JP4978729B2 - Electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor capable of preventing increase of electric resistance of a separator and leakage of an electrolyte even when an electrode is expanded or contracted by charge/discharge. <P>SOLUTION: In this electric double-layer capacitor, a porous electrolyte reservoir 8 capable of impregnating an electrolyte therein is arranged in an armoring case 1 in contact with a separator 7. The electrolyte reservoir 8 extends up to an area between a release valve 2 and a cell portion 9, and a space between the release valve 2 and the extending electrolyte reservoir 8 is continuously connected to a space for housing the cell portion 9 in the armoring case 1 therein. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an electric double layer capacitor.

  As disclosed in Patent Document 1 below, an electric double layer capacitor is provided with polarizable electrodes (positive electrode and negative electrode) facing each other across a separator, and is formed on the surface of the polarizable electrode in an electrolyte solution. It utilizes the double layer capacitance. Electric double layer capacitors are characterized by extremely large capacitance compared to ordinary capacitors such as aluminum capacitors. They are used for backup of electronic devices, power storage for home appliances and copiers, and for automobiles. A wide range of uses has begun, including power supplies for starting during idle stops, power supplies for hybrid vehicles, and power storage for peak shaving and leveling of wind power and solar power generation. This is a key to save energy and reduce carbon dioxide. Expected as a device.

  The electric double layer capacitor has different shapes such as a button type, a laminated type, and a wound type, but in each case, a positive electrode and a negative electrode composed of polarizable electrodes mainly composed of carbon particles such as activated carbon, and these Separators that separate the two electrodes are alternately stacked in an outer case provided with a release valve, and impregnated with an electrolytic solution (such as an electrolyte dissolved in a solution or an ionic liquid).

  Since the electric double layer capacitor does not involve a chemical reaction during charging and discharging, there is an advantage that a large current can be charged and discharged instantaneously and charging and discharging efficiency is good. In addition, it has the advantages that it can be charged and discharged more than 100,000 times, has a lifetime of 10 years or more, and is highly reliable. On the other hand, compared with a lithium ion battery etc., there exists a fault that an energy density is low.

  Therefore, in order to increase the energy density of the electric double layer capacitor, a device for optimizing the combination of the pore diameter of carbon and the size of the electrolyte, or increasing the energy density by using nanogate carbon or nanocarbon has been devised. For example, Patent Document 2 below discloses that the energy density can be improved to nearly six times that of the prior art by using nonporous charcoal with a developed multilayer graphene layer. It is also known that the energy density can be increased by using nanocarbon such as carbon nanotubes.

Japanese Patent Laid-Open No. 11-150042 JP 2004-289130 A

  However, when carbon having a high energy density is used as the electrode material, the electrode expands during charging and contracts during discharging. This is because intercalation causes the volume to expand due to the electrolyte being absorbed by the carbon of the electrode during charging, and the electrolyte absorbed by the electrode is discharged outside the electrode during discharging. This is because the volume shrinks. For example, when nanogate carbon is used as an electrode material, expansion of about 10% occurs during charging, and contraction of about 10% occurs during discharging.

  When the electrode expands during charging, the electrolyte solution impregnated in the separator moves to the electrode side, so that the electrolyte solution impregnated in the separator is insufficient and voids are generated in the pores of the separator. As a result, there exists a problem that the electrical resistance of a separator becomes high.

  Further, when the electrode contracts during discharge, the electrolyte discharged from the electrode moves to the separator side, and the electrolyte that cannot be stored in the separator overflows from the discharge valve to the outside of the outer case. As a result, there is a problem in that the electrolyte in the outer case is insufficient and the life is shortened, and the overflowed electrolyte causes an electrical short circuit or corrosion of the external circuit.

  The problem of insufficient electrolyte can also occur when the operating temperature of the electric double layer capacitor becomes high. This is because the liquid electrolyte leaks from the release valve to the outside of the exterior case together with the electrolyte gasified by decomposition and carbon dioxide generated by the decomposition of carbon.

  The present invention has been made to solve the above-described problems, and maintains a certain amount of electrolyte impregnated in the separator even when the electrode expands and contracts due to charge and discharge. Thus, an object of the present invention is to obtain an electric double layer capacitor that can avoid an increase in the electrical resistance of the separator and a leakage of the electrolyte to the outside of the outer case. In addition, even when the operating temperature is high, the electrolyte in the outer case is suppressed or avoided from leaking outside from the discharge valve, and even if it leaks, the electrolyte impregnated in the separator An object of the present invention is to obtain an electric double layer capacitor that can avoid a situation in which the amount of liquid immediately decreases.

The electric double layer capacitor according to the present invention is opposed to each other with a porous separator impregnated with an electrolytic solution interposed therebetween, absorbs the electrolytic solution by charging, expands, and discharges and contracts the electrolytic solution absorbed by discharging. A cell portion having a positive electrode and a negative electrode using carbon; an outer case in which the cell portion is housed; a discharge valve provided at a position away from the cell portion of the outer case; a side surface and a bottom surface of the cell portion; And a porous sheet-like electrolyte reservoir that is disposed in a gap with the inner wall and can be impregnated with the electrolyte. The separator has a protruding portion from between the positive electrode and the negative electrode, and is disposed so as to cover the outermost cell portion, the electrolyte reservoir, extend to between the discharge valve and the cell unit In addition , the separator is in contact with the side surface and the bottom surface of the cell portion .

  According to the electric double layer capacitor of the present invention, even when the electrode expands / contracts due to charge / discharge, the electrolyte solution impregnated in the separator can be maintained at a constant amount by the electrolyte reservoir. It is possible to avoid an increase in electrical resistance or leakage of the electrolyte solution outside the outer case. In addition, even when the electrolyte in the outer case leaks to the outside due to high temperature operation, the electrolyte reservoir can avoid a situation where the amount of electrolyte impregnated in the separator immediately decreases. it can.

It is sectional drawing which shows the structure of the electric double layer capacitor which concerns on Embodiment 1 of this invention. It is a front view which shows the structure of the electric double layer capacitor which concerns on Embodiment 1 of this invention. It is a side view which shows typically the positional relationship of a positive electrode, a negative electrode, a separator, and an electrolyte solution reservoir. It is a figure which shows the pore diameter distribution of a separator, the pore diameter distribution of an electrolyte solution reservoir, and the pore occupancy rate of an electrolyte solution at the time of complete charge. It is a figure which shows the pore diameter distribution of a separator, the pore diameter distribution of an electrolyte solution reservoir, and the pore occupation rate of an electrolyte solution at the time of complete discharge. It is a perspective view which shows the structure of the electric double layer capacitor which concerns on Embodiment 2 of this invention. FIG. 7 is a cross-sectional view schematically showing a cross-sectional structure when the electric double layer capacitor shown in FIG. 6 is cut along a virtual plane.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, the element which attached | subjected the same code | symbol shall show the same or an equivalent element.

Embodiment 1 FIG.
1 and 2 are a cross-sectional view and a front view, respectively, showing the structure of the electric double layer capacitor according to Embodiment 1 of the present invention. Referring to FIGS. 1 and 2, a cell portion 9 is configured by laminating a plurality of sets of positive electrodes 6 a and negative electrodes 6 b facing each other with a porous separator 7 interposed therebetween. As the positive electrode 6a and the negative electrode 6b, a layer having a thickness of several hundreds μm is used in which activated carbon or nanogate carbon having a diameter of about 10 μm is fixed using a fluorine-based resin such as PTFE (polytetrafluoroethylene) as a binder. It is done.

  The positive electrode 6a is formed on the positive electrode current collector plate 5a, and the negative electrode 6b is formed on the negative electrode current collector plate 5b. Aluminum foil is used as the positive electrode current collector plate 5a, and the positive electrode 6a is formed on one or both surfaces of the positive electrode current collector plate 5a. Similarly, an aluminum foil is used as the negative electrode current collector plate 5b, and the negative electrode 6b is formed on one or both surfaces of the negative electrode current collector plate 5b. The positive electrode current collector plate 5a is connected to the positive electrode terminal 3a, and the positive electrode terminal 3a is drawn out of the outer case 1 while being sealed by the seal portion 4a. Similarly, the negative electrode current collector plate 5b is connected to the negative electrode terminal 3b, and the negative electrode terminal 3b is drawn out of the outer case 1 while being sealed by the seal portion 4b.

  The cell unit 9 is accommodated in the outer case 1. As the outer case 1, a laminate film in which a resin such as polyethylene is bonded to the surface of an aluminum foil is used. The outer case 1 is provided with a discharge valve 2. The discharge valve 2 is provided with a small through hole, and this through hole is normally closed by the valve. When the internal pressure of the outer case 1 increases, the valve opens and the through hole is opened. The gas in the outer case 1 is released to the outside.

  Examples of the separator 7 include celluloses such as natural pulp, natural cellulose, solvent-spun cellulose, and bacterial cellulose, and non-woven fabric containing glass fiber and non-fibrillated organic fiber, as well as nylon 66, aromatic polyamide, wholly aromatic polyamide, Aromatic polyester, wholly aromatic polyester, wholly aromatic polyester amide, wholly aromatic polyether, wholly aromatic polyazo compound, polyphenylene sulfide (PPS), poly-p-phenylenebenzobisthiazole (PBZT), poly-p-phenylene Philylated forms such as benzobisoxazole (PBO), polybenzimidazole (PBI), polyetheretherketone (PEEK), polyamideimide (PAI), polyimide, polytetrafluoroethylene (PTFE), and many Quality film is used. The separator 7 has a thickness of about 20 μm to 50 μm, a porosity (porosity) of about 60% to 80%, and an average pore diameter of several μm to several tens of μm. There are various average pore diameters, and the same material can be easily changed with the basis weight. The average pore diameter can be easily measured using an analytical instrument such as a commercially available mercury intrusion porosimeter or gas adsorption. It is also possible to entrust the analysis by handing the sample to the analysis manufacturer.

  In the outer case 1, a porous electrolyte reservoir 8 that is in contact with the separator 7 and can be impregnated with the electrolyte is disposed. In the example shown in FIG. 1, the electrolyte reservoir 8 is disposed in the gap between the side surface and bottom surface of the cell portion 9 and the inner wall of the outer case 1. As the electrolyte reservoir 8, the same material as that of the separator 7 can be used.

  Examples of the electrolyte include a combination of a cation and an anion, and the cation is quaternary ammonium, 1,3-dialkylimidazolium, or 1,2,3-trialkylimidazolium, and the anion is BF4-, PF6-, ClO4-, Or a salt of CF3SO3- or a salt of 1-ethyl-3-methylimidazolium (EMI), 1,2-dimethyl-3-propylimidazolium (DMPI) such as AlCl4- or BF4- As the solvent, one kind selected from propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxymethane, diethoxyethane, γ-butyllactone, acetonitrile, propionitrile, or a mixed solvent of two or more of these is used. . In the present invention, the electrolytic solution means a liquid electrolyte solution containing these.

  FIG. 3 is a side view schematically showing the positional relationship between the positive electrode 6 a, the negative electrode 6 b, the separator 7, and the electrolyte reservoir 8. The positive electrode 6 a and the negative electrode 6 b are alternately sandwiched between the folded separator 7, and the electrolyte reservoir 8 is disposed so as to cover the bottom surface and the side surface of the separator 7.

  FIG. 4 is a diagram showing the pore size distribution (S7) of the separator 7, the pore size distribution (S8) of the electrolyte reservoir 8, and the pore occupancy rate of the electrolyte during full charge. FIG. 5 is a diagram showing the pore size distribution (S7) of the separator 7, the pore size distribution (S8) of the electrolyte reservoir 8, and the pore occupancy rate of the electrolyte during complete discharge. Here, the pore occupation ratio (hereinafter simply referred to as “occupancy ratio”) means the pore volume filled with the electrolyte with respect to the total pore volume.

  As shown in FIGS. 4 and 5, the average pore diameter of the electrolyte reservoir 8 is set larger than the average pore diameter of the separator 7. Therefore, the occupancy rate of the electrolyte solution in the pores of the separator 7 is kept high by the difference in pore suction force. This is because when the contact angle with the electrolytic solution is less than 90 degrees, a force for drawing the electrolytic solution is generated by capillary action, and the force becomes stronger as the pore diameter becomes smaller. If the contact angle is the same, the electrolyte solution is filled in order from the pores with the smallest pore diameter. Therefore, as shown in FIG. 4, if the amount of the electrolytic solution is smaller than the total pore volume of the electrolytic solution reservoir 8 and the separator 7, pores having a large diameter of the electrolytic solution reservoir 8 are left as a region not filled with the electrolytic solution.

  During charging, when the electrolyte is sucked into the carbon of the positive electrode 6a and the negative electrode 6b by a mechanism such as intercalation and the volume of the positive electrode 6a and the negative electrode 6b increases, the electrolyte moves from the separator 7 to the positive electrode 6a and the negative electrode 6b. A void is generated in a part of the pores of the separator 7. If voids are generated in the separator 7, the electrical resistance increases, the charging efficiency decreases, the heat generated by charging increases, the temperature increases, and the life may be shortened. However, according to the electric double layer capacitor according to the first embodiment, the electrolyte present in the large pores of the electrolyte reservoir 8 moves to the gap of the separator 7, and the gap of the separator 7 becomes the electrolyte. Will be satisfied.

  In the example shown in FIG. 4, the occupation ratio of the electrolyte solution to the pores of the separator 7 at the time of full charge is 100%. In this case, the electrical resistance of the separator 7 does not increase at all. However, if the occupancy ratio of the electrolyte in the pores of the separator 7 is 50% or more, the electrolytes in the adjacent pores of the separator 7 are connected to each other, and the increase in electric resistance is within an allowable range. Since the electrolyte solution in the separator 7 is the least during full charge, if the occupancy rate of the electrolyte solution in the pores of the separator 7 during full charge is 50% or more, the increase in the electrical resistance of the separator 7 is It will be within the allowable range.

  On the other hand, when the positive electrode 6a and the negative electrode 6b contract during discharge, the electrolyte discharged from the positive electrode 6a and the negative electrode 6b moves to the separator 7 side. When the occupancy rate of the electrolytic solution in the pores of the separator 7 exceeds 100%, the electrolytic solution that cannot be accommodated in the separator 7 is absorbed by the electrolytic solution reservoir 8. As a result, it is possible to avoid a situation in which the electrolyte overflows from the discharge valve 2 to the outside of the outer case 1. Since the electrolytic solution in the separator 7 has the largest amount at the time of complete discharge, as shown in FIG. 5, if the occupancy rate of the electrolytic solution in the pores of the electrolytic solution reservoir 8 at the time of complete discharge is 100% or less Thus, leakage of the electrolyte solution to the outside of the outer case 1 can be prevented.

  As described above, the electrolyte reservoir 8 has an electrolyte occupancy ratio of 50% or more in the pores of the separator 7 when fully charged, and an occupancy ratio of 100% of the electrolyte solution in the pores of the electrolyte reservoir 8 when fully discharged. It suffices that the electrolyte solution is impregnated with a predetermined amount so as to be not more than%. Thereby, the leakage of the electrolyte solution to the outside at the time of discharging can be prevented while keeping the increase in the electrical resistance of the separator 7 at the time of charging within an allowable range.

  It is desirable that the average pore diameter of the electrolyte reservoir 8 is larger than the average pore diameter of the separator 7, but conversely, if the contact angle with the electrolyte is smaller than that of the electrolyte reservoir 8, Since the pore suction force is higher in the separator 7 than in the electrolyte reservoir 8, the same effect as that obtained when the average pore diameter is different can be obtained.

  Referring to FIG. 1, the electrolyte reservoir 8 is disposed in the gap between the outer case 1 and the cell portion 9. The electrolyte reservoir 8 is in contact with the separator 7 a of the positive electrode 6 a at the left end of the cell part 9 and the separator 7 b of the negative electrode 6 b at the right end of the cell part 9. Specifically, the electrolyte reservoir 8 and the separators 7a and 7b are in close contact with each other in a large area because the main surfaces thereof are in contact with each other.

  The electrolyte solution is transferred at a portion where the electrolyte solution reservoir 8 and the separators 7a and 7b are in contact with each other. Since the main surfaces of the electrolytic solution reservoir 8 and the separators 7a and 7b are in close contact with each other, the electrolytic solution can be delivered efficiently. During charging, the electrolytic solution moves from the electrolytic solution reservoir 8 to the separators 7a and 7b via the contact surface between the electrolytic solution reservoir 8 and the separators 7a and 7b. The electrolyte also moves to the separator 7 at the center of the cell portion 9 by the pore suction force. On the contrary, at the time of discharging, the electrolytic solution moves from the separators 7a and 7b to the electrolytic solution reservoir 8 through the contact surface between the electrolytic solution reservoir 8 and the separators 7a and 7b. Further, as shown in FIG. 1, the electrolyte reservoir 8 and the separators 7, 7a, 7b are in contact with each other even at the bottom surface, and the electrolyte is delivered also at this portion.

  In the electric double layer capacitor, the resistance loss due to charging / discharging generates heat and the temperature rises. Depending on the installation environment for automobiles, the temperature may rise to 70 ° C. or higher. In such a case, when the electrolytic solution is gasified by oxidative decomposition and the internal pressure of the outer case 1 becomes higher than a predetermined value, the gaseous electrolytic solution is released from the release valve 2. At that time, if the liquid electrolyte is discharged from the discharge valve 2, the amount of the electrolyte is gradually reduced. However, according to the electric double layer capacitor according to the first embodiment, as shown in FIG. 1, the electrolyte reservoir 8 extends between the discharge valve 2 and the cell portion 9. Yes. Accordingly, the liquid electrolytic solution to be discharged from the discharge valve 2 is absorbed by the portion of the electrolyte reservoir 8 extending in the vicinity of the discharge valve 2. As a result, it is possible to suppress or avoid the situation where the liquid electrolyte is released to the outside of the outer case 1. Moreover, even if a part of the electrolytic solution is released, since the excess electrolytic solution is stored in the electrolytic solution reservoir 8, the amount of the electrolytic solution in the separator 7 can be kept sufficiently. Therefore, according to the electric double layer capacitor according to the first embodiment, higher life reliability can be ensured even in high temperature operation.

  As described above, according to the electric double layer capacitor according to the first embodiment, in the outer case 1, the porous electrolyte reservoir 8 that can be impregnated with the electrolyte is disposed in contact with the separator 7. Yes. Therefore, even when the positive electrode 6a and the negative electrode 6b are expanded and contracted by charging / discharging, the amount of the electrolyte solution impregnated in the separator 7 can be kept within a certain range. As a result, an increase in the electrical resistance of the separator 7 and leakage of the electrolyte solution to the outside of the outer case 1 can be avoided. Further, even when the operating temperature is high, leakage of the electrolyte in the outer case 1 from the discharge valve 2 to the outside can be suppressed or avoided. Even if it leaks, the separator 7 is impregnated. It is possible to avoid a situation in which the amount of the electrolyte solution immediately decreases.

Embodiment 2. FIG.
FIG. 6 is a perspective view showing the structure of the electric double layer capacitor according to the second embodiment of the present invention, in which a part of the outer case 1 and the electrolyte reservoir 8 is cut away. FIG. 7 is a cross-sectional view schematically showing a cross-sectional structure of the electric double layer capacitor shown in FIG.

  In the first embodiment, an example of a multilayer electric double layer capacitor has been described. However, as shown in FIGS. 6 and 7, the present invention can also be applied to a wound electric double layer capacitor.

  In the wound type electric double layer capacitor, unlike the stacked type, the cell portion 9 is configured by overlapping and winding the sheets of the positive electrode 6a, the separator 7, and the negative electrode 6b a plurality of times. In the electric double layer capacitor according to the second embodiment, the length of the sheet of the separator 7 is made longer than the length of each sheet of the positive electrode 6 a and the negative electrode 6 b, and the separator 7 is wound around the outermost periphery of the cell portion 9. Is configured to do. An electrolyte reservoir 8 is disposed in the gap between the outer case 1 and the cell portion 9. As shown in FIG. 7, the inner surface of the electrolyte reservoir 8 and the outer surface of the outermost separator 7 are in contact with each other. Although not shown in FIGS. 6 and 7, as in the first embodiment, the electrolyte reservoir 8 and the separator 7 are in contact with each other even on the bottom surfaces.

  In the wound type electric double layer capacitor, as in the case of the multilayer type electric double layer capacitor, the electrolyte reservoir 8 is disposed, so that the electrolysis in the separator 7 caused by the expansion / contraction of the positive electrode 6a and the negative electrode 6b is achieved. The increase and decrease of the liquid is absorbed, and the amount of the electrolytic solution in the separator 7 can be kept long even when the electrolytic solution decreases due to high temperature operation or the like. As a result, it is possible to obtain an effect of suppressing the deterioration of the performance of the electric double layer capacitor and improving the life reliability.

  In the first and second embodiments, the multilayer type and the wound type electric double layer capacitor have been described. However, the present invention can also be applied to a button type or box type electric double layer capacitor. Similar effects can be obtained.

  1 exterior case, 2 release valve, 6a positive electrode, 6b negative electrode, 7 separator, 8 electrolyte reservoir, 9 cell part.

Claims (6)

It has a positive electrode and a negative electrode containing carbon that are opposed to each other across a porous separator impregnated with an electrolytic solution, and that absorbs the electrolytic solution by charging and expands and discharges and shrinks the electrolytic solution that has been absorbed by discharging. Cell part,
An outer case in which the cell portion is stored;
A discharge valve provided at a position away from the cell portion of the outer case;
A porous sheet-like electrolyte reservoir that is disposed in a gap between a side surface and a bottom surface of the cell portion and an inner wall of the exterior case, and is capable of impregnating the electrolyte solution;
The separator has a portion protruding from between the positive electrode and the negative electrode, and is disposed so as to cover the outermost portion of the cell portion,
2. The electric double layer capacitor according to claim 1 , wherein the electrolyte reservoir extends between the discharge valve and the cell part, and is in contact with the separator on a side surface and a bottom surface of the cell part . 2. The electric double layer capacitor according to claim 1 , wherein the separator is stronger in drawing the electrolyte than the electrolyte reservoir, and pores that are not filled with the electrolyte remain in the electrolyte reservoir during charging. The electric double layer capacitor according to claim 2 , wherein an average pore diameter of the electrolyte reservoir is larger than an average pore diameter of the separator. The electrolyte reservoir has an occupancy rate of the electrolyte in the pores of the separator of 50% or more during full charge, and an occupancy rate of the electrolyte in the pores of the electrolyte reservoir of 100% or less during complete discharge. comprising such, characterized in that the electrolyte of a predetermined amount is impregnated, the electric double layer capacitor according to claim 2 or 3. The electric double layer capacitor according to claim 2 , wherein a contact angle of the porous material of the electrolytic solution reservoir with the electrolytic solution is larger than that of the separator. The solvent of the electrolytic solution is selected from propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxymethane, diethoxyethane, γ-butyllactone, acetonitrile, propionitrile, or a mixed solvent of two or more of these, The electric double layer capacitor according to any one of claims 1 to 5 , characterized in that:

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