JPWO2017073474A1 - Electrode, capacitor using the electrode, and method of manufacturing electrode - Google Patents

Abstract

An electrode with reduced electrical resistance, an electric double layer capacitor using the electrode, and a method for manufacturing the electrode are provided. It contains fibrous cellulose and carbon powder, and the carbon powder is entangled between the fibers of fibrous cellulose and supported. The fibrous cellulose and the carbon powder are deposited on a filter paper to form a sheet. A carbon powder, a dispersion step of dispersing the fibrous cellulose in the solvent, and a sheet electrode forming step of removing the solvent of the solution obtained in the dispersion step to obtain a sheet electrode of the carbon powder and the fibrous cellulose.

Description

  The present invention relates to an electrode using a carbon material, a capacitor using the electrode, and a method for manufacturing the electrode.

  Conventionally, a capacitor such as an electric double layer capacitor is composed of a pair of electrodes, a separator existing therebetween, and a current collecting layer of each electrode. A carbon material such as carbon powder is used for a typical electrode used for an electric double layer capacitor.

  The following methods are known as methods for producing electrodes used for the electric double layer capacitor. That is, after adding and mixing a conductive material such as acetylene black and a resin such as polytetrafluoroethylene and tetrafluoroethylene resin to activated carbon powder, which is a representative electrode material, press molding. A sheet-like polarizable electrode is formed. 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.

JP 2001-237149 A

  As described above, in the electrode of the electric double layer capacitor, a resin-based binder is used when pressure molding or when a mixed solution such as activated carbon powder is applied to the current collector. In particular, when the particle size of the activated carbon powder is nano-sized, a large amount of a resin-based binder is required when a sheet-like polarizable electrode is formed by applying to a current collector. Considering the aspect of reducing the resistance of the electrode, an electrode using a large amount of a resin-based binder has a problem that the resistance becomes high.

  The present invention has been proposed to solve the above problems. The object is to provide an electrode with reduced electrical resistance, a capacitor using the electrode, and a method of manufacturing the electrode.

  In order to achieve the above-mentioned goal, the electrode of the present invention includes fibrous cellulose and carbon powder, and the carbon powder is entangled and supported between fibers of the fibrous cellulose. .

  The fibrous cellulose and the carbon powder may be deposited on a filter paper and formed into a sheet shape.

  The fibrous cellulose may be cellulose nanofiber. The carbon powder may be activated carbon black.

  A silane coupling agent may be bonded to the surface of the fibrous cellulose. The silane coupling agent may have an alkyl group as a functional group.

  You may make it contain the said fibrous cellulose in the ratio of 5 to 40 weight% with respect to the total amount of the said fibrous cellulose and the said carbon powder. Moreover, you may make it contain the said fibrous cellulose in the ratio of 5 to 15 weight% with respect to the total amount of the said fibrous cellulose and the said carbon powder.

  A capacitor in which the electrode described above is formed over a current collector is also one embodiment of the present invention.

  In addition, a method for manufacturing the above electrode is also one embodiment of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode which made electric resistance small, the capacitor using the electrode, and the manufacturing method of an electrode can be provided.

It is sectional drawing which shows an example of a structure of the coin-shaped electric double layer capacitor of 1st Embodiment. It is a SEM (x10.0k) image of the sheet electrode of carbon powder and fibrous cellulose produced from the solution which disperse | distributed carbon powder and fibrous cellulose. It is the graph showing the relationship between the charging voltage and capacity density in the electric double layer capacitor of an Example. It is the graph showing the relationship between the charging voltage and DC resistance in the electric double layer capacitor of an Example. It is the graph showing the relationship between the load time and a capacity | capacitance maintenance factor in the electric double layer capacitor of an Example. It is the graph showing the relationship between load time and DC resistance in the electric double layer capacitor of an Example. It is the graph showing the relationship between the load time and a capacity | capacitance maintenance factor in the electric double layer capacitor of an Example. It is the graph showing the change of the capacity density based on the difference in the content rate of the fibrous cellulose in the electric double layer capacitor of an Example. It is the graph showing the change of internal resistance based on the difference in the content rate of the fibrous cellulose in the electric double layer capacitor of an Example.

[1. Constitution]
Hereinafter, embodiments of an electrode and an electrode manufacturing method according to the present invention will be described in detail. First, a capacitor to which the electrode of this embodiment is applied will be described taking a coin-shaped electric double layer capacitor as an example. The electrode and the electrode manufacturing method according to the present invention are applicable not only to electric double layer capacitors. For example, it can be applied to power storage devices such as various capacitors and secondary batteries such as electrochemical capacitors including lithium ion capacitors.

  The electrode and the electrode manufacturing method according to the present invention are not limited to the coin-type electric double layer capacitor, and may be applied to a laminate type heat sealed using a laminate film. Moreover, you may apply to the cylindrical element wound through the separator between the positive electrode and the negative electrode. Furthermore, the present invention can also be applied to power storage devices such as various capacitors and secondary batteries using a stacked element that is stacked between a positive electrode and a negative electrode via a separator.

(1) Electric Double Layer Capacitor FIG. 1 is a cross-sectional view of a coin type electric double layer capacitor in which a sheet electrode using carbon powder and fibrous cellulose is applied to a coin type cell as an example of an electric double layer capacitor. The coin-shaped electric double layer capacitor includes a negative electrode case 1, an electrolyte 2, an electrode 3, a separator 4, an electrode 5, a positive electrode case 6, and a gasket 7.

  The negative electrode case 1 and the positive electrode case 6 are cell casings that overlap to form a space therein. The negative electrode case 1 serves as a negative electrode current collector and a negative electrode terminal. The positive electrode case 6 serves as a positive electrode current collector and a positive electrode terminal. The gasket 7 is interposed in the caulking between the negative electrode case 1 and the positive electrode case 6. The gasket 7 maintains electrical insulation between the negative electrode and the positive electrode, and seals and seals the cell contents.

  The electrolyte 2, the electrode 3, the electrode 5, and the separator 4 are cell contents and are accommodated in the space formed by the negative electrode case 1 and the positive electrode case 6. The electrodes 3 and 5 are sheet-like electrodes using carbon powder and fibrous cellulose. The sheet-like electrodes 3 and 5 are integrated with a current collector (not shown).

  The electrode 3 is fixed and electrically connected to the positive electrode case 6 by a conductive resin adhesive, press bonding, or the like. The electrode 5 is fixed and electrically connected to the negative electrode case 1 by a conductive resin adhesive, press bonding, or the like. The separator 4 is disposed so as to be interposed between the electrode 3 and the electrode 5 in order to prevent a short circuit due to contact between the opposing electrode 3 and the electrode 5. The electrolyte 2 is impregnated in the electrode 3, the electrode 5, and the separator 7. Hereinafter, each component of the electric double layer capacitor will be described in detail.

(2) Electrode In the electric double layer capacitor as described above, the electrode 3 and the electrode 5 include a mixture of fibrous cellulose and carbon powder. Specifically, the carbon powder is entangled and supported between fibers of fibrous cellulose. The electrode 3 and the electrode 5 are sheet-like electrodes obtained by dispersing carbon powder and fibrous cellulose in a solvent and then removing the solvent.

(Fibrous cellulose)
Fibrous cellulose is cellulose that can efficiently entangle extremely small nano-sized carbon powder between fibers. Examples of fibrous cellulose include cellulose nanofibers. The cellulose nanofiber is preferably fibrous cellulose having a width of 4 to 100 nm and a length of 50 to 1000 μm.

  A silane coupling agent may be bonded to the surface of the fibrous cellulose. As the silane coupling agent, a silane coupling agent having a methacryl group and an alkyl group as functional groups can be used. In particular, it is preferable to use a silane coupling agent having an alkyl group, since the initial equivalent series resistance is lowered and the capacity retention after the load test is improved.

  Bonding of the silane coupling agent to the fibrous cellulose can be performed by the following procedure. For example, after adding fibrous cellulose and a silane coupling agent to isopropyl alcohol at a mass ratio of 100: 1, the resulting liquid is stirred using a homogenizer. Next, by drying the stirred solution, fibrous cellulose having a silane coupling agent bonded to the surface can be obtained.

(Carbon powder)
The carbon powder 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, acetylene black, channel black, etc. And carbon black, carbon nanohorn, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, activated carbon, mesoporous carbon, and the like.

  The carbon powder is preferably used after being subjected to a porous treatment such as an activation treatment or an 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 100 nm, and particularly preferably less than 50 nm. If the average particle size of the carbon powder is less than 100 nm, the diffusion resistance is low and the conductivity is high because of the extremely small particle size. Moreover, since the specific surface area by the porous treatment is large, an effect of expressing a high capacity 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 size 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.

(Content)
The electrode of the present embodiment includes a mixture of carbon powder and fibrous cellulose as described above. When carbon powder and fibrous cellulose are mixed, the content is 5 to 40% by weight, particularly 5 to 15% by weight, based on the total amount of carbon powder and fibrous cellulose. Is preferred.

  In the range up to 40% by weight of fibrous cellulose, the range of high capacity density and low internal resistance is maintained, but when the content of fibrous cellulose increases to 50% by weight, the internal resistance of the capacitor is in the range of low internal resistance. And the capacity density tends to decrease outside the range of the high capacity density. On the other hand, if it is smaller than this range, the carbon powder tends to be aggregated, making it difficult to form the electrode 3 and the electrode 5 in a sheet form. Furthermore, the range of 5% by weight to 15% by weight of the fibrous cellulose achieves outstanding high capacity density and low internal resistance even within the range of 5% by weight to 40% by weight of the fibrous cellulose. preferable.

(Dispersion solution)
As a solvent for dispersing carbon powder and fibrous cellulose, alcohols such as methanol, ethanol and 2-propanol, hydrocarbon solvents, aromatic solvents, N-methyl-2-pyrrolidone (NMP), N, N- Various solvents such as an amide solvent such as dimethylformamide (DMF), water, a solvent using these solvents alone or a mixture of two or more solvents can be used. Moreover, you may add additives, such as a dispersing agent, in this solvent.

(Current collector)
As the current collector integrated with the sheet electrode 3 and the electrode 5, a conductive material such as aluminum foil, platinum, gold, nickel, titanium, steel, and carbon can be used. 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. The surface of the current collector may be formed with an uneven surface by etching or the like, or may be a plain surface.

(3) Negative electrode case, positive electrode case The negative electrode case 1 is formed by drawing a stainless steel plate whose outer surface is plated with Ni. Further, the positive electrode case 6 is made of stainless steel plated with Ni on the outer side surface serving as the cell case main body or a valve action metal such as Al or Ti.

  As the negative electrode case 1 and the positive electrode case 6, Mo-containing stainless steels such as SUS316, 316L and double-layer stainless steel, and valve action metals such as Al and Ti have high corrosion resistance and can be suitably used. Further, it is particularly preferable to use a clad material in which stainless steel and a valve metal such as Ai or Ti are bonded by crimping by cold rolling or the like, with the valve metal side being the inner surface of the cell. This is because a cell having high corrosion resistance against high voltage application, high mechanical strength at the time of sealing, and high reliability of sealing can be obtained. The negative electrode case 1 and the positive electrode case 6 may be made of the materials described as the above-described current collector, or may be applied in the form.

(4) Separator The separator 4 can be a cellulose separator, a synthetic fiber nonwoven fabric separator, a mixed paper separator made by mixing cellulose and synthetic fibers, or the like. Polyester, polyphenylene sulfide, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyimide, fluororesin, polyolefin resins such as polypropylene and polyethylene, non-woven fabrics made of fibers such as ceramics and glass, mixed paper or porous films are preferably used. Can do. 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. In the capacitor, it is preferable to use an acid-resistant material (synthetic fiber nonwoven fabric or glass material).

(5) Electrolyte Electrolyte 2 is a chain sulfone such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl isopropyl sulfone, ethyl methyl sulfone, 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, Solvents such as ethylene glycol diethyl ether, water or mixtures thereof can be used. That. In particular, when the electrolyte 2 is a mixture of sulfolane and a sulfolane compound having a side chain in the sulfolane skeleton or a chain sulfone, the influence of the electrode capacity of the electric double layer capacitor over time can be reduced. it can. The sulfolane compound has a cyclic sulfone structure of tetrahydrothiophene-1,1-dioxide, and is, for example, a compound having a side chain of an alkyl group on a sulfolane skeleton such as sulfolane or 3-methylsulfolane, or a mixture thereof. The chain sulfone has a chain structure in which two alkyl groups are bonded to a sulfonyl group, and examples thereof include ethyl isopropyl sulfone, ethyl methyl sulfone, and ethyl isobutyl sulfone.

The electrolyte 2 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, trimethyl ammonium BF _4, diethyldimethylammonium BF _4, triethylmethylammonium BF _4, tetraethylammonium BF _4, spiro - (N, N ') - bipyrrolidinium BF _4, methyl ethyl pyrrolidinium _BF 4, 1-ethyl - 3-methylimidazolium BF ₄ , 1-ethyl-2,3-dimethylimidazolium BF ₄ , ethyltrimethylammonium PF ₆ , diethyldimethylammonium PF ₆ , triethylmethylammonium PF ₆ , tetraethylammonium PF ₆ , spiro- (N, N ') - bipyrrolidinium PF _6, tetramethylammonium bis (oxalato) borate, trimethyl ammonium bis (oxalato) borate, diethyl-dimethyl ammonium bis (oxalato) borate Triethylmethylammonium bis (oxalato) borate, tetraethylammonium bis (oxalato) borate, spiro- (N, N ′)-bipyrrolidinium bis (oxalato) borate, tetramethylammonium difluorooxalatoborate, ethyltrimethylammonium difluoro Oxalatoborate, diethyldimethylammonium difluorooxalatoborate, triethylmethylammonium difluorooxalatoborate, tetraethylammonium difluorooxalatoborate, spiro- (N, N ′)-bipyrrolidinium difluorooxalatoborate, LiBF ₄ , LiPF ₆ Lithium bis (oxalato) borate, lithium difluorooxalatoborate and the like are preferable.

  Moreover, you may contain various additives in electrolyte. Examples of additives include phosphoric acids and derivatives thereof (phosphoric acid, phosphorous acid, phosphoric esters, phosphonic acids, etc.), boric acids and derivatives thereof (boric acid, boric oxide, boric esters, boron and hydroxyl groups, And / or a complex with a compound having a carboxyl group), a nitrate (such as lithium nitrate), a nitro compound (such as nitrobenzoic acid, nitrophenol, nitrophenetole, nitroacetophenone, and an aromatic nitro compound). The amount of the additive is preferably 10% by weight or less, more preferably 5% by weight or less of the total electrolyte from the viewpoint of conductivity. The electrolyte may contain a gas absorbent. The absorbent for the gas generated from the electrode is not particularly limited as long as it does not react with each component of the electrolyte (solvent, electrolyte salt, various additives, etc.) and does not remove (adsorb). Specific examples include zeolite and silica gel.

(6) Gasket The gasket 7 is mainly composed of a resin that is insoluble in the electrolyte 2 and has an electrical insulation property. For example, the gasket 7 is usually made of a resin such as polypropylene or nylon. 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, liquid crystal polymer (LCP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), polyether ether ketone resin (PEEK), polyether nitrile resin (PEN), Polyetherketone resin (PEK), polyarylate resin, polybutylene terephthalate resin, polycyclohexanedimethylene terephthalate resin, polyethersulfone resin, polyaminobismaleimide resin, polyetherimide resin, fluorine resin, and the like can be used. In addition, a material obtained by adding glass fibers, My Cowisker, ceramic fine powder and the like to these materials in an addition amount of about 30% by weight or less can be suitably used.

[2. Electrode manufacturing method]
The manufacturing method of the electrode of this embodiment as described above includes the following steps.
(1) Dispersing step of dispersing carbon powder and fibrous cellulose in a solvent (2) Removing the solvent of the solution obtained in the dispersing step to obtain an electrode of carbon powder and fibrous cellulose

(1) Dispersing step In the dispersing step, carbon powder and fibrous cellulose are dispersed in a solvent. That is, in the dispersion step, a dispersion treatment is performed on a mixed solution obtained by mixing carbon powder and fibrous cellulose. By performing the dispersion treatment, the carbon powder and the fibrous cellulose in the mixed solution are subdivided and homogenized, and dispersed in the solution. That is, the fibrous cellulose in the mixed solution before the dispersion treatment is in a state where the cellulose fibers are entangled (bundle shape). By performing the dispersion treatment, the bundle of fibrous cellulose is broken and the fibrous cellulose is dispersed in the solution.

  As a dispersion method, a mixer, jet mixing (jet collision), ultracentrifugation, or other ultrasonic treatment is used. Considering the improvement in the degree of dispersion of the carbon powder and the fibrous cellulose in the solvent and the improvement in the electrode density of the obtained sheet electrode, the dispersion method is preferably jet mixing or ultracentrifugation. In particular, by using such jet mixing or ultracentrifugation treatment, aggregation of carbon powder having a very small particle diameter and fibrous cellulose is suppressed, and an electrode having a low internal resistance can be obtained.

  In the dispersion method using a mixer, a physical force is applied to a mixed solution containing carbon powder and fibrous cellulose by a ball mill, a homogenizer, a homomixer, or the like, and the carbon powder and fibrous cellulose in the solution are stirred. Subdivide. By applying an external force to the carbon powder, the agglomerated carbon powder and fibrous cellulose can be subdivided and homogenized, and the entangled carbon powder and fibrous cellulose can be solved.

  In the dispersion method by jet mixing, a pair of nozzles are provided at positions facing each other on the inner wall of a cylindrical chamber. A mixed solution containing carbon powder and fibrous cellulose 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 cellulose 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 by ultracentrifugation, ultracentrifugation is performed on a mixed solution containing carbon powder and fibrous cellulose. In ultracentrifugation, shear stress and centrifugal force are applied to the carbon powder and fibrous cellulose in the mixed solution in a rotating container. For example, in ultracentrifugation, the mixed solution is introduced into the inner cylinder of the container, and the inner cylinder is swirled so that the centrifugal force causes carbon powder and fibrous cellulose inside the inner cylinder to pass through the through hole of the inner cylinder. It collides with the inner wall of the cylinder, forms a thin film, and slides 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 cellulose, and a large mechanical energy is applied to the carbon powder and the fibrous cellulose in the mixed solution. Become.

It is thought that this ultracentrifugation can be realized by the mechanical energy of shear stress and centrifugal force applied to the carbon powder and fibrous cellulose in the mixed solution, but this shear stress and centrifugal force can be realized by the mixed solution in the inner cylinder. It is generated by the centrifugal force applied to the carbon powder and fibrous cellulose inside. Thus, the centrifugal force applied to the carbon powder and the fibrous cellulose in the inner cylinder necessary for the present invention is 1500 N (kgms ^-2) or more, preferably 60000N (kgms ^-2) or more, more preferably 270000N (kgms ^-2) That's it.

  In this ultracentrifugation process, mechanical energy of both shear stress and centrifugal force is simultaneously applied to the carbon powder and fibrous cellulose in the mixed solution, so that this mechanical energy is combined with the carbon powder in the mixed solution. Fibrous cellulose is homogenized and subdivided.

  The dispersion treatment as described above is preferably performed on a mixed solution in which carbon powder and fibrous cellulose are mixed. However, a solution in which fibrous cellulose is added separately is prepared, a dispersion treatment is performed on this solution to obtain a fibrous cellulose in which the bundle is unwound, and a mixed solution is obtained by mixing the fibrous cellulose and carbon powder. May be. 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 cellulose may be mixed to obtain a mixed solution. . Furthermore, a solution in which fibrous cellulose is added separately is prepared, and a dispersion treatment is performed on this solution to obtain a fibrous cellulose in which the bundle is unwound. Similarly, a solution in which carbon powder is additionally added is prepared. Alternatively, dispersion treatment may be performed to obtain a finely divided carbon powder, and these fibrous cellulose and carbon powder may be mixed to obtain a mixed solution. These mixed solutions may be subjected to dispersion treatment.

(2) Sheet Electrode Formation Step In the sheet electrode formation step, sheet-like electrodes 3 and 5 made of carbon powder and fibrous cellulose are obtained by papermaking. In papermaking molding, the solvent of the mixed solution that has passed through the dispersing step is removed by filtering the mixed solution that has passed through the dispersing step. In papermaking molding, filter paper such as glass fiber nonwoven fabric, organic nonwoven fabric (polytetrafluoroethylene, polyethylene, etc.) or metal fiber nonwoven fabric can be used. The solvent in the mixed solution is removed by filtering and drying the mixed solution under reduced pressure using a filter paper. Therefore, carbon powder and fibrous cellulose are deposited on the filter paper, and the sheet electrode 3 and the electrode 5 are obtained. The carbon powder is dispersed and supported between the fiber celluloses. The sheet-like electrode 3 and the electrode 5 are preferably used by being peeled from the filter paper.

  The carbon powder and fibrous cellulose sheet-like electrode 3 and electrode 5 produced in this sheet electrode forming step are cut to the same size as the current collector. The cut sheet-like electrode 3 and electrode 5 are placed on an etched aluminum foil to be a current collector, and are pressed from above and below the foil and the sheet electrode to bite into the uneven surface of the aluminum foil. Integrated. For the integration, the aforementioned press may be used, or a conductive adhesive may be used. In addition, the electrode 5 and the electrode 7 may be subjected to a flattening process by pressing or the like before being integrated with the current collector, if necessary.

[3. Effect]
The effect which the electrode of this embodiment shows is as follows.
(1) The electrode of this embodiment includes fibrous cellulose and carbon powder, and the carbon powder is entangled and supported between fibers of fibrous cellulose.
In the electrode of this embodiment as described above, fibrous cellulose plays a role as a binder and can hold the carbon powder in a small amount, so that an electrode with reduced resistance can be provided.

(2) Fibrous cellulose and carbon powder are deposited on the filter paper to form a sheet.
The resistance can be reduced by preparing a sheet-like electrode on the filter paper by filtering the mixed solution without using a resin binder.

(3) Fibrous cellulose is cellulose nanofiber.
By using the cellulose nanofiber, the carbon powder can be surely entangled between the fibers of the cellulose nanofiber. Therefore, an increase in internal resistance can be suppressed.

(4) The carbon powder is activated carbon black.
Since the carbon black made porous by the activation treatment has a large specific surface area, a high capacity expression effect can be expected. Carbon black is dispersed and supported in a network of fibrous cellulose as small aggregates. Therefore, the dispersion degree of carbon black in fibrous cellulose can be improved. Therefore, an increase in internal resistance can be suppressed.

(5) A silane coupling agent is bonded to the surface of the fibrous cellulose.
Fibrous cellulose has OH groups on the surface. Therefore, for example, when fibrous cellulose is used in a non-aqueous electric double layer capacitor, hydrolysis may occur due to water caused by OH groups, which may cause deterioration of the capacitor. When the silane coupling agent is bonded to the surface of the fibrous cellulose, the functional group of the silane coupling agent is oriented on the surface. Since the functional group of the silane coupling agent is hydrophobic, deterioration due to the OH group of the fibrous cellulose can be prevented.

(6) The silane coupling agent has an alkyl group as a functional group.
When a silane coupling agent having an alkyl group is used, the initial equivalent series resistance can be reduced and the capacity retention rate after the load test can be improved.

  According to the electric double layer capacitor in which the electrodes as described above are formed on the current collector, the equivalent series resistance can be reduced.

Moreover, the effect which the manufacturing method of the electrode of this embodiment show | plays is as follows.
(7) The manufacturing method of the electrode of this embodiment includes carbon powder and a dispersion step of dispersing fibrous cellulose in a solvent, and removing the solvent of the solution obtained in the dispersion step, so that the carbon powder and fibrous cellulose are removed. A sheet electrode forming step of obtaining the sheet electrode.

  By forming the electrode by dispersing carbon powder and fibrous cellulose in the mixed solution and removing the solvent of the solution, the fibrous cellulose plays a role as a binder. Therefore, since a resin-based binder that increases resistance is not necessary, the resistance of the electrode can be reduced. Further, by using a dispersion method such as jet mixing or ultracentrifugation, the degree of dispersion in the mixed solution of carbon powder and fibrous cellulose is improved, so that the sheet electrode is made into a dense and homogeneous form and the electrode density is increased. Therefore, an excellent sheet electrode capable of obtaining the same level of capacity as that of an electrode using conventional micron-sized carbon powder is realized.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited to the following Example.

(1) Characteristic evaluation <Preparation of electric double layer capacitor of Example 1>
First, 40 mg of carbon black having an average particle diameter of 12 nm subjected to the steam activation treatment was weighed so that the total amount of carbon powder and fibrous cellulose contained in the electrode was 80 wt%. Next, 10 mg of cellulose nanofibers having an outer diameter of 20 nm and a length of 150 μm were measured as fibrous cellulose so that the total amount of carbon powder and fibrous cellulose contained in the electrode was 20 wt%. Carbon black having a total amount of 50 mg and cellulose nanofibers were mixed with 50 ml of methanol to prepare a mixed solution.

In the ultracentrifugal dispersion treatment, the above mixed solution was subjected to a dispersion treatment at a peripheral speed of 40 m / s for 30 seconds to prepare a carbon powder / fibrous cellulose / methanol dispersion. This dispersion was filtered under reduced pressure using PTFE filter paper (diameter: 80 mm, average pore 0.2 μm) to obtain a paper electrode and a carbon powder / fibrous cellulose sheet electrode. This was placed on an aluminum plate, sandwiched between other aluminum plates, and pressed for 1 minute at a pressure of 1 t / cm ² from the vertical direction of the plate to obtain a sheet electrode of carbon powder and fibrous cellulose.

The carbon powder and fibrous cellulose sheet electrodes were peeled from the aluminum plate and cut into the same size as the current collector. The cut sheet electrode was attached to an aluminum foil serving as a current collector with a conductive adhesive and dried at 120 ° C. for 1 hour under normal pressure to obtain two electrode bodies. The obtained two electrode bodies were arranged via a cellulose separator to produce an electric double layer capacitor element (electrode area: 2.1 cm ² ). Then, after impregnating the element with 1.4 mol of TEMABF ₄ as an electrolyte (1.4 M TEMABF ₄ / SL) in 1 L of sulfolane (SL) solvent, the element was heat sealed using a laminate film and evaluated. Cell (electric double layer capacitor) was prepared.

<Preparation of Electric Double Layer Capacitor of Example 2>
The carbon powder was prepared in the same manner as in Example 1 except that activated carbon having an average particle diameter of several μm was used.

<Creation of electric double layer capacitor of Comparative Example 1>
Except for the addition of conductive materials such as acetylene black and resins such as polytetrafluoroethylene and tetrafluoroethylene resin as binders to the activated carbon powder, mixing, and then press molding to form a sheet electrode Prepared as in Example 1.

(A) SEM image of sheet electrode FIG. 2 shows an SEM (× 10.0 k) image of the sheet electrode of carbon black and cellulose nanofiber obtained in Example 1. As is clear from FIG. 2, the carbon black is supported so as to be entangled between the fibers of cellulose nanofibers. Further, in the sheet electrode of Example 1 in which the dispersion treatment is performed by ultracentrifugation, the bundle of cellulose nanofibers is sufficiently unwound and the network of cellulose nanofibers is dense. Furthermore, the aggregate state of carbon black collapses and is subdivided into small aggregates. The dense mesh-like cellulose nanofibers are supported in the form of agglomerated carbon black, and the cellulose nanofibers and carbon black are uniformly dispersed. Therefore, the surface shape of the sheet electrode is dense.

  For the evaluation cell, the results of the calculation of the capacitance and the measurement of the initial DC resistance are shown below as the initial characteristic evaluation.

(B) Calculation of Capacitance FIG. 3 is a graph showing the relationship between the charging voltage and the capacity density in Examples 1 and 2 and Comparative Example 1. FIG. 3 shows the result of measuring two samples for each example. From this graph, it was found that the capacity density of Examples 1 and 2 was not significantly different from the capacity density of Comparative Example 1 in the range of the charging voltage from 2.7 V to 3.3 V. That is, in the electric double layer capacitor containing fibrous cellulose and carbon powder of Examples 1 and 2, an electric double layer capacitor having a high capacitance per electrode unit volume can be obtained as in the conventional case.

(C) Measurement of Initial DC Resistance FIG. 4 is a graph showing the relationship between the charging voltage and DC resistance (DCIR) in Examples 1 and 2 and Comparative Example 1. The results measured after voltage application for 30 minutes at 2.7 V, 3 V, and 3.3 V, respectively, are shown. FIG. 4 shows the results of measuring two samples for each example. From this graph, it was found that the DC resistance of Comparative Example 1 using a resinous binder that acts as an impurity was high in the range of the charging voltage of 2.7 V to 3.3 V. On the other hand, in Examples 1 and 2 in which a mixed solution in which carbon powder and fibrous cellulose are dispersed is filtered, the carbon powder is entangled and supported between fibers of fibrous cellulose. That is, since the fibrous cellulose plays a role as a binder, the direct current resistance is an extremely excellent value as compared with Comparative Example 1 using a resin binder.

  The evaluation cell was subjected to a 3.3V constant voltage load test at 60 degrees as an acceleration test, and the results of measuring the capacity retention rate and direct current resistance (DCIR) at an arbitrary time are shown below.

(D) Measurement of Capacity Maintenance Rate FIG. 5 is a graph showing the relationship between the load time and the capacity maintenance rate in Examples 1 and 2 and Comparative Example 1. The capacity retention ratio was determined by measuring the electrode capacity after voltage application at 3.3 V for 30 minutes and the electrode capacity after voltage application at each measurement time, and the ratio of the capacity (capacity after voltage application at each measurement time). / Capacity after voltage application for 30 minutes) × 100%. As shown in FIG. 5, in the evaluation cell of Comparative Example 1, the capacity maintenance rate after 500 hours is extremely lowered. On the other hand, it was found that in Examples 1 and 2 in which the mixed solution in which the carbon powder and the fibrous cellulose were dispersed was filtered, a decrease in the capacity retention rate was suppressed as compared with Comparative Example 1.

(E) Measurement of DC Resistance FIG. 6 is a graph showing the relationship between load time and DC resistance (DCIR) in Examples 1 and 2 and Comparative Example 1. As shown in FIG. 6, in the evaluation cell of Comparative Example 1, since the resin-based binder that acts as an impurity is used, the direct current resistance increases extremely as the load time becomes longer. On the other hand, in Example 1 and 2 which filtered the mixed solution which disperse | distributed carbon powder and fibrous cellulose, compared with the comparative example 1 using a resin binder, the increase in direct-current resistance is suppressed. I understood.

(2) Characteristic Evaluation of Silane Coupling Agent <Preparation of Electric Double Layer Capacitor of Example 3>
Cellulose nanofibers and a silane coupling agent having a methacryl group as a functional group were added to isopropyl alcohol at a mass ratio of 9: 1. The obtained liquid was stirred for 5 minutes at a rotation speed of 9500 rpm using a homogenizer. Cellulose nanofibers were collected and dried to obtain fibrous cellulose having a silane coupling agent bonded to the surface.

  45 mg of carbon black having an average particle diameter of 12 nm subjected to the steam activation treatment was weighed out so that the total amount of carbon powder and fibrous cellulose contained in the electrode was 90 wt%. Next, 5 mg of the obtained cellulose nanofiber was weighed so as to be 10 wt% with respect to 50 mg of the total amount of carbon powder and fibrous cellulose contained in the electrode. Carbon black having a total amount of 50 mg and cellulose nanofibers were mixed with 50 ml of methanol to prepare a mixed solution.

In the ultracentrifugation dispersion treatment, the above mixed solution was subjected to a dispersion treatment at a peripheral speed of 40 m / s for 30 seconds to prepare a fibrous cellulose / methanol dispersion. The dispersion was filtered under reduced pressure using PTFE filter paper (diameter: 80 mm, average pore 0.2 μm) to obtain a sheet electrode of fibrous cellulose formed by papermaking. This was placed on an aluminum plate, sandwiched between other aluminum plates, and pressed from the vertical direction of the plate at a pressure of 1 t / cm ² for 1 minute to obtain a fibrous cellulose sheet electrode.

The carbon powder and fibrous cellulose sheet electrodes were peeled from the aluminum plate and cut into the same size as the current collector. The cut sheet electrode was attached to an aluminum foil serving as a current collector with a conductive adhesive and dried at 120 ° C. for 1 hour under normal pressure to obtain two electrode bodies. The obtained two electrode bodies were arranged via a cellulose separator to produce an electric double layer capacitor element (electrode area: 2.1 cm ² ). Then, after impregnating the element with 1.4 mol of TEMABF ₄ as an electrolyte (1.4 M TEMABF ₄ / SL) in 1 L of sulfolane (SL) solvent, the element was heat sealed using a laminate film and evaluated. Cell (electric double layer capacitor) was prepared.

<Preparation of Electric Double Layer Capacitor of Example 4>
A silane coupling agent was prepared in the same manner as in Example 3 except that a silane coupling agent having an alkyl group as a functional group was used.

<Production of Electric Double Layer Capacitor of Comparative Example 2>
It was created in the same manner as in Example 3 except that the silane coupling agent was not added.

(A) Measurement of capacitance and initial DC resistance Table 1 shows the calculation of capacitance and measurement of DC resistance (DCIR) at charging voltage of 3.3 V for Example 3, Example 4, and Comparative Example 2. The results are shown.

  From Table 1, in Example 4 using the silane coupling agent which has an alkyl group in a functional group, compared with the comparative example 2 which does not use a silane coupling agent, a capacity density is high and direct current | flow resistance is low. An electric double layer capacitor could be obtained. In Example 3 using a silane coupling agent having a methacrylic group as a functional group, the capacity density is lower and the direct current resistance is higher than in Comparative Example 2 where no silane coupling agent is used. I understood.

(B) Measurement of capacity retention rate The evaluation cell was subjected to a 3.3V constant voltage load test at 60 degrees as an acceleration test, and the capacity retention rate was measured at an arbitrary time. The capacity retention ratio was determined by measuring the electrode capacity after voltage application at 3.3 V for 30 minutes and the electrode capacity after voltage application at each measurement time, and the ratio of the capacity (capacity after voltage application at each measurement time). / Capacity after voltage application for 30 minutes) × 100%.

  FIG. 7 is a graph showing the relationship between the load time and the capacity retention rate in Examples 3 to 4 and Comparative Example 2. As described above, Example 3 using a silane coupling agent having a methacryl group as a functional group was inferior to Comparative Example 2 in terms of initial characteristics. However, from FIG. 7, it was found that Example 3 had a higher capacity retention rate than Example 4 and Comparative Example 2. In addition, it was found that Example 4, which had good initial characteristics, was able to obtain a good capacity retention rate as compared with Comparative Example 2. From the above, it was found that the silane coupling agent having an alkyl group as a functional group can provide good results in both initial characteristics and capacity retention.

(3) Content rate evaluation of fibrous cellulose The ratio of fibrous cellulose is 9 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% with respect to 50 mg of the total amount of carbon powder and fibrous cellulose. Thus, each of carbon powder and fibrous cellulose was weighed and mixed with 50 ml of methanol to prepare a total of seven types of mixed solutions having different fibrous cellulose contents. The carbon powder is carbon black having an average particle diameter of 12 nm subjected to steam activation treatment, and the fibrous cellulose is cellulose nanofiber having an outer diameter of 20 nm and a length of 150 μm.

  In the ultracentrifugation dispersion treatment, these mixed solutions were subjected to a dispersion treatment at a peripheral speed of 40 m / s for 30 seconds to prepare carbon powder / fibrous cellulose / methanol dispersion liquids, respectively. The dispersion was filtered under reduced pressure using PTFE filter paper to obtain carbon paper / fibrous cellulose sheet electrodes formed by papermaking. This was placed on an aluminum plate, sandwiched between other aluminum plates, and pressed from above and below to obtain a sheet electrode of carbon powder and fibrous cellulose.

Each sheet electrode of this carbon powder and fibrous cellulose was peeled from the aluminum plate, and cut into the same size as the current collector. Each of the cut sheet electrodes was attached to an aluminum foil serving as a current collector with a conductive adhesive and dried at 120 ° C. for 1 hour under normal pressure to obtain two electrode bodies. The obtained two electrode bodies were arranged via a cellulose separator to produce each electric double layer capacitor element (electrode area: 2.1 cm ² ). Each electric double layer capacitor element was impregnated with 1.4 M TEMABF ₄ / PC electrolyte prepared by adding 1.4 mol of 1.4 M TEMABF ₄ as an electrolyte to 1 L of propylene carbonate (PC) solvent. Then, it heat-sealed using the laminate film and produced each cell for evaluation (electric double layer capacitor).

(A) Calculation of Capacitance Density FIG. 8 shows that the content of fibrous cellulose is 9 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 40 wt% and the total amount of carbon powder and fibrous cellulose. It is a graph which shows an electrostatic capacity density about each cell for evaluation produced with the electrode body made into 50 wt%, A horizontal axis is a content rate (%) of fibrous cellulose with respect to the total amount of carbon powder and fibrous cellulose. The vertical axis indicates the capacitance density (F / cc). In measuring the capacitance density, each evaluation cell was charged and discharged with a voltage range of 3-0 V and a constant current density of ² mA / cm ² .

  As shown in FIG. 8, in the range up to 40% by weight of fibrous cellulose, a capacitance density of 10 F / cc or more was achieved, but when the content of fibrous cellulose increased to 50% by weight, 8 F / cc. The capacitance density was. That is, it was confirmed that high capacity density was achieved in the range of up to 40% by weight of fibrous cellulose. Furthermore, in the range which made the content rate of fibrous cellulose 5-15 weight%, the electrostatic capacitance density of 13 F / cc or more was achieved. That is, it was confirmed that an outstanding high capacity density was achieved in the range where the content of fibrous cellulose was 5 to 15% by weight.

(B) Calculation of internal resistance FIG. 9 shows 9 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% of the content of fibrous cellulose with respect to the total amount of carbon powder and fibrous cellulose. Is a graph showing the internal resistance with respect to each cell for evaluation produced using an electrode body as, the horizontal axis indicates the content (%) of fibrous cellulose relative to the total amount of carbon powder and fibrous cellulose, The vertical axis represents the internal resistance (Ω · cm ² ). When measuring the internal resistance, each evaluation cell was charged and discharged with a voltage range of 3-0 V and a constant current density of ² mA / cm ² .

As shown in FIG. 9, an internal resistance value of 5 Ω · cm ² or less was achieved in the range up to 40% by weight of fibrous cellulose, but when the content of fibrous cellulose increased to 50% by weight, 6 weak Ω of · cm ² rose to the internal resistance value. That is, it was confirmed that low internal resistance was achieved when the content of fibrous cellulose was in the range of up to 40% by weight. Furthermore, an internal resistance value of less than 4 Ω · cm ² was achieved when the fibrous cellulose content was in the range of 5-15 wt%. That is, it was confirmed that an outstanding high capacity density was achieved when the fibrous cellulose content was in the range of 5 to 15% by weight.

1 Negative electrode case 2 Electrolyte 3, 5 Electrode 4 Separator 6 Positive electrode case 7 Gasket

Claims (17)

Fibrous cellulose and carbon powder,
The carbon powder is supported by being entangled between the fibers of the fibrous cellulose.   The electrode according to claim 1, wherein the fibrous cellulose and the carbon powder are deposited on a filter paper and formed into a sheet shape.   The electrode according to claim 1, wherein the fibrous cellulose is a cellulose nanofiber.   The electrode according to claim 1, wherein the carbon powder is activated carbon black.   The electrode according to any one of claims 1 to 4, wherein a silane coupling agent is bonded to the surface of the fibrous cellulose.   6. The electrode according to claim 5, wherein the silane coupling agent has an alkyl group as a functional group. The fibrous cellulose is contained in a proportion of 5 wt% to 40 wt% with respect to the total amount of the fibrous cellulose and the carbon powder,
The electrode according to claim 1, wherein: The fibrous cellulose is contained in a proportion of 5 wt% to 15 wt% with respect to the total amount of the fibrous cellulose and the carbon powder;
The electrode according to claim 1, wherein:   A capacitor comprising the electrode according to any one of claims 1 to 8 formed on a current collector. A dispersion step of dispersing carbon powder and fibrous cellulose in a solvent;
Removing the solvent of the solution obtained in the dispersion step to obtain an electrode containing carbon powder and fibrous cellulose; and
A method for producing an electrode, comprising:   The said electrode formation process is a process of removing a solvent by filtering the solution obtained at the said dispersion | distribution process, and obtaining the sheet-like electrode of carbon powder and a fibrous cellulose, It is characterized by the above-mentioned. Electrode manufacturing method.   The method for producing an electrode according to claim 10 or 11, wherein the fibrous cellulose is cellulose nanofiber.   The method for producing an electrode according to any one of claims 10 to 12, wherein the carbon powder is obtained by activating carbon black.   The method for producing an electrode according to any one of claims 10 to 13, wherein a silane coupling agent is bonded to the surface of the fibrous cellulose.   The method for producing an electrode according to claim 14, wherein the silane coupling agent has an alkyl group as a functional group. The fibrous cellulose is contained in a proportion of 5% by weight to 40% by weight with respect to the total amount of the fibrous cellulose and the carbon powder,
The method for producing an electrode according to claim 10, wherein: The fibrous cellulose is contained in a proportion of 5 wt% or more and 15 wt% with respect to the total amount of the fibrous cellulose and the carbon powder,
The method for producing an electrode according to claim 10, wherein: