JP2008192695A - Electrode body, manufacturing method thereof and electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode body preventing the separation of carbon nano-tubes from a conductor. <P>SOLUTION: The electrode body comprises the conductor, and a carbon nano-tube layer provided on the surface of the conductor. The carbon nano-tube layer includes a plurality of first carbon nano-tubes erected on the surface of the conductor, and second carbon nano-tubes each crosslinking between at least two first carbon nano-tubes. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode used for an energy device, a manufacturing method thereof, and an electric double layer capacitor.

  Energy devices can be broadly divided into energy storage devices and energy power generation devices. Typical examples of the energy storage device include an electrochemical capacitor and a battery, which have already been used in the market utilizing their respective characteristics. As an electrochemical capacitor, activated carbon is used as a polarizable electrode, and an electric double layer capacitor using only an electric double layer formed at the interface between the surface of the activated carbon pores and the electrolyte, or a continuous valence such as ruthenium nitrate. Examples thereof include a transition metal oxide that changes and a redox capacitor using a conductive polymer that can be doped. Batteries are broadly classified into secondary batteries that can be charged / discharged using intercalation or chemical reaction of active materials, and primary batteries that are basically non-rechargeable once discharged.

  The most basic structure common to all of these various energy storage devices is an electrode active material that can release energy in principle, but in order to extract the energy stored in the electrode active material to the outside, electron conduction And a current collector (conductor) electrically connected to the electrode active material. The current collector needs to propagate the energy of the electrode active material with high efficiency. Therefore, metal materials with low resistance such as aluminum, copper, and stainless steel are generally used. In some cases, a rubber-based material imparted with conductivity may be used.

In recent years, as energy storage devices are widely used, there has been a demand for a device having excellent characteristics capable of discharging a large current with a lower resistance. Conventionally, an electric double layer capacitor mainly uses activated carbon having a large specific surface area as an electrode active material. However, activated carbon generally has a low electrical conductivity, and the activated carbon alone has a problem that the internal resistance of the polarizable electrode is increased and a large current cannot be taken out. For this reason, in order to reduce the internal resistance of the polarizable electrode, an attempt was made to increase the capacity by increasing the electric conductivity by incorporating carbon nanotubes into the polarizable electrode (see, for example, Patent Document 1). . In addition, as an effort to further increase the specific surface area of the electrode to improve the capacity, an electrode body is disclosed in which a plurality of carbon nanotubes are formed in a brush shape on the surface of a conductor (see, for example, Patent Document 2).
JP 2000-124079 JP 2004-30926 A

  However, in an electrode body in which a plurality of carbon nanotubes are formed in a brush shape on the surface of a conductor, there is a problem in that the carbon nanotubes are released from the conductor in the manufacturing process of the energy storage device. . In the energy storage device, if the carbon nanotubes on the electrodes are released from the conductor, it may cause a short circuit between the electrodes.

  The present invention solves the above problem, and provides an electrode body having a structure in which a plurality of carbon nanotubes are erected on the surface of a conductor, in which the release of carbon nanotubes from the conductor is reduced. With the goal. Furthermore, it aims at providing the electrical double layer capacitor carrying the said electrode body.

  The inventors of the present invention believe that the carbon nanotubes are released from the conductor because the contact portion between the carbon nanotubes and the conductor is as small as nanometers in diameter, so the connection force of the carbon nanotubes to the conductor is small, and therefore the connection As a result of earnest research that the carbon nanotubes are peeled off even by a small load applied to the part, the carbon nanotubes provided between the carbon nanotubes standing on the conductor surface are provided, The present inventors have found that the problem can be solved and have reached the present invention.

  That is, the first present invention is an electrode body comprising a conductor and a carbon nanotube layer provided on the surface of the conductor, wherein the carbon nanotube layer is erected on the surface of the conductor. A plurality of first carbon nanotubes and at least two second carbon nanotubes are provided between the second carbon nanotubes.

  In one aspect of the electrode body, one end of the first carbon nanotube is connected to the surface of the conductor. For example, the first carbon nanotube can be synthesized on the surface of the conductor via the first catalytic metal. The first catalytic metal is preferably selected from the group consisting of iron, nickel, cobalt, platinum, gold, yttrium, rhodium, palladium, and alloys containing combinations thereof.

  In one embodiment of the electrode body, one end of the second carbon nanotube is connected to the side surface of the first carbon nanotube, and the other end is connected to the side surface of the other first carbon nanotube. The second carbon nanotube can be synthesized, for example, on the side surface of the first carbon nanotube via the second catalytic metal. The second catalytic metal is preferably selected from the group consisting of iron, nickel, cobalt, platinum, gold, yttrium, rhodium, palladium, and alloys containing combinations thereof.

  2nd this invention is a method of manufacturing the electrode body which concerns on 1st this invention, Comprising: The process of providing the 1st catalyst metal particle which consists of a 1st catalyst metal on the surface of the said conductor, 1st catalyst metal particle A step of synthesizing the first carbon nanotube through the first carbon nanotube, a step of providing the second catalytic metal particle made of the second catalytic metal on the side surface of the first carbon nanotube, and a second carbon nanotube through the second catalytic metal particle. Process.

  In the manufacturing method, the first carbon nanotube and the second carbon nanotube are preferably synthesized by a vapor phase chemical vapor deposition method.

  The third aspect of the present invention includes a pair of polarizable electrodes comprising the electrode body according to the first aspect of the present invention, and the pair of polarizable electrodes are provided so that the carbon nanotube layers face each other in a non-contact manner. An electric double layer capacitor.

  According to the electrode body of the present invention, it is possible to prevent the carbon nanotubes from being released from the conductor without using a binder made of resin or the like. Therefore, in an energy device such as an electric double layer capacitor using the present invention, a high capacity can be obtained and at the same time the failure rate can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
1. Electrode Configuration The first embodiment is an electrode body according to the present invention. FIG. 1 is a schematic view conceptually showing the electrode body of the first embodiment. The electrode body 10 includes a conductive substrate 11 and a carbon nanotube layer 15 provided on the surface of the conductive substrate 11. The carbon nanotube layer 15 includes a plurality of carbon nanotubes (first carbon nanotubes) 12 erected on the surface of the conductive substrate 11 and a carbon nanotube (second carbon nanotube) laid between at least two carbon nanotubes 12. ) 13.

  The carbon nanotubes 12 and 13 are extremely fine tube (tube) -like substances having a hole diameter of nanometers and formed by bonding carbon atoms in a network. Each of the carbon nanotubes 12 and 13 may have a single-layer structure, that is, a single tube, or a multi-layer structure, that is, a concentric plurality of different diameter tubes. As the “carbon nanotube” in the present invention, a multi-walled carbon nanotube having a large diameter generally called “carbon nanofiber” may be used. The diameters of the carbon nanotubes 12 and 13 are not limited. For example, the carbon nanotubes 12 and 13 can take values in the range of 0.4 nm to 10 μm. However, lithium ions having an ionic radius of 0.074 nm and electrolyte solvents having an ionic radius of about 0.5 nm are possible. Considering that the sum enters the inside, the inner diameter is preferably in the range of 0.4 nm to 100 nm.

  The first carbon nanotubes 12 are erected on the surface of the conductive substrate 11. It is preferable that one end of the first carbon nanotube 12 is connected to the surface of the conductive substrate 11, and the other end or the side surface is erected so as to be substantially free from the conductive substrate 11. This is because the interface with the electrolytic solution formed by one carbon nanotube can be maximized.

  The second carbon nanotubes 13 are constructed between at least two first carbon nanotubes 12. Here, “erection” means a state in which the second carbon nanotubes 13 are connected to at least two first carbon nanotubes 12. In addition, although the connection site | part with the 1st carbon nanotube 12 in the 1st carbon nanotube 12 is not specifically limited, For example, one end is connected to the side surface of the 1st carbon nanotube 12, and the other end is the other 1st carbon nanotube 12 There may be a form of connection to the side surface.

  As described above, since the first carbon nanotube 12 has a plurality of connection portions, the load applied to the entire carbon nanotube 12 is dispersed, and the load applied to the connection portion with the conductive substrate 11 is expected to be reduced. . That is, the possibility of occurrence of peeling of the first carbon nanotubes 12 from the conductive substrate 11 is reduced. Even if the first carbon nanotube 12 is peeled off at the connection portion with the conductive substrate 11, the first carbon nanotube 12 is completely released as long as the connection state at the connection portion with the second carbon nanotube 13 is maintained. It does not become a state. Therefore, the possibility that the first carbon nanotubes 12 are released (dropped off) from the conductive substrate 11 is reduced. By using the electrode body having such a configuration, the possibility of occurrence of a short circuit between the electrodes in the energy device is reduced.

  As the conductive substrate 11 serving as a current collector, for example, a flat plate made of copper, aluminum, silicon, titanium, stainless steel, tantalum, or graphite can be used. In order to increase the current collection efficiency, a punching metal, an expanded metal, a metal net, an aluminum etching foil, or the like can be preferably used. Alternatively, a conductive substrate on which different materials are bonded can be used. It can select suitably according to the use of an electrode body.

2. Method for Forming Carbon Nanotube Layer A method for forming the carbon nanotube layer 15 on the surface of the conductive substrate 11 will be described. As a method of forming the carbon nanotube layer 15 on the surface of the conductive substrate 11, even if the carbon nanotube layer 15 is directly formed on the surface of the conductive substrate 11, the carbon nanotube layer 15 is formed on another substrate. It may be a transfer method in which it is formed and transferred onto the conductive substrate 11. Hereinafter, the case of the direct method will be described. First, catalyst metal particles (first catalyst metal particles) are provided on the conductive substrate 11, and the first carbon nanotubes 12 are synthesized on the conductive substrate 11 via the catalyst metal particles. Thereafter, catalytic metal particles (second catalytic metal particles) are provided on the side surfaces of the first carbon nanotubes 12, and the second carbon nanotubes are synthesized on the side surfaces of the first carbon nanotubes 12 through the catalytic metal particles. Growing so as to connect to the first carbon nanotubes 12.

  As a method of synthesizing the first carbon nanotube 12 and the second carbon nanotube 13, there are a vapor phase chemical vapor deposition (CVD) method, a laser ablation method, an arc discharge, an electrolytic synthesis method in solution, and the like. Preferably by the CVD method. Examples of the catalyst metal used for the synthesis of the first carbon nanotube 12 and the second carbon nanotube 13 include iron, nickel, cobalt, platinum, gold, yttrium, rhodium, palladium, or an alloy containing a combination thereof. The selection is determined by the desired carbon nanotube diameter and its synthesis method. Catalyst metal particles are enlarged by heating or preheating during the synthesis of carbon nanotubes. It is generally said that there is a correlation between the catalyst metal particle diameter and the synthesized carbon nanotube diameter. When a carbon nanotube diameter of 0.4 nm to 100 nm is desired, the catalyst metal particle diameter is preferably 0.4 nm to 100 nm. The catalyst metal particles can be formed first by, for example, vacuum-depositing the catalyst metal layer. In this case, the thickness of the catalyst metal layer is preferably 0.1 nm to 10 nm.

  Although the length of the 1st carbon nanotube 12 is not specifically limited, In order to increase the energy density per weight, so long is desirable. Further, the length of the second carbon nanotube 13 is not particularly limited as long as at least two carbon nanotubes are cross-linked.

  The electrode body according to the present invention is applicable to all energy storage devices including electric double layer capacitors, electrochemical capacitors, lithium ion capacitors, lithium ion secondary batteries, organic batteries and the like.

  In the electric double layer capacitor or the electrochemical capacitor, the electrode body according to the present invention can be used for both positive and negative electrodes.

  In a lithium ion secondary battery, an electrode body carrying lithium metal oxide such as lithium cobaltate, silicon compound, or lithium metal is used as the positive electrode, and an electrode body carrying graphite or the like is used as the negative electrode. Here, the electrode body according to the present invention can be used as the negative electrode.

  In lithium ion capacitors, it has been proposed to use an electrode body carrying activated carbon as a positive electrode and an electrode body carrying graphite as a negative electrode. Here, the electrode body according to the present invention is used for both positive and negative electrodes. Can do.

(Second Embodiment)
Below, the energy device using the electrode body of 1st Embodiment is demonstrated. As an example of such an energy device, first, the electric double layer capacitor of the second embodiment will be described with reference to FIG.

  FIG. 2 is a vertical sectional view schematically showing the coin-type electric double layer capacitor of the second embodiment. The electric double layer capacitor 20 includes a positive electrode 10a and a negative electrode 10b which are polarizable electrodes, and the positive electrode 10a and the negative electrode 10b have the same configuration as the electrode body 10 of the first embodiment. That is, it consists of conductive substrates 11a and 11b and carbon nanotube layers 15a and 15b, respectively. In the electric double layer capacitor 20, the case 25 and the lid 27 are arranged to face each other, and the positive electrode 10a fixed to the upper surface of the case 25 and the negative electrode 10b fixed to the lower surface of the lid 27 are respectively carbon nanotubes. The layers 15a and 15b are arranged so as to face each other with the separator 23 interposed therebetween. The case 25 and the lid 27 are caulked and sealed using a gasket 26. A space formed by the case 25 and the lid 27 is filled with the electrolytic solution 24.

  The separator does not depend on the type of energy device in principle, but heat resistance is required particularly when reflow treatment is required. Polypropylene or the like can be used when heat resistance is not required, and cellulosic material can be used when heat resistance is required.

  It is necessary to select different materials for the electrolyte depending on the type of energy device. A solvent having an appropriate potential window is selected so that electrochemical decomposition does not occur depending on the operating voltage range. General propylene carbonate, ethylene carbonate, ethyl methyl carbonate, hexane, pure water, ethylene, ethylene glycol, or a mixed solvent thereof can be used. A high boiling point solvent such as sulfolane is used so that it does not boil.

  As the electrolyte, various known materials, for example, tetraethylammonium tetrafluoroborate for electric double layer capacitor use, lithium pentafluorophosphate, etc. for lithium ion secondary battery use can be used. By synthesizing carbon nanotubes having a diameter corresponding to the ionic diameter of these ionic electrolytes, it is possible to produce an energy storage device in which the energy density per unit weight is close to the maximum.

  Hereinafter, the present invention will be described with reference to examples.

(Example 1)
1. Production of Electrode Body of Example 1 1) Synthesis of First Carbon Nanotube As Example 1, an electrode body according to the first embodiment is produced. With reference to FIG. 1, the manufacturing process of the electrode body of Example 1 will be described. First, a catalytic metal layer is formed on the conductive substrate 11. A 0.05 mm thick substrate made of Cu is used as the conductive substrate 11, and Fe is used as the catalyst metal. Using an electron beam (EB) vapor deposition apparatus, Fe is supplied onto the conductive substrate 11 at room temperature so that the instruction of the crystal vibrator type film thickness meter is 1.2 mm, and a catalytic metal layer made of Fe is formed.

  Next, the conductive substrate 11 on which the catalytic metal layer is formed is introduced into a thermal CVD apparatus and heated at 500 ° C. for 3 minutes. Through this process, Fe aggregates to form nanometer-sized catalytic metal particles.

Next, the temperature is raised to 600 ° C., and a gas obtained by diluting ethylene five times with argon is supplied onto the conductive substrate 11 at a flow rate of 1 liter / min for 5 minutes. By this step, a plurality of carbon nanotubes 12 having a length of about 1 μm are erected on the surface of the conductive substrate 11.
2) Synthesis of Second Carbon Nanotube Thereafter, the conductive substrate 11 is taken out and mounted again on the EB vapor deposition apparatus, and Fe is supplied at room temperature so that the instruction of the crystal vibrator type film thickness meter is 1.2 nm. Here, the conductive substrate 11 is mounted at an angle of 60 degrees with respect to the vapor deposition source so that Fe is supplied to the side surfaces of the carbon nanotubes 12.

  Next, it is again introduced into the thermal CVD apparatus and heated at 500 ° C. for 3 minutes. Through this step, Fe adhered to the side surface aggregates to form nanometer-sized catalytic metal particles.

  Finally, the temperature is raised to 600 ° C. under the same conditions as in the carbon nanotube 12 synthesis step, and a gas obtained by diluting ethylene five times with argon is supplied onto the conductive substrate 11 at a flow rate of 1 liter / min for 5 minutes. By this step, the carbon nanotube 12 grows longer and finally has a length of about 2 μm. In addition, carbon nanotubes are newly synthesized in the lateral direction using Fe particles attached to the side surfaces of the carbon nanotubes 12 as seeds, and some of the carbon nanotubes 12 grow from the surface of the conductive substrate 11, Carbon nanotubes 13 are formed. Although Fe is supplied from only one direction, the growth direction of the carbon nanotubes from the side surfaces of the carbon nanotubes 12 extends in multiple directions. It can be considered that this is because the position of the Fe particles is not limited to one direction through the Fe aggregation step.

  Here, although the mechanism of bonding between the carbon nanotubes is not known in detail, for example, when Fe exists at the tip of the growing carbon nanotube 13 and the tip of the carbon nanotube 13 contacts another carbon nanotube 12. In addition, there is a possibility that a chemical bond is formed through Fe at the tip.

2. Production of Electrode Body of Comparative Example 1 The production process of the electrode body of Comparative Example 1 is the same as the production process of the electrode body of Example 1. 1) A gas obtained by diluting ethylene five times with argon in the first carbon nanotube synthesis step Is produced in the same manner as the electrode body of Example 1 except that the second carbon nanotube synthesis step of 2) is not performed and the second carbon nanotube synthesis step of 2) is not performed.

3. Confirmation of characteristics of electrode body The characteristics of the electrode body of Example 1 can be confirmed as follows. The electrode bodies of Example 1 and Comparative Example 1 were subjected to ultrasonic cleaning with ethanol for 10 minutes, and then the number of carbon nanotubes that had fallen off was measured by concentrating the cleaning solution. By comparing the measurement results of Example 1 and Comparative Example 1, the electrode body of Example 1 having the second carbon nanotubes was compared with the electrode body of Comparative Example 1 having no second carbon nanotubes. It can be confirmed that the amount of dropping-out of the nanotube is small.

(Example 2)
1. Production of Electric Double Layer Capacitor of Example 2 As Example 2, the electric double layer capacitor of the second embodiment is produced using the electrode body of Example 1. The manufacturing process of the electric double layer capacitor of Example 2 will be described with reference to FIGS. Two electrode bodies 10 of Example 1 are prepared, and are set as a positive electrode 10a and a negative electrode 10b, which are polarizable electrodes, respectively. The surface of the positive electrode 10a on the side of the conductive substrate 11a where the carbon nanotube layer 15a is not formed is bonded to the upper surface of the case 25 of the stainless steel container using a conductive adhesive. The surface of the negative electrode 10b on the side of the conductive substrate 11b where the carbon nanotube layer 15b is not formed is bonded to the lower surface of the lid 27 of the stainless steel container using a conductive adhesive.

  After drying the case 25 together with the positive electrode 10a and the lid 27 together with the negative electrode 10b, the positive electrode 10a and the negative electrode 10b are impregnated with an electrolytic solution. As the electrolyte, a 1 mol / l tetraethylammonium tetrafluoroborate propylene carbonate solution was used. The positive electrode 10 a and the negative electrode 10 b impregnated with the electrolytic solution are opposed to each other through a separator 23 made of a cellulose-based nonwoven fabric, and the case 25 and the lid 27 are caulked and sealed using a gasket 26. Thus, the coin-type electric double layer capacitor 20 is manufactured.

2. Production of Electric Double Layer Capacitor of Comparative Example 2 The electric double layer capacitor of Comparative Example 2 is the electric double layer of Example 2 except that the electrode body of Comparative Example 1 is used instead of the electrode body of Example 1. It is manufactured by the same method as the capacitor.

3. Confirmation of defective rate of electric double layer capacitor For the defective rate of electric double layer capacitor, a plurality of electric double layer capacitors having the same configuration are manufactured, the capacitance of each electric double layer capacitor is measured, and the average value of the capacitance is 50% or less. It can be evaluated based on the probability of occurrence of those having a capacity. By comparing the above-mentioned occurrence probabilities in Example 2 and Comparative Example 2, it is confirmed that the electric double layer capacitor of Example 2 has a lower defect rate than the electric double layer capacitor of Comparative Example 1. Can do.

  The electrode body according to the present invention has a form of use as an electrode body having a large specific surface area, and is useful not only for energy storage devices but also for gas sensors and the like.

The schematic diagram shown notionally of the electrode body of 1st Embodiment. The vertical sectional view showing typically the coin type electric double layer capacitor of a 2nd embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electrode body 10a Positive electrode 10b Negative electrode 11, 11a, 11b Conductive substrate 12 First carbon nanotube 13 Second carbon nanotube 15, 15a, 15b Carbon nanotube layer 20 Electric double layer capacitor 23 Separator 24 Electrolytic solution 25 Case 26 Gasket 27 Lid

Claims (10)

An electrode body comprising a conductor and a carbon nanotube layer provided on the surface of the conductor,
The said carbon nanotube layer is an electrode body containing the several 1st carbon nanotube standingly arranged by the surface of the said conductor, and the 2nd carbon nanotube spanned between the at least 2nd 2nd carbon nanotube.   The electrode body according to claim 1, wherein one end of the first carbon nanotube is connected to the surface of the conductor.   The electrode body according to claim 2, wherein the first carbon nanotube is synthesized on the surface of the conductor via a first catalyst metal.   The electrode body according to claim 3, wherein the first catalyst metal is selected from the group consisting of iron, nickel, cobalt, platinum, gold, yttrium, rhodium, palladium, and an alloy containing a combination thereof.   5. The electrode body according to claim 1, wherein one end of the second carbon nanotube is connected to a side surface of the first carbon nanotube and the other end is connected to a side surface of another first carbon nanotube.   The electrode body according to claim 5, wherein the second carbon nanotube is synthesized on the side surface of the first carbon nanotube via the second catalytic metal.   The electrode body according to claim 6, wherein the second catalyst metal is selected from the group consisting of iron, nickel, cobalt, platinum, gold, yttrium, rhodium, palladium, and an alloy containing a combination thereof. A method for producing the electrode body according to any one of claims 1 to 7,
Providing first catalytic metal particles comprising a first catalytic metal on the surface of the conductor;
Synthesizing first carbon nanotubes through first catalytic metal particles;
Providing a second catalytic metal particle comprising a second catalytic metal on the side surface of the first carbon nanotube; and synthesizing a second carbon nanotube via the second catalytic metal particle;
A manufacturing method comprising:   The manufacturing method according to claim 8, wherein the first carbon nanotube and the second carbon nanotube are synthesized by a vapor phase chemical vapor deposition method. A pair of polarizable electrodes comprising the electrode body according to any one of claims 1 to 7,
The pair of polarizable electrodes are electric double layer capacitors provided so that the carbon nanotube layers are opposed to each other in a non-contact manner.

Images