WO2022198583A1 - 碳集流体及包括该碳集流体的电化学装置和电子装置 - Google Patents

碳集流体及包括该碳集流体的电化学装置和电子装置 Download PDF

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WO2022198583A1
WO2022198583A1 PCT/CN2021/083054 CN2021083054W WO2022198583A1 WO 2022198583 A1 WO2022198583 A1 WO 2022198583A1 CN 2021083054 W CN2021083054 W CN 2021083054W WO 2022198583 A1 WO2022198583 A1 WO 2022198583A1
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current collector
carbon
conductive fibers
carbon current
present application
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French (fr)
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刘宏威
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Priority to CN202180004872.3A priority Critical patent/CN114531925B/zh
Priority to PCT/CN2021/083054 priority patent/WO2022198583A1/zh
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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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
    • 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
    • H01M4/04—Processes of manufacture in general
    • 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

Definitions

  • the present application relates to the field of energy storage, and in particular, to a carbon current collector, a preparation method thereof, and electrochemical devices and electronic devices using the same.
  • Lithium-ion batteries have the advantages of high energy density, long cycle life and small self-discharge, and have been widely used; with the continuous advancement of technology, people have higher and higher requirements for the energy density of lithium-ion batteries.
  • the energy density of ion batteries has become a research hotspot.
  • Fluid can improve the gravimetric energy density of the battery; the use of a thinner carbon current collector can simultaneously increase the weight energy density and volumetric energy density of the battery; however, when the thickness of the carbon current collector becomes thinner, its strength is greatly reduced, which cannot meet the capacity of the battery
  • the conductivity of graphite is worse than that of traditional metal current collectors, and the polarization of electrons in the length direction of the pole piece is serious during the charge and discharge process, which affects the overall charge and discharge consistency of the pole piece, and affects the rate performance of the battery.
  • the present application provides a carbon current collector, the carbon current collector has higher tensile strength and lower internal resistance, and a lithium ion battery using the current collector can have a higher energy density and better rate performance.
  • the present application also provides electrochemical devices and electronic devices including the carbon current collectors.
  • the present application provides a carbon current collector comprising a carbon material film and conductive fibers, wherein the conductive fibers are distributed in the carbon material film along a length direction of the carbon current collector.
  • the included angle between the projection of the conductive fibers on the carbon material film and the length direction of the carbon current collector is 0° to 5°.
  • the tensile strength of the carbon current collector in the length direction is 200 MPa to 500 MPa.
  • the electrical resistance of the carbon current collector along the length direction is 3 m ⁇ to 30 m ⁇ .
  • the conductive fibers are in the form of sheets.
  • the conductive fibers have a width of 0.01 mm to 5 mm.
  • the conductive fibers have a thickness of 0.5 ⁇ m to 20 ⁇ m.
  • the conductive fibers satisfy at least one of the following characteristics: the spacing between adjacent conductive fibers in the width direction of the carbon current collector is 0.1 mm to 9 mm; the conductivity of the conductive fibers is 0.1 mm to 9 mm. 30 ⁇ 10 6 S/m to 60 ⁇ 10 6 S/m; the strength of the conductive fiber is 220 MPa to 1400 MPa.
  • the projected area of the conductive fibers on the carbon material film accounts for 10% to 90% of the total area of the carbon material film.
  • the conductive fibers are metal fibers.
  • the material of the metal fiber includes at least one of copper, aluminum or nickel.
  • the thickness of the carbon current collector is 2 ⁇ m to 10 ⁇ m.
  • the present application also provides a method for preparing a carbon current collector as described above in the first aspect, comprising the following steps:
  • the polymer in the polymer solution includes at least one of polyimide, polyacrylonitrile, carboxymethyl cellulose or polyvinyl alcohol.
  • the polymer solution may further include a carbon material.
  • the carbon material includes at least one of acetylene black, carbon nanotubes, or graphene.
  • the mass percentage of the carbon material is 1% to 80% based on the total mass of the polymer and the carbon material.
  • the present application provides an electrochemical device comprising the carbon current collector of the first aspect or the carbon current collector prepared by the method of the second aspect.
  • the present application provides an electronic device comprising the electrochemical device of the third aspect.
  • the carbon current collector of the present application has higher tensile strength (fiber length direction) and lower internal resistance;
  • Li-ion batteries using this current collector can have higher energy density and better rate performance.
  • FIG. 1 is a schematic top-view structure diagram of a carbon current collector according to an embodiment of the present application, and the symbols in the schematic diagram are as follows: 1-conductive fiber; 2-carbon material film.
  • FIG. 2 is a left-view structural schematic diagram of a carbon current collector according to an embodiment of the present application, and the symbols in the schematic diagram are as follows: 1-conductive fiber; 2-carbon material film.
  • a term may refer to a range of variation less than or equal to ⁇ 10% of the numerical value, such as less than or equal to ⁇ 5%, less than or equal to ⁇ 4%, less than or equal to ⁇ 3%, Less than or equal to ⁇ 2%, less than or equal to ⁇ 1%, less than or equal to ⁇ 0.5%, less than or equal to ⁇ 0.1%, or less than or equal to ⁇ 0.05%.
  • a list of items linked by the term "at least one of” can mean any combination of the listed items.
  • the phrase "at least one of A and B” means A only; B only; or A and B.
  • the phrase "at least one of A, B, and C” means A only; or B only; C only; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.
  • Item A may contain a single element or multiple elements.
  • Item B may contain a single element or multiple elements.
  • Item C may contain a single element or multiple elements.
  • the present application provides a carbon current collector comprising a carbon material film and conductive fibers, wherein the conductive fibers are distributed in the carbon material film along a length direction of the carbon current collector.
  • the conductive fibers in the carbon current collector of the present application are distributed in the carbon material film along the length direction of the carbon current collector.
  • the conductive fibers distributed along the length direction of the carbon current collector can utilize fiber Its own strength provides the strength required by the current collector in the process of lithium-ion battery processing and transport, which solves the problem of low tensile strength of traditional carbon current collectors after thinning, which is insufficient for mass production and processing of lithium-ion batteries;
  • the direction of the conductive fibers is consistent with the length direction of the current collector, and the conductive fibers with high conductivity improve the conductivity in the length direction of the pole piece, which solves the problem of poor long-range conductivity of traditional carbon current collectors. Therefore, the carbon current collector of the present application has lower internal resistance and higher tensile strength, so that the thinner carbon current collector has better mass production processability and higher application feasibility. Lithium ions using this current collector can have higher energy density and better rate capability.
  • the included angle between the projection of the conductive fibers on the carbon material film and the length direction of the carbon current collector is 0° to 5°, such as 0.1°, 0.5°, 1.0°, 1.5°, 2.0° , 2.5°, 3.0°, 4.0°, 4.5°, or any value in between. If the included angle is too large, on the one hand, to prepare carbon current collectors of the same length, the required fiber length increases, the electron transmission distance increases, and the difficulty increases; on the other hand, the tensile strength of the current collector in the length direction is affected, and it will Creating a force component perpendicular to the length of the current collector increases the risk of tearing of the current collector perpendicular to its length. In addition, if the included angle is too large, the number of fibers running through the head and tail ends of a single pole piece is reduced, which is not conducive to long-range conduction and affects the conduction effect.
  • the included angle between the projection of the conductive fibers on the carbon material film and the length direction of the carbon current collector is 0°, that is, the conductive fibers are distributed parallel to the carbon current collector along the length direction of the carbon current collector. material film.
  • the strength of the conductive fibers distributed parallel to each other can more effectively improve the strength of the current collector along the fiber direction, and the amount of fibers used is less, which reduces the weight of the current collector.
  • the length direction of the carbon current collector is consistent with the coating direction of each material layer (such as electrode active material layer) in the process of pole piece processing, and is also consistent with the direction of the pole piece in the process of manufacturing electrochemical devices (such as batteries).
  • the winding direction is the same.
  • the width direction is perpendicular to the length direction.
  • the carbon current collector is shown in FIG. 1, which includes conductive fibers 1 and carbon material films 2, wherein the conductive fibers 1 are distributed in the carbon material films 2 at equal intervals along the MD direction.
  • the MD direction is consistent with the length direction of the carbon current collector.
  • the tensile strength of the carbon current collector in the length direction is 200 MPa to 500 MPa. In some embodiments, the tensile strength of the carbon current collector along the length direction is 220 MPa, 250 MPa, 270 MPa, 300 MPa, 330 MPa, 350 MPa, 380 MPa, 400 MPa, 450 MPa, 470 MPa, or any value therebetween.
  • the electrical resistance of the carbon current collector along the length direction is 3 m ⁇ to 30 m ⁇ .
  • the resistance along the length direction of the carbon current collector is 3.1m ⁇ , 3.3m ⁇ , 3.5m ⁇ , 3.7m ⁇ , 4.0m ⁇ , 4.3m ⁇ , 4.5m ⁇ , 4.7m ⁇ , 5.0m ⁇ , 5.3m ⁇ , 5.5m ⁇ m ⁇ , 5.7m ⁇ , 6.0m ⁇ , 6.5m ⁇ , 7.0m ⁇ , 7.5m ⁇ , 8.0m ⁇ , 8.5m ⁇ , 9.0m ⁇ , 10m ⁇ , 13m ⁇ , 15m ⁇ , 17m ⁇ , 20m ⁇ , 25m ⁇ , or any value in between.
  • the conductive fibers are in the form of sheets. Compared with other shapes such as cylindrical shape, sheet-shaped conductive fibers can obtain a current collector with a higher fiber projected area. The increase in the projected area of the fiber is beneficial to improve the tensile strength of the current collector and reduce the internal resistance in the length direction.
  • the thin thickness of the current collector restricts the diameter of cylindrical fibers from being too large, while the manufacturing of cylindrical fibers with too small diameter is difficult, and its uniform and dense arrangement is difficult, so it is difficult to prepare Current collectors with high fiber projected area.
  • the conductive fibers have a width of 0.01 mm to 5 mm. According to some embodiments of the present application, the conductive fibers have a width of 0.05mm, 0.1mm, 0.3mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.3mm, 1.5mm , 1.7mm, 1.9mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm, 4.0mm, 4.5mm or any value in between. In some embodiments of the present application, the conductive fibers have a width of 0.5 mm to 3 mm. Too wide fiber width may lead to too much fiber proportion, reducing the advantage of weight energy density, and too small width may lead to higher cost and difficulty in making current collectors.
  • the conductive fibers have a thickness of 0.5 ⁇ m to 20 ⁇ m.
  • the thickness of the conductive fibers is 0.5 ⁇ m, 1.0 ⁇ m, 1.5 ⁇ m, 2.0 ⁇ m, 2.5 ⁇ m, 3.0 ⁇ m, 4.0 ⁇ m, 4.5 ⁇ m, 5.0 ⁇ m, 7.0 ⁇ m, 9.0 ⁇ m, 10 ⁇ m, 11 ⁇ m, 13 ⁇ m, 15m, 17 ⁇ m, 19 ⁇ m or any value in between.
  • the conductive fibers have a thickness of 0.5 ⁇ m to 10 ⁇ m. Too thick fiber thickness will increase the thickness of the current collector, which will affect the volume energy density. Too small thickness will increase the cost and difficulty of fiber fabrication, reduce the tensile strength of the composite current collector, and increase the internal resistance.
  • the length direction of the conductive fibers is consistent with the length direction of the carbon current collector.
  • the direction perpendicular to the length direction of the conductive fibers is the width direction of the conductive fibers, and the dimension corresponding to this direction is the width of the conductive fibers.
  • the direction perpendicular to the length direction of the conductive fibers is the thickness direction of the conductive fibers, and the dimension corresponding to this direction is the thickness of the conductive fibers.
  • the spacing between adjacent conductive fibers along the width direction of the carbon current collector is 0.1 mm to 9 mm, such as 0.5 mm, 1.0 mm, 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm , 7.0mm or 8.0mm.
  • the spacing between adjacent conductive fibers along the width direction of the carbon current collector is 0.5 mm to 5 mm. If the interval is too small, the process is difficult and the cost is high; if the interval is too large, the proportion of fibers decreases, the tensile strength of the current collector decreases, and the internal resistance increases.
  • adjacent conductive fibers have the same spacing along the width direction of the carbon current collector.
  • the electrical conductivity of the conductive fibers is 30 ⁇ 10 6 S/m to 60 ⁇ 10 6 S/m, such as 40 ⁇ 10 6 S/m or 50 ⁇ 10 6 S/m.
  • the conductive fibers have a strength of 220 MPa to 1400 MPa, such as 300 MPa, 500 MPa, 700 MPa, 900 MPa, 1100 MPa or 1300 MPa.
  • the projected area of the conductive fibers on the carbon material film accounts for 10% to 90% of the total area of the carbon material film.
  • the proportion of the projected area of the conductive fibers on the carbon material film to the total area of the carbon material film is 20%, 25%, 30%, 35%, 40%, 45%, 50% , 60%, 70% or 80% etc.
  • the projected area of the conductive fibers on the carbon material film accounts for 20% to 50% of the total area of the carbon material film.
  • the conductive fibers are metal fibers.
  • the material of the metal fiber includes at least one of copper, aluminum or nickel.
  • the thickness of the carbon current collector is 2 ⁇ m to 10 ⁇ m. In some embodiments of the present application, the thickness of the carbon current collector is 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, or any value therebetween. If the thickness of the current collector is too low, it is difficult to process and has many defects. If the thickness is too high, the volume energy density will be lost.
  • the present application also provides a method for preparing a carbon current collector as described above in the first aspect, comprising the following steps:
  • the polymer in the polymer solution includes at least one of polyimide, polyacrylonitrile, carboxymethyl cellulose or polyvinyl alcohol.
  • the polymer solution may further include a carbon material.
  • the carbon material includes at least one of acetylene black, carbon nanotubes, or graphene.
  • adding carbon material to the polymer solution can further reduce the resistance in the length direction of the current collector, which is due to the very high electrical conductivity of carbon materials such as acetylene black, carbon nanotubes or graphene, which can promote the carbon current collector.
  • the conductivity of itself and the conductivity of the current collector in the length direction are improved.
  • adding carbon nanotubes with a one-dimensional structure and graphene with a two-dimensional structure will form a richer conductive network and increase the electrical conductivity along the length of the current collector.
  • the mass percentage of the carbon material is 1% to 80% based on the total mass of the polymer and the carbon material. In some embodiments, based on the total mass of the polymer and the carbon material, the mass percentage of the carbon material is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% %, 45%, 50%, 60%, 70% or any value in between. As the mass content of carbon material increases, the electrical resistance decreases, but the tensile strength also decreases. This is due to the interface between the carbon material and the polymer.
  • the mass percentage of the carbon material is 1% to 50% based on the total mass of the polymer and the carbon material.
  • the substrate in step (1) is selected from glass, polytetrafluoroethylene plate, polypropylene plate, marble plate, and the like.
  • the carbonization atmosphere in step (3) is carbonization under the protection of an inert gas, such as a nitrogen atmosphere.
  • the carbonization temperature is 500°C to 800°C, such as 600°C, 650°C, 700°C or 750°C, and the like.
  • the carbonization time is 60 min to 150 min, such as 70 min, 90 min, 110 min, 130 min, and the like.
  • the pressing described in step (3) is cold pressing.
  • the carbonized film is cold-pressed by a cold press at a pressure of 5 tons and a speed of 1 m/min.
  • the present application further provides an electrochemical device comprising the carbon current collector provided by the present application.
  • the carbon current collector provided in the present application can be used as a current collector for the positive electrode and the negative electrode.
  • the positive electrode sheet includes the carbon current collector provided herein. According to some embodiments, the positive electrode sheet further includes a positive active material disposed on the carbon current collector.
  • the positive active material of the present application may include lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganate, iron manganese phosphate At least one of lithium or lithium titanate.
  • the negative pole piece includes the carbon current collector provided herein. According to some embodiments, the negative pole piece further includes a negative active material disposed on the carbon current collector.
  • the negative active material in the present application may include at least one of artificial graphite, natural graphite, mesocarbon microspheres, soft carbon, hard carbon, silicon, silicon carbon, lithium titanate, and the like.
  • the electrochemical device of the present application such as a lithium ion battery, further includes an electrolyte, and the electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the lithium salt is selected from LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2.
  • LiPF 6 may be chosen as the lithium salt because it gives high ionic conductivity and improves cycling characteristics.
  • the non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.
  • the above-mentioned carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
  • Examples of the above-mentioned chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), carbonic acid Methyl ethyl ester (MEC) and combinations thereof.
  • Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), and combinations thereof.
  • fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate Ethyl carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-dicarbonate Fluoro-1-methylethylene, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.
  • FEC fluoroethylene carbonate
  • 1,2-difluoroethylene carbonate 1,1-difluoroethylene carbonate
  • 1,1,2-trifluoroethylene carbonate Ethyl carbonate 1,1,2,2-tetrafluoroethylene carbonate
  • 1-fluoro-2-methylethylene carbonate 1-fluoro-1-methylethylene carbonate
  • 1,2-dicarbonate Fluoro-1-methylethylene 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethyl
  • carboxylate compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone , caprolactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.
  • ether compounds examples include dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethyl ether Oxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.
  • Examples of the above-mentioned other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, Formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.
  • the material and shape of the separator used in the electrochemical device of the present application are not particularly limited, and it may be any technique disclosed in the prior art.
  • the separator includes a polymer or inorganic or the like formed from a material that is stable to the electrolyte of the present application.
  • the release film may include a substrate layer and a surface treatment layer.
  • the base material layer is a non-woven fabric, film or composite film with a porous structure, and the material of the base material layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.
  • At least one surface of the base material layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic material layer, or a layer formed by mixing a polymer and an inorganic material.
  • the inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, At least one of yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.
  • the binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxy , at least one of polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer is selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxy, polyvinylidene fluoride, At least one of poly(vinylidene fluoride-hexafluoropropylene).
  • the present application further provides an electronic device comprising the electrochemical device described herein.
  • the electronic equipment or device of the present application is not particularly limited.
  • the electronic devices of the present application include, but are not limited to, notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets , VCR, LCD TV, Portable Cleaner, Portable CD Player, Mini CD, Transceiver, Electronic Notepad, Calculator, Memory Card, Portable Recorder, Radio, Backup Power, Motor, Automobile, motorcycle, Power-assisted Bicycle, Bicycle , lighting equipment, toys, game consoles, clocks, power tools, flashes, cameras, large household batteries and lithium-ion capacitors, etc.
  • Test method for resistance in the length direction of the current collector using an internal resistance tester, clamp the two clips connected to the internal resistance tester on the current collector respectively, and the size of the junction between the clip and the current collector is 0.5cm ⁇ 3cm, The 3cm long side is perpendicular to the length direction of the current collector, the two clips are spaced 30cm apart along the length direction of the current collector, and the long sides of the two clips are clamped on both sides of the pole piece.
  • Tensile strength test in the length direction of the current collector Use an Instron universal testing machine for tensile test to prepare a current collector spline with a width of 20mm and a length of 100mm, in which the length direction of the current collector is the same as the length direction of the conductive fiber, and the tension is set. The speed is 5mm/min, the test is stopped after breaking, and the average value of 3 tests is taken.
  • Thickness and width of conductive fibers use a micrometer for thickness measurement, randomly select 5 fibers with a length of 30cm, and measure at 4-6cm intervals, and take the average value of 25 measurements;
  • the width was measured using a laser microscope. Three fibers with a length of 30 cm were randomly selected and measured at 7-10 cm intervals. Each sample was measured three times, and the average value of nine measurements was finally taken.
  • Spacing distance of conductive fibers The spacing distance is measured with a laser microscope. Take a 10cm ⁇ 20cm current collector sample, cut it perpendicular to the fiber length direction, cut it into two samples of similar size, and measure the two fibers on the cross section. The distance between each sample is measured 3 values, and the average value of 6 measurements is taken.
  • Projected area of conductive fibers The projected area is tested by CT scanning. A 10cm ⁇ 10cm current collector is randomly selected and scanned perpendicular to the surface of the current collector to calculate the fiber projection ratio.
  • PI polyimide
  • PAN polyacrylonitrile
  • PVA polyvinyl alcohol
  • CMC carboxymethyl cellulose
  • SP acetylene black
  • CNT carbon nanotube
  • the copper conductive fibers with a thickness of 3 ⁇ m and a width of 1 mm were laid flat on the glass with a gap of 2 mm and straightened, and the PI polymer solution with a solid content of 1% was scraped on the release film. After drying, a PI copper fiber composite membrane with a thickness of 7 ⁇ m was obtained.
  • a carbon current collector in which the copper fibers are distributed in the composite film parallel to each other along the length direction of the carbon current collector, that is, the included angle between the projection of the copper fibers on the carbon material film and the length direction of the carbon current collector is 0°.
  • Example 1 the difference from the Example is that the parameters of each raw material in the synthesis process of the carbon current collector are adjusted, and the specific parameter changes are shown in the tables corresponding to each Example and Comparative Example.
  • Preparation of positive electrode Lithium cobaltate, acetylene black and polyvinylidene fluoride are fully stirred and mixed uniformly in N-methylpyrrolidone solvent system according to the weight ratio of 98:1:1 to prepare positive electrode slurry.
  • the prepared positive electrode slurry is coated on the above-mentioned carbon current collector, dried, and cold-pressed to obtain a positive electrode.
  • Preparation of negative electrode Graphite, polymethacrylic acid and styrene-butadiene rubber were fully stirred and mixed in an appropriate amount of deionized water solvent according to the weight ratio of 98:1:1 to form a uniform negative electrode slurry.
  • the prepared negative electrode slurry is coated on the carbon current collector, dried, and cold pressed to obtain a negative electrode.
  • Preparation of lithium ion battery stack the positive electrode, the separator and the negative electrode in order, so that the separator is placed between the positive electrode and the negative electrode for isolation.
  • a bare cell is obtained by winding.
  • the bare cell is placed in the outer package, and after vacuum drying, the electrolyte is injected and packaged.
  • the lithium-ion battery is obtained through the process of formation, degassing, trimming and other processes.
  • Table 1 shows the effect of the conductive fibers and the polymer species in the polymer solution on the performance of the prepared carbon current collectors and lithium-ion batteries containing the same.
  • the conductive fibers in Examples 2-5 are copper fibers, which are the same as those in Example 1, and the shape is sheet-like.
  • the thickness of the fibers is 3 ⁇ m and the width is 1 mm.
  • the distance between the fibers is 2 mm
  • the projected area ratio of the conductive fibers on the carbon material mold is 33.3%
  • the angle between the projection of the conductive fibers on the carbon material film and the length direction of the carbon current collector is 0°.
  • Comparative Examples 1-4 did not contain conductive fibers.
  • Example 1 and Comparative Examples 1-3 in Table 1 that the current collectors of Examples 1-5 containing conductive fibers have lower current collectors than the current collectors of Comparative Examples 1-4 without conductive fibers internal resistance and higher tensile strength.
  • the conductive fibers provide the strength required by the current collector during the processing and transport of lithium-ion batteries, which solves the problem that the traditional carbon current collectors have low strength after thinning and are insufficient for mass production of lithium-ion batteries; fiber orientation Consistent with the length direction of the current collector, the conductive fiber with high conductivity improves the conductivity in the length direction of the pole piece, which solves the problem of poor long-range conductivity of the traditional carbon current collector.
  • Table 2 shows the effects of the types and contents of carbon materials in the polymer solution on the performance of the prepared carbon current collectors and lithium-ion batteries comprising the same.
  • the conductive fibers are copper fibers, which are the same as in Example 1.
  • the shape is sheet-like.
  • the thickness of the fibers is 3 ⁇ m, the width is 1 mm, and the distance between adjacent conductive fibers is 2 mm.
  • the projected area ratio of the conductive fibers on the carbon material mold is 33.3%, and the included angle between the projection of the conductive fibers on the carbon material film and the length direction of the carbon current collector is 0°.
  • the mass content of the carbon material refers to the mass percentage content of the carbon material in the total amount of the carbon material and the polymer.
  • Example 6 and Examples 9-11 in Table 2 It can be seen from Example 6 and Examples 9-11 in Table 2 that the mass content of carbon material in the polymer has a certain influence on the strength and resistance of the current collector. As the mass content of carbon material increases, the resistance decreases, but the strength Also decreased, because there is an interface between the carbon material and the polymer, the interface will be slightly peeled off when the polymer is carbonized, resulting in the weakening of the force between the carbon material and the carbonized polymer, and the excessive addition of carbon material will This leads to poor polymer continuity and insufficient internal connection points after carbonization, resulting in reduced tensile strength.
  • Table 3 shows the effect of various parameters of the conductive fibers on the performance of the prepared carbon current collectors and lithium-ion batteries containing the same.
  • the polymer in the polymer solution in Examples 12-30 shown in Table 3 was the same as Example 1 and was PI.
  • the sheet-shaped conductive fibers have better effects than other shapes such as cylindrical shapes, because the sheet-shaped conductive fibers can obtain a current collector with a higher fiber projected area .
  • the increase in the projected area of the fiber is beneficial to improve the tensile strength of the current collector and reduce the internal resistance in the length direction.
  • the thin thickness of the current collector restricts the diameter of cylindrical fibers from being too large, while the manufacture of cylindrical fibers with too small diameters is difficult, and its uniform and dense arrangement is difficult, so it is difficult to prepare Current collectors with high fiber projected area.
  • the carbon current collector has high tensile strength and low internal resistance. If the thickness of the fiber is too thick, the thickness of the current collector will increase, which will affect the volume energy density; if the thickness is too small, the cost and difficulty of fiber fabrication will increase, the tensile strength of the composite current collector will decrease, and the internal resistance will increase.
  • the carbon current collector has high tensile strength and low internal resistance. Too wide fiber width may lead to too much fiber proportion, reducing the advantage of weight energy density; too small width will lead to higher cost and difficulty in making current collectors.

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Abstract

本申请涉及一种碳集流体和包含所述碳集流体的电化学装置和电子装置。本申请的碳集流体包括碳材料膜和导电纤维，其中，所述导电纤维沿所述碳集流体的长度方向分布在碳材料膜中。本申请的碳集流体具有更高的拉伸强度(纤维长度方向)和更低的内阻。使用该集流体的锂离子电池可以具有更高的能量密度和更好的倍率性能。

Description

碳集流体及包括该碳集流体的电化学装置和电子装置 技术领域
本申请涉及储能领域，具体涉及一种碳集流体、其制备方法及使用其的电化学装置和电子装置。
背景技术
锂离子电池具有能量密度高，循环寿命长、自放电小等优势，得到了非常广泛的应用；随着技术的不断进步，人们对锂离子电池的能量密度的要求越来越高，如何提升锂离子电池的能量密度成为了人们研究的热点。
随着锂离子电池材料的克容量和上限电压趋向于极限，电池能量密度的提升变得越来越困难。更薄的金属集流体如铜箔和铝箔，在满足电池使用要求的前提下，其厚度基本达到工艺上限，再继续减薄会极大的增加成本；使用密度更低的石墨纸替代传统金属集流体可提升电池的重量能量密度；使用厚度更薄的碳集流体可以同时提升电池的重量能量密度和体积能量密度；然而当碳集流体厚度变薄时其强度大幅度降低，无法满足电池的量产加工要求；此外石墨电导率差于传统金属集流体，充放电过程中电子在极片长度方向上的极化严重，影响极片整体充放电的一致性，影响电池倍率性能。
发明内容
针对现有技术存在的问题，本申请提供一种碳集流体，该碳集流体具有更高的拉伸强度、更低的内阻，使用该集流体的锂离子电池可以具有更高的能量密度和更好的倍率性能。本申请还提供了包括该碳集流体的电化学装置和电子装置。
在第一方面，本申请提供了一种碳集流体，其包括碳材料膜和导电纤维，其中，所述导电纤维沿所述碳集流体的长度方向分布在碳材料膜中。
根据本申请的一些实施方式，所述导电纤维在碳材料膜上的投影与碳集流体长度方向的夹角为0°至5°。
根据本申请的一些实施方式，所述碳集流体沿长度方向的拉伸强度为200MPa至500MPa。
根据本申请的一些实施方式，所述碳集流体沿长度方向的电阻为3mΩ至30mΩ。
根据本申请的一些实施方式，所述导电纤维为片状。在一些实施方式中，所述导电纤维的宽度为0.01mm至5mm。根据本申请的一些实施例，所述导电纤维的厚度为0.5μm至20μm。
根据本申请的一些实施方式，所述导电纤维满足以下特征中的至少一者：相邻的导电纤维沿所述碳集流体宽度方向的间距为0.1mm至9mm；所述导电纤维的电导率为30×10 6S/m至60×10 6S/m；所述导电纤维的强度为220MPa至1400MPa。
根据本申请的一些实施方式，所述导电纤维在所述碳材料膜上的投影面积占所述碳材料膜的总面积的比例为10％至90％。
根据本申请的一些实施方式，所述导电纤维为金属纤维。在本申请的一些实施方式中，所述金属纤维的材质包括铜、铝或镍中的至少一种。
根据本申请的一些实施方式，所述碳集流体的厚度为2μm至10μm。
在第二方面，本申请还提供了如上述第一方面的碳集流体的制备方法，其包括以下步骤：
(1)将导电纤维平铺在基体表面，得到负载导电纤维的基体；
(2)将聚合物溶液涂覆至所述负载导电纤维的基体上，干燥后得到聚合物和导电纤维复合的薄膜；
(3)将所述聚合物和导电纤维复合的薄膜从基体表面脱离，进行碳化；
(4)将碳化后的薄膜进行压制，得到所述碳集流体。
根据本申请的一些实施方式，所述聚合物溶液中的聚合物包括聚酰亚胺、聚丙烯腈、羧甲基纤维素或聚乙烯醇中的至少一种。
根据本申请的一些实施方式，所述聚合物溶液还可以包括碳材料。在本申请的一些实施方式中，所述碳材料包括乙炔黑、碳纳米管或石墨烯中的至少一种。
根据本申请的一些实施方式，基于所述聚合物和碳材料的总质量，所述碳材料的质量百分含量为1％至80％。
在第三方面，本申请提供了一种电化学装置，其包括第一方面所述的碳集流体或第二方面所述的方法制备的碳集流体。
在第四方面，本申请提供了一种电子装置，其包括第三方面所述的电化学装置。
本申请的有益效果：
1)本申请的碳集流体具有更高的拉伸强度(纤维长度方向)和更低的内阻；
2)使更薄的碳集流体具有更好的量产加工性能和更高应用可行性；
3)使用该集流体的锂离子电池可以具有更高的能量密度和更好的倍率性能。
附图说明
图1为根据本申请的一个实施方式的碳集流体的俯视结构示意图，示意图中的标记如下：1-导电纤维；2-碳材料膜。
图2为根据本申请的一个实施方式的碳集流体的左视结构示意图，示意图中的标记如下：1-导电纤维；2-碳材料膜。
具体实施方式
本申请的实施例将会被详细的描示在下文中。本申请的实施例不应该被解释为对本申请的限制。
如本文中所使用，术语“约”用以描述及说明小的变化。当与事件或情形结合使用时，所述术语可指代其中事件或情形精确发生的例子以及其中事件或情形极近似地发生的例子。举例来说，当结合数值使用时，术语可指代小于或等于所述数值的±10％的变化范围，例如小于或等于±5％、小于或等于±4％、小于或等于±3％、小于或等于±2％、小于或等于±1％、小于或等于±0.5％、小于或等于±0.1％、或小于或等于±0.05％。另外，有时在本文中以范围格式呈现量、比率和其它数值。应理解，此类范围格式是用于便利及简洁起见，且应灵活地理解，不仅包含明确地指定为范围限制的数值，而且包含涵盖于所述范围内的所有个别数值或子范围，如同明确地指定每一数值及子范围一般。
在具体实施方式及权利要求书中，由术语“中的至少一种”连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一种”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一种”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个元件或多个元件。项目B可包含单个元件或多个元件。项目C可包含单个元件或多个元件。
整个说明书中对“实施例”、“部分实施例”、“一个实施例”、“另一举例”、“举例”、“具体举例”或“部分举例”的引用，其所代表的意思是在本申请中的至少一个实施例或举例包含了该实施例或举例中所描述的特定特征、结构、材料或特性。因 此，在整个说明书中的各处所出现的描述，例如：“在一些实施例中”、“在实施例中”、“在一个实施例中”、“在另一个举例中”，“在一个举例中”、“在特定举例中”或“举例“，其不必然是引用本申请中的相同的实施例或示例。此外，本文中的特定特征、结构、材料或特性可以以任何合适的方式在一个或多个实施例或举例中结合。
在第一方面，本申请提供了一种碳集流体，其包括碳材料膜和导电纤维，其中，所述导电纤维沿所述碳集流体的长度方向分布在碳材料膜中。
与传统的碳集流体相比，本申请的碳集流体中导电纤维沿所述碳集流体的长度方向分布在碳材料膜中，一方面沿碳集流体的长度方向分布的导电纤维可以利用纤维自身的强度提供集流体在锂离子电池加工走带过程中所需的强度，解决了传统碳集流体变薄后拉伸强度低而不足以应用于锂离子电池量产加工的问题；另一方面，导电纤维方向与集流体长度方向一致，高电导率的导电纤维提升了极片长度方向上的电导率，解决了传统碳集流体长程电导率差的问题。因此本申请的碳集流体具有更低的内阻和更高拉伸强度，使更薄的碳集流体具有更好的量产加工性能和更高应用可行性。使用该集流体的锂离子可以具有更高的能量密度和更好的倍率性能。
根据本申请的一些实施方式，所述导电纤维在碳材料膜上的投影与碳集流体长度方向的夹角为0°至5°，例如0.1°、0.5°、1.0°、1.5°、2.0°、2.5°、3.0°、4.0°、4.5°或它们之间的任意值。夹角过大，一方面制备相同长度的碳集流体，所需纤维长度增加，电子传输距离增加，难度增加；另一方面，影响集流体在长度方向的拉伸强度，在拉伸时还会在垂直于集流体长度方向上产生分力，增加集流体在垂直于其长度方向上发生撕裂的风险。此外，夹角过大，贯穿单个极片头尾两端的纤维数量降低，不利于长程导电，影响导电效果。
根据本申请的一些实施例，所述导电纤维在碳材料膜上的投影与碳集流体长度方向的夹角为0°，即所述导电纤维沿所述碳集流体的长度方向平行分布在碳材料膜中。相互平行分布的导电纤维其本身的强度可以更有效的提升集流体的沿纤维方向上的强度，并且所用的纤维量更少，降低集流体重量。
本申请中，碳集流体的长度方向与极片加工过程中的各个材料层(例如电极活性材料层)的涂覆方向是一致的，也与电化学装置(例如电池)制造过程中极片的卷绕方向是一致的。而宽度方向是与长度方向垂直的。
在本申请的一个实施方式中，所述碳集流体如图1所示，其包括导电纤维1和碳 材料膜2，其中导电纤维1沿着MD方向，等间距分布于碳材料膜2中。其中MD方向与碳集流体的长度方向一致。
根据本申请的一些实施方式，所述碳集流体沿长度方向的拉伸强度为200MPa至500MPa。在一些实施例中，所述碳集流体沿长度方向的拉伸强度为220MPa、250MPa、270MPa、300MPa、330MPa、350MPa、380MPa、400MPa、450MPa、470MPa或它们之间的任意值。
根据本申请的一些实施方式，所述碳集流体沿长度方向的电阻为3mΩ至30mΩ。根据本申请的一些实施方式，所述碳集流体沿长度方向的电阻为3.1mΩ、3.3mΩ、3.5mΩ、3.7mΩ、4.0mΩ、4.3mΩ、4.5mΩ、4.7mΩ、5.0mΩ、5.3mΩ、5.5mΩ、5.7mΩ、6.0mΩ、6.5mΩ、7.0mΩ、7.5mΩ、8.0mΩ、8.5mΩ、9.0mΩ、10mΩ、13mΩ、15mΩ、17mΩ、20mΩ、25mΩ或它们之间的任意值。
根据本申请的一些实施方式，所述导电纤维为片状。采用片状的导电纤维相比于其他形状例如圆柱状，片状的导电纤维可以获得具有更高纤维投影面积的集流体。纤维投影面积增大，有利于提升集流体的拉伸强度，降低其长度方向上的内阻。而对于圆柱状纤维来说，集流体的薄厚度特性限制圆柱状纤维的直径不能过大，而直径过小的圆柱状纤维的制造困难，且其均匀密集排布困难，因此难以用于制备具有高纤维投影面积的集流体。
根据本申请的一些实施方式，所述导电纤维的宽度为0.01mm至5mm。根据本申请的一些实施例，所述导电纤维的宽度为0.05mm、0.1mm、0.3mm、0.5mm、0.6mm、0.7mm、0.8mm、0.9mm、1.0mm、1.1mm、1.3mm、1.5mm、1.7mm、1.9mm、2.0mm、2.5mm、3.0mm、3.5mm、4.0mm、4.5mm或它们之间的任意值。在本申请的一些实施方式中，所述导电纤维的宽度为0.5mm至3mm。纤维宽度过宽可能导致纤维占比过多，降低重量能量密度优势，宽度过小导致集流体制成成本及难度变高。
根据本申请的一些实施例，所述导电纤维的厚度为0.5μm至20μm。根据本申请的一些实施例，所述导电纤维的厚度为0.5μm、1.0μm、1.5μm、2.0μm、2.5μm、3.0μm、4.0μm、4.5μm、5.0μm、7.0μm、9.0μm、10μm、11μm、13μm、15m、17μm、19μm或它们之间的任意值。在本申请的一些实施方式中，所述导电纤维的厚度为0.5μm至10μm。纤维厚度过厚会导致集流体厚度增加，影响体积能量密度，厚度过小导致纤维制成成本及难度变高，复合集流体的拉伸强度降低，内阻增加。
本申请中，导电纤维沿所述碳集流体的长度方向分布在碳材料膜时，导电纤维的长度方向与碳集流体的长度方向一致。在与碳集流体平行的平面中，与导电纤维长度方向垂直的方向为导电纤维的宽度方向，此方向上对应的尺寸为导电纤维的宽度。在与碳集流体垂直的平面中，与导电纤维长度方向垂直的方向为导电纤维的厚度方向，此方向上对应的尺寸为导电纤维的厚度。
根据本申请的一些实施方式，相邻的导电纤维沿所述碳集流体宽度方向的间距为0.1mm至9mm，例如0.5mm、1.0mm、2.0mm、3.0mm、4.0mm、5.0mm、6.0mm、7.0mm或8.0mm。在本申请的一些实施例中，相邻的导电纤维沿所述碳集流体宽度方向的间距为0.5mm至5mm。间隔过小制程困难，成本高；间隔过大，纤维占比降低，集流体的拉伸强度降低，内阻增加。在一些实施例中，相邻的导电纤维沿所述碳集流体宽度方向的间距相同。
根据本申请的一些实施方式，所述导电纤维的电导率为30×10 6S/m至60×10 6S/m，例如40×10 6S/m或50×10 6S/m。根据本申请的一些实施方式，所述导电纤维的强度为220MPa至1400MPa，例如300MPa、500MPa、700MPa、900MPa、1100MPa或1300MPa。
根据本申请的一些实施方式，所述导电纤维在所述碳材料膜上的投影面积占所述碳材料膜的总面积的比例为10％至90％。在一些实施方式中，导电纤维在所述碳材料膜上的投影面积占所述碳材料膜的总面积的比例为20％、25％、30％、35％、40％、45％、50％、60％、70％或80％等。在一些实施例中，导电纤维在所述碳材料膜上的投影面积占所述碳材料膜的总面积的比例为20％至50％。
根据本申请的一些实施方式，所述导电纤维为金属纤维。在本申请的一些实施方式中，所述金属纤维的材质包括铜、铝或镍中的至少一种。
根据本申请的一些实施方式，所述碳集流体的厚度为2μm至10μm。在本申请的一些实施方式中，所述碳集流体的厚度为3μm、4μm、5μm、6μm、7μm、8μm、9μm或它们之间的任意值。集流体的厚度过低，加工困难，缺陷多，厚度过高会损失体积能量密度。
在第二方面，本申请还提供了如上述第一方面的碳集流体的制备方法，其包括以下步骤：
(1)将导电纤维平铺在基体表面，得到负载导电纤维的基体；
(2)将聚合物溶液涂覆至所述负载导电纤维的基体上，干燥后得到聚合物和导电纤维复合的薄膜；
(3)将所述聚合物和导电纤维复合的薄膜从基体表面脱离，进行碳化；
(4)将碳化后的薄膜进行压制，得到所述碳集流体。
根据本申请的一些实施方式，所述聚合物溶液中的聚合物包括聚酰亚胺、聚丙烯腈、羧甲基纤维素或聚乙烯醇中的至少一种。
根据本申请的一些实施方式，所述聚合物溶液还可以包括碳材料。在本申请的一些实施方式中，所述碳材料包括乙炔黑、碳纳米管或石墨烯中的至少一种。本申请中在聚合物溶液中添加碳材料可以进一步降低集流体长度方向上的电阻，这是由于乙炔黑、碳纳米管或石墨烯等碳材料具有非常高的电导率，从而可以促进碳集流体本身的电导率以及集流体长度方向上的电导率的提高。尤其是，添加具有一维结构的碳纳米管以及具有二维结构的石墨烯后，会形成更丰富的导电网络，增加集流体长度方向上的电导率。
根据本申请的一些实施方式，基于所述聚合物和碳材料的总质量，所述碳材料的质量百分含量为1％至80％。在一些实施例中，基于所述聚合物和碳材料的总质量，所述碳材料的质量百分含量为5％、10％、15％、20％、25％、30％、35％、40％、45％、50％、60％、70％或它们之间的任意值。随着碳材料质量含量的增加，电阻降低，但拉伸强度也下降，这是由于碳材料和聚合物之间具有界面，聚合物碳化时界面会有轻微的剥离，导致碳材料和碳化后的聚合物间的作用力减弱，同时碳材料的过多加入会导致聚合物连续性变差，碳化后内部连接点不足，导致拉伸强度降低。
根据本申请的一些实施例，基于所述聚合物和碳材料的总质量，所述碳材料的质量百分含量为1％至50％。
根据本申请的一些实施方式，步骤(1)中所述基体选自玻璃、聚四氟乙烯板、聚丙烯板或大理石板等。
根据本申请的一些实施方式，步骤(3)中的碳化氛围为在惰性气体保护下进行碳化，例如氮气氛围。碳化温度为500℃至800℃，例如600℃、650℃、700℃或750℃等。在一些实施例中，所述碳化的时间为60min至150min，例如70min、90min、110min、130min等。
根据本申请的一些实施方式，步骤(3)中所述的压制为冷压。在本申请的一些实施例中，冷压机以5吨的压力，1m/min的速度对碳化后的薄膜进行冷压。
本申请进一步提供了一种电化学装置，所述电化学装置包括本申请提供的碳集流体。本申请提供的碳集流体可以作为正极极片与负极极片的集流体。
根据一些实施例，所述正极极片包括本申请提供的碳集流体。根据一些实施例，所述正极极片还包括设置在所述碳集流体上的正极活性物质。本申请的正极活性物质可以包括镍钴锰酸锂(811、622、523、111)、镍钴铝酸锂、磷酸铁锂、富锂锰基材料、钴酸锂、锰酸锂、磷酸锰铁锂或钛酸锂中的至少一种。
根据一些实施例，所述负极极片包括本申请提供的碳集流体。根据一些实施例，所述负极极片还包括设置在所述碳集流体上的负极活性物质。本申请中的负极活性物质可以包括人造石墨、天然石墨、中间相碳微球、软碳、硬碳、硅、硅碳、钛酸锂等中的至少一种。
本申请的电化学装置，例如锂离子电池，还包括电解质，电解质可以是凝胶电解质、固态电解质和电解液中的一种或多种，电解液包括锂盐和非水溶剂。
在本申请一些实施方案中，锂盐选自LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiB(C 6H 5) 4、LiCH 3SO 3、LiCF 3SO 3、LiN(SO 2CF 3) 2、LiC(SO 2CF 3) 3、LiSiF 6、LiBOB和二氟硼酸锂中的一种或多种。举例来说，锂盐可以选用LiPF 6，因为它可以给出高的离子导电率并改善循环特性。
非水溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、其它有机溶剂或它们的组合。
上述碳酸酯化合物可为链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或其组合。
上述链状碳酸酯化合物的实例为碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸甲乙酯(MEC)及其组合。环状碳酸酯化合物的实例为碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)、碳酸乙烯基亚乙酯(VEC)及其组合。氟代碳酸酯化合物的实例为碳酸氟代亚乙酯(FEC)、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯、碳酸三氟甲基亚乙酯及其组 合。
上述羧酸酯化合物的实例为甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯、甲瓦龙酸内酯、己内酯及其组合。
上述醚化合物的实例为二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、乙氧基甲氧基乙烷、2-甲基四氢呋喃、四氢呋喃及其组合。
上述其它有机溶剂的实例为二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、甲酰胺、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯、磷酸三辛酯、和磷酸酯及其组合。
本申请的电化学装置中使用的隔离膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。在一些实施例中，隔离膜包括由对本申请的电解液稳定的材料形成的聚合物或无机物等。
例如隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。
无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的至少一种。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的至少一种。
聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚偏氟乙烯、聚(偏氟乙烯-六氟丙烯)中的至少一种。
本申请进一步提供了一种电子装置，其包括本申请所述的电化学装置。
本申请的电子设备或装置没有特别限定。在一些实施例中，本申请的电子设备包括但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、 便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
下面结合实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。
测试方法
1、集流体长度方向电阻测试方法：采用内阻测试仪，将连接内阻测试仪的两个夹子分别夹在集流体上，其中夹子与集流体的相接处的尺寸为0.5cm×3cm，其3cm的长边垂直于集流体长度方向，两个夹子沿集流体长度方向间隔30cm，两个夹子的长边正对的夹在极片的两侧，三次测试取平均值。
2、集流体长度方向拉伸强度测试：使用Instron万能试验机进行拉伸测试，制备宽度为20mm，长度为100mm的集流体样条，其中集流体长度方向与导电纤维长度方向相同，设置拉伸速度为5mm/min，拉断后停止测试，取3次测试平均值。
3、导电纤维的厚度、宽度：厚度测量使用万分尺进行测试，随机取5条长度为30cm的纤维，间隔4-6cm取点测量，取25次测量的平均值；
宽度使用激光显微镜进行测量，随机取3条长度为30cm的纤维，间隔7-10cm取点测量，每条样品测量3次，最终取9次测量的平均值。
4、导电纤维的间隔距离：间隔距离使用激光显微镜进行测量，取10cm×20cm的集流体样品，垂直于纤维长度方向进行激光切割，切割成2份大小相近的样品，测量其截面上两条纤维间的距离，每份样品测量3个值，取6次测量的平均值。
5、导电纤维的投影面积：投影面积采用CT扫描测试，随机取10cm×10cm的集流体，垂直于集流体表面进行扫描，计算得出纤维投影占比。
6、2C放电容量/0.2C放电容量
25℃环境下，静置30min；0.5C恒流充电至4.45V，4.45V恒压充电至0.02C；静置5min；0.2C恒流放电至3.0V，此步放电容量为“0.2C放电容量”，静置30min；0.5C恒流充电至4.45V，4.45V恒压充电至0.02C；静置5min；2C恒流放电至3.0V，此步放电容量为“2C放电容量”；静置5min；测试完成。
实施例
实施例和对比例中：PI代表聚酰亚胺、PAN代表聚丙烯腈、PVA代表聚乙烯醇、CMC代表羧甲基纤维素、SP代表乙炔黑、CNT代表碳纳米管。
实施例1
将厚度为3μm、宽度为1mm的铜导电纤维，以2mm的间隙平铺在玻璃上并拉直，将固含量为1％的PI聚合物溶液刮涂在离型膜上。烘干后，制得7μm的PI铜纤维复合膜。将此膜揭下，放置于高温炉中以氮气做保护气800℃烧结90min，降温后取出，用冷压机以5吨的压力，1m/min的速度冷压，冷压至6μm，即得碳集流体，所述碳集流体中铜纤维沿碳集流体的长度方向相互平行分布在复合膜中，即铜纤维在碳材料膜上的投影与碳集流体长度方向的夹角为0°。
实施例2-30以及对比例1-4
参照实施例1，与实施例的不同之处在于，调整碳集流体合成过程中各原料的参数，具体参数变化详见各实施例及对比例所对应的表格。
锂离子电池的制备
正极的制备：将钴酸锂、乙炔黑和聚偏氟乙烯按照98:1:1的重量比在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀，制得正极浆料。将制得的正极浆料涂布在上述碳集流体上，烘干，冷压，得到正极。
负极的制备：将石墨、聚甲基丙烯酸和丁苯橡胶按照98:1:1的重量比在适量的去离子水溶剂中充分搅拌混合，使其形成均匀的负极浆料。将制得的负极浆料涂布在上述碳集流体上，烘干，冷压，得到负极。
电解液的制备：在含水量<10ppm的氩气气氛手套箱中，在碳酸丙烯酯(PC)，碳酸乙烯酯(EC)，碳酸二乙酯(DEC)(重量比约1:1:1)混合而成的溶剂中，加入LiPF 6混合均匀得到电解液，其中LiPF 6的浓度为约1.15mol/L。
隔离膜的制备：以7μm的PE作为隔离膜。
锂离子电池的制备：将正极、隔离膜、负极按顺序叠好，使隔离膜处于正极和负极中间以起到隔离的作用。卷绕得到裸电芯。将裸电芯置于外包装中，经真空干燥后，注入电解液，封装。经过化成、脱气、切边等工艺流程得到锂离子电池。
表1示出了导电纤维以及聚合物溶液中的聚合物种类对所制备得到的碳集流体以及包含所述集流体的锂离子电池的性能影响。在表1所示的各实施例和对比例中，实施例2-5中导电纤维与实施例1相同为铜纤维，形状为片状，纤维的厚度为3μm、宽度为1mm，相邻的导电纤维之间的间距为2mm，导电纤维在碳材料模上的投影面积比例为33.3％，导电纤维在碳材料膜上的投影与碳集流体长度方向的夹角为0°。对比例1-4中不含有导电纤维。
表1
Figure PCTCN2021083054-appb-000001
通过表1的实施例1与对比例1-3可以看出，含有导电纤维的实施例1-5的集流体相比于不含导电纤维的对比例1-4的集流体，其具有更低的内阻和更高拉伸强度。这是由于导电纤维提供了集流体在锂离子电池加工走带过程中所需的强度，解决了传统碳集流体变薄后强度低而不足以应用于锂离子电池量产加工的问题；纤维方向与集流体长度方向一致，高电导率的导电纤维提升了极片长度方向上的电导率，解决了传统碳集流体长程电导率差的问题。
通过表1的实施例1-5可以看出，导电纤维在采用不同种类的聚合物生成的碳集流体中具有普适性。
表2示出了聚合物溶液中的碳材料种类、含量对所制备得到的碳集流体以及包含所述集流体的锂离子电池的性能影响。在表2所示的实施例6-11中导电纤维与实施例1 相同为铜纤维，形状为片状，纤维的厚度为3μm、宽度为1mm，相邻的导电纤维之间的间距为2mm，导电纤维在碳材料模上的投影面积比例为33.3％，导电纤维在碳材料膜上的投影与碳集流体长度方向的夹角为0°。其中，碳材料质量含量指碳材料占碳材料与聚合物总量的质量百分含量。
表2
Figure PCTCN2021083054-appb-000002
通过表2的实施例6-8可以看出，在聚合物溶液中添加碳材料可以进一步降低集流体长度方向上的电阻。这是由于乙炔黑、碳纳米管或石墨烯具有非常高的电导率，从而可以促进碳集流体本身的电导率以及集流体长度方向上的电导率的提高，尤其是，添加具有一维结构的碳纳米管以及具有二维结构的石墨烯后，会形成更丰富的导电网络，增加集流体长度方向上的电导率。
通过表2的实施例6与实施例9-11可以看出，聚合物中碳材料的质量含量对集流体的强度和电阻有一定影响，随着碳材料质量含量的增加，电阻降低，但强度也下降，这是由于碳材料和聚合物之间具有界面，聚合物碳化时界面会有轻微的剥离，导致碳材料和碳化后的聚合物间的作用力减弱，同时碳材料的过多加入会导致聚合物连续性变差，碳化后内部连接点不足，导致拉伸强度降低。
表3示出了导电纤维的各参数对制备得到的碳集流体以及包含所述集流体的锂离子电池的性能影响。在表3所示实施例12-30中聚合物溶液中的聚合物与实施例1相同为PI。
表3
Figure PCTCN2021083054-appb-000003
通过表3的实施例12-14可以看出，片状的导电纤维相比于其他形状例如圆柱状具有好的效果，这是由于片状的导电纤维可以获得具有更高纤维投影面积的集流体。纤维投影面积增大，有利于提升集流体的拉伸强度，降低其长度方向上的内阻。对于圆柱状纤维来说，集流体的薄厚度特性限制了圆柱状纤维的直径不能过大，而直径过小的圆柱状纤维的制造困难，且其均匀密集排布困难，因此难以用于制备具有高纤维投影面积的集流体。
通过实施例15-18可以看出，纤维厚度在0.5μm至20μm范围内时，碳集流体具有高的拉伸强度和低的内阻。纤维厚度过厚会导致集流体厚度增加，影响体积能量密度； 厚度过小导致纤维制成成本及难度变高，复合集流体的拉伸强度降低，内阻增加。
通过实施例19-22可以看出，纤维宽度在0.01mm至5mm范围内时，碳集流体具有高的拉伸强度和低的内阻。纤维宽度过宽可能导致纤维占比过多，降低重量能量密度优势；宽度过小导致集流体制成成本及难度变高。
通过实施例23-26可以看出，相邻的纤维之间的间隔在0.1mm至9mm范围内时，碳集流体具有高的拉伸强度和低的内阻。间隔增大，纤维占比降低，集流体的强度降低，内阻增加；间隔过小，制成困难，成本高。
通过实施例27-30可以看出，导电纤维在碳材料膜上的投影与碳集流体长度方向的夹角为0°至5°时，碳集流体具有高的拉伸强度和低的内阻。夹角过大，一方面制备相同长度的碳集流体，所需纤维长度增加，电子传输距离增加，难度增加；另一方面，影响集流体在长度方向的拉伸强度，在拉伸时还会在垂直于集流体长度方向上产生分力，增加集流体在垂直于其长度方向上发生撕裂的风险。此外，夹角过大，贯穿单个极片头尾两端的纤维数量降低，不利于长程导电，影响导电效果。
尽管已经演示和描述了说明性实施例，本领域技术人员应该理解上述实施例不能被解释为对本申请的限制，并且可以在不脱离本申请的精神、原理及范围的情况下对实施例进行改变，替代和修改。

Claims (15)

  1. 一种碳集流体，包括碳材料膜和导电纤维，其中，所述导电纤维沿所述碳集流体的长度方向分布在所述碳材料膜中。
  2. 根据权利要求1所述的碳集流体，其中，所述导电纤维在所述碳材料膜上的投影与所述碳集流体长度方向的夹角为0°至5°。
  3. 根据权利要求1所述的碳集流体，其中，所述碳集流体沿长度方向的拉伸强度为200MPa至500MPa。
  4. 根据权利要求1所述的碳集流体，其中，所述碳集流体沿长度方向的电阻为3mΩ至30mΩ。
  5. 根据权利要求1所述的碳集流体，其中，所述导电纤维为片状，所述导电纤维的宽度为0.01mm至5mm，所述导电纤维的厚度为0.5μm至20μm。
  6. 根据权利要求1所述的碳集流体，其中，所述导电纤维满足以下特征中的至少一者：
    相邻的所述导电纤维沿所述碳集流体宽度方向的间距为0.1mm至9mm；
    所述导电纤维的电导率为30×10 6S/m至60×10 6S/m；
    所述导电纤维的强度为220MPa至1400MPa。
  7. 根据权利要求1所述的碳集流体，其中，所述导电纤维在所述碳材料膜上的投影面积占所述碳材料膜的总面积的比例为10％至90％。
  8. 根据权利要求1所述的碳集流体，其中，所述导电纤维为金属纤维，所述金属纤维的材质包括铜、铝或镍中的至少一种。
  9. 根据权利要求1所述的碳集流体，其中，所述碳集流体的厚度为2μm至10μm。
  10. 一种如所述权利要求1-9中任一项所述的碳集流体的制备方法，包括以下步骤：
    (1)将导电纤维平铺在基体表面，得到负载导电纤维的基体；
    (2)将聚合物溶液涂覆至所述负载导电纤维的基体上，干燥后得到聚合物和导电纤维复合的薄膜；
    (3)将所述聚合物和导电纤维复合的薄膜从基体表面脱离，进行碳化；
    (4)将所述碳化后的薄膜进行压制，得到所述碳集流体。
  11. 根据权利要求10所述的制备方法，其中，所述聚合物溶液中的聚合物包 括聚酰亚胺、聚丙烯腈、羧甲基纤维素或聚乙烯醇中的至少一种。
  12. 根据权利要求11所述的制备方法，其中，所述聚合物溶液还可以包括碳材料，所述碳材料包括乙炔黑、碳纳米管或石墨烯中的至少一种。
  13. 根据权利要求12所述的制备方法，其中，基于所述聚合物和所述碳材料的总质量，所述碳材料的质量百分含量为1％至80％。
  14. 一种电化学装置，包括权利要求1-9中任一项所述的碳集流体或权利要求10-13中任一项所述的制备方法制备的碳集流体。
  15. 一种电子装置，包括根据权利要求14所述的电化学装置。
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