JP2010103152A - Electrode material for electric double layer capacitor, electrode for electric double layer capacitor and electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode material for an electric double layer capacitor, which produces less gas and has superior long-period life characteristics, and to provide an electrode for the electric double layer capacitor and an electric double layer capacitor that use the same. <P>SOLUTION: The electrode material for the electric double layer capacitor has a surface function group concentration of 0.3 to 0.6 mmol/g, a half-value width (Δν) of 68 to 75 at a peak (G1) of approximately 1,580 cm-1 observed in a Raman spectrum, and an average pore diameter of ≥1.73 nm. It is preferable that the electrode for the electric double layer capacitor has a surface area of 1,800 to 2,800 m<SP>2</SP>/g, a pore capacity of 0.5 to 1.5 ml/g, and an average particle size of 1 to 10 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode material for an electric double layer capacitor, an electrode for an electric double layer capacitor using the same, and an electric double layer capacitor.

Since electric double layer capacitors do not involve chemical reactions during charging and discharging, they have the advantage of superior input / output characteristics, life characteristics, and safety compared to lithium ion secondary batteries and nickel metal hydride secondary batteries. . Conventionally, the main application of electric double layer capacitors has been for small products such as memory backup, but in recent years, taking advantage of these features, development and commercialization of medium and large products have been promoted. Medium and large products include industrial applications such as copiers, instantaneous power failure compensation power supplies, and construction machinery, and automotive applications such as automotive electronic control system compensation and hybrid power supplies.
Such industrial and in-vehicle electric double layer capacitors are required to have better life characteristics than small products. Conventionally, in order to improve the life characteristics, it has been regarded as important to reduce the surface functional group concentration of activated carbon as an electrode material. This is because the surface functional group attached to the electrode material decomposes the electrolyte solution due to charging / discharging of the battery to generate gas, or the functional group itself decomposes and gasifies, thereby reducing the long-term life characteristics. (For example, Patent Documents 1 to 3)
Certainly, reducing the amount of functional groups on the surface is effective for improving the life characteristics, but activated carbons with different precursor types, such as activated carbon with a precursor of soft carbon, will significantly reduce the life characteristics due to expansion and contraction. It is known to do. That is, there is a limit to improving the life characteristics only by reducing the surface functional group amount (for example, Patent Document 4).
The electric double layer capacitor exhibits a capacity when a solvent or an electrolyte acts electrochemically on activated carbon. Therefore, the performance of the electric double layer capacitor greatly depends on the physical properties, pore structure and surface characteristics of the activated carbon.

  In order to produce a high performance electric double layer capacitor, it is important to improve the specific surface area, pore structure, etc., which are the physical properties of activated carbon. The increase in the specific surface area of the activated carbon is a technique which is expected and attempted to increase the electrode density and the capacitance because it increases the amount of adsorbed electrolyte ions. However, in recent years, electric double layer capacitors have been used in various fields such as in-vehicle use, and there is a demand for higher capacity electrode materials and higher output. In order to increase the capacity and output of the capacitor electrode material, it is common to use a technique for controlling the pore diameter, such as developing mesopores of activated carbon. However, when the pore diameter is enlarged, the bulk density is inevitably lowered, and there is a problem that a capacitor having a low volume capacity is obtained.

  As described above, conventionally, in order to improve the performance of activated carbon, a method of optimizing the specific surface area and the pore diameter by controlling the activation conditions has been mainly used. However, in designing an electric double layer capacitor, performance development is insufficient only by the structural design of the electrode material before charging and discharging. In the electric double layer capacitor electrode material, surface functional groups attached to the carbon electrode material are generated as a gas inside the capacitor during charge and discharge, thereby causing an internal pressure increase and possibly rupturing the metal case. Further, a material having soft carbon as a precursor expands and contracts during charge and discharge, and causes an increase in pressure inside the capacitor (for example, Patent Document 4). In particular, the surface functional group may change in initial characteristics and cycle characteristics. There is an attempt to improve initial characteristics and cycle characteristics by controlling surface functional groups (see, for example, Patent Document 3).

JP 2004-67498 A JP 2000-235939 A JP 2003-243265 A JP 2002-265215 A

This invention makes it a subject to achieve the following objectives from the problem of the said description.
An object of the present invention is to provide an electrode material for an electric double layer capacitor that generates less gas and has excellent long-term life characteristics, an electrode for an electric double layer capacitor, and an electric double layer capacitor using the electrode material.

  As a result of intensive studies, the inventors have found that the amount of surface functional groups of the electrode material and the electrode material affect the long-term life characteristics. That is, by controlling the amount of functional groups on the surface of the electrode material to be reduced, it is possible to suppress the decomposition of the electrolyte solution at the beginning of the lifetime, and by further increasing the crystallinity of the electrode material, It was found that it can be suppressed.

That is, specifically, the features described in the following [1] to [5] are characterized.
[1] The surface functional group concentration is 0.3 to 0.6 mmol / g, the half-width (Δν) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is 68 to 75, and the average pore diameter is An electrode material for an electric double layer capacitor having a thickness of 1.73 nm or more.
[2] The electrode material for an electric double layer capacitor according to [1], wherein the specific surface area is 1800 to 2800 m ² / g, the pore volume is 0.5 to 1.5 ml / g, and the average particle size is 1 to 10 μm.
[3] The electrode material for an electric double layer capacitor according to the above [1] or [2], which is produced by alkali activation of non-graphitizable carbon.
[4] An electric double layer capacitor electrode using the electric double layer capacitor electrode material according to any one of [1] to [3].
[5] An electric double layer capacitor using the electric double layer capacitor electrode according to any one of [1] to [4].

  According to the present invention, it is possible to obtain an electrode material for an electric double layer capacitor, an electrode for an electric double layer capacitor, and a battery double layer capacitor that generate less gas and have excellent long-term life characteristics.

Hereinafter, the present invention will be described in detail.
The electrode material for an electric double layer capacitor of the present invention has a surface functional group concentration of 0.3 to 0.6 mmol / g, and a half-value width (Δν1) of a peak (G1) near 1580 cm ⁻¹ observed in a Raman spectrum. Is 68 to 75, and the average pore diameter is 1.73 nm or more.

  The electrode material for electric double layer capacitors in the present invention has a surface functional group concentration of 0.3 to 0.6 mmol / g, preferably 0.35 to 0.55 mmol / g, 0.4 to 0 More preferably, it is 5 mmol / g. When the surface functional group concentration exceeds 0.6 mmol / g, a large amount of gas is generated during charge and discharge, and the life characteristics of the electric double layer capacitor tend to be deteriorated. If it is less than 0.3 mmol / g, it is difficult to produce an electrode, and as a result, battery characteristics tend to be lowered. The surface functional group concentration can be reduced, for example, by subjecting the obtained activated carbon to a heat treatment in an inert atmosphere.

The surface functional group concentration in the present invention is measured by the following 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 filtering this electrode material and sodium hydroxide mixed solution, 50 ml of the filtrate is accurately weighed with a whole pipette and put into 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 amount of surface functional groups (surface functional group concentration) 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
The amount of surface functional groups calculated in this method is the amount of functional groups attached to and attached to the carbon network surface. For example, the total amount of functional groups such as lactone groups, hydroxyl groups, and carboxyl groups present on the electrode material surface. It becomes.

In the electrode material for an electric double layer capacitor of the present invention, the half-value width (Δν) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is 68 to 75, preferably 70 to 74. . The full width at half maximum (Δν) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum represents the crystal structure of the carbon crystallite, and it is possible to determine the fine structure of carbon by looking at this value. It is. When the value of Δν exceeds 75, the crystallinity is lowered, and the reactivity between the electrolytic solution and the electrode material is increased, and the life characteristics of EDLC (electric double layer capacitor) tend to be lowered. The reason why the lower limit of Δν is set to 68 is that the value of carbon before activation is 68, and since the value of Δν increases by activation, 68 is set as the lower limit value.

(Half width (Δν) 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 around 1580 cm ⁻¹ The half width is calculated using the peak of G as the G band (see FIG. 1), and the average value of the three measurements is set as the target value.

  The electrode material for electric double layer capacitors in the present invention is characterized in that the average pore diameter is 1.73 or more. The solvated ion diameter of the electrolytic solution is about 1 nm, and if the average pore diameter is less than 1.73 nm, the ion diffusion is insufficient. The upper limit of the average pore diameter is not limited, but if it exceeds 1.9 nm, the bulk density tends to decrease and the volume capacity tends to decrease, and therefore it is preferably 1.9 nm. In addition, the average pore diameter in the present invention can be calculated by the following formula from the BET specific surface area and the pore volume measured by nitrogen gas adsorption.

Average pore diameter D (nm) = 4 V / S (V: pore volume, S: BET specific surface area)
It electric double layer capacitor electrode material in the present invention preferably has a BET specific surface area of 1800~2800m 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 0.5 to 1.5 ml / g, more preferably 0.9 to 1.2 ml / g, and still more preferably 0.95 to 1.15 ml / g. . When the pore volume is less than 0.5 ml / g, pore development is insufficient, ion diffusibility is lowered, and sufficient output characteristics tend not to be obtained. If it exceeds 1.5 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 particle diameter of the electrode material is preferably 1 to 10 μm, more preferably 1 to 9 μm, and even more preferably 2 to 8 μm. When the average particle size is less than 1 μm, the bulk density is remarkably lowered and the volume capacity tends to be lowered. When it exceeds 10 μm, the life characteristics tend to be lowered. 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, It can obtain as follows.
The raw material is preferably a precursor that becomes non-graphitizable carbon, more preferably a phenol resin is used as the precursor, and even more preferably a novolac type phenol resin. The novolac type phenolic resin is preferably subjected to a curing treatment with a curing agent. The electrode material produced using carbon obtained by carbonizing the novolak type phenolic resin suppresses structural changes that occur during charging, and outputs characteristics. It is preferable because deterioration of is suppressed.

  Although there is no restriction | limiting in particular as a hardening | curing agent of a novolak type phenol resin, 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. About carbonization, it is preferable to carry out in the range of 500-1000 degreeC normally in inert atmosphere, such as nitrogen, argon, helium, and a vacuum, it is more preferable to carry out at 600-900 degreeC, and to carry out at 700-800 degreeC. Is more preferable. 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.

  After carbonization of the resin, alkali activation is performed. 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 a temperature of 500 to 1000 ° C. for 0.5 to 3 hours under an inert atmosphere such as nitrogen, argon or helium. As for the activation temperature in this case, 600-900 degreeC is more preferable. The activation time is more preferably 1 to 2 hours. If the activation temperature is less than 500 ° 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 1000 ° 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 largely removed by magnetic washing, and then dissolved and extracted with an acid. Although this method is not particularly limited, for example, the mixture after activation is stirred in 4% by mass of hydrochloric acid while heating to 80 ° C. or more 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. 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 life characteristics over a long period of time. 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. After the application, a rolling process using a flat plate press, a calendar roll, or the like is performed as necessary.

  The binder is not particularly limited, but fluorine resins 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, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a 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 (propylene carbonate). 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 to the electric double layer capacitor, the electrode material for electric double layer capacitor of the present invention can be applied to electrode materials for various power storage devices, electrochemical elements and the like.

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 in a nitrogen stream in an atmosphere baking furnace at a flow rate of 300 ml / min from room temperature (25 ° C.) to 750 ° C., and held 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, and metal impurities were removed by the method of dissolving and extracting with the acid described in the above alkali activation, 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 600 ° C. in a nitrogen atmosphere and then heat treated for 1 hour to obtain an electrode material.
The BET specific surface area, pore volume, and average pore diameter of the electrode material were measured using an N ₂ gas adsorption measuring device (ASAP-2010 manufactured by Shimadzu Corporation). The average particle size was measured using a laser diffraction particle size measuring device (SALD-3000J, manufactured by Shimadzu Corporation). The surface functional group amount (concentration) was evaluated by the method described above (surface functional group measurement method).
The value of half width (Δν) is determined by using a laser Raman spectrophotometer (NRS-1000 type manufactured by JASCO Corporation) for the obtained electrode material and the electrode material heat-treated at 600 ° C. for 1 hour in a nitrogen atmosphere. Then, it was determined by the method described above (half-value width (Δν) measurement 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. The change rate of the surface functional group amount of the electrode material was 13%, and the Δν value was 72.5.

In Table 2, the value of “Δν1” is the value of the half width (Δν) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum.
(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% by weight aqueous solution, 60% by weight PTFE aqueous dispersion (M-390 manufactured by Daikin Industries, Ltd.) ) Was mixed at a ratio (mass ratio) of 100: 10: 200: 5, and water was added to prepare a slurry, which was then applied to an aluminum etching foil (having a film thickness of 20 μm) to an electrode thickness of 70 μm. The coated electrode was dried with a dryer at 80 ° C. for 5 hours, 120 ° C. for 3 hours, and then the electrode was punched into a circular shape with a diameter of 16 mm to produce an electrode. Prepare two electrodes for the positive electrode and the negative electrode, and vacuum dry at 120 ° C for 3 hours using a vacuum separator together with a paper separator (TF40 manufactured by Nippon Advanced Paper Industries Co., Ltd.), a SUS coin cell upper and lower lid, and an aluminum spacer. It was. After drying, a coin-type capacitor cell was produced in an argon-substituted glove box. The cell was prepared by placing two electrodes facing each other through a separator and then inserting an aluminum spacer to fill the space in the cell. After adding about 0.03 ml of the electrolytic solution, the coin cell was 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 was connected to a charge / discharge tester (TOSCAT manufactured by Toyo System Co., Ltd.), and a charge / discharge test was performed. Although a 1.4 mol / l propylene carbonate solution of triethylmethylammonium tetrafluoroborate (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as the electrolytic solution, the effects of the present invention are not particularly limited to the type and concentration of the electrolytic solution. Not.

(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: 6 mA
・ Charging voltage: 2.5V
・ Charging time: 2 hours ・ Discharging conditions: constant voltage ・ Discharging current: 6 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) × 0.006 / (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 / 0.006
Moreover, lifetime measurement evaluation was measured by repeatedly performing charging / discharging at 60 degreeC, after performing the charging / discharging measurement shown above at 25 degreeC and -30 degreeC. Detailed conditions for cycle characteristic evaluation are shown below. FIG. 1 shows the Coulomb efficiency (capacity retention) with respect to the number of cycles.
・ Charging conditions: constant current / constant voltage ・ Charging current: 6 mA
・ Charging voltage: 2.5V
・ Charging time: 2 hours ・ Discharging conditions: constant voltage ・ Discharging current: 6 mA
・ Discharge voltage: 0V
Coulomb efficiency in charging / discharging was calculated | required with the following formula | equation from the charging capacity (C1) and the discharge capacity (C2).

Coulomb efficiency (%) = (C2 / C1) × 100
Furthermore, the cell expansion coefficient was obtained by the following equation by measuring the cell thickness (A1) before the test and the cell thickness (A2) after the test.
Cell expansion rate (%) = (A2 / A1) × 100

(Example 2)
The same operation as in Example 1 was performed except that the temperature after the heat treatment was set to 700 ° C. The Δν value was 73.0.
(Example 3)
The same procedure as in Example 1 was performed except that the temperature after the heat treatment was 800 ° C. The Δν value was 72.7.
Example 4
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 during alkali activation was 2.7 times the weight of the carbide. The Δν value was 72.4.

(Comparative Example 1)
The procedure was the same as Example 1 except that no heat treatment was performed. The Δν value was 72.5.
(Comparative Example 2)
The same procedure as in Example 1 was performed except that the carbonization temperature of the cured resin was 600 ° C., and the amount of potassium hydroxide during alkali activation was 2.15 times the amount of the carbide. The Δν value was 87.6.
(Comparative Example 3)
The same operation as in Example 4 was conducted except that the amount of potassium hydroxide at the time of alkali activation was 2.5 times the amount of carbide. The Δν value was 72.1.

  As shown in Table 2, for Examples 1 to 4, the surface functional group concentration was 0.6 mmol / g or less, and the initial efficiency in life evaluation at 60 ° C. was higher than that of Comparative Example 1 where heat treatment was not performed. It has become. FIG. 1 shows that the initial life characteristics are better when heat treatment is performed.

  Further, as shown in Table 2, the cell expansion coefficient is high in Comparative Example 1 having a high functional group concentration, whereas the Examples are low, and it is understood that gas generation is suppressed. Further, it can be seen that the capacity is high at low temperatures and high output characteristics are exhibited.

As shown in Table 1, the examples in which the half-value width (Δν1) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is 68 to 75 are from the beginning of the lifetime measurement (after the 20th cycle). ) Shows high efficiency. In contrast, Comparative Example 2 did not improve the charge / discharge efficiency even after the beginning of the lifetime, and showed a relatively lower charge / discharge efficiency than the Examples. That is, it can be seen that the control of Δν1 works effectively for improving long-term life characteristics.

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

It is a figure which shows a lifetime measurement, and is a figure which shows the Coulomb efficiency (capacity retention, a vertical axis | shaft) at the time of repeating charging / discharging (horizontal axis; number of cycles). 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 (5)

The surface functional group concentration is 0.3 to 0.6 mmol / g, the half width (Δν) of the peak (G1) near 1580 cm ⁻¹ observed in the Raman spectrum is 68 to 75, and the average pore diameter is 1.73 nm. The electrode material for an electric double layer capacitor as described above. ^{2. The} electrode material for an electric double layer capacitor according to claim 1, wherein the specific surface area is 1800 to 2800 m ² / g, the pore volume is 0.5 to 1.5 ml / g, and the average particle size is 1 to 10 μm.   The electrode material for an electric double layer capacitor according to claim 1, wherein the electrode material is produced by alkali activation of non-graphitizable carbon.   The electrode for electric double layer capacitors using the electrode material for electric double layer capacitors in any one of Claims 1-3.   The electric double layer capacitor which uses the electrode for electric double layer capacitors in any one of Claims 1-4.

Images