CN112768693A - Binder for lithium ion battery and preparation method thereof - Google Patents

Binder for lithium ion battery and preparation method thereof Download PDF

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CN112768693A
CN112768693A CN202110028291.5A CN202110028291A CN112768693A CN 112768693 A CN112768693 A CN 112768693A CN 202110028291 A CN202110028291 A CN 202110028291A CN 112768693 A CN112768693 A CN 112768693A
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binder
formula
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polyfluorinated ethylene
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CN112768693B (en
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陈云
蒋天天
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Wuhai Ruisen New Energy Materials Co ltd
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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
    • 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
    • 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
    • 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
    • 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 discloses a binder for a lithium ion battery and a preparation method thereof, wherein the binder comprises polyfluorinated ethylene, carboxymethyl cellulose gel and modified sodium polyacrylate; wherein, the carboxymethyl cellulose gel is modified by graphene oxide, and the sodium polyacrylate is modified by a carbon nano tube and sodium dodecyl benzene sulfonate. The prepared binder has good conductivity and stability, the expansion rate of the binder is very small after the binder is soaked in electrolyte, the reduction rate of the binding strength is small, meanwhile, the assembled battery has better cycle rate performance and cycle life, and the performance of the lithium ion battery can be integrally improved by the binder.

Description

Binder for lithium ion battery and preparation method thereof
Technical Field
The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a binder for a lithium ion battery and a preparation method thereof.
Background
The lithium ion battery has the advantages of large specific capacity, good cycle performance, small volume and the like, is widely applied in the electronic field, becomes the best choice of the power battery of the electric automobile, and has increasingly growing demand for the power lithium ion battery along with the development of the technology. The anode material, the cathode material, the electrolyte and the diaphragm are the keys of the lithium ion battery. Preparing active slurry from the positive and negative electrode active substances, a conductive agent and a binder, uniformly coating the active slurry on an aluminum foil or a copper foil, and forming the lithium ion battery by baking, rolling, flaking and other processes. The binder is used as one of important components of the anode material and the cathode material, has the main functions of ensuring the uniformity and safety during pulping, plays an effective bonding role between active substance particles and a current collector, forms a stable solid electrolyte interface film (SEI) on the surface of the cathode carbon material, and has better ionic and electronic conductivity.
The current binders for electrode materials of lithium ion batteries are mainly: carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), and the like. However, these binders are different from the electrolyte (mainly carbonate) components, and reduce compatibility with electrode materials and SEI films. The polycarbonate is a novel polymer with biodegradability and low toxicity, and the molecular structure of the polycarbonate is similar to the components of the conventional electrolyte, so that a more stable SEI film is formed on the surface of an electrode, and the electrochemical performance of the battery is improved.
Disclosure of Invention
The invention aims to provide a binder for a lithium ion battery, which comprises polyfluorinated ethylene, carboxymethyl cellulose gel and modified sodium polyacrylate; the polyfluorinated ethylene comprises polymers of structural units shown in a formula I, a formula II, a formula III and a formula IV:
Figure BDA0002891017560000011
Figure BDA0002891017560000021
wherein R is1Is C unsubstituted by a substituent1～4The linear alkyl group of (1); r2Is C unsubstituted by a substituent2～6Carboxylic acid groups of (a); r3Is C unsubstituted by a substituent3～8The linear alkyl group of (1); r4Is C4～8Carboxylic acid groups of (a); r5Is C unsubstituted or substituted by a substituent1～8Carboxylic acid groups of (a); r6Is C unsubstituted or substituted by a substituent6～16The linear alkyl group of (1); r7Is C unsubstituted or substituted by a substituent4～16Carboxylic acid group of (1).
Further, the structural unit shown in the formula I accounts for 30-45% of the mass of the polyfluorinated ethylene, the structural unit shown in the formula II accounts for 20-30% of the mass of the polyfluorinated ethylene, the structural unit shown in the formula III accounts for 10-15% of the mass of the polyfluorinated ethylene, and the structural unit shown in the formula IV accounts for 20-30% of the mass of the polyfluorinated ethylene.
Still further, the polyfluorinated ethylene has the formula I: n is more than or equal to 330 and less than or equal to 390; formula II: n is more than or equal to 290 and less than or equal to 350; formula II: n is more than or equal to 240 and less than or equal to 310; formula II: n is more than or equal to 300 and less than or equal to 400.
Further, the binder comprises 45-60 parts of polyfluorinated ethylene, 20-35 parts of carboxymethyl cellulose gel and 16-22 parts of modified sodium polyacrylate.
Another object of the present invention is to provide a method for preparing a binder for a lithium ion battery, the method comprising the steps of:
s1: and uniformly mixing the polymers I, II, III and IV, adding the mixture into a ball mill, grinding for 2-4 hours, sieving the mixture with a 500-600 mesh sieve, and extruding the mixture in an extruder to obtain polyfluorinated ethylene powder, wherein the extrusion temperature is 310-335 ℃.
S2: adding the polyfluorinated ethylene powder, the carboxymethyl cellulose gel and the modified sodium polyacrylate in the step S1 into a mortar, uniformly mixing and grinding, then heating to 105-120 ℃, stirring for 0.5-2 h, shearing, and grinding to obtain the binder.
Preferably, the carboxymethyl cellulose gel is prepared by the following method:
1) adding sodium carboxymethylcellulose into distilled water, then adding graphene oxide, heating to 55-70 ℃, stirring and ultrasonically treating for 2-4 h, wherein the mass-to-volume ratio of the sodium carboxymethylcellulose to the distilled water to the graphene oxide is (2-4) g, (25-38) mL, (0.16-0.39) g.
2) Adding a complexing agent into the mixed solution obtained in the step 1), continuously stirring for 0.5-1 h, moving into a high-pressure reaction kettle, reacting for 8-10 h at 90-105 ℃, cooling, and freeze-drying to obtain the carboxymethyl cellulose gel, wherein the mass ratio of the complexing agent to the graphene oxide is 2.6-3.4: 1.
More preferably, the complexing agent is any one of citric acid and L-ascorbic acid.
Preferably, the modified sodium polyacrylate is prepared by the following method:
adding deionized water and isopropanol into a three-neck flask, stirring uniformly, raising the temperature to 75-85 ℃, then dropwise adding an aqueous solution of acrylic acid and potassium persulfate, after dropwise adding for 3.5h, preserving heat at the temperature for reflux reaction for 3-3.5 h, cooling to room temperature, dropwise adding an aqueous solution of sodium hydroxide into the mixed solution, stirring to adjust the pH value to 7.2-8.8, then adding carbon nano tubes and sodium dodecyl benzene sulfonate, heating to boiling, continuously stirring, drying in vacuum at 60 ℃ after water is basically volatilized, and crushing to obtain the modified sodium polyacrylate.
More preferably, the mass ratio of the isopropanol to the acrylic acid to the potassium persulfate is (1-1.6): (1-4.2): 0.26-0.89); the mass fraction of the sodium hydroxide aqueous solution is 30-36%.
More preferably, the mass ratio of the carbon nano tube, the sodium dodecyl benzene sulfonate and the acrylic acid is (1-2): (0.65-1.7): (8.6-16.9).
Compared with the prior art, the invention has the following beneficial effects:
(1) in the invention, the binder prepared by using the four types of polyfluorinated ethylene, carboxymethyl cellulose gel and modified sodium polyacrylate has excellent stability, the expansion rate of the binder after being soaked in electrolyte is very small, the reduction rate of the binding strength is small, meanwhile, the assembled battery has better cycle rate performance and cycle life, and the binder can improve the performance of the lithium ion battery on the whole.
(2) In the invention, the graphene oxide modified carboxymethyl cellulose gel, the carbon nano tube and the sodium dodecyl benzene sulfonate modified sodium polyacrylate have better conductivity, and meanwhile, the modified acrylic acid and the carboxymethyl cellulose gel have abundant functional groups on the surface, can generate hydrogen bond action with F atoms in polyfluorinated ethylene, effectively improve the stability of the binder and avoid the stripping phenomenon in the use process.
(3) The binder disclosed by the invention can be used in a lithium ion battery anode material and a lithium ion battery cathode material, and has universality.
Detailed Description
The following embodiments of the present invention are described in detail, and the embodiments are implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, it should be noted that, for those skilled in the art, a plurality of modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Example 1
A preparation method of a binder for a lithium ion battery specifically comprises the following steps:
the binder comprises 45 parts of polyfluorinated ethylene, 20 parts of carboxymethyl cellulose gel and 16 parts of modified sodium polyacrylate.
The structural unit shown in the formula I of the polyfluorinated ethylene accounts for 30 percent of the mass of the polyfluorinated ethylene, the structural unit shown in the formula II accounts for 30 percent of the mass of the polyfluorinated ethylene, the structural unit shown in the formula III accounts for 10 percent of the mass of the polyfluorinated ethylene, and the structural unit shown in the formula IV accounts for 30 percent of the mass of the polyfluorinated ethylene.
Wherein R in the polyfluoroethylene1Is C unsubstituted by a substituent1The linear alkyl group of (1); r2Is C unsubstituted by a substituent2Carboxylic acid groups of (a); r3Is C unsubstituted by a substituent3The linear alkyl group of (1); r4Is C4Carboxylic acid groups of (a); r5Is C unsubstituted by a substituent1Carboxylic acid groups of (a); r6Is unsubstituted or substituted C6The linear alkyl group of (1); r7Is C unsubstituted by a substituent4Carboxylic acid group of (1).
Wherein the polyfluoroethylene has the formula I: n is more than or equal to 380 and less than or equal to 390; formula II: n is more than or equal to 330 and less than or equal to 350; formula II: n is more than or equal to 290 and less than or equal to 310; formula II: n is more than or equal to 380 and less than or equal to 400.
The preparation method comprises the following steps:
s1: the polymers I, II, III and IV are mixed uniformly and added into a ball mill for grinding for 2 hours, then the mixture is sieved by a 500-mesh sieve, and the mixture is extruded in an extruder to obtain polyfluorinated ethylene powder, wherein the extrusion temperature is 310 ℃.
S2: adding the polyfluorinated ethylene powder, the carboxymethyl cellulose gel and the modified sodium polyacrylate in the step S1 into a mortar, uniformly mixing and grinding, then heating to 105 ℃, stirring for 0.5h, shearing, and grinding to obtain the binder.
The carboxymethyl cellulose gel is prepared by the following method:
1) adding sodium carboxymethylcellulose into distilled water, then adding graphene oxide, raising the temperature to 55 ℃, stirring and ultrasonically treating for 2h, wherein the mass-volume ratio of the carboxymethylcellulose to the distilled water to the graphene oxide is 2g:25mL:0.16 g.
2) Adding citric acid into the mixed solution obtained in the step 1), continuously stirring for 0.5h, moving into a high-pressure reaction kettle, reacting for 8h at 90 ℃, cooling, and freeze-drying to obtain the carboxymethyl cellulose gel, wherein the mass ratio of the complexing agent to the graphene oxide is 2.6: 1.
The modified sodium polyacrylate is prepared by the following method:
adding deionized water and isopropanol into a three-neck flask, stirring uniformly, raising the temperature to 75 ℃, then dropwise adding an aqueous solution of acrylic acid and potassium persulfate, after dropwise adding for 3.5 hours, preserving heat at the temperature for reflux reaction for 3 hours, cooling to room temperature, dropwise adding an aqueous solution of sodium hydroxide into the mixed solution, stirring to adjust the pH value to 7.2, then adding a carbon nano tube and sodium dodecyl benzene sulfonate, heating to boiling and stirring continuously, drying in vacuum at 60 ℃ after water is basically volatilized, and crushing to obtain modified sodium polyacrylate, wherein the mass ratio of the isopropanol, the acrylic acid and the potassium persulfate is 1:1: 0.26; the mass fraction of the sodium hydroxide aqueous solution is 30 percent; the mass ratio of the carbon nano tube to the sodium dodecyl benzene sulfonate to the acrylic acid is 1:0.65: 8.6.
Example 2
A preparation method of a binder for a lithium ion battery specifically comprises the following steps:
the binder comprises 60 parts of polyfluorinated ethylene, 35 parts of carboxymethyl cellulose gel and 22 parts of modified sodium polyacrylate.
The structural unit shown in the formula I of the polyfluorinated ethylene accounts for 45% of the mass of the polyfluorinated ethylene, the structural unit shown in the formula II accounts for 20% of the mass of the polyfluorinated ethylene, the structural unit shown in the formula III accounts for 15% of the mass of the polyfluorinated ethylene, and the structural unit shown in the formula IV accounts for 20% of the mass of the polyfluorinated ethylene.
Wherein R in the polyfluoroethylene1Is C unsubstituted by a substituent4The linear alkyl group of (1); r2Is C unsubstituted by a substituent6Carboxylic acid groups of (a); r3Is C unsubstituted by a substituent8The linear alkyl group of (1); r4Is C8Carboxylic acid groups of (a); r5Is C unsubstituted by a substituent8Carboxylic acid groups of (a); r6Is C unsubstituted by a substituent16The linear alkyl group of (1); r7Is C unsubstituted or substituted by a substituent16Carboxylic acid group of (1).
Wherein the polyfluoroethylene has the formula I: n is more than or equal to 330 and less than or equal to 340; formula II: n is more than or equal to 290 and less than or equal to 310; formula II: n is more than or equal to 240 and less than or equal to 260; formula II: n is more than or equal to 300 and less than or equal to 320.
The preparation method comprises the following steps:
s1: and uniformly mixing the polymers I, II, III and IV, adding the mixture into a ball mill for grinding for 4 hours, then sieving the mixture through a 600-mesh screen, and extruding the mixture in an extruder to obtain polyfluorinated ethylene powder, wherein the extrusion temperature is 335 ℃.
S2: adding the polyfluorinated ethylene powder, the carboxymethyl cellulose gel and the modified sodium polyacrylate in the step S1 into a mortar, uniformly mixing and grinding, then heating to 120 ℃, stirring for 2 hours, shearing, and grinding to obtain the binder.
The carboxymethyl cellulose gel is prepared by the following method:
1) adding sodium carboxymethylcellulose into distilled water, then adding graphene oxide, raising the temperature to 70 ℃, and carrying out ultrasonic stirring for 4 hours, wherein the mass-volume ratio of the carboxymethylcellulose to the distilled water to the graphene oxide is 4g:38mL:0.39 g.
2) Adding L-ascorbic acid into the mixed solution obtained in the step 1), continuously stirring for 1h, moving the mixed solution into a high-pressure reaction kettle, reacting for 10h at 105 ℃, cooling, and freeze-drying to obtain the carboxymethyl cellulose gel, wherein the mass ratio of the complexing agent to the graphene oxide is 3.4: 1.
The modified sodium polyacrylate is prepared by the following method:
adding deionized water and isopropanol into a three-neck flask, stirring uniformly, raising the temperature to 85 ℃, then dropwise adding an aqueous solution of acrylic acid and potassium persulfate, after dropwise adding for 3.5 hours, carrying out heat preservation reflux reaction for 3.5 hours at the temperature, cooling to room temperature, dropwise adding an aqueous solution of sodium hydroxide into the mixed solution, stirring to adjust the pH value to 8.8, then adding a carbon nano tube and sodium dodecyl benzene sulfonate, heating to boiling and continuously stirring until water is basically volatilized, then carrying out vacuum drying at 60 ℃, and crushing to obtain modified sodium polyacrylate, wherein the mass ratio of the isopropanol, the acrylic acid and the potassium persulfate is 1.6:4.2: 0.89; the mass fraction of the sodium hydroxide aqueous solution is 36 percent; the mass ratio of the carbon nano tube to the sodium dodecyl benzene sulfonate to the acrylic acid is 2:1.7: 16.9.
Example 3
A preparation method of a binder for a lithium ion battery specifically comprises the following steps:
the binder comprises 50 parts of polyfluorinated ethylene, 25 parts of carboxymethyl cellulose gel and 18 parts of modified sodium polyacrylate.
The structural unit shown in the formula I of the polyfluorinated ethylene accounts for 35% of the mass of the polyfluorinated ethylene, the structural unit shown in the formula II accounts for 25% of the mass of the polyfluorinated ethylene, the structural unit shown in the formula III accounts for 10% of the mass of the polyfluorinated ethylene, and the structural unit shown in the formula IV accounts for 30% of the mass of the polyfluorinated ethylene.
Wherein R in the polyfluoroethylene1Is C unsubstituted by a substituent3The linear alkyl group of (1); r2Is C unsubstituted by a substituent3Carboxylic acid groups of (a); r3Is C unsubstituted by a substituent5The linear alkyl group of (1); r4Is C6Carboxylic acid groups of (a); r5Is C substituted by a substituent4Carboxylic acid groups of (a); r6Is C unsubstituted by a substituent12Linear chain of (2)An alkyl group; r7Is C unsubstituted by a substituent8Carboxylic acid group of (1).
Wherein the polyfluoroethylene has the formula I: n is more than or equal to 350 and less than or equal to 360; formula II: n is more than or equal to 310 and less than or equal to 320; formula II: n is more than or equal to 260 and less than or equal to 280; formula II: n is more than or equal to 320 and less than or equal to 350.
The preparation method comprises the following steps:
s1: and uniformly mixing the polymers I, II, III and IV, adding the mixture into a ball mill for grinding for 3 hours, then sieving the mixture through a 550-mesh screen, and extruding the mixture in an extruder to obtain polyfluorinated ethylene powder, wherein the extrusion temperature is 320 ℃.
S2: adding the polyfluorinated ethylene powder, the carboxymethyl cellulose gel and the modified sodium polyacrylate in the step S1 into a mortar, uniformly mixing and grinding, then heating to 110 ℃, stirring for 1h, pouring out, shearing, and grinding to obtain the binder.
The carboxymethyl cellulose gel is prepared by the following method:
1) adding sodium carboxymethylcellulose into distilled water, then adding graphene oxide, heating to 60 ℃, stirring and ultrasonically treating for 3h, wherein the mass-volume ratio of the carboxymethylcellulose to the distilled water to the graphene oxide is 3g:30mL:0.22 g.
2) Adding citric acid into the mixed solution obtained in the step 1), continuously stirring for 1h, moving into a high-pressure reaction kettle, reacting for 9h at 95 ℃, cooling, and freeze-drying to obtain the carboxymethyl cellulose gel, wherein the mass ratio of the complexing agent to the graphene oxide is 2.9: 1.
The modified sodium polyacrylate is prepared by the following method:
adding deionized water and isopropanol into a three-neck flask, stirring uniformly, raising the temperature to 80 ℃, then dropwise adding an aqueous solution of acrylic acid and potassium persulfate, after dropwise adding for 3.5 hours, carrying out heat preservation reflux reaction for 3.2 hours at the temperature, cooling to room temperature, dropwise adding an aqueous solution of sodium hydroxide into a mixed solution, stirring to adjust the pH value to 7.8, then adding a carbon nano tube and sodium dodecyl benzene sulfonate, heating to boiling and continuously stirring, carrying out vacuum drying at 60 ℃ after water is basically volatilized, and crushing to obtain modified sodium polyacrylate, wherein the mass ratio of the isopropanol, the acrylic acid and the potassium persulfate is 1.2:2.6: 0.44; the mass fraction of the sodium hydroxide aqueous solution is 32 percent; the mass ratio of the carbon nano tube to the sodium dodecyl benzene sulfonate to the acrylic acid is 1.4:0.96: 11.6.
Example 4
A preparation method of a binder for a lithium ion battery specifically comprises the following steps:
the binder comprises 55 parts of polyfluorinated ethylene, 30 parts of carboxymethyl cellulose gel and 20 parts of modified sodium polyacrylate.
The structural unit shown in the formula I of the polyfluorinated ethylene accounts for 40% of the mass of the polyfluorinated ethylene, the structural unit shown in the formula II accounts for 30% of the mass of the polyfluorinated ethylene, the structural unit shown in the formula III accounts for 10% of the mass of the polyfluorinated ethylene, and the structural unit shown in the formula IV accounts for 20% of the mass of the polyfluorinated ethylene.
Wherein R in the polyfluoroethylene1Is C unsubstituted by a substituent3The linear alkyl group of (1); r2Is C unsubstituted by a substituent5Carboxylic acid groups of (a); r3Is C unsubstituted by a substituent7The linear alkyl group of (1); r4Is C7Carboxylic acid groups of (a); r5Is C unsubstituted by a substituent7Carboxylic acid groups of (a); r6Is C unsubstituted by a substituent15The linear alkyl group of (1); r7Is C unsubstituted by a substituent14Carboxylic acid group of (1).
Wherein the polyfluoroethylene has the formula I: n is more than or equal to 370 and less than or equal to 380; formula II: n is more than or equal to 330 and less than or equal to 340; formula II: n is more than or equal to 2900 and less than or equal to 300; formula II: n is more than or equal to 370 and less than or equal to 380.
The preparation method comprises the following steps:
s1: and uniformly mixing the polymers I, II, III and IV, adding the mixture into a ball mill, grinding for 2-4 h, then sieving the mixture through a 600-mesh screen, and extruding the mixture in an extruder to obtain polyfluorinated ethylene powder, wherein the extrusion temperature is 330 ℃.
S2: adding the polyfluorinated ethylene powder, the carboxymethyl cellulose gel and the modified sodium polyacrylate in the step S1 into a mortar, uniformly mixing and grinding, then heating to 115 ℃, stirring for 1.5h, pouring out, shearing, and grinding to obtain the binder.
The carboxymethyl cellulose gel is prepared by the following method:
1) adding sodium carboxymethylcellulose into distilled water, then adding graphene oxide, raising the temperature to 65 ℃, and carrying out ultrasonic stirring for 4 hours, wherein the mass-volume ratio of the carboxymethylcellulose to the distilled water to the graphene oxide is 3.6g to 34mL to 0.36 g.
2) Adding citric acid or L-ascorbic acid into the mixed solution obtained in the step 1), continuously stirring for 1h, moving the mixed solution into a high-pressure reaction kettle, reacting for 10h at 100 ℃, cooling, and freeze-drying to obtain the carboxymethyl cellulose gel, wherein the mass ratio of the complexing agent to the graphene oxide is 3.2: 1.
The modified sodium polyacrylate is prepared by the following method:
adding deionized water and isopropanol into a three-neck flask, stirring uniformly, raising the temperature to 85 ℃, then dropwise adding an aqueous solution of acrylic acid and potassium persulfate, after dropwise adding for 3.5 hours, carrying out heat preservation reflux reaction for 3.4 hours at the temperature, cooling to room temperature, dropwise adding an aqueous solution of sodium hydroxide into a mixed solution, stirring to adjust the pH value to 8.4, then adding a carbon nano tube and sodium dodecyl benzene sulfonate, heating to boiling and continuously stirring until water is basically volatilized, then carrying out vacuum drying at 60 ℃, and crushing to obtain modified sodium polyacrylate, wherein the mass ratio of the isopropanol, the acrylic acid and the potassium persulfate is 1.4:3.9: 0.78; the mass fraction of the sodium hydroxide aqueous solution is 34 percent; the mass ratio of the carbon nano tube to the sodium dodecyl benzene sulfonate to the acrylic acid is 1.9:1.48: 14.8.
Comparative example 1
Polyvinylidene fluoride was purchased commercially.
Comparative example 2
Polyvinylidene fluoride is commercially purchased.
Comparative example 3
Carboxymethyl cellulose is commercially purchased.
Comparative example 4
Sodium polyacrylate was purchased commercially.
Experimental example:
performance test (1) electrode sliceAdhesive force test- -before soaking in electrolyte, the positive pole piece after coating and cold pressing is cut into a rectangle with a length of 100mm and a width of 10mm, a stainless steel plate with a width of 25mm is taken, a double-sided adhesive tape (with a width of 11mm) is attached, the cut pole piece is attached to the double-sided adhesive tape on the stainless steel plate, a 2000g compression roller is used for rolling back and forth three times (300mm/min) on the surface of the stainless steel plate, the pole piece is bent at 180 degrees and manually stripped for 25mm, the sample is fixed on a testing machine, the stripping surface is consistent with the force line of the testing machine, the testing machine continuously strips at 300mm/min to obtain a stripping force curve, and the average value of stable fracture is taken as the stripping force F0And then the adhesive force of the tested positive pole piece is as follows: f ═ F0/0.01＝100F0(N/m)，
After soaking the electrolyte: remove coating, the positive pole piece after the cold pressing, cut into the rectangle that length is 100mm, width is 10mm, soak in electrolyte, electrolyte includes organic solvent and lithium salt, and organic solvent is diethyl carbonate, dimethyl carbonate, the mixture of ethylene carbonate, and the volume ratio of three kinds of solvents is 1:1: 1, the lithium salt is LiPF61mol/L, and placing in a dry environment (relative humidity)<5 percent) and soaking for 24 hours at room temperature, naturally volatilizing in a dry environment, and testing the pole piece adhesive force after the solvent on the surface of the pole piece is completely volatilized. The test method and the adhesion calculation method were the same as above, and the results are shown in table 1; (2) the electrode sheet was tested for stability in terms of expansion rate before and after being immersed in the electrolyte, and the results are shown in table 1,
(3) the positive electrode active material is lithium iron phosphate, the binder is the binder in the embodiments 1-4 and the comparative examples 1-4, the current collector is aluminum foil, the negative electrode active material is artificial graphite, the binder is the same as the above, the current collector is copper foil, the electrolyte is a mixture of diethyl carbonate, dimethyl carbonate and ethylene carbonate, and the volume ratio of the three solvents is 1:1: 1, the lithium salt is LiPF6The concentration is 1mol/L, the discharge rate performance of the battery is tested at normal temperature by using constant current electric quantity of 0.5C, 1.0C, 1.5C and 2.0C respectively, the results are shown in Table 2,
(4) the battery cycle life performance test is carried out at normal temperature, the constant current charging at 0.5C is carried out to 4.35V, and the constant voltage charging is carried out to 0.05C, so that the battery is stopped; discharging at constant current of 0.5C to 3.0V, and recording the capacity, wherein the capacity of the first battery is 100%; the percentage of remaining capacity of the battery was repeatedly recorded, and the results are shown in table 3,
table 1. test results:
Figure BDA0002891017560000101
as can be seen from table 1, the binder of the present invention used in the electrode material had a slower decrease in the binding strength before and after soaking in the electrolyte, and a smaller expansion rate and higher stability than the binder of the comparative example.
Table 2. results of battery performance testing:
Figure BDA0002891017560000102
Figure BDA0002891017560000111
as can be seen from Table 2, the binders prepared in inventive examples 1-4 have superior discharge rate performance compared to the binders in the comparative examples.
Table 3. test results:
Figure BDA0002891017560000112
as can be seen from Table 3, the binders prepared in inventive examples 1-4 have superior cycle life performance of the battery as compared to the binder in the comparative example.

Claims (10)

1. The binder for the lithium ion battery is characterized by comprising polyfluorinated ethylene, carboxymethyl cellulose gel and modified sodium polyacrylate; the polyfluorinated ethylene comprises polymers of structural units shown in a formula I, a formula II, a formula III and a formula IV:
Figure FDA0002891017550000011
wherein R is1Is C unsubstituted by a substituent1～4The linear alkyl group of (1); r2Is C unsubstituted by a substituent2～6Carboxylic acid groups of (a); r3Is C unsubstituted by a substituent3～8The linear alkyl group of (1); r4Is C4～8Carboxylic acid groups of (a); r5Is C unsubstituted or substituted by a substituent1～8Carboxylic acid groups of (a); r6Is C unsubstituted or substituted by a substituent6～16The linear alkyl group of (1); r7Is C unsubstituted or substituted by a substituent4～16Carboxylic acid group of (1).
2. The binder for lithium ion batteries according to claim 1, wherein the structural unit represented by formula I in the polyfluorinated ethylene accounts for 30-45% by mass of the polyfluorinated ethylene, the structural unit represented by formula II accounts for 20-30% by mass of the polyfluorinated ethylene, the structural unit represented by formula III accounts for 10-15% by mass of the polyfluorinated ethylene, and the structural unit represented by formula IV accounts for 20-30% by mass of the polyfluorinated ethylene.
3. The binder for lithium ion batteries according to claim 1, wherein said polyfluoro ethylene has the formula I: n is more than or equal to 330 and less than or equal to 390; formula II: n is more than or equal to 290 and less than or equal to 350; formula II: n is more than or equal to 240 and less than or equal to 310; formula II: n is more than or equal to 300 and less than or equal to 400.
4. The binder for the lithium ion battery as claimed in claim 1, wherein the binder comprises 45-60 parts by weight of polyvinyl fluoride, 20-35 parts by weight of carboxymethyl cellulose gel and 16-22 parts by weight of modified sodium polyacrylate.
5. The method for preparing the binder for the lithium ion battery according to claim 1, wherein the preparation method comprises the following steps:
s1: uniformly mixing the polymers I, II, III and IV, adding the mixture into a ball mill, grinding for 2-4 hours, then screening the mixture through a 500-600 mesh screen, and extruding the mixture in an extruder to obtain polyfluorinated ethylene powder, wherein the extrusion temperature is 310-335 ℃;
s2: adding the polyfluorinated ethylene powder, the carboxymethyl cellulose gel and the modified sodium polyacrylate in the step S1 into a mortar, uniformly mixing and grinding, then heating to 105-120 ℃, stirring for 0.5-2 h, shearing, and grinding to obtain the binder.
6. The method of claim 5, wherein the carboxymethyl cellulose gel is prepared by the following steps:
1) adding sodium carboxymethylcellulose into distilled water, then adding graphene oxide, heating to 55-70 ℃, stirring and ultrasonically treating for 2-4 h, wherein the mass-to-volume ratio of the sodium carboxymethylcellulose to the distilled water to the graphene oxide is (2-4) g, (25-38) mL, (0.16-0.39) g;
2) adding a complexing agent into the mixed solution obtained in the step 1), continuously stirring for 0.5-1 h, moving into a high-pressure reaction kettle, reacting for 8-10 h at 90-105 ℃, cooling, and freeze-drying to obtain the carboxymethyl cellulose gel, wherein the mass ratio of the complexing agent to the graphene oxide is 2.6-3.4: 1.
7. The method of claim 6, wherein the complexing agent is any one of citric acid and L-ascorbic acid.
8. The method for preparing the binder for the lithium ion battery according to claim 5, wherein the modified sodium polyacrylate is prepared by the following method:
adding deionized water and isopropanol into a three-neck flask, stirring uniformly, raising the temperature to 75-85 ℃, then dropwise adding an aqueous solution of acrylic acid and potassium persulfate, after dropwise adding for 3.5h, preserving heat at the temperature for reflux reaction for 3-3.5 h, cooling to room temperature, dropwise adding an aqueous solution of sodium hydroxide into the mixed solution, stirring to adjust the pH value to 7.2-8.8, then adding carbon nano tubes and sodium dodecyl benzene sulfonate, heating to boiling, continuously stirring, drying in vacuum at 60 ℃ after water is basically volatilized, and crushing to obtain the modified sodium polyacrylate.
9. The method of claim 8, wherein the mass ratio of the isopropyl alcohol, the acrylic acid and the potassium persulfate is (1-1.6): (1-4.2): 0.26-0.89); the mass fraction of the sodium hydroxide aqueous solution is 30-36%.
10. The method of claim 8, wherein the mass ratio of the carbon nanotubes to the sodium dodecylbenzenesulfonate to the acrylic acid is (1-2): (0.65-1.7): (8.6-16.9).
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CN108878886A (en) * 2018-07-10 2018-11-23 东莞市迈科新能源有限公司 A kind of battery thickness pole piece and its water base compound binding agent
CN110233265A (en) * 2019-06-13 2019-09-13 华中科技大学 Application and corresponding binder of the carragheen based binder in lithium ion battery

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5468938A (en) * 1977-11-12 1979-06-02 Furukawa Battery Co Ltd Preparation of cadmium cathode for alkaline battery
CN1047324A (en) * 1989-05-16 1990-11-28 罗姆和哈斯公司 The propylene ester adhesive composition that contains linking agent and impact modifying agent
CN1529917A (en) * 2001-04-10 2004-09-15 三菱麻铁里亚尔株式会社 Lithium ion polymer secondary battery, its electrode and method for synthesizing polymer compound in binder used in adhesion layer thereof
CN106170879A (en) * 2014-01-13 2016-11-30 杜拉塞尔美国经营公司 Preparation cathode slurry and the method for negative electrode
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