JP2007186411A - Activated carbon, process of making the same and use of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide activated carbon the deterioration of whose capacitance is lowered at particularly low temperature (in the vicinity of -30°C) and which has excellent low-temperature characteristics and to provide an electric double layer capacitor. <P>SOLUTION: The activated carbon has peak (a) within the range of 2.1-2.4 nm pore size, peak (b) within the range of 1.7-2.1 nm pore size, peak (c) within the range of 1.4-1.7 nm pore size and peak (d) within the range of 1.1-1.4 nm pore size in a pore volume distribution. When area (a) of a portion surrounded by a curved line of peak (a) and the pore size axis within the range of 2.1-2.4 nm pore size is calculated, area (b), area (c) and area (d) are calculated in the same manner as area (a) is calculated and area (a) is defined as 1, area (d), area (c) and area (b) are 3.7-4.8, 1.6-2.3 and 1.6-2.1, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to activated carbon useful as an electric double layer capacitor (also referred to as an electric double layer capacitor), a method for producing the same, and a polarizable electrode. In particular, the present invention relates to the use of activated carbon typified by an electric double layer capacitor having excellent charge / discharge characteristics and internal resistance characteristics at low temperatures.

  Electric double layer capacitors are capable of rapid charge and discharge, are resistant to overcharge and discharge, have no chemical reaction, have a long life, can be used in a wide temperature range, and do not contain heavy metals. It has characteristics not found in batteries. Electric double layer capacitors have been used for memory backup power supplies. Furthermore, in recent years, the development of large capacity has progressed rapidly, the development of applications for high-performance energy devices has been promoted, and the use for power storage systems combined with solar cells and fuel cells, engine assistance for hybrid cars, etc. has been considered. Yes.

  The electric double layer capacitor has a structure in which a pair of positive and negative polarizable electrodes made of activated carbon or the like are opposed to each other through a separator in a solution containing electrolyte ions. When a DC voltage is applied to the electrode, the anion in the solution is attracted to the electrode polarized to the positive (+) side, and the cation in the solution is attracted to the electrode polarized to the negative (−) side. The electric double layer formed at the interface is used as electric energy.

Therefore, in order to form more electric double layers, the use of activated carbon having a large specific surface area has been studied, but such activated carbon is superior to the electric capacity per mass (F / g), but the electrode density is lowered. Therefore, the electric capacity per volume (F / cm ³ ) is not so large.

On the other hand, it has been proposed to use activated carbon having graphite-like microcrystals produced by alkali activation and having an interlayer distance of 0.365 nm to 0.385 nm as raw materials for polarizable electrodes (Patent Documents 1, 2, 3). An electric double layer capacitor using activated carbon as a raw material for a polarizable electrode can be said to be an excellent raw material in that the capacitance per volume (F / cm ³ ) is large.

  In the method of producing activated carbon by forming pores in the carbonized product by alkali activation with potassium hydroxide (KOH), it is considered difficult to control the pore diameter of the activated carbon, and pores mixed in large and small are formed, It is difficult to control and form pores having an optimal size for the electrolyte ions of the electrolytic solution of the electric double layer capacitor to operate at a low temperature.

  On the other hand, the activated carbon pore ratio controlled to the mesopore distribution (bore diameter 2 to 50 nm) by the steam activation treatment of the low softening point firing raw material obtained by mixing the low softening point pitch and the metal compound, and the manufacturing method thereof are proposed. (Patent Documents 4 and 5).

JP 11-317333 A JP 2000-68164 A JP 2000-68165 A Japanese Patent No. 319563 JP 2004-182511 A

The electric double layer capacitor is premised on a room temperature of about 25 ° C., and exhibits a relatively high capacity at room temperature. Resistance increases. The main reason is that the mobility of the electrolyte ions in the pores of the activated carbon decreases due to the increase in the viscosity of the electrolyte solution at a low temperature.
Until now, increasing the pore volume (cm ³ / g) of activated carbon has been performed as means for improving the mobility of electrolyte ions at low temperatures. However, if only the pore volume (cm ³ / g) of the activated carbon is increased to reduce the internal resistance at low temperatures, the density of the activated carbon electrode will decrease, and eventually the capacity per volume (F / cm ³ ). Will be lower.
Accordingly, an object of the present invention is to provide an activated carbon and an electric double layer capacitor that are excellent in charge / discharge characteristics and internal resistance characteristics particularly at a low temperature (under about −30 ° C.).

As a result of intensive studies to achieve the above object, the present inventors have found that the pore volume distribution by the BJH method determined by the nitrogen adsorption method is 1.1 to 1.4 nm, 1.4 to 1 Activated carbon having the pore volume peaks d, c, b and a in the range of 1.7 nm, 1.7 to 2.1 nm and 2.1 to 2.4 nm, respectively, or the pore diameter is 0.4 to 0. The pore volume in the range of 8 nm, 0.8-1.1 nm, 1.1-1.4 nm, 1.4-1.7 nm, 1.7-2.1 nm, and 2.1-2.4 nm, respectively. Activated carbon having the peak f, e, d, c, b, and a and the ratio of the area surrounded by the respective peak curve, pore diameter range, and pore diameter axis within a specific range is low temperature. Polarity for electric double layer capacitors with excellent charge / discharge characteristics and internal resistance characteristics (under -30 ° C) It found that the electrode material, and have completed the present invention.
That is, the present invention has the following configuration.

[1] In the pore distribution, there is a peak D indicating the maximum value of the pore volume in the pore diameter range of 1.0 to 1.5 nm, and the value of the peak D is 0.012 to 0.050 cm ³ / g. Activated carbon having a size of 2 to 32% of the total pore volume value.
[2] The activated carbon according to [1], wherein the BET specific surface area is 1100 to 2200 m ² / g.
[3] The activated carbon according to [1] or [2], wherein the peak D is in the range of a pore diameter of 1.2 to 1.4 nm.
[4] The activated carbon according to any one of [1] to [3], wherein a peak C is present in a pore diameter range of 1.5 to 1.7 nm.
[5] The activated carbon according to any one of [1] to [4], wherein there is a peak B in a pore diameter range of 1.7 to 2.0 nm.
[6] The activated carbon according to any one of [1] to [5], wherein a peak A is present in a pore diameter range of 2.0 to 2.5 nm.

[7] In the pore volume distribution determined by the BJH method from the nitrogen adsorption isotherm of 77.4 K, the pore volume distribution has a peak a in the range of 2.1 to 2.4 nm, and the pore size is 1.7 to 2.1 nm. Having a peak b in the range of pore diameter 1.4 to 1.7 nm, a peak c in the range of pore diameter 1.1 to 1.4 nm, and a peak a, The area (area a, area b, area c, and area d) of the portion surrounded by the peak curve of each of peak b, peak c, and peak d, each pore diameter range, and pore diameter axis is defined as area a being 1. Sometimes activated carbon having an area d in the range of 3.7 to 4.8, an area c of 1.6 to 2.3, and an area b of 1.6 to 2.1.
[8] In the pore volume distribution determined by the BJH method from the nitrogen adsorption isotherm of 77.4K, the pore volume distribution has a peak a in the range of 2.1 to 2.4 nm, and the pore size is 1.7 to 2.1 nm. Having a peak b in the range of pore diameters of 1.4 to 1.7 nm, a peak d in the range of pore diameters of 1.1 to 1.4 nm, and a pore diameter of 0.8. Has a peak e in the range of ~ 1.1 nm, a peak f in the range of pore diameters of 0.4 to 0.8 nm, and each of peak a, peak b, peak c, peak d, peak e and peak f When the area (area a, area b, area c, area d, area e, and area f) of the portion surrounded by the peak curve, each pore diameter range and the pore diameter axis is defined as 1, The area f is 2.2 to 2.5, the area e is 2.3 to 2.5, the area d is 4.6 to 4.8, and the area c is 2.1 to 2 .3, and activated carbon having an area b in the range of 1.9 to 2.1.

[9] The pitch is carbonized in the presence of a compound Z containing any element of Group 4 to Group 11 of Periodic Table 4 or Group 5 of Periodic 5 of Periodic Table having an element concentration of 7000 ppm or more. Including obtaining an easily graphitizable carbonized material having a true density of 1.44 to 1.52 g / cm ³ , activating the mixture in the presence of an alkali metal compound, and then washing the activated mixture A method for producing activated carbon.
[10] Carbonize the pitch to obtain a graphitizable carbonized product having a true density of 1.44 to 1.52 g / cm ³ , and the carbonized product has a concentration of 7000 ppm or more in the periodic table in the 4th period of the periodic table. ~ A compound Z containing any element of Group 11 or Group 5 element of 5th period was mixed to obtain a mixture, and the mixture was activated in the presence of an alkali metal compound, and then this activated A method for producing activated carbon, comprising washing the mixture.
[11] The method for producing activated carbon according to [9] or [10], wherein the pitch softening point is 100 ° C. or lower.
[12] The method for producing activated carbon according to [9] or [10], wherein the pitch is coal-based pitch or petroleum-based pitch or an organic solvent-soluble component thereof.

[13] Any of [9] to [12], wherein the compound Z is a compound containing at least one metal element selected from the group consisting of calcium, titanium, manganese, iron, cobalt, nickel, copper, and zirconium. The manufacturing method of activated carbon as described.
[14] Compound Z is at least one selected from the group consisting of simple metals, oxides, hydroxides, chlorides, bromides, iodides, fluorides, phosphates, carbonates, sulfides, sulfates and nitrates. The method for producing activated carbon according to any one of [9] to [13], which is a seed compound.
[15] The method for producing activated carbon according to any one of [9] to [14], wherein the maximum temperature during the activation treatment is in the range of 700 ° C to 760 ° C.
[16] The method for producing activated carbon according to any one of [9] to [15], wherein the holding time at the maximum temperature during the activation treatment is within 30 minutes.
[17] The method for producing activated carbon according to any one of the above [9] to [16], wherein a cooling rate when cooling from the maximum temperature during the activation treatment to 590 ° C. is 60 ° C./hr or more.
[18] The method for producing activated carbon according to any one of [9] to [17], wherein the alkali metal compound is an alkali metal hydroxide.
[19] The method for producing activated carbon according to any one of [9] to [18], wherein the alkali metal compound is a compound containing at least one metal element selected from the group consisting of potassium, sodium, and cesium.

[20] A polarizable electrode comprising the activated carbon according to any one of [1] to [8], carbon black, and a binder.
[21] A polarizable electrode comprising the activated carbon according to any one of [1] to [8], vapor grown carbon fiber, carbon black, and a binder.
[22] The polarizable electrode according to [21], wherein the amount of vapor grown carbon fiber mixed with activated carbon is 0.1 to 20% by mass.
[23] The above [21] or [22], wherein the vapor-grown carbon fiber has a hollow structure therein, a specific surface area of 10 to 50 m ² / g, an average fiber diameter of 50 to 500 nm, and an aspect ratio of 5 to 1000. A polarizable electrode according to 1.
[24] The polarizable electrode according to any one of [20] to [23], wherein the binder is polytetrafluoroethylene, polyvinylidene fluoride, acrylate rubber, or butadiene rubber.

[25] An electric double layer capacitor using the polarizable electrode according to any one of [20] to [24].
[26] Using an electrolytic solution in which an electrolyte salt containing at least one selected from the group consisting of a quaternary ammonium salt, a quaternary imidazolium salt, a quaternary pyridinium salt, and a quaternary phosphonium salt is added to an organic solvent, an electrolyte ion The electric double layer capacitor according to [25], wherein the cation diameter is 3 to 15 mm and the anion diameter is 5 to 10 mm.

[27] A slurry containing the activated carbon according to any one of [1] to [8].
[28] A paste containing the activated carbon according to any one of [1] to [8].
[29] An electrode sheet on which the activated carbon according to any one of [1] to [8] is applied.
[30] A power supply system including the electric double layer capacitor according to [25] or [26].
[31] An automobile using the power supply system according to [30].
[32] A railway using the power supply system according to [30].
[33] A ship using the power supply system according to [30].
[34] An aircraft using the power supply system according to [30].
[35] A mobile phone using the power supply system according to [30].
[36] Office equipment using the power supply system according to [30].
[37] A solar cell power generation system using the power supply system according to [30].
[38] A wind power generation system using the power supply system according to [30].
[39] A communication device using the power supply system according to [30].
[40] An electronic tag using the power supply system according to [30].

(1) Activated carbon The activated carbon of the present invention has a pore diameter of 1.0 to 1.5 nm, preferably 1.2 to 1.2 nm in the pore distribution determined by the BJH method based on the nitrogen adsorption method. There is a peak D indicating the maximum value of the pore volume in the range of 1.4 nm.

The pore distribution of the activated carbon is calculated by the BJH method based on the nitrogen adsorption isotherm. Specifically, nitrogen gas is introduced in a state where the activated carbon is cooled to 77.4 K (the boiling point of nitrogen), and the adsorption amount V [cc / g] of the nitrogen gas is measured by a volumetric method. The ratio of the nitrogen gas pressure (adsorption equilibrium pressure) P [mmHg] and the saturated vapor pressure P ₀ [mmHg] of nitrogen gas (relative pressure: P / P ₀ ) in the adsorption equilibrium state is plotted on the horizontal axis. A nitrogen adsorption isotherm is obtained by plotting the quantity on the vertical axis. Based on this nitrogen adsorption isotherm, pore distribution analysis was performed by the BJH (Barrett-Joyner-Halenda) method. The BJH method itself is a known method. Amer. Chem. Soc. 73.373. (1951).
By this pore distribution analysis, as shown in FIG. 2 or FIG. 3, a diagram showing the pore distribution with the pore diameter on the horizontal axis and the pore volume on the vertical axis can be obtained. FIG. 2 or FIG. 3 is a diagram showing the pore distribution of the example of the present invention.

The activated carbon of the present invention has a peak D value of 0.012 to 0.050 cm ³ / g, preferably 0.020 to 0.035 cm ³ / g and a total pore volume value of 2 The size is ~ 32%. When the value of the peak D is smaller than 0.012 cm ³ / g, the mobility of electrolyte ions in the pores decreases when the electrolyte viscosity increases at low temperature. As a result, charge / discharge characteristics at low temperature and internal Resistance characteristics are likely to deteriorate. If the value of peak D is larger than 0.050 cm ³ / g, the capacity per volume for the electrode density of the activated carbon is reduced (F / cm ³⁾ is likely to be low.

  The preferred activated carbon of the present invention has a peak C in the pore diameter range of 1.5 to 1.7 nm, a peak B in the pore diameter range of 1.7 to 2.0 nm, and a pore diameter of 2.0 to 2. One or more of peaks A in the range of 5 nm are included.

  The activated carbon of the present invention has a peak a in a pore diameter range of 2.1 to 2.4 nm in a pore volume distribution determined by the BJH method based on a nitrogen adsorption isotherm of 77.4 K, and a pore diameter of 1.7. Having a peak b in the range of ~ 2.1 nm, a peak c in the range of pore diameter 1.4-1.7 nm, a peak d in the range of pore diameter 1.1-1.4 nm, and , Peak a, peak b, peak c, and peak d, the area (area a, area b, area c, and area d) of the portion surrounded by the respective peak curves, each pore diameter range, and the pore diameter axis is expressed as area a. Where d is 3.7 to 4.8, area c is 1.6 to 2.3, and area b is 1.6 to 2.1.

  Further, the activated carbon of the present invention has a peak a in the pore diameter range of 2.1 to 2.4 nm in the pore volume distribution determined by the BJH method from the nitrogen adsorption isotherm of 77.4K, and the pore diameter of 1. It has a peak b in the range of 7 to 2.1 nm, a peak c in the range of pore diameter 1.4 to 1.7 nm, a peak d in the range of pore diameter 1.1 to 1.4 nm, It has a peak e in the pore diameter range of 0.8 to 1.1 nm, a peak f in the pore diameter range of 0.4 to 0.8 nm, and peak a, peak b, peak c, peak d, peak The area (area a, area b, area c, area d, area e, and area f) of the portion surrounded by the peak curve of each of e and peak f, each pore diameter range and the pore diameter axis is 1 The area f is 2.2 to 2.5, the area e is 2.3 to 2.5, the area d is 4.6 to 4.8, Product c is 2.1-2.3, and the area b is in the range of 1.9 to 2.1.

Activated carbon of the present invention is preferably a BET specific surface area determined by a nitrogen adsorption method 1100~2200m ² / g, more preferably 1500~2200m ² / g, particularly preferably 1800~2100m ² / g. If the BET specific surface area of the activated carbon is less than 1100 m ² / g, the total pore volume is small, so the mobility of electrolyte ions at low temperatures is lowered, and the charge / discharge characteristics at low temperatures are likely to be low. On the other hand, if it exceeds 2200 m ² / g, the electrode density is lowered, and the capacitance per volume (F / cm ³ ) required as an electric double layer capacitor tends to be lowered.

The tap density (50 taps) of the activated carbon of the present invention is preferably 0.35 to 0.70 g / cm ³ , and the powder resistance is preferably 1.0 MPa and 0.4 Ωcm or less. The tap density can be measured with a tap density meter (manufactured by Kuramochi Scientific Instruments).

(2) Manufacturing method of activated carbon Although the manufacturing method of the activated carbon of this invention is not restrict | limited in particular, As a suitable manufacturing method,
(A) The pitch is carbonized in the presence of a compound Z containing any element of Group 4 to Group 11 of Periodic Table 4 or Group 5 of Periodic Table 5 of Periodic Table having an element concentration of 7000 ppm or more. To obtain a graphitizable carbonized product having a true density of 1.44 to 1.52 g / cm ³ , subjecting the mixture to an activation treatment in the presence of an alkali metal compound, and then washing the activated mixture. A method for producing activated carbon containing,
(B) The pitch is carbonized to obtain an easily graphitizable carbonized product having a true density of 1.44 to 1.52 g / cm ³ , and the carbonized product has a periodic table in the periodic table 4th period 2nd in the periodic table having an element concentration of 7000 ppm or more. A compound Z containing any element of Group 11 to Group 11 or Group 5 element of the 5th period is mixed to obtain a mixture, and the mixture is activated in the presence of an alkali metal compound. And a method for producing activated carbon including washing the mixture.

  The electrical characteristics of activated carbon are greatly influenced by structural characteristics such as specific surface area, pore distribution, and crystal structure of activated carbon. Such structural characteristics of activated carbon are determined by the structure of raw materials, carbonization conditions, and activation conditions. Therefore, in order to obtain activated carbon useful as an electrode material, it is necessary to optimize the raw material structure, carbonization conditions, and activation conditions.

The pitch used in the method for producing activated carbon of the present invention is preferably a low softening point pitch. The pitch includes petroleum-based pitch, coal-based pitch, and their organic solvent-soluble components. In the present invention, organic solvent-soluble components of petroleum pitch and coal pitch are particularly preferably used.
Such a component has fewer side chains than the non-graphitizable carbon material, has a high ratio of aromatic compounds, and contains polycyclic aromatic compounds of various molecular structures. It is considered that the activated carbon is derived from a polycyclic aromatic compound and forms various complicated microcrystalline structures and the like, thereby exhibiting excellent electrical characteristics.
The pitch used in the present invention has a softening point of preferably 100 ° C. or lower, more preferably 60 ° C. to 90 ° C.

In the present invention, in the pre-stage or post-stage of the above-mentioned carbonization, the compound Z containing any element of Group 4 to Group 11 of the periodic table or Group 4 element of Period 5 is used as the metal element concentration. Mix more than 7000ppm.
As the compound Z, any of a simple metal, an inorganic compound, and an organic compound can be used. Examples of inorganic compounds include oxides, hydroxides, chlorides, bromides, iodides, fluorides, phosphates, carbonates, sulfides, sulfates and nitrates. Examples of the organic compound include organometallic complexes with acetylacetone and cyclopentadiene.

  The compound Z is preferably a compound containing at least one element selected from the group consisting of calcium, titanium, manganese, iron, cobalt, nickel, copper, and zirconium. Specific examples include calcium oxide, titanium oxide, iron oxide, nickel oxide, and zirconium oxide. These compounds Z may be used alone or in combination of two or more.

  The method of mixing the compound Z with pitch or an easily graphitizable carbonized product obtained by carbonizing and heat treating it is not particularly limited as long as it can be uniformly mixed. The powder of compound Z can be added to the graphitizable carbonized powder as a solid-solid and mixed with a stirrer. The apparatus used for mixing is not particularly limited as long as it can be uniformly mixed, such as a V-shaped mixer, a Henschel mixer, and a Nauter mixer.

  The pitch is carbonized by heat treatment to obtain an easily graphitizable carbonized product. The carbonization heat treatment is preferably performed at 400 ° C. or more and less than 600 ° C. and second heat treatment at 600 ° C. or more and less than 700 ° C. The heat treatment causes a thermal decomposition reaction, gas and light fractions are desorbed, and the residue is heavy. Condensation occurs and eventually solidifies. In the first heat treatment in this carbonization step, the micro bond state between the carbon atoms is almost determined. Further, the structure of the carbon crystallite determined in this carbonization step determines the basis of the structure of the activated carbon that is the final product.

If the heating temperature of the first heat treatment is less than 400 ° C., the thermal decomposition reaction is insufficient and carbonization is difficult to proceed. On the other hand, when the heat treatment temperature is 600 ° C. or higher, it becomes the same as the heating temperature of the second heat treatment, and it becomes difficult to obtain a stepwise heating effect.
In the first heat treatment, the rate of temperature rise is preferably 3 to 10 ° C./hr, and more preferably 4 to 6 ° C./hr. The holding time at the maximum temperature is preferably 5 to 20 hr, more preferably 8 to 12 hr.

If the heating temperature of the second heat treatment is less than 600 ° C., it becomes the same as the heating temperature of the first heat treatment, and it becomes difficult to obtain the heating effect by the second heat treatment. On the other hand, when the heat treatment temperature is 700 ° C. or higher, the microcrystalline structure portion similar to graphite is excessively formed, and alkali activation tends to be difficult.
In the second heat treatment, the rate of temperature rise is preferably 10 to 100 ° C./hr, and more preferably 40 to 80 ° C./hr. The holding time at the maximum temperature is preferably 1 to 20 hours, more preferably 1 to 12 hours.

  It is also effective to carry out these carbonization steps in an alkali metal vapor. The alkali metal acts as a catalyst in the carbonization process. That is, the cross-linking between aromatics in the pitch is promoted, and the carbonization reaction proceeds.

The graphitizable carbonized product obtained by carbonization of pitch preferably has a true density of 1.44 to 1.52 g / cm ³ by a liquid phase substitution method. When the true density is less than 1.44 g / cm ^3, many functional groups remain on the activated carbon surface after alkali activation, and thus durability and reliability may be lowered when used as a capacitor material. On the other hand, when the true density is larger than 1.52 g / cm ³ , the alkali activation reaction is hardly performed, and activated carbon having a high electric capacity may not be obtained.

  In a graphitizable carbonized product in which a microcrystalline structure part similar to graphite is formed, there are many gaps between the layers formed by the metal potassium generated by reducing KOH during the alkali activation reaction. The Therefore, when the capacitor voltage is applied, the electrolyte ions (solvated ion radius 3.7 半径) intercalate the gaps between the carbon layers of 3.35 to 4.0Å, and are adsorbed in the pores. Therefore, it is estimated that a high electric capacity can be exhibited. On the other hand, in a graphitizable carbonized material in which a microcrystalline structure portion similar to graphite is not formed, pores formed due to consumption of carbon by water or carbon dioxide gas during an alkali activation reaction are increased, which is caused by metal potassium. There are fewer gaps between the carbon layers, and fewer can exhibit high electric capacity.

  The graphitizable carbonized material obtained as described above is preferably pulverized to an average particle size of 1 to 30 μm before alkali activation. The pulverization method may be a normal pulverization method such as a jet mill, a vibration mill, or a balberizer.

  By mixing and heating an easily graphitizable carbonized material pulverized to a particle size of 1 to 30 μm with an alkali metal compound, pores can be formed to obtain activated carbon. When alkali-activated without easily pulverizing the graphitizable carbonized material, it becomes difficult to wash the metal impurities contained in the activated carbon to reduce the metal impurities in the activated carbon after activation. Mixing in activated carbon may adversely affect the durability of the capacitor.

As described above, an easily activated graphitizable carbonized product obtained by carbonizing pitch in the presence of compound Z or a mixture obtained by carbonizing pitch and then mixing compound Z is subjected to an alkali activation reaction, thereby performing a nitrogen adsorption method. The peak D value of the pore volume with a pore diameter of 1.0 to 1.5 nm determined by the BJH method is 0.012 to 0.050 cm ³ / g, preferably 0.020 to 0.035 cm ³ / g. Furthermore, the peak a, peak b, peak c and peak d of the pore volume are 2.1 to 2.4 nm, 1.7 to 2.1 nm, 1.4 to 1.7 nm and 1.1 to 1. The area (area d, area c, area of the portion that is in the range of 4 nm and surrounded by the peak curve of each of peak d, peak c, peak b, and peak a, each pore diameter range, and pore diameter axis) b and area a) are surfaces Activated carbon having an area d of 3.7 to 4.8, an area c of 1.6 to 2.3, and an area b of 1.6 to 2.1, where the product a is 1.
Or the pore volume peak a, peak b, peak c, peak d, peak e and peak f are 2.1 to 2.4 nm, 1.7 to 2.1 nm, 1.4 to 1.7 nm, 1.1. -1.4 nm, 0.8-1.1 nm and 0.4-0.8 nm, respectively, and peak curves of peak f, peak e, peak d, peak c, peak b, peak a, respectively When the area (area f, area e, area d, area c, area b, and area a) of the portion surrounded by each pore diameter range and the pore diameter axis is area a, the area f is 2.2 to 2.5, area e is 2.3 to 2.5, area d is 4.6 to 4.8, area c is 2.1 to 2.3, and area b is 1.9 to 2 Activated carbon in the range of .1 can be obtained.

The alkali metal compound used for the alkali activation reaction is not particularly limited, but a hydroxide is preferable. Specifically, sodium hydroxide, potassium hydroxide, cesium hydroxide and the like are preferable. The maximum temperature during the activation treatment is usually in the range of 600 ° C to 800 ° C, and preferably in the range of 700 ° C to 760 ° C.
If the maximum temperature during the activation process becomes too high, the amount of metal (for example, K) that enters the carbon layer during activation of the alkali (for example, KOH) increases too much, and the metal that remains in the activated carbon after the activation (for example, K) ) Increases in quantity and tends to adversely affect the reliability of the electric double layer capacitor. On the other hand, if the maximum temperature during the activation treatment is too low, the alkali activation reaction does not proceed, so that it becomes difficult to obtain activated carbon having a desired specific surface area and electric capacity.

  The holding time at the maximum temperature during the activation process is preferably within 30 minutes. If the holding time at the maximum temperature is too long, the pore peaks a, b, c, and d (FIG. 2) tend to disappear, and as a result, the charge / discharge characteristics and internal resistance characteristics at low temperatures tend to deteriorate. Become. Note that the temperature does not have to be strictly constant at the maximum temperature during the holding time, and there may be some fluctuation within the range of the maximum temperature.

After holding at the maximum temperature as described above, cool. In the manufacturing method of this invention, it is preferable to make the temperature-fall rate at the time of cooling from the maximum temperature at the time of an activation process to 590 degreeC more than 60 degreeC / hr. If the rate of temperature decrease is too slow, the pore peaks a, b, c, and d (FIG. 2) of the activated carbon of the present invention tend to disappear, and as a result, the charge / discharge characteristics and internal resistance characteristics at low temperatures tend to decrease.
The above alkali activation treatment conditions are any of the batch type vertical reactor, roller hearth kiln type continuous furnace, trayscher type continuous furnace, tunnel kiln type continuous production furnace, rotary kiln type moving bed type reactor, etc. It can also be applied to other manufacturing apparatuses.

  The alkali metal compound is mixed in an amount of usually 1.5 to 5.0 times, more preferably 1.7 to 3.0 times the mass of the carbonaceous material.

The alkali activation treatment is performed in an inert gas atmosphere such as N ₂ or Ar gas, but water vapor, carbon dioxide gas or the like may be introduced as necessary.

  In the event that the melt of the reactant foams or bumps due to the gas generated during alkali activation (melt expansion), vapor-grown carbon fiber is added to the graphitizable carbonized material to suppress the phenomenon. You can also

After the alkali activation treatment, washing is performed with water, acid or the like.
For the acid cleaning, mineral acids such as sulfuric acid, phosphoric acid, hydrochloric acid and nitric acid, and organic acids such as formic acid, acetic acid and citric acid can be used. Hydrochloric acid and citric acid are preferred from the standpoint of washing efficiency and residue. The acid concentration is usually from 0.01 to 20 N, preferably from 0.1 to 1 N. As a washing method, stirring may be performed after addition of the acid, but washing efficiency is improved by boiling or heating at 50 to 90 ° C. It is more effective to use an ultrasonic cleaner.

The washing time is 0.5 to 24 hours, preferably 1 to 5 hours.
The number of washings is preferably about 1 to 5 times for boiling acid washing and about 1 to 5 times for hot water boiling washing for removing residual chlorine. The container used for cleaning is preferably glass lining, tantalum, Teflon (registered trademark) or the like in the case of acid cleaning.

  Further, a fully automatic stirring and warming filter dryer such as a multi-function filter WD filter (manufactured by Nissen), an FV dryer (manufactured by Okawara Seisakusho) or the like can be used for these washing steps. The water used for the cleaning uses pure water having an ionic electrical conductivity of 1.0 μS / cm or less, and the cleaning waste liquid in the process can be recycled and used for these cleaning waters.

The alkali-activated activated carbon thus obtained had characteristics that it exhibited a high electric capacity from the first cycle without giving an excessive voltage and had a high retention rate of the electric capacity.
Furthermore, when the graphitizable carbonized product undergoes a sufficient carbonization step, the amount of functional groups on the carbon surface is reduced, and deterioration of electric capacity is suppressed.

(2) Activated carbon (carbon composite powder) containing vapor grown carbon fiber
A further improvement in characteristics can be achieved by blending vapor grown carbon fiber with the activated carbon of the present invention. The method of blending the vapor grown carbon fiber with the activated carbon is not particularly limited, but the carbon composite powder composed of the vapor grown carbon fiber and the activated carbon is obtained by mixing and activating the vapor grown carbon fiber with the graphitizable carbonized product. It is preferable to do. By this method, the contact resistance between particles is reduced, the conductivity and the electrode strength are improved, and the effect of reducing the electrode expansion coefficient when a voltage is applied is also exhibited. Moreover, it can also be set as carbon composite powder by the method of mixing vapor grown carbon fiber with activated carbon. By using carbon composite powder, the thermal conductivity is improved as compared with the case of activated carbon alone.

  The vapor grown carbon fiber blended with the activated carbon can be produced, for example, by spraying benzene and metal catalyst particles at about 1000 ° C. in a hydrogen stream. As the vapor grown carbon fiber, it is possible to use a carbon fiber obtained by the above-described production method and then calcined at 1000 to 1500 ° C. or graphitized at a temperature of 2500 ° C. or higher.

The vapor grown carbon fiber preferably has a hollow structure inside, a specific surface area of 10 to 50 m ² / g, an average fiber diameter of 50 to 500 nm, and an aspect ratio of 5 to 1000. As the vapor grown carbon fiber, any of a branched fiber, a straight chain, or a mixture thereof can be used.

  The vapor grown carbon fiber preferably has a fiber length in the range of 0.5 to 2 times the average particle diameter of the activated carbon. If the length of the vapor grown carbon fiber is shorter than 0.5 times, the particles may not be bridged with each other and the conductivity may be insufficient. If the length exceeds 2 times, the gas phase is formed in the gap between the activated carbon particles. There is a possibility that the strength of the polarizable electrode may be reduced due to the absence of the carbon fiber.

Vapor-grown carbon fiber has a concentric circular orientation structure, so gas activation (steam, CO ₂ etc.), chemical activation (zinc chloride, phosphoric acid, calcium carbonate etc.), alkali activation (potassium hydroxide, water) It is also possible to use a material activated in advance with sodium oxide or the like. In this case, it is preferable to control the surface structure so that the micropore volume (pores of 2.0 nm or less) is 0.01 to 0.4 cm ³ / g and the BET specific surface area is 10 to 500 m ² / g. . If the micropore volume is too large, the ion diffusion resistance inside the electrode may increase, which may be undesirable.

The amount of vapor grown carbon fiber is preferably 0.02 to 20% by mass, more preferably 0.1 to 20% by mass, and particularly preferably 0.5 to 10% by mass with respect to the activated carbon. If it is less than 0.02% by mass, the effect of increasing the thermal conductivity of the composite powder mixed with the graphitizable carbonized material is small, and the heat uniformity during activation becomes insufficient, making uniform activation difficult. The activated carbon having a large capacitance per volume (F / cm ³ ) and excellent quality stability may be difficult to industrially produce. If it exceeds 20% by mass, the electrode density is lowered, and the electric capacity per volume (F / cm ³ ) may be lowered.

In addition to improving the heat conductivity by utilizing the good conductivity and heat conduction of vapor grown carbon fiber, the role as an electrode expansion cushion material due to the mixture of fibrous materials in the bulk activated carbon particles is enhanced, so the voltage It is also effective in suppressing an increase in the electrode expansion coefficient during application.
The activated carbon of the present invention can be suitably used for polarizable electrodes and electric double layer capacitors.

(3) Polarizable electrode and electric double layer capacitor The polarizable electrode of the present invention contains the activated carbon of the present invention, carbon black, and a binder, and preferably further contains vapor grown carbon fiber. is there.
As the carbon black used for the polarizable electrode of the present invention, a carbon material known as a conductive material used for an electrode of an electrochemical element can be used. Examples thereof include acetylene black, channel black, and furnace black. The amount of carbon black is usually 0.1 to 20 parts by mass, preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the polarizable electrode.

  The vapor grown carbon fiber is as described above. In addition to the method of mixing vapor grown carbon fiber, activated carbon, carbon black, and binder, as a method of incorporating the vapor grown carbon fiber into the polarizable electrode, the carbon composite powder described above is mixed with carbon black and the binder. There is a way to mix.

  A polarizable electrode is usually a method in which a conductive agent and a binder are added to activated carbon and kneaded and rolled; a conductive agent, a binder and, if necessary, a solvent are added to activated carbon, and then applied to a conductive material in a slurry or paste form. Method: It can be produced by a method in which uncarbonized resins are mixed with activated carbon and sintered.

  For example, carbon black or the like is added as a conductive agent to the activated carbon powder of the present invention having an average particle size of 1 to 50 μm, and a binder such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride, acrylate rubber, or butadiene rubber is added. In addition, dry blending is performed with a blender, and then an organic solvent having a boiling point of 200 ° C. or lower is added to the mixed powder to swell and knead to form a sheet having a thickness of about 0.1 to 0.5 mm. A polarizable electrode can be obtained by vacuum drying at a temperature of about 0C.

  The organic solvent is not particularly limited as long as it is an organic solvent having a boiling point of 200 ° C. or lower. Examples thereof include hydrocarbons such as toluene, xylene and benzene, ketones such as acetone, methyl ethyl ketone and butyl methyl ketone, alcohols such as methanol, ethanol and butanol, esters such as ethyl acetate and butyl acetate, and the like. Of these, toluene, acetone, and ethanol are preferred. Use of an organic solvent having a boiling point of 200 ° C. or higher is not preferable because the organic solvent remains in the sheet when dried at 100 to 200 ° C. after the sheet is formed.

  This sheet is punched into a predetermined shape and used as an electrode. A metal plate as a current collector is laminated on this electrode, two metal plates are stacked with a separator interposed therebetween, and immersed in an electrolytic solution to form an electric double layer capacitor.

As the electrolytic solution of the electric double layer capacitor, any known non-aqueous solvent electrolyte solution or water-soluble electrolyte solution can be used, and in addition to other electrolyte solutions, polymer solid electrolytes and polymers that are non-aqueous electrolytes Gel electrolytes and ionic liquids can also be used.
Examples of the aqueous (water-soluble electrolyte solution) include sulfuric acid aqueous solution, sodium sulfate aqueous solution, sodium hydroxide aqueous solution and the like.

In addition, as a non-aqueous (non-aqueous solvent electrolyte solution), a cation (R ¹ , R ² , R ³⁾ represented by R ¹ R ² R ³ R ⁴ N ⁺ or R ¹ R ² R ³ R ⁴ P ⁺ , R ⁴ are each independently an alkyl group or an allyl group having 1 to 10 carbon atoms) and an anion such as BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ^−, or the like. Examples of the electrolyte include those using a carbonate non-aqueous solvent such as ethylene carbonate and propylene carbonate as a solvent. In addition, two or more electrolytes or solvents can be used in combination.

  The separator interposed between the electrodes as needed may be a porous separator that transmits ions, such as a microporous polyethylene film, a microporous polypropylene film, an ethylene nonwoven fabric, a polypropylene nonwoven fabric, and a glass fiber mixed nonwoven fabric. It can be preferably used.

  The electric double layer capacitor of the present invention is a coin type housed in a metal case together with an electrolyte through a separator between a pair of sheet electrodes, a winding type formed by winding a pair of positive and negative electrodes through a separator, Any configuration such as a stacked type in which a large number of sheet-like electrodes are stacked via a separator can be used.

  The electric double layer capacitor of the present invention can be applied to a power supply system. And this power supply system includes: a power supply system for vehicles such as automobiles and railways; a power supply system for ships; a power supply system for aircraft; a power supply system for portable electronic devices such as mobile phones, personal digital assistants and portable electronic computers; System: Power supply system for power generation system such as solar cell power generation system, wind power generation system; communication device, electronic tag, etc.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples.
The measuring method of each characteristic in this example and the manufacturing method of the electrode and the electric double layer capacitor are as follows.

[Measurement of BET specific surface area and pore volume]
Using a NOVA1200 manufactured by Quantachrome, the BET method and the BJH method were calculated from an adsorption isotherm of nitrogen at a liquid nitrogen temperature (77.4 K).

[Production of electrodes]
10 parts by mass of PTFE (polytetrafluoroethylene) and 10 parts by mass of carbon black were added to 80 parts by mass of activated carbon having an average particle size of 10 μm, kneaded and rolled into a sheet having a thickness of 0.5 mm. This sheet was punched into a disk having a diameter of 20 mm, and vacuum-dried at 200 ° C. overnight to obtain a polarizable electrode.

[Assembly of electric double layer capacitor]
An evaluation cell as shown in FIG. 1 was assembled in a glove box in which high purity argon was circulated through the electrode. In FIG. 1, 1 is an aluminum top cover, 2 is a fluororubber O-ring, 3 is a current collector made of aluminum, 4 is an insulating material made of Teflon (registered trademark), 5 is an aluminum container, and 6 is aluminum. A leaf spring, 7 is a polarizable electrode, and 8 is a 1 mm thick separator made of glass fiber.
In the electrolytic solution, PC (propylene carbonate) is used as a solvent, (CH ₃ ) (C ₂ H ₅ ) ₃ NBF ₄ , (C ₂ H ₅ ) ₄ NBF ₄ is 1 mol / liter, or EC / DEC (ethylene carbonate / diethylene). An electrolytic solution manufactured by Toyama Pharmaceutical Co., Ltd. was used with carbonate as a solvent and LiBF ₄ and LiPF ₆ as 1 mol / liter electrolyte.

[Charge / discharge measurement]
The charge / discharge measurement was performed using a charge / discharge test apparatus HJ-101SM6 manufactured by Hokuto Denko Co., Ltd., and charged and discharged at 0 mA to 2.7 V at 5 mA. From the discharge curve obtained by the second constant current discharge, The capacitance per mass (F / g) and the capacitance per volume (F / cm ³ ) of the bipolar activated carbon of the electric double layer capacitor were calculated.

Example 1:
The first carbonization treatment was performed by heating the coal-based pitch at 500 ° C. in a nitrogen atmosphere. Next, as a second carbonization treatment, carbonization treatment was performed at 630 ° C. for 1 hour to obtain a raw material carbide having a true density of 1.47 [g / cm ³ ]. The obtained raw material carbide was pulverized until the particle size became 0.5 mm or less.

10 [g] of water was added to 71.5 [mg] of ferric trioxide, which is a compound containing a fourth periodic group 8 element, to obtain an iron oxide slurry. The raw material carbide 5.0 [g] was added to this iron oxide slurry and mixed well to prepare a raw material carbide / iron oxide mixed slurry. The obtained mixed slurry was dried at 110 ° C. overnight to obtain a mixture of raw material carbide and iron oxide.
A raw material carbide / iron oxide mixture 5 [g] and potassium hydroxide (95%) 15.7 [g] were charged in a nickel container (φ = 40 mm) and placed in a batch type activation reactor. The inside of the activation reaction furnace was replaced with nitrogen, and then the temperature increase was started. While the reaction furnace was heated, nitrogen gas was bubbled into water at 50 ° C. at a flow rate of 0.5 [L / min], and nitrogen was supplied into the reaction furnace along with saturated steam.

In the activation reaction, the reactor temperature was raised from room temperature to 400 ° C. at a rate of 6.3 [° C./min], held at 400 ° C. for 30 minutes, and then up to 720 ° C. at a rate of 5.3 [° C./min]. The temperature was raised and held at 720 ° C. for 15 minutes. After the activation was completed, the temperature of the reactor was decreased from 720 ° C. to 590 ° C. at 350 ° C./hr (about 22 minutes), and further cooled to room temperature over about 98 minutes.
The activated carbon taken out from the reactor was filtered and washed with water to remove alkali components. Next, by boiling and washing with 0.1 mol / L hydrochloric acid at 100 ° C., metal impurities such as iron and nickel adhering to the activated carbon were dissolved and removed. Next, the activated carbon was repeatedly subjected to boiling washing treatment with hot water at 100 ° C. and filtration / water washing treatment to reduce the residual chlorine of the activated carbon to 10 ppm or less, and the obtained activated carbon was dried at 110 ° C. overnight.
The obtained activated carbon had a BET specific surface area of 1960 [m ² / g], and the pore volume distribution determined by the BJH method was as shown in FIG.

  As shown in FIG. 2, the peak a is in the range of pore diameter 2.1 to 2.4 nm, the peak b is in the range of pore diameter 1.7 to 2.1 nm, and the peak b is in the range of pore diameter 1.4 to 1.7 nm. It can be seen that the peak c has a peak d in the pore diameter range of 1.1 to 1.4 nm. The area (area a, area b, area c and area d) of the portion surrounded by the peak curve of each of peak a, peak b, peak c and peak d, each pore diameter range and the pore diameter axis is expressed as area a. When 1, the area d was 3.90, the area c was 1.66, and the area b = 1.66.

Compared with Comparative Example 1 in which the metal compound was not added to the raw material carbide, the effect of controlling the pore volume distribution by adding ferric trioxide is recognized.
(C ₂ H ₅ ) ₄ BF ₄ system / PC system electrolyte solution has an electrode capacity of 27.7 F / cm ³ at 25 ° C. during charge / discharge of 2.7 V, and an electrode capacity at −30 ° C. of 24.5 F / cm ^{3. 3} . The capacity retention ((−30 ° C. electrode capacity) / (25 ° C. electrode capacity)) was 0.88.

Example 2:
The first carbonization treatment was performed by heating the coal-based pitch at 500 ° C. in a nitrogen atmosphere. Next, as a second carbonization treatment, carbonization treatment was performed at 630 ° C. for 1 hour to obtain a raw material carbide having a true density of 1.47 [g / cm ³ ]. The obtained raw material carbide was pulverized until the particle size became 0.5 mm or less.

10 [g] of water was added to 62.2 [mg] of copper oxide, which is a compound containing the fourth group 11 element, to obtain a copper oxide slurry. The raw material carbide 5.0 [g] was added to this copper oxide slurry and mixed well to prepare a raw material carbide / copper oxide mixed slurry. The resulting mixed slurry was dried at 110 ° C. overnight to obtain a raw material carbide / copper oxide mixture.
A raw material carbide / copper oxide mixture 5 [g] and potassium hydroxide (95%) 15.7 [g] were charged into a nickel container (φ = 40 mm) and placed in a batch type activation reactor. The inside of the activation reaction furnace was replaced with nitrogen, and then the temperature increase was started. While the reaction furnace was heated, nitrogen gas was bubbled into water at 50 ° C. at a flow rate of 0.5 [L / min], and nitrogen was supplied into the reaction furnace along with saturated steam.

In the activation reaction, the reactor temperature was raised from room temperature to 400 ° C. at a rate of 6.3 [° C./min], held at 400 ° C. for 30 minutes, and then up to 720 ° C. at a rate of 5.3 [° C./min]. The temperature was raised and held at 720 ° C. for 15 minutes. After the activation was completed, the temperature of the reactor was decreased from 720 ° C. to 590 ° C. at 350 ° C./hr (about 22 minutes), and further cooled to room temperature over about 98 minutes.
The activated carbon taken out from the reactor was filtered and washed with water to remove alkali components. Next, by boiling and washing with 0.1 mol / L hydrochloric acid at 100 ° C., metal impurities such as copper and nickel adhering to the activated carbon were dissolved and removed. Next, the activated carbon was repeatedly subjected to boiling washing treatment with hot water at 100 ° C. and filtration / water washing treatment to reduce the residual chlorine of the activated carbon to 10 ppm or less, and the obtained activated carbon was dried at 110 ° C. overnight.
The obtained activated carbon had a BET specific surface area of 1707 [m ² / g], and the pore volume distribution determined by the BJH method was as shown in FIG.

As shown in FIG. 2, the peak a is in the range of pore diameter 2.1 to 2.4 nm, the peak b is in the range of pore diameter 1.7 to 2.1 nm, and the peak b is in the range of pore diameter 1.4 to 1.7 nm. It can be seen that the peak c has a peak d in the pore diameter range of 1.1 to 1.4 nm. The area (area a, area b, area c and area d) of the portion surrounded by the peak curve of each of peak a, peak b, peak c and peak d, each pore diameter range and the pore diameter axis is expressed as area a. When 1, the area d was 4.41, the area c was 1.91, and the area b = 1.87.
Compared with the comparative example in which the metal compound was not added to the raw material carbide, the effect of controlling the pore volume distribution by adding copper oxide is recognized.
(C ₂ H ₅ ) ₄ BF ₄ system / PC system electrolyte solution has an electrode capacity of 27.1 F / cm ³ at 25 ° C. during charge / discharge of 2.7 V, and an electrode capacity of −33.9 F / cm at −30 ° C. ³ . The capacity retention ((−30 ° C. electrode capacity) / (25 ° C. electrode capacity)) was 0.88.

Example 3:
The first carbonization treatment was performed by heating the coal-based pitch to 500 ° C. in a nitrogen atmosphere. Next, as a second carbonization treatment, carbonization treatment was performed at 630 ° C. for 1 hour to obtain a raw material carbide having a true density of 1.47 [g / cm ³ ]. The obtained raw material carbide was pulverized until the particle size became 0.5 mm or less.
10 [g] of water was added to 83.2 [mg] of titanium dioxide, which is a compound containing the fourth periodic group 4 element, to obtain a titanium dioxide slurry. The raw material carbide 5.0 [g] was added to the titanium dioxide slurry and mixed well to prepare a raw material carbide / titanium dioxide mixed slurry. The obtained mixed slurry was dried at 110 ° C. overnight to obtain a mixture of raw material carbide / titanium dioxide.
A raw material carbide / titanium dioxide mixture 5 [g] and potassium hydroxide (95%) 15.7 [g] were charged into a nickel container (φ = 40 mm) and placed in a batch type activation reactor. The inside of the activation reaction furnace was replaced with nitrogen, and then the temperature increase was started. While the reaction furnace was heated, nitrogen gas was bubbled into water at 50 ° C. at a flow rate of 0.5 [L / min], and nitrogen was supplied into the reaction furnace along with saturated steam.

In the activation reaction, the reactor temperature was raised from room temperature to 400 ° C. at a rate of 6.3 [° C./min], held at 400 ° C. for 30 minutes, and then up to 720 ° C. at a rate of 5.3 [° C./min]. The temperature was raised and held at 720 ° C. for 15 minutes. After completion of activation, the temperature of the reactor was decreased from 720 ° C. to 590 ° C. at 350 ° C./hr (about 22 minutes), and further cooled to room temperature over about 98 minutes.
The activated carbon taken out from the reactor was filtered and washed with water to remove alkali components. Subsequently, metal impurities such as titanium and nickel adhering to the activated carbon were dissolved and removed by boiling and washing with 0.1 mol / L hydrochloric acid at 100 ° C. Next, the activated carbon was repeatedly subjected to boiling washing treatment with hot water at 100 ° C. and filtration / water washing treatment to reduce the residual chlorine of the activated carbon to 10 ppm or less, and the obtained activated carbon was dried at 110 ° C. overnight.
The obtained activated carbon had a BET specific surface area of 1707 [m ² / g], and the pore volume distribution determined by the BJH method was as shown in FIG.

  As shown in FIG. 2, it has a peak a in the pore diameter range of 2.1 to 2.4 nm, a peak b in the pore diameter range of 1.7 to 2.1 nm, and a pore diameter of 1.4 to 1.7 nm. Having a peak c in the range of pore diameter 1.1 to 1.4 nm, a peak e in the range of pore diameter 0.8 to 1.1 nm, and a pore diameter of 0.4 A portion having a peak f in a range of ˜0.8 nm and surrounded by a peak curve of each of peak a, peak b, peak c, peak d, peak e, and peak f, each pore diameter range, and a pore diameter axis Area (area a, area b, area c, area d, area e, and area f) where area a is 1, area f is 2.4, area e is 2.38, and area d is 4 0.73, area c was 2.21, and area b was 2.03.

Compared with the comparative example in which the metal compound was not added to the raw material carbide, the effect of controlling the pore volume distribution by adding titanium dioxide is recognized.
(C ₂ H ₅ ) ₄ BF ₄ system / PC system electrolyte solution has an electrode capacity of 24.9 F / cm ³ at 25 ° C. during charge / discharge of 2.7 V, and an electrode capacity at −30 ° C. of 23.2 F / cm ^{3. 3} . The capacity retention ((−30 ° C. electrode capacity) / (25 ° C. electrode capacity)) was 0.93.

Comparative Example 1:
Commercially available alkali-activated activated carbon MSP-20 (manufactured by Kansai Heat Chemical Co., Ltd.) using phenol resin as a raw material was used as a sample. The specific surface area of this activated carbon was 2210 m ² / g. After 9% by mass of carbon black and 10% by mass of PTFE are dry-mixed with respect to the activated carbon, an organic solvent is added to the mixed powder to swell, knead, roll, and vacuum dry at 200 ° C. to obtain an electrode material. Produced. (C ₂ H ₅ ) ₄ NBF ₄ / PC system 2.5 V charge / discharge electric capacity (25 ° C.) 39.2 F / g, 24.3 F / cm ³ , capacity retention ratio ((−30 ° C. electrode (Capacity) / (electrode capacity at 25 ° C.)) was 0.61. The pore distribution of the activated carbon is shown in FIG.

Example 4:
The first carbonization treatment was performed at 560 ° C on a coal pitch having a softening point of 86 ° C. Next, the second carbonization treatment was performed at 630 ° C. to obtain a graphitizable carbonized product. 25 g of calcium carbonate powder was added to 1000 g of the easily graphitizable carbonized material (average particle size after pulverization 3.5 μm) and mixed for 60 seconds with a Henschel mixer. The mixed carbon powder was mixed with 2.8 times the mass KOH fine powder by a ball mill and filled in a Ni container (300 mm × 300 mm × 3 t × height 10 mm). The vessel was heat-treated in a batch activation furnace (split heating furnace, manufactured by Fuji Denpa Kogyo). The activation conditions were as follows: the temperature was raised at a rate of temperature increase of 5 ° C./min in an N ₂ atmosphere, held at 400 ° C. for 30 minutes, further raised to the maximum activation temperature of 720 ° C. and held for 15 minutes, and then from 720 ° C. to 590 ° C. The temperature was lowered to 80 ° C./hr (about 98 minutes). Furthermore, the temperature in the furnace was lowered to 100 ° C. or lower under an N ₂ atmosphere, and the Ni container was taken out from the furnace into the air. The reaction product (activated carbon powder is hereinafter referred to as activated carbon) was neutralized with 1N hydrochloric acid, and boiled and washed twice with 0.1N hydrochloric acid to remove metal impurities. Next, boiling boiling was performed twice with distilled water to remove residual Cl and metal impurities. This was dried with hot air at 110 ° C., and activated carbon having an average particle size of 4.6 μm was obtained through a 330 mesh sieve and a magnetic separator (magnetic force 12000 G).

This activated carbon had a specific surface area of 2020 m ² / g and a pore volume of 0.033 cc / g with a pore diameter of 10 to 15 mm. Carbon black 9 mass% and PTFE (polytetrafluoroethylene) 10 mass% were dry-mixed with respect to the activated carbon. An organic solvent was added to the dry mixed powder to swell, then kneaded, rolled, and vacuum dried at 200 ° C. to produce an electrode material. (C ₂ H ₅ ) ₄ NBF ₄ system / PC system electrolyte at 2.5V charge / discharge at 25 ° C. is 41.0 F / g, 23.8 F / cm ³ , at −30 ° C. low temperature The capacity was 22.1 F / cm ³ and the capacity retention was 93%. The pore distribution of the activated carbon was as shown in FIG.

Example 5:
3% by mass of calcium carbonate was added to a coal pitch having a softening point of 86 ° C., and a first carbonization treatment was performed at 560 ° C. (temperature increase rate: 5 ° C./hr, retention time at 560 ° C .: 10 hours). Subsequently, a second carbonization treatment (temperature increase rate: 50 ° C./hr, holding time at 640 ° C .: 1 hour) was performed at 640 ° C. to obtain an easily graphitizable carbonized product. To 1000 g of this graphitizable carbonized product (average particle diameter after grinding: 3.5 μm), KOH fine powder of 3.0 times the mass ratio is added and mixed with a ball mill, and a Ni container (600φ × 3t × height 1050 mm) ). The container was heat-treated in a continuous activation furnace (Roller Hearth Kiln, manufactured by Noritake Company). The activation conditions were as follows: the temperature was increased at a rate of temperature increase of 5 ° C./min in an N ₂ atmosphere, the temperature was maintained at 400 ° C. for 30 minutes, the temperature was further increased to the maximum activation temperature of 740 ° C. and held for 15 minutes, The temperature was decreased from 740 ° C. to 590 ° C. at 280 ° C./hr (about 32 minutes). The temperature in the furnace was lowered to 100 ° C. or lower under an N ₂ atmosphere, and the Ni container was taken out of the furnace into the air. The reaction product (activated carbon powder is hereinafter referred to as activated carbon) was neutralized with 1N-hydrochloric acid, and washed with boiling with 0.1N-hydrochloric acid four times to remove metal impurities. Next, boiling boiling was performed 5 times with distilled water to remove residual Cl and metal impurities. This was dried with hot air at 110 ° C., and activated carbon having an average particle diameter of 4.5 μm was obtained through a 330 mesh sieve and a magnetic separator (magnetic force 12000 G).

The specific surface area of this activated carbon was 2030 m ² / g, and the peak value of the pore volume with a pore diameter of 1.0 to 1.5 nm was 0.034 cm ³ / g. Carbon black 9 mass% and PTFE (polytetrafluoroethylene) 10 mass% were dry-mixed with respect to the activated carbon. An organic solvent was added to the mixed powder to swell, then kneaded, rolled, and further vacuum dried at 200 ° C. to produce an electrode material. The capacitance of LiPF ₆ / EC / DEC electrolyte was 40.6 F / g and 23.6 F / cm ³ when charged and discharged at 2.5 V, and the capacity retention rate at low temperature of −30 ° C. was 85%. . The pore distribution of the activated carbon was as shown in FIG.

  As shown in Table 1 or Table 2, the pitch carbonized in the presence of the compound Z containing elements such as iron and copper is the pore determined by the BJH method from the nitrogen adsorption isotherm of 77.4K. The volume distribution has a peak a in the range of pore diameter 2.1 to 2.4 nm, a peak b in the range of pore diameter 1.7 to 2.1 nm, and a pore diameter of 1.4 to 1.7 nm. It has a peak c in the range, a peak d in the pore diameter range of 1.1 to 1.4 nm, a peak curve of each of peak a, peak b, peak c and peak d, and each pore size range When the area (area a, area b, area c, and area d) of the portion surrounded by the hole diameter axis is 1, the area d is 3.7 to 4.8 and the area c is 1. Activated carbon having 6 to 2.3 and area b in the range of 1.6 to 2.1 is obtained.

In addition, when carbonizing the pitch in the presence of the compound Z containing an element such as titanium, the pore diameter distribution is 2.1 to 2 in the pore volume distribution determined by the BJH method from the nitrogen adsorption isotherm of 77.4K. It has a peak a in the range of 0.4 nm, a peak b in the range of pore diameter 1.7 to 2.1 nm, a peak c in the range of pore diameter 1.4 to 1.7 nm, and a pore diameter of 1 .Has a peak d in the range of 1 to 1.4 nm, has a peak e in the range of pore diameters of 0.8 to 1.1 nm, and has a peak f in the range of pore diameters of 0.4 to 0.8 nm. , And the areas (area a, area b, area c, and the area surrounded by the peak curve of each of peak a, peak b, peak c, peak d, peak e, and peak f and each pore diameter range and pore diameter axis). Area d, area e, and area f) where area a is 1, area f is 2.2-2. Activated carbon having an area e of 2.3 to 2.5, an area d of 4.6 to 4.8, an area c of 2.1 to 2.3, and an area b of 1.9 to 2.1. It turns out that it is obtained.
And when such activated carbon is used, it turns out that the electrical double layer capacitor excellent in the capacity | capacitance retention under low temperature is obtained.

Sectional drawing of the electric double layer capacitor evaluation cell. The distribution diagram of the pore diameter of the activated carbon obtained in Examples 1 to 3 and Comparative Example 1. The distribution diagram of the pore diameter of the activated carbon obtained in Examples 4 and 5.

Explanation of symbols

1: O-ring; 2: O-ring; 3: Current collector; 4: Insulator; 5: Container; 6: Leaf spring; 7: Electrode; 8: Separator a: Peak a; b: Peak b; D: peak d

Claims (34)

  In the pore volume distribution determined by the BJH method from the nitrogen adsorption isotherm of 77.4K, it has a peak a in the pore diameter range of 2.1 to 2.4 nm, and the pore diameter is in the range of 1.7 to 2.1 nm. Having a peak b, having a peak c in the range of pore diameter 1.4 to 1.7 nm, having a peak d in the range of pore diameter 1.1 to 1.4 nm, and peak a, peak b, When the area (area a, area b, area c, and area d) of the portion surrounded by the peak curve of each of peak c and peak d, each pore diameter range and the pore diameter axis is area a is 1, Activated carbon having an area d of 3.7 to 4.8, an area c of 1.6 to 2.3, and an area b of 1.6 to 2.1.   In the pore volume distribution determined by the BJH method from the nitrogen adsorption isotherm of 77.4K, it has a peak a in the pore diameter range of 2.1 to 2.4 nm, and the pore diameter is in the range of 1.7 to 2.1 nm. It has a peak b, has a peak c in the pore diameter range of 1.4 to 1.7 nm, has a peak d in the pore diameter range of 1.1 to 1.4 nm, and has a pore diameter of 0.8 to 1. A peak e in the range of 1 nm, a peak f in the pore diameter range of 0.4 to 0.8 nm, and a peak curve of each of peak a, peak b, peak c, peak d, peak e and peak f When the area (area a, area b, area c, area d, area e, and area f) of the portion surrounded by each pore diameter range and the pore diameter axis is set to 1, the area f is 2.2 to 2.5, area e is 2.3 to 2.5, area d is 4.6 to 4.8, area c is 2.1 to 2.3, Activated carbon fine area b is in the range of 1.9 to 2.1. True density is obtained by carbonizing the pitch in the presence of a compound Z containing any element of Group 4 to Group 11 of Periodic Table 4 or Group 5 of Periodic Table 5 of Periodic Table having an element concentration of 7000 ppm or more. 1.44 to 1.52 g / cm ^{3 of} an easily graphitizable carbonized product is obtained, activated in the presence of an alkali metal compound, and the mixture is activated, and then the activated mixture is washed. Production method. The pitch is carbonized to obtain an easily graphitizable carbonized product having a true density of 1.44 to 1.52 g / cm ³ , and the carbonized product has an element concentration of 7000 ppm or more in the periodic table 4th periodic group 2nd to 4th periodic table. A compound Z containing any element of Group 11 or Group 5 element of 5th period is mixed to obtain a mixture, and the mixture is activated in the presence of an alkali metal compound. The manufacturing method of activated carbon including washing | cleaning.   The method for producing activated carbon according to claim 3 or 4, wherein the pitch has a softening point of 100 ° C or lower.   The method for producing activated carbon according to claim 3 or 4, wherein the pitch is coal-based pitch or petroleum-based pitch or an organic solvent-soluble component thereof.   The compound Z is a compound containing at least one element selected from the group consisting of calcium, titanium, manganese, iron, cobalt, nickel, copper, and zirconium. Method.   Compound Z is at least one compound selected from the group consisting of simple metals, oxides, hydroxides, chlorides, bromides, iodides, fluorides, phosphates, carbonates, sulfides, sulfates and nitrates. The method for producing activated carbon according to any one of claims 3 to 7.   The manufacturing method of the activated carbon in any one of Claims 3-8 which makes the maximum temperature at the time of an activation process into the range of 700 to 760 degreeC.   The manufacturing method of the activated carbon in any one of Claims 3-9 which makes holding time in the maximum temperature at the time of activation processing within 30 minutes.   The manufacturing method of the activated carbon in any one of Claims 3-10 which makes the temperature-fall rate at the time of cooling to 590 degreeC from the maximum temperature at the time of an activation process 60 degreeC / hr or more.   The method for producing activated carbon according to any one of claims 3 to 11, wherein the alkali metal compound is an alkali metal hydroxide.   The method for producing activated carbon according to any one of claims 3 to 12, wherein the alkali metal compound is a compound containing at least one metal element selected from the group consisting of potassium, sodium and cesium.   A polarizable electrode comprising the activated carbon according to claim 1 or 2, carbon black, and a binder.   A polarizable electrode comprising the activated carbon according to claim 1 or 2, vapor-grown carbon fiber, carbon black, and a binder.   The polarizable electrode according to claim 15, wherein the mixed amount of the vapor grown carbon fiber with respect to the activated carbon is 0.1 to 20% by mass. The vapor grown carbon fiber has a hollow structure therein, a specific surface area of 10 to 50 m ² / g, an average fiber diameter of 50 to 500 nm, and an aspect ratio of 5 to 1000. Polarized electrode.   The polarizable electrode according to any one of claims 14 to 17, wherein the binder is polytetrafluoroethylene, polyvinylidene fluoride, acrylate rubber or butadiene rubber.   The electric double layer capacitor using the polarizable electrode in any one of Claims 14-18.   A cation of an electrolyte ion using an electrolytic solution in which an electrolyte salt containing at least one selected from the group consisting of a quaternary ammonium salt, a quaternary imidazolium salt, a quaternary pyridinium salt, and a quaternary phosphonium salt is added to an organic solvent. The electric double layer capacitor according to claim 19, wherein the electric double layer capacitor has a diameter of 3 to 15 mm and an anion diameter of 5 to 10 mm.   A slurry containing the activated carbon according to claim 1 or 2.   A paste containing the activated carbon according to claim 1.   An electrode sheet on which the activated carbon according to claim 1 or 2 is applied.   A power supply system including the electric double layer capacitor according to claim 1.   An automobile using the power supply system according to claim 24.   A railway using the power supply system according to claim 24.   A ship using the power supply system according to claim 24.   An aircraft using the power supply system according to claim 24.   A mobile phone using the power supply system according to claim 24.   An office device using the power supply system according to claim 24.   A solar cell power generation system using the power supply system according to claim 24.   A wind power generation system using the power supply system according to claim 24.   A communication device using the power supply system according to claim 24.   An electronic tag using the power supply system according to claim 24.

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