Binder emulsion, preparation method of binder emulsion, coating slurry, lithium ion battery diaphragm and preparation method of lithium ion battery diaphragm

Abstract

The invention provides a binder emulsion and a preparation method thereof, coating slurry, a lithium ion battery diaphragm and a preparation method thereof, and the binder emulsion is prepared from the following raw materials in parts by weight: 1-50 parts of functional monomer, 50-99 parts of skeleton monomer and 50-900 parts of water; wherein the sum of the parts by weight of the functional monomer and the skeleton monomer is 100. The binder emulsion provided by the invention has proper emulsion particle size, proper (I) content and proper glass transition temperature, so that when the binder emulsion is applied to diaphragm coating slurry, the binder emulsion has excellent cohesiveness, and the thermal stability of a diaphragm coating can be improved. # imgabs0 #

Description

Binder emulsion and preparation method thereof, coating slurry, lithium ion battery separator and preparation method thereof Technical Field

[0001] The present application belongs to the technical field of lithium-ion batteries and relates to a binder emulsion and a preparation method thereof, a coating slurry, a lithium-ion battery separator and a preparation method thereof. Background Art

[0002] The water-based ceramic slurry coating process is a low-cost, environmentally friendly coating technology that can effectively improve the thermomechanical stability deficiencies of battery separators. The ceramic particles in the slurry are connected or encapsulated by a binder, forming a rigid inorganic coating layer after drying, which effectively inhibits thermal shrinkage at high temperatures. However, because the ceramic particles in the rigid inorganic coating are connected by non-cross-linked linear coating polymers, there is a risk of complete melt shrinkage at high temperatures, leading to battery short circuits.

[0003] Therefore, in the art, it is desired to develop a binder emulsion that, when applied to a coating slurry for a lithium-ion battery separator, has excellent adhesion and can improve the thermal stability of the separator coating.

[0004] Summary of the Invention

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

[0006] In view of the deficiencies in the prior art, the purpose of the present application is to provide a binder emulsion and a preparation method thereof, a coating slurry, a lithium-ion battery separator and a preparation method thereof, and a preparation method of a lithium-ion battery separator.

[0007] To achieve this goal, this application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a binder emulsion, wherein the raw materials for preparing the binder emulsion include the following components in parts by weight:

[0009] 1-50 parts of functional monomer

[0010] 50-99 parts of backbone monomer

[0011] 50-900 parts water;

[0012] The total weight of the functional monomer and the skeleton monomer is 100 parts.

[0013] The present invention controls the selection and dosage of various raw materials to prepare a binder emulsion having a suitable latex particle size, suitable content and glass transition temperature, which makes it have excellent storage stability. When it is applied to the diaphragm coating slurry, it has excellent adhesion and can improve the thermal stability of the diaphragm coating.

[0014] In the embodiments of the present application, the raw materials for preparing the binder emulsion are calculated in parts by weight, and the amount of functional monomer used can be 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts or 50 parts, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] In the embodiments of the present application, the raw materials for preparing the binder emulsion are calculated in parts by weight, and the amount of the backbone monomer used can be 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, 95 parts or 99 parts, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] In the embodiments of the present application, the raw materials for preparing the binder emulsion are calculated in parts by weight, and the amount of water used can be 50 parts, 100 parts, 200 parts, 300 parts, 400 parts, 500 parts, 600 parts, 700 parts, 800 parts or 900 parts, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] Preferably, the functional monomers include and -C=C- monomers.

[0018] Preferably, the functional monomer includes any one of acrylic acid, diacetone acrylamide and its derivatives, itaconic acid or maleic acid, or a combination of at least two thereof.

[0019] Preferably, the backbone monomer includes any one or a combination of at least two of (meth)acrylate, styrene, (meth)acrylamide, (meth)acrylonitrile or vinyl acetate.

[0020] It should be noted that, in the embodiments of the present application, the (methyl)... refers to the corresponding monomers whose α-carbon atoms may or may not be connected to a methyl group. For example, (meth)acrylate includes acrylate and methacrylate, and (meth)acrylamide includes acrylamide and methacrylamide. Other cases with (methyl) have the same meaning and are not described in detail.

[0021] Preferably, the water comprises deionized water and / or ultrapure water.

[0022] Preferably, the raw materials for preparing the binder emulsion further include any one of an emulsifier, a pH buffer or an initiator, or a combination of at least two of them.

[0023] Preferably, the weight portion of the emulsifier is 0.1-10 parts, the weight portion of the pH buffer is 0.05-5 parts, and the weight portion of the initiator is 0.5-5 parts.

[0024] Preferably, the amount of emulsifier used can be 0.1 parts, 0.5 parts, 0.8 parts, 1 parts, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, etc., but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the amount of the pH buffer can be 0.05 parts, 0.08 parts, 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1 parts, 2 parts, 3 parts, 4 parts or 5 parts, etc., but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the amount of the initiator can be 0.2 parts, 0.4 parts, 0.5 parts, 1 parts, 2 parts, 3 parts, 4 parts, 5 parts or 8 parts, etc., but is not limited to the values ​​listed above. Other values ​​not listed within the numerical range are also applicable. Preferably, the emulsifier includes any one or a combination of at least two of anionic emulsifiers, cationic emulsifiers, nonionic emulsifiers, amphoteric emulsifiers, ionic-nonionic composite emulsifiers or polymeric emulsifiers (reactive emulsifiers).

[0027] Preferably, the emulsifier comprises sodium lauryl sulfate (SDS) and / or alkylphenol polyoxyethylene ether (OP-10).

[0028] Preferably, the pH buffer comprises any one or a combination of at least two of sodium bicarbonate, dipotassium hydrogen phosphate, ammonium bicarbonate, sodium dihydrogen phosphate, sodium sulfite or sodium acetate, preferably ammonium bicarbonate.

[0029] Preferably, the initiator is a water-soluble initiator, including ammonium persulfate.

[0030] Preferably, the raw materials for preparing the binder emulsion further include a post-elimination initiator and / or a pH regulator.

[0031] Preferably, the weight proportion of the post-elimination initiator is 0.05-3 parts, such as 0.05 parts, 0.08 parts, 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1 parts, 2 parts or 3 parts, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0032] Preferably, the post-elimination initiator comprises sodium formaldehyde sulfoxylate (SFS) and / or tert-butyl hydroperoxide (TBHP).

[0033] Preferably, the pH adjuster is used in an amount to adjust the pH value of the binder emulsion to 8-9.5, such as 8, 8.3, 8.5, 8.8, 9, 9.3 or 9.5, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, the pH adjuster includes any one or a combination of at least two of ammonia water, 2-amino-2-methyl-1-propanol (AMP-95), N-methylethanolamine (MMAE), dimethylethanolamine (DMAE), monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), 2-sec-butylaminoethanol (Alpamine N41), butylethanolamine (Advantex), N-aminopropyl-methylethanolamine, 2-amino-2-ethyl-1,3-propanediol (AEPD VOX 1000) or butyldiethanolamine (Vantex-T).

[0035] In the embodiments of the present application, adding a pH regulator to the binder emulsion can improve the storage stability of the binder emulsion and extend the shelf life.

[0036] Preferably, the particle size D50 of the latex particles of the binder emulsion is ≥60nm (for example, 60nm, 100nm, 150nm, 200nm, 250nm, 300nm, 500nm, 800nm, 1μm, 1.5μm or 2μm, etc., but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable), preferably 60nm~1μm (for example, one of 60nm, 100nm, 150nm, 200nm, 250nm, 300nm, 500nm, 800nm, 1μm or a range value between two of them), and further preferably 100~300nm (for example, one of 100nm, 150nm, 200nm, 250nm, 300nm or a range value between two of them).

[0037] Preferably, the latex particle size D90 of the binder emulsion is ≤3.5×D50 (for example, D90 can be 3.5×D50, 3.0×D50, 2.5×D50, 2.0×D50, 1.5×D50 or 1.0×D50, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable), preferably D90≤2.5×D50.

[0038] If the particle size of the latex particles in the binder emulsion is less than 60nm, it is easy to cause pore blockage and a high Gurley permeability value. If the particle size of the latex particles in the binder emulsion is greater than 1μm, the gravity sedimentation effect will be greater than the electrostatic stabilization effect between the latex particles, resulting in a decrease in the stability of the binder (the particle sizes mentioned above are all D50 median particle sizes measured by a laser particle size analyzer). On the other hand, the D90 particle size of the binder latex particles should be controlled at D90≤3.5×D50 (preferably ≤2.5×D50). If D90 is too high, the particle size distribution is too wide, and both too large and too small latex particles exist in the binder system, which can easily have an adverse effect on the storage stability of the binder and the Gurley permeability value of the coated diaphragm.

[0039] Preferably, the binder emulsion The content is 0.8wt% to 26wt%, for example, 0.8wt%, 1wt%, 3wt%, 5wt%, 8wt%, 10wt%, 13wt%, 15wt%, 18wt%, 20wt%, 23wt%, 25wt% or 26wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 1.4wt% to 9.7wt%, for example, 1.6wt%, 1.8wt%, 3wt%, 5wt%, 8wt%, 9wt%, 9.3wt%, 9.6wt% or 9.7wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] It should be noted that the binder emulsion in the embodiment of the present application The content refers to the mass proportion relative to all monomers in the binder emulsion. Since the mass of functional monomers and backbone monomers does not change after reacting with other raw materials to form the binder emulsion, although there are almost no monomers in the binder emulsion, for the sake of convenience, it is still described as "all monomers in the binder emulsion."

[0041] if If the content is too low, the binder emulsion used for coating the slurry has a low catalytic efficiency for the cross-linking reaction, and the adhesive force of the binder emulsion on the ceramic powder and / or one-dimensional nanomaterial becomes poor; if If the content is too high, emulsion polymerization will be difficult, the alkaline pH regulator will be difficult to fully volatilize, and it will also easily lead to a high moisture content in the coated diaphragm (the above The contents are all in percentage by mass).

[0042] Preferably, the glass transition temperature of the adhesive film formed by the adhesive emulsion after cross-linking is 50 to 200°C, for example, 50°C, 80°C, 100°C, 130°C, 150°C, 180°C or 200°C, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable, preferably 80 to 160°C.

[0043] If the glass transition temperature of the adhesive film formed by the adhesive emulsion after cross-linking is lower than 50°C, when it is applied to the coating slurry of lithium-ion battery separators, the heat resistance of the coating layer will be reduced, resulting in a high thermal shrinkage rate and reduced thermal mechanical stability of the coated separator; and if the glass transition temperature of the adhesive film formed after cross-linking is higher than 200°C, the adhesive molecular chain will be too rigid and difficult to adhere to the surface of the base film, significantly reducing the peel strength of the coating layer.

[0044] In a second aspect, the present application provides a method for preparing the binder emulsion according to the first aspect, the preparation method comprising the following steps:

[0045] (1) Pre-emulsification of monomers: functional monomers and backbone monomers are mixed and added to a reactor, followed by addition of a portion of water and an optional portion of an emulsifier, emulsified to obtain a pre-emulsion, which is then removed and set aside;

[0046] (2) Seed emulsion polymerization: adding the remaining water, an optional pH buffer, and an optional remaining emulsifier to a reactor, raising the temperature, and then adding a portion of the optional initiator and a portion of the pre-emulsion obtained in step (1), reacting to obtain a seed emulsion;

[0047] (3) Emulsion polymerization: the system temperature is controlled at 70-90° C., the remaining pre-emulsion and the optional remaining initiator are added to the seed emulsion obtained in step (2), the reaction is carried out at the temperature, the temperature is lowered, and then the optional post-elimination initiator is added, the temperature is lowered again, and then the optional pH adjuster is added to obtain the binder emulsion.

[0048] It should be noted that the embodiment of the present application does not impose any specific restrictions on the amount of the partial water in step (1). For example, the weight ratio of the partial water to the mixed monomer (i.e., the sum of the functional monomer and the backbone monomer) is 1:1.

[0049] Preferably, the portion of the emulsifier in step (1) is 50-70% of the total amount of the emulsifier, such as 50%, 55%, 60%, 65% or 70%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] Preferably, the weight portion of the initiator in step (2) is 0.3-1 part, for example, 0.3 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part or 1 part, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0051] Preferably, the portion of the pre-emulsion obtained in step (1) in step (2) accounts for 5 to 10% of the total amount of the pre-emulsion obtained in step (1), for example, 5%, 6%, 7%, 8%, 9% or 10%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] Preferably, the temperature in step (2) is raised to 70-90°C, such as 70°C, 75°C, 80°C, 85°C or 90°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] Preferably, the reaction temperature in step (2) is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable. The reaction time is 20-40 min, for example, 20 min, 25 min, 30 min, 35 min or 40 min, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0054] Preferably, the temperature of the insulation reaction in step (3) is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable. The insulation reaction time is 1-2h, for example, 1h, 1.5h or 2h, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0055] Preferably, the cooling in step (3) is to 60-65°C, for example, 60°C, 61°C, 62°C, 63°C, 64°C or 65°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] Preferably, the cooling again in step (3) is cooling to 30-40°C, such as 30°C, 33°C, 35°C, 38°C or 40°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0057] Preferably, the adding and reaction of step (2) and step (3) are carried out under an inert atmosphere.

[0058] Preferably, the inert atmosphere includes nitrogen, argon, etc.

[0059] As a preferred technical solution of the embodiment of the present application, the preparation method of the binder emulsion comprises the following steps:

[0060] (1) Pre-emulsification of monomers: functional monomers and backbone monomers are mixed and added to a reaction kettle, followed by addition of a portion of water and then an optional portion of an emulsifier, emulsified to obtain a pre-emulsion, which is then removed and set aside; wherein the portion of the emulsifier is 50-70% of the total amount of the emulsifier;

[0061] (2) Seed emulsion polymerization: argon is introduced into the reaction kettle, and the remaining water, optional pH buffer, and optional remaining emulsifier are added, and the temperature is raised to 70-90° C., and then a portion of the optional initiator and a portion of the pre-emulsion obtained in step (1) are added, and the reaction is carried out at 70-90° C. for 20-40 minutes to obtain a seed emulsion; wherein the weight portion of the portion of the initiator is 0.3-1 parts, and the portion of the pre-emulsion obtained in step (1) is 5-10% of the total amount of the pre-emulsion obtained in step (1);

[0062] (3) Emulsion polymerization: In an argon atmosphere, the system temperature is controlled at 70-90°C, and the remaining pre-emulsion and the optional remaining initiator are added to the seed emulsion obtained in step (2). The pre-emulsion is controlled to be dripped in about 3 hours, and the initiator is controlled to be dripped in about 3.5 hours. The reaction is kept at 70-90°C for 1-2 hours, cooled to 60-65°C, and then an optional post-elimination initiator is added. The temperature is again cooled to 30-40°C, and then an optional pH adjuster is added to obtain the binder emulsion.

[0063] In a third aspect, the present application provides a coating slurry, wherein the raw materials for preparing the coating slurry include the following components in parts by weight:

[0064]

[0065] The binder emulsion includes the binder emulsion described in the first aspect or the binder emulsion prepared according to the second aspect;

[0066] The cross-linking agent includes any one of a hydrazide cross-linking agent, an aziridine cross-linking agent or a carbodiimide cross-linking agent, or a combination of at least two of them.

[0067] The cross-linking agents selected in the embodiments of the present application include hydrazide cross-linking agents, aziridine cross-linking agents or carbodiimide cross-linking agents. The ketone hydrazine cross-linking reaction, aziridine cross-linking reaction and carbodiimide cross-linking reaction have the following common characteristics: the functional monomers are copolymerized in the molecular chain and are located in the latex particles of the binder emulsion; the cross-linking agent is a water-soluble cross-linking agent, and the diffusion rate from the water phase to the oil phase of the latex particles is slow.

[0068] In the embodiments of the present application, the raw materials for preparing the coating slurry are measured in parts by weight, and the amount of binder emulsion used can be 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts, 8.5 parts, 9 parts, 9.5 parts or 10 parts, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0069] In the embodiments of the present application, the raw materials for preparing the coating slurry are measured in parts by weight, and the amount of the crosslinking agent used can be 0.0025 parts, 0.003 parts, 0.005 parts, 0.008 parts, 0.01 parts, 0.03 parts, 0.05 parts, 0.08 parts, 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1 parts, 2 parts, 3 parts, 4 parts or 5 parts, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0070] In the embodiments of the present application, the raw materials for preparing the coating slurry are calculated in parts by weight, and the amount of water used can be 100 parts, 200 parts, 300 parts, 400 parts, 500 parts, 600 parts, 700 parts, 800 parts or 900 parts, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0071] In the embodiments of the present application, the amount of the alkaline pH regulator in the raw materials for preparing the coating slurry is to adjust the pH value of the system to 8-9.5, for example, 8, 8.3, 8.5, 8.8, 9, 9.3 or 9.5, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0072] In the embodiments of the present application, the raw materials for preparing the coating slurry are calculated in parts by weight, and the amount of the additive used can be 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts or 3 parts, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0073] Preferably, the ceramic powder includes alumina and / or boehmite.

[0074] Preferably, the one-dimensional nanomaterial includes a one-dimensional non-conductive inorganic nanomaterial and / or a one-dimensional organic nanomaterial.

[0075] Preferably, the aspect ratio of the one-dimensional nanomaterial is ≥5, such as 5, 6, 7, 8, 9 or 10, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0076] Preferably, the one-dimensional non-conductive inorganic nanomaterial includes any one of inorganic nanowires, nanotubes, nanorods or nanowhiskers, or a combination of at least two of them.

[0077] Preferably, the thermal conductivity of the one-dimensional non-conductive inorganic nanomaterial is ≥50W / m·K, for example, 50W / m·K, 60W / m·K, 70W / m·K, 80W / m·K, 90W / m·K or 100W / m·K, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. For example, the one-dimensional non-conductive inorganic nanomaterial can be a high-temperature inorganic ceramic fiber such as BN, SiC, Si3N4 or AlN.

[0078] Preferably, the one-dimensional organic nanomaterial comprises natural nanofibers and / or polymer nanofibers.

[0079] Preferably, the natural nanofibers include any one of nanocellulose, nanolignin fibers, nanoalginate fibers or nanochitosan fibers, or a combination of at least two thereof, preferably nanocellulose.

[0080] Preferably, the cross-linking agent includes any one of adipic dihydrazide, carbonate dihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, N-aminoacrylamide, SV-02, V-10, SW-12G, 2-(trimethylolpropane-tris[3-(3-aziridine)]propionate), 7-(pentaerythritol-tris(3-aziridine)propionate) or trimethylolpropane-tris[3-(2-methylaziridine)propionate] or a combination of at least two thereof.

[0081] Preferably, the crosslinking agent also includes a silane crosslinking agent. Silane crosslinking agents have the following characteristics: (1) The crosslinking reaction rate of silane crosslinking agents is slow, and it takes 72h to 7d for a complete reaction at room temperature. However, the addition of silane crosslinking agents can increase the crosslinking density of the coating layer on the basis of other types of crosslinking reactions, improve the thermal stability of the coated diaphragm and reduce the moisture content. (2) Epoxysilane crosslinking agents or double-bond silane functional monomers are usually used. The epoxy groups contained in the former are grafted onto the binder molecular chain by reacting with functional monomers containing carboxyl and amino groups; the latter are copolymerized in the main chain of the binder molecular chain. The alkoxy groups contained in this type of crosslinking agent can be hydrolyzed to form Si-OH, which can condense with each other to form siloxane crosslinks or react with the surface hydroxyl groups of the ceramic powder (or one-dimensional nanomaterial), thereby enhancing the bonding force of the binder to the ceramic powder (or one-dimensional nanomaterial).

[0082] Preferably, the epoxysilane crosslinking agent includes any one of A-186 (β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane), A-187 (γ-glycidyloxypropyltrimethoxysilane), A-1871 (3-(2,3-epoxypropyloxy)propyltriethoxysilane), WetLink 78 (3-glycidyletherpropylmethyldiethoxysilane) or CoatOsil 1770 (β-(3,4-epoxycyclohexyl)ethyltriethoxysilane) or a combination of at least two thereof.

[0083] Preferably, the water comprises deionized water and / or ultrapure water.

[0084] Preferably, the auxiliary agent includes any one of a dispersant, a wetting agent, a thickener or a defoaming agent, or a combination of at least two of them.

[0085] Preferably, the coating slurry further comprises an alkaline pH regulator, and the alkaline pH regulator is used to adjust the pH value of the coating slurry system to 8-9.5, for example, 8, 8.5, 9 or 9.5.

[0086] In the embodiments of this application, the coating slurry includes an alkaline pH regulator, which improves its storage stability. Furthermore, when used in lithium-ion battery separators, the alkaline pH regulator evaporates during the drying process, promoting a cross-linking reaction and introducing a cross-linked structure into the coating layer. Compared to currently mainstream aqueous slurries formulated with non-cross-linking binders, this significantly improves the thermomechanical stability of the coating layer and achieves a higher membrane rupture temperature.

[0087] In the embodiment of the present application, when the pH of the coating slurry is weakly alkaline, the reaction activity is low and cross-linking is inhibited, while when the pH is weakly acidic, the reaction activity is high and the cross-linking reaction is promoted. Therefore, the system should meet the following pH conditions: the system contains Functional groups, and the pH is adjusted to 8-9.5 with an alkaline regulator. During the drying process of the system, the water is gradually evaporated and the pH of the system is reduced to 5-6.

[0088] Preferably, the alkaline pH regulator includes any one or a combination of at least two of ammonia water, 2-amino-2-methyl-1-propanol (AMP-95), N-methylethanolamine (MMAE), dimethylethanolamine (DMAE), monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), 2-sec-butylaminoethanol (Alpamine N41), butylethanolamine (Advantex), N-aminopropyl-methylethanolamine, 2-amino-2-ethyl-1,3-propanediol (AEPD VOX 1000) or butyldiethanolamine (Vantex-T).

[0089] It should be noted that the pH adjuster and the alkaline pH adjuster mentioned in the examples of the present application can be the same adjuster or different adjusters.

[0090] Preferably, the raw materials for preparing the coating slurry also include a cross-linking catalyst.

[0091] Preferably, the cross-linking catalyst comprises any one or a combination of at least two of ammonium acetate, potassium fluoride, potassium carbonate, aniline, p-methoxyaniline, m-phenylenediamine, p-phenylenediamine, o-aminophenylphosphonic acid or o-aminophenol.

[0092] Preferably, the raw materials for preparing the coating slurry also include an acidic pH regulator.

[0093] Preferably, the acidic pH regulator is used in an amount to adjust the pH value of the system to 5-6.5, such as 5, 5.3, 5.5, 5.8, 6, 6.3 or 6.5, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0094] Preferably, the acidic pH regulator includes any one or a combination of at least two of glacial acetic acid, citric acid, lactic acid, malic acid, tartaric acid, metatartaric acid, sorbic acid, fumaric acid, succinic acid, ascorbic acid, adipic acid, oxalic acid, ammonium chloride, ammonium sulfate, ammonium phosphate, ammonium nitrate, sodium dihydrogen phosphate or sodium bisulfite.

[0095] It should be noted that the present invention does not impose any specific restrictions on the preparation method of the coating slurry. For example, the coating slurry can be prepared by the following method:

[0096] The formulated amount of water, ceramic powder and / or one-dimensional nanomaterial are mixed and dispersed, and then the additive is added and dispersed. Then, the binder emulsion is added and stirred, and then the crosslinking agent, alkaline pH regulator and optional crosslinking catalyst are added and mixed to obtain the coating slurry.

[0097] In a fourth aspect, the present application provides a lithium-ion battery separator, comprising a base membrane and a coating layer coated on one or both sides of the base membrane, wherein the raw materials for preparing the coating layer include the coating slurry described in the third aspect.

[0098] Typically, for a base film with a thickness of 7 to 12 μm, the coating thickness is controlled at 2 to 3 μm on one side, and 1.5 + 1.5 μm on both sides for the best overall effect. If the coating is too thin, the mechanical strength is insufficient, making it difficult to suppress the thermal shrinkage of the base film at high temperatures, resulting in excessive thermal shrinkage. If the coating is too thick, the separator's areal density is too high, reducing the mass energy density of the lithium-ion battery. It can also lead to high moisture content, reducing the lithium-ion battery's electrochemical stability.

[0099] Preferably, the mass proportion of the organic solvent extract of the lithium-ion battery separator after washing with pure water and soaking in an organic solvent for 24 hours is ≤3.5%, for example, 3.5%, 3%, 2%, 1%, 0.5%, 0.3%, 0.15% or 0.1%, etc., but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable, preferably 0.15% to 3.5%.

[0100] The mass ratio of the organic solvent extract described in this application is obtained by testing using the following method:

[0101] (1) A certain weight (M0) of lithium-ion battery separator was soaked in ultrapure water, stirred for 24 h, and rinsed with ultrapure water for more than 3 times to fully wash away the water-soluble additive components, such as CMC, dispersant and wetting agent. After being fully dried, the separator was weighed and recorded as M1.

[0102] (2) Soaking the washed lithium-ion battery separator in an organic solvent for 24 hours and fully rinsing it to fully wash away the uncrosslinked binder components, and then fully drying and weighing it, which is recorded as M2. The organic solvent is a common solvent for lithium-ion battery electrolyte such as dichloromethane, toluene, acetone, dimethyl carbonate, propylene carbonate, etc., preferably dichloromethane;

[0103] (3) Calculate the mass ratio of organic solvent extract (M1-M2) / M0.

[0104] In a fifth aspect, the present application provides a method for preparing the lithium-ion battery separator according to the fourth aspect, the preparation method comprising the following steps:

[0105] 1) coating the coating slurry described in the third aspect on one side or both sides of the base film to obtain a coating layer;

[0106] 2) drying the coating layer to obtain the lithium-ion battery separator.

[0107] Preferably, the drying temperature in step 2) is 60-80°C, such as 60°C, 65°C, 70°C, 75°C or 80°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0108] Preferably, after step 2), step 3) aging is further included: the lithium-ion battery separator is placed at room temperature for 72h to 7d (for example, 72h, 4d, 5d, 6d or 7d, but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable) or at 50 to 70°C (for example, 50°C, 55°C, 60°C, 65°C or 70°C, but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable) for 24h.

[0109] Preferably, step 3) further includes step 4): unwinding and then rewinding the lithium-ion battery separator.

[0110] The lithium-ion battery separators of the present invention can be coated using various coating equipment, such as roller coating, spray coating, extrusion coating, dip coating, or blade coating, to apply the mixed slurry to one or both surfaces of the base film. Single-layer coating or multi-layer coating with other coating materials can be used. The coated separator is dried in a drying oven to dry out moisture, and the pH decreases during the drying process, making it suitable for cross-linking reactions.

[0111] The reaction mechanisms involved in the embodiments of the present application include ketone-hydrazine cross-linking mechanism, carbodiimide cross-linking mechanism, aziridine cross-linking mechanism, and may also include siloxane cross-linking mechanism, epoxy cross-linking mechanism, etc. depending on actual conditions.

[0112] Among them, the ketone-hydrazine cross-linking reaction mechanism is as follows:

[0113] The carbonyl-functional monomers (e.g., diacetone acrylamide (DAAM)) in the copolymerized linear polymer possess a multi-carbonyl structure. Under acidic conditions and at room temperature, they can react with an externally added water-soluble crosslinker (e.g., adipic dihydrazide (ADH)) to form a hydrazone, forming a three-dimensional network structure. In the aforementioned coating slurry, the functional monomers are only present in the latex particles, while the crosslinker is water-soluble and primarily resides in the aqueous phase, making it difficult to diffuse into the latex particles in the oil phase, resulting in poor contact between the two. By adding an alkaline pH adjuster beforehand, the carboxyl groups in the carboxyl-functional monomers are converted into carboxylate structures, adjusting the pH of the coating slurry system to a weakly alkaline state, which is unfavorable for the ketone-hydrazine crosslinking reaction. Therefore, the aforementioned coating slurry is less likely to react during storage and exhibits excellent storage stability. During the drying process of the coating layer, the pH adjuster gradually evaporates along with the water, and the carboxylates in the carboxyl-functional monomers are converted back into carboxyl groups, gradually decreasing the pH of the system. At the same time, as the water evaporates, the latex particles contact and merge with each other, breaking the emulsion to form a film. The cross-linking agent originally in the water phase diffuses into the oil phase in large quantities and undergoes a cross-linking reaction with the cross-linkable groups of the linear polymer to form a network cross-linked structure.

[0114] In order to increase the rate of the ketone-hydrazine cross-linking reaction, an appropriate amount of catalyst, such as ammonium acetate, aniline, p-phenylenediamine, etc., can be added during the preparation of the binder or the preparation of the slurry, or an acidic pH regulator can be added to lower the pH before the slurry is coated, such as glacial acetic acid, ammonium salt, hydrochloric acid, etc. to adjust the pH to 5-6.5 in advance.

[0115] The cross-linking mechanism of carbodiimide is as follows:

[0116] The carboxyl groups in the (meth)acrylic acid monomer react with carbodiimide at room temperature under acidic conditions to form a cross-linked network structure. Carbodiimide can be formulated into the form of an emulsion or an aqueous solution as needed. The cross-linking reaction between carbodiimide and carboxyl groups is affected by pH. The cross-linking reaction activity is low under alkaline conditions, while the cross-linking reaction rate is accelerated under neutral or acidic conditions. Similar to the above-mentioned ketone-hydrazine cross-linking mechanism, during the drying process of the coating layer, the pH regulator is gradually volatilized along with the water, while the carboxyl groups of the (meth)acrylic acid are retained, and the pH of the system gradually decreases. At the same time, as the water evaporates, the latex particles contact and merge with each other, breaking the emulsion to form a film. The cross-linking agent originally in the aqueous phase or in different latex particles accelerates contact with the linear polymer and gradually undergoes a cross-linking reaction with the cross-linkable groups to form a network cross-linked structure.

[0117] Similar to the above-mentioned ketone-hydrazine crosslinking mechanism, adding a pH regulator to lower the pH near the slurry coating, such as glacial acetic acid, ammonium phosphate, ammonium chloride, etc. to adjust the pH to 5-6.5 can accelerate the rate of the carbodiimide crosslinking reaction.

[0118] The cross-linking mechanism of aziridine is as follows:

[0119] The carboxyl groups in the (meth)acrylic acid monomer react with the aziridine crosslinker to form a crosslinked network structure. The optimal pH for adding the aziridine crosslinker is 9.0-9.5. Lower pH levels can lead to premature crosslinking and gelation, while higher pH levels can prolong crosslinking time. Due to the high reactivity of the aziridine crosslinker, it must be miscible with water (usually in a 1:1 ratio) before addition to the aqueous slurry. Otherwise, hydrolysis can lead to poor crosslinking or premature gelation. Similar to the keto-hydrazine and carbodiimide crosslinking mechanisms described above, as the coating dries, the pH adjuster gradually evaporates along with the water, and the carboxylate structures in the carboxyl-functional monomers reconvert to carboxyl groups, gradually decreasing the pH of the system. Simultaneously, as the water evaporates, the latex particles contact and merge, breaking the emulsion to form a film. The crosslinker, originally in the aqueous phase, rapidly comes into contact with the linear polymer, rapidly crosslinking with the crosslinkable groups to form a network of crosslinked structures. Although the aziridine crosslinking agent has a high reaction activity, similar to the above-mentioned ketone-hydrazine crosslinking or carbodiimide crosslinking mechanism, adding a pH regulator to lower the pH near the slurry coating, such as glacial acetic acid, ammonium phosphate, ammonium chloride, etc. to adjust the pH to 5-6.5, can accelerate the rate of the aziridine crosslinking reaction.

[0120] Compared with the prior art, this application has at least the following beneficial effects:

[0121] (1) The present invention controls the selection and dosage of various raw materials so that the prepared binder emulsion has a suitable latex particle size and a suitable content and glass transition temperature, which makes it have excellent storage stability. When it is applied to the diaphragm coating slurry, it has excellent adhesion and can improve the thermal stability of the diaphragm coating.

[0122] (2) In this application, the coating slurry includes a binder emulsion, a crosslinking agent, and an alkaline pH regulator. These three agents work together to improve the storage stability of the coating slurry. On the other hand, when used in lithium-ion battery separators, they can promote the crosslinking reaction while drying the coating film, introducing a crosslinked structure into the coating layer. Compared with the current mainstream water-based slurry formulated with non-crosslinking binders, the thermomechanical stability of the coating layer can be greatly improved, achieving a higher film rupture temperature, while also meeting the performance requirements of a lower water content.

[0123] (3) In the present application, the cross-linking process can be completed simultaneously with the drying process, which effectively avoids the upgrade and transformation of the existing water-based coating production line. At the same time, it is only necessary to ensure that the coated diaphragm is evenly heated to ensure the uniformity of the cross-linking reaction at all parts of the diaphragm.

[0124] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0125] The inventors discovered that the thermomechanical stability of lithium-ion battery separator coatings is influenced by the glass transition temperature of the polymer in the coating, which in turn determines the separator's thermal shrinkage properties. Furthermore, the high-temperature insulation properties of non-crosslinked linear polymers are influenced by their glass transition temperature and molecular chain structure, which in turn determines the separator's membrane rupture temperature (high-temperature melting failure). Both of these effects can lead to the potential safety hazard of short circuits in batteries.

[0126] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0127] Binder emulsion

[0128] In Examples 1-5 and Comparative Examples 1-3, a binder emulsion is provided respectively. The raw materials and amounts (parts by weight) of the binder emulsion are shown in Table 1.

[0129] The preparation method comprises the following steps:

[0130] (1) Pre-emulsification of monomers: Mix the functional monomers and backbone monomers in the formulated amount, add them to a reactor, then add some water, and then add some emulsifier (60% of the total amount of emulsifier), emulsify to obtain a pre-emulsion, remove it, and set aside;

[0131] (2) Seed emulsion polymerization: Argon was introduced into the reactor, and the remaining water, pH buffer, and remaining emulsifier (40% of the total amount of the emulsifier) ​​were added, and the temperature was raised to 80° C., and then part of the initiator (0.3 parts) and part of the pre-emulsion obtained in step (1) (5% of the total amount of the pre-emulsion) were added, and the mixture was reacted at 80° C. for 30 minutes to obtain a seed emulsion;

[0132] (3) Emulsion polymerization: In an argon atmosphere, the system temperature is controlled at 85° C., and the remaining pre-emulsion (95% of the total amount of the pre-emulsion) and the remaining initiator are added to the seed emulsion obtained in step (2). The pre-emulsion is controlled to be dripped in about 3 hours, and the initiator is controlled to be dripped in about 3.5 hours. The reaction is kept at 85° C. for 1.5 hours, cooled to 65° C., and then a post-elimination initiator is added to eliminate unreacted monomers. The mixture is stirred for 20 minutes and filtered to obtain the binder emulsion.

[0133] Table 1

[0134]

[0135]

[0136] In Table 1, “ / ” indicates that the corresponding raw materials were not added or the corresponding tests were not performed.

[0137] During the binder emulsion preparation process, the diacetone acrylamide in Comparative Example 2 was difficult to fully dissolve in the monomer mixture, resulting in a turbid system. Phase separation was evident during the pre-emulsification process, making it impossible to successfully prepare a pre-emulsion. The diacetone acrylamide in Comparative Example 3 was difficult to dissolve in the monomer mixture, resulting in a large amount of precipitate at the bottom of the mixture, making it impossible to successfully prepare a pre-emulsion. Therefore, neither Comparative Examples 2 nor 3 successfully produced binder emulsions with the properties described herein.

[0138] The test method is described as follows:

[0139] (1) Latex particle size D50 and D90: tested by laser particle size analyzer;

[0140] (2) In binder emulsion system Content: For the ketone carbonyl groups contained, the hydroxylamine hydrochloride method can be used to determine the carbonyl content: the ketone carbonyl content is determined by potassium hydroxide titration based on the principle of hydrochloric acid released when the carbonyl compound undergoes oximation reaction with hydroxylamine hydrochloride; for the carboxyl groups contained, KOH-ethanol solution can be used for titration, or according to the Boehm titration method, a NaHCO3 solution of known concentration is mixed with the binder sample and then titrated with hydrochloric acid; if the carboxyl groups exist in the form of carboxylates, excess hydrochloric acid can be added to the binder first to reduce the carboxyl groups to carboxyl groups, and then the system can be dried to volatilize the excess hydrochloric acid. The remaining carboxylic acids can be titrated using the above method.

[0141] Cross-linked adhesive film

[0142] The adhesive emulsions provided in Examples 1-5 and Comparative Example 1 were cross-linked with the corresponding cross-linking agents in Table 2 to form adhesive films. The adhesive films formed after cross-linking the adhesive emulsions were subjected to performance tests, and the results are shown in Table 2.

[0143] Table 2

[0144]

[0145] In Table 2, (1) carbodiimide crosslinker: purchased from Nisshinbo, brand SV-02; aziridine crosslinker: purchased from DSM, brand NeoCryl CX-100; (2) it can be understood that the selection and amount of the crosslinker here are only for the purpose of reacting with the binder emulsion to form a film and used to characterize the performance of the binder. When actually used in lithium-ion batteries, the proportion can be determined according to the weight percentage of the slurry mentioned in this application.

[0146] As can be seen from Table 1 and Table 2, the binder emulsions provided in Examples 1-5 of the present application all have suitable latex particle sizes (D50: 87.3-575.4 nm, D90: (1.7-2.4) × D50), and all have suitable content (1.4-18.0wt%) and glass transition temperature (85.3-150.2℃), and has a lower mass swelling degree (31.7-45.4%). The particle size D50 of the binder emulsion provided in Comparative Example 1 is smaller, The content and glass transition temperature are both low, while the mass swelling degree is significantly larger. That is, the present application controls the content of the binder emulsion system. The amount and type of added -C=C- monomers are of great significance for obtaining the ideal latex particle size and particle size distribution, the appropriate glass transition temperature after the cross-linking reaction, and the lower mass swelling degree.

[0147] The test method is described as follows:

[0148] (1) Glass transition temperature: The glass transition temperature of the film was tested using a DSC tester;

[0149] (2) Mass swelling: The film was immersed in an electrolyte at 65°C for 72 h to test the mass swelling of the film.

[0150] Application Examples 1-5

[0151] In Application Examples 1-5, a coating slurry is provided respectively. The raw materials and dosage (parts by weight) of the coating slurry are shown in Table 3.

[0152] Table 3

[0153]

[0154] In Table 3, (1) “ / ” indicates that the corresponding raw material is not added; (2) the binder emulsions used in Application Examples 1-5 are the binder emulsions provided in Examples 1-5 respectively; (3) nanocellulose: purchased from Nippon Paper Industries, Ltd., brand name cellenpia; carbodiimide crosslinker: purchased from Nisshinbo, brand name SV-02; aziridine crosslinker: purchased from DSM, brand name NeoCryl CX-100; dispersant: purchased from Akzo Nobel, brand name Bermodol SPS 2543; wetting agent: purchased from Cognis, brand name Hydropalat 885; defoamer: purchased from San Nopco, brand name SN-Defoamer 1349.

[0155] The preparation method of the coating slurry can refer to the content of the above invention.

[0156] In Application Examples 1-5, a lithium-ion battery separator is also provided respectively, which includes a base film (PE wet-process base film) and a coating layer coated on one side of the base film. The raw material for preparing the coating layer is the coating slurry of Application Examples 1 to 5 described above.

[0157] The preparation method of the lithium ion battery separator comprises the following steps:

[0158] The coating slurry is coated on one side of the base film and dried at 70° C. to obtain the lithium ion battery separator.

[0159] Application Example 6

[0160] The only difference between this application example and application example 1 is that the raw materials for preparing the coating slurry do not include an alkaline pH adjuster (ammonia water).

[0161] Comparative Application Example 1

[0162] The only difference between this comparative application example and application example 1 is that the amount of adipic acid dihydrazide used is 6 parts by weight.

[0163] Comparative Application Example 2

[0164] The only difference between this comparative application example and application example 1 is that the binder emulsion is replaced with an equal amount of the binder emulsion provided in comparative example 1.

[0165] Comparative Application Example 3

[0166] The only difference between this comparative application example and application example 1 is that adipic acid dihydrazide is replaced by an equal amount of 1,8-octanediamine.

[0167] Comparative Application Example 4

[0168] The only difference between this comparative application example and application example 1 is that the raw materials for preparing the coating slurry do not include a cross-linking agent.

[0169] The performance tests of the lithium-ion battery separators provided in Example 1-6 and Comparative Example 1-4 were conducted, and the results are shown in Table 4:

[0170] Table 4

[0171]

[0172] As can be seen from Table 4, the lithium-ion battery separators provided in Application Examples 1-6 of this application all have a higher membrane rupture temperature (177.2-191.0°C), a lower moisture content (436.7-859.5 ppm), a higher bonding strength (70.3-109.9 N / m), and excellent dissolution resistance (the content of organic solvent extract is 0.15-3.5%).

[0173] Compared with Application Example 1, the lithium-ion battery separator provided in Application Example 6 also has excellent comprehensive performance, but the coating slurry for preparing the lithium-ion battery separator has poor storage properties. After being placed for a period of time, ceramic particles are prone to agglomeration and sedimentation, resulting in the final coating bulk density and thickness uniformity being difficult to control; the membrane rupture temperature of the lithium-ion battery separator provided in Comparative Application Example 1 is improved, but due to the high proportion of cross-linking agent in the slurry, its moisture content is significantly increased; the membrane rupture temperature of the lithium-ion battery separator provided in Comparative Application Example 2 is low, the bonding strength is poor, and the dissolution resistance is significantly reduced; the membrane rupture temperature of the lithium-ion battery separator provided in Comparative Application Example 3 is reduced, the moisture content is significantly increased, and the bonding strength and dissolution resistance are significantly reduced; the membrane rupture temperature, bonding strength and dissolution resistance of the lithium-ion battery separator provided in Comparative Application Example 4 are significantly reduced;

[0174] That is, the emulsion adhesive of the present application contains The type and amount of monomers containing -C=C-; the type and amount of cross-linking agents in the coating slurry; all play a key role in the membrane rupture temperature, moisture content, bonding strength and dissolution resistance of lithium-ion battery separators; and the alkaline pH adjuster has a significant impact on the storage properties of the coating slurry.

[0175] The test method is described as follows:

[0176] (1) Membrane rupture temperature:

[0177] The test requires a multi-channel temperature tester, a digital bridge, an oven, and a dedicated test fixture. The membrane to be tested is cut into 2cm long and wide specimens, placed in a sealable fixture with upper and lower electrodes, injected with electrolyte, and sealed. The fixture is then placed in an oven and heated at a constant rate. The resistance between the two electrodes of the fixture is recorded as a function of temperature. As the temperature rises, the pores of the membrane gradually close, and the resistance increases sharply. When the resistance reaches 100Ω, the temperature at that point is recorded as the closed-pore temperature, T. shut-down As the temperature continues to rise, the diaphragm melts and breaks, and the resistance drops rapidly. When the resistance drops back to 1000Ω, the temperature at that point is recorded as the membrane breaking temperature T break down .

[0178] (2) Moisture content:

[0179] The test requires an electronic balance, a liquid-filled glove box, and a Karl-Fischer moisture meter. Accurately weigh 0.15±0.05g of the membrane sample to be tested using an electronic balance. Place the sample in the glove box for 10 minutes to maintain a constant moisture content (glove box temperature 25±5°C, relative humidity <1%). The treated sample is then tested using a Karl-Fischer moisture meter to determine its moisture content.

[0180] (3) Bonding strength between coating and base film:

[0181] This test requires a universal testing machine. Cut the membrane into 15mm strips and adhere them to a glass slide using 3M double-sided tape. Place the coated surface of the strip on the double-sided tape, gently pressing with your fingers to secure the bond. Ensure the effective bond length is ≥ 100mm. Fold the free end of the specimen 180° and pre-tear approximately 10mm. Using a universal testing machine, peel the adhesive surface at a speed of 300mm / min. Record the average peel strength as the bond strength.

[0182] (4) Organic solvent extracts:

[0183] (a) A certain weight (M0) of lithium-ion battery separator was immersed in ultrapure water, stirred for 24 h, and rinsed with ultrapure water for more than three times to thoroughly remove water-soluble additives such as CMC, dispersants, and wetting agents. After thorough drying, the separator was weighed and recorded as M1.

[0184] (b) soaking the washed lithium-ion battery separator in an organic solvent for 24 hours and thoroughly rinsing it to remove the uncrosslinked binder component, and then fully drying and weighing it, which is recorded as M2. The organic solvent is a common solvent for lithium-ion battery electrolyte such as dichloromethane, toluene, acetone, dimethyl carbonate, propylene carbonate, etc., preferably dichloromethane;

[0185] (c) Organic solvent extract (dichloromethane) = (M1-M2) / M0.

[0186] The applicant declares that this application uses the above-mentioned embodiments to illustrate the binder emulsion and its preparation method, coating slurry, lithium-ion battery separator and its preparation method, but this application is not limited to the above-mentioned embodiments, that is, it does not mean that this application must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent replacement of various raw materials of the products of this application, addition of auxiliary ingredients, selection of specific methods, etc., all fall within the scope of protection and disclosure of this application.

Claims

1. A binder emulsion, wherein The raw materials for preparing the binder emulsion include the following components in parts by weight: 1-50 parts of functional monomer 50-99 parts of backbone monomer 50-900 parts water; The total weight of the functional monomer and the skeleton monomer is 100 parts.

2. The binder emulsion according to claim 1, wherein The functional monomers include and -C=C- monomers; The functional monomers include any one or a combination of at least two of acrylic acid, diacetone acrylamide and its derivatives, itaconic acid or maleic acid; The backbone monomer includes any one or a combination of at least two of (meth)acrylate, styrene, (meth)acrylamide, (meth)acrylonitrile or vinyl acetate The water includes deionized water and / or ultrapure water.

3. The binder emulsion according to claim 1 or 2, wherein The raw materials for preparing the binder emulsion further include any one or a combination of at least two of an emulsifier, a pH buffer or an initiator; The weight portion of the emulsifier is 0.1-10 parts, the weight portion of the pH buffer is 0.05-5 parts, and the weight portion of the initiator is 0.2-8 parts; The emulsifier includes any one or a combination of at least two of anionic emulsifiers, cationic emulsifiers, nonionic emulsifiers, amphoteric emulsifiers, ionic-nonionic composite emulsifiers or polymeric emulsifiers; Optionally, the emulsifier includes sodium lauryl sulfate and / or alkylphenol polyoxyethylene ether; The pH buffer comprises any one or a combination of at least two of sodium bicarbonate, dipotassium hydrogen phosphate, ammonium bicarbonate, sodium dihydrogen phosphate, sodium sulfite or sodium acetate, preferably ammonium bicarbonate; Optionally, the initiator is a water-soluble initiator, including ammonium persulfate.

4. The binder emulsion according to any one of claims 1 to 3, wherein The raw materials for preparing the binder emulsion also include a post-elimination initiator and / or a pH regulator; Optionally, the weight portion of the post-elimination initiator is 0.05-3 parts; Optionally, the post-elimination initiator comprises sodium formaldehyde sulfoxylate and / or tert-butyl hydroperoxide; Optionally, the pH adjuster is used in an amount to adjust the pH value of the binder emulsion to 8-9.5; Optionally, the pH regulator includes any one or a combination of at least two of ammonia water, 2-amino-2-methyl-1-propanol, N-methylethanolamine, dimethylethanolamine, monoethanolamine, diethanolamine, triethanolamine, 2-sec-butylaminoethanol, butylethanolamine, N-aminopropyl-methylethanolamine, 2-amino-2-ethyl-1,3-propanediol or butyldiethanolamine.

5. The binder emulsion according to any one of claims 1 to 4, wherein The particle size D50 of the latex particles of the binder emulsion is ≥60 nm, preferably 60 nm to 1 μm, and more preferably 100 to 300 nm; Optionally, the particle size of the latex particles of the binder emulsion is D90≤3.5×D50, preferably D90≤2.5×D50; Optionally, the binder emulsion The content is 0.8wt% to 26wt%, preferably 1.4wt% to 9.7wt%; Optionally, the adhesive film formed by the adhesive emulsion after cross-linking has a glass transition temperature of 50 to 200°C, preferably 80 to 160°C.

6. A binder emulsion, characterized in that: The particle size of the latex particles of the binder emulsion is D50 ≥ 60 nm, preferably 60 nm to 1 μm, more preferably 100 to 300 nm; the particle size of the latex particles of the binder emulsion is D90 ≤ 3.5 × D50, preferably D90 ≤ 2.5 × D50; The content is 0.8wt% to 26wt%, preferably 1.4wt% to 9.7wt%; the glass transition temperature of the adhesive film formed by the adhesive emulsion after cross-linking is 50 to 200°C, preferably 80 to 160°C.

7. A method for preparing the binder emulsion according to any one of claims 1 to 6, wherein: The preparation method comprises the following steps: (1) Pre-emulsification of monomers: functional monomers and backbone monomers are mixed and added to a reactor, followed by addition of a portion of water and an optional portion of an emulsifier, emulsified to obtain a pre-emulsion, which is then removed and set aside; (2) Seed emulsion polymerization: adding the remaining water, an optional pH buffer, and an optional remaining emulsifier to a reactor, raising the temperature, and then adding a portion of the optional initiator and a portion of the pre-emulsion obtained in step (1), reacting to obtain a seed emulsion; (3) Emulsion polymerization: the system temperature is controlled at 70-90° C., the remaining pre-emulsion and the optional remaining initiator are added to the seed emulsion obtained in step (2), the reaction is carried out at the temperature, the temperature is lowered, and then the optional post-elimination initiator is added, the temperature is lowered again, and then the optional pH adjuster is added to obtain the binder emulsion.

8. The preparation method according to claim 7, characterized in that The portion of the emulsifier in step (1) is 50-70% of the total amount of the emulsifier; Optionally, the weight portion of the initiator in step (2) is 0.3-1 parts; Optionally, the portion of the pre-emulsion obtained in step (1) in step (2) is 5 to 10% of the total amount of the pre-emulsion obtained in step (1); Optionally, the heating in step (2) is to 70-90° C.; Optionally, the reaction temperature in step (2) is 70-90° C., and the reaction time is 20-40 min; Optionally, the temperature of the insulation reaction in step (3) is 70-90° C., and the insulation reaction time is 1-2 h; Optionally, the cooling in step (3) is to cool to 60-65°C; Optionally, the cooling again in step (3) is cooling to 30-40°C.

9. A coating slurry, wherein: The raw materials for preparing the coating slurry include the following components in parts by weight: The binder emulsion comprises the binder emulsion according to any one of claims 1 to 6 or the binder emulsion prepared according to claim 7 or 8; The cross-linking agent includes any one of a hydrazide cross-linking agent, an aziridine cross-linking agent or a carbodiimide cross-linking agent, or a combination of at least two of them.

10. The coating slurry according to claim 9, wherein The ceramic powder includes alumina and / or boehmite; Optionally, the one-dimensional nanomaterial includes a one-dimensional non-conductive inorganic nanomaterial and / or a one-dimensional organic nanomaterial; Optionally, the aspect ratio of the one-dimensional nanomaterial is ≥5; Optionally, the one-dimensional non-conductive inorganic nanomaterial includes any one or a combination of at least two of inorganic nanowires, nanotubes, nanorods or nanowhiskers; Optionally, the thermal conductivity of the one-dimensional non-conductive inorganic nanomaterial is ≥50 W / m·K; Optionally, the one-dimensional organic nanomaterial comprises natural nanofibers and / or polymer nanofibers; Optionally, the natural nanofibers include any one of nanocellulose, nanolignin fibers, nanoalginate fibers or nanochitosan fibers, or a combination of at least two thereof, preferably nanocellulose; 11. The coating slurry according to claim 9 or 10, wherein the crosslinking agent comprises any one of adipic dihydrazide, carbonate dihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, N-aminoacrylamide, SV-02, V-10, SW-12G, 2-(trimethylolpropane-tris[3-(3-aziridinyl)]propionate), 7-(pentaerythritol-tris(3-aziridinyl)propionate), or trimethylolpropane-tris[3-(2-methylaziridinyl)propionate], or a combination of at least two thereof; Optionally, the cross-linking agent further comprises a silane cross-linking agent; The water includes deionized water and / or ultrapure water; The auxiliary agent includes any one or a combination of at least two of a dispersant, a wetting agent, a thickener or a defoaming agent; Optionally, the coating slurry further comprises an alkaline pH regulator, and the alkaline pH regulator is used to adjust the pH value of the coating slurry system to 8-9.5; Optionally, the alkaline pH regulator includes any one or a combination of at least two of ammonia water, 2-amino-2-methyl-1-propanol, N-methylethanolamine, dimethylethanolamine, monoethanolamine, diethanolamine, triethanolamine, 2-sec-butylaminoethanol, butylethanolamine, N-aminopropyl-methylethanolamine, 2-amino-2-ethyl-1,3-propanediol or butyldiethanolamine; Optionally, the raw materials for preparing the coating slurry further include a cross-linking catalyst; Optionally, the cross-linking catalyst comprises any one or a combination of at least two of ammonium acetate, potassium fluoride, potassium carbonate, aniline, p-methoxyaniline, m-phenylenediamine, p-phenylenediamine, o-aminophenylphosphonic acid or o-aminophenol; Optionally, the raw materials for preparing the coating slurry further include an acidic pH regulator; The acidic pH regulator is used in an amount to adjust the pH value of the system to 5-6.5; Optionally, the acidic pH regulator includes any one or a combination of at least two of glacial acetic acid, citric acid, lactic acid, malic acid, tartaric acid, metatartaric acid, sorbic acid, fumaric acid, succinic acid, ascorbic acid, adipic acid, oxalic acid, ammonium chloride, ammonium sulfate, ammonium phosphate, ammonium nitrate, sodium dihydrogen phosphate or sodium bisulfite.

12. A lithium ion battery separator, wherein: The lithium-ion battery separator comprises a base film and a coating layer coated on one side or both sides of the base film, and the raw material for preparing the coating layer comprises the coating slurry according to claim 9, 10 or 11; The weight ratio of the organic solvent extract of the lithium ion battery separator after washing with pure water and soaking in the organic solvent for 24 hours is ≤3.5%, preferably 0.15% to 3.5%.

13. A method for preparing a lithium-ion battery separator according to claim 12, wherein: The preparation method comprises the following steps: 1) coating the coating slurry according to claim 9, 10 or 11 on one side or both sides of the base film to obtain a coating layer; 2) drying the coating layer to obtain the lithium ion battery separator; Step 2) the drying temperature is 60-80°C; Optionally, after step 2), the method further comprises step 3) aging: placing the lithium-ion battery separator at room temperature for 72 hours to 7 days or at 50 to 70° C. for 24 hours; Optionally, step 3) further includes step 4): unwinding and then rewinding the lithium-ion battery separator.

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