WO2016031423A1

WO2016031423A1 - Activated carbon, carbon starting material for activated carbon, method for producing activated carbon, and method for producing carbon starting material for activated carbon

Info

Publication number: WO2016031423A1
Application number: PCT/JP2015/070417
Authority: WO
Inventors: 正利西田; 政喜藤井; 慶三猪飼; 正剛小関; 陽介大津
Original assignee: Ｊｘ日鉱日石エネルギー株式会社; 南開工業株式会社
Priority date: 2014-08-28
Filing date: 2015-07-16
Publication date: 2016-03-03
Also published as: JP2016051728A

Abstract

Provided is activated carbon which is capable of achieving sufficiently high electrostatic capacitance under low temperature conditions if used in an electric double layer capacitor or in a lithium ion capacitor. Specifically provided is activated carbon for capacitors, which has a sodium content of 20 ppm or more but less than 4,000 ppm, a phosphorus content of 100 ppm or more but less than 2,000 ppm, and an average particle diameter of 1 μm or more but less than 50 μm as determined by a laser scattering particle size distribution measuring instrument, and a BET specific surface area of 1,400 m²/g or more but less than 3,300 m²/g.

Description

Activated carbon, carbon raw material of activated carbon, and production method thereof

The present invention relates to activated carbon and a carbon raw material of activated carbon, and more particularly to an activated carbon and a carbon raw material of activated carbon that are optimal for use in electrodes of electric double layer capacitors and lithium ion capacitors.

Electric double layer capacitors (EDLC) and lithium ion capacitors (LIC) are characterized by superior power density and charge / discharge cycle life compared to general secondary batteries. Its applications are expanding, such as being used in stop systems.

The electric double layer capacitor has a structure in which a pair of polarizable electrodes made of activated carbon are opposed to each other through a separator as a positive electrode and a negative electrode. Each polarizable electrode is impregnated with a water-soluble electrolyte solution or a non-aqueous solvent electrolyte solution, and each polarizable electrode is in contact with a collecting electrode.

Among the characteristics of electric double layer capacitors, the performance such as resistance, low temperature characteristics and life depends on the performance of activated carbon used as a polarizable electrode. As the carbon material for the polarizable electrode of the electric double layer capacitor, activated carbon having a large specific surface area is usually used.

Activated carbon is usually produced by carbonizing a carbonaceous material at a temperature of 800 ° C. or lower and then performing an activation treatment. Here, the activation treatment is, for example, a method of heating in an atmosphere such as water vapor or carbon dioxide (gas activation method), a method of mixing zinc chloride, potassium hydroxide, etc. and heating in an inert atmosphere (chemical activation method). (For example, Patent Documents 1 and 2). In this activation process, many pores suitable for adsorption are generated on the surface of the carbon material generated in the carbonization process. The polarizable electrode is produced by a method of adding a conductive agent and a binder to activated carbon and kneading and rolling, a method of mixing activated carbon with uncarbonized resins, and sintering.

International Publication No. 2012/074054 JP 2011-136856 A Japanese Patent Laid-Open No. 2005-104148

In recent years, with the expansion of applications of electric double layer capacitors and lithium ion capacitors, not only output characteristics but also capacity has been required for capacitors. This is because there is a restriction on the installation location in an application such as an automobile, and therefore a capacitor having the same volume and a high capacity or a capacitor having the same capacity and a small volume is desired. When used in transportation equipment such as automobiles, the external environment temperature is exposed to a wide temperature range from below freezing to about 70 ° C., so that it exhibits the same capacity as room temperature even at low temperatures where the electrolyte viscosity increases. There is a need.

The capacity of the electric double layer capacitor or lithium ion capacitor is determined by the electric double layer capacity of the activated carbon electrode. When the conventional alkali activation method was used, the capacitance of the activated carbon could be increased. However, when activated carbon produced by an alkali activation method that is mainly activated using potassium hydroxide is used, the capacitor exhibits high capacitance at room temperature, but it cannot fully demonstrate capacitance under low temperature conditions. There was a problem.

An object of the present invention is to provide activated carbon, a carbon raw material for activated carbon, and a method for producing the same that can exhibit sufficiently high capacitance even under low temperature conditions in an electric double layer capacitor and a lithium ion capacitor. .

Investigate the activated carbon that can maintain the capacitance of electric double layer capacitors and lithium ion capacitors even under low temperature conditions. As a result, after carbonizing petroleum-based delayed coke, a carbon raw material oxidized by adding a phosphorus compound or a carbon raw material carbonized by heating a mixture of cellulose acetate and a phosphorus compound in an inert atmosphere is used as an activator. The inventors have found that activated carbon obtained by activation treatment using sodium oxide can be a capacitor exhibiting a sufficiently high capacitance even under low temperature conditions, and have arrived at the present invention.

That is, in one aspect of the present invention, the sodium content is 20 ppm or more and less than 4000 ppm, the phosphorus content is 100 ppm or more and less than 2000 ppm, and the average particle size measured by a laser scattering particle size distribution analyzer is 1 μm or more and 50 μm. The activated carbon for capacitors having a BET specific surface area of 1400 m ² / g or more and less than 3300 m ² / g.
Another aspect of the present invention is a carbon raw material for activated carbon. The carbon raw material has a phosphorus content of 0.3% by mass to 2.0% by mass and an oxygen content of 10% by mass to 30%. Carbon for producing activated carbon having a mass ratio H / C of hydrogen atom to carbon atom of 0.05 to 0.54 and a BET specific surface area of 100 m ² / g or more and less than 600 m ² / g It is a raw material.
In another aspect, the present invention is a method for producing a carbon raw material for activated carbon, the carbonizing coke is obtained by heating a graphitizable carbon material in an inert atmosphere to obtain carbonized coke. It is a manufacturing method including at least an oxidation step of adding a phosphorus compound and heating to an oxide, and a cleaning step of cleaning the oxide.
The present invention is a method for producing a carbon raw material of activated carbon different from the above in another aspect, and the production method includes a carbonization step of heating and carbonizing a mixture containing at least cellulose acetate and a phosphorus compound in an inert atmosphere. It is a manufacturing method including at least.
Another aspect of the present invention is a method for producing activated carbon, the production method including at least an activation treatment step of activating the mixture of the carbon raw material and sodium hydroxide under an inert atmosphere, The mass ratio of the carbon raw material and the sodium hydroxide is 1: 1.5 to 3.5, and the activated carbon has a sodium content of 20 ppm or more and less than 4000 ppm, and a phosphorus content of 100 ppm or more and less than 2000 ppm. , average particle diameter measured by a laser scattering type particle size distribution meter is less than 50μm more than 1 [mu] m, BET specific surface area of the manufacturing method of the activated carbon is less than 1400 m ² / g or more 3300 m ² / g.
Another aspect of the present invention is an electric double layer capacitor using the activated carbon as an electrode.
Another aspect of the present invention is a lithium ion capacitor using the activated carbon as an electrode.

According to the present invention, when used in an electric double layer capacitor and a lithium ion capacitor, it is possible to provide activated carbon that can exhibit a sufficiently high capacitance even under low temperature conditions.

It is a perspective view explaining the structure of a laminate cell. It is a graph which shows the relationship of charging / discharging of a laminate cell.

Hereinafter, one aspect of the embodiment of the present invention will be described. However, the present invention is not limited to the embodiments described below.

(1) Activated carbon First, activated carbon is demonstrated. The activated carbon for the capacitor has a sodium content of 20 ppm or more and less than 4000 ppm, a phosphorus content of 100 ppm or more and less than 2000 ppm, and an average particle size measured by a laser scattering particle size distribution meter of 1 μm or more and less than 50 μm, The BET specific surface area is 1400 m ² / g or more and less than 3300 m ² / g.

When the sodium content of the activated carbon is 20 ppm or more and less than 4000 ppm, a sufficiently high capacitance can be exhibited even under low temperature conditions when used in a capacitor. It is considered that sodium can penetrate into the carbon crystals during activation and push between the crystals of the activated carbon, and as a result, ions can easily enter and exit even at low temperatures when the viscosity of the electrolytic solution increases. When the sodium content of the activated carbon is less than 20 ppm, the effect of pushing the gap between the crystals of the activated carbon is not sufficient, and thus the capacitance under low temperature conditions tends to decrease. On the other hand, when the sodium content is greater than 4000 ppm, the pores are blocked by an excessive amount of sodium, and the specific surface area itself tends to decrease and the capacitance tends to decrease. When the sodium content of the activated carbon is 40 ppm to 3500 ppm, a higher capacitance can be expressed under low temperature conditions.

When the phosphorus content of the activated carbon is 100 ppm or more and less than 2000 ppm, a sufficiently high capacitance can be exhibited even under low temperature conditions when used in a capacitor. When the phosphorus content is less than 100 ppm, the capacitance under low temperature conditions tends to decrease. When the phosphorus content is 2000 ppm or more, the specific surface area tends to decrease and the capacitance tends to decrease. When the phosphorus content of the activated carbon is 200 ppm or more and less than 1500 ppm, higher capacitance can be developed under low temperature conditions.

When the average particle diameter of the activated carbon is 1 μm or more and less than 50 μm, a sufficiently high capacitance can be exhibited even under low temperature conditions when used in a capacitor. When the average particle diameter of the activated carbon is smaller than 1 μm, it becomes difficult to process as a capacitor electrode. On the other hand, when the average particle diameter is larger than 50 μm, it is difficult to produce a thin electrode, which is not preferable. If the average particle diameter of the activated carbon is 2 μm or more and less than 20 μm, a higher capacitance can be expressed under low temperature conditions. The average particle diameter of the activated carbon is measured with a laser scattering particle size distribution meter.

When the activated carbon has a BET specific surface area of 1400 m ² / g or more and less than 3300 m ² / g, a sufficiently high capacitance can be exhibited even under low temperature conditions when used in a capacitor. When the BET specific surface area is less than 1400 m ² / g, since the pore volume itself is small, the capacitance tends to decrease under low temperature conditions when the capacitor is used. Moreover, when the BET specific surface area is 3300 m ² / g or more, the pore volume is too large, and a sufficient capacitance cannot be obtained per volume, which is not preferable.

If the activated carbon satisfies the above conditions of sodium and phosphorus contents, average particle diameter, and BET specific surface area, it can exhibit a sufficiently high capacitance even under low temperature conditions when used in a capacitor. If any one of these conditions is out of the above range, the electrostatic capacity cannot be sufficiently exhibited under low temperature conditions when used for a capacitor.

(2) Carbon raw material for activated carbon production Next, the carbon raw material for activated carbon production will be described. The carbon raw material of activated carbon has a phosphorus content of 0.3% to 2.0% by mass, an oxygen content of 10% by mass to less than 30% by mass, and a molar ratio of hydrogen atoms to carbon atoms. H / C is 0.05 to 0.54, and the BET specific surface area is 100 m ² / g or more and less than 600 m ² / g.

If the content of phosphorus, H / C, and oxygen in the carbon raw material are within the above ranges, the activation activity of the alkali activator, particularly sodium hydroxide can be increased. Moreover, since it is possible to prevent spills and expansions in the activation process, it is possible to increase the production efficiency of activated carbon and to obtain a sufficient capacitance when used in a capacitor. In particular, when used in a capacitor, it is possible to provide activated carbon that can exhibit a sufficiently high capacitance even under low temperature conditions.

When the content of phosphorus in the carbon raw material is 0.3% to 2.0% by mass, the activation activity of the alkali activator, especially sodium hydroxide is increased, and it is sufficient even under low temperature conditions when used in a capacitor. In addition, it is possible to provide activated carbon that can exhibit a high electrostatic capacity. When the content of phosphorus is less than 0.3% by mass, it is possible to obtain only activated carbon having a small specific surface area as compared with the case of using a raw material containing phosphorus in the above range, which is likely to spill during the activation process. Can not. On the other hand, when the phosphorus content exceeds 2.0 mass%, the target activated carbon cannot be obtained because the alkali activation reaction does not proceed sufficiently.

When the molar ratio H / C of hydrogen atoms to carbon atoms in the carbon raw material is 0.05 to 0.54, a sufficiently high capacitance can be exhibited even under low temperature conditions when used in a capacitor. The activated carbon which can be provided can be provided. On the other hand, when the H / C ratio is less than 0.05, the carbon raw material is too high in carbonization, so that the capacitor cannot sufficiently obtain pores for expressing a high capacitance under low temperature conditions. On the other hand, when the H / C ratio is larger than 0.54, the desired activated carbon cannot be obtained because the foam is violently foamed and blown out during alkali activation.

When the content of oxygen in the carbon raw material is 10% by mass or more and less than 30% by mass, it is possible to provide activated carbon that can exhibit a sufficiently high capacitance even under low temperature conditions when used in a capacitor. it can. When the oxygen content is less than 10% by mass, the reactivity with the alkali activator, particularly sodium hydroxide is poor, and activated carbon with a large specific surface area that can provide a large capacitance when used in a capacitor cannot be obtained. . An oxygen content of 30% by mass or more is not preferable because the activated carbon has a larger specific surface area than the intended activated carbon. Moreover, since an activation reaction yield falls extremely, it is remarkably inferior to industrial productivity.

When the carbon raw material has a BET specific surface area of 100 m ² / g or more and less than 600 m ² / g, it provides activated carbon that can exhibit a sufficiently high capacitance even under low temperature conditions when used in a capacitor. be able to. When the BET specific surface area of the carbon raw material is less than 100 m ² / g, activated carbon that is poorly reactive with an alkali activator, particularly sodium hydroxide, and sufficiently develops capacitance even under low temperature conditions when used in a capacitor. Difficult to get. In addition, when the carbon material has a BET specific surface area of 600 m ² / g or more, carbonization proceeds excessively in the majority of the carbon material, so that fine pores are not easily generated, and a high electrostatic capacity when used in a capacitor. It is difficult to obtain activated carbon that exhibits capacity.

If the carbon raw material satisfies the conditions of the phosphorus and oxygen content, the hydrogen / carbon molar ratio H / C and the BET specific surface area, the carbon raw material is activated using a predetermined amount of sodium hydroxide. By doing so, it is possible to provide activated carbon that can exhibit a sufficiently high capacitance even under low temperature conditions when used in a capacitor. If any one of these conditions is out of the above range, the electrostatic capacity cannot be sufficiently exhibited under low temperature conditions when used for a capacitor.

(3) Carbon Raw Material Production Method Using Easily Graphitizable Carbon Material Next, a carbon raw material production method will be described. The method for producing a carbon raw material includes at least a carbonization step, an oxidation step, and a cleaning step.

The carbonization step is a step of heating the graphitizable carbon material in an inert atmosphere to obtain carbonized coke. The reason for carbonizing the graphitizable carbon material is to reduce the volatile matter. When the volatile matter is removed, the carbonized coke and the phosphorus compound are more in contact with each other in the subsequent oxidation step, and are easily oxidized. Carbonization of the graphitizable carbon material is carried out by heating in an inert atmosphere with an inert gas so that coke is not oxidized in this step. Nitrogen gas, rare gas, etc. can be used as the inert gas. The heating can be performed in a temperature range of 500 ° C. to 900 ° C., more preferably 500 ° C. to 800 ° C. At that time, there is no particular restriction on the rate of temperature rise, but if it is too slow, it takes time for the treatment process, and conversely, if the temperature rises too rapidly, explosive volatilization of volatile components will occur, destroying the crystal structure. There is. Considering these points, the temperature is raised from an unheated state (for example, an air temperature of about 25 ° C.), usually 30 ° C./hour to 600 ° C./hour, more preferably about 60 ° C./hour to 300 ° C./hour. It is desirable to use speed. After reaching the target temperature, the temperature is maintained for a certain time. This holding time is, for example, about 10 minutes to 2 hours. These carbonization conditions make it easy to remove volatile components.

The graphitizable carbon material used as a starting material is a carbon material that can be graphitized by high-temperature heat treatment. As the graphitizable carbon material, peat, grass coal, lignite, lignite, bituminous coal, anthracite and other coal, coal tar, petroleum, coal pitch, coke and other mineral raw materials can be used. The pitch may be an isotropic pitch or an anisotropic pitch (such as a mesophase pitch). These carbon materials can be used alone or in combination of two or more. The graphitizable carbon material is a carbon material that is easily graphitized. Among the above carbon materials, there are petroleum coke and coal coke, etc. Also, mesophase pitch and mesophase pitch fiber spun from it are infusible. Carbonized materials can be mentioned. Of these, petroleum coke is preferred. By using the graphitizable carbon material, the capacitance of the obtained activated carbon is increased, and if it is needle coke, activation is easy with high purity.

Petroleum coke is a product mainly composed of solid carbon obtained by pyrolyzing (coking) a heavy oil fraction under conditions of a temperature of 450 ° C. to 550 ° C. and a pressure of 0.01 to 1.00 MPa. Yes, it is called petroleum coke compared to normal coal-based coke. There are two types of petroleum coke, the delayed coking method and the fluid coking method, and the former is the majority. As a starting material for the carbon raw material, it is preferable to use raw petroleum coke (raw coke) that has been taken out from the coker with this petroleum coke. The raw coke produced by the delayed coking method usually has a volatile content of 6 to 13% by mass, and the raw coke produced by the fluid coke method usually has a volatile content of 4 to 7% by mass. is there. Raw coke by any method may be used, but raw coke that is easily available and is produced by a delayed coking method with stable quality is particularly suitable.

The heavy fraction of petroleum is not particularly limited. Heavy oil obtained as residual oil when petroleum is distilled under reduced pressure, heavy oil obtained when fluids are cracked by fluid catalytic cracking, petroleum Examples thereof include heavy oils obtained by hydrodesulfurization, and mixtures thereof. Examples of the vacuum distillation conditions include a method in which crude oil is changed in a range of 320 to 360 ° C. at a furnace outlet temperature under a reduced pressure of 10 to 30 Torr. The conditions for fluid catalytic cracking include, for example, a method in which atmospheric distillation residual oil is reacted in a fluid catalytic cracking apparatus with a reactor reaction temperature of 510 to 540 ° C. and a catalyst / residual oil ratio of 6 to 8. Is mentioned. The hydrodesulfurization conditions include, for example, a method in which a residual oil having a sulfur content of 2.0 to 5.0% is reacted in the presence of a catalyst at a total pressure of 180 MPa, a hydrogen partial pressure of 160 MPa, and a temperature of 380 ° C. Is mentioned.

The oxidation step in the carbon raw material production method is a step in which a phosphorus compound is added to the carbonized coke and heated to form an oxide. By adding a phosphorus compound to carbonized coke to oxidize and modify it, sodium hydroxide that is relatively inexpensive and weakly activating can be used as an activator. The activated carbon after activation can exhibit a sufficiently high capacitance even under low temperature conditions when used in a capacitor.

As the phosphorus compound, phosphoric acid, phosphorous acid, peroxomonophosphoric acid, diphosphorus pentoxide and the like can be used. In particular, phosphoric acid used industrially is desirable. The phosphorus compound can be added so that the mass ratio of the carbonized coke to the phosphorus compound is preferably 1: 3 to 10. Heating is preferably performed at 80 ° C. to 150 ° C. for 30 minutes to 2 hours. As an example of the oxidation step, a step in which carbonized coke is added to the phosphorous compound aqueous solution and heated at 120 ° C. for 1 hour with stirring to oxidize it is mentioned.

The cleaning step in the carbon raw material manufacturing method is a step of cleaning the oxide. If impurities remain in the oxide, the impurities may be adversely affected when the activated carbon is manufactured or the capacitor is used. Therefore, the impurities are removed by washing. In this cleaning step, for example, if cleaning is performed until the pH of the cleaning wastewater reaches about 6 to 7, impurities can be sufficiently removed. As a method of cleaning the oxide, a method of cleaning the oxide with a cleaning liquid and performing solid-liquid separation can be employed. For example, a method of immersing the oxide in a cleaning solution, stirring and heating as necessary, mixing with the cleaning solution, and then removing the cleaning solution can be mentioned.

In addition to the above steps, the carbon raw material production method can be easily mixed with a phosphorus compound after the carbonization step, a particle size adjustment step for adjusting the particle size to 2 mm or less so that petroleum-based delayed coke can be easily pulverized before the carbonization step, Therefore, a pulverizing step for pulverizing the carbonized coke so as to have an average particle diameter of 5 μm to 10 μm can be included. The average particle diameter can be adjusted by a usual method, for example, by a method such as a jet mill, a ball mill, a high-pressure pulverizing roll, a disk mill, a bead mill, or the like.

(4) Carbon Raw Material Production Method Using Cellulose Acetate Next, a carbon raw material production method different from the above will be described. The method for producing a carbon raw material includes at least a carbonization step of heating and carbonizing a mixture containing at least cellulose acetate and a phosphorus compound in an inert atmosphere. Activated carbon produced using a carbonized carbon raw material can exhibit a sufficiently high capacitance even under low temperature conditions when used in a capacitor.

In the carbon raw material manufacturing method, a mixture containing at least cellulose acetate and a phosphorus compound is used as a starting raw material. An example of the starting material is a mixture (for example, a film) mainly composed of cellulose acetate, in which a phosphorus compound is added as a plasticizer to cellulose acetate. Cellulose acetate having a substitution degree of acetic acid in the range of 2 to 3 is preferred because it is commercially available. Cellulose not substituted with acetic acid is not preferred as a starting material because it does not melt by heating. Moreover, there is no restriction | limiting in particular in the form of a cellulose acetate, For example, forms, such as a flake, a pellet, a fiber, a woven fabric, a tow, a film, can be taken. The amount of cellulose acetate in the starting material is preferably high in purity considering that extra impurities are mixed into the carbide or activated carbon. The amount of cellulose acetate in the starting material can be used as a starting material as long as it is 50% by mass or more, more preferably 80% by mass or more, and still more preferably 85 to 99.5% by mass. .

Moreover, examples of the phosphorus compound contained in the starting material include phosphoric acid, phosphate, and phosphate ester. Examples of phosphoric acid include orthophosphoric acid and condensed phosphoric acid. Examples of the phosphate include ammonium salts, alkali metal salts, and alkaline earth metal salts. Examples of the phosphate ester include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, and tributyl phosphate. It is preferable that phosphorus is dispersed in molecules in cellulose acetate as a phosphorus compound. When phosphorus is present in the starting material, the amount of phosphorus in the carbon material can be appropriately controlled. The preferable amount of phosphorus in the starting material is 0.1% by mass to 5% by mass, although it varies depending on the carbonization temperature and time. If the amount is less than 0.1% by mass, the amount of phosphorus required in the carbon material cannot be obtained. If the amount is more than 5% by mass, the amount of phosphorus in the carbon material becomes excessive. The amount of phosphorus in the carbon material is particularly preferably 0.1% by mass to 2.0% by mass because the carbonization temperature and time can be set over a wide range.

The starting material may contain components other than cellulose acetate and a phosphorus compound, and is preferably a component that melts together with cellulose acetate by heating. Examples of such components include plasticizers, deterioration inhibitors, ultraviolet absorbers (UV agents), optical anisotropy control agents, retardation control agents, dyes, matting agents, release agents, release accelerators, and the like. . Details of cellulose acetate are described in paragraphs 0140 to 0195 of Patent Document 3. Similarly, additives such as solvents and plasticizers, deterioration inhibitors, ultraviolet absorbers (UV agents), optical anisotropy control agents, retardation control agents, dyes, matting agents, release agents, release accelerators, The details are described in paragraphs 0196 to 0516 of Patent Document 3.

As a starting material, defective products generated during the production of industrial products containing cellulose acetate and wastes discarded as used products can be used. Examples of such industrial products include photographic films, polarizing plates, cigarette filters, and water purification filter membranes. These industrial products containing cellulose acetate may contain phosphorus, for example, a photographic film contains a phosphate ester as a plasticizer. When industrial product waste containing cellulose acetate is used as a starting material, it is preferable to remove unnecessary components other than cellulose acetate and phosphorus compounds in advance from waste by means such as washing, separation, and separation. For example, in the case of tobacco waste, it is preferable to remove portions other than the filter, such as wrapping paper and cigarettes. When the phosphorus compound is not contained in the waste or the like, the starting material can be obtained by adding the phosphorus compound to the waste or the like. In addition, a waste material containing a phosphorus compound and a waste material not containing a phosphorus compound can be appropriately mixed and adjusted to a predetermined phosphorus amount to be used as a starting material.

The starting material is adjusted to an appropriate size and shape by crushing or cutting before being heated in the carbonization step, so that the carbonization can be made uniform and the carbonization step can be shortened.

In the carbonization step, the mixture is heated at a temperature of 250 ° C. to 600 ° C. to melt the cellulose acetate and then carbonize. As the cellulose acetate melts, the phosphorus compound is uniformly dispersed in the mixture. Examples of the inert gas used for the inert atmosphere include noble gases such as nitrogen gas, argon gas, helium gas, xenon gas, and neon gas. The heating time is usually in the range of 5 minutes to 600 minutes, for example, 5 minutes to 30 minutes if the heating temperature is about 500 ° C, and 30 minutes to 500 minutes if the heating temperature is about 300 ° C. In addition, it may be performed until the mixture is carbonized. The heating temperature is preferably 300 ° C. to 500 ° C., particularly preferably 350 ° C. to 450 ° C. The carbon material treated at a heating temperature lower than 250 ° C. tends to expand in the activation raw material mixture during activation, and the carbon material treated at a heating temperature higher than 600 ° C. spills out of the container during activation. In either case, it becomes difficult to obtain activated carbon.

For the carbonization of the mixture, it is preferable to perform the heat treatment in a stationary state without stirring, because a carbide having developed pores can be obtained. For this reason, the carbonization step is preferably performed using a continuous heating furnace in which the heating object in the furnace is conveyed by a roller or a belt conveyor. In the continuous heating furnace, it is more preferable to use a roller-type roller hearth kiln as a method for conveying the heating object because the temperature in the furnace can be easily controlled.

The carbon raw material production method may include an acetic acid removing step of removing the acetic acid by heating the carbide after the carbonizing step, if necessary. For example, when the heating temperature in the carbonization step is 250 ° C. to 350 ° C., acetic acid may remain in the carbide after the carbonization step. If acetic acid remains, acetic acid gas is generated at the time of alkali activation, which is liable to cause spillage, and the activity of the alkali activator is reduced. Acetic acid is removed by heating the carbide at a temperature of 380 ° C. to 700 ° C., preferably 500 ° C. to 650 ° C. Thereby, acetic acid volatilizes and is removed. Many passages when acetic acid volatilizes from the carbide are formed as pores in the carbide. The heating of the carbide is preferably performed in an inert atmosphere using an inert gas. Examples of the inert gas include nitrogen gas, argon gas, helium gas, xenon gas, rare gas such as neon gas, and the like. Further, CO gas generated during the carbonization process can also be used as an inert gas. The heating time for removing acetic acid is generally in the range of 10 minutes to 10 hours, preferably in the range of 30 minutes to 5 hours.

The removal of acetic acid is preferably performed in a stationary state without stirring, because a carbide with developed pores is obtained. For this reason, the acetic acid removing step is preferably performed using a continuous heating furnace in which the heating object is transported in the furnace by a roller type or a belt conveyor type. In the continuous heating furnace, it is more preferable to use a roller-type roller hearth kiln as a method for conveying the heating object because the temperature in the furnace can be easily controlled.

(5) Manufacturing method of activated carbon Next, the manufacturing method of activated carbon is demonstrated. The method for producing activated carbon includes at least an activation treatment step. In the activation treatment step, the mixture of the carbon raw material and sodium hydroxide is activated in an inert atmosphere.

Sodium hydroxide is used as an alkali metal hydroxide used for the activation reaction. Although sodium hydroxide is less expensive than other alkali metal hydroxides, sodium hydroxide is not preferable because it has a weak activation power and requires an excessive amount when used in a normal alkali activation treatment. However, in the case of a carbon raw material that has been oxidized and modified with phosphorus, inexpensive activated sodium hydroxide is used as an activator, so that activated carbon can be sufficiently static even under low temperature conditions when used in a capacitor. The capacity can be demonstrated.

The mass ratio of the carbon raw material to the sodium hydroxide in the mixture is 1: 1.5 to 3.5. Within this range, the activated carbon after activation can exhibit a sufficiently high capacitance even under low temperature conditions when used in a capacitor. When the mass ratio is smaller than the above range, the activated BET specific surface area of activated carbon becomes small, and a sufficiently high capacitance cannot be exhibited under low temperature conditions. On the other hand, when the mass ratio is larger than the above range, the activated BET specific surface area of the activated carbon increases, and the electrode density of the capacitor decreases.

Also, the reason for setting the reaction condition as an inert atmosphere is to prevent the carbon raw material from being oxidized during the activation treatment. In order to obtain an inert atmosphere, an inert gas can be used. For example, a rare gas such as nitrogen gas, argon gas, helium gas, xenon gas, or neon gas can be used.

The activation treatment process is a process that can be performed by any equipment as long as the equipment can seal the mixture of the carbon material and sodium hydroxide in an inert atmosphere and heat the mixture. For example, the activation process can be performed by using a tubular furnace or the like equipped with a heater.

The heating of the mixture includes a temperature raising step for raising the temperature of the mixture from 700 ° C. to 900 ° C. from an unheated state (for example, an air temperature of about 25 ° C.), and then a temperature holding step for keeping the temperature of the mixture. It can be heating. Sodium hydroxide increases its activation activity in a high temperature range of about 700 ° C to 900 ° C. Therefore, it is possible to provide a temperature raising step for raising the temperature of the room temperature mixture to a temperature at which the activity of the alkali activator is increased.

The temperature raising condition in the temperature raising stage can be a normal condition used for the activation treatment, and if it is within the range of 1 ° C./min to 50 ° C./min, there is no problem in the activation treatment. Considering the efficiency of the activation process and the load on the equipment used for the activation process, the temperature raising condition can be set to 5 ° C./min to 30 ° C./min.

After the temperature is raised to a high temperature range of about 700 ° C. to 900 ° C., the activation process proceeds sufficiently by maintaining the temperature of the mixture for about 10 minutes to 2 hours, more preferably for 30 minutes to 1 hour.

The average particle diameter of the carbon raw material can be adjusted in advance before mixing with sodium hydroxide. For example, by adjusting the average particle diameter of the carbon raw material to 1 μm to 50 μm, a uniform activation process is facilitated. The average particle diameter can be adjusted by a usual method, for example, by a method such as a jet mill, a ball mill, a high-pressure pulverizing roll, a disk mill, a bead mill, or the like.

The mixture of the carbon raw material and sodium hydroxide can be obtained by, for example, a mechanical mixing method such as a ball mill Henschel mixer or a method of mixing an alkali activator in a molten state. A particularly preferred method is a method in which sodium hydroxide is blended with the carbon raw material, and then the mixture is pulverized with a ball mill and mixed. Sodium hydroxide is preferably mixed with the carbon raw material as a powder. If the carbon material and sodium hydroxide are sufficiently mixed, uniform activation treatment is facilitated. This mixing step is preferably performed at room temperature (for example, 25 ° C.) where the activation activity of sodium hydroxide is low in order to avoid the activation process from starting.

The activated carbon described above is used for electrodes of electric double layer capacitors and lithium ion capacitors.

(6) Electric Double Layer Capacitor Next, the electric double layer capacitor will be described. The electric double layer capacitor includes an electrode including the activated carbon of the present invention. For example, the electrode may be configured by adding the activated carbon of the present invention and a binder, more preferably a conductive agent, and may be an electrode integrated with a current collector.

As the binder, known ones can be used, for example, polyolefins such as polyethylene and polypropylene, fluorinated polymers such as polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin / vinyl ether copolymer cross-linked polymers, and carboxy. Examples thereof include celluloses such as methylcellulose, vinyl polymers such as polyvinylpyrrolidone and polyvinyl alcohol, and polyacrylic acid. The content of the binder in the electrode is not particularly limited, but is appropriately selected within the range of usually about 0.1% by mass to 30% by mass with respect to the total amount of the activated carbon and the binder of the present invention.

As the conductive agent, powders of carbon black, powder graphite, titanium oxide, ruthenium oxide, etc. are used. The blending amount of the conductive agent in the electrode is appropriately selected according to the blending purpose, but is usually 1% by mass to 50% by mass, preferably based on the total amount of the activated carbon, the binder and the conductive agent of the present invention. It is appropriately selected within the range of about 2% by mass to 30% by mass.

As a method of mixing the activated carbon, the binder, and the conductive agent of the present invention, a known method can be appropriately applied. For example, there is a method in which a solvent having a property of dissolving a binder is added to the activated carbon, the binder, and the conductive agent to form a slurry, which is uniformly applied on the current collector. In addition, there is a method in which the activated carbon, the binder, and the conductive agent are kneaded without adding a solvent, and then pressure-molded at room temperature or under heating.

As the current collector, a known material and shape can be used. For example, a metal such as aluminum, titanium, tantalum, or nickel, or an alloy such as stainless steel can be used.

A unit cell of an electric double layer capacitor is generally formed by using a pair of the above electrodes as a positive electrode and a negative electrode, facing each other through a separator (polypropylene fiber nonwoven fabric, glass fiber nonwoven fabric, synthetic cellulose paper, etc.), and immersing in an electrolytic solution. Is done.

As the electrolytic solution, a known aqueous electrolytic solution or organic electrolytic solution can be used. More preferably, an organic electrolyte is used as the electrolyte. As such an organic electrolytic solution, one used as a solvent for an electrochemical electrolytic solution can be used. For example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, sulfolane derivatives, 3-methylsulfolane, 1,2-dimethoxyethane, acetonitrile, glutaronitrile, valeronitrile, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, dimethoxy Examples include ethane, methyl formate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. In addition, these electrolyte solutions can be mixed and used.

Further, the supporting electrolyte in the organic electrolyte is not particularly limited, and various kinds of salts, acids, alkalis, and the like that are usually used in the field of electrochemistry or the field of batteries can be used. Examples include inorganic ion salts such as alkali metal salts and alkaline earth metal salts, quaternary ammonium salts, cyclic quaternary ammonium salts, quaternary phosphonium salts, and the like. (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , (C ₂ H ₅ ) ₄ PBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) PBF _{4 and the} like are preferable.

The concentration of these salts in the electrolytic solution is appropriately selected within the range of usually about 0.1 mol / l to 5 mol / l, preferably about 0.5 mol / l to 3 mol / l. The specific configuration of the electric double layer capacitor is not particularly limited. For example, the electric double layer capacitor is accommodated in a metal case via a separator between a pair of thin sheet or disk electrodes (positive electrode and negative electrode) having a thickness of 10 μm to 500 μm. A coin type, a wound type in which a pair of electrodes are wound through a separator, and a stacked type in which a large number of electrode groups are stacked through a separator.

(7) Lithium Ion Capacitor Next, a lithium ion capacitor will be described. The lithium ion capacitor includes a positive electrode including the activated carbon of the present invention and a negative electrode capable of absorbing and releasing lithium ions. The positive electrode is constituted, for example, by adding the activated carbon of the present invention and a binder, more preferably a conductive agent. The negative electrode is configured by adding, for example, hard carbon, a binder, and a conductive agent. Both the positive electrode and the negative electrode may be electrodes integrated with the current collector.

As the positive electrode binder, known materials can be used, for example, polyolefins such as polyethylene and polypropylene, fluorinated polymers such as polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin / vinyl ether copolymer cross-linked polymers, Examples thereof include celluloses such as carboxymethyl cellulose, styrene-butadiene rubbers, vinyl polymers such as polyvinyl pyrrolidone and polyvinyl alcohol, and polyacrylic acid. The content of the binder in the electrode is not particularly limited, but is appropriately selected within a range of usually about 0.1% by mass to 30% by mass with respect to the total amount of the activated carbon and the binder of the present invention. .

As the positive electrode conductive agent, powders such as carbon black, powdered graphite, and titanium oxide are used. The blending amount of the conductive agent in the electrode is appropriately selected according to the blending purpose. The content of the conductive agent in the electrode is usually in the range of about 1% to 50% by weight, preferably about 2% to 30% by weight, based on the total amount of the activated carbon, the binder and the conductive agent of the present invention. Is appropriately selected.

A known material and shape can be used as the positive electrode current collector. For example, a metal such as aluminum, titanium, tantalum, or nickel, or an alloy such as stainless steel can be used.

As the negative electrode active material, a known material capable of absorbing and releasing lithium ions can be used. Examples thereof include organic compounds such as hard carbon, coke, graphite and polyolefin, or inorganic compounds containing lithium in the structure such as lithium titanate. The particle diameter is preferably about 0.01 μm to 100 μm, more preferably 0.1 μm to 30 μm for convenience of electrode forming.

As the negative electrode binder, known materials can be used, for example, polyolefins such as polyethylene and polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, fluorinated polymers such as fluoroolefin / vinyl ether copolymer crosslinked polymers, Examples thereof include celluloses such as carboxymethyl cellulose, styrene-butadiene rubbers, vinyl polymers such as polyvinyl pyrrolidone and polyvinyl alcohol, and polyacrylic acid. The content of the binder in the electrode is not particularly limited, but is appropriately selected within the range of usually about 0.1% by mass to 30% by mass with respect to the total amount of the activated carbon and the binder of the present invention.

As the negative electrode conductive agent, powders such as carbon black, powdered graphite and titanium oxide are used. The addition of the conductive auxiliary agent to the negative electrode is not essential, and the blending amount of the conductive agent in the electrode is appropriately selected according to the blending purpose, but with respect to the total amount of the negative electrode active material, the binder and the conductive agent, It is appropriately selected within the range of about 1 to 50% by mass, preferably about 2 to 30% by mass.

As a method of mixing the negative electrode active material, the binder, and the conductive agent, a known method can be appropriately applied. For example, there is a method in which a solvent having a property of dissolving a binder is added to the activated carbon, the binder, and the conductive agent to form a slurry, which is uniformly applied on the current collector. In addition, there is a method in which the activated carbon, the binder, and the conductive agent are kneaded without adding a solvent, and then pressure-molded at room temperature or under heating.

As the negative electrode current collector, known materials and shapes can be used. For example, a metal such as copper, titanium, tantalum, or nickel, or an alloy such as stainless steel can be used.

In the case of a negative electrode used for a lithium ion capacitor, it is necessary to pre-dope lithium ions into the negative electrode before charging for the first time. As a pre-doping method, there are a method of bringing a lithium source such as lithium metal into contact with a negative electrode in an inert atmosphere, and a method of performing electrochemical pre-doping in a solution containing lithium. In the practice of the present invention, there is no particular limitation, and any method can be used. In addition, the pre-doping step may be performed either before or after the cell assembly in which the positive electrode, the electrolyte, and the separator are housed in the case. For example, when a compound containing lithium in the structure in advance, such as lithium titanate, is used for the negative electrode, pre-doping is not essential.

A unit cell of a lithium ion capacitor is generally formed by using a pair of the positive electrode and the negative electrode, facing each other through a separator, and immersing in an electrolytic solution. As a material for the separator, polypropylene fiber nonwoven fabric, glass fiber nonwoven fabric, synthetic cellulose paper, or the like can be used.

Further, the supporting electrolyte in the organic electrolytic solution is not particularly limited, but in general, various lithium salts can be used. Lithium salts include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) There are ₂ etc.

The concentration of these salts in the electrolytic solution is appropriately selected within the range of usually about 0.1 mol / l to 5 mol / l, preferably about 0.5 mol / l to 3 mol / l. The specific configuration of the lithium ion capacitor is not particularly limited. For example, the lithium ion capacitor is accommodated in a metal case via a separator between a pair of thin sheet or disk electrodes (positive electrode and negative electrode) having a thickness of 10 μm to 500 μm. A coin type, a wound type in which a pair of electrodes are wound through a separator, and a stacked type in which a large number of electrode groups are stacked through a separator.

Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

The analysis methods used in the examples are as follows.
<Oxygen content, hydrogen atom / carbon atom ratio>
Remaining carbon content (mass%), hydrogen content (mass%) and nitrogen content (mass%) of the sample using an elemental analyzer (manufactured by Sumika Chemical Analysis Co., Ltd., NCH-22F type) Using the X-ray fluorescence analyzer (manufactured by Techno-X Co., Ltd., WED-100), the phosphorous content calculated by subtracting the phosphorus content calculated from the calibration curve of each element by the fluorescent X-ray method Amount (mass%). Moreover, the molar ratio (H / C) of a hydrogen atom and a carbon atom was computed from said carbon content and hydrogen content.

<Specific surface area>
Using an automatic specific surface area measuring device (BELSORP-mini II type, manufactured by Nippon Bell Co., Ltd.), the BET method was used to calculate the adsorption isotherm obtained from nitrogen gas adsorption.

<Average particle size>
Using a laser diffraction particle size distribution measuring device (LA-950, manufactured by Horiba, Ltd.), a small amount of a surfactant was added using water as a dispersion medium, and the measurement was performed after irradiating ultrasonic waves. The 50% particle diameter (average particle diameter) was determined from the obtained volume-based particle size integration curve.

<Sodium and phosphorus content>
Using a fluorescent X-ray analyzer (manufactured by Techno-X Co., Ltd., WED-100), the respective contents were calculated from calibration curves of sodium and phosphorus by the fluorescent X-ray method.

[Manufacture of activated carbon]
[Example 1]
Using raw petroleum coke as a starting material, a carbon raw material for activated carbon was produced. The oil raw coke was adjusted to a particle size of 2 mm or less so as to be easily pulverized, heated at 600 ° C. in an inert atmosphere with nitrogen gas for 1 hour using a rotary kiln, and carbonized to obtain carbonized coke (carbonization step). The obtained carbonized coke was pulverized by a jet mill so that the average particle size was 8 μm. Carbonized coke is added to 85 mass% phosphoric acid aqueous solution so that the mass ratio of carbonized coke to 85 mass% phosphoric acid aqueous solution is 1: 5, and heated at 120 ° C. for 1 hour with stirring. Was obtained (oxidation step). The obtained oxide was washed several times with pure water (washing step) and then dried at 100 ° C. to obtain a carbon raw material for activated carbon. Then, activated carbon was manufactured using the carbon raw material of the obtained activated carbon. Sodium hydroxide was added to the obtained carbon raw material so that the mass ratio of the carbon raw material of activated carbon and sodium hydroxide was 1: 2.8, and the mixture was mixed for 30 minutes with a ball mill (mixing step). ). The obtained mixture was filled in a nickel container and placed in a ceramic electric furnace, and after purging nitrogen gas in the furnace to an inert atmosphere, The temperature of the furnace was raised from room temperature to 750 ° C., and the activation treatment was performed by maintaining the temperature at 750 ° C. for 30 minutes from the time when the temperature in the furnace reached 750 ° C. (activation treatment step). After the activation treatment, heating of the electric furnace was stopped, and natural cooling was performed in a nitrogen gas atmosphere. After cooling to below 170 ° C., the activated product was taken out from the electric furnace, and the activated product was repeatedly washed with water and acid washed with hydrochloric acid to remove residual impurities, and then dried to obtain activated carbon of Example 1.

[Example 2]
A carbon raw material for activated carbon was produced using a flaky ground product of a mixture containing 12% by mass of triphenyl phosphate and the balance of cellulose acetate as the starting material. The amount of phosphorus in the mixture is about 1% by weight. The starting material was put in a heat-resistant container, and the container was put in a batch electric furnace equipped with a thermometer, an oxygen gas detector, a nitrogen gas inlet, and a gas exhaust port. Next, nitrogen gas is supplied to the nitrogen gas inlet at a supply rate of 2.0 L / min to bring the inside of the electric furnace and the heat-resistant container to an inert atmosphere, and the temperature is raised until the internal temperature of the heat-resistant container reaches 350 ° C. Then, the temperature was maintained for 3 hours and 45 minutes to carbonize the mixture (carbonization step). After the heat treatment, the mixture was allowed to cool to room temperature and the carbide was taken out from the heat-resistant container. The obtained carbide was pulverized with a cyclone mill so that the average particle size became 8 μm, and a carbon raw material for activated carbon was obtained. Then, activated carbon was manufactured using the carbon raw material of the obtained activated carbon. The mixture was obtained with a ball mill for 30 minutes so that the mixing ratio of the carbon raw material and sodium hydroxide was 1: 2.8 in terms of mass ratio (mixing step). Using the obtained mixture, an activation treatment process, washing, and drying were performed under the same conditions as in Example 1, and activated carbon of Example 2 was obtained.

[Example 3]
Activated carbon of Example 3 was obtained under the same production conditions as in Example 2 except that the mixing ratio of the carbon raw material and sodium hydroxide was 1: 2.4 by mass ratio.

[Example 4]
Activated carbon of Example 4 was obtained under the same production conditions as in Example 2 except that the mixing ratio of the carbon raw material and sodium hydroxide was 1: 2.0 by mass ratio.

[Example 5]
Activated carbon of Example 5 was obtained under the same production conditions as in Example 2 except that the mixing ratio of the carbon raw material and sodium hydroxide was 1: 1.6.

[Example 6]
The activated carbon of Example 6 is obtained under the same production conditions as in Example 2 except that the mixing ratio of the carbon raw material and sodium hydroxide is 1: 2.2 by mass ratio, and the temperature of the activation treatment process is 800 ° C. It was.

[Comparative Example 1]
The starting material for the carbon material of the activated carbon was the same as in Example 2 except that a pulverized pulverized product of cellulose acetate was used without adding a phosphorus compound, but spilling occurred during the activation process. I couldn't get a sample.

[Comparative Example 2]
Without adding a phosphorus compound, coconut-based cellulose carbide originating in Southeast Asia was used as a carbon raw material for activated carbon. In order to make it easy to grind cellulose carbide, the particle size was adjusted to 2 mm or less using a sieve, and the average particle size was ground to about 7 μm using a ball mill. The steps after the mixing step with sodium hydroxide were carried out under the same production conditions as in Example 2. However, spraying occurred during the activation treatment, and a sample could not be obtained.

[Comparative Example 3]
Activated carbon was produced using the same mixture of activated carbon carbon material and sodium hydroxide as in Example 2. The mixture was filled in an alumina boat and placed in a ceramic tubular electric furnace and sealed. From the time when the electric furnace was heated from room temperature to 900 ° C. under a temperature rising condition of 4 ° C./min by passing 1000 cm ³ of carbon dioxide gas through the tubular electric furnace, and the temperature in the furnace became 900 ° C. The activation process was performed by maintaining 900 ° C. for 60 minutes. After the activation treatment, the heating of the electric furnace was stopped, and it was naturally cooled to room temperature by switching to a nitrogen gas atmosphere. The activated material obtained was sieved with a 45 μm sieve to obtain activated carbon of Comparative Example 3.

[Comparative Example 4]
Without carrying out the oxidation step of adding a phosphorus compound, carbonized coke was used as a carbon raw material for activated carbon, and activated carbon was produced under the same production conditions as in Example 1 to obtain activated carbon of Comparative Example 4.

[Comparative Example 5]
Comparative Example 5 was carried out under the same production conditions as in Example 2, except that potassium hydroxide was used as the activator instead of sodium hydroxide, and the mixing ratio of the carbon raw material and potassium hydroxide was 1: 2.4. Of activated carbon was obtained.

[Comparative Example 6]
Activated carbon of Comparative Example 6 was obtained under the same production conditions as in Example 2 except that the mixing ratio of the carbon raw material and sodium hydroxide was 1: 1.2 by mass ratio.

[Comparative Example 7]
Activated carbon of Comparative Example 7 was obtained under the same production conditions as in Example 2 except that the mixing ratio of the carbon raw material and sodium hydroxide was 1: 4.0 by mass ratio.

[Comparative Example 8]
In the carbonization step of the starting material, the temperature is increased and maintained until the internal temperature of the heat-resistant container reaches 310 ° C., and the mixing ratio of the carbon material and sodium hydroxide in the mixing step of the carbon material and alkali is 1: 2. Except for 2, it was carried out under the same production conditions as in Example 2. However, spraying occurred during the activation treatment, and a sample could not be obtained.

Table 1 shows the properties of the starting materials, the carbon materials of the activated carbon produced, the activation conditions, and the properties of the activated carbon when activated carbon was produced in Examples 1 to 6 and Comparative Examples 1 to 8.

[Production of laminate cell]
Electric double layer capacitors were produced using the activated carbon produced in Examples 1 to 6 and Comparative Examples 1 to 8. 7 parts by weight of carbon black (manufactured by Lion Corporation, ECP600JD) and 86 parts by weight of activated carbon as a conductive additive, granular polytetrafluoroethylene as a binder (manufactured by Daikin Industries, Ltd., PTFE Polyflon F-104) 7 parts by weight and water were added and mixed using an agate mortar, and the mixture was pressed into a sheet using a roll press machine until the thickness became 150 μm to prepare a carbon electrode sheet. This carbon electrode sheet was cut into a size of 14 mm × 20 mm and attached to an aluminum current collector to form an electrode. As shown in FIG. 1, the prepared two electrodes are a positive electrode 2 and a negative electrode 3, and a current collector 4 is attached to these electrodes, and a cellulose separator 5 (manufactured by Nippon Kogyo Paper Industries Co., Ltd., TF40-50). The laminate cell 1 was manufactured by covering the outside with a laminate film 6, injecting an electrolytic solution, and sealing with a heat sealer. A 1.5M triethylmethylammonium tetrafluoroborate (TEMA-BF ₄ ) solution in propylene carbonate (PC) was used as the electrolyte.

[Capacitance evaluation of capacitors]
In order to evaluate the capacitor performance of the laminate cell, the electrode density, capacitance at 20 ° C. and −30 ° C. were measured. The electrode density was determined by measuring the sheet weight and the vertical and horizontal dimensions × thickness. The capacitance (C) was obtained by measuring the total amount of discharge energy (U) stored in the capacitor and calculating the value by the energy conversion method. Formula (1) is shown below as a formula for calculating the capacitance. The total discharge energy amount of the capacitor is constant voltage and constant voltage charging with a current of 3.6 mA / cm ² from 0 V to 2.8 V, and after a predetermined time of rest, it is fixed to 0 V with a current of 3.6 mA / cm ^2. Obtained by current discharge. Further, regarding the charge / discharge relationship, FIG. 2 shows a graph in which the vertical axis represents voltage (V) and the horizontal axis represents time (S).

Table 2 shows the electrode density and capacitance results of the laminate cells prepared using the activated carbons of Examples 1 to 6 and Comparative Examples 1 to 8.

The laminate cells using the activated carbons of Examples 1 to 6 exhibited a capacitance of 90% or more under 20 ° C. conditions even at a low temperature of −30 ° C. (Table 2).

In the case of Comparative Example 1, Comparative Example 2, and Comparative Example 8, the mixture was ejected from the container during the activation process, and activated carbon could not be obtained. The laminate cells using the activated carbons of Comparative Examples 3 to 6 had a result that the capacitance under the −30 ° C. condition was inferior to the capacitance under the 20 ° C. condition. In addition, the laminate cell using the activated carbon of Comparative Example 7 exhibited 96% capacitance under the low temperature condition of −30 ° C. even under the low temperature condition of −30 ° C., but due to the large specific surface area of the activated carbon, The electrode density was smaller than the practical level (about 0.40 g / cm ³ ).

According to the present invention, a capacitor electrode that can exhibit a sufficiently high capacitance even under a low temperature condition can be provided, which is industrially useful.

DESCRIPTION OF SYMBOLS 1 Laminate cell 2 Positive electrode 3 Negative electrode 4 Current collector 5 Separator 6 Laminate film

Claims

The content of sodium is 20 ppm or more and less than 4000 ppm,
The phosphorus content is 100 ppm or more and less than 2000 ppm,
The average particle size measured with a laser scattering particle size distribution meter is 1 μm or more and less than 50 μm,
Activated carbon for capacitors having a BET specific surface area of 1400 m 2 / g or more and less than 3300 m 2 / g.
A carbon raw material for producing the capacitor activated carbon according to claim 1,
The phosphorus content is 0.3% by mass to 2.0% by mass,
The oxygen content is 10% by mass or more and less than 30% by mass,
The molar ratio H / C of hydrogen atoms to carbon atoms is 0.05 to 0.54,
A carbon raw material having a BET specific surface area of 100 m 2 / g or more and less than 600 m 2 / g.
A method for producing a carbon raw material according to claim 2,
A carbonization step in which an easily graphitizable carbon material is heated in an inert atmosphere to form carbonized coke;
An oxidation step of adding a phosphorus compound to the carbonized coke and heating it to an oxide;
And a cleaning step of cleaning the oxide.
A method for producing a carbon raw material according to claim 2,
A production method comprising at least a carbonization step of heating and carbonizing a mixture containing at least cellulose acetate and a phosphorus compound in an inert atmosphere.
The production method according to claim 4, further comprising an acetic acid removing step of removing acetic acid by heating the carbide after the carbonizing step.
A method for producing activated carbon,
At least an activation treatment step of activating the mixture of the carbon raw material according to claim 2 and sodium hydroxide under an inert atmosphere;
The mass ratio of the carbon raw material to the sodium hydroxide in the mixture is 1: 1.5 to 3.5,
The activated carbon has a sodium content of 20 ppm or more and less than 4000 ppm, a phosphorus content of 100 ppm or more and less than 2000 ppm, an average particle size measured by a laser scattering particle size distribution meter of 1 μm or more and less than 50 μm, and a BET ratio surface area of less than 1400 m 2 / g or more 3300 m 2 / g, the manufacturing method of the activated carbon.
An electric double layer capacitor using the activated carbon according to claim 1 as an electrode.
A lithium ion capacitor using the activated carbon according to claim 1 as an electrode.