Patent Publication Number: US-2017358785-A1

Title: Power supply device and vehicle including the same

Description:
TECHNICAL FIELD 
     The present invention relates to a power supply device in which a plurality of secondary batteries capable of charging and discharging are stacked, and to a vehicle including the power supply device. 
     BACKGROUND ART 
     In a power supply device for a vehicle, multiple secondary batteries capable of charging and discharging are connected in series into a battery block, and the output voltage of the battery block is set high to increase power to be supplied to a motor for running the vehicle. This power supply device is discharged by supplying power to the motor in a running state of the vehicle, and is charged by a power generator in regenerative braking of the vehicle. The discharging current of the batteries specifies the driving torque of the motor, and the charging current of the batteries specifies the braking force for regenerative braking. Therefore, it is necessary to increase the discharging current of the batteries in order to increase the driving torque of the motor for accelerating the vehicle, and it is necessary to charge the batteries with a large current in order to increase regenerative braking of the vehicle. Accordingly, the batteries in the power supply device for the vehicle are discharged or charged with a large current. To improve safety in discharging and charging the batteries with a large current, there has been developed a battery including a mechanism that interrupts the current when the internal pressure of the battery abnormally increases, that is, a current interrupt device. 
     As a battery including such a current interrupt device, for example, there has been proposed a secondary battery including a device that interrupts the current by fusing a contained fuse part when the internal pressure of the battery exceeds a set pressure (see PTL 1). As illustrated in  FIG. 14 , this secondary battery  101  includes an electrode body  115 , a collector plate  116  connected to the electrode body  115 , an outer can  111  that contains the electrode body  115 , a sealing plate  112  that hermetically seals the outer can  111 , an inverting plate  122  having an edge connected to the sealing plate  112  and made of a conductive material, and a connection plate  123  insulated from the sealing plate  112  by an insulating member  124  and having a different polarity. The collector plate  116  has a fuse part  121  to be melted by heat of an overcurrent. The inverting plate  122  normally bulges toward an inner region of the outer can  111 , and inverts when the pressure in the battery exceeds the set pressure. In the secondary battery  101 , when the internal pressure of the outer can  111  rises, the inverting plate  122  inverts and comes into contact with the connection plate  123 , and a short circuit is made inside the secondary battery  101 . At this time, inside the battery, the fuse part  121  provided in the collector plate  116  is melted by heat, and this breaks the electrical connection between electrode terminals of the battery and the electrode body  115 . 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Published Unexamined Patent Application No. 2012-195278 
     SUMMARY OF INVENTION 
     Technical Problem 
     The current can be reliably interrupted by fusing of the fuse part contained in the secondary battery by completely fusing and cutting off the fuse part. In an actual secondary battery, however, it is difficult to completely fuse the fuse part in a limited narrow space inside the battery. It is conceivable that a spark will occur at the time of fusing and that a spark will be caused by reconduction resulting from the contact between fused portions. 
     Particularly when the fuse part is fused in the vehicular power supply device, the current is interrupted and motor driving cannot be performed, but, for example, a hybrid car can run by using the engine. However, it is conceivable that, if engine driving is performed in this state, the fused portions may come into contact with each other inside the secondary battery and a spark may be caused by reconduction. In particular, in the secondary battery mounted in the vehicle, vibration due to driving of the vehicle cannot be completely removed. It is conceivable that the fused portions may be brought into contact with each other by external vibration and a spark may be easily caused by reconduction. From these, the present inventors considered that, in the secondary battery including the current interrupt device for interrupting the current by fusing the fuse part, the occurrence of the spark at the time of fusing and reconduction could not be completely avoided and that it was necessary to take measures to prevent scattering of the spark to the outside of the secondary battery. 
     The present invention has been made in view of these problems of the related art. An object of the invention is to provide a power supply device that can effectively prevent a spark from scattering to the outside of a secondary battery even if the spark occurs at fused portions and damages an outer can when a fuse part contained in the second battery is fused and reconducted, and a vehicle including the power supply device. 
     Solution to Problem and Advantageous Effects of Invention 
     To achieve the above object, a power supply device according to the present invention includes a battery stack in which a plurality of secondary batteries are stacked, and a binding member that binds the battery stack. Each of the secondary batteries includes an electrode body having a positive electrode and a negative electrode, an outer can having an opening and shaped like a bottomed cylinder to contain the electrode body, a sealing plate that closes the opening of the outer can, a pair of electrode terminals disposed on the sealing plate, and a current interrupt device that operates when an internal pressure of the secondary battery exceeds a set pressure. The pair of electrode terminals include a first electrode terminal insulated from the sealing plate and a second electrode terminal electrically connected to the sealing plate, and are electrically connected to the electrode body through a collector member inside the secondary battery. The current interrupt device includes a short-circuit part that short-circuits the first electrode terminal and the sealing plate when the internal pressure of the secondary battery exceeds the set pressure, and a fuse part provided in the collector member. The fuse part is disposed close to an upper end corner portion serving as a boundary portion between an upper surface and a side surface of the secondary battery, and is fused by an overcurrent in a short-circuit state of the short-circuit part. The binding member includes a protective cover portion located on each side of the battery stack to cover the upper end corner portion of the secondary battery. The protective cover portion includes an upper-surface covering part that covers an upper surface of the upper end corner portion and a side-surface covering part that covers a side surface of the upper end corner portion. 
     In this description, the up-down direction of the secondary battery is specified in the drawings. The side surface of the second battery refers to a narrow surface on each side of a battery stack in which a plurality of secondary batteries are stacked with wide principal surfaces opposed to each other. 
     The present invention is effective particularly when the fuse part is located in a region at a direct distance of 2 cm or less from the upper end corner portion. Further, the present invention is more effective when the fuse part is located in a region at a direct distance of 1 cm or less from the upper end corner portion. Preferably, the collector member has a platelike portion, and the fuse part is constituted by a portion having a small cross-sectional area obtained by forming an opening in the platelike portion. The present invention is more effective when the fuse part is located in a region of the collector member between the sealing plate and the electrode body. Further, the present invention is more effective when the platelike portion of the collector member having the fuse part is located parallel to the sealing plate. 
     According to the power supply device having the above-described structure, the fuse part in the current, interrupt device is located close to the upper end corner portion of the secondary battery, and the binding member that binds the battery stack has the protective cover portion that covers the upper end corner portion of the secondary battery. Hence, even if a spark occurs at fused portions and damages the outer can during fusing and reconduction of the contained fuse part, the spark can be effectively prevented from scattering to the outside of the second battery. In particular, since the protective cover portion includes the upper-surface covering part that covers the upper surface of the upper end corner portion and the side-surface covering part that covers the side surface, the protective cover portion can reliably cover the upper end corner portion of the secondary battery and can effectively prevent scattering of the spark from the upper end corner portion. 
     In the power supply device of the present invention, the binding member can be a bind bar formed by bending a metal plate having a predetermined thickness. According to the above structure, the binding member can be easily produced at low cost by bending the metal plate. 
     In the power supply device of the present invention, an insulating member can be provided on an inner surface of the bind bar. According to the above structure, while the binding member is the metal plate, a portion thereof opposed to the battery stack can be insulated and safely used. 
     In the power supply device of the present invention, the bind bar can include an upper bind bar that covers an upper portion of a side surface of the battery stack and a lower bind bar that covers a lower portion of the side surface of the battery stack, and the upper bind bar can also function as the protective cover portion. According to the structure, since the battery stack is connected by four bind bars, four corners of the battery stack can be bound in an ideal state by the bind bars. 
     In the power supply device of the present invention, the bind bar can have a body portion opposed to a side surface of the battery stack, and the body portion can cover the entire side surface of the battery stack. According to the above structure, the mechanical strength can be increased by widening the bind bar opposed to the side surface of the battery stack. Moreover, since the side surface of the battery stack is entirely covered, the spark can be reliably prevented from scattering toward the side surface of the battery stack. 
     In the power supply device of the present invention, the bind bar can have a body portion opposed to a side surface of the battery stack, and the body portion can have an open window. According to the above structure, the weight of the bind bar opposed to the side surface of the battery stack can be reduced, and heat can be effectively dissipated by exposing the side surface of the secondary battery from the open window. 
     In the power supply device of the present invention, the bind bar can have a horizontal portion that covers at least a part of a bottom surface of the battery stack. According to the above structure, since at least a part of the bottom surface of the battery stack is covered with the horizontal portion, a plurality of stacked secondary batteries can be bound while positioning the bottom surfaces of the secondary batteries, and the vibration-resistant strength can be further increased by further suppressing the relative movement in the up-down direction. 
     A vehicle according to the present invention includes any of the above-described power supply devices. 
     According to the vehicle having the above-described structure, while the power supply device having a plurality of secondary batteries is mounted in the vehicle, the binding member that, binds the battery stack is provided with the protective cover portion that covers the upper end corner portion of each of the secondary batteries. Hence, even if a spark occurs at fused portions and damages the outer can at the time of fusing and reconduction of the contained fuse part, the spark can be effectively prevented from scattering to the outside of the second battery. In particular, since the protective cover portion of the binding member includes the upper-surface covering part that covers the upper surface of the upper-end corner portion and the side-surface covering part that covers the side surface, the protective cover portion can reliably cover the upper end corner portion of the secondary battery and can effectively prevent the spark from scattering from the upper end corner portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded perspective view of a power supply device according to a first embodiment of the present, invention. 
         FIG. 2  is a perspective view of an assembled battery in the power supply device illustrated in  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the assembled battery illustrated in  FIG. 2 . 
         FIG. 4  is a vertical cross-sectional view of the assembled battery illustrated in  FIG. 2 , and illustrates an internal structure of a secondary battery. 
         FIG. 5  is a cross-sectional view illustrating an operating state of a current interrupt device in the secondary battery illustrated in  FIG. 4 . 
         FIG. 6  is an enlarged perspective view of a fuse part provided in a collector member. 
         FIG. 7  is an enlarged perspective view of another example of the fuse part. 
         FIG. 8  is a schematic sectional view of an assembled battery according to a second embodiment of the present invention. 
         FIG. 9  is a vertical cross-sectional view of the assembled battery of  FIG. 8 . 
         FIG. 10  is a vertical cross-sectional view of an assembled battery according to a third embodiment of the present invention. 
         FIG. 11  is a vertical cross-sectional view of an assembled battery according to a fourth embodiment of the present invention. 
         FIG. 12  is a perspective view of another example of binding members. 
         FIG. 13  is a perspective view of a further example of the binding members. 
         FIG. 14  is a schematic sectional view illustrating an example of a current interrupt device in a conventional secondary battery. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIGS. 1 to 5  illustrate a power supply device  100  according to a first embodiment of the present invention. The power supply device  100  illustrated in these figures is an example of a vehicle-mounted power supply device. Specifically, the power supply device  100  is mainly mounted in an electrically driven vehicle such as a hybrid car or an electric car, and is used as a power supply that supplies power to a running motor of the vehicle to run the vehicle. The power supply device of the present invention can be used in electrically driven vehicles other than the hybrid car and the electric car, and can also be used for applications requiring large output other than the electrically driven vehicles. 
     (Power Supply Device  100 ) 
     As illustrated in an exploded perspective view of  FIG. 1 , the power supply device  100  has an outer shape like a box having a rectangular upper surface. A box-shaped outer case  70  of the power supply device  100  is divided to store a plurality of assembled batteries  10  therein. The outer case  70  includes a lower case  71 , an upper case  72 , and end face plates  73  connected to both ends of each of the lower case  71  and the upper case  72 . The end face plates  73  are connected to both ends of each of the lower case  71  and the upper case  72  to close both ends of the outer case  70 . The upper case  72  has flanges  74  projecting outward, and is fixed to the lower case  71  by bolts and nuts through screw holes opening in the flanges  74 . The screw holes of the flanges  74  can also be used to fix the power supply device  100 . For example, the power supply device  100  is fixed to the vehicle by screwing using the screw holes. 
     The assembled batteries  10  are fixed at determined positions inside the outer case  70 . In the example of  FIG. 1 , two assembled batteries  10  arranged in the longitudinal direction and two assembled batteries  10  arranged in the lateral direction, that is, a total of four assembled batteries  10  are stored in the outer case  70 . The number and layout of the assembled batteries are not limited to those of this example. For example, one assembled battery may be stored in the outer case. 
     (Assembled Batteries  10 ) 
     As illustrated in  FIGS. 2 and 3 , each assembled battery  10  includes a plurality of secondary batteries  1 , separators  2  interposed between surfaces of the plurality of stacked secondary batteries  1  to isolate the secondary batteries  1 , a pair of end plates  3  disposed on end faces of a battery stack  5  in a stacking direction in which the plurality of secondary batteries  1  and the separators  2  are alternately stacked, and a plurality of metallic binding members  4  disposed on a side surface or an upper surface of the battery stack  5  to bind the end plates  3 . The assembled battery  10  is also fixed to the lower case  71 . For example, bottom surfaces of the secondary batteries  1  are fixed onto the lower case  71  by adhesion using an adhesive. 
     The lower case  71  also functions as a cooling plate that cools the battery stack  5 . That is, heat generated by the secondary batteries  1  is thermally conducted to the lower case  71  to promote heat dissipation by thermally bonding the bottom surfaces of the secondary batteries  1  to the lower case  71 . A cooling pipe for circulating a refrigerant may be disposed on a lower surface or an inner side of the lower case  71 . The separators  2  may have grooves through which a cooling gas is passed to cool the secondary batteries  1 . 
     (Battery Stack  5 ) 
     In each assembled battery  10 , a plurality of secondary batteries  1  are stacked with insulating separators  2  interposed therebetween to form a battery stack  5 , a pair of end plates  3  are disposed on both end faces of the battery stack  5 , and the pair of end plates  3  are connected by binding members  4 . In the assembled battery  10  illustrated in these figures, the separators  2  for insulating the adjacent secondary batteries  1  are interposed between stacking surfaces of the secondary batteries  1 , and the secondary batteries  1  and the separators  2  are alternately stacked to constitute the battery stack  5 . 
     In the assembled battery, the separators do not always need to be interposed between the secondary batteries. For example, the separators can be omitted by insulating the adjacent second batteries by means of a method of forming outer cans of the secondary batteries of an insulating material such as resin, or a method of covering outer peripheries of the outer cans of the secondary batteries with heat-shrinkage tubes, insulating sheets, or an insulating paint. Particularly in a structure that adopts a method of cooling the battery stack through a cooling pipe cooled by, for example, a refrigerant, without using an air cooling method of cooling the secondary batteries by forcibly blowing cooling air between the secondary batteries, it is not always necessary to interpose the separators between the secondary batteries. 
     (Secondary Batteries  1 ) 
     As illustrated in  FIG. 3 , the secondary batteries  1  are square batteries having an outer shape that is smaller in thickness than in width. The secondary batteries  1  are chargeable and dischargeable batteries such as lithium-ion secondary batteries, nickel-hydrogen secondary batteries, or nickel-cadmium secondary batteries. Particularly when lithium-ion secondary batteries are used as the secondary batteries  1 , it is possible to increase the charging capacity with respect to the total volume or mass of the secondary batteries. 
     As illustrated in  FIG. 4 , each of the secondary batteries  1  includes an electrode body  15  having a positive electrode and a negative electrode, an outer can  11  shaped like a bottomed cylinder having an opening in one surface and containing the electrode body  15 , a sealing plate  12  that closes the opening of the outer can  11 , and a pair of electrode terminals  13  disposed at both ends of the sealing plate  12 . The positive electrode and the negative electrode of the electrode body  15  are helically wound with a separator interposed therebetween, are pressed to a predetermined thickness, and are inserted in the outer can  11 . The outer can  11  is shaped like a rectangular cylinder having a closed bottom and both opposed wide surfaces, and is open upward in the figure. The outer can  11  having this shape is produced by pressing a metal plate made of, for example, aluminum or an aluminum alloy. The opening of the outer can  11  is closed by laser-welding the flat sealing plate  12  formed by pressing a metal plate. 
     The sealing plate  12  has a gas discharge valve  14  between the pair of electrode terminals  13 . The gas discharge valve  14  opens to discharge inner gas when the internal pressure of the outer can  11  rises to a pressure higher than or equal to a predetermined pressure. By opening the gas discharge valve  14 , the rise of the internal pressure of the outer can  11  can be suppressed. The gas discharge valve  14  is preferably disposed at almost, the longitudinal center of the sealing plate  12 . Thus, even if the adjacent secondary batteries  1  are stacked while being alternately reversed in the lateral direction, the gas discharge valve  14  can be always aligned with the center of the sealing plate  12 . Further, the sealing plate  12  has a liquid injection portion  19  adjacent to the gas discharge valve and allowing injection of an electrolyte therethrough. The secondary battery  1  is produced by inserting the electrode body  15  in the outer can  11 , hermetically sealing the opening of the outer can  11  with the sealing plate  12 , and then injecting an electrolyte (not illustrated) from the liquid injection portion  19 . 
     The pair of electrode terminals  13  includes a first electrode terminal  13 A insulated from the sealing plate  12  and a second electrode terminal  13 B electrically connected to the sealing plate  12 . The pair of electrode terminals  13  are fixed to determined positions on the sealing plate  12  with gaskets  17  interposed therebetween. The first electrode terminal  13 A is connected to the sealing plate  12  in an insulated state with the gasket  17  interposed therebetween. The second electrode terminal  13 B is connected to the sealing plate  12  with the gasket  17  interposed therebetween, and is electrically connected to an upper surface side of the sealing plate  12  with a metallic fixed member  18 , which is fixed to the second electrode terminal  13 B, interposed therebetween. Inside the secondary battery  1 , the positive and negative electrode terminals  13  fixed to the sealing plate  12  are electrically connected to the electrode body  15  with collector members  16  interposed therebetween. In the secondary battery  1 , the second electrode terminal  13 B connected to the sealing plate  12  and the outer can  11  serves as a positive terminal, and the first electrode terminal  13 A serves as a negative terminal. 
     (Current Interrupt Device  7 ) 
     To avoid a thermal runaway, for example, due to overcharging, each of the secondary batteries  1  includes a current interrupt device  7  that breaks electric connection between the electrode body  15  and the second electrode terminal  13 B in response to the rise of the internal pressure of the outer can  11 . The illustrated current interrupt device  7  includes a short-circuit part  20  that short-circuits the first electrode terminal  13 A and the sealing plate  12  when the internal pressure of the secondary battery  1  exceeds the set pressure, and a fuse part  21  provided in the collector member  16  connected to the second electrode terminal  13 B. In the current interrupt device  7 , in a state in which the internal pressure of the battery exceeds the set pressure and the short-circuit part  20  makes a short circuit, the fuse part  21  is fused by an overcurrent flowing through the fuse part  21 . As a result, the electrical connection between the electrode body  15  and the second electrode terminal  13 B is broken and the current is interrupted. 
     (Short-Circuit Part  20 ) 
     When the internal pressure of the secondary battery  1  exceeds the set pressure, for example, owing to overcharging, the short-circuit part  20  serves to induce a short circuit so that a large current flows through the fuse part  21 . The short-circuit part  20  illustrated in  FIG. 3  includes an inverting plate  22  fixed to the sealing plate  12  and made of a conductive material and a metallic connection plate  23  disposed on the upper side of the sealing plate  12  to be opposed to the inverting plate  22 . 
     (Inverting Plate  22 ) 
     As illustrated in  FIG. 4 , the inverting plate  22  is attached at a short-circuit hole  12 A opening in the sealing plate  12 , for example, by welding. An outer peripheral edge portion of the inverting plate  22  is electrically connected to the sealing plate  12 , and a center portion of the inverting plate  22  is curved to project toward the inside of the outer can  11 . When overcharging occurs in the secondary battery  1  and the internal pressure of the secondary battery  1  exceeds the set pressure, as illustrated in  FIG. 5 , the inverting plate  22  inverts and bulges upward, that is projects in a direction apart from the electrode body  15  and comes into contact with the connection plate  23 , so that a short-circuit is induced. 
     While one inverting plate  22  is provided in the short-circuit part  20  of this example, a plurality of inverting plates may be stacked. In a short-circuit part including a plurality of stacked inverting plates, when the inverting plates are made different in thickness and set inverting pressure, it is possible to more smoothly respond to the rise of the internal pressure of the battery and to continue the fuse function of the fuse part while maintaining a short circuit of one of the inverting plates even when the other inverting plate is fused by heat. 
     The connection plate  23  is disposed on the upper surface of the sealing plate  12  with an insulating portion  24  interposed therebetween, and is connected to the sealing plate  12  in an insulated state. The connection plate  23  is electrically connected to the first electrode terminal  13 A. Specifically, the first electrode terminal  13 A is passed through a hole opening in a part of the connection plate  23 , and the connection plate  23  and the first electrode terminal  13 A are electrically connected through the fixed member  18  fixed to the first electrode terminal  13 A on the upper side of the connection plate  23 . 
     (Fuse Part  21 ) 
     The fuse part  21  is to be fused and cut off by heat generated by an overcurrent flowing through the battery in a short-circuit state of the short-circuit part  20 , and is disposed in a conduction path of the current at the time of a short circuit. The fuse part  21  illustrated in  FIG. 3  is disposed in the collector member  16  connected to the second electrode terminal  13 B. The fuse part  21  provided in the collector member  16  is to be fused by an overcurrent flowing through the collector member  16  in the short-circuit state of the short-circuit part  20 . 
     The fuse part  21  illustrated in  FIG. 3  is constituted by a fuse hole  21 A opening in the collector member  16 , and specifically, is constituted by a connecting portion  21 B on both sides of the fuse hole  21 A opening in a platelike portion  16 A of the collector member  16 , as illustrated in  FIG. 6 . The connecting portion  21 B has a cross-sectional area that is reduced by the opening of the fuse hole  21 A, and the electric resistance thereof locally increases. Thus, the connecting portion  21 B functions as a fuse that interrupts the current by being fused by heat generated by a large current flowing in the short circuit of the secondary battery  1 . In the collector member  16  illustrated in  FIG. 6 , one fuse hole  21 A is open in the platelike portion  16 A, and the connecting portion  21 B is located on both sides of the fuse hole  21 A. In the collector member  16 , as illustrated in  FIG. 7 , a plurality of (two in  FIG. 7 ) fuse holes  21 A can open in the platelike portion  16 A and a connecting portion  21 B can be located in a portion between the fuse holes  21 A and in both side portions of the platelike portion  16 A. While the planar shape of the fuse hole  21 A is elliptic or circular in  FIGS. 6 and 7 , the shape, such as an oval shape, a rectangular shape, a polygonal shape, an arc shape, or a slit shape, and layout of the fuse hole  21 A can be changed variously. Although not illustrated, in the fuse part, cutouts can be provided in both side portions of the platelike portion and a narrow portion in a center portion of the platelike portion can serve as a connecting portion, a cutout can be provided in one side portion of the platelike portion and the other remaining side portion can serve as a connecting portion, or a cutout can be provided on a side portion of the platelike portion and a fuse hole can be provided in a center portion of the platelike portion so that an obtained narrow portion serves as a connecting portion. 
     In the above-described fuse part  21 , the connecting portion  21 B is fused and cut off in the region where the fuse hole  21 A or the cutout are provided. This electrically separates the platelike portion  16 A of the collector member  16  and interrupts the current. As illustrated in  FIG. 3 , the fuse part  21  is disposed in a region on an upper side of the electrode body  15  stored in the outer can  11  and on an outer side of the electrode terminal  13 . That is, the fuse part  21  is disposed close to an upper end corner portion  1 T serving as a boundary portion between the upper surface and the side surface of the secondary battery  1 . 
     The fuse part  21  is preferably obtained by forming an opening in the platelike portion  16 A of the collector member  16 . Further, the thickness of the sealing plate  12  is preferably more than or equal to double the thickness of the platelike portion  16 A of the collector member  16 . 
     In the current interrupt device  7  illustrated in  FIG. 3 , the fuse part  21  is provided in the collector member  16  connected to the second electrode terminal  13 B. This structure can reduce the adverse effect on the short-circuit part  20  resulting from the spark caused during fusing and reconduction of the fuse part  21  because the short-circuit part  20  and the fuse part  21  are arranged apart from each other. However, the fuse part, can be provided in the collector member connected to the first electrode terminal. 
     In the above-described current interrupt device  7 , when the internal pressure of the secondary battery  1  becomes higher than or equal to the set pressure, as illustrated in  FIG. 5 , the inverting plate  22  is pushed up by the internal pressure, and is thereby deformed and inverted. When the inverting plate  22  is inverted and comes into contact with the connection plate  23 , the inverting plate  22  and the connection plate  23  are conductively connected and the short-circuit part  20  makes a short circuit. When the short-circuit part  20  makes the short circuit, a large current flows inside the secondary battery  1  along a path shown by a bold line arrow in  FIG. 5 . At this time, the fuse part  21  in the conduction path is heated, melted, and cut off by the Joule heat due to the large current, and this interrupts the current. Thus, when the internal pressure of the second battery  1  abnormally rises, the current flowing through the secondary battery  1  is interrupted to ensure safety of the secondary battery  1 . 
     As illustrated in  FIG. 3 , the above-described secondary batteries  1  are stacked into the battery stack  5  in such a posture that wide surfaces serving as principal surfaces  1 X are opposed to each other and that upper surfaces  1 A thereof are flush with one another and side surfaces  1 B thereof are flush with one another. The plurality of secondary batteries  1  stacked to constitute the battery stack  5  are connected in series with the adjacent positive and negative electrode terminals  13  connected by bus bars  6 . When the adjacent secondary batteries  1  are connected in series, the output voltage and output of the assembled battery  10  can be increased. In the assembled battery, however, the adjacent secondary batteries can be connected in parallel or can be connected in a multi-serial parallel manner by combination of serial connection and parallel connection. 
     In the assembled battery  10  in which the secondary batteries  1  are connected in series, as illustrated in the perspective views of  FIGS. 2 and 3 , the secondary batteries  1  are stacked in such a posture that the positive and negative electrode terminals  13  of the adjacent secondary batteries  1  are close to each other, in other words, in such a posture that the secondary batteries  1  are alternately reversed in the lateral direction. This can reduce the size of the bus bars  6  that connect the electrode terminals  13 . In this structure, the fuse parts  21  contained in the secondary batteries  1  are different in position between the adjacent secondary batteries  1 . 
     (Separators  2 ) 
     The secondary batteries  1  are constituted by the metallic outer cans  11 . The secondary batteries  1  hold the insulating separators  2  therebetween to prevent a short, circuit between the outer cans  11  of the adjacent secondary batteries  1 . The separators  2  are spacers that allow the adjacent secondary batteries  1  to be stacked while being electrically and thermally insulated from each other. The separators  2  are made of an insulating material such as resin, and are disposed between the adjacent secondary batteries  1  to insulate the adjacent secondary batteries  1 . 
     (End Plates  3 ) 
     A pair of end plates  3  are disposed on both end surfaces of the battery stack  5  in which the secondary batteries  1  and the separators  2  are alternately stacked, and the pair of end plates  3  bind the battery stack  5 . The end plates  3  are made of a material that exhibits a sufficient strength, for example, metal. The end plates  3  have fixing structures to be fixed to the lower case  71  illustrated in  FIG. 1 . Alternatively, the end plates may be made of resin, and further, the resin end plates may be reinforced by members made of a metal material. 
     (Binding Members  4 ) 
     As illustrated in  FIGS. 2 to 5 , the binding members  4  are disposed on the side surfaces and the upper surface of the battery stack  5  with the end plates  3  stacked on both ends, and are each fixed at both ends to the pair of end plates  3  to bind the battery stack  5 . The illustrated binding members  4  are provided as bind bars  40  each obtained by bending a metal plate of a predetermined thickness into a predetermined shape. These bind bars  40  can be made of a material having a sufficient strength, for example, a metal plate of iron, and preferably a steel plate. By thus using the bind bars  40  each formed by bending the metal plate as the binding members  4 , the cost can be reduced. 
     The binding members  4  serving as the bind bars  40  extend in the stacking direction of the battery stack  5 , and are each fixed at. both ends to the pair of end plates  3 . Each of the bind bars  40  has a body portion  41  disposed along the side surface of the battery stack  5 , and connecting pieces  42  disposed at both ends of the body portion  41  and fixed to the end plates  3 . Bind bars  40 A illustrated in  FIGS. 2 to 5  are disposed opposed to upper portions and lower portions of side surfaces of the battery stack  5  and the end plates  3 . That is, the pair of end plates  3  are bound by four bind bars  40 A. The four bind bars  40 A include two upper bind bars  40 X disposed on the upper portions of the side surfaces of the battery stack  5  and two lower bind bars  40 Y disposed on the lower portions of the side surfaces of the battery stack  5 . 
     Each of the upper bind bars  40 X has an L-shaped cross section defined by connecting pieces  42  at both ends of a body portion  41  of a predetermined width and a horizontal portion  43  at an upper end of the body portion  41  to cover the upper surface of the battery stack  5 . In each of the upper bind bars  40 X illustrated in  FIG. 4 , the body portion  41  is extended upward and the extended portion is bent onto the upper surface of the battery stack  5  to form the horizontal portion  43 . The horizontal portion  43  is bent substantially perpendicularly to the body portion  41  to take a horizontal posture along the upper surfaces of the secondary batteries  1 . The horizontal portion  43  of the upper bind bar  40 X serves as a holding portion for holding the upper surface of the battery stack  5 . As illustrated in  FIG. 3 , each of the lower bind bars  40 Y has connecting pieces  42  at both ends of a body portion  41  having a predetermined width. 
     The connecting pieces  42  at both ends of the body portion  41  are bent perpendicularly to the body portion  41  to be in surface contact with outer side surfaces of the end plates  3 . Although not illustrated, both ends of each bind bar  40  are fixed to the end plates  3  by connectors such as setscrews, are fixed to the end plates  3  by a retaining structure, or are fixed to the end plates  3  by bonding or welding. In each bind bar  40  illustrated in  FIGS. 2 and 3 , the connecting pieces  42  are formed by bending both ends of the bind bar  40 , and can be fixed to the outer side surfaces of the end plates  3  by the connecting pieces  42 . However, the bind bar does not always need to have the connecting pieces at both ends. A bind bar having no connecting piece can be fixed by screwing connectors, such as setscrews, penetrating both ends of the bind bar into the side surfaces of the end plates or penetrating the connectors through the end plates in the up-down direction or the right-left direction. This structure can shorten the total length of the assembled battery. 
     The binding members  4  further include protective cover portions  8  that cover upper end corner portions  1 T at boundaries of the upper surfaces  1 A and the side surfaces  1 B of the secondary batteries  1 . The protective cover portions  8  are disposed to cover the upper end corner portions  1 T of the secondary batteries  1  close to the fuse parts  21  contained in the outer cans  11 . In each illustrated secondary battery  1 , since the fuse part  21  is provided in the collector member  16  that connects the second electrode terminal  13 B at the end of the sealing plate  12  and the electrode body  15 , the protective cover portion  8  is disposed to cover an edge where the second electrode terminal  13 B is disposed in a connecting portion between the sealing plate  12  and the outer can  11 . In the binding member  4  of this example, the upper bind bar  40 X also functions as the protective cover portion  8 . 
     The protective cover portion  8  illustrated in  FIG. 4  includes an upper-surface covering part  8 A that covers an upper surface of the upper end corner portion  1 T and a side-surface covering part  8 B that covers a side surface of the upper end corner portion  1 T. That is, in the upper bind bar  40 X illustrated in  FIG. 4 , the body portion  41  covering the upper portion of the side surface of the battery stack  5  functions as the side-surface covering part  8 B of the protective cover portion  8 , and the horizontal portion  43  covering the upper surface of the battery stack  5  functions as the upper-surface covering part  8 A of the protective cover portion  8 . 
     When a spark occurs inside the secondary battery  1 , a portion near the joint portion between the opening of the outer can  11  and the sealing plate  12  is most subject to breakage. Therefore, the shape and size of the protective cover portion  8  are such as to cover a region provided near the upper end corner portion  1 T of the secondary battery  1  and including at least a welded portion  25  between the opening of the outer can  11  and the edge of the sealing plate  12 . In the illustrated secondary battery  1 , the boundary portion is welded at the opening of the outer can  11  in a state in which the outer peripheral edge of the sealing plate  12  is fitted inside the edge of the opening of the outer can  11 . Therefore, in the secondary battery  1 , the welded portion  25  between the outer can  11  and the sealing plate  12  is provided on the upper surface of the secondary battery  1 . In the protective cover portion  8  illustrated in  FIG. 4 , the welded portion  25  inside the opening edge of the outer can  11  is covered with the upper-surface covering part  8 A covering the upper surface of the upper end corner portion  1 T. The upper-surface covering part  8 A preferably extends to a position that is close to the electrode terminal  13 , but is out of contact with the electrode terminal  13 , and covers the upper surface of the upper end corner portion  1 T. Therefore, a length (S) of the secondary battery  1  in the width direction, along which the upper-surface covering part  8 A covers the upper surface of the upper end corner portion  1 T, is larger than the thickness of the outer can  11  and is 2 mm or more, and preferably 5 mm or more. A length (H) in the vertical direction, along which the side-surface covering part  8 B covers the side surface of the upper end corner portion  1 T, is 1 cm or more, and preferably 3 cm or more. 
     In the secondary battery, however, the welded portion does not always need to be provided on the upper surface. Although not illustrated, the boundary portion can also be welded in a state in which the outer peripheral edge of the sealing plate is in contact with the opening edge of the opening of the outer can. In this secondary battery, a welded portion between the outer can and the sealing plate is provided on an outer peripheral surface (side surface and principal surface) of the secondary battery along the outer peripheral edge of the sealing plate. In the secondary battery having this structure, the side-surface covering part covering the side surface of the upper end corner portion covers the welded portion outside the opening edge of the outer can. 
     In the assembled battery  10  in which the plurality of secondary batteries  1  are connected in series, as described above, the adjacent secondary batteries  1  are stacked in such a posture to be alternately reversed in the lateral direction to connect the adjacent positive and negative electrode terminals  13  by the bus bars  6  in the shortest distance. For this reason, the positions of the fuse parts  21  contained in the secondary batteries  1  alternately differ between the adjacent secondary batteries  1 . Therefore, in this assembled battery  10 , as illustrated in  FIGS. 2 to 4 , the protective cover portions  8  are disposed on both sides of the battery stack  5  to cover the upper end corner portions  1 T of the secondary batteries  1 . Thus, in any of the secondary batteries  1 , the upper end corner portion  1 T close to the fuse part  21  is covered with the protective cover portion  8 . Even if a spark occurs inside the battery, the protective cover portion  8  suppresses scattering of the spark to the outside of the battery. This can improve safety. 
     (Insulating Member  45 ) 
     The assembled battery  10  illustrated in  FIG. 4  has insulating members  45  on inner surfaces of the bind bars  40 . The insulating members  45  insulate the metallic bind bars  40  and the outer can  11  of each secondary battery  1 , and, for example, insulating sheets, insulating plates, or an insulating paint can be used. In particular, the insulating members  45  on the inner surfaces of the protective cover portions  8  are each preferably constituted by a sheet material or a plate material made of a heat-resistant or flame-resistant resin, and this can reduce breakage and adverse effects due to the spark. The insulating members  45  are preferably provided all over the inner surfaces of the bind bars  40  to insulate the surfaces opposed to the battery stack  5 . In the illustrated assembled battery  10 , the insulating members  45  are disposed on the inner surfaces of the upper bind bars  40 X and the inner surfaces of the lower bind bars  40 Y. Some of the separators  2  disposed between the secondary batteries  1  can also function as the insulating members  45 . In the secondary battery in which the outer can and the surface of the sealing plate are covered with, for example, a heat-shrinkage tube, an insulating sheet, or an insulating point, as described above, the insulating members on the inner surfaces of the bind bars can be omitted. 
     In the above-described embodiment, the binding members  4  are constituted by four bind bars  40 A, the upper bind bars  40 X bind the upper portions of the side surfaces of the battery stack  5 , and the lower bind bars  40 Y bind the lower portions of the battery stack  5 . Although not illustrated, according to this structure, in an air-cooled power supply device that cools secondary batteries by forcibly blowing cooling air between the secondary batteries, the cooling air can be passed and blown through ventilations defined by gaps serving between the upper bind bars and the lower bind bars. However, in the present invention, the binding members  4  on each side of the battery stack  5  can also be constituted by one bind bar  40 B. 
     Second Embodiment 
     In an assembled battery  10  illustrated in  FIGS. 8 and 9 , bind bars  40 B include their respective body portions  41  opposed to side surfaces of a battery stack  5 , and the body portions  41  cover the entire side surfaces of the battery stack  5 . The illustrated bind bars  40 B each have an L-shaped cross section defined by connecting pieces  42  at both ends of each of the body portions  41  having such a width as to cover the entire side surfaces of the battery stack  5  and horizontal portions  43  at upper ends of the body portions  41  to cover an upper surface of the battery stack  5 . The bind bars  40 B also function as protective cover portions  8  that cover upper end corner portions  1 T of secondary batteries  1 . That is, the body portions  41  covering upper portions of the side surfaces of the battery stack  5  function as side-surface covering parts  8 B of the protective cover portions  8 , and the horizontal portions  43  covering the upper surface of the battery stack  5  function as upper-surface covering parts  8 A of the protective cover portions  8 . Further, the bind bars  40 B have insulating members  45  all over inner surfaces thereof to cover the entire side surfaces and both end portions of the upper surface of the battery stack  5 . In the bind bars  40 B having this structure, the body portions  41  opposed to the side surfaces of the battery stack  5  are made wide, and this can increase the mechanical strength. Also, the side surfaces of the battery stack  5  are entirely covered, and this can reliably prevent scattering of the spark toward the side surfaces of the battery stack  5 . 
     Alternatively, the binding members  4  can be configured to cover at least a part of the bottom surface of the battery stack  5 . For example, the binding members  4  can cover corner portions on the bottom side of the battery stack  5  by providing horizontal portions  43  at lower ends of the bind bars  40 . 
     Third Embodiment 
     Bind bars  40 C illustrated in  FIG. 10  include two upper bind bars  40 X disposed at corner portions on an upper side of a battery stack  5  and two lower bind bars  40 Y disposed at corner portions on a lower side of the battery stack  5 . The upper bind bars  40 X each have an L-shaped cross section defined by connecting pieces  42  at both ends of each of body portions  41  having a predetermined width and horizontal portions  43  at upper ends of the body portions  41  to cover the upper surface of the battery stack  5 , similarly to the above-described upper bind bars  40 X. The upper bind bars  40 X also function as protective cover portions  8 . The lower bind bars  40 Z each have an L-shaped cross section defined by connecting pieces  42  at both ends of each of body portions  41  having a predetermined width and horizontal portions  43  at lower ends of the body portions  4  to cover a bottom surface of the battery stack  5 . The horizontal portions  43  are bent substantially perpendicularly to the body portions  41  to take a horizontal posture along bottom surfaces  1 C of secondary batteries  1 . In the four bind bars  4 C at four corner portions of the battery stack  5 , the body portions  41  are disposed on both sides of the battery stack  5  to prevent the horizontal movement of the secondary batteries  1 , and the horizontal portions  43  are disposed on the upper and lower sides of the battery stack  5  to prevent the up-down movement of the secondary batteries  1 . 
     Fourth Embodiment 
     Bind bars  40 D illustrated in  FIG. 11  each have an angular U-shaped cross section defined by horizontal portions  43  at upper ends and lower ends of body portions  41  covering the entire side surfaces of the battery stack  5  to cover an upper surface and a lower surface of the battery stack  5 . In the bind bars  40 D, the body portions  41  and the horizontal portions  43  at the upper ends of the body portions  41  constitute protective cover portions  8  that cover upper end corner portions  1 T of secondary batteries  1 . That is, the body portions  41  covering the side surfaces of the battery stack  5  function as side-surface covering parts  8 B of the protective cover portions  8 , and the horizontal portions  43  covering the upper surface of the battery stack  5  function as upper-surface covering parts  8 A of the protective cover portions  8 . In the bind bars  40 D having this structure, the body portions  41  opposed to the side surfaces of the battery stack  5  are made wide, and this can increase the mechanical strength. Moreover, the body portions  41  cover the entire side surfaces of the battery stack  5 , and this can reliably prevent scattering of the spark toward the side surfaces of the battery stack  5 . In the bind bars  40 D disposed on both side surfaces of the battery stack  5  and having the angular U-shaped cross section, the body portions  41  are disposed on both sides of the battery stack  5  to prevent horizontal movement of the secondary batteries  1  and the horizontal portions  43  are disposed on the upper and lower sides of the battery stack  5  to prevent up-down movement of the secondary batteries  1 . 
     Fifth and Sixth Embodiments 
     Further, in the binding members  4 , the body portions  41  covering the side surfaces of the battery stack  5  can have open windows. In bind bars  40 E and  40 F illustrated in  FIGS. 12 and 13 , body portions  41  covering side surfaces of a battery stack  5  have open windows  44  in center portions thereof. The illustrated open windows  44  are open to be opposed to intermediate portions of the side surfaces of the battery stack  5  except for upper portions and lower portions. 
     In the bind bars  40 E of  FIG. 10 , connecting pieces  42  are provided at both ends of each of the body portions  41  having the open windows  44  in the center portions, and horizontal portions  43  covering the upper surface of the battery stack are provided at upper ends of the body portions  41 . In the bind bars  40 E, the body portions  41  are frame-shaped, and upper parts of the body portions  41  and the horizontal portions  43  function as protective cover portions  8  that cover upper end corner portions  1 T of secondary batteries  1 . 
     In the bind bars  40 F of  FIG. 11 , connecting pieces  42  are provided at both ends of each of the body portions  41  having the open windows  44  in center portions thereof, and horizontal portions  43  covering an upper surface and a lower end of the battery stack are provided at upper ends and lower ends of the body portions  41 . In the bind bars  40 F, the body portions  41  are also frame-shaped, and upper parts of the body portions  41  and the horizontal portions  43  at the upper ends function as protective cover portions  8  that cover upper end corner portions  1 T of secondary batteries  1 . 
     Since these bind bars  40 E and  40 F have the open windows  44 , the weight and cost of the bind bars  40 E and  40 F are reduced. Further, heat can be efficiently dissipated from the secondary batteries by exposing the side surfaces of the battery stack from the open windows  44 . Although not illustrated, in particular, in an air-cooled power supply device that cools secondary batteries by forcibly blowing cooling air between the secondary batteries, the cooling air can be passed and blown through the open windows provided as ventilations in the bind bars. 
     The above-described power supply devices can be used as a vehicle-mounted power supply. As vehicles in which the power supply device is mounted, electrically driven vehicles, such as a hybrid car and a plug-in hybrid car that run by using both an engine and a motor and an electric car that runs by using only a motor can be used. The power supply device is used as a power supply for these vehicles. 
     The embodiments and examples of the present invention have been described above with reference to the drawings. However, the above-described embodiments and examples are just illustrative examples for embodying the technical idea of the present invention, and the present, invention is not limited to the above embodiments and examples. This description does not specify the members in the scope of the claims to the members in the embodiments. In the above description, the same names and symbols denote the same or equivalent members, and detailed descriptions thereof are appropriately omitted. Further, in the elements that constitute the present invention, a plurality of elements may be constituted by the same member so that one member functions as a plurality of elements. Conversely, the function of one member may be shared and realized by a plurality of members. 
     INDUSTRIAL APPLICABILITY 
     The power supply device and the vehicle including the power supply device according to the present invention can be suitably used as a power supply device for, for example, a plug-in hybrid electric car and a hybrid electric car capable of switching an EV running mode and an HEV running mode and an electric car. The power supply device can be appropriately used for applications as a backup power supply device mountable in a computer server rack, a backup power supply device for a wireless base station of, for example, a mobile phone, a power storage device used in combination with a solar battery, such as a domestic or factory storage power supply or a power supply of a street light, and a backup power supply of a traffic light. 
     REFERENCE SIGNS LIST 
     
         
           100  power supply device 
           1  secondary battery 
           1 A upper surface 
           1 B side surface 
           1 C bottom surface 
           1 X principal surface 
           1 T upper end corner portion 
           2  separator 
           3  end plate 
           4  binding member 
           5  battery stack 
           6  bus bar 
           7  current interrupt device 
           8  protective cover portion 
           8 A upper-surface covering part 
           8 B side-surface covering part 
           10  assembled battery 
           11  outer can 
           12  sealing plate 
           12 A short-circuit hole 
           13  electrode terminal 
           13 A first electrode terminal 
           13 B second electrode terminal 
           14  gas discharge valve 
           15  electrode body 
           16  collector member 
           16 A platelike portion 
           17  gasket 
           18  fixed member 
           19  liquid injection portion 
           20  short-circuit part 
           21  fuse part 
           21 A fuse hole 
           21 B connecting portion 
           22  inverting plate 
           23  connection plate 
           24  insulating portion 
           25  welded portion 
           45  insulating member 
           40 ,  40 A,  40 B,  40 C,  40 D,  40 E,  40 F bind bar 
           40 X upper bind bar 
           40 Y,  40 Z lower bind bar 
           41  body portion 
           42  connecting piece 
           43  horizontal portion 
           44  open window 
           45  insulating member 
           70  outer case 
           71  lower case 
           72  upper case 
           73  end face plate 
           74  flange 
           101  secondary battery 
           111  outer can 
           112  sealing plate 
           115  electrode body 
           116  collector plate 
           121  fuse part 
           122  inverting plate 
           123  connection plate 
           124  insulating member