Abstract:
Disclosed herein is a battery pack including secondary batteries which can be charged and discharged. The battery pack is configured such that secondary batteries having different sizes are stacked to form a stair-like structure having a width and a height.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a battery pack including a battery cell stack of secondary batteries which can be charged and discharged. 
       BACKGROUND ART 
       [0002]    With remarkable development of information technology (IT), a great variety of portable information communication devices has been popularized. As a result, in the 21 st  century, we are moving toward a ubiquitous society in which high-quality information service is possible regardless of time and place. 
         [0003]    Meanwhile, lithium secondary batteries are very important to extend such a ubiquitous society. Specifically, lithium secondary batteries, which can be charged and discharged, have been widely used as an energy source for wireless mobile devices. In addition, lithium secondary batteries have also been used as an energy source for electric vehicles and hybrid electric vehicles, which have been proposed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. 
         [0004]    As devices, to which the lithium secondary batteries are applicable, are diversified as described above, the lithium secondary batteries have also been diversified such that the lithium secondary batteries can provide powers and capacities suitable for devices to which the lithium secondary batteries are applied. In addition, there is a strong need to reduce the size and weight of lithium secondary batteries. 
         [0005]    For example, small-sized mobile devices, such as mobile phones, personal digital assistants (PDAs), digital cameras, and laptop computers, use one or several small-sized, lightweight battery cells for each device according to the reduction in size and weight of the corresponding products. 
         [0006]    On the other hand, middle or large-sized devices, such as electric bicycles, electric motorcycles, electric vehicles, and hybrid electric vehicles, use a middle or large-sized battery module (middle or large-sized battery pack) having a plurality of battery cells electrically connected with each other because high power and large capacity are necessary for the middle or large-sized devices. The size and weight of the battery module is directly related to an accommodation space and power of a corresponding middle or large-sized device. For this reason, manufacturers are trying to manufacture small-sized, lightweight battery modules. 
         [0007]    A cylindrical battery cell, a prismatic battery cell, and a pouch-shaped battery cell, which are classified based on their shapes, are used as a unit cell of a battery module or battery pack. Especially, the pouch-shaped battery cell, which can be stacked with high integration, has a high energy density per weight, and is inexpensive, has attracted considerable attention. 
         [0008]      FIGS. 1A and 1B  are exploded perspective views typically showing the general structure of a conventional representative pouch-shaped secondary battery. 
         [0009]    Referring to  FIG. 1A , a pouch-shaped secondary battery  10  includes an electrode assembly  20  having pluralities of electrode tabs  21  and  232  protruding therefrom, two electrode leads  30  and  31  respectively connected to the electrode tabs  21  and  232 , and a battery case  40  to receive the electrode assembly  20  in a sealed state such that portions of the electrode leads  30  and  31  are exposed outward from the battery case  40 . 
         [0010]    The battery case  40  includes a lower case  42  having a depressed receiving part  41 , in which the electrode assembly  20  is located, and an upper case  43  to cover the lower case  42  such that the electrode assembly  20  is sealed in the battery case  40 . The upper case  43  and the lower case  42  are connected to each other by thermal welding in a state in which the electrode assembly is mounted therein to form an upper end sealed part  44 , side sealed parts  45  and  46 , and a lower end sealed part  47 . 
         [0011]    As shown in  FIG. 1A , the upper case  43  and the lower case  42  may be configured as separate members. As shown in  FIG. 1B , on the other hand, one end of the upper case  43  may be integrally formed at a corresponding end of the lower case  42  such that the upper case  43  and the lower case  42  may be hingedly connected to each other. 
         [0012]    Also, as shown in  FIGS. 1A and 1B , the pouch-shaped battery cell is configured to have a structure in which electrode terminals constituted by the electrode tabs and the electrode leads are formed at one end of the electrode assembly. However, a pouch-shaped battery cell configured to have a structure in which electrode terminals are formed at opposite ends of an electrode assembly may also be manufactured using the above method. 
       DISCLOSURE 
     Technical Problem 
       [0013]    As shown in  FIGS. 1A and 1B , a pouch-shaped battery cell is generally manufactured so as to have an almost rectangular parallelepiped structure. A plurality of such pouch-shaped battery cells is stacked to constitute a battery pack having a rectangular parallelepiped structure. 
         [0014]    However, a device, to which the battery cell or the battery pack having the rectangular parallelepiped structure is applied, is not generally formed in the shape of a rectangular parallelepiped. For example, sides of a smartphone are curved to improve grip. 
         [0015]    In a case in which the battery cell or the battery pack having the rectangular parallelepiped structure is mounted in a device designed so as to have such curved portions, space utilization of the device may be deteriorated. 
         [0016]    That is, the curved portions of the device have dead spaces, in which the battery cell or the battery pack cannot be mounted. Eventually, such dead spaces lower the capacity of the device per volume. 
         [0017]    Therefore, the present invention has been made to solve the above problems, and it is an object of the present invention to provide a battery pack wherein the capacity of a device per volume is maximized. 
       Technical Solution 
       [0018]    In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a battery pack including two or more battery cells stacked in a height direction on the basis of a plane, wherein one or more battery cells have the same size as or different sizes than one or more other battery cells and the battery cells having different sizes are stacked to form a one or more stair-like structure having a width and a height. 
         [0019]    In the above description, the plane means any plane. That is, the plane may be the ground or a plane perpendicular to the ground. Consequently, the battery cells may be stacked on the ground in the height direction. Alternatively, the battery cells may be stacked on the plane perpendicular to the ground in the height direction. 
         [0020]    Hereinafter, the plane may be referred to as the ground for ease of understanding. In this case, the height direction from the plane may be referred to as an antigravity direction, and the direction opposite to the height direction may be referred to as a gravity direction. 
         [0021]    For example, “the battery cells are stacked in the height direction on the basis of the plane” in the above description may mean that the battery cells may be stacked from the ground in the gravity direction and/or in the antigravity direction. 
         [0022]    Consequently, the stacked direction of the battery cells may be the gravity direction and/or in the antigravity direction. 
         [0023]    In a case in which the battery cells are stacked in the height direction and in the direction opposite to the height direction, i.e. in opposite directions, on the basis of the plane, the battery cells stacked in the height direction on the basis of the plane and the battery cells stacked in the direction opposite to the height direction on the basis of the plane may be arranged in a symmetrical fashion or in an asymmetrical fashion. 
         [0024]    The battery pack may be configured to have a structure in which two or more battery cells are stacked and electrode terminals of the battery cells are electrically connected to each other. In this case, at least one selected from among a total length, a total width, and a total height of one of the electrode terminals may be different from that of the other electrode terminal or the total length, the total width, and the total height of one of the electrode terminals may be equal to those of the other electrode terminal. Also, the battery cells may be stacked such that the electrode terminals are stacked in an overlapped state to electrically connect the electrode terminals to each other. 
         [0025]    The battery pack may include two or more battery cells. In this case, the two or more battery cells may have different sizes. Alternatively, one of the battery cells may have a size different from that of the other battery cells having the same size. Also, the battery pack may include a combination of two or more battery cells (A) having the same size and two or more battery cells (B) having the same size, the size of the battery cells (B) being different from that of the battery cells (A). Alternatively, the battery pack may include a combination of two or more battery cells (A) having the same size, two or more battery cells (B) having the same size, the size of the battery cells (B) being different from that of the battery cells (A), and two or more battery cells (C) having the same size, the size of the battery cells (C) being different from those of the battery cells (A) and the battery cells (B). 
         [0026]    In order to form the stair-like structure, the battery pack according to the present invention may include one or more battery cells have different widths and/or lengths. Battery cells having different sizes may be battery cells having different widths and/or lengths. 
         [0027]    The stair-like structure has a width and a height. The width of the stair-like structure may correspond to the difference between the widths or the lengths of the stacked battery cells, and the height of the stair-like structure may be the sum of heights of stairs. The height of each stair may correspond to the height of each of the stacked battery cells. 
         [0028]    The stair-like structure may have (i) the same stair height and different widths or (ii) different widths and stair heights. 
         [0029]    Specifically, a plurality of battery cells having the same length, the same stair height, and different widths, a plurality of battery cells having the same width, the same stair height, and different lengths, or a plurality of battery cells having different widths, lengths, and stair heights may be stacked to form a stair-like structure. 
         [0030]    The width and/or stair height of the stair-like structure may be changed based on the radius of curvature of a device in which the battery pack is mounted. 
         [0031]    Specifically, in the battery pack according to the present invention, the stair-like structure may be configured such that the stair height is gradually decreased from the lower end to the upper end of the stair-like structure in the height direction on the basis of the plane. The stair-like structure may be configured such that the stair height is gradually increased from the lower end to the upper end of the stair-like structure in the height direction on the basis of the plane. The stair-like structure may be configured such that the width is gradually increased from the lower end to the upper end of the stair-like structure in the height direction on the basis of the plane. The stair-like structure may be configured such that the width is gradually decreased from the lower end to the upper end of the stair-like structure in the height direction on the basis of the plane. The stair-like structure may be configured such that both the width and the stair height are gradually increased or decreased from the lower end to the upper end of the stair-like structure in the height direction on the basis of the plane. 
         [0032]    A region at which the stair-like structure is formed is not particularly restricted. Specifically, the stair-like structure may be formed at an electrode terminal non-formation region or an electrode terminal formation region. Alternatively, the stair-like structure may be formed at both the electrode terminal non-formation region and the electrode terminal formation region. 
         [0033]    In a case in which the stair-like structure is formed at both the electrode terminal non-formation region and the electrode terminal formation region, the stair-like structure may be formed in the shape of a frustum of a quadrangular pyramid or a frustum of an octagonal pyramid. The frustum of the octagonal pyramid may be a symmetric frustum of an octagonal pyramid or an asymmetric frustum of an octagonal pyramid. 
         [0034]    A system component of a device, in which the battery pack is mounted, is located at the stair-like structure. 
         [0035]    Each of the battery cells may be a prismatic battery cell, a cylindrical battery cell, or a pouch-shaped battery cell. However, the shape of the battery cells according to the present invention is not particularly restricted. Consequently, the battery pack according to the present invention may include a structure in which the battery cells are stacked in a mixed fashion. 
         [0036]    Hereinafter, each of the battery cells may be referred to as a pouch-shaped battery cell configured to have a structure in which a stack of cathodes, separators, and anodes, i.e. an electrode assembly, is received in a cell case, the cell case is sealed by thermal welding after the electrode assembly is impregnated with an electrolyte for ease of understanding. However, the present invention is not limited thereto. 
         [0037]    The plate-shaped battery cell may be a pouch-shaped battery cell configured to have a structure in which a stack of cathodes, separators, and anodes, i.e. an electrode assembly, is received in a cell case, the cell case is sealed by thermal welding in a state in which a cathode terminal and an anode terminal protrude outward from the cell case after the electrode assembly is impregnated with an electrolyte. 
         [0038]    The cell case may include a receiving part to receive the electrode assembly and a sealed part formed around the receiving part by thermal welding. According to circumstances, the sealed part may be bent toward the receiving part. 
         [0039]    In a concrete example, the pouch-shaped battery cell may be a first type pouch-shaped battery cell having a circular structure in plane, a polygonal structure in plane, a polygonal structure in plane, at least one corner of which is curved, or a polygonal structure in plane, at least one side of which is curved, and configured to have a structure in which the cathode terminal and the anode terminal are formed at one end of the battery cell. 
         [0040]    In another concrete example, the pouch-shaped battery cell may be a second type pouch-shaped battery cell having a circular structure in plane, a polygonal structure in plane, a polygonal structure in plane, at least one corner of which is curved, or a polygonal structure in plane, at least one side of which is curved, and configured to have a structure in which the cathode terminal and the anode terminal are formed at one end of the battery cell and the other end of the battery cell opposite to one end of the battery cell, respectively. 
         [0041]    In a further concrete example, the pouch-shaped battery cell may be a third type pouch-shaped battery cell having a circular structure in plane, a polygonal structure in plane, a polygonal structure in plane, at least one corner of which is curved, or a polygonal structure in plane, at least one side of which is curved, and configured to have a structure in which the cathode terminal and the anode terminal are located at adjacent sides of the battery cell. 
         [0042]    The first type pouch-shaped battery cell, the second type pouch-shaped battery cell, and the third type pouch-shaped battery cell may be electrically connected to one another while being stacked in a mixed fashion. 
         [0043]    The electrode assembly is configured to have a structure including a cathode, an anode, and a separator disposed between the cathode and the anode. The electrode assembly may be a stacked type electrode assembly, which is manufactured by sequentially stacking a cathode plate, a separator plate, and an anode plate such that the separator plate is disposed between the cathode plate and the anode plate, a wound type electrode assembly, which is manufactured by sequentially stacking a sheet type cathode, a sheet type separator, and a sheet type anode and winding the sheet type cathode, the sheet type separator, and the sheet type anode such that the sheet type separator is disposed between the sheet type cathode and the sheet type anode, or a combination (stacked/folded) type electrode assembly, which is manufactured by arranging one or more polarized bodies selected from a group consisting of a cathode plate, an anode plate, and a stacked type electrode assembly on a sheet type separator and winding or folding the sheet type separator. The stacked/folded type electrode assembly may be manufactured using two or more sheet type separators. 
         [0044]    Meanwhile, in order to achieve stable coupling between the battery cells stacked in the height direction on the basis of the plane, the battery pack may further include an adhesion means or a bonding means to couple the battery cells. 
         [0045]    The adhesion means or the bonding means is not particularly restricted so long as the coupling between the battery cells is easily achieved. For example, the adhesion means or the bonding means may be an adhesive, a bonding agent, a double-sided adhesive tape, or a double-sided bonding tape. 
         [0046]    According to circumstances, a spacer may be disposed between battery cells having different sizes and a system component of a device may be located at a portion of the spacer. 
         [0047]    In the above structure, the spacer may be formed in a frame shape corresponding to outer circumferential regions of the battery cells facing each other. 
         [0048]    An adhesion means or a bonding means of a predetermined thickness to couple the battery cells may be applied to the top and the bottom of the spacer or a double-sided adhesive or bonding tape may be attached to the top and the bottom of the spacer such that the spacer is easily mounted to a corresponding top and a corresponding bottom of the battery cells. Also, the battery cells may be fixed in position using ultraviolet (UV) gel or UV glue in a state in which the battery cells are stacked. The spacer may be a heat sink. 
         [0049]    In accordance with another aspect of the present invention, there is provided a device comprising the battery pack with the above-stated construction as a power source. 
         [0050]    An example of the device, for which the battery pack according to the present invention is used, may be selected from among a mobile phone, a portable computer, a smartphone, a smart pad, a laptop computer, a light electronic vehicle (LEV), an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage unit. However, the device is not limited thereto. 
         [0051]    The structure of each device and a method of manufacturing each device are well known in the art to which the present invention pertains, and therefore, a detailed description thereof will be omitted. 
       Effects of the Invention 
       [0052]    As is apparent from the above description, the battery pack according to the present invention includes a stair-like structure changed based on the radius of curvature of a device. Consequently, the present invention has an effect of increasing the capacity of the device per volume utilizing a dead space defined in the device unlike a conventional battery pack. 
         [0053]    In addition, a system component of the device, in which the battery pack is mounted, is located at the stair-like structure. Consequently, the dead space of the device is further utilized. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0054]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0055]      FIGS. 1A and 1B  are exploded perspective views showing a conventional representative pouch-shaped secondary battery; 
           [0056]      FIG. 2  is a perspective view showing a battery pack, including pouch-shaped battery cells each having angled corners, according to an embodiment of the present invention; 
           [0057]      FIG. 3  is a perspective view showing a battery pack including pouch-shaped battery cells each having a curved corner as a modification of the battery pack shown in  FIG. 2 ; 
           [0058]      FIGS. 4 and 5  are perspective views showing a battery pack according to another embodiment of the present invention; 
           [0059]      FIG. 6  is a view typically showing a method of manufacturing the battery pack shown in  FIGS. 4 and 5 ; 
           [0060]      FIG. 7  is a perspective view showing a battery pack according to another embodiment of the present invention; 
           [0061]      FIG. 8  is a sectional view taken along line A-A of  FIG. 2 ; 
           [0062]      FIGS. 9 to 12  are views typically showing the battery pack according to the embodiment of the present invention using the sectional view of  FIG. 8 ; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0063]    Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted, however, that the scope of the present invention is not limited by the illustrated embodiments. 
         [0064]    In  FIGS. 2 to 7 , there are shown battery packs configured such that three pouch-shaped battery cells  110 ,  120 , and  130  having diffident lengths are stacked to form a stair-like structure at an electrode terminal non-formation region  150 . 
         [0065]    Referring to  FIG. 2 , there is shown a battery pack  200  configured to have a structure in which three first type pouch-shaped battery cells  110 ,  120 , and  130  are stacked in the height direction on the basis of a plane parallel to the ground. A stair-like structure is formed at an electrode terminal non-formation region  150 . 
         [0066]    Also, electrode terminals of the pouch-shaped battery cells  110 ,  120 , and  130  are connected to each other by welding in a stacked state to form electrode terminal connection parts  140  and  141 . The electrode terminal connection parts  140  and  141  may be connected in series or in parallel. The electrode terminal connection parts  140  and  141  are formed at one side on the basis of a virtual center line C-C of the battery cell  130 . 
         [0067]    Referring to  FIG. 3 , there is shown a battery pack  200  including three first type pouch-shaped battery cells  110 ,  120 , and  130  each having a curved corner. The radius of curvature of the curved corner may be properly adjusted based on a curved device. 
         [0068]    Only one corner of each of the battery cells  110 ,  120 , and  130  is curved. However, each of the battery cells  110 ,  120 , and  130  may have two or more curved corners based on the shape of a curved device, which falls within the scope of the present invention. 
         [0069]    Referring to  FIG. 4 , there is shown a battery pack  200  configured to have a structure in which three second type pouch-shaped battery cells  110 ,  120 , and  130  are stacked in the height direction on the basis of a plane parallel to the ground. In the same manner as in  FIG. 2 , a stair-like structure is formed at an electrode terminal non-formation region  150 . Electrode terminal connection parts  140  and  141  may be connected in series or in parallel. According to circumstances, both or one of the electrode terminal connection parts  140  and  141  may be formed at one side on the basis of a virtual center line (not shown) of the battery cell  130 . 
         [0070]    A battery pack shown in  FIG. 5  is identical to the battery pack shown in  FIG. 4  except that an electrode terminal, i.e. a cathode terminal or an anode terminal, of a battery cell  130 , which is stacked at the lowermost end is bent. The battery pack of  FIG. 4  may be a small-sized battery pack which may be used as a power source of a device, such as a mobile phone, and the battery pack of  FIG. 5  may be a middle or large-sized battery pack which may be used as a power source of an electric vehicle. 
         [0071]      FIG. 6  is a view typically showing a method of manufacturing the battery pack  200  shown in  FIGS. 4 and 5 . As shown in  FIG. 6 , the battery cell  120  is folded as indicated by an arrow such that the battery cell  120  is stacked on the battery cell  130 , and then the battery cell  110  is folded as indicated by an arrow such that the battery cell  110  is stacked on the battery cell  120 . As a result, the battery cells  110 ,  120 , and  130  are folded in a Z shape. 
         [0072]    Referring to  FIG. 7 , there is typically shown a battery pack  200  configured to have a structure in which three third type pouch-shaped battery cells  110 ,  120 , and  130 , each of which has an angle of 90 degrees between a cathode terminal and an anode terminal, are stacked. 
         [0073]    The battery pack of  FIG. 7  is identical to the battery pack of  FIGS. 2 and 4  except that the third type pouch-shaped battery cells  110 ,  120 , and  130  are stacked. 
         [0074]      FIG. 8  is a vertical sectional view taken along line A-A of  FIG. 2 . 
         [0075]    Referring to  FIG. 8 , it can be clearly seen that the battery pack  200 , in which the three battery cells  110 ,  120 , and  130  having the same height and different lengths are stacked, has a stair-like structure formed at the electrode terminal non-formation region. 
         [0076]    Also, referring to  FIG. 8 , it can be seen that the stair-like structure of the battery pack  200  is configured such that the height is gradually decreased and the width is gradually increased from the lower end to the upper end of the stair-like structure. 
         [0077]      FIG. 9  is a sectional view showing a battery pack in which battery cells  110 ,  120 , and  130  having different heights and lengths are stacked unlike  FIG. 8 . 
         [0078]    A straight line L 2 -L 2  tangent to the battery cell  130  having the greatest height and length and to the battery cell  120 , stacked on the battery cell  130 , having a height and a length less than those of the battery cell  130  is inclined at a predetermined angle to a central axis H-H. 
         [0079]    Also, a straight line L 1 -L 1  tangent to the battery cell  120  and to the battery cell  110 , stacked on the battery cell  120 , having a height and a length less than those of the battery cell  120  is inclined at another predetermined angle to the central axis H-H. 
         [0080]    It can be seen from  FIG. 9  that in the battery pack  200 , in which the three battery cells  110 ,  120 , and  130  having different heights and lengths are stacked, the angle between the straight line and the central axis is gradually increased from the lower end to the upper end of the stair-like structure. That is, the angle between the straight line L 1 -L 1  and the central axis H-H is greater than that between the straight line L 2 -L 2  and the central axis H-H. 
         [0081]      FIG. 10  typically shows a battery pack  200  configured to have a structure in which three battery cells  130  having the same length are located at the lowermost end, two battery cells  120  having the same size and a length less than that of the battery cells  130  are located on the battery cells  130 , and a battery cell  110  having a length less than that of the battery cells  120  is located at the uppermost end. 
         [0082]    Referring to  FIG. 10 , an angle between a straight line L 1 -L 1  and a central axis H-H is greater than that between a straight line L 2 -L 2  and the central axis H-H in the same manner as in  FIG. 9 . 
         [0083]    In the above description, the battery packs including battery cells having different lengths and/or heights have been described in detail with reference to  FIGS. 2 to 10 . However, it can be easily understood from the above description that the present invention may be applied to a battery cell stack in which battery cells having different widths and/or heights are stacked or a battery cell stack in which battery cells having different widths, lengths, and heights are stacked. 
         [0084]      FIG. 11  is a vertical sectional view typically showing a battery pack configured to have a structure in which battery cells  110 ,  120 , and  130  are stacked in the shape of a frustum of a quadrangular pyramid, and  FIG. 12  is a vertical sectional view typically showing a battery pack configured to have a structure in which battery cells  110 ,  111 ,  120 ,  121 ,  130 , and  131  are stacked in the shape of a frustum of an octagonal pyramid. 
         [0085]    In the battery pack of  FIG. 11  formed in the shape of the frustum of the quadrangular pyramid and the battery pack of  FIG. 12  formed in the shape of the frustum of the octagonal pyramid, stair-like structures may be formed at both an electrode terminal formation region and an electrode terminal non-formation region. That is, in the battery pack of  FIG. 11  formed in the shape of the frustum of the quadrangular pyramid and the battery pack of  FIG. 12  formed in the shape of the frustum of the octagonal pyramid, the battery cells having different widths and lengths are stacked. 
         [0086]    Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.