Modified polyethyleneimine binder

Abstract

The invention discloses a modified polyethyleneimine binder, and relates to the technical field of lithium ion battery negative electrode materials. The molecular chain of the prepared polyethyleneimine is simultaneously connected with a cyano group and an organic acid group, the organic acid group and cations are matched to form salt, and the modified polyethyleneimine binder is prepared by uniformly mixing polyethyleneimine and water, adding an organic acid salt monomer to carry out primary reaction, and then adding a cyano monomer to carry out secondary reaction. The molar ratio of the ethyleneimine unit to the organic acid salt monomer to the cyano monomer in the polyethyleneimine is 10: (0.1-5): (5-15). According to the modified polyethyleneimine binder prepared by the preparation method disclosed by the invention, by introducing a cyano unit, the adhesiveness can be improved, active hydrogen groups can be eliminated, and the dielectric constant performance can be improved; meanwhile, a stable hydrophobic cyano structure of the organic acid salt is introduced, so that the organic acid salt can be uniformly distributed in the negative electrode slurry, and the binding agent has excellent binding strength and electrochemical performance when being applied to the negative electrode plate of the lithium ion battery due to the combination of the organic acid salt and the negative electrode slurry.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery negative electrode materials, and more specifically to a modified polyethyleneimine binder. Background Art

[0002] In recent years, with the public's increasing attention to environmental protection, lithium batteries, as the leader in the new energy industry, have been widely used in various electronic products, electric vehicles and other energy storage equipment. Lithium-ion batteries are mainly composed of positive electrodes, negative electrodes, diaphragms, and electrolytes. The positive and negative electrodes both contain binders. As an important component of lithium-ion batteries, the binder mainly adheres the electrode active material and the conductive agent to the current collector, stabilizes the structure of the pole piece, makes the pole piece have good processability, and prevents the active material from falling off during the battery charging and discharging process. More importantly, it ensures that the manufactured battery cell can maintain its electrochemical properties for a long time. The role of the binder in the negative electrode of the lithium-ion battery is extremely critical, and the quality of its performance will directly affect the electrochemical performance of the battery.

[0003] Polyethyleneimine is a water-soluble polymer with good flexibility and adhesion. It can be used as a binder in various fields. However, polyethyleneimine has strong water absorption and is not suitable for use in devices that are sensitive to moisture. At the same time, polyethyleneimine has a large number of active hydrogen groups. When used as a binder in lithium-ion batteries, long-term contact with electrolytes will produce side reactions, resulting in poor chemical and electrochemical stability of lithium-ion batteries. Therefore, it is hoped that a binder with further improved adhesion performance can be developed that can be stably used in lithium-ion batteries. Summary of the invention

[0004] In order to solve the above-mentioned defects of the prior art, the object of the present invention is to provide a modified polyethyleneimine binder.

[0005] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0006] A modified polyethyleneimine binder, wherein a cyano group and an organic acid group are simultaneously connected to the molecular chain of the polyethyleneimine, and the organic acid group is combined with a cation to form a salt. The modified polyethyleneimine binder is prepared by uniformly mixing polyethyleneimine and water, adding an organic acid salt monomer for a primary reaction, and then adding a cyano monomer for a secondary reaction. The molar ratio of the polyethyleneimine unit, the organic acid salt monomer, and the cyano monomer in the polyethyleneimine is 10:(0.1-5):(5-15).

[0007] The modified polyethyleneimine binder of the present invention can increase the adhesion and hydrophobicity of polyethyleneimine by introducing a cyano unit. In addition, cyano modification can also eliminate active hydrogen groups in polyethyleneimine, which can improve the dielectric properties of the binder and facilitate the transmission of lithium ions. However, when preparing the negative electrode sheet of a lithium battery, it is necessary to mix and slurry the negative electrode active material, the conductive agent and the binder in an aqueous solution system. During the slurrying process, the hydrophobic binder will cause its stability in the aqueous solution to be poor, and it is easy to settle and stratify in the aqueous solution, thereby causing the binder to be unevenly distributed in the pole piece, thereby reducing the electrochemical performance of the lithium ion battery. In addition, by first introducing an organic acid salt unit into polyethyleneimine and then introducing a cyano unit, since the organic acid salt used in the present invention is a polar molecule, the charge repulsion effect of the organic acid salt is conducive to stabilizing the hydrophobic cyano structure, so that its dispersion performance in the aqueous solution is improved, and the negative electrode sheet is more evenly distributed, which is conducive to improving the cycle performance of the lithium ion battery. At the same time, the organic acid salt, as an ion conductor, can also improve the conductivity of the binder, which is conducive to improving the transmission efficiency of lithium ions. The synergistic effect of cyano units and organic acid salts can increase the adhesion and electrochemical performance of polyethyleneimine binder when applied to negative electrode sheets.

[0008] Furthermore, the cation is any one of sodium ion, potassium ion, lithium ion or ammonium ion.

[0009] Furthermore, the molar ratio of the ethyleneimine unit, the organic acid salt monomer, and the cyano monomer in the polyethyleneimine is 10:(0.8-4.5):(5-12).

[0010] Too much organic acid group content in the modified polyethyleneimine binder will reduce the adhesion of the modified polyethyleneimine binder, and too little organic acid group content will reduce the dispersibility of the modified polyethyleneimine binder in the negative electrode slurry, thereby affecting the electrochemical performance of the binder when applied to the negative electrode plate. Therefore, when preparing the polyethyleneimine binder, the molar ratio of polyethyleneimine, organic acid salt monomer, and cyano monomer is within this range. The prepared modified polyethyleneimine binder can maintain a higher adhesion and at the same time make the modified polyethyleneimine binder evenly distributed when preparing the negative electrode slurry.

[0011] Furthermore, the organic acid group is one or more of a carboxylic acid group, a sulfonic acid group, and a phosphonic acid group.

[0012] Furthermore, the organic acid group is one or more of an acrylic acid group, a methacrylic acid group, a carboxyethyl acrylate group, a vinyl sulfonic acid group, and a 2-acrylamide-dimethylpropane sulfonic acid group.

[0013] Furthermore, the cyano monomer is acrylonitrile and / or methacrylonitrile.

[0014] Furthermore, the reaction temperature of the primary reaction and the secondary reaction is 55-65°C.

[0015] Furthermore, the time of the primary reaction is ≥1h, and the time of the secondary reaction is ≥4h.

[0016] In some embodiments of the present invention, the preparation method of the modified polyethyleneimine binder is: add polyethyleneimine and water to a reaction container, stir and dissolve evenly, heat to 55-65°C, slowly add an organic acid salt, add the addition after 0.5-1.5 hours, continue to react for 1-4 hours, then slowly add a cyano monomer, add the addition after 0.5-1.5 hours, and continue to react for 4-12 hours.

[0017] Furthermore, the molecular weight of the polyethyleneimine is 5,000 to 100,000.

[0018] Furthermore, after the reaction is completed, unreacted cyano monomer is removed by evaporation under reduced pressure.

[0019] Furthermore, the organic acid salt monomer is one or more of carboxylates, sulfonates, and phosphonates.

[0020] Furthermore, the cation in the organic acid salt monomer is any one of sodium ion, potassium ion, lithium ion or ammonium ion.

[0021] Furthermore, the carboxylate is one or more of acrylate, methacrylate, and carboxyethyl acrylate. Specifically, the structural formulas of acrylate (a) and carboxyethyl acrylate (b) are as follows:

[0022]

[0023] M is any one of NH4, Li, Na, and K

[0024] Further, the sulfonate is vinyl sulfonate and / or 2-acrylamide-dimethylpropane sulfonate. Specifically, the structural formulas of vinyl sulfonate (a) and 2-acrylamide-dimethylpropane sulfonate (b) are as follows:

[0025]

[0026] M is any one of NH4, Li, Na, and K

[0027] Another object of the present invention is to provide a negative electrode sheet, wherein the negative electrode sheet comprises the modified polyethyleneimine binder.

[0028] Furthermore, the weight percentage of the modified polyethyleneimine binder in the negative electrode sheet is 0.5-2.0%.

[0029] Furthermore, the negative electrode sheet also includes a current collector, a negative electrode active material and a conductive agent.

[0030] The present invention has no particular limitation on the negative electrode active material. Without violating the inventive concept of the present application, any known negative electrode active material for lithium batteries can be used in the present invention, including but not limited to one or more of carbon-based materials, silicon-based materials, tin-based materials, lithium titanate materials, metal oxide materials, and lithium metal materials.

[0031] The present invention has no particular limitation on the conductive agent. Without violating the inventive concept of the present application, any known conductive agent can be used in the present invention, including but not limited to one or more of carbon black, conductive graphite, carbon fiber, carbon nanotubes, and graphene.

[0032] The present invention has no particular limitation on the negative electrode current collector. Without violating the inventive concept of the present invention, any known negative electrode current collector can be used in the present invention. The negative electrode current collector can be a metal foil, metal grid or wire mesh, or mesh metal containing copper or any other suitable conductive material known to those skilled in the art.

[0033] Furthermore, the present invention also provides a method for preparing a negative electrode sheet: artificial graphite as a negative electrode active material, acetylene black as a conductive agent, styrene butadiene emulsion as an adhesive, sodium carboxymethyl cellulose as a dispersant, and the modified polyethyleneimine binder provided by the present invention are fully stirred and mixed in a deionized water solvent system, and then coated on a negative electrode current collector copper foil, dry pressed, and then rolled, slit, and welded to the tabs to obtain a negative electrode sheet.

[0034] Another object of the present invention is to provide a lithium-ion battery, wherein the lithium-ion battery comprises the negative electrode sheet.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention provides a modified polyethyleneimine binder, which has cyano groups and organic acid groups on the polyethyleneimine molecular chain. Polyethyleneimine has good flexibility and processability; cyano groups, as a polar functional group, have good adhesion to various materials. Cyanide modification on polyethyleneimine can improve hydrophobicity and adhesion while eliminating more active hydrogen groups, so that it has good dielectric constant performance; the organic acid salt unit is an ionic salt unit, and the introduction of such ionic structure can increase the conductivity of the binder. At the same time, through the charge effect of ions, the hydrophobic cyano structure can be more stabilized and its dispersibility in aqueous solution can be increased. The synergistic effect of cyano groups and organic acid groups can significantly increase the adhesion and conductivity of polyethyleneimine while improving its dispersibility in negative electrode slurry, thereby improving the consistency of negative electrode sheets. The modified polyethyleneimine binder of the present invention is applied to the negative electrode of lithium ion batteries and exhibits excellent adhesion, conductivity and consistency, which is beneficial to improving the cycle stability and rate performance of lithium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the hydrogen NMR spectrum of polyethyleneimine.

[0038] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of polyethyleneimine grafted with organic acid groups in Example 1.

[0039] Figure 3 This is the hydrogen nuclear magnetic resonance spectrum of polyethyleneimine after grafting organic acid groups and cyano groups in Example 1. DETAILED DESCRIPTION

[0040] The content of the present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present embodiment are conventional reagents, methods and equipment in the art.

[0041] Example 1

[0042] A modified polyethyleneimine binder is prepared as follows: In a three-mouth inverted glass reactor, add 15g of polyethyleneimine (Mw=100,000, solid content 36%) aqueous solution and 10g of deionized water, stir evenly, and heat to 60°C to obtain a polyethyleneimine primer solution. Take 2.60g of 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and add it to 90g of water. After gradually adding 10% ammonia water for neutralization, a 2-acrylamide-2-methylpropane sulfonate solution is obtained. Slowly add the 2-acrylamide-2-methylpropane sulfonate solution to the polyethyleneimine primer solution. After 1h of adding, continue the reaction for 4h. Take a sample of the reaction solution for the first nuclear magnetic resonance test. The test results are as follows: Figure 2 As shown. Then, 5.99 g of acrylonitrile monomer was slowly added. After the addition was completed gradually over 1 hour, the reaction was continued for 8 hours to obtain a cyano-modified aqueous polyethyleneimine solution. The cyano-modified aqueous polyethyleneimine solution was evaporated under reduced pressure to remove residual acrylonitrile monomer to obtain a modified polyethyleneimine binder. The product solution was sampled for the second NMR test, and the test results were as follows: Figure 3 As shown. The first H-NMR spectrum test results showed that the monomer double bond peak at the chemical shift of 6.0-7.0 ppm completely disappeared, indicating that the 2-acrylamide-2-methylpropane sulfonate monomer was completely reacted. The second H-NMR spectrum test results showed that acrylonitrile had reacted, and the polyethyleneimine molecular chain contained both 2-acrylamide-2-methylpropane sulfonic acid group and cyano group.

[0043] The present embodiment also provides a method for preparing a negative electrode sheet, wherein the negative electrode material artificial graphite, the conductive agent acetylene black, the adhesive styrene butadiene emulsion (SBR), the dispersant sodium carboxymethyl cellulose (CMC) and the modified polyethyleneimine binder provided in the present embodiment are fully stirred and mixed in a deionized water solvent system at a mass ratio of 96.0:0.8:1.2:1.0:1.0, and then coated on the negative electrode current collector copper foil, dry pressed, and then subjected to rolling, slitting, and welding of the pole ears to obtain a negative electrode sheet.

[0044] Example 2

[0045] A modified polyethyleneimine binder is prepared as follows: in a three-mouth glass reactor, 15g of polyethyleneimine (Mw=5000, solid content 36%) aqueous solution and 10g of deionized water are added and stirred evenly, and the temperature is raised to 60°C to obtain a polyethyleneimine primer solution. 4.07g of acrylic acid is added to 90g of water, and 2.37g of lithium hydroxide monohydrate is gradually added for neutralization to obtain a lithium acrylate solution. The lithium acrylate solution is slowly added to the polyethyleneimine primer solution, and the reaction is continued for 1h after the addition is completed for 1h, and then 3.66g of acrylonitrile monomer is slowly added, and the reaction is continued for 12h after the gradual addition is completed for 1h to obtain a cyano-modified aqueous polyethyleneimine solution. The cyano-modified aqueous polyethyleneimine solution is evaporated under reduced pressure to remove residual acrylonitrile monomer to obtain a modified polyethyleneimine binder.

[0046] This embodiment also provides a method for preparing a negative electrode of a lithium battery. The difference between the negative electrode of the lithium battery and that of Embodiment 1 is only that the modified polyethyleneimine binder in the negative electrode plate is the modified polyethyleneimine binder provided in this embodiment.

[0047] Example 3

[0048] A modified polyethyleneimine binder is prepared as follows: in a three-mouth glass reactor, 15g of polyethyleneimine (Mw=100,000, solid content 36%) aqueous solution and 10g of deionized water are added and stirred evenly, and the temperature is raised to 60°C to obtain a polyethyleneimine primer solution. 1.45g of carboxyethyl acrylate is added to 90g of water, and 0.4g of sodium hydroxide is gradually added for neutralization to obtain a sodium salt solution. The sodium salt solution is slowly added to the polyethyleneimine primer solution, and the reaction is continued for 4h after the addition is completed for 1h, and then 4.21g of methacrylonitrile monomer is slowly added, and the reaction is continued for 8h after the gradual addition is completed for 1h to obtain a cyano-modified aqueous polyethyleneimine solution. The cyano-modified aqueous polyethyleneimine solution is subjected to reduced pressure evaporation to remove residual acrylonitrile monomer to obtain a modified polyethyleneimine binder.

[0049] This embodiment also provides a method for preparing a negative electrode of a lithium battery. The difference between the negative electrode of the lithium battery and that of Embodiment 1 is only that the modified polyethyleneimine binder in the negative electrode plate is the modified polyethyleneimine binder provided in this embodiment.

[0050] Example 4

[0051] A modified polyethyleneimine binder is prepared as follows: in a three-mouth glass reactor, 15g of polyethyleneimine (Mw=100,000, solid content 36%) aqueous solution and 10g of deionized water are added and stirred evenly, and the temperature is raised to 60°C to obtain a polyethyleneimine primer solution. 2.71g of vinyl sulfonic acid is added to 90g of water, and 1.41g of potassium hydroxide is gradually added for neutralization to obtain a potassium salt solution. The potassium salt solution is slowly added to the polyethyleneimine primer solution, and the reaction is continued for 4h after the addition is completed for 1h, and then 5.99g of acrylonitrile monomer is slowly added, and the reaction is continued for 8h after the gradual addition is completed for 1h to obtain a cyano-modified aqueous polyethyleneimine solution. The cyano-modified aqueous polyethyleneimine solution is evaporated under reduced pressure to remove residual acrylonitrile monomer to obtain a modified polyethyleneimine binder.

[0052] This embodiment also provides a method for preparing a negative electrode of a lithium battery. The difference between the negative electrode of the lithium battery and that of Embodiment 1 is only that the modified polyethyleneimine binder in the negative electrode plate is the modified polyethyleneimine binder provided in this embodiment.

[0053] Example 5

[0054] A modified polyethyleneimine binder is prepared as follows: in a three-mouth glass reactor, 15g of polyethyleneimine (Mw=5000, solid content 36%) aqueous solution and 10g of deionized water are added and stirred evenly, and the temperature is raised to 60°C to obtain a polyethyleneimine primer solution. 0.18g of acrylic acid is added to 90g of water, and 0.11g of lithium hydroxide monohydrate is gradually added for neutralization to obtain a lithium acrylate solution. The lithium acrylate solution is slowly added to the polyethyleneimine primer solution, and the reaction is continued for 4h after the addition is completed for 1h, and then 7.98g of acrylonitrile monomer is slowly added, and the reaction is continued for 8h after the gradual addition is completed for 1h to obtain a cyano-modified aqueous polyethyleneimine solution. The cyano-modified polyethyleneimine solution is evaporated under reduced pressure to remove residual acrylonitrile monomer to obtain a modified polyethyleneimine binder.

[0055] This embodiment also provides a method for preparing a negative electrode of a lithium battery. The difference between the negative electrode of the lithium battery and that of Embodiment 1 is only that the modified polyethyleneimine binder in the negative electrode plate is the modified polyethyleneimine binder provided in this embodiment.

[0056] Comparative Example 1

[0057] This comparative example also provides a method for preparing a negative electrode of a lithium battery. The difference between the negative electrode of the lithium battery and Example 1 is that the modified polyethyleneimine binder in the negative electrode plate in Example 1 is replaced by unmodified polyethyleneimine.

[0058] Comparative Example 2

[0059] A modified polyethyleneimine binder, which differs from Example 1 only in that the polyethyleneimine binder does not contain a cyano unit. The preparation method is as follows: in a three-mouth reverse glass reactor, add 15g polyethyleneimine (Mw=100,000, solid content 36%) aqueous solution and 10g deionized water and stir evenly, heat to 60°C, and obtain a polyethyleneimine primer solution. Take 2.60g 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and add it to 90g water, gradually add 10% ammonia water for neutralization, and obtain a 2-acrylamide-2-methylpropane sulfonate solution. Slowly add the 2-acrylamide-2-methylpropane sulfonate solution to the polyethyleneimine primer solution, continue to react for 4h after the addition is completed for 1h, and obtain a modified polyethyleneimine binder.

[0060] This comparative example also provides a method for preparing a negative electrode of a lithium battery. The difference between the negative electrode of the lithium battery and Example 1 is only that the modified polyethyleneimine binder in the negative electrode plate is the modified polyethyleneimine binder provided in this comparative example.

[0061] Comparative Example 3

[0062] A modified polyethyleneimine binder, which differs from Example 1 only in that the polyethyleneimine binder does not contain a 2-acrylamide-2-methylpropanesulfonate structure. The preparation method is as follows: in a three-mouth reverse glass reactor, 15g of polyethyleneimine (Mw=100,000, solid content 36%) aqueous solution and 10g of deionized water are added and stirred evenly, and the temperature is raised to 60°C to obtain a polyethyleneimine primer solution. Subsequently, 5.99g of acrylonitrile monomer is slowly added, and after the gradual addition is completed in 1h, the reaction is continued for 8h to obtain a cyano-modified aqueous polyethyleneimine solution, and the residual acrylonitrile monomer is removed by reduced pressure evaporation to obtain a modified polyethyleneimine binder.

[0063] This comparative example also provides a method for preparing a negative electrode of a lithium battery. The difference between the negative electrode of the lithium battery and Example 1 is only that the modified polyethyleneimine binder in the negative electrode plate is the modified polyethyleneimine binder provided in this comparative example.

[0064] Performance Testing

[0065] Peel strength test:

[0066] The negative electrode sheets obtained in the examples and comparative examples were cut into strips of 20×200mm in size. One side of the electrode sheet sample was bonded to the 3M double-sided tape, and the other side of the double-sided tape was bonded to the surface of a 25×200mm stainless steel plate. A 2kg rubber roller was used to roll the double-sided tape bonding area back and forth 3 times to make the electrode sheet, double-sided tape and steel plate completely fit together and bend in the opposite direction at an angle of 180°. A universal electronic tensile testing machine was used for testing. One end of the stainless steel plate was fixed to the lower fixture of the tensile testing machine, and the bent end of the sample was fixed to the upper fixture. The angle of the sample was adjusted to ensure that the upper and lower ends were in a vertical position. Then, the sample was stretched at a speed of 50mm / min until the sample was completely peeled off from the substrate. The displacement and force during the process were recorded. It is generally believed that the force when the force is balanced is the adhesion of the electrode sheet. The results are shown in Table 1.

[0067] Lithium-ion battery assembly and performance testing:

[0068] Take 97% solid mass percentage content of lithium nickel cobalt manganese oxide (NCM 622) active material, 0.8% conductive agent (SP) and 1.2% polyvinylidene fluoride (PVDF), gradually add N-methyl pyrrolidone (NMP) in sequence and stir and mix thoroughly to obtain positive electrode slurry, adjust the solid content of the slurry to 50% with NMP, evenly coat the positive electrode slurry on both sides of aluminum foil, dry and roll to obtain positive electrode sheet. The diaphragm is selected from single-sided ceramic PE film (base film 9um, Al2O3 ceramic layer 3um), and the electrolyte is prepared by mixing 1.0M LiPF6 / ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and the volume ratio of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) is EC:EMC:DEC=30:50:30. The positive electrode sheet, the negative electrode sheet obtained in the embodiment of the present invention and the comparative example, and the separator are vacuum dried at 100° C. for 24 hours, and then cut, stacked, shelled, injected, pre-sealed, formed, double-sealed, and constant capacity are obtained to obtain a lithium-ion battery.

[0069] Battery capacity test:

[0070] At 25±5℃, the lithium-ion battery was discharged at a constant current of 0.33C to 3.0V and left to stand for 10min; then charged at a constant current of 0.33C to 4.3V; then changed to constant voltage charging until the charging current was ≤0.02C; among which, the capacity of the constant current charging stage was Q1, and the capacity of the constant voltage charging stage was Q2, then the battery capacity was Q1+Q2, and the results were shown in Table 1.

[0071] Internal resistance test:

[0072] When the lithium-ion battery is charged to 50% capacity, the internal resistance of the battery is tested using a 1kHz voltage internal resistance tester. The results are shown in Table 1.

[0073] Rate discharge capacity retention test:

[0074] At 25±5℃, the lithium-ion battery was charged to 4.3V at a constant current of 0.33C, and then left to stand for 10 minutes; then it was changed to constant voltage charging until the charging current was ≤0.02C, and after standing for 10 minutes, it was discharged to 3.0V at a rate of 3C. Among them, the constant current charging stage capacity is Q1, the constant voltage charging stage capacity is Q2, and the 2C discharge stage capacity is Q3, then the 2C discharge capacity retention rate = Q3 / (Q1+Q2), and the results are shown in Table 1.

[0075] Table 1

[0076]

[0077] According to the data in Table 1, the present invention prepares a modified polyethyleneimine binder by introducing a cyano unit and an organic acid salt structure into polyethyleneimine. The prepared binder can significantly improve the adhesion of the negative electrode sheet, and the peeling force reaches more than 15.1 N / m, which can effectively improve the processing performance of the electrode sheet. When applied to lithium-ion batteries, the battery capacity reaches more than 2.5 Ah, the internal resistance is less than 4.28 mΩ, the conductivity is significantly improved, the 3C rate charging capacity retention rate reaches more than 85.3%, and the cycle stability is significantly improved.

[0078] The above embodiments are preferred experimental methods of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A modified polyethyleneimine binder, characterized in that: The polyethyleneimine molecular chain is connected with cyano groups and organic acid groups at the same time, and the organic acid groups are combined with cations to form salts; the modified polyethyleneimine binder is prepared by uniformly mixing polyethyleneimine and water, adding an organic acid salt monomer for a primary reaction, and then adding a cyano monomer for a secondary reaction; the molar ratio of the polyethyleneimine unit, the organic acid salt monomer, and the cyano monomer in the polyethyleneimine is 10:(0.1-5):(5-15).

2. The modified polyethyleneimine binder according to claim 1, characterized in that The molar ratio of the ethyleneimine unit, the organic acid salt monomer and the cyano monomer in the polyethyleneimine is 10:(0.8-4.5):(5-12).

3. The modified polyethyleneimine binder according to claim 1, characterized in that The organic acid group is one or more of a carboxylic acid group, a sulfonic acid group, and a phosphonic acid group.

4. The modified polyethyleneimine binder according to claim 1, characterized in that: The organic acid group is one or more of an acrylic acid group, a methacrylic acid group, a carboxyethyl acrylate group, a vinyl sulfonic acid group, and a 2-acrylamide-dimethylpropane sulfonic acid group.

5. The modified polyethyleneimine binder according to claim 1, characterized in that: The cyano monomer is acrylonitrile and / or methacrylonitrile.

6. The modified polyethyleneimine binder according to claim 1, characterized in that: The reaction temperature of the primary reaction and the secondary reaction is 55-65°C.

7. The modified polyethyleneimine binder according to claim 1, characterized in that: The time of the primary reaction is ≥1h, and the time of the secondary reaction is ≥4h.

8. A negative electrode sheet, characterized in that: The negative electrode sheet comprises the modified polyethyleneimine binder according to any one of claims 1 to 7.

9. The negative electrode sheet according to claim 8, characterized in that: The weight percentage of the modified polyethyleneimine binder in the negative electrode sheet is 0.5-2.0%.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 8 or 9.

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