CN115594783B - Method for preparing lithium battery binder - Google Patents
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- CN115594783B CN115594783B CN202211244652.0A CN202211244652A CN115594783B CN 115594783 B CN115594783 B CN 115594783B CN 202211244652 A CN202211244652 A CN 202211244652A CN 115594783 B CN115594783 B CN 115594783B
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F114/00—Homopolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
- C08F114/18—Monomers containing fluorine
- C08F114/22—Vinylidene fluoride
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
- C08F2/12—Polymerisation in non-solvents
- C08F2/16—Aqueous medium
- C08F2/18—Suspension polymerisation
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
- C08F2/12—Polymerisation in non-solvents
- C08F2/16—Aqueous medium
- C08F2/20—Aqueous medium with the aid of macromolecular dispersing agents
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
- H01M4/623—Binders being polymers fluorinated polymers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The invention discloses a method for preparing a high-purity lithium battery binder, wherein the high-purity lithium battery binder is polyvinylidene fluoride resin with extremely low impurity content, and the preparation method is that a specific dispersing agent is adopted for suspension polymerization process preparation of vinylidene fluoride monomers, and the method comprises the following steps: (a) preparation of a dispersing agent: firstly, preparing vinylidene fluoride resin particles through emulsion polymerization, adding a surfactant containing two hydrophilic groups into slurry of the resin particles after coagulation and washing, adding the slurry into a centrifuge after uniform mixing to improve the sphericity of the particles, and drying and screening the resin particles after centrifugation to obtain dispersing agent particles for suspension polymerization; (b) suspension polymerization: and d, adding an initiator, a chain transfer agent and a vinylidene fluoride monomer into a reaction kettle, adding the dispersing agent prepared in the step a, heating to perform suspension polymerization, removing unreacted monomers after polymerization, and filtering, washing and drying to obtain the polyvinylidene fluoride resin. The polymerization adopts a novel dispersion system, the high sphericity polyvinylidene fluoride resin particles prepared by emulsion polymerization are used as dispersing agents, the prepared polyvinylidene fluoride resin has high purity, excellent heat stability, low manufacturing cost and recoverable dispersing agents.
Description
Technical Field
The invention relates to the field of polymers, in particular to a method for preparing a lithium battery binder
Background
Polyvinylidene fluoride (PVDF) resin refers to a vinylidene fluoride (VDF) homopolymer or a copolymer of vinylidene fluoride and other fluorovinyl monomers. It has very balanced performance and can be applied to various fields. The molecular structure of the CH2 and CF2 groups in PVDF along the carbon chain is alternately arranged, so that the PVDF has the characteristics of polyethylene and polytetrafluoroethylene. Among the fluoropolymers, PVDF has the best abrasion resistance, mechanical strength and toughness, excellent permeation resistance and stain resistance, good heat resistance and chemical resistance, etc., and is widely used in the directions of photovoltaic back sheets, fluorocarbon coatings, water treatment films, lithium electric binders, etc. The application with the highest added value is a lithium battery binder, and has very strict requirements on purity, molecular weight, distribution, binding performance and the like of PVDF.
The most commonly used polymerization methods for polymerizing vinylidene fluoride monomers are emulsion polymerization and suspension polymerization, and the emulsion polymerization has the advantages of high reaction rate, good stability, high yield and the like, but the post-treatment process is complex, the impurity removal is difficult, and the cost is high; the suspension polymerization and post-treatment process is simple, the production efficiency is high, the molecular weight of the prepared polyvinylidene fluoride product is high, and the molecular weight distribution is narrow, and the defect is that impurities can be introduced when a dispersing agent is added in the suspension polymerization, so that the prepared polyvinylidene fluoride product can be used as a lithium battery binder to generate potential safety hazards.
Funo lin (CN 102336854) is prepared into polyvinylidene fluoride resin by adopting a suspension polymerization process, magnesium hydroxide is used as a dispersing agent, water, an initiator, a chain transfer agent, magnesium hydroxide and vinylidene fluoride monomers are added into a reaction system for suspension polymerization, solid-liquid separation is carried out after the reaction is finished, and washing operation is carried out for a plurality of times to separate the dispersing agent magnesium hydroxide from the resin. The invention reduces the kettle sticking amount and production, but the residue of magnesium hydroxide still has influence on the purity of the product.
The giant group (CN 105924554) is also prepared into polyvinylidene fluoride resin through suspension polymerization process, and the polyvinylidene fluoride resin is prepared through suspension polymerization reaction of adding organic and inorganic compound dispersant into suspension system, washing and stoving. Although an inorganic dispersant such as calcium phosphate is used instead of a part of the organic dispersant, there is also a problem of dispersant residue, and the problem of impurity introduction is not fundamentally avoided.
The polyvinylidene fluoride resin for the lithium battery binder has very strict purity requirements, on one hand, the lower purity can lead to the reduction of the energy density of the lithium battery and influence the service performance, and on the other hand, the lower purity can lead to the reduction of the thermal stability of the product and even bring potential safety hazard, so that the improvement of the purity of the polyvinylidene fluoride resin is the key of the preparation process. At present, no matter the emulsion process or the suspension process is adopted to prepare the polyvinylidene fluoride resin, an emulsifying agent or a dispersing agent is added, then the emulsifying agent and the dispersing agent are removed through multiple times of washing, and a small amount of impurities still remain in the polyvinylidene fluoride resin in actual production, so that the problem is not solved from the source.
In summary, it is found that a dispersing agent with better dispersing capability, no impurity introduced and low cost is important for the method for preparing polyvinylidene fluoride by suspension polymerization, and the high sphericity polyvinylidene fluoride resin particles prepared by emulsion polymerization are used as the dispersing agent.
Disclosure of Invention
The invention aims to provide a preparation method of a high-purity lithium battery binder, which adopts a novel dispersion system, takes high sphericity polyvinylidene fluoride resin particles prepared by emulsion polymerization as a dispersing agent to prepare polyvinylidene fluoride resin by suspension polymerization, and the polyvinylidene fluoride resin prepared by the method has higher purity, excellent thermal stability, low manufacturing cost and recoverable dispersing agent.
The invention provides a method for preparing a high-purity lithium battery binder, which comprises the following steps:
(a) Preparing a dispersing agent: firstly, preparing vinylidene fluoride resin particles through emulsion polymerization, adding a surfactant containing two hydrophilic groups into slurry of the resin particles after coagulation and washing, adding the slurry into a centrifuge after uniform mixing to improve the sphericity of the particles, and drying and screening the resin particles after centrifugation to obtain the dispersing agent particles for suspension polymerization.
(b) Suspension polymerization: and d, adding an initiator, a chain transfer agent and a vinylidene fluoride monomer into a reaction kettle, adding the dispersing agent prepared in the step a, heating to perform suspension polymerization, removing unreacted monomers after polymerization, and filtering, washing and drying to obtain the polyvinylidene fluoride resin.
The invention further comprises the steps of recovering the dispersing agent: the filtered liquid is sequentially passed through a filter press and a dryer to recover the dispersant particles.
In the present invention, the sphericity of the dispersant particle for suspension polymerization obtained in the step (a) is 0.68 to 1; the particle size is 0.3-1.2 microns.
The coagulant used in the coagulation operation in the preparation of the dispersing agent in the step (a) is calcium chloride aqueous solution, and the dosage of the coagulant is 0.25-0.50% of that of vinylidene fluoride; the concentration of the calcium chloride aqueous solution is 5-10wt%.
The surfactant containing two hydrophilic groups in the step (a) is one or more of sodium dodecyl diphenyl ether disulfonate, dimethyl phenyl benzyl quaternary ammonium disulfonate and sodium 5, 6-dibutyl naphthalene-2-sulfonate, and the addition amount of the surfactant is 0.32-0.75wt% of the resin particles.
The centrifugal force of the centrifugal machine in the preparation of the dispersing agent in the step (a) is 32-65G.
The suspension polymerization initiator in the step (b) is one or more of dibenzoyl peroxide, diethyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-tert-butyl peroxide, tert-butyl peroxypivalate, tert-butyl hydroperoxide, diisopropyl azodicarboxylate, azobisisobutyronitrile or azobisisoheptonitrile, and the initiator is 0.13-0.46 wt% of vinylidene fluoride monomer.
The chain transfer agent in the step (b) is one or more of dodecyl mercaptan, tridecyl mercaptan, tetradecyl mercaptan, octane mercaptan, acetone, ethyl propionate, butyl propionate, diethyl malonate, ethyl acetate, butyl acetate, diethyl succinate and dipropyl succinate, and the use level of the chain transfer agent is 0.2-0.58 wt% of vinylidene fluoride monomer.
The dispersant dosage in the step (b) is 0.4-1.2wt% of vinylidene fluoride monomer; the suspension polymerization temperature in step (b) is 44 to 60℃and preferably 50 to 55 ℃.
The invention has the beneficial effects that:
the inventor finds that the polyvinylidene fluoride resin particles prepared by emulsion polymerization are moderate in particle size and density and can be used as a solid powder dispersing agent for dispersion of vinylidene fluoride monomer suspension technology, and the polyvinylidene fluoride resin particles prepared by emulsion polymerization are adsorbed on the surfaces of vinylidene fluoride oil drops to form an isolation layer, so that the contact of the vinylidene fluoride oil drops is avoided, and the purpose of dispersion is realized. The dispersing agent is the polyvinylidene fluoride resin, no impurity is introduced, the prepared product has high purity and good thermal stability, and the dispersing agent is solid powder which is insoluble in water and can be recovered through filtration, pressure filtration and drying, so that the use cost of the dispersing agent is reduced.
Meanwhile, the inventor further found that the sphericity of the polyvinylidene fluoride resin particles as a dispersing agent influences the dispersing effect, and when the sphericity is poor, the arrangement of the resin particles is not compact and can not fully play a role in isolation, and the sphericity of the resin particles prepared by emulsion polymerization needs to be further improved, so that the dispersing effect of the resin particles as a dispersing agent is improved. And adding a surfactant containing two hydrophilic groups into the coagulated particle slurry prepared by emulsion polymerization, wherein after the surfactant is added, a hydration layer and a double-electron layer are formed on the surface of the coagulated particles to play a role in protecting the particles from coalescence, adding the slurry into a centrifugal machine, centrifuging to reduce the inter-particle distance and increase the intermolecular acting force, weakly adhering primary particles in the coagulated resin particles, and reshaping the particles to be more approximate to a sphere under the action of external force, wherein the particles exist stably under the action of the surfactant. The sphericity of the emulsion polymerization prepared particles is improved by further processing the emulsion polymerization prepared particles, so that the emulsion polymerization prepared particles have better dispersing capability.
The method for preparing the polyvinylidene fluoride resin by suspension synthesis of the novel dispersion system provided by the invention is different from the conventional suspension and emulsion polymerization process, breaks through the bottleneck of the conventional preparation process, and provides a better method for preparing the high-purity polyvinylidene fluoride.
Detailed Description
The process according to the invention is further illustrated by the following specific examples, but the invention is not limited to the examples listed but encompasses any other known modifications within the scope of the claims.
The main raw material information is as follows:
vinylidene fluoride: vanhua chemical group Co., ltd., industrial products;
potassium persulfate: aladine, analytically pure;
ammonium perfluorooctanoate: beijing enokie, analytically pure;
10% calcium chloride solution: beijing enokie, analytically pure;
sodium dodecyl diphenyl ether disulfonate: analytical grade of Tokyo Hao chemical industry Co., ltd;
dimethyl phenyl benzyl quaternary ammonium disulfonate calcium: analytical grade of Tokyo Hao chemical industry Co., ltd;
dodecyl mercaptan: beijing enokie, analytically pure;
ethyl acetate: aladine, analytically pure;
tert-butyl peroxypivalate: beijing enokie, analytically pure;
diisopropyl peroxydicarbonate: zibo Red chemical Co., ltd.
The main test method is as follows:
1. impurity content
The product was tested for impurity content using HNMR and nmr analysis was performed on a Bruker 400 nmr.
2. Thermal stability YI
About 15g of the polymer powder was weighed into a 20ml container and heated in an oven at 230℃for 30min. And a Hunterlab Labscan XE yellow index instrument is selected for testing, the yellow index is used for representing the degree of yellowing, and the lower the index is, the better the thermal stability is.
3. Bond strength
The adhesive strength of the polymers after preparation into electrodes was determined according to IS04624 standard (adhesion pull-off test).
The preparation process of the electrode is as follows: 1g of the resin produced in the example was dissolved in 50g of NMP at room temperature under mechanical stirring. 2g of conductive carbon black and 30g of lithium cobalt oxide (LiCo 02) were added with stirring, and thoroughly mixed to ensure uniformity. Then the mixture was degassed under vacuum and spread on an aluminum foil with a doctor blade, finally the aluminum foil on which the electrode material mixture was spread was placed in a vacuum oven and dried for 12 hours at 60 ℃ to prepare an electrode sheet. And measuring the bonding strength of the electrode material on the electrode plate by using an INSTRON tensile machine measuring instrument.
4. Sphericity and particle size
Sample particle sphericity and particle size were tested using a dandong baud 3000plus laser particle size analyzer.
Dispersant 1 preparation:
and (3) vacuumizing a 5L polymerization kettle, supplementing nitrogen to positive pressure, adding 2000g of deionized water, 850g of vinylidene fluoride monomer, 1.2g of emulsifier ammonium perfluorooctanoate and 1.9g of initiator potassium persulfate into the kettle after the oxygen content in the kettle is tested to be lower than 20ppm, heating to 78 ℃ for reaction for 8 hours, cooling to 20 ℃ after the conversion rate reaches 80%, adding 3.4g of flocculant 10% calcium chloride solution into the kettle, and washing resin particles after flocculation. And adding 3.94G of surfactant sodium dodecyl diphenyl ether disulfonate into the kettle, uniformly mixing, adding the slurry into a centrifuge, setting centrifugal force 40G for 10min, drying and screening to obtain the dispersing agent for suspension polymerization, and testing the dispersing agent to have the average sphericity of 0.84 and the average particle diameter of 0.82 microns by using a Dandongbaite 3000plus laser particle size analyzer.
Dispersant 2 preparation:
and (3) vacuumizing a 5L polymerization kettle, supplementing nitrogen to positive pressure, adding 2000g of deionized water, 850g of vinylidene fluoride monomer, 1.2g of emulsifier ammonium perfluorooctanoate and 1.9g of initiator potassium persulfate into the kettle after the oxygen content in the kettle is lower than 20ppm, reacting for 8 hours at 78 ℃, cooling to 20 ℃ after the conversion rate reaches 80%, adding 4.17g of flocculant 5.4% calcium chloride solution into the kettle, and washing resin particles after flocculation. 2.24G of surfactant sodium dodecyl diphenyl ether disulfonate is added into the kettle, the slurry is added into a centrifuge after being uniformly mixed, centrifugal force 34G is set for 10min to treat, drying and screening are carried out, and the dispersing agent for suspension polymerization is obtained, wherein the average sphericity is 0.7 and the average particle diameter is 1.08 by using a dandong hundred 3000plus laser particle size analyzer.
Dispersant 3 preparation:
and (3) vacuumizing a 5L polymerization kettle, supplementing nitrogen to positive pressure, adding 2000g of deionized water, 850g of vinylidene fluoride monomer, 1.2g of emulsifier ammonium perfluorooctanoate and 1.9g of initiator potassium persulfate into the kettle after the oxygen content in the kettle is lower than 20ppm, reacting for 8 hours after the temperature is raised to 78 ℃, cooling to 20 ℃ after the conversion rate reaches 80%, adding 2.3g of flocculant 7.4% calcium chloride solution into the kettle, and washing resin particles after flocculation. And adding 5.03G of surfactant sodium dodecyl diphenyl ether disulfonate into the kettle, uniformly mixing, adding the slurry into a centrifuge, setting centrifugal force 63G, treating for 10min, drying and screening to obtain the dispersing agent for suspension polymerization, and testing the dispersing agent to have the average sphericity of 0.93 and the average particle diameter of 0.35 microns by using a Dandongbaite 3000plus laser particle size analyzer.
Dispersant 4 preparation:
and (3) vacuumizing a 5L polymerization kettle, supplementing nitrogen to positive pressure, adding 2000g of deionized water, 850g of vinylidene fluoride monomer, 1.2g of emulsifier ammonium perfluorooctanoate and 1.9g of initiator potassium persulfate into the kettle after the oxygen content in the kettle is tested to be lower than 20ppm, heating to 78 ℃ for reaction for 8 hours, cooling to 20 ℃ after the conversion rate reaches 80%, adding 6.46g of flocculant 10% calcium chloride solution into the kettle, and washing resin particles after flocculation. Then adding 4.25G of dimethyl phenyl benzyl quaternary ammonium disulfonate serving as a surfactant into the kettle, uniformly mixing, adding the slurry into a centrifuge, setting a centrifugal force of 35G for 10min, drying and screening to obtain the dispersing agent for suspension polymerization, and testing the dispersing agent to have an average sphericity of 0.71 and an average particle diameter of 2.3 microns by using a Dandong hundred 3000plus laser particle analyzer.
Dispersant 5 preparation:
and (3) vacuumizing a 5L polymerization kettle, supplementing nitrogen to positive pressure, adding 2000g of deionized water, 850g of vinylidene fluoride monomer, 1.2g of emulsifier ammonium perfluorooctanoate and 1.9g of initiator potassium persulfate into the kettle after the oxygen content in the kettle is lower than 20ppm, reacting for 8 hours at 78 ℃, cooling to 20 ℃ after the conversion rate reaches 80%, adding 0.94g of flocculant 7.4% calcium chloride solution into the kettle, and washing resin particles after flocculation. Adding 4.25G of surfactant sodium dodecyl diphenyl ether disulfonate into a kettle, uniformly mixing, adding the slurry into a centrifuge, setting centrifugal force 62G for 10min, drying and screening to obtain the dispersing agent for suspension polymerization, and testing the dispersing agent to have the average sphericity of 0.76 and the average particle diameter of 0.14 microns by using a Dandong hundred 3000plus laser particle size analyzer.
Dispersant 6 preparation:
and (3) vacuumizing a 5L polymerization kettle, supplementing nitrogen to positive pressure, adding 2000g of deionized water, 850g of vinylidene fluoride monomer, 1.2g of emulsifier ammonium perfluorooctanoate and 1.9g of initiator potassium persulfate into the kettle after the oxygen content in the kettle is lower than 20ppm, reacting for 8 hours at 78 ℃, cooling to 20 ℃ after the conversion rate reaches 80%, adding 3.4g of flocculant 5.4% calcium chloride solution into the kettle, and washing resin particles after flocculation. And adding 1.02G of surfactant sodium dodecyl diphenyl ether disulfonate into the kettle, uniformly mixing, adding the slurry into a centrifuge, setting centrifugal force 25G for 10min, drying and screening to obtain the dispersing agent for suspension polymerization, and testing the dispersing agent to have the average sphericity of 0.47 and the average particle diameter of 0.91 microns by using a Dandong hundred 3000plus laser particle size analyzer.
Example 1
The experiment was performed in a 5L reactor equipped with a stirrer, the reactor was evacuated and then filled with nitrogen to positive pressure, and the experiment was started after several cycles of testing the oxygen content in the reactor below 20 ppm. 1800g of deionized water, 1100g of vinylidene fluoride monomer, 1.5g of dispersing agent prepared by emulsion polymerization, 2.8g of chain transfer agent dodecyl mercaptan and 1.5g of initiator tert-butyl pivalate peroxide are added into a reaction kettle. And then heating the reaction kettle to 50 ℃ to start polymerization reaction, cooling and recovering unreacted monomers after 7 hours of reaction, filtering, washing and drying the product to obtain polyvinylidene fluoride resin, and then filtering, press-filtering and drying the washing liquid to recover the dispersing agent.
Example 2
The experiment was performed in a 5L reactor equipped with a stirrer, the reactor was evacuated and then filled with nitrogen to positive pressure, and the experiment was started after several cycles of testing the oxygen content in the reactor below 20 ppm. 1800g of deionized water, 1100g of vinylidene fluoride monomer, 2.8g of dispersing agent prepared by emulsion polymerization, 3.7g of chain transfer agent ethyl acetate and 4.9g of initiator diisopropyl peroxydicarbonate are added into a reaction kettle. And then heating the reaction kettle to 54 ℃ to start polymerization reaction, cooling and recovering unreacted monomers after 7 hours of reaction, filtering, washing and drying the product to obtain polyvinylidene fluoride resin, and then filtering, press-filtering and drying the washing liquid to recover the dispersing agent.
Example 3
The experiment was performed in a 5L reactor equipped with a stirrer, the reactor was evacuated and then filled with nitrogen to positive pressure, and the experiment was started after several cycles of testing the oxygen content in the reactor below 20 ppm. 1800g of deionized water, 1100g of vinylidene fluoride monomer, 3.9 g of dispersing agent prepared by emulsion polymerization, 6.1g of chain transfer agent ethyl acetate and 3.2g of initiator tert-butyl peroxypivalate are added into a reaction kettle. And then heating the reaction kettle to 52 ℃ to start polymerization reaction, cooling and recovering unreacted monomers after reacting for 9 hours, filtering, washing and drying the product to obtain polyvinylidene fluoride resin, and then filtering, press-filtering and drying the washing liquid to recover the dispersing agent.
Comparative example 1
Dispersant 1 of example 1 was replaced with hydroxypropyl methylcellulose, with the other conditions unchanged.
Comparative example 2
The dispersant 1 of example 1 was replaced with a dispersant 4 having an excessively large particle diameter, and the other conditions were unchanged.
Comparative example 3
The dispersant 1 of example 1 was replaced with a dispersant 5 having a particle size too small, and the other conditions were unchanged. Comparative example 4
The dispersant 1 of example 1 was replaced with a dispersant 6 having too low a sphericity, with the other conditions unchanged.
The properties of the polyvinylidene fluoride resins obtained in the above examples and comparative examples are shown in the following table 1:
table 1 example and comparative example performance parameters
As can be seen from the table, the polyvinylidene fluoride resin prepared by suspension polymerization of the novel dispersion system has lower impurity content and better thermal stability, and meanwhile, the production cost is low, and the dispersing agent can be recycled.
Those skilled in the art will appreciate that certain modifications and adaptations of the invention are possible and can be made under the teaching of the present specification. Such modifications and adaptations are intended to be within the scope of the present invention as defined in the appended claims.
Claims (10)
1. A method of preparing a high purity lithium electric binder, the method comprising the steps of:
(a) Preparing a dispersing agent: firstly, preparing vinylidene fluoride resin particles through emulsion polymerization, adding a surfactant containing two hydrophilic groups into slurry of the resin particles after coagulation and washing, adding the slurry into a centrifuge after uniform mixing to improve the sphericity of the particles, and drying and screening the resin particles after centrifugation to obtain dispersing agent particles for suspension polymerization; the addition amount of the surfactant is 0.32-0.75wt% of the resin particles;
(b) Suspension polymerization: adding an initiator, a chain transfer agent and a vinylidene fluoride monomer into a reaction kettle, adding the dispersing agent prepared in the step a, heating to perform suspension polymerization, removing unreacted monomers after polymerization, and filtering, washing and drying to obtain polyvinylidene fluoride resin, wherein the sphericity of the dispersing agent particles for suspension polymerization obtained in the step (a) is 0.68-1; the particle size of the particles is 0.3-1.2 microns; the dispersant in the step (b) is used in an amount of 0.4 to 1.2wt% of the vinylidene fluoride monomer.
2. The method of claim 1, further comprising the step of recovering the dispersant: the filtered liquid is sequentially passed through a filter press and a dryer to recover the dispersant particles.
3. The method of claim 1, wherein the coagulant used in the coagulation operation in the preparation of the dispersant of step (a) is an aqueous solution of calcium chloride, and the amount of the coagulant is 0.25 to 0.50% of the amount of vinylidene fluoride; the concentration of the calcium chloride aqueous solution is 5-10wt%.
4. A method according to any one of claims 1 to 3, wherein the surfactant containing two hydrophilic groups in step (a) is one or more of sodium dodecyl diphenyl ether disulfonate, calcium dimethyl phenyl benzyl quaternary ammonium disulfonate, sodium 5, 6-dibutyl naphthalene-2-sulfonate.
5. A process according to any one of claims 1 to 3, wherein the suspension polymerization initiator of step (b) is one or more of dibenzoyl peroxide, diethyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-t-butyl peroxide, t-butyl peroxypivalate, t-butyl hydroperoxide, diisopropyl azodicarboxylate, azobisisobutyronitrile or azobisisoheptonitrile.
6. The method of claim 4, wherein the suspension polymerization initiator of step (b) is one or more of dibenzoyl peroxide, diethyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-t-butyl peroxide, t-butyl peroxypivalate, t-butyl hydroperoxide, diisopropyl azodicarboxylate, azobisisobutyronitrile, or azobisisoheptonitrile.
7. A process according to any one of claims 1 to 3, wherein the initiator is present in an amount of 0.13 to 0.46% by weight of vinylidene fluoride monomer.
8. A process according to any one of claims 1 to 3, wherein the chain transfer agent of step (b) is one or more of dodecyl mercaptan, tridecyl mercaptan, tetradecyl mercaptan, octanethiol, acetone, ethyl propionate, butyl propionate, diethyl malonate, ethyl acetate, butyl acetate, diethyl succinate, dipropyl succinate.
9. A process according to any one of claims 1 to 3 wherein the chain transfer agent in step (b) is used in an amount of 0.2 to 0.58wt% of vinylidene fluoride monomer.
10. A process according to any one of claims 1 to 3, wherein the suspension polymerization in step (b) is carried out at a temperature of 44 to 60 ℃.
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