WO2014192776A1

WO2014192776A1 - Electrode, electric double-layer capacitor using said electrode, and method for manufacturing said electrode

Info

Publication number: WO2014192776A1
Application number: PCT/JP2014/064035
Authority: WO
Inventors: 大輔堀井; 修一石本; 覚爪田
Original assignee: 日本ケミコン株式会社
Priority date: 2013-05-27
Filing date: 2014-05-27
Publication date: 2014-12-04
Also published as: JP2014229886A; CN105247640A; JP6375593B2; CN105247640B

Abstract

This invention provides the following: an electrode comprising a mix of a carbon powder and fibrous carbon wherein the impact of a resin binder or the like is eliminated, the electrical resistance of said electrode is reduced, and said electrode exhibits superb capacity characteristics; an electric double-layer capacitor using said electrode; and a method for manufacturing said electrode. Said method has the one of following steps: a dispersion step in which fibrous carbon and a carbon powder having a grain diameter of less than 100 nm are dispersed in a solvent; or a dispersion step in which fibrous carbon and a carbon powder that has a grain diameter of at least 100 nm but less than 10 µm and has been treated so as to be made porous are dispersed in a solvent via either a process in which jets of a solution are made to collide with each other or a process in which shear stress and centrifugal force are applied to said solution. Said method also has an electrode formation step, after the dispersion step, in which a collector is coated with the solution resulting from the dispersion step, yielding a layer comprising a carbon-powder/fibrous-carbon mix.

Description

Electrode, electric double layer capacitor using the electrode, and method for manufacturing electrode

The present invention relates to an electrode using a carbon material, an electric double layer capacitor using the electrode, and a method for manufacturing the electrode. In particular, carbon powder and fibrous carbon are used as the carbon material.

Conventionally, an electric double layer capacitor is composed of a pair of electrodes, a separator existing between them, and a current collecting layer of each electrode. Activated carbon is used as a typical electrode used in the electric double layer capacitor.

The manufacturing method of the electrode used for this electric double layer capacitor is a binder of a conductive material such as acetylene black and a resin such as polytetrafluoroethylene or tetrafluoroethylene resin to activated carbon powder which is a typical electrode material. A method of forming a sheet-like polarization electrode by press molding after adding and mixing is known. In addition to this, there is a method (coating method) in which the mixture is contained in a solvent and applied to a current collector.

Such an electric double layer capacitor has a problem of a decrease in capacity during standing at high temperature, which is considered to be caused by a reaction due to a functional group on the surface of activated carbon. Proposals have been made to solve this problem (Patent Document 1).

Therefore, for the purpose of increasing the capacity, an attempt has been made to create a polarizable electrode by mixing activated carbon with a particle size exceeding 1 μm and a resin binder and then applying the mixture on a current collector, and using it for an electric double layer capacitor. Yes (Patent Document 2).

JP 2001-237149 A JP 2000-1224079 A

In the electrode of such an electric double layer capacitor, the activated carbon has a large particle diameter, so the diffusion resistance increases, and the internal resistance and low temperature characteristics deteriorate. Further, when forming an electrode with activated carbon having a large particle size and a binder, if a resin binder is used alone as the binder, it is difficult to increase the electrode density, which is disadvantageous in terms of lowering the resistance.

Accordingly, an object of the present invention is to provide an electrode having a high electrode density and a low diffusion resistance, an electric double layer capacitor using the electrode, and an electrode manufacturing method in an electrode in which carbon powder and fibrous carbon are mixed. It is.

In order to achieve the above object, the electrode of the present invention is applied to a current collector by applying a solution in which porous carbon powder having an average particle diameter of less than 100 nm and fibrous carbon are dispersed to a current collector. It was obtained by drying. In the electrode obtained by applying a mixed solution of carbon powder and fibrous carbon on the current collector and removing the solvent, the fibrous carbon plays a role as a binder, and the carbon powder is uniformly dispersed. Can be held in. Fibrous carbon can also be used in combination with resin binders, so even when resin binders are used, resin binders can be used at a rate that is less likely to affect electrical resistance. Since it is possible to eliminate the influence of the resin binder on the electric resistance, it is possible to reduce the electric resistance of the obtained electrode.

The carbon powder may be obtained by activating carbon black.

Carbon powder and fibrous carbon are highly dispersed, and the electrode density can be 0.48 g / cc or more.

The fibrous carbon may be contained in an amount of 10 to 55% by weight based on the total amount of carbon powder and fibrous carbon.

The proportion of mesopores in the pores in the porous carbon powder may be in the range of 5 to 30%.

The particle size distribution of the carbon powder constituting the electrode and the aggregate of fibrous carbon has a single peak, and the ratio between the particle size of 50% cumulative value D50 and the particle size of 90% cumulative value D90 of the particle size distribution. D90 / D50 may be 2.5 or less.

The particle diameter of the 90% cumulative value D90 of the particle size distribution may be less than 150 μm.

The interval between the fibrous carbons constituting the electrode may be 2 μm or less.

Also, a treatment for causing the jetting of the solution to collide with the porous carbon powder having an average particle size of 100 nm or more and less than 10 μm and fibrous carbon, or a treatment for applying shear stress and centrifugal force to the solution The dispersion may be obtained by dispersing in a solution and applying the dispersed solution on a current collector and removing the solvent.

An electric double layer capacitor in which this electrode is formed on a current collector is also an embodiment of the present invention.

Furthermore, since the said objective can be achieved, the manufacturing method of the electrode of this invention includes the following processes.
(1) A dispersion step of dispersing a porous carbon powder having an average particle diameter of less than 100 nm and fibrous carbon in a solvent.
(2) An electrode forming step of applying the solution obtained in the dispersing step onto a current collector, removing the solvent, and forming a carbon powder / fibrous carbon mixed layer on the current collector.

According to the present invention, in an electrode obtained by applying a solution in which carbon powder and fibrous carbon are dispersed on a current collector and removing the solvent, the electrode density can be increased and the internal resistance can be decreased. it can. Therefore, an excellent electrode having a large capacity and a small electric resistance and an electric double layer capacitor using the electrode can be obtained.

It is a flowchart which shows the manufacturing process of the electrode which concerns on this embodiment. An SEM (× 40.00k) image of the coating layer of carbon powder / fibrous carbon obtained by applying a solution in which carbon powder and fibrous carbon are dispersed on a current collector by a mixer and removing the solvent. is there. A SEM (× 40.00k) image of a coating layer of carbon powder / fibrous carbon obtained by applying a solution in which carbon powder and fibrous carbon are dispersed by a ball mill on a current collector and removing the solvent. is there. SEM (× 40.00k) of coating layer of carbon powder / fibrous carbon obtained by applying a solution in which carbon powder and fibrous carbon are highly dispersed by jet mixing on a current collector and removing the solvent It is a statue. An SEM (× 40.00k) of a coating layer of carbon powder / fibrous carbon obtained by applying a solution in which carbon powder and fibrous carbon are highly dispersed by ultracentrifugation to a current collector and removing the solvent. ) It is a conceptual diagram which shows the structure of the laminate type electrical double layer capacitor which concerns on this embodiment. It is a figure which shows the particle size distribution of the carbon powder of Examples 1-3 of this embodiment.

Hereinafter, embodiments for carrying out the present invention will be described. In addition, this invention is not limited to embodiment described below.

As shown in FIG. 1, the electrode of this embodiment is manufactured by the following steps (1) and (2).
(1) A dispersion step of dispersing carbon powder and fibrous carbon in a solvent.
(2) A coating layer forming step of applying the solution obtained in the dispersing step onto a current collector, removing the solvent, and forming a carbon powder / fibrous carbon coating layer on the current collector.
Hereinafter, the steps (1) and (2) will be described in detail.

(1) Dispersing step In the dispersing step, carbon powder and fibrous carbon are dispersed in a solvent.

The carbon powder used in the present embodiment expresses the main capacity of the electrode. The types of carbon powder include natural plant tissues such as palm, synthetic resins such as phenol, activated carbon derived from fossil fuels such as coal, coke and pitch, ketjen black (hereinafter referred to as KB), acetylene. Examples thereof include carbon black such as black and channel black, carbon nanohorn, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, activated carbon, and mesoporous carbon.

The carbon powder is preferably used after being subjected to a porous treatment such as activation treatment or opening treatment. The carbon powder activation method varies depending on the raw material used, but conventionally known activation treatments such as a gas activation method and a drug activation method can be usually used. Examples of the gas used in the gas activation method include water vapor, air, carbon monoxide, carbon dioxide, hydrogen chloride, oxygen, or a gas composed of a mixture thereof. In addition, as a chemical used in the chemical activation method, alkali metal hydroxide such as sodium hydroxide and potassium hydroxide; alkaline earth metal hydroxide such as calcium hydroxide; boric acid, phosphoric acid, sulfuric acid, hydrochloric acid Inorganic acids such as zinc chloride; or inorganic salts such as zinc chloride. In this activation treatment, the carbon powder is heat-treated as necessary. In addition to these activation treatments, an opening treatment for forming holes in the carbon powder may be used.

The carbon powder preferably has a specific surface area in the range of 600 to 2000 m ² / g. The carbon powder preferably has an average primary particle size of less than 10 μm, and particularly preferably less than 100 nm. In particular, when the average particle size of the carbon powder is less than 100 nm, the diffusion resistance is low and the conductivity is high because the particle size is very small. Moreover, since the specific surface area by the porous treatment is large, a high capacity expression effect can be expected. If the average particle diameter of the carbon powder is larger than 100 nm, the ion diffusion resistance in the carbon powder particles increases, and the resistance of the resulting capacitor increases. On the other hand, considering the agglomeration state of the carbon powder, the average particle diameter is preferably 5 nm or more. In addition, the improvement of electrical conductivity is obtained by taking the form which connected the very small carbon powder which made the average particle diameter less than 100 nm individually (in a daisy chain form). As the carbon powder, activated carbon black is particularly preferable. Moreover, even when the average particle diameter of the carbon powder is less than 10 μm, the effects of the present invention can be achieved by the ultracentrifugation process and the jet mixing process described later as the dispersion method.

The electrical conductivity of the carbon powder is preferably in the range of 20 to 1000 S / cm. By setting it as such high conductivity, the obtained electrode can be made low resistance. As a method for evaluating the conductivity of the carbon powder, the following electrical conductivity during compression is used. Here, the electrical conductivity during compression refers to the thickness when the carbon powder is sandwiched between the electrodes having a cross-sectional area A (cm ² ) and then compressed and held by applying a constant load to h (cm). Then, the resistance R (Ω) of the compressed carbon powder was determined by applying a voltage to both ends of the electrode to measure the current, and the value was calculated using the following calculation formula (1).

Electrical conductivity during compression (S / cm) = h / (A x R) ··· Formula (1)
In the formula (1), A indicates the cross-sectional area (cm ² ) of the electrode, and h indicates the thickness when the carbon powder is sandwiched between the electrodes and a certain load is applied to this to compress and hold until the volume does not change. (Cm), R represents the resistance (Ω) of the compressed carbon powder.

The weight of the carbon material used for the measurement may be an amount that is compressed and held between the electrodes, and the load during compression is such that the shape of the carbon powder does not break and the volume change of the carbon powder. Any load that can be compressed to such an extent that there is no need is present.

Furthermore, when the average particle diameter of the carbon powder is less than 100 nm, the proportion of the mesopores (diameter 2 to 50 nm) occupied in the pores of the carbon powder is preferably in the range of 5 to 55%. When the proportion of mesopores is less than 5%, there is a problem that it is difficult to expect a reduction in resistance, and when the proportion of mesopores exceeds 55%, there is a problem that it is difficult to manufacture. In general activated carbon, the proportion of micropores (diameter less than 2 nm) is 95% or more, whereas carbon powder having an average particle size of carbon powder of less than 100 nm is mesopore (diameter 2-50 nm), macropores. The ratio (over 50 nm in diameter) is relatively large.

In general activated carbon, a large average particle diameter of several microns is used to increase the surface area, and many fine diameters (micropores) are provided. A large number of pores are formed inside the particle, and the area of the inner surface of the particle is about 80% of the entire particle (specific surface area). Ions in the electrolyte must enter the deep part of the pores of the particles, and the diffusion resistance tends to be high. With this activated carbon, it is difficult to reduce the resistance.

On the other hand, when the average particle diameter of the carbon powder is less than 100 nm, since the diameter is extremely small, the distance to the deep part of the pores of the particles is short, and ions in the electrolytic solution easily move. Therefore, the diffusion resistance is low and the conductivity is high. Further, the specific surface area is large due to the porous treatment. In particular, by increasing the ratio of the small particle diameter and relatively large pores (mesopores) to the above 5 to 55%, ions are more easily moved and diffusion resistance can be further reduced.

The fibrous carbon used in this embodiment can efficiently entangle extremely small nano-sized carbon powder between the fibers, and plays a role of a binder. Examples of the type of fibrous carbon include fibrous carbon such as carbon nanotubes (hereinafter referred to as CNT) and carbon nanofibers (hereinafter referred to as CNF). In addition, you may use the opening process and activation process which make a hole in the front-end | tip and wall surface of fibrous carbon also with respect to this fibrous carbon.

The CNT used as the fibrous carbon may be a single-walled carbon nanotube with a single graphene sheet, or a multi-walled carbon nanotube (MWCNT) in which two or more graphene sheets are rounded coaxially and the tube wall forms a multilayer, May be mixed. Moreover, since the capacity density of CNT itself is so high that there are few layers of the graphene sheet of CNT, CNT of the number of layers is 50 layers or less, Preferably the range of 10 layers or less is preferable from the point of capacity density.

The outer diameter of the fibrous carbon is desirably 1 to 100 nm, preferably 2 to 70 nm, and more preferably 3 to 40 nm. The length of the fibrous carbon is preferably 50 to 1000 μm, preferably 70 to 500 μm, more preferably 100 to 200 μm.

The specific surface area of the fibrous carbon is 100 to 2600 m ² / g, preferably 200 to 2000 m ² / g. If the specific surface area is larger than 2600 m ² / g, the formed electrode tends to expand, and if it is smaller than 100 m ² / g, the desired electrode density is hardly increased.

Note that the particle diameter and outer shape of the carbon powder and fibrous carbon were measured by ASTM D3849-04 (also referred to as ASTM particle diameter).

The content of the carbon powder and the fibrous carbon is preferably 5 to 50% by weight, particularly 10 to 30% by weight of the fibrous carbon based on the total amount of the carbon powder and the fibrous carbon. If the fibrous carbon exceeds 50% by weight, the electrode itself swells when it is impregnated with the electrolytic solution, which presses the outer case and easily causes the case to swell. On the other hand, if the amount of fibrous carbon is less than 5% by weight, the aggregate of the carbon powder tends to be large and the internal resistance tends to increase. In addition, you may contain the arbitrary component in the range which does not impair the objective of this invention. For example, a dispersing agent, other binders, etc. are mentioned. Other binders include polyvinyl alcohol, carboxymethyl cellulose, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, acrylonitrile butadiene rubber, and tetrafluoroethylene-hexafluoropropylene. Polymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PEA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer Polymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafur Ethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, and There is a mixture of them. Of these, polytetrafluoroethylene and polyvinylidene fluoride are preferable. These resin binders are desirably 3% or less based on the total amount of carbon powder, fibrous carbon, and resin binder. If it exceeds this, the internal resistance tends to increase due to the resin binder.

Examples of the solvent for dispersing carbon powder and fibrous carbon in the present embodiment include alcohols such as methanol, ethanol and 2-propanol, hydrocarbon solvents, aromatic solvents, N-methyl-2-pyrrolidone (NMP), and the like. Various solvents such as amide solvents such as N, N-dimethylformamide (DMF), water, those using these solvents singly or those containing two or more types can be used. Moreover, you may add additives, such as a dispersing agent, in this solvent.

In the dispersion step of the present embodiment, carbon powder and fibrous carbon are added to a solvent, and a dispersion treatment is performed on the mixed solution. In addition, you may perform a dispersion process in the state which added the above-mentioned resin binder as an arbitrary component to this mixed solution. By performing the dispersion treatment, the carbon powder and the fibrous carbon in the mixed solution are subdivided and homogenized, and dispersed in the solution. That is, the fibrous carbon in the mixed solution before the dispersion treatment is in a state where the carbon fibers are entangled (bundle shape). By performing the dispersion treatment, the bundle of fibrous carbon is broken and the fibrous carbon is dispersed in the solution. As a dispersion method, a mixer, jet mixing (jet collision), ultracentrifugation, or other ultrasonic treatment is used. Among these, considering the high dispersion of carbon powder and fibrous carbon and the improvement of the electrode density of the obtained electrode, the mixing method is preferably jet mixing or ultracentrifugation. By using such jet mixing or ultracentrifugation, the aggregate of the carbon material is subdivided and the aggregation of the carbon material having an extremely small particle diameter is suppressed, and an electrode having a low internal resistance can be obtained.

In the dispersion method using a mixer, physical force is applied to a mixed solution containing carbon powder and fibrous carbon by a bead mill, rod mill, roller mill, stirring mill, planetary mill, vibration mill, ball mill, homogenizer, homomixer, etc. In addition, the carbon powder and the fibrous carbon in the solution are subdivided by stirring. By applying an external force to the carbon powder, the agglomerated carbon powder can be subdivided and homogenized, and entangled fibrous carbon can be solved. Among these, a ball mill capable of obtaining a grinding force is preferable.

In the dispersion method by jet mixing, a pair of nozzles are provided at positions facing each other on the inner wall of the cylindrical chamber. A mixed solution containing carbon powder and fibrous carbon is pressurized by a high-pressure pump and sprayed from a pair of nozzles to cause a frontal collision in the chamber. Thereby, the bundle of fibrous carbon is pulverized, and can be dispersed and homogenized. As conditions for jet mixing, the pressure is preferably 100 MPa or more and the concentration is less than 5 g / l.

In the dispersion method using ultracentrifugation, ultracentrifugation is performed on a mixed solution containing carbon powder and fibrous carbon. In ultracentrifugation, shear stress and centrifugal force are applied to the carbon powder and fibrous carbon of the mixed solution in a rotating container.

The ultracentrifugation process is performed, for example, by a container including an outer cylinder having a claw plate at an opening and a rotating inner cylinder having a through hole. By introducing the mixed solution into the inner cylinder of this container and turning the inner cylinder, the carbon powder and fibrous carbon inside the inner cylinder move to the inner wall of the outer cylinder through the through hole of the inner cylinder by the centrifugal force. . At this time, the carbon powder and the fibrous carbon collide with the inner wall of the outer cylinder by the centrifugal force of the inner cylinder, and form a thin film and slide up to the upper part of the inner wall. In this state, both the shear stress between the inner wall and the centrifugal force from the inner cylinder are simultaneously applied to the carbon powder and the fibrous carbon, and a large mechanical energy is applied to the carbon powder and the fibrous carbon in the mixed solution. Become.

In this ultracentrifugation process, mechanical energy of both shear stress and centrifugal force is simultaneously applied to the carbon powder and fibrous carbon in the mixed solution, so that the mechanical energy is reduced to the carbon powder and Uniform and subdivide the fibrous carbon.

The dispersion treatment is preferably performed on a mixed solution in which carbon powder and fibrous carbon are mixed. However, a solution in which fibrous carbon is added separately is prepared, the dispersion treatment is performed on this solution, and the bundle is formed. The melted fibrous carbon may be obtained, and the fibrous carbon and carbon powder may be mixed to obtain a mixed solution. Alternatively, a solution in which carbon powder is separately added is prepared, and a dispersion treatment is performed on the solution to obtain a finely divided carbon powder. The carbon powder and fibrous carbon may be mixed to obtain a mixed solution. . Furthermore, a solution in which fibrous carbon is separately added is prepared, and dispersion treatment is performed on this solution to obtain a fibrous carbon in which the bundle has been broken. Similarly, a solution in which carbon powder is separately added is prepared. Alternatively, dispersion treatment may be performed to obtain finely divided carbon powder, and these fibrous carbon and carbon powder may be mixed to obtain a mixed solution. These mixed solutions may be subjected to dispersion treatment.

Further, this electrode may contain various additives. Examples thereof include solid acids such as amorphous silica alumina and amorphous silica magnesia, gas absorbents, and the like.

(2) Coating layer forming step In the coating layer forming step, the mixed solution that has been subjected to the dispersion step is applied onto the current collector, and the solvent is removed by drying, thereby coating the current collector with carbon powder / fibrous carbon. An electrode having a layer formed can be obtained.

As a method of applying the mixed solution on the current collector, there is a method of coating the current collector with the mixed solution (various coating methods such as dip coating, spray coating, and ink jet coating are used). In the coating, a bar coater or a coater is used to apply the mixed solution on the current collector with a uniform thickness. Thereafter, the mixed solution is dried. As a result, the solvent in the mixed solution is removed, and a coating layer as a mixed layer of carbon powder / fibrous carbon in which carbon powder and fibrous carbon are deposited is formed on the current collector. Furthermore, an electrode is produced by pressing from the up-down direction of the current collector and the coating layer, so that the coating layer bites into the uneven surface of the current collector and is integrated. The thickness of the coating layer formed on this current collector is preferably about 10-40 μm. When the SEM image of this coating layer is observed, the distance between the fibrous carbon and the fibrous carbon is 2 μm or less. The carbon powder is dispersed and supported in fibrous carbon with an interval of 2 μm or less. For pressing the current collector and the coating layer, a vertical press or a roll press can be used.

The current collector used in this embodiment can use a conductive material. Examples of the conductive material used as the current collector include aluminum foil, platinum, gold, nickel, titanium, steel, and carbon. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted. Further, the surface of the current collector may be formed with an uneven surface by etching or the like in advance, or may be a plain surface. In addition, in order to improve the adhesiveness with the coating layer of carbon powder / fibrous carbon on the surface of these current collectors, an adhesive layer made of a conductive material can be formed in advance.

FIG. 2 is an SEM (× 40.00 k) of a coating layer of carbon powder / fibrous carbon prepared from a solution in which carbon powder (carbon black) and fibrous carbon (CNT) are dispersed by a mixer in the dispersion step. It is a statue.
FIG. 3 is an SEM (× 40.00 k) image of a coating layer of carbon powder / fibrous carbon produced from a solution in which carbon powder (carbon black) and fibrous carbon (CNT) are highly dispersed by a ball mill. is there.
FIG. 4 shows an SEM (× 40.00k) image of a coating layer of carbon powder / fibrous carbon produced from a solution in which carbon powder (carbon black) and fibrous carbon (CNT) are highly dispersed by jet mixing. It is.
FIG. 5 shows an SEM (× 40.00 k) of a coating layer of carbon powder / fibrous carbon prepared from a solution in which carbon powder (carbon black) and fibrous carbon (CNT) are highly dispersed by ultracentrifugation. It is a statue.

As shown in FIGS. 3 to 5, in the carbon powder / fibrous carbon coating layer, the fibrous carbon is carried around the carbon powder. Carbon powder / fibrous carbon coating layer prepared from a mixed solution dispersed by a mixer, carbon powder / fibrous carbon coating layer prepared from a mixed solution dispersed by jet mixing, dispersion by ultracentrifugation It can be seen that the shape of the surface of the coating layer becomes denser in the order of the carbon powder / fibrous carbon coating layer produced from the treated mixed solution.

Moreover, as shown in FIG. 2, in the carbon powder / fibrous carbon coating layer prepared from the solution dispersed by the mixer (homogenizer), the fibrous carbon (CNT) is sparse and the fibrous carbon (CNT) is The interval is wide. That is, in the dispersion treatment by the mixer, the amount of bundled fibrous carbon (CNT) bundles that can be unwound is small, so that the fibrous carbon (CNT) becomes sparse and the gap between the CNTs becomes large. For this reason, it is difficult for the carbon powder to be uniformly dispersed and supported on the fibrous carbon.

In FIG. 2, there is a portion where the distance between the CNTs is short, such as a gap A between the CNT (1) and the CNT (2). However, like the region B between the CNT (1) and the CNT (4), the CNT There is a region where is not observed in the SEM image. In such a region B, the gap C between the CNTs is not less than 2 μm. That is, it can be seen that CNTs are not sufficiently dispersed and sparse. Further, the carbon powder is not sufficiently subdivided, and the aggregate of the carbon powder exists in a large state exceeding 3 μm. Since large aggregate carbon powder is supported on sparse CNTs, the carbon powder is not uniformly dispersed and supported on the CNTs, and it is difficult to improve electrode capacity and internal resistance. The gap between the CNTs in the region B was observed with an SEM image and calculated as the maximum linear distance in the region where no CNTs existed.

On the other hand, as shown in FIGS. 3 to 5, in the carbon powder / fibrous carbon coating layer formed from a solution dispersed by a ball mill, jet mixing, or ultracentrifugation, fibrous carbon (CNT) is used. Are dense and the spacing between fibrous carbons (CNTs) is also narrow. That is, in the dispersion process by ball milling, jet mixing, or ultracentrifugation, bundles of fibrous carbon (CNT) are sufficiently unwound, so that the network of fibrous carbon (CNT) is dense. Also, the carbon powder itself is broken by these dispersion treatments, and the aggregate state of the carbon powder is broken down into small aggregates. The dense mesh-like fibrous carbon is supported in a state of agglomerated carbon powder, and the carbon powder and fibrous carbon are uniformly dispersed.

Further, in FIGS. 3 to 5, the gap between CNTs was 2 μm or less, and a gap exceeding 2 μm could not be confirmed. Since the carbon powder (carbon black) is dispersed and supported on the network fibrous carbon (CNT) as small aggregates of 3 μm or less, the carbon powder can be highly dispersed.

As for the SEM image, the carbon powder / fibrous carbon coating layer formed on the current collector under the same conditions as in FIGS. Also confirmed that the above-mentioned form was obtained.

In an electrode in which this carbon powder / fibrous carbon coating layer is formed on a current collector, a mixed solution using fibrous carbon, which plays a role of a binder, is applied on the current collector and dried to remove the solvent. By doing so, it is possible to reduce the resistance by preparing a coating layer on the current collector and suppressing the addition amount of the resin binder. Furthermore, by setting the average particle size of the carbon powder to a very small particle size of less than 100 nm, the diffusion resistance of the carbon powder itself can be reduced, and the resistance of the electrode can be further reduced. In addition, since an extremely small particle diameter is used as the carbon powder, the carbon powder tends to aggregate, and the resulting coating layer tends to have a low density. However, the carbon powder and fibrous carbon in the mixed solution are highly dispersed using a dispersion technique such as jet mixing or ultracentrifugation, thereby increasing the electrode density with a dense and homogeneous coating layer. An excellent electrode capable of obtaining the same level of capacity as an electrode using micron-sized carbon powder can be realized.

Next, the state of this electrode will be examined. The carbon powder / fibrous carbon coating layer prepared by applying a mixed solution in which the carbon material and the fibrous carbon are dispersed on the current collector and removing the solvent is peeled off from the current collector in a predetermined amount. When the particle size distribution (50% cumulative value: D50 (median diameter), 90% cumulative value: D90) when dispersed in the solution was examined, a so-called normal distribution having a single peak was shown. It turned out that the structure which D90 / D50 shows 2.5 or less is preferable. That is, by using the carbon powder / fibrous carbon coating layer in this range, a uniform surface state and high density are obtained. Moreover, by setting D90 to 150 μm or less, a sharp particle size distribution can be obtained, and a uniform surface state and a high-density carbon powder / fibrous carbon coating layer can be obtained. The lower limit of D90 is 1 μm, and the optimum range is 1 to 50 μm. It should be noted that the particle size distribution was determined by adding a carbon powder / fibrous carbon coating layer (1 cm ² ) to an isopropyl alcohol (IPA) solution and dispersing using a homogenizer (24000 rpm, 5 minutes). (Measurement method of particle size distribution).

FIG. 6 is a conceptual diagram showing a configuration of a laminated electric double layer capacitor in which an electrode in which a coating layer of carbon powder / fibrous carbon is formed on a current collector is laminated and sealed as an example of the electric double layer capacitor. The laminated electric double layer capacitor includes a positive electrode and a negative electrode 3, a separator 4, an electrolytic solution 5, a laminate film 6, and an external terminal 7.

The electrode 3 is an electrode in which the carbon powder / fibrous carbon coating layer of the present embodiment is formed on a current collector. An external terminal 7 for connection to the outside is formed on a part of the electrode 3.

As the separator 4, a cellulose separator, a synthetic fiber nonwoven fabric separator, a mixed paper separator made by mixing cellulose and synthetic fibers, or the like can be used. Polyester, polyphenylene sulfide, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyimide, fluororesin, polyolefin resin such as polypropylene and polyethylene, non-woven fabric made of fibers such as ceramics and glass, kraft paper, manila paper, esparto paper, and a mixture of these Papermaking or a porous film can be preferably used. When performing reflow soldering, a resin having a heat distortion temperature of 230 ° C. or higher is used. For example, polyphenylene sulfide, polyethylene terephthalate, polyamide, fluororesin, ceramics, glass, or the like can be used.

As the electrolyte 5 impregnated in the positive electrode and negative electrode 3 and the separator 4 interposed between the electrodes, ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl isopropyl sulfone, Chain sulfones such as ethyl methyl sulfone and ethyl isobutyl sulfone, sulfolane, 3-methyl sulfolane, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, 2-methyltetrahydrofuran 1,3-dioxolane, nitromethane, ethylene glycol, ethylene glycol dimethyl ether, ethylene glycol die It can be used ether, water or mixtures thereof. The electrolyte 4 contains one or more electrolytes selected from the group consisting of quaternary ammonium salts or lithium salts. Any quaternary ammonium salt or lithium salt can be used as long as the electrolyte can generate quaternary ammonium ions and lithium ions. It is more preferable to use one or more selected from the group consisting of quaternary ammonium salts and lithium salts. In particular, ethyl trimethyl ammonium BF ₄ , diethyl dimethyl ammonium BF ₄ , triethyl methyl ammonium BF ₄ , tetraethyl ammonium BF ₄ , spiro- (N, N ′)-bipyrrolidinium BF ₄ , ethyl trimethyl ammonium PF ₆ , diethyl dimethyl ammonium PF ₆ , Triethylmethylammonium PF ₆ , tetraethylammonium PF ₆ , spiro- (N, N ′)-bipyrrolidinium PF ₆ , tetramethylammonium bis (oxalato) borate, ethyltrimethylammonium bis (oxalato) borate, diethyldimethylammonium bis (oxalato) borate , Triethylmethylammonium bis (oxalato) borate, tetraethylammonium bis (oxalato) borate, spiro -(N, N ')-bipyrrolidinium bis (oxalato) borate, tetramethylammonium difluorooxalatoborate, ethyltrimethylammonium difluorooxalatoborate, diethyldimethylammonium difluorooxalatoborate, triethylmethylammonium difluorooxalatoborate, Tetraethylammonium difluorooxalatoborate, spiro- (N, N ′)-bipyrrolidinium difluorooxalatoborate, LiBF ₄ , LiPF ₆ , lithium bis (oxalato) borate, lithium difluorooxalatoborate, methylethylpyrrolidinium tetra Fluoroborate and the like are preferable.

The laminate film 6 may be of this type as long as it has flexibility and can seal the capacitor element formed of the electrode 3 and the separator 4 by heat fusion so that the electrolyte does not leak. Generally used films can be used. A typical layer structure used for the laminate film 6 is a structure in which a non-venting layer made of a metal thin film and a heat-sealing layer made of a heat-fusible resin are laminated, or a heat-sealing layer of a non-venting layer. Further, a configuration in which a protective layer made of a film of polyester such as polyethylene terephthalate or nylon is laminated on the surface opposite to the surface. When sealing the capacitor element, the capacitor element is surrounded by facing the heat sealing layer. Further, the number of electrodes 3 and separators 4 forming the capacitor element to be sealed can be arbitrarily set. For example, a capacitor element may be constituted by one electrode and two separators, or a capacitor element may be constituted by a combination of other numbers.

As the metal thin film constituting the non-breathing layer, for example, a foil of Al, Ti, Ti alloy, Fe, stainless steel, Mg alloy or the like having a thickness of 10 μm to 100 μm can be used. The heat-sealable resin used for the heat-sealable layer is not particularly limited as long as it is a resin that can be heat-sealable. For example, polyesters such as polypropylene, polyethylene, acid modified products thereof, polyphenylene sulfide, and polyethylene terephthalate. And polyamide, ethylene-vinyl acetate copolymer and the like.

(3) Electrode Density of Electrode The electrode according to the present invention can provide good results in electrode capacity when the electrode density is 0.48 g / cc or more.

The “electrode density” described in the present specification is the mass per unit volume of the coating layer obtained by dispersing carbon powder and fibrous carbon in a solvent and coating the current collector. Specifically, in the thickness region (volume) of the coating layer at 1 cm ² of the coating layer, a value obtained by dividing the weight of the solid content including the electrode material by the volume.

(4) Application Form of Electrode According to the Present Invention The electrode and the electrode manufacturing method according to the present invention can be applied not only to an electric double layer capacitor but also to various capacitors such as an electrochemical capacitor such as a lithium ion capacitor.
In addition, the electrode and the electrode manufacturing method according to the present invention are not limited to the laminate type electric double layer capacitor, and may be applied to a coin type. Further, the electrode is wound between the positive electrode and the negative electrode via a separator. The present invention can also be applied to various types of capacitors using a cylindrical element or a laminated element laminated with a separator between a positive electrode and a negative electrode.

[First characteristic comparison]
(Comparison of electrode characteristics in carbon black having an average particle diameter of 12 nm)
The characteristics of the electric double layer capacitor using the electrode of the present invention will be confirmed. In this example and comparative example, an electrode was prepared under the following conditions, an electric double layer capacitor was prepared using the electrode, and various characteristics were measured. Examples 1 to 8 used in this characteristic comparison, Comparative Example 1 and Conventional Example 1 were produced by the following method.

(Preparation of mixed solution)
In Examples 1 to 4, carbon black having an average particle size of 12 nm (hereinafter referred to as CB) subjected to water vapor activation treatment is used as carbon particles having an average particle size of 100 nm. CB having an average particle diameter of 12 nm is measured so as to be 80 wt% with respect to the total amount of carbon powder and fibrous carbon in the electrode. Next, CNT as a fibrous carbon having an outer diameter of 20 nm and a length of 150 μm is measured so as to be 20 wt% with respect to the total amount of CB and CNT in the electrode. 1.6 g of CB and 0.4 g of CNT were put into 1 L of a solvent (NMP) to prepare a mixed solution.
In Examples 4 to 6 and Conventional Example 1, 0.02 g of polyvinylidene fluoride (PVDF) was further added to the mixed solution and mixed. The proportion of PVDF in the mixed solution is 1 wt%.

(Example 1)
In Example 1, the above mixed solution was subjected to dispersion treatment by ultracentrifugation dispersion treatment at a centrifugal force of 200000 N (kgms ⁻² ) for 5 minutes to prepare a CB / CNT / NMP dispersion. The dispersion was concentrated by removing the solvent by filtration, and this dispersion was applied onto an aluminum foil as a current collector using a bar coater. Then, it dried at 120 degreeC under normal pressure for 1 hour, NMP used as a solvent was removed, and two electrodes which formed the coating layer of CB / CNT on aluminum foil were obtained, and an electric double layer was passed through a cellulosic separator. A capacitor element was produced (electrode area: 2.1 cm ² ). Then, after impregnating the element with a propylene carbonate solution containing 1M (= 1 mol / dm ³ ) tetraethylammonium tetrafluoroborate as an electrolytic solution, the element was heat sealed using a laminate film, and an evaluation cell (electric double layer) Capacitor).

(Example 2)
In Example 2, the above mixed solution was subjected to dispersion treatment three times by jet mixing at a pressure and concentration of 200 MPa, 0.5 g / l, and a carbon powder / fibrous carbon / NMP dispersion was produced. Produced an evaluation cell in the same manner as in Example 1.

(Example 3)
In Example 3, the above mixed solution was stirred for about 30 seconds with a ball mill for dispersion treatment, and the evaluation cell was prepared in the same manner as in Example 1 except that a carbon powder / fibrous carbon / NMP dispersion was produced. Produced.

Example 4
In Example 4, the above mixed solution was stirred for about 30 seconds with a mixer for dispersion treatment, and the evaluation cell was prepared in the same manner as in Example 1 except that a carbon powder / fibrous carbon / NMP dispersion was produced. Produced.

(Example 5)
In Example 5, carbon powder / fibrous carbon / NMP dispersion was further mixed with PVDF as a binder, and carbon powder / fibrous carbon / NMP dispersion was used for evaluation in the same manner as in Example 1 A cell was produced. The amount of PVDF added is 1% with respect to the total amount of carbon powder, fibrous carbon, and PVDF.

(Example 6)
In Example 6, carbon powder / fibrous carbon / NMP dispersion was further mixed with PVDF as a binder and carbon powder / fibrous carbon / NMP dispersion was used for evaluation in the same manner as in Example 2 except that it was used. A cell was produced. The amount of PVDF added is 1% with respect to the total amount of carbon powder, fibrous carbon, and PVDF.

(Example 7)
In Example 7, for evaluation in the same manner as in Example 3 except that carbon powder / fibrous carbon / NMP dispersion was further mixed with PVDF as a binder and carbon powder / fibrous carbon / NMP dispersion was used. A cell was produced. The amount of PVDF added is 1% with respect to the total amount of carbon powder, fibrous carbon, and PVDF.

(Example 8)
In Example 8, carbon powder / fibrous carbon / NMP dispersion was further mixed with PVDF as a binder, and carbon powder / fibrous carbon / NMP dispersion was used for evaluation in the same manner as in Example 4 A cell was produced. The amount of PVDF added is 1% with respect to the total amount of carbon powder, fibrous carbon, and PVDF.

(Comparative Example 1)
In Comparative Example 1, an evaluation cell was produced in the same manner as in Example 3 except that the mixed solution was changed. Specifically, the activated carbon (raw material: Yasakara) having an average particle diameter of 1 μm subjected to the steam activation treatment is measured so as to be 80 wt% with respect to the total amount of the activated carbon and CNT in the electrode. Next, CNT is measured as fibrous carbon having an outer diameter of 20 nm and a length of 150 μm so as to be 20 wt% with respect to the total amount of activated carbon and CNT in the electrode. The total amount of activated carbon and CNT is 50 mg. A total of 50 mg of activated carbon and CNT were mixed with 50 ml of NMP to prepare a mixed solution. An evaluation cell was produced in the same manner as in Example 1 except that this mixed solution was stirred for about 30 seconds with a mixer and dispersed to produce a carbon powder / fibrous carbon / NMP dispersion.

(Conventional example 1)
In Conventional Example 1, activated carbon (raw material: Yasugara) having an average particle diameter of 1 μm subjected to steam activation treatment and ketjen black (hereinafter referred to as KB) is 95 wt% with respect to the total amount of carbon powder and resin binder in the electrode. Measure so that Next, PVDF as a resin binder is measured so that it may become 5 wt% with respect to the total amount of activated carbon and PVDF in an electrode. The total amount of activated carbon and PVDF is 50 mg. A mixed solution prepared by mixing a total of 50 mg of activated carbon and PVDF with 50 ml of NMP is used. This mixed solution is applied onto an aluminum foil serving as a current collector and dried at 120 ° C. for 1 hour under normal pressure to obtain two electrode bodies, and an electric double layer capacitor element is produced through a cellulose separator. (Electrode area: 2.1 cm ² ). Then, after impregnating the element with a propylene carbonate solution containing 1M (= 1 mol / dm ³ ) tetraethylammonium tetrafluoroborate as an electrolytic solution, the element was heat sealed using a laminate film, and an evaluation cell (electric double layer) Capacitor).

In Table 1, the electrode dispersion methods of Examples 1 to 8, Comparative Example 1 and Conventional Example 1, the ratio of binder or fibrous carbon, the ratio of carbon black in the electrode, the electrode density, the electrode capacity of the evaluation cell, the internal It is the table | surface which showed resistance and a low temperature characteristic. For the evaluation cells of Examples 1 to 8 and Conventional Example 1, the electrode capacity and the internal resistance show the measurement results after applying voltage at 3 V for 30 minutes. For the low temperature characteristics, the electrode capacity of the evaluation cell was measured in each environment of 20 ° C. and −30 ° C., and the ratio of the capacities (capacity at −30 ° C./capacity at 20 ° C.) × 100% did.

From Table 1, the characteristics of Examples 1 to 8, Comparative Example 1 and Conventional Example 1 are compared. In Conventional Example 1, which is a coating electrode using PVDF as a binder, a resin-based binder is used. Despite the small amount of the resin binder, the internal resistance and the low temperature characteristics were deteriorated. Moreover, about the comparative example 1 which coated the mixed solution similarly to this invention, the electrode density and the electrode capacity are showing the high value. However, since the activated carbon particle size is large, the diffusion resistance increases despite the fact that no resin binder is used, and the internal resistance and low-temperature characteristics are degraded.

In contrast, in Examples 1 to 8, carbon powder having an extremely small particle diameter was used, and the mixed solution was coated on the current collector, so that the internal resistance and the low temperature characteristics were extremely excellent.

In particular, the electrode density of Examples 1 and 5 in which the dispersion process was performed by ultracentrifugation was 0.62 g / cc, and the electrode density of Examples 2 and 6 in which jet mixing was performed was 0.55 g / cc. The electrode density of Examples 3 and 7 performed by the ball mill is 0.60 g / cc, which is higher than 0.50 g / cc. That is, Examples 1 to 3, 5 to 7 in which carbon powder and fibrous carbon are highly dispersed are examples in which internal resistance and low-temperature characteristics are good and the electrode density is high and dispersed by a mixer. It can be seen that the electrode capacity is significantly improved as compared with 4 and 8.

[Second characteristic comparison]
(Comparison with Ketjen Black having an average particle size of 34 nm)
In this characteristic comparison, instead of using the CB having an average particle diameter of 12 nm subjected to the steam activation treatment in the first characteristic comparison, the characteristics of the electric double layer capacitor using the electrode using the ketjen black having an average particle diameter of 34 nm are used. Confirm. In this example and comparative example, an electrode was prepared under the following conditions, an electric double layer capacitor was prepared using the electrode, and various characteristics were measured.

(Preparation of mixed solution)
In Examples 9 to 10, ketjen black (hereinafter referred to as KB) having an average particle diameter of 34 nm subjected to the steam activation treatment is measured so as to be 80 wt% with respect to the total amount of carbon powder and fibrous carbon in the electrode. Next, CNT is measured as fibrous carbon having an outer diameter of 20 nm and a length of 150 μm so as to be 20 wt% with respect to the total amount of KB and CNT in the electrode. 1.6 g of KB and 0.4 g of CNT were put into 1 L of a solvent (NMP) to prepare a mixed solution.

Example 9
In Example 9, an electric double layer capacitor element was produced for the above mixed solution under the same conditions as in Example 1 (electrode area: 2.1 cm ² ). Then, after impregnating the element with a propylene carbonate solution containing 1M (= 1 mol / dm ³ ) tetraethylammonium tetrafluoroborate as an electrolytic solution, the element was heat sealed using a laminate film, and an evaluation cell (electric double layer) Capacitor).

(Example 10)
In Example 10, the above mixed solution was dispersed three times by jet mixing at a pressure and concentration of 200 MPa, 0.5 g / l, and a carbon powder / fibrous carbon / NMP dispersion was produced. Produced an evaluation cell in the same manner as in Example 9.

(Example 11)
In Example 11, the above mixed solution was stirred for about 30 seconds with a ball mill for dispersion treatment, and the evaluation cell was prepared in the same manner as in Example 9 except that a carbon powder / fibrous carbon / NMP dispersion was produced. Produced.

Example 12
In Example 12, the above mixed solution was stirred for about 30 seconds with a mixer for dispersion treatment, and the evaluation cell was prepared in the same manner as in Example 9 except that a carbon powder / fibrous carbon / NMP dispersion was produced. Produced.

Table 2 is a table showing the electrode dispersion method, binder or fibrous carbon ratio, ratio of carbon black in the electrode, electrode density, electrode capacity of the evaluation cell, internal resistance, and low temperature characteristics of Examples 9 to 12. It is. For the evaluation cells of Examples 9 to 12, the electrode capacity and the internal resistance show the measurement results after voltage application at 3 V for 30 minutes. For the low temperature characteristics, the electrode capacity of the evaluation cell was measured in each environment of 20 ° C. and −30 ° C., and the ratio of the capacities (capacity at −30 ° C./capacity at 20 ° C.) × 100% did.

From Table 2, in Examples 9 to 12, as in Examples 1 to 4, carbon powder having an extremely small particle diameter was used, and the mixed solution was coated on the current collector, whereby the internal resistance and low temperature characteristics were reduced. The value was extremely excellent.

In particular, Example 9 in which the dispersion process was performed by ultracentrifugation to highly disperse carbon powder and fibrous carbon, Example 10 in which carbon powder and fibrous carbon were highly dispersed by jet mixing, Carbon powder by ball mill About Example 11 which carried out the high dispersion | distribution of carbon fiber and carbon, internal resistance and a low temperature characteristic are favorable. Moreover, as can be seen from the electrode density of Example 9 of 0.56 g / cc, the electrode density of Example 10 of 0.50 g / cc, and the electrode density of Example 11 of 0.54 g / cc, the electrode density increases. For this reason, it turns out that the electrode capacity is significantly improved as compared with Example 12 dispersed by the mixer.

As described above, even in an electric double layer capacitor prepared by replacing CB with an average particle diameter of 12 nm with KB with an average particle diameter of 34 nm, the internal resistance and low temperature characteristics can be extremely increased to an electrode density of 0.48 g / cc or more. .

[Third characteristic comparison]
In this characteristic comparison, a comparison is made regarding the state of carbon particles and the particle size distribution of the carbon powder and aggregates constituting the electrode.
(State of carbon particles)
When the carbon materials used for the electrodes of Example 1 and Comparative Example 1 were analyzed, it was as follows. The measurement method was a nitrogen gas adsorption method. The specific surface area was calculated by the BET method.

In Table 3, when the characteristics of Examples 1 and 9 and Comparative Example 1 are compared, Comparative Example 1 in which internal resistance and low-temperature characteristics have deteriorated has a lower proportion of mesopores than Examples 1 and 9. I understand that. On the other hand, in Examples 1 and 9 in which the internal resistance and the low-temperature characteristics are extremely excellent values, it can be seen that the resistance is reduced by increasing the proportion of mesopores having a large pore size. By setting the proportion of mesopores to 5 to 55%, the internal resistance and the low temperature characteristics become extremely excellent values.

(Particle size distribution of carbon powder and aggregates at the electrode)
Next, the electrode obtained by applying the highly dispersed mixed solution on the current collector and removing the solvent will be examined. The carbon materials used for the electrodes of Examples 1 to 3 were analyzed. Table 4 is a table showing 50% cumulative value: D50 (median diameter) and 90% cumulative value: D90 of Examples 1 to 3, and FIG. 7 is a diagram showing the particle size distribution of Examples 1 to 3. . The measurement method was that the carbon powder / fibrous carbon mixed layer (1 cm ² ) of Examples 1 to 3 was taken out from the current collector, placed in an isopropyl alcohol (IPA) solution, and a homogenizer (24000 rpm, 5 minutes) was used. In the dispersed state, the particle size distribution was measured.

FIG. 7 shows that Examples 1 and 2 are so-called normal distributions having a single peak in the particle size distribution. This shows that the electrodes obtained in Examples 1 and 2 have a uniform surface state and high density.

Furthermore, from Table 4, a sharper particle size distribution can be obtained by setting D90 to be less than 138 μm. In Example 1 and Example 2, it is possible to obtain an optimum electrode with extremely excellent internal resistance and capacity. I understand. Similarly, even when D90 is 150 μm or less, excellent internal resistance and capacitance can be obtained. On the other hand, when D90 exceeds 150 μm, the internal resistance and the capacity decrease.

Further, D90 / D50, electrode density, capacity, and internal resistance of the electrodes of Examples 1 to 3 were analyzed. Table 5 is a table showing D90 / D50, electrode density, capacity, and internal resistance of the electrodes of Examples 1 to 3.

From Table 5, by setting the value of D90 / D50 to 2.5 or less and making it a sharp peak in the particle size distribution, the electrode has a uniform surface state and high density. Therefore, in Examples 1 and 2, the internal resistance and the capacitance can be made excellent values. On the other hand, when the value of D90 / D50 is 2.6 or more, the uniformity of the surface state of the electrode is partially broken, so that the electrode density is lowered.

From the above, in the aggregate of carbon powder and fibrous carbon having an average particle diameter of less than 100 nm, the value of D90 / D50 in the particle size distribution is 2.5 or less, and a sharp peak is obtained to obtain a uniform surface state and high It can be a density. Thereby, the value of internal resistance and a capacity | capacitance can be made excellent. In particular, by setting the D90 of the aggregate to 150 μm or less, a sharper particle size distribution can be obtained, and the internal resistance and capacity of the electrode can be made excellent.

[Fourth characteristic comparison]
(Characteristic comparison based on binder ratio)
(Example 1-1 to Example 1-1)
It was fabricated in the same manner as the evaluation cell described in Example 1. However, the ratio of CB and CNT contained in the mixed solution is changed as shown in Table 6.

Table 6 shows the electrode dispersion method of Example 1-1 to Example 1-6, the ratio of fibrous carbon in the electrode, the ratio of the carbon material in the electrode, the electrode density, the electrode capacity of the evaluation cell, and the internal resistance. It is the table | surface which showed the case swelling condition. For the case swelling, the thickness of the cell for evaluation before voltage application is used as a standard, and compared with the thickness after voltage application at 3 V for 30 minutes, the case where the swelling is more than 20% is “x”, in the range of 20 to 10% What was swollen with “△” was evaluated as “◯” when it was swollen with less than 10%.

From Table 6, it can be seen that, when the characteristics of Examples 1-1 to 1-6 are compared, good results are obtained with respect to electrode density and capacitance in any of the Examples. As for the internal resistance, Examples 1-2 to 1-6 in which the ratio of CNTs was 10 wt% or more showed better results than Example 1-1. As for the case swelling, Examples 1-1 to 1-4 having a CNT ratio of 30 wt% or less showed better results than Examples 1-5 and 1-6. Moreover, in the electrode density, a favorable result was obtained for the electrode capacity in any example as compared with Example 4 dispersed by the mixer described in Table 1.

(Example 2-1 to Example 2-6)
Next, the electrode filtered using the mixed solution highly dispersed by jet mixing will be examined. In Examples 2-1 to 2-6, the cells were manufactured in the same manner as the evaluation cell described in Example 2. However, the ratio of CB and CNT contained in the mixed solution is changed as shown in Table 7.

Table 7 shows the electrode dispersion methods of Examples 2-1 to 2-6, the ratio of fibrous carbon in the electrodes, the ratio of the carbon material in the electrodes, the electrode density, the electrode capacity of the evaluation cell, and the internal resistance. It is the table | surface which showed the case swelling condition.

From Table 7, when the characteristics of Examples 2-1 to 2-6 are compared, good results are obtained with respect to electrode density and capacitance in any of the Examples. As for the internal resistance, Examples 2-2 to 2-6 in which the ratio of CNT was 10 wt% or more were better than those of Example 2-1. Regarding the swollen state of the case, Examples 2-1 to 2-4 having a CNT ratio of 30 wt% or less showed better results than Examples 2-5 and 2-6. Further, the electrode density is 0.48 g / cc or more in any of the examples, and good results are obtained for the electrode capacity as compared with Example 3 dispersed by the mixer described in Table 1. ing.

[Fifth characteristic comparison]
(Characteristic comparison based on electrolyte)
In the fifth characteristic comparison, an electric double layer capacitor was prepared by impregnating an electrolyte prepared in Table 8 with an electrode prepared by highly dispersing carbon powder and fibrous carbon by a dispersion process by ultracentrifugation. Various characteristics were measured.

(Examples 1-7 to 1-9)
It was fabricated in the same manner as the evaluation cell described in Example 1. However, the electrolyte solution impregnating the electric double layer capacitor element was SLF (sulfolane) containing 1.4 M (= 1.4 mol / dm 3) TEMABF 4 (triethylmethylammonium tetrafluoroborate) in Example 1-7. Changed to EiPS (ethyl isopropyl sulfone). Similarly, in Example 1-8, SLF and 3-MeSLF (3-methylsulfolane) containing 1.4 M TEMABF4 were used, and in Example 1-9, PC (propylene carbonate) containing 1.4 M TEMABF4 was used. .

Table 8 shows the dispersion method of the electrodes of Examples 1-7 to 1-9, the type of the electrolyte, the proportion of fibrous carbon in the electrodes, the proportion of the carbon material in the electrodes, the electrode capacity of the evaluation cell, and the low temperature characteristics And a table showing the capacity maintenance rate after 250 hours. The electrode capacity indicates a measurement result after applying a voltage at 3.5 V for 30 minutes. The capacity retention ratio was determined by measuring the electrode capacity after applying voltage at 3.5 V for 30 minutes and the electrode capacity after applying voltage at 3.5 V for 250 hours, and the ratio of the capacity (capacity after applying voltage for 250 hours). / Capacity after voltage application for 30 minutes) × 100%. For the low temperature characteristics, the electrode capacity of the evaluation cell was measured in each environment of 20 ° C. and −30 ° C., and the ratio of the capacities (capacity at −30 ° C./capacity at 20 ° C.) × 100% did.

From Table 8, the characteristics of Examples 1-7 to 1-9 are compared. In Example 1-9 in which no sulfolane, sulfolane compound or chain sulfone is used in the electrolyte, the capacity retention rate after 250 hours is shown. Extremely reduced. On the other hand, in Example 1-7 using EiPS which is sulfolane and chain sulfone as the electrolyte, and in Example 1-8 using 3-MeSLF which is a sulfolane compound having a side chain in the sulfolane and sulfolane skeleton, 250 hours The subsequent capacity retention rate was 95%, and the decrease in electrode capacity over time was suppressed to a small level, and good low temperature characteristics of 90% or more were exhibited. In this characteristic comparison, a dispersion method by ultracentrifugation dispersion treatment was used. Even when jet mixing and a ball mill dispersion method were used, sulfolane and a sulfolane compound having a side chain in the sulfolane skeleton or a chain-like structure were used. By using sulfone, the same effect can be obtained.

As described above, by using sulfolane as an electrolyte for impregnating the electric double layer capacitor element and using a sulfolane compound having a side chain in the sulfolane skeleton or a combination of sulfolane and a chain sulfone, low temperature characteristics and after a long time have passed. It is possible to produce an electric double layer capacitor that is superior in terms of capacity retention.

[Sixth characteristic comparison]
In the first and second characteristic comparisons, the characteristics of carbon powder having an average particle diameter of 12 nm and an average particle diameter of 34 nm were compared. In this characteristic comparison, characteristics of an electric double layer capacitor using a carbon powder electrode having an average particle diameter of 1 μm are confirmed. In Examples and Comparative Examples of this characteristic comparison, an electrode was prepared under the following conditions, an electric double layer capacitor was prepared using the electrode, and various characteristics were measured. Examples 10-1, 10-2 and Conventional Example 1 used in this characteristic comparison were manufactured by the following method.

(Preparation of mixed solution)
First, the activated carbon (raw material: Yasakara) having an average particle diameter of 1 μm subjected to the steam activation treatment is measured so as to be 80 wt% with respect to the total amount of carbon powder and fibrous carbon in the electrode. Next, CNT is measured as fibrous carbon having an outer diameter of 20 nm and a length of 150 μm so as to be 20 wt% with respect to the total amount of activated carbon and CNT in the electrode. 1.6 g of activated carbon and 0.4 g of CNT were put into a NMP1L solvent to prepare a mixed solution.

(Example 10-1)
In Example 10-1, the above mixed solution was subjected to a dispersion treatment by ultracentrifugation for 5 minutes at a centrifugal force of 200000 N (kgms ⁻² ) to produce an activated carbon / CNT / NMP dispersion. The dispersion is concentrated by removing a part of the solvent by filtration, and this dispersion is coated on an aluminum foil as a current collector using a bar coater, and dried at 120 ° C. for 1 hour under normal pressure. NMP was removed to obtain two electrodes in which a mixed layer of activated carbon / CNT was formed on an aluminum foil, and an electric double layer capacitor element was produced through a cellulose-based separator (electrode area: 2.1 cm ² ) . Then, after impregnating the element with a propylene carbonate solution containing 1M (= 1 mol / dm ³ ) tetraethylammonium tetrafluoroborate as an electrolytic solution, the element was heat sealed using a laminate film, and an evaluation cell (electric double layer) Capacitor).

(Example 10-2)
In Example 10-2, the above mixed solution was dispersed three times by jet mixing at a pressure and concentration of 200 MPa and 0.5 g / l to prepare a carbon powder / fibrous carbon / NMP dispersion. An evaluation cell was produced in the same manner as in Example 10-1, except that

Table 9 shows the electrode dispersion method of Examples 10-1, 10-2 and Conventional Example 1, the ratio of fibrous carbon, the ratio of activated carbon in the electrode, the electrode density, the electrode capacity of the evaluation cell, and the internal resistance. It is a table. For the evaluation cells of Examples 10-1 and 10-2 and Conventional Example 1, the electrode capacity and internal resistance show the measurement results after applying voltage at 3 V for 30 minutes.

In Table 9, the characteristics of Examples 10-1 and 10-2 and Conventional Example 1 are compared. For Conventional Example 1, the internal resistance and the low temperature characteristics were degraded. On the other hand, in Example 10-1 and Example 10-2 in which ultracentrifugation and jet mixing were performed, activated carbon and CNTs can be highly dispersed, and the electrode density of the obtained electrode was improved. The capacity and internal resistance were excellent values. That is, from Table 9, even when carbon powder having an average particle diameter of 1 μm is used, an electrode having excellent electrode capacity and low internal resistance can be produced by performing ultracentrifugation and jet mixing as a dispersion method. It is understood that is possible.

As described above, in this characteristic comparison, the characteristics of carbon powder having an average particle diameter of 1 μm were compared. However, even when carbon powder having an average particle diameter of less than 10 μm was used, the dispersion method was changed to ultracentrifugation and jet. The effects of the present invention can be achieved by performing processing by mixing.

DESCRIPTION OF SYMBOLS 1 ... Negative electrode case 2 ... Electrolyte 3 ... Electrode 4 ... Separator 5 ... Electrode 6 ... Positive electrode case 7 ... Gasket

Claims

An electrode obtained by applying a solution in which a porous carbon powder having a particle size of less than 100 nm and fibrous carbon is dispersed on a current collector and removing the solvent.
The electrode according to claim 1, wherein the carbon powder is obtained by activating carbon black.
The electrode according to claim 1 or 2, wherein the carbon powder and the fibrous carbon are highly dispersed, and the electrode density is 0.48 g / cc or more.
4. The electrode according to claim 1, wherein the fibrous carbon is contained in an amount of 10 to 55% by weight based on the total amount of carbon powder and fibrous carbon.
The electrode according to any one of claims 1 to 4, wherein the proportion of mesopores in the pores of the carbon powder subjected to the porous treatment is in the range of 5 to 30%.
The particle size distribution of the aggregate of carbon powder and fibrous carbon constituting the electrode has a single peak,
The ratio D90 / D50 between the particle diameter of the 50% cumulative value D50 and the particle diameter of the 90% cumulative value D90 of the particle size distribution is 2.5 or less. The electrode according to item.
The electrode according to claim 6, wherein a particle diameter of a 90% cumulative value D90 of the particle size distribution is 150 µm or less.
The electrode according to any one of claims 1 to 7, wherein an interval between the fibrous carbons constituting the electrode is 2 µm or less.
In the treatment of making the porous carbon powder having a particle diameter of 100 nm or more and less than 10 μm and fibrous carbon collide with the jets of the solution, or the treatment of applying shear stress and centrifugal force to the solution An electrode obtained by applying the dispersed solution on a current collector and removing the solvent.
An electric double layer capacitor in which the electrode according to any one of claims 1 to 9 is formed on a current collector.
The electric double layer capacitor according to claim 10, wherein an electrolytic solution containing a mixture of the electrode, sulfolane, and a sulfolane compound having a side chain in the sulfolane skeleton or a chain sulfone is used.
A dispersion step of dispersing a porous carbon powder having a particle diameter of less than 100 nm and fibrous carbon in a solvent;
An electrode forming step of applying the solution obtained in the dispersion step onto a current collector and removing the solvent to form a mixed layer of carbon powder / fibrous carbon on the current collector. A method for manufacturing an electrode.
The method for producing an electrode according to claim 12, wherein the carbon powder is obtained by activating carbon black.
14. The electrode manufacturing method according to claim 12, wherein the dispersion step is a process of causing the jets of the solution to collide with each other.
14. The method for manufacturing an electrode according to claim 12, wherein the dispersing step is a process of applying a shear stress and a centrifugal force to the solution.
14. The method for producing an electrode according to claim 12, wherein the dispersing step is a process of applying a physical force to the solution by a ball mill.
A dispersion step of dispersing a porous carbon powder having a particle diameter of 100 nm or more and less than 10 μm and fibrous carbon in a solvent;
An electrode forming step of applying the solution obtained in the dispersion step onto a current collector, removing the solvent, and forming a carbon powder / fibrous carbon mixed layer on the current collector;
With
The dispersion step is a process of causing the jets of the solution to collide with each other, or a process of applying shear stress and centrifugal force to the solution;
An electrode manufacturing method characterized by the above.