Patent Publication Number: US-2023155254-A1

Title: Battery module

Description:
This nonprovisional application is based on Japanese Patent Application No. 2021-187141 filed on Nov. 17, 2021, with the Japan Patent Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a battery module. 
     Description of the Background Art 
     For example, Japanese Patent Laying-Open No. 2017-216095 discloses a battery module including: a battery cell stack formed by stacking a plurality of battery cells; and a plurality of bus bars that each connect between positive electrode external terminal and negative electrode external terminal of battery cells adjacent to each other in the stacking direction. Each of the bus bars is provided with a fragile portion, which is a portion weak in compressive strength in the stacking direction of the battery cells. 
     Japanese Patent Laying-Open No. 2012-59451 discloses a bus bar module including: a plurality of bus bars that each electrically connects between adjacent power storage elements; a plurality of bus bar holding portions that hold the plurality of bus bars; and a coupling portion that couples adjacent bus bar holding portions to each other. The coupling portion is provided with a notch such that the cross sectional area of a predetermined portion thereof is smaller than that of a portion adjacent to the predetermined portion. 
     Japanese Patent Laying-Open No.  2011 - 253735  discloses an battery pack including: a plurality of unit cells each having a gas-discharge valve and stacked in a predetermined direction; and a bus bar module into which a plurality of bus bars that connect between unit cells adjacent to each other in the predetermined direction are unitized. The bus bar module is provided with a fragile portion, which is melted by heat when gas is discharged from the gas-discharge valve. 
     SUMMARY OF THE INVENTION 
     As disclosed in each of the pieces of the patent literature described above, there has been known a battery module including a plurality of battery cells stacked in one direction, wherein a bus bar is used as means for electrically connecting the plurality of battery cells together. 
     On the other hand, in some situations such as maintenance of the battery module, one may wish to disassemble the battery module by disconnecting a plurality of battery cells connected by a bus bar. However, in the conventional battery module, the disassembling of the battery module is not sufficiently taken into consideration in terms of connection made between the plurality of battery cells by the bus bar. 
     In view of the above, it is an object of the present invention to solve the above-described problem and provide a battery module allowing for excellent workability at the time of disassembling. 
     A battery module according to the present invention includes: a plurality of battery cells stacked in a predetermined direction; and a plurality of bus bars that electrically connect the plurality of battery cells together. The plurality of bus bars includes a first bus bar extending between a first battery cell and a second battery cell of the plurality of battery cells, the first battery cell and the second battery cell being adjacent to each other in the predetermined direction. The first bus bar has a first base portion connected to the first battery cell, a second base portion connected to the second battery cell, and a rising portion that has a shape to rise from the first base portion and the second base portion and that connects between the first base portion and the second base portion. A fragile portion is provided in a root region of the rising portion. 
     According to the battery module thus configured, by breaking the fragile portion, an operator can disconnect the connection made between the first base portion and the second base portion by the rising portion, thereby separating the first battery cell and the second battery cell. In this case, since the fragile portion is provided in the root region of the rising portion, the operator can readily break the fragile portion. Thus, workability at the time of disassembling the battery module can be improved. 
     Preferably, the fragile portion has a thin structure in which a thickness of the rising portion is locally small. 
     According to the battery module thus configured, the operator can readily break the fragile portion having such a thin structure. 
     Preferably, restraint force along the predetermined direction is applied to the plurality of battery cells. A thickness direction of the rising portion at the fragile portion is parallel to the predetermined direction. 
     According to the battery module thus configured, when the operator applies, to the rising portion, force in the thickness direction of the rising portion in order to break the fragile portion having the thin structure, the direction in which the force is applied is parallel to the direction in which the restraint force is applied to the plurality of battery cells. Therefore, the restraining force serves to suppress the postures of the first battery cell and the second battery cell from leaning in the direction of the force applied to the rising portion, with the result that the force can be more efficiently transmitted to the fragile portion. Thus, the operator can break the fragile portion more readily. 
     Preferably, the fragile portion is constituted of a notched structure or a perforated structure, the notched structure being a structure in which a notch is provided in a width direction of the rising portion, the width direction of the rising portion being orthogonal to a rising direction of the rising portion and a thickness direction of the rising portion, the perforated structure being a structure in which cut portions each extending through the rising portion in the thickness direction of the rising portion are intermittently provided in a form of a line. 
     According to the battery module thus configured, the operator can readily break the fragile portion constituted of the notched structure or the perforated structure. 
     Preferably, the fragile portion is provided to overlap with a predetermined plane that constitutes a boundary between the first battery cell and the second battery cell. The first bus bar has a symmetrical shape with respect to the predetermined plane. 
     According to the battery module thus configured, the first has bar is supported in a balanced manner by the first battery cell and the second battery cell on both sides beside the fragile portion. Therefore, when the operator applies force to the rising portion in order to break the fragile portion, the first bus bar is suppressed from being deformed, with the result that the force can be more efficiently transmitted to the fragile portion. Thus, the operator can break the fragile portion more readily. 
     Preferably, the rising portion and includes a dividable portion that connects between the first base portion and the second base portion and that is dividable from the first base portion and the second base portion with the fragile portion serving as a boundary. 
     According to the battery module thus configured, the operator can efficiently apply force to the rising portion while holding the dividable portion until the fragile portion becomes broken. Thus, the operator can break the fragile portion more readily. 
     Preferably, the rising portion further includes a first remaining portion and a second remaining portion, the first remaining portion remaining on the first base portion side in a state in which the dividable portion is divided from the first base portion and the second base portion, the second remaining portion remaining on the second base portion side and being placed on the first remaining portion in the state in which the dividable portion is divided from the first base portion and the second base portion. 
     According to the battery module thus configured, after disconnecting the connection made between the first base portion and the second base portion by the rising portion so as to separate the first battery cell and the second battery cell, the disassembled battery module may be assembled again. Even in such a case, the first base portion and the second base portion can be connected to each other by using the first remaining portion and the second remaining portion that are placed on each other. 
     Preferably, the battery module includes a plurality of battery cell units arranged side by side in the predetermined direction and fed with restraining force along the predetermined direction. Each of the battery cell units has the plurality of battery cells arranged side by side continuously in the predetermined direction, and a holding member that collectively holds the plurality of battery cells arranged side by side continuously in the predetermined direction. The first bus bar electrically connects between battery cells adjacent to each other in the predetermined direction between a first battery cell unit of the plurality of battery cell units and a second battery cell unit of the plurality of battery cell units, the second battery cell unit being adjacent to the first battery cell unit in the predetermined direction. The plurality of bus bars further include a second bus bar that electrically connects between battery cells adjacent to each other in the predetermined direction in each of the battery cell units. 
     According to the battery module thus configured, the first battery cell unit and the second battery cell unit can be separated by a simple operation. 
     Preferably, each of the battery cells has an output density of 8000 W/L or more. 
     According to the battery module thus configured, workability at the time of disassembling can be improved in the battery module including the battery cells each having a high output density of 8000 W/L or more. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view showing a battery module according to an embodiment of the present invention. 
         FIG.  2    is a perspective view showing an internal structure of the battery module in  FIG.  1   . 
         FIG.  3    is a perspective view showing a battery cell unit included in the battery module in  FIG.  1   . 
         FIG.  4    is a perspective view showing a battery cell included in the battery cell unit in  FIG.  3   . 
         FIG.  5    is an exploded assembly diagram showing a connection structure for a plurality of battery cells. 
         FIG.  6    is a perspective view showing a connection structure for battery cells between adjacent battery cell units. 
         FIG.  7    is a perspective view showing a connection structure for battery cells in a battery cell unit. 
         FIG.  8    is a diagram showing the connection structure for the battery cells when viewed in a direction indicated by an arrow VIII in  FIG.  6   . 
         FIG.  9    is a perspective view showing a first form change of the connection structure for the battery cells in  FIG.  6   . 
         FIG.  10    is a diagram showing the connection structure for the battery cells when viewed in a direction indicated by an arrow X in  FIG.  9   . 
         FIG.  11    is a perspective view showing a second form change of the connection structure for the battery cells in  FIG.  6   . 
         FIG.  12    is a diagram showing a first modification of a fragile portion in  FIG.  8   . 
         FIG.  13    is a diagram showing a second modification of the fragile portion in  FIG.  8   . 
         FIG.  14    is a perspective view showing a modification of a first bus bar in  FIG.  6   . 
         FIG.  15    is a diagram showing the first bus bar when viewed in a direction indicated by an arrow XV in  FIG.  14   . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described with reference to figures. It should be noted that in the figures referred to below, the same or corresponding members are denoted by the same reference characters. 
       FIG.  1    is a perspective view showing a battery module according to an embodiment of the present invention.  FIG.  2    is a perspective view showing an internal structure of the battery module in  FIG.  1   .  FIG.  3    is a perspective view showing a battery cell unit included in the battery module in  FIG.  1   . 
     Referring to  FIGS.  1  to  3   , a battery module  100  is used as a power supply for driving a vehicle such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or a battery electric vehicle (BEV). 
     In the present specification, for convenience of description of the structure of battery module  100 , the “Y axis” represents an axis extending in parallel with a stacking direction of a plurality of below-described battery cells  11 , the “X axis” represents an axis extending in a direction orthogonal to the Y axis, and the “Z axis” represents an axis extending in a direction orthogonal to the Y axis and the X axis. An obliquely rightward upward direction in the plane of sheet of  FIG.  1    is “+Y axis direction”, and an obliquely leftward downward direction in the plane of sheet of  FIG.  1    is “−Y axis direction”. An obliquely rightward downward direction in the plane of sheet of  FIG.  1    is “+X axis direction” and an obliquely leftward upward direction in the plane of sheet of  FIG.  1    is “−X axis direction”. An upward direction in the plane of sheet of  FIG.  1    is “+Z axis direction” and a downward direction in the plane of sheet of  FIG.  1    is “−Z axis direction”. 
     Typically, battery module  100  is mounted on a vehicle in such a posture that the +Z axis direction corresponds to the upward direction and the −Z axis direction corresponds to the downward direction. 
     First, an overall structure of battery module  100  will be described. As shown in  FIG.  1   , battery module  100  includes a plurality of battery cell units  21  ( 21 A,  21 B,  21 C,  21 D,  21 E,  21 F) and a restraint member  41 . 
     The plurality of battery cell units  21  are stacked in the Y axis direction. Battery cell unit  21 A, battery cell unit  21 B, battery cell unit  21 C, battery cell unit  21 D, battery cell unit  21 E, and battery cell unit  21 F are arranged side by side in this order from the negative side to the positive side in the Y axis direction. It should be noted that the number of battery cell units  21  included in battery module  100  is not particularly limited as long as two or inure battery cell units  21  are included. 
     The plurality of battery cell units  21  are collectively held by restraint member  41 . Restraint member  41  applies, to the plurality of battery cell units  21 , restraint force along the Y axis direction. Restraint member  41  has a pair of end plates  42  ( 42 P,  42 Q), a pair of first restraint bands  43 , and a second restraint band (not shown). 
     The pair of end plates  42  are disposed on both sides beside the plurality of battery cell units  21  stacked in the Y axis direction. End plate  42 P is disposed to face battery cell unit  21 A in the Y axis direction. End plate  42 Q is disposed to face battery cell unit  21 F in the Y axis direction. Each of end plates  42  is composed of a plate material having a thickness direction corresponding to the Y axis direction. 
     The pair of first restraint bands  43  are disposed on both sides beside the plurality of battery cell units  21  in the X axis direction. The second restraint band (not shown) is provided at a position facing the plurality of battery cell units  21  in the Z axis direction. Each of first restraint bands  43  and the second restraint band extends in the Y axis direction. An end portion of each of first restraint hands  43  and the second restraint band in the −Y axis direction is connected to end plate  42 P. An end portion of each of first restraint bands  43  and the second restraint band in the +Y axis direction is connected to end plate  42 Q. 
     Each of first restraint bands  43  is provided with a plurality of openings  44 . The plurality of openings  44  are provided at intervals in the Y axis direction, and each of openings  44  is constituted of a through hole extending through first restraint band  43  in the X axis direction. Opening  44  is provided to expose ventilation ports  32  provided in a case body  31  described later. 
     Battery module  100  further has a pair of collective terminals  91  ( 91   p ,  91   q ), a wiring member  92 , a plurality of voltage detection wires  96 , and an exhaust duct  93 . 
     The pair of collective terminals  91  are disposed on both sides beside the plurality of battery cell units  21  stacked in the Y axis direction. Collective terminal  91   p  is provided at a position overlapping with end plate  42 P when viewed in the Z axis direction. Collective terminal  91   q  is provided at a position overlapping with end plate  42 Q when viewed in the Z axis direction. Each of collective terminals  91  is a terminal for connecting battery module  100  to an external wiring such as a cable disposed outside battery module  100 . 
     Wiring member  92  is provided at a position facing the plurality of battery cell units  21  in the Z axis direction. Wiring member  92  is disposed opposite to the second restraint band (not shown) with the plurality of battery cell units  21  being interposed therebetween. Wiring member  92  extends, in the Y axis direction, through the central portions of battery cell units  21  in the X axis direction. Wiring member  92  is composed of, for example, a flexible printed circuit board. The plurality of voltage detection wires  96  extend from wiring member  92  and are respectively connected to a plurality of below-described bus bars  50 . 
     Exhaust duct  93  extends in the Y axis direction. Exhaust duct  93  extends at a position overlapping with wiring member  92  when viewed in the Z axis direction. Exhaust duct  93  is disposed between each of the plurality of battery cell units  21  and wiring member  92  in the Z axis direction. 
     As shown in  FIGS.  2  and  3   , each of battery cell units  21  has a plurality of battery cells  11  and a holding member  30 . 
     Battery cell unit  21  has four battery cells  11  ( 11   a ,  11   b ,  11   c ,  11   d ). Battery cell unit  21  has an even number of battery cells  11 . It should be noted that the number of battery cells  11  included in each battery cell unit  21  is not particularly limited as long as two or more battery cells  11  are included. An odd number of battery cells  11  may be included. 
     In each battery cell unit  21 , i.e., in each of battery cell unit  21 A, battery cell unit  21 B, battery cell unit  21 C, battery cell unit  21 D, battery cell unit  21 E, and battery cell unit  21 F, the plurality of battery cells  11  are arranged side by side continuously in the Y axis direction. Battery cell  11   a , battery cell  11   b , battery cell  11   c , and battery cell  11   d  are arranged side by side in this order from the negative side to the positive side in the Y axis direction. 
     The stacking direction of the plurality of battery cells  11  in each battery cell unit  21  is the same as the stacking direction of the plurality of battery cell units  21 . Restraint member  41  applies, to the plurality of battery cells  11 , restraint force along the Y axis direction. 
     Holding member  30  collectively holds the plurality of battery cells  11  ( 11   a ,  11   b ,  11   c ,  11   d ). Holding member  30  includes case body  31 . Case body  31  has an external appearance having a rectangular parallelepiped shape. The plurality of battery cells  11  are accommodated in case body  31 . 
     Case body  31  is provided with the plurality of ventilation ports  32 . The plurality of ventilation ports  32  are provided in the both side surfaces of case body  31  orthogonal to the X axis direction. Each of ventilation ports  32  is constituted of a through hole extending through case body  31  in the X axis direction. Ventilation port  32  is provided as a path for introducing cooling air into a space between battery cells  11  adjacent to each other in the Y axis direction and discharging the cooling air from the space. 
       FIG.  4    is a perspective view showing a battery cell included in the battery cell unit in  FIG.  3   .  FIG.  5    is an exploded assembly diagram showing a connection structure for a plurality of battery cells. 
     Referring to  FIGS.  4  and  5   , battery cell  11  is a lithium ion battery. Battery cell  11  has an output density of 8000 W/L or more. Battery cell  11  has a prismatic shape and has a thin plate shape in the form of a rectangular parallelepiped. The plurality of battery cells  11  are stacked such that the Y axis direction corresponds to the thickness direction of each battery cell  11 . 
     Each of battery cells  11  has an exterior package  12 . Exterior package  12  is constituted of a housing having a rectangular parallelepiped shape, and forms the external appearance of battery cell  11 . An electrode assembly and an electrolyte solution are accommodated in exterior package  12 . 
     Exterior package  12  has a first side surface  13 , a second side surface  14 , and a third side surface  15 . Each of first side surface  13  and second side surface  14  is constituted of a flat surface orthogonal to the Y axis direction. First side surface  13  and second side surface  14  are oriented oppositely in the Y axis direction. Each of first side surface  13  and second side surface  14  has the largest area among the areas of the plurality of side surfaces of exterior package  12 . Each of first side surface  13  and second side surface  14  has a rectangular shape when viewed in the Y axis direction. Each of first side surface  13  and second side surface  14  has a rectangular shape in which the X axis direction corresponds to the long-side direction and the Z axis direction corresponds to the short-side direction when viewed in the Y axis direction. Third side surface  15  is constituted of a flat surface orthogonal to the Z axis direction. Third side surface  15  is oriented in the +Z axis direction. 
     Battery cell  11  further includes a gas-discharge valve  17 . Gas-discharge valve  17  is provided in third side surface  15 . When internal pressure of exterior package  12  becomes more than or equal to a predetermined value due to gas generated inside exterior package  12 , gas-discharge valve  17  discharges the gas to the outside of exterior package  12 . The gas from gas-discharge valve  17  flows through exhaust duct  93  in  FIG.  1    and is discharged to the outside of battery module  100 . 
     Battery cell  11  further has electrode terminals  16  including a pair of a positive electrode terminal  16 P and a negative electrode terminal  16 N. Each of electrode terminals  16  is composed of a metal. Electrode terminal  16  is provided on third side surface  15 . Positive electrode terminal  16 P and negative electrode terminal  16 N are provided to be separated from each other in the X axis direction. Positive electrode terminal  16 P and negative electrode terminal  16 N are provided beside wiring member  92  and exhaust duct  93  in the X axis direction. 
     The plurality of battery cells  11  are stacked such that first side surfaces  13  of battery cells  11 ,  11  adjacent to each other in the Y axis direction face each other and second side surfaces  14  of battery cells  11 ,  11  adjacent to each other in the Y axis direction face each other. Thus, positive electrode terminals  16 P and negative electrode terminals  16 N are alternately arranged in the Y axis direction in which the plurality of battery cells  11  are stacked. 
     It should be noted that when an odd number of battery cells  11  are included in battery cell unit  21 , the posture of battery cell unit  21  may be turned by 180° with respect to the Z axis between battery cell units  21  adjacent to each other in the Y axis direction. 
     Next, a connection structure for the plurality of battery cells  11  will be described. Referring to  FIGS.  1  to  5   , battery module  100  further has the plurality of bus bars  50 . Each of bus bars  50  is composed of an electric conductor. The plurality of bus bars  50  are provided to electrically connect the plurality of battery cells  11  of battery module  100  together. 
     Each of bus bars  50  extends in the Y axis direction. Bus bar  50  has ends that both extend in the Y axis direction and that are connected to battery cells  11 ,  11  adjacent to each other in the Y axis direction. Bus bar  50  is provided between battery cells  11 ,  11  adjacent to each other in the Y axis direction so as to connect positive electrode terminal  16 P and negative electrode terminal  16 N arranged side by side in the Y axis direction. The plurality of battery cells  11  are electrically connected together in series by the plurality of bus bars  50 . 
       FIG.  6    is a perspective view showing a connection structure for battery cells between adjacent battery cell units.  FIG.  7    is a perspective view showing a connection structure for battery cells in a battery cell unit. 
     Referring to  FIGS.  5  to  7   , the plurality of bus bars  50  include one or more first bus bars  51  and one or more second bus bars  52 . In the present embodiment, the plurality of bus bars  50  include a plurality of first bus bars  51  and a plurality of second bus bars  52 . 
     As shown in  FIGS.  5  and  6   , each of first bus bars  51  extends between first battery cell  11   d  and second battery cell  11   a  of the plurality of battery cells  11 , first battery cell  11   d  and second battery cell  11   a  being adjacent to each other in the Y axis direction. First bus bar  51  electrically connects between battery cells  11 ,  11  adjacent to each other in the Y axis direction between a first battery cell unit of the plurality of battery cell units  21  and a second battery cell unit of the plurality of battery cell units  21 , the second battery cell unit being adjacent to the first battery cell unit in the Y axis direction. 
     First bus bar  51  has a first base portion  226 , a second base portion  221 , and a rising portion  231 . First base portion  226  is connected to first battery cell  11   d . Second base portion  221  is connected to second battery cell  11   a . Rising portion  231  has a shape to rise from first base portion  226  and second base portion  221 . Rising portion  231  connects between first base portion  226  and second base portion  221 . 
     For explanation in the range shown in  FIG.  6   , battery cell unit  21 B corresponds to the first battery cell unit, battery cell unit  21 C corresponds to the second battery cell unit, battery cell  11   d  in battery cell unit  21 B corresponds to the first battery cell, and battery cell  11   a  in battery cell unit  21 C corresponds to the second battery cell. 
     First base portion  226  is connected to negative electrode terminal  16 N of battery cell lid in battery cell unit  21 B. Second base portion  221  is connected to positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C. Between battery cell units  21 B,  21 C, first bus bar  51  electrically connects negative electrode terminal  16 N of battery cell  11   d  in battery cell unit  21 B to positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C. 
     As shown in  FIGS.  5  and  7   , in each battery cell unit  21 , second bus bar  52  electrically connects between battery cells  11 ,  11  adjacent to each other in the Y axis direction. For explanation in a range shown in  FIG.  7   , second bus bar  52  electrically connects negative electrode terminal  16 N of battery cell  11   b  to positive electrode terminal  16 P of battery cell  11   c  in battery cell unit  21 C. 
       FIG.  8    is a diagram showing the connection structure for the battery cells when viewed in a direction indicated by an arrow VIII in  FIG.  6   . The following describes a more specific structure of first bus bar  51  while focusing on the ranges shown in  FIGS.  6  and  8   . 
     Referring to  FIGS.  6  and  8   , first bus bar  51  is formed by combining a first bus-bar-divided body  211  and a second bus-bar-divided body  212 . 
     First bus-bar-divided body  211  and second bus-bar-divided body  212  are composed of electric conductors (metal plates) separated from each other. First bus-bar-divided body  211  is connected to negative electrode terminal  16 N of battery cell  11   d  in battery cell unit  21 B. Second bus-bar-divided body  212  is connected to positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C. First bus-bar-divided body  211  and second bus-bar-divided body  212  are joined to each other by welding. 
     First bus-bar-divided body  211  is provided at a position overlapping with battery cell  11   d  in battery cell unit  21 B when viewed in the Z axis direction. First bus-bar-divided body  211  has a first plate portion  227 , a second plate portion  228 , a third plate portion  229 , and a fourth plate portion  233 . 
     First plate portion  227  has a plate shape having a thickness direction corresponding to the Z axis direction, and is disposed in parallel with an X-Y-axes plane. First plate portion  227  is placed on negative electrode terminal  16 N of battery cell  11   d  in battery cell unit  21 B in the Z axis direction. First plate portion  227  is joined to negative electrode terminal  16 N of battery cell  11   d  in battery cell unit  21 B by welding. Second plate portion  228  has a plate shape having a thickness direction corresponding to the X axis direction, and is disposed in parallel with a Y-Z-axes plane. Second plate portion  228  extends in the +Z axis direction from the end portion of first plate portion  227  in the −X axis direction. 
     Third plate portion  229  has a plate shape having a thickness direction corresponding to the Z axis direction, and is disposed in parallel with the X-Y-axes plane. Third plate portion  229  extends in the −X axis direction from the end portion of second plate portion  228  in the +Z axis direction. Fourth plate portion  233  has a plate shape having a thickness direction corresponding to the Y axis direction, and is disposed in parallel with the X-Z-axes plane. Fourth plate portion  233  extends in the +Z axis direction from the end portion of third plate portion  229  in the +Y axis direction. 
     Second bus-bar-divided body  212  is provided at a position overlapping with battery cell  11   a  in battery cell unit  21 C when viewed in the Z axis direction. Second bus-bar-divided body  212  has a fifth plate portion  222 , a sixth plate portion  223 , a seventh plate portion  224 , and an eighth plate portion  232 . 
     Fifth plate portion  222 , sixth plate portion  223 , seventh plate portion  224 , and eighth plate portion  232  respectively have shapes symmetrical to first plate portion  227 , second plate portion  228 , third plate portion  229 , and fourth plate portion  233  with respect to the X-Z-axes plane that constitutes a boundary between battery cell  11   d  in battery cell unit  21 B and battery cell  11   a  in battery cell unit  21 C. 
     Fifth plate portion  222  is placed on positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C in the Z axis direction. Fifth plate portion  222  is joined to positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C by welding. Eighth plate portion  232  is placed on fourth plate portion  233  in the Y axis direction. Fourth plate portion  233  and eighth plate portion  232  are in surface contact with each other in a plane parallel to the X-Z-axes plane. Fourth plate portion  233  and eighth plate portion  232  are joined to each other by welding. 
     In first bus bar  51  having such a configuration, first base portion  226  is constituted of first plate portion  227 , second plate portion  228 , and third plate portion  229 . First plate portion  227  of first base portion  226  is connected to negative electrode terminal  16 N of battery cell  11   d  in battery cell unit  21 B. Second base portion  221  is constituted of fifth plate portion  222 , sixth plate portion  223 , and seventh plate portion  224 . Fifth plate portion  222  of second base portion  221  is connected to positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C. 
     Rising portion  231  is constituted of a portion at which fourth plate portion  233  and eighth plate portion  232  are placed on each other. Rising portion  231  has a shape to rise from third plate portion  229  of first base portion  226  and seventh plate portion  224  of second base portion  221  in the +Z axis direction. 
     Rising portion  231  rises from third plate portion  229  of first base portion  226  and seventh plate portion  224  of second base portion  221  in the axis direction orthogonal to the X-Y-axes plane in which third plate portion  229  and seventh plate portion  224  are disposed. Rising portion  231  rises from first base portion  226  and second base portion  221  in a direction further away from battery cells  11 ,  11  to which first base portion  226  and second base portion  221  are connected. Rising portion  231  is provided at a position separated in the +Z axis direction from third side surface  15  of exterior package  12  on which electrode terminal  16  is provided. 
     The Z axis direction in which rising portion  231  rises from first base portion  226  (third plate portion  229 ) and second base portion  221  (seventh plate portion  224 ) corresponds to the rising direction of rising portion  231 . The Y axis direction in which fourth plate portion  233  and eighth plate portion  232  are placed on each other corresponds to the thickness direction of rising portion  231 . The X axis direction orthogonal to the rising direction of rising portion  231  and the thickness direction of rising portion  231  corresponds to the width direction of rising portion  231 . 
     Rising portion  231  is provided with a fragile portion  240 . Fragile portion  240  is provided in a root region  236  of rising portion  231 . Fragile portion  240  has a rigidity smaller than those of the other portions of rising portion  231  except for fragile portion  240 . Fragile portion  240  has a rigidity smaller than that of a tip region  237  of rising portion  231 . 
     As shown in  FIG.  8   , root region  236  of rising portion  231  is defined on the root side of rising portion  231  having the shape to rise from first base portion  226  and second base portion  221 . Tip region  237  of rising portion  231  is defined on the tip side of rising portion  231  having the shape to rise from first base portion  226  and second base portion  221 . 
     More specifically, rising portion  231  has a root portion  231   j  and a tip portion  231   k , and extends between root portion  231   j  and tip portion  231   k . Root portion  231   j  is located on the first base portion  226  and second base portion  221  side in the rising direction (Z axis direction) of rising portion  231 , and tip portion  231   k  is located opposite to root portion  231   j . Root region  236  of rising portion  231  corresponds to a region close to root portion  231   j  with respect to tip portion  231   k  in the rising direction of rising portion  231 . Tip region  237  of rising portion  231  corresponds to a region close to tip portion  231   k  with respect to root portion  231   j  in the rising direction of rising portion  231 . 
     Rising portion  231  has a rising length La. In this case, root region  236  of rising portion  231  has a length range of La/ 2  from root portion  231   j  in the +Z axis direction. Tip region  237  of rising portion  231  has a length range of La/ 2  from tip portion  231   k  in the −Z axis direction. 
     Fragile portion  240  is provided at a position separated from root portion  231   j  in the +Z axis direction. Fragile portion  240  is provided at a position separated from tip region  237  of rising portion  231  in the −Z axis direction. 
     Fragile portion  240  is constituted of a thin structure  241  in which the thickness of rising portion  231  is locally small. Rising portion  231  has a thickness Tb in the Y axis direction at a position other than fragile portion  240 . Fragile portion  240  has a thickness Ta smaller than thickness Tb in the Y axis direction (Ta&lt;Tb). Groove portions  242  are formed in root region  236  of rising portion  231 . Groove portions  242  have such shapes of grooves that are respectively recessed from the surface of fourth plate portion  233  oriented in the −Y axis direction and the surface of eighth plate portion  232  oriented in the +Y axis direction and extend in the +X axis direction. Thin structure  241  is constituted of groove portions  242 . 
     The thickness direction of rising portion  231  at fragile portion  240  is parallel to the Y axis direction in which the restraint force by restraint member  41  is applied to the plurality of battery cells  11 . 
     Fragile portion  240  is provided at a position overlapping with the X-Z-axes plane (predetermined plane) that constitutes the boundary between battery cell  11   d  in battery cell unit  21 B and battery cell  11   a  in battery cell unit  21 C. First bus bar  51  has a symmetrical shape with respect to the X-Z-axes plane that constitutes the boundary between battery cell  11   d  in battery cell unit  21 B and battery cell  11   a  in battery cell unit  21 C. 
       FIG.  9    is a perspective view showing a first form change of the connection structure for the battery cells in  FIG.  6   .  FIG.  10    is a diagram showing the connection structure for the battery cells when viewed in a direction indicated by an arrow X in  FIG.  9   .  FIG.  11    is a perspective view showing a second form change of the connection structure for the battery cells in  FIG.  6   . 
     Referring to  FIGS.  6  and  8  to  11   , rising portion  231  has a dividable portion  251 , a first remaining portion  252 , and a second remaining portion  253 . 
     Dividable portion  251  connects between first base portion  226  and second base portion  221 . Dividable portion  251  is dividable from first base portion  226  and 
     second base portion  221  with fragile portion  240  serving as a boundary. In a state in which dividable portion  251  is divided from first base portion  226  and second base portion  221 , first remaining portion  252  remains on the first base portion  226  side, and second remaining portion  253  remains on the second base portion  221  side. First remaining portion  252  and second remaining portion  253  are placed on each other. 
     Dividable portion  251  is connected to first remaining portion  252  and second remaining portion  253  at fragile portion  240 . Dividable portion  251  is constituted of: fourth plate portion  233  located on the tip side of rising portion  231  with respect to fragile portion  240 ; and eighth plate portion  232  located on the tip side of rising portion  231  with respect to fragile portion  240 . Fourth plate portion  233  and eighth plate portion  232  are joined to each other at dividable portion  251 . 
     First remaining portion  252  is constituted of fourth plate portion  233  located on the root side of rising portion  231  with respect to fragile portion  240 . Second remaining portion  253  is constituted of eighth plate portion  232  located on the root side of rising portion  231  with respect to fragile portion  240 . Fourth plate portion  233  and eighth plate portion  232  are not joined to each other at first remaining portion  252  and second remaining portion  253 . 
     Battery module  100  mays be disassembled for maintenance or the like. In such a case, an operator holds dividable portion  251  of rising portion  231  using a tool such as pliers and applies force along the Y axis direction to rising portion  231 , thereby breaking fragile portion  240 . Thus, the connection made between first base portion  226  and second base portion  221  by rising portion  231  can be disconnected, thereby separating adjacent battery cell units  21 . For example, as shown in  FIG.  11   , the operator separates battery cell unit  21 C from battery cell units  21 B,  21 D located beside battery cell unit  21 C so as to repair a component of battery cell unit  21 C or replace a battery cell  11  in battery cell unit  21 C. 
     In the present embodiment, fragile portion  240  is provided in root region  236  of rising portion  231 . With such a configuration, the operator can readily hold rising portion  231  using pliers or the like or can readily apply force to fragile portion  240 , with the result that breaking fragile portion  240  can be readily broken. Thus, workability at the time of disassembling battery module  100  can be improved. 
     Further, in fragile portion  240  constituted of thin structure  241 , the thickness direction of rising portion  231  in fragile portion  240  is parallel to the Y axis direction in which the plurality of battery cells  11  (battery cell units  21 ) are stacked. In this case, the restraint force in the Y axis direction is applied from restraint member  41  to the plurality of battery cells  11  (battery cell units  21 ), so that battery cells  11  can be suppressed from leaning in the Y axis direction when the operator applies force along the Y axis direction to rising portion  231  in order to break fragile portion  240 . Thus, the force applied to rising portion  231  can be more efficiently transmitted to fragile portion  240 , thereby improving workability at the time of breaking fragile portion  240  by the operator. 
     Further, fragile portion  240  is disposed to overlap with the X-Z-axes plane that constitutes a boundary between battery cells  11 ,  11  connected by first bus bar  51 , and first bus bar  51  has a symmetrical shape with respect to the X-Z-axes plane. With such a configuration, first bus bar  51  is supported by battery cell  11  in a balanced manner between the first base portion  226  side connected to first battery cell  11   d  and the second base portion  221  side connected to second battery cell  11   a  with fragile portion  240 , to which the force from the operator is transmitted, being interposed therebetween. Therefore, when the operator applies force along the Y axis direction to rising portion  231  in order to break fragile portion  240 , first bus bar  51  can be suppressed from being elastically deformed. Thus, the force applied to rising portion  231  can be more efficiently transmitted to fragile portion  240 , thereby improving workability at the time of breaking fragile portion  240  by the operator. 
     Further, rising portion  231  has dividable portion  251  that is dividable from first base portion  226  and second base portion  221  with fragile portion  240  serving as a boundary. With such a configuration, the operator can continuously apply force to rising portion  231  while holding dividable portion  251  until fragile portion  240  becomes broken, thereby improving workability at the time of breaking fragile portion  240  by the operator. 
     Further, rising portion  231  further has first remaining portion  252  and second remaining portion  253  shown in  FIGS.  9  and  10   . With such a configuration, when assembling, to battery module  100 , a battery cell unit  21  having been through maintenance, connection between first base portion  226  and second base portion  221  of first bus bar  51  can be made again by performing welding onto first remaining portion  252  and second remaining portion  253 . 
       FIG.  12    is a diagram showing a first modification of the fragile portion in  FIG.  8   . Referring to  FIG.  12   , in the present modification, fragile portion  240  is constituted of a notched structure  243 . Notches  244  are provided in root region  236  of rising portion  231 . 
     Notches  244  are provided to notch rising portion  231  in the width direction (X axis direction) of rising portion  231  orthogonal to the rising direction (Z axis direction) of rising portion  231  and the thickness direction (Y axis direction) of rising portion  231 . Notches  244  have such shapes of notches that are recessed from the respective side surfaces of rising portion  231  oriented in the +X axis direction and the −X axis direction and extend through rising portion  231  in the Y axis direction. A width Sa of rising portion  231  at fragile portion  240  is smaller than a width Sb of rising portion  231  at a position other than fragile portion  240  (Sa&lt;Sb). 
       FIG.  13    is a diagram showing a second modification of the fragile portion in  FIG.  8   . Referring to  FIG.  13   , in the present modification, fragile portion  240  is constituted of a perforated structure  246 . Cut portions  247  are provided in root region  236  of rising portion  231 . 
     Each of cut portions  247  is constituted of a through hole extending through rising portion  231  in the thickness direction of rising portion  231 . Cut portions  247  are provided intermittently in the form of a line. Cut portions  247  extend in the form of a straight line. Cut portions  247  extend in the X axis direction. 
       FIG.  14    is a perspective view showing a modification of a first bus bar in  FIG.  6   .  FIG.  15    s a diagram showing a first bus bar when viewed in a direction indicated by an arrow XV in  FIG.  14   . 
     Referring to  FIGS.  14  and  15   , in the present modification, first bus-bar-divided body  211  is provided at a position overlapping with battery cell  11   d  in battery cell unit  21 B when viewed in the Z axis direction. First bus-bar-divided body  211  has a first plate portion  284  and a second plate portion  283 . 
     First plate portion  284  has a plate shape having a thickness direction corresponding to the Z axis direction, and is disposed in parallel with the X-Y-axes plane. First plate portion  284  is placed on negative electrode terminal  16 N of battery cell  11   d  in battery cell unit  21 B in the Z axis direction. First plate portion  284  is joined to negative electrode terminal  16 N of battery cell  11   d  in battery cell unit  21 B by welding. Second plate portion  283  has a plate shape having a thickness direction corresponding to the X axis direction, and is disposed in parallel with the Y-Z-axes plane. Second plate portion  283  extends in the +Z axis direction from the end portion of first plate portion  284  in the −X axis direction. 
     When viewed in the Z axis direction, second bus-bar-divided body  212  is provided to extend over a position overlapping with battery cell  11   a  in battery cell unit  21 C and a position overlapping with battery cell  11   d  in battery cell unit  21 B. Second bus-bar-divided body  212  has a third plate portion  262 , a fourth plate portion  263 , a fifth plate portion  264 , an elastic portion  265 , a sixth plate portion  266 , and a seventh plate portion  282 . 
     Third plate portion  262  has a plate shape having a thickness direction corresponding to the Z axis direction, and is disposed in parallel with the X-Y-axes plane. Third plate portion  262  is placed on positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C in the Z axis direction. Third plate portion  262  is joined to positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C by welding. Fourth plate portion  263  has a plate shape having a thickness direction corresponding to the X axis direction, and is disposed in parallel with the Y-Z-axes plane. Fourth plate portion  263  extends in the +Z axis direction from the end portion of third plate portion  262  in the −X axis direction. 
     Each of fifth plate portion  264  and sixth plate portion  266  has a plate shape having a thickness direction corresponding to the Z axis direction, and is disposed in parallel with the X-Y-axes plane. Fifth plate portion  264  extends in the −X axis direction from the end portion of fourth plate portion  263  in the +Z axis direction. Sixth plate portion  266  is provided at a position displaced from fifth plate portion  264  in the −Y axis direction. Fifth plate portion  264  is provided at a position overlapping with battery cell  11   a  in battery cell unit  21 C when viewed in the Z axis direction, and sixth plate portion  266  is provided at a position overlapping with battery cell  11   d  in battery cell unit  21 B when viewed in the Z axis direction. 
     Elastic portion  265  extends between fifth plate portion  264  and sixth plate portion  266 . When viewed in the Z axis direction, elastic portion  265  is provided at a position overlapping with the boundary between battery cell  11   a  in battery cell unit  21 C and battery cell  11   d  in battery cell unit  21 B. Elastic portion  265  extends in the −Z axis direction from the end portion of fifth plate portion  264  in the −Y axis direction, is curved to reverse in the Z axis direction, and further extends in the +Z axis direction so as to be contiguous to the end portion of sixth plate portion  266  in the +Y axis direction. Elastic portion  265  can be elastically deformed to change a distance between fifth plate portion  264  and sixth plate portion  266  in the Y axis direction. 
     Seventh plate portion  282  has a plate shape having a thickness direction corresponding to the X axis direction, and is disposed in parallel with the Y-Z-axes plane. Seventh plate portion  282  extends in the +Z axis direction front an end portion of sixth plate portion  266  in the +X axis direction. Seventh plate portion  282  is placed on second plate portion  283  in the X axis direction. Seventh plate portion  282  is in surface contact with second plate portion  283  in a plane parallel to the Y-Z-axes plane. Second plate portion  283  and seventh plate portion  282  are joined to each other by welding. 
     In first bus bar  51  having such a configuration, first base portion  226  is constituted of first plate portion  284 . First plate portion  284  of first base portion  226  is connected to negative electrode terminal  16 N of battery cell  11   d  in battery cell unit  21 B. Second base  221  is constituted of third plate portion  262 , fourth plate portion  263 , fifth plate portion  264 , elastic portion  265 , and sixth plate portion  266 . Third plate portion  262  of second base portion  221  is connected to positive electrode terminal  16 P of battery cell  11   a  in battery cell unit  21 C. 
     Rising portion  231  is constituted of a portion at which second plate portion  283  and seventh plate portion  282  are placed on each other. Rising portion  231  is a portion on the positive side in the Z axis direction with respect to the corner portions of sixth plate portion  266  and seventh plate portion  282 . 
     Fragile portion  240  is provided in root region  236  of rising portion  231 . Rising portion  231  has a rising length Lb. Root region  236  of rising portion  231  has a length range of Lb/ 2  from root portion  231   j  of rising portion  231  in the −Z axis direction. Tip region  237  of rising portion  231  has a length range of Lb/ 2  from tip portion  231   k  of rising portion  231  in the −Z axis direction. 
     The thickness direction of rising portion  231  in fragile portion  240  is the X axis direction orthogonal to the Y axis direction in which the restraint force by restraint member  41  is applied to the plurality of battery cells  11 . First bus bar  51  has an asymmetrical shape with respect to the X-Z-axes plane that constitutes the boundary between battery cell  11   d  in battery cell unit  21 B and battery cell  11   a  in battery cell unit  21 C. 
     The above-described structure of battery module  100  according to the embodiment of the present invention is summarized as follows: battery module  100  according to the present embodiment includes: the plurality of battery cells  11  stacked in the Y axis direction serving as the predetermined direction; and the plurality of bus bars  50  that electrically connect the plurality of battery cells  11  together. The plurality of bus bars  50  include first bus bar  51  extending between first batten cell  11   d  and second battery cell  11   a  of the plurality of battery cells  11 , first battery cell  11   d  and second battery cell  11   a  being adjacent to each other in the Y axis direction. First bus bar  51  has first base portion  226  connected to first battery cell  11   d , second base portion  221  connected to second battery cell  11   a , and rising portion  231  that has a shape to rise from first base portion  226  and second base portion  221  and that connects between first base portion  226  and second base portion  221 . Fragile portion  240  is provided in root region  236  of rising portion  231 . 
     According to battery module  100  of the embodiment of the present invention thus configured, since fragile portion  240  is provided in root region  236  of rising portion  231 , the operator can readily break fragile portion  240  to separate first battery cell  11   d  and second battery cell  11   a  adjacent to each other in the predetermined direction. Thus, workability at the time of disassembling battery module  100  can be improved. 
     It should be noted that in addition to first bus bar  51 , the fragile portion of the present invention may be also provided in second bus bar  52  that connects between battery cells  11 ,  11  in battery cell unit  21 . 
     Although the embodiments of the present invention have been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.