KR20110049471A - The carbon nanofiber coated aluminum current collector with improved adhesion strength and contact conductivity and the fabrication method thereof - Google Patents

Abstract

PURPOSE: A current collector in which carbon nanofiber with improved adhesive strength and electric conductivity is coated is provided to enable the application to a electric double layer capacitor required for high energy density suing carbon nano fiber with wide specific surface area as a carbon layer. CONSTITUTION: A current collector in which carbon nanofiber is coated includes a metal film(200) and a carbon nanofiber layer(300) equipped on one side of the metal film. The metal film forms a metal-carbon fiber synthesizing layer(400) by impregnating one side of molten metal film to pores of the carbon nanofiber layer. The metal film is welded with the carbon nanofiber layer.

Description

The carbon nanofiber coated aluminum current collector with improved adhesion strength and contact conductivity and the fabrication method

The present invention relates to a current collector of a capacitor or a secondary battery with improved adhesive strength and electrical conductivity. The carbon nanofibers obtained by the electrospinning method are welded onto a metal foil (aluminum foil), and the carbon nanofibers with improved adhesive strength and electrical conductivity are coated. It relates to a current collector and a method of manufacturing the same.

The current collector accumulates electrons generated by an electrochemical reaction of an active material in a battery or an electrochemical capacitor and transfers them to an external circuit. Since the current collector must receive as much electrons generated from the active material as possible, the current collector and the active material must be strongly bound, and the larger the contact area is, the better. In addition, in order to smoothly transfer electrons from the active material to the external circuit, the current collector requires high conductivity. Finally, the electrode structure of the current collector must be stable to the electrochemical reactions occurring in the cell or capacitor.

The current collector used for the positive electrode and electrochemical capacitor of a lithium ion battery is generally manufactured by applying a slurry made of a mixture of an active material or activated carbon powder, a binder, and a conductive material to aluminum foil, followed by drying or pressing at room temperature. However, when manufactured by such a method, there is a problem that the applied material is peeled off from aluminum over time due to insufficient adhesion between the current collector and the coating material, and since the commonly used binder is non-conductive, the conductivity of the current collector There is a problem of lowering. In addition, a high oxidation voltage is applied to the aluminum during charging and discharging. At this time, an oxide film, which is a non-conductor, is formed on the surface of the aluminum, thereby degrading the electrical conductivity of the current collector.

In order to solve the problems of the existing current collector, the following inventions have been proposed.

International Patent PCT / JP2004 / 003239 discloses a method for producing carbon-coated aluminum foil by arranging aluminum coated with carbon in a hydrocarbon atmosphere, applying heat below an aluminum melting temperature, and forming an aluminum carbide deposition layer. posting. A whisker vapor-grown using aluminum carbide holds the carbon layer and the aluminum surface to improve the surface adhesion strength, and at the same time serves as an electrical conduction path between the two layers to improve the electrical conductivity.

US Patent US577428 discloses a method for manufacturing a current collector by coating aluminum on a carbon fiber cloth by a plasma spray method and then thermally compressing the coated carbon fiber cloth on an aluminum foil at a temperature of about 300 ° C.

In Japanese Patent JP2009 / 123664, after removing the oxide on the aluminum surface, a conductive titanium carbide is sprayed on the aluminum foil at high speed to form a bonding layer diffused in aluminum on a molecular scale. As a result, a method of manufacturing a current collector having excellent bonding strength with an active material and improving durability by suppressing surface oxide formation has been disclosed.

Korean Patent KR10-0511363 discloses a current collector manufactured by attaching a mixture of carbon nanotubes or carbon nanofibers and metal nanoparticles or metal oxides to aluminum and then thermocompressing them.

The present invention is to improve the performance of the current collector through the new design described below in consideration of the existing technical improvements to solve the problems of the prior art.

 After attaching the polymer nanofibers to the metal foil (aluminum foil) having a uniform concave-convex structure by electrospinning, carbonizing them near the melting temperature of the aluminum, and simultaneously welding the aluminum foil to the carbonized fiber to form a composite layer of carbonized fiber and aluminum. By doing so, the adhesive strength and durability are improved, and the current collector with minimal interfacial contact resistance is produced.

The carbon nanofiber coated current collector according to the present invention

Metal foil and carbon nanofiber layer provided on one surface of the metal foil,

The metal foil is characterized in that one surface of the molten metal foil penetrates into the pores of the carbon nanofiber layer to form a metal-carbon fiber composite layer and is welded with the carbon nanofiber layer.

At this time, the metal foil is one or more of the main material selected from aluminum, copper and nickel is electroplated or ion deposited by a surface material selected from at least one selected from aluminum, copper, nickel, platinum, gold, silver and palladium,

It is preferable that the nanoparticles of the surface material are coated on the main material by any one of spraying, dipping and pressing.

On the other hand, the manufacturing method of the current collector coated with carbon nanofiber according to the present invention,

A first step of forming an uneven structure on one surface of the metal foil by an anodizing method;

A second step of coating the polymer nanofibers on the uneven structure;

A third step of fabricating a current collector by heating the metal foil coated with the polymer nanofibers in air containing oxygen; And

And a fourth step of applying pressure to the current collector in an inert atmosphere and carbonizing the polymer nanofibers with conductive carbon fibers through heat treatment, and simultaneously infiltrating the molten metal foil into the pores of the carbon fibers and welding them.

At this time, in the fourth step, the heat treatment is preferably performed to increase the specific surface area by performing heat treatment at a temperature of 300 ° C. or more and below the melting point of the metal foil in a steam atmosphere.

Since the present invention uses carbon nanofibers having a large specific surface area as a carbon layer, the present invention can be applied to an electric double layer capacitor requiring high energy density. In addition, since the carbon fiber layer and the composite layer of aluminum forms a strong adhesion, it is possible to prevent the performance degradation of the battery and the capacitor due to the peeling phenomenon, and to improve the output performance by minimizing the contact resistance.

Hereinafter, with reference to the accompanying drawings will be described in detail the current collector and its manufacturing method coated with carbon nanofibers.

1 is a flowchart illustrating a method of manufacturing a current collector coated with carbon nanofibers, and FIG. 2 is a schematic cross-sectional view of a current collector coated with carbon nanofibers. 3a and 4 are the results of the evaluation of the adhesive strength and the interface resistance for each of the embodiments.

The carbon nanofiber coated current collector 100 according to the present invention includes a metal foil 200 and a carbon nanofiber layer 300 provided on one surface of the metal foil 200 as shown in FIG. 2, wherein the metal foil 200 is One surface of the molten metal foil 200 penetrates into the pores of the carbon nanofiber layer 300 to form a metal-carbon fiber composite layer 400 and is welded with the carbon nanofiber layer 300.

At this time, the metal foil 200 is one or more of the main material selected from aluminum, copper and nickel is electroplated or ion deposited by a surface material selected from at least one selected from aluminum, copper, nickel, platinum, gold, silver and palladium, It is preferable that the nanoparticles of the surface material are coated on the main material by any one of spraying, dipping and pressing.

Hereinafter, the characteristics of the carbon nanofiber-coated current collector 100 using the aluminum metal foil 200 will be described in detail through the manufacturing method of FIG. 1.

The carbon nanofiber coated current collector 100 of the present invention

A first step of forming the uneven structure 210 on one surface of the metal foil 200 by an anodization method;

A second step of coating the polymer nanofibers on the uneven structure 210;

A third step of fabricating the current collector 100 by heating the polymer nanofiber coated metal foil 200 in air containing oxygen; And

A fourth step of applying pressure to the current collector 100 in an inert atmosphere and carbonizing the polymer nanofibers with conductive carbon fibers through heat treatment and simultaneously infiltrating the molten metal foil 200 into the pores of the carbon fibers and welding them; It is manufactured through.

First, in the first step, through the anodization, a wide and uniform uneven structure 210 having a specific surface area of about 100 to 500 nm in width is formed on the surface of the aluminum metal foil 200.

Thereafter, in the second step, the polymer nanofibers are formed on the surface on which the uneven structure 210 is formed by electrospinning, silk screen, doctor blade, and spray method. The polymer nanofibers of 1 to 200 ㎛ thick coating.

For example, the electrospun polymer nanofibers are entangled with the concave-convex structure 210 having a large surface area to serve to physically hold the fiber layer. Polymers used for nanofiber electrospinning may include polyacrylonitrile (PAN), pitch, rayon, and cellulose-based polymers. Among them, carbides of pitch nanofibers are particularly preferred because they exhibit high conductivity compared to other types of polymer-based carbon fibers.

In the third step, the polymer nanofibers attached to the aluminum metal foil 200 having the uneven structure 210 are heat-treated for 1 to 2 hours at a temperature of 200 to 300 ° C. in air with oxygen.

In the heat treatment, it is preferable to increase the specific surface area by performing heat treatment at a temperature of 300 ° C. or more and below the melting point of the metal foil 200 in a steam atmosphere. In ionicity, the polymer nanofibers are at a temperature above the glassy temperature and are in a fluid state, so that the fibrous layer binds well to the surface of aluminum. Over time, as the molecules of nanofibers react with oxygen, the molecular structure changes from chain to cyclic. The fiber with cyclic structure no longer undergoes deformation by heat, and stable carbonization with minimal loss of mass even at high temperatures above 600 ℃. Is possible. The polymer fibers may be peeled off the aluminum surface as shrinkage occurs due to the change in molecular structure during oxidation for cyclization. In order to prevent peeling of the polymer nanofiber layer due to shrinkage, a pressure of 0.2-1 kgf / cm 2 is applied during stabilization.

Finally, the fourth step is 600 ~ in the range of +40 ℃ from the melting point of the aluminum metal foil 200 while applying a pressure of 0.5 ~ 1kgf / ㎠ to the heated current collector 100 in an inert atmosphere of nitrogen or argon By heat treatment at a temperature of 700 ℃, while carbonizing the polymer nanofibers into the conductive carbon fiber and the molten surface of the aluminum metal foil 200 to penetrate into the pores of the carbon fiber, the metal-carbon as shown in FIG. The fiber composite layer 400 is generated and welded.

The following is a manufacturing example of the current collector 100 coated with carbon nanofibers according to the manufacturing method.

(Example 1)

Anodized aluminum metal foil 200 having a purity of 99.9% and a thickness of 100 μm with an phosphate solution as an electrolyte to form a uniform uneven structure 210 having a diameter of 300 to 500 nm on the surface, and then a surface formed by anodization. The oxide was immersed in sodium hydroxide or chromic acid solution for 5 hours to strip off the aluminum oxide formed on the surface.

PAN and dimethyl formamide (DMF) 1:10 by weight ratio to prepare an electrospinning precursor. The prepared precursor is placed in a syringe having a diameter of 1 μm and a volume of 10 ml, and +10 kV is applied to the syringe tip portion and -10 kV to the collecting metal surface to give the PAN precursor to the metal foil 200 attached to the collecting metal surface. Electrospinning was performed for a minute. The thickness of the spun polymer fiber was 300-500 nm, and the thickness of the electrode material to which the polymer fiber was attached was 120 μm.

After applying nanofiber-attached aluminum metal foil 200 to a muffle furnace with a stainless steel sheet at a pressure of 0.2-1 kgf / cm 2 and heat-treating at 300 ° C. for 1 hour in an air atmosphere at a temperature rising rate of 5 ° C./min, Heat treatment was performed while applying a pressure of 0.5-1kgf / ㎠ for 1 hour at 700 ° C. at the same temperature rising rate in a nitrogen atmosphere. In the process, the polymer fibers were converted into conductive carbon fibers. Finally, heat treatment was performed at a temperature of 300 ° C. in a nitrogen atmosphere containing 30% moisture.

(Example 2)

The same process as in the above embodiment was performed on the aluminum metal foil 200 having the uneven structure 210 having a diameter of about 100 nm.

(Reference Example 1)

The same process as Example 1 was performed on the commercial aluminum metal foil 200 which surface-etched.

(Reference Example 2)

The same process as Example 1 was performed on the commercial aluminum metal foil 200 which did not have any treatment on the surface.

(Adhesive evaluation)

The electrode prepared by the method of the above examples was cut out to a size of 1 cm × 2.5 cm, and then the Scotch Magic tape was attached and detached to measure the mass of the detached coating to evaluate adhesion using the following equation. The evaluation results are shown in FIG. 3A. As can be seen in the drawings presented, Example 1 showed the best adhesion.

(Interface contact resistance evaluation)

The prepared electrode was cut into a size of 2 cm × 2 cm, sandwiched between copper plates, a pressure of 100 kgf / cm 2 was applied using a crimping machine, and the interfacial contact resistance of each sample was evaluated by measuring the resistance between the copper plates using a high frequency ohmmeter. The evaluation results are shown in FIG. 4. As can be seen in Figure 4, the results of Example 1 showed the lowest interfacial contact resistance.

 The present invention is not limited to the above-described embodiments, and the scope of application of the present invention is not limited to those of ordinary skill in the art to which the present invention pertains without departing from the gist of the present invention as claimed in the claims. Of course, various modifications can be made.

1 is a flowchart illustrating a method of manufacturing a current collector coated with carbon nanofibers

2 is a schematic cross-sectional view of a current collector coated with carbon nanofibers

Figure 3a is a result of evaluation of the adhesive strength for each embodiment

4 is a result of evaluating the interfacial contact resistance for each embodiment

*** Explanation of symbols in the drawings ***

100: current collector

200: metal foil

210: uneven structure

300: carbon nano fiber layer

400: metal-carbon fiber composite layer

Claims (4)

It includes a metal foil 200 and the carbon nanofiber layer 300 provided on one surface of the metal foil 200, The metal foil 200 is one surface of the molten metal foil 200 penetrates into the pores of the carbon nanofiber layer 300 to form a metal-carbon fiber composite layer 400 and is deposited with the carbon nanofiber layer 300. Carbon nanofiber coated current collector 100, characterized in that. The method of claim 1, The metal foil 200 is one or more of the main material selected from aluminum, copper and nickel is electroplated or ion deposited by a surface material selected from at least one selected from aluminum, copper, nickel, platinum, gold, silver and palladium, Carbon nanofiber-coated current collector (100), characterized in that the nanoparticles of the surface material is coated on the main material by any one of spraying, dip and pressing. A first step of forming the uneven structure 210 on one surface of the metal foil 200 by an anodization method; A second step of coating the polymer nanofibers on the uneven structure 210; A third step of fabricating the current collector 100 by heating the polymer nanofiber coated metal foil 200 in air containing oxygen; And A fourth step of applying pressure to the current collector 100 in an inert atmosphere and carbonizing the polymer nanofibers with conductive carbon fibers through heat treatment and simultaneously infiltrating the molten metal foil 200 into the pores of the carbon fibers and welding them; Carbon nanofibers coated with a current collector (100) manufacturing method comprising a. The method of claim 3, wherein In the fourth step, the heat treatment is a carbon nanofiber coated current collector, characterized in that to increase the specific surface area by applying a pressure at a temperature of 300 ℃ or more below the melting point of the metal foil 200 in a water vapor atmosphere ( 100) Production method.

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