JP2002260970A - Activated carbonaceous structure and electric double- layer capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an activated carbonaceous structure which can be improved in the charging density of activated carbon powder and reduced in internal resistance and forms a polarized electrode of an electric double-layer capacitor with large electrostatic capacitor through short-time charging. SOLUTION: The electric double-layer capacitor 11 is manufactured by arranging a couple of polarized electrodes 12 and 12 impregnated with an electrolytic solution, in an activated carbonaceous structure formed by charging coconut shell activated carbon powder 2 of 0.1 to 0.4 r1 in mean particle size (r2 ) in phenol-resin based activated carbon powder 2 to 20 to 50 μm in mean particle size (r1 ) across a separator 13, and also by arranging charge collectors 14 and 14 on the external surfaces of the polarized electrodes 12 and 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an activated carbonaceous structure capable of easily increasing the packing density of activated carbon powder, and more particularly to an activated carbonaceous structure suitable for use as a polarizable electrode of an electric double layer capacitor, and to a use thereof. Related to the electric double-layer capacitor.

[0002]

2. Description of the Related Art An electric double layer capacitor is a capacitor using an electric double layer formed by polarization of ions at an interface between an electrode and an electrolytic solution, and has both functions of a capacitor and a battery. Compared to a large electrostatic capacity and a rapid charge / discharge capability, it is attracting attention as an auxiliary power supply for a large-capacity motor, such as a small memory backup power supply or a drive source for an automobile.

As an example of a conventional electric double layer capacitor, a plate-like separator is interposed between a pair of plate-like polarizable electrodes, and a plate-like separator is provided on each surface of the polarizable electrodes opposite to the separator laminated surface. There is known a multilayer electric double layer capacitor having a configuration in which current collectors are stacked and the stacked body is sealed with a sealing material.

In such an electric double layer capacitor,
It is required to improve the capacitance while reducing the internal resistance of the polarizing electrode.
In JP-A-6 (1999), as an activated carbonaceous structure constituting a polarizable electrode, a particle size of 3 to 10% by weight of a number (3 to 8) μm is mainly based on an activated carbon powder mainly having a particle size of 20 to 30 μm. It is described that an electric double layer capacitor having a high capacitance can be obtained while reducing internal resistance by forming a mixture of mesocarbon powder.

[0005]

However, in the electric double layer capacitor disclosed in Japanese Patent Laid-Open Publication No. Hei 3-201516, the mesocarbon having a small electric double layer capacity is added, so that the electrostatic capacity of the electric double layer capacitor can be sufficiently improved. Rather, there has been a demand for further improvement in capacitance while suppressing an increase in internal resistance.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to be suitable as a polarizable electrode of an electric double layer capacitor having a low internal resistance and capable of improving the capacitance per unit volume. It is to provide an activated carbonaceous structure and an electric double layer capacitor using the same.

[0007]

Means for Solving the Problems The present inventors have examined the powder constituting the activated carbonaceous structure to solve the above-mentioned problems, and as a result, have found that the average particle diameter (r ₁ ) of the phenolic resin-based activated carbon is 20 to 50 μm. between powder, excessive milling conditions easily obtained regardless, coconut shell contributes an average particle size in reduction of internal resistance (r ₂₎ is having a relatively small particle size of 0.1r ₁ ~0.4r ₁ By filling the activated carbon, the dispersibility of the activated carbon powder in the activated carbon structure is improved, and the packing density of the activated carbon powder is easily improved. By using a phenolic resin-based activated carbon powder that easily exhibits capacitance and a coconut shell-based activated carbon powder having a relatively small average particle size (r ₂ ), the internal resistance of the electric double layer capacitor is reduced. Short time It has been found that the internal resistance of the electric double layer capacitor during charging can be reduced and the capacitance per unit volume can be increased.

That is, the activated carbonaceous structure of the present invention has an average particle size (r ₂ ) of 0.1r _{1 to} 0.4r between phenolic resin-based activated carbon powders having an average particle size (r ₁ ) of 20 to 50 μm.
It is characterized by being filled with the coconut shell activated carbon powder of _{No. 1} .

The phenolic resin-based activated carbon powder is 55 to 75% by weight, and the coconut shell activated carbon powder is 25 to 75% by weight.
It is desirable that the content is 45% by weight and that the total content of Fe, Cr, Ni, Na, K and Cl relative to the total amount of the structure is 450 ppm or less.

Further, the electric double layer capacitor of the present invention comprises:
A pair of the activated carbonaceous structures is provided with a polarizable electrode impregnated with an electrolyte through a separator, and a current collector is provided on each of the outer surfaces of the pair of polarizable electrodes. Things.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The activated carbonaceous structure of the present invention will be described with reference to FIG. According to FIG. 1, the activated carbonaceous structure 1 has an average particle size (r ₁ ) of 20 to 5.
Between phenolic resin activated carbon powder 2 0 .mu.m, the average particle diameter (r ₂₎ is 0.1r ₁ ~0.4r ₁ of coconut shell-based activated carbon powder 3 that a large technical feature made by filling a, thereby, There is no large void remaining between the activated carbon powders, and no large voids remain in the aggregated particles due to the aggregation of the activated carbon powders. The structure can be improved, and the structure has high mechanical strength.

Further, in the coconut shell-based activated carbon powder 3 having a small average particle diameter (r ₂ ), the electrolyte ions can easily diffuse into the pores formed extending to the inside of the powder. Since the resistance is reduced, the exchange speed of the electric double layer can be increased, and the responsiveness of the current at the initial stage of charging and discharging is particularly improved, so that the responsiveness of the current at the initial stage of charging and discharging is particularly increased to reduce the internal resistance. be able to.

Further, according to the present invention, phenolic resin-based activated carbon powder 2 having an average particle size (r ₁ ) of 20 to 50 μm as activated carbon, and an average particle size (r ₂ ) of 0.1 r _{1 to} 0.4 r
Are those allowed to contain a combination of a ₁ coconut shell based activated carbon powder 3.

That is, phenolic resin-based activated carbon powder 2
Has a high capacitance, but the powder itself is hard, and the powder itself is fed from a pulverizer or a pulverizing medium to Fe, Cr, Ni,
Contaminants such as Na, K, and Cl are easily mixed. For this reason, when the average particle diameter (r ₁ ) of the phenolic resin-based activated carbon powder 2 is smaller than 20 μm, a large amount of the above impurities are mixed into the activated carbon powder, and a gas is generated by the reaction with the electrolytic solution to form the electrolytic solution. And the capacitance of the electric double layer capacitor decreases.

Conversely, when the average particle size (r ₁ ) of the phenolic resin-based activated carbon powder 2 exceeds 50 μm, the content ratio of the activated carbon powder in the structure decreases. Desirable range of the average particle diameter of the phenol resin-based activated carbon powder 2 (r ₁₎ is 35 to 45
μm.

If the phenolic resin-based activated carbon powder 2 having an average particle diameter of 20 to 50 μm is not added, aggregation occurs between the coconut shell-based activated carbon powders 3 having a small average particle diameter, and large voids are formed inside the aggregated particles. As a result, the packing density of the activated carbon in the structure decreases, and the strength and the capacitance decrease.

Conversely, when the average particle size (r ₂ ) is between 0.1 r _{1 and} 0.1.
If 4r ₁ coconut shell activated carbon powder 3 is not added,
Many voids are formed between the phenolic resin-based activated carbon powders 2 to lower the capacitance and increase the internal resistance particularly at the beginning of charging and discharging. In addition, coconut shell activated carbon powder 3
When the average particle size (r ₂ ) of is less than 0.1 r ₁ ,
As the cohesive force between the powders increases, the dispersibility decreases and the coconut shell-based activated carbon powders 3 aggregate, so that the voids between the phenolic resin-based activated carbon powders 2 cannot be effectively filled and the internal resistance increases. Resulting in.

Further, when the average particle size (r ₂ ) of the coconut shell activated carbon powder 3 is larger than 0.4 r ₁ , the voids formed between the phenolic resin activated carbon powders 2 cannot be sufficiently filled. In addition, the fillability of the activated carbon decreases. The desirable range of the average particle size (r ₂ ) of the coconut shell activated carbon powder 3 is 0.15r ₁
０．３0.3 r ₁ .

Further, according to the present invention, the activated carbonaceous structure 1
In order to increase the packing density of the activated carbon therein, to reduce the internal resistance of the electric double layer capacitor and to improve the capacitance, 55 to 75% by weight of the phenol resin-based activated carbon powder 2 and the coconut shell activated carbon powder 3 were used. Desirably, the content is 25 to 45% by weight.

Further, according to the present invention, Fe, Cr, Ni, Na,
K and Cl are 450 ppm in total amount with respect to the total amount of the structure
It is desirable to have the following.

In the activated carbonaceous structure 1, for example,
Conductive carbon such as Ketjen black having an average particle diameter of 200 nm or less, particularly 50 to 100 nm, or Teflon (registered trademark) resin such as polytetrafluoroethylene (PTFE) may be contained as the binder 4, It is desirable that a part of Ketjen Black has a toughness and is in a fibrous form from the viewpoint of improving the strength of the structure. In addition, the content of each component is, for example, the total amount of activated carbon powder 80 to 85.
Wt%, Ketjen Black 5-10 wt% and PTF
It is desirable to have a ratio of E5 to 10% by weight.

Further, as the binder, in addition to the above components, polyvinylidenefluorite (PVDF), phenol, coal tar, polybutylbutyral (PVB)
And the like, and these binders 4
May be carbonized to exist as a carbon.

In addition, the capacitance of the capacitor is increased,
In order to maximize the properties of the activated carbonaceous structure and obtain the required strength as a structure, the activated carbonaceous structure 1
It is desirable that the specific surface area is 1000 to 2500 m ² / g.

(Structure of Electric Double Layer Capacitor) Next, as a preferred application example of the above-mentioned activated carbonaceous structure, an active carbonaceous structure 1 is impregnated with an electrolytic solution, and this is used as a polarizable electrode of the electric double layer capacitor. One example used will be described with reference to the schematic sectional view of FIG.

According to FIG. 2, the electric double layer capacitor 11
Is a pair of two polarizable electrodes 1 via a separator 13.
2 and 12, and the polarizable electrodes 12 and 12
An electrode body cell 15 of a current collector 14, a polarizable electrode 12, a separator 13, a polarizable electrode 12, and a current collector 14 in which current collectors 14 and 14 are laminated on the outer surfaces of the current collector 14, respectively is provided.

Here, since the polarizable electrode 12 is made of the above-described activated carbonaceous structure 1 impregnated with an electrolytic solution, as described above, the electric double layer capacitor 11 has a low internal resistance, The capacitance is high, and the capacitance of the electric double layer capacitor 11 can be increased particularly in short-time charging.

The electrolytic solution impregnated in the polarizable electrode 12 may be an aqueous solution such as sulfuric acid or nitric acid, ethylene carbonate (EC), propylene carbonate (PC), or the like.
Non-aqueous solvents such as butylene carbonate (BC), γ-butyrolactone (γ-BL), N, N-dimethylformamide, sulfolane, and 3-methylsulfolane; and quaternary ammonium salts such as tetraammonium tetrafluoroborate and quaternary sulfonium salts Although a non-aqueous electrolytic solution in which an electrolyte such as a quaternary phosphonium salt is combined can be used, it is particularly preferable to use a non-aqueous electrolytic solution having a high decomposition voltage. Furthermore, in order to obtain a stable and high capacitance, the amount of the electrolyte dissolved in the solvent is 0.5 to 2 mol / mol.
It is desirable to be 1.

On the other hand, the separator 13 disposed between the polarizable electrodes 12, 12 is formed of an organic film such as pulp or polyethylene or polypropylene, a glass fiber nonwoven fabric, ceramics, or the like, and a pair of polarizers forming a positive electrode and a negative electrode. The separator 12 is formed to insulate the electrodes 12 from each other, and is formed of a porous material through which ions in the electrolytic solution can pass.
The electrolyte is also impregnated inside.

The current collector 14 is made of a conductive metal such as aluminum, silver, gold, nickel, stainless steel, or the like.
In particular, it is formed of a metal foil or stainless steel having a thickness of 20 to 100 μm, and exchanges electric charges with the polarizable electrode 12.

Further, the electrode assembly cell 15 is provided with the polarizable electrode 12.
In order to prevent the electrolyte solution impregnated in the laminate from leaking to the outside and to fix and protect the laminate, the laminate is housed and sealed in the exterior material 16. The exterior material 16 is made of a non-conductive material, for example, a plastic such as polypropylene or acrylic, glass, ceramics, or a so-called laminate film in which both surfaces of a metal foil such as an aluminum foil are covered with an organic resin film. It is formed.

In FIG. 2, the polarizable electrode 12,
Although the separator 13 and the current collector 14 were formed of a plate-like body and these plate-like bodies were laminated, the present invention is not limited to this, and the length of the current collector-polarizable electrode-separator It may be formed by winding a length tape-shaped laminate.

(Manufacturing Method) Next, a method for manufacturing the above-described electric double layer capacitor will be described. First, in order to produce a solid activated carbon structure (hereinafter, abbreviated as activated carbon structure) forming a polarizable electrode, two types of activated carbon raw materials having different particle sizes are prepared. Average particle size (r ₁ ) of 20 to
The phenolic resin-based activated carbon having a thickness of 50 μm is produced by using a phenolic resin as a starting material, being steam-activated, chemical-activated or gas-activated, and roughly pulverized if desired. On the other hand, coconut shell activated carbon having an average particle size (r ₂ ) of 0.1 r _{1 to} 0.4 r ₁ is
It is produced by using a cheap coconut shell as a starting material by steam activation, chemical activation, or gas activation, and pulverized if necessary.

The above two types of activated carbon powders are blended so as to be in a predetermined range, thoroughly mixed in a wet or dry system using a high-speed mixing stirrer, a ball mill or the like, and uniformly mixed to disperse the two types of activated carbon powders. After that, a predetermined amount of a binder such as conductive carbon such as Ketjen black or a Teflon resin such as polytetrafluoroethylene (PTFE) is added to the activated carbon mixed raw material, and mixed with a high-speed mixing stirrer. In addition, as the binder, in addition to the above, polyvinylidene fluoride (PVDF), phenol, coal tar,
Polyvinyl butyral (PVB) or the like can be suitably added, but polytetrafluoroethylene (PTFE) is most suitable from the viewpoint of moldability and the strength of the obtained solid activated carbonaceous structure.

The obtained mixed powder is formed into a sheet-like activated carbonaceous structure by a known molding method such as press molding, extrusion molding, roll molding, or a tape molding method such as a doctor blade method or a calendar roll method. Further, a plurality of the sheet-like activated carbonaceous structures may be laminated and pressure-bonded. Also,
If desired, the activated carbonaceous structure may be carbonized.

By arranging a separator between the obtained two activated carbonaceous structures and disposing a current collector on each of the outer surfaces of the activated carbonaceous structures, a current collector-activated carbonaceous structure (polarizable electrode) -)-Separator-Activated carbonaceous structure (polarizable electrode)-A current collector electrode body cell is formed, and a plurality of the electrode body cells are laminated as required. The electrode body cell is formed by winding a long tape-shaped laminate of a current collector-activated carbonaceous structure (polarizable electrode) -separator-activated carbonaceous structure (polarizable electrode). You may.

Then, the electrode body cell was housed in an exterior material, and an electrolyte was injected into the activated carbonaceous structure in the exterior material to form a polarizable electrode, and an electrolyte was also injected into the separator. Thereafter, the electric double layer capacitor can be manufactured by sealing the exterior material.

[0037]

EXAMPLE A phenolic resin-based activated carbon powder having a BET value of 1500 m ² / g and an average particle size (r ₁ ) shown in Table 1 obtained by carbonizing a phenol resin, and a BET value obtained by carbonizing a coconut shell were obtained. A coconut shell-based activated carbon powder having an average particle size (r ₂ ) shown in Table 1 at 1500 m ² / g is mixed at a weight ratio shown in Table 1 and mixed with a high-speed mixing stirrer.

Next, 10% by weight of Ketjen black and 10% by weight of polytetrafluoroethylene (PTFE) were mixed with 80% by weight of the obtained mixed activated carbon, and the mixture was again stirred by a high-speed mixing stirrer. The obtained powder was subjected to a mesh pass with 40 mesh, and then roll-formed to form a powder.
A sheet-like activated carbonaceous molded article having a thickness of 0 μm was prepared, and
It was cut into a shape of 00 mm x 100 mm.

In the obtained activated carbonaceous structure, 1 mo was added.
1 / l of tetraethoxyammonium tetrafluoroborate (Et ₄ NBF ₄ ) propylene carbonate (P
C) After the solution is impregnated as an electrolyte, the laminate is formed through a porous separator made of a glassy nonwoven fabric to form a laminate cell, and the laminate cell is sealed with aluminum laminate to form an electric double layer capacitor. Produced.

Then, the obtained electric double layer capacitor was charged at a voltage of 2.7 V for 30 minutes, and then charged at 3 mA.
The capacitance (F) of the capacitor was determined by a constant current discharge method at a current of / cm ² . In addition, the internal resistance is such that the discharge voltage is 0.
Discharge is stopped immediately after it becomes, and from the voltage rise at that time,
The voltage V 10 minutes after the discharge was stopped was measured to determine the internal resistance (R) =
It was determined from V / I.

[0041]

[Table 1]

As is clear from Table 1, coconut shell activated carbon
Sample No. containing no powder 1, the capacitance is low.
Partial resistance was high. In addition, phenolic resin-based
Sample No. containing no charcoal powder 8 is coconut shell activated carbon
Low capacitance and increased internal resistance due to agglomeration of powders
Great. Furthermore, the average particle size of the coconut shell activated carbon powder
(R _Two) Is 0.1r₁(R₁: Phenolic resin activated carbon powder
(Average particle size of the powder). 2, 0.4r₁
Sample no. In 10 and 11, powder filling
However, the internal resistance increased.

Further, the phenolic resin-based activated carbon powder having the average particle size (r ₁ ) of less than 20 μm was used for sample No. 11
In this case, a large amount of impurity components were mixed by pulverization at the time of powder production, the internal resistance increased, and the capacitance decreased. Conversely, the average particle size (r ₁ ) of the phenolic resin-based activated carbon powder is 50 μm.
Sample no. In No. 14, the packing property of the activated carbon powder was reduced, the capacitance was low, and the internal resistance was high.

On the other hand, when the average particle size (r ₁ ) is 20 to
A phenolic resin-based activated carbon powder (A powder) of 50 μm and a coconut shell-based activated carbon powder (B powder) having an average particle size (r ₂ ) of 0.1r1 to 0.4r1 are used in combination. Sample No. 3-7, 9, 12,
In No. 13, the dispersibility and the filling property of the activated carbon powder can be enhanced, and in each case, the internal resistance is 31Ω or less, and the capacitance is 14
It had excellent characteristics of F / cc or more. As a result of the ICP analysis, the sample No. For samples other than 11, Fe, Cr, Ni, Na, K and Cl
Was 450 ppm or less in total.

[0045]

As described above in detail, according to the activated carbon quality structures of the present invention, the average particle diameter (r ₁₎ is between phenolic resin activated carbon powder of 20 to 50 m, an average particle diameter (r ₂₎ Is filled with 0.1 r _{1 to} 0.4 r ₁ of coconut shell activated carbon powder, so that no large voids remain between the activated carbon powders and the activated carbon powders aggregate to form large aggregated particles. Since no voids remain, the density of the activated carbon powder can be increased and the capacitance of the electric double layer capacitor can be improved, and the internal resistance can be reduced. And the internal resistance can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one example of the activated carbonaceous structure of the present invention.

FIG. 2 is a schematic cross-sectional view of an example of an electric double layer capacitor using the activated carbonaceous structure of the present invention as a polarizable electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Activated carbonaceous structure 2 Phenolic resin type activated carbon powder 3 Coconut shell type activated carbon powder 4 Binder 11 Electric double layer capacitor 12 Polarized electrode 13 Separator 14 Current collector 15 Electrode cell 16 Exterior material

Claims (4)

[Claims] To 1. A mean particle diameter (r ₁₎ is between phenolic resin activated carbon powder of 20 to 50 m, an average particle diameter (r ₂₎ is 0.
Activated carbon membrane structure characterized by comprising filling a coconut shell based activated carbon powder 1r ₁ ~0.4r _1. 2. The phenolic resin-based activated carbon powder 55 to 7
5% by weight, and 25-45% by weight of the coconut shell activated carbon powder
The activated carbonaceous structure according to claim 1, which is contained in a ratio of: 3. Fe, Cr, Ni, N based on the total amount of the structure
3. The activated carbonaceous structure according to claim 1, wherein the total content of a, K, and Cl is 450 ppm or less. 4. A pair of claim 1 through 3 via a separator.
And a current collector disposed on each of the outer surfaces of the pair of polarizable electrodes, and a polarizable electrode obtained by impregnating the activated carbonaceous structure with an electrolytic solution. Multilayer capacitors.