CN111082062A - Water-soluble binder for lithium ion battery and preparation method thereof - Google Patents
Water-soluble binder for lithium ion battery and preparation method thereof Download PDFInfo
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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
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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
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
- C08F220/04—Acids; Metal salts or ammonium salts thereof
- C08F220/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
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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
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
- C08F220/10—Esters
- C08F220/20—Esters of polyhydric alcohols or phenols, e.g. 2-hydroxyethyl (meth)acrylate or glycerol mono-(meth)acrylate
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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
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
- C08F220/10—Esters
- C08F220/26—Esters containing oxygen in addition to the carboxy oxygen
- C08F220/28—Esters containing oxygen in addition to the carboxy oxygen containing no aromatic rings in the alcohol moiety
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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
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
- C08F220/42—Nitriles
- C08F220/44—Acrylonitrile
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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
- C08F222/00—Copolymers 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 carboxyl radical and containing at least one other carboxyl radical in the molecule; Salts, anhydrides, esters, amides, imides, or nitriles thereof
- C08F222/02—Acids; Metal salts or ammonium salts thereof, e.g. maleic acid or itaconic acid
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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
- C08F222/00—Copolymers 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 carboxyl radical and containing at least one other carboxyl radical in the molecule; Salts, anhydrides, esters, amides, imides, or nitriles thereof
- C08F222/04—Anhydrides, e.g. cyclic anhydrides
- C08F222/06—Maleic anhydride
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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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
Abstract
The invention provides a water-soluble binder for a lithium ion battery and a preparation method thereof, wherein the water-soluble binder comprises an acrylic polymer, and the acrylic polymer is prepared by copolymerizing 20-95 wt%, 1-75 wt% and 1-75 wt% of an ethylenically unsaturated water-soluble flexible polymer by mass percentage, wherein the ethylenically unsaturated nitrile monomer is at least one of ethylenically unsaturated carboxylic acid and ethylenically unsaturated carboxylic anhydride, and the ethylenically unsaturated hydrophilic monomer does not contain carboxyl. The water-soluble binder which can be completely dissolved in water, has low swelling degree of electrolyte and high binding power can improve the high-temperature storage and high-temperature cycle performance of the lithium ion battery and reduce the cost.
Description
Technical Field
The invention relates to a lithium ion battery material and a preparation method thereof, in particular to a lithium ion secondary battery binder and a preparation method thereof.
Background
Currently, lithium ion batteries are considered to be the most promising mobile energy storage technology in mobile electronic products, the electric automobile industry and other energy recycling systems. Common binders for lithium ion batteries are polyvinylidene fluoride (PVDF for short) and styrene-butadiene emulsion (SBR for short). However, the conventional common adhesives have the following problems: (1) when PVDF is used as a binder, an organic solvent used for dissolving PVDF, such as N-methyl pyrrolidone (NMP for short), is harmful to the environment and human body and is expensive; (2) when SBR is used as a binder, cellulose (CMC for short) is required to be added as a thickening agent, but the CMC has general viscosity, large brittleness and poor flexibility, and a pole piece is easy to crack during charging and discharging; meanwhile, when the SBR serving as a binder electrolyte has high swelling degree and is applied to a graphite cathode and a silicon-based novel cathode based on a point-point binding mechanism, the volume of the graphite cathode and the silicon-based cathode repeatedly expands and contracts during charge and discharge cycles, and the point binding easily loses the binding property, so that the capacity loss is caused, and particularly the high-temperature storage and high-temperature cycle performance are deteriorated; in addition, the SBR has a large swelling degree (50% to 200%) in the electrolyte, resulting in an increase in the distance between the negative electrode active materials, and at the same time, a large swelling of the electrolyte results in a decrease in the adhesion of the binder to the copper foil or the active material, resulting in deterioration of the battery performance.
In summary, the conventional SBR binder has poor flexibility due to the addition of a CMC thickener, is very prone to losing cohesiveness due to high swelling degree of an electrolyte, and has adverse effects on high-temperature storage and high-temperature cycle performance of a lithium ion battery manufactured by using the conventional SBR binder due to the decrease in adhesion to a copper foil or an active material due to high swelling degree of the electrolyte.
Disclosure of Invention
The invention aims to provide a water-soluble binder for a lithium ion battery, which can be completely dissolved in water, has low swelling degree of electrolyte and high binding power, and a preparation method thereof, so that the high-temperature storage and high-temperature cycle performance of the lithium ion battery are improved, and the cost can be reduced.
In order to solve the technical problems, the invention provides a water-soluble binder for a lithium ion battery, which comprises an acrylic polymer, wherein the acrylic polymer is prepared by copolymerizing 20-95 wt%, 1-75 wt% and 1-75 wt% of an ethylenically unsaturated water-soluble flexible polymer by mass percentage, at least one of ethylenically unsaturated carboxylic acid and ethylenically unsaturated carboxylic anhydride, an ethylenically unsaturated nitrile-based monomer, an ethylenically unsaturated hydrophilic monomer without a carboxyl group.
Preferably, the acrylic polymer has a molecular weight of 1000 to 100000000, a 1% aqueous solution viscosity of 1 to 10000 mPas, and a swelling degree in an electrolyte of 10% or less.
Preferably, the ethylenically unsaturated carboxylic acid is at least one selected from the group consisting of unsaturated monocarboxylic acids and unsaturated dicarboxylic acids, and the ethylenically unsaturated carboxylic acid anhydride monomer is selected from the group consisting of unsaturated dicarboxylic acid anhydrides.
Preferably, the unsaturated monocarboxylic acid is at least one selected from the group consisting of acrylic acid and methacrylic acid; the unsaturated dicarboxylic acid is at least one selected from maleic acid and itaconic acid; the unsaturated dicarboxylic acid anhydride is at least one of maleic anhydride and itaconic anhydride.
Preferably, the ethylenically unsaturated nitrile monomer is at least one selected from the group consisting of acrylonitrile, α -haloacrylonitrile, and α -alkylacrylonitrile.
Preferably, the α -halogenated acrylonitrile is at least one selected from α -chloroacrylonitrile and α -bromoacrylonitrile, and the α -alkylacrylonitrile is at least one selected from methacrylonitrile and ethacrylonitrile.
Preferably, the ethylenically unsaturated hydrophilic monomer having no carboxyl group is at least one selected from the group consisting of acrylamide, hydroxyethyl acrylate, ethoxyethoxyethyl acrylate, hydroxypropyl acrylate, methacrylamide, hydroxyethyl methacrylate, and sodium vinylsulfonate.
Preferably, the ethylenically unsaturated water-soluble flexible polymer is at least one selected from the group consisting of methoxy polyethylene glycol acrylate, polyethylene glycol diacrylate, urethane acrylate and polyester acrylate.
The invention also provides a preparation method of the water-soluble binder for the lithium ion battery, which is characterized by comprising the following steps of:
placing a water-soluble solvent into a reaction kettle, sealing the reaction kettle, introducing nitrogen into the reaction kettle, and stirring at least one of ethylenically unsaturated carboxylic acid and ethylenically unsaturated carboxylic anhydride, an ethylenically unsaturated nitrile-based monomer, an ethylenically unsaturated hydrophilic monomer without carboxyl, and an ethylenically unsaturated water-soluble flexible polymer according to the mass percentage: 20-95 wt%, 1-75 wt% and 1-75 wt% of the water-soluble solvent, adding alkali liquor, and stirring to uniformly mix to obtain a mixed solution;
step two, heating the mixed solution prepared in the step one to 30-85 ℃, keeping the temperature constant, adding a water-soluble initiator, stirring, and carrying out copolymerization reaction;
step three, removing residual monomers under reduced pressure;
and step four, adding the alkali liquor again, and adjusting the pH value to 5-9 to obtain the viscous water-soluble binder.
Preferably, the water-soluble solvent is water; the alkali liquor is inorganic strong alkali weak acid salt, inorganic strong alkali and inorganic weak alkali.
The lithium ion battery water-soluble binder prepared by the method and the preparation method thereof have the beneficial effects that: the adhesive disclosed by the invention adopts a water-soluble acrylic polymer system with the molecular weight of 1000-100000000, can be completely dissolved in water, has excellent adhesive force by controlling the reasonable mass percentage of each monomer, can form a surface-surface adhesive mechanism, has lower electrolyte swelling degree, better dispersion characteristic and good suspension stability, can be used as an electrode slurry dispersing agent and a viscosity regulator at the same time, enables a pole piece to keep flexible at normal temperature, and keeps the adhesive action between active materials and between current collectors in the manufacturing process and the circulating process of the electrode pole piece.
Drawings
Fig. 1 is a rheological graph of a negative electrode slurry prepared using the binder of the present invention after standing for 48 hours.
Fig. 2 is a graph of the high temperature cycle retention of a simulated battery prepared using the binder of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The invention provides a water-soluble adhesive for a lithium ion battery, which comprises an acrylic polymer. The acrylic polymer is prepared from at least one of ethylenically unsaturated carboxylic acid and ethylenically unsaturated carboxylic anhydride (component A for short), an ethylenically unsaturated nitrile monomer (component B for short), an ethylenically unsaturated hydrophilic monomer without carboxyl (component C for short), and an ethylenically unsaturated water-soluble flexible polymer (component D for short) by mass percent: 20-95 wt%, 1-75 wt%, and copolymerizing. The molecular weight of the acrylic polymer is 1000-100000000, the viscosity of 1% aqueous solution is 1-10000 mPa.s, preferably 10-2800 mPa.s, the glass transition temperature is less than or equal to 50 ℃, the pH value is 5-9, and the swelling degree in the electrolyte is less than or equal to 10%.
The ethylenically unsaturated carboxylic acid is selected from at least one of unsaturated monocarboxylic acid and unsaturated dicarboxylic acid, and the ethylenically unsaturated carboxylic anhydride monomer is selected from unsaturated dicarboxylic anhydride.
Further, the unsaturated monocarboxylic acid is at least one selected from acrylic acid and methacrylic acid. The unsaturated dicarboxylic acid is at least one selected from maleic acid and itaconic acid; the unsaturated dicarboxylic acid anhydride is at least one of maleic anhydride and itaconic anhydride.
The ethylenically unsaturated nitrile monomer is selected from at least one of acrylonitrile, α -halogenated acrylonitrile and α -alkyl acrylonitrile, the α -halogenated acrylonitrile is selected from at least one of α -chloroacrylonitrile and α -bromoacrylonitrile, and the α -alkyl acrylonitrile is selected from at least one of methacrylonitrile and ethacrylonitrile.
The ethylenically unsaturated hydrophilic monomer having no carboxyl group must have the following characteristics: has a solubility in 100g of water at room temperature of not less than 0.5g, contains no carboxyl group, no carboxylic anhydride, and has an ethylenically unsaturated bond. Further, the ethylenically unsaturated hydrophilic monomer having no carboxyl group is at least one selected from the group consisting of acrylamide, hydroxyethyl acrylate, ethoxyethoxyethyl acrylate, hydroxypropyl acrylate, methacrylamide, hydroxyethyl methacrylate, and sodium vinylsulfonate.
The ethylenically unsaturated water-soluble flexible polymer must have the following characteristics: a glass transition temperature of not more than 30 ℃ and a solubility in 100g of water at room temperature of not less than 0.5g, an ethylenically unsaturated bond, and a molecular weight of 100 to 100000.
Further, the ethylenically unsaturated water-soluble flexible polymer is selected from at least one of methoxy polyethylene glycol acrylate, polyethylene glycol diacrylate, polyurethane acrylate and polyester acrylate.
The invention also provides a preparation method of the water-soluble binder of the lithium ion battery, which adopts soap-free emulsion polymerization and comprises the following steps:
step one, batching; at room temperature (20 ℃), placing a solvent in a reaction kettle, introducing nitrogen under the stirring state of the rotating speed of 10-1000 rpm, ensuring that the gas in the kettle is replaced for 2 times for 2 hours by ensuring the flow rate of the nitrogen to be 1-2 kettle volumes/hour and the ventilation time to be 1-2 hours, removing dissolved oxygen of a system, and mixing at least one of ethylenically unsaturated carboxylic acid and ethylenically unsaturated carboxylic anhydride, an ethylenically unsaturated nitrile-based monomer, an ethylenically unsaturated hydrophilic monomer without carboxyl, and an ethylenically unsaturated water-soluble flexible polymer according to mass percent: 20-95 wt%, 1-75 wt% and 1-75 wt% of a water-soluble solvent, adding an alkali liquor, stirring at a rotation speed of 10-1000 rpm for 1-2 h, and uniformly mixing to obtain a solution with a pH of 1-5, wherein the mass concentration of the solution is 10-90%. The alkali liquor is inorganic strong alkali weak acid salt, inorganic strong alkali and inorganic weak alkali. The water-soluble solvent is water.
And step two, heating the solution prepared in the step one to 30-85 ℃ at a heating rate of 1 min/DEG C, keeping the temperature constant, adding a water-soluble initiator which is 0.1-1% of the total amount of the monomers in the mixed solution obtained in the step one, such as persulfate, hydrogen peroxide, azobisisobutylamidine hydrochloride and the like, stirring at the rotating speed of 10-1000 rpm, reacting for 5-10 hours, and carrying out copolymerization.
The effect of this step is that the monomers copolymerize to form the desired product.
And step three, removing residual monomers under reduced pressure, and vacuumizing for 2 hours, wherein the vacuum degree is less than or equal to-0.1 MPa.
The step is used for eliminating unreacted monomers and improving the purity of the product.
And fourthly, adding alkali liquor (inorganic strong base and weak acid salt such as carbonate, phosphate, oxalate, acetate and the like; inorganic strong base such as lithium hydroxide, sodium hydroxide, potassium hydroxide and the like; inorganic weak base such as ammonia water) again, and adjusting the pH to 5-9 to obtain a viscous water-soluble binder, wherein the viscosity of 1% aqueous solution with the viscosity meeting the requirement is 1-10000 mPa & s, preferably 10-1000 mPa & s, namely the water-soluble binder for the lithium ion battery.
The step is used for neutralizing, and anionizing carboxyl groups to improve the water solubility of the product.
The compositions and weights of examples 1 to 8 and comparative examples 1 to 5 are shown in Table 1, and some experimental parameters of examples 1 to 8 and comparative examples 1 to 5 are shown in Table 2.
TABLE 1
TABLE 2
The test results of examples 1 to 8 and comparative examples 1 to 5 are shown in Table 3.
The water-soluble binder for the lithium ion battery prepared by the method judges the water solubility by turbidity. The method comprises the following steps: diluting the sample to 1 w% concentration, testing the turbidity value by using a turbidity meter, and judging that the water solubility of the sample is poor if the turbidity value is more than 100 NTU; if the turbidity value is less than or equal to 100NTU, the water solubility of the sample can be judged to be good, and the test result is shown in Table 3. Reference standard: JJG880-2006 turbidimeter.
And the water-soluble binder is used for testing the swelling degree of the electrolyte:
the water-soluble binder of the film-formed example and the binder of the comparative example were cut into a square film having a side length of 1cm, dried in an oven at a temperature of 105 ℃ and a vacuum degree of-0.075 MPa for 2 hours, weighed as M1, placed in a glass-sealed bottle with a lid containing an electrolyte of ethylene carbonate EC, ethyl methyl carbonate EMC and diethyl carbonate DEC in a volume ratio of EC: EMC: DEC of 3:2:5, kept at 70 ℃ for 7 days, weighed as M2 after the electrolyte on the surface of the film was gently sucked off in a drying room, and weighed as M2, and the Swelling degree of the electrolyte, Swelling:
when the steel is in the range of (M2-M1)/M1 × 100%, the test results are shown in Table 3;
the weighed film was further baked in an oven at 105 ℃ and a vacuum of-0.075 MPa for 2 hours, the weight was recorded as M3, and the electrolyte dissolution disorder was:
distol. (M1-M3)/M1 × 100%, the test results are shown in table 3.
The invention also provides a battery pole piece manufactured by using the water-soluble binder for the lithium ion battery. The water-soluble binder for the lithium ion battery prepared in the embodiments 1-8 and the binder in the comparative examples 1-5 are respectively used for preparing the positive electrode pole piece and the negative electrode pole piece of the lithium ion battery with the conventional positive electrode active material and the conventional negative electrode active material.
Further, the water-soluble binder for the lithium ion battery obtained in the embodiment is used for manufacturing the silicon-based and graphite composite negative electrode material electrode plate. The silicon-based and graphite composite negative electrode material is preferably SiOx, wherein x is more than 1 and less than 2, or C or Si-C composite material containing Si and C and natural graphite or artificial graphite, and the gram volume of the silicon-based and graphite composite negative electrode material is 600 mAh/g.
Preparing cathode electrode plate slurry: the silicon-based composite negative electrode material, the conductive carbon black, the water-soluble binder (based on solid content) for the lithium ion batteries of the embodiment and the comparative example are mixed according to the mass fractions of 95.5 wt%, 2.0 wt% and 2.5 w%, and deionized water is added according to the proportion that the total solid content is 45 wt% to prepare the negative electrode pole piece slurry. The slurry which is uniformly dispersed is screened by a 100-mesh screen according to the prior art, then coated on a copper foil with the thickness of 10 mu m which is used as a current collector, directly put into a furnace for drying for 5 minutes at the temperature of 120 ℃, naturally cooled to the room temperature in the furnace, and then the temperature is 10 multiplied by 104And (3) calendering the load of N/m unit length to obtain an electrode piece which is used as a lithium ion battery cathode.
And (3) measuring the stability of the negative electrode pole piece slurry:
the negative electrode pole piece slurry prepared by the examples and the comparative examples is kept still for 48 hours, a rheologic diagram is measured by a rheometer, the slurry shows a trend of increasing stress and decreasing viscosity along with the increase of the shear rate, and the test result is shown in figure 1.
And (3) determining the peel strength of the negative pole piece:
the rolled and non-rolled electrode sheets of examples and comparative examples were cut into a 20cm × 2.5cm strip, a steel sheet 1mm thick was adhered to the collector side with a double-sided tape, a transparent adhesive tape was adhered to the coated layer side, and the sheet was peeled at a speed of 100mm/min in a 180 ° direction by a tensile tester, and the peel stress was measured, and the test results are shown in table 3.
And evaluating the flexibility of the negative pole piece:
a mandrel with the diameter phi of 1.5mm is placed on one side of the current collector of the rolled pole piece in the example and the comparative example, a bending experiment is carried out, the state of the pole piece at the moment is observed through an optical microscope, the pole piece is intact and is marked as ○, the pole piece is peeled off or cracked and is marked as x, and the test result is shown in table 3.
The invention also provides a simulated lithium ion battery which is made by using the silicon-based and graphite composite negative electrode pole piece made of the water-soluble binder for the lithium ion battery, and a conventional positive electrode pole piece, electrolyte and diaphragm.
And evaluating the performance of the simulated lithium ion battery:
the first coulombic efficiency of the charge-discharge cycle of the simulated lithium ion battery and the coulombic efficiency and the capacity retention rate after 50 cycles are tested by a constant current method, the ratio of the thickness increase value of the pole piece to the thickness of the pole piece before charge-discharge is recorded as the expansion rate of the pole piece after 50 cycles of charge-discharge and in a lithium-embedded state of the pole piece, and the obtained results are shown in a table 3.
The simulated high-temperature cycle performance of the lithium ion battery is as follows:
the simulated lithium ion battery is directly placed in an oven environment at 60 ℃, and after 50 weeks of circulation, the circulation capacity retention rate is determined, and the test result is shown in figure 2.
TABLE 3
As shown in Table 3, the binders in the embodiments 1 to 8 of the present invention have the characteristics of good water solubility, small swelling of the electrolyte, high peel strength, and the like, i.e., compared with the electrodes and the simulated batteries using the binders in the comparative examples 1 to 5, the binders in the embodiments 1 to 8 of the present invention have the advantages of high pole piece binding power, good flexibility, low swelling degree of the electrolyte, high capacity retention rate after 50-week charge and discharge cycles, and lower pole piece swelling ratio than that in the comparative examples 1 to 5.
From fig. 1, the rheological curve of the negative electrode plate slurry prepared by the embodiments 1 to 8 of the present invention almost completely coincides with that of the slurry after standing for 0 hour, which indicates that the slurry prepared by the binder of the present invention has good stability.
From fig. 2, it is found that the high temperature performance of the simulated battery prepared by using the water-soluble binder having high intrinsic viscosity and low electrolyte swelling according to examples 1 to 8 of the present invention is improved.
Claims (10)
1. The water-soluble binder for the lithium ion battery is characterized by comprising an acrylic polymer, wherein the acrylic polymer is prepared by copolymerizing 20-95 wt%, 1-75 wt% and 1-75 wt% of an ethylenically unsaturated water-soluble flexible polymer by mass percentage, at least one of ethylenically unsaturated carboxylic acid and ethylenically unsaturated carboxylic anhydride, an ethylenically unsaturated nitrile-based monomer, an ethylenically unsaturated hydrophilic monomer without a carboxyl group.
2. The aqueous binder for lithium ion battery according to claim 1, wherein the acrylic polymer has a molecular weight of 1000 to 100000000, a 1% aqueous solution viscosity of 1 to 10000mPa · s, and a swelling degree in an electrolyte of 10% or less.
3. The water-soluble binder for lithium ion batteries according to claim 1, wherein said ethylenically unsaturated carboxylic acid is at least one selected from the group consisting of unsaturated monocarboxylic acids and unsaturated dicarboxylic acids, and said ethylenically unsaturated carboxylic acid anhydride monomer is selected from the group consisting of unsaturated dicarboxylic acid anhydrides.
4. The water-soluble binder for lithium ion batteries according to claim 3, wherein said unsaturated monocarboxylic acid is at least one member selected from the group consisting of acrylic acid and methacrylic acid; the unsaturated dicarboxylic acid is at least one selected from maleic acid and itaconic acid; the unsaturated dicarboxylic acid anhydride is at least one of maleic anhydride and itaconic anhydride.
5. The water-soluble binder for lithium ion batteries according to claim 1, wherein said ethylenically unsaturated nitrile monomer is at least one monomer selected from the group consisting of acrylonitrile, α -haloacrylonitrile, and α -alkylacrylonitrile.
6. The water-soluble binder for the lithium ion battery as claimed in claim 5, wherein the α -halogenated acrylonitrile is selected from at least one of α -chloroacrylonitrile and α -bromoacrylonitrile, and the α -alkylacrylonitrile is selected from at least one of methacrylonitrile and ethacrylonitrile.
7. The water-soluble binder for lithium ion batteries according to claim 1, wherein said ethylenically unsaturated hydrophilic monomer containing no carboxyl group is at least one monomer selected from the group consisting of acrylamide, hydroxyethyl acrylate, ethoxyethoxyethoxyethyl acrylate, hydroxypropyl acrylate, methacrylamide, hydroxyethyl methacrylate, and sodium vinylsulfonate.
8. The water-soluble binder for lithium ion batteries according to claim 1, wherein said ethylenically unsaturated water-soluble flexible polymer is at least one selected from the group consisting of methoxypolyethylene glycol acrylate, polyethylene glycol diacrylate, urethane acrylate, and polyester acrylate.
9. The preparation method of the water-soluble binder for the lithium ion battery is characterized by comprising the following steps of:
placing a water-soluble solvent into a reaction kettle, sealing the reaction kettle, introducing nitrogen into the reaction kettle, and stirring at least one of ethylenically unsaturated carboxylic acid and ethylenically unsaturated carboxylic anhydride, an ethylenically unsaturated nitrile-based monomer, an ethylenically unsaturated hydrophilic monomer without carboxyl, and an ethylenically unsaturated water-soluble flexible polymer according to the mass percentage: 20-95 wt%, 1-75 wt% and 1-75 wt% of the water-soluble solvent, adding alkali liquor, and stirring to uniformly mix to obtain a mixed solution;
step two, heating the mixed solution prepared in the step one to 30-85 ℃, keeping the temperature constant, adding a water-soluble initiator, stirring, and carrying out copolymerization reaction;
step three, removing residual monomers under reduced pressure;
and step four, adding the alkali liquor again, and adjusting the pH value to 5-9 to obtain the viscous water-soluble binder.
10. The method for preparing a water-soluble binder for a lithium ion battery according to claim 9, wherein the water-soluble solvent is water; the alkali liquor is inorganic strong alkali weak acid salt, inorganic strong alkali and inorganic weak alkali.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111697234A (en) * | 2020-06-19 | 2020-09-22 | 中国地质大学（武汉） | Water-based crosslinking binder for lithium ion battery and preparation method and application thereof |
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| CN111697234A (en) * | 2020-06-19 | 2020-09-22 | 中国地质大学（武汉） | Water-based crosslinking binder for lithium ion battery and preparation method and application thereof |
| CN114560973A (en) * | 2021-01-29 | 2022-05-31 | 深圳市研一新材料有限责任公司 | Lithium ion battery anode aqueous binder and preparation method thereof |
| CN114560973B (en) * | 2021-01-29 | 2023-05-16 | 深圳市研一新材料有限责任公司 | Water-based binder for positive electrode of lithium ion battery and preparation method thereof |
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Application publication date: 20200428 |