Patent Publication Number: US-2022216552-A1

Title: Pack case, battery pack, and method for manufacturing pack case

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This divisional application claims the benefit to U.S. patent application Ser. No. 16/773,111, filed Jan. 27, 2020, which claims benefit of Japanese Patent Application No. 2019-021418 filed on Feb. 8, 2019 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a pack case that accommodates a battery stack in which a plurality of batteries are stacked, a battery pack in which the pack case houses the battery stack, and a method for manufacturing a pack case. 
     2. Description of Related Art 
     As a battery pack accommodating a plurality of batteries, a battery pack may be required in which the batteries are restrained by applying in a stacking direction a predetermined compression force to a battery stack, in which the batteries are stacked. Examples of the battery pack of this type includes a battery pack in which bolts are provided to extend between end plates arranged at both ends of a battery stack in a stacking direction and fastened with nuts, and a compression force is applied to the battery stack (see, Japanese Unexamined Patent Application Publication No. 2005-339929 (JP 2005-339929 A)). 
     SUMMARY 
     A battery pack is also conceivable that is formed by inserting, in a pack case formed by aluminum die casting or the like to have a bottomed rectangular box shape, a battery stack compressed with a compression force larger than a desired compression force, and then, loosening the compression so that the battery stack is accommodated in the battery pack in a compressed state with the desired compression force using rigidity of the pack case. 
     However, when the battery stack is restrained by using the bolts and the nuts, the size of the battery pack increases, and the weight of the battery pack as a whole increases due to the weights of the end plates, the bolts, and the like. On the other hand, the battery pack including the aluminum die-cast pack case accommodating the battery stack can be made relatively light. However, in order to maintain an appropriate compression force, the rigidity of each part must be increased by increasing a thickness of walls of the pack case. Thus, the pack case itself tends to be heavy. 
     The present disclosure provides a pack case that is lightweight and can accommodate a battery stack while applying a compression force to the battery stack, a battery pack including the pack case accommodating the battery stack, and a method for manufacturing the pack case. 
     A first aspect of the present disclosure relates to a pack case. The pack case accommodates a battery stack in which a plurality of batteries are stacked in a stacking direction, and compresses and restrains the battery stack in the stacking direction. The pack case includes a first wall that is located on a first side of the accommodated battery stack in the stacking direction, contacts a first end of the battery stack, and presses the battery stack toward a second side in the stacking direction, and a second wall that is located on the second side of the accommodated battery stack in the stacking direction, contacts a second end of the battery stack, and presses the battery stack toward the first side in the stacking direction. At least one of the first wall and the second wall is a panel structure wall including a first metal plate, a second metal plate, and an interposed member. The second metal plate is located outward of the first metal plate in the stacking direction and faces the first metal plate. The interposed member is interposed between the first metal plate and the second metal plate, is fixed to the first metal plate and the second metal plate, and has a density lower than that of a metal forming the first metal plate and the second metal plate. 
     In the above pack case that accommodates the battery stack and compresses and restrains the battery stack in the stacking direction, at least one of the first wall and the second wall that press the battery stack in the stacking direction is the panel structure wall that includes the first metal plate, the second metal plate, and the interposed member interposed between and fixed to the first metal plate and the second metal plate, and that has a so-called sandwich panel structure. Thus, the first wall or the second wall that is the panel structure wall has higher flexural rigidity and higher torsional rigidity compared to the case where the wall is formed of only the first metal plate or the case where the wall is formed of only the first metal plate and the interposed member fixed thereto. Therefore, it is possible to suppress deformation of the panel structure wall (first wall or second wall) due to a reaction force with respect to a compression force that compresses the battery stack in the stacking direction, and thus, to suppress reduction of the compression force that compresses the battery stack in the stacking direction. Moreover, the interposed member interposed between the first metal plate and the second metal plate has the density lower than that of the metal forming the first metal plate and the second metal plate. Therefore, it is possible to make the panel structure wall lightweight compared to the case where a solid metal plate having the same thickness as the panel structure wall is used instead of the sandwich panel structure. Thus, it is also possible to make the pack case lightweight. 
     The pack case may have a rectangular frame shape surrounding the battery stack from four sides, or may have a bottomed rectangular frame shape (bottomed rectangular box shape) having a bottom, for example. The pack case may have a U shape (shape of a rectangle with one open side) having no lateral side wall and having a bottom in addition to the first wall and the second wall. The first metal plate and the second metal plate forming the panel structure wall may be separate metal plates, or may be provided by bending one metal plate into a U-shape. 
     As a material for the first metal plate and the second metal plate forming the panel structure wall (first wall or second wall), an appropriate metal plate may be used. Example of the material include a steel plate, a galvanized steel plate, a nickel plated steel plate, a stainless steel plate, an aluminum plate, etc. 
     Further, as the interposed member, a resin material made from thermoplastic resin such as polyamide, thermosetting resin such as epoxy, fiber reinforced plastic such as glass fiber reinforced polyamide, or the like can be used. In this case, besides using a solid interposed member made from resin, the interposed member may be provided with a lightening portion such as a hole (lightening hole), in order to reduce a weight of the panel structure wall and further a weight of the pack case. Further, a foamed resin material made of urethane foam, foamed polyamide, etc., a honeycomb material for a core material, in which a metal such as aluminum or stainless steel, or resin such as polypropylene or aramid is formed in a honeycomb shape, can also be used for the interposed member. The interposed member may be formed of a single member extending over the entire panel structure wall. Alternatively, the interposed member may be formed of a plurality of members. For example, in the interposed member, a portion close to the four corners of the pack case having a rectangular frame shape and a central portion may be formed of different members. 
     For fixing the interposed member to the first metal plate and the second metal plate of the panel structure wall, a primer is applied to the first metal plate and the second metal plate, to which the interposed member is fixed. Alternatively, after the first metal plate and the second metal plate are subjected to surface roughing such as chemical etching or laser processing, resin may be injected by injection molding between the first metal plate and the second metal plate to form the interposed member and bond the interposed member to the first metal plate and the second metal plate together. 
     In the first aspect, the panel structure wall may include a first metal plate portion that is the first metal plate, a second metal plate portion that is the second metal plate, and a connecting portion connecting the first metal plate portion and the second metal plate portion. The first metal plate portion, the second metal plate portion and the connecting portion are formed by bending one metal plate into a U-shape. 
     In the pack case, the first metal plate portion and the second metal plate portion that are the first metal plate and the second metal plate are provided by bending one metal plate into a U-shape. Therefore, it is possible to reduce the number of parts forming the pack case and to provide an inexpensive pack case. In addition, compared to the case where the first metal plate and the second metal plate are separate members, the first metal plate portion and the second metal plate portion are connected via the connecting portion (the first metal plate portion, the second metal plate portion, and the connecting portion connecting the first metal plate portion and the second metal plate portion are formed of one metal plate). Therefore, it is possible to further improve the flexural rigidity and the torsional rigidity of the panel structure wall (first wall, second wall). 
     As a U-shaped bending form in the connecting portion of the metal plate, the connecting portion may have a semicircular (rounded) bending form. The connecting portion may have a bending form having the shape of a rectangle with one open side (form in which opposite ends of the flat connecting portion are bent at an angle of 90 degrees to extend in the same direction). This is because the flexural rigidity and the torsional rigidity of the panel structure wall (first wall, second wall) can be further improved by connecting the respective parts by bending at an angle of 90 degrees. 
     In the first aspect, the pack case may include a third wall and a fourth wall that are each located on an outer side of the accommodated battery stack in a lateral direction orthogonal to the stacking direction, that form, together with the first wall and the second wall, a rectangular frame surrounding the battery stack from four sides, and that connects the first wall and the second wall. The third wall and the fourth wall may each include a lateral metal plate extending in the stacking direction, and the lateral metal plate may be connected to the first metal plate and the second metal plate via a corner connecting resin portion made from resin. 
     In the pack case, each of the third wall and the fourth wall includes the lateral metal plate extending in the stacking direction, and the lateral metal plate is connected to the panel structure wall (first wall, second wall) via the corner connecting resin portion. Therefore, part of the reaction force with respect to a compression force applied by the panel structure wall (first wall, second wall) to the battery stack can be transmitted to the third wall and the fourth wall each including the lateral metal plate via the corner connecting resin portions to be carried by the third wall and the fourth wall as a tensile force in the stacking direction. 
     The pack case may be configured such that the lateral metal plate is not directly connected to the first metal plate or the second metal plate forming the panel structure wall. That is, the pack case may be configured such that the lateral metal plate and the first and second metal plates are separate members or the lateral metal plate and the first metal plate are formed by individually bending at respective fold lines orthogonal to each other and raising upright from a bottom plate to which the lateral metal plate and the first plate are connected. Alternatively, the pack case may be configured such that one metal plate is bent so that the lateral metal plate is directly connected (continuous) to the first metal plate or the second metal plate forming the panel structure wall. 
     In the pack case according to the first aspect, the lateral metal plate may have an extending portion extending outward of the first metal plate of the panel structure wall in the stacking direction, in which the panel structure wall is the first wall or the second wall. The extending portion may include a panel engagement portion that is located outward of the first metal plate in the stacking direction and inward of a lateral edge of the first metal plate in the lateral direction, and that engages with the first metal plate via the corner connecting resin portion. 
     In the pack case, the panel engagement portion provided in the extending portion of the lateral metal plate is engaged with the first metal plate via the corner connecting resin portion. Thus, the lateral side wall including the lateral metal plate and the panel structure wall (first wall, second wall) can be more firmly connected, which enables the pack case to have higher rigidity and higher strength. 
     Examples of the panel engagement portion include a bulging portion that is formed by bulging a part of the extending portion of the lateral metal plate in a plate thickness direction (inward in the lateral direction) so that the bulging portion is located inward of a lateral edge of the first metal plate in the lateral direction and engages with the first metal plate via the corner connecting resin portion. The examples of the panel engagement portion further include a bending protruding portion that is formed by protruding a part of the extending portion so that the bending protruding portion engages with the first metal plate via the corner connecting resin portion. 
     In the pack case according to the above aspect, at least one of the third wall and the fourth wall may be a panel structure lateral side wall including the lateral metal plate, the second lateral metal plate, and a lateral interposed member. The second lateral metal plate may extend in the stacking direction and may be located outward or inward of the lateral metal plate in the lateral direction so as to face the lateral metal plate. The lateral interposed member may be interposed between the lateral metal plate and the second lateral metal plate, may be fixed to the lateral metal plate and the second lateral metal plate, and may have a density lower than that of a metal forming the lateral metal plate and the second lateral metal plate. 
     In the pack case, at least one of the third wall and the fourth wall is the panel structure lateral side wall having the sandwich panel structure. The panel structure lateral side wall has high flexural rigidity and torsional rigidity, compared to the case of using a single lateral metal plate as the lateral side wall or using only the lateral metal plate and the lateral interposed member as the lateral side wall. Therefore, the rigidity and the strength of the rectangular frame-shaped pack case can be further improved. 
     Here, the lateral metal plate and the second lateral metal plate may be separate metal plates, or may be formed by bending one metal plate into a U-shape for use. In addition, the sandwich panel structure composed of the lateral metal plate, the second lateral metal plate, and the lateral interposed member may be employed only in a part of the lateral side wall in the height direction that is orthogonal to the stacking direction and the lateral direction. 
     In the pack case according to the first aspect, each of the third wall and the fourth wall may be the panel structure lateral side wall. 
     In the pack case, each of the third wall and the fourth wall has the sandwich panel structure. Therefore, it is possible to provide the lightweight pack case having even higher rigidity. 
     In the pack case according to the first aspect, each of the first wall and the second wall may be the panel structure wall. 
     In the pack case, each of the first wall and the second wall has the sandwich panel structure. Therefore, it is possible to provide the lightweight pack case having even higher rigidity. 
     A second aspect of the present disclosure relates to a battery pack. The battery pack includes the pack case according to the first aspect and the battery stack accommodated in the pack case so as to be compressed and restrained in the stacking direction. 
     In the battery pack, at least one of the first wall and the second wall of the pack case compressing and restraining the battery stack is the panel structure wall having the sandwich panel structure with high flexural rigidity and high torsional rigidity. Therefore, it is possible to provide the battery pack that is lightweight but does not easily deform, at the first wall or the second wall that is the panel structure wall, with a reaction force to the compression force applied to the battery stack in order to compress and restrain the battery stack, while suppressing the reduction of the compression force due to deformation of the first wall or the second wall. 
     A third aspect of the present disclosure relates to a method for manufacturing a pack case. The pack case accommodates a battery stack in which a plurality of batteries are stacked in a stacking direction, and compresses and restrains the battery stack in the stacking direction. The pack case includes a first wall and a second wall. The first wall is located on a first side of the accommodated battery stack in the stacking direction, contacts a first end of the battery stack, and presses the battery stack toward a second side in the stacking direction. The second wall is located on the second side of the accommodated battery stack in the stacking direction, contacts a second end of the battery stack, and presses the battery stack toward the first side in the stacking direction. At least one of the first wall and the second wall is a panel structure wall including a first metal plate, a second metal plate, and an interposed member. The second metal plate is located outward of the first metal plate in the stacking direction and faces the first metal plate. The interposed member is interposed between the first metal plate and the second metal plate, is fixed to the first metal plate and the second metal plate, and has a density lower than that of a metal forming the first metal plate and the second metal plate. The method includes: setting the first metal plate and the second metal plate in a mold; and performing an injection molding for forming the panel structure wall by charging resin between the set first metal plate and the set second metal plate and molding the interposed member. 
     In the above method, the interposed member is formed by injection molding. Therefore, it is possible to easily manufacture the pack case including the panel structure wall (first wall, second wall). In the injection molding, besides using a solid interposed member made from resin, the interposed member may be provided with a lightening portion such as a lightening hole, in order to reduce the weight of the panel structure wall and further the weight of the pack case. 
     The method according to the third aspect further includes, prior to the setting, bending one metal plate into a U-shape to form a first metal plate portion that is the first metal plate, a second metal plate portion that is the second metal plate, and a connecting portion connecting the first metal plate portion and the second metal plate portion. 
     In the method, in the bending, the first metal plate portion that is the first metal plate and the second metal plate portion that is the second metal plate are formed by bending one metal plate into a U-shape. Thus, it is possible to reduce the number of parts of the panel structure walls, and therefore, reduce the number of parts of the pack case. Accordingly, it is possible to reduce man-hours required in the setting and the like, which facilitates the manufacture of the pack case. Further, the first metal plate portion and the second metal plate portion are connected. Therefore, it is possible to further improve the flexural rigidity and the torsional rigidity of the panel structure wall (first wall, second wall). 
     In the method according to the third aspect, the pack case may include a third wall and a fourth wall that are each located on an outer side of the accommodated battery stack in a lateral direction orthogonal to the stacking direction, that form, together with the first wall and the second wall, a rectangular frame surrounding the battery stack from four sides, and that connects the first wall and the second wall. The third wall and the fourth wall each may include a lateral metal plate extending in the stacking direction. The lateral metal plate may be connected to the first metal plate and the second metal plate via a corner connecting resin portion made from resin. In the setting, the lateral metal plate forming the third wall and the lateral metal plate forming the fourth wall may also be set in the mold. In the injection molding, the panel structure wall may formed and the corner connecting resin portion may be formed. 
     In the above method, the panel structure wall is formed and the corner connecting resin portion is formed in the injection molding, which further facilitates the manufacture of the pack case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is an explanatory diagram illustrating a battery pack according to a first embodiment; 
         FIG. 2  is a perspective view of a pack case according to the first embodiment and a first modification; 
         FIG. 3  is an enlarged sectional perspective view of the pack case according to the first embodiment, taken along line in  FIG. 2 ; 
         FIG. 4  is a perspective view of a metal case member used for the pack case according to the first embodiment and the first modification; 
         FIG. 5  is an enlarged perspective view of a corner (a part B in  FIG. 4 ) of the metal case member used for the pack case according to the first embodiment and the first modification; 
         FIG. 6  is a developed view of the metal case member used for the pack case according to the first embodiment and the first modification; 
         FIG. 7  is a flowchart showing processes of manufacturing the pack case and the battery pack according to the first and second embodiments and the first to fourth modifications; 
         FIG. 8  is a perspective view of the pack case according to the first modification, as viewed from a bottom side; 
         FIG. 9  is an enlarged sectional perspective view of the pack case according to the first modification, taken along line IX-IX in  FIG. 8 ; 
         FIG. 10  is a perspective view of a metal case member used for the pack case according to the second modification; 
         FIG. 11  is an enlarged perspective view of a corner (a part D in  FIG. 10 ) of the metal case member used for the pack case according to the second modification; 
         FIG. 12  is an enlarged sectional perspective view of the corner of the metal case member used for the pack case according to the second modification, taken along line XII-XII in  FIG. 11 ; 
         FIG. 13  is a perspective view of the pack case according to the second modification; 
         FIG. 14  is an enlarged perspective view of a corner (a part F in  FIG. 13 ) of the pack case according to the second modification; 
         FIG. 15  is an enlarged sectional perspective view of the corner of the pack case according to the second modification, taken along line XV-XV in  FIG. 14 ; 
         FIG. 16  is a perspective view of the pack case according to the third modification; 
         FIG. 17  is an enlarged sectional perspective view of a corner of the pack case according to the third modification, taken along line XVII-XVII in  FIG. 16 ; 
         FIG. 18  is a perspective view of a metal case member used for the pack case according to the third modification; 
         FIG. 19  is an enlarged perspective view of a corner (a part I in  FIG. 18 ) of the metal case member used for the pack case according to the third modification; 
         FIG. 20  is a perspective view of a metal case member used for the pack case according to the fourth modification; 
         FIG. 21  is an enlarged perspective view of a corner (a part J in  FIG. 20 ) of the metal case member used for the pack case according to the fourth modification; 
         FIG. 22  is a perspective view of the pack case according to the fourth modification; 
         FIG. 23  is an enlarged perspective view of a corner (a part K in  FIG. 22 ) of the pack case according to the fourth modification; 
         FIG. 24  is a perspective view of the pack case according to the second embodiment; 
         FIG. 25  is a sectional perspective view of the pack case according to the second embodiment, taken along line XXV-XXV in  FIG. 24 ; and 
         FIG. 26  is a perspective view of a metal case member used for the pack case according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings.  FIG. 1  shows a battery pack  1  according to the first embodiment. The battery pack  1  is an in-vehicle battery pack that is mounted on a vehicle such as a hybrid car, a plug-in hybrid car, and an electric vehicle. The battery pack  1  includes: a battery stack  5  in which batteries (cells)  2 , spacers  3  and end plates  4  are stacked in a stacking direction SH (right-left direction in  FIG. 1 ); and a pack case  10  accommodating the battery stack  5  while compressing the battery stack  5  in the stacking direction SH with a compression force KF. 
     Among these, the battery stack  5  includes the rectangular (cuboid) batteries  2  and the rectangular plate-shaped spacers  3  stacked alternately, as well as the rectangular plate-shaped metal end plates  4  arranged at the opposite ends in the stacking direction SH. 
     The batteries  2  are sealed rectangular lithium ion secondary batteries. The batteries  2  are connected in series via a bus bar (not shown). Each battery  2  contains electrodes (not shown) together with a non-aqueous electrolyte solution in a battery case  2   a  made of metal (aluminum in the first embodiment) and having a cuboid box shape. A positive terminal member  2   b  and a negative terminal member  2   c  are fixed to an upper surface  2   au  of the battery case  2   a  while being insulated from the battery case  2   a . The terminal members  2   b ,  2   c  are connected to and electrically connected to a positive electrode plate or a negative electrode plate of an electrode (not shown) in the battery case  2   a , and pass through the upper surface  2   au  of the battery case  2   a  to the upper part of the battery. 
     The spacers  3  are rectangular plate-shaped members made from insulating resin. Each spacer  3  is interposed between two batteries  2  adjacent to each other in the stacking direction SH to insulate the battery cases  2   a  of the batteries  2  and forms a heat dissipation path for each battery  2 . The end plates  4  are rectangular plate-shaped members made of metal (aluminum in the first embodiment), and disposed on the outer side of the batteries  2  at the opposite ends in the stacking direction SH. 
     The pack case  10  (see also  FIG. 2 ) has the shape of a bottomed rectangular tube opening only on an upper side HHU in a height direction HH that is orthogonal to the stacking direction SH. The pack case  10  includes a rectangular plate-shaped bottom wall  11  and four walls  12  to  15  extending upright from four side edges of the bottom wall  11  toward the upper side HHU to form a rectangular frame shape. Among these, a first side wall  12  is located on a first side SH 1  (right side in  FIG. 1 , lower right side in  FIG. 2 ) in the stacking direction SH, and a second side wall  13  is located on a second side SH 2  (left side in  FIG. 1 , upper left side in  FIG. 2 ) in the stacking direction SH and faces the first side wall  12 . A third side wall  14  and a fourth side wall  15  extend in the stacking direction SH so as to be orthogonal to a lateral direction YH orthogonal to the stacking direction SH and the height direction HH and so as to face each other, as shown in  FIG. 2 . The four walls  12  to  15  are connected to each other by corner connecting resin portions  36  (described later) located at the four corners. 
     The pack case  10  includes a metal case member  20  shown in  FIGS. 4 and 5  and a resin case member  30  provided so as to cover the metal case member  20  from outside. The resin case member  30  is formed by resin injection molding, and is fixed to and integrated with the metal case member  20 . 
     The metal case member  20  (see  FIGS. 4 and 5 ) is formed by bending a flat metal plate  20 M made of a galvanized steel plate shown in  FIG. 6 , and includes a rectangular bottom metal plate portion  21  and rectangular side wall metal plate portions  22  to  25  extending upright from the four side edges of the bottom metal plate portion  21  to the upper side HHU. A first side wall metal plate portion  22  is located on the first side SH 1  (lower right side in  FIG. 4 ) in the stacking direction SH, and a second side wall metal plate portion  23  is located on the second side SH 2  (upper left side in  FIG. 4 ) in the stacking direction SH and faces the first side wall metal plate portion  22 . A third side wall metal plate portion  24  and a fourth side wall metal plate portion  25  extend in the stacking direction SH so as to be orthogonal to the lateral direction YH and to face each other, as shown in  FIG. 4 . The four side wall metal plate portions  22  to  25  are not directly connected to each other but are connected via the bottom metal plate portion  21  as shown in  FIG. 4 . 
     As shown in  FIG. 5 , the first side wall metal plate portion  22  is formed by bending one metal plate  20 M into a U shape (shape of a rectangle with one open side), and has an inner metal plate portion  22   a , a connecting portion  22   b , and an outer metal plate portion  22   c . The inner metal plate portion  22   a  is formed by bending the metal plate  20 M at an angle of 90 degrees so as to be connected to the bottom metal plate portion  21  and extend upright to the upper side HHU. The connecting portion  22   b  has a plate shape and is formed by further bending the metal plate  20 M at an angle of 90 degrees so as to be connected to the inner metal plate portion  22   a  and extend to the first side SH 1  in the stacking direction SH. The outer metal plate portion  22   c  is formed by further bending the metal plate  20 M at an angle of 90 degrees so as to be connected to the connecting portion  22   b  and extend to a lower side HHD while facing the inner metal plate portion  22   a . The connecting portion  22   b  connects the inner metal plate portion  22   a  and the outer metal plate portion  22   c.    
     Similarly to the first side wall metal plate portion  22 , the second side wall metal plate portion  23  has an inner metal plate portion  23   a , a connecting portion  23   b , and an outer metal plate portion  23   c . The inner metal plate portion  23   a  is formed by bending the metal plate  20 M at an angle of 90 degrees so as to be connected to the bottom metal plate portion  21  and extend upright to the upper side HHU. The connecting portion  23   b  has a plate shape and is formed by further bending the metal plate  20 M at an angle of 90 degrees so as to be connected to the inner metal plate portion  23   a  and extend to the second side SH 2  in the stacking direction SH. The outer metal plate portion  23   c  is formed by further bending the metal plate  20 M at an angle of 90 degrees so as to be connected to the connecting portion  23   b  and extend to the lower side HHD while facing the inner metal plate portion  23   a . The connecting portion  23   b  connects the inner metal plate portion  23   a  and the outer metal plate portion  23   c . Further, the third side wall metal plate portion  24  and the fourth side wall metal plate portion  25  have their respective end portions bent at an angle of 90 degrees in order to increase their rigidity. 
     The resin case member  30  is made from glass fiber reinforced polyamide and is formed in a bottomed rectangular tube shape so as to cover the metal case member  20  from outside, as shown in  FIGS. 2 to 4 . That is, in the bottom wall  11 , a bottom plate portion  31  is formed on the lower side HHD of the bottom metal plate portion  21  so as to be fixed to the bottom metal plate portion  21 . In the third side wall  14 , a third side wall resin portion  34  is formed on a first side YH 1  of the third side wall metal plate portion  24  in the lateral direction YH so as to be fixed to the third side wall metal plate portion  24 . Similarly in the fourth side wall  15 , a fourth side wall resin portion  35  is provided on a second side YH 2  of the fourth side wall metal plate portion  25  in the lateral direction YH so as to be fixed to the fourth side wall metal plate portion  25 . 
     In the first side wall  12 , a first side wall resin portion  32  is formed outward SHO of the inner metal plate portion  22   a  of the first side wall metal plate portion  22  in the stacking direction SH (on the first side SH 1  in the stacking direction SH) and inward SHI of the outer metal plate portion  22   c  of the first side wall metal plate portion  22  in the stacking direction SH (on a second side SH 2  in the stacking direction SH) i.e., between the inner metal plate portion  22   a  and the outer metal plate portion  22   c , so as to be fixed to the inner metal plate portion  22   a  and the outer metal plate portion  22   c . In the second side wall  13 , a second side wall resin portion  33  is formed outward SHO of the inner metal plate portion  23   a  of the second side wall metal plate portion  23  in the stacking direction SH (on the second side SH 2  in the stacking direction SH) and inward SHI of the outer metal plate portion  23   c  of the second side wall metal plate portion  23  in the stacking direction SH (on the first side SH 1  in the stacking direction SH), i.e., between the inner metal plate portion  23   a  and the outer metal plate portion  23   c , so as to be fixed to the inner metal plate portion  23   a  and the outer metal plate portion  23   c.    
     The bottom plate portion  31  and the four side wall resin portions  32  to  35  are connected to each other by the corner connecting resin portions  36  located at the four corners. Thus, as described above, the four walls  12  to  15  including the four side wall resin portions  32  to  35  are connected to each other by the corner connecting resin portions  36 . 
     In the first embodiment, the above-mentioned portions of the metal case member  20  and the above-mentioned portions of the resin case member  30  are fixed to each other by applying a primer (for example, VESTAMELT Hylink (registered trademark) manufactured by Daicel-Evonik, Ltd., etc.) to the portions of the metal case member  20 , which serve as fixing surfaces to which the portions of the resin case member  30  are fixed, followed by injection molding such that resin adheres to the fixing surfaces of the metal case member  20 . 
     As described above, the first side wall  12  has a so-called sandwich panel structure, in which the first side wall resin portion  32  is interposed between and fixed to the inner metal plate portion  22   a  and the outer metal plate portion  22   c . Thus, compared to a case of using, instead of the first side wall  12 , a wall including only the inner metal plate portion  22   a  or a wall including only the inner metal plate portion  22   a  and the first side wall resin portion  32  fixed to the inner metal plate portion  22   a , flexural rigidity and torsional rigidity of the first side wall  12  are high. Thus, it is possible to suppress deformation of the first side wall  12  due to a reaction force RKF to the compression force KF that compresses the battery stack  5  in the stacking direction SH thereby lowering the compression force KF that presses the battery stack  5 . In addition, the first side wall resin portion  32  (glass fiber reinforced polyamide, density: 1.35 g/cm 3 ) interposed between the inner metal plate portion  22   a  and the outer metal plate portion  22   c  has a density lower than that of a metal (galvanized steel plate, density: 7.8 g/cm 3 ) forming the inner metal plate portion  22   a  and the outer metal plate portion  22   c . Therefore, the first side wall  12  can be made lightweight compared to the case of using a solid metal plate having the same thickness instead of the sandwich panel structure. Thus, the pack case  10  can be also made lightweight. Note that the second side wall  13  having the same sandwich panel structure provides the same effects as those of the first side wall  12  described above, and therefore description thereof will be omitted. 
     In the pack case  10 , the first side wall metal plate portion  22  that is a part of one metal plate  20 M is bent into a U shape (shape of a rectangle with one open side) to provide the inner metal plate portion  22   a  and the outer metal plate portion  22   c  functioning as a first metal plate and a second metal plate, respectively, to form the first side wall  12 . Therefore, it is possible to form the pack case  10  with a small number of parts and make the pack case  10  inexpensive. In contrast to the case where the first metal plate and the second metal plate are formed as separate parts, the inner metal plate portion  22   a  and the outer metal plate portion  22   c  are connected via the connecting portion  22   b . That is, a part of one metal plate  20 M forms the inner metal plate portion  22   a , the outer metal plate portion  22   c , and the connecting portion  22   b  connecting the inner metal plate portion  22   a  and the outer metal plate portion  22   c . Therefore, it is possible to further improve the flexural rigidity and the torsional rigidity of the first side wall  12 . In particular, in the first side wall  12  of the first embodiment, the inner metal plate portion  22   a , the connecting portion  22   b , and the outer metal plate portion  22   c  are connected by bending at an angle of 90 degrees. Thus, it is possible to further improve the flexural rigidity and the torsional rigidity of the first side wall  12 . Note that the second side wall  13  having the same sandwich panel structure provides the same effects as those of the first side wall  12  described above, and therefore description thereof will be omitted. 
     Moreover, in the pack case  10 , both the first side wall  12  and the second side wall  13  located on the first side SH 1  and the second side SH 2 , respectively, in the stacking direction SH have the sandwich panel structure. Therefore, it is possible to provide the lightweight pack case  10  having even higher rigidity. 
     Further, in the battery pack  1  of the first embodiment, which includes the pack case  10 , the first side wall  12  and the second side wall  13  of the pack case  10  compressing and restraining the battery stack  5  are panel structure walls each having the sandwich panel structure with high flexural rigidity and high torsional rigidity. Therefore, it is possible to provide the battery pack  1  that is lightweight but does not easily deform with the reaction force RKF to the compression force KF applied to the battery stack  5  in order to compress and restrain the battery stack  5 , while suppressing the reduction of the compression force KF due to deformation. 
     In the first embodiment, unlike the first side wall  12  and the second side wall  13 , each of the third side wall  14  and the fourth side wall  15  does not have the sandwich panel structure. However, the sandwich panel structure may be adopted that is similar to those of the first side wall  12  and the second side wall  13 , or similar to those of third side walls  514 A,  514 B and a fourth side wall  515  in a pack case  510  of a second embodiment to be described later. In such a pack case, each of the third side wall and the fourth side wall has the sandwich panel structure. Therefore, it is possible to provide the lightweight pack case having even higher rigidity. 
     The pack case  10  of the first embodiment is manufactured by the following procedure (see  FIG. 7 ). First, in a stamping step S 1 , the metal plate  20 M is formed by stamping from a hoop-shaped metal plate (not shown). Next, in an application step S 2 , a primer is applied to a portion of the metal plate  20 M, which serves as a fixing surface that is fixed to resin, and is dried. Next, in a bending step S 3 , the metal case member  20  is formed by bending the metal plate  20 M. The metal plate  20 M may be obtained by stamping in the stamping step, after the application step in which the primer is applied to the metal plate that has not been subjected to the stamping. 
     Next, in a setting step S 4 , the metal case member  20  is set at a predetermined position in a mold (not shown) provided in an injection molding apparatus (not shown). Subsequently, in an injection molding step S 5 , the injection molding apparatus is operated to inject resin and the resin case member  30  is molded so as to be fixed to the metal case member  20 . Thus, the pack case  10  is completed. 
     In the method for manufacturing the pack case  10  described above, the first side wall resin portion  32  and the second side wall resin portion  33  are formed by injection molding. Therefore, it is possible to easily manufacture the pack case  10  having the first side wall  12  and the second side wall  13  that are the panel structure walls. 
     Further, in the bending step S 3 , a part of one metal plate  20 M is bent into a U shape (shape of a rectangle with one open side) to form the inner metal plate portion  22   a , the outer metal plate portion  22   c , and the connecting portion  22   b  of the first side wall metal plate portion  22 . The same applies to the second side wall metal plate portion  23 . Thus, it is possible to reduce the number of parts of the first side wall metal plate portion  22  and the second side wall metal plate portion  23  that are the panel structure walls, and therefore, to reduce the number of parts of the pack case  10 . Accordingly, it is possible to reduce man-hours required in the subsequent setting step S 4  and the like, which facilitates the manufacture of the pack case  10 . In addition, the inner metal plate portion  22   a  and the outer metal plate portion  22   c  (the inner metal plate portion  23   a  and the outer metal plate portion  23   c ) are connected. Therefore, it is possible to further improve the flexural rigidity and the torsional rigidity of the first side wall  12  and the second side wall  13  that are the panel structure walls. 
     In addition, in the setting step S 4 , the metal case member  20  is set in the mold, whereby the third side wall metal plate portion  24  and the fourth side wall metal plate portion  25  that function as lateral side metal plates can be set in the mold. In the injection molding step S 5 , the first side wall  12  and the second side wall  13  that are the panel structure walls are formed, and the corner connecting resin portion  36  is formed at each corner. Thus, in this manufacturing method, the pack case  10  can be manufactured more easily. 
     Next, the manufacture of the battery pack  1  will be described (see  FIGS. 1 and 7 ). First, in a battery stack forming step S 11 , the battery stack  5  is formed. That is, the batteries  2  and the spacers  3  that have been separately manufactured are alternately arranged to be stacked, and the end plates  4  are arranged outward SHO of the outermost batteries  2  in the stacking direction SH (the outermost battery  2  on the first side SH 1  in the stacking direction SH and the outermost battery  2  on the second side SH 2  in the stacking direction SH). Thus, the battery stack  5  is formed. 
     Next, in an insertion and restraint step S 12 , the battery stack  5  is compressed in the stacking direction SH with a compression force larger than the compression force KF, which is applied by a compression tool (not shown), the battery stack  5  is inserted into the pack case  10  with battery stack  5  compressed in length (dimension in the stacking direction SH), and then, the compression force of the compression tool is released. Then, the length of the battery stack  5  slightly increases, and the battery stack  5  is restrained by the pack case  10  with the compression force KF. Thereafter, the compression tool is removed from the battery stack  5 . 
     Thereafter, in a connection step S 13 , the positive terminal member  2   b  and the negative terminal member  2   c  of each battery  2  are connected to each other in a predetermined connection pattern (for example, in series) using a bus bar (not shown) or the like. Thus, the battery pack  1  is completed. Pack cases  110 ,  210 ,  310 ,  410 ,  510  and battery packs  101 ,  201 ,  301 ,  401 ,  501  according to first to fourth modifications and the second embodiment described later are also manufactured by the same manufacturing method. 
     First Modification 
     Next, the pack case  110  according to the first modification will be described with reference to  FIGS. 2, 8, and 9 . The pack case  110  according to the first modification has the same appearance as the pack case  10  of the first embodiment (see  FIG. 2 ), and includes the metal case member  20  that is the same as that of the first embodiment (see  FIGS. 4 and 5 ). 
     However, in the pack case  10  of the first embodiment, the first side wall resin portion  32  of the first side wall  12  that is the panel structure wall and the second side wall resin portion  33  of the second side wall  13  that is the panel structure wall are formed as solid resin members (see  FIG. 3 ). 
     In contrast, in the pack case  110  of the first modification, each of a first side wall resin portion  132  of a first side wall  112  and a second side wall resin portion  133  of a second side wall  113  has a number of lightening portions  132   h ,  133   h  that are substantially rectangular columnar-shaped holes and arranged side by side in the lateral direction YH (see  FIGS. 8 and 9 ). 
     Thus, the first side wall  112  has the inner metal plate portion  22   a , the outer metal plate portion  22   c , and the first side wall resin portion  132  interposed between and fixed to the inner metal plate portion  22   a  and the outer metal plate portion  22   c , and is the panel structure wall having the sandwich panel structure. In addition, since the first side wall resin portion  132  has the lightening portions  132   h , it is possible to reduce the weight of the first side wall resin portion  132  by the weight of the lightening portions  132   h , compared to the first side wall resin portion  32  of the first embodiment. Therefore, it is possible to reduce the weight of the first side wall  112  and further, reduce the weight of the pack case  110 . The same applies to the second side wall  113  having the lightening portions  133   h.    
     When the first side wall resin portion  132  and the second side wall resin portion  133  are provided with the lightening portions  132   h ,  133   h , the form and the amount of the lightening portions  132   h ,  133   h  to be provided may be determined, considering a merit of weight reduction of the first side wall  112  and the second side wall  113  and the degree of degradation of the flexural rigidity and the torsional rigidity. Further, in forming the pack case  110  of the first modification by injection molding, the first side wall resin portion  132  and the second side wall resin portion  133  may be provided with the lightening portions  132   h ,  133   h  using pins or the like. 
     Second Modification 
     Next, the pack case  210  according to the second modification will be described with reference to  FIGS. 10 to 15 . The pack case  210  according to the second modification and a metal case member  220  included in the pack case  210  have substantially the same appearances as the pack case  10  and the metal case member  20 , respectively, of the first embodiment (see  FIGS. 2, 4 and 5 ). 
     However, in the pack case  10  of the first embodiment, the first side wall  12  and the second side wall  13  are connected with the third side wall  14  and the fourth side wall  15  at the four corners of the bottom wall  11  with only the corner connecting resin portions  36  made from resin. Therefore, when the battery stack  5  is inserted into the pack case  10  and the compression force KF is applied to the battery stack  5  from the first side wall  12  and the second side wall  13 , the reaction force RKF to the compression force KF is applied to the first side wall  12  and the second side wall  13  (see  FIG. 1 ). The reaction force RKF is further transmitted to the third side wall  14  and the fourth side wall  15  in addition to the bottom wall  11 , and large stresses are also applied to portions that connect the first and second side walls  12 ,  13  and the third and fourth side walls  14 ,  15  (corner connecting resin portions  36 ). Thus, with only the corner connecting resin portions  36  made from resin, creep or cracking is likely to occur, and it is difficult to maintain the compression force KF. 
     In contrast, as can be easily understood from  FIGS. 11, 12, and 15 , in the pack case  210  of the second modification, connection between first and second side walls  212 ,  213 , and third and fourth side walls  214 ,  215  is improved. 
     Specifically, a third side wall metal plate portion  224  of the metal case member  220  has an extending portion  224 A extending further outward SHO in the stacking direction SH (more toward the first side SH 1  in the stacking direction SH, lower right side in  FIGS. 11 and 12 ) than an inner metal plate portion  222   a  of the first side wall  212 . The extending portion  224 A has panel engagement portions  224 Ak that are located outward SHO of the inner metal plate portion  222   a  in the stacking direction SH (on the first side SH 1  in the stacking direction SH) and inward YHI of an edge  222   at  of the inner metal plate portion  222   a  in the lateral direction YH (on the second side YH 2  in the lateral direction YH, upper right side in  FIGS. 11 and 12 ) and that engage with the inner metal plate portion  222   a  via a corner connecting resin portion  236 . 
     In the second modification, the panel engagement portions  224 Ak are two bulging portions each formed by making parallel cuts extending in the height direction HH in the extending portion  224 A and bulging a portion between the cuts inward YHI in the lateral direction YH (on the second side YH 2  in the lateral direction YH, upper right side in  FIGS. 11 and 12 ). 
     Further, in the metal case member  220  of the pack case  210  (see  FIG. 10 ) according to the second modification, panel engagement portions are formed at the other three corners. That is, an extending portion  224 B of the third side wall metal plate portion  224  is also provided with panel engagement portions  224 Bk that are bulging portions similar to the panel engagement portions  224 Ak. In addition, extending portions  225 A,  225 B of a fourth side wall metal plate portion  225  are also provided with panel engagement portions (not shown) formed of bulging portions similar to the panel engaging portions  224 Ak. 
     Thus, in the pack case  210  of the second modification, the panel engagement portions  224 Ak etc. provided in the extending portions  224 A,  224 B,  225 A,  225 B of the third side wall metal plate portion  224  and the fourth side wall metal plate portion  225  are engaged with the inner metal plate portions  222   a ,  223   a  via the corner connecting resin portions  236 . Thus, the third side wall  214  and the fourth side wall  215  including the third side wall metal plate portion  224  and the fourth side wall metal plate portion  225  can be more firmly connected with the first side wall  212  and the second side wall  213  that are the panel structure walls, which enables the pack case  210  to have higher rigidity and higher strength. 
     As shown in  FIG. 15 , in the pack case  210  of the second modification, a first side wall resin portion  232  of the first side wall  212  is provided with lightening portions  232   h  as in the first modification. Therefore, it is possible to reduce the weight of the first side wall  212 , and further, to reduce the weight of the pack case  210 . Although not shown, a second side wall resin portion of the second side wall  213  is similarly provided with lightening portions. 
     Third Modification 
     Next, a pack case  310  according to a third modification will be described with reference to  FIGS. 16 to 19 . The pack case  310  according to the third modification and the metal case member  320  included therein also have substantially the same appearances as the pack case  10  and the metal case member  20  (see  FIGS. 2, 4, and 5 ) of the first embodiment. 
     However, in the pack case  10  of the first embodiment, the first side wall  12  and the second side wall  13  are connected with the third side wall  14  and the fourth side wall  15  at the four corners of the bottom wall  11  with only the corner connecting resin portions  36  made from resin. 
     In contrast, as can be easily understood from  FIGS. 17 and 19 , in the pack case  310  of the third modification, connection between first and second side walls  312 ,  313 , and third and fourth side walls  314 ,  315  is improved. 
     Specifically, a third side wall metal plate portion  324  of the metal case member  320  has an extending portion  324 A extending further outward SHO in the stacking direction SH (more toward the first side SH 1  in the stacking direction SH, lower right side in  FIGS. 17 and 19 ) than an inner metal plate portion  322   a  of the first side wall  312 . The extending portion  324 A has a panel engagement portion  324 Ak that is located outward SHO of the inner metal plate portion  322   a  in the stacking direction SH (on the first side SH 1  in the stacking direction SH) and inward YHI of an edge  322   at  of the inner metal plate portion  322   a  in the lateral direction YH (on the second side YH 2  in the lateral direction YH, upper right side in  FIGS. 17 and 19 ) and that engages with the inner metal plate portion  322   a  via a corner connecting resin portion  336 . 
     In the third modification, the panel engagement portion  324 Ak is a bending protruding portion formed by bending an end of the extending portion  324 A inward YHI in the lateral direction YH (toward the second side YH 2  in the lateral direction YH, upper right side in  FIGS. 17 and 19 ) and protruding the end inward YHI in the lateral direction YH (toward the second side YH 2  in the lateral direction YH) between the inner metal plate portion  322   a  and an outer metal plate portion  322   c.    
     Also in the metal case member  320  of the pack case  310  (see  FIG. 18 ) according to the third modification, panel engagement portions are formed at the other three corners. That is, an extending portion  324 B of the third side wall metal plate portion  324  is also provided with a panel engagement portion  324 Bk that is a bending protruding portion similar to the panel engagement portion  324 Ak. Also, extending portions  325 A,  325 B of the fourth side wall metal plate portion  325  are each provided with a panel engagement portion (not shown) formed of a bending protruding portion similar to the panel engagement portion  324 Ak. 
     Thus, in the pack case  310  of the third modification, the panel engagement portion  324 Ak etc. provided in the extending portions  324 A,  324 B,  325 A,  325 B of the third side wall metal plate portion  324  and the fourth side wall metal plate portion  325  are engaged with the inner metal plate portions  322   a ,  323   a  via the corner connecting resin portions  336 . Thus, the third side wall  314  and the fourth side wall  315  including the third side wall metal plate portion  324  and the fourth side wall metal plate portion  325  can be more firmly connected with the first side wall  312  and the second side wall  313  that are the panel structure walls, which enables the pack case  310  to have higher rigidity and higher strength. 
     Fourth Modification 
     Next, the pack case  410  according to the fourth modification will be described with reference to  FIGS. 20 to 23 . The pack case  410  according to the fourth modification and a metal case member  420  included therein also have substantially the same appearances as the pack case  10  and the metal case member  20  (see  FIGS. 2, 4 and 5 ) of the first embodiment. 
     However, in the pack case  10  of the first embodiment, the first side wall  12  and the second side wall  13  are connected with the third side wall  14  and the fourth side wall  15  at the four corners of the bottom wall  11  with only the corner connecting resin portions  36  made from resin. 
     In contrast, as can be easily understood from  FIGS. 21 and 23 , in the pack case  410  of the fourth modification, connection between first and second side walls  412 ,  413 , and third and fourth side walls  414 ,  415  is improved. 
     Specifically, a third side wall metal plate portion  424  of the metal case member  420  has an extending portion  424 A extending further outward SHO in the stacking direction SH (more toward the first side SH 1  in the stacking direction SH, lower right side in  FIGS. 21 and 23 ) than an inner metal plate portion  422   a  of the first side wall  412 . The extending portion  424 A has a panel engagement portion  424 Ak that is located outward SHO of the inner metal plate portion  422   a  in the stacking direction SH (on the first side SH 1  in the stacking direction SH) and inward YHI of an edge  422   at  of the inner metal plate portion  422   a  in the lateral direction YH (on the second side YH 2  in the lateral direction YH, upper right side in  FIGS. 21 and 23 ) and that engages with the inner metal plate portion  422   a  via a corner connecting resin portion  436 . 
     In the fourth modification, the panel engagement portion  424 Ak is a bending protruding portion formed by bending an end of the extending portion  424 A to the second side YH 2  in the lateral direction YH (inward YHI in the lateral direction YH, upper right side in  FIGS. 21 and 23 ) and protruding the end inward YHI in the lateral direction YH (toward the second side YH 2  in the lateral direction YH) at the same position in the stacking direction SH as an outer metal plate portion  422   c . The outer metal plate portion  422   c  is provided with a notch  422 Ck that can accommodate the panel engagement portion  424 Ak. 
     In the metal case member  420  of the pack case  410  (see  FIG. 20 ) according to the fourth modification, panel engagement portions are formed at the other three corners. That is, the extending portion  424 B of the third side wall metal plate portion  424  is also provided with a panel engagement portion  424 Bk that is a bending protruding portion similar to the panel engagement portion  424 Ak. Also, extending portions  425 A,  425 B of the fourth side wall metal plate portion  425  are each provided with a panel engagement portion  425 Ak etc. formed of a bending protruding portion similar to the panel engagement portion  424 Ak etc. 
     Thus, in the pack case  410  of the fourth modification, the panel engagement portion  424 Ak etc. provided in the extending portions  424 A,  424 B,  425 A,  425 B of the third side wall metal plate portion  424  and the fourth side wall metal plate portion  425  are engaged with the inner metal plate portions  422   a ,  423   a  via the corner connecting resin portions  436 . Thus, the third side wall  414  and the fourth side wall  415  including the third side wall metal plate portion  424  and the fourth side wall metal plate portion  425  can be more firmly connected with the first side wall  412  and the second side wall  413  that are the panel structure walls, which enables the pack case  410  to have higher rigidity and higher strength. 
     Second Embodiment 
     Next, the pack case  510  according to the second embodiment will be described with reference to  FIGS. 24 to 26 . Unlike the pack case  10  and the metal case member  20  (see  FIGS. 2, 4 and 5 ) of the first embodiment, the pack case  510  and the metal case member  520  included in the pack case  510  according to the second embodiment have a pair of accommodating portions  510 A,  510 B such that two battery stacks  5  can be accommodated therein while being arranged side by side. 
     As can be understood from  FIG. 26 , a metal case member  520  is also formed by bending a flat metal plate, and includes a pair of bottom metal plate portions  521 A,  521 B, each having a rectangular plate shape, and side wall metal plate portions  522 A,  522 B,  523 A,  523 B,  524 A,  524 B, and  525  each having a rectangular shape and extending upright from four sides of the bottom metal plate portions  521 A,  521 B to the upper side HHU. 
     Among these, in the accommodating portion  510 A, the first side wall metal plate portion  522 A is located on the first side SH 1  in the stacking direction SH (lower right side in  FIG. 26 ), and the second side wall metal plate portion  523 A is located on the second side SH 2  in the stacking direction SH (upper left side in  FIG. 26 ) and faces the first side wall metal plate portion  522 A. The third side wall metal plate portion  524 A and a fourth side wall metal plate portion  525 A extend in the stacking direction SH so as to be orthogonal to the lateral direction YH and to face each other. 
     In the accommodating portion  510 B, the first side wall metal plate portion  522 B is located on the first side SH 1  in the stacking direction SH (lower right side in  FIG. 26 ), and the second side wall metal plate portion  523 B is located on the second side SH 2  in the stacking direction SH (upper left side in  FIG. 26 ) and faces the first side wall metal plate portion  522 B. The third side wall metal plate portion  524 B and a fourth side wall metal plate portion  525 B extend in the stacking direction SH so as to be orthogonal to the lateral direction YH and to face each other. However, in the metal case member  520  of the second embodiment, the fourth side wall metal plate portions  525 A,  525 B are shared by the accommodating portions  510 A,  510 B. Further, the side wall metal plate portions  522 A to  524 A,  525  arranged on the four sides are not directly connected to one another and are connected via the bottom metal plate portion  521 A, and the side wall metal plate portions  522 B to  524 B,  525  arranged on the four sides are not directly connected to one another and are connected via the bottom metal plate portion  521 B. 
     Here, since the first side wall metal plate portions  522 A,  522 B and the second side wall metal plate portions  523 A,  523 B are similar to the first side wall metal plate portion  22  and the second side wall metal plate portion  23  of the first embodiment (see  FIGS. 4 and 5 ), description thereof will be omitted. 
     The third side wall metal plate portion  524 A has, unlike the third side wall metal plate portion  24  of the first embodiment, an inner metal plate portion  524 Aa bent from a bottom metal plate portion  521 A and standing upright, an outer metal plate portion  524 Ac located outward YHO of the inner metal plate portion  524 Aa in the lateral direction YH (on the first side YH 1  in the lateral direction YH) and facing the inner metal plate portion  524 Aa, and a connecting portion  524 Ab connecting the inner metal plate portion  524 Aa and the outer metal plate portion  524 Ac. Similarly, the third side wall metal plate portion  524 B has an inner metal plate portion  524 Ba bent from a bottom metal plate portion  521 B and standing upright, an outer metal plate portion  524 Bc located outward YHO of the inner metal plate portion  524 Ba in the lateral direction YH (on the second side YH 2  in the lateral direction YH) and facing the inner metal plate portion  524 Ba, and a connecting portion  524 Bb connecting the inner metal plate portion  524 Ba and the outer metal plate portion  524 Bc. 
     The third side wall  514 A of the pack case  510  has a third side wall resin portion  534 A interposed between and fixed to the inner metal plate portion  524 Aa and the outer metal plate portion  524 Ac and having a density lower than that of the metal forming the inner metal plate portion  524 Aa and the outer metal plate portion  524 Ac. Thus, the third side wall  514 A is a panel structure lateral side wall having the sandwich panel structure. Similarly, the third side wall  514 B has a third side wall resin portion  534 B between the inner metal plate portion  524 Ba and the outer metal plate portion  524 Bc, and is the panel structure lateral side wall having the sandwich panel structure. 
     The fourth side wall metal plate portion  525  has, unlike the fourth side wall metal plate portion  25  of the first embodiment, the fourth side wall metal plate portion  525 A bent from the bottom metal plate portion  521 A and standing upright, the fourth side wall metal plate portion  525 B located outward YHO of the fourth side wall metal plate portion  525 A in the lateral direction YH (on the second side YH 2  in the lateral direction YH) and facing the fourth side wall metal plate portion  525 A while being bent from the bottom metal plate portion  521 B and standing upright, and a connecting portion  525 C connecting the fourth side wall metal plate portion  525 A and the fourth side wall metal plate portion  525 B. 
     The fourth side wall  515  of the pack case  510  has a fourth side wall resin portion  535  interposed between and fixed to the fourth side wall metal plate portion  525 A and the fourth side wall metal plate portion  525 B and having a density lower than that of the metal forming the fourth side wall metal plate portion  525 A and the fourth side wall metal plate portion  525 B. Thus, the fourth side wall  515  is the panel structure lateral side wall having the sandwich panel structure. 
     As described above, in the pack case  510 , all the third side walls  514 A,  514 B and the fourth side wall  515  are the panel structure lateral side walls. Thus, compared to the case using, instead of the third side walls  514 A,  514 B and the fourth side wall  515 , only the inner metal plate portions  524 Aa,  524 Ba,  525 Aa each formed of a single metal plate, or using only the inner metal plate portions  524 Aa,  524 Ba,  525 Aa, the third side wall resin portions  534 A,  534 B, and the fourth side wall resin portion  535 , the third side wall  514 A,  514 B and the fourth side wall  515  have higher flexural rigidity and torsional rigidity. Therefore, the rigidity and the strength of the pack case  510  can be further improved. In particular, in the pack case  510  of the second embodiment, both the third side wall  514 A and the fourth side wall  515 , and both the third side wall  514 B and the fourth side wall  515  are the panel structure lateral side walls having the sandwich panel structure. Therefore, it is possible to provide the pack case  510  that is lightweight but has even higher rigidity. 
     In the pack case  510  of the second embodiment, as in the pack case  10  of the first embodiment, the first side walls  512 A,  512 B and the second side walls  513 A,  513 B are also the panel structure walls having the sandwich panel structure. Therefore, it is possible to provide the pack case  510  that is lightweight but has even higher rigidity. 
     In the above, description has been made with the first and second embodiments and the first to fourth modifications. However, needless to say, the present disclosure is not limited to the embodiments and the like, and may be appropriately changed for application without departing from the scope of the present disclosure. For example, the first and second embodiments and the first to fourth modifications describe the pack case  10  and the like, in which the metal case member  20  and the like are each formed by bending the single metal plate  20 M or the like. However, the present disclosure is not limited to this, and the metal case member constituting the pack case  10  and the like may be formed of a plurality of metal plates. 
     In the second to fourth modifications, the extending portions  224 A,  324 A,  424 A, etc. of the third side wall metal plate portions  224 ,  324 ,  424 , etc. are provided with the panel engagement portions  224 Ak,  324 Ak,  424 Ak, etc., and the third side wall metal plate portions  224 ,  324 ,  424 , etc. themselves do not have the sandwich panel structure. However, the third side wall  214  etc. may be the panel structure lateral side wall having the sandwich panel structure, with the panel engagement portion  224 Ak provided in the extending portion  224 A etc. of the third side wall metal plate portion  224  etc. Thereby, it is possible to provide a pack case with even higher rigidity and strength. 
     The first and second embodiments and the first to fourth modifications show examples in which the first side wall  12  etc. and the second side wall  13  etc. have the inner metal plate portion  22   a  etc. and the outer metal plate portion  22   c  etc. with the same dimension in the height direction HH and have the sandwich panel structure over the entire length along the height direction HH. However, for example, in the pack case  510  of the second embodiment, the outer metal plate portions may have a dimension in the height direction HH shorter than that of the inner metal plate portions, as in the third side walls  514 A,  514 B, so that each of the first side wall and the second side wall has the sandwich panel structure only at a part thereof in the height direction. Moreover, each of the third side wall and the fourth side wall may have the sandwich panel structure only at a part thereof in the height direction.