogenizer at a speed of 1000 rpm;

[0049] Step 4: After nitrogen is introduced for 30 minutes, the temperature is raised to polymerize at a polymerization temperature of 75° C. and a polymerization time of 6 hours. After the polymerization is completed, an aqueous dispersion of polymer particles A with a solid content of 10% is obtained.

[0050] The glass transition temperature of the polymer particles A in this embodiment is 90° C., and the particle size of the polymer particles A is 10 μm.

[0051] The preparation process of polymer adhesive B is the same as that of Example 1, except that the amount of sodium lauryl sulfate used is 0.08 parts, and the monomer composition is a mixture of acrylonitrile, butyl acrylate, and ethylene glycol diacrylate in a mass ratio of 9:90:1.

[0052] The polymer adhesive B of this embodiment has a glass transition temperature of -41°C and a particle size of 1 μm.

[0053] The emulsion of polymer particles A and the emulsion of polymer binder B were mixed at a solid mass ratio of 100:30 to obtain a separator adhesive composition with a solid content of 10 wt %. The surface tension of a 5 wt % dilution was 39.35 mN / m.

[0054] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0055] Example 3

[0056] Compared with Example 2, the deionized water dosage, monomer ratio, and homogenizer speed were adjusted to achieve a glass transition temperature of 40°C for polymer particles A, a particle size of 2 μm, and a particle size of 0.5 μm and a glass transition temperature of -41°C for polymer binder B. The separator adhesive composition had a solids content of 25 wt %, with a mass ratio of polymer particles A to polymer binder B of 100:15. The surface tension of a 5 wt % dilution was 31.28 mN / m.

[0057] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0058] Example 4

[0059] Compared with Example 3, the glass transition temperature of polymer particles A is 50°C, the particle size of polymer particles A is 4 μm, the solid content of the diaphragm adhesive composition is 15 wt %, and the mass ratio of polymer particles A to polymer adhesive B is 100:15. The surface tension of the 5 wt % dilution is 31.39 mN / m.

[0060] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0061] Example 5

[0062] Compared with Example 3, the glass transition temperature of polymer particles A is 60°C, the particle size of polymer particles A is 5 μm, the solid content of the diaphragm adhesive composition is 15 wt %, and the mass ratio of polymer particles A to polymer adhesive B is 100:15. The surface tension of the 5 wt % dilution is 30.46 mN / m.

[0063] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0064] Example 6

[0065] Compared with Example 3, the glass transition temperature of polymer particles A is 70°C, the particle size of polymer particles A is 6 μm, the solid content of the diaphragm adhesive composition is 15 wt %, and the mass ratio of polymer particles A to polymer adhesive B is 100:15. The surface tension of the 5 wt % dilution is 30.84 mN / m.

[0066] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0067] Example 7

[0068] Compared with Example 3, the glass transition temperature of polymer particles A is 80°C, the particle size of polymer particles A is 8 μm, the solid content of the diaphragm adhesive composition is 15 wt%, and the mass ratio of polymer particles A to polymer adhesive B is 100:15. The surface tension of the 5 wt% dilution is 31.32 mN / m.

[0069] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0070] Example 8

[0071] Compared with Example 1, the glass transition temperature of polymer particles A is 30°C, the particle size of polymer particles A is 9 μm, the solid content of the diaphragm adhesive composition is 15 wt%, and the mass ratio of polymer particles A to polymer adhesive B is 100:15. The surface tension of the 5 wt% dilution is 30.95 mN / m.

[0072] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0073] Example 9

[0074] Compared with Example 3, the separator adhesive composition is the same, except that the separator adhesive is coated on the surface of the coated separator containing the boehmite coating, and the thickness of the boehmite coating is 2 μm.

[0075] Comparative Example 1

[0076] Compared with Example 3, the glass transition temperature of polymer particles A is 20° C., and the remaining steps are the same as those in Example 3. The surface tension of the 5 wt % dilution is 31.33 mN / m.

[0077] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0078] Comparative Example 2

[0079] Compared with Example 3, the glass transition temperature of polymer particles A is 100° C., and the remaining steps are the same as those in Example 3. The surface tension of the 5 wt % dilution is 31.52 mN / m.

[0080] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0081] Comparative Example 3

[0082] Compared with Example 3, the particle size of polymer particles A was 0.1 μm, and the remaining steps were the same as in Example 3. The surface tension of the 5 wt % dilution was 30.76 mN / m.

[0083] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0084] Comparative Example 4

[0085] Compared with Example 3, the particle size of polymer particles A was 11 μm, and the remaining steps were the same as in Example 3. The surface tension of the 5 wt % dilution was 30.93 mN / m.

[0086] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0087] Comparative Example 5

[0088] Compared with Example 3, the surface tension of the diluted solution of the diaphragm adhesive composition is 26.89 mN / m, and the remaining steps are the same as those in Example 3.

[0089] The diaphragm adhesive composition is coated on the surface of the diaphragm base film.

[0090] Comparative Example 6

[0091] Compared with Comparative Example 5, the separator adhesive composition is the same, except that the separator adhesive is coated on the surface of the coated separator containing the boehmite coating, and the boehmite coating has a thickness of 2 μm.

[0092] In all the above examples and comparative examples, the membrane adhesive composition is coated on the surface of the substrate in a dot matrix manner, the design diameter of the coating point is 300 μm, and the surface density of the membrane adhesive composition is 0.2 g / m 2 .

[0093] This embodiment also provides a lithium-ion battery, which uses the separator of this embodiment.

[0094] The battery preparation method is as follows: assemble the negative electrode sheet, the positive electrode sheet, the electrolyte and the separator into a battery.

[0095] The polymers of Examples 1-9 and Comparative Examples 1-6 were characterized and tested for performance. The test results are shown in Table 1.

[0096] Particle size: Laser particle size analyzer (Model: LS-909E, Zhuhai OMEC Instrument Co., Ltd.) was used for detection.

[0097] Glass transition temperature: Differential scanning calorimetry (DSC-100, Shanghai Qunhong Instrument Co., Ltd.) was used for detection.

[0098] Surface tension test: The surface tension of the membrane adhesive composition dilution solution was tested at 23±1°C using a platinum plate method, with the unit being mN / m.

[0099] Peel strength test: The coated separator and negative electrode sheet prepared by the scheme described in the present invention were cut into 20mm*100mm strips respectively, cold pressed for 60s at 95℃ and 2MPa, and subjected to a 180° peel strength test using an electronic tensile testing machine. The test results were taken as the average value of three samples.

[0100] The test method for air permeability value-added is: refer to the air permeability test in GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries":

[0101] Cut three pieces of membrane from the film roll, spaced 150mm apart longitudinally. If the membrane width is ≥100mm, the sample size should be 100mm x 100mm. If the membrane width is <100mm, the sample size should be 100mm x membrane width. Place the membrane in the test head of a permeability tester suitable for the test range and test the permeability time. The average of the three test results is used as the membrane permeability time, expressed in seconds per 100cc.

[0102] The membrane permeability increment is the difference between the permeability time of the membrane after applying the adhesive and the permeability time of the membrane before applying the adhesive, and the unit is s / 100cc;

[0103] Contact angle test: The contact angle of 5wt% dilution was tested using a contact angle meter. 3μl of 5wt% dilution was dropped onto the diaphragm base film and photographed after 5 seconds. The unit is °.

[0104] Glue dot diameter change rate: After the adhesive-coated diaphragm dries, measure the increase in the adhesive dot diameter relative to the theoretical diameter, that is, (actual measured diameter - 300) / 300 * 100%.

[0105] Table 1

[0106] Sample Group Particle size (μm) Glass transition temperature (℃) Diaphragm ventilation value added s / 100cc Peel strength (N / m) Glue coating point diameter change rate (%) Contact angle (°) Example 1 0.2 30 13 8 18 30.35 Example 2 10 90 14 7 12 43.13 Example 3 2 40 7 15 11 32.89 Example 4 4 50 9 13 12 32.80 Example 5 5 60 7 12 12 31.92 Example 6 6 70 8 12 11 32.10 Example 7 8 80 9 11 13 32.78 Example 8 9 30 7 16 12 32.57 Example 9 2 40 35 13 10 / Comparative Example 1 2 20 18 13 15 32.73 Comparative Example 2 2 100 7 3 13 33.65 Comparative Example 3 0.1 40 19 5 11 32.45 Comparative Example 4 11 40 8 4 11 32.31 Comparative Example 5 2 40 17 13 35 27.10 Comparative Example 6 2 40 44 12 33 /

[0107] Test results show that when the surface tension of the adhesive diluent is above 28 mN / m, the change in the diameter of the adhesive dot after application and drying of the separator adhesive composition is minimal. When the surface tension is too low, the change in the diameter of the adhesive dot is greater, and the permeability value-added increases. When the polymer A particle size is between 0.2 and 10 μm and the glass transition temperature is between 30 and 90°C, the separator exhibits both low permeability value-added and improved peel strength. If the polymer A particle size is too small, it can easily clog the separator pores, resulting in increased permeability value-added and weaker peel strength. If the polymer A particle size is too large, the polymer A particles tend to fall off after application, reducing peel strength. If the glass transition temperature of polymer A is too high, it cannot soften during hot pressing, resulting in low peel strength. On the other hand, if the glass transition temperature is too low, the polymer A particles tend to form a film, resulting in increased permeability value-added.

[0108] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in this field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A diaphragm adhesive composition, characterized in that The solid content of the diaphragm adhesive composition is 10wt%~40wt%. When the solid content of the diaphragm adhesive composition is diluted to 5wt%, the surface tension of the diluted liquid of the diaphragm adhesive composition is not less than 28mN / m; the diaphragm adhesive composition includes polymer particles A and polymer adhesive B, and the solid mass ratio of the polymer particles A to the polymer adhesive B is 100:(3~30); the particle size of the polymer particles A is 0.2~10μm, and the glass transition temperature of the polymer particles A is 30~90°C; the polymer adhesive B is an aqueous emulsion-type adhesive, the particle size of the polymer microparticles contained therein is 0.1~1μm, and the glass transition temperature of the polymer adhesive B is -50~20°C.

2. The separator adhesive composition according to claim 1, characterized in that When the solid content of the separator adhesive composition is diluted to 5 wt %, the surface tension of the diluted solution of the separator adhesive composition is 28-60 mN / m.

3. The separator adhesive composition according to claim 1, characterized in that After the diaphragm adhesive composition is applied, the change rate of the adhesive coating point diameter is less than 30%.

4. The separator adhesive composition according to claim 1, characterized in that When the solid content of the separator adhesive composition is diluted to 5 wt %, the contact angle between the separator adhesive composition and the separator base film is greater than 30°.

5. The separator adhesive composition according to claim 1, characterized in that When the solid content of the diaphragm adhesive composition is diluted to 5 wt %, the contact angle between the diaphragm adhesive composition and the diaphragm base film is 30° to 70°.

6. The separator adhesive composition according to claim 4 or 5, characterized in that The diaphragm base film is selected from one of a polyethylene base film, a polypropylene base film, a polypropylene-polyethylene-polypropylene laminated base film, and a non-woven fabric base film.

7. A diaphragm, characterized in that: The diaphragm comprises the diaphragm adhesive composition according to any one of claims 1 to 6 and a substrate, wherein the substrate is a diaphragm base film and / or a coated diaphragm with non-conductive particles coated on the diaphragm base film, and the diaphragm adhesive composition is coated on the substrate by dot matrix coating.

8. The diaphragm according to claim 7, characterized in that The diaphragm base film is selected from one of a polyethylene base film, a polypropylene base film, a polypropylene-polyethylene-polypropylene laminated base film, and a non-woven fabric base film.

9. The diaphragm according to claim 7, characterized in that The non-conductive particles are selected from at least one of hydrated alumina, aluminum oxide, boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, and heat-resistant organic polymer particles.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the separator adhesive composition according to any one of claims 1 to 6, or the separator according to any one of claims 7 to 9.