Composite binder, preparation method thereof, diaphragm and secondary battery

Abstract

The invention belongs to the field of new energy, and particularly provides a composite binder, a preparation method thereof, a diaphragm and a secondary battery. The composite binder comprises a raspberry-shaped binder and a linear binder, and the raspberry-shaped binder and the linear binder at least partially form a cross-linked structure; the raspberry-shaped binder is a raspberry-shaped microsphere with a core-shell structure, and comprises a polymer microsphere serving as a core and a polymer nanosphere serving as a shell on at least part of the surface of the core; the linear binder comprises a linear polymer; the mass ratio of the raspberry-shaped binder to the linear binder is (3: 7)-(7: 3). According to the composite binder provided by the invention, the raspberry-shaped binder and the linear binder are cross-linked, so that the synergistic effect of the raspberry-shaped binder and the linear binder can be fully exerted, and the heat resistance and the use reliability of the diaphragm are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of new energy and relates to a composite adhesive, a preparation method thereof, a diaphragm and a secondary battery, and more particularly to a composite adhesive with high heat resistance and bonding strength, a preparation method thereof, a diaphragm containing the adhesive and a secondary battery containing the diaphragm. Background Art

[0002] The separator is an indispensable component of lithium-ion battery systems. It prevents short circuits between the positive and negative electrodes, ensuring battery safety, while also providing an effective channel for the rapid migration of lithium ions. Currently, polyolefin microporous membranes are widely used in the lithium-ion battery industry due to their excellent chemical stability and mechanical strength. However, due to the inherent properties of polyethylene (PE) and polypropylene (PP) separators, their melting points (Tm) are only around 135°C and 165°C, respectively. These membranes experience severe thermal shrinkage under overheating, limiting their use in high-temperature applications. This can lead to internal short circuits and potential explosion hazards.

[0003] To improve the thermal shrinkage and temperature resistance of diaphragms, a common method is to apply ceramic coating to the diaphragm surface. To ensure the adhesion and uniformity of the coating, a binder is usually added to bond the ceramic particles to the base film.

[0004] However, the current commercial conventional adhesives can only achieve heat shrinkage resistance of 130℃~150℃, and have limited improvement on the heat shrinkage performance of the diaphragm. In addition, the coating has low bonding strength and is prone to uneven shedding, which reduces the heat resistance of the diaphragm in the battery and causes the diaphragm to shrink in a high temperature environment, ultimately affecting battery safety.

[0005] To improve the adhesive's adhesion and heat resistance, some literature has disclosed a heat-resistant separator adhesive. The adhesive comprises polymer particles with a core-shell structure, comprising a core polymer and a shell polymer. The core polymer has a glass transition temperature of 80°C or higher, while the shell polymer has a glass transition temperature of 0°C or lower. This core-shell structure improves the bond strength between the separator and the electrode, as well as the separator's heat resistance.

[0006] Some literature discloses a method for preparing raspberry-structured polymer microspheres. This method uses amino-activated microspheres as a carrier. Epoxy-activated nanoparticles are added to the amino-activated microspheres, causing a ring-opening reaction between the amino and epoxy groups to produce polymer particles. Using these raspberry-structured polymer microspheres as a binder can improve thermal stability and bond strength between the diaphragm and the electrode.

[0007] It can be seen that although the existing technology has explored adhesive materials with high heat resistance to a certain extent, it cannot be said to be sufficient and there is still room for further improvement. Summary of the Invention

[0008] Problems to be solved by the invention

[0009] As mentioned above, the currently commonly used polyolefin separators have a problem of poor heat shrinkage performance due to their low melting point, which affects their safety in use. In order to improve the heat shrinkage performance and low melting point of the separator, it has been reported in the prior art that raspberry-shaped binders and inorganic particles are used to improve their performance. Among them, by the high elasticity and rigidity of the raspberry-shaped structure, high spherical shape-keeping ability and good bonding strength are guaranteed, thereby improving the heat resistance of the separator. However, it is also found in practice that for the raspberry-shaped core-shell structure, whether the kernel is a hard core and the shell is a soft shell, or the kernel is a soft core and the shell is a hard shell, in the charge and discharge cycle, due to the presence of the electrolyte, certain swelling will occur, therefore, there is a risk of swelling and pore blocking, and the binder will lose a certain adhesive force when swelling, which will eventually cause the binder to fall off, affecting the heat resistance of the separator.

[0010] To address the above-mentioned problems, the present invention provides a composite binder comprising a raspberry-shaped binder and a linear binder. The raspberry-shaped binder at least partially forms a cross-linked structure with the linear binder, and preferably, the core-shell structure of the raspberry-shaped binder is connected by covalent bonds. This structure can effectively inhibit micropore blockage caused by swelling of the raspberry-shaped binder. Furthermore, the raspberry-shaped binder can also give the composite binder a larger specific surface area, increasing the bonding strength with the inorganic particles and the electrode. Therefore, by cross-linking the raspberry-shaped binder and the linear binder, the synergistic effect of the two can be fully utilized, greatly improving the heat resistance and reliability of the diaphragm.

[0011] In addition, the present invention also provides a method for preparing the composite adhesive according to the present invention.

[0012] In addition, the present invention also provides a separator, which includes the composite binder of the present invention.

[0013] Furthermore, the present invention also provides a secondary battery comprising the separator of the present invention.

[0014] Solutions for solving problems

[0015] The present invention first provides a composite adhesive, wherein the composite adhesive comprises a raspberry-shaped adhesive and a linear adhesive, and the raspberry-shaped adhesive at least partially forms a cross-linked structure with the linear adhesive;

[0016] The raspberry-shaped adhesive is a raspberry-shaped microsphere having a core-shell structure, and includes polymer microspheres as cores and polymer nanospheres as shells on at least a portion of the surface of the cores;

[0017] The linear binder comprises a linear polymer;

[0018] The mass ratio of the raspberry-shaped adhesive to the linear adhesive is 3:7 to 7:3.

[0019] According to the composite adhesive of the present invention, the particle size of the polymer microspheres is 0.5-10 μm, and the particle size of the polymer nanospheres is less than 100 nm; preferably, the particle size of the polymer microspheres is 1-10 μm, and the particle size of the polymer nanospheres is 1-100 nm.

[0020] According to the composite adhesive of the present invention, the polymer microspheres are at least partially connected to the polymer nanospheres through covalent bonds.

[0021] According to the composite adhesive of the present invention, the Tg of the polymer A forming the polymer microspheres is greater than the Tg of the polymer B forming the polymer nanospheres.

[0022] According to the composite adhesive of the present invention, the polymer microspheres are at least partially connected to the polymer nanospheres via sulfur-containing covalent bonds.

[0023] According to the composite adhesive of the present invention, the monomer forming the linear polymer includes an olefin having an amino group.

[0024] Secondly, the present invention also provides a method for preparing the composite adhesive according to the present invention, which comprises the following steps:

[0025] The steps for synthesizing the raspberry-shaped adhesive are as follows: monomer 1 is initially polymerized to obtain polymer microspheres, and monomer 2 is added to continue the polymerization reaction to obtain the raspberry-shaped adhesive;

[0026] The linear binder synthesis step is as follows: monomer 3 is polymerized to obtain the linear binder;

[0027] The step of synthesizing the composite adhesive is as follows: mixing the obtained raspberry-shaped adhesive with the linear adhesive to carry out a cross-linking reaction.

[0028] According to the preparation method of the present invention, the monomer 1 comprises a combination of one or more of styrene, vinyl ether, terephthalic acid, 1,4-dicyanobenzene, N-vinylcarbazole, maleic anhydride, N-substituted maleimide, dialkyl maleate, and maleonitrile;

[0029] and / or, the monomer 2 comprises an aromatic compound having two or more thiol groups;

[0030] And / or, the monomer 3 includes an olefin having an amino group.

[0031] According to the preparation method of the present invention, in the step of synthesizing the raspberry-shaped binder, the molar ratio of monomer 1 to monomer 2 is 1:0.95 to 1:1.05;

[0032] And / or, the reaction temperature of the initial polymerization is 50-70° C., and the reaction time is 0.5-1.5 h;

[0033] And / or, the reaction temperature of the polymerization reaction is 50-70° C.; and the reaction time is 3-5 hours.

[0034] According to the preparation method of the present invention, in the step of synthesizing the linear binder, the reaction temperature of the polymerization reaction is 30 to 50° C. and the reaction time is 1 to 3 hours.

[0035] According to the preparation method of the present invention, in the step of synthesizing the composite binder, the reaction temperature of the cross-linking reaction is 50-60° C. and the reaction time is 1-3 hours.

[0036] In addition, the present invention also provides a separator for a secondary battery, wherein the separator comprises a base film and a coating layer coated on at least one surface of the base film;

[0037] Wherein, the coating comprises inorganic particles and the composite binder according to the present invention;

[0038] Wherein, the content of the composite binder in the coating is 3-8%; the content of the inorganic particles is 85-95%.

[0039] According to the separator of the present invention, the base film includes at least one of a polyolefin base film, a polyimide base film, and a polyester base film.

[0040] Furthermore, the present invention also provides a secondary battery, which includes the separator according to the present invention, and the secondary battery includes a power battery or an energy storage battery for an energy storage power station.

[0041] Effects of the Invention

[0042] 1) The composite adhesive provided by the present invention includes a combination of a raspberry-shaped microsphere polymer adhesive and a linear adhesive. By forming a cross-linked network structure between the linear adhesive and the raspberry-shaped adhesive, the strong chemical bond interaction between the linear adhesive and the raspberry-shaped adhesive can prevent the spherical adhesive with a raspberry-shaped structure from deforming after swelling due to liquid absorption, and can maintain better structural stability, thereby preventing the raspberry-shaped adhesive from clogging due to swelling due to liquid absorption.

[0043] 2) The raspberry-shaped binder, due to its large specific surface area and roughness, can provide more contact sites. After cross-linking with the linear binder, the raspberry-shaped binder can synergistically enhance the bonding between the diaphragm and the electrode, resulting in stronger adhesion and higher mechanical strength, and improving the wettability of the diaphragm. Furthermore, the composite binder's larger specific surface area provides abundant contact sites, while also improving the flexibility of the diaphragm. This prevents the raspberry-shaped binder from losing its adhesive force and falling off the diaphragm due to electrolyte absorption in high-silicon battery systems. This ensures that the inorganic particles in the coating will not shed, thus preventing the diaphragm from rupturing due to high temperatures, which could lead to battery short circuits. The composite binder improves the heat resistance and safety of the battery.

[0044] 3) The polymer nanospheres, which serve as shells in the raspberry-shaped binder, bond the electrode to the separator. The resulting polymer, cross-linked with the linear binder, forms a strong surface layer at the positive / negative electrode interface, preventing degradation and migration of the positive electrode material to the negative electrode. This protects the negative electrode SEI (Solid Electrolyte Interface) layer, while also inhibiting the growth of lithium dendrites, thereby improving the battery's cycling stability. Furthermore, the cross-linked network structure mitigates stress caused by volume expansion at the negative electrode, while the linear network structure disperses and alleviates this stress, ensuring that the separator surface coating remains structurally intact during expansion.

[0045] 4) In a preferred embodiment, the raspberry-shaped microsphere polymer of the present invention is configured to have a hard core-soft shell structure, which not only takes into account heat resistance and flexibility, but also the nano-sized soft shell can further increase the crosslinking property of the raspberry-shaped microspheres and the linear binder. DETAILED DESCRIPTION

[0046] The following is a detailed description of the present invention. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0047] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0048] In this specification, the numerical range expressed using "above" or "below" means a numerical range including the number.

[0049] In this specification, the use of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0050] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0051] In this specification, "normal temperature" or "room temperature" refers to an indoor ambient temperature of "23±2°C".

[0052] In this specification, the term "plurality" refers to a number of 2 or more.

[0053] In this specification, the unit names used are all international standard unit names, and unless otherwise stated, the "%" used means weight or mass percentage.

[0054] In this specification, the use of “substantially” or “essentially” means that the standard deviation from a theoretical model, theoretical data or target data is within a numerical range of 1%, preferably 0.8%, and more preferably 0.5%.

[0055] When the terms “include” and / or “comprising” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0056] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "embodiments," etc., mean that the specific elements (e.g., features, structures, properties, and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0057] The present invention primarily provides a separator comprising a base film and a coating applied to at least one surface of the base film. The coating comprises a composite binder and inorganic particles. The composite binder comprises a raspberry-shaped binder and a linear binder. The raspberry-shaped binder is a raspberry-shaped microsphere having a core-shell structure, and the raspberry-shaped binder at least partially forms a cross-linked structure with the linear binder. This composite binder effectively improves the separator's heat resistance and adhesion to electrode components.

[0058] The present invention is mainly obtained through the following insights:

[0059] The composite use of core-shell polymer particles and inorganic particles has been used to improve the heat resistance and dimensional stability of polyolefin separators. However, it has been found that during the repeated thermal experience of the charge and discharge cycle, the core-shell polymer structure swells due to the presence of the electrolyte. As a result, not only does it lead to poor adhesion with the inorganic particles and electrode sheets, but it may also cause blockage of the micropores of the separator. Through long-term research, the inventors found that the composite binder obtained by cross-linking a raspberry-shaped binder with specific structural characteristics with a linear binder can synergistically give full play to the advantages of both while making up for the shortcomings of both. The cross-linking of the two can inhibit the occurrence of the above-mentioned swelling, so that the composite binder has high heat resistance, high adhesion and stability, and at the same time makes the separator highly flexible, preventing the inorganic particles from easily falling off in high temperature, electrolyte and other environments, greatly improving the heat resistance and stability of the separator.

[0060] (First aspect)

[0061] A first aspect of the present invention provides a composite adhesive, comprising a raspberry-shaped adhesive and a linear adhesive, wherein the raspberry-shaped adhesive at least partially forms a cross-linked structure with the linear adhesive.

[0062] Raspberry-shaped adhesive

[0063] The raspberry-shaped adhesive of the present invention is a raspberry-shaped microsphere having a core-shell structure. The raspberry-shaped microsphere comprises a polymer microsphere as a core and a polymer nanosphere as a shell present on at least a portion of the surface of the core. The polymer microsphere is at least partially covalently bonded to the polymer nanosphere. In some specific embodiments, both the polymer microsphere and the polymer nanosphere have a solid structure.

[0064] In a preferred embodiment, a raspberry-like structure can be constructed with a hard core inside to provide cohesion and swelling electrolyte and a certain proportion of soft spheres outside to provide mechanical strength and thermal stability, thereby simultaneously ensuring excellent adhesion and spherical shape retention at high temperatures.

[0065] Furthermore, in some specific embodiments, the particle size of the raspberry-shaped microspheres can be 0.5 to 10 μm, for example, 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 9 μm, etc. When the particle size of the raspberry-shaped microspheres is 0.5 to 10 μm, they can have a high specific surface area and can bond the separator and electrode without blocking the pores of the separator. Because the particle size of the raspberry-shaped microspheres is primarily determined by the polymer microspheres that serve as their cores, the particle size of the polymer microspheres is used as the particle size of the raspberry-shaped microspheres in the present invention.

[0066] In addition, the particle size of the polymer nanospheres in the raspberry-shaped microspheres can generally be 100 nm or less and 1 nm or more, preferably 5 to 80 nm, and more preferably 10 to 60 nm.

[0067] In some specific embodiments of the present invention, the raspberry-shaped microspheres of the present invention have a rigid core and a flexible shell. Therefore, the Tg of polymer A forming the polymer microspheres is greater than the Tg of polymer B forming the polymer nanospheres. In some preferred embodiments, the Tg of polymer A is above 80°C, preferably above 90°C, and more preferably above 100°C, while the Tg of polymer B is below 20°C, preferably below 10°C, and more preferably below 0°C. Tg (glass transition temperature) represents the glass transition temperature.

[0068] The polymer microspheres used as the core of the present invention can preferably provide cohesive force through a rigid hard core to ensure the spherical shape retention of the raspberry-shaped binder at high temperatures, thereby improving heat resistance. In some specific embodiments, the polymer microspheres used as the core can be formed by polymer A obtained by polymerization of monomers including monomer 1. The type of monomer 1 can be selected from those monomers generally considered to form hard segment structures in the art. Preferably, the monomer 1 can be selected from one or more combinations of styrene, vinyl ether, terephthalic acid, 1,4-dicyanobenzene, N-vinylcarbazole, maleic anhydride, N-substituted maleimide, dialkyl maleate (the alkyl group may include methyl, ethyl, etc.), and maleic dinitrile.

[0069] The polymer nanospheres used as the shell in the present invention may preferably be soft spheres with high elasticity, thereby increasing the bonding strength of the raspberry-shaped adhesive.

[0070] In some preferred embodiments of the present invention, the core and shell of the raspberry-shaped microspheres can be connected by covalent bonds. The method of covalent connection is not particularly limited in principle. To facilitate the formation of the polymer nanospheres, the covalent connection can be via sulfur-containing covalent bonds.

[0071] For example, the residual double bonds in the core polymer microsphere component can react with the thiol functional groups in the shell-forming substance through click chemistry reaction to achieve the above covalent bonding.

[0072] The aforementioned thiol-functional substance is preferably an aromatic compound having multiple thiol groups. Such aromatic compounds may be carboaromatic or heteroaromatic, preferably carboaromatic, such as phenyl or biphenyl. The thiol group is preferably directly bonded to the aromatic group. Furthermore, the number of thiol groups in the aromatic compound molecule may generally be 2 to 4, preferably 2.

[0073] In some specific embodiments, the polymer nanospheres as the shell can be formed by polymerizing monomers including monomer 2 or polymer B obtained by self-polymerization of monomer 2, wherein the monomer 2 is selected from the compound shown in formula (A):

[0074]

[0075] Here, R1 to R4 are the same or different and each independently represents a hydrogen atom or a monovalent organic group.

[0076] In some specific embodiments, the monovalent organic group may be a hydrophilic group. Preferably, the hydrophilic group may be selected from a group having a hydroxyl group, an amino group, or a carboxyl group. Preferably, the monovalent organic group may be any of these groups or a hydrocarbon group substituted with these groups. The hydrocarbon group may preferably be an alkyl group, an alkenyl group, an alkynyl group, or the like having 1 to 10 carbon atoms.

[0077] In some preferred embodiments, the monomer 2 is selected from one or more combinations of compounds represented by the following formulae:

[0078]

[0079]

[0080] The thiol group in monomer 2 can form a disulfide bond, thereby gradually polymerizing to form a polymer chain. At the same time, the π-π stacking between the benzene rings causes the polymer chain to assemble into supramolecular nanospheres. At the same time, the thiol group reacts with the above-mentioned polymer microspheres as the core through groups such as carbon-carbon double bonds, thereby obtaining nano-scale shell spheres and wrapping them on the surface of the polymer microspheres as the core, finally forming raspberry-shaped microspheres.

[0081] Linear binder

[0082] The linear binder of the present invention includes a linear polymer, which is a polymer with a basically two-dimensional straight chain linear structure. By cross-linking the linear polymer with the above-mentioned raspberry-shaped microspheres, the adhesion and mechanical properties of the binder can be improved through the synergistic effect of the two, while preventing the raspberry-shaped binder from falling off due to volume expansion due to absorption of electrolyte, thereby significantly improving the heat resistance of the diaphragm.

[0083] The linear polymer can be obtained by polymerizing monomer 3 or a monomer mixture including monomer 3. The monomer 3 may include an olefin having an amino group. In some specific embodiments, the monomer 3 may be selected from one or more of C2 to C10 olefin amines, for example, ethylene amine, propylene amine, butylene amine, etc. A linear polymer can be obtained by polymerization or self-polymerization of the above monomer 3, and a network cross-linked structure is formed by cross-linking reaction between the amino group in the molecular structure and the functional group in the above raspberry-shaped binder.

[0084] Composition of composite adhesive

[0085] In principle, there is no particular restriction on the mass ratio of the raspberry-shaped binder to the linear binder in the composite binder. From the perspective of better cross-linking of the raspberry-shaped binder and the linear binder or more conducive to the effects of both, in some preferred embodiments, the mass ratio of the raspberry-shaped binder to the linear binder in the composite binder can be 3:7 to 7:3, for example, 3.8:6.2, 4:6, 4.5:5.5, 5:5, 5.5:4.5, 6:4, 6.2:3.8, etc.

[0086] (Second aspect)

[0087] A second aspect of the present invention provides a method for preparing the composite adhesive according to the first aspect, comprising the following steps:

[0088] The steps for synthesizing the raspberry-shaped adhesive are as follows: monomer 1 is initially polymerized to obtain polymer microspheres, and monomer 2 is added to continue the polymerization reaction to obtain the raspberry-shaped adhesive;

[0089] The steps of synthesizing the linear binder are as follows: monomer 3 is polymerized to obtain the linear binder;

[0090] The steps of synthesizing the composite adhesive are as follows: the obtained raspberry-shaped adhesive is mixed with the linear adhesive to carry out a cross-linking reaction.

[0091] The types of monomer 1, monomer 2, and monomer 3 are the same as those described above and will not be described again here.

[0092] Steps for synthesizing raspberry-like adhesives

[0093] In the present invention, the synthesis of the raspberry-shaped adhesive is mainly through the initial polymerization of monomer 1 to form polymer microspheres as the core, and then adding monomer 2 to continue the polymerization reaction. During this process, monomer 1 and monomer 2 can simultaneously undergo self-polymerization and copolymerization reactions to finally obtain the raspberry-shaped adhesive.

[0094] In some specific embodiments, the molar ratio of the monomer 1 to the monomer 2 is 1:0.95 to 1:1.05, for example, 1:0.98, 1:1, 1:1.02, etc.

[0095] In some specific embodiments, the initial polymerization specifically includes: mixing monomer 1 with an emulsifier solution to form a pre-emulsion, and mixing the pre-emulsion with an initiator solution in a reactor and heating to a preliminary polymerization temperature. At this temperature, the initiator decomposes to generate free radicals, which initiate the preliminary polymerization of monomer 1. Preferably, to ensure the stability of the system, a certain amount of deionized water can be pre-added to the reactor.

[0096] The present invention does not impose any particular limitation on the types and amounts of the emulsifier and initiator, which can be selected based on existing synthesis experience.

[0097] In some specific embodiments, the reaction temperature of the initial polymerization is 50-70°C, for example, 55°C, 60°C, 65°C, etc.; the reaction time is 0.5-1.5h, for example, 0.8h, 1h, 1.2h, etc.

[0098] In some specific embodiments, the continued polymerization specifically includes: adding monomer 2 to the reaction solution of the initial polymerization to carry out continued polymerization reaction. During the polymerization process, the temperature and pressure in the reactor are kept stable, and the reaction is stirred by a stirrer to ensure uniform reaction.

[0099] In some more specific embodiments, the polymerization reaction temperature is 50-70°C, for example, 55°C, 60°C, 65°C, etc.; the reaction time is 3-5h, for example, 3.5h, 4h, 4.5h, etc.

[0100] Steps for synthesizing linear binders

[0101] In the present invention, the linear binder is synthesized by polymerizing monomer 3 to obtain the linear binder.

[0102] In some specific embodiments, the steps for synthesizing the linear binder include: uniformly mixing monomer 3 with an emulsifier solution to form a pre-emulsion; mixing the pre-emulsion with an initiator solution in a reactor and heating to a polymerization temperature. At this temperature, the initiator decomposes to generate free radicals, initiating polymerization of the monomers. During the polymerization process, the temperature and pressure in the reactor are maintained stable, and a stirrer is used to ensure uniform reaction. Preferably, a certain amount of deionized water may be pre-added to the reactor to ensure system stability.

[0103] The present invention does not particularly limit the types and amounts of the emulsifier and initiator, and they can be selected based on existing experience.

[0104] In some specific embodiments, the reaction temperature of the polymerization reaction is 30-50°C, for example, 35°C, 40°C, 45°C, etc.; the reaction time is 1-3h, for example, 1.5h, 2h, 2.5h, etc.

[0105] Steps in the synthesis of composite binders

[0106] In the present invention, the step of synthesizing the composite adhesive is to mix the raspberry-shaped adhesive obtained above with the linear adhesive and perform a cross-linking reaction to obtain the composite adhesive.

[0107] The mixing ratio of the raspberry-shaped adhesive and the linear adhesive is the same as that described in the first aspect and will not be repeated here.

[0108] In some specific embodiments, the reaction temperature of the cross-linking reaction is 50-60°C, for example, 52°C, 55°C, 58°C, etc., and the reaction time is 1-3h, for example, 1.5h, 2h, 2.5h, etc.

[0109] (Third aspect)

[0110] The third aspect of the present invention provides a secondary battery separator, which includes a base film and a coating coated on at least one side of the base film, wherein the coating includes inorganic particles and the composite binder according to the first aspect or the composite binder obtained according to the preparation method described in the second aspect.

[0111] In addition, various functional additive components can also be used in the coating without hindering the realization of the technical effects of the present invention.

[0112] Inorganic particles

[0113] The inorganic particles described in the present invention are mainly provided as high-temperature resistant materials in the coating. The use of inorganic particles can effectively improve the heat resistance of the diaphragm. In addition, this component can also play a role in improving the wettability and dimensional stability of the diaphragm.

[0114] The type of the inorganic particles can be selected as needed, and preferably various ceramic particles can be used, for example, at least one of boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, titanium dioxide, silicon dioxide, titanium oxide, barium titanate, zinc oxide, nickel oxide, magnesium fluoride, zirconium oxide, cerium oxide, and barium sulfate particles.

[0115] The particle size Dv50 of the inorganic particles or ceramic particles can be 0.5 to 2 μm, for example, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, etc.

[0116] Other components

[0117] There is no particular limitation on other additives that can be used in the coating of the present invention. For example, the coating may include one or more of a wetting agent, a dispersant, and a thickener.

[0118] There is no particular limitation on the type of the wetting agent, and the wetting agent may be selected as needed. For example, the wetting agent may include a silicone nonionic surfactant.

[0119] There is no particular limitation on the type of the dispersant, and it can be selected as needed. For example, it can include hydrolyzed maleic anhydride dispersants.

[0120] There is no particular limitation on the type of the thickener, and it can be selected as needed. For example, it can include sodium carboxymethyl cellulose thickeners.

[0121] basement membrane

[0122] The base film of the present invention is provided as a basis for a separator.

[0123] There is no particular limitation on the type of the base film, and it may be a diaphragm base film commonly used in the art, for example, it may include at least one of a polyolefin base film, a polyimide base film, and a polyester base film.

[0124] In some preferred embodiments, the base film may be a porous film such as polyethylene or polypropylene.

[0125] In some specific embodiments, the base film may have a thickness of 5 to 9 μm, for example, 6 μm, 7 μm, 8 μm, etc.

[0126] Coating and its composition

[0127] In the present invention, the thickness of the coating is 0.5 to 3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, etc., and a coating with the same or different thickness / composition can be formed on one side or both sides of the base film.

[0128] Regarding the composition of the coating of the present invention, in terms of improving heat resistance and electrical properties, the content of each component of the present invention can be arranged as follows:

[0129] The content of the composite binder is 3% to 8% of the total mass of the coating, for example, 4%, 5%, 6%, 7%, etc.

[0130] The content of the inorganic particles is 85% to 95% of the total mass of the coating, for example, 88%, 90%, 92%, 94%, etc.

[0131] Method for preparing diaphragm

[0132] The present invention does not particularly limit the preparation method of the diaphragm. In some preferred embodiments, the method includes the following steps:

[0133] Mixing step: mixing the composite binder, inorganic particles and optional additives in a solvent to obtain a coating liquid;

[0134] The coating step comprises coating the coating liquid on at least one surface of the base film, and drying the base film to obtain a separator.

[0135] The types and amounts of the composite binder, inorganic particles, additives, and base film are the same as those described above and will not be described in detail here.

[0136] Furthermore, there is no particular limitation on other additives or equipment used in the above-mentioned mixing and coating, and they can be carried out in accordance with existing experience in the field.

[0137] (Fourth aspect)

[0138] A fourth aspect of the present invention provides a secondary battery comprising the separator according to the third aspect.

[0139] The secondary battery described in the present invention includes various secondary batteries with ion conduction, and in particular, refers to lithium secondary batteries, including non-aqueous electrolyte lithium secondary batteries, semi-solid lithium secondary batteries, quasi-solid lithium secondary batteries, etc.

[0140] The secondary battery of the present invention may be a power battery, i.e. a battery used to provide power for transportation or vehicles, or a secondary battery used in energy storage equipment such as wind power, hydropower, solar power or traditional petrochemical energy.

[0141] In some specific embodiments, the battery of the present invention appears and is used in a single form. In other specific embodiments, the battery of the present invention can be used in parallel or in series in any number of scales.

[0142] The lithium secondary battery of the present invention may include a positive electrode, a negative electrode, an electrolyte and the composite separator.

[0143] The positive electrode includes a current collector, a positive electrode active material, and optionally an auxiliary agent. In principle, there is no particular limitation on the positive electrode active material. For example, it can be a lithium oxide doped with a transition metal, typically a ternary lithium positive electrode active material doped with nickel, manganese, or cobalt.

[0144] The negative electrode may include a current collector, a negative electrode active material, and optional auxiliary agents, etc. The negative electrode active material may include carbon-based materials and non-carbon-based materials.

[0145] The carbon-based materials include graphite materials (natural graphite, artificial graphite and mesophase carbon spheres) and other carbon-based materials (hard carbon, soft carbon and graphene); the non-carbon-based materials can be further divided into titanium-based materials, silicon-based materials, tin-based materials, nitrides and metallic lithium, etc.

[0146] Furthermore, in principle, there is no particular limitation on the electrolyte solution that can be used in the secondary battery of the present invention.

[0147] In some specific embodiments, the electrolyte solution includes an electrolyte and a non-aqueous solvent.

[0148] The present invention does not particularly limit the type of the non-aqueous solvent, as long as it is a non-aqueous solvent commonly used as a non-aqueous electrolyte solution.

[0149] In some specific embodiments, the non-aqueous solvent can be selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, and ketone solvents.

[0150] The cyclic carbonate solvent can be selected from ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); the linear carbonate solvent can be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), trifluoroethyl methyl carbonate (FEMC), di(2,2,2-trifluoroethyl) carbonate (DFDEC); The ester solvent can be selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, and methyl pivalate; the ether solvent can be selected from dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), dioxane (DX), dioxolane (DOL), etc.; the ketone solvent can be selected from polymethyl vinyl ketone, etc. These non-aqueous solvents can be used alone or in the form of a mixture of two or more.

[0151] In some preferred embodiments, the non-aqueous solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl acetate, propyl acetate, ethyl propionate, propyl ester, methyl butyrate, and ethyl butyrate.

[0152] The electrolyte of the present invention can generally be various lithium salts. The present invention does not specifically limit the type of lithium salt, and can be a lithium salt commonly used in the art. In some specific embodiments, the lithium salt can be selected from one or more salts formed by lithium ions and the following anions: PF6 - 、BF4 - 、Cl - Br - , I - 、ClO4 - 、AsF6 - 、SiF6 2- 、AlCl4 - 、B(C2O4)2 - 、CH3CO2 - CF3SO3 - 、N(CF3SO2)2 - 、N(FSO2)2 - 、C(CF2SO2)3 - 、C2BF2O4 - .

[0153] In principle, there is no particular limitation on other functional additives that can be used in the electrolyte of the present invention. For example, the use of some additives can promote film formation.

[0154] Examples of such additives include vinyl ethylene carbonate (VC), lithium difluorophosphate (LiPO2F2), fluoroethylene carbonate (FEC), boron-containing additives, sulfur-containing additives, or oxalate-containing additives. The boron-containing additive may be selected from lithium tetrafluoroborate (LiBF4), trimethylsilyl phosphate (TMSP), trimethylsilyl borate (TMSB), etc.; the sulfur-containing additive may be selected from 1,3-propane sultone (1,3PS), 1,4-butane sultone (1,4-BS), 2,4-butane sultone (2,4-BS), 1,3-propene sultone (PST), vinyl sulfate (DTD), methylene methanedisulfonate (MMDS), vinyl sulfite (ES), etc.; and the oxalate-containing additive may be selected from lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium tetrafluorooxalatophosphate (LiTFOP), lithium difluorobis(oxalatophosphate) (LiDFOP), etc. These additives may be used alone or in combination of two or more.

[0155] Example

[0156] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be obtained commercially.

[0157] Example 1

[0158] (1) Preparation of composite adhesive:

[0159] Mix monomer 1 styrene and emulsifier solution evenly to form a pre-emulsion. Add the pre-emulsion and initiator solution to the reactor. A certain amount of deionized water should be added to the reactor in advance to ensure the stability of the system. Heat the reactor to the set polymerization temperature (60°C). At this temperature, the initiator decomposes to produce free radicals, which initiate the polymerization reaction of monomer 1. After 1 hour of reaction, add monomer 2 (structure shown in formula (A-1)), where the molar ratio of monomer 1 to monomer 2 is 1:1. During the polymerization process, keep the temperature and pressure in the reactor stable, and stir with a stirrer to ensure that the reaction proceeds evenly. Continue the polymerization reaction for 4 hours. Obtain emulsion 1.

[0160] Then, monomer 3 (propylene ammonia) is mixed evenly with the emulsifier solution to form a pre-emulsion. This pre-emulsion and initiator solution are added to the reactor. A certain amount of deionized water should be pre-added to the reactor to ensure system stability. The reactor is heated to the set polymerization temperature (40°C). At this temperature, the initiator decomposes to produce free radicals, initiating the polymerization of monomer 3. During the polymerization process, the temperature and pressure in the reactor are maintained stable, and a stirrer is used to ensure uniform reaction. The polymerization reaction lasts for 2 hours. This results in Emulsion 2.

[0161] Afterwards, emulsion 1 and emulsion 2 were mixed in the same reactor at a mass ratio of raspberry-shaped binder to linear binder of 4:6, and the reactor was heated to a set crosslinking temperature (55°C). The crosslinking reaction was carried out for 2 hours, and a composite binder was obtained after the reaction was completed.

[0162] (2) Preparation of the diaphragm: 90% by mass of aluminum oxide, 0.5% of sodium dodecyl sulfate (dispersant), 2% of sodium carboxymethyl cellulose (thickener), 7% of a composite binder, and 0.5% of a phosphate ester were uniformly dispersed in water to obtain a uniform ceramic coating solution. The solution was then applied to a polyethylene film and dried at 40°C to form a diaphragm. The coating thickness was 2 μm.

[0163] Example 2

[0164] (1) Preparation of composite adhesive: The preparation method is the same as that of Example 1, except that monomer 1 in Example 2 is replaced with N-vinylcarbazole, and monomers 2 and 3 remain unchanged.

[0165] (2) Diaphragm Preparation: 89% by mass of aluminum oxide, 0.5% sodium dodecyl sulfate (dispersant), 2.5% sodium carboxymethyl cellulose (thickener), 7.5% of a composite binder, and 0.5% of a phosphate ester were uniformly dispersed in water to obtain a uniform ceramic coating solution. The solution was then applied to a polypropylene film and dried at 40°C to form a diaphragm. The coating thickness was 1 μm.

[0166] Example 3

[0167] (1) Preparation of composite adhesive: The preparation method is the same as that of Example 1, except that monomer 1 in Example 3 is replaced with maleic anhydride, and monomers 2 and 3 remain unchanged.

[0168] (2) Preparation of the diaphragm: 89% by mass of aluminum oxide, 0.5% of sodium dodecyl sulfate (dispersant), 3% of sodium carboxymethyl cellulose (thickener), 7% of a composite binder, and 0.5% of a phosphate ester were uniformly dispersed in water to obtain a uniform ceramic coating solution. The solution was then applied to a non-woven fabric base membrane and dried at 40°C to form a diaphragm. The coating thickness was 3 μm.

[0169] Example 4

[0170] (1) Preparation of composite adhesive: The preparation method is the same as that of Example 1, except that monomer 1 in Example 4 is replaced with N-substituted maleimide, and monomers 2 and 3 remain unchanged.

[0171] (2) Diaphragm Preparation: 89% by mass of aluminum oxide, 1% sodium dodecyl sulfate (dispersant), 2% sodium carboxymethyl cellulose (thickener), 7% of a composite binder, and 0.1% of a phosphate ester were uniformly dispersed in water to obtain a uniform ceramic coating solution. The solution was then applied to a polyimide-based film and dried at 40°C to form a diaphragm. The coating thickness was 2 μm.

[0172] Example 5

[0173] (1) Preparation of composite adhesive:

[0174] Mix monomer 2 (structure as shown in formula (A-1)) with the emulsifier solution to form a pre-emulsion. Add the pre-emulsion and initiator solution to the reactor. A certain amount of deionized water should be added to the reactor in advance to ensure the stability of the system. Heat the reactor to the set polymerization temperature (60°C). At this temperature, the initiator decomposes to produce free radicals, which initiate the polymerization reaction of monomer 2. After 1 hour of reaction, monomer 1 styrene is added, where the molar ratio of monomer 1 to monomer 2 is 1:1. During the polymerization process, keep the temperature and pressure in the reactor stable, and stir with a stirrer to ensure that the reaction proceeds evenly. Continue the polymerization reaction for 4 hours. Obtain emulsion 1.

[0175] Then, monomer 3 (propylene ammonia) is mixed evenly with the emulsifier solution to form a pre-emulsion. This pre-emulsion and initiator solution are added to the reactor. A certain amount of deionized water should be pre-added to the reactor to ensure system stability. The reactor is heated to the set polymerization temperature (40°C). At this temperature, the initiator decomposes to produce free radicals, initiating the polymerization of monomer 3. During the polymerization process, the temperature and pressure in the reactor are maintained stable, and a stirrer is used to ensure uniform reaction. The polymerization reaction lasts for 2 hours. This results in Emulsion 2.

[0176] Afterwards, emulsion 1 and emulsion 2 were mixed in the same reactor at a mass ratio of raspberry-shaped binder to linear binder of 4:6. The reactor was heated to a set crosslinking temperature (55° C.) and the crosslinking reaction was carried out for 2 hours. After the reaction was completed, a composite binder was obtained.

[0177] (2) Preparation of diaphragm: The method is the same as that in Example 1.

[0178] Example 6

[0179] Except that the mass ratio of the raspberry-shaped binder to the linear binder is 5:5, the rest is the same as that in Example 1.

[0180] Example 7

[0181] Except that the mass ratio of the raspberry-shaped binder to the linear binder is 6:4, the rest is the same as that in Example 1.

[0182] Comparative Example 1

[0183] A uniform ceramic coating solution was prepared by uniformly dispersing 90% aluminum oxide, 0.5% sodium dodecyl sulfate (dispersant), 2% sodium carboxymethyl cellulose (thickener), 7% polyacrylate (common binder), and 0.5% phosphate in water. The solution was then applied to a polyethylene film and dried at 40°C to form a separator. The coating had a thickness of 2 μm.

[0184] Comparative Example 2

[0185] (1) Preparation method of raspberry adhesive: Monomer 1 styrene is mixed evenly with the emulsifier solution to form a pre-emulsion. The pre-emulsion and initiator solution are added to the reactor. A certain amount of deionized water should be added to the reactor in advance to ensure the stability of the system. The reactor is heated to the set polymerization temperature (60°C). At this temperature, the initiator decomposes to produce free radicals, which initiate the polymerization reaction of monomer 1. After the reaction for 1 hour, monomer 2 (the structure is shown in formula (A-1)) is added, wherein the molar ratio of monomer 1 to monomer 2 is 1:1. During the polymerization process, the temperature and pressure in the reactor are kept stable, and the reaction is stirred by a stirrer to ensure uniform reaction. The polymerization reaction is continued for 4 hours. The raspberry adhesive is obtained.

[0186] (2) Diaphragm Preparation Method: 89% by mass of aluminum oxide, 0.5% of sodium dodecyl sulfate (dispersant), 2.5% of sodium carboxymethyl cellulose (thickener), 7.5% of raspberry binder, and 0.5% of phosphate ester were uniformly dispersed in water to obtain a uniform ceramic coating liquid. The liquid was then coated onto a polypropylene base film and dried at 40°C to form a diaphragm. The coating thickness was 1 μm.

[0187] Comparative Example 3

[0188] (1) Preparation method of raspberry adhesive: the same as that of comparative example 2;

[0189] (2) Preparation of the diaphragm: 89% by mass of aluminum oxide, 0.5% of sodium dodecyl sulfate (dispersant), 3% of sodium carboxymethyl cellulose (thickener), 7% of raspberry binder, and 0.5% of phosphate ester were uniformly dispersed in water to obtain a uniform ceramic coating solution. The solution was then applied to a non-woven fabric base film and dried at 40°C to form a diaphragm. The coating thickness was 3 μm.

[0190] Comparative Example 4

[0191] (1) Preparation of composite adhesive:

[0192] Mix monomer 1 (styrene) and the emulsifier solution evenly to form a pre-emulsion. Add the pre-emulsion and initiator solution to a reactor. A certain amount of deionized water should be pre-added to the reactor to ensure system stability. Heat the reactor to the set polymerization temperature (60°C). At this temperature, the initiator decomposes to produce free radicals, initiating polymerization of monomer 1. After one hour of reaction, Emulsion 1 (the spherical binder) is obtained.

[0193] Then, monomer 3 (propylene ammonia) is mixed evenly with the emulsifier solution to form a pre-emulsion. This pre-emulsion and initiator solution are added to the reactor. A certain amount of deionized water should be pre-added to the reactor to ensure system stability. The reactor is heated to the set polymerization temperature (40°C). At this temperature, the initiator decomposes to produce free radicals, initiating the polymerization of monomer 3. During the polymerization process, the temperature and pressure in the reactor are maintained stable, and a stirrer is used to ensure uniform reaction. The polymerization reaction lasts for 2 hours. This results in Emulsion 2.

[0194] Afterwards, emulsion 1 and emulsion 2 were mixed in a reactor with a mass ratio of spherical binder to linear binder being 4:6. The reactor was heated to a set crosslinking temperature (55° C.) and the crosslinking reaction was carried out for 2 hours. After the reaction was completed, a composite binder was obtained.

[0195] (2) Diaphragm Preparation: 89% by mass of aluminum oxide, 1% sodium dodecyl sulfate (dispersant), 2% sodium carboxymethyl cellulose (thickener), 7% of a composite binder, and 0.1% of a phosphate ester were uniformly dispersed in water to obtain a uniform ceramic coating solution. The solution was then applied to a polyimide-based film and dried at 40°C to form a diaphragm. The coating thickness was 2 μm.

[0196] Performance Testing

[0197] 1. Diaphragm Thermal Shrinkage Test: The membrane was cut into 10×10 square sheets, secured with an A4 sheet, placed in an oven, and heated at 180°C for 1 hour. The thermal shrinkage of the membrane was measured. The results are shown in Table 1, where TD (Transverse Direction) represents the transverse shrinkage, and MD (Machine Direction) represents the longitudinal shrinkage.

[0198] 2. Diaphragm rupture temperature test: This method primarily utilizes a thermomechanical analyzer. The specific steps are as follows: Take a 20-30 mm diaphragm sample. Use a thermomechanical analyzer to record the diaphragm length versus temperature curve until the diaphragm ruptures. The temperature at which the diaphragm length increases instantaneously is the rupture temperature. The results are shown in Table 1.

[0199] 3. Air Permeability Test: Under a constant pressure differential (usually 1.22 kPa), measure the time required for a certain volume of gas (e.g., 100 mL) to pass through the membrane. The specific steps are as follows: Cut membrane samples longitudinally from the membrane roll at a certain distance. The sample size is determined by the membrane width. Place the membrane sample in the test head of the air permeability tester. Measure the time required for 100 mL of air to pass through the membrane under a pressure of 1.22 kPa. The average of these multiple test results is used as the membrane air permeability. The results are shown in Table 1.

[0200] 4. Adhesion Test: Overlay the coated diaphragm and electrode, and heat-press the diaphragm and electrode together using a roller press, with the coated side facing the electrode. The hot-pressing temperature and pressure are adjusted based on the diaphragm material and coating type, for example, 80°C and 1 MPa. Cut the bonded diaphragm and electrode into strips. Use a universal tensile testing machine to peel the strips apart, record the force at separation, and calculate the bond strength between the diaphragm and electrode. The results are shown in Table 1.

[0201] Table 1: Test results of Examples and Comparative Examples

[0202]

[0203] It can be seen from the performance test data of Examples 1 to 7 in Table 1 that the diaphragm prepared using the composite adhesive of the present invention has a low thermal shrinkage rate at 180°C and a film rupture temperature as high as 179 to 210°C, and has excellent heat resistance. At the same time, the adhesive has good adhesion to the electrode and has good air permeability.

[0204] When the traditional adhesive polyacrylate is used in Comparative Example 1, the heat resistance is poor and it is difficult to maintain good stability at 180°C. There is no bonding function between the adhesive and the electrode, and the air permeability is poor.

[0205] When the adhesive used in Comparative Examples 2 and 3 is a raspberry-shaped adhesive, although the bonding force is improved compared to the traditional adhesive, the heat resistance is still poor and the air permeability is reduced.

[0206] The adhesive used in Comparative Example 4 is a composite adhesive obtained by combining a spherical adhesive and a linear adhesive. Although the adhesive force and heat resistance are improved compared with the traditional adhesive, the improvement effect is limited and the air permeability is reduced.

[0207] It should be noted that, although the technical solutions of the present invention are described with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0208] While various embodiments of the present invention have been described above, the above descriptions are intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or technological improvements in the marketplace, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A composite adhesive, characterized in that: The composite adhesive includes a raspberry-shaped adhesive and a linear adhesive, and the raspberry-shaped adhesive at least partially forms a cross-linked structure with the linear adhesive; The raspberry-shaped adhesive is a raspberry-shaped microsphere having a core-shell structure, and includes a polymer microsphere as a core and a polymer nanosphere as a shell on at least a portion of the surface of the core; The linear binder comprises a linear polymer; The mass ratio of the raspberry-shaped adhesive to the linear adhesive is 3:7 to 7:

3.

2. The composite adhesive according to claim 1, characterized in that The particle size of the polymer microspheres is 0.5 to 10 μm, and the particle size of the polymer nanospheres is less than 100 nm.

3. The composite adhesive according to claim 1 or 2, characterized in that: The polymer microspheres are at least partially connected to the polymer nanospheres via covalent bonds.

4. The composite adhesive according to claim 3, characterized in that The Tg of the polymer A forming the polymer microspheres is greater than the Tg of the polymer B forming the polymer nanospheres.

5. The composite adhesive according to claim 3 or 4, characterized in that: The polymer microspheres are at least partially connected to the polymer nanospheres via sulfur-containing covalent bonds.

6. The composite adhesive according to any one of claims 1 to 5, characterized in that: The monomers forming the linear polymer include an olefin having an amino group.

7. A method for preparing the composite adhesive according to any one of claims 1 to 6, characterized in that: The following steps are involved: The steps for synthesizing the raspberry-shaped adhesive are as follows: monomer 1 is initially polymerized to obtain polymer microspheres, and monomer 2 is added to continue the polymerization reaction to obtain the raspberry-shaped adhesive; The linear binder synthesis step is as follows: monomer 3 is polymerized to obtain the linear binder; The step of synthesizing the composite adhesive is as follows: mixing the obtained raspberry-shaped adhesive with the linear adhesive to carry out a cross-linking reaction.

8. The preparation method according to claim 7, characterized in that The monomer 1 comprises one or more of styrene, vinyl ether, terephthalic acid, 1,4-dicyanobenzene, N-vinylcarbazole, maleic anhydride, N-substituted maleimide, dialkyl maleate, and maleonitrile; and / or, the monomer 2 comprises an aromatic compound having two or more thiol groups; And / or, the monomer 3 includes an olefin having an amino group.

9. The preparation method according to claim 7 or 8, characterized in that In the step of synthesizing the raspberry-shaped binder, the molar ratio of monomer 1 to monomer 2 is 1:0.95 to 1:1.05; And / or, the reaction temperature of the initial polymerization is 50-70° C., and the reaction time is 0.5-1.5 h; And / or, the reaction temperature of the polymerization reaction is 50-70° C.; and the reaction time is 3-5 hours.

10. The preparation method according to any one of claims 7 to 9, characterized in that: In the step of synthesizing the linear binder, the reaction temperature of the polymerization reaction is 30 to 50° C., and the reaction time is 1 to 3 hours.

11. The preparation method according to any one of claims 7 to 10, characterized in that: In the step of synthesizing the composite adhesive, the reaction temperature of the cross-linking reaction is 50 to 60° C., and the reaction time is 1 to 3 hours.

12. A separator for a secondary battery, characterized in that: The diaphragm includes a base film and a coating layer coated on at least one side of the base film; Wherein, the coating comprises inorganic particles and the composite binder according to any one of claims 1 to 6 or the composite binder obtained by the preparation method according to any one of claims 7 to 11; Wherein, the content of the composite binder in the coating is 3-8%; the content of the inorganic particles is 85-95%.

13. The diaphragm according to claim 12, characterized in that The base film includes at least one of a polyolefin base film, a polyimide base film, and a polyester base film.

14. A secondary battery, characterized in that: The secondary battery comprises the diaphragm according to claim 12 or 13, wherein the secondary battery comprises a power battery or an energy storage battery for an energy storage power station.

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