Abstract:
A secondary battery includes an electrode assembly, a case accommodating the electrode assembly and including an opening, an electrode terminal connected to the electrode assembly and protruding outwardly from the case; a cap assembly including a cap plate in sealing engagement with the opening of the case, and a switch plate connected to the electrode terminal.

Description:
BACKGROUND  
       [0001]    1. Field 
         [0002]    Embodiments relate to a secondary battery. 
         [0003]    2. Description of the Related Art 
         [0004]    Secondary batteries are rechargeable, unlike primary batteries. Among such secondary batteries, a low capacity battery including a battery cell in the form of a pack may be used for small portable electronic devices such as cellular phones and camcorders, and a high capacity battery including dozens of battery cells connected to one another may be used as a motor-driving power source for electric scooters, hybrid vehicles, or electric vehicles. 
         [0005]    Secondary batteries are manufactured in various shapes such as a cylindrical shape and a prismatic shape. A secondary battery is constructed as follows: an electrode assembly formed by disposing an insulating separator between a positive electrode plate and a negative electrode plate is placed in a case together with electrolyte, and a cap plate is disposed on the case. The electrode assembly is connected to electrode terminals which protrude from the cap plate and are exposed to the exterior of the secondary battery. 
       SUMMARY  
       [0006]    According to an embodiment, there is provided a secondary battery including an electrode assembly, a case accommodating the electrode assembly and including an opening, an electrode terminal connected to the electrode assembly and protruding outwardly from the case, a cap assembly including a cap plate in sealing engagement with the opening of the case, and a switch plate connected to the electrode terminal. 
         [0007]    One part of the switch plate may be connected to the electrode terminal and another part of the switch plate may face a bottom surface of the cap plate. 
         [0008]    The electrode terminal may include a first protrusion inserted in a collecting plate connected to the electrode assembly and a second protrusion inserted in the switch plate. 
         [0009]    The switch plate may include a temperature sensing part through which the second protrusion is inserted, the temperature sensing part being disposed between the electrode terminal and the collecting plate, and a switch part extending from a side of the temperature sensing part and having a bent shape. 
         [0010]    The switch plate may further include a terminal hole through which the second protrusion of the electrode terminal is inserted. 
         [0011]    The switch part may be formed of a shape-memory alloy. 
         [0012]    The switch part may be bent upward and downward in an S-shape. 
         [0013]    The switch plate may be brought into contact with a bottom surface of the cap plate when the secondary battery is in a temperature range from 80° C. to 150° C. 
         [0014]    The switch plate may be brought into contact with a bottom surface of the cap plate if the secondary battery is heated to 80° C. or higher. 
         [0015]    The switch plate may include a shape-memory alloy that changes shape when a temperature of the shape-memory alloy rises from a temperature that is less than a predetermined temperature to a temperature that is equal to or greater than the predetermined temperature, and the switch plate may be configured and disposed to face, but not contact, a bottom surface of the cap plate when the temperature of the switch plate has not risen above the predetermined temperature and to contact the bottom surface of the cap plate when the temperature of the switch plate has risen to the predetermined temperature. 
         [0016]    The predetermined temperature may be 80° C. or higher. 
         [0017]    The predetermined temperature may be in a range of from about 80° C. to about 150° C. 
         [0018]    The cap assembly may further include an insulating member disposed at a bottom surface of the cap plate. 
         [0019]    The insulating member may include a switch hole that allows the switch plate to make contact with the bottom surface of the cap plate. 
         [0020]    The insulating member may define a space that accommodates a portion of the electrode terminal and the switch plate inside the case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0021]    The above and other features and advantages will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which: 
           [0022]      FIG. 1  illustrates a perspective view relating to a secondary battery according to an embodiment; 
           [0023]      FIG. 2  illustrates a sectional view of  FIG. 1 ; 
           [0024]      FIG. 3  illustrates an enlarged sectional view relating to portion A of  FIG. 2 ; 
           [0025]      FIG. 4  illustrates an exploded perspective view of  FIG. 3 ; 
           [0026]      FIG. 5  illustrates a perspective view relating to a switch plate depicted in  FIG. 4 ; 
           [0027]      FIG. 6  illustrates a perspective view relating to the switch plate depicted in  FIG. 3 , without an insulating member being present; and 
           [0028]      FIG. 7  illustrates a perspective view illustrating a state where the switch plate shown in  FIG. 5  makes contact with the bottom side of a cap plate. 
       
    
    
     DETAILED DESCRIPTION  
       [0029]    Korean Patent Application No. 10-2010-0125166 filed on Dec. 8, 2010, in the Korean Intellectual Property Office, and entitled: “Secondary Battery” is incorporated by reference herein in its entirety. 
         [0030]    Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0031]    In the drawing figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout. 
         [0032]    In addition, it will be understood that when a part is referred to as being electrically connected to another part, it can be directly connected to the other part, or intervening parts may also be present. 
         [0033]      FIG. 1  illustrates a perspective view relating to a secondary battery according to an embodiment.  FIG. 2  illustrates a sectional view of  FIG. 1 .  FIG. 3  illustrates an enlarged sectional view relating to portion A of  FIG. 2 .  FIG. 4  illustrates an exploded perspective view of  FIG. 3 .  FIG. 5  illustrates a perspective view relating to a switch plate depicted in  FIG. 4 .  FIG. 6  illustrates a perspective view relating to the switch plate depicted in  FIG. 3 , without an insulating member being present.  FIG. 7  illustrates a perspective view relating to a state where the switch plate shown in  FIG. 5  makes contact with the bottom side of a cap plate. 
         [0034]    Referring to  FIGS. 1 through 4 , a secondary battery  100  of the current embodiment includes an electrode assembly  110 , first and second collecting plates  120  and  130 , a case  140 , a cap assembly  150 , and a switch plate  176 . 
         [0035]    The electrode assembly  110  may be formed by winding or stacking a first electrode plate  111 , a separator  113 , and a second electrode plate  112 , which may have a thin plate or film shape. The first electrode plate  111  may function as a negative electrode, and the second electrode plate  112  may function as a positive electrode. Alternatively, the first electrode plate  111  and the second electrode plate  112  may function oppositely. 
         [0036]    The electrode assembly  110  may be accommodated in the case  140  together with an electrolyte. The electrolyte may include an organic solvent such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC); and a lithium salt such as LiPF 6  or LiBF 4 . The electrolyte may be a liquid, solid, or gel. 
         [0037]    The first electrode plate  111  may be formed by applying a first electrode active material, such as graphite or carbon, to a first electrode collector formed of metal foil such as copper or nickel foil. The first electrode plate  111  may include a first electrode non-coating portion to which the first electrode active metal is not applied. The first electrode non-coating portion may function as a current flow passage between the first electrode plate  111  and the outside of the first electrode plate  111 . Materials that can be used to form the first electrode plate  111  are not limited to the above-mentioned materials. 
         [0038]    The second electrode plate  112  may be formed by applying a second electrode active material, such as a transition metal oxide, to a second electrode collector formed of metal foil, such as aluminum foil. The second electrode plate  112  may include a second electrode non-coating portion to which the second electrode active metal is not applied. The second electrode non-coating portion may function as a passage for current between the second electrode plate  112  and the outside of the second electrode plate  112 . Materials that can be used to form the second electrode plate  112  are not limited to the above-mentioned materials. 
         [0039]    The polarities of the first and second electrode plates  111  and  112  may be changed with each other. 
         [0040]    The separator  113  is disposed between the first electrode plate  111  and the second electrode plate  112 . The separator  113  prevents a short circuit and allows movement of lithium ions. The separator  113  may be formed of a polyethylene film or a film including polyethylene and polypropylene. Materials that can be used to form the separator  113  are not limited to the above-mentioned materials. 
         [0041]    The electrode assembly  110  may be formed by winding the first electrode plate  111 , the separator  113 , and the second electrode plate  112  in a manner such that the first electrode non-coating portion protrudes from an upper end of the electrode assembly  110  and the second electrode non-coating portion protrudes from a lower end of the electrode assembly  110 . The first electrode plate  111 , the separator  113 , and the second electrode plate  112  of the electrode assembly  110  may be wound in a vortex shape. 
         [0042]    The first and second collecting plates  120  and  130  may be coupled to respective end parts of the electrode assembly  110  in a manner such that the first and second collecting plates  120  and  130  are electrically connected to the first and second electrode plates  111  and  112 , respectively. 
         [0043]    The first collecting plate  120  may include a first terminal coupling part  121 , a second terminal coupling part  122 , and a base. The first collecting plate  120  may be formed of a metal or an equivalent thereof. For example, the first collecting plate  120  may be formed of copper or a copper alloy. However, the material of the first collecting plate  120  is not limited thereto. The first collecting plate  120  may have an approximately reverse L-shape. For example, the first terminal coupling part  121  and the second terminal coupling part may extend parallel to the cap plate and the base part may extend perpendicular to the first terminal coupling part  121  and the second terminal coupling part in a direction toward the bottom of the case. The first and second terminal coupling parts  121  and  122  may be electrically connected to a terminal by inserting lower protrusions of the terminal into the first and second terminal coupling parts  121  and  122 . The base may be connected to the first electrode non-coating portion of the electrode assembly  110 . 
         [0044]    The second collecting plate  130  may have the same structure as that of the first collecting plate  120 . Thus, a detailed description of the second collecting plate  130  will be omitted. 
         [0045]    The case  140  may be formed of a conductive metal such as aluminum, aluminum alloy, or steel plated with nickel. The case  140  may have an approximately hexahedral shape with an opening so that the electrode assembly  110 , a first electrode terminal  170 , and a second electrode terminal  160  can be inserted and placed in the case  140 . The secondary battery  100  may be sealed by coupling the cap assembly  150  to the opening of the case  140 . The inner surface of the case  140  may be treated to be electrically insulated from the electrode assembly  110 , the first electrode terminal  170 , the second electrode terminal  160 , and the cap assembly  150 . 
         [0046]    The cap assembly  150  may include a cap plate  151 , a safety vent  152 , and a plug  153 . The cap plate  151  seals the case  140 . The cap plate  151  may include a bottom surface facing the interior of the case  140 . The cap plate  151  may include a hole so that the first electrode terminal  170  connected to the first collecting plate  120  can be inserted through the cap plate  151 . In addition, the cap plate  151  may include a hole so that the second electrode terminal  160  connected to the second collecting plate  130  can be inserted through the cap plate  151 . The electrode terminals  160  and  170  may include upper gaskets  162  and  172 , and lower gaskets  163  and  173  so that the cap plate  151  can be insulated from the electrode terminals  160  and  170 . In addition, the electrode terminals  160  and  170  may include nuts  161  and  171  so that the electrode terminals  160  and  170  can be fixed to the cap plate  151  by tightening the nuts  161  and  171  on the electrode terminals  160  and  170 . After electrode is injected through an electrolyte injection hole (not shown) of the cap plate  151 , the electrode injection hole may be closed with the plug  153  of the cap assembly  150 . The cap plate  151  may include the safety vent  152 . The safety vent  152  may have a thin thickness, and thus if pressure increases to a set value, the safety vent  152  may be broken to release gas. 
         [0047]    First and second insulating members  174  and  164  may be disposed on the bottom side of the cap plate  151 . Electrode terminal accommodation spaces (refer to  174   a  in  FIG. 2 ) may be defined inside the first and second insulating members  174  and  164 . 
         [0048]    The first and second insulating members  174  and  164  may prevent a short circuit between the cap plate  151  and the electrode terminals  170  and  160 . The first insulating member  174  may prevent a short circuit between the first collecting plate  120  and the cap plate  151 . The second insulating member  164  may prevent a short circuit between the second collecting plate  130  and the cap plate  151 . The first and second insulating members  174  and  164  may be formed of polyphenylene sulfide (PPS). However, the current embodiment is not limited thereto. 
         [0049]    The first insulating member  174  may include a switch hole  175 . The switch plate  176  may make contact with the bottom surface of the cap plate  151  through the switch hole  175 . 
         [0050]    The switch plate  176  may include a terminal hole  176   a,  a temperature sensing part  176   e,  and a switch part  176   f.    
         [0051]    The switch plate  176  is formed of a conductive material. The switch plate  176  is connected to the first electrode terminal  170  and has the same polarity as that of the first electrode terminal  170 . If the inside cell temperature increases to a predetermined temperature, such as, for example, 80° C. or higher, an end of the switch plate  176  comes into contact with the bottom surface of the cap plate  151 . The cap plate  151  and the switch plate  176  have different electrical polarities. The switch plate  176  makes contact with a portion of the bottom surface of the cap plate  151  to cause an electric short circuit. 
         [0052]    A protrusion  170   b  formed on the bottom surface of the first electrode terminal  170  may be inserted through the terminal hole  176   a  of the switch plate  176 . The protrusion  170   b  may also be inserted in the second terminal coupling part  122  of the first collecting plate  120 . The first electrode terminal  170 , the switch plate  176 , and the first collecting plate  120  are electrically connected to each other. 
         [0053]    The temperature sensing part  176   e  may be disposed between the first electrode terminal  170  and the first collecting plate  120 . The temperature sensing part  176   e  may have a large contact area with the first electrode terminal  170  and the first collecting plate  120  so that the temperature sensing part  176   e  can be sensitive to the inside cell temperature. If the inside cell temperature is a predetermined temperature, such as, for example, 80° C. or higher, an end of the switch part  176   f  is brought into contact with the bottom surface of the cap plate  151 . For example, when the inside cell temperature is in the range from 80° C. to 150° C., the end of the switch part  176   f  may be brought into contact with the bottom surface of the cap plate  151 . 
         [0054]    The switch part  176   f  may have a bent shape. The switch part  176   f  may be formed of a shape-memory alloy. Shape-memory alloys are easily deformed at a low temperature, and if heated to a certain temperature or higher, the shape-memory alloys return to their original shape. That is, the switch part  176   f  may have the above-described characteristics of shape-memory alloys. The switch part  176   f  may be curved in an S-shape, such as an S-shape in a horizontal orientation. By forming the switch part  176   f  in an S-shape, desired effects may be obtained with minimal deformation of the shape-memory alloy. The switch part  176   f  may include a first bent part  176   b  and a second bent part  176   c.  The first bent part  176   b  may be a gradually bent part extending from the temperature sensing part  176   e  and having a predetermined radius of curvature. The first bent part  176   b  may be bent in a manner such that the first bent part  176   b  protrudes toward the cap plate  151 . The second bent part  176   c  may be bent from the first bent part  176   b  and may have a concave shape. The front end of the concave second bent part  176   c  is spaced apart from the cap plate  151  as long as the inside cell temperature has not reached the predetermined temperature. If the cell temperature increases to the predetermined temperature, such as, for example, 80° C. or higher, the end of the second bent part  176   c  is brought into contact with the bottom surface of the cap plate  151 . 
         [0055]    As described above, according to the embodiments, overcharging of the secondary battery may be prevented. Overcharging of the secondary battery may be prevented due to action of the switch plate in response to an increase in temperature that may occur in connection with an overcharging. 
         [0056]    The switch plate and the cap plate have different polarities. If the inside cell temperature increases, the switch plate formed of a shape-memory alloy is brought into contact with the bottom surface of the cap plate. Due to the contacting of the switch plate and the cap plate in response to the temperature increase, overcharging of the secondary battery can be prevented, and thus the electric stability of the secondary battery can be improved. 
         [0057]    Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.