CN116675800A - Fluorine-containing polymer, preparation method, positive electrode plate, secondary battery and electricity utilization device - Google Patents
Fluorine-containing polymer, preparation method, positive electrode plate, secondary battery and electricity utilization device Download PDFInfo
- Publication number
- CN116675800A CN116675800A CN202310968961.0A CN202310968961A CN116675800A CN 116675800 A CN116675800 A CN 116675800A CN 202310968961 A CN202310968961 A CN 202310968961A CN 116675800 A CN116675800 A CN 116675800A
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- Prior art keywords
- fluoropolymer
- positive electrode
- molar content
- formula
- fluorine
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- 239000011737 fluorine Substances 0.000 title claims abstract description 57
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- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- 230000005611 electricity Effects 0.000 title description 2
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- 239000001257 hydrogen Substances 0.000 claims abstract description 20
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 20
- BQCIDUSAKPWEOX-UHFFFAOYSA-N 1,1-Difluoroethene Chemical compound FC(F)=C BQCIDUSAKPWEOX-UHFFFAOYSA-N 0.000 claims abstract description 12
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims abstract description 10
- 239000000460 chlorine Substances 0.000 claims abstract description 10
- 229910052801 chlorine Inorganic materials 0.000 claims abstract description 10
- 125000001153 fluoro group Chemical group F* 0.000 claims abstract description 8
- 238000012360 testing method Methods 0.000 claims description 33
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- PWLNAUNEAKQYLH-UHFFFAOYSA-N butyric acid octyl ester Natural products CCCCCCCCOC(=O)CCC PWLNAUNEAKQYLH-UHFFFAOYSA-N 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 125000002057 carboxymethyl group Chemical group [H]OC(=O)C([H])([H])[*] 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 229920001688 coating polymer Polymers 0.000 description 1
- 238000010280 constant potential charging Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000007334 copolymerization reaction Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 239000010431 corundum Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 125000004093 cyano group Chemical group *C#N 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- VUPKGFBOKBGHFZ-UHFFFAOYSA-N dipropyl carbonate Chemical compound CCCOC(=O)OCCC VUPKGFBOKBGHFZ-UHFFFAOYSA-N 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 229940093499 ethyl acetate Drugs 0.000 description 1
- QKBJDEGZZJWPJA-UHFFFAOYSA-N ethyl propyl carbonate Chemical compound [CH2]COC(=O)OCCC QKBJDEGZZJWPJA-UHFFFAOYSA-N 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000005621 ferroelectricity Effects 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 238000005755 formation reaction Methods 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 238000001879 gelation Methods 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 229910021385 hard carbon Inorganic materials 0.000 description 1
- 125000001072 heteroaryl group Chemical group 0.000 description 1
- 238000004128 high performance liquid chromatography Methods 0.000 description 1
- 235000019447 hydroxyethyl cellulose Nutrition 0.000 description 1
- 239000003999 initiator Substances 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 125000001972 isopentyl group Chemical group [H]C([H])([H])C([H])(C([H])([H])[H])C([H])([H])C([H])([H])* 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- 229910002102 lithium manganese oxide Inorganic materials 0.000 description 1
- FRMOHNDAXZZWQI-UHFFFAOYSA-N lithium manganese(2+) nickel(2+) oxygen(2-) Chemical compound [O-2].[Mn+2].[Ni+2].[Li+] FRMOHNDAXZZWQI-UHFFFAOYSA-N 0.000 description 1
- MHCFAGZWMAWTNR-UHFFFAOYSA-M lithium perchlorate Chemical compound [Li+].[O-]Cl(=O)(=O)=O MHCFAGZWMAWTNR-UHFFFAOYSA-M 0.000 description 1
- 229910001486 lithium perchlorate Inorganic materials 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical class 0.000 description 1
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 description 1
- IGILRSKEFZLPKG-UHFFFAOYSA-M lithium;difluorophosphinate Chemical compound [Li+].[O-]P(F)(F)=O IGILRSKEFZLPKG-UHFFFAOYSA-M 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- VLXXBCXTUVRROQ-UHFFFAOYSA-N lithium;oxido-oxo-(oxomanganiooxy)manganese Chemical compound [Li+].[O-][Mn](=O)O[Mn]=O VLXXBCXTUVRROQ-UHFFFAOYSA-N 0.000 description 1
- URIIGZKXFBNRAU-UHFFFAOYSA-N lithium;oxonickel Chemical compound [Li].[Ni]=O URIIGZKXFBNRAU-UHFFFAOYSA-N 0.000 description 1
- MCVFFRWZNYZUIJ-UHFFFAOYSA-M lithium;trifluoromethanesulfonate Chemical compound [Li+].[O-]S(=O)(=O)C(F)(F)F MCVFFRWZNYZUIJ-UHFFFAOYSA-M 0.000 description 1
- 229910001425 magnesium ion Inorganic materials 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229940017219 methyl propionate Drugs 0.000 description 1
- KKQAVHGECIBFRQ-UHFFFAOYSA-N methyl propyl carbonate Chemical compound CCCOC(=O)OC KKQAVHGECIBFRQ-UHFFFAOYSA-N 0.000 description 1
- YKYONYBAUNKHLG-UHFFFAOYSA-N n-Propyl acetate Natural products CCCOC(C)=O YKYONYBAUNKHLG-UHFFFAOYSA-N 0.000 description 1
- UUIQMZJEGPQKFD-UHFFFAOYSA-N n-butyric acid methyl ester Natural products CCCC(=O)OC UUIQMZJEGPQKFD-UHFFFAOYSA-N 0.000 description 1
- 125000003136 n-heptyl group Chemical group [H]C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])* 0.000 description 1
- 125000001280 n-hexyl group Chemical group C(CCCCC)* 0.000 description 1
- 229910021382 natural graphite Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 1
- 125000000449 nitro group Chemical group [O-][N+](*)=O 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- 239000010450 olivine Substances 0.000 description 1
- 229910052609 olivine Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 1
- 229920001495 poly(sodium acrylate) polymer Polymers 0.000 description 1
- 229920002961 polybutylene succinate Polymers 0.000 description 1
- 239000004631 polybutylene succinate Substances 0.000 description 1
- 229920002223 polystyrene Polymers 0.000 description 1
- 229920000036 polyvinylpyrrolidone Polymers 0.000 description 1
- 239000001267 polyvinylpyrrolidone Substances 0.000 description 1
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 description 1
- 229910001414 potassium ion Inorganic materials 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 229940090181 propyl acetate Drugs 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000004537 pulping Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000012488 sample solution Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000002153 silicon-carbon composite material Substances 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- NNMHYFLPFNGQFZ-UHFFFAOYSA-M sodium polyacrylate Chemical compound [Na+].[O-]C(=O)C=C NNMHYFLPFNGQFZ-UHFFFAOYSA-M 0.000 description 1
- 229910021384 soft carbon Inorganic materials 0.000 description 1
- 238000013112 stability test Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- HXJUTPCZVOIRIF-UHFFFAOYSA-N sulfolane Chemical compound O=S1(=O)CCCC1 HXJUTPCZVOIRIF-UHFFFAOYSA-N 0.000 description 1
- 238000010408 sweeping Methods 0.000 description 1
- 239000012085 test solution Substances 0.000 description 1
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 1
- 229920001169 thermoplastic Polymers 0.000 description 1
- 239000004416 thermosoftening plastic Substances 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- 108010032276 tyrosyl-glutamyl-tyrosyl-glutamic acid Proteins 0.000 description 1
- NQPDZGIKBAWPEJ-UHFFFAOYSA-N valeric acid Chemical compound CCCCC(O)=O NQPDZGIKBAWPEJ-UHFFFAOYSA-N 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
- C08F214/18—Monomers containing fluorine
- C08F214/22—Vinylidene fluoride
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
- C09J127/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Adhesives based on derivatives of such polymers
- C09J127/02—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Adhesives based on derivatives of such polymers not modified by chemical after-treatment
- C09J127/12—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Adhesives based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
- C09J127/16—Homopolymers or copolymers of vinylidene fluoride
-
- 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
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
- C08F214/18—Monomers containing fluorine
- C08F214/28—Hexyfluoropropene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
- C08F220/10—Esters
- C08F220/12—Esters of monohydric alcohols or phenols
- C08F220/14—Methyl esters, e.g. methyl (meth)acrylate
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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
- 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)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Health & Medical Sciences (AREA)
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- Polymers & Plastics (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The application provides a fluorine-containing polymer, a preparation method, a positive electrode plate, a secondary battery and an electric device, and relates to the technical field of secondary batteries. The fluoropolymer comprises structural units derived from vinylidene fluoride, derived from formula IStructural units of the monomers, structural units derived from monomers of formula II, wherein R 1 、R 2 、R 3 Each independently selected from hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1‑3 Alkyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from hydrogen, substituted or unsubstituted C 1‑5 Alkyl, R 7 Selected from substituted or unsubstituted C 1‑9 And alkyl, wherein the molar content of the alpha crystal form of the fluoropolymer is more than or equal to 60%, and the crystallinity of the fluoropolymer is 40-45% based on the total molar content of the alpha crystal form, the beta crystal form and the gamma crystal form of the fluoropolymer. The positive electrode plate prepared from the fluorine-containing polymer has good flexibility.
Description
Technical Field
The application relates to the technical field of secondary batteries, in particular to a fluorine-containing polymer, a preparation method, a positive pole piece, a secondary battery and an electric device.
Background
Many types of binders for lithium ion batteries are used, polyvinylidene fluoride (PVDF) is used as a binder, and polyvinylidene fluoride is a thermoplastic binder, so that good adhesion can be formed between two surfaces when heating, but the positive electrode sheet prepared by using polyvinylidene fluoride as the binder has relatively poor flexibility, such as thick coating, and the positive electrode sheet has high possibility of cracking, so that it is needed to provide a binder suitable for thick coating.
Disclosure of Invention
The present application has been made in view of the above problems, and an object of the present application is to provide a fluoropolymer which can be added to a positive electrode slurry as a binder to make a thick coating on a positive electrode sheet, thereby contributing to an improvement in energy density of the positive electrode sheet.
In order to achieve the above object, the present application provides a fluorine-containing polymer comprising a structural unit derived from vinylidene fluoride, a structural unit derived from a monomer represented by formula I, a structural unit derived from a monomer represented by formula II,
formula I->II (II)
Wherein R is 1 、R 2 、R 3 Each independently selected from hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1-3 Alkyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from hydrogen, substituted or unsubstituted C 1-5 Alkyl, R 7 Selected from substituted or unsubstituted C 1-9 An alkyl group, a hydroxyl group,
the molar content of the alpha crystal form of the fluoropolymer is greater than or equal to 60%, based on the total molar content of the alpha crystal form, the beta crystal form and the gamma crystal form of the fluoropolymer; the crystallinity of the fluoropolymer is 40% -45%.
The stability of the positive electrode slurry can be improved and the gel phenomenon can be relieved by introducing the structural unit of which the substituted part is derived from vinylidene fluoride in the formula I, and the modified polyvinylidene fluoride can be applied to bonding high-nickel ternary positive electrode materials; in addition, the content of alpha crystal form in the fluorine-containing polymer is controlled within the range, so that the flexibility of the pole piece can be improved, the pole piece is suitable for thick coating, and the energy density of the positive pole piece is improved. When the crystallinity of the fluoropolymer is less than 40%, the electrolyte is likely to absorb liquid and swell, and even dissolve, and the adhesion is deteriorated, and when the crystallinity of the fluoropolymer is more than 45%, the brittleness of the electrode sheet is increased, resulting in deterioration of the cycle performance of the battery.
In any embodiment, the molar content of the alpha crystalline form of the fluoropolymer is 60% to 81% based on the total molar content of the alpha, beta and gamma crystalline forms of the fluoropolymer.
If the molar content of the alpha crystal form in the fluorine-containing polymer is too high, the binding force of the fluorine-containing polymer to the ternary cathode material is reduced, and if the molar content of the alpha crystal form in the fluorine-containing polymer is too low, the improvement effect on the flexibility of the polar plate is relatively weak.
In any embodiment, R in formula I 1 、R 2 、R 3 Each independently selected from one or more of hydrogen, fluorine, chlorine, trifluoromethyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from one or two of hydrogen and methyl.
In any embodiment, the molar content of structural units derived from the monomer of formula I is 1% to 3% based on the total moles of structural units of the fluoropolymer.
In any embodiment, the molar content of structural units derived from the monomer of formula II is 15% to 30% based on the total moles of structural units of the fluoropolymer.
In any embodiment, the fluoropolymer has a weight average molecular weight of 120 ten thousand to 185 ten thousand.
In any embodiment, the monomer of formula I comprises one or more of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene.
In any embodiment, the monomer of formula II comprises one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, and ethyl methacrylate.
In a second aspect of the present application, there is provided a method for producing a fluoropolymer, the method comprising the steps of:
Polymerization: under the polymerizable condition, the vinylidene fluoride monomer, the monomer shown in the formula I and the monomer shown in the formula II are polymerized to obtain the initial fluorine-containing polymer,
formula I->II (II)
Wherein R is 1 、R 2 、R 3 Each independently selected from hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1-3 Alkyl group, andthe molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from hydrogen, substituted or unsubstituted C 1-5 Alkyl, R 7 Selected from substituted or unsubstituted C 1-9 An alkyl group;
and (5) recrystallizing: recrystallizing the initial fluorine-containing polymer to obtain a fluorine-containing polymer;
the molar content of the alpha crystal form of the fluoropolymer is more than or equal to 60%, and the crystallinity of the fluoropolymer is 40% -45% based on the total molar content of the alpha crystal form, the beta crystal form and the gamma crystal form of the fluoropolymer.
The application can prepare the fluorine-containing polymer with the alpha crystal form molar content higher than 60% and the crystallinity of 40% -45% by a suspension method and a recrystallization method, and the fluorine-containing polymer is used as a binder to improve the flexibility of the pole piece and reduce the possibility of brittle failure of the pole piece in the processing process.
In any embodiment, the recrystallization includes the steps of:
and (3) heat treatment: heating and melting the initial fluoropolymer;
And (3) crystallization: cooling to 130-150 ℃ at a cooling rate of 30-50 ℃/min, preserving heat for 2-5 h, and cooling to room temperature to obtain the fluorine-containing polymer.
In any embodiment, the heat treatment process specifically includes:
heating the initial fluoropolymer to 200-250 ℃ at a rate of not higher than 20 ℃/min, and preserving the temperature for at least 1h.
In a third aspect of the present application, there is provided a positive electrode sheet comprising 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 comprising a positive electrode active material, a conductive agent and a binder, the binder being the fluoropolymer of the first aspect of the present application or the fluoropolymer prepared by the preparation method of the second aspect of the present application.
In any embodiment, the positive electrode active material is lithium transition metal oxide and modified material thereof, and the modified material is prepared by one or more modification modes of doping, conductive carbon coating, conductive metal coating and conductive polymer coating, and is selected from lithium nickel cobalt manganese oxide and modified material thereof.
In any embodiment, the positive electrode film layer has a compacted density of 3.5g/cm 3 -4.1g/cm 3 。
In any embodiment, the binding force per unit length between the positive electrode film layer and the positive electrode current collector is not less than 30N/m.
In any embodiment, after the positive electrode plate is subjected to bending test for at least 3 times, the positive electrode plate has a light transmission phenomenon.
In a fourth aspect of the present application, there is provided a secondary battery comprising a separator, a negative electrode tab, an electrolyte, and a positive electrode tab, the positive electrode tab being the positive electrode tab of the third aspect of the present application.
In a fifth aspect of the present application, there is provided an electric device comprising the secondary battery of the fourth 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 an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.
Reference numerals:
5 a secondary battery; 51 a housing; 52 electrode assembly; 53 cover plates.
Detailed Description
Embodiments of the fluoropolymer, the method for producing the fluoropolymer, the positive electrode sheet, the secondary battery and the electric device according to the present application are specifically disclosed below in detail with reference to the drawings. 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 the 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 the present 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 of the application and alternative embodiments may be combined with each other to form new solutions, unless otherwise specified.
All technical features and optional technical features of the application may be combined with each other to form new technical solutions, unless specified otherwise.
All the steps of the present application may be performed sequentially or randomly, preferably sequentially, unless otherwise specified. 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.
The terms "comprising" and "including" as used herein mean open ended or 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).
The ternary positive electrode material has been widely used in the field of lithium ion batteries due to its high energy density, but for the ternary positive electrode material, the gel phenomenon easily occurs when the conventional binder polyvinylidene fluoride is used in the pulping process, and in addition, with the development of the secondary battery, higher requirements are also put on the energy density and other properties of the secondary battery.
[ fluoropolymer ]
Based on this, the present application proposes a fluoropolymer comprising structural units derived from vinylidene fluoride, structural units derived from a monomer of formula I, structural units derived from a monomer of formula II,
formula I->II (II)
Wherein R is 1 、R 2 、R 3 Each independently selected from hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1-3 Alkyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from hydrogen, substituted or unsubstituted C 1-5 Alkyl, R 7 Selected from the group consisting ofSubstituted or unsubstituted C 1-9 An alkyl group, a hydroxyl group,
the molar content of the alpha crystal form of the fluoropolymer is more than or equal to 60%, and the crystallinity of the fluoropolymer is 40% -45% based on the total molar content of the alpha crystal form, the beta crystal form and the gamma crystal form of the fluoropolymer. In some embodiments, the molar content of the alpha crystalline form of the fluoropolymer is greater than or equal to 60% and less than or equal to 100% based on the total molar content of the alpha crystalline form, the beta crystalline form, the gamma crystalline form of the fluoropolymer; in some embodiments, the molar content of the alpha crystalline form of the fluoropolymer is 60% -70%, 70% -80%, 80% -90%, 90% -96%, 60% -81% based on the total molar content of the alpha crystalline form, the beta crystalline form, and the gamma crystalline form in the fluoropolymer.
The flexibility of the pole piece can be effectively improved by controlling the molar content of the alpha crystal form of the fluorine-containing polymer within the range; the structural unit derived from the monomer shown in the formula I is introduced, so that the gel phenomenon can be relieved, the stability of the sizing agent is improved, the short circuit risk caused by the fact that the surface is not uniformly coated with the active material in the use process of the pole piece is reduced, and the safety of the pole piece is improved; the introduction of structural units derived from the monomer shown in formula II can further improve the flexibility of the pole piece, is suitable for thick coating and improves the energy density of the pole piece. When the crystallinity of the fluorine-containing polymer is less than 40%, the fluorine-containing polymer is easy to absorb liquid and swell in electrolyte and even dissolve, the cohesive force can be deteriorated, and when the crystallinity of the fluorine-containing polymer is higher than 45%, the brittleness of the pole piece can be increased, the cycle performance of the battery can be deteriorated, and the cohesive force and the flexibility of the pole piece can be both considered when the crystallinity of the fluorine-containing polymer is controlled within 40% -45%. When the crystallinity of the fluorine-containing polymer and the molar content of the alpha crystal form meet the above-mentioned limit, the positive electrode plate with good binding force between the positive electrode film layer and the current collector and good flexibility can be prepared.
In this context, the term "polymer" includes, on the one hand, macromolecular assemblies prepared by polymerization but differing in terms of degree of polymerization, molar mass and chain length, and, on the other hand, also derivatives of such macromolecular assemblies formed by polymerization, i.e. compounds which can be obtained by reaction of functional groups in the macromolecules mentioned, for example addition or substitution, and which can be chemically uniform or chemically non-uniform.
As used herein, the term "fluoropolymer" refers to a macromolecular aggregate or derivative thereof formed by the copolymerization of fluorine-containing monomers and ester-containing monomers.
Herein, the term "monomer" refers to a compound that synthesizes a polymer, the monomer being converted into a structural unit of a macromolecule by polymerization.
Herein, the term "structural unit" refers to repeating units that can be linked to each other by covalent bonds; many building blocks are linked to form linear macromolecules, resembling a chain, and are therefore commonly known as links.
Herein, the term "C 1-3 Alkyl "refers to a straight or branched chain alkane group consisting of only carbon and hydrogen atoms, no unsaturation present in the group, having one, two or three carbon atoms, and attached to the remainder of the molecule by a single bond. C (C) 1-3 Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, 1-methylethyl (isopropyl).
Herein, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is substituted with another chemical moiety with a substituent, wherein each substituent is independently selected from the group consisting of: hydroxy, mercapto, amino, cyano, nitro, aldehyde, halogen, alkenyl, alkynyl, aryl, heteroaryl, C 1-6 Alkyl, C 1-6 An alkoxy group.
Herein, the term "C 1-5 Alkyl "refers to a straight or branched chain alkane group consisting of only carbon and hydrogen atoms, no unsaturation present in the group, having one, two, three, four or five carbon atoms, and attached to the remainder of the molecule by a single bond. C (C) 1-5 Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), n-butyl, dimethylpropyl (isobutyl), n-pentyl, isopentyl (2-methylbutyl).
Herein, the term "C 1-9 Alkyl "means a straight or branched chain alkyl group consisting of only carbon and hydrogen atoms, a groupNo unsaturation is present in the group, having one, two, three, four, five, six, seven, eight, or nine carbon atoms, and is attached to the remainder of the molecule by a single bond. C (C) 1-9 Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), n-butyl, 2-methylpropyl (isobutyl), n-pentyl, 2-methylbutyl (isopentyl), n-hexyl, 2-methylpentyl (isohexane), n-heptyl, 2-methylhexyl (isoheptyl), n-octyl, 2-methylheptyl (isooctyl).
As used herein, the term "alpha form" refers to the molecular chain-CH 2 -CF 2 -crystalline forms with alternating units and antiparallel spatial arrangement, in TGTG' conformation, with a net dipole moment of 0, which is not polar to the outside, belonging to monoclinic system, unit cell parameters: a=0.496 nm, b=0.964 nm, c=0.462 nm.
The term "beta crystal form" refers to a crystal form with a planar zigzag molecular chain, is in a TTTT all-trans conformation, has high polarity, good piezoelectricity and ferroelectricity, belongs to an orthorhombic system and has unit cell parameters: a=0.858 nm, b=0.491 nm, c=0.256 nm.
In this context, the term "gamma crystal form" refers to TTTGTTTG' conformation, having a certain polarity, its unit cell parameters: a=0.496 nm, b=0.967 nm, c=0.920 nm.
In some embodiments, the molar content of the alpha crystalline form of the fluoropolymer is 60% -81% based on the total molar content of the alpha, beta and gamma crystalline forms of the fluoropolymer. In some embodiments, the molar content of the alpha crystalline form of the fluoropolymer is 60% -66%, 66% -71%, 66% -75%, 75% -81% based on the total molar content of the alpha crystalline form, the beta crystalline form, and the gamma crystalline form of the fluoropolymer.
When the molar content of the alpha crystal form in the fluorine-containing polymer is higher than 80%, the binding force between the positive electrode film layer prepared by the ternary positive electrode material and the current collector is reduced, and the circulation stability of the positive electrode plate is reduced. The positive electrode plate prepared from the fluorine-containing polymer meeting the conditions has good flexibility and binding force.
In some embodiments, R in formula I 1 、R 2 、R 3 Each independently selected from one or more of hydrogen, fluorine, chlorine, trifluoromethyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from one or two of hydrogen and methyl.
In some embodiments, the molar content of structural units derived from the monomer of formula I is 1% -3% based on the total moles of structural units of the fluoropolymer. In some embodiments, the molar content of structural units derived from the monomer of formula I is 1% -2%, 2% -3%.
Controlling the molar content of the structural units derived from the monomer of formula I in the fluoropolymer within the above ranges can alleviate the gelation that is easily caused by the simple use of polyvinylidene fluoride as a binder, while also contributing to the improvement of the flexibility and adhesion of the pole piece. When the molar content of the structural unit derived from the monomer represented by formula I is too high, flexibility is lowered, and when the molar content is too low, the slurry is liable to agglomerate.
In some embodiments, the molar content of structural units derived from the monomer of formula II is 15% -30% based on the total moles of structural units of the fluoropolymer. In some embodiments, the molar content of structural units derived from the monomer of formula II is 15% -18%, 18% -21%, 21% -24%, 24% -27%, 27% -30%, 15% -20%, 20% -30%.
Controlling the molar content of structural units derived from the monomer of formula II in the fluoropolymer within the above ranges may further improve the flexibility of the pole piece.
In some embodiments, the fluoropolymer has a weight average molecular weight of 120 ten thousand to 185 ten thousand. In some embodiments, the fluoropolymer has a weight average molecular weight of 124 ten thousand to 154 ten thousand, 154 ten thousand to 185 ten thousand.
The binding property between particles and a current collector of the ternary positive electrode material is slightly poorer than that of other positive electrode materials, and when the weight average molecular weight of the fluorine-containing polymer meets the requirement, the ternary positive electrode material and the current collector have good binding force.
Herein, the "weight average molecular weight" is the sum of the weight fraction of each molecule of different molecular weight and the product of the molecular weights corresponding thereto.
In some embodiments, the monomer of formula I comprises one or more of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene.
In some embodiments, the monomer of formula II comprises one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate.
The raw materials are simple and easy to obtain, the production cost can be greatly reduced, and the yield is improved.
In one embodiment of the present application, there is provided a method for producing a fluoropolymer, the method comprising the steps of:
polymerization: under the polymerizable condition, the vinylidene fluoride monomer, the monomer shown in the formula I and the monomer shown in the formula II are polymerized to obtain the initial fluorine-containing polymer,
formula I->II (II)
Wherein R is 1 、R 2 、R 3 Each independently selected from hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1-3 Alkyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from hydrogen, substituted or unsubstituted C 1-5 Alkyl, R 7 Selected from substituted or unsubstituted C 1-9 An alkyl group;
and (5) recrystallizing: recrystallizing the initial fluorine-containing polymer to obtain a fluorine-containing polymer;
The molar content of the alpha crystal form of the fluoropolymer is more than or equal to 60%, and the crystallinity of the fluoropolymer is 40% -45% based on the total molar content of the alpha crystal form, the beta crystal form and the gamma crystal form of the fluoropolymer.
The application can prepare the fluorine-containing polymer with the alpha crystal form molar content higher than 60% by a suspension method and a recrystallization method, and the fluorine-containing polymer is used as a binder to improve the flexibility of the pole piece and reduce the possibility of brittle failure of the pole piece in the processing process.
In some embodiments, the recrystallization includes the steps of:
and (3) heat treatment: heating and melting the initial fluoropolymer;
and (3) crystallization: cooling to 130-150 ℃ at a cooling rate of 30-50 ℃/min, preserving heat for 2-5 h, and cooling to room temperature to obtain the fluorine-containing polymer. In some embodiments, the cooling rate may be 30 ℃/min, 35 ℃/min, 40 ℃/min, 45 ℃/min, 50 ℃/min.
The fluoropolymer with the alpha crystal form molar content of more than or equal to 60% and the crystallinity of 40-45% can be prepared by controlling the crystallization conditions within the range.
In some embodiments, the heat treatment process is specifically:
Heating the initial fluoropolymer to 200-250 ℃ at a rate of not higher than 20 ℃/min, and preserving the temperature for at least 1h.
The heat treatment under the above conditions allows the initial fluoropolymer to be completely melted in preparation for the subsequent crystallization process.
In some embodiments, the fluoropolymer may be used in a secondary battery. Optionally, the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.
[ Positive electrode sheet ]
The positive electrode plate 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 binder and a conductive agent, and the binder is fluorine-containing polymer in some embodiments or fluorine-containing polymer prepared by a preparation method in some embodiments.
The positive pole piece has excellent flexibility and binding force.
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 be a positive electrode active material for a battery known in the art, such as lithium transition metal oxide and modified materials thereof, which are prepared by one or more modification modes of doping, conductive carbon coating, conductive metal coating, conductive polymer coating, and may be selected from lithium nickel cobalt manganese oxide and modified materials thereof. 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 electrode active materials 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 film layer has a compacted density of 3.5g/cm 3 -4.1g/cm 3 。
For ternary positive electrode materials, the fluorine-containing polymer can be used as a binder to prepare the positive electrode film layer with the compaction density, has high energy density and can be applied to a plurality of fields.
Herein, the "compacted density" refers to a ratio of a coating surface density to a thickness of the positive electrode film layer, and the "coating surface density" refers to a ratio of a weight of the positive electrode film layer, which is dried and rolled after coating, to a coating area.
In some embodiments, the adhesion force per unit length between the positive electrode film layer and the positive electrode current collector is not less than 30N/m.
In some embodiments, the positive electrode sheet is subjected to bending test for at least 3 times, and the positive electrode sheet has a light transmission phenomenon.
In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode film layer, such as a positive electrode active material, a conductive agent, a binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and obtaining a positive electrode film layer and a positive electrode plate after the procedures of drying, cold pressing and the like.
[ negative electrode sheet ]
The negative electrode tab includes a negative electrode current collector, a negative electrode active material layer and an insulating coating layer disposed on at least one surface of the negative electrode current collector.
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 anode active material 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 anode active material layer may further optionally include 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 anode active material layer may also optionally include other adjuvants, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.
[ electrolyte ]
The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The application is not particularly limited in the kind of electrolyte, 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 can 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, referring to fig. 2, the outer package may include a housing 51 and a cover 53. 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 addition, the application also provides an electric device, which comprises the secondary battery provided by the application. The secondary battery 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.
Fig. 3 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 following examples are illustrative only and are not to be construed as limiting the 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 fluoropolymers
Polymerization process: adding 30kg of deionized water (the conductivity is less than or equal to 2 mu s/cm) and 10g of hydroxyethyl cellulose into a reaction kettle in sequence, and closing the reaction kettle; vacuumizing the reactor, filling nitrogen, and repeating the operation until the oxygen concentration in the reactor is less than 100ppm; introducing vinylidene fluoride monomer into the reaction kettle until the pressure in the kettle is 5.0MPa; heating to 40 ℃ in a kettle, adding 40g of diisopropyl peroxydicarbonate and 150g of acetone, and starting to react, wherein vinylidene fluoride monomers, hexafluoropropylene and methyl methacrylate monomers are continuously introduced in proportion in the reaction process, and the reaction pressure in the kettle is kept unchanged, wherein the mass of the introduced vinylidene fluoride is 3420g, the mass of the hexafluoropropylene is 205.5g, and the mass of the methyl methacrylate is 1370g; the total monomer addition time is 10 hours; adding all monomers and continuing to react for 8 hours; when the reaction is completed, the pressure in the kettle is reduced to 0.2MPa, and unreacted vinylidene fluoride monomer is recovered; and centrifuging, washing and drying the reaction product to obtain the initial fluorine-containing polymer.
And (5) recrystallizing: 50g of the initial fluoropolymer powder was charged into a 250mL corundum crucible; placing the crucible into a muffle furnace, replacing gas in the furnace chamber with nitrogen, and keeping the furnace chamber closed; heating to 210 ℃ at a speed of 5 ℃/min, and keeping for 1h to eliminate heat history; cooling to 150 ℃ at the speed of 45 ℃/min, and keeping the temperature for 3 hours; the product was taken out of the muffle furnace and cooled to room temperature to obtain a fluoropolymer.
2) Preparation of positive electrode plate
LiNi is added to 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811), conductive carbon black, fluoropolymer of example 1, polyvinylpyrrolidone dispersant, N-methylpyrrolidone (NMP) at a weight ratio of 96.9:2:1:0.1:25 stirring, wherein the solid content of the positive electrode slurry is 75%; then uniformly coating the anode slurry on an anode current collector, and then drying, cold pressing and cutting to obtain an anode plate, wherein the density of a coating surface is 20mg/cm 2 A compaction density of3.5g/cm 3 。
3) Preparation of negative electrode plate
Dissolving active material artificial graphite, conductive agent carbon black, binder Styrene Butadiene Rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC-Na) in a weight ratio of 96.2:0.8:0.8:1.2 in deionized water, and uniformly mixing to prepare negative electrode slurry; and uniformly coating the negative electrode slurry on a negative electrode current collector copper foil once or a plurality of times, and drying, cold pressing and cutting to obtain a negative electrode plate.
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 12.5% LiPF 6 The lithium salt was dissolved in an organic solvent and stirred uniformly to obtain an electrolyte of example 1.
6) Preparation of a Battery
The positive electrode plate, the isolating film and the negative electrode plate of the embodiment 1 are sequentially stacked, the isolating film is positioned between the positive electrode plate and the negative electrode plate to play a role of isolation, then the bare cell is obtained by winding, the tab is welded on the bare cell, the bare cell is arranged in an aluminum shell, baking and dewatering are carried out at 80 ℃, and then electrolyte is injected and sealed, so that the uncharged battery is obtained. The uncharged battery was subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity test and the like in sequence to obtain the lithium ion battery product of example 1.
In examples 2 to 5, the cooling rate, crystallization temperature and crystallization time in the recrystallization process were adjusted, and further the molar content and crystallinity of the alpha crystal form of the fluoropolymer were adjusted, and other parameters were kept consistent with example 1, and specific parameters are shown in table 1.
The molar content of structural units derived from methyl methacrylate and structural units derived from hexafluoropropylene in the fluoropolymers was adjusted in examples 6 to 13, and other parameters were consistent with example 1, and specific parameters are shown in table 1.
The polymerization temperature for preparing the fluoropolymers and the quality of the initiator diisopropyl peroxydicarbonate were adjusted in examples 14-17 so that the fluoropolymers had different weight average molecular weights, and other parameters were consistent with example 1, and specific parameters are shown in table 1.
In example 14, the polymerization temperature was adjusted to 45℃and the mass of diisopropyl peroxydicarbonate was adjusted to 44g.
In example 15, the polymerization temperature was adjusted to 45℃and the mass of diisopropyl peroxydicarbonate was adjusted to 42g.
In example 16, the polymerization temperature was adjusted to 35℃and the mass of diisopropyl peroxydicarbonate was adjusted to 38g.
In example 17, the polymerization temperature was adjusted to 35℃and the mass of diisopropyl peroxydicarbonate was adjusted to 36g.
In example 18, methyl methacrylate was replaced with ethyl acrylate, and other parameters were the same as in example 1, and specific parameters are shown in tables 1 and 2.
The hexafluoropropylene was replaced with chlorotrifluoroethylene in example 19 and the other parameters were the same as in example 1, with specific parameters shown in tables 1 and 2.
In example 20, the positive electrode active material NCM811 was replaced with lithium iron phosphate (LFP), and other parameters were the same as in example 1, and specific parameters are shown in tables 1 and 2.
In comparative example 1, polyvinylidene fluoride was used as the fluoropolymer, and other parameters were the same as in example 1, and specific parameters are shown in table 1.
The cooling rate, crystallization temperature and crystallization time during recrystallization were adjusted in comparative example 2, and further the molar content and crystallinity of the alpha-form of the fluoropolymer were adjusted, and other parameters were the same as in example 1, and specific parameters are shown in table 1.
Hexafluoropropylene was not added during the polymerization in comparative example 3, and other parameters were the same as in example 1, and specific parameters are shown in tables 1 and 2.
The polymerization process in comparative example 4 was carried out without adding methyl methacrylate, and other parameters were the same as in example 1, and specific parameters are shown in tables 1 and 2.
The cooling rate, crystallization temperature and crystallization time during recrystallization were adjusted in comparative example 5, and further the molar content and crystallinity of the alpha-form of the fluoropolymer were adjusted, and other parameters were the same as in example 1, and specific parameters are shown in table 1.
2. Test method
1. Property testing of fluoropolymers
(1) Weight average molecular weight of fluoropolymer
A Waters2695 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: styragelHT5 DMF7.8X 300mm+Styragel HT4) was selected. Preparing a 3.0% fluoropolymer solution 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.
(2) Molar content of fluoropolymer alpha form
The molar content of the alpha crystal form is tested by FTIR, and the method specifically comprises the following steps: the FTIR tester is a Nieolet5700 infrared spectrometer, and scans for 32 times, and the wave number range of the spectrum is 700-4000cm -1 . From the spectrum obtained, the wave number 795cm as characteristic absorption of the alpha crystal form was obtained -1 Wave number 839cm as characteristic absorption of beta crystal form -1 Absorption intensity of (c), wave number 811cm as characteristic absorption of gamma crystal form -1 Is not limited, and the absorption intensity of (a) is not limited. The start point and the end point of each peak corresponding to the above wave number are connected by a straight line, the intersection point of the straight line and the peak wave number is A, the point at which the spectrum intersects the peak wave number is B, the point at which the transmittance at the peak wave number is 0% is C, the lengths between ACs and between BC are obtained, and Log (AC/BC) is taken as the absorption intensity of each wave number.
The molar content of the alpha form was determined, as described above, to obtain the wave numbers 795cm corresponding to the alpha form, the beta form and the gamma form -1 、839cm -1 、811cm -1 The absorption intensity is calculated by substituting the following formula,
molar content of alpha form = 795cm -1 Absorption intensity/(795 cm) -1 Is +839cm -1 Is +811cm -1 The absorption strength of (c) x 100%.
(3) Crystallinity of fluoropolymer
Crystallinity was measured using a Differential Scanning Calorimeter (DSC) of american TA instrument model Discovery 250, specifically: dissolving fluorine-containing polymer in N-methyl pyrrolidone solution to prepare a glue solution with the mass fraction of the fluorine-containing polymer being 10%, drying the glue solution for 2 days at the temperature of 100 ℃, cutting a glue film into small pieces with the mass fraction of 2cm, placing the small pieces in an aluminum crucible, shaking the small pieces flat, covering a crucible cover, sweeping gas at the speed of 50mL/min under nitrogen atmosphere, ensuring the gas flow rate of protective gas to be 70mL/min, setting the heating rate to be 10 ℃/min, and testing the temperature range to be-100 ℃ -400 ℃. The test can obtain a curve of the heat absorption or heat release rate of the adhesive film along with the temperature, and the peak area is calculated by integration, wherein the peak area is the melting enthalpy delta H (J/g) of the adhesive film, and the crystallinity of the adhesive film is=delta H/(delta Hm 100%). 100%, wherein delta Hm100% is the standard melting enthalpy (crystalline melting heat) of PVDF, and delta Hm100% = 104.7J/g.
2. Property test of positive electrode slurry
Slurry stability test
And (3) after the slurry is stirred for 30 minutes again, pouring a certain amount of slurry into a sample bottle of the stability instrument, closing a test tower cover after the slurry is put into the sample bottle, opening the test tower cover, starting to generate a scanning curve on a test interface, starting to test the stability of the sample, and continuously testing for more than 48 hours to finish the test.
3. Property test of positive electrode sheet
(1) Cohesive force
The battery is disassembled in a full-discharge state after being charged and discharged at 25 ℃ and 1C for 100 times, a cathode plate is taken, washed in dimethyl carbonate for three times, dried, and the binding force of the plate is tested:
referring to national standard GB/T2790-1995 Experimental method for 180 DEG peel strength of adhesive, the adhesion test procedure of the examples and comparative examples of the application is as follows:
cutting a pole piece sample with the width of 30mm and the length of 100-160mm by a blade, and sticking 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 pole piece sample intercepted in the front is stuck on a double-sided adhesive tape with the test surface facing downwards, and then is rolled three times along the same direction by a pressing roller.
A paper tape with the width equal to the width of the pole piece sample and the length of 250mm is inserted below the pole piece current collector and 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 sample, by using a lower clamp. The paper tape is turned upwards and fixed by an upper clamp, 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, and then the test is carried out and the numerical value is read. The adhesive force between the positive electrode film layer and the current collector is represented by dividing the force of the pole piece when the pole piece is stressed and balanced by the width of the adhesive tape.
(2) Flexible and flexible
Cutting the cold-pressed positive pole piece into a test sample with the size of 20mm multiplied by 100 mm; after the positive folding, flattening by using 2kg of pressing rollers, unfolding to check whether the gap has light transmission or not, if not, reversely folding, flattening by using 2kg of pressing rollers, checking again by using light, repeating the test for three times, and if not, indicating that the positive pole piece has certain flexibility.
(3) Maximum compaction density
And cutting the positive electrode plate into a test sample with the size of 20mm and 100mm for later use. The pole piece is bent, folded and fixed well, a rolling roller with the weight of 2kg is used for rolling once, whether the folded part of the pole piece transmits light and leaks metal is checked, if not, the pole piece is folded and fixed reversely, the same method is used for rolling once, whether the folded part of the pole piece transmits light and leaks metal is checked, if the folded part of the pole piece does not transmit light and leaks metal repeatedly for three times, the thickness of the pole piece is reduced, the compaction density is increased, the test is carried out again until the phenomenon of transmitting light and leaking metal appears after the folded part and the rolled part of the pole piece are repeatedly folded and rolled for three times, and the compaction density of the positive pole piece which does not generate the phenomenon of transmitting light and leaking metal finally is obtained The degree is taken as the maximum compaction density. The initial compaction density was the same as for the examples and comparative examples, with an increase in compaction density of 0.02g/cm per test 3 。
4. Performance test of a battery
Mass energy density of battery
Capacity test of battery cell: the battery cell was allowed to stand at 25℃for 2 hours, ensuring the temperature of the battery cell to be 25 ℃. After the battery cell was charged to the charge cutoff voltage at 25C at 0.1C, constant voltage charging was continued at the charge cutoff voltage until the current was 0.05C, and the charge was cut off (where C represents the rated capacity of the battery cell). The cell was allowed to stand at 25℃for 1h. At 25 ℃, the battery cell is discharged to a discharge cut-off voltage at 0.1C, and the total discharge capacity C0 discharged by the battery cell is recorded, and the total discharge energy is E0.
And (3) measuring the weight of the battery cell: and placing the battery cell on an electronic balance until the weight is stable, and reading the weight value M0 of the battery cell.
Mass energy density calculation: the battery cell discharge energy E0/the battery cell weight M0 is the mass energy density of the battery cell.
3. Analysis of test results for examples and comparative examples
The fluoropolymer, positive electrode sheet, and battery of each example and comparative example were prepared according to the above method, respectively, and each property was measured, wherein the Y value of the flexibility test result represents the light-tightness repeated three times, and the specific results are shown in tables 1 and 2.
TABLE 1
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TABLE 2
As shown by the test results, the molar content of the alpha crystal form of the fluorine-containing polymer in the examples 1-20 is higher than 60%, the crystallinity is 40% -45%, wherein the ternary positive electrode material nickel cobalt lithium manganate NCM811 used for the positive electrode active materials in the examples 1-19 can reach the maximum compaction density of 3.6g/cm 3 The positive electrode active material in example 20 was lithium iron phosphate, and the maximum compacted density thereof was also 2.5g/cm 3 Above, compared with the positive electrode sheet prepared by the fluorine-containing polymer with low alpha crystal form molar content, the maximum compaction density is improved to a certain extent, but the fluorine-containing polymer has relatively weak effect of improving the binding force and flexibility of the lithium iron phosphate positive electrode active material, and is still difficult to thick coat, and the mass energy density is obviously lower than that of the embodiment 1.
The molar content of the alpha crystal form of the fluoropolymer in comparative examples 1-2 was too low to achieve a compacted density of 3.6g/cm for the prepared pole piece 3 The improvement effect on energy density is weak. The fluoropolymer of comparative example 3, which does not contain structural units derived from the monomer of formula I, produces a severe paste gel that is more difficult to uniformly coat on the surface of a current collector and presents a risk of short circuits during subsequent use. The fluoropolymer of comparative example 4, which does not contain structural units derived from the monomer of formula II, is difficult to effectively improve the flexibility of the pole piece, has relatively poor thickness coating properties, and has a maximum compacted density of only 3.52g/cm 3 . The fluoropolymer of comparative example 5 has too low crystallinity and tends to absorb liquid during circulation to swell, resulting in a significant decrease in adhesion.
In addition, the test results of comparative examples 1 to 5 show that when the molar content of the alpha crystal form in the fluorine-containing polymer is 60% -81%, the positive electrode plate has good flexibility and binding force, and when the molar content of the alpha crystal form is too high, the binding force can be reduced to below 35N/m, and the cycle performance of the battery can be influenced to a certain extent.
As can be seen from the test results of examples 1 and examples 6 to 9, the content of the structural unit derived from the monomer of formula I in the fluoropolymer also has a large influence on the performance of the electrode sheet, and when the molar content of the structural unit derived from the monomer of formula I is 1% -3%, the prepared positive electrode sheet has good adhesion and flexibility, and the maximum compaction density can reach 3.8g/cm 3 The above helps to increase the energy density of the battery. When the content of structural units derived from the monomer of formula I is too low, the slurry is a 48-hour moderate gel, and when the content of structural units derived from the monomer of formula I is too high, the flexibility of the pole piece is relatively poor, and the maximum compacted density is less than 3.8g/cm 3 。
As can be seen from the test results of comparative examples 1 and examples 10 to 13, the overall performance of the positive electrode sheet is relatively good, the adhesion force can reach 34.5N/m, and the maximum compaction density can reach 3.8g/cm when the molar content of the structural unit derived from the monomer represented by formula II in the fluoropolymer is 15% -30% 3 . When the molar content is less than 15%, the flexibility of the pole piece is reduced, and when the molar content is more than 30%, the adhesive force of the pole piece is greatly attenuated.
As a result of the test of comparative examples 1 and examples 14 to 17, it was found that the weight average molecular weight of the fluoropolymer greatly affects the adhesion and flexibility of the pole piece, and when the weight average molecular weight of the fluoropolymer is less than 120 ten thousand, the adhesion is less than 34N/m, and when the weight average molecular weight of the fluoropolymer is more than 185 ten thousand, the flexibility of the pole piece is reduced, and the maximum compacted density is less than 3.7g/cm 3 。
As can be seen from the test results of comparative example 1 and examples 18 to 19, the fluoropolymers of the formula I of hexafluoropropylene or chlorotrifluoroethylene and the formula II of ethyl acrylate or methyl methacrylate can be used for preparing positive electrode plates with good adhesion and flexibility.
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 (19)
1. A fluorine-containing polymer comprising a structural unit derived from vinylidene fluoride, a structural unit derived from a monomer represented by formula I, a structural unit derived from a monomer represented by formula II,
formula I->II (II)
Wherein R is 1 、R 2 、R 3 Each independently selected from hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1-3 Alkyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from hydrogen, substituted or unsubstituted C 1-5 Alkyl, R 7 Selected from substituted or unsubstituted C 1-9 An alkyl group, a hydroxyl group,
the molar content of the alpha crystal form of the fluoropolymer is more than or equal to 60%, and the crystallinity of the fluoropolymer is 40% -45% based on the total molar content of the alpha crystal form, the beta crystal form and the gamma crystal form of the fluoropolymer.
2. Fluoropolymer according to claim 1 characterized in that the molar content of the alpha, beta and gamma crystalline forms of the fluoropolymer is 60-81% based on the total molar content of the alpha, beta and gamma crystalline forms of the fluoropolymer.
3. The fluoropolymer according to claim 1 or 2 wherein R in formula I 1 、R 2 、R 3 Each independently selected from one or more of hydrogen, fluorine, chlorine, trifluoromethyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from one or two of hydrogen and methyl.
4. Fluoropolymer according to claim 1 or 2, characterized in that the molar content of the structural units derived from the monomer of formula I is 1-3% based on the total moles of structural units of the fluoropolymer.
5. Fluoropolymer according to claim 1 or 2, characterized in that the molar content of the structural units derived from the monomer of formula II is 15-30% based on the total moles of structural units of the fluoropolymer.
6. The fluoropolymer according to claim 1 or 2 wherein the fluoropolymer has a weight average molecular weight of 120-185 tens of thousands.
7. The fluoropolymer according to claim 1 or 2 wherein the monomer of formula I comprises one or more of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene.
8. The fluoropolymer according to claim 1 or 2 wherein the monomer of formula II comprises one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate.
9. A method for preparing a fluoropolymer comprising the steps of:
polymerization: under the polymerizable condition, the vinylidene fluoride monomer, the monomer shown in the formula I and the monomer shown in the formula II are polymerized to obtain the initial fluorine-containing polymer,
formula I->II (II)
Wherein R is 1 、R 2 、R 3 Each independently selected from hydrogen, fluorine, chlorine or C containing at least one fluorine atom 1-3 Alkyl, and the molar content of C-F bonds in formula I is higher than the molar content of C-H bonds, R 4 、R 5 、R 6 Each independently selected from hydrogen, substituted or unsubstituted C 1-5 Alkyl, R 7 Selected from substituted or unsubstituted C 1-9 An alkyl group;
and (5) recrystallizing: recrystallizing the initial fluorine-containing polymer to obtain a fluorine-containing polymer;
the molar content of the alpha crystal form of the fluoropolymer is more than or equal to 60%, and the crystallinity of the fluoropolymer is 40% -45% based on the total molar content of the alpha crystal form, the beta crystal form and the gamma crystal form of the fluoropolymer.
10. The method of preparation according to claim 9, wherein the recrystallisation comprises the steps of:
and (3) heat treatment: heating and melting the initial fluoropolymer;
and (3) crystallization: cooling to 130-150 ℃ at a cooling rate of 30-50 ℃ per minute, preserving heat for 2-5 h, and cooling to room temperature to obtain the fluorine-containing polymer.
11. The preparation method according to claim 10, wherein the heat treatment process specifically comprises:
heating the initial fluoropolymer to 200-250 ℃ at a rate of not higher than 20 ℃/min, and preserving the temperature for at least 1h.
12. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed 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 and a binder, and the binder is the fluoropolymer according to any one of claims 1 to 8 or the fluoropolymer prepared by the preparation method according to any one of claims 9 to 11.
13. The positive electrode sheet according to claim 12, wherein the positive electrode active material comprises at least one of a lithium transition metal oxide and a modified material thereof, the modified material being prepared by one or more modification modes of doping, conductive carbon coating, conductive metal coating, conductive polymer coating.
14. The positive electrode sheet according to claim 13, wherein the positive electrode active material comprises one or more of lithium nickel cobalt manganese oxide and modified materials thereof.
15. The positive electrode sheet according to any one of claims 12 to 14, wherein the positive electrode film layer has a compacted density of 3.5g/cm 3 -4.1g/cm 3 。
16. The positive electrode sheet according to any one of claims 12 to 14, wherein the adhesion force per unit length between the positive electrode film layer and the positive electrode current collector is not less than 30N/m.
17. The positive electrode sheet according to any one of claims 12 to 14, wherein the positive electrode sheet exhibits a light transmission phenomenon after being subjected to a bending test no less than 3 times.
18. A secondary battery comprising a separator, a negative electrode sheet, an electrolyte, and the positive electrode sheet according to any one of claims 12 to 17.
19. An electric device comprising the secondary battery according to claim 18.
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