Patent Publication Number: US-2021194085-A1

Title: Power storage device

Description:
This application is based on and claims the benefit of priority from Japanese Patent Application 2019-231624, filed on 23 Dec. 2019, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a power storage device. 
     Related Art 
     Since hybrid vehicles or electric vehicles require a larger amount of power than typical gasoline vehicles, a power storage device in which a plurality of battery cells such as lithium ion secondary batteries are stacked is mounted in the hybrid vehicles or electric vehicles. The plurality of battery cells need to be held in the power storage device to be prevented from vibrating due to vibration of a vehicle or the like. 
     There has been conventionally known a battery device in which a pin-shaped fastening protrusion is provided on a bottom surface of a cell casing of an individual battery cell, and the individual battery cell mounted on a cooling plate is fastened to the cooling plate using the fastening protrusion passing through the cooling plate (see Patent Document 1). 
     Patent Document 1: Japanese Unexamined Patent Application (Translation of PCT Application), Publication No. 2015-520924 
     SUMMARY OF THE INVENTION 
     However, in the above-described conventional technique, the battery cells need to be individually fastened to the cooling plate to hold the battery cells, resulting in poor assembly workability of the battery device. 
     The present invention has an object to provide a power storage device in which a plurality of battery cells can be easily held, resulting in good assembly workability. 
     (1) A power storage device according to the present invention (for example, a power storage device  1  described later) comprises: a cell group (for example, a cell group  3  described later) in which a plurality of battery cells (for example, battery cells  31  described later) each having a terminal (for example, a terminal  32  described later) on a first surface (for example, an upper surface  31   a  described later) are stacked; a cylindrical housing part (for example, a housing part  2  described later) that houses the cell group; a first plate member (for example, an upper plate member  5  described later) extending from the first surface of each of the battery cells in the cell group to side surfaces (for example, side surfaces  31   c  described later) of each of the battery cells, the side surfaces being adjacent to the first surface, the first plate member being housed in the housing part together with the cell group; a cell side protrusion portion (for example, a cell side protrusion portion  54  described later) protruding from a portion extending on each of the side surfaces of each of the battery cells toward an inner wall surface (for example, an inner surface  23   a,    24   a  described later) of the housing part in the first plate member; and an insertion member (for example, an insertion member  8  described later) that is press-fitted to contact both of the cell side protrusion portion and the inner wall surface disposed closer to the first surface side than the cell side protrusion portion, and presses the cell group against an opposite side of a side facing the first surface via the cell side protrusion portion. 
     According to the above-described (1), since the cell group can be pressed and held in the housing part just by press-fitting the insertion member between the cell side protrusion portion of the first plate member housed in the housing part together with the cell group and the inner wall surface of the housing part, there can be provided the power storage device in which the plurality of battery cells can be easily held, resulting in good assembly workability. 
     (2) In the power storage device according to (1), an elastic member (for example, an elastic member  64  described later) that receives a load from the cell group pressed by the insertion member may be provided between the cell group and the inner wall surface of the housing part. 
     According to the above-described (2), the cell group can be stably held when the elastic member is compressed. In addition, since a vibration applied to the cell group can be absorbed by the elastic member, noise and impacts caused by such vibration can be prevented from occurring. 
     (3) In the power storage device according to (2), the elastic member may be disposed in a corner portion at a diagonal position of the insertion member via the cell group. 
     According to the above-described (3), vibrations in an up-down direction and a left-right direction of the cell group can be absorbed by the elastic member. 
     (4) The power storage device according to (2) or (3) comprises a second plate member (for example, a lower plate member  6  described later) disposed to cover a second surface (for example, a bottom surface  31   d  described later) side of each of the battery cells disposed at an opposite side of the first surface in the cell group, the second plate member being housed in the housing part together with the cell group, wherein the elastic member may be provided in the second plate member. 
     According to the above-described (4), the elastic member can be easily disposed in the housing part by the second plate member. 
     (5) In the power storage device according to (4), the second plate member includes a pair of side frame portions (for example, side frame portions  61  described later) extending at both ends along a length direction of a lower surface of the cell group, the elastic member is held between upper claw portions (for example, upper claw portions  61   a  described later) and lower claw portions (for example, lower claw portions  61   b  described later) that are alternately disposed on an upper side and a lower side of each of the pair of side frame portions along the length direction, and the upper claw portions each may include a contact portion (for example, a contact portion  61   c  described later) that contacts the side surface of the battery cell. 
     According to the above-described (5), since the upper claw portions are deformed toward the side surfaces of the battery cell and the side surfaces of the battery cell are sandwiched from both sides by the contact portions, the lower portion of the battery cell is firmly held. 
     (6) In the power storage device according to any one of (1) to (5), the cell side protrusion portion may be disposed in the first plate member on each of both side surface sides of the battery cell. 
     According to the above-described (6), the cell group in the housing part can be more stably held. 
     (7) in the power storage device according to any one of (1) to (6), a contact recess portion (for example, a contact recess portion  27  described later) having an inner surface (for example, an inner surface  27   a  described later) sandwiching the insertion member between the contact recess portion and the cell side protrusion portion may be provided in the inner wall surface of the housing part disposed closer to the first surface side than the cell side protrusion portion. 
     According to the above-described (7), the insertion member is smoothly guided in an insertion direction by the contact recess portion. Since the insertion member press-fitted to be fitted into the contact recess portion is held in the contact recess portion, a pressing force can be stably applied to the cell side protrusion portion. In addition, since it is simply required that the insertion member is made small to an extent capable of being fitted into the contact recess portion, the power storage device can be reduced in size and weight. 
     (8) In the power storage device according to (7), an inner wall side protrusion portion (for example, an inner wall side protrusion portion  28  described later) protruding toward the cell group side is provided in the inner wall surface of the housing part facing the cell side protrusion portion, and the inner wall side protrusion portion is disposed on an opposite side of the cell side protrusion portion via the insertion member, and at least a part of the inner wall side protrusion portion overlaps with the cell side protrusion portion as viewed from a side facing the first surface. 
     According to the above-described (8), since a movement o the cell group in a direction in which the cell side protrusion portion and the inner wall side protrusion portion approach each other is restricted by contact between the cell side protrusion portion and the inner wall side protrusion portion, the terminal of the battery cell can be protected. 
     The present invention can provide a power storage device in which a plurality of battery cells can be easily held, resulting in good assembly workability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating a power storage device according to one embodiment; 
         FIG. 2  is a cross-sectional view along line A-A in  FIG. 1 ; 
         FIG. 3  is an exploded perspective view illustrating components in a housing part in the power storage device; 
         FIG. 4  is a perspective view illustrating a portion of an upper plate member when viewed obliquely from above; 
         FIG. 5  is a cross-sectional view along line B-B in  FIG. 4 ; 
         FIG. 6  is a perspective view illustrating a portion of a lower plate member when viewed obliquely from below; 
         FIG. 7  is an enlarged perspective view illustrating a portion of the lower plate member; 
         FIG. 8  is an enlarged cross-sectional view illustrating a portion of an insertion member in one cell group in a housing part; 
         FIG. 9  is an enlarged cross-sectional view illustrating a portion of an elastic member in one cell group in the housing part; 
         FIG. 10  is a cross-sectional view illustrating a state in which one cell group is fixed in the housing part; and 
         FIG. 11  is a diagram illustrating a state in which a lower portion of a battery cell is fixed by an upper claw portion of the lower plate member. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings.  FIG. 1  is an exploded perspective view illustrating a power storage device according to one embodiment.  FIG. 2  is a cross-sectional view along line A-A in  FIG. 1 .  FIG. 3  is an exploded perspective view illustrating components in a housing part in the power storage device. As illustrated in  FIG. 1 , a power storage device  1  includes a housing part  2 , cell groups  3 ,  3  to be housed in the housing part  2 , and end plates  4 ,  4 . Note that in directions indicated by arrows in each drawing, a direction along an X direction indicates a length direction of the power storage device  1  and the housing part  2 . A direction along a Y direction indicates a width direction of the power storage device  1  and the housing part  2 . A direction along a Z direction indicates a height direction of the power storage device  1  and the housing part  2 . 
     The housing part  2  illustrated in the present embodiment is a case made of metal such as aluminum or an aluminum alloy, and is formed in a horizontally long quadrangular cylindrical shape in which a dimension in the width direction (Y direction) is larger than that in the height direction (Z direction). The housing part  2  is an extrusion-molded product formed by extrusion molding along one direction (X direction). Since the housing part  2  constituted by the extrusion-molded product can be easily formed and does not have a joint portion in which plate members are joined to each other, assembly variation or thermal distortion arising from the joint portion does not occur. Hence, the housing part  2  has a stable shape. 
     The housing part  2  includes an upper wall portion  21  and a lower wall portion  22  facing each other in the height direction, two side wall portions  23 ,  23  facing each other in the width direction, and one middle wall portion  24  disposed between the side wall portions  23 ,  23  and extending in parallel with the side wall portions  23 ,  23  from the upper wall portion  21  to the lower wall portion  22 . In the housing part  2 , two rows of housing spaces  20 ,  20  each tor housing the cell group  3  are formed as spaces surrounded by the upper wall portion  21 , the lower wall portion  22 , the side wall portions  23 ,  23 , and the middle wall portion  24 . Openings  20   a,    20   a  formed in a horizontally long rectangular shape are open in both ends of the housing part  2  in the length direction (X direction), respectively, so that the housing spaces  20 ,  20  communicate with the outside. 
     Heat exchange medium flow paths  25 ,  26  through which heat exchange media to be subjected to heat exchange with the battery cells  31  (described later) forming the cell groups  3 ,  3  flow are provided inside the side wall portions  23 ,  23  and inside the middle wall portion  24  of the housing part  2 , respectively. The heat exchange medium flow paths  25 ,  26  extend along the entire length of the housing part  2  in the length direction, and each is opened to both ends of the housing part  2  in the length direction. As illustrated in FIG.  2 , the heat exchange medium flow paths  25 ,  26  are divided into the upper flow paths  252 ,  261  and the lower flow paths  252 ,  262  by flow path partition walls  25   a,    26   a  extending along the length direction of the housing part  2  at a substantially center portion of the housing part  2  in the height direction, respectively. The upper flow path  251  and the lower flow path  252  are aligned with the upper flow path  261  and the lower flow path  262  in the height direction of the housing part  2 , respectively. 
     As illustrated in  FIG. 3 , each of the cell groups  3 , 3  housed in the respective housing spaces  20 ,  20  of the housing part  2  is configured by stacking along the X direction a plurality of battery cells  31  formed in a rectangular parallelepiped shape, for example, lithium ion secondary batteries. The battery cell  31  is configured by housing an electrode body (not illustrated) in a cell case made of aluminum, an aluminum alloy or the like, and has a pair of positive and negative terminals  32 ,  32  on an upper surface  31   a  (first surface) disposed to face in the Z direction. The terminals  32 ,  32  of the battery cells  31 ,  31  adjacent to each other in the stacking direction are electrically connected by a bus bar  33 . Accordingly, all the battery cells  31  configuring one cell group  3  are electrically connected in series or in parallel. Each of the bus bars  33  is electrically connected to a common flexible printed circuit board  34  extending in the stacking direction (X direction) of the battery cells  31  on the upper surface  31   a  side of the battery cells  31 . The flexible printed circuit board  34  serves as a voltage detection line to be connected to a voltage sensor (not illustrated) for detecting a voltage of each of the battery cells  31 . 
     An upper plate member  5  (first plate member) is disposed above the cell group  3 , and a lower plate member  6  (second plate member) is disposed below the cell group  3 . The upper plate member  5  and the lower plate member  6  will be further described with reference to  FIG. 4  to  FIG. 7 .  FIG. 4  is a perspective view illustrating a portion of the upper plate member when viewed obliquely from above.  FIG. 5  is a cross-sectional view along line B-B in  FIG. 4 .  FIG. 6  is a perspective view illustrating a portion of the lower plate member when viewed obliquely from below.  FIG. 7  is an enlarged perspective view illustrating a portion of the lower plate member. 
     The upper plate member  5  is formed of, for example, an insulating resin such as polypropylene or polyethylene. The upper plate member  5  integrally includes a rectangular frame portion  51  dimensioned to surround an upper surface of the cell group  3  (a surface including the upper surfaces  31   a  of the plurality of stacked battery cells  31 ), a plurality of upper partition plate portions  52  that partition the inside of the rectangular frame portion  51  along the width direction (Y direction) of the cell group  3 , and an upper plate portion  53  forming an upper surface of the upper plate member  5 . 
     The rectangular frame portion  51  is formed by assembling a pair of end frames  51   a,    51   a  disposed at both ends of the cell, group  3  in the length direction (X direction), and a pair of side frames  51   b,    51   b  extending along the length direction of the cell group  3  to form a rectangular shape. The end frames  51   a,    51   a  are disposed on end surfaces  31   b,    31   b  facing in the stacking direction of the two battery cells  31 ,  31  disposed at the outermost ends of the cell group  3 , to extend at a predetermined height (a height along the Z direction). The side frames  51   b,    51   b  are disposed on side surfaces  31   c ,  31   c  which are both end surfaces of all the battery cells  31  in the cell group  3  in the width direction, to extend at a substantially same height as the end frames  51   a,    51   a.    
     The upper partition plate portions  52  are provided between the pair of side frames  51   b,    51   b,  to be in parallel with the end frames  51   a,    51   a.  The upper partition plate portions  52  are disposed so that the surface direction thereof is in parallel with the height direction (Z direction) of the cell group  3 . The height of the upper partition plate portions  52  along the Z direction is substantially the same as that of the rectangular frame portion  51 . The upper partition plate portions  52  are disposed at a predetermined interval in parallel with one another, to correspond to respective portions between the battery cells  31 ,  31  adjacent to each other. 
     The upper plate portion  53  is provided over an upper end of the rectangular frame portion  51  and upper ends of the upper partition plate portions  52 , thereby being disposed to extend in parallel with the upper surfaces  31   a  of the respective battery cells  31 . The upper plate portion  53  has rectangular openings  53   a  formed between each of the end frames  51   a,    51   a  and the adjacent upper partition plate portion  52  and between the upper partition plate portions  52 ,  52  adjacent to each other. Each of the openings  53   a  is provided between the upper partition plate portions  52 ,  52  adjacent to each other so that the upper surface  31   a  including the two terminals  32 ,  32  of one battery cell  31  is exposed upward. The area of one opening  53   a  is slightly smaller than that of the upper surface  31   a  of one battery cell  31 . Therefore, the upper plate portion  53  extends along outer peripheral portions of the respective upper surfaces  31   a  of the battery cells  31 , in the peripheries of the openings  53   a.    
     Cell side protrusion portions  54 ,  54  protruding in the width direction (the width direction of the cell group  3 ) of the upper plate member  5  are provided on the pair of side frames  51   b,    51   b  of the rectangular frame portion  51 , respectively. The cell side protrusion portions  54 ,  54  extend along substantially the entire length of the upper plate member  5  in the length direction (the length direction of the cell group  3 ). 
     As illustrated in  FIG. 5 , the cell side protrusion portion  54  has substantially triangular cross section in which a vertex  54   a  protrudes in the width direction (Y direction). A surface disposed above the vertex  54   a  in the cell side protrusion portion  54  has a receiving surface  54   b  that contacts an insertion member  8  (described later) and receives a load (pressing force) from the insertion member  8 . As illustrated in  FIG. 5 , the receiving surface  54   b  is slightly recess-curved, and faces above the cell group  3  and outward in the width direction. 
     The lower plate member  6  is formed of, for example, an insulating resin such as polypropylene or polyethylene. The lower plate member  6  integrally includes a pair of side frame portions  61 ,  61  extending in parallel with each other at both side portions along the length direction of the lower surface (a surface including bottom surfaces  31   d  of the battery cells  31 ) of the cell group  3 , and a plurality of lower partition plate portions  62  and support plate portions  63  that connect the pair of side frame portions  61 ,  61  to each other along the width direction of the cell group  3 . 
     The lower partition plate portions  62  partition the inside of the lower plate member  6  (between the pair of side frame portions  61 ,  61 ) along the width direction of the cell group  3 . The lower partition plate portions  62  are disposed so that the surface direction thereof is in parallel with the height direction of the cell group  3 . The lower partition plate portions  62  are disposed at a predetermined interval in parallel with one another, to correspond to the end surfaces  31   b,    31   b  facing in the stacking direction of the two battery cells  31 ,  31  disposed at the outermost ends of the cell group  3  and portions between the battery cells  31 ,  31  adjacent to one another, respectively. 
     Each of the support plate portions  63  is disposed between the lower partition plate portions  62 ,  62  adjacent to each other. The support plate portions  63  are disposed so that the surface direction thereof is in parallel with the bottom surface  31   d  (second surface) of the battery cell  31  in the cell group  3 , and are provided in one-to-one correspondence with the respective battery cells  31  in the cell group  3 . The support plate portions  63  contact the respective bottom surfaces  31   d  of the battery cells  31 , thereby supporting the respective battery cells  31  from below. 
     Elastic members  64 ,  64  made of rubber or the like are attached to the outside of the side frame portions  61 ,  61 , respectively, to extend along the entire length of the side frame portions  61 ,  61 . The elastic member  64  is held between upper claw portions  61   a  and lower claw portions  61   b  that are alternately disposed on the upper side and the lower side of the side frame portion  61  in the length direction. The elastic member  64  protrudes toward the outside of the corresponding side frame portion  61 , specifically, toward the outside of the lower plate member  6  in the width direction and obliquely downward. 
     The upper claw portions  61   a  are provided in one-to-one correspondence with the respective side surfaces  31   c  of the battery cells  31  configuring the cell group  3 . As illustrated in  FIG. 7 , each of the upper claw portions  61   a  rises upward from the side frame portion  61  corresponding to the end portion of the support plate portion  63  along the side surface  31   c  of the battery cell  31 . The upper claw portion  61   a  is provided to be easily elastically deformable in such a direction to approach the side surface  31   c  of the battery cell  31 . Therefore, the back surface of the upper claw portion  61   a  facing the side surface  31   c  of the battery cell  31  serves as a contact portion  61   c  that contacts the side surface  31   c  of the battery cell  31  to be mounted on the support plate portion  63  when the upper claw portion  61   a  is elastically deformed. 
     The upper side of the cell group  3  is covered with the upper plate member  5 . In addition, the lower side of the cell group  3  is covered with and supported by the lower plate member when the battery cells  31  are mounted on the respective support plate portions  63 . The upper partition plate portions  52  of the upper plate member  5  and the lower partition plate portions  62  of the lower plate member  6  each are held between the battery cells  31 ,  31  adjacent to each other, which insulates between the battery cells  31 ,  31 . The terminals  32  of each of the battery cells  31  are exposed from the opening  53   a  in the upper plate member  5 , and are connected to the respective bus bars  33 . The flexible printed circuit board  34  is disposed on the upper surface of the upper plate member  5 . Furthermore, as illustrated in  FIG. 3 , the upper side of the cell group  3  is covered with a cover member  7  from above the upper plate member  5 . 
     The cell group  3  is inserted into each of the housing spaces  20 ,  20  in the housing part  2  from each of the openings  20   a,    20   a  in the stacking direction of the battery cells  31 , together with the upper plate member  5 , the lower plate member  6 , and the cover member  7 , thereby being housed in the housing part  2 . As illustrated in  FIG. 2 , the cell side protrusion portions  54  of the upper plate member  5  protrude toward an inner surface  23   a  of the side wall portion  23  and an inner surface  24   a  of the middle wall portion  24 , respectively. In each of the housing spaces  20 ,  20 , the elastic members  64  of the lower plate member  6  contact a corner portion  20   b  between the lower wall portion  22  and the side wall portion  23  and a corner portion  20   c  between the lower wall portion  22  and the middle wall portion  24 , respectively. Note that portions that the elastic members  64  contact are not limited to the corner portions  20   b,    20   c,  and may be portions closer to the lower wall portion  22  or portions closer to the side wall portion  23  and the middle wall portion  24 . That is, it is only required that the elastic members  64  contact the inner surface of the housing space  20  from the lower wall portion  22  to the side wall portion  23  and the middle wall portion  24  via the corner portions  20   b,    20   c.    
     As illustrated in  FIG. 2 , each of the cell groups  3 ,  3  housed in the housing part  2  is sandwiched between the side wall portion  23  and the middle wall portion  24  via respective heat transfer sheets  35 . Therefore, even when two rows of cell groups  3 ,  3  are housed in one housing part  2 , heat can be efficiently exchanged with the heat exchange media flowing through the heat exchange medium flow paths  25 ,  26  at both sides of each of the battery cells  31  in the width direction. The cell groups  3 ,  3  housed in the housing part  2  may be integrated by a restraining band or the like (not illustrated) in order to maintain the state in which the battery cells  31  are stacked. One housing part  2  illustrated in the present embodiment includes two rows of housing spaces  20 ,  20  via the middle wall portion  24 , and houses the two cell groups  3 ,  3  in parallel. However, it is only required that one housing part  2  includes at least one housing space  20 . 
     The end plates  4 ,  4  are disposed so that each covers the two openings  20   a,    20   a  at each end of the housing part  2 , and are fixed to both end surfaces of the housing part  2 , respectively, using a plurality of bolts  41  passing through each of the end plates  4 ,  4 . 
     Next, a configuration for fixing the cell groups  3 ,  3  housed inside of the housing part  2  will be further described with reference to  FIG. 8  to  FIG. 11 .  FIG. 8  is an enlarged cross-sectional view illustrating a portion of the insertion member in one cell group in the housing part.  FIG. 9  is an enlarged cross-sectional view illustrating a portion of the elastic member in one cell group in the housing part.  FIG. 10  is a cross-sectional view illustrating a state in which one cell group is fixed in the housing part.  FIG. 11  is a diagram illustrating a state in which a lower portion of the battery cell is fixed by the upper claw portion of the lower plate member. As illustrated in  FIG. 1  and  FIG. 8 , each of the cell groups  3 ,  3  housed inside of the housing part  2  is fixed by two insertion members  8 ,  8 . 
     The insertion member  8  is formed of, for example, metal such as stainless steel, and is a cylindrical bar-shaped body having a length extending the entire length of the housing part  2  and the cell group  3  in the length direction. The insertion members  8  are press-fitted from the opening  20   a  of the housing part  2 , to contact the respective cell side protrusion portions  54  of the upper plate member  5 , and respective inner wall surfaces of the housing space  20  disposed closer to the upper surface  31   a  side of the battery cells  31  than the cell side protrusion portions  54 , specifically, the inner surface  23   a  of the side wall portion  23  and the inner surface  24   a  of the middle wall portion  24 , respectively. Note that  FIG. 8  illustrates an arrangement structure of the insertion member  3  between the cell side protrusion portion  54  and the side wall portion  23 , but the insertion member  8  between the cell side protrusion portion  54  and the middle wall portion  24  also has the same structure and appears symmetrically to  FIG. 8 . In addition,  FIG. 9  illustrates an arrangement structure of the elastic member  64  between the lower plate member  6  and the middle wall portion  24 , but the elastic member  64  between the lower plate member  6  and the side wall portion  23  also has the same structure and appears symmetrically to  FIG. 9 . 
     As illustrated in  FIG. 8 , the insertion member  8  contacts the receiving surface  54   b  disposed on the upper side in the cell side protrusion portion  54  of the upper plate member  5  and contacts the inner surface  23   a  of the side wall portions  23  made of metal (or the inner surface  24   a  of the middle wall portion  24 ), thereby pressing the cell group  3  against the opposite side of a side facing the upper surface  31   a  of the battery cell  31 , via the cell side protrusion portion  54 . Specifically, the insertion member  8  contacts the inner surface  23   a  of the side wall portion  23  (or the inner surface  24   a  of the middle wall portion  24 ), thereby applying a pressing force in a diagonal direction D of the battery cell  31  indicated by a dashed-dotted line in  FIG. 8  and  FIG. 9  with respect to a contact point  54   c  with the receiving surface  54   b , to press the cell group  3  in the diagonal direction D via the upper plate member  5 . 
     As illustrated in  FIG. 9 , a load of the cell group  3  pressed by the insertion member  8  in the diagonal direction D is applied to the elastic member  64  of the lower plate member  6  disposed at a diagonal position of the cell side protrusion portion  54 . The elastic member  64  is compressed upon receipt of the load from the cell group  3 , and applies a reaction force to the cell group  3 , thereby stably holding the cell group  3 . That is, in the power storage device  1 , the cell group  3  can be pressed and held in the housing part  2  just by press-fitting the insertion members  8 ,  8  between the respective cell side protrusion portions  54  of the upper plate member  5  housed in the housing part  2  together with the cell group  3  and the respective inner wall surfaces of the housing part  2  (the inner surface  23   a  of the side wall portion  23  and the inner surface  24   a  of the middle wall portion  24 ). Therefore, the power storage device  1  can be provided in which the plurality of battery cells  31  can be easily held in the housing part  2 , resulting in good assembly workability. 
     Since the cell group  3  is held when the elastic member  64  is compressed, the vibration applied to the cell group  3  can be absorbed by the elastic member  64 , whereby noise and impacts caused by such vibration can be prevented from occurring. Moreover, since the elastic members  64  are disposed in the corner portions  20   b,    20   c  at the diagonal positions of the insertion members  8 ,  8  via the cell group  3 , respectively, the vibrations in the up-down direction and the left-right direction of the cell group  3  can be absorbed just by disposing the elastic members  64 ,  64  at portions of the cell group  3  in the width direction, respectively. Since the elastic members  64  are provided in the lower plate member  6 , the elastic members  64  can be easily disposed in the housing part  2  by housing the lower plate member  6  in the housing space  20  of the housing part  2  together with the cell group  3 . 
     The cell side protrusion portions  54 ,  54  of the present embodiment are disposed in the upper plate member  5  on respective sides of both side surfaces  31   c,    31   c  of the battery cell  31 , and are pressed by the respective insertion members  8 ,  8 . Therefore, as illustrated in  FIG. 10 , the pressing forces applied by the respective insertion members  8 ,  8  are applied to the cell group  3  in the two diagonal directions D, D. Thus, the cell group  3  can be more stably held in the housing space  20  of the housing part  2 . 
     As indicated by a dashed-dotted line in  FIG. 11 , when the elastic member  64  is compressed, the elastic member  64  presses the upper claw portion  61   a  of the lower plate member  6  toward the side surface  31   c  of the battery cell  31  by the reaction force. Thus, the upper claw portion  61   a  is elastically deformed toward the side surface  31   c  of the battery cell  31 , and the contact portion  61   c  on the back surface side of the upper claw portion  61   a  contacts the side surface  31   c  of the battery cell  31 . Since the upper claw portions  61   a  are disposed on the pair of side frame portions  61 ,  61 , respectively, to sandwich the battery cell  31  from both sides, the pair of upper claw portions  61   a,    61   a  sandwich the side surfaces  31   c  of the battery cell  31  from both sides when being elastically deformed, whereby the lower portion of the battery cell  31  is firmly held. 
     As illustrated in  FIG. 2 ,  FIG. 8 , and  FIG. 10 , a contact recess portion  27  having an inner surface  27   a  sandwiching the insertion member  8  between the contact recess portion  27  and the cell side protrusion portion  54  is provided in the inner wall surface of the housing part  2  disposed closer to the upper surface  31   a  side of the battery cell  31  than the cell side protrusion portion  54 , that is, the inner surface  23   a  of the side wall portion  23  (or the inner surface  24   a  of the middle wall portion  24 ). The contact recess portion  27  is formed in the inner surface  23   a  of the side wall portion  23  (or the inner surface  24   a  of the middle wall portion  24 ) closer to the upper wall portion  21  of the housing part  2  than the cell side protrusion portion  54 , to face the receiving surface  54   b  of the cell side protrusion portion  54  along the entire length of the housing part  2  in the length direction. Accordingly, the inner surface  27   a  of the contact recess portion  27  faces the receiving surface  54   b  of the cell side protrusion portion  54  via the insertion member  8 . 
     The insertion member  8  is press-fitted along the contact recess portion  27  while contacting the receiving surface  54   b  of the cell side protrusion portion  54  and being housed in the contact recess portion  27 . Therefore, the insertion member  8  is smoothly guided in the insertion direction by the contact recess portion  27 . Since the insertion member  8  press-fitted to be fitted into the contact recess portion  27  is held in the contact recess portion  27 , the pressing force can be stably applied to the receiving surface  54   b  of the cell side protrusion portion  54 . In addition, since it is simply required that the insertion member  8  is made small to an extent capable of being fitted into the contact recess portion  27 , the power storage device  1  can be reduced in size and weight. 
     As illustrated in  FIG. 8 , an inner wall side protrusion portion  28  protruding toward the cell group  3  side is provided in the inner wall surface of the housing part  2  facing the cell side protrusion portion  54 , that is, the inner surface  23   a  of the side wall portion  23  (or the inner surface  24   a  of the middle wall portion  24 ). The inner wall side protrusion portion  28  is smoothly continued from the inner surface  27   a  of the contact recess portion  27 , and protrudes toward the cell group  3  along the entire length of the housing part  2  in the length direction to cover above the cell side protrusion portion  54  (or the upper wall portion  21  side of the housing part  2 ) via the insertion member  8 . 
     The inner wall side protrusion portion  28  is disposed on the opposite side of the cell side protrusion portion  54  via the insertion member  8 , and at least a part of the inner wall side protrusion portion  28  overlaps with the cell side protrusion portion  54  as viewed from the side facing the upper surface  31   a  of the battery cell  31 . That is, as illustrated in  FIG. 8 , the inner wall side protrusion portion  28  protrudes toward the cell group  3 , and therefore overlaps with the cell side protrusion portion  54  at a distance L. Therefore, the insertion member  8  is prevented from coming off upward from the contact recess portion  27 . Furthermore, since the movement of the cell group  3  in a direction in which the cell side protrusion portion  54  and the inner wall side protrusion portion  28  approach each other (movement of the cell group  3  toward the upper wall portion  21 ) is restricted by contact between the cell side protrusion portion  54  and the inner wall side protrusion portion  28 , the terminals  32  of the battery cell  31  can be prevented from contacting the upper wall portion  21  and the like, whereby the terminals  32  can be protected. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1  Power storage device 
           2  Housing part 
           23   a  Inner surface (of side wall portion) (inner wall surface of housing part) 
           24   a  Inner surface (of middle wall portion) (inner wall surface of housing part) 
           27  Contact recess portion 
           27   a  Inner surface (of contact recess portion) 
           28  Inner wall side protrusion portion 
           3  Cell group 
           31  Battery cell 
           31   a  Upper surface (first surface) (of battery cell) 
           31   c  Side surface (of battery cell) 
           31   d  Bottom surface (second surface) (of battery cell) 
           32  Terminal 
           5  Upper plate member (first plate member) 
           54  Cell side protrusion portion 
           6  Lower plate member (second plate member) 
           61  Side frame portion 
           61   a  Upper claw portion 
           61   c  Contact portion 
           64  Elastic member 
           8  Insertion member