KR20170130999A - Pouch-type electric double layer capacitor - Google Patents

Abstract

The present invention relates to a pouch-type electric double layer capacitor which comprises: a pouch; a device composed of a plurality of current collectors disposed in the pouch, a separation film disposed between the current collectors to isolate the plurality of current collectors, and a pair of electrodes disposed on both sides of the current collector; and an electrolyte filled in the pouch. A gas absorbing layer for absorbing gas is included in the pouch. Therefore, the volume expansion of the pouch can be restrained by absorbing gas generated in charging and discharging processes for a long period of time from the pouch-type electric double layer capacitor through the gas absorbing layer. In addition, deterioration in characteristics such as an increase in resistance of capacitance and an increase in ESR is small, thereby improving excellent long-term reliability.

Description

[0001] Pouch-type electric double layer capacitor [0002]

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 a pouch by absorbing gas generated in a pouch electric double layer capacitor during a long- .

In an electric double layer capacitor (EDLC), a separator having an excellent insulating property is disposed between a pair of polarizable electrodes made of a carbon material to form a double layer between the electrode and the electrolyte to form an energy storage device Lt; / RTI > Such an electric double layer capacitor uses an electric double layer having a thickness of several nanometers, which is formed at the interface between a solid having a charge and an electrolyte in contact therewith, as a dielectric. The capacity of the electric double layer is several tens of micro F per cm ^2, but 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 is capable of inputting and outputting energy in an energy storage device in a short time, and is applied to a rectifier circuit, noise attenuation, and pulse generation for power supply. In recent years, electric double layer capacitors have been developed which have a dramatically increased capacity as compared with conventional electrochemical capacitors used in electronic devices. Due to high output pulse power capability and high capacity energy storage capability, a small and lightweight electrochemical energy storage device, And application for load equalization of large output pulse power and peak power. In addition, among the various energy storage devices, the use of environmentally friendly materials, long lifespan and high discharge efficiency, and the importance of technology in environmental and economical aspects have been emphasized as the applications of electric double layer capacitors in military, aerospace, It is expected to be used as main power and auxiliary power for large output pulse power of high value equipment such as automobiles.

Such an electric double layer capacitor is manufactured in a cylinder type, a prismatic type or a pouched type according to a method of accommodating a device composed of a polarized electrode and a separator. In the case of a pouch type, free. A cylindrical or prismatic electric double layer capacitor is generally manufactured by winding a unit laminate structure in which a separator is disposed between a pair of polarizable electrodes to form an element, impregnating the element with an electrolytic solution, sealing the opening of the metal container with a sealing member do. On the other hand, in the pouch type electric double layer capacitor, a plurality of unit laminate structures in which a separator is disposed between a pair of polarizable electrodes are stacked in parallel, and then the same polarizable electrodes are connected to each other by lead tabs and then packed in an aluminum laminate film together with an electrolytic solution do. Since the pouch type electric double layer capacitor can easily bend or bend, it is configured to be used for a long time by combining a rigid case on the outside.

These pouch-type capacitors are manufactured by adding organic solvents and plasticizers to improve output or capacity characteristics. In this case, when the overcharge occurs in the charge and discharge processes, or the temperature inside the cell rises instantaneously due to the occurrence of an internal short-circuit due to the failure of the specific cell among several cells, and the swelling of the pouch ) Phenomenon may occur. That is, the moisture and the acidic functional groups present in the pores of the activated carbon which is a polar material react with the electrolyte to generate gas such as carbon monoxide (CO) and carbon dioxide (CO ₂ ), thereby increasing the resistance and capacity of the interior of the cell . Therefore, in order to minimize the generation of gas by electrochemical side reaction, the surface treatment of activated carbon and the treatment for minimizing the water introduction in the cell assembling process are mainly carried out. However, to control the generation of gas by long- It is near impossible. Therefore, if the swelling phenomenon continues due to the generation of gas, a large amount of flammable gas is discharged at the same time as the side surface of the pouch is blown. Therefore, there is a need for a technique to prevent the pouch from bursting by removing the flammable gas in the pouch.

Conventionally, a technique for preventing a pouch from blowing through a structure including a gas discharge port such that an ignitable gas in the pouch is discharged to the outside of the pouch is known as in Korean Patent Application No. 10-2012-0146430 supercapacitor and its manufacturing method have. However, in such conventional technologies, there is a problem in that the process of attaching and sealing the membrane for the gas outlet to the pouch is complicated and the air is introduced into the pouch to the outside, resulting in a low long-term reliability.

Korean Patent Publication No. 10-2012-0146430

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

It is another object of the present invention to provide a pouch-type electric double layer capacitor which is excellent in long-term reliability with less characteristic deterioration such as a resistance of capacitance and an increase in ESR.

The above object is achieved by a pouch comprising: a pouch; A plurality of current collectors disposed in the pouch, a separation layer disposed between the current collectors to isolate the plurality of current collectors, and a pair of electrodes disposed on both sides of each current collector; The pouch type electric double layer capacitor includes an electrolyte filled in the pouch. The pouch type electric double layer capacitor includes a gas absorbing layer for absorbing gas inside the pouch.

Here, the gas absorbing layers are formed as a pair, and are disposed between the pouch and the device, respectively, and the gas absorbing layer preferably includes a metal form and an absorbing powder embedded in the metal foam.

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

The absorbing powder may be sodium carbonate (Na ₂ CO ₃ ) or potassium carbonate (K ₂ CO ₃ ) which is an alkali of solid carbonate, and the gas absorbing layer may be formed such that after the absorbing powder is introduced into the metal foam, It is preferable to reduce the thickness of the gas absorption layer by at least 20% in comparison with the thickness of the metal foam, and it is preferable that the gas absorption layer has a thickness of 1 to 2 mm.

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

The carbon material may be selected from the group consisting of active carbon, carbon black, graphite, graphene, hard carbon, carbon nano fiber, carbon nano tube ), And mixtures thereof.

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

Further, deterioration in characteristics such as capacitance resistance and ESR increase is small and excellent long-term reliability can be improved.

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

1, the pouch type electric double layer capacitor 100 includes a pouch 110, an element 120, an electrolyte 130, a lead tab 140, and a gas absorbing layer 150. [

The pouch 110 is disposed so as to surround the electric double layer capacitor 100 and includes therein an element 120, an electrolyte 130, a lead tab 140 and a gas absorption layer 150, The electrolyte 130 is not discharged to the outside but air or moisture existing in the outside is sealed so as not to be introduced into the pouch 110. The pouch 110 may be an aluminum laminate pouch, but is not limited thereto.

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

In the present invention, the electrode 121 means a carbon material electrode including a carbon material powder, and is made of a carbon material, a conductive material, and a binder. The carbon material is generally known to have a large specific surface area as compared with other materials. When the carbon material is applied to the electrode 121, the capacity of the electric double layer capacitor 100 can be increased. Therefore, in the present invention, a 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. When the carbon material exceeds 3,000 m ² / g, the specific surface area is large, Which is not suitable for application to the present invention.

The carbon material may be selected from the group consisting of active carbon, carbon black, graphite, graphene, hard carbon, carbon nano fiber, carbon nano tube, and a mixture thereof. Of these, activated carbon is most preferable. Activated carbon can be used as the activated carbon. Examples of the activated carbon include waste activated fiber-based activated carbon, woody activated carbon using coconut shell as a raw material, activated carbon of petroleum coke type, etc., and an average particle size of 20 탆 or less for powder and 10 to 20 탆 .

Examples of the conductive material include carbon black, graphite, graphene, hard carbon, carbon nano fiber, carbon nano tube, metal powder, and the like. And mixtures thereof, and it is preferable that the diameter is 0.01 to 10 탆. When the diameter of the conductive material is less than 0.01 탆, the conductivity may be deteriorated, and when it exceeds 10 탆, the conductive material may not be uniformly mixed with the carbon material.

The binder is most preferably a polytetrafluoroethylene (PTFE) binder. PTFE having a diameter of 0.1 to 0.5 탆 may be used and may be used in a solid state alone or in a solid state in the form of water (H ₂ O), xylene, methanol, ethanol, isopropanol, toluene toluene, butyl acetate, or the like. Since PTFE has excellent chemical resistance, heat resistance and mechanical strength, the network structure of PTFE develops as the rolling is repeated to construct electrodes. As the network structure develops, the carbon material and the conductive material are adhered to each other, thereby increasing the filling density and reducing the contact resistance between the carbon material and the conductive materials, thereby improving the electrical characteristics of the electrode.

The electrodes 121 made of such materials are formed as a pair, and the pair of electrodes are disposed on both sides of the current collector 122. A plurality of current collectors 122 are disposed inside the pouch 110. That is, the current collectors 122 and the pair of electrodes 121 are formed as a unit, and a plurality of the current collectors 122 are disposed inside the pouch 110. The current collector 122 is most preferably an aluminum foil but is not limited thereto. As described above, the current collector 122 is disposed between the pair of electrodes 121, and the positive electrode and the negative electrode are determined by the initial applied voltage condition of the electrodes 122 spaced apart from each other.

The isolation layer 123 is spaced apart from the current collectors 122 to isolate the plurality of current collectors 122 and is preferably disposed between the current collectors 122 and the electrodes 121 The electrodes 121 disposed in the different current collectors 122 do not contact 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 arranged close to the separation layer 123. The most preferable material is polypropylene, Nonwoven fabric.

The device 120 made of the electrode 121, the current collector 122 and the separator 123 must be in contact with the electrolyte solution 130 and the electrolyte 130 is filled in the pouch 110. The electrolytic solution 130 is not particularly limited, and one that is generally used for the electric double layer capacitor 100, that is, one in which an electrochemically stable electrolyte is dissolved in a polar organic solvent, may be used. (C ₂ H ₅ ) ₄ N ⁺ , (C ₃ H ₇ ) ₄ N ⁺ , (C ₄ H ₉ ) ₄ N ⁺ , and (C ₂ H ₅ ) ₃ CH ₃ N ⁺ , (C ₂ H ₅ ) ₄ P ⁺ , and anions BF ₄ ^- , PH ₆ ^- , ClO ₄ ^- , and CF ₃ SO ₃ ^- can be used. The organic solvent is preferably selected from the group consisting of carbonate-based ones such as propylene carbonate, butylene carbonate, ethylene carbonate, acetonitrile, and mixtures thereof.

The lead tabs 140 are composed of a positive electrode tab and a negative electrode tab, and one end of each of the positive electrode tab and the negative electrode tab is coupled to the same polarizable electrodes 121 inside the pouch 110 and the other end is drawn out. Therefore, the pouch 110 is formed to enclose only the region except the lead tab 140 to seal it. The lead tab 140 serves to transfer a current generated when the device 120 discharges or a current that flows when the device 120 is charged to the outside.

The gas absorbing 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 or discharged for a long period of time or is used at a high voltage, the gas is generated by the reaction between the electrode 121 and the electrolyte 130. Particularly, the carbon material contained in the electrode 121 is used to improve the performance of the electric double layer capacitor 100 because of its wide specific surface area. However, the water or acidic functional group attached to the surface of the carbon material reacts with the electrolyte 130 It generates a gas such as carbon monoxide (CO) or carbon dioxide (CO ₂ ). The resistance of the electric double layer capacitor 100 is increased by the swelling phenomenon and the capacity is decreased. Therefore, a technique for controlling the gas inside the pouch 110 is needed. Accordingly, the present invention includes a gas absorbing layer 150 that absorbs carbon monoxide or carbon dioxide present in the pouch 110 to prevent swelling.

The gas absorption layer 150 is made of metal foam and absorbing powder. The metal form refers to a porous sheet made of a metal material. Such a metal foam is preferably made of aluminum (Al), nickel (Ni), or stainless steel, and has an average porosity of 80% or more. When the average porosity is less than 80%, the absorbing powder is not sufficiently absorbed therein, and the gas absorbing function can not be performed properly. It is preferable that the thickness of the metal foam is made 1 to 2 mm so as not to significantly increase the volume of the electric double layer capacitor 100 while sufficiently containing the absorbing powder.

The metal foams may be disposed within the pouch 110 in a single manner, but it is most preferable that the metal foams are disposed between the pouch 110 and the element 120 in pairs so that gas absorption can be smoothly performed. That is, on both sides of the device 120 to effectively absorb the gas exiting the device 120. These metal foams are disposed at both ends of the element 120 in the pouch 110 so as to support the element 120 and exhibit a pressing effect to minimize the contact resistance between the electrodes 121 of the element 120 have.

The absorbing powder contained in the metal foam in the gas absorbing layer 150 acts as an active ingredient that absorbs carbon monoxide or carbon dioxide to perform a chemical reaction. In order to prevent the absorbing powder from being detached from the metal foam after being embedded in the metal foam, the metal foam containing the absorbing powder is vertically pressed so that the thickness of the absorbent powder is reduced by 20% or more compared to the initial metal foam thickness desirable. The solid alkali carbonate powder in which the absorbing powder absorbs carbon monoxide or carbon dioxide to perform the chemical reaction is most preferable. Here, the solid alkali carbonate powder refers to sodium carbonate (Na ₂ CO ₃ ) or potassium carbonate (K ₂ CO ₃ ). For example, a small amount of water contained in sodium carbonate, carbon dioxide and carbonaceous material is subjected to chemical reaction .

<Reaction Scheme>

Na ₂ CO ₃ + H ₂ O + CO _{2 -} > 2NaHCO ₃

That is, a small amount of moisture present in the electrode 121 and a gas generated from the electrode 121 react with the absorbed powder to turn into a sodium hydrogencarbonate (NaHCO ₃ ) powder, thereby causing a swelling phenomenon of the pouch 110 .

The average particle size of the absorbent powder is preferably 100 탆 or less. If the particle size exceeds 100 탆, it is difficult to insert the metal foam into the metal foam, so that a proper gas absorbing layer 150 can not be obtained.

The pouch type electric double layer capacitor 100 of the present invention and the conventional pouch type electric double layer capacitor having the above structure will be described as follows.

<Comparative Example>

Of the pouch type electric double layer capacitors according to the comparative example, the electrodes were made of coke-based active carbon, carbon black and binder having a specific surface area of 2,000 m ² / g, and polytetrafluoroethylene as an active carbon: Carbon black: binder = 85: 10: 5 by weight, and kneaded together with a certain amount of isopropyl alcohol, followed by roll pressing to produce a 150 μm thick activated carbon sheet. The activated carbon sheet thus prepared was bonded to an etched aluminum current collector having a thickness of 30 탆 by using a conductive adhesive to prepare an activated carbon sheet electrode including an activated carbon sheet.

The activated carbon sheet electrode is arranged to be symmetrical with a separator made of polypropylene nonwoven fabric interposed therebetween, and then the anode and the cathode are determined under the initial applied voltage condition. The active carbon sheet electrodes of the same polarity were laminated in parallel according to the required production capacity, and then a separator was disposed between the electrodes, and a device wrapped with a separator was manufactured. At this time, each polarity terminal was drawn out in the opposite direction, and these terminals were ultrasonically welded to the aluminum lead tab.

This device was packed in a sealed _three- ply laminated film pouch, and then an electrolyte solution of 1.5 M of spirobipyridinium tetrafluoroborate (SBPBF ₄ ) was injected and the other surface was sealed to prepare a pouch electric double layer capacitor.

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

<Examples>

The manufacturing method of the pouch type electric double layer capacitor according to the embodiment is manufactured by the same method as the manufacturing method of the comparative example except that the gas absorbing layer is used.

The gas-absorbing layer was prepared by dispersing sodium carbonate (Na ₂ CO ₃ ) powder having a particle size of 100 μm in a 1 mm-thick nickel foam having a porosity of 90% and impregnating the powder with an applied load of ¹ ton / Respectively. Thereafter, the gas absorbing layer was disposed on both sides of the element composed of the electrode and the separator, and a pouch-shaped electric double layer capacitor including the element and the gas absorbing layer was produced. The electrochemical characteristics 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 the ESR of the comparative example and the example show similar values. However, in the results after the floating test, the capacity decrease of the comparative example was reduced by 5.3% compared with 12.9%, and the resistance change showed a smaller value in the embodiment. Also, it can be seen that the volume expansion rate shows a smaller value in the embodiment than in 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 is possible to suppress the volume expansion of the electric double layer capacitor 100 by absorbing the gas generated in the long term deterioration process, This minimizes the change in capacitance and resistance.

100: electric double layer capacitor
110: Pouch
120: element
121: Electrode
122: The whole house
123:
130: electrolyte
140: Lead tab
150: gas absorbing layer

Claims (12)

A pouch; A plurality of current collectors disposed in the pouch, a separation layer disposed between the current collectors to isolate the plurality of current collectors, and a pair of electrodes disposed on both sides of each current collector; A pouch type electric double layer capacitor comprising an electrolyte filled in the pouch,
And a gas absorbing layer for absorbing gas in the pouch. The method according to claim 1,
Wherein the gas absorbing layers are formed as a pair and are disposed between the pouch and the device, respectively. The method according to claim 1,
Wherein the gas absorbing layer comprises a metal form and an absorbing powder embedded in the metal foam. The method of claim 3,
Wherein the metal foil is made of aluminum (Al), nickel (Ni), or stainless steel. The method of claim 3,
Wherein the metal foam has an average porosity of 80% or more. The method of claim 3,
It said absorbing powder is a solid alkali carbonate is sodium carbonate (Na ₂ CO _3), or a pouch-shaped electric double layer capacitor, characterized in that potassium carbonate (K ₂ CO _3). The method of claim 3,
Wherein the gas absorption layer reduces the thickness of the gas absorption layer by 20% or more compared to the thickness of the metal foam to prevent the absorption powder from being separated after the absorption powder is introduced into the metal foam. . The method according to claim 1,
Wherein the gas absorbing layer has a thickness of 1 to 2 mm. The method according to claim 1,
Wherein the pouch is an aluminum laminate pouch. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 1,
Wherein the electrode comprises a carbon material, a conductive material, and a binder. 11. The method of claim 10,
Wherein the carbon material has a specific surface area of 1,000 to 3,000 m ² / g. 11. The method of claim 10,
The carbon material may be selected from the group consisting of active carbon, carbon black, graphite, graphene, hard carbon, carbon nano fiber, carbon nano tube ), And mixtures thereof. &Lt; Desc / Clms Page number 18 &gt;

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