PVDF material with dispersion anti-gel function for positive electrode slurry and preparation method thereof

Abstract

The present application relates to a kind of positive electrode slurry with dispersing anti-gel function PVDF material, wherein the PVDF material has the following structural formula:;Wherein, in the above structural formula, G1 is co-grafted functional part, including but not only limited to vinyl trimethoxysilane, styrene ethyl trimethoxysilane, 3- (methacryloyloxy) propyl trimethoxysilane, vinyl tri (2-methoxyethoxy) silane, (4-vinylphenylmethyl) trimethylsilane and so on one or more. The PVDF material can significantly improve the dispersion stability of existing lithium battery positive electrode slurry without introducing more additive functional parts, enhance the anti-gel properties of slurry, and increase the applicability of lithium battery positive electrode adhesive in different slurry systems.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a PVDF material with dispersion and anti-gelling function for positive electrode slurry and its preparation method. Background Technology

[0002] With the popularization of new energy vehicles, the performance requirements for power batteries are increasing. Lithium-ion batteries are currently the most commonly used batteries in the electric vehicle industry. In the manufacturing process of lithium-ion batteries, the quality of the electrode sheets directly affects the battery's electrochemical performance and safety stability. The preparation of the electrode slurry is the first and most crucial step in lithium-ion battery production. The viscosity, solid content, uniformity, and stability of the slurry directly affect subsequent slurry coating, electrode sheet rolling, and electrode performance; therefore, slurry dispersion is paramount. Furthermore, in actual production, an abnormal slurry gelation phenomenon is often observed in different slurry systems. Once gelation occurs during electrode synthesis, the electrode changes from a slurry to a gel, losing its fluidity and adhesive properties. This not only severely affects slurry coating but also leads to the separation of the aluminum foil and electrode material, ultimately causing the positive electrode material to fail. Therefore, gelation should be prevented or slowed down as much as possible during the preparation of the positive electrode material. Current improvement methods mainly involve eliminating gel by adding one or two additives or changing the pulping process. However, the introduction of additional additives not only reduces the proportion of active battery materials but also raises a series of issues such as stability and compatibility. Furthermore, complex processes are not what factories require.

[0003] Polyvinylidene fluoride (PVDF) is currently a mainstream binder for lithium-ion battery cathodes. Although its proportion in the slurry is small (generally 2-5 wt%), it is an indispensable material in lithium-ion batteries. PVDF is a semi-crystalline functional fluorine-containing polymer composed of -CH2-CF2- repeating units. Its molecular chains are closely arranged and have strong hydrogen bonding interactions. However, PVDF is an inert compound with poor solubility, high viscosity, poor compatibility with other substrate materials, and relies solely on weak van der Waals forces for adhesion, thus limiting its application in today's competitive market. Further reducing the viscosity of the slurry system, improving its stability, and its applicability in different slurry systems without introducing more additives is a problem that must be addressed.

[0004] Therefore, it is necessary to modify PVDF, and the main modification methods currently are copolymerization, grafting, and blending. Copolymerization generally involves copolymerizing PVDF with other fluorinated monomers, but this often requires the use of various additives and catalysts in solution, inevitably resulting in residual metal ions in the final product. This clearly cannot meet the increasingly demanding requirements of the high-energy-density battery industry. Blending, on the other hand, requires consideration of the compatibility between the modified material and PVDF. Poor compatibility leads to uneven dispersion or even agglomeration of the modified material in the PVDF matrix, resulting in unsatisfactory product performance. Furthermore, with blending, there are no chemical bonds between the modified material and PVDF, making the modified material prone to continuous loss during use, failing to provide excellent and stable modification effects.

[0005] Existing patent CN117603634A discloses a PVDF binder applicable to high-alkalinity ternary cathode or sodium battery cathode systems. While it effectively solves the gelation problem of slurry, the PVDF copolymer obtained by suspension polymerization not only uses a large amount of solvent but also has harsh reaction conditions and cumbersome post-processing, which is not conducive to industrial production. Patent CN117946338A discloses a PVDF material with high compatibility and adhesion and its preparation method, which uses reactive extrusion to melt-graft methacryloxypropyltriethoxysilane (MPTES) onto polyvinylidene fluoride (PVDF). Although this method can effectively enhance the adhesion of PVDF coatings, its impact on the battery field is unknown.

[0006] In light of the above issues, there is an urgent need for a modification method for PVDF, a lithium-ion battery cathode binder material, that is easy to industrialize. This method should significantly improve the dispersion stability of existing lithium-ion battery cathode slurries, enhance the anti-gel properties of the slurries, and increase the applicability of lithium-ion battery cathode binders in different slurry systems without introducing additional functional components. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a PVDF material with dispersion and anti-gelling functions for positive electrode slurries. This PVDF material, without introducing additional functional components, can significantly improve the dispersion stability of existing lithium-ion battery positive electrode slurries, enhance the anti-gelling properties of the slurry, and increase the applicability of lithium-ion battery positive electrode binders in different slurry systems.

[0008] The present invention also provides a method for preparing the above-mentioned dispersion and antigelling functional PVDF material for positive electrode slurry.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A PVDF material with dispersion and anti-gelling function for positive electrode slurry, wherein the PVDF material has the following structural formula:

[0011] in,

[0012] In the above structural formula, G1 is the co-grafted functional part, including but not limited to one or more of vinyltrimethoxysilane, styrene ethyltrimethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, and (4-vinylphenylmethyl)trimethylsilane;

[0013] In the above structural formula, G2 is the distributed functional part, and its structure is as follows:

[0014]

[0015] In the dispersive functional part G2, the R1 and R2 groups can be long-chain alkane structures with 1-8 carbon atoms, olefins containing unsaturated bonds, or cyclic structures, wherein at least one chain is carboxyl-terminated; the number of repeating units x can be 10-40.

[0016] In the above structural formula, G3 is the anti-gel functional part, and its structure is as follows:

[0017]

[0018] In the antigel functional part G3, the R3 group can be a hydrogen atom, a methyl or acetyl group with 1-2 carbon atoms; the R4 and R5 groups can be alkyl groups with 1-7 carbon atoms, alkyl groups with 1-4 carbon atoms and hydroxyl-terminated, or aromatic groups with 6-8 carbon atoms.

[0019] Furthermore, in the dispersive functional part G2, the monomers composed of R1 and R2 groups include, but are not limited to, one or more of maleic anhydride, maleic acid, α-linolenic acid, oleic acid, linoleic acid, arachidonic acid, etc.; the monomers composed of repeating units x can be allyl polyethylene glycol, preferably with a molecular weight of 500-1800.

[0020] Furthermore, in the antigel functional part G3, the substances composed of R3 and R4 groups include, but are not limited to, one or more of the following: phenylhydrazine, acetylphenylhydrazine, 2-hydrazinoethanol, ethylhydrazine, benzylhydrazine, etc.; the substances composed of R5 groups include, but are not limited to, one or more of the following: acetylhydrazine, butyrylhydrazine, 4-hydroxybenzoylhydrazine, 4-hydroxyphenylacetylhydrazine, hexanoylhydrazine, octanoylhydrazine, benzoylhydrazine, phenylacetylhydrazine, phenoxyacetylhydrazine, etc.

[0021] This invention provides a method for preparing the above-mentioned PVDF material with dispersion and anti-gelling function for positive electrode slurry, which includes the following steps:

[0022] S1. Dry the PVDF powder in an oven;

[0023] S2. Use a high-speed mixer to mix the PVDF powder with the initiator, dispersant, co-grafted, and antigel components evenly.

[0024] S3. Start the twin-screw extruder to preheat and set the parameters;

[0025] S4. The uniformly mixed sample is fed into the inlet of the twin-screw extruder. After being extruded by the twin-screw shearing and mixing reaction, the material is gradually transferred from the first zone of the extruder to the sixth zone and discharged.

[0026] S5. After thoroughly drying the extruded product in a cooling water tank, use a pelletizer to pelletize the water-cooled product to obtain the final product.

[0027] Specifically, in step S1, the molecular weight of the PVDF powder is 200,000-500,000; the temperature of the drying oven is 80-120℃; and the drying time is 12-24h.

[0028] Further, in step S2, the mass fractions of each reaction component are as follows: PVDF 100 parts; initiator 0.1-0.3 parts; dispersing functional part 5-10 parts; co-grafting functional part 1-5 parts; anti-gelling functional part 2-5 parts; the initiator can be one or more combinations of benzoyl peroxide, dicumyl peroxide, dodecyl peroxide, di-tert-butyl cumyl peroxide, tert-butyl peroxide, etc., preferably dodecyl peroxide.

[0029] Furthermore, in step S4, the twin-screw extruder is provided with six temperature control zones, which are as follows: Zone I 80±2℃, Zone II 100±2℃, Zone III 150±2℃, Zone IV 170±2℃, Zone V 170±2℃, and Zone VI 175±2℃.

[0030] Furthermore, in step S4, the screw speed of the twin-screw extruder can be 30-50 rpm, and the feeding speed can be 50-60 rpm. The average residence time of the material in the twin-screw extruder is 3-5 minutes.

[0031] This invention provides a PVDF material with dispersion and antigelling function for positive electrode slurry prepared by the above method.

[0032] The present invention also provides the application of the above-mentioned dispersible and anti-gelling PVDF material as a positive electrode slurry for lithium batteries.

[0033] Taking one of the systems as an example, the grafting reaction principle is as follows:

[0034]

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) The method for preparing the dispersion-antigel functional PVDF material of the present invention is by reactive extrusion. Utilizing the strong shearing action of a twin-screw extruder at high temperature, the various functional components can be thoroughly and uniformly mixed. Grafting is initiated by free radicals from an initiator, and the covalently grafted small molecules are inseparable from the PVDF backbone. This effectively avoids phase separation / aggregation, providing excellent and stable modification effects, while also increasing its compatibility and applicability with different systems. Furthermore, it boasts high production efficiency, avoids the use of large amounts of organic solvents, and allows for continuous industrial production, greatly enriching the existing modification systems for lithium-ion battery cathode binders.

[0037] (2) In the preparation process of modified PVDF material, the present invention introduces a water cooling system, which not only avoids the problem of uneven crystallization caused by natural cooling of extruded products, but also removes the water-soluble functional parts that did not participate in the grafting during the reaction extrusion process, further increasing the proportion of the main components of the modified PVDF material; in addition, some grafted functional parts will be further hydrolyzed, thereby introducing more reaction sites, which will further enhance the comprehensive performance of PVDF material.

[0038] (3) In the process of modifying PVDF, the present invention introduces a dispersing functional part by grafting. Its long chain structure can provide sufficient steric hindrance in the positive electrode slurry, reduce the chain entanglement of the PVDF molecular chain, and form a stable barrier. Therefore, the positive electrode slurry prepared by it has a lower viscosity and can maintain stability for a longer time. In addition, due to the introduction of carboxyl groups, strong hydrogen bonds can be formed with hydroxyl groups on the surface of the active material, which further enhances the bonding performance of PVDF material. Furthermore, the partially ionized carboxylic acid groups can also generate an electrostatic repulsion, which further enhances the dispersion stability of the slurry.

[0039] (4) In the process of PVDF modification, the present invention introduces an anti-gelling functional part through amidation reaction, which enables the adhesive material to have a strong metal ion chelating ability, which can effectively alleviate the slurry gelation problem.

[0040] (5) In the process of PVDF modification, the present invention introduces a co-grafted functional part. Its inorganic functional group is reactive to inorganic materials, and its organic functional group is compatible and reactive to organic materials. It plays a coupling role in the whole material system, which further enhances the compatibility between the various systems in the slurry. Its co-grafting effect is not only conducive to the grafting of the dispersion functional part, but also the hydrolyzed silanol group can further react with the anti-gel functional part, so that the prepared adhesive material has better performance.

[0041] (6) The dispersible and anti-gelling PVDF material prepared by this invention undergoes high-temperature and high-pressure twin-screw shearing, causing the PVDF crystal form to transform from α to β crystals. This improves the slow dissolution rate and high viscosity of existing PVDF while enhancing its conductivity. This method not only maintains the original comprehensive performance of PVDF but also significantly improves its dispersion performance, stability, and anti-gelling properties, while increasing its applicability in different slurry systems and solving the gelling problem existing in existing high-solids-content lithium-ion battery cathode slurries. Attached Figure Description

[0042] Figure 1 FT-IR spectra of PVDF and Examples 1-5;

[0043] Figure 2 The XRD patterns are for PVDF and Examples 1-5. Detailed Implementation

[0044] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0045] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention are further described below with reference to embodiments. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0046] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0047] In the examples, the PVDF powder used has a molecular weight of 200,000-500,000 and is a commercially available product.

[0048] Example 1, the preparation method of PVDF material with dispersion and anti-gelling function for positive electrode slurry includes the following steps:

[0049] (1) Place 400g of PVDF in an 80℃ oven and dry for 24 hours;

[0050] (2) Use a high-speed mixer to thoroughly mix 400g PVDF, 0.4g dodecyl peroxide, 20g dispersing functional part (α-linolenic acid), 4g co-grafted functional part (3-(methacryloyloxy)propyltrimethoxysilane), and 8g antigel functional part (phenylhydrazine);

[0051] (3) Start the twin-screw extruder. Set the six temperature control zones as follows: Zone I 80±2℃, Zone II 100±2℃, Zone III 150±2℃, Zone IV 170±2℃, Zone V 170±2℃, and Zone VI 175±2℃. After reaching the set temperature, start the screw, set the rotation speed to 40 rpm, and the feeding speed to 60 rpm.

[0052] (4) The mixture is fed into the feed port of the twin-screw extruder. The material is gradually transferred from the first section to the sixth section and extruded by the high temperature shearing reaction of the twin screw. The average residence time of the material in the twin-screw extruder is 3 minutes. Then the material is discharged, cooled by the cooling water tank, and pelletized by the pelletizer to finally obtain the PVDF material with dispersion and anti-gelling function.

[0053] Example 2, the preparation method of PVDF material with dispersion and anti-gelling function for positive electrode slurry includes the following steps:

[0054] (1) Place 400g of PVDF in a 120℃ oven and dry for 12 hours;

[0055] (2) Use a high-speed mixer to thoroughly mix 400g PVDF, 0.8g benzoyl peroxide, 40g dispersing functional part (oleic acid), 8g co-grafting functional part (vinyltrimethoxysilane), and 16g antigel functional part (acetylphenylhydrazine);

[0056] (3) Start the twin-screw extruder. Set the six temperature control zones as follows: Zone I 80±2℃, Zone II 100±2℃, Zone III 150±2℃, Zone IV 170±2℃, Zone V 170±2℃, Zone VI 175±2℃. After reaching the set temperature, start the screw, set the rotation speed to 50 rpm, and the feeding speed to 50 rpm.

[0057] (4) The mixture is fed into the feed inlet of the twin-screw extruder. The material is gradually transferred from the first section to the sixth section and extruded through the high-temperature shearing and mixing reaction of the twin screw. The average residence time of the material in the twin-screw extruder is 4 minutes. Then the material is discharged, cooled by the cooling water tank, and pelletized by the pelletizer to finally obtain the PVDF material with dispersion and anti-gelling function.

[0058] Example 3, the preparation method of PVDF material with dispersion and anti-gelling function for positive electrode slurry includes the following steps:

[0059] (1) Place 400g of PVDF in a 120℃ oven and dry for 12 hours;

[0060] (2) Use a high-speed mixer to thoroughly mix 400g PVDF, 0.4g di-tert-butyl cumene peroxide, 30g dispersing functional part (linoleic acid), 8g co-grafted functional part (styrene ethyltrimethoxysilane), and 16g antigel functional part (4-hydroxybenzoyl hydrazine);

[0061] (3) Start the twin-screw extruder. Set the six temperature control zones as follows: Zone I 80±2℃, Zone II 100±2℃, Zone III 150±2℃, Zone IV 170±2℃, Zone V 170±2℃, Zone VI 175±2℃. After reaching the set temperature, start the screw, set the rotation speed to 50 rpm, and the feeding speed to 50 rpm.

[0062] (4) The mixture is fed into the feed port of the twin-screw extruder. The material is gradually transferred from the first section to the sixth section and extruded by high-temperature shearing and mixing reaction of the twin screw. The average residence time of the material in the twin-screw extruder is 5 minutes. Then the material is discharged, cooled by a cooling water tank, and pelletized by a pelletizer to finally obtain the PVDF material with dispersion and anti-gelling function.

[0063] Example 4, the preparation method of PVDF material with dispersion and anti-gelling function for positive electrode slurry includes the following steps:

[0064] Referring to Example 1, the difference is that the initiator is changed to tert-butyl peroxide, and the dispersing component is replaced with maleic anhydride.

[0065] Example 5, the preparation method of PVDF material with dispersion and anti-gelling function for positive electrode slurry includes the following steps:

[0066] Referring to Example 2, the difference is that the antigel function part is changed to hexanohydrazide, and the co-grafting function part is changed to vinyltris(2-methoxyethoxy)silane.

[0067] Comparative Example 1: A common commercially available PVDF.

[0068] Performance testing:

[0069] 1. Viscosity of the adhesive solution. Weigh 7g of the prepared dispersible anti-gelling PVDF material into 93g of N-methylpyrrolidone (NMP), and dissolve it by magnetic stirring in an oil bath at 70℃ to obtain the dispersible anti-gelling PVDF material adhesive solution. Then, transfer 30ml of the adhesive solution to a 50ml centrifuge tube and place it in a constant temperature water bath at 25℃. Measure the viscosity using an RVDV-1 digital rotational viscometer with a No. 3 rotor at 30rpm and a measurement temperature of 25℃.

[0070] 2. Slurry preparation process.

[0071] First, the positive electrode active material, lithium iron phosphate, and the conductive agent were dried in an oven at 120℃ for 4 hours. Then, the organic solvent N-methylpyrrolidone, the prepared PVDF material solution, and the conductive agent were sequentially placed into a 250ml plastic beaker and sheared using a high-speed shearing machine at 1200 rpm for 10 minutes. Finally, the positive electrode active material, lithium iron phosphate, was added, and shearing continued at 1500 rpm for 20 minutes to obtain the positive electrode slurry. The raw materials were weighed according to a mass ratio of lithium iron phosphate: conductive agent: dispersing and anti-gelling PVDF material = 96:2:2, with the PVDF material being the corresponding mass of the solution. The organic solvent N-methylpyrrolidone accounted for 32 wt% of the positive electrode slurry.

[0072] In the above slurry preparation process, the conductive agent selected for the sample in Example 1 was KS-15; the conductive agent selected for the sample in Example 2 was acetylene black; the conductive agent selected for the sample in Example 3 was carbon nanotubes; the conductive agent selected for the sample in Example 4 was SFG-15; and the conductive agent selected for the sample in Example 5 was Ketjen black.

[0073] 3. Slurry viscosity and gelation test. Transfer 30 ml of slurry to a 50 ml centrifuge tube and place it in a 25°C constant temperature water bath. Use an RVDV-1 digital rotational viscometer with a No. 4 rotor at 12 rpm and a test temperature of 25°C. Measure the viscosity at regular intervals and observe whether the slurry gels.

[0074] 4. Peel strength and folding endurance tests. The uniformly dispersed slurry was coated onto a substrate with aluminum foil as the positive electrode sheet using a coating machine to a thickness of 200 μm. The fabricated positive electrode sheet was then dried in an oven at 105℃ for 1 hour. The dried electrode sheet with a wet thickness of 200 μm was then rolled and tested for peel strength. Rolling was continued until the compacted density reached 2.4 g / m³. 3 The electrode sheets were cut into 15mm × 200mm sample strips and tested using a 180° horizontal peel strength tester at a speed of 150mm / min and a test temperature of 25℃. The coated side and the aluminum foil side of the sample strip were folded in half once, and the result was recorded as one fold until the sample strip cracked. This folding endurance was then measured.

[0075] Figure 1 The figures show the FT-IR spectra of Examples 1-5. As can be seen from the figures, compared to pure PVDF, the infrared spectra of each example show a higher FT-IR value at 1244 cm⁻¹. -1 New characteristic absorption peaks appear at all locations, corresponding to the symmetric stretching vibration peaks of the Si-OC co-grafted functional part; at 1730 cm⁻¹... -1 A new characteristic absorption peak appears nearby, which is attributed to the carbonyl peak of the dispersed functional moiety; at 1600 cm⁻¹ -1A new peak appears nearby, which is attributed to the benzene ring vibration peak of the antigel functional moiety, and the 3300 cm⁻¹ peak. -1 The new characteristic peaks appearing on the left and right sides are attributed to the -NH- peak of the antigelling component, indicating that all functional components have been successfully grafted. Further testing revealed that, based on the amount of PVDF, the grafting amount of co-grafted functional component G1 was 0.05-1 wt%; the grafting amount of dispersing functional component G2 was 0.05-1 wt%; and the grafting amount of antigelling functional component G3 was 0.05-1 wt%. Additionally, we observed that after reactive extrusion, compared to the example, the 975 cm⁻¹ of pure PVDF... -1 and 762cm -1 The characteristic peaks belonging to α crystals are significantly weakened; instead, the peak at 1276 cm⁻¹ in the example is used as a substitute. -1 and 839cm -1 The enhancement of the peak is attributed to the β characteristic peak of PVDF, indicating that after modification by this method, PVDF has completed the transformation from α crystal to β crystal. β crystal has strong polarity and excellent ferroelectric and piezoelectric properties, which helps to improve the conductivity of PVDF materials.

[0076] Figure 2 The XRD patterns of Examples 1-5 are shown in the figures. It can be seen from the figures that in pure PVDF, characteristic diffraction peaks of the nonpolar α-phase crystal appear at 17.612°, 18.16°, 19.765°, and 26.658°. However, after modification using the method of this invention, the diffraction peaks in the examples appear at 18.50° and 20.15°, which belong to the diffraction peaks of the polar β-phase crystal, consistent with the aforementioned FT-IR patterns.

[0077] Table 1. Solubility test results of Examples 1-5 and Comparative Example 1

[0078]

[0079] In this invention, specifically, as can be seen from the comparison between Examples 1-5 and Comparative Example 1:

[0080] 1) Compared with the dissolution time of commercially available PVDF, the dissolution time of the PVDF material with dispersion and anti-gel function of the present invention is reduced;

[0081] 2) Compared with commercially available PVDF, the viscosity of the adhesive liquid prepared by the present invention is significantly reduced, by 41%-63%, and remains stable after standing for 24 hours.

[0082] Table 2. Slurry performance test results of Examples 1-5 and Comparative Example 1

[0083]

[0084] In this invention, specifically, as can be seen from the comparison between Examples 1-5 and Comparative Example 1:

[0085] 1) The positive electrode slurry prepared using the dispersion antigel functional PVDF material prepared in this invention has a low viscosity after standing for 1 hour, with a maximum decrease of 82.7%;

[0086] 2) After standing for 8 hours, compared with Comparative Example 1, the viscosity of the slurry in the embodiment of the present invention increased by only 16.6-35.4%, while the viscosity of the slurry in the comparative example increased by nearly 135%.

[0087] 3) After standing for 24 hours, the positive electrode slurry prepared by the present invention did not show any gelation phenomenon, while Comparative Example 1 had already gelled after standing for 8 hours.

[0088] Table 3 Comparison of peel strength between Examples 1-5 and Comparative Example 1

[0089] sample Peel strength N / m flexural strength Example 1 13.28 5 Example 2 14.56 5 Example 3 12.35 5 Example 4 10.26 4 Example 5 8.37 4 Comparative Example 1 6.32 1

[0090] In this invention, specifically, as can be seen from the comparison between Examples 1-5 and Comparative Example 1:

[0091] 1) The peel strength of the positive electrode sheet prepared using the dispersion anti-gel functional PVDF material prepared by the present invention is improved, with an improvement of 32.43-130.38% compared with the comparative example, and it also has excellent folding resistance; thus, it reflects the excellent bonding performance of PVDF material as a binder, and further reflects the excellent performance of lithium battery positive electrode sheet.

[0092] In summary, the preparation method of the dispersion-antigel functional PVDF material and the preparation method of the positive electrode slurry of the present invention have the following beneficial effects:

[0093] The method for preparing the PVDF material with dispersion and anti-gel function of the present invention is carried out by reactive extrusion. Utilizing the strong shearing action of a twin-screw extruder at high temperature, a dispersion functional component is introduced through grafting. Its long-chain structure provides sufficient steric hindrance in the positive electrode slurry, reducing chain entanglement of the PVDF molecular chains and forming a stable barrier. Therefore, the prepared positive electrode slurry has lower viscosity and can maintain stability for a longer period. The water-cooling system not only makes the modified PVDF material more uniformly crystallized but also increases the proportion of the main components of the modified PVDF material and increases the number of reaction sites. The introduction of co-grafted functional components further enhances the compatibility between various functional components and increases the grafting rate of other functional components, allowing more beneficial functional groups to be linked. The introduction of the anti-gel functional component gives the binder a strong metal ion chelating ability, effectively mitigating the slurry gelation problem. Furthermore, due to the high-temperature and high-pressure twin-screw shearing, the crystal function of PVDF is transformed from α to β crystals, improving the slow dissolution rate and high system viscosity of existing PVDF while enhancing the conductivity of PVDF. It not only maintains the original comprehensive performance of PVDF, but also significantly improves its dispersion performance, stability, and anti-gelling properties.

[0094] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a PVDF material with anti-gelling function for cathode slurry, characterized in that, It comprises the following steps: S1, drying the PVDF powder in an oven; S2, mixing the PVDF powder with initiators, dispersion functional parts, co-grafting functional parts, and anti-gel functional parts uniformly; S3, starting the preheating of the twin-screw extruder and setting the parameters; S4, feeding the uniformly mixed sample into the twin-screw extruder from the feeding port, extruding through the twin-screw shearing mixing reaction, and transferring the material from the first zone to the sixth zone of the extruder gradually, and discharging; S5, cooling the extruded product in a cooling water tank, and cutting the dried product after water cooling using a pelletizer, thereby obtaining the product. In step S2, the mass fraction of each reaction component is as follows: 100 parts of PVDF, 0.1-0.3 parts of initiator, 5-10 parts of dispersion functional part, 1-5 parts of co-grafting functional part, and 2-5 parts of anti-gel functional part. The co-grafting functional part comprises one or more of vinyltrimethoxysilane, styrene ethyltrimethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, vinyltri(2-methoxyethoxy)silane, and (4-vinylphenylmethyl)trimethylsilane. The dispersion functional part comprises one or more of maleic anhydride, maleic acid, α-linolenic acid, oleic acid, linoleic acid, and arachidonic acid, or is allyl polyethylene glycol with a molecular weight of 500-1800. The anti-gel functional part comprises one or more of phenylhydrazine, acetylphenylhydrazine, 2-hydrazinoethanol, ethylhydrazine, and benzylhydrazine, or comprises one or more of acetylhydrazine, butyrylhydrazine, 4-hydroxybenzoylhydrazine, 4-hydroxyphenylacetylhydrazine, hexanoylhydrazine, octanoylhydrazine, benzoylhydrazine, phenylacetylhydrazine, and phenoxyacetylhydrazine.

2. The preparation method of the PVDF material for positive electrode slurry with dispersion and anti-gelling function as described in claim 1, characterized in that, In step S1, the molecular weight of the PVDF powder is 200000-500000, the temperature of the oven is 80-120℃, and the drying time is 12-24h.

3. The preparation method of the PVDF material for positive electrode slurry with dispersion and anti-gelling function as described in claim 1, characterized in that, The initiator is one or more of benzoyl peroxide, dicumyl peroxide, dodecanoyl peroxide, di-tert-butylcumyl peroxide, and tert-butyl peroxybenzoate.

4. The preparation method of the PVDF material for positive electrode slurry with dispersion and anti-gelling function as described in claim 1, characterized in that, In step S4, the twin-screw extruder is provided with six temperature control zones, which are sequentially: the first zone 80±2℃, the second zone 100±2℃, the third zone 150±2℃, the fourth zone 170±2℃, the fifth zone 170±2℃, and the sixth zone 175±2℃.

5. A dispersion anti-gel functional PVDF material for positive electrode slurry prepared by the method of any one of claims 1 to 4.

6. The dispersion anti-gel functional PVDF material of claim 5 for use as a positive electrode slurry for lithium batteries.

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