Vinyl phosphonic acid-acrylonitrile copolymer binder, its preparation method and application

Abstract

This invention discloses a vinylphosphonic acid-acrylonitrile copolymer adhesive, its preparation method, and its application. The vinylphosphonic acid-acrylonitrile copolymer adhesive comprises the following components by mass: 76%–92% acrylonitrile, 4%–12% acrylic monomers, and 4%–12% vinylphosphonic acid monomers. The vinylphosphonic acid-acrylonitrile copolymer adhesive is prepared by subjecting each monomer to a free radical polymerization reaction. By simultaneously introducing flexible acrylic segments and vinylphosphonic acid functional units into a rigid acrylonitrile skeleton, the copolymer adhesive possesses strong adhesion, flexibility, electrochemical stability under high pressure conditions, and applicability to different metal ion systems.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage materials technology, specifically to the design of a vinylphosphonic acid-acrylonitrile copolymer binder, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, sodium-ion batteries, and other metal-ion batteries are widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems due to their high energy density and long cycle life. Battery electrodes typically consist of active materials, conductive agents, and binders. While the binder does not contribute capacity, it is a crucial component for maintaining the integrity of the electrode structure. It is responsible for firmly bonding the active materials and conductive agents to the current collector and for withstanding the volume changes caused by ion insertion / extraction during charging and discharging.

[0003] Currently, the selection of polymer binders is particularly important in the field of metal-ion battery cathodes. Polyvinylidene fluoride (PVDF) is one of the most widely used binder materials, mainly due to its good electrochemical stability and compatibility with various electrode components. However, PVDF still has many limitations in practical applications: First, its bonding strength is limited, making it difficult to provide sufficient mechanical strength in high-load electrodes; second, the molecular structure of PVDF determines its insufficient flexibility, making it unable to effectively adapt to the significant volume changes of high-capacity electrode materials during cycling; furthermore, as a fluoropolymer, PVDF may decompose under high temperature or extreme electrochemical conditions, seriously affecting the safety performance and lifespan of the battery.

[0004] Polyacrylonitrile (PAN) is another promising binder material that can form a strong interaction with electrode components. However, PAN also has significant drawbacks: its high glass transition temperature results in considerable brittleness, making it difficult to meet the flexibility requirements of high-performance batteries after film formation. Especially under high-rate charge-discharge conditions, PAN-based electrodes are prone to cracking due to stress concentration, leading to the shedding of active material and severe performance degradation of the battery.

[0005] To overcome the shortcomings of PAN, researchers have attempted to improve its properties through copolymerization modification. Existing technologies typically introduce acrylate monomers to adjust the polymer's flexibility, but these improvements often focus only on optimizing mechanical properties, neglecting the electrochemical stability of the binder under high pressure conditions and its applicability to different metal ion systems.

[0006] Therefore, there is an urgent need in this field to develop a novel binder that, when used in the positive electrode of a battery, not only needs to have good bonding performance and suitable flexibility, but also should have excellent electrochemical stability and applicability to different metal ion systems, so as to meet the development needs of high-performance metal-ion batteries. Summary of the Invention

[0007] The purpose of this invention is to provide a vinylphosphonic acid-acrylonitrile copolymer binder, its preparation method and application, in order to solve the technical problem that the binder used in the prior art cannot simultaneously possess bonding performance, flexibility, electrochemical stability and applicability to different metal ion systems when used in battery cathodes.

[0008] According to a first aspect of the invention, a vinylphosphonic acid-acrylonitrile copolymer adhesive is provided, comprising the following components in parts by mass: 76%–92% acrylonitrile, 4%–12% acrylic monomers, and 4%–12% vinylphosphonic acid monomers. The vinylphosphonic acid-acrylonitrile copolymer adhesive is prepared by free radical polymerization of the monomers. This vinylphosphonic acid-acrylonitrile copolymer adhesive possesses bonding properties, flexibility, electrochemical stability, and suitability for various metal ion systems.

[0009] Specifically, the introduction of phosphate groups with antioxidant properties enables the binder to operate stably under high voltage conditions, avoiding oxidative decomposition. At the same time, the introduction of flexible acrylic segments alleviates the stress caused by volume changes in the electrodes during charging and discharging, preventing interface failure. In addition, the binder has a suitable degree of swelling in the electrolyte, providing ion channels while avoiding structural damage, effectively maintaining the electrochemical cycle stability of the battery system.

[0010] The improved applicability of the binder system in this invention is attributed to the chemical anchoring ability of the phosphate groups, which can form a strong bond with the surfaces of different cathode materials through hydrogen bonds or coordination bonds, adapting to various material properties. Simultaneously, the flexible acrylic segments enhance the binder's buffering capacity against volume changes in the cathode material, preventing electrode cracking or detachment. Furthermore, the monomer composition and proportions of this invention make the binder widely applicable to different cathode material systems in lithium / sodium-ion batteries.

[0011] The binder provided by this invention, which is obtained by copolymerizing three monomers, has the advantages of bonding performance, flexibility and electrochemical stability, and is suitable for different metal ion systems, thereby meeting the requirements of high-performance metal ion batteries.

[0012] In some embodiments, to improve the performance and compatibility of the lithium / sodium ion battery cathode binder, the monomers are in the following proportions by mass: 80%–88% acrylonitrile, 6%–10% acrylic acid monomers, and 6%–10% vinylphosphonic acid monomers.

[0013] In some embodiments, the acrylic monomer is acrylic acid, and the vinylphosphonic monomer is vinylphosphonic acid.

[0014] In some embodiments, the weight-average molecular weight of the vinylphosphonic acid-acrylonitrile copolymer binder is 150,000–300,000 g / mol, preferably 180,000–240,000 g / mol. This suitable molecular weight ensures that the binder possesses both good film-forming properties and mechanical strength, as well as suitable solution processing performance. When the weight-average molecular weight is below 150,000 g / mol, the mechanical strength and adhesion of the binder decrease significantly; when the weight-average molecular weight is above 300,000 g / mol, the solution viscosity is too high, the processing performance deteriorates, and it is difficult to form a uniform electrode coating.

[0015] In some embodiments, the polydispersity index (PDI) of the vinylphosphonic acid-acrylonitrile copolymer binder is 1.2 to 2.0.

[0016] According to a second aspect of the present invention, a method for preparing a vinylphosphonic acid-acrylonitrile copolymer adhesive is provided, comprising the following steps: First, acrylonitrile, vinylphosphonic acid monomers and acrylic acid monomers are added sequentially to a solvent, and the mixture is heated and stirred under a nitrogen atmosphere to obtain mixture a; Secondly, while maintaining a nitrogen atmosphere, heat mixture a to 70℃~80℃ for 10~30 minutes. When the temperature is constant, add an initiator to dissolve it in mixture a to carry out a polymerization reaction, and obtain mixture b. Then, the mixture b is vacuumed and then nitrogen is introduced to remove oxygen. The mixture is reacted at a constant temperature of 70℃~80℃ for 6~12 hours with continuous stirring at a speed of 100~500rpm. After the reaction is completed, the polymerization product is obtained. Finally, the polymer product is vacuum dried at a temperature of 100℃ to 160℃, then pulverized and sieved with a mesh size of 100 to 300 mesh to obtain the vinylphosphonic acid-acrylonitrile copolymer binder.

[0017] In some embodiments, the solvent is at least one of dimethyl sulfoxide, deionized water, and N-methylpyrrolidone.

[0018] The initiator is selected based on the type of solvent. When the solvent is oil-based, an oil-based initiator is used, selected from at least one of azobisisobutyronitrile (AIBN) and benzoyl peroxide. When the solvent is water-based, an water-based initiator is used, selected from at least one of potassium persulfate, ammonium persulfate, and sodium persulfate. Selecting the appropriate oil-based or water-based initiator according to the type of solvent ensures the compatibility of the initiator with the system, optimizes the polymerization efficiency, and reduces the possibility of side reactions, thereby contributing to product quality stability and adaptability to multiple processes.

[0019] In some embodiments, the amount of initiator is 0.01% to 0.3% of the total weight of the monomer, preferably 0.02% to 0.15%. By limiting the amount of initiator, the appropriate amount of initiator is ensured when realizing free radical polymerization, which can effectively initiate the reaction and avoid the problems of uneven polymerization products or increased reaction by-products caused by excessive amount.

[0020] According to a third aspect of the invention, the use of a vinylphosphonic acid-acrylonitrile copolymer binder in the preparation of a lithium / sodium ion battery cathode is provided.

[0021] According to a fourth aspect of the present invention, a lithium / sodium ion battery positive electrode is provided, which is prepared by the following steps: S1: Dissolve the vinylphosphonic acid-acrylonitrile copolymer adhesive in an organic solvent to prepare an adhesive solution; S2: Mix the active material, conductive agent and binder solution and shake well to obtain the positive electrode slurry; S3: The positive electrode slurry is uniformly coated on the conductive current collector, and then dried and sliced ​​to obtain a lithium / sodium ion positive electrode sheet; S4: After drying the lithium / sodium ion positive electrode sheet, the positive electrode of the lithium / sodium ion battery is obtained.

[0022] In some embodiments, the organic solvent is N-methylpyrrolidone.

[0023] In some embodiments, the mass ratio of vinylphosphonic acid-acrylonitrile copolymer adhesive to N-methylpyrrolidone is (5-20):(80-95).

[0024] In some embodiments, the active material is at least one of the following: ternary materials NCM523, NCM622, NCM811, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, copper-iron-manganese-based, nickel-manganese-based morphological oxides, sodium vanadium phosphate, sodium fluorophosphate, and lithium-rich manganese-based materials.

[0025] In some embodiments, the conductive agent is at least one of acetylene black, Ketjen black, and Super P.

[0026] In some embodiments, the conductive current collector is one of carbon-coated aluminum foil, carbon cloth, and nickel foam.

[0027] In some embodiments, the mass ratio of the active substance, the conductive agent and the copolymer binder is (70-96):(2-20):(1-10).

[0028] In some embodiments, the amount of binder used accounts for 1 wt% to 10 wt% of the total solid content of the lithium / sodium ion battery cathode, preferably 2 wt% to 5 wt%.

[0029] The beneficial effects of this invention are as follows: (1) The vinylphosphonic acid-acrylonitrile copolymer adhesive of the present invention, through molecular structure design, simultaneously introduces flexible acrylic segments and vinylphosphonic acid functional units into the rigid acrylonitrile skeleton, thereby achieving the control of the mechanical properties of the adhesive. Among them, the phosphate groups of the vinylphosphonic acid unit can form a strong chemical anchor with the surface of the active material of the electrode through strong hydrogen bonding and coordination bonding, which enhances the interfacial bonding force between the adhesive and the various components of the electrode, and can effectively solve the problem of insufficient bonding strength of traditional PVDF adhesives; (2) Through the synergistic effect of the three monomers, the resulting binder maintains the inherent strong adhesion of acrylonitrile while also possessing flexibility and elasticity, enabling it to effectively buffer the volume change caused by ion insertion or extraction during the charging and discharging process of high-capacity cathode materials, prevent electrode cracking and active material shedding, thereby improving the structural stability of the electrode, especially the capacity retention rate under high-rate charging and discharging conditions. (3) The binder of the present invention exhibits a suitable degree of swelling in the electrolyte, which can be synthesized and adjusted to a degree of swelling that can be stabilized within the range of 15% to 65%. When the degree of swelling is below 15%, the binder cannot provide sufficient channels for ion transport; while when the degree of swelling is above 65%, it will lead to excessive expansion of the electrode and an increase in internal resistance. The present invention, through the control of monomer ratio, enables the binder to maintain good ion conductivity in the electrolyte while avoiding damage to the electrode structure due to excessive swelling, thereby maintaining the structural integrity of the electrode while ensuring high ion conductivity; (4) The vinylphosphonic acid unit introduced in this invention not only provides strong adhesion, but its phosphate group also exhibits excellent electrochemical stability, especially under high voltage conditions (>4.3V vs. Li+ / Li), it can maintain the performance stability of the battery and is not prone to oxidation and decomposition. This characteristic makes this binder particularly suitable for high voltage cathode material systems, broadening its application prospects in high energy density batteries; (5) The binder of the present invention has wide system applicability. It not only exhibits excellent performance in lithium-ion batteries, but also shows good application effect in sodium-ion batteries, providing a universal binder solution for metal-ion batteries of different systems. (6) The preparation method of the present invention is simple and reproducible, can be achieved using conventional polymerization equipment, and the solvent can be recycled. It has good industrialization prospects and provides important material support for the development of metal-ion batteries. Attached Figure Description

[0030] Figure 1 This is a synthesis route diagram of the vinylphosphonic acid-acrylonitrile copolymer adhesive provided in Example 1 of the present invention; Figure 2This is a GPC curve molecular weight distribution diagram of the vinylphosphonic acid-acrylonitrile copolymer adhesive provided in Example 6 of the present invention; Figure 3 This is a dynamic mechanical analysis diagram of the vinylphosphonic acid-acrylonitrile copolymer adhesive provided in Example 6 of the present invention; Figure 4 This is a comparison chart of the cycle performance of lithium-ion button batteries prepared using the same proportion of binder as in Examples 5 and 6 of this invention and Comparative Example 1. Figure 5 This is a comparison chart of the cycle performance of nickel-manganese base layer sodium oxide button batteries prepared using the same proportion of binder as in Example 6 of the present invention and Comparative Example 1. Figure 6 These are SEM images of the electrodes prepared using the same binder as in Example 6 and Comparative Example 1 before cycling. Figure 7 The image shows an SEM image of an electrode prepared using the same binder as in Example 6 and Comparative Example 1 after 200 cycles. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the raw materials and reagents involved in the following embodiments are all commercially available.

[0032] Figure 1 This invention illustrates the synthetic route of a vinylphosphonic acid-acrylonitrile copolymer adhesive, obtained by free radical polymerization of three monomers: acrylonitrile, acrylic acid monomers, and vinylphosphonic acid monomers. By simultaneously introducing flexible acrylic acid segments and vinylphosphonic acid functional units into the rigid acrylonitrile backbone, the copolymer adhesive possesses strong adhesion, flexibility, electrochemical stability under high pressure conditions, and applicability to different metal ion systems. The vinylphosphonic acid-acrylonitrile copolymer adhesive obtained by free radical copolymerization in this invention avoids the problems of uncontrollable grafting efficiency, uneven functional group distribution, and cumbersome two-step synthesis in grafted adhesives.

[0033] Example 1 This embodiment provides a vinylphosphonic acid-acrylonitrile copolymer adhesive, the preparation method of which includes the following steps: (1) First, add 30 mL of dimethyl sulfoxide as solvent to a 100 mL three-necked flask, and add 8.0 g acrylonitrile, 1.0 g acrylic acid and 1.0 g vinylphosphonic acid in sequence. Heat to 73 °C under nitrogen protection and stir at 300 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 73°C for 10 hours. The mixture was stirred continuously at a speed of 300 rpm. After the reaction was completed, a viscous polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain a white powdery vinylphosphonic acid-acrylonitrile copolymer binder.

[0034] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 1 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively. The method for preparing the lithium-ion battery cathode includes the following steps: S1: Weigh 0.3g of vinylphosphonic acid-acrylonitrile copolymer adhesive and add it to 9.7g of N-methylpyrrolidone (NMP) solvent to prepare a 3wt% adhesive dilution solution; S2: Mix the active material NCM811, the conductive agent Super P, and the binder solution from step S1 in a mass ratio of 92:5:3, and then put the mixture into a 2mL centrifuge tube. Place the centrifuge tube into a ball mill and shake it. The ball mill speed is 3000rad / s, and the homogenization time is 15min to obtain the positive electrode slurry.

[0035] S3: The positive electrode slurry obtained in step S2 is evenly coated onto the conductive current collector carbon-coated aluminum foil using a scraper to obtain the positive electrode sheet; S4: After drying the positive electrode sheet obtained in step S3 in a 90°C oven for 12 hours, cut the electrode sheet with a diameter of 12mm on a slicing machine, which is the positive electrode of the lithium-ion battery.

[0036] When preparing the positive electrode for a sodium-ion battery, it is only necessary to replace the active material with the same mass of nickel-manganese base oxide Na. 0.73 Ni 0.22 Zn 0.05 Li 0.06 Mn 0.66 Zr 0.01 O2 is sufficient.

[0037] It should be noted that during slurry preparation, the ball mill speed should be maintained at 2000–3000 rad / s, and the homogenization time should be 9–15 min to ensure sufficient dispersion of the conductive agent, binder, and active material, forming a uniform slurry. Insufficient homogenization may lead to uneven material distribution, while excessive homogenization may damage the material particle structure. Furthermore, controlling the drying temperature at 80–120°C for 10–16 h allows the solvent to evaporate, preventing degradation of the electrode material's chemical properties and improving the adhesion of the current collector to the battery's positive electrode.

[0038] Based on the above-mentioned lithium-ion battery positive electrode, using the corresponding lithium metal sheet as the negative electrode, Celgard's polypropylene membrane 2500 as the separator, and the corresponding lithium-ion battery-specific electrolyte (KLD-1230C ternary electrolyte) purchased from KELOD as the electrolyte, the CR2025 type button cell was assembled in an anhydrous glove box filled with argon gas (H2O<0.01ppm, O2<0.01ppm) to obtain a lithium-ion button cell.

[0039] Based on the above sodium-ion battery positive electrode, using the corresponding metallic sodium sheet as the negative electrode, Celgard's polypropylene membrane 2500 as the separator, and the corresponding sodium-ion battery-specific electrolyte (MA-EN-HS-1016) purchased from Krohde as the electrolyte, the CR2025 type button cell was assembled in an anhydrous glove box filled with argon gas (H2O<0.01ppm, O2<0.01ppm) to obtain a lithium-ion button cell.

[0040] The assembly method for the CR2025 button cell battery is as follows: First, remove the positive electrode casing of the CR2025 coin cell battery and place the lithium / sodium ion battery positive electrode stably in the center of the casing, ensuring that the lithium / sodium ion battery positive electrode is not in contact with the casing wall and is centered. Then, using a pipette, add 30 μL of KLD-1230C ternary electrolyte / MA-EN-HS-1016 to the center of the lithium / sodium ion battery positive electrode surface and let it stand for 2 minutes to allow the electrolyte to fully wet the lithium / sodium ion battery positive electrode. Next, place the Celgard... A 2500mm separator is smoothly applied to the positive electrode of the lithium / sodium-ion battery, ensuring complete coverage without misalignment or wrinkles. Next, 30μL of KLD-1230C ternary electrolyte / MA-EN-HS-1016 is added to the separator surface to ensure thorough wetting. Then, lithium / sodium sheets are smoothly stacked on top of the separator, their positions adjusted to ensure alignment with the positive electrode and centered within the battery casing. Stainless steel gaskets and springs are then placed horizontally and centered on the lithium / sodium sheets. Finally, the CR2025 coin cell negative electrode casing is smoothly attached to the positive electrode casing, resulting in a lithium / sodium-ion coin cell battery.

[0041] Example 2 The vinylphosphonic acid-acrylonitrile copolymer adhesive provided in this embodiment is prepared in a basically the same way as that in Example 1, except for the monomer ratio. The specific preparation steps are as follows: (1) First, add 30 mL of dimethyl sulfoxide as solvent to a 100 mL three-necked flask, and add 8.8 g acrylonitrile, 0.6 g acrylic acid and 0.6 g vinylphosphonic acid in sequence. Heat to 75 °C under nitrogen protection and stir at 300 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 75°C for 10 hours. The mixture was stirred continuously at a speed of 300 rpm. After the reaction was completed, a viscous polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain a white powdery vinylphosphonic acid-acrylonitrile copolymer binder.

[0042] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 2 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and the sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 1.

[0043] Example 3 The preparation steps of the vinylphosphonic acid-acrylonitrile copolymer adhesive provided in this embodiment are as follows: (1) First, add 30 mL of N-methylpyrrolidone as a solvent to a 100 mL three-necked flask, and then add 8.4 g of acrylonitrile, 0.8 g of acrylic acid and 0.8 g of vinylphosphonic acid in sequence. Heat to 70 °C under nitrogen protection and stir at 300 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 70°C for 12 hours. The mixture was stirred continuously at a speed of 200 rpm. After the reaction was completed, a viscous polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain a white powdery vinylphosphonic acid-acrylonitrile copolymer binder.

[0044] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 3 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and the sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 1.

[0045] Example 4 The preparation steps of the vinylphosphonic acid-acrylonitrile copolymer adhesive provided in this embodiment are as follows: (1) First, add 30 mL of deionized water as a solvent to a 100 mL three-necked flask, and add 8.4 g acrylonitrile, 0.8 g acrylic acid and 0.8 g vinylphosphonic acid in sequence. Heat to 70 °C under nitrogen protection and stir at 200 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.003 g of potassium persulfate initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 70°C for 12 hours. The mixture was stirred continuously at a speed of 200 rpm. After the reaction was completed, a viscous polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain a white powdery vinylphosphonic acid-acrylonitrile copolymer binder.

[0046] It should be noted that the solvent of this invention is selected from at least one of dimethyl sulfoxide, deionized water, and N-methylpyrrolidone. The solvent in this embodiment is an aqueous solvent, requiring the use of an aqueous initiator for the polymerization reaction. The aqueous initiator is selected from at least one of potassium persulfate, ammonium persulfate, and sodium persulfate. In contrast, the solvent in Example 1 is an oil-based solvent, requiring the use of an oil-based initiator for the polymerization reaction. The oil-based initiator is selected from at least one of azobisisobutyronitrile (AIBN) and benzoyl peroxide.

[0047] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 4 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and the sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 1.

[0048] Example 5 This embodiment provides a vinylphosphonic acid-acrylonitrile copolymer adhesive, the preparation method of which includes the following steps: (1) First, add 30 mL of dimethyl sulfoxide as solvent to a 100 mL three-necked flask, and then add 9.2 g acrylonitrile, 0.4 g acrylic acid and 0.4 g vinylphosphonic acid in sequence. Heat to 73 °C under nitrogen protection and stir at 200 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 73°C for 10 hours. The mixture was stirred continuously at a speed of 200 rpm. After the reaction was completed, a viscous polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain a white powdery vinylphosphonic acid-acrylonitrile copolymer binder.

[0049] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 5 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and the sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 1.

[0050] Example 6 This embodiment provides a vinylphosphonic acid-acrylonitrile copolymer adhesive, the preparation method of which includes the following steps: (1) First, add 30 mL of dimethyl sulfoxide as solvent to a 100 mL three-necked flask, and then add 8.4 g of acrylonitrile, 0.8 g of acrylic acid and 0.8 g of vinylphosphonic acid in sequence. Heat to 73 °C under nitrogen protection and stir at 200 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 73°C for 10 hours. The mixture was stirred continuously at a speed of 200 rpm. After the reaction was completed, a viscous polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain a white powdery vinylphosphonic acid-acrylonitrile copolymer binder.

[0051] The weight-average molecular weight of the vinylphosphonic acid-acrylonitrile copolymer binder in this embodiment was determined by gel permeation chromatography (GPC), and the results are as follows: Figure 2 As shown, its weight-average molecular weight was measured to be 192,772 g / mol, which is within the preferred range of 180,000–240,000 g / mol. The polydispersity index (PDI) was 1.358, indicating that the binder has a concentrated molecular chain length distribution and excellent batch stability, which is beneficial to ensuring the uniformity of the cathode slurry and the reproducibility of electrochemical performance.

[0052] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 6 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and the sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 1.

[0053] Example 7 This embodiment provides a vinylphosphonic acid-acrylonitrile copolymer adhesive, the preparation method of which includes the following steps: (1) First, add 26.7 mL of dimethyl sulfoxide and 3.3 mL of deionized water as solvents to a 100 mL three-necked flask, and then add 8.4 g of acrylonitrile, 0.8 g of acrylic acid and 0.8 g of vinylphosphonic acid in sequence. Heat to 73 °C under nitrogen protection and stir at 200 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 73°C for 10 hours. The mixture was stirred continuously at a speed of 200 rpm. After the reaction was completed, a viscous polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain a white powdery vinylphosphonic acid-acrylonitrile copolymer binder.

[0054] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 7 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and the sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 1.

[0055] Example 8 This embodiment provides a vinylphosphonic acid-acrylonitrile copolymer adhesive, the preparation method of which is basically the same as that of Example 1, the difference being that the proportion of vinylphosphonic acid monomers is increased in this embodiment. The specific preparation steps are as follows: (1) First, add 30 mL of dimethyl sulfoxide as solvent to a 100 mL three-necked flask, and then add 7.6 g acrylonitrile, 0.4 g acrylic acid and 2.0 g vinylphosphonic acid (monomer mass ratio of 76:4:20) in sequence. Heat to 73 °C under nitrogen protection and stir at 300 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 73°C for 10 hours. The mixture was stirred continuously at a speed of 300 rpm. After the reaction was completed, a viscous polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain a white powdery vinylphosphonic acid-acrylonitrile copolymer binder.

[0056] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 8 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and the sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 1.

[0057] Example 9 This embodiment provides a vinylphosphonic acid-acrylonitrile copolymer binder, the preparation method of which is basically the same as that of Example 6, the difference being that the amount of initiator used is increased in this embodiment. The specific preparation steps are as follows: (1) First, add 30 mL of dimethyl sulfoxide as solvent to a 100 mL three-necked flask, and then add 8.4 g of acrylonitrile, 0.8 g of acrylic acid and 0.8 g of vinylphosphonic acid in sequence. Heat to 73 °C under nitrogen protection and stir at 300 rpm for 30 minutes to obtain mixture a. (2) Next, while maintaining a nitrogen atmosphere, add 0.015g of azobisisobutyronitrile initiator (accounting for 0.15% of the total weight of the monomer), and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 73°C for 10 hours. The mixture was stirred continuously at a speed of 300 rpm. After the reaction was completed, the polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain vinylphosphonic acid-acrylonitrile copolymer binder.

[0058] The vinylphosphonic acid-acrylonitrile copolymer binder prepared in Example 9 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 6. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and the sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 6.

[0059] In other embodiments, the active material may be at least one of the following: ternary materials NCM523, NCM622, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, copper-iron-manganese based materials, sodium vanadium phosphate, sodium vanadium fluorophosphate, and lithium-rich manganese based materials; the conductive agent may be at least one of acetylene black and Ketjen black; and the conductive current collector may be carbon cloth or nickel foam.

[0060] Comparative Example 1 In this embodiment, polyvinylidene fluoride (PVDF) is used as a binder to prepare lithium-ion batteries and sodium-ion batteries, respectively.

[0061] The preparation of lithium-ion batteries using polyvinylidene fluoride (PVDF) binder includes the following steps: (1) Add 0.3g of polyvinylidene fluoride to 9.7g of N-methylpyrrolidone (NMP) solvent to prepare an adhesive solution with a 3wt% ratio; (2) Mix the active material NCM811, conductive carbon black and the binder solution from step (1) in a mass ratio of 92:5:3, put them into a 2mL centrifuge tube, and then put the centrifuge tube into a ball mill for shaking. The ball mill speed is 3000rad / s and the homogenization time is 15min to obtain the positive electrode slurry.

[0062] (3) The positive electrode slurry obtained in step (2) is evenly coated onto the conductive current collector carbon-coated aluminum foil using a scraper to obtain the positive electrode sheet; (4) After drying the positive electrode sheet obtained in step (3) in a 90°C oven for 12 hours, cut the electrode sheet with a diameter of 12 mm on a slicing machine, which is the positive electrode of the lithium-ion battery. (5) Based on the positive electrode of the lithium-ion battery in step (4), a lithium metal sheet is used as the negative electrode, a polypropylene membrane 2500 from Celgard is used as the membrane, and the corresponding lithium-ion battery electrolyte purchased from KELOD is used as the electrolyte. The CR2025 button battery is assembled in an anhydrous glove box filled with argon (H2O<0.01ppm, O2<0.01ppm) to obtain a lithium-ion button battery. The assembly method of the lithium-ion button battery is the same as that in Example 1.

[0063] The preparation of sodium-ion batteries using polyvinylidene fluoride (PVDF) binder includes the following steps: (1) Add 0.3g of polyvinylidene fluoride to 9.7g of N-methylpyrrolidone (NMP) solvent to prepare an adhesive solution with a 3wt% ratio; (2) The active material nickel-manganese base layer oxide Na 0.73 Ni 0.22 Zn 0.05 Li 0.06 Mn 0.66 Zr 0.01 O2, conductive carbon black, and the binder solution from step (1) are mixed in a mass ratio of 92:5:3 and then placed into a 2mL centrifuge tube. The centrifuge tube is then placed on a ball mill and shaken. The ball mill rotates at 3000 rad / s and the homogenization time is 15 min to obtain the positive electrode slurry.

[0064] (3) The positive electrode slurry obtained in step (2) is evenly coated onto the conductive current collector carbon-coated aluminum foil using a scraper to obtain the positive electrode sheet; (4) After drying the positive electrode sheet obtained in step (3) in a 90°C oven for 12 hours, cut the electrode sheet with a diameter of 12 mm on a slicer, which is the positive electrode of sodium-ion battery; (5) Based on the sodium-ion battery positive electrode of step (4), a sodium metal sheet is used as the negative electrode, a polypropylene membrane 2500 from Celgard is used as the membrane, and the corresponding sodium-ion battery electrolyte purchased from Kelode is used as the electrolyte. The CR2025 button battery is assembled in an anhydrous glove box filled with argon gas (H2O<0.01ppm, O2<0.01ppm) to obtain a sodium-ion button battery. The assembly method of the sodium-ion button battery is the same as that in Example 1.

[0065] Comparative Example 2 (Single Acrylonitrile Polymer Binder) This comparative example provides a single acrylonitrile homopolymer binder to illustrate the performance defects of binders lacking flexible segments and functional monomers. The specific preparation steps are as follows: (1) First, add 30 mL of dimethyl sulfoxide as solvent to a 100 mL three-necked flask, add 10.0 g of acrylonitrile (without acrylic monomers and vinyl phosphonic acid monomers), heat to 73 °C under nitrogen protection, and stir at 300 rpm for 30 minutes to obtain mixture a; (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 73°C for 10 hours. The mixture was stirred continuously at a speed of 300 rpm. After the reaction was completed, the polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain polyacrylonitrile binder.

[0066] The polyacrylonitrile binder prepared in Comparative Example 2 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then used to assemble lithium-ion button batteries, and sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were used to assemble sodium-ion button batteries, using the same assembly method as in Example 1.

[0067] Comparative Example 3 (Acrylonitrile-Acrylic Binary Copolymer Adhesive) This comparative example provides an acrylonitrile-acrylic acid binary copolymer adhesive to illustrate the performance defects of adhesives lacking vinylphosphonic acid functional units. The specific preparation steps are as follows: (1) First, add 30 mL of dimethyl sulfoxide as solvent to a 100 mL three-necked flask, then add 9.2 g of acrylonitrile and 0.8 g of acrylic acid (mass ratio 92:8, without vinylphosphonic acid monomers) in sequence, heat to 73 °C under nitrogen protection, and stir at 300 rpm for 30 minutes to obtain mixture a; (2) Next, while maintaining a nitrogen atmosphere, add 0.003g of azobisisobutyronitrile initiator and continue stirring to completely dissolve the initiator to obtain mixture b; (3) Then, the mixture b was vacuumed, and nitrogen was introduced to remove oxygen. The mixture was kept in a nitrogen atmosphere and reacted at a constant temperature of 73°C for 10 hours. The mixture was stirred continuously at a speed of 300 rpm. After the reaction was completed, the polymer product was obtained. (4) Finally, the polymer product was vacuum dried at 120°C for 12 hours, then pulverized by a pulverizer and passed through a 200-mesh sieve to obtain the acrylonitrile-acrylic acid copolymer binder.

[0068] The acrylonitrile-acrylic acid binary copolymer binder prepared in Comparative Example 3 was used to prepare lithium-ion battery cathodes and sodium-ion battery cathodes, respectively, using the same preparation method as in Example 1. The lithium-ion battery cathodes, lithium metal sheets, separators, and electrolytes were then assembled into lithium-ion button batteries, and sodium-ion battery cathodes, sodium metal sheets, separators, and electrolytes were assembled into sodium-ion button batteries, using the same assembly method as in Example 1.

[0069] Performance testing (1) Adhesive viscosity test The binders of each embodiment and comparative example were diluted with DMOSO solution to a solid content of 22%, and their viscosity was measured using a rotational viscometer under constant temperature of 25°C. Each set of embodiments was prepared three times and tested separately, and the average viscosity was taken as the final result. The viscosity test results are shown in Table 1.

[0070] The results show that, within the monomer composition range, the viscosity of the binder system increases with the increase of the proportion of acrylonitrile monomer in the copolymer. Specifically, the formulation of Example 6 exhibits the best overall performance balance: its viscosity is more suitable, ensuring good processing rheology, sufficient intermolecular forces, and achieving an optimal balance between suitable swelling degree and best cycling performance.

[0071] (2) Adhesive swelling test The adhesives of each embodiment and comparative example were vacuum dried at 100°C to constant weight to form a film of uniform thickness. These films were then cut into circular samples with a radius of 6 mm using a cutting machine and accurately weighed (recorded as m1). The samples were placed in a sealed container, and KLD-1230C electrolyte with a mass 20 times the sample mass was added. After soaking at a constant temperature of 25°C for 48 hours, the samples were removed, and residual electrolyte was quickly wiped off with filter paper. The mass was immediately weighed (recorded as m2). The degree of swelling was calculated using the formula: Swelling degree (%) = (m2 - m1) / m1 × 100%. Three parallel experiments were conducted for each adhesive, and the average value was taken. The swelling test data for each embodiment are shown in Table 1.

[0072] The results show that the binder of this invention exhibits a suitable and adjustable degree of swelling in the electrolyte, which can be stably maintained within an optimized range of 5% to 20%. When the swelling degree is below 5%, the binder cannot provide sufficient channels for ion transport; while when the swelling degree is above 20%, it leads to excessive electrode expansion and increased internal resistance. This invention, through precise control of the monomer ratio, enables the binder to maintain good ionic conductivity in the electrolyte while avoiding damage to the electrode structure due to excessive swelling, thereby maintaining the structural integrity of the electrode while ensuring high ionic conductivity.

[0073] Table 1: Viscosity and swelling test results of the binders in each example and comparative example

[0074] (3) Adhesive peel strength test The lithium-ion battery cathodes prepared in each embodiment and comparative example were subjected to a 180° peel strength test. The width of the lithium-ion battery cathode was uniformly 2.5 cm. The specific test results are shown in Table 2.

[0075] Test results show that, under the same component ratio, the peel strength of the battery cathode prepared using the binder of Example 6 of this invention reaches 4.1 N / m, which is significantly higher than the 2 N / m of the PVDF binder in Comparative Example 1. This demonstrates that the vinylphosphonic acid-acrylonitrile copolymer binder provided by this invention exhibits superior bonding performance in battery cathodes compared to traditional PVDF binders, demonstrating better interfacial bonding strength and thus better ensuring the structural integrity of the electrode during cycling.

[0076] (4) Dynamic mechanical analysis (DMA) of the adhesive The adhesives used in each embodiment and comparative example were made into films of uniform thickness, cut into strips, and tested in tensile mode. The test temperature range was -50 to 200°C, the heating rate was 5°C / min, the frequency was 1 Hz, and the tensile stress was 0.1 MPa. The test results are shown in Table 2. The dynamic mechanical analysis diagram for Example 6 is shown below. Figure 3 .

[0077] According to the test results, the energy storage modulus of the binder in Example 6 at room temperature reaches 597.61 MPa, indicating excellent mechanical strength. The loss factor (tanδ) curve shows a sharp peak (maximum value 0.595) at 48.8℃, corresponding to its glass transition temperature (Tg), indicating that the binder has high rigidity and structural stability, which can effectively support the electrode skeleton and resist mechanical stress during rolling and cycling. At the same time, the moderate Tg value enables the binder to have both dimensional stability and moderate flexibility within the battery operating temperature range. It can maintain the integrity of the electrode structure and buffer the volume expansion and contraction of the active material during charging and discharging through slight deformation of the molecular chain, avoiding structural damage caused by interface stress concentration.

[0078] Table 2: Peel strength and dynamic mechanical analysis test results of adhesives in each embodiment and comparison.

[0079] (5) High-voltage cycling test of binder in lithium-ion button cell The cycle performance of the assembled lithium-ion coin cells of each embodiment and comparative example was tested using a Neware CT2001A battery testing system at 30°C. The test conditions were: active material loading of 2.1 mg / cm², charge / discharge window of 2.7–4.4 V for lithium-ion batteries, and a current density of 0.5 C. The test results are shown in Table 3. Figure 4 The cycle performance of lithium-ion button batteries assembled using the binders of Example 6 and Comparative Example 1 is compared under the same test conditions.

[0080] Table 3: High-voltage cycle test results of lithium-ion button batteries in each embodiment and comparison

[0081] The test results show that after 300 cycles, the button cell using the binder from Example 6 exhibits excellent electrochemical stability, and its reversible specific capacity remains at 155 mAh g⁻¹. ‐1 The capacity retention rate reached 87.93%, and the coulombic efficiency was 99.88%. In contrast, the reversible specific capacity of the coin cell using Comparative Example 1 (PVDF) binder after cycling was only 110 mAhg. ‐1 The capacity retention rate was 70.02%, and the coulombic efficiency was 99.51%; the reversible specific capacity of the button cell using the single acrylonitrile polymer binder in Comparative Example 2 was only 85 mAh g after cycling. ‐1 The capacity retention rate was 48.6%, and the coulombic efficiency was 99.35%.

[0082] (6) High-rate cycle test of binder in sodium-ion button cell The cycle performance of the assembled sodium-ion button batteries of each embodiment and comparative example was tested using a Neware CT2001A battery testing system at 30°C. The test conditions were: active material loading of 2.02 mg / cm², charge / discharge window of lithium-ion batteries selected within the voltage window of 2.0–4.3V, and current density of 10C. The test results are shown in Table 4. Figure 5 The study demonstrates a comparison of the long-cycle performance of sodium-ion button batteries assembled using the binders of Example 6 and Comparative Example 1 at a high rate of 10 C.

[0083] The test results show that after 1000 cycles, the button cell using the binder from Example 6 exhibits excellent structural stability and interface characteristics, maintaining a reversible specific capacity of 77.28 mAh g⁻¹. ‐1 The capacity retention rate reached 65.31%, and the coulombic efficiency was 99.96%. In contrast, the coin cell using Comparative Example 1 (PVDF) binder showed a reversible specific capacity decrease to 67.01 mAh g after the same number of cycles. ‐1The capacity retention rate was 59.66%, and the coulombic efficiency was 99.91%; the reversible specific capacity of the button cell using the single acrylonitrile polymer binder in Comparative Example 2 was only 42.3 mAh g⁻¹ after cycling. ‐1 The capacity retention rate was 32.5%, and the coulombic efficiency was 99.48%. The coin cell using the comparative example 3 acrylonitrile-acrylic acid binary copolymer binder had a reversible specific capacity of 62.8 mAh g after cycling. ‐1 The capacity retention rate was 52.3%, and the coulombic efficiency was 99.78%.

[0084] Table 4: High-rate cycle test results of sodium-ion button batteries in various examples and comparisons

[0085] (7) Morphological analysis of the battery cathode was performed using SEM before cycling. First, the positive electrodes of the batteries in Example 6 and Comparative Example 1 were subjected to gold sputtering for 30 seconds to enhance conductivity. Then, surface images were taken at magnifications of 100 μm and 10 μm using an accelerating voltage of 5 kV.

[0086] Depend on Figure 6 It can be seen that both sets of battery cathodes exhibit a state of uniform particle dispersion, but the surface of the cathode of Example 6 is flatter and denser, the binder coating of NCM811 particles is more continuous and complete, there are fewer gaps between particles, and the overall structure is more compact; while the surface of the cathode of Comparative Example 1 has slight particle agglomeration and local pores, and the continuity of the skeleton is slightly weaker.

[0087] (8) Morphological analysis of the battery positive electrode was performed using SEM after 200 cycles. First, the positive electrodes of the batteries in Example 6 and Comparative Example 1 were subjected to gold sputtering for 30 seconds to enhance conductivity. Then, surface images were taken at magnifications of 100 μm and 10 μm using an accelerating voltage of 5 kV.

[0088] Depend on Figure 7 As can be seen, multiple through cracks appeared on the surface of the positive electrode of the battery in Comparative Example 1, and some areas experienced particle peeling and skeleton collapse. The originally continuous conductive network was severely damaged, exposing a large number of bare NCM811 particles. In contrast, the surface of the positive electrode of the battery in Example 6 had only a very small number of tiny wrinkles, no obvious cracks or particle detachment, and the particles remained tightly bonded. The integrity of the overall microstructure was well maintained, and the conductive network did not experience significant breakage.

[0089] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A vinylphosphonic acid-acrylonitrile copolymer adhesive, characterized in that, It comprises the following components by mass: 76%–92% acrylonitrile, 4%–12% acrylic monomers, and 4%–12% vinylphosphonic acid monomers, wherein the vinylphosphonic acid-acrylonitrile copolymer adhesive is prepared by free radical polymerization of each of the monomers.

2. The vinylphosphonic acid-acrylonitrile copolymer adhesive according to claim 1, characterized in that, The monomers, by mass percentage, are: 80%–88% acrylonitrile, 6%–10% acrylic acid monomers, and 6%–10% vinylphosphonic acid monomers.

3. The vinylphosphonic acid-acrylonitrile copolymer adhesive according to claim 1, characterized in that, The acrylic monomer is acrylic acid, and the vinylphosphonic monomer is vinylphosphonic acid.

4. The vinylphosphonic acid-acrylonitrile copolymer adhesive according to claim 1, characterized in that, The weight-average molecular weight of the vinylphosphonic acid-acrylonitrile copolymer binder is 150,000 to 300,000 g / mol.

5. The method for preparing the vinylphosphonic acid-acrylonitrile copolymer adhesive according to any one of claims 1 to 4, characterized in that, Includes the following steps: First, acrylonitrile, vinylphosphonic acid monomers and acrylic acid monomers are added sequentially to a solvent, and the mixture is heated and stirred under a nitrogen atmosphere to obtain mixture a; Next, while maintaining a nitrogen atmosphere, heat the mixture a to 70°C to 80°C for 10 to 30 minutes. When the temperature reaches a constant level, add an initiator to dissolve the mixture a to obtain mixture b. Then, the mixture b is vacuumed and then nitrogen is introduced to remove oxygen. The mixture is reacted at a constant temperature of 70℃~80℃ for 6~12 hours with continuous stirring at a speed of 100~500rpm. After the reaction is completed, the polymer product is obtained. Finally, the polymer product is vacuum dried at a temperature of 100℃ to 160℃, then pulverized and sieved with a mesh size of 100 to 300 mesh to obtain a vinylphosphonic acid-acrylonitrile copolymer binder.

6. The method for preparing the vinylphosphonic acid-acrylonitrile copolymer adhesive according to claim 5, characterized in that, The solvent is at least one of dimethyl sulfoxide, deionized water, and N-methylpyrrolidone.

7. The method for preparing the vinylphosphonic acid-acrylonitrile copolymer adhesive according to claim 5, characterized in that, The initiator is selected according to the type of solvent; When the solvent is an oil-based solvent, the initiator is an oil-based initiator selected from at least one of azobisisobutyronitrile and benzoyl peroxide; When the solvent is an aqueous solvent, the initiator is an aqueous initiator selected from at least one of potassium persulfate, ammonium persulfate, and sodium persulfate.

8. The method for preparing the vinylphosphonic acid-acrylonitrile copolymer adhesive according to claim 5 or 7, characterized in that, The amount of the initiator is 0.01% to 0.3% of the total weight of the monomer.

9. The application of the vinylphosphonic acid-acrylonitrile copolymer binder according to any one of claims 1 to 4 in the preparation of the positive electrode of a lithium / sodium ion battery.

10. A lithium / sodium ion battery positive electrode, characterized in that, It is prepared through the following steps: S1: Dissolve the vinylphosphonic acid-acrylonitrile copolymer adhesive according to any one of claims 1 to 4 in an organic solvent to obtain an adhesive solution; S2: Mix the active material, conductive agent and binder solution and shake well to obtain positive electrode slurry; S3: The positive electrode slurry is uniformly coated on a conductive current collector, and then dried and sliced ​​to obtain a lithium / sodium ion positive electrode sheet; S4: After drying the lithium / sodium ion positive electrode sheet, the positive electrode of the lithium / sodium ion battery is obtained.

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