A separator adhesive composition, a separator, and a lithium ion secondary battery

Abstract

The application discloses a separator adhesive composition, which comprises a main adhesive and an auxiliary adhesive, the main adhesive comprises polymer microparticles A, the polymer microparticles A comprise first main monomer structural units and first post-reaction structural units containing post-reaction groups; the auxiliary adhesive comprises polymer microparticles B, the polymer microparticles B comprise second main monomer structural units and second post-reaction structural units containing post-reaction groups; the first post-reaction structural units and the second post-reaction structural units are connected with each other through chemical bonds. The application increases the post-reaction groups in the polymer microparticles A and the polymer microparticles B, and the post-reaction groups react in the vacuum baking stage of the electric core, so that the post-curing between the main adhesive and the auxiliary adhesive is realized, the adhesive strength of the main adhesive and the auxiliary adhesive is improved, the adhesive strength between the separator and the pole piece interface is improved, the wettability of the separator and the electrolyte is improved, and the performance and reliability of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and particularly relates to a separator binder composition, a separator and a lithium ion secondary battery. BACKGROUND

[0002] A lithium ion secondary battery is generally composed of a positive electrode, a negative electrode, a separator, an electrolyte and a battery shell. Among them, the separator is one of the key inner components, and its main function is to separate the positive electrode and the negative electrode of the battery to prevent the two from contacting and causing short circuit. At present, the commonly used separator material in lithium ion batteries is polyolefin porous film. However, the melting point of this material is relatively low, and when the temperature of the battery rises due to internal or external factors, the polyolefin porous film may shrink or melt, causing the positive and negative electrodes to directly contact, triggering a short circuit, and further possibly causing safety accidents such as battery combustion or explosion.

[0003] The adhesion between the separator and the electrode sheet interface has a great influence on the hardness and safety of the battery cell. The adhesion between the separator and the electrode sheet interface is mainly realized by the separator adhesive composition. The adhesion strength of the current market separator adhesive between the electrode sheet and the main adhesive is higher than that between the auxiliary adhesive and the main adhesive. Therefore, improving the adhesion strength between the main adhesive and the auxiliary adhesive is a key factor to improve the adhesion between the separator and the electrode sheet interface.

[0004] In order to solve the above problems, a polymer binder is usually used to coat inorganic particles on the surface of the separator substrate to make a composite separator. For example, ceramic particles are coated on the surface of the separator substrate to form a ceramic / polymer composite separator, which utilizes the heat resistance of the ceramic particles to reduce the thermal shrinkage of the separator; at the same time, the polymer is used to improve the adhesion between the separator and the electrode sheet interface, so as to prevent the positive and negative electrodes of the battery from short circuiting and improve the hardness of the battery cell.

[0005] However, this composite separator still has different degrees of deficiencies. First, the composite separator needs to use NMP, acetone, ethanol and other organic solvents to prepare slurry for multiple coating, which not only pollutes the environment but also makes the process complex, resulting in a decrease in yield and an increase in cost. More seriously, the adhesion between the composite separator and the electrode sheet is not high, which cannot effectively improve the hardness of the battery cell. Second, if a fluoropolymer such as PVDF is dissolved in NMP or other organic solvents to prepare a slurry for coating on the surface of the separator substrate, and then the NMP or other organic solvents are washed away with water or other solvents to form a porous coating, a large amount of organic solvents is required to manufacture this composite separator, and a large amount of wastewater containing organic solvents is generated, which causes serious environmental pollution and greatly increases the manufacturing cost.

[0006] Therefore, there is an urgent need for a separator adhesive that can improve the adhesion between the separator and the pole piece, while also improving the hardness of the battery cell, reducing the deformation of the battery cell, and thus improving the rate, cycle, safety, and other performance of the battery, and improving the production efficiency and reducing the cost of the battery. SUMMARY

[0007] To solve the problems of the existing separator, the present application provides a separator adhesive composition, a separator and a lithium ion secondary battery.

[0008] In a first aspect, the present application provides a separator adhesive composition, comprising a main adhesive and an auxiliary adhesive, the main adhesive comprising polymer particles A, the polymer particles A comprising a first main monomer structural unit and a first post-reaction structural unit containing a post-reaction group; the auxiliary adhesive comprising polymer particles B, the polymer particles B comprising a second main monomer structural unit and a second post-reaction structural unit containing a post-reaction group; the first post-reaction structural unit and the second post-reaction structural unit are connected to each other by a chemical bond.

[0009] Further, the post-reaction group is a carboxyl group, an epoxy group or an amino group; when the post-reaction group in the first post-reaction structural unit is a carboxyl group, the post-reaction group in the second post-reaction structural unit is an epoxy group or an amino group; when the post-reaction group in the first post-reaction structural unit is an amino group, the post-reaction group in the second post-reaction structural unit is an epoxy group or a carboxyl group; when the post-reaction group in the first post-reaction structural unit is an epoxy group, the post-reaction group in the second post-reaction structural unit is a carboxyl group or an amino group.

[0010] Further, the weight percentage content of the first post-reaction structural unit in the polymer particles A is 1-5%.

[0011] Further, the weight percentage content of the second post-reaction structural unit in the polymer particles B is 1-5%.

[0012] Further, the average particle size D A of the polymer particles A is 0.6-1.3 μm, and the glass transition temperature Tg of the polymer particles A is 50-80℃.

[0013] Further, the average particle size D B of the polymer particles B is 0.1-0.3 μm; and the glass transition temperature Tg of the polymer particles B is -50-10℃.

[0014] Further, the solid mass ratio of the main adhesive to the auxiliary adhesive is 100: (15-25).

[0015] Further, the first and second main monomer structure units are independently selected from at least one of an acrylic ester structure unit, an aromatic vinyl structure unit, and an acrylamide structure unit.

[0016] In a second aspect, the present application provides a separator comprising a substrate and a separator binder composition as described in the first aspect coated on the substrate, wherein the substrate is a separator base film and / or a coated separator in which non-conductive particles are coated on the separator base film.

[0017] In a third aspect, the present application provides a lithium ion secondary battery comprising the separator binder composition as described in the first aspect or the separator as described in the second aspect.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] The separator binder composition of the present application comprises a main binder and an auxiliary binder, which are first coated and dried, and then the main binder is fixed on the separator by the auxiliary binder, and the main binder is bonded to the electrode sheet after heat pressing. In the peeling process, the two adhesion forces of the electrode sheet and the main binder and the auxiliary binder and the main binder play a key role.

[0020] By increasing the post-reaction groups in the polymer microparticles A of the main binder and the polymer microparticles B of the auxiliary binder, the post-reaction groups of the polymer microparticles A and the polymer microparticles B react during the vacuum baking stage of the battery cell, achieving post-curing between the main binder and the auxiliary binder, improving the adhesion strength of the main binder and the auxiliary binder, thereby improving the adhesion strength between the separator and the electrode sheet interface, and improving the wettability of the separator and the electrolyte, and improving the performance and safety reliability of the battery.

[0021] By optimizing the particle size and glass transition temperature of the polymer microparticles A and the polymer microparticles B, the adhesion strength between the separator and the electrode sheet interface is further improved, and the wettability of the separator and the electrolyte is improved, and the performance and safety reliability of the battery are improved. DETAILED DESCRIPTION

[0022] In order to make the technical problems solved by the present application, the technical solutions and beneficial effects more clear and explicit, the present application will be further described in detail below in combination with specific embodiments. It should be understood that the embodiments described herein are part of the embodiments of the present application, rather than all the embodiments, which are used to explain the present application, and do not limit the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0023] In the present application, each structural unit represents a moiety corresponding to the monomer participating in the polymerization reaction, as is well known to those skilled in the art of chemical synthesis. The mass ratio of each structural unit is the mass ratio of the monomer providing the structural unit.

[0024] In a first aspect, the present application provides a separator adhesive composition, comprising a main adhesive and an auxiliary adhesive, the main adhesive comprising polymer microparticles A, the polymer microparticles A comprising first main monomer structural units and first post-reaction structural units containing post-reaction groups; the auxiliary adhesive comprising polymer microparticles B, the polymer microparticles B comprising second main monomer structural units and second post-reaction structural units containing post-reaction groups; the first post-reaction structural units and the second post-reaction structural units are connected to each other by chemical bonds.

[0025] In the vacuum baking stage of the battery cell, such as baking at 100-115℃ for 8-12h, the first post-reaction structural units in the polymer microparticles A and the second post-reaction structural units in the polymer microparticles B undergo a chemical reaction and are connected to each other by chemical bonds, achieving post-curing between the main adhesive and the auxiliary adhesive, thereby improving the bonding strength.

[0026] The present application improves the bonding strength and inhibits the deformation of the battery by the separator adhesive composition, and the key lies in the post-reaction groups. The bonding strength between the electrode sheet and the separator is determined by the bonding strength F1 between the polymer microparticles A and the electrode sheet and the bonding strength F2 between the polymer microparticles A and the separator; and the bonding strength between the polymer microparticles A and the separator is provided by F2 of the polymer microparticles B. From the phenomenon observed in the peel strength test, it can be known that F1>F2 after the polymer microparticles A adhere to the electrode sheet after the peel strength test, and the peel strength tested at this time is also F2. If it is necessary to improve the peel strength between the electrode sheet and the separator, it is necessary to improve F2. Therefore, post-curing between the polymer microparticles A and the polymer microparticles B can improve F2, thereby increasing the bonding strength between the separator and the electrode sheet interface, and further inhibiting the deformation of the battery.

[0027] In some embodiments, the post-reaction groups are carboxyl, epoxy or amino; when the post-reaction groups in the first post-reaction structural units are carboxyl, the post-reaction groups in the second post-reaction structural units are epoxy or amino; when the post-reaction groups in the first post-reaction structural units are amino, the post-reaction groups in the second post-reaction structural units are epoxy or carboxyl; when the post-reaction groups in the first post-reaction structural units are epoxy, the post-reaction groups in the second post-reaction structural units are carboxyl or amino.

[0028] The first post-reaction structural unit and the second post-reaction structural unit are derived from a post-reaction group monomer, i.e., a carboxyl monomer, an epoxy monomer, or an amino monomer. The carboxyl monomer includes at least one of acrylic acid, methacrylic acid, β-acryloyloxypropionic acid, itaconic acid, and butyl itaconate; the epoxy monomer includes at least one of glycidyl methacrylate, allyl glycidyl ether, and 3,4-epoxycyclohexylmethyl methacrylate; and the amino monomer includes at least one of amino polyethylene glycol acrylate, 2-(tert-butylamino)ethyl methacrylate, amino (meth) acrylate, and N-methylallylamine.

[0029] In some embodiments, the first post-reaction structural unit has a weight percentage content of 1-5% in the polymer microparticle A; and the second post-reaction structural unit has a weight percentage content of 1-5% in the polymer microparticle B. In this way, the bonding strength between the separator and the pole piece can be improved.

[0030] In some embodiments, the average particle size D A of the polymer microparticle A is 0.6-1.3 μm, and the glass transition temperature Tg of the polymer microparticle A is 50-80 °C.

[0031] In some embodiments, the average particle size D B of the polymer microparticle B is ≤0.3 μm, preferably 0.1-0.3 μm, and the glass transition temperature Tg of the polymer microparticle B is -50-10 °C.

[0032] If the particle size of the polymer microparticle A is too small, it may block a large area of the hole, affecting the air permeability of the separator, and if the particle size is too large, the polymer microparticle A may fall off. The particle size of the polymer microparticle B is small, which can effectively bond the polymer microparticle A; if the particle size of the polymer microparticle B is too large and the Tg is too low, the polymer microparticle B is prone to film formation, resulting in hole blocking and self-adhesion of the separator. The polymer A is a hot-pressing type adhesive, which has no bonding force before being coated, baked, and hot-pressed, and the bonding between the pole piece and the separator needs to be realized after hot-pressing. However, the polymer microparticle A itself cannot be bonded to the separator, and the polymer microparticle B is needed to realize the bonding between the polymer microparticle A and the separator after being coated and dried.

[0033] The Tg of the polymer microparticle A is lower than the hot-pressing temperature (85 °C), and the polymer microparticle A can be deformed at the hot-pressing temperature, so that the pole piece can be in contact with the separator

[0034] In some embodiments, the first main monomer structural unit and the second main monomer structural unit are independently selected from at least one of an acrylate structural unit, an aromatic vinyl structural unit, and an acrylamide structural unit.

[0035] The aromatic vinyl structural unit is selected from at least one of styrene structural units and methylstyrene structural units.

[0036] The acrylate structural units are selected from one or more of the following structural units: methyl acrylate, ethyl acrylate, n-butyl acrylate, isooctyl acrylate, hexyl acrylate, cyclohexyl methacrylate, and isobornyl acrylate.

[0037] The acrylamide structural unit is selected from at least one of (meth)acrylamide, N-methyl(meth)acrylamide, hydroxyethylacrylamide, N-butylacrylamide, acetylacetoneacrylamide, N-hydroxymethyl(meth)acrylamide, N,N'-methylenebis[(meth)acrylamide], N,N-dimethylacrylamide, and N,N-dibenzylacrylamide. Introducing an acrylamide structural unit can improve the stability of the adhesive system.

[0038] There are no particular restrictions on the first main monomer structural unit in polymer particle A and the second main monomer structural unit in polymer particle B. It is only necessary to select several monomers and corresponding mass ratios. After polymerization, the structural units in the polymers may be the same or different. The resulting polymer particles A and B satisfy the following: the glass transition temperature Tg of polymer particle A is 50~80℃, and the glass transition temperature Tg of polymer particle B is -50~10℃.

[0039] In some specific embodiments, the solid mass ratio of the primary binder to the secondary binder is 100:(15~25). The solid mass of the primary binder is the mass of the polymer contained in polymer particles A, and the solid mass of the secondary binder is the mass of the polymer contained in polymer particles B. Therefore, the mass ratio of polymer particles A to polymer particles B is 100:(15~25).

[0040] The preparation method of the diaphragm adhesive composition of the present invention:

[0041] Using deionized water as a solvent, add 0.1-0.8% by weight of an organic salt and selected monomers that meet the requirements of polymer microparticle A / polymer microparticle B. Sodium dodecylbenzenesulfonate can be used as the organic salt. Mix and stir to form a pre-emulsion. In another container, add an aqueous solution containing an initiator, with the initiator accounting for 0.1-1% by weight of the total monomers. Potassium persulfate can be used as the initiator. Add the pre-emulsion dropwise and react at 80-90℃ for 10-18 hours to obtain the main binder and auxiliary binder. The solid in the main binder is polymer microparticle A, and the solid in the auxiliary binder is polymer microparticle B. Mix the main binder and auxiliary binder to obtain the diaphragm binder composition.

[0042] The method for preparing the above-mentioned polymer, the glass transition temperature, and the method for controlling the particle size are known to those skilled in the art or can be known by those skilled in the art based on the prior art. For example, the glass transition temperature can be controlled by controlling the composition and ratio of the polymerization monomers, and the particle size of the polymer microparticles can be controlled by controlling the solid content, the stirring speed (for example, the speed can be selected from 200 rpm to 20,000 rpm according to the different material compositions of the polymer microparticles) and the stirring time during the synthesis, and the temperature and time of the polymerization reaction. Generally, the higher the stirring speed, the smaller the particle size of the polymer microparticles; the longer the stirring time, the smaller the particle size of the polymer microparticles; and the longer the reaction time, the smaller the particle size of the polymer microparticles.

[0043] In a second aspect, the present application provides a separator comprising a substrate and the separator binder composition as described in the first aspect coated on the substrate, wherein the substrate is a separator base film and / or a coated separator in which non-conductive particles are coated on the separator base film.

[0044] The separator base film is selected from one of a polyethylene base film, a polypropylene base film, a polypropylene-polyethylene-polypropylene laminated base film, and a non-woven fabric base film.

[0045] In some embodiments, the non-conductive particles are selected from at least one of hydrated aluminum oxide, aluminum trioxide, boehmite, silicon dioxide, titanium dioxide, zirconium dioxide, calcium oxide, magnesium oxide, magnesium hydroxide, calcium carbonate, barium titanate, barium sulfate, and heat-resistant organic polymer particles.

[0046] The method for preparing the separator using the aforementioned separator binder composition is known in the art. When used, the separator binder composition is mixed with a wetting agent, a defoaming agent, and other conventional additives that are beneficial for coating, and a solvent (deionized water). After dispersion, a coating slurry of the separator binder composition is obtained, which is then coated on the surface of the substrate and dried before being wound up. The mass ratio of the polymer microparticles A: the polymer microparticles B: the wetting agent: the defoaming agent is 100:(15-25):(0.3-0.6):(0.3-0.6), and is preferably 100:20:0.5:0.5.

[0047] In a third aspect, the present application provides a lithium ion secondary battery comprising the separator binder composition as described in the second aspect or the separator as described in the second aspect. The method for preparing the battery is to assemble a negative electrode sheet, a positive electrode sheet, an electrolyte, and a separator into a battery.

[0048] The specific embodiments of the present application will be further explained by the following examples and comparative examples.

[0049] The reagents, materials and instruments used in the following description are conventional reagents, conventional materials and conventional instruments, which are commercially available, and the reagents involved can also be synthesized by conventional synthesis methods. The methods in the examples are conventional methods in the art, unless otherwise specified. The monomers meeting the present application can be commercially available.

[0050] Example 1

[0051] 1) Preparation of the separator binder composition:

[0052] The main binder: in a pre-emulsification kettle, 150 parts of deionized water, 0.8 parts of sodium dodecyl benzene sulfonate, 78 parts of styrene, 17 parts of isooctyl acrylate, 2 parts of acrylamide and 3 parts of methacrylic acid were added and mixed and stirred into a pre-emulsion. In a reaction kettle, 100 parts of deionized water and 0.3 parts of potassium persulfate were added, and the pre-emulsion was added dropwise, and reacted at 85°C for 12h. The main binder was obtained, and the solid was polymer microparticles A with an average particle size of 0.9μm and a glass transition temperature Tg of 64°C.

[0053] The auxiliary binder: in a pre-emulsification kettle, 150 parts of deionized water, 0.8 parts of sodium dodecyl benzene sulfonate, 33 parts of styrene, 62 parts of isooctyl acrylate, 2 parts of acrylamide and 3 parts of glycidyl methacrylate were added and mixed and stirred into a pre-emulsion. In a reaction kettle, 100 parts of deionized water and 0.3 parts of potassium persulfate were added, and the pre-emulsion was added dropwise, and reacted at 85°C for 12h. The auxiliary binder was obtained, and the solid was polymer microparticles B with an average particle size of 0.2μm and a glass transition temperature Tg of -22°C.

[0054] The main binder and the auxiliary binder were mixed to obtain the separator binder composition.

[0055] 2) Separator

[0056] The separator binder composition was mixed with wetting agents and defoaming agents and other conventional beneficial assistants and solvents (deionized water) to obtain a coating slurry containing the separator binder composition, wherein the mass ratio of polymer microparticles A: polymer microparticles B: wetting agent: defoaming agent was 100:20:0.5:0.5.

[0057] A polyvinyl film was selected as the separator base film, and the coating slurry containing the separator binder composition was coated on the surface of the separator base film to obtain a separator, and the coating surface density was controlled to be 0.2g / m 2 .

[0058] 3) Lithium ion secondary battery

[0059] The negative electrode sheet, the positive electrode sheet, the electrolyte solution of the lithium ion battery prepared according to the conventional method in the art, the positive electrode sheet, the separator of the application, and the negative electrode sheet are sequentially stacked, and then are wound and hot-pressed to obtain a battery core. The battery core is placed in an aluminum plastic film, and is subjected to vacuum baking, liquid injection, formation, capacity test, and other processes to obtain a lithium ion secondary battery.

[0060] Example 2

[0061] The separator adhesive composition, the separator, and the lithium ion secondary battery are prepared according to the method of Example 1. The main difference between this example and Example 1 is that the preparation of the separator adhesive composition is adjusted by adjusting the types and amounts of the polymerization monomers, so that the glass transition temperature Tg of the polymer microparticle A is 80°C, and the glass transition temperature Tg of the polymer microparticle B is 12°C. The rest is the same as Example 1. Details are as follows:

[0062] The monomers used for the polymer microparticle A are 68 parts of methylstyrene, 27 parts of butyl acrylate, 2 parts of methacrylamide, and 3 parts of acrylic acid; the glass transition temperature Tg of the polymer microparticle A is 80°C.

[0063] The monomers used for the polymer microparticle B are 45 parts of methylstyrene, 50 parts of isooctyl acrylate, 2 parts of methacrylamide, and 3 parts of allyl glycidyl ether; the glass transition temperature Tg of the polymer microparticle B is 12°C.

[0064] Example 3

[0065] The separator adhesive composition, the separator, and the lithium ion secondary battery are prepared according to the method of Example 1. The main difference between this example and Example 1 is that the preparation of the separator adhesive composition is adjusted by adjusting the types and amounts of the polymerization monomers, so that the glass transition temperature Tg of the polymer microparticle A is 69°C, and the glass transition temperature Tg of the polymer microparticle B is -36°C. The rest is the same as Example 1. Details are as follows:

[0066] The monomers used for the polymer microparticle A are 72 parts of styrene, 23 parts of ethyl acrylate, 2 parts of acrylamide, and 3 parts of acrylic acid; the glass transition temperature Tg of the polymer microparticle A is 69°C.

[0067] The monomers used for the polymer microparticle B are 15 parts of styrene, 82 parts of butyl acrylate, 2 parts of methacrylamide, and 3 parts of N-methylallylamine; the glass transition temperature Tg of the polymer microparticle B is -36°C.

[0068] Example 4

[0069] A separator adhesive composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this example and Example 1 being that the glass transition temperature Tg of the polymer fine particles A was 51°C and the glass transition temperature Tg of the polymer fine particles B was -50°C by adjusting the kind and amount of the polymerization monomers in the preparation of the separator adhesive composition. The rest was the same as Example 1. Specifically as follows:

[0070] The monomers used for the polymer fine particles A were 73 parts of styrene, 24 parts of n-butyl acrylate, 2 parts of acrylamide and 3 parts of glycidyl methacrylate; and the glass transition temperature Tg of the polymer fine particles A was 51°C.

[0071] The monomers used for the polymer fine particles B were 95 parts of n-butyl acrylate, 2 parts of acrylamide and 3 parts of acrylic acid; and the glass transition temperature Tg of the polymer fine particles B was -50°C.

[0072] Example 5

[0073] A separator adhesive composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this example and Example 1 being that:

[0074] The glass transition temperature Tg of the polymer fine particles A was 64°C and the glass transition temperature Tg of the polymer fine particles B was -22°C by adjusting the kind and amount of the polymerization monomers in the preparation of the separator adhesive composition; and the post-reaction group monomer used for the polymer fine particles A was 1 part of 3,4-epoxycyclohexylmethyl methacrylate and the post-reaction group monomer used for the polymer fine particles B was 1 part of amino polyethylene glycol acrylate. The rest was the same as Example 1.

[0075] Example 6

[0076] A separator adhesive composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this example and Example 1 being that:

[0077] The glass transition temperature Tg of the polymer fine particles A was 64°C and the glass transition temperature Tg of the polymer fine particles B was -22°C by adjusting the kind and amount of the polymerization monomers in the preparation of the separator adhesive composition; and the post-reaction group monomer used for the polymer fine particles A was 5 parts of 2-(tert-butylamino)ethyl methacrylate and the post-reaction group monomer used for the polymer fine particles B was 5 parts of glycidyl methacrylate; and the average particle diameter of the polymer fine particles A was 0.6 μm and the average particle diameter of the polymer fine particles B was 0.1 μm by adjusting the amount of the deionized water, the mixing and stirring speed, the reaction temperature and time. The rest was the same as Example 1.

[0078] Example 7

[0079] A separator adhesive composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this example and Example 1 being that:

[0080] In the preparation of the separator adhesive composition, the post-reacting group monomer used for the polymer fine particles A was an amino (meth) acrylate and the post-reacting group monomer used for the polymer fine particles B was a β-acryloyloxy propionic acid; by adjusting the amount of deionized water, the mixing and stirring speed, the reaction temperature and time, the average particle diameter of the polymer fine particles A was 1.1 μm and the average particle diameter of the polymer fine particles B was 0.15 μm. The rest was the same as Example 1.

[0081] Example 8

[0082] A separator adhesive composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this example and Example 1 being that:

[0083] In the preparation of the separator adhesive composition, the average particle diameter of the polymer fine particles A was 1.3 μm and the average particle diameter of the polymer fine particles B was 0.3 μm by adjusting the amount of deionized water, the mixing and stirring speed, the reaction temperature and time.

[0084] In the preparation of the separator, the mass ratio of the polymer fine particles A: polymer fine particles B: wetting agent: defoaming agent in the coating slurry containing the separator adhesive composition was 100: 15: 0.3: 0.3. The rest was the same as Example 1.

[0085] Example 9

[0086] A separator adhesive composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this example and Example 1 being that:

[0087] In the preparation of the separator adhesive composition, the average particle diameter of the polymer fine particles A was 0.75 μm and the average particle diameter of the polymer fine particles B was 0.22 μm by adjusting the amount of deionized water, the mixing and stirring speed, the reaction temperature and time.

[0088] In the preparation of the separator, the mass ratio of the polymer fine particles A: polymer fine particles B: wetting agent: defoaming agent in the coating slurry containing the separator adhesive composition was 100: 25: 0.6: 0.6.

[0089] Comparative Example 1

[0090] A separator adhesive composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this example and Example 1 being that: there was no post-reacting structural unit in the polymer fine particles A and the polymer fine particles B of the separator adhesive composition, the rest being the same as Example 1.

[0091] Comparative Example 2

[0092] A separator binder composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this comparative example and Example 1 being that the glass transition temperature Tg of the polymer fine particles A was adjusted to 55°C and the glass transition temperature Tg of the polymer fine particles B was adjusted to 0°C by adjusting the types and amounts of the polymerization monomers, the weight percentage content of the post-reaction structure units in the polymer fine particles A and the polymer fine particles B of the separator binder composition were both 8%, and the rest was the same as in Example 1.

[0093] Comparative Example 3

[0094] A separator binder composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this comparative example and Example 1 being that the glass transition temperature Tg of the polymer fine particles A was adjusted to 40°C and the glass transition temperature Tg of the polymer fine particles B was adjusted to -60°C by adjusting the types and amounts of the polymerization monomers, and the rest was the same as in Example 1.

[0095] Comparative Example 4

[0096] A separator binder composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this comparative example and Example 1 being that the glass transition temperature Tg of the polymer fine particles A was adjusted to 90°C and the glass transition temperature Tg of the polymer fine particles B was adjusted to 20°C by adjusting the types and amounts of the polymerization monomers, and the rest was the same as in Example 1.

[0097] Comparative Example 5

[0098] A separator binder composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this comparative example and Example 1 being that the average particle size of the polymer fine particles A was adjusted to 0.2 μm by adjusting the amount of deionized water, the mixing and stirring speed, the reaction temperature and time, and the rest was the same as in Example 1.

[0099] Comparative Example 6

[0100] A separator binder composition, a separator and a lithium ion secondary battery were prepared according to the method of Example 1, the main difference between this comparative example and Example 1 being that the average particle size of the polymer fine particles B was adjusted to 1.2 μm by adjusting the amount of deionized water, the mixing and stirring speed, the reaction temperature and time, and the rest was the same as in Example 1.

[0101] Comparative Example 7

[0102] The membrane binder composition, the membrane, and the lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between this comparative example and Example 1 is that in the preparation of the membrane, the mass ratio of polymer particles A: polymer particles B: wetting agent: defoamer in the coating slurry containing the membrane binder composition is 20:100:0.5:0.5. The rest is the same as in Example 1.

[0103] Comparative Example 8

[0104] The separator coating uses an existing ceramic coating. Ceramic particles are coated onto the surface of the separator base membrane using a polymer binder to form a ceramic / polymer composite separator. The base membrane is 9 μm thick, and the ceramic coating is a single layer of 2 μm. The resulting composite separator is used to prepare a lithium-ion secondary battery according to the same method as in Example 1.

[0105] Comparative Example 9

[0106] The main difference between this comparative example and Example 1 is that the membrane binder is derived from the commercially available product SWA5205; otherwise, it is the same as Example 1, and the membrane and lithium-ion secondary battery are prepared according to the method of Example 1.

[0107] The membrane adhesive compositions (or membrane coatings) and membranes of Examples 1-9 and Comparative Examples 1-9 were characterized and their performance was tested. The test results are shown in Table 1.

[0108] [Average Particle Size]: The average particle size of polymer particles A and polymer particles B during the preparation of the diaphragm adhesive composition was measured using a laser particle size analyzer (Zhuhai Omec Instrument Co., Ltd., model: LS-909E).

[0109] [Glass transition temperature]: The glass transition temperatures of polymer particles A and polymer particles B during the preparation of the diaphragm binder composition were measured using a differential scanning calorimeter (Shanghai Qunhong Instrument Equipment Co., Ltd., model: DSC-100) in accordance with GB / T 19466.1-2004.

[0110] [Peel Strength Test]: The separator and negative electrode sheet were cut into strips of 20mm*100mm each. They were hot-pressed at 95℃ and 2MPa for 60s, and then subjected to a 180° peel strength test using an electronic tensile testing machine. The peel strength of the separator-electrode interface was tested under three conditions: 1) After coating the separator adhesive composition onto the separator substrate, the dry-bonded peel strength of the coated separator and electrode sheet was tested; 2) After coating and hot-pressing, the separator and electrode sheet were placed in a vacuum oven at 115℃ for 12 hours (simulating vacuum baking) for post-curing, and the dry-bonded peel strength of the cured separator and electrode sheet was tested; 3) Electrolyte was injected, and the wet-bonded peel strength of the separator and electrode sheet was tested under actual battery cell usage scenarios. The test results were taken as the average of three samples.

[0111]

Separation membrane air permeability

[0112]

Electrolyte wettability

[0113] Table 1

[0114]

[0115]

Electrical performance test

[0116] Table 2

[0117]

[0118] From the performance test results in Tables 1 and 2, it can be seen that the use of the separation membrane adhesive composition provided by the present application and the separation membrane and battery prepared from the separation membrane adhesive composition can effectively improve the adhesion strength of the electrode sheet and the separation membrane and the performance of the battery. When the weight percentage of the post-reaction structural unit, the average particle size, the glass transition temperature, and the mass ratio of the two after the polymer particles A and the polymer particles B in the coating of the separation membrane are selected outside the range disclosed in the present application, the adhesion strength of the negative electrode sheet and the separation membrane and the performance of the battery decrease to varying degrees. The specific analysis is as follows.

[0119] From the test results of Comparative Examples 1, 5 to 7 and Comparative Examples 1 to 2, it can be seen that the weight percentage of the post-reaction structural unit in the polymer particles A and the polymer particles B of the separation membrane adhesive composition is > 5%, the separation membrane adhesive emulsion has insoluble substances after being stored for 1 month, and is not a qualified stable product. The short shelf life will affect production. There is no post-reaction structural unit in the separation membrane adhesive composition, and the dry and wet peel strengths of the cured separation membrane and the electrode sheet are significantly reduced, and the capacity during high-temperature storage and high-rate cycling is also decreased; when the weight percentage of the post-reaction structural unit in the polymer is 1% to 5%, the performance is better.

[0120] From the test results of Examples 1-4 and Comparative Examples 3-4, it can be seen that the lower the Tg of the polymer microparticles A, the higher the dry adhesion peeling strength and the wet adhesion peeling strength; but when the Tg of the polymer A is less than 50℃, the separator has self-adhesion phenomenon during winding, resulting in the peeling of the coating; the higher the Tg of the polymer microparticles B, the smaller the dry adhesion strength, the wet adhesion peeling strength decreases significantly, and the capacity during high-temperature storage and high-rate cycling process also decreases, and when the Tg of the polymer B is greater than 10℃, the separator is not adhered to the pole piece after injection of electrolyte; when the Tg of the polymer microparticles A is 50-80℃ and the glass transition temperature Tg of the polymer microparticles B is -50-10℃, the performance is better.

[0121] From the test results of Examples 1, 6-9 and Comparative Examples 5-6, it can be seen that when the average particle size of the polymer microparticles A is in the range of 0.6-1.3 μm and the average particle size of the polymer microparticles B is in the range of 0.1-0.3 μm, the separator has both low air permeability and better peeling strength. If the average particle size of the polymer microparticles A is not in the range disclosed in the present application, the smaller the particle size, the higher the air permeability of the separator, which is prone to film formation and causes hole blocking, and the adhesion strength between the separator and the pole piece decreases significantly, and the capacity during high-temperature storage and high-rate cycling process also decreases; if the average particle size of the polymer microparticles B is not in the range disclosed in the present application, the larger the particle size, the higher the air permeability of the separator, which is prone to film formation and causes hole blocking, and the separator has obvious self-adhesion during winding, and the coating peels off.

[0122] From the test results of Examples 1-9 and Comparative Example 7, it can be seen that when the proportion of the polymer microparticles B is large, the air permeability of the separator is high, which is prone to film formation and causes hole blocking, and the separator has obvious self-adhesion during winding, and the coating peels off; when the mass ratio of the polymer microparticles A to the polymer microparticles B is 100: (15-25), the performance is better.

[0123] From the test results of Examples 1-9 and Comparative Example 8, it can be seen that the separator adhesive composition used in the present application can replace the existing ceramic coating as the separator coating, which can significantly improve the adhesion between the separator and the pole piece, especially the wet adhesion peeling strength, thereby improving the processing performance and safety performance of the battery and improving the cycle performance of the battery cell.

[0124] From the test results of Examples 1-9 and Comparative Example 9, it can be seen that the separator adhesive composition used in the present application can replace SWA5205 as the separator coating, which can significantly improve the adhesion between the separator and the pole piece, especially the wet adhesion peeling strength, thereby improving the processing performance and safety performance of the battery and improving the cycle performance of the battery cell.

[0125] Moreover, it is found in performance test that: when testing the dry adhesion peeling strength between the coated separator and the pole piece, the separator adhesive provided by the application is mainly located on the pole piece side after the pole piece and the separator are peeled off; when testing the dry adhesion peeling strength of the cured separator and the pole piece and the wet adhesion peeling strength after the electrolyte is injected, the separator adhesive provided by the application is mainly located on the separator side; however, in the peeling strength test under the three conditions, the separator adhesive of all the comparative examples is mainly located on the pole piece side. This also shows that the application improves the adhesion strength of the main adhesive and the auxiliary adhesive through post-curing, thereby improving the adhesion strength between the separator and the pole piece interface.

[0126] The application is further described above by means of specific examples, but it should be understood that the specific description herein should not be construed as limiting the essence and scope of the application, and various modifications made to the above examples by those skilled in the art after reading the specification are within the scope of the application.

Claims

1. A separator binder composition characterized by, The separator adhesive composition comprises a main adhesive and an auxiliary adhesive; the main adhesive comprises polymer microparticles A, the polymer microparticles A comprising first main monomer structural units and first post-reaction structural units containing post-reaction groups; the auxiliary adhesive comprises polymer microparticles B, the polymer microparticles B comprising second main monomer structural units and second post-reaction structural units containing post-reaction groups; the first post-reaction structural units and the second post-reaction structural units are connected to each other through chemical bonds; The average particle size D of the polymer particles A A The particle size is 0.6~1.3μm, and the glass transition temperature Tg of the polymer particles A is 50~80℃; The average particle size D of the polymer particles B B The particle size is 0.1~0.3μm, and the glass transition temperature Tg of the polymer particles B is -50~10℃; The post-reaction groups are carboxyl groups, epoxy groups or amino groups; when the post-reaction groups in the first post-reaction structural units are carboxyl groups, the post-reaction groups in the second post-reaction structural units are epoxy groups or amino groups; when the post-reaction groups in the first post-reaction structural units are amino groups, the post-reaction groups in the second post-reaction structural units are epoxy groups or carboxyl groups; when the post-reaction groups in the first post-reaction structural units are epoxy groups, the post-reaction groups in the second post-reaction structural units are carboxyl groups or amino groups; The first post-reaction structural units have a content of 1-5% by weight in the polymer microparticles A; The second post-reaction structural units have a content of 1-5% by weight in the polymer microparticles B; The solid mass ratio of the main adhesive to the auxiliary adhesive is 100: (15-25); The first main monomer structural units and the second main monomer structural units are independently selected from at least one of acrylate structural units, aromatic vinyl structural units and acrylamide structural units.

2. A diaphragm, characterized by The separator comprises a substrate and the separator adhesive composition as claimed in claim 1 coated on the substrate, the substrate being a separator base film and / or a coated separator with non-conductive particles coated on the separator base film.

3. A lithium ion secondary battery, which is obtained by sequentially stacking a positive electrode sheet, a separator, and a negative electrode sheet, then roll-winding and hot-pressing to obtain a battery core, and then placing the battery core in an aluminum plastic film, and then performing vacuum baking, liquid injection, formation, capacity test, and capacity test procedures, characterized in that, The lithium ion secondary battery comprises the separator adhesive composition as claimed in claim 1 or the separator as claimed in claim 2; in the vacuum baking stage of the battery cell, the first post-reaction structural units in the polymer microparticles A and the second post-reaction structural units in the polymer microparticles B in the separator adhesive composition chemically react and are connected to each other through chemical bonds.

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