Copolymers and binders for lithium batteries

Abstract

The present application discloses a copolymer and a binder for a lithium battery. The copolymer comprises a polymerized unit derived from the following monomers: vinylidene fluoride, a first modified monomer shown in formula I, and a second modified monomer shown in formula II. The copolymer of the present application can be used as a binder with excellent adhesion and ionic conductivity, and the binder can be used to prepare a positive electrode plate of a lithium battery, and a lithium battery with low internal resistance, high rate performance and excellent cycle life can be prepared.

Description

Technical Field

[0001] The present application relates to the field of copolymer synthesis, and more specifically to a modified polyvinylidene fluoride copolymer, a synthesis process of the copolymer, and use of the copolymer as a binder for lithium battery manufacturing. Background Art

[0002] As a traditional electrochemical energy storage and conversion device, lithium batteries are widely used in the electronics industry, national power grid system, and even power vehicles due to their advantages of high energy density, stable cycle, and fast charge and discharge. However, with the rapid development of new energy technologies, people are currently putting forward higher requirements on the performance of lithium batteries, such as cycle life, discharge rate, and rate performance.

[0003] In order to improve the energy density without changing the volume of lithium batteries, various improved active positive electrode materials for lithium batteries are constantly being developed. On the one hand, the defects of these materials themselves still limit the improvement of battery performance. On the other hand, the research and development cycle of this technical route is long and it is difficult to meet the immediate needs of the market. Therefore, in addition to modifying the material itself, using targeted binders to make up for the defects of positive electrode materials is also a solution worth looking forward to. In the positive electrode of lithium batteries, binders are mainly used to stabilize the electrode structure. Although the content is small, it has a greater impact on battery performance. High-energy-density lithium batteries also put forward new requirements for the current mainstream positive electrode binders. On the one hand, in high-energy-density lithium batteries, the positive electrode binder is required to reduce the amount of addition while maintaining the same peeling force; on the other hand, it is required to minimize the negative impact of the positive electrode binder, which is inherently insulating, on the transmission of ions and electrons. In order to improve the competitiveness of their own products, major lithium battery manufacturers hope to develop new positive electrode binders that can solve the above technical problems. To this end, many scientific research institutions and R&D centers of enterprises have invested a lot of energy, time and resources in recent years to develop modification technologies that can overcome the above problems or new alternative materials that can be truly industrialized, but so far, no satisfactory results have been achieved. Therefore, the field still urgently hopes to develop a new technology that can solve the above technical problems. Summary of the invention

[0004] In view of the above problems, the inventors of the present application have conducted a lot of in-depth research and successfully developed a copolymer with excellent performance, which can be used as a binder to manufacture positive electrode plates of lithium batteries, effectively solving the long-standing problem that urgently needs to be solved in the prior art.

[0005] The first aspect of the present application provides a copolymer comprising polymerized units derived from the following monomers:

[0006] Vinylidene fluoride;

[0007] The first modified monomer has a structural formula shown in Formula I:

[0008]

[0009] In Formula I, R1 represents a hydrogen atom, a methyl group or an ethyl group; R2 represents a (C1-C16)alkylene group, a (C3-C16)cycloalkylene group, a (C6-C16)arylene group, a (C6-C16)heteroarylene group, or -[(C1-C16)alkylene-O] n -, -(C1-C16)alkylene-(ethylene oxide)-, or -(ethylene oxide)-(C1-C16)alkylene-; R3 represents hydroxyl, -(C1-C6 alkyl)hydroxyl, -O-(C1-C6 alkyl)hydroxyl, amino, -(C1-C6 alkyl)amino, -O-(C1-C6 alkyl)amino, -ethylene oxide, -O-ethylene oxide, -(C1-C6 alkyl)ethylene oxide, or -O-(C1-C6 alkyl)ethylene oxide; wherein n represents an integer from 1 to 20;

[0010] The second modified monomer has the structural formula shown in Formula II:

[0011]

[0012] In formula II, R4 represents hydrogen or (C1-C6) alkyl; R5 represents (C2-C12) alkylene or (C2-C12) alkylene substituted by one or more substituents selected from the following: (C1-C12) alkyl, (C1-C12) alkoxy, (C3-C12) cycloalkyl, (C3-C12) cycloalkoxy, (C6-C12) aryl, (C6-C12) aryloxy, (C7-C12) aralkyl, (C7-C12) aralkyloxy, fluorine, chlorine, bromine, and iodine; R6 represents a hydrogen atom, a methyl or ethyl group; wherein m represents an integer from 2 to 20.

[0013] According to an embodiment of the first aspect of the present application, based on 100 parts by weight of the vinylidene fluoride, the content of the first modified monomer is 0.1 to 16 parts by weight, and the content of the second modified monomer is 0.1 to 18 parts by weight. According to another embodiment of the first aspect of the present application, the weight average molecular weight Mw of the copolymer is 5,000 to 1,200,000.

[0014] According to another embodiment of the first aspect of the present application, the first modifying monomer is selected from one or more of the following: hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 1-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, hydroxyisopropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 1-hydroxybutyl (meth)acrylate, hydroxyisobutyl (meth)acrylate, hydroxy-tert-butyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, 3-hydroxycyclohexyl (meth)acrylate, 2-hydroxycyclohexyl (meth)acrylate, (4-hydroxycyclohexyl)methyl (meth)acrylate, glycidyl (meth)acrylate, oligoethylene glycol (meth)acrylate, Acrylates (wherein the degree of polymerization of the oligoethylene glycol is 2 to 20), aminomethyl (meth)acrylate, 2-aminoethyl (meth)acrylate, 1-aminoethyl (meth)acrylate, 2-aminopropyl (meth)acrylate, 3-aminopropyl (meth)acrylate, aminoisopropyl (meth)acrylate, 4-aminobutyl (meth)acrylate, 3-aminobutyl (meth)acrylate, 2-aminobutyl (meth)acrylate, 1-aminoethyl (meth)acrylate, The invention also includes aminobutyl (meth)acrylate, aminoisobutyl (meth)acrylate, aminotert-butyl (meth)acrylate, 5-aminopentyl (meth)acrylate, 6-aminohexyl (meth)acrylate, 4-aminocyclohexyl (meth)acrylate, 3-aminocyclohexyl (meth)acrylate, 2-aminocyclohexyl (meth)acrylate, (4-aminocyclohexyl)methyl (meth)acrylate, and amino-terminated oligoethylene glycol (meth)acrylate (wherein the degree of polymerization of the oligoethylene glycol is 2 to 20).

[0015] According to another embodiment of the first aspect of the present application, the second modified monomer has a structural formula shown in Formula II, wherein R4 represents hydrogen or methyl; R5 represents ethylene; R6 represents a hydrogen atom or a methyl; and m represents an integer of 3-10.

[0016] According to another embodiment of the first aspect of the present application, the copolymer further comprises one or more of the following components or their residues: a dispersant, a chain transfer agent, an initiator. According to another embodiment of the first aspect of the present application, the dispersant is selected from one or more of the following: methyl hydroxymethyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxymethyl cellulose, ethyl hydroxyethyl cellulose, polyvinyl alcohol. According to another embodiment of the first aspect of the present application, the chain transfer agent is selected from one or more of the following: ethyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl malonate, acetone, methyl propionate, ethyl propionate, diethyl succinate. According to another embodiment of the first aspect of the present application, the initiator is selected from one or more of the following: diethylhexyl peroxydicarbonate, tert-butyl peroxyneodecanoate, diisopropyl peroxydicarbonate, dodecyl peroxide, dibenzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate.

[0017] The second aspect of the present application provides a binder, which is a binder for manufacturing positive electrode plates of lithium batteries, and the binder contains the copolymer of the present application.

[0018] The third aspect of the present application provides a method for preparing the copolymer of the present application, the method comprising: copolymerizing the vinylidene fluoride, a first modified monomer and a second modified monomer to form the copolymer.

[0019] According to one embodiment of the third aspect of the present application, the method includes: in the presence of a dispersant, a chain transfer agent and an initiator, continuously adding the vinylidene fluoride, the first modified monomer and the second modified monomer into a reactor, so that the vinylidene fluoride, the first modified monomer and the second modified monomer undergo a copolymerization reaction to form the copolymer.

[0020] The fourth aspect of the present application provides a lithium battery, which includes a housing, a negative electrode collector, a negative electrode plate, a separator, a positive electrode plate, a positive electrode collector and an electrolyte, and the positive electrode plate contains the binder of the present application.

[0021] A fifth aspect of the present application provides a method for manufacturing a lithium battery, the method comprising:

[0022] (a) providing a positive electrode slurry, wherein the positive electrode slurry comprises a solvent, a positive electrode active material and a positive electrode binder, and using the positive electrode slurry to manufacture the positive electrode sheet;

[0023] (b) manufacturing a negative electrode sheet;

[0024] (c) applying a positive electrode current collector to the positive electrode sheet, applying a negative electrode current collector to the negative electrode sheet, forming a stacked structure including the negative electrode current collector, the negative electrode sheet, the separator, the positive electrode sheet and the positive electrode current collector, placing the stacked structure in a housing, and pouring electrolyte into the housing to form the lithium battery;

[0025] The positive electrode binder is the binder of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the following paragraphs, various embodiments of the present application are discussed in conjunction with the accompanying drawings. However, it should be noted that the embodiments shown in the accompanying drawings and described in detail below are only some preferred embodiments of the present application, and the scope of protection of the present application is defined by the claims, but not limited to these preferred embodiments. In addition, for the purpose of clear display, the various components shown in the drawings of the specification are not drawn according to the true scale.

[0027] Figure 1 The structure of a lithium battery manufactured according to one embodiment of the present application is shown, in which the positive electrode sheet of the lithium battery is manufactured using the copolymer of the present invention as a binder. DETAILED DESCRIPTION

[0028] "Range" disclosed herein is in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges that can be defined in this way are inclusive and combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0029] In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.

[0030] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0031] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0032] In this application, if there is no special explanation, the "including" mentioned herein means open or closed. For example, the "including" may mean that other components not listed may also be included, or only the listed components may be included.

[0033] The copolymer of the present application is prepared by copolymerization of the vinylidene fluoride, the first modified monomer and the second modified monomer, and the copolymer prepared in this way contains polymerization units (copolymerization units) derived from the vinylidene fluoride, the first modified monomer and the second modified monomer.

[0034] In the present application, the vinylidene fluoride refers to 1,1-difluoroethylene.

[0035] According to one embodiment of the present application, the first modified monomer has a structural formula shown in Formula I:

[0036]

[0037] In Formula I, R1 represents a hydrogen atom, a methyl group or an ethyl group; R2 represents a (C1-C16)alkylene group, a (C3-C16)cycloalkylene group, a (C6-C16)arylene group, a (C6-C16)heteroarylene group, or -[(C1-C16)alkylene-O] n -, -(C1-C16)alkylene-(ethylene oxide)-, or -(ethylene oxide)-(C1-C16)alkylene-; R3 represents hydroxyl, -(C1-C6 alkyl)hydroxyl, -O-(C1-C6 alkyl)hydroxyl, amino, -(C1-C6 alkyl)amino, -O-(C1-C6 alkyl)amino, -ethylene oxide, -O-ethylene oxide, -(C1-C6 alkyl)ethylene oxide, or -O-(C1-C6 alkyl)ethylene oxide; wherein n represents an integer of 1-20, for example 2-18, or 3-16, or 4-12, or 4-10, or 4-8, or 4-6.

[0038] According to another embodiment of the present application, R1 represents a hydrogen atom or a methyl group; wherein R2 represents a (C1-C12) alkylene group, a (C3-C12) cycloalkylene group, a (C6-C12) arylene group, a (C6-C12) heteroarylene group, -[(C1-C12) alkylene-O] n-, -(C1-C12)alkylene-(ethylene oxide)-, or -(ethylene oxide)-(C1-C12)alkylene-; R3 represents hydroxyl, -(C1-C4 alkyl)hydroxyl, -O-(C1-C4 alkyl)hydroxyl, amino, -(C1-C4 alkyl)amino, -O-(C1-C4 alkyl)amino, -ethylene oxide, -O-ethylene oxide, -(C1-C4 alkyl)ethylene oxide, or -O-(C1-C4 alkyl)ethylene oxide. According to another embodiment of the present application, R1 represents a hydrogen atom or a methyl group; wherein R2 represents (C1-C6)alkylene, (C3-C6)cycloalkylene, (C6-C8)arylene, (C6-C8)heteroarylene, -[(C1-C6)alkylene-O] n -, -(C1-C6)alkylene-(ethylene oxide)-, or -(ethylene oxide)-(C1-C6)alkylene-; R3 represents hydroxyl, -(C1-C3 alkyl)hydroxyl, -O-(C1-C3 alkyl)hydroxyl, amino, -(C1-C3 alkyl)amino, -O-(C1-C3 alkyl)amino, -ethylene oxide, -O-ethylene oxide, -(C1-C3 alkyl)ethylene oxide, or -O-(C1-C3 alkyl)ethylene oxide.

[0039] According to another embodiment of the present application, the first modifying monomer is selected from one or more of the following: hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 1-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, hydroxyisopropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 1-hydroxybutyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate. Hydroxyisobutyl acrylate, hydroxy-tert-butyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, 3-hydroxycyclohexyl (meth)acrylate, 2-hydroxycyclohexyl (meth)acrylate, (4-hydroxycyclohexyl)methyl (meth)acrylate, glycidyl (meth)acrylate, oligoethylene glycol (meth)acrylate (wherein the degree of polymerization of the oligoethylene glycol is 2 to 20, for example, the degree of polymerization of the oligoethylene glycol can be 3 to 16, or 4-12, or 4-10, or 4-8, or 4-6), aminomethyl (meth)acrylate, 2-aminoethyl (meth)acrylate, 1-aminoethyl (meth)acrylate, 2-aminopropyl (meth)acrylate, 3-aminopropyl (meth)acrylate, aminoisopropyl (meth)acrylate, 4-aminobutyl (meth)acrylate, 3-aminobutyl (meth)acrylate, 2-aminobutyl (meth)acrylate, 1-aminobutyl (meth)acrylate, amino isobutyl ester, amino-tert-butyl (meth)acrylate, 5-aminopentyl (meth)acrylate, 6-aminohexyl (meth)acrylate, 4-aminocyclohexyl (meth)acrylate, 3-aminocyclohexyl (meth)acrylate, 2-aminocyclohexyl (meth)acrylate, (4-aminocyclohexyl)methyl (meth)acrylate, amino-terminated oligoethylene glycol (meth)acrylate (wherein the degree of polymerization of the oligoethylene glycol is 2 to 20, for example 3-16, or 4-12, or 4-10, or 4-8, or 4-6).

[0040] In the present application, when describing oligoethylene glycol (meth)acrylate or amino-terminated oligoethylene glycol (meth)acrylate, the expression "oligoethylene glycol" is used to describe the structure in these compounds, that is, two or more ethylene glycols are polymerized to form an oligoethylene glycol chain, and the hydroxyl group at one end of the oligoethylene glycol chain is esterified with (meth)acrylic acid; while amino-terminated oligoethylene glycol (meth)acrylate means that the hydroxyl group at one end of the above oligoethylene glycol chain is esterified with (meth)acrylic acid, and the hydroxyl group at the other end is replaced by an amino group. The degree of polymerization of the oligoethylene glycol (meth)acrylate or amino-terminated oligoethylene glycol (meth)acrylate is as described above, and the "degree of polymerization" means the number of ethylene glycol molecules that condense (condensation reaction or polycondensation reaction) with each other to form the oligoethylene glycol.

[0041] According to one embodiment of the present application, in the copolymer, when the total weight of vinylidene fluoride is 100 parts by weight, the amount of the first modifying monomer can be 0.1-16 parts by weight, for example, 0.2-15 parts by weight, or 0.3-12 parts by weight, or 0.4-10 parts by weight, or 0.5-8 parts by weight, or 0.6-6 parts by weight, or 0.7-5 parts by weight, or 0.8-4 parts by weight, or 1-3 parts by weight, or 1.1-2.5 parts by weight, or 1.2-2 parts by weight, or 1.3-1.5 parts by weight, or can be within the numerical range obtained by combining any two of the above end values.

[0042] According to one embodiment of the present application, the second modified monomer has a structure shown in Formula II:

[0043]

[0044] In formula II, R4 represents hydrogen or (C1-C6) alkyl; R5 represents (C2-C12) alkylene or (C2-C12) alkylene substituted by one or more substituents selected from the following: (C1-C12) alkyl, (C1-C12) alkoxy, (C3-C12) cycloalkyl, (C3-C12) cycloalkyloxy, (C6-C12) aryl, (C6-C12) aryloxy, (C7-C12) aralkyl, (C7-C12) aralkyloxy, fluorine, chlorine, bromine, and iodine; R6 represents a hydrogen atom, a methyl or ethyl group; wherein m represents an integer of 2-20, for example 2-18, or 3-16, or 4-12, or 4-10, or 4-8, or 4-6.

[0045] According to another embodiment of the present application, R4 represents hydrogen or (C1-C4) alkyl; R5 represents (C2-C10) alkylene or (C2-C10) alkylene substituted by one or more substituents selected from the following: (C1-C10) alkyl, (C1-C10) alkoxy, (C3-C10) cycloalkyl, (C3-C10) cycloalkoxy, (C6-C10) aryl, (C6-C10) aryloxy, (C7-C10) aralkyl, (C7-C10) aralkyloxy, fluorine, chlorine, bromine, and iodine; R6 represents a hydrogen atom or a methyl group. According to another embodiment of the present application, R4 represents hydrogen or (C1-C3) alkyl; R5 represents (C2-C8) alkylene or (C2-C8) alkylene substituted by one or more substituents selected from the following: (C1-C8) alkyl, (C1-C8) alkoxy, (C3-C8) cycloalkyl, (C3-C8) cycloalkyloxy, (C6-C8) aryl, (C6-C8) aryloxy, (C7-C8) aralkyl, (C7-C8) aralkyloxy, fluorine, chlorine, bromine, and iodine; R6 represents a hydrogen atom or a methyl group.

[0046] According to another embodiment of the present application, the second modified monomer has a structural formula shown in Formula II, wherein R4 represents hydrogen or methyl; R5 represents ethylene; and R6 represents a hydrogen atom or a methyl. According to a preferred embodiment, the second modified monomer may be polyethylene glycol (meth) acrylate or polyethylene glycol monomethyl ether (meth) acrylate, wherein the degree of polymerization of the polyethylene glycol is as described above.

[0047] According to one embodiment of the present application, in the copolymer, when the total weight of vinylidene fluoride is 100 parts by weight, the amount of the second modifying monomer can be 0.1-18 parts by weight, for example, 0.2-16 parts by weight, or 0.3-14 parts by weight, or 0.4-12 parts by weight, or 0.5-11 parts by weight, or 0.6-10 parts by weight, or 0.7-9 parts by weight, or 0.8-8 parts by weight, or 0.9-7 parts by weight, or 1-6 parts by weight, or 1.1-5 parts by weight, or 1.2-4 parts by weight, or 1.25-3 parts by weight, or 1.3-2 parts by weight, or 1.3-1.5 parts by weight, or can be within the numerical range obtained by combining any two of the above end values.

[0048] According to one embodiment of the present application, the molecular weight (expressed as weight average molecular weight Mw) of the copolymer of the present application is 5,000 to 1,200,000, for example, it can be 10,000 to 1,100,000, or 20,000 to 1,050,000, or 50,000 to 1,000,000, or 100,000 to 950,000, or 200,000 to 900,000, or 500,000 to 850,000, or 600,000 to 800,000, or 650,000 to 780,000, or 700,000 to 750,000, or it can be within the numerical range obtained by combining any two of the above end values. In the present invention, the Mw of the copolymer can be characterized by techniques known in the art. For example, the Mw testing techniques of the copolymer can include light scattering, small-angle laser light scattering, gel filtration chromatography, etc., and can be tested according to various standard testing processes at home and abroad, such as GB / T 6598-1986, ASTM D4001-20, HG / T 4744-2014, etc.

[0049] According to another embodiment of the present application, during the preparation of the copolymer, one or more of the following components may be added to the reaction system: dispersant, chain transfer agent, initiator, etc. These components may be physically mixed in the copolymer or connected to the main chain of the copolymer, or components such as initiators may have reacted, and their residual parts may be physically mixed in the copolymer or connected to the main chain of the copolymer.

[0050] According to one embodiment of the present application, the dispersant is selected from one or more of the following: methyl hydroxymethyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxymethyl cellulose, ethyl hydroxyethyl cellulose, polyvinyl alcohol. According to another embodiment of the present application, based on the total weight of vinylidene fluoride added in the copolymerization reaction as 100 parts by weight, the amount of the dispersant added during the copolymerization reaction is 0.01-7 parts by weight.

[0051] According to one embodiment of the present application, the chain transfer agent is selected from one or more of the following: ethyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl malonate, acetone, methyl propionate, ethyl propionate, diethyl succinate. According to another embodiment of the present application, based on the total weight of vinylidene fluoride added in the copolymerization reaction as 100 parts by weight, the amount of the chain transfer agent added during the copolymerization reaction is 0.01-8 parts by weight.

[0052] According to one embodiment of the present application, the initiator is selected from one or more of the following: diethylhexyl peroxydicarbonate, tert-butyl peroxyneodecanoate, diisopropyl peroxydicarbonate, dodecyl peroxide, dibenzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate. According to another embodiment of the present application, based on the total weight of vinylidene fluoride added in the copolymerization reaction as 100 parts by weight, the amount of the initiator added during the copolymerization reaction is 0.5-12 parts by weight.

[0053] The method for preparing the copolymer of the present invention comprises the steps of respectively adding the vinylidene fluoride, the first modified monomer and the second modified monomer into a reactor continuously to make them copolymerize to form the copolymer.

[0054] According to another specific embodiment of the present application, the copolymerization reaction is carried out under an inert atmosphere, such as a nitrogen or argon atmosphere, preferably a nitrogen atmosphere. According to another specific embodiment of the present application, the copolymerization reaction is carried out by suspension polymerization.

[0055] According to another embodiment of the present application, the copolymerization reaction is carried out in the following manner: water, a dispersant and a chain transfer agent are added to a reactor, vinylidene fluoride is introduced into the reactor, and then an initiator is added into the reactor to initiate the reaction, at which time the first modified monomer and the second modified monomer are added into the reactor in a continuous manner, and vinylidene fluoride is continuously added into the reactor, so that the copolymerization reaction continues. The initiator is added into the reactor in a continuous or intermittent manner during the copolymerization reaction.

[0056] According to one embodiment of the present application, the water used in the copolymerization reaction may be deionized water. According to another embodiment of the present application, after the copolymerization reaction is completed, the copolymerization product is purified (eg, washed with water) to obtain the target copolymerization product.

[0057] According to an exemplary embodiment of the present application, the copolymer of the present invention is prepared in the following manner:

[0058] First, deionized water, dispersant and chain transfer agent are added to the reactor, the materials are stirred evenly and purged with nitrogen until the oxygen content in the reactor is less than 80ppm, then the reactor is heated to 50-75°C, vinylidene fluoride monomer is introduced into the reactor to increase the pressure in the reactor to 3.5-8.5Mpa, and an initiator is injected into the reactor through a compression pump to initiate the reaction.

[0059] After the initiation reaction, the second modified monomer and the third modified monomer are continuously added to the reactor through a metering pump for copolymerization reaction, and at the same time, the compression pump is turned on to add vinylidene fluoride monomer to keep the pressure in the reactor constant, and the initiator is injected into the reactor every 30-50 minutes, and the addition can be adjusted several times, for example, 2-10 times, or 3-8 times, or 4-6 times;

[0060] After the reaction is completed, the reactor is cooled and depressurized to discharge the remaining gas in the reactor. The slurry obtained after the reaction is then filtered, centrifuged, and washed until the conductivity of the wastewater is reduced to below 2 μs / cm. After drying, a white solid powder is obtained, which is the vinylidene fluoride copolymer.

[0061] According to one embodiment of the present application, the copolymer of the present invention can be used as a binder for preparing a lithium battery (also called a lithium ion battery), for example, for preparing a positive electrode sheet in a lithium battery. Figure 1 An example of a lithium ion battery prepared using the copolymer of the present invention as a binder according to one embodiment of the present application is shown. Figure 1 As shown, the lithium battery includes a battery cell, which includes a stacked structure consisting of a negative electrode current collector, a negative electrode sheet, a separator, a positive electrode sheet and a positive electrode current collector, and the stacked structure can be installed in a shell in the form of a flat stack or a roll. After the stacked structure is installed in the shell, an electrolyte is added into the shell and the shell is sealed, a lithium battery can be obtained.

[0062] According to one embodiment of the present application, the positive electrode plate of the lithium battery can be prepared using the copolymer of the present application as a binder. For example, according to an exemplary embodiment, the method for manufacturing a lithium battery includes the following steps:

[0063] (a) providing a positive electrode slurry, wherein the positive electrode slurry comprises a solvent, a positive electrode active material and a positive electrode binder, and using the positive electrode slurry to manufacture the positive electrode sheet;

[0064] (b) manufacturing a negative electrode sheet;

[0065] (c) applying a positive electrode current collector to the positive electrode sheet, and applying a negative electrode current collector to the negative electrode substrate to form a stacked structure including the negative electrode current collector, the negative electrode sheet, the separator, the positive electrode sheet and the positive electrode current collector, placing the stacked structure in a housing, and pouring electrolyte into the housing to form the lithium battery;

[0066] The positive electrode binder is the binder of the present invention, that is, the copolymer of the present invention is used as the binder.

[0067] According to some embodiments of the present application, the negative electrode sheet can be synthesized by conventional techniques, for example, it can be prepared by coating and drying the negative electrode slurry. The negative electrode sheet may contain a negative electrode active material, a negative electrode binder, a conductive agent and other auxiliary additives. For example, examples of negative electrode active materials may include one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, and the silicon-based materials may be selected from one or more of elemental silicon, silicon oxide, and silicon-carbon composites, and the tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. Examples of conductive agents may include one or more of superconducting carbon, carbon black (such as acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). Other optional additives include, for example, thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, and the like.

[0068] In the lithium battery of the present application, the negative electrode current collector may be a metal foil or a composite current collector, for example, the metal foil may be a copper foil, a silver foil, an iron foil, or a foil composed of an alloy of the above metals. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer, and may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material base layer (such as a base layer made of materials such as polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE and copolymers thereof).

[0069] In the lithium battery of the present application, the positive electrode current collector may be a metal foil or a composite current collector, for example, the metal foil may be an aluminum foil, and the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE and copolymers thereof).

[0070] In the lithium battery of the present application, the positive electrode sheet can be synthesized by applying the positive electrode slurry and then drying it. The positive electrode slurry may contain the binder of the present invention, the positive electrode active material, the solvent and other additives that may need to be used. The positive electrode active material may adopt the known positive electrode active material for lithium batteries. For example, the positive electrode active material may include one or more of the following: lithium-containing phosphates with olivine structure, lithium transition metal oxides and their respective modified compounds. Examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811)), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. One or more. Examples of lithium phosphates containing olivine structures may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. In some embodiments, the positive electrode plate may also optionally include a conductive agent. Examples of conductive agents for positive electrode film layers may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0071] The electrolyte is dissolved in a solvent to form an electrolytic solution, and then the electrolytic solution is injected into the housing, and the electrolyte plays the role of conducting ions between the positive electrode plate and the negative electrode plate. The electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte). In some embodiments, the electrolyte uses an electrolyte. The electrolyte includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt can be selected from LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonyl imide), LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro oxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluoro dioxalate phosphate) and LiTFOP (lithium tetrafluoro oxalate phosphate) One or more. In one embodiment of the present application, the solvent may be selected from one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0072] In one embodiment of the present application, the lithium battery includes a separator, which separates the positive electrode side of the lithium battery from the negative electrode side, and provides selective permeation or blocking for substances of different types, sizes and charges in the system. For example, the separator can insulate electrons, physically isolate the positive and negative active substances of the lithium battery, prevent internal short circuits and form an electric field in a certain direction, and at the same time allow ions in the battery to pass through the separator and move between the positive and negative electrodes. In one embodiment of the present application, the material used to prepare the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0073] Without wishing to be limited to any particular theory, the copolymer of the present application is improved in composition to obtain a binder with excellent bonding properties. The positive electrode plate prepared using the copolymer has excellent bonding properties, and the lithium battery prepared thereby has extremely low plate internal resistance, rate performance and cycle life.

[0074] The present application is described below in the form of specific examples, and its purpose is to better understand the content of the present application. It should be understood that these examples are merely illustrative and non-restrictive. The reagents used in the examples are conventionally purchased from the market unless otherwise specified. The methods and conditions used in the examples are conventional methods and conditions unless otherwise specified.

[0075] Example

[0076] In the following examples, the copolymer of the present invention was synthesized, and the copolymer was used as a positive electrode binder to manufacture a lithium battery, and the performance of the copolymer and the lithium battery of the present invention was characterized. However, it should be noted that the following example is only a specific example listed in this application, but the technical features of this application are not limited thereto. Any simple changes, equivalent substitutions or other modifications made based on this application to solve basically the same technical problems and achieve basically the same technical effects are all covered within the scope of protection of this application.

[0077] Example 1: Synthesis of copolymers of the present invention

[0078] 3 kg of deionized water and 2 g of hydroxypropyl methylcellulose were added to a 5L stainless steel horizontal reactor, and nitrogen was purged and stirred while stirring to make the oxygen content in the reactor less than 80 ppm, and the temperature in the reactor was raised to 65°C. After reaching the above-mentioned set temperature, vinylidene fluoride monomer was added to the closed reactor from the VDF storage tank with a diaphragm pump until the pressure reached 6.9 MPa, and 2.3 g of ethyl acetate and 1.5 g of diisopropyl peroxydicarbonate were added with a metering pump to start the reaction, and the pressure in the reactor was maintained constant by a pressure automatic control system. During the entire reaction, glycidyl acrylate (GMA) with a feed rate of 1.3% by weight of the VDF feed rate and polyethylene glycol monomethyl ether acrylate (OEGMA, molecular weight of about 300) with a feed rate of 1.3% by weight of the VDF feed rate were continuously added to the reactor through a diaphragm pump. Diisopropyl peroxydicarbonate was added to the reactor every 45 minutes for a total of four times, and the amount of diisopropyl peroxydicarbonate added each time was 4g, 3g, 3g, and 3g respectively. The reaction ended after 8.5 hours. The entire polymerization process consumed a total of 950 grams of vinylidene fluoride. The polymer slurry was degassed in a degassing tank and unreacted monomers were recovered. The polymer slurry was stirred and washed with deionized water at a temperature of about 85°C until the conductivity of the wastewater was reduced to below 2μs / cm, and the concentrated polymer slurry was spray-dried to obtain a finished product.

[0079] The Mw of the product was tested by gel permeation chromatography (GPC), the viscosity of the product was tested by a rotational viscometer, the melting point and crystallization enthalpy of the product were tested by DSC, and the peel strength of the pole piece was tested by a tensile tester. The test results are listed in Table 1.

[0080] Example 2: Synthesis of copolymers of the present invention

[0081] 3 kg of deionized water and 2 g of hydroxypropyl methylcellulose were added to a 5L stainless steel horizontal reactor, and nitrogen was purged and stirred while stirring to make the oxygen content in the reactor less than 80 ppm, and the temperature in the reactor was raised to 65°C. After reaching the above-mentioned set temperature, vinylidene fluoride monomer was added to the closed reactor from the VDF storage tank with a diaphragm pump until the pressure reached 6.9 MPa, 2.3 g of ethyl acetate and 1.5 g of diisopropyl peroxydicarbonate were added with a metering pump to start the reaction, and the pressure in the reactor was maintained constant by a pressure automatic control system. During the entire reaction, glycidyl acrylate (GMA) with a feed rate of 1.5% by weight of the VDF feed rate and polyethylene glycol monomethyl ether acrylate (OEGMA, molecular weight of about 300) with a feed rate of 1.1% by weight of the VDF feed rate were continuously added to the reactor through a diaphragm pump. Diisopropyl peroxydicarbonate was added to the reactor every 45 minutes for a total of four times, and the amount of diisopropyl peroxydicarbonate added each time was 4g, 3g, 3g, and 3g, respectively. The reaction ended after 8.9 hours. The entire polymerization process consumed a total of 950 grams of vinylidene fluoride. The polymer slurry was degassed in a degassing tank and unreacted monomers were recovered. The polymer slurry was stirred and washed with deionized water at a temperature of about 85°C until the conductivity of the wastewater was reduced to below 2μs / cm, and the concentrated polymer slurry was spray-dried to obtain a finished product.

[0082] The various properties of the copolymer product were characterized in the same manner as in Example 1. The test results are listed in Table 1.

[0083] Comparative Example 1: Synthesis of polyvinylidene fluoride without adding the first modified monomer and the second modified monomer

[0084] Add 3 kg of deionized water and 2 g of hydroxypropyl methylcellulose to a 5L stainless steel horizontal reactor, purge and stir with nitrogen while stirring, so that the oxygen content in the reactor is less than 80 ppm, and raise the temperature in the reactor to 65 ° C. After reaching the above set temperature, add vinylidene fluoride monomer from the VDF storage tank to the closed reactor with a membrane pump until the pressure reaches 6.9 MPa, add 2.3 g of ethyl acetate and 1.5 g of diisopropyl peroxydicarbonate with a metering pump, so that the reaction starts, and the pressure in the reactor is maintained constant by the pressure automatic control system. Add diisopropyl peroxydicarbonate to the reactor every 45 minutes, and add it four times in total. The amount of diisopropyl peroxydicarbonate added each time is 4g, 3g, 3g, and 3g respectively. The reaction ends after 9.1 hours. The entire polymerization process consumes a total of 950 grams of vinylidene fluoride. The polymer slurry is degassed in the degassing tank and the unreacted monomer is recovered. The polymer slurry is stirred and washed with deionized water at a temperature of about 85° C. until the conductivity of the wastewater is reduced to below 2 μs / cm, and the concentrated polymer slurry is spray-dried to obtain a finished product.

[0085] The various properties of the copolymer product were characterized in the same manner as in Example 1. The test results are listed in Table 1.

[0086] Comparative Example 2: Synthesis of polyvinylidene fluoride with the addition of the first modifying monomer but without the addition of the second modifying monomer

[0087] Add 3 kg of deionized water and 2 g of hydroxypropyl methylcellulose to a 5L stainless steel horizontal reactor, purge and stir with nitrogen while stirring, so that the oxygen content in the reactor is less than 80ppm, and raise the temperature in the reactor to 65°C. After reaching the above-mentioned set temperature, add vinylidene fluoride monomer to the closed reactor from the VDF storage tank with a diaphragm pump until the pressure reaches 6.9MPa, add 2.3 g of ethyl acetate and 1.5 g of diisopropyl peroxydicarbonate with a metering pump, so that the reaction starts, and the pressure in the reactor is maintained constant by the pressure automatic control system. During the entire reaction, glycidyl acrylate (GMA) with a feed rate of 1.3% by weight of the VDF feed rate is continuously added to the reactor through a diaphragm pump. Add diisopropyl peroxydicarbonate to the reactor every 45 minutes, and add it four times in total, and the amount of diisopropyl peroxydicarbonate added each time is 4g, 3g, 3g, and 3g respectively. The reaction ends after 8.7 hours. The whole polymerization process consumes 950 grams of vinylidene fluoride in total. The polymer slurry is degassed in a degassing tank to recover unreacted monomers. The polymer slurry is stirred and washed with deionized water at a temperature of about 85°C until the conductivity of the wastewater is reduced to below 2μs / cm, and the concentrated polymer slurry is spray-dried to obtain a finished product.

[0088] The various properties of the copolymer product were characterized in the same manner as in Example 1. The test results are listed in Table 1.

[0089] Comparative Example 3: Synthesis of polyvinylidene fluoride with the addition of the second modifying monomer but without the addition of the first modifying monomer

[0090] 3 kg of deionized water and 2 g of hydroxypropyl methylcellulose were added to a 5L stainless steel horizontal reactor, and nitrogen was purged and stirred while stirring to make the oxygen content in the reactor less than 80ppm, and the temperature in the reactor was raised to 65°C. After reaching the above-mentioned set temperature, vinylidene fluoride monomer was added to the closed reactor from the VDF storage tank with a diaphragm pump until the pressure reached 6.9MPa, and 2.3 g of ethyl acetate and 1.5 g of diisopropyl peroxydicarbonate were added with a metering pump to start the reaction, and the pressure in the reactor was maintained constant by the pressure automatic control system. During the entire reaction, polyethylene glycol monomethyl ether acrylate (OEGMA, molecular weight of about 300) with a feed rate of 1.3% by weight of the VDF feed rate was continuously added to the reactor by a diaphragm pump. Diisopropyl peroxydicarbonate was added to the reactor every 45 minutes, and four additions were made, and the amount of diisopropyl peroxydicarbonate added each time was 4g, 3g, 3g, and 3g, respectively. The reaction ended after 9.0 hours. The whole polymerization process consumes 950 grams of vinylidene fluoride in total. The polymer slurry is degassed in a degassing tank to recover unreacted monomers. The polymer slurry is stirred and washed with deionized water at a temperature of about 85°C until the conductivity of the wastewater is reduced to below 2μs / cm, and the concentrated polymer slurry is spray-dried to obtain a finished product.

[0091] The various properties of the copolymer product were characterized in the same manner as in Example 1. The test results are listed in Table 1.

[0092] Table 1: Polymer performance test

[0093]

[0094] Example 3: Fabrication and performance characterization of lithium batteries

[0095] In this embodiment, an experimental lithium battery is manufactured by the following steps:

[0096] Preparation of positive electrode layer: The positive electrode active material lithium iron phosphate, the conductive agent Ketjen black, and the positive electrode binder are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone at a weight ratio of 91:5:4 to form a uniform positive electrode slurry with a solid content of about 60%. The positive electrode slurry is coated on one surface of the aluminum foil as the positive electrode current collector. After drying and cold pressing, a positive electrode active layer is formed on the positive electrode current collector. The surface density of the positive electrode active layer is about 255 mg / cm 2 , compacted density is about 2.3g / cm 3 .

[0097] Preparation of negative electrode layer: Graphite powder, conductive agent Ketjen black, binder styrene butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na) are mixed in a proper amount of deionized water at a weight ratio of 97:1:1:1 to form a negative electrode slurry with a solid content of about 60%; the negative electrode slurry is applied to one surface of the negative electrode current collector copper foil, and then dried and cold pressed to obtain a negative electrode sheet. The surface density of the negative electrode sheet is about 1800 mg / m 2 , compacted density is about 1.8g / cm 3 .

[0098] A PE porous polymer film with a thickness of 20 μm was selected as the separator. Ethylene carbonate and propylene carbonate were mixed evenly in a volume ratio of 1:1, and then the electrolyte lithium salt LiPF6 was dissolved in the above solvent to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L. The positive electrode sheet, separator and negative electrode sheet prepared above were stacked in sequence and wound to obtain an experimental battery core, which was placed in a plastic casing, injected with electrolyte and packaged to obtain an experimental battery.

[0099] The battery cell was charged at a constant current of 0.1C to a rated voltage of 4.0V and maintained at a constant voltage for 30 minutes, and then discharged at a constant current of 0.1C to 2.5V, and the discharge capacity was recorded. The battery cell was left to stand for 10 minutes, and then the charging and discharging process was repeated. The cycle performance attenuation rate after 100 cycles was calculated according to the following formula:

[0100]

[0101] In addition, before the battery cell is loaded into the casing, the ionic conductivity of the unfolded membrane-form battery cell (that is, the ionic conductivity of the 0th battery cell) is tested according to the standard method NB / T10827-2021. After 100 charge and discharge cycles, the casing is opened, the battery cell is taken out, and the ionic conductivity of the unfolded membrane-form battery cell is tested again according to the above method. The attenuation rate of the ionic conductivity of the battery cell after 100 cycles is calculated according to the following formula:

[0102]

[0103] The characterization results are summarized in the following table:

[0104] Table 2: Lithium battery performance

[0105]

Claims

1. A copolymer comprising polymerized units derived from the following monomers: Vinylidene fluoride; A first modifying monomer, which is glycidyl (meth)acrylate; A second modified monomer, which is polyethylene glycol monomethyl ether (meth)acrylate, wherein the degree of polymerization of the polyethylene glycol is 2-20; Based on 100 parts by weight of the vinylidene fluoride, the content of the first modifying monomer is 0.1 to 16 parts by weight, and the content of the second modifying monomer is 0.1 to 18 parts by weight; and The weight average molecular weight Mw of the copolymer is 5,000 to 1,200,000.

2. The copolymer according to claim 1, characterized in that The copolymer further comprises one or more of the following components or their residues: a dispersant, a chain transfer agent, an initiator; The dispersant is selected from one or more of the following: methyl hydroxymethyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxymethyl cellulose, ethyl hydroxyethyl cellulose, polyvinyl alcohol; The chain transfer agent is selected from one or more of the following: ethyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl malonate, acetone, methyl propionate, ethyl propionate, diethyl succinate; The initiator is selected from one or more of the following: diethylhexyl peroxydicarbonate, tert-butyl peroxyneodecanoate, diisopropyl peroxydicarbonate, dodecyl peroxide, dibenzoyl peroxide, and tert-butyl peroxy-2-ethylhexanoate.

3. A binder for manufacturing a positive electrode plate of a lithium battery, the binder comprising the copolymer as claimed in any one of claims 1 to 2.

4. A method for preparing a copolymer as claimed in any one of claims 1 to 2, comprising: The vinylidene fluoride, the first modified monomer and the second modified monomer are copolymerized to form the copolymer.

5. The method according to claim 4, characterized in that In the presence of a dispersant, a chain transfer agent and an initiator, the vinylidene fluoride, the first modified monomer and the second modified monomer are continuously added into a reactor, so that the vinylidene fluoride, the first modified monomer and the second modified monomer undergo copolymerization to form the copolymer.

6. A lithium battery comprising a housing, a negative electrode collector, a negative electrode plate, a separator, a positive electrode plate, a positive electrode collector and an electrolyte, wherein the positive electrode plate comprises the binder according to claim 3.

7. A method for manufacturing a lithium battery, the method comprising: (a) providing a positive electrode slurry, wherein the positive electrode slurry comprises a solvent, a positive electrode active material and a positive electrode binder, and using the positive electrode slurry to manufacture the positive electrode sheet; (b) manufacturing a negative electrode sheet; (c) applying a positive electrode current collector to the positive electrode sheet, applying a negative electrode current collector to the negative electrode sheet, forming a stacked structure including the negative electrode current collector, the negative electrode sheet, the separator, the positive electrode sheet and the positive electrode current collector, placing the stacked structure in a housing, and pouring electrolyte into the housing to form the lithium battery; The positive electrode binder is the binder according to claim 3.

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