Modified vinylidene fluoride polymer, preparation method therefor, and use thereof

Abstract

The present invention relates to a technique for preparing a vinylidene fluoride polymer and provides a modified vinylidene fluoride polymer, a preparation method therefor, and use thereof. Using the method of the present invention to prepare a modified vinylidene fluoride polymer can further improve the mechanical properties of the obtained polymer and improve the application performance of the polymer as an electrode binder. The preparation method for the modified vinylidene fluoride polymer comprises reacting components including vinylidene fluoride and an acrylic acid raw material to prepare the modified vinylidene fluoride polymer, wherein the mass content of a dimer in the acrylic acid raw material is 0.1-1000 ppm, the mass content of acetic acid is 0.1-2000 ppm, and the mass content of a polymerization inhibitor is 50-200 ppm.

Description

A modified vinylidene fluoride polymer, its preparation method and application Technical Field

[0001] This invention relates to the preparation technology of vinylidene fluoride polymers, specifically to a modified vinylidene fluoride polymer, its preparation method, and its applications. Background Technology

[0002] The main unique characteristic of polyvinylidene fluoride (PVDF) within the family of fluorinated polymers lies in the presence of both CF and CH bonds. The CF bonds provide structural stability, excellent mechanical properties, aging resistance, high and low temperature resistance, insulation, chemical resistance, sun resistance, and flame retardancy. The CH bonds provide solubility, making it easy to process. Therefore, PVDF resin is particularly suitable for use in coatings and viscous adhesives, such as in the preparation of coatings, lithium-ion battery separator coatings, photovoltaic backsheet coatings, and lithium-ion battery cathode adhesives.

[0003] Polyvinylidene fluoride (PVDF) is known in the art to be suitable as an adhesive for manufacturing electrodes (particularly positive electrodes), for manufacturing composite membranes, and / or for coating porous membranes for use in non-aqueous electrochemical devices such as batteries. Fluoropolymers have traditionally been used for applications requiring specific properties, such as low surface energy, high chemical resistance, aging resistance, and electrochemical stability. However, these advantageous properties also make fluoropolymers difficult to handle and limit their applications. For example, the lack of polar functional groups on fluoropolymers makes them difficult to adhere to substrates, difficult to promote crosslinking, difficult to provide sites for subsequent chemical modifications, difficult to wet with water, and difficult to improve hydrophilicity.

[0004] Therefore, it is necessary to copolymerize or graft the molecular chain segments of polyvinylidene fluoride to add polar functional groups of fluoropolymers to the molecular chain segments of the polymer in various ways, so as to enhance the special properties of fluoropolymers, such as improving their adhesion to polar substrates such as metals and glass.

[0005] Patent CN101679563B discloses a method for preparing a linear semi-crystalline fluoropolymer. The method involves copolymerizing vinylidene fluoride with 0.05-10% of a hydrophilic (meth)acrylic acid monomer (preferably acrylic acid or hydroxyethyl acrylate). Under a polymerization pressure greater than the VDF critical pressure of 4.43 MPa, an aqueous solution of the (meth)acrylic acid comonomer is continuously fed into the fluoropolymer, ultimately resulting in a fluoropolymer with at least 40% randomly distributed (meth)acrylic acid comonomer units. The resulting fluoropolymer exhibits significantly improved bonding strength and thermal stability, making it suitable as a binder for lithium-ion batteries.

[0006] Patent CN 109075343 B discloses an adhesive composition, an electrode mixture, an electrode, and a non-aqueous electrolyte secondary battery. The vinylidene fluoride copolymer composition comprises vinylidene fluoride and an acrylic acid monomer, wherein the acrylic acid monomer is at least one selected from acrylic acid and methacrylic acid. The ratio (Mn2 / Mnl) of the number-average molecular weight of the vinylidene fluoride copolymer composition after adsorption onto alumina to the number-average molecular weight (Mnl) of the vinylidene fluoride copolymer composition before adsorption onto alumina is less than 2, and the melting point of the vinylidene fluoride copolymer composition is above 160°C. The prepared vinylidene fluoride copolymer exhibits sufficient adhesiveness and achieves excellent dispersibility of conductive additives in the adhesive composition.

[0007] Patent CN104497190B discloses a method for preparing a vinylidene fluoride polymer (VDF) for use as a binder in lithium-ion battery electrode materials. The method involves adding deionized water, a dispersant (sodium carboxymethyl cellulose), a pH adjuster (sodium pyrophosphate, sodium acid pyrophosphate), a chain transfer agent (diethyl carbonate), vinylidene fluoride, and a second monomer (acrylic acid monomer) to a polymerization reactor. The reactor is heated to 32–52°C, the reaction pressure is 6.0–9.0 MPa, the rotation speed is 800–1600 r / min, an initiator (perfluoroacyl peroxide) is added, and the reaction is terminated after 4–8 hours. The resulting VDF polymer has a slurry concentration of 30–50% and is spray-dried at 80–130°C. This yields a VDF polymer with ultra-high molecular weight, fine particle size, high purity, and high high-temperature resistance and colorability. Lithium-ion batteries made from this polymer have advantages such as low binder usage, high peel strength, high energy density, and high cycle capacity retention.

[0008] Patent CN 103282393 B discloses a hydrophilic vinylidene fluoride polymer and relates to a method for manufacturing a grafted fluorinated polymer comprising at least one grafted side chain containing one or more glycoside repeating units. The method comprises polymerizing vinylidene fluoride (VDF), optionally one or more additional fluorinated monomers, and optionally one or more (meth)acrylic acid monomers, in the presence of at least one polysaccharide derivative having a dynamic viscosity of less than 15 mpax, as measured according to ASTM D445 in a 2% by weight aqueous solution at 20°C. The provided polymer exhibits excellent hydrophilic surface properties while retaining other excellent properties of the vinylidene fluoride polymer, such as thermal stability and mechanical properties, and can be manufactured in an easy manner without involving subsequent grafting or blending or other chemical modifications.

[0009] In addition, many other patents describe methods for improving the adhesion of vinylidene fluoride polymers. For example, patent US2020190239A1 uses acrylate monomers to copolymerize and modify vinylidene fluoride, and through precise process control, avoids sudden heat generation that could cause uncontrolled exceeding of the set reaction temperature to obtain a vinylidene fluoride polymer further containing repeating units derived from (meth)acrylic acid monomers, exhibiting good thermal stability. Patent US5415958A discloses copolymerization of vinylidene fluoride with unsaturated dicarboxylic acid monoester polar monomers, introducing carbonyl groups into the PVDF backbone to improve its adhesion to different substrates.

[0010] The aforementioned patents, employing different processes and methods, have achieved some positive results in copolymerizing and modifying vinylidene fluoride polymers with acrylic monomers. However, there is still room for improvement in the existing technology for copolymerizing and modifying vinylidene fluoride polymers.

[0011] Summary of the Invention

[0012] This invention provides a modified vinylidene fluoride polymer, its preparation method, and its application. The modified vinylidene fluoride polymer prepared by the method of this invention can further improve the mechanical properties of the obtained polymer and its application performance as an electrode adhesive.

[0013] To achieve its objective, the present invention provides the following technical solution:

[0014] This invention provides a method for preparing a modified vinylidene fluoride polymer, wherein the modified vinylidene fluoride polymer is prepared by reacting components including vinylidene fluoride and acrylic acid raw materials.

[0015] The acrylic acid raw material contains 0.1-1000 ppm of dimer, 0.1-2000 ppm of acetic acid, and 50-200 ppm of polymerization inhibitor.

[0016] Preferably, the dimer content in the acrylic acid raw material is 90-1000 ppm, more preferably 90-700 ppm.

[0017] Preferably, the mass content of acetic acid in the acrylic acid raw material is 350-2000 ppm, more preferably 350-1000 ppm.

[0018] Preferably, the mass content of the polymerization inhibitor in the acrylic acid raw material is 50-100 ppm;

[0019] In some embodiments, the polymerization inhibitor is selected from one or more of hydroquinone, phenothiazine, and p-hydroxyanisole.

[0020] Preferably, the purity of the acrylic acid raw material is ≥99.8%, more preferably ≥99.9%, and even more preferably ≥99.95%.

[0021] In some embodiments, the amount of acrylic acid raw material used is 0.01-5 wt% of the amount of vinylidene fluoride used, preferably 0.01-2 wt%.

[0022] Preferably, the intrinsic viscosity of the modified vinylidene fluoride polymer in an N,N-dimethylacetamide solution at 25°C is 2.0-4.0 dL / g.

[0023] In some embodiments, the components used to prepare the polymer optionally include other fluorinated monomers;

[0024] Preferably, the other fluorinated monomers are selected from one or more of vinyl fluoride, trifluoroethylene, tetrafluoroethylene, trifluorochloroethylene, 2,3,3,3-tetrafluoropropylene, hexafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropylene, 3,3,3-trifluoro-1-propylene, 2-trifluoromethyl-3,3,3-trifluoropropylene, and fluorinated vinyl ethers; preferably, the fluorinated vinyl ethers are one or more of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, and perfluorobutyl vinyl ether.

[0025] Preferably, the amount of the other fluorinated monomers is 0-10 wt% of the amount of vinylidene fluoride, more preferably 0.1-10 wt%, and even more preferably 0.1-5 wt%.

[0026] In some embodiments, the components used to prepare the polymer further include one or more of a polymerization stabilizer, an initiator, and optional other auxiliaries;

[0027] Preferably, the polymerization stabilizer is selected from one or more of cellulose compounds, polyvinyl alcohol, polyethylene glycol, and polyacrylic acid; preferably, the cellulose compound is selected from one or more of methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose; preferably, the amount of the polymerization stabilizer is 0.01-1.5 wt% of the amount of vinylidene fluoride.

[0028] Preferably, the initiator is an organic peroxide initiator, preferably one or more of the following: diisopropyl peroxide, diethyl peroxide, dicyclohexyl peroxide, di-2-ethylhexyl peroxide, 2,2'-azobis(2,4-dimethylpentanolyl), 2,2'-azobis(4-methoxy-2,4-dimethylpentanolyl), tert-butyl peroxyneodecanate, tert-butyl peroxynepentanoate, tert-pentyl peroxynepentanoate, benzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxymaleate, dicumyl peroxide, cumyl hydroperoxide, tert-butyl peracetic acid, 2,2'-di(tert-butylperoxy)butane, tert-butyl cumyl peroxide, and tert-butyl peroxyisopropyl carbonate; preferably, the amount of the initiator is 0.01-2 wt% of the amount of vinylidene fluoride, more preferably 0.1-1 wt%.

[0029] Preferably, the other additives include pH adjusters and / or chain transfer agents; preferably, the chain transfer agent is 0.01-1 wt% of the amount of vinylidene fluoride added; preferably, the reaction is carried out in the pH range of 4-8 by adding the pH adjuster.

[0030] In some embodiments, the polymer is prepared by one or more processes selected from suspension polymerization, emulsion polymerization, and supercritical CO2 polymerization, with suspension polymerization being the preferred method.

[0031] In some embodiments, the polymerization reaction temperature for preparing the polymer is 40-100°C, and the pressure is gauge pressure 3.0-15.0 MPa.

[0032] The present invention also provides a modified vinylidene fluoride polymer prepared by the preparation method described above.

[0033] The present invention also provides the application of the modified vinylidene fluoride polymer as described above in battery electrode adhesives or in the preparation of battery electrode adhesive compositions; the battery being, for example, a non-hydrolyzable electrolyte secondary battery;

[0034] Preferably, the adhesive composition comprises the modified vinylidene fluoride polymer, the electrode active material, the non-aqueous solvent, and optionally a conductive additive;

[0035] More preferably, the adhesive composition comprises, by weight, 0.5 to 10 parts, preferably 1 to 5 parts, of a modified vinylidene fluoride polymer, and 90 to 99.5 parts, preferably 95 to 99 parts, of an electrode active material; the amount of the non-aqueous solvent is 4 to 100 times, more preferably 6 to 50 times, the mass of the modified vinylidene fluoride polymer; and the amount of the conductive additive is 0.02 to 4 times, more preferably 0.1 to 2 times, the mass of the modified vinylidene fluoride polymer.

[0036] The technical solution provided by this invention has the following beneficial effects:

[0037] The modified vinylidene fluoride polymer prepared by the method of the present invention has excellent mechanical properties and thermal stability, as well as excellent product purity. Using the modified vinylidene fluoride polymer provided by the present invention in electrode adhesives can improve the application effect of electrode adhesives.

[0038] This invention controls the dimer content, acetic acid content, and polymerization inhibitor content in the acrylic monomer used to prepare the modified vinylidene fluoride polymer within the above-mentioned range, which is beneficial to improving reaction efficiency, while also taking into account the good application performance of the resulting polymer in electrode adhesives, such as improved mechanical properties and improved battery cycle performance. Detailed Implementation

[0039] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0041] This invention provides a method for preparing a modified vinylidene fluoride polymer, wherein the modified vinylidene fluoride polymer is prepared by reacting components including vinylidene fluoride and acrylic acid raw materials.

[0042] The acrylic acid raw material contains 0.1-1000 ppm of dimer (e.g., 0.1, 10, 50, 90, 200, 500, 700, 1000 ppm), 0.1-2000 ppm of acetic acid (e.g., 0.1, 10, 50, 90, 200, 350, 500, 700, 1000, 1500, 2000 ppm), and 50-200 ppm of polymerization inhibitor (e.g., 50, 90, 100, 150, 200 ppm).

[0043] The modified vinylidene fluoride polymer prepared by the method of the present invention has excellent mechanical properties and thermal stability, as well as excellent product purity. Using the modified vinylidene fluoride polymer provided by the present invention in electrode adhesives can improve the application effect of electrode adhesives.

[0044] Through extensive research, the inventors discovered that the dimer content, acetic acid content, and polymerization inhibitor content in the acrylic acid monomer raw material affect the reaction efficiency of the copolymerization of acrylic acid and vinylidene fluoride, as well as the properties of the prepared modified vinylidene fluoride polymer, such as mechanical properties and thermal stability, ultimately impacting the performance of the resulting polymer as an electrode binder. The inventors found that simultaneously controlling the dimer content, acetic acid content, and polymerization inhibitor content in the acrylic acid monomer used to prepare the modified vinylidene fluoride polymer within the aforementioned ranges improves reaction efficiency while also ensuring good performance of the resulting polymer as an electrode binder, such as improved mechanical properties and improved battery cycle performance.

[0045] As is well known, the main industrial methods for manufacturing acrylic acid include acetylene carbonylation, 3-hydroxypropionitrile, ketene, acrylonitrile hydrolysis, high-pressure Rapper process, modified Rapper process, and propylene oxidation. Among these, the most widely used is the propylene gas-phase oxidation method. This method uses propylene, air, and water as raw materials, and produces acrylic acid through an oxidation reaction under the action of a catalyst. The process includes three steps: oxidation reaction, absorption, and separation. The oxidation reactor is generally a tubular or tower reactor, with the reaction temperature controlled at 140-180℃ and the pressure controlled at 0.2-0.4 MPa. The gas generated in the reaction is cooled and absorbed to obtain an aqueous solution of acrylic acid, which is then separated by distillation to obtain pure acrylic acid. However, the production of acrylic acid inevitably produces byproducts and impurities such as acetic acid. Acetic acid, as one of the main impurities, has a boiling point (118℃) and physical properties very close to those of acrylic acid (boiling point 142℃), making it difficult to remove. Furthermore, acrylic acid is a vinyl monomer that polymerizes very easily. During its production, transportation, and storage, it readily undergoes polymerization reactions, such as forming acrylic acid dimers or generating large-molecule, insoluble, white flocculent or gel-like substances. This affects the product quality of acrylic acid and the polymerization reaction, and can even lead to serious safety accidents. Therefore, a certain amount of polymerization inhibitor needs to be added to acrylic acid to prevent or slow down its self-polymerization reaction. The preferred polymerization inhibitors for acrylic acid are one or more of hydroquinone, phenothiazine, and p-hydroxyanisole. The inventors have discovered that in the process of preparing modified vinylidene fluoride polymers, the acetic acid content, dimer content (i.e., acrylic acid dimer content), and polymerization inhibitor content in the acrylic acid monomer have a significant impact on the reaction and polymerization rate of acrylic acid and vinylidene fluoride, the quality of the vinylidene fluoride polymer product, and its performance as an electrode binder. By controlling the dimer content in the acrylic acid raw material to 0.1-1000 ppm, the acetic acid content to 0.1-2000 ppm, and the polymerization inhibitor content to 50-200 ppm, not only can the polymerization efficiency be improved, but also the mechanical properties of the resulting vinylidene fluoride polymer can be improved, as well as its performance as an electrode binder, which helps to improve battery cycle performance.

[0046] Preferably, the mass content of the dimer in the acrylic acid raw material is 90-1000 ppm, more preferably 90-700 ppm; preferably, the mass content of the acetic acid in the acrylic acid raw material is 350-2000 ppm, more preferably 350-1000 ppm; this is beneficial for obtaining high-performance vinylidene fluoride polymers and for keeping the production and refining costs of acrylic acid within a reasonable range.

[0047] In this invention, the mass content of the polymerization inhibitor in the acrylic acid raw material is controlled at 50-200 ppm, preferably 50-100 ppm. Excessive polymerization inhibitor content in acrylic acid can affect the polymerization efficiency of acrylic acid and vinylidene fluoride, or prolong the induction period of the reaction. Conversely, insufficient polymerization inhibitor content in acrylic acid leads to excessively rapid polymerization, resulting in an overly vigorous reaction and adversely affecting the quality and performance of the resulting polymer. It can also cause an excessively rapid dimer formation rate, affecting the quality of the acrylic acid product and even leading to self-polymerization, posing significant safety risks. Controlling the polymerization inhibitor content in acrylic acid within the above-mentioned range, along with controlling the dimer content and acetic acid content, not only achieves good polymerization efficiency but also results in a polymer with optimal mechanical properties required as an electrode binder, and improves the cycle performance of the battery.

[0048] In a preferred embodiment, the mass content of dimer in the acrylic acid raw material is controlled to be 90-700 ppm, the mass content of acetic acid to be 350-1000 ppm, and the mass content of polymerization inhibitor to be 50-100 ppm. This not only eliminates the need for more stringent purification requirements on the acrylic acid raw material and avoids excessively high purification costs, but also allows for the preparation of modified vinylidene fluoride polymers based on this acrylic acid raw material. The required reaction induction period is short, and the reaction efficiency is high. Furthermore, the resulting polymer, when used as an electrode adhesive, not only has better bonding strength but also facilitates better battery cycle performance.

[0049] In a preferred embodiment, the acrylic acid has a purity of ≥99.8%, preferably ≥99.9%, and more preferably ≥99.95%.

[0050] In some embodiments, the amount of acrylic acid raw material used is 0.01-5 wt% of the amount of vinylidene fluoride used, for example, 0.01, 0.5, 1, 1.5, 2 wt%, etc., preferably 0.01-2 wt%.

[0051] Preferably, the intrinsic viscosity of the modified vinylidene fluoride polymer in an N,N-dimethylacetamide solution at 25°C is 2.0-4.0 dL / g. The inventors have found that modified vinylidene fluoride polymers with the above-mentioned intrinsic viscosity range have a relatively ideal molecular weight level, which helps to balance good melt processing characteristics and solubility in polar solvents, while also facilitating good mechanical properties and structural stability. Intrinsic viscosity that is too high or too low may lead to difficulties in melt processing and incomplete dissolution in polar solvents, resulting in processing and usage problems; while controlling the specific viscosity within the above range helps to further ensure that mechanical properties and structural stability meet usage requirements.

[0052] In some embodiments, the components used to prepare the polymer optionally include other fluorinated monomers; these other fluorinated monomers are selected, for example, from, but not limited to, vinyl fluoride, trifluoroethylene, tetrafluoroethylene, trifluorochloroethylene, 2,3,3,3-tetrafluoropropylene, hexafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropylene, 3,3,3-trifluoro-1-propylene, 2-trifluoromethyl-3,3,3-trifluoropropylene, and fluorinated vinyl ethers; preferably, the fluorinated vinyl ether is one or more of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, and perfluorobutyl vinyl ether; preferably, the amount of the other fluorinated monomers is 0-10 wt% of the amount of vinylidene fluoride, more preferably 0.1-10 wt%, and more preferably 0.1-5 wt%.

[0053] In some embodiments, the components used to prepare the polymer further include polymerization stabilizers and / or initiators, and optionally other auxiliaries;

[0054] The addition of a polymerization stabilizer is beneficial for improving the dispersibility of vinylidene fluoride and other fluorinated and non-fluorinated comonomers in water. Preferably, the polymerization stabilizer is selected from one or more of cellulose compounds, polyvinyl alcohol, polyethylene glycol, and polyacrylic acid. More preferably, the cellulose compounds are selected from one or more of methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose. Preferably, the amount of the polymerization stabilizer is 0.01-1.5 wt% of the amount of vinylidene fluoride.

[0055] Preferably, the initiator is an organic peroxide initiator, preferably one or more of the following: diisopropyl peroxide, diethyl peroxide, dicyclohexyl peroxide, di-2-ethylhexyl peroxide, 2,2'-azobis(2,4-dimethylpentanolyl), 2,2'-azobis(4-methoxy-2,4-dimethylpentanolyl), tert-butyl peroxyneodecanate, tert-butyl peroxynepentanoate, tert-pentyl peroxynepentanoate, benzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxymaleate, dicumyl peroxide, cumyl hydroperoxide, tert-butyl peracetic acid, 2,2'-di(tert-butylperoxy)butane, tert-butyl cumyl peroxide, and tert-butyl peroxyisopropyl carbonate; preferably, the amount of the initiator is 0.01-2 wt% of the amount of vinylidene fluoride, more preferably 0.1-1 wt%.

[0056] Preferably, the other auxiliaries include pH adjusters and / or chain transfer agents. The chain transfer agent is used to adjust the molecular weight of the resulting vinylidene fluoride polymer. The chain transfer agent can be suitably selected from known compounds capable of adjusting the molecular weight of fluoropolymers, such as, but not limited to, oxygen-containing compounds, such as one or more of alcohols, carbonates, ketones, esters, and ethers; halogenated hydrocarbons, such as one or more of chlorinated hydrocarbons, hydrochlorocarbons, chlorofluorocarbons, and hydrochlorofluorocarbons; and alkanes, such as ethane and propane. Preferably, the chain transfer agent is one or more of diethyl carbonate, ethyl acetate, and diethyl malonate, and its addition amount is preferably 0.01-1 wt% of the vinylidene fluoride addition. Optionally, a pH adjuster may be included in the polymerization reaction mixture to maintain a controlled pH throughout the polymerization reaction, generally preferably controlled in the range of about 4-8, to minimize the formation of undesirable colors in the product. The pH adjuster may include one or more of organic acids and their alkali metal salts, inorganic acids and their alkali metal salts, and preferably one or more of phosphates and acetates. The phosphate can be a single salt of phosphate or a mixture of multiple salts of phosphate.

[0057] Specifically, the polymer can be prepared using one or more processes selected from suspension polymerization, emulsion polymerization, and supercritical CO2 polymerization. These processes are common in the art for preparing vinylidene fluoride polymers, and can be carried out using existing processes in the art, without any particular limitation. Preferably, the polymer is prepared using a suspension polymerization process, specifically, the modified vinylidene fluoride polymer of the present invention is prepared by suspension polymerization in an aqueous solution. More preferably, the amount of vinylidene fluoride in the polymer is not less than 80 wt%, which is beneficial for obtaining a vinylidene fluoride polymer with excellent chemical resistance, weather resistance, and heat resistance.

[0058] Generally, oxygen removal is required when the polymerization reactor is empty or after the polymerization reaction aids are added. This is usually done by multiple nitrogen purgings under negative pressure. It is preferable to control the oxygen content below 20 ppm, and more preferably below 10 ppm.

[0059] It is known that in the polymerization system, an appropriate amount of water is added to form a suspension. Preferably, the amount of water added is such that the solid content of the polyvinylidene fluoride polymer dispersion obtained by polymerization is 20-50%, and more preferably 20-40%.

[0060] As an example, the specific steps for preparing the modified vinylidene fluoride polymer of the present invention using suspension polymerization include, for example:

[0061] (a) Add deionized water, polymerization stabilizer and optional chain transfer agent to the polymerization reactor, stir and mix evenly, and purge with nitrogen to remove oxygen;

[0062] (b) Add an initiator to the polymerization reactor, and add vinylidene fluoride, acrylic acid, or / and other fluorinated monomers, and heat to start the polymerization reaction;

[0063] (c) Continue to add the remaining monomers and optional initiators and optional chain transfer agents as needed, and keep the polymerization temperature and polymerization pressure stable within the required range;

[0064] (d) When the addition of the monomers is completed and the polymerization pressure is less than the set value, the polymerization reaction ends and a fluoropolymer dispersion is obtained;

[0065] (e) Degas, wash, filter, and dry as needed to obtain the desired modified vinylidene fluoride polymer.

[0066] In this invention, the polymerization reactor used for the polymerization reaction can be a type of polymerization reactor known in the art, such as, but not limited to, a high-pressure spherical reactor, a high-pressure horizontal reactor, and a high-pressure vertical reactor. In some examples, the length-to-diameter ratio (L / D) of the polymerization reactor is less than 2, more preferably less than 1.5, which is beneficial to ensuring the heat and mass transfer effect of the polymerization reaction. In addition, the stirring method in the polymerization reactor can be one or more of the following: a three-bladed inclined impeller, a four-bladed inclined impeller, an anchor impeller, a frame impeller, and a ribbon impeller.

[0067] Preferably, the polymerization reaction temperature for preparing the polymer is 40-100℃, and the pressure is gauge pressure 3.0-15.0 MPa.

[0068] The pressure inside the polymerization reactor is sufficiently exceeded by the temperature rise within the reactor to the initial polymerization temperature, thus exceeding the critical pressure of vinylidene fluoride (4.38 MPa). Vinylidene fluoride is primarily used in the polymerization reaction as a supercritical fluid. The pressure within the reaction system generally decreases as vinylidene fluoride monomer is used for polymerization, therefore, a continuous supply of vinylidene fluoride monomer is usually required to maintain a stable pressure within the polymerization reactor. If the pressure inside the reactor when the reaction system is heated to the initial polymerization temperature is too high, a high-pressure-resistant container may be required; if the pressure is too low, the polymerization reaction time may be prolonged, reducing productivity. From the viewpoint of shortening the reaction time, the pressure inside the reactor when the reaction system is heated to the initial polymerization temperature is preferably 3 MPa or higher, more preferably 4.4 MPa or higher. Furthermore, from the viewpoint of reducing the cost of the polymerization reactor, the pressure is preferably 15 MPa or lower, more preferably 13 MPa or lower. This pressure can be adjusted based on various key factors such as the supply rate of vinylidene fluoride and comonomer, the initial polymerization temperature, and the monomer density.

[0069] Meanwhile, the initial polymerization temperature can be appropriately determined within a temperature range sufficient to bring vinylidene fluoride in the reactor to a supercritical state. Within this range, if the initial polymerization temperature is too low, the reaction time of suspension polymerization becomes longer, which sometimes results in a lower yield of vinylidene fluoride polymer. If the initial polymerization temperature is too high, the pressure of the suspension polymerization reaction system increases, sometimes requiring a reactor with higher pressure resistance. From the viewpoint of improving the yield of vinylidene fluoride polymer, the initial polymerization temperature is preferably 40°C or higher, more preferably 45°C or higher. Furthermore, from the viewpoint of suppressing the pressure surge of the reaction system, the initial polymerization temperature is preferably 100°C or lower, more preferably 70°C or lower.

[0070] In this invention, the endpoint control of suspension polymerization is appropriately selected by considering the balance between reducing the amount of unreacted monomers and extending the polymerization time (i.e., the productivity of the product polymer). For example, in addition to sampling the reaction products, the endpoint of suspension polymerization can also be determined based on the temperature rise and accompanying pressure changes within the reaction system.

[0071] In some examples, the modified vinylidene fluoride polymer is obtained in powder form, which is obtained by dehydrating, washing, and drying the polymer slurry after suspension polymerization. The preparation process provided by the present invention can improve reaction efficiency and shorten polymerization time. Specifically, the polymerization time from the point at which the initial polymerization temperature is reached after the raw materials are supplied to the reactor to the end of polymerization is preferably within 20 hours, more preferably within 15 hours.

[0072] The present invention also provides a modified vinylidene fluoride polymer prepared by the preparation method described above.

[0073] The present invention also provides the application of the modified vinylidene fluoride polymer prepared by the preparation method described above in electrode adhesives for batteries, or in the preparation of electrode adhesive compositions for batteries, for example, positive electrode adhesive compositions; wherein the battery is, for example, a non-hydrolyzable electrolyte secondary battery, and the modified vinylidene fluoride polymer provided by the present invention is particularly suitable for use in electrode adhesives for non-hydrolyzable electrolyte secondary batteries.

[0074] Preferably, the electrode binder composition comprises the modified vinylidene fluoride polymer, electrode active material, non-aqueous solvent, and optional conductive additives, etc.

[0075] More preferably, the electrode adhesive composition comprises, by weight, 0.5 to 10 parts, preferably 1 to 5 parts, of a modified vinylidene fluoride polymer, and 90 to 99.5 parts, preferably 95 to 99 parts, of an electrode active material; the amount of the non-aqueous solvent is 4 to 100 times, more preferably 6 to 50 times, the mass of the modified vinylidene fluoride polymer; and the amount of the conductive additive is 0.02 to 4 times, more preferably 0.1 to 2 times, the mass of the modified vinylidene fluoride polymer.

[0076] An electrode for a non-aqueous electrolyte secondary battery can be obtained by coating the above-described electrode binder composition onto a metal current collector and then drying it. The metal current collector is the electrode substrate and serves as the terminal for extracting electricity. Materials used for the metal current collector include, for example, iron, stainless steel, steel, copper, aluminum, nickel, and titanium; aluminum foil is preferred. The thickness of the metal current collector is typically 5–100 μm, preferably 5–20 μm. The coating method for the electrode binder composition can be selected from wire rod coating machines, blade coating machines, and roller coating machines. The electrode binder composition is coated on at least one side of the current collector, preferably both sides. The drying temperature of the electrode binder composition is preferably 50–150°C, and the drying time is preferably 30–300 minutes. The drying pressure is not particularly limited and is usually carried out under atmospheric pressure or reduced pressure. Furthermore, after the electrode binder composition is dried, it can be pressed to increase the electrode energy density.

[0077] The electrode active material is not particularly limited, and known negative electrode active materials and positive electrode active materials can be used. As a negative electrode active material, it can be carbon material, silicon material, metal / alloy material, metal oxide, etc., with carbon material being preferred, including artificial graphite, natural graphite, difficult-to-graphitize carbon, and easily-graphitize carbon. One type of carbon material can be used, or two or more can be used. As a positive electrode active material, it is generally a lithium-based positive electrode active material containing lithium, such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and nickel-cobalt-manganese ternary materials.

[0078] The non-aqueous solvent is used to dissolve the modified vinylidene fluoride polymer, and may be selected from one or more of N-methyl-2-pyrrolidone, dimethylformamide, N,N-dimethylacetamide, N,N-dimethyl sulfoxide, hexamethylphosphoramide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate, acetone, methyl ethyl ketone, and tetrahydrofuran. The amount of non-aqueous solvent used is, for example, 4-100 times the mass of the modified vinylidene fluoride polymer, more preferably 6-50 times. Within this range, the solution viscosity of the electrode adhesive composition can be made moderate, and the handling can be made easy.

[0079] The conductive additive is mainly used to improve the electrochemical performance of the electrode binder composition. The conductive additive may be selected from one or more carbonaceous materials such as carbon black, carbon nanotubes, graphite powder, and graphite fibers, as well as metal powders or fibers such as nickel and aluminum. The amount of conductive additive used is, for example, 0.02-4 times the mass of the modified vinylidene fluoride polymer, more preferably 0.1-2 times.

[0080] There is no particular limitation on the manufacturing method of the electrode binder composition for non-aqueous electrolyte secondary batteries. The components can be mixed using known methods, and there is no particular limitation on the order in which the components are mixed.

[0081] The present invention will be further illustrated by the following embodiments, but it should not be construed as the present invention being limited to these embodiments.

[0082] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0083] The main test methods involved in the following embodiments are as follows:

[0084] <1> Conductivity test

[0085] An aqueous solution of the vinylidene fluoride polymer after the polymerization reaction was completed was taken and its conductivity was tested using a Mettler Toledo S230K conductivity meter.

[0086] <2> Testing of acrylic acid monomer content

[0087] The content of acrylic acid monomer in the prepared vinylidene fluoride polymer was determined by NMR (Bruker 600MHz liquid nuclear magnetic resonance spectrometer) H-s spectrometry analysis.

[0088] <3> Intrinsic viscosity test

[0089] Weigh 0.02 g of vinylidene fluoride polymer sample, accurate to 0.0001 g, and place it in a 25 mL volumetric flask. Add 15-20 mL of N,N-dimethylacetamide, seal the flask, shake, and place it in a 120℃ drying oven for 4-6 hours to dissolve. Visually inspect the sample; if it appears as a clear, transparent liquid, it is considered completely dissolved. Then, transfer the volumetric flask to a constant temperature water bath at 25℃±0.2℃ until it reaches a constant temperature. Add the pre-concentrated N,N-dimethylacetamide at 25℃ to the mark and shake well. Use an Ubbelohde viscometer with an inner diameter of 0.56-0.60 mm. Calculation of test results:

[0090] Intrinsic viscosity is denoted by [η], and the result is calculated using the following formula:

[0091] In the formula:

[0092] [η]—intrinsic viscosity, in dL / g; t—time for the solution to flow through the viscometer, in s; t0—time for the pure solvent to flow through the viscometer, in s; m—mass of the substance to be measured, in g; 0.25—dissolved volume of the substance to be measured, in dL.

[0093] <4> Preparation of electrodes for non-aqueous electrolyte secondary batteries

[0094] Add 5g of the prepared vinylidene fluoride polymer to 100g of N-methylpyrrolidone and stir until the fluorinated polymer is completely dissolved. Then add 3.75g of ultrafine carbon powder Super P and 1.25g of carbon nanotubes to the solution and continue mixing with a mechanical stirrer until homogeneous. Then add 240g of electrode active material (nickel-cobalt-manganese ternary material LiNi) to the mixture. x Co y Mn z O2 (where x+y+z=1) is mixed, degassed, and allowed to stand to obtain a paste-like electrode adhesive composition for secondary batteries with the required viscosity and fineness (viscosity between 4000-8000cp, fineness ≤20 micrometers), free of oil stains, bubbles, and suspended particles. The obtained electrode adhesive composition is then uniformly coated onto aluminum foil with a wet thickness of 350μm using a coating machine. The foil is heated in a vacuum oven at 120℃ for 150 minutes and then compacted using a roller press to obtain a coated non-aqueous electrolyte secondary battery electrode.

[0095] <5> Bond strength test

[0096] Will <4> The electrodes for non-aqueous electrolyte secondary batteries prepared in this manner were cut into strips of 20cm × 2.5cm. These strips were bonded to a rigid aluminum plate using a double-sided adhesive (the adhesive was applied to the coated side of the strip). A GOTECH AI-7000-LA tensile testing machine was used to perform a peel test, fixing one end to the rigid aluminum plate and the other end to the strip. The test standard was ISO 4624 Adhesion Pull-Off Test, with a peel angle of 180° and a clamp displacement rate set to 100mm / min, to determine the peel strength between the electrode adhesive composition for non-aqueous electrolyte secondary batteries and the metal current collector (aluminum foil).

[0097] <6> Battery cycle performance test

[0098] In an argon atmosphere glove box meeting environmental standards (water content <1 ppm, oxygen content <1 ppm), 30 parts by mass of ethylene carbonate, 20 parts by mass of diethyl carbonate, and 45 parts by mass of methyl ethyl carbonate were mixed thoroughly, and then 5.0 parts by mass of lithium hexafluorophosphate were added to prepare the electrolyte. The separator was a 12 μm thick polyethylene film with a 4 μm thick ceramic coating. The non-aqueous electrolyte secondary battery prepared above was assembled with electrodes (as positive electrodes), electrolyte, separator, and lithium sheet to obtain a simulated lithium-ion battery (half-cell). The cycle performance of the prepared lithium-ion battery was tested using an electrochemical workstation at a current density of 0.5C. The capacity retention rate of the battery after 100 cycles was calculated using the following formula:

[0099] Capacity retention rate (%) after 100 cycles = Discharge capacity after 100 cycles / Discharge capacity after the first cycle.

[0100] <7> Determination of acrylic acid dimer, polymerization inhibitor and acetic acid content in acrylic acid raw materials

[0101] First, take approximately 1 mL of acrylic acid raw material sample, add 10 mL of methanol, and shake at room temperature for 5 minutes to ensure complete dissolution. Then, take 1 mL of the solution and pipette it into a sample vial of the gas chromatograph (Shimadzu GCMS-QP 2020). Add 1 mL of diclofenac internal standard solution (100 μg / mL methanol solution) and mix thoroughly. Place the sample vial in the gas chromatograph for testing. Through detection and calculation by the gas chromatograph, the content and purity of each component in the acrylic acid can be obtained.

[0102] The raw materials required for the experiment are as follows:

[0103] Hydroxypropyl methylcellulose: HPMC, Shandong Heda Chemical, product brand HEADCEL 75HD100;

[0104] tert-butyl peroxypentanoate (TBPP): Hubei Kanos Technology Co., Ltd.

[0105] Acrylic acid raw material a: AA, Wanhua Chemical, product purity ≥99%, p-hydroxyanisole content ≤200ppm.

[0106] The test methods in the examples and comparative examples are as follows:

[0107] Prefabricated Example 1 (Acrylic Raw Material D1)

[0108] Acrylic acid feedstock a and hydrazine hydrate (N2H4 mass fraction 75%) were injected into the acrylic acid purification unit at a mass ratio of 2000:1 and mixed evenly at 25-30℃. During the mixing process, impurities such as aldehydes and ketones in acrylic acid feedstock a reacted with the hydrazine hydrate. The resulting mixture was then fed into a distillation unit. The reactants first entered a distillation column at a temperature of 60-65℃ and a top pressure of 3.0-4.5 kPa for distillation. The gaseous material collected from the distillation column was condensed at a condensation temperature of 21-24℃ to obtain the first condensate. Simultaneously, the liquid material collected from the distillation column was sent to a recovery column. The temperature of the inner tower bottom is maintained at 60-65℃. The gas phase generated in the recovery tower is collected and condensed at 21-24℃ to obtain the second condensate. Both the first and second condensates are passed into the falling film crystallization purification unit for falling film crystallization at a temperature of -23 to -17℃. The uncrystallized liquid phase enters the condensation and sweating heating unit for sweating and cooling at a temperature of 14-17℃. The sweated material and the crystallized material are combined to form high-purity acrylic acid raw material D1, which contains 5 ppm of p-hydroxyanisole, 97 ppm of acrylic acid dimer, 384 ppm of acetic acid, and has a purity of 99.95%.

[0109] Prefabricated Example 2 (Acrylic Raw Material A1)

[0110] A small amount of p-hydroxyanisole was added to the high-purity acrylic acid raw material D1 obtained in Preparative Example 1, so that the mass content of p-hydroxyanisole was 55 ppm, to obtain acrylic acid raw material A1 with an acrylic acid purity of 99.94%.

[0111] Example 1

[0112] The acrylic raw material used in this embodiment is acrylic raw material A1 obtained in pre-preparation example 2, which is prepared into an acrylic aqueous solution with a mass concentration of 1.2%.

[0113] At room temperature, 3350g of deionized water and 2.4g of hydroxypropyl methylcellulose were added to an 8-liter high-pressure polymerization reactor. The reactor was stirred at 600 rpm to ensure thorough mixing. Under vacuum, nitrogen was repeatedly purged to remove oxygen (oxygen content <20 ppm). Then, 7.2g of tert-butyl peroxypentanoate, 85g of acrylic acid aqueous solution, and 2100g of 1,1-vinylidene fluoride were added. The temperature was raised to 50℃ (initial reaction temperature) and the pressure to 10.0 MPa (initial reaction pressure) to begin the polymerization reaction. The temperature was lowered using circulating water. After the reaction temperature stabilized, 1630g of acrylic acid aqueous solution was continuously added, maintaining the reaction pressure at 10.0 MPa. After the monomer replenishment was completed, the reaction temperature was maintained at 50℃. When the reaction pressure dropped to 5.0 MPa, the polymerization reaction ended. The resulting polymer dispersion was then degassed, washed with water, filtered, and dried at 80℃ for 12 hours to obtain vinylidene fluoride polymer resin powder.

[0114] Example 2

[0115] The procedure was carried out in accordance with Example 1, except that the acrylic acid used was acrylic acid raw material A2. This raw material was prepared by adding a small amount of p-hydroxyanisole to acrylic acid raw material A1 prepared in Preparatory Example 2, so that the mass content of p-hydroxyanisole in the raw material reached 95 ppm, and the purity of acrylic acid in the raw material was 99.94%.

[0116] Example 3

[0117] The procedure was carried out in accordance with Example 1, except that the acrylic acid used was acrylic acid raw material A3. This raw material was prepared by adding a small amount of p-hydroxyanisole to acrylic acid raw material A1 prepared in Preparatory Example 2, so that the mass content of p-hydroxyanisole in the raw material reached 155 ppm, and the purity of the acrylic acid in the raw material was 99.93%.

[0118] Example 4

[0119] The procedure was carried out in accordance with Example 1, except that the acrylic acid used was acrylic acid raw material A4. This raw material was obtained by storing acrylic acid raw material A1 prepared in Preparatory Example 2, after which the mass content of acrylic acid dimer in the raw material was 500 ppm and the purity of acrylic acid was 99.91%.

[0120] Example 5

[0121] The procedure was carried out in accordance with Example 1, except that the acrylic acid used was acrylic acid raw material A5. This raw material was obtained by storing acrylic acid raw material A1 prepared in Preparatory Example 2, after which the mass content of acrylic acid dimer in the raw material was 900 ppm and the purity of acrylic acid was 99.87%.

[0122] Example 6

[0123] The procedure was carried out in accordance with Example 1, except that the acrylic acid used was acrylic acid raw material A6. This raw material was obtained by adding a small amount of acetic acid to acrylic acid raw material A1 prepared in Preparatory Example 2. The acetic acid content of this raw material was 884 ppm, and the purity of the acrylic acid was 99.9%.

[0124] Example 7

[0125] The procedure was carried out in accordance with Example 1, except that the acrylic acid used was acrylic acid raw material A7. This raw material was obtained by adding a small amount of acetic acid to acrylic acid raw material A1 prepared in Preparatory Example 2. The acetic acid content in this raw material was 1884 ppm, and the purity of the acrylic acid was 99.8%.

[0126] Comparative Example 1

[0127] The procedure was carried out in accordance with Example 1, except that the acrylic acid raw material used was replaced with industrial acrylic acid (acrylic acid raw material D2), which had a product purity of 99.2%, and contained 185 ppm of p-hydroxyanisole, 2600 ppm of acrylic acid dimer, and 3530 ppm of acetic acid.

[0128] Comparative Example 2

[0129] The procedure was carried out in accordance with Example 1, except that the acrylic acid raw material used was acrylic acid raw material D3. This raw material was obtained by adding a small amount of p-hydroxyanisole to acrylic acid raw material A1 prepared in Preparatory Example 2, wherein the p-hydroxyanisole content was 305 ppm by mass and the acrylic acid purity was 99.92%.

[0130] Comparative Example 3

[0131] The procedure was carried out in accordance with Example 1, except that the acrylic acid raw material used was acrylic acid raw material D4. This raw material was obtained by storing acrylic acid raw material A1 prepared in Preparatory Example 2, after which the acrylic acid dimer content in the raw material was 2000 ppm and the acrylic acid purity was 99.75%.

[0132] Comparative Example 4

[0133] The procedure was carried out in accordance with Example 1, except that the acrylic acid raw material used was acrylic acid raw material D5. This raw material was obtained by adding a small amount of acetic acid to acrylic acid raw material A1 prepared in Preparatory Example 2. The acetic acid content in this raw material was 2800 ppm, and the purity of the acrylic acid was 99.7%.

[0134] Comparative Example 5

[0135] The procedure was carried out in accordance with Example 1, except that the acrylic acid raw material was replaced with the acrylic acid raw material D1 prepared in Preparatory Example 1.

[0136] The vinylidene fluoride polymer resins prepared in each embodiment and comparative example were tested according to the method described above, and electrodes for non-aqueous electrolyte secondary batteries were prepared respectively. The bonding strength between the electrode binder composition and the metal current collector (aluminum foil) was tested, and lithium-ion batteries were prepared and battery cycle performance was tested. The test results are shown in Table 1.

[0137] Table 1. Performance Test Results

[0138] In Table 1, "reaction induction period" refers to the time from when the polymerization reactor temperature reaches the required initial reaction temperature and the pressure reaches the initial reaction pressure until the polymerization reaction begins to start. The criteria for judging the start of the polymerization reaction are: the time when the reaction temperature begins to rise from the initial reaction temperature and the reaction pressure begins to fall from the initial reaction pressure.

[0139] The test results above show that the performance of the vinylidene fluoride polymer prepared in the examples is significantly better than that of the comparative examples. By controlling the content of the polymerization inhibitor, dimer, and acetic acid in the acrylic monomer used to prepare the vinylidene fluoride polymer, the present invention can achieve both high reaction efficiency and a relatively short reaction induction period. At the same time, the prepared vinylidene fluoride polymer has better application performance in electrode binders. Using the polymer obtained in the examples of the present invention as an electrode binder for non-aqueous electrolyte secondary batteries can improve the bonding strength between the electrode binder composition for non-aqueous electrolyte secondary batteries and the metal current collector (aluminum foil), thereby improving the electrochemical performance and service life of the electrode for non-aqueous electrolyte secondary batteries, and exhibiting better cycle capacity retention.

[0140] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a modified vinylidene fluoride polymer, comprising reacting components including vinylidene fluoride and acrylic acid raw materials to obtain the modified vinylidene fluoride polymer; characterized in that, The acrylic acid raw material contains 0.1-1000 ppm of dimer, 0.1-2000 ppm of acetic acid, and 50-200 ppm of polymerization inhibitor.

2. The preparation method according to claim 1, characterized in that, The dimer content in the acrylic acid raw material is 90-1000 ppm, more preferably 90-700 ppm.

3. The preparation method according to claim 1 or 2, characterized in that, The mass content of acetic acid in the acrylic acid raw material is 350-2000 ppm, more preferably 350-1000 ppm.

4. The preparation method according to any one of claims 1-3, characterized in that, The mass content of the polymerization inhibitor in the acrylic acid raw material is 50-100 ppm; And / or, the polymerization inhibitor is selected from one or more of hydroquinone, phenothiazine, and p-hydroxyanisole.

5. The preparation method according to any one of claims 1-4, characterized in that, The purity of the acrylic acid raw material is ≥99.8%, preferably ≥99.9%, and more preferably ≥99.95%; And / or, the amount of the acrylic acid raw material used is 0.01-5 wt% of the amount of the vinylidene fluoride used, preferably 0.01-2 wt%.

6. The preparation method according to any one of claims 1-5, characterized in that, The modified vinylidene fluoride polymer has an intrinsic viscosity of 2.0-4.0 dL / g in an N,N-dimethylacetamide solution at 25°C.

7. The preparation method according to any one of claims 1-5, characterized in that, The components used to prepare the polymer also include polymerization stabilizers and / or initiators, and optionally one or more of other fluorinated monomers and other auxiliaries; Preferably, the other fluorinated monomers are selected from one or more of vinyl fluoride, trifluoroethylene, tetrafluoroethylene, trifluorochloroethylene, 2,3,3,3-tetrafluoropropylene, hexafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropylene, 3,3,3-trifluoro-1-propylene, 2-trifluoromethyl-3,3,3-trifluoropropylene, and fluorinated vinyl ethers; preferably, the fluorinated vinyl ether is perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, etc. One or more of perfluoropropyl vinyl ether and perfluorobutyl vinyl ether; Preferably, the amount of the other fluorinated monomers is 0-10 wt% of the amount of vinylidene fluoride, more preferably 0.1-10 wt%, and even more preferably 0.1-5 wt%. Preferably, the polymerization stabilizer is selected from one or more of cellulose compounds, polyvinyl alcohol, polyethylene glycol, and polyacrylic acid; preferably, the cellulose compound is selected from one or more of methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose; preferably, the amount of the polymerization stabilizer is 0.01-1.5 wt% of the amount of vinylidene fluoride. Preferably, the initiator is an organic peroxide initiator, preferably one or more of the following: diisopropyl peroxide, diethyl peroxide, dicyclohexyl peroxide, di-2-ethylhexyl peroxide, 2,2'-azobis(2,4-dimethylpentanolyl), 2,2'-azobis(4-methoxy-2,4-dimethylpentanolyl), tert-butyl peroxyneodecanate, tert-butyl peroxynepentanoate, tert-pentyl peroxynepentanoate, benzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxymaleate, dicumyl peroxide, cumyl hydroperoxide, tert-butyl peracetic acid, 2,2'-di(tert-butylperoxy)butane, tert-butyl cumyl peroxide, and tert-butyl peroxyisopropyl carbonate; preferably, the amount of the initiator is 0.01-2 wt% of the amount of vinylidene fluoride, more preferably 0.1-1 wt%. Preferably, the other additives include pH adjusters and / or chain transfer agents; preferably, the chain transfer agent is 0.01-1 wt% of the amount of vinylidene fluoride added; preferably, the reaction is carried out in the pH range of 4-8 by adding the pH adjuster.

8. The preparation method according to any one of claims 1-7, characterized in that, The polymer is prepared by one or more processes selected from suspension polymerization, emulsion polymerization, and supercritical CO2 polymerization, with suspension polymerization being the preferred method. And / or, the polymerization reaction temperature for preparing the polymer is 40-100℃, and the pressure is gauge pressure 3.0-15.0 MPa.

9. A modified vinylidene fluoride polymer prepared by the preparation method according to any one of claims 1-8.

10. The use of the modified vinylidene fluoride polymer of claim 9 in a battery electrode binder or in the preparation of a battery electrode binder composition; wherein the battery is, for example, a non-hydrolyzable electrolyte secondary battery; Preferably, the adhesive composition comprises the modified vinylidene fluoride polymer, the electrode active material, the non-aqueous solvent, and optionally a conductive additive; More preferably, the adhesive composition comprises, by weight, 0.5 to 10 parts, preferably 1 to 5 parts, of a modified vinylidene fluoride polymer, and 90 to 99.5 parts, preferably 95 to 99 parts, of an electrode active material; the amount of the non-aqueous solvent is 4 to 100 times, more preferably 6 to 50 times, the mass of the modified vinylidene fluoride polymer; and the amount of the conductive additive is 0.02 to 4 times, more preferably 0.1 to 2 times, the mass of the modified vinylidene fluoride polymer.

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