CN114514642A - Carbon current collector and electrochemical device - Google Patents

Carbon current collector and electrochemical device Download PDF

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Publication number
CN114514642A
CN114514642A CN202180004955.2A CN202180004955A CN114514642A CN 114514642 A CN114514642 A CN 114514642A CN 202180004955 A CN202180004955 A CN 202180004955A CN 114514642 A CN114514642 A CN 114514642A
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current collector
carbon
carbon current
precursor
fabric
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CN202180004955.2A
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Chinese (zh)
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李志愿
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—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
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F11/00—Chemical after-treatment of artificial filaments or the like during manufacture
    • D01F11/04—Chemical after-treatment of artificial filaments or the like during manufacture of synthetic polymers
    • D01F11/06—Chemical after-treatment of artificial filaments or the like during manufacture of synthetic polymers of macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
    • D01F6/44—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds as major constituent with other polymers or low-molecular-weight compounds
    • D01F6/54—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds as major constituent with other polymers or low-molecular-weight compounds of polymers of unsaturated nitriles
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06C—FINISHING, DRESSING, TENTERING OR STRETCHING TEXTILE FABRICS
    • D06C7/00—Heating or cooling textile fabrics
    • D06C7/04—Carbonising or oxidising
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/70—Carriers or collectors characterised by shape or form
    • H01M4/80—Porous plates, e.g. sintered carriers
    • H01M4/806—Nonwoven fibrous fabric containing only fibres
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

The present application relates to a carbon current collector, an electrochemical device, and an electronic device. The carbon current collector comprises carbon fibers, wherein the carbon fibers are of a hollow tubular structure, a pipe wall of the hollow fiber tubular structure is provided with a through hole, and the through hole penetrates through the pipe wall along the direction from the inner diameter to the outer diameter of the pipe wall. The carbon current collector has high liquid retention capacity, and battery multiplying power and low-temperature performance are improved.

Description

Carbon current collector and electrochemical device
Technical Field
The application relates to the field of energy storage, in particular to a carbon current collector and an electrochemical device.
Background
In recent years, portable electronic products such as smart phones, notebook computers, tablet computers and the like are continuously updated, and more electronic devices such as curved surface display screens, smart clothes, electronic skins, implantable medical devices and the like are developing towards being light, thin, flexible and wearable. At present, an electrochemical device for supplying power to electronic products comprises a battery, a super capacitor and the like, flexible bending is difficult to realize, and the requirement of future flexible electronic technology development is difficult to meet. Therefore, the development of flexible electronic technology must develop a new lithium ion battery that is light, thin and flexible. The main difficulty in developing flexible lithium ion batteries is how to obtain high-performance flexible light electrode plates.
The current collector of the current lithium ion battery mainly comprises copper foil and aluminum foil, which are the heaviest parts in the battery except for anode and cathode materials, and the metal material has poor flexibility and is not suitable for being used in a flexible electrode. The flexible matrix of the bendable flexible lithium ion battery mainly comprises 2 types: (1) non-conductive flexible substrates such as high molecular polymers, paper, woven cloth. (2) The conductive flexible substrate mainly adopts a carbon material film such as graphene or carbon nano tubes and the like as the flexible substrate, and active substances are attached to the structural units of the flexible substrate to form flexible electrodes. The flexible battery has obvious advantages in quality, and is the mainstream development direction of high energy density and light weight of the flexible battery.
In order to meet the characteristics of long standby time and short charging time of the flexible electronic device, the flexible energy storage device is required to have high energy density and power density. The electrochemical performance of the flexible lithium ion battery reported at present, particularly in the aspect of high power performance, still far reaches the level of the conventional lithium ion battery, and also far cannot meet the requirements of practical application. Therefore, the improvement of high power performance is a difficult point in the research field of the current flexible lithium ion battery, and as with the conventional lithium ion battery, the lower lithium ion mobility is an important reason for limiting the high power performance.
Disclosure of Invention
To the problem that prior art exists, this application provides a carbon mass flow body, and this carbon mass flow body not only light is flexible but also can promote battery rate performance. The present application also provides an electrochemical device and an electronic device including the carbon current collector.
In a first aspect, the present application provides a carbon current collector comprising carbon fibers, wherein the carbon fibers are of a hollow tubular structure, and a tube wall of the hollow tubular structure has through holes. According to the application, the through hole penetrates through the inner wall surface and the outer wall surface of the pipe wall.
According to some embodiments of the present application, the through-hole has a hole diameter of 0.02 μm to 0.05 μm.
According to some embodiments of the present application, the porosity of the carbon current collector is 5% to 60%.
According to some embodiments of the present application, the carbon current collector has at least one of the following characteristics a) to d): a) resistance of 3 to 100m omega, b) tensile strength of 300 to 1000MPa, c) elongation of 2 to 8%, d) resistance of more than 98% of initial resistance and tensile strength of more than 98% of initial tensile strength after baking at 120 ℃ for 15 min.
According to some embodiments of the present application, the carbon current collector has a thickness of 3 to 30 μm.
According to some embodiments of the application, the hollow tubular structure has an outer diameter of 0.1 μm to 5 μm, and/or the ratio of the inner diameter to the outer diameter of the hollow tubular structure is 10% to 80%.
According to some embodiments of the present application, the carbon current collector satisfies at least one of the following conditions: e) the strength of the carbon fiber is 100MPa to 1000 MPa; f) the elongation of the carbon fiber is 1% to 5%; g) the total porosity of the carbon fiber is 5% to 70%, wherein the porosity of the through hole is 4% to 60%, and the porosity of the hollow pipe is 1% to 66%; h) the carbon fiber has an electrolyte flux of 1 L.m-2·h-1To 50 L.m-2·h-1。
According to some embodiments of the present application, the surface of the carbon current collector is further provided with a metal layer. According to some embodiments of the present application, the carbon current collector satisfies at least one of the following conditions: the orthographic projection area of the metal layer on the surface of the carbon current collector is less than 70%; the thickness of the metal layer is <2 μm; the metal in the metal layer comprises at least one of copper, aluminum, gold, silver or nickel.
In a second aspect, the present application also provides a method for preparing a carbon current collector as described in the first aspect above, comprising the steps of: spinning a precursor into precursor fiber, wherein the precursor comprises a polymer and a pore-forming agent; stretching and shaping the precursor fiber, and removing the pore-forming agent; weaving the precursor fiber after removing the pore-forming agent into a precursor fabric; and carbonizing the precursor fabric.
According to some embodiments of the present application, the polymer is selected from one or more of polyacrylonitrile, polyimide, polybenzimidazole, polybenzoxazole, polybenzothiazole, and polyquinoxaline.
According to some embodiments of the present application, the precursor fabric comprises one or more of a unidirectional fabric, a bidirectional fabric, a multiaxial fabric.
According to some embodiments of the present application, the pore former is selected from at least one of polyvinyl alcohol (PVA) and polyethylene glycol (PEG).
According to some embodiments of the present application, carbonizing the precursor fabric includes calcining the precursor fabric at 1000-1500 ℃ at a heating rate of 1-10 ℃/min in a nitrogen atmosphere.
In a third aspect, the present application also provides an electrochemical device comprising the carbon current collector of the first aspect.
In a fourth aspect, the present application also provides an electronic device comprising the electrochemical device of the third aspect.
Drawings
Fig. 1 is a schematic illustration of a cross-section of a carbon current collector according to an embodiment of the present application.
Fig. 2 is a schematic view of a surface of a carbon current collector according to an embodiment of the present application.
Fig. 3 shows a schematic diagram of electrolyte migration in a carbon current collector according to an embodiment of the present application.
Fig. 4 is an electron micrograph of a current collector cross-section according to an embodiment of the present application.
Detailed Description
The present application is further described below in conjunction with the detailed description. It should be understood that these specific embodiments are merely illustrative of the present application and are not intended to limit the scope of the present application.
In a first aspect, the present application provides a carbon current collector comprising carbon fibers, wherein the carbon fibers are of a hollow tubular structure, and a tube wall of the hollow tubular structure has through holes that pass through along an inner diameter to an outer diameter direction of the tube wall.
According to an embodiment of the application, the hollow tubular structure comprises a hollow pipe and a pipe wall, the through hole being located in said pipe wall. As shown in fig. 1 and 2, wherein fig. 1 is a schematic cross-sectional view of a carbon current collector according to an embodiment of the present application, and fig. 2 is a schematic surface view of the carbon current collector.
Compared with the existing metal foil current collector, the carbon material can improve the flexibility and energy density of the electrode as the current collector, and the prepared pole piece is suitable for batteries for flexible electronic devices. To the relatively poor shortcoming of high power performance of current flexible lithium ion battery, the carbon fiber hollow structure of the mass flow body of this application makes the mass flow body have the liquid retention ability, and electrolyte gathers in hollow fiber's internal diameter, and the through-hole that the inside and outside wall link up makes electrolyte can migrate to the outside (as shown in fig. 3) from hollow pipeline rapidly on the pipe wall, promotes multiplying power and low temperature performance.
According to some embodiments of the present application, the through-hole has a hole diameter of 0.02 μm to 0.05 μm. Through holes with the aperture smaller than 0.02 μm are difficult to prepare, and when the aperture is larger than 0.05 μm, the influence on the mechanical properties of the fibers is large, which can cause the tensile strength of the current collector to be reduced. In some embodiments, the aperture of the via is 0.02 μm, 0.025 μm, 0.03 μm, 0.035 μm, 0.04 μm, or 0.05 μm.
According to some embodiments of the present application, the carbon fiber has an electrolyte flux of 1L · m-2·h-1To 50 L.m-2·h-1The electrolyte flux refers to the amount of electrolyte transported per hour per unit area of carbon fiber at a pressure of 1 bar. The electrolyte flux can represent the transportation capacity of the through holes on the pipe wall to the electrolyte, and represents the penetration degree of the through holes on the pipe wall to a certain extent. In some embodiments, the carbon fibers have an electrolyte flux of 2L · m-2·h-1、4L·m-2·h-1、8L·m-2·h-1、12L·m-2·h-1、15L·m-2·h-1、18L·m-2·h-1、、20L·m-2·h-1And so on.
According to some embodiments of the present application, the carbon fibers have a total porosity of 5 to 70%, wherein the porosity of the through-holes of the tube wall is 4 to 60%, and the porosity of the hollow tube is 1 to 66%. The higher the porosity of the hollow pipeline, the stronger the liquid retention capacity, and the higher the porosity of the through holes on the wall, the stronger the electrolyte transportation capacity.
According to some embodiments of the present application, the porosity of the carbon current collector is 5% to 60%. In some embodiments, the porosity of the carbon current collector is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or 55%. The increase of the porosity of the carbon current collector is beneficial to improving the liquid retention capacity, but the mechanical property is reduced when the porosity is too high.
According to some embodiments of the present application, the carbon current collector has a resistance of 3 to 100m Ω. According to some embodiments, the resistance of the carbon current collector is tested using a four-probe method. In some embodiments, the resistance of the carbon current collector is 5m Ω, 10m Ω, 15m Ω, 20m Ω, 30m Ω, 40m Ω, 50m Ω, 55m Ω, 60m Ω, 80m Ω, or 90m Ω.
According to some embodiments of the present application, the carbon current collector has a tensile strength of 300 to 1000MPa and an elongation of 2 to 8%.
According to some embodiments of the present application, after the carbon current collector is baked at 120 ℃ for 15min, the resistance is more than 98% of the initial resistance, and the tensile strength is more than 98% of the initial tensile strength.
According to some embodiments of the present application, the carbon current collector has a thickness of 3 to 30 μm. The thickness of the current collector is increased, the mechanical property is not affected, the electrolyte retaining amount is increased to a certain extent, and the performance is improved. However, an increase in the thickness of the current collector results in a loss of volumetric energy density, and therefore, it is preferable not to exceed 30 μm in combination. The thickness of the carbon current collector may be measured at 12 locations using a ten-thousandth ruler, and averaged.
According to some embodiments of the application, the hollow tubular structure has an outer diameter of 0.1 μm to 5 μm. The outer diameter is the diameter of the overall carbon fiber. The current collector is prepared in a woven structure, if the outer diameter of the carbon fiber is larger, the number of woven layers required by the current collector reaching the target thickness is less, and finally the thickness uniformity of the current collector is difficult to achieve; if the outer diameter of the fiber is smaller, the tortuosity of the internal pore structure is very high, which is not beneficial to lithium ion conduction, and the electronic conduction is influenced by a lot of contact among the fibers. In some embodiments, the outer diameter of the hollow tubular structure is 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 2.0 μm, 2.2 μm, 2.5 μm, 3.0 μm, or the like.
According to some embodiments of the application, the hollow tubular structure has a ratio of inner diameter to outer diameter (inner diameter/outer diameter) of 10% to 80%. The inner diameter is the diameter of the hollow tubular structure. The increase of the inner diameter/outer diameter of the carbon fiber of the current collector is beneficial to improving the liquid retention capacity, but if the inner diameter is too large, the mechanical property of the current collector is reduced, and the hollow through structure of the section of the current collector is difficult to maintain in the compaction process and the cold pressing process of the pole piece in the subsequent preparation. In some embodiments, the ratio of the inner diameter to the outer diameter of the hollow tubular structure is 10%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%, etc.
According to some embodiments of the present application, the carbon fiber has a strength of 100MPa to 1000MPa and an elongation of 1% to 5%.
According to some embodiments of the present application, the surface of the carbon current collector is further provided with a metal layer. The surface of the carbon current collector is provided with the metal coating, which is beneficial to improving the electronic conduction of the carbon current collector and can be used under the condition of low conductivity of the main material. In some embodiments, the metal in the metal layer includes at least one of copper, aluminum, gold, silver, or nickel, and the metal layer may be introduced by electroplating, deposition, or spraying. The metal layer has an orthographic area ratio of < 70% on the surface of the carbon current collector and a thickness of <2 μm in consideration of thickness influence and electrolyte retention.
In a second aspect, the present application also provides a method for preparing a carbon current collector as described in the first aspect above, comprising the steps of: spinning a precursor into precursor fiber, wherein the precursor comprises a polymer and a pore-forming agent; stretching and shaping the precursor fiber, and removing the pore-forming agent; weaving the precursor fiber after removing the pore-forming agent into a precursor fabric; and carbonizing the precursor fabric.
According to some embodiments of the present disclosure, the carbon current collector of the present disclosure is obtained after the precursor fabric is carbonized, washed, and compacted.
According to some embodiments of the present application, the hollow tubular structure of the carbon fiber is prepared by adjusting the shape of the spinning assembly, and the through hole of the tube wall is obtained by adding pore-forming agent to make the hole.
According to some embodiments of the present application, the polymer is selected from one or more of polyacrylonitrile, polyimide, polybenzimidazole, polybenzoxazole, polybenzothiazole, and polyquinoxaline. The polymer type has little influence on the performance, and common carbon fiber precursors are all suitable for the application.
According to some embodiments of the present application, the precursor fabric comprises one or more of a unidirectional fabric, a bidirectional fabric, a multiaxial fabric. According to some embodiments of the present application, the pore former is selected from at least one of PVA, PEG.
According to some embodiments of the present application, carbonizing the precursor fabric includes calcining the precursor fabric at 1000-1500 ℃ at a heating rate of 1-10 ℃/min in a nitrogen atmosphere.
The present application further provides an electrochemical device comprising the carbon current collector provided herein. The application provides a carbon current collector can regard as the mass flow body of positive pole piece and negative pole piece.
According to some embodiments, the positive electrode sheet comprises a carbon current collector as provided herein. According to some embodiments, the positive electrode sheet further comprises a positive active material disposed on the carbon current collector. The positive electrode active material of the present application is not particularly limited, and any positive electrode active material known in the art may be used, and for example, may include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, a lithium rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate.
According to some embodiments, the negative electrode sheet comprises a carbon current collector as provided herein. According to some embodiments, the negative electrode sheet further comprises a negative active material disposed on the carbon current collector. The negative electrode active material in the present application is not particularly limited, and any negative electrode active material known in the art may be used. For example, at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon carbon, lithium titanate, and the like may be included.
The electrochemical device of the present application, such as a lithium ion battery, further includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent.
In some embodiments herein, the lithium salt is selected from LiPF6、LiBF4、LiAsF6、LiClO4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiC(SO2CF3)3、LiSiF6One or more of LiBOB and lithium difluoroborate. For example, the lithium salt may be LiPF6Since it can give high ionic conductivity and improve cycle characteristics.
The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.
The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.
Examples of the above chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), and combinations thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.
Examples of the above carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.
Examples of the above ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.
Examples of such other organic solvents are dimethylsulfoxide, 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 may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.
For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.
At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.
The inorganic layer includes inorganic particles selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate, and a binder. The binder is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
The polymer layer comprises a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).
The present application further provides an electronic device comprising the electrochemical device described herein.
The electronic device or apparatus of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.
For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each separately disclosed point or individual value may itself, as a lower or upper limit, be combined with any other point or individual value or with other lower or upper limits to form ranges not explicitly recited.
In the description herein, "above" and "below" include the present numbers unless otherwise specified.
Unless otherwise indicated, terms used in the present application have well-known meanings that are commonly understood by those skilled in the art. Unless otherwise indicated, the numerical values of the parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, the test can be performed according to the methods given in the examples of the present application).
A list of items to which the term "at least one of," "at least one of," or other similar term is connected may imply any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item A may comprise a single component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.
Polymers used in examples and comparative examples
Polyacrylonitrile: a molecular weight of 15 ten thousand;
polyimide (I): a molecular weight of 40 ten thousand;
polybenzimidazole: molecular weight 50 ten thousand;
polybenzoxazole: the molecular weight is 50 ten thousand.
Second, testing method
Strength and elongation of single carbon fiber filament: reference standard GB/T14337-. And testing the single fiber by using an XQ-1 electronic single fiber strength tester, wherein the distance between the clamps is 10mm, testing 12 sample strips, averaging, and calculating the strength and the elongation rate of the sample when the sample is broken.
Inner diameter and outer diameter of carbon fiber: taking 12 hollow carbon fibers, cutting the hollow carbon fibers by using IB-09010CP to obtain a cross section, testing the inner diameter and the outer diameter of each hollow carbon fiber by using a SIGMA/X-max field emission scanning electron microscope, selecting 3 positions for each hollow carbon fiber, and taking the average value of all data.
Aperture of carbon fiber pipe wall through hole: and (3) taking 12 hollow carbon fibers, testing the pore diameter of the outer diameter surface of the fiber by using a SIGMA/X-max field emission scanning electron microscope, selecting 3 positions for each hollow carbon fiber, and taking the average value of all data.
Porosity of carbon fiber: and (3) determining the pore size distribution and porosity of the solid material by reference to the GB/T21650 mercury intrusion method and the gas adsorption method. Weighing 100 carbon fiber samples with the length of 20 mm; testing by using an Autopore V9620 mercury intrusion instrument, and placing a sample into a sample tube for sealing; the equipment is started, the sample tube is placed in the low-pressure bin for low-pressure mercury filling, after the low-pressure mercury filling is completed, the sample tube is placed in the high-pressure bin for high-pressure mercury filling, and after the high-pressure mercury filling is completed, mercury removing is performed. And (3) outputting a pore distribution curve, wherein the pore diameter of the pore distribution curve is larger than 50nm and is contributed by a large pore hollow pipeline of the carbon fiber, the pore diameter of the pore distribution curve is smaller than 50nm and is contributed by a small pore through hole of the carbon fiber pipe wall, the total volume of 100 carbon fibers is calculated to be V0, the volume of the large pore is calculated to be V1, the volume of the small pore is calculated to be V2, the porosity of the carbon fiber hollow pipeline is calculated to be V1/V0, and the porosity of the carbon fiber pipe wall through hole is calculated to be V2/V0.
Electrolyte flux of carbon fiber: reference is made to the standard HY/T049-. Placing 20 carbon fibers with the length of 20cm in a membrane module, fixing two sides of a hollow fiber to ensure that no bending and wrinkling phenomenon exists, connecting the membrane module with a liquid collection module to ensure that no leakage occurs in a closed state, and carrying out electrolyte (EC/DMC (1/1), lithium salt is 1mol/L LiPF (lithium ion plasma) on one side of the membrane module at the pressure of 1bar6) And the inner diameter surface of the membrane is passed through at a certain flow rate, and due to the pipe wall through hole structure of the carbon fiber, a part of electrolyte can penetrate into the liquid collection assembly from the through hole, and the rest of electrolyte is recycled. The collection amount of the electrolyte in 48h of the test is V, the total area of the inner diameters of the 20 hollow carbon fibers is A, and the flux calculation formula is V/(48 multiplied by A).
Average thickness of current collector: collecting a collection with a length of 40cm and a width of 20cmAnd (3) the fluid ensures that the current collector is smooth and has no wrinkles, and the thickness of 12 different positions in the size range is tested by using a Mitutoyo ten-thousandth micrometer, and the average value is taken.
Current collector resistor: and taking a current collector with the length of 40cm and the width of 20cm, ensuring that the current collector is smooth and free of wrinkles, testing 12 resistors at different positions in the size range by using a BER1300 resistor meter and selecting a four-probe method, and averaging.
Tensile strength and elongation of current collector: taking a current collector with the length of 40cm and the width of 20cm, ensuring that the current collector is smooth and free of wrinkles, the thickness of the current collector is d, cutting the current collector into sample strips with the width of 12mm and the length of 100mm along the length direction, using an Instron3365 universal testing machine, selecting a tensile fixture for testing, wherein the distance between the fixtures, namely the length of a testing section, is 50mm, the tensile rate is 10mm/min, the length of the sample when the sample is broken is L, the tensile force is F, the elongation rate is calculated to be (L-100)/100, the tensile strength is calculated to be F/(d 12), testing 12 sample strips, taking an average value, and calculating the tensile strength and the elongation rate when the sample is broken.
Fluid-collecting body pore structure: and (3) determining the pore size distribution and porosity of the solid material by reference to the GB/T21650 mercury intrusion method and the gas adsorption method. Taking 3 current collector samples with the width of 20mm and the length of 300mm, and weighing; testing by using an Autopore V9620 mercury porosimeter, rolling up a sample along the length direction, and placing the sample into a sample tube for sealing; the equipment is started, the sample tube is placed in the low-pressure bin for low-pressure mercury filling, after the low-pressure mercury filling is completed, the sample tube is placed in the high-pressure bin for high-pressure mercury filling, and after the high-pressure mercury filling is completed, mercury removing is performed. The sample volume was V0, the total pore volume was V1, and the porosity was V1/V0, taking the average of 3 samples.
Coverage of the metal coating layer (The orthographic area ratio of the metal coating on the surface of the carbon current collector): taking 12 current collector samples with the size of 10mm multiplied by 10mm, testing by using KEYENCE VHX5000 with the magnification of 500 times, calculating the coverage degree by an automatic area measurement mode, and taking the average value of 12 current collectors.
Thickness of metallic coating: taking 12 current collector samples with the size of 10mm multiplied by 10mm, cutting the current collectors by IB-09010CP to obtain sections, testing the thickness of the section metal coating of the 12 current collectors by using a SIGMA/X-max field emission scanning electron microscope,each slice was taken for 3 positions and averaged over all data.
1.5C charge capacity retention: at 25 ℃, the battery cell with the SOC of 0% is charged to 100% SOC at a constant current of 0.2C, charged to 0.05C at a constant voltage, charged to the capacity of C0, discharged to 0% SOC at a direct current of 0.5C, charged to 100% SOC at a constant current of 1.5C, charged to the capacity of C1, and charged to C1/C0.
2C discharge Capacity conservation Rate: at 25 ℃, the battery cell with SOC of 0% is charged to 100% SOC at a constant current of 0.2C, charged to 0.05V at a constant voltage, discharged to 0% SOC at a direct current of 0.2C, and discharged at a discharge capacity of D0, charged to 100% SOC at a constant current of 0.2C, charged to 0.05V at a constant voltage, discharged to 0% SOC at a direct current of 2C, and discharged at a discharge capacity of D1 and D1/D0.
Capacity retention rate of-20 ℃ C. _0.5C: charging the battery cell with SOC of 0% to 100% SOC at a constant current of 0.2C, charging to 0.05V at a constant voltage, discharging to 0% SOC at a direct current of 0.5C at 25 ℃, wherein the discharge capacity is D0; the battery cell with SOC of 0% is charged to 100% SOC at a constant current of 0.2C and charged to 0.05V at a constant voltage at 25 ℃, and is discharged to 0% SOC at a direct current of 0.5C at-20 ℃, and the discharge capacity is D1 and D1/D0.
Thirdly, preparing a carbon current collector:
dissolving a polymer in a solvent DMAc to prepare a polymer solution, adding an extracting agent (at least one of PVA and PEG) and uniformly mixing, wherein the solid content of the solution is 3-20%;
carrying out wet spinning on the polymer solution by using a hollow wet spinning assembly and a coagulating bath by using a saturated sodium sulfate solution to obtain hollow fibers (hollow through structures), and carrying out hot stretching and shaping on the hollow fibers by using fiber hot stretching equipment;
placing the hollow fiber in water at 85 ℃ to wash off the extractant, so that the wall of the hollow fiber is provided with through holes;
the hollow fiber is woven into a fabric, and the fabric structure can be one or more of a unidirectional fabric, a bidirectional fabric and a multiaxial fabric;
calcining the hollow fiber fabric for 3 hours in a nitrogen protective atmosphere at the temperature of 1000-1500 ℃ and at the temperature rise rate of 1-10 ℃/min for carbonization to prepare the hollow fiber fabric, and cleaning the fabric by using acetone;
and rolling the hollow carbon fiber fabric to a target thickness, and cutting the hollow carbon fiber fabric into a target width to obtain the hollow carbon fiber current collector.
Example 1
1. Preparing a carbon current collector:
dissolving polyacrylonitrile in a solvent DMAc to prepare a polymer solution, adding PVA (with the polymerization degree of 400-500 and the alcoholysis degree of 88%) and uniformly mixing, wherein the solid content of the solution is 10%, and the mass ratio of the polymer to the extracting agent is 1: 3. and (3) carrying out wet spinning on the polymer solution by using a hollow wet spinning assembly and a coagulating bath by using a saturated sodium sulfate solution to obtain a hollow fiber (hollow through structure), and carrying out hot drawing and shaping on the hollow fiber by using fiber hot drawing equipment. The hollow fiber is put into water with the temperature of 85 ℃ to wash away PVA, so that the wall of the hollow fiber is provided with through holes. The hollow fibers are woven into a fabric, the fabric structure being a bidirectional fabric. And calcining the hollow fiber fabric for 3 hours at 1100 ℃ and at the heating rate of 5 ℃/min in a protective atmosphere to carbonize, thus preparing the hollow carbon fiber fabric. Cleaning the fabric by using acetone; and rolling the hollow carbon fiber fabric to a target thickness to obtain the carbon current collector.
Carbon current collector prepared in this example: the carbon fiber has an outer diameter of 0.2 μm and an inner diameter/outer diameter of 40%, the carbon fiber tube wall has through holes with a hole diameter of 0.04 μm, a porosity of 40%, and a current collector thickness of 5 μm, and other parameters are shown in table 1.
2. Preparing a positive pole piece:
mixing the positive electrode active material lithium cobaltate, acetylene black and polyvinylidene fluoride (PVDF) according to a mass ratio of 94: 3: 3, adding N-methyl pyrrolidone (NMP) as a solvent to prepare slurry with the solid content of 75%, and uniformly stirring. And uniformly coating the slurry on the carbon current collector, drying at 90 ℃, cold-pressing to obtain a positive pole piece with the thickness of a positive active material layer of 100 mu m, and repeating the steps on the other surface of the positive pole piece to obtain the positive pole piece with the positive active material layer coated on the two surfaces. Cutting the positive pole piece into the specification of 74mm multiplied by 867mm, and welding the pole lugs for later use.
3. Preparation of negative pole piece
Preparing a negative electrode active material of artificial graphite, acetylene black, styrene butadiene rubber and sodium carboxymethyl cellulose according to a mass ratio of 96: 1: 1.5: 1.5, adding deionized water as a solvent to prepare slurry with the solid content of 70%, and uniformly stirring. And uniformly coating the slurry on the carbon current collector, drying at 110 ℃, cold-pressing to obtain a negative pole piece with a negative active material layer of which the thickness is 150 mu m and the single surface is coated with the negative active material layer, and repeating the coating steps on the other surface of the negative pole piece to obtain the negative pole piece with the double surfaces coated with the negative active material layer. Cutting the negative pole piece into a size of 74mm multiplied by 867mm, and welding a pole lug for later use.
4. Preparation of the electrolyte
Under the environment that the water content is less than 10ppm, non-aqueous organic solvents such as Ethylene Carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Propyl Propionate (PP) and Vinylene Carbonate (VC) are mixed according to the mass ratio of 20: 30: 20: 28: 2 mixing and then adding lithium hexafluorophosphate (LiPF) to the non-aqueous organic solvent6) Dissolving and mixing uniformly to obtain electrolyte, wherein the LiPF is6The mass ratio of the organic solvent to the non-aqueous organic solvent is 8: 92.
5. preparation of lithium ion battery
And (3) sequentially stacking the prepared positive pole piece, the prepared isolating membrane and the prepared negative pole piece, contacting one surface of the isolating membrane with the first coating with the positive pole piece, contacting one surface of the isolating membrane with the second coating with the negative pole piece, and winding to obtain the electrode assembly. And (3) putting the electrode assembly into an aluminum-plastic film packaging bag, dehydrating at 80 ℃, injecting the prepared electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.
Comparative example 1
The difference from example 1 is only in the current collector, wherein the copper foil is used as the negative electrode current collector and the aluminum foil is used as the positive electrode current collector.
Comparative example 2
The difference from example 1 is only that the current collector is different, and carbon nanotubes and polyethylene (the mass ratio of the carbon nanotubes to the polyethylene is 30/70) are cast into a conductive composite film by melt extrusion. The conductive composite film is thermally stretched to a thickness of 5 μm without a porous structure.
Comparative example 3
The only difference from comparative example 2 was that the anode active material was replaced with silicon oxide.
Comparative example 4
The difference from example 1 is that the carbon fiber has no through hole in the tube wall, and is only the carbon fiber with a hollow tubular structure, other parameters are not changed, and the comparative example can be prepared without adding an extracting agent.
Comparative example 5
The difference from example 1 is that the carbon fiber tube wall had a pore structure, but had no pores penetrating the inner and outer walls, and had a thickness of 5 μm. The preparation method refers to the prior proposal CN 106898778B.
TABLE 1
Figure BDA0003505514950000121
Figure BDA0003505514950000131
Examples 2 to 15
Referring to example 1, the difference from example 1 is that the outer diameter of the carbon fiber, the inner/outer diameter of the carbon fiber, the hole diameter of the through hole in the wall of the carbon fiber, and the carbon fiber precursor material are adjusted, specifically, see tables 2-1 and 2-2.
Examples 16 to 24
Examples 16-22 referring to example 3, the difference from example 3 is that the carbon fiber fabric structure, the current collector thickness or the metal coating on the surface of the current collector is adjusted. Specifically, example 23 is different from example 3 in that the negative electrode active material was replaced with silica from graphite, and example 24 is different from example 22 in that the negative electrode active material was replaced with silica from graphite, the current collector porosities were all 40%, the carbon fiber filament elongations were all 2.2%, and the carbon fiber filament strengths were all 350MPa, in example 3. See table 3 for details.
TABLE 2-1
Figure BDA0003505514950000132
Figure BDA0003505514950000141
Tables 2 to 2
Figure BDA0003505514950000142
TABLE 3
Figure BDA0003505514950000151
As can be seen from table 1, compared with the existing metal foil current collector, the carbon current collector provided by the application can improve the flexibility and energy density of the electrode, and the introduced porous structure can enable the current collector to have the liquid retention capacity, so that the multiplying power and the low-temperature performance are improved; in addition, through holes with through inner diameters and outer diameters on the wall of the current collector tube enable electrolyte to rapidly migrate to the outside from the inside of the hollow fiber, and therefore compared with comparative examples 4 and 5, the performance of the current collector tube is improved.
According to examples 1 to 5 of table 2, as the outer diameter of the carbon fiber increases (0.2 μm to 2 μm, since the number of fiber layers required for the current collector to reach the target thickness decreases, the contact resistance between fibers decreases, so that the resistance decreases to some extent, and since the porosity is uniform, the lithium ion migration path decreases, the tortuosity decreases and increases, and the performance improves to some extent.
Examples 6-9 changed the carbon fiber inner/outer diameter compared to example 3. According to table 2, as the inner diameter/outer diameter of the carbon fiber of the current collector is increased, the porosity of the current collector is increased, which is beneficial to improving the liquid retention capacity and improving the performance to a certain extent. However, since an excessively large inner/outer diameter causes a certain reduction in mechanical properties, it is preferable that the inner/outer diameter is 40% to 60%, in view of the above.
Examples 10-12 changed the pore size of the through-holes in the fiber wall compared to example 3. It can be seen from table 2 that the increase in the pore diameter of the through-holes in the fiber wall has little effect on the performance while ensuring consistent porosity. The size of the through hole is mainly influenced by pore-forming agent, the preparation of the hole with the aperture smaller than 0.02 μm is difficult, and when the aperture is larger than 0.05 μm, the mechanical property of the fiber is greatly influenced, so that the strength of the current collector is reduced.
Examples 13-15 changed the polymer species compared to example 3. As can be seen from table 2, the polymer species have little influence on the properties, and therefore, the commonly used carbon material precursor polymers are all suitable for the present application.
Examples 16-18 changed the braid structure compared to example 3. It can be seen from table 3 that, compared with bidirectional and multiaxial, the carbon fiber contact resistance of the unidirectional fabric structure is slightly larger, the mechanical property of the current collector is slightly poor, but the influence degree on the performance is limited, so that the common braided fabric structure is suitable for the application.
Examples 19-21 varied the current collector thickness compared to example 3. As can be seen from Table 3, the thickness of the current collector is increased, the mechanical properties are not affected, the retention amount of the electrolyte is increased to a certain extent, and the properties are slightly improved.
By comparing example 3 with example 22 and example 23 with example 24, the electron conduction of the carbon current collector can be increased by adding the metal coating on the surface of the carbon current collector, but for the anode with the graphite as the main material, the electron conduction of the graphite is better, and the influence is smaller; for the anode with the main material of silicon material, the introduction of the metal coating on the surface of the current collector is beneficial to improving the performance due to poor electronic conduction of the silicon material.

Claims (15)

1. A carbon current collector comprises carbon fibers, wherein the carbon fibers are of a hollow tubular structure, a tube wall of the hollow tubular structure is provided with through holes, and the through holes penetrate through the inner wall surface and the outer wall surface of the tube wall.
2. The carbon current collector of claim 1, wherein the pore size of the through-holes is 0.02 to 0.05 μ ι η.
3. The carbon current collector of claim 1, wherein the porosity of the carbon current collector is from 5% to 60%.
4. The carbon current collector of claim 1, wherein the carbon current collector has at least one of the following characteristics a) to d):
a) the resistance is 3m omega to 100m omega,
b) the tensile strength is 300MPa to 1000MPa,
c) the elongation is 2 to 8 percent,
d) after baking for 15min at 120 ℃, the resistance is more than 98 percent of the initial resistance, and the tensile strength is more than 98 percent of the initial tensile strength.
5. The carbon current collector of claim 1, wherein the thickness of the carbon current collector is 3 μ ι η to 30 μ ι η.
6. The carbon current collector of claim 1, wherein the hollow tubular structure has an outer diameter of 0.1 to 5 μ ι η, and/or a ratio of inner diameter to outer diameter of 10 to 80%.
7. The carbon current collector of claim 1, wherein at least one of the following conditions e) to h) is satisfied:
e) the strength of the carbon fiber is 100MPa to 1000 MPa;
f) the elongation of the carbon fiber is 1% to 5%;
g) the total porosity of the carbon fiber is 5-70%, wherein the porosity of the through hole of the pipe wall is 4-60%, and the porosity of the hollow pipeline is 1-66%;
h) the carbon fiber has an electrolyte flux of 1 L.m-2·h-1To 50 L.m-2·h-1。
8. The carbon current collector of claim 1, wherein the surface of the carbon current collector is further provided with a metal layer.
9. The carbon current collector of claim 8, wherein at least one of the following conditions is met:
the metal layer has an orthographic area ratio of < 70% on the surface of the carbon current collector;
the thickness of the metal layer is <2 μm;
the metal in the metal layer comprises at least one of copper, aluminum, gold, silver or nickel.
10. A method of preparing a carbon current collector as claimed in any one of claims 1 to 9, comprising the steps of:
spinning a precursor into precursor fiber, wherein the precursor comprises a polymer and a pore-forming agent;
stretching and shaping the precursor fiber, and removing the pore-forming agent;
weaving the precursor fiber after removing the pore-forming agent into a precursor fabric;
and carbonizing the precursor fabric.
11. The preparation method according to claim 10, wherein the polymer is selected from one or more of polyacrylonitrile, polyimide, polybenzimidazole, polybenzoxazole, polybenzothiazole, and polyquinoxaline.
12. The preparation method of claim 10, wherein the precursor fabric comprises one or more of a unidirectional fabric, a bidirectional fabric and a multiaxial fabric, and the pore-forming agent is selected from at least one of polyvinyl alcohol (PVA) and polyethylene glycol (PEG).
13. The method as claimed in claim 10, wherein carbonizing the precursor fabric includes calcining the precursor fabric in a nitrogen atmosphere at a temperature rise rate of 1 ℃/min to 10 ℃/min at 1500 ℃.
14. An electrochemical device comprising the carbon current collector of any one of claims 1-9.
15. An electronic device comprising the electrochemical device of claim 14.
CN202180004955.2A 2021-03-30 2021-03-30 Carbon current collector and electrochemical device Pending CN114514642A (en)

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