Patent Publication Number: US-2017365839-A1

Title: Energy storage device

Description:
TECHNICAL FIELD 
     The present invention relates to an energy storage device including a non-electrolyte secondary battery such as a lithium ion secondary battery. 
     BACKGROUND ART 
     Patent document 1 discloses an energy storage device which includes an electrode assembly formed by winding a positive electrode sheet, a negative electrode sheet and a separator in an elongated circular shape as viewed in a plan view in a state where the separator is interposed between the positive electrode sheet and the negative electrode sheet. Out of a pair of opposedly facing straight line portions of the electrode assembly, a positive electrode current collecting tab and a negative electrode current collecting tab are formed on the first straight line portion on one side in a spaced-apart manner. A spacer is disposed above the current collecting tabs, and the current collecting tabs are electrically connected to current collectors above the spacer. 
     The energy storage device disclosed in patent document 1 requires a large space for arranging the current collectors above the first straight line portion on which the current collecting tabs of the electrode assembly are formed in a projecting manner. Accordingly, in the case where energy storage devices having the same height are manufactured, it is necessary to form the electrode assembly in a small compact shape and hence, a capacity of the energy storage device becomes small. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: JP-A-2011-70918 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     It is an object of the present invention to provide a technique which allows an energy storage device to have large capacity. 
     Means for Solving the Problems 
     The present invention provides an energy storage device which includes: an electrode assembly having a positive electrode sheet and a negative electrode sheet stacked alternately with a separator interposed therebetween, and a positive electrode current collecting tab and a negative electrode current collecting tab formed of projecting portions which project from a first portion on one side in a stacking direction of the respective electrode sheets, the electrode assembly being housed in a case; a positive electrode external terminal and a negative electrode external terminal disposed on the case; and a positive electrode current collector and a negative electrode current collector disposed between the electrode assembly and the case, electrically connected to the respective external terminals, and electrically connected to the respective current collecting tabs on the other side in the stacking direction of the respective electrode sheets, the other side being a second portion side of the respective electrode sheets. 
     In the energy storage device of the present invention, the current collecting tabs project from the first portion side of the electrode assembly, and connecting portions between the current collecting tabs and the current collectors are positioned on the second portion side where the current collecting tabs do not project. With such a configuration, a height of the current correcting tab at the end portion of the electrode assembly can be lowered and hence, a distance between the electrode assembly and a case can be decreased. Accordingly, when the energy storage devices having the same height are manufactured, the electrode assembly can be formed with a large size and hence, the energy storage device can acquire a large capacity. 
     Advantages of the Invention 
     According to an energy storage device of the present invention, by lowering a height of an end portion of an electrode assembly, a capacity of the energy storage can be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view of a non-electrolyte secondary battery according to a first embodiment of the present invention. 
         FIG. 2  is an exploded perspective view of the non-electrolyte secondary battery shown in  FIG. 1 . 
         FIG. 3  is a perspective view of an electrode assembly. 
         FIG. 4  is a developed view of the electrode assembly. 
         FIG. 5  is an enlarged view of a portion V in  FIG. 1   
         FIG. 6  is an enlarged view of a portion VI in  FIG. 1 . 
         FIG. 7  is a perspective view of the electrode assembly and a current collector. 
         FIG. 8  is a perspective view with a part broken away of the non-electrolyte secondary battery shown in  FIG. 1 . 
         FIG. 9  is an exploded side view with a part broken away of the non-electrolyte secondary battery shown in  FIG. 1 . 
         FIG. 10  is a partially transverse cross-sectional view of the non-electrolyte secondary battery shown in  FIG. 1 . 
         FIG. 11A  is a cross-sectional view showing an assembling step of a current collecting tab. 
         FIG. 11B  is a cross-sectional view showing a state where the current collecting tab is assembled. 
         FIG. 12  is a plan view of the electrode assembly and the current collector. 
         FIG. 13A  is a perspective view of an upper spacer as viewed from above. 
         FIG. 13B  is a perspective view of the upper spacer as viewed from below. 
         FIG. 14A  is a cross-sectional view showing an assembling step of the electrode assembly and a lid. 
         FIG. 14B  is a cross-sectional view showing another assembling step of the electrode assembly and the lid. 
         FIG. 15  is a partially transverse cross-sectional view of a non-electrolyte secondary battery according to a second embodiment. 
         FIG. 16  is a partially transverse cross-sectional view of a non-electrolyte secondary battery according to a third embodiment. 
         FIG. 17  is a plan view of an electrode assembly and a current collector according to the third embodiment. 
         FIG. 18  is a partially transverse cross-sectional view showing a modification of the non-electrolyte secondary battery. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the present invention are described with reference to attached drawings. In the following description, although terms (terms containing “upper”, “lower”, “side”, and “end”, for example) indicating specific directions or positions are used when necessary, these terms are merely used for facilitating understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by meanings of these terms. Further, the description made hereinafter represents just an essential example of the present invention and is not intended to limit the present invention, applications of the present invention, and the usages of the present invention. 
     First Embodiment 
       FIG. 1  and  FIG. 2  show a lithium ion secondary battery (hereinafter simply referred to as a battery)  1  according to a first embodiment of the present invention. 
     (Overall Configuration) 
     With reference to  FIG. 1  and  FIG. 2 , the battery  1  includes an outer case  10 , an electrode assembly  20 , an insulation sheet  30 , a bottom spacer  40 , an external terminal  50 A for a positive electrode and an external terminal  50 B for a negative electrode, positive and negative current collectors  60 A,  60 B, upper packings  70 A,  70 B, lower packings  80 A,  80 B, and an upper spacer  90 . 
     The outer case (case)  10  includes a case body  11 , and a lid  12  which closes an opening  11   a  of the case body  11 . In this embodiment, the case body  11  and the lid  12  are made of aluminum or an aluminum alloy. The case body  11  has a rectangular plate-like bottom wall portion  11   b , a pair of long-side wall portions  11   c ,  11   c  which is raised from long sides of the bottom wall portion  11   b , and a pair of short-side wall portions  11   d ,  11   d  which is raised from short sides of the bottom wall portion  11   b . The lid  12  has an approximately rectangular plate shape. Upper ends of the long-side wall portions  11   c  and upper ends of the short-side wall portions  11   d  define the opening  11   a  of the case body  11 . The electrode assembly  20  is stored in the inside of the case body  11  which is filled with an electrolyte solution. The electrode assembly  20  is covered by the insulation sheet  30 . The bottom spacer  40  is interposed between the electrode assembly  20  and the bottom wall portion  11   b  of the case body  11 . The lower packings  80 A,  80 B and the upper spacer  90  are also stored in the inside of the case body  11 . 
     Also with reference to  FIG. 3  and  FIG. 4 , the electrode assembly  20  is configured such that a positive electrode sheet  21 , a negative electrode sheet  22 , and two separators  23 ,  23  all of which have an elongated strip shape and a fixed width are made to overlap with each other, and are wound into an approximately elongated circular shape with a high flatness ratio. The separators  23 ,  23  are formed using a microporous resin sheet. Either one of two separators  23 ,  23  is interposed between one layer of the positive electrode sheet  21  and one layer of the negative electrode sheet  22  disposed adjacently to one layer of the positive electrode sheet  21 . An axis of winding (winding axis) of the positive electrode sheet  21 , the negative electrode sheet  22  and two separators  23 ,  23  is conceptually indicated by symbol A in  FIG. 3 . The electrode assembly  20  is stored in the inside of the case body  11  in a posture where the winding axis A extends substantially in a direction that the bottom wall portion  11   b  and the opening  11   a  of the case body  11  face each other in an opposed manner (in a vertical direction in  FIG. 1 ). 
     As shown in  FIG. 3 , end portions  20   a ,  20   b  of the electrode assembly  20  as viewed in a direction that the winding axis A extends respectively have a pair of opposedly facing straight line portions  20   c ,  20   d , and a pair of opposedly facing curved portions  20   e ,  20   e  so as to connect these straight line portions  20   c ,  20   d  to each other. 
     The positive electrode sheet  21  includes: a strip-shaped positive electrode metal foil  24 ; and positive active material layers  25  which are formed on both surfaces of the positive electrode metal foil  24  respectively. On one end portion of the positive electrode sheet  21  in a width direction of the positive electrode sheet  21  (on a lower side in  FIG. 3  and  FIG. 4 ), the positive active material layer  25  is formed so as to reach a side edge of the positive electrode metal foil  24 . On the other end portion of the positive electrode sheet  21  in the width direction of the positive electrode sheet  21  (on an upper side in  FIG. 3  and  FIG. 4 ), the positive active material layer  25  is not formed, and a non-coated portion  24   a  is formed where the positive electrode metal foil  24  is exposed. 
     The negative electrode sheet  22  includes: a strip-shaped negative electrode metal foil  26 ; and negative active material layers  27  which are formed on both surfaces of the negative electrode metal foil  26  respectively. On one end portion of the negative electrode sheet  22  in a width direction of the negative electrode sheet  22  (on a lower side in  FIG. 3  and  FIG. 4 ), the negative active material layer  27  is formed so as to reach a side edge of the negative electrode metal foil  26 . On the other end portion of the negative electrode sheet  22  in the width direction of the negative electrode sheet  22  (on an upper side in  FIG. 3  and  FIG. 4 ), the negative active material layer  27  is not formed, and a non-coated portion  26   a  is formed where the negative electrode metal foil  26  is exposed. 
     A plurality of projecting portions  24   b  which project outward in the width direction from the non-coated portion  24   a  are formed on the positive electrode metal foil  24  at intervals in the longitudinal direction. In a state where the positive electrode sheet  21 , the negative electrode sheet  22 , and the separators  23 ,  23  are made to overlap with each other and are wound together, the plurality of projecting portions  24   b  are made to overlap with each other thus forming a tab-shaped portion (positive electrode current collecting tab  28 ) which projects from the electrode assembly  20 . A plurality of projecting portions  26  are formed also on the negative electrode metal foil  26  in the same manner as the projecting portions  24   b  of the positive electrode metal foil  24 . By making the projecting portions  26   b  overlap with each other, a negative electrode current collecting tab  29  which projects from the electrode assembly  20  is formed. 
     With reference to  FIG. 3 , the positive electrode current collecting tab  28  and the negative electrode current collecting tab  29  project from one end portion  20   a  (an end portion on an upper side in  FIG. 3 ) of the electrode assembly  20 . When the end portion  20   a  of the electrode assembly  20  is viewed in a direction that the winding axis A extends, the positive electrode current collecting tab  28  and the negative electrode current collecting tab  29  project from the first straight line portion  20   c  which is one of the pair of straight line portions  20   c ,  20   d  (a viewer&#39;s side in  FIG. 3 ) with respect to a center line B in the longitudinal direction. 
     The external terminal  50 A for the positive electrode is disposed on one end side (a left side in  FIG. 1 ) of the lid  12 , and the external terminal  50 B for the negative electrode is disposed on the other end side (right side in  FIG. 1 ) of the lid  12 . The external terminals  50 A,  50 B respectively have a plate-like portion  51 A,  51 B which is disposed on an outer surface (upper surface)  12   a  of the lid  12 . A connecting member such as a bus bar is welded to the plate-like portions  51 A,  51 B respectively so that the external terminals  50 A,  50 B are connected to an external circuit. 
     With reference to  FIG. 5  in addition to  FIG. 1  and  FIG. 2 , the external terminal  50 A for the positive electrode includes: the plate-like portion  51 A which is disposed on the outer surface  12   a  of the lid  12 ; and a circular cylindrical shaft portion  52  which projects downward from a lower surface of the plate-like portion  51 A. The plate-like portion  51 A and the shaft portion  52  are formed as an integral body. The shaft portion  52  penetrates the lid  12  and projects to the inside of the case body  11 . 
     A large diameter portion  52   a  is formed on a lower end of the shaft portion  52  of the external terminal  50 A for the positive electrode. With the formation of the large diameter portion  52   a , the external terminal  50 A for the positive electrode is fixed to the lid  12  by swaging. To be more specific, the external terminal  50 A for the positive electrode and the current collector  60 A are fixed to the lid  12  in such a manner that the insulating-resin-made upper packing  70 A, the lid  12 , the insulating-resin-made lower packing  80 A, and the current collector  60 A for the positive electrode (a swaged portion  62 A described later) are sandwiched between the plate-like portion  51 A and the large-diameter portion  52   a  of the external terminal  50 A. The upper packing  70 A is interposed between the outer surface  12   a  of the lid  12  and the external terminal  50 A, and the lower packing  80 A is interposed between an inner surface (lower surface)  12   b  of the lid  12  and the current collector  60 A. In this embodiment, the external terminal  50 A for the positive electrode and the current collector  60 A are made of aluminum or an aluminum alloy. 
     With reference to  FIG. 6  in addition to  FIG. 1  and  FIG. 2 , the external terminal  50 B for the negative electrode includes the plate-like portion  51 B which is disposed on the outer surface  12   a  of the lid  12 , and a rivet  53  which is a member provided as a separate body from the plate-like portion  51 B. A flange portion  53   a  formed on an upper end of the rivet  53  is press-fitted into a through hole formed in the plate-like portion  51 B so that the rivet  53  is fixed to the plate-like portion  51 B. The rivet  53  projects downward from a lower surface of the plate-like portion  51 B, penetrates the lid  12 , and projects to the inside of the case body  11 . 
     An enlarged-diameter portion  53   b  is formed on a lower end of the rivet  53  of the external terminal  50 B for the negative electrode. With the formation of the enlarged-diameter portion  53   b , the external terminal  50 B for the negative electrode is fixed to the lid  12  by swaging. To be more specific, the external terminal  50 B for the negative electrode and the current collector  60 B are fixed to the lid  12  in such a manner that the insulating-resin-made upper packing  70 B, the lid  12 , the insulating-resin-made upper packing  70 B, and the current collector  60 B for the negative electrode are sandwiched between the plate-like portion  51 B and the enlarged-diameter portion  53   b  of the external terminal  50 B. The lower packing  80 B is interposed between the outer surface  12   a  of the lid  12  and the external terminal  50 B, and the lower packing  80 B is interposed between the inner surface  12   b  of the lid  12  and the current collector  60 B of the negative electrode. In this embodiment, the plate-like portion  51 B of the external terminal  50 B for the negative electrode is made of aluminum or an aluminum alloy, the rivet  53  of the external terminal  50 B for the negative electrode is made of copper or a copper alloy, and the current collector  60 B for the negative electrode is made of copper or a copper alloy. 
     As shown most clearly in  FIG. 7 , the current collector  60 A for the positive electrode includes: a welded portion  61 A; and the swaged portion  62 A. The welded portion  61 A is welded to the positive electrode current collector tab  28  of the electrode assembly  20 . That is, the welded portion  61 A is electrically and mechanically connected to the positive electrode current collecting tab  28 . As described above, the swaged portion  62 A is fixed to the lid  12  by swaging by way of the enlarged diameter portion  52   a  formed on the shaft portion  52  of the external terminal  50 A for the positive electrode. In the same manner, the current collector  60 B for the negative electrode includes: a welded portion  61 B; and a swaged portion  62 B. The welded portion  61 B is welded to the negative electrode current collecting tab  29  of the electrode assembly  20 . That is, the welded portion  61 B is electrically and mechanically connected to the negative electrode current collecting tab  29 . As described above, the swaged portion  62 B is fixed to the lid  12  by swaging by way of the enlarged diameter portion  53   b  formed on the rivet  53  of the external terminal  50 B for the negative electrode. 
     As shown most clearly in  FIG. 8  and  FIG. 9 , the upper spacer  90  is interposed between the electrode assembly  20  and the inner surface  12   b  of the lid  12 . 
     (Detailed Description of Current Collecting Tab) 
     As shown most clearly in  FIG. 10 , with respect to the current collecting tabs  28 ,  29 , a proximal portion side of each current collecting tab  28 ,  29  is positioned on the straight line portion (first portion)  20   c  on one side out of the pair of straight line portions  20   c ,  20   d  where the electrode sheets  21 ,  22  are stacked together by winding, the proximal portion side of the current collecting tab  28 ,  29  is bent toward the straight line portion (second portion)  20   d  on the other side, and a distal end side of the current collecting tab  28 ,  29  is electrically connected to the current collector  60 A,  60 B which is arranged in a stacking direction of the electrode sheets  21 ,  22  on a straight line portion  20   d  side. 
     With reference to  FIG. 11A  and  FIG. 11B  in addition to  FIG. 10 , the current collecting tabs  28 ,  29  respectively include: a joint portion  28   a ,  29   a  on a distal end side where projecting portions  24   b ,  26   b  are joined to each other by welding; and a non-joint portion  28   b ,  29   b  on a proximal end side where projecting portions  24   b ,  26   b  are not joined to each other. In the joint portion  28   a ,  29   a , the respective projecting portions  24   b ,  26   b  are integrally bent by folding. In the non-joint portion  28   b ,  29   b , the respective projecting portions  24   b ,  26   b  can be freely bent at different curvatures by folding. 
     A total length L of the current collecting tab  28 ,  29  is set to a size which allows the current collecting tab  28 ,  29  to be bent two times between the electrode assembly  20  and the lid  12 . A first bent portion  28   c ,  29   c  is positioned on a stacked electrode sheet  21 ,  22  side, and is bent toward a second straight line portion  20   d  side from a first straight line portion  20   c  side. A second bent portion  28   d ,  29   d  is positioned closer to a current collector  60 A,  60 B side than the first bent portion  28   c ,  29   c , and is bent toward the first straight line portion  20   c  side from the second straight line portion  20   d  side. The second bent portion  28   d ,  29   d  is positioned in the vicinity of a second welded portion  61 A,  61 B which is a connecting portion where current correcting tab  28 ,  29  is connected to the current collector  60 A,  60 B. These bent portions  28   c ,  29   c ,  28   d ,  29   d  are named as the first bent portion and the second bent portion from a proximal portion side of the current collecting tab  28 ,  29 . However, “first” and “second” are not intended to be used for indicating the order that these portions are bent. 
     The total length L of the current collecting tab  28 ,  29  is set to a size which allows the first and second bent portions  28   c ,  29   c ,  28   d ,  29   d  to possess predetermined flexibility (play). To be more specific, a size L 2  from the first bent portion  28   c ,  29   c  to the second bent portion  28   d ,  29   d  is set larger than a size (distance) L 1  from the first bent portion  28   c ,  29   c  to an end portion of the second welded portion  61 A,  61 B on a proximal portion side of the current collecting tab  28 ,  29 . A size difference L 3  between the sizes L 1  and L 2  is set to a length which can prevent the interference between the second bent portion  28   d ,  29   d  and the connecting portion  95 A,  95 B of the upper spacer  90 . 
     The non-joint portion  28   b ,  29   b  of the current collecting tab  28 ,  29  is configured such that, using a total length of a first projecting portion  24   b ′,  26   b ′ positioned at the center of the non-joint portion  28   b ,  29   b  in the stacking direction as a reference, total lengths of the projecting portions  24   b ,  26   b  which are positioned outside the first projecting portion  24   b ′,  26   b ′ are gradually increased. To be more specific, the current collecting tab  28 ,  29  is formed in a line-symmetrical shape with respect to the first projecting portion  24   b ′,  26   b ′ positioned at the center of the first straight line portion  20   c  in the stacking direction of the electrode sheets  21 ,  22 . As shown most clearly in  FIG. 11A , the first projecting portion  24   b ′,  26   b ′ is disposed so as to extend coplanar with the electrode sheets  21 ,  22  with which the first projecting portion  24   b ′,  26   b ′ is continuously formed, and a projecting size of the first projecting portion  24   b ′,  26   b ′ from the end portion  20   a  is set as the total length L. Other projecting portions  24   b ,  26   b  are disposed in an inclined manner toward a distal end of the first projecting portion  24   b ′,  26   b ′ from the electrode sheets  21 ,  22 , and projecting sizes of other projecting portions  24   b ,  26   b  are set such that distal ends of other projecting portions  24   b ,  26   b  agree with each other. Then, as shown in  FIG. 11B , the joint portions  28   a ,  29   a  are formed by welding the distal end sides of all projecting portions  24   b ,  26   b  to each other. With such a configuration, the projecting portions  24   b ,  26   b  of the non-joint portion  28   b ,  29   b  which forms the first bent portion  28   c ,  29   c  can respectively have individually different optimum plays. The number of projecting portions  24   b ,  26   b  is not limited to an odd number and may be an even number. When the number of projecting portions  24   b ,  26   b  is an even number, the projecting portions  24   b ,  26   b  are formed into a line-symmetrical shape using a pair of first projecting portions  24   b ′,  26   b ′ positioned at the center in the stacking direction as a reference. 
     (Detail of Current Collectors) 
     With reference to  FIG. 7  and  FIG. 12  in addition to  FIG. 10 , the current collectors  60 A,  60 B are configured such that the current collecting tabs  28 ,  29  are electrically connected to the external terminals  50 A,  50 B of the lid  12  respectively. The current collector  60 A,  60 B further includes, in addition to a welded portion  61 A,  61 B which is a joining portion and the swaged portion  62 A,  62 B which is a connecting portion, an escape portion  66 A,  66 B which prevents the interference of the first bent portion  28   c ,  29   c  of the current collecting tab  28 ,  29 . 
     As shown most clearly in  FIG. 12 , in the current collector  60 A,  60 B, the welded portion  61 A,  61 B and an edge  63 A,  63 B of a swaged portion  62 A,  62 B on one end side are positioned on a straight line. The welded portion  61 A,  61 B and the swaged portion  62 A,  62 B respectively have a quadrangular shape as viewed in a plan view. A width H 1  of the welded portion  61 A,  61 B in a direction that the current collecting tab  28 ,  29  projects is narrower than a width H 2  of the swaged portion  62 A,  62 B. The swaged portion  62 A,  62 B and the welded portion  61 A,  61 B are disposed adjacently to each other in a direction which intersects with the direction that the current collecting tab  28 ,  29  projects (outside of the center line B in  FIG. 3 ). 
     As shown most clearly in  FIG. 7 , between the welded portion  61 A,  61 B and the swaged portion  62 A,  62 B, a stepped portion  64 A,  64 B for arranging the swaged portion  62 A,  62 B above the upper spacer  90  is provided. The current collecting tab  28 ,  29  is welded to the welded portion  61 A,  61 B on a lower surface  61   a  side opposite to a side where the stepped portion  64 A,  64 B projects. In the swaged portion  62 A,  62 B, a through hole  65 A,  65 B which allows the shaft portion  52  and the rivet  53  of the external terminal  50 A,  50 B to pass therethrough is formed. 
     As shown most clearly in  FIG. 12 , due to the difference between the width H 1  of the welded portion  61 A,  61 B and the width H 2  of the swaged portion  62 A,  62 B, a space is formed adjacently to the welded portion  61 A,  62 A in a direction that the current collecting tab  28 ,  29  projects. That is, the escape portion  66 A,  66 B is formed. The width H 2  of the swaged portion  62 A,  62 B is larger than a width of the straight line portion  20   c ,  20   d  of the electrode assembly  20  in the stacking direction. The swaged portion  62 A,  62 B is positioned at the end portion  20   a  of the electrode assembly  20  in a state where the swaged portion  62 A,  62 B straddles over the first and second straight line portions  20   c ,  20   d . The escape portion  66 A,  66 B is formed in a portion of the welded portion  61 A,  61 B positioned above the first straight line portion  20   c . That is, the escape portion  66 A,  66 B is formed by cutting out a portion of the welded portion  61 A,  61 B having the same width as the swaged portion  62 A,  62 B positioned above the first straight line portion  20   c  (a distal end (joint portion  28   a ,  29   a ) side in a direction that the current collecting tab  28 ,  29  projects in  FIG. 12 ). 
     (Detail of Upper Spacer) 
     With reference to  FIG. 9 ,  FIG. 13A  and  FIG. 13B  in addition to  FIG. 10 , the upper spacer  90  has an elongated rectangular shape in the same manner as the lid  12  as a whole. The upper spacer  90  includes: a center portion  91 ; and a pair of current collector housing portions  92 A,  92 B which extends from the center portion  91 . The current collector housing portion  92 A,  92 B has one end thereof connected to the center portion  91 , and the other end thereof connected to swaged portion arranging portion  97 A,  97 B positioned above the bent portion  20   e ,  20   e  of the electrode assembly  20  respectively. At the center portion  91 , an opening  91   a  which opposedly faces a safety valve provided to the lid  12  is formed. 
     The current collector housing portion  92 A,  92 B includes: a side wall portion  93 A,  93 B; an upper wall portion  94 A,  94 B which extends from an upper end of the side wall portion  93 A,  93 B; and a lower wall portion  95 A,  95 B which extends from a lower end of the side wall portion  93 A,  93 B substantially parallel to the upper wall portion  94 A,  94 B. Between a distal end  94   a  of the upper wall portion  94 A,  94 B and a distal end  95   a  of the lower wall portion  95 A,  95 B, a transversely-elongated opening portion  98 A,  98 B is formed. The welded portion  61 A,  61 B of the current collector  60 A,  60 B and a distal end side of the current collecting tab  28 ,  29  including the second bent portion  28   d ,  29   d  are inserted into the transversely-elongated opening portion  98 A,  98 B. 
     The side wall portions  93 A,  93 B are positioned on a second straight line portion  20   d  side of the electrode assembly  20 . The upper wall portion  94 A,  94 B extends toward a first straight line portion  20   c  side from the second straight line portion  20   d  side between the welded portion  61 A,  61 B of the current collector  60 A,  60 B and the inner surface  12   b  of the lid  12 . The distal end  94   a  of the upper wall portion  94 A,  94 B is positioned in the vicinity of the escape portion  66 A,  66 B so as to cover the welded portion  61 A,  61 B of the current collector  60 A,  60 B. The lower wall portion  95 A,  95 B extends toward the first straight line portion  20   c  side from the second straight line portion  20   d  side between the end portion  20   a  of the electrode assembly  20  and the current collecting tab  28 ,  29 . The distal end  95   a  of the lower wall portion  95 A,  95 B is positioned on the first straight line portion  20   c  of the electrode assembly  20  between the second projecting portion  24   b ″,  26   b ″ positioned at an end portion on a second straight line portion  20   d  side and the first projecting portion  24   b ′,  26   b ′ positioned at the center. That is, the lower wall portion  95 A,  95 B is not formed above the first straight line portion  20   c  thus forming a space where the current collecting tab  28 ,  29  can be disposed toward the opening portion  98 A,  98 B. 
     With reference to  FIG. 8  and  FIG. 13A . An insertion groove  96 A,  96 B is formed on an end portion of the upper wall portion  94 A,  94 B on a swaged portion arranging portion  97 A,  97 B side. When the welded portion  61 A,  61 B of the current collector  60 A,  60 B is disposed in the inside of the current collector housing portion  92 A,  92 B, the stepped portion  64 A,  64 B of the current collector  60 A,  60 B is positioned in the inside of the insertion groove  96 A,  96 B. With such a configuration, the swaged portion  62 A,  62 B of the current collector  60 A,  60 B is positioned on the swaged portion arranging portion  97 A,  97 B. 
     As shown most clearly in  FIG. 13A  and  FIG. 13B , the swaged portion arranging portion  97 A,  97 B includes: a bottom wall portion  97   a ; and an inner peripheral wall portion  97   b  which is formed on the bottom wall portion  97   a . The enlarged diameter portion  52   a ,  53   b  of the external terminal  50 A,  50 B is positioned in the inside of the inner peripheral wall portion  97   b . On the bottom wall portion  97   a , an outer peripheral wall portion  97   c  on which the swaged portion  62 A,  62 B of the current collector  60 A,  60 B is disposed is further provided so as to surround the inner peripheral wall portion  97   b.    
     Next, assembling steps of the battery  1  are described. 
     As shown in  FIG. 7  and  FIG. 12 , the electrode assembly  20  is disposed transversely such that a first straight line portion  20   c  side of the electrode assembly  20  from which the current collecting tabs  28 ,  29  project is positioned downward. Next, the current collectors  60 A,  60 B are disposed such that the swaged portions  62 A,  62 B are positioned above the welded portions  61 A,  61 B respectively, and the electrode assembly  20  is positioned on an edge  63 A,  63 B side of the welded portions  61 A,  61 B. Then, the welded portions  61 A,  61 B of the current collectors  60 A,  60 B are disposed on upper surfaces of the distal ends of the current collecting tabs  28 ,  29  respectively, and the current collecting tabs  28 ,  29  are connected to a lower surface  61   a  side of the welded portions  61 A,  61 B respectively by ultrasonic welding. 
     Then, as shown in  FIG. 14A , the electrode assembly  20  is disposed such that the first straight line portion  20   c  from which the current collecting tabs  28 ,  29  project is positioned upward. Next, the upper packings  70 A,  70 B and the external terminals  50 A,  50 B are mounted on the outer surface  12   a  of the lid  12 , and the lid  12  is disposed such that the inner surface  12   b  is positioned upward. Subsequently, the lower packings  80 A,  80 B and the swaged portions  62 A,  62 B of the current collectors  60 A,  60 B are disposed on an inner surface  12   b  side of the lid  12 . Then, the shaft portions  52  and the rivets  53  of the external terminals  50 A,  50 B are caulked thus electrically connecting the external terminals  50 A,  50 B and the current collectors  60 A,  60 B to each other respectively. In accordance with such steps, the electrode assembly  20  and the external terminals  50 A,  50 B are electrically connected to each other through the current collecting tabs  28 ,  29  and the current collectors  60 A,  60 B. 
     When the lid  12  is assembled to the electrode assembly  20 , subsequently, as shown in  FIG. 11B  and  FIG. 14A , the current collecting tabs  28 ,  29  are bent to 180 degrees about bending positions C 1  in the vicinity of the welded portions  61 A,  61 B of the current collectors  60 A,  60 B respectively. The bending direction of the current collecting tabs  28 ,  29  is a direction toward a side opposite to the second straight line portion  20   d  such that the lid  12  is positioned at an upper side in an assembled state. Next, as shown in  FIG. 11B  and  FIG. 14B , the current collecting tabs  28 ,  29  are bent to 90 degrees about bending positions C 2  on a proximal portion side respectively. The bending direction of the current collecting tabs  28 ,  29  is a direction toward a second straight line portion  20   d  side such that the lid  12  is positioned at an upper side in an assembled state. 
     In accordance with such steps, as shown in  FIG. 9 , the lid  12  is disposed parallel to the end portion  20   a  of the electrode assembly  20 . In such a state, the first bent portions  28   c ,  29   c  of the current collecting tabs  28 ,  29  are positioned above the first straight line portion  20   c , and bulged upper peak portions of the first bent portions  28   c ,  29   c  are positioned above the lower surfaces  61   a  of the current collectors  60 A,  60 B through the escape portions  66 A,  66 B respectively. That is, the peak portions of the first bent portion  28   c ,  29   c  are positioned between the lower surfaces (opposedly facing surfaces)  61   a  of the current collectors  60 A,  60 B which opposedly face the electrode assembly  20  and the lid  12  of the outer case  10  respectively. The second bent portions  28   d ,  29   d  of the current collecting tabs  28 ,  29  are positioned above the second straight line portion  20   d , and the welded portions  61 A,  61 B to which the current collecting tabs  28 ,  29  are joined respectively are also positioned above the second straight line portion  20   d.    
     Next, the upper spacer  90  is disposed on a side of the electrode assembly  20   a  second straight line portion  20   d  side, and the upper spacer  90  is inserted between the electrode assembly  20  and the lid  12  from a side. To be more specific, the distal ends  94   a ,  95   a  of the current collector housing portions  92 A,  92 B are disposed to face the electrode assembly  20  in an opposed manner respectively. Next, as shown in  FIG. 8  and  FIG. 10 , the upper wall portions  94 A,  94 B are inserted between the welded portions  61 A,  61 B and the inner surface  12   b  of the lid  12  respectively, and the lower wall portions  95 A,  95 B are inserted between the current collecting tabs  28 ,  29  and the end portion  20   a  of the electrode assembly  20  respectively. In accordance with such steps, joint portions each of which includes the welded portion  61 A,  61 B of the current collector  60 A,  60 B and the second bent portion  28   d ,  29   d  are disposed in the inside of the current collector housing portions  92 A,  92 B respectively. 
     Next, as shown in  FIG. 1  and  FIG. 10 , the electrode assembly  20  and the outer peripheral portion of the upper spacer  90  are covered by the insulation sheet  30  and, thereafter, the electrode assembly  20  is housed in the inside of the case body  11  together with the insulation sheet  30 . Finally, the lid  12  is pressed to a case body  11  side, and the case body  11  is sealed by welding the lid  12  to the opening  11   a  of the case body  11 . 
     On an end portion  20   a  side of the electrode assembly  20  of the battery  1  assembled as described above, a proximal portion (non-joint portions  28   b ,  29   b ) side of the current collecting tabs  28 ,  29  is positioned on a first straight line portion  20   c  side of the electrode assembly  20 , and a distal end (joint portions  28   a ,  29   a ) side of the current collecting tabs  28 ,  29  is positioned on a second straight line portion  20   d  side. With such a configuration, the first bent portions  28   c ,  29   c  of the current collecting tabs  28 ,  29  are positioned on the first straight line portion  20   c  side, and the welded portions  61 A,  61 B of the current collectors  60 A,  60 B which are joined to the current collecting tabs  28 ,  29  respectively are positioned on the second straight line portion  20   d  side. That is, the portion where the first bent portion  28   c ,  29   c  which bulges due to imparting of play is disposed and the portion where the bulky joint portion  28   a ,  29   a  is disposed are disposed adjacently to each other in a transverse direction at the end portion  20   a  of the electrode assembly  20 . With such a configuration, a height of the electrode assembly  20  at the end portion  20   a  can be lowered and hence, a distance between the electrode assembly  20  and the lid  12  can be decreased. Accordingly, when the energy storage devices  1  having the same height are manufactured, the electrode assembly  20  can be formed with a large size and hence, the energy storage  1  can acquire a large capacity. 
     Further, the current collecting tabs  28 ,  29  are formed with the total length L which allows the current collecting tabs  28 ,  29  to be bent two times at the end portion  20   a  of the electrode assembly  20 . Accordingly, operability of an operation of connecting the current collectors  60 A,  60 B which are connected to the current collecting tabs  28 ,  29  and the external terminals  50 A  50 B to each other can be enhanced. To be more specific, in swaging the shaft portion  52  and the rivet  53  of the external terminals  50 A,  50 B, a swaging device can be easily disposed such that the swaging device is not brought into contact with the electrode assembly  20 . Further, the current collecting tabs  28 ,  29  respectively have the total length L which allows the second bent portions  28   d ,  29   d  to be disposed in the vicinity of the welded portions  61 A,  61 B of the current collectors  60 A,  60 B and hence, the lengths of the current collecting tabs  28 ,  29  are set as short as possible while enhancing assembling property of the current collectors  60 A,  60 B and the external terminals  50 A,  50 B. Accordingly, a resistance during energization of the battery  1  can be minimized. 
     The size L 2  from the first bent portion  28   c ,  29   c  to the second bent portion  28   d ,  29   d  is set larger than the size L 1  from the first bent portion  28   c ,  29   c  of the current collecting tab  28 ,  29  to the welded portion  61 A,  61 B of the current collector  60 A,  60 B. Accordingly, it is possible to impart flexibility to the current collecting tabs  28 ,  29  per se, that is, to the first bent portions  28   c ,  29   c  and the second bent portions  28   d ,  29   d . As a result, vibrations and an impact which are applied to the current collecting tabs  28 ,  29  at the time of assembling the battery  1  or during traveling of a vehicle after the battery  1  is mounted on the vehicle can be decreased. Accordingly, it is possible to prevent the elongation and breaking of the current collecting tabs  28 ,  29 . 
     In the first bent portions  28   c ,  29   c  of the current collecting tabs  28 ,  29 , using the total length of the first projecting portion  24   b ′,  26   b ′ positioned at the center in the stacking direction as a reference, the total lengths of the projecting portions  24   b ,  26   b  positioned outside the first projecting portion  24   b ′,  26   b ′ are gradually increased. Further, the first bent portion  28   c ,  29   c  is formed by bending the non-joint portion  28   b ,  29   b  of the current collecting tab  28 ,  29 . With such a configuration, it is possible to set individually different optimum plays to the respective projecting portions  24   b ,  26   b . Accordingly, it is possible to prevent with certainty the elongation and breaking of the respective projecting portions  24   b ,  26   b.    
     Second Embodiment 
       FIG. 15  shows a battery  1  of a second embodiment. The second embodiment differs from the first embodiment with respect to a point that second bent portions  28   d ,  29   d  are bent below welded portions  61 A,  61 B of current collectors  60 A,  60 B respectively. The second embodiment can acquire the same manner of operation and the same advantageous effects as the first embodiment. Further, in the second embodiment, total lengths of current collecting tabs  28 ,  29  can be set as short as possible and hence, electric resistance at the time of energization can be made small. Still further, there is no possibility that the current collecting tabs  28 ,  29  which are connected to the current collectors  60 A,  60 B respectively are brought into contact with an outer case  10  and hence, as shown in the drawing, it is unnecessary to arrange an upper spacer  90  in the inside of the outer case  10 . Alternatively, in the second embodiment, it may be possible to use an upper spacer  90  where a current collector housing portion  92 A,  92 B has no side wall portion  93 A,  93 B. With such configurations, the number of parts can be decreased or the structure of the upper spacer  90  can be simplified and hence, the reduction in cost can be realized. 
     Third Embodiment 
       FIG. 16  shows a battery  1  of a third embodiment. The third embodiment differs from the first embodiment with respect to a point that current collecting tabs  28 ,  29  are joined to upper surfaces  61   b  of welded portions  61 A,  61 B of current collectors  60 A,  60 B, and edges  63 A,  63 B of the welded portions  61 A,  61 B are utilized for bending of second bent portions  28   d ,  29   d.    
     As shown in  FIG. 17 , in assembling the current collectors  60 A,  60 B to the current collecting tabs  28 ,  29 , in the same manner as the first embodiment, an electrode assembly  20  is disposed transversely such that a first straight line portion  20   c  side is positioned downward, and the current collectors  60 A,  60 B are disposed such that swaged portions  62 A,  62 B are positioned above the welded portions  61 A,  61 B respectively. Further, the electrode assembly  20  is disposed on an edge  63 A,  63 B side of the welded portions  61 A,  61 B, and the current collecting tabs  28 ,  29  are disposed on an upper surfaces  61   b  side of the welded portions  61 A,  61 B of the current collectors  60 A,  60 B. Then, the current collecting tabs  28 ,  29  are connected to the upper surface  61   b  side of the welded portions  61 A,  61 B respectively by ultrasonic welding. 
     Next, in the same manner as the first embodiment, the current collectors  60 A,  60 B connected to the current collecting tabs  28 ,  29  are disposed on an inner surface  12   b  of a lid  12  on which upper packings  70 A,  70 B, external terminals  50 A,  50 B, and lower packings  80 A,  80 B are disposed, and the current collectors  60 A,  60 B and the external terminals  50 A,  50 B are connected to each other by welding respectively. 
     Next, in arranging the lid  12  on an end portion  20   a  of the electrode assembly  20  by bending the current collecting tabs  28 ,  29 , firstly, the current collecting tabs  28 ,  29  are bent so as to be wound around the edges  63 A,  63 B of the current collectors  60 A,  60 B respectively thus forming the second bent portions  28   d ,  29   d . Subsequently, by bending the current collecting tabs  28 ,  29  to 90 degrees at a proximal portion side, the lid  12  is disposed on the end portion  20   a  of the electrode assembly  20 . 
     Then, in the same manner as the first embodiment, an upper spacer  90  is disposed between the electrode assembly  20  and the lid  12  and, thereafter, an insulation sheet  30  is disposed on an outer peripheral portion of the outer spacer  90 . Next, the electrode assembly  20  is disposed in the inside of the case body  11 , and an opening  11   a  of the case body  11  is sealed by the lid  12 . 
     The third embodiment having the above-mentioned configuration can acquire substantially the same manner of operation and advantageous effects as the first embodiment. The second bent portions  28   d ,  29   d  can be formed so as to be wound around the current collectors  60 A,  60 B respectively and hence, operability of the assembling operation can be enhanced. In the same manner as the second embodiment, total lengths of the current collecting tabs  28 ,  29  can be set as short as possible. Since there is no possibility that the current collecting tabs  28 ,  29  are brought into contact with the outer case  10 , a configuration may be adopted where an upper spacer  90  is not disposed in the inside of the outer case  10  or a configuration may be adopted where side wall portions  93 A,  93 B of current collector housing portions  92 A,  92 B are not provided. 
     The battery  1  of the present invention is not limited to the above-mentioned embodiments, and various modifications are conceivable. 
     For example, although the current collecting tabs  28 ,  29  are bent two times between the electrode assembly  20  and the lid  12  in the embodiments, as shown in  FIG. 18 , the current collecting tabs  28 ,  29  may be bent only one time (first bent portions  28   c ,  29   c ). Alternatively, the current collecting tabs  28 ,  29  may be bent three or more times. That is, in the current collectors  60 A,  60 B, by adopting the configuration where first bent portions  28   c ,  29   c  are disposed on a first straight line portion  20   c  side from which current collecting tabs  28 ,  29  project, and welded portions  61 A,  61 B of the current collectors  60 A,  60 B are disposed on a second straight line portion  20   d  side from which the current collecting tabs  28 ,  29  do not project, the number of bending times of the current collecting tabs  28 ,  29  may be changed as desired. 
     Further, in the embodiments, with respect to the current collecting tabs  28 ,  29 , total lengths of the projecting portions  24   b ,  26   b  positioned outside the projecting portions  24   b ′,  26   b ′ are set such that the total lengths are gradually increased. However, the total lengths of all projecting portions  24   b ,  26   b  may be set equal to each other. Further, in the embodiments, the joint portions  28   a ,  29   a  and the non-joint portions  28   b ,  29   b  are formed by welding the projecting portions  24   b ,  26   b . However, the joint portions  28   a ,  29   a  may not be formed in advance. 
     The electrode assembly  20  is housed in the inside of the case body  11  such that the current collecting tabs  28 ,  29  are positioned on an opening  11   a  side. However, the electrode assembly  20  may be housed in the inside of the case body  11  such that the current collecting tabs  28 ,  29  are positioned on one short-side wall portion  11   d  side. In this case, the external terminals  50 A,  50 B may be disposed on the case body  11 . 
     The present invention is not limited to the winding-type electrode assembly  20  which is formed by winding the positive electrode sheet  21 , the negative electrode sheet  22  and the separators  23  each having a strip shape about the winding axis A, and the present invention is also applicable to a stacking-type electrode assembly which is formed by stacking, in one direction, positive electrode sheets, negative electrode sheets and separators which respectively have a rectangular shape. 
     The present invention is not limited to a secondary battery such as a non-electrolyte secondary battery such as a lithium ion battery, and is also applicable to a primary battery or various kinds of energy storage devices including a capacitor. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
         
           
               1 : battery (energy storage device) 
               10 : outer case (case) 
               11 : case body 
               11   a : opening 
               11   b : bottom wall portion 
               11   c : long-side wall portion 
               11   d : short-side wall portion 
               12 : lid 
               12   a : outer surface 
               12   b : inner surface 
               20 : electrode assembly 
               20   a : end portion 
               20   b : end portion 
               20   c : first straight line portion 
               20   d : second straight line portion 
               20   e : bent portion 
               21 : positive electrode sheet 
               22 : negative electrode sheet 
               23 : separator 
               24 : positive electrode metal foil 
               24   a : non-coated portion 
               24   b : projecting portion 
               24   b ′: first projecting portion 
               24   b ″: second projecting portion 
               25 : positive active material layer 
               26 : negative electrode metal foil 
               26   a : non-coated portion 
               26   b : projecting portion 
               26   b ′: first projecting portion 
               26   b ″: second projecting portion 
               27 : negative active material layer 
               28 : positive electrode current collecting tab 
               28   a : joint portion 
               28   b : non-joint portion 
               28   c : first bent portion 
               28   d : second bent portion 
               29 : negative electrode current collecting tab 
               29   a : joint portion 
               29   b : non-joint portion 
               29   c : first bent portion 
               29   d : second bent portion 
               30 : insulation sheet 
               40 : bottom spacer 
               50 A,  50 B: external terminal 
               51 A,  51 B: plate-like portion 
               52 : shaft portion 
               52   a : enlarged diameter portion 
               53 : rivet 
               53   a : flange portion 
               53   b : enlarged diameter portion 
               60 A,  60 B: current collector 
               61 A,  61 B: welded portion (joining portion) 
               61   a : lower surface 
               61   b : upper surface 
               62 A,  62 B: swaged portion 
               63 A,  63 B: edge 
               64 A,  64 B: stepped portion 
               65 A,  65 B: through hole 
               66 A,  66 B: escape portion 
               70 A,  70 B: upper packing 
               80 A,  80 B: lower packing 
               90 : upper spacer 
               91 : center portion 
               91   a : opening 
               92 A,  92 B: current collector housing portion 
               93 A,  93 B: side wall portion 
               94 A,  94 B: upper wall portion 
               94   a : distal end 
               95 A,  95 B: lower wall portion 
               95   a : distal end 
               96 A,  96 B: insertion groove 
               97 A,  97 B: swaged portion arranging portion 
               97   a : bottom wall portion 
               97   b : inner peripheral wall portion 
               97   c : outer peripheral wall portion 
               98 A,  98 B: opening portion 
             A: winding axis 
             B: center line 
             C 1 , C 2 : bending position