Patent Publication Number: US-2022231384-A1

Title: Secondary battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of PCT patent application no. PCT/JP2020/033537, filed on Sep. 4, 2020, which claims priority to Japanese patent application no. JP2019-186909 filed on Oct. 10, 2019, the entire contents of which are being incorporated herein by reference. 
    
    
     BACKGROUND 
     The present technology generally relates to a secondary battery. 
     Various electronic apparatuses such as mobile phones have been widely used. Such widespread use has promoted development of a secondary battery as a power source that is smaller in size and lighter in weight and allows for a higher energy density. A configuration of the secondary battery influences a battery characteristic. Accordingly, various considerations have been given to the configuration of the secondary battery. 
     Specifically, in order to obtain a favorable characteristic such as high productivity, a group of electrodes is contained inside a positive electrode case and a negative electrode case that are opposed to each other. All of positive electrode tabs are disposed above the group of electrodes and are electrically coupled to the positive electrode case, and all of negative electrode tabs are disposed below the group of electrodes and are electrically coupled to the negative electrode case. Further, in order to prevent variations in gaps in an electrode body (positive electrodes and negative electrodes), the electrode body is contained inside a positive electrode can and a negative electrode can that are opposed to each other. All of positive electrode leads are disposed on a side of the electrode body and are electrically coupled to each other, and all of negative electrode leads are disposed on another side of the electrode body opposite from the positive electrode leads and are electrically coupled to each other. 
     SUMMARY 
     The present technology generally relates to a secondary battery. 
     Various considerations have been made to solve problems of a secondary battery; however, the secondary battery has not yet achieved a sufficient energy density per unit volume, and there is still room for improvement in terms thereof. 
     The technology has been made in view of such an issue and it is an object of the technology to provide a secondary battery that makes it possible to increase an energy density per unit volume. 
     A secondary battery according to an embodiment of the technology includes a power generation element including a plurality of electrodes. The electrodes are stacked on each other in a stacking direction with a separator interposed therebetween. Each of the electrodes includes a current collector led out in a first direction intersecting the stacking direction. Each of a plurality of current collectors led out in the first direction includes an end part, and the end part includes a first bent part that is bent in a second direction intersecting the first direction. Each of a plurality of first bent parts overlaps and is in contact with an adjacent first bent part in the second direction. At least one of the first bent parts terminates at a middle point on an end face along the second direction of the power generation element. 
     According to the secondary battery of the embodiment of the technology, each of the plurality of electrodes stacked on each other with the separator interposed therebetween includes the current collector led out in the first direction. Each of the plurality of current collectors led out in the first direction includes the first bent part bent in the second direction. Each of the plurality of first bent parts overlaps and is in contact with an adjacent first bent part in the second direction. At least one of the first bent parts terminates at a middle point on the end face along the second direction of the power generation element. This makes it possible to increase the energy density per unit volume. 
     It should be understood that effects of the technology are not necessarily limited to those described above and may include any of a series of effects described below in relation to the technology. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a sectional view of a configuration of a secondary battery according to an embodiment of the technology. 
         FIG. 2  is a perspective view of a configuration of a main part of the secondary battery illustrated in  FIG. 1 . 
         FIG. 3  is an enlarged sectional view of the configuration of the main part of the secondary battery illustrated in  FIG. 1 . 
         FIG. 4  is another enlarged sectional view of the configuration of the main part of the secondary battery illustrated in  FIG. 1 . 
         FIG. 5  is a sectional diagram for describing a process of manufacturing the secondary battery according to an embodiment of the technology. 
         FIG. 6  is another sectional diagram for describing the process of manufacturing the secondary battery according to an embodiment of the technology. 
         FIG. 7  is a sectional diagram for describing a configuration of a secondary battery of a comparative example. 
         FIG. 8  is another sectional diagram for describing the configuration of the secondary battery of the comparative example. 
         FIG. 9  is a perspective view of a configuration of a secondary battery according to a second embodiment of the technology. 
         FIG. 10  is a sectional view of a configuration of a main part of the secondary battery illustrated in  FIG. 9 . 
         FIG. 11  is another sectional view of the configuration of the main part of the secondary battery illustrated in  FIG. 9 . 
         FIG. 12  is a perspective view of a configuration of a secondary battery according to an embodiment of the technology. 
         FIG. 13  is a sectional view of a configuration of a secondary battery according to an embodiment of the technology. 
         FIG. 14  is a perspective view of the configuration of the secondary battery illustrated in  FIG. 13 . 
         FIG. 15  is a sectional view of a configuration of a secondary battery according to an embodiment of the technology. 
         FIG. 16  is a sectional view of a configuration of a secondary battery according to an embodiment of the technology. 
         FIG. 17  is a perspective view of the configuration of the secondary battery illustrated in  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION 
     As described herein, the present disclosure will be described based on examples with reference to the drawings, but the present disclosure is not to be considered limited to the examples, and various numerical values and materials in the examples are considered by way of example. 
     A description is given first of a secondary battery according to a first embodiment of the technology. 
     Described here is a secondary battery having a flat and columnar shape. Examples of such a secondary battery include a so-called coin-type secondary battery and a so-called button-type secondary battery. As will be described later, the secondary battery having a flat and columnar shape includes a pair of bottom parts and a sidewall part. The bottom parts are opposed to each other. The sidewall part lies between the bottom parts. This secondary battery has a height that is small relative to an outer diameter. 
     A charge and discharge principle of the secondary battery is not particularly limited. The secondary battery described below obtains a battery capacity by utilizing insertion and extraction of an electrode reactant. The secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. In the secondary battery, in order to prevent precipitation of the electrode reactant on a surface of the negative electrode in the middle of charging, a charge capacity of the negative electrode is greater than a discharge capacity of the positive electrode. In other words, an electrochemical capacity per unit area of the negative electrode is set to be greater than an electrochemical capacity per unit area of the positive electrode. 
     Although not limited to a particular kind, the electrode reactant is a light metal, such as an alkali metal or an alkaline earth metal. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the alkaline earth metal include beryllium, magnesium, and calcium. 
     In the following, a description is given of an example case where the electrode reactant is lithium. A secondary battery that obtains a battery capacity by utilizing insertion and extraction of lithium is a so-called lithium-ion secondary battery. In the lithium-ion secondary battery, lithium is inserted and extracted in an ionic state. 
       FIG. 1  is a sectional view of a configuration of the secondary battery. 
       FIG. 2  is a perspective view of a configuration of a main part of the secondary battery illustrated in  FIG. 1 . It should be understood that  FIG. 2  illustrates a battery device  20 , a positive electrode tab  30 , and a negative electrode tab  40  to be described later as the main part of the secondary battery, and also illustrates a state where the positive electrode tab  30  and the negative electrode tab  40  are each separated from the battery device  20 . 
     In the following, for the sake of convenience, an up direction, a down direction, a right direction, and a left direction in  FIGS. 1 and 2  are taken as corresponding to positions above, below, to the right, and to the left of the secondary battery, respectively. Further, a direction in which a positive electrode  21 , a negative electrode  22 , and a separator  23  to be described later are stacked, i.e., an up-and-down direction, will be referred to as a stacking direction S. 
     This secondary battery is a button-type secondary battery, and therefore, as illustrated in  FIG. 1 , has a flat and columnar three-dimensional shape with a height H thereof small relative to an outer diameter D thereof. Here, the secondary battery has a flat and cylindrical (circular columnar) three-dimensional shape. Dimensions of the secondary battery are not particularly limited; however, for example, the outer diameter (here, the diameter of the circular shape) D is from 3 mm to 30 mm both inclusive, and the height H is from 0.5 mm to 70 mm both inclusive. It should be understood that a ratio of the outer diameter D to the height H, i.e., D/H, is greater than 1 and smaller than or equal to 25. 
     Specifically, as illustrated in  FIGS. 1 and 2 , the secondary battery includes a battery can  10 , the battery device  20 , the positive electrode tab  30 , the negative electrode tab  40 , and a gasket  50 . 
     As illustrated in  FIG. 1 , the battery can  10  is an outer package member having a flat and columnar shape and containing the battery device  20 . This battery can  10  has a flat and cylindrical three-dimensional shape in accordance with the three-dimensional shape of the secondary battery described above. The battery can  10  thus includes a pair of bottom parts N 1  and N 2  and a sidewall part N 3 . The sidewall part N 3  is coupled to the bottom part N 1  at one end, and is coupled to the bottom part N 2  at the other end. Because the battery can  10  is cylindrical as described above, the bottom parts N 1  and N 2  are each circular in plan shape, and a surface of the sidewall part N 3  is a convex curved surface. 
     Here, the battery can  10  includes an outer package can  11  and an outer package cup  12 . 
     The outer package can  11  has a hollow, flat and cylindrical three-dimensional shape with one end open and the other end closed, and is a first outer package part shaped like a so-called handleless mug. The outer package can  11  includes a bottom part  11 M and a sidewall part  11 W, and thus has an opening  11 K. Further, the outer package can  11  contains the battery device  20  inside. 
     The outer package cup  12  has a hollow, flat and cylindrical three-dimensional shape with one end open and the other end closed, as with the outer package can  11 , and is a second outer package part shaped like a so-called handleless mug. The outer package cup  12  includes a bottom part  12 M and a sidewall part  12 W, and thus has an opening  12 K. Further, the outer package cup  12  is opposed to the outer package can  11  in the stacking direction S with the battery device  20  interposed therebetween, and thus seals the opening  11 K of the outer package can  11 . 
     In the battery can  10 , in a state where the battery device  20  is contained inside the outer package can  11  and where the outer package can  11  and the outer package cup  12  are disposed to allow the openings  11 K and  12 K to be opposed to each other, the outer package can  11  and the outer package cup  12  are fitted to each other in such a manner that the bottom part  12 M covers the opening  11 K and that the sidewall part  12 W lies over the sidewall part  11 W from an outer side. The sidewall part  12 W is thereby crimped to the sidewall part  11 W with the gasket  50  interposed therebetween. A so-called crimp part C (crimped part) is thus provided. The battery can  10  including the outer package can  11  and the outer package cup  12  is sealed by means of the crimp part C, and the battery device  20  is thus enclosed in the battery can  10 . In other words, the battery can  10  described here is a so-called crimp-type battery can. However, in  FIG. 1 , the illustration of the crimp part C (a crimp structure) is simplified. 
     The outer package can  11  is electrically conductive, and has one of a positive polarity and a negative polarity. The outer package cup  12  is electrically conductive, and has the other of the positive polarity and the negative polarity. Here, the outer package can  11  is coupled via the positive electrode tab  30  to the positive electrode  21  of the battery device  20  to be described later, and thus serves as a positive electrode terminal for external coupling of the secondary battery. Further, the outer package cup  12  is coupled via the negative electrode tab  40  to the negative electrode  22  of the battery device  20  to be described later, and thus serves as a negative electrode terminal for external coupling of the secondary battery. Thus, the outer package can  11  has the positive polarity, and the outer package cup  12  has the negative polarity which is opposite to the polarity of the outer package can  11 . 
     In order to serve as the positive electrode terminal, the outer package can  11  includes one or more of electrically conductive materials including, without limitation, metals (including stainless steel) and alloys. Here, the outer package can  11  includes one or more of materials including, without limitation, aluminum, an aluminum alloy, and stainless steel. 
     In order to serve as the negative electrode terminal, the outer package cup  12  includes one or more of electrically conductive materials including, without limitation, metals (including stainless steel) and alloys. Here, the outer package cup  12  includes one or more of materials including, without limitation, iron, copper, nickel, stainless steel, an iron alloy, a copper alloy, and a nickel alloy. The kinds of the stainless steel employable include SUS304 and SUS316, but are not particularly limited thereto. 
     It should be understood that the outer package can  11  (the sidewall part  11 W) and the outer package cup  12  (the sidewall part  12 W) are electrically separated (insulated) from each other via the gasket  50 . 
     The battery device  20  is a power generation element causing charging and discharging reactions to proceed, and includes, as illustrated in  FIGS. 1 and 2 , the positive electrode  21 , the negative electrode  22 , the separator  23 , and an electrolytic solution which is a liquid electrolyte. It should be understood that  FIG. 2  omits the illustration of the electrolytic solution. 
     It should be understood that  FIG. 2  also illustrates a stacked body  120  to be used to fabricate the battery device  20  in a process of manufacturing the secondary battery to be described later. The stacked body  120  has a configuration similar to that of the battery device  20  except that the positive electrode  21 , the negative electrode  22 , and the separator  23  are each yet to be impregnated with the electrolytic solution. 
     The battery device  20  has a three-dimensional shape corresponding to the three-dimensional shape of the battery can  10 . The “three-dimensional shape corresponding to the three-dimensional shape of the battery can  10 ” refers to a three-dimensional shape substantially similar to that of the battery can  10 . A reason for allowing the battery device  20  to have such a three-dimensional shape is that this makes it harder for a so-called dead space (a gap between the battery can  10  and the battery device  20 ) to result upon placing the battery device  20  in the battery can  10  than in a case where the battery device  20  has a three-dimensional shape different from that of the battery can  10 . This allows for efficient use of an internal space of the battery can  10 , resulting in an increase in device space volume, and accordingly an increase in energy density per unit volume. The “device space volume” refers to a volume of an internal space of the battery can  10  available for containing the battery device  20  therein. 
     Here, the battery can  10  has a flat and cylindrical three-dimensional shape as described above, and the battery device  20  thus has a flat and generally cylindrical three-dimensional shape. 
     In the battery device  20 , a plurality of positive electrodes  21  and a plurality of negative electrodes  22  are stacked on each other with the separators  23  interposed therebetween. More specifically, the positive electrodes  21  and the negative electrodes  22  are alternately stacked in the stacking direction S with the separators  23  interposed therebetween. Thus, the battery device  20  described here is a so-called stacked electrode body. It should be understood that each of an uppermost layer and a lowermost layer of the battery device  20  is one of the separators  23 . The respective numbers of the positive electrodes  21 , the negative electrodes  22 , and the separators  23  to be stacked are not particularly limited, and may be freely chosen. 
     The positive electrode  21 , the negative electrode  22 , and the separator  23  each have a generally circular plan shape with a plane taper. Thus, the battery device  20  as a whole has a flat and generally cylindrical three-dimensional shape with a plane taper surface M 3 T. More specifically, the battery device  20  includes a pair of bottom parts M 1  and M 2  and a sidewall part M 3 . The bottom parts M 1  and M 2  are opposed to each other. The sidewall part M 3  is coupled to each of the bottom parts M 1  and M 2 . A surface of the sidewall part M 3  includes a curved surface M 3 C, and the taper surface M 3 T coupled to the curved surface M 3 C. 
     It should be understood that a description will be given later regarding a detailed configuration of each of the positive electrode  21 , the negative electrode  22 , and the separator  23  (see  FIGS. 3 and 4 ). 
     The positive electrode tab  30  is an electrode wiring line for electrically coupling a plurality of positive electrode current collectors  21 A (see  FIG. 3 ) described later to each other, and is coupled to the positive electrode current collectors  21 A. 
     Here, as illustrated in  FIG. 2 , the positive electrode tab  30  is bent to be along the battery device  20 , and more specifically, bent to be along the bottom part M 1  and the sidewall part M 3  (the taper surface M 3 T). The positive electrode tab  30  thus includes a tab part  30 A, and a tab part  30 B coupled to the tab part  30 A. The tab part  30 A extends along the bottom part M 1  in a direction intersecting the stacking direction S, and has a plan shape similar to that of each of the positive electrode  21 , the negative electrode  22 , and the separator  23 . The tab part  30 B extends along the sidewall part M 3  (the taper surface M 3 T) in a direction along the stacking direction S, i.e., in the down direction, and has a strip-like plan shape. 
     The positive electrode tab  30  includes a material similar to a material included in the positive electrode current collector  21 A. It should be understood that the material included in the positive electrode tab  30  may be the same as or different from the material included in the positive electrode current collector  21 A. 
     A description will be given later regarding a coupling form of the positive electrode tab  30  to the positive electrode current collectors  21 A (see  FIG. 3 ). 
     The negative electrode tab  40  is another electrode wiring line for electrically coupling a plurality of negative electrode current collectors  22 A (see  FIG. 4 ) described later to each other, and is coupled to the negative electrode current collectors  22 A. 
     Here, the negative electrode tab  40  has a configuration similar to that of the positive electrode tab  30  described above. In other words, as illustrated in FIG.  2 , the negative electrode tab  40  is bent to be along the battery device  20 , and more specifically, bent to be along the bottom part M 2  and the sidewall part M 3  (the taper surface M 3 T). The negative electrode tab  40  thus includes a tab part  40 A, and a tab part  40 B coupled to the tab part  40 A. The tab part  40 A extends along the bottom part M 2  in the direction intersecting the stacking direction S, and has a plan shape similar to that of each of the positive electrode  21 , the negative electrode  22 , and the separator  23 . The tab part  40 B extends along the sidewall part M 3  (the taper surface M 3 T) in a direction along the stacking direction S, i.e., in the up direction, and has a strip-like plan shape. 
     The negative electrode tab  40  includes a material similar to a material included in the negative electrode current collector  22 A. It should be understood that the material included in the negative electrode tab  40  may be the same as or different from the material included in the negative electrode current collector  22 A. 
     A description will be given later regarding a coupling form of the negative electrode tab  40  to the negative electrode current collectors  22 A (see  FIG. 4 ). 
     The gasket  50  is an insulating member interposed between the outer package can  11  (the sidewall part  11 W) and the outer package cup  12  (the sidewall part  12 W), as illustrated in  FIG. 1 . The gasket  50  seals a space between the outer package can  11  and the outer package cup  12 , and insulates the outer package can  11  and the outer package cup  12  from each other, as described above. 
     The gasket  50  includes one or more of insulating materials including, without limitation, polypropylene and polyethylene. A mounting range of the gasket  50  is not particularly limited. Here, the mounting range of the gasket  50  is not limited to the space between the sidewall parts  11 W and  12 W but is extended to the inside of the battery can  10 , that is, onto an inner surface of the sidewall part  11 W. 
     It should be understood that the secondary battery may further include one or more of other unillustrated components. 
     Specifically, the secondary battery includes a safety valve mechanism. The safety valve mechanism cuts off the electrical coupling between the battery can  10  and the battery device  20  if an internal pressure of the battery can  10  reaches a certain level or higher due to, e.g., an internal short circuit or heating from outside. A mounting position of the safety valve mechanism is not particularly limited. The safety valve mechanism may thus be provided at the outer package can  11  or at the outer package cup  12 . 
     Further, the secondary battery includes an insulator between the battery can  10  and the battery device  20 . The insulator includes one or more of materials including, without limitation, an insulating film and an insulating sheet. The insulator prevents a short circuit between the outer package can  11  and the negative electrodes  22 , and prevents a short circuit between the outer package cup  12  and the positive electrodes  21 . A mounting range of the insulator is not particularly limited, and may thus be freely chosen. 
     It should be understood that the battery can  10  is provided with, for example, a liquid injection hole and a cleavage valve. The liquid injection hole is used for injecting the electrolytic solution into the battery can  10 , and is sealed after use. In a case where the internal pressure of the battery can  10  reaches a certain level or higher due to, e.g., an internal short circuit or heating from outside as described above, the cleavage valve cleaves to release the internal pressure. There is no limitation on the respective positions at which the liquid injection hole and the cleavage valve are to be provided. Each of the liquid injection hole and the cleavage valve may thus be provided at the outer package can  11  or at the outer package cup  12 . 
       FIGS. 3 and 4  each illustrate an enlarged sectional configuration of the main part of the secondary battery (the battery device  20 , the positive electrode tab  30 , and the negative electrode tab  40 ) illustrated in  FIG. 1 . 
     It should be understood that  FIG. 3  illustrates a section along the positive electrode tab  30 , and  FIG. 4  illustrates a section along the negative electrode tab  40 . Further,  FIG. 3  illustrates a state where the positive electrode tab  30  is separated from the battery device  20  for easy viewing of the coupling form of the positive electrode tab  30 , and  FIG. 4  illustrates a state where the negative electrode tab  40  is separated from the battery device  20  for easy viewing of the coupling form of the negative electrode tab  40 . 
     In the following, the detailed configuration of each of the positive electrode  21 , the negative electrode  22 , and the separator  23  will be described first, and thereafter the coupling form of each of the positive electrode tab  30  and the negative electrode tab  40  will be described. In this case,  FIGS. 1 and 2  described already will be referred to when necessary. 
     In the battery device  20  which is a stacked electrode body, as described above, the positive electrodes  21  and the negative electrodes  22  are alternately stacked in the stacking direction S with the separators  23  interposed therebetween. The battery device  20  thus includes the separators  23  together with the positive electrodes  21  and the negative electrodes  22 . 
     Here, as one example, six positive electrodes  21  and seven negative electrodes  22  are alternately stacked with the separators  23  interposed therebetween in such a manner that each of a lowermost layer and an uppermost layer among the positive electrodes  21  and the negative electrodes  22  is one of the negative electrodes  22 . It should be understood that the respective numbers of the positive electrodes  21  and the negative electrodes  22  to be stacked are not particularly limited, and may thus be freely chosen. 
     The positive electrodes  21  are electrodes included in the battery device  20 . Each of the positive electrodes  21  includes the positive electrode current collector  21 A and a positive electrode active material layer  21 B, as illustrated in  FIG. 3 . Here, the positive electrode active material layer  21 B is provided on each of both sides of the positive electrode current collector  21 A. It should be understood that the positive electrode active material layer  21 B may be provided only on one side of the positive electrode current collector  21 A. 
     The positive electrode current collector  21 A includes a material similar to the material included in the outer package can  11 . It should be understood that the material included in the positive electrode current collector  21 A may be the same as or different from the material included in the outer package can  11 . As will be described later, the positive electrode current collector  21 A is led more outward than the positive electrode active material layer  21 B. 
     The positive electrode active material layer  21 B includes a positive electrode active material into which lithium is insertable and from which lithium is extractable. The positive electrode active material includes one or more of lithium-containing compounds including, without limitation, a lithium-containing transition metal compound. Examples of the lithium-containing transition metal compound include an oxide, a phosphoric acid compound, a silicic acid compound, and a boric acid compound each including lithium and one or more transition metal elements as constituent elements. It should be understood that the positive electrode active material layer  21 B may further include, without limitation, a positive electrode binder and a positive electrode conductor. 
     The negative electrodes  22  are the other electrodes included in the battery device  20 . Each of the negative electrodes  22  includes the negative electrode current collector  22 A and a negative electrode active material layer  22 B, as illustrated in  FIG. 4 . Here, the negative electrode active material layer  22 B is provided on each of both sides of the negative electrode current collector  22 A. It should be understood that the negative electrode active material layer  22 B may be provided only on one side of the negative electrode current collector  22 A. 
     The negative electrode current collector  22 A includes a material similar to the material included in the outer package cup  12 . It should be understood that the material included in the negative electrode current collector  22 A may be the same as or different from the material included in the outer package cup  12 . As will be described later, the negative electrode current collector  22 A is led more outward than the negative electrode active material layer  22 B. It should be understood that the negative electrode current collector  22 A is led out to a position not overlapping a position to which the positive electrode current collector  21 A is led out. In other words, the negative electrode current collector  22 A is so led out as not to come into contact with the positive electrode current collector  21 A. This is for the purpose of preventing a short circuit between the positive electrode current collector  21 A and the negative electrode current collector  22 A. 
     The negative electrode active material layer  22 B includes a negative electrode active material into which lithium is insertable and from which lithium is extractable. The negative electrode active material includes one or more of materials including, without limitation, a carbon material and a metal-based material. Examples of the carbon material include graphite. The metal-based material is a material that includes, as a constituent element or constituent elements, one or more elements among metal elements and metalloid elements that are each able to form an alloy with lithium. Specifically, the metal-based material includes one or more of elements including, without limitation, silicon and tin, as a constituent element or constituent elements. The metal-based material may be a simple substance, an alloy, a compound, or a mixture of two or more thereof. It should be understood that the negative electrode active material layer  22 B may further include, without limitation, a negative electrode binder and a negative electrode conductor. 
     The separator  23  is an insulating porous film interposed between the positive electrode  21  and the negative electrode  22 . The separator  23  allows lithium to pass therethrough in an ionic state while preventing a short circuit between the positive electrode  21  and the negative electrode  22 . This separator  23  includes one or more of polymer compounds, including polyethylene. 
     It should be understood that the positive electrode  21  preferably has an outer diameter smaller than an outer diameter of the separator  23 . A reason for this is that this prevents a short circuit between the positive electrode  21  and the outer package cup  12 . The negative electrode  22  preferably has a height smaller than the outer diameter of the separator  23  and greater than a height of the positive electrode  21 . A reason for this is that this prevents a short circuit between the negative electrode  22  and the outer package can  11  and also prevents a short circuit between the positive electrode  21  and the negative electrode  22  caused by precipitation of lithium upon charging and discharging. 
     The positive electrode  21 , the negative electrode  22 , and the separator  23  are each impregnated with the electrolytic solution. The electrolytic solution includes a solvent and an electrolyte salt. The solvent includes one or more of nonaqueous solvents (organic solvents) including, without limitation, a carbonic-acid-ester-based compound, a carboxylic-acid-ester-based compound, and a lactone-based compound. The electrolyte salt includes one or more of light metal salts, including a lithium salt. 
     Here, a detailed configuration of the positive electrode current collector  21 A will be described first as a precondition for describing a configuration of the positive electrode tab  30 , and thereafter the coupling form of the positive electrode tab  30  will be described. This order of descriptions applies also to the descriptions of a detailed configuration of the negative electrode current collector  22 A and the coupling form of the negative electrode tab  40 . 
     The positive electrodes  21  each include the positive electrode current collector  21 A as described above. The battery device  20  therefore includes a plurality of positive electrode current collectors  21 A. Here, respective lengths of the positive electrode current collectors  21 A are equal. 
     In each of the positive electrodes  21 , the positive electrode current collector  21 A is led more outward than the positive electrode active material layer  21 B, as described above. More specifically, the positive electrode current collector  21 A is led out in a leading-out direction D 211  (a first direction, i.e., the right direction) intersecting the stacking direction S. Thus, as illustrated in  FIG. 3 , the positive electrode current collector  21 A includes a non-led-out part  21 AX, and a led-out part  21 AY coupled to the non-led-out part  21 AX. The non-led-out part  21 AX is a part that is covered with the positive electrode active material layer  21 B and is thus not led more outward than the positive electrode active material layer  21 B. The led-out part  21 AY is a part that is not covered with the positive electrode active material layer  21 B and is thus led more outward than the positive electrode active material layer  21 B. 
     The positive electrode current collector  21 A led out in the leading-out direction D 211  includes an end part that is bent in a first bending direction D 212  (a second direction, i.e., the up direction) intersecting the leading-out direction D 211 . In other words, the led-out part  21 AY led out in the leading-out direction D 211  is bent in the first bending direction D 212  at some middle point. Here, the led-out part  21 AY which is a part of the positive electrode current collector  21 A having the positive polarity is bent in a direction away from the outer package cup  12  having the negative polarity opposite to the positive polarity, that is, the outer package cup  12  serving as the negative electrode terminal. The first bending direction D 212  is therefore a direction from the outer package cup  12  toward the outer package can  11 , that is, the up direction. This is for the purpose of preventing a short circuit between the led-out part  21 AY and the outer package cup  12 . 
     As the battery device  20  includes the plurality of positive electrodes  21 , each of the positive electrodes  21  includes the non-led-out part  21 AX and the led-out part  21 AY. The battery device  20  thus includes a plurality of led-out parts  21 AY. 
     Each of the led-out parts  21 AY bent in the first bending direction D 212  overlaps and is in contact with another one of the led-out parts  21 AY adjacent thereto (in front thereof) in the first bending direction D 212 , and is therefore coupled to the adjacent one of the led-out parts  21 AY. Here, each of the led-out parts  21 AY is joined to the adjacent one of the led-out parts  21 AY by means of a method such as a welding method. 
     Here, of the plurality of led-out parts  21 AY, one or more led-out parts  21 AY that are located on a rear side in the first bending direction D 212  are bent once and thus terminate at some middle point along the first bending direction D 212 . In other words, the one or more led-out parts  21 AY each terminate at some middle point on an end face along the first bending direction D 212  of the battery device  20 , i.e., the taper surface M 3 T of the sidewall part M 3 . As a result, the one or more led-out parts  21 AY are bent only in the first bending direction D 212 , and are thus bent to be along the battery device  20  (the taper surface M 3 T). 
     The one or more led-out parts  21 AY each include a non-bent part  21 AY 1 , and a first bent part  21 AY 2  coupled to the non-bent part  21 AY 1 . The non-bent part  21 AY 1  is disposed on a side closer to the positive electrode active material layer  21 B than the first bent part  21 AY 2 , and extends in the leading-out direction D 211 . The first bent part  21 AY 2  is disposed on a side farther from the positive electrode active material layer  21 B than the non-bent part  21 AY 1 , and extends in the first bending direction D 212 . 
     The number of the one or more led-out parts  21 AY that are bent once is not particularly limited, and may thus be freely chosen. In other words, the number of the one or more led-out parts  21 AY may be one, or may be two or more but is less than the total number of the plurality of led-out parts  21 AY. 
     Further, in each of the one or more led-out parts  21 AY that are bent once, the position of an end of the first bent part  21 AY 2  may be freely chosen. In other words, respective ends of a plurality of first bent parts  21 AY 2  may be at the same position or at different positions from each other. Here, the positions of the respective ends of the first bent parts  21 AY 2  are gradually recessed toward a direction opposite to the first bending direction D 212 . 
     Here, in a case where the six positive electrodes  21  and the seven negative electrodes  22  are alternately stacked with the separators  23  interposed therebetween, three led-out parts  21 AY located on the rear side in the first bending direction D 212  are bent once. Further, the positions of the ends of the respective first bent parts  21 AY 2  of the three led-out parts  21 AY are gradually recessed toward the direction opposite to the first bending direction D 212 . 
     Besides, of the plurality of led-out parts  21 AY, the remaining one or more led-out parts  21 AY that are located on a front side in the first bending direction D 212  are bent twice, and are thus bent in the first bending direction D 212  and thereafter bent further in a second bending direction D 213  (a third direction, i.e., the left direction) opposite to the leading-out direction D 211 . In other words, the remaining one or more led-out parts  21 AY are bent in the first bending direction D 212  and thereafter bent in the second bending direction D 213 , and are therefore bent to be along the sidewall part M 3  (the taper surface M 3 T) and thereafter bent to be along the bottom part M 1 . 
     Accordingly, the remaining one or more led-out parts  21 AY each include, together with the non-bent part  21 AY 1  and the first bent part  21 AY 2 , a second bent part  21 AY 3  coupled to the first bent part  21 AY 2 , unlike the foregoing one or more led-out parts  21 AY. The second bent part  21 AY 3  is disposed on a side farther from the non-bent part  21 AY 1  than the first bent part  21 AY 2 , and extends in the second bending direction D 213 . 
     The number of the remaining one or more led-out parts  21 AY that are bent twice is not particularly limited, and may thus be freely chosen. In other words, the number of the remaining one or more led-out parts  21 AY may be one, or may be two or more but is less than the total number of the plurality of led-out parts  21 AY. 
     Further, the position of an end of the led-out part  21 AY bent twice may be freely chosen. In other words, respective ends of a plurality of second bent parts  21 AY 3  may be at the same position, or at different positions from each other. Here, the positions of the respective ends of the second bent parts  21 AY 3  are gradually recessed toward a direction opposite to the second bending direction D 213 . 
     Here, in the case where the six positive electrodes  21  and the seven negative electrodes  22  are alternately stacked with the separators  23  interposed therebetween, three led-out parts  21 AY located on the front side in the first bending direction D 212  are bent twice. Further, the positions of the ends of the respective second bent parts  21 AY 3  of the three led-out parts  21 AY are gradually recessed toward the direction opposite to the second bending direction D 213 . 
     As described above, the positive electrode tab  30  includes the tab part  30 A along the bottom part M 1  and the tab part  30 B along the sidewall part M 3  (the taper surface M 3 T). Thus, in the positive electrode tab  30 , the tab part  30 A is coupled to the remaining one or more led-out parts  21 AY (the second bent part(s)  21 AY 3  of the led-out part(s)  21 AY that are bent twice) of the plurality of led-out parts  21 AY, and the tab part  30 B is coupled to the one or more led-out parts  21 AY (the first bent part(s)  21 AY 2  of the led-out part(s)  21 AY that are bent once) of the plurality of led-out parts  21 AY. In this case, the tab part  30 A is joined to the remaining one or more led-out parts  21 AY by means of a method such as a welding method, and the tab part  30 B is joined to the one or more led-out parts  21 AY by means of a method such as a welding method. 
     The positive electrode tab  30  is coupled to the outer package can  11  (the bottom part  11 M) at the tab part  30 A. The outer package can  11  is thereby coupled to the positive electrodes  21  (the positive electrode current collectors  21 A) via the positive electrode tab  30  (the tab part  30 A and the tab part  30 B), and thus serves as the positive electrode terminal. 
     The negative electrode current collector  22 A has a configuration similar to that of the positive electrode current collector  21 A described above, and the negative electrode tab  40  has a configuration similar to that of the positive electrode tab  30  described above. It should be understood that the coupling method (the joining method) has already been described, and the description thereof will thus be omitted from the following. 
     The negative electrodes  22  each include the negative electrode current collector  22 A as described above. The battery device  20  therefore includes a plurality of negative electrode current collectors  22 A. Here, respective lengths of the negative electrode current collectors  22 A are equal. 
     In each of the negative electrodes  22 , the negative electrode current collector  22 A is led more outward than the negative electrode active material layer  22 B as described above. More specifically, the negative electrode current collector  22 A is led out in a leading-out direction D 221  (a first direction, i.e., the right direction) intersecting the stacking direction S. Thus, as illustrated in FIG.  4 , the negative electrode current collector  22 A includes a non-led-out part  22 AX, and a led-out part  22 AY coupled to the non-led-out part  22 AX. The non-led-out part  22 AX is a part that is covered with the negative electrode active material layer  22 B and is thus not led more outward than the negative electrode active material layer  22 B. The led-out part  22 AY is a part that is not covered with the negative electrode active material layer  22 B and is thus led more outward than the negative electrode active material layer  22 B. 
     The negative electrode current collector  22 A led out in the leading-out direction D 221  includes an end part that is bent in a first bending direction D 222  (a second direction, i.e., the down direction) intersecting the leading-out direction D 221 . In other words, the led-out part  22 AY led out in the leading-out direction D 221  is bent in the first bending direction D 222  at some middle point. Here, the led-out part  22 AY which is a part of the negative electrode current collector  22 A having the negative polarity is bent in a direction away from the outer package can  11  having the positive polarity opposite to the negative polarity, that is, the outer package can  11  serving as the positive electrode terminal. The first bending direction D 222  is therefore a direction from the outer package can  11  toward the outer package cup  12 , that is, the down direction. This is for the purpose of preventing a short circuit between the led-out part  22 AY and the outer package can  11 . 
     As the battery device  20  includes the plurality of negative electrodes  22 , each of the negative electrodes  22  includes the non-led-out part  22 AX and the led-out part  22 AY. The battery device  20  thus includes a plurality of led-out parts  22 AY. 
     Each of the led-out parts  22 AY bent in the first bending direction D 222  overlaps and is in contact with another one of the led-out parts  22 AY adjacent thereto (in front thereof) in the first bending direction D 222 , and is therefore coupled to the adjacent one of the led-out parts  22 AY. 
     Here, of the plurality of led-out parts  22 AY, one or more led-out parts  22 AY that are located on the rear side in the first bending direction D 222  are bent once and therefore terminate at some middle point along the first bending direction D 222 . In other words, the one or more led-out parts  22 AY each terminate at some middle point on the end face along the first bending direction D 222  of the battery device  20 , i.e., the taper surface M 3 T of the sidewall part M 3 . As a result, the one or more led-out parts  22 AY are bent only in the first bending direction D 222 , and are thus bent to be along the battery device  20  (the taper surface M 3 T). 
     The one or more led-out parts  22 AY each include a non-bent part  22 AY 1 , and a first bent part  22 AY 2  coupled to the non-bent part  22 AY 1 . The non-bent part  22 AY 1  is disposed on a side closer to the negative electrode active material layer  22 B than the first bent part  22 AY 2 , and extends in the leading-out direction D 221 . The first bent part  22 AY 2  is disposed on a side farther from the negative electrode active material layer  22 B than the non-bent part  22 AY 1 , and extends in the first bending direction D 222 . 
     The number of the one or more led-out parts  22 AY that are bent once is not particularly limited, and may thus be freely chosen. In other words, the number of the one or more led-out parts  22 AY may be one, or may be two or more but is less than the total number of the plurality of led-out parts  22 AY. 
     Further, in each of the one or more led-out parts  22 AY that are bent once, the position of an end of the first bent part  22 AY 2  may be freely chosen. In other words, respective ends of a plurality of first bent parts  22 AY 2  may be at the same position or at different positions from each other. Here, the positions of the respective ends of the first bent parts  22 AY 2  are gradually recessed toward a direction opposite to the first bending direction D 222 . 
     Here, in the case where the six positive electrodes  21  and the seven negative electrodes  22  are alternately stacked with the separators  23  interposed therebetween, four led-out parts  22 AY located on the rear side in the first bending direction D 222  are bent once. Further, the positions of the ends of the respective first bent parts  22 AY 2  of the four led-out parts  22 AY are gradually recessed toward the direction opposite to the first bending direction D 222 . 
     Besides, of the plurality of led-out parts  22 AY, the remaining one or more led-out parts  22 AY that are located on the front side in the first bending direction D 222  are bent twice, and are thus bent in the first bending direction D 222  and thereafter bent further in a second bending direction D 223  (a third direction, i.e., the left direction) opposite to the leading-out direction D 221 . In other words, the remaining one or more led-out parts  22 AY are bent in the first bending direction D 222  and thereafter bent in the second bending direction D 223 , and are therefore bent to be along the sidewall part M 3  (the taper surface M 3 T) and thereafter bent to be along the bottom part M 2 . 
     Accordingly, the remaining one or more led-out parts  22 AY each include, together with the non-bent part  22 AY 1  and the first bent part  22 AY 2 , a second bent part  22 AY 3  coupled to the first bent part  22 AY 2 , unlike the foregoing one or more led-out parts  22 AY. The second bent part  22 AY 3  is disposed on a side farther from the non-bent part  22 AY 1  than the first bent part  22 AY 2 , and extends in the second bending direction D 223 . 
     The number of the remaining one or more led-out parts  22 AY that are bent twice is not particularly limited, and may thus be freely chosen. In other words, the number of the remaining one or more led-out parts  22 AY may be one, or may be two or more but is less than the total number of the plurality of led-out parts  22 AY. 
     Further, the position of an end of the led-out part  22 AY bent twice may be freely chosen. In other words, respective ends of a plurality of second bent parts  22 AY 3  may be at the same position, or at different positions from each other. Here, the positions of the respective ends of the second bent parts  22 AY 3  are gradually recessed toward a direction opposite to the second bending direction D 223 . 
     Here, in the case where the six positive electrodes  21  and the seven negative electrodes  22  are alternately stacked with the separators  23  interposed therebetween, three led-out parts  22 AY located on the front side in the first bending direction D 222  are bent twice. Further, the positions of the ends of the respective second bent parts  22 AY 3  of the three led-out parts  22 AY are gradually recessed toward the direction opposite to the second bending direction D 223 . 
     As described above, the negative electrode tab  40  includes the tab part  40 A along the bottom part M 2  and the tab part  40 B along the sidewall part M 3  (the taper surface M 3 T). Thus, in the negative electrode tab  40 , the tab part  40 A is coupled to the remaining one or more led-out parts  22 AY (the second bent part(s)  22 AY 3  of the led-out part(s)  22 AY that are bent twice) of the plurality of led-out parts  22 AY, and the tab part  40 B is coupled to the one or more led-out parts  22 AY (the first bent part(s)  22 AY 2  of the led-out part(s)  22 AY that are bent once) of the plurality of led-out parts  22 AY. 
     The negative electrode tab  40  is coupled to the outer package cup  12  (the bottom part  12 M) at the tab part  40 A. The outer package cup  12  is thereby coupled to the negative electrodes  22  (the negative electrode current collectors  22 A) via the negative electrode tab  40  (the tab part  40 A and the tab part  40 B), and thus serves as the negative electrode terminal. 
     Here, as illustrated in  FIG. 2 , the led-out parts  21 AY and  22 AY are disposed to be adjacent to each other at the sidewall part M 3  (the taper surface M 3 T). Thus, the leading-out direction D 211  for the led-out part  21 AY and the leading-out direction D 221  for the led-out part  22 AY are a common direction. More specifically, the leading-out direction D 211  for the led-out part  21 AY is the right direction, and the leading-out direction D 221  for the led-out part  22 AY is also the right direction. 
     Upon charging the secondary battery, in the battery device  20 , lithium is extracted from the positive electrode  21 , and the extracted lithium is inserted into the negative electrode  22  via the electrolytic solution. Upon discharging the secondary battery, in the battery device  20 , lithium is extracted from the negative electrode  22 , and the extracted lithium is inserted into the positive electrode  21  via the electrolytic solution. In these cases, the lithium is inserted and extracted in an ionic state. 
     Upon charging and discharging, the positive electrode current collectors  21 A are electrically coupled to each other by means of the positive electrode tab  30 , and the negative electrode current collectors  22 A are electrically coupled to each other by means of the negative electrode tab  40 . 
     For describing a process of manufacturing the secondary battery,  FIGS. 5 and 6  each illustrate a sectional configuration of the secondary battery in the course of manufacture. It should be understood that  FIG. 5  corresponds to  FIG. 3 , and  FIG. 6  corresponds to  FIG. 4 . 
     In a case of manufacturing the secondary battery, the secondary battery is assembled by a procedure described below. In this case, the stacked body  120  described above is used to fabricate the battery device  20 . In the following,  FIGS. 1 to 4  described already will be referred to when necessary. 
     First, prepared is a slurry including, without limitation, the positive electrode active material in a solvent such as an organic solvent, following which the slurry is applied on both sides of the positive electrode current collector  21 A (the non-led-out part  21 AX) to thereby form the positive electrode active material layers  21 B. The positive electrode  21  which includes the positive electrode current collector  21 A and the positive electrode active material layers  21 B and in which the led-out part  21 AY is led more outward than the positive electrode active material layers  21 B is thereby fabricated. 
     Thereafter, prepared is a slurry including, without limitation, the negative electrode active material in a solvent such as an organic solvent, following which the slurry is applied on both sides of the negative electrode current collector  22 A (the non-led-out part  22 AX) to thereby form the negative electrode active material layers  22 B. The negative electrode  22  which includes the negative electrode current collector  22 A and the negative electrode active material layers  22 B and in which the led-out part  22 AY is led more outward than the negative electrode active material layers  22 B is thereby fabricated. 
     Thereafter, the electrolyte salt is added to a solvent. The electrolytic solution including the solvent and the electrolyte salt is thereby prepared. 
     Thereafter, a plurality of positive electrodes  21  and a plurality of negative electrodes  22  are alternately stacked with the separators  23  interposed therebetween to thereby fabricate the stacked body  120 . 
     Thereafter, each of a plurality of led-out parts  21 AY is bent. In this case, one or more, but not all, of the led-out parts  21 AY are each bent once to include the non-bent part  21 AY 1  and the first bent part  21 AY 2 , and the remaining one or more led-out parts  21 AY are each bent twice to include the non-bent part  21 AY 1 , the first bent part  21 AY 2 , and the second bent part  21 AY 3 . The plurality of led-out parts  21 AY is bent in such a manner that each of the led-out parts  21 AY overlaps and comes into contact with another one of the led-out parts  21 AY adjacent thereto in the first bending direction D 212 . 
     Further, each of a plurality of led-out parts  22 AY is bent. In this case, one or more, but not all, of the led-out parts  22 AY are each bent once to include the non-bent part  22 AY 1  and the first bent part  22 AY 2 , and the remaining one or more led-out parts  22 AY are each bent twice to include the non-bent part  22 AY 1 , the first bent part  22 AY 2 , and the second bent part  22 AY 3 . The plurality of led-out parts  22 AY is bent in such a manner that each of the led-out parts  22 AY overlaps and comes into contact with another one of the led-out parts  22 AY adjacent thereto in the first bending direction D 222 . 
     Thereafter, the led-out parts  21 AY are coupled to each other, and the led-out parts  22 AY are coupled to each other. Here, the led-out parts  21 AY are joined to each other by means of a method such as a welding method, and the led-out parts  22 AY are joined to each other by means of a method such as a welding method. The welding method includes one or more kinds of welding methods including, without limitation, a laser welding method and a resistance welding method. Details of the welding method described here apply also to the following. 
     Thereafter, the positive electrode tab  30  (the tab parts  30 A and  30 B) and the negative electrode tab  40  (the tab parts  40 A and  40 B) are each coupled to the stacked body  120  (the led-out parts  21 AY and  22 AY). Here, the positive electrode tab  30  and the negative electrode tab  40  are each joined to the stacked body  120  by means of a method such as a welding method. 
     In this case, at the bottom part M 1 , the tab part  30 A is coupled to the remaining one or more led-out parts  21 AY that are bent twice, i.e., to the second bent part(s)  21 AY 3 , and at the side wall part M 3  (the taper surface M 3 T), the tab part  30 B is coupled to the one or more led-out parts  21 AY that are bent once, i.e., to the first bent part(s)  21 AY 2 . Further, at the bottom part M 2 , the tab part  40 A is coupled to the remaining one or more led-out parts  22 AY that are bent twice, i.e., to the second bent part(s)  22 AY 3 , and at the side wall part M 3  (the taper surface M 3 T), the tab part  40 B is coupled to the one or more led-out parts  22 AY that are bent once, i.e., to the first bent part(s)  22 AY 2 . 
     Thereafter, the stacked body  120  is placed into the outer package can  11  through the opening  11 K. In this case, the positive electrode tab  30  (the tab part  30 A) is coupled to the outer package can  11  (the bottom part  11 M). Here, the tab part  30 A is joined to the bottom part  11 M by means of a method such as a welding method. 
     Thereafter, the outer package can  11  and the outer package cup  12  are disposed to allow the openings  11 K and  12 K to be opposed to each other, following which the outer package cup  12  is fitted to the outer package can  11  with the gasket  50  interposed therebetween. In this case, the opening  11 K is covered with the bottom part  12 M, and the sidewall part  12 W is placed over the sidewall part  11 W from an outer side. Further, the negative electrode tab  40  (the tab part  40 A) is coupled to the outer package cup  12  (the bottom part  12 M). Here, the tab part  40 A is joined to the bottom part  12 M by means of a method such as a welding method. 
     Thereafter, the sidewall parts  11 W and  12 W are crimped to each other with the gasket  50  interposed therebetween. The outer package cup  12  is thereby fixed to the outer package can  11  with the gasket  50  interposed therebetween. As a result, the battery can  10  is sealed and the stacked body  120  is enclosed inside the battery can  10 . 
     Lastly, the electrolytic solution is injected into the battery can  10  through the unillustrated liquid injection hole, following which the liquid injection hole is sealed. This causes the stacked body  120  (the positive electrodes  21 , the negative electrodes  22 , and the separators  23 ) to be impregnated with the electrolytic solution, thereby fabricating the battery device  20 . The battery device  20  is thus sealed inside the battery can  10 . As a result, the secondary battery is completed. 
     According to the secondary battery, the positive electrode current collectors  21 A (the led-out parts  21 AY) are led out in the leading-out direction D 211  from the respective positive electrodes  21  stacked over each other with the separators  23  interposed therebetween, and the led-out parts  21 AY led out in the leading-out direction D 211  include the respective first bent parts  21 AY 2  bent in the first bending direction D 212 . Further, each of the first bent parts  21 AY 2  overlaps and is in contact with another one of the first bent parts  21 AY 2  adjacent thereto in the first bending direction D 212 . Furthermore, one or more, but not all, of the first bent parts  21 AY 2  terminate at some middle point on the end face along the first bending direction D 212  of the battery device  20 , i.e., the taper surface M 3 T of the sidewall part M 3 . As a result, for a reason described below, it is possible to increase the energy density per unit volume. 
       FIG. 7  is a sectional view of a configuration of a secondary battery of a comparative example, and corresponds to  FIG. 3 . The secondary battery of the comparative example has a configuration similar to that of the secondary battery of the present embodiment ( FIG. 3 ) except that, as illustrated in  FIG. 7 , all of the led-out parts  21 AY in the positive electrodes  21  (the positive electrode current collectors  21 A) are bent twice and therefore none of the first bent parts  21 AY 2  terminates at some middle point along the first bending direction D 212 , that is, none of the first bent parts  21 AY 2  terminates at some middle point on the end face along the first bending direction D 212  of the battery device  20 , i.e., the taper surface M 3 T of the sidewall part M 3 . Thus, all of the led-out parts  21 AY each include the non-bent part  21 AY 1 , the first bent part  21 AY 2 , and the second bent part  21 AY 3 . 
     In the secondary battery of the comparative example, all of the led-out parts  21 AY are bent twice. Accordingly, as illustrated in  FIG. 7 , all of the led-out parts  21 AY (the first bent parts  21 AY 2 ) overlap each other at the sidewall part M 3  (the taper surface M 3 T) of the battery device  20 . As a result, a total thickness (a maximum thickness) T 11  of the first bent parts  21 AY 2  overlapping each other at the sidewall part M 3  is markedly large. Here, the maximum thickness T 11  is the sum of the respective thicknesses of six first bent parts  21 AY 2 . 
     Here, a space occupied by the first bent parts  21 AY 2  at the sidewall part M 3 , that is, a space determined on the basis of the maximum thickness T 11 , is a space that is not available for containing the battery device  20  in the battery can  10 , that is, a non-device space. 
     From the foregoing, the secondary battery of the comparative example is markedly large in maximum thickness T 11  due to the configuration in which all of the first bent parts  21 AY 2  overlap each other at the sidewall part M 3 . This increases a volume of the non-device space (a non-device space volume). As a result, a space available for containing the battery device  20  in the battery can  10  (a device space) becomes small in volume (device space volume). Accordingly, it is difficult to increase the energy density per unit volume. 
     In contrast, according to the secondary battery of the present embodiment, one or more, but not all, of the led-out parts  21 AY are bent once, and only the remaining one or more led-out parts  21 AY are bent twice. As a result, as illustrated in  FIG. 3 , only some of the led-out parts  21 AY (the first bent parts  21 AY 2 ) overlap each other at the sidewall part M 3 . Accordingly, a total thickness (a maximum thickness) T 1  of the first bent parts  21 AY 2  overlapping each other at the sidewall part M 3  is smaller than the maximum thickness T 11  in the secondary battery of the comparative example. Here, the maximum thickness T 1  is the sum of the respective thicknesses of almost three first bent parts  21 AY 2 . 
     From the foregoing, the secondary battery of the present embodiment is smaller in maximum thickness T 1  by virtue of the configuration in which only some of the first bent parts  21 AY 2  overlap each other at the sidewall part M 3 . This reduces the non-device space volume. As a result, the device space volume increases to make it possible to increase the energy density per unit volume. 
     The action and effects based on the configuration of the positive electrode  21  described here are similarly achievable also on the basis of the configuration of the negative electrode  22 . More specifically, according to the secondary battery of the comparative example illustrated in  FIG. 8  corresponding to  FIG. 4 , the led-out parts  22 AY (the first bent parts  22 AY 2 ) overlap each other at the sidewall part M 3 , causing a maximum thickness T 12  to be markedly large. This results in a greater non-device space volume and a smaller device space volume, causing also the energy density per unit volume to be smaller. In contrast, according to the secondary battery of the present embodiment illustrated in  FIG. 4 , only some of the led-out parts  22 AY (the first bent parts  22 AY 2 ) overlap each other at the sidewall part M 3 , and therefore a maximum thickness T 2  is smaller than the maximum thickness T 12 . This results in a smaller non-device space volume and a greater device space volume, causing also the energy density per unit volume to be greater. The secondary battery of the present embodiment thus makes it possible to achieve similar effects also in terms of the configuration of the negative electrode  22 . 
     In addition, in the secondary battery of the present embodiment, the respective lengths of the positive electrode current collectors  21 A may be equal. This allows for uniformization of respective electrical resistances of the positive electrodes  21  and allows a wiring structure using the positive electrode current collectors  21 A described above to be provided easily without a need for changing the respective lengths of the positive electrode current collectors  21 A. Accordingly, it is possible to achieve higher effects. 
     The action and effects based on the configuration of the positive electrode  21  described here are similarly achievable also on the basis of the configuration of the negative electrode  22 . More specifically, the respective lengths of the negative electrode current collectors  22 A may be equal. This allows for uniformization of respective electrical resistances of the negative electrodes  22  and allows a wiring structure using the negative electrode current collectors  22 A described above to be provided easily. Accordingly, it is possible to achieve higher effects. 
     Further, the positions of the respective ends of the first bent parts  21 AY 2  that each terminate at some middle point along the first bending direction D 212  may be gradually recessed toward the direction opposite to the first bending direction D 212 . In such a case, an increase in maximum thickness T 1  is suppressed as compared with a case where the ends are located at the same position. This helps to prevent the non-device space volume from becoming smaller, and accordingly helps to increase the device space volume, making it possible to achieve higher effects. 
     The action and effects based on the configuration of the positive electrode  21  described here are similarly achievable also on the basis of the configuration of the negative electrode  22 . More specifically, the positions of the respective ends of the first bent parts  22 AY 2  that each terminate at some middle point along the first bending direction D 222  may be gradually recessed toward the direction opposite to the first bending direction D 222 . This suppresses an increase in maximum thickness T 2 , making it possible to achieve higher effects. 
     Further, one or more, but not all, of the led-out parts  21 AY may each further include the second bent part  21 AY 3  bent in the second bending direction D 213 . This allows for a further increase in energy density per unit volume for a reason described below. Accordingly, it is possible to achieve even higher effects. 
     In the secondary battery of the comparative example ( FIG. 7 ), all of the led-out parts  21 AY are bent twice, and therefore all of the led-out parts  21 AY (the second bent parts  21 AY 3 ) overlap each other at the bottom part M 1  of the battery device  20 . As a result, the total thickness of the second bent parts  21 AY 3  overlapping each other at the bottom part M 1 , i.e., a maximum thickness T 13 , is markedly large. The non-device space volume thus increases to reduce the device space volume. This results in a smaller energy density per unit volume. 
     In contrast, in the secondary battery of the present embodiment ( FIG. 3 ), one or more, but not all, of the led-out parts  21 AY are bent once, and only the other or remaining one or more of the led-out parts  21 AY are bent twice. As a result, only some of the led-out parts  21 AY (the second bent parts  21 AY 3 ) overlap each other at the bottom part Ml. The total thickness of the second bent parts  21 AY 3  overlapping each other at the bottom part M 1 , i.e., a maximum thickness T 3 , is therefore smaller than the maximum thickness T 13 . This results in a smaller non-device space volume and accordingly a greater device space volume. The energy density per unit volume therefore increases. 
     From the foregoing, the secondary battery of the present embodiment achieves a further increase in energy density per unit volume not only in terms of the maximum thickness T 1  at the sidewall part M 3  but also in terms of the maximum thickness T 3  at the bottom part M 1 . Accordingly, it is possible to achieve even higher effects. 
     The action and effects based on the configuration of the positive electrode  21  described here are similarly achievable also on the basis of the configuration of the negative electrode  22 . More specifically, in the secondary battery of the comparative example ( FIG. 7 ), all of the led-out parts  22 AY (the second bent parts  22 AY 3 ) overlap each other at the bottom part M 2 , and a maximum thickness T 14  is thus markedly large. In contrast, in the secondary battery of the present embodiment ( FIG. 3 ), only some of the led-out parts  22 AY (the second bent parts  22 AY 3 ) overlap each other at the bottom part M 2 , and therefore a maximum thickness T 4  is smaller than the maximum thickness T 14 . This results in a smaller non-device space volume and a greater device space volume, thus allowing the energy density per unit volume to increase. Accordingly, it is possible to achieve even higher effects. 
     Further, in the secondary battery of the present embodiment, the positions of the respective ends of the second bent parts  21 AY 3  may be gradually recessed toward the direction opposite to the second bending direction D 213 . In such a case, an increase in maximum thickness T 3  is suppressed as compared with a case where the ends are located at the same position. This helps to prevent the non-device space volume from becoming smaller, and accordingly helps to increase the device space volume, making it possible to achieve higher effects. 
     The action and effects based on the configuration of the positive electrode  21  described here are similarly achievable also on the basis of the configuration of the negative electrode  22 . More specifically, the positions of the respective ends of the second bent parts  22 AY 3  may be gradually recessed toward the direction opposite to the second bending direction D 223 . This suppresses an increase in maximum thickness T 4 , making it possible to achieve higher effects. 
     Further, the positive electrode tab  30  may be coupled to each of the first bent parts  21 AY 2  and the second bent parts  21 AY 3 . This allows the positive electrode current collectors  21 A (the led-out parts  21 AY) to be electrically coupled to each other easily and stably by means of the positive electrode tab  30 . Accordingly, it is possible to achieve higher effects. 
     The action and effects based on the configuration of the positive electrode tab  30  described here are similarly achievable also on the basis of the configuration of the negative electrode tab  40 . More specifically, the negative electrode tab  40  may be coupled to each of the first bent parts  22 AY 2  and the second bent parts  22 AY 3 . This allows the negative electrode current collectors  22 A (the led-out parts  22 AY) to be electrically coupled to each other easily and stably by means of the negative electrode tab  40 . Accordingly, it is possible to achieve higher effects. 
     Further, the bending direction (the first bending direction D 212 ) of each of the led-out parts  21 AY may be a direction away from the outer package cup  12  (the negative electrode terminal). This prevents a short circuit between the led-out parts  21 AY having the positive polarity and the outer package cup  12  having the negative polarity, making it possible to achieve higher effects. 
     The action and effects based on the configuration of the led-out parts  21 AY described here are similarly achievable also on the basis of the configuration of the led-out parts  22 AY. More specifically, the bending direction (the first bending direction D 222 ) of each of the led-out parts  22 AY may be a direction away from the outer package can  11  (the positive electrode terminal). This prevents a short circuit between the led-out parts  22 AY having the negative polarity and the outer package can  11  having the positive polarity, making it possible to achieve higher effects. 
     Further, the leading-out direction D 211  in each of the positive electrodes  21  (the led-out parts  21 AY) and the leading-out direction D 221  in each of the negative electrodes  22  (the led-out parts  22 AY) may be a common direction. This makes it easier for the secondary battery to be coupled to an electronic apparatus in that direction via the positive electrodes  21  and the negative electrodes  22 . Accordingly, it is possible to achieve higher effects. 
     Further, the secondary battery may include the battery can  10  having a flat and columnar shape. In other words, the secondary battery may be a button-type secondary battery. In such a case, it is possible to achieve higher effects because the energy density per unit volume effectively increases in the small-sized secondary battery which is highly constrained in terms of size. 
     Next, a description will be given of a secondary battery according to a second embodiment of the technology. 
     In the secondary battery of the present embodiment, some of the plurality of positive electrode current collectors  21 A (the positive electrode current collector  21 A of an uppermost layer to be described later) and some of the plurality of negative electrode current collectors  22 A (the negative electrode current collector  22 A of a lowermost layer to be described later) are used to electrically couple the led-out parts  21 AY to each other and to electrically couple the led-out parts  22 AY to each other, unlike in the secondary battery of the first embodiment that uses the positive electrode tab  30  and the negative electrode tab  40  to electrically couple the led-out parts  21 AY to each other and to electrically couple the lead-out parts  22 AY to each other. 
     The secondary battery of the present embodiment has a configuration similar to that of the secondary battery of the first embodiment except for what is described below. 
       FIG. 9  is a perspective view of the configuration of the secondary battery of the present embodiment, and corresponds to  FIG. 2 .  FIGS. 10 and 11  each illustrate a sectional configuration of a main part of the secondary battery of the present embodiment. It should be understood that  FIG. 10  corresponds to  FIG. 3 , and  FIG. 11  corresponds to  FIG. 4 . In each of  FIGS. 9 to 11 , the same components as those described in the first embodiment are denoted with the same reference signs. 
     For easy viewing of the coupling form of the led-out part  21 AY of the lowermost layer,  FIG. 10  illustrates a state where the led-out part  21 AY of the lowermost layer is separated from the other led-out parts  21 AY. For easy viewing of the coupling form of the led-out part  22 AY of the uppermost layer,  FIG. 11  illustrates a state where the led-out part  22 AY of the uppermost layer is separated from the other led-out parts  22 AY. 
     As illustrated in  FIGS. 9 to 11 , this secondary battery includes insulating layers  51  and  52  instead of the positive electrode tab  30  and the negative electrode tab  40 . In the battery device  20 , a plurality of positive electrodes  21  and a plurality of negative electrodes  22  are alternately stacked with the separators  23  interposed therebetween. The uppermost layer is one of the positive electrodes  21 , and the lowermost layer is one of the negative electrodes  22 . 
     The positive electrode  21  of the uppermost layer of the plurality of positive electrodes  21 , that is, the positive electrode  21  closest to the outer package can  11  among the positive electrodes  21  stacked over each other in the stacking direction S, is an additional electrode as illustrated in  FIG. 10 . The positive electrode  21  of the uppermost layer includes the positive electrode current collector  21 A (hereinafter referred to as “positive electrode current collector  21 A of the uppermost layer”) led out in the leading-out direction D 211  (the right direction). This positive electrode current collector  21 A is an additional current collector which also serves as the positive electrode tab  30 . 
     In each of the positive electrodes  21  other than the positive electrode  21  of the uppermost layer, the positive electrode current collector  21 A is led out in the leading-out direction D 211  (the right direction) intersecting the stacking direction S, and includes the non-led-out part  21 AX and the led-out part  21 AY. The led-out part  21 AY led out in the leading-out direction D 211  is bent in the first bending direction D 212  at some middle point. Here, the led-out part  21 AY is bent in a direction away from the positive electrode  21  of the uppermost layer, i.e., in the down direction. In other words, the bending direction (the first bending direction D 212 ) of the led-out part  21 AY is opposite to the bending direction (the first bending direction D 212 ) of the led-out part  21 AY of the first embodiment. A reason for this is that, even if attempts are made to bend the led-out part  21 AY in a direction closer to the outer package can  11 , no space for the first bent part  21 AY 2  to be disposed therein lies in that direction and therefore there is no choice but to bend the led-out part  21 AY in a direction opposite to that direction. 
     Each of the led-out parts  21 AY bent in the first bending direction D 212  overlaps and is in contact with another one of the led-out parts  21 AY adjacent thereto (lying in front thereof) in the first bending direction D 212 , thus being coupled to the adjacent one of the led-out parts  21 AY. 
     Here, of the plurality of led-out parts  21 AY, one or more led-out parts  21 AY that are located on the rear side in the first bending direction D 212  are bent once and thus terminate at some middle point along the first bending direction D 212 . Accordingly, the one or more led-out parts  21 AY each include the non-bent part  21 AY 1  and the first bent part  21 AY 2 . The non-bent part  21 AY 1  extends in the leading-out direction D 211 . The first bent part  21 AY 2  extends in the first bending direction D 212 . 
     Here, in a case where five positive electrodes  21  (except the positive electrode  21  of the uppermost layer) and five negative electrodes  22  (except the negative electrode  22  of the lowermost layer) are alternately stacked with the separators  23  interposed therebetween, two led-out parts  21 AY located on the rear side in the first bending direction D 212  are bent once. Further, the positions of the respective ends of two first bent parts  21 AY 2  are gradually recessed toward the direction opposite to the first bending direction D 212 . 
     Besides, of the plurality of led-out parts  21 AY, the remaining one or more led-out parts  21 AY that are located on the front side in the first bending direction D 212  are bent twice, and thus each include the non-bent part  21 AY 1 , the first bent part  21 AY 2 , and the second bent part  21 AY 3 . The second bent part  21 AY 3  extends in the second bending direction D 213 . 
     Here, in the case where the five positive electrodes  21  (except the positive electrode  21  of the uppermost layer) and the five negative electrodes  22  (except the negative electrode  22  of the lowermost layer) are alternately stacked with the separators  23  interposed therebetween, three led-out parts  21 AY located on the front side in the first bending direction D 212  are bent twice. Further, the positions of the respective ends of three second bent parts  21 AY 3  are gradually recessed toward the direction opposite to the second bending direction D 213 . 
     In the positive electrode  21  of the uppermost layer, the positive electrode active material layer  21 B is provided only on one side of the positive electrode current collector  21 A of the uppermost layer, and therefore the positive electrode current collector  21 A (the non-led-out part  21 AX) of the uppermost layer is exposed at a side closer to the outer package can  11 . However, the positive electrode active material layer  21 B may be provided on each of both sides of the positive electrode current collector  21 A of the uppermost layer; therefore, the positive electrode current collector  21 A (the non-led-out part  21 AX) of the uppermost layer need not necessarily be exposed at the side closer to the outer package can  11 . 
     An end part (the led-out part  21 AY) of the positive electrode current collector  21 A of the uppermost layer is bent twice, and therefore includes the non-bent part  21 AY 1 , the first bent part  21 AY 2 , and the second bent part  21 AY 3 . The first bent part  21 AY 2  and the second bent part  21 AY 3  are additional bent parts. As a result, the positive electrode current collector  21 A of the uppermost layer is coupled to the remaining one or more led-out parts  21 AY (the second bent part(s)  21 AY 3  of the led-out part(s)  21 AY that are bent twice) of the plurality of led-out parts  21 AY, and is also coupled to the one or more led-out parts  21 AY (the first bent part(s)  21 AY 2  of the led-out part(s)  21 AY that are bent once) of the plurality of led-out parts  21 AY. 
     Besides, the positive electrode current collector  21 A of the uppermost layer is coupled to the outer package can  11  (the bottom part  11 M) at the non-led-out part  21 AX and the led-out part  21 AY (the non-bent part  21 AY 1 ). The outer package can  11  is thereby coupled to the other positive electrodes  21  (the positive electrode current collectors  21 A) via the positive electrode current collector  21 A of the uppermost layer which also serves as the positive electrode tab  30 . The outer package can  11  thus serves as the positive electrode terminal. 
     It should be understood that there is no particular limitation on the thickness of the positive electrode current collector  21 A of the uppermost layer which also serves as the positive electrode tab  30 . The thickness of the positive electrode current collector  21 A of the uppermost layer is preferably greater than the thickness of each of the other positive electrode current collectors  21 A which do not also serve as the positive electrode tab  30 , in particular. A reason for this is that this reduces the electrical resistance of the positive electrode current collector  21 A of the uppermost layer, resulting in an improved electrical coupling characteristic of the positive electrode current collector  21 A of the uppermost layer. 
     The plurality of negative electrodes  22  has a configuration similar to that of the plurality of positive electrodes  21  described above. More specifically, the negative electrode  22  of the lowermost layer of the plurality of negative electrodes  22 , that is, the negative electrode  22  closest to the outer package cup  12  among the negative electrodes  22  stacked over each other in the stacking direction S, is another additional electrode as illustrated in  FIG. 11 . The negative electrode  22  of the lowermost layer includes the negative electrode current collector  22 A (hereinafter referred to as “negative electrode current collector  22 A of the lowermost layer”) led out in the leading-out direction D 221  (the right direction). This negative electrode current collector  22 A is another additional current collector which also serves as the negative electrode tab  40 . 
     In each of the negative electrodes  22  other than the negative electrode  22  of the lowermost layer, the negative electrode current collector  22 A is led out in the leading-out direction D 221  (the right direction) intersecting the stacking direction S, and includes the non-led-out part  22 AX and the led-out part  22 AY. The led-out part  22 AY led out in the leading-out direction D 221  is bent in the first bending direction D 222  at some middle point. Here, the led-out part  22 AY is bent in a direction away from the negative electrode  22  of the lowermost layer, i.e., in the up direction. In other words, the bending direction (the first bending direction D 222 ) of the led-out part  22 AY is opposite to the bending direction (the first bending direction D 222 ) of the led-out part  22 AY of the first embodiment. A reason for this is that, even if attempts are made to bend the led-out part  22 AY in a direction closer to the outer package cup  12 , no space for the first bent part  22 AY 2  to be disposed therein lies in that direction and therefore there is no choice but to bend the led-out part  22 AY in a direction opposite to that direction. 
     Each of the led-out parts  22 AY bent in the first bending direction D 222  overlaps and is in contact with another one of the led-out parts  22 AY adjacent thereto (lying in front thereof) in the first bending direction D 222 , thus being coupled to the adjacent one of the led-out parts  22 AY. 
     Here, of the plurality of led-out parts  22 AY, one or more led-out parts  22 AY that are located on the rear side in the first bending direction D 222  are bent once and thus terminate at some middle point along the first bending direction D 222 . Accordingly, the one or more led-out parts  22 AY each include the non-bent part  22 AY 1  and the first bent part  22 AY 2 . The non-bent part  22 AY 1  extends in the leading-out direction D 221 . The first bent part  22 AY 2  extends in the first bending direction D 222 . 
     Here, in the case where the five positive electrodes  21  (except the positive electrode  21  of the uppermost layer) and the five negative electrodes  22  (except the negative electrode  22  of the lowermost layer) are alternately stacked with the separators  23  interposed therebetween, two led-out parts  22 AY located on the rear side in the first bending direction D 222  are bent once. Further, the positions of the respective ends of two first bent parts  22 AY 2  are gradually recessed toward the direction opposite to the first bending direction D 212 . 
     Besides, of the plurality of led-out parts  22 AY, the remaining one or more led-out parts  22 AY that are located on the front side in the first bending direction D 222  are bent twice, and thus each include the non-bent part  22 AY 1 , the first bent part  22 AY 2 , and the second bent part  22 AY 3 . The second bent part  22 AY 3  extends in the second bending direction D 223 . 
     Here, in the case where the five positive electrodes  21  (except the positive electrode  21  of the uppermost layer) and the five negative electrodes  22  (except the negative electrode  22  of the lowermost layer) are alternately stacked with the separators  23  interposed therebetween, three led-out parts  22 AY located on the front side in the first bending direction D 222  are bent once. Further, the positions of the respective ends of three second bent parts  22 AY 3  are gradually recessed toward the direction opposite to the second bending direction D 223 . 
     In the negative electrode  22  of the lowermost layer, the negative electrode active material layer  22 B is provided only on one side of the negative electrode current collector  22 A of the lowermost layer, and therefore the negative electrode current collector  22 A (the non-led-out part  22 AX) of the lowermost layer is exposed at a side closer to the outer package cup  12 . However, the negative electrode active material layer  22 B may be provided on each of both sides of the negative electrode current collector  22 A of the lowermost layer; therefore, the negative electrode current collector  22 A (the non-led-out part  22 AX) of the lowermost layer need not necessarily be exposed at the side closer to the outer package cup  12 . 
     An end part (the led-out part  22 AY) of the negative electrode current collector  22 A of the lowermost layer is bent twice, and therefore includes the non-bent part  22 AY 1 , the first bent part  22 AY 2 , and the second bent part  22 AY 3 . The first bent part  22 AY 2  and the second bent part  22 AY 3  are other additional bent parts. As a result, the negative electrode current collector  22 A of the lowermost layer is coupled to the remaining one or more led-out parts  22 AY (the second bent part(s)  22 AY 3  of the led-out part(s)  22 AY that are bent twice) of the plurality of led-out parts  22 AY, and is also coupled to the one or more led-out parts  22 AY (the first bent part(s)  22 AY 2  of the led-out part(s)  22 AY that are bent once) of the plurality of led-out parts  22 AY. 
     Besides, the negative electrode current collector  22 A of the lowermost layer is coupled to the outer package cup  12  (the bottom part  12 M) at the non-led-out part  22 AX and the led-out part  22 AY (the non-bent part  22 AY 1 ). The outer package cup  12  is thereby coupled to the other negative electrodes  22  (the negative electrode current collectors  22 A) via the negative electrode current collector  22 A of the lowermost layer which also serves as the negative electrode tab  40 . The outer package cup  12  thus serves as the negative electrode terminal. 
     It should be understood that there is no particular limitation on the thickness of the negative electrode current collector  22 A of the lowermost layer which also serves as the negative electrode tab  40 . The thickness of the negative electrode current collector  22 A of the lowermost layer is preferably greater than the thickness of each of the other negative electrode current collectors  22 A which do not also serve as the negative electrode tab  40 , in particular. A reason for this is that this reduces the electrical resistance of the negative electrode current collector  22 A of the lowermost layer, resulting in an improved electrical coupling characteristic of the negative electrode current collector  22 A of the lowermost layer. 
     The insulating layer  51  is disposed between the positive electrode current collector  21 A (the second bent part  21 AY 3 ) of the uppermost layer which also serves as the positive electrode tab  30  and the outer package cup  12 , and prevents a short circuit between the second bent part  21 AY 3  and the outer package cup  12 . The insulating layer  52  is disposed between the negative electrode current collector  22 A (the second bent part  22 AY 3 ) of the lowermost layer which also serves as the negative electrode tab  40  and the outer package can  11 , and prevents a short circuit between the second bent part  22 AY 3  and the outer package can  11 . Each of the insulating layers  51  and  52  is an insulating resin tape. The resin tape includes one or more of insulating materials including, without limitation, a polymer material, such as polyimide, polyethylene terephthalate (PET), or poly olefin. 
     The secondary battery of the present embodiment performs operations (charging and discharging operations) similar to those of the secondary battery of the first embodiment. Upon charging and discharging, as the positive electrode current collector  21 A of the uppermost layer also serves as the positive electrode tab  30 , the other positive electrode current collectors  21 A are electrically coupled to each other by means of the positive electrode current collector  21 A of the uppermost layer, and as the negative electrode current collector  22 A of the lowermost layer also serves as the negative electrode tab  40 , the other negative electrode current collectors  22 A are electrically coupled to each other by means of the negative electrode current collector  22 A of the lowermost layer. 
     A method of manufacturing the secondary battery of the present embodiment is similar to the method of manufacturing the secondary battery of the first embodiment, except for what is described below. 
     In the case of fabricating the positive electrodes  21 , the bending direction of the positive electrode current collectors  21 A (the led-out parts  21 AY) except the positive electrode current collector  21 A of the uppermost layer is changed to the opposite direction, and the positive electrode current collector  21 A (the led-out part  21 AY) of the uppermost layer is bent twice in the same direction. Further, in the positive electrode  21  of the uppermost layer, the positive electrode active material layer  21 B is formed only on one side of the positive electrode current collector  21 A. In addition, the positive electrode current collector  21 A of the uppermost layer is coupled to the other positive electrode current collectors  21 A. 
     In the case of fabricating the negative electrodes  22 , the bending direction of the negative electrode current collectors  22 A (the led-out parts  22 AY) except the negative electrode current collector  22 A of the lowermost layer is changed to the opposite direction, and the negative electrode current collector  22 A (the led-out part  22 AY) of the lowermost layer is bent twice in the same direction. Further, in the negative electrode  22  of the lowermost layer, the negative electrode active material layer  22 B is formed only on one side of the negative electrode current collector  22 A. In addition, the negative electrode current collector  22 A of the lowermost layer is coupled to the other negative electrode current collectors  22 A. 
     In the case of assembling the secondary battery, the positive electrode current collector  21 A of the uppermost layer is joined to the outer package can  11 , and the negative electrode current collector  22 A of the lowermost layer is joined to the outer package cup  12 . 
     The secondary battery of the present embodiment has a configuration similar to that of the secondary battery of the first embodiment except that the positive electrode current collector  21 A of the uppermost layer, instead of the positive electrode tab  30 , is coupled to the other positive electrode current collectors  21 A, and the negative electrode current collector  22 A of the lowermost layer, instead of the negative electrode tab  40 , is coupled to the other negative electrode current collectors  22 A. 
     In this case, for a reason similar to that described in relation to the secondary battery of the first embodiment, the maximum thickness T 1  becomes smaller than the maximum thickness T 11 , and the maximum thickness T 2  becomes smaller than the maximum thickness T 12 , as compared with the secondary battery of the comparative example. This reduces the non-device space volume, thus increasing the device space volume. Accordingly, it is possible to increase the energy density per unit volume. 
     Further, by making the maximum thickness T 3  smaller than the maximum thickness T 13  and making the maximum thickness T 4  smaller than the maximum thickness T 14 , the non-device space volume is further reduced and therefore a further increase in device space volume results. Accordingly, it is possible to further increase the energy density per unit volume. 
     Furthermore, coupling the positive electrode current collector  21 A of the uppermost layer to the other positive electrode current collectors  21 A allows the positive electrode current collector  21 A of the uppermost layer to also serve as the positive electrode tab  30 , and coupling the negative electrode current collector  22 A of the lowermost layer to the other negative electrode current collectors  22 A allows the negative electrode current collector  22 A of the lowermost layer to also serve as the negative electrode tab  40 . As a result, the positive electrode current collectors  21 A are electrically coupled to each other and the negative electrode current collectors  22 A are electrically coupled to each other even without the use of any separate positive electrode tab  30  or any separate negative electrode tab  40 . Accordingly, it is possible to achieve higher effects. 
     In particular, the bending direction (the first bending direction D 212 ) of each of the led-out parts  21 AY may be a direction away from the positive electrode current collector  21 A of the uppermost layer. In such a case, a space for disposing the first bent parts  21 AY 2  therein is secured. This allows for easy and stable bending of each of the led-out parts  21 AY, making it possible to achieve higher effects. 
     The action and effects based on the configuration of the led-out parts  21 AY described here are similarly achievable also on the basis of the configuration of the led-out parts  22 AY. More specifically, the bending direction (the first bending direction D 222 ) of each of the led-out parts  22 AY may be a direction away from the negative electrode current collector  22 A of the lowermost layer. This allows for easy and stable bending of each of the led-out parts  22 AY, making it possible to achieve higher effects. 
     Further, the positive electrode current collector  21 A of the uppermost layer may be exposed. This allows for easy coupling of the positive electrode current collector  21 A of the uppermost layer to the outer package can  11 , making it possible to achieve higher effects. In this case, because no positive electrode active material layer  21 B is interposed between the positive electrode current collector  21 A of the uppermost layer and the outer package can  11 , it is possible to improve an electrical conductivity characteristic between the positive electrode current collector  21 A of the uppermost layer and the outer package can  11 . 
     The action and effects based on the configuration of the positive electrode current collector  21 A of the uppermost layer described here are similarly achievable also on the basis of the configuration of the negative electrode current collector  22 A of the lowermost layer. More specifically, the negative electrode current collector  22 A of the lowermost layer may be exposed. This allows for easy coupling of the negative electrode current collector  22 A of the lowermost layer to the outer package cup  12 , making it possible to achieve higher effects. Needless to say, this also makes it possible to improve an electrical conductivity characteristic between the negative electrode current collector  22 A of the lowermost layer and the outer package cup  12 . 
     For the secondary battery of the first embodiment ( FIGS. 1 to 4 ) and the secondary battery of the comparative example ( FIGS. 7 and 8 ), the respective device space volumes (mm 3 ) were logically (mathematically) calculated, and the calculated device space volumes were compared with each other. Table 1 provides the results obtained. 
     The “Configuration” column in Table 1 indicates the kinds of the secondary batteries. More specifically, “Comparative” represents the secondary battery of the comparative example, and “Embodiment” represents the secondary battery of the first embodiment. 
     Conditions for calculating the device space volumes were as follows. Various dimensions of the battery device  20 , i.e., the number of the positive electrodes  21  stacked, the number of the negative electrodes  22  stacked, a thickness (μm) of the positive electrode current collector  21 A, a maximum overlap thickness (μm) of the positive electrode current collectors  21 A, a thickness (μm) of the negative electrode current collector  22 A, and a maximum overlap thickness (μm) of the negative electrode current collectors  22 A were set as listed in Table 1. Here, attention was focused on the maximum thicknesses T 1 , T 2 , T 11 , and T 12  as parameters influencing the device space volume; therefore, the maximum overlap thickness of the positive electrode current collectors  21 A was taken as the maximum thickness T 1  or T 11 , and the maximum overlap thickness of the negative electrode current collectors  22 A was taken as the maximum thickness T 2  or T 12 . In other words, for the sake of convenience, neither the thickness of the positive electrode tab  30  nor the thickness of the negative electrode tab  40  was taken into account. 
     The battery can  10  has a flat and generally cylindrical three-dimensional shape with the sidewall part M 3  (the taper surface M 3 T). The battery can  10  thus has a generally cylindrical internal space for the battery device  20  to be contained therein. Various dimensions of the battery can  10  were set as follows: the outer diameter D=12.1 mm and the height H=4.0 mm (the number of the positive electrodes  21  stacked=the number of the negative electrodes  22  stacked=15); or the outer diameter D=12.1 mm and the height H =5.4 mm (the number of the positive electrodes  21  stacked=20, and the number of the negative electrodes  22  stacked=20). Further, a recess distance of the taper surface M 3 T was set to 1.8 mm. 
     To calculate the device space volume, first, a maximum volume of the internal space (the cylindrical space), that is, a space volume (mm 3 ), of the battery can  10  was calculated on the basis of the outer diameter D and the height H of the battery can  10 . For the sake of convenience, the thickness (wall thickness) of the battery can  10  was not taken into account in calculating the space volume. Thereafter, the non-device space volume (mm 3 ) was calculated on the basis of the number of the positive electrodes  21  stacked, the number of the negative electrodes  22  stacked, the thickness of the positive electrode current collector  21 A, the maximum overlap thickness of the positive electrode current collectors  21 A, the thickness of the negative electrode current collector  22 A, and the maximum overlap thickness of the negative electrode current collectors  22 A. Lastly, the non-device space volume was subtracted from the space volume to thereby calculate the device space volume. The device space volume corresponds to an area of the plan shape of the negative electrode  22  (excluding a portion where the negative electrode current collectors  22 A overlap each other) multiplied by the height of the battery device  20 . As described above, the height H of the battery can  10  was varied to be of two different values, and thereby the number of the positive electrodes  21  stacked and the number of the negative electrodes  22  stacked were also each varied to be of two different values, as listed in Table 1. 
     For easy understanding of an influence of the difference in device space volume, Table 1 also lists battery capacity (mAh). The battery capacity is one that is obtainable in a case of increasing the area of each of the positive electrodes  21  and the negative electrodes  22  to its maximum without changing the number of each of the positive electrodes  21  and the negative electrodes  22  stacked. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Positive electrode 
                 Negative electrode 
                   
               
               
                   
                 current collector 
                 current collector 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 Positive 
                 Negative 
                   
                 Maximum 
                   
                 Maximum 
                 Device 
                   
               
               
                   
                 electrode 
                 electrode 
                   
                 overlap 
                   
                 overlap 
                 space 
                 Battery 
               
               
                   
                 Number 
                 Number 
                 Thickness 
                 thickness 
                 Thickness 
                 thickness 
                 volume 
                 capacity 
               
               
                 Configuration 
                 stacked 
                 stacked 
                 (μm) 
                 (μm) 
                 (μm) 
                 (μm) 
                 (mm 3 ) 
                 (mAh) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                 15 
                 15 
                 12 
                 180 
                 10 
                 150 
                 47.9 
                 50.3 
               
               
                 Embodiment 
                 15 
                 15 
                 12 
                 48 
                 10 
                 100 
                 49.8 
                 53.1 
               
               
                 Comparative 
                 20 
                 20 
                 12 
                 240 
                 10 
                 200 
                 66.0 
                 69.8 
               
               
                 Embodiment 
                 20 
                 20 
                 12 
                 48 
                 10 
                 100 
                 69.8 
                 75.5 
               
               
                   
               
            
           
         
       
     
     As indicated in Table 1, the device space volume varied depending on the configuration of the secondary battery. Specifically, the secondary battery of the comparative example was smaller in device space volume. This is attributable to a greater non-device space volume resulting from each of the maximum overlap thickness of the positive electrode current collectors  21 A and the maximum overlap thickness of the negative electrode current collectors  22 A being markedly large. In contrast, the secondary battery of the embodiment was greater in device space volume. This is attributable to a smaller non-device space volume resulting from each of the maximum overlap thickness of the positive electrode current collectors  21 A and the maximum overlap thickness of the negative electrode current collectors  22 A being greatly reduced as compared with the secondary battery of the comparative example. 
     The results presented in Table 1 indicate that, as compared with the secondary battery of the comparative example, the secondary battery of the embodiment achieves an increased device space volume owing to a reduction in non-device space volume in terms of the electrical coupling form of each of the positive electrode current collectors  21 A and the negative electrode current collectors  22 A. As a result, an increased energy density per unit volume is achieved. 
     Next, modifications of the foregoing secondary battery will be described. The configuration of the secondary battery is appropriately modifiable, as will be described below. It should be understood that any two or more of the following series of modifications may be combined. 
     [Modification 1] 
     In the first embodiment ( FIGS. 3 and 4 ), the remaining one or more of the plurality of led-out parts  21 AY include the respective second bent parts  21 AY 3 , and the remaining one or more of the plurality of led-out parts  22 AY include the respective second bent parts  22 AY 3 . 
     However, the remaining one or more of the plurality of led-out parts  21 AY need not necessarily include the respective second bent parts  21 AY 3 , and the remaining one or more of the plurality of led-out parts  22 AY need not necessarily include the respective second bent parts  22 AY 3 . Needless to say, a case is possible in which the remaining one or more of the plurality of led-out parts  21 AY include the respective second bent parts  21 AY 3  whereas the remaining one or more of the plurality of led-out parts  22 AY include no second bent parts  22 AY 3 ; alternatively, a case is possible in which the remaining one or more of the plurality of led-out parts  21 AY include no second bent parts  21 AY 3  whereas the remaining one or more of the plurality of led-out parts  22 AY include the respective second bent parts  22 AY 3 . 
     In these cases also, as described above, the device space volume increases owing to the maximum thicknesses T 1  and T 2  being smaller than the maximum thicknesses T 11  and T 12 , respectively. Accordingly, it is possible to achieve similar effects. However, in order to achieve a greatest possible electrical coupling area and a greatest possible device space volume, it is preferable that the remaining one or more of the plurality of led-out parts  21 AY include the respective second bent parts  21 AY 3  and the remaining one or more of the plurality of led-out parts  22 AY include the respective second bent parts  22 AY 3  to make the maximum thicknesses T 3  and T 4  smaller than the maximum thicknesses T 13  and T 14 , respectively. 
     Although not specifically illustrated here, Modification  1  described here may be applied to the second embodiment ( FIGS. 10 and 11 ). In this case also, it is possible to achieve similar effects owing to the maximum thicknesses T 1  and T 2  being smaller than the maximum thicknesses T 11  and T 12 , respectively. 
     [Modification 2] 
     In the first embodiment ( FIG. 2 ), the battery device  20  has one taper surface M 3 T, and the led-out parts  21 AY and  22 AY are each disposed at the sidewall part M 3  (the taper surface M 3 T). As a result, the led-out parts  21 AY and  22 AY are disposed to be adjacent to each other, and accordingly, the tab part  30 B of the positive electrode tab  30  and the tab part  40 B of the negative electrode tab  40  are disposed to be adjacent to each other. In this case, the leading-out direction D 211  in the positive electrodes  21  (the led-out parts  21 AY) and the leading-out direction D 221  in the negative electrodes  22  (the led-out parts  22 AY) are a common direction. 
     However, as illustrated in  FIG. 12  corresponding to  FIG. 2 , the battery device  20  may have two taper surfaces M 3 T disposed opposite to each other, with the led-out parts  21 AY being disposed on one sidewall part M 3  (taper surface M 3 T) and the led-out parts  22 AY being disposed on the other sidewall part M 3  (taper surface M 3 T). The led-out parts  21 AY and  22 AY may thus be disposed opposite to each other and accordingly, the tab part  30 B of the positive electrode tab  30  and the tab part  40 B of the negative electrode tab  40  may be disposed opposite to each other. In this case, the leading-out direction D 211  in the positive electrodes  21  (the led-out parts  21 AY) and the leading-out direction D 221  in the negative electrodes  22  (the led-out parts  22 AY) are opposite to each other. 
     In this case also, it is possible for the positive electrode tab  30  to electrically couple the led-out parts  21 AY to each other, and it is possible for the negative electrode tab  40  to electrically couple the led-out parts  22 AY to each other. Accordingly, it is possible to achieve similar effects. In this case, in particular, by making use of the configuration in which respective positions of the positive electrode tab  30  and the negative electrode tab  40  are opposite to each other, it is possible to increase flexibility for the coupling form of the secondary battery to an electronic apparatus. 
     Although not specifically illustrated here, Modification  2  described here may be applied to the second embodiment ( FIG. 9 ). More specifically, the positive electrode current collector  21 A (the led-out part  21 AY) of the uppermost layer which also serves as the positive electrode tab  30  may be disposed at one side wall part M 3  (taper surface M 3 T), and the negative electrode current collector  22 A (the led-out part  22 AY) of the lowermost layer which also serves as the negative electrode tab  40  may be disposed at the other side wall part M 3  (taper surface M 3 T). In this case also, it is possible to achieve similar effects. 
     [Modification 3] 
     In the first embodiment ( FIGS. 1 and 2 ), the positive electrode tab  30  includes the tab part  30 A having a generally circular shape and the tab part  30 B having a strip-like shape, and the negative electrode tab  40  includes the tab part  40 A having a generally circular shape and the tab part  40 B having a strip-like shape. However, the configuration of each of the positive electrode tab  30  and the negative electrode tab  40  is not particularly limited as long as it is possible for the positive electrode tab  30  to electrically couple the positive electrode current collectors  21 A to each other and it is possible for the negative electrode tab  40  to electrically couple the negative electrode current collectors  22 A to each other. 
     Specifically, as illustrated in  FIG. 13  corresponding to  FIG. 1  and in  FIG. 14  corresponding to  FIG. 2 , the positive electrode tab  30  may include a tab part  30 C having a strip-like shape instead of the tab part  30 A having a generally circular shape, and the negative electrode tab  40  may include a tab part  40 C having a strip-like shape instead of the tab part  40 A having a generally circular shape. 
     The tab part  30 C extends in a direction away from the battery device  20 . The positive electrode tab  30  thus has a three-dimensional shape that is bent in the direction away from the battery device  20  at some middle point. Although not particularly limited, an angle at which the positive electrode tab  30  is bent (an angle defined by the tab parts  30 B and  30 C) is, e.g., 90°. 
     The tab part  40 C has a configuration similar to that of the tab part  30 C described above. More specifically, the tab part  40 C extends in a direction away from the battery device  20 . The negative electrode tab  40  thus has a three-dimensional shape that is bent in the direction away from the battery device  20  at some middle point. Although not particularly limited, an angle at which the negative electrode tab  40  is bent (an angle defined by the tab parts  40 B and  40 C) is, e.g., 90°. 
     The positive electrode tab  30  is coupled to the outer package can  11  at the tab part  30 C, and the outer package can  11  thus serves as the positive electrode terminal. The negative electrode tab  40  is coupled to the outer package cup  12  at the tab  40  part C, and the outer package cup  12  thus serves as the negative electrode terminal. 
     In this case also, it is possible for the positive electrode tab  30  to electrically couple the led-out parts  21 AY to each other, and it is possible for the negative electrode tab  40  to electrically couple the led-out parts  22 AY to each other. Accordingly, it is possible to achieve similar effects. 
     However, in a case of using the tab part  30 C that is shaped like a strip and small in area, a contact area between the tab part  30 C and the outer package can  11  becomes smaller, and this can result in an increase in electrical resistance of the positive electrode tab  30 . In order to achieve a lowest possible electrical resistance of the positive electrode tab  30 , it is thus preferable that the positive electrode tab  30  include the tab part  30 A that is generally circular in shape and large in area. A reason for this is that this allows for a large contact area between the tab part  30 A and the outer package can  11  and consequently reduces the electrical resistance of the positive electrode tab  30 . 
     The action and effects based on the configuration of the positive electrode tab  30  (the tab part  30 C) described here are similarly achievable also on the basis of the configuration of the negative electrode tab  40  (the tab part  40 C). In other words, similar effects are achievable also in the case where the negative electrode tab  40  includes the tab part  40 C, and it is preferable that the negative electrode tab  40  include the tab part  40 A in order to reduce the electrical resistance of the negative electrode tab  40 . 
     It should be understood that in the case of using the tab parts  30 C and  40 C, it is necessary to provide an excess space  10 J, as illustrated in  FIG. 13 , for disposing the tab parts  30 C and  40 C inside the battery can  10 . The excess space  10 J is a space that is not available for disposing the battery device  20  therein, that is, a non-device space, resulting in a smaller device space volume. In contrast, in the case of using the tab parts  30 A and  30 B, as illustrated in  FIG. 1 , hardly any excess space  10 J is involved and therefore the device space volume increases. In order to achieve a greater device space volume, it is thus preferable to use the tab parts  30 A and  30 B rather than the tab parts  30 C and  40 C. 
     Needless to say, although not specifically illustrated here, the positive electrode tab  30  including the tab part  30 A and the negative electrode tab  40  including the tab part  40 C may be used in combination, or the positive electrode tab  30  including the tab part  30 C and the negative electrode tab  40  including the tab part  40 A may be used in combination. In these cases also, it is possible to achieve similar effects. 
     [Modification 4] 
     In the process of manufacturing the secondary battery, the stacked body  120  is placed into the outer package can  11 , and the outer package can  11  and the outer package cup  12  (the sidewall parts  11 W and  12 S) are crimped to each other, following which the electrolytic solution is injected into the battery can  10  (the outer package can  11  and the outer package cup  12 ) through the liquid injection hole. In other words, the stacked body  120  is impregnated with the electrolytic solution by injecting the electrolytic solution into the battery can  10  after the battery can  10  is formed. 
     However, the outer package can  11  and the outer package cup  12  may be crimped to each other after the stacked body  120  is placed into the outer package can  11  and the electrolytic solution is injected into the outer package can  11 . In other words, the stacked body  120  may be impregnated with the electrolytic solution by injecting the electrolytic solution into the outer package can  11  before the battery can  10  is formed. In this case, the battery can  10  does not have to be provided with the liquid injection hole. 
     In this case also, the battery device  20  is fabricated by impregnation of the stacked body  120  with the electrolytic solution, and the battery device  20  is sealed inside the battery can  10 . Accordingly, it is possible to achieve similar effects. In this case, in particular, it is possible to simplify the configuration of the battery can  10  because it is unnecessary for the battery can  10  to have the liquid injection hole. Further, because the electrolytic solution is injected into the outer package can  11  through an opening having an opening area larger than that of the liquid injection hole, it is possible to improve efficiency of injection of the electrolytic solution for the stacked body  120 , and to simplify the process of injecting the electrolytic solution. 
     [Modification 5] 
     In the first embodiment ( FIG. 1 ), the battery can  10  is a battery can of a crimped type; however, the battery can  10  is not limited to a particular kind. 
     Specifically, as illustrated in  FIG. 15  corresponding to  FIG. 1 , a battery can  60  of a welded type may be used instead of the battery can  10  of the crimped type. The battery can  60  includes an outer package can  61  and an outer package cover  62 . The secondary battery using the battery can  60  has a configuration similar to that of the secondary battery illustrated in  FIG. 1  except that an electrode terminal  70  and a gasket  80  are provided in addition. 
     The outer package can  61  has a configuration similar to that of the outer package can  11 . More specifically, the outer package can  61  includes a bottom part  61 M, a sidewall part  61 W, and an opening  61 K, and contains the battery device  20  inside. The negative electrode tab  40  is coupled to the outer package can  61  (the bottom part  61 M), and the outer package can  61  thus serves as the negative electrode terminal. Accordingly, the outer package can  61  includes a material similar to the material included in the negative electrode tab  40 . 
     The outer package cover  62  is a plate-shaped member that seals the opening  61 K of the outer package can  61 , and is joined to the outer package can  61  by means of a method such as a welding method. The outer package cover  62  is thereby firmly coupled to the outer package can  61 , and is not separable from the outer package can  61  after being joined thereto. The outer package cover  62  has a through hole  60 K, and the electrode terminal  70  is attached to the through hole  60 K with the gasket  80  interposed therebetween. 
     The positive electrode tab  30  is coupled to the electrode terminal  70 , and the electrode terminal  70  thus serves as the positive electrode terminal. Accordingly, the electrode terminal  70  includes a material similar to the material included in the positive electrode tab  30 . The electrode terminal  70  extends from the inside of the battery can  60  to the outside of the battery can  60  via the through hole  60 K, and has a generally cylindrical three-dimensional shape with an outer diameter thereof locally reduced inside the through hole  60 K. However, the electrode terminal  70  may have another three-dimensional shape such as a generally polygonal prismatic shape. The gasket  80  is disposed between the battery can  60  and the electrode terminal  70 , and includes one or more of insulating materials including, without limitation, polypropylene and polyethylene. 
     In a process of manufacturing the secondary battery using the battery can  60  of the welded type, the electrolytic solution may be injected into the battery can  60  (the outer package can  61  and the outer package cover  62 ) through the liquid injection hole after the stacked body  120  is placed into the outer package can  61  and the outer package cover  62  is joined to the outer package can  61  by means of a method such as a welding method. In other words, the stacked body  120  may be impregnated with the electrolytic solution by injecting the electrolytic solution into the battery can  60  after the battery can  60  is formed, that is, after the outer package cover  62  is joined to the outer package can  61 . 
     Alternatively, the outer package cover  62  may be joined to the outer package can  61  by means of a method such as a welding method after the stacked body  120  is placed into the outer package can  61  and the electrolytic solution is injected into the outer package can  61 . In other words, the stacked body  120  may be impregnated with the electrolytic solution by injecting the electrolytic solution into the outer package can  61  before the battery can  60  is formed, that is, before the outer package cover  62  is joined to the outer package can  61 . In this case, the battery can  60  does not have to be provided with the liquid injection hole. 
     In this case also, the device space volume increases to increase the energy density per unit volume. Accordingly, it is possible to achieve similar effects. In this case, the absence of the crimp part C allows the increase in device space volume to be greater accordingly than in the case of using the battery can  10  of the crimped type, thus making it possible to achieve higher effects. 
     It should be understood that in the case of using the battery can  60  of the welded type, a portion of the electrode terminal  70  is placed inside the battery can  60  and therefore the device space volume decreases by a volume based on the height of the portion of the electrode terminal  70 . However, the decrease in device space volume resulting from the portion of the electrode terminal  70  is sufficiently smaller than a decrease in device space volume resulting from the presence of the crimp part C. Accordingly, the use of the battery can  60  of the welded type increases the device space volume as compared with the case of using the battery can  10  of the crimped type, thus making it possible to achieve further higher effects. 
     In particular, in a case where the electrolytic solution is injected into the outer package can  61  before the battery can  60  is formed, it is unnecessary to provide the battery can  60  with the liquid injection hole, and therefore it is possible to simplify the configuration of the battery can  60 . Furthermore, because the electrolytic solution is injected into the outer package can  61  through the opening having an opening area larger than that of the liquid injection hole, it is possible to improve efficiency of injection of the electrolytic solution for the stacked body  120 , and it is also possible to simplify the process of injecting the electrolytic solution. 
     Although not specifically illustrated here, Modification  4  described here may be applied to the second embodiment. More specifically, the battery can  60  of the welded type may be used in the case where the positive electrode current collector  21 A of the uppermost layer also serves as the positive electrode tab  30  and the negative electrode current collector  22 A of the lowermost layer also serves as the negative electrode tab  40 . This makes it possible to achieve similar effects. 
     [Modification 6] 
     Also in the case of using the battery can  60  of the welded type described above, as described in Modification  3 , there is no particular limitation on the configuration of each of the positive electrode tab  30  and the negative electrode tab  40 . 
     Specifically, as illustrated in  FIG. 16  corresponding to  FIG. 15  and in  FIG. 17  corresponding to  FIG. 2 , the positive electrode tab  30  including the tab part  30 C and the negative electrode tab  40  including the tab part  40 A may be combined. In this case, the attachment position of the electrode terminal  70  on the battery can  60  may be changed depending on the combination of the positive electrode tab  30  and the negative electrode tab  40  described above. 
     Here, the battery can  60  has the through hole  60 K at the outer package can  61  (the sidewall part  61 W) instead of the outer package cover  62  (a bottom part  62 M), and the electrode terminal  70  is therefore attached to the through hole  60 K provided at the sidewall part  61 W, with the gasket  80  interposed between the electrode terminal  70  and the through hole  60 K. 
     The positive electrode tab  30  includes the tab parts  30 B and  30 C as described above, and is thus bent at some middle point. Here, the positive electrode tab  30  is bent at an angle of less than 90°. The positive electrode tab  30  is thereby coupled to the electrode terminal  70 , and the electrode terminal  70  thus serves as the positive electrode terminal. 
     In this case also, the device space volume increases to increase the energy density per unit volume. Accordingly, it is possible to achieve similar effects. 
     Although the technology has been described above with reference to some embodiments and examples, configurations of the technology are not limited to those described with reference to the embodiments and examples above, and are therefore modifiable in a variety of ways. 
     Specifically, while a description has been given of a case where the electrode reactant is lithium, the electrode reactant is not particularly limited. Specifically, the electrode reactant may be, as described above, another alkali metal, such as sodium or potassium, or may be an alkaline earth metal, such as beryllium, magnesium, or calcium. Other than the above, the electrode reactant may be another light metal, such as aluminum. 
     The effects described herein are mere examples. Therefore, the effects of the technology are not limited to the effects described herein. Accordingly, the technology may achieve any other effect. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and alterations may occur depending on design requirements and other factors. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.