Binder and preparation method thereof, negative electrode slurry, negative electrode pole piece and battery

Abstract

The invention provides a binder and a preparation method thereof, negative electrode slurry, a negative electrode plate and a battery. The binder comprises ester-modified styrene-butadiene rubber, the ester-modified styrene-butadiene rubber comprises a main chain skeleton and a plurality of branched chains, the main chain skeleton is a main chain structure of styrene-butadiene rubber, and the branched chains are obtained by polymerizing acrylate monomers. A branched chain containing an ester group is grafted and introduced to a main chain of butadiene styrene rubber, so that a lithium ion transmission channel can be effectively constructed in the binder, the ionic conductivity is improved, the transmission of lithium ions is promoted, the binder is used in a battery, and the binder can effectively reduce the internal resistance of the battery and remarkably improve the fast charge performance and high-rate discharge performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to binders and their preparation methods, negative electrode slurry, negative electrode sheet, and battery. Background Technology

[0002] Currently, the commonly used negative electrode binder is the styrene-butadiene rubber (SBR) system. However, this system has some technical defects and shortcomings when facing high-power applications. For example, the ion transport efficiency of traditional SBR binders is low, which leads to severe polarization and increased internal resistance when large currents pass through, affecting high-power performance. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in the related art. To this end, one object of this invention is to provide a binder with superior ion conductivity, which is beneficial for reducing battery internal resistance.

[0004] In one aspect of the invention, an adhesive is provided. According to an embodiment of the invention, the adhesive comprises ester-modified styrene-butadiene rubber (SBR), said ester-modified SBR comprising a main chain backbone and multiple branches connected to said main chain backbone, said main chain backbone being the main chain structure of SBR, and said branches being obtained by polymerization of acrylate monomers. Thus, by grafting branches containing ester (-COOR) polar functional groups onto the main chain of SBR, the ester groups enhance the adhesion of lithium ions (Li... + It has a certain solubilizing effect, which can effectively build lithium-ion transport channels inside the binder, improve ion conductivity, and promote lithium-ion transport. When used in batteries, this binder can effectively reduce the internal resistance of the battery and significantly improve the fast charging performance and high-rate discharge performance of the battery.

[0005] According to an embodiment of the present invention, the ester-modified styrene-butadiene rubber is obtained by polymerization of the styrene-butadiene rubber and the acrylate monomer.

[0006] According to embodiments of the present invention, the acrylate monomer includes at least one of butyl acrylate, methyl methacrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, and glycidyl methacrylate.

[0007] According to an embodiment of the present invention, the glass transition temperature of the ester-modified styrene-butadiene rubber is -15°C to 5°C.

[0008] According to embodiments of the present invention, the adhesive further includes styrene-butadiene rubber, an emulsifier, a crosslinking agent, and a dispersion medium, optionally comprising, based on the total mass of the styrene-butadiene rubber, the ester-modified styrene-butadiene rubber, the emulsifier, and the crosslinking agent: styrene-butadiene rubber: 45% to 90%; the ester-modified styrene-butadiene rubber: 5% to 30%; the emulsifier: 0.5% to 2%; and the crosslinking agent: 0.1% to 1%.

[0009] In another aspect of the invention, a method for preparing the aforementioned adhesive is provided. According to an embodiment of the invention, the method for preparing the adhesive includes: uniformly dispersing an acrylate monomer and an emulsifier in a dispersion medium to obtain a functional monomer emulsion; mixing a styrene-butadiene rubber emulsion with the functional monomer emulsion and adding an initiator thereto to perform a copolymerization reaction to obtain a polymer mixture containing ester-modified styrene-butadiene rubber; adding a crosslinking agent to the polymer mixture, and after a crosslinking reaction, obtaining the adhesive. Thus, in the above preparation method, by grafting a branch containing ester (-COOR) polar functional groups onto the main chain of styrene-butadiene rubber, the ester groups have a strong affinity for lithium ions (Li... + This material possesses a certain solubilizing effect, effectively constructing lithium-ion transport channels within the binder and improving ionic conductivity. When used in batteries, this binder can significantly enhance the battery's fast-charging and high-rate discharge performance. Simultaneously, the ester-modified styrene-butadiene rubber (SBR) retains the original high bonding strength, flexibility, and elasticity of SBR. In the ester-modified SBR, the cross-linking of the branches helps construct a network structure, enabling the ester-modified SBR to effectively buffer the volume changes of silicon-based materials, suppress electrode rebound, and improve the stability of the electrode structure. Moreover, compared to unmodified SBR, the aforementioned ester-modified SBR can better promote electrolyte wetting and lithium-ion transport, thereby helping to improve the battery's internal resistance.

[0010] According to an embodiment of the present invention, the method for preparing the adhesive further includes: adding a reducing agent to the polymer mixture before adding the crosslinking agent to remove unreacted acrylate monomers, and / or, after the crosslinking reaction, adding an alkaline neutralizing agent to the mixture to adjust the pH to 6-8.

[0011] According to embodiments of the present invention, the method for preparing the adhesive further satisfies at least one of the following conditions: the mass ratio of the acrylate monomer to the styrene-butadiene rubber in the styrene-butadiene rubber emulsion is (1:5) to (1:1); the mass ratio of the acrylate monomer to the emulsifier is (5~30):(0.5~2); the solid content of the styrene-butadiene rubber emulsion is 40%~50%; the amount of the crosslinking agent is 0.5%~3% of the total mass of polymerizable monomers in the reaction system; and the amount of the initiator is 0.1%~1.0% of the total mass of polymerizable monomers in the reaction system.

[0012] According to an embodiment of the present invention, the temperature of the copolymerization reaction is 50~80°C and the time is 4~12 hours; and / or, the temperature of the crosslinking reaction is 60~80°C and the time is 1~3 hours.

[0013] In another aspect, the present invention provides a negative electrode slurry. According to an embodiment of the present invention, the negative electrode slurry comprises: an active material, a conductive agent, a first binder, and a solvent, wherein the first binder is the binder described above, or a binder prepared by the method described above. Therefore, the negative electrode slurry has good ionic conductivity, as well as good high bonding strength, flexibility, and high elasticity; the negative electrode slurry can effectively buffer the volume change of silicon-based materials, suppress electrode rebound, and improve the stability of the electrode structure; moreover, it can better promote electrolyte wetting and lithium-ion transport, thereby helping to improve the internal resistance of the battery.

[0014] According to an embodiment of the present invention, the solid content of the first adhesive is 35% to 45%.

[0015] According to an embodiment of the present invention, the amount of the first binder is 1% to 3% based on the total weight of the remaining components in the negative electrode slurry after removing the solvent.

[0016] In another aspect, the present invention provides a negative electrode sheet. According to an embodiment of the present invention, the negative electrode sheet includes a current collector and a negative electrode active layer located on at least one surface of the current collector, the negative electrode active layer being prepared from the aforementioned negative electrode slurry. Thus, the negative electrode slurry has good ionic conductivity, which helps to improve the internal resistance of the battery; the negative electrode sheet can effectively suppress electrode rebound and improve the stability of the electrode structure. Those skilled in the art will understand that the negative electrode sheet possesses all the features and advantages of the aforementioned binder and negative electrode slurry, which will not be elaborated further here.

[0017] In another aspect, the present invention provides a battery. According to an embodiment of the invention, the battery includes the aforementioned negative electrode sheet. Therefore, the battery exhibits good electrical performance, excellent fast-charging performance, and superior high-rate discharge performance. Those skilled in the art will understand that the battery possesses all the characteristics and advantages of the aforementioned binder and negative electrode slurry, which will not be elaborated further here.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of the preparation of the adhesive in one embodiment of the present invention; Figure 2 The image shows the infrared spectrum of the ester-modified SBR prepared in Example 1. Detailed Implementation

[0020] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0021] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0022] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0023] The terms "first" and "second" used in this document are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature marked "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0024] In one aspect of the invention, an adhesive is provided. According to an embodiment of the invention, the adhesive comprises ester-modified styrene-butadiene rubber (SBR), which includes a main chain backbone and multiple branches connected to the main chain backbone. The main chain backbone is the SBR main chain structure, and the branches are obtained by polymerization of acrylate monomers. Thus, by grafting branches containing ester (-COOR) polar functional groups onto the SBR main chain, the ester groups enhance the adhesion of lithium ions (Li... + This binder exhibits a certain solubilizing effect, effectively constructing lithium-ion transport channels within the binder, enhancing ionic conductivity, and promoting lithium-ion transport. When used in batteries, this binder effectively reduces battery internal resistance, significantly improving fast-charging and high-rate discharge performance. Simultaneously, the ester-modified styrene-butadiene rubber retains the original high bonding strength, flexibility, and elasticity of styrene-butadiene rubber. In the ester-modified styrene-butadiene rubber, the cross-linking of the branches helps construct a network structure, enabling it to effectively buffer volume changes in silicon-based materials, suppress electrode rebound, and improve electrode structure stability. Moreover, compared to unmodified styrene-butadiene rubber, the aforementioned ester-modified styrene-butadiene rubber better promotes electrolyte wetting and lithium-ion transport, further contributing to improved battery internal resistance.

[0025] According to embodiments of the present invention, ester-modified styrene-butadiene rubber (ester-modified SBR) is obtained by polymerizing styrene-butadiene rubber (SBR) and acrylate monomers. During the preparation of ester-modified SBR, although the SBR is a polymerized macromolecule, unreacted double bonds (especially on butadiene units) or active sites may still exist on its chains. Under heating and the action of an initiator, the free radicals generated by the initiator attack the SBR macromolecular chain, "snatching" a hydrogen atom from it, thereby generating a free radical active site on the SBR chain. This free radical active site can initiate the polymerization reaction of the surrounding acrylate monomers. Ultimately, branches of acrylate monomer polymers are grafted onto the original SBR backbone. Therefore, it can be said that the ester-modified SBR of the present invention is essentially achieved through "graft copolymerization," forming a modified SBR with an "SBR backbone-g-ester polymer branch" structure.

[0026] According to some embodiments of the present invention, the acrylate monomers include at least one of butyl acrylate (BA), methyl methacrylate (MMA), ethyl acrylate (EA), hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), and glycidyl methacrylate (GMA). All of the above-mentioned acrylate monomers are functional monomers containing ester groups, which can polymerize under relatively mild conditions and graft onto the main chain of styrene-butadiene rubber (SBR) to obtain ester-modified SBR. Specifically, butyl acrylate (BA) can help improve the flexibility of ester-modified SBR; methyl methacrylate (MMA) and ethyl acrylate (EA) can help improve the hardness of ester-modified SBR; hydroxyethyl acrylate (HEA) and hydroxyethyl methacrylate (HEMA), by introducing hydroxyl groups into the branched chain, can provide additional crosslinking points and hydrogen bonding, further enhancing the adhesive strength and network structure of the binder; glycidyl methacrylate (GMA) can introduce epoxy groups, which have high reactivity and readily react with carboxyl groups and other groups on the SBR chain, contributing to efficient grafting modification.

[0027] According to some embodiments of the present invention, the glass transition temperature (Tg) of ester-modified styrene-butadiene rubber is -15°C to 5°C, for example, the glass transition temperatures of ester-modified styrene-butadiene rubber are -15°C, -12°C, -10°C, -8°C, -6°C, -5°C, -4°C, -2°C, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, etc. Therefore, the glass transition temperature Tg characterizes the temperature at which the polymer transitions from a glassy state to a highly elastic state, directly affecting the flexibility and low-temperature performance of the adhesive. The aforementioned glass transition temperature ensures that the ester-modified styrene-butadiene rubber remains in its highly elastic state at extremely low temperatures, retaining a certain degree of chain segment mobility and preventing complete freezing. This ensures the electrode maintains a certain level of flexibility at low temperatures, preventing the lithium-ion transport resistance in the binder from increasing indefinitely, thereby improving the battery's low-temperature discharge performance and guaranteeing its performance in cold regions. At higher temperatures (such as during hot summer days or when the battery heats up), the ester-modified styrene-butadiene rubber does not become too soft and lose its binding force on the active material in the negative electrode. The binder retains sufficient rigidity to prevent softening and deformation of the electrode structure, better suppressing electrode rebound and maintaining the stability of the electrode structure at high temperatures, while also meeting the high stability requirements of fast charging. In some embodiments, the glass transition temperature of the ester-modified styrene-butadiene rubber can be adjusted by selecting the type and proportion of acrylate monomers used in the preparation process.

[0028] According to some embodiments of the present invention, the adhesive further includes styrene-butadiene rubber, an emulsifier, a crosslinking agent, and a dispersion medium. The adhesive is an emulsion system, and the dispersion medium may be water.

[0029] In some specific embodiments, based on the total mass of styrene-butadiene rubber, ester-modified styrene-butadiene rubber, emulsifier, and crosslinking agent (i.e., based on the total mass of the remaining components in the binder excluding the dispersion medium), the binder comprises: styrene-butadiene rubber: 45%~90% (e.g., 45%, 48%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.); ester-modified styrene-butadiene rubber: 5%~30% (e.g., 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, etc.); emulsifier: 0.5%~2% (e.g., 0.5%, 0.7%, 0.9%, 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, etc.); crosslinking agent: 0.1%~ 1% (e.g., 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.). In the above binders, styrene-butadiene rubber is unmodified styrene-butadiene rubber. The binders in the above proportions have high bonding strength and flexibility, can effectively construct ion transport channels, improve ion conductivity, effectively buffer volume changes in silicon-based materials, suppress electrode rebound, and improve the stability of the electrode structure. Moreover, the presence of crosslinking agents helps to construct a crosslinked three-dimensional network structure in the binder, which can significantly improve the mechanical strength and elastic recovery ability of the binder (reducing electrode rebound) while maintaining good flexibility.

[0030] In some embodiments, the monomers of the above-mentioned styrene-butadiene rubber (SBR) and ester-modified SBR include butadiene and styrene, wherein the molar proportion of styrene is 20-35%, which can effectively ensure the film-forming properties and mechanical strength of the adhesive. Introducing styrene segments into the SBR can effectively improve the cohesive strength, hardness, and tensile strength of the adhesive; simultaneously, it can also adjust the glass transition temperature (Tg) of the SBR. Butadiene homopolymers have a very low Tg (approximately -100°C), are very soft but have poor strength, and the introduction of styrene systematically increases the Tg of the entire SBR copolymer.

[0031] In some embodiments, the emulsifier may be an allyl sulfonate, such as sodium allyl sulfonate, which is beneficial for forming a uniform emulsion system.

[0032] In some embodiments, there are no special requirements for the specific material of the crosslinking agent, and those skilled in the art can make flexible choices according to the actual situation. For example, the crosslinking agent can be an acrylate monomer with a polymerizable acrylate double bond at each end of the molecule, such as ethylene glycol diacrylate (EGDMA).

[0033] In another aspect of the invention, a method for preparing the aforementioned adhesive is provided. According to an embodiment of the invention, the method for preparing the adhesive includes: S100: Acrylic ester monomers and emulsifiers are uniformly dispersed in a dispersion medium to obtain a functional monomer emulsion.

[0034] According to some embodiments of the present invention, the acrylate monomers include at least one of butyl acrylate (BA), methyl methacrylate (MMA), ethyl acrylate (EA), hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), and glycidyl methacrylate (GMA). All of the above-mentioned acrylate monomers are functional monomers containing ester groups, which can polymerize under relatively mild conditions and be grafted onto the main chain of styrene-butadiene rubber to obtain ester-modified styrene-butadiene rubber.

[0035] According to some embodiments of the present invention, the emulsifier can be an allyl sulfonate, such as sodium allyl sulfonate, which is beneficial for forming a uniform emulsion system.

[0036] According to some embodiments of the present invention, a specific method for obtaining a functional monomer emulsion may be as follows: adding acrylate monomers and emulsifiers to deionized water and mixing them, heating the mixture to 50-70°C, and stirring until homogeneous to obtain the functional monomer emulsion.

[0037] According to some embodiments of the present invention, the mass ratio of acrylate monomer to emulsifier is (5~30):(0.5~2), for example, a mass ratio of 5:2, 5:1, 5:0.5, 10:0.5, 15:2, 15:1, 15:0.5, 20:0.5, 30:0.5, etc. This helps to form a good emulsion system.

[0038] S200: Styrene-butadiene rubber emulsion is mixed with functional monomer emulsion, and an initiator is added to carry out a copolymerization reaction to obtain a polymer mixture containing ester-modified styrene-butadiene rubber.

[0039] According to some embodiments of the present invention, although styrene-butadiene rubber (SBR) is a polymerized macromolecule, unreacted double bonds (especially on butadiene units) or active sites still exist on its chain. Under heating and the action of an initiator, the free radicals generated by the initiator attack the SBR macromolecular chain, "snatching" a hydrogen atom from it, thereby generating a free radical active site on the SBR chain. This free radical active site can initiate the polymerization reaction of the surrounding acrylate monomers, ultimately resulting in the grafting of branches of acrylate monomer polymers onto the original SBR backbone. Therefore, it can be said that the ester-modified SBR of the present invention is essentially achieved through "graft copolymerization," forming a modified SBR with an "SBR backbone-g-ester polymer branch" structure.

[0040] According to some embodiments of the present invention, the specific method for carrying out the copolymerization reaction can be as follows: adding styrene-butadiene rubber emulsion and functional monomer emulsion into a reaction vessel, then adding an initiator into the reaction vessel, and then carrying out a copolymerization reaction at a certain temperature to obtain a polymer mixture containing ester-modified styrene-butadiene rubber.

[0041] In some embodiments, the copolymerization reaction is carried out at a temperature of 50-80°C for 4-12 hours. Under these conditions, the free radicals generated by the initiator attack the SBR macromolecular chain, generating a free radical active site on the SBR chain. This free radical active site can initiate the polymerization reaction of the surrounding acrylate monomers and graft them onto the side chains of the styrene-butadiene rubber to obtain ester-modified styrene-butadiene rubber.

[0042] In some embodiments, the monomers of the above-mentioned styrene-butadiene rubber include butadiene and styrene, wherein the molar proportion of styrene is 20-35%, which can effectively ensure the film-forming properties and mechanical strength of the adhesive.

[0043] In some embodiments, the solid content of the styrene-butadiene rubber latex is 40% to 50%, such as 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, and 50%. Styrene-butadiene rubber with the above-mentioned solid content has a stable latex system, and the mixed latex obtained after mixing with the functional monomer emulsion still maintains a good latex system, facilitating the polymerization reaction.

[0044] In some embodiments, the mass ratio of acrylate monomer to styrene-butadiene rubber in the styrene-butadiene rubber emulsion is (1:5) to (1:1), such as 1:1, 1:2, 1:3, 1:4, 1:5, etc. Within the above-mentioned ratio range, it is helpful to obtain ester-modified styrene-butadiene rubber with better ester group density, which helps to improve the overall performance of the binder. While maintaining the good adhesion and elasticity of SBR, it can significantly introduce an appropriate amount of ester groups, effectively construct lithium-ion transport channels, optimize the interface, and achieve a balance between fast charging and cycle life. If the amount of acrylate monomer is relatively low, the branching rate of styrene-butadiene rubber will be low and the ester group content will be low, thus having a limited effect on improving ionic conductivity and interface properties. If the amount of acrylate monomer is relatively high, the branching density of styrene-butadiene rubber will be high and the ester group content will be high. Although it can further improve ionic conductivity, excessive modification may destroy the original flexible network structure of SBR, causing the binder itself to become brittle, reducing mechanical properties, and affecting the structural integrity of the electrode.

[0045] In some embodiments, the specific material of the initiator is not particularly required, and those skilled in the art can flexibly select it according to actual needs. For example, the initiator can be at least one of potassium persulfate and azobisisobutyronitrile. In some embodiments, the amount of initiator used is 0.1% to 1.0% of the total mass of polymerizable monomers in the reaction system, such as 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, etc. In this way, the copolymerization reaction of the monomers can be effectively initiated. The polymerizable monomers include acrylate monomers, emulsifiers, or, the polymerizable monomers include acrylate monomers.

[0046] According to some embodiments of the present invention, before proceeding to subsequent steps, i.e., before adding the crosslinking agent, the method for preparing the adhesive further includes: adding a reducing agent to the polymer mixture to remove unreacted acrylate monomers. A purified polymer mixture can be obtained.

[0047] In some specific embodiments, the reducing agent can be sodium bisulfite (NaHSO3), which is slowly added dropwise to the copolymer polymer mixture at 50°C-70°C while continuously stirring for 1-2 hours. Under these temperature conditions, sodium bisulfite can undergo an addition reaction with the carbon-carbon double bonds in the acrylate monomers, converting the polymerizable, reactive vinyl monomers into inert, water-soluble sulfonates, thus rendering them inactive. Subsequent washing or purification steps can easily remove these modified molecules.

[0048] S300: A crosslinking agent is added to the polymer mixture. After the crosslinking reaction, an adhesive is obtained. With the addition of the crosslinking agent, the crosslinking agent reacts and connects with the free radical active sites of the ester-modified styrene-butadiene rubber formed in the above steps, tightly covalently bonding the two originally independent, linear or branched ester-modified styrene-butadiene rubbers together. Countless such crosslinking points are formed in the entire system, eventually constructing a huge, three-dimensional network structure, which can significantly improve the mechanical strength and elastic recovery ability of the adhesive (reducing electrode rebound) while maintaining good flexibility.

[0049] In some embodiments, the crosslinking agent can be ethylene glycol diacrylate (EGDMA), whose molecules each have a polymerizable acrylate double bond at both ends. Under heating and the action of a residual initiator, one double bond of EGDMA reacts and connects with the active site of a free radical on an ester-modified styrene-butadiene rubber polymer chain (SBR-g-ester polymer). Subsequently, its other double bond reacts with the active site on another ester-modified styrene-butadiene rubber polymer chain. In this way, an EGDMA molecule acts as a "chemical bridge," tightly covalently bonding two originally independent, linear or branched ester-modified styrene-butadiene rubber polymer macromolecular chains together. Moreover, multiple crosslinking sites are formed throughout the system, ultimately constructing a huge, three-dimensional network structure.

[0050] In some embodiments, the amount of crosslinking agent used is 0.5% to 3% of the total mass of polymerizable monomers in the reaction system. In this way, the amount of crosslinking agent can help form a moderately tight crosslinking network, significantly improve the mechanical strength and elastic recovery ability of the binder (reduce electrode rebound), while maintaining good flexibility, thereby improving the battery's lifespan, rate performance, cycle performance, etc.

[0051] In some embodiments, the crosslinking reaction is carried out at a temperature of 60-80°C for 1-3 hours. These conditions facilitate the smooth progress of the crosslinking reaction.

[0052] In some embodiments, after the crosslinking reaction, an alkaline neutralizing agent is added to the mixture to adjust the pH to 6-8 (neutral to weakly alkaline). The addition of the alkaline neutralizing agent terminates the reaction and stabilizes the system, effectively stopping any potential free radical polymerization reactions, ensuring stable product performance, preventing continued reaction during storage that could lead to gelation or deterioration, and maintaining the stability of the emulsion system. Furthermore, when the prepared binder is used in the negative electrode slurry, the negative electrode slurry will not corrode the copper foil (negative electrode), ensuring the compatibility of the binder with the battery manufacturing process.

[0053] In some embodiments, the alkaline neutralizing agent may be an alkaline reagent such as potassium hydroxide, sodium hydroxide, ammonia, or sodium carbonate.

[0054] According to embodiments of the present invention, in the above preparation method, a branch containing an ester group (-COOR) polar functional group is grafted onto the main chain of styrene-butadiene rubber. The ester group has a positive effect on lithium ions (Li... + This material possesses a certain solubilizing effect, effectively constructing lithium-ion transport channels within the binder and improving ionic conductivity. When used in batteries, this binder can significantly enhance the battery's fast-charging and high-rate discharge performance. Simultaneously, the ester-modified styrene-butadiene rubber (SBR) retains the original high bonding strength, flexibility, and elasticity of SBR. In the ester-modified SBR, the cross-linking of the branches helps construct a network structure, enabling the ester-modified SBR to effectively buffer the volume changes of silicon-based materials, suppress electrode rebound, and improve the stability of the electrode structure. Moreover, compared to unmodified SBR, the aforementioned ester-modified SBR can better promote electrolyte wetting and lithium-ion transport, thereby helping to improve the battery's internal resistance.

[0055] In another aspect, the present invention provides a negative electrode slurry. According to an embodiment of the present invention, the negative electrode slurry comprises: an active material, a conductive agent, a first binder, and a solvent, wherein the first binder is the binder described above, or a binder prepared by the method described above. Therefore, the negative electrode slurry has good ionic conductivity, as well as good high bonding strength, flexibility, and high elasticity; the negative electrode slurry can effectively buffer the volume change of silicon-based materials, suppress electrode rebound, and improve the stability of the electrode structure; moreover, it can better promote electrolyte wetting and lithium-ion transport, thereby helping to improve the internal resistance of the battery.

[0056] According to some embodiments of the present invention, the solid content of the first binder is 35% to 45% (e.g., 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, etc.), that is, the solid content of the above-mentioned binder or the binder prepared by the above method can be adjusted to 35% to 45% by means of a dispersion medium (e.g., water) before it is used to prepare the negative electrode slurry.

[0057] According to some embodiments of the present invention, based on the total weight of the remaining components in the negative electrode slurry after removing the solvent, the amount of the first binder is 1% to 3%, such as 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, etc. The above-mentioned amounts of first binder can better construct lithium-ion transport channels in the negative electrode sheet, which helps to improve the rate performance and fast charging performance of the battery; it can effectively address the expansion problem of silicon-based materials, effectively suppress electrode rebound, and improve the stability of the electrode structure.

[0058] According to some embodiments of the present invention, in addition to the first binder, the above-mentioned negative electrode slurry may further include a second binder, which may be at least one of polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0059] According to some embodiments of the present invention, the active material can be at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, etc. Further, the silicon-based material can be selected from at least one selected from elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0060] According to some embodiments of the present invention, the conductive agent may be at least one of conductive carbon black (Super P), acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0061] According to some embodiments of the present invention, the negative electrode slurry may further include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0062] According to some embodiments of the present invention, the solvent may be water.

[0063] In another aspect, the present invention provides a negative electrode sheet. According to an embodiment of the present invention, the negative electrode sheet includes a current collector and a negative electrode active layer located on at least one surface of the current collector, the negative electrode active layer being prepared from the aforementioned negative electrode slurry. Thus, the negative electrode slurry has good ionic conductivity, which helps to improve the internal resistance of the battery; the negative electrode sheet can effectively suppress electrode rebound and improve the stability of the electrode structure. Those skilled in the art will understand that the negative electrode sheet possesses all the features and advantages of the aforementioned binder and negative electrode slurry, which will not be elaborated further here.

[0064] In some embodiments, the current collector may be copper foil.

[0065] In another aspect, the present invention provides a battery. According to an embodiment of the invention, the battery includes the aforementioned negative electrode sheet. Therefore, the battery exhibits good electrical performance, excellent fast-charging performance, and superior high-rate discharge performance. Those skilled in the art will understand that the battery possesses all the characteristics and advantages of the aforementioned binder and negative electrode slurry, which will not be elaborated further here.

[0066] Those skilled in the art will understand that, in addition to the aforementioned negative electrode, the battery also includes the essential structures and components found in conventional batteries. For example, a lithium-ion battery will also include the essential structures and components such as the positive electrode, separator, electrolyte, and casing.

[0067] According to some embodiments of the present invention, there is no specific requirement for the type of battery, and it can be any type of battery that can use the above-mentioned negative electrode sheet, such as lithium-ion battery, sodium-ion battery, solid-state battery, etc.

[0068] In some embodiments, the battery can be a single-junction battery, or a battery pack or battery stack formed by connecting multiple single-junction batteries in series.

[0069] In some embodiments, the specific shape of the battery is not limited in this invention, and the battery may be a cylindrical battery, a square battery, a blade battery, or other shaped battery structures.

[0070] Example Example 1 1. Preparation of adhesive: 118g of butyl acrylate monomer, 30g of methyl methacrylate monomer and 6.3g of emulsifier sodium allyl sulfonate were added to deionized water and mixed. The mixture was heated to 60°C and stirred until homogeneous to obtain a functional monomer emulsion. 592g of styrene-butadiene rubber latex and the functional monomer emulsion obtained above were added to a reaction vessel, and then 0.9g of potassium persulfate initiator was added to the reaction vessel. After that, a copolymerization reaction was carried out at 65°C for 8 hours to obtain a polymer mixture containing ester-modified styrene-butadiene rubber. The solid content of the styrene-butadiene rubber latex was 50%, and the mass ratio of acrylate monomer to SBR was 1:2. Add 6.7g of reducing agent NaHSO3 to the polymer mixture to remove unreacted acrylate monomers and obtain a purified polymer mixture. 4.0 g of ester-containing crosslinking agent ethylene glycol diacrylate was added to the purified polymer mixture, and the mixture was reacted at 70 °C for 2 hours to form a three-dimensional network structure. Then, the pH was adjusted to 7 with ammonia water, and the total mass of the product was adjusted to 1097.5 g with deionized water, with a solid content of 40%, to obtain the final product binder, namely ester-modified SBR emulsion. Based on the total mass of SBR, ester-modified SBR, emulsifier and crosslinking agent included in the ester-modified SBR emulsion, it includes: 68.56% SBR, 29.20% ester-modified SBR, 1.40% emulsifier and 0.84% ​​crosslinking agent. 2. Preparation of negative electrode slurry and negative electrode sheet First, the thickener CMC-Na was dissolved in deionized water to prepare a 1.5% solution. Then, artificial graphite, Super P, and polyacrylic acid (PAA) were added sequentially under high-speed stirring for 120 minutes to form a homogeneous slurry. Next, the binder ester-modified SBR emulsion was added, and the mixture was stirred at low speed for 60 minutes to obtain a negative electrode slurry with stable viscosity. Finally, the negative electrode slurry was coated onto copper foil, rolled, dried, and slit to obtain the negative electrode sheet. The mass ratio of artificial graphite, Super P, CMC-Na, polyacrylic acid (PAA), and ester-modified SBR emulsion was 96.5:1.0:0.5:1.0:1.0.

[0071] 3. Preparation of positive electrode slurry and positive electrode sheet The positive electrode active material, NCM111, is combined with PVDF binder and conductive carbon black in a mass ratio of 97.5:1.5:1.0 and coated onto aluminum foil. After coating, rolling, and slitting, the positive electrode sheet is obtained.

[0072] 4. Battery assembly In a dry environment, the positive electrode sheet, separator, and negative electrode sheet are wound into a core, then assembled into a casing, injected with electrolyte, and subjected to standard processes such as vacuum sealing, settling, formation, and capacity testing to finally produce a cylindrical battery.

[0073] Among them, the diaphragm is a porous polyethylene (PE) diaphragm; Electrolyte: LiPF6 is dissolved in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) in a volume ratio of 1:1:1, and 2% vinylene carbonate (VC) is added as a film-forming additive.

[0074] Example 2 The difference from Example 1 is that the mass ratio of acrylate monomer to SBR is 1:1 (by changing the amount of styrene-butadiene rubber latex). The final ester-modified SBR latex contains, based on the total mass of SBR, ester-modified SBR, emulsifier, and crosslinker, 52.65% SBR, 44.72% ester-modified SBR, 1.58% emulsifier, and 1.05% crosslinker.

[0075] Example 3 The difference from Example 1 is that the mass ratio of acrylate monomer to SBR is 1:3 (by changing the amount of styrene-butadiene rubber latex). The final ester-modified SBR latex contains, based on the total mass of SBR, ester-modified SBR, emulsifier, and crosslinker, 76.09% SBR, 21.49% ester-modified SBR, 1.52% emulsifier, and 0.90% crosslinker.

[0076] Example 4 The difference from Example 1 is that the mass ratio of acrylate monomer to SBR is 1:4 (by changing the amount of styrene-butadiene rubber latex). The final ester-modified SBR latex contains, based on the total mass of SBR, ester-modified SBR, emulsifier, and crosslinker, 80.92% SBR, 17.14% ester-modified SBR, 1.21% emulsifier, and 0.73% crosslinker.

[0077] Example 5 The difference from Example 1 is that the mass ratio of acrylate monomer to SBR is 1:5 (by changing the amount of styrene-butadiene rubber latex). The final ester-modified SBR latex contains, based on the total mass of SBR, ester-modified SBR, emulsifier, and crosslinker, 84.05% SBR, 14.34% ester-modified SBR, 1.01% emulsifier, and 0.60% crosslinker.

[0078] Example 6 The difference from Example 1 is that the mass ratio of acrylate monomer to SBR is 1:6 (by changing the amount of styrene-butadiene rubber latex). The final ester-modified SBR latex contains, based on the total mass of SBR, ester-modified SBR, emulsifier, and crosslinker, 85.20% SBR, 12.06% ester-modified SBR, 1.71% emulsifier, and 1.03% crosslinker.

[0079] Example 7 The difference from Example 1 is that the mass ratio of acrylate monomer to SBR is 1.5:1 (by changing the amount of styrene-butadiene rubber latex). The final ester-modified SBR latex contains, based on the total mass of SBR, ester-modified SBR, emulsifier, and crosslinker, 43.31% SBR, 55.03% ester-modified SBR, 0.87% emulsifier, and 0.79% crosslinker.

[0080] Example 8 The difference from Example 1 is that the acrylate monomers are 118g of butyl acrylate (BA) and 30g of hydroxyethyl acrylate (HEA).

[0081] Example 9 The difference from Example 1 is that the acrylate monomers are 118g of ethyl acrylate (EA) and 30g of glycidyl methacrylate (GMA).

[0082] Example 10 The difference from Example 1 is that the acrylate monomer is 148g of butyl acrylate (BA).

[0083] Example 11 The difference from Example 1 is that the acrylate monomer is 148g of methyl methacrylate (MMA).

[0084] Example 12 The difference from Example 1 is that the mass ratio of artificial graphite, Super P, CMC-Na, polyacrylic acid (PAA) and ester-modified SBR emulsion is 95.5:1.0:0.5:1.0:2.0 during the preparation of negative electrode slurry and negative electrode sheet.

[0085] Example 13 The difference from Example 1 is that the mass ratio of artificial graphite, Super P, CMC-Na, polyacrylic acid (PAA) and ester-modified SBR emulsion is 94.5:1.0:0.5:1.0:3.0 during the preparation of negative electrode slurry and negative electrode sheet.

[0086] Example 14 The difference from Example 1 is that the mass ratio of artificial graphite, Super P, CMC-Na, polyacrylic acid (PAA) and ester-modified SBR emulsion is 93.5:1.0:0.5:1.0:4.0 during the preparation of negative electrode slurry and negative electrode sheet.

[0087] Example 15 The difference from Example 1 is that the mass ratio of artificial graphite, Super P, CMC-Na, polyacrylic acid (PAA) and ester-modified SBR emulsion is 97:1.0:0.5:1.0:0.5 during the preparation of negative electrode slurry and negative electrode sheet.

[0088] Comparative Example 1 1. Preparation of negative electrode slurry and negative electrode sheet First, the thickener CMC-Na was dissolved in deionized water to prepare a 1.5% solution. Then, artificial graphite, Super P, and polyacrylic acid (PAA) were added sequentially under high-speed stirring for 120 minutes to form a homogeneous slurry. Next, the binder SBR emulsion was added, and the mixture was stirred at low speed for 60 minutes to obtain a negative electrode slurry with stable viscosity. Finally, the negative electrode slurry was coated onto copper foil, rolled, dried, and slit to obtain the negative electrode sheet. The mass ratio of artificial graphite, Super P, CMC-Na, polyacrylic acid (PAA), and SBR emulsion was 96.5:1.0:0.5:1.0:1.0.

[0089] 2. Preparation of positive electrode slurry and positive electrode sheet The positive electrode active material, NCM111, is combined with PVDF binder and conductive carbon black in a mass ratio of 97.5:1.5:1.0 and coated onto aluminum foil. After coating, rolling, and slitting, the positive electrode sheet is obtained.

[0090] 3. Assemble the battery In a dry environment, the positive electrode sheet, separator, and negative electrode sheet are wound into a core, then assembled into a casing, injected with electrolyte, and subjected to standard processes such as vacuum sealing, settling, formation, and capacity testing to finally produce a cylindrical battery.

[0091] Among them, the diaphragm is a porous polyethylene (PE) diaphragm; Electrolyte: LiPF6 is dissolved in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) in a volume ratio of 1:1:1, and 2% vinylene carbonate (VC) is added as a film-forming additive.

[0092] Infrared spectroscopy was performed on the ester-modified SBR prepared in Example 1. The test results can be found in [reference needed]. Figure 2 , Figure 2 The text appears to be a mix of Chinese characters and symbols, possibly representing a corrupted or incomplete translation. A direct translation wouldn't be meaningful without further context. 2917cm -1 and 2850cm -1 The peaks are CH stretching vibration peaks of -CH2- and -CH3-, respectively, which are characteristic peaks shared by the SBR backbone and alkane segments of ester monomers, proving the existence of the organic SBR backbone. 1730cm -1 Characteristic peak of strong stretching vibration of C=O in ester group (-COOR); 1601cm -1 1583cm -1 1492cm -1 and 1451cm -1 The C=C skeletal vibration, which belongs to the benzene ring, originates from the styrene unit in the SBR and is one of the characteristic peaks of the SBR. 1152cm -1 The stretching vibration of COC (from the ester group) further corroborates the existence of the ester group.

[0093] The electrodes and batteries prepared in Examples 1-15 and Comparative Example 1 were subjected to performance tests, and the test results are shown in Table 1. The test methods for the relevant performance are as follows: Tensile strength (MPa): The ester-modified SBR emulsion or the SBR emulsion in Comparative Example 1 is cast onto a polytetrafluoroethylene (PTFE) plate and dried into a complete adhesive film of uniform thickness (~0.5 mm). The adhesive film is cut into standard dumbbell-shaped specimens and tested using a universal testing machine at a fixed tensile rate until the adhesive film breaks. Tensile strength = maximum tensile force / initial cross-sectional area of ​​the specimen. This indicator reflects the mechanical strength of the adhesive matrix.

[0094] Roller peel force (N): A small piece of standard masking tape is tightly adhered to the surface of the freshly rolled negative electrode sheet, and then the electrode sheet is torn at a constant speed and at a 180° angle using a tensile testing machine. Note: The two sets of roller peel force data represent the two sides of the electrode sheet, i.e., sides A and B. This is used to evaluate the cohesive force of the adhesive and its adhesion to the current collector.

[0095] 24h negative electrode sheet rebound rate (%): Immediately after rolling, the thickness of the negative electrode sheet is measured and recorded as H0; the negative electrode sheet is placed unrestrained at room temperature for 24 hours, and the thickness at the same location is measured again under the same conditions and recorded as H1. Rebound rate = [(H1-H0) / H0] × 100%. This reflects the elastic recovery and stress relaxation characteristics of the binder system.

[0096] Battery internal resistance DCR (mΩ): The battery was placed in a constant temperature environment at 25℃ until the temperature stabilized, and then charged to 50% SOC. The current open-circuit voltage U0 of the battery was recorded. The battery was continuously discharged at a constant current of 1C for 30 seconds. Record again: Immediately after the pulse ends, the battery voltage U1 is recorded. According to Ohm's law, DC internal resistance DCR = (U0 - U1) / I, where I is the pulse current value.

[0097] Cycle capacity retention (%): At 25°C, the battery is charged and discharged at a rate of 0.5C, and the initial discharge capacity is recorded as C0. At the same temperature, the battery is continuously charged and discharged at 0.5C / 0.5C. After a certain number of cycles (100 cycles), the current discharge capacity C is tested again at a rate of 0.2C. n Capacity retention rate = (C n / C0)×100%.

[0098] Rate performance (%): At 25℃, the battery is charged and discharged at a low rate of 0.2C, and the discharge capacity is measured as the baseline capacity C1. After charging the same battery to the same state, it is discharged at different high rates (0.33C, 0.5C, 1C, 2C, 3C, etc.). The actual discharge capacity C2 at each high rate is recorded. Rate performance (capacity retention) = (C2 / C1)×100%.

[0099] Table 1

[0100] As can be seen from the data in Table 1, compared with Comparative Example 1, the ester-modified styrene-butadiene rubber in the embodiments of the present invention has a lower glass transition temperature, which results in a lower rebound rate of the corresponding negative electrode sheet and better improves the stability of the electrode structure. Furthermore, the ester-modified SBR film in the embodiments exhibits excellent tensile strength, indicating that the modification of styrene-butadiene rubber with ester groups in the present invention does not damage the original mechanical strength of the styrene-butadiene rubber.

[0101] Compared to Comparative Example 1, the negative electrode sheet in the embodiments of the present invention has a higher roll-press peeling force, indicating that the styrene-butadiene rubber of the present invention has better adhesion after ester group modification.

[0102] Compared to Comparative Example 1, the battery in this embodiment can achieve a better balance between rate capability and cycle life, indicating that the battery in this embodiment can better achieve a balance between fast charging and cycle life, thus comprehensively improving battery performance.

[0103] As can be seen from Examples 1 to 7, when the mass ratio of acrylate monomer to SBR is between (1:5) and (1:1), the performance of the negative electrode and the battery can be balanced in all aspects, thus comprehensively improving the battery's performance. If the amount of SBR is too high (as in Example 6), the tensile strength of the ester-modified SBR film and the peel force of the negative electrode are adversely affected, and the rate and cycle life are also affected to a certain extent. If the amount of monomer is too high (as in Example 7), the cycle life of the battery may be significantly affected.

[0104] As can be seen from Examples 1 and 12-15, when the amount of ester-modified SBR emulsion in the negative electrode slurry is between 1% and 3%, it can balance the performance of the negative electrode sheet and the battery in various aspects, thus comprehensively improving the battery's performance. If the amount of ester-modified SBR emulsion is too high (as in Example 14), the cycle life of the battery may be significantly affected. If the amount of ester-modified SBR emulsion is too low (as in Example 15), the rolling peeling force of the negative electrode sheet will be low, which will affect the stability of the electrode structure.

[0105] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0106] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An adhesive, characterized in that, The invention includes ester-modified styrene-butadiene rubber, wherein the ester-modified styrene-butadiene rubber comprises a main chain backbone and multiple branches connected to the main chain backbone, wherein the main chain backbone is the main chain structure of styrene-butadiene rubber, and the branches are obtained by polymerization of acrylate monomers.

2. The adhesive according to claim 1, characterized in that, The ester-modified styrene-butadiene rubber is obtained by polymerizing the styrene-butadiene rubber and the acrylate monomer.

3. The adhesive according to claim 1 or 2, characterized in that, The acrylate monomers include at least one of butyl acrylate, methyl methacrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, and glycidyl methacrylate.

4. The adhesive according to claim 1 or 2, characterized in that, The glass transition temperature of the ester-modified styrene-butadiene rubber is -15°C to 5°C.

5. The adhesive according to claim 1 or 2, characterized in that, It also includes styrene-butadiene rubber, emulsifiers, crosslinking agents, and dispersion media. Optionally, based on the total mass of the styrene-butadiene rubber, the ester-modified styrene-butadiene rubber, the emulsifier, and the crosslinking agent, it includes: The styrene-butadiene rubber: 45% ~ 90%; The ester-modified styrene-butadiene rubber is 5% to 50%; The emulsifier: 0.5% ~ 3%; The crosslinking agent: 0.1% ~ 2%.

6. A method for preparing the adhesive according to any one of claims 1 to 5, characterized in that, include: The acrylate monomer and emulsifier are uniformly dispersed in a dispersion medium to obtain a functional monomer emulsion. The styrene-butadiene rubber emulsion is mixed with the functional monomer emulsion, and an initiator is added to carry out a copolymerization reaction to obtain a polymer mixture containing ester-modified styrene-butadiene rubber. A crosslinking agent is added to the polymer mixture, and after the crosslinking reaction, an adhesive is obtained.

7. The method according to claim 6, characterized in that, Also includes: Before adding the crosslinking agent, a reducing agent is added to the polymer mixture to remove unreacted acrylate monomers. And / or, after the crosslinking reaction, an alkaline neutralizing agent is added to the mixture to adjust the pH to 6-8.

8. The method according to claim 6 or 7, characterized in that, At least one of the following conditions must be met: The mass ratio of the acrylate monomer to the styrene-butadiene rubber in the styrene-butadiene rubber emulsion is (1:5) to (1:1). The mass ratio of the acrylate monomer to the emulsifier is (5~30):(0.5~2). The solid content of the styrene-butadiene rubber latex is 40%~50%; The amount of the crosslinking agent is 0.5% to 3% of the total mass of polymerizable monomers in the reaction system; The amount of the initiator is 0.1% to 1.0% of the total mass of polymerizable monomers in the reaction system.

9. The method according to claim 6 or 7, characterized in that, The copolymerization reaction is carried out at a temperature of 50-80°C for 4-12 hours. And / or, the crosslinking reaction is carried out at a temperature of 60-80°C for 1-3 hours.

10. A negative electrode slurry, characterized in that, include: The active substance, conductive agent, first binder, and solvent, wherein the first binder is the binder according to any one of claims 1 to 5, or the binder prepared by the method according to any one of claims 6 to 9.

11. The negative electrode slurry according to claim 10, characterized in that, The solid content of the first adhesive is 35% to 45%.

12. The negative electrode slurry according to claim 10 or 11, characterized in that, Based on the total weight of the remaining components in the negative electrode slurry after removing the solvent, the amount of the first binder is 1% to 3%.

13. A negative electrode sheet, characterized in that, It includes a current collector and a negative electrode active layer located on at least one surface of the current collector, the negative electrode active layer being prepared from the negative electrode slurry according to any one of claims 10 to 12.

14. A battery, characterized in that, Includes the negative electrode sheet as described in claim 13.

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