Negative electrode binder as well as preparation method and application thereof

Abstract

The invention relates to a negative electrode binder and a preparation method and application thereof, the negative electrode binder comprises modified polyethyleneimine, and the modified polyethyleneimine comprises a first structure, a second structure and a third structure according to a molar ratio of 100: (10-20): (10-40); the first structure is a structural unit of ethyleneimine; the second structure is a structural unit containing an amide group; the third structure is a cyano group-containing structural unit; the weight-average molecular weight of the modified polyethyleneimine ranges from 10,000 g / mol to 300,000 g / mol. The negative electrode binder has the characteristics of good flexibility, strong binding power and good stability in negative electrode slurry, and can improve the anti-cracking performance of a negative electrode active layer and the performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a negative electrode binder, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, as a highly promising type of rechargeable battery, are favored for their high energy density, long lifespan, small size, and environmental friendliness.

[0003] Cracking is a common problem during the drying process of lithium-ion battery negative electrode sheets. The negative electrode slurry is coated onto the current collector and dried. During drying, the solvent in the slurry evaporates on the surface, while the active materials and other particles deposit downwards, causing the overall shrinkage of the negative electrode active layer. This reduction in the volume of the negative electrode active layer generates various stresses on the negative electrode sheet, which cannot be released through the current collector. When the accumulated stress exceeds the bonding force between particles, cracks form to release these stresses. Traditional binders such as sodium alginate (SA), acrylic acid (AA), and sodium carboxymethyl cellulose (CMC-Na) are prone to forming microcracks during rapid drying, making it impossible to guarantee that the manufactured battery cell can maintain its electrochemical performance for a long time.

[0004] CN119275287A discloses a method for reducing cracking in negative electrode slurry. The method includes the following steps: S1, improving the negative electrode slurry formulation: Based on the original raw materials of the negative electrode slurry—graphite, conductive agent, thickener, binder, and deionized water—0.5% by weight of a specific additive—N-methylpyrrolidone. This technical solution effectively improves the coating cracking problem of the negative electrode slurry by adding a specific proportion of N-methylpyrrolidone, increasing the yield and quality of the negative electrode sheet. However, N-methylpyrrolidone is a volatile organic compound (VOC), which can have adverse effects on human health and the environment.

[0005] Therefore, there is a need to develop a negative electrode binder that has good flexibility, strong adhesion, good stability in negative electrode slurry, does not require the addition of N-methylpyrrolidone, and can improve the crack resistance of the negative electrode active layer and the performance of lithium-ion batteries. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a negative electrode binder, its preparation method, and its application. The negative electrode binder features good flexibility, strong adhesion, and good stability in negative electrode slurry, thereby improving the crack resistance of the negative electrode active layer and the performance of lithium-ion batteries.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a negative electrode binder comprising modified polyethyleneimine, wherein the modified polyethyleneimine comprises a first structure, a second structure, and a third structure in a molar ratio of 100:(10-20):(10-40); the first structure is a structural unit of ethyleneimine; the second structure is a structural unit containing an amide group; the third structure is a structural unit containing a cyano group; the weight-average molecular weight of the modified polyethyleneimine is 10,000-300,000 g / mol, for example 30,000 g / mol, 60,000 g / mol, 90,000 g / mol, 120,000 g / mol, 150,000 g / mol, 180,000 g / mol, 210,000 g / mol, 240,000 g / mol, or 270,000 g / mol, etc.

[0009] To achieve optimal crack resistance, an ideal negative electrode binder should possess appropriate yield stress to reduce the overall stress of the negative electrode active layer, moderate hardness to balance volume changes and prevent viscous creep, and high elasticity and moderate adhesion strength to effectively inhibit crack propagation. Polyethyleneimine is a water-soluble polymer with good flexibility and adhesion, making it suitable as a binder in various fields. However, polyethyleneimine contains a large number of alkaline amine groups, which are detrimental to the stability of the negative electrode slurry, leading to processing difficulties.

[0010] In this invention, the negative electrode binder comprises modified polyethyleneimine, which includes ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units. The polymer chains containing ethyleneimine structural units contribute to better flexibility and high adhesion performance, while the amide-containing structural units contribute to enhanced structural rigidity and cyano-containing structural units contribute to enhanced bonding performance. The combination of the polymer chains containing ethyleneimine structural units, the amide-containing structural units, and the cyano-containing structural units makes the modified polyethyleneimine structurally both rigid and flexible, which helps to release various stresses generated by the reduction in the volume of the negative electrode active layer during drying. In the negative electrode active layer, the negative electrode binder can form hydrogen bonds with other components (such as sodium carboxymethyl cellulose and styrene-butadiene rubber) in the negative electrode active layer through cyano and amine groups, resulting in stronger bonding strength between active materials in the negative electrode active layer, inhibiting the formation of microcracks, and also exhibiting good stability in the negative electrode slurry.

[0011] In this invention, the amino group refers to any one or a combination of at least two of primary, secondary, or tertiary amino groups.

[0012] In this invention, the structural units of the ethyleneimine include -CH2-CH2-NH-, -CH2-CH2-NH2 and -CH2-CH2-N-.

[0013] In this invention, the weight-average molecular weight of the modified polyethyleneimine is obtained through theoretical calculations based on the reaction raw materials and conversion rate.

[0014] For example, the molar ratio of the first structure and the second structure is 100:11, 100:12, 100:13, 100:14, 100:15, 100:16, 100:17, 100:18 or 100:19, etc.

[0015] For example, the molar ratio of the first structure to the third structure is 100:13, 100:16, 100:19, 100:22, 100:25, 100:28, 100:31, 100:34 or 100:37, etc.

[0016] In this invention, when the molar ratio of the first structure to the second structure is 100:(10-20), the resulting negative electrode binder exhibits high electrolyte resistance and is not easily dissolved in the electrolyte. When fabricating battery electrodes, this prevents the negative electrode active layer from shedding powder due to the dissolution of the negative electrode binder during electrolyte wetting. If the molar ratio is too low, the second structure accounts for a high proportion, introducing excessive amide bonds, resulting in strong structural rigidity and exacerbating electrode cracking. If the molar ratio is too high, the second structure accounts for a low proportion, introducing fewer amide bonds, reducing the electrolyte swelling rate, and failing to provide sufficient structural rigidity.

[0017] In this invention, when the molar ratio of the first structure to the third structure is 100:(10-40), the prepared negative electrode binder exhibits high bonding performance and ionic conductivity, which enhances the bonding effect between negative electrode active material particles in the negative electrode active layer during battery electrode fabrication. If the molar ratio is too low, the proportion of the third structure is high, resulting in a high cyano content. The hydrophobic effect of the cyano groups causes the structure to spontaneously form granules, leading to a decrease in bonding performance as the particle size increases, which is detrimental to Mn ion adsorption. Conversely, if the molar ratio is too high, the proportion of the third structure is low, resulting in a low cyano content, which is also detrimental to improving bonding performance.

[0018] Preferably, the modified polyethyleneimine has a weight-average molecular weight of 30,000 to 200,000 g / mol, and more preferably 100,000 to 200,000 g / mol.

[0019] Preferably, the second structure is derived from the reaction of a monomer having the structure shown in Formula I with polyethyleneimine.

[0020]

[0021] R1 is selected from any one of carboxyl, substituted or unsubstituted C1-C7 (e.g., C2, C3, C4, C5 or C6) alkyl or substituted or unsubstituted C2-C7 (e.g., C3, C4, C5 or C6) alkenyl, R2 is selected from hydrogen or C1-C7 (e.g., C2, C3, C4, C5 or C6) alkyl, and the substituted substituent is selected from carboxyl and / or hydroxyl.

[0022] In this invention, the second structure is derived from the reaction of a monomer having the structure shown in Formula I and polyethyleneimine, meaning that the monomer having the structure shown in Formula I reacts with the primary amine group in polyethyleneimine to form a structural unit containing an amide group, which is the second structure. The group participating in the reaction in the monomer having the structure shown in Formula I is a carboxyl group or an ester group.

[0023] Preferably, R2 is hydrogen and R1 is a carboxyl group.

[0024] Preferably, R2 is hydrogen, and R1 is a substituted C1 to C7 (e.g., C2, C3, C4, C5, or C6) alkyl group, wherein the substituted substituent includes a carboxyl group.

[0025] In this invention, R2 is hydrogen and R1 is carboxyl, or R2 is hydrogen and R1 is a substituted C1-C7 (e.g., C2, C3, C4, C5 or C6) alkyl group. When the substituted substituent includes a carboxyl group, the monomer having the structure shown in Formula I is a polybasic acid with high reactivity, which can also increase crosslinking and improve adhesion.

[0026] Preferably, the monomer having the structure shown in Formula I includes any one or a combination of at least two of acetic acid, propionic acid, tartaric acid, acrylic acid, butenoic acid, oxalic acid, malic acid, citric acid, methyl acrylate, methyl methacrylate, or butyl acrylate.

[0027] Preferably, the monomer having the structure shown in Formula I has ≤4 carbon atoms, for example, 2 or 3.

[0028] Preferably, the third structure is derived from the reaction of a monomer having the structure shown in Formula II with polyethyleneimine.

[0029]

[0030] R3 is selected from substituted or unsubstituted C2-C7 (e.g., C2, C3, C4, C5 or C6) alkenyl groups, and the substituted substituents are selected from C6-C15 (e.g., C8, C10, C12 or C14) aryl groups or C2-C7 (e.g., C2, C3, C4, C5 or C6) ester groups.

[0031] In this invention, the third structure is derived from the reaction of a monomer having the structure shown in Formula II and polyethyleneimine. This means that the monomer having the structure shown in Formula II undergoes Michael addition with the amino group in polyethyleneimine to form a cyano-containing structural unit, which is the third structure. The group participating in the reaction in the monomer having the structure shown in Formula I is a carbon-carbon double bond.

[0032] Preferably, the monomer having the structure shown in Formula II includes any one or a combination of at least two of acrylonitrile, methacrylonitrile, cyanostyrene, or cyanoacrylate.

[0033] Preferably, the molar ratio of primary amine groups, secondary amine groups, and tertiary amine groups in the modified polyethyleneimine is 1:(6-20):(3-15).

[0034] For example, the molar ratio of the primary amine group to the secondary amine group is 1:8, 1:10, 1:12, 1:14, 1:16, or 1:18, etc.

[0035] For example, the molar ratio of the primary amine group to the tertiary amine group is 1:5, 1:7, 1:9, 1:11, or 1:13, etc.

[0036] In this invention, the secondary amine group in the structural unit of the ethyleneimine still possesses basicity, which can remove hydrofluoric acid (HF) formed by the oxidative decomposition reaction caused by trace amounts of water during the electrolyte cycle and reduce the dissolution of transition metals in the cathode material during the cycle.

[0037] In this invention, the second structure is formed by reacting the carboxyl or ester group in the monomer having the structure shown in Formula I with the primary amine group on the structural unit of ethyleneimine to generate an amide group. This partial amidation treatment helps to enhance the structural rigidity. The third structure introduces a cyano group by Michael addition of the carbon-carbon double bond in the monomer having the structure shown in Formula II with the primary or secondary amine group on polyethyleneimine, which helps to enhance the adhesive properties.

[0038] Preferably, the electrolyte swelling rate of the negative electrode binder is 64% to 85%, such as 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, or 84%.

[0039] In this invention, the electrolyte swelling rate of the negative electrode binder refers to the swelling rate of the negative electrode binder after being soaked in an electrolyte at 60°C for 10 days. The electrolyte is a 1 mol / L LiPF6 solution, wherein the solvent is ethylene carbonate: methyl ethyl carbonate: diethyl carbonate in a volume ratio of 3:5:2.

[0040] Preferably, the elongation at break of the negative electrode binder is 33% to 57%, such as 35%, 40%, 45%, 50%, or 55%.

[0041] In a second aspect, the present invention provides an adhesive solution comprising a negative electrode adhesive as described in the first aspect and water.

[0042] Preferably, the negative electrode binder in the binder solution is dispersed in a completely dissolved state or in particulate form, and more preferably dispersed in a completely dissolved state.

[0043] In this invention, although both dispersing the negative electrode binder in a completely dissolved state or dispersing it in particulate form in the binder solution can improve the flexibility of the negative electrode sheet, the improvement effect of dispersing in particulate form is not as good as that of dispersing in a completely dissolved state. This is because when the negative electrode binder is dispersed in a completely dissolved state, the molecular chains of the modified polyimide are more extended, and more hydrogen bonds are formed between the cyano groups and other components in the negative electrode slurry (such as sodium carboxymethyl cellulose or styrene-butadiene rubber), resulting in stronger bonding strength and higher cohesive energy among the components.

[0044] Preferably, the negative electrode binder in the binder solution is dispersed in particulate form, and the D of the particulates is... v 50 Particle size <80nm, such as 10nm, 20nm, 30nm, 40nm, 50nm, 60nm or 70nm, etc.

[0045] In this invention, the dispersion state of the negative electrode binder in the binder solution is related to the weight-average molecular weight of the first structure and the mass ratio of the first, second, and third structures. The negative electrode binder is dispersed in a completely dissolved state or in particulate form, and the particle size distribution (D) is... v The bonding effect is good when the particle size is <80nm, and when D v If the particle size is too large, the contact area between the negative electrode binder and the negative electrode active material in the prepared negative electrode material coating will be reduced, and the bonding effect will decrease.

[0046] Preferably, the solid content of the adhesive solution is 10% to 25%, such as 12%, 14%, 16%, 18%, 20%, 22%, or 24%.

[0047] Preferably, the adhesive solution further includes a neutralizing agent.

[0048] Preferably, the pH of the adhesive solution is 6 to 8, such as 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.4, 7.6 or 7.8.

[0049] Thirdly, the present invention provides a method for preparing an adhesive solution as described in the second aspect, the method comprising the following steps: mixing polyethyleneimine, a monomer having the structure shown in Formula I, a monomer having the structure shown in Formula II, optionally a neutralizing agent and water, reacting to obtain the adhesive solution.

[0050] Preferably, the preparation method includes the following steps:

[0051] (1) Mix polyethyleneimine, a monomer having the structure shown in Formula I, water and a catalyst, and react to obtain an amidated modified polyethyleneimine solution.

[0052] (2) The amidated modified polyethyleneimine solution obtained in step (1) is mixed with a monomer having the structure shown in Formula II and reacted to obtain the adhesive solution.

[0053] Preferably, the polyethyleneimine comprises linear polyethyleneimine and / or branched polyethyleneimine, and more preferably branched polyethyleneimine.

[0054] In this invention, both linear polyethyleneimine and / or branched polyethyleneimine can provide reaction sites for monomers having the structure shown in Formula I and monomers having the structure shown in Formula II. Preferably, the negative electrode binder prepared with branched polyethyleneimine has better structural strength and bonding effect.

[0055] In this invention, the reaction of the polyethyleneimine with monomers having the structure shown in Formula I and the structure shown in Formula II can effectively reduce the content of primary amine groups in the polyethyleneimine, lower the alkalinity, and increase the stability of the negative electrode slurry prepared using the negative electrode binder. The remaining amine structures in the modified polyethyleneimine, such as secondary amines, still possess a certain degree of alkalinity, which can eliminate hydrofluoric acid formed by the oxidative decomposition reaction caused by trace amounts of water during electrolyte cycling, reduce the dissolution of transition metals in the positive electrode material during cycling, and effectively improve the overall performance of the lithium-ion secondary battery.

[0056] Preferably, the weight-average molecular weight of the polyethyleneimine is 10,000 to 200,000 g / mol, such as 30,000 g / mol, 50,000 g / mol, 70,000 g / mol, 90,000 g / mol, 110,000 g / mol, 130,000 g / mol, 150,000 g / mol, 170,000 g / mol, or 190,000 g / mol.

[0057] Preferably, step (1) further includes a step of removing unreacted monomers having the structure shown in Formula I after the reaction.

[0058] Preferably, the mixing in step (1) further includes mixing with a double bond inhibitor.

[0059] In this invention, when the monomer having the structure shown in Formula I contains carbon-carbon double bonds, a double bond inhibitor can be added in step (1). Under the action of oxygen and the double bond inhibitor and at a lower reaction temperature, the carbon-carbon double bond addition reaction of the double bond monomer can be suppressed. In step (2), the double bond inhibitor is deactivated by raising the temperature, and the double bond reaction is initiated.

[0060] Preferably, the double bond polymerization inhibitor includes any one or a combination of at least two of hydroquinone, p-tert-butylcatechol, 2,6-di-tert-butyl-p-methylphenol, or 4,4'-dihydroxybiphenyl and bisphenol A.

[0061] Preferably, the reaction temperature in step (1) is 40 to 65°C, for example, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C or 64°C.

[0062] Preferably, the reaction time in step (1) is 10 to 15 hours, such as 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours or 14.5 hours.

[0063] Preferably, the solid content of the amidation-modified polyethyleneimine solution in step (1) is 10% to 25%, such as 12%, 14%, 16%, 18%, 20%, 22%, or 24%.

[0064] Preferably, the reaction in step (2) is carried out in an inert gas or nitrogen atmosphere.

[0065] Preferably, the reaction temperature in step (2) is 50 to 65°C, such as 52°C, 54°C, 56°C, 58°C, 60°C, 62°C or 64°C.

[0066] Preferably, the reaction time in step (2) is 10 to 15 hours, such as 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours or 14.5 hours.

[0067] Preferably, step (2) further includes a step of removing unreacted monomers having the structure shown in Formula II after the reaction;

[0068] Preferably, after the reaction described in step (2), the reaction further includes a step of adding a neutralizing agent to neutralize to a pH of 6-8 (e.g., 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.4, 7.6 or 7.8, etc.);

[0069] In this invention, taking polyethyleneimine, monocarboxylic acid, and acrylonitrile as examples, the reaction formula for preparing modified polyethyleneimine is as follows. The reaction sites in the reaction formula are merely examples and are not intended to be limiting.

[0070]

[0071] In this formula, formula III represents polyethyleneimine, formula IV represents a monocarboxylic acid, R in formula IV is selected from C1 to C7 alkyl groups, R2 is selected from hydrogen or C1 to C7 alkyl groups, formula V represents amidated modified polyethyleneimine, formula VI represents acrylonitrile, and formula VII represents modified polyethyleneimine.

[0072] For example, the negative electrode binder is prepared by drying the binder solution as described in the second aspect or the binder solution prepared by the preparation method as described in the third aspect to obtain the negative electrode binder.

[0073] It should be noted that the molar ratio of the first structure, the second structure, and the third structure in this invention is calculated by the amount of polyethyleneimine, monomer having the structure shown in Formula I, and monomer having the structure shown in Formula II that participate in the reaction.

[0074] Fourthly, the present invention provides a negative electrode slurry, the negative electrode slurry comprising a negative electrode binder as described in the first aspect or a binder solution as described in the second aspect.

[0075] Preferably, the negative electrode slurry comprises a negative electrode active material, a conductive agent, a thickener, a binder solution as described in the second aspect, a styrene-butadiene rubber binder, and water.

[0076] Preferably, the mass ratio of the adhesive solution to the thickener is 1:(1-4), for example, 1:1.5, 1:2, 1:2.5, 1:3 or 1:3.5, etc.

[0077] Preferably, the viscosity of the negative electrode slurry at 25°C is 8000–12000 mPa·s, such as 8500 mPa·s, 9000 mPa·s, 9500 mPa·s, 10000 mPa·s, 10500 mPa·s, 11000 mPa·s, or 11500 mPa·s.

[0078] In this invention, the preferred mass ratio of binder solution to thickener in the negative electrode slurry is 1:(1-4). If the mass of the negative electrode slurry is too low, the bonding strength will be weak, and the effect on improving the cracking of the negative electrode active layer will be poor. If the mass of the binder solution is too high, the negative electrode binder will adhere to the surface of the styrene-butadiene rubber binder during the preparation of the negative electrode slurry, causing the surface charge of the styrene-butadiene rubber binder to lose balance, thereby destroying its stability and causing the viscosity of the negative electrode slurry to increase, affecting subsequent processing.

[0079] Fifthly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on the current collector, the negative electrode active layer comprising a negative electrode binder as described in the first aspect or made from a negative electrode slurry as described in the fourth aspect.

[0080] Preferably, the negative electrode active layer is disposed on one or both surfaces of the current collector.

[0081] Exemplarily, the negative electrode sheet is prepared by the following method: coating the negative electrode slurry as described in the fourth aspect onto both surfaces of the current collector, drying, and forming a negative electrode active layer on the current collector, wherein the areal density of the negative electrode active layer formed on both surfaces of the current collector is independently 80-120 g / cm³. 2 (e.g. 85g / cm) 2 90g / cm 2 95g / cm 2 100g / cm 2 105g / cm 2 110g / cm 2 Or 115g / cm 2 (etc.), rolled and pressed to obtain the negative electrode sheet, the density of the negative electrode sheet being 1.50~1.65g / cm³. 3 (e.g., 1.52 g / cm³) 3 1.54g / cm 3 1.56g / cm 3 1.58g / cm 3 1.60g / cm 3 1.62g / cm 3 Or 1.64 g / cm 3 wait).

[0082] In a sixth aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet as described in the fifth aspect.

[0083] Compared with the prior art, the present invention has at least the following beneficial effects:

[0084] The negative electrode binder of the present invention comprises modified polyethyleneimine, which includes ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units. The negative electrode binder has the characteristics of good flexibility, strong adhesion, and good stability in negative electrode slurry. It can improve the crack resistance of the negative electrode active layer, has an adsorption effect on hydrofluoric acid, reduces the dissolution of transition metals during the cycling process of positive electrode material, and can improve the performance of lithium-ion batteries. Detailed Implementation

[0085] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0086] The following are some of the raw materials used in the examples below:

[0087] Acrylonitrile: purchased from Maclean's, molecular weight 53.

[0088] Styrene-butadiene rubber adhesive: Manufacturer: Ruiweng, Brand: BM-451B.

[0089] (1) Polyethyleneimine solution

[0090] Polyethyleneimine solution A: weight average molecular weight of 70000 g / mol, Japanese Shokubai EPOMIN, brand: P-1050, solid content of 50%, amine value of 18, diluted with water to a solid content of 36%;

[0091] Polyethyleneimine solution B: weight average molecular weight of 10000 g / mol, Japanese Shokubai EPOMIN, brand name: SP-200, solid content of 98%, amine value of 18, diluted with water to a solid content of 36%;

[0092] Polyethyleneimine solution C: weight average molecular weight of 30000 g / mol, Japanese Shokubai EPOMIN, brand: HM-2000, solid content of 50%, amine value of 18, diluted with water to a solid content of 36%;

[0093] Polyethyleneimine solution D: weight average molecular weight is 100,000 g / mol, Japanese Shokubai EPOMIN, brand name: P-3000, amine value is 19, solid content is 36%;

[0094] Polyethyleneimine solution E: weight average molecular weight of 1800 g / mol, Japanese Shokubai EPOMIN, brand name: SP-018, solid content of 99%, amine value of 19, diluted with water to a solid content of 36%;

[0095] Polyethyleneimine solution F: weight average molecular weight 250,000 g / mol, Aladdin, solid content 98%, diluted with water to a solid content of 36%.

[0096] Example 1

[0097] This embodiment provides a negative electrode binder, a binder solution, a negative electrode slurry, and a negative electrode sheet. The binder solution is prepared by the following method:

[0098] (1) Add acetic acid to a container with a stirrer, add polyethyleneimine solution (polyethyleneimine solution A) and deionized water to make the solid content reach 20%. The molar ratio of the ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is 1628:271. Keep warm and stir at 60℃ for 12 h and control the conversion rate of acetic acid to 91%. Remove the residual acetic acid monomer by vacuum rotary evaporation to obtain the amidation modified polyethyleneimine solution.

[0099] (2) Acrylonitrile and deionized water are added dropwise to the amidated modified polyethyleneimine solution prepared in step (1) using a peristaltic pump to make the solid content reach 20%. The molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 1628:453. Nitrogen gas is introduced into the container to remove oxygen for 30 min. The reaction is carried out at 60 °C for 12 h, and the conversion rate of acrylonitrile is controlled at 91%. The residual acrylonitrile monomer is removed by rotary evaporation under reduced pressure. The pH is adjusted to 7 by adding a neutralizing agent (hydrochloric acid) to obtain the binder solution. The binder solution contains modified polyethyleneimine in which the molar ratio of ethyleneimine structural units, amide-containing structural units and cyano-containing structural units is 100:15:25.

[0100] The negative electrode binder is prepared by drying the above binder solution to obtain the negative electrode binder.

[0101] The negative electrode slurry was prepared by the following method: 94.5 parts by weight of graphite, 0.5 parts by weight of carbon black conductive agent (SP), 2 parts by weight of thickener (sodium carboxymethyl cellulose), 1 part by weight of the above binder solution and 2 parts by weight of styrene-butadiene rubber binder were added to a planetary mixing tank and stirred for 1 hour at a stirring speed of 35 Hz revolution and 1500 Hz rotation. Subsequently, an appropriate amount of deionized water was added to adjust the viscosity to 10000 mPa·s at 25°C to obtain the negative electrode slurry.

[0102] The negative electrode sheet is prepared by the following method: the above-mentioned negative electrode slurry is coated on both sides of the current collector (copper foil), and dried in a vacuum drying oven at 80°C to form a negative electrode active layer on the current collector. The areal density of the negative electrode active layer on both sides of the current collector is 100 g / cm³. 2 The negative electrode sheet is obtained by rolling and pressing, and the density of the negative electrode sheet is 1.6 g / cm³. 3 .

[0103] Example 2

[0104] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that, in the preparation of the binder solution, the polyethyleneimine solution (polyethyleneimine solution A) is replaced with a polyethyleneimine solution (polyethyleneimine solution B), and the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 233:39; the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 233:65, and the molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units in the modified polyethyleneimine contained in the prepared binder solution is 100:15:25. Other conditions are the same as in Embodiment 1.

[0105] Example 3

[0106] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that, in the preparation of the binder solution, the polyethyleneimine solution (polyethyleneimine solution A) is replaced with a polyethyleneimine solution (polyethyleneimine solution C), and the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 698:116; the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 698:194, and the molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units in the modified polyethyleneimine contained in the prepared binder solution is 100:15:25. Other conditions are the same as in Embodiment 1.

[0107] Example 4

[0108] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference from Embodiment 1 is that in the preparation of the binder solution, the polyethyleneimine solution (polyethyleneimine solution A) is replaced with a polyethyleneimine solution (polyethyleneimine solution D). The molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 2326:388; the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 2326:646; and the molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units in the modified polyethyleneimine contained in the obtained binder solution is 100:15:25. Other conditions are the same as in Embodiment 1.

[0109] Example 5

[0110] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that, in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 1628:179, the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 1628:179, the reaction time is adjusted to maintain a constant conversion rate, and the binder solution contains a modified polyethyleneimine containing ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units in a molar ratio of 100:10:10. Other conditions are the same as in Embodiment 1.

[0111] Example 6

[0112] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that, in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 1628:358, and the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 1628:716. The reaction time is adjusted to maintain a constant conversion rate. The binder solution contains modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:20:40. Other conditions are the same as in Embodiment 1.

[0113] Example 7

[0114] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that, in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 1628:358, and the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 1628:179. The reaction time is adjusted to maintain a constant conversion rate. The binder solution contains modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:20:10. Other conditions are the same as in Embodiment 1.

[0115] Example 8

[0116] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that, in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 1628:179, and the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 1628:716. The reaction time is adjusted to maintain a constant conversion rate. The binder solution contains modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:10:40. Other conditions are the same as in Embodiment 1.

[0117] Example 9

[0118] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that the binder solution is prepared using the following method:

[0119] (1) Methyl acrylate is added to a container equipped with a stirrer, followed by polyethyleneimine solution (polyethyleneimine solution A), a polymerization inhibitor (hydroquinone) equivalent to 0.1% of the mass of methyl acrylate, and deionized water, so that the solid content reaches 20%. The molar ratio of the ethyleneimine structural units in the added polyethyleneimine solution to methyl acrylate is 1628:268. The mixture is kept at 45°C and stirred to disperse and react. The conversion rate of methyl acrylate is controlled to reach 91%. The residual methyl acrylate is removed by rotary evaporation under reduced pressure to obtain an amidated modified polyethyleneimine solution.

[0120] (2) Acrylonitrile and deionized water were added dropwise to the amidated modified polyethyleneimine solution prepared in step (1) using a peristaltic pump to make the solid content reach 20%. The molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution was 1628:453. Nitrogen gas was introduced into the container to remove oxygen for 30 minutes. The reaction was carried out at 60°C, and the acrylonitrile conversion rate was controlled to reach 91%. The residual acrylonitrile monomer was removed by rotary evaporation under reduced pressure. The pH was adjusted to 7 by adding a neutralizing agent (hydrochloric acid) to obtain the binder solution. The binder solution contained ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units in the modified polyethyleneimine with a molar ratio of 100:15:25. Other conditions were the same as in Example 1.

[0121] Example 10

[0122] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference from Example 1 is that acetic acid is replaced with hexanoic acid in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to hexanoic acid in the added polyethyleneimine solution is 1628:272, the reaction time is adjusted to keep the conversion rate constant, and the binder solution contains modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:15:25. Other conditions are the same as in Example 1.

[0123] Example 11

[0124] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that, in the preparation of the negative electrode slurry, the weight percentage of the binder solution is adjusted to 1.5 parts, the weight percentage of the thickener (sodium carboxymethyl cellulose) is adjusted to 1.5 parts, and other conditions are the same as in Embodiment 1.

[0125] Example 12

[0126] This embodiment provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this embodiment and Embodiment 1 is that, in the preparation of the negative electrode slurry, the weight percentage of the binder solution is adjusted to 0.6 parts, and the weight percentage of the thickener (sodium carboxymethyl cellulose) is adjusted to 2.4 parts. Other conditions are the same as in Embodiment 1.

[0127] Comparative Example 1

[0128] This comparative example provides a negative electrode binder, a negative electrode slurry, and a negative electrode sheet, which differ from Example 1 in that the negative electrode binder is sodium carboxymethyl cellulose.

[0129] In the preparation of the negative electrode slurry, 1 part by weight of binder solution and 2 parts by weight of thickener (sodium carboxymethyl cellulose) were replaced with 3 parts by weight of sodium carboxymethyl cellulose, and other conditions were the same as in Example 1.

[0130] Comparative Example 2

[0131] This comparative example provides a negative electrode binder, a negative electrode slurry, and a negative electrode sheet. The difference between this example and Example 1 is that the negative electrode binder is polyacrylic acid (Kelode, lithium-ionized acrylic acid binder, molecular weight 300,000).

[0132] In the preparation of the negative electrode sheet, 1 part by weight of binder solution and 2 parts by weight of thickener (sodium carboxymethyl cellulose) were replaced with 3 parts by weight of polyacrylic acid (Klude, lithium-ionized acrylic acid binder, molecular weight 300,000), and other conditions were the same as in Example 1.

[0133] Comparative Example 3

[0134] This comparative example provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this example and Example 1 is that, in the preparation of the binder solution, the polyethyleneimine solution (polyethyleneimine solution A) is replaced with a polyethyleneimine solution (polyethyleneimine solution E), and the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 42:7; the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 42:11.6, and the resulting binder solution contains modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:15:25. Other conditions are the same as in Example 1.

[0135] Comparative Example 4

[0136] This comparative example provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this example and Example 1 is that, in the preparation of the binder solution, the polyethyleneimine solution (polyethyleneimine solution A) is replaced with a polyethyleneimine solution (polyethyleneimine solution F). The molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 5814:971; the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 5814:1616. The reaction time is adjusted to maintain the conversion rate. The binder solution contains modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:15:25. Other conditions are the same as in Example 1.

[0137] Comparative Example 5

[0138] This comparative example provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this example and Example 1 is that the binder solution is polyethyleneimine solution A, while the other conditions are the same as in Example 1.

[0139] Comparative Example 6

[0140] This comparative example provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this example and Example 1 is that, in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 1628:537; the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 1628:895; the reaction time is adjusted to maintain the conversion rate; and the resulting binder solution contains a modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:30:50. Other conditions are the same as in Example 1.

[0141] Comparative Example 7

[0142] This comparative example provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this example and Example 1 is that acetic acid is not added in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acrylonitrile in the added polyethyleneimine solution is 1628:724, the reaction time is adjusted to maintain the conversion rate, and the molar ratio of ethyleneimine structural units to cyano-containing structural units in the modified polyethyleneimine in the obtained binder solution is 100:40. Other conditions are the same as in Example 1.

[0143] Comparative Example 8

[0144] This comparative example provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this example and Example 1 is that acrylonitrile is not added in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 1628:724, the reaction time is adjusted to maintain the conversion rate, and the resulting binder solution contains a modified polyethyleneimine with a molar ratio of ethyleneimine structural units to amide-containing structural units of 100:40. Other conditions are the same as in Example 1.

[0145] Comparative Example 9

[0146] This comparative example provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this example and Example 1 is that, in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 1628:89.5, and the reaction time is adjusted to maintain the conversion rate. This results in the binder solution containing a modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:5:25. Other conditions are the same as in Example 1.

[0147] Comparative Example 10

[0148] This comparative example provides a negative electrode binder, binder solution, negative electrode slurry, and negative electrode sheet. The difference between this example and Example 1 is that in the preparation of the binder solution, the molar ratio of ethyleneimine structural units to acetic acid in the added polyethyleneimine solution is adjusted to 1628:544, the reaction time is adjusted to maintain the conversion rate, and the resulting binder solution contains a modified polyethyleneimine with a molar ratio of ethyleneimine structural units, amide-containing structural units, and cyano-containing structural units of 100:30:25. Other conditions are the same as in Example 1.

[0149] The negative electrode binder, binder solution, negative electrode slurry and negative electrode sheet prepared in Examples 1 to 12 and Comparative Examples 1 to 10 were subjected to the following performance tests.

[0150] (1) State of the binder solution: visual inspection of the state, and testing of the D of the polymer in the binder solution using a laser particle size analyzer. v 50 particle size.

[0151] (2) Electrolyte swelling rate: About 1g of negative electrode binder was immersed in 60℃ electrolyte (the electrolyte is a 1mol / L LiPF6 solution, in which the solvent is ethylene carbonate: methyl ethyl carbonate: diethyl carbonate in a volume ratio of 3:5:2); after immersion for 10 consecutive days, it was taken out, wiped clean, and then weighed; swelling rate = (M-M0) / M0×100%, where M is the test mass after immersion and M0 is the initial mass.

[0152] (3) Elongation at break: The elongation at break of the strip negative electrode adhesive of 80mm×10mm×4mm was tested by tensile testing machine at a tensile rate of 50mm / min.

[0153] (4) Electrolyte color change: The electrolyte is a 1 mol / L LiPF6 solution, in which the solvent is ethylene carbonate: methyl ethyl carbonate: diethyl carbonate in a volume ratio of 3:5:2; 1000 ppm water and 1 g negative electrode binder are added to the electrolyte, and the solution is vacuum-insulated in a 60℃ oven for 72 h, and the electrolyte color is observed.

[0154] The water resistance test involved adding 1000 ppm of water to the electrolyte and vacuum heating it in a 60°C oven for 72 hours as a blank control; the electrolyte in this blank turned yellow.

[0155] (5) Stability of negative electrode slurry: After the negative electrode slurry is left to stand for 24 hours, 0.5 g of solid content is tested from the upper and lower layers of the negative electrode slurry at 0h, 2h, 4h, 6h, 12h, 18h and 24h respectively. If the solid content of the upper and lower layers is within ±1%, it is considered stable; otherwise, it is considered gelled.

[0156] (7) Primary, secondary and tertiary amine ratio test: The ratio of primary, secondary and tertiary amines in the negative electrode binder was measured by ISO 9702:1996.

[0157] (6) Average peel strength of negative electrode sheet: The surface of one side of the negative electrode sheet is tightly attached to the center of a flat steel plate with double-sided adhesive. The length of the double-sided adhesive is greater than the test length of the negative electrode sheet sample and the same width as the negative electrode sheet sample. Then, a 180° peel test is performed on the negative electrode sheet. The peel length of the negative electrode sheet is 100 mm and the peel speed is 100 mm / min. The peel strength curve and the average peel strength of the negative electrode sheet are obtained.

[0158] (7) Average cohesive energy of negative electrode sheet: One side of the negative electrode sheet is tightly attached to the center of a flat steel plate with double-sided tape. The length of the double-sided tape is greater than the test length of the negative electrode sheet sample and the same width as the negative electrode sheet sample. The negative electrode sheet is fixed on the steel plate. Transparent tape is attached to the negative active layer on the other side of the negative electrode sheet. Then, a 180° peel test is performed on the transparent tape. The peel length is 100 mm and the peel speed is 100 mm / min. The cohesive energy curve and the average cohesive energy of the negative electrode sheet are obtained.

[0159] (8) Softness of negative electrode sheet: The softness of the electrode sheet was tested by using a winding needle with a diameter of 0.5 to 5 mm to determine the diameter of the winding needle used when the electrode sheet cracked. The smaller the value, the better the softness.

[0160] (9)Mn2+ Dissolution test: A single-cell battery was assembled from the negative electrode, the positive electrode (composed of aluminum foil and a positive electrode material coating, the positive electrode material coating consisting of lithium manganese oxide, PVDF and conductive carbon black SP in a mass ratio of 96:2:2), the separator (a polyethylene separator with a thickness of 7 μm), and the electrolyte (a 1 mol / L LiPF6 solution, in which the solvent is ethylene carbonate: methyl ethyl carbonate: diethyl carbonate in a volume ratio of 3:5:2). The battery was then subjected to 100 charge-discharge cycles at 3.0-4.3V and 0.5C at 60℃. The process involves immersing the separator in a single battery cell in a solution using ICP testing. Specifically, the separator is soaked in aqua regia (10 ml of aqua regia in a microwave digestion vessel) and pre-digested at 120°C for half an hour. Microwave digestion follows the same procedure: 150°C, 3 min heating time, 10 min stabilization time; 180°C, 3 min heating time, 30 min stabilization time. After cooling to 60°C, the solution is removed using an acid removal apparatus until approximately 1 ml of acid remains. This is then transferred to a 25 ml colorimetric tube and diluted to 25 ml with deionized water. The Mn content is then measured. 2+ The mass content.

[0161] The test results are shown in Tables 1 and 2 below.

[0162] Table 1

[0163]

[0164]

[0165] In Table 1, “\” indicates that the test was not performed.

[0166] Table 2

[0167]

[0168]

[0169] In Table 2, “\” indicates that the test was not performed.

[0170] The test results show that the negative electrode slurry prepared in Examples 1-12 has good stability, and the resulting negative electrode sheets have high peel strength, high cohesive energy, and good flexibility. After charge-discharge cycling, the Mn... 2+ Low dissolution concentration.

[0171] Compared to Examples 1-4, when the weight-average molecular weight of modified polyethyleneimine in the binder solution is 10,000-200,000 g / mol, the resulting negative electrode binder exhibits high peel strength and good flexibility, resulting in a better Mn content after battery cycling. 2+ Lower dissolution concentration results in better performance.

[0172] When a small amount of water is present in the electrolyte, lithium hexafluorophosphate in the electrolyte undergoes hydrolysis to form highly corrosive hydrofluoric acid, causing the electrolyte to appear yellow and turbid. High temperature can accelerate this process. When any of the negative electrode binders provided in Examples 1 to 12 are added to the electrolyte, it can still remain a clear, colorless liquid at high temperatures, demonstrating good hydrofluoric acid adsorption, which in turn helps to improve the cycle life of lithium-ion batteries. This effect is positively correlated with the amount of primary and secondary amine groups remaining in the modified polyethyleneimine.

[0173] Compared to Example 1, if no binder solution is added to the negative electrode slurry, and sodium carboxymethyl cellulose (Comparative Example 1) or polyacrylic acid (Comparative Example 2) is used instead, the prepared negative electrode sheet has low peel strength and poor flexibility. When sodium carboxymethyl cellulose or polyacrylic acid is added to the aqueous electrolyte at high temperature, the color turns yellow, failing to adsorb hydrofluoric acid and thus failing to improve the manganese ion deposition problem in lithium manganese oxide batteries. The resulting battery exhibits poor manganese ion deposition after cycling. 2+ High dissolution concentration.

[0174] Compared with Example 1, if the weight-average molecular weight of polyethyleneimine is too small (Comparative Example 3), the weight-average molecular weight of the prepared modified polyethyleneimine is small, the peel strength of the negative electrode sheet decreases, the flexibility of the prepared negative electrode sheet decreases, and the ability to remove hydrofluoric acid decreases. This may be because the weight-average molecular weight of polyethyleneimine is small, the molecular stretching effect is good, the amine groups participating in the reaction on the polyethyleneimine molecular chain are more uniformly distributed, and the reaction is sufficient. However, as the cyano group in the modified polyethyleneimine increases, its hydrophobic effect and the hydrogen bonding effect between molecular chains are enhanced, causing the molecular chains of the modified polyethyleneimine to entangle and form nanoparticles, which encapsulates some primary and secondary amines, reducing alkalinity, and at the same time reducing adhesion. If the weight-average molecular weight of polyethyleneimine is too large (Comparative Example 4), the negative electrode slurry made from the prepared negative electrode binder will have poor stability. This may be because the large weight-average molecular weight of polyethyleneimine results in poor molecular expansion, and the entanglement of polyethyleneimine molecular chains leads to uneven distribution of amine groups participating in the reaction. The high-alkalinity primary amines at some positions of the polyethyleneimine molecular chain cannot participate in the reaction, resulting in high alkalinity and low stability of the negative electrode slurry.

[0175] Compared with Example 1, the negative electrode slurry prepared without the addition of acetic acid and acrylonitrile (Comparative Example 5) has poor stability.

[0176] Compared to Example 1, if the amount of acetic acid and acrylonitrile added is too high (Comparative Example 6), the D of the polymer particles in the prepared binder solution will be lower. v The larger particle size of Mn results in a negative electrode sheet with low peel strength and poor flexibility, leading to poor performance after battery cycling. 2+ High dissolution concentration.

[0177] Compared to Example 1, if acetic acid is not added (Comparative Example 7), the D of modified polyethyleneimine in the prepared adhesive solution is higher. v The larger particle size of Mn results in a negative electrode sheet with low peel strength and poor flexibility, leading to poor performance after battery cycling. 2+ The dissolution concentration is high; if acrylonitrile is not added (Comparative Example 8), the prepared binder has high rigidity, the resulting negative electrode sheet has low peel strength and poor flexibility.

[0178] Compared to Example 1, if the amount of acetic acid added is too low (Example 9), the D of the modified polyethyleneimine in the prepared adhesive solution will be lower. v The larger particle size of Mn results in a negative electrode sheet with low peel strength and poor flexibility, leading to poor performance after battery cycling. 2+ The dissolution concentration is high; if the amount of acetic acid added is too high (Example 10), the prepared binder will have greater rigidity and the negative electrode sheet will have poor flexibility.

[0179] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A negative electrode binder, characterized in that, The negative electrode binder includes modified polyethyleneimine, which includes a first structure, a second structure, and a third structure in a molar ratio of 100:(10-20):(10-40). The first structure is a structural unit of ethyleneimine; The second structure is a structural unit containing an amide group; The third structure is a cyano-containing structural unit; The modified polyethyleneimine has a weight-average molecular weight of 10,000 to 300,000 g / mol.

2. The negative electrode binder according to claim 1, characterized in that, The modified polyethyleneimine has a weight-average molecular weight of 30,000 to 200,000 g / mol, and is more preferably 100,000 to 200,000 g / mol. Preferably, the second structure is derived from the reaction of a monomer having the structure shown in Formula I and polyethyleneimine; R1 is selected from any one of carboxyl, substituted or unsubstituted C1-C7 alkyl or substituted or unsubstituted C2-C7 alkenyl, R2 is selected from hydrogen or C1-C7 alkyl, and the substituted substituent is selected from carboxyl and / or hydroxyl. Preferably, the monomer having the structure shown in Formula I includes any one or a combination of at least two of acetic acid, propionic acid, tartaric acid, acrylic acid, butenoic acid, oxalic acid, malic acid, citric acid, methyl acrylate, methyl methacrylate or butyl acrylate. Preferably, the monomer having the structure shown in Formula I has ≤4 carbon atoms; Preferably, the third structure is derived from the reaction of a monomer having the structure shown in Formula II with polyethyleneimine; R3-C≡N Equation II; R3 is selected from substituted or unsubstituted C2-C7 alkenyl groups, and the substituted substituents are selected from C6-C15 aryl groups or C2-C7 ester groups; Preferably, the monomer having the structure shown in Formula II includes any one or a combination of at least two of acrylonitrile, methacrylonitrile, cyanostyrene, or cyanoacrylate; Preferably, the molar ratio of primary amine groups, secondary amine groups, and tertiary amine groups in the modified polyethyleneimine is 1:(6-20):(3-15).

3. The negative electrode binder according to claim 1 or 2, characterized in that, The electrolyte swelling rate of the negative electrode binder is 64% to 85%; Preferably, the elongation at break of the negative electrode binder is 33% to 57%.

4. An adhesive solution, characterized in that, The binder solution comprises the negative electrode binder as described in any one of claims 1 to 3 and water.

5. The adhesive solution according to claim 4, characterized in that, The negative electrode binder in the binder solution is dispersed in a completely dissolved state or in particulate form. Preferably, the negative electrode binder in the binder solution is dispersed in particulate form, and the D of the particulates is... v 50 Particle size <80nm; Preferably, the solid content of the adhesive solution is 10% to 25%; Preferably, the adhesive solution further includes a neutralizing agent; Preferably, the pH of the adhesive solution is 6 to 8.

6. A method for preparing an adhesive solution as described in claim 4 or 5, characterized in that, The preparation method includes the following steps: mixing polyethyleneimine, a monomer having the structure shown in Formula I, a monomer having the structure shown in Formula II, an optional neutralizing agent, and water, and reacting them to obtain the adhesive solution.

7. The preparation method according to claim 6, characterized in that, The preparation method includes the following steps: (1) Mix polyethyleneimine, a monomer having the structure shown in Formula I and water, and react to obtain an amidated modified polyethyleneimine solution; (2) The amidated modified polyethyleneimine solution obtained in step (1) is mixed with a monomer having the structure shown in Formula II and reacted to obtain the adhesive solution; Preferably, the weight-average molecular weight of the polyethyleneimine is 10,000 to 200,000 g / mol; Preferably, the reaction in step (1) further includes a step of removing unreacted monomers having the structure shown in Formula I; Preferably, the mixing in step (1) further includes mixing with a double bond polymerization inhibitor; Preferably, the double bond polymerization inhibitor includes any one or a combination of at least two of hydroquinone, p-tert-butylcatechol, 2,6-di-tert-butyl-p-methylphenol, or 4,4'-dihydroxybiphenyl and bisphenol A; Preferably, the reaction temperature in step (1) is 40–65°C; Preferably, the reaction time in step (1) is 10-15 hours; Preferably, the solid content of the amidation-modified polyethyleneimine solution in step (1) is 10% to 25%; Preferably, the reaction in step (2) is carried out under an inert gas or nitrogen atmosphere; Preferably, the reaction temperature in step (2) is 50–65°C; Preferably, the reaction time in step (2) is 10-15 hours; Preferably, step (2) further includes a step of removing unreacted monomers having the structure shown in Formula II after the reaction; Preferably, step (2) further includes a step of adding a neutralizing agent to neutralize to a pH of 6-8 after the reaction.

8. A negative electrode slurry, characterized in that, The negative electrode slurry includes the negative electrode binder as described in any one of claims 1 to 3 or the binder solution as described in claim 4 or 5; Preferably, the negative electrode slurry comprises a negative electrode active material, a conductive agent, a thickener, a binder solution as described in claim 4 or 5, a styrene-butadiene rubber binder, and water; Preferably, the mass ratio of the binder solution to the thickener is 1:(1-4).

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active layer disposed on the current collector, wherein the negative electrode active layer includes the negative electrode binder as described in any one of claims 1 to 3 or is made from the negative electrode slurry as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 9.

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