A vinylidene fluoride polymer dispersant and use thereof

Abstract

The application discloses a vinylidene fluoride polymer dispersant and application thereof, wherein the dispersant has a relative weight average molecular weight of 100,000-600,000 and is a vinylidene fluoride homopolymer or a copolymer formed by vinylidene fluoride and a comonomer. The comonomer of the vinylidene fluoride copolymer is a C2-C10 olefin containing at least one polar functional group selected from at least one of a carboxyl group, an ester group, a hydroxyl group, a sulfonic acid group, a phosphoric acid group, an amide group, a cyano group, an amino group, a mercapto group, an aldehyde group or a halogen, and the comonomer accounts for 0.1-50 mol% of vinylidene fluoride repeating units. The vinylidene fluoride polymer dispersant of the application is applied to preparation of lithium battery electrodes or capacitor electrodes, can not only play a role in stabilizing positive active materials and conductive agents, but also can improve the adhesion between the positive active materials and electrode sheets.

Description

Technical Field

[0001] This invention relates to the field of alkali metal secondary batteries, and in particular to a dispersant used in the preparation process of alkali metal battery electrode or capacitor electrode slurry, employing a low molecular weight vinylidene fluoride polymer. Background Technology

[0002] Alkali metal secondary batteries have advantages such as long cycle life, environmental friendliness, and high efficiency, and are widely used in digital 3C products, power batteries, energy storage, and other fields. The structure of an alkali metal secondary battery typically consists of a positive electrode, a separator, a negative electrode, and an electrolyte. During charging, the active material is extracted from the positive electrode, flows through the electrolyte and separator, and then flows into the negative electrode; the discharge process is exactly the opposite.

[0003] As a crucial component of alkali metal secondary batteries, the cathode plays a vital role in the battery's energy density, safety, and lifespan. During cathode preparation, the active material, conductive agent, and binder are mixed in a solvent to form a suspension slurry. Due to inter-material interactions, collisions occur between the active material and conductive agent under static or slowly stirred conditions, leading to agglomeration and physical gelation. This phenomenon is particularly pronounced in current nano-lithium iron phosphate and lithium manganese iron phosphate systems. In lithium-ion batteries, high-nickel ternary materials and sodium-ion batteries, due to their high residual alkali content, undergo chemical reactions with the binder, causing cross-linking and chemical gelation. In recent years, to improve battery energy density and electrochemical performance, the particle size of active materials has been continuously reduced. Smaller particle sizes and larger specific surface areas increase the likelihood of particle collisions, making slurry agglomeration and gelation more likely. This reduces slurry flowability, making slurry transport and coating difficult, and even resulting in uneven dispersion of the main material and conductive agent, ultimately degrading electrochemical performance.

[0004] Currently, the main methods for improving slurry stability include: ① physical dispersion methods: high-speed shear dispersion, ultrasonic dispersion, etc.; ② chemical dispersion methods: adding dispersants. Because traditional physical dispersion methods use large dispersion equipment, consume a lot of energy, and cannot fundamentally solve the dispersion problem of slurry, they are not used as a standalone dispersion method. They are usually combined with chemical dispersion methods to synergistically improve the overall slurry stability, that is, by adding dispersants to improve slurry stability.

[0005] Patent CN116314819A discloses a dispersant for styrene-based and ethylene-based copolymers. Adding this dispersant to the cathode slurry helps to improve the overall dispersion effect of the slurry and reduce the occurrence of slurry agglomeration, but it cannot solve the chemical gelation phenomenon caused by chemical reactions between slurry components.

[0006] Patent CN117716541A discloses a hydrogenated nitrile rubber dispersant. Adding this dispersant to the positive electrode slurry can reduce the slurry viscosity. After the electrode is made, it helps to improve DCR and cycle performance. However, it still cannot solve the chemical gelation phenomenon caused by chemical reactions between slurry components.

[0007] Patent CN116589671A discloses a block copolymer dispersant, wherein the segments are PPO and PEO segments, and the chain ends contain polar groups. This dispersant, when applied to the positive electrode slurry, can improve the dispersion effect of the slurry, slow down the gelation phenomenon, and improve the overall electrical performance of the battery after it is made into an electrode. However, it still cannot solve the chemical gelation phenomenon caused by chemical reactions between slurry components.

[0008] In summary, commonly used dispersants mainly consist of hydrophilic and lipophilic groups, and their primary mechanisms of action are steric hindrance or electrostatic repulsion. While they can improve the dispersion performance of positive electrode active materials and conductive agents, thus preventing physical gelation, they cannot address chemical gelation caused by chemical reactions. Therefore, it is essential to develop a dispersant that can both improve slurry stability and prevent chemical cross-linking of slurry components, thereby breaking with conventional methods to further enhance slurry stability. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention proposes a polyvinylidene fluoride polymer dispersant with a low weight-average molecular weight and containing polar groups. When used in the preparation of positive electrode slurry, it not only improves physical and chemical gelation issues and further enhances slurry stability and solid content, but also unexpectedly improves the adhesion between the positive electrode active material and the electrode sheet.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A dispersant, wherein the dispersant is a vinylidene fluoride polymer and has a relative weight-average molecular weight of 10,000 to 600,000, preferably a relative weight-average molecular weight of 50,000 to 400,000.

[0012] The vinylidene fluoride polymer is a vinylidene fluoride homopolymer or a vinylidene fluoride copolymer.

[0013] The vinylidene fluoride copolymer is a copolymer formed by vinylidene fluoride and a comonomer, comprising vinylidene fluoride repeating units and comonomer repeating units, wherein the comonomer accounts for 0.1 to 50 mol% of the vinylidene fluoride repeating units; preferably, the comonomer accounts for 0.5 to 10 mol% of the vinylidene fluoride repeating units.

[0014] The comonomer is a C2-C10 olefin containing at least one polar functional group, preferably a C2-C8 olefin containing at least one polar functional group. The polar functional group is selected from at least one of carboxyl, ester, hydroxyl, sulfonic acid, phosphate, amide, cyano, amino, mercapto, aldehyde, or halogen; preferably, the polar functional group is selected from at least one of carboxyl, hydroxyl, amide, phosphate, or halogen.

[0015] In a preferred embodiment, the comonomer is selected from at least one of acrylic acid, 2-(dimethylamino)ethyl acrylate, hydroxyethyl acrylate, 2-vinylpyridine, trifluorochloroethylene, tetrafluoroethylene, 2-acrylamido-2-methylpropanesulfonic acid, 2-trifluoromethacrylic acid, diethyl vinylphosphonate, or N,N-dimethylacrylamide. Preferably, the comonomer is selected from at least one of acrylic acid, 2-(dimethylamino)ethyl acrylate, hydroxyethyl acrylate, trifluorochloroethylene, tetrafluoroethylene, or N,N-dimethylacrylamide.

[0016] The vinylidene fluoride copolymer described in this invention can be a random copolymer or a graft copolymer, and can be prepared by emulsion polymerization or suspension polymerization.

[0017] In one embodiment, a random copolymer of vinylidene fluoride is prepared using an emulsion polymerization process. The reaction temperature is 50-120°C, the reaction pressure is ≥2.5 MPa, and the feeding method is either a single-pass feeding or batch feeding. Specific steps include:

[0018] A1. Add pure water and emulsifier to the reactor, purge with nitrogen three times, and heat to 50-120℃; the emulsifier is selected from at least one of alkyl sulfonates, polyoxyethylene ethers, perfluoropolyethers, and polyethylene glycol-propylene glycol copolymers.

[0019] A2. Add chain transfer agent M and initiator, and continue to maintain the temperature for 5-20 minutes; the chain transfer agent M is selected from at least one of ester compounds (such as ethyl acetate, methyl acetate, butyl butyrate, etc.), alcohol compounds (such as ethanol, methanol, isopropanol, etc.), and ketone compounds (such as acetone); the initiator is selected from at least one of persulfate compounds (such as ammonium persulfate), peroxide compounds (such as diisopropyl peroxide), redox compounds (such as potassium persulfate combined with sodium sulfite), and azo compounds (such as azobisisobutyronitrile).

[0020] A3. Add at least one reaction monomer, including vinylidene fluoride, and increase the reaction pressure. The reaction begins when the reaction pressure is ≥2.5 MPa.

[0021] A4. During the reaction, continuously add comonomer or pure water to maintain a stable reaction pressure;

[0022] A5. The reaction ends when the total amount of comonomers fed reaches the preset value or the pressure cannot be maintained normally.

[0023] In another embodiment, a suspension polymerization process is used to prepare a random copolymer of vinylidene fluoride, with a reaction temperature of 25-70°C, a reaction pressure ≥2.5 MPa, and a feeding method of either one-time feeding or batch feeding.

[0024] B1. Add pure water and dispersant to the reactor, purge with nitrogen three times, and heat to 25-70℃; the dispersant is selected from at least one of sodium carboxymethyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose.

[0025] B2. Add chain transfer agent M and initiator, and continue to maintain the temperature for 5-20 minutes; the chain transfer agent M is selected from at least one of ester compounds (such as ethyl acetate, methyl acetate, butyl butyrate, etc.), alcohol compounds (such as ethanol, methanol, isopropanol, etc.), and ketone compounds (such as acetone); the initiator is selected from at least one of peroxide compounds (such as diisopropyl peroxide) and azo compounds (such as azobisisobutyronitrile).

[0026] B3. Add at least one reaction monomer, including vinylidene fluoride, and increase the reaction pressure. The reaction begins when the reaction pressure is ≥2.5 MPa.

[0027] B4. During the reaction, continuously add comonomer or pure water to maintain a stable reaction pressure;

[0028] B5. The reaction ends when the total amount of comonomers fed reaches the preset value or the pressure cannot be maintained normally.

[0029] In another embodiment, a vinylidene fluoride graft copolymer is prepared using an emulsion polymerization process. The reaction temperature is 50-120°C, the reaction pressure is ≥2.5 MPa, and the feeding method is either a single-pass feeding or batch feeding. Specific steps include:

[0030] C1. Add pure water and emulsifier to the reactor, purge with nitrogen three times, and heat to 50-120℃; the emulsifier is selected from at least one of alkyl sulfonates, polyoxyethylene ethers, perfluoropolyethers, and polyethylene glycol-propylene glycol copolymers.

[0031] C2. Add chain transfer agent M, chain transfer agent N, and initiator, and continue to maintain the temperature for 5-20 minutes; the chain transfer agent M is selected from at least one of ester compounds (such as ethyl acetate, methyl acetate, butyl butyrate, etc.), alcohol compounds (such as ethanol, methanol, isopropanol, etc.), and ketone compounds (such as acetone); the chain transfer agent N is selected from at least one of polyacrylic acid, polyacrylate, polyvinylpyrrolidone, and polyvinyl alcohol; the initiator is selected from at least one of persulfate compounds (such as ammonium persulfate), peroxide compounds (such as diisopropyl peroxide), redox compounds (such as potassium persulfate combined with sodium sulfite), and azo compounds (such as azobisisobutyronitrile).

[0032] C3. Add at least one reaction monomer, including vinylidene fluoride, and increase the reaction pressure. The reaction begins when the reaction pressure is ≥2.5 MPa.

[0033] C4. During the reaction, the comonomer or pure water is continuously added to maintain a stable reaction pressure;

[0034] C5. The reaction ends when the total amount of comonomers fed reaches the preset value or the pressure cannot be maintained normally.

[0035] In another embodiment, a suspension polymerization process is used to prepare a vinylidene fluoride graft copolymer, with a reaction temperature of 25-70°C, a reaction pressure ≥2.5 MPa, and a feeding method of either one-time feeding or batch feeding.

[0036] D1. Add pure water and dispersant to the reactor, purge with nitrogen three times, and heat to 25-70℃; the dispersant is selected from at least one of sodium carboxymethyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose.

[0037] D2. Add chain transfer agent M, chain transfer agent N, and initiator, and continue to maintain the temperature for 5-20 minutes; the chain transfer agent M is selected from at least one of ester compounds (such as ethyl acetate, methyl acetate, butyl butyrate, etc.), alcohol compounds (such as ethanol, methanol, isopropanol, etc.), and ketone compounds (such as acetone); the chain transfer agent N is selected from at least one of polyacrylic acid, polyacrylate, polyvinylpyrrolidone, and polyvinyl alcohol; the initiator is selected from at least one of peroxide compounds (such as diisopropyl peroxide) and azo compounds (such as azobisisobutyronitrile).

[0038] D3. Add at least one reaction monomer, including vinylidene fluoride, and increase the reaction pressure. The reaction begins when the reaction pressure is ≥2.5 MPa.

[0039] D4. During the reaction, continuously add comonomer or pure water to maintain a stable reaction pressure;

[0040] D5. The reaction ends when the total amount of comonomers fed reaches the preset value or the pressure cannot be maintained normally.

[0041] The present invention also provides the application of any of the above-described dispersants in the preparation process of alkali metal battery electrodes or capacitor electrodes.

[0042] The present invention also provides an electrode composition comprising: any of the dispersants, electrode active substances, conductive agents and binders described above, wherein the dispersant accounts for 0.005-0.4% of the total mass of the electrode composition, preferably 0.02-0.2% of the total mass of the electrode composition.

[0043] The electrode active material constitutes 80-98% of the total mass of the electrode composition and is a composite metal compound represented by the general formula MNY, wherein M is selected from Li, Na, or K, N is selected from one or more of Co, Ni, Fe, Mn, Cr, or V, and Y is selected from O, S, SO4, PO4, or SiO3. For example, the electrode active material is selected from lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, Prussian blue, sodium iron phosphate, etc.

[0044] The conductive agent accounts for 1-10% of the total mass of the electrode composition and is selected from at least one of carbon black, acetylene black, carbon nanotubes, carbon fibers, Super S, Super P or graphene; preferably, the conductive agent is selected from carbon black, carbon nanotubes, carbon fibers, Super P and accounts for 2-5% of the total mass of the electrode composition.

[0045] The binder comprises 1-10% of the total mass of the electrode composition and is selected from at least one of polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyvinyl alcohol, styrene-butadiene rubber, or carboxymethyl cellulose; preferably, the binder is selected from polyvinylidene fluoride, polyacrylic acid, or polytetrafluoroethylene and comprises 1.2-3% of the total mass of the electrode composition; more preferably, the binder is selected from polyvinylidene fluoride.

[0046] The electrode composition of this invention is obtained by coating, baking, and rolling an electrode slurry. Unlike the electrode composition, the electrode slurry contains, in addition to the vinylidene fluoride polymer dispersant, electrode active material, conductive agent, and binder, a solvent selected from at least one of N-methylpyrrolidone, dimethylacetamide, or dimethylformamide.

[0047] The electrode slurry prepared by this invention has a viscosity of 1000-50000 cp and a solid content of 40-82%; preferably, the slurry viscosity is 10000-15000 cp and the solid content is 55-80%.

[0048] Specifically, taking the lithium iron phosphate system as an example, the slurry prepared by this invention has a solid content of 65-68%, which is 2-5% higher than the highest solid content of about 63% in the prior art; taking the lithium nickel cobalt manganese oxide system as an example, the slurry prepared by this invention has a solid content of 77-80%, which is also 2-5% higher than the highest solid content of about 75% in the prior art; taking the sodium nickel iron manganese oxide system as an example, the slurry prepared by this invention has a solid content of 64-65%, which is 2-3% higher than the highest solid content of about 62% in the prior art; taking the sodium iron phosphate system as an example, the slurry prepared by this invention has a solid content of 55-58%, which is 5-8% higher than the highest solid content of about 50% in the prior art.

[0049] The present invention also provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode film layer on at least one surface of the positive current collector, the positive electrode film layer comprising any of the electrode compositions described above.

[0050] The present invention also provides an alkali metal secondary battery, wherein the alkali metal secondary battery comprises the aforementioned positive electrode plate. Preferably, the alkali metal secondary battery is a lithium-ion battery or a sodium-ion battery.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] 1. This invention is the first to propose the application of low molecular weight vinylidene fluoride polymer as a dispersant in the preparation process of alkali metal battery electrodes or capacitor electrodes.

[0053] 2. The vinylidene fluoride polymer dispersant of the present invention can not only greatly improve the stability of the electrode slurry and improve the physical gelation of the slurry during the preparation of the electrode slurry, but also consume residual alkali through the polar groups contained in the dispersant and improve the chemical gelation.

[0054] 3. This invention uses a low molecular weight polyvinylidene fluoride polymer as a dispersant, which can form a eutectic with the polyvinylidene fluoride binder, further improving the adhesion between the positive electrode active material and the electrode sheet. In the lithium iron phosphate system, the adhesion can be improved by about 30% compared to the prior art; in the lithium nickel cobalt manganese oxide system, the adhesion can be improved by about 30% compared to the prior art. Detailed Implementation

[0055] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0056] Various performance tests were conducted during the implementation of this invention, as detailed below:

[0057] (1) Weight-average molecular weight: Gel permeation chromatography (GPC) was used to determine the weight-average molecular weight of polyvinylidene fluoride (PVDF). N,N-dimethylformamide was used as the mobile phase at a flow rate of 1 ml / min and the test temperature was 50 °C. A standard curve was plotted using narrow-distribution polystyrene with a molecular weight of 10,000 to 10,000,000 as the standard sample. The relative weight-average molecular weight of PVDF is a relative value to the molecular weight of polystyrene.

[0058] (2) Adhesion strength: The adhesion strength of the polymer after it is made into an electrode was determined according to ISO 4624 standard (adhesion pull test), at 25°C and 50% relative humidity;

[0059] (3) Stability of slurry: After preparing the slurry, use a spatula to scoop up the slurry at different time periods and observe the slurry's falling state to judge the stability of the slurry.

[0060] Stabilized slurry: The slurry falls continuously in a linear stream without interruption or unstable flow.

[0061] Medium-gel slurry: The slurry falls in a linear stream, occasionally with interruptions or lumps.

[0062] Heavy gelling slurry: The slurry has a jelly-like consistency and cannot fall.

[0063] Example 1

[0064] (1) Preparation of polyvinylidene fluoride polymer dispersant

[0065] Add 2800g of deionized water and 1g of methylcellulose to a 5L vertical polymerization reactor. Vacuum the reactor and replace it with nitrogen three times until the oxygen content in the reactor is less than 10ppm.

[0066] 1000g of polyvinylidene fluoride monomer was added to the reactor, and the temperature inside the reactor was raised to 50℃. 20g of ethyl acetate and 15g of diisopropyl peroxide were added, and the mixture was kept at this temperature for 10 minutes. Then, stirring was started at 580 rpm, while simultaneously adding an acrylic acid solution (20g of acrylic acid to make 1600g of acrylic acid solution) at a constant rate of approximately 4.5g / min. After the acrylic acid was added, the reaction was stopped after waiting for half an hour. After the reaction was complete, the polyvinylidene fluoride resin was collected, washed, and dried to obtain polyvinylidene fluoride resin powder. A sample was taken and the relative weight-average molecular weight was measured to be 180,000.

[0067] (2) Electrode paste preparation

[0068] At room temperature, under mechanical stirring, 0.7725g of polyvinylidene fluoride resin powder prepared in this example, 30.1275g of polyvinylidene fluoride binder (HSV900), 9.9g of SUPER P, and 1360.4g of lithium iron phosphate were slowly dry-mixed for 30 minutes in a double planetary mixer. After being thoroughly mixed, 659.4g of N-methylpyrrolidone was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0069] Take a small amount of slurry, weigh it using an analytical balance to obtain the mass m1, and place it in an oven to dry; after drying, weigh it to obtain the mass m2, and m2 ÷ m1 is the solid content of the slurry.

[0070] Slurry stability test: The flow state of the slurry was observed at 1, 2, 3, 6, 12, 18 and 24 hours respectively.

[0071] Adhesion strength test: The prepared slurry was uniformly coated onto the current collector using a transfer coating machine to obtain the electrode sheet. The electrode adhesion strength was measured using a tensile testing machine at 25°C and 50% relative humidity according to ISO 4624 standard (adhesion pull-off test). At least 5 current collectors were tested to obtain the average value.

[0072] Example 2

[0073] The operation of this embodiment is the same as that of Embodiment 1, the only difference being:

[0074] In the preparation of vinylidene fluoride polymer dispersant, 1g of hydroxypropyl methylcellulose was used instead of 1g of methylcellulose, and other operations remained unchanged. The relative weight-average molecular weight was measured to be 210,000.

[0075] In the preparation of the electrode slurry, the amount of polyvinylidene fluoride polymer dispersant prepared in this embodiment was reduced to 0.495g, the polyvinylidene fluoride binder was replaced with Solef5130 and the amount was reduced to 19.305g, the amount of SUPER P was increased to 16.5g, and 1613.7g of lithium nickel cobalt manganese oxide was used instead of 1360.4g of lithium iron phosphate as the positive electrode active material. The mixture was slowly dry-mixed in a double planetary mixer for 30min. After thorough mixing, 412.5g of N-methylpyrrolidone was added and slowly kneaded for 30min. Then, it was dispersed at high speed for 3h. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0076] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0077] Example 3

[0078] The operation of this embodiment is the same as that of Embodiment 1, the only difference being:

[0079] In the preparation of the polyvinylidene fluoride polymer dispersant, 40g of acrylic acid was used to prepare 1600g of solution, and the feed rate was reduced to about 3.8g / min; the amount of diisopropyl peroxide was increased to 25g, and other operations remained unchanged. The relative weight average molecular weight was measured to be 240,000.

[0080] In the preparation of the electrode slurry, 1.545g of polyvinylidene fluoride resin powder prepared in this embodiment was used, and the amount of polyvinylidene fluoride binder was reduced to 29.355g, while other conditions remained unchanged.

[0081] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0082] Example 4

[0083] (1) Preparation of polyvinylidene fluoride polymer dispersant

[0084] Add 2800g of deionized water and 1g of hydroxypropyl cellulose to a 5L vertical polymerization reactor. Vacuum the reactor and replace it with nitrogen three times until the oxygen content in the reactor is less than 10ppm.

[0085] Add 1300g of vinylidene fluoride monomer to the reactor, raise the temperature of the reactor to 40℃, add 25g of isopropanol and 35g of diisopropyl peroxide, maintain the temperature for 10 minutes, then start stirring at a rate of 580rpm, while simultaneously adding hydroxyethyl acrylate solution (40g of hydroxyethyl acrylate to prepare 1600g of hydroxyethyl acrylate solution) to the reactor at a constant rate of about 3.8g / min. After the acrylic acid is added, wait for half an hour. After the reaction is completed, collect the polyvinylidene fluoride resin, and obtain polyvinylidene fluoride resin powder by washing and drying. The relative weight average molecular weight was measured to be 180,000.

[0086] (2) Electrode paste preparation

[0087] Under mechanical stirring at room temperature, 0.7725g of polyvinylidene fluoride resin powder prepared in this example, 30.1275g of polyvinylidene fluoride binder (HSV900), 9.9g of SUPER P, and 1360.4g of lithium iron phosphate were slowly dry-mixed for 30 minutes in a double planetary mixer. After thorough mixing, 659.4g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0088] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0089] Example 5

[0090] (1) Preparation of polyvinylidene fluoride polymer dispersant

[0091] Add 3200g of deionized water and 1g of polyethylene glycol-propylene glycol copolymer to a 5L vertical polymerization reactor. Vacuum the reactor and replace it with nitrogen three times until the oxygen content in the reactor is less than 10ppm.

[0092] Add 300g of vinylidene fluoride monomer to the reactor, raise the temperature to 80℃, add 12g of isopropanol and 5g of ammonium persulfate, maintain the temperature for 10 minutes, then start stirring at 350rpm. Add acrylic acid solution (6g acrylic acid to make 360g acrylic acid solution) to the reactor at a constant rate of approximately 3g / min, and replenish vinylidene fluoride monomer to maintain stable pressure until the cumulative amount of vinylidene fluoride added reaches 1000g, at which point the reaction is stopped. After the reaction is complete, collect the emulsion, filter, demulsify, wash, and dry to obtain polyvinylidene fluoride resin powder. A sample was taken and the relative weight-average molecular weight was measured to be 190,000.

[0093] (2) Electrode paste preparation

[0094] At room temperature, 0.99g of polyvinylidene fluoride resin powder prepared in this example, 18.81g of polyvinylidene fluoride binder (Solef5130), 16.5g of SUPER P, and 1613.7g of lithium nickel cobalt manganese oxide material were slowly dry-mixed for 30 minutes in a double planetary mixer. After being thoroughly mixed, 412.5g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0095] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0096] Example 6

[0097] (1) Preparation of polyvinylidene fluoride polymer dispersant

[0098] Add 3200g of deionized water and 1g of polyethylene glycol-propylene glycol copolymer to a 5L vertical polymerization reactor. Vacuum the reactor and replace it with nitrogen three times until the oxygen content in the reactor is less than 10ppm.

[0099] Add 300g of vinylidene fluoride monomer to the reactor, raise the reactor temperature to 80℃, add 12g of isopropanol and 5g of ammonium persulfate, maintain the temperature for 10 minutes, then start stirring at 350rpm. Add 2-vinylpyridine solution (6g of 2-vinylpyridine prepared to 360g of 2-vinylpyridine solution) to the reactor at a constant rate of approximately 3g / min, and replenish vinylidene fluoride monomer to maintain stable pressure until the cumulative amount of vinylidene fluoride added reaches 1000g, at which point the reaction is stopped. After the reaction is complete, collect the emulsion, filter, demulsify, wash, and dry to obtain polyvinylidene fluoride resin powder. A sample was taken and the relative weight-average molecular weight was measured to be 200,000.

[0100] (2) Electrode paste preparation

[0101] Under stirring conditions at room temperature, 1.545g of polyvinylidene fluoride resin powder prepared in this example, 29.355g of polyvinylidene fluoride binder (HSV900), 9.9g of SUPER P, and 1360.4g of lithium iron phosphate were slowly dry-mixed for 30 minutes in a double planetary mixer. After thorough mixing, 659.4g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0102] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0103] Example 7

[0104] (1) Preparation of polyvinylidene fluoride polymer dispersant

[0105] Add 3200g of deionized water and 1g of perfluoropolyether to a 5L vertical polymerization reactor. Vacuum the reactor and replace it with nitrogen three times until the oxygen content in the reactor is less than 10ppm.

[0106] 100g of trifluorochloroethylene monomer and 220g of vinylidene fluoride monomer were added to the reactor. The temperature inside the reactor was raised to 80℃, and 12g of isopropanol and 5g of ammonium persulfate were added. The mixture was kept at a constant temperature for 10 minutes, and then stirred at 300rpm. A mixture of trifluorochloroethylene and vinylidene fluoride monomers (mass ratio 1:2.19) was added to the reactor through a premixing tank to maintain stable pressure until the cumulative amount of vinylidene fluoride added reached 1000g, at which point the reaction was stopped. After the reaction was complete, the emulsion was collected, filtered, demulsified, washed, and dried to obtain polyvinylidene fluoride resin powder. A sample was taken and the relative weight-average molecular weight was measured to be 190,000.

[0107] (2) Electrode paste preparation

[0108] At room temperature, 0.99g of polyvinylidene fluoride resin powder prepared in this example, 18.81g of polyvinylidene fluoride binder (Solef5130), 16.5g of SUPER P, and 1613.7g of sodium nickel iron manganese oxide were slowly dry-mixed for 30 minutes in a double planetary mixer. After being thoroughly mixed, 888.5g of N-methylpyrrolidone was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0109] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0110] Example 8

[0111] (1) Preparation of polyvinylidene fluoride polymer dispersant

[0112] Add 2800g of deionized water and 1g of hydroxypropyl methylcellulose to a 5L vertical polymerization reactor. Vacuum the reactor and replace it with nitrogen three times until the oxygen content in the reactor is less than 10ppm.

[0113] 1000g of vinylidene fluoride monomer was added to the reactor, and the temperature inside the reactor was raised to 50℃. 30g of ethyl acetate and 35g of diisopropyl peroxide were added, and the temperature was kept constant for 10 minutes. Then, stirring was started at a rate of 580 rpm, and acrylic acid solution (60g of acrylic acid was used to prepare 1600g of acrylic acid solution) was added to the reactor at a constant rate of about 3.8g / min. After the acrylic acid was added, the reaction was stopped for half an hour. After the reaction was completed, the polyvinylidene fluoride resin was collected, and polyvinylidene fluoride resin powder was obtained by washing and drying. The relative weight average molecular weight was measured to be 200,000.

[0114] (2) Electrode paste preparation

[0115] At room temperature, 0.99g of polyvinylidene fluoride resin powder prepared in this example, 18.81g of polyvinylidene fluoride binder (Solef5130), 16.5g of SUPER P, and 1613.7g of sodium iron phosphate were slowly dry-mixed for 30 minutes in a double planetary mixer. After thorough mixing, 1100g of N-methylpyrrolidone was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0116] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0117] Example 9

[0118] (1) Preparation of polyvinylidene fluoride polymer dispersant

[0119] Add 3200g of deionized water and 1g of polyethylene glycol-propylene glycol copolymer to a 5L vertical polymerization reactor. Vacuum the reactor and replace it with nitrogen three times until the oxygen content in the reactor is less than 10ppm.

[0120] 100g of tetrafluoroethylene monomer and 250g of vinylidene fluoride monomer were added to the reactor. The temperature inside the reactor was raised to 80℃, and 12g of isopropanol and 5g of ammonium persulfate were added. The mixture was kept at a constant temperature for 10 minutes, and then stirred at 300rpm. A mixture of tetrafluoroethylene and vinylidene fluoride monomers (mass ratio 1:2.56) was added to the reactor through a premixing tank to maintain stable pressure until the cumulative amount of vinylidene fluoride added reached 1000g, at which point the reaction was stopped. After the reaction was complete, the emulsion was collected, filtered, demulsified, washed, and dried to obtain polyvinylidene fluoride resin powder. A sample was taken and the relative weight-average molecular weight was measured to be 200,000.

[0121] (2) Electrode paste preparation

[0122] Under room temperature stirring conditions, 0.99g of polyvinylidene fluoride resin powder prepared in this example, 18.81g of polyvinylidene fluoride binder (Solef5130), 16.5g of SUPER P, and 1613.7g of sodium nickel iron manganese oxide material were slowly dry-mixed for 30 minutes in a double planetary mixer. After being thoroughly mixed, 888.5g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0123] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0124] Example 10

[0125] (1) Preparation of polyvinylidene fluoride polymer dispersant

[0126] Add 3200g of deionized water and 1g of polyethylene glycol-propylene glycol copolymer to a 5L vertical polymerization reactor. Vacuum the reactor and replace it with nitrogen three times until the oxygen content in the reactor is less than 10ppm.

[0127] 300g of vinylidene fluoride monomer was added to the reactor, and the temperature inside the reactor was raised to 80℃. 30g of polyacrylic acid and 5g of ammonium persulfate were added, and the mixture was kept at a constant temperature for 10 minutes. Then, stirring was started at 350 rpm, and vinylidene fluoride monomer was added to the reactor to maintain stable pressure until the cumulative amount of vinylidene fluoride added reached 1000g, at which point the reaction was stopped. After the reaction was completed, the emulsion was collected, and polyvinylidene fluoride resin powder was obtained by filtration, demulsification, washing, and drying. The relative weight-average molecular weight was measured to be 170,000.

[0128] (2) Electrode paste preparation

[0129] Under stirring conditions at room temperature, 0.7725g of polyvinylidene fluoride resin powder prepared in this example, 30.1275g of polyvinylidene fluoride binder (HSV900), 9.9g of SUPER P, and 1360.4g of lithium iron phosphate were slowly dry-mixed for 30 minutes in a double planetary mixer. After thorough mixing, 659.4g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0130] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0131] Comparative Example 1

[0132] At room temperature with stirring, 30.1275g of polyvinylidene fluoride binder (HSV900), 9.9g of SUPER P, and 1360.4g of lithium iron phosphate were slowly dry-mixed for 30 minutes in a double planetary mixer. After thorough mixing, 659.4g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0133] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0134] Comparative Example 2

[0135] At room temperature with stirring, 19.305g of polyvinylidene fluoride binder (Solef5130), 16.5g of SUPER P, and 1613.7g of lithium nickel cobalt manganese oxide were slowly dry-mixed for 30 minutes in a double planetary mixer. After thorough mixing, 412.5g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0136] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0137] Comparative Example 3

[0138] At room temperature with stirring, 18.81g of polyvinylidene fluoride binder (Solef5130), 16.5g of SUPER P, and 1613.7g of sodium nickel iron manganese oxide were slowly dry-mixed for 30 minutes in a double planetary mixer. After thorough mixing, 888.5g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0139] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0140] Comparative Example 4

[0141] At room temperature with stirring, 18.81g of polyvinylidene fluoride binder (Solef5130), 16.5g of SUPER P, and 1613.7g of sodium iron phosphate were slowly dry-mixed for 30 minutes in a double planetary mixer. After thorough mixing, 1100g of N-methylpyrrolidone solution was added and slowly kneaded for 30 minutes, followed by high-speed dispersion for 3 hours. After discharge, N-methylpyrrolidone was further added to make the final slurry viscosity approximately 12000cp.

[0142] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0143] Comparative Example 5

[0144] The operation of this comparative example is the same as that of comparative example 1, except that 0.7725 PVP dispersant was added during the preparation of the electrode slurry. All other operations remain unchanged.

[0145] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0146] Comparative Example 6

[0147] The operation of this comparative example is the same as that of comparative example 1, except that 0.7725g of nitrile rubber dispersant is added during the preparation of the electrode slurry. All other operations remain unchanged.

[0148] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0149] Comparative Example 7

[0150] The operation of this comparative example is the same as that of Example 10, except that:

[0151] In the preparation of polyvinylidene fluoride polymer dispersant, the amount of polyacrylic acid was adjusted from 6g to 2g, and the relative weight average molecular weight was measured to be 640,000.

[0152] The solid content test, stability test, and adhesion test of the slurry were conducted in the same manner as in Example 1, and the test results are shown in Table 1.

[0153] Table 1 Performance Test Results

[0154]

[0155]

[0156] As can be seen from the data in Table 1 above, the polyvinylidene fluoride dispersant prepared by the present invention has a good dispersion effect in the positive electrode slurry of secondary batteries, which can improve the overall solid content of the slurry and improve the stability of the slurry. At the same time, when used in conjunction with polyvinylidene fluoride binder, it can significantly enhance the adhesion.

[0157] Comparative Examples 1-4 did not contain any dispersant. The test results showed that the overall solid content was low and the slurry stability was poor. At the same time, compared with the samples containing polyvinylidene fluoride dispersant, the adhesion strength decreased to varying degrees.

[0158] Comparative Examples 5-6 added mainstream positive electrode dispersants (PVP and nitrile rubber). Compared with Comparative Example 1 without dispersants, the overall solid content was only slightly improved, the slurry stability was average, and the adhesion was not improved or even slightly deteriorated.

[0159] Comparing Comparative Example 1 and Comparative Example 7, it can be seen that using a higher molecular weight vinylidene fluoride polymer dispersant, although the solid content is slightly increased, the adhesion cannot be improved. Therefore, only low molecular weight vinylidene fluoride polymer dispersants within a specific range can simultaneously achieve an increase in solid content and an improvement in adhesion.

Claims

1. A dispersant, characterized in that: The dispersant is a vinylidene fluoride polymer with a relative weight-average molecular weight of 10,000 to 600,000.

2. The dispersant according to claim 1, characterized in that: The relative weight-average molecular weight of the vinylidene fluoride polymer is 50,000 to 400,000.

3. The dispersant according to claim 1 or 2, characterized in that: The vinylidene fluoride polymer is a vinylidene fluoride homopolymer or a copolymer formed by vinylidene fluoride and a comonomer, wherein the comonomer is a C2-C10 olefin containing at least one polar functional group.

4. The dispersant according to claim 3, characterized in that: The polar functional group is selected from at least one of carboxyl, ester, hydroxyl, sulfonic acid, phosphate, amide, cyano, amino, mercapto, aldehyde or halogen.

5. The dispersant according to claim 3, characterized in that: The comonomer accounts for 0.1–50 mol of the vinylidene fluoride repeating unit.

6. The dispersant according to claim 5, characterized in that: The comonomer accounts for 0.5–10 mol of the vinylidene fluoride repeating unit.

7. The dispersant according to any one of claims 4-6, characterized in that: The comonomer is selected from at least one of acrylic acid, 2-(dimethylamino)ethyl acrylate, hydroxyethyl acrylate, 2-vinylpyridine, trifluorochloroethylene, tetrafluoroethylene, 2-acrylamido-2-methylpropanesulfonic acid, 2-trifluoromethylacrylic acid, diethyl vinylphosphonate, or N,N-dimethylacrylamide.

8. The dispersant according to any one of claims 1-7, characterized in that: The vinylidene fluoride polymer is prepared by emulsion polymerization, with a reaction temperature of 50-120℃, a reaction pressure ≥2.5 MPa, and feeding methods of one-time feeding or batch feeding.

9. The dispersant according to any one of claims 1-7, characterized in that: The vinylidene fluoride polymer is prepared by suspension polymerization, with a reaction temperature of 25-70℃, a reaction pressure ≥2.5 MPa, and feeding methods of one-time feeding or batch feeding.

10. The use of the dispersant according to any one of claims 1-7 in the preparation process of alkali metal battery electrodes or capacitor electrodes.

11. An electrode composition, characterized in that: The electrode composition comprises: a dispersant, an electrode active material, a conductive agent, and a binder as described in any one of claims 1-7, wherein the dispersant accounts for 0.005-0.4% of the total mass of the electrode composition.

12. The electrode composition according to claim 11, characterized in that: The electrode active material accounts for 80-98% of the total mass of the electrode composition and is a composite metal compound represented by the general formula MNY, wherein M is selected from Li, Na or K, N is selected from one or more of Co, Ni, Fe, Mn, Cr or V, and Y is selected from O, S, SO4, PO4 or SiO3.

13. The electrode composition according to claim 11, characterized in that: The conductive agent accounts for 1-10% of the total mass of the electrode composition and is selected from at least one of carbon black, acetylene black, carbon nanotubes, carbon fibers, Super S, Super P or graphene.

14. The electrode composition according to claim 11, characterized in that: The binder accounts for 1-10% of the total mass of the electrode composition and is selected from at least one of polyvinylidene fluoride, polyacrylic acid, and polyvinyl alcohol.

15. A positive electrode plate, characterized in that: The positive electrode includes a positive current collector and a positive electrode film layer on at least one surface of the positive current collector, the positive electrode film layer comprising the electrode composition according to any one of claims 11-14.

16. An alkali metal secondary battery, characterized in that: The alkali metal secondary battery includes the positive electrode sheet as described in claim 15.

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