KR102410490B1 - Pouch-type electric double layer capacitor - Google Patents

Abstract

The present invention, a pouch; an element comprising a plurality of current collectors disposed inside the pouch, a separator disposed spaced apart between the current collectors to isolate the plurality of current collectors, and a pair of electrodes disposed on both surfaces of each of the current collectors; In the pouch-type electric double layer capacitor comprising an electrolyte to be charged inside the pouch, it is a technical gist of the pouch to include a gas absorbing layer for absorbing gas inside the pouch. Accordingly, it is possible to suppress the volume expansion of the pouch by absorbing the gas generated in the long-term charging and discharging process from the pouch-type electric double layer capacitor through the gas absorption layer. In addition, excellent long-term reliability can be improved because there is little deterioration in characteristics such as increase in capacitance resistance and ESR.

Description

Pouch-type electric double layer capacitor

The present invention relates to a pouch-type electric double-layer capacitor, and more particularly, to a pouch-type electric double-layer capacitor capable of suppressing the volume expansion of the pouch by absorbing gas generated in the long-term charging and discharging process from the pouch-type electric double-layer capacitor through the gas absorption layer. is about

An electric double layer capacitor (EDLC) is an energy storage device in which a separator with excellent insulation is disposed between a pair of polarizable electrodes made of a carbon material to form a double layer between the electrode and an electrolyte to express capacity. one of them The electric double layer capacitor uses, as a dielectric, an electric double layer having a thickness of several nm formed at an interface between a solid having an electric charge and an electrolyte in contact with it. Although the electric double layer has a capacity of several tens of μF per 1 cm ² , it is possible to obtain a very large capacity of several hundred to several thousand F by using activated carbon having a surface area of 2,000 to 2,500 m ² as an electrode. Such an electric double layer capacitor can input and output energy in a short time among energy storage devices, so it is applied to a rectifier circuit, noise attenuation, and power pulse generation. In recent years, electric double layer capacitors have been developed, which have dramatically increased capacity compared to conventional electrochemical capacitors used in electronic devices. Applications are being promoted for load leveling of high power pulse power and peak power. In addition, among various energy storage devices, the use of eco-friendly materials, long lifespan, and high charging and discharging efficiency, etc. It is expected to be used as the main power and auxiliary power for high-output pulse power of high value-added equipment such as automobiles.

Such an electric double layer capacitor is manufactured in a cylindrical type, a prismatic type, or a pouched type according to a method of accommodating an element composed of a polarizable electrode and a separator, and in the case of a pouch type, the shape is relatively free. Cylindrical or prismatic electric double layer capacitors are generally manufactured by winding a unit stack structure in which a separator is disposed between a pair of polarizable electrodes to form a device, impregnating the device with an electrolyte, and sealing the opening of a metal container with a sealing member do. On the other hand, pouch-type electric double-layer capacitors are manufactured by stacking a plurality of unit stack structures in which a separator is disposed between a pair of polarizable electrodes in parallel, connecting the same polarized electrodes with lead tabs, and packaging with an aluminum laminate film together with an electrolyte. do. In the case of a pouch-type electric double layer capacitor, it can be easily bent or bent.

Such pouch-type capacitors are manufactured by adding organic solvents and plasticizers to improve output or capacity characteristics. At this time, the temperature inside the cell rises in an instant due to overcharge occurring during the charging and discharging process or an internal short circuit due to a failure of a specific cell among several cells, and the pouch swells due to the generation of ignitable gas. ) may occur. That is, gases such as carbon monoxide (CO) and carbon dioxide (CO ₂ ) are generated by the reaction of water and acid functional groups in the pores of activated carbon, which is a polarizable material, with the electrolyte, which increases the resistance and reduces the capacity inside the cell. . Therefore, in order to minimize gas generation due to electrochemical side reactions, the surface treatment of activated carbon and treatment to minimize the introduction of moisture in the cell assembly process are being carried out, but it is difficult to completely control the gas generation due to long-term charge and discharge. close to impossible Therefore, when gas is generated and the swelling phenomenon continues, a large amount of flammable gas is discharged at once as the side of the pouch bursts, so a technology for preventing the pouch from bursting by removing the flammable gas in the pouch is required.

Accordingly, in the prior art, a technique for preventing the pouch from bursting through a configuration including a gas outlet so that the ignitable gas in the pouch is discharged to the outside of the pouch is known, such as 'Korea Patent Office Laid-Open Patent Publication No. 10-2012-0146430 Supercapacitor and Manufacturing Method thereof' have. However, in the case of these prior arts, the process of attaching and sealing the membrane for the gas outlet to the pouch is complicated, and there is a problem in that long-term reliability is low because there is a possibility that external air may be introduced into the pouch.

Korean Patent Office Laid-Open Patent 10-2012-0146430

Accordingly, it is an object of the present invention to provide a pouch-type electric double-layer capacitor capable of suppressing volume expansion of the pouch by absorbing gas generated in the long-term charging and discharging process from the pouch-type electric double-layer capacitor through the gas absorption layer.

Another object of the present invention is to provide a pouch-type electric double layer capacitor that improves excellent long-term reliability due to less deterioration in characteristics such as increase in capacitance resistance and ESR.

The above object, the pouch; an element comprising a plurality of current collectors disposed inside the pouch, a separator disposed spaced apart between the current collectors to isolate the plurality of current collectors, and a pair of electrodes disposed on both surfaces of each of the current collectors; In the pouch-type electric double-layer capacitor comprising an electrolyte to be charged inside the pouch, the pouch-type electric double-layer capacitor comprises a gas-absorbing layer for absorbing gas inside the pouch.

Here, the gas absorption layer is made of a pair and is disposed between the pouch and the device, respectively, and the gas absorption layer preferably includes a metal form and an absorption powder embedded in the metal form.

The metal foam is made of aluminum (Al), nickel (Ni) or stainless steel material, and the metal foam preferably has an average porosity of 80% or more.

In addition, the absorption powder is sodium carbonate (Na ₂ CO ₃ ) or potassium carbonate (K ₂ CO ₃ ), which is a solid alkali carbonate, and the absorption powder is released from the gas absorption layer after the absorption powder is embedded in the metal foam. It is preferable to reduce the thickness by 20% or more compared to the initial thickness of the metal foam to prevent it from being formed, and it is preferable that the gas absorption layer has a thickness of 1 to 2 mm.

The pouch is an aluminum laminate pouch, and the electrode is preferably made of a carbon material, a conductive material and a binder, and the carbon material preferably has a specific surface area of 1,000 to 3,000 m ² /g.

The carbon material is activated carbon (active carbon), carbon black (carbon black), graphite (graphite), graphene (graphene), hard carbon (hard carbon), carbon nano fiber (carbon nano fiber), carbon nano tube (carbon nano tube) ) and mixtures thereof.

According to the above-described configuration of the present invention, it is possible to suppress the volume expansion of the pouch by absorbing the gas generated in the long-term charging and discharging process from the pouch-type electric double layer capacitor through the gas absorption layer.

In addition, excellent long-term reliability can be improved because there is little deterioration in characteristics such as increase in capacitance resistance and ESR.

1 is a perspective view of a pouch-type electric double layer capacitor according to an embodiment of the present invention;
2 is a cross-sectional view of a pouch-type electric double layer capacitor.

Hereinafter, the pouch-type electric double layer capacitor 100 according to an embodiment of the present invention will be described in detail.

As shown in FIG. 1 , the pouch-type electric double layer capacitor 100 includes a pouch 110 , a device 120 , an electrolyte 130 , a lead tab 140 , and a gas absorption layer 150 .

The pouch 110 is disposed to surround the electric double layer capacitor 100 and includes a device 120, an electrolyte 130, a lead tab 140, and a gas absorption layer 150 therein. While the electrolyte 130 is not discharged to the outside, it is sealed so that air or moisture existing outside does not flow into the pouch 110 . The pouch 110 is most preferably an aluminum laminate pouch, but is not limited thereto.

The device 120 disposed inside the pouch 110 is charged and discharged with electricity, and includes an electrode 121 , a current collector 122 , and a separator 123 .

In the present invention, the electrode 121 means a carbon material electrode including a carbon material powder, and is composed of a carbon material, a conductive material, and a binder. Carbon material is generally known to have a larger specific surface area than other materials, and when this is applied to the electrode 121 , the capacity of the electric double layer capacitor 100 can be increased. Therefore, in the present invention, the carbon material electrode 121 having a large specific surface area is used. Here, it is preferable to use a carbon material having a specific surface area of 1,000 to 3,000 m ² /g. When the specific surface area of the carbon material is less than 1,000 m ² /g, the performance of the capacitor 100 is poor, and when it exceeds 3,000 m ² /g, the moisture content on the surface of the carbon material increases as the specific surface area is large, or gas from the carbon material increases. Since a lot of is generated, it is not suitable for application to the present invention.

Such carbon materials include active carbon, carbon black, graphite, graphene, hard carbon, carbon nano fiber, and carbon nanotube. tube) and mixtures thereof, and among them, activated carbon is most preferred. Activated carbon may be phenol fiber-based activated carbon, lignocellulosic activated carbon using coconut shell as a raw material, petroleum coke-based activated carbon, etc. In the case of powder, the average particle size is 20 μm or less, and in the case of fiber, the fiber diameter is 10 to 20 μm. it is preferable

In the case of conductive materials, carbon black, graphite, graphene, hard carbon, carbon nano fiber, carbon nano tube, metal powder and its It is used by selecting one selected from the group consisting of mixing, and preferably has a diameter of 0.01 to 10 μm. If the diameter of the conductive material is less than 0.01㎛, conductivity may be reduced, and if it exceeds 10㎛, it is not possible to mix evenly with the carbon material.

Here, the binder is most preferably a polytetrafluoroethylene (PTFE, polytetrafluoroethylene)-based binder. PTFE can be used with a diameter of 0.1 to 0.5㎛, solid content alone or solid content is water (H ₂ O), xylene (xylene), methanol (methanol), ethanol (ethanol), isopropanol (isopropanol), toluene ( toluene), it can be used in the form of an emulsion dispersed in butyl acetate, etc. Since PTFE has excellent chemical resistance, heat resistance and mechanical strength, the network structure of PTFE develops as rolling is repeated to compose the electrode. When the network structure develops, since the carbon material and the conductive material are fixed inside, the filling density is increased and the contact resistance between the carbon material and the conductive material is reduced, thereby improving the electrical properties of the electrode.

The electrodes 121 made of these materials are formed as a pair, and the pair of electrodes are disposed on both surfaces of the current collector 122 . A plurality of current collectors 122 are disposed inside the pouch 110 , that is, the current collector 122 and a pair of electrodes 121 are formed as a unit, and a plurality of current collectors 122 are disposed inside the pouch 110 . The current collector 122 is preferably an aluminum foil (Al foil), but is not limited thereto. As described above, the current collector 122 is disposed between the pair of electrodes 121 , and the electrodes 122 spaced apart from each other have an anode and a cathode determined by an initial applied voltage condition.

The separator 123 is spaced apart between the current collectors 122 and serves to isolate the plurality of current collectors 122 , and is preferably disposed spaced apart between the units including the current collector 122 and the electrode 121 . It serves to prevent the electrodes 121 disposed on different current collectors 122 from contacting each other. The current collector 122 is preferably made of a material through which the electrolyte 130 passes so that the electrolyte can contact the electrode 121 disposed close to the separator 123, and the most preferable material is polypropylene. Non-woven fabric.

As described above, the device 120 including the electrode 121 , the current collector 122 and the separator 123 must be in contact with the electrolyte 130 , and for this, the electrolyte 130 is filled in the pouch 110 . The electrolyte 130 is not particularly limited, and those commonly used for the electric double layer capacitor 100 , that is, an electrochemically stable electrolyte dissolved in a polar organic solvent may be used. Here, the electrolyte is a quaternary onium cation (C ₂ H ₅ ) ₄ N ⁺ , (C ₃ H ₇ ) ₄ N ⁺ , (C ₄ H ₉ ) ₄ N ⁺ , (C ₂ H ₅ ) ₃ CH ₃ N ⁺ , (C ₂ H ₅ ) ₄ P ⁺ and the anion may be a salt composed of BF ₄ ^- , PH ₆ ^- , ClO ₄ ^- , CF ₃ SO ₃ ^- . In addition, the organic solvent is preferably selected from the group consisting of carbonate-based propylene carbonate, butyrene carbonate, ethylene carbonate, acetonitrile, and mixtures thereof.

The lead tab 140 includes a positive electrode tab and a negative electrode tab, and each of the positive and negative electrode tabs has one end coupled to the same polarizable electrode 121 inside the pouch 110 and the other end is drawn out. Therefore, the pouch 110 is formed in a shape of enclosing only the area excluding the lead tab 140 to seal. The lead tab 140 serves to transmit a current generated during discharging from the device 120 or a current flowing in during charging to the outside.

The gas absorption layer 150 disposed inside the pouch 110 absorbs gas generated inside the sealed pouch 110 to prevent swelling of the pouch. When the electric double layer capacitor 100 is charged and discharged for a long time or is used at a high voltage, gas is generated due to a reaction between the electrode 121 and the electrolyte 130 . In particular, since the carbon material included in the electrode 121 has a large specific surface area, it is used to improve the performance of the electric double layer capacitor 100 , but a water or acid functional group attached to the surface of the carbon material reacts with the electrolyte 130 , There is a disadvantage of generating a gas such as carbon monoxide (CO) or carbon dioxide (CO ₂ ). Since the resistance of the electric double layer capacitor 100 increases and the capacity decreases due to this swelling phenomenon, a technique for controlling the gas inside the pouch 110 is required. Therefore, in the present invention, the pouch 110 includes a gas absorption layer 150 that absorbs carbon monoxide or carbon dioxide to prevent swelling.

The gas absorption layer 150 is made of metal foam and absorption powder. The metal form means a porous sheet made of a metal material. The metal foam is made of aluminum (Al), nickel (Ni) or stainless steel material, and it is preferable to use a material having an average porosity of 80% or more. If the average porosity is less than 80%, the absorption powder is not sufficiently incorporated into the interior, so that the gas absorption role cannot be properly performed. The thickness of the metal foam is preferably 1 to 2 mm so that the volume of the electric double layer capacitor 100 is not increased much while sufficiently containing the absorbent powder.

Although the metal foam may be disposed inside the pouch 110 as a single piece, it is most preferable to be disposed between the pouch 110 and the device 120 as a pair in order to smoothly absorb gas. That is, it is disposed on both sides of the device 120 to effectively absorb the gas discharged from the device 120 . This metal foam is disposed at both ends of the device 120 in the pouch 110 to support the device 120 and at the same time exert a pressing effect to minimize the contact resistance between the electrodes 121 of the device 120. have.

The absorption powder embedded in the metal foam in the gas absorption layer 150 absorbs carbon monoxide or carbon dioxide and acts as an active ingredient for a chemical reaction. In order to prevent such absorbent powder from being separated from the metal foam after being embedded in the metal foam, it is recommended to reduce the thickness by 20% or more compared to the initial thickness of the metal foam by pressing the metal foam with the absorption powder up and down. desirable. A solid alkali carbonate powder in which a chemical reaction occurs by absorbing carbon monoxide or carbon dioxide in the absorption powder is most preferable. Here, the solid alkali carbonate powder means sodium carbonate (Na ₂ CO ₃ ) or potassium carbonate (K ₂ CO ₃ ), for example, sodium carbonate, carbon dioxide, and a small amount of moisture contained in the carbon material are chemically reacted through the following reaction formula this is done

<reaction formula>

Na ₂ CO ₃ + H ₂ O + CO ₂ → 2NaHCO ₃

That is, a small amount of moisture present in the electrode 121 and the gas generated from the electrode 121 react with the absorption powder to change to sodium bicarbonate (NaHCO ₃ ) powder, thereby preventing the swelling of the pouch 110 . can be prevented.

It is preferable that the average particle size of the absorbent powder is 100 μm or less, because when the particle size exceeds 100 μm, it is not easy to insert into the metal foam, so that a proper gas absorption layer 150 cannot be obtained.

An embodiment in which the pouch-type electric double-layer capacitor 100 of the present invention and the conventional pouch-type electric double-layer capacitor having such a structure were manufactured and then tested will be described as follows.

<Comparative example>

Among the pouch-type electric double layer capacitors according to the comparative example, the electrode was made of coke-based activated carbon, carbon black, and polytetrafluoroethylene as a binder with a specific surface area of 2,000 m ² /g. Carbon black: Binder = 85: 10: Mixed in a weight ratio of 5, kneaded with a certain amount of isopropyl alcohol, and then an activated carbon sheet having a thickness of 150 μm was prepared through roll pressing. The prepared activated carbon sheet was bonded to an etched aluminum current collector with a thickness of 30 μm using a conductive adhesive to prepare an activated carbon sheet electrode including the activated carbon sheet.

After the activated carbon sheet electrode is symmetrically disposed with a separator made of polypropylene nonwoven therebetween, the positive electrode and the negative electrode are determined in the initial applied voltage condition. After stacking in parallel according to the required manufacturing capacity of the activated carbon sheet electrodes of the same polarity, a separator was disposed between the electrodes, and an externally wrapped device with the separator was manufactured. At this time, each polarity terminal was drawn out in the opposite direction, and these terminals were ultrasonically welded to an aluminum lead tab.

After these devices were charged in a laminate film pouch sealed on three sides, 1.5M spirobipyrrolidium tetrafluoroborate (SBPBF ₄ ) electrolyte was injected, and the other side was sealed to prepare a pouch electric double layer capacitor.

The prepared pouch electric double layer capacitor was measured for initial capacitance and equivalent series resistance (ESR) when charged at an applied voltage of 2.7V and discharged at 1A. Subsequently, the pouch electric double layer capacitor was applied at 2.7V at 60°C, and after a high temperature load test (floating test) maintained for 1,000 hours, capacitance and equivalent series resistance were measured.

<Example>

The manufacturing method of the pouch-type electric double layer capacitor according to the embodiment was manufactured through the same method as the manufacturing method of the comparative example, except that a gas absorption layer was used.

The gas absorption layer was prepared by dispersing sodium carbonate (Na ₂ CO ₃ ) powder with a particle size of 100 μm in a 1 mm thickness and a nickel foam having a porosity of 90% and impregnating it in a dry manner, and then pressurizing it with an applied load of 1 ton/cm ² to obtain a final thickness of 0.8 mm. did Thereafter, a gas absorption layer was disposed on both sides of the device composed of an electrode and a separator, and a pouch-type electric double layer capacitor including the device and a gas absorption layer was manufactured. Electrochemical properties were measured in the same manner as in Comparative Example.

Table 1 shows the electrochemical properties of these Comparative Examples and Examples.

Early Floating test @ 2.7V, 60℃, 1000hr capacitance
(F) ESR
(mΩ) capacitance
(F) ESR
(mΩ) Volume expansion rate (%) comparative example 1,100 0.8 958 2.5 15 Example 1,120 0.8 1,060 1.0 3

It can be seen from Table 1 that the initial capacitance and ESR of the comparative example and the example show similar values. However, in the results after the high temperature load (floating test), the capacity reduction of the comparative example was 12.9%, but the example showed a decrease of 5.3%, and the example showed a smaller value due to the change in resistance. In addition, it can be seen that the volume expansion ratio of the Example shows a smaller value than that of the Comparative Example.

Therefore, when manufacturing the pouch-type electric double-layer capacitor 100 including the gas absorption layer 150 as described in the present invention, it absorbs the gas generated during the long-term deterioration process to suppress the volume expansion of the electric double-layer capacitor 100, As a result, it can be seen that changes in capacitance and resistance are minimized.

100: electric double layer capacitor
110: pouch
120: element
121: electrode
122: current collector
123: separator
130: electrolyte
140: lead tab
150: gas absorption layer

Claims (12)

pouch; an element comprising a plurality of current collectors disposed inside the pouch, a separator disposed spaced apart between the current collectors to isolate the plurality of current collectors, and a pair of electrodes disposed on both surfaces of each of the current collectors; In the pouch-type electric double layer capacitor comprising an electrolyte to be charged inside the pouch,
The pouch includes a gas absorption layer for absorbing gas,
The gas absorption layer includes a metal form (metal form), and an absorption powder impregnated in the metal form,
The gas absorption layer is a pouch-type electric double layer capacitor, characterized in that the thickness is reduced by at least 20% compared to the initial thickness of the metal foam to prevent the absorption powder from being separated after the absorption powder is embedded in the metal foam . The method of claim 1,
The gas absorption layer is made of a pair and is respectively disposed between the pouch and the device. delete The method of claim 1,
The metal foam is a pouch type electric double layer capacitor, characterized in that made of aluminum (Al), nickel (Ni) or stainless steel (stainless steel) material. The method of claim 1,
The metal foam is a pouch-type electric double layer capacitor, characterized in that the average porosity is 80% or more. The method of claim 1,
The absorbing powder is a solid alkali carbonate sodium carbonate (Na ₂ CO ₃ ) or potassium carbonate (K ₂ CO ₃ ) Pouch-type electric double layer capacitor, characterized in that. delete The method of claim 1,
The gas absorption layer is a pouch-type electric double layer capacitor, characterized in that made of a thickness of 1 to 2mm. The method of claim 1,
The pouch type electric double layer capacitor, characterized in that the aluminum laminate pouch (aluminum laminate pouch). The method of claim 1,
The electrode is a pouch type electric double layer capacitor, characterized in that made of a carbon material, a conductive material and a binder. 11. The method of claim 10,
The carbon material is a pouch-type electric double layer capacitor, characterized in that the specific surface area of 1,000 to 3,000 m ² /g. 11. The method of claim 10,
The carbon material is activated carbon (active carbon), carbon black (carbon black), graphite (graphite), graphene (graphene), hard carbon (hard carbon), carbon nano fiber (carbon nano fiber), carbon nano tube (carbon nano tube) ) and a pouch type electric double layer capacitor, characterized in that it is selected from the group consisting of mixtures thereof.

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