Patent Publication Number: US-2018053962-A1

Title: Bipolar battery

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2016-159430 filed on Aug. 16, 2016 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a bipolar battery, and particularly to a bipolar battery including multiple unit cells. 
     2. Description of Related Art 
     A bipolar battery described in Japanese Patent Application Publication No. 2011-151016 includes an electrode stacked body formed by alternatingly stacking bipolar electrodes and electrolyte layers in multiple stories. The bipolar electrode includes current collectors, positive electrodes formed on one surfaces of the current collectors, and negative electrodes on the other surfaces thereof. 
     Each electrolyte layer is formed on each separator, and a sealed portion in a frame shape is formed on an outer circumference of each separator. The electrolyte layer is formed on a portion of each separator, the portion being surrounded by each seal member. 
     The seal member is formed, using a mold or the like, by filling, pouring, or applying a resin for sealing into or to the separator, or impregnating the separator with the resin for sealing. The seal member is formed in the separator in a manner as to project from a front surface and a back surface of the separator. In formation of the seal member, a height (thickness) of the seal member is formed to be thicker than respective thicknesses of the positive electrode and the negative electrode. 
     After the bipolar electrodes and separators are stacked, pressure or heat is applied thereto so as to pressurize and deform or heat-seal the sealed portions to be in tight contact with each sealed current collector. 
     SUMMARY 
     In the bipolar battery described in JP 2011-151016 A, the seal member in a frame shape formed on each separator prevents the electrolytic solution contained in each electrolyte layer from oozing out of the separator. 
     Unfortunately, it is difficult to completely impregnate each separator with the resin in a thickness direction of the separator, and also difficult to prevent the leakage of the electrolytic solution from occurring in the seal member with the separator impregnated with the resin. 
     The present disclosure is a bipolar battery capable of promoting suppression of leakage of an electrolytic solution. 
     A bipolar battery of the present disclosure includes: a first end portion; a second end portion; a stacked body and a fastening tool. The stacked body includes: plurality of unit cells that are stacked between the first end portion and the second end portion. The fastening tool presses the first end portion and the second end portion such that the fastening tool fastens the stacked body. Each of the plurality of unit cells includes a current collecting plate, a unit battery, and a seal member. The current collecting plate includes a first main surface and a second main surface that are arranged in a stacking direction of the plurality of unit cells. The unit battery includes a separator impregnated with an electrolytic solution, the unit battery being disposed on the first main surface. The seal member is provided on the first main surface. The seal member surrounds a periphery of the unit battery, and the seal member is in tight contact with the current collecting plates adjacent to the seal member in the stacking direction by a pressing force from the fastening tool. 
     According to the above bipolar battery, unit battery is surrounded by the seal member. The seal member is in tight contact with the adjacent current collecting plates in the stacking direction by the pressing force from the fastening tool. Accordingly, the seal member suppresses the electrolytic solution with which the separator of the unit battery is impregnated from leaking out to the outside. 
     The above fastening tool may include: a first pressing plate pressing the first end portion of the stacked body; a second pressing plate pressing the second end surface; and plurality of connecting members connecting the first pressing plate and the second pressing plate. The above plurality of connecting members may be arranged such that the plurality of connecting members ( 23 ) are apart from each other, and the stacked body may be exposed to the outside. 
     According to the bipolar battery, a pressing force is applied to each seal member by the pressing force from the first pressing member and the second pressing member so that the seal member comes into tight contact with the current collecting plates. In addition, the connecting members are disposed with a distance therebetween, so that the stacked body is exposed to the outside air, to thus cool the stacked body. 
     When each current collecting plate and each seal member are viewed from a position apart from the stacking direction, the seal member may be located in an inner side of the current collecting plate, and the current collecting plate may include a heat-dissipating portion that outwardly protrudes from the seal member, and may be exposed to the outside air. 
     According to the above bipolar battery, it is possible to dissipate more heat from the heat-dissipating portion of the current collecting plate. 
     The above current collecting plate may include an electric insulating member covering a portion of the current collecting plate located more outward than the seal member. 
     According to the above bipolar battery, at more outward positions than the seal member, even when the current collecting plates become warped so that the adjacent current collecting plates in the stacking direction come into contact with each other, the electric insulating member can suppress occurrence of short-circuit. 
     The above fastening tool may include: a first metallic pressing plate pressing the first end portion of the stacked body; and a second metallic pressing plate pressing the second end portion. The bipolar battery may further include a heat insulating member disposed at least one of between the first pressing plate and the first end portion and between the second pressing plate and the second end portion. 
     According to the above bipolar battery, since the heat insulating members are provided between the pressing plates and the unit cell, to thereby reduce variation in temperature of the respective unit cell adjacent to the corresponding pressing plates due to the temperature of the pressing plates. The battery characteristics such as charging property, discharging property, and battery capacity vary depending on the temperature; thus, it is possible to suppress that the battery characteristics of the unit battery adjacent to the pressing plates vary due to the temperatures of the pressing plates. Through this, it is possible to suppress variation in battery characteristics of the entire bipolar battery. 
     The above heat insulating member may be an electric insulating material. According to this bipolar battery, it is possible to secure electric insulation between the pressing plates and the stacked body by the heat insulating members. 
     When each above unit battery is viewed from the stacking direction, the separator may cover a portion of the first main surface of each current collecting plate that is located between a placement part of each unit battery and a placement position of seal member. 
     According to the above bipolar battery, of the first main surface of the current collecting plate, the inside of the seal member is covered by the separator. Hence, for example, even when a gas is generated from the unit battery and the current collecting plate become warped in the inner side of the seal member, it is possible to suppress that the adjacent current collecting plates in the stacking direction come into direct contact with each other, to thus suppress occurrence of short-circuit. 
     The seal member may include a stepped portion on which an outer circumferential edge of the separator is placed. During the manufacturing process of the positive electrodes or the negative electrodes, needle-like burrs might be formed on the positive electrodes or the negative electrodes. According to the above bipolar battery, it is possible to suppress that each separator comes into contact with these needle-like burrs. 
     The above stacked body may include first current collecting plates and second current collecting plates arranged in the stacking direction. Each of the unit batteries may be held between each first current collecting plate and each second current collecting plate. Each of the unit batteries may include a positive electrode formed on the first main surface of each first current collecting plate, and a negative electrode formed on the second main surface of each second current collecting plate. The bipolar battery may include a rough portion having recesses and projections, the recesses and the projections being formed in at least either of a portion of the first current collecting plate in which the positive electrode is formed and a portion of the second current collecting plate in which the negative electrode is formed. The above the current collecting plate may include a positive electrode arranged on the first main surface of the current collecting plate, a negative electrode arranged on the second main surface of the current collecting plate, and a rough portion having recesses and projections. The rough portion may be arranged in at least one of a portion of each of the first main surface in which the positive electrode is arranged and a portion of the second main surface in which the negative electrode is arranged. 
     According to the above bipolar battery, for example, it is possible to increase a contact area of at least either the positive electrode or the negative electrode with the current collecting plate, and promote reduction of electric resistance of at least either the positive electrode or the negative electrode as well as tight contact thereof with the current collecting plate. 
     The above stacked body may include first current collecting plates and second current collecting plates arranged in the stacking direction. Each of the unit batteries may be held between each first current collecting plate and each second current collecting plate. Each of the unit batteries may include a positive electrode formed on the first main surface of each the first current collecting plate, and a negative electrode formed on the second main surface of each the second current collecting plate. The bipolar battery may include an electric conductive film formed between at least one of the first main surface and the positive electrode of each first current collecting plate, and the second main surface and the negative electrode of each second current collecting plate. The current collecting plate may include a positive electrode arranged on the first main surface of the current collecting plate, and a negative electrode arranged on the second main surface of the current collecting plate, and the unit battery may include an electric conductive film arranged in at least one of between the first main surface and the positive electrode and between the second main surface and the negative electrode. 
     According to the above bipolar battery, it is possible to promote reduction of the contact resistance and enhancement of the tight contact of at least one of the positive electrodes and the negative electrodes with each corresponding current collecting plate. As the aforementioned electric conductive film, a carbon film is employed. 
     The current collecting plate may include a recess located between a placement position of the unit battery and the seal member in the current collecting plate. An electrolytic solution may be stored in the recess. The separator may be in contact with the electrolytic solution in the recess. 
     According to the above bipolar battery, it is possible to suppress exhaustion of the electrolytic solution. 
     According to the bipolar battery of the present disclosure, it is possible to suppress leakage of the electrolytic solution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a schematic view schematically showing a vehicle in which a bipolar battery according to a present embodiment 1 is installed; 
         FIG. 2  is a cross sectional view showing the bipolar battery; 
         FIG. 3  is an exploded perspective view of the bipolar battery; 
         FIG. 4  is a perspective view showing a unit cell; 
         FIG. 5  is a plan view showing the unit cell; 
         FIG. 6  is a cross sectional view showing a bipolar battery according to an embodiment 2; 
         FIG. 7  is a cross sectional view showing a bipolar battery according to a comparative example; 
         FIG. 8  is a cross sectional view showing a bipolar battery according to an embodiment 3; 
         FIG. 9  is a plan view showing the unit cell; 
         FIG. 10  is a plan view showing a variation of the unit cell; 
         FIG. 11  is a cross sectional view showing a bipolar battery according to an embodiment 4; 
         FIG. 12  is a cross sectional view showing a configuration of a stepped portion and a periphery thereof; 
         FIG. 13  is a plan view showing a seal member and a current collecting plate; 
         FIG. 14  is a plan view showing the seal member, the current collecting plate, and a separator; 
         FIG. 15  is a cross sectional view showing a configuration of each unit cell and a periphery thereof; 
         FIG. 16  is a cross sectional view showing a part of a bipolar battery according to an embodiment 5; 
         FIG. 17  is a cross sectional view showing a configuration of a rough surface portion of each current collecting plate and a periphery thereof; 
         FIG. 18  is a cross sectional view showing a current collecting plate provided with no rough surface; 
         FIG. 19  is a cross sectional view showing a part of a bipolar battery according to a variation of the present embodiment 5; 
         FIG. 20  is a cross sectional view showing a part of a bipolar battery according to a present embodiment 6; 
         FIG. 21  is a partial cross sectional view showing a variation of the bipolar battery; and 
         FIG. 22  is a perspective view showing the bipolar battery. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     With reference to  FIG. 1  to  FIG. 22 , a bipolar battery according to each embodiment will be described. In  FIG. 1  to  FIG. 22 , the same or substantially the same configurations will be denoted with the same reference numerals, and overlapped description thereof might be omitted.  FIG. 1  is a schematic view schematically showing a vehicle  2  in which bipolar batteries  1  according to the present embodiment  1  are installed. As shown in  FIG. 1 , the vehicle  2  includes a battery unit  3 . 
     The battery unit  3  includes a battery case  4  housing the multiple bipolar batteries  1  therein, and a fan  5  supplying a cooling air into the battery case  4 . 
       FIG. 2  is a cross sectional view showing the bipolar battery  1 , and  FIG. 3  is an exploded perspective view of the bipolar battery  1 . As shown in  FIG. 2 , the bipolar battery  1  includes a stacked body  11  formed by stacking multiple unit cells  10  in a stacking direction D 1 , and a fastening tool  12  to fasten the stacked body  11  in the stacking direction D 1 . 
     The stacked body  11  includes an end surface (a first end portion)  13  and an end surface (a second end portion)  14  that are arranged in the stacking direction D 1 . 
     The fastening tool  12  includes a metallic pressing plate (a first pressing plate)  20  pressing the end surface  13 , a metallic pressing plate (a second pressing plate)  21  pressing the end surface  14 , and multiple connecting members  23  connecting the pressing plate  20  and the pressing plate  21 . 
     The pressing plate  20  is formed with multiple through-holes  24 , and the pressing plate  21  is also formed with multiple through-holes  25 . 
     Each connecting member  23  includes a connecting shaft  26  disposed between the pressing plate  20  and the pressing plate  21 , a bolt  27  connecting one end of the connecting shaft  26  to the pressing plate  20 , a bolt  28  connecting the other end of the connecting shaft  26  to the pressing plate  21 , and electric insulating members  29 ,  30 . 
     The electric insulating member  29  is formed with a through-hole into which a shaft portion of the bolt  27  is inserted. The electric insulating member  29  includes a cylindrical portion  31  in a cylindrical shape to be inserted into the through-hole  24  and a flange portion  32  formed at a lower end of the cylindrical portion  31 . The flange portion  32  is disposed on a bottom surface of the pressing plate  20 . 
     The electric insulating member  29  is a member to electrically insulate the pressing plate  20  from the bolt  27 , and the flange portion  32  electrically insulates the pressing plate  20  from a head portion of the bolt  27 , and the cylindrical portion  31  electrically insulates the pressing plate  20  from the shaft portion of the bolt  27 . 
     The electric insulating member  30  is also configured to be the same as the electric insulating member  29 , and the electric insulating member  30  includes a cylindrical portion  33  to be inserted into a through-hole  25 , and a flange portion  34  disposed on a top surface of the pressing plate  21 . The electric insulating member  30  electrically insulates the pressing plate  21  from the bolt  28 . 
     One end of the connecting shaft  26  is formed with a female-threaded portion to be screwed with the shaft portion of the bolt  27 , and the other end of the connecting shaft  26  is formed with a female-threaded portion to be screwed with a shaft portion of the bolt  28 . 
     The bolts  27 ,  28  are screwed with the connecting shaft  26 , and the bolts  27 ,  28  are then fastened so that the pressing plates  20 ,  21  press the end surfaces  13 ,  14  of the stacked body  11 . 
     The pressing plates  20 ,  21  are connected to each connecting shaft  26  with the electric insulating members  29 ,  30  interposed therebetween, and the electric insulating members  29 ,  30  electrically insulate the pressing plates  20 ,  21  from the bolts  27 ,  28 , respectively. In this manner, the connecting shafts  26  are out of contact with the pressing plates  20 ,  21 , so that the connecting shafts  26  are electrically insulated from the pressing plates  20 ,  21 . The pressing plate  20  and the pressing plate  21  are electrically connected to the stacked body  11 , while the connecting shafts  26  are electrically insulated from the pressing plates  20 ,  21 ; therefore, short-circuit between the pressing plate  20  and the pressing plate  21  is suppressed. Thus, the pressing plate  20  and the pressing plate  21  can be used as current collecting terminals. 
     Here, as shown in  FIG. 3 , the connecting shafts  26  are so disposed as to surround a periphery of the stacked body  11  with a distance therebetween. Hence, a cooling air from the fan  5  passes through between the connecting shafts  26  to reach the stacked body  11 , thus cooling the stacked body  11 . 
     Specifically, the stacked body  11  is exposed to the outside air so as to directly dissipate heat of the stacked body  11  to the outside air. 
     The configuration of the fastening tool  12  is not limited to the aforementioned configuration. For example, instead of the connecting members  23 , there may be employed fastening bands to fasten the pressing plates  20 ,  21 , or elastic members such as springs to urge the pressing plates  20 ,  21  such that the pressing plates  20 ,  21  come closer to each other. The electric insulating members  29 ,  30  may be omitted, and resin bolts may be used as the bolts  27 ,  28 . 
     In  FIG. 2 , the bipolar battery  1  is formed by stacking current collecting plates  40  each having a negative electrode  45  on a lower surface  36  thereof and a positive electrode  43  on an upper surface  35  thereof, and a seal member  42  and a separator  44  disposed on each current collecting plate  40  one by one in this order, and thereafter, fastening the stacked body  11  by the fastening tool  12 . A so-called bipolar electrode is formed by the current collecting plates  40 , the negative electrodes  45  formed on the lower surfaces  36  of the current collecting plates  40 , and the positive electrodes  43  formed on the upper surfaces  35  of the current collecting plates  40 . Through the stacking in the above manner, there is formed each unit cell  10  that includes: the current collecting plate  40  including the upper surface  35  (first main surface) and the lower surface  36  (second main surface) that are arranged in the stacking direction D 1 ; the unit battery  41  disposed on the upper surface  35  of the current collecting plate  40 ; and the seal member  42  formed on the upper surface  35  so as to surround the periphery of the unit battery  41 . Each unit cell  10  further includes seal members  53 ,  54  formed on respective outer circumferential surfaces of the seal members  42 , and hydrophobic insulating films  55 ,  56  formed in respective inner sides of the seal members  42 . 
     The current collecting plates  40  are made of metallic plates such as nickel plates and nickel-plated steel plates. A thickness of each current collecting plate  40  is 50 to 700 μm, for example. In this manner, each current collecting plate  40  has a predetermined thickness, and thus even if the multiple current collecting plates  40  are arranged with a distance therebetween, an outer circumferential edge of each current collecting plate  40  is suppressed from being warped. 
     Each unit battery  41  includes a separator  44  including: an upper surface (a third main surface)  46  and a lower surface (a fourth main surface)  47  that are arranged in the stacking direction D 1 ; a negative electrode  45  disposed on the upper surface  46 ; and a positive electrode  43  disposed on the lower surface  47 . A unit battery  41 G of a unit cell  10 G shown in  FIG. 2  is held between a current collecting plate  40 G and a current collecting plate  40 H that are adjacent to each other in the stacking direction. The positive electrode  43  of the unit battery  41 G is formed on the upper surface  35  of the current collecting plate  40 G, and the negative electrode  45  of the current collecting plate  40 G is formed on the lower surface  36  of the current collecting plate  40 H. The separator  44  of the unit battery  41 G is disposed between the positive electrode  43  and the negative electrode  45 . 
     The positive electrode  43  contains a positive-electrode active material of approximately 80 to 99 mass %. The positive-electrode active material is nickel hydroxide (Ni(OH) 2 ). The nickel hydroxide is changed into nickel oxyhydroxide (NiOOH) by charging. The nickel oxyhydroxide returns to the nickel hydroxide by discharging. That is, the positive electrode  43  contains at least one of nickel hydroxide and nickel oxyhydroxide. 
     The positive electrode  43  may contain an electric conductive material and a binder other than the positive-electrode active material. The positive electrode  43  may contain an electric conductive material of approximately 0.5 to 10 mass %, for example. The electric conductive material may be, for example, cobalt oxide (CoO), cobalt hydroxide (Co(OH) 2 ), or the like. The positive electrode  43  may contain a binder of approximately 0.5 to 10 mass %, for example. The binder may be, for example, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), or the like. 
     The negative electrode  45  contains a hydrogen absorbing alloy. The hydrogen absorbing alloy is a negative-electrode active material. The hydrogen absorbing alloy may be, for example, an ABS-type alloy or the like. An example of the ABS-type alloy may include LaNi 5 , MmNi 5 (“Mm” indicates a mixture of rare earth metals referred to as “mischmetal”), for example. The negative electrode  45  may be a compact of a hydrogen absorbing alloy, or one including a base material on which a hydrogen absorbing alloy is supported. An example of the base material may include a punching metal or the like, for example. 
     An active material supporter may be used so as to form the positive electrode  43  or the negative electrode  45 . The positive electrode  43  or the negative electrode  45  may be formed by joining the active material supporter to the upper surface  35  and the lower surface  36  of each current collecting plate  40  through welding, pressure-welding or the like, and also filling the active material supporter with a positive-electrode active material paste or a negative-electrode active material paste, for example. An example of the active material supporter may include a punching metal, a metal mesh, or the like, for example. 
     The separator  44  is non-woven fabric made of polyolefin, or the like, for example. The separator  44  is impregnated with an electrolytic solution. The electrolytic solution is a potassium hydroxide (KOH) solution, or the like, for example. 
     Note that the bipolar battery  1  according to the present embodiment is an aqueous battery. An aqueous battery is a battery containing an aqueous solution as the electrolytic solution, and a battery containing an alkaline electrolytic solution as the electrolytic solution is included in the aqueous battery. 
       FIG. 4  is a perspective view showing each unit cell  10 . As shown in  FIG. 4 , the separator  44  is the largest in the unit battery  41 , the entire outer circumferential edge of the separator  44  outwardly protrudes from outer circumferential edges of the positive electrode  43  and the negative electrode  45 . 
     The seal member  42  is formed in a loop shape that surrounds the periphery of the unit battery  41 . The seal member  42  includes: a resin frame  50  in a loop shape; a resin frame  51  in a loop shape disposed in the inner side of the resin frame  50 ; and a gasket  52  disposed between the resin frame  50  and the resin frame  51 . 
     The gasket  52  is formed by a resin having a long-term high air-tightness and excellent in heat-resistance, chemical resistance, and electric insulation, and is formed by a polyarylene sulfide resin, a thermoplastic elastomer, or a resin containing a polyarylene sulfide resin, or the like, for example. 
     As shown in  FIG. 2 , each seal member  42  is tightly held between the two adjacent current collecting plates  40  in the stacking direction D 1  by a pressing force applied by the fastening tool  12  onto the stacked body  11 . A height of the gasket  52  is reduced to be lower than a height thereof in a natural state by the holding force applied from the two adjacent current collecting plates  40 , and each gasket  52  is in tight contact with the adjacent current collecting plates  40  in the stacking direction D 1 . 
     Since each gasket  52  is in tight contact with each corresponding current collecting plate  40 , the electrolytic solution of each unit battery  41  is suppressed from leaking out to the outside. The configuration of the seal member  42  is not limited to the configuration of including the resin frames  50 ,  51  and the gasket  52 . For example, the gasket  52  may be used as the seal member  42 , or a sealing material may be employed other than the gasket  52 . 
     Further, each unit cell  10  includes the seal members  53 ,  54  formed on the outer circumferential surfaces of the resin frame  50 . Each resin frame  50  is held between the two adjacent current collecting plates  40 G,  40 H in the stacking direction D 1 , and the seal member  53  is formed in a loop shape in a manner as to fill a corner formed by the current collecting plate  40 G on one side and the resin frame  50 . The seal member  54  is formed in a manner as to fill a corner formed by the current collecting plate  40 H on the other side and the resin frame  50 . This configuration promotes enhancement of sealing property of the electrolytic solution. 
       FIG. 5  is a plan view showing each unit cell  10 . Specifically, this is a plan view of the current collecting plate  40 , the seal member  42 , and others as viewed from a position apart therefrom in the stacking direction D 1 . In this  FIG. 5 , the negative electrode  45  is not illustrated. 
     As shown in this  FIG. 5 , each unit cell  10  includes the hydrophobic insulating film  55  formed on the upper surface  35  in a manner as to surround the periphery of the unit battery  41 . 
     The hydrophobic insulating film  55  is formed of a hydrophobic material, and is formed of a preferable hydrophobic material such as fluoropolymer or a similar material, for example. For example, the hydrophobic insulating film  55  is formed of a material realizing that a contact angle of the electrolytic solution in the hydrophobic insulating film  55  becomes 90° or more. 
     An outer circumferential edge of the hydrophobic insulating film  55  is located more outward than an outer circumferential edge of the separator  44 , and the outer circumferential edge of the separator  44  is located on the hydrophobic insulating film  55 . 
     Hence, even if the electrolytic solution tends to ooze out from the outer circumferential edge of the separator  44  onto the hydrophobic insulating film  55 , the hydrophobic insulating film  55  having a hydrophobic property repels the electrolytic solution. As a result, the electrolytic solution with which the separator  44  is impregnated becomes hard to leak out from the separator  44 , to thus suppress the electrolytic solution from reaching the seal member  42 . Accordingly, it is possible to suppress leakage of the electrolytic solution to the outside. 
     Note that it is not always essential that the outer circumferential edge of the separator  44  be in contact with the hydrophobic insulating film  55 , and the hydrophobic insulating film  55  may be located outside the separator  44 , as viewed in a plan view. 
     Each unit cell  10 , as shown in  FIG. 2 , includes the hydrophobic insulating film  56  that is formed on the lower surface  36  of each current collecting plate  40  in a manner as to surround the periphery of the unit battery  41 . 
     The above configured bipolar battery  1  is formed by alternately stacking the current collecting plates  40  each having the negative electrode  45  formed on the lower surface  36  thereof and the positive electrode  43  formed on the upper surface  35  thereof, and the seal members  42 , one by one on the upper surface of the pressing plate  20 , and thereafter fastening the stacked body  11  by the fastening tool  12 . At this time, it is necessary to arrange each current collecting plate  40  at a predetermined position. For this reason, in the bipolar battery  1  according to the present embodiment 1, as shown in  FIG. 5 , a cutout  57  is formed on the outer circumferential edge of each current collecting plate  40 . When the current collecting plates  40  are stacked, the respective current collecting plates  40  are stacked one by one such that the cutouts  57  overlap one another. The cutouts  57  function as a mark, and thus a round hole or a rectangular hole may be employed instead of the cutout  57 , and various other shapes may be employed as a cutout shape. 
     As aforementioned, the bipolar battery  1  according to the present embodiment  1  includes the unit batteries  41  on the upper surfaces  35  of the respective current collecting plates  40 , and the seal members  42  surrounding peripheries of the respective unit batteries  41 , and each of the seal members  42  is held between each two adjacent current collecting plates  40  by the pressing force from the fastening tool  12 , to thereby suppress leakage of the electrolytic solution. 
     Further, the fastening tool  12  does not close the stacked body  11 , so that circumferential surfaces of the stacked body  11  are exposed to the outside air, and the stacked body  11  can be directly cooled by cooling air or the like. In the present embodiment  2 , there will be described a configuration to provide heat insulating members between the stacked body and the pressing plates so as to reduce variation in temperature of the unit batteries at the uppermost position and the lowermost position, to thereby stabilize electric characteristics of the bipolar battery. 
       FIG. 6  is a cross sectional view showing a bipolar battery  1 A according to the embodiment  2 . As shown in  FIG. 6 , the bipolar battery  1 A includes the stacked body  11 , a heat insulating member  70  disposed between the stacked body  11  and the pressing plate  20 , and a heat insulating member  71  disposed between the stacked body  11  and the pressing plate  21 . 
     The stacked body  11  includes: a unit cell  10 A adjacent to the pressing plate  20 ; a unit cell  10 B adjacent to the pressing plate  21 ; and unit cells  10 C,  10 D,  10 E that are located in the vicinity of a middle part of the stacked body  11  in the stacking direction D 1 . 
     The heat insulating member  70  is disposed between the end surface  13  of the stacked body  11  and the pressing plate  20 . The heat insulating member  71  is disposed between the end surface  14  of the stacked body  11  and the pressing plate  21 . 
     Each of the heat insulating members  70 ,  71  is formed of polyurethane, polyethylene, a phenol resin, foamed styrene, glass wool, cellulose fiber, rock wool, or the like, and is also formed by a material having a heat insulation property and an electric insulation property. Each of the heat insulating members  70 ,  71  may be formed by a metallic plate, the above described heat insulating member, and a heat insulating member having an electric insulation property. In this case, the metallic plates are disposed on the pressing plates  20 ,  21  side and the heat insulating members are disposed on the stacked body  11  side. 
     The heat insulating member  70  electrically insulates the pressing plate  20  from the unit cell  10 A, and the heat insulating member  71  electrically insulates the pressing plate  21  from the unit cell  10 B. The stacked body  11  and the fastening tool  12  are electrically insulated from each other by the heat insulating members  70 ,  71 . Hence, the bipolar battery  1 A does not include the electric insulating members  29 ,  30  that are provided in the bipolar battery  1  according to the aforementioned embodiment. 
       FIG. 7  is a cross sectional view showing a bipolar battery  1 B according to a comparative example. In the bipolar battery  1 B shown in  FIG. 7 , each of the connecting shafts  26  is formed by an electrically insulating material, and the bipolar battery  1 B is not provided with the heat insulating member  70  and the heat insulating member  71 . When charging and discharging are performed in this bipolar battery  1 B, each unit battery  41  generates heat, and thus the temperature of each unit cell  10  is increased. 
     At this time, the unit cells  10 D,  10 E adjacent to the unit cell  10 C also generate heat; thus the temperature of the unit cell  10 C is likely to become the same temperature as those of the unit cells  10 D,  10 E. As a result, the unit cells  10  located at and near the middle part of the stacked body  11  in the stacking direction D 1  are unlikely to experience variation in temperature among them. 
     Battery characteristics such as charging characteristics, discharging characteristics, and battery capacity of each unit cell  10  vary depending on the temperature; therefore, the unit cells  10  located near the middle part of the stacked body  11  are more unlikely to experience variation in battery characteristics. 
     In the meantime, the temperatures of the unit cells  10 A,  10 B are more likely to vary by influence of the temperatures of the metallic pressing plates  20 ,  21 , and the temperatures of the pressing plates  20 ,  21  are more likely to vary by influence of the ambient temperature. As a result, the unit cells  10 A,  10 B are more likely to have variation in temperature thereof, and the unit cells  10 A,  10 B are also more likely to have variation in electric characteristics thereof. Consequently, the electric characteristics of the bipolar battery  1 B are more likely to vary by influence of the ambient environment. 
     In the meantime, in the bipolar battery  1 A according to the embodiment 2, as shown in  FIG. 6 , the heat insulating member  70  is disposed between the pressing plate  20  and the unit cell  10 A so as to reduce influence on the unit cell  10 A from the pressing plate  20  to be smaller. Similarly, the heat insulating member  71  is disposed between the pressing plate  21  and the unit cell  10 B so as to reduce influence on the unit cell  10 B from the pressing plate  21  to be smaller. 
     Through this, it is possible to suppress variation in electric performance of the unit cells  10 A,  10 B, to thus suppress variation in electric characteristics of the bipolar battery  1 B. 
     In the above example, the case in which both the heat insulating members  70 ,  71  are provided has been explained, but one of the heat insulating members  70 ,  71  may be provided. In this case, the electric insulating member  29  or the electric insulating member  30  is provided. In the present embodiment  3 , there will be described a configuration that for the sake of promoting enhancement of the heat dissipation of the stacked body  11 , each of the current collecting plates  40  is formed with a heat-dissipating portion greatly protruding from the seal member  42 , to thereby promote enhancement of the heat dissipation of the stacked body  11 . 
       FIG. 8  is a cross sectional view showing a bipolar battery  1 C according to the embodiment  3 . As shown in  FIG. 8 , the outer circumferential edge of each current collecting plate  40  is so formed as to protrude more outward than each seal member  42 . Of each current collecting plate  40 , a portion protruding more outward than the seal member  42  is readily cooled by the cooling air from the fan  5 , thus suppressing increase in temperature of each unit cell  10 . 
       FIG. 9  is a plan view showing each unit cell  10 . Specifically, this is a plan view of each unit cell  10 , as viewed from a position apart therefrom in the stacking direction D 1 . 
     As shown in  FIG. 9 , the seal member  42  is located in an inner side of the current collecting plate  40 , and a part of the current collecting plate  40  is formed to greatly protrude outwardly from the outer circumferential edge of the seal member  42 . 
     The seal member  42  is formed in a substantially rectangular shape. The outer circumferential edge of the seal member  42  includes a side surface  60  and a side surface  61  that are arranged in an X direction, and a side surface  62  and a side surface  63  that are arranged in a Y direction. 
     The current collecting plate  40  includes proximate portions  64 ,  65  extending along the side surfaces  62 ,  63 , heat-dissipating portions  66 ,  67  greatly protruding outward from the side surfaces  60 ,  61 , and insulating films  68 ,  69  covering the heat-dissipating portions  66 ,  67 . 
     Respective distances between the outer circumferential edges of the heat-dissipating portions  66 ,  67  and the side surfaces  60 ,  61  are longer than respective distances between the outer circumferential edges of the proximate portions  64 ,  65  and the side surfaces  62 ,  63 , and respective exposed areas of the heat-dissipating portions  66 ,  67  are greater than respective exposed areas of the proximate portions  64 ,  65 . Accordingly it is possible to favorably dissipate heat from the heat-dissipating portions  66 ,  67 . 
     As shown in  FIG. 10 , the entire outer circumferential edge of each current collecting plate  40  may be configured to protrude from the seal member  42 . 
     In  FIG. 9 , the insulating films  68 ,  69  are so formed as to cover front surfaces of the heat-dissipating portions  66 ,  67  so that mutual electric insulation between the adjacent heat-dissipating portions  66 ,  67  in the stacking direction D 1  can be secured even when these heat-dissipating portions  66 ,  67  come into contact with each other. Formation of the insulating film  68  is not limited to the case of applying the insulating film  68  onto the entire surfaces of the heat-dissipating portions  66 ,  67 , but the insulating film  68  may be formed on the outer circumferential edge of the current collecting plate  40  or the outer circumferential edges of the heat-dissipating portions  66 ,  67  and the peripheries thereof, for example. 
     As long as the insulating films  68 ,  69  are formed on portions of the current collecting plate  40  where the current collecting plate  40  comes into contact with the other current collecting plate  40  adjacent in the stacking direction D 1  when the heat-dissipating portions  66 ,  67  are warped, it is possible to secure the electric insulation between the adjacent current collecting plates  40 . 
     The insulating film  68  can be formed by various methods such as application of an insulating tape, and caulking, thermal-spraying application, or coating of an insulating material, or resin-molding. In the embodiment 4, a configuration of suppressing short-circuit between the adjacent current collecting plates  40  in the stacking direction D 1  inside each seal member  42  is described. 
       FIG. 11  is a cross sectional view showing a bipolar battery  1 D according to the embodiment  4 . As shown in  FIG. 11 , a stepped portion  80  is formed on an inner circumferential surface of each seal member  42  so that the outer circumferential edge of each separator  44  is placed on this stepped portion  80 . 
       FIG. 12  is a cross sectional view showing a configuration of the stepped portion  80  and the periphery thereof. As shown in  FIG. 12 , the resin frame  51  includes: a frame portion  81  extending along an inner circumferential surface of the gasket  52 ; and the stepped portion  80  formed on an inner circumferential surface of the frame portion  81 . 
     The stepped portion  80  is disposed on the upper surface  35  of the current collecting plate  40 , and the outer circumferential edge of the separator  44  is placed on the stepped portion  80  so as to suppress the separator  44  from coming into contact with the positive electrode  43 . 
     If each positive electrode  43  is formed by the active material supporter, needle-like burrs might be formed on the circumferential surface of the positive electrode  43  when the active material supporter is sheared. If the separator  44  comes into contact with the burrs, the burrs might break through this separator  44 . 
     However, in the bipolar battery  1 D, each separator  44  is placed on each corresponding stepped portion  80 , to thereby suppress the separator  44  from coming into contact with the burrs. 
       FIG. 13  is a plan view showing the positive electrode  43 , the seal member  42 , and the current collecting plate  40 . In this  FIG. 13 , the negative electrode  45  and the separator  44  are not illustrated. In  FIG. 13 , the stepped portion  80  is formed in a loop shape. Here, a portion where the positive electrode  43  is placed is a placement part of the unit battery  41 . In the upper surface  35  of each current collecting plate  40 , a portion located between the outer circumferential edge of the positive electrode  43  and the inner circumferential edge of the seal member  42  is exposed. 
       FIG. 14  is a plan view showing the separator  44 , the positive electrode  43 , the seal member  42 , and the current collecting plate  40 . As shown in this  FIG. 14 , the outer circumferential edge of the separator  44  is placed on the stepped portion  80 , and in the upper surface  35  of the current collecting plate  40 , a portion located between the positive electrode  43  and the seal member  42  is covered by the separator  44 . 
       FIG. 15  is a cross sectional view showing a configuration of the unit cell  10 A and the periphery thereof. As shown in  FIG. 15 , the unit cell  10 G is provided on the upper surface side of the unit cell  10 A. 
     When the electrolytic solution of the unit cell  10 G is decomposed, a gas might be generated; and at the time of overcharge, for example, electrolysis of water contained in the electrolytic solution is caused as a side reaction of the electrode; thus a gas (hydrogen) might be generated. 
     Since the gas (hydrogen) is suppressed from leaking out to the outside by the seal member  42  of the unit cell  10 G, an inner pressure inside the unit cell  10 G is increased, the current collecting plate  40 G is deformed to swell out, so that the current collecting plate  40 G and a current collecting plate  40 A might come to closer to each other. 
     Specifically, of the current collecting plate  40 G, a portion located between a seal member  42 G and a positive electrode  43 G is not supported by a unit battery  41 A, and thus this portion might be deformed to swell downward. 
     On the other hand, a separator  44 A of the unit cell  10 A is disposed so as to cover the upper surface  35  of the current collecting plate  40 A located between a positive electrode  43 A and the seal member  42 . 
     Hence, even if the current collecting plate  40 G is deformed in the above manner, the separator  44 A suppresses that the current collecting plate  40 G and the current collecting plate  40 A come into direct contact with each other, thereby suppressing occurrence of short-circuit between the current collecting plate  40 A and the current collecting plate  40 G. 
     In this manner, in the bipolar battery  1 D according to the present embodiment  4 , even if the inner pressure inside each unit cell  10  becomes increased, the current collecting plates  40  of the adjacent unit cells  10  in the stacking direction D 1  can be suppressed from coming into contact with each other to be short-circuited. In the present embodiment  5 , there will be described a configuration that in spite of occurrence of a phenomenon such as deformation of the current collecting plate  40 , which encourages separation of the positive electrode  43  and the negative electrode  45  from the current collecting plate  40 , a tight contact of the positive electrode  43  and the negative electrode  45  to the current collecting plates  40  is secured. 
       FIG. 16  is a cross sectional view showing a part of a bipolar battery  1 E according to the embodiment 5. As shown in  FIG. 16 , a rough surface portion  82 G is formed on the upper surface  35  of the current collecting plate  40 G, and a rough surface portion  83 G is formed on the lower surface  36 . 
     The rough surface portion  82 G is formed with the positive electrode  43 G, and the rough surface portion  83 G is formed with a negative electrode  45 A. 
       FIG. 17  is a cross sectional view showing a configuration of the rough surface portions  82 G,  83 G of the current collecting plate  40 G and the periphery thereof; and  FIG. 18  is a cross sectional view showing the current collecting plate  40 H provided with no rough surface portions  82 G,  83 G. 
     In  FIG. 17  and  FIG. 18 , the rough surface portions  82 G,  83 G include multiple recesses and projections, and a height H 1  of each projection of the rough surface portion  82 G is higher than a height H 2  of each projection of the rough surface portion  83 G. 
     Since the rough surface portion  82 G is provided with the multiple recesses and projections, a contact area between the positive electrode  43 G and a rough surface portion  82 G is greater than a contact area between the current collecting plate  40 H and the positive electrode  43 G. Similarly, a contact area between the rough surface portion  83 G and the negative electrode  45 A is greater than a contact area between the current collecting plate  40 H and the negative electrode  45 A. As a result, an adhesive strength between the positive electrode  43 G and the rough surface portion  82 G is greater than an adhesive strength between the current collecting plate  40 H and the positive electrode  43 G; and an adhesive strength between the rough surface portion  83 G and the negative electrode  45 A is greater than an adhesive strength between the current collecting plate  40 H and the negative electrode  45 A. 
     Through this, even if the current collecting plate  40 G becomes warped, or the like, the positive electrode  43 G and the negative electrode  45 G can be suppressed from being separated from the current collecting plate  40 G. In order to enhance the tight contact between the positive electrode  43 G and the current collecting plate  40 G and the tight contact between the negative electrode  45 A and the current collecting plate  40 G, a positive electrode material and a negative electrode material may be thermal-sprayed or the positive electrode material may be sintered so as to enhance the tight contact. 
     The projections of the rough surface portion  82 G come into the positive electrode  43 , a current collecting distance between the positive electrode  43 G and the current collecting plate  40 G is shorter than a current collecting distance between the current collecting plate  40 H and the positive electrode  43 G; thus an electric resistance of the positive electrode  43 G can be reduced to be lower. Similarly, the electric resistance of the negative electrode  45 A can be reduced to be lower by the rough surface portion  83 G. 
     Here, the positive electrode  43 G contains nickel hydroxide as the positive electrode active material. Nickel hydroxide has a lower electric conductivity. Hence, if the nickel positive electrode becomes thicker, an electric resistance in the thickness direction becomes increased; consequently, a desired battery performance might not be obtained. 
     In the bipolar battery according to the embodiment 5, the height H 1  of each projection of the rough surface portion  82 G is higher than the height H 2  of each projection of the rough surface portion  83 G so that the positive electrode  43 G partially has a thinner thickness, to thereby attain reduction in electric resistance of the positive electrode  43 G. 
     The aforementioned rough surface portions  82 G,  83 G may be formed through press working such as embossing, physical surface treatment such as shot blasting, chemical surface treatment such as etching, electroplating treatment such as dispersal plating, etc., for example. 
     In an example shown in  FIG. 17 , there has been described the example of providing both the rough surface portion  82 G and the rough surface portion  83 G, but one of the rough surface portion  82 G and the rough surface portion  83 G may be provided, instead. 
       FIG. 19  is a cross sectional view showing a part of a bipolar battery  1 F according to the present embodiment  5 . As shown in  FIG. 19 , an electric conductive layer  84  is formed on the upper surface  35  of the current collecting plate  40 G, and the positive electrode  43 G is formed on this electric conductive layer  84 . Similarly, an electric conductive layer  85  is formed on the lower surface  36 , and the negative electrode  45 A is formed on this electric conductive layer  85 . 
     The electric conductive layers  84 ,  85  are made of electric conductive carbon, and carbon black, CNT (carbon nanotubes or a material including carbon nanotubes and fullerene) or the like may be employed. The electric conductive layers  84 ,  85  are formed by blending carbon black or CNT with a binder and water, and applying this on the surface of the current collecting plate  40 G through screen printing or the like, for example. 
     An electric resistance of the positive electrode  43 G is high, so that a contact resistance between the positive electrode  43 G and the current collecting plate  40 G is likely to be high. On the other hand, by forming the electric conductive layer  84  between the positive electrode  43 G and the current collecting plate  40 G, it is possible to reduce the contact resistance between the positive electrode  43 G and the current collecting plate  40 G. In addition, by bringing the positive electrode  43 G and the current collecting plate  40 G to adhere to each other via the electric conductive layer  84 , it is possible to promote enhancement of the tight contact of the positive electrode  43 . 
     Similarly, by the electric conductive layer  85 , it is possible to reduce the contact resistance between the negative electrode  45 A and the current collecting plate  40 G, while it is possible to promote enhancement of the tight contact of the negative electrode  45 A. In an aqueous battery such as a nickel hydrogen battery, for example, at the charging time, electrolysis of water contained in the electrolytic solution is caused as the side reaction of the electrode, so that the electrolytic solution might be exhausted. In the embodiment  6 , a bipolar battery promoting suppression of exhaustion of the electrolytic solution will be described. 
       FIG. 20  is a cross sectional view showing a part of a bipolar battery  1 G according to the present embodiment 6. As shown in this  FIG. 20 , a recess  90 G is formed in an upper surface  35 G of the current collecting plate  40 G of the unit cell  10 G. The recess  90 G is located between the placement position of the unit battery  41 G (the contact portion between the positive electrode  43 A and the upper surface  35 G) and the seal member  42 G. An electrolytic solution  91 G is stored in the recess  90 G. 
     The electrolytic solution  91 G may be stored in the recess  90 G in a state in which a liquid holding material such as a gel polymer sponge is permeated with the electrolytic solution  91 G, for example. 
     The outer circumferential edge of a separator  44 G is disposed on the stepped portion  80 . The separator  44 G includes a bent portion  92  that is bent in a manner as to come out between the positive electrode  43 G and the negative electrode  45 G, and then go into the recess  90 G, and thereafter, go toward the stepped portion  80 . An apex of the bent portion  92  is soaked in an electrolytic solution  91 G. 
     Even if the electrolytic solution with which the separator  44 G is impregnated is decomposed, the electrolytic solution  91 G in the recess  90 G is supplied to the separator  44 G, thus suppressing exhaustion of the electrolytic solution in the separator  44 G. 
     By configuring the other unit cells  10  in the same manner as that of the unit cell  10 G, in the bipolar battery  1 G, it is possible to suppress occurrence of exhaustion of the electrolytic solution. 
       FIG. 21  is a partial cross sectional view showing a variation of the bipolar battery  1 G. As shown in the  FIG. 21 , the outer circumferential edge of the separator  44 G may be thermal-welded in the recess  90 G. 
     In the aforementioned embodiments 1 to 6, there has been described the case in which the plan shape of each unit cell  10  is a rectangular shape, but the shape of each unit cell  10  may be formed in a circular shape as with that of a bipolar battery  1 H of  FIG. 22 ; and various shape may be employed. 
     As aforementioned, the embodiments 1 to 6 have been described, but the configurations described in the respective embodiments 1 to 6 may be combined with one another. 
     For example, the heat insulating members  70 ,  71  described in the embodiment  2  may be combined to the bipolar battery  1  of the embodiment 1. In addition, the configuration of the heat-dissipating portions  66 ,  67 , and the configuration of the insulating film  68  described in the embodiment 3 may be combined to the configuration of the bipolar battery  1  or  1 A. 
     The shape of the separator  44  and the configuration of the stepped portion  80  described in the embodiment 4 may be applied to the configuration of the bipolar battery  1 ,  1 A, or  1 C. 
     The configuration of the rough surface portions  82 G,  83 G and the configuration of the electric conductive layer  84  described in the embodiment 5 may be applied to the configurations of the bipolar batteries  1  to  1 D. 
     The configuration of the recess  90 G and others described in the embodiment 6 may be applied to the configurations of the bipolar batteries  1  to  1 E. 
     The embodiments described above are merely examples in all aspects and should not be considered to be limiting. It is intended that the scope of the present disclosure is defined not by the description presented above but by the claims below and includes meanings equivalent to the scope of the claims and all modifications within the scope. 
     The bipolar battery disclosed in the present disclosure may be applied to an electric vehicle or a fuel cell vehicle such as a hybrid vehicle and an electric vehicle, for example.