Patent Publication Number: US-11387493-B2

Title: Secondary battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of International application No. PCT/JP2017/044966, filed Dec. 14, 2017, which claims priority to Japanese Patent Application No. 2017-004477, filed Jan. 13, 2017, the entire contents of each of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a secondary battery. 
     BACKGROUND OF THE INVENTION 
     Secondary batteries that can be repeatedly charged and discharged have conventionally been used for various purposes. For example, a secondary battery is used as a power source for electronic equipment, such as a smartphone and a notebook computer. 
     In recent years, there has been a growing demand for thinner and smaller electronic equipment, and along with this, there has been a demand for efficient provision of a substrate and the like in secondary batteries in electronic equipment. With respect to this, Patent Document 1 discloses a secondary battery having a step structure. More specifically, Patent Document 1 discloses that an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, which are constituents of the secondary battery, forms a step structure in a cross-sectional view. 
     Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2014-523629. 
     SUMMARY OF THE INVENTION 
     Here, the inventors of the present application have found that a problem described below may occur when a secondary battery including an electrode assembly having a step structure in a cross-sectional view is used. Specifically, the inventors of the present invention have found that when an electrode assembly having a step structure in a cross-sectional view is used, each positive electrode and each negative electrode as its constituents need to be electrically connected, which causes a restriction on an installation location of an external terminal. 
     The present invention has been devised in view of such circumstances. Specifically, it is an object of the present invention to provide a secondary battery in which a restriction on an installation location of an external terminal can be avoided. 
     In order to achieve the above object, one embodiment of the present invention provides a secondary battery including an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and an electrolyte, the electrode assembly and the electrolyte being housed in an exterior body. The electrode assembly includes a step structure including a first region being relatively high in a cross-sectional view and a second region being relatively low adjacent to the first region. The electrode assembly further includes at least one of a positive electrode side connecting portion that mutually connects each of positive electrode side connecting tabs of all positive electrodes in the first region and a negative electrode side connecting portion that mutually connects each of the negative electrode side connecting tabs of all negative electrodes in the first region, and at least one of a positive electrode side extended tab of at least one of the positive electrodes and a negative electrode side extended tab of at least one of the negative electrodes in the second region are configured to be electrically connected to an external terminal. 
     According to one embodiment of the present invention, it is possible to avoid restriction on an installation location of an external terminal. 
    
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         FIG. 1  is a perspective view schematically showing a secondary battery according to one embodiment of the present invention. 
         FIG. 2  is a cross-sectional view schematically showing an electrode assembly having a step structure of one mode. 
         FIG. 3  is a cross-sectional view schematically showing a mode in which a positive electrode side extended tab and/or a negative electrode side extended tab positioned in a second region of the electrode assembly are electrically connected to an external terminal. 
         FIG. 4  is a cross-sectional view schematically showing a mode of a positive electrode side connecting portion which mutually connects positive electrode side connecting tabs positioned in a first region of the electrode assembly. 
         FIG. 5  is a cross-sectional view schematically showing a mode of a negative electrode side connecting portion which mutually connects negative electrode side connecting tabs positioned in the first region of the electrode assembly. 
         FIG. 6  is a cross-sectional view schematically showing a mode in which the positive electrode side extended tab and/or the negative electrode side extended tab positioned in the second region of the electrode assembly are electrically connected to an external terminal via a current collector lead. 
         FIG. 7  is a cross-sectional view schematically showing another mode in which the positive electrode side extended tab and/or the negative electrode side extended tab positioned in the second region of the electrode assembly are electrically connected to an external terminal. 
         FIG. 8  is a cross-sectional view schematically showing a mode of a positive electrode side extended portion which mutually connects the positive electrode side extended tabs positioned in the second region of the electrode assembly. 
         FIG. 9  is a cross-sectional view schematically showing a mode of a negative electrode side extended portion which mutually connects the negative electrode side extended tabs positioned in the second region of the electrode assembly. 
         FIG. 10  is a cross-sectional view schematically showing the electrode assembly having a step structure of another mode. 
         FIG. 11  is a cross-sectional view schematically showing a basic configuration of an electrode assembly having a planar lamination structure. 
         FIG. 12  is a cross-sectional view schematically showing a basic configuration of an electrode assembly having a wound structure. 
         FIG. 13  is a cross-sectional view schematically showing a specific configuration of the electrode assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, before a secondary battery according to an embodiment of the present invention is described, a basic configuration of a secondary battery will be described. 
     [Basic Configuration of Secondary Battery] 
     The secondary battery has a structure in which an electrode assembly and an electrolyte are accommodated and enclosed in an exterior body as described in an embodiment of the present invention below. In the present description, the term “secondary battery” refers to a battery that can be repeatedly charged and discharged. Therefore, the secondary battery of the present invention is not excessively bound by its name, and for example, “electric storage device” and the like may be included in the subject of the present invention. The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. Types of the electrode assembly include types described below. In a first type, an electrode assembly  10 A has a planar lamination structure, in which a plurality of unit electrode units including positive electrodes  1 ,  1 A, negative electrodes  2 ,  2 A, and separators  3 ,  3 A are laminated (see  FIG. 11 ). In a second type, an electrode assembly  10 B has a wound structure in which electrode units including positive electrodes  1 ,  1 B, negative electrodes  2 ,  2 B, and separators  3 ,  3 B are wound in a roll (see  FIG. 12 ). Furthermore, as a third type, the electrode assembly may have what is called a stack-and-fold structure that is formed by folding an electrode unit of a positive electrode, a negative electrode, a separator, and a negative electrode (particularly preferably an electrode unit (a laminate body) extending longer in one direction). Further, the exterior body may take a form of a conductive hard case or a flexible case (such as a pouch). When the form of the exterior body is a flexible case (such as a pouch), each of a plurality of positive electrodes is connected to the positive electrode external terminal with a positive electrode current collector lead interposed between them. The positive electrode external terminal is fixed to the exterior body by a seal portion, and the seal portion prevents leakage of the electrolyte. Similarly, each of a plurality of negative electrodes is connected to a negative terminal external terminal with a negative electrode current collector lead interposed between them. The negative terminal external terminal is fixed to the exterior body by a seal portion, and the seal portion prevents leakage of the electrolyte. The positive electrode current collector lead connected to each of a plurality of positive electrodes may have a function of the positive electrode external terminal, and the negative electrode current collector lead connected to each of a plurality of negative electrodes may have a function of the negative terminal external terminal. When the form of the exterior body is a conductive hard case, each of a plurality of positive electrodes is connected to the positive electrode external terminal with a positive electrode current collector lead interposed between them. The positive electrode external terminal is fixed to the exterior body by a seal portion, and the seal portion prevents leakage of the electrolyte. 
     A positive electrode  1  is configured with at least a positive electrode current collector  11  and a positive electrode material layer  12  (see  FIG. 13 ), and the positive electrode material layer  12  is provided on at least one side of the positive electrode current collector  11 . In a location of the positive electrode current collector  11  where the positive electrode material layer  12  is not provided, that is, an end portion of the positive electrode current collector  11 , a positive electrode side extended tab  13  is positioned. The positive electrode material layer  12  contains a positive electrode active material as an electrode active material. A negative electrode  2  is configured with at least a negative electrode current collector  21  and a negative electrode material layer  22  (see  FIG. 13 ), and the negative electrode material layer  22  is provided on at least one side of the negative electrode current collector  21 . In a location of the negative electrode current collector  21  where the negative electrode material layer  22  is not provided, that is, an end portion of the negative electrode current collector  21 , a negative electrode side extended tab  23  is positioned. The negative electrode material layer  22  contains a negative electrode active material as an electrode active material. 
     The positive electrode active material contained in the positive electrode material layer  12  and the negative electrode active material contained in the negative electrode material layer  22  are substances directly involved in the transfer of electrons in the secondary battery, and are main substances of the positive and negative electrodes which are responsible for charging and discharging, that is, cell reaction. More specifically, ions are brought in an electrolyte due to “the positive electrode active material contained in the positive electrode material layer  12 ” and “the negative electrode active material contained in the negative electrode material layer  22 ”, and such ions move between the positive electrode  1  and the negative electrode  2  so that electrons are transferred, and charging and discharging are performed. The positive electrode material layer  12  and the negative electrode material layer  22  are preferably layers particularly capable of occluding and releasing lithium ions. That is, the secondary battery, in which lithium ions move between the positive electrode  1  and the negative electrode  2  through an electrolyte to charge and discharge the battery, is preferable. When lithium ions are involved in charging and discharging, the secondary battery corresponds to what is called a “lithium ion battery”. 
     As the positive electrode active material of the positive electrode material layer  12  is made of, for example, a granular body, a binder (which is also referred to as a “binding material”) is preferably included in the positive electrode material layer  12  for grains to be in contact with each other sufficiently and retaining a shape. Furthermore, a conductive auxiliary agent may be included in the positive electrode material layer  12  in order to facilitate transmission of electrons promoting a cell reaction. Likewise, as the negative electrode active material of the negative electrode material layer  22  is made of, for example, a granular body, a binder is preferably included for grains to be in contact with each other sufficiently and retaining a shape, and a conductive auxiliary agent may be included in the negative electrode material layer  22  in order to facilitate transmission of electrons promoting a cell reaction. As described above, since a plurality of components are contained, the positive electrode material layer  12  and the negative electrode material layer  22  can also be referred to as a “positive electrode mixture layer” and a “negative electrode mixture layer”, respectively. 
     The positive electrode active material is preferably a substance that contributes to occlusion and releasing of lithium ions. In this respect, it is preferable that the positive electrode active material be, for example, a lithium-containing composite oxide. More specifically, it is preferable that the positive electrode active material be a lithium transition metal composite oxide containing lithium and at least one kind of transition metal selected from a group consisting of cobalt, nickel, manganese, and iron. That is, in the positive electrode material layer  12  of the secondary battery, such a lithium transition metal composite oxide is preferably included as a positive electrode active material. For example, the positive electrode active material may be lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium iron phosphate, or part of their transition metals replaced with another metal. Although one kind of such a positive electrode active material may be included, two or more kinds of such a positive electrode active material may also be contained in combination. In a more preferable mode, the positive electrode active material contained in the positive electrode material layer  12  is lithium cobalt oxide. 
     The binder which may be contained in the positive electrode material layer  12  is not particularly limited, and can be at least one kind selected from a group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and polytetrafluoroethylene. The conductive auxiliary agent which may be contained in the positive electrode material layer  12  is not particularly limited, and can be at least one kind selected from carbon black, such as thermal black, furnace black, channel black, ketjen black, acetylene black, and the like, graphite, a carbon fiber, such as carbon nanotube and vapor phase growth carbon fiber, metal powder of copper, nickel, aluminum, silver, and the like, polyphenylene derivative, and the like. For example, the binder of the positive electrode material layer  12  may be polyvinylidene fluoride. Although it is merely an example, the conductive auxiliary agent of the positive electrode material layer  12  is carbon black. In a more preferably mode, the binder and the conductive auxiliary agent of the positive electrode material layer  12  may be a combination of polyvinylidene fluoride and carbon black. 
     The negative electrode active material is preferably a substance that contributes to occlusion and releasing of lithium ions. In this respect, it is preferable that the negative electrode active material be, for example, various carbon materials, oxides or lithium alloys. 
     As the various carbon materials of the negative electrode active material, graphite (natural graphite, artificial graphite), hard carbon, soft carbon, diamond-like carbon, and the like can be mentioned. In particular, graphite is preferable because it has high electron conductivity and excellent adhesion to the negative electrode current collector  21 . As the oxide of the negative electrode active material, at least one kind selected from a group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, and the like can be mentioned. The lithium alloy of the negative electrode active material may be any metal which may be alloyed with lithium, and is preferably, for example, a binary, ternary or higher alloy of a metal, such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, and the like, and lithium. It is preferable that such an oxide be amorphous as its structural form. This is because degradation due to nonuniformity, such as crystal grain boundaries or defects, is hardly generated. Although it is merely an example, the negative electrode active material of the negative electrode material layer  22  may be artificial graphite. 
     The binder which may be contained in the negative electrode material layer  22  is not particularly limited, and can be at least one kind selected from a group consisting of styrene butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resin, and polyamide imide resin. For example, the binder contained in the negative electrode material layer  22  may be styrene butadiene rubber. The conductive auxiliary agent which may be contained in the negative electrode material layer  22  is not particularly limited, and can be at least one kind selected from carbon black, such as thermal black, furnace black, channel black, ketjen black, acetylene black, and the like, graphite, a carbon fiber, such as carbon nanotube and vapor phase growth carbon fiber, metal powder of copper, nickel, aluminum, silver, and the like, polyphenylene derivative, and the like. Note that the negative electrode material layer  22  may contain a component derived from a thickener component (for example, carboxymethyl cellulose) used at the time of manufacturing a battery. 
     Although it is merely an example, the negative electrode active material and the binder in the negative electrode material layer  22  may be a combination of artificial graphite and styrene butadiene rubber. 
     The positive electrode current collector  11  and the negative electrode current collector  21  used for the positive electrode  1  and the negative electrode  2  are members that contribute to collecting and supplying electrons generated in the active material due to a cell reaction. Such a current collector may be a sheet-like metal member and may have a porous or perforated form. For example, the current collector may be a metal foil, a punching metal, a net, an expanded metal, or the like. The positive electrode current collector  11  used for the positive electrode  1  is preferably made from a metal foil containing at least one kind selected from a group consisting of aluminum, stainless steel, nickel, and the like, and may be, for example, an aluminum foil. On the other hand, the negative electrode current collector  21  used for the negative electrode  2  is preferably made from a metal foil containing at least one kind selected from a group consisting of copper, stainless steel, nickel, and the like, and may be, for example, a copper foil. 
     The separator  3  used for the positive electrode  1  and the negative electrode  2  is a member provided from the viewpoints of prevention of short circuit due to contact of the positive and negative electrodes, holding of the electrolyte, and the like. In other words, the separator  3  can be considered as a member that allows ions to pass through while preventing electronic contact between the positive electrode  1  and the negative electrode  2 . Preferably, the separator  3  is a porous or microporous insulating member and has a film form due to its small thickness. Although it is merely an example, a microporous film made from polyolefin may be used as the separator. In this regard, the microporous film used as the separator  3  may contain, for example, only polyethylene (PE) or polypropylene (PP) as polyolefin. Furthermore, the separator  3  may be a laminate body configured with a “microporous film made from PE” and a “microporous film made from PP”. A surface of the separator  3  may be covered with an inorganic particle coat layer, and/or an adhesive layer, or the like. The surface of the separator may have adhesive properties. Note that, the separator  3  should not be particularly restricted by its name, and may be a solid electrolyte, a gel electrolyte, an insulating inorganic particle, or the like having a similar function. Note that, from the viewpoint of further improving the handling of the electrode, the separator  3  and the electrode (the positive electrode  1 /the negative electrode  2 ) are preferably adhered. The adhesion between the separator  3  and the electrode may be performed by using an adhesive separator as the separator  3 , applying an adhesive binder on the electrode material layer (the positive electrode material layer  12 /the negative electrode material layer  22 ), and/or thermocompression bonding, and the like. Examples of the adhesive agent that provides adhesiveness to the separator  3  or the electrode material layer include polyvinylidene fluoride, an acrylic adhesive, and the like. 
     When the positive electrode  1  and the negative electrode  2  have a layer capable of occluding and releasing lithium ions, the electrolyte is preferably a “non-aqueous” electrolyte, such as an organic electrolyte and/or an organic solvent (that is, the electrolyte is preferably a non-aqueous electrolyte). In the electrolyte, metal ions released from the electrode (the positive electrode  1  or the negative electrode  2 ) exist, and hence the electrolyte helps transfer of metal ions in the cell reaction. 
     The non-aqueous electrolyte is an electrolyte containing a solvent and a solute. A specific solvent of the non-aqueous electrolyte preferably include at least a carbonate. Such a carbonate may be cyclic carbonates and/or chain carbonates. Although not particularly limited, as the cyclic carbonates, at least one selected from a group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC) can be mentioned. As the chain carbonates, at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC) can be mentioned. Although it is merely an example, a combination of cyclic carbonates and chain carbonates may be used as the non-aqueous electrolyte, and, for example, a mixture of ethylene carbonate and diethyl carbonate may be used. Further, as a specific solute of the non-aqueous electrolyte, for example, a Li salt, such as LiPF 6 , LiBF 4 , or the like is used. Further, as a specific solute of the non-aqueous electrolyte, for example, a Li salt, such as LiPF 6  and/or LiBF 4 , is preferably used. 
     As the positive electrode current collector lead and the negative electrode current collector lead, any current collector lead used in the field of the secondary battery can be used. Such a current collector lead is preferably made from a material by which electron transfer may be performed, and is made from, for example, a conductive material, such as aluminum, nickel, iron, copper, stainless steel, or the like. The positive electrode current collector lead is preferably made from aluminum and the negative electrode current collector lead is preferably made from nickel. The form of the positive electrode current collector lead and the negative electrode current collector lead is not particularly limited, and may be, for example, a line or a plate shape. 
     Any external terminal used in the field of secondary batteries can be used as the external terminal. Such an external terminal is preferably made from a material by which electron transfer may be performed, and is normally made from a conductive material, such as aluminum, nickel, iron, copper, stainless steel, or the like. An external terminal  5  may be electrically and directly connected to a substrate, or may be electrically and indirectly connected to the substrate with another device interposed between them. Note that the configuration is not limited to the above, and the positive electrode current collector lead connected to each of a plurality of positive electrodes may have a function of the positive electrode external terminal, and the negative electrode current collector lead connected to each of a plurality of negative electrodes may have a function of the negative terminal external terminal. 
     The exterior body may be in the form of a conductive hard case or a flexible case (such as a pouch) as described above. 
     The conductive hard case is composed of a main body portion and a lid portion. The main body portion is composed of a bottom portion and a side portion constituting a bottom surface of the exterior body. The main body portion and the lid portion are sealed after the electrode assembly, the electrolyte, the current collector lead and the external terminal are accommodated. The sealing method is not particularly limited, and for example, a laser irradiation method or the like can be mentioned. As a material constituting the main body portion and the lid portion, any material which may constitute a hard case type exterior body in the field of secondary batteries can be used. Such a material may be any material as long as electron transfer can be performed, and examples of such a material include conductive materials such as aluminum, nickel, iron, copper, and stainless steel. Dimensions of the main body portion and the lid portion are mainly determined according to dimensions of the electrode assembly, and are preferably such that, for example, movement (displacement) of the electrode assembly in the exterior body is prevented when the electrode assembly is accommodated. By preventing movement of the electrode assembly, destruction of the electrode assembly is prevented and the safety of the secondary battery is improved. 
     The flexible case is composed of a flexible sheet. The flexible sheet is preferably as soft as allowing the seal portion to be bent, and is preferably a plastic sheet. The plastic sheet is a sheet having such a characteristic that deformation by an external force is maintained when the external force is applied and then removed, and for example, what is called a laminate film can be used as the plastic sheet. For example, a flexible pouch made from a laminate film can be manufactured by laminating two laminate films and heat-sealing a peripheral portion of the laminate films. As the laminate film, a film formed by laminating a metal foil and a polymer film is generally used. Specifically, a three-layer film composed of an outer layer polymer film/a metal foil/an inner layer polymer film is exemplified. The outer layer polymer film is for preventing the metal foil from being damaged due to permeation of moisture and the like, contact, and the like, and polymers, such as polyamide and polyester, can be suitably used. The metal foil is for preventing permeation of moisture and gas, and foil of copper, aluminum, stainless steel, or the like can be suitably used. The inner layer polymer film protects the metal foil from the electrolyte contained in the inside and is for melting and sealing at the time of heat sealing, and polyolefin or acid-modified polyolefin can be suitably used. 
     [Secondary Battery of the Present Invention] 
     The secondary battery according to one embodiment of the present invention will be described hereinafter in consideration of the basic configuration of the secondary battery described above. It is to be noted in advance that the secondary battery according to one embodiment of the present invention is assumed to be a secondary battery having a step structure. 
       FIG. 1  is a perspective view schematically showing the secondary battery according to one embodiment of the present invention. 
     A secondary battery  100  according to one embodiment of the present invention has a structure in which an electrode assembly and an electrolyte are accommodated and sealed in an exterior body  20 . The exterior body  20  is provided with at least two step portions which are continuous with each other and have top surfaces at height levels different from each other. For example, as an example, as shown in  FIG. 1 , the exterior body  20  may include at least two step portions (a first step portion  20   a  and a second step portion  20   b ). Specifically, the first step portion  20   a  and the second step portion  20   b  are continuous to each other, and a height h 2  of a top surface  20   b   1  of the second step portion  20   b  is larger than a height h 1  of a top surface  20   a   1  of the first step portion  20   a . The height level of the top surface  20   a   1  of the first step portion  20   a  and the height level of the top surface  20   b   1  of the second step portion  20   b  are different from each other, so that a step surface  20   b   2  is formed between the top surface  20   a   1  of the first step portion  20   a  and the top surface  20   b   1  of the second step portion  20   b . On the other hand, in one embodiment, the first step portion  20   a  and the second step portion  20   b  are configured so that a width dimension W 2  (longitudinal direction) of the top surface  20   b   1  of the second step portion  20   b  is equal to a width dimension W 1  (longitudinal direction) of the top surface  20   a   1  of the first step portion  20   a.    
     A step surface  20   b   2  has a height h 3  and a width dimension (longitudinal direction) W 3 . The height h 3  of the step surface  20   b   2  is equal to a difference between the height h 2  of the top surface  20   b   1  of the second step portion  20   b  and the height h 1  of the top surface  20   a   1  of the first step portion  20   a . On the other hand, the width W 3  (longitudinal direction) of the step surface  20   b   2  is equal to the width dimension W 2  (longitudinal direction) of the top surface  20   b   1  of the second step portion  20   b  and the width dimension W 1  (longitudinal direction) of the top surface  20   a   1  of the first step portion  20   a.    
     The step surface  20   b   2  is configured to be continuous with the top surface  20   a   1  of the first step portion  20   a . Specifically, the top surface  20   a   1  of the first step portion  20   a  is continuous with the step surface  20   b   2  in a manner extending in a direction different from an extending direction of the step surface  20   b   2 . 
     Although not particularly limited, the top surface  20   a   1  of the first step portion  20   a  may extend in a direction perpendicular to the extending direction of the step surface  20   b   2 . That is, an angle θ between the step surface  20   b   2  and the top surface  20   a   1  of the first step portion  20   a  may be 90 degrees. Note that the configuration is not limited to the above, and the angle θ between the step surface  20   b   2  and the top surface  20   a   1  of the first step portion  20   a  may be 30 to 150 degrees in consideration of an arrangement form of a substrate, and is preferably 50 to 130 degrees, and more preferably 70 to 110 degrees. 
     In this manner, the exterior body has a step structure formed between the step surface and the top surface  20   a   1  of the first step portion  20   a . A substrate is preferably provided in the step structure, specifically a spatial region on the top surface  20   a   1  of the first step portion  20   a  from the viewpoint of efficient utilization of the region. 
     The above-mentioned substrate may be what is called a rigid substrate or a flexible substrate, and is preferably a rigid substrate. As the rigid substrate, any rigid substrate used in the field of substrates used together with a secondary battery can be used, and, for example, a glass-epoxy resin substrate can be mentioned. Examples of the substrate include circuit boards, such as a printed circuit board and a protective circuit board, a semiconductor substrate, such as a silicon wafer, a glass substrate, such as a display panel, and the like. When the substrate is what is called a protective circuit board for preventing overcharge, overdischarge, and overcurrent of the secondary battery, a secondary battery pack is configured with the protective circuit board and the secondary battery. 
     External terminals  30  (a positive electrode external terminal  30   a  and a negative electrode external terminal  30   b ) for a secondary battery are provided on a surface of the exterior body  20 . Although not particularly limited, for example, the external terminal  30  may be configured to be exposed on an end portion side surface  20   a   2  of the first step portion  20   a.    
     Hereinafter, an electrode assembly which is a constituent of the secondary battery according to one embodiment of the present invention will be described. 
     As described above, the exterior body which is a constituent of the secondary battery according to one embodiment of the present invention has at least two step portions (a low step portion having a top surface at a relatively low position and a high step portion having a top surface, which is continuous with the low step portion and at a relatively high position). Since the top surface of the low step portion and the top surface of the high step portion are at height levels different from each other, a step surface is formed between the top surface of the low step portion and the top surface of the high step portion due to the difference. In this manner, the exterior body has a step structure formed between the step surface and the top surface of the low step portion. In one embodiment of the present invention, from the viewpoint of preventing movement (displacement) of the electrode assembly in the exterior body and the like, the electrode assembly disposed in the exterior body having the step structure preferably has a step structure having substantially the same shape as the exterior body in a cross-sectional view. 
     The content of description below is merely an example, and it is confirmed that the electrode assembly is presumed to be provided inside the exterior body having two steps. 
     The electrode assembly, which is a constituent of the secondary battery, includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode as described above. Types of the electrode assembly include types described below. In a first type (planar lamination structure type), the electrode assembly  10 A is formed by laminating a plurality of unit electrode units including the positive electrodes  1 , LA, the negative electrodes  2 ,  2 A and the separators  3 ,  3 A (see  FIG. 11 ), and in a second type (wound structure type), the electrode assembly  10 B is formed by winding an electrode unit including a positive electrode  1 ,  1 B, a negative electrode  2 ,  2 B and a separator  3 ,  3 B in a roll form (see  FIG. 12 ). Furthermore, as a third type, the electrode assembly may have what is called a stack-and-fold structure that is formed by folding an electrode unit of a positive electrode, a negative electrode, a separator, and a negative electrode (particularly preferably an electrode unit (a laminate body) extending longer in one direction). 
     In one mode, the electrode assembly  10  may include at least two sub-electrode assemblies of planar lamination structure type (see  FIG. 2 ). For example, the electrode assembly  10  may include a first planar lamination structure type sub electrode assembly  10 A 1  and a second planar lamination structure type sub electrode assembly  10 A 2 . The first planar lamination structure type sub electrode assembly  10 A 1  is formed by laminating a plurality of unit electrode units including a positive electrode  1 A 1 , a negative electrode  2 A 1 , and a separator  3 A 1 . Similarly, the second planar lamination structure type sub electrode assembly  10 A 2  is formed by laminating a plurality of unit electrode units including a positive electrode  1 A 2 , a negative electrode  2 A 2 , and a separator  3 A 2 . 
     In this case, for example, in the electrode assembly  10 , the second planar lamination structure type sub electrode assembly  10 A 2  has a width dimension larger than a width dimension of the first planar lamination structure type sub electrode assembly  10 A 1  in a cross-sectional view as shown in  FIG. 2 , and may be mutually in contact with the first planar lamination structure type sub electrode assembly  10 A 1  in such as manner as being positioned below the first planar lamination structure type sub electrode assembly  10 A 1 . By having such a structure, the electrode assembly  10  may have a step structure in the cross-sectional view. 
     Hereinafter, the electrode assembly which is a constituent of the secondary battery according to one embodiment of the present invention will be described on the premise that it has a step structure in a cross-sectional view. Note that, hereinafter, the term “connecting tab” referred to in the present description means a portion corresponding to an uncoated portion of an electrode (positive electrode/negative electrode) and not joined to a current collector lead. The term “connecting portion” as used in the present description means one in which each of a plurality of connecting tabs can be connected to each other. The term “extended tab” in the present description means a portion corresponding to an uncoated portion of an electrode (positive electrode/negative electrode) and joined to a current collector lead. Further, the term “extended portion” as used in the present description is one in which each of a plurality of extended tabs can be connected to each other. 
     In such a case, in one embodiment of the present invention, the electrode assembly  10  having the step structure has a first region  10 X being relatively high and a second region  10 Y being relatively low adjacent to the first region  10 X in a cross-sectional view as shown in  FIG. 3 . 
     The term “adjacent” as used here may include not only a state in which the first region  10 X and the second region  10 Y which are constituents of a single electrode assembly are continuous, but also a state in which one electrode assembly (corresponding to the first region) and the other electrode assembly (corresponding to the second region) functioning as separate constituent bodies are continuous. In other words, from the viewpoint that the electrode assembly  10  including the first region  10 X and the second region  10 Y can be electrically connected as a whole, each of the positive electrode and the negative electrode in the second region  10 Y and each of the positive electrode and the negative electrode in the first region  10 X may be configured to be continuous with each other. 
     In one embodiment of the present invention, each of positive electrode side connecting tabs  13 X included in each of “all” positive electrodes configured with the positive electrode  1 A 1  of the first planar lamination structure type sub electrode assembly  10 A 1  in the first region  10 X and the positive electrode  1 A 2  of the second planar lamination structure type sub electrode assembly  10 A 2  in the first region  10 X is joined to each other, so that a positive electrode side connecting portion  14 X is formed as shown in  FIG. 3 . Specifically, for example, as shown in  FIG. 4 , the positive electrode side connecting portion  14 X is formed by joining end portions of a plurality of the positive electrode side connecting tabs  13 X so as to form a bundle as a whole. A joining method is not particularly limited, but laser welding, ultrasonic welding, and the like can be mentioned. 
     Similarly, in one embodiment of the present invention, each of negative electrode side connecting tabs  23 X included in each of “all” negative electrodes configured with the negative electrode  2 A 1  of the first planar lamination structure type sub electrode assembly  10 A 1  in the first region  10 X and the negative electrode  2 A 2  of the second planar lamination structure type sub electrode assembly  10 A 2  in the first region  10 X is joined to each other, so that a negative electrode side connecting portion  24 X is formed as shown in  FIG. 3 . Specifically, for example, as shown in  FIG. 5 , the negative electrode side connecting portion  24 X is formed by joining end portions of a plurality of the negative electrode side connecting tabs  23 X so as to form a bundle as a whole. A joining method is not particularly limited, but laser welding, ultrasonic welding, and the like can be mentioned. 
     In one embodiment of the present invention, as shown in  FIGS. 3 and 6 , a single positive electrode side extended tab  13 Y included in at least one positive electrode in the second region  10 Y, for example, the positive electrode  1 A 2  of the second planar lamination structure type sub electrode assembly  10 A 2  may be electrically connected to the external terminal  30   a  via a positive electrode side current collector lead  40   a . For example, the positive electrode side extended tab  13 Y may be electrically connected to the external terminal  30   a  “provided on the end portion side surface  20   a   2  of the first step portion  20   a ” via the positive electrode side current collector lead  40   a . Note that the single positive electrode side extended tab  13 Y is not limited to be connected to the external terminal  30   a  with the positive electrode side current collector lead  40   a  interposed between them. For example, the single positive electrode side extended tab  13 Y may be connected to the positive electrode side collector lead having a function of an external terminal. 
     Similarly, in one embodiment of the present invention, as shown in  FIGS. 3 and 6 , a single negative electrode side extended tab  23 Y included in at least one negative electrode in the second region  10 Y, for example, the negative electrode  2 A 2  of the second planar lamination structure type sub electrode assembly  10 A 2  may be electrically connected to the external terminal  30   b  via a negative electrode side current collector lead  40   b . For example, the negative electrode side extended tab  23 Y may be electrically connected to the external terminal  30   b  “provided on the end portion side surface  20   a   2  of the first step portion  20   a ” via the negative electrode side current collector lead  40   b . Note that the single negative electrode side extended tab  23 Y is not limited to be connected to the external terminal  30   b  with the negative electrode side current collector lead  40   b  interposed between them. For example, the single negative electrode side extended tab  23 Y may be connected to the negative electrode side collector lead having a function of an external terminal. 
     As shown in  FIGS. 3 and 6 , in a state where all the positive electrode side connecting tabs  13 X are joined to each other in the first region  10 X of the electrode assembly  10  so that the positive electrode side connecting portion  14 X is formed, in order to be electrically connected to the positive electrode side external terminal  30   a  via the positive electrode side current collector lead  40   a  joined to the positive electrode side extended tab  13 Y positioned in the second region  10 Y, at least one positive electrode needs to include both the positive electrode side connecting tab  13 X and the positive electrode side extended tab  13 Y in the plan view. Similarly, as shown in  FIGS. 3 and 6 , in a state where all the negative electrode side connecting tabs  23 X are joined to each other in the first region  10 X of the electrode assembly  10  so that the negative electrode side connecting portion  24 X is formed, in order to be electrically connected to the negative electrode side external terminal  30   b  via the negative electrode side current collector lead  40   b  joined to the negative electrode side extended tab  23 Y positioned in the second region  10 Y, at least one negative electrode needs to include both the negative electrode side connecting tab  23 X and the negative electrode side extended tab  23 Y in the plan view. 
     That is, in one embodiment of the present invention, the extended tab from the side of the second region  10 Y is electrically connected to, for example, the external terminal  30  “provided on the end portion side surface  20   a   2  of the first step portion  20   a ” via the current collector lead. By employing such a configuration, an external terminal electrically connected to the extended tab via the current collector lead does not always need to be provided on the second step portion  20   b  side of the exterior body  20 . In other words, even if all the positive electrodes are connected to each other with each of the positive electrode side connecting tabs  13 X interposed between them by formation of the positive electrode side connecting portion  14 X in the first region  10 X, and all the negative electrodes are connected to each other with each of the negative electrode side connecting tabs  23 X interposed between them by formation of the negative electrode side connecting portion  24 X in the first region  10 X, the external terminal  30  may be provided not on the second step portion  20   b  side of the exterior body  20  but on the first step portion  20   a  side. In view of the above, according to one embodiment of the present invention, it is possible to prevent an installation location of the external terminal from being limited to the second step portion  20   b  side of the exterior body  20 . That is, according to one embodiment of the present invention, the degree of freedom of installation of the external terminal can be increased. 
     For example, as shown in  FIG. 1 ,  FIG. 3 , and  FIG. 6 , when the positive electrode side extended tab  13 Y may be electrically connected to a single positive electrode side external terminal  30   a  via the positive electrode side current collector lead  40   a , the number of wires connecting the positive electrode side external terminal  30   a  and the substrate can also be set to only one. Therefore, it is possible to suppress the complication of a wiring structure which may occur when a plurality of positive electrode side external terminals are used. In other words, the wire structure connecting the positive electrode side external terminal  30   a  and the substrate can be simplified. Similarly, for example, as shown in  FIG. 1 ,  FIG. 3 , and  FIG. 6 , when the negative electrode side extended tab  23 Y may be electrically connected to a single negative electrode side external terminal  30   b  via the negative electrode side current collector lead  40   b , the number of wires connecting the negative electrode side external terminal  30   b  and the substrate can also be set to only one. Therefore, it is possible to suppress the complication of a wiring structure which may occur when a plurality of negative electrode side external terminals are used. In other words, the wiring structure connecting the negative electrode side external terminal  30   b  and the substrate can be simplified. 
     Further, in one embodiment of the present invention, instead of the second region  10 Y of the electrode assembly  10  electrically connected to an external terminal, in the first region  10 X not electrically connected to the external terminal, all the positive electrodes are connected to each other with each of the positive electrode side connecting tabs  13 X interposed between them by formation of the positive electrode side connecting portion  14 X, and all the negative electrodes are connected to each other with the negative electrode side connecting tabs  23 X interposed between them by formation of the negative electrode side connecting portion  24 X. That is, since all the positive electrodes are mutually connected by formation of the single positive electrode side connecting portion  14 X, the electrical connection between the positive electrodes can be stabilized. Further, since all of the negative electrodes are mutually connected by formation of the single negative electrode side connecting portion  24 X, the electrical connection between the negative electrodes can be stabilized. As described above, it is possible to stably generate a cell reaction in all the electrodes, so that the battery characteristics may be improved. 
     In one embodiment of the present invention, at least one of the positive electrodes  1 A 2  in the second region  10 Y may be electrically connected to the external terminal  30   a  via the positive electrode side current collector lead  40   a . For example, in a case where only a single one of the positive electrodes  1 A 2  is electrically connected to an external terminal in the second region  10 Y, as shown in  FIG. 6 , the positive electrode side extended tab  13 Y may be directly connected to the positive electrode side current collector lead  40   a  without the positive electrode side extended portion, so that electrical connection between the positive electrode side extended tab  13 Y and the external terminal  30   a  via the positive electrode side current collector lead  40   a , that is, electrical connection between the positive electrode  1 A 2  and the external terminal  30   a , may be relatively simplified. Further, similarly, in one embodiment of the present invention, at least one of the negative electrodes  2 A 2  in the second region  10 Y may be electrically connected to the external terminal  30   b  via the negative electrode side current collector lead  40   b . For example, in a case where only a single one of the negative electrodes  2 A 2  is electrically connected to an external terminal in the second region  10 Y, as shown in  FIG. 6 , the negative electrode side extended tab  23 Y may be directly connected to the negative electrode side current collector lead  40   b  without the negative electrode side extended portion, so that electrical connection between the negative electrode side extended tab  23 Y and the external terminal  30   b  via the negative electrode side current collector lead  40   b , that is, electrical connection between the negative electrode  2 A 2  and the external terminal  30   b , may be relatively simplified. 
     Further, as shown in  FIG. 3 , when only the positive electrode side extended tab  13 Y of a single one of the positive electrodes  1 A 2  is electrically connected to the external terminal  30   a  in the second region  10 Y, excessive decrease in the electric resistance of the positive electrode can be suppressed. In this manner, it is possible to suppress heat generation that may occur, for example, during internal short circuit of the secondary battery according to one embodiment of the present invention, thereby making it possible to improve the safety of the secondary battery. 
     The configuration is not limited to the above mode, and, for example, as shown in  FIGS. 7 and 8 , the positive electrode side extended portion  14 Y may be formed by mutually joining the positive electrode side extended tabs  13 Y of at least two positive electrodes in the second region  10 Y, for example, the positive electrodes  1 A 2  of the second planar lamination structure type sub electrode assembly  10 A 2 . Specifically, for example, as shown in  FIG. 8 , the positive electrode side extended portion  14 Y is formed by joining end portions of the positive electrode side extended tabs  13 Y so as to form a bundle as a whole. A joining method is not particularly limited, but laser welding, ultrasonic welding, and the like can be mentioned. 
     In one mode, part of the positive electrode side extended tab  13 Y in the formation region of the positive electrode side extended portion  14 Y may be configured to be electrically connected to the external terminal  30   a  via the positive electrode side current collector lead  40   a . For example, part of the positive electrode side extended tab  13 Y in the formation region of the positive electrode side extended portion  14 Y may be electrically connected to the external terminal  30   a  “provided on the end portion side surface  20   a   2  of the first step portion  20   a ” via the positive electrode side current collector lead  40   a . Note that part of the positive electrode side extended tab  13 Y in the formation region of the positive electrode side extended portion  14 Y does not need to be always electrically connected to the external terminal  30   a  via the positive electrode side current collector lead  40   a . For example, on the premise that the positive electrode side extended portion  14 Y is formed, part of the positive electrode side extended tab  13 Y in another region other than the formation region of the positive electrode side extended portion  14 Y may be configured to be electrically connected to the external terminal  30   a  via the positive electrode side current collector lead  40   a . Further, part of the positive electrode side extended tab  13 Y is not limited to be connected to the external terminal  30   a  with the positive electrode side current collector lead  40   a  interposed between them. For example, part of the positive electrode side extended tab  13 Y may be connected to the positive electrode side current collector lead having the function of the external terminal. 
     Similarly, for example, as shown in  FIGS. 7 and 9 , the negative electrode side extended portion  24 Y may be formed by mutually joining the negative electrode side extended tabs  23 Y of at least two negative electrodes in the second region  10 Y, for example, the negative electrodes  2 A 2  of the second planar lamination structure type sub electrode assembly  10 A 2 . Specifically, for example, as shown in  FIG. 7 , the negative electrode side extended portion  24 Y is formed by joining end portions of the negative electrode side extended tabs  23 Y so as to form a bundle as a whole. A joining method is not particularly limited, but laser welding, ultrasonic welding, and the like can be mentioned. 
     In one mode, part of the negative electrode side extended tab  23 Y in the formation region of the negative electrode side extended portion  24 Y may be configured to be electrically connected to the external terminal  30   b  via the negative electrode side current collector lead  40   b . For example, part of the negative electrode side extended tab  23 Y in the formation region of the negative electrode side extended portion  24 Y may be electrically connected to the external terminal  30   b  “provided on the end portion side surface  20   a   2  of the first step portion  20   a ” via the negative electrode side current collector lead  40   b . Note that part of the negative electrode side extended tab  23 Y in the formation region of the negative electrode side extended portion  24 Y does not need to be always electrically connected to the external terminal  30   b  via the negative electrode side current collector lead  40   b . For example, on the premise that the negative electrode side extended portion  24 Y is formed, part of the negative electrode side extended tab  23 Y in another region other than the formation region of the negative electrode side extended portion  24 Y may be configured to be electrically connected to the external terminal  30   b  via the negative electrode side current collector lead  40   b . Further, part of the negative electrode side extended tab  23 Y is not limited to be connected to the external terminal  30   b  with the negative electrode side current collector lead  40   b  interposed between them. For example, part of the negative electrode side extended tab  23 Y may be connected to the negative electrode side current collector lead having the function of the external terminal. 
     As shown in  FIGS. 7 and 8 , in a state where all the positive electrode side connecting tabs  13 X are joined to each other in the first region  10 X of the electrode assembly  10  by the formation of the positive electrode side connecting portion  14 X, in order to be electrically connected to the positive electrode side external terminal  30   a  via the positive electrode side current collector lead  40   a  joined to the positive electrode side extended portion  14 Y positioned in the second region  10 Y, at least two positive electrodes need to include both the positive electrode side connecting tab  13 X and the positive electrode side extended tab  13 Y in the plan view. Similarly, as shown in  FIGS. 7 and 9 , in a state where all the negative electrode side connecting tabs  23 X are joined to each other in the first region  10 X of the electrode assembly  10  by the formation of the negative electrode side connecting portion  24 X, in order to be electrically connected to the negative electrode side external terminal  30   b  via the negative electrode side current collector lead  40   b  joined to the negative electrode side extended portion  24 Y positioned in the second region  10 Y, at least two negative electrodes need to include both the negative electrode side connecting tab  23 X and the negative electrode side extended tab  23 Y in the plan view. 
     As shown in  FIG. 7  and  FIG. 8 , in the present mode, the positive electrode side extended tab  13 Y of at least two of the positive electrodes  1 A 2  in the second region  10 Y is electrically connected to the external terminal  30   a  via the positive electrode side extended portion  14 Y, therefore it is possible to suppress the concentration of electric resistance on one positive electrode compared to a case where only a single one of the positive electrodes  1 A 2  is electrically connected to the external terminal  30   a  in the second region  10 Y. Further, similarly, as shown in  FIG. 7  and  FIG. 9 , in the present mode, the negative electrode side extended tab  23 Y of at least two of the negative electrodes  2 A 2  in the second region  10 Y is electrically connected to the external terminal  30   b  via the negative electrode side extended portion  24 Y, therefore it is possible to suppress the concentration of electric resistance on one negative electrode compared to a case where only a single one of the negative electrodes  2 A 2  is electrically connected to the external terminal  30   b  in the second region  10 Y. From the above, it is possible to relatively reduce the electric resistance generated in the secondary battery  100  according to one embodiment of the present invention as a whole. 
     In one mode, as shown in  FIGS. 1 and 7 , the positive electrode side connecting portion  14 X and the negative electrode side connecting portion  24 X, and the positive electrode side extended portion  14 Y and the negative electrode side extended portion  24 Y are preferably configured to be arranged only on one side in the exterior body  20 . 
     When such a configuration is employed, as compared with a case where, for example, the positive electrode side connecting portion  14 X and the positive electrode side extended portion  14 Y are arranged on one side of the electrode assembly  10 , and the negative electrode side connecting portion  24 X and the negative electrode side extended portion  24 Y are disposed on the other side facing the one side of the electrode assembly  10 , a width dimension of the electrode assembly  10  can be relatively reduced in the plan view due to that, for example, the negative electrode side connecting portion  24 X and the negative electrode side extended portion  24 Y do not exist on the other side of the electrode assembly  10 . Therefore, due to the relative reduction of the width dimension of the electrode assembly  10 , it is possible to relatively reduce dimensions of the exterior body  20  accommodating the electrode assembly  10  therein. That is, dimensions of the secondary battery  100  according to one embodiment of the present invention can be made relatively small. 
     The above description is made based on the electrode assembly  10  including the first planar lamination structure type sub electrode assembly  10 A 1  and the second planar lamination structure type sub electrode assembly  10 A 2 . However, the present invention is not limited to the above, and a mode described below may be employed if the electrode assembly has a step structure in the cross-sectional view. 
     For example, as shown in  FIG. 10 , a configuration of an electrode assembly  10 ′ including a planar lamination structure type sub electrode assembly and a wound structure type sub electrode assembly may be employed. A planar lamination structure type sub electrode assembly  10 A 1 ′ is formed by laminating a plurality of unit electrode units including a positive electrode  1 A 1 ′, a negative electrode  2 A 1 ′, and a separator  3 A 1 ′. On the other hand, a wound structure type sub electrode assembly  10 B 1 ′ is an electrode unit including the positive electrode  1 B 1 ′, the negative electrode  2 B 1 ′ and the separator  3 B 1 ′ wound in a roll. In this case, for example, in the electrode assembly  10 ′, the wound structure type sub electrode assembly  10 B 1  has a width dimension larger than a width dimension the planar lamination structure type sub electrode assembly  10 A 1  in the cross-sectional view as shown in  FIG. 10 , and may be mutually in contact with the planar lamination structure type sub electrode assembly  10 A 1  in such as manner as being positioned below the planar lamination structure type sub electrode assembly  10 A 1 . 
     The configuration is not limited to the above, and, in still another mode, the planar laminate structure type sub electrode assembly has a width dimension larger than the width dimension of the wound structure type sub electrode assembly in the cross-sectional view, and may be in contact with the wound structure type sub electrode assembly in such a manner as being positioned below the wound structure type sub electrode assembly. 
     In yet another mode, the electrode assembly may include at least two wound structure type sub electrode assemblies (not shown). For example, the electrode assembly may include a first wound structure type sub electrode assembly and a second wound structure type sub electrode assembly. Both of the first wound structure type sub electrode assembly and the second wound structure type sub electrode assembly are formed by winding an electrode unit including a positive electrode, a negative electrode, and a separator in a roll. In this case, for example, in the electrode assembly, the second wound structure type sub electrode assembly has a width dimension larger than a width dimension of the first wound structure type sub electrode assembly in the cross-sectional view, and may be mutually in contact with the first wound structure type sub electrode assembly in such a manner as being positioned below the first wound structure type sub electrode assembly. 
     Note that, although detailed description, which overlaps the content described in the mode (see  FIG. 3 ) in which at least two planar lamination structure type sub electrode assemblies are included, is avoided, if the electrode assembly has a step structure in the cross-sectional view, a characteristic configuration is preferably employed from two viewpoints described below also in the mode (see  FIG. 10 ) in which the electrode assembly includes at least the planar lamination structure type sub electrode assembly and the wound structure type sub electrode assembly. Specifically, in this mode as well, from the viewpoint of “avoiding that the installation location of the external terminal is limited to the second step portion  20   b  side of the exterior body  20 , thereby increasing the degree of freedom in installation of the external terminal”, and the viewpoint of “stably generating a cell reaction in all electrodes and thereby improving battery characteristics”, a configuration described below is preferably employed. 
     Specifically, the positive electrode side connecting tabs included in all the positive electrodes configured with the positive electrode  1 A 1 ′ of the planar lamination structure type sub electrode assembly  10 A 1 ′ in the first region being relatively high of the electrode assembly  10 ′ in the cross-sectional view and the positive electrode  1 B 1 ′ of the wound structure type sub electrode assembly  10 B 1 ′ in the first region are preferably connected to each other by formation of the positive electrode side connecting portion. Further, at the same time, the positive electrode side extended tab included in the positive electrode  1 B 1 ′ of the wound structure type sub electrode assembly  10 B 1 ′ in the second region being relatively low of the electrode assembly  10 ′ is preferably electrically connected to the positive electrode side external terminal  30   a  (see  FIG. 1 , for example) via the positive electrode side current collector lead. Similarly, the negative electrode side connecting tabs included in all the negative electrodes configured with the negative electrode  2 A 1 ′ of the planar lamination structure type sub electrode assembly  10 A 1 ′ in the first region being relatively high of the electrode assembly  10 ′ in the cross-sectional view and the negative electrode  2 B 1 ′ of the wound structure type sub electrode assembly  10 B 1 ′ in the first region are preferably connected to each other by formation of the negative electrode side connecting portion. Further, at the same time, the negative electrode side extended tab included in the negative electrode  2 B 1 ′ of the wound structure type sub electrode assembly  10 B 1 ′ in the second region being relatively low of the electrode assembly  10 ′ is preferably electrically connected to the negative electrode side external terminal  30   b  (see  FIG. 1 , for example) via the negative electrode side current collector lead. 
     Similarly, from the above two viewpoints, a characteristic configuration is preferably employed also in a mode (not shown) in which the electrode assembly includes at least two wound structure type sub electrode assemblies in which width dimensions are different from each other in the cross-sectional view. Specifically, the positive electrode side connecting tabs included in all the positive electrodes configured with the positive electrode of the first wound structure type sub electrode assembly in the first region being relatively high of the electrode assembly in the cross-sectional view and the positive electrode of the second wound structure type sub electrode assembly in the first region are preferably connected to each other by formation of the positive electrode side connecting portion. Further, at the same time, the positive electrode side extended tab included in the positive electrode of the second wound structure type sub electrode assembly in the second region being relatively low of the electrode assembly is preferably electrically connected to the positive electrode side external terminal  30   a  (see  FIG. 1 , for example) via the positive electrode side current collector lead. Similarly, the negative electrode side connecting tabs included in all the negative electrodes configured with the negative electrode of the first wound structure type sub electrode assembly in the first region being relatively high of the electrode assembly in the cross-sectional view and the negative electrode of the second wound structure type sub electrode assembly in the first region are preferably connected to each other by formation of the negative electrode side connecting portion. Further, at the same time, the negative electrode side extended tab included in the negative electrode of the second wound structure type sub electrode assembly in the second region being relatively low of the electrode assembly is preferably electrically connected to the negative electrode side external terminal  30   b  (see  FIG. 1 , for example) via the negative electrode side current collector lead. 
     The secondary battery according to one embodiment of the present invention can be used in various fields in which storage of electricity is expected. Although it is merely an example, the secondary battery according to one embodiment of the present invention, in particular, a non-aqueous electrolyte secondary battery, can be used in the fields of electric, information and communications (for example, mobile equipment fields, such as mobile phones, smart phones, notebook computers, digital cameras, activity meters, arm computers, electronic papers, and the like) in which mobile equipment is used, home and small industrial applications (for example, electric tools, golf carts, domestic, nursing care, and industrial robot fields), large industrial applications (for example, forklifts, elevators, harbor port crane fields), transportation system fields (for example, fields of hybrid vehicles, electric vehicles, buses, trains, electric assisted bicycles, electric motorcycles, and the like), electric power system applications (for example, fields of various electric power generation, load conditioners, smart grids, general home electric storage systems, and the like), IoT fields, space and deep-sea applications (for example, fields of space explorers, research submarines, and the like), and the like. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
         
         
           
               1 : Positive electrode 
               2 : Negative electrode 
               3 : Separator 
               1 A: Positive electrode 
               2 A: Negative electrode 
               3 A: Separator 
               1 A 1 : Positive electrode 
               2 A 1 : Negative electrode 
               3 A 1 : Separator 
               1 A 1 ′: Positive electrode 
               2 A 1 ′: Negative electrode 
               3 A 1 ′: Separator 
               1 A 2 : Positive electrode 
               2 A 2 : Negative electrode 
               3 A 2 : Separator 
               1 B: Positive electrode 
               2 B: Negative electrode 
               3 B: Separator 
               1 B 1 ′: Positive electrode 
               2 B 1 ′: Negative electrode 
               3 B 1 ′: Separator 
               10 : Electrode assembly 
               10 X: First region of the electrode assembly 
               10 Y: Second region of the electrode assembly 
               10 A: Planar lamination structure type electrode assembly 
               10 A 1 : First planar lamination structure type sub electrode assembly 
               10 A 1 ′: Planar lamination structure type sub electrode assembly 
               10 A 2 : Second planar lamination structure type sub electrode assembly 
               10 B 1 ′: Wound structure type sub electrode assembly 
               11 : Positive electrode current collector 
               12 : Positive electrode material layer 
               13 : Positive electrode side extended tab 
               13 X: Positive electrode side connecting tab 
               13 Y: Positive electrode side extended tab 
               14 X: Positive electrode side connecting portion 
               14 X 1 : First positive electrode side connecting portion 
               14 X 2 : Second positive electrode side connecting portion 
               14 Y: Positive electrode side extended portion 
               14 Y 1 : First positive electrode side extended portion 
               14 Y 2 : Second positive electrode side extended portion 
               20 : Exterior body 
               20   a : First step portion of the exterior body 
               20   a   1 : Top surface of the first step portion 
               20   a   2 : End portion side surface of the first step portion 
               20   b : Second step portion of the exterior body 
               20   b   1 : Top surface of the second step portion 
               20   b   2 : Step surface 
               21 : Negative electrode current collector 
               22 : Negative electrode material layer 
               23 : Negative electrode side extended tab 
               23 X: Negative electrode side connecting tab 
               23 Y: Negative electrode side extended tab 
               24 X: Negative electrode side connecting portion 
               24 X 1 : First negative electrode side connecting portion 
               24 X 2 : Second negative electrode side connecting portion 
               24 Y: Negative electrode side extended portion 
               24 Y 1 : First negative electrode side extended portion 
               24 Y 2 : Second negative electrode side extended portion 
               30 : External terminal 
               30   a : Positive electrode side external terminal 
               30   b : Negative electrode side external terminal 
               40   a : Positive electrode side current collector lead 
               40   b : Negative electrode side current collector lead 
               100 : Secondary battery 
             W 1 : Width dimension of the top surface of the first step portion 
             W 2 : Width dimension of the top surface of the second step portion 
             W 3 : Width dimension of the step surface 
             h 1 : Height dimension of the top surface of the first step portion 
             h 2 : Height dimension of the top surface of the second step portion 
             h 3 : Height dimension of the step surface 
             θ: Angle between the step surface and the top surface of the first step portion