Electrochemical capacitor

Abstract

The electrochemical capacitor comprises a polarizable electrode layer. The polarizable electrode layer comprises activated carbon. The activated carbon has a BET specific surface area Sb of less than 2000 m 2 / g. The ratio Sa / Sb of the external specific surface area Sa of the activated carbon with respect to the BET specific surface area Sb of the activated carbon, as determined by the t-plot method, is 0.10 or more.

Description

Technical Field

[0001] This disclosure relates to electrochemical capacitors. Background Technology

[0002] Electrochemical capacitors are characterized by long lifespan and rapid charging capability. Various schemes have been proposed regarding electrochemical capacitors in the past.

[0003] Claim 1 of Patent Document 1 (Japanese Patent Application Publication No. 2008-60457) discloses "a double-layer capacitor, characterized in that it comprises a polarized electrode layer containing activated carbon, a conductive auxiliary material, and a binder, wherein the external specific surface area of ​​the activated carbon (the specific surface area after removing micropores with a pore diameter of less than 20 Å, calculated from the nitrogen adsorption isotherm by the t-plot method) is 450-800 m² / unit volume of the polarized electrode layer." 2 / cm 3 Within this range, and the volume per unit volume of the polarized electrode layer based on interparticle voids is between 0.05 and 0.12 cm³. 3 / cm 3 Within the range.

[0004] Claim 1 of Patent Document 2 (Japanese Patent Application Publication No. 2021-170568) discloses "a carbonaceous material, characterized in that its BET specific surface area is 2000 m²". 2 / g or more and 3500m 2 For particles with a surface area of ​​ / g or less, 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 particle is defined as the internal specific surface area in the total specific surface area obtained by t-plot analysis, the ratio of the external specific surface area to the total specific surface area, i.e., the external specific surface area ratio, is 4.8% or more and 14.5% or less.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-60457

[0008] Patent Document 2: Japanese Patent Application Publication No. 2021-170568 Summary of the Invention

[0009] One aspect of this disclosure relates to an electrochemical capacitor. The electrochemical capacitor includes a polarized electrode layer. The polarized electrode layer includes activated carbon with a BET specific surface area (Sb) less than 2000 m². 2 / g. The ratio of the external specific surface area Sa of the activated carbon to the BET specific surface area Sb, as determined by the t-plot method, is greater than or equal to 0.10.

[0010] According to this disclosure, electrochemical capacitors with minimal degradation can be obtained. Attached Figure Description

[0011] Figure 1 This is a perspective view schematically illustrating an example of the electrochemical capacitor of Embodiment 1. Detailed Implementation

[0012] In recent years, there has been a demand for electrochemical capacitors with low degradation. This disclosure provides an electrochemical capacitor with low degradation.

[0013] The following examples illustrate embodiments of this disclosure, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes illustrated, but other numerical values ​​and materials can be applied as long as the effects of this disclosure are achieved. In this specification, the description of "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower." In the following description, when lower and upper limits are illustrated for numerical values ​​relating to specific physical properties, conditions, etc., any of the illustrated lower limits and any of the illustrated upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. In the following description, when examples of constituent elements or methods are listed, unless specifically stated otherwise, only one of the listed examples can be used, or multiple of the listed examples can be used together.

[0014] (Electrochemical capacitor)

[0015] The following describes an example of the electrochemical capacitor of this embodiment. Sometimes the electrochemical capacitor of this embodiment is referred to as "electrochemical capacitor (C)" or "capacitor (C)".

[0016] The electrochemical capacitor (C) includes a polarized electrode layer. The polarized electrode layer contains activated carbon. The BET specific surface area (Sb) of the activated carbon is less than 2000 m². 2 / g. The ratio of the external specific surface area Sa to the BET specific surface area Sb of the activated carbon, calculated by the t-plot method, is greater than 0.10.

[0017] In a polarized electrode layer, capacity is achieved by adsorbing ions onto activated carbon (the active material). Therefore, the properties of the activated carbon influence the characteristics of the electrochemical capacitor. Based on our research, the inventors of this application have newly discovered that by using activated carbon with a BET specific surface area Sb and a Sa / Sb ratio within the aforementioned ranges, an electrochemical capacitor with minimal degradation can be achieved. This disclosure is based on this new insight.

[0018] The capacitor (C) includes a first electrode and a second electrode. At least one of the first electrode and the second electrode includes the aforementioned polarization electrode layer. Typically, both the first electrode and the second electrode include the aforementioned polarization electrode.

[0019] The BET specific surface area (Sb) of activated carbon is less than 2000 m². 2 / g, which can be 1800m 2 / g or less, 1700m 2 / g or less, 1600m 2 / g or less, 1500m 2 / g or less or 1150m 2 / g or less. The specific surface area of ​​BET Sb can be 900m². 2 / g or more, 1000m 2 / g or more, 1150m 2 / g or more or 1500m 2 / g or more. The specific surface area of ​​BET Sb can be 1000~1700m². 2 The range is / g. If the BET specific surface area Sb of activated carbon is large, the capacity increases; on the other hand, the internal resistance increases. This is achieved by making the BET specific surface area Sb of activated carbon less than a specified value (e.g., 2000m²). 2 / g), which can reduce internal resistance.

[0020] The external specific surface area Sa of activated carbon can be 170 m². 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 / g or more. The external specific surface area Sa can be 1000m². 2 / g or less, 730m 2 / g or less, 400m 2 / g or less, 250m 2 / g or less or 200m 2 / g or less. External specific surface area Sa can range from 170 to 1000 m². 2 The range is defined as / g. As long as the lower limit does not exceed the upper limit, the lower and upper limits of this range can be changed to the aforementioned lower and upper limits. For example, the external specific surface area Sa of activated carbon can be between 180 and 1000 m². 2 / g range (e.g., 280~1000m) 2 / g range). By setting the external specific surface area Sa to a specified value (e.g., 180m²). 2 / g、280m 2By setting the external specific surface area Sa to a value below a specified value (e.g., 400 m²), the rate of change of the internal resistance of the capacitor (C) can be reduced. 2 (Below / g) can increase the capacitance of capacitor (C).

[0021] The ratio Sa / Sb is 0.10 or higher, and can be 0.15 or higher, or 0.29 or higher. The ratio Sa / Sb can be 0.70 or lower, 0.65 or lower, 0.36 or lower, or 0.16 or lower. By setting the ratio Sa / Sb to 0.10 or higher, the degradation of the capacitor (C) can be suppressed. By setting the ratio Sa / Sb to a specified value or lower (e.g., 0.30 or lower), the capacitance of the capacitor (C) can be increased.

[0022] The average pore size of activated carbon can be above 2.0 nm, above 2.5 nm, above 3.0 nm, or above 3.2 nm. The average pore size of activated carbon can also be below 4.0 nm.

[0023] The capacitor (C) satisfies the following condition (1). The capacitor (C) may further satisfy condition (2) and / or (3).

[0024] (1) The BET specific surface area Sb of activated carbon is less than 2000 m². 2 / g, the ratio of the external specific surface area Sa to the BET specific surface area Sb, calculated by the t-plot method, is greater than 0.10.

[0025] (2) The external specific surface area Sa of activated carbon is between 180 and 1000 m². 2 The range of / g.

[0026] (3) The average pore size of activated carbon is above 3.0 nm.

[0027] The numerical ranges recorded in conditions (1) to (3) can be replaced with other numerical ranges mentioned above. It should be noted that the evaluation value of activated carbon in a polarized electrode layer can be regarded as the value when evaluating all activated carbon contained in that polarized electrode layer.

[0028] (BET specific surface area)

[0029] The BET specific surface area Sb of activated carbon was determined using the nitrogen adsorption isotherm.

[0030] (External specific surface area)

[0031] The external specific surface area Sa of activated carbon is determined using the t-plot method based on the nitrogen adsorption isotherm. The external specific surface area, calculated using the t-plot method based on the nitrogen adsorption isotherm, refers to the specific surface area after removing micropores with a diameter less than 20 Å. Analysis based on the t-plot method involves comparing / transforming the adsorption isotherm data with standard isotherms, and plotting the relationship between the adsorption layer thickness t and the adsorption amount. The t-plot method is used for micropore analysis.

[0032] (Average aperture)

[0033] The average pore size of activated carbon can be calculated using the BET specific surface area Sb and the total pore volume V by the following formula.

[0034] Average pore size = 4 × V / Sb

[0035] BET specific surface area Sb, external specific surface area Sa, and total pore volume V can be measured, for example, using the Tristar II Plus 3020 from Shimadzu Corporation.

[0036] (Activated carbon)

[0037] Activated carbon possessing the aforementioned properties can be prepared by mixing commercially available activated carbon with the specified properties. Alternatively, activated carbon can be produced by heat-treating the raw materials to transform them into carbonides, and then activating the carbonides to make them porous. Examples of raw materials include wood, coconut shells, pulp waste liquor, coal-based pitch, petroleum-based pitch, phenolic resins, petroleum coke, and coal coke.

[0038] Activation treatment can be performed using gases (such as water vapor). Alternatively, activation can be achieved using chemicals such as zinc chloride (ZnCl2), acids (such as phosphoric acid), or bases (such as potassium hydroxide). The activated carbon obtained from the activation treatment can then be pulverized. After pulverization, it can be graded. Pulverization can be performed using ball mills, spray mills, etc. By heat-treating the pulverized activated carbon at high temperatures, the functional groups on the surface of the activated carbon can be removed.

[0039] The pore structure can be controlled by the starting materials and / or activation methods. By activating woody materials with chemicals (zinc chloride, phosphoric acid, etc.), mesopores with a diameter of 2-50 nm can be easily formed, which can increase the external specific surface area Sa. On the other hand, by activating coconut shells with gases (water vapor, carbon dioxide, etc.), the BET specific surface area Sb can be increased. Therefore, in order to obtain activated carbon that meets the above condition (1), activated carbon activated with zinc chloride or phosphoric acid is preferred.

[0040] The components of a capacitor (C) other than those required are not particularly limited, and components known to be used in electrochemical capacitors may be used. Examples of the components of a capacitor (C) are described below. However, the capacitor (C) is not limited to the examples described below.

[0041] A capacitor (C) typically comprises a first electrode, a second electrode, a separator, and an electrolyte. These are housed in an external casing. Depending on the requirements, a capacitor (C) may include other components such as leads.

[0042] (First electrode and second electrode)

[0043] The first electrode and the second electrode are a pair of electrodes. The first electrode and the second electrode are opposite each other separated by a separator. The first electrode and the second electrode can be positive and negative electrodes, respectively. The configuration of the first electrode and the second electrode can be the same or different.

[0044] The first and second electrodes are polarized electrodes. Polarized electrodes contain active materials capable of adsorbing and desorbing ions. Capacitance is achieved by adsorbing ions onto the active material. A non-Radaic current flows when ions desorb from the active material. In one view, an electrochemical capacitor (C) is an electrically double-layer capacitor (EDLC) that forms an electric double layer by adsorbing ions onto the active material.

[0045] A polarized electrode includes a polarized electrode layer. A polarized electrode may also include a current collector and a polarized electrode layer disposed on the current collector. A positive electrode may include a positive current collector and a polarized electrode layer disposed on the positive current collector. A negative electrode may include a negative current collector and a polarized electrode layer disposed on the negative current collector.

[0046] The polarization electrode layer of the capacitor (C) contains activated carbon as the active material. The proportion of activated carbon in the active material of the polarization electrode layer can be 80% by mass or more, 90% by mass or more, or 95% by mass or more. The active material of the polarization electrode layer of the capacitor (C) can be activated carbon alone. The polarization electrode layer may contain other components (binder, conductive material, etc.) as needed.

[0047] Examples of binders include polymers such as polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). Examples of conductive materials include carbon black (acetylene black, Ketjen black, etc.).

[0048] The current collector can be made of conductive sheet or metal foil (such as aluminum foil). For example, metal foil such as aluminum foil can be used. The surface of the current collector can be roughened by methods such as etching.

[0049] There is no particular limitation on the method for forming the electrode. The electrode can also 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 coated onto the surface of a current collector and dried, thereby forming a laminate of the current collector and the coating (polarized electrode layer). Then, the laminate is calendered as needed. In this way, an electrode comprising a current collector and a polarized electrode layer disposed on the current collector is obtained.

[0050] (electrolyte)

[0051] An electrolyte comprises a solvent (non-aqueous), ionic substances, and a buffer. The ionic substances include cations and anions. An electrolyte can be prepared by dissolving the ionic substances in a solvent. The concentration of the ionic substances in the electrolyte can be greater than 0.5 mol / L and between 2.0 mol / L. The electrolyte may contain one or more types of cations. Similarly, the electrolyte may contain one or more types of anions.

[0052] Examples of solvents include lactones and compounds other than lactones. A solvent can consist of only one compound or a mixture of two compounds. Examples of lactones include γ-butyrolactone, γ-valerolactone, and γ-caprolactone.

[0053] Examples of solvents other than lactones include: cyclic carbonates such as ethylene carbonate, propylene carbonate, and butyl carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; polyols 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.

[0054] By using acetonitrile-based solvents, degradation under high voltage can be suppressed. On the other hand, acetonitrile-based solvents are sometimes flammable. According to capacitor (C), degradation under high voltage can be suppressed even without using acetonitrile-based solvents.

[0055] As a cation constituting an ionic substance, considering its high voltage resistance and high solubility in aprotic solvents, NR4 is preferred. + (R stands for alkyl) represents a quaternary alkylammonium ion. The four alkyl groups R bonded to N can be the same or different. Each of the four alkyl groups R can be an alkyl group with 1 to 4 carbon atoms. Each alkyl group R can be a straight-chain alkyl group. Examples of cations include tetramethylammonium ion, tetraethylammonium ion, diethyldimethylammonium ion, ethyltrimethylammonium ion, and triethylmethylammonium ion. Diethyldimethylammonium ion (N(C2H5)2(CH3)2) +OH- is easily decomposed with trace amounts of water to produce - It is preferred in terms of its reaction rate and ease of maintaining a constant pH in the electrolyte.

[0056] Examples of anions that constitute ionic substances include BF4. - PF6 - AsF6 - SbF6 - N(FSO2)2 - (FSI), N(F3C) S O2)2 - (TFSI), etc. From the perspective of improving withstand voltage characteristics, BF4 is preferred. - and PF6 - Fluorine-containing anions.

[0057] Organic salts can be composed of quaternary alkylammonium cations and fluorinated acid anions. Examples of such organic salts include diethyldimethylammonium tetrafluoroborate (DEDMABF4) and triethylmethylammonium tetrafluoroborate (TEMABF4).

[0058] (Separator)

[0059] A separator is typically disposed between the positive and negative electrodes. The separator is both ion-permeable and insulating. It prevents short circuits between the first and second electrodes. The separator can be made of woven fabric, 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 can range from 8 to 300 µm (e.g., from 8 to 40 µm).

[0060] (other)

[0061] 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 the positive electrode, negative electrode, and separator with a separator between the positive and negative electrodes. An electrochemical capacitor (C) includes an outer casing housing the capacitor element and electrolyte. The outer casing is not particularly limited and known outer casings can be used. The outer casing may include an outer housing and a sealing member that seals the opening of the outer housing. The outer housing may also be formed of metals such as aluminum, stainless steel, copper, iron, and brass. The sealing member may also be formed of an elastic material such as rubber (butyl rubber). The capacitor (C) may include other components (leads, etc.) as needed.

[0062] The shape of the capacitor (C) is not particularly limited. The capacitor (C) can also be a cylindrical capacitor containing wound capacitor elements. The capacitor (C) can also be a square capacitor containing stacked capacitor elements. Alternatively, the capacitor (C) can also be a coin-shaped capacitor.

[0063] (Manufacturing method of electrochemical capacitor (C))

[0064] The method for manufacturing the capacitor (C) is not particularly limited except for using activated carbon as described above to form the polarization electrode layer. In addition to using activated carbon as described above to form the polarization electrode layer, the capacitor (C) can also be manufactured using known methods.

[0065] Hereinafter, an example of the capacitor (C) of this disclosure will be described with reference to the accompanying drawings. The constituent elements of the example described below can be applied using the constituent elements described above. Furthermore, the constituent elements of the example described below can be modified based on the above description. Additionally, the matters to be described below can also be applied to the above-described embodiments. Furthermore, in the example described below, constituent elements that are not essential to the capacitor (C) of this disclosure may be omitted.

[0066] (Implementation Method 1)

[0067] Figure 1 The electrochemical capacitor 10 of Embodiment 1 is shown schematically. Figure 1 This is a three-dimensional view of a portion of the electrochemical capacitor 10 cut open.

[0068] The electrochemical capacitor 10 is a 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 in between. The first electrode 2, the second electrode 3, and the separator 4 are all strip-shaped. The first electrode 2 and the second electrode 3 each include a current collector and polarized electrode layers disposed on both sides of the current collector. The polarized electrode layers include the aforementioned activated carbon.

[0069] A lead 5a is connected to the first electrode 2. A lead 5b is connected to the second electrode 3. The capacitor element 1, along with the electrolyte (not shown), is housed in a bottomed cylindrical outer casing 6. The opening of the outer casing 6 is sealed by a sealing member 7. Leads 5a and 5b pass through the sealing member 7.

[0070] (Postscript)

[0071] The following technology is disclosed through the above description.

[0072] (Technology 1)

[0073] An electrochemical capacitor comprising a polarized electrode layer,

[0074] The polarized electrode layer contains activated carbon.

[0075] The activated carbon has a BET specific surface area (Sb) of less than 2000 m². 2 / g,

[0076] The ratio of the external specific surface area Sa of the activated carbon to the BET specific surface area Sb, as determined by the t-plot method, is greater than 0.10 (Sa / Sb).

[0077] (Technology 2)

[0078] According to the electrochemical capacitor of technology 1, the external specific surface area Sa of the activated carbon is 180 m². 2 / g or more and 1000m 2 / g or less.

[0079] (Technology 3)

[0080] According to the electrochemical capacitor of technique 1 or 2, the ratio Sa / Sb is 0.28 or higher.

[0081] (Technology 4)

[0082] According to the electrochemical capacitor of technique 1 or 3, the external specific surface area Sa of the activated carbon is 280 m². 2 / g or more and 1000m 2 / g or less.

[0083] (Technology 5)

[0084] The electrochemical capacitor according to any one of techniques 1 to 4, wherein the average pore size of the activated carbon is 3.0 nm or more.

[0085] Example

[0086] The electrochemical capacitor of this disclosure will now be described in more detail through examples. This disclosure is not limited to the following examples. In these examples, multiple electrochemical capacitors were fabricated for evaluation.

[0087] (Capacitor A1)

[0088] Make capacitor A1 (double-layer capacitor) according to the following steps.

[0089] (1) Preparation of activated carbon

[0090] Activated carbon with the properties shown in Table 1 was prepared as the 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 size of the activated carbon were measured by the method described above. Specifically, the measurements were performed using a Tristar II Plus 3020 from Shimadzu Corporation.

[0091] (2) Electrode fabrication

[0092] A slurry was prepared by dispersing activated carbon (active material), conductive material (acetylene black: AB), dispersant (carboxymethyl cellulose: CMC), and binder (styrene-butadiene rubber: SBR) in water at a mass ratio of activated carbon:AB:CMC:SBR = 100:6.6:5.6:1.0. This slurry was then coated onto a current collector and dried to form a laminate consisting of a current collector and a coating (polarized electrode layer). The current collector was made of aluminum foil (thickness: 20 µm) with a roughened surface achieved through etching. The resulting laminate was calendered to obtain an electrode sheet containing a current collector and polarized electrode layers (thickness: 70 µm) on both sides of the current collector. The electrode sheet was cut to specified dimensions to obtain positive and negative electrodes. Aluminum leads were then connected to each electrode.

[0093] (3) Fabrication of capacitor components

[0094] The positive and negative electrodes are wound together with a separator in between, thereby forming a capacitor element. The separator is made of cellulose nonwoven fabric. The formed capacitor element is dried by heating.

[0095] (4) Preparation of electrolyte

[0096] Dissolve organic salts (diethyldimethylammonium tetrafluoroborate: DEDMA) in γ-butyrolactone (GBL). + BF4 - An electrolyte was prepared. The concentration of organic salts in the electrolyte was set to 1 mol / L.

[0097] (5) Capacitor assembly

[0098] The dry capacitor element is impregnated with electrolyte. The electrolyte-impregnated capacitor element is then placed in an aluminum casing. Next, the opening of the aluminum casing is sealed with a sealing member. While applying a voltage of 2.7V to the capacitor thus formed, it is aged at 60°C for 5.5 hours. In this way, capacitor A1 (electrochemical capacitor) is obtained.

[0099] (Evaluation of the resistance change ratio)

[0100] The change in the internal resistance of capacitor A1 is evaluated using the following method.

[0101] (1) Initial internal resistance (initial DC resistance)

[0102] At -30°C, capacitor A1 was charged with a constant current of 2700mA until its voltage reached 2.7V. Then, the 2.7V voltage was maintained on capacitor A1 for 7.5 minutes. Next, capacitor A1 was discharged with a constant current of 1350mA at -30°C. The discharge voltage during discharge was measured to obtain the discharge curve (vertical axis: discharge voltage, horizontal axis: discharge time).

[0103] Based on an approximate straight line in the discharge curve within the range of 0.05 seconds to 0.2 seconds from the start of discharge, calculate the voltage V at the intercept of this approximate straight line. S Subtract voltage V from the voltage V0 at the start of discharge (0 seconds after the start of discharge). S The obtained value (V0-V) S The initial internal resistance R1 of capacitor A1 is determined using ΔV and the discharge current (1350mA).

[0104] Initial internal resistance R1 = ΔV / Id

[0105] (2) Internal resistance change ratio

[0106] At 50°C, capacitor A1 was charged with a constant current of 1A until the voltage reached 2.7V. Then, with capacitor A1 at 2.7V, it was maintained at 50°C for 1000 hours (float charge test). Next, at 25°C, capacitor A1 was discharged with a constant current of 1A until the voltage reached 1V. Then, the internal resistance R2 of capacitor A1 after the float charge test was determined using the same method as for determining the initial internal resistance. Finally, the resistance change ratio (R2 / R1) was calculated from the initial internal resistance R1 and the internal resistance R2. A resistance change ratio closer to 1 indicates a smaller change in internal resistance and better float charge characteristics.

[0107] Furthermore, for capacitor A1, the voltage applied during the float charge test was changed to 2.9V, and the test was performed using the same method as described above. From this, the resistance change ratio under high voltage was determined.

[0108] (Capacitors A2~A7 and C1)

[0109] By modifying the activated carbon (active material), capacitors A2 to A7 and C1 are manufactured under the same methods and conditions as those used for capacitor A1. The activated carbon is manufactured using the methods described above. The characteristics (resistance change ratio) of the manufactured capacitors are evaluated using the same methods as those used for capacitor A1.

[0110] The physical properties and evaluation results of the activated carbon used in the manufacture of capacitors are shown in Table 1.

[0111] [Table 1]

[0112]

[0113] 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 exhibit small resistance changes, demonstrating good characteristics. Capacitors A5 to A7 also show small resistance changes even during float charge tests with applied high voltages.

[0114] Industrial availability

[0115] This disclosure can be used in electrochemical capacitors.

[0116] Explanation of reference numerals in the attached figures

[0117] 1: Capacitor Components

[0118] 2: First electrode

[0119] 3: Second electrode

[0120] 4: Divider

[0121] 6: External casing

[0122] 7: Sealing components

[0123] 10: Electrochemical capacitors

Claims

1. An electrochemical capacitor comprising a polarized electrode layer, The polarized electrode layer contains activated carbon. The activated carbon has a BET specific surface area (Sb) of less than 2000 m². 2 / g, The ratio of the external specific surface area Sa of the activated carbon to the BET specific surface area Sb, as determined by the t-plot method, is greater than 0.10 (Sa / Sb).

2. The electrochemical capacitor according to claim 1, wherein, The external specific surface area Sa of the activated carbon is 180 m². 2 / g or more and 1000m 2 / g or less.

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

4. The electrochemical capacitor according to claim 3, wherein, The external specific surface area Sa of the activated carbon is 280 m². 2 / g or more and 1000m 2 / g or less.

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

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