JP2002289481A - Activated carbonaceous structure and electric double layer capacitor using the same - Google Patents

Abstract

(57) [Object] To provide an electric double layer capacitor having a high capacitance and a low internal resistance by increasing the conductivity of an activated carbonaceous structure. SOLUTION: A potassium titanate whisker 3 is added to activated carbon powder 2 through a separator 13 in a total amount of 0.5 to 20%.
In addition to disposing a pair of polarizable electrodes 12 made of the activated carbonaceous structure 1 containing at a ratio of weight%, an electrode laminate 15 in which a pair of current collectors 14 is disposed on each outer surface of the polarizable electrode 12 is used as an exterior material. The electric double layer capacitor 11 housed in the housing 16 is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an activated carbonaceous structure having high conductivity and an electric double layer capacitor using the same as a polarizable electrode.

[0002]

2. Description of the Related Art Activated carbonaceous structures are used for various purposes such as absorbent materials, deodorants, and catalyst carriers. Among them, an electric double layer formed by polarization of ions at the interface between a polarizable electrode and an electrolytic solution. It is used as a polarizable electrode material of an electric double-layer capacitor using the same.

[0003] Such an electric double layer capacitor has a structure in which a pair of polarizable electrodes are arranged via a separator, and a pair of current collectors are arranged on the outer surfaces of the polarizable electrodes, respectively. It is housed in a material and sealed, and such an electric double layer capacitor has both functions of a capacitor and a battery, and can exhibit a large capacitance as compared with a conventional capacitor. Because of its rapid charge / discharge capability, it is attracting attention as a battery for large-capacity motors, such as a small memory backup power supply and a drive source for automobiles. Rarely, the improvement of the capacitance and the reduction of the internal resistance are attempted.

In an electric double layer capacitor, for example, in Japanese Patent Application Laid-Open No. 63-186414, a valve metal such as titanium is added to activated carbon and mixed to lower the contact resistance between the activated carbons to reduce the internal resistance. It describes that the resistance can be reduced.
No. 250 describes that by electrically connecting activated carbon particles with carbon whiskers, the capacitance of an electric double layer capacitor can be increased and the internal resistance can be reduced.

[0005]

However, in the electric double layer capacitor to which metal titanium or the like is added in JP-A-63-186414, although the internal resistance of the polarizable electrode can be reduced, it is described in the same publication. As described above, the capacitance becomes small, which is not suitable for producing a large-capacity electric double layer capacitor.

Further, in the electric double layer capacitor to which carbon whiskers are added as disclosed in JP-A-7-307250, the specific resistance of the carbon whiskers is 1 × 10 ⁻³ Ω · cm.
Due to the low degree, the effect of reducing the internal resistance is small, and further reduction in the internal resistance has been demanded.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide an activated carbonaceous structure having a high capacitance and a low internal resistance, and an electric double layer using the same as a polarizable electrode. It is to provide a capacitor.

[0008]

Means for Solving the Problems The present inventors have studied the composition of an activated carbonaceous structure constituting a polarizable electrode with respect to the above problem, and found that a predetermined amount of potassium titanate whiskers was dispersed between activated carbons. Thus, it was found that while maintaining the capacitance of the electric double layer capacitor, the conductivity between the activated carbons was significantly increased, the contact resistance was reduced, and the internal resistance could be reduced.

That is, in the activated carbonaceous structure of the present invention, potassium titanate whiskers are contained in activated carbon powder in a total amount of 0.1%.
It is characterized in that it is contained at a ratio of 5 to 20% by weight.

Here, it is desirable to coat the surface of the potassium titanate whisker with carbon.

The ratio (r ₂ / r ₁ ) of the average major axis diameter r ₂ of the potassium titanate whisker to the average particle diameter r ₁ of the activated carbon powder is 0.2 to 20, and the potassium titanate It is desirable that the whisker has an average aspect ratio of 10 to 70.

Further, the activated carbonaceous structure has a thickness of 50
It is preferable that the plate-like activated carbonaceous structure is oriented in a direction orthogonal to the thickness direction of the plate-like activated carbonaceous structure.

Further, the electric double layer capacitor of the present invention comprises:
A pair of polarizable electrodes made of the activated carbonaceous structure were disposed via a separator, and an electrode laminate in which a pair of current collectors was disposed on each of outer surfaces of the polarizable electrodes was housed in an exterior material. It is characterized by the following.

[0014]

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, for example, an average particle size of 1 to 5
Activated carbon powder 2 having a spherical shape, hollow shape, irregular shape or the like of 0 μm, particularly 5 to 20 μm, contains potassium titanate whisker 3 dispersed and contained in a ratio of 0.5 to 20% by weight based on the total amount of activated carbonaceous structure 1. It is a great feature that the specific resistance between the activated carbon powders 2 is 1 × 10 ^{−1 to −2} Ω ·
cm of potassium titanate whiskers can be bridged and the electrical connection between the activated carbon powders 2 can be improved by the potassium titanate whiskers 3. Therefore, the internal resistance in the activated carbonaceous structure 1 is reduced, and the electric double layer capacitor is rapidly charged. Discharge becomes possible, and the capacitance can be increased.

Here, if the content of potassium titanate whisker is less than 0.5% by weight of the total amount, activated carbon powder 2
When the contact resistance is high and the internal resistance increases, and when the content of potassium titanate whisker exceeds 20% by weight, the content ratio of the activated carbon decreases and the capacitance of the electric double layer capacitor decreases. Activated carbonaceous structure 1
Characteristics are impaired. The desirable content of potassium titanate whisker is 5 to 10% by weight based on the total amount.

Further, according to the present invention, the shape of the potassium titanate whisker 3 is such that the content of the activated carbon powder 2 is extremely reduced and the capacitance of the electric double layer capacitor is not reduced. In order to improve the electrical connection between the activated carbon powders 2 and improve the connection between the activated carbon powders 2 by breaking through an insulator such as a binder 5 described later, the average major axis diameter r of the potassium titanate whisker 3 is improved. ₂ is 10-2
0 μm, and the ratio (r ₂ / r ₁ ) of the average major axis diameter r ₂ of the potassium titanate whisker 3 to the average particle diameter r ₁ (for example, _{1 to} 50 μm) of the activated carbon powder 2 is:
Desirably, it is 0.2 to 20.

In order to increase the mechanical strength of the activated carbonaceous structure 1, the average aspect ratio R of the potassium titanate whiskers 3, that is, the average major axis diameter r ₂ and the average minor axis diameter r ₂ of the potassium titanate whiskers 3 are set. ₃ and the ratio of (r ₂ / r ₃₎ 15
To 70, particularly preferably 20 to 50, and
Average desirably short axis diameter r ₃ is 0.3 to 0.6 .mu.m. Further, the potassium titanate whiskers need not necessarily be arranged linearly, and may be partially curved along the arrangement of the activated carbon powder 2 as shown in FIG.

The average aspect ratio R of the potassium titanate whisker 3 in the present invention is defined as the activated carbonaceous structure 1
An average major axis diameter r ₂ of ten or more potassium titanate whiskers 3 in an internal SEM photograph (however, when the activated carbonaceous structure 1 is plate-shaped, the polished surface in the main plane direction of the activated carbonaceous structure 1) And the average minor axis diameter r ₃ (r ₂ / r ₃ ).

Further, according to the present invention, it is desirable to coat the surface of potassium titanate whisker 3 with carbon in order to suppress the reaction between the polarizable electrode (activated carbonaceous structure 1) and the electrolyte. . The thickness of the carbon coating on the surface of the potassium titanate whisker 3 is preferably 0.1 to 0.5 μm. Further, the degree of graphitization of carbon coated on the surface of the potassium titanate whisker 3 is 30% or more, particularly 50%.
% Is desirable from the viewpoint of improving conductivity. According to the present invention, since the potassium titanate whisker 3 plays the role of a reinforcing material, the strength of the potassium titanate whisker 3 can be increased even if the degree of graphitization of carbon coated on the surface of the potassium titanate whisker 3 increases. The conductivity can be improved without lowering.

Further, according to the present invention, Fe, Cr, Ni, N contained in the activated carbon powder are improved in terms of improving the capacitance of the electric double layer capacitor and reducing the internal resistance.
It is desirable that the impurities of a, K, and Cl are 450 ppm or less in total with respect to the total amount of the structure.

In the activated carbonaceous structure 1, for example,
Conductive carbon 4 such as Ketjen black having an average particle size of 200 nm or less, particularly 50 to 100 nm, and Teflon (registered trademark) such as polytetrafluoroethylene (PTFE).
A resin may be contained as the binder 5, and a part of the conductive carbon 4 such as Ketjen black has a toughness and is in a fibrous form in view of improving the strength of the structure. desirable. The content of each component is, for example, 60 to 94.
5% by weight and potassium titanate whisker 3 0.5 to 2%
It is desirable that the conductive carbon 4 including carbon coated on the surface of the potassium titanate whisker 3 has a ratio of 0 to 10% by weight, and the binder 5 has a ratio of 5 to 10% by weight.

Further, as the binder 5, in addition to the above components, polyvinylidenefluorite (PVDF), phenol, coal tar, polybutylbutyral (PV
B), ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride copolymer, tetrafluoroethylene-perfluoroalkylene vinyl ether copolymer, phenol resin, cellulose resin, coal Tar, polybutyl butyral (PVB), polyvinyl formal (PVFM)
Polyvinyl acetal, vinyl acetate, and the like can be suitably added, and these binders 5 may be carbonized to exist as carbon.

In addition, the capacitance of the capacitor is increased,
In order to obtain the necessary strength as a structure while maximizing the properties of the activated carbon structure 1, the activated carbon structure 1
Has a specific surface area of 700 to 3000 m ² / g, especially 120
Desirably, it is 0 to 2500 m ² / g.

Further, according to the present invention, by forming the activated carbonaceous structure 1 in a plate shape having a thickness of 50 to 150 μm, the activated carbonaceous structure 1 has a uniform thickness without defects such as pinholes and cracks, and particularly has a rapid filling rate. The internal resistance during discharge can be reduced, and the potassium titanate whiskers 3 are oriented in the main plane direction (the direction orthogonal to the thickness direction) of the plate-shaped activated carbonaceous structure 1. In order to increase the packing density and mechanical strength of the electrolyte, it is desirable to be able to quickly impregnate the electrolyte.

In the present invention, the phrase that the potassium titanate whiskers 3 are oriented in a direction orthogonal to the thickness direction of the plate-like activated carbonaceous structure 1 means that the plate-like activated carbonaceous structure 1
The aspect ratio (average major axis diameter r ₂ / average minor axis diameter r ₃ ) _{RL of the} potassium titanate whisker 3 observed in the EM photograph and the aspect ratio R in the thickness (cross section) direction are shown.
It indicates that the ratio ( _RL / Rt) to t is 0.2 or more, and it is particularly desirable that this ratio ( _RL / Rt) be 0.4 or more.

(Structure of Electric Double Layer Capacitor) Next, as a preferable application example of the above-mentioned activated carbonaceous structure, the activated carbonaceous structure 1 is impregnated with an electrolytic solution, and this is used as a polarizable electrode of the electric double layered 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
A current collector 14, a polarizable electrode 12, a separator 13, a polarizable electrode 12, and a current collector 14, each having a current collector 14, 14 laminated on the outer surface of the device, are provided.

Here, since the polarizable electrode 12 is formed by impregnating the above-described activated carbonaceous structure 1 with an electrolytic solution, the electric double layer capacitor 11 has a low internal resistance and 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 of 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, a separator 13 disposed between the polarizable electrodes 12 and 12 is formed of pulp, an organic film of polyethylene, polypropylene or the like, 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, and stainless steel.
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 laminate 15 is formed of 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 electrodes 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 an activated carbon structure) forming a polarizable electrode, for example, an activated carbon powder raw material having an average particle size of 1 to 50 μm and a potassium titanate whisker are used. prepare.

Activated carbon powder includes phenol resin, coconut shell,
It is produced by using wood, coal, petroleum pitch, petroleum coke, or the like as a starting material, steam-activated, chemical-activated, or gas-activated, and if necessary, coarsely pulverized.

On the other hand, potassium titanate whiskers (K ₂ O)
NTiO ₂ , n = ₂ , 4, 6, 8) is, for example, K ₂ M
using oO _4, the raw material at 1150 ° C. (TiO ₂ and K ₂ C
A predetermined mixture of O ₃ ) and flux is melted and
A flux method of gradually cooling to 0 ° C. to synthesize K ₂ Ti ₄ O ₉ whiskers as a primary compound, or mixing raw materials to a stoichiometric composition ratio corresponding to K ₂ Ti ₂ O ₃ and melting at 1100 ° C. The melt is quenched and solidified to synthesize needle-like K ₂ Ti ₂ O ₅ as a primary compound, and then synthesized by a melt method in which it is converted into K ₂ Ti ₄ O ₉ whiskers or K ₂ Ti ₆ O ₁₃ whiskers by firing or the like. Is done.

To coat the surface of the potassium titanate whisker with carbon, a thin film forming method such as a CVD method may be used.

The above two kinds of powders are blended so as to be within a predetermined range, sufficiently mixed in a wet or dry system using a high-speed mixing stirrer or a ball mill, etc., and uniformly mixed to disperse the two kinds of activated carbon powder. After that, a predetermined amount of a binder such as a 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.

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.

According to the present invention, it is particularly desirable to form the activated carbonaceous structure having a predetermined thickness and to form the activated carbonaceous structure by a roll forming method in order to increase the degree of orientation of potassium titanate whiskers in the activated carbonaceous structure.

A plurality of the sheet-like activated carbonaceous structures may be laminated and pressed, and if desired, the activated carbonaceous structures may be carbonized.

By arranging a separator between the obtained two activated carbonaceous structures and arranging a current collector on each of the outer surfaces of the activated carbonaceous structures, a current collector-activated carbonaceous structure (polarizable electrode) A) -separator-activated carbonaceous structure (polarizable electrode) -current collector electrode stack, and a plurality of the electrode stacks are stacked as desired. The electrode laminate is formed by winding a long tape-like laminate of a current collector, an activated carbonaceous structure (polarizable electrode), a separator, and an activated carbonaceous structure (polarizable electrode). You may.

Then, the electrode laminate 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 the electrolyte was also injected into the separator. Thereafter, the electric double layer capacitor can be manufactured by sealing the exterior material.

[0044]

EXAMPLE Coconut shell activated carbon powder having an average particle size of 20 μm (specific surface area: 1500 m ² / g), Ketjen black, and polytetrafluoroethylene (PTF) as a binder
E) was mixed at a ratio shown in Table 1 and stirred by a high-speed mixing stirrer. The obtained powder was subjected to a mesh pass with a 40 mesh, and then an amount of potassium titanate whisker shown in Table 1 was added. Then, the mixture was again stirred by the high-speed mixing stirrer. The surface of the potassium titanate whisker was coated with carbon having an average thickness of 100 nm by a CVD method. Then, this was roll-formed to form a sheet-like activated carbonaceous structure having the thickness shown in Table 1, and cut into a 25 x 25 mm shape.

With respect to the obtained activated carbonaceous structure, SEM observation was performed on the main plane of the sheet, and the average major axis diameter r ₂ and the average minor axis diameter r ₃ of the potassium titanate whisker were measured. It was calculated aspect ratio R _L is r ₂ / r _3).
Further, SEM observation was performed on the cross section (thickness) of the sheet, and the aspect ratio R of the potassium titanate whisker was determined in the same manner as described above.
_t was calculated, and the ratio (R _L / R _t ) was calculated as the degree of orientation. The results are shown in Table 1.

[0046]

[Table 1]

Further, the sheet-shaped activated carbonaceous structure is used as a polarizable electrode, and an etched aluminum foil is laminated on the outer surface of the polarizable electrode via a cellulosic separator between the two polarizable electrodes. An electrode laminate was produced.
After joining the current collector and the terminal of the electrode laminate, the electrode laminate was inserted into a bag-shaped aluminum laminate sealing material, and 1 mol / l of tetraethoxyammonium tetrafluoro was inserted into the bag-shaped sealing material. After a polarizable electrode and a separator were impregnated with a propylene carbonate (PC) solution of borate (Et ₄ NBF ₄ ) as an electrolyte, the sealing material at the opening was hermetically sealed to produce an electric double layer capacitor.

With respect to the obtained electric double layer capacitor,
After charging at a voltage of 2.7 V for 15 minutes, 3 mA / cm ²
Capacitance of capacitor by constant current discharge method (F)
I asked. The internal resistance (Ω) was determined from R = V / I from the voltage V 10 minutes after the discharge was stopped, when the discharge was stopped immediately after the discharge voltage became 0. Also, after charging at 25 ° C. and 2.7 V for 15 minutes,
Find the voltage between terminals when left unloaded for 24 hours,
The voltage was calculated as a voltage holding characteristic (self-discharge characteristic). The results are shown in Table 2.

[0049]

[Table 2]

As is clear from Tables 1 and 2, Sample No. 1 containing no potassium titanate whisker was used. Sample Nos. 1 and 2 and the addition amount of potassium titanate whisker of 0.5% by weight or less. In No. 5, the internal resistance was high and the voltage holding characteristics were poor. In addition, potassium titanate whisker is used for 20
Sample No. to which more than% by weight was added. In No. 12, the capacitance decreased.

On the other hand, in Samples 3, 4, 6 to 11 and 1314 in which the activated carbon powder contained a predetermined amount of potassium titanate whisker according to the present invention, the capacitance was 2.7 F or more. It had excellent characteristics such as an internal resistance of 18.0 Ω or less and a voltage holding characteristic of 2.58 V or more.

[0052]

As described in detail above, according to the activated carbonaceous structure of the present invention and the electric double layer capacitor using the same as a polarizable electrode, a predetermined amount of potassium titanate whiskers can be dispersed between activated carbons. Accordingly, while maintaining the capacitance of the electric double layer capacitor, the conductivity between the activated carbons is significantly increased, the contact resistance is reduced, and the internal resistance can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a schematic 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 Activated carbon powder 3 Potassium titanate whisker 4 Conductive carbon 5 Binder 11 Electric double layer capacitor 12 Polarized electrode 13 Separator 14 Current collector 15 Electrode laminate 16 Exterior material

Claims (6)

[Claims] 1. An activated carbonaceous structure characterized in that activated carbon powder contains potassium titanate whiskers in a ratio of 0.5 to 20% by weight based on the total amount. 2. The activated carbonaceous structure according to claim 1, wherein the surface of said potassium titanate whisker is coated with carbon. 3. The ratio (r ₂₎ of the average major axis diameter r ₂ of the potassium titanate whisker to the average particle diameter r ₁ of the activated carbon powder.
/ R ₁₎ activated carbon quality structure according to claim 1 or 2, wherein it is 0.2 to 20. 4. The method according to claim 1, wherein said potassium titanate whisker has an average aspect ratio of 10 to 70.
4. The activated carbonaceous structure according to any one of claims 1 to 3. 5. A plate having a thickness of 50 to 150 μm, wherein said potassium titanate whiskers are oriented in a direction orthogonal to a thickness direction of said plate-like activated carbonaceous structure. 5. The activated carbonaceous structure according to any one of 1 to 4. 6. A pair of polarizable electrodes comprising the activated carbonaceous structure according to any one of claims 1 to 5 is disposed via a separator, and a pair of current collectors is provided on each of the outer surfaces of the polarizable electrodes. An electric double layer capacitor characterized in that the arranged electrode laminate is housed in an exterior material.