JP2012235041A - Positive electrode and lithium-ion capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode which, when used for a power storage device, allows the power storage device to have high energy density and high capacity, and a lithium-ion capacitor having high energy density and high capacity.SOLUTION: The positive electrode comprises a positive electrode active material layer which has a BET specific surface area of 2400 to 3000 m/g inclusive and an electrode density of 0.41-0.49 g/cm. The lithium-ion capacitor comprises the positive electrode.

Description

  The present invention relates to a positive electrode and a lithium ion capacitor, and more particularly to a positive electrode suitable as a positive electrode of a lithium ion capacitor and a lithium ion capacitor provided with the positive electrode.

In recent years, lithium-ion capacitors have attracted attention as power storage devices that support applications that require high energy density and high output characteristics.
Since lithium ion capacitors are required to have higher performance, various proposals for higher performance have been made (for example, see Patent Document 1).

Specifically, in Patent Document 1, for the purpose of obtaining a high energy density and a high output density, as a positive electrode active material constituting the positive electrode, a pore volume having a pore radius of 1 to 40 mm has a total pore volume. It has been proposed to use activated carbon particles that are 80% or more and have a total pore volume of 0.4 to 1.5 cc / g.
However, in a lithium ion capacitor provided with a positive electrode using such activated carbon particles as a positive electrode active material, there is a problem that sufficient energy density and capacity cannot be increased.
The reason is that the positive electrode of the lithium ion capacitor has a structure in which, for example, a positive electrode active material layer containing a positive electrode active material is formed on a current collector, and the positive electrode active material layer is formed of a positive electrode active material and a binder. And, as necessary, additives such as a conductive agent and a thickener are formed by a method in which a slurry in which an additive is dispersed in an aqueous medium or an organic solvent is applied to a current collector, In the manufacturing process, the surface pores of the activated carbon particles constituting the positive electrode active material are covered or blocked by entering a binder and, if necessary, an additive such as a thickener, and the resulting positive electrode active material This is because the pore volume related to the activated carbon particles in the layer becomes small.
In the process of preparing a slurry for producing an electrode for an electric double layer capacitor, the surface fineness of a porous material such as activated carbon constituting the active material is improved for the purpose of improving the peel resistance of the active material layer. Although a method for suppressing the binder from entering the hole has been proposed (see Patent Document 2), no attempt has been made to increase the capacity.

  On the other hand, in an electric double layer capacitor, for the purpose of obtaining a high capacity and a high capacity retention rate, it has been proposed to use a combination of two types of activated carbons having different BTE specific surface areas as active materials constituting electrodes. (Patent Document 3).

JP 2006-286923 A Japanese Patent No. 3511943 JP 2005-243933 A

  Therefore, the present inventors can increase the capacity by using only activated carbon having a large specific surface area as the active material constituting the electrode in the lithium ion capacitor, but the positive electrode active material layer in the positive electrode is bulky. In view of the fact that the energy density is reduced with the increase in the density, and that the energy density can be increased by using only activated carbon with a small specific surface area, the capacity is reduced. As the positive electrode active material to be configured, it was examined that two types of activated carbons having different BTE specific surface areas were used in combination. As a result, by simply using a combination of two types of activated carbons, further enhancement of performance can be achieved. It became clear that it was not possible to achieve a sufficiently high energy density and capacity.

The present invention has been made on the basis of the circumstances as described above, and the object thereof is a positive electrode capable of making the power storage device have a high energy density and a high capacity when used in the power storage device. Is to provide.
Another object of the present invention is to provide a lithium ion capacitor having a high energy density and a high capacity.

The positive electrode of the present invention has a positive electrode active material layer having a BET specific surface area of 2400 m ² / g or more and 3000 m ² / g or less and an electrode density of 0.41 to 0.49 g / cm ^3. Features.

In the positive electrode of the present invention, the positive electrode active material layer has a first positive electrode active material having a BET specific surface area of more than 2500 m ² / g and not more than 3200 m ² / g, and a BET specific surface area of 1500 m ² / g or more. And a second positive electrode active material that is 2000 m ² / g or less.

  The lithium ion capacitor of the present invention has the above positive electrode.

According to the positive electrode of the present invention, since the positive electrode active material layer has a specific BET specific surface area and a specific density, when used as a positive electrode of an electric storage device, Energy density and high capacity are obtained.
Such a positive electrode of the present invention has a remarkable effect when applied to a lithium ion capacitor.

  The positive electrode of the present invention has a large BET specific surface area by combining two types of positive electrode active materials each having a specific BET specific surface area as the positive electrode active material constituting the positive electrode active material layer. The capacity of the positive electrode active material is increased by the action of the first positive electrode active material, and the density of the positive electrode active material is increased by the action of the second positive electrode active material having a small BET specific surface area. In the process of forming the slurry and a slurry in which an additive such as a conductive agent and a thickener, if necessary, is dispersed in an aqueous medium or an organic solvent, the surface fineness of the positive electrode active material having a particularly large BET specific surface area. Additives such as binders and thickeners added as needed are less likely to enter the pores, and the surface of the positive electrode active material can be controlled by controlling the slurry preparation process. As a result, it is possible to suppress the penetration of the binder into the pores, and as a result, the surface pores in the positive electrode active material layer are covered or blocked by the binder or the like. Since the decrease in the pore volume is suppressed, the positive electrode active material layer can have a desired BET specific surface area and density.

  According to the lithium ion capacitor of the present invention, since the positive electrode of the present invention is used, high energy density and high capacity can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail.

The positive electrode of the present invention has a positive electrode active material layer in a state where the positive electrode active material is bound by a binder, and the positive electrode active material layer has a BET specific surface area of 2400 m ² / g or more. It is 3000 m < ² > / g or less, and an electrode density is 0.41-0.49 g / cm < ³ >, It is characterized by the above-mentioned.
This positive electrode of the present invention is suitably used as a positive electrode of a lithium ion capacitor, and has a configuration in which a positive electrode active material layer is laminated on one surface or both surfaces on a current collector, for example. The structure is suitable for a lithium ion capacitor.
Here, in the present specification, the “positive electrode” refers to an electrode on the side from which a current flows during discharge.

  Below, the case where the positive electrode of this invention is used as a positive electrode of a lithium ion capacitor is demonstrated.

In positive electrode of the present invention, BET specific surface area of the positive electrode active material layer, it is required a at 2400 m ² / g or more 3000 m ² / g or less, preferably the 2500~3000m ² / g More preferably, it is 2600-3000 m < ² > / g.

  When the BET specific surface area of the positive electrode active material layer is too small, when applied to a lithium ion capacitor, the capacity of the lithium ion capacitor is reduced and the internal resistance is increased. On the other hand, when the BET specific surface area of the positive electrode active material layer is excessive, the electrode density becomes small, and accordingly, when applied to the lithium ion capacitor, the energy density of the lithium ion capacitor becomes small. In addition, since the binding state of the positive electrode active material layer with the binder becomes insufficient, the electrode strength is reduced, which causes difficulty in the manufacturing process of the lithium ion capacitor.

  The BET specific surface area of the positive electrode active material layer in the positive electrode of the present invention is sufficiently pulverized using, for example, an agate mortar, and specifically, pulverized so that the resulting pulverized body has a diameter of 100 μm or less. The positive electrode active material layer pulverized product obtained by drying under reduced pressure conditions is used as a BET specific surface area measurement sample, and a specific surface measurement device (specifically, for example, This is a value measured by “BELSORP-miniII” (manufactured by Nippon Bell Co., Ltd.).

In the positive electrode of the present invention, the density of the positive electrode active material layer is required to be 0.41 to 0.49 g / cm ³ .

  When the electrode density of the positive electrode active material layer is too low, the energy density of the lithium ion capacitor becomes small when applied to the lithium ion capacitor. On the other hand, when the electrode density of the positive electrode active material layer is excessive, the positive electrode active material layer has a low porosity, and when applied to a lithium ion capacitor, the electrolyte does not easily penetrate into the positive electrode active material layer. As a result, the movement of lithium ions becomes difficult and the transfer of electrons becomes difficult, so that the internal resistance of the lithium ion capacitor increases and the capacity retention rate may decrease.

The electrode density of the positive electrode active material layer in the positive electrode of the present invention is based on the mass and outer volume of the positive electrode active material layer in a dry state, and the mass of the positive electrode active material layer is divided by the outer volume of the positive electrode active material layer. Is the value obtained by
Here, the “external volume of the positive electrode active material layer” is a volume calculated based on the measurement values obtained by measuring the vertical dimension, the horizontal dimension, and the thickness dimension of the positive electrode active material layer.

The positive electrode active material constituting the positive electrode active material layer in the positive electrode of the present invention is a substance that can reversibly carry lithium ions and / or anions such as tetrafluoroborate.
Preferable specific examples of the positive electrode active material constituting the positive electrode active material layer include, for example, a polyacene-based material (hereinafter also referred to as “PAS”), which is a heat-treated product of activated carbon and an aromatic condensation polymer.

In the activated carbon used as the positive electrode active material constituting the positive electrode active material layer, the average particle diameter D50 (50% volume cumulative diameter) is preferably 2 to 12 μm, particularly preferably 2 to 8 μm.
When the average particle diameter D50 is too small, the capacity retention rate of the lithium ion capacitor may be reduced when applied to the lithium ion capacitor. The reason for this is presumed that the porosity between the activated carbon particles decreases as the electrode density of the positive electrode active material layer in the positive electrode increases excessively, and therefore the electrolyte is easily depleted. . On the other hand, when the average particle diameter D50 is excessive, it is difficult to form the positive electrode because the electrode density required for forming the positive electrode active material layer cannot be obtained. Even if the electrode can be formed, the energy density of the lithium ion capacitor may decrease when applied to the lithium ion capacitor.
Here, the average particle diameter D50 (50% volume cumulative diameter) of the activated carbon is measured by, for example, the X-ray microtrack method.

  Moreover, activated carbon used as a positive electrode active material constituting the positive electrode active material layer is obtained by, for example, calcination treatment by firing an activated carbon raw material, activation treatment, and further pulverization treatment.

As the activated carbon raw material, for example, phenol resin, petroleum pitch, petroleum coke, coconut husk and coal-based coke are used. Of these, phenol resin and coal-based coke are preferred because the specific surface area can be increased.
Moreover, as said activation process, an alkali activation process and a water vapor activation process are preferable. As the alkali activator used for this alkali activation treatment, salts of alkali metals such as lithium, sodium and potassium or hydroxides are preferably used, and potassium hydroxide is particularly preferable.
Moreover, the said grinding | pulverization process is performed by using known crushers, such as a ball mill, for example. The average particle diameter D50 (50% volume cumulative diameter) of the pulverized product obtained by this pulverization treatment is measured by a laser diffraction microtrack method.

In the positive electrode of the present invention, the positive electrode active material constituting the positive electrode active material layer is preferably used in combination of two or more kinds of materials in order to adjust the BET specific surface area of the positive electrode active material layer to a desired range. In particular, the first positive electrode active material having a BET specific surface area of more than 2500 m ² / g and not more than 3200 m ² / g, and the second positive electrode active material having a BET specific surface area of not less than 1500 m ² / g and not more than 2000 m ² / g. It is preferable to use a combination of two or more substances including the substance.

In the first positive electrode active material constituting the positive electrode active material layer, the BET specific surface area is required to be more than 2500 m ² / g and not more than 3200 m ² / g, preferably 2600 to 3200 m ² / g. Yes, more preferably 2800-3200 m ² / g.

When the BET specific surface area of the first positive electrode active material is too small, the BET specific surface area of the positive electrode active material layer is small, and when applied to a lithium ion capacitor, the capacity of the lithium ion capacitor is small and the internal resistance is high. Tend to be. On the other hand, when the BET specific surface area of the first positive electrode active material is excessively large, the bulk density becomes very large, and the energy density per cell volume becomes small when applied to a lithium ion capacitor. Since the amount of the electrolytic solution to be applied is larger than usual, the energy density per cell mass may be reduced. A positive electrode active material having a BET specific surface area exceeding 3200 m ² / g is difficult to manufacture and is not realistic.

In the second positive electrode active material constituting the positive electrode active material layer, the BET specific surface area, it is required a at 1500 m ² / g or more 2000 m ² / g or less, preferably 1700～2000M ² / g, more preferably 1800 to 2000 m ² / g.

  When the BET specific surface area of the second positive electrode active material is too small, the BET specific surface area of the positive electrode active material layer is small, and when applied to a lithium ion capacitor, the capacity of the lithium ion capacitor is small and the internal resistance is high. Tend to be. On the other hand, when the BET specific surface area of the second positive electrode active material is excessive, the bulk density increases, and there is a possibility that a sufficient energy density cannot be obtained when applied to a lithium ion capacitor.

Moreover, it is preferable that the content rate of the 1st positive electrode active material in the positive electrode active material which comprises a positive electrode active material layer is 80-95 mass%, and the content rate of a 2nd positive electrode active material is 5-20 mass%.
When the content ratio of the first positive electrode active material is excessively small, that is, when the content ratio of the second positive electrode active material is excessively large, a sufficient capacity may not be obtained when applied to a lithium ion capacitor. On the other hand, when the content ratio of the first positive electrode active material is excessive, that is, when the content ratio of the second positive electrode active material is excessively small, the electrode density of the positive electrode active material layer is remarkably decreased, and the application to the lithium ion capacitor is performed. At this time, there is a possibility that a sufficient energy density cannot be obtained.

Specifically, activated carbon is preferably used as the first positive electrode active material and the second positive electrode active material constituting the positive electrode active material layer in the positive electrode of the present invention.
That is, the positive electrode active material constituting the positive electrode active material layer includes a first positive electrode active material made of activated carbon having a BET specific surface area of more than 2500 m ² / g and not more than 3200 m ² / g, and a BET specific surface area of 1500 m ² / g. It is preferable to use in combination with the second positive electrode active material made of activated carbon that is 2000 m ² / g or less.

In the activated carbon constituting the first positive electrode active material, the average pore diameter is preferably 10 nm or less, particularly preferably greater than 0.5 nm and 10 nm or less.
When the average pore diameter of the activated carbon constituting the first positive electrode active material is within the above range, good discharge characteristics can be obtained when applied to a lithium ion capacitor.
Here, the average pore diameter of the activated carbon is obtained by subjecting 0.2 g of activated carbon as a measurement target to a dry treatment under reduced pressure conditions as a measurement sample, and using a specific surface measuring device (specifically, for example, “BELSORP-miniII” ( The adsorption isotherm is obtained using Nippon Bell Co., Ltd.), and based on the specific surface area and total pore volume obtained by the BET method, the pore shape formed in the activated carbon is assumed to be cylindrical, and the following formula This is a value calculated by (1).

Formula (1):
Average pore diameter = (4 × total pore volume (cm ³ / g) / specific surface area (m ² / g)) × 1000

Moreover, in the activated carbon which comprises a 1st positive electrode active material, it is preferable that a bulk density (tap density) is 0.3 g / cm < ³ > or less.
When the bulk density (tap density) of the activated carbon constituting the first positive electrode active material is excessive, the amount of liquid absorption of the positive electrode active material layer is remarkably reduced, and thus, when applied to a lithium ion capacitor, Internal resistance may increase.
Here, the measuring method of the bulk density (tap density) is a tap denser (specifically, for example, “KYT-4000” (manufactured by Seishin Enterprise Co., Ltd.), cylinder volume 200 ml, tapping distance 50 mm, tapping frequency 2000. Measured under the measurement conditions.

In the second activated carbon constituting the second positive electrode active material, the average pore diameter is preferably smaller than the average pore diameter of the activated carbon constituting the first positive electrode active material, specifically 5 nm or less. Preferably it is less than 2 nm.
When the average pore diameter of the activated carbon constituting the first positive electrode active material is within the above range, good discharge characteristics can be obtained when applied to a lithium ion capacitor.

Moreover, in the activated carbon which comprises a 2nd positive electrode active material, it is preferable that a bulk density (tap density) is 0.3 g / cm < ³ > or more.
When the bulk density (tap density) of the activated carbon constituting the second positive electrode active material is too small, there is a possibility that a desired electrode density cannot be obtained in the formed positive electrode active material layer.
There is a fear.

  In the activated carbon constituting the first positive electrode active material and the activated carbon constituting the second positive electrode active material as described above, the BET specific surface area, average pore diameter and bulk density (tap density) are, for example, the type of activated carbon raw material and the activation treatment. In particular, alkali activation treatment or steam activation treatment is selected as the activation treatment.

Examples of the binder constituting the specific positive electrode active material layer in the present invention include rubber binders such as styrene / butadiene rubber (SBR), fluorine-containing resins such as polytetrafluoroethylene and polyvinylidene fluoride, polypropylene, and polyethylene. A polymer material having oxidation resistance and resistance to dissolution with respect to an electrolytic solution, such as a hydrocarbon resin such as an acrylic polymer, can be suitably used.
In addition, in the manufacturing method of the positive electrode mentioned later, in order to form a positive electrode active material layer, it does not use the binder consisting of the said polymeric material, but is used as a positive electrode active material and thickeners, such as carboxymethylcellulose, for example. In the case of using only a polymer material that does not have oxidation resistance, the obtained positive electrode is an aprotic organic material in which a thickener constitutes an electrolyte in a capacitor cell when applied to a lithium ion capacitor. Due to the solvent absorbing and swelling, the binding force of the positive electrode active material layer to the current collector is insufficient, and the positive electrode active material layer peels off from the current collector.

  In the positive electrode of the present invention, if the positive electrode active material layer is in a state in which the positive electrode active material is bound by the binder, the positive electrode active material in the state bound by the binder exists. In addition to the layer portion to be formed, a layer portion having no positive electrode active material such as a conductive layer made of carbon or the like may be used.

  The thickness of the conductive layer constituting the positive electrode active material layer is preferably 5 to 20% with respect to the total thickness of the positive electrode active material layer. Specifically, it is usually preferably 1 to 20 μm.

  Moreover, it is preferable that the thickness of the positive electrode active material layer in the positive electrode of this invention is 30-350 micrometers.

As the current collector in the positive electrode of the present invention, various materials generally used for lithium batteries can be used as long as they have through holes penetrating the front and back surfaces, such as expanded metal. .
Specific examples of the material include aluminum and stainless steel.
The shape and number of through holes provided in the current collector are not particularly limited as long as the lithium ions can be moved between the front and back of the electrode without being blocked by the current collector.

  The thickness of the current collector in the positive electrode is not particularly limited, but is usually 1 to 50 μm, preferably 5 to 40 μm, and particularly preferably 10 to 40 μm.

  The positive electrode of the present invention is prepared by, for example, preparing a slurry by dispersing additives such as a positive electrode active material, a binder, and a conductive agent and a thickener used as necessary in an aqueous medium, A method of applying the obtained slurry to a current collector formed with a conductive layer or the like as necessary, or forming the prepared slurry into a sheet in advance, and preferably using a conductive adhesive The method of sticking to a collector can be mentioned.

In the production process for producing the positive electrode of the present invention, a slurry is prepared when a combination of two or more kinds of materials including the first positive electrode active material and the second positive electrode active material is used as the positive electrode active material. In the process, a binder is added to the dispersion containing the positive electrode active material. Specifically, the positive electrode active material dispersion containing the positive electrode active material and the binder dispersion containing the binder. Are preferably prepared separately, and the binder dispersion is added to the positive electrode active material dispersion.
Here, the positive electrode active material dispersion may contain substances other than the binder (specifically, additives such as a conductive agent and a thickener used) together with the positive electrode active material.

  Thus, the positive electrode active material layer obtained by using a combination of the first positive electrode active material and the second positive electrode active material by adding a binder to the dispersion containing the positive electrode active material is used as a desired BTE. It has a specific surface area and can have a desired electrode density, that is, a specific positive electrode active material layer can be obtained.

In the case where a thickener is contained in the positive electrode material dispersion, a thickener may be added to the dispersion containing the positive electrode active material (however, no thickener is contained) The positive electrode active material may be added to the dispersion containing the thickener, but the thickener may be added to the dispersion containing the positive electrode active material (but not containing the thickener). preferable. By adding a thickener to the dispersion containing the positive electrode active material, additives such as a binder and a thickener added as needed penetrate into the surface pores of the positive electrode active material. As a result, when applied to a lithium ion capacitor, when applied to a lithium ion capacitor, the capacity can be further increased and the internal resistance can be further reduced.
In addition, when the positive electrode active material is added to the dispersion containing the thickener, a dispersion containing the positive electrode active material is prepared separately from the dispersion containing the thickener, and the positive electrode active material is It is preferable to add the containing dispersion to the dispersion containing the thickener.

  The amount of the binder used varies depending on the electrical conductivity of the positive electrode active material, the shape of the positive electrode to be formed, and the like, but is preferably 1 to 15% by mass with respect to 100% by mass of the positive electrode active material.

Examples of the conductive agent used as necessary to form the positive electrode include acetylene black, ketjen black, furnace black, channel black, lamp black, graphite, and metal powder.
The amount of the conductive agent used varies depending on the electrical conductivity of the positive electrode active material, the shape of the positive electrode to be formed, and the like, but is preferably 1 to 40 parts by mass with respect to 100 parts by mass of the positive electrode active material.

Examples of the thickener used as necessary to form the positive electrode include carboxymethyl cellulose (CMC), polyethylene oxide (PEO), and polyvinyl alcohol (PVA).
It is preferable that the usage-amount of a thickener is 1-10 mass% in 100 mass% of the whole slurry.

  According to the positive electrode of the present invention as described above, since the positive electrode active material layer has a specific BET specific surface area and a specific electrode density, when used in a lithium ion capacitor, High energy density and high capacity can be obtained in the ion capacitor.

  In the positive electrode of the present invention, two positive electrode active materials each having a specific BET specific surface area (first positive electrode active material and second positive electrode active material) are used as the positive electrode active material constituting the positive electrode active material layer. In combination, the capacity of the first positive electrode active material having a large BET specific surface area can be increased, and the density of the second positive electrode active material having a small BET specific surface area can be increased. Moreover, in the process of forming the positive electrode active material layer from a slurry in which an additive such as a positive electrode active material, a binder and, if necessary, a conductive agent and a thickener is dispersed in an aqueous medium or an organic solvent, Additives such as binders and thickeners added as needed are less likely to enter into the surface pores of the first positive electrode active material having a particularly large BET specific surface area, and a slurry is prepared. By controlling the process, it becomes possible to suppress the penetration of the binder into the surface pores of the positive electrode active material. As a result, the surface pores in the positive electrode active material layer are covered or blocked by the binder or the like. Since the decrease in the pore volume of the positive electrode active material resulting from the above is suppressed, the positive electrode active material layer can have a desired BET specific surface area and electrode density.

  When the positive electrode of the present invention is applied to a lithium ion capacitor, the effect becomes remarkable. Therefore, the positive electrode is preferably used as a positive electrode of a lithium ion capacitor, but may be applied to an electricity storage device other than the lithium ion capacitor. it can.

The lithium ion capacitor of the present invention is characterized in that the positive electrode of the present invention is provided as a positive electrode.
This lithium ion capacitor of the present invention basically comprises the positive electrode and the negative electrode of the present invention, and an electrolyte containing an electrolyte capable of transporting lithium ions, and is accompanied by the movement of lithium ions, The positive electrode includes a current collector having through holes penetrating the front and back surfaces, contains a substance capable of reversibly supporting lithium ions and / or anions as a positive electrode active material, and the negative electrode is A capacitor cell having a current collector with a through-hole penetrating the back surface, containing a material capable of reversibly carrying lithium ions as a negative electrode active material, and comprising a capacitor cell in which lithium is electrochemically doped on the negative electrode It is.
Here, in this specification, the “negative electrode” refers to an electrode on the side into which a current flows during discharge. The “positive electrode” is an electrode on the side from which a current flows during discharge as described above.

  The doping of lithium ions in the capacitor cell is preferably an amount that does not cause such inconvenience in consideration of the type of active material constituting the negative electrode and the positive electrode.

In addition, the capacitor cell constituting the lithium ion capacitor of the present invention particularly has a capacitance per unit mass of the negative electrode active material of three times or more than a capacitance per unit mass of the positive electrode active material, and the positive electrode The mass of the active material is preferably 1.1 to 10 times greater than the mass of the negative electrode active material.
According to such a capacitor cell, a high voltage and a large capacity are achieved. In addition, according to the capacitor cell using the negative electrode having a capacitance per unit mass that is extremely large relative to the capacitance per unit mass of the positive electrode, a high voltage is achieved, and at the same time, the negative electrode is designed. Since the negative electrode active material can be reduced in mass while maintaining the amount of potential change, the amount of the positive electrode active material can be increased, so that the capacitor cell has a large capacitance and capacity. The
Here, when the mass of the positive electrode active material is less than 1.1 times the mass of the negative electrode active material, the difference between the capacity of the positive electrode and the capacity of the negative electrode is reduced, and the mass of the positive electrode active material is If it exceeds 10 times the mass of the active material, the capacity of the capacitor cell may be reduced, and the difference in thickness between the positive electrode and the negative electrode becomes excessively large, which is not preferable in terms of the structure of the capacitor cell.

In the present invention, the capacitance and capacitance are defined as follows.
The capacitance of a capacitor cell indicates the amount of electricity (inclination of the discharge curve) flowing through the cell per unit voltage of the capacitor cell (unit: F).
The capacitance per unit mass of the capacitor cell is indicated by the division of the total mass of the positive electrode active material and the negative electrode active material with respect to the capacitance of the capacitor cell (unit: F / g).
The capacitance of the positive electrode or the negative electrode indicates the amount of electricity (inclination of the discharge curve) flowing through the capacitor cell per unit voltage of the positive electrode or the negative electrode (unit: F).
The capacitance per unit mass of the positive electrode or the negative electrode is obtained by dividing the capacitance of the positive electrode or the negative electrode by the mass of the positive electrode or the negative electrode active material (unit: F / g). .

Further, the capacity of the capacitor cell is the difference between the discharge start voltage and the discharge end voltage of the capacitor cell, that is, the product of the voltage change amount and the capacitance of the capacitor cell (unit: C).
Since 1.0 C is the amount of charge when a current of 1.0 A flows per second, it is converted into mAh in this specification.
The capacity of the positive electrode is the product of the difference between the potential of the positive electrode at the start of discharge and the potential of the positive electrode at the end of discharge (potential change amount of the positive electrode) and the capacitance of the positive electrode (unit: C or mAh). Similarly, the capacity of the negative electrode is the product of the difference between the potential of the negative electrode at the start of discharge and the potential of the negative electrode at the end of discharge (potential change amount of the negative electrode) and the capacitance of the negative electrode (unit: C or mAh).
The capacities of these capacitor cells coincide with the capacities of the positive electrode and the negative electrode.

In the lithium ion capacitor of the present invention, the means for doping lithium into the negative electrode is not particularly limited. For example, a method of arranging a lithium ion supply source such as metal lithium capable of supplying lithium ions in the capacitor cell as a lithium electrode. And so on. The lithium electrode may be placed in physical contact (short circuit) with the negative electrode, or may be placed at a position where it can be electrochemically doped.
When lithium ions are electrochemically doped, the current collector constituting the positive electrode and the negative electrode is provided with through holes, so that the capacitor cell is configured as a wound cell or a stacked cell. Even so, if the lithium electrode is provided only in a part of the outermost or outermost capacitor cell, specifically, for example, at a position facing one positive electrode or negative electrode, all the negative electrodes are electrochemically provided. In addition, lithium ions can be doped smoothly and uniformly.

As the lithium electrode, for example, one in which a lithium ion supply source is formed on a current collector made of a conductive porous body can be used. As the conductive porous body serving as the current collector of the lithium electrode, a metal porous body that does not react with a lithium ion supply source such as a stainless steel mesh can be used.
In addition, when electrochemically doping from a lithium ion source, the lithium ion source is a substance containing at least lithium and capable of supplying lithium ions, such as lithium metal and a lithium-aluminum alloy. Say.
The amount of lithium ion supply source (the mass of lithium metal or the like) may be an amount that provides a predetermined negative electrode capacity.

  In the negative electrode constituting the lithium ion capacitor of the present invention, for example, a negative electrode active material layer in which a negative electrode active material is bound by a binder is laminated on one surface or both surfaces on a current collector. It has the composition which becomes.

In the lithium ion capacitor of the present invention, the negative electrode active material is a material that can reversibly carry lithium ions.
Preferable specific examples of the negative electrode active material include carbon materials such as graphite (hard graphite), non-graphitizable carbon (hard carbon), or heat-treated products of aromatic condensation polymers such as polyacene-based materials (PAS). Is preferred.

  Examples of the binder constituting the negative electrode active material layer of the negative electrode include the same binders as those constituting the positive electrode active material layer of the positive electrode described above.

  Moreover, it is preferable that the thickness of the negative electrode active material layer in a negative electrode is 20-250 micrometers.

As the current collector, as in the case of the current collector constituting the positive electrode described above, various types of lithium batteries generally used for lithium-based batteries can be used as long as they have through holes penetrating the front and back surfaces, such as expanded metal. The thing of a material can be used.
Specific examples of the material include stainless steel, copper, and nickel.
The shape and number of through holes provided in the current collector are not particularly limited as long as the lithium ions can be moved between the front and back of the electrode without being blocked by the current collector.

  The thickness of the current collector in the negative electrode is not particularly limited, but is usually 1 to 50 μm, preferably 5 to 40 μm, and particularly preferably 10 to 40 μm.

The negative electrode constituting the lithium ion capacitor of the present invention is manufactured from a negative electrode active material, a binder, and a conductive agent used as necessary.
Specifically, for example, a negative electrode active material, a binder, and additives such as a conductive agent and a thickener used as needed are dispersed in an aqueous medium to form a slurry, and the slurry is a current collector And a method in which the slurry is formed into a sheet shape in advance, and this is preferably attached to a current collector using a conductive adhesive.

  The amount of the binder used to form the negative electrode can be in the same range as the amount of the binder used to form the positive electrode described above.

  Examples of the conductive agent used as necessary to form the negative electrode include those similar to the conductive agent used as necessary to form the positive electrode described above. A similar range can be used.

  Thickeners used as necessary to form the negative electrode can include the same thickeners used as necessary to form the positive electrode described above, and their use The amount can be in the same range.

  In the lithium ion capacitor of the present invention, an aprotic organic solvent electrolyte solution (lithium salt electrolyte solution using an aprotic organic solvent) is used as the electrolytic solution.

Examples of the aprotic organic solvent constituting the electrolytic solution in the present invention include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride, sulfolane. Etc.
This can also be used individually or in combination of 2 or more types.

The electrolyte constituting the electrolytic solution in the present invention may be any electrolyte that can generate lithium ions, and various electrolytes can be used.
Specific examples of the electrolyte include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) _{2 and the} like.

The concentration of the electrolyte in the aprotic organic solvent electrolyte solution as the electrolytic solution is preferably at least 0.1 mol / l or more because low internal resistance is obtained.
Here, the aprotic organic solvent electrolyte solution constituting the electrolytic solution is obtained by mixing a sufficiently dehydrated electrolyte and an aprotic organic solvent.

As the structure of the lithium ion capacitor according to the present invention, in particular, a wound type cell in which a strip-like positive electrode and a negative electrode are wound through a separator, and a plate-like positive electrode and a negative electrode are provided through a separator. In a large capacity capacitor cell such as a laminated cell in which three or more layers are laminated, or a film type cell in which a laminate of three or more layers each having a plate-like positive electrode and negative electrode interposed via a separator is enclosed in an exterior film. Suitable structures are mentioned.
The structures of these capacitor cells are known from International Publication WO 00/07255, International Publication WO 03/003395, Japanese Patent Application Laid-Open No. 2004-266091, etc., and the capacitor cell of the present invention is similar to the existing cell. It can be configured.

According to the lithium ion capacitor of the present invention, since the positive electrode of the present invention is used, high energy density and high capacity can be obtained.
Such a lithium ion capacitor of the present invention is extremely effective as a driving power source or auxiliary power source for electric vehicles, hybrid electric vehicles, and the like. Further, it can be suitably used as a driving power source for electric bicycles, electric wheelchairs, etc., an energy storage device such as a solar energy generator and a wind power generator, or a storage power source for process electric appliances.

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

(Preparation Example 1 of Negative Electrode Slurry)
First, a thermosetting phenol resin molded plate having a thickness of 0.5 mm is placed in an electric furnace, heated to 1100 ° C. at a heating rate of 10 ° C./hour in a nitrogen atmosphere, and held at a temperature of 1100 ° C. for 2 hours. Heat carbon was used to synthesize hard carbon. The obtained hard carbon was pulverized to a mean particle size of 3 μm using a disk mill to obtain a hard carbon powder.
Next, 6 parts by mass of acetylene black powder, 5 parts by mass of a water-soluble acrylate copolymer binder, 4 parts by mass of carboxymethylcellulose, and 200 parts by mass of ion-exchanged water are added to 92 parts by mass of the obtained hard carbon powder. The mixture was sufficiently mixed with a mixing stirrer to obtain a negative electrode slurry (hereinafter also referred to as “negative electrode slurry (1)”).

(Preparation example 1 of positive electrode slurry)
First, as a first positive electrode active material, a BET specific surface area of 2900 m ² / g, an average pore diameter of 1.1 nm, a bulk density (tap density) of 0.23 g / cm ³ , and an average particle diameter (average particle diameter D50) of 4 μm are commercially available. 73.6 parts by mass of activated carbon powder, a BET specific surface area of 1800 m ² / g as a second positive electrode active material, an average pore diameter of 0.8 nm, a bulk density (tap density) of 0.58 g / cm ³ , and an average particle diameter of D504 μm. The positive electrode active material and the conductive agent are dispersed by mixing 18.4 parts by mass of the activated carbon powder, 6 parts by mass of acetylene black powder as a conductive agent, and 120 parts by mass of ion-exchanged water using a biaxial planetary stirrer. A dispersion was obtained.
Next, 4 parts by mass of carboxymethyl cellulose as a thickener dissolved in 36 parts by mass of ion-exchanged water was added to the obtained dispersion and mixed using a biaxial planetary stirrer. A positive electrode slurry (hereinafter, also referred to as “positive electrode slurry (1)”) was obtained by adding 6 parts by weight of a water-soluble acrylic copolymer binder and mixing with a biaxial planetary stirrer. .
Hereinafter, this method of preparing the positive electrode slurry is referred to as “Preparation Method A”.

(Preparation example 2 of positive electrode slurry)
In Preparation Example 1 of the positive electrode slurry, 82.8 parts by mass of commercially available activated carbon powder having a BET specific surface area of 2900 m ² / g and a bulk density (tap density) of 0.23 g / cm ³ as the first positive electrode active material, Except for using 9.2 parts by mass of a commercially available activated carbon powder having a BET specific surface area of 1800 m ² / g and a bulk density (tap density) of 0.58 g / cm ³ as a substance, the same as in Preparation Example 1 of the positive electrode slurry. A positive electrode slurry (hereinafter also referred to as “positive electrode slurry (2)”) was obtained.

(Preparation example 3 of positive electrode slurry)
In Preparation Example 1 of the positive electrode slurry, 82.8 parts by mass of commercially available activated carbon powder having a BET specific surface area of 3200 m ² / g and a bulk density (tap density) of 0.22 g / cm ³ as the first positive electrode active material, Except that 9.2 parts by mass of a commercially available activated carbon powder having a BET specific surface area of 1750 m ² / g and a bulk density (tap density) of 0.59 g / cm ³ as a substance was used, the same procedure as in Preparation Example 1 of the positive electrode slurry was performed. A positive electrode slurry (hereinafter also referred to as “positive electrode slurry (3)”) was obtained.

(Preparation example 4 of positive electrode slurry)
First, 196 parts by mass of ion-exchanged water and 4 parts by mass of carboxymethyl cellulose as a thickener were mixed using a biaxial planetary stirrer, and then 6 parts by mass of acetylene black powder as a conductive agent was added. By mixing using a stirrer, a dispersion liquid in which the thickener and the conductive agent were dispersed was obtained.
Next, 82.8 parts by mass of commercially available activated carbon powder having a BET specific surface area of 3200 m ² / g and a bulk density (tap density) of 0.22 g / cm ³ as the first positive electrode active material was added to the obtained dispersion, After adding 9.2 parts by mass of a commercial activated carbon powder having a BET specific surface area of 1750 m ² / g as an active material and a bulk density (tap density) of 0.59 g / cm ³ , and mixing using a biaxial planetary stirrer, 4 parts by mass of ion-exchanged water and 6 parts by mass of a water-soluble acrylic copolymer binder were added and mixed using a biaxial planetary stirrer to obtain a positive electrode slurry (positive electrode slurry (4)).
Hereinafter, this method of preparing the positive electrode slurry is referred to as “Preparation Method B”.

(Preparation Example 5 of Positive Electrode Slurry)
In Preparation Example 1 of the positive electrode slurry, 87.4 parts by mass of commercially available activated carbon powder having a BET specific surface area of 2700 m ² / g and a bulk density (tap density) of 0.23 g / cm ³ as the first positive electrode active material, A positive electrode slurry (hereinafter referred to as “positive electrode slurry (5)”) was prepared in the same manner as Preparation Example 1 of the positive electrode slurry, except that 4.6 parts by mass of a commercially available activated carbon powder having a BET specific surface area of 1950 m ² / g as a substance was used. Say).

(Preparation Example 6 of Positive Electrode Slurry (Preparation of Comparative Positive Electrode Slurry))
In Production Example 1 of the positive electrode, except that 92.0 parts by mass of commercially available activated carbon powder having a BET specific surface area of 2150 m ² / g and a bulk density (tap density) of 0.28 g / cm ³ was used as the positive electrode active material. A positive electrode slurry (hereinafter also referred to as “positive electrode slurry (6)”) was obtained in the same manner as in Preparation Example 1 of the positive electrode slurry.

(Preparation Example 7 of Positive Electrode Slurry (Preparation of Comparative Positive Electrode Slurry))
In Preparation Example 1 of positive electrode slurry, as the positive electrode active material, a commercially available activated carbon powder 73.6 parts by weight of the BET specific surface area of 2900 m ² / g, bulk density (tap density) 0.23 g / cm ^3, a specific surface area of 2150m ² / g, positive electrode slurry (hereinafter referred to as “positive electrode slurry (hereinafter referred to as“ positive electrode slurry ”), except that 18.4 parts by mass of commercially available activated carbon powder having a bulk density (tap density) of 0.28 g / cm ³ was used. 7) ".

(Preparation Example 8 of Positive Electrode Slurry (Preparation of Comparative Positive Electrode Slurry))
In Preparation Example 1 of the positive electrode slurry, except that 92.0 parts by mass of commercially available activated carbon powder having a BET specific surface area of 2900 m ² / g and a bulk density (tap density) of 0.23 g / cm ³ was used as the positive electrode active material. A positive electrode slurry (hereinafter also referred to as “positive electrode slurry (8)”) was obtained in the same manner as in Preparation Example 1 of the positive electrode slurry.

(Preparation Example 9 of Positive Electrode Slurry (Preparation of Comparative Positive Electrode Slurry))
In Preparation Example 1 of the positive electrode slurry, except that 92.0 parts by mass of commercially available activated carbon powder having a BET specific surface area of 1800 m ² / g and a bulk density (tap density) of 0.58 g / cm ³ was used as the positive electrode active material. A positive electrode slurry (hereinafter also referred to as “positive electrode slurry (9)”) was obtained in the same manner as in Preparation Example 1 of the positive electrode slurry.

(Preparation Example 10 of Positive Electrode Slurry (Preparation of Comparative Positive Electrode Slurry))
In Preparation Example 1 of the positive electrode slurry, except that 92.0 parts by mass of commercially available activated carbon powder having a BET specific surface area of 3400 m ² / g and a bulk density (tap density) of 0.23 g / cm ³ was used as the positive electrode active material. A positive electrode slurry (hereinafter also referred to as “positive electrode slurry (10)”) was obtained in the same manner as in Preparation Example 1 of the positive electrode slurry.

(Negative electrode test sample production example 1)
First, a copper expanded metal (manufactured by Nippon Metal Industry Co., Ltd.) having a thickness of 35 μm and a porosity of 50% is prepared as a current collector, and a negative electrode slurry (1) is prepared on both sides of the copper expanded metal using a roll coater. After coating, a negative electrode active material layer was formed on the current collector by pressing, thereby preparing a negative electrode sheet (hereinafter also referred to as “negative electrode test sample (1)”).
By using the obtained negative electrode test sample (1), a lithium ion capacitor was produced according to a production example of a lithium ion capacitor described later.

(Preparation Examples 1 to 10 of a positive electrode test sample)
First, an aluminum expanded metal (manufactured by Nippon Metal Industry Co., Ltd.) having a thickness of 35 μm and a porosity of 50% is prepared as a current collector, and a non-aqueous carbon-based conductive paint “EB-815” is provided on both surfaces of the aluminum expanded metal. A conductive layer having a thickness of 5 μm was formed on the current collector by coating (manufactured by Japan Atchison Co., Ltd.) by a spray method and drying. In the current collector in which the conductive layer is formed, the through hole of the copper expanded metal is in a state of being substantially closed by the conductive layer.
Next, a positive electrode slurry (1) to a positive electrode slurry (10) are respectively applied to both surfaces of the current collector on which the conductive layer is formed using a roll coater, and then pressed to form the current collector. A positive electrode active material layer made of a laminate of a conductive layer and a positive electrode slurry layer is formed on a current collector by forming a layer made of a positive electrode slurry (hereinafter also referred to as “positive electrode slurry layer”) on the conductive layer formed. (Hereinafter, also referred to as “positive electrode test sample (1)” to “positive electrode test sample (10)”).
By using the obtained positive electrode test sample (1) to positive electrode test sample (10), a lithium ion capacitor was produced according to a production example of a lithium ion capacitor described later, and the BET ratio of the positive electrode active material layer was obtained by the following method. The surface area and electrode density were measured. The results are shown in Table 1.
As for the positive electrode test sample (10), the positive electrode active material layer could not be formed because the amount of the binder to the positive electrode active material was insufficient, so the positive electrode active material in this positive electrode test sample (10) The BET specific surface area and electrode density of the layer could not be measured.

(Method for measuring the specific surface area of the positive electrode active material layer in the positive electrode)
First, the positive electrode active material layer of each of the positive electrode test sample (1) to the positive electrode test sample (10) is scraped off, and the scraped material is ground using an agate mortar until the diameter of the obtained pulverized body becomes 100 μm or less. Thus, a pulverized body made of a mixture of components of the positive electrode active material layer (specifically, a positive electrode active material, a binder, a conductive agent, a thickener, and a conductive layer, which are components of the positive electrode slurry layer) is obtained. .
Next, 0.2 g of the obtained pulverized body was sampled and charged into a sample tube, dried under reduced pressure over a period of 24 hours at a temperature of 200 ° C., and then the BET specific surface area of the pulverized body subjected to the reduced pressure drying was determined as the specific surface area. Measurement is performed using a measuring apparatus “BELSORP-miniII” (manufactured by Nippon Bell Co., Ltd.)

(Measurement of the electrode density of the positive electrode active material layer in the positive electrode)
A sample for measuring electrode density having a vertical and horizontal dimension of 40 mm × 60 mm is cut out from each of the positive electrode test sample (1) to the positive electrode test sample (10), and the mass and the external volume of the electrode density measurement sample are measured. Based on the mass of the positive electrode active material layer and the outer volume of the positive electrode active material layer, the mass value of the positive electrode active material layer and the outer volume of the positive electrode active material layer were calculated. The electrode density is calculated by dividing by the volume value.

[Example 1: Production Example 1 of lithium ion capacitor]
(Preparation of negative electrode capacity evaluation sample)
A copper foil having a thickness of 18 μm was prepared as a current collector, and the negative electrode slurry (1) was applied to one side of the copper foil under a coating condition of 7 mg / cm ² (in terms of solid content), followed by drying treatment and A negative electrode (hereinafter also referred to as “negative electrode capacity evaluation sample (1)”) was produced by performing a press treatment.

(Measurement of capacitance per unit mass of negative electrode)
First, a sample for measuring capacitance having a size of 1.5 cm × 2.0 cm (area: 3.0 cm ² ) was cut out from the negative electrode capacity evaluation sample (1) to obtain a negative electrode for measuring capacitance. As a counter electrode of the negative electrode, a lithium metal having a size of 1.5 cm × 2.0 cm (area 3.0 cm ² ) and a thickness of 200 μm is prepared, and a non-woven fabric made of polyethylene having a thickness of 50 μm is prepared as a separator. A counter cell was disposed on both sides of the substrate with a separator interposed therebetween, and a simulated cell having a configuration in which a lithium metal as a reference electrode and a propylene carbonate solution in which LiPF ₆ was dissolved at a concentration of 1 mol / l was used as an electrolyte solution was produced. .
Subsequently, after charging lithium ions of 400 mAh / g with respect to the mass of the negative electrode active material at a charging current of 1 mA, the cell voltage (capacitor voltage) is 1.5 V under the condition of a charging current of 1 mA. The battery was charged until Thereafter, the electrostatic capacity per unit mass of the negative electrode was calculated from the potential of the negative electrode 1 minute after the start of discharge based on the discharge time during which the cell voltage (capacitor voltage) changed by 0.2 V. / G.

(Preparation of positive electrode capacity evaluation sample)
An aluminum foil having a thickness of 20 μm is prepared as a current collector, and a conductive layer having a thickness of 5 μm is formed by coating a carbon-based conductive paint, and a positive electrode is formed on one side of the 30 μm-thick aluminum foil coated with the carbon-based conductive paint. After applying the slurry (1) under coating conditions of 7 mg / cm ² (in terms of solid content), a drying treatment and a pressing treatment are performed, whereby a positive electrode sample for capacitance measurement (hereinafter referred to as “positive electrode capacity”). An evaluation sample (also referred to as “1”) was prepared.

(Measurement of capacitance per unit mass of positive electrode)
First, a sample for measuring capacitance having a size of 1.5 cm × 2.0 cm (area: 3.0 cm ² ) was cut out from the positive electrode capacity evaluation sample (1) to obtain a positive electrode for measuring capacitance. As a counter electrode of the positive electrode, a lithium metal having a size of 1.5 cm × 2.0 cm (area: 3.0 cm ² ) and a thickness of 200 μm is prepared, and a polyethylene nonwoven fabric having a thickness of 50 μm is prepared as a separator. A counter cell was disposed on both sides of the substrate with a separator interposed therebetween, and a simulated cell having a configuration in which a lithium metal as a reference electrode and a propylene carbonate solution in which LiPF ₆ was dissolved at a concentration of 1 mol / l was used as an electrolyte solution was produced. .
Next, the obtained simulated cell was charged under the condition of a charging current of 1 mA until the cell voltage reached 3.6 V, and then constant voltage charging was performed until the total charging time reached 1 hour. Thereafter, discharging was performed under the condition of a discharge current of 1 mA until the cell voltage (capacitor voltage) reached 2.5V. The capacitance per unit mass was found to be 92 F / g based on the discharge time when the cell voltage (capacitor voltage) was 3.5 V to 2.5 V during this discharge.

<Preparation of electrode laminate>
First, by cutting the negative electrode test sample (1), a negative electrode provided with an electrode body having a size of 6.0 cm × 7.5 cm (area 45 cm ² ) and a terminal connection portion continuous to the electrode body was obtained. A sheet was produced. Moreover, the positive electrode provided with the electrode main body which has a dimension of 5.8 cm x 7.3 cm (area 42.34 cm < ² >), and the terminal connection part which continues to the said electrode main body by cutting a positive electrode test sample (1) 10 sheets were produced.
Next, 10 positive electrodes and 11 negative electrodes were used as separators using a cellulose / rayon mixed nonwoven fabric having a thickness of 35 μm, and the terminal welded portion in the positive electrode and the terminal welded portion in the negative electrode were on opposite sides. Also, there are 20 opposing surfaces of the positive electrode active material layer in the positive electrode and the negative electrode active material layer in the negative electrode, and between the lowermost part and the positive electrode and negative electrode inside thereof (hereinafter referred to as “lowermost inner side”). (Also referred to as “between the positive and negative electrodes”). Each of the two separators is disposed, and one separator is disposed between the positive electrode and the negative electrode other than between the uppermost and lowermost inner positive and negative electrodes. Laminated and taped on 4 sides. Thereafter, each of the terminal welded portion in the 10 positive electrodes and the terminal welded portion in the 11 negative electrodes constituting the obtained laminate was made into an aluminum positive electrode having a size of 50 mm × 50 mm and a thickness of 0.2 mm. The electrode laminate was fabricated by ultrasonic welding to a terminal and a copper negative electrode terminal having a thickness of 50 mm × 50 mm and having a thickness of 0.2 mm.
In the obtained electrode laminate, the positive electrode active material mass was 1.4 times the negative electrode active material mass.

<Production of lithium ion capacitor>
First, as a lithium electrode, a lithium metal foil having a dimension of 6.0 cm × 7.5 cm (area 45 cm ² ) and having a thickness of 80 μm (equivalent to 200 mAh / g) is used as a lithium electrode current collector made of a copper mesh having a thickness of 80 μm. Two sheets having a structure formed by pressure bonding were prepared. The two lithium electrodes are arranged on each of the uppermost and lowermost parts of the electrode stack so as to be completely opposite to the negative electrode located on the outermost side, and the lithium electrode current collector at each lithium electrode is arranged. A three-pole laminated unit was produced by resistance-welding the terminal welded part of the body to a copper negative electrode terminal.
Next, two rectangular exterior films having dimensions suitable for the obtained three-pole laminated unit were prepared, and three of the two exterior films were deeply drawn at the center of one exterior film by 6.5 mm. An electrode laminate unit is disposed, and the other exterior film is overlapped on the three electrode laminate unit. The three electrode laminate unit is covered with the exterior film, and the three sides are fused, and then an electrolyte solution (ethylene carbonate, diethyl carbonate, and propylene). A tripolar unit was vacuum impregnated with a solution of LiPF ₆ dissolved at a concentration of 1 mol / l in a mixed solvent of carbonate at a mass ratio of 3: 4: 1. Thereafter, four film type lithium capacitors (hereinafter also referred to as “lithium ion capacitors (1)”) were produced by fusing the remaining one side.
In addition, the lithium metal arrange | positioned inside the obtained lithium ion capacitor is equivalent to 400 mAh / g per negative electrode active material mass.

<Initial evaluation of lithium ion capacitors>
After the four lithium ion capacitors (1) thus prepared were left to stand for 20 days, when one of the lithium ion capacitors (1) was disassembled, the lithium metal foil relating to the lithium electrode disappeared. It was confirmed. Therefore, after 20 days from the production, the negative electrode is doped with an expected amount of lithium ions with a capacitance per unit mass of the negative electrode of 1021 F / g or more with respect to the negative electrode ( Preliminary charging) is determined.

<Measurement of initial capacity and energy density of lithium ion capacitor>
Each of the three lithium ion capacitors (1) is charged with a constant current of 1.5 A until the cell voltage (capacitor voltage) reaches 3.8 V, and then a constant voltage of 3.8 V is applied. Current-constant voltage charging was performed for 1 hour. Next, the battery was discharged with a constant current of 150 mA until the cell voltage (capacitor voltage) became 2.2V. This operation was repeated as one cycle, and the capacity (initial capacity) and energy density of the capacitor in the discharge at the 10th cycle were measured, and the average value for the three lithium ion capacitors (1) was calculated. The results are shown in Table 1 below.

<Measurement of internal resistance of lithium ion capacitor>
Using an “AC milliohm HiTester 3560” (manufactured by Hioki Electric Co., Ltd.), each of the three lithium ion capacitors (1) was measured for an AC internal resistance of 1 KHz under an environmental condition of a temperature of 25 ° C. The average value for the ion capacitor (1) was calculated. The results are shown in Table 1 below.

[Example 2: Production Example 2 of lithium ion capacitor]
In Production Example 1 of a lithium ion capacitor, the same procedure as in Production Example 1 of the lithium ion capacitor except that the positive electrode test sample (2) was used instead of the positive electrode test sample (1) in the production of the electrode laminate. Four lithium ion capacitors (hereinafter also referred to as “lithium ion capacitor (2)”) were obtained.
About the obtained lithium ion capacitor (2), when an initial evaluation of the lithium ion capacitor was performed by the same method as in Production Example 1 of the lithium ion capacitor, after 20 days from the production, It was determined that the negative electrode was doped (preliminarily charged) with an intended amount of lithium ions with an electrostatic capacity per unit mass of the negative electrode of 1021 F / g or more.
For the lithium ion capacitor (2), the initial capacity, energy density, and internal resistance were measured by the same method as in Production Example 1 of the lithium ion capacitor. The results are shown in Table 1.

[Example 3: Production Example 3 of lithium ion capacitor]
In Production Example 1 of a lithium ion capacitor, the same procedure as in Production Example 1 of the lithium ion capacitor except that the positive electrode test sample (3) was used instead of the positive electrode test sample (1) in the production of the electrode laminate. Four lithium ion capacitors (hereinafter also referred to as “lithium ion capacitor (3)”) were obtained.
About the obtained lithium ion capacitor (3), when an initial evaluation of the lithium ion capacitor was performed by the same method as in Production Example 1 of a lithium ion capacitor, after 20 days from the production, It was determined that the negative electrode was doped (preliminarily charged) with an intended amount of lithium ions with an electrostatic capacity per unit mass of the negative electrode of 1021 F / g or more.
For the lithium ion capacitor (3), the initial capacity, energy density, and internal resistance were measured by the same method as in Production Example 1 of the lithium ion capacitor. The results are shown in Table 1.

[Example 4: Production Example 4 of lithium ion capacitor]
In Production Example 1 of a lithium ion capacitor, the same procedure as in Production Example 1 of the lithium ion capacitor except that the positive electrode test sample (4) was used instead of the positive electrode test sample (1) in the production of the electrode laminate. Four lithium ion capacitors (hereinafter also referred to as “lithium ion capacitor (4)”) were obtained.
About the obtained lithium ion capacitor (4), when an initial evaluation of the lithium ion capacitor was performed by the same method as in Production Example 1 of the lithium ion capacitor, after 20 days from the production, It was determined that the negative electrode was doped (preliminarily charged) with an intended amount of lithium ions with an electrostatic capacity per unit mass of the negative electrode of 1021 F / g or more.
For the lithium ion capacitor (4), the initial capacity, energy density, and internal resistance were measured by the same method as in Production Example 1 of the lithium ion capacitor. The results are shown in Table 1.

[Example 5: Production Example 5 of lithium ion capacitor]
In Production Example 1 of a lithium ion capacitor, the same procedure as in Production Example 1 of the lithium ion capacitor except that the positive electrode test sample (5) was used instead of the positive electrode test sample (1) in the production of the electrode laminate. Four lithium ion capacitors (hereinafter also referred to as “lithium ion capacitor (5)”) were obtained.
About the obtained lithium ion capacitor (5), when an initial evaluation of the lithium ion capacitor was performed by the same method as in Production Example 1 of the lithium ion capacitor, after 20 days from the production, It was determined that the negative electrode was doped (preliminarily charged) with an intended amount of lithium ions with an electrostatic capacity per unit mass of the negative electrode of 1021 F / g or more.
For the lithium ion capacitor (5), the initial capacity, energy density, and internal resistance were measured by the same method as in Production Example 1 of the lithium ion capacitor. The results are shown in Table 1.

[Comparative Example 1: Production Example 1 for Comparative Lithium Ion Capacitor]
In Production Example 1 of a lithium ion capacitor, the same procedure as in Production Example 1 of the lithium ion capacitor except that the positive electrode test sample (6) was used instead of the positive electrode test sample (1) in the production of the electrode laminate. Four lithium ion capacitors (hereinafter also referred to as “comparative lithium ion capacitor (1)”) were obtained.
With respect to the obtained comparative lithium ion capacitor (1), when an initial evaluation of the lithium ion capacitor was performed by the same method as in Production Example 1 of the lithium ion capacitor, Thus, it was determined that the negative electrode was doped (preliminarily charged) with an expected amount of lithium ions having an electrostatic capacity per unit mass of 1021 F / g or more.
For the comparative lithium ion capacitor (1), the initial capacity, energy density, and internal resistance were measured by the same method as in Production Example 1 of the lithium ion capacitor. The results are shown in Table 1.

[Comparative example 2: Production example 2 of comparative lithium ion capacitor]
In Production Example 1 of a lithium ion capacitor, the same procedure as in Production Example 1 of the lithium ion capacitor except that the positive electrode test sample (7) was used instead of the positive electrode test sample (1) in the production of the electrode laminate. Four lithium ion capacitors (hereinafter also referred to as “comparative lithium ion capacitor (2)”) were obtained.
With respect to the obtained comparative lithium ion capacitor (2), an initial evaluation of the lithium ion capacitor was performed by the same method as in Production Example 2 of the lithium ion capacitor. Thus, it was determined that the negative electrode was doped (preliminarily charged) with an expected amount of lithium ions having an electrostatic capacity per unit mass of 1021 F / g or more.
For the comparative lithium ion capacitor (2), the initial capacity, energy density, and internal resistance were measured by the same method as in Production Example 2 of the lithium ion capacitor. The results are shown in Table 1.

[Comparative Example 3: Production Example 3 of Comparative Lithium Ion Capacitor]
In the manufacture example 1 of a lithium ion capacitor, it was carried out similarly to the manufacture example 1 of the said lithium ion capacitor except having used the positive electrode test sample (8) instead of the positive electrode test sample (1) in preparation of an electrode laminated body. Four lithium ion capacitors (hereinafter also referred to as “comparative lithium ion capacitor (3)”) were obtained.
With respect to the obtained comparative lithium ion capacitor (3), when an initial evaluation of the lithium ion capacitor was performed by the same method as in Production Example 1 of the lithium ion capacitor, after the lapse of 20 days from the production, Thus, it was determined that the negative electrode was doped (preliminarily charged) with an expected amount of lithium ions having an electrostatic capacity per unit mass of 1021 F / g or more.
For the comparative lithium ion capacitor (3), the initial capacity, energy density, and internal resistance were measured in the same manner as in Production Example 1 of the lithium ion capacitor. The results are shown in Table 1.

[Comparative Example 4: Production Example 4 for Comparative Lithium Ion Capacitor]
In Production Example 1 of a lithium ion capacitor, the same procedure as in Production Example 1 of the lithium ion capacitor except that the positive electrode test sample (9) was used instead of the positive electrode test sample (1) in the production of the electrode laminate. Four lithium ion capacitors (hereinafter also referred to as “comparative lithium ion capacitor (4)”) were obtained.
With respect to the obtained comparative lithium ion capacitor (4), when an initial evaluation of the lithium ion capacitor was performed by the same method as in Production Example 1 of the lithium ion capacitor, after 20 days from the production, Thus, it was determined that the negative electrode was doped (preliminarily charged) with an expected amount of lithium ions having an electrostatic capacity per unit mass of 1021 F / g or more.
For the comparative lithium ion capacitor (4), the initial capacity, energy density, and internal resistance were measured in the same manner as in Production Example 1 of the lithium ion capacitor. The results are shown in Table 1.

[Comparative Example 5: Production Example 5 for Comparative Lithium Ion Capacitor]
In Production Example 1 of a lithium ion capacitor, the same procedure as in Production Example 1 of the lithium ion capacitor except that the positive electrode test sample (10) was used instead of the positive electrode test sample (1) in the production of the electrode laminate. As a result, the positive electrode test sample (10) was not able to form the positive electrode active material layer because the amount of the binder to the positive electrode active material was insufficient. Since it could not be formed, characteristics (initial capacity, energy density and internal resistance in the lithium ion capacitor) when the positive electrode made of the positive electrode test sample (10) was applied to the lithium ion capacitor could not be measured. There wasn't.

In Table 1, the “high specific surface area positive electrode active material” means a first positive electrode active material (a positive electrode active material having a BET specific surface area of 2500 m ² / g or more and 3200 m ² / g or less in the production example of the positive electrode. In the production example of the comparative positive electrode, when two types of positive electrode active materials are used, the positive electrode active material having the larger BET specific surface area is shown. When only one kind of material is used, a positive electrode active material having a BET specific surface area of 2000 m ² / g or more is shown. In addition, the “content ratio” related to the “high specific surface area positive electrode active material” indicates a ratio (mass) with respect to a total of 100 mass% of the positive electrode active material constituting the positive electrode active material layer.
In addition, the “low specific surface area positive electrode active material” means a second positive electrode active material (a positive electrode active material having a BET specific surface area of 1500 m ² / g or more and 2000 m ² / g or less) in the production example of the positive electrode. In the production example of the comparative positive electrode, when two types of positive electrode active materials are used, the positive electrode active material having the smaller BET specific surface area is shown. When only one type is used, a positive electrode active material having a BET specific surface area of less than 2000 m ² / g is shown. Further, the “content ratio” relating to the “low specific surface area positive electrode active material” indicates a ratio (mass) with respect to a total of 100 mass% of the positive electrode active material constituting the positive electrode active material layer.

As is clear from the results in Table 1, it was confirmed that the lithium ion capacitors according to Examples 1 to 5 had a high cell capacity and a large energy density.
On the other hand, in the lithium ion capacitor according to Comparative Example 1, since the positive electrode had a small BET specific surface area and a high electrode density, the capacity and energy density were small, and the internal resistance was large.
Since the lithium ion capacitor according to Comparative Example 2 has a small electrode density, the energy density is small.
In Comparative Example 2, although two types of activated carbon were used as the positive electrode active material for forming the positive electrode active material layer of the positive electrode, the activated carbon having the smaller specific surface area had a larger BET specific surface area. As a result, the obtained positive electrode active material layer had a large BET specific surface area but a small electrode density. As a result, the lithium ion capacitor had a large capacity but a small energy density.
The lithium ion capacitor according to Comparative Example 3 has a low energy density because it has a low electrode density.
Moreover, in Comparative Example 3, since only the activated carbon having a large specific surface area related to the first positive electrode active material was used as the positive electrode active material for forming the positive electrode active material layer of the positive electrode, the obtained positive electrode active material Although the BET specific surface area of the lithium ion capacitor increased, the electrode density decreased. As a result, in the lithium ion capacitor, although the capacity increased, the energy density decreased and the internal resistance increased.
The lithium ion capacitor according to Comparative Example 4 had a small capacity and energy density because the positive electrode had a small BET specific surface area and a large electrode density.
Moreover, in Comparative Example 4, since only the activated carbon having a small specific surface area related to the second positive electrode active material was used as the positive electrode active material for forming the positive electrode active material layer of the positive electrode, the obtained positive electrode active material However, the BET specific surface area was small and the electrode density was large. As a result, in the lithium ion capacitor, although the internal resistance was small, the capacity and energy density were small.

Claims (3)

A positive electrode having a positive electrode active material layer having a BET specific surface area of 2400 m ² / g or more and 3000 m ² / g or less and an electrode density of 0.41 to 0.49 g / cm ³ . The positive electrode active material layer has a first positive electrode active material having a BET specific surface area of more than 2500 m ² / g and not more than 3200 m ² / g, and a BET specific surface area of not less than 1500 m ² / g and not more than 2000 m ² / g. The positive electrode according to claim 1, comprising a second positive electrode active material.   A lithium ion capacitor comprising the positive electrode according to claim 1.