A negative electrode binder, a negative electrode coating composition, a negative electrode sheet and a secondary battery

Abstract

The present invention relates to the technical field of lithium ion batteries, and in particular to a negative electrode binder, a negative electrode coating composition, a negative electrode plate and a secondary battery. The negative electrode binder is composed of a carboxylate monomer unit, a cyano monomer unit, a polyether monomer unit and a crosslinking monomer unit; the carbon number of the cyano monomer unit is between 3 and 10. By using the above copolymer as a negative electrode binder, CMC can be completely eliminated and the amount of SBR can be reduced. In addition, the negative electrode binder is in powder form, which is convenient for transportation and reduces transportation costs.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a negative electrode binder, a negative electrode coating composition, a negative electrode pole piece and a secondary battery. Background Art

[0002] As a rechargeable battery with broad application prospects, lithium-ion secondary batteries have shown their unique advantages in many fields. These advantages include high energy density, long life, compact size, maintenance-free and environmental friendliness, and are therefore widely welcomed by various industries. Lithium-ion batteries were initially used in small electronic devices such as mobile phones and laptops. With the advancement of technology, their application scope has rapidly expanded to electric bicycles, electric vehicles, large-scale energy storage systems and various portable devices, becoming an ideal mobile power solution.

[0003] The negative electrode materials of commercial lithium-ion secondary batteries are mostly graphite or graphite-based carbon materials. In order to fix the active material on the electrode, a binder needs to be added to ensure good contact between the electrode material and the current collector and enhance mechanical stability. Commonly used negative electrode binders include carboxymethyl cellulose (CMC), styrene-butadiene latex (SBR) and polyacrylic acid (PAA).

[0004] Currently, most PAA negative electrode binders on the market are sold in the form of aqueous solutions with a solid content of 5% to 10%. As the solid content of PAA increases, its viscosity will also increase, which brings certain difficulties to the actual operation. In addition, since the solid content of the binder in the form of aqueous solution is low, this not only increases the weight during transportation, but also indirectly increases the transportation cost. Summary of the invention

[0005] In view of the shortcomings of the prior art, how to provide a negative electrode binder that does not require neutralization during use and can simultaneously provide dispersion, suspension, thickening and bonding effects has become a technical problem that needs to be solved urgently. Based on this, the present invention provides a negative electrode binder, a negative electrode coating composition, a negative electrode plate and a secondary battery. In the present invention, the specific composition of the negative electrode binder is designed, and further monomers containing carboxylate groups and functional monomers are introduced to improve the bonding strength of the negative electrode binder. In addition, the negative electrode binder of the present invention is in powder form, which can reduce transportation costs.

[0006] To achieve this object, in a first aspect, the present invention adopts the following technical solutions:

[0007] A negative electrode binder, wherein the negative electrode binder is composed of a carboxylate monomer unit, a cyano monomer unit, a polyether monomer unit and a crosslinking monomer unit; the cyano monomer unit has a carbon atom number between 3 and 10;

[0008] The polyether monomer unit is selected from one or more of a (meth)acrylate-based polyether monomer unit and a (meth)allyl ether-based polyether monomer unit.

[0009] In the negative electrode binder, the weight ratio of the carboxylate monomer unit, the cyano group-containing monomer unit, the polyether monomer unit and the crosslinking monomer unit is (68-89.9): (5-15): (5-15): (0.1-2), and more preferably (72-85): (6-12): (6-12): (0.12-1.8).

[0010] In the present invention, the mass ratio of the above monomers is the ratio of their masses to each other, not the percentage ratio.

[0011] In the present invention, the negative electrode binder contains a carboxylate monomer unit, which can make the negative electrode binder have good adhesion, so that the active material can be firmly attached to the current collector, and also has better interface bonding force, which can enhance the bonding strength between the electrode material and the current collector, and the prepared negative electrode binder does not need to be neutralized when used, and can be used directly. In the negative electrode binder provided by the present invention, the carboxylic acid in the carboxylate monomer unit has been neutralized with the alkaline substance. Under the composition provided by the present invention, the negative electrode binder has good resistance to electrolyte erosion and prolongs the service life of the battery.

[0012] According to the present invention, the carboxylate monomer unit is selected from one or more of a lithium salt monomer unit of a carboxylic acid, a lithium sodium salt monomer unit of a carboxylic acid, and a lithium ammonium salt monomer unit of a carboxylic acid. Wherein, the carboxylic acid is selected from one or more of acrylic acid, methacrylic acid, β-(acryloyloxy) propionic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, crotonic acid, C1~C18 alkyl monoesters of 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] As known to those skilled in the art, the above C1-C18 means that the number of carbon atoms is 1-18.

[0014] In the present invention, when the negative electrode binder contains the carboxylate monomer unit, it can provide excellent peel strength due to its large polarity. Moreover, after the carboxylic acid is neutralized into the carboxylate, it has extremely low electrolyte swelling degree, which can provide the battery with excellent long-term performance.

[0015] Specifically, the carboxylate monomer unit is obtained based on a carboxylate monomer formed by an acid-base neutralization reaction between a carboxylic acid monomer and an alkaline substance. Preferably, the carboxylic acid monomer is selected from one or more of acrylic acid, methacrylic acid, β-(acryloyloxy) propionic acid, itaconic acid, and maleic acid, and the alkaline substance can be selected from various alkaline substances commonly used in the art, for example, it can be one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, lithium carbonate, lithium bicarbonate, lithium hydroxide, and ammonia water.

[0016] Under the composition provided by the present invention, the cyano group-containing monomer unit in the negative electrode binder can increase the rigidity and mechanical strength of the negative electrode binder, improve its toughness, reduce cracks and shedding when the volume of the electrode material changes, improve the conductivity of the polymer, and improve the conductive network of the electrode material, thereby improving the rate performance of the battery, helping to form a more uniform and stable solid electrolyte interface (SEI) layer, reducing the occurrence of side reactions, and improving the cycle stability of the battery.

[0017] Under the composition provided by the present invention, the polyether monomer unit in the negative electrode binder can give the negative electrode binder better flexibility. Especially when the weight average molecular weight of the polyether monomer unit is 500~2000, it is helpful to absorb the stress generated by the electrode material during the charge and discharge process, help to improve the electrochemical stability of the negative electrode binder, reduce the decomposition of the electrolyte, extend the service life of the battery, help to improve the dispersibility and fluidity of the negative electrode binder in the electrode slurry, make the slurry easier to apply evenly, and also have good temperature resistance, can maintain good mechanical properties in a wide temperature range, and can absorb the internal stress generated by the electrode material during the charge and discharge process, reducing internal damage. In addition, the polyether monomer unit in the negative electrode binder provided by the present invention has good lithium ion conductivity, which is conducive to reducing the internal resistance of the battery.

[0018] Preferably, the cyano group-containing monomer unit is selected from one or more of acrylonitrile monomer unit, methacrylonitrile monomer unit and cyanostyrene monomer unit.

[0019] In the present invention, the cyano-containing monomer unit in the negative electrode binder can improve the cohesive force of the prepared negative electrode plate, make the electrode material adhere better to the current collector, and reduce shedding during the battery cycle, which is helpful to maintain the integrity of the electrode after multiple charge and discharge cycles, and also helps to form a more stable solid electrolyte interface (SEI) layer, inhibit side reactions on the electrode surface, reduce electrolyte decomposition, and reduce the risk of thermal runaway, thereby improving the cycle stability and safety of the battery; at the same time, the negative electrode binder with the above-mentioned cyano-containing monomer unit provided by the present invention has good temperature resistance, can maintain good mechanical properties in a wide temperature range, and has excellent fluidity and dispersibility, so that the electrode slurry is easier to apply evenly; and it has good conductivity, can improve the conductive network of the electrode material, and improve the rate performance of the battery.

[0020] Preferably, the polyether monomer unit is selected from one or more of polyethylene oxide monomer units, polypropylene oxide monomer units, and ethylene oxide-propylene oxide copolymer monomer units.

[0021] Further, the polyether monomer unit is selected from one or more of a (meth)acrylate-based polyether monomer unit and a (meth)allyl ether-based polyether monomer unit. For example, the polyether monomer unit is selected from one or more of a (meth)acrylate-based polyethylene oxide monomer unit, a (meth)acrylate-based polypropylene oxide monomer unit, a (meth)acrylate-based ethylene oxide-propylene oxide copolymer monomer unit, a (meth)allyl ether-based polyethylene oxide monomer unit, a (meth)allyl ether-based polypropylene oxide monomer unit, and a (meth)allyl ether-based ethylene oxide-propylene oxide copolymer monomer unit.

[0022] In the present invention, the (meth)acrylate-based polyether monomer unit can promote the formation of a more uniform and stable solid electrolyte interface (SEI) layer, reduce the occurrence of side reactions, and enhance the interaction between the negative electrode binder and the active material, improve wettability, and help promote the uniform dispersion of the components in the electrode slurry, thereby ensuring the uniform distribution of the negative electrode binder in the entire electrode.

[0023] According to the present invention, in a further preferred case, the weight average molecular weight of the polyether monomer unit is 500-2000, more preferably 800-1800.

[0024] In the present invention, the cross-linked monomer unit is selected from one or more of a (meth) acrylate cross-linked monomer unit, a (meth) acrylamide cross-linked monomer unit, and an allyl cross-linked monomer unit. It is understandable that the cross-linked monomer unit is obtained by polymerizing a monomer having two or more polymerizable double bonds. In this case, the negative electrode binder containing the cross-linked monomer unit has a three-dimensional network structure, and this three-dimensional network cross-linked structure can increase the molecular weight, so that the prepared negative electrode slurry has a suitable viscosity, which is conducive to coating, and the cross-linked structure increases the cohesive force of the negative electrode binder, making the electrode material more stable during the charge and discharge process, reducing cracks and falling off, so that it can better withstand the volume change of the electrode material during the cycle.

[0025] Preferably, the cross-linking monomer unit is selected from one or more of ethylene glycol diacrylate monomer unit, polyethylene glycol diacrylate monomer unit, propylene glycol diacrylate monomer unit, dipropylene glycol diacrylate monomer unit, tripropylene glycol diacrylate monomer unit, trimethylolpropane triacrylate monomer unit, glycerol triacrylate monomer unit, pentaerythritol triacrylate monomer unit, ethylene glycol dimethacrylate monomer unit, polyethylene glycol dimethacrylate monomer unit, propylene glycol dimethacrylate monomer unit, dipropylene glycol dimethacrylate monomer unit, tripropylene glycol dimethacrylate monomer unit, trimethylolpropane trimethacrylate monomer unit, glycerol trimethacrylate monomer unit, pentaerythritol trimethacrylate monomer unit, glycerol diallyl ether monomer unit, pentaerythritol diallyl ether monomer unit, pentaerythritol triallyl ether monomer unit, and methacrylic acid allyl ether monomer unit. More preferably, it is at least one of N,N-methylenebisacrylamide monomer units, polyethylene glycol diacrylate monomer units, and polyethylene glycol dimethacrylate monomer units.

[0026] It is understandable that in the above-mentioned negative electrode binder disclosed in the present invention, the carboxylate monomer unit, the cyano group-containing monomer unit, the polyether monomer unit and the cross-linked monomer unit are respectively obtained by double bond polymerization of the carboxylate monomer, the cyano group-containing monomer, the polyether monomer and the cross-linked monomer. The various monomer units mentioned above can be understood as the various monomers that can be used to prepare the negative electrode binder, and will not be repeated here. Similarly, the weight ratio of the carboxylate monomer unit, the cyano group-containing monomer unit, the polyether monomer unit and the cross-linked monomer unit in the negative electrode binder as described above can be regarded as the ratio of the addition amount of the corresponding various monomers when preparing the negative electrode binder.

[0027] According to the present invention, the negative electrode binder can be prepared by double bond polymerization, which is commonly used in the art. For example, the preparation method of the negative electrode binder includes the following steps:

[0028] (1) Preparation of aqueous phase: the aforementioned carboxylic acid monomer, cyano group-containing monomer, polyether monomer and cross-linking monomer are added to water to dissolve, an alkaline substance is added, and the pH is adjusted to 6-8, so that the carboxylic acid monomer reacts with the alkaline substance to obtain a carboxylate monomer; and then an oxidant is added to complete the preparation; wherein, the amount of alkaline substance added is such that the pH value of the solution is 6-8;

[0029] (2) Preparation of oil phase: Add the water-in-oil emulsifier to the organic solvent, stir and dissolve to form the oil phase to complete the preparation; wherein the amount of the water-in-oil emulsifier is 5%-15% of the total weight of the organic solvent;

[0030] (3) Preparation of reducing aqueous solution: dissolve the reducing agent in water to form a reducing agent aqueous solution with a concentration of 0.1% to 5%;

[0031] (4) The water phase and the oil phase are mixed and homogenized in a weight ratio of 50-80:50-20 to form an oil-in-water emulsion, nitrogen is introduced into the emulsion to remove oxygen in the air, and then an aqueous solution of a reducing agent is added dropwise to carry out a polymerization reaction to obtain an oil-in-water polymer emulsion, and then water and organic solvents are removed by distillation or spray drying to finally obtain a powdered acrylate copolymer, which is the negative electrode binder.

[0032] The amount of the oxidant is 0.01%-0.5% of the total weight of the monomers, and the amount of the reducing agent is 0.02%-2% of the total weight of the monomers. In the aqueous phase configuration, the weight ratio of the total weight of the monomers to water is 1-3:1.

[0033] The negative electrode binder prepared in the present invention pre-neutralizes the carboxylic acid-containing monomer before polymerization, and then removes water and solvent to obtain the negative electrode binder powder after the reverse emulsion polymerization is completed. The negative electrode binder powder does not need to be neutralized again when used, and can provide dispersion, suspension, thickening and bonding effects at the same time, and CMC can be completely eliminated, and the amount of SBR can be reduced. The negative electrode binder is in powder form, which is convenient for transportation and reduces transportation costs.

[0034] In the present invention, the oxidant is selected from at least one of persulfate, hydrogen peroxide or tert-butyl hydroperoxide, and the water-in-oil emulsifier is selected from but not limited to sorbitan monooleate, sorbitan monostearate or commercial emulsifiers, such as Span emulsifiers (Span 80, Span 60, Span 40) and Hypermer sold by Croda Company. TM A series of polymer emulsifiers, the reducing agent is selected from at least one of sodium bisulfite, sodium pyrosulfite, Rongalite or ascorbic acid, and the organic solvent is selected from at least one of pentane, hexane, heptane, octane, cyclohexane, cycloheptane, and C13~C16 isomeric alkanes.

[0035] In the second aspect, a negative electrode coating composition includes the negative electrode binder as described above. Preferably, the negative electrode coating composition also includes a styrene-butadiene rubber binder. Further preferably, the mass ratio of the negative electrode binder to the styrene-butadiene rubber binder is 0.5~0.7:1~1.4. According to the present invention, more preferably, 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. Among them, the mass ratio of the negative electrode binder, styrene-butadiene rubber binder, conductive carbon black Super P and artificial graphite is (0.5~0.7): (1~1.4): 1: (96.9~97.5).

[0036] The steps of preparing the negative electrode coating composition include adding the negative electrode binder described in this patent into water and dispersing it, adding conductive carbon black and artificial graphite and dispersing them at high speed, and finally adding styrene-butadiene rubber binder and stirring to obtain it.

[0037] The viscosity of the negative electrode coating composition is 3000-5000 mPa·s.

[0038] In a third aspect, the present invention provides a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode coating composition of the second aspect. Specifically, the negative electrode sheet is obtained by coating, drying, and rolling the negative electrode coating composition prepared in the second aspect. The surface density of the negative electrode sheet is 80-100 g / m 2 , compacted density is 1.4~1.8g / cm 3 .

[0039] In a fourth aspect, the present invention provides a secondary battery, wherein the secondary battery comprises the negative electrode sheet as described in the third aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The carboxylate monomer units in the negative electrode binder of the present invention improve the adhesion and stability of the negative electrode binder, the cyanide monomer units improve the mechanical strength and heat resistance of the negative electrode binder, the polyether monomer units enhance the flexibility and crack resistance of the negative electrode binder, and the cross-linking monomer units further enhance the cross-linking structure of the polymer, thereby improving the durability and stability of the negative electrode binder.

[0042] (2) The negative electrode coating composition of the present invention uses a negative electrode binder. The combination of the negative electrode binder and the SBR binder can further improve the softness and enhance the cohesion between the electrode materials, so that the electrode materials can maintain better structural stability during the charge and discharge process. The conductive carbon black Super P can improve the conductivity of the electrode sheet and reduce the resistivity.

[0043] (3) The negative electrode binder provided by the present invention can significantly improve the mechanical properties, electrochemical properties, processing properties, environmental adaptability and safety of lithium-ion batteries. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0045] Example 1

[0046] This embodiment provides a negative electrode binder, which is obtained by polymerization of a carboxylate monomer, a cyanide-containing monomer, a polyether monomer and a cross-linking monomer;

[0047] The above monomers and their mass ratios are: sodium acrylate: acrylonitrile: polyethylene oxide acrylate (weight average molecular weight 1000): polyethylene glycol diacrylate is 68:15:15:2;

[0048] This embodiment provides a negative electrode coating composition, wherein the mass ratio of the negative electrode binder, the SBR binder, the conductive carbon black SuperP, and the artificial graphite is 0.5:1:1:97.5.

[0049] This embodiment provides a negative electrode sheet, wherein the negative electrode coating composition is made into a uniform negative electrode slurry, which is passed through a 100-mesh screen and then coated on a negative electrode current collector Cu foil, and then dried at 80° C. and rolled to obtain a negative electrode sheet.

[0050] This embodiment provides a secondary battery, using the negative electrode sheet of the embodiment as the negative electrode in the battery.

[0051] The present invention provides a method for preparing a negative electrode binder:

[0052] (1) Preparation of aqueous phase: a total of 200 parts of a monomer mixture of acrylic acid, acrylonitrile, polyethylene oxide acrylate and polyethylene glycol diacrylate having the above-mentioned composition of this embodiment is added to 100 parts of water to dissolve, sodium carbonate is added, the pH is adjusted to 8, and 0.2 parts of hydrogen peroxide is added to complete the preparation;

[0053] (2) Preparation of oil phase: 10 parts of Span is dissolved in 80 to 100 parts of pentane solvent, stirred and dissolved to form an oil phase;

[0054] (3) Preparation of reducing aqueous solution: Dissolve 0.4 parts of sodium bisulfite in water to form a reducing agent aqueous solution with a concentration of 0.5%;

[0055] (4) The water phase and the oil phase are mixed and homogenized in a weight ratio of 70:30 to form an oil-in-water emulsion. Nitrogen is introduced into the emulsion to remove oxygen in the air. Then, an aqueous solution of a reducing agent is added dropwise to carry out a polymerization reaction to obtain an oil-in-water polymer emulsion. The water and organic solvent are then removed by distillation or spray drying to finally obtain a powdered acrylate copolymer, which is the negative electrode binder.

[0056] Example 2

[0057] The difference from Example 1 is that the mass fractions of the monomers are: 89.9 parts of sodium acrylate, 5 parts of acrylonitrile, 5 parts of polyethylene oxide acrylate (weight average molecular weight 1600) and 0.1 parts of N,N-methylenebisacrylamide;

[0058] Negative electrode coating composition: the mass ratio of negative electrode binder, SBR binder, conductive carbon black SuperP and artificial graphite is 0.7:1.4:1:96.9.

[0059] Example 3

[0060] The difference from Example 1 is that the mass fractions of the monomers are: 75 parts of sodium acrylate, 12 parts of acrylonitrile, 12 parts of polyethylene oxide acrylate (weight average molecular weight 1000) and 1 part of polyethylene glycol (600) diacrylate;

[0061] Negative electrode coating composition: the mass ratio of negative electrode binder, SBR binder, conductive carbon black SuperP and artificial graphite is 0.6:1.2:1:97.2.

[0062] Example 4

[0063] The difference from Example 1 is that the mass fractions of the monomers are: 80 parts of sodium acrylate, 9 parts of methacrylonitrile, 9 parts of polyethylene oxide acrylate (weight average molecular weight 1000) and 2 parts of polyethylene glycol (600) diacrylate;

[0064] Negative electrode coating composition: the mass ratio of negative electrode binder, SBR binder, conductive carbon black SuperP and artificial graphite is 0.6:1.2:1:97.2.

[0065] Example 5

[0066] The difference from Example 1 is that the mass fractions of the monomers are: 72 parts of methacrylic acid, 13 parts of cyanostyrene, 13 parts of polypropylene oxide acrylate (weight average molecular weight 800) and 2 parts of propylene glycol diacrylate;

[0067] Negative electrode coating composition: the mass ratio of negative electrode binder, SBR binder, conductive carbon black SuperP and artificial graphite is 0.7:1:1:97.3.

[0068] Comparative Example 1

[0069] Compared with Example 3, acrylate is selected to replace acrylonitrile, and the remaining steps are the same as those in Example 3.

[0070] Comparative Example 2

[0071] Compared with Example 3, except that acrylonitrile is not added, the remaining steps are the same as those of Example 3.

[0072] Comparative Example 3

[0073] Compared with Example 3, except that polyethylene oxide acrylate is not added, the remaining steps are the same as those of Example 3.

[0074] Comparative Example 4

[0075] Compared with Example 1, CMC is used as the negative electrode binder, and the mass ratio of the negative electrode binder, SBR binder, conductive carbon black SuperP, and artificial graphite is 0.5:1:1:97.5.

[0076] Performance Test:

[0077] Slurry viscosity test: After the prepared negative electrode coating composition was kept at a constant temperature of 25° C. in a thermostat for 2 hours, a rotational viscometer was used to test the viscosity, with the unit being mPa·s.

[0078] Dispersibility (fineness) test: The fineness of the prepared negative electrode coating composition is tested using a fineness scraper. The smaller the value, the better the dispersibility, and the unit is μm.

[0079] Stability test of negative electrode coating composition: Place 40g of negative electrode coating composition in a 50ml glass bottle of the same shape, let it stand at 25℃ for 24 hours, take the lower and upper layer samples respectively to test the solid content, and calculate the difference between the solid content of the lower layer and the solid content of the upper layer. The smaller the difference, the better the stability, the unit is wt%.

[0080] Negative electrode peeling strength test: An electronic tensile testing machine is used to test the electrode interface peeling strength, with a tensile angle of 180°C, a tensile rate of 50mm / min, and a unit of N / m.

[0081] Pole piece softness test: Use winding needles with different diameters of 0.5~5mm to test the softness of the pole piece. The diameter of the winding needle used to determine when the pole piece cracks. The smaller the value, the better the softness.

[0082] The test results obtained are entered in Table 1.

[0083] Table 1

[0084] The test results show that: It can be seen from the test results in Table 1 that the negative electrode coating composition prepared by the negative electrode binder provided by the present invention has low fineness, good dispersibility and good stability. Importantly, the negative electrode sheet prepared thereby has high peel strength and good flexibility.

[0085] Among them, by comparing the results of Example 1 and Comparative Example 1, it can be seen that compared with the traditional CMC, the negative electrode coating composition prepared by the negative electrode binder provided by the present invention has better dispersibility and stability, and the prepared electrode sheet has higher peel strength and better flexibility.

[0086] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description here should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in the field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A negative electrode binder, characterized in that: The negative electrode binder is prepared by reverse emulsion polymerization, and the negative electrode binder is composed of a carboxylate monomer unit, a cyano monomer unit, a polyether monomer unit and a crosslinking monomer unit; the carbon number of the cyano monomer unit is between 3 and 10; the weight average molecular weight of the polyether monomer unit is 800-1800; in the negative electrode binder, the weight ratio of the carboxylate monomer unit, the cyano monomer unit, the polyether monomer unit and the crosslinking monomer unit is (68-89.9): (5-15): (5-15): (0.1-2); The polyether monomer unit is selected from one or more of a (meth)acrylate polyether monomer unit and a (meth)allyl ether polyether monomer unit; The cross-linking monomer unit is selected from one or more of ethylene glycol diacrylate monomer unit, polyethylene glycol diacrylate monomer unit, propylene glycol diacrylate monomer unit, dipropylene glycol diacrylate monomer unit, tripropylene glycol diacrylate monomer unit, trimethylolpropane triacrylate monomer unit, glycerol triacrylate monomer unit, pentaerythritol triacrylate monomer unit, ethylene glycol dimethacrylate monomer unit, polyethylene glycol dimethacrylate monomer unit, propylene glycol dimethacrylate monomer unit, dipropylene glycol dimethacrylate monomer unit, tripropylene glycol dimethacrylate monomer unit, trimethylolpropane trimethacrylate monomer unit, glycerol trimethacrylate monomer unit, pentaerythritol trimethacrylate monomer unit, glycerol diallyl ether monomer unit, pentaerythritol diallyl ether monomer unit, and pentaerythritol triallyl ether monomer unit.

2. The negative electrode binder according to claim 1, characterized in that: The carboxylate monomer unit is selected from one or more of a lithium salt monomer unit of a carboxylic acid, a sodium salt monomer unit of a carboxylic acid, and an ammonium salt monomer unit of a carboxylic acid; The carboxylic acid is selected from one or more of acrylic acid, methacrylic acid, β-(acryloyloxy)propionic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, crotonic acid, C1~C18 alkyl monoesters of 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.

3. The negative electrode binder according to any one of claims 1 to 2, characterized in that: The cyano group-containing monomer unit is selected from one or more of acrylonitrile monomer units, methacrylonitrile monomer units, and cyanostyrene monomer units.

4. A negative electrode coating composition, characterized in that: The invention comprises the negative electrode binder as claimed in any one of claims 1 to 3.

5. A negative electrode plate, characterized in that: The negative electrode plate is prepared from the negative electrode coating composition as claimed in claim 4.

6. A secondary battery, characterized in that: The secondary battery comprises the negative electrode sheet as claimed in claim 5.

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