Abstract:
Disclosed is a battery module which comprises a cell unit that comprises cells, and a case that contains the cell unit. The case comprises: a first member which has a first guide portion, and a second member which has a second guide portion that is fitted into the first guide portion by being slid on the first guide portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese patent application serial no. JP2010-131877, filed Jun. 9, 2010, which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present invention relates to a battery module. 
     BACKGROUND 
     A battery receiving container is known in which a metal container main body or case with an opening and that houses a flat battery pack of laminated cells inside and a metal lid that closes the opening formed in the metal container main body, wherein an open end periphery of the metal container main body and a lid end periphery of the metal lid are joined each other by seam rolling. 
     BRIEF SUMMARY 
     However, there has been a problem for recycling or the like that, in the case of dismantling the binding portion formed by tightening or seam-rolling of that conventional battery, substantial man-hours are required for dismantling or disassembly. 
     The problem that the present invention attempts to solve is to provide a battery module that facilitates disassembly. 
     The present invention solves the above problem by storing the cell unit by a first member having a first guide portion and a second member having a second guide portion that mates or engages with the first guide portion by sliding on the first guide portion. 
     According to the present invention the man-hours for dismantling may be reduced by sliding the second member to dismantle at least part of the case when disassembling the battery module 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
         FIG. 1  is an exploded perspective view showing a battery module of an embodiment according to present invention. 
         FIG. 2  is a plan view of the battery in dismantled state. 
         FIG. 3  is a partial cross-sectional view along the line A-A of the battery module of  FIG. 1   
         FIG. 4  is a partial cross-sectional view along the line A-A of the battery module of  FIG. 1   
         FIG. 5  is an enlarged view of portion B of the battery module in  FIGS. 3 and 4 . 
         FIG. 6  is a partial cross-sectional view showing a modification of the battery module of  FIG. 4 . 
         FIG. 7  is an enlarged view of a portion C of the battery module in  FIG. 6 . 
         FIG. 8  is an exploded side view showing a modification of the battery module of  FIG. 1   
         FIG. 9  is a perspective view of a battery module of an embodiment according to the present invention. 
         FIG. 10  is an enlarged view of portion D of the battery module of  FIG. 8 . 
         FIG. 11  is an enlarged view of the portion E of the battery module of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Described below with reference to the accompanying drawings is an embodiment of the present invention. 
       FIG. 1  is an exploded perspective view of a battery module according to the first embodiment, and  FIG. 2  is an exploded plan view of the battery module in this example. The battery cell module  1  of this embodiment has a cell unit  40  consisting of a plurality of unit cells  41  stacked on one another, and a container or case accommodating the cell unit  40 . The unit cells  41  constituting the cell unit  40  (a stacked body of unit cells) can employ a lithium ion secondary battery with high energy density and sealing ability for example of a sheet-like shape battery in which a power generating element housing therein a pair of internal electrodes, separator, and electrolyte sealed inside a flexible bag-like outer casing member of generally rectangular shape in plan view. Principles of charging and discharging and the internal structure of the lithium ion flat secondary battery are known and therefore omitted for a detailed description thereof. The bag-like outer casing member is composed of laminated films with an inner layer of thermoplastic resin, an intermediate layer of metal foil, and an outer layer of insulating resin and houses the power generation element in a sealing way. Therefore the electrical insulation is ensured except for electrode terminals derived to the outside of the pouched case or package member. 
     As shown in  FIG. 1 , the cell unit  40  which is a stack of unit cells  41  is constructed by stacking a plurality of unit cells  41  (“four” in the example shown in  FIG. 1 ). Though not shown, a positive electrode terminal (positive electrode tab) and the negative terminal (negative electrode tab) are sequentially connected directly or by a bus bar. Thus a circuit configuration of four cells  41  connected in series is formed in this example. 
     The case or container is a rectangular parallelepiped member and includes a first case  10 , a pair of second cases  20 , and a third case  30 , each being made of aluminum alloy or plastic. 
     The first case  10  is a housing formed in a rectangular shape as shown in  FIG. 1 , and includes a bottom surface  12  of the first case, a ceiling surface  13  of the first case, and a side wall  14  (also referred to as an end wall) formed by extension from the bottom surface or bottom wall  12  and ceiling surface or top wall  13  of the first case  12 . The bottom surface  12  of first case presents a main or principle surface of first case  12  and contacts a main or principle surface  42  of cell unit  40 , while the ceiling surface  13  of first case presents another main or principle surface of the first case  10  and contact the other main surface  43  of the cell unit  40  and side wall surface  14  of first case abuts on side wall surface  44  on the short side edge of the cell unit  40 . In addition, at both sides of the side wall surface  14  are provided with first opening portions  15 . A second opening portion  16  is provided and counter-faces the side wall surface  14  of first case. Thus, the first case  10  is formed as a housing shaped in a U-shape. 
     The ceiling surface  13  of the first case is provided with a first guide portion  17  at the part of the side of one first opening portion  15  along the side edge of the opening portion  15 , while another first guide portion  17  is formed at the part of the side of the other first opening portion  15  along the side edge as well. Similarly, the bottom surface  12  of the first case is provided with a first guide portion  17  at the portion of the side of one first opening portion  15  along the side of the side edge, while another first guide portion  17  is formed at the part of the side of the other first opening portion  15  along the side edge as well. The first guide portion  17  are recessed inwardly from either ceiling surface  13  or bottom surface  14  of first case to form the shape of the rail by cutting out grooves parallel to the first openings  15 . The one end of the first guide portion on the side of the second opening  16  is formed to face an opening surface of the second opening portion  16 , while the other end of first guide portion  17  on the side wall surface  14  of first case is not formed to be flush with side wall surface  14  of first case but dammed or terminated on the ceiling surface  13  of first case. Since both the ceiling surface  13  of the first case and the bottom surface  12  of the first case are the surfaces extending in the vertical plane with respect to the stacking direction of unit cell  41  (the surface direction of the main or principle surface of the cell unit  40 ), the first guide portion  17  is formed in a direction perpendicular to the stacking direction of the unit cell  41 . 
     As shown in  FIG. 1 , the third case  30  is a case that is attached to the short side of the cell unit  40 , and holds the side surface of the short side of the cell unit  40 . In addition, though not shown, an insulating cover made of insulating material such as plastic may be provided in the third case  30  to ensure the insulation between the cell unit  40  and the third case  30  by the insulating cover. The third case  30  may hold the cell unit  40  through the insulating cover. 
     The third case  30  is a housing formed in the shape of a rectangular parallelepiped, and provided with a bottom surface  32  of third case, a ceiling surface  33  of third case, a side wall surface  34  of third case (also referred to as an end wall), and opposing side wall surfaces  35  of third case. The third case  30  is provided with a connector (not shown) for electrically connecting the cell unit  40  and external connection terminals (not shown). The side wall surface  34  of third case is formed as an extension from bottom surface  32  of third case and ceiling surface  35  of third case respectively, while side wall surfaces  35  are the side walls formed by extending respectively from short edge of bottom surface  32  of third case and short edge of ceiling surface  33  of third case. 
     The ceiling surface  33  of third case is provided with a first guide portion  37  at about the edge portion on the side of third side wall surface  35  and formed along the edge, while about the edge of the other third side wall surface  35  is provided with another first guide portion  37  along the edge. Similarly, the bottom surface  32  of third case is provided with a first guide portion  37  at about the edge of the one third side wall surface  35  and formed along the edge, while the bottom surface is further provided with a first guide portion  37  at about the edge of the other third surface  35  along the edge. The first guide portion  37  of ceiling surface  33  of third case extends from a part of the long side edge of third side wall surface  34  toward cell unit  40  along third ceiling surface  33  to form a groove with a recessed railed shape. In addition, the one end of first guide portion  37  is flush with the side wall surface  34  of third case while the other end of first guide portion  37  is flush with sidewall surface (a face opposing side wall surface  34  of third case) on the side of cell unit of third case  30 . Moreover, since both ceiling surface  33  and of third case and bottom surface  32  of third case are perpendicular to the stacking direction of unit cells  41  (the surface direction of main surface of cell unit  40 ), the first guide portion  37  is configured to extend perpendicular to the stacking direction of unit cells  41 . 
     By inserting the third case  30  holding cell unit  40  into first case  10  through an entry provided by the second opening  16 , the cell unit  40  will be housed in first case  10  to establish mating or fitting relationship between first case  10  and third case  30 . 
     As shown in  FIG. 2 , when the first case  10  is fitted to the third case  30 , part of the ceiling surface  13  of the first case is flush with the ceiling surface  33 , first guide portion  17  and the third case  37  are joined, and the first guide portion  17  and the third guide portion  37  corresponding to the first guide portion  17  jointly form the rail groove. Regarding the bottom part of first guide portion  17  and the first guide portion  37 , though not shown, the construction is similar to that at part of the ceiling surface, the description is thus omitted. 
     Next, description will be made with reference to  FIGS. 3 to 5 , of the fitting portion of the first case  10  and third case  30 .  FIGS. 3 and 4  are each cross-sectional views along the line A-A of  FIG. 1  of the tip portion of first case  10  together with third case.  FIG. 3  shows a state before being fitted, while  FIG. 4  after fitting.  FIG. 5  is an enlarged view of the portion surrounded by line B in  FIG. 3  and  FIG. 4 . Note that the dotted line shows a state before fitting (corresponding to  FIG. 3 ), while the solid line indicates a state after fitting (corresponding to  FIG. 4 ). 
     As shown in  FIG. 3 , a side wall surface or end surface  36  of each of the ceiling surface  35  and the bottom surface  32  of the third case  30  is formed on the side of cell unit  40  with an engaging portion  38  with a protruding shape. The engaging portion  38  is formed to advance from side wall surface  36  of third case toward first case  10  to form a convex shape. The tip of the ceiling surface  13  of first case is bent so as to be easily caught on the engaging portion  38 , and is configured to have a plane extending parallel to the main surface of ceiling surface of first case such that a surface lower than the main surface is processed to be formed. Similarly, the tip of bottom surface  12  of first case on the side of second opening  12  is bent so as to be easily engaged with the engaging portion  38  and is configured to have a plane parallel to a main surface of bottom surface of first case such that a surface higher than the main surface is processed to be formed. 
     Because the ceiling surface  13  of the first case and the bottom surface  12  of the first case are each formed in plate-shaped by a metal material to exert elasticity with respect to the direction of each surface. Therefore, by clamping and pressurizing ceiling surface  13  of first case and bottom surface  12  of first case to apply pressure in the direction of main surface of first case, thereby narrowing the second opening  16 . Subsequently, by first holding the distance formed by a tip or an end of ceiling surface  13  of first case and a tip of bottom surface  12  of first case smaller than that of engaging portions  38  and abutting the tips against side wall surface  36  of third case, and then releasing the pressure applied in the direction of main surface of first case  10 , by elasticity, respective tips of ceiling surface  13  of first case and bottom surface  12  of first case are engaged or caught by the corresponding engaging portion  38 . Therefore, the respective tips of second opening  16  are engaged by engaging portions  38 . Thus, the tips of second opening  16  are engaged by engaging portions  38  so as for the first case  10  and third case  30  to be fitted or locked to each other. 
     Returning to  FIG. 1 , the second case  20  is provided with side wall surfaces  20 ,  24 ,  25 ,  26  of the second case, ceiling surface  23  of second case, and bottom surface  22  of second case. Each second case  20  abuts on the side surface on the side of longer edge and is configured to enclose or cover from the both side surfaces. The ceiling surface  23  of second case is formed with a second guide portion  27  projecting downward along a surface opposing to wall surface  28  of second case. Similarly, the bottom surface  22  of second case is formed with a second guide portion  27  projecting upward along a surface opposing side wall surface  25  of second case. Each second guide portion  27  is formed with a single rail in a projection shape extending from side wall surface  26  of second case along bottom surface  22  of second case and ceiling surface  23  of second case toward sidewall surface  24  of second case. One end or tip of each second guide portion  27  is flush with side wall surface  26  of second case while the other end or tip of each second guide portion  27  is flush with side wall surface  24  of second case. The projection portion of second guide portion  27  is fitted into recessed portions of first guide portion  17  and second guide portion  37 . 
     The length of the rail of the second guide portion  27  equals to a sum of the length of rail of first guide portion  17  and the length of first guide portion  37 . Since ceiling surface  23  of second case and bottom surface  22  of second case are such surfaces perpendicular to the stacking direction of unit cells  41  (the surface direction of main surface of cell unit  40 ), the second guide portion  27  is formed perpendicular to the stacking direction of unit cells  41 . 
     Moreover, as shown in  FIGS. 1 and 2 , by inserting respective second case  20  from the side of side wall surface  34  of third case, the second guide portion  27  slides on the first guide portion  17  and the first guide portion  37  to establish fitting among first guide portions  17 ,  37  and second guide portion  27 . Thus, the second cases  20  cover the first opening  15  and are abutted on side surface of cell unit  40  to accommodate cell unit  40 . 
     As has been described above, the present embodiment is configured to provide a first guide portion  17  in first case  10  and a second guide portion  27  in second case  20 , respectively and by sliding second guide portion  27  on the first guide portion  17  to thereby fit the second case  20  into first case  10  for accommodating the cell unit  40 . In this configuration, when dismantling or dissembling the battery cell module in the present embodiment, cell module will be disassembled by sliding second case  20  off the first case  10 . Therefore, the man-hours for dismantling may be reduced. In other words, in the conventional battery module in which case is joined by a wound tightening as in the prior art, the effort for dismantling tends to be increased due to cutting through the case by such tool as can opener, deforming the case and separate each case. In contrast, in the present embodiment, the dismantling man-hours will be reduced with a decreased cost of demolition. In addition, when opening the case using a general-purpose tool such as a can opener, conventionally, there is a possibility of damaging the cell unit  40 . Since, during dismantling, it is not necessary to frequently use tools such as a can opener, it is possible to reduce the possibility of damaging the cell unit  40 . As a result, in this example, working safety may be improved. 
     Furthermore, by reducing the effort of demolition, the cost of recycling of rare metals contained in the cell unit  40  may be reduced. 
     Also, in the present embodiment, by providing the sliding mechanism composed of first guide portion  17  and the second guide portion  27 , the expansion of the cell unit  40  due to deterioration may be suppressed. Specifically, in the present embodiment, when accommodating cell unit  40  by sliding the second guide portion  27  on the first guide portion  17 , the second case  20  would not be subjected to deform and fitted to first case  10  with holding the shape of second case  20 . Since the second case is not required to deform when sliding, the rigidity of second case  20  may be enhanced. In addition, with a higher rigidity of second case  20 , since the first guide portion  17  and second guide portion  27  function to suppress expansion of cell unit  40 . Thus, in the present embodiment, provision of the sliding mechanism may serve to suppress the expansion of cell unit  40  by configuring such that the second case  20  will not deform due to pressure associated with expansion of cell unit  40 . 
     By providing a slide mechanism which consists of first guide portion  17  and second guide portion  27 , since the projection portion that projects from the side of the battery module  1  is not formed, when assembling a battery pack by disposing a plurality of battery modules, the degree of freedom in the layout of the battery with reduction of size of the battery. 
     More specifically, when housing cell unit  40  by locking mechanism projecting from side surface of battery module  1 , at the time of dismantling the cell module  1 , unlocking the locking mechanism may separate the cell unit  40  from the case. However, in the configuration having the locking mechanism, a projection portion projecting from side surface of the battery module would be formed. On the other hand, in this embodiment, in order to accommodate the cell unit  40  the slide mechanism is used, and the protruding portion which protrudes from the side of the battery module  1  is not formed, thus increasing of the degree of freedom of the layout of the cell will be achieved, while reducing the disassembly labor. 
     In the present embodiment, the first guide portion  17  is provided in a direction perpendicular to the main surface of a unit cell  41  of flat type along with a second guide portion  27 . As in this embodiment, the battery module with flat lithium ion secondary batteries stacked may expand in the direction of the main surface over time due to deterioration. However, with a fitting structure configured to slide second guide portion on the first guide portion  17  disposed in a direction perpendicular to the main surface direction of unit cell  41 , a pressure associated with expansion in the main surface direction may be suppressed. Therefore, while ensuring the holding state of the cell unit  40 , as described above, a battery module may be achieved with an ease of dismantling. 
     In the present embodiment, the first guide portion  17  and second guide portion  27  are formed respectively in first case  10  and second case  20  along the edge of first opening  15 , thus the second case is configured to clamp or sandwich cell unit  40  via first case  10  from a vertical main surface direction of cell unit  40  to cover the first opening  15  of second case  20 . Thus, due to expansion of cell unit  40 , the pressure applied on first guide portion  17  and second guide portion  27  will be equalized or uniform. That is, for example, when as compared to the length of the side edge of the ceiling surface of first case on side of the first side opening  15 , the length of the first guide portion  17  parallel to the side edge is set extremely short, the length of engagement between the first guide portion  17  and the second guide portion  17  will be caused to be short, the majority part of opening section will not be covered by the case having the sliding mechanism. In this instance, when the cell unit  40  expands, the portion of slide mechanism, i.e., the portion of first opening not covered by second case  20 , is subjected to be concentrated application of pressure such that expansion of cell unit  40  may not suppressed. Moreover, when the cell unit  40  expands due to deterioration and the pressure due to expansion is applied locally, there is a possibility that the gas generated within the cell unit  40  will be retained, resulting in reduction in the output of the battery. 
     On the other hand, in the present embodiment, since the slide mechanism composed of first guide portion  17  and second guide portion  27  is configured to cover the entire first opening  15 , the pressure applied on the slide mechanism generated due to expansion of cell unit  40  will be made uniform so that the expansion of cell unit  40  may be suppressed. In addition, due to the uniformed application of pressure in response to expansion by the deteriorated cell unit  40 , an output decrease in battery may be prevented that would lead to a longer battery life. 
     Moreover, in the present embodiment, by engaging the end or tip of second opening  16  of first case with engaging portion  38  of third case  30 , the first case  10  is fitted to third case  30 . Thus, when disassembling for recycling purpose, the battery module  1  in the present embodiment will be configured for ease of dismantling with reduced man-hours associated. 
     In the present embodiment, as shown in  FIG. 8 , the ceiling surface  13  of the first case and the bottom surface  12  of the first case may be provided with a recess  131  and a recess  121  respectively.  FIG. 8  is an exploded side view of the first case  10 , the third case  30  and the cell unit  40  in the modification according to the present invention, which shows a state before inserting the second case. The recess  131  and recess  121  are provided in the center portion of main surface of ceiling surface  13  of first case and in the center portion of main surface of bottom surface  12  of first case respectively, and are configured to be recessed inwardly from ceiling surface  13  of first case and bottom surface of first case, respectively. Further, as described above, ceiling surface  13  of first case and bottom surface  12  of first case are formed by plate-shaped metal material to provide elasticity by forming a leaf spring with respect to the direction of the surface of each surface. In the state where the external force is not applied, the ceiling surface  13  of the first case and the bottom surface  12  of first case expand or widen toward the second opening  16  from the side wall  14  of the first case, i.e. to be open with respect to each major surface. 
     Then by exerting pressure on both the ceiling surface  13  of first case and bottom surface  12  of first case thereby narrowing the second opening  16  to engage engaging portion  38  with the respective tips of ceiling surface  13  of first case and bottom surface  12  of first case. The engaging portions  38  restrict the spread of the bottom surface  12  of first case and the ceiling surface  13  of the first case toward the surface direction. In this state, since the recess  131  and recess  121  are recessed toward the cell unit  40 , therefore by having recess  131  and recess  121  contact main surface  43  and  44  of cell unit  40 , cell unit  40  will be sandwiched by recess  131  and recess  121  to be held in first case. 
     As described above, the first case  10  is formed so as to extend toward the second opening  16  from the side wall surface  14  of the first case. Thus, the ceiling surface  13  of the first case and bottom surface  12  of the first case are sandwiched to accommodate cell unit  40 , thus the assembly of battery module will be made easier. 
     Further, in this embodiment, the engaging portion  38  restricts an expansion of ceiling surface  13  of first case and bottom surface of first case in the main surface direction. Thus, when disassembling the battery module, by removing the restriction by the engaging portions of the spread of the first case  10 , the first case  10  and cell unit  40  may be disassembled with ease, which leads to an easily disassembly of the battery module. 
     In addition, in the present embodiment, the ceiling surface  13  of the first case and the bottom surface  12  of first case are provided with recess  131  and  121  respectively to be recessed toward cell unit  40 . Thus, by having recess  131  and recess  121  in contact with main surface  43  and main surface  42  of cell unit  40  respectively thereby clamping cell unit  40  in the direction of main surface, the main surface of cell unit  40  and the inner surface of first case  10  may be held securely. 
     In addition, the battery module may expand in the stacking direction due to deterioration over time. In the present invention, by providing the recess  121  and the recess  131  respectively on the ceiling surface  13  of first case and bottom surface  12  of first case, ceiling surface of first case  13  and bottom surface  12  of first case may be increased in rigidity in the direction of main surface such that the expansion of battery module may be suppressed. 
     In addition, in the present embodiment, a layered adhesive member may be provided between the recess  131  and the cell unit  40 , or, between the recesses  121  and the cell unit  40  so that the main surface of the cell unit  40  can be bonded and fixed firmly to the inner surface of the first case  10 . Disassembly of cell model may be performed easily. 
     It should be noted that this embodiment forms the engaging portion  38  in a convex shape. However, as shown in  FIGS. 6 and 7 , fitting portion may be formed in a flange.  FIG. 6  is a figure of modification corresponding to the sectional view along A-A in  FIG. 1 , and illustrates the state after the first case  10  and third case  30  have been fitted together.  FIG. 7  is a partial exploded view of the portion enclosed by the line C in  FIG. 6 . Note that the dotted line indicates a state before fitting while the solid line indicates the state after fitting (corresponding to  FIG. 4 ). 
     As shown in  FIGS. 6 and 7 , the sidewall of third case  30  is opened on the side of the cell unit  40  and ceiling surface  33  of third case is provided with an engaging portion  38   a  projecting downward while the bottom surface  32  of third surface with engagement portion  38   a  projecting upward. In addition, the cross section of third case in generally formed in “U” shape. Similarly, ceiling surface  10  of first case has at its edge on the side of opening  16  formed with a recess-shaped engaging portion  38   b  along the projection of engaging portion  38   a . Furthermore, as in  FIGS. 1 to 3 , by engaging portion  38   a  and engaging portion  38   b  with holding under pressure ceiling surface  13  of first case and bottom surface  12  of first case such that fitting between first case  10  and third case  30  may be established. 
     It should be noted that, although in this embodiment, the first guide portion  17 ,  37  and second guide portion  27  are provided in a direction perpendicular to the stacking direction of unit cells  41 , they may be in parallel thereto or may be in a direction other than the perpendicular or parallel direction. 
     The configuration need not necessarily be that four first guide portion  17 ,  37  and four second guide portions  27  are not necessarily required, but only one would suffice. 
     In addition, in this embodiment, the configuration of case is not necessarily limited to a composition of first case  10 , second case  20  and third case  30 . The first case must not in the form of a U-shape. In addition, bottom surface  12  of first case and ceiling surface  13  of first case may be separately provided from side wall surface  14  of first case. 
     The first case  10  corresponds to the “first member” according to the present invention while the second case  20  corresponds to the “second member”. 
       FIG. 9  shows an exploded perspective view of a battery module according to another embodiment according to the present invention. The point of difference over the battery module in the first embodiment resides in provision of fixing portion. The description regarding the first embodiment is incorporated appropriately for the remaining elements.  FIG. 10  is an enlarged plan view of the portion encircled by D in  FIG. 8 . 
     As shown in  FIGS. 9 and 10 , the fixing portion  50  includes a fixing portion  50   a  which is provided on the first guide portion  17  and a fixed portion  50   b  provided in the second guide portion  27 . Fixing portion  50   a  is formed by recessing a portion of side wall surface of first guide portion  17  outward of first guide portion  17  and the shape of recess has a triangular shape when viewed from ceiling surface  13  of first case. When viewed from ceiling surface  13  of first case, the inclination of edge of fixing portion  50   a  on the side of direction of insertion of second case (see the direction of arrow in  FIG. 10 ) is set smaller than the inclination on the side of opposite direction (see  FIG. 10 , reversed direction from the arrow). 
     The fixing portion  50   b  is formed with a shape protruding a portion of side wall surface  27  of second guide portion  27  outwardly from first guide portion  17 . The protruded shape has a triangular shape when viewed from ceiling surface  23  of second case. When viewed from ceiling surface of second case, the inclination of edge of fixing portion  50   b  in the direction of insertion of second case  20  (direction of arrow in  FIG. 10 ) is set smaller than the inclination of the edge in the direction opposite to the direction of insertion (opposite to the arrow in  FIG. 10 ). 
     When inserting second case  20  in first case  10 , the edge of smaller inclination of fixing portion  50   b  is brought into contact with first guide groove  17 , the fixing portion  50  is configured to allow the insertion of second case  20  in first case  10 . On the other hand, when withdrawing second case  20  from the first case  10 , since the edge of large inclination of fixing portion  50   b  is in contact with the side of a large inclination of the fixing portion  50   a  to restrict the movement, fixing portion  50  is formed to prevent second case  20  from being withdrawn from first case  10 . 
     Thus, in the present embodiment, since second case  20  may be configured to be hard to slide, the function of holding the cell unit  40  may be sustained. 
     Incidentally, in this embodiment, in addition to the fixing portion  50  shown in  FIG. 10 , a fixing portion  50  may be provided as shown in  FIG. 11 .  FIG. 11  shows an enlarged perspective view of a portion surrounded by E in  FIG. 9 . As shown in  FIG. 11 , the fixing portion  50  is formed by cutting out a portion of the bottom surface of the first guide portion  17  and deflecting toward the inside of the first guide portion  17  of the bottom surface. When inserting second case  20  into the first case  10 , the fixing portion  50  is flush with the bottom surface of first guide portion  17  so that fixing portion  50  is configured to allow for the second case  20  to be inserted into first case  10 . On the other hand, when withdrawing second case  20  from first case  10 , the tip of fixing portion  50  abuts against the side wall of second guide portion  27  and is subjected to movement restriction so that fixing portion  50  is configured to inhibit the withdrawal of second case  20  form first case  10 . 
     Note that the fixing portions  50  as shown in  FIGS. 10 and 11  need not necessarily be provided both, but only one fixing portion may be sufficient. 
     As described above, in the present embodiment, since at least one of first guide portion  17  and second guide portion  27  is provided with fixing portion  50 , during normal use, the second case  20  may be configured to be difficult to side and the function of maintain the ability for holding cell unit  40  may be maintained.