Patent Publication Number: US-2005130026-A1

Title: Electrochemical battery, electrode therefor and method for manufacturing the same

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an electrochemical battery and, more particularly, to an electrode of an electrochemical battery.  
      2. Description of the Conventional Art  
      In general, a battery is to convert chemical energy to electric energy by using a contact potential difference between suitable materials.  
      There are various kinds of batteries which can be technically classified into a primary battery, a secondary battery, a fuel cell and solar battery.  
      The primary battery, such as, a manganese battery, an alkali battery, a mercury battery, a silver oxide battery,. performs only a discharging reaction to convert chemical energy into electric energy. The secondary battery can be used by being repeatedly charged and discharged differing from the primary battery having only one time discharging reaction. The fuel cell converts combustion heat of fuel such as hydrogen or hydrocarbon as it is into electric energy. The solar battery converts light energy to electric energy.  
       FIG. 1  is a schematic view showing an example of a general fuel cell.  
      As shown in  FIG. 1 , the fuel cell includes a fuel electrode (anode)  14  and an oxygen electrode (cathode)  16  with electrolyte interposed therebetween.  
      In the fuel cell with such a structure, a fuel such as hydrogen is supplied to the fuel electrode  14  through a fuel supply pipe  13  and at the same time oxidant such as oxygen or air is supplied to the oxygen electrode  16  through an oxidant supply pipe  17 .  
      At this time, electrons are discharged with the aid of a catalyst and oxidation takes place in the anode  14 . The electrons generated from the anode  14  are transferred to the cathode  16  by way of a load  18  connected to the anode  14  and the cathode  16 .  
      In the cathode  16 , as a reduction reaction takes place with the electrons transferred by the aid of the catalyst, the oxidant is reduced.  
      Positive ions/negative ions are transferred from the anode  14  to the cathode  16  or from the cathode  16  to the anode  14  through the electrolyte  12  interposed between the anode  14  and the cathode  16 .  
      In particular, if hydrogen is used as the fuel, as the fuel cell operates, ionization of hydrogen proceeds to hydrogen ions H +  and electrons e −  in the anode  14 , and H +  generated in the anode  14  is moved to the cathode  16  through the electrolyte and the electrons e − are transferred to an external load 18 through the anode 14.    
      In the cathode  16 , H +  transferred through the electrolyte  12  reacts with oxygen in the air, generating water together with heat of reaction, which is expressed as the following reaction formula: 
 
Fuel electrode/anode: H 2 (g)→2H + +2e − 
 
Oxygen electrode/cathode: ½O 2 (g)+2H + +2e − →H 2 O(I) 
 
Total reaction formula: H 2 (g)+½O 2 (g)→H 2 O(I) 
 
      In the fuel cell, generally, a load is connected to the anode  14  and the cathode  16 . When the fuel cell operates, electrons e −  are continuously generated from the anode  14  and flows to the cathode  16  through the load, that is, as electrons are transferred from the anode  14  to the cathode  16 , a current is generated to operate an electric device or the like.  
      Meanwhile, the type of electrode used as the cathode or the anode of the electrochemical battery such as the fuel cell greatly affects the performance of the battery such as a lifespan of the battery or its output according to its material and characteristics.  
       FIG. 2  shows a structure of the electrode of the conventional fuel cell.  
      As shown in  FIG. 2 , the electrode  20  of the conventional fuel cell includes a foam body  23  made of Ni in which mixture of electrode catalyst particles  21  made of metal halide (MH), and polytetrafluoro ethylene  22 , as fluoride polymer, is infiltrated, and a mesh  24  made of Ni enclosing the foam body  23 .  
      In detail, the granule type electrode catalyst  21  and PTFE(Poly Tetrafluoro Ethylene)  22  are mixed to a mixture  25  which is infiltrated in the foam body  23  to fill the void parts of the foam body  23 .  
      The foam body  23  filled with the mixture  25  of electrode catalyst  21  and PTFE  22  is enclosed by the mesh  24  which maintains the shape of the foam body  23 , protects the foam body  23  and has fine holes for preventing the electrode catalyst  21  and PTFE  22  from being separated, and then is pressed by using a roller to thereby process the electrode  20 .  
      However, the electrode  20  constructed and fabricated as described above has a problem that since the mesh  24  is additionally used to prevent the electrode atalyst  21  or PTFE  22  from being separated from the foam body  23 , a specific surface area of the electrode catalyst  21  is reduced, to cause the volume and weight of the electrode to be relatively increased in its fabrication to meet a required performance.  
      In addition, an incomplete combination between the electrode catalyst  21  and PTFE  22  weakens durability, and in case of being used as the electrode  20 , the electrode catalyst  21  is separated from the electrode  20 , thus degrading the performance as the electrode.  
     SUMMARY OF THE INVENTION  
      Therefore, it is an object of the present invention to provide an electrochemical battery, an electrode therefore and a method for manufacturing the electrode that are capable of providing a simple manufacturing method, reducing volume, increasing flexibility, durability and specific surface area of an electrode catalyst, and heightening an efficiency of a battery.  
      To achieve the above object, there is provided an electrode of an electrochemical battery including: an electrode catalyst; and a catalyst holding body for holding and confining the electrode catalyst by being entangled with the electrode catalyst.  
      To achieve the above object, there is also provided a method for fabricating an electrode of electrochemical battery, including: a first step of fabricating a catalyst holding body having fine spaces; and a second step of holding and confining an electrode catalyst in the catalyst holding body, the catalyst holding body and the power type electrode catalyst being entangled with each other.  
      To achieve the above objects, there is also provided a battery having such an electrode as described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
      In the drawings:  
       FIG. 1  is a schematic view showing an example of a general fuel cell;  
       FIG. 2  is a view showing a structure of an electrode of a fuel cell in accordance with a conventional art;  
       FIG. 3A  is a schematic view showing a construction of an electrode of an electrochemical battery in accordance with the first embodiment of the present invention;  
       FIG. 3B  is a view showing an enlarged portion of  FIG. 3A ;  
       FIG. 4  is a schematic view showing a modification of the electrode of an electrochemical battery of  FIG. 3A ;  
       FIG. 5  is a sectional view showing the electrode having a housing enclosing the electrode of  FIG. 3A ;  
       FIG. 6  is a schematic view showing a construction of an electrode of an electrochemical battery in accordance with the second embodiment of the present invention;  
       FIG. 7  is a flow chart of a process of manufacturing the electrochemical battery of  FIG. 3A ; and  
       FIG. 8  is a flow chart of a process of manufacturing the electrochemical battery of  FIG. 6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      An electrochemical battery, electrode therefore and a method for manufacturing the same will now be described in detail with reference to the accompanying drawings.  
       FIG. 3A  is a schematic view showing a construction of an electrode of an electrochemical battery in accordance with the first embodiment of the present invention; and  FIG. 3B  is a view showing an enlarged portion of  FIG. 3A .  
      As shown in  FIGS. 3A and 3B , an electrode  30  of an electrochemical battery in accordance with the first embodiment of the present invention includes an electrode catalyst  31 , and, i.e., a catalyst holding body  32  made of a fiber stack of conductive metal material to which the electrode catalyst  31  is attached.  
      As the electrode catalyst  31 , a hydrogen storage alloy such as metal halide is preferably used.  
      The electrode catalyst  31  can be transformed to various forms. It has a fiber form such as a filament, and preferably a granule form.  
      Preferably, the electrode catalyst  31  is coated with nickel on its surface. Especially, if the catalyst holding body  32  (to be described) is made of nickel or nickel alloy material, the electrode catalyst  31  and the catalyst holding body  32  are made of the same material so that the electrode catalyst  31  can be more firmly adhered in the catalyst holding body  32  and confined within the catalyst holding body  32 , and thus, separation of the electrode catalyst  31  from the catalyst holding body  32  can be prevented.  
      In particular, the electrode catalyst  31  needs to be subjected to a surface processing for improvement of performance. If the electrode catalyst  31  is coated with Ni, which is the same material as that of the catalyst holding body  32 , the adhesiveness of the electrode catalyst  31  to the catalyst holding body  32  is increased compared to the electrode catalyst processed with fluoride.  
      The catalyst holding body  32  is made of conductive metal material, and preferably, it is made of nickel or nickel alloy. Especially, the electrode  31  itself can be a fiber stack to constitute the catalyst holding body  32 .  
      A diameter and a length of each of the fibers constituting the catalyst holding body  32  can be determined depending on usage conditions of the electrode. In the preferred embodiment of the present invention, the diameter of the fiber of the catalyst holding body  32  is 1 to 100 μm and its length is 10 to 10,000 μm.  
      As shown in  FIG. 3B , the catalyst holding body  32  can be a fiber sintered body resulting from sintering fibers  32   a  of conductive metal material or a non-woven fabric made of conductive metal material.  
      Especially, as the catalyst holding body and its manufacturing method, the present invention uses a method for fabricating a stack of fine metallic threads and metal fiber sintered body as disclosed in Korean Patent Publication No. 10-2001-0086569 or Korean Patent Publication No. 10-2001-0018726, but it is not limited thereto.  
      Accordingly, the catalyst holding body  32  can be formed as a porous tissue and the porous tissue can be implemented as one line.  
      As shown in  FIG. 4 , the catalyst holding body  32  can be constructed as a pair of sheets  41  with the electrode catalyst  31  infiltrated with a certain depth and attached only at one side. The pair of sheets  41  can be mutually overlapped in such a manner that the sides where the electrode catalyst  31  is attached meet together.  
      As shown in  FIG. 5 , the electrode  50  of the electrochemical battery in accordance with the present invention may additionally include a housing  55  which accommodates the catalyst holding body  32 , is made of conductive metal material and has a plurality of holes.  
      The housing  55  having a plurality of holes may be a mesh, and the housing  55  is preferably fabricated with nickel or nickel alloy.  
      The catalyst holding body  32  may additionally include a fluoro polymer (not shown) such as PTFE.  
       FIG. 6  is a schematic view showing a construction of an electrode of an electrochemical battery in accordance with the second embodiment of the present invention.  
      The electrode of an electrochemical battery of the present invention can be constructed with the electrode catalyst and the catalyst holding body each formed as a layer. That is, as shown in  FIG. 6 , an electrode  60  of an electrochemical battery in accordance with the second embodiment of the present invention includes an electrode catalyst layer  61  having electrode catalyst  31  and a pair of first and second catalyst holding bodies  62  and  63  which are formed with the electrode catalyst layer  61  interposed therebetween and made of a fiber stack.  
      As the electrode catalyst  31 , a hydrogen storage alloy such as metal halide (MH) is preferably used. The electrode catalyst layer  61  may contain a fluoro polymer  64  such as PTFE in addition to the electrode catalyst  31 . PTFE has the effect of restraining the generation of hydrogen. That is, the electrode catalyst layer  61  can be constructed with a mixture of the electrode catalyst  31  and PTFE.  
      The electrode catalyst  31  can be transformed to various forms. It has a fiber form such as a filament, and preferably a granule form.  
      Preferably, the electrode catalyst  31  is coated with nickel on its surface. In this respect, especially, if the first and second catalyst holding bodies  62  and  63  are made of nickel or nickel alloy material, the electrode catalyst  31  and the first and second catalyst holding bodies  62  and  63  are made of the same material, so that the electrode catalyst  31  can be more firmly adhered to the first and second catalyst holding bodies  62  and  63 , thus, separation of the electrode catalyst  31  from the catalyst holding bodies  62  and  63  can be prevented.  
      In particular, the electrode catalyst  31  needs to be subjected to a surface processing for improvement of a performance. If the electrode catalyst  31  is coated with Ni, which is the same material as that of the first and second catalyst holding bodies  62  and  63 , the adhesiveness of the electrode catalyst  31  to the catalyst holding body  32  is increased compared to the electrode catalyst processed with fluoride.  
      The first and second catalyst holding bodies  62  and  63  are made of conductive metal material, and preferably, they are made of nickel or nickel alloy.  
      A diameter and a length of each of the fibers constituting the first and second catalyst holding bodies  62  and  63  can be determined depending on usage conditions of the electrode. In the preferred embodiment of the present invention, the diameters of the fiber of the first and second catalyst holding bodies  62  and  63  are 1 to 100 μm and the lengths are 10 to 10,000 μm.  
      As shown in  FIG. 6 , the first and second catalyst holding bodies  62  and  63  can be a fiber sintered body resulting from sintering fibers  32   a  of conductive metal material or a non-woven fabric made of a conductive metal material.  
      Especially, as the catalyst holding body and its manufacturing method, the present invention uses a method for fabricating a fine metallic thread and metal fiber sintered body as disclosed in Korean Patent Publication No. 10-2001-0086569 or Korean Patent Publication No. 10-2001-0018726, but it is not limited thereto.  
      As shown in  FIG. 6 , the electrode  50  of the electrochemical battery in accordance with the second embodiment of the present invention may additionally include a housing  65  which accommodates the catalyst holding body  32 , is made of conductive metal material and has a plurality of holes.  
      The housing  65  having a plurality of holes may be a mesh, and the housing  65  is preferably fabricated with nickel or nickel alloy.  
      The battery in accordance with the second embodiment of the present invention can be applied in the same way except for the descriptions for the battery in accordance with the first embodiment.  
      The method for manufacturing an electrode of an electrochemical battery in accordance with the present invention will now be described in detail.  
       FIG. 7  is a flow chart of a process of manufacturing an electrochemical battery of  FIG. 3A .  
      First of all, fabrication of the catalyst holding body  32  is of importance. As described above, it needs to be fabricated to form a fiber stack made of conductive metal material, especially, nickel or nickel alloy material. The fiber stack and its manufacturing method are as disclosed in Korean Patent Publication No. 10-2001-0086569 and Korean Patent Publication No. 10-2001-0018726.  
      As shown in  FIG. 7 , the method for manufacturing the electrode of an electrochemical battery in accordance with the first embodiment of the present invention including the steps of: attaching the electrode catalyst  31  to the catalyst holding body  32  made of a fiber stack of conductive metal material; and forming the electrode catalyst-attached catalyst holding body  32  as an electrode  30  of an electrochemical battery.  
      The electrode catalyst  31  preferably can have a filament form, and more preferably a granule form.  
      In the attaching step, the catalyst holding body  32  is put in a solution, and them onto which the electrode catalyst  31  is dispersed, thereby attaching the electrode catalyst  31  to the catalyst holding body  32 .  
      For dispersion of the electrode catalyst  31 , reactivity and viscosity with respect to the electrode catalyst  31  are taken into consideration and a solution such as alcohol which does not react with the electrode catalyst  31  is used. That is, in a state that the catalyst holding body  32  is put in the solution, the electrode catalyst  31  is dispersed so as to be introduced into and attached to the fiber stack constituting the catalyst holding body  32 , as well as being attached to a surface layer of the fiber stack.  
      In a different method for the attaching step, liquid particles including the granule type electrode catalyst  31  are dispersed onto the catalyst holding body  32  in order to attach the electrode catalyst  31  to the catalyst holding body  32 .  
      The attaching step includes a sub-step of drying the catalyst holding body  32  after the liquid particles are dispersed or after the electrode catalyst  31  is dispersed.  
      Besides, various methods such as liquid phase infiltration, precipitation, liquid particle spray, dry spray, etc. can be used to attach the electrode catalyst  31  to the catalyst holding body  32 .  
      The forming step includes the steps of: press-molding the catalyst holding body  32  with the electrode catalyst  31  attached to the catalyst holding body  32  by using a roller; and processing the press-molded electrode catalyst support member catalyst holding body  32  to an electrode  30  in a desired size.  
      The pressed catalyst holding body  32  confines the electrode catalyst therein, and even if a fluid is transmitted through the catalyst holding body  32 , the electrode catalyst  31  cannot flow out.  
      In the press-molding step, the pair of catalyst holding bodies  32  with the electrode catalyst  31  attached to the catalyst holding body  32  can be press-molded in such a manner that the surfaces on which the electrode catalyst is attached mutually overlap with each other.  
       FIG. 8  is a flow chart of a process of manufacturing the electrochemical battery of  FIG. 6 .  
      A method for manufacturing an electrode of an electrochemical battery in accordance with the second embodiment of the present invention includes the steps of: forming an electrode catalyst layer  61  made of an electrode catalyst  31  on a first catalyst holding body  62  made of a fiber stack of conductive metal material; and forming a second catalyst holding body  63  made of a fiber stack of conductive metal material on the electrode catalyst layer  61  formed on the first catalyst holding body  62 , the second catalyst holding body  63  making a pair with the first catalyst holding body  62 .  
      The electrode catalyst  31  preferably may have a filament form, and more preferably a granule form.  
      In the method for manufacturing a battery in accordance with the second embodiment of the present invention, after the step of forming the catalyst holding bodies, a molding and processing step can be additionally provided in which the first and second catalyst holding bodies  62  and  63  with the electrode catalyst  31  attached thereto are press-molded by using a roller or the like, and processed into the electrode  30  of a desired size.  
      The battery in accordance with the second embodiment of the present invention can be applied in the same way except for the descriptions for the battery in accordance with the first embodiment.  
      As so far described, the electrochemical battery, its electrode and the method for manufacturing the electrode of the present invention have the following advantages.  
      That is, the manufacturing method is simple and the battery can be small in volume and has a high flexibility and durability. In addition, the specific surface area of the electrode catalyst is high.  
      The battery of the present invention has an improved efficiency compared to that of the conventional art.  
      In addition, since the catalyst holding body of the electrode is made of the fiber stack, alkali fuel with a low surface tension can be easily infiltrated due to a capillary phenomenon, thereby enhancing an efficiency of the battery.  
      It will be apparent to those skilled in the art that various modifications and variations can be made in electrochemical battery of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.