CN117638070A - Positive electrode slurry, preparation method, secondary battery and electricity utilization device - Google Patents

Positive electrode slurry, preparation method, secondary battery and electricity utilization device Download PDF

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Publication number
CN117638070A
CN117638070A CN202310179551.8A CN202310179551A CN117638070A CN 117638070 A CN117638070 A CN 117638070A CN 202310179551 A CN202310179551 A CN 202310179551A CN 117638070 A CN117638070 A CN 117638070A
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China
Prior art keywords
polyvinylidene fluoride
positive electrode
binder
battery
electrode slurry
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CN202310179551.8A
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Chinese (zh)
Inventor
段连威
孙成栋
刘会会
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to CN202310179551.8A priority Critical patent/CN117638070A/en
Publication of CN117638070A publication Critical patent/CN117638070A/en
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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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The application provides positive electrode slurry, a preparation method, a secondary battery and an electric device. The positive electrode slurry includes a binder including a first polyvinylidene fluoride having a weight average molecular weight of 500 to 900 tens of thousands and a second polyvinylidene fluoride having a weight average molecular weight smaller than that of the first polyvinylidene fluoride. The positive electrode plate prepared from the positive electrode slurry has high binding force and can improve the cycle performance of the battery.

Description

Positive electrode slurry, preparation method, secondary battery and electricity utilization device
The present application is a divisional application based on the invention application with application number 202211045483.8, application date 2022, month 08 and 30, and the invention name of "binder, preparation method, positive electrode sheet, secondary battery and electric device".
Technical Field
The application relates to the technical field of secondary batteries, in particular to positive electrode slurry, a preparation method, a secondary battery and an electric device.
Background
In recent years, secondary batteries are widely used in energy storage power supply systems such as hydraulic power, thermal power, wind power and solar power stations, and in various fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment, aerospace, and the like. With the popularization of secondary battery applications, higher demands are also being made on its cycle performance, service life, etc.
The binder is a common material in secondary batteries, and there is a great demand for pole pieces, separator films, packaging parts, and the like of the batteries. However, the existing adhesive is poor in adhesion, and a large amount of adhesive is often required to be added to meet the requirement of the adhesive force of the pole piece, so that the improvement of the energy density of the battery is limited. Thus, the existing adhesives remain to be improved.
Disclosure of Invention
The present invention has been made in view of the above problems, and an object thereof is to provide an adhesive that can exert excellent adhesive force at a low addition amount, can provide a pole piece with sufficient adhesive strength, and can improve cycle performance of a battery.
In order to achieve the above object, the present application provides an adhesive, the adhesive comprising a first polyvinylidene fluoride and a second polyvinylidene fluoride, the first polyvinylidene fluoride having a weight average molecular weight of 500 to 900 ten thousand, the second polyvinylidene fluoride having a weight average molecular weight smaller than that of the first polyvinylidene fluoride.
The adhesive can ensure that the pole piece has enough adhesive force under the condition of low addition amount, and improves the cycle performance of the battery.
In any embodiment, the first polyvinylidene fluoride has a polydispersity of 1.8 to 2.5.
The polydispersion coefficient of the first polyvinylidene fluoride is in a proper range, the weight average molecular weight of the first polyvinylidene fluoride is uniformly distributed, the performance variance is small, the stability is high, the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can ensure that the pole piece has enough binding force under the condition of low addition, and the capacity retention rate of the battery in the circulation process is further improved.
In any embodiment, the first polyvinylidene fluoride has a Dv50 particle size of 100 μm to 200 μm.
The Dv50 particle size of the first polyvinylidene fluoride is controlled within a proper range, and the first polyvinylidene fluoride has good processing performance, so that the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is easy to process, and the production efficiency of the pole piece and the battery can be ensured.
In any embodiment, the crystallinity of the first polyvinylidene fluoride is 40% to 45%.
The crystallinity of the first polyvinylidene fluoride is controlled within a proper range, so that the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can meet the adhesive force of the pole piece and the cycle performance of the battery on the basis of low addition, the flexibility of the pole piece is not greatly influenced, and the use requirement of the pole piece can be met.
In any embodiment, the first polyvinylidene fluoride is dissolved in N-methyl pyrrolidone to prepare a glue solution with the viscosity of 2000 mPas to 5000 mPas, wherein the mass content of the first polyvinylidene fluoride is 2% based on the total mass of the glue solution.
The viscosity of the glue solution of the first polyvinylidene fluoride is controlled within a proper range, and the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride with low addition amount can ensure that the pole piece has excellent adhesive force.
In any embodiment, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 to 4:1.
the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is controlled within a proper range, so that the pole piece has good processability and binding force, and the capacity retention rate of the battery in the circulation process can be further improved. In addition, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is controlled within a proper range, so that the usage amount of the first polyvinylidene fluoride is reduced under the condition that the pole piece has enough binding force, the cost of the binding agent is saved, and the industrial production is facilitated.
In any embodiment, the second polyvinylidene fluoride has a weight average molecular weight of 60 to 110 tens of thousands.
The weight average molecular weight of the second polyvinylidene fluoride is controlled within a proper range, the low-addition amount of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can ensure that the pole piece has excellent binding force, and the capacity retention rate of the battery in the circulating process can be further improved.
The second aspect of the present application also provides a method for preparing an adhesive, comprising the steps of:
preparation of first polyvinylidene fluoride: providing vinylidene fluoride monomer and solvent, and performing first-stage polymerization reaction to obtain a first product; carrying out second-stage polymerization reaction on the first product in the water-insoluble gas atmosphere; adding a chain transfer agent to perform a third-stage polymerization reaction to obtain first polyvinylidene fluoride with a weight average molecular weight of 500-900 ten thousand; blending: and blending the first polyvinylidene fluoride with the second polyvinylidene fluoride to prepare the adhesive, wherein the weight average molecular weight of the second polyvinylidene fluoride is smaller than that of the first polyvinylidene fluoride.
According to the preparation method of the adhesive, the first polyvinylidene fluoride with ultra-high molecular weight can be prepared through sectional polymerization, so that the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can meet the requirement of the adhesive force of the pole piece under the condition of low addition, the loading capacity of the positive electrode active material in the pole piece can be improved, and the capacity retention rate of the battery in the circulating process can be improved. In addition, the adhesive is prepared by blending the first polyvinylidene fluoride with the ultrahigh molecular weight and the second polyvinylidene fluoride with relatively low molecular weight, so that the use amount of the first polyvinylidene fluoride with the ultrahigh molecular weight is reduced, the cost of the adhesive is reduced, and the industrial production is facilitated.
In any embodiment, the reaction temperature of the first stage polymerization is 45 ℃ to 60 ℃, the reaction time is 4 hours to 10 hours, and the initial pressure is 4MPa to 6MPa.
In any embodiment, the reaction temperature of the second stage polymerization reaction is 60 ℃ to 80 ℃, the reaction time is 2 hours to 4 hours, and the reaction pressure is 6MPa to 8MPa.
In any embodiment, the reaction time of the third stage polymerization reaction is 1 to 2 hours.
The reaction pressure, reaction time and reaction temperature of polymerization reaction at each stage of preparing the first polyvinylidene fluoride are controlled within proper ranges, the improvement of the weight average molecular weight of the first polyvinylidene fluoride is realized, the uniformity of the weight average molecular weight of the first polyvinylidene fluoride can be ensured, the product is ensured to have a lower polydispersion coefficient, the uniformity and stability of the performance of the first polyvinylidene fluoride are improved, the uniformity of the performances in batches and between batches of the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is further ensured, the pole piece has excellent adhesive force under the condition of low addition of the adhesive, and the cycle capacity retention rate of the battery can be further improved.
In any embodiment, the chain transfer agent comprises one or more of cyclohexane, isopropanol, methanol, acetone.
In any embodiment, the water insoluble gas is selected from any one of nitrogen, oxygen, hydrogen, and methane.
In any embodiment, the amount of chain transfer agent is 1.5% to 3% of the total mass of vinylidene fluoride monomer.
In any embodiment, the first stage polymerization reaction comprises the steps of:
adding a solvent and a dispersing agent into a container, and removing oxygen in a reaction system;
adding an initiator and a pH regulator into a container, regulating the pH value to 6.5-7, and then adding vinylidene fluoride monomer to enable the pressure in the container to reach 4-6 MPa;
stirring for 30-60 min, heating to 45-60 deg.c, and first stage polymerization.
In any embodiment, the solvent is used in an amount of 2 to 8 times the total mass of vinylidene fluoride monomers.
In any embodiment, the dispersant comprises one or more of a cellulose ether and a polyvinyl alcohol.
In any embodiment, the cellulose ether comprises one or more of a methyl cellulose ether and a carboxyethyl cellulose ether.
In any embodiment, the dispersant is used in an amount of 0.1% to 0.3% by weight of the total vinylidene fluoride monomer mass.
In any embodiment, the initiator is an organic peroxide.
In any embodiment, the organic peroxide comprises one or more of t-amyl peroxypivalate, 2-ethyl peroxydicarbonate, diisopropyl peroxydicarbonate, and t-butyl peroxypivalate.
In any embodiment, the initiator is used in an amount of 0.15% to 1% of the total mass of vinylidene fluoride monomer.
In any embodiment, the pH adjuster comprises one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and aqueous ammonia.
In any embodiment, the pH adjustor is used in an amount of 0.05 to 0.2% of the total mass of the vinylidene fluoride monomer.
In any embodiment, in the blending step, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 to 4:1.
the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is controlled within a proper range, so that the pole piece has excellent binding force, and the capacity retention rate of the battery in the circulation process can be further improved. In addition, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is controlled within a proper range, so that the usage amount of the first polyvinylidene fluoride can be reduced under the condition that the pole piece has enough binding force, the cost of the binding agent is saved, and the industrial production is facilitated.
A third aspect of the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, a conductive agent, and a binder in any embodiment or a binder prepared by a preparation method in any embodiment.
In any embodiment, the mass fraction of the binder is 0.6% to 0.8% based on the total mass of the positive electrode film layer.
Controlling the mass fraction of the binder within a suitable range helps to improve the capacity retention of the battery during cycling and allows the battery to have a high positive electrode energy density.
In a fourth aspect of the present application, there is provided a secondary battery comprising an electrode assembly comprising the positive electrode tab of the third aspect of the present application, a separator, and a negative electrode tab, and an electrolyte. Alternatively, the secondary battery is a lithium ion battery or a sodium ion battery.
In a fifth aspect of the present application, there is provided a battery module including the secondary battery of the fourth aspect of the present application.
In a sixth aspect of the present application, there is provided a battery pack comprising the battery module of the fifth aspect of the present application.
In a seventh aspect of the present application, there is provided an electric device including at least one of the secondary battery of the fourth aspect, the battery module of the fifth aspect, or the battery pack of the sixth aspect of the present application.
Drawings
Fig. 1 is a schematic view of a secondary battery according to an embodiment of the present application;
fig. 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in fig. 1;
FIG. 3 is a schematic view of a battery module according to an embodiment of the present application;
FIG. 4 is a schematic view of a battery pack according to an embodiment of the present application;
FIG. 5 is an exploded view of the battery pack of one embodiment of the present application shown in FIG. 4;
fig. 6 is a schematic view of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source;
FIG. 7 is a graph of adhesion versus displacement for example 24 and comparative example 2;
fig. 8 is a graph of battery capacity retention versus cycle number for example 24 and comparative example 2.
Reference numerals illustrate:
1, a battery pack; 2, upper box body; 3, lower box body; 4, a battery module; 5 a secondary battery; 51 a housing; 52 electrode assembly; 53 cover plates.
Detailed Description
Hereinafter, embodiments of the positive electrode active material and the method of manufacturing the same, the positive electrode tab, the secondary battery, the battery module, the battery pack, and the electrical device of the present application are specifically disclosed with reference to the accompanying drawings as appropriate. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of the actual same structure may be omitted. This is to avoid that the following description becomes unnecessarily lengthy, facilitating the understanding of those skilled in the art. Furthermore, the drawings and the following description are provided for a full understanding of the present application by those skilled in the art, and are not intended to limit the subject matter recited in the claims.
The "range" disclosed herein is defined in terms of lower and upper limits, with a given range being defined by the selection of a lower and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges that are defined in this way can be inclusive or exclusive of the endpoints, and any combination can be made, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise indicated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is simply a shorthand representation of a combination of these values. When a certain parameter is expressed as an integer of 2 or more, it is disclosed that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12 or the like.
All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, unless specifically stated otherwise.
All technical features and optional technical features of the present application may be combined with each other to form new technical solutions, unless specified otherwise.
All steps of the present application may be performed sequentially or randomly, preferably sequentially, unless otherwise indicated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), and the like.
Reference herein to "comprising" and "including" means open ended, as well as closed ended, unless otherwise noted. For example, the terms "comprising" and "comprises" may mean that other components not listed may be included or included, or that only listed components may be included or included.
The term "or" is inclusive in this application, unless otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or absent); a is false (or absent) and B is true (or present); or both A and B are true (or present).
Polyvinylidene fluoride is one of the most widely used types of binders in secondary batteries at present. However, the conventional polyvinylidene fluoride has low viscosity, and a large amount of addition is often required to ensure effective bonding of the active materials, so that the pole piece achieves effective bonding force. However, the increase of the dosage of the traditional polyvinylidene fluoride can reduce the load capacity of the active material in the pole piece, influence the improvement of the power performance of the battery, and hardly meet the requirement on the cycle performance of the battery.
[ adhesive ]
The application provides a binder, which comprises first polyvinylidene fluoride and second polyvinylidene fluoride, wherein the weight average molecular weight of the first polyvinylidene fluoride is 500-900 ten thousand, and the weight average molecular weight of the second polyvinylidene fluoride is smaller than that of the first polyvinylidene fluoride.
In this context, the term "binder" refers to a chemical compound, polymer or mixture that forms a colloidal solution or colloidal dispersion in a dispersing medium.
In some embodiments, the dispersion medium of the adhesive is an oily solvent, examples of which include, but are not limited to, dimethylacetamide, N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethylcellulose, polycarbonate. That is, the binder is dissolved in an oily solvent.
In some embodiments, a binder is used to fix the electrode active material and/or the conductive agent in place and adhere them to the conductive metal component to form an electrode.
In some embodiments, the binder serves as a positive electrode binder for binding the positive electrode active material and/or the conductive agent to form an electrode.
In some embodiments, the binder serves as a negative electrode binder for binding a negative electrode active material and/or a conductive agent to form an electrode.
In this context, the term "polyvinylidene fluoride" refers to polymers based on vinylidene fluoride as the main synthetic monomer, which on the one hand comprises an assembly of chemically homogeneous macromolecules prepared by polymerization, but differing in terms of degree of polymerization, molar mass and chain length. The term on the other hand also includes derivatives of such macromolecular assemblies formed by polymerization, i.e. compounds which can be obtained by reaction of functional groups in the macromolecules described above, for example addition or substitution, and which can be chemically homogeneous or chemically inhomogeneous. Polyvinylidene fluoride herein includes both homopolymers and copolymers.
In this context, the term "weight average molecular weight" refers to the sum of the weight fractions of the polymer occupied by molecules of different molecular weights multiplied by their corresponding molecular weights.
In some embodiments, the first polyvinylidene fluoride has a structural formula shown in formula I, the second polyvinylidene fluoride has a structural formula shown in formula II,
wherein m and n are integers, and respectively represent the polymerization degree of the first polyvinylidene fluoride and the second polyvinylidene fluoride, and m is larger than n, namely the polymerization degree and the weight average molecular weight of the first polyvinylidene fluoride are respectively larger than those of the second polyvinylidene fluoride.
In some embodiments, the first polyvinylidene fluoride has a weight average molecular weight of 500 to 900 tens of thousands. In some embodiments, the upper or lower limit of the weight average molecular weight of the first polyvinylidene fluoride is selected from any one of 510 tens of thousands, 550 tens of thousands, 600 tens of thousands, 650 tens of thousands, 700 tens of thousands, 750 tens of thousands, 800 tens of thousands, 850 tens of thousands, 900 tens of thousands.
The fluorine element contained in the first polyvinylidene fluoride and the second polyvinylidene fluoride form hydrogen bond action with the hydroxyl or/and carboxyl on the surface of the active material and the surface of the current collector, so that the pole piece has good cohesive force. The first polyvinylidene fluoride with the weight average molecular weight of 500-900 ten thousand has extremely high cohesive force and intermolecular acting force, can improve the adhesive force of the pole piece under the condition of low-level addition, and improves the capacity retention rate of the battery in the circulating process. The addition of the second polyvinylidene fluoride in the binder can greatly reduce the cost of the binder, and meanwhile, as the structural units of the first polyvinylidene fluoride and the second polyvinylidene fluoride are the same and have excellent compatibility, the pole piece cannot be layered in the drying process of preparing the pole piece, and the high-quality pole piece can be obtained.
The adhesive can ensure that the pole piece has enough adhesive force under the condition of low addition amount, and is beneficial to improving the energy density of the battery and the cycle performance of the battery.
In this application, the first polyvinylidene fluoride may be tested for its weight average molecular weight by methods known in the art, such as gel chromatography, e.g., using a Waters 2695 Isocric HPLC-type gel chromatograph (differential refractive detector 2141). In some embodiments, the test method is to select a matched chromatographic column (oiliness: styragel HT5DMF7.8 x 300mm+Styragel HT4) with a polystyrene solution sample of 3.0% mass fraction as reference. Preparing a glue solution of 3.0% of a binder by using a purified N-methylpyrrolidone (NMP) solvent, and standing the prepared solution for one day for later use. During the test, tetrahydrofuran is firstly sucked by a syringe, and then the syringe is washed, and the test is repeated for several times. Then, 5ml of the test solution was aspirated, the air in the syringe was removed, and the needle tip was wiped dry. And finally, slowly injecting the sample solution into the sample inlet. And after the indication is stable, acquiring data, and reading the weight average molecular weight.
In some embodiments, the first polyvinylidene fluoride has a polydispersity of 1.8 to 2.5. In some embodiments, the polydispersity of the first polyvinylidene fluoride may be selected to be any of 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5.
As used herein, the term "polydispersity" refers to the ratio of the weight average molecular weight of a polymer to the number average molecular weight of the polymer.
As used herein, the term "number average molecular weight" refers to the sum of the mole fractions of the polymer taken up by molecules of different molecular weights multiplied by their corresponding molecular weights.
If the polydispersity coefficient of the first polyvinylidene fluoride is too large, the polymerization degree of the first polyvinylidene fluoride is dispersed, so that the uniformity of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is affected, the binder cannot uniformly adhere the positive electrode active material to the current collector, the cycle performance of the battery is affected, the solid content of the slurry is reduced, and the energy density of the battery cannot be further improved; if the polydispersion coefficient of the first polyvinylidene fluoride is too small, the preparation process is difficult, the high-quality rate is low, and the production cost is high.
The polydispersion coefficient of the first polyvinylidene fluoride is in a proper range, the weight average molecular weight of the first polyvinylidene fluoride is uniformly distributed, the performance is uniform, the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can be ensured to have enough binding force under the condition of low addition amount, and the capacity retention rate of the battery in the circulation process is further improved. In addition, the polyvinylidene fluoride has proper polydispersity, so that the solid content of the slurry can be effectively improved, and the production cost is reduced.
In this application, the polydisperse coefficient may be tested by methods known in the art, such as gel chromatography, e.g., using a Waters 2695 Isocric HPLC-type gel chromatograph (differential refractive detector 2141). In some embodiments, a matched chromatographic column (oiliness: styragel HT5DMF7.8 x 300mm+Styragel HT4) is selected as a reference with a polystyrene solution sample having a mass fraction of 3.0%. Preparing 3.0% binder glue solution with purified N-methyl pyrrolidone (NMP) solvent, and standing the prepared solution for one day for later use. During the test, tetrahydrofuran is firstly sucked by a syringe, and then the syringe is washed, and the test is repeated for several times. Then, 5ml of the test solution was aspirated, the air in the syringe was removed, and the needle tip was wiped dry. And finally, slowly injecting the sample solution into the sample inlet. And obtaining data after the indication is stable. The weight average molecular weight a and the number average molecular weight b, polydispersity=a/b, were read separately.
In some embodiments, the first polyvinylidene fluoride has a Dv50 particle size of 100 μm to 200 μm. In some embodiments, the Dv50 particle size of the first polyvinylidene fluoride may be selected to be any of 120 μm to 200 μm, 120 μm to 160 μm, 120 μm to 180 μm, 160 μm to 200 μm.
As used herein, the term "Dv50 particle size" refers to the particle size corresponding to a cumulative particle size distribution of 50% in the particle size distribution curve, in the physical sense that the particle size is less than (or greater than) 50% of its particles.
If the Dv50 particle size of the first polyvinylidene fluoride is too large, the first polyvinylidene fluoride is relatively difficult to dissolve, the dispersibility of a binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is reduced, the uniform distribution of the positive electrode active material on a current collector is affected, the cycle performance of a battery is affected, and meanwhile, the first polyvinylidene fluoride is difficult to dissolve, so that the speed of a pulping process is reduced; if the Dv50 particle size of the first polyvinylidene fluoride is too small, the adhesive force of the adhesive containing the first and second polyvinylidene fluorides is lowered, so that the adhesive force of the pole piece is lowered.
The Dv50 particle size of the first polyvinylidene fluoride is controlled within a proper range, so that the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride has good processability, and the production efficiency of the pole piece and the battery is ensured. Meanwhile, the Dv50 particle size of the first polyvinylidene fluoride in a proper range can also enable the dosage of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride to be controlled at a lower level, and the binding performance is not excessively and negatively affected, so that the condition that the performance of a pole piece and a battery is limited due to the high dosage of the binder in the prior art is effectively improved.
With reference to GB/T19077-2016 particle size distribution laser diffraction method, weighing 0.1 g-0.13 g of first polyvinylidene fluoride powder with a 50ml beaker, weighing 5g of absolute ethyl alcohol, adding into the beaker filled with the first polyvinylidene fluoride powder, placing a stirrer with the length of about 2.5mm, and sealing with a preservative film. The sample is put into an ultrasonic machine for ultrasonic treatment for 5 minutes, and is transferred to a magnetic stirrer to be stirred for more than 20 minutes at the speed of 500 revolutions per minute, and 2 samples are extracted from each batch of products for testing and averaging. The measurement is performed using a laser particle size analyzer, such as a Mastersizer 2000E laser particle size analyzer from malvern instruments, england.
In some embodiments, the crystallinity of the first polyvinylidene fluoride is 40% to 45%. In some embodiments, the crystallinity of the first polyvinylidene fluoride may be selected to be any of 41%, 42%, 43%, 44%, or 45%.
If the crystallinity of the first polyvinylidene fluoride is too small, the degree of ordered close packing of the molecular chains of the first polyvinylidene fluoride is reduced, affecting the chemical stability and thermal stability of the first polyvinylidene fluoride, and thus of the adhesive comprising the first and second polyvinylidene fluorides. However, if the crystallinity of the first polyvinylidene fluoride is too high, the crystallinity of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is increased, so that the flexibility of the pole piece is reduced, and meanwhile, the first polyvinylidene fluoride is difficult to dissolve, so that the speed of the pulping process is reduced.
The crystallinity of the first polyvinylidene fluoride is in a proper range, and the adhesive can meet the requirements of the adhesive force of the pole piece and the battery cycle performance on the basis of low addition, so that the flexibility of the pole piece is not greatly influenced.
In this application, the crystallinity may be tested by methods known in the art, such as differential scanning thermal analysis. In some embodiments, 0.5g of the first polyvinylidene fluoride was placed in an aluminum crucible, shaken flat, covered with a crucible lid, purged under nitrogen at 50 ml/min with 70 ml/min of shielding gas at a temperature ramp rate of 10 ℃ per minute, a test temperature range of-100 ℃ to 400 ℃, and a Differential Scanning Calorimeter (DSC) of american TA instruments model Discovery 250 was used to test and eliminate heat history.
This test will result in a DSC curve of the first polyvinylidene fluoride, the curve being integrated, the peak area being the melting enthalpy of the polymer Δh (J/g), the crystallinity of the first polyvinylidene fluoride = Δh/(Δhm) ×100%, where Δhm is the standard melting enthalpy of the polyvinylidene fluoride (crystalline heat of fusion), Δhm = 104.7J/g.
In some embodiments, the first polyvinylidene fluoride is dissolved in N-methyl pyrrolidone to produce a gum solution having a viscosity of 2000 mPa-s to 5000 mPa-s, wherein the first polyvinylidene fluoride is present in an amount of 2% by mass based on the total mass of the gum solution. In some embodiments, the viscosity of the gum solution prepared by dissolving the first polyvinylidene fluoride in the N-methylpyrrolidone may be selected to be any one of 2100 mPas to 2700 mPas, 2700 mPas to 3400 mPas, 3400 mPas to 3800 mPas, 3800 mPas to 4300 mPas, 4300 mPas to 4800 mPas, 2100 mPas to 3400 mPas, 2100 mPas to 4800 mPas, 3400 mPas to 4800 mPas.
If the viscosity of the glue solution of the first polyvinylidene fluoride is too high, the viscosity of the prepared binder solution containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is too high, stirring is difficult, the dispersibility of the binder is reduced, so that the binder is difficult to uniformly adhere the positive electrode active material to the current collector, the cycle performance of the battery is affected, and meanwhile, if the viscosity of the prepared binder solution containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is too high, the speed of the pulping process is reduced; if the viscosity of the glue solution of the first polyvinylidene fluoride is too low, the viscosity of the prepared adhesive solution containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is too low, and the pole piece is difficult to have enough adhesive force under the condition of low addition amount.
In addition, when preparing the positive electrode slurry, the binder solution needs to have a certain viscosity to prevent the sedimentation of the positive electrode active material and the conductive agent, so that the slurry can be placed more stably. In the prior art, in order to achieve the glue solution viscosity of 2500 mPas-5000 mPas, at least the mass fraction of the binder in the glue solution is required to achieve 7%, but the first polyvinylidene fluoride can achieve the expected viscosity of the glue solution at the dosage of 2%, and a foundation is provided for reducing the content of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride in the positive electrode film layer.
The viscosity of the glue solution of the first polyvinylidene fluoride is controlled within a proper range, and the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride with low addition amount can ensure that the pole piece has excellent adhesive force.
In this application, the viscosity of the binder solution may be measured using methods known in the art, such as a rotational viscometer test. As an example, 7g of first polyvinylidene fluoride and 343g N-methylpyrrolidone (NMP) were weighed respectively in 500ml beakers, prepared as a glue solution with a mass fraction of 2%, stirred and dispersed by a forced high-speed grinder at a rotation speed of 800 rpm, and after a stirring time of 120 minutes, air bubbles were removed by ultrasonic vibration for 30 minutes. At room temperature, using a force technology NDJ-5S rotary viscometer to test, selecting a No. 3 rotor to insert glue solution, ensuring that a rotor liquid level mark is level with the glue solution, testing viscosity at a rotor rotating speed of 12 revolutions per minute, and reading viscosity data after 6 minutes.
In some embodiments, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 to 4:1. in some embodiments, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride may be selected to be 1: 1. 2: 1. 3: 1. 4:1.
If the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is too large, namely the mass of the first polyvinylidene fluoride is too high, the aim of reducing the cost cannot be achieved; if the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is too small, namely the mass of the first polyvinylidene fluoride is too low, the adhesive force of the pole piece is reduced, and the cycle performance of the battery is affected.
The mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is controlled within a proper range, and the adhesive enables the pole piece to have excellent adhesive force under the condition of low addition amount, so that the capacity retention rate of the battery in the circulation process can be improved. In addition, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is controlled within a proper range, so that the usage amount of the first polyvinylidene fluoride is reduced under the condition that the pole piece has enough binding force, the cost of the binding agent is saved, and the industrial production is facilitated.
In some embodiments, the second polyvinylidene fluoride has a weight average molecular weight of 60 to 110 tens of thousands. In some embodiments, the weight average molecular weight of the second polyvinylidene fluoride may be selected to be any of 60 ten thousand, 70 ten thousand, 80 ten thousand, 90 ten thousand, 100 ten thousand, 110 ten thousand.
If the weight average molecular weight of the second polyvinylidene fluoride is too large, the aim of reducing the cost cannot be achieved; if the weight average molecular weight of the second polyvinylidene fluoride is too small, the adhesive force of the adhesive containing the first and second polyvinylidene fluorides is lowered, thereby causing the lowering of the adhesive force of the pole piece.
The weight average molecular weight of the second polyvinylidene fluoride is controlled within a proper range, the low-addition amount of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can ensure that the pole piece has excellent binding force, and the capacity retention rate of the battery in the circulating process can be further improved.
In one embodiment of the present application, a method for preparing an adhesive is provided, including the steps of: preparation of first polyvinylidene fluoride: providing vinylidene fluoride monomer and solvent, and performing first-stage polymerization reaction to obtain a first product; carrying out second-stage polymerization reaction on the first product in the water-insoluble gas atmosphere; adding a chain transfer agent to perform a third-stage polymerization reaction to obtain first polyvinylidene fluoride with a weight average molecular weight of 500-900 ten thousand; blending: and blending the first polyvinylidene fluoride with the second polyvinylidene fluoride to prepare the adhesive, wherein the weight average molecular weight of the second polyvinylidene fluoride is smaller than that of the first polyvinylidene fluoride.
As used herein, the term "blend" refers to a process of forming a macroscopically homogeneous material under conditions of temperature and/or shear stress, etc., from two or more materials.
It is understood that the first product may refer to a reaction solution obtained after the first-stage polymerization of the vinylidene fluoride monomer and the solvent, or may refer to a polymer obtained after the first-stage polymerization.
In some embodiments, multiple parts of the first product are mixed and the second stage polymerization is carried out under an atmosphere of a water insoluble gas. It is understood that multiple parts of the first product can be prepared simultaneously by multiple reaction kettles, or can be prepared multiple times by one reaction kettle. The uniformity of the polymerization product can be improved by a multi-time and sectional synthesis method.
According to the preparation method of the adhesive, the first polyvinylidene fluoride with ultra-high molecular weight can be prepared through sectional polymerization, so that the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can meet the requirement of the adhesive force of the pole piece under the condition of low addition, the loading capacity of the positive electrode active material in the pole piece can be improved, and the capacity retention rate of the battery in the circulating process can be improved. Meanwhile, a first product is formed in the first-stage polymerization reaction, a molecular chain segment with target molecular weight is formed in the second-stage polymerization reaction, the third-stage polymerization reaction is used for regulating and controlling the molecular weight of the first polyvinylidene fluoride, the condition that the molecular weight is too high to reduce the uniformity of the weight average molecular weight of the first polyvinylidene fluoride is avoided, and the uniformity of the product is improved. And the utilization rate of the reactor in the preparation process of the first polyvinylidene fluoride can be improved by the sectional polymerization, so that the time is saved, and the residence time of the first polyvinylidene fluoride in the reactor is reduced. The first stage polymerization reaction, the second stage polymerization reaction and the third stage polymerization reaction are matched with each other to further improve the production efficiency of the first polyvinylidene fluoride.
In addition, the adhesive is prepared by blending the first polyvinylidene fluoride with the ultrahigh molecular weight and the second polyvinylidene fluoride with relatively low molecular weight, so that the use amount of the first polyvinylidene fluoride with the ultrahigh molecular weight is reduced, the cost of the adhesive is reduced, and the industrial production is facilitated.
In some embodiments, the reaction temperature of the first stage polymerization is 45 ℃ to 60 ℃. In some embodiments, the reaction temperature of the first stage polymerization reaction may be selected to be any one of 45℃to 50℃to 55℃and 55℃to 60℃and 45℃to 55 ℃.
In some embodiments, the reaction time for the first stage polymerization is from 4 hours to 10 hours. In some embodiments, the reaction time of the first stage polymerization reaction may be selected to be any of 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours.
In some embodiments, the initial pressure of the first stage polymerization reaction is from 4MPa to 6MPa. In some embodiments, the initial pressure of the first stage polymerization reaction is from 4MPa to 5MPa or from 5MPa to 6MPa. In some embodiments, the initial pressure of the first stage polymerization reaction is above the critical pressure of vinylidene fluoride.
In some embodiments, the reaction temperature of the second stage polymerization reaction is from 60 ℃ to 80 ℃. In some embodiments, the reaction temperature of the second stage polymerization reaction is 60 ℃ to 70 ℃ or 70 ℃ to 80 ℃.
In some embodiments, the second stage polymerization reaction time is from 2 hours to 4 hours. In some embodiments, the second stage polymerization reaction time is 2 hours to 3 hours or 3 hours to 4 hours.
In some embodiments, the reaction pressure of the second stage polymerization is from 6MPa to 8MPa. In some embodiments, the reaction pressure of the second stage polymerization is from 6MPa to 7MPa or from 7MPa to 8MPa.
In some embodiments, the reaction time for the third stage polymerization is from 1 hour to 2 hours.
The reaction pressure, reaction time and reaction temperature of polymerization reaction at each stage are controlled within proper ranges, the uniformity of the weight average molecular weight of the first polyvinylidene fluoride can be controlled while the improvement of the weight average molecular weight of the first polyvinylidene fluoride is realized, the product is ensured to have lower polydispersity, the uniformity of the performance of the first polyvinylidene fluoride is improved, the stability of the performance of the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is further ensured, the pole piece has excellent adhesive force under the condition of low addition of the adhesive, and the cycle capacity retention rate of the battery can be further improved.
In some embodiments, the chain transfer agent comprises one or more of cyclohexane, isopropanol, methanol, acetone.
The water-insoluble gas means a gas having a gas solubility of less than 0.1L. The solubility of the gas means that the pressure of the gas is 1.013X10 at 20 DEG C 5 Pa, the volume of gas when dissolved in 1L of water to saturation.
In some embodiments, the water insoluble gas is selected from any one of nitrogen, oxygen, hydrogen, methane.
In some embodiments, the chain transfer agent is used in an amount of 1.5% to 3% of the total mass of vinylidene fluoride monomer. The amount of chain transfer agent may also be 2% or 2.5% of the total mass of vinylidene fluoride monomer, for example.
The chain transfer agent is controlled in a proper range, so that the chain length of the polymer can be controlled, and the first polyvinylidene fluoride with proper molecular weight range and uniform distribution can be obtained.
In some embodiments, the first stage polymerization reaction comprises the steps of: adding a solvent and a dispersing agent into a container, and removing oxygen in a reaction system; adding an initiator and a pH regulator into a container, regulating the pH value to 6.5-7, and then adding vinylidene fluoride monomer to enable the pressure in the container to reach 4-6 MPa; stirring for 30-60 min, heating to 45-60 deg.c, and first stage polymerization.
Before the polymerization reaction is carried out by heating, the materials are uniformly mixed, so that the reaction can be carried out more thoroughly, and the weight average molecular weight, the crystallinity and the particle size of the prepared first polyvinylidene fluoride are more uniform.
In some embodiments, the solvent is used in an amount of 2 to 8 times the total mass of vinylidene fluoride monomer. The solvent may also be used, for example, in an amount of 3, 4, 5, 6 or 7 times the total mass of vinylidene fluoride monomers. In some embodiments, the solvent is deionized water.
In some embodiments, the dispersant comprises one or more of a cellulose ether and a polyvinyl alcohol.
In some embodiments, the cellulose ether comprises one or more of a methyl cellulose ether and a carboxyethyl cellulose ether.
In some embodiments, the dispersant is used in an amount of 0.1% to 0.3% of the total mass of vinylidene fluoride monomer. The dispersant may also be used in an amount of, for example, 0.2% by weight of the total vinylidene fluoride monomer mass.
In some embodiments, the initiator is an organic peroxide.
In some embodiments, the organic peroxide comprises one or more of t-amyl peroxypivalate, 2-ethyl peroxydicarbonate, diisopropyl peroxydicarbonate, and t-butyl peroxypivalate.
In some embodiments, the initiator is used in an amount of 0.15% to 1% of the total mass of vinylidene fluoride monomer. The initiator may also be used in an amount of, for example, 0.2%, 0.4%, 0.6% or 0.8% of the total mass of vinylidene fluoride monomers.
In some embodiments, the pH adjuster comprises one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and aqueous ammonia.
In any embodiment, the pH adjustor is used in an amount of 0.05 to 0.2% of the total mass of the vinylidene fluoride monomer. The amount of the pH adjustor can also be, for example, 0.1% or 0.15% of the total mass of the vinylidene fluoride monomer.
In some embodiments, in the blending step, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 to 4:1. in some embodiments, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride may be selected to be 1: 1. 2: 1. 3: 1. 4:1.
If the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is too large, namely the mass of the first polyvinylidene fluoride is too high, the aim of reducing the cost cannot be achieved; if the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is too small, namely the mass of the first polyvinylidene fluoride is too low, the adhesive force of the pole piece is reduced, and the cycle performance of the battery is affected.
The mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is controlled within a proper range, so that the pole piece has excellent binding force, and the capacity retention rate of the battery in the circulating process can be further improved. In addition, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is controlled within a proper range, so that the usage amount of the first polyvinylidene fluoride is reduced under the condition that the pole piece has enough binding force, the cost of the binding agent is saved, and the industrial production is facilitated.
[ Positive electrode sheet ]
The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, a conductive agent, a binder in some embodiments or a binder prepared by a preparation method in some embodiments.
The positive electrode plate has excellent adhesive force under the condition of low addition amount of the adhesive.
In some embodiments, the mass fraction of the binder is 0.6% to 0.8% based on the total mass of the positive electrode film layer. In some embodiments, the binder comprises 0.6% to 0.7% or 0.7% to 0.8% by mass of the total mass of the positive electrode film layer.
If the mass fraction of the binder is too high, the excessive binder can cause the load of the positive electrode active material in the pole piece to be reduced, so that the energy density of the battery is reduced, and the capacity of the battery is reduced.
If the mass fraction of the binder is too low, a sufficient bonding effect cannot be achieved, on one hand, enough conductive agent and positive electrode active material cannot be bonded together, and the bonding force of the pole piece is small; on the other hand, the adhesive cannot be tightly combined with the surface of the active material, so that the surface of the pole piece is easy to be destoner, and the cycle performance of the battery is reduced.
The mass fraction of the binder is controlled within a proper range, so that the active material loading capacity in the battery pole piece can be improved while the pole piece has effective binding force, and the power performance of the battery can be further improved.
As an example, the positive electrode current collector has two surfaces opposing in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two surfaces opposing the positive electrode current collector.
In some embodiments, the positive current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, the positive electrode active material may employ a positive electrode active material for a battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may be used. These positive electrodes The active material may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) 2 ) Lithium nickel oxide (e.g. LiNiO) 2 ) Lithium manganese oxide (e.g. LiMnO 2 、LiMn 2 O 4 ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM) 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also referred to as NCM) 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (also referred to as NCM) 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (also referred to as NCM) 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM) 811 ) Lithium nickel cobalt aluminum oxide (e.g. LiNi 0.85 Co 0.15 Al 0.05 O 2 ) And at least one of its modified compounds and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO 4 (also abbreviated as LFP)), composite material of lithium iron phosphate and carbon, and manganese lithium phosphate (such as LiMnPO) 4 ) At least one of a composite material of lithium manganese phosphate and carbon, and a composite material of lithium manganese phosphate and carbon.
In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and (3) coating the positive electrode slurry on a positive electrode current collector, and obtaining a positive electrode plate after the procedures of drying, cold pressing and the like.
[ negative electrode sheet ]
The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material.
As an example, the anode current collector has two surfaces opposing in its own thickness direction, and the anode film layer is provided on either one or both of the two surfaces opposing the anode current collector.
In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, the anode active material may employ an anode active material for a battery, which is well known in the art. As an example, the anode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like. The silicon-based material may be at least one selected from elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery anode active material may be used. These negative electrode active materials may be used alone or in combination of two or more.
In some embodiments, the negative electrode film layer further optionally includes a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).
In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent is at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
In some embodiments, the negative electrode film layer may optionally further include other adjuvants, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.
In some embodiments, the negative electrode sheet may be prepared by: dispersing the above components for preparing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and obtaining a negative electrode plate after the procedures of drying, cold pressing and the like.
[ electrolyte ]
The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The type of electrolyte is not particularly limited in this application, and may be selected according to the need. For example, the electrolyte may be liquid, gel, or all solid.
In some embodiments, the electrolyte is an electrolyte. The electrolyte includes an electrolyte salt and a solvent.
In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium difluorodioxaato phosphate, and lithium tetrafluorooxalato phosphate.
In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethyl sulfone, methyl sulfone, and diethyl sulfone.
In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, and the like.
[ isolation Membrane ]
In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known porous separator having good chemical stability and mechanical stability may be used.
In some embodiments, the material of the isolating film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.
In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.
In some embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte described above.
In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The exterior package of the secondary battery may also be a pouch type pouch, for example. The material of the flexible bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
The shape of the secondary battery is not particularly limited in the present application, and may be cylindrical, square, or any other shape. For example, fig. 1 is a secondary battery 5 of a square structure as one example.
In some embodiments, the overwrap may include a housing 51 and a cover 53 with reference to fig. 2. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate enclose a receiving chamber. The housing 51 has an opening communicating with the accommodation chamber, and the cover plate 53 can be provided to cover the opening to close the accommodation chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is enclosed in the accommodating chamber. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art may select according to specific practical requirements.
In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, and the specific number may be selected by one skilled in the art according to the application and capacity of the battery module.
Fig. 3 is a battery module 4 as an example. Referring to fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be sequentially arranged in the longitudinal direction of the battery module 4. Of course, the arrangement may be performed in any other way. The plurality of secondary batteries 5 may be further fixed by fasteners.
Alternatively, the battery module 4 may further include a case having an accommodating space in which the plurality of secondary batteries 5 are accommodated.
In some embodiments, the above battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and a specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.
Fig. 4 and 5 are battery packs 1 as an example. Referring to fig. 4 and 5, a battery case and a plurality of battery modules 4 disposed in the battery case may be included in the battery pack 1. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.
In addition, the application also provides an electric device, which comprises at least one of the secondary battery, the battery module or the battery pack. The secondary battery, the battery module, or the battery pack may be used as a power source of the power consumption device, and may also be used as an energy storage unit of the power consumption device. The power utilization device may include mobile devices (e.g., cell phones, notebook computers, etc.), electric vehicles (e.g., electric-only vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.
As the electricity consumption device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirements thereof.
Fig. 6 is an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or the like. In order to meet the high power and high energy density requirements of the secondary battery by the power consumption device, a battery pack or a battery module may be employed.
As another example, the device may be a cell phone, tablet computer, notebook computer, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.
Examples
Hereinafter, embodiments of the present application are described. The embodiments described below are exemplary only for the purpose of illustrating the present application and are not to be construed as limiting the present application. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
1. Preparation method
Example 1
1) Preparation of the adhesive
Preparation of first polyvinylidene fluoride: first stage polymerization 4kg of deionized water and 2g of methyl cellulose ether were charged into an autoclave of No. 1, no. 2 and N was used while evacuating 2 Replacement O 2 Three times, 5g of tert-butyl peroxypivalate and 2 were again addedg of sodium bicarbonate, and charging 1kg of vinylidene fluoride monomer to enable the pressure to reach 5MPa, mixing and stirring for 30min, heating to 45 ℃ and reacting for 4h; the second stage of polymerization reaction, namely transferring the reaction liquid in the reaction kettles 1 and 2 into a reaction kettle 3, charging nitrogen to the pressure of 7MPa, heating to 70 ℃, and stirring for reaction for 3 hours; in the third polymerization stage, 40g of cyclohexane was added to continue the reaction for 1 hour, and the reaction was stopped. And centrifuging, washing and drying the polymer to obtain the first polyvinylidene fluoride.
Second polyvinylidene fluoride: the viscosity of the glue solution which is purchased from Shandong De Yi New Material Co., ltd, model DY-5, weight average molecular weight of 80 ten thousand, polydispersity of 1.85, dv50 of 15 μm and crystallinity of 40%, and is prepared into 7% by mass after being dissolved in N-methylpyrrolidone is 2300 mpa.s.
And blending the first polyvinylidene fluoride and the second polyvinylidene fluoride, wherein the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1, and the adhesive containing the first polyvinylidene fluoride and the second polyvinylidene fluoride is obtained.
2) Preparation of positive electrode plate
3961.8g of lithium iron phosphate, 24.6g of binder and 57.4g of acetylene black are placed in a planetary stirring tank, and the mixture is stirred for 25 minutes at a revolution speed of 25r/min, wherein the mass fraction of the binder is 0.6% based on the total mass of the positive electrode film layer;
2.4kg of N-methylpyrrolidone (NMP) solution is added into a stirring tank, the revolution speed is 25r/min, the rotation speed is 900r/min, and stirring is carried out for 70min;
adding 12.3g of dispersing agent into a stirring tank, and stirring for 60min at revolution speed of 25r/min and rotation speed of 1250 r/min;
after the stirring, the viscosity of the slurry is tested and controlled to 8000-15000 mPa.s.
If the viscosity is higher, NMP solution is added to reduce the viscosity to the above viscosity interval, and then the positive electrode slurry is obtained according to revolution speed of 25r/min and rotation speed of 1250r/min and stirring for 30 min. And (3) scraping the prepared positive electrode slurry on a carbon-coated aluminum foil, baking for 15min at 110 ℃, cold pressing, and cutting into wafers with the diameter of 15mm to obtain the positive electrode plate.
3) Negative pole piece
And taking the metal lithium sheet as a negative electrode sheet.
4) Isolation film
A polypropylene film was used as a separator.
5) Preparation of electrolyte
In an argon atmosphere glove box (H 2 O<0.1ppm，O 2 <0.1 ppm), mixing organic solvent Ethylene Carbonate (EC)/methyl ethyl carbonate (EMC) according to volume ratio of 3/7, adding LiPF 6 Dissolving lithium salt in organic solvent, stirring uniformly, and preparing 1M LiPF 6 The EC/EMC solution yields the electrolyte.
6) Preparation of a Battery
The positive electrode tab, the negative electrode tab, the separator and the electrolyte in example 1 were assembled into a button cell in a button cell box.
Examples 2 to 3
The procedure was substantially as in example 1, except that the reaction times in the first polymerization stage of the first polyvinylidene fluoride were adjusted to 6h and 8h, respectively, and the cyclohexane in the third polymerization stage was adjusted to 30g and 20g, respectively, with the specific parameters shown in Table 1.
Examples 4 to 7
Substantially the same as in example 1, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, the specific parameters are shown in table 1.
Examples 8 to 11
Substantially the same as in example 1, except that the mass fraction of the binder was adjusted, the specific parameters are shown in table 1 based on the total mass of the positive electrode film layer.
Example 12
The procedure is substantially as in example 1, except that the second polyvinylidene fluoride is 605 purchased from Huaan Corp, has a weight average molecular weight of 60 ten thousand, a polydispersity of 2.05, a Dv50 of 13.4 μm, a crystallinity of 42%, and a viscosity of a dope prepared by dissolving in N-methylpyrrolidone to 7% by mass is 3000 mPa.s, and the specific parameters are shown in Table 1.
Example 13
Substantially the same as in example 1, except that the second polyvinylidene fluoride was 202E purchased from Shenzhou corporation, had a weight average molecular weight of 110 ten thousand, a polydispersity of 2.0, a dv50 of 11.5 μm, a crystallinity of 42%, and a viscosity of a dope prepared by dissolving in N-methylpyrrolidone to 7% by mass was 4100 mPas.
Examples 14 to 16
Substantially the same as in example 1, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, and the mass fraction of the binder was adjusted to 0.7% based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Examples 17 to 19
Substantially the same as in example 1, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, and the mass fraction of the binder was adjusted to 0.8% based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Examples 20 to 22
Substantially the same as in example 2, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, and the mass fraction of the binder was adjusted to 0.6% based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Example 23
Substantially the same as in example 2, except that the mass fraction of the binder was adjusted to 0.7% based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Examples 24 to 26
Substantially the same as in example 2, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, and the mass fraction of the binder was adjusted to 0.7% based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Example 27
Substantially the same as in example 2, except that the mass fraction of the binder was adjusted to 0.8%, based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Examples 28 to 30
Substantially the same as in example 2, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, and the mass fraction of the binder was adjusted to 0.8% based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Examples 31 to 33
Substantially the same as in example 3, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, the specific parameters are shown in table 1.
Example 34
Substantially the same as in example 3, except that the mass fraction of the binder was adjusted to 0.7% based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Examples 35 to 37
Substantially the same as in example 3, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, and the mass fraction of the binder was adjusted to 0.7% based on the total mass of the positive electrode film layer, the specific parameters are shown in table 1.
Example 38
Substantially the same as in example 3, except that the mass fraction of the binder was adjusted to 0.8% based on the total mass of the positive electrode film layer during blending, the specific parameters are shown in table 1.
Examples 39 to 41
Substantially the same as in example 3, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the blending process was adjusted, the mass fraction of the binder was adjusted to 0.8% based on the total mass of the positive electrode film layer, and specific parameters are shown in table 1.
Comparative example 1
Substantially the same as in example 1, the binder contained only the second polyvinylidene fluoride, and the specific parameters are shown in table 1.
Comparative example 2
The mass fraction of the binder was adjusted to 2.5% based on the total mass of the positive electrode film layer, substantially the same as in comparative example 1, and specific parameters are shown in table 1.
2. Performance testing
1. Adhesive property test
1) Weight average molecular weight test
A Waters 2695 Isocric HPLC gel chromatograph (differential refractive detector 2141) was used. A sample of a polystyrene solution with a mass fraction of 3.0% was used as a reference, and a matched column (oiliness: styragel HT5DMF7.8X 300mm+Styragel HT4) was selected. Preparing 3.0% binder solution with purified N-methyl pyrrolidone (NMP) solvent, and standing the prepared solution for one day for use. During the test, tetrahydrofuran is firstly sucked by a syringe, and then the syringe is washed, and the test is repeated for several times. Then, 5ml of the test solution was aspirated, the air in the syringe was removed, and the needle tip was wiped dry. And finally, slowly injecting the sample solution into the sample inlet. And after the indication is stable, acquiring data, and reading the weight average molecular weight.
2) Polydisperse coefficient testing
A Waters 2695 Isocric HPLC gel chromatograph (differential refractive detector 2141) was used. A sample of a polystyrene solution with a mass fraction of 3.0% was used as a reference, and a matched column (oiliness: styragel HT5DMF7.8X 300mm+Styragel HT4) was selected. Preparing 3.0% binder solution with purified N-methyl pyrrolidone (NMP) solvent, and standing the prepared solution for one day for use. During the test, tetrahydrofuran is firstly sucked by a syringe, and then the syringe is washed, and the test is repeated for several times. Then, 5ml of the test solution was aspirated, the air in the syringe was removed, and the needle tip was wiped dry. And finally, slowly injecting the sample solution into the sample inlet. And obtaining data after the indication is stable. The weight average molecular weight a and the number average molecular weight b were read separately. Polydisperse coefficient = a/b.
3) Dv50 test
With reference to GB/T19077-2016 particle size distribution laser diffraction method, weighing 0.1 g-0.13 g of first polyvinylidene fluoride powder with a 50ml beaker, weighing 5g of absolute ethyl alcohol, adding into the beaker filled with the first polyvinylidene fluoride powder, placing a stirrer with the length of about 2.5mm, and sealing with a preservative film. And (3) putting the sample into an ultrasonic machine for ultrasonic treatment for 5min, transferring the sample into a magnetic stirrer, stirring for more than 20min by using 500r/min, and taking 2 samples from each batch of products for testing and averaging. The measurement is performed using a laser particle size analyzer, such as a Mastersizer 2000E laser particle size analyzer from malvern instruments, england.
4) Crystallinity test
0.5g of the first polyvinylidene fluoride was placed in an aluminum crucible, shaken flat, covered with a crucible cover, purged with 50ml/min under a nitrogen atmosphere, and heated with a protective gas of 70ml/min at a heating rate of 10 ℃/min, at a test temperature ranging from-100 ℃ to 400 ℃, using a Differential Scanning Calorimeter (DSC) of American TA instrument model Discovery 250, and the heat history was eliminated.
This test will give a DSC curve of the first polyvinylidene fluoride and integrate the curve, the peak area being the melting enthalpy Δh (J/g) of the first polyvinylidene fluoride, the crystallinity of the first polyvinylidene fluoride = (Δh/Δhm) ×100%, where Δhm is the standard melting enthalpy (crystalline heat of fusion) of the polyvinylidene fluoride, Δhm=104.7J/g.
5) Glue viscosity test
7g of first polyvinylidene fluoride and 343g N-methyl pyrrolidone (NMP) are weighed by a 500ml beaker respectively to prepare glue solution with the mass fraction of 2%, a high-speed grinding machine is used for stirring and dispersing, the rotating speed is 800r/min, and after the stirring time is 120min, air bubbles are removed by ultrasonic vibration for 30 min. At room temperature, using a force technology NDJ-5S rotary viscometer to test, selecting a No. 3 rotor to insert glue solution, ensuring that a rotor liquid level mark is level with the glue solution, testing viscosity at a rotor rotating speed of 12r/min, and reading viscosity data after 6 min.
2. Pole piece performance test
1) Adhesion test
Referring to GB-T2790-1995 national standard "180 DEG peel Strength test method of adhesive", the adhesion test procedure of the examples and comparative examples of the present application is as follows:
cutting a sample with the width of 30mm and the length of 100-160mm by a blade, and sticking a special double-sided adhesive tape on a steel plate, wherein the width of the adhesive tape is 20mm and the length of the adhesive tape is 90-150mm. The positive electrode film layer surface of the pole piece sample intercepted in the front is stuck on a double-sided adhesive tape, and then is rolled three times along the same direction by a 2kg press roller. Paper tape with the width equal to the width of the pole piece and the length of 250mm is fixed on the pole piece current collector and is fixed by using crepe adhesive. And (3) turning on a power supply (sensitivity is 1N) of the three-thinking tensile machine, turning on an indicator lamp, adjusting a limiting block to a proper position, and fixing one end of the steel plate, which is not attached with the pole piece, by using a lower clamp. The paper tape is turned upwards and fixed by an upper clamp, and the position of the upper clamp is adjusted by using an 'up' button and a 'down' button on a manual controller attached to a pulling machine. Then testing is performed and the values are read. The force at which the pole pieces are forced to balance was divided by the width of the tape as the binding force of the pole pieces per unit length to characterize the binding strength between the positive electrode film layer and the current collector, resulting in the binding force-displacement diagram of example 24 and comparative example 2 as shown in fig. 7.
3. Battery performance test
1) Battery capacity retention test
The battery capacity retention test procedure was as follows: at 25 ℃, the button cell was charged to 3.65V at a constant current of 1/3C, then charged to 0.05C at a constant voltage of 3.65V, left for 5min, then discharged to 2.5V at 1/3C, and the resulting capacity was recorded as initial capacity C0. The above procedure was repeated for the same battery and the discharge capacity Cn of the battery after the nth cycle was recorded at the same time, and the battery capacity retention pn=cn/c0 after each cycle was 100%, and the graphs of the battery capacity retention and the cycle numbers of example 24 and comparative example 2 shown in fig. 8 were obtained with the 500 point values P1 and P2 … … P500 being on the ordinate and the corresponding cycle numbers being on the abscissa.
In this test procedure, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and the 500 th cycle of … … corresponds to n=500. The battery capacity retention rate data corresponding to examples 1 to 41 or comparative examples 1 to 2 in table 1 are data measured after 500 cycles under the above test conditions, i.e., P500 values.
The results of performance tests of the binders, pole pieces and batteries obtained in examples 1 to 41 and comparative examples 1 to 2 described above are shown in table 1.
3. Analysis of test results for examples and comparative examples
Batteries of each example and comparative example were prepared separately according to the above-described methods, and each performance parameter was measured, and the results are shown in table 1 below.
Table 1 parameters and performance tests for examples 1-41 and comparative examples 1-2
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Fig. 7 is a graph of adhesion versus displacement for example 24 and comparative example 2, and it can be seen from the graph that at the same displacement, the adhesion of example 24 is significantly higher than that of comparative example 2, indicating that the adhesive comprising the first polyvinylidene fluoride and the second polyvinylidene fluoride provided in the present application provides a pole piece with excellent adhesion at a lower amount of adhesive. Fig. 8 is a graph of the capacity retention rate and the cycle number of the batteries of example 24 and comparative example 2, and it can be seen from the graph that the capacity retention rate of the batteries of example 24 is significantly higher than that of comparative example 2 after 500 cycles of the batteries, which indicates that the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride provided in the application can improve the capacity retention rate of the batteries in the cycle process under the condition of lower binder addition, and effectively improve the situations of limited performance of the pole pieces and the batteries caused by high-usage of the binder in the conventional technology.
From the above results, it is understood that the binders in examples 1 to 41 each include a first polyvinylidene fluoride having a weight average molecular weight of 500 to 900 tens of thousands and a second polyvinylidene fluoride having a weight average molecular weight smaller than that of the first polyvinylidene fluoride.
As is apparent from comparison of examples 1 to 7, examples 12 to 13, examples 20 to 22, and examples 31 to 33 with comparative example 1, the binder comprising the first polyvinylidene fluoride and the second polyvinylidene fluoride provides the pole piece with excellent adhesive force at a low addition amount, and improves the capacity retention rate of the battery during the cycle.
As is clear from the comparison between examples 1 to 41 and comparative example 2, the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride provides the pole piece with excellent adhesion under the condition of low binder addition, improves the capacity retention rate of the battery during the cycle, and effectively improves the situation of limited pole piece and battery performance caused by high binder consumption in the conventional technology.
As is apparent from examples 1 to 41, the polydisperse coefficient of the first polyvinylidene fluoride in the binder is 1.8 to 2.5, and the low addition of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can give the pole piece excellent adhesion, and the battery has a high capacity retention during the cycle.
As is known from examples 1 to 41, the Dv50 particle size of the first polyvinylidene fluoride in the binder is 100 μm to 200 μm, and the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride in a low addition amount can give excellent adhesion to the pole piece, and the battery has a high capacity retention during the cycle.
As is known from examples 1 to 41, the crystallinity of the first polyvinylidene fluoride in the binder was 40% to 45%, and the low addition of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride enabled the pole piece to have excellent adhesion and the battery to have a high capacity retention during the cycle.
From examples 1 to 41, it was found that the viscosity of the first polyvinylidene fluoride glue solution prepared by dissolving the first polyvinylidene fluoride in N-methylpyrrolidone, which has a mass content of 2%, was 2000 mPas to 5000 mPas, so that the adhesive comprising the first polyvinylidene fluoride and the second polyvinylidene fluoride can ensure that the pole piece has sufficient adhesive force at a low addition amount.
As can be seen from the comparison of example 1, examples 5 to 7 and example 4, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the adhesive is 1:1 to 4:1, the low addition of the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride enables the pole piece to have excellent binding force, and the capacity retention rate of the battery during the circulation process can be further improved.
As is clear from examples 1 and 12 to 13, the weight average molecular weight of the second polyvinylidene fluoride in the binder is 60 to 110 tens of thousands, and the binder containing the first polyvinylidene fluoride and the second polyvinylidene fluoride can provide the pole piece with excellent adhesion at a low addition amount, and the capacity retention rate of the battery during the cycle is improved.
From comparison of examples 1, 9 to 10 and 8, when the mass fraction of the binder is 0.6% to 0.8%, the binder comprising the first polyvinylidene fluoride and the second polyvinylidene fluoride can ensure that the electrode sheet has sufficient binding power based on the total mass count of the positive electrode film layer, and the capacity retention rate of the battery during the cycle is further improved. As is clear from the comparison of examples 1, 9 to 10 and 11, when the mass fraction of the binder is 0.9%, the battery cycle performance is not significantly improved, but rather, the improvement of the battery energy density is not facilitated.
The present application is not limited to the above embodiment. The above embodiments are merely examples, and embodiments having substantially the same configuration and the same effects as those of the technical idea within the scope of the present application are included in the technical scope of the present application. Further, various modifications that can be made to the embodiments and other modes of combining some of the constituent elements in the embodiments, which are conceivable to those skilled in the art, are also included in the scope of the present application within the scope not departing from the gist of the present application.

Claims (29)

1. The positive electrode slurry is characterized by comprising a binder, wherein the binder comprises first polyvinylidene fluoride and second polyvinylidene fluoride, the weight average molecular weight of the first polyvinylidene fluoride is 500-900 ten thousand, and the weight average molecular weight of the second polyvinylidene fluoride is smaller than that of the first polyvinylidene fluoride.
2. The positive electrode slurry according to claim 1, wherein the first polyvinylidene fluoride has a polydispersity of 1.8 to 2.5.
3. The positive electrode slurry according to claim 1, wherein the first polyvinylidene fluoride has a Dv50 particle size of 100 μm to 200 μm.
4. The positive electrode slurry according to any one of claims 1 to 3, wherein the crystallinity of the first polyvinylidene fluoride is 40% to 45%.
5. A cathode slurry according to any one of claims 1 to 3, wherein the viscosity of a dope prepared by dissolving the first polyvinylidene fluoride in N-methylpyrrolidone is 2000 mPa-s to 5000 mPa-s, and the mass content of the first polyvinylidene fluoride in the dope is 2% based on the total mass of the dope.
6. The positive electrode slurry according to any one of claims 1 to 3, wherein a mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 to 4:1.
7. the positive electrode slurry according to any one of claims 1 to 3, wherein the second polyvinylidene fluoride has a weight average molecular weight of 60 to 110 tens of thousands.
8. A positive electrode slurry according to any one of claims 1 to 3, wherein the mass fraction of the binder is 0.6% to 0.8% based on the total mass of solid matter of the positive electrode slurry.
9. The preparation method of the positive electrode slurry is characterized in that the positive electrode slurry comprises a binder, and the preparation method of the binder comprises the following steps:
preparation of first polyvinylidene fluoride: providing vinylidene fluoride monomer and solvent, and performing first-stage polymerization reaction to obtain a first product; carrying out second-stage polymerization reaction on the first product under the water-insoluble gas atmosphere; adding a chain transfer agent to perform a third-stage polymerization reaction to obtain first polyvinylidene fluoride with a weight average molecular weight of 500-900 ten thousand;
blending: and blending the first polyvinylidene fluoride with second polyvinylidene fluoride to prepare the adhesive, wherein the weight average molecular weight of the second polyvinylidene fluoride is smaller than that of the first polyvinylidene fluoride.
10. The process according to claim 9, wherein the reaction temperature of the first stage polymerization is 45 to 60 ℃, the reaction time is 4 to 10 hours, and the initial pressure is 4 to 6MPa.
11. The process according to claim 9, wherein the second polymerization stage is carried out at a reaction temperature of 60 to 80 ℃ for a reaction time of 2 to 4 hours and a reaction pressure of 6 to 8MPa.
12. The process according to claim 9, wherein the reaction time of the third polymerization stage is 1 to 2 hours.
13. The production method according to any one of claims 9 to 12, wherein the chain transfer agent is selected from one or more of cyclohexane, isopropanol, methanol, acetone.
14. The production method according to any one of claims 9 to 12, wherein the water-insoluble gas is selected from any one of nitrogen, oxygen, hydrogen, methane.
15. The production method according to any one of claims 9 to 12, wherein the chain transfer agent is used in an amount of 1.5% to 3% of the total mass of the vinylidene fluoride monomer.
16. The method of claim 9, wherein the first stage polymerization reaction comprises the steps of:
adding a solvent and a dispersing agent into a container, and removing oxygen in a reaction system;
adding an initiator and a pH regulator into the container, regulating the pH value to 6.5-7, and then adding vinylidene fluoride monomer to enable the pressure in the container to reach 4-6 MPa;
stirring for 30-60 min, heating to 45-60 deg.c, and first stage polymerization.
17. The method according to claim 16, wherein the solvent is used in an amount of 2 to 8 times the total mass of the vinylidene fluoride monomer.
18. The method of preparation of claim 16, wherein the dispersant comprises one or more of a cellulose ether and a polyvinyl alcohol.
19. The method of preparation of claim 18, the cellulose ether comprising one or more of a methyl cellulose ether and a carboxyethyl cellulose ether.
20. The method of claim 16, wherein the dispersant is used in an amount of 0.1% to 0.3% of the total mass of the vinylidene fluoride monomer.
21. The method of claim 16, wherein the initiator is an organic peroxide.
22. The method of preparation of claim 21, wherein the organic peroxide comprises one or more of t-amyl peroxypivalate, 2-ethyl peroxydicarbonate, diisopropyl peroxydicarbonate, and t-butyl peroxypivalate.
23. The method of claim 16, wherein the initiator is used in an amount of 0.15% to 1% of the total mass of the vinylidene fluoride monomer.
24. The method of claim 16, wherein the pH adjuster comprises one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and aqueous ammonia.
25. The method of claim 16, wherein the pH adjuster is used in an amount of 0.05% to 0.2% of the total mass of the vinylidene fluoride monomer.
26. The method according to claim 9, wherein in the blending step, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 to 4:1.
27. a secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a separator, a negative electrode sheet, and a positive electrode sheet prepared from the positive electrode slurry according to any one of claims 1 to 8 or the positive electrode slurry prepared by the preparation method according to any one of claims 9 to 26.
28. The secondary battery according to claim 28, wherein the secondary battery is a lithium ion battery or a sodium ion battery.
29. An electric device comprising the secondary battery according to claim 27 or 28.
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Family Cites Families (12)

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Publication number Priority date Publication date Assignee Title
JPH09274920A (en) * 1996-04-05 1997-10-21 Sony Corp Nonaqueous electrolyte battery
CN101276895B (en) * 2007-03-27 2013-05-29 比亚迪股份有限公司 Composition for lithium ion secondary battery porous diaphragm layer and lithium ion secondary battery
CN101241988A (en) * 2008-02-03 2008-08-13 深圳市比克电池有限公司 A making method for anode slice of lithium ion battery
CN101760154A (en) * 2009-11-09 2010-06-30 南京双登科技发展研究院有限公司 Binding agent for super capacitor electrode paste
CN103113501B (en) * 2013-03-01 2014-01-08 江苏九九久科技股份有限公司 Method for preparing polyvinylidene fluoride in pressure change way
KR101904296B1 (en) * 2015-12-22 2018-11-13 삼성에스디아이 주식회사 A separator comprising porous bonding layer and an electrochemical battery comprising the separator
TWI654269B (en) * 2017-12-19 2019-03-21 財團法人工業技術研究院 Adhesive composition
KR102437371B1 (en) * 2018-09-28 2022-08-26 주식회사 엘지에너지솔루션 A separator for an electrochemical device and a method for manufacturing the same
CN110183562B (en) * 2019-05-30 2020-06-30 浙江孚诺林化工新材料有限公司 Vinylidene fluoride polymer for lithium ion power battery binder and preparation method and application thereof
CN112952092B (en) * 2019-12-10 2022-11-11 惠州比亚迪电池有限公司 Positive electrode binder and preparation method thereof, positive electrode slurry, positive electrode and lithium ion battery
CN111205707B (en) * 2020-01-10 2022-04-08 武汉中兴创新材料技术有限公司 Aqueous polyvinylidene fluoride coating slurry, battery diaphragm and preparation method
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WO2024045553A1 (en) 2024-03-07
CN115133033B (en) 2023-04-07

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