Abstract:
A secondary battery which reduces production cost and improves productivity by excluding the process of attaching an insulating washer and, instead, insulating a cap plate by forming an UV-curing insulation layer on an external surface of the cap plate after sealing the electrolyte inlet.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 2006-18707, filed on Feb. 27, 2006, the entire content of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Aspects of the present invention relates to a secondary battery, and more particularly, a secondary battery and fabricating process thereof to reduce production cost and improve manufacturing productivity by excluding the process of attaching a washer, the exclusion effected by insulating a cap plate with an insulation coating on the surface of the cap plate. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, a secondary battery is different from other batteries as the secondary battery is discharged through a reversible process and is therefore rechargeable. Secondary batteries are used widely in devices such as cell phones, notebook computers, camcorders, etc. Operating or nominal voltage of lithium secondary batteries is about 3.6V and the lithium secondary battery is 3 times more powerful than nickel, cadmium, or nickel-hydrogen batteries. Additionally, the energy density per unit weight of the lithium secondary battery is greater than other secondary cells. 
         [0006]    In the lithium secondary battery, lithium oxide is generally used as the positive electrode, and carbon is generally used as the negative electrode. Depending upon the sort of electrolyte used, the lithium secondary battery is classified as either a liquid electrolyte battery or high molecular weight electrolyte (polymer electrolyte) battery. Liquid electrolyte batteries are described as lithium-ion batteries; and polymer electrolyte batteries are termed lithium-ion polymer batteries. Also, lithium-ion batteries are produced in many shapes, the typical of which are cylinders, polygonal prisms, and pouch types. The shape of lithium-ion polymer batteries may be custom made as the internal electrodes and separator are laminated together and do not require external pressure, supplied by the case, to force such internal components together. 
         [0007]      FIG. 1  illustrates a conventional polygonal shape of a secondary battery according to the related art. As in  FIG. 1 , the secondary battery  10  includes a can  11 , an electrode assembly  12  disposed in the can  11 , and a can assembly  20  connected to the can  11 . 
         [0008]    The electrode assembly  12 , including a positive electrode plate  13 , a separator  14 , and a negative electrode plate  15 , is wound in series to form a jelly-roll-like shape. And the positive electrode plate  13  and the negative electrode plate  15  are connected to the positive electrode tab  16  and the negative electrode tab  17 , respectively. The positive electrode tab  16  and the negative electrode tab  17  are extended outwardly from the electrode assembly  12  to the cap plate  21  and the negative terminal  23 , respectively. 
         [0009]    The cap assembly  20  includes a cap plate  21 , connected to the upper end of the can  11 , a negative terminal  23 , a gasket  22  to insulate the negative terminal  23  from the cap plate  21 , an insulation plate  24  installed on the lower surface of the cap plate  21 , and a terminal plate  25 , which is installed on the surface of the insulation plate  24 . The negative terminal  23  extends through the cap plate  21 , insulated therefrom by the gasket  22  and the insulation plate  24 , to connect to the terminal plate  25 , which is insulated from the cap plate  21  by the insulation plate  24 . 
         [0010]    The positive electrode tab  16  is electrically connected to the cap plate  21 , and the negative electrode tab  17  is electrically connected to the negative terminal  23 . The negative electrode tab  17  may be directly connected to the negative terminal  23  (as shown) or connected via the terminal plate  25 . 
         [0011]    In addition, the cap plate  21  contains an electrolyte inlet  26  which provides a channel for infusing an electrolyte into the can  11 . The sealing element  27  is inserted into the electrolyte inlet  26  so as to seal the cap assembly  20  and prevent electrolyte from escaping the secondary battery  10 . Also, there is a UV-cured coating layer  28  on the upper surface of the sealing element  27 . 
         [0012]    The conventional secondary battery  10  includes an insulating paper washer  29  on the external surface of the cap plate  12 . The insulating paper washer  29  prevents short circuits that often occur when the positively-charged cap plate  12  contacts a recharge/discharge terminal and the negative terminal  23  does not contact the recharge/discharge terminal during chemical processing of the secondary battery  10 . 
         [0013]    Or, in the conventional secondary battery  10 , when there is a battery protection circuit on the side of the bare cell, the insulating paper washer  29  prevents short circuits even though the lead wire of the battery protection circuit contacts with the cap plate  21 . 
         [0014]    However, despite the protective nature of the insulating paper washer  29 , the attachment of the insulating paper washer  29  increases the cost of production and decreases the manufacturing rate of the secondary batteries. 
       SUMMARY OF THE INVENTION 
       [0015]    In view of the above-mentioned and other limitations, aspects of the present invention provide a method of fabricating a secondary battery to attain insulation of the cap plate. 
         [0016]    A secondary battery according to aspects of the present invention includes an electrode assembly including a positive electrode plate, a separator, and a negative electrode plate wounded in series; a can including the electrode assembly; a cap plate connected to an upper opening portion of the can and including a terminal opening portion and an electrolyte infusion inlet, an electrode terminal connected to the terminal opening portion, a gasket disposed between the electrode terminal and the cap plate, and insulating the electrode terminal, and a plug to plug an electrolyte opening of the cap plate and to seal the electrolyte opening hole, wherein the insulation layer is on an upper plane of the cap plate. The insulation layer is UV-cured coating layer and the curing paint of the UV-cured coating layer is a photo-curing resin. 
         [0017]    Also, a method of fabricating a secondary battery is provided, the method including placing an electrode assembly in a can; forming a cap assembly on an upper opening of the can; injecting an electrolyte in an electrolyte opening hole of a cap plate of the cap assembly; sealing the electrolyte opening hole with a plug; and forming an insulation layer on an upper plane of the cap plate after sealing the electrolyte opening hole. 
         [0018]    According to further aspects of the current invention, a secondary battery is provided including a cap assembly with an electrolyte inlet therethrough; a plug to fit into and seal the electrolyte inlet; and a UV-crosslinked insulation layer, wherein the UV-crosslinked insulation layer is formed on an external surface of the cap assembly and an external surface of the plug. 
         [0019]    According to further aspects of the current invention, a secondary battery is provided including a cap assembly with an electrolyte inlet therethrough; and a UV-crosslinked insulation layer, wherein the UV-crosslinked insulation layer is formed on an external surface of the cap assembly. 
         [0020]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0022]      FIG. 1  is a cross-sectional view of the upper end of a secondary battery of the related art; 
           [0023]      FIG. 2  is a cross-sectional view of the upper end of a secondary battery according to aspects of the present invention; and 
           [0024]      FIG. 3  is a process flow chart of a secondary battery according to aspects of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0025]    Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
         [0026]      FIG. 2  is a cross sectional view of the upper surface of the secondary battery and  FIG. 3  is a process flow chart of manufacturing the secondary battery according to aspects of the present invention. 
         [0027]    As illustrated in  FIG. 2 , the secondary battery  30  according to aspects of the present invention includes a can  31 , an electrode assembly  32 , contained within the can  31 , and a cap assembly  40  to enclose the exposed inner surface of the can  31 . 
         [0028]    The can  31  is a polygonal prism or an extended cylindrical shape having one end sealed and one end exposing the internal surfaces of the can  31 . The can  31  can be manufactured of metal as the can  31  may be one of the electrode terminals. 
         [0029]    The electrode assembly  32  within the can  31  includes a positive electrode plate  33 , a separator  34 , and a negative electrode plate  35  which are stacked and wound into a cylindrical shape such that a separator  34  is disposed between the positive electrode plate  33  and the negative electrode plate  35 . The wound positive electrode plate  33 , separator  34 , and negative electrode plate  35  form a jelly-roll type electrode assembly  32 . 
         [0030]    Generally in lithium secondary batteries, the positive electrode plate  33  includes a positive electrode collector constructed of sheet aluminum that is coated on both sides with a lithium oxide slurry. The negative electrode plate  35  generally includes a negative electrode collector constructed of sheet copper that is coated on both sides with a carbon-based slurry. 
         [0031]    From the positive electrode plate  33 , a portion of the positive electrode tab  36  is disposed to extend from the upper end of the electrode assembly  32  to the cap plate  41 . The negative electrode tab  37  is disposed to extend from the negative electrode plate  35  at the upper end of the electrode assembly  32  to the negative terminal  43 , as shown in  FIG. 2 . However, the negative electrode tab  37  may also extend to and contact the electrode plate  45 . The positive electrode collector and negative electrode collector are stabilized by and welded to the positive electrode tab  36  and negative electrode tab  37 , respectively. The positive electrode tab  36  and the negative electrode tab  37  can have the opposite polarity. 
         [0032]    The cap assembly  40  is installed at the open upper end of the can  31 , and the cap assembly  40  includes the cap plate  41 , the insulation plate  44  installed on the lower surface of the cap plate  41 , and the electrode plate  45  which contacts the lower surface of the insulation plate  44 . 
         [0033]    A terminal opening  41   a  is formed in the middle of the cap plate  41 , and the negative terminal  43  is installed in the terminal opening  41   a  to extend therethrough to the inside of the can  31 . A gasket  42  is installed about the outside surface of the negative terminal  43  and between the negative terminal  43  and the cap plate  41  at the terminal opening  41   a . The gasket  42  insulates the negative terminal  43  from the cap plate  41 . The electrode plate  45  connects to the portion of the negative terminal  43  that is disposed inside the can  31 . According to aspects of the invention, the electrode plate  45  may complete the electrical connection between the negative electrode plate  35 , the negative electrode tab  37 , and the negative terminal  43 . 
         [0034]    The positive electrode tab  36  is welded to the cap plate  41 . The negative electrode tab  37  is welded to the negative terminal  43 , as shown in  FIG. 2 . Again, the negative electrode tab  37  may be welded to the terminal plate  45 , which is electrically connected and welded to the negative terminal  43 . Adversely, there may be a design of a secondary battery  30  which represents opposite polarity meaning that the negative electrode tab  37  is electrically connected to the cap plate  41 , and the positive electrode tab  36  is connected to the terminal, which would then be a positive terminal. 
         [0035]    Furthermore, the construction of the cap assembly  40  may include varying components not herein described. 
         [0036]    The cap plate  41  includes the electrolyte inlet  46  allowing the injection of electrolyte into the can  31  when the cap plate  41  is installed, and the electrolyte inlet  46  can be sealed off with plug  47 . 
         [0037]    The plug  47  may be a ball or pin type and be constructed of aluminum, an aluminum alloy, or stainless steel. 
         [0038]    While or after the electrolyte inlet  46  is pressed and sealed with the plug  47 , the UV coating layer  48 , an ultraviolet ray hardening layer, is formed on the upper surface of the cap plate  41 . 
         [0039]    The UV coating layer  48  is hardened and stabilized by the application of UV radiation. The UV coating layer  48  may be a UV sclerosing paint. The UV sclerosing paint may be applied by spraying the paint on the surface of the cap plate  41 . The UV coating layer  48 , in response to excitation by UV radiation, forms new bonds between the individual polymer chains within the UV coating layer  48 . The UV coating  48  crosslinks to become a hardened polymer coating. The sclerosing or curing paint may be a photo-hardening resin, but it is not limited thereto. Although the UV coating layer  48  is described as hardening in response to excitation by UV radiation, the UV coating layer  48  may include a material that hardens in response to any form of electromagnetic radiation, including x-ray and visible light. 
         [0040]    The characteristics of the UV coating layer  48  include the capacity to crosslink at lower temperatures, harden or cure quickly, protect from and resist pollution, and electrically insulate the cap plate  41 . The UV coating  48  prevents short circuits on the upper surface of the cap plate  41  by protecting the cap plate  41  from any undesired electrical connections. 
         [0041]    Referring to  FIG. 3 , the process  50  to manufacture the secondary battery according to an embodiment of the present invention will be explained. 
         [0042]    First of all, the electrode assembly  32  is constructed and positioned on the inside of the can  31  ( 51 ); the cap assembly  40  is assembled ( 52 ) and attached to the upper opening of the can  31  ( 53 ); and the electrolyte liquid is injected through the electrolyte inlet  46  ( 54 ), which is formed in the cap plate  41  of the cap assembly  40 . 
         [0043]    Thereafter, the electrolyte inlet  46  of the cap plate  41  is plugged and sealed with the plug  47  ( 55 ); the plug  47  is externally compressed from the upper side. Then, the periphery of the plug  47  is welded to the surface of the electrolyte inlet  46 , thereby sealing the cap plate  41 . 
         [0044]    Next, the UV coating layer  48  is formed on the whole upper surface of the cap plate  41  and the plug  47  ( 56 ). In the related art, the UV coating layer is formed only on the upper side of the sealing element  27  (of  FIG. 1 ). Here, the UV coating layer  48  is formed on the whole surface of the cap plate  41  and acts as an insulator thereby replacing the need for the insulating paper washer  29  (of  FIG. 1 ). Therefore, the application of the insulating paper washer  29  can be eliminated from the battery manufacturing process in favor of the UV coating process. 
         [0045]    Finally, an amount of UV radiation is applied to the UV coating layer  48  so that the UV coating layer hardens or crosslinks. 
         [0046]    As described above, the exclusion of the washer attachment process reduces the production cost and increases the productivity of manufacturing the secondary battery. 
         [0047]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.