Separator binder composition, separator binder powder, separator, and battery

Abstract

The present invention relates to the technical field of battery materials, and in particular to a separator binder composition, separator binder powder, a separator, and a battery. The separator binder composition comprises polymer particles A and polymer particles B, wherein the glass transition temperature Tg of the polymer particles A is -10°C or below, the glass transition temperature Tg of the polymer particles B is 60°C or above, the median particle size D50 of the polymer particles A is 500 nm or above, and the median particle size D50 of the polymer particles B is 300 nm or below. The separator binder composition in the present invention not only can effectively bond an electrode sheet and the separator, but also helps maintain the uniformity and stability of a coating layer on the surface of the separator, ensuring that the separator has high air permeability and good wetting performance for an electrolyte solution, thereby prolonging the cycle life of the battery.

Description

A membrane binder composition, membrane binder powder, membrane, and battery Technical Field

[0001] This invention relates to the field of battery materials technology, and more particularly to a membrane binder composition, membrane binder powder, membrane, and battery. Background Technology

[0002] With socio-economic development and technological progress, people's demand for energy is constantly increasing. The consumption of traditional fossil fuels has not only caused resource depletion but also triggered serious environmental problems. Among numerous new energy technologies, lithium-ion batteries have become one of the most prominent research subjects due to their advantages such as high energy density, long lifespan, and lack of memory effect.

[0003] A lithium-ion battery is a rechargeable battery (secondary battery) that operates based on the movement of lithium ions between the positive and negative electrodes. A typical lithium-ion battery structure includes a positive electrode material, a negative electrode material, an electrolyte, and a separator between the positive and negative electrodes. The separator is not only a key component that physically isolates the positive and negative electrodes, but also an important medium that ensures lithium ions can freely pass through for charging and discharging reactions. The quality of the separator directly affects the battery's safety, cycle life, and charge / discharge efficiency. The main function of the separator is to physically prevent direct contact between the positive and negative electrodes, which could lead to a short circuit, while allowing lithium ions to pass through smoothly. Furthermore, the separator must possess good chemical stability, mechanical strength, and thermal stability to withstand the complex electrochemical environment inside the battery.

[0004] Currently, most lithium-ion battery separators widely used in the market are porous membranes made of polyolefin materials, such as polyvinylidene fluoride (PVDF). While these materials have good thermal stability and chemical inertness, they suffer from high cost, complex production processes, and environmental unfriendliness. Furthermore, the preparation of fluoropolymer coatings requires the use of organic solvents, which not only increases production costs but may also lead to environmental pollution and safety hazards. More importantly, traditional fluoropolymer coatings struggle to achieve effective adhesion at room temperature. While commonly used hot-pressing processes can achieve good adhesion, they also introduce problems such as micro-deformation of the separator and pore blockage, affecting the migration path of lithium ions, reducing battery charge and discharge efficiency, and even posing safety risks.

[0005] Therefore, it is of great significance to develop a diaphragm adhesive that can achieve good bonding between the diaphragm and the electrode at room temperature. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a separator adhesive composition, separator adhesive powder, separator, and battery that can achieve good adhesion between the separator and the electrode at room temperature.

[0007] In a first aspect, a membrane adhesive composition includes polymer particles A and polymer particles B, wherein the glass transition temperature Tg of polymer particles A is below -10°C, the glass transition temperature Tg of polymer particles B is above 60°C, the average particle size D50 of polymer particles A is above 500 nm, and the average particle size D50 of polymer particles B is below 300 nm.

[0008] In this invention, when the diaphragm binder composition contains polymer particles A with a glass transition temperature (Tg) below -10°C and an average particle size (D50) above 500 nm, and polymer particles B with a glass transition temperature (Tg) above 60°C and an average particle size (D50) below 300 nm, after the powder formed by this diaphragm binder composition is used to prepare a diaphragm slurry and coated onto the surface of the base membrane, the surface of the larger polymer particles A is covered with polymer particles B. Under unpressurized diaphragm preparation and winding processes, the diaphragm will not self-adhere, greatly improving processing performance. Furthermore, when bonding the diaphragm to the electrode to prepare the battery cell, only a certain pressure needs to be applied at room temperature to achieve effective bonding between the diaphragm and the electrode.

[0009] Furthermore, the use of polymer particles A and B, which have glass transition temperatures and average particle sizes within the aforementioned specific range, can effectively suppress the coating layer from clogging the micropores of the base film, thereby suppressing the decrease in the air permeability of the prepared diaphragm.

[0010] Preferably, in the diaphragm adhesive composition, the mass ratio of polymer particles A to polymer particles B is (5-9):(1-5).

[0011] In this invention, when the mass ratio of polymer particles A to polymer particles B is within the above-mentioned range, it is more beneficial to ensure that self-adhesion does not occur during the membrane processing, and that effective bonding between the membrane and the electrode is achieved by applying pressure at room temperature during the preparation of the battery cell. Preferably, the mass ratio of polymer particles A to polymer particles B is (6-8):(2-4).

[0012] Preferably, the average particle size ratio of polymer particle A to polymer particle B is (5~15):3.

[0013] In this invention, the ratio of the average particle size of polymer particles A to polymer particles B within the aforementioned range is highly advantageous for further achieving the objectives of this invention. Specifically, it facilitates effective bonding between the diaphragm and the electrode under room temperature pressure and effectively prevents self-adhesion during diaphragm processing. Furthermore, it helps to further suppress the decline in the diaphragm's air permeability. In a further preferred embodiment, the ratio of the average particle size of polymer particles A to polymer particles B is (8~12):3.

[0014] Preferably, the glass transition temperature (Tg) of polymer particle A is -70 to -10°C, and the average particle size (D50) of polymer particle A is 500 to 1500 nm. The glass transition temperature (Tg) of polymer particle B is 60 to 150°C, and the average particle size (D50) of polymer particle B is 100 to 300 nm.

[0015] Specifically, the glass transition temperature Tg of polymer particles A can be -10℃, -15℃, -20℃, -25℃, -30℃, -35℃, -40℃, -45℃, -50℃, -55℃, -60℃, -65℃, or -70℃.

[0016] The average particle size D50 of polymer particles A can be 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1000nm, 1050nm, 1100nm, 1150nm, 1200nm, 1250nm, 1300nm, 1350nm, 1400nm, 1450nm, or 1500nm.

[0017] The glass transition temperature (Tg) of polymer particles B can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, or 150℃.

[0018] The average particle size D50 of polymer particles B can be 100nm, 150nm, 200nm, 250nm, or 300nm.

[0019] Preferably, polymer particles B are distributed on the surface of polymer particles A, and the surface of polymer particles A is at least partially covered by polymer particles B.

[0020] In this invention, when the aforementioned polymer particles A and B have the above-described distribution, during the membrane processing, polymer particles B, with the aforementioned glass transition temperature and particle size, can provide effective structural support. Furthermore, polymer particles B encapsulate polymer particles A, which primarily provide the adhesive effect, while the exposed polymer particles do not provide adhesive force at room temperature, thus preventing self-adhesion. However, when preparing the battery cell, polymer particles A, with the aforementioned glass transition temperature and particle size, are softer and provide the main adhesive force. Upon applying pressure, polymer particles A are exposed and come into contact with the base membrane and electrode of the membrane, achieving adhesion. Simultaneously, since polymer particles B are mainly distributed on the surface of polymer particles A rather than discretely distributed, this is highly advantageous for maintaining the porosity of the coating layer containing the membrane binder and for avoiding clogging of the micropores of the membrane base membrane, thus suppressing the decrease in membrane permeability.

[0021] In this invention, the specific materials of polymer particles A and B are not particularly limited, and various polymer materials commonly used in the prior art can be used.

[0022] To better achieve the objectives of this invention, preferably, the polymer particles A include vinyl structural units, acrylate structural units, and functional structural units;

[0023] The vinyl structural unit is selected from one or more of styrene structural units, acrylonitrile structural units, methylstyrene structural units, ethylstyrene structural units, acrylamide structural units, and methacrylamide structural units; in this invention, the vinyl structural unit is preferably selected from styrene structural units and / or acrylamide structural units.

[0024] In this invention, styrene structural units can form polymers with good transparency, rigidity, and chemical resistance. The presence of styrene structural units can improve the hardness and modulus of the final material, while also enhancing its gloss and surface smoothness. Acrylamide structural units, on the other hand, have good water solubility and hydrophilicity, which can improve the polymer's water absorption and wettability, and promote the absorption and transport of electrolytes. Both styrene and acrylamide have good reactivity and are easily subjected to emulsion polymerization, which not only simplifies the production process but also improves production efficiency.

[0025] The acrylate structural units are selected from one or more of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, lauryl methacrylate, and cyclohexyl methacrylate.

[0026] The functional structural unit is selected from one or more of the following: acrylic acid structural unit, methacrylic acid structural unit, vinyl acrylate structural unit, β-acryloyloxypropionic acid structural unit, hydroxyacrylic acid, maleic acid structural unit, itaconic acid structural unit, itaconic acid monobutyl ester structural unit, hydroxyethyl acrylate structural unit, hydroxypropyl acrylate structural unit, hydroxyethyl methacrylate structural unit, hydroxypropyl methacrylate structural unit, hydroxymethylacrylamide structural unit, hydroxyethylacryloylurea structural unit, caprolactone acrylate structural unit, polyethylene glycol monomethacrylate structural unit, and phenyl glycidyl ether acrylate structural unit.

[0027] Preferably, in polymer particles A, the mass ratio of vinyl structural units, acrylate structural units and functional structural units is (0-35):(60-95):(1-5).

[0028] Preferably, the polymer particle B comprises a main structural unit and a cross-linked structural unit;

[0029] The main structural unit is selected from one or more of the following structural units: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, styrene, methylstyrene, acrylamide, methacrylamide, methyl methacrylate, glycerol formaldehyde methacrylate, isoborneol acrylate, isoborneol methacrylate, acrylic acid, methacrylic acid, and itaconic acid.

[0030] The crosslinking structural unit is selected from one or more of the following: diol diacrylate structural unit, bisphenol A diacrylate structural unit, heterocycloalkane diacrylate structural unit, divinyl aromatic hydrocarbon structural unit, diol dimethacrylate structural unit, bisphenol A dimethacrylate structural unit, trimethylolpropane triacrylate structural unit, trimethylolpropane trimethacrylate structural unit, and pentaerythritol tetraacrylate structural unit.

[0031] Preferably, in polymer particles B, the mass ratio of the main structural unit to the cross-linked structural unit is 100:(2-10).

[0032] As is known to those skilled in the art, in the aforementioned polymer particles A and B, "a certain" structural unit refers to a structural unit present in the polymer obtained by polymerizing "a certain monomer". For example, an acrylate structural unit refers to a structural unit derived from an acrylate monomer in polymer particle A obtained after the polymerization of acrylate monomers. Similarly, in this invention, the mass ratio of various structural units in the aforementioned polymer particles is based on the mass ratio of various monomers that participated in the polymerization to obtain the polymer particles.

[0033] The aforementioned polymer particles A and B can be prepared using conventional methods in the field of chemical synthesis, which will not be described in detail in this invention.

[0034] When the materials of polymer particles A and B meet the above conditions, it is more beneficial to further improve the adhesion and avoid self-adhesion.

[0035] The diaphragm binder composition provided by this invention is typically in the form of an emulsion, with polymer particles A and B distributed in the solvent as suspended particles. Generally, the solvent content is not limited; the relative amounts of polymer particles A and B to the solvent can be adjusted according to the actual solid content requirements.

[0036] Typically, the solvent mentioned above is deionized water.

[0037] In a second aspect, the present invention provides a diaphragm binder powder, wherein the diaphragm binder powder is a secondary particle formed from the diaphragm binder composition as described above, the secondary particle comprising polymer particles A and polymer particles B distributed on the surface of polymer particles A, wherein the surface of polymer particles A is at least partially covered by polymer particles B.

[0038] The aforementioned diaphragm binder powder can be prepared by spray drying using the diaphragm binder composition provided by the present invention. For example, a spray drying agent can be used to spray dry the aforementioned diaphragm binder composition. The specific conditions for spray drying can be those known in the prior art, such as an inlet air temperature of 180°C or higher and an outlet air temperature of 80~100°C.

[0039] By using the aforementioned diaphragm binder composition and spray drying, diaphragm binder powder with the aforementioned structure can be obtained.

[0040] Thirdly, the present invention provides a diaphragm comprising the diaphragm binder powder as described above.

[0041] The method of preparing a diaphragm using the aforementioned diaphragm adhesive composition or diaphragm adhesive powder is known in the prior art. For example, the diaphragm adhesive powder, auxiliary adhesive, additives and solvent are mixed in a mass ratio of (10-15):(1-3):(0.5-2):(80-90), dispersed to obtain a coating slurry, and then the coating slurry is coated on the surface of the diaphragm substrate, dried and wound up.

[0042] Because the diaphragm adhesive composition or diaphragm adhesive powder provided by this invention hardly adheres under normal temperature and without pressure, an auxiliary adhesive needs to be added during diaphragm preparation to achieve stable adhesion of the coating slurry to the diaphragm base membrane surface. In this invention, the auxiliary adhesive can be selected from one or more commonly used acrylic adhesives, SBR (styrene-butadiene rubber) adhesives, PAA (polyacrylic acid) adhesives, and PAN (polyacrylonitrile) adhesives, for example, SWA610 from Shenzhen Haodian Technology Co., Ltd. can be used.

[0043] The aforementioned additives can be of various types commonly used in the field, such as surfactants and defoamers. Specifically, additives can be one or more of fluorocarbon surfactants, polysiloxane defoamers, and white mineral oil.

[0044] Deionized water can be used as the solvent.

[0045] Fourthly, the present invention provides a battery comprising the separator as described above.

[0046] The method for preparing batteries using the separator provided by this invention can be a conventional method in the prior art, and will not be described in detail here. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. Example 1

[0048] This embodiment provides a method for preparing diaphragm binder powder, including the following steps: polymer particles A and polymer particles B are compounded at a mass ratio of 5:1 and obtained by spray drying (inlet air temperature 180°C, outlet air temperature 90°C).

[0049] The preparation method of polymer particles A includes: adding 80 parts of water and 1 part of sodium bicarbonate into a reaction vessel, purging with nitrogen for 30 min, heating the sealed container to 75℃ and reacting for 15 min, adding 1 part of ammonium persulfate, 0.2 parts of sodium dodecylbenzenesulfonate, 80 parts of water, 50 parts of butyl acrylate, 20 parts of isooctyl acrylate, 38 parts of styrene, and 3 parts of methacrylic acid, reacting at 75℃ for 2 h, holding at that temperature for 1 h, heating to 85℃ and reacting for 1 h, holding at that temperature for 2 h, cooling to 40℃ and ending the reaction, and obtaining an emulsion of polymer particles A. The glass transition temperature of polymer particles A is -15℃, and the particle size D of polymer particles A is 551 nm.

[0050] The preparation method of polymer particles B involves adding 80 parts of water, 1 part of sodium bicarbonate, and 0.5 parts of emulsifier to a reaction vessel, purging with nitrogen for 30 minutes, heating the sealed container to 85°C and reacting for 15 minutes, then adding 1 part of ammonium persulfate, 1 part of sodium dodecylbenzenesulfonate, 80 parts of water, 85 parts of styrene, 15 parts of isooctyl acrylate, 3 parts of acrylic acid, and 3 parts of divinylbenzene. The reaction is carried out at 80-90°C for 4 hours, maintained at this temperature for 2 hours, and then cooled to 40°C to terminate the reaction, thus obtaining an emulsion of polymer particles B. The glass transition temperature of polymer particles B is 70°C, and the particle size D of polymer particles B is 256 nm.

[0051] The emulsions of polymer particles A and polymer particles B are mixed at a mass ratio of polymer particles A:polymer particles B of 5:1 to obtain the diaphragm adhesive composition of the present invention. This embodiment provides a method for preparing a diaphragm coating composition, comprising the following steps: mixing the above-mentioned diaphragm adhesive powder, auxiliary binder (SWA610 from Shenzhen Haodian Technology Co., Ltd., by solid mass), polysiloxane defoamer, and water at a mass ratio of 10:2:2:83, and dispersing the mixture to obtain the diaphragm coating composition.

[0052] This embodiment provides a method for preparing a ceramic diaphragm, comprising the following steps: coating the above-mentioned diaphragm coating composition and winding it up to obtain a ceramic diaphragm.

[0053] This embodiment provides a battery, which further includes a positive electrode, a negative electrode, a ceramic separator, and an electrolyte.

[0054] The preparation of the positive electrode sheet involves weighing each raw material according to the mass ratio (lithium cobalt oxide: carbon black: polyvinylidene fluoride = 90:5:5), adding lithium cobalt oxide, carbon black, and polyvinylidene fluoride to a solvent, mixing thoroughly with a high-speed stirrer to obtain a uniform slurry, uniformly coating the obtained slurry onto an aluminum foil current collector, and then drying it in an oven to remove the solvent and form a uniform positive electrode sheet.

[0055] Preparation of negative electrode sheet: Weigh each raw material according to the mass ratio (graphite: carbon black: sodium carboxymethyl cellulose = 90:5:5), add graphite, carbon black and sodium carboxymethyl cellulose to the solvent, mix thoroughly with a high-speed stirrer to obtain a uniform slurry, coat the prepared slurry evenly on the copper foil current collector, and then dry in an oven to remove the solvent and form a uniform negative electrode sheet.

[0056] Preparation of electrolyte: Weigh each raw material according to the mass ratio (lithium hexafluorophosphate: ethylene carbonate = 1:10), dissolve lithium hexafluorophosphate in ethylene carbonate, stir evenly, and the electrolyte is obtained.

[0057] Battery assembly: Prepare the positive electrode, negative electrode, ceramic separator, and electrolyte. Stack the positive electrode, ceramic separator, and negative electrode in sequence and press them at 4-5 MPa for 60 seconds at room temperature to form a battery cell. Ensure that the positive and negative electrode cells are separated by a ceramic separator to prevent short circuits. Place the battery cell into the battery case, inject the electrolyte, and seal the battery case to ensure airtightness. Perform an aging treatment on the assembled battery, usually by placing it at room temperature for 24 hours. Example 2

[0058] Compared with Example 1, the raw materials for preparing polymer particles A include: 13 parts acrylonitrile, 13 parts styrene, 54 parts butyl acrylate, 28 parts isooctyl acrylate, and 3 parts methacrylic acid; its glass transition temperature Tg is -30°C and its average particle size D50 is 763 nm.

[0059] The raw materials for preparing polymer particles B include: 96 parts styrene, 4 parts isooctyl acrylate, 3 parts acrylic acid, and 3 parts divinylbenzene; its glass transition temperature Tg is 90°C and its average particle size D50 is 231 nm.

[0060] The mass ratio of polymer particle A to polymer particle B is 7:3, and the remaining steps are the same as in Example 1. Example 3

[0061] Compared with Example 2, the stirring speed during the preparation of polymer particles A and polymer particles B was adjusted; the glass transition temperature Tg of the prepared polymer particles A was tested to be -30° and the average particle size D50 was 1408 nm; the glass transition temperature Tg of polymer particles B was 90° and the average particle size D50 was 291 nm; the remaining steps were the same as in Example 2. Example 4

[0062] Compared with Example 2, the stirring speed during the preparation of polymer particles A and polymer particles B was adjusted; the glass transition temperature Tg of the prepared polymer particles A was tested to be -30° and the average particle size D50 was 516 nm; the glass transition temperature Tg of polymer particles B was 90° and the average particle size D50 was 297 nm; the remaining steps were the same as in Example 2. Example 5

[0063] Compared with Example 2, the stirring speed during the preparation of polymer particles A and polymer particles B was adjusted; the glass transition temperature Tg of the prepared polymer particles A was tested to be -30° and the average particle size D50 was 656 nm; the glass transition temperature Tg of polymer particles B was 90° and the average particle size D50 was 128 nm; the remaining steps were the same as in Example 2. Example 6

[0064] Compared with Example 1, the raw materials for preparing polymer particles A include: 5 parts acrylonitrile, 25 parts styrene, 30 parts butyl acrylate, 50 parts isooctyl acrylate, 2 parts hydroxyethyl acrylate, and 1 part methacrylic acid; its glass transition temperature Tg is -30°C and its average particle size D50 is 752 nm.

[0065] The raw materials for preparing polymer particles B include: 96 parts styrene, 4 parts isooctyl acrylate, 3 parts acrylic acid, and 3 parts divinylbenzene; its glass transition temperature Tg is 90°C and its average particle size D50 is 226 nm.

[0066] The mass ratio of polymer particle A to polymer particle B is 9:5, and the remaining steps are the same as in Example 1. Example 7

[0067] Compared with Example 6, the mass ratio of polymer particle A to polymer particle B is 12:1, and the remaining steps are the same as in Example 6. Example 8

[0068] Compared with Example 6, the mass ratio of polymer particle A to polymer particle B is 3:5, and the remaining steps are the same as in Example 6. Example 9

[0069] Compared with Example 1, the raw materials for preparing polymer particles A include: 3 parts styrene, 5 parts butyl acrylate, 95 parts isooctyl acrylate, and 2 parts methacrylic acid; its glass transition temperature Tg is -60°C and its average particle size D50 is 803 nm.

[0070] The raw materials for preparing polymer particles B include: 90 parts styrene, 10 parts isobornyl methacrylate, 5 parts acrylic acid, and 5 parts ethylene glycol dimethacrylate; its glass transition temperature Tg is 120°C and its average particle size D50 is 263 nm.

[0071] The mass ratio of polymer particle A to polymer particle B is 7:3, and the remaining steps are the same as in Example 1. Example 10

[0072] Compared with Example 1, the raw materials for preparing polymer particles A include: 3 parts styrene, 5 parts butyl acrylate, 95 parts isooctyl acrylate, and 2 parts methacrylic acid; its glass transition temperature Tg is -30°C and its average particle size D50 is 957 nm.

[0073] The raw materials for preparing polymer particles B include: 96 parts styrene, 4 parts isooctyl acrylate, 3 parts acrylic acid, and 3 parts ethylene glycol dimethacrylate; its glass transition temperature Tg is 90°C and its average particle size D50 is 285 nm.

[0074] The mass ratio of polymer particle A to polymer particle B is 7:3, and the remaining steps are the same as in Example 1.

[0075] Comparative Example 1

[0076] Compared with Example 1, the raw materials for preparing polymer particles A include: 13 parts acrylonitrile, 45 parts styrene, 30 parts butyl acrylate, 22 parts isooctyl acrylate, and 3 parts methacrylic acid; its glass transition temperature Tg is 5° and its average particle size D50 is 533 nm.

[0077] The raw materials for preparing polymer particles B include: 85 parts styrene, 15 parts isooctyl acrylate, 3 parts acrylic acid, and 2 parts divinylbenzene; its glass transition temperature Tg is 70°C and its average particle size D50 is 256 nm.

[0078] The mass ratio of polymer particle A to polymer particle B is 5:1, and the remaining steps are the same as in Example 1.

[0079] Comparative Example 2

[0080] Compared with Example 1, the raw materials for preparing polymer particles A include: 38 parts styrene, 50 parts butyl acrylate, 20 parts isooctyl acrylate, and 3 parts methacrylic acid; its glass transition temperature Tg is -15°C and its average particle size D50 is 551 nm.

[0081] The raw materials for preparing polymer particles B include: 75 parts styrene, 25 parts isooctyl acrylate, 3 parts acrylic acid, and 2 parts divinylbenzene; its glass transition temperature Tg is 30°C and its average particle size D50 is 264 nm.

[0082] The mass ratio of polymer particle A to polymer particle B is 5:1, and the remaining steps are the same as in Example 1.

[0083] Comparative Example 3

[0084] Compared with Example 1, the raw materials for preparing polymer particles A include: 38 parts styrene, 50 parts butyl acrylate, 20 parts isooctyl acrylate, and 3 parts methacrylic acid; by changing the stirring speed, polymer particles A were prepared, and their glass transition temperature Tg was tested to be -15° and the average particle size D50 was 353 nm.

[0085] The polymer particles B used in Comparative Example 1 have a glass transition temperature Tg of 70° and an average particle size D50 of 256 nm.

[0086] The mass ratio of polymer particle A to polymer particle B is 5:1, and the remaining steps are the same as in Example 1.

[0087] Comparative Example 4

[0088] Compared with Example 1, the polymer particles A of Comparative Example 1 have a glass transition temperature Tg of -15° and an average particle size D50 of 551 nm.

[0089] The raw materials for preparing polymer particles B include: 85 parts styrene, 15 parts isooctyl acrylate, 3 parts acrylic acid, and 2 parts divinylbenzene; by changing the stirring speed, polymer particles B were prepared, and their glass transition temperature Tg was tested to be 70° and their average particle size D50 was 486 nm.

[0090] The mass ratio of polymer particle A to polymer particle B is 5:1, and the remaining steps are the same as in Example 1.

[0091] Comparative Example 5

[0092] Compared with Example 1, PVDF was used to replace the membrane adhesive composition provided by the present invention, and the remaining steps were the same as in Example 1.

[0093] The diaphragms prepared in Examples 1-10 and Comparative Examples 1-5 were wound up, and it was observed whether any sticking occurred.

[0094] The air permeability of Examples 1-10 and Comparative Examples 1-5 was tested using a Gurley air permeability meter, and the test results are shown in Table 1.

[0095] The bonding strength of Examples 1-10 and Comparative Examples 1-5 was tested, and the results are shown in Table 1.

[0096] The peel force and interfacial peel strength of the electrode and diaphragm coating were tested using an electronic tensile testing machine in accordance with the national standard GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tape".

[0097] Table 1

[0098] Particle size ratio of sample group A:B; air permeability time (s / 100ml); diaphragm winding and peel strength of positive electrode sheet (N / m); peel strength of negative electrode sheet (N / m); Example 1: 2.15 20 1.6 Non-stick 11.5 6.7; Example 2: 3.30 20 2.6 Non-stick 10.9 5.3; Example 3: 4.84 20 2.7 Non-stick 10.2 5.6; Example 4: 1.74 20 5.4 Non-stick 11.3 6.5; Example 5: 5.13 20 3.7 Slightly sticky 10.7 6; Example 6: 3.33 20 0.1 Non-stick 11.3 5.5; Example 73.33 239.8 Adhesive 14.1 8.9 Example 8 3.33 200.1 Non-adhesive 2.11 Example 9 3.05 202.4 Non-adhesive 11.2 5.9 Example 10 3.36 208.5 Non-adhesive 12.8 7.2 Comparative Example 12.08 201.7 Non-adhesive 4.2 2.5 Comparative Example 2 2.09 23 3.5 Slightly Adhesive 10.5 5.4 Comparative Example 3 1.38 203.3 Non-adhesive 5.6 3.1 Comparative Example 4 1.13 201.9 Non-adhesive 1.81 Comparative Example 5 / 25 0.7 Severely Adhesive 12.1 5.3

[0099] As can be seen from the results in Table 1, the membrane binder powder prepared by the membrane binder composition provided by the present invention is applied to the coating of the membrane surface. The resulting membrane has good air permeability and no membrane sticking occurs during winding. It has good adhesion and stability for both positive and negative electrode systems, suppresses deformation generated during cell cycling, and extends the service life of the cell.

[0100] Comparing the test results of Example 5 and Example 2, it can be seen that when the particle size ratio of polymer particles A and polymer particles B is too large, it will cause slight sticking when the diaphragm is wound up.

[0101] Comparing the test results of Example 7 and Example 2, it can be seen that when the amount of polymer particles A relative to polymer particles B is too large, it will cause the membrane to stick together when it is wound up, and the air permeability of the membrane will increase. It is speculated that the reason is that, on the one hand, if there are too few polymer particles B, they cannot be effectively distributed on the surface of polymer particles A, and the effect of inhibiting the sticking phenomenon is not obvious; on the other hand, if there are too many polymer particles A, film formation will occur, thereby increasing the air permeability.

[0102] Comparing the test results of Example 1 and Comparative Example 1, it can be seen that the glass transition temperature of polymer particles A is too high, and the peel strength is significantly reduced.

[0103] Comparing the test results of Example 1 and Comparative Example 2, it can be seen that the glass transition temperature of polymer particles B is too low, which will cause the membrane to roll up and stick together, and the air permeability of the membrane will increase.

[0104] Comparing the test results of Example 1 and Comparative Examples 3 and 4, it can be seen that if the particle size of polymer particle A is too small, or the particle size of polymer particle B is too large, it will result in insufficient peel strength.

[0105] Comparing the test results of Example 1 and Comparative Example 5, it can be seen that, compared with traditional PVDF adhesives, the diaphragm adhesive provided by the present invention can effectively improve the phenomenon of diaphragm winding and adhesion, and the air permeability of the diaphragm is significantly better.

[0106] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A separator binder composition characterized by, It includes polymer particles A and polymer particles B, wherein the glass transition temperature Tg of polymer particles A is below -10℃, the glass transition temperature Tg of polymer particles B is above 60℃, the average particle size D50 of polymer particles A is above 500nm, and the average particle size D50 of polymer particles B is below 300nm.

2. The separator binder composition of claim 1, wherein, In the diaphragm adhesive composition, the mass ratio of polymer particles A to polymer particles B is (5-9):(1-5).

3. The separator binder composition of claim 1, wherein, The average particle size ratio of polymer particle A to polymer particle B is (5~15):

3.

4. The separator binder composition of claim 1, wherein, The glass transition temperature (Tg) of polymer particle A is -70 to -10°C, and the average particle size (D50) of polymer particle A is 500 to 1500 nm; the glass transition temperature (Tg) of polymer particle B is 60 to 150°C, and the average particle size (D50) of polymer particle B is 100 to 300 nm.

5. The separator binder composition of claim 1, wherein, The surface of polymer particle A is distributed with polymer particles B, and the surface of polymer particle A is at least partially covered by polymer particles B.

6. The separator binder composition of claim 1, wherein, The polymer particles A include vinyl structural units, acrylate structural units, and functional structural units; The vinyl structural unit is selected from one or more of the following: styrene structural unit, acrylonitrile structural unit, methylstyrene structural unit, ethylstyrene structural unit, acrylamide structural unit, and methacrylamide structural unit; The acrylate structural units are selected from one or more of the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, lauryl methacrylate, and cyclohexyl methacrylate. The functional structural unit is selected from one or more of the following: acrylic acid structural unit, methacrylic acid structural unit, vinyl acrylate structural unit, β-acryloyloxypropionic acid structural unit, hydroxyacrylic acid, maleic acid structural unit, itaconic acid structural unit, itaconic acid monobutyl ester structural unit, hydroxyethyl acrylate structural unit, hydroxypropyl acrylate structural unit, hydroxyethyl methacrylate structural unit, hydroxypropyl methacrylate structural unit, hydroxymethylacrylamide structural unit, hydroxyethylacryloylurea structural unit, caprolactone acrylate structural unit, polyethylene glycol monomethacrylate structural unit, and phenyl glycidyl ether acrylate structural unit.

7. The separator binder composition of claim 1, wherein The polymer particles B include main structural units and cross-linked structural units; The main structural unit is selected from one or more of the following structural units: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, isooctyl acrylate, styrene, methylstyrene, acrylamide, methacrylamide, methyl methacrylate, glycerol formaldehyde methacrylate, isoborneol acrylate, isoborneol methacrylate, acrylic acid, methacrylic acid, and itaconic acid. The crosslinking structural unit is selected from one or more of the following: diol diacrylate structural unit, bisphenol A diacrylate structural unit, heterocycloalkane diacrylate structural unit, divinyl aromatic hydrocarbon structural unit, diol dimethacrylate structural unit, bisphenol A dimethacrylate structural unit, trimethylolpropane triacrylate structural unit, trimethylolpropane trimethacrylate structural unit, and pentaerythritol tetraacrylate structural unit.

8. A diaphragm binder powder, characterized in that, The diaphragm binder powder is a secondary particle formed from the diaphragm binder composition as described in any one of claims 1-7, the secondary particle comprising polymer particles A and polymer particles B distributed on the surface of polymer particles A, wherein the surface of polymer particles A is at least partially covered by polymer particles B.

9. A diaphragm, characterized in that, The diaphragm includes the diaphragm binder powder as described in claim 8.

10. A battery, characterized in that, The battery includes the separator as described in claim 9.