JP2001155972A - Electrochemical capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical for sealing packages through thermal welding, regardless of the thickness or the shape of the electrode terminal, and improving reliability in strength and airtightness of the package. SOLUTION: A laminate (single capacitor cell 12) includes a pair of metallic collectors and polarized electrode, made of partly oxidized carbon material with minute crystal carbon similar to graphite, with an electrically insulating separator between the polarized electrode. The laminate is put at the collectors and dipped in organic electrolyte and sealed in a package 60 of an electrochemical capacitor. Electrode terminals 44 and 45, connected to the collectors, are an electrode unit 50 made in a body with a support member 54. The electrode unit 50 is interposed therein the package 60 and is then sealed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention uses a carbon material having graphite-like microcrystalline carbon as a polarizable electrode material,
The present invention relates to an electrochemical capacitor that exhibits a high capacitance density based on pseudo capacitance by using a product of an electrochemical reaction as an active material.

[0002]

2. Description of the Related Art Electrochemical capacitors (hereinafter, referred to as “capacitors”) have farad-class large capacities and excellent charge / discharge cycle characteristics. In addition to being used as batteries for transport aircraft, from the viewpoint of effective use of energy, use in applications such as storage of nighttime power is also being studied.

As shown in FIG. 5, a single-electrode cell 10, which is one of the basic structures of such a capacitor, generally has polarizers on the positive electrode side on current collectors 20 and 22 each made of a metal material. An electrode 24 and a polarizable electrode 26 on the negative electrode side are formed, and have a structure in which the polarizable electrodes 24 and 26 are separated by a separator 28. The liquid is impregnated.

FIG. 6 shows the structure of a single capacitor cell 12 in which a plurality of single electrode cells 10 are connected to a current collector 20.
・ Electrode extraction portions 30 and 32 formed at 22 are electrically connected in parallel. Relatively large capacitors used for automobiles, etc.
Such a single capacitor cell 12 is preferably used.
Each of the single electrode cell 10 and the single capacitor cell 12 is a flat plate type, and has a feature that high filling and large area can be easily performed.

When the above-described capacitor is actually used, strict packaging suitability (sealing properties, barrier properties, abrasion resistance, expansion resistance, etc.) is required for parts other than the electrode terminals in order to prevent leakage or deterioration of the electrolytic solution. It is important to package in.
For this reason, as shown in FIG. 4, for example, as shown in FIG. 4, a single electrode cell 10 or a single capacitor cell 12 and an organic electrolytic solution are mounted in a package 60 which is a pouch made of an aluminum laminated film or the like. Then, the tape-shaped electrode terminals 40 and 42 covered with the heat-sealing film are taken out of the package 60, and then heat-sealed together with the seal part 62 of the package to seal.

However, in the above-described packaging method, the shape of the electrode terminals 40 and 42 that can be used is limited to a tape-shaped one. When the thickness of the electrode terminals 40 and 42 becomes too large, the sealing of the package is performed. It was difficult to seal at the part 62. In addition, as the capacity of the capacitor increases in recent years, the stacking of the single capacitor cells 12 progresses, and the self-weight of the capacitor increases, so that the stress concentration of the seal portion 62 of the package increases.
However, there is a problem that the strength reliability is significantly reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the related art,
The purpose is to provide an electrochemical capacitor that can seal the package by heat without being affected by the thickness and shape of the electrode terminal and can improve the strength reliability and airtightness of the package. To provide.

[0008]

Means for Solving the Problems According to the present invention, a pair of current collectors made of a metal material are formed as a main material by partially oxidizing a carbon material having microcrystalline carbon similar to graphite. An electrochemical capacitor in which at least one laminate having an electrically insulating separator sandwiched between the polarizable electrodes is sealed in a package while being immersed in an organic electrolyte. Thus, an electrochemical capacitor is provided in which electrode terminals respectively connected to the current collector are electrode units integrated with a holding material, and the electrode units are sealed by being interposed in a package. . At this time, in the present invention,
The electrode unit preferably has a shape that minimizes the contact area with the outside of the package, and the holding material is preferably a resin having excellent bonding properties with the electrode terminals and the package.

In such an electrochemical capacitor of the present invention, it is preferable to use, as the carbon material, one obtained by heat-treating a graphitizable carbon material at 500 ° C. to 1000 ° C. in an inert gas atmosphere. As one method of the partial oxidation, a method of heat-treating a carbon material in the presence of at least one of an alkali metal compound containing an alkali metal and oxygen in an inert atmosphere at a temperature not lower than a temperature at which an alkali metal vapor is generated. Can be In addition, as another partial oxidation method, it is preferable to use a method of immersing a carbon material in an oxidizing agent that can form graphite when dipping graphite.Furthermore, the carbon material is oxidized in an oxidizing atmosphere containing an oxidizing gas. Alternatively, a method of performing heat treatment at a temperature lower than the carbonization temperature of the graphitizable carbon raw material may be employed.

The electrochemical reaction for developing the capacitance is performed by immersing a sheet-like electrode made using a material obtained by partially oxidizing a carbon material, a separator and a current collector in an organic electrolytic solution, and immersing the capacitor in the organic electrolyte. It is preferable to carry out the current supply after the configuration. At this time, it is also possible to use different electrolyte solutions for performing an electrochemical reaction and for operating as a capacitor.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An electrochemical capacitor according to the present invention is characterized in that a pair of current collectors made of a metal material are formed mainly by partially oxidizing a carbon material having microcrystalline carbon similar to graphite. At least one polar electrode is provided, and at least one of the polarizable electrodes is sandwiched between electronically insulating separators.
An electrochemical capacitor in which two laminates are sealed in a package in a state of being immersed in an organic electrolyte, and the electrode terminals respectively connected to the current collector are integrated with a holding material to form an electrode unit. In this case, the electrode unit is sealed (sealed) with the package interposed in the package. Thereby, without being affected by the thickness or shape of the electrode terminal,
It is possible to seal the package by heat sealing and to improve the strength reliability and airtightness of the package.

Hereinafter, the present invention will be described in more detail with reference to the drawings. 1 and 2 show examples of an electrode unit used in the electrochemical capacitor of the present invention, and FIG.
FIG. 2 is a schematic perspective view showing an example of a package in the electrochemical capacitor of the present invention. Here, the main feature of the electrochemical capacitor of the present invention is to use the electrode units 50 and 52 in which the electrode terminals 44 and 46 are integrated with the holding member 54 as shown in FIGS. Thus, the package 60 can be thermally sealed without being affected by the thickness and shape of the electrode terminals 44 and 46, and the stress concentration of the package sealing portion 62 due to the weight of the capacitor can be reduced. Therefore, the strength reliability and airtightness of the package 60 can be improved.

In particular, the electrode unit 52 shown in FIG.
In order to minimize the contact area of the package 60 with the outside and increase the bonding area between the electrode unit 52 and the package 60, a taper 55 is provided around the electrode unit 52 so that the electrode unit 52 can be Because it can be heat-sealed to surround
The strength reliability and airtightness of the package 60 can be further improved.

The holding member 54 used in the present invention is not particularly limited as long as it is a resin having excellent bonding properties with the electrode terminals 44 and 46 and the package 60. For example, a functional group having good adhesion to metal is used. An added modified resin or the like can be suitably used. The material of the electrode terminal used in the present invention is not particularly limited as long as it has high electric conductivity and high-temperature deformation resistance. For example, high-purity aluminum or the like can be preferably used.

Furthermore, the package 60 used in the present invention
In order to have a function according to the purpose, a laminated film in which films with different characteristics are laminated is used,
In particular, an aluminum laminate film can be suitably used.

Next, an example of a method for packaging an electrochemical capacitor according to the present invention will be described. For example, the electrode extraction portions 30, 32 of the single capacitor cell 12 shown in FIG.
And the electrode terminals 44 and 46 of the electrode unit 50 are connected respectively. Next, after the single capacitor cell 12 connected to the electrode unit 50 and the organic electrolyte are charged into a package 60 which is a pouch made of an aluminum laminated film or the like, the electrode unit 50 is placed at a predetermined position of the package 60. By heat-sealing with the interposition, the single capacitor cell 12 and the organic electrolyte are sealed (sealed), and the package of the electrochemical capacitor is completed as shown in FIG.

The single capacitor cell 12, which is one of the basic structures of the electrochemical capacitor of the present invention, has a pair of current collectors 20, 2 made of a metal material, for example, as shown in FIG.
2, a positive electrode-side polarizable electrode 24 and a negative electrode-side electrode 26 are formed, each of which is formed mainly by partially oxidizing a carbon material having microcrystalline carbon similar to graphite, and the polarizable electrodes 24 and 26 are formed. A laminate (single-electrode cell) 10 having an electronic insulating separator 28 interposed therebetween is laminated, and the electrode take-out portions 3 formed on the current collectors 20 and 22 are stacked.
The structures 0 and 32 are electrically connected in parallel.

Next, the polarizable electrode used in the present invention will be described in more detail. In producing a carbon material as a main material of the polarizable electrode used in the present invention, first, petroleum coke, coal coke, petroleum pitch (tar), coal pitch (tar), mesophase carbon, polyvinyl chloride, polyimide, etc. The graphitized carbon material is heat-treated and carbonized. This carbonization treatment is performed in an inert gas atmosphere for about 50 minutes.
It is suitably performed in a temperature range of 0 ° C to 1000 ° C. One of these easily graphitizable carbon materials may be used alone, or a mixture of a plurality of types may be used. As the inert gas, nitrogen gas and rare gases such as argon gas and helium gas are preferably used.

FIG. 7 is an explanatory view of the microstructure of the carbon material 90 thus obtained. The carbon material 90 is made of graphite-like microcrystalline carbon 94 (the net plane of the microcrystalline carbon 94 is perpendicular to the paper surface).
Are mainly composed of a structural body 96 which is laminated in layers. The structure 96 itself has a structure in which the microcrystalline carbons 94 are stacked substantially parallel and at substantially equal intervals, but the arrangement between the structures 96 is such that the layer planes are substantially parallel, but completely parallel. They are stacked at random angles without any orientation.

Next, the obtained carbon material is preferably pulverized so as to have a predetermined particle size. Here, when the carbon material is obtained in the form of a powder because the easily graphitizable carbon raw material is in the form of a powder or the like, the pulverization treatment is not necessarily required. By this pulverizing process, the reaction of the partial oxidation process in the next step can be made uniform and the processing time can be shortened. In addition, various well-known methods can be used for the pulverization treatment regardless of a dry type or a wet type.

Next, the carbon material is partially oxidized. One method of this partial oxidation is to form a carbon material in the presence of at least one alkali metal compound containing an alkali metal and oxygen (hereinafter referred to as “alkali metal compound”), in an inert atmosphere, in an alkali metal vapor. Heat treatment at a temperature higher than the temperature at which

Here, as the alkali metal compound,
Potassium, sodium, lithium, and alkali metal elements
Oxides, hydroxides, nitrates, sulfates, carbonates, and the like using rubidium can be used, and examples thereof include potassium hydroxide, sodium hydroxide, potassium carbonate, and sodium carbonate. These alkali metal compounds may be used in combination of two or more.

The “in the presence” of the alkali metal compound
This means that the carbon material is directly mixed with the alkali metal compound or that the carbon material is placed in an environment in contact with the alkali metal vapor generated from the alkali metal compound. Further, the treatment at a temperature at which an alkali metal vapor is generated means that the treatment is performed by heating to a temperature at which an alkali metal vapor is generated in the presence of a carbon material and an alkali metal compound. Such a heat treatment is performed in an inert gas atmosphere.

Now, as described above, the carbon material heat-treated in the presence of the alkali metal compound and partially oxidized is
Unnecessary alkali metal compounds are attached to the carbon material or the like, and need to be removed. Therefore, an alkali metal compound unnecessarily attached to the carbon material is dissolved using an alcohol-based solvent such as methanol or ethanol, distilled water, or the like, and the carbon material is washed and filtered. Thus, a carbon material used for the polarizable electrode is obtained.

Another method of partially oxidizing a carbon material is a method of heat-treating a carbon material in an oxidizing atmosphere containing an oxidizing gas at a temperature lower than the carbonization temperature of the graphitizable carbon material. Examples of the oxidizing gas include oxygen, NO _x , CO _x , water vapor, and air. By controlling the partial pressure and the oxidizing temperature of the oxidizing gas, extreme oxidation of carbon material, that is, while suppressing combustion, Oxidation can be performed.

Still another method of partially oxidizing a carbon material is a method of immersing a carbon material in an oxidizing agent capable of forming and dissolving graphite acid when graphite is immersed, and oxidizing the carbon material. Oxidizing agents include hot nitric acid and potassium chlorate (KCl
Mixture of O _3), mixed acid and the like in the mixture and hot nitric acid and hot sulfuric thermal nitric acid and perchloric acid (HClO ₄₎ and the like, can be carried out partial oxidation by controlling the temperature and the immersion time.

Now, a polarizable electrode is manufactured using the carbon material manufactured as described above as a main material. For the production of this polarizable electrode, after adding a conductive agent such as an organic binder or carbon black to a carbon material, mixing, kneading, etc.,
It is performed by processing into various shapes such as a plate shape and a sheet shape. In particular, high performance as a capacitor can be obtained by forming a sheet into a polarizable electrode.

The organic electrolyte used in the present invention is a solute, that is, an electrolyte, a quaternary ammonium tetrafluoroborate (BF ₄ ⁻ ) salt or a hexafluorophosphoric acid (PF ₆ ⁻ ) salt, or tetraethylammonium (PF ₆ ⁻ ) salt. TEA ⁺⁾ or BF ₄ salt or PF ₆ salt of tetrabutylammonium (TBA ^+), BF ₄ salt or a PF ₆ salt of triethylmethylammonium (TEMA ^+), or quaternary phosphonium salt of BF ₄ salt or P
F ₆ salt, BF _{4 of} tetraethylphosphonium (TEP ⁺ )
Salt or PF ₆ salt, or general formula

[0029]

Embedded image

(Wherein R ₁ and R ₂ are alkyl groups having 1 to 5 carbon atoms, and R ₁ and R ₂ may be the same or different groups). _Four
Salts or PF ₆ salts, and BF ₄ salts or PF ₆ salts of 1-ethyl-3-methyliridazolium (EMI ⁺ ) can be suitably used.

Further, the organic electrolyte solution used in the present invention includes propylene carbonate (PC), γ-butyl lactone (GBL), ethylene carbonate (E
Those containing at least one of C) and sulfolane (SL) are preferably used. In addition, the PC, GBL, EC,
It is also possible to use a solvent containing at least one of SL as a main solvent and a solvent containing at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) as a secondary solvent. is there.

Here, the main solvent refers to a solvent capable of obtaining sufficient performance as an electrolyte solvent even when the substance is used alone, and the auxiliary solvent refers to a solvent having a low performance as an electrolyte solvent when the substance alone is used. It refers to a solvent that, when used in combination with the main solvent, can attain a performance higher than that of the main solvent alone or the auxiliary solvent alone. The amount of the auxiliary solvent added is not limited to, for example, 50% or less.

Now, after a polarizable electrode formed into a predetermined shape, a separator and a current collector are combined and immersed in an organic electrolytic solution to form a capacitor, an electrochemical reaction is performed by energization. Here, the “configuration of the capacitor” has a meaning of manufacturing a capacitor as a product, but is not limited to such a meaning, and also indicates setting in an environment in which the capacitor operates. Therefore, the polarizable electrode after the electrochemical reaction can be used as a polarizable electrode of a capacitor using a different organic electrolyte for a product capacitor.

The capacitance developed by this electrochemical reaction is characterized in that it is much larger than the case where activated carbon whose main component is the same carbon is used. Therefore, in the capacitor of the present invention, it is considered that the capacitance mainly expresses the pseudo capacitance based on the redox reaction involving the product of the electrochemical reaction.

That is, the capacitor of the present invention is distinguished from a conventional capacitor based on the development of an electric double layer capacitance, and the active material in the polarizable electrode is not actually a carbon material but is formed by an electrochemical reaction. It can be regarded as a thing. Conversely, the capacitor of the present invention also has an electric double layer capacitance, but it is difficult to explain the capacitance characteristics of the capacitor unless the pseudo capacitance involving such an electrochemical reaction product is mainly considered. It is. Although this product has not yet been identified, the partially oxidized graphite and the partially oxidized graphite are placed on the surface of the structure composed of partially oxidized graphite-like microcrystalline carbon in the carbon material and / or the gaps between the structures. It is presumed to be formed by electrochemical reaction with similar microcrystalline carbon.

By the way, as shown in Examples described later, after the above-described electrochemical reaction is performed once to generate a substance contributing to the appearance of pseudo capacitance, the organic electrolyte is replaced with another type. It is also possible to constitute a capacitor by exchanging.

It should be noted that an organic electrolyte solution that is optimal for generating a substance contributing to the development of a pseudo capacitance by performing an electrochemical reaction once and an electrolyte solution that operates optimally as a capacitor are not necessarily the same. It is also possible to obtain a capacitor with higher capacity by optimizing the use of different electrolytes for the operation of the capacitor and the capacitor.

[0038]

As described above, according to the electrochemical capacitor of the present invention, the package can be heat-sealed without being affected by the thickness or shape of the electrode terminal, and the package can have a high reliability and a high reliability. The airtightness can be improved.

[Brief description of the drawings]

FIG. 1 is an example of an electrode unit used in the present invention,
(A) is a schematic perspective view, (b) is a schematic perspective view showing an example of mounting on a package.

FIG. 2 shows another example of the electrode unit used in the present invention, wherein (a) is a plan view, (b) is a front view, (c) is a side view, and (d) shows an example of mounting on a package. It is a schematic perspective view.

FIG. 3 is a schematic perspective view showing an example of a package in the electrochemical capacitor of the present invention.

FIG. 4 is a schematic perspective view showing an example of a package in a conventional electrochemical capacitor.

FIG. 5 is a perspective view showing an example of the structure of a single electrode cell.

FIG. 6 is a perspective view showing an example of the structure of a single capacitor cell.

FIG. 7 is an explanatory view schematically showing a microstructure of a carbon material suitably used for the electrochemical capacitor of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Single electrode cell (laminated body), 12 ... Single capacitor cell, 22, 24 ... Current collector, 26 ... Polarizable electrode, 28 ... Separator, 30, 32 ... Electrode extraction part, 40, 42 ...
Electrode terminals, 44, 46: Electrode terminals, 50, 52: Electrode unit, 54: Holding material, 55: Taper, 60: Package, 62: Seal portion of package, 90: Carbon material,
94: microcrystalline carbon, 96: structure.

Claims (9)

[Claims] 1. A pair of current collectors comprising a metal material, a polarizable electrode formed mainly of a carbon material having a microcrystalline carbon similar to graphite, which is partially oxidized, is disposed,
An electrochemical capacitor in which at least one laminate in which an electronic insulating separator is sandwiched between the polarizable electrodes is sealed in a package while being immersed in an organic electrolyte, and connected to the current collector, respectively. An electrochemical capacitor, wherein an electrode terminal is an electrode unit integrated with a holding material, and the electrode unit is sealed in a package. 2. The electrochemical capacitor according to claim 1, wherein the electrode unit has a shape that minimizes a contact area with the outside of the package. 3. The electrochemical capacitor according to claim 1, wherein the holding material is a resin having excellent bonding properties with the electrode terminals and the package. 4. The electrochemical according to claim 1, wherein the carbon material is obtained by heat-treating a graphitizable carbon raw material in an inert gas atmosphere at 500 ° C. to 1000 ° C. Capacitors. 5. The method of partial oxidation, wherein the carbon material is heat-treated in an inert atmosphere in the presence of at least one of an alkali metal and an alkali metal compound containing oxygen at a temperature not lower than a temperature at which an alkali metal vapor is generated. The electrochemical capacitor according to any one of claims 1 to 4, which is a method. 6. The electrochemical capacitor according to claim 1, wherein the method of partial oxidation is a method of immersing the carbon material in an oxidizing agent that can form graphite when immersed in graphite. . 7. The partial oxidation method according to claim 1, wherein the carbon material is heat-treated in an oxidizing atmosphere containing an oxidizing gas at a temperature lower than a heat treatment temperature of the graphitizable carbon material. 5. The electrochemical capacitor according to any one of items 4 to 5. 8. A method in which a sheet-like electrode prepared by using a partially oxidized carbon material, a separator, and a current collector are combined, immersed in an organic electrolytic solution, a capacitor is formed, and electricity is supplied to the capacitor. 2. The reaction is performed.
The electrochemical capacitor according to any one of claims 1 to 7, wherein 9. The electrochemical capacitor according to claim 8, wherein an electrolyte for performing the electrochemical reaction and an electrolyte for operating as a capacitor are different from each other.