JP4116657B2 - Separator for electric double layer capacitor having a dense structure and electric double layer capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator that has not only improved impregnation properties of an electrolyte and ion mobility as in a conventional separator containing cellulose but also mechanical strength and oxidation-resistant reducing properties. <P>SOLUTION: In the separator for electric double layer capacitors made of a porous sheet, the porous sheet has a high-density layer with approximately 20-50% porosity and a low-density layer with approximately 50-80% porosity. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a separator for positive and negative electrode insulation (hereinafter abbreviated as “separator”) of an electric double layer capacitor, and more particularly to a separator having a dense structure in which a high-density porous layer and a low-density porous layer are laminated.

  In an electric double layer capacitor, a separator made of a porous sheet is used in order to hold an electrolytic solution and insulate a pair of positive and negative electrodes.

For example, Non-Patent Document 1 pages 34 to 37 include a tank partitioned into two compartments by a separator, an organic electrolyte filled in the tank, and two carbonaceous electrodes immersed in each compartment. A multilayer capacitor is described. An organic electrolytic solution is a solution in which a solute is dissolved in an organic solvent. Tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ) and the like are described as the solute, and propylene carbonate is described as the solvent. Activated carbon is used as the carbonaceous electrode. Activated carbon refers to amorphous carbon having a very large specific surface area because it has countless fine pores. In the present specification, amorphous carbon having a specific surface area of about 1000 m ² / g or more is referred to as activated carbon. Nonwoven fabrics such as cellulose and glass fiber are described as the material of the separator.

  Patent Documents 1 and 2 describe non-porous carbonaceous materials as polarizable electrodes used in electric double layer capacitors. This carbonaceous material has microcrystalline carbon similar to graphite, and its specific surface area is smaller than that of activated carbon. When a voltage is applied to the non-porous carbonaceous material, it is considered that electrolyte ions are inserted between layers of microcrystalline carbon similar to graphite with a solvent to form an electric double layer. Glass fiber and Japanese paper are described as the material of the separator.

  Patent Document 3 describes an electric double layer capacitor in which a non-porous carbonaceous electrode is immersed in an organic electrolyte. The organic electrolyte must exhibit ionic conductivity, and the solute is a salt in which a cation and an anion are combined. As the cation, lower aliphatic quaternary ammonium, lower aliphatic quaternary phosphonium, imidazolium and the like are described. As anions, tetrafluoroboric acid and hexafluorophosphoric acid are described. The solvent of the organic electrolyte is a polar aprotic organic solvent. Specifically, ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane and the like are described.

  Patent Document 4 describes a carbonaceous material containing graphite as a polarizable electrode used for an electric double layer capacitor. In this carbonaceous material, the rate of change in voltage becomes smaller than the voltage change curve based on the time constant due to adsorption of ions in the electrolyte from the middle of charging, and charging / discharging by adsorption and desorption of ions is performed. As a material for the separator, a porous sheet made of cellulose is described.

  Patent Document 5 describes that a porous sheet made of cellulose is used as a separator for an electric double layer capacitor. A porous sheet made of cellulose is excellent in electrolyte impregnation and ion mobility, and the internal resistance of the electric double layer capacitor can be kept low. However, cellulose is easily deteriorated by the influence of the oxidation-reduction reaction, and a separator containing cellulose is inferior in durability. This tendency becomes more prominent when the usage environment of the electric double layer capacitor becomes high. That is, a voltage drop or a short circuit is likely to occur over time.

  In particular, some carbonaceous electrodes using a non-porous carbonaceous material or a graphite-based carbonaceous material exhibit a volume change during charge / discharge, and have a high rated voltage. Therefore, a conventional separator made from cellulose has insufficient mechanical strength and chemical stability.

  On the other hand, a separator made of a synthetic resin porous sheet is known as an electronic component separator in which an electrode is immersed in an electrolytic solution. For example, Patent Document 6 describes a separator for a lithium ion secondary battery. This separator is a polyamideimide porous sheet or a composite porous sheet in which a polyamideimide porous layer and a polyolefin porous layer are laminated. This synthetic resin porous sheet is excellent in the shutdown characteristics and meltdown characteristics of the lithium ion secondary battery.

However, Patent Document 6 does not describe a separator of an electric double layer capacitor as a use of a synthetic resin porous sheet. Further, there is no description of the electrolyte retention characteristics, mechanical strength, and chemical stability as a function of the synthetic resin porous sheet, and the necessity and means for making these compatible are not described.
JP 11-317333 A JP2002-25867 JP 2000-77273 A JP-A-2005-294780 Japanese Patent Laid-Open No. 10-256088 JP 2005-281669 A JP 2005-286178 A Ikuo Okamura "Electric Double Layer Capacitor and Power Storage System" 3rd Edition, Nikkan Kogyo Shimbun, 2005

  The present invention solves the above-mentioned conventional problems, and the object of the present invention is to provide mechanical strength and oxidation resistance while being excellent in impregnation and ion mobility of an electrolytic solution in the same manner as conventional cellulose-containing separators. An object of the present invention is to provide a separator for an electric double layer capacitor that also has reducibility.

The present invention is an electrical double layer capacitor separator comprising a porous sheet,
The porous sheet has a dense structure composed of a high density layer having a porosity of about 20 to 50% and a low density layer having a porosity of about 50 to 80%.
The object of the present invention is to provide a separator for an electric double layer capacitor.

  The separator of the present invention is excellent in mechanical strength and oxidation-reduction resistance while being excellent in impregnation of the electrolytic solution and ion mobility. Therefore, for example, when used for an electric double layer capacitor, low internal resistance and high durability, particularly high durability in a high temperature environment are realized.

  FIG. 1 is a cross-sectional view showing an example of the structure of a porous sheet used in the present invention. A high density layer 101 and a low density layer 102 are laminated to form one porous sheet 103. However, the layer structure is not limited to this example, a structure in which a plurality of high-density layers and low-density layers are stacked, a structure in which two low-density layers are provided on the front and back surfaces of the high-density layer, and the surface of the low-density layer In addition, a structure in which two high-density layers are provided on the back surface is also included in the scope of the present invention.

  The high-density layer is a porous layer and has a structure in which pores are almost uniformly dispersed in a matrix of a synthetic resin or a structure in which voids are held between a large number of fibers. The porosity of the high density layer is about 20-50%, preferably about 30-50%, more preferably about 40-50%. The porosity here means the ratio of the volume of the space to the volume of the layer. The value of the porosity is determined, for example, by a known method as described in paragraph 0047 of Patent Document 6 (porosity (%) = {1−separator density / material true density} × 100).

  Measure the area of the pore cross section (void) and the area of the matrix cross section (synthetic resin) appearing on the surface of the porous layer and divide the pore cross section by the matrix cross section. It is good. For example, the cross-sectional area of the pores and the cross-sectional area of the matrix are obtained by optically observing the surface of the porous layer as image data, and performing binarization processing of the image data using a computer to obtain bright and dark areas. And the area of both parts can be calculated and measured.

  When the porosity of the high-density layer is less than about 20%, the electrolyte solution retention rate is deteriorated, the ion conductivity is deteriorated, and the internal resistance of the capacitor is increased. When the porosity of the high-density layer exceeds about 60%, self-discharge becomes large when a thin film separator is used.

  The low density layer is a porous layer having a structure similar to that of the high density layer. The porosity of the low density layer is about 50-80%, preferably about 60-75%, more preferably about 65-70%. If the porosity of the low density layer is less than about 50%, the internal resistance increases, and if it exceeds about 80%, self-discharge due to an internal short circuit increases.

  The thickness of the high-density layer (the total thickness when there are a plurality of high-density layers) is about 4 to 50%, preferably about 10 to 40%, more preferably the thickness of the synthetic resin porous sheet. It accounts for about 10-20%. If the high-density layer becomes too thin, self-discharge due to an internal short circuit increases, and if it becomes too thick, the internal resistance increases.

  The thickness of the entire porous sheet is about 15 to 100 μm, preferably about 20 to 50 μm, more preferably about 25 to 35 μm. When the thickness of the entire porous sheet is less than about 15 μm, the strength is insufficient and the insulating property is lowered. Further, when the thickness of the entire porous sheet exceeds about 100 μm, the internal resistance increases.

  The porous sheet is produced, for example, by laminating two porous sheets each having an appropriate porosity as a high density layer and a low density layer. Examples of the porous sheet suitable as the high-density layer include, for example, a polyethylene porous sheet, a polypropylene porous sheet, a polyethylene-polypropylene laminated porous sheet, a polyamideimide porous sheet, an aramid fiber porous sheet, There is a synthetic resin porous sheet. As the low density layer, the above-mentioned synthetic resin porous sheet can be used, but besides these, for example, a porous sheet containing cellulose such as paper, mixed paper, etc., an aramid fiber porous sheet, glass A fiber porous sheet, a polyvinylidene fluoride porous sheet, or the like may be used.

  A preferred porous sheet is a laminate obtained by laminating and combining a polyamideimide porous sheet and a polyolefin porous sheet. A preferred polyamideimide porous sheet includes a polyamideimide resin layer having a glass transition temperature of 70 ° C. or higher and a logarithmic viscosity of 0.5 dl / g or higher, and has an overall absorbance of 700 nm or higher and a film thickness of 0.5 or higher. The air permeability is 1 to 2000 sec / 100 cc Air, and the porosity is 35 to 80%.

  A method for producing a polyamide porous sheet is known, and is described, for example, in paragraphs 0030 to 0032 of Patent Document 6.

  The polyolefin porous sheet is made of a polyethylene or polypropylene film by, for example, a stretched hole opening method or a phase separation method described in 7th Polymer Material Forum (1998) Abstract 1 BIL09. A preferred polyolefin porous sheet has a porosity of 30 to 50%.

  In the case of laminating the polyamideimide porous sheet and the polyolefin porous sheet, if the polyamideimide porous sheet is A and the polyolefin porous sheet is B, A / B, A / B / A or B / The configuration is A / B.

The production of these composite porous sheets is not particularly limited, but the following method is preferred.
(1) A polyamideimide porous sheet and a polyolefin porous sheet are simply stacked.
(2) Using a polyolefin porous sheet as a support, a polyamideimide resin solution is impregnated or coated on one or both sides of the support, and the solution is put into a coagulation bath and solidified.

  That is, after applying or immersing a polyamideimide resin solution having a specific composition on one or both surfaces of a polyolefin porous sheet, it is mixed with a solvent in which the polyamideimide resin is dissolved, but is a poor solvent for the polyamideimide resin. Throw in and solidify.

  In this case, the porosity is adjusted so that the polyolefin-based porous film corresponds to the high-density layer, and the porosity is adjusted so that the polyamide-imide resin layer corresponds to the low-density layer. The porosity can be controlled by the impregnation time of the extraction solvent.

  In the case of a composite porous sheet, the total film thickness is 10 to 100 μm, preferably 15 to 70 μm. The porosity is 30 to 80%, and the air permeability is 1 to 2000 sec / 100 cc Air.

  The manufacturing method of such a composite porous sheet is well-known, For example, it describes in the 0035-0037 paragraph of patent document 6, and the 0050-0055 paragraph.

  The obtained porous sheet has a dense structure and can be suitably used as a separator of an electric double layer capacitor.

  The structure of the electric double layer capacitor is shown, for example, in FIGS. 5 and 6 of Patent Document 1, FIG. 6 of Patent Document 2, FIGS. 1 to 4 of Patent Document 3, and the like. In general, such an electric double layer capacitor can be assembled by impregnating an electrolytic solution after constituting a positive electrode and a negative electrode by overlapping electrode members with a separator interposed therebetween.

  What is necessary is just to use what has been conventionally used for the electric double layer capacitor as an electrode member. For example, a polarizable electrode can be formed using a polarizable electrode material such as activated carbon particles, non-porous carbonaceous particles, and graphite, and bonded to a collector electrode to obtain an electrode member.

  The polarizable electrode material may include a carbon material that substantially expands when the electric double layer capacitor is charged. For example, the non-porous carbonaceous particles are graphite-like microcrystalline carbon, and when a voltage is applied, electrolyte ions intercalate with a solvent between the graphite-like microcrystalline carbon layers, resulting in the electrode It is believed that substantial expansion occurs.

  A preferable non-porous carbon is, for example, described in Patent Document 7, and can be produced as follows.

  The powder of needle coke green powder is baked at 500 to 900 ° C., preferably 600 to 800 ° C., more preferably 650 to 750 ° C. for 2 to 4 hours in an inert atmosphere, for example, an atmosphere of nitrogen or argon. It is considered that a crystal structure of a carbon structure is formed in this firing step.

  The calcined carbon powder is mixed with an alkali hydroxide having a weight ratio of 1.8 to 2.2 times, preferably about 2 times. The powder mixture is calcined at 650 to 850 ° C., preferably 700 to 750 ° C. for 2 to 4 hours under an inert atmosphere. This process is called alkali activation, and it is considered that the alkali metal vapor penetrates the carbon structure and has the effect of loosening the crystal structure of carbon.

  The resulting powder mixture is then washed to remove the alkali hydroxide. In the washing, for example, particles are collected from the carbon after the alkali treatment, filled in a stainless steel column, 120 to 150 ° C., 10 to 100 kgf, preferably 10 to 50 kgf of pressurized water vapor is introduced into the column, This can be done by continuing to introduce pressurized steam until the pH is ˜7 (usually 6-10 hours). After completion of the alkali removal step, an inert gas such as argon or nitrogen is passed through the column and dried to obtain the desired non-porous carbon powder.

  In addition to carbon black, powdered graphite and the like can be used as the conductive auxiliary for the polarizable electrode, and PVDF, PE, PP and the like can be used in addition to PTFE as the binding resin. In this case, the blending ratio of non-porous carbon, conductive auxiliary agent (carbon black) and binder resin (PTFE) is generally about 10: 1: 0.5-10: 0.5-0.25. is there.

  As the electrolytic solution, a so-called organic electrolytic solution obtained by dissolving an electrolyte as an solute in an organic solvent can be used. As electrolyte, what is normally used by those skilled in the art as described in patent document 3 can be used. Specifically, lower aliphatic quaternary ammonium such as triethylmethylammonium (TEMA), tetraethylammonium (TEA) and tetrabutylammonium (TBA), lower aliphatic quaternary phosphonium such as tetraethylphosphonium (TEP), or Examples thereof include a salt of an imidazolium derivative such as 1-ethyl-3-methylimidazolium (EMI) and tetrafluoroboric acid or hexafluorophosphoric acid.

  Among them, preferred electrolytes are pyrrolidinium compounds and their derivatives. Preferred pyrrolidinium compound salts have the formula

[Wherein, each R is independently an alkyl group or an alkylene group linked together, and X ⁻ is a counter anion. ]
It has the structure shown by. The pyrrolidinium compound salt is known and may be synthesized by a method known to those skilled in the art.

  Preferred for the ammonium component of the pyrrolidinium compound salt is that in the above formula, each R is independently an alkyl group having 1 to 10 carbon atoms or an alkylene group having 3 to 8 carbon atoms linked together. More preferably, R is an alkylene group having 4 carbon atoms linked together (spirobipyrrolidinium) or an alkylene group having 5 carbon atoms (piperidine-1-spiro-1′-pyrrolidinium). It is. This is because the use of such a compound provides the advantage that the decomposition voltage has a wide potential window and dissolves in a large amount in a solvent. However, the alkylene group may have a substituent.

The counter anion X ⁻ may be any one that has been conventionally used as an electrolyte ion of an organic electrolyte. For example, a tetrafluoroborate anion, a fluoroborate anion, a fluorophosphate anion, a hexafluorophosphate anion, a perchlorate anion, a borodisalicylate anion, and a borodisoxalate anion. Preferred counter anions are tetrafluoroborate anion and hexafluorophosphate anion.

  An organic electrolyte for an electric double layer capacitor is obtained by dissolving the above electrolyte as a solute in an organic solvent. The concentration of the electrolyte in the organic electrolyte is adjusted to 0.8 to 3.5 mol%, preferably 1.0 to 2.5 mol%. When the concentration of the electrolyte is less than 0.8 mol%, the number of ions contained is insufficient and sufficient capacity cannot be obtained. Moreover, even if it exceeds 2.5 mol%, it does not contribute to the capacity and is meaningless. The electrolyte may be used alone or a plurality of types may be mixed. You may use together the electrolyte conventionally used for the organic electrolyte solution.

  As the organic solvent, those conventionally used for organic electric double layer capacitors may be used. For example, ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), sulfolane (SL), and the like are preferable because of their excellent electrolyte solubility and high safety. Also useful are those containing these as a main solvent and at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as a sub-solvent. This is because the low temperature characteristics of the electric double layer capacitor are improved. Further, when acetonitrile (AC) is used as the organic solvent, the conductivity of the electrolytic solution is increased, which is preferable in terms of characteristics. However, the use may be limited.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “part” or “%” is based on weight unless otherwise specified.

Reference example 1
The potassium hydroxide pellets were pulverized in advance with a mill to obtain powder. Nippon Steel-made coal-based needle coke green powder (NCGP) was calcined at about 800 ° C. for 3 hours while being naturally cooled in an alumina crucible while circulating nitrogen in a muffle furnace. Next, the roughly fired product was mixed with 1.5 times the potassium hydroxide powder per weight ratio. Each was put in a nickel crucible and covered with a nickel lid to shut off the outside air. This was activated for 4 hours at 750 ° C. while circulating nitrogen in a muffle furnace. The fired product was taken out, washed lightly with pure water, and then washed by applying ultrasonic waves. The time is 1 minute. Next, water was separated using a Buchner funnel. The same washing operation was repeated until the pH of the washing water reached around 7. This was dried in a vacuum dryer at 200 ° C. for 10 hours.

The obtained carbon was pulverized for 1 hour with 10 mmφ alumina balls using a ball mill (AV-1 manufactured by Fujiwara Seisakusho). When the particle size was measured with a Coulter counter, all of them became powdery with a center particle diameter of about 10 microns. It was 80 m < ² > / g when the specific surface area of the obtained powdery carbon was measured by BET method. The pore volume with a pore diameter of 0.8 nm or less was 0.04 ml / g.

  Powdered carbon (CB) was mixed at a mixing ratio of 10: 1: 1 of acetylene black (AB) and polytetrafluoroethylene powder (PTFE), and kneaded in a mortar. In about 10 minutes, PTFE was stretched and formed into flakes. This was pressed with a press machine to obtain a carbon sheet having a thickness of 200 microns. This carbo sheet was punched into a 20 mmφ disk to obtain a positive electrode and a negative electrode.

  Paper-based porous sheet (“TF paper separator” manufactured by Nippon Kogyo Paper Industries Co., Ltd., thickness 35 μm, porosity 73%) and synthetic resin porous sheet (“Polypropylene separator” manufactured by Celgard Co., Ltd., thickness 25 μm, porosity 37% ( Catalog value)) was prepared.

  Image data was obtained by optically observing the surface of the synthetic resin porous sheet with an Omron microscope VC-4500. Using a computer and image processing software, the binarization processing of the image data was performed, and the void portion and the resin portion were separated. Using the function of the software, the ratio of the area of both parts (void area / resin area) was calculated. As a result, the porosity was 34%.

  The above two types of porous sheets were punched into a 22.5 mmφ disk, and two sheets were stacked to form a separator having a dense structure.

A three-electrode cell as shown in FIG. 2 was assembled using the obtained electrode and separator. Note that either the high-density layer or the low-density layer may be disposed on any electrode side. The reference electrode used was a sheet of # 1711 activated carbon formed by the same method as above. These cells were dried in a vacuum at 220 ° C. for 24 hours and cooled. An electrolyte solution was prepared by dissolving spirobipyrrolidinium tetrafluoroborate (SBPBF ₄ ) in propylene carbonate so as to be 2.0 mol%. And the obtained electrolyte solution was inject | poured into the cell, and the electrical double layer capacitor was produced.

Power system charge / discharge test device “CDT-RD20” is connected to the assembled electric double layer capacitor, and after electric field activation, the ambient temperature is kept at 25 ° C. and constant current charging is performed at 5 mA for 7200 seconds. After reaching the set voltage, constant current discharge at 5 mA was performed. The set voltage was 3.5 V, 3 cycles were performed, and the data for the third cycle was adopted.
The capacity (F / cc) was calculated from the discharge power.
The DC resistance (Ω) was calculated from the IR drop during constant current discharge.

  Next, the ambient temperature was raised to 70 ° C., and charging / discharging under the above conditions was performed 100 cycles. Thereafter, the ambient temperature was returned to 25 ° C., charging and discharging were performed for 3 cycles, and the capacity and internal resistance were calculated. The capacity retention rate (%) after 106 cycles of the electric double layer capacitor, the initial internal resistance (Ω) after 3 cycles, and the internal resistance increase rate (%) after 106 cycles are shown in Table 1 together with the calculation formula.

Reference example 2
Reference except that a porous sheet made of synthetic resin (“Aramid fiber separator” manufactured by Nippon Vilene Co., Ltd., thickness 35 μm, porosity 59%) is used in place of the paper separator (“TF paper separator” manufactured by Nippon Kogyo Paper Industries) In the same manner as in Example 1 , an electric double layer capacitor was produced and tested. The test results are shown in Table 1.

EXAMPLE A composite porous sheet made of synthetic resin (“PAI porous membrane sheet” manufactured by Toyobo Co., Ltd., thickness 22 μm, average porosity 65%) was prepared. One separator has a low density layer and a high density layer.

  First, the surface of the porous sheet on the low density layer side was optically observed with a microscope VC-4500 manufactured by OMRON Corporation to obtain image data. Using a computer and image processing software, the binarization processing of the image data was performed, and the void portion and the resin portion were separated. Using the function of the software, the ratio of the area of both parts (void area / resin area) was calculated. As a result, the porosity of the low density layer was 69%. Subsequently, the surface on the high-density layer side of the porous sheet was observed and processed in the same manner, and calculation was performed. As a result, the porosity of the high density layer was 38%.

An electric double layer capacitor was produced and tested in the same manner as in Reference Example 1 except that this synthetic resin composite porous sheet was used. The test results are shown in Table 1.

Comparative Example 1
An electric double layer capacitor was prepared and tested in the same manner as in Reference Example 1 except that two sheets of “TF paper separator” manufactured by Nippon Kogyo Paper Industries Co., Ltd., thickness 35 μm, porosity 73%) were used. The test results are shown in Table 1.

Comparative Example 2
An electric double layer capacitor was fabricated in the same manner as in Reference Example 1 except that two sheets of a synthetic resin porous sheet (“Polypropylene Separator” manufactured by Celgard, thickness 25 μm, porosity 37%) were laminated and used. Tested. The test results are shown in Table 1.

Comparative Example 3
An electric double layer capacitor was produced and tested in the same manner as in Reference Example 1 except that one separator of Comparative Example 1 was used. The test results are shown in Table 1.

Comparative Example 4
An electric double layer capacitor was prepared and tested in the same manner as in Reference Example 1 except that one separator of Comparative Example 2 was used. The test results are shown in Table 1.

容量維持率(%)=C106/C3×100
抵抗増加率(%)=(R106/R3-1)×100
C3:3サイクル目容量(25℃)、C106:106サイクル目容量(25℃)
R3:3サイクル目抵抗(25℃)、R106:106サイクル目抵抗(25℃)
[Table 1]

Capacity maintenance rate (%) = C106 / C3 × 100
Resistance increase rate (%) = (R106 / R3-1) x 100
C3: 3rd cycle capacity (25 ° C), C106: 106th cycle capacity (25 ° C)
R3: 3rd cycle resistance (25 ° C), R106: 106th cycle resistance (25 ° C)

  According to the results of the examples, the electric double layer capacitor using the separator of the present invention is more excellent in durability under a high temperature environment than that using a paper material as the separator.

It is sectional drawing which shows an example of the structure of the synthetic resin porous sheet | seat used by this invention. It is an assembly drawing which shows the structure of the electric double layer capacitor of an Example.

Explanation of symbols

101 ... high density layer,
102 ... low density layer,
103 ... porous sheet,
1, 11 ... Insulating washer,
2 ... Top cover,
3 ... Spring,
4, 8 ... collector electrode,
5, 7 ... carbonaceous electrode,
6 ... separator,
9 ... Guide,
10, 13 ... O-ring,
12 ... the body,
14 ... Presser plate,
15 ... Reference electrode,
16 ... Bottom cover.

Claims (4)

After applying or immersing the polyamideimide resin solution on one or both sides of the polyolefin porous sheet, mix with the solvent in which the polyamideimide resin is dissolved, but inject into a poor solvent for the polyamideimide resin. A separator for an electric double layer capacitor comprising a composite porous sheet obtained by solidification,
The porous sheet has a dense structure composed of a high-density layer with a porosity of 20 to 50% and a low-density layer with a porosity of 50 to 80% .
The thickness of the high-density layer accounts for 4 to 50% of the thickness of the porous sheet,
The high-density layer is a porous layer having a structure in which pores are almost uniformly dispersed in a polyolefin matrix,
The low density layer is a porous layer having a structure in which pores are substantially uniformly dispersed in a matrix of polyamideimide.
The electric double layer capacitor is obtained by immersing a non-porous carbon having graphite-like microcrystalline carbon or a carbonaceous electrode containing graphite in an electrolytic solution in which a solute is dissolved in a non-aqueous solvent.
Electric double layer capacitor separator.   The separator for an electric double layer capacitor according to claim 1, wherein the high-density layer is a polyolefin porous sheet produced by a stretch-opening method or a phase separation method.   A carbonaceous positive electrode, the separator according to claim 1 and a carbonaceous negative electrode are immersed in an electrolytic solution in which a solute is dissolved in a nonaqueous solvent, and the carbonaceous positive electrode and the carbonaceous negative electrode are immersed in the electrolyte. An electric double layer capacitor, wherein at least one of the electrodes is a carbonaceous electrode containing non-porous carbon having graphite-like microcrystalline carbon or graphite.   A carbonaceous positive electrode, the separator according to claim 1 and a carbonaceous negative electrode are immersed in an electrolytic solution in which a solute is dissolved in a nonaqueous solvent, and the carbonaceous positive electrode and the carbonaceous negative electrode are immersed in the electrolyte. An electric double layer capacitor, wherein the electrode is a carbonaceous electrode containing non-porous carbon having microcrystalline carbon similar to graphite.

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