Abstract:
A battery is provided with a base portion provided on the base end side of a columnar rivet portion. A terminal rivet is formed, on that surface of the base portion on which the rivet portion is located, with a sloped seat surface having a height which increases as one moves closer to the rivet section and provided at the entire circumference around the rivet section. The battery is also provided with an annular elastic member and a hard member having higher hardness than the elastic member and provided with a first hole having a diameter greater than the outer diameter of the elastic member and smaller than the outer diameter of the sloped seat surface. The terminal rivet is mounted such that the base portion and a current collecting part are located inside a battery case and such that the rivet portion penetrates through a hole in the battery case to project outward. The hard member is mounted such that the elastic member is located in the first hole and is sandwiched between the base portion and the battery case. When the rivet section is riveted, the elastic member is compressed in the thickness direction between the base portion and the battery case, and as a result, reliable sealing ability is maintained for a long period.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a national phase application based on the PCT International Patent Application No. PCT/JP2009/059154 filed on May 19, 2009, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a battery including an electrode group housed in a battery case in a hermetically sealed manner while positive and negative external terminals are protruding out of the battery case. More particularly, the present invention relates to a battery in which a terminal rivet electrically connected to an external terminal is fixed to the battery case by riveting, a vehicle mounted with the battery, and a device mounted with the battery. 
     BACKGROUND ART 
     Heretofore, there has been used a sealed battery having an electrode group housed in a case in a hermetically sealed manner. The electrode group includes positive and negative electrode plates, electrolyte, etc. Positive and negative external terminals connected to the positive and negative electrode plates respectively are arranged to protrude outside through the through holes and others of the case. Each terminal is fixed to the through hole of the case by for example riveting a rivet-like member. Usually, a seal member is placed between a base portion of the rivet member and the case to seal the inside of the case. 
     For instance, Patent Literature 1 proposes an electrode structure in which a gasket is sandwiched between a base portion of a rivet member and a case (a cover). Patent Literature 2 discloses a structure that a protrusion is formed in a seat surface so that the protrusion bites into a seal member, thereby improving sealing ability. Further, Patent Literature 3 discloses an electrode structure that an annular protrusion is formed in a seal member. In this literature, the protrusion is compressed to make sure sealing. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2008-192552 A 
         Patent Literature 2: JP 2003-173767 A 
         Patent Literature 3: JP 2006-216411 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the above structure disclosed in Patent Literature 1, the base portion of the rivet member, the gasket, and the cover are in contact with each other through respective flat surfaces. This structure can maintain normal sealing ability for a long period under normal conditions. However, in case depressions or warps occur in the base portion of the rivet member during manufacture thereof, the sealing ability may deteriorate over time. 
     In the structures disclosed in Patent Literatures 2 and 3, stress is liable to concentrate on a specific portion of the seal member. Thus, cracks and breakage may occur in the seal member due to age deterioration. Accordingly, the sealing ability can be reliably provided in the short term but cannot be stably achieved in the long term. 
     The present invention has been made to solve the above problems and has a purpose to provide a battery including a structure of an electrode terminal capable of maintaining reliable sealing ability for a long term, a vehicle mounted with the battery, and a device mounted with the battery. 
     Solution to Problem 
     To achieve the above purpose, one aspect of the invention provides a battery comprising a battery case, an electrode group housed in the battery case in a hermetically sealed manner, and an external terminal electrically connected to an electrode body of the electrode group and exposed to outside of the battery case, wherein the battery comprises: a terminal rivet including a columnar rivet portion, a base portion provided at a base end of the rivet portion, and a current collecting part connected to the electrode body of the electrode group, a surface of the base portion provided with the rivet portion having a sloped seat surface with a height increasing toward the rivet portion and the raised seat surface being formed over an entire circumference of the rivet portion; an annular elastic member; and a hard member having higher hardness than the elastic member, the hard member being formed with a first hole having a diameter larger than an outer diameter of the elastic member and smaller than an outer diameter of the sloped seat surface, the battery case is formed with a second hole through which the rivet portion is inserted, the terminal rivet is placed such that the base portion and the current collecting part are located inside the battery case and the rivet portion passes through the second hole and protrudes out of the battery case, the hard member is placed so that the elastic member is located in the first hole and the hard member is sandwiched between the base portion and the battery case, the rivet portion is riveted so that the external terminal is fixed to the battery case and electrically connected to the terminal rivet, and the elastic member is compressed in a thickness direction between the base portion and the battery case. 
     According to the battery in the above aspect, the base portion of the terminal rivet is formed with the raised (sloped) seat surface having a height increasing toward the inner circumferential side. The elastic member is sandwiched between the base portion and the battery case and in the inner circumferential side than the hard member. The elastic member is located in a narrower place than the hard member in a thickness direction and thus is entirely compressed. Further, the raised seat surface of the base portion, contributes to smoothly increasing a compression amount of the elastic member toward the inner circumferential side. Accordingly, even when the seat surface of the base portion has been deformed or inclined slightly, good sealing ability can be maintained. In addition, no stress concentrates on any portion of the elastic member, so that the sealing ability can be reliably maintained for a long term. 
     In the above aspect of the invention, preferably, a difference in height between a portion of the sloped seat surface that contacts with a peripheral edge of the first hole and a portion of the sloped seat surface on a most inner circumference side is in a range of 0.001 mm to 0.2 mm. 
     When a compression amount of the elastic member is in the above range, the elastic member can maintain sufficient sealing ability and is less likely to be so deformed as to lose its elasticity. 
     Another aspect of the invention provides a vehicle comprising an electric motor to be driven to rotate wheels upon receiving supply of electric power and a power source for supplying the electric power to the motor, the power source including a battery mentioned above. 
     Further, another aspect of the invention provides a device comprising an operating part to be operated upon receiving supply of electric power and a power source for supplying the electric power to the operating part, the power source including a battery mentioned above. 
     Advantageous Effects of Invention 
     According to the battery, the vehicle and the device each mounted with the battery in the aforementioned aspects, an electrode terminal can be configured to maintain reliable sealing ability for a long term. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partial cross-sectional view of a secondary battery in an embodiment; 
         FIG. 2  is an exploded perspective view showing a riveting section in the embodiment; 
         FIG. 3  is an end view of the riveting section; 
         FIG. 4  is an explanatory view showing an example of a vehicle mounted with a secondary battery; and 
         FIG. 5  is an explanatory view showing an example of a hammer drill mounted with a secondary battery. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A detailed description of a preferred embodiment of the present invention will now be given referring to the accompanying drawings. In the present embodiment, the invention is applied to a flat-type lithium ion secondary battery. 
     A secondary battery  10  in the present embodiment is arranged such that a power generating element  16  is housed in a battery case  11  in a hermetically sealed manner as shown in  FIG. 1 . The battery case  11  includes a box-like main body  13  having one open end and a closing plate  12  for closing the open end. On the upper surface of the closing plate  12  in the figure, a positive terminal  14  and a negative terminal  15 , each serving as an external electrode terminal, are attached to protrude therefrom. Those positive terminal  14  and negative terminal  15  are respectively connected to positive and negative electrode plates and others included in the power generating element  16 . 
     An attaching section of the positive terminal  14  to the closing plate  12  in the present embodiment is explained referring to  FIG. 2 .  FIG. 2  is an exploded view showing a state where the positive terminal  14  is not attached yet. An attaching section of the negative terminal  15  is almost symmetric to that of the positive terminal  14 . The positive terminal  14  is attached to the closing plate  12  by use of an external terminal  21  which is a stepped metal member as shown in  FIG. 2 . This external terminal  21  is fixed to the closing plate  12  together with an insulation gasket  22 , an insulation spacer  23 , and a seal gasket  24  by a terminal rivet  31 . 
     The positive terminal  14  includes, as shown in  FIG. 2 , a bolt portion  14   a  protruding outside and a base portion  14   b  having a larger diameter than the bolt portion  14   a . The external terminal  21  includes an upper step portion  21   a  and a lower step portion  21   b  integrally formed in a stepped shape. The upper step portion  21   a  is formed with a through hole  21   c  through which the bolt portion  14   a  of the positive terminal  14  is inserted. The lower step portion  21   b  is formed with a through hole  21   d  through which the terminal rivet  31  is inserted. In this embodiment, the base portion  14   b  of the positive terminal  14  has an almost rectangular parallelepiped shape. The shape of the base portion  14   b  may be any shape not allowed to pass through the through hole  21   c.    
     The insulation gasket  22 , the closing plate  12 , the insulation spacer  23 , and the seal gasket  24  are provided with through holes respectively for insertion of the terminal rivet  31  as shown in  FIG. 2 . The insulation gasket  22 , the closing plate  12 , and the insulation spacer  23  are components each of which further continuously extends rightward from the illustrated range up to the position of the negative terminal  15 . The seal gasket  24  is an annular member as illustrated. 
     As shown in  FIG. 2 , the insulation gasket  22  is formed with a through hole  22   a  and also a depression in the upper surface to receive the lower step portion  21   b  of the external terminal  21 . The closing plate  12  is formed with a through hole  12   a . An inner wall  22   b  (see  FIG. 3 ) of the through hole  22   a  of the insulation gasket  22  extends downward in the figure enough to pass through the through hole  12   a  of the closing plate  12 . The insulation spacer  23  is also formed with a through hole  23   a  having a relatively large diameter. The inner diameter of the through hole  23   a  is larger than the outer diameter of the seal gasket  24 . The insulation spacer  23  is formed with an outer peripheral wall  23   b  extending downward in the figure. 
     The insulation gasket  22 , the insulation spacer  23 , and the seal gasket  24  are all insulating bodies. The insulation gasket  22  and the insulation spacer  23  are made of relatively hard synthetic resin. On the other hand, the seal gasket  24  is made of a softer and more deformable material than the gasket  22  and the spacer  23 . For instance, an elastic body such as synthetic rubber is suitable. The seal gasket  24  is an annular component having an almost uniform thickness before attachment. The seal gasket  24  is formed with a through hole  24   a . The thickness of this seal gasket  24  before attachment is almost equal to the thickness of a peripheral edge portion around the through hole  23   a  of the insulation spacer  23 . 
     The terminal rivet  31  before riveting has a rivet portion  32 , a base portion  33 , and a current collecting part  34  as shown in  FIG. 2 . This rivet portion  32  has an almost columnar shape formed with a recess  32   a  at the center of an upper end in the figure. The rivet portion  32  is riveted by expanding this recess  32   a . The base portion  33  is configured such that an almost rectangular flat plate portion  33   a  is provided with a truncated cone-shaped raised portion  33   b  centered about the rivet portion  32 . The flat plate portion  33   a  is located substantially perpendicular to the rivet portion  32 . 
     The current collecting part  34  is of an almost flat plate-like shape extending downward from one side of the flat plate portion  33   a  in  FIG. 2 . The shape of the flat plate portion  33   a  is not limited thereto and may be any shape firmly connected to the current collecting part  34 . In the present embodiment, the current collecting part  34  is connected to a positive electrode plate of the power generating element  16  by for example welding within the battery case  11 . 
       FIG. 3  is a cross-sectional view of a riveting section of the above components after secured. The rivet portion  32  of the terminal rivet  31  is inserted, from below in the figure, in the through hole  24   a  of the seal gasket  24 , the through hole  23   a  of the insulation spacer  23 , the through hole  12   a  of the closing plate  12 , the through hole  22   a  of the insulation gasket  22 , and the through hole  21   d  of the lower step portion  21   b  of the external terminal  21 . The rivet portion  32  is then riveted on the upper surface of the lower step portion  21   b  in the figure. 
     In the present embodiment, as shown in  FIG. 3 , the external terminal  21 , the closing plate  12 , and the terminal rivet  31  of the stacked components are conductive members such as aluminum. The lower step portion  21   b  of the external terminal  21  is in contact with the terminal rivet  31  in conductive relation. As mentioned above, furthermore, the current collecting part  34  of the terminal rivet  31  is connected to the positive electrode plate of the power generating element  16 , so that the external terminal  21  is connected to the positive electrode plate of the power generating element  16  in the battery case  11  through the terminal rivet  31 . 
     As shown in  FIG. 2 , since the external terminal  21  is connected to the positive terminal  14 , the positive terminal  14  is connected to the positive electrode plate. Accordingly, the positive terminal  14  functions as a terminal of a positive electrode. The closing plate  12  is insulated from the terminal rivet  31  by the insulation gasket  22  and the seal gasket  24 . The closing plate  12  is also insulated from the inside of the secondary battery  10  by the insulation spacer  23 . 
     As shown in  FIG. 3 , the through hole  21   d  formed in the lower step portion  21   b  of the external terminal  21  has a funnel-like shape whose hole diameter gradually increases upward in the figure. Thus, the terminal rivet  31  can be riveted smoothly. A minimum inner diameter of the through hole  21   d  and an inner diameter of each of the through hole  22   a  of the insulation gasket  22  and the through hole  24   a  of the seal gasket  24  are determined to allow the rivet portion  32  of the terminal rivet  31  to just pass through those through holes. 
     In the present embodiment, furthermore, the outer diameter of the raised portion  33   b  is slightly larger then the inner diameter of the through hole  23   a  of the insulation spacer  23 . As shown in  FIG. 3 , therefore, a peripheral portion around the through hole  23   a  of the insulation spacer  23  contacts with a peripheral edge portion of the raised portion  33   b  over the entire circumference. This ensures a distance between the lower surface of the closing plate  12  and an upper surface of the raised portion  33   b  of the terminal rivet  31  in the figure after riveting. Further, the terminal rivet  31  is prevented from being attached in an inclined posture with respect to the closing plate  12  and others. Alternatively, the insulation spacer  23  may be arranged to contact with the flat plate portion  33   a.    
     The inner diameter of the through hole  23   a  of the insulation spacer  23  is larger than the outer diameter of the seal gasket  24 . Accordingly, the seal gasket  24  is placed inside the through hole  23   a  of the insulation spacer  23  as shown in  FIG. 3 . In other words, the seal gasket  24  is positioned on the terminal rivet  31  at a portion that is closer to the rivet portion  32  and has a raised upper surface. At the portion of the terminal rivet  31  on which the seal gasket  24  is placed, the distance between the closing plate  12  and the terminal rivet  31  is shorter than the distance defined by the insulation spacer  23 . 
     In the attached state shown in  FIG. 3 , the seal gasket  24  is entirely compressed in the thickness direction. The width of a space in a vertical direction in the figure between the lower surface of the closing plate  12  and the upper surface of the raised portion  33   b  is wider toward the outer peripheral side and narrower toward the inner peripheral side. This width of the space smoothly changes. Since the seal gasket  24  is an elastic member, the seal gasket  24  is placed easily in a compressed state to conform to the shape of the space. Thus, good sealing ability can be achieved. 
     The space in which the seal gasket  24  is placed includes no area having drastically changing shape, so that no stress concentration occurs on a specific portion of the seal gasket  24 . The terminal rivet  31  is prevented from inclining by the insulation spacer  23  as above. Even when the rivet  31  is attached with a slight inclination within an allowable range, the sealing ability is maintained well. For the above arrangement, it is preferable that the lower surface of the inner wall  22   b  of the through hole  22   a  of the insulation gasket  22  in  FIG. 3  is flush with the lower surface of the closing plate  12  in the figure. 
     In the space between the lower surface of the closing plate  12  and the upper surface of the raised portion  33   b , the width of an area in which the peripheral portion around the through hole  23   a  of the insulation spacer  23  contacts with the closing plate  12  and the raised portion  33   b  is assumed as L 1 . This width is a dimension to be realized when the rivet portion  32  is to be riveted. The width of an area in which the outer peripheral edge of the seal gasket  24  contacts with the closing plate  12  and the raised portion  33   b  is assumed as L 2 . In the present embodiment, as shown in  FIG. 3 , a relation of L 1 ≧L 2  is provided over the entire circumference. Specifically, the seal gasket  24  is surely compressed in the thickness direction over its entire circumference. 
     Furthermore, as shown in  FIG. 3 , the seal gasket  24  is compressed gradually more strongly toward the inner peripheral side. The width in an area of the space having a minimum width, that is, in an area in which the seal gasket  24  contacts with the rivet portion  32 , is assumed as L 3 . At this area, the seal gasket  24  is compressed most strongly. The original width of the seal gasket  24  is equal to that of the peripheral portion around the through hole  23   a  of the insulation spacer  23 , i.e., almost equal to L 1 . The compression amount of the seal gasket  24  is preferably determined in the following range:
 
0.001 mm≦L1 −L 2 ≦L 1 −L 3≦0.2 mm
 
     Since the seal gasket  24  is an elastic member, a portion thereof compressed to some extent can ensure sealing ability. On the other hand, if it is held as compressed too strongly for a long period, the elasticity is lost, decreasing the sealing ability. In the present embodiment, the compression amount is determined as above, so that the sealing ability can be maintained for a long period of time. 
     According to the secondary battery  10  in the present embodiment explained in detail above, the raised portion  33   b  having a truncated cone shape centered about the rivet portion  32  is provided on the flat plate portion  33   a  of the terminal rivet  31 . Further, the relatively hard insulation spacer  23  contacts with the raised portion  33   b  on the outer circumferential side thereof and the seal gasket  24  which is an elastic member is held on the raised portion  33   b  on the inner circumferential side thereof. Accordingly, the seal gasket  24  is smoothly compressed along the shape of the raised portion  33   b . Thus, no stress concentration occurs on a specific portion of the seal gasket  24  which is an elastic member. The reliable sealing ability can therefore be maintained for a long term. 
     The secondary battery  10  in the aforementioned embodiment can be combined in plurality as an assembled battery, which can be mounted in a vehicle. An example of such vehicle is shown in  FIG. 4 . This vehicle  200  is a hybrid vehicle that drives wheels by a combination of an engine  240 , a front electric motor  220 , and a rear electric motor  230 . This vehicle  200  includes a vehicle body  290 , the engine  240 , the front electric motor  220  attached to the engine  240 , the rear electric motor  230 , a cable  250 , an inverter  260 , and an assembled battery  100  containing a plurality of the secondary batteries  10 . Electric power is supplied from the assembled battery  100  to the front electric motor  220  and the rear electric motor  230  through the inverter  260 . 
     The vehicle may be any vehicle using electric energy of the battery in the whole or part of its power source. For instance, the vehicle may be an electric vehicle, a plug-in hybrid vehicle, a hybrid railroad vehicle, a forklift, an electric-driven wheel chair, an electric bicycle, an electric scooter, etc. 
     The secondary battery  10  in the aforementioned embodiment can be mounted on various electric devices. One example of such electric devices, a hammer drill, is shown in  FIG. 5 . This hammer drill  300  is mounted with a battery pack  310  including the aforementioned secondary battery  10 . The hammer drill  300  is a battery-mounting device having the battery pack  310 , a main body  320 , and an operating part  323 . Electric power is supplied from the battery pack  310  to the operating part  323 . It is to be noted that the battery pack  310  is removably accommodated in a bottom part  321  of the main body  320  of the hammer drill  300 . 
     The battery-mounting device may be any device mounted with a battery and arranged to utilize this battery as at least one of energy sources. For instance, the device may be any one of various battery-driven home electric appliances, office equipment, and industrial equipment such as a personal computer, a cell phone, a battery-driven electric tool, an uninterruptible power supply system. 
     The embodiment is a mere example and does not give any limitations to the present invention. The present invention therefore may be embodied in other specific forms without departing from the essential characteristics thereof. 
     For instance, all the shapes of the rivet portion  32 , the lower surface of the base portion  33 , and the current collecting part  34  of the terminal rivet  31  are mere examples and are not limited to the above mentioned ones. The lower surface of the base portion  33  does not always need to be flat and the current collecting part  34  does not always need to have a flat plate shape. In this embodiment, the present invention is applied to the positive terminal  14  but of course may be applied to a negative terminal. 
     REFERENCE SIGNS LIST 
     
         
           10  Secondary battery 
           11  Battery case 
           12  Closing plate 
           12   a  Through hole 
           14  Positive terminal 
           16  Power generating element 
           23  Insulation spacer 
           23   a  Through hole 
           24  Seal gasket 
           31  Terminal rivet 
           32  Rivet portion 
           33  Base portion 
           33   b  Raised portion 
           34  Current collecting part 
           200  Vehicle 
           300  Hammer drill