JPWO2011046173A1 - Electrode active material and use thereof, and method for producing electrode active material - Google Patents

Abstract

The method for producing an electrode active material of the present invention includes an activation treatment step in which a carbon material is activated in the presence of water at a temperature of 250 ° C. or higher and a pressure of 3.9 MPa or higher. Thereby, the electrode active material which can provide the electrode excellent in durability is realizable.

Description

  The present invention relates to an electrode active material, its use, and a method for producing an electrode active material.

  An electric double layer capacitor is a kind of power storage device, and is a capacitor that uses a power storage phenomenon in an electric double layer that occurs at the interface between a carbon electrode and an electrolyte. An electric double layer capacitor generally has a container and a pair of carbon electrodes and a pair of current collectors, which are accommodated in the container and are arranged with a separator interposed therebetween. An ion conductive electrolyte is introduced.

  It is known that such an electric double layer capacitor has a very large capacitance, and the energy density is 100 to 1000 times that of a conventional capacitor. In addition, unlike general storage batteries that store electric charge by chemical reaction, it is possible to charge and discharge in an extremely short time because it physically stores electric charge, and to maintain power storage capacity semipermanently. .

  Due to the above characteristics, the electric double layer capacitor is attracting a great deal of attention as a next-generation power storage means, and in particular as a power storage that needs to be repeatedly charged and discharged with a large current at a high frequency.

  There are generally known two types of electric double layer capacitors, one using activated carbon having a very large specific surface area as an electrode and one using nonporous carbon having a relatively small specific surface area as an electrode. Among these, those using non-porous carbon as an electrode have been demonstrated to have a higher electrostatic capacity and withstand voltage per electrode volume than those using an activated carbon having an extremely large specific surface area as an electrode.

  Examples of the non-porous carbon include an alkali activation step in which calcined coke obtained by calcining petroleum needle coke is mixed with an alkali agent having a mass ratio of 2.5 to 4 times, and calcined coke after the alkali activation step. An electrode active material produced by a method including washing and drying, and further a post-baking step of baking in an inert atmosphere is known (see, for example, Patent Document 1).

  In addition, as a method that does not use an alkali agent, an electrode active material is produced by heat treating the extraction residue when extracting coke derived from substances such as heavy coal oil with an organic solvent, and then removing the organic solvent. There is a known method (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication "JP 2008-205173 Patent Publication No. (September 4, 2008 published)" Japanese Unexamined Patent Publication "JP 2008-135587 Patent Publication No. (June 12, 2008 published)"

  However, an electrode having higher durability than the conventional configuration is desired.

  The present invention has been made in view of the above problems, and an object thereof is to use an electrode active material capable of providing an electrode having excellent durability, an electrode obtained using the electrode active material, and the electrode. It is to realize the electrical storage device, the electronic device including the electrical storage device, and the method for manufacturing the electrode active material.

  In order to solve the above problems, the present inventor has intensively studied an electrode active material that can provide an electrode having excellent durability.

  The present inventor has the reason that the durability of the electrode obtained from the electrode active material described in Patent Document 1 is reduced because the activation treatment is performed with a large amount of alkali during the production of the electrode active material. It was thought that it remained in the electrode active material.

  Further, when the activation treatment is performed with a large amount of alkali, the alkali metal is gasified by heating and penetrated to the depth of the carbon structure. For example, when the alkali is KOH, the activation treatment is performed in a temperature range of 700 to 800 ° C. in order to gasify the metal K. For this reason, it was considered that alkali metals such as K that had penetrated deep into the carbon structure were confined inside the carbon structure, making it difficult to remove.

  In particular, when the specific surface area is activated greatly, the carbon structure becomes porous, so that alkali metals are easily removed to some extent. However, in the case of a non-porous structure with a small specific surface area, there is almost no space leading to the outside, which makes it extremely difficult to remove. It is thought that it becomes.

  As a result, when the activation treatment was performed with alkali, it was considered that these alkalis were not completely removed even if post-treatment was performed after the activation treatment.

  And when impurities, such as an alkali, remain in an electrode active material, an alkali component etc. will remain in the electrode to produce, As a result, gas may be generated from an electrode, and an electrode produced from an electrode active material It was thought that the durability of can be reduced.

  Moreover, it was thought that the cause that the durability of the electrode obtained from the electrode active material described in Patent Document 2 was reduced was that the activation treatment was performed with a large amount of an organic solvent during the production of the electrode active material. In other words, since the conventional electrode active material is activated by a large amount of organic solvent, it was considered that the organic solvent was not completely removed even after post-treatment after activation. And when the organic solvent remained in the electrode, it thought that the durability of the electrode produced from the electrode active material could be reduced.

  In addition, when the activation process is performed with a solvent, the solvent penetrates deep into the carbon structure while dissolving a part of the carbon structure, so that the solvent that penetrates into the carbon structure is confined inside the carbon structure. Removal is considered difficult. In addition, when the specific surface area is greatly activated, the carbon structure becomes porous, so the solvent is easy to remove.However, in the case of the non-porous structure having a small specific surface area, there is almost no space leading to the outside, so that removal is extremely difficult. Conceivable.

  Furthermore, as a result of the study by the present inventor, it has been clarified that when an organic solvent remains in the electrode, the leakage current of the electrode manufactured from the electrode active material increases. For this reason, in the structure of patent document 2, energy efficiency may deteriorate.

  From the above viewpoint, as a result of examining the activation treatment method using a substance that can be easily removed after the activation treatment, the present inventor obtained an activation agent after the activation treatment if the activation treatment was performed with subcritical water or supercritical water. As a result, it has been found that an electrode active material that can provide an electrode having excellent durability can be obtained, and the present invention has been completed.

  That is, the method for producing an electrode active material according to the present invention includes an activation treatment step of activating a carbon material in the presence of water at a temperature of 250 ° C. and a pressure of 3.9 MPa in order to solve the above-described problem. It is characterized by including.

  According to the above method, since the activation treatment is performed with subcritical water or supercritical water that can be easily removed after the treatment, impurities such as water can be removed from the electrode active material only by performing a simple treatment after the activation treatment. it can. Moreover, in the said activation process process, since an activator does not osmose | permeate the back of a carbon structure | tissue like an alkali activation process, impurities, such as water, are easily removed after an activation process.

  For this reason, in the electrode active material obtained by the above method, it is considered that when the electrode is produced, the impurities are unlikely to cause a decrease in durability such as a decrease in withstand voltage or a performance deterioration due to a change with time. Therefore, according to the said method, there exists an effect that the electrode active material which can provide the electrode excellent in durability can be manufactured.

  Moreover, in the said activation process process, since the specific surface area of the electrode active material obtained becomes comparatively small, when producing an electrode, an electrode density becomes high and the electrostatic capacitance per electrode volume does not fall.

  Furthermore, in the said method, since an activator does not osmose | permeate the back of a carbon structure, an activator can be removed easily, a work process becomes simple and production efficiency can be improved.

  In addition, since a large amount of alkaline substance is not used in the production process of the electrode active material, there is little risk of corrosion of the reaction vessel, ignition by explosion of by-product alkali metal, explosion, and the like.

The electrode active material according to the present invention has a specific surface area of 0.01 to 30 m ² / g, a content of each alkali metal atom of 50 ppm or less, and 2. The leakage current measured at 7V is 50 μA / cm ² or less.

  According to the above arrangement, an effect that it is possible to provide a superior electrode durability.

  The electrode according to the present invention is obtained by using any one of the electrode active materials according to the present invention.

  According to the said structure, since it is obtained using the said electrode active material which concerns on this invention, there exists an effect that the electrode excellent in durability can be provided.

  Electricity storage device according to the present invention is characterized by comprising the electrode according to the present invention.

  According to the said structure, since the said electrode which concerns on this invention is provided, there exists an effect that the electrical storage device excellent in durability can be provided.

  An electronic device according to the present invention includes any one of the power storage devices according to the present invention and an integrated circuit.

  According to the said structure, since the said electrical storage device which concerns on this invention is provided, there exists an effect that the electronic device excellent in durability can be provided. In particular, the electric storage device for withstand voltage is high, it is possible to suitably drive the driving voltage is high integrated circuits.

  As described above, the method for producing an electrode active material according to the present invention includes an activation treatment step using subcritical water or supercritical water.

  For this reason, there exists an effect that the electrode active material which can provide the electrode excellent in durability can be manufactured.

The electrode active material according to the present invention has a specific surface area of 0.01 to 30 m ² / g, a content of each alkali metal atom of 50 ppm or less, and 2. The leakage current measured at 7V is 50 μA / cm ² or less.

  For this reason, there exists an effect that the electrode excellent in durability can be provided.

It is sectional drawing which shows schematic structure of an example of the electrical storage device which concerns on this Embodiment. It is sectional drawing which shows schematic structure of the other example of the electrical storage device which concerns on this Embodiment. It is a block diagram which shows typically an example of the electronic device which concerns on this Embodiment.

  The present invention will be described in detail below. In addition, unless otherwise indicated, the various physical properties mentioned in this specification mean values measured by the methods described in Examples described later.

[I] Method for Producing Electrode Active Material The method for producing an electrode active material according to the present embodiment includes an activation treatment step using subcritical water or supercritical water. Since the production method includes the activation treatment step, it is not necessary to perform conventional alkali treatment or solvent treatment, and there is almost no extra impurity remaining. For this reason, the electrode active material which can provide the electrode excellent in durability can be manufactured.

  In the method for producing an electrode active material according to the present embodiment, for example, a firing step, a pulverization step, and a drying step may be included. Each step will be described below.

<Baking process>
The firing step is a step of heating the carbon material at a high temperature in the presence of an inert gas.

  Examples of the inert gas include nitrogen gas and argon gas. Although the heating temperature in a baking process is not specifically limited, For example, it can carry out within the temperature range of 450-900 degreeC.

  Examples of the carbon material include soft carbon, and more specifically, pitch-based materials, coke-based materials, synthetic resin-based materials, and the like.

<Crushing process>
The pulverization step is a step of pulverizing the carbon material after the firing step. As a result, the subsequent activation process can be performed efficiently. The pulverization method is not particularly limited, and a conventionally known pulverization method can be employed.

<Activation process>
The activation treatment step is a step in which the carbon material after pulverization is activated in the presence of water at a temperature of 250 ° C. or higher and a pressure of 3.9 MPa or higher, that is, the carbon material is subcritical water or supercritical water. This is a process of activation treatment. The activation treatment step is a step of activating the carbon material after pulverization at a temperature of 374 ° C. or higher and a pressure of 22.1 MPa or higher in the presence of water, that is, a step of activating the carbon material with supercritical water. It is preferable that

  In the activation treatment process, it is considered that no extra pores are formed because the low molecular component in the carbon material reacts with subcritical water or supercritical water. For this reason, an electrode active material with a small specific surface area can be produced. As a result, an electrode having a high electrode density and a high capacitance per volume can be produced.

  The temperature in the activation treatment step is more preferably 374 ° C. or higher, and further preferably 450 ° C. or higher. Moreover, although it does not specifically limit about an upper limit, For example, it can carry out at 900 degrees C or less.

  Moreover, the pressure in the said activation process process is 3.9 Mpa or more, It is more preferable that it is 22.1 Mpa or more, It is still more preferable that it is 35 Mpa or more. Although there is no particular limitation on the upper limit, for example, it can be carried out by the following 50 MPa.

  The activation treatment step, from the viewpoint of performing more efficiently process is preferably carried out in the presence of an oxidizing accelerator.

The oxidation accelerator is not particularly limited as long as it has an effect of promoting the oxidation of the carbon material by subcritical water or supercritical water in the activation treatment step. For example, at least one selected from the group consisting of hydrogen peroxide, oxygen, alkaline substances, alkali salts, ZrO ₂ , transition metals and transition metal oxides can be used, and among these, hydrogen peroxide is preferable. .

  Examples of the alkaline substance, for example, hydroxides and alkaline earth metal of the alkali metal. Examples of the alkali metal hydroxide include lithium hydroxide, potassium hydroxide, and sodium hydroxide. Examples of the alkaline earth hydroxide include potassium hydroxide, strontium hydroxide, and barium hydroxide. Etc.

  The alkali salt is not particularly limited as long as it is a salt generated by neutralization of an alkali metal hydroxide and an acid. For example, a halogenated salt, carbonate, phosphorus, or the like of an alkali metal such as lithium, potassium, or sodium. Examples include acid salts.

  Examples of the transition metal include cobalt, nickel, palladium, platinum and the like. Examples of the transition metal oxide include ruthenium dioxide and aluminum oxide.

  In the activation treatment step, the amount of water used is preferably in the range of 100 to 1500% by mass with respect to the carbon material to be treated. Moreover, it is preferable that the quantity of the said oxidation accelerator exists in the range of 10-100 mass% with respect to the carbon material to process.

  Although the processing time of the said activation process process should just be suitably changed according to the kind of carbon material and the performance of the electrode active material to request | require, it can set within the range of 0.1 to 2 hours, for example.

<Drying process>
A drying process is a process of removing the water | moisture content (a water | moisture content and an oxidation promoter, when an oxidation promoter is used) by drying the carbon material after the said activation process.

  The drying conditions are not particularly limited as long as the conditions can remove moisture (in the case of using an oxidation accelerator, moisture and an oxidation accelerator). For example, it can be performed under conditions of 110 ° C. under vacuum.

  In the activation treatment in the present invention, even if an oxidation accelerator is used, the treatment temperature range is lower than the temperature range in the alkali activation treatment, so that the alkali metal is gasified in the alkali activation treatment to the back of the carbon structure. Like the permeation, the oxidation accelerator does not penetrate deep into the carbon structure, and the oxidation accelerator can be easily removed.

  For this reason, even when an alkaline substance or an alkali salt is used as the oxidation accelerator, it can be easily removed by performing a simple cleaning process.

  As described above, the method for producing an electrode active material according to the present embodiment can be carried out without using a large amount of an alkaline substance that causes corrosion of the container, so that the life of the reaction container can be extended. be able to. In addition, since the activator does not penetrate deep into the carbon structure, the activator can be easily removed, the work process is simplified, and the production efficiency can be increased.

  Furthermore, when an alkaline substance is not used, the neutralization step is unnecessary, no extra chemicals are required, the treatment time can be shortened, and the environmental burden can be reduced.

  As described above, in the method for producing an electrode active material according to the present invention, it is preferable to perform the activation treatment step in the presence of the water and the oxidation accelerator.

  According to the above method, the oxidation in the activation treatment step is promoted and the activation treatment can be performed more efficiently, so that the production efficiency can be further increased.

  In addition, since the said activation treatment process is not a reaction that penetrates to the back of the carbon structure but a reaction that oxidatively decomposes the surface of the carbon material, no impurities remain inside the carbon structure even if it is non-porous. . For this reason, since most of the oxidation accelerator and water are attached to the surface of the carbon material, they can be easily removed.

  In the method for producing an electrode active material according to the present invention, the oxidation accelerator is preferably hydrogen peroxide.

[II] Electrode Active Material The electrode active material according to the present embodiment has a specific surface area within a range of 0.01 to 30 m ² / g, and the content of each alkali metal atom is 50 ppm or less to produce an electrode. In this case, the leakage current measured at 2.7 V is 50 μA / cm ² or less. In addition, the electrode active material which concerns on this Embodiment can be obtained with the manufacturing method mentioned above.

Electrode active material according to the present embodiment, in the range of 0.01~30m ² / g, a specific surface area preferably in the range of 3~30m ² / g, of 4 to 20 m ² / g More preferably, it is within the range, and further preferably within the range of 5 to 10 m ² / g.

  When the specific surface area is within the above range, the electrode density, the capacitance per electrode volume, and the withstand voltage can be increased when the electrode is manufactured.

  Further, if the specific surface area is within the above range, it is considered that moisture in the carbon material can be easily removed because there are few pores. For this reason, as a result of being able to reduce the residual amount of moisture that is a cause of a decrease in withstand voltage, the withstand voltage can be increased.

  Furthermore, it is considered that by reducing the specific surface area, the contact between the edge portion of the graphene sheet causing the decomposition of the electrolytic solution and the electrolytic solution can be reduced. For this reason, decomposition | disassembly of electrolyte solution can be suppressed and a withstand voltage can be made high. For example, a capacitor including an electrode using the electrode active material according to the present embodiment can be used even at 3.2V.

  In addition, the said specific surface area can be made into the said range by adjusting the processing time of an activation process, for example.

The electrode active material according to the present embodiment has a content of each alkali metal atom of 50 ppm or less, and the leakage current measured at 2.7 V when the electrode is produced is 50 μA / cm ² or less.

  The above-mentioned “content of each alkali metal atom is 50 ppm or less” specifically means that, for example, if the electrode active material contains potassium atoms and sodium atoms as alkali metal atoms, the content of potassium atoms the amount is at 50ppm or less and the content of sodium atoms means that is 50ppm or less.

  When the content of the alkali atom and the organic solvent is within the above range, an electrode active material that is unlikely to change with time, is excellent in long-term reliability, and can provide an electrode with high withstand voltage can be realized.

  The alkali atom content and the leakage current can be within the above ranges by using the production method according to the present invention.

  As described above, the electrode active material according to the present invention is obtained by any one of the above production methods according to the present invention.

  According to the said structure, since it is obtained by the manufacturing method which concerns on this invention, there exists an effect that the electrode excellent in durability can be provided.

In addition, the electrode active material according to the present invention has a specific surface area in the range of 3 to 30 m ² / g, the content of each alkali metal atom is 50 ppm or less, and is 2.7 V when the electrode is produced. In other words, the measured leakage current is 100 μA or less.

[III] Electrode The electrode according to the present embodiment can be obtained by using the above-described electrode active material. For example, the electrode active material can be configured by adding a binder and a conductive material.

  The electrode according to the present embodiment can be manufactured according to a known manufacturing method (for example, Japanese Patent Application Laid-Open No. 2008-205173). For example, the electrode active material, the conductive material, and the binder are kneaded and molded. Can be produced.

  As the binder, it may be used polytetrafluoroethylene, carboxymethyl cellulose, and polyvinyl alcohol. Among these, polytetrafluoroethylene is preferable.

  As the conductive material, acetylene black, conductive carbon black of ketjen black, natural graphite, artificial graphite or the like can be used.

  The kneading and molding can be performed by press molding or roll molding after adding and mixing a binder to the mixture of the electrode active material and the conductive material. As another method, a thin coating film may be formed by making a mixture of an electrode active material, a conductive material, and a binder into a slurry and coating it.

  The compounding ratio of the electrode active material, the conductive material, and the binder can be within a range of 8 to 10: 0.5 to 1.5: 0.5 to 1.5, for example, as a mass ratio.

[IV] Electric storage device The electric storage device according to the present embodiment includes the electrode according to the present embodiment.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an example of the electricity storage device according to the present embodiment, and FIG. 2 is a cross-sectional view showing a schematic configuration of another example of the electricity storage device according to the present embodiment.

  As shown in FIG. 1, the electrical storage device according to the present embodiment includes a pair of electrodes 1 and a separator 2 that physically insulates the electrodes. Moreover, these are provided in the electrolyte solution (not shown) which supplies ion to the electrode 1. FIG. Moreover, in another example, as shown in FIG. 2, the electroconductive adhesive 3 and the electrical power collector 4 are further provided in this order on the outer side of each electrode 1 in the structure shown in FIG. , Provided in an electrolyte solution (not shown) for supplying ions to the electrode 1.

  Examples of the electrolyte constituting the electrolytic solution include triethylmethylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, and a pyrrolidinium compound salt. Examples of the solvent constituting the electrolytic solution include ethylene carbonate, propylene carbonate, γ-butyl lactone, sulfolane and the like. Moreover, you may mix at least 1 sort (s) of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate as a co-solvent.

  The separator can be formed from a polyolefin-based separator, a nonwoven fabric, or the like, and the collector electrode can be formed from aluminum, an aluminum alloy, or the like. The conductive adhesive may be a conventionally known conductive adhesive used in the electric storage device.

  Electricity storage device according to this embodiment is preferably an electric double layer capacitor or a lithium ion capacitor.

  As an example of the electric double layer capacitor, for example, in the configuration shown in FIG. 1 or FIG. 2, a configuration in which the electrodes according to the present embodiment are used as positive and negative electrodes can be given. Note that the electrode according to the present embodiment may be used as only one of positive and negative electrodes, and the other electrode may be a conventionally known electrode.

  As the electrolytic solution, for example, a known electrolytic solution used in a conventional electric double layer capacitor can be used.

  As an example of the lithium ion capacitor, for example, in the configuration shown in FIG. 1 or 2, the electrode according to the present embodiment is used as a positive electrode, and lithium ions are occluded in the electrode active material according to the present embodiment. Examples include a configuration in which an electrode using a material as a negative electrode active material is used as a negative electrode, and an electrolytic solution having a lithium salt as a solute is used, and the electrode is manufactured using a conventionally known technique (for example, JP 2009-130066 A). Can do. Incidentally, it may for any one of the positive and negative electrodes be used an electrode of conventional construction.

  As the electrolytic solution, current collector, separator, and the like, a conventionally known configuration used for a lithium ion capacitor as described in, for example, JP-A-2009-130066 can be employed.

[V] Electronic Device An electronic device according to the present embodiment includes the above-described power storage device and an integrated circuit.

  Since the electronic device includes the above-described power storage device according to the present invention, a high driving voltage can be supplied to the integrated circuit. Therefore, as the electronic device, for example, it can be suitably used for various sensors or the like provided with a power storage device.

  Figure 3 shows a plan view schematically showing an example of an electronic device according to the present embodiment. As shown in FIG. 3, the electronic device according to the present embodiment includes a power generation device 5, a rectification and voltage conversion circuit 6, a power storage device 7, a sensor 8, an integrated circuit 9, and a wireless module 10. ing. In the electronic device, electricity generated by the power generation device 5 is converted by the rectification and voltage conversion circuit 6 and sent to the power storage device 7 from the power storage device 7 to the sensor 8, the integrated circuit 9, and the wireless module 10, respectively. When electricity is supplied, it functions as a sensor.

  In addition, since the said electronic device is not different from a well-known structure except providing the electrical storage device which concerns on this invention mentioned above, if it is an expert, it can be produced with a conventionally well-known manufacturing method.

  In the above description, the electronic device includes a sensor and a wireless module. However, as a matter of course, the configuration of the present invention is not limited to such a configuration, and at least the present invention is provided. If the electrical storage device which concerns on, and an integrated circuit are provided, there exists an effect of this invention.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example.

[Measurement of capacitance]
The produced electrode active material, acetylene black (product name: Denka Black (powder), manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive agent, and tetrafluoroethylene (product name: F-104, Daikin Industries Ltd.) as a binder Was manufactured at a mass ratio of 10: 1: 1, and formed into a sheet shape to prepare an electrode sheet having a thickness of 100 μm.

  A disk-shaped disk having a diameter of 15.95 mm is punched from the electrode sheet, dried in vacuum, and then propylene containing 1.5 mol / L triethylmethylammonium tetrafluoroborate in a glove box in a nitrogen gas atmosphere. Carbonate was vacuum impregnated, then the molded body was made into a positive electrode and a negative electrode, glass filter paper was placed between both electrodes, and a cell was assembled to obtain an electric double layer capacitor.

  The cell was charged at 0.23 mA at room temperature and held for 2 hours, and then a constant current discharge was performed at 0.6 mA, and the capacitance of the electric double layer capacitor was measured. The capacitance was calculated by the energy conversion method from the discharge start voltage of the discharge curve to 0V.

〔Specific surface area〕
Using a fully automatic gas adsorption amount apparatus (product name: Autosorb-1-C / VP / TCD / MS, manufactured by Yuasa Ionics), the specific surface area was measured by the BET multipoint method.

[Content of each alkali metal atom]
Using a fluorescent X-ray analyzer (product name: ZSX100e, manufactured by Rigaku), the alkali element concentration was quantified by the fundamental parameter method.

(Measurement of leakage current)
Using a charge / discharge measuring device (product name: HJ1001SM8A, manufactured by Hokuto Denko Co., Ltd.), the current flowing between the positive electrode and the negative electrode when the voltage is increased to a specified voltage by constant current charging and then held at the specified voltage for 30 minutes. Measured as leakage current.

(Measurement of resistance)
Using an LCR meter (product name: LCR HiTester 3511-50, manufactured by Hioki Electric Co., Ltd.), the equivalent series resistance at 1 kHz of the electric double layer capacitor was measured at room temperature. The resistivity was calculated by dividing the equivalent series resistance by the electrode area.

[Float test]
The float test was performed by leaving it to stand in an oven at 70 ° C. for 140 hours in a state where a voltage of 2.7 V was applied to the electrode active material.

[Electrode density]
The electrode density was calculated from the mass of the electrode and the volume determined from the diameter and thickness.

[Example 1]
The carbon raw material (soft carbon of petroleum coke) was heat-treated at 450 ° C. or higher for 1 hour in a nitrogen atmosphere in a baking furnace, and the obtained fired body was pulverized to 32 mesh or lower.

  Then, 2 g of the fired body after pulverization and 25 g of water were filled in a SUS container. Thereafter, the SUS container was immersed in a molten salt at 450 ° C. for 1 hour to perform supercritical processing at an internal pressure of 35 MPa, and then the SUS container was immersed in water and cooled.

  After cooling, the contents of the SUS container were filtered under reduced pressure, and further dried under reduced pressure at 110 ° C. and −0.1 MPa for 6 hours to prepare an electrode active material. Table 1 shows the results of measuring various physical properties of the obtained electrode active material.

[Example 2]
The same operation as in Example 1 except that instead of filling the SUS container with 2 g of fired body and 25 g of water, 2 g of fired body, 21 g of water and 4 g of hydrogen peroxide (concentration: 31% by mass) were filled. To produce an electrode active material. Table 1 shows the results of measuring various physical properties of the obtained electrode active material.

[Comparative Example 1]
Example 1 described in Japanese Patent Application Laid-Open No. 2008-135587 was additionally tested. Table 1 shows the results of measuring various physical properties of the obtained electrode active material.

[Comparative Example 2]
S42 in Table 2 of JP 2008-205173 A was additionally tested. Table 1 shows the results of measuring various physical properties of the obtained electrode active material.

  In addition, paragraph [0059] of Japanese Patent Application Laid-Open No. 2008-205173 describes that “... the impurity amount of the carbon material obtained through the fourth step has been reduced to 100 ppm”. In this comparative example, the K content was 3304 ppm and the Na content was 24 ppm. This is probably due to the difference in the measurement conditions for alkali content between the present application and Japanese Patent Application Laid-Open No. 2008-205173.

Example 3
The same operation as in Example 1 was performed to produce an electrode active material. Table 2 shows the results obtained by measuring various physical properties of the obtained electrode active material.

Example 4
The same operation as in Example 2 was performed to produce an electrode active material. Table 2 shows the results obtained by measuring various physical properties of the obtained electrode active material.

[Comparative Example 3]
The same operation as in Comparative Example 1 was performed to prepare an electrode active material. Table 2 shows the results obtained by measuring various physical properties of the obtained electrode active material.

As shown in Table 2, the electrode active materials obtained in Examples 3 and 4 have a resistivity increase of 7.4 to 10.8 Ω / cm ² before and after the float test, whereas the comparative examples The electrode active material obtained in 3 increased by 19.0 Ω / cm ² , and the electrode active material obtained in Comparative Example 3 was about 2 to 3 more than the electrode active material obtained in Examples 3 and 4. It was confirmed that the double resistivity increased. Therefore, from these results, it was confirmed that the electrode active material according to the present invention is excellent in durability.

  Although the electrode active material obtained in Comparative Example 2 has not been evaluated in the float test, activated carbon having a large amount of metal such as alkali metal is generally used as the electrode material for the electric double layer capacitor. In such a case, it is known that durability reduction is induced when charging / discharging of the electric double layer capacitor is repeated (see, for example, paragraph [0003] of Japanese Patent Application Laid-Open No. 2008-207982). For this reason, it is easily estimated that the electrode active material obtained in Comparative Example 2 has low durability.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The electrode active material of the present invention can be suitably used as an electrode used for various capacitors.

DESCRIPTION OF SYMBOLS 1 Electrode 2 Separator 3 Conductive adhesive 4 Current collector 5 Power generation device 6 Rectification and voltage conversion circuit 7 Power storage device 8 Sensor 9 Integrated circuit 10 Wireless module

Examples of the alkaline substance include alkali metal hydroxides and alkaline earth metal hydroxides. Examples of the alkali metal hydroxide include lithium hydroxide, potassium hydroxide, and sodium hydroxide. Examples of the alkaline earth metal hydroxide include calcium hydroxide, strontium hydroxide, and hydroxide. Barium etc. are mentioned.

Claims (10)

  A method for producing an electrode active material comprising an activation treatment step of activating a carbon material in the presence of water at a temperature of 250 ° C. or higher and a pressure of 3.9 MPa or higher.   2. The production of an electrode active material according to claim 1, wherein the activation treatment step is a step of activating the carbon material in the presence of water at a temperature of 374 ° C. or higher and a pressure of 22.1 MPa or higher. Method.   The method for producing an electrode active material according to claim 1 or 2, wherein the activation treatment step is performed in the presence of water and an oxidation accelerator.   The method for producing an electrode active material according to claim 3, wherein the oxidation accelerator is hydrogen peroxide.   The electrode active material obtained by the manufacturing method of any one of Claims 1-4. The specific surface area is in the range of 0.01 to 30 m ² / g,
The content of each alkali metal atom is 50 ppm or less,
An electrode active material having a leakage current of 50 μA / cm ² or less measured at 2.7 V when an electrode is produced.   An electrode obtained using the electrode active material according to claim 5.   An electricity storage device comprising the electrode according to claim 7.   The electricity storage device according to claim 8, wherein the electricity storage device is an electric double layer capacitor or a lithium ion capacitor. The electricity storage device according to claim 8 or 9,
An electronic device comprising an integrated circuit.