Abstract:
A secondary battery includes an electrode assembly; a cap plate and a case accommodating the electrode assembly; an electrode terminal protruding above the cap plate; a current collecting member that electrically connects the electrode assembly to the electrode terminal; and a fuse unit on the current collecting member and configured to block a current beyond a preset blocking point, wherein the fuse unit includes a fracture unit surrounding a through hole in the current collecting member; and a blocking point control unit formed as a notch on the fracture unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0023943, filed on Mar. 6, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     One or more embodiments of the present invention relate to a secondary battery. 
     2. Description of the Related Art 
     Generally, unlike a primary battery that is not rechargeable, a secondary battery is a rechargeable and dischargeable battery. Secondary batteries are typically used as an energy source of mobile equipment, electrical vehicles, hybrid vehicles, electrical bicycles, and uninterruptible power supplies. Depending on the type of external equipment to which the secondary battery is applied, the secondary battery is used in a single cell type or in a cell module in which a plurality of cells are bound to a single unit by electrically connecting the cells. 
     However, when an excessive current is charged or discharged in the secondary battery, high heat may be generated or an electrolyte may be decomposed. In this case, an internal pressure may be increased, and as a result, the secondary battery may ignite or explode. Therefore, there is a need to develop a structure of a secondary battery that can perform a safety operation in advance by sensing an abnormal situation, such as an overcurrent. 
     SUMMARY 
     One or more embodiments of the present invention include a secondary battery that ensures a high reliability of current blocking at a designed overcurrent blocking point and precisely controls the point at which a current flow is blocked. 
     One or more embodiments of the present invention include a secondary battery that provides a safety structure as described above and can minimize the reduction of structural strength that can occur due to the safety structure. Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description. 
     According to one or more embodiments of the present invention, there is provided a secondary battery including: an electrode assembly; a cap plate disposed on the electrode assembly; an electrode terminal protruding above the cap plate; a current collecting member that electrically connects the electrode assembly to the electrode terminal; and a fuse unit that is formed on the current collecting member to block a current beyond a preset blocking point, wherein the fuse unit includes: a fracture unit formed to surround a through hole formed in the current collecting member; and a blocking point control unit formed in a notch shape on the fracture unit. 
     The through hole may have a slim shape that extends long in a direction perpendicular to the extending direction of the current collecting member. 
     The blocking point control unit may be formed on an external surface of the fracture unit that is on an opposite side to the through hole. 
     The blocking point control unit may be formed in a region that is projected in a length direction of the through hole of the external surface of the fracture unit. 
     The blocking point control unit may be formed in a concave shape from the external surface of the fracture unit towards the through hole. 
     The blocking point control unit may be formed in a pair on both side surfaces of the fracture unit that are opposite to each other with the through hole therebetween. 
     The blocking point control unit may be formed outside a region of the external surface of the fracture unit outside the region that is projected in a length direction of the through hole. 
     The blocking point control units may be formed in plural numbers along the external surface of the fracture unit, wherein some portions of the blocking point control units are formed in the region of the fracture unit that is projected in a length direction of the through hole, and the other portions of the blocking point control units are formed outside the region of the fracture unit that is projected in a length direction of the through hole. 
     The blocking point control unit may be formed on an inner surface of the fracture unit facing the through hole. 
     The blocking point control unit may form a single opening together with the through hole by being connected to the through hole. 
     The blocking point control unit may be formed in a pair on both side surfaces of the fracture unit facing the through hole. 
     The blocking point control unit is formed inside a region of an inner surface of the fracture unit that is projected in a length direction of the through hole. 
     The blocking point control unit may include a first control unit formed on an external surface of the fracture unit that is opposite to the through hole and a second control unit formed on an inner surface of the fracture unit facing the through hole. 
     The first and second control units may be formed inside a region of the fracture unit that is projected in a length direction of the through hole. 
     According to one or more embodiments of the present invention, there is provided a secondary battery including: an electrode assembly; a cap plate disposed on the electrode assembly; an electrode terminal protruding above the cap plate; a current collecting member that electrically connects the electrode assembly to the electrode terminal; and a fuse unit that is formed on the current collecting member to block a current beyond a preset blocking point, wherein the fuse unit includes: a fracture unit formed to surround a through hole formed in the current collecting member; and a blocking point control unit formed in a hole shape on the fracture unit. 
     The through hole may have a slim shape that extends long in a direction perpendicular to the extending direction of the current collecting member. 
     The blocking point control unit may be separately formed from the through hole. 
     The blocking point control unit may be formed inside a region of the fracture unit that is projected in a length direction of the through hole. 
     The blocking point control unit may be formed as a pair on both sides of the fracture unit that are opposite to each other with the through hole therebetween. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of the secondary battery of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 1 ; 
         FIG. 4  is a perspective view of a fuse unit that is applied to the secondary battery according to an embodiment of the present invention; 
         FIG. 5  is a plan view of a planar structure of the fuse unit of  FIG. 4 ; 
         FIG. 6  is a perspective view of a modified version of the fuse unit of  FIG. 4 ; 
         FIG. 7  is a perspective view of a fuse unit that is applied to the secondary battery according to another embodiment of the present invention; 
         FIG. 8  is a magnified perspective view of the fuse unit of  FIG. 7 ; 
         FIG. 9  is a plan view of a planar structure of the fuse unit of  FIG. 7 ; 
         FIG. 10  is a perspective view of a fuse unit that is applied to the secondary battery according to another embodiment of the present invention; 
         FIG. 11  is a plan view of a planar structure of the fuse unit of  FIG. 10 ; 
         FIG. 12  is a perspective view of a fuse unit that is applied to the secondary battery according to another embodiment of the present invention; 
         FIG. 13  is a plan view of a planar structure of the fuse unit of  FIG. 12 ; 
         FIG. 14  is a perspective view of a fuse unit that is applied to the secondary battery according to another embodiment of the present invention; 
         FIG. 15  is a plan view of a planar structure of the fuse unit of  FIG. 14 ; 
         FIG. 16  is a perspective view of a fuse unit that is applied to the secondary battery according to another embodiment of the present invention; and 
         FIG. 17  is a plan view of a planar structure of the fuse unit of  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. 
       FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention.  FIG. 2  is an exploded perspective view of the secondary battery of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the secondary battery includes a case  190  that accommodates an electrode assembly  150  therein, and a cap plate  100  that closes the case  190  in which the electrode assembly  150  is accommodated. For example, the cap plate  100  may be combined on the case  190 , and a welding unit may be formed along edges where the cap plate  100  and the case  190  contact each other to seal the cap plate to the case. The welding unit may be formed by a laser welding between the cap plate  100  and the case  190 . 
     A pair of electrode terminals, for example, first and second electrode terminals  110  and  120  having polarities opposite to each other may be formed on the cap plate  100 . In one embodiment, the first and second electrode terminals  110  and  120  are electrically connected to the electrode assembly  150  that is accommodated in the secondary battery. The first and second electrode terminals  110  and  120  respectively may function as a positive terminal and a negative terminal for supplying discharging power stored in the secondary battery to the outside or for receiving charging power from the outside by being electrically connected to the electrode assembly  150 . For example, the first and second electrode terminals  110  and  120  may be formed on both sides of the secondary battery. 
     In the current embodiment, the cap plate  100  may function as a terminal by being electrically connected to the electrode assembly  150 . However, in other embodiments, one of the first and second electrode terminals  110  and  120  may be omitted. 
     In  FIG. 1 , the cap plate  100  may include a safety vent  108 . The safety vent  108  may be formed relatively weaker than other portions of the cap plate  100 . When an internal pressure is greater than a predetermined level, the internal pressure may be released by fracturing the safety vent  108 . The cap plate  100  also includes a sealing member  109 . After injecting an electrolyte into the case  190  through an electrolyte injection hole, the sealing member  109  seals the electrolyte injection hole by being assembled in the electrolyte injection hole. 
       FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 1 . 
     Referring to  FIGS. 2 and 3 , the secondary battery includes the electrode assembly  150 , the first and second electrode terminals  110  and  120 , and current collecting members  117  and  127  that intermediate the electrical connections of the electrode assembly  150  and the first and second electrode terminals  110  and  120 . Also, the secondary battery may include the case  190  that accommodates the electrode assembly  150  and the cap plate  100  that seals an opening of the case  190  in which the electrode assembly  150  is accommodated. 
     The electrode assembly  150  may be accommodated in the case  190  of the secondary battery, and may include first and second electrode plates  151  and  152  having polarities opposite to each other and a separator  153  located therebetween. The electrode assembly  150  may be formed in a stack form in which the first and second electrode plates  151  and  152  and the separator  153  are alternately stacked. 
     The cap plate  100  may be assembled on an upper opening of the case  190  that accommodates the electrode assembly  150  to seal the electrode assembly  150 . In order to make an electrical connection between the electrode assembly  150  and an external circuit or between the electrode assembly  150  and a neighboring secondary battery, the first and second electrode terminals  110  and  120  that are electrically connected to the electrode assembly  150  are formed outside the cap plate  100 . The electrode terminals may have first and second electrode terminals  110  and  120  having different polarities and that may be respectively electrically connected to the first and second electrode plates  151  and  152 . 
     The first electrode terminal  110  may include a first current collecting terminal  115  and a first terminal plate  111  connected to the first current collecting terminal  115 . Likewise, the second electrode terminal  120  may include a second current collecting terminal  125  and a second terminal plate  121  connected to the second current collecting terminal  125 . 
     The first and second current collecting terminals  115  and  125  may protrude outside of the cap plate  100  through the cap plate  100 . For this purpose, terminal holes  100 ′ into which the first and second current collecting terminals  115  and  125  are inserted may be formed in the cap plate  100 . More specifically, the first and second current collecting terminals  115  and  125  are upwardly inserted from a lower side of the cap plate  100  through the terminal holes  100 ′ of the cap plate  100 . 
     The first and second current collecting terminals  115  and  125  may be inserted into the terminal holes  100 ′ and electrically insulated from the cap plate  100 . For example, seal gaskets  113  and  123  may be inserted into the terminal holes  100 ′. Since the first and second current collecting terminals  115  and  125  are inserted into the terminal holes  100 ′ along with the seal gaskets  113  and  123 , the first and second current collecting terminals  115  and  125  may be insulated from the cap plate  100 . The seal gaskets  113  and  123  seal around the terminal holes  100 ′, and thus, leaking of an electrolyte accommodated in the case  190  may be prevented and penetration of external impurities into the case  190  is blocked. 
     The first and second current collecting terminals  115  and  125  may be electrically connected to the electrode assembly  150  through the current collecting members  117  and  127 . The current collecting members  117  and  127  mutually electrically connect between the electrode assembly  150  and the first and second current collecting terminals  115  and  125 . The current collecting members  117  and  127  may include electrode assembly combining units  135  that combine with the electrode assembly  150  at a lower side of the current collecting members  117  and  127 , current collecting terminal combining units  131  that combine with the first and second current collecting terminals  115  and  125  on an upper side of the current collecting members  117  and  127 , and fuse units  180  formed between the electrode assembly combining units  135  and the current collecting terminal combining units  131  along a length direction of the current collecting members  117  and  127 . 
     The electrode assembly combining units  135  may be combined with both edges of the electrode assembly  150 . More specifically, the electrode assembly combining units  135  may be combined with the electrode assembly  150  by welding on active-material-non-coated portions formed on the edges of the electrode assembly  150 , that is, the active-material-non-coated portions on which an electrode active material is omitted on the first and second electrode plates  151  and  152 . For example, the electrode assembly combining units  135  of the current collecting members  117  and  127  respectively may be combined with the active-material-non-coated portions of the first and second electrode plates  151  and  152 . 
     The current collecting terminal combining units  131  extend in a direction bending from the electrode assembly combining units  135  and may be formed on the current collecting members  117  and  127  that face the first and second current collecting terminals  115  and  125 . The current collecting terminal combining units  131  may include holes for combining with the first and second current collecting terminals  115  and  125 . For example, lower sides of the first and second current collecting terminals  115  and  125  are inserted into the holes of the current collecting terminal combining units  131 , and thus, the first and second current collecting terminals  115  and  125  and the current collecting terminal combining units  131  may be assembled facing each other. Then, the first and second current collecting terminals  115  and  125  and the current collecting terminal combining units  131  may be combined with each other by welding along a circumference where the first and second current collecting terminals  115  and  125  and the current collecting terminal combining units  131  contact each other. 
     The fuse units  180  may be formed between the electrode assembly combining units  135  and the current collecting terminal combining units  131 , and may form a charging and discharging current path between the electrode assembly  150  and the first and second current collecting terminals  115  and  125 . The fuse units  180  forcedly block the charging and discharging current path when an overcurrent greater than a set blocking point flows. For example, the fuse units  180  perform a safety operation for preventing a safety accident such as explosion or fire ignition of the secondary battery due to an overcurrent by forcedly blocking the charging and discharging current path during the occurrence of an abnormal circumstance. 
     For example, the charging and discharging current path through the fuse units  180  may be blocked by melting due to resistance heat, and a blocking point may be established according to a heating value determined by an electrical resistance and current of the fuse units  180 . For example, in the current collecting members  117  and  127  that are formed of a uniform material, the fuse units  180  may be formed with a minimum cross-sectional area along a length of the current collecting members  117  and  127  and may be designed to have an electrical resistance corresponding to the blocking point. 
       FIG. 4  is a perspective view of the fuse unit  180  that is applied to the secondary battery according to an embodiment of the present invention.  FIG. 5  is a plan view of a planar structure of the fuse unit  180  of  FIG. 4 . 
     Referring to  FIGS. 4 and 5 , the fuse unit  180  may include a fracture unit  181  formed around a through hole  180 ′ and a blocking point control unit  185  formed on the fracture unit  181 . For example, the fracture unit  181  may be formed in a shape surrounding the through hole  180 ′ formed in the current collecting member  117  ( 127 ). 
     The through hole  180 ′ may be formed in a slim shape in which a length side thereof extends in a direction perpendicular to the extending direction of the current collecting member  117  ( 127 ). For example, the current collecting member  117  ( 127 ) generally extends in a vertical direction to connect the electrode assembly  150  on a lower side thereof and the first or second current collecting terminal  115  ( 125 ) on an upper side thereof. In one embodiment, the through hole  180 ′ extends in a direction perpendicular to the vertical direction and may block a charging and discharging current path that is formed by the current collecting member  117  ( 127 ). 
     For example, the through hole  180 ′ may be formed in a slim shape in which a length L is relatively longer than a width W. For example, the through hole  180 ′ may be formed in a rectangular shape having a length L having a maximum length and a width W having a minimum length. Since the fracture unit  181  is fractured along the length direction of the through hole  180 ′, the charging and discharging current path may be blocked. 
     The blocking point control unit  185  may be formed on the fracture unit  181 . For example, the blocking point control unit  185  may be formed on a location separated from the through hole  180 ′ in the fracture unit  181 . For example, the blocking point control unit  185  may be formed on an external surface of the fracture unit  181 . More specifically, the blocking point control unit  185  may be formed as a plurality along the external surface of the fracture unit  181 , for example, may be formed in pairs on both external surfaces of the fracture unit  181 . 
     The blocking point control unit  185  may be formed in a region W of the external surface of the fracture unit  181  that is projected in a length direction of the through hole  180 ′. According to the current embodiment, the projected region W may be a region corresponding to the width W of the through hole  180 ′. 
     When the through hole  180 ′ is formed in a slim shape in which a length L is longer than a width W, the blocking point control unit  185  is formed in a region W of the fracture unit  181  that is projected in a length direction of the through hole  180 ′. Thus, the blocking point control unit  185  may induce a fracture of the current collecting members  117  ( 127 ) along the length direction of the through hole  180 ′. As depicted in  FIG. 4 , the blocking point control unit  185  may be formed in a notch shape, and may have a shape grooved from an external surface of the fracture unit  181  towards the through hole  180 ′. Also, the blocking point control unit  185  may be formed to have a minute size (i.e., it is significantly smaller) compared with the through hole  180 ′. 
     The blocking point control unit  185  ensures current blocking at a designed blocking point. For example, when a safety operation is not started in a circumstance when an overcurrent beyond the blocking point flows, there is a high risk of explosion or fire ignition of the secondary battery. Therefore, there is a need to start a safety operation of the blocking point control unit  185  at a designed blocking point. Since the blocking point control unit  185  forms a discontinuous notch with respect to a charging and discharging current, the blocking point control unit  185  may induce a bottleneck of the charging and discharging current. Accordingly, the current is concentrated at the blocking point control unit  185 , and thus, an initiation point for thermal melting is provided. 
     Also, the blocking point control unit  185  provides a structure for precisely controlling the blocking point of the charging and discharging current path. For example, when a safety operation starts in a circumstance when a normal current below the blocking point flows, a normal charging and discharging operation of the secondary battery may not be performed. Since the fracture unit  181  is formed around the through hole  180 ′ having a relatively large size, the precise control of the blocking point may not be controlled. Also, when the through hole  180 ′ is large, the mechanical strength of the current collecting member  117  ( 127 ) may be reduced. Since the blocking point control unit  185  is formed in a size smaller than the fracture unit  181 , the blocking point may be precisely controlled, and the reduction of the mechanical strength of the current collecting member  117  ( 127 ) may be mitigated to some degree. 
       FIG. 6  is a perspective view of a modified version of the fuse unit  180  of  FIG. 4 . Referring to  FIG. 6 , a fuse unit  280  may include a fracture unit  281  formed around the through hole  180 ′ and a blocking point control unit  285  formed on the fracture unit  281 . The blocking point control unit  285  is formed in a region W of the fracture unit  281  that is projected in a length direction of the through hole  180 ′, and thus, may induce a fracture of the current collecting member  117 ( 127 ) along the length direction of the through hole  180 ′. 
     The blocking point control unit  285  may be formed in a notch shape, and may have a shape grooved from an external surface of the fracture unit  281  towards the through hole  180 ′. In  FIG. 6 , the blocking point control unit  285  may be optionally formed in a portion of a thickness of the current collecting member  117  ( 127 ) from a lower surface of the current collecting member  117  ( 127 ) without passing through the entire thickness of the current collecting member  117  ( 127 ). Since the blocking point control unit  285  provides a structure for precisely controlling the blocking point of the charging and discharging current path, if necessary, the blocking point control unit  285  may be formed in a minute size with respect to a portion of the thickness without passing through the entire thickness of the current collecting member  117  ( 127 ). 
       FIG. 7  is a perspective view of a fuse unit  380  that is applied to the secondary battery according to another embodiment of the present invention.  FIG. 8  is a magnified perspective view of the fuse unit  380  of  FIG. 7 .  FIG. 9  is a plan view of a planar structure of the fuse unit  380  of  FIG. 7 . 
     Referring to  FIGS. 7, 8, and 9 , the fuse unit  380  includes a fracture unit  381  formed around the through hole  180 ′ and a blocking point control unit  385  formed on the fracture unit  381 . The fracture unit  381  may be formed in a shape surrounding the through hole  180 ′ formed in the current collecting member  117  ( 127 ). Also, the blocking point control unit  385  is formed on the fracture unit  381 . More specifically, the blocking point control unit  385  is formed on an inner surface of the fracture unit  381 , that is, on the inner surface facing the through hole  180 ′. The blocking point control unit  385  may form an opening together with the through hole  180 ′ by being connected to the through hole  180 ′. For example, the blocking point control unit  385  is formed in a notch shape connected together with the through hole  180 ′. 
     When the through hole  180 ′ is formed in a slim shape, a longitudinal side extends along a length direction of the through hole  180 ′, the blocking point control unit  385  is formed in a region W of the fracture unit  381  that is projected in a length direction of the through hole  180 ′, and thus, the fracture of the current collecting member  117  ( 127 ) along the length direction of the through hole  180 ′ may be induced. In  FIGS. 7, 8, and 9 , the blocking point control unit  385  may be a region corresponding to a width W of the through hole  180 ′. For example, the blocking point control unit  385  may be formed in a notch shape at an edge of the through hole  180 ′, and may be formed in a minute size, compared with the through hole  180 ′. 
     The blocking point control unit  385  may be formed as a plurality along an inner surface of the fracture unit  381 . For example, the blocking point control unit  385  may be formed as a pair on both side surfaces of the fracture unit  381  facing the through hole  180 ′. 
       FIG. 10  is a perspective view of a fuse unit  480  that is applied to the secondary battery according to another embodiment of the present invention.  FIG. 11  is a plan view of a planar structure of the fuse unit  480  of  FIG. 10 . 
     Referring to  FIGS. 10 and 11 , the fuse unit  480  may include a fracture unit  481  formed around the through hole  180 ′ and a blocking point control unit  482  formed on the fracture unit  481 . The fracture unit  481  may be formed to surround the through hole  180 ′ formed in the current collecting member  117  ( 127 ), and an area of the fracture unit  481  may be controlled by the size of the through hole  180 ′. The blocking point control unit  482  is formed on the fracture unit  481 , and may include first and second control units  482   a  and  482   b  that are formed on different locations. 
     More specifically, the first control unit  482   a  may be formed on an external surface of the fracture unit  481 , and the second control unit  482   b  may be formed on an inner surface of the fracture unit  481 , that is, the inner surface facing the through hole  180 ′. For example, the first and second control units  482   a  and  482   b  respectively may be formed in a notch shape on the inner and external surfaces of the fracture unit  481 . The first and second control units  482   a  and  482   b  may induce a fracture of the current collecting member  117  ( 127 ) in a length direction of the through hole  180 ′ by forming the first and second control units  482   a  and  482   b  in a region W of the fracture unit  481  that is projected in a length direction of the through hole  180 ′. 
     The first and second control units  482   a  and  482   b  may precisely control the blocking point by cooperating with each other. Since the fracture unit  481  is formed through a relatively large through hole  180 ′, the fracture unit  481  may not be suitable for precisely controlling the blocking point, and also, when the through hole  180 ′ is enlarged, the strength of the current collecting member  117  ( 127 ) may be reduced. In this embodiment, the blocking point may be precisely controlled through the first and second control units  482   a  and  482   b  having a minute size and the strength of the current collecting member  117  ( 127 ) may be maintained. 
       FIG. 12  is a perspective view of a fuse unit  580  that is applied to the secondary battery according to another embodiment of the present invention.  FIG. 13  is a plan view of a planar structure of the fuse unit  580  of  FIG. 12 . 
     Referring to  FIGS. 12 and 13 , the fuse unit  580  may include a fracture unit  581  formed around a through hole  180 ′ and a blocking point control unit  582  formed on the fracture unit  581 . The fracture unit  581  may be formed in a shape surrounding the through hole  180 ′ formed in the current collecting member  117  ( 127 ). The blocking point control unit  582  may be formed on an external surface of the fracture unit  581 . In particular, in the current embodiment, the blocking point control unit  582  may be formed outside the region W of the fracture unit  581  that is projected in a length direction of the through hole  180 ′. 
     The blocking point control unit  582  does not control a passing area of a charging and discharging current at the same cross-sectional surface as the through hole  180 ′. However, since the blocking point control unit  582  is formed in a notch shape, the blocking point control unit  582  provides a discontinuous point to a flow of the charging and discharging current. As a bottleneck phenomenon of the blocking point control unit  185 , the charging and discharging current is concentrated on the blocking point control unit  582 , and thus, an initiation point for thermal melting is provided. In this point of view, the blocking point control unit  582  may provide an environment for blocking the charging and discharging current at the designed blocking point. 
     The blocking point control unit  582  may be located as a plurality along an external surface of the fracture unit  581 . For example, as depicted in  FIG. 13 , the blocking point control unit  582  may be formed in pairs on different surfaces of the fracture unit  581 , or may be arranged adjacent to each other of the same surface of the fracture unit  581 . 
       FIG. 14  is a perspective view of a fuse unit  680  that is applied to the secondary battery according to another embodiment of the present invention.  FIG. 15  is a plan view of a planar structure of the fuse unit  680  of  FIG. 14 . 
     Referring to  FIGS. 14 and 15 , the fuse unit  680  may include a fracture unit  681  formed around the through hole  180 ′ and a blocking point control unit  682  formed on the fracture unit  681 . The fracture unit  681  may be formed to surround the through hole  180 ′ formed in the current collecting member  117  ( 127 ). The blocking point control unit  682  may be formed on the fracture unit  681 , and may be formed on an external surface of the fracture unit  581  opposite to the through hole  180 ′. In this embodiment, the blocking point control unit  682  may be formed as a plurality along an external surface of the fracture unit  581  and may include first and second control units  682   a  and  682   b . The first control unit  682   a  is formed in a projected region W that is formed along a length direction of the through hole  180 ′, and may induce a fracture of the current collecting member  117  ( 127 ) in the length direction of the through hole  180 ′. Also, the second control unit  682   b  is formed outside the region W of the fracture unit  681  that is projected in a length direction of the through hole  180 . Therefore, the second control unit  682   b  may induce a bottleneck of a charging and discharging current, and thus, may provide an initiation point for thermal melting. 
       FIG. 16  is a perspective view of a fuse unit  780  that is applied to the secondary battery according to another embodiment of the present invention.  FIG. 17  is a plan view of a planar structure of the fuse unit  780  of  FIG. 16 . 
     Referring to  FIGS. 16 and 17 , the fuse unit  780  may include a fracture unit  781  formed around the through hole  180 ′ and a blocking point control unit  782  formed on the fracture unit  781 . The fracture unit  781  may be formed to surround the through hole  180 ′ formed in the current collecting member  117  ( 127 ). The blocking point control unit  782  may be formed in the fracture unit  781  as a through hole. 
     For example, the blocking point control unit  782  may be formed as a hole in a location separated from the through hole  180 ′, and may be formed in a size relatively minute compared to that of the through hole  180 ′. The blocking point control unit  782  may be formed on a side of the through hole  180 ′ or may be formed as a pair on opposite sides of the through hole  180 ′. The blocking point control unit  782  may be formed in a region W of the fracture unit  781  that is projected in a length direction of the through hole  180 ′, and may induce a fracture in the length direction of the through hole  180 ′. 
     Hereinafter, the configuration of constituent elements of the secondary battery will be described in detail with reference to  FIG. 3 . Referring to  FIG. 3 , the current collecting members  117  and  127  electrically connected to the electrode assembly  150  are connected to the first and second terminal plates  111  and  121  disposed on the cap plate  100  through the first and second current collecting terminals  115  and  125 . 
     The first and second current collecting terminals  115  and  125  may include first and second current collecting terminal fixing units  115   a  and  125   a  and first and second current collecting terminal flange units  115   b  and  125   b , which are respectively formed in an upper and lower portion of the first and second current collecting terminals  115  and  125  along a length direction of the first and second current collecting terminals  115  and  125 . For example, the first and second current collecting terminals  115  and  125  may be assembled through the cap plate  100 , and may include the first and second current collecting terminal fixing units  115   a  and  125   a  exposed upwards from the cap plate  100  and the first and second current collecting terminal flange units  115   b  and  125   b  disposed on a lower side of the cap plate  100 . 
     The first and second current collecting terminal fixing units  115   a  and  125   a  formed for fixing the first and second current collecting terminals  115  and  125  may be fixed, for example, by using a riveting method with respect to upper surfaces of the first and second terminal plates  111  and  121 . For example, the first and second current collecting terminal fixing units  115   a  and  125   a  form flange units that widely extend in lateral directions from the main bodies of the first and second current collecting terminals  115  and  125 , and may be fixed on upper surfaces of the first and second terminal plates  111  and  121 . Grooves concavely dug according to a pressure applied by a processing tool that rotates at a high speed may be formed in upper ends of the first and second current collecting terminal fixing units  115   a  and  125   a . According to the pressure applied by the processing tool, the upper ends of the first and second current collecting terminal fixing units  115   a  and  125   a  are pushed in the lateral direction, and thus, the first and second current collecting terminal fixing units  115   a  and  125   a  may tightly contact with respect to the upper surfaces of the first and second terminal plates  111  and  121 . 
     The first and second current collecting terminal flange units  115   b  and  125   b  may have a flange shape extending outwards greater than the terminal holes  100 ′ so that the first and second current collecting terminals  115  and  125  will not disengage through the terminal holes  100 ′ of the cap plate  100 . In one embodiment, the first and second current collecting terminals  115  and  125  are assembled in the terminal holes  100 ′ by inserting them into the terminal holes  100 ′ from the lower side of the cap plate  100 . Also, the positions of the first and second current collecting terminals  115  and  125  may be fixed by riveting the first and second current collecting terminal fixing units  115   a  and  125   a  that are exposed upwards from the cap plate  100  in a state that the first and second current collecting terminals  115  and  125  are supported on a lower side of the cap plate  100  by the first and second current collecting terminal flange units  115   b  and  125   b.    
     The first and second current collecting terminals  115  and  125  may be inserted into the terminal holes  100 ′ of the cap plate  100  such that they are electrically insulated from the cap plate  100 . For example, the seal gaskets  113  and  123  may be inserted into the terminal holes  100 ′, and since the first and second current collecting terminals  115  and  125  are inserted into the terminal holes  100 ′ by locating the seal gaskets  113  and  123  therein, the first and second current collecting terminals  115  and  125  may be insulated from the cap plate  100 . 
     Lower insulating members  114  and  124  may be located between the first and second current collecting terminals  115  and  125  and the cap plate  100 , and the lower insulating members  114  and  124  may insulate the first and second current collecting terminals  115  and  125  from the cap plate  100 . Accordingly, the seal gaskets  113  and  123  are located around the terminal holes  100 ′ through which the first and second current collecting terminals  115  and  125  pass and the lower insulating members  114  and  124  are located between the first and second current collecting terminals  115  and  125  and the cap plate  100 , and thus, the first and second current collecting terminals  115  and  125  may be insulated from the cap plate  100 . The formation of the lower insulating members  114  and  124  may extend between the current collecting members  117  and  127  and the cap plate  100 . 
     The first and second terminal plates  111  and  121  may be formed on the cap plate  100 . The first and second terminal plates  111  and  121  are electrically connected to the first and second current collecting terminals  115  and  125  and may provide terminal regions greater than that of the first and second current collecting terminals  115  and  125 . The first and second terminal plates  111  and  121  may be connected to the first and second current collecting terminals  115  and  125  by a riveting process, but the present invention is not limited thereto. For example, the first and second terminal plates  111  and  121  may be connected to the first and second current collecting terminals  115  and  125  in various combining ways such as welding or a screw combination. 
     Upper insulating members  112  and  122  may be located between the first and second terminal plates  111  and  121  and the cap plate  100 . The upper insulating members  112  and  122  may insulate the first and second terminal plates  111  and  121  from the cap plate  100 . According to an embodiment of the present invention, when the first and second terminal plates  111  and  121  and the cap plate  100  have the same polarities, the upper insulating members  112  and  122  may be omitted. 
     According to the present invention, a safety accident of a secondary battery, such as an explosion or ignition of fire due to an overcurrent, may be prevented by performing a safety operation that forcedly blocks a charging and discharging current path in a circumstance when an overcurrent greater than a preset blocking point flows. In particular, according to the present invention, the current blocking at a preset blocking point may be ensured with high reliability, and a point at which the current path is blocked may be precisely controlled. Also, the reduction of structural strength of the secondary battery due to the safety structure may be minimized. 
     It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.