Abstract:
A battery pack includes: a plurality of unit batteries each having a rectangular-solid sealed metal unit battery case and two voltage terminals protruding from a terminal surface of the unit battery case; a spacer arranged between two main surfaces of adjacent unit batteries opposing to each other so as to maintain a gap between the main surfaces; and a connection portion which electrically connects the voltage terminals of different unit batteries. The spacer has a plurality of protrusions for supporting the corner portions of the unit battery cases and through holes formed at positions opposing to the main surfaces which can receive expanded portions when the main surfaces of the unit battery cases are expanded by inner pressure of the unit battery cases.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part (CIP) application based upon the International Application PCT/JP2008/002245, the International Filing Date of which is Aug. 20, 2008, the entire content of which is incorporated herein by reference, and claims the benefit of priority from the prior Japanese Patent Application No. 2007-251599, filed in the Japanese Patent Office on Sep. 27, 2007, the entire content of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a battery pack formed by arranging and connecting a plurality of unit batteries and, more particularly, to a battery pack having a structure capable of maintaining safety and efficiency even after a long-term use. 
         [0003]    There is known a battery pack formed by arranging a plurality of unit batteries and electrically and mutually connecting the electrodes of the unit batteries, as disclosed in Japanese Patent Application Laid-Open Publications No. 2006-339032 and No. 2007-200758, the entire contents of which are incorporated herein by reference. In this battery pack, it is preferable that the unit batteries be arranged close to each other in order to reduce the size of the entire battery pack. 
         [0004]    In the case of, e.g., a lithium-ion battery, it is necessary to prevent entering of water in terms of characteristics of a material thereof and thus a metal unit battery case that does not transmit water is employed. 
         [0005]    For example, in the case where an aluminum unit battery case of a sealed type that does not transmit water is employed in the lithium-ion battery, there is a possibility that gas may accumulate in the unit battery case due to a long-term use to increase the inner pressure, resulting in inflation of the unit battery case. Thus, it is necessary to estimate the deformation of the unit battery case and design the structure thereof so as to allow for the deformation. Otherwise, the battery pack may be destroyed before the end of the life of each unit battery, disabling the subsequent use. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention has been made in view of the above situation, and an object thereof is to provide a battery pack formed by arranging and connecting a plurality of unit batteries capable of maintaining safety and efficiency even after a long-term use. 
         [0007]    In order to solve the problems, according to the present invention, there is presented a battery pack comprising: a plurality of unit batteries each provided with a rectangular-solid shaped sealed type metal unit battery case and two voltage terminals, the unit battery case having two main surfaces which are larger than other surfaces and extend in parallel and the two voltage terminals projecting from one surface which is not the main surface of the unit battery case; a spacer disposed between two of the main surfaces of two of the unit batteries which are adjacent and opposed to each other so as to maintain the interval between the main surfaces; and a connection unit which electrically connects the voltage terminals of different unit batteries, wherein the spacer has a plurality of protrusions for supporting corner portions of the unit battery cases, and cut portions formed at positions opposed to the main surfaces which can receive inflated portions when the main surfaces of the unit battery cases are inflated by inner pressure of the unit battery cases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The above and other features and advantages of the present invention will become apparent from the discussion hereinbelow of specific, illustrative embodiments thereof presented in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a perspective view showing an embodiment of a battery pack according to the present invention; 
           [0010]      FIG. 2  is a sectional elevation view of the battery pack taken along the II-II line of  FIG. 1 ; 
           [0011]      FIG. 3  is a plan view showing an example of a spacer used in the battery pack of  FIG. 1 ; 
           [0012]      FIG. 4  is a sectional elevation view taken along the IV-IV line of  FIG. 3 ; 
           [0013]      FIG. 5  is a sectional elevation view taken along the V-V line of  FIG. 3 . 
           [0014]      FIG. 6  is a plan view showing an example of an upper/lower plate used in the battery pack of  FIG. 1 ; 
           [0015]      FIG. 7  is a sectional elevation view taken along the VII-VII line of  FIG. 6 ; 
           [0016]      FIG. 8  is an elevation view showing an example of an insulating plate used in the battery pack of  FIG. 1 ; 
           [0017]      FIG. 9  is a perspective view showing a state during assembly of the battery pack of  FIG. 1 ; 
           [0018]      FIG. 10  is a perspective view showing a state during assembly of the battery pack of  FIG. 1  continued from  FIG. 9 ; 
           [0019]      FIG. 11  is a perspective view showing a state during assembly of the battery pack of  FIG. 1  continued from  FIG. 10 ; and 
           [0020]      FIG. 12  is a perspective view showing a state during assembly of the battery pack of  FIG. 1  continued from  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    With reference to the accompanying drawings, an embodiment of a battery pack according to the present invention will be described.  FIG. 1  is a perspective view showing a battery pack according to the present embodiment, and  FIG. 2  is a sectional elevation view of the battery pack taken along the II-II line of  FIG. 1 .  FIG. 3  is a plan view showing an example of a spacer used in the battery pack according to the present embodiment,  FIG. 4  is a sectional elevation view taken along the IV-IV line of  FIG. 3 , and  FIG. 5  is a sectional elevation view taken along the V-V line of  FIG. 3 .  FIG. 6  is a plan view showing an example of an upper/lower plate used in the battery pack according to the present embodiment, and  FIG. 7  is a sectional elevation view taken along the VII-VII line of  FIG. 6 .  FIG. 8  is an elevation view showing an example of an insulating plate used in the battery pack according to the present embodiment.  FIGS. 9 to 12  are perspective views showing a procedure of assembling the battery pack according to the present embodiment. 
         [0022]    In the battery pack of the present embodiment, four unit batteries  1  are arranged horizontally and three unit batteries  1  are arranged vertically. That is, twelve unit batteries  1  are arranged in total. Each unit battery  1  is, e.g., a lithium-ion battery and has a rectangular-solid shaped unit battery case  2  made of aluminum. The unit battery case  2  has a flattened shape, and the upper and lower surfaces (main surfaces) are larger than other surfaces. Two voltage terminals  5  project from one surface (terminal surface)  4  of the two smallest surfaces of each unit battery  1 . 
         [0023]    A spacer  6  is disposed between the two main surfaces  3  of two adjacent unit batteries  1  which are opposed to each other. The spacer  6  is made of electrically insulating material such as polypropylene or polycarbonate resin and has substantially a rectangular flat plate shape. A plurality of projections  7  for retaining the corner portions of the plurality of unit batteries  1  are formed on both sides of the spacer  6 . Further, at the positions facing the main surfaces  3  of each of the unit batteries  1 , cut portions are formed. The cut portions may be through holes  8  shaped in rectangles, each having a size slightly smaller than the main surface  3   
         [0024]    Two upper/lower plates  10  are disposed in parallel to the spacer  6  so as to be opposed to the outermost main surfaces  3  of the unit batteries  1  that are not opposed to the main surfaces  3  of the other unit batteries  1 . That is, the entire arrangement of the unit batteries  1  is sandwiched between the two upper/lower plates  10 . Like the spacers  6 , the upper/lower plates  10  are made of electrically insulating material such as polypropylene or polycarbonate resin, and each has substantially a rectangular flat plate shape. A plurality of projections  11  for retaining the corner portions of the unit batteries  1  are formed on the surfaces of each of the upper/lower plates  10  that are opposed to the main surfaces  3  of the unit batteries  1 . Further, at the positions facing the main surfaces  3 , cut portions are formed. The cut portion may be through holes  12  shaped in rectangles, each having a size slightly smaller than the main surface  3 . 
         [0025]    The unit batteries  1  are arranged between one of the upper/lower plates  10  and one of the spacers  6  or between two of the spacers  6  such that elongated surfaces  13  of the unit batteries  1  adjacent to the main surfaces  3  and the terminal surfaces  4  are opposed to each other in parallel. 
         [0026]    The terminal surfaces  4  of the unit batteries  1  are positioned in the same plane, and a rectangular insulating plate  14  ( FIG. 12 ) is disposed so as to cover the entire terminal surface  4 . The insulating plate  14  is made of, e.g., epoxy resin or a paper having a slightly higher stiffness and has a plurality of terminal holes  15  through which the voltage terminals  5  penetrate the insulating plate  14 . Preferably, the insulating plate  14  is a circuit board on which a circuit is printed, through which respective elements on the circuit board and voltage terminals  5  are electrically connected to each other so as to establish electrical connection between the voltage terminals  5 . 
         [0027]    A rectangular connector substrate  17  ( FIGS. 1 and 2 ) is disposed outside relative to the one of the side surfaces  13  of the outermost unit batteries  1 . A discharge connector  18 , a charge connector  19 , and a communication/voltage measurement connector  20  are mounted on the connector substrate  17 . The discharge connector  18  and the charge connector  19  each have positive and negative electrodes each of which are electrically connected (not shown) to the voltage terminals  5  of each unit battery  1 . The communication/voltage measurement connector  20  includes a number of terminals (not shown) which are individually connected to the voltage terminals  5  of each unit battery  1 , and the voltage of each unit battery  1  can be individually measured by means of an external measurement device (not shown). 
         [0028]    The outer peripheral portions of the upper/lower plates  10  sandwiching the entire arrangement of the unit batteries  1  is covered by, e.g., a heat-shrinkable shrink tube  22 . However, the outside of the portion of the connector substrate  17  is not covered by the shrink tube  22 . Further, a plurality of sponge pads  23  are adhered to the outside of the shrink tube  22  so as to protect the battery pack from a mechanical impact applied at the time when the battery pack is inserted into a device. 
         [0029]    An assembly procedure of the battery pack according to the embodiment will next be described with reference to  FIGS. 9 to 12 . 
         [0030]    First, as shown in  FIG. 9 , one of the upper/lower plate  10  is set such that the projections  11  face upward. On the upper/lower plate  10 , the unit batteries  1  of the first row from the bottom are arranged such that the main surfaces  3  thereof face upward, the side surfaces  13  of the adjacent unit batteries  1  are opposed to each other, and the terminal surfaces  4  of the unit batteries  1  are positioned on a same plane. The corner portions of each unit battery  1  are retained by the projections  11 . 
         [0031]    Then, as shown in  FIG. 10 , a lower spacer  6  is disposed on the unit batteries  1  of the first row from the bottom. Further, the unit batteries  1  of the second from the bottom are arranged on the lower spacer  6  so as to make them parallel to the unit batteries  1  of the first row from the bottom and make the terminal surfaces  4  thereof be positioned in the same plane as those of the unit batteries  1  of the first row from the bottom. Similarly, an upper spacer  6  is disposed on the unit batteries  1  of the second row from the bottom, and unit batteries  1  of the third row are arranged on the upper spacer  6 . 
         [0032]    Then, as shown in  FIG. 11 , the remaining one of the upper/lower plates  10  is disposed on the unit batteries  1  of the third row such that the projections  11  face downward. 
         [0033]    Subsequently, as shown in  FIG. 12 , the insulating plate  14  is disposed so as to cover the terminal surfaces  4  and make the voltage terminals  5  penetrate the insulating plate  14  through the terminal holes  5 . 
         [0034]    Thereafter, the voltage terminals  5  are electrically connected (not shown) appropriately, and the connector substrate  17  is disposed outside relative to the side surfaces  13  of the outermost unit batteries  1 . Then, the outside of the resultant structure, including the outer peripheral portions of the upper/lower plates  10  sandwiching the entire arrangement of the unit batteries  1  but except for the outside of the connector substrate  17 , is covered by the shrink tube  22 . Further, the plurality of sponge pads  23  are adhered to the outside of the shrink tube  22 , whereby the state shown in  FIGS. 1 and 2  is obtained. 
         [0035]    According to the embodiment described above, when the inner pressures of the unit batteries  1  are increased to cause the main surfaces  3  thereof are inflated outward after a long term use of the battery pack, existence of the through holes  8  and  12  of the spacer  6  and upper/lower plates  10  can prevent the inflated portions of the main surfaces  3  from interfering with each other or with spacer  6  and the upper/lower plates  10 . As a result, it is possible to prevent the entire battery pack from being mechanically destroyed, thereby maintaining safety and efficiency of the battery pack. 
         [0036]    In the above embodiment, the cut portions such as the through holes are formed in the spacer  6  and the upper/lower plates  10  so as to prevent the interference of the inflated portions of the main surfaces  3 . Alternatively, however, depressions or the like may be formed in place of the through holes as a modification of the cut portions. Also in this case, the same effect as above can be obtained. 
         [0037]    Although the terms “upper” and “lower” are used for convenience of the explanation in the above description, either side may face up from the structural view pint of the battery pack.