Electrochemical capacitor

Abstract

This electrochemical capacitor includes a polarizable electrode layer. The polarizable electrode layer contains activated carbon. The BET specific surface area Sb of the activated carbon is less than 2,000 m2 / g. The ratio Sa / Sb of the external specific surface area Sa of the activated carbon obtained through the t-plot method to the BET specific surface area Sb of the activated carbon is 0.10 or more.

Description

electrochemical capacitor

[0001] The present disclosure relates to electrochemical capacitors.

[0002] Electrochemical capacitors have the advantages of long life and rapid charging. Various proposals have been made for electrochemical capacitors.

[0003] Claim 1 of Patent Document 1 (JP 2008-60457 A) describes an electric double layer capacitor comprising a polarizable electrode layer containing activated carbon, a conductive auxiliary material, and a binder, wherein the external specific surface area of ​​the activated carbon (specific surface area excluding micropores with a pore diameter of less than 20 Å calculated from a nitrogen adsorption isotherm by the t-plot method) is 450 to 800 m per unit volume of the polarizable electrode layer. ２ / cm ３ and the volume based on the interparticle voids per unit volume of the polarizable electrode layer is in the range of 0.05 to 0.12 cm ３ / cm ３ The document discloses an electric double layer capacitor characterized by being in the range of

[0004] Claim 1 of Patent Document 2 (JP 2021-170568 A) states that "BET specific surface area is 2000 m ２ / g or more 3500m ２ / g or less, and when the specific surface area of ​​the particle surface is defined as the external specific surface area and the specific surface area of ​​the pores inside the particles is defined as the internal specific surface area, of the total specific surface area determined by t-plot analysis, the external specific surface area ratio, which is the ratio of the external specific surface area to the total specific surface area, is 4.8% or more and 14.5% or less.

[0005] JP 2008-60457 A JP 2021-170568 A

[0006] One aspect of the present disclosure relates to an electrochemical capacitor. The electrochemical capacitor includes a polarizable electrode layer. The polarizable electrode layer includes activated carbon, and the activated carbon has a BET specific surface area Sb of 2000 m ２ The ratio Sa / Sb of the external specific surface area Sa of the activated carbon determined by the t-plot method to the BET specific surface area Sb is 0.10 or more.

[0007] According to the present disclosure, an electrochemical capacitor with little deterioration can be obtained.

[0008] FIG. 1 is a perspective view schematically illustrating an example of an electrochemical capacitor according to a first embodiment.

[0009] In recent years, there has been a demand for electrochemical capacitors that deteriorate less. The present disclosure provides an electrochemical capacitor that deteriorates less.

[0010] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0011] (Electrochemical Capacitor) An example of an electrochemical capacitor according to this embodiment will be described below. The electrochemical capacitor according to this embodiment may be referred to as an "electrochemical capacitor (C)" or a "capacitor (C)."

[0012] The electrochemical capacitor (C) includes a polarizable electrode layer. The polarizable electrode layer includes activated carbon. The activated carbon has a BET specific surface area Sb of 2000 m ２ The ratio Sa / Sb of the external specific surface area Sa of the activated carbon determined by the t-plot method to the BET specific surface area Sb is 0.10 or more.

[0013] In polarizable electrode layers, capacitance is generated by the adsorption of ions onto activated carbon (active material). Therefore, the physical properties of activated carbon affect the characteristics of electrochemical capacitors. As a result of investigations, the present inventors have newly discovered that an electrochemical capacitor with minimal degradation can be realized by using activated carbon with a BET specific surface area Sb and a ratio Sa / Sb within the above ranges. The present disclosure is based on this new finding.

[0014] The capacitor (C) includes a first electrode and a second electrode. At least one of the first electrode and the second electrode includes the polarizable electrode layer described above. Typically, both the first electrode and the second electrode include the polarizable electrode described above.

[0015] The BET specific surface area Sb of activated carbon is 2000 m ２ / g or less, and ２ / g or less, 1700m ２ / g or less, 1600m ２ / g or less, 1500m ２ / g or less, or 1150m ２ The BET specific surface area Sb may be 900 m ２ / g or more, 1000m ２ / g or more, 1150m ２ / g or more, or 1500m ２ / g or more. The BET specific surface area Sb is 1000 to 1700 m ２ / g. When the BET specific surface area Sb of the activated carbon is large, the capacity increases but the internal resistance also increases. ２ / g), the internal resistance can be reduced.

[0016] The external specific surface area Sa of the activated carbon is 170 m ２ / g or more, 180m ２ / g or more, 200m ２ / g or more, 240m ２ / g or more, 280m ２ / g or more, or 420m ２ The external specific surface area Sa may be 1000 m / g or more. ２ / g or less, 730m ２ / g or less, 400m ２ / g or less, 250m ２ / g or less, or 200m ２ The external specific surface area Sa may be 170 to 1000 m ２ / g. The lower and upper limits of this range may be changed to the lower and upper limits as long as the lower limit is not greater than or equal to the upper limit. For example, the external specific surface area Sa of the activated carbon may be in the range of 180 to 1000 m ２ / g range (e.g., 280 to 1000 m ２ The external specific surface area Sa may be in the range of 180 m / g. ２ / g, 280m ２ On the other hand, by making the external specific surface area Sa a predetermined value or less (for example, 400 m ２ / g or less), the capacitance of the capacitor (C) can be increased.

[0017] The ratio Sa / Sb is 0.10 or more, and may be 0.15 or more, or 0.29 or more. The ratio Sa / Sb may be 0.70 or less, 0.65 or less, 0.36 or less, or 0.16 or less. By setting the ratio Sa / Sb to 0.10 or more, deterioration of the capacitor (C) can be suppressed. By setting the ratio Sa / Sb to a predetermined value or less (e.g., 0.30 or less), the capacitance of the capacitor (C) can be increased.

[0018] The activated carbon may have an average pore diameter of 2.0 nm or more, 2.5 nm or more, 3.0 nm or more, 3.2 nm or more, or 4.0 nm or less.

[0019] The capacitor (C) satisfies the following condition (1): The capacitor (C) may further satisfy the conditions (2) and / or (3): (1) The BET specific surface area Sb of the activated carbon is 2000 m ２ / g, and the ratio Sa / Sb of the external specific surface area Sa determined by the t-plot method to the BET specific surface area Sb is 0.10 or more. (2) The external specific surface area Sa of the activated carbon is 180 to 1000 m ２(3) The average pore diameter of the activated carbon is 3.0 nm or more.

[0020] The numerical ranges described in conditions (1) to (3) may be replaced with other numerical ranges described above. Note that the evaluation value for activated carbon in one polarizable electrode layer can be considered to be the value obtained when all activated carbons contained in that polarizable electrode layer are evaluated together.

[0021] (BET Specific Surface Area) The BET specific surface area Sb of activated carbon is measured using the adsorption isotherm of nitrogen gas.

[0022] (External Specific Surface Area) The external specific surface area Sa of activated carbon is determined by the t-plot method based on the nitrogen gas adsorption isotherm. The external specific surface area is the specific surface area calculated using the t-plot method based on the nitrogen adsorption isotherm, and refers to the specific surface area excluding micropores with a pore diameter of less than 20 Å. Analysis using the t-plot method is performed by comparing and converting the data of the adsorption isotherm with a standard isotherm and graphing the relationship between the thickness t of the adsorption layer and the amount of adsorption. The t-plot method is used to analyze micropores.

[0023] (Average Pore Diameter) The average pore diameter of activated carbon can be calculated using the BET specific surface area Sb and the total pore volume V according to the following formula.

[0024] Average pore diameter=4×V / Sb The BET specific surface area Sb, the external specific surface area Sa, and the total pore volume V can be measured using, for example, a Tristar II Plus 3020 manufactured by Shimadzu Corporation.

[0025] (Activated Carbon) Activated carbon having the above physical properties may be prepared by mixing commercially available activated carbons having the specified physical properties. Alternatively, activated carbon may be produced by heat treating a raw material to convert it into a carbonized product, and then activating the carbonized product to make it porous. Examples of raw materials include wood, coconut shells, pulp waste liquor, coal-based pitch, petroleum-based pitch, phenolic resin, petroleum coke, and coal coke.

[0026] The activation treatment may be gas activation using a gas (such as water vapor). Alternatively, the activation treatment may be zinc chloride (ZnCl ２The activated carbon obtained by the activation treatment may be subjected to a pulverization treatment. After the pulverization treatment, classification may be performed. The pulverization treatment may be performed using a ball mill, a jet mill, or the like. After the pulverization treatment, the activated carbon may be heat-treated at a high temperature to remove functional groups on the surface of the activated carbon.

[0027] The pore structure can be controlled by the starting material and / or activation method. Activating wood with chemicals (e.g., zinc chloride, phosphoric acid) facilitates the formation of mesopores with diameters of 2 to 50 nm, making it possible to increase the external specific surface area Sa. On the other hand, activating coconut shell with gas (e.g., water vapor, carbon dioxide) makes it possible to increase the BET specific surface area Sb. Therefore, in order to obtain activated carbon that satisfies the above condition (1), it is preferable to use activated carbon activated with zinc chloride or phosphoric acid.

[0028] The components other than the essential components of the capacitor (C) are not particularly limited, and components used in known electrochemical capacitors may be applied. Examples of the components of the capacitor (C) are described below. However, the capacitor (C) is not limited to the examples described below.

[0029] The capacitor (C) typically includes a first electrode, a second electrode, a separator, and an electrolyte, all of which are housed in an exterior housing. If necessary, the capacitor (C) may also include other components (lead wires).

[0030] (First and Second Electrodes) The first electrode and the second electrode are a pair of electrodes. The first electrode and the second electrode face each other with a separator interposed therebetween. The first electrode and the second electrode may be a positive electrode and a negative electrode, respectively. The configuration of the first electrode and the configuration of the second electrode may be the same or different.

[0031] The first and second electrodes are polarizable electrodes. The polarizable electrodes contain an active material capable of adsorbing and desorbing ions. The adsorption of ions to the active material generates capacitance. The desorption of ions from the active material causes a non-Faradic current to flow. From one perspective, the electrochemical capacitor (C) is an electric double layer capacitor (EDLC) in which an electric double layer is formed by the adsorption of ions to the active material.

[0032] The polarizable electrode includes a polarizable electrode layer. The polarizable electrode may include a current collector and a polarizable electrode layer disposed on the current collector. The positive electrode may include a positive electrode current collector and a polarizable electrode layer disposed on the positive electrode current collector. The negative electrode may include a negative electrode current collector and a polarizable electrode layer disposed on the negative electrode current collector.

[0033] The polarizable electrode layer of the capacitor (C) contains the above-mentioned activated carbon as an active material. The proportion of activated carbon in the active material in the polarizable electrode layer may be 80 mass % or more, 90 mass % or more, or 95 mass % or more. Activated carbon alone may be used as the active material in the polarizable electrode layer of the capacitor (C). The polarizable electrode layer may contain other components (such as a binder or a conductive material) as necessary.

[0034] Examples of binders include polymers such as polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), etc. Examples of conductive materials include carbon black (acetylene black, ketjen black, etc.).

[0035] The current collector may be a conductive sheet, such as a metal foil (e.g., aluminum foil). The surface of the current collector may be roughened by etching or other methods.

[0036] The method for forming the electrode is not particularly limited. The electrode may be formed by the following method. First, a slurry is prepared by mixing activated carbon, a binder and / or a conductive material, and a dispersion medium. Next, the slurry is applied to the surface of a current collector and dried to form a laminate of the current collector and the coating film (polarizable electrode layer). Next, the laminate is rolled as necessary. In this manner, an electrode including a current collector and a polarizable electrode layer disposed on the current collector is obtained.

[0037] (Electrolyte) The electrolyte contains a solvent (non-aqueous solvent), an ionic substance, and a buffer. The ionic substance contains a cation and an anion. The electrolyte can be prepared by dissolving the ionic substance in a solvent. The concentration of the ionic substance in the electrolyte may be 0.5 mol / L or more and may be 2.0 mol / L or more. The cation contained in the electrolyte may be one type or multiple types. The anion contained in the electrolyte may be one type or multiple types.

[0038] Examples of the solvent include lactone compounds and compounds other than lactone compounds. The solvent may consist of only one type of compound or a mixture of two types of compounds. Examples of the lactone compound include γ-butyrolactone, γ-valerolactone, and γ-caprolactone.

[0039] Examples of the solvent other than the lactone compound include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; polyhydric alcohols such as ethylene glycol and propylene glycol; cyclic sulfones such as sulfolane; amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone; ethers such as 1,4-dioxane; ketones such as methyl ethyl ketone; and formaldehyde.

[0040] By using an acetonitrile-based solvent, deterioration when a high voltage is applied can be suppressed. On the other hand, acetonitrile-based solvents can be flammable. With the capacitor (C), deterioration when a high voltage is applied can be suppressed without using an acetonitrile-based solvent.

[0041] As a cation constituting an ionic substance, NR is preferred because it has high voltage resistance and high solubility in aprotic solvents. ４ ＋ Quaternary alkylammonium ions represented by (R is an alkyl group) are preferred. The four alkyl groups R bonded to N may be the same or different. Each of the four alkyl groups R may independently be an alkyl group having 1 to 4 carbon atoms. Each of the alkyl groups R may be a straight-chain alkyl group. Examples of the cation include tetramethylammonium ion, tetraethylammonium ion, diethyldimethylammonium ion, ethyltrimethylammonium ion, and triethylmethylammonium ion. Diethyldimethylammonium ion (N(C ２ H ５ ) ２ (CH ３ ) ２ ＋ ) is generated by decomposing a small amount of water. － This is preferable in that it easily reacts with the above and the pH of the electrolyte can be easily maintained constant.

[0042] Examples of anions that constitute the ionic substance include BF ４ － , P.F. ６ － , AsF ６ － , SbF ６ － , N(FSO ２ ) ２ － (FSI), N(F ３ C Ｓ O ２ ) ２ － (TFSI) and others. ４ － and P.F. ６ －Fluorine-containing anions such as the above are preferred in that they improve the withstand voltage characteristics.

[0043] The organic salt may be composed of a quaternary alkyl ammonium cation and a fluorine-containing acid anion. Examples of such organic salts include diethyldimethylammonium tetrafluoroborate (DEDMABF ４ ), triethylmethylammonium tetrafluoroborate (TEMABF ４ ) etc.

[0044] (Separator) A separator is usually disposed between the positive electrode and the negative electrode. The separator has ion permeability and insulating properties. The separator prevents short-circuiting between the first electrode and the second electrode. The separator may be a woven fabric, a nonwoven fabric, or a microporous membrane. Examples of separator materials include polymers and glass. Examples of polymers include polyolefins (such as polyethylene) and cellulose. Examples of separators include nonwoven fabrics made of cellulose fibers, nonwoven fabrics made of glass fibers, and microporous membranes made of polyolefins. The thickness of the separator may be in the range of 8 to 300 μm (e.g., in the range of 8 to 40 μm).

[0045] (Others) A capacitor element is formed by a positive electrode, a negative electrode, and a separator. For example, a wound capacitor element is formed by winding a positive electrode, a negative electrode, and a separator so that the separator is disposed between the positive electrode and the negative electrode. The electrochemical capacitor (C) includes an exterior body that houses a capacitor element and an electrolyte. The exterior body is not particularly limited, and a known exterior body may be used. The exterior body may include an exterior case and a sealing member that seals the opening of the exterior case. The exterior case may be formed of a metal such as aluminum, stainless steel, copper, iron, or brass. The sealing member may be formed of an elastic material such as rubber (butyl rubber). The capacitor (C) may include other members (such as lead wires) as necessary.

[0046] The shape of the capacitor (C) is not particularly limited. The capacitor (C) may be a cylindrical capacitor including a wound capacitor element. The capacitor (C) may be a prismatic capacitor including a stacked capacitor element. Alternatively, the capacitor (C) may be a coin-type capacitor.

[0047] (Method for manufacturing electrochemical capacitor (C)) The method for manufacturing the capacitor (C) is not particularly limited, except that the polarizable electrode layer is formed using the activated carbon described above. The capacitor (C) may be manufactured by a known method, except that the polarizable electrode layer is formed using the activated carbon described above.

[0048] An example of a capacitor (C) according to the present disclosure will be described below with reference to the drawings. The components described above can be applied to the components of the example described below. The components of the example described below can be modified based on the above description. The matters described below may also be applied to the above embodiment. In the example described below, components that are not essential for the capacitor (C) according to the present disclosure may be omitted.

[0049] Embodiment 1 An electrochemical capacitor 10 according to embodiment 1 is shown schematically in Fig. 1. Fig. 1 is a perspective view of the electrochemical capacitor 10 with a portion cut away.

[0050] The electrochemical capacitor 10 is an electric double layer capacitor. The electrochemical capacitor 10 includes a wound capacitor element 1. The capacitor element 1 is formed by winding a first electrode (positive electrode) 2 and a second electrode (negative electrode) 3 with a separator 4 interposed therebetween. The first electrode 2, the second electrode 3, and the separator 4 are each strip-shaped. The first electrode 2 and the second electrode 3 each include a current collector and polarizable electrode layers disposed on both sides of the current collector. The polarizable electrode layers include the activated carbon described above.

[0051] A lead wire 5a is connected to the first electrode 2. A lead wire 5b is connected to the second electrode 3. The capacitor element 1 is housed in a cylindrical outer case 6 with a bottom together with an electrolyte (not shown). The opening of the outer case 6 is sealed with a sealing member 7. The lead wires 5a and 5b pass through the sealing member 7.

[0052] (Additional Note) The above description discloses the following techniques.

[0053] (Technology 1) An electrochemical capacitor including a polarizable electrode layer, wherein the polarizable electrode layer includes activated carbon, and the BET specific surface area Sb of the activated carbon is 2000 m ２ / g, and a ratio Sa / Sb of the external specific surface area Sa of the activated carbon determined by a t-plot method to the BET specific surface area Sb is 0.10 or more.

[0054] (Technology 2) The external specific surface area Sa of the activated carbon is 180 m ２ / g or more 1000m ２ / g or less.

[0055] (Technology 3) The electrochemical capacitor according to Technology 1 or 2, wherein the ratio Sa / Sb is 0.28 or more.

[0056] (Technology 4) The external specific surface area Sa of the activated carbon is 280 m ２ / g or more 1000m ２ / g or less.

[0057] (Technology 5) The electrochemical capacitor according to any one of Technologies 1 to 4, wherein the activated carbon has an average pore diameter of 3.0 nm or more.

[0058] The electrochemical capacitor according to the present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples. In these examples, a plurality of electrochemical capacitors were fabricated and evaluated.

[0059] (Capacitor A1) Capacitor A1 (electric double layer capacitor) was fabricated by the following procedure.

[0060] (1) Preparation of activated carbon Activated carbon having the physical properties shown in Table 1 was prepared as an active material. The activated carbon was produced by the method described above. The BET specific surface area Sb, external specific surface area Sa, and average pore diameter of the activated carbon were measured by the methods described above. Specifically, the measurements were performed using a Tristar II Plus 3020 manufactured by Shimadzu Corporation.

[0061] (2) Electrode Preparation Activated carbon (active material), conductive material (acetylene black: AB), dispersant (carboxymethyl cellulose: CMC), and binder (styrene butadiene rubber: SBR) were dispersed in water in a mass ratio of activated carbon: AB: CMC: SBR = 100: 6.6: 5.6: 1.0 to prepare a slurry. The slurry was then applied to a current collector and dried to form a laminate consisting of the current collector and the coating film (polarizable electrode layer). Aluminum foil (thickness: 20 μm) whose surface had been roughened by etching was used as the current collector. The resulting laminate was rolled to obtain an electrode sheet comprising a current collector and polarizable electrode layers (thickness: 70 μm) on both sides of the current collector. The electrode sheet was cut to a predetermined size to obtain positive and negative electrodes. Aluminum leads were connected to each electrode.

[0062] (3) Preparation of Capacitor Element The positive electrode and negative electrode were wound with a separator interposed therebetween to form a capacitor element. The separator was a cellulose nonwoven fabric. The formed capacitor element was dried by heating.

[0063] (4) Preparation of Electrolyte Solution: γ-butyrolactone (GBL) was dissolved in an organic salt (diethyldimethylammonium tetrafluoroborate: DEDMA) ＋ BF ４ － The concentration of the organic salt in the electrolyte solution was 1 mol / L.

[0064] (5) Assembly of Capacitor The dried capacitor element was impregnated with an electrolyte solution. The capacitor element impregnated with the electrolyte solution was housed in an aluminum case. The opening of the aluminum case was then sealed with a sealing material. The capacitor thus formed was subjected to an aging treatment at 60°C for 5.5 hours while a voltage of 2.7 V was applied. In this way, Capacitor A1 (electrochemical capacitor) was obtained.

[0065] (Evaluation of Resistance Change Ratio) The change ratio of the internal resistance of the capacitor A1 was evaluated by the following method.

[0066] (1) Initial Internal Resistance (Initial DC Resistance) Capacitor A1 was charged at a constant current of 2700 mA in an environment of −30° C. until the voltage reached 2.7 V. Next, the state in which a voltage of 2.7 V was applied to capacitor A1 was maintained for 7.5 minutes. Thereafter, capacitor A1 was discharged at a constant current of 1350 mA in an environment of −30° C. The discharge voltage during discharge was measured to obtain a discharge curve (vertical axis: discharge voltage, horizontal axis: discharge time).

[0067] The voltage V of the intercept of the linear approximation line in the range of 0.05 seconds to 0.2 seconds after the start of discharge of the discharge curve Ｓ The voltage V at the start of discharge (0 seconds after the start of discharge) was calculated. ０ minus the voltage Vs (V ０ -V Ｓ ) was calculated as ΔV. Using ΔV and the current value (1350 mA) during discharge, the initial internal resistance R1 of capacitor A1 was calculated by the following formula.

[0068] Initial internal resistance R1 = ΔV / Id (2) Internal Resistance Change Ratio Capacitor A1 was charged at a constant current of 1 A in a 50°C environment until the voltage reached 2.7 V. Next, capacitor A1 was held at 50°C for 1000 hours with a voltage of 2.7 V applied (float test). After that, capacitor A1 was discharged at a constant current of 1 A in a 25°C environment until the voltage reached 1 V. Next, the internal resistance R2 of capacitor A1 after the float test was determined using the same method as for measuring the initial internal resistance. Next, the resistance change ratio (R2 / R1) was calculated from the initial internal resistance R1 and the internal resistance R2. The closer the resistance change ratio is to 1, the smaller the change in internal resistance and the better the float characteristics.

[0069] Furthermore, the capacitor A1 was subjected to a test in the same manner as above, except that the voltage applied during the float test was changed to 2.9 V. This resulted in determining the resistance change ratio when a high voltage was applied.

[0070] (Capacitors A2 to A7 and C1) Capacitors A2 to A7 and C1 were fabricated using the same method and conditions as for Capacitor A1, except that the activated carbon (active material) was changed. The activated carbon was fabricated using the method described above. The characteristics (resistance change ratio) of the fabricated capacitors were evaluated using the same method as for Capacitor A1.

[0071] Table 1 shows the physical properties of the activated carbon used in the production of the capacitor and the evaluation results.

[0072]

[0073] Capacitors A1 to A7 are examples of electrochemical capacitors (C). Capacitor C1 is a comparative example. As shown in Table 1, capacitors A1 to A7 exhibited small resistance changes and good characteristics. Capacitors A5 to A7 also exhibited small resistance changes in a float test in which a high voltage was applied.

[0074] The present disclosure can be used in electrochemical capacitors.

[0075] 1: Capacitor element 2: First electrode 3: Second electrode 4: Separator 6: Outer case 7: Sealing member 10: Electrochemical capacitor

Claims

1. An electrochemical capacitor including a polarizable electrode layer, wherein the polarizable electrode layer includes activated carbon, and the BET specific surface area Sb of the activated carbon is 2000 m ２ / g, and a ratio Sa / Sb of the external specific surface area Sa of the activated carbon determined by a t-plot method to the BET specific surface area Sb is 0.10 or more.

2. The external specific surface area Sa of the activated carbon is 180 m ２ / g or more 1000m ２ 2. The electrochemical capacitor according to claim 1, wherein the capacitance is 0.1 / g or less.

3. The electrochemical capacitor according to claim 1, wherein the ratio Sa / Sb is 0.28 or greater.

4. The external specific surface area Sa of the activated carbon is 280 m ２ / g or more 1000m ２ 4. The electrochemical capacitor according to claim 3, wherein the capacitance is 0.1 / g or less.

5. The electrochemical capacitor according to claim 3 or 4, wherein the activated carbon has an average pore diameter of 3.0 nm or more.

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