JPH0620520A - Solid electrode composition - Google Patents

Abstract

PURPOSE:To provide a solid electrode composition for constituting an electric double layer capacitor of large capacity, which excels in mechanical strength and workability. CONSTITUTION:This solid electrode composition is what is composed by carrying a solid electrolyte and an activated carbon on a conductive or non-conductive woven cloth or unwoven cloth for composition, which is composed by forming into a gel an aprotic organic solvent in which an alkaline metal salt and an ammonium salt are dissalved, by using a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate. Hydroxide group and carboxylic acid group on the surface of an activated carbon, woven cloth and the like reacts to a copolymer to accelerate the gel formation of a solid electrolyte, and an organic solvent with a salt melted inside the fine hole of an activated carbon is effectively held to allow the inner surface of the fine hole to get wet, and an electric double layer is effectively formed along the inner surface of the fine hole in an activated carbon on a large area to obtain a large electric double layer capacity. And an activated carbon and a fixed electrolyte are firmly held on a woven cloth and the like with the reaction between activated carbon particles and also between a woven cloth and the like and a solid electrolyte in an electrode slurry.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrode composition used for an electrochemical device such as a solid or solid electric double layer capacitor or a secondary battery.

[0002]

2. Description of the Related Art Electrochemical devices such as light-weight and high energy density capacitors, electrochromic devices, and biochemical sensors using microelectrodes can be expected.
Active carbon electrodes are being actively studied. A liquid electrolyte is exclusively used as the electrolyte, and representative ones include organic solvent solutions such as sulfuric acid and propylene carbonate in which a salt is dissolved. It has also been proposed to use a solid electrolyte at room temperature, such as a copper ion conductive solid electrolyte or a silver ion conductive solid electrolyte. If a solid electrolyte is used, the entire element can be solidified, and a highly reliable element with no electrolyte leakage can be obtained. In particular, a flexible sheet-like activated carbon electrode can be obtained by using a flexible polymer electrolyte represented by polyethylene oxide among solid electrolytes. By using this electrode, a solid electric double layer capacitor having a large area and excellent flexibility can be constructed.

[0003]

However, the polymer electrolyte used by mixing with activated carbon does not have to be any polymer electrolyte, and it is necessary that it sufficiently penetrates into the pores of activated carbon and sufficiently covers the surface of activated carbon. Becomes Polyethylene oxide, polyethylene imine,
A polymer electrolyte in which a salt is dissolved in polyether or polyphosphazene has a problem in that it has a high viscosity and does not sufficiently penetrate into the pores of the activated carbon, making it difficult to obtain a large capacity. Furthermore, the solubility of salts in these polymer electrolytes is as low as about 0.05 mol / liter, and a large amount of polymer electrolyte must be mixed in the electrode in order to form a double layer. It has a drawback that the capacity is one-tenth or less as compared with that using a liquid electrolyte, and the advantage of using a flexible solid polymer electrolyte has not necessarily been utilized. On the other hand, a polymer electrolyte using a low molecular weight polyethylene oxide chain that can sufficiently penetrate into the pores of activated carbon or a polymer electrolyte with a low degree of crosslinking has too low a viscosity, and it is difficult to fix the activated carbon and maintain the sheet shape. There is a problem that it is difficult to obtain sufficient mechanical strength.

[0004]

In the electrode composition of the present invention, a solid electrolyte having an appropriate viscosity that can sufficiently enter inside the pores of activated carbon is used. This solid electrolyte is a copolymer of an aprotic organic solvent in which an alkali metal salt or an ammonium salt is dissolved and acrylonitrile and methyl acrylate or methyl methacrylate (hereinafter referred to as AN).
It was made into a gel using. After applying or impregnating a sheet-like conductive or non-conductive sheet with the mixture of the solid electrolyte and activated carbon, the solvent is removed to integrate the solid electrolyte, activated carbon, and woven or non-woven fabric into a solid electrode. Obtain the composition.

[0005]

In the electrode composition of the present invention, hydroxyl groups and carboxylic acid groups on the surface of activated carbon act on AN to promote gelation of the solid electrolyte. As a result, the organic solvent in which the salt is dissolved is effectively retained inside the pores, the inner surface of the pores can be uniformly wetted with the organic solvent, and the electric double layer is effectively formed along the inner surface. On the outer surface of the activated carbon, the AN strongly binds the activated carbon particles together by a gelling reaction with the hydroxyl groups or carboxylic acid groups on the activated carbon particles. Such an action is also obtained between the sheet-shaped woven or non-woven fabric and the solid electrolyte in the electrolyte slurry, and the activated carbon is firmly held by the woven or non-woven fabric. A solid electrode composition having excellent mechanical strength and high workability can be obtained by a relatively simple method such as slurry coating / impregnation and solvent removal.

[0006]

[Examples] Activated carbon has an average particle size of 5 μm or less, a specific surface area of 1000 m ² / g, and a pore volume of 0.5 ml / g.
A powdery material or a fibrous material is preferably used. Any of those activated with natural coconut husks and those activated with synthetic resins such as phenolic resins can be used.

The copolymer of acrylonitrile and methyl acrylate or methyl methacrylate can be obtained by polymerizing an acrylonitrile monomer and methyl acrylate or methyl methacrylate by a conventional polymerization method. Those having a molecular weight of 30,000 to 100,000 are preferably used. The copolymerization ratio (AN / MA) of acrylonitrile (AN) and methyl acrylate or methyl methacrylate (MA) is 50: 1 to 2: 1 (molar ratio).
A degree is preferable.

As the aprotic organic solvent, ethylene carbonate (EC), propylene carbonate (P
C), butylene carbonate (BC), diethylene carbonate (DEC), sulfolane (SL), methyl sulfolane (MSL), tetrahydrofuran (THF),
Dioxane (DOX), dioxolane (DOS), etc. may be used alone or in combination. In particular, a mixed solvent of EC and SL or EC and PC is preferable because it has relatively high conductivity and good oxidation stability.

Salts MX which are soluble in aprotic organic solvents include lithium iodide (LiI), lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium borofluoride (LiB).
F ₄ ), such as a lithium salt in which M is an alkali metal Li, tetraethylammonium perchlorate [(C ₂ H ₅ ) ₄ NClO ₄ ] in which M is tetraalkylammonium,
Tetrabutylammonium perchlorate _{[(n-C 4 H 9} ) 4
NClO ₄ ] or tetraethylammonium borofluoride [(C ₂ H ₅ ) ₄ NBF ₄ ] and the like.

The conductive or non-conductive woven or non-woven fabric is obtained by carbonizing the activated carbon fiber activated by woven fabric of phenol resin or polyacrylonitrile resin fiber, activated carbon short fiber paper-making. Conductive material such as woven or non-woven carbon fiber,
Alternatively, a polyolefin non-woven fabric, a microporous polyolefin film which is uniaxially or biaxially stretched to make it porous, and a composite film in which a microporous polyolefin film is integrated with a polyolefin non-woven fabric are used. A surface-treated surface of which is hydrophilized with a surfactant such as low-molecular-weight polyethylene or polyalkyleneamine is preferably used. Further, a film obtained by filling such a microporous polyolefin film with an inorganic filler such as calcium carbonate fine powder can be used. Also,
It is also possible to use a composite of a conductive woven fabric or a non-woven fabric and a non-conductive woven fabric or a non-woven fabric such as a laminated film obtained by laminating a polypropylene microporous membrane on an activated carbon fiber woven fabric. The thickness of the woven or non-woven fabric is not particularly limited, but is preferably about several tens of μm to several mm. The aperture ratio is preferably about 20% to 60%.

The solid electrolyte composition of the present invention is manufactured, for example, as follows. First, for example, lithium trifluoromethanesulfonate as a salt is dissolved by heating in a mixed solvent of EC and PC as an aprotic organic solvent to obtain an organic solvent solution of the salt. Next, a powder of a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate is added to this solution and heated at 150 ° C to 180 ° C to dissolve the powder to obtain a uniform transparent solution. This solution is diluted 2-3 times by weight with acetonitrile.
The diluted solution and activated carbon powder that has been heated and dried in advance are mixed in a slurry in a mortar. Next, in the obtained electrode slurry,
An activated carbon fiber woven fabric having an opening ratio of 25% obtained by activating a woven fabric made of a phenol resin fiber by heating at 450 ° C. is immersed, and the electrode slurry is vacuum impregnated into the activated carbon fiber woven fabric,
After pulling up from the electrode slurry and passing through a slit made of stainless steel to remove excess electrode slurry, 60 ° C
To remove acetonitrile under reduced pressure at 1-10 hours. By shaping the thus dried electrode composition with a pressure roller, a sheet-shaped electrode composition having a constant thickness can be obtained.

<Example 1> 3.58 g of lithium trifluorosulfonate, 10.47 of propylene carbonate
g, ethylene carbonate 7.86 g are mixed, and 120
It heated at 0 degreeC and the homogeneous solution was obtained. 3 g of powder of a copolymer of polyacrylonitrile having a molecular weight of 60,000 and methyl acrylate (AN / MA = 10/1, molar ratio) was mixed with this solution,
Heat to 150 ° C in a sealed 100 ml Erlenmeyer flask,
The copolymer powder was completely dissolved to obtain a viscous transparent liquid. 30 g of acetonitrile was added to this liquid to obtain a diluted solution. BET obtained by activating phenolic resin
Specific surface area 2500 m ² / gr, pore volume 0.86 m
Activated carbon powder 1.25 with 1 / gr and an average particle size of 3.0 μm
An electrode slurry was obtained by mixing gr and 10 gr of the diluted solution in a mortar. Activated carbon fiber woven cloth (made by Nippon Kynol, trade name: Kynol activated carbon fiber cloth A in this electrode slurry
CC-507, thickness 0.4 mm, specific surface area 2000 m ²
/ G) and the electrode slurry was vacuum impregnated. next,
The excess electrode slurry was removed by passing through a slit having a gap of 0.5 mm. Acetonitrile was removed by drying at 60 ° C. for about 3 hours under a reduced pressure of 1 Torr, and then shaped with a roller having a linear pressure of 20 kg / cm to obtain a sheet-like electrode composition A having a thickness of 0.4 mm. The electrode composition A thus obtained was in an apparently dry state, showed no exudation of the liquid, had good flexibility and mechanical strength without being damaged even after 500 times of repeated bending tests with a radius of 10 mm. Was given. In addition, as an electrolyte for forming the electric double layer capacitor A for electrode characteristic measurement, a diluted solution of 10 gr was used.
Cast only into a glass dish with a diameter of 90 mm, 40 ℃
Dried in an argon stream for 1 hour and then at 80 ° C for 5
By vacuum drying for a period of time, a sheet-like solid electrolyte A having a thickness of about 0.3 mm was obtained.

Example 2 3.58 g of lithium trifluorosulfonate, 11.5 g of sulfolane and 7.86 g of ethylene carbonate were mixed and heated to 120 ° C. to obtain a uniform solution. A copolymer of polyacrylonitrile having a molecular weight of 60,000 and methyl acrylate (AN / MA = 2) was added to this solution.
(0/1, molar ratio) 3 g of powder were mixed and heated to 170 ° C. in a sealed 100 ml Erlenmeyer flask to completely dissolve the copolymer powder to obtain a viscous transparent liquid. 30 g of acetonitrile was added to this liquid to obtain a diluted solution.

The BET specific surface area obtained by activating coconut husks is 1300 m ² / gr, and the pore volume is 1.14 ml /
1.25 gr of activated carbon powder having an average particle size of 4.2 μm
And 10 g of the diluted solution were mixed in a mortar to obtain an electrode slurry. A carbon fiber non-woven fabric (made by Nippon Kynol, trade name: Kynol carbon fiber paper CP0 in this electrode slurry
2, thickness 0.26 mm, basis weight 35 g / cm ² ) was immersed and the electrode slurry was vacuum impregnated. Next, the gap is 0.
The excess electrode slurry was removed by passing through a 3 mm slit. After removing acetonitrile by drying at 60 ° C. for about 5 hours under a reduced pressure of 1 Torr, a linear pressure of 20 k
The sheet was shaped with a g / cm roller to obtain a sheet-shaped electrode composition B having a thickness of 0.25 mm. The electrode composition B thus obtained was apparently in a dry state, had no oozing out of the liquid, and had good flexibility and mechanical strength without being damaged even after 500 times of repeated bending tests with a radius of 10 mm. Was given. As an electrolyte for constructing the electric double layer capacitor B for electrode characteristic measurement, only 10 gr of the diluted solution was cast on a glass dish having a diameter of 90 mm, dried in a dry argon gas stream at 40 ° C. for 1 hour, and further 80 ° C. By vacuum drying for 5 hours, a sheet-like solid electrolyte B having a thickness of about 0.3 mm was obtained.

Example 3 Tetraethylammonium perchlorate 3.75 g, 3-methylsulfolane 10.4 g,
7.86 g of ethylene carbonate was mixed and heated to 120 ° C. to obtain a uniform solution. A copolymer of polyacrylonitrile having a molecular weight of 60,000 and methyl acrylate (A
(N / MA = 5/1, molar ratio) 3.5 g of powder were mixed and heated to 170 ° C. in a sealed 100 ml Erlenmeyer flask to completely dissolve the copolymer powder and obtain a viscous transparent liquid. It was 30 g of acetonitrile was added to this liquid to obtain a diluted solution. BET obtained by activating phenolic resin
Specific surface area 2500 m ² / gr, pore volume 0.86 m
Activated carbon powder 1.25 with 1 / gr and an average particle size of 3.0 μm
An electrode slurry was obtained by mixing gr and 10 gr of the diluted solution in a mortar. A composite film obtained by laminating a polypropylene microporous film and a polypropylene non-woven fabric in this electrode slurry (manufactured by Daicel Chemical Industries, trade name: Celgard Microporous Membrane 5511, thickness 175 μm, porosity 45%)
Was dipped and vacuum impregnated with the electrode slurry. Next, the excess electrode slurry was removed by passing through a slit having a gap of 0.2 mm. After removing acetonitrile by drying under reduced pressure of 1 Torr at 60 ° C. for about 5 hours, a linear pressure of 2
The sheet was shaped with a 0 kg / cm roller to obtain a sheet-shaped electrode composition C having a thickness of 0.22 mm. The electrode composition C thus obtained was in an apparently dry state, showed no exudation of the liquid, had good flexibility and mechanical strength without being damaged even after 500 times of repeated bending tests with a radius of 10 mm. Was given. The electric double layer capacitor B for measuring electrode characteristics
As an electrolyte for constituting the above, only a diluted solution of 10 gr was cast on a glass petri dish having a diameter of 90 mm, dried in an atmosphere of dry argon at 40 ° C. for 1 hour, and further vacuum dried at 80 ° C. for 5 hours to obtain a thickness of about A 0.3 mm sheet-shaped solid electrolyte C was obtained.

Comparative Example Polyethylene triol having a molecular weight of about 3000, 6.6 gr, tolylene diisocyanate 0.5 ml, and lithium trifluoromethanesulfonate 0.3 gr were dissolved in 10 ml of methyl ethyl ketone to obtain a diluent 10 gr. And 1.25 gr of activated carbon powder having a BET specific surface area of 2500 m 2 / gr, a pore volume of 0.86 ml / gr and an average particle diameter of 3.0 μm, obtained by activating the phenol resin in a mortar. A slurry was obtained. About 5 gr of the electrode slurry was cast on a glass petri dish having a diameter of 90 mm, dried in a dry argon gas stream at 40 ° C. for 1 hour, and further vacuum dried at 80 ° C. for 5 hours to obtain a sheet-shaped product having a thickness of about 0.35 mm. Solid electrode composition D
Got The electrode composition D thus obtained was subjected to a repeated bending test with a radius of 10 mm in the same manner as in Example 1, and it was broken after 280 times.

As an electrolyte for forming the electric double layer capacitor D for measuring electrode characteristics, 10 g of a dilute solution was used.
Cast only r into a glass dish with a diameter of 90 mm,
A sheet-like solid electrolyte D having a thickness of about 0.3 mm was obtained by drying in a dry argon stream at 0 ° C. for 1 hour and further vacuum drying at 80 ° C. for 5 hours.

Evaluation of Electrical Properties The electrode compositions A, B, C and D and the solid electrolytes A, B, C and D obtained in Examples 1, 2, 3 and Comparative Example were punched out into a disk shape having a diameter of 13 mm. It was A solid electrolyte disc was sandwiched between two electrode composition discs, the whole was sandwiched between two platinum discs, and the disc was placed in a cylinder made of Teflon having an inner diameter of 13 mm to form an electric double layer capacitor. The electrical characteristics were evaluated in a state where the entire element was pressed from above and below via a spring by a Steres rod for electrode terminals having a diameter of 13 mm. 0.
Charging and discharging were repeatedly performed between 0.0 and 3.5 V at a constant current of 27 mA. The capacity calculated from the weight of powdered activated carbon per electrode and the linear portion where the voltage is 1.5 V to 2.5 V is shown in (Table 1) below. All evaluations were performed at 20 ° C.

[0019]

[Table 1]

As shown in (Table 1), the electric double layer capacitors A, B, and C of the embodiment give much larger capacitance than the capacitor D of the comparative example.

Although only the application to the electric double layer capacitor was shown as an example, by using the solid electrode composition of the present invention as a counter electrode in addition to the electric double layer capacitor, excellent charge / discharge cycle characteristics were obtained. It is possible to obtain a biochemical sensor such as a secondary battery, an electrochromic element having a fast coloring / fading speed, and a glucose sensor having a fast response speed, and it is also possible to configure an electrochemical analog memory having a fast writing / reading speed. .

[0022]

INDUSTRIAL APPLICABILITY In the present invention, that is, activated carbon, an alkali metal salt or an ammonium salt, a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, and an aprotic organic solvent are combined. The solidified electrode composition thus obtained has an extremely large capacity, and is excellent in mechanical strength and processability, as compared with an electrode using a conventional polymer solid electrolyte. By using this solid electrode composition, it is possible to construct a large-capacity electric double layer capacitor which does not leak in a solid state.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Uemachi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Kenichi Takeyama 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A conductive or non-conductive material carrying an electrode containing activated carbon, a salt represented by MX, a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, and an aprotic organic solvent. A solid electrode composition comprising a conductive woven fabric or a non-woven fabric.
(However, M is selected from alkali metal ions or ammonium ions, and X represents its counter anion.) 2. The solid electrode composition according to claim 1, wherein the sheet-shaped woven fabric or nonwoven fabric is an activated carbon woven fabric or an activated carbon nonwoven fabric. 3. The solid electrode composition according to claim 1, wherein the sheet-shaped woven fabric or nonwoven fabric is a composite film of a microporous polyolefin porous membrane and a polyolefin nonwoven fabric.