A flexible acrylonitrile copolymer positive electrode binder and its preparation method and application

Abstract

The present application relates to the field of lithium-ion battery adhesives, and in particular to a flexible acrylonitrile copolymer positive electrode binder and its preparation method and application. A flexible acrylonitrile copolymer positive electrode binder, calculated by mass, is prepared from raw materials including: 68-72 parts of acrylonitrile, 0.4-0.6 parts of polyvinyl alcohol, 9-11 parts of a strong polar monomer, 97-103 parts of a polyoctene copolymer emulsion, 2.4-2.6 parts of an initiator aqueous solution, and 395-400 parts of deionized water. The flexible acrylonitrile copolymer positive electrode binder of the present application exhibits significant technical advantages in terms of improving bonding strength, optimizing electrolyte swelling, improving processing performance, providing chemical stability, and promoting lithium ion conduction. It also has the advantage of being suitable for large-scale production, providing important material and technical support for the development of lithium-ion batteries.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion battery adhesives, and in particular to a flexible acrylonitrile copolymer positive electrode binder and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density, long cycle life, and high operating voltage, are widely used in mobile electronics, electric vehicles, and energy storage. Lithium-ion batteries operate by storing and initially discharging energy through redox reactions involving the insertion and removal of lithium ions from the electrode active materials. Lithium-ion batteries primarily consist of a positive electrode, a negative electrode, a separator, and an electrolyte. Although the binder content is small, it is an essential material in the battery, bonding the active material, conductive carbon, and current collector together to ensure proper function. Currently, positive electrode binders include polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA). PVDF binders produce electrode sheets with good processing properties and battery performance, but they are expensive, have weak bonding strength, exhibit high electrolyte swelling, and pose the risk of hydrogen fluoride release upon high-temperature decomposition. PAA binders offer strong bonding, low electrolyte swelling, and excellent battery cycle performance, but they produce hard and brittle electrode sheets with poor processing properties. These binders no longer meet the demands of high-performance lithium-ion batteries.

[0003] The PVDF cathode binder currently available on the market is a fluorine-containing material, primarily imported. It is expensive, exhibits weak binding properties, exhibits high electrolyte swelling, and carries the risk of releasing hydrogen fluoride upon high-temperature decomposition. Therefore, there is an urgent need to develop a binder with excellent processability, high bonding strength, moderate electrolyte swelling, and superior battery performance. Summary of the Invention

[0004] In response to the deficiencies in the prior art, the present application provides a flexible acrylonitrile copolymer positive electrode binder, and its preparation method and application. The present application uses acrylonitrile as the main monomer, and introduces highly polar lithium acrylate, acrylamide, dimethylaminoethyl acrylate monomers and long-chain polyoctene copolymers through free radical copolymerization. The strong polar groups give the binder a strong bonding ability to the current collector aluminum foil, and the complexation and decomplexation effect of the strongly electronegative elements oxygen and nitrogen with lithium ions is beneficial to lithium ion conduction and reduces the internal resistance of the battery. The long-chain polyoctene copolymer makes the electrolyte swelling degree moderate, the prepared positive electrode sheet has good processing performance, and the polyfluorine structure provides excellent chemical stability. The strong peeling force and moderate electrolyte swelling degree of the binder ensure that the electrode active material does not fall off from the current collector during the charge and discharge process as the volume changes periodically with the insertion / extraction of lithium ions, thereby improving the cycle performance of the lithium-ion battery. At the same time, the preparation method of the present application is simple and easy to implement, and is suitable for large-scale production.

[0005] In the first aspect, the present application provides a flexible acrylonitrile copolymer positive electrode binder, which adopts the following technical solution: a flexible acrylonitrile copolymer positive electrode binder, wherein the raw materials for preparation include, by weight: 68-72 parts of acrylonitrile, 0.4-0.6 parts of polyvinyl alcohol, 9-11 parts of strong polar monomer, 97-103 parts of polyoctene copolymer emulsion, 2.4-2.6 parts of initiator aqueous solution, and 395-400 parts of deionized water.

[0006] By adopting the above technical solution, acrylonitrile serves as the primary monomer, providing the basic structure of the polymer backbone. The cyano group (-CN) in acrylonitrile is a highly polar group, which helps improve the binder's adhesion to the current collector aluminum foil. Its electronegativity interacts with lithium ions, promoting lithium ion conduction and reducing the battery's internal resistance. Polyvinyl alcohol, a multifunctional additive, improves the binder's film-forming properties and adhesion, while also providing additional hydroxyl (-OH) groups to enhance hydrogen bonding with the current collector aluminum foil. Highly polar monomers introduce highly polar groups such as lithium carboxylate, amino, and amide groups, enhancing the binder's bond strength and forming ionic and hydrogen bonds with oxygen-containing groups on the surface of the current collector aluminum foil. Furthermore, the complexation and decomplexation between the highly electronegative elements oxygen and nitrogen and lithium ions facilitates lithium ion conduction. Polyoctene copolymer emulsion provides long-chain non-polar octanyl groups, increasing the binder's flexibility and providing moderate electrolyte swelling, resulting in excellent positive electrode sheet processing performance. The polyfluorinated structure also provides excellent chemical stability. Initiator aqueous solution: used to initiate free radical copolymerization reaction, control the polymerization process and molecular weight distribution, and ensure the performance consistency of the binder. Deionized water: as a reaction medium, it provides a pure environment to avoid unnecessary side reactions or pollution, and facilitates subsequent product purification and drying. In summary, the flexible acrylonitrile copolymer positive electrode binder of the present application achieves high bonding strength, moderate electrolyte swelling, good processing performance and excellent cycle capacity retention rate through the precise ratio and synergistic effect of each component, thereby significantly improving the performance of lithium-ion batteries.

[0007] Preferably, the highly polar monomer is selected from two of lithium acrylate monomers, acrylamide monomers and dimethylaminoethyl acrylate monomers.

[0008] By adopting the above technical solution, two highly polar monomers from the group consisting of lithium acrylate, dimethylaminoethyl acrylate, and acrylamide were selected as the binder for the preparation of a flexible acrylonitrile copolymer positive electrode binder. These monomers are introduced into the polymer chain via free radical copolymerization, endowing the binder with strong adhesion to the current collector aluminum foil. Furthermore, through the complexation and decomplexation of the highly electronegative elements oxygen and nitrogen with lithium ions, they facilitate lithium ion conduction and reduce the battery's internal resistance. The lithium carboxylate groups in the highly polar monomers have excellent adhesion, effectively enhancing the binding force between the binder and the aluminum foil current collector. The amino groups in the acrylamide monomers can form strong chemical bonds with the oxide layer on the aluminum foil surface, further enhancing the bonding effect. The highly polar monomers exhibit good weather resistance in the electrolyte, significantly reducing the binder's swelling and solubility in lithium-ion battery electrolytes. A moderate swelling degree helps maintain the integrity of the electrode active material during volume changes during charge and discharge, thereby improving the battery's cycling performance. Strongly electronegative elements such as oxygen and nitrogen can complex with lithium ions, facilitating their conduction within the electrode and reducing the battery's internal resistance. These polar monomers also help increase the rate of lithium ion decomplexation, further enhancing the battery's charge and discharge efficiency. Strongly polar monomers can improve the coating and uniformity of electrode slurries, facilitating the preparation of high-performance electrode sheets. By regulating the type and ratio of strong polar monomers, the mechanical properties of the binder can be optimized, imparting excellent flexibility and meeting the processing requirements of different electrode materials. Strongly polar monomers not only enhance bonding performance but also bring new functionalities, such as self-healing, to the binder, further optimizing the battery's overall performance. They also improve the binder's stability in the electrolyte and reduce performance degradation during long-term use. In summary, strong polar monomers play a crucial role in flexible acrylonitrile copolymer positive electrode binders, not only improving the binder's adhesion and electrochemical stability but also promoting lithium ion conduction, enhancing the processing properties of the electrode sheet, and ultimately improving the battery's overall performance. These combined advantages ensure the performance stability and reliability of the battery during long-term cycling, which is of great significance for improving the cycle capacity retention rate of lithium batteries.

[0009] Preferably, the mass ratio of the lithium acrylate monomer to the acrylamide monomer is 1:1.

[0010] By employing the above-mentioned technical solution, a flexible acrylonitrile copolymer positive electrode binder is prepared using lithium acrylate and acrylamide monomers as part of the highly polar monomers. These monomers are incorporated into the polymer chain via free radical copolymerization, imparting strong adhesion to the current collector aluminum foil. Furthermore, their highly electronegative elements, oxygen and nitrogen, complex and decomplex with lithium ions, facilitating lithium ion conduction and reducing battery internal resistance. The following details the role and synergistic effect of these monomers at a 1:1 weight ratio. When the weight ratio of lithium acrylate to acrylamide is 1:1, the combination of the two monomers effectively enhances the binding strength of the binder to the aluminum foil current collector. The lithium carboxylate groups in the lithium acrylate and the amino groups in the acrylamide form strong chemical and hydrogen bonds, respectively, with the oxide layer on the current collector surface, significantly enhancing the bond strength. This balanced weight ratio helps to create a balanced structure in the binder, maintaining sufficient bonding strength while maintaining good flexibility, ensuring that it does not fall off when the electrode material changes volume. Strongly polar monomers exhibit excellent weather resistance in electrolytes, significantly reducing the binder's swelling and dissolution rate in lithium-ion battery electrolytes. This mass ratio, particularly at high temperatures, allows for better control of swelling and maintains stable battery performance. A moderate swelling ratio helps maintain the integrity of the electrode active material during volume changes during charge and discharge, thereby improving battery cycling performance. Highly electronegative elements such as oxygen and nitrogen can complex with lithium ions, facilitating lithium ion conduction within the electrode and reducing battery internal resistance. This effect is particularly pronounced at a mass ratio of 1:1, contributing to improved battery charge and discharge efficiency. These polar monomers also increase the rate of lithium ion decomplexation, further enhancing battery charge and discharge efficiency. By adjusting the type and ratio of the strongly polar monomers, the binder's mechanical properties can be optimized, resulting in excellent flexibility and meeting the processing requirements of different electrode materials. A mass ratio of 1:1 significantly improves slurry coating and uniformity, facilitating the preparation of high-performance electrode sheets. This mass ratio can increase the flexibility of the binder while maintaining the bonding strength, making the electrode sheet less likely to break during repeated charge and discharge, and maintaining good electrochemical performance. The strong polar monomer not only improves the bonding performance, but also brings new functions such as self-repair to the binder, further optimizing the overall performance of the battery. At a mass ratio of 1:1, this self-repairing ability is more significant, which helps to extend the service life of the battery. It improves the stability of the binder in the electrolyte and reduces performance degradation during long-term use. In summary, when the mass ratio of lithium acrylate monomers to acrylamide monomers is 1:1, they play a vital role in the flexible acrylonitrile copolymer positive electrode binder. It not only improves the adhesion and electrochemical stability of the binder, but also promotes the conduction of lithium ions, enhances the processing performance of the electrode sheet, and ultimately improves the overall performance of the battery.These combined advantages ensure the performance stability and reliability of the battery during long-term cycling, which is of great significance for improving the cycle capacity retention rate of lithium batteries.

[0011] Preferably, the mass ratio of the lithium acrylate monomer to the dimethylaminoethyl acrylate monomer is 1:1.

[0012] By adopting the above technical solution, in the preparation of a flexible acrylonitrile copolymer positive electrode binder, lithium acrylate monomers and dimethylaminoethyl acrylate monomers are mixed in a mass ratio of 1:1. This specific combination has a significant impact on the performance of the binder. 1. Enhanced Adhesion Performance: 1) Adhesion of Lithium Acrylate: Lithium acrylate monomers contain highly polar lithium carboxylate groups, which can form strong chemical bonds with the surface of the current collector aluminum foil, thereby providing excellent adhesion and ensuring the stability of the electrode material during battery charging and discharging. 2) Additional Adhesion of Dimethylaminoethyl Acrylate: Dimethylaminoethyl Acrylate monomers introduce additional polar groups, such as tertiary amino groups, which can also interact with the surface of the current collector aluminum foil, further enhancing the overall adhesion of the binder. 2. Improved Electrochemical Stability: 1) Weathering Resistance of Lithium Acrylate: Lithium acrylate monomers have good weathering resistance in electrolytes, which helps reduce the swelling and dissolution of the binder in lithium-ion battery electrolytes, thereby improving the electrochemical stability of the battery. 2) Electrolyte compatibility of dimethylaminoethyl acrylate: The polar groups in dimethylaminoethyl acrylate monomers have a large difference in polarity from electrolyte solvents (such as carbonates), which helps reduce the corrosion of the electrolyte on the binder and maintain the stability of the binder's performance. 3. Promote lithium ion conduction: 1) Ion conduction of lithium acrylate: The lithium carboxylate groups in lithium acrylate monomers can complex with lithium ions, reduce the internal resistance of the battery, and promote the conduction of lithium ions in the electrode. 2) Decomplexation rate of dimethylaminoethyl acrylate: The polar groups in dimethylaminoethyl acrylate monomers help increase the decomplexation rate of lithium ions, further improving the charge and discharge efficiency of the battery. 4. Improve electrode sheet processing performance: 1) Coating properties of lithium acrylate: Lithium acrylate monomers can improve the coating and uniformity of electrode slurry, which is conducive to the preparation of high-performance electrode sheets. 2) Flexibility of dimethylaminoethyl acrylate: Dimethylaminoethyl acrylate monomers increase the flexibility of the binder, enabling it to better adapt to the processing requirements of different electrode materials. 5. Improve the overall performance of the battery: 1) Functionality of lithium acrylate: Lithium acrylate monomers not only improve the bonding performance, but also bring new functions such as self-repair to the binder, further optimizing the overall performance of the battery. 2) Stability of dimethylaminoethyl acrylate: Dimethylaminoethyl acrylate monomers improve the stability of the binder in the electrolyte and reduce performance degradation during long-term use. In summary, lithium acrylate monomers and dimethylaminoethyl acrylate monomers are mixed in a mass ratio of 1:1, and play a vital role in the flexible acrylonitrile copolymer positive electrode binder, which not only improves the adhesion and electrochemical stability of the binder, but also promotes the conduction of lithium ions, enhances the processing performance of the electrode sheet, and ultimately improves the overall performance of the battery.The choice of this ratio is based on the respective characteristics of the two monomers and the synergistic effect between them, which ensures the performance stability and reliability of the battery during long-term cycling, and is of great significance for improving the cycle capacity retention rate of lithium batteries.

[0013] Preferably, the mass ratio of the acrylamide monomer to the dimethylaminoethyl acrylate monomer is 1:1.

[0014] By adopting the above technical solution, in the preparation of the flexible acrylonitrile copolymer positive electrode binder, acrylamide monomers and dimethylaminoethyl acrylate monomers are mixed in a mass ratio of 1:1. This specific combination has a significant impact on the performance of the binder. 1. Enhanced bonding performance: 1) Adhesion of acrylamide: Acrylamide monomers contain highly polar amide groups that can form strong chemical bonds with the surface of the current collector aluminum foil, thereby providing excellent adhesion and ensuring the stability of the electrode material during battery charging and discharging. 2) Additional adhesion of dimethylaminoethyl acrylate: Dimethylaminoethyl acrylate monomers introduce additional polar groups, such as tertiary amino groups, which can also interact with the surface of the current collector aluminum foil, further enhancing the overall adhesion of the binder. 2. Improved electrochemical stability: 1) Weather resistance of acrylamide: Acrylamide monomers have good weather resistance in electrolytes, which helps reduce the swelling and dissolution of the binder in lithium-ion battery electrolytes, thereby improving the electrochemical stability of the battery. 2) Electrolyte compatibility of dimethylaminoethyl acrylate: The polar groups in dimethylaminoethyl acrylate monomers have a large difference in polarity from electrolyte solvents (such as carbonates), which helps reduce the corrosion of the electrolyte on the binder and maintain the stability of the binder's performance. 3. Promote lithium ion conduction: 1) Ion conduction of acrylamide: The amide groups in acrylamide monomers can complex with lithium ions, reduce the internal resistance of the battery, and promote the conduction of lithium ions in the electrode. 2) Decomplexation rate of dimethylaminoethyl acrylate: The polar groups in dimethylaminoethyl acrylate monomers help to increase the decomplexation rate of lithium ions, further improving the charge and discharge efficiency of the battery. 4. Improve electrode sheet processing performance: 1) Coating properties of acrylamide: Acrylamide monomers can improve the coating and uniformity of electrode slurry, which is conducive to the preparation of high-performance electrode sheets. 2) Flexibility of dimethylaminoethyl acrylate: Dimethylaminoethyl acrylate monomers increase the flexibility of the binder, enabling it to better adapt to the processing requirements of different electrode materials. 5. Improve the overall performance of the battery: 1) Functionality of acrylamide: Acrylamide monomers not only improve the bonding performance, but also bring new functions such as self-repair to the binder, further optimizing the overall performance of the battery. 2) Stability of dimethylaminoethyl acrylate: Dimethylaminoethyl acrylate monomers improve the stability of the binder in the electrolyte and reduce performance degradation during long-term use. In summary, acrylamide monomers and dimethylaminoethyl acrylate monomers are mixed in a mass ratio of 1:1, and play a vital role in the flexible acrylonitrile copolymer positive electrode binder, which not only improves the adhesion and electrochemical stability of the binder, but also promotes the conduction of lithium ions, enhances the processing performance of the electrode sheet, and ultimately improves the overall performance of the battery.The choice of this ratio is based on the respective characteristics of the two monomers and the synergistic effect between them, which ensures the performance stability and reliability of the battery during long-term cycling, and is of great significance for improving the cycle capacity retention rate of lithium batteries.

[0015] Preferably, the lithium acrylate monomer is selected from at least one of lithium acrylate and lithium methacrylate; the acrylamide monomer is selected from at least one of acrylamide and methacrylamide; and the dimethylaminoethyl acrylate monomer is selected from at least one of dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate.

[0016] Preferably, the preparation method of the polyoctene copolymer emulsion is as follows: 390 parts of deionized water and 0.5 parts of emulsifier are added to a glass reactor in parts by mass, high-purity nitrogen is introduced, and the mixture is stirred at a stirring speed of 250-300 rpm for 1-1.5 hours, and then 15 parts of 1-octene are added, stirred at a stirring speed of 250-300 rpm for 0.5-0.7 hours, heated to 58-60°C and kept constant temperature, and then 1 part of a 10% initiator aqueous solution is added and reacted at 58-60°C for 2-2.5 hours, and then 70 parts of 1-octene, 15 parts of perfluoromethyl vinyl ether, and 4 parts of a 10% initiator aqueous solution are respectively added dropwise to the reactor through a peristaltic pump, the addition time is 3-3.5 hours, and the mixture is reacted at 58-60°C for 5-6 hours. After the reaction is completed, the mixture is cooled to room temperature and filtered with a 150-mesh sieve to obtain a polyoctene copolymer emulsion.

[0017] By adopting the above technical solution, the resulting polyoctene copolymer emulsion exhibits the following benefits and synergistic effects in a flexible acrylonitrile copolymer positive electrode binder: 1. Enhanced Adhesion: The long-chain polyoctene copolymer emulsion provides excellent adhesion, ensuring a tight bond between the electrode active material and the current collector. Its long-chain structure provides sufficient flexibility, allowing the binder to adapt to volume changes in the electrode material, thereby maintaining electrode integrity. 2. Optimized Electrolyte Swelling: The non-polar octyl groups in the polyoctene copolymer emulsion have a significant polarity difference with electrolyte solvents (such as carbonates), which helps control the binder's swelling in the electrolyte, reduce dissolution, and thus improve battery cycling stability. 3. Improved Processability: The addition of the polyoctene copolymer emulsion significantly improves the processing performance of the positive electrode sheet, making the electrode slurry easier to coat and evenly distribute, facilitating the preparation of high-performance electrode sheets. 4. Provided Chemical Stability: The polyfluorinated structures in the emulsion, such as perfluoromethyl vinyl ether, provide excellent chemical stability, enhancing the stability of the binder in the electrolyte and reducing performance degradation during long-term use. 5. Promote lithium ion conduction: The complexation and decomplexation of highly electronegative elements such as oxygen and nitrogen in the polyoctene copolymer emulsion with lithium ions facilitates the conduction of lithium ions within the electrode, reduces the internal resistance of the battery, and improves the battery's charge and discharge efficiency. In summary, the specific preparation method of the polyoctene copolymer emulsion enables it to play a key role in the flexible acrylonitrile copolymer positive electrode binder. It not only provides good bonding properties and chemical stability, but also optimizes electrolyte swelling and processing properties, promotes lithium ion conduction, and thus significantly improves the overall performance and cycle capacity retention of lithium-ion batteries.

[0018] Preferably, the initiator is ammonium persulfate, and the emulsifier is selected from one of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate.

[0019] Preferably, the polyvinyl alcohol is PVA 1799.

[0020] Preferably, the mass concentration of the initiator aqueous solution is 20%, and the initiator is selected from one of ammonium persulfate, potassium persulfate and sodium persulfate.

[0021] In a second aspect, the present application provides a method for preparing a flexible acrylonitrile copolymer positive electrode binder, using the following technical solution:

[0022] As a general technical concept, the present application also provides a method for preparing the above-mentioned flexible acrylonitrile copolymer positive electrode binder, comprising the following steps:

[0023] Deionized water and polyvinyl alcohol were added to a glass reactor in parts by mass, high-purity nitrogen was introduced, and the mixture was stirred at a stirring speed of 250-300 rpm for 1-1.2 hours. Then, acrylonitrile, a strong polar monomer, and a polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 58-60°C and kept constant. Then, an initiator aqueous solution was added to initiate the reaction. After the reaction lasted for 8-9 hours, the heating was stopped, and the mixture was cooled to room temperature. The mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

[0024] In a third aspect, the present application provides an application of a flexible acrylonitrile copolymer positive electrode binder, using the following technical solution:

[0025] As a general technical concept, the present application also provides the use of the above-mentioned flexible acrylonitrile copolymer positive electrode binder in a lithium battery.

[0026] In summary, this application includes at least one of the following beneficial technical effects:

[0027] 1. Enhanced Adhesion: Strongly polar monomers introduced through free radical copolymerization, such as lithium acrylate, acrylamide, and dimethylaminoethyl acrylate, contain highly polar groups such as lithium carboxylate, amino, amide, and cyano groups. These groups can form ionic and hydrogen bonds with oxygen-containing groups on the surface of the current collector aluminum foil, significantly enhancing the adhesive's bonding strength. This strong bonding prevents the electrode active material from falling off the current collector during charge and discharge, maintaining the integrity of the electrode even under periodic volume changes caused by lithium ion insertion and extraction.

[0028] 2. Optimizing electrolyte swelling: The polarity difference between the non-polar octanyl group in the binder and the electrolyte solvent (such as carbonates) is significant, which provides the binder with a certain degree of weather resistance, thereby significantly reducing the swelling and dissolution of the binder in lithium-ion battery electrolytes. Moderate swelling helps maintain the integrity of the electrode material and avoids structural damage caused by excessive swelling.

[0029] 3. Improved Processing: The introduction of long-chain polyoctene copolymers allows for moderate electrolyte swelling while also imparting excellent coating and flexibility to the binder, making the processing of positive electrode sheets simpler and more efficient. This superior processing performance facilitates the production of uniform, high-performance electrode sheets, improving production efficiency and product quality.

[0030] 4. Provide chemical stability: The polyfluorinated structures in the polyoctene copolymer emulsion, such as perfluoromethyl vinyl ether, provide the binder with excellent chemical stability. This stability enhances the stability of the binder in the electrolyte, reduces performance degradation during long-term use, and extends the battery life.

[0031] 5. Promote lithium ion conduction: The complexation and decomplexation of highly electronegative elements such as oxygen and nitrogen with lithium ions facilitates the conduction of lithium ions within the electrode, reducing the internal resistance of the battery and improving the battery's charge and discharge efficiency. This characteristic is crucial for improving the energy density and power density of lithium-ion batteries.

[0032] 6. Suitable for large-scale production: The adhesive preparation method of this application is simple and easy to implement, suitable for large-scale production. This easy-to-scale production process helps reduce production costs, improve product consistency, and meet the needs of commercial applications. DETAILED DESCRIPTION

[0033] The embodiments of the present application will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0034] In the following Examples, Preparation Examples, and Comparative Examples, 1 part represents 10 g.

[0035] Preparation Example 1 Preparation of polyoctene copolymer emulsion

[0036] The preparation method of the polyoctene copolymer emulsion comprises the following steps: adding 390 parts by mass of deionized water and 0.5 parts of sodium dodecylbenzenesulfonate to a glass reactor, introducing high-purity nitrogen, stirring at a stirring speed of 250 rpm for 1.5 hours, then adding 15 parts of 1-octene, stirring at a stirring speed of 250 rpm for 0.7 hours, heating to 58° C. and maintaining the temperature, then adding 1 part of a 10% aqueous solution of ammonium persulfate by mass and reacting at 58° C. for 2.5 hours, then respectively adding 70 parts of 1-octene, 15 parts of perfluoromethyl vinyl ether, and 4 parts of a 10% aqueous solution of ammonium persulfate by mass to the reactor through a peristaltic pump, the addition time being 3.5 hours, reacting at 58° C. for 6 hours, cooling to room temperature after the reaction, and filtering through a 150-mesh sieve to obtain a polyoctene copolymer emulsion having a solid content of 19.8% and a viscosity of 46 mPa·s at 25° C.

[0037] The polyoctene copolymer emulsion prepared above was applied to Example 1 and Example 2.

[0038] Preparation Example 2 Preparation of polyoctene copolymer emulsion

[0039] The preparation method of the polyoctene copolymer emulsion comprises the following steps: adding 390 parts by mass of deionized water and 0.5 parts by mass of sodium lauryl sulfate to a glass reactor, introducing high-purity nitrogen, stirring at a stirring speed of 300 rpm for 1 hour, then adding 15 parts of 1-octene, stirring at a stirring speed of 300 rpm for 0.5 hour, heating to 60° C. and maintaining the temperature, then adding 1 part of a 10% aqueous solution of ammonium persulfate at 60° C. and reacting for 2 hours, then adding 70 parts of 1-octene, 15 parts of perfluoromethyl vinyl ether, and 4 parts of a 10% aqueous solution of ammonium persulfate at 60° C. dropwise to the reactor via a peristaltic pump for 3 hours, reacting at 60° C. for 5 hours, cooling to room temperature after the reaction, and filtering through a 150-mesh sieve to obtain a polyoctene copolymer emulsion having a solid content of 20% and a viscosity of 45 mPa·s at 25° C.

[0040] The polyoctene copolymer emulsion prepared above was applied to Examples 3 to 10.

[0041] Example 1

[0042] 395 parts of deionized water and 0.4 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and the mixture was stirred at 250 rpm for 1.2 hours. Then, 68 parts of acrylonitrile, 4.5 parts of lithium acrylate, 4.5 parts of acrylamide, and 97 parts of a polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 58° C. and kept constant. Then, 20% potassium persulfate and 2.4 parts of a sodium persulfate aqueous solution were added to initiate the reaction. After reacting for 8 hours, heating was stopped, the mixture was cooled to room temperature, and a flexible acrylonitrile copolymer positive electrode binder was obtained by filtering, washing, drying, crushing, and sieving.

[0043] Example 2

[0044] 400 parts of deionized water and 0.6 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and the mixture was stirred at 280 rpm for 1.1 hours. Then, 72 parts of acrylonitrile, 5.5 parts of lithium acrylate, 5.5 parts of acrylamide, and 103 parts of a polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 59° C. and kept constant. Then, 2.6 parts of a 20% aqueous sodium persulfate solution was added to initiate the reaction. After reacting for 8.5 hours, heating was stopped, the mixture was cooled to room temperature, and a flexible acrylonitrile copolymer positive electrode binder was obtained by filtering, washing, drying, crushing, and sieving.

[0045] Example 3

[0046] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and stirring was carried out at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of lithium acrylate, 5 parts of acrylamide, and 100 parts of a polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After reacting for 8 hours, heating was stopped, and a flexible acrylonitrile copolymer positive electrode binder was obtained by filtering, washing, drying, crushing, and sieving.

[0047] Example 4

[0048] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and stirring was carried out at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of lithium methacrylate, 5 parts of acrylamide, and 100 parts of a polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After reacting for 8 hours, heating was stopped, and the temperature was cooled to room temperature. The mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

[0049] Example 5

[0050] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and stirring was carried out at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of dimethylaminoethyl acrylate, 5 parts of acrylamide, and 100 parts of a polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After reacting for 8 hours, heating was stopped, and the temperature was cooled to room temperature. The mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

[0051] Example 6

[0052] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and stirring was carried out at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of dimethylaminoethyl methacrylate, 5 parts of acrylamide, and 100 parts of a polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After reacting for 8 hours, heating was stopped, and the temperature was cooled to room temperature. The mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

[0053] Example 7

[0054] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA1799) were added to a glass reactor, high-purity nitrogen was introduced, and stirring was carried out at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of lithium acrylate, 5 parts of methacrylamide, and 100 parts of polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 60°C and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After the reaction was completed for 8 hours, heating was stopped, the temperature was cooled to room temperature, and the mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

[0055] Example 8

[0056] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and stirring was carried out at 300 rpm for 1 hour. Then, 70 parts of methacrylonitrile, 5 parts of lithium methacrylate, 5 parts of methacrylamide, and 100 parts of polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 60°C and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After the reaction was carried out for 8 hours, heating was stopped, and the temperature was cooled to room temperature. The mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

[0057] Example 9

[0058] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and stirring was carried out at 300 rpm for 1 hour. Then, 70 parts of methacrylonitrile, 5 parts of dimethylaminoethyl acrylate, 5 parts of methacrylamide, and 100 parts of polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After the reaction was carried out for 8 hours, heating was stopped, and the temperature was cooled to room temperature. The mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

[0059] Example 10

[0060] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and stirring was carried out at 300 rpm for 1 hour. Then, 70 parts of methacrylonitrile, 5 parts of dimethylaminoethyl methacrylate, 5 parts of methacrylamide, and 100 parts of polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 60°C and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After the reaction was carried out for 8 hours, heating was stopped, and the temperature was cooled to room temperature. The mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

[0061] Comparative Example 1

[0062] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and the mixture was stirred at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of lithium acrylate, 5 parts of acrylamide, and 20 parts of butyl acrylate were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After reacting for 8 hours, heating was stopped, the mixture was cooled to room temperature, and a binder was obtained by filtering, washing, drying, crushing, and sieving.

[0063] Comparative Example 2

[0064] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, and high-purity nitrogen was introduced and stirred at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of lithium acrylate, 5 parts of acrylamide, and 20 parts of isooctyl acrylate were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After reacting for 8 hours, heating was stopped, the temperature was cooled to room temperature, and a binder was obtained by filtering, washing, drying, crushing, and sieving.

[0065] Comparative Example 3

[0066] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, high-purity nitrogen was introduced, and the mixture was stirred at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of lithium acrylate, 5 parts of acrylamide, and 20 parts of lauryl acrylate were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After reacting for 8 hours, heating was stopped, the mixture was cooled to room temperature, and a binder was obtained by filtering, washing, drying, crushing, and sieving.

[0067] Comparative Example 4

[0068] 397.5 parts of deionized water and 0.5 parts of polyvinyl alcohol (PVA 1799) were added to a glass reactor, and high-purity nitrogen was introduced and stirred at 300 rpm for 1 hour. Then, 70 parts of acrylonitrile, 5 parts of dimethylaminoethyl acrylate, 5 parts of acrylamide, and 20 parts of butyl acrylate were added in sequence, and the temperature was raised to 60° C. and kept constant. Then, 2.5 parts of a 20% aqueous solution of ammonium persulfate was added to initiate the reaction. After reacting for 8 hours, heating was stopped, the temperature was cooled to room temperature, and a binder was obtained by filtering, washing, drying, crushing, and sieving.

[0069] Comparative Example 5

[0070] The adhesive is a PVDF adhesive, specifically adhesive 5130 produced by Solvay Corporation of the United States.

[0071] Performance testing

[0072] 1. Binder swelling and dissolution performance test

[0073] The binders prepared in each example and comparative example were added to NMP at 60°C and stirred at 500 rpm until the solution became transparent. The solution was then filtered through a 200-mesh sieve to yield a 5% light yellow transparent solution. 15 g of this solution was added to a polytetrafluoroethylene mold with an inner diameter of 9 cm × 6 cm × 1.5 cm and an outer diameter of 10 cm × 7 cm × 2 cm. The mold was then dried in an oven at 55°C for 24 hours to form a film. The film was then dried at 100°C for 2 hours and 120°C for 2 hours. The film was cut into 1 cm squares, dried in a vacuum oven at 120°C for 2 hours, and weighed, denoted as M1. The film was then placed in an electrolyte solution (EC:PC:EMC:DEC = 3:3:2:2) at 70°C for 24 hours. The film was then removed and the surface solvent was blotted off with filter paper. The weight of the film was then recorded as M2. The formula for calculating electrolyte swelling is: Swelling = (M2 - M1) / M1 × 100%. After the second weighing, the film was dried in a vacuum drying oven at 120°C for 2 hours and weighed, recording it as M3. The formula for electrolyte dissolution is: Dissolving = (M1 - M3) / M1 × 100%. See Table 1 for detailed results.

[0074] 2. Flexibility test of positive electrode

[0075] The flexibility of each embodiment and comparative example sample was measured with reference to "GB / T 1731-93 Determination of paint film flexibility". The positive electrode sheet was cut into 2.5cm×0.5cm strips, and then the positive electrode sheet was pressed upward on a shaft rod of a specified diameter with both hands. The positive electrode sheet was bent around the shaft rod within 2-3 seconds using the strength of the two thumbs. After bending, the two thumbs should be symmetrical to the center line of the shaft rod. After bending, the positive electrode sheet was observed with a 4x magnifying glass to see if there were any damage phenomena such as reticulation, cracks and peeling. The radius or curvature radius of the shaft rod 1 to the shaft rod 7 is R1=7.5mm, R2=5.0mm, R3=2.5mm, R4=2.0mm, R5=1.5mm, R6=1.0mm, and R7=0.5mm. The specific results are shown in Table 1.

[0076] 3. Peel strength test of positive electrode

[0077] The positive electrode sheet was cut into 20 cm × 2.5 cm strips. The current collector aluminum foil side was adhered to a 1 mm thick steel plate using double-sided tape. The coating layer side was affixed with transparent tape. The coating layer was peeled off in a 180° direction using a tensile testing machine at a speed of 100 mm / min, and the peel stress was measured. The results are shown in Table 1.

[0078] 4. Battery preparation and performance testing

[0079] (1) Preparation of positive electrode sheets

[0080] The active material lithium cobalt oxide, conductive carbon SP, and binder are dissolved in NMP in a weight ratio of 97:1:2, mixed evenly and prepared into a positive electrode slurry, and the slurry is evenly coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained after drying, hot pressing, and slitting.

[0081] (2) Preparation of negative electrode sheets

[0082] The active material graphite, conductive carbon SP, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are dissolved in deionized water at a weight ratio of 96.5:1:1:1.5, mixed evenly to prepare a negative electrode slurry, and the slurry is evenly coated on the negative electrode current collector copper foil. After drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0083] (3) Preparation of diaphragm

[0084] Using PE porous polymer film as separator

[0085] (4) Preparation of electrolyte

[0086] Lithium hexafluorophosphate was dissolved in a carbonate solvent (ethylene carbonate, propylene carbonate, and ethyl methyl carbonate in a volume ratio of 2:2:2) to prepare a 1 mol / L electrolyte.

[0087] (5) Preparation of batteries

[0088] The positive electrode sheet, separator, and negative electrode sheet are wound in sequence to form a battery cell. The battery cell is encapsulated with aluminum plastic film, baked at 85°C for 24 hours, and then injected with electrolyte after dehydration. After vacuum packaging, storage, formation, secondary sealing, and shaping, the lithium-ion battery is produced.

[0089] (6) Battery cycle test at room temperature

[0090] The lithium-ion battery was charged at a constant current of 1C to 4.35V, then charged at a constant voltage at 4.35V to a cutoff current of 0.02C, left for 5 minutes, and then discharged at a constant current of 1C to 3.0V, left for 5 minutes, and the first cycle discharge capacity was measured. This cycle was repeated for 500 cycles, and the 500th cycle discharge capacity was measured. The 500th cycle capacity retention rate was calculated using the following formula: 500th cycle capacity retention rate (%) = (500th cycle discharge capacity / first cycle discharge capacity) × 100%. Specific results are shown in Table 1.

[0091] Table 1 Performance test

[0092]

[0093] Analyzing the data in Table 1, we can see that:

[0094] 1) The electrolyte swelling and solubility of the flexible acrylonitrile copolymer positive electrode binder prepared in Examples 1 to 10 are relatively small, while the electrolyte swelling and solubility of the binder prepared in Comparative Examples 1 to 4 are very large. This is because the strong polar groups (lithium carboxylate, amino, amide, cyano) in the strong polar monomers in Examples 1 to 10 and the non-polar octyl groups in the polyoctene copolymer emulsion have a large difference in polarity with the electrolyte solvent (carbonates) and have a certain weather resistance to the electrolyte solvent, while the acrylate groups in Comparative Examples 1 to 4 have a similar polarity to the electrolyte solvent and good compatibility with the electrolyte, resulting in excessive electrolyte swelling and solubility of the binder.

[0095] 2) The positive electrode sheets prepared in Examples 1 to 10 and Comparative Examples 1 to 5 have good flexibility, giving the electrode sheets excellent processing performance.

[0096] 3) The peeling force of the positive electrode sheets prepared in Examples 1 to 10 and Comparative Examples 1-4 is greater than that in Comparative Example 5. This is because the strong polar groups (lithium carboxylate, amino, amide, cyano) in the binders obtained in Examples 1 to 10 and Comparative Examples 1-4 have ionic bonds, hydrogen bonds and other forces with the oxygen-containing groups on the surface of the current collector aluminum foil, while the binder in Comparative Example 5 only has van der Waals forces with the surface of the current collector aluminum foil, resulting in a smaller peeling force.

[0097] 4) The battery cycle capacity retention rates prepared in Examples 1 to 10 are very high, while the battery cycle capacity retention rates prepared in Comparative Examples 1 to 4 are relatively low. This is because the binders in Examples 1 to 10 have suitable swelling degrees and stronger peeling forces to adapt to the periodic volume changes of the electrode active materials during the charge and discharge process as lithium ions are inserted / extracted without falling off from the current collector, thereby improving the cycle performance of the lithium-ion battery.

[0098] 5) A comparative analysis of the performance of the flexible acrylonitrile copolymer positive electrode binder prepared in Example 3 and the binders obtained in Comparative Examples 1 to 3 shows that the polyoctene copolymer emulsion prepared in the present application has the following effects and synergistic effects in the flexible acrylonitrile copolymer positive electrode binder: The long-chain polyoctene copolymer emulsion can provide good bonding properties to ensure a close bond between the electrode active material and the current collector. Its long-chain structure provides sufficient flexibility so that the binder can adapt to the volume changes of the electrode material, thereby maintaining the integrity of the electrode. Optimize the swelling degree of the electrolyte: The polarity difference between the non-polar octyl group in the polyoctene copolymer emulsion and the electrolyte solvent (such as carbonates) is large, which helps to control the swelling degree of the binder in the electrolyte, reduce the dissolution rate, and thus improve the cycle stability of the battery. Provide chemical stability: The polyfluorinated structure in the emulsion, such as perfluoromethyl vinyl ether, provides excellent chemical stability, enhances the stability of the binder in the electrolyte, and reduces performance degradation during long-term use. Promote lithium ion conduction: The complexation and decomplexation effect of strongly electronegative elements such as oxygen and nitrogen in the polyoctene copolymer emulsion with lithium ions is beneficial to the conduction of lithium ions in the electrode, reducing the internal resistance of the battery and improving the charge and discharge efficiency of the battery, thereby significantly improving the comprehensive performance and cycle capacity retention rate of the lithium ion battery.

[0099] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the above embodiments provide a detailed description of the present application, relevant technical personnel should understand that the specific implementation methods of the present application may still be modified or replaced by equivalents. Any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. A flexible acrylonitrile copolymer positive electrode binder, characterized in that: The raw materials for the preparation include, by weight, 68-72 parts of acrylonitrile, 0.4-0.6 parts of polyvinyl alcohol, 9-11 parts of a strongly polar monomer, 97-103 parts of a polyoctene copolymer emulsion, 2.4-2.6 parts of an initiator aqueous solution, and 395-400 parts of deionized water; the strongly polar monomer is selected from two of a lithium acrylate monomer, an acrylamide monomer, and a dimethylaminoethyl acrylate monomer; The mass ratio of the lithium acrylate monomer to the acrylamide monomer is 1:1; or the mass ratio of the lithium acrylate monomer to the dimethylaminoethyl acrylate monomer is 1:1; or the mass ratio of the acrylamide monomer to the dimethylaminoethyl acrylate monomer is 1:1; The lithium acrylate monomer is selected from at least one of lithium acrylate and lithium methacrylate; the acrylamide monomer is selected from at least one of acrylamide and methacrylamide; the dimethylaminoethyl acrylate monomer is selected from at least one of dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate; The preparation method of the polyoctene copolymer emulsion comprises the following steps: adding 390 parts by mass of deionized water and 0.5 parts of an emulsifier into a glass reactor, introducing high-purity nitrogen, stirring at a stirring speed of 250-300 rpm for 1-1.5 hours, then adding 15 parts of 1-octene, stirring at a stirring speed of 250-300 rpm for 0.5-0.7 hours, heating to 58-60° C. and maintaining the temperature, then adding 1 part of an initiator aqueous solution with a mass concentration of 10% and reacting at 58-60° C. for 2-2.5 hours, then respectively adding 70 parts of 1-octene, 15 parts of perfluoromethyl vinyl ether, and 4 parts of an initiator aqueous solution with a mass concentration of 10% into the reactor through a peristaltic pump, the addition time being 3-3.5 hours, reacting at 58-60° C. for 5-6 hours, cooling to room temperature after the reaction, and filtering through a 150-mesh sieve to obtain the polyoctene copolymer emulsion.

2. The flexible acrylonitrile copolymer positive electrode binder according to claim 1, characterized in that: In the preparation method of the polyoctene copolymer emulsion, the initiator is ammonium persulfate, and the emulsifier is selected from one of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate.

3. The flexible acrylonitrile copolymer positive electrode binder according to claim 1, characterized in that: The polyvinyl alcohol is PVA 1799.

4. The flexible acrylonitrile copolymer positive electrode binder according to claim 1, characterized in that: In the preparation of raw materials, the mass concentration of the initiator aqueous solution is 20%, and the initiator is selected from one of ammonium persulfate, potassium persulfate and sodium persulfate.

5. A method for preparing a flexible acrylonitrile copolymer positive electrode binder according to any one of claims 1 to 4, characterized in that: The following steps are involved: Deionized water and polyvinyl alcohol were added to a glass reactor in parts by mass, high-purity nitrogen was introduced, and the mixture was stirred at a stirring speed of 250-300 rpm for 1-1.2 hours. Then, acrylonitrile, a strong polar monomer, and a polyoctene copolymer emulsion were added in sequence, and the temperature was raised to 58-60°C and kept constant. Then, an initiator aqueous solution was added to initiate the reaction. After the reaction lasted for 8-9 hours, the heating was stopped, and the mixture was cooled to room temperature. The mixture was filtered, washed, dried, crushed, and sieved to obtain a flexible acrylonitrile copolymer positive electrode binder.

6. Use of the flexible acrylonitrile copolymer positive electrode binder according to any one of claims 1 to 4 in a lithium battery.

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