Abstract:
A high-capacity battery pack attachable to a small-sized electronic device in which a lithium-polymer cell and a lithium-ion cell are physically coupled and to be electrically connected in parallel, and an electronic device using the battery pack maximize a battery mounting space while providing a high-capacity battery pack useful for the small-sized electronic device. The battery pack is arranged such that the lithium-polymer cell having a thin thickness in a large cross-sectional area and a lithium-ion cell having a thick thickness in a small cross-sectional area are appropriately arranged to maximize the space of the battery accommodating portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 2007-113804, filed Nov. 8, 2007, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Aspects of the present invention relate to a battery pack and an electronic device using the same, and more particularly, to a high-capacity battery pack, which can be joined to a small-sized set for use by allowing a lithium-polymer cell and a lithium-ion cell to be physically coupled and to be electrically connected in parallel, and an electronic device using the battery pack. 
     2. Description of the Related Art 
     As camcorders, mobile phones, notebook computers, and the like are widely used together with the rapid development of electronic, communication, and computer industries, it has been recently necessary to develop high-capacity secondary batteries which are light and have a long lifetime and provide high performance. 
     As a possible solution to environmental and energy problems, large-sized secondary batteries for electric vehicles and effective use of power at night are being developed. Thus, lithium secondary batteries have come into the spotlight, and their application range has been widely extended. 
     A lithium secondary battery may be mounted onto an electronic device and may be a battery pack in which a protective circuit board connects to at least one bare cell. The bare cell is formed by accommodating an electrode assembly including a positive electrode plate, a negative electrode plate, and a separator disposed therebetween together with an electrolyte in a can and then sealing an opening of the can with a cap assembly. The protective circuit board is provided with safety devices such as a positive temperature coefficient (PTC) thermistor, a thermal fuse, and a protective circuit module. 
     A battery pack may be a hard pack which is received in an outer case for at least one bare cell, a safety device, and the like, or an inner pack in which a gap between the bare cell and the protective circuit board is filled with hot-melt resin and which is tubed and labeled with a thin casing. 
     Depending on the types of electrolyte, lithium secondary batteries may be classified into lithium-metal batteries and lithium-ion batteries in which an organic solvent electrolyte is used and lithium-polymer batteries in which a solid polymer electrolyte is used. 
     The lithium secondary batteries may be further classified into cylinder-type batteries, prismatic-type batteries, and pouch-type batteries according to the shape of the can. 
     When the lithium secondary battery is a lithium-polymer battery in which a solid polymer electrolyte is used, the external shape is generally formed in a pouch shape. When the lithium secondary battery is a lithium-ion battery in which an organic solvent electrolyte is used, the external shape is generally formed in a cylindrical shape or a prismatic shape. 
     The conventional lithium-polymer cell that is formed in a pouch shape having a thickness that is relatively thin in a relatively large cross-sectional area compared to a conventional lithium-ion cell that is formed in a cylindrical or prismatic shape has a thickness that is relatively thick in a relatively small cross-sectional area. 
     Lithium-polymer cells have been used for small-sized devices, such as mobile phones or MP3 players, rather than high-capacity devices, and cylinder-type lithium-ion cells have been used for devices which need high-capacity batteries. However, as small-sized devices, such as mobile phones or MP3 players, also have various functions and a high frequency of use, small-sized devices are requiring higher capacity batteries. 
     SUMMARY OF THE INVENTION 
     According to aspects of the present invention, a battery pack includes a battery assembly including a lithium-ion cell and a lithium-polymer cell connected in parallel to the lithium-ion cell. 
     According to aspects of the present invention, an electronic device includes a battery accommodating portion in which a battery pack is accommodated to receive or supply power, the battery pack having a battery assembly including a lithium-ion cell and a lithium-polymer cell electrically connected in parallel to the lithium-ion cell. According to aspects of the present invention, the lithium-ion cell may be formed in a prismatic shape. According to aspects of the present invention, the lithium-polymer cell may be formed in a pouch shape. 
     According to aspects of the present invention, a protective circuit board may have a primary protective circuit including a switching element positioned between the battery assembly and the external connection terminal unit, and a switching control unit to control the switching element. 
     According to aspects of the present invention, the switching element may have one current path with the external connection terminal unit, and have first and second paths respectively connected to the lithium-ion cell and lithium-polymer cell of the battery assembly. 
     According to aspects of the present invention, a charge/discharge operation may be performed in only one of the lithium-ion cell and lithium-polymer cell. 
     According to aspects of the present invention, a lithium-polymer cell having a thin thickness in a large cross-sectional area and a lithium-ion cell having a thick thickness in a small cross-sectional area are physically coupled and electrically connected in parallel, thus maximizing a battery mounting space and providing a high-capacity battery pack useful for a small-sized set. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is an exploded perspective view illustrating a constitution of a battery pack according to an exemplary embodiment of the present invention; 
         FIG. 2  is an assembled view of a lithium-ion cell and a lithium-polymer cell in  FIG. 1 ; 
         FIG. 3  is an assembled view of the battery pack in  FIG. 1 ; 
         FIG. 4  is a circuit diagram illustrating a constitution of a battery pack according to an exemplary embodiment of the present invention; 
         FIG. 5  is a circuit diagram illustrating a constitution of a battery pack according to another exemplary embodiment of the present invention; and 
         FIG. 6  is a cross-sectional view of an electronic device using a battery pack according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. It will be understood that when an element is referred to as being electrically or physically “connected” or “coupled” to another element, it may be directly connected or coupled, electrically or physically, to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, electrically or physically, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). 
       FIG. 1  is an exploded perspective view illustrating a battery pack according to an exemplary embodiment of the present invention,  FIG. 2  is an assembled view of the lithium-ion cell and the lithium-polymer cell in  FIG. 1 , and  FIG. 3  is an assembled view of the battery pack in  FIG. 1 . Referring to  FIGS. 1 through 3 , the battery pack  100  includes a lithium-ion cell  10 , a lithium-polymer cell  20 , a double adhesive tape  30  disposed between the lithium-ion cell  10  and lithium-polymer cell  20 , a protective circuit board  40 , and first and second leads  50  and  60  to electrically connect the lithium-ion and  10  cell and the protective circuit board  40 . 
     The battery pack  100  further includes a coverlay  70  to insulate the first and second leads  50  and  60  from the exterior. The battery pack  100  also includes upper and lower cases  80  and  90 . 
     When the lithium-ion cell  10  is formed in a prismatic shape, the lithium-ion cell  10  is formed by accommodating an electrode assembly in a can formed of a metallic material, such as aluminum formed by a deep drawing method; finishing the top end of the can with a cap assembly; and then injecting an electrolyte into the can. 
     In this case, a cap-up  11  is a negative terminal that protrudes from a top portion of the lithium-ion cell  10 , and a positive terminal is disposed on a cap plate. A positive temperature coefficient (PTC) thermistor  13  can be formed at the positive terminal  15 . The positive terminal  15  is formed of a material such as nickel on the cap plate by laser welding. 
     Alternatively, when it is difficult to connect the positive terminal  15  directly to the cap plate due to an insulating material formed on the cap plate, the positive terminal  15  may be disposed on the insulating material and electrically connected to the cap plate through a connection tab  17  connected to the can, which may be an electrode terminal. 
     When the lithium-polymer cell  20  is formed in a pouch shape, the lithium-polymer cell  20  is formed by accommodating the electrode assembly (not shown) on a lower surface of a pouch casing with a space for accommodating the electrode assembly, covering the lower surface with an upper surface of the pouch casing, and then sealing the pouch casing. In this case, positive and negative electrode tabs  21  and  23  electrically connected to the protective circuit board  40  protrude outside of the pouch casing. 
     The double adhesive tape  30  is disposed between the lithium-ion cell  10  and the lithium-polymer cell  20  to allow them to be physically adhered to each other. In this case, the double adhesive tape  30  may have a notch (not shown) formed by removing a central portion of the double adhesive tape  30 . The notch can minimize a thickness increase when a central portion of the can is swelled in charge as well as accommodate the first and second leads  50  and  60 . 
     The protective circuit board  40  is disposed at one side of the lithium-ion cell  10  and lithium-polymer cell  20  and the protective circuit board  40  couple the lithium-ion cell  10  and the lithium-polymer cell  20 . The protective circuit board  40  includes protective elements, such as a protective circuit, a charge/discharge element unit, a PTC thermistor, a fuse, and the like, but is not limited thereto. The protective circuit board  40  may be formed on a printed circuit board (PCB) and have an interconnection pattern. The protective circuit board  40  further includes an external connection terminal unit  41  to connect the lithium-ion cell  10  and the lithium-polymer cell  20  to an external device. 
     The external connection terminal unit  41  may have one or a plurality of terminals, and may include a power terminal, a ground terminal, an input/out terminal, and a thermistor terminal but is not limited thereto. 
     The protective circuit board  40  further includes positive and negative terminals  43  and  45  to electrically connect the lithium-ion cell  10  and lithium-polymer cell  20 . In this case, respective positive and negative terminals  43  and  45  are disposed on the protective circuit board  40  such that the positive terminal  15  of the lithium-ion cell  10  and the positive electrode tab  21  of the lithium-polymer cell  20  are electrically connected to the positive terminal  43 , and the negative terminal  11  of the lithium-ion cell  10  and the negative electrode tab  23  of the lithium-polymer cell  20  are electrically connected to the one negative terminal  45 . Specifically, the positive electrode terminal  15  of the lithium-ion cell  10  is electrically connected to the positive terminal  43  of the protective circuit board  40  via the first lead  50 ; and the negative electrode terminal  11  of the lithium-ion cell  10  is electrically connected to the negative terminal  45  of the protective circuit board  40 . However, aspects of the present invention are not limited thereto. 
     Alternatively, a plurality of the positive terminals  43  and a plurality of the negative terminals  45  may be disposed on the protective circuit board  40  such that the positive terminal  15  of the lithium-ion cell  10  (via the first lead  50 ) and the positive electrode tab  21  of the lithium-polymer cell  20  are electrically connected to different positive terminals  43 , respectively, and the negative terminal  11  of the lithium-ion cell  10  (via the second lead  60 ) and the negative electrode tab  23  of the lithium-polymer cell  20  are electrically connected to different negative terminals  45 , respectively. 
     Alternatively, the positive terminal  15  of the lithium-ion cell  10  (via the first lead  50 ) and the positive electrode tab  21  of the lithium-polymer cell  20  may be electrically connected to one positive terminal  43  disposed on the protective circuit board  40 , and the negative terminal  11  of the lithium-ion cell  10  (via the second lead  60 ) and the negative electrode tab  23  of the lithium-polymer cell  20  are electrically connected to different negative terminals  45 , respectively. 
     On the other hand, the positive terminal  15  of the lithium-ion cell  10  (via the first lead  50 ) and the positive electrode tab  21  of the lithium-polymer cell  20  may be electrically connected to different positive terminals  43 , respectively, and the negative terminal  11  of the lithium-ion cell  10  (via the second lead  60 ) and the negative electrode tab  23  of the lithium-polymer cell  20  are electrically connected to one negative terminal  45 . 
     Thus, the lithium-ion cell  10  and lithium-polymer cell  20  connected to the protective circuit board  40  are electrically connected in parallel to each other, and constitute a core-pack-type secondary battery. When the lithium-ion cell  10  and lithium-polymer cell  20  connected in parallel and are connected to an external device, a charge or discharge operation is performed. That is, when the external device to which the lithium-ion cell  10  and the lithium-polymer cell  20  are connected via the protective circuit board  40  is a power source, such as a charger, the charge operation is performed and when the external device is a load, the discharge operation is performed. In such case, the charge and discharge operations are not performed simultaneously but performed sequentially by the protective circuit formed on the protective circuit board  40  in the lithium-ion cell  10  and lithium-polymer cell  20  connected in parallel. That is, when the charge or discharge operation is performed in any one of the lithium-ion cell  10  and lithium-polymer cell  20 , the charge or discharge operation is not performed in the other cell. Further, the lithium-ion cell  10  and lithium-polymer cell  20  may be sequentially controlled by an electronic device employing the battery alone or in addition to the protective circuit formed on the protective circuit board  40 . 
     Detailed description of the charge and discharge operations will be described later with reference to a circuit of a battery pack in  FIG. 4  according to an exemplary embodiment of the present invention. 
     The protective circuit board  40  may be connected to any one of the lithium-ion cell  10  and lithium-polymer cell  20  before they are adhered to each other, and then connected to the other cell after they are coupled to each other. Alternatively, the protective circuit board  40  may be connected to the lithium-ion cell  10  and lithium-polymer cell  20  after they are adhered to each other. 
     The first and second leads  50  and  60  are provided for electrical connection between the protective circuit board  40  and one of the lithium-ion cell  10  and the lithium-polymer cell  20 . In this exemplary embodiment, as illustrated in  FIG. 2 , the first lead  50  connects the positive electrode terminal  43  of the protective circuit board  40  to the positive electrode terminal  15  of the lithium-ion cell  10 , and the second lead  60  connects the negative electrode terminal  45  of the protective circuit board  40  to the cap-up  11  that is a negative electrode terminal of the lithium-ion cell, so that the protective circuit board  40  and the lithium-ion cell  10  are electrically connected to each other. In this case, the first and second leads  50  and  60  are preferably adhered to a portion of the double adhesive tape  30 . The coverlay  70  that is an insulating film for circuit protection is then attached on the first and second leads  50  and  60  to insulate them from the exterior and to enhance adhesion with the cell. However, aspects of the present invention are not limited thereto such that at least one of the lithium-ion cell  10  and the lithium-polymer cell  20  may include electrode tabs electrically connected to respective terminals of the protective circuit board  40 , at least one of the lithium-ion cell  10  and the lithium-polymer cell  20  may include leads electrically connected to respective terminals of the protective circuit board  40 , or the lithium-ion cell  10  may have electrode tabs electrically connected to respective terminals of the protective circuit board  40  while the lithium-polymer cell  20  has leads electrically connected to the respective terminals of the protective circuit board  40 . 
     After the lithium-ion cell  10  and lithium-polymer cell  20  are physically joined and electrically connected to the protective circuit board  40 , the lithium-ion cell  10 , the lithium-polymer cell  20 , and the protective circuit board  40  are accommodated in or housed in an external case including the upper and lower cases  80  and  90 , thus completing a battery pack  100  as illustrated in  FIG. 3 . In this case, a hole  81  is formed on the upper case  80  such that the external connection terminal unit  41  formed on the protective circuit board  40  is connectable to an external device. Although the hole  81  is formed in the upper case  80 , aspects of the present invention are not limited thereto such that the hole  81  may be formed in the upper or lower case  80  and  90  according to the location of the external connection terminal unit  41 , which may further be located elsewhere according to a configuration of the external device to which the battery pack  100  is connectable. 
       FIG. 4  is a circuit diagram illustrating circuitry of a battery pack according to an exemplary embodiment of the present invention. The battery pack includes a battery assembly  200 , a protective circuit board  300 , and an external connection terminal unit  400 . 
     The battery assembly  200  includes different types of first and second cells  210  and  220  connected in parallel, i.e., when the first cell  210  is a lithium-ion cell, the second cell  220  is a lithium-polymer cell; and when the first cell  210  is a lithium-polymer cell, the second cell  220  is a lithium-ion cell. 
     Positive electrodes of the first and second cells  210  and  220  are connected to a power terminal B+ of the external connection terminal unit  400  through a switching element  330 , and negative electrodes of the first and second cells  210  and  220  are connected to a ground terminal B− of the external connection terminal unit  400  through a charge/discharge element unit  320 . 
     The battery assembly  200  transmits various information about the battery assembly  200 , i.e., a charge potential of the cell and an amount of current that flows through the cell, to a primary protective circuit  310 . When a secondary protective circuit  340  is provided in the battery pack, the battery assembly  200  may also transmit such information to the secondary protective circuit  340 . 
     The protective circuit board  300  is formed by disposing electric elements on a printed circuit board (PCB) by such methods as spot welding, soldering, or the like. The protective circuit board  300  may include a primary protective circuit  310 , a charge/discharge element unit  320 , and a switching element  330 . The protective circuit board  300  may further include a secondary protective circuit  340 , a fuse  350 , and a temperature sensor  360 . 
     The primary protective circuit  310  receives signals transmitted from the battery assembly  200  and controls charge and discharge operations according to the information received from the battery assembly  200 . 
     The charge/discharge control unit  311  in the primary protective circuit  310  outputs charge/discharge control signals to control the charge/discharge element unit  320  to be turned off when over-charge, over-discharge, or over-current occurs or is about to occur so as to interrupt electrical flow such that a charge or discharge operation does not occur. 
     The switching control unit  313  in the primary protective circuit  310  outputs switching control signals to control the switching element  330  such that a charge or discharge operation is performed in any one of the first and second cells  210  and  220 . 
     The charge/discharge element unit  320  may be disposed in a high current path between the battery assembly  200  and the power terminal B+ or between the battery assembly  200  and the ground terminal B−. The charge/discharge element unit  320  includes charge and discharge elements  321  and  323  operated by control signals of the charge/discharge control unit  311  in the primary protective circuit  310 . That is, when the battery assembly  200  is connected to an external power supply through the external connection terminal unit  400  and the charge element  321  is turned on, the battery assembly  200  is charged. When the battery assembly  200  is connected to a load through the external connection terminal unit  400  and the discharge element  323  is turned on, the battery assembly  200  is discharged to supply power to the load. 
     When an abnormal operation such as over-charge, over-discharge, or over-current occurs or is about to occur, the charge/discharge element unit  320  is turned off by control signals from the charge/discharge control unit  311  so as to interrupt charge and discharge operations. Preferably, the charge and discharge elements  321  and  323  include metal oxide semiconductor field effect transistors (MOSFET), which have small power consumption and are easily implementable. The charge and discharge elements  321  and  323  may be NMOSFETs or PMOSFETs. 
     The switching element  330  is positioned on a high current path between the battery assembly  200  and the external connection terminal unit  400 . However, aspects of the present invention are not limited thereto such that the switching element  330  may be positioned between the battery assembly  200  and the ground terminal B−. The switching element  330  is operated by control signals from the switching control unit  313 . The switching element  330  has one current path with the external connection terminal unit  400 , and has first and second paths respectively connected to the first and second cells  210  and  220  with the battery assembly  200 . Thus, the switching element  330  is switched to select the first or second path depending on a control signal from the switching control unit  313 , thereby electrically connecting only one of the first and second cells  210  and  220  to the external connection terminal unit  400 . Accordingly, a charge or discharge operation is performed only in one of the first and second cells  210  and  220 . Preferably, a field effect transistor (FET), which has easy switching and a small power consumption, is used as the switching element  330 . 
     The secondary protective circuit  340  is operated in response to signals input from the battery assembly  200 . When an abnormal operation such as over-current occurs, the secondary protective circuit  340  cuts the fuse  350  positioned on a high current path between the battery assembly  200  and the power terminal B+ or between the battery assembly  200  and the ground terminal B− so as to interrupt electrical flow and thus protect an accident such as firing or blasting. 
     The fuse  350  is positioned on a high current path between the battery assembly  200  and the external connection terminal unit  400 . When an abnormal operation such as over-charge, over-discharge or over-current occurs or is about to occur, the fuse  350  is melted and/or cut by force, to open a circuit and thus interrupt electrical flow. However, aspects of the present invention are not limited thereto such that the fuse  350  may be positioned between the battery assembly  200  and the ground terminal B−. The fuse  350  is connected to the secondary protective circuit  340  to operate in accordance with control signals from the secondary protective circuit  340 . The fuse  350  may be a self-control protector (SCP). When the temperature used in a process of manufacturing a typical battery pack is below 110° C. and the internal temperature of the battery pack is over 130° C., the fuse  350  may be heated or blasted due to a swelling phenomenon. For this reason, the fuse  350  is preferably melted and cut at a temperature of 110 to 130° C. 
     The temperature sensor  360  is an element in which resistance is changed according to a temperature. The temperature sensor  360  is positioned on a high current path between the battery assembly  200  and the external connection terminal unit  400 . However, aspects of the present invention are not limited thereto such that the temperature sensor  360  may be positioned between the battery assembly  200  and the ground terminal B−. The temperature sensor  360  may be a positive temperature coefficient (PTC) thermistor. When temperature increases due to an abnormal operation, such as over-heat or over-current, resistance increases to reduce electrical flow, thus ensuring stability of the battery pack. 
     The external connection terminal unit  400  may include one or a plurality of terminals as described above. The external connection terminal unit  400  may include a power terminal B+, a ground terminal B−, an input/output terminal (not shown) and a thermistor terminal (not shown) but is not limited thereto. Although it has been described in  FIG. 4  that the external connection terminal unit  400  is a separate component from the protective circuit board  300 , the external connection terminal unit  400  may be provided at one side of the protective circuit board  300 . 
       FIG. 5  is a circuit diagram illustrating circuitry of a battery pack according to another exemplary embodiment of the present invention. The battery pack includes first and second core packs  510  and  530  connected in parallel and an external connection terminal unit  550 . 
     The first core pack  510  includes a first cell  511  and a first protective circuit board  513 . Since the first cell  511  and the first protective circuit board  513  are the same components as the first cell  210  and the protective circuit board  300  in  FIG. 4 , detailed descriptions thereof will be omitted. 
     The second core pack  530  includes a second cell  531  and a second protective circuit board  533 . Since the second cell  531  and the second protective circuit board  533  are the same components as the second cell  220  and the protective circuit board  300  in  FIG. 4 , detailed descriptions thereof will be omitted. 
     In this case, the first and second core packs  510  and  530  are connected in parallel to each other, so that a positive electrode terminal P 1 + of the first core pack  510  and a positive electrode terminal P 2 + of the second core pack  530  are connected to a power terminal B+ of the external connection terminal unit  550 , and a negative electrode terminal P 1 − of the first core pack  510  and a negative electrode terminal P 2 − of the second core pack  530  are connected to a ground terminal B− of the external connection terminal unit  550 . 
     While two different cells are connected to one protective circuit board  300  in  FIG. 4 , two different cells are respectively connected to two different protective circuit boards  513  and  533  in  FIG. 5 , thus ensuring electrical stability. 
     Accordingly, when any one of the first and second protective circuit boards  513  and  533  is damaged, only the one cell connected to the damaged protective circuit board is not operable but the other cell may be operable, thus ensuring electrical stability as compared with a battery pack including one protective circuit board. 
       FIG. 6  is a cross-sectional view of an electronic device using a battery pack according to an exemplary embodiment of the present invention and illustrates the electronic device  600  and the battery pack  100  provided with the electronic device  600 . 
     The electronic device  600  may be a load of a portable device that receives power supplied by the battery pack  100  or a charger that supplies power to the battery pack  100 . 
     The electronic device  600  has a battery accommodating portion  610  for accommodating the battery pack  100 , and an external terminal portion  615  connected to an external connection terminal portion  41  of the battery pack  100  is provided at one side of the battery accommodating portion  610 . 
     When the battery pack  100  is accommodated in the battery accommodating portion  610  of the electronic device  600 , a lithium-ion cell  10  having a thick thickness in a small cross-sectional area may first be inserted into the battery accommodating portion  610  rather than a lithium-polymer cell  20  having a thin thickness in a large cross-sectional area such that the lithium-ion cell  10  is positioned inside the battery accommodating portion  610 . In this case, the external connection terminal portion  41  of the battery pack  100  is electrically connected to the external terminal portion  615  provided in the battery accommodating portion  610 . 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.