Patent Publication Number: US-2022216545-A1

Title: Flat secondary battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of PCT patent application no. PCT/JP2020/033535 filed on Sep. 4, 2020, which claims priority to Japanese patent application no. JP2019-179466 filed on Sep. 30, 2019, the entire contents of which are being incorporated herein by reference. 
    
    
     BACKGROUND 
     The present technology relates to a flat 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. As such a secondary battery, for example, a small-sized flat secondary battery is known. 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 increase utilization of an internal space of a battery case, an electrode assembly is contained inside the battery case made of a laminated film having a side surface including a curved surface and a plane surface, and a positive electrode terminal and a negative electrode terminal are led from the plane surface to the outside of the battery case. 
     In order to allow for easy installation of a header insulator, an electrode assembly is contained inside a case having a side surface including a curved surface and a plane surface, and a feed-through pin coupled to a positive electrode is led from the plane surface to the outside of the case. In this case, the case is coupled to a negative electrode. 
     In order to achieve a higher capacity, a group of electrodes is contained inside an outer case and a sealing case that are crimped to each other. The group of electrodes includes a positive electrode and a negative electrode stacked with a separator interposed therebetween. 
     In order to improve a characteristic such as a load characteristic, a group of electrodes is contained inside a positive electrode case and a negative electrode case fitted to each other. The group of electrodes includes a positive electrode and a negative electrode wound with a separator interposed therebetween. 
     In order to improve a battery characteristic, an electrode assembly is contained inside two exterior bodies crimped to each other. The electrode assembly includes a positive electrode and a negative electrode stacked with a separator interposed therebetween. The electrode assembly has a circular shape with a notch in a plan view. In this case, in the notch part of the circular shape, a positive electrode tab and a negative electrode tab are coupled to the electrode assembly. The positive electrode tab and the negative electrode tab are contained inside the respective two exterior bodies. The positive electrode tab is coupled to one of the exterior bodies, and the negative electrode tab is coupled to the other of the exterior bodies. 
     SUMMARY 
     The present disclosure relates a secondary battery. 
     Various considerations have been made to solve problems of a secondary battery; however, a flat 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 of the present disclosure has been made in view of such an issue, and thus, to provide a flat secondary battery that makes it possible to increase an energy density per unit volume according to an embodiment. 
     A flat secondary battery according to an embodiment of the technology includes an outer package member, a battery device, and an electrode terminal. The outer package member has a flat and columnar shape, and 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. At least a portion of a surface of the sidewall part is a curved surface. The battery device is contained inside the outer package member and includes a positive electrode and a negative electrode. The electrode terminal is provided to be exposed at the sidewall part and is coupled to one of the positive electrode and the negative electrode. 
     According to the flat secondary battery of the embodiment of the technology, the battery device is contained inside the outer package member having a flat and columnar shape and in which at least a portion of the surface of the sidewall part is a curved surface. The electrode terminal coupled to one of the positive electrode and the negative electrode is provided at the sidewall part. This makes it possible to increase the energy density per unit volume. 
     Note that effects of the technology are not necessarily limited to those described above and may include any of a series of suitable effects including described below in relation to the technology. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a configuration of a flat secondary battery according to an embodiment of the technology of the present disclosure. 
         FIG. 2  is a sectional view of the configuration of the flat secondary battery illustrated in  FIG. 1 . 
         FIG. 3  is another sectional view of the configuration of the flat secondary battery illustrated in  FIG. 1 . 
         FIG. 4  is an enlarged sectional view of a configuration of an electrode terminal illustrated in  FIG. 2 . 
         FIG. 5  is a perspective view of a configuration of a battery device illustrated in  FIG. 1 . 
         FIG. 6  is a perspective view of a configuration of a battery can to be used in a process of manufacturing the flat secondary battery. 
         FIG. 7  is a sectional view of a configuration of a flat secondary battery of a comparative example. 
         FIG. 8  is a schematic diagram for describing a device space volume of the flat secondary battery of the comparative example. 
         FIG. 9  is a schematic diagram for describing a device space volume of the flat secondary battery according to the embodiment of the technology. 
         FIG. 10  is a sectional view of a configuration of a flat secondary battery of Modification 1. 
         FIG. 11  is a perspective view of a configuration of a flat secondary battery of Modification 2. 
         FIG. 12  is a sectional view of the configuration of the flat secondary battery of Modification 2. 
         FIG. 13  is a sectional view of a configuration of a flat secondary battery of Modification 3. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the technology of the present disclosure are described below in detail with reference to the drawings. 
     A description is given first of a flat secondary battery according to an embodiment of the technology. 
     The flat secondary battery 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 flat secondary battery 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 description will be given later of specific dimensions (the outer diameter and the height) of the flat secondary battery. Specifically, the flat secondary battery may be flat and cylindrical, or may be flat and generally cylindrical, as will be described later. 
     Further, the flat secondary battery does not have any crimp part C (see  FIG. 7 ) to be described later. In the illustrated crimp part C, an end of a containing part  111  is bent outward and is thus folded over itself. Further, a portion of the containing part  111  and a portion of a cover part  112  are crimped to each other in a state of being placed over each other. The two members (the containing part  111  and the cover part  112 ) are thereby placed over each other. 
     A charge and discharge principle is not particularly limited. The following will describe a case where a battery capacity is obtained by utilizing insertion and extraction of an electrode reactant. The flat secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. In the flat 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 flat secondary battery that obtains the 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 perspective view of a configuration of the flat secondary battery.  FIGS. 2 and 3  each illustrate a sectional configuration of the flat secondary battery illustrated in  FIG. 1 .  FIG. 4  is an enlarged sectional view of a configuration of an electrode terminal  30  illustrated in  FIG. 2 .  FIG. 5  is a perspective view of a configuration of a battery device  20  illustrated in  FIG. 1 . Note that  FIG. 2  illustrates a section of the flat secondary battery along a plane intersecting a height direction (a vertical direction in  FIG. 1 ), and  FIG. 3  illustrates a section of the flat secondary battery along a plane along the height direction. 
     For the sake of convenience, the following description is given with an up direction in  FIG. 1  as an upper side of the flat secondary battery, and a down direction in  FIG. 1  as a lower side of the flat secondary battery. 
     As illustrated in  FIGS. 1 to 3 , the flat secondary battery has a flat and columnar three-dimensional shape with a height (a maximum height) thereof small relative to an outer diameter (a maximum outer diameter) thereof. Dimensions of the flat secondary battery are not particularly limited; however, for example, the outer diameter is from 3 mm to 30 mm both inclusive, and the height is from 0.5 mm to 70 mm both inclusive. Note that a ratio of the outer diameter to the height, i.e., outer diameter/height, is greater than 1 and smaller than or equal to 25. The outer diameter is a dimension in a horizontal direction in  FIGS. 1 and 3 , and the height is, as described above, a dimension in the vertical direction in  FIGS. 1 and 3 . 
     Specifically, as illustrated in  FIGS. 1 to 5 , the flat secondary battery includes a battery can  10 , the battery device  20 , the electrode terminal  30 , a gasket  40 , a positive electrode lead  51 , and a negative electrode lead  52 . 
     As illustrated in  FIGS. 1 to 3 , the battery can  10  is an outer package member that contains the battery device  20  inside. 
     The battery can  10  has a hollow, flat and cylindrical three-dimensional shape in accordance with the three-dimensional shape of the flat secondary battery described above. The battery can  10  thus 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  lies between the bottom parts M 1  and M 2 . The sidewall part M 3  is coupled to the bottom part M 1  at one end, and is coupled to the bottom part M 2  at the other end. 
     Here, the battery can  10  has a generally cylindrical three-dimensional shape. Specifically, a portion of a surface of the sidewall part M 3  is a curved surface M 3 C that is convex toward the outside of the battery can  10 , and the other portion of the surface of the sidewall part M 3  is a plane surface M 3 F. In other words, the surface of the sidewall part M 3  includes the curved surface M 3 C and the plane surface M 3 F. Thus, one end of the plane surface M 3 F is coupled to one end of the curved surface M 3 C, and the other end of the plane surface M 3 F is coupled to the other end of the curved surface M 3 C to thereby provide the sidewall part M 3 . As will be described later, the electrode terminal  30  is provided at the sidewall part M 3  (the plane surface M 3 F). 
     A circumscribed circle G illustrated in  FIG. 2  represents a circular outline along the sidewall part M 3  (the curved surface M 3 C) of the battery can  10 , that is, an outline of a circular shape defined by the curved surface M 3 C. The curved surface M 3 C is thus curved along a portion (an arc R) of the circumscribed circle G. 
     A range of the surface of the sidewall part M 3  occupied by the curved surface M 3 C is determined on the basis of a range of the circumscribed circle G occupied by the arc R. Although not particularly limited, a ratio of the arc R to the circumscribed circle G, that is, a ratio of a length of the arc R to a length (a circumference) of the circumscribed circle G is preferably as high as possible within a range allowing for mounting of the electrode terminal  30  to the battery can  10 , in particular. A reason for this is that increasing the ratio of the arc R increases a device space volume, and consequently increases also the energy density per unit volume. The “device space volume” refers to a volume (an effective volume) of an internal space of the battery can  10  available for containing the battery device  20  therein. 
     The battery can  10  includes a containing part  11  and a cover part  12 . The containing part  11  is a flat and generally cylindrical (handleless mug-shaped) member with one end open and the other end closed. The containing part  11  contains the battery device  20 . More specifically, to allow the battery device  20  to be contained therein, the containing part  11  has an opening  11 K (see  FIG. 6 ) to be described later. The cover part  12  is a generally plate-shaped member, and is joined to the containing part  11  to cover the opening  11 K. 
     Here, as will be described later, the cover part  12  is joined to the containing part  11  by a method such as a welding method. More specifically, the battery can  10  is a welded can including two members (the containing part  11  and the cover part  12 ) welded to each other. The battery can  10  after the cover part  12  has been joined to the containing part  11  is a single member as a whole, that is, not separable into two or more members. Note that the battery can  10  may be a can (a single member as a whole) including three or more members welded to each other. 
     As a result, the battery can  10  is a single member including no folded-over portion or no portion in which two or more members are placed over each other. What is meant by “including no folded-over portion in the middle” is that the battery can  10  is not so processed as to include a portion folded over another portion. What is meant by “including no portion in which two or more members are placed over each other” is that the battery can  10  is physically a single member and is therefore not a composite body in which two or more members including a container and a cover are so fitted to each other as to be separable later. More specifically, as described above, the “folded-over portion” and the “portion in which two or more members are placed over each other” each correspond to the crimp part C provided in a flat secondary battery of a comparative example (see  FIG. 7 ) to be described later. 
     Thus, the battery can  10  described here is without the foregoing crimp part C, and is therefore a so-called crimpless can. A reason for employing the crimpless can is that this increases the device space volume inside the battery can  10 , and accordingly, increases also the energy density per unit volume. 
     The battery can  10  is electrically conductive. The battery can  10  thus serves as a negative electrode terminal because the battery can  10  is coupled to a negative electrode  22 , which will be described later, of the battery device  20 . A reason for employing such a configuration is that allowing the battery can  10  to serve as the negative electrode terminal makes it unnecessary to provide a negative electrode terminal separate from the battery can  10  in the flat secondary battery. A decrease in device space volume resulting from the presence of a negative electrode terminal is thereby avoided. This results in an increase in device space volume, and accordingly an increase in energy density per unit volume. 
     Further, the battery can  10  has a through hole  10 K at the sidewall part M 3  (the plane surface M 3 F). The through hole  10 K is used to attach the electrode terminal  30  to the battery can  10 . 
     The battery can  10  includes one or more of electrically conductive materials including, without limitation, metals (including stainless steel) and alloys. Here, in order to serve as the negative electrode terminal, the battery can  10  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. 
     Note that, as will be described later, the battery can  10  is insulated via the gasket  40  from the electrode terminal  30  serving as a positive electrode terminal. A reason for this is that a contact (a short circuit) between the battery can  10  and the electrode terminal  30  is thereby prevented. 
     The battery device  20  is a device causing charging and discharging reactions to proceed, and includes, as illustrated in  FIGS. 1 to 3  and  FIG. 5 , a positive electrode  21 , the negative electrode  22 , a separator  23 , and an electrolytic solution which is a liquid electrolyte. Note that the battery device  20  is shaded in  FIG. 2 , and the illustration of the electrolytic solution is omitted from each of FIGS.  3  and  5 . 
     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 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 the 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. Here, the battery can  10  has a generally cylindrical three-dimensional shape as described above, and therefore the battery device  20  also has a generally cylindrical three-dimensional shape. 
     Specifically, as described above, the battery can  10  has a generally cylindrical three-dimensional shape with the pair of bottom parts M 1  and M 2  and the sidewall part M 3  (the curved surface M 3 C and the plane surface M 3 F), and the battery device  20  thus has a generally cylindrical three-dimensional shape, as with the battery can  10 . In this case, the battery device  20  includes a pair of bottom parts N 1  and N 2  corresponding to the pair of bottom parts M 1  and M 2 , and a sidewall part N 3  (a curved surface N 3 C and a plane surface N 3 F) corresponding to the sidewall part M 3  (the curved surface M 3 C and the plane surface M 3 F). Accordingly, the positive electrode  21 , the negative electrode  22 , and the separator  23  each have a plan shape defined by the curved surface N 3 C and the plane surface N 3 F, in other words, a generally circular plan shape with a taper surface at one location. 
     Here, the positive electrode  21  and the negative electrode  22  are stacked with the separator  23  interposed therebetween. More specifically, a plurality of positive electrodes  21  and a plurality of negative electrodes  22  are alternately stacked in the height direction with the separators  23  interposed therebetween. Thus, the battery device  20  is a stacked electrode body including the positive electrode  21  and the negative electrode  22  that are stacked with the separator  23  interposed therebetween. The number of each of the positive electrodes  21 , the negative electrodes  22 , and the separators  23  to be stacked is not particularly limited, and may be freely chosen. 
     The plan shape of each of the positive electrode  21  and the negative electrode  22  is preferably smaller in area than the plan shape of the separator  23 . In this case, an outer edge of each of the positive electrode  21  and the negative electrode  22  is preferably recessed back from an outer edge of the separator  23  toward an inner side. A reason for this is that this prevents a short circuit between the battery can  10  serving as the negative electrode terminal and the positive electrode  21 . Further, the plan shape of the negative electrode  22  is preferably larger in area than the plan shape of the positive electrode  21 . A reason for this is that this 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  includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer may be provided on each of both sides of the positive electrode current collector, or may be provided only on one side of the positive electrode current collector. The positive electrode current collector includes a material similar to a material included in the electrode terminal  30 . Note that the material included in the positive electrode current collector may be the same as or different from the material included in the electrode terminal  30 . The positive electrode active material layer 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. Note that the positive electrode active material layer may further include, without limitation, a positive electrode binder and a positive electrode conductor. 
     The negative electrode  22  includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer may be provided on each of both sides of the negative electrode current collector, or may be provided only on one side of the negative electrode current collector. The negative electrode current collector includes a material similar to the material included in the battery can  10 . Note that the material included in the negative electrode current collector may be the same as or different from the material included in the battery can  10 . The negative electrode active material layer 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. Note that the negative electrode active material layer 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 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. 
     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. 
     Note that  FIG. 5  also illustrates a stacked body  20 Z to be used to fabricate the battery device  20  in a process of manufacturing the flat secondary battery to be described later. The stacked body  20 Z has a configuration similar to that of the battery device  20 , which is a wound electrode body, 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 electrode terminal  30  is an external coupling terminal to be coupled to an electronic apparatus on which the flat secondary battery is mountable. Here, as illustrated in  FIGS. 1 to 4 , the electrode terminal  30  is coupled to the positive electrode  21  (the positive electrode current collector) of the battery device  20 . The electrode terminal  30  thus serves as the positive electrode terminal. As a result, upon use of the flat secondary battery, the flat secondary battery is coupled to the electronic apparatus via the electrode terminal  30  (the positive electrode terminal) and the battery can  10  (the negative electrode terminal), and the electronic apparatus thereby becomes operable using the flat secondary battery as a power source. 
     The electrode terminal  30  is provided at the sidewall part M 3  (the plane surface M 3 F) of the battery can  10 , as described above. In this case, the electrode terminal  30  is placed through the through hole  10 K provided at the sidewall part M 3 . The electrode terminal  30  is thus attached to the battery can  10  via the through hole  10 K. Note that a portion of the electrode terminal  30  is exposed from the sidewall part M 3  in order to serve as an external coupling terminal. In this case, the electrode terminal  30  preferably protrudes from the plane surface M 3 F. A reason for this is that this makes it easier for the flat secondary battery to be coupled to an electronic apparatus via the electrode terminal  30 . 
     In a case where the electrode terminal  30  protrudes from the battery can  10  (the plane surface M 3 F), the protrusion range of the electrode terminal  30  is not particularly limited. 
     In particular, the electrode terminal  30  preferably lies inside the circumscribed circle G defined by the curved surface M 3 C described above. In other words, the electrode terminal  30  is preferably recessed relative to the circumference of the circumscribed circle G toward the inner side without any portion lying outside the circumscribed circle G. A reason for this is that this increases the energy density per unit volume. 
     Specifically, if the electrode terminal  30  extends to the outside of the circumscribed circle G, the flat secondary battery increases in outer diameter due to the presence of the electrode terminal  30 , and this results in a lower energy density per unit volume. In contrast, in a case where the electrode terminal  30  is recessed relative to the circumference of the circumscribed circle G toward the inner side, the presence of the electrode terminal  30  causes no increase in outer diameter of the flat secondary battery, and this results in a higher energy density per unit volume. 
     Note that the electrode terminal  30  includes one or more of electrically conductive materials including, without limitation, metals (including stainless steel) and alloys. Here, in order to serve as the positive electrode terminal, the electrode terminal  30  includes one or more of materials including, without limitation, aluminum, an aluminum alloy, and stainless steel. 
     The three-dimensional shape of the electrode terminal  30  is not particularly limited. Here, the electrode terminal  30  includes terminal parts  31 ,  32 , and  33 . The terminal parts  32  and  33  are coupled to respective opposite ends of the terminal part  31 . 
     Specifically, the terminal part  31  is a first terminal part having a cylindrical shape and disposed in the through hole  10 K. The terminal part  31  has an outer diameter D (D 1 ) smaller than an inner diameter of the through hole  10 K. The terminal part  32  is a second terminal part having a cylindrical shape, and is disposed on a rear side in a direction from the electrode terminal  30  toward the inside of the battery can  10 , that is, toward the left in  FIG. 3 . The terminal part  32  is coupled to one end of the terminal part  31 . The terminal part  32  has an outer diameter D (D 2 ) larger than the inner diameter of the through hole  10 K. The terminal part  33  is a third terminal part having a cylindrical shape, and is disposed on a front side in the direction from the electrode terminal  30  toward the inside of the battery can  10 . The terminal part  33  is coupled to the other end of the terminal part  31 . The terminal part  33  has an outer diameter D (D 3 ) larger than the inner diameter of the through hole  10 K. Here, the terminal part  32  is disposed outside the battery can  10 , and the terminal part  33  is disposed inside the battery can  10 . Note that the outer diameters D 2  and D 3  may be equal, or may be different from each other. 
     Thus, the electrode terminal  30  has such a three-dimensional shape that the outer diameter D is reduced locally in the middle. A reason for employing such a shape is that the outer diameter D 2  of the terminal part  32  larger than the inner diameter of the through hole  10 K helps to prevent the terminal part  32  from passing through the through hole  10 K, and the outer diameter D 3  of the terminal part  33  larger than the inner diameter of the through hole  10 K helps to prevent the terminal part  33  from passing through the through hole  10 K. A further reason is that the electrode terminal  30  is fixed to the battery can  10  by utilizing a pressing force of the terminal part  32  on the battery can  10  and a pressing force of the terminal part  33  on the battery can  10 . This helps to prevent the electrode terminal  30  from falling out of the battery can  10 . 
     The gasket  40  is an insulating member disposed between the battery can  10  and the electrode terminal  30 , as illustrated in  FIGS. 1 to 3 . The gasket  40  insulates the electrode terminal  30  from the battery can  10 . The electrode terminal  30  is thus fixed to the battery can  10  with the gasket  40  interposed therebetween. 
     The gasket  40  includes one or more of insulating materials including, without limitation, polypropylene and polyethylene. 
     A mounting range of the gasket  40  is not particularly limited. Here, the gasket  40  is disposed in a gap between the battery can  10  and the electrode terminal  30 . 
     As illustrated in  FIGS. 2 and 3 , the positive electrode lead  51  is a wiring member that couples the electrode terminal  30  and the positive electrode  21  (the positive electrode current collector) to each other, and includes a material similar to the material included in the electrode terminal  30 . Note that the material included in the positive electrode lead  51  may be the same as or different from the material included in the electrode terminal  30 . A coupling position of the positive electrode lead  51  to the positive electrode  21  is not particularly limited, and may be freely chosen. The number of the positive electrode leads  51  is not particularly limited, and may be freely chosen. Here, the number of the positive electrode leads  51  is one. 
     As illustrated in  FIGS. 2 and 3 , the negative electrode lead  52  is a wiring member that couples the battery can  10  and the negative electrode  22  (the negative electrode current collector) to each other, and includes a material similar to the material included in the battery can  10 . Note that the material included in the negative electrode lead  52  may be the same as or different from the material included in the battery can  10 . A coupling position of the negative electrode lead  52  to the negative electrode  22  is not particularly limited, and may be freely chosen. The number of the negative electrode leads  52  is not particularly limited, and may be freely chosen. Here, the number of the negative electrode leads  52  is one. 
     Note that the flat secondary battery may further include one or more of other unillustrated components. 
     Specifically, the flat 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. Although a mounting position of the safety valve mechanism is not particularly limited, the safety valve mechanism is provided at one of the bottom parts M 1  and M 2 , preferably the bottom part M 2  at which the electrode terminal  30  is not provided. 
     Further, the flat 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, and prevents a short circuit between the battery can  10  and the battery device  20  (the positive electrode  21 ). A mounting range of the insulator is not particularly limited, and may be freely chosen. 
     Note 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. Although there is no limitation on the respective positions at which the liquid injection hole and the cleavage valve are to be provided, the liquid injection hole and the cleavage valve are each provided at one of the bottom parts M 1  and M 2 , preferably the bottom part M 2  at which the electrode terminal  30  is not provided, as with the mounting position of the safety valve mechanism described above. 
     The flat secondary battery operates in a manner described below. Upon charging, 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, 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. 
       FIG. 6  is a perspective view of the configuration of the battery can  10  to be used in a process of manufacturing the flat secondary battery, and corresponds to  FIG. 1 . Note that  FIG. 6  illustrates a state where the cover part  12  is separated from the containing part  11 . In the following,  FIGS. 1 to 5  described already will be referred to when necessary. 
     In a case of manufacturing the flat secondary battery, the flat secondary battery is assembled by a procedure described below. In this case, the stacked body  20 Z described above is used to fabricate the battery device  20 , and the cover part  12  with the electrode terminal  30  attached thereto with the gasket  40  therebetween in advance is used to assemble the battery can  10 . 
     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 the positive electrode current collector to thereby form the positive electrode active material layer. The positive electrode  21  including the positive electrode current collector and the positive electrode active material layer 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 the negative electrode current collector to thereby form the negative electrode active material layer. The negative electrode  22  including the negative electrode current collector and the negative electrode active material layer 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, the positive electrode  21  and the negative electrode  22  are alternately stacked with the separator  23  interposed therebetween to thereby fabricate the stacked body  20 Z. 
     Thereafter, the stacked body  20 Z is placed into the containing part  11  through the opening  11 K. In this case, one end of the negative electrode lead  52  is coupled to the stacked body  20 Z (the negative electrode current collector of the negative electrode  22 ) and the other end of the negative electrode lead  52  is coupled to the battery can  10  by a method such as a welding method. Note that one or more of welding methods including, without limitation, a laser welding method and a resistance welding method may be used. Details of the welding method described here apply also to the following. 
     Thereafter, the cover part  12  with the electrode terminal  30  attached thereto with the gasket  40  therebetween in advance is placed on the containing part  11  to cover the opening  11 K, following which the cover part  12  is joined to the containing part  11  by a method such as a welding method. In this case, one end of the positive electrode lead  51  is coupled to the stacked body  20 Z (the positive electrode current collector of the positive electrode  21 ) and the other end of the positive electrode lead  51  is coupled to the electrode terminal  30  by a method such as a welding method. The stacked body  20 Z is thereby enclosed inside the battery can  10  (the containing part  11  and the cover part  12 ). 
     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  20 Z (the positive electrode  21 , the negative electrode  22 , and the separator  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 flat secondary battery is completed. 
     According to the flat secondary battery, the battery device  20  is contained inside the battery can  10  having a columnar shape and including the sidewall part M 3  (the curved surface M 3 C and the plane surface M 3 F), and the electrode terminal  30  coupled to the positive electrode  21  of the battery device  20  is provided at the sidewall part M 3  (the plane surface M 3 F). As a result, for a reason described below, it is possible to increase the energy density per unit volume. 
       FIG. 7  illustrates a sectional configuration of a flat secondary battery of a comparative example, and corresponds to  FIG. 3 .  FIGS. 8 and 9  each schematically illustrate a configuration of a flat secondary battery for describing the device space volume. Note that  FIG. 8  illustrates the flat secondary battery of the comparative example, and  FIG. 9  illustrates the flat secondary battery according to the present embodiment. 
     As illustrated in  FIG. 7 , the flat secondary battery of the comparative example includes a battery can  110  (the containing part  111  and the cover part  112 ) and a battery device  120  (a positive electrode  121 , a negative electrode  122 , and a separator  123 ) that respectively correspond to the battery can  10  (the containing part  11  and the cover part  12 ) and the battery device  20  (the positive electrode  21 , the negative electrode  22 , and the separator  23 ). The flat secondary battery of the comparative example further includes a gasket  130 . 
     Each of the containing part  111  and the cover part  112  is a flat and cylindrical (handleless mug-shaped) member with one end open and the other end closed. The containing part  111  contains the battery device  120 . The containing part  111  and the cover part  112  are disposed to be opposed to each other. The containing part  111  and the cover part  112  are fitted to each other with the battery device  120  contained inside the containing part  111 , and are also crimped to each other with the gasket  130  interposed therebetween. In this case, an end of the containing part  111  on a side opposed to the cover part  112  is bent outward, and a portion of the containing part  111  and a portion of the cover part  112  are crimped to each other with the gasket  130  interposed therebetween. The so-called crimp part C (crimped part) is thus provided. The battery device  120  (the positive electrode  121 , the negative electrode  122 , and the separator  123 ) has a configuration similar to that of the battery device  20  (the positive electrode  21 , the negative electrode  22 , and the separator  23 ). 
     The positive electrode  121  of the battery device  120  is coupled to the containing part  111  via an unillustrated positive electrode lead. The containing part  111  thus serves as the positive electrode terminal. Besides, the negative electrode  122  of the battery device  120  is coupled to the cover part  112  via an unillustrated negative electrode lead. The cover part  112  thus serves as the negative electrode terminal. 
     As illustrated in  FIGS. 8 and 9 , in a case where the height H is fixed, the device space volume is determined not on the basis of the maximum outer diameter DM but on the basis of an effective outer diameter DY. 
     Specifically, for the flat secondary battery of the comparative example illustrated in  FIG. 7 , a schematic illustration of an internal configuration of the battery can  110  necessary for calculating the device space volume is as in  FIG. 8 . As is apparent from a correspondence relationship between  FIGS. 7 and 8 , a circumscribed rectangle K illustrated in  FIG. 8  represents an outline of a rectangle defined by the height H and the maximum outer diameter DM. 
     In the flat secondary battery of the comparative example, due to the battery can  110  having the crimp part C, it is not possible to dispose the battery device  120  at a location (a space) where the crimp part C lies. Therefore, the volume of the internal space of the battery can  110  available for containing the battery device  120 , i.e., the device space volume of the battery can  110 , is determined not on the basis of the maximum outer diameter DM but on the basis of the effective outer diameter DY which is determined by subtracting a loss outer diameter DR corresponding to the crimp part C from the maximum outer diameter DM. The effective outer diameter DY is calculated in accordance with the following equation: Effective outer diameter DY=Maximum outer diameter DM−(Loss outer diameter DR×2). Note that the loss outer diameter DR is determined on the basis of the thickness of the containing part  111 , the thickness of the cover part  112 , and the thickness of the gasket  130 . The loss outer diameter DR increases as the thickness of the gasket  130  is increased to improve the sealing property of the battery can  110 . 
     In this case, inside the battery can  110 , a loss space RS resulting from the loss outer diameter DR is large in volume because the loss outer diameter DR occurs at each of two locations. As a result, the volume of an effective space YS (the device space volume) corresponding to the effective outer diameter DY decreases. The “loss space RS” is an internal space that is not available for containing the battery device  120 . The “effective space YS” is an internal space that is available for containing the battery device  120 . Thus, due to the decrease in device space volume, the energy density per unit volume also decreases. This results in degradation of a characteristic such as a battery capacity characteristic, thus making it difficult to obtain a superior battery characteristic. 
     In contrast, for the flat secondary battery according to the present embodiment illustrated in  FIG. 3 , a schematic illustration of an internal configuration of the battery can  10  necessary for calculating the device space volume is as in  FIG. 9 . 
     In the flat secondary battery according to the present embodiment, unlike in the flat secondary battery of the comparative example, the battery can  10  includes no crimp part C. However, in the flat secondary battery according to the present embodiment, the battery can  10  has the plane surface M 3 F, and also has an excess space  10 S between the plane surface M 3 F and the battery device  20  for disposing, e.g., a portion of the electrode terminal  30  therein. Thus, inside the battery can  10 , it is not possible to dispose the battery device  20  in the excess space  10 S. Needless to say, it is not possible to dispose the battery device  20  in a space outside the battery can  10  (the plane surface M 3 F), i.e., a space between the plane surface M 3 F and the circumscribed circle G, either. 
     Therefore, the volume of the internal space of the battery can  10  available for containing the battery device  20 , i.e., the device space volume of the battery can  10 , is determined not on the basis of the maximum outer diameter DM but on the basis of the effective outer diameter DY which is determined by subtracting the loss outer diameter DR corresponding to, e.g., the excess space  10 S from the maximum outer diameter DM. The effective outer diameter DY is calculated in accordance with the following equation: Effective outer diameter DY =Maximum outer diameter DM−Loss outer diameter DR. 
     In this case, inside the battery can  10 , the loss space RS resulting from the loss outer diameter DR is smaller in volume because the loss outer diameter DR occurs only at one location. As a result, the volume of the effective space YS (the device space volume) corresponding to the effective outer diameter DY increases. Thus, by virtue of the increase in device space volume, it is possible to increase the energy density per unit volume. This improves a characteristic such as a battery capacity characteristic. Accordingly, it is possible to achieve a superior battery characteristic. 
     In addition, in the flat secondary battery according to the present embodiment, a portion of the surface of the sidewall part M 3  of the battery can  10  may be the plane surface M 3 F, and the electrode terminal  30  may be provided at the plane surface M 3 F. This suppresses a decrease in device space volume resulting from the electrode terminal  30  provided on the battery can  10 . Accordingly, it is possible to achieve higher effects. In this case, the electrode terminal  30  may lie inside the circumscribed circle G defined on the basis of the curved surface M 3 C. This further suppresses a decrease in device space volume, thus making it possible to achieve even higher effects. 
     Further, the battery can  10  may be a crimpless can without the crimp part C. This avoids a large decrease in effective space YS (effective outer diameter DY) resulting from the presence of the crimp part C. As a result, it becomes easier to secure the device space volume, and it is thus possible to achieve higher effects. In this case, the battery can  10  may be a welded can. This makes it easy to provide the battery can  10  including no crimp part C. Accordingly, it is possible to achieve higher effects. 
     Further, the electrode terminal  30  may include the terminal part  31  having a small outer diameter (D 1 ) and the terminal parts  32  and  33  having large outer diameters (D 2  and D 3 ). This helps to prevent the electrode terminal  30  from falling out of the battery can  10 . Accordingly, stable charging and discharging operations are secured while the device space volume is secured. It is thus possible to achieve higher effects. 
     Further, the battery device  20  may have a three-dimensional shape corresponding to the three-dimensional shape of the battery can  10 . This helps to prevent a dead space from resulting upon placing the battery device  20  in the battery can  10 , thereby facilitating efficient use of the effective space YS inside the battery can  10 . Accordingly, an area over which the positive electrode  21  and the negative electrode  22  are opposed to each other is secured. It is thus possible to achieve higher effects. 
     Further, the negative electrode  22  may be coupled to the battery can  10 . This allows the battery can  10  to serve as the negative electrode terminal, making it unnecessary to separately provide a negative electrode terminal in the flat secondary battery. Accordingly, a decrease in effective volume due to the presence of the negative electrode terminal is avoided, and it is thus possible to achieve higher effects. In this case, the gasket  40  may be disposed between the battery can  10  and the electrode terminal  30 . This prevents a short circuit between the electrode terminal  30  and the battery can  10  also in the case where the battery can  10  serves as the negative electrode terminal. Accordingly, stable charging and discharging operations are secured even if the battery can  10  is used as the negative electrode terminal. It is thus possible to achieve higher effects. 
     In particular, the electrode terminal  30  may serve as the positive electrode terminal and the battery can  10  may serve as the negative electrode terminal. This allows for easy coupling of the flat secondary battery to an electronic apparatus through the use of the electrode terminal  30  and the battery can  10 . Accordingly, it is possible to improve convenience at the time of using the flat secondary battery. 
     Specifically, in the flat secondary battery of the comparative example ( FIG. 7 ), the containing part  111  serves as the positive electrode terminal and the cover part  112  serves as the negative electrode terminal. In this case, because the containing part  111  and the cover part  112  are opposed to each other with the battery device  120  interposed therebetween, the positive electrode terminal and the negative electrode terminal are disposed in mutually opposite directions (the up direction and the down direction in  FIG. 7 ) along the height direction. This makes it difficult to couple the flat secondary battery (the positive electrode terminal and the negative electrode terminal) of the comparative example to an electronic apparatus. 
     In contrast, in the flat secondary battery according to the present embodiment ( FIG. 3 ), the electrode terminal  30  serves as the positive electrode terminal and the battery can  10  serves as the negative electrode terminal. In this case, because the electrode terminal  30  is provided on the battery can  10 , the positive electrode terminal and the negative electrode terminal are disposed in a common direction (the horizontal direction in  FIG. 3 ) along the height direction. This makes it possible to easily couple the flat secondary battery (the positive electrode terminal and the negative electrode terminal) according to the present embodiment to an electronic apparatus. 
     Further, in the battery device  20 , the positive electrode  21  and the negative electrode  22  may be stacked with the separator  23  interposed therebetween (the stacked electrode body). This makes it harder for a dead space to occur in the battery device  20  than in a case where the positive electrode  21  and the negative electrode  22  are wound with the separator  23  interposed therebetween (a wound electrode body). The dead space is a space such as one formed at a winding core part of the wound electrode body. Thus, the energy density per unit volume further increases to make it possible to achieve higher effects. 
     Next, modifications of the foregoing flat secondary battery will be described. The configuration of the flat secondary battery is appropriately modifiable, for example, as will be described below. Note that any two or more of the following series of modifications may be combined. 
     [Modification 1] 
     In  FIG. 2 , the electrode terminal  30  lies inside the circumscribed circle G. However, as illustrated in  FIG. 10  corresponding to  FIG. 2 , the position of the plane surface M 3 F may be shifted in a direction from the electrode terminal  30  toward the outside of the circumscribed circle G to allow a portion of the electrode terminal  30  to protrude to the outside of the circumscribed circle G. In this case also, the device space volume increases as compared with that in the flat secondary battery of the comparative example illustrated in  FIG. 7 . Accordingly, it is possible to achieve similar effects. 
     In the case illustrated in  FIG. 10 , however, while the shift in position of the plane surface M 3 F increases the volume of the internal space of the battery can  10  and accordingly increases also the device space volume, the energy density per unit volume can decrease due to an increase in outer diameter D. In order to secure the device space volume to thereby secure also the energy density per unit volume, it is therefore preferable that the electrode terminal  30  lie inside the circumscribed circle G as illustrated in  FIG. 2 . 
     Note that in  FIG. 10 , the position of the plane surface M 3 F is shifted to allow a portion of the electrode terminal  30  to protrude to the outside of the circumscribed circle G. However, instead of shifting the position of the plane surface M 3 F, the terminal part  32  may be increased in dimension in the direction of protrusion of the electrode terminal  30  to thereby allow a portion of the electrode terminal  30  to protrude to the outside of the circumscribed circle G. In this case also, the device space volume increases as compared with that in the flat secondary battery of the comparative example illustrated in  FIG. 7 . Accordingly, it is possible to achieve similar effects. 
     However, in a case of allowing a portion of the electrode terminal  30  to protrude to the outside of the circumscribed circle G without a shift in position of the plane surface M 3 F, the outer diameter D increases, although the device space volume does not change. As a result, the energy density per unit volume can decrease. In order to secure the device space volume to thereby secure also the energy density per unit volume, it is therefore preferable that the electrode terminal  30  lie inside the circumscribed circle G, as described above. 
     [Modification 2] 
     In  FIGS. 1 and 2 , the surface of the sidewall part M 3  of the battery can  10  includes the curved surface M 3 C and the plane surface M 3 F, and the electrode terminal  30  is thus provided at the plane surface M 3 F. 
     However, as illustrated in  FIG. 11  corresponding to  FIG. 1  and in  FIG. 12  corresponding to  FIG. 2 , the surface of the sidewall part M 3  may entirely be the curved surface M 3 C without including the plane surface M 3 F, and the electrode terminal  30  may thus be provided at the curved surface M 3 C. In other words, the battery can  10  may have a flat and cylindrical three-dimensional shape. In this case also, the device space volume increases as compared with that in the flat secondary battery of the comparative example illustrated in  FIG. 7 . Accordingly, it is possible to achieve similar effects. 
     However, in the case illustrated in  FIGS. 11 and 12 , the outer diameter D increases due to the configuration in which the electrode terminal  30  is provided at the curved surface M 3 C. This results in a relative decrease in device space volume with respect to the outer diameter D, causing the energy density per unit volume to decrease. In order to increase the energy density per unit volume as much as possible, it is therefore preferable that the electrode terminal  30  be provided at the plane surface M 3 F as illustrated in  FIG. 2 . 
     Note that in the case where the surface of the sidewall part M 3  includes the curved surface M 3 C and the plane surface M 3 F, the electrode terminal  30  may be provided at the curved surface M 3 C; however, for the above-described reason, it is preferable that the electrode terminal  30  be provided at the plane surface M 3 F in order to secure the energy density per unit volume. 
     [Modification 3] 
     In  FIG. 3 , the battery device  20  is a stacked electrode body. Accordingly, in the battery device  20 , the positive electrode  21  and the negative electrode  22  are stacked with the separator  23  interposed therebetween. 
     However, as illustrated in  FIG. 13  corresponding to  FIG. 3 , the flat secondary battery may include a battery device  60  which is a wound electrode body, in place of the battery device  20  which is a stacked electrode body. In the battery device  60 , a positive electrode  61  and a negative electrode  62  are wound with a separator  63  interposed therebetween. More specifically, in the battery device  60  which is a wound electrode body, the positive electrode  61  and the negative electrode  62  are wound with the separator  63  interposed therebetween. More specifically, the positive electrode  61  and the negative electrode  62  are stacked on each other with the separator  63  interposed therebetween, and are wound in the state of the stack with the separator  23  interposed between the positive electrode  61  and the negative electrode  62 . The battery device  60  has, at the winding core part, a space (a winding center space  60 S) in which none of the positive electrode  61 , the negative electrode  62 , and the separator  63  is present. The positive electrode  61 , the negative electrode  62 , and the separator  63  have configurations similar to those of the positive electrode  21 , the negative electrode  22 , and the separator  23 , respectively. 
     A method of manufacturing the flat secondary battery illustrated in  FIG. 13  is similar to the method of manufacturing the flat secondary battery illustrated in  FIG. 3  except that, after the positive electrode  61  and the negative electrode  62  are alternately stacked with the separator  63  interposed therebetween, the stack of the positive electrode  61 , the negative electrode  62 , and the separator  63  is wound to thereby fabricate a wound body  160  to be used to fabricate the battery device  60 . In this case, the wound body  160  is enclosed inside the battery can  10  (the containing part  11  and the cover part  12 ), and thereafter the wound body  160  is impregnated with an electrolytic solution injected into the battery can  10 . The battery device  60  is thereby fabricated. 
     In this case also, the device space volume increases as compared with that in the flat secondary battery of the comparative example illustrated in  FIG. 7 . Accordingly, it is possible to achieve similar effects. However, as described above, in order to avoid a decrease in energy density per unit volume due to the occurrence of a dead space (the winding center space  60 S), the battery device  20  which is a stacked electrode body causing no dead space is preferable to the battery device  60  which is a wound electrode body causing the dead space. 
     [Modification 4] 
     In  FIG. 3 , the electrode terminal  30  is coupled to the battery device  20  (the positive electrode  21 ) via the positive electrode lead  51 , and the battery device  20  (the negative electrode  22 ) is coupled to the battery can  10  via the negative electrode lead  52 . Thus, the electrode terminal  30  serves as the positive electrode terminal, and the battery can  10  serves as the negative electrode terminal. 
     However, the electrode terminal  30  may be coupled to the battery device  20  (the negative electrode  22 ) via the negative electrode lead  52 , and the battery device  20  (the positive electrode  21 ) may be coupled to the battery can  10  via the positive electrode lead  51 . Thus, the electrode terminal  30  may serve as the negative electrode terminal, and the battery can  10  may serve as the positive electrode terminal. 
     In this case, in order to serve as the negative electrode terminal, the electrode terminal  30  includes one or more of materials including, without limitation, iron, copper, nickel, stainless steel, an iron alloy, a copper alloy, and a nickel alloy. In order to serve as the positive electrode terminal, the battery can  10  includes one or more of materials including, without limitation, aluminum, an aluminum alloy, and stainless steel. 
     In this case also, the device space volume increases as compared with that in the flat secondary battery of the comparative example illustrated in  FIG. 7 . Accordingly, it is possible to achieve similar effects. 
     [Modification 5] 
     In  FIGS. 2 to 4 , the terminal parts  31  to  33  of the electrode terminal  30  all have a cylindrical three-dimensional shape, and therefore the electrode terminal  30  as a whole has a generally cylindrical three-dimensional shape. However, the three-dimensional shape of each of the terminal parts  31  to  33  is not particularly limited as long as the electrode terminal  30  is able to serve as the positive electrode terminal. Specifically, the terminal parts  31  to  33  may each have another three-dimensional shape, such as a shape of a polygonal prism, and the electrode terminal  30  as a whole may thus have another, generally polygonal prismatic three-dimensional shape. The polygonal prism is not particularly limited, and examples thereof include a triangular prism, a rectangular prism, and a pentagonal prism. In this case also, the device space volume increases, making it possible to achieve similar effects. 
     Note that although not specifically illustrated here, other different variations are possible for the three-dimensional shape of the electrode terminal  30 . Specifically, the electrode terminal  30  may include only the terminal parts  31  and  32  without the terminal part  33 , or may include only the terminal parts  31  and  33  without the terminal part  32 . Alternatively, the electrode terminal  30  may have a substantially uniform outer diameter D as a whole, and therefore the electrode terminal  30  may be substantially constant in outer diameter D. In this case also, it is possible to achieve similar effects. 
     [Modification 6] 
     The positive electrode lead  51  may be physically separated from the positive electrode current collector and thereby provided as a component separate from the positive electrode current collector. Alternatively, the positive electrode lead  51  may be physically coupled to the positive electrode current collector and thereby integrated with the positive electrode current collector. In the latter case, in a process of forming the positive electrode  21  by means of a punching process on a metal foil, the positive electrode current collector after forming the positive electrode active material layer thereon may be punched into a configuration in which the positive electrode lead  51  and the positive electrode current collector are integrated with each other. It is thereby possible to form the positive electrode  21  including the positive electrode current collector integrated with the positive electrode lead  51 . In this case also, electrical conduction between the positive electrode lead  51  and the positive electrode current collector is secured. Accordingly, it is possible to achieve similar effects. 
     Note that, in a case where the positive electrode lead  51  is integrated with the positive electrode current collector, the positive electrode  21  need not have a foil winding structure, and therefore the positive electrode active material layer may be provided on the entire positive electrode current collector. In other words, the positive electrode current collector does not have to be exposed at each of the ends of the positive electrode  21  on the inner side and the outer side of the winding. 
     Modification  6  described here is also applicable to the negative electrode lead  52  and the negative electrode current collector. More specifically, the negative electrode lead  52  may be separate from the negative electrode current collector or may be integrated with the negative electrode current collector. In this case also, electrical conduction between the negative electrode lead  52  and the negative electrode current collector is secured. Accordingly, it is possible to achieve similar effects. Needless to say, in a case where the negative electrode lead  52  is integrated with the negative electrode current collector, the negative electrode  22  need not have the foil winding structure, and the negative electrode active material layer may thus be provided on the entire negative electrode current collector. 
     [Modification 7] 
     In the process of manufacturing the secondary battery, the stacked body  20 Z is placed into the containing part  11 , and the cover part  12  is joined to the containing part  11  by a method such as a welding method, following which the electrolytic solution is injected into the battery can  10  (the containing part  11  and the cover part  12 ) through the liquid injection hole. In other words, the stacked body  20 Z is impregnated with the electrolytic solution by injecting the electrolytic solution into the battery can  10  after the battery can  10  is formed, that is, after the cover part  12  is joined to the containing part  11 . 
     However, the cover part  12  may be joined to the containing part  11  by a method such as a welding method after the stacked body  20 Z is placed into the containing part  11  and the electrolytic solution is injected into the containing part  11 . In other words, the stacked body  20 Z may be impregnated with the electrolytic solution by injecting the electrolytic solution into the containing part  11  before the battery can  10  is formed, that is, before the cover part  12  is joined to the containing part  11 . 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  20 Z 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 containing part  11  through the opening  11 K 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  20 Z, and to simplify the process of injecting the electrolytic solution. 
     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 of using a liquid electrolyte (an electrolytic solution), the electrolyte is not limited to a particular kind. Thus, a gel electrolyte (an electrolyte layer) may be used, or an electrolyte in a solid form (a solid electrolyte) may be used. 
     Further, while a description has been given of a case where the battery device has a wound-type device structure (a wound electrode body) and a case where the battery device has a stacked-type device structure (a stacked electrode body), the device structure of the battery device is not particularly limited, and any other device structure, such as a zigzag-folded-type device structure where the electrodes (the positive electrode and the negative electrode) are folded in a zigzag shape, may be chosen. 
     Further, 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 suitable effect. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. 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.