JP2008181949A - Electrode material for electric double-layer capacitor and the electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode material for an electric double-layer capacitor, exhibiting high output characteristics in a low-temperature region, and to provide the electric double-layer capacitor. <P>SOLUTION: In the electrode material for the electric double-layer capacitor, a half width value (Δν1) of a peak (G1) in the vicinity of 1,580 cm<SP>-1</SP>observed in Raman spectrum is less than or equal to 77. The half width value (Δν1) is increased by 1 or larger, when the electrode material is heat treated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode material for an electric double layer capacitor and an electric double layer capacitor.

  The electric double layer capacitor is configured by facing two pairs of electrodes in a liquid electrolyte via a separator. Charging / discharging is performed by applying a voltage to the cell so that ions in the electrolytic solution are electrically adsorbed / desorbed on the electrode surface. In this way, since the electric double layer capacitor does not involve a chemical reaction between the electrode and the electrolyte, compared with other secondary batteries such as lithium ion secondary battery and nickel metal hydride battery, high output, high life, Furthermore, it is characterized by high safety.

  The electric double layer capacitor has been put to practical use as a backup power source for semiconductor memories, and then has been used for road signs, lighting, etc. combined with a solar cell with an increase in capacity. In recent years, electric double layer capacitors that are attracting attention are in-vehicle power supplies and instantaneous power outages. In particular, in automotive applications, demands for reliability, life, and output characteristics of power sources are increasing along with electronic control and hybridization of automobiles, and electric double layer capacitors that are excellent in these characteristics are attracting attention.

  Activated carbon having a high specific surface area is used for the electrode material of the electric double layer capacitor. Activated carbon is porous carbon composed of nano-sized pores. Since electric double layer formation and ion migration occur in the pores, improvement of activated carbon as an electrode material has been actively studied for the purpose of improving the characteristics of the electric double layer capacitor.

  Electric double layer capacitors for on-vehicle power supplies are required to have high output characteristics, particularly high output at low temperatures. In general, in order to increase the output of an electric double layer capacitor from an electrode material, (1) reduce the electric resistance inherent to the electrode material, (2) reduce the contact resistance between the electrode materials, and (3) the activated carbon fine For example, the diffusion resistance of the electrolytic solution in the pores is reduced. In particular, in the low temperature range, the diffusion resistance of ions in the pores of (3) is the main factor of the resistance component, and many attempts to improve the output characteristics by controlling the pore diameter of activated carbon have been reported.

For example, activated carbon obtained by steam activation of coconut carbide, and its BET specific surface area is 2000-2500 m ² / g, the average pore diameter is 1.95 nm-2.20 nm, and the fineness calculated by Cranston inclay method. There is a report that a pore volume with a pore diameter of 5 nm to 30 nm of 0.05 to 0.15 cm 3 / g is excellent in volume capacity, output characteristics, and life characteristics (see Patent Document 1). In addition, the activated carbon obtained by alkali activation has a total specific surface area of 1000 m ² / g or more, and the pore volume distribution has a pore diameter of 12 to 40 mm and a pore diameter of 400 μl / g or more and a diameter of 40 mm or more. Have been reported to be excellent in volume capacity, low temperature characteristics, and output characteristics when the total pore volume is controlled to 50 μl / g or more and the total pore volume is 1000 μl / g or less (see Patent Document 2).

  It is known that the increase in the pore diameter greatly contributes to the improvement of the output characteristics of the electric double layer capacitor. However, the increase in the pore diameter of the activated carbon causes a decrease in the bulk density, which inevitably results in a volume as an electrode material. This causes a problem that the capacity decreases. In the above report, for this problem, a decrease in volume capacity is suppressed by designating a certain region and the amount of the specific surface area, pore diameter, and pore volume of the activated carbon. However, these are intended to achieve high output characteristics at the expense of volume capacity. In order to maintain high volume capacity and obtain high output characteristics, it does not depend on the expansion of the pore diameter as in the past. There is a need to develop high-power electrode materials.

JP 2002-033249 A JP 2001-118753 A

  As described above, in order to achieve both high volume capacity and high output as an electrode material for an electric double layer capacitor, there is a limit to a technique based on pore improvement such as pore diameter expansion. The present invention provides an electrode material for an electric double layer capacitor and an electric double layer capacitor having high capacity and high output characteristics at low temperature.

As a result of intensive studies, the inventors have solved the above problems and have reached the present invention. Specifically, the items described in [1] to [5] below are characterized.
[1] Electricity in which the half-value width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is 77 or less, and the half-value width (Δν1) increases by 1 or more by heat treatment. Electrode material for double layer capacitors.
[2] BET specific surface area of 1800-2500 m ² / g, pore volume of 0.8-1.2 ml / g, average pore size of 1.6-2.0 nm, average particle size of 0.5-15 μm, surface The electrode material for electric double layer capacitors according to [1], wherein the functional group amount is 0.25 to 0.60 mmol / g.
[3] The electrode material for an electric double layer capacitor according to [1] or [2], which is subjected to a surface modification treatment.
[4] The electrode material for an electric double layer capacitor according to any one of [1] to [3], which is manufactured by alkali activation using a phenol resin carbide as a carbon raw material.
[5] The electrode material for an electric double layer capacitor according to any one of [1] to [4], wherein the heat treatment condition is 1 hour at 800 ° C. in a nitrogen atmosphere.
[6] The electrode material for an electric double layer capacitor according to any one of [3] to [5], wherein the surface modification treatment is performed by a compressive force and a shearing force.
[7] An electric double layer capacitor using the electric double layer capacitor electrode material according to any one of [1] to [6].

  According to the present invention, it is possible to obtain an electrode material for an electric double layer capacitor and an electric double layer capacitor that have a high capacity and high output characteristics in a low temperature range.

Hereinafter, the present invention will be described in detail.
In the electrode material for an electric double layer capacitor of the present invention, the half-value width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is 77 or less. ) Increases by 1 or more. The value of the half width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum represents the crystalline state of the carbon structure, and the smaller the value, the higher the crystallinity of the electrode material. The value of the half width (Δν1) is preferably in the range of 65 to 77, more preferably in the range of 65 to 76, and still more preferably in the range of 65 to 75. When the value of the half width (Δν1) exceeds 77, the crystallinity is low and the output characteristics are deteriorated. In addition, the higher the crystal, the more excellent the output characteristics. Therefore, the lower half-value width (Δν1) is preferable, but the lower limit value is limited by the raw material, processing method, and the like. For example, when alkali activation is performed using a phenol resin carbide as a carbon raw material, the full width at half maximum (Δν1) is preferably 68 or more. In addition, the half value width (Δν1) in the present invention is usually measured by the following method.

(Half width (Δν1) measurement method)
The sample powder (electrode material of the present invention) is placed on the preparation, and the powder surface is flattened with a slide glass. Set this to measurement port, the measurement is carried out in the wavelength range ^{830cm -1 ~1940cm} -1 according to the procedure of the program. For the measurement, a laser Raman spectrophotometer (excitation light: argon ion laser 514.5 nm) is used. The obtained spectra, using a fitting analysis software analysis software (spectra manager), component a (peak: 1595cm ^-1 half-width: 75 cm ^-1), component b (peak: 1510 cm ^-1 half width: 65cm ^-1) , Component c (peak: 1355 cm ⁻¹ half-value width: 175 cm ⁻¹ ), component d (peak: 1200 cm ⁻¹ half-value width: 200 cm ⁻¹ ) are temporarily set, four-component fitting is performed, and 1580 cm ⁻¹ The full width at half maximum is calculated with the peak near the G band as shown in FIG. 1 (see FIG. 1), and the average value of three measurements is set as the target value.

In addition, when the electrode material for an electric double layer capacitor of the present invention is subjected to heat treatment, the value of the full width at half maximum (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is increased by 1 or more. The condition for the heat treatment is usually 1 hour at 800 ° C. in a nitrogen atmosphere. In the present invention, the value of the half width (Δν1) increases when the value of the half width (Δν1) measured after the heat treatment is 1 with respect to the value of the half width (Δν1) measured before the heat treatment. That means more. As for the increasing value, in consideration of the variation due to the measurement, if it is less than 1, there is a possibility that it does not change (increase). Moreover, it is preferable that it is 1-5 about an increase value, It is more preferable that it is 1-4, It is further more preferable that it is 1-3. When the increase value exceeds 5, the output characteristics tend to be lowered.

Examples of the increase in the half-value width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum before and after the heat treatment include, for example, an electrode material in which the crystal state of the electrode material surface is different from the bulk crystal state And electrode materials whose surface condition is modified. As such an electrode material, for example, a material in which the surface is coated with a material having a different crystal state from a bulk, a composite material, etc., a surface treatment is performed by applying mechanical treatment to the electrode material surface, etc. It is done. Among these, an electrode material obtained by subjecting the electrode material to a surface modification treatment is preferable. Here, the surface modification usually indicates that the surface state is modified by applying a compressive force and a shearing force to the electrode material surface. In addition, it is preferable that a compressive force and a shear force are strong.

The apparatus used for the surface modification treatment is not particularly limited as long as it can apply a compressive force and a shearing force to the surface. Specifically, for example, mechanofusion (manufactured by Hosokawa Micron Co., Ltd.), nobilta (manufactured by Hosokawa Micron Co., Ltd.), hybridization system (manufactured by Nara Machinery Co., Ltd.), mechano macros (Nara Machinery Co., Ltd.) Manufactured). By such surface modification treatment, it is possible to modify the surface state while maintaining the state of the electrode material bulk. The electrode material whose surface state has been modified undergoes a heat treatment, so that the surface state returns to the state before the modification. Therefore, the full width at half maximum (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum. ) Value increases. Further, the value of the half width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum can be adjusted, for example, by appropriately adjusting the conditions of the surface modification treatment.

  The conditions for the surface modification treatment vary depending on the equipment used, the physical properties of the material to be treated, and the like. When the surface modification treatment is performed by the above apparatus, the oxidation reaction of the particles proceeds from the heat generated by the applied energy, and when the treatment is excessive, the amount of surface functional groups tends to increase. Since the surface functional group causes a decrease in the life characteristics of the electric double layer capacitor, it is preferable to select the surface modification treatment condition so that the rate of change of the surface functional group amount is 30% or less, and 25% or less. Is more preferable, and it is further more preferable that it is 20% or less. The surface functional group amount can be measured by the following method.

(Surface functional group measurement method)
1 g of electrode material and 100 ml of 0.1 mol / l sodium hydroxide are placed in a volumetric flask and stirred at 25 ° C. for 20 hours. After filtration of this mixture, 50 ml of the filtrate is accurately weighed with a whole pipette and placed in a volumetric flask. As an indicator, 3 drops of methyl orange are appropriately applied to the filtrate, and this aqueous solution is back titrated with 0.1 mol / l hydrochloric acid. The surface functional group amount of the electrode material can be evaluated from the following formula.
Electrode material surface functional group amount (mmol / g) = (50-hydrochloric acid dropping amount (ml)) × 0.1 × 2

It electric double layer capacitor electrode material in the present invention preferably has a BET specific surface area of 1800~2500m ² / g, more preferably 1900~2500m ² / g, a 2000~2500m ² / g Is more preferable. When the BET specific surface area is less than 1800 m ² / g, there is a tendency that sufficient capacitance cannot be obtained, and when it exceeds 2500 m ² / g, the bulk density decreases and the volume capacity of the electric double layer capacitor decreases. In addition, the BET specific surface area in this invention can be measured by nitrogen gas adsorption measurement.

  The pore volume is preferably 0.8 to 1.2 ml / g, more preferably 0.9 to 1.2 ml / g, and even more preferably 0.95 to 1.15 ml / g. . If the pore volume is less than 0.8 ml / g, pore development is insufficient, ion diffusibility tends to be lowered, and high output characteristics tend not to be obtained. When it exceeds 1.2 ml / g, the volume capacity tends to decrease due to the decrease in bulk density. The pore volume in the present invention can be measured by nitrogen gas adsorption measurement, and the pore volume is calculated from the nitrogen adsorption amount at a relative pressure value of 0.995.

The average pore diameter is preferably 1.6 to 2.0 nm, more preferably 1.6 to 1.9 nm, and even more preferably 1.65 to 1.85 nm. If the average pore diameter is less than 1.6 nm, the diffusion of ions existing in the pores is insufficient, and the output characteristics tend to be lowered. If it exceeds 2.0 nm, the bulk density tends to be low, and the volume capacity tends to decrease. In addition, the average pore diameter in the present invention can be calculated from the BET specific surface area and the pore volume of nitrogen gas adsorption measurement by the following formula.
Average pore diameter D (nm) = 4 V / S (V: pore volume, S: BET specific surface area)

  The electrode material for electric double layer capacitors in the present invention preferably has a surface functional group amount of 0.25 to 0.6 mmol / g, more preferably 0.25 to 0.55 mmol / g, More preferably, it is 0.25 to 0.5 mmol / g. When the surface functional group amount exceeds 0.6 mmol / g, the life characteristics of the electric double layer capacitor tend to be lowered. In addition, the surface functional group amount in the present invention can be measured by the method described above.

  The average particle diameter is preferably 0.5 to 15 μm, more preferably 1 to 12 μm, and further preferably 2 to 10 μm. When the average particle diameter is less than 0.5 μm, the bulk density is remarkably lowered and the volume capacity tends to be lowered. If it exceeds 15 μm, the output characteristics tend to deteriorate. In addition, the average particle diameter of an electrode material can be measured using a laser diffraction particle size measuring apparatus, for example. The average particle diameter is set to 50% of the cumulative particle size distribution based on the volume standard.

  Although there is no restriction | limiting in particular in the manufacturing method of the electrode material for electric double layer capacitors of this invention, For example, it can obtain by carbonizing in inert atmosphere by using phenol resin as a raw material, and carrying out alkali activation after that. When a phenol resin is used as a raw material, it is preferable to use a novolac type phenol resin, and the novolac type phenol resin is preferably subjected to a curing treatment with a curing agent prior to carbonization. An electrode material produced using carbon obtained by carbonizing a novolak resin is preferable because structural changes that occur during charging are suppressed, and deterioration of output characteristics is suppressed.

  Although there is no restriction | limiting in particular as a hardening | curing agent of the novolak-type phenol resin used as a raw material, Specifically, formaldehyde supply sources, such as hexamethylenetetramine and paraformaldehyde, are mentioned. These are used individually or in combination of 2 or more types. Also, as a curing method, melt curing in which a novolak type phenol resin is melted and mixed with a curing agent is generally used. After the novolac type phenol resin is suspended in an aqueous solution, a curing agent is added and the aqueous solution is added. Examples thereof include a suspension curing method in which heat treatment is performed, and heat curing using a heat treatment apparatus such as a dryer. These are used alone or in combination of two or more. The cured resin is preferably used after being pulverized. For pulverization, a normal pulverizer is used, and specific examples include pulverization with a cutter mill, a pin mill, a jet mill or the like. These may be performed alone or in combination of two or more methods.

  The cured and pulverized resin is preferably carbonized. The carbonization is usually preferably performed in an inert atmosphere such as nitrogen, argon, helium, vacuum, etc. in the range of 500 to 1000 ° C., more preferably 600 to 900 ° C., and 700 to 800 ° C. Further preferred. When the carbonization temperature is less than 500 ° C., the obtained electrode material tends to have poor output characteristics because of low crystallinity. When the carbonization temperature exceeds 1000 ° C., a large amount of alkali compound is required at the time of activation, and the improvement in crystallinity tends not to greatly contribute to the output characteristics. The obtained carbide is preferably further pulverized to the target particle size. Examples of the pulverizer include a pin mill, a jet mill, a ball mill, and a bead mill. These may be performed alone or in combination of two or more methods.

It is preferable to perform alkali activation after carbonization of the resin. The alkali activation can be performed by a usual method. The alkali activation is preferably performed as follows. Hereinafter, activation refers to alkali activation.
The carbide and the alkali compound are mixed using a mixer such as a planetary mixer. Although there is no restriction | limiting in particular about the alkaline compound used in this invention, For example, potassium hydroxide, sodium hydroxide, potassium carbonate etc. are mentioned. Of these, potassium hydroxide is preferable because an electrode material having a high specific surface area can be obtained. This mixture is put into a Ni container and heat-treated at 700 to 900 ° C. for 0.5 to 3 hours in an inert atmosphere such as nitrogen, argon or helium. The activation temperature at this time is more preferably 750 to 850 ° C, and further preferably 780 to 830 ° C. The activation time is more preferably 1 to 2 hours. If the activation temperature is less than 700 ° C., activation does not proceed easily, and activated carbon having a desired specific surface area tends not to be obtained. If the activation temperature exceeds 900 ° C., the corrosion of the container due to the alkali compound in the Ni container is remarkable. Tend to be. In addition, if the activation time is less than 0.5 hours, activation tends to be insufficient, and an electrode material having a desired specific surface area tends not to be obtained. Even if the activation time exceeds 3 hours, there is a tendency that the pore formation hardly changes.

  After activation, the metal impurities mixed from the alkali compound or Ni container are dissolved and extracted with an acid. Although there is no particular limitation on this method, for example, the mixture after activation is stirred in 4% by weight hydrochloric acid while heating to 80 ° C. or higher to dissolve the metal impurities. Thereafter, the acid solution is filtered, and the above process is repeated again 5 times using the same concentration of hydrochloric acid. Subsequently, the same process as described above is performed 5 times or more using pure water, and hydrochloric acid adhering to the electrode material is removed, whereby a high-purity electrode material is obtained.

  The purified electrode material is preferably further heat-treated in an inert atmosphere in order to reduce surface functional groups. The heat treatment temperature is preferably 500 to 1000 ° C, more preferably 600 to 900 ° C, and further preferably 700 to 800 ° C. When the temperature is lower than 500 ° C., the surface functional groups tend not to be sufficiently reduced, and the life characteristics tend to be lowered. On the other hand, when the heat treatment temperature exceeds 1000 ° C., the specific surface area and pore volume tend to decrease, and the capacitance and output characteristics tend to decrease.

  The electrode material for electric double layer capacitors obtained by the present invention is suitable as an electrode material for electric double layer capacitors that require high output characteristics and capacity at low temperatures. Although there is no restriction | limiting in particular about the structure of the electrical double layer capacitor which uses the electrode material of this invention, a manufacturing method, For example, an electrical double layer capacitor is producible as follows.

  The electrode is prepared by mixing and dispersing the electrode material for an electric double layer capacitor of the present invention, a binder, various additives, and the like together with a solvent with a stirrer, a kneader, or the like. An electrode can be produced by applying this to a current collector. Further, it is possible to produce an electrode by forming a paste-like paint into a sheet shape, a pellet shape, or the like and integrating it with a current collector.

  Although there is no limitation in particular as said binder, fluorinated resin, such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and styrene butadiene rubber (SBR) Or the like. These binders are usually used in the form of powder dissolved or dispersed in a solvent, but it is also possible to use the powder as it is without using a solvent. The electrode is preferably mixed with a conductive additive. As the conductive assistant, graphite, carbon black such as acetylene black, ketjen black, or the like can be used.

  About the said electrical power collector, the strip | belt-shaped thing which made aluminum, nickel, stainless steel etc. into foil shape, perforated foil shape, mesh shape, etc. can be used, for example. A porous material such as porous metal (foamed metal) or carbon paper can also be used.

  The method for applying the electrode slurry is not particularly limited. For example, a metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, doctor blade method, gravure coating method, screen printing method, etc. A well-known method is mentioned. After the application, a rolling process using a flat plate press, a calendar roll, or the like is performed as necessary. Further, the integration of the electrode material formed into a sheet shape or a pellet shape and the current collector can be performed by a known method such as a roll press.

  The electric double layer capacitor of the present invention can be produced by injecting an electrode using the electrode material of the present invention with a separator interposed therebetween and injecting an electrolytic solution. In addition, it is preferable to carry out in an inert atmosphere using a glove box etc. so that moisture mixing may not occur at the time of capacitor cell production. The electrode is preferably used after sufficiently removing the adsorbed moisture.

The electrolytic solution can be broadly classified into an aqueous type and an organic type, but it is preferable to use an organic electrolytic solution from the viewpoint that it can be used at a high voltage. No particular limitation is imposed on the type of electrolyte and the electrolyte, for _{example, (C 2 H 5) 4} NBF 4, (C 2 H 5) 3 CH 3 NBF 4 quaternary ammonium salts such as, 1-ethyl-3 It is possible to use a room temperature molten salt such as methylimidazolium BF ₄ or a lithium-containing salt such as LiBF ₄ dissolved in an organic solvent such as propylene carbonate. As the anion species of the electrolyte, in addition to BF ₄ , ClO ₄ ⁻ , PF ₄ ⁻ , AsF ₆ ^{− and the} like can be used. As the organic solvent for dissolving the electrolyte, γ-butyrolactone, acetonitrile, sulfolane and the like can be used in addition to PC. About the structure of these electrolyte solutions, it is preferable to select suitably from use conditions. As said separator, the nonwoven fabric, cloth, microporous film, paper, etc. which have polyolefins, such as polyethylene and a polypropylene, as a main component can be used.

  The structure of the electric double layer capacitor of the present invention is not particularly limited. Usually, the positive and negative electrodes and the separator are wound in a flat spiral shape to form a wound electrode plate group, or these are laminated in a flat plate shape to form a laminated electrode. In general, a plate group is used, and the electrode plate group is enclosed in an exterior body.

  The electric double layer capacitor of the present invention is used as a coin type, multilayer type, cylindrical cell or the like. In addition, the electrode material for electric double layer capacitors of the present invention can be applied to electrode materials for various power storage devices, electrochemical elements, etc. in addition to electric double layer capacitors.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples.

(Example 1)
500 g of phenol formaldehyde resin was weighed and ground and mixed with 50 g of hexamine. The mixture was melt-mixed with a vat coated with PTFE (polytetrafluoroethylene) on a hot plate to obtain a semi-cured product of a phenol resin. The obtained phenol resin semi-cured product was after-cured at 180 ° C. for 2 hours with a hot air dryer to obtain a cured resin product. The obtained resin cured product is pulverized to about 100 μm with a cutter mill, heated from room temperature (25 ° C.) to 750 ° C. at a flow rate of 300 ml / min in an atmosphere baking furnace, and kept for 2 hours to phenol. Resin carbide was produced. The obtained carbide was pulverized to an average particle size of 4 μm, mixed with 3.3 times the amount of potassium hydroxide with respect to the weight of the carbide, and room temperature (25 ° C. at a flow rate of 300 ml / min in a nitrogen stream in a box furnace. ) To 800 ° C. and held for 2 hours to activate the alkali. When the temperature returned to room temperature (25 ° C.), a sample was taken out, metal impurities were removed by the method of dissolving and extracting with the acid described above, and this was dried at 120 ° C. for 40 hours to obtain activated carbon. The obtained activated carbon was heated from room temperature (25 ° C.) to 800 ° C. in a nitrogen atmosphere and then heat treated for 1 hour to obtain an electrode material. The obtained electrode material was subjected to a surface modification treatment for 1 minute by a compression shear type surface modification device (device name: Nobilta NOB-130, manufactured by Hosokawa Micron Corporation).

The BET specific surface area, pore volume, and average pore diameter of the surface-modified electrode material were measured using ASAP-2010 manufactured by Shimadzu Corporation in an N ₂ gas adsorption measuring device. The average particle size was measured using a SALD-3000J manufactured by Shimadzu Corporation with a laser diffraction particle size measuring apparatus. The amount of surface functional groups was evaluated by the method described above (surface functional group measurement method). The value of half width (Δν1) is described above using the NRS-1000 model manufactured by JASCO as a laser Raman spectrophotometer for the obtained electrode material and the electrode material heat-treated at 800 ° C. for 1 hour in a nitrogen atmosphere. (The half-value width (Δν1) measuring method). For the capacitance and output characteristics, an electrode cell was prepared and evaluated by the following method. The results are shown in Tables 1 and 2. In addition, the change rate of the surface functional group amount of the electrode material was 19%.
In Table 2, the value of “Δν1” is the half-value width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum, and “before heat treatment” means “before heat treatment”. “After heat treatment” is an electrode material that is heat-treated at 800 ° C. for 1 hour in a nitrogen atmosphere, and “change amount” is an increase in the half-value width (Δν1) due to the heat treatment. .

(Electrode cell manufacturing method)
Electrode material and conductive additive (HS100 manufactured by Denki Kagaku Kogyo Co., Ltd.) and carboxymethylcellulose (DN-10L manufactured by Daicel Chemical Industries, Ltd.) 2 wt% aqueous solution, 60 wt% PTFE aqueous dispersion (Daikin Kogyo Co., Ltd. M-390) ) Is mixed at a ratio of 100: 10: 200: 5 and water is added to prepare a slurry, which is then applied to an aluminum etching foil (film pressure 20 μm manufactured by Hosen) to an electrode thickness of 70 μm. The coated electrode is dried in a dryer at 80 ° C. for 5 hours and 120 ° C. for 3 hours, and then the electrode is punched into a circular shape having a diameter of 16 mm to produce an electrode. Two of these electrodes are prepared for the negative electrode for the positive electrode, and are vacuum-dried at 120 ° C. for 3 hours using a vacuum separator together with a paper separator (TF40 manufactured by Nippon Advanced Paper Industry Co., Ltd.), a SUS coin cell upper and lower lid, and an aluminum spacer. After drying, a coin-type capacitor cell is produced in an argon-substituted glove box. In the cell, two electrodes are opposed to each other via a separator, and then an aluminum spacer is inserted to fill the space in the cell. After adding about 0.03 ml of the electrolytic solution, the coin cell is sealed after performing a reduced pressure impregnation treatment in a side box at a reduced pressure of 10 torr or less for 10 minutes. The produced cell is connected to a charge / discharge tester (TOSCAT manufactured by Toyo System Co., Ltd.), and a charge / discharge test is performed. Although 1.5 mol / l propylene carbonate solution of ethylmethylimidazolium tetrafluoroborate (manufactured by Guangei Chemical Industry Co., Ltd.) was used as the electrolytic solution, the effects of the present invention are particularly limited to the type and concentration of the electrolytic solution. Not done.

(Evaluation method of electrode characteristics)
The capacitor cell prepared above was left in a thermostatic chamber at a predetermined temperature for 3 hours or more, and then subjected to a charge / discharge test under the following conditions to evaluate electrode characteristics at 25 ° C. (room temperature) and −30 ° C. (low temperature). went. The results are shown in Table 2.
・ Charging conditions: constant current / constant voltage ・ Charging current: 2 mA
・ Charging voltage: 2V
・ Charging time: 2 hours ・ Discharging conditions: constant voltage ・ Discharging current: 2 mA
・ Discharge voltage: 0V
The capacitance is 1.7 V (voltage: V1, time: T1 (seconds)) to 1.3 V (voltage: V2, time: T2 (seconds)) of the discharge curve obtained in the charge / discharge test described above. Calculate from the slope (see next formula).
Capacitance (F / g) = (T2-T1) × 0.002 / (V1-V2) / G
(G: active material amount (g))

The output characteristics were evaluated using the DC resistance value as an index. For the DC resistance value, an approximate straight line was drawn for the curve from 10 seconds to 40 seconds of the discharge curve, and the difference between the intercept value and the full charge voltage value was defined as a voltage drop ΔV, and the resistance value was obtained by the following equation.
Resistance value (Ω) = ΔV / 0.002

(Example 2)
The same procedure as in Example 1 was performed except that the carbonization temperature of the cured resin was 730 ° C., and the amount of potassium hydroxide during alkali activation was 3 times the amount of the carbide. In addition, the change rate of the surface functional group amount of the electrode material was 17%.

(Example 3)
The same procedure as in Example 1 was performed except that the carbonization temperature of the cured resin was 700 ° C., and the amount of potassium hydroxide at the time of alkali activation was 2.5 times the weight of the carbide. In addition, the change rate of the surface functional group amount of the electrode material was 10%.

(Comparative Example 1)
The same procedure as in Example 3 was performed except that the surface modification treatment was not performed. The change rate of the surface functional group amount of the electrode material was 0%.

(Comparative Example 2)
The same procedure as in Example 1 was performed except that the carbonization temperature of the cured resin was 600 ° C., the amount of potassium hydroxide during alkali activation was 2.15 times the weight of the carbide, and the surface modification treatment was not performed. It was. The change rate of the surface functional group amount of the electrode material was 0%.

(Comparative Example 3)
The same procedure as in Comparative Example 2 was performed except that the surface modification treatment time was 1 minute. The change rate of the surface functional group amount of the electrode material was 2%.

As shown in Table 2, the half-value width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is 77 or less, and the half-value width (Δν1) is increased by 1 or more by heat treatment. In Examples 1 to 3, the capacitance at −30 ° C. (low temperature) is almost the same as that at 25 ° C. (normal temperature). Moreover, Examples 1-3 show that resistance value in -30 degreeC (low temperature) is low compared with Comparative Examples 1-3. In contrast, Comparative Example 1 in which the increase value (change amount) after the heat treatment is 0.4 has a high resistance value at −30 ° C. (low temperature), and the half width (Δν1) before the heat treatment exceeds 77. In Comparative Examples 2 and 3, the resistance value at −30 ° C. (low temperature) is remarkably high, and the capacitance is also reduced.

  According to the present invention, it has been found that an electrode material for an electric double layer capacitor and an electric double layer capacitor having a high capacity and high output characteristics in a low temperature range can be obtained.

It is a diagram illustrating a method for calculating the half value width of the peak around 1580 cm ^-1 and near 1360 cm ^-1 by Raman spectra as G-band and D-band.

Claims (7)

Electric double layer capacitor in which the half-value width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is 77 or less, and the half-value width (Δν1) is increased by 1 or more by heat treatment Electrode material. BET specific surface area of 1800-2500 m ² / g, pore volume of 0.8-1.2 ml / g, average pore size of 1.6-2.0 nm, average particle size of 0.5-15 μm, surface functional group content The electrode material for an electric double layer capacitor according to claim 1, wherein is from 0.25 to 0.60 mmol / g.   The electrode material for an electric double layer capacitor according to claim 1 or 2, which has been subjected to a surface modification treatment.   The electrode material for an electric double layer capacitor according to any one of claims 1 to 3, wherein a carbonized material of phenol resin is used as a carbon raw material and is produced by alkali activation.   The electrode material for an electric double layer capacitor according to any one of claims 1 to 4, wherein the heat treatment condition is 800 ° C in a nitrogen atmosphere for 1 hour.   The electrode material for an electric double layer capacitor according to any one of claims 3 to 5, wherein the surface modification treatment is performed by a compressive force and a shearing force.   The electric double layer capacitor formed using the electrode material for electric double layer capacitors in any one of Claims 1-6.

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