JP2010109355A - Electrical double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrical double layer capacitor having stable capacitor characteristics even at 85°C. <P>SOLUTION: In the electrical double-layer capacitor including a pair of polarizing electrodes and a separator which is arranged between these polarizing electrodes and holds an electrolyte, an organic solvent mainly containing a γ-butyrolactone is used as a solvent of the electrolyte, and a water content ratio of the electrolyte is 1,000 mass ppm or less of the whole electrolyte, thereby the electrical double-layer capacitor having stable capacitor characteristics even at 85°C is acquired. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor using a non-aqueous electrolyte.

  In general, an electric double layer capacitor is wound or laminated by interposing a separator between a pair of polarizable electrode bodies in which a polarizable electrode layer (for example, a carbon layer) is provided on a current collector such as an aluminum foil. Thus, a capacitor cell is obtained, and the capacitor cell is impregnated with an electrolytic solution and accommodated in a metal case, and the opening end is sealed.

  Such an electric double layer capacitor is required to have a high capacity and excellent long-term reliability. However, in the conventional electric double layer capacitor, a nonaqueous electrolytic solution using a carbonate-based solvent such as propylene carbonate has been used. It was. This is because an electric double layer capacitor having a high capacity and excellent load characteristics under high temperature can be obtained by using a carbonate-based solvent.

  However, when an electrolytic solution containing a carbonate-based solvent is used at a high temperature, carbon monoxide (CO) gas is generated due to the decomposition of the solvent, so that the internal pressure of the container containing the polarizable electrode body or the electrolytic solution increases. Problem arises. For this reason, the maximum use temperature of such an electric double layer capacitor is limited to 60 ° C., and there is a problem that it cannot cope with further high temperature use of 70 to 85 ° C. On the other hand, there is an attempt to enable use of an electric double layer capacitor at 70 ° C. by using γ-butyrolactone, which is less likely to generate gas due to electrolysis, as a solvent (Patent Document 1).

JP 2001-217150 A

  In the electric double layer capacitor disclosed in Patent Document 1, the internal pressure in the capacitor does not increase in a high-temperature load test in which 2.5 V is applied between polarizable electrode bodies at 70 ° C. However, as a result of investigations by the inventors, when a load test at 85 ° C. is performed on an electric double layer capacitor using a non-aqueous electrolytic solution using γ-butyrolactone as a solvent, the variation in durability is large, and the capacitor characteristics are large. There were many things that deteriorated.

  Therefore, an object of the present invention is to solve this problem and provide an electric double layer capacitor that can be used at 85 ° C.

  As a result of intensive studies, the inventors found that the variation in durability of the 85 ° C. load test of the electric double layer capacitor using the non-aqueous electrolyte containing γ-butyrolactone is the variation in the moisture content of the electrolyte. As a result, it was discovered that by using an electrolyte solution having a low water content, variation in durability can be suppressed, and an electric double layer capacitor having stable capacitor characteristics can be obtained even in an 85 ° C. load test.

  Therefore, the present invention provides an electric double layer capacitor having a pair of polarizable electrode bodies and a separator holding the electrolytic solution disposed between these polarizable electrode bodies, wherein the solvent of the electrolytic solution is γ-butyrolactone. And an organic solvent, wherein the water content of the electrolytic solution is 1000 mass ppm or less of the whole electrolytic solution.

  In the electric double layer capacitor of the present invention, since an electrolytic solution using γ-butyrolactone as a main solvent is used, deterioration of capacitor characteristics due to electrolysis of the solvent is suppressed, and the moisture content of the electrolytic solution is extremely low. Deterioration caused by moisture is suppressed, and as a result, stable capacitor characteristics can be obtained even in an 85 ° C. load test. The water content of 1000 mass ppm or less in the electrolytic solution of the electric double layer capacitor of the present invention is that the water content of the polarizable electrode body (both electrodes) used in the assembly of the electric double layer capacitor is 150 ppm or less of the entire polarizable electrode body. This can be suitably achieved.

  In the present invention, an electrolytic solution using γ-butyrolactone as a main solvent is used, and the moisture contained in the electrolytic solution is extremely low, so that deterioration of capacitor characteristics due to electrolysis of the solvent is suppressed. Further, deterioration of capacitor characteristics caused by moisture is suppressed, and an electric double layer capacitor having stable capacitor characteristics even when used at 85 ° C. can be obtained.

  In the electric double layer capacitor of the present invention, a pair of polarizable electrode bodies each having a polarizable electrode layer provided on a current collector such as an aluminum foil are opposed to each other via a separator, and a capacitor cell is manufactured. It is obtained by the step of housing in the outer case in a state impregnated with the electrolytic solution. The electric double layer capacitor of the present invention may be of any known shape such as a coin type, a wound type, and a laminated type.

  As the current collector, a conductive thin film such as aluminum, titanium, or stainless steel can be used, and an aluminum etching foil can be suitably used. As the aluminum foil, a high-purity aluminum foil having a purity of 99.9% or more, and usually an aluminum foil having a thickness of about 10 to 50 μm is used.

  A polarizable electrode body is obtained by forming a polarizable electrode layer on the current collector. In the present invention, for example, a paste obtained by mixing activated carbon powder, a conductive additive and a binder with an organic solvent or a solvent such as water is applied to a current collector and dried at 100 to 300 ° C. for 10 to 60 minutes. Thus, a polarizable electrode body can be obtained. Moreover, it can be set as a polarizable electrode body by shape | molding the said paste in a sheet form, press-contacting this sheet | seat to a collector, and drying for 10 to 60 minutes at 100-300 degreeC.

  The raw material of activated carbon constituting the polarizable electrode layer is plant-based wood, sawdust, coconut husk, pulp waste liquor, fossil fuel-based coal, petroleum heavy oil, or coal and petroleum-based pitch obtained by pyrolyzing them, For example, petroleum coke. Activated carbon is obtained by carbonizing these raw materials and then activating them.

  As the conductive assistant, carbon black and graphite, which are conductive carbon materials, can be used. Examples of carbon black include acetylene black, ketjen black, channel black, furnace black, and thermal black. These may be used alone or in combination of two or more. In particular, it is preferable to use ketjen black having a hollow shell structure. Examples of graphite include natural graphite and artificial graphite.

  Any binder may be used as long as it is usually used, for example, rubbers such as fluorine rubber, diene rubber and styrene rubber, fluorine-containing polymers such as polytetrafluoroethylene and polyvinylidene fluoride, and the like. , Polyolefin resin, acrylic resin, nitrile resin, polyester resin, phenol resin, polyvinyl acetate resin, polyvinyl alcohol resin, epoxy resin and the like. These may be used alone or in combination of two or more.

  In the present invention, the water content of the polarizable electrode body used in the assembly of the electric double layer capacitor is 150 mass ppm or less, preferably 120 mass ppm or less of the entire polarizable electrode body. When the water content of the polarizable electrode body exceeds 150 mass ppm, this water moves into the electrolytic solution, and the deterioration of capacitor characteristics caused by the water becomes remarkable. The lower the moisture content of the polarizable electrode body, the better. However, according to the above-described manufacturing method, water of about 70 ppm by mass is usually contained. The water content of the polarizable electrode body is determined by placing the polarizable electrode body in the water vaporizer of the Karl Fischer device and heating it to vaporize the water. It can be measured by introducing it into.

  In the present invention, an organic solvent containing γ-butyrolactone is used as a solvent for the nonaqueous electrolytic solution. The solvent is preferably only γ-butyrolactone, but a mixed solvent with another organic solvent may be used as long as the effects of the present invention are not impaired. As a co-solvent, carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate; trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, etc. Ethers; sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; nitrogen-containing compounds such as acetonitrile and nitromethane; methyl formate, methyl acetate, ethyl acetate, butyl acetate Organic acid esters such as methyl propionate and ethyl propionate; inorganic acid esters such as phosphoric acid triesters and carbonic acid diesters such as dimethyl carbonate, diethyl carbonate and dipropyl carbonate Diglymes; triglymes; sulfones such as sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; 1,3-propane sultone, 1,4- Sultone such as butane sultone and naphtha sultone can be used. These subsolvents may be used independently and 2 or more types may be used. The content of γ-butyrolactone in the solvent is generally 90% by mass or more, preferably 98% by mass or more, particularly preferably 100% by mass, based on the entire solvent.

Examples of the electrolyte dissolved in the solvent include metal cations, quaternary ammonium cations, carbonium cations, and the like, BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , and AlCl _4. ^-, or ^{_{RfSO 3 -, (RfSO 2)}} 2 N -, RfCO 2 - (Rf is a fluoroalkyl group having 1 to 8 carbon atoms) can be exemplified salts of anions selected from. These may be used alone or in combination of two or more.

  In the present invention, the water content of an electrolytic solution obtained by dissolving an electrolyte in an organic solvent mainly composed of γ-butyrolactone is 1000 ppm by mass or less, preferably 500 ppm by mass or less of the entire electrolytic solution. When the water content of the electrolytic solution exceeds 1000 mass ppm of the entire electrolytic solution, the deterioration of the capacitor characteristics due to the water becomes remarkable. The smaller the moisture content of the electrolyte solution, the better, but generally about 10 ppm by weight of moisture is contained. The water content of the electrolytic solution is determined by disassembling the assembled electric double layer capacitor, collecting the electrolytic solution by centrifuging the capacitor cell containing the electrolytic solution, and curling the collected electrolytic solution. It can be measured by performing a Fisher titration.

  The electric double layer capacitor of the present invention suppresses the deterioration of the capacitor characteristics due to the electrolysis of the solvent, and also suppresses the deterioration of the capacitor characteristics caused by moisture, and exhibits stable capacitor characteristics even in the 85 ° C. load test. .

  The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples.

1: Preparation of an electric double layer capacitor Example 1
A slurry is prepared by stirring activated carbon and ketjen black in an aqueous carboxymethyl cellulose (CMC) solution and mixing an acrylic elastomer into the solution. The resulting slurry is collected using a coating machine. A sheet was prepared by coating the both sides of the aluminum etching foil with a thickness of 160 μm on one side of the coated film after drying. Further, this sheet was roll-pressed so that the thickness of one surface of the coating film was 150 μm, and dried in air at 150 ° C. for 20 minutes to obtain a polarizable electrode body serving as a positive electrode and a negative electrode. The obtained polarizable electrode body is placed in the moisture vaporizer of the Karl Fischer device, heated at 200 ° C. for 60 minutes to vaporize the moisture, and the vaporized moisture is introduced into the Karl Fischer titration cell with a dry inert gas. When the water content of the polarizable electrode body was measured, it was 100 ppm by mass.

  Next, a connection terminal is connected to the polarizable electrode body, and two sheet-like polarized electrode bodies of positive and negative electrodes are arranged so as to face each other, and a cell separator is interposed between them to create a capacitor cell. did.

  This capacitor cell is impregnated with 1.5M boron tetrafluoride triethylmethylammonium / γ-butyrolactone solution as an electrolytic solution, and further inserted into a cylindrical aluminum outer case having an open end, and the opening is opened by a sealing member. The connection terminal provided on the aluminum etching foil of the polarizable electrode body was joined to the external terminal of the sealing member. An electric double layer capacitor having a diameter of 35 mm and a length of 105 mm was produced by discharging after applying voltage and aging. The electrolytic double layer capacitor is disassembled, the electrolytic solution is collected by centrifuging the capacitor cell containing the electrolytic solution, and the collected electrolytic solution is subjected to Karl Fischer titration to obtain the moisture content of the electrolytic solution. When the content rate was measured, it was 100 mass ppm.

Examples 2-3 and Comparative Examples 1-3
The procedure of Example 1 was repeated using polarizable electrode bodies with different drying conditions. Comparative Example 3 is an example in which the polarizable electrode body was not dried. Table 1 below collectively shows the water content of the polarizable electrode body used when the electric double layer capacitor was prepared and the water content of the electrolytic solution collected by disassembling the electric double layer capacitor. As the water content of the polarizable electrode body increases, the water content of the electrolytic solution also tends to increase. In Example 1 and Example 2, although the water content of the polarizable electrode body is the same, the electrolytic solution In Comparative Example 1 and Comparative Example 2, the water content of the polarizable electrode body is different, although the water content of the electrolyte solution is the same. This is considered to reflect the difference in the amount of water mixed in the electrolyte in the process of producing the electric double layer capacitor.

Example 4
The procedure of Example 1 was repeated using styrene butadiene elastomer instead of acrylic elastomer and using the polarizable electrode body used in Example 2. Table 1 below shows the moisture content of the polarizable electrode body used at the time of producing the electric double layer capacitor and the moisture content of the electrolyte collected by disassembling the electric double layer capacitor.

Example 5
The procedure of Example 1 was repeated by using a styrene butadiene elastomer instead of the acrylic elastomer and using the polarizable electrode body used in Example 3. Table 1 below shows the moisture content of the polarizable electrode body used at the time of producing the electric double layer capacitor and the moisture content of the electrolyte collected by disassembling the electric double layer capacitor.

(Conventional example)
A 1M boron tetrafluoride tetraethylammonium / propylene carbonate solution was used as the electrolyte, and an electric double layer capacitor similar to that of Example 1 was produced.

2: 85 degreeC load test About the electric double layer capacitor of Examples 1-3 obtained by said method, Comparative Examples 1-3, and a prior art example, the load test which applies 2.3V at 85 degreeC was done. The electric double layer capacitor of the conventional example was also subjected to a load test in which 2.5 V was applied at 60 ° C. The increase rate of capacitance (Cap) and the increase rate of DC internal resistance (DCIR) after 500 hours and 1000 hours from the start of the load test were measured. The results are shown in Table 1.

  All of the conventional electric double layer capacitors were opened in the 85 ° C. load test. The values of the increase rate of capacitance (Cap) and the increase rate of DC internal resistance (DCIR) of the conventional electric double layer capacitor in Table 1 are values in a 60 ° C. load test.

  As can be seen from Table 1, in the electric double layer capacitor of the present invention, in the 85 ° C. load test, the moisture content in the electrolyte is 1000 ppm or less of the entire electrolyte, and the moisture content of the polarizable electrode body When it was 150 ppm or less of the whole electrode body, excellent characteristic stability equivalent to the characteristic stability at the time of a 60 ° C. load test of the electric double layer capacitor of the conventional example was shown. Therefore, it can be seen that the use temperature of the electric double layer capacitor is improved to 85 ° C. by the present invention. In addition, when the styrene butadiene elastomer is used as the binder (Examples 4 and 5), the increase in direct current internal resistance (DCIR) is suppressed as compared with the case where the acrylic elastomer is used (Examples 2 and 3). I found out that

  The present invention provides an electric double layer capacitor that can be used even at 85 ° C.

Claims (2)

In an electric double layer capacitor having a pair of polarizable electrode bodies and a separator holding an electrolytic solution disposed between these polarizable electrode bodies,
The solvent of the electrolytic solution is an organic solvent containing γ-butyrolactone,
The electric double layer capacitor characterized in that the water content of the electrolytic solution is 1000 mass ppm or less of the entire electrolytic solution.   The electric double layer capacitor according to claim 1, wherein a polarizable electrode body having a moisture content of 150 mass ppm or less of the entire polarizable electrode body is used as the polarizable electrode body.