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CN113498558B - Electrochemical device and electronic device - Google Patents

Electrochemical device and electronic device Download PDF

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Publication number
CN113498558B
CN113498558B CN202080016363.8A CN202080016363A CN113498558B CN 113498558 B CN113498558 B CN 113498558B CN 202080016363 A CN202080016363 A CN 202080016363A CN 113498558 B CN113498558 B CN 113498558B
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Prior art keywords
material layer
binder
electrochemical device
positive electrode
current collector
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CN202080016363.8A
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CN113498558A (en
Inventor
刘晓欠
刘胜奇
韩冬冬
王可飞
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Dongguan Amperex Technology Ltd
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Dongguan 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The present application provides an electrochemical device and an electronic device, comprising a positive electrode including a current collector, a first material layer and a second material layer, wherein the second material layer is arranged on at least one surface of the current collector, the first material layer is arranged between the current collector and the second material layer, the second material layer comprises a second active material, a second conductive agent and a second binder, and the specific surface area of the second active material is 0.05m 2 /g to 20m 2 /g; the first material layer comprises a first active material, a first conductive agent, and a first binder comprising a polymer polymerized from at least one monomer of an acrylate or an acrylamide. Through the design, the content of the second binder in the second material layer of the positive electrode is reduced, the relative content ratio of the second active material is increased, and the positive electrode is applied to the electrochemical device, so that the energy density of the electrochemical device can be effectively improved.

Description

Electrochemical device and electronic device
Technical Field
The present application relates to the field of electrochemistry, and in particular, to an electrochemical device and an electronic device.
Background
The lithium ion battery has the advantages of high energy storage density, high open circuit voltage, low self-discharge rate, long cycle life, good safety performance and the like, and is widely applied to various fields of electric energy storage, mobile electronic equipment, electric automobiles, aerospace equipment and the like. As mobile electronic devices and electric vehicles enter a high-speed development stage, the market has raised higher and higher requirements on energy density, safety, service life and the like of lithium ion batteries.
Lithium ion batteries generally include a positive electrode, a negative electrode, and a separator positioned between the positive and negative electrodes. The positive electrode contains an active material layer, and the existing active material layer often influences the feasibility of the positive electrode process and the performance (such as capacity, power, cycle and the like) of the lithium ion battery due to the selection of the type and the increase of the content of the binder.
Disclosure of Invention
The present application is directed to an electrochemical device and an electronic device to increase the energy density of the electrochemical device.
In the following, the present application will be explained with reference to a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.
The specific technical scheme is as follows:
the first aspect of the present application provides an electrochemical device comprising a positive electrode including a current collector, a first material layer and a second material layer, the second material layer being disposed on at least one surface of the current collector, the first material layer being disposed between the current collector and the second material layer, the second material layer comprising a second active material, a second conductive agent and a second binder, the second active material having a specific surface area of 0.05m 2 /g to 20m 2 /g; the first material layer comprises a first active material, a first conductive agent and a first binder, wherein the first binder comprises a polymer formed by polymerizing at least one monomer of acrylate or acrylamide.
In one embodiment of the present application, a first material layer and a second material layer are provided on at least one surface of the above-mentioned current collector, the first material layer being provided between the current collector and the second material layer. The "surface" herein may be the entire area of the current collector surface or may be a partial area of the current collector surface, and the present application is not particularly limited as long as the object of the present application can be achieved.
In some embodiments of the present application, the first material layer and the second material layer are sequentially disposed on one surface of the current collector. In some embodiments of the application, the first material layer and the second material layer are sequentially disposed on both surfaces of the current collector.
In the present application, the specific surface area of the second active material is 0.05m 2 /g to 20m 2 And/g. Without being limited to any theory, the specific surface area of the second active material is too small, e.g., less than 0.05m 2 And/g, the second active material cannot be fully contacted with the electrolyte, so that more oxide active sites cannot be provided, and the dynamics of the lithium ion battery can be influenced; the specific surface area of the second active material is too large, e.g. greater than 20m 2 And/g, the slurry is not easy to disperse uniformly, excessive active sites can be caused, side reactions are increased to deteriorate the stability of the battery cell, a larger proportion of the second binder is required to be consumed, the bonding force between the second material layer and the first material layer is easily reduced, and the internal resistance growth rate is increased.
In the present application, the first binder comprises a polymer polymerized from at least one monomer of an acrylate or an acrylamide. The polymer is soaked in electrolyte for 24 hours at 85 ℃ or soaked for 7 days at 25 ℃, the swelling rate is less than 5%, and the first material layer and the current collector or the first material layer and the second material layer can have good binding force.
In the present application, "swelling" means a phenomenon in which the above polymer expands in volume in an electrolyte. Swelling ratio= (post-soak volume-pre-soak volume)/pre-soak volume×100%.
In summary, the use of the first binder in the first material layer improves the adhesion of the first material layer, increases the adhesion between the first material layer and the second material layer, and reduces the amount of the second binder in the second material layer. At the same time, the specific surface area of the second active material is controlled within the scope of the present application, and the content of the second binder is also reduced. The reduction of the content of the second binder in the second material layer increases the relative content ratio of the second active material in the second active material layer, thereby effectively improving the energy density of the lithium ion battery.
In one embodiment of the present application, the first binder is present in the first material layer in an amount a of 1wt% to 20wt%. Without being limited to any theory, when the first binder content is too low, for example, less than 1wt%, the first positive electrode active layer has poor film forming properties, which is disadvantageous for improvement of coverage; when the first binder content is too high, for example, higher than 20wt%, the first material layer is shrunk to an increased extent during the drying and film forming process due to the high binding power of the first binder itself, and the current collector substrate (for example, aluminum foil) is not substantially shrunk, the difference in shrinkage rates between the two is large, resulting in the first material layer falling off from the current collector substrate in a large area. By controlling the content of the first binder within the above-described content range, it is advantageous to improve the adhesion between the current collector and the first material layer.
In one embodiment of the application, the polymer in the first binder further comprises an acrylonitrile monomer.
In one embodiment of the application, the acrylonitrile is present in an amount of 30 to 70% by mass, based on the total mass of the polymer, and the sum of the mass percentages of acrylate and acrylamide is present in an amount of 30 to 70%. Preferably, the acrylonitrile is present in an amount of 40 to 60% by mass, based on the total mass of the polymer, and the sum of the mass percentages of acrylate and acrylamide is present in an amount of 40 to 60%. By controlling acrylonitrile, acrylic acid salt and acrylamide within the above-mentioned ranges of the total mass of the polymer, the first adhesive can be made to have a better adhesion in use.
In the present application, the weight average molecular weight of the first binder is not particularly limited as long as the object of the present application can be achieved, and for example, the weight average molecular weight of the first binder is 100000 to 2000000. Without being limited by any theory, the weight average molecular weight of the first binder is too large, the thickening effect of the first binder is enhanced, the slurry viscosity is too high, the fluidity is poor, and the slurry of the first positive electrode active layer is liable to be leaked and coated; too small a weight average molecular weight of the first binder results in too low a paste viscosity and poor paste film forming properties, and also results in paste overcoating of the insulating layer. By controlling the weight average molecular weight of the first binder within the above range, the slurry of the first material layer can be formed into a thin film having a uniform thickness on the surface of the current collector substrate, thereby forming the first material layer, and the adhesion between the first material layer and the current collector can be improved.
In one embodiment of the present application, the second binder comprises at least one of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene-hexafluoropropylene, sodium polyacrylate, nitrile rubber, or polyacrylate. Preferably, the second binder comprises at least one of polyacrylic acid, polyvinylidene fluoride or nitrile rubber.
In the present application, the weight average molecular weight of the second binder is not particularly limited as long as the object of the present application can be achieved, and for example, the weight average molecular weight of the second binder is 100000 to 2000000.
In one embodiment of the present application, the content B of the second binder in the second material layer is 0.5wt% to 10wt%. Without being limited by any theory, when the content of the second binder is too low, for example, less than 0.5wt%, the adhesion of the second material layer is too low, the film is easy to be removed, the film forming property of the second material layer is poor, which is unfavorable for the coverage improvement; when the content of the second binder is too high, for example, higher than 10wt%, the second material layer is easily dropped from the first material layer in a large area due to the difference between the shrinkage degree of the second material layer and the shrinkage degree of the first material layer in the drying film forming process, so that the energy density of the battery core is reduced, and meanwhile, the ion diffusion resistance in the positive electrode is increased due to the too high content of the second binder, so that the power performance of the lithium ion battery is deteriorated. By controlling the content of the second binder within the above-described content range, it is advantageous to improve the adhesion between the first material layer and the second material layer.
In one embodiment of the present application, the adhesion between the first material layer and the second material layer is 5N/m or more, indicating excellent adhesion between the first material layer and the second material layer.
In one embodiment of the application, the second binder is present inThe content B in the second material layer is 0.5wt% to 3.99wt%; the content A of the first binder in the first material layer and the content B of the second binder in the second material layer satisfy the following conditions: b=n 1 ×A+n 2 And n is more than or equal to-0.4 1 ≤-0.01、0.8％≤n 2 Less than or equal to 4 percent. When the content of the first binder and the content of the second binder satisfy the above relationship, the increase of the content of the first binder in the first material layer can reduce the amount of the second binder in the second material layer, so that the relative content of the second active material in the second material layer is increased, thereby increasing the energy density of the lithium ion battery.
In one embodiment of the application, the monolayer thickness of the first material layer is 0.01 μm to 20 μm, and when the thickness of the first material layer is too low, for example, below 0.01 μm, the first material layer is too thin, and the safety performance is affected; when the thickness of the first material layer is too high, for example, higher than 20 μm, the relative content of the first active material in the positive electrode decreases, affecting the energy density of the lithium ion battery.
In one embodiment of the application, the second material layer has a monolayer thickness of 20 μm to 300 μm, and when the thickness of the second material layer is too low, for example below 20 μm, the energy density of the lithium ion battery is affected and the processing is not easy under the condition of certain capacity; when the thickness of the second material layer is too high, for example, above 300 μm, lithium ion battery kinetics are deteriorated.
In one embodiment of the present application, the resistance of the positive electrode after full charge of the electrochemical device is 10Ω or more, preferably 30Ω to 100deg.OMEGA. The positive electrode resistance is controlled within the range, so that the internal resistance of the lithium ion battery during short circuit can be increased, the short circuit current is reduced, the temperature rise is reduced, and the safety of the lithium ion battery is improved.
In one embodiment of the present application, the first conductive agent and the second conductive agent each independently comprise at least one of lamellar, network, linear, or zero-dimensional conductive agents. Preferably, the first conductive agent and the second conductive agent each independently comprise at least one of graphene, reticulated graphite fibers, carbon nanotubes, ketjen black, graphite fibers, or nanoparticulate conductive carbon. By adding the first conductive agent in the first material layer and the second conductive agent in the second material layer, the migration rate of lithium ions in the first active material and the second active material can be effectively improved, and therefore the charge and discharge efficiency of the lithium ion battery is improved.
The preparation method of the first binder of the present application is not particularly limited, and a preparation method known to those skilled in the art may be employed, for example, the following preparation method may be employed:
Adding distilled water into a reaction kettle, starting stirring, introducing nitrogen to remove oxygen, adding at least one of the components such as acrylonitrile, acrylate and acrylamide according to different mass ratios, heating to about 65 ℃ under inert atmosphere and keeping the temperature, then adding an initiator to initiate reaction, and ending the reaction after about 20 hours.
The initiator is not particularly limited as long as it can initiate polymerization of the monomer, and may be, for example, a 20% ammonium persulfate solution. The present application is not particularly limited in the addition amount of distilled water and an initiator, as long as the added monomer is ensured to undergo polymerization. After the reaction, alkali liquor is added to the precipitate of the reaction for neutralization to a pH of 6.5 to 9. Then, the reaction product is subjected to filtration, washing, drying, crushing, sieving and the like.
The method for preparing the second binder of the present application is not particularly limited, and a method known to those skilled in the art may be used, for example, the following method may be used:
and vacuumizing a reaction kettle containing a stirrer, pumping nitrogen to replace oxygen, adding deionized water, vinylidene fluoride, an initiator, an emulsifier and a chain transfer agent into the reaction kettle, and performing polymerization reaction to obtain the second binder.
Among them, the initiator is not particularly limited, and may be selected from, for example, diisopropylbenzene hydroperoxide; the emulsifier is not particularly limited and may be selected from, for example, perfluoroalkyl carboxylates; the chain transfer agent is not particularly limited and may be selected from, for example, isopropyl alcohol. So long as the object of the present application is achieved.
In the positive electrode of the present application, the current collector is not particularly limited, and may be a current collector known in the art, such as an aluminum foil, an aluminum alloy foil, or a composite current collector. The first material layer includes a first active material, the second material layer includes a second active material, and in the present application, the first active material and the second active material are not particularly limited, and active materials well known in the art may be used, for example, the first active material may include at least one of lithium iron phosphate, lithium iron manganese phosphate, or lithium manganate, and the second active material may include at least one of lithium cobalt oxide, lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium iron manganese phosphate, or lithium manganate. In the present application, the thickness of the current collector is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the current collector is 8 μm to 12 μm.
In the positive electrode of the present application, the surface of the current collector is provided with the first material layer and the second material layer, and the first material layer and the second material layer generally do not entirely coat the surface of the current collector. The insulating layer may be provided in a region where the first material layer and the second material layer are not provided on the surface of the current collector according to actual needs by those skilled in the art, and is not particularly limited in the present application as long as the object of the present application can be achieved.
The negative electrode of the present application is not particularly limited as long as the object of the present application can be achieved. For example, the negative electrode typically includes a current collector and a material layer. In the negative electrode of the present application, the current collector is not particularly limited, and a current collector known in the art, such as a copper foil, a copper alloy foil, a composite current collector, and the like, may be used. The material layer is not particularly limited, and active materials known in the art may be used. For example, at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon carbon, silicon oxygen compounds, soft carbon, hard carbon, lithium titanate, niobium titanate, or the like may be included. In the negative electrode of the present application, the thicknesses of the current collector and the material layer are not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the current collector is 4 μm to 10 μm and the thickness of the material layer is 30 μm to 120 μm.
Optionally, the negative electrode may further comprise a conductive layer between the conductive layer current collector and the material layer. The composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.
The above-mentioned conductive agent is not particularly limited as long as the object of the present application can be achieved. For example, the conductive agent may include at least one of conductive carbon black (Super P), carbon Nanotubes (CNTs), carbon fibers, graphene, or the like. The binder is not particularly limited, and binders known in the art may be used as long as the object of the present application can be achieved. For example, the binder may include at least one of styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC-Na), or the like. For example, styrene Butadiene Rubber (SBR) may be used as the binder.
The lithium ion battery also comprises a separation membrane for separating the positive electrode from the negative electrode, preventing the internal short circuit of the lithium ion battery, allowing electrolyte ions to pass freely, and completing the electrochemical charge and discharge process. In the present application, the separator is not particularly limited as long as the object of the present application can be achieved.
For example, a Polyolefin (PO) based separator mainly composed of Polyethylene (PE) and polypropylene (PP), a polyester film (for example, a polyethylene terephthalate (PET) film), a cellulose film, a polyimide film (PI), a polyamide film (PA), a spandex or aramid film, a woven film, a nonwoven film (nonwoven fabric), a microporous film, a composite film, a separator paper, a laminate film, a spun film, or the like.
For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and the like. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic material.
For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, and may be 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, barium sulfate, and the like, for example. The binder is not particularly limited and may be, for example, one or a combination of several selected from polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylic polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene) and the like.
The lithium ion battery of the present application further comprises an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution, which includes a lithium salt and a nonaqueous solvent.
In some embodiments of the application, 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 、LiC(SO 2 CF 3 ) 3 、LiSiF 6 One or more of LiBOB and lithium difluoroborate. For example, the lithium salt may be LiPF 6 Since it can give high ionic conductivity and improve cycle characteristics.
The nonaqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.
The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
Examples of such chain carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), vinyl Ethylene Carbonate (VEC) and combinations thereof. Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1, 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, trifluoromethyl ethylene 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, gamma-butyrolactone, decalactone, valerolactone, mevalonic acid lactone, 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 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 phosphoric acid esters and combinations thereof.
A second aspect of the application provides an electronic device comprising the electrochemical device provided in the first aspect of the application.
The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-compact disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable audio recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large-sized battery, a lithium ion capacitor, and the like.
The process for preparing the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, the electrochemical device may be manufactured by: the positive electrode and the negative electrode are overlapped via a separator, wound, folded, and the like as needed, and then placed in a case, and an electrolyte is injected into the case and sealed. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the case as needed, thereby preventing the pressure inside the electrochemical device from rising and overcharging and discharging.
The present application provides an electrochemical device and an electronic device, comprising a positive electrode including a current collector, a first material layer and a second material layer, wherein the second material layer is disposed on at least one surface of the current collector, the first material layer is disposed between the current collector and the second material layer, the second material layer comprises a second active material, a second conductive agent and a second binder, and the specific surface area of the second active material is 0.05m 2 /g to 20m 2 /g; the first material layer comprises a first active material, a first conductive agent and a first binder, wherein the first binder comprises a polymer formed by polymerizing at least one monomer of acrylate or acrylamide. Through the design, the binding force of the first material layer to the second material layer in the positive electrode is obviously increased, the content of the second binder in the second material layer of the positive electrode is reduced, the relative content ratio of the second active material is increased, and the positive electrode is applied to an electrochemical device, so that the energy density of the electrochemical device can be effectively improved.
Drawings
In order to more clearly illustrate the technical solutions of the present application and the prior art, the following description briefly describes embodiments and drawings that are required to be used in the prior art, and it is apparent that the drawings in the following description are only some embodiments of the present application.
FIG. 1 is a schematic view of a positive electrode structure according to an embodiment of the present application;
FIG. 2 is a schematic view of a positive electrode structure according to another embodiment of the present application;
fig. 3 is a relationship between adhesion and travel in an adhesion test.
Reference numerals: 10. current collector 21. First material layer 22. Second material layer.
Detailed Description
The present application will be described in further detail below with reference to the drawings and examples in order to make the objects, technical solutions, and advantages of the present application more apparent. It will be apparent that the described embodiments are only some, but not all, embodiments of the application. All other technical solutions obtained by a person skilled in the art based on the embodiments of the present application fall within the scope of protection of the present application.
In the specific embodiment of the present application, the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.
Fig. 1 shows a schematic view of a positive electrode structure according to an embodiment of the present application, in which a first surface and a second surface of a current collector 10 are provided with a first material layer 21 and a second material layer 22, wherein the area of the first surface of the current collector 10 where the first material layer 21 and the second material layer 22 are provided is larger than that of the second surface of the current collector 10, and of course, the area of the first surface of the current collector 10 where the first material layer 21 and the second material layer 22 are provided may be smaller than that of the second surface of the current collector 10; and the first material layers 21 are each disposed between the current collector 10 and the second material layer 22.
Fig. 2 shows a schematic view of a positive electrode structure of another embodiment of the present application, in which only a first material layer 21 and a second material layer 22 are provided on a first surface of a current collector 10. Of course, the first material layer 21 and the second material layer 22 may be provided on the second surface of the current collector 10.
Fig. 3 shows the relationship between the adhesion and the stroke at the time of the adhesion test of the present application.
Examples
Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. The various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "parts" and "%" are mass references.
Test method and apparatus:
first binder weight average molecular weight test:
the weight average molecular weight of the first binder in the first material layer was tested using Gel Permeation Chromatography (GPC). In the present application, the weight average molecular weight means a molecular weight which is statistically averaged by mass.
Specific surface area (BET) test:
the specific surface area of the second active material was tested using a nitrogen adsorption method.
Adhesive force test:
the adhesion between the first and second material layers was tested using a high-speed rail tensile machine, 90 ° angle method: and cutting the positive electrode plate provided with the first material layer part in the finished lithium ion battery into a strip sample with the length and width of 20mm multiplied by 60mm, wherein the length and width value can be adjusted proportionally according to the actual situation. Adhering a part of the sample to a steel plate through double-sided tape from one end of the sample along the length direction of the sample, wherein the adhering length is not less than 40mm; then fixing the steel plate at the corresponding position of the high-speed rail tensile machine, pulling up the other end which is not adhered to the steel plate, and clamping the sample in a clamping head through a connector or directly, wherein the space included angle between the pulled sample part and the steel plate is 90 degrees. The chuck pulls the sample at a speed of 5mm/min to separate the first material layer from the second material layer, and the average value of the pulling force in the final measured plateau area is recorded as the binding force between the first material layer and the second material layer. As shown in fig. 3, the ratio of the standard deviation to the average value of the adhesion force data of the above plateau region is required to be not more than 10%.
Thickness test of the first and second material layers:
1) Removing the positive electrode coated with the first material layer and the second material layer from the finished lithium ion battery;
2) Cutting the positive electrode obtained in 1) along the thickness direction of the positive electrode by using a plasma cutting technology to obtain cross sections of the first material layer and the second material layer;
3) And (3) observing the cross sections (required to be observed to be not less than 2 cm) of the first material layer and the second material layer obtained in the step (2) under an SEM (electron microscope), respectively testing the single-sided thickness of the first material layer and the single-sided thickness of the second material layer under the SEM, spacing adjacent test points by 2mm to 3mm, testing at least 15 different points, and recording the thickness average value of all the test positions of each layer as the thickness value of the corresponding layer.
And (3) testing the full charge internal resistance of the positive electrode:
1) Constant current charging at 0.05C rate to 4.45V (i.e. full charge voltage), and then constant voltage charging at 4.45V to 0.025C (off current) to make the lithium ion battery reach full charge state
2) Disassembling the lithium ion battery to obtain a positive electrode;
3) Soaking the anode obtained in the step 2) in DMC (dimethyl carbonate) at 25 ℃ for 1h, and then airing in a fume hood;
4) And (3) testing the resistance of the positive electrode plate obtained in 3) by using a BER1200 type diaphragm resistance tester, wherein the distance between adjacent test points is 2mm to 3mm, at least 15 different points are tested, and the average value of the resistance of all the test points is recorded as the diaphragm resistance of the positive electrode plate. Wherein the parameters are as follows: area of ram 153.94mm 2 Pressure 3.5t, hold time 50s.
Impact test:
and (3) in the environment of 20+/-5 ℃, charging the lithium ion battery to be tested to a voltage of 4.45V (namely full charge voltage) at a constant current of 0.05C, and then charging to a current of 0.025C (cut-off current) at a constant voltage of 4.45V to enable the lithium ion battery to reach a full charge state, and recording the appearance of the lithium ion battery before the test. In the process that a round bar with the diameter of 15.8 plus or minus 0.1mm is placed at the center of the battery, an iron block with the weight of 9.1 plus or minus 0.46kg is dropped onto the battery from the height of 610 plus or minus 25mm, and the impacted sample does not fire or explode during the process, and the impacted sample passes the impact test.
Example 1
< preparation of first Binder >
Adding distilled water into a reaction kettle, starting stirring, introducing nitrogen to deoxidize for 2 hours, adding the following monomers of acrylonitrile, sodium acrylate and acrylamide into the reaction kettle according to the mass ratio of 40:45:15, heating to 65 ℃ under an inert atmosphere, keeping the temperature constant, adding 20% ammonium persulfate solution as an initiator to start reaction, taking out a precipitate after 22 hours of reaction, and adding alkali liquor to neutralize the pH to 6.5. Wherein the mass ratio of distilled water, monomer and initiator is 89.5:10:0.5. And after the reaction, filtering, washing, drying, crushing, sieving and the like are carried out on the reaction product to obtain the first binder.
< preparation of second Binder >
Vacuumizing a reaction kettle containing a stirrer, after replacing oxygen with nitrogen, adding deionized water, vinylidene fluoride, initiator diisopropylbenzene hydroperoxide, emulsifier perfluoroalkyl carboxylate and chain transfer agent isopropanol into the reaction kettle until the pressure of the reaction kettle is 3.5MPa, wherein the deionized water is 7 times of the mass of the vinylidene fluoride monomer, the initiator accounts for 0.2% of the mass of the vinylidene fluoride monomer, the emulsifier accounts for 0.5% of the mass of the vinylidene fluoride monomer, and the chain transfer agent accounts for 5% of the mass of the vinylidene fluoride monomer. Then heating to 60 ℃, starting polymerization reaction at the rotation speed of 80r/min, continuously adding vinylidene fluoride monomer, keeping the pressure of the reaction kettle at 3.5MPa until the solid content of emulsion in the reactor reaches 25%, stopping reaction, recovering unreacted monomer, discharging polymer emulsion, and obtaining polyvinylidene fluoride after centrifugation, washing and drying.
< preparation of Positive electrode >
Mixing the first active material lithium iron phosphate, a first binder, the first conductive agent nanoparticle conductive carbon and the carbon nano tube according to the mass ratio of 95.8:3.0:0.7:0.5, then adding N-methyl pyrrolidone (NMP) as a solvent, preparing into slurry with the solid content of 35%, and uniformly stirring. Uniformly coating the slurry on a current collector aluminum foil with the thickness of 10 mu m, and drying at 90 ℃ to obtain a first material layer with the thickness of 5 mu m; wherein the weight average molecular weight of the first binder is 500000;
The second active material Lithium Cobalt Oxide (LCO), second binder polyvinylidene fluoride (PVDF), second conductive agent conductive carbon black and carbon nano tube are mixed according to mass percentMixing at a ratio of 97.3:1.6:0.6:0.5, adding N-methylpyrrolidone (NMP) as solvent, preparing into slurry with solid content of 75%, and stirring uniformly. Uniformly coating the slurry on the first material layer, and drying at 90deg.C to obtain a second material layer with a thickness of 85 μm, wherein the specific surface area of the second active material is 2.0m 2 /g；
And repeating the steps on the other surface of the positive electrode to obtain the positive electrode with the first material layer and the second positive electrode layer coated on the two sides. And cutting the positive electrode into the specification of 74mm multiplied by 867mm, and welding the tab for later use.
< preparation of negative electrode >
Mixing active materials graphite, styrene-butadiene polymer and sodium carboxymethylcellulose at a weight ratio of 97.5:1.3:1.2, adding deionized water as solvent, blending to obtain slurry with solid content of 70%, and stirring uniformly. And uniformly coating the slurry on a copper foil of a negative electrode current collector, drying at 110 ℃, and cold pressing to obtain the negative electrode with the single-sided coating material layer, wherein the thickness of the material layer is 150 mu m.
After the steps are finished, the steps are finished on the back of the negative electrode by adopting the same method, and the negative electrode with the double-sided coating is obtained. After the coating is completed, the negative electrode is cut into sheets with the specification of 76mm×851mm and the tabs are welded for use.
< preparation of electrolyte >
In a dry argon atmosphere, mixing organic solvents of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate at a mass ratio of EC:EMC DEC=30:50:20 to obtain an organic solution, and then adding lithium hexafluorophosphate lithium salt into the organic solvent to dissolve and uniformly mix to obtain an electrolyte with a lithium salt concentration of 1.15 Mol/L.
< preparation of isolation Membrane >
Alumina was mixed with polyvinylidene fluoride in a mass ratio of 90:10 and dissolved in deionized water to form a ceramic slurry having a solids content of 50%. Subsequently, the ceramic slurry was uniformly coated on one surface of a porous substrate (polyethylene, thickness 7 μm, average pore diameter 0.073 μm, porosity 26%) by a gravure coating method, and dried to obtain a double-layer structure of a ceramic coating layer and the porous substrate, the thickness of the ceramic coating layer being 50 μm.
Polyvinylidene fluoride (PVDF) was mixed with polyacrylate in a mass ratio of 96:4 and dissolved in deionized water to form a polymer syrup having a solids content of 50%. And then uniformly coating the polymer slurry on two surfaces of the ceramic coating and porous substrate double-layer structure by adopting a micro-concave coating method, and drying to obtain the isolating film, wherein the thickness of a single-layer coating formed by the polymer slurry is 2 mu m.
< preparation of lithium ion Battery >
And stacking the prepared positive electrode, the prepared isolating film and the prepared negative electrode in sequence, enabling the isolating film to be positioned in the middle of the positive electrode and the negative electrode to play a role of isolation, and winding to obtain the electrode assembly. And (3) filling the electrode assembly into an aluminum plastic film packaging bag, dehydrating at 80 ℃, injecting the prepared electrolyte, and carrying out the procedures of vacuum packaging, standing, formation, shaping and the like to obtain the lithium ion battery.
Example 2
Except at<Preparation of the Positive electrode>In which the specific surface area of the second active material is controlled to be 0.05m 2 The procedure of example 1 was repeated except for the ratio of/g.
Example 3
Except at<Preparation of the Positive electrode>In which the specific surface area of the second active material is controlled to be 0.1m 2 The procedure of example 1 was repeated except for the ratio of/g.
Example 4
Except at<Preparation of the Positive electrode>In which the specific surface area of the second active material is controlled to be 4.0m 2 The procedure of example 1 was repeated except for the ratio of/g.
Example 5
Except at<Preparation of the Positive electrode>In which the specific surface area of the second active material is controlled to be 8.0m 2 The procedure of example 1 was repeated except for the ratio of/g.
Example 6
Except at<Preparation of the Positive electrode>In which the specific surface area of the second active material is controlled to be 15m 2 The procedure of example 1 was repeated except for the ratio of/g.
Example 7
Except at <Preparation of the Positive electrode>In which the specific surface area of the second active material is controlled to be 20m 2 The procedure of example 1 was repeated except for the ratio of/g.
Example 8
The procedure of example 1 was repeated except that sodium polyacrylate was used as the binder in the < preparation of the first binder >.
Example 9
The procedure of example 1 was repeated except that in the < preparation of the first binder >, acrylamide and sodium acrylate were used in a mass ratio of 40:60.
Example 10
The procedure of example 1 was repeated except that in the < preparation of the first binder >, acrylonitrile and acrylamide were used in a mass ratio of 40:60.
Example 11
The procedure of example 1 was repeated except that in the < preparation of the first binder >, acrylonitrile and sodium acrylate were used in a mass ratio of 40:60.
Example 12
The procedure of example 1 was repeated except that acrylonitrile, sodium acrylate and acrylamide were used in a mass ratio of 30:60:10 as the monomers in < preparation of the first binder >.
Example 13
The procedure of example 1 was repeated except that acrylonitrile, sodium acrylate and acrylamide were used in a mass ratio of 30:10:60 as the monomers in < preparation of the first binder >.
Example 14
The procedure of example 1 was repeated except that in the < preparation of the first binder >, acrylonitrile, sodium acrylate and acrylamide were used in a mass ratio of 50:40:10.
Example 15
The procedure of example 1 was repeated except that in the < preparation of the first binder >, acrylonitrile, sodium acrylate and acrylamide were used in a mass ratio of 60:10:30.
Example 16
The procedure of example 1 was repeated except that in the < preparation of the first binder >, acrylonitrile, sodium acrylate and acrylamide were used in a mass ratio of 70:20:10.
Example 17
The procedure of example 1 was repeated except that the mass ratio of the first active material to the first binder in the < preparation of positive electrode > was 97.8:1.0.
Example 18
The procedure of example 1 was repeated except that the mass ratio of the first active material to the first binder in the < preparation of positive electrode > was 93.8:5.0.
Example 19
The procedure of example 1 was repeated except that the mass ratio of the first active material to the first binder in the < preparation of positive electrode > was 88.8:10.0.
Example 20
The procedure of example 1 was repeated except that the mass ratio of the first active material to the first binder in the < preparation of positive electrode > was 83.8:15.0.
Example 21
The procedure of example 1 was repeated except that the mass ratio of the first active material to the first binder in the < preparation of positive electrode > was 78.8:20.0.
Example 22
The procedure of example 1 was repeated except that the weight-average molecular weight of the first binder was 100000 in the < preparation of positive electrode >.
Example 23
The procedure of example 1 was repeated except that the weight-average molecular weight of the first binder was 800000.
Example 24
The procedure of example 1 was repeated except that the weight-average molecular weight of the first binder was 1000000 in the < preparation of positive electrode >.
Example 25
The procedure of example 1 was repeated except that the weight-average molecular weight of the first binder was 1400000 in the < preparation of positive electrode >.
Example 26
The procedure of example 1 was repeated except that the weight average molecular weight of the first binder was 2000000 in the < preparation of positive electrode >.
Example 27
The procedure of example 1 was repeated except that nitrile rubber was used as the second binder in the procedure of < preparation of positive electrode >.
Example 28
The procedure of example 1 was repeated except that the mass ratio of the second active material to the second binder in the < preparation of positive electrode > was 98.4:0.5.
Example 29
The procedure of example 1 was repeated except that the mass ratio of the second active material to the second binder in the < preparation of positive electrode > was 93.9:5.0.
Example 30
The procedure of example 1 was repeated except that the mass ratio of the second active material to the second binder in the < preparation of positive electrode > was 88.9:10.
Example 31
The procedure of example 1 was repeated except that in < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 97.8:1.0, the mass ratio of lithium cobalt oxide to the second binder was 96.3:2.6, n1= -0.4, n2=3%.
Example 32
The procedure of example 31 was repeated except that in < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 96.8:2.0 and the mass ratio of lithium cobalt oxide to the second binder was 96.7:2.2.
Example 33
The procedure of example 1 was repeated except that the mass ratio of lithium cobaltate to the second binder was 97.1:1.8, n1= -0.2, n2=2.4% in < preparation of positive electrode >.
Example 34
The procedure of example 33 was repeated except that in < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 94.8:4.0 and the mass ratio of lithium cobalt oxide to the second binder was 97.3:1.6.
Example 35
The procedure of example 33 was repeated except that in < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 93.8:5.0 and the mass ratio of lithium cobalt oxide to the second binder was 97.5:1.4.
Example 36
The procedure of example 1 was repeated except that in < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 82.8:16, and the mass ratio of lithium cobalt oxide to the second binder was 98.26:0.64, n1= -0.01, n2=0.8%.
Example 37
The procedure of example 36 was repeated except that in < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 80.8:18, and the mass ratio of lithium cobalt oxide to the second binder was 98.28:0.62.
Example 38
The procedure of example 36 was repeated except that in < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 78.8:20 and the mass ratio of lithium cobalt oxide to the second binder was 98.3:0.6.
Example 39
The procedure of example 1 was repeated except that in < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 97.8:1.0, the mass ratio of lithium cobalt oxide to the second binder was 94.91:3.99, n1= -0.01, n2=4.0%.
Example 40
The procedure of example 39 was repeated except that in the < preparation of positive electrode >, the mass ratio of lithium iron phosphate to the first binder was 78.8:20 and the mass ratio of lithium cobalt oxide to the second binder was 95.1:3.8.
Comparative example 1
Except at<Preparation of the Positive electrode >In which the specific surface area of the second active material is 40m 2 The procedure of example 1 was repeated except for the ratio of/g.
Comparative example 2
The procedure of example 1 was repeated except that polyvinylidene fluoride was used as the binder in the < preparation of the first binder >.
Comparative example 3
The procedure of example 1 was repeated except that the weight-average molecular weight of the first binder was 2500000 in the < preparation of positive electrode >.
The preparation parameters and test results of each example and comparative example are shown in tables 1 to 3 below.
TABLE 1 preparation parameters and test results for examples 1-21 and comparative examples 1-2
Table 2 preparation parameters and test results for examples 22-30 and comparative example 3
TABLE 3 preparation parameters and test results for examples 31-40
As can be seen from examples 1 to 7 and comparative example 1, the specific surface area of the second active material of the present application is within the scope of the present application, the adhesion between the first material layer and the second material layer is significantly improved, and especially in example 3, the adhesion between the first material layer and the second material layer reaches more than 35N/m, which results in a decrease in the content of the second binder in the second material layer and an increase in the relative content of the second active material in the second material layer, which is beneficial to the improvement of the energy density of the lithium ion battery; and the passing rate of the penetrating nail test is obviously improved, and the safety of the lithium ion battery can be effectively improved.
As can be seen from examples 8-21 and comparative example 2, the first material layer contains the first binder of the present application, and the content of the first binder is within the scope of the present application, so that the adhesion between the first material layer and the second material layer is obviously improved, especially examples 14-15 and examples 18-21, the adhesion between the first material layer and the second material layer reaches more than 30N/m, and up to 55N/m, which reduces the content of the second binder in the second material layer, and increases the relative content ratio of the second active material in the second material layer, thereby being beneficial to improving the energy density of the lithium ion battery; and the passing rate of the penetrating nail test is obviously improved, and the safety of the lithium ion battery can be effectively improved.
As can be seen from examples 22 to 26 and comparative example 3, in the case of the lithium ion battery having the same components and the same content of the second binder according to the present application, the weight average molecular weight of the first binder according to the present application is within the scope of the present application, the adhesion between the first material layer and the second material layer is significantly improved, and in particular, in examples 25 to 26, the adhesion between the first material layer and the second material layer is up to 40N/m or more, which results in a decrease in the content of the second binder in the second material layer and an increase in the relative content of the second active material in the second material layer, thereby facilitating the improvement of the energy density of the lithium ion battery; and the passing rate of the penetrating nail test is obviously improved, and the safety of the lithium ion battery can be effectively improved.
As can be seen from examples 27 to 30, controlling the content of the second binder within the scope of the present application can effectively improve the adhesion between the first material layer and the second material layer, thereby improving the energy density and safety of the lithium ion battery.
As can be seen from examples 31 to 40, when n1 and n2 take the same values, the increase of the first binder content a increases the binding force between the first material layer and the second material layer, and simultaneously decreases the content B of the second binder in the second material layer, so that the relative content of the second active material in the second material layer increases, which is beneficial to the improvement of the energy density of the lithium ion battery; and the passing rate of the penetrating nail test is obviously improved, and the safety of the lithium ion battery can be effectively improved.
The foregoing description of the preferred embodiments of the application is not intended to limit the application to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the application are intended to be included within the scope of the application.

Claims (9)

1. An electrochemical device comprising a positive electrode comprising a current collector, a first material layer and a second material layer, the second material layer being disposed on at least one surface of the current collector, the first material layer being disposed between the current collector and the second material layer; the second material layer comprises a second active material, a second conductive agent, and a second binder; wherein the specific surface area of the second active material is 0.05m 2 /g to 20m 2 /g; the first material layer comprises a first active material, a first conductive agent and a first binder, wherein the first binder comprises a polymer formed by polymerizing at least one monomer of acrylate or acrylamide;
the polymer in the first binder further comprises an acrylonitrile monomer;
the acrylonitrile is 30 to 70% by mass, and the sum of the acrylic acid salt and the acrylamide is 30 to 70% by mass, based on the total mass of the polymer;
the content A of the first binder in the first material layer is 1wt% to 20wt%;
the weight average molecular weight of the first binder is 100000 to 2000000;
the content B of the second binder in the second material layer is 0.5wt% to 10wt%.
2. The electrochemical device of claim 1, wherein the second binder comprises at least one of polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene-hexafluoropropylene, sodium polyacrylate, nitrile rubber, or polyacrylate.
3. The electrochemical device according to claim 1, wherein an adhesion force of the first material layer and the second material layer is 5N/m or more.
4. The electrochemical device according to claim 1, wherein a content B of the second binder in the second material layer is 0.5wt% to 3.99wt%;
The content A of the first binder in the first material layer and the content B of the second binder in the second material layer satisfy the following conditions:
b=n1×a+n2, and-0.4.ltoreq.n1.ltoreq.0.01, 0.8.ltoreq.n2.ltoreq.4%.
5. The electrochemical device according to claim 1, wherein the first material layer has a single layer thickness of 0.01 μm to 20 μm and the second material layer has a single layer thickness of 20 μm to 300 μm.
6. The electrochemical device according to claim 1, wherein the positive electrode has a resistance of 10Ω or more after the electrochemical device is fully charged.
7. The electrochemical device of claim 1, wherein the first and second conductive agents each independently comprise at least one of lamellar, network, linear, or zero-dimensional conductive agents.
8. The electrochemical device of claim 1, wherein the electrochemical device meets at least one of the following characteristics:
(a) The acrylonitrile is 40 to 60% by mass, and the sum of the acrylic acid salt and the acrylamide is 40 to 60% by mass, based on the total mass of the polymer;
(b) The second binder comprises at least one of polyacrylic acid, polyvinylidene fluoride or nitrile rubber;
(c) The first conductive agent and the second conductive agent each independently comprise at least one of graphene, reticulated graphite fibers, carbon nanotubes, ketjen black, graphite fibers, or nanoparticulate conductive carbon.
9. An electronic device comprising the electrochemical device of any one of claims 1 to 8.
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