Abstract:
A battery module is fabricated as follows. A plurality of elements for electromotive force is accommodated in a one-piece cylindrical case and is arranged in series in an axial direction of the case. The elements for electromotive force are electrically connected through an electric connector passing through a resin partition wall which separates the elements for electromotive force from one another. The both ends of the case are sealed with sealing plates.

Description:
The present disclosure relates to subject matter contained in priority Japanese Patent Application No. 2000-272815, filed on Sep. 8, 2000, the contents of which is herein expressly incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     The present invention relates to a battery module, and more particularly to a battery module used as a battery power source for an electric vehicle. 
     2. Description of Related Art 
     FIG. 1 shows a conventional battery module disclosed in Japanese Laid-open Patent Application No. 10-106533, the battery module made by connecting a plurality of cells and coupling them integrally so as to obtain a necessary power capacity. In the conventional battery module, a plurality of cylindrical cell A shown in FIG. 2 are arranged in series in the axial direction thereof, and adjacent cells are connected together through a connector  1  shown in FIGS. 3A to  3 C, by welding. 
     As shown in FIGS. 3A to  3 C, the connector  1  is formed like a circular dish having two steps in a depth direction. An opening  17  is concentrically formed in a bottom plate  5  of the connector  1 , the opening  17  for inserting a protruding portion  14  of an electrode  10  of the cell A therethrough. As shown in FIG. 4, four projections  2  formed on the bottom plate  5  of the connector  1  are welded to the electrode  10  of the cell A. Subsequently, four projections  3  formed on a cylindrical wall  4  of the connector  1  are welded to a cell case  11  of another cell A, thereby connecting the cells electrically and mechanically together. 
     Another conventional battery module is disclosed in Japanese Laid-open Patent Application No. 10-112299. As shown in FIG.  5  and FIG. 6, the battery module includes a tube body  21 , a plurality of elements for electromotive force (i.e., unit cells).  25   a,    25   b,  and  25   c  fitted on the peripheral surface of the body  21 , and a case  22  for covering them. In other words, the battery module is made by accommodating a plurality of elements for electromotive force in a single case. 
     Furthermore, Japanese Laid-open Patent Application. No. 8-329971 discloses another battery module. As shown in FIG. 7, the battery module includes a plurality of sealed elements for electromotive force  31 , a single case  36  for accommodating the elements  31 , and a connector  35  for connecting the elements  31 . 
     However, the conventional battery modules have some disadvantages. The battery module disclosed in Japanese Laid-open Patent Application No. 10-106533 necessitates a number of connectors. Moreover, it is difficult to ensure a desired mechanical strength of the battery module, since the battery module is made by connecting a plurality of cells. Furthermore, the connectors are exposed in an external atmosphere, so that they may be progressively subjected to corrosion when condensation occurs thereon due to sudden changes in environmental temperature. 
     Regarding the battery module disclosed in Japanese Laid-open Patent Application No. 10-112299, it is very difficult to electrically connect between collector leads  26   b,    26   c  and a collector lead fixing member  27   c  for connecting between the collector leads  26   b,    26   c,  while reducing a dead space between them. 
     Furthermore, the battery module disclosed in Japanese Laid-open Patent Application No. 8-329971 has a low resistance to pressure of gas generated from the element for electromotive force, since each of the elements is sealed with a sealing sheet. What is worse, such a battery module is unsuitable for a large capacity electric discharge because a current-feeding portion is made of a thin metal plate in order to seal each of the elements. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a battery module having a high mechanical strength, a high weight energy density, a high volume energy density, and a corrosion-free connection between cells. 
     To achieve the above object, according to the present invention, there is provided a battery module which includes a cylindrical or columnar case; a plurality of elements for electromotive force accommodated in the case, the elements being placed in series in the axial direction of the case; a partition wall for spatially isolating the elements from one another; an electric connector for connecting the elements through the partition wall; and sealing plates placed on both ends of the case. In the battery module, a desired mechanical strength is obtained because the plurality of elements for electromotive force is accommodated in a single case. Moreover, since the connecting portion between the elements for electromotive force is positioned inside the case, a corrosion-free connection between the elements is achieved and the dead space is minimized, resulting in a high weight energy density and a high volume energy density. Preferably the electric connector is loaded into the partition wall by pressing, so that the boundary face therebetween is sealed to prevent liquid or gas leakage. 
     These and other objects and characteristics of the present invention will become further clear from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an external view of a conventional battery module; 
     FIG. 2 is an external view of a conventional rechargeable cell; 
     FIG. 3A is a plan view of a conventional connector; 
     FIG. 3B is a side view of the conventional connector shown in FIG. 3A; 
     FIG. 3C is a perspective view of the conventional connector shown in FIG.  3 A and FIG. 3B; 
     FIG. 4 is a cross sectional view of a connecting portion of the conventional battery module; 
     FIG. 5 is a cross sectional view of another conventional battery module; 
     FIG. 6 is a perspective view of essential components of the conventional battery module; 
     FIG. 7 is a cross sectional view of yet another conventional battery module; 
     FIG. 8 is a cross sectional view of a battery module according to a first embodiment of the present invention; 
     FIG. 9 is a cross sectional view of a terminal portion of the battery module according to the first embodiment of the invention; 
     FIG. 10 is an exploded perspective view illustrating the structure of the battery module according to the first embodiment of the invention; 
     FIG. 11 is a cross sectional view showing a plate group and collector plates of the battery module according to the first embodiment of the invention; 
     FIG. 12 is a cross sectional view of a battery module according to a second embodiment of the present invention; 
     FIG. 13 is a cross sectional view of a terminal portion of the battery module according to the second embodiment of the invention; and 
     FIG. 14 is a perspective view of a battery module according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be hereinafter described in the form of a battery module employing a nonaqueous electrolyte secondary battery as examples. 
     First Embodiment 
     FIG. 8 to FIG. 11 show a battery module according to a first embodiment of the present invention. FIG. 8 shows a cross sectional view of the battery module. FIG. 9 shows an enlarged cross sectional view of a terminal portion of the battery module. FIG. 10 shows a perspective view of the components of the battery module, and FIG. 11 shows a cross sectional view of a part of the battery module, the part including collector plates and a plate group. 
     The battery module of the present embodiment includes various components and a cylindrical case  100  for accommodating the components. The components include a plate group  110 , a negative collector plate  117  being welded to the plate group  110 , an electric connector  120  for connecting between the plate groups  110 , a partition wall  130  for spatially isolating the plate groups  110 , battery terminals  139 ,  140 , and sealing plates  150 . 
     As shown in FIG. 11, the plate group  110  is formed by overlaying a positive electrode plate and a negative electrode plate with a separator  115  interposed between them, and winding them in a spiral fashion. The positive electrode plate includes a positive collector  111  on which a positive active material  112  is coated, and the negative electrode plate includes a negative collector  113  on which a negative active material  114  is coated. The plate group  110  has protruded portions  111   a,    113   a  on both ends thereof. The protruded portion  111   a  is a bared portion of the positive collector  111 , on which the positive active material  112  is not coated. The protruded portion  113   a  is a bared portion of the negative collector  113 , on which the negative active material  114  is not coated. 
     A flat portion  111   b  is formed by plastic deformation by pressing the protruded portion  111   a  of the positive collector  111 . The positive collector plate  116  is welded to the flat portion  111   b  so that they are electrically connected to each other. A flat portion  113   b  is formed by plastic deformation by pressing the protruded portion  113   a  of the negative collector  113 . The negative collector plate  117  is welded to the flat portion  113   b  so that they are electrically connected to each other. 
     The partition wall  130  is in the shape of a disk made of resin such as polypropylene and polyethylene. In the partition wall  130 , a through hole  131  is concentrically formed for inserting the electric connector  120  therethrough. On the peripheral portion of the partition wall  130 , there is formed a retaining groove  132  for holding an O-ring  160  being press-contacted on the inner surface of the case  100 . 
     The electric connector  120  is made of a combining material of aluminum and copper, an aluminum portion being located on the positive side of the element for electromotive force, and a copper portion being located on the negative side thereof. The electric connector  120  is loaded into the partition wall  130  through the hole  131 . The electric connector  120  has a retaining groove  121  for holding the O-ring  160  being pressed on the inner surface of the through hole  131 . 
     The positive collector plate  116  and the negative collector plate  117  are electrically connected to the battery terminals  139 ,  140  or the electric connector  120  by means of welding at a welding point  122 . 
     The sealing plate  150  is in the shape of a disk made of resin such as polypropylene and polyethylene. In the sealing plate  150 , a through hole  151  is concentrically formed for inserting the battery terminal therethrough. On the peripheral portion of the sealing plate  150 , there is formed a retaining groove  152  for holding an O-ring  160  being press-contacted on the inner surface of the case  100 . Furthermore, an annular thin portion  153  which breaks at the predetermined internal pressure is formed in the sealing plate  150  to prevent the battery from explosion caused by an abnormal increase in the internal pressure of the battery. 
     Each end of the cylindrical case  100  is bent inwardly to form a terminal portion  101  for retaining the sealing plate  150  in place. 
     Each of the battery terminals  139  and  140  has a retaining groove  141  on its peripheral portion, the retaining groove  141  for holding the O-ring  160  being press-contacted on the inner periphery of the through hole  151  of the sealing plate  150 . The battery terminals  139  and  140  also have a screw portion  142  for electrically connecting the batteries. The battery terminal  139  on the positive side is made of aluminum or the like, and the battery terminal  140  on the negative side is made of copper or the like. 
     Each of the battery terminals  139  and  140  is inserted into the through hole  151  and is fixed on the sealing plate  150  by an annular press spring  155 . 
     The O-rings  160  respectively placed in the retaining grooves of the partition wall  130 , the sealing plate  150 , and the battery terminals  139  and  140  spatially isolate the elements for electromotive force. Preferably, a soft viscous sealant is applied on the surface of the O-ring  160  on which the component of the battery is touched. 
     A method of fabricating the battery module of the present invention includes the following steps. First, two plate groups  110  are manufactured, and then a positive collector plate  116  and a negative collector plate  117  are welded to opposite ends of each plate group  110 . In parallel with the step of manufacturing the plate groups  110 , an electric connector  120  provided with an O-ring  160  placed in a retaining groove  121  is loaded into a partition wall  130 . In this case, a soft viscous sealant is previously applied in the groove  121  and on a portion of the partition wall  130  where the O-ring  160  is press-contacted. The negative collector plate  117  and the positive collector plate  116  both welded to the plate groups  110  are welded to the electric connector  120  at predetermined welding points  112 , respectively. Then, each of battery terminals  139 ,  140  is welded to the positive collector plate  116  and the negative collector plate  117  at a predetermined welding point. The battery terminals  139 ,  140  are inserted into a through hole  151  of a sealing plate  150  and are fixed thereon with a washer  154  and an annular press spring  155 . In this case, a soft viscous sealant is previously applied in a retaining groove of each of the battery terminals  139 ,  140 , followed by placing an O-ring  160  in the retaining groove. Then, a soft viscous sealant is applied in retaining grooves  132 ,  152  formed on the outer peripheries of the partition wall  130  and the sealing plate  150 , respectively. Subsequently, an O-ring  160  is placed in each of the retaining grooves  132 ,  152 . Such an assembly of these components is accommodated in a case  100 , in which a soft viscous sealant is previously applied on a portion to be press contacted with the O-ring  160 . Then, a terminal portion  101  of the case  100  is inwardly bent at a predetermined position. 
     According to the invention, due to the use of a single case, the battery module has a higher mechanical strength than that of the conventional one. Moreover, connecting portion of the battery module is protected from corrosion damage since the portion is accommodated in the case. Furthermore, a mass energy density and a volume energy density of the battery module are higher than those of the conventional one since a dead space in the battery module is minimized. 
     Second Embodiment 
     A battery module of the present embodiment is configured just as the battery module of the first embodiment except for the configuration thereof shown in FIG.  12  and FIG.  13 . In the present embodiment, a positive electrode plate is prepared by coating a positive active material on a positive collector, and a negative electrode plate is prepared by coating a negative active material on a negative collector. These electrode plates are overlaid together with a separator interposed between them and are wound around an internal tube  170  made of stainless steel, aluminum, or the like in a spiral fashion to form a plate group. Then, the internal tube  170  is held between the battery terminal and the electric connector through an insulator  171 , whereby the battery module is made vibration resistant. 
     Third Embodiment 
     A battery module of the present embodiment is configured just as the battery module of the first embodiment except for the configuration thereof shown in FIG.  14 . In the present embodiment, a portion  103  of the case, which corresponds to the position of a partition wall, is pressed down to decrease a diameter thereof. Thereby, an adhesion between the case and the partition wall is increased, and the reliability of the spatial isolation between the elements for electromotive force is increased. 
     Although the battery module including two elements for electromotive force is explained in each of the above embodiments, it is to be understood that the present invention is not limited to any particular number of batteries in the battery module. The invention is not limited to the battery module employing a nonaqueous electrolyte rechargeable battery. It is also possible to employ a case in an oval shape in a battery module. Further, the electric connector may be fixed to the partition wall by insert molding. Furthermore, an insulating layer may be applied on the inner surface of the case to prevent a short circuit to be developed by contacting the element for electromotive force with the case. 
     According to the present invention, a battery module offering resistance to corrosion and showing a high mechanical strength, a high reliability, a high voltage energy density, and a high volume energy density is realized. 
     Although the present invention has been fully described in connection with the preferred embodiment thereon, it is to be noted that various changes and modifications apparent to those skilled in the art are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.