Abstract:
A rechargeable battery including an electrode assembly including a negative electrode and a positive electrode; a case housing the electrode assembly; a cap plate coupled to an opening of the case; a negative terminal and a positive terminal penetrating the cap plate and connected to the negative electrode and the positive electrode, respectively; an external short-circuit unit separately provided between the negative terminal and the cap plate and configured to short-circuit the negative terminal on the cap plate; and a thermistor for connecting the positive terminal and the cap plate, wherein the thermistor is configured to have reduced resistance when its temperature is increased.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0097884 filed in the Korean Intellectual Property Office on Sep. 4, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The described technology relates generally to a rechargeable battery for controlling charging resistance of a case depending on temperature for a perforation characteristic of a conductor. 
     2. Description of the Related Art 
     Unlike a primary battery that cannot be recharged, a rechargeable battery may be repeatedly charged and discharged. A small-capacity rechargeable battery is used for small portable electronic devices such as mobile phones, notebook computers, camcorders, and the like, while a large-capacity rechargeable battery is used as a motor-driving power source for hybrid vehicles and electric vehicles. 
     The rechargeable battery may include an electrode assembly having a positive electrode and a negative electrode provided on either side of a separator, a case accommodating the electrode assembly, a cap plate sealing an opening of the case, and an electrode terminal penetrating the cap plate and electrically connected to the electrode assembly. 
     When a conductive material penetrates the case of the rechargeable battery to pierce the electrode assembly, a high-voltage current flowing through the electrode terminal flows again toward the electrode assembly through the cap plate, the case, and the conductive material. If the amount of high-voltage current is large, the electrode assembly may be ignited or explode. 
     When a case is charged with a positive electrode in the rechargeable battery and charging resistance for connecting a positive terminal and a cap plate at room temperature is great, a current that flows to the electrode assembly through the case and the conductor is restricted when perforating the conductor so a possibility of ignition and explosion is reduced, but the charging resistance is low so the possibility of ignition and explosion is increased. 
     Also, when the charging resistor for connecting the positive terminal and the cap plate becomes lower in the overcharge and high temperature condition, an external short circuit by an external short-circuit unit provided between the negative terminal and the cap plate becomes easier but it cannot reduce the predetermined charging resistor so the external short circuit becomes difficult. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     The described technology has been made in an effort to provide a rechargeable battery for improving a perforation characteristic of a conductor by controlling charging resistance of a case according to temperature. 
     An exemplary embodiment provides a rechargeable battery including: an electrode assembly including a negative electrode and a positive electrode; a case for receiving the electrode assembly; a cap plate combined to an opening of the case; a negative terminal and a positive terminal penetrating the cap plate and connected to the negative electrode and the positive electrode; an external short-circuit unit separately provided between the negative terminal and the cap plate and short-circuiting the negative terminal on the cap plate; and a thermistor for connecting the positive terminal and the cap plate, resistance thereof being reduced when temperature is increased. 
     The thermistor has resistance of 1 mohm to 100 ohm at 25° C. and 0.1 mohm to 10 ohm at 60° C. 
     The external short-circuit unit includes a short-circuit tab and a short-circuit member that are separated or short-circuited according to an internal pressure, the short-circuit tab is disposed outside the cap plate in an insulated state and is electrically connected to the negative terminal, and the short-circuit member is installed in a short-circuit hole formed in the cap plate facing the short-circuit tab. 
     The rechargeable battery further includes: a metal support plate electrically connected to the negative electrode and disposed on at least one side of the electrode assembly; a first insulation member provided between the electrode assembly and the metal support plate; and a second insulation member provided between the metal support plate and the case. 
     The positive terminal includes: a rivet terminal installed in a terminal hole of the cap plate; and a plate terminal disposed outside the cap plate and connected to the rivet terminal, and the thermistor is provided between the plate terminal and the cap plate and perforates the rivet terminal. 
     A gasket provided between the terminal hole and the rivet terminal is extended between the rivet terminal and the thermistor to have an insulation configuration. 
     According to the embodiment, the positive terminal and the cap plate are connected through the thermistor so the perforation characteristic of the conductor is improved by controlling the charging resistance of the case connected to the cap plate according to the temperature. 
     For example, resistance of the thermistor is increased at room temperature at which the rechargeable battery is normally operable to control the current that flows to the electrode assembly through the case and the conductor and increase safety of conductor perforation, and the resistance of the thermistor is reduced through overcharging at a high temperature to allow fluent external short circuit operation by the external short-circuit unit provided between the negative terminal and the cap plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a rechargeable battery according to an exemplary embodiment of the present invention. 
         FIG. 2  shows a cross-sectional view with respect to a line II-II of  FIG. 1 . 
         FIG. 3  shows an exploded perspective view of an electrode assembly, a first insulation member, a metal support plate, and a second insulation member. 
         FIG. 4  shows a cross-sectional view with respect to a line IV-IV of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
       FIG. 1  shows a perspective view of a rechargeable battery according to an exemplary embodiment of the present invention, and  FIG. 2  shows a cross-sectional view with respect to a line II-II of  FIG. 1 . Referring to  FIG. 1  and  FIG. 2 , the rechargeable battery  100  includes an electrode assembly  10  for charging and discharging a current, a case  15  for receiving the electrode assembly  10 , a cap plate  20  combined to an opening of the case  15 , a first electrode terminal (hereinafter, a negative terminal)  21  and a second electrode terminal (hereinafter, a positive terminal)  22  installed on the cap plate  20 , and an external short-circuit unit  40  provided to the negative terminal  21 . 
     For example, the electrode assembly  10  is formed by disposing a first electrode (hereinafter, a negative electrode)  11  and a second electrode (hereinafter, a positive electrode)  12  on respective sides of a separator  13 , i.e., an insulator, and winding the negative electrode  11 , the separator  13 , and the positive electrode  12  as a jellyroll. 
     Also, the electrode assembly may be assembled by laminating a negative electrode and a positive electrode each of which is formed by a single plate with the separator located therebetween, or by bending and laminating the negative electrode, the separator, and the positive electrode in a zigzag form. 
     The negative electrode  11  and the positive electrode  12  include coated regions  11   a  and  12   a  that are formed by applying an active material to a current collector on a metal plate, and uncoated regions  11   b  and  12   b  that are formed without application of the active material thereto. 
     The uncoated region  11   b  of the negative electrode  11  is formed at an end of the negative electrode  11  along the spirally wound negative electrode  11 . The uncoated region  12   b  of the positive electrode  12  is formed at an end of the positive electrode  12  along the spirally wound positive electrode  12 . The uncoated regions  11   b  and  12   b  are located on respective ends of the electrode assembly  10 . 
     In one embodiment, the case  15  is formed to be cuboidal so as to provide a space for receiving the electrode assembly  10  and an electrolyte solution, and an opening for communicating the outside and the inner space on one side of the cuboid. The opening allows the electrode assembly  10  to be inserted inside the case  15 . 
     The cap plate  20  is installed in the opening of the case  15  to close and seal the case  15 . In one embodiment, the case  15  and the cap plate  20  can be made of aluminum and may be welded to each other. 
     Also, the cap plate  20  includes an electrolyte injection opening  29 , a vent hole  24 , and terminal holes H 1  and H 2 . The electrolyte injection opening  29  places the outside of the cap plate  20  and the inside of the case  15  in fluid communication to allow the electrolyte solution to be injected into the case  15 . After the electrolyte solution is injected, the electrolyte injection opening  29  is sealed with a sealing cap  27 . 
     The vent hole  24  is closed and sealed by a vent plate  25  so as to discharge an internal pressure of a rechargeable battery. When the internal pressure of the rechargeable battery reaches a predetermined pressure, the vent plate  25  is incised to open the vent hole  24 . The vent plate  25  includes a notch  25   a  for generating an incision. 
     The negative terminal  21  and the positive terminal  22  are installed in the terminal holes H 1  and H 2  of the cap plate  20  and are electrically connected to the electrode assembly  10 . That is, the negative terminal  21  is electrically connected to the negative electrode  11  of the electrode assembly  10 , and the positive terminal  22  is electrically connected to the positive electrode  12  of the electrode assembly  10 . Therefore, the electrode assembly  10  is drawn out to the outside of the case  15  through the negative terminal  21  and the positive terminal  22 . 
     The negative terminal  21  and the positive terminal  22  form the same configuration inside the cap plate  20 , and they form different configurations outside the cap plate  20 , which will now be described. 
     The negative and positive terminals  21  and  22  include rivet terminals  21   a  and  22   a  installed in the terminal holes H 1  and H 2  of the cap plate  20 , flanges  21   b  and  22   b  widely formed as a single body on the rivet terminals  21   a  and  22   a  inside the cap plate  20 , and plate terminals  21   c  and  22   c  located outside the cap plate  20  and connected to the rivet terminals  21   a  and  22   a  through riveting or welding. 
     Negative and positive gaskets  36  and  37  are installed between the rivet terminals  21   a  and  22   a  of the negative and positive terminals  21  and  22  and the insides of the terminal holes H 1  and H 2  of the cap plate  20  to seal and electrically insulate a space between the rivet terminals  21   a  and  22   a  of the negative and positive terminals  21  and  22  and the cap plate  20 . 
     The negative and positive gaskets  36  and  37  are extended to be installed between the flanges  21   b  and  22   b  and the inside of the cap plate  20  to further seal and electrically insulate the space between the flanges  21   b  and  22   b  and the cap plate  20 . That is, the negative and positive gaskets  36  and  37  prevent an electrolyte solution from being leaked through the terminal holes H 1  and H 2  when installing the negative and positive terminals  21  and  22  in the cap plate  20 . 
     Negative and positive lead tabs  51  and  52  electrically connect the negative and positive terminals  21  and  22  to the negative and positive electrodes  11  and  12  of the electrode assembly  10 . That is, the negative and positive lead tabs  51  and  52  are combined to bottoms of the rivet terminals  21   a  and  22   a  and the bottoms are caulked so that the negative and positive electrode lead tabs  51  and  52  are supported by the flanges  21   b  and  22   b  and are connected to the rivet terminals  21   a  and  22   a.    
     Negative and positive insulation members  61  and  62  are installed between the negative and positive electrode lead tabs  51  and  52  and the cap plate  20  to electrically insulate the negative and positive electrode lead tabs  51  and  52  from the cap plate  20 . Further, the negative and positive electrode insulating members  61  and  62  are combined to the cap plate  20  on a first end and wrap the negative and positive electrode lead tabs  51  and  52 , the rivet terminals  21   a  and  22   a , and the flanges  21   b  and  22   b  thereby stabilizing their connection structure. 
     The external short-circuit unit  40  will now be described with regard to a plate terminal  21   c  of the negative terminal  21  and a thermistor  46  with regard to a plate terminal  22   c  of the positive terminal  22 . 
     The external short-circuit unit  40  of the negative terminal  21  includes a short-circuit tab  41  and a short-circuit member  43  that are separated or short-circuited according to an internal pressure. The short-circuit tab  41  is electrically connected to the rivet terminal  21   a  of the negative terminal  21 , is provided with an insulation member  31 , and is located on the outside of the cap plate  20 . 
     The insulation member  31  is installed between the short-circuit tab  41  and the cap plate  20  to electrically insulate the short-circuit tab  41  and the cap plate  20 . That is, the cap plate  20  maintains electrical insulation from the negative terminal  21 . 
     The short-circuit tab  41  and the plate terminal  21   c  are combined to an upper portion of the rivet terminal  21   a  to caulk the upper portion so the short-circuit tab  41  and the plate terminal  21   c  are combined to the upper portion of the rivet terminal  21   a . Therefore, the short-circuit tab  41  and the plate terminal  21   c  are fixed to the cap plate  20  with the provision of the insulation member  31 . 
     The short-circuit member  43  is installed in a short-circuit hole  42  formed in the cap plate  20 . The short-circuit tab  41  is connected to the negative terminal  21  and is extended along an outer part of the short-circuit member  43 . Therefore, the short-circuit tab  41  and the short-circuit member  43  correspond to the short-circuit hole  42 , they face each other to maintain a solid line state, and when internal pressure of the rechargeable battery is increased, the short circuit state (imaginary line state) is formed by inversion of the short-circuit member  43 . 
     The thermistor  46  on the side of the positive terminal  22  electrically connects the plate terminal  22   c  of the positive terminal  22  and the cap plate  20 , and resistance is changed according to the temperature of the rechargeable battery. For example, the thermistor  46  can be formed with a negative temperature coefficient (NTC) thermistor having resistance that is reduced when the temperature is increased. 
     For example, when the rechargeable battery is normally operated, that is, when the rechargeable battery is operated at room temperature, the thermistor  46  maintains high resistance. When the resistance of the thermistor  46  is high, the current is controlled to flow between the positive terminal  22  and the cap plate  20 , and the current flowing to the electrode assembly  10  through the case  15  and the conductor is controlled to thus increase safety on perforation of the conductor (by, for example, a nail). 
     When the rechargeable battery is overcharged, that is, when the temperature of the rechargeable battery is increased, resistance of the thermistor  46  is reduced. When the resistance of the thermistor  46  is reduced, the current easily flows between the positive terminal  22  and the cap plate  20  so the external short-circuit operation of the external short-circuit unit  40  between the negative terminal  21  and the cap plate  20  performs suitably. 
     For example, the thermistor  46  has resistance of about 1 mohm to about 100 ohm at room temperature between about 15 to about 35° C. (for example, about 25° C.), and it has resistance of about 0.1 mohm to about 10 ohm at a high temperature from about 50 to about 70° C. (for example, about 60° C.). 
     For example, the thermistor  46  is provided between the plate terminal  22   c  and the cap plate  20  and penetrates the rivet terminal  22   a . Therefore, the thermistor  46  and the plate terminal  22   c  are combined to an upper portion of the rivet terminal  22   a  to caulk the upper portion so the thermistor  46  and the plate terminal  22   c  are combined to the upper portion of the rivet terminal  22   a.    
     The plate terminal  22   c  is installed outside the cap plate  20  while being provided with the thermistor  46 . That is, the plate terminal  22   c  is connected as a variable resistor to the cap plate  20  through the thermistor  46  having resistance that is variable by the temperature. Resistance of the thermistor  46  can be set according to a thickness that is set between the plate terminal  22   c  and the cap plate  20 . 
     The positive gasket  37  is extended between the rivet terminal  22   a  and the thermistor  46 . That is, the positive gasket  37  prevents direct electrical connection of the rivet terminal  22   a  and the thermistor  46 . That is, the rivet terminal  22   a  is electrically connected to the thermistor  46  through the plate terminal  22   c.    
       FIG. 3  shows an exploded perspective view of an electrode assembly, a first insulation member, a metal support plate, and a second insulation member, and  FIG. 4  shows a cross-sectional view with respect to a line IV-IV of  FIG. 2 . Referring to  FIG. 3  and  FIG. 4 , the rechargeable battery includes metal support plates  71  and  72  that are provided between the electrode assembly  10  and the case  15  as an insulating configuration. 
     The metal support plates  71  and  72  are provided on respective sides of the electrode assembly  10  in the present exemplary embodiment, and they can be located on either side thereof. For the insulating configuration of the metal support plates  71  and  72 , a first insulation member  81  and a second insulation member  82  are located on both ends of the metal support plates  71  and  72 . 
     The metal support plates  71  and  72  are provided between the electrode assembly  10  and the case  15  so that they may cause a short circuit outside the electrode assembly  10  before the electrode assembly  10  is short-circuited inside them when the conductor is perforated. For this purpose, the metal support plates  71  and  72  are electrically connected to the negative electrode  11  of the electrode assembly  10  and have negative polarity. 
     The metal support plates  71  and  72  are bent along the uncoated region  11   b  of the negative electrode  11  of the electrode assembly  10  and are connected to the uncoated region  11   b . In this case, the negative electrode lead tab can be connected to the uncoated region, or it can also be connected to the metal support plate so that it may be connected to the uncoated region through the metal support plate. 
     For example, the conductor can perforate the case  15  and then the electrode assembly  10 . In this instance, the metal support plates  71  and  72  located between the case  15  and the electrode assembly  10  generate a short circuit outside the electrode assembly  10  before they generate a short circuit inside the electrode assembly  10 . The voltage charged into the electrode assembly  10  is passed through the case  15 , the conductor, and the metal support plates  71  and  72  and is quickly reduced outside the electrode assembly  10 . 
     The first insulation member  81  is located between the electrode assembly  10  and the metal support plate  71  and  72  to form an insulation configuration. That is, the first insulation member  81  includes an insulation plate  811  located between the metal support plate  71  and a first side of the electrode assembly  10 , and an insulation plate  812  located between the metal support plate  72  and a second side of the electrode assembly  10  and forming an insulation configuration. 
     The second insulation member  82  is located between the metal support plates  71  and  72  and the case  15  to form an insulation configuration. The top of the second insulation member  82  is closed so as to insulate the tops of the metal support plate  71  and  72  from the cap plate  20 . Therefore, the second insulation member  82  includes outlets  821  and  822  for drawing out the negative and positive lead tabs  51  and  52  at the top. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.