Water-based binder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium batteries, and particularly provides a water-based binder as well as a preparation method and application thereof. The invention aims to solve the problem that the existing aqueous binder for the negative electrode of the lithium battery cannot give consideration to electrolyte resistance and flexibility at the same time. Therefore, the water-based adhesive comprises an inner core structure and a shell structure, the outer side of the inner core structure is coated with the shell structure, the inner core structure comprises an inner core main body structure and a polyurea structural unit grafted on the inner core main body structure, and the shell structure comprises a shell main body structure and a polyurethane structural unit grafted on the shell main body structure. According to the water-based adhesive disclosed by the invention, the polyurea structural unit is grafted in the core structure, the polyurethane structural unit is grafted in the shell structure, and the polyurea structural unit and the polyurethane structural unit are matched, so that the prepared water-based adhesive has good electrolyte resistance and flexibility.

Description

Technical Field

[0001] This application relates to the technical field of lithium batteries, and specifically provides an aqueous binder, a preparation method thereof, and uses thereof. Background Art

[0002] Currently, policies in the fields of energy conservation and emission reduction have driven the booming development of the lithium battery industry. As one of the essential materials in lithium battery manufacturing, the binder is also continuously undergoing technological iteration and upgrading. For the aqueous binder for the negative electrode, a common choice is to use styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in combination. This is because SBR is difficult to disperse by itself and CMC needs to be added as a dispersant. However, CMC has high hardness, low flexibility, and general viscosity. When the dosage of the binder is limited, the bonding strength is insufficient, which easily causes the conductive agent and graphite to fall off after long-term cycling, and the battery performance drops sharply. Therefore, using modified polyacrylic acid (PAA) alone as a binder or mixing PAA with SBR and CMC has gradually become a mainstream choice. This is because after modification, PAA has functional groups such as cyano, carbonyl, ester group, and carboxyl group in its structure, which can provide certain hardness and flexibility, and carboxyl groups can form hydrogen bonds with the hydroxyl groups on the surface of the copper current collector to increase the bonding strength.

[0003] Currently, most binders for long-term cycling performance are linear structures. The design ratio of hard monomers in the structure is relatively high to pursue high hardness, thereby reducing swelling loss and improving the electrolyte resistance performance. This leads to a decrease in flexibility, easy cracking of the electrode sheet during production, and a decrease in the yield rate, thus increasing the production cost of enterprises.

[0004] Correspondingly, the art needs a new technical solution to solve the above technical problems. Summary of the Invention

[0005] This application aims to solve the above technical problems, that is, to solve the problem that the existing aqueous binder for the negative electrode of a lithium battery cannot balance the electrolyte resistance performance and flexibility.

[0006] In a first aspect, this application provides an aqueous binder. The aqueous binder includes a core structure and a shell structure. The shell structure covers the outside of the core structure. The core structure includes a core main structure and a polyurea structural unit obtained by polymerizing a first acrylate monomer, a first acrylamide monomer, and a first acrylonitrile. The polyurea structural unit is grafted on the core main structure. Among them, the first acrylate monomer and / or the first acrylamide monomer contains a hydroxyl group; the shell structure includes a shell main structure and a polyurethane structural unit obtained by polymerizing a second acrylate monomer, a second acrylamide monomer, and a second acrylonitrile. The polyurethane structural unit is grafted on the shell main structure. Among them, the second acrylate monomer and / or the second acrylamide monomer contains a hydroxyl group.

[0007] In a second aspect, the present application provides a method for preparing an aqueous binder, and the preparation method includes the following steps: S1: providing a core main structure; S2: grafting a polyurea structural unit onto the core main structure to obtain a core structure; S3: coating a shell main structure outside the core structure; S4: grafting a polyurethane structural unit onto the shell main structure to obtain an aqueous binder.

[0008] In a preferred technical solution of the above method for preparing an aqueous binder, step S1 specifically includes: reacting a first core reaction raw material with a second core reaction raw material to obtain a core main structure, where the first core reaction raw material includes a mixture of a first acrylate monomer, a first acrylamide monomer, first acrylonitrile and water, and the second core reaction raw material includes a mixture of a first emulsifier, a first initiator and water; and / or, step S2 specifically includes: mixing a reaction system in which the core main structure is formed with a polyurea reaction raw material and a first catalyst to react, so as to graft a polyurea structural unit onto the core main structure to obtain the core structure, where the first catalyst is used to catalyze the polyurea reaction raw material to react to generate a polyurea structural unit; and / or, step S3 specifically includes: mixing a reaction system in which the core structure is formed with a first shell reaction raw material and a second shell reaction raw material to react, to obtain a shell main structure, and coating the shell main structure outside the core structure, where the first shell reaction raw material includes a mixture of a second acrylate monomer, a second acrylamide monomer, second acrylonitrile and water, and the second shell reaction raw material includes a mixture of a second emulsifier, a second initiator and water, where the mass of the second emulsifier is greater than the mass of the first emulsifier in the raw materials used in the reaction system in which the core structure is formed; and / or, step S4 specifically includes: mixing a reaction system in which the shell main structure is formed with a polyurethane reaction raw material and a second catalyst to react, so as to graft a polyurethane structural unit onto the shell main structure to obtain an aqueous binder, where the shell main structure in the reaction system is coated outside the core structure, and the second catalyst is used to catalyze the polyurethane reaction raw material to react to generate a polyurethane structural unit.

[0009] In the preferred technical solution of the above preparation method of the aqueous binder, the polyurea reaction raw materials include an aromatic polyurea resin and a first isophorone diisocyanate. Step S2 specifically includes: first, uniformly mixing the reaction system having the inner core main structure with the aromatic polyurea resin, and then mixing and reacting with the first isophorone diisocyanate and the first catalyst to obtain an inner core structure grafted with polyurea structural units; and / or, the polyurethane reaction raw materials include a hydroxy acrylic emulsion and a second isophorone diisocyanate. Step S4 specifically includes: first, uniformly mixing the reaction system having the outer shell main structure with the hydroxy acrylic emulsion, and then mixing and reacting with the second isophorone diisocyanate and the second catalyst to obtain an outer shell structure grafted with polyurethane structural units.

[0010] In the preferred technical solution of the above preparation method of the aqueous binder, the polyurea reaction raw materials include an aromatic polyurea resin and a first isophorone diisocyanate. The aromatic polyurea resin is added to the first inner core reaction raw material in step S1 and uniformly mixed with the first inner core reaction raw material. Step S2 specifically includes: mixing the reaction system having the inner core main structure with the first isophorone diisocyanate and the first catalyst to carry out a reaction to obtain an inner core structure grafted with polyurea structural units; and / or, the polyurethane reaction raw materials include a hydroxy acrylic emulsion and a second isophorone diisocyanate. The hydroxy acrylic emulsion is added to the first outer shell reaction raw material in step S3 and uniformly mixed with the first outer shell reaction raw material. Step S4 specifically includes: mixing the reaction system having the outer shell main structure with the second isophorone diisocyanate and the second catalyst to carry out a reaction to obtain an outer shell structure grafted with polyurethane structural units.

[0011] In the preferred technical solution of the above preparation method of the aqueous binder, step S1 specifically includes: S11: providing a mixture of a first acrylate monomer, a first acrylamide monomer, a first acrylonitrile, an aromatic polyurea resin, and a first solvent water to obtain a first core reaction raw material; S12: providing a mixture of a first emulsifier, a first initiator, and a second solvent water to obtain a second core reaction raw material; S13: taking a part of the second core reaction raw material and mixing it with a third solvent water, slowly stirring, and heating to 80°C to 90°C to form a reaction system; S14: uniformly dropping the first core reaction raw material and the remaining second core reaction raw material into the reaction system of step S3, and after the dropping is completed, maintaining the temperature at a first temperature for a first preset time to obtain the core main structure; and / or, step S2 specifically includes: cooling the reaction system with the core main structure formed to 45°C to 50°C, and then adding the first isophorone diisocyanate and the first catalyst to the reaction system, maintaining the temperature at a second temperature for a second preset time, and grafting a polyurea structural unit on the core main structure to obtain a core structure; and / or, step S3 specifically includes: S31: providing a mixture of a second acrylate monomer, a second acrylamide monomer, a second acrylonitrile, a hydroxy acrylic emulsion, and a fourth solvent water to obtain a first shell reaction raw material; S32: providing a mixture of a second emulsifier, a second initiator, and a fifth solvent water to obtain a second shell reaction raw material; S33: adjusting the temperature of the reaction system with the core structure formed to 80°C to 90°C, and then uniformly dropping the first shell reaction raw material and the second shell reaction raw material into the reaction system, and after the dropping is completed, maintaining the temperature at a third temperature for a third preset time; and / or, step S4 specifically includes: cooling the reaction system with the shell main structure formed to 45°C to 50°C, and then adding the second isophorone diisocyanate and the second catalyst to the reaction system, maintaining the temperature at a fourth temperature for a fourth preset time, and grafting a polyurethane structural unit on the shell main structure to obtain the aqueous binder.

[0012] In the preferred technical solution of the above preparation method of the aqueous binder, in step S13, 5% to 30% of the second core reaction raw material is mixed with the third solvent water; in step S14, before dropping the first core reaction raw material and the second core reaction raw material, the rotation speed of the reaction system in step S13 is first adjusted to 200 rpm to 400 rpm; and / or, in step S14, the reaction temperature is controlled not to exceed 95°C during the dropping of the first core reaction raw material and the second core reaction raw material; and / or, in step S14, the first core reaction raw material and the second core reaction raw material are dropped within 0.5 h to 1 h; and / or, in step S14, the first temperature is 88°C to 92°C, and the first preset time is 1 h to 1.5 h; and / or, in step S2, the reaction temperature is controlled not to exceed 65°C during the addition of the first isophorone diisocyanate and the first catalyst; and / or, in step S2, the second temperature is 58°C to 62°C, and the second preset time is 1 h to 1.5 h; and / or, in step S33, before dropping the first shell reaction raw material and the second shell reaction raw material, the rotation speed of the reaction system with the core structure formed is first adjusted to 200 rpm to 400 rpm; and / or, in step S33, the reaction temperature is controlled not to exceed 95°C during the dropping of the first shell reaction raw material and the second shell reaction raw material; and / or, in step S33, the first shell reaction raw material and the second shell reaction raw material are dropped within 1 h to 2 h; and / or, in step S33, the third temperature is 88°C to 92°C, and the third preset time is 1.5 h to 2.5 h; and / or, in step S4, the reaction temperature is controlled not to exceed 65°C during the addition of the second isophorone diisocyanate and the second catalyst; and / or, in step S4, the fourth temperature is 58°C to 62°C, and the fourth preset time is 1 h to 1.5 h.

[0013] In the preferred technical solution of the above preparation method of the aqueous binder, in step S11, the first core reaction raw material includes the following components in parts by weight: 50-150 parts of a first acrylate monomer, 10-50 parts of a first acrylamide monomer, 5-20 parts of a first acrylonitrile, 20-50 parts of an aromatic polyurea resin, and 50-150 parts of a first solvent water; and / or, in step S12, the second core reaction raw material includes the following components in parts by weight: 5-10 parts of a first emulsifier, 2-5 parts of a first initiator, and 50-200 parts of a second solvent water; and / or, in step S13, the weight of the third solvent water is 100-200 parts; and / or, in step S2, the weight of the first isophorone diisocyanate is 5-20 parts, and the weight of the first catalyst is 2-5 parts; and / or, in step S31, the first shell reaction raw material includes the following components in parts by weight: 100-300 parts of a second acrylate monomer, 20-80 parts of a second acrylamide monomer, 5-30 parts of a second acrylonitrile, 50-100 parts of a hydroxy acrylic emulsion, and 50-100 parts of a fourth solvent water; and / or, in step S32, the second shell reaction raw material includes the following components in parts by weight: 10-20 parts of a second emulsifier, 2-5 parts of a second initiator, and 50-100 parts of a fifth solvent water; and / or, in step S4, the weight of the second isophorone diisocyanate is 5-20 parts, and the weight of the second catalyst is 2-5 parts.

[0014] In the preferred technical solution of the above preparation method of the aqueous binder, the first acrylate monomer and / or the first acrylamide monomer contains a hydroxyl group, and the second acrylate monomer and / or the second acrylamide monomer contains a hydroxyl group; and / or, the mass of the aromatic polyurea resin is 15%-30% of the total mass of the first acrylate monomer, the first acrylamide monomer and the first acrylonitrile, and the mass ratio of the first isophorone diisocyanate to the aromatic polyurea resin is 1:(2-3); and / or, the mass of the hydroxy acrylic emulsion is 12%-80% of the total mass of the second acrylate monomer, the second acrylamide monomer and the second acrylonitrile, and the mass ratio of the second isophorone diisocyanate to the hydroxy acrylic emulsion is 1:(5-10); and / or, the aromatic polyurea resin is in powder form.

[0015] In a preferred technical solution of the above preparation method of the aqueous binder, one or more of hydroxyethyl acrylate, hydroxymethyl acrylate, and hydroxyethyl methacrylate are included in the first acrylate monomer and / or the second acrylate monomer; and / or, one or more of N-methylolacrylamide and N-hydroxyethyl acrylamide are included in the first acrylamide monomer and / or the second acrylamide monomer; and / or, the mass of the hydroxy acrylic emulsion is 30% to 40% of the total mass of the second acrylate monomer, the second acrylamide monomer, and the second acrylonitrile.

[0016] In a preferred technical solution of the above preparation method of the aqueous binder, the first acrylate monomer and / or the second acrylate monomer further includes one or more of ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isooctyl acrylate, lauryl methacrylate, butyl methacrylate, and n-octyl methacrylate; and / or, the first acrylamide monomer and / or the second acrylamide monomer further includes one or more of methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, methyl-acryloyloxyethyl trimethyl ammonium chloride, diacetone acrylamide, and N-butoxymethyl acrylamide; and / or, the first emulsifier and the second emulsifier are respectively selected from one or more of sodium p-styrenesulfonate, sodium vinylsulfonate, and sodium dodecylsulfonate; and / or, the first initiator and the second initiator are persulfates, and preferably the persulfates include one or more of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0017] In a preferred technical solution of the above preparation method of the aqueous binder, the aromatic polyurea resin is selected from one or more of phenyl polyurea and dichlorobenzene polyurea; and / or, the first isophorone diisocyanate and the second isophorone diisocyanate are respectively selected from one or several of Covestro Bayhydur ultra 2759, Bayhydur 2858 XP, and Bayhydurultra 401-70 MPA / X; and / or, the hydroxy acrylic emulsion is selected from one or several of Dow Prospersetm200, Huaguoshan Houshan 0880, and DSM Neocryl XK-540; and / or, the first catalyst and the second catalyst are respectively selected from one or more of bismuth isooctanoate, benzoyl chloride, and triethylenediamine; and / or, the crosslinking agent is one or more of adipic dihydrazide and aziridine.

[0018] In a third aspect, the present application provides the use of the aqueous binder as a negative electrode binder in a lithium ion battery.

[0019] Compared with the prior art, the technical solution of the present application has the following beneficial effects: 1. The aqueous binder of the present application has a core-shell structure, specifically including a core structure and a shell structure coated on the outer side of the core structure. The core structure includes a core main structure and a polyurea structural unit grafted on the core main structure. The shell structure includes a shell main structure and a polyurethane structural unit grafted on the shell main structure. The prepared aqueous binder has good electrolyte resistance and flexibility through the cooperation of the polyurea structural unit and the polyurethane structural unit.

[0020] 2. The preparation method of the aqueous binder of the present application first reacts core reaction raw material one and core reaction raw material two to generate a core main structure, and then reacts with a polyurea reaction raw material to generate a polyurea structural unit and graft it on the core main structure. Then, it is mixed with shell reaction raw material one and shell reaction raw material two to make shell reaction raw material one react with shell reaction raw material two to generate a shell main structure coated on the outer side of the core structure. Then, it reacts with a polyurethane reaction raw material to generate a polyurethane structural unit and graft it on the shell main structure, and finally obtains an aqueous binder with a core-shell structure. This preparation method can sequentially complete the synthesis of the core structure and the shell structure in steps in one device, without the need to separately synthesize the core and the shell using two devices and then mix them. The preparation process is simple and convenient to operate, and the shell coating effect of the prepared aqueous binder is good and the performance is good.

[0021] 3. During the preparation of the aqueous binder of the present application, by controlling and adjusting the dosage of the polyurea reaction raw material relative to the reaction raw material of the core structure, the proportion of the polyurea structural unit in the core structure is controlled, and by controlling the dosage of the polyurethane reaction raw material relative to the reaction raw material of the shell structure, the proportion of the polyurethane structural unit in the shell structure is controlled, so that the prepared aqueous binder has excellent flexibility and electrolyte resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The following describes the preferred embodiments of the present invention with reference to the drawings, in which: Figure 1 is the Fourier transform infrared spectrum of the aqueous binder of Example 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The following describes the preferred embodiments of the present application. Those skilled in the art should understand that these embodiments are only used to explain the technical principle of the present application and are not intended to limit the protection scope of the present application.

[0024] In the present application, the term "and / or" describes the association relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B may be singular or plural. The character " / " generally represents an "or" relationship between the front and back associated objects.

[0025] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or a similar expression means any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can each be single or multiple.

[0026] It should be understood that in various embodiments of this application, the magnitudes of the serial numbers of the above - mentioned processes do not mean the sequence of execution. Some or all of the steps can be executed in parallel or sequentially. The execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0027] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms "a", "the", and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0028] The weights of the relevant components mentioned in the specification of the embodiments of this application not only can refer to the specific contents of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the contents of the relevant components in the specification of the embodiments of this application are scaled up or down in proportion, they are within the scope disclosed in the specification of the embodiments of this application. Specifically, the mass described in the specification of the embodiments of this application can be mass units well - known in the chemical industry such as μg, mg, g, kg, etc.

[0029] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of this application, the first XX can also be called the second XX, and similarly, the second XX can also be called the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features.

[0030] The experimental methods in the following embodiments are all conventional methods unless otherwise specified, and the materials, reagents, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified.

[0031] Based on the problem pointed out in the background technology that the existing water - based binders for the negative electrodes of lithium - ion batteries cannot balance the electrolyte resistance performance and flexibility.

[0032] The present application provides an aqueous binder. The aqueous binder has a core-shell structure, specifically including a core structure and a shell structure coated on the outer side of the core structure. The core structure includes a core main structure and a polyurea structural unit grafted on the core main structure. The shell structure includes a shell main structure and a polyurethane structural unit grafted on the shell main structure. The prepared aqueous binder has good electrolyte resistance and flexibility through the cooperation of the polyurea structural unit and the polyurethane structural unit.

[0033] Specifically, in the first aspect of the present application, an aqueous binder is provided. The aqueous binder has a core-shell structure, which specifically includes a core structure and a shell structure, and the shell structure is coated on the outer side of the core structure. Among them, the core structure includes a core main structure obtained by polymerizing a first acrylate monomer, a first acrylamide monomer, and a first acrylonitrile, and a polyurea structural unit, and the polyurea structural unit is grafted on the core main structure. The polyurea structural unit is , where at least one of the first acrylate monomer and / or the first acrylamide monomer contains a hydroxyl group, so that at least one of the first acrylate monomer and the first acrylamide monomer contains a hydroxyl group, which can enable the polyurea structural unit to be grafted on the core main structure; the shell structure includes a shell main structure obtained by polymerizing a second acrylate monomer, a second acrylamide monomer, and a second acrylonitrile, and a polyurethane structural unit, and the polyurethane structural unit is grafted on the shell main structure. The polyurethane structural unit is , where at least one of the second acrylate monomer and / or the second acrylamide monomer contains a hydroxyl group, so that at least one of the second acrylate monomer and the second acrylamide monomer contains a hydroxyl group, which can enable the polyurethane structural unit to be grafted on the shell main structure.

[0034] In the second aspect of the present application, a preparation method of an aqueous binder is provided for preparing the aqueous binder provided in the first aspect.

[0035] Specifically, the preparation method of the aqueous binder of the present application includes the following steps: S1: Provide a core main structure; S2: Graft the polyurea structural unit onto the core main structure to obtain a core structure; S3: Coat the shell main structure on the outer side of the core structure; S4: Graft the polyurethane structural unit onto the shell main structure to obtain an aqueous binder.

[0036] Preferably, step S1 specifically includes: reacting a first core reaction raw material with a second core reaction raw material to obtain a core main structure. The first core reaction raw material includes a mixture of a first acrylate monomer, a first acrylamide monomer, a first acrylonitrile, and water, and the second core reaction raw material includes a mixture of a first emulsifier, a first initiator, and water.

[0037] Preferably, step S2 specifically includes: mixing a reaction system in which a core main structure is generated with a polyurea reaction raw material and a first catalyst for reaction to graft polyurea structural units onto the core main structure to obtain a core structure, wherein the first catalyst is used to catalyze the polyurea reaction raw material to generate polyurea structural units. Specifically, the reaction system in which the core main structure is generated can be the reaction system after the completion of the reaction in step S1.

[0038] Preferably, step S3 specifically includes: mixing a reaction system in which a core structure is generated with a first outer shell reaction raw material and a second outer shell reaction raw material for reaction to obtain an outer shell main structure, and causing the outer shell main structure to coat the outside of the core structure. The first outer shell reaction raw material includes a mixture of a second acrylate monomer, a second acrylamide monomer, and second acrylonitrile and water. The second outer shell reaction raw material includes a mixture of a second emulsifier, a second initiator, and water, wherein the mass of the second emulsifier is greater than the mass of the first emulsifier in the raw materials used in the reaction system for generating the core structure. Specifically, the reaction system in which the core structure is generated can be the reaction system after the completion of the reaction in step S2.

[0039] Preferably, step S4 includes: mixing a reaction system in which an outer shell main structure is generated with a polyurethane reaction raw material and a second catalyst for reaction to graft polyurethane structural units onto the outer shell main structure to obtain an aqueous binder, wherein the outer shell main structure in the reaction system coats the outside of the core structure, and the second catalyst is used to catalyze the polyurethane reaction raw material to react to generate polyurethane structural units. Specifically, the reaction system in which the outer shell main structure is generated can be the reaction system after the completion of the reaction in step S3.

[0040] In addition, adjust the pH of the reaction system in step S4 to 7.0 - 7.5. Specifically, add a neutralizing base dropwise to the reaction system in step S4 to adjust the pH to 7.0 - 7.5. Then mix with a crosslinking agent, cool down to below 40°C, and screen and discharge to remove insoluble large particles to obtain an emulsion of the aqueous binder.

[0041] The preparation method of the aqueous binder of the present application first reacts the first core reaction raw material and the second core reaction raw material to form a core main structure, and then reacts with the polyurea reaction raw material to form a polyurea structural unit and graft it onto the core main structure. Then, it is mixed with the first shell reaction raw material and the second shell reaction raw material, and the first shell reaction raw material reacts with the second shell reaction raw material to form a shell main structure covering the outside of the core structure. Then, it reacts with the polyurethane reaction raw material to form a polyurethane structural unit and graft it onto the shell main structure, and finally obtains an aqueous binder with a core-shell structure. This preparation method can sequentially complete the synthesis of the core structure and the shell structure in one device, without the need to use two devices to separately synthesize the core and the shell and then mix them. The preparation process is simple and convenient to operate, and the coating effect of the shell of the aqueous binder obtained is good and the performance is good.

[0042] Preferably, the polyurea reaction raw material includes an aromatic polyurea resin and the first isophorone diisocyanate. Specifically, the aromatic polyurea resin and the first isophorone diisocyanate can react under the catalysis of the first catalyst to form a polyurea structural unit, and at the same time, the first isophorone diisocyanate can react with the hydroxyl group in the core main structure so that the generated polyurea structural unit is grafted onto the core main structure. Further preferably, the aromatic polyurea resin is in powder form.

[0043] It should be noted that in the present application, there is no restriction on the time node for adding the aromatic polyurea resin of the polyurea reaction raw material to the reaction system. In actual use, those skilled in the art can set the time node for adding the aromatic polyurea resin to the reaction system according to actual needs.

[0044] In some embodiments, the aromatic polyurea resin is added to the reaction system in step S2. The specific steps of S2 include: first mixing the reaction system with the generated core main structure and the aromatic polyurea resin evenly, and then mixing and reacting with the first isophorone diisocyanate and the first catalyst to obtain a core structure grafted with a polyurea structural unit. Specifically, the reaction system with the generated core main structure can be the reaction system obtained after the reaction in step S1.

[0045] In some other embodiments, the aromatic polyurea resin is added to the first core reaction raw material in step S1 and mixed evenly with the first core reaction raw material. The specific steps of S2 include: mixing the reaction system with the generated core main structure, the first isophorone diisocyanate and the first catalyst and reacting to obtain a core structure grafted with a polyurea structural unit. Specifically, the reaction system with the generated core main structure can be the reaction system obtained after the reaction in step S1.

[0046] Since the aromatic polyurea resin does not participate in the reaction in the process of generating the core main structure, adding the aromatic polyurea resin to the core reaction raw material 1 in step S1 can effectively shorten the preparation time and improve the preparation efficiency compared to adding the aromatic polyurea resin dropwise in step S2.

[0047] In a specific embodiment, step S1 specifically includes: S11: providing a mixture of a first acrylate monomer, a first acrylamide monomer, a first acrylonitrile, an aromatic polyurea resin and a first solvent water to obtain a first core reaction raw material.

[0048] S12: providing a mixture of a first emulsifier, a first initiator and a second solvent water to obtain a second core reaction raw material.

[0049] S13: Take a portion of the second core reaction raw material and mix it with the third solvent water, slowly stir it, and heat it to 80° C. to 90° C. to form a reaction system.

[0050] Preferably, 5% to 30% of the second core reaction raw material is mixed with the third solvent water to form a reaction system.

[0051] S14: adding the inner core reaction raw material 1 and the remaining inner core reaction raw material 2 to the reaction system of step S13 at a uniform speed, and maintaining the temperature at a first temperature for a first preset time after the addition is completed, to obtain an inner core main structure.

[0052] Preferably, in step S14, before dropping the core reaction raw material 1 and the core reaction raw material 2, the rotation speed of the reaction system in step S13 is adjusted to 200 rpm to 400 rpm. Reducing the rotation speed to 200 to 400 rpm can disperse the dropped raw materials in the reaction system to avoid excessive local concentration, and can also prevent the reaction emulsion system from breaking due to excessive rotation speed.

[0053] Preferably, in step S14, the reaction temperature is controlled not to exceed 95° C. during the process of dripping the core reaction raw material 1 and the core reaction raw material 2. During the dripping process, the reaction will release heat, and the temperature is controlled not to exceed 95° C. to avoid excessive reaction speed and increase side reactions, thereby helping to make the particle size distribution of the final product wider and increase the fineness.

[0054] Preferably, in step S14, the inner core reaction raw material 1 and the inner core reaction raw material 2 are dripped within 0.5 h to 1 h.

[0055] Preferably, in step S14, the first temperature is 88°C to 92°C, and the first preset time is 1h to 1.5h. After all the reaction materials are added, the temperature is controlled to about 90°C, and the reaction is continued for 1 to 1.5h, so that the inner core reaction material 1 and the inner core reaction material 2 can fully react.

[0056] Step S2 specifically includes: cooling the reaction system with the generated kernel main structure to 45°C - 50°C, then adding the first isophorone diisocyanate and the first catalyst to the reaction system, keeping it at a second temperature for a second preset time, grafting polyurea structural units onto the kernel main structure to obtain the kernel structure. Specifically, the reaction system with the generated kernel main structure can be the reaction system obtained from step S1.

[0057] Preferably, in step S2, during the process of adding the first isophorone diisocyanate and the first catalyst, the reaction temperature is controlled not to exceed 65°C. Heat is generated during the dropping process, and controlling the temperature not to exceed 65°C can avoid too fast reaction speed and increase side reactions.

[0058] Preferably, in step S2, the second temperature is 58°C - 62°C, and the second preset time is 1h - 1.5h. After dropping all the reaction raw materials, the temperature is controlled to be about 60°C and the reaction continues for 1 - 1.5h, so that the first isophorone diisocyanate can fully react with the hydroxyl groups in the aromatic polyurea resin and the first kernel reaction raw material.

[0059] Preferably, the polyurethane reaction raw materials include hydroxy acrylic emulsion and the second isophorone diisocyanate. Specifically, the hydroxy polyacrylic emulsion and the second isophorone diisocyanate can react under the catalysis of the second catalyst to generate polyurethane structural units, and at the same time, the second isophorone diisocyanate can react with the hydroxyl groups in the shell main structure so that the generated polyurethane structural units are grafted onto the shell main structure.

[0060] It should be noted that in this application, there is no limitation on the time node for adding the hydroxy acrylic emulsion of the polyurethane reaction raw materials to the reaction system. In actual use, those skilled in the art can set the time node for adding the hydroxy acrylic emulsion to the reaction system according to actual needs.

[0061] In some embodiments, the hydroxy acrylic emulsion is added to the reaction system in step S4. Step S4 specifically includes: first mixing the reaction system with the generated shell main structure and the hydroxy acrylic emulsion evenly, and then mixing and reacting with the second isophorone diisocyanate and the second catalyst to obtain the shell structure grafted with polyurethane structural units. Specifically, the reaction system with the generated shell main structure can be the reaction system after step S3.

[0062] In some other embodiments, the hydroxy acrylic emulsion is added to the first outer shell reaction raw material in step S3 and mixed evenly with the first outer shell reaction raw material. Step S4 specifically includes: reacting the reaction system with the formed outer shell main structure with the second isophorone diisocyanate and the second catalyst to obtain an outer shell structure grafted with polyurethane structural units. Specifically, the reaction system with the formed outer shell main structure can be the reaction system after the reaction in step S3.

[0063] Since the hydroxy acrylic emulsion does not participate in the reaction during the formation of the outer shell main structure, adding the hydroxy acrylic emulsion to the first outer shell reaction raw material in step S3 can effectively shorten the preparation time and improve the preparation efficiency compared with dropping the hydroxy acrylic emulsion in step S4.

[0064] In a specific embodiment, step S3 specifically includes: S31: Providing a mixture of a second acrylate monomer, a second acrylamide monomer, a second acrylonitrile, a hydroxy acrylic emulsion and a fourth solvent water to obtain the first outer shell reaction raw material.

[0065] S32: Providing a mixture of a second emulsifier, a second initiator and a fifth solvent water to obtain the second outer shell reaction raw material.

[0066] S33: Adjusting the temperature of the reaction system with the formed inner core structure to 80°C - 90°C, and then uniformly dropping the first outer shell reaction raw material and the second outer shell reaction raw material into the reaction system. After the dropping is completed, keep it warm at a third temperature for a third preset time. Specifically, the reaction system with the formed inner core structure can be the reaction system after the reaction in step S2.

[0067] Preferably, in step S33, before dropping the first outer shell reaction raw material and the second outer shell reaction raw material, first adjust the rotation speed of the reaction system with the formed inner core structure to 200 rpm - 400 rpm. Reducing the rotation speed to 200 - 400 rpm can not only disperse the dropped raw materials in the reaction system to avoid too high local concentration, but also avoid the emulsion system of the reaction from breaking due to too fast rotation speed.

[0068] Preferably, in step S33, control the reaction temperature not to exceed 95°C during the dropping of the first outer shell reaction raw material and the second outer shell reaction raw material. Heat is released during the dropping process. Controlling the temperature not to exceed 95°C can avoid too fast reaction speed and increase side reactions.

[0069] Preferably, in step S33, drop the first outer shell reaction raw material and the second outer shell reaction raw material within 1 h - 2 h.

[0070] Preferably, in step S33, the third temperature is 88°C to 92°C, and the third preset time is 1.5 h to 2.5 h. After all the reaction raw materials are added dropwise, the temperature is controlled at about 90°C and the reaction is continued for 1.5 to 2.5 h, so that the first outer shell reaction raw material and the second outer shell reaction raw material can react sufficiently.

[0071] Step S4 specifically includes: cooling the reaction system with the outer shell main structure generated to 45°C to 50°C, and then adding the second isophorone diisocyanate and the second catalyst to the reaction system, and keeping it warm for the fourth preset time at the fourth temperature, so that a polyurethane structural unit is grafted on the outer shell main structure. Specifically, the reaction system with the outer shell main structure generated can be the reaction system after step S3.

[0072] Preferably, in step S4, the reaction temperature is controlled not to exceed 65°C during the addition of the second isophorone diisocyanate and the second catalyst. Heat is released during the dropping process, and the temperature is controlled not to exceed 65°C to avoid too fast reaction rate and increase side reactions.

[0073] Preferably, in step S4, the fourth temperature is 58°C to 62°C, and the fourth preset time is 1 h to 1.5 h. After all the reaction raw materials are added dropwise, the temperature is controlled at about 60°C and the reaction is continued for 1 to 1.5 h, so that the second isophorone diisocyanate can react sufficiently with the hydroxyl groups in the hydroxyl acrylic emulsion and the first outer shell reaction raw material.

[0074] In some preferred embodiments, in step S11, the first inner core reaction raw material includes the following components in parts by weight: 50 to 150 parts of the first acrylate monomer, 10 to 50 parts of the first acrylamide monomer, 5 to 20 parts of the first acrylonitrile, 20 to 50 parts of the aromatic polyurea resin, and 50 to 150 parts of the first solvent water.

[0075] In some preferred embodiments, in step S12, the second inner core reaction raw material includes the following components in parts by weight: 5 to 10 parts of the first emulsifier, 2 to 5 parts of the first initiator, and 50 to 200 parts of the second solvent water.

[0076] In some preferred embodiments, in step S13, the weight of the third solvent water is 100 to 200 parts.

[0077] In some preferred embodiments, in step S2, the weight of the first isophorone diisocyanate is 5 to 20 parts, and the weight of the first catalyst is 2 to 5 parts.

[0078] In some preferred embodiments, in step S31, the first outer shell reaction raw material comprises the following components in parts by weight: 100 - 300 parts of a second acrylate monomer, 20 - 80 parts of a second acrylamide monomer, 5 - 30 parts of a second acrylonitrile, 50 - 100 parts of a hydroxy acrylic emulsion, and 50 - 100 parts of a fourth solvent water.

[0079] In some preferred embodiments, in step S32, the second outer shell reaction raw material comprises the following components in parts by weight: 10 - 20 parts of a second emulsifier, 2 - 5 parts of a second initiator, and 50 - 100 parts of a fifth solvent water.

[0080] In some preferred embodiments, in step S4, the weight part of the second isophorone diisocyanate is 5 - 20 parts, and the weight part of the second catalyst is 2 - 5 parts.

[0081] In some preferred embodiments, the weight part of the cross - linker is 5 - 10 parts.

[0082] In this application, by controlling and adjusting the amounts of the polyurea reaction raw materials (the first isophorone diisocyanate and the aromatic polyurea resin), the proportion of polyurea structural units in the core structure of the prepared aqueous binder is controlled, and by controlling and adjusting the amounts of the polyurethane reaction raw materials (the second isophorone diisocyanate and the hydroxy acrylic emulsion), the proportion of polyurethane structural units in the outer shell structure of the prepared aqueous binder is controlled, so that the prepared aqueous binder has better flexibility and electrolyte resistance. In addition, by regulating the components and amounts of the reaction raw materials of the core structure (the first core reaction raw material and the second core reaction raw material) and regulating the components and amounts of the reaction raw materials of the outer shell structure (the first outer shell reaction raw material and the second outer shell reaction raw material), the outer shell actively wraps the core during the synthesis of the outer shell to form an aqueous binder with a better - shaped core - shell structure.

[0083] In some preferred embodiments, the mass of the aromatic polyurea resin is 15% - 30% of the total mass of the first acrylate monomer, the first acrylamide monomer, and the first acrylonitrile, and the mass ratio of the first isophorone diisocyanate to the aromatic polyurea resin is 1:(2 - 3).

[0084] In some preferred embodiments, the mass of the hydroxy acrylic emulsion is 12% - 80% of the total mass of the second acrylate monomer, the second acrylamide monomer, and the second acrylonitrile, and the mass ratio of the second isophorone diisocyanate to the hydroxy acrylic emulsion is 1:(5 - 10).

[0085] In some further preferred embodiments, the mass of the hydroxy acrylic emulsion is 30% - 40% of the total mass of the second acrylate monomer, the second acrylamide monomer, and the second acrylonitrile.

[0086] In this application, by further controlling and adjusting the dosage of the aromatic polyurea resin in the polyurea reaction raw materials relative to the total mass of the first acrylate monomer, the first acrylamide monomer, and the first acrylonitrile, the proportion of polyurea structural units in the core structure is controlled, and by controlling the dosage of the hydroxyl acrylic emulsion in the polyurethane reaction raw materials relative to the total mass of the second acrylate monomer, the second acrylamide monomer, and the second acrylonitrile, the proportion of polyurethane structural units in the shell structure is controlled, so that the prepared aqueous binder has excellent flexibility and electrolyte resistance performance.

[0087] Preferably, the first acrylate monomer and / or the first acrylamide monomer contain hydroxyl groups, and the second acrylate monomer and / or the second acrylamide monomer contain hydroxyl groups.

[0088] Specifically, making both the reaction raw materials of the core structure and the reaction raw materials of the shell structure contain hydroxyl groups, which can react with isophorone diisocyanate, so that the generated polyurea structural units are grafted onto the core structure, and the generated polyurethane structural units are grafted onto the shell structure, thereby improving the electrolyte resistance performance and flexibility of the aqueous binder.

[0089] Further preferably, the first acrylate monomer and / or the second acrylate monomer include one or more of hydroxyethyl acrylate, hydroxymethyl acrylate, and hydroxyethyl methacrylate.

[0090] Further preferably, the first acrylamide monomer and / or the second acrylamide monomer include one or more of N-methylolacrylamide and N-hydroxyethylacrylamide.

[0091] Further preferably, the first acrylate monomer and / or the second acrylate monomer also include one or more of ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isooctyl acrylate, lauryl methacrylate, butyl methacrylate, and n-octyl methacrylate.

[0092] Further preferably, the first acrylamide monomer and / or the second acrylamide monomer also include one or more of methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, methyl-acryloyloxyethyltrimethylammonium chloride, diacetone acrylamide, and N-butoxymethylacrylamide.

[0093] Preferably, the first emulsifier and the second emulsifier are respectively selected from one or more of sodium p-styrenesulfonate, sodium vinylsulfonate, and sodium dodecylsulfonate.

[0094] Preferably, the first initiator and the second initiator are persulfates. Among them, the persulfates include one or more of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0095] Preferably, the aromatic polyurea resin is selected from one or more of phenyl polyurea and dichlorobenzene polyurea.

[0096] Preferably, the first isophorone diisocyanate and the second isophorone diisocyanate are respectively selected from one or several of Covestro Bayhydur ultra 2759, Bayhydur 2858 XP, and Bayhydur ultra 401-70 MPA / X.

[0097] Preferably, the hydroxy acrylic emulsion is selected from one or several of Dow Prospersetm 200, Huaguoshan Houshan 0880, and DSM Neocryl XK-540.

[0098] Preferably, the first catalyst and the second catalyst are respectively selected from one or more of bismuth isooctanoate, benzoyl chloride, and triethylenediamine.

[0099] Preferably, the neutralizing base is selected from one or several of sodium hydroxide, lithium hydroxide, ammonia water, sodium carbonate, and sodium bicarbonate.

[0100] Preferably, the crosslinking agent is one or more of adipic dihydrazide and aziridine.

[0101] In a third aspect, the present application provides the use of the aqueous binder provided in the first aspect as a negative electrode binder in a lithium-ion battery.

[0102] The aqueous binder of the present application will be described in detail below through several specific examples.

[0103] Example 1 The emulsion of the aqueous binder in this example was prepared by the following steps: S101: Mix 70 g of the first acrylate monomer (10 g of ethyl acrylate, 15 g of isooctyl acrylate, 15 g of hydroxyethyl acrylate, 10 g of lauryl methacrylate, 20 g of butyl methacrylate), 21 g of the first acrylamide monomer (5 g of methacrylamide, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 6 g of diacetone acrylamide), 11 g of the first acrylonitrile, 25 g of the aromatic polyurea resin (phenyl polyurea), and 70 g of deionized water, and disperse and stir at 500 rpm for 5 minutes with a disperser under normal temperature and pressure to obtain the first core reaction raw material.

[0104] S102: Mix 7 g of the first emulsifier (sodium dodecyl sulfate), 4 g of the first initiator (ammonium persulfate), and 80 g of deionized water, and disperse and emulsify at 6000 rpm for 1 minute with a high-speed disperser under normal temperature and pressure to obtain the second core reaction raw material.

[0105] S103: Take 22% of the second core reaction raw material (i.e., 20 g of the second core reaction raw material) and mix it with 200 g of deionized water. Stir with a stirring paddle at a speed of 50 rpm and heat up to 82 °C to form a reaction system.

[0106] S104: Adjust the stirring speed of the reaction system in step S103 to 300 rpm, and uniformly drip the first core reaction raw material and the remaining second core reaction raw material into the reaction system. Among them, the first core reaction raw material is dripped out within 45 minutes, and the remaining second core reaction raw material is dripped out within 50 minutes. During the dripping process, control the reaction temperature not to exceed 95 °C. After all are dripped out, start timing and keep it warm at 90 °C for 1 hour to polymerize the first core reaction raw material to obtain the core main structure.

[0107] S105: Cool the reaction system after the reaction in step S104 to 45 °C, add 10 g of the first isophorone diisocyanate (Covestro Bayhydur ultra 2759) and 3 g of the first catalyst (triethylenediamine) to the reaction system, and at the same time control the reaction temperature not to exceed 65 °C. Then keep it warm at 60 °C for 1 hour to generate a polyurea structural unit, and the polyurea structural unit is grafted onto the core main structure to obtain the core structure.

[0108] S106: Mix 100 g of the second acrylate monomer (20 g of ethyl acrylate, 15 g of isooctyl acrylate, 25 g of 2-hydroxyethyl acrylate, 20 g of lauryl methacrylate, 20 g of butyl methacrylate), 39 g of the second acrylamide monomer (5 g of methacrylamide, 18 g of 2-acrylamido-2-methylpropanesulfonic acid, 16 g of diacetone acrylamide), 14 g of the second acrylonitrile, 100 g of the hydroxyacrylate emulsion (Dow Prospersetm 200) and 60 g of deionized water, and disperse and stir at 500 rpm with a disperser at normal temperature and pressure for 15 minutes to obtain the first outer shell reaction raw material.

[0109] S107: Mix 15 g of the second emulsifier (sodium dodecyl sulfonate), 4 g of the second initiator (ammonium persulfate) and 80 g of deionized water, and disperse and emulsify at 6000 rpm with a high-speed disperser at normal temperature and pressure for 1 minute to obtain the second outer shell reaction raw material.

[0110] S108: Adjust the temperature of the reaction system after the reaction in step S105 to 86 °C, and adjust the stirring speed to 300 rpm. Uniformly drip the first outer shell reaction raw material and the second outer shell reaction raw material into the reaction system. The first outer shell reaction raw material is dripped out within 1 hour and 30 minutes, and the second outer shell reaction raw material is dripped out within 1 hour and 20 minutes. During the dripping process, control the reaction temperature not to exceed 95 °C. After all are dripped out, start timing and keep it warm at 90 °C for 2 hours to polymerize the first outer shell reaction raw material to obtain the outer shell main structure, and the outer shell main structure covers the outside of the core structure.

[0111] S109: Cool down the reaction system after the reaction in step S108 to 45°C, then add 20 g of the second isophorone diisocyanate (Covestro Bayhydur ultra 2759) and 3 g of the second catalyst (triethylenediamine), while controlling the reaction temperature not to exceed 65°C, and then keep it at 60°C for 1 hour. A polyurethane structural unit is formed and grafted onto the outer shell main structure, thus obtaining the aqueous binder.

[0112] S110: Dropwise add lithium hydroxide to the reaction system after the reaction in step S109 to adjust the pH to 7.2.

[0113] S111: Add 5 g of the crosslinking agent (3 g of adipic dihydrazide and 2 g of aziridine) to the reaction system obtained in step S110, cool it down to below 40°C, and discharge it through a 300-mesh sieve to obtain the emulsion of the aqueous binder.

[0114] Perform FT-IR test on the aqueous binder obtained in Example 1 to obtain the Figure 1 shown Fourier transform infrared spectrum. Figure 1 The FT-IR test spectrum shows that there are peaks at 3300 - 3500, indicating the presence of N-H structure; there are peaks at 1600 - 1700, indicating the presence of C=O structure. Both the polyurea structural unit and the polyurethane structural unit contain these two structures. Therefore, it can be known that the aqueous binder of this application contains polyurea structural unit and polyurethane structural unit. In addition, the aqueous binder of this Example 1 shows a core-shell structure by scanning electron microscopy test, where the outer shell structure covers the outside of the inner core structure.

[0115] Example 2 The preparation method of the emulsion of the aqueous binder in this example is the same as that in Example 1. The difference between this example and Example 1 is only that: the types of the first isophorone diisocyanate in step S105 and the second isophorone diisocyanate in step S109 are different.

[0116] Specifically, in this example, both the first isophorone diisocyanate and the second isophorone diisocyanate are Covestro Bayhydur 2858 XP.

[0117] Example 3 The preparation method of the emulsion of the aqueous binder in this example is the same as that in Example 1. The difference between this example and Example 1 is only that: the types of the first isophorone diisocyanate in step S105 and the second isophorone diisocyanate in step S109 are different.

[0118] Specifically, in this embodiment, both the first isophorone diisocyanate and the second isophorone diisocyanate are Covestro Bayhydur ultra 401-70 MPA / X.

[0119] Example 4 The preparation method of the emulsion of the aqueous binder in this embodiment is the same as that in Example 1. The difference between this embodiment and Example 1 is only that: the types of the aromatic polyurea resin in step S101 and the hydroxy acrylic emulsion in step S106 are different.

[0120] Specifically, in this embodiment, the aromatic polyurea resin is dichlorobenzene polyurea, and the hydroxy acrylic emulsion is DSM Neocryl XK-540.

[0121] The preparation method of the emulsion of the aqueous binder in Examples 5 to 7 is the same as that in Example 1. The difference between them and Example 1 is that the components and dosages of the raw materials are different. The components and dosages of the raw materials in Examples 5 to 7 are shown in Table 1.

[0122] Table 1 Raw material ratio table of Examples 5 to 7

[0123] Example 8 The emulsion of the aqueous binder in this embodiment is prepared by the following steps: S101: Mix 100 g of the first acrylate monomers (10 g of ethyl acrylate, 10 g of isooctyl acrylate, 10 g of n-propyl acrylate, 20 g of 2-hydroxyethyl acrylate, 10 g of lauryl methacrylate, 20 g of butyl methacrylate, 20 g of n-octyl methacrylate), 30 g of the first acrylamide monomers (10 g of N-methylolacrylamide, 5 g of methacrylamide, 10 g of methacryloyloxyethyl trimethyl ammonium chloride, 5 g of N-butoxymethyl acrylamide), 15 g of the first acrylonitrile, 25 g of the aromatic polyurea resin (dichlorobenzene polyurea) and 100 g of deionized water, and disperse and stir at 500 rpm with a disperser for 5 minutes under normal temperature and pressure to obtain the first core reaction raw material.

[0124] S102: Mix 7 g of the first emulsifier (sodium p-styrenesulfonate), 3 g of the first initiator (potassium persulfate) and 120 g of deionized water, and disperse and emulsify at 6000 rpm with a high-speed disperser for 1 minute under normal temperature and pressure to obtain the second core reaction raw material.

[0125] S103: Take 22% of the second core reaction raw material (i.e., 28.6 g of the second core reaction raw material) and mix it with 150 g of deionized water, stir with a stirring paddle at a speed of 50 rpm, and heat up to 82 °C to form a reaction system.

[0126] S104: Adjust the stirring speed of the reaction system in step S103 to 300 rpm, and uniformly drip the first core reaction raw material and the remaining second core reaction raw material into the reaction system. Among them, the first core reaction raw material is dripped out within 45 minutes, and the remaining second core reaction raw material is dripped out within 50 minutes. During the dripping process, control the reaction temperature not to exceed 95 °C. After all are dripped, start timing and keep it warm at 90 °C for 1 hour. The first core reaction raw material undergoes polymerization to obtain the core main structure.

[0127] S105: Cool the reaction system after the reaction in step S104 to 45 °C, add 12 g of the first isophorone diisocyanate (Covestro Bayhydur ultra 2759) and 3 g of the first catalyst (bismuth isooctanoate) to the reaction system, and at the same time control the reaction temperature not to exceed 65 °C. Then keep it warm at 60 °C for 1 hour. The reaction generates polyurea structural units, and the polyurea structural units are grafted onto the core main structure to obtain the core structure.

[0128] S106: Mix 200 g of the second acrylate monomer (35 g of ethyl acrylate, 15 g of isooctyl acrylate, 50 g of 2-hydroxyethyl acrylate, 20 g of lauryl methacrylate, 20 g of butyl methacrylate, 20 g of n-propyl acrylate, 20 g of n-butyl acrylate, 20 g of n-octyl methacrylate), 50 g of the second acrylamide monomer (5 g of methacrylamide, 13 g of 2-acrylamido-2-methylpropanesulfonic acid, 16 g of diacetone acrylamide, 16 g of N-methylolacrylamide), 17 g of the second acrylonitrile, 75 g of the hydroxy acrylic emulsion (Dow Prospersetm 200) and 75 g of deionized water, and disperse and stir at 500 rpm for 15 minutes under normal temperature and pressure to obtain the first shell reaction raw material.

[0129] S107: Mix 15 g of the second emulsifier (sodium p-styrenesulfonate), 3 g of the second initiator (potassium persulfate) and 75 g of deionized water, and disperse and emulsify at 6000 rpm for 1 minute under normal temperature and pressure to obtain the second shell reaction raw material.

[0130] S108: Adjust the temperature of the reaction system after the reaction in step S105 to 86 °C, and adjust the stirring speed to 300 rpm. Uniformly drip the first shell reaction raw material and the second shell reaction raw material into the reaction system. The first shell reaction raw material is dripped out within 1 hour and 30 minutes, and the second shell reaction raw material is dripped out within 1 hour and 20 minutes. During the dripping process, control the reaction temperature not to exceed 95 °C. After all are dripped, start timing and keep it warm at 90 °C for 2 hours to polymerize the first shell reaction raw material to obtain the shell main structure, and the shell main structure covers the outside of the core structure.

[0131] S109: The reaction system after the reaction in step S108 is cooled to 45°C, and then 15g of the second isophorone diisocyanate (Covestro Bayhydur ultra 2759) and 3g of the second catalyst (bismuth isooctanoate) are added, and the reaction temperature is controlled not to exceed 65°C. Then, the temperature is kept at 60°C for 1 hour to react to generate a polyurethane structural unit, and the polyurethane structural unit is grafted onto the main structure of the shell to obtain a water-based adhesive.

[0132] S110: Sodium hydroxide is added dropwise to the reaction system after the reaction in step S109 to adjust the pH to 7.2.

[0133] S111: adding 7 g of a cross-linking agent (7 g of adipic acid dihydrazide) to the reaction system obtained in step S110, cooling the temperature to below 40° C., and discharging the material through a 300-mesh sieve to obtain an emulsion of a water-based binder.

[0134] The preparation method of the aqueous binder emulsion of Examples 9 to 14 is the same as that of Example 8, and the difference between them and Example 8 is that the amount of the aromatic polyurea resin and the first isophorone diisocyanate is different, and the other raw material components and amounts are the same as those of Example 8. Specifically, the amount of the aromatic polyurea resin and the first isophorone diisocyanate in Examples 9 to 14 is shown in Table 2.

[0135] Table 2 Proportions of different dosages of Examples 9 to 14 and Example 8

[0136] The preparation method of the aqueous binder emulsion of Examples 15 to 18 is the same as that of Example 8, and the difference between them and Example 8 is that the amount of the first isophorone diisocyanate is different, and the other raw material components and amounts are the same as those of Example 8. Specifically, the amount of the first isophorone diisocyanate used in Examples 15 to 18 is shown in Table 3.

[0137] Table 3 Proportions of different dosages of Examples 15 to 18 and Example 8

[0138] The preparation method of the aqueous binder emulsion of Examples 19 to 24 is the same as that of Example 8, and the difference from Example 8 is that the amount of hydroxyl acrylic emulsion and the second isophorone diisocyanate is different, and the other raw material components and amounts are the same as those of Example 8. Specifically, the amounts of hydroxyl acrylic emulsion and the second isophorone diisocyanate in Examples 19 to 24 are shown in Table 4.

[0139] Table 4 Proportions of different dosages of Examples 19 to 24 and Example 8

[0140] The preparation method of the aqueous binder emulsion of Examples 25 to 28 is the same as that of Example 8, and the difference between them and Example 8 is that the amount of the second isophorone diisocyanate is different, and the other raw material components and amounts are the same as those of Example 8. Specifically, the amount of the second isophorone diisocyanate used in Examples 25 to 28 is shown in Table 5.

[0141] Table 5 Proportions of different dosages of Examples 25 to 28 and Example 8

[0142] Comparative Example 1 The aqueous binder emulsion of this comparative example was prepared by the following steps: S101: 70 g of the first acrylic ester monomer (10 g of ethyl acrylate, 15 g of isooctyl acrylate, 15 g of hydroxyethyl acrylate, 10 g of lauryl methacrylate, 20 g of butyl methacrylate), 21 g of the first acrylamide monomer (5 g of methacrylamide, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 6 g of diacetone acrylamide), 11 g of the first acrylonitrile and 70 g of deionized water are mixed, and dispersed and stirred at 500 rpm for 5 minutes in a disperser at room temperature and pressure to obtain a core reaction raw material one.

[0143] S102: 7 g of the first emulsifier (sodium dodecyl sulfate), 4 g of the first initiator (ammonium persulfate) and 80 g of deionized water were mixed, and dispersed and emulsified at 6000 rpm for 1 minute using a high-speed disperser at room temperature and pressure to obtain the second core reaction raw material.

[0144] S103: 22% of the core reaction raw material 2 (ie, 20 g of the core reaction raw material 2) was mixed with 200 g of deionized water, stirred at a stirring speed of 50 rpm, and heated to 82° C. to form a reaction system.

[0145] S104: The stirring speed of the reaction system of step S103 is adjusted to 300 rpm, and the inner core reaction raw material 1 and the remaining inner core reaction raw material 2 are uniformly dripped into the reaction system, wherein the inner core reaction raw material 1 is dripped within 45 minutes, and the remaining inner core reaction raw material 2 is dripped within 50 minutes. During the dripping process, the reaction temperature is controlled not to exceed 95°C. After all the dripping is completed, the timing is started, and the temperature is kept at 90°C for 1 hour to polymerize the inner core reaction raw material 1 to obtain the inner core structure.

[0146] S105: Mix 100 g of the second acrylate monomer (20 g of ethyl acrylate, 15 g of isooctyl acrylate, 25 g of 2-hydroxyethyl acrylate, 20 g of lauryl methacrylate, 20 g of butyl methacrylate), 39 g of the second acrylamide monomer (5 g of methacrylamide, 18 g of 2-acrylamido-2-methylpropane sulfonic acid, 16 g of diacetone acrylamide), 14 g of the second acrylonitrile, 100 g of a hydroxy acrylic emulsion (Dow Prospersetm 200), and 60 g of deionized water, and disperse and stir at 500 rpm for 15 minutes under normal temperature and pressure using a disperser to obtain the first raw material for the shell reaction.

[0147] S106: Mix 15 g of the second emulsifier (sodium dodecyl sulfonate), 4 g of the second initiator (ammonium persulfate), and 80 g of deionized water, and disperse and emulsify at 6000 rpm for 1 minute under normal temperature and pressure using a high-speed disperser to obtain the second raw material for the shell reaction.

[0148] S107: Adjust the temperature of the reaction system after the reaction in step S104 to 86 °C, adjust the stirring speed to 300 rpm, and uniformly dropwise add the first raw material for the shell reaction and the second raw material for the shell reaction to the reaction system. The first raw material for the shell reaction is added dropwise within 1 hour and 30 minutes, and the second raw material for the shell reaction is added dropwise within 1 hour and 20 minutes. During the dropping process, control the reaction temperature not to exceed 95 °C. After both are added dropwise, start timing, and keep warm at 90 °C for 2 hours to polymerize the first raw material for the shell reaction to obtain the main structure of the shell, and the main structure of the shell is coated on the outside of the core structure.

[0149] S108: Cool the reaction system after the reaction in step S107 to 45 °C, then add 20 g of the second isophorone diisocyanate (Covestro Bayhydur ultra 2759) and 3 g of the second catalyst (triethylenediamine), while controlling the reaction temperature not to exceed 65 °C, and then keep warm at 60 °C for 1 hour. The polyurethane structural unit is generated by reaction and grafted onto the main structure of the shell, that is, the water-based binder is obtained.

[0150] S109: Dropwise add lithium hydroxide to the reaction system after the reaction in step S108 to adjust the pH to 7.2.

[0151] S110: Add 5 g of the crosslinking agent (3 g of adipic dihydrazide, 2 g of aziridine) to the reaction system obtained in step S109, cool to below 40 °C, and discharge through a 300-mesh sieve to obtain the emulsion of the water-based binder.

[0152] Comparative Example 2 The emulsion of the water-based binder in this comparative example is prepared by the following steps: S101: Mix 70 g of the first acrylate monomers (10 g of ethyl acrylate, 15 g of isooctyl acrylate, 15 g of 2-hydroxyethyl acrylate, 10 g of lauryl methacrylate, 20 g of butyl methacrylate), 21 g of the first acrylamide monomers (5 g of methacrylamide, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 6 g of diacetone acrylamide), 11 g of the first acrylonitrile, 25 g of an aromatic polyurea resin (phenyl polyurea) and 70 g of deionized water, and disperse and stir at 500 rpm for 5 minutes under normal temperature and pressure using a disperser to obtain the first core reaction raw material.

[0153] S102: Mix 7 g of the first emulsifier (sodium dodecyl sulfonate), 4 g of the first initiator (ammonium persulfate) and 80 g of deionized water, and disperse and emulsify at 6000 rpm for 1 minute under normal temperature and pressure using a high-speed disperser to obtain the second core reaction raw material.

[0154] S103: Take 22% of the second core reaction raw material (i.e., 20 g of the second core reaction raw material) and mix it with 200 g of deionized water, stir with a stirring paddle at a speed of 50 rpm, and heat up to 82 °C to form a reaction system.

[0155] S104: Adjust the stirring speed of the reaction system in step S103 to 300 rpm, and uniformly drip the first core reaction raw material and the remaining second core reaction raw material into the reaction system. Among them, the first core reaction raw material is dripped within 45 minutes, and the remaining second core reaction raw material is dripped within 50 minutes. During the dripping process, control the reaction temperature not to exceed 95 °C. After all are dripped, start timing and keep it warm at 90 °C for 1 hour to polymerize the first core reaction raw material to obtain the core main structure.

[0156] S105: Cool the reaction system after step S104 to 45 °C, add 10 g of the first isophorone diisocyanate (Covestro Bayhydur ultra 2759) and 3 g of the first catalyst (triethylenediamine) to the reaction system, while controlling the reaction temperature not to exceed 65 °C, and then keep it warm at 60 °C for 1 hour to react to generate a polyurea structural unit, and the polyurea structural unit is grafted onto the core main structure to obtain the core structure.

[0157] S106: Mix 100 g of the second acrylate monomers (20 g of ethyl acrylate, 15 g of isooctyl acrylate, 25 g of 2-hydroxyethyl acrylate, 20 g of lauryl methacrylate, 20 g of butyl methacrylate), 39 g of the second acrylamide monomers (5 g of methacrylamide, 18 g of 2-acrylamido-2-methylpropanesulfonic acid, 16 g of diacetone acrylamide), 14 g of the second acrylonitrile and 60 g of deionized water, and disperse and stir at 500 rpm for 15 minutes under normal temperature and pressure using a disperser to obtain the first shell reaction raw material.

[0158] S107: Mix 15 g of the second emulsifier (sodium dodecyl sulfonate), 4 g of the second initiator (ammonium persulfate), and 80 g of deionized water, and disperse and emulsify them at 6000 rpm for 1 minute under normal temperature and pressure using a high-speed disperser to obtain the second raw material for the shell reaction.

[0159] S108: Adjust the temperature of the reaction system after the reaction in step S105 to 86 °C, adjust the stirring speed to 300 rpm, and uniformly drip the first raw material for the shell reaction and the second raw material for the shell reaction into the reaction system. The first raw material for the shell reaction is dripped out within 1 hour and 30 minutes, and the second raw material for the shell reaction is dripped out within 1 hour and 20 minutes. During the dripping process, control the reaction temperature not to exceed 95 °C. After all are dripped, start timing and keep it warm at 90 °C for 2 hours to polymerize the first raw material for the shell reaction to obtain the shell structure, and the shell structure is coated on the outside of the core structure, that is, the aqueous binder is obtained.

[0160] S109: Dropwise add lithium hydroxide to the reaction system after the reaction in step S108 to adjust the pH to 7.2.

[0161] S110: Add 5 g of the crosslinking agent (3 g of adipic dihydrazide, 2 g of aziridine) to the reaction system obtained in step S109, cool down to below 40 °C, and discharge through a 300-mesh sieve to obtain the emulsion of the aqueous binder.

[0162] Comparative Example 3 The emulsion of the aqueous binder in this comparative example is prepared through the following steps: S101: Mix 70 g of the first acrylate monomer (10 g of ethyl acrylate, 15 g of isooctyl acrylate, 15 g of 2-hydroxyethyl acrylate, 10 g of lauryl methacrylate, 20 g of butyl methacrylate), 21 g of the first acrylamide monomer (5 g of methacrylamide, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 6 g of diacetone acrylamide), 11 g of the first acrylonitrile, and 70 g of deionized water, and disperse and stir them at 500 rpm for 5 minutes under normal temperature and pressure using a disperser to obtain the first raw material for the core reaction.

[0163] S102: Mix 7 g of the first emulsifier (sodium dodecyl sulfonate), 4 g of the first initiator (ammonium persulfate), and 80 g of deionized water, and disperse and emulsify them at 6000 rpm for 1 minute under normal temperature and pressure using a high-speed disperser to obtain the second raw material for the core reaction.

[0164] S103: Take 22% of the second raw material for the core reaction (i.e., 20 g of the second raw material for the core reaction) and mix it with 200 g of deionized water, stir with a stirring paddle at a speed of 50 rpm, and heat up to 82 °C to form a reaction system.

[0165] S104: Adjust the stirring speed of the reaction system in step S103 to 300 rpm, and uniformly drop the first core reaction raw material and the remaining second core reaction raw material into the reaction system. Among them, the first core reaction raw material is dropped within 45 minutes, and the remaining second core reaction raw material is dropped within 50 minutes. During the dropping process, control the reaction temperature not to exceed 95°C. After all are dropped, start timing and keep it warm at 90°C for 1 hour to polymerize the first core reaction raw material to obtain the core structure.

[0166] S105: Mix 100 g of the second acrylate monomer (20 g of ethyl acrylate, 15 g of isooctyl acrylate, 25 g of 2-hydroxyethyl acrylate, 20 g of lauryl methacrylate, 20 g of butyl methacrylate), 39 g of the second acrylamide monomer (5 g of methacrylamide, 18 g of 2-acrylamido-2-methylpropanesulfonic acid, 16 g of diacetone acrylamide), 14 g of the second acrylonitrile and 60 g of deionized water, and disperse and stir at 500 rpm for 15 minutes under normal temperature and pressure with a disperser to obtain the first shell reaction raw material.

[0167] S106: Mix 15 g of the second emulsifier (sodium dodecyl sulfonate), 4 g of the second initiator (ammonium persulfate) and 80 g of deionized water, and disperse and emulsify at 6000 rpm for 1 minute under normal temperature and pressure with a high-speed disperser to obtain the second shell reaction raw material.

[0168] S107: Adjust the temperature of the reaction system after the reaction in step S104 to 86°C, adjust the stirring speed to 300 rpm, and uniformly drop the first shell reaction raw material and the second shell reaction raw material into the reaction system. The first shell reaction raw material is dropped within 1 hour and 30 minutes, and the second shell reaction raw material is dropped within 1 hour and 20 minutes. During the dropping process, control the reaction temperature not to exceed 95°C. After all are dropped, start timing and keep it warm at 90°C for 2 hours to polymerize the first shell reaction raw material to obtain the shell structure, and the shell structure is coated on the outside of the core structure, that is, the water-based binder is obtained.

[0169] S108: Drop lithium hydroxide into the reaction system after the reaction in step S107 to adjust the pH to 7.2.

[0170] S109: Add 5 g of the cross-linking agent (3 g of adipic dihydrazide, 2 g of aziridine) to the reaction system obtained in step S108, cool down to below 40°C, and discharge through a 300-mesh sieve to obtain the emulsion of the water-based binder.

[0171] Comparative Example 4 The preparation method of the water-based binder in this comparative example is the same as that in Example 1. The difference between this comparative example and Example 1 is only that: the components and contents of the first core reaction raw material and the first shell reaction raw material are different.

[0172] Specifically, in this comparative example, the first core reaction raw material consists of the following components: 70 g of the first acrylate monomer (15 g of ethyl acrylate, 20 g of isooctyl acrylate, 15 g of lauryl methacrylate, 20 g of butyl methacrylate), 21 g of the first acrylamide monomer (5 g of methacrylamide, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 6 g of diacetone acrylamide), 11 g of the first acrylonitrile, 25 g of aromatic polyurea resin (phenyl polyurea), and 70 g of deionized water.

[0173] The first shell reaction raw material consists of the following components: 100 g of the second acrylate monomer (30 g of ethyl acrylate, 20 g of isooctyl acrylate, 30 g of lauryl methacrylate, 20 g of butyl methacrylate), 39 g of the second acrylamide monomer (5 g of methacrylamide, 18 g of 2-acrylamido-2-methylpropanesulfonic acid, 16 g of diacetone acrylamide), 14 g of the second acrylonitrile, 100 g of hydroxyacrylate emulsion (Dow Prospersetm 200), and 60 g of deionized water.

[0174] Test Examples The water-based binders prepared in Examples 1 to 28 and Comparative Examples 1 to 4 were subjected to electrolyte resistance performance testing and flexibility performance testing, and the test results are shown in Table 6.

[0175] Among them, the specific method for testing the electrolyte resistance performance is as follows: Pour the emulsion of the prepared water-based binder into a Teflon mold and bake it at 85 °C for 24 hours to make a dry glue. Then, at 60 °C, take 3 ± 0.2 g (initial mass) of the dry glue and soak it in the electrolyte of Macklin L769384 sold on the market. Record the mass of the dry glue before soaking. Then take out the glue every 24 hours, dry the surface electrolyte with lint-free paper, measure and record the mass of the glue. The test lasts for 30 days, and record the mass of the dry glue measured last time as the termination mass. Calculate the dissolution mass ratio of the dry glue after the last measurement. The dissolution mass ratio = (initial mass - termination mass) ÷ initial mass × 100%.

[0176] The specific method for testing the flexibility performance is as follows: Use a wet film applicator to coat a binder emulsion with a thickness of 200 μm, a width of 10 cm, and a length of 30 cm on the surface of the copper foil, and immediately place it in an oven and bake at 60 °C for 24 hours. Then take it out and cut it into a copper foil with a width of 16 cm and a length of 36 cm that completely contains the dry film of the binder. Then use coiling needles with different diameters for the flexibility test. The diameters of the coiling needles used in the test are 5 mm, 4 mm, 3 mm, 2 mm, 1.5 mm, and 1 mm, and the smallest coiling needle diameter is 1 mm. The specific operation is as follows: Bend the copper foil with the dry film 180° around the coiling needle, observe whether there are cracks on the outer side of the bend. If there are no cracks, reduce the diameter of the coiling needle, and change the position of the copper foil and bend it again for testing until cracks appear on the outer side of the bent part of the dry film, or until the test is carried out with a 1 mm coiling needle. Record the diameter of the coiling needle used in the previous test when cracks appear as the flexibility test result, that is, the smallest coiling needle diameter without cracks is the flexibility test result (for example: if cracks appear when testing with a 1.5 mm coiling needle, the flexibility test result is 2 mm).

[0177] Table 6 Detection Results of Examples and Comparative Examples It can be seen from the experimental data in Table 6 that: 1. Comparing Example 1 with Comparative Examples 1-3, and comparing Comparative Examples 2 and 3, it can be seen that when only introducing a polyurea structural unit into the core structure of the aqueous binder, the electrolyte resistance performance can be significantly improved, but the flexibility cannot be improved; comparing Comparative Examples 1 and 3, it can be seen that when only introducing a polyurethane structural unit into the shell structure of the aqueous binder, the flexibility can be significantly improved, but there is almost no improvement in the electrolyte resistance performance; comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that the electrolyte resistance performance of Example 1 is better than that of Comparative Example 2 and the flexibility of Example 1 is better than that of Comparative Example 1. From this, it can be known that only by introducing a polyurea structural unit into the core structure of the aqueous binder and introducing a polyurethane structural unit into the shell structure at the same time can an aqueous binder with good flexibility and good electrolyte resistance performance be prepared, and the technical effect obtained when the polyurethane structural unit and the polyurea structural unit act synergistically is far better than the technical effects of the individual polyurea structural unit and the individual polyurethane structural unit acting alone.

[0178] 2. Comparing Examples 1 to 3, it can be seen that the electrolyte resistance performance and flexibility of Example 1 are the best. From this, it can be known that the best technical effect is obtained when isophorone diisocyanate is Covestro Bayhydur ultra 2759. Therefore, it is most preferred that the first isophorone diisocyanate and the second isophorone diisocyanate are Covestro Bayhydur ultra 2759.

[0179] 3. Compare Examples 8 to 14. The electrolyte resistance performance of Examples 10, 9, 8, 11, 12, and 13 gradually increases, and the electrolyte resistance performance of Example 14 drops significantly compared to Example 13. From this, it can be seen that as the percentage of the mass of the aromatic polyurea resin in the total mass of the first acrylate monomer, the first acrylamide monomer, and the first acrylonitrile increases, that is, as the proportion of the polyurea structural unit in the aqueous binder increases, the electrolyte resistance performance of the aqueous binder first increases and then drops rapidly. Therefore, it is necessary to control the proportion of the polyurea structural unit in the aqueous binder within a certain range. Preferably, the mass of the aromatic polyurea resin is 15% - 30% of the total mass of the first acrylate monomer, the first acrylamide monomer, and the first acrylonitrile. More preferably, the mass of the aromatic polyurea resin is 20% - 30% of the total mass of the first acrylate monomer, the first acrylamide monomer, and the first acrylonitrile.

[0180] 4. Compare Examples 8, 15 to 18. The electrolyte resistance performance of Examples 15, 8, 16, and 17 gradually increases, and the electrolyte resistance performance of Example 18 drops significantly compared to Example 17. From this, it can be seen that when the dosage of the first isophorone diisocyanate is the same, as the dosage of the aromatic polyurea resin increases, the electrolyte resistance performance of the aqueous binder first increases and then drops rapidly. Therefore, it is necessary to control the mass ratio of the first isophorone diisocyanate to the aromatic polyurea resin within a certain range. Preferably, the ratio of the first isophorone diisocyanate to the aromatic polyurea resin is 1:(2 - 3). More preferably, the ratio of the first isophorone diisocyanate to the aromatic polyurea resin is 1:(2.5 - 3).

[0181] 5. Compare Examples 8, 19 - 24. The flexibility of Examples 19, 20, 8, and 21 gradually increases, and the flexibility of Examples 23 and 24 drops compared to Examples 21 and 22. From this, it can be seen that as the percentage of the mass of the hydroxy acrylic emulsion in the total mass of the second acrylate monomer, the second acrylamide monomer, and the second acrylonitrile increases, that is, as the proportion of the polyurethane structural unit in the aqueous binder increases, the flexibility of the aqueous binder first increases and then drops. Therefore, it is necessary to control the proportion of the polyurethane structural unit in the aqueous binder within a certain range. Preferably, the mass of the hydroxy acrylic emulsion is 12% - 80% of the total mass of the second acrylate monomer, the second acrylamide monomer, and the second acrylonitrile. More preferably, the mass of the hydroxy acrylic emulsion is 30% - 40% of the total mass of the second acrylate monomer, the second acrylamide monomer, and the second acrylonitrile.

[0182] 6. Comparing Examples 8, 25 to 28, it can be seen that the electrolyte resistance performance of Examples 25, 8, 26, and 27 gradually increases, while the electrolyte resistance performance of Example 28 drops significantly compared to Example 27. Thus, it can be known that when the dosage of the second isophorone diisocyanate is the same, with the increase in the dosage of the hydroxy acrylic emulsion, the flexibility of the water-based binder first increases and then decreases. Therefore, it is necessary to control the mass ratio of the second isophorone diisocyanate to the hydroxy acrylic emulsion within a certain range, and preferably the second isophorone diisocyanate:hydroxy acrylic emulsion is 1:(5 - 10).

[0183] 7. Comparing Example 1 and Comparative Example 4, it can be seen that both the electrolyte resistance performance and flexibility of Comparative Example 4 are worse than those of Example 1. Thus, it can be known that when neither the first acrylate monomer nor the first acrylamide monomer contains a hydroxyl group, and neither the second acrylate monomer nor the second acrylamide monomer contains a hydroxyl group, the generated polyurea structural unit cannot be grafted onto the inner core main structure and exists independently in the system, and the generated polyurethane structural unit cannot be grafted onto the outer shell main structure and exists independently in the system. The polyurea structural unit and the polyurethane structural unit are free in the emulsion and cannot improve the electrolyte resistance and flexibility of the water-based binder. Only when the polyurea structural unit is grafted onto the inner core main structure and the polyurethane structural unit is grafted onto the outer shell main structure can the electrolyte resistance and flexibility of the water-based binder be effectively improved.

[0184] So far, the technical solutions of the present application have been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Without departing from the principle of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present application.

Claims

1. A water-based adhesive, characterized in that: The water-based binder comprises a core structure and a shell structure, wherein the shell structure is coated on the outside of the core structure. The core structure includes a core main structure and a polyurea structural unit obtained by polymerizing a first acrylate monomer, a first acrylamide monomer and a first acrylonitrile, wherein the polyurea structural unit is grafted onto the core main structure, wherein the first acrylate monomer and / or the first acrylamide monomer contains a hydroxyl group; The shell structure includes a shell main body structure and a polyurethane structural unit obtained by polymerizing a second acrylate monomer, a second acrylamide monomer and a second acrylonitrile, and the polyurethane structural unit is grafted on the shell main body structure, wherein the second acrylate monomer and / or the second acrylamide monomer contains a hydroxyl group.

2. A method for preparing a water-based adhesive, for preparing the water-based adhesive according to claim 1, characterized in that: The preparation method comprises the following steps: S1: Provides the kernel main structure; S2: Grafting a polyurea structural unit onto the core main structure to obtain a core structure; S3: Covering the outer shell main structure on the outer side of the inner core structure; S4: Grafting the polyurethane structural unit onto the main structure of the shell to obtain a water-based adhesive.

3. The method for preparing the aqueous binder according to claim 2, characterized in that: Step S1 specifically comprises: reacting a first core reaction raw material with a second core reaction raw material to obtain a core main structure, wherein the first core reaction raw material comprises a first acrylate monomer, a first acrylamide monomer, a first acrylonitrile and a mixture of water, and the second core reaction raw material comprises a first emulsifier, a first initiator and a mixture of water; And / or, step S2 specifically comprises: mixing a reaction system having the core main structure, a polyurea reaction raw material and a first catalyst to react, so as to graft a polyurea structural unit onto the core main structure to obtain the core structure, wherein the first catalyst is used to catalyze the reaction of the polyurea reaction raw material to generate the polyurea structural unit; And / or, step S3 specifically comprises: mixing and reacting a reaction system having the core structure with a shell reaction raw material 1 and a shell reaction raw material 2 to obtain a shell main body structure, and coating the shell main body structure on the outside of the core structure, wherein the shell reaction raw material 1 comprises a mixture of a second acrylate monomer, a second acrylamide monomer, a second acrylonitrile and water, and the shell reaction raw material 2 comprises a mixture of a second emulsifier, a second initiator and water, wherein the mass of the second emulsifier is greater than the mass of the first emulsifier in the raw materials used in the reaction system having the core structure; And / or, step S4 specifically includes: mixing a reaction system having a shell main structure with a polyurethane reaction raw material and a second catalyst for reaction, so as to graft a polyurethane structural unit onto the shell main structure to obtain a water-based adhesive, wherein the shell main structure in the reaction system is coated on the outside of the core structure, and the second catalyst is used to catalyze the reaction of the polyurethane reaction raw material to generate a polyurethane structural unit.

4. The method for preparing the aqueous binder according to claim 3, characterized in that: The polyurea reaction raw materials include aromatic polyurea resin and first isophorone diisocyanate, and step S2 specifically includes: firstly uniformly mixing the reaction system having the core main structure with the aromatic polyurea resin, and then mixing with the first isophorone diisocyanate and the first catalyst to react, so as to obtain a core structure grafted with polyurea structural units; And / or, the polyurethane reaction raw materials include hydroxyl acrylic emulsion and second isophorone diisocyanate, and step S4 specifically includes: firstly uniformly mixing the reaction system having the shell main structure with the hydroxyl acrylic emulsion, and then mixing with the second isophorone diisocyanate and the second catalyst for reaction to obtain a shell structure grafted with a polyurethane structural unit.

5. The method for preparing the aqueous binder according to claim 3, characterized in that: The polyurea reaction raw materials include an aromatic polyurea resin and a first isophorone diisocyanate, the aromatic polyurea resin is added to the core reaction raw material one in step S1 and is uniformly mixed with the core reaction raw material one, and step S2 specifically includes: mixing the reaction system having the core main structure with the first isophorone diisocyanate and the first catalyst to react, so as to obtain a core structure grafted with a polyurea structural unit; And / or, the polyurethane reaction raw materials include hydroxyl acrylic emulsion and second isophorone diisocyanate, the hydroxyl acrylic emulsion is added to the shell reaction raw material one in step S3 and mixed evenly with the shell reaction raw material one, and step S4 specifically includes: mixing the reaction system having the shell main structure with the second isophorone diisocyanate and the second catalyst for reaction to obtain a shell structure grafted with a polyurethane structural unit.

6. The method for preparing the aqueous binder according to claim 5, characterized in that: Step S1 specifically includes: S11: providing a mixture of a first acrylate monomer, a first acrylamide monomer, a first acrylonitrile, an aromatic polyurea resin and a first solvent water to obtain a first core reaction raw material; S12: providing a mixture of a first emulsifier, a first initiator and a second solvent water to obtain a second core reaction raw material; S13: taking part of the second core reaction raw material and mixing it with the third solvent water, slowly stirring, and heating it to 80° C. to 90° C. to form a reaction system; S14: uniformly dripping the core reaction raw material 1 and the remaining core reaction raw material 2 into the reaction system of step S13, and maintaining the temperature at a first temperature for a first preset time after the dripping is completed, to obtain the core main structure; And / or, step S2 specifically comprises: cooling the reaction system having the core main structure to 45° C. to 50° C., then adding the first isophorone diisocyanate and the first catalyst to the reaction system, keeping the temperature at a second temperature for a second preset time, and grafting a polyurea structural unit onto the core main structure to obtain a core structure; And / or, step S3 specifically includes: S31: providing a mixture of a second acrylate monomer, a second acrylamide monomer, a second acrylonitrile, a hydroxy acrylic emulsion and a fourth solvent water to obtain a first shell reaction raw material; S32: providing a mixture of a second emulsifier, a second initiator and a fifth solvent, water, to obtain a second shell reaction raw material; S33: adjusting the temperature of the reaction system in which the core structure is generated to 80° C. to 90° C., then dripping the shell reaction raw material 1 and the shell reaction raw material 2 into the reaction system at a uniform speed, and keeping the temperature at a third temperature for a third preset time after the dripping is completed; And / or, step S4 specifically includes: cooling the reaction system having the shell main structure to 45°C~50°C, then adding the second isophorone diisocyanate and the second catalyst to the reaction system, keeping the system warm at a fourth temperature for a fourth preset time, and grafting a polyurethane structural unit on the shell main structure to obtain a water-based adhesive.

7. The method for preparing the aqueous binder according to claim 6, characterized in that: In step S13, 5% to 30% of the second core reaction raw material is mixed with the third solvent water; And / or, in step S14, before the core reaction raw material 1 and the core reaction raw material 2 are added dropwise, the rotation speed of the reaction system in step S13 is adjusted to 200 rpm to 400 rpm; and / or, in step S14, the reaction temperature is controlled not to exceed 95° C. during the process of dropwise adding the core reaction raw material 1 and the core reaction raw material 2; and / or, in step S14, the inner core reaction raw material 1 and the inner core reaction raw material 2 are dripped within 0.5 h to 1 h; And / or, in step S14, the first temperature is 88°C to 92°C, and the first preset time is 1h to 1.5h; and / or, in step S2, controlling the reaction temperature to not exceed 65° C. during the process of adding the first isophorone diisocyanate and the first catalyst; and / or, in step S2, the second temperature is 58°C to 62°C, and the second preset time is 1h to 1.5h; And / or, in step S33, before the shell reaction raw material 1 and the shell reaction raw material 2 are added dropwise, the rotation speed of the reaction system having the core structure is adjusted to 200 rpm to 400 rpm; and / or, in step S33, the reaction temperature is controlled not to exceed 95° C. during the process of dropwise adding the shell reaction raw material 1 and the shell reaction raw material 2; and / or, in step S33, the shell reaction raw material 1 and the shell reaction raw material 2 are dripped within 1 h to 2 h; And / or, in step S33, the third temperature is 88°C to 92°C, and the third preset time is 1.5h to 2.5h; and / or, in step S4, controlling the reaction temperature to not exceed 65° C. during the process of adding the second isophorone diisocyanate and the second catalyst; And / or, in step S4, the fourth temperature is 58° C. to 62° C., and the fourth preset time is 1 h to 1.5 h.

8. The method for preparing the aqueous binder according to claim 6, characterized in that: In step S11, the core reaction raw material 1 includes the following components in parts by weight: 50-150 parts of a first acrylate monomer, 10-50 parts of a first acrylamide monomer, 5-20 parts of a first acrylonitrile, 20-50 parts of an aromatic polyurea resin, and 50-150 parts of a first solvent water; And / or, in step S12, the second core reaction raw material comprises the following components in parts by weight: 5-10 parts of a first emulsifier, 2-5 parts of a first initiator, and 50-200 parts of a second solvent, water; And / or, in step S13, the weight parts of the third solvent water are 100-200 parts; And / or, in step S2, the weight parts of the first isophorone diisocyanate are 5 to 20 parts, and the weight parts of the first catalyst are 2 to 5 parts; And / or, in step S31, the shell reaction raw material 1 includes the following components in parts by weight: 100-300 parts of a second acrylate monomer, 20-80 parts of a second acrylamide monomer, 5-30 parts of a second acrylonitrile, 50-100 parts of a hydroxylated acrylic emulsion, and 50-100 parts of a fourth solvent, water; And / or, in step S32, the shell reaction raw material 2 includes the following components in parts by weight: 10-20 parts of a second emulsifier, 2-5 parts of a second initiator, and 50-100 parts of a fifth solvent, water; And / or, in step S4, the weight proportion of the second isophorone diisocyanate is 5 to 20 parts, and the weight proportion of the second catalyst is 2 to 5 parts.

9. The method for preparing the aqueous binder according to any one of claims 4 to 8, characterized in that: The first acrylate monomer and / or the first acrylamide monomer contains a hydroxyl group, and the second acrylate monomer and / or the second acrylamide monomer contains a hydroxyl group; and / or, the mass of the aromatic polyurea resin is 15% to 30% of the total mass of the first acrylate monomer, the first acrylamide monomer and the first acrylonitrile, and the mass ratio of the first isophorone diisocyanate to the aromatic polyurea resin is 1:(2 to 3); and / or, the mass of the hydroxylated acrylic emulsion is 12% to 80% of the total mass of the second acrylic ester monomer, the second acrylamide monomer and the second acrylonitrile, and the mass ratio of the second isophorone diisocyanate to the hydroxylated acrylic emulsion is 1:(5 to 10); And / or, the aromatic polyurea resin is in powder form.

10. The method for preparing the aqueous binder according to claim 9, characterized in that: The first acrylic acid ester monomer and / or the second acrylic acid ester monomer comprises one or more of hydroxyethyl acrylate, hydroxymethyl acrylate, and hydroxyethyl methacrylate; and / or, the first acrylamide monomer and / or the second acrylamide monomer include one or more of N-hydroxymethyl acrylamide and N-hydroxyethyl acrylamide; And / or, the mass of the hydroxy acrylic emulsion is 30% to 40% of the total mass of the second acrylate monomer, the second acrylamide monomer and the second acrylonitrile.

11. The method for preparing the aqueous binder according to claim 10, characterized in that: The first acrylic acid ester monomer and / or the second acrylic acid ester monomer further comprises one or more of ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isooctyl acrylate, lauryl methacrylate, butyl methacrylate, and n-octyl methacrylate; And / or, the first acrylamide monomer and / or the second acrylamide monomer further comprises one or more of methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, methyl-acyloxyethyltrimethylammonium chloride, diacetone acrylamide, and N-butoxymethyl acrylamide; And / or, the first emulsifier and the second emulsifier are respectively selected from one or more of sodium p-styrene sulfonate, sodium vinyl sulfonate and sodium dodecyl sulfonate; And / or, the first initiator and the second initiator are persulfates, and preferably the persulfate includes one or more of ammonium persulfate, potassium persulfate and sodium persulfate.

12. The method for preparing the aqueous binder according to any one of claims 4 to 8, characterized in that: The aromatic polyurea resin is selected from one or more of phenyl polyurea and dichlorophenyl polyurea; and / or, the first isophorone diisocyanate and the second isophorone diisocyanate are selected from one or more of Bayhydur ultra 2759, Bayhydur 2858 XP and Bayhydur ultra 401-70MPA / X respectively; And / or, the hydroxylated acrylic emulsion is selected from one or more of Dow Prospersetm 200, Huaguoshan Houshan 0880 and DSM Neocryl XK-540; And / or, the first catalyst and the second catalyst are respectively selected from one or more of bismuth isooctanoate, benzoyl chloride and triethylenediamine.

13. Use of the aqueous binder according to claim 1 as a negative electrode binder in a lithium ion battery.

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