Abstract:
A battery includes a cover for sealing an opening of a battery case which contains an electrode assembly therein and current collectors for electrically connecting external terminals whose at least parts are disposed outside of the cover to the electrode assembly, respectively. Gaskets are interposed between a lower surface of the cover and the current collectors, respectively. In the gasket, a caulked portion is contained in an engagement recess formed at the lower surface of the cover. In contrast, the entire gasket is contained in another engagement recess formed at the lower surface.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a battery including a nonaqueous electrolytic secondary battery. 
         [0003]    2. Description of the Related Art 
         [0004]    A battery such as a nonaqueous electrolytic secondary battery includes a positive current collector and a negative current collector for electrically connecting a positive electrode and a negative electrode in an electrode assembly contained inside of a battery case to a positive external terminal and a negative external terminal, respectively. A base of the current collector is fixed to a cover for sealing an upper opening of the battery case by means such as caulking using, for example, a rivet. A lower gasket for securing sealability or the like is interposed between the base of the current collector and a lower surface of the cover (see Japanese Unexamined Patent Application Publication No. 2003-346882 (FIG. 1)). 
         [0005]    The higher the occupancy of an electrode assembly with respect to the volume of a battery case, the higher the energy density. Consequently, from the viewpoint of energy efficiency, it is preferable that the upper end of the electrode assembly should be disposed as proximately to the lower surface of a cover as possible. However, when the lower gasket formed into a substantially merely flat plate disclosed in Japanese Unexamined Patent Application Publication No. 2003-346882 is disposed at the lower surface of the cover, the upper end of the electrode assembly cannot be disposed sufficiently proximately to the lower surface of the cover, and therefore, a high energy density cannot be achieved. Moreover, the flat cover and the flat lower gasket are brought into mere contact with each other on the plane, and therefore, the gasket is liable to be rotated. The rotation of the gasket exerts a load on a portion where an external terminal and a current collector are electrically connected to each other (e.g., a portion caulked and joined by a rivet). 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention is to enhance the occupancy of an electrode assembly with respect to the volume of a battery case so as to improve energy density. 
         [0007]    The present invention provides a battery including: a package containing an electrode assembly therein; a current collector which electrically connects an external terminal whose at least part is disposed outside of the package to the electrode assembly; and a gasket interposed between the inner surface of the package and the current collector, the gasket including a contained portion which is contained in a recess formed at the inner surface of the package. 
         [0008]    The contained portion of the gasket interposed between the current collector and the package is contained in the recess formed at the inner surface of the package. Consequently, the projection of the gasket from the inner surface of the package can be suppressed to the minimum. The suppression of the projection of the gasket enables the end of the electrode assembly to be disposed sufficiently in the proximity of the inner surface of the package. Thus, energy density can be enhanced by increasing the occupancy of the electrode assembly with respect to the volume of the battery case. 
         [0009]    Moreover, the wall surface defining the recess of the package is formed into not a flat shape but a recessed shape. The recessed wall surface restricts or restrains the position of the contained portion of the gasket which is contained in the recess. In other words, the recess of the package and the contained portion of the gasket are not brought into contact with each other on the plane. Consequently, the gasket can be prevented from being rotated with respect to the package. Therefore, a load can be prevented from exerting on a part of the gasket (e.g., a caulked and joined portion via a rivet) which may be caused by such rotation of the gasket. 
         [0010]    The current collector preferably includes a base which is electrically connected to the external terminal and a connector which projects from the base and is electrically connected to the electrode assembly; and the contained portion of the gasket should preferably include a caulked portion which is caulked and joined to the package together with the base, the thickness of the caulked portion being greater than those of other portions of the gasket. 
         [0011]    With the configuration, the weight of the gasket and a material required for fabricating the gasket can be reduced while enhancing air-tightness of the gasket. 
         [0012]    A clearance is preferably defined between the surroundings of the contained portion of the gasket and the wall surface of the recess of the package. 
         [0013]    With the configuration, a clearance for deformation (relief) in a planar direction with respect to compression in a thickness direction of a caulked portion can be secured at the time of caulking and joining, so that a damage such as a crack of the gasket can be securely prevented at the time of caulking and joining. 
         [0014]    The gasket preferably includes a rib which is disposed at least at a portion corresponding to a position at the outer peripheral edge of the body where the connector projects from the base of the current collector and has a height more than a thickness of the base of the current collector. 
         [0015]    With the configuration, the rib satisfactorily ensures an insulation distance between the current collector and the package, thus securely insulating the current collector from the package. 
         [0016]    In this case, as the fixed portion of the base is inside of the recess of the package, the projection of the current collector from the surface of the inner surface of the package can be further suppressed to the minimum. The suppression of the projection of the current collector enables the end of the electrode assembly to be disposed further sufficiently in the proximity of the inner surface of the package. Thus, energy density can be further enhanced by increasing the occupancy of the electrode assembly with respect to the volume of the battery case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a vertical cross-sectional view of a battery in an embodiment according to the present invention; 
           [0018]      FIG. 2  is a perspective view of a cover; 
           [0019]      FIG. 3  is an enlarged view of a section III of  FIG. 1 ; 
           [0020]      FIG. 4  is an enlarged view of a section IV of  FIG. 1 ; 
           [0021]      FIG. 5  is a perspective view of the surroundings of a lower gasket on the side of a lower surface of the cover; 
           [0022]      FIG. 6  is a partly cross-sectional perspective view of the surroundings of the lower gasket on the side of the lower surface of the cover; 
           [0023]      FIG. 7  is a cross-sectional view taken along a line VII-VII of  FIG. 2 ; 
           [0024]      FIG. 8  is a cross-sectional view taken along a line VIII-VIII of  FIG. 2 ; 
           [0025]      FIG. 9  is an exploded perspective view of the lower gasket and a negative current collector, as viewed from the bottom; and 
           [0026]      FIG. 10  is an exploded perspective view of the lower gasket and the negative current collector, as viewed from the top. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    A detailed description will be given below of an embodiment according to the present invention with reference to the attached drawings. 
         [0028]      FIG. 1  shows a nonaqueous electrolytic secondary battery  1  (hereinafter simply referred to as a battery) in an embodiment according to the present invention. An electrode assembly  3  of the battery  1  is housed in a battery case  2  which is made of aluminum or an aluminum alloy and is formed into a rectangular parallelepiped shape. An upper opening of the battery case  2  is sealed by a cover  4 . The battery case  2  and the cover  4  constitute a package. The upper surfaces of a negative external terminal  14  and a positive external terminal  15  are exposed to the outside of the cover  4 . 
         [0029]    The electrode assembly  3  includes a negative electrode formed of a copper foil, a positive electrode formed of an aluminum foil, and a separator  7  formed of a porous resin film and interposed in a wound manner between the negative electrode and the positive electrode. In the electrode assembly  3 , the negative electrode is electrically connected to the negative external terminal  14  via a negative current collector  12  whereas the positive electrode is electrically connected to the positive external terminal  15  via a positive current collector  13 . 
         [0030]    As shown in  FIG. 2 , the cover  4  is made of an elongated metallic plate formed into a rectangular shape, as viewed on plane. The cover  4  includes a safe valve  8  near the center thereof in a longitudinal direction and a liquid injection hole  9  formed at one end thereof. 
         [0031]    An engagement receiving portion  11  formed into a substantially rectangular shape, as viewed on plane, is formed at both ends of the cover  4  so as to expand upward from an upper surface  4   b . The engagement receiving portion  11  has an engagement recess  11   a  formed by depressing a lower surface  4   a  of the cover  4 . Moreover, a through hole  11   b  is formed at the center of a ceiling constituting the engagement recess  11   a.    
         [0032]    As shown in  FIGS. 3 and 5  to  8 , the negative external terminal  14  and the negative current collector  12  are fitted to the engagement receiving portion  11  on the left via an upper gasket  16  and a negative lower gasket  17  which are made of an insulating resin, respectively. 
         [0033]    Referring to  FIGS. 2 to 4 ,  6 , and  7 , explanation will be made on the upper gasket  16 . The upper gasket  16  is a resin part having a terminal holding recess  16   b  on the upper side and a mounting recess  16   c  on the lower side which are partitioned by a partition wall  16   a . A cylindrical portion  16   d  extending downward and having openings at both ends thereof is formed at the center of the partition wall  16   a . The upper gasket  16  is put on the engagement receiving portion  11  from above, and then, attached to the cover  4  by containing the engagement receiving portion  11  in the mounting recess  16   c . The cylindrical portion  16   d  is inserted into the through hole lib to intrude into the engagement recess  11   a . Moreover, engagement projections  19  projecting from the upper surface  4   b  of the cover  4  are inserted into engagement holes  16   f  formed at two tongue pieces  16   e  provided in the upper gasket  16 . 
         [0034]    Referring to  FIGS. 3 and 5  to  10 , explanation will be made on the negative lower gasket  17 . The negative lower gasket  17  includes an expanded portion  17   a  which is to be contained inside of the engagement recess  11   a  of the cover  4 , and a flat portion  17   b  which is disposed in a region adjacent to the engagement recess  11   a  at the lower surface  4   a  of the cover  4  and is formed into a substantially rectangular shape. 
         [0035]    As most clearly shown in  FIGS. 9 and 10 , the expanded portion  17   a  of the negative lower gasket  17  includes a caulked portion  17   c  which is disposed with a step in a height direction with respect to the flat portion  17   b  and extends in parallel to the flat portion  17   b.    
         [0036]    The caulked portion  17   c  in the negative lower gasket  17  is disposed on one short side of the flat portion  17   b , and further, is connected via three vertical walls  17   d ,  17   e , and  17   f  to the flat portion  17   b . A through hole  17   g  penetrating in a thickness direction is formed in the caulked portion  17   c . As shown in  FIGS. 3 and 6 , the cylindrical portion  16   d  of the upper gasket  16  is inserted into the through hole  17   g  around the lower end thereof. 
         [0037]    As most clearly shown in  FIG. 9 , a rib  17   h  projecting downward is disposed at the outer peripheral edge of the flat portion  17   b  of the negative lower gasket  17  except a part of one short side (a short side forward in  FIG. 9 ). 
         [0038]    Referring to  FIGS. 3 and 5  to  7 , a description will be given of the negative external terminal  14 . The negative external terminal  14  includes an aluminum plate-like member  21  having a rectangular shape, as viewed on plane, and a copper rivet  22 . A flange  22   a  is press-fitted into a through hole  21   a  formed at the center of the plate-like member  21  so that the rivet  22  is fixed to the plate-like member  21  in the state in which a shaft  22   b  projects. The plate-like member  21  is contained in the terminal holding recess  16   b  of the upper gasket  16 . 
         [0039]    Referring to  FIGS. 3 and 5  to  10 , explanation will be made on the negative current collector  12 . The copper negative current collector  12  includes a base  12   a  and a pair of legs (connectors)  12   b  and  12   b . The base  12   a  includes a fixed portion  12   c , which is contained inside of the engagement recess  11   a  formed at the lower surface  4   a  of the cover  4  and is fitted to the lower side of the caulked portion  17   c  in the expanded portion  17   a  of the negative lower gasket  17 , and a mount  12   d  to be fitted onto the lower side of the flat portion  17   b  of the negative lower gasket  17  at a position adjacent to the engagement recess  11   a . A through hole  12   e  penetrating in a thickness direction is formed in the fixed portion  12   c . The fixed portion  12   c  and the mount  12   d , which are stepwise different in the height direction, are connected via a vertical wall  12   f . The legs  12   p  and  12   b  extend downward from the mount  12   d . The legs  12   b  and  12   b  are electrically connected to and mechanically coupled to the negative electrode in the electrode assembly  3  via a clip  10  schematically shown only in  FIG. 1 . 
         [0040]    The shaft  22   b  of the rivet  22  in the negative external terminal  14  is inserted into the cylindrical portion  16   d  of the upper gasket  16 , the through hole  17   g  formed in the caulked portion  17   c  of the negative lower gasket  17 , and the through hole  12   e  formed in the fixed portion  12   c  of the negative current collector  12 , and then, the tip is widened under pressure, thereby forming a large-diameter portion  22   c . Consequently, the negative external terminal  14 , the upper gasket  16 , the caulked portion  17   c  of the negative lower gasket  17 , and the base  12   a  of the negative current collector  12  are securely caulked and joined to the cover  4 . Moreover, owing to the caulking and joining, the negative current collector  12  is electrically connected to the negative external terminal  14 . 
         [0041]    Referring to  FIGS. 1 to 3 , the positive external terminal  15  and the positive current collector  13  are fixed to the engagement receiving portion  11  on the right side via the upper gasket  16  and a positive lower gasket  18  which are made of an insulating resin, respectively. 
         [0042]    In the same manner as the side of the negative electrode, the upper gasket  16  is attached to the engagement receiving portion  11 . Moreover, the positive lower gasket  18  is formed into a plate having a through hole  18   a , and is disposed inside of the engagement recess  11   a.    
         [0043]    The aluminum positive external terminal  15  includes a plate-like member  15   a  formed into a rectangular shape, as viewed on plane, and a cylindrical shaft  15   b  projecting from the center of the lower surface of the member  15   a . The plate-like member  15   a  is contained in a terminal holding recess  16   b  of the upper gasket  16 . 
         [0044]    The aluminum positive current collector  13  includes a base  13   a  and a pair of legs (connectors)  13   b  and  13   b . The base  13   a  includes a fixed portion  13   c , which is contained inside of the engagement recess  11   a  and is fitted to the lower side of the positive lower gasket  18 , and a mount  13   d  to be fitted to the lower surface  4   a  of the cover  4  at a position adjacent to the engagement recess  11   a . A through hole  13   e  penetrating in a thickness direction is formed in the fixed portion  13   c . The fixed portion  13   c  and the mount  13   d  which are stepwise disposed are connected via a vertical wall  13   f . The legs  12   b  and  12   b  are electrically connected to and mechanically coupled to the electrode assembly  3  via a clip  10  schematically shown only in  FIG. 1 . 
         [0045]    The shaft  15   b  of the positive external terminal  15  is inserted into the cylindrical portion  16   d  of the upper gasket  16 , the through hole  18   a  formed in the positive lower gasket  18 , and the through hole  13   e  formed in the fixed portion  13   c  in the positive current collector  13 , and then, the tip is widened under pressure, thereby forming a large-diameter portion  15   c . Consequently, the positive external terminal  15 , the upper gasket  16 , the positive lower gasket  18 , and the base  13   a  of the positive current collector  13  are securely caulked and joined to the cover  4 . Moreover, owing to the caulking and joining, the positive current collector  13  is electrically connected to the positive external terminal  15 . 
         [0046]    The battery  1  in the present embodiment is particularly featured by the following points. 
         [0047]    First, referring to  FIGS. 3 and 5  to  9 , the rib  17   h  is disposed at the outer peripheral edge of the flat portion  17   b  in the negative lower gasket  17  interposed between the lower surface  4   a  of the cover  4  and the negative current collector  12 . The height H of the rib  17   h  (see  FIGS. 5 and 9 ) is more than the thickness of the base  12   a  of the negative current collector  12 . The rib  17   h  sufficiently ensures an insulation distance defined between the negative current collector  12  and the cover  4 , thus securely insulating the negative current collector  12  from the cover  4 . 
         [0048]    In particular, at the flat portion  17   b  of the negative lower gasket  17 , the rib  17   h  having the thickness more than that of the base  12   a  is disposed at a portion corresponding to a position at which the legs  12   b  an  12   b  project from the mount  12   d  at a portion at which the electrode assembly  3  is electrically connected to the negative current collector  12 , and therefore, the negative lower gasket  17  can effectively insulate the negative current collector  12   c  from the cover  4 . At the base  12   a  of the negative current collector  12 , the position, in particular, at which the legs  12   b  and  12   b  project from the mount  12   d , need be securely insulated from the cover  4 . Consequently, even if the rib  17   h  is not disposed over substantially the entire outer peripheral edge of the flat portion  17   b  of the negative lower gasket  17 , unlike the present embodiment, but only at the portion corresponding to the position at which the legs  12   b  and  12   b  project from the mount  12   d  of the negative current collector  12  on the outer periphery of the flat portion  17   b , the negative lower gasket  17  can effectively insulate the negative current collector  12   c  from the cover  4 . 
         [0049]    Next, the expanded portion  17   a  of the negative lower gasket  17  interposed between the negative current collector  12  and the cover  4  is contained in the engagement recess ha formed at the lower surface  4   a  of the cover  4 . Consequently, only the flat portion  17   b  formed into a thin plate in the negative lower gasket  17  projects from the lower surface  4   a  of the cover  4 , thereby suppressing the projection of the negative lower gasket  17  from the lower surface  4   a  of the cover  4  to the minimum. In contrast, the entire positive lower gasket  18  is contained in the engagement recess  11   a  formed at the lower surface  4   a  of the cover  4 . In this manner, the projection of each of the negative lower gasket  17  and the entire positive lower gasket  18  from the lower surface  4   a  of the cover  4  is suppressed to the minimum, and consequently, the upper end of the electrode assembly  3  can be disposed sufficiently near the lower surface  4   a  of the cover  4 . Thus, it is possible to increase the occupancy of the electrode assembly  3  with respect to the volume of the battery cell  2 , so as to enhance energy density. 
         [0050]    Moreover, the wall surface constituting the engagement recess  11   a  at the lower surface  4   a  of the cover  4  is formed into a recess. The recessed wall surface defines or restrains the position of the expanded portion  17   a  of the negative lower gasket  17  contained in the engagement recess  11   a . Specifically, the engagement recess  11   a  formed at the cover  4  and the expanded portion  17   a  of the negative lower gasket  17  are brought into contact with each other not on the plane but in mutual engagement. As a consequence, the negative lower gasket  17  can be prevented from being rotated with respect to the cover  4 . In the present embodiment, the negative external terminal  14 , the upper gasket  16 , the caulked portion  17   c  of the negative lower gasket  17 , and the base  12   a  of the negative current collector  12  are caulked and joined with respect to the cover  4  via the rivet  22 . The expanded portion  17   a  of the negative lower gasket  17  is contained in the engagement recess  11   a , so that the rivet  22  can prevent the rotation of the negative lower gasket  17  with respect to the caulked and joined portions. As described above, the rivet  22  is concerned in electrically connecting the negative current collector  12  and the negative external terminal  14 , and therefore, the rotation of the negative lower gasket  17  at the caulked and joined portions via the rivet  22  is undesirable in view of the secureness of the favorable electric connection between the negative current collector  12  and the negative external terminal  14 . The prevention of the rotation of the negative lower gasket  17  with the simple configuration in which the expanded portion  17   a  of the negative lower gasket  17  is contained in the engagement recess  11   a  of the cover  4  has a great advantage from the viewpoint of the favorable secureness of the electric connection between the negative current collector  12  and the negative external terminal  14 . 
         [0051]    In addition, as shown in  FIGS. 3 ,  6 , and  7 , the thickness T of the caulked portion  17   c  caulked and connected to the cover  4  in the negative lower gasket  17  is set to be more than those of other portions in the negative lower gasket  17 . In this manner, only the thickness T of the caulked portion  17   c  where a large force exerts by caulking is set to be large, so that the negative lower gasket  17  is reduced in weight and a material required for fabricating the negative lower gasket  17  is reduced while air tightness of the negative lower gasket  17  can be enhanced. 
         [0052]    Additionally, referring to  FIGS. 3 and 6 , a clearance  31  is defined by the wall surface (i.e., the engagement receiving portion  11 ) surrounding the engagement recess  11   a  at the lower surface  4   a  of the cover  4  near a corner defined by the caulked portion  17   c  and the vertical wall  17   d  in the negative lower gasket  17 . In particular, a clearance having a dimension indicated by reference numeral S 1  is defined between side wall surfaces surrounding the vertical wall  17   d  of the negative lower gasket  17  and the engagement recess  11   a . Moreover, a clearance having a greater dimension indicated by reference numeral S 2  is defined between the tip of the caulked portion  17   c  of the negative lower gasket  17  and the side wall surface surrounding the engagement recess  11   a  at the lower surface  4   a  of the cover  4 . In this manner, the clearances  31 , S 1 , and S 2  are defined between both ends of the caulked portion  17   c  of the negative lower gasket  17  and the wall surface (i.e., the engagement receiving portion  11 ) surrounding the engagement recess  11   a , and therefore, room can be secured such that the caulked portion  17   c  is deformed (relieved) in a planar direction when the caulked portion  17   c  is compressed in a thickness direction during caulking and joining. Consequently, it is possible to securely prevent a damage such as a crack on the negative lower gasket  17  during caulking and joining. 
         [0053]    The present invention is not limited to the embodiment, various modifications can be implemented. For example, although the present invention has been described by way of the configuration in which the expanded potion  17   a  of the negative lower gasket  17  is contained in the engagement recess  11   a  of the cover  4 , a part of a gasket (i.e., a contained portion) may be contained in a recess formed at not the cover but the inner surface of a battery case.