Negative electrode modified binder as well as preparation method and application thereof

Abstract

The invention provides a negative electrode modified binder and a preparation method and application thereof. The negative electrode modified binder comprises a first unit, a second unit, a third unit and a fourth unit, the structure of the first unit is as shown in a formula (I), the structure of the second unit is as shown in a formula (II), the structure of the third unit is as shown in a formula (III), and the structure of the fourth unit is as shown in a formula (IV): # imgabs 0 #, # imgabs 1 #-CH2-CR5R6--(IV). The negative electrode modified binder has multiple functions of dispersing, thickening and binding, has excellent ionic conductivity, is beneficial to improving the bonding strength between negative electrode active materials in a negative electrode plate and between the negative electrode active materials and a negative electrode current collector, enhances the flexibility of the negative electrode plate, and comprehensively improves the electrochemical performance of the battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode modified binder and a preparation method and application thereof. Background Art

[0002] At present, in the production of battery pole pieces, the positive and negative electrode slurries have a significant impact on the performance of the battery pole pieces. A variety of organic additives are usually added in the preparation of positive and negative electrode slurries, which mainly play the role of dispersion, thickening and bonding. Due to the poor ionic conductivity of organic additives and the addition of too many additives, the proportion of active materials in the battery pole pieces is reduced, resulting in an increase in battery impedance, affecting the capacity and power performance of the battery. Therefore, it is necessary to develop an organic additive that integrates the functions of dispersion, thickening and bonding and has good ionic conductivity, so as to reduce the proportion of organic additives used, increase the proportion of active materials in the battery pole pieces, enhance the flexibility of the negative electrode pole pieces, and improve the electrochemical performance of the battery. Summary of the invention

[0003] In view of this, the present application provides a negative electrode modified binder and a preparation method and application thereof. The negative electrode modified binder, as an organic additive for a negative electrode slurry, can not only play a dispersing, thickening and bonding role, but also increase the ion conduction speed, reduce battery impedance, and improve the overall performance of the battery, which is conducive to the wide application of the battery.

[0004] In a first aspect, the present application provides a negative electrode modified binder, the negative electrode modified binder comprising a first unit, a second unit, a third unit and a fourth unit, the structure of the first unit is shown in formula (I), the structure of the second unit is shown in formula (II), the structure of the third unit is shown in formula (III), the structure of the fourth unit is shown in formula (IV),

[0005]

[0006] The R1 is selected from -H, -Na or -Li, the R2 and the R4 are independently selected from -H or -CH3, the R3 is an alkylene group, the R5 is selected from -H, -CH3 or -CH2CH3, the R6 is selected from -CN, -CH=CH2, -COOR 1 、-OCOR 2 ,-CONHR 3 、-COOR 4 OH, -OCOR 5 OH or -Ph-R 6 , the R 1 , the R 2 and the R 3 is an alkyl group, the R 4 and the R 5 is an alkylene group, said R6 is -H, -OH, -SO3H or -OP=O(OH)2, and m is an integer greater than or equal to 1.

[0007] Optionally, the repetition numbers of the first unit, the second unit, the third unit and the fourth unit in the negative electrode modified binder are independently selected from integers ranging from 1 to 2000.

[0008] Optionally, m is an integer from 1 to 18.

[0009] The different units in the negative electrode modified binder provided in the present application enable the negative electrode modified binder to have the functions of dispersing, thickening and bonding, and have good bonding ability and ionic conductivity, which is beneficial to reduce the use of organic additives in the negative electrode plate, enhance the bonding strength between active materials and between active materials and current collectors, improve the flexibility of the negative electrode plate, and enhance the electrochemical performance of the battery.

[0010] In a second aspect, the present application provides a method for preparing a negative electrode modified binder, comprising:

[0011] A negative electrode binder, a first water-soluble monomer, a second water-soluble monomer, a third water-soluble monomer and a hydrophobic monomer are mixed to form a mixture, and a negative electrode modified binder is obtained after a polymerization reaction; the negative electrode modified binder includes a first unit, a second unit, a third unit and a fourth unit, the structure of the first unit is shown in formula (I), the structure of the second unit is shown in formula (II), the structure of the third unit is shown in formula (III), and the structure of the fourth unit is shown in formula (IV),

[0012]

[0013]

[0014] The R1 is selected from -H, -Na or -Li, the R2 and the R4 are independently selected from -H or -CH3, the R3 is an alkylene group, the R5 is selected from -H, -CH3 or -CH2CH3, the R6 is selected from -CN, -CH=CH2, -COOR 1 、-OCOR 2 ,-CONHR 3 、-COOR 4 OH, -OCOR 5 OH or -Ph-R 6 , the R 1 , the R 2 and the R 3 is an alkyl group, the R 4 and the R 5 is an alkylene group, said R 6is -H, -OH, -SO3H or -OP=O(OH)2, and m is an integer greater than or equal to 1.

[0015] Optionally, the structural formula of the first water-soluble monomer is CH2=CHCOOR1, the structural formula of the second water-soluble monomer is CHR2=CHCOOR3OH, and the structural formula of the third water-soluble monomer is CHR4=CHCOO(CH2CH2O) m CH2CH3, the structural formula of the hydrophobic monomer is CH2=CR5R6.

[0016] Optionally, the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:(0.001-0.5):(0.001-0.5):(0.001-0.5):(0.001-0.5).

[0017] Optionally, the negative electrode binder includes at least one of a synthetic polymer and a biomass polymer, the synthetic polymer includes at least one of polyvinyl alcohol, polyvinyl butyral, polyethylene glycol and polypropylene glycol, the biomass polymer includes at least one of a lithium salt, a sodium salt and a potassium salt of a cellulose derivative, and the degree of substitution of the biomass polymer is 0.6 to 1.5.

[0018] Optionally, the mixture also includes an initiator; the initiator includes at least one of benzoyl peroxide, methyl ethyl ketone peroxide, potassium persulfate, ammonium persulfate, ammonium sulfate, sodium sulfite and ferrous chloride; the mass ratio of the initiator to the negative electrode binder is 0.1% to 20%.

[0019] Optionally, the polymerization reaction temperature is 20°C to 60°C.

[0020] The preparation method of the negative electrode modified binder provided in the present application is simple, easy to operate, and has high production efficiency. It can realize large-scale production of the negative electrode modified binder, which is beneficial to the use of the negative electrode modified binder.

[0021] In a third aspect, the present application provides a negative electrode plate, which includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material and the negative electrode modified binder described in the first aspect or the negative electrode modified binder prepared by the preparation method described in the second aspect.

[0022] Optionally, the mass ratio of the negative electrode modification binder to the negative electrode active material is 0.1:100 to 5:100.

[0023] Optionally, the negative electrode plate further includes a negative electrode current collector, the negative electrode active material layer is arranged on the surface of the negative electrode current collector, and the peeling strength between the negative electrode current collector and the negative electrode active material layer is 5N / m to 50N / m.

[0024] The negative electrode plate provided in the present application uses a negative electrode modified binder with good bonding ability and good ion conductivity, which reduces the large-scale use of other organic additives in the negative electrode active material layer, increases the proportion of negative electrode active materials in the negative electrode active layer, improves the peeling strength between the negative electrode current collector and the negative electrode active material layer, and enhances the flexibility of the negative electrode plate, thereby helping to improve the product competitiveness of the negative electrode plate.

[0025] In a fourth aspect, the present application provides a battery, comprising a positive electrode plate and the negative electrode plate described in the third aspect.

[0026] The battery provided in this application has low impedance, excellent comprehensive performance and strong product competitiveness.

[0027] In a fifth aspect, the present application provides an electrical device, wherein the electrical device comprises the battery described in the fourth aspect.

[0028] The electrical equipment provided in this application has excellent performance and strong product competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the prior art description. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0030] Figure 1 A schematic cross-sectional view of a negative electrode sheet provided in one embodiment of the present application.

[0031] Figure 2 A schematic cross-sectional view of a negative electrode sheet provided in another embodiment of the present application.

[0032] Figure 3 A schematic diagram of a peel strength test of a negative electrode current collector and a negative electrode active material layer provided in one embodiment of the present application.

[0033] Figure 4 Schematic diagram of the peel strength test process of the negative electrode current collector and the negative electrode active material layer provided in an embodiment of the present application.

[0034] Description of labels:

[0035] Negative electrode sheet-100, negative electrode current collector-10, negative electrode active material layer-20, double-sided tape-30, resin plate-40. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] In the related art, in order to obtain a battery electrode with excellent performance, it is necessary to regulate the components of the active material layer. In the preparation process of the active material layer, it is necessary to add organic additives with various functions. For example, organic additives with dispersing functions can promote the uniform distribution of active materials, and organic additives with thickening and bonding functions can meet the bonding strength requirements between the active material layer and the current collector. However, the large-scale use of organic additives with various functions will reduce the proportion of active materials in the active material layer, thereby reducing the ion conduction efficiency, increasing the battery impedance, and having an adverse effect on the battery capacity and power.

[0038] In order to solve the above technical problems, the present application provides a negative electrode modified binder, which, as an organic additive for negative electrode slurry, can simultaneously have the functions of dispersing, thickening and bonding, and has excellent bonding ability and good ion conductivity. It can reduce the usage ratio of different functional additives in the active material layer, reduce battery impedance, improve battery ion conduction efficiency, enhance the flexibility of the negative electrode sheet, and improve the overall performance of the battery.

[0039] In the present application, the negative electrode modified binder includes a first unit, a second unit, a third unit and a fourth unit, the structure of the first unit is shown in formula (I), the structure of the second unit is shown in formula (II), the structure of the third unit is shown in formula (III), and the structure of the fourth unit is shown in formula (IV). R1 is selected from -H, -Na or -Li, R2 and R4 are independently selected from -H or -CH3, R3 is an alkylene group, R5 is selected from -H, -CH3 or -CH2CH3, R6 is selected from -CN, -CH=CH2, -COOR 1 、-OCOR 2 ,-CONHR 3 、-COOR 4 OH, -OCOR 5 OH or -Ph-R 6 , R 1 , R 2 and R 3 is an alkyl group, R 4 and R 5 is an alkylene group, R 6is -H, -OH, -SO3H or -OP=O(OH)2, and m is an integer greater than or equal to 1.

[0040] The negative electrode modified binder provided in the present application has units with different structures, and the negative electrode modified binder is modified, wherein the first unit, the second unit, and the third unit can form intermolecular and intramolecular hydrogen bonds with the negative electrode active material to construct a network structure, so that the negative electrode modified binder has a strong bonding ability; the first unit, the second unit, and the third unit all contain unbonded oxygen arc electron pairs, which can associate and disassociate with cations, provide more paths for cation transport, accelerate the transmission rate of cations on the electrochemical interface, and reduce the electrochemical reaction impedance of the negative electrode pole piece; the second unit and the third unit can reduce the glass transition temperature, adjust the flexibility of the negative electrode binder, and prevent the winding and cracking of the negative electrode pole piece; the fourth unit has good dispersibility, can improve the wetting and dispersibility of the negative electrode active material layer, adjust the viscosity and thixotropic ability of the negative electrode slurry, and meet production needs; in this way, the negative electrode modified binder has high bonding, good ionic conductivity, thickening and dispersing effects, which is conducive to the use of the negative electrode modified binder. The characteristic groups of units with different structures in the negative electrode modified binder can be detected by, but not limited to, infrared spectroscopy and other means.

[0041] The first unit, the second unit, the third unit and the fourth unit are used as modified structural units of the negative electrode modified binder, which greatly improves the dispersibility, thickening ability and bonding ability of the negative electrode modified binder, and enhances the ionic conductivity, which is conducive to reducing the use of other organic additives in the negative electrode sheet, enhancing the flexibility of the negative electrode sheet, and improving the electrochemical performance of the battery. The negative electrode binder is an unmodified substance. The active groups in the negative electrode binder are replaced by modified structural units to form a negative electrode modified binder. The negative electrode modified binder is a modified negative electrode binder. The negative electrode modified binder includes a negative electrode binder group and a modified structural unit connected to the negative electrode binder active group. The negative electrode binder active group is the hydroxyl group in the negative electrode binder.

[0042] In one embodiment of the present application, the negative electrode binder includes at least one of the structures shown in formula (V-1) to formula (V-5),

[0043]

[0044] R7, R8 and R9 are independently selected from -H or R 7 Selected from alkylene, R 8Selected from alkyl, -H, -OH, -ONa, -OLi, -OK, -NH2 or -OCH3, n and n1 are integers greater than or equal to 100, n2 is an integer greater than 1, and R7, R8 and R9 include at least one hydroxyl group. It can be seen that the negative electrode binder group includes at least one functional group (i.e., an active group) that can undergo a substitution reaction, and the modified structural unit is connected to the substitutable functional group to modify the negative electrode binder. Exemplarily, n can be, but is not limited to, 100, 150, 300, 700, 1000, 10000, 15000 or 20000, etc., n1 can be, but is not limited to, 100, 120, 140, 160, 200, 500 or 1000, etc., and n2 can be, but is not limited to, 1, 5, 10, 50, 100, 200, 300 or 500, etc. In one embodiment, n can be an integer from 150 to 1000, n1 can be an integer from 100 to 500, and n2 can be an integer from 150 to 300. When the negative electrode binder is connected to the modified structural unit, the modified structural unit can replace the hydrogen atoms of the active groups in the negative electrode binder, thereby obtaining a negative electrode modified binder. In one embodiment of the present application, the negative electrode binder is n is 720. In another embodiment of the present application, the negative electrode binder is n is 1000. In another embodiment of the present application, the negative electrode binder is n1 is 120 and n2 is 50.

[0045] In the present application, the structure of the first unit is shown in formula (I),

[0046]

[0047] R1 is selected from -H, -Na or -Li. The first unit contains carboxyl, lithiated or sodiumated carboxyl, which can form intermolecular and intramolecular hydrogen bonds with other units or negative electrode active materials, thereby enhancing the bonding strength of the negative electrode modified binder, and can also accelerate the transmission rate of cations at the electrochemical interface, thereby improving the ionic conductivity of the negative electrode modified binder. Specifically, the first unit can be, but is not limited to, In one embodiment of the present application, the first unit can be In another embodiment of the present application, the first unit may be In another embodiment of the present application, the first unit can be

[0048] In the present application, the structure of the second unit is shown in formula (II),

[0049]

[0050] R2 is selected from -H or -CH3, and R3 is an alkylene group. The second unit has an ester group and a hydroxyl functional group, which can form a hydrogen bond network structure with other units, improve the bonding ability of the negative electrode modified binder, and enhance the flexibility of the negative electrode modified binder. Specifically, the second unit can be but is not limited to One or more of the above.

[0051] In the present application, the structure of the third unit is shown in formula (III),

[0052]

[0053] R4 is selected from -H or -CH3, and m is an integer from 1 to 18. The third unit can improve the cation conductivity, reduce the glass transition temperature of the negative electrode binder, and improve the ionic conductivity and flexibility of the negative electrode modified binder. Exemplarily, the value of m can be, but is not limited to, 1, 2, 4, 7, 9, 10, 14, 16 or 18. Specifically, the third unit can be, but is not limited to, One or more of the above.

[0054] In the present application, the structure of the fourth unit is shown in formula (IV),

[0055] -CH2-CR5R6-(IV)

[0056] R5 is -H, -CH3 or -CH2CH3, and R6 is selected from -CN, -CH=CH2, -COOR 1 、-OCOR 2 ,-CONHR 3 、-COOR 4 OH, -OCOR 5 OH or -Ph-R 6 , R 1 , R 2 and R 3 is an alkyl group, R 4 and R 5 is an alkylene group, R 6 The fourth unit can enhance the hydrophobic interaction strength between the negative electrode binder and the active graphite particles and improve the dispersion ability of the graphite particles. Specifically, the fourth unit can be, but is not limited to,

[0057] One or more of the above.

[0058] In the present application, the connection position and connection order of the first unit, the second unit, the third unit and the fourth unit with the active group in the negative electrode modified binder are not limited; in the structural formula of the negative electrode modified binder, the units are randomly and non-fixedly connected to the active group. In one embodiment of the present application, the first unit, the second unit, the third unit or the fourth unit is connected to an active group of a negative electrode binder. In one embodiment of the present application, at least two of the first unit, the second unit, the third unit and the fourth unit can be connected to the same active group of the negative electrode binder, and the connection order and number of the connected units are not limited. In other words, the multiple units connected to the same active group and the order and number of the units can be the same or different. In one embodiment of the present application, the first unit, the second unit, the third unit and the fourth unit can be connected to the same active group of the negative electrode binder, and the connection order of the four units is not limited. The same negative electrode binder active group can be a homopolymer of the same unit or a random copolymer of at least two units. In one embodiment of the present application, one unit (first unit, second unit, third unit or fourth unit) can be connected to some of the active groups in the negative electrode binder, and multiple units (two or more of the first unit, second unit, third unit and fourth unit) can be connected to some of the active groups in the negative electrode binder. That is to say, all units can be connected to the same active group position in the negative electrode binder, or they can be connected to different active group positions in the negative electrode binder; at the same time, the negative electrode modified binder can also have unmodified active groups. In one embodiment of the present application, the structural formula of the negative electrode modified binder can be, but is not limited to, as shown in Formula (VI-1) to Formula (VI-6), n is an integer greater than 100, a1, a2, a3, a4, b, c, d are independently selected from integers between 10 and 10000, and a1+a2≤a, a3+a4≤a.

[0059]

[0060]

[0061] In one embodiment of the present application, the number of carbon atoms of the alkyl group is 1 to 18. Exemplarily, the number of carbon atoms of the alkyl group may be, but not limited to, 1, 2, 5, 7, 9, 10, 12, 15 or 18. The alkyl group may be a straight chain alkyl group or a branched chain alkyl group. Specifically, the alkyl group may be, but not limited to, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a dodecyl group or a heptadecyl group. In one embodiment of the present application, the alkyl group is an ethyl group. In another embodiment of the present application, the alkyl group is a dodecyl group. In another embodiment of the present application, the alkyl group is a pentyl group. The above R 1 , R 2 , R 3 or R 8When it is an alkyl group, it can be selected according to the range of the alkyl group.

[0062] In one embodiment of the present application, the number of carbon atoms of the alkylene group is 1 to 18. Exemplarily, the number of carbon atoms of the alkylene group may be, but not limited to, 1, 3, 6, 7, 9, 10, 11, 14 or 18. The alkylene group may be a straight chain alkylene group or a branched chain alkylene group. Specifically, the alkylene group may be, but not limited to, a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a dodecylene group or a heptadecanylene group. In one embodiment of the present application, the alkylene group is an ethylene group. In another embodiment of the present application, the alkylene group is a dodecylene group. In yet another embodiment of the present application, the alkylene group is a pentylene group. The above R3, R 4 , R 5 or R 7 In the case of an alkylene group, it can be selected according to the range of the alkylene group.

[0063] In one embodiment of the present application, the repetition number of the first unit, the second unit, the third unit and the fourth unit in the negative electrode modified binder is independently selected from an integer from 1 to 2000. Specifically, the repetition number may be, but is not limited to, 1, 10, 100, 500, 800, 1000, 1500 or 2000, etc., and the repetition number of each unit may be the same or different. In one embodiment of the present application, the repetition number of the first unit, the second unit, the third unit and the fourth unit is independently selected from an integer from 100 to 1000, which can further improve the bonding ability of the negative electrode modified binder. In another embodiment of the present application, the unit numbers of the first unit, the second unit, the third unit and the fourth unit are 1500, 100, 400 and 200, respectively.

[0064] The present application also provides a method for preparing a negative electrode modified binder, comprising: mixing a negative electrode binder, a first water-soluble monomer, a second water-soluble monomer, a third water-soluble monomer and a hydrophobic monomer, and then performing a polymerization reaction to obtain a negative electrode modified binder; the negative electrode modified binder comprises a first unit, a second unit, a third unit and a fourth unit, the structure of the first unit is shown in formula (I), the structure of the second unit is shown in formula (II), the structure of the third unit is shown in formula (III), and the structure of the fourth unit is shown in formula (IV). The preparation method can prepare the negative electrode modified binder in any of the above embodiments.

[0065] In the preparation method of the negative electrode modified binder provided in the present application, the water-soluble monomer (including the first water-soluble monomer, the second water-soluble monomer, and the third water-soluble monomer) modifies the negative electrode binder so that the negative electrode modified binder can be used in an aqueous slurry system and has good water solubility; a variety of intramolecular and intermolecular hydrogen bonds can be generated between the water-soluble monomer and the negative electrode active material to form a network structure, thereby improving the bonding strength of the negative electrode modified binder; each water-soluble monomer includes a carbonyl group and an ether bond, which contains unbonded oxygen arc pairs of electrons, and can improve the cation transport capacity of the negative electrode modified binder; the second water-soluble monomer and the third water-soluble monomer have good flexibility, which enhances the flexibility of the negative electrode binder and prevents the negative electrode electrode sheet from cracking during winding; the hydrophobic monomer can enhance the dispersion performance of the negative electrode modified binder. The preparation method of the negative electrode modified binder provided in the present application is simple, and the prepared negative electrode modified binder can have the functions of dispersing, thickening and bonding, and has good bonding performance, excellent ionic conductivity, and the negative electrode sheet is wound without cracking, and the battery has excellent electrical performance. In one embodiment of the present application, the negative electrode binder includes synthetic polymers or biomass polymers, and the synthetic polymers include one or more of polyvinyl alcohol, poly (vinyl butyral-vinyl alcohol) copolymers, polyethylene glycol and polypropylene glycol, and the biomass polymers include one or more of lithium salts, sodium salts and potassium salts of cellulose derivatives. In one embodiment of the present application, the negative electrode binder can be sodium carboxymethyl cellulose. Sodium carboxymethyl cellulose itself has certain dispersing and thickening effects, which can improve the comprehensive performance of the negative electrode modified binder. In another embodiment of the present application, the negative electrode binder can be a mixture of polyethylene glycol and polypropylene glycol.

[0066] In one embodiment of the present application, the degree of substitution of the biomass polymer is 0.6 to 1.5. The degree of substitution refers to the number of hydroxyl groups substituted by other groups on each biomass unit. Specifically, the degree of substitution of the biomass polymer can be, but is not limited to, 0.6, 0.7, 0.8, 1, 1.2, 1.4, 1.5 or 1.6, etc. In one embodiment of the present application, the degree of substitution of the biomass polymer is 0.7. In another embodiment of the present application, the degree of substitution of the biomass polymer is 1.0.

[0067] In one embodiment of the present application, the particle size of the negative electrode binder is 100nm to 1000μm. Specifically, the particle size of the negative electrode binder may be, but is not limited to, 100nm, 200nm, 500nm, 50μm, 100μm, 500μm, 700μm or 1000μm, etc. In one embodiment of the present application, the particle size of the negative electrode binder is 300μm to 500μm. In another embodiment of the present application, the particle size of the negative electrode binder is 10μm to 50μm. In yet another embodiment of the present application, the particle size of the negative electrode binder is 500nm to 1000nm.

[0068] In one embodiment of the present application, the first water-soluble monomer has a structural formula of CH2=CHCOOR1, and R1 is selected from -H, -Na or -Li. The first water-soluble monomer has ester and carboxyl functional groups, which can form intermolecular and intramolecular hydrogen bonds with other monomers and negative electrode active materials, and can improve the bonding ability; at the same time, the first water-soluble monomer also includes unbonded oxygen lone pairs of electrons, and the oxygen lone pairs of electrons can continuously associate and disassociate with cations, thereby improving the interfacial transport capacity of cations. Specifically, the first water-soluble monomer can be one or more of acrylic acid, sodium acrylate and lithium acrylate. In one embodiment of the present application, the first water-soluble monomer is acrylic acid. In another embodiment of the present application, the first water-soluble monomer is acrylic acid and lithium acrylate.

[0069] In one embodiment of the present application, the second water-soluble monomer has a structural formula of CHR2=CHCOOR3OH, R2 is -H or -CH3, and R3 is an alkylene group. The flexible second water-soluble monomer can form intermolecular and intramolecular hydrogen bonds with other monomers and negative electrode active materials to form a network structure, further improving the bonding strength and flexibility. Specifically, the second water-soluble monomer is 2-hydroxyalkyl acrylate or 2-hydroxyalkyl methacrylate. In one embodiment of the present application, when R2 is -H and R3 is ethylene, the second water-soluble monomer is 2-hydroxyethyl acrylate. In another embodiment of the present application, when R2 is -CH3 and R3 is ethylene, the second water-soluble monomer is 2-hydroxyethyl methacrylate. In yet another embodiment of the present application, when R2 is -H and R3 is propylene, the second water-soluble monomer is 2-hydroxypropyl acrylate.

[0070] In one embodiment of the present application, the structural formula of the third water-soluble monomer is CHR4=CHCOO(CH2CH2O) m CH2CH3, m is a positive integer greater than or equal to 1, and R4 is -H or -CH3. The third water-soluble monomer includes a carbonyl group or an ether bond containing an unbonded oxygen arc electron pair, which can improve the ion transmission capacity. The third water-soluble monomer has excellent flexibility and a low glass transition temperature, which can improve the flexibility of the negative electrode binder and prevent the negative electrode sheet from winding and cracking. Specifically, the third water-soluble monomer is polyethoxyethyl (meth)acrylate or polyethoxyethyl acrylate, and m is an integer from 1 to 18. Specifically, m can be, but is not limited to, 2, 3, 4, 5, 10, 15 or 18. In one embodiment of the present application, when m is 2, R4 is -H, and the third water-soluble monomer is 2-(2-ethoxyethoxy)ethyl acrylate. In another embodiment of the present application, when m is 2, R4 is -CH3, and the third water-soluble monomer is 2-(2-ethoxyethoxy)ethyl methacrylate. In another embodiment of the present application, when m is 4, R4 is -H, and the third water-soluble monomer is 2-(4-ethoxyethoxy)ethyl acrylate.

[0071] In one embodiment of the present application, the structural formula of the hydrophobic monomer is CH2=CR5R6, R5 is selected from -H, -CH3 or -CH2CH3, and R6 is selected from -CN, -CH=CH2, -COOR 1 、-OCOR 2 ,-CONHR 3 、-COOR 4 OH, -OCOR 5 OH or -Ph-R 6 , R 1 , R 2 and R 3 is an alkyl group, R 4 and R 5 is an alkylene group, R 6 is -H, -OH, -SO3H or -OP=O(OH)2. 1 , R 2 and R 3 is an alkyl group, R 4 and R 5 It is an alkylene group. Specifically, the hydrophobic monomer can be, but is not limited to, styrene, dodecyl methacrylate or octadecyl methacrylate, etc. The hydrophobic monomer can disperse the negative electrode active material, provide the uniformity of the negative electrode active material, and at the same time, enhance the hydrophobic interaction strength on the surface of the negative electrode active material, which helps to improve the bonding ability. Specifically, the hydrophobic monomer can be selected according to the material of the negative electrode active material. In one embodiment of the present application, when the negative electrode active material is natural graphite, the hydrophobic monomer is styrene. In another embodiment of the present application, when the negative electrode active material is artificial graphite, the hydrophobic monomer is dodecyl methacrylate. In this way, it is more conducive to the dispersion of the negative electrode active material.

[0072] In one embodiment of the present application, the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:(0.001-0.5):(0.001-0.5):(0.001-0.5):(0.001-0.5). In this way, the reaction process can be promoted and the reaction time can be shortened. Specifically, the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer can be, but is not limited to, 1:0.001:0.001:0.001:0.001, 1:0.005:0.005:0.005:0.005, 1:0.01:0.01:0.01:0.01, 1:0.05:0.05:0.05:0.05, 1:0.08:0.04:0.04:0.001, 1:0.1:0.2:0.08:0.07, 1:0.5:0.2:0.5:0.3 or 1:0.5:0.5:0.5:0.5, etc. In one embodiment of the present application, the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1: (0.05-0.2): (0.01-0.05): (0.05-0.1): (0.01-0.05), which improves the uniformity of the reaction, avoids the occurrence of local cross-linking reactions, and is conducive to improving the thickening and dispersibility of the negative electrode modified binder. In another embodiment of the present application, the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1: (0.08-0.1): (0.02-0.04): (0.04-0.07): (0.02-0.05). In another embodiment of the present application, the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:(0.03-0.2):(0.02-0.1):(0.02-0.3):(0.01-0.09).

[0073] In one embodiment of the present application, a negative electrode binder, a first water-soluble monomer, a second water-soluble monomer, a third water-soluble monomer and a hydrophobic monomer are added to a solvent and mixed, and a polymerization reaction is carried out to obtain a negative electrode modified binder. The solvent may be, but is not limited to, one or more of deionized water, alcohols (such as methanol, ethanol, isopropanol, etc.). In one embodiment of the present application, the mass ratio of the negative electrode binder to the solvent may be 1: (1 to 40). Specifically, the mass ratio of the negative electrode binder to the solvent may be, but is not limited to, 1: 1, 1: 5, 1: 10, 1: 15, 1: 20, 1: 25, 1: 30 or 1: 40, etc. In some embodiments of the present application, a kneader is used for mixing, the negative electrode binder includes at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose, the mass ratio of the negative electrode binder to the solvent can be 1: (1-40), and the volume ratio of water to alcohol in the solvent can be 1: (0.1-9) (such as 1: 0.2, 1: 1, 1: 1.5, 1: 3, 1: 5 or 1: 8, etc.). In other embodiments of the present application, the negative electrode binder includes a synthetic polymer, the mass ratio of the negative electrode binder to the solvent can be 1: (1-5) (such as 1: 1, 1: 2, 1: 4 or 1: 5, etc.), and the volume ratio of water to alcohol in the solvent can be 1: (0.5-2.5), which can improve the solubility of the negative electrode binder. In one embodiment of the present application, a kneader is used for mixing, the negative electrode binder includes at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose, and the solvent can be a mixed solvent of deionized water and ethanol, the volume ratio of deionized water and ethanol is 2: 3, and the mass ratio of the negative electrode binder to the solvent is 1: 3. In another embodiment of the present application, a stirred reactor is used for mixing, the negative electrode binder includes at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose, and the solvent can be a mixed solvent of deionized water and ethanol, the volume ratio of deionized water to ethanol is 2:3, and the mass ratio of the negative electrode binder to the solvent is 1:10. In another embodiment of the present application, a stirred reactor is used for mixing, and when the negative electrode binder is polyvinyl alcohol, the solvent can be deionized water, and the mass ratio of the negative electrode binder to the solvent is 1:1. During the mixing process, argon gas can be introduced into the reaction system to remove dissolved oxygen.

[0074] In one embodiment of the present application, the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer are mixed with an initiator; the initiator may be, but is not limited to, one or more of an organic peroxide initiator, an inorganic peroxide initiator or a redox initiator. The organic peroxide initiator includes at least one of benzoyl oxide and methyl ethyl ketone peroxide, the inorganic peroxide initiator includes at least one of potassium sulfate and ammonium persulfate, and the redox initiator includes at least one of a combination of ammonium sulfate and sodium sulfite and a combination of potassium persulfate and ferrous chloride. The mass ratio of the initiator to the negative electrode binder is 0.1% to 20%. Specifically, the mass ratio of the initiator to the negative electrode binder can be 0.1%, 0.5%, 1%, 5%, 7%, 10%, 15%, 20%, etc. In one embodiment of the present application, the initiator is benzoyl peroxide, and the mass ratio of the initiator to the negative electrode binder is 0.1% to 5%, which can increase the reaction rate. In another embodiment of the present application, the initiator is ammonium sulfate and sodium sulfite, and the mass ratio of the initiator to the negative electrode binder is 5% to 7%. In another embodiment of the present application, the initiator is ammonium persulfate, and the mass ratio of the initiator to the negative electrode binder is 10% to 15%.

[0075] The present application adopts a heterogeneous, free radical polymerization reaction, and the free radical polymerization is carried out by free radical random graft copolymerization or free radical block graft copolymerization according to the addition method of the modified monomer, thereby obtaining a negative electrode modified binder. The method adjusts the proportion of the solvent so that the negative electrode binder is in an incompletely dissolved state, and the addition of an initiator and other modified monomers will cause a polymerization reaction, which can reduce the viscosity of the negative electrode binder during the reaction process, is conducive to the extraction of polymerization reaction heat, and increases the output of the negative electrode modified binder. The generated negative electrode modified binder can be washed, separated and dried to obtain a negative electrode modified binder powder, which is suitable for large-scale production and is conducive to reducing transportation costs.

[0076] In one embodiment of the present application, the polymerization temperature is 20°C to 60°C, which can accelerate the reaction speed of the polymerization reaction. Specifically, the polymerization temperature can be 20°C, 30°C, 40°C, 50°C, 60°C, etc. In one embodiment of the present application, the polymerization temperature is 30°C to 60°C. In another embodiment of the present application, the polymerization temperature is 40°C to 50°C.

[0077] In one embodiment of the present application, after the polymerization reaction is completed, an acid or alkaline solution is used to adjust the pH value of the reaction system to 4 to 9, which can neutralize the carboxyl or hydroxyl groups that are not completely polymerized after the polymerization reaction, so that they form salts, thereby improving the water solubility of the negative electrode modified binder. Specifically, the acid may be, but is not limited to, one or more of acetic acid, hydrochloric acid, nitric acid, and sulfuric acid, and the base may be, but is not limited to, one or more of ammonia water, sodium hydroxide, potassium hydroxide, and lithium hydroxide. In one embodiment of the present application, acetic acid can be used to adjust the pH value of the reaction system to 6. In one embodiment of the present application, lithium hydroxide can be used to adjust the pH value of the reaction system to 8. The addition of lithium hydroxide provides additional lithium ions, which can further reduce the electrochemical reaction impedance and improve the electrochemical performance of the negative electrode sheet.

[0078] See also Figure 1 , is a schematic cross-sectional view of a negative electrode sheet provided in one embodiment of the present application, wherein the negative electrode sheet 100 comprises a negative electrode current collector 10 and a negative electrode active material layer 20 disposed on the surface of the negative electrode current collector, wherein the negative electrode active material layer 20 comprises a negative electrode active material and a negative electrode modified binder. Figure 2 , is a cross-sectional schematic diagram of a negative electrode plate provided in another embodiment of the present application, wherein the negative electrode plate 100 includes a negative electrode current collector 10 and a negative electrode active material layer 20 disposed on both sides of the negative electrode current collector, wherein the negative electrode active material layer 20 includes a negative electrode active material and a negative electrode modified binder. Specifically, the negative electrode current collector is copper foil or aluminum foil, and the negative electrode active material may be, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon carbon and silicon dioxide. In one embodiment of the present application, the negative electrode active material is natural graphite. In another embodiment of the present application, the negative electrode active material is hard carbon.

[0079] In one embodiment of the present application, the mass ratio of the negative electrode modified binder to the negative electrode active material is 0.1:100 to 5:100. Adding a small amount of negative electrode modified binder can improve the uniform distribution of the negative electrode active material in the negative electrode active material layer, enhance the bonding strength between the negative electrode active material layer and the current collector, improve the flexibility of the negative electrode active material layer, and enhance the ion conductivity. Specifically, the mass ratio of the negative electrode modified binder to the negative electrode active material can be but is not limited to 0.01:100, 0.1:100, 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, or 5:100. In one embodiment of the present application, the mass ratio of the negative electrode modified binder to the negative electrode active material is 0.01:100 to 2:100. In another embodiment of the present application, the mass ratio of the negative electrode modified binder to the negative electrode active material is 0.8:100 to 5:100.

[0080] In one embodiment of the present application, the negative electrode active material layer further includes a conductive agent, and the mass ratio of the conductive agent to the negative electrode active material is 0.01% to 5%. Specifically, the conductive agent includes one or more of conductive carbon black, conductive graphite, graphene, carbon nanotubes and carbon fibers, and the mass ratio of the conductive agent to the negative electrode active material can be, but is not limited to, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4% or 5%, etc.

[0081] In one embodiment of the present application, the negative electrode active material layer also includes an auxiliary binder, and the mass ratio of the auxiliary binder to the negative electrode active material is 0.01% to 5%. The addition of the auxiliary binder can further improve the bonding ability and flexibility of the negative electrode active material layer. Specifically, the auxiliary binder can be a styrene-butadiene rubber emulsion or a styrene-acrylic emulsion, and the mass ratio of the auxiliary binder to the negative electrode active material can be, but is not limited to, 0.01%, 0.05%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 1.8%, 2%, 3%, 4% or 5%, etc. In one embodiment of the present application, a negative electrode modified binder is obtained by modifying one or more negative electrode binders of lithium salts, sodium salts and potassium salts of cellulose derivatives, and the negative electrode active material layer includes a negative electrode active material, a negative electrode modified binder and an auxiliary binder styrene-butadiene rubber emulsion.

[0082] In one embodiment of the present application, the negative electrode slurry is coated on the surface of the negative electrode current collector, and after drying, a negative electrode material layer is formed to obtain a negative electrode plate. In one embodiment of the present application, the negative electrode slurry includes a negative electrode active material, a negative electrode modified binder and a negative electrode solvent. In another embodiment of the present application, the negative electrode slurry may also include at least one of a conductive agent and an auxiliary binder. Specifically, the above components can be added to the negative electrode solvent and mixed to obtain a negative electrode slurry. In one embodiment, the solid content of the negative electrode slurry can be 45% to 55%. In one embodiment, the negative electrode modified binder is stirred and dissolved in deionized water to obtain a mixed solution, and the mass concentration range of the mixed solution is 0.1% to 3.0% (such as 0.4%, 0.8%, 1.5%, 1.9%, 2.5%, 3%, etc.); the negative electrode active material and the conductive agent are placed in a double planetary agitator, and the mixed solution configured above is added after sufficient stirring and mixing to obtain a solid content of 60% to 80% (such as 60%, 62%, 65%, 6 7%, 70%, 75%, 80%, etc.); then add the mixed solution configured above again to make the solid content of the mixed slurry 50% to 60% (such as 50%, 52%, 54%, 55%, 58%, 60%, etc.); then add the auxiliary binder, continue to stir evenly, add deionized water to obtain the negative electrode slurry, and the solid content of the negative electrode slurry is 45% to 55% (such as 45%, 48%, 52%, 50%, 55%, etc.).

[0083] In one embodiment of the present application, the peel strength between the negative electrode current collector and the negative electrode active material layer is 5N / m to 50N / m. Specifically, the peel strength between the negative electrode current collector and the negative electrode active material layer may be, but is not limited to, 5N / m, 10N / m, 15N / m, 20N / m, 30N / m, 35N / m, 40N / m, 45N / m or 50N / m, etc. Please refer to Figure 3 , is a schematic diagram of the peeling strength test of the negative electrode current collector and the negative electrode active material layer provided in one embodiment of the present application. A negative electrode active material layer 20 is provided on the negative electrode current collector 10, and the negative electrode active material layer 20 is bonded to the resin plate 40 by a double-sided adhesive tape 30 (such as 3M double-sided adhesive tape) to form a test group. The test group was repeatedly rolled and placed in a 180° peeling machine for a peeling strength test. The length of the negative electrode current collector and the negative electrode active material layer tested was 200 mm and the width was 20 mm. The length of the resin plate was 250 mm, the width was 40 mm, the thickness was 5 mm, and the width of the 3M double-sided adhesive tape was 20 mm. In one embodiment of the present application, the peeling strength between the negative electrode current collector and the negative electrode active material layer is 15 N / m. In another embodiment of the present application, the peeling strength between the negative electrode current collector and the negative electrode active material layer is 45 N / m.

[0084] In one embodiment of the present application, the electrochemical reaction impedance of the negative electrode plate is 20Ω to 140Ω. The smaller the electrochemical reaction impedance, the smaller the resistance during charge transfer and the better the battery performance. The electrochemical reaction impedance of the negative electrode plate is obtained by electrochemical impedance spectroscopy test. The test button assembly model is CR2025, the test conditions are 25°C, 50% SOC, and the test frequency is 0.05Hz-100000Hz. Specifically, the electrochemical reaction impedance of the negative electrode plate may be, but is not limited to, 20Ω, 30Ω, 40Ω, 50Ω, 60Ω, 70Ω, 80Ω, 90Ω, 100Ω, 110Ω, 120Ω or 140Ω, etc. In one embodiment of the present application, the electrochemical reaction impedance of the negative electrode plate may be 40Ω. In another embodiment of the present application, the electrochemical reaction impedance of the negative electrode plate may be 70Ω.

[0085] The present application provides a battery, the battery comprising a positive electrode sheet and a negative electrode sheet in any one of the above embodiments. The battery has low electrochemical reaction impedance and excellent performance, which is conducive to the wide application of the battery. Specifically, the battery can be, but is not limited to, a lithium ion battery, a sodium ion battery, etc.

[0086] In one embodiment of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. Specifically, the positive electrode current collector includes aluminum foil, and the positive electrode active material layer includes a positive electrode active material and a positive electrode binder. In one embodiment of the present application, the battery also includes a separator disposed between the positive electrode plate and the negative electrode plate. Specifically, the separator may be, but is not limited to, a woven film, a non-woven fabric, a microporous film, a composite film, a rolled film or a separator paper, etc. In one embodiment of the present application, the battery also includes an electrolyte. Among them, at least part of the positive electrode plate and at least part of the negative electrode plate are immersed in the electrolyte. The electrolyte of the present application is not particularly limited, and may be, but is not limited to, a substance that can be used as a battery electrolyte in the art.

[0087] The present application also provides an electric device, including a battery in any of the above embodiments. The electric device provided by the present application has excellent performance and strong product competitiveness. The electric device of the present application may refer to a vehicle, an electronic device, an energy storage system, etc., and the above electrochemical device may be arranged in the electric device in the form of a single cell, a battery module, a battery pack, a capacitor, etc.

[0088] The effect of the applied technical solution is further explained below through specific examples.

[0089] Example 1

[0090] After mixing the negative electrode binder (sodium carboxymethyl cellulose), the first water-soluble monomer (acrylic acid), the second water-soluble monomer (2-hydroxypropyl acrylate), the third water-soluble monomer (2-(2-ethoxyethoxy)ethyl acrylate) and the hydrophobic monomer (styrene), an initiator (ammonium persulfate) was added, and a polymerization reaction was carried out at 40°C. After the polymerization reaction, LiOH was added to adjust the pH value to 7 to obtain a negative electrode modified binder. The mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:0.1:0.02:0.05:0.02, and the mass ratio of the initiator to the negative electrode binder is 1%.

[0091] Example 2

[0092] The difference from Example 1 is that the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:0.05:0.02:0.1:0.02.

[0093] Example 3

[0094] The difference from Example 1 is that the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:0.03:0.01:0.03:0.01.

[0095] Example 4

[0096] The difference from Example 1 is that the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:0.25:0.1:0.15:0.1.

[0097] Example 5

[0098] The difference from Example 1 is that the negative electrode binder is polyvinyl alcohol.

[0099] Comparative Example 1

[0100] The difference from Example 1 is that the negative electrode binder is used directly without modification.

[0101] Comparative Example 2

[0102] The difference from Example 1 is that the first water-soluble monomer is not added, and the mass ratio of the negative electrode binder, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:0.02:0.05:0.02.

[0103] Comparative Example 3

[0104] The difference from Example 1 is that the second water-soluble monomer is not added, and the mass ratio of the negative electrode binder, the first water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:0.1:0.05:0.02.

[0105] Comparative Example 4

[0106] The difference from Example 1 is that the third water-soluble monomer is not added, and the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer and the hydrophobic monomer is 1:0.1:0.02:0.02.

[0107] Comparative Example 5

[0108] The difference from Example 1 is that no hydrophobic monomer is added, and the mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer and the third water-soluble monomer is 1:0.1:0.02:0.05.

[0109] Comparative Example 6

[0110] The difference from Example 1 is that the third water-soluble monomer is used alone to modify the negative electrode binder, and the mass ratio of the negative electrode binder to the third water-soluble monomer is 1:0.05.

[0111] Performance Testing

[0112] The negative electrode modified binder prepared in the above Examples 1 to 5 and Comparative Examples 1 to 6 was mixed with a negative electrode active material (artificial graphite), a conductive agent (carbon black), and an auxiliary binder (styrene-butadiene rubber latex) to prepare a negative electrode slurry. The negative electrode slurry was coated on a negative electrode current collector (copper foil, 8 um) and dried and rolled to prepare a negative electrode sheet. The obtained negative electrode sheet had a thickness of 128 um and a compaction density of 1.5 g / cm 3 .

[0113] The peel strength between the negative electrode current collector and the negative electrode active material layer in the negative electrode sheet is tested. The length of the negative electrode current collector and the negative electrode active material layer tested is 200mm, the width is 20mm, the length of the resin plate is 250mm, the width is 40mm, the thickness is 5mm, and the width of the 3M double-sided tape is 20mm. Please refer to Figure 4 , a schematic diagram of a peel strength test process of a negative electrode current collector and a negative electrode active material layer provided in an embodiment of the present application, wherein the negative electrode active material layer 20 is peeled off from the negative electrode current collector 10 to obtain a peel strength, and the specific test results are shown in Table 1.

[0114] The above negative electrode sheet and positive electrode sheet (lithium iron phosphate), electrolyte (propylene carbonate, dimethyl carbonate and ethyl methyl carbonate, volume ratio of 1:1:1, 1 mol / L lithium hexafluorophosphate), and separator (polypropylene separator) were made into CR2025 type button half-cell. The button cell was subjected to electrochemical impedance spectroscopy test at 25°C and 50% SOC, and the electrochemical reaction impedance results are shown in Table 1.

[0115] Table 1 Performance test results

[0116] Peel strength (N / m) Electrochemical reaction impedance (Ω) Example 1 48 36 Example 2 42 22 Example 3 33 43 Example 4 28 63 Example 5 43 85 Comparative Example 1 10 135 Comparative Example 2 18 82 Comparative Example 3 24 53 Comparative Example 4 43 115 Comparative Example 5 28 72 Comparative Example 6 13 75

[0117] It can be seen that compared with the comparative example, the negative electrode modified binder prepared in the embodiment of the present application has high peeling strength, low electrochemical reaction impedance, and excellent battery binding performance and electrochemical performance. Among them, it can be seen from the comparison between Example 1 and Comparative Examples 2-6 that the first water-soluble monomer can improve the peeling strength of the pole piece, the second water-soluble monomer plays an auxiliary role, further enhancing the bonding ability of the negative electrode modified binder, and the addition of the third water-soluble monomer can significantly reduce the electrochemical reaction impedance. The hydrophobic monomer helps to enhance the interaction between the negative electrode modified binder and graphite, and indirectly improves the peeling strength; compared with Example 4, the amount of modified monomer added in Example 1 is more appropriate, which can further improve the peeling strength and electrochemical reaction impedance of the negative electrode modified binder.

[0118] The above is a preferred embodiment of the present application, but it should not be understood as limiting the scope of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application, and these improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A negative electrode modified binder, characterized in that: The negative electrode modified binder comprises a first unit, a second unit, a third unit and a fourth unit, wherein the structure of the first unit is shown in formula (I), the structure of the second unit is shown in formula (II), the structure of the third unit is shown in formula (III), and the structure of the fourth unit is shown in formula (IV), The R1 is selected from -H, -Na or -Li, the R2 and the R4 are independently selected from -H or -CH3, the R3 is an alkylene group, the R5 is selected from -H, -CH3 or -CH2CH3, the R6 is selected from -CN, -CH=CH2, -COOR 1 、-OCOR 2 ,-CONHR 3 、-COOR 4 OH, -OCOR 5 OH or -Ph-R 6 , the R 1 , the R 2 and the R 3 is an alkyl group, the R 4 and the R 5 is an alkylene group, said R 6 is -H, -OH, -SO3H or -OP=O(OH)2, and m is an integer greater than or equal to 1.

2. The negative electrode modified binder according to claim 1, characterized in that The repetition numbers of the first unit, the second unit, the third unit and the fourth unit in the negative electrode modified binder are independently selected from integers ranging from 1 to 2,000.

3. The negative electrode modified binder according to claim 1, characterized in that: The m is an integer from 1 to 18.

4. A method for preparing a negative electrode modified binder, characterized in that: include: A negative electrode binder, a first water-soluble monomer, a second water-soluble monomer, a third water-soluble monomer and a hydrophobic monomer are mixed to form a mixture, and a negative electrode modified binder is obtained after a polymerization reaction; the negative electrode modified binder includes a first unit, a second unit, a third unit and a fourth unit, the structure of the first unit is shown in formula (I), the structure of the second unit is shown in formula (II), the structure of the third unit is shown in formula (III), and the structure of the fourth unit is shown in formula (IV), The R1 is selected from -H, -Na or -Li, the R2 and the R4 are independently selected from -H or -CH3, the R3 is an alkylene group, the R5 is selected from -H, -CH3 or -CH2CH3, the R6 is selected from -CN, -CH=CH2, -COOR 1 、-OCOR 2 ,-CONHR 3 、-COOR 4 OH, -OCOR 5 OH or -Ph-R 6 , the R 1 , the R 2 and the R 3 is an alkyl group, the R 4 and the R 5 is an alkylene group, said R 6 is -H, -OH, -SO3H or -OP=O(OH)2, and m is an integer greater than or equal to 1.

5. The preparation method according to claim 4, characterized in that: The structural formula of the first water-soluble monomer is CH2=CHCOOR1, The structural formula of the second water-soluble monomer is CHR2=CHCOOR3OH, The structural formula of the third water-soluble monomer is CHR4=CHCOO(CH2CH2O) m CH2CH3, The structural formula of the hydrophobic monomer is CH2=CR5R6.

6. The preparation method according to claim 4, characterized in that: The mass ratio of the negative electrode binder, the first water-soluble monomer, the second water-soluble monomer, the third water-soluble monomer and the hydrophobic monomer is 1:(0.001-0.5):(0.001-0.5):(0.001-0.5):(0.001-0.5).

7. The preparation method according to claim 4, characterized in that: The negative electrode binder includes at least one of a synthetic polymer and a biomass polymer. The synthetic polymer includes at least one of polyvinyl alcohol, polyvinyl butyral, polyethylene glycol and polypropylene glycol, and the biomass polymer includes at least one of lithium salt, sodium salt and potassium salt of cellulose derivatives. The degree of substitution of the biomass macromolecule is 0.6 to 1.

5.

8. The preparation method according to claim 4, characterized in that: The mixture also includes an initiator; the initiator includes at least one of benzoyl peroxide, methyl ethyl ketone peroxide, potassium persulfate, ammonium persulfate, ammonium sulfate, sodium sulfite and ferrous chloride; The mass ratio of the initiator to the negative electrode binder is 0.1% to 20%.

9. The preparation method according to claim 4, characterized in that: The polymerization temperature is 20°C to 60°C.

10. A negative electrode plate, characterized in that: The negative electrode sheet comprises a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active material and the negative electrode modified binder according to any one of claims 1 to 3 or the negative electrode modified binder prepared by the preparation method according to any one of claims 4 to 9.

11. The negative electrode sheet according to claim 10, characterized in that: The mass ratio of the negative electrode modification binder to the negative electrode active material is 0.1:100 to 5:

100.

12. The negative electrode sheet according to claim 10, characterized in that: The negative electrode sheet further includes a negative electrode current collector, the negative electrode active material layer is disposed on the surface of the negative electrode current collector, and the peel strength between the negative electrode current collector and the negative electrode active material layer is 5N / m to 50N / m.

13. A battery, characterized in that: The battery comprises a positive electrode sheet and a negative electrode sheet as claimed in any one of claims 10 to 12.

14. An electrical device, characterized in that: The electrical device comprises the battery according to claim 13.

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