WO2014077393A1

WO2014077393A1 - Cnt/non-woven composite capacitor

Info

Publication number: WO2014077393A1
Application number: PCT/JP2013/081058
Authority: WO
Inventors: 俊雄阿部
Original assignee: スペースリンク株式会社
Priority date: 2012-11-19
Filing date: 2013-11-18
Publication date: 2014-05-22
Also published as: JP3182172U

Abstract

In order to increase the electrostatic capacitance of electrodes in an electric double-layer capacitor, said electric double-layer capacitor comprises a separator, a pair of polarizable electrodes arranged on both surfaces of the separator, and a pair of collectors arranged in contact with the pair of polarizable electrodes on the side that is not facing the separator. The electric double-layer capacitor has an electrolyte impregnated into the polarizable electrodes and a carbon nanotube (CNT)-impregnated non-woven composite body is used for the polarizable electrodes.

Description

CNT / nonwoven composite capacitors

The present invention relates to a CNT / nonwoven fabric composite capacitor using carbon nanotubes having high electrical characteristics.

An electric double layer capacitor is an electric double layer capacitor that accumulates electricity by electrostatic adsorption and desorption of ions. Unlike a battery using a chemical reaction, an electric double layer capacitor uses a simple ion transfer to an electrode and an electrolyte and a charging phenomenon by physical adsorption. Rapid charge and discharge is possible, and it has high charge and discharge efficiency and semi-permanent cycle life characteristics.

As a structure of a general electric double layer capacitor, for example, a polarizable electrode material is applied on a collector electrode provided with a metal foil, and a polarizable electrode (anode) on the positive electrode side and an electrode (cathode) on the negative electrode side And these polarizable electrodes are combined with a separator (separation membrane) interposed therebetween. In this way, the capacitor composed of the anode / separation membrane / cathode is housed in a container, and then manufactured by injecting an electrolytic solution therein.

In the electric double layer capacitor having such a configuration, when a voltage of several volts is applied to the electrode where both ends of the polarizable electrode are connected, an electric field is formed, which causes ions in the electrolyte to move to the electrode surface. It is adsorbed and accumulates electricity.

The collector electrode is the base of the first polarizable electrode and is a component that plays an important role in collecting electricity. The collector electrode collects the charge of the polarizable electrode. In general, an aluminum foil or a copper foil is used as the metal foil to be joined to the collector electrode. Metal foil is used to improve conductivity.

An electric double layer capacitor is an electric double layer capacitor utilizing an interface phenomenon, and its capacitance increases as the surface area of the polarizable electrode interface increases. Therefore, conventionally, the electrode material has a large specific surface area. Activated carbon has been mainly used.

However, activated carbon having a large specific surface area generally has low electrical conductivity, and when only activated carbon is used as an electrode material for an electric double layer capacitor, the internal resistance of the electrode becomes too large, so that it can be used for taking out a large current. Is not suitable. Moreover, there existed the subject that a thing with a large electrostatic capacitance was not obtained and the vulnerability of a structure.

For this reason, carbon black or the like is generally mixed in the electrode in addition to activated carbon as a main component, mainly for the purpose of lowering the internal resistance of the electrode.

However, the higher the mixing ratio of materials other than activated carbon to increase conductivity, the lower the internal resistance, whereas the lower the mixing ratio of activated carbon, the lower the capacitance per unit mass of the capacitor. End up.

Therefore, in order to increase the conductivity and lower the internal resistance of the electrode and to improve the capacitance per unit mass, the following Patent Document 1 discloses that carbon nanotubes are mixed with activated carbon powder and carbon black. It has been proposed to obtain an electric double layer capacitor with improved capacitance by forming an electrode.

Further, Patent Document 2 below proposes to obtain a capacitor with high capacity and high charge / discharge speed by using a carbon nanotube film impregnated with an electrolyte as an electrode.

However, in spite of these ideas, until now, the performance of carbon nanotubes could not be fully exhibited, and commercialization has not progressed.

In recent years, electric double layer capacitors with high response have been expected for applications such as solar energy and wind power generation, which are used for clean energy storage systems. Development of an electric double layer capacitor that can be taken out is desired. Furthermore, many ignition and explosion accidents have occurred in secondary batteries that are currently mainstream, such as nickel-cadmium batteries, sodium-sulfur batteries, nickel-metal hydride batteries, and lithium-ion batteries. There are many accidents involving lithium-ion batteries. Therefore, at present, a safe large-capacity storage means cannot be found. For this reason, a safe electric storage element that does not use dangerous materials such as lithium, sodium, sulfur, and hydrogen is desired. Thus, although a capacitor using carbon nanotubes has been researched and developed, a capacitor having a low internal resistance, a large capacity, and a low cost has not yet been realized.

JP 2000-1224079 A JP 2008-44820 A

In view of the above background, the present invention eliminates the conventional problems and uses a carbon nanotube to reduce the internal resistance and to reduce the polarizable electrode capable of improving the capacitance per unit mass. The goal is to realize a high-performance electric double layer capacitor that is realized at low cost.

As a result of conducting various experimental studies to improve the performance of the electric double layer capacitor, the present inventor has immersed a multi-walled carbon nanotube (MWCNT) or a single-walled carbon nanotube (SWCNT) in a non-woven fabric, thereby obtaining a high-performance electrode. The present invention has been completed.

That is, the present invention is characterized by the following.

1. An electric double layer capacitor comprising a separator, a pair of polarizable electrodes on the positive electrode side and negative electrode side disposed on both sides of the separator, and a pair of polarizable electrodes on the side not facing the separator. A pair of collector electrodes on the positive electrode side and the negative electrode side, wherein the polarizable electrode is impregnated with an electrolyte solution, wherein the polarizable electrodes on the positive electrode side and the negative electrode side are carbon nanotubes ( CNT) impregnated in a nonwoven fabric. CNT. Which is a non-woven fabric composite. Nonwoven composite capacitor.

2. The non-woven fabric is a conductive non-woven fabric. Nonwoven composite capacitor.

3. The carbon nanotube is a multi-walled carbon nanotube. Nonwoven composite capacitor.

4. Any one of the above CNT. A non-woven composite capacitor, wherein the end surfaces of the pair of polarizable electrodes, the separator, and the pair of collector electrodes are hermetically bonded with an insulating material. Nonwoven composite capacitor.

5. Similarly, any one of the above CNT. A non-woven composite capacitor, in which CNT. Positive and negative polarizable electrodes made of a non-woven fabric composite are arranged, these are housed in a conductive case, a gasket is interposed between the case and the conductive lid, and the lid is covered And CNT. Nonwoven composite capacitor.

6. The CNT. Characterized in that a wave washer and a space are interposed between a positive polarizable electrode and a lid. Nonwoven composite capacitor.

As described above, the electric double layer CNT of the present invention. In the non-woven fabric composite capacitor, it has been confirmed that the use of the CNT / non-woven fabric composite as a polarizable electrode can realize a capacitance more than double that of a conventional CNT capacitor. This is considered to be due to the improved connection between CNTs, which has been a conventional problem, improved ion conductivity, and increased the amount of ions attached to the CNT surface. This effect is exhibited regardless of whether it is multilayer or single layer. In particular, multi-walled carbon nanotubes are inexpensive (about 30,000 yen per kilogram), and are overwhelmingly less expensive than expensive single-walled carbon nanotubes (200 million yen per kilogram). Therefore, the effect is great if the capacitor can be made stably with multi-walled carbon nanotubes.

By using a CNT / nonwoven fabric composite, it is possible to increase the storage capacity of an electric double layer capacitor using a conventional carbon nanotube electrode to nearly double. This has the effect of increasing the capacity in the present invention regardless of whether it is a multilayer or a single layer. Also, the internal resistance can be lowered to about 1/10 of the conventional one. This structure can be commonly used regardless of whether the CNT is a multilayer or a single layer.

That is, it is considered that CNTs are firmly bonded to each other on the fiber surface by adhering to the fiber surface of the nonwoven fabric by intermolecular force.

Nonwoven fabrics in CNT / nonwoven fabric composites (sheets entangled without weaving fibers) fibers include aramid fibers, glass fibers, cellulose fibers, nylon fibers, vinylon fibers, polyester fibers, polyolefin fibers, rayon fibers Inorganic, such as titanium oxide fiber, or various conductive polymer fibers such as polyaniline, polythiophene, and polyacetylene are used. In particular, titanium oxide fibers, cellulose fibers, and conductive polymer fibers are preferably used. This is because the lifetime of the device can be extended and the performance can be improved due to the fact that there is little reaction with the electrolytic solution and the conductivity is good. Among conductive non-woven fabrics, in particular, in the case of titanium oxide (TiO ₂ ) fiber, since the relative dielectric constant is as large as 40, there is an effect of increasing the dielectric constant in the electric double layer region. Therefore, there is an effect of increasing the capacitance.

As a method of impregnating a carbon nanotube into a nonwoven fabric, in the present invention, a method of generally immersing the nonwoven fabric in a solution of carbon nanotubes dispersed in water or a method of injecting a paste mixed with carbon nanotubes in water into the nonwoven fabric is preferably employed. Is done. For example, specifically, 1 g of carbon nanotube dispersed in 10 liters of water is mixed. The nonwoven fabric is dipped in this solution, taken out, dried and dipped. By repeating this cycle 5 times or more, the carbon nanotubes are attached to the non-woven fibers, and the conductivity is increased. Further, a paste in which 1 g of carbon nanotubes is mixed with 100 cc of water is prepared and injected into the nonwoven fabric with a syringe. The electrode is produced by drying the CNT / nonwoven fabric composite thus obtained. In such a process, since no chemicals are used, an effect of not deteriorating the electrolytic solution is produced.

According to the CNT / nonwoven fabric composite capacitor using the electrode according to the present invention, the internal resistance can be reduced, the capacitance can be increased several times, and a CNT / nonwoven fabric composite capacitor having a very large capacitance is realized. The Particularly important in this technology is that multi-walled carbon nanotubes can be supported by a nonwoven fabric, so that a low-cost (tens of tens of thousands of yen per kilogram), structurally strong, and large-capacity practical capacitors can be stably manufactured. It can be mass-produced with. Since the price of the material is about the same as that of the activated carbon capacitor, the performance ratio is excellent and it is competitive in the market.

It is a block diagram which shows the structural example of the conventional electrical double layer capacitor. It is sectional drawing which illustrated the CNT and the nonwoven fabric composite capacitor as embodiment of this invention. It is sectional drawing which illustrated the coin type CNT * nonwoven fabric composite capacitor which is other embodiments of the present invention. It is the assembly exploded view which illustrated the embodiment of another coin type CNT and nonwoven fabric composite capacitor. It is an example of a photograph of a measurement jig and an electrode. It is an example of experimental data which shows the discharge characteristic of the electrode in connection with this invention.

DESCRIPTION OF SYMBOLS 100 Electrode 101 Metal foil 102 Graphene layer 103 Carbon nanotube / graphene layer 104 Carbon nanotube layer 200 CNT / nonwoven fabric composite capacitor 201 CNT / nonwoven fabric composite positive electrode 202 CNT / nonwoven fabric composite negative electrode 203 Separator 204 Positive electrode collecting electrode 205 Negative electrode side collector electrode 206 Metal foil 207 Insulating material 300 Coin type CNT / nonwoven fabric composite capacitor 302 CNT / nonwoven fabric composite positive electrode 303 CNT / nonwoven fabric composite negative electrode 304 Conductive adhesive 305 Case 306 Lid 307 Separator 308 Gasket 309 Wave washer 310 Spacer 401 Discharge Characteristics of Multi-Wall Carbon Nanotube Capacitor 402 Discharge Characteristics of CNT / Nonwoven Fabric Composite Capacitor Using Multi-Wall Carbon Nanotubes 403 Single-Wall Carbon Nano Discharge characteristics of CNT · nonwoven composite capacitor using a discharge characteristic 404 SWNTs Yubukyapashita

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, FIG. 1 illustrates a configuration of a conventional capacitor in a cross-sectional view.
In the conventional electrode, a graphene layer 102 is formed by applying graphene dispersed in an extremely fine manner with ultrasonic waves on the surface of the metal foil 101 to form a graphene layer 102, and further, a slurry is obtained by combining carbon nanotubes and graphene on the surface. A method of forming and applying the carbon nanotube / graphene layer 103 to form the carbon nanotube layer 104 on the surface of the carbon nanotube / graphene layer 103 has been adopted. In this method, the ionic conductivity of the carbon nanotube layer 104 is inhibited, and the amount of stored charge cannot be increased as expected. Therefore, the limit of the electrostatic capacity that can be realized is 20 F / g to 40 F / g in terms of electrode material. Moreover, since the connection of CNT does not work well, it is difficult to increase the size and the structure is unstable. That is, when trying to make a business card size or larger electrode, the CNT connection in the surface direction could not be sufficiently secured, and the internal resistance did not increase or the capacitance did not increase.

On the other hand, FIG. 2 is a sectional view of a CNT / nonwoven fabric composite capacitor 200 as one embodiment of the present invention.

The positive side CNT / nonwoven fabric composite positive electrode 201 is disposed on the front side of the separator 203, and the negative side CNT / nonwoven fabric composite negative electrode 202 is disposed on the back side. These polarizable electrodes are joined to positive and negative polarizable electrodes, each of a positive collector electrode 204 and a negative collector electrode 205. Further, a metal foil 206 is bonded to the surfaces of these collector electrodes.

The insulating material 207 is applied and sealed along the end surfaces of the CNT / nonwoven fabric composite positive electrode 201, the CNT / nonwoven fabric composite negative electrode 202, the separator 203, and the

collector electrodes

204 and 205. As the insulating material, a silicon adhesive, an acrylic, a Teflon (registered trademark) adhesive, or the like can be used, and a silicon or Teflon (registered trademark) adhesive having excellent chemical resistance is preferably used.

FIG. 3 is a cross-sectional view of a CNT / nonwoven fabric composite capacitor 300 as another embodiment of the present invention. As shown in the figure, a CNT / nonwoven fabric composite positive electrode 302 and a CNT / nonwoven fabric composite negative electrode 303 made of a CNT / nonwoven fabric composite are formed by shaping a CNT / nonwoven fabric composite into a circle having a diameter of about 13 mm.

The CNT / nonwoven fabric composite negative electrode 303 and the CNT / nonwoven fabric composite positive electrode 302 are respectively bonded to a stainless steel container case 305 and a stainless steel container lid 306 using a conductive adhesive 304.

A cellulose-based or conductive polymer-based material is suitably used for the nonwoven fabric. A two-component epoxy / silver adhesive is preferably used as the conductive adhesive.

The CNT / nonwoven fabric composite negative electrode 303 adhered to the case 305 and the CNT / nonwoven fabric composite negative electrode 302 adhered to the lid 306 are annealed with ultraviolet rays and further dried at 120 to 200 ° C. under reduced pressure for 2 to 4 hours. After that, both electrodes are impregnated with an electrolyte in a glove box in a dry nitrogen atmosphere. The electrolytic solution can be produced by dissolving tetraethylammonium tetrafluoroborate in propylene carbonate at a concentration of 2 to 3 mol / L. There are various variations of this electrolytic solution, such as adding an ionic liquid or sulfonic acid.

Next, the CNT / nonwoven fabric composite electrode impregnated with the electrolytic solution is opposed to each other through a nonwoven fabric separator 307 and caulked with a polypropylene gasket 308, and the coin-shaped CNT / nonwoven fabric composite capacitor according to this embodiment is used. 300 is configured.

The obtained coin-shaped CNT / nonwoven fabric composite capacitor 300 according to the present embodiment is charged and discharged with a constant current of an upper limit voltage of 3 V and 1 mA as shown in FIG. When the capacitance and the internal resistance were measured, the result was, for example, that the capacitance was 3 V, the voltage was 3 V, the discharge current was 1 mA, the discharge time was 88 minutes, and the CNT / nonwoven fabric composite was used 80 mg. . Based on this numerical value, the electrostatic capacity per gram is calculated according to the following formula (1), and the large capacity of 88 F / g greatly exceeds 30-40 F / g, which is the typical performance of the conventional carbon nanotube capacitor. Realized. The energy density is calculated by the following formula (2). When calculated including the separator and the electrolyte, the energy density is 92 to 179 Wh / Kg. The internal resistance was confirmed to be within 2 milliohms. FIG. 6 compares the characteristics of various batteries and the CNT / nonwoven fabric composite capacitor of the present invention. As can be seen, it is possible to exhibit sufficient performance without using metal.

Also, since it has a large capacity and the internal resistance can be reduced to 2 milliohms or less, the conventional sense that the internal resistance of the large-capacitance capacitor is large and the internal resistance of the small-capacitance capacitor is small.

Thus, it was confirmed that it was possible to stably produce card-type or coin-shaped CNT / nonwoven fabric composite capacitors. Although the structure is simple, the performance is extremely excellent and stable, and the value of the present invention is considered high.

Furthermore, the CNT / nonwoven fabric composite capacitor is resistant to charge / discharge cycle deterioration, and the storage capacity is only deteriorated within 2% even after 10,000 charge / discharge cycles. Furthermore, the carbon nanotubes that are formed are nonflammable, and the electrolyte can be made nonflammable when an ionic liquid is used. This can be avoided from the danger of heating and ignition.

In the manufacturing process, the electrode material is subjected to an acid treatment, the purpose of which is to remove impurities and add functional groups. Next, as an annealing process, the electrodes are irradiated with ultraviolet rays in an ammonia atmosphere. This step is to reduce the functional group. By performing such treatment, the electrode exhibits high conductivity, the internal resistance can be reduced, and the performance is improved.

FIG. 4 illustrates still another embodiment. The structure is slightly different from the coin-shaped CNT / nonwoven fabric composite capacitor of FIG. 3, and a spacer and a wave washer are added.

As shown in the figure, a CNT / nonwoven fabric composite positive electrode 302 and a CNT / nonwoven fabric composite negative electrode 303 made of a CNT / nonwoven fabric composite electrode are formed by shaping a CNT / nonwoven fabric composite into a circle having a diameter of about 13 mm. The configuration up to this point is the same as in FIG.

The CNT / nonwoven fabric composite negative electrode 303 is adhered to the case 305 with a conductive adhesive 304 using a conductive adhesive 304. The CNT / nonwoven fabric composite positive electrode 302 is similarly bonded to a stainless steel spacer 307. A wave washer 310 having a spring structure is placed on the upper portion of the spacer, and a lid 306 is further covered. The lid 306 and the case 305 are joined and integrated by caulking.

The CNT / nonwoven fabric composite negative electrode 303 is electrically connected to the case 305 of the stainless steel container, and the CNT / nonwoven fabric composite negative electrode 302 is electrically connected to the cover 306 of the stainless steel container.

A cellulose-based or conductive polymer-based material is suitably used for the nonwoven fabric. Further, the two-component epoxy / silver adhesive is preferably used as the conductive adhesive zs agent as in the second embodiment.

The manufacturing process is the same as in Example 2. The difference is that a spacer 310 and a wave washer 309 are inserted between the lid 306 on the positive electrode side and the CNT / nonwoven fabric composite positive electrode 302.
As a result, electrical connection between the electrode and the cap 306 and the case 305 is ensured, and stable performance is exhibited.

In order to measure the capacitance of the electric double layer capacitor, the electrode and separator were housed in a measurement jig as shown in FIG. The result is shown in FIG.

When a conventional capacitor using multi-walled carbon nanotubes was measured for comparison, as shown by 401 in FIG. 6, the discharge current was 1 mA, the discharge time was 60 minutes, and the discharge start voltage was 3 v. When calculated by the following formula (1) and converted per unit gram, it is about 15 F / g. When the CNT / nonwoven fabric composite capacitor using the multi-walled carbon nanotube of the present invention was measured, a discharge characteristic having a curve 402 was obtained. From this, it was confirmed that it increased to 30 F / g.

Furthermore, the measurement result of a conventional single-walled carbon nanotube capacitor was 403, and 40 F / g was obtained. When the CNT / nonwoven fabric composite capacitor using single-walled carbon nanotubes was measured, the discharge characteristic indicated by curve 404 was obtained, and 50 F / g was obtained.

It was confirmed that the use of the nonwoven fabric-impregnated CNT electrode increased the electrostatic capacity. In addition to this effect, it was confirmed that the internal resistance was reduced to a fraction of the conventional value.
Further, since this CNT / nonwoven fabric composite capacitor is made of a non-combustible material, there is no risk of explosion or combustion unlike a lithium ion battery. Looking at the current situation in which lithium-ion batteries have caused many fires and explosions and many recalls have occurred around the world, it is highly necessary to develop and put into practical use safe batteries as soon as possible.

The present invention is not limited to the above-described embodiments, and various modifications can be made.

If a CNT / nonwoven fabric composite capacitor is provided to society, a conventional storage battery can be reduced in size and weight, and can be used as an ideal storage element having a long life and high safety. The market availability is as follows.
(1) New energy vehicle market Effective as a storage battery for hybrid cars, electric cars, and fuel cell cars.
(2) Effective for leveling the amount of power generated by wind turbine generators, where the wind power market is volatile.
(3) Solar power generation market Same as wind power.

In addition, the use will be expanded to long-life batteries for aerospace and safe and long-life batteries for medical use.

Claims

An electric double layer capacitor having a separator, a pair of polarizable electrodes on the positive electrode side and negative electrode side disposed on both surfaces of the separator, and a side of each of the pair of polarizable electrodes that does not face the separator An electric double layer capacitor having a pair of positive electrode and negative electrode collectors disposed therein, the electrode being impregnated with an electrolyte, wherein the polarizable electrodes on the positive electrode side and the negative electrode side are carbon nanotubes (CNT ) And a non-woven fabric composite impregnated in a non-woven fabric. Nonwoven composite capacitor.
The CNTs according to claim 1, wherein the nonwoven fabric is a conductive nonwoven fabric. Nonwoven composite capacitor.
The carbon nanotubes are multi-walled carbon nanotubes. Nonwoven composite capacitor.
The CNT according to any one of claims 1 to 3. A non-woven fabric composite capacitor, characterized in that the pair of polarizable electrodes, the separator, and the end surfaces of the pair of collector electrodes are hermetically bonded with an insulating material.
The CNT according to any one of claims 1 to 3. A non-woven fabric composite capacitor, characterized in that it has a structure in which a conductive case is sealed between conductive caps with a gasket.
6. The CNT / nonwoven fabric composite capacitor according to claim 5, wherein a wave washer and a spacer are inserted between the CNT / nonwoven fabric composite positive electrode and the lid.