A negative electrode binder, a negative electrode coating composition, a negative electrode sheet, and a lithium ion battery

Abstract

The present invention relates to a negative electrode binder, a negative electrode coating composition, a negative electrode sheet and a lithium ion battery. The negative electrode binder is obtained by reacting an acrylic monomer, a cyanide group-containing polymerizable monomer, a polyether monomer and a polymerizable double bond monomer; the cyanide group-containing polymerizable monomer is selected from monomers containing vinyl and cyanide groups with 3 to 10 carbon atoms; the polyether monomer is selected from at least one of polyethylene oxide with a polymerizable double bond, polypropylene oxide with a polymerizable double bond or an ethylene oxide-propylene oxide copolymer with a polymerizable double bond; the polymerizable double bond monomer includes at least one of acrylate monomers with two or more polymerizable double bonds, methacrylate monomers with two or more polymerizable double bonds, and allyl monomers with two or more polymerizable double bonds. The negative electrode binder can provide functions such as dispersion, suspension, thickening power and adhesion superior to carboxymethyl cellulose, simplifies the production process, and improves the performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a negative electrode binder, a negative electrode coating composition, a negative electrode sheet and a lithium-ion battery. Background Art

[0002] As a highly potential rechargeable battery, lithium-ion secondary batteries are widely popular in the market. This kind of battery is favored for its high energy density, long life, small size, maintenance-free and environmental protection characteristics. Initially applied to mobile phones and laptop computers, it has now been extended to the fields of electric bicycles, electric vehicles, energy storage systems and various portable electronic devices, becoming an ideal mobile power solution.

[0003] The basic structure of a lithium-ion secondary battery includes a positive electrode, a negative electrode, a separator, an electrolyte and a battery case. In currently commercialized lithium-ion batteries, the negative electrode material mostly uses graphite or carbon materials synthesized based on graphite. Commonly used negative electrode binders include carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and polyacrylic acid (PAA). Among them, the main function of CMC is to stabilize the dispersion system and adjust the viscosity; SBR provides flexibility and adhesion, and the two are usually used in combination to achieve the best effect. As another negative electrode binder, PAA is usually used in combination with CMC and SBR, which helps to improve the peel strength and other performance indicators of the battery electrode sheet.

[0004] Currently, the PAA negative electrode binder on the market is usually provided in the form of an aqueous solution with a solid content of 5%-10%, and its viscosity is generally above 3000 mPa·s. A higher PAA solid content will lead to too high viscosity, which not only increases the complexity of the manufacturing process, but also may cause difficulties in the coating process. In addition, a lower solid content also means that more solvents are needed for dilution, which not only increases the production and transportation costs, but also has an adverse impact on the environment. Therefore, developing a more efficient powder-like PAA binder with excellent comprehensive performance is of great significance for improving the overall performance of lithium-ion secondary batteries. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a negative electrode binder, a negative electrode coating composition, a negative electrode sheet and a lithium-ion battery, using the negative electrode binder and the negative electrode coating composition, negative electrode sheet and lithium-ion battery prepared with this binder. This binder shows unique performance advantages in the manufacturing process of lithium-ion batteries, and can simultaneously provide various functions such as dispersion, suspension, thickening power and adhesion superior to carboxymethyl cellulose (CMC), thus simplifying the production process, reducing the amount of binder used, and improving the overall performance of the battery.

[0006] In a first aspect, the present invention provides a negative electrode binder, which is obtained by polymerizing an acrylic monomer, a cyanide group-containing polymerizable monomer, a polyether monomer, and a polymerizable double bond monomer;

[0007] Among them, the cyanide group-containing polymerizable monomer is selected from monomers containing vinyl and cyanide groups with 3 to 10 carbon atoms;

[0008] The polyether monomer is selected from at least one of polyethylene oxide with a polymerizable double bond, polypropylene oxide with a polymerizable double bond, or an ethylene oxide-propylene oxide copolymer with a polymerizable double bond;

[0009] The polymerizable double bond monomer includes at least one of acrylate monomers with two or more polymerizable double bonds, methacrylate monomers with two or more polymerizable double bonds, and allyl monomers with two or more polymerizable double bonds.

[0010] In the present invention, the acrylic monomer serves as the basic monomer to provide the basic binding performance of the binder; the cyanide group-containing polymerizable monomer is selected from monomers containing vinyl and cyanide groups with 3 to 10 carbon atoms and is used to improve the binding force of the binder; the polyether monomer is used to increase the flexibility of the binder; the polymerizable double bond monomer is used as a crosslinking agent to adjust the viscosity of the binder. Among them, introducing the cyanide group-containing polymerizable monomer can significantly improve the binding force of the binder because after polymerization of monomers containing vinyl and cyanide groups with 3 to 10 carbon atoms, the intermolecular interaction force can be enhanced, thereby improving the adhesion ability between the binder and the active material; by introducing the polyether monomer, the flexibility of the binder can be effectively increased. This flexibility is particularly important for the electrode sheet that undergoes various processing steps (such as rolling, slicing, and winding) during battery manufacturing, and can effectively prevent the phenomena of powder falling or fracture; the polymerizable double bond monomer containing two or more polymerizable double bonds is used as a crosslinking agent to adjust the viscosity of the binder to be within a reasonable range, which is crucial for preparing the negative electrode sheet because it ensures the uniformity and stability of the electrode sheet during the manufacturing process.

[0011] Preferably, the mass ratio of the acrylic monomer, the cyanide group-containing polymerizable monomer, the polyether monomer, and the polymerizable double bond monomer is (66~98):(3~10):(3~10):(0.5~2). More preferably, it is (69~90):(5~8):(5~8):(0.8~1.6). In the present invention, the mass ratio of the above-mentioned monomers is the ratio of the masses to each other, not the percentage content ratio.

[0012] Preferably, the acrylic monomer can be various acrylic monomers commonly used in the art. For example, it can be at least one of C1-C18 alkyl monoesters of acrylic acid, methacrylic acid, β-(acryloyloxy) propionic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, crotonic acid, and aconitic acid, C1-C18 alkyl monoesters of maleic acid, C1-C18 alkyl monoesters of fumaric acid, C1-C18 alkyl monoesters of itaconic acid, and C1-C18 alkyl monoesters of aconitic acid.

[0013] Preferably, the vinyl monomer is selected from at least one of acrylonitrile, methacrylonitrile, cyanostyrene, and cyanoacrylate.

[0014] In the present invention, acrylonitrile has good heat resistance and chemical stability, and acrylonitrile-based polymers can improve the solvent resistance and mechanical strength of the binder; methacrylonitrile is similar to acrylonitrile but has higher heat resistance. It can also improve the heat resistance and mechanical properties of the binder; cyanostyrene polymers have good thermal stability and chemical stability and can be used to improve the high-temperature resistance of the binder; polymers of monomers such as cyanoacrylate have the characteristics of rapid curing and good bonding properties, and they can be used to improve the bonding speed and strength of the binder.

[0015] Preferably, the molecular weight of the polyethylene oxide with a polymerizable double bond, the polypropylene oxide with a polymerizable double bond, or the ethylene oxide-propylene oxide copolymer with a polymerizable double bond is selected from 500 to 2000, preferably 800 to 1600.

[0016] In the present invention, the molecular weight range is selected from 500 to 2000, which generally makes the negative electrode slurry prepared from the above polymers have a suitable viscosity, is easier to process and handle, and further enables the negative electrode sheet to have better flexibility and bonding strength.

[0017] Preferably, the polymerizable double bond groups in the polyether monomer are selected from at least one of acrylate groups, methacrylate groups, allyl ether groups, and methallyl ether groups.

[0018] In the present invention, the acrylate functional group has a vinyl (C=C) double bond, which enables the polyether monomer to copolymerize with other monomers through a free radical polymerization reaction. The acrylate functional group can provide good adhesion and flexibility; the methacrylate functional group is similar to the acrylate, but has an additional methyl group substituting a hydrogen atom of the vinyl group, which results in the methacrylate being more hydrolysis-resistant than the acrylate and also having higher thermal stability. The allyl ether functional group also has a vinyl double bond and can participate in the free radical polymerization reaction. The allyl ether functional group can improve the reactivity of the polymer and, in some cases, can also provide good weather resistance and chemical resistance; the methallyl ether functional group is similar to the allyl ether but has an additional methyl substituent, which can improve its mechanical properties and thermal stability.

[0019] Preferably, the acrylate monomer with two or more polymerizable double bonds is selected from at least one of ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, glycerol triacrylate, and pentaerythritol triacrylate.

[0020] In the present invention, ethylene glycol diacrylate has two acrylate groups and can increase the crosslinking degree of the polymer. Diethylene glycol diacrylate is similar to EGDA but has a longer flexible chain segment, which may affect the flexibility and crosslinking density of the polymer. Propylene glycol diacrylate is similar to the above two but has a slightly different structure and may have different performance characteristics; dipropylene glycol diacrylate has a longer chain segment and can provide better flexibility. Tripropylene glycol diacrylate has an even longer flexible chain segment and is suitable for applications that require higher flexibility; trimethylolpropane triacrylate has three acrylate groups and can form a highly crosslinked network structure, improving the hardness and heat resistance of the polymer; glycerol triacrylate also has three acrylate groups and can increase the crosslinking density of the polymer; pentaerythritol triacrylate has three acrylate groups and is suitable for applications that require high crosslinking.

[0021] Preferably, the methacrylate monomer with two or more polymerizable double bonds is selected from at least one of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, propylene glycol dimethacrylate, dipropylene glycol dimethacrylate, tripropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, glycerol trimethacrylate, and pentaerythritol trimethacrylate.

[0022] In the present invention, ethylene glycol dimethacrylate has two methacrylate groups, which can increase the crosslinking degree of the polymer; diethylene glycol dimethacrylate is similar to EGDMA but has a longer flexible chain segment, which may affect the flexibility and crosslinking density of the polymer; propylene glycol dimethacrylate is similar to the above two but has a slightly different structure and may have different performance characteristics; dipropylene glycol dimethacrylate has a longer chain segment and can provide better flexibility; tripropylene glycol dimethacrylate has an even longer flexible chain segment and is suitable for applications that require higher flexibility; trimethylolpropane trimethacrylate has three methacrylate groups and can form a highly crosslinked network structure to improve the hardness and heat resistance of the polymer; glycerol trimethacrylate also has three methacrylate groups and can increase the crosslinking density of the polymer; pentaerythritol trimethacrylate has three methacrylate groups and is suitable for applications that require high crosslinking.

[0023] The allyl monomers with two or more polymerizable double bonds are selected from at least one of diallyl phthalate, glycerol diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, and diallyl adipate.

[0024] Preferably, the above-mentioned acrylate monomers with two or more polymerizable double bonds and methacrylate monomers with two or more polymerizable double bonds are used to manufacture adhesives. They copolymerize with the main-chain polymer to form a crosslinked network, thereby improving the mechanical properties, thermal stability, and chemical stability of the adhesives.

[0025] The negative electrode binder provided by the present invention is obtained by polymerizing the above-mentioned acrylic monomers, cyanide-containing polymerizable monomers, polyether monomers, and polymerizable double-bond monomers. Its preparation method can be a conventional double-bond polymerization method. Preferably, the specific steps for preparing the negative electrode binder include adding the raw materials of the first aspect and a reaction solvent into a reaction flask, purging with nitrogen and heating up. After the temperature reaches the reaction temperature, an initiator is added for polymerization reaction, and the reaction is continued while maintaining the temperature until the end. After filtration and drying, a binder powder is obtained.

[0026] Among them, the reaction solvent is selected from a mixture composed of one or more organic solvents and one or more hydrocarbon solvents. The organic solvents include ketones, esters, ethers, and saturated alcohols, preferably alkyl acetates with 1 to 6 carbon atoms, more preferably alkyl acetates with 2 to 4 carbon atoms, including ethyl acetate, isopropyl acetate, and butyl acetate. The hydrocarbon solvents are selected from straight-chain, branched-chain, or cyclic hydrocarbons with 4 to 10 carbon atoms, more preferably straight-chain, branched-chain, or cyclic hydrocarbons with 5 to 8 carbon atoms, including pentane, hexane, heptane, octane, cyclopentane, cyclohexane, and cycloheptane. The ratio of the organic solvent to the hydrocarbon solvent is 80:20 - 5:95, preferably 2:1 - 1:2; the ratio of the monomer to the reaction solvent is 10:9-20:80, the polymerization reaction temperature is 40 - 8℃, the initiator is a peroxide, specifically but not limited to one or more of benzoyl peroxide, lauroyl peroxide, di-sec-butyl peroxydicarbonate, diisooctyl peroxydicarbonate, diisopropyl peroxydicarbonate, and dicyclohexyl peroxydicarbonate, and the dosage of the initiator is 0.1 - 3 wt% of the total weight of the monomer.

[0027] In a second aspect, a negative electrode coating composition includes the negative electrode binder as described above. Preferably, the negative electrode coating composition further includes a styrene-butadiene rubber binder. More preferably, the mass ratio of the negative electrode binder to the styrene-butadiene rubber binder is 0.5 - 1.5:0.5 - 1.5. According to the present invention, in a more preferred case, the negative electrode coating composition includes the negative electrode binder, styrene-butadiene rubber binder, conductive carbon black Super P, and artificial graphite as described above.

[0028] Among them, the mass ratio of the negative electrode binder, styrene-butadiene rubber binder, conductive carbon black Super P, and artificial graphite is (0.5 - 1.5):(0.5 - 1.5):1:(96 - 98).

[0029] The steps for preparing the negative electrode coating composition include dispersing the negative electrode binder described in the present application in water, adding an alkali to adjust the pH value to 6.5 - 7.5, then adding conductive carbon black and artificial graphite and dispersing them at high speed, and finally adding the styrene-butadiene rubber binder, and stirring evenly to obtain it.

[0030] The alkali can be at least one of sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, lithium carbonate, lithium bicarbonate, or ammonia water.

[0031] The viscosity of the negative electrode coating composition is 3000 - 5000 mPa·s.

[0032] In a third aspect, a negative electrode sheet is obtained by coating, drying, and rolling the negative electrode coating composition prepared as in the second aspect. The areal density of the negative electrode sheet is 80 - 100 g / m 2 , and the tap density is 1.4 - 1.8 g / cm3 。

[0033] In a fourth aspect, the negative electrode sheet of the third aspect is used for assembling a lithium-ion battery.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. The negative electrode binder prepared by the present invention can simultaneously provide functions such as dispersion, suspension, thickening, and adhesion, which means that it can replace multiple components in the traditional binder system, such as carboxymethyl cellulose and styrene-butadiene latex, and can completely avoid using CMC. This not only simplifies the process flow but also helps improve the battery performance. Compared with the traditional binder system, this negative electrode binder can significantly reduce the usage amount of SBR, thereby reducing costs and at the same time reducing the impact on the environment. This binder is provided in powder form, which is not only convenient for transportation but also can significantly reduce transportation costs. In addition, the binder in powder form is easier to control the addition amount during use, which is beneficial to improving production efficiency.

[0036] 2. In the raw materials of the negative electrode binder prepared by the present invention, acrylic acid is used to provide the basic adhesion performance of the binder, a cyanide-containing polymerizable monomer is used to improve the adhesion of the binder, a polyether monomer is used to increase the flexibility of the binder, and a polymerizable double-bond monomer is used as a crosslinking agent to adjust the viscosity of the binder. Detailed Embodiments

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] Example 1

[0039] This example provides a negative electrode binder, which is obtained by the polymerization reaction of an acrylic acid monomer, a cyanide-containing polymerizable monomer, a polyether monomer, and a polymerizable double-bond monomer. The preparation steps specifically include the following: adding the acrylic acid monomer, the cyanide-containing polymerizable monomer, the polyether monomer, the polymerizable double-bond monomer, and the reaction solvent into a reaction flask, passing nitrogen and heating up, carrying out precipitation polymerization reaction, adding an initiator after the temperature reaches the reaction temperature and keeping warm to continue the reaction until the end, thus obtaining the negative electrode binder.

[0040] Among them, the mass ratio of acrylic acid, the cyanide-containing polymerizable monomer, the polyether monomer, and the polymerizable double-bond monomer is 66:3:3:0.5;

[0041] The acrylic monomer is acrylic acid, the cyano-containing polymerizable monomer is acrylonitrile, the polyether monomer is methoxypolyethylene glycol (molecular weight 600) methacrylate, and the polymerizable double bond monomer is trimethylolpropane triacrylate.

[0042] The organic solvent is ethyl acetate, and the hydrocarbon solvent is cyclohexane. The ratio of the organic solvent to the hydrocarbon solvent is 2:1; the ratio of the total mass of the monomers to the reaction solvent is 10:90, and the polymerization reaction temperature is 40 °C.

[0043] The initiator is bis(2-ethylhexyl) peroxydicarbonate, and the dosage is 0.1 wt% of the total mass of the monomers.

[0044] This example provides a negative electrode coating composition, and the specific raw material ratio is as follows: the mass ratio of the negative electrode binder, styrene-butadiene rubber binder, conductive carbon black Super P, and artificial graphite is 1:1:1:97.

[0045] This example provides a negative electrode sheet, which is prepared by coating with the negative electrode coating composition.

[0046] This example provides a lithium-ion battery equipped with the negative electrode sheet.

[0047] Example 2

[0048] This example provides a negative electrode binder, which is obtained by polymerizing an acrylic monomer, a cyano-containing polymerizable monomer, a polyether monomer, and a polymerizable double bond monomer. The preparation steps specifically include the following: adding the acrylic monomer, the cyano-containing polymerizable monomer, the polyether monomer, the polymerizable double bond monomer, and the reaction solvent into a reaction flask, purging with nitrogen and heating up, carrying out precipitation polymerization reaction, adding the initiator after the temperature reaches the reaction temperature and maintaining the temperature to continue the reaction until the end to obtain the negative electrode binder.

[0049] Among them, the mass ratio of the acrylic monomer, the cyano-containing polymerizable monomer, the polyether monomer, and the polymerizable double bond monomer is 70:7:6:1;

[0050] The acrylic monomer is acrylic acid, the cyano-containing polymerizable monomer is methacrylonitrile, the polyether monomer is allyl polyoxyethylene ether (molecular weight 1000), and the polymerizable double bond monomer is pentaerythritol triallyl ether.

[0051] The organic solvent is butyl acetate, and the hydrocarbon solvent is hexane. The ratio of the organic solvent to the hydrocarbon solvent is 1:1; the ratio of the total mass of the monomers to the reaction solvent is 15:85, and the polymerization reaction temperature is 60 °C.

[0052] The initiator is dilauroyl peroxide, and the dosage is 0.5 wt% of the total mass of the monomers.

[0053] This embodiment also provides a negative electrode coating composition, and the specific raw material ratios are as follows: the mass ratio of the negative electrode binder, styrene-butadiene rubber binder, conductive carbon black Super P, and artificial graphite is 0.5:0.5:1:98.

[0054] This embodiment provides a negative electrode plate, which is prepared by coating, drying, and rolling with the negative electrode coating composition.

[0055] This embodiment provides a lithium-ion battery equipped with the negative electrode plate.

[0056] Example 3

[0057] This embodiment provides a negative electrode binder, which is obtained by polymerizing acrylic acid monomers, cyanide-containing polymerizable monomers, polyether monomers, and polymerizable double-bond monomers. The specific preparation steps are as follows: Add acrylic acid monomers, cyanide-containing polymerizable monomers, polyether monomers, polymerizable double-bond monomers, and a reaction solvent into a reaction flask, pass nitrogen and raise the temperature, and carry out precipitation polymerization. After the temperature reaches the reaction temperature, add an initiator and keep the temperature for continuous reaction until the end to obtain the negative electrode binder.

[0058] Among them, the mass ratio of the acrylic acid monomer, cyanide-containing polymerizable monomer, polyether monomer, and polymerizable double-bond monomer is 98:10:10:2;

[0059] The acrylic acid monomer is methacrylic acid, the cyanide-containing polymerizable monomer is acrylonitrile, the polyether monomer is allyl polyoxyethylene ether (molecular weight 2000), and the polymerizable double-bond monomer with two or more polymerizable double bonds is glycerol triacrylate.

[0060] The organic solvent is butyl acetate, and the hydrocarbon solvent is heptane. The ratio of the organic solvent to the hydrocarbon solvent is 2:1; the ratio of the total mass of the monomers to the reaction solvent is 20:80, and the polymerization reaction temperature is 80 °C.

[0061] The initiator is benzoyl peroxide, and the dosage of the initiator is 1 wt% of the total mass of the monomers.

[0062] This embodiment also provides a negative electrode coating composition, and the specific raw material ratios are as follows: the mass ratio of the negative electrode binder, styrene-butadiene rubber binder, conductive carbon black Super P, and artificial graphite is 1.5:1.5:1:96.

[0063] This embodiment provides a negative electrode plate, which is prepared by coating with the negative electrode coating composition.

[0064] This embodiment provides a lithium-ion battery equipped with the negative electrode plate.

[0065] Example 4

[0066] The difference from Example 2 lies in that the mass ratio of the acrylic monomer, the polymerizable monomer containing a cyano group, the polyether monomer, and the polymerizable double bond monomer is 70:4:6:1.

[0067] Example 5

[0068] The difference from Example 2 lies in that the mass ratio of the acrylic monomer, the polymerizable monomer containing a cyano group, the polyether monomer, and the polymerizable double bond monomer is 70:9:6:1.

[0069] Example 6

[0070] The difference from Example 2 lies in that the mass ratio of the acrylic monomer, the polymerizable monomer containing a cyano group, the polyether monomer, and the polymerizable double bond monomer is 70:7:4:1.

[0071] Example 7

[0072] The difference from Example 2 lies in that the mass ratio of the acrylic monomer, the polymerizable monomer containing a cyano group, the polyether monomer, and the polymerizable double bond monomer is 70:7:9:1.

[0073] Example 8

[0074] The difference from Example 2 lies in that the mass ratio of the acrylic monomer, the polymerizable monomer containing a cyano group, the polyether monomer, and the polymerizable double bond monomer is 70:7:6:0.8.

[0075] Example 9

[0076] The difference from Example 2 lies in that the mass ratio of the acrylic monomer, the polymerizable monomer containing a cyano group, the polyether monomer, and the polymerizable double bond monomer is 70:7:6:1.8.

[0077] Comparative Example 1

[0078] The difference from Example 2 lies in that a traditional SBR-CMC system is used as the binder. The mass ratio of CMC, styrene-butadiene rubber binder, conductive carbon black Super P, and artificial graphite is 0.5:0.5:1:98.

[0079] Comparative Example 2

[0080] The difference from Example 3 lies in that a traditional SBR-CMC system is used as the binder. The mass ratio of CMC, styrene-butadiene rubber binder, conductive carbon black Super P, and artificial graphite is 1.5:1.5:1:96.

[0081] Performance test:

[0082] Negative electrode binder 1wt% solid content aqueous solution viscosity test: Disperse 2g of the negative electrode binder or CMC prepared in this application in 198g of water, adjust the pH value to 6.5 - 7.5 using sodium hydroxide, stir and dissolve evenly to form an aqueous solution. After keeping it in a constant temperature oven at 25°C for 2 hours, measure the viscosity using a rotational viscometer, with the unit of mPa·s.

[0083] Dispersion ability (fineness) test: Use a fineness squeegee to test the fineness of the prepared negative electrode coating composition. The smaller the value, the better the dispersion, with the unit of μm.

[0084] Negative electrode coating composition stability test: Place 40g of the negative electrode coating composition in a 50ml glass bottle of the same shape, let it stand at 25°C for 24 hours, take the lower-layer and upper-layer samples respectively to measure the solid content, and calculate the difference between the lower-layer solid content and the upper-layer solid content. The smaller the difference, the better the stability, with the unit of wt%.

[0085] Negative electrode sheet peeling strength test: Use an electronic tensile testing machine to test the peeling strength of the sheet interface, with a tensile angle of 180°C and a tensile rate of 50mm / min, with the unit of N / m.

[0086] Sheet flexibility test: Use coiling needles with different diameters from 0.5 - 5mm to test the flexibility of the sheet, and judge the diameter of the coiling needle used when the sheet cracks. The smaller the value, the better the flexibility.

[0087] Fill the test results into Table 1.

[0088] Table 1

[0089] Sample group Aqueous solution viscosity (mPa·s) Fineness (μm) Stability (wt%) Pole piece peeling strength (N / m) Flexibility (mm) Example 1 10590 7 0.7 15 1.5 Example 2 14800 9 0.3 12 1 Example 3 13600 6 0.2 21 0.5 Example 4 15780 8 0.3 11 1 Example 5 14560 8 0.3 15 1.5 Example 6 16890 9 0.2 13 2 Example 7 13370 7 0.4 12 0.5 Example 8 12800 6 0.5 11 1 Example 9 17980 10 0.3 13 1 Comparative example 1 1550 17 2 5 3 Comparative example 2 1550 14 1.5 9 2

[0090] It can be seen from the test results in Table 1 that the negative electrode binder provided by the present invention can provide excellent dispersion and thickening properties, and is very beneficial for improving the bonding force. Specifically, by comparing the effects of Examples 1 - 9 and Comparative Examples 1 - 2, in the system where it is used in common with the styrene-butadiene rubber binder, compared with carboxymethyl cellulose, the negative electrode binder provided by the present invention has excellent thickening effects, high slurry dispersion and stability, and the peeling strength of the sheet prepared therefrom is high and the flexibility is also better.

[0091] The above further describes the present invention with the aid of specific embodiments. However, it should be understood that this specific description should not be construed as a limitation on the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A negative electrode binder, characterized in that: The negative electrode binder is obtained by polymerization of an acrylic monomer, a cyanide group-containing polymerizable monomer, a polyether monomer, and a polymerizable double bond monomer; wherein, the cyanide group-containing polymerizable monomer is selected from monomers containing vinyl and cyanide groups with 3 to 10 carbon atoms; the polyether monomer is selected from at least one of polyethylene oxide with a polymerizable double bond, polypropylene oxide with a polymerizable double bond, or an ethylene oxide-propylene oxide copolymer with a polymerizable double bond; the polymerizable double bond groups in the polyether monomer are selected from at least one of allyl ether groups and methallyl ether groups; the polymerizable double bond monomer includes at least one of acrylate monomers with two or more polymerizable double bonds, methacrylate monomers with two or more polymerizable double bonds, and allyl monomers with two or more polymerizable double bonds; the mass ratio of the acrylic monomer, the cyanide group-containing polymerizable monomer, the polyether monomer, and the polymerizable double bond monomer is (66~98):(3~10):(3~10):(0.5~2).

2. The negative electrode binder according to claim 1, characterized in that, the cyanide group-containing polymerizable monomer is selected from at least one of acrylonitrile, methacrylonitrile, cyanostyrene, and cyanoacrylate; 3. The negative electrode binder according to claim 1, characterized in that, the molecular weight of the polyethylene oxide with a polymerizable double bond, the polypropylene oxide with a double bond, or the ethylene oxide-propylene oxide copolymer with a double bond is selected from 500~2000; 4. The negative electrode binder according to claim 1, wherein the acrylate monomers with two or more polymerizable double bonds are selected from at least one of ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, dipropylene glycol triacrylate, trimethylolpropane triacrylate, glycerol triacrylate, and pentaerythritol triacrylate; the methacrylate monomers with two or more polymerizable double bonds are selected from at least one of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, propylene glycol dimethacrylate, dipropylene glycol dimethacrylate, dipropylene glycol trimethacrylate, trimethylolpropane trimethacrylate, glycerol trimethacrylate, and pentaerythritol trimethacrylate; the allyl monomers with two or more polymerizable double bonds are selected from at least one of diallyl phthalate, glycerol diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, and diallyl adipate; 5. A negative electrode coating composition, characterized in that, containing the negative electrode binder according to any one of claims 1~4.

6. The coating composition according to claim 5, characterized in that, It also contains a styrene-butadiene rubber binder; wherein, the mass ratio of the negative electrode binder to the styrene-butadiene rubber binder is 0.5-1.5:0.5-1.

5.

7. A negative electrode sheet, characterized in that, Coated by the negative electrode coating composition according to claim 5 or 6.

8. A lithium-ion battery, characterized in that, Including the negative electrode sheet according to claim 7.