Abstract:
A protection circuit board, a secondary battery, and a battery pack including a secondary battery. In embodiments of a protection circuit board, as well as a secondary battery and a battery pack including a protection circuit board, a secondary protection device is disposed in a board body of the protection circuit board for facilitating fabrication and improving performance of the secondary protection device without using an additional structure for insulating the secondary protection device and the secondary battery.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 2009-0060165, filed on Jul. 2, 2009 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments of the present invention relate to a secondary battery, and more particularly, to a protection circuit board including a secondary protection device, a secondary battery including the protection circuit board, and a battery pack including the secondary battery. 
         [0004]    2. Description of the Related Art 
         [0005]    Secondary batteries are rechargeable batteries that can be repeatedly used and recharged. Secondary batteries are used in various portable multimedia devices such as cellular phones, laptop computers, and camcorders. 
         [0006]    A secondary battery typically includes a can, an electrode assembly disposed in the can, and a bare cell. The bare cell may includes a cap assembly connected to an opening of the can and electrically connected to an external terminal. The secondary battery may include a protection circuit board electrically connected to the bare cell. A secondary battery may be included in a battery pack. Additionally, a protection circuit may be provided at the protection circuit board for preventing over-charging and over-discharging of the bare cell. 
         [0007]    A protection device such as a positive temperature coefficient (PTC) device or a thermal fuse is often installed at a protection circuit board. The protection device may be referred to as “a secondary protection device” to distinguish it from a primary protection device, such as a safety vent. 
         [0008]    A typical secondary protection device breaks a current when the temperature of the secondary battery increases excessively or the voltage of the secondary battery increases excessively due to over-charging or over-discharging. Breakage or deterioration of the secondary battery may thereby be prevented by a secondary protection device. A primary protection device is typically installed in a bare cell such that the primary protection device may be sensitive to the temperature of the bare cell. 
         [0009]    The secondary protection device is typically installed in a space between the bare cell and the protection circuit board, and providing a structure at the secondary protection device for electrically connecting the protection circuit board and the bare cell. As such, the manufacturing process of the protection circuit board, and/or the assembling process of the protection circuit board and the bare cell is typically complicated. 
         [0010]    In addition, the secondary protection device is electrically connected to a first electrode of the bare cell and is insulated from a second electrode of the bare cell. Therefore, in a conventional secondary battery, an additional structure is formed to insulate the secondary protection device from the outer surface of the bare cell, thereby complicating manufacturing processes and increasing cost. If the secondary protection device is not insulated, the secondary protection device cannot perform its function, and moreover, the secondary battery is susceptible to malfunction. 
         [0011]    Moreover, because a secondary protection device is typically installed in a space between the bare cell and the protection circuit board, the size of a battery pack may be increased, or the space may not be used for other purposes. 
       SUMMARY 
       [0012]    Embodiments of the present invention are directed to a protection circuit board, a secondary battery, and a battery pack, which overcome or substantially overcome one or more of the problems resulting from the limitations and disadvantages of the related art. 
         [0013]    Aspects of embodiments of the present invention provide a protection circuit board having a simple structure by disposing a secondary protection device therein. 
         [0014]    Aspects of other embodiments of the present invention provide a secondary battery in which a secondary protection device is disposed inside a protection circuit board for insulating the secondary protection device from a bare cell. 
         [0015]    Aspects of still other embodiments of the present invention provide a battery pack in which a secondary protection device is disposed inside a protection circuit board, thereby saving space between the protection circuit board and a bare cell. 
         [0016]    According to one exemplary embodiment of the present invention, a protection circuit board includes a board body, and a secondary protection device inside the board body. 
         [0017]    The board body may have a generally rectangular parallelepiped shape and a hole at a central portion, and the protection circuit board may further include an external terminal at one surface of the board body, and a charge/discharge device on another surface of the board body. 
         [0018]    The board body may include at least two circuit layers, and a first end part of the secondary protection device may be connected to an uppermost layer of the circuit layers, and a second end part of the secondary protection device may be connected to a lowermost layer of the circuit layers. 
         [0019]    The protection circuit board may further include insulating layers on top and bottom surfaces of the board body. 
         [0020]    The insulating layers may include photoimageable solder resist (PSR) layers. 
         [0021]    The secondary protection device may not be exposed outside the board body. 
         [0022]    The secondary protection device may include a positive temperature coefficient (PTC) device or a protection device substantially equivalent to the PTC device. 
         [0023]    The PTC device may include a PTC main body having a generally rectangular parallelepiped shape; a first conductive part on at least one surface of the PTC main body; and a second conductive part spaced apart from the first conductive part and on at least one surface of the PTC main body that does not have the first conductive part thereon. 
         [0024]    According to another exemplary embodiment, a secondary battery includes a bare cell, and a protection circuit board electrically connected to the bare cell, wherein the protection circuit board includes a board body and a secondary protection device inside the board body. 
         [0025]    The bare cell may include a can; an electrode assembly in the can; and a cap assembly closing an opening of the can. 
         [0026]    The protection circuit board may further include an electrode terminal at a center part of the board body and connected to a first electrode of the bare cell; and electrodes at end parts of the board body and connected to a second electrode of the bare cell. 
         [0027]    The secondary protection device may not be exposed outside the board body. 
         [0028]    The protection circuit board may further include insulating layers on top and bottom surfaces of the board body. 
         [0029]    The insulating layers may include PSR layers. 
         [0030]    The secondary protection device may include a PTC device or a protection device substantially equivalent to the PTC device. 
         [0031]    According to another exemplary embodiment, a battery pack includes: a bare cell; a protection circuit board electrically connected to the bare cell; and a top case coupling the protection circuit board to a side of the bare cell, wherein the protection circuit board includes a board body and a secondary protection device inside the board body. 
         [0032]    The bare cell may include a can; an electrode assembly in the can; and a cap assembly closing an opening of the can. 
         [0033]    The protection circuit board may further include an electrode terminal at a center part of the board body and connected to a first electrode of the bare cell; and electrodes at end parts of the board body and connected to a second electrode of the bare cell. 
         [0034]    The secondary protection device may not be exposed outside the board body. 
         [0035]    The protection circuit board may further include insulating layers on top and bottom surfaces of the board body. 
         [0036]    The insulating layers may include PSR layers. 
         [0037]    The secondary protection device may include a PTC device or a protection device substantially equivalent to the PTC device. 
         [0038]    The battery pack may further include a bottom case coupled to another side of the bare cell. The battery pack may further include a label sheet enclosing lateral surfaces of the bare cell, the top case, and the bottom case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    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: 
           [0040]      FIG. 1  is a side view of a protection circuit board according to one embodiment of the present invention; 
           [0041]      FIG. 2  is a perspective view of the protection circuit board of  FIG. 1 ; 
           [0042]      FIG. 3  is a cross-sectional view of a positive temperature coefficient (PTC) device of the protection circuit board of  FIG. 1 ; 
           [0043]      FIG. 4  is an exploded partial perspective view of a secondary battery according to one embodiment of the present invention; 
           [0044]      FIG. 5  is a partial front view of the secondary battery of  FIG. 4 , showing an assembled state of the secondary battery; and 
           [0045]      FIG. 6  is an exploded perspective view of a battery pack according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    Certain exemplary embodiments are described more fully herein with reference to the accompanying drawings; however, embodiments of the present invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided by way of example for understanding of the invention and to convey the scope of the invention to those skilled in the art. 
         [0047]    In the drawings, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being “on” another layer or substrate, it may be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it may be directly under, or one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or one or more intervening layers may also be present. Further, like reference numerals refer to like elements throughout the following description. 
         [0048]    Hereinafter, certain exemplary embodiments will be described in detail with reference to the accompanying drawings. 
         [0049]      FIG. 1  is a side view of a protection circuit board according to one exemplary embodiment of the present invention.  FIG. 2  is a perspective view of the protection circuit board of  FIG. 1 .  FIG. 3  is a cross-sectional view of a positive temperature coefficient (PTC) device according to one exemplary embodiment of the present invention. 
         [0050]    With reference to  FIGS. 1 to 3 , according to one exemplary embodiment, a protection circuit board  100  includes a board body  110  and a secondary protection device  120  disposed in the board body  110 . 
         [0051]    The board body  110 , in one embodiment, has a shape generally or approximately of a rectangular parallelepiped. A hole  111  is formed in a center part of the board body  110 . In one embodiment, external terminals  112  are mounted on a surface (e.g., a top surface) of the board body  110  to transmit a current to an external part, and a charge/discharge device  113  is mounted on another surface (e.g., a bottom surface) of the board body  110 . 
         [0052]    The secondary protection device  120 , in one exemplary embodiment, is disposed in the board body  110  such that the secondary protection device  120  is embedded in the board body  110  and not exposed to the outside of the board body  110 . 
         [0053]    The secondary protection device  120  may be installed during a manufacturing process of a printed circuit board that constitutes the board body  110 . At least two or four circuit layers  114   a ,  114   b ,  144   c ,  114   d  may be formed in the board body  110 . In one exemplary embodiment, an upper end part of the secondary protection device  120  is connected to an uppermost layer  114   a  of the circuit layers, and a lower end part of the secondary protection device  120  is connected to a lowermost layer  114   d  of the circuit layers. In this way, the secondary protection device  120  is electrically connected to the circuit layers  114   a ,  114   d  of the board body  110  to form a circuit structure. 
         [0054]    The top and bottom surfaces of the board body  110 , in an exemplary embodiment, are coated with photoimageable solder resist (PSR) mask ink. When the printed circuit board is fabricated, the PSR treatment process is performed to form an insulating layer on the circuitry of the printed circuit board. As a result of the PSR treatment, when a component is mounted on the printed circuit board in a later soldering process, formation of a solder bridge between circuits may be prevented or substantially prevented. That is, by performing such a PSR treatment process, the secondary protection device  120  can be insulated. 
         [0055]    A PTC device or a protection device equivalent or substantially equivalent to a PTC device may be used as the secondary protection device  120  (hereinafter, also referred to as a PTC device  120 ). However, the secondary protection device  120  is not limited thereto and may alternatively include any other suitable protection device. 
         [0056]    With further reference to  FIG. 3 , the PTC device  120 , in one embodiment, includes a PTC main body  121  having a shape generally or approximately of a rectangular parallelepiped, a first conductive part  122  enclosing at least one surface of the PTC main body  121 , and a second conductive part  123  spaced apart from the first conductive part  122  and enclosing at least one remaining surface of the PTC main body  121 . The first conductive part  122  is connected to one circuit layer  114   a  of the circuit layers of the board body  110 , and the second conductive part  123  is connected to another circuit layer  114   d  of the circuit layers of the board body  110 . 
         [0057]    The PTC main body  121 , in one embodiment, is fabricated by dispersing conductive particles in a crystalline polymer. Carbon particles may be used as the conductive particles, and a synthetic resin such as a polyolefine-based polymer may be used as the crystalline polymer. At temperatures equal to or less than a reference, or preselected, temperature, the conductive particles of the PTC main body  121  clump together such that the first conductive part  122  and the second conductive part  123  are electrically connected through the PTC main body  121 . However, at temperatures greater than the reference temperature, the crystalline polymer of the PTC main body  121  expands, and the conductive particles of the PTC main body  121  are separated to increase the electric resistance of the PTC main body  121 . Therefore, no current, or only a small amount of current, may flow between the first conductive part  122  and the second conductive part  123 . That is, in this case, no current, or only a small amount of current, may flow in the PTC main body  121  that connects the first conductive part  122  and the second conductive part  123 . 
         [0058]    Therefore, the PTC device  120  can be used as a safety device for preventing breakage of a battery. For example, due to heat generated by overcurrent, overvoltage, or over power consumption, the temperature of the battery can increase higher than a preset, or reference, temperature. Thereafter, if the temperature of the PTC main body  121  decreases to a temperature equal to or lower than the preset temperature, the crystalline polymer of the PTC main body  121  shrinks to clump the conductive particles, and thus the PTC main body  121  becomes conductive. 
         [0059]    In the described exemplary embodiment, since the PTC device  120  (secondary protection device) is disposed inside the board body  110  of the protection circuit board  100 , an additional insulation structure is unnecessary. In addition, the size of the protection circuit board  100  is not increased by the PTC device  120 . 
         [0060]    A secondary battery according to another exemplary embodiment of the present invention is described below. 
         [0061]      FIG. 4  is an exploded partial perspective view of a secondary battery according to one exemplary embodiment of the present invention.  FIG. 5  is a partial front view of the secondary battery of  FIG. 4 , showing an assembled state of the secondary battery. 
         [0062]    With reference to  FIGS. 4 and 5 , in one exemplary embodiment, a secondary battery  200  includes a bare cell  210  and a protection circuit board  100  electrically connected to the bare cell  210 . The protection circuit board  100  includes a board body  110  in which a PTC device  120  is disposed. The protection circuit board  100  and the PTC device  120 , in one embodiment, have the same or substantially similar structures as the protection circuit board  100  and the PTC device  120  described above. Therefore, like reference numerals are used for the protection circuit board  100  and the PTC device  120 , and detailed descriptions thereof will not be repeated herein. 
         [0063]    The bare cell  210  includes a can  211 , an electrode assembly  212  accommodated in the can  211 , and a cap assembly  220  configured to close an opening of the can  211 . 
         [0064]    The can  211 , in one embodiment, is a container generally or approximately shaped as a rectangular parallelepiped and having an opening formed in an end part of the can  211 . The can  211  may be formed by a method such as deep drawing. The can  211 , in one embodiment, functions as a terminal. The can  211  may be formed of a light conductive metal such as aluminum, an aluminum alloy, or any other suitable material. The can  211  is configured to accommodate, or contain, the electrode assembly  212  and electrolyte, and the opening of the can  211  is closed by the cap assembly  220  after the electrode assembly  212  is inserted into the can  211  through the opening. 
         [0065]    The electrode assembly  212  includes a positive electrode plate  213 , a separator  214 , a negative electrode plate  215 , a positive electrode tab  216  extending from the positive electrode plate  213 , a negative electrode tab  217  extending from the negative electrode plate  215 , and insulating tapes  218  attached to the positive electrode tab  216  and the negative electrode tab  217 . 
         [0066]    The separator  214  is disposed between the positive electrode plate  213  and the negative electrode plate  215 , and the positive electrode plate  213 , the separator  214 , and the negative electrode plate  215  are wound in a so-called “jelly roll” shape. The positive electrode plate  213  may be formed by coating an aluminum-foil collector with a positive electrode active material such as a lithium cobalt dioxide (LiCoO 2 ), and the negative electrode plate  215  may be formed by coating a copper-foil collector with a negative electrode active material such as carbon. The separator  214  may be formed of polyethylene, polypropylene, or a copolymer of polyethylene and polypropylene. The separator  214  may be wider than the positive and negative electrode plates  213  and  215  for reliably providing insulation between the positive and negative electrode plates  213  and  215 . 
         [0067]    The positive electrode tab  216  connected to the positive electrode plate  213 , and the negative electrode tab  217  connected to the negative electrode plate  215  are extended from the electrode assembly  212 . The insulating tapes  218  are wound around the positive electrode tab  216  and the negative electrode tab  217  at positions from which the positive electrode tab  216  and the negative electrode tab  217  extend from the electrode assembly  212 , so as to provide insulation between the positive electrode plate  213  and the negative electrode plate  215 . 
         [0068]    The cap assembly  220 , in one embodiment, includes a cap plate  221 , a gasket  222 , an electrode terminal  223 , an insulating plate  224 , a terminal plate  225 , and an insulating case  226 . 
         [0069]    A terminal penetration hole  221   a  is formed through a center part of the cap plate  221 , in one embodiment, for receiving the electrode terminal  223 , and the gasket  222  is disposed around the electrode terminal  223  for insulating the electrode terminal  223  from the cap plate  221 . An electrolyte injection hole  221   b , in one embodiment, is formed in a side of the cap plate  221  for injecting electrolyte into the can  211 . After the electrolyte is injected into the can  211 , the electrolyte injection hole  221   b  is closed using a stopple  227 . 
         [0070]    The electrode terminal  223 , in one embodiment, is electrically connected to the negative electrode tab  217  and functions as a negative terminal. Alternatively, the electrode terminal  223  may be electrically connected to the positive electrode tab  216  and used as a positive terminal. 
         [0071]    The insulating plate  224  is disposed at the bottom surface of the cap plate  221 , and the terminal plate  225  is disposed at the bottom surface of the insulating plate  224 . That is, the insulating plate  224  insulates the cap plate  221  from the terminal plate  225 . 
         [0072]    The terminal plate  225  is coupled to a lower end part of the electrode terminal  223 . In one embodiment, the negative electrode plate  215  of the electrode assembly  212  is electrically connected to the terminal plate  225  and the electrode terminal  223  through the negative electrode tab  217 . The positive electrode plate  213  of the electrode assembly  212  may be electrically connected to the bottom surface of the cap plate  221 , such as by welding the positive electrode tab  216  to the bottom surface of the cap plate  221 . 
         [0073]    The insulating case  226  is disposed at the top surface of the electrode assembly  212 . The insulating case  226  includes a negative electrode tab penetration part  226   a , a positive electrode tab penetration part  226   b , and an electrolyte injection hole  226   c  corresponding to the electrolyte injection hole  221   b  for injecting the electrolyte into the can  211 . 
         [0074]    After the electrolyte is injected into the can  211  through the electrolyte injection holes  221   b  and  226   c , the electrolyte injection hole  221   b  is closed using the stopple  227 . 
         [0075]    The protection circuit board  100  includes the board body  110  and the PTC device  120  disposed in the board body  110 . In one embodiment, an electrode terminal  114  is provided at a lower end of the hole  111  formed in the center part of the board body  110 , and lead plates  115  and  116  are disposed at both sides of the bottom surface of the board body  110 . In one embodiment, the electrode terminal  114  is used as a negative terminal, and the lead plates  115  and  116  are used as positive terminals. Alternatively, the electrode terminal  114  may be used as a positive terminal, and the lead plates  115  and  116  may be used as negative terminals. 
         [0076]    In the above-described secondary battery  200 , the protection circuit board  100  is electrically connected to the bare cell  210 . 
         [0077]    In one embodiment, the electrode terminal  114  is spot-welded to the electrode terminal  223  of the bare cell  210  through the hole  111  of the board body  110 . Also, in one embodiment, the lead plates  115  and  116  are connected to the top surface of the bare cell  210  by laser welding. In one embodiment, the electrode terminal  223  is a negative terminal, the cap plate  221  is a positive terminal of the bare cell  210 , and at least one of the lead plates  115  and  116  is welded to the top surface of the cap plate  221  and is electrically connected to a positive terminal of the board body  110 . 
         [0078]    In the above-described secondary battery  200 , the PTC device  120  (secondary protection device) is disposed inside the board body  110  so as to prevent fire or explosion of the secondary battery  200  by breaking a current when the temperature of the secondary battery  200  increases excessively due to either an internal or an external cause. 
         [0079]    Because the PTC device  120  is disposed inside the board body  110 , the PTC device  120  can be effectively insulated from the bare cell  210 . Moreover, the PTC device  120  can be efficiently insulated from the bare cell  210  without requiring an additional component. 
         [0080]    Furthermore, since the PTC device  120  is not located in a space between the protection circuit board  100  and the bare cell  210 , other components or devices may be arranged in the space between the protection circuit board  100  and the bare cell  210 . 
         [0081]    A battery pack according to another exemplary embodiment of the present invention is described below. 
         [0082]      FIG. 6  is an exploded perspective view of a battery pack according to one exemplary embodiment of the present invention. 
         [0083]    With reference to  FIG. 6 , in an exemplary embodiment, a battery pack  300  includes a bare cell  210 , a protection circuit board  100  electrically connected to the bare cell  210 , a top case  310  coupling the protection circuit board  100  to the top side of the bare cell  210 , a bottom case  320  coupled to the bottom side of the bare cell  210 , and a label sheet  330  wrapped around the sidewall of the bare cell  210  so as to couple the top case  310  and the bottom case  320  to the bare cell  210  and protect the sidewall of the bare cell  210 . 
         [0084]    The protection circuit board  100  includes a board body  110  in which a PTC device  120  is disposed. The protection circuit board  100  and the PTC device  120 , in an exemplary embodiment, have the same or substantially similar structures as those of the protection circuit board  100  and the PTC device  120  described above. Therefore, in the following description, like reference numerals are used for the protection circuit board  100  and the PTC device  120 , and detailed descriptions thereof are not repeated. 
         [0085]    The top case  310  has a shape generally or approximately of a rectangular parallelepiped. An inner space of the top case  310  is sufficiently large for receiving the protection circuit board  100 , and the bottom side of the top case  310  is open. In one embodiment, terminal holes  311  are formed in one side of the top case  310  so that external terminals  112  of the protection circuit board  100  can be exposed through the terminal holes  311 , and a sheet attachment part  312  is formed at the other side of the top case  310  for attaching a submersion indication sheet  340  to the sheet attachment part  312 . 
         [0086]    Lateral ribs  321  are formed on both longitudinal sides of the bottom case  320 , in one embodiment, for supporting lower portions of longitudinal sides of the bare cell  210 . 
         [0087]    A double-sided tape  350  is disposed between the bare cell  210  and the bottom case  320  for bonding the bottom side of the bare cell  210  and the top side of the bottom case  320  together. In this way, the bottom case  320  is coupled to the bottom side of the bare cell  210 . 
         [0088]    The label sheet  330 , in one embodiment, is wrapped around the lower end part of the top case  310 , the lateral ribs  321  of the bottom case  320 , and the sidewall of the bare cell  210 . 
         [0089]    In the battery pack  300 , the bare cell  210  and the protection circuit board  100  are electrically connected to each other. That is, in an exemplary embodiment, the electrode terminal  223  (e.g., the negative terminal) of the bare cell  210  is electrically connected to the electrode terminal  114  of the protection circuit board  100 . In addition, the cap plate  221  (e.g., the positive terminal) of the bare cell  210  is electrically connected to the lead plates  115  and  116  of the protection circuit board  100 . 
         [0090]    In the battery pack  300 , heat can be transferred to the PTC device  120  disposed in the protection circuit board  100  through the electrode terminal  223 . Therefore, if the temperature of the battery pack  300  increases excessively, the PTC device  120  can break a current to prevent fire or explosion of the battery pack  300 . 
         [0091]    The PTC device  120  is installed inside the board body  110 , and the top and bottom surfaces of the board body  110 , in one embodiment, are coated with PSR to form an insulating layer. As such, more reliable insulation can be provided between the protection circuit board  100  and the bare cell  210 . Further, an additional component is not needed for insulating the PTC device  120  from the bare cell  210 . 
         [0092]    In addition, a space between the protection circuit board  100  and the bare cell  210  can be saved. Therefore, another component or device can be placed in the saved space, or the size of the battery pack  300  can be reduced. 
         [0093]    As described above, according to one exemplary embodiment of the present invention, a protection circuit board has a simple structure having a secondary protection device disposed therein. The secondary protection device can be simply installed at the protection circuit board. 
         [0094]    According to another exemplary embodiment of the present invention, a secondary battery includes a protection circuit board having a secondary protection device disposed therein for effectively insulating the secondary protection device from a bare cell. As such, a process for insulating the secondary protection device from the bare cell may be unnecessary. 
         [0095]    According to another exemplary embodiment of the present invention, a battery pack includes a secondary protection device disposed inside a protection circuit board for saving a space between the protection circuit board and a bare cell. As such, the size of the battery pack may be reduced. 
         [0096]    Certain exemplary embodiments of the present invention 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 ordinary 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.