Patent Publication Number: US-2005118499-A1

Title: Secondary battery

Description:
CLAIM OF PRIORITY  
      This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 from an application for SECONDARY BATTERY earlier filed in the Korean Intellectual Property Office on 29 Nov. 2003 and there duly assigned the Serial No. 2003-86086.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a secondary battery, and more particularly, to a secondary battery with a structure for preventing a short circuit between a collecting member and a container.  
      2. Description of the Related Art  
      Unlike the primary battery, the secondary battery may be recharged. Common types of secondary batteries may be made into a battery pack and used as the power source for various portable electronic devices such as cellular phones, laptop computers, and camcorders. In particular, the lithium secondary battery among the secondary batteries is more suitable for the portable electronic devices since it has a high driving voltage and a high energy density per unit weight.  
      Furthermore, bulk size batteries which have several to tens of battery cells connected to each other to be used as a battery pack unit, are suitable for the power source of motor drive of hybrid electric vehicles.  
      Depending on the external shape, secondary batteries maybe classified into different types, for example, square and cylindrical batteries. The cylindrical-shaped secondary battery includes an electrode assembly (jellyroll) in which a positive plate and a negative plate of a long belt shape, and a separator as an insulator interposed therebetween are spiral-wound, a cylindrical container receiving the electrode assembly, and a cap assembly fixed to the container and electrically connected to the electrode assembly to thereby seal the container.  
      The positive and negative plates have lead members, i.e. tabs for collecting the current produced from the positive and negative plates when the battery is operated. The tab is fixed to the cap assembly or the container to induce the current produced from the positive and negative plates to the positive and negative terminals.  
      In that case, if only a single tab is provided, the resistance against the tab is increased and, accordingly, the power of the battery can be decreased. In an effort to overcome this difficulty, there has been provided a secondary battery which has the positive and negative plates with plural tabs.  
      In the meantime, there has been provided a secondary battery in which an uncoated region being left uncoated with the active material corresponding to each of collectors of the positive and negative plates is formed on the one end of the positive and negative plates, and the uncoated region is directly fixed to the collector plate by a method such as laser welding. That is, the collector plate for collecting the current from the positive and negative plates is electrically contacted with as large an area as possible of the positive and negative plates to improve the power of the battery.  
      However, such secondary batteries have a problem in that there is a high possibility that a short circuit can occur by contacting plural tabs or collector plates with the inside wall of the container, when or after the electrode assembly fixed to plural tabs and collector plates is inserted into the container during the manufacturing process.  
     SUMMARY OF THE INVENTION  
      It is, therefore, an object of the present invention to provide a method and an apparatus that can prevent a short circuit between a collecting member and a container.  
      It is another object to provide a secondary battery that can provide a highly reliable source of power with reduced faults over a period of use and can be used as the power source for a plurality of devices including for example but not limited to hybrid electric vehicles, electric vehicles, wireless vacuum cleaners, motorbikes, and motor scooters.  
      It is yet another object to provide a secondary battery that is more reliable and yet be efficient and cost effective.  
      It is still another object to provide an a apparatus and technique for a secondary battery that can prevent a short circuit during manufacture and after manufacture of the secondary battery.  
      There is provided a secondary battery which can prevent a short circuit between a collecting member and a container.  
      According to one aspect of the present invention, a secondary battery includes an electrode assembly having a positive plate, a negative plate, and a separator interposed between the positive plate and the negative plate; a container receiving the electrode assembly; a cap assembly fixed to the container to seal the container; a collecting member electrically connected to at least one of the positive and negative plates; and an insulating member disposed between the container and the collecting member to insulate the container from the collecting member.  
      The insulating member can be fixed to the outer portion of the electrode assembly, and one end of the electrode assembly can be placed in the insulating member.  
      The insulating member can be fixed to the outer portion of the electrode assembly, and one end of the electrode assembly and the collecting member can be placed in the insulating member.  
      The insulating member can be fixed to the outer portion of the electrode assembly, and can be placed to cover at least a portion of the collecting member.  
      The collecting member can be formed in a plate shape, and the collecting member can be contacted with an uncoated region which is formed by not coating with the active material on at least a portion of a collector of the positive or negative plate.  
      The collecting member can be formed in a ring shape, and the collecting member can be electrically connected with plural tabs which are electrically connected to the positive or negative plate. In addition, the insulating member wraps the collecting member to contact one end thereof with at least a portion of the collecting member.  
      The insulating member is formed in a tape or film shape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
       FIG. 1  is a cross-sectional view of a secondary battery according to the first embodiment of the present invention;  
       FIG. 2  is a schematic partial exploded perspective view of an electrode assembly according to the embodiment of the present invention;  
       FIG. 3  is a partial perspective view illustrating the structure of fixing the insulating member to the electrode assembly according to the first embodiment of the present invention;  
       FIG. 4  is a cross-sectional view of a secondary battery according to the second embodiment of the present invention;  
       FIG. 5  is a plan view illustrating the structure of welding lines formed on the collecting members according to the first and second embodiments of the present invention;  
       FIG. 6  is a cross-sectional view of a secondary battery according to the third embodiment of the present invention; and  
       FIG. 7  is a partial perspective view of the secondary battery according to the third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      Reference will now be made in detail to the 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 to explain the present invention by referring to the figures.  
       FIG. 1  is a cross-sectional view of a secondary battery according to the first embodiment of the present invention.  
      As shown in  FIG. 1 , the secondary battery includes an electrode assembly  10  having a positive plate  11 , a negative plate  12  and a separator  13  interposed between those two plates, positive plate  11  and negative plate  12 ; a container  20  having an opening formed on one of its sides to receive the electrode assembly  10  together with an electrolyte; a cap assembly  30  mounted to the opening of the container  20  through a gasket  31  to thereby close off and seal the container  20 ; a positive collecting member  40  electrically connected to the positive plate  11  of the electrode assembly  10 ; and a negative collecting member  50  electrically connected to the negative plate  12  of the electrode assembly  10 .  
      More specifically, the container  20  is made of conductive metal such as aluminum, aluminum alloy, and steel plated with nickel, and it has a cylindrical shape which has an inner space to receive the electrode assembly  10 .  
      Although the secondary battery explained in the exemplary embodiment has a cylindrical shape, its shape is not limited to this shape and can be other than cylindrical, for example, square.  
      The electrode assembly  10  has a stacked layer structure such that the separator  13  is placed between the positive plate  11  and the negative plate  12 , the collectors of which are coated with the corresponding active materials, or it has a jellyroll structure such that the positive plate  11 , the negative plate  12  and the separator  13  in a stacked layer are wound into a jellyroll configuration ( FIG. 2 ).  FIG. 1  shows a structure that the electrode assembly  10  in a round jellyroll configuration is mounted inside the cylindrical container  20 .  
      In the exemplary embodiment of the present invention, the collecting members  40 ,  50  are made with a plate-shaped conductive member, and are respectively fixed (secured) to the uncoated regions  11   c,    12   c  of the positive plate  11  and the negative plate  12 , respectively, by welding.  
      That is, in the lower end (for  FIG. 1 ) of the negative plate  12 , the uncoated region  12   c  of the collector  12   a  of the negative plate  12  which is not coated with the negative active material  12   b  is formed along the longitudinal direction of the negative plate  12  to contact with the negative collecting member  50 . In the upper end (for  FIG. 1 ) of the positive plate  11 , the uncoated region  11   c  at the edge of the collector  11   a  of the positive plate  11  which is not coated with the positive active material  11   b  is formed along the longitudinal direction of the positive plate  11  to electrically connected with the positive collecting member  40 .  
      The cap assembly  30  includes a cap plate  32  having an external terminal  32   a,  and a gasket  31  insulating the cap plate  32  from the container  20 . It can further include a vent plate  33  which is broken at a prescribed pressure level to discharge the gas, thereby preventing the explosion of the battery. The vent plate  33  is electrically connected to the positive collecting member  40  through a lead  35 .  
      The vent plate  33  can be modified into various configurations as long as it performs cutoff of the electrical connection between the external terminal  32   a  and the electrode assembly  10  through the lead  35  at a prescribed pressure level.  
      Each of the uncoated regions  11   c,    12   c  of the positive and negative plates, when the electrode assembly  10  is formed, is arranged to project from the separator  13 .  
      Furthermore, an insulating member  60  is arranged between at least one of the collecting members  40 ,  50  (the positive collecting member  40  in the exemplary embodiment) and the container  20  of the secondary battery to insulate each other.  
      The insulating member  60  has a role in preventing a short circuit which can occur by contacting the collecting members  40 ,  50  with the inside wall of the container  20  when or after the electrode assembly  10 , having the collecting members  40 ,  50  at its both ends, is inserted into the container  20 .  
      The insulating member  60  can be formed with a tape or a film consisting of the conductive material.  
      As shown in  FIG. 3 , the insulating member  60  of the present exemplary embodiment is fixed (or secured) to the outer portion of the electrode assembly  10 , and when the insulating member  60  is arranged between the collecting member  40  and the container  20 , the insulating member  60  enables its upper end to be located at a higher position than the upper end of the electrode assembly  10  or the upper end of the collecting member  40 .  
      That is, while the insulating member  60  is fixed to the electrode assembly  10 , one end of the electrode assembly  10  (the upper portion for  FIG. 1 ) or the collecting member  40  is placed in the insulating member  60 .  
      The structure of the insulating member  60  of the present invention which is fixed to the electrode assembly  10  is not limited to the above.  FIG. 4  shows another exemplary embodiment, in which the insulating member  60  can be fixed to cover at least a portion of the collecting member  40  (the upper surface of the collecting member  40  for  FIG. 1 ).  
      If the electrode assembly  10  is inserted into the container  20  while the insulating member  60  is fixed to the electrode assembly  10 , the collecting member  40  can maintain the coverage with the insulating member  60 . Therefore, it can prevent contacting with the inside wall of the container  20 , and also prevent the short circuit, and thereby prevent the manufacture of faulty batteries.  
      The above effects of the insulating member  60  can be expected not only when the electrode assembly  10  is inserted into the container  20  upon manufacturing of the battery, but also after the insertion, i.e. when the battery is operated after the completion of manufacturing the battery.  
      In the meantime, the collecting members  40 ,  50  are respectively fixed to the uncoated regions  11   c,    12   c  of the positive and negative plates  11 ,  12  by laser welding and thereby welding lines are formed on the collecting members  40 ,  50  of the above secondary battery.  
       FIG. 5  is a plan view illustrating the structure of welding lines formed on the positive collecting member  40  of the collecting members  40 ,  50 . As shown in  FIG. 5 , the welding lines L are formed in plural on the collecting member  40 , and include main welding lines L main  and sub welding lines L sub .  
      The main welding lines L main  are arranged on a virtual straight lines extending from the center of the electrode assembly  10  toward the outermost of the electrode assembly  10 , and the sub welding lines L sub  are arranged between the main welding lines L main . Then, the sub welding lines L sub  are formed with a predetermined length not extending from the outermost toward the center of the electrode assembly  10 , rather than a full length.  
      It is preferable that the length ( 1 ) of the sub welding line L sub  extends as long as the gap (a) between the sub welding line L sub  and the adjacent main welding line L main  equals the least gap (b) between each of the main welding lines L main .  
      If the length ( 1 ) of the sub welding line L sub  is shorter than the least gap (b) of the main welding lines L main , the collection against the center of the electrode assembly  10  becomes more dependent on the collecting member  40  based on the main welding lines L main . Accordingly, it causes the power against the center of the electrode assembly  10  to decrease, and thereby the life span of the battery is decreased.  
      Another exemplary example in which the structure of the collecting member is modified will be described in the following.  
      As shown in  FIG. 6  and  FIG. 7 , the collecting member  70  for collecting the current from the positive plate  11  of the electrode assembly  10  is formed with a ring shaped conductive material. The collecting member  70  is arranged at the one end of the electrode assembly  10 , and has plural tabs  72  electrically connected to the collector of the positive plate  11 .  
      Then, a special member can be provided with the inside of the container  20  receiving the electrode assembly  10  to support and fix the collecting member  70 .  
      For the secondary battery having the above collecting member  70 , an insulating member  74  as mentioned above can be placed between the collecting member  70  and the container  20 .  
      The structure and material of the insulating member  74  can be achieved as mentioned above, and  FIG. 6  and  FIG. 7  show that the insulating member  74  wraps entirely the collecting member  70  and covers a portion of the upper surface of the collecting member  70 .  
      The secondary battery of the present invention can also be used as the power source for the hybrid electric vehicles, electric vehicles, wireless vacuum cleaners, motorbikes, and motor scooters.  
      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.