A solvent-based negative electrode binder, a preparation method and application thereof

Abstract

This invention discloses a solvent-based negative electrode binder, its preparation method, and its application. The binder comprises the following raw materials in parts by weight: 2-10 parts of acrylic monomers; 70-95 parts of acrylonitrile monomers; 5-20 parts of oil-soluble monomers; and 0-6 parts of water-soluble monomers. After the binder is prepared into a negative electrode slurry, 0-0.1% of a crosslinking agent is added. Compared with the prior art, this invention, through crosslinking modification and copolymerization unit design, enables the binder to possess both high strength and high toughness. High strength effectively restrains the volume expansion of the silicon negative electrode, while high toughness achieves stress dissipation and maintains the integrity of the electrode sheet. At the same time, this binder effectively suppresses the volume expansion of the high-silicon negative electrode during charge and discharge, slows down capacity decay, and improves the cycle life of lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and particularly relates to a solvent-based negative electrode binder, its preparation method, and its application. Background Technology

[0002] In lithium-ion batteries, silicon anodes have attracted much attention due to their extremely high theoretical specific capacity. However, silicon undergoes drastic volume expansion during charging and discharging, leading to the pulverization of active materials, damage to the electrode structure, and repeated reconstruction of the solid electrolyte interface film, resulting in rapid capacity decay.

[0003] Binders are one of the key materials for suppressing the volume expansion of silicon anodes. Current industrial anode binders are mainly aqueous systems, including sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyurethane (PU). These binders perform well in graphite anodes, but have significant drawbacks in high-silicon systems: PAA, while possessing high modulus and strength, has excessively rigid molecular chains and poor flexibility, leading to electrode brittleness; SBR has good flexibility but low strength, failing to effectively restrain silicon expansion; PU, while possessing both strength and toughness, swells severely in carbonate electrolytes, causing a rapid decrease in adhesion. These defects make it difficult for existing binders to suppress the volume expansion of high-silicon anodes, resulting in excessively rapid capacity decay.

[0004] To alleviate the aforementioned problems, existing research has attempted to improve the overall performance of binders through crosslinking modification or the introduction of interpenetrating network structures. Existing technologies disclose methods for preparing crosslinked polyacrylic acid (PAA) binders using suspension polymerization. However, these crosslinked PAA binders still suffer from insufficient resistance to electrolyte swelling and rapid modulus decay during long-term cycling, making it difficult to meet the long-life requirements of high-silicon anodes.

[0005] Therefore, developing a novel binder that combines high strength, high toughness, and low swelling properties is key to improving the cycle stability of silicon-based lithium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a solvent-based anode binder, its preparation method, and its application, to solve the problems that existing high-silicon anode binders cannot simultaneously achieve high strength and high flexibility, and have poor resistance to electrolyte swelling, so as to effectively suppress the volume expansion of high-silicon anodes during charging and discharging, and improve the cycle life of lithium-ion batteries.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a solvent-based negative electrode binder, comprising the following raw materials in parts by weight: 2-10 parts of acrylic monomers; 70-95 parts of acrylonitrile monomer; 5-20 parts of oil-soluble monomer; 0-6 parts of water-soluble monomers.

[0008] Preferably, the acrylic monomer is selected from acrylic acid or methacrylic acid, and the degree of neutralization is 10% to 100%.

[0009] Preferably, the acrylonitrile monomer is selected from one or more of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile.

[0010] Preferably, the oil-soluble monomer is selected from one or more of methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, octadecyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, styrene, vinyl acetate, alkoxyphenol acrylate, and glycidyl methacrylate.

[0011] Preferably, the water-soluble monomer is selected from one or more of methacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, itaconic acid, and hydroxyethyl methacrylate.

[0012] Preferably, the solvent-based negative electrode binder is a cross-linked network copolymer with a molecular weight of 600,000 to 2,000,000.

[0013] Secondly, the present invention provides a method for preparing a solvent-based negative electrode binder, comprising the following steps: S1. The acrylic monomers are pre-neutralized to the set degree of neutralization with alkali solution, and then acrylonitrile monomer, oil-soluble monomer, water-soluble monomer and deionized water are added and stirred evenly to form a mixture. S2. Add the initiator to the mixture, and heat it to 30~100℃ under an inert atmosphere to carry out a suspension polymerization reaction for 4~24 hours; S3. After the reaction is complete, filter, wash and dry to obtain the solvent-based negative electrode binder.

[0014] Preferably, the alkaline solution comprises a sodium hydroxide solution or a lithium hydroxide solution, and the pre-neutralization needs to be carried out under a chilled water circulation system.

[0015] Preferably, the stirring rate in step S1 is 300~500 rpm.

[0016] Preferably, the inert atmosphere is a nitrogen atmosphere, and nitrogen is introduced before heating to remove oxygen for 1-2 hours.

[0017] Preferably, the initiator is selected from at least one of ammonium sulfate, potassium persulfate, sodium persulfate, azobisisobutyramidine hydrochloride, persulfate, sodium sulfite, and hydrogen peroxide, and its amount is 0.1% to 2% of the total mass of the solvent-based negative electrode binder.

[0018] Thirdly, the present invention provides a negative electrode sheet comprising a negative electrode active material, a conductive agent, and the solvent-based negative electrode binder described above, wherein the negative electrode active material is a mixture of silicon-based material and graphite, and the silicon-based material is a silicon-oxygen material or a silicon-carbon material.

[0019] Preferably, the method for preparing the negative electrode sheet includes the following steps: Solvent-based negative electrode binder is dissolved in N-methylpyrrolidone to obtain a mixed solution with a solid content of 3-7%; The mixed solution, the negative electrode active material, and the conductive agent are mixed to prepare a negative electrode slurry; Add 0-0.1% of polycarbodiimide crosslinking agent by mass to the negative electrode slurry, mix evenly, coat onto the current collector, and dry at 75-110°C to obtain the negative electrode sheet.

[0020] Fourthly, the present invention provides a lithium-ion battery comprising the aforementioned negative electrode sheet.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: This invention, through the synergistic design of a cross-linked network structure and flexible comonomers, endows the solvent-based negative electrode binder with excellent mechanical properties and toughness. Specifically, the tensile strength of the solvent-based negative electrode binder can reach 60~150MPa, and the elongation at break can reach 100~300%. This high strength ensures that the solvent-based negative electrode binder can effectively restrain the expansion of the electrode sheet during long-term charge-discharge cycles of the silicon negative electrode; at the same time, the high toughness ensures that the solvent-based negative electrode binder can effectively dissipate the stress generated during charge-discharge, preventing the electrode sheet from becoming brittle or detaching due to stress concentration. The synergistic effect of these two characteristics allows the electrode sheet to maintain its integrity during long cycles, significantly reducing the risk of coating powdering and detachment, and the rate of cyclic expansion.

[0022] The solvent-based negative electrode binder of this invention exhibits minimal swelling in commonly used carbonate electrolytes, with a swelling rate significantly lower than that of existing aqueous PU and cross-linked PAA binders. This low swelling characteristic ensures the stability of the adhesive strength and modulus of the solvent-based negative electrode binder during long-term cycling, preventing electrode structure instability and rapid capacity decay caused by swelling, thereby granting the battery a longer cycle life. Detailed Implementation

[0023] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0024] In this invention, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0025] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0026] It should be understood that in various embodiments of the present invention, the order of the above-mentioned processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0027] According to a first aspect of the present invention, a solvent-based negative electrode binder is provided, comprising the following raw materials in parts by weight: 2-10 parts of acrylic monomers; 70-95 parts of acrylonitrile monomer; 5-20 parts of oil-soluble monomer; 0-6 parts of water-soluble monomers.

[0028] The component content of the above formula can be adjusted proportionally according to requirements; for example, the weight parts of acrylic monomers can be 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., the weight parts of acrylonitrile monomers can be 70, 72, 75, 78, 80, 82, 85, 88, 90, 92, 95, etc., the weight parts of oil-soluble monomers can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc., and the weight parts of water-soluble monomers can be 0, 1, 2, 3, 4, 5, 6, etc.

[0029] Among them, acrylic monomers, after pre-neutralization, provide carboxyl functional groups, giving the binder excellent adhesion to the surface of silicon particles and resistance to electrolytes. Simultaneously, hydrogen bonds can form between carboxyl groups to enhance cohesion. Acrylonitrile monomers introduce highly polar cyano groups, which significantly improve the interaction forces between polymer molecular chains, increasing the modulus and tensile strength of the binder. Furthermore, the solvent resistance of the cyano groups effectively inhibits the swelling of the binder in carbonate electrolytes. Oil-soluble monomers are embedded in the polymer backbone, providing a flexible chain segment structure, giving the binder good toughness and stress dissipation capabilities, avoiding electrode brittleness caused by excessive crosslinking or rigidity. Water-soluble monomers improve the dispersion stability of the polymerization system in the aqueous phase, while enhancing the wetting and adhesion of the binder to hydrophilic silicon oxide surfaces. These four monomers form a crosslinked network structure through suspension polymerization, achieving a synergistic balance of high strength, high toughness, and low swelling.

[0030] In some embodiments of the present invention, the acrylic monomer is selected from acrylic acid or methacrylic acid, and the degree of neutralization is 10% to 100%. For example, the degree of neutralization of the acrylic monomer can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc.

[0031] The neutralization degree of acrylic monomers is controlled between 10% and 100% because: partial neutralization converts carboxyl groups into carboxylate salts, increasing the solubility of monomers in the aqueous phase, which is beneficial to the stable dispersion of oil droplets in the initial stage of suspension polymerization; an appropriate degree of neutralization can regulate the balance between electrostatic repulsion and hydrogen bonding between polymer molecular chains; if the neutralization is too low (<10%), it will lead to excessive coiling of molecular chains, abnormal increase in viscosity of the polymerization system, and easy agglomeration; if the neutralization is too high (complete neutralization), it will weaken the hydrogen bond anchoring effect formed by carboxyl groups and hydroxyl groups on the surface of silicon particles, reducing the adhesion of the binder to the silicon anode.

[0032] In some embodiments of the present invention, the acrylonitrile monomer is selected from one or more of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile.

[0033] In some embodiments of the present invention, the oil-soluble monomer is selected from one or more of methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, octadecyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, styrene, vinyl acetate, alkoxyphenol acrylate, and glycidyl methacrylate. The water-soluble monomer is selected from one or more of methacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, itaconic acid, and hydroxyethyl methacrylate.

[0034] In some embodiments of the present invention, the solvent-based negative electrode binder is a copolymer with a cross-linked network structure and a molecular weight of 600,000 to 2,000,000. For example, the molecular weight of the solvent-based negative electrode binder can be 600,000, 800,000, 1,000,000, 1,200,000, 1,500,000, 1,800,000, 2,000,000, etc.

[0035] The molecular weight of the solvent-based negative electrode binder is controlled within the range of 600,000 to 2 million because: when the molecular weight is below 600,000, the entanglement between polymer molecular chains is insufficient, resulting in a significant decrease in the bulk strength and cohesive force of the binder, making it difficult to provide sufficient outward binding force when the silicon negative electrode expands in volume; while when the molecular weight is above 2 million, although the strength is further improved, the excessive entanglement of molecular chains leads to excessively high solution viscosity, which easily causes droplet aggregation and uneven particle size distribution during suspension polymerization, and makes coating difficult and dispersibility poor during electrode preparation.

[0036] According to a second aspect of the present invention, a method for preparing a solvent-based negative electrode binder is provided, comprising the following steps: S1. The acrylic monomers are pre-neutralized to the set degree of neutralization with alkali solution, and then acrylonitrile monomer, oil-soluble monomer, water-soluble monomer and deionized water are added and stirred evenly to form a mixture. S2. Add the initiator to the mixture, heat to 30~100℃ under an inert atmosphere, and carry out suspension polymerization reaction for 4~24 hours; S3. After the reaction is complete, filter, wash and dry to obtain solvent-based negative electrode binder.

[0037] In some embodiments of the invention, the alkali solution comprises a sodium hydroxide solution or a lithium hydroxide solution, and pre-neutralization needs to be carried out under a chilled water circulation system.

[0038] In some embodiments of the present invention, the stirring rate in step S1 is 300~500 rpm.

[0039] In some embodiments of the present invention, the inert atmosphere is a nitrogen atmosphere, and nitrogen is introduced before heating to remove oxygen for a period of 1 to 2 hours.

[0040] Suspension polymerization requires an inert atmosphere, the core purpose of which is to remove oxygen from the reaction system. Oxygen is a typical free radical polymerization inhibitor, and its mechanism of action is as follows: oxygen molecules readily react with chain free radicals to generate peroxide free radicals or relatively stable peroxides. These species cannot continue to initiate monomer polymerization, leading to a prolonged polymerization induction period and a significant decrease in the reaction rate. More seriously, the presence of oxygen prematurely terminates the growing polymer molecular chains, causing a significant reduction in the molecular weight of the product, making it difficult to reach the target range of 600,000 to 2,000,000 required by this invention. At the same time, the randomness of chain termination leads to defects in the crosslinking network structure, causing the tensile strength and elongation at break of the binder to fall short of expectations.

[0041] In some embodiments of the present invention, the initiator is selected from at least one of ammonium sulfate, potassium persulfate, sodium persulfate, azobisisobutyramidine hydrochloride, persulfate, sodium sulfite, and hydrogen peroxide, and its amount is 0.1% to 2% of the total mass of the solvent-based negative electrode binder. For example, the amount of initiator can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc.

[0042] The amount of initiator is directly related to the polymerization kinetics and the molecular weight of the product: when the amount is less than 0.1%, the free radical generation rate is too low, the polymerization reaction time is significantly prolonged, and the insufficient number of active centers can easily lead to low monomer conversion rate, excessively large product molecular weight, or incomplete polymerization; when the amount is more than 2%, the free radical concentration is too high, the probability of chain termination reaction increases, resulting in a decrease in polymer molecular weight. At the same time, the reaction is exothermic and can easily cause explosive polymerization or uneven cross-linking, which can damage the mechanical properties of the binder.

[0043] According to a third aspect of the present invention, the present invention provides a negative electrode sheet comprising a negative electrode active material, a conductive agent and the above-mentioned solvent-based negative electrode binder, wherein the negative electrode active material is a mixture of silicon-based material and graphite, and the silicon-based material is a silicon-oxygen material or a silicon-carbon material.

[0044] In some embodiments of the present invention, the method for preparing the negative electrode sheet includes the following steps: Solvent-based negative electrode binder is dissolved in N-methylpyrrolidone to obtain a mixed solution with a solid content of 3-7%; A negative electrode slurry is prepared by mixing a mixed solution, a negative electrode active material, and a conductive agent. Add 0-0.1% of polycarbodiimide crosslinking agent by mass to the negative electrode slurry, mix evenly, coat it onto the current collector, and dry it at 75-110℃ to obtain the negative electrode sheet.

[0045] According to a fourth aspect of the present invention, the present invention provides a lithium-ion battery comprising the above-described negative electrode sheet.

[0046] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0047] Example 1

[0048] The solvent-based negative electrode binder provided in this embodiment comprises the following raw materials: 4g of acrylic monomer (acrylic acid); 80g of acrylonitrile monomer (acrylonitrile); 14g of oil-soluble monomer (isooctyl methacrylate); and 2g of water-soluble monomer (hydroxyethyl methacrylate). The preparation method of this binder is as follows: S1. Neutralize 4g of acrylic acid with 5M NaOH solution to a neutralization degree of 80%, add 80g of acrylonitrile, 14g of isooctyl methacrylate, 2g of hydroxyethyl methacrylate and 200mL of deionized water, and stir until a mixture is formed. S2. Add 0.5g of potassium persulfate to the mixture, heat to 70°C under nitrogen, and carry out suspension polymerization reaction for 6 hours; S3. After the reaction is complete, filter, wash and dry to obtain solvent-based negative electrode binder.

[0049] Preparation of negative electrode sheet The solvent-based negative electrode binder was dissolved in N-methylpyrrolidone to obtain a mixed solution with a solid content of 3%. The mixed solution, silicon carbon material and carbon nanotubes were mixed to prepare a negative electrode slurry. 0.01% of polycarbodiimide by mass of the negative electrode slurry was added to the negative electrode slurry, mixed evenly and then coated onto the current collector. The mixture was dried at 75°C to obtain the negative electrode sheet.

[0050] Example 2

[0051] The difference from Example 1 is that the raw materials in step S1 are 3g acrylic acid, 84g acrylonitrile, 12g butyl acrylate and 1g acrylamide, and the initiator in step S2 is 0.4g sodium persulfate. The remaining steps are the same as in Example 1.

[0052] Example 3

[0053] Unlike Example 1, the raw materials in step S1 are 9g acrylic acid, 85g acrylonitrile, and 6g methyl acrylate, and no water-soluble monomers are added. The initiator in step S2 is 0.7g sodium persulfate. The remaining steps are the same as in Example 1.

[0054] Example 4

[0055] The difference from Example 1 is that the raw materials in step S1 are 3g acrylic acid, 78g acrylonitrile, 18g isooctyl acrylate, and 1g edaconic acid, while the remaining steps are the same as in Example 1.

[0056] Example 5

[0057] Unlike Example 1, the raw materials in step S1 are 4g acrylic acid, 90g acrylonitrile, and 6g butyl acrylate, without the addition of water-soluble monomers. The remaining steps are the same as in Example 1.

[0058] Example 6

[0059] The difference from Example 1 is that the neutralization degree in step S1 is 10%, while the other steps are the same as in Example 1.

[0060] Example 7

[0061] The difference from Example 1 is that the neutralization degree in step S1 is 50%, while the other steps are the same as in Example 1.

[0062] Example 8

[0063] Unlike Example 1, the neutralization degree in step S1 is 100%, while the remaining steps are the same as in Example 1.

[0064] Example 9

[0065] Unlike Example 1, 0.05% polycarbodiimide was added during the preparation of the negative electrode sheet; the remaining steps were the same as in Example 1.

[0066] Example 10

[0067] Unlike Example 1, 0.1% of polycarbodiimide was added during the preparation of the negative electrode sheet, while the remaining steps were the same as in Example 1.

[0068] Comparative Example 1 Unlike Example 1, the raw materials in step S1 are 25g acrylic acid, 72g acrylonitrile, and 3g acrylamide, without the addition of oil-soluble monomers. The remaining steps are the same as in Example 1.

[0069] Comparative Example 2 The difference from Example 1 is that the raw materials in step S1 are 30g acrylic acid, 60g acrylonitrile, 6g butyl acrylate and 4g acrylamide, and the initiator in step S2 is 0.3g potassium persulfate. The remaining steps are the same as in Example 1.

[0070] Comparative Example 3 A crosslinked PAA binder was prepared using only acrylic acid (80% neutralization) and crosslinking agent N,N'-methylenebisacrylamide, following the same suspension polymerization process, and then used to fabricate a negative electrode sheet.

[0071] Comparative Example 4 The negative electrode sheet is made using commercially available SBR binder.

[0072] The negative electrode sheets obtained from the above embodiments and comparative examples were subjected to the following performance tests, and the test results are shown in Table 1.

[0073] 1) Tensile strength: The polymer was dissolved in NMP and cast onto a polytetrafluoroethylene release film. After curing and peeling, a self-supporting film with a thickness of 0.5-1 mm was obtained, and then cut into national standard type 3 tensile test strips using a dumbbell-shaped cutter. The test was conducted using an electronic universal testing machine with a tensile speed of 50 mm / min and a gauge length of 25 mm.

[0074] 2) Elongation at break: Tensile strength is calculated by dividing the maximum tensile force by the initial cross-sectional area of ​​the specimen (MPa), and elongation at break is calculated as (gauge length at break - initial gauge length) / initial gauge length × 100%. Three parallel specimens are tested for each sample, and the final result is the average value.

[0075] 3) Swelling rate: Cut the polymer film into 2×2cm pieces and weigh the initial mass m1. Then immerse them in commercial silicon-based electrolyte, seal them, and let them stand in a 70℃ oven for 48 h. After taking them out, wipe off the residual electrolyte on the surface and weigh the mass m2. The swelling rate is calculated as (m2-m1) / m1×100%. Similarly, test 3 samples and take the average value.

[0076] 4) Cycle life: Perform 1C / 0.5C cyclic charge and discharge test. When the cell capacity retention rate drops to 80%, stop the test. The number of cycles at this time is the cycle life of the cell.

[0077] 5) Cyclic expansion rate: Charge the cell to 100% SOC at a 1C rate; record the initial thickness d1 using a PPG thickness gauge. Afterward, after every 100 charge-discharge cycles, charge to 100% SOC at 1C and measure the thickness d at that number of cycles. n (n is the number of cycles). The cyclic expansion rate is calculated using the formula (d n Calculated as -d1) / d1×100%.

[0078] Table 1 Performance test results of the negative electrode sheets in Examples 1-8 and Comparative Examples 1-4

[0079] As shown in Table 1, the test results of Examples 1-5 indicate that the tensile strength of this type of adhesive sample ranges from 23.6 to 45.7 MPa, the elongation at break ranges from 42.1% to 260.5%, and the swelling rate ranges from 16.32% to 41.23%. Overall, it exhibits moderate strength and good flexibility, effectively suppressing cell cyclic expansion. After 500 cycles, the expansion rate of the cell thickness at 100% SOC compared to the initial 100% SOC state is controlled within 10%.

[0080] As can be seen from the test results of Examples 6-8 in Table 1, when the acrylic acid content is low, the change in the degree of neutralization has little impact on the performance. The tensile strength of the three examples is 26.6~30.4MPa, the elongation at break is 163.2%~212.3%, the swelling rate is 22.45%~31.87%, and the cyclic expansion rate is 7.2%~9.2%, with limited fluctuations in various indicators.

[0081] Compared with Example 1, Comparative Examples 1-3, due to the higher proportion of rigid monomers added, showed a significant reduction in film elongation at break to 3.6%~18.2% and swelling rate to 5.2%~21.43%, but the tensile strength was greatly increased to 52.1~80.8 MPa; however, the sacrifice in flexibility was too great, resulting in a cell thickness expansion rate of more than 20% after 500 cycles.

[0082] Compared to Example 1, Comparative Example 4, using pure SBR binder, exhibits a tensile strength of only 1.2 MPa, an elongation at break as high as 450%, and a swelling rate of 39.21%, demonstrating extremely low stiffness and high swelling characteristics. This system has a cycle life of less than 500 cycles compared to polyacrylonitrile.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A solvent-based negative electrode binder, characterized in that, The raw materials consist of the following parts by weight: 2-10 parts of acrylic monomers; 70-95 parts of acrylonitrile monomer; 5-20 parts of oil-soluble monomer; 0-6 parts of water-soluble monomers.

2. The solvent-based negative electrode binder according to claim 1, characterized in that, The acrylic monomers are selected from acrylic acid or methacrylic acid, with a degree of neutralization of 10% to 100%.

3. The solvent-based negative electrode binder according to claim 1, characterized in that, The acrylonitrile monomer is selected from one or more of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile; And / or, the oil-soluble monomer is selected from one or more of methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, octadecyl methacrylate, isooctyl methacrylate, isobornyl methacrylate, styrene, vinyl acetate, alkoxyphenol acrylate, and glycidyl methacrylate. And / or, the water-soluble monomer is selected from one or more of methacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, itaconic acid, and hydroxyethyl methacrylate.

4. The solvent-based negative electrode binder according to claim 1, characterized in that, The solvent-based negative electrode binder is a cross-linked network copolymer with a molecular weight of 600,000 to 2,000,000.

5. A method for preparing the solvent-based negative electrode binder according to any one of claims 1-4, characterized in that, Includes the following steps: S1. The acrylic monomers are pre-neutralized to the set degree of neutralization with alkali solution, and then acrylonitrile monomer, oil-soluble monomer, water-soluble monomer and deionized water are added and stirred evenly to form a mixture. S2. Add the initiator to the mixture, and heat it to 30~100℃ under an inert atmosphere to carry out a suspension polymerization reaction for 4~24 hours; S3. After the reaction is complete, filter, wash and dry to obtain the solvent-based negative electrode binder.

6. The method according to claim 5, characterized in that, The alkaline solution includes sodium hydroxide solution or lithium hydroxide solution, and pre-neutralization needs to be carried out under chilled water circulation; And / or, the stirring rate in step S1 is 300~500 rpm; And / or, the inert atmosphere is a nitrogen atmosphere, and nitrogen is introduced before heating for deoxygenation treatment, the deoxygenation time being 1~2 hours.

7. The method according to claim 5, characterized in that, The initiator is selected from at least one of ammonium sulfate, potassium persulfate, sodium persulfate, azobisisobutyramidine hydrochloride, persulfate, sodium sulfite, and hydrogen peroxide, and its amount is 0.1% to 2% of the total mass of the solvent-based negative electrode binder.

8. A negative electrode sheet, characterized in that, The invention comprises a negative electrode active material, a conductive agent, and a solvent-based negative electrode binder as described in any one of claims 1-4, wherein the negative electrode active material is a mixture of a silicon-based material and graphite, and the silicon-based material is a silicon-oxygen material or a silicon-carbon material.

9. The negative electrode sheet according to claim 8, characterized in that, The method for preparing the negative electrode sheet includes the following steps: Solvent-based negative electrode binder is dissolved in N-methylpyrrolidone to obtain a mixed solution with a solid content of 3-7%; The mixed solution, the negative electrode active material, and the conductive agent are mixed to prepare a negative electrode slurry; Add 0-0.1% of polycarbodiimide crosslinking agent by mass to the negative electrode slurry, mix evenly, coat onto the current collector, and dry at 75-110°C to obtain the negative electrode sheet.

10. A lithium-ion battery, characterized in that, It includes the negative electrode sheet as described in claim 8 or 9.

Images