Patent Publication Number: US-2019180948-A1

Title: Electric double layer capacitor

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an electric double layer capacitor (EDLC) and, more particularly, to an EDLC in which a negative electrode foil is disposed on the outside of an electrode body included in the EDLC and a porous current collector is used as the negative electrode foil disposed on the outside, whereby both electrode materials coated on surfaces of one side and the other side of the negative electrode foil can implement capacitance. 
     2. Description of the Related Art 
     An electric double layer capacitor (EDLC) is applied to an energy storage device for a smartphone, a hybrid vehicle, an electric vehicle and the generation of solar light. The EDLC uses activated carbon as a positive material or negative material. The activated carbon is coated on a current collector. A technology related to the current collector on which the activated carbon is coated is disclosed in Korean Patent Application Publication No. 10-2011-0000234 (Patent Document 1). 
     Korean Patent Application Publication No. 10-2011-0000234 relates to a method of manufacturing a current collector. When performing etching by applying an alternating current to an hydrochloric acid electrolyte including chlorine ions in an aluminum foil as a method of improving efficiency by controlling a concentration of aluminum dissolved upon performing the electrolysis etching of a current collector for an EDLC, electrolysis etching according to a frequency is performed by adding AlCl 3 .6H 2 O and controlling the concentration. Accordingly, the supply of aluminum ions and chlorine ions is made smooth by controlling a proper amount of molten AlCl 3 .6H 2 O, thereby increasing a surface area and capacitance. 
     In a convention EDLC, such as that disclosed in Korean Patent Application Publication No. 10-2011-0000234, an etching foil is used, and an electrode material such as activated carbon is coated on a surface of one side of the etching foil and a surface of the other side of the etching foil opposite the one side. In the EDLC, an electrode body is fabricated by stacking two or more etching foils on which the electrode material has been coated. In the etching foil located on the outside of the electrode body, an electrode material that belongs to the electrode materials formed on the surfaces of one side and the other side of the etching foil and that is formed on the outermost side of the electrode body cannot implement capacitance. Accordingly, the convention EDLC has a problem in that energy storage density is generally low compared to the volume of the EDLC. 
     PRIOR ART DOCUMENT 
     [Patent Document] 
     (Patent Document 1): Korean Patent Application Publication No. 10-2011-0000234 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an EDLC in which a negative electrode foil is disposed on the outside of an electrode body included in the EDLC and a porous current collector is used as the negative electrode foil disposed on the outside, whereby both electrode materials coated on surfaces of one side and the other side of the negative electrode foil can implement capacitance. 
     Another object of the present invention is to provide an EDLC capable of improving energy storage density in proportion to the volume while reducing a manufacturing cost because a negative electrode foil is disposed on the outside of an electrode body included in the EDLC and a porous current collector is used as the negative electrode foil disposed on the outside, whereby both electrode materials coated on surfaces of one side and the other side of the negative electrode foil can implement capacitance. 
     An EDLC according to an embodiment of the present invention includes a casing and an electrode body disposed within the casing and having an electrolyte impregnated therein. The electrode body includes one or more positive electrode foils having an electrode material coated on surfaces of one side and the other side of the positive electrode foil, one or more negative electrode foils disposed and stacked to face the positive electrode foil and having an electrode material coated on surfaces of one side and the other side of the negative electrode foil, and one or more isolation films disposed between the positive electrode foil and the negative electrode foil and stacked on the surface of one side or the other side of the positive electrode foil or the negative electrode foil. A porous current collector in which a plurality of through holes is arranged and formed is used as a negative electrode foil belonging to the one or more negative electrode foils and disposed on an outside of the electrode body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view showing an EDLC according to an embodiment of the present invention. 
         FIG. 2  is a perspective view showing an electrode body shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along line A-A of  FIG. 2 . 
         FIG. 4  is an enlarged cross-sectional view of a positive electrode foil shown in  FIG. 3 . 
         FIG. 5  is an enlarged cross-sectional view of the positive electrode foil shown in  FIG. 4  according to an embodiment. 
         FIG. 6  is an enlarged cross-sectional view of a negative electrode foil shown in  FIG. 3 . 
         FIG. 7  is an enlarged cross-sectional view of the negative electrode foil shown in  FIG. 6  according to an embodiment. 
         FIG. 8  is a plan view of a porous current collector shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. Exemplary embodiments are described below to explain the present invention by referring to the figures. 
     Hereinafter, an EDLC according to an embodiment of the present invention is described below with reference to the accompanying drawings. 
     As shown  FIGS. 1 to 3 , an EDLC according to an embodiment of the present invention is configured to include a casing  110  and an electrode body  120 . 
     The casing  110  has the electrode body  120  disposed therein and sealed, and generally supports the EDLC according to an embodiment of the present invention. The electrode body  120  has an electrolyte impregnated therein and is disposed within the casing  110 . The electrode body  120  is configured to include one or more positive electrode foils  121 , one or more negative electrode foils  122 , and one or more isolation films  123 . An electrode material  121   a  is coated on surfaces of one side and the other side of the one or more positive electrode foils  121 . The one or more negative electrode foils  122  are stacked to face the one or more positive electrode foils  121 , respectively. The electrode material  121   a  is coated on the surfaces of one side and the other side of the one or more positive electrode foils  121 . The one or more isolation films  123  are disposed between the positive electrode foil  121  and the negative electrode foil  122  and are stacked on the surface of one side or the other side of the positive electrode foil  121  or negative electrode foil  122 . A porous current collector  20  (see  FIG. 7 ) in which a plurality of through holes  21  is arranged is used as a negative electrode foil  122  that belongs to the one or more negative electrode foils  122  and that is located on the outside of the electrode body  120 . 
     The configuration of the EDLC according to an embodiment of the present invention is described in more detail below. 
     As shown in  FIG. 1 , the casing  110  includes a cylindrical casing  111 , a metal cover  112 , and a pair of external electrodes  113  and  114 . The electrode body  120  having an electrolyte impregnated therein is disposed in the cylindrical casing  111 . A curling part  111   a  is formed on one side of the cylindrical casing  111 . The curling part  111   a  supports the metal cover  112  in the state in which the electrode body  120  having the electrolyte impregnated therein is disposed within the cylindrical casing  111 , thereby sealing the inside of the cylindrical casing  111 . In an embodiment of the present invention, as shown in  FIG. 1 , the casing  110  has been illustrated as being a cylindrical shape, but may be a rectangular casing (not shown) or a pouch (not shown). In an embodiment of the present invention, since the casing  110  has a cylindrical shape, the electrode body  120  is wound in a cylindrical form. Accordingly, when a rectangular casing or a pouch is used as the casing  110 , the electrode body  120  may be fabricated by simply winding the positive electrode foil  121 , the negative electrode foil  122 , and the isolation film  123  or may be fabricated by winding the positive electrode foil  121 , the negative electrode foil  122 , and the isolation film  123  in an oval. 
     As shown in  FIGS. 2 and 3 , the electrode body  120  is fabricated by being wound in a cylindrical shape because the casing  110  of a cylindrical shape is used. After the electrode body  120  is wound in a cylindrical shape, it is disposed within the casing  110  after the electrolyte is impregnated in the electrode body  120  and is sealed by the metal cover  112  of the casing  110 . The electrode body  120  is configured to include the one or more positive electrode foils  121 , the one or more negative electrode foils  122 , and the one or more isolation films  123 . One positive electrode foil  121 , one negative electrode foil  122  and one isolation film  123  have been illustrated as being used in  FIG. 3 , but two or more positive electrode foils  121 , negative electrode foils  122  and isolation films  123  may be used to form the electrode body  120 . 
     As shown in  FIG. 4 , the electrode material  121   a  is coated on the surfaces of one side and the other side of the one or more positive electrode foils  121 . An etching foil  10  shown in  FIG. 5  is used as the one or more positive electrode foils  121 . The one or more positive electrode foils  121  are made of a mixture of one or two or more of aluminum (Al), nickel (Ni) and copper (Cu) materials. A plurality of grooves  11  is formed in a surface of the one or more positive electrode foils  121  using a known etching method in order to improve a surface area. As described above, the etching foil  10  is used as the one or more positive electrode foils  121 , and a foil on a surface of which the porous current collector  20  or the grooves  11  have not been formed, that is, a non-etched foil (not shown), in addition to the etching foil  10  may be used as the one or more positive electrode foils  121 . 
     As shown in  FIG. 6 , the one or more negative electrode foils  122  are disposed to face the one or more positive electrode foils  121 , respectively, and are stacked along with the positive electrode foils  121 . An electrode material  122   a  is coated on the surfaces of one side and the other side of the one or more negative electrode foils  122 . A porous current collector  20  having a plurality of through holes  21  arranged and formed therein as shown in  FIG. 7  is used as a negative electrode foil  122  that belongs to the one or more negative electrode foils  122  and that is located on the outside of the electrode body  120 . That is, the porous current collector  20  having the plurality of through holes  21  arranged and formed therein is used as the one or more negative electrode foils  122 . The electrode material  122   a  is coated to fill the plurality of through holes  21  when it is coated on a surface of one side of the porous current collector  20  and a surface of the other side opposite one side. The negative electrode foil  122  is made of a mixture of one or two or more of aluminum (Al), nickel (Ni) and copper (Cu) materials. The plurality of through holes  21  is arranged and formed in the negative electrode foil  122 . In this case, the porous current collector  20  has an opening ratio of 1 to 24%. As shown in  FIG. 8 , if the center of adjacent through holes  21  is 90 degrees, the diameter of each through hole  21  is D, and the length between the centers of the through holes  21  is P, the opening ratio is calculated as (78.5×D 2 )/P 2 . 
     The plurality of through holes  21  is arranged and formed in the porous current collector  20  applied to the one or more positive electrode foils  121  and the one or more negative electrode foils  122 . The plurality of through holes  21  is buried in the electrode materials  121   a  and  122   a  coated on the surfaces of one side and the other sides of the porous current collector  20  and are electrically connected. That is, the plurality of through holes  21  is formed so that the surfaces of one side and the other side of the porous current collector  20  communicate with each other. A foil (not shown) on which etching processing has not been performed and in which the plurality of grooves  11 ,  22  are formed in surfaces of one side and the other side of the foil as shown in  FIGS. 5 and 7  or in which the grooves  11 ,  22  are not formed on the surfaces of one side and the other side may be used. 
     The electrode materials  121   a  and  122   a  coated on the one or more positive electrode foils  121  and the one or more negative electrode foils  122 , respectively, are made of a mixture of activated carbon, a conductive agent and a binder. One of Super-P, ketjen black and carbon black is used as the conductive agent. One or more of polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR) and carboxymethylcellulose (CMC) are used as the binder. 
     If the one or more positive electrode foils  121  and the one or more negative electrode foils  122  according to an embodiment of the present invention are applied to a hybrid capacitor, the electrode material  121   a  coated on the one or more positive electrode foils  121  includes a mixture of the activated carbon, the conductive agent and the binder. The electrode material  122   a  coated on the one or more negative electrode foils  122  includes a mixture of Li 4 Ti 5 O 12 , a conductive agent and a binder. In this case, one of Super-P, ketjen black and carbon black is used as the conductive agent. One or more of polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR) and carboxymethylcellulose (CMC) are used as the binder. That is, one or two or more of PVDF, PTFE, SBR and CMC are mixed and used as the binder. 
     The one or more isolation films  123  are disposed between the positive electrode foil  121  and the negative electrode foil  122  and stacked on the surface of one side or the other side of the positive electrode foil  121  or the negative electrode foil  122 . A known technology is applied to the isolation film  123 , and a detailed description of the isolation film is omitted. 
     In order to test capacitance performance of the EDLC according to an embodiment of the present invention, embodiments were performed as in the following table. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 
               
               
                   
               
               
                   
                   
                   
                 Opening 
                   
               
               
                   
                   
                   
                 ratio [%] 
               
               
                   
                   
                   
                 of porous 
               
               
                 Classi- 
                 Type of positive 
                 Type of negative 
                 current 
                 Capacitance 
               
               
                 fication 
                 electrode foil 
                 electrode foil 
                 collector 
                 [F/g] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 etching foil 
                 etching foil 
                 — 
                 34.34 
               
               
                 2 
                 porous current 
                 etching foil 
                 1 
                 35.38 
               
               
                   
                 collector 
               
               
                 3 
                 porous current 
                 etching foil 
                 3 
                 35.22 
               
               
                   
                 collector 
               
               
                 4 
                 porous current 
                 etching foil 
                 24 
                 37.75 
               
               
                   
                 collector 
               
               
                 5 
                 porous current 
                 porous current 
                 1 
                 38.99 
               
               
                   
                 collector 
                 collector 
               
               
                 6 
                 porous current 
                 porous current 
                 3 
                 37.75 
               
               
                   
                 collector 
                 collector 
               
               
                 7 
                 porous current 
                 porous current 
                 24 
                 42.41 
               
               
                   
                 collector 
                 collector 
               
               
                 8 
                 etching foil 
                 porous current 
                 1 
                 37.16 
               
               
                   
                   
                 collector 
               
               
                 9 
                 etching foil 
                 porous current 
                 3 
                 38.18 
               
               
                   
                   
                 collector 
               
               
                 10 
                 etching foil 
                 porous current 
                 24 
                 41.41 
               
               
                   
                   
                 collector 
               
               
                   
               
            
           
         
       
     
     As indicated by “Classification” in the items shown in the table in order to test performance of the EDLC according to an embodiment of the present invention, ten types of the electrode bodies  120  were fabricated and capacitance [F/g] of the electrode bodies  120  was tested. In a method of manufacturing the electrode body  120 , as shown in  FIGS. 2 and 3 , the casing  110  of a cylindrical shape was used, and thus the electrode body  120  was also wound in a cylindrical shape. That is, the size of the electrode body  120  was set so that the electrode body  120  was received in the casing  110  of a 1020 cell having a diameter of 10 mm and height of 20 mm. After the electrode body  120  was fabricated, an electrolyte was impregnated into the electrode body, and the electrode body was sealed within the casing  110  to fabricate the EDLC. In a method of fabricating the positive electrode foil  121  or the negative electrode foil  122  used when fabricating the electrode body  120  included in the EDLC, first, after the electrode materials  121   a  and  122   a  were fabricated in a slurry state, they were coated on the surfaces of one side and the other side of the positive electrode foil  121  or the negative electrode foil  122  and were then dried under a vacuum state at a temperature of 120° C. for 24 hours. After the electrode material  121   a  was coated, the isolation film  123  was interposed between the positive electrode foil  121  and the negative electrode foil  122 , which were wound in a cylindrical shape to form the electrode body  120 . 
     In the first of “Classification” of the items of the table, the etching foil  10  was used as both the positive electrode foil  121  and the negative electrode foil  122 . The positive electrode foil  121  and the negative electrode foil  122  using the etching foil  10  were wound with the isolation film  123  interposed therebetween, thereby fabricating the electrode body  120 . After electrolyte was impregnated into the fabricated electrode body  120 , an EDLC was fabricated by receiving the electrode body  120  into the casing  110  of a 1020 cell having a diameter of 10 mm and height of 20 mm. Capacitance of the fabricated EDLC was measured using capacitance measurement equipment (not shown), and the measured results were 34.34 F/g as in the table. 
     In the second of “Classification” of the items of the table, the porous current collector  20  was used as the positive electrode foil  121 , and the etching foil  10  was used as the negative electrode foil  122 . If the porous current collector  20  was used as the positive electrode foil  121 , the porous current collector  20  was wound to be located on the outside of the electrode body  120 . In this case, in the porous current collector  20  used in the positive electrode foil  121 , each of the plurality of through holes  21  had a diameter of 100 μm and an opening ratio thereof was 1%. The porous current collector  20  formed to have the opening ratio of 1% was disposed on the outside, thereby fabricating the electrode body  120 . After the electrode body  120  was fabricated, electrolyte was impregnated into the electrode body  120 . An EDLC was fabricated by receiving the electrode body  120  into the casing  110  of a 1020 cell having a diameter of 10 mm and height of 20 mm. Capacitance of the fabricated EDLC was measured using capacitance measurement equipment, and the measured results were 35.38 F/g as in the table. 
     In the third of “Classification” of the items of the table, the porous current collector  20  was used as the positive electrode foil  121 , and the etching foil  10  was used as the negative electrode foil  122 . In this case, the porous current collector  20  used in the positive electrode foil  121  had an opening ratio of 3%. An EDLC was fabricated using the same method as that of the second using the positive electrode foil  121  using the porous current collector  20  having the opening ratio of 3%. Capacitance of the fabricated EDLC was measured as 35.22 F/g. 
     In the fourth of “Classification” of the items of the table, the porous current collector  20  was used as the positive electrode foil  121 , and the etching foil  10  was used as the negative electrode foil  122 . In the porous current collector  20  used in the positive electrode foil  121 , the through hole  21  had a diameter of 100 μm and an opening ratio of 24%. The electrode body  120  was fabricated so that the porous current collector  20  having the opening ratio of 24% is disposed on the outside of the electrode body  120 . After the electrode body  120  was fabricated, electrolyte was impregnated into the electrode body  120 . An EDLC was fabricated by receiving the electrode body  120  into the casing  110  of a 1020 cell having a diameter of 10 mm and height of 20 mm. Capacitance of the EDLC using the electrode body  120  including the porous current collector  20  having the opening ratio of 24% was measured as 37.75 F/g. 
     In each of the fifth to seventh of “Classification” of the items of the table, the porous current collector  20  was used as both the positive electrode foil  121  and the negative electrode foil  122 . In the fifth, the porous current collector  20  had an opening ratio of 1%. In the sixth, the porous current collector  20  had an opening ratio of 3%. In the seventh, the porous current collector  20  had an opening ratio of 24%. An EDLC was fabricated by receiving the electrode body  120  using the porous current collector  20  having the opening ratio of 1% into the casing  110  of a 1020 cell. Capacitance of the EDLC was measured as 38.99 F/g as in the table. An EDLC was fabricated using the porous current collector  20  having the opening ratio of 3%, and capacitance of the EDLC was measured as 37.75 F/g as in the table. An EDLC was fabricated by receiving the electrode body  120  using the porous current collector  20  having the opening ratio of 24% into the casing  110  of a 1020 cell. The results of the measurement of capacitance of the EDLC were 42.41 F/g as in the table. 
     In the eighth of “Classification” of the items of the table, the etching foil  10  was used as the positive electrode foil  121 , and the porous current collector  20  was used as the negative electrode foil  122 . In the porous current collector  20  used in the negative electrode foil  122 , the through hole  21  had a diameter of 100 μm and an opening ratio of 1%. The electrode body  120  was fabricated so that the porous current collector  20  is disposed on the outside using the porous current collector  20  having the opening ratio of 1% in the negative electrode foil  122  only. An EDLC was fabricated using the fabricated electrode body  120 . Capacitance of the EDLC fabricated according to the eighth embodiment was measured as 37.16 F/g. 
     In the ninth of “Classification” of the items of the table, the etching foil  10  was used as the positive electrode foil  121 , and the porous current collector  20  was used as the negative electrode foil  122 . The porous current collector  20  had an opening ratio of 3%. After the electrode body  120  was fabricated so that the porous current collector  20  is disposed on the outside, an EDLC was fabricated using the electrode body  120 . Capacitance of the EDLC was measured as 38.18 F/g as in the table. 
     In the tenth of “Classification” of the items of the table, the etching foil  10  was used as the positive electrode foil  121 , and the porous current collector  20  was used as the negative electrode foil  122 . In the porous current collector  20  used in the negative electrode foil  122 , the through hole  21  had a diameter of 100 μm and an opening ratio of 24%. As described above, the porous current collector  20  having the opening ratio of 24% was used in the negative electrode foil  122  only, and the electrode body  120  was fabricated so that the porous current collector  20  is disposed on the outside. An EDLC was fabricated using the electrode body  120 . Capacitance of the fabricated EDLC was measured 41.41 F/g. 
     From the table, it may be seen that capacitance is great if the porous current collector  20  is used as the negative electrode foil  122 . That is, by disposing the negative electrode foil  122  on the outside of the electrode body  120  and using the porous current collector  20  as the negative electrode foil  122  disposed on the outside, both the electrode materials  122   a  coated on the surfaces of one side and the other side of the negative electrode foil  122  can implement capacitance. Accordingly, a rise of a manufacturing cost can be prevented and energy storage density can be improved because both the positive electrode foil  121  and the negative electrode foil  122  are applied to the porous current collector  20 . 
     The EDLC according to the embodiments of the present invention may be applied to a capacitor or cell fabrication industrial field. 
     In the EDLC according to the embodiments of the present invention, the negative electrode foil is disposed on the outside of the electrode body included in the EDLC, and the porous current collector is used as the negative electrode foil disposed on the outside. Accordingly, there is an advantage in that both the electrode materials coated on the surfaces of one side and the other side of the negative electrode foil can implement capacitance. Furthermore, both the electrode materials coated on the surfaces of one side and the other side of the negative electrode foil can implement capacitance because the porous current collector is used as the negative electrode foil disposed on the outside. Accordingly, there are advantages in that a manufacturing cost can be reduced and energy storage density can be improved in proportion to the volume.