Patent Publication Number: US-2023163433-A1

Title: Secondary battery, electronic equipment, and electric tool

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of PCT patent application no. PCT/JP2021/031913, filed on Aug. 31, 2021, which claims priority to Japanese patent application no. JP2020-150288, filed on Sep. 8, 2020, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present application relates to a secondary battery, electronic equipment, and an electronic tool. 
     Development of lithium ion batteries has expanded to applications that require high output power, including electric tools and electric automobiles. One of methods to achieve high output power is a high-rate discharge in which a relatively large current is fed from a battery. 
     For example, a structure and a manufacturing method of a battery is provided that makes it possible to increase current collection efficiency and reduce a temperature rise during charging and discharging, as compared with existing techniques. Such a battery is obtained by providing an electrode wound body in which a positive electrode and a negative electrode are stacked on each other with a separator interposed therebetween and are wound, bending a part of the positive electrode not covered with an active material toward a center hole of the electrode wound body, and welding a current collector plate. See, for example, Japanese Unexamined Patent Application Publication No. 2000-294222. 
     SUMMARY 
     The present application relates to a secondary battery, electronic equipment, and an electronic tool. 
     Employing a technique as described in the Background section can sometimes generate an outwardly turned-up state of a winding end part of a positive electrode in the course of a process after forming an electrode plate group by winding electrodes in a spiral shape, or in the course of a conveyance process. When the electrode plate group is placed into a molding jig and pressed with a pressing tool through an opening at an end of the molding jig, the turned-up portion can break through a separator located in an outermost wind of an electrode wound body to thereby come into contact with a negative electrode. This can result in the occurrence of an internal short circuit. 
     The present application relates to providing a battery that suppresses the occurrence of an internal short circuit due to a turned-up portion generated in the positive electrode according to an embodiment. 
     In order to solve the above-described problem, the present application, in an embodiment, provides a secondary battery including an electrode wound body, a positive electrode current collector plate, and an outer package can. The electrode wound body includes a positive electrode having a band shape and a negative electrode having a band shape. The positive electrode and the negative electrode are stacked on each other with a separator interposed therebetween, and are wound. The outer package can contains the electrode wound body and the positive electrode current collector plate. The positive electrode includes a positive electrode active material covered part in which a positive electrode foil is covered with a positive electrode active material layer, and a positive electrode active material uncovered part. The secondary battery includes a flat surface formed by the positive electrode active material uncovered part that protrudes from one end of the electrode wound body being bent toward a central axis of the electrode wound body and portions of the positive electrode active material uncovered part overlapping each other. The flat surface is joined to the positive electrode current collector plate. The positive electrode active material uncovered part has a cutout at one end on an outer periphery side of the electrode wound body. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a sectional view of a battery according to an embodiment. 
         FIG.  2    is a diagram illustrating an example of an arrangement relationship between a positive electrode, a negative electrode, and a separator in an electrode wound body. 
         FIG.  3    includes views A and B, where view A is a plan view of a positive electrode current collector plate, and where view B is a plan view of a negative electrode current collector plate. 
         FIG.  4    includes views A to F which are diagrams describing an assembly process of the battery according to an embodiment. 
         FIG.  5    is a diagram for describing positions of laser welding marks. 
         FIG.  6    is a diagram for describing a cutout according to one embodiment. 
         FIG.  7    includes views A to C which are diagrams for describing Example 1, Comparative example 1, and Comparative example 2. 
         FIG.  8    includes views A to C which are diagrams for describing Comparative example 1 and Comparative example 2. 
         FIG.  9    includes views A-1 to D-1 and views A-2 to D-2 which are diagrams for describing Examples 2 to 5. 
         FIG.  10    is a diagram for describing a modification. 
         FIG.  11    is a coupling diagram for use to describe a battery pack as an application example of the present technology. 
         FIG.  12    is a coupling diagram for use to describe an electric tool as an application example of the present technology. 
         FIG.  13    is a coupling diagram for use to describe an electric vehicle as an application example of the present technology. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the present technology are described below in further detail, without limitation, including with reference to the drawings and examples. 
     In an embodiment, a lithium ion battery having a cylindrical shape will be described as an example of a secondary battery. 
     Description is given first of an overall configuration of the lithium ion battery.  FIG.  1    is a schematic sectional view of a lithium ion battery  1 . The lithium ion battery  1  is, for example, a cylindrical lithium ion battery  1  in which an electrode wound body  20  is contained inside a battery can  11 , as illustrated in  FIG.  1   . 
     Specifically, the lithium ion battery  1  includes, for example, a pair of insulating plates  12  and  13  and the electrode wound body  20  inside the battery can  11  having a cylindrical shape. Note that the lithium ion battery  1  may further include, for example, one or more of devices and members including, without limitation, a thermosensitive resistive device or a PTC device and a reinforcing member, inside the battery can  11 . 
     The battery can  11  is a member that contains the electrode wound body  20 , for example. The battery can  11  is, for example, a cylindrical container with one end face open and another end face closed. That is, the battery can  11  has one open end face (an open end face  11 N). The battery can  11  includes, for example, one or more of metal materials including, without limitation, iron, aluminum, and alloys thereof. Further, for example, the battery can  11  may have a surface plated with one or more of metal materials including, without limitation, nickel. 
     The insulating plates  12  and  13  are disk-shaped plates each having a surface that is generally perpendicular to a central axis of the electrode wound body  20 . Further, the insulating plate  12  and  13  are disposed with the wound electrode body  20  interposed therebetween, for example. 
     A battery cover  14  and a safety valve mechanism  30  are crimped to the open end face  11 N of the battery can  11  via a gasket  15  to thereby provide a crimp structure  11 R. The battery can  11  is thus sealed in a state where the electrode wound body  20  and other components are contained inside the battery can  11 . 
     The battery cover  14  is a member that closes the open end face  11 N of the battery can  11  in the state where the electrode wound body  20  and the other components are contained inside the battery can  11 , for example. The battery cover  14  includes, for example, a material similar to the material included in the battery can  11 . A middle region of the battery cover  14  protrudes in a +Z direction, for example. A region other than the middle region, that is, a peripheral region, of the battery cover  14  is thus in contact with the safety valve mechanism  30 , for example. 
     The gasket  15  is a member that is interposed, for example, between the battery can  11  (a bent part  11 P) and the battery cover  14  to thereby seal a gap between the bent part  11 P and the battery cover  14 . Note that the gasket  15  may have a surface coated with a material such as asphalt. 
     The gasket  15  includes, for example, one or more of insulating materials. Although not particularly limited in kind, the insulating material may be, for example, a polymer material such as polybutylene terephthalate (PBT) or polypropylene (PP). In particular, the insulating material may be polybutylene terephthalate. A reason for this is that the gap between the bent part  11 P and the battery cover  14  is sufficiently sealed while the battery can  11  and the battery cover  14  are electrically separated from each other. 
     The safety valve mechanism  30  releases the sealed state of the battery can  11  on an as-needed basis when, for example, a pressure inside the battery can  11 , i.e., an internal pressure of the battery can  11 , is increased. Examples of a cause of the increase in the internal pressure of the battery can  11  include a gas generated due to a decomposition reaction of an electrolytic solution during charging and discharging. 
     In the cylindrical lithium ion battery, a positive electrode  21  having a band shape and a negative electrode  22  having a band shape that are stacked on each other with a separator  23  interposed therebetween and are wound in a spiral shape are contained in the battery can  11  in a state of being impregnated with the electrolytic solution. The positive electrode  21  includes a positive electrode foil  21 A with a positive electrode active material layer provided on one of or each of both sides of the positive electrode foil  21 A. The positive electrode foil  21 A includes a metal foil including, for example, aluminum or an aluminum alloy. The negative electrode  22  includes a negative electrode foil  22 A with a negative electrode active material layer provided on one of or each of both sides of the negative electrode foil  22 A. The negative electrode foil  22 A includes a metal foil including, for example, nickel, a nickel alloy, copper, or a copper alloy. The separator  23  is a porous insulating film. The separator  23  electrically insulates the positive electrode  21  and the negative electrode  22  from each other, and allows movement of substances including, without limitation, ions and the electrolytic solution. 
     The positive electrode active material layer and the negative electrode active material layer cover most of the positive electrode foil  21 A and most of the negative electrode foil  22 A, respectively, but do not cover, on purpose, respective parts of the foils located at and near respective one ends in a short-axis direction of the bands. Hereinafter, where appropriate, the parts not covered with the respective active material layers will be referred to as active material uncovered parts  21 C and  22 C, and parts covered with the respective active material layers will be referred to as active material covered parts  21 B and  22 B. In the electrode wound body  20  of the cylindrical battery, the positive electrode  21  and the negative electrode  22  are laid over each other and wound with the separator  23  interposed therebetween in such a manner that the active material uncovered part  21 C of the positive electrode and the active material uncovered part  22 C of the negative electrode face toward opposite directions. 
       FIG.  2    illustrates an example of a pre-winding structure in which the positive electrode  21 , the negative electrode  22 , and the separator  23  are stacked on each other. The active material uncovered part  21 C of the positive electrode (a shaded portion on the upper side in  FIG.  2   ) has a width A, and the active material uncovered part  22 C of the negative electrode (a shaded portion on the lower side in  FIG.  2   ) has a width B. In an embodiment, A may be greater than B. For example, A is 7 (mm), and B is 4 (mm). A portion of the active material uncovered part  21 C of the positive electrode protruding from one end in a width direction of the separator  23  has a length C. A portion of the active material uncovered part  22 C of the negative electrode protruding from another end in the width direction of the separator  23  has a length D. In an embodiment, C may be greater than D. For example, C is 4.5 (mm), and D is 3 (mm). 
     The active material uncovered part  21 C of the positive electrode includes, for example, aluminum, and the active material uncovered part  22 C of the negative electrode includes, for example, copper. Thus, the active material uncovered part  21 C of the positive electrode is typically softer, that is, lower in Young&#39;s modulus, than the active material uncovered part  22 C of the negative electrode. Accordingly, in an embodiment, both A&gt;B and C&gt;D may be satisfied. In such a case, when the active material uncovered part  21 C of the positive electrode and the active material uncovered part  22 C of the negative electrode are simultaneously bent with equal pressures from both electrode sides, respective heights of the bent portions as measured from respective ends of the separator  23  are almost the same between the positive electrode  21  and the negative electrode  22  in some cases. At this time, the active material uncovered parts  21 C and  22 C are bent and portions of each of the active material uncovered parts  21 C and  22 C appropriately overlap each other. This makes it possible to easily join the active material uncovered parts  21 C and  22 C to current collector plates  24  and  25 , respectively, by laser welding. In an embodiment, joining refers to coupling electrically; however, a method of joining is not limited to laser welding. 
     In the positive electrode  21 , a section of a 3-mm width including a boundary between the active material uncovered part  21 C and the active material covered part  21 B is covered with an insulating layer  101  (a gray region in  FIG.  2   ). In addition, all of a region of the active material uncovered part  21 C of the positive electrode that is opposed to the active material covered part  22 B of the negative electrode with the separator interposed therebetween is covered with the insulating layer  101 . The insulating layer  101  has an effect of preventing an internal short circuit of the battery  1  with reliability when foreign matter enters between the active material covered part  22 B of the negative electrode and the active material uncovered part  21 C of the positive electrode. In addition, the insulating layer  101  has, when the battery  1  undergoes an impact, an effect of absorbing the impact on the battery  1  and thereby preventing bending of the active material uncovered part  21 C of the positive electrode and a short circuit with the negative electrode  22 , with reliability. 
     The electrode wound body  20  has a through hole  26  at a center thereof. The through hole  26  is a hole through which a winding core for assembling the electrode wound body  20  and an electrode rod for welding are to be placed. In the electrode wound body  20 , the positive electrode  21  and the negative electrode  22  are laid over each other and wound in such a manner that the active material uncovered part  21 C of the positive electrode and the active material uncovered part  22 C of the negative electrode face toward opposite directions. Thus, the active material uncovered part  21 C of the positive electrode is localized to one end face, i.e., an end face  41 , of the electrode wound body, and the active material uncovered part  22 C of the negative electrode is localized to another end face, i.e., an end face  42 , of the electrode wound body  20 . In order to improve contact with the current collector plates  24  and  25  which serve to extract currents, the active material uncovered parts  21 C and  22 C are bent and the end faces  41  and  42  are thus made into flat surfaces. The direction of bending is from an outer edge part  27  of the end face  41  toward the through hole  26  or from an outer edge part  28  of the end face  42  toward the through hole  26 . Thus, portions of the active material uncovered part that are located in adjacent winds in a wound state overlap each other and are bent. As used herein, the “flat surface” includes not only a completely flat surface but also a surface having some asperities or surface roughness to the extent that it is possible to join the active material uncovered parts to the current collector plates. 
     It may seem to be possible to make the end faces  41  and  42  into flat surfaces by bending each of the active material uncovered parts  21 C and  22 C in such a manner that portions thereof overlap each other; however, without any processing in advance of bending, creases or voids (gaps or spaces) will develop in the end faces  41  and  42  upon bending, thus making it difficult for the end faces  41  and  42  to become flat surfaces. Here, “wrinkles” and “voids” are unevenness in the active material uncovered parts  21 C and  22 C occurring when they are bent, resulting in non-flatness of the end faces  41  and  42 . To prevent the occurrence of the wrinkles and voids, grooves  43  (see, for example  FIG.  4 B ) are formed in advance in radial directions from the through hole  26 . The grooves  43  each extend from the outer edge part  27  of the end face  41  to the through hole  26  or from the outer edge part  28  of the end face  42  to the through hole  26 . The through hole  26  is positioned at the center of the electrode wound body  20 . The through hole  26  is used as a hole through which a welding tool is to be placed in the assembly process of the lithium ion battery  1 . Respective portions of the active material uncovered parts  21 C and  22 C at the beginning of winding of the positive electrode  21  and the negative electrode  22  near the through hole  26  are provided with cutouts. This is to prevent the through hole  26  from being closed by the active material uncovered parts  21 C and  22 C when they are bent toward the through hole  26 . The grooves  43  remain in each of the flat surfaces even after the active material uncovered parts  21 C and  22 C are bent, and portions of each flat surface having no grooves  43  are thus joined (e.g., welded) to corresponding one of the positive electrode current collector plate  24  and the negative electrode current collector plate  25 . Note that the grooves  43 , as well as the flat surface, may be joined to portions of the current collector plate  24  or  25 . A detailed configuration of the electrode wound body  20 , that is, a detailed configuration of each of the positive electrode  21 , the negative electrode  22 , the separator  23 , and the electrolytic solution will be described later. 
     In a typical lithium ion battery, for example, a lead for current extraction is welded at one location on each of the positive electrode and the negative electrode; however, this is not suitable for a high-rate discharge because a high internal resistance of the battery will result and cause the lithium ion battery to generate heat and become high in temperature during discharging. To cope with this, in the lithium ion battery according to one embodiment, the internal resistance of the battery is kept low by disposing the positive electrode current collector plate  24  at the end face  41  and the negative electrode current collector plate  25  at the end face  42 , and welding, at multiple points, the positive electrode current collector plate  24  and the negative electrode current collector plate  25  respectively to the active material uncovered part  21 C of the positive electrode located at the end face  41  and the active material uncovered part  22 C of the negative electrode located at the end face  42 . The configuration in which the end faces  41  and  42  are formed by bending into flat surfaces also contributes to reduction in resistance. 
       FIGS.  3 A and  3 B  illustrate an example of the current collector plates.  FIG.  3 A  illustrates the positive electrode current collector plate  24 .  FIG.  3 B  illustrates the negative electrode current collector plate  25 . The positive electrode current collector plate  24  includes, for example, a metal plate including a simple substance or a composite material of aluminum or an aluminum alloy. The negative electrode current collector plate  25  includes, for example, a metal plate including a simple substance or a composite material of nickel, a nickel alloy, copper, or a copper alloy, that is, a cladding material. As illustrated in  FIG.  3 A , the positive electrode current collector plate  24  has a shape in which a band-like part  32  having a rectangular shape is attached to a plate-like part  31  having a flat fan shape. The plate-like part  31  has a hole  35  at a position near a middle thereof. The position of the hole  35  corresponds to that of the through hole  26 . 
     A shaded region in  FIG.  3 A  represents an insulating part  32 A where an insulating tape or an insulating material is attached or applied to the band-like part  32 . A region below the shaded region in  FIG.  3 A  represents a coupling part  32 B to be coupled to a sealing plate that also serves as an external terminal. Note that in a case of a battery structure without a metallic center pin (not illustrated) in the through hole  26 , the insulating part  32 A may be omitted because there is a low possibility that the band-like part  32  comes into contact with a part having a negative electrode potential. In such a case, it is possible to increase charge and discharge capacities by increasing a width of each of the positive electrode  21  and the negative electrode  22  by an amount corresponding to a thickness of the insulating part  32 A. 
     The negative electrode current collector plate  25  has a shape that is almost the same as the shape of the positive electrode current collector plate  24 , but is different in band-like part. A band-like part  34  of the negative electrode current collector plate  25  in  FIG.  3 B  is shorter than the band-like part  32  of the positive electrode current collector plate, and includes no portion corresponding to the insulating part  32 A. The band-like part  34  includes circular projections  37  depicted as multiple circles. Upon resistance welding, current is concentrated on the projections, and the projections thus melt to allow the band-like part  34  to be welded to the bottom of the battery can  11 . Like the positive electrode current collector plate  24 , the negative electrode current collector plate  25  has a hole  36  at a position near a middle of a plate-like part  33 . The position of the hole  36  corresponds to that of the through hole  26 . The plate-like part  31  of the positive electrode current collector plate  24  and the plate-like part  33  of the negative electrode current collector plate  25  each have a fan shape, and thus cover respective portions of the end faces  41  and  42 . A reason for not covering all of each of the end faces is to allow the electrolytic solution to smoothly permeate the electrode wound body in assembling the battery, or to allow gas generated when the battery comes into an abnormally high-temperature state or an overcharged state to be easily released to the outside of the battery. 
     The positive electrode active material layer includes at least a positive electrode material (a positive electrode active material) into which lithium is insertable and from which lithium is extractable, and may further include, for example, a positive electrode binder and a positive electrode conductor. The positive electrode material may be a lithium-containing composite oxide or a lithium-containing phosphoric acid compound. The lithium-containing composite oxide has, for example, a layered rock-salt crystal structure or a spinel crystal structure. The lithium-containing phosphoric acid compound has, for example, an olivine crystal structure. 
     The positive electrode binder includes a synthetic rubber or a polymer compound. Examples of the synthetic rubber include a styrene-butadiene-based rubber, a fluorine-based rubber, and ethylene propylene diene. Examples of the polymer compound include polyvinylidene difluoride (PVdF) and polyimide. 
     The positive electrode conductor is a carbon material such as graphite, carbon black, acetylene black, or Ketjen black. Note that the positive electrode conductor may be a metal material or a polymer compound. 
     The positive electrode foil  21 A may have a thickness within a range from 5 μm to 20 μm both inclusive. A reason for this is that setting the thickness of the positive electrode foil  21 A to 5 μm or more allows manufacturing without breakage of the positive electrode  21  when the positive electrode  21 , the negative electrode  22 , and the separator  23  are laid over each other and wound. A further reason is that setting the thickness of the positive electrode foil  21 A to 20 μm or less makes it possible to prevent a decrease in energy density of the battery  1  and allows the positive electrode  21  and the negative electrode  22  to be opposed to each other over a large area, thus allowing the battery  1  to have high output power. 
     The negative electrode foil  22 A may have a surface roughened for improved adherence to the negative electrode active material layer. The negative electrode active material layer includes at least a negative electrode material (a negative electrode active material) into which lithium is insertable and from which lithium is extractable, and may further include, for example, a negative electrode binder and a negative electrode conductor. 
     The negative electrode material includes, for example, a carbon material. The carbon material is graphitizable carbon, non-graphitizable carbon, graphite, low-crystalline carbon, or amorphous carbon. The carbon material has a fibrous shape, a spherical shape, a granular shape, or a scale-like shape. 
     Further, the negative electrode material includes, for example, a metal-based material. Examples of the metal-based material include Li (lithium), Si (silicon), Sn (tin), Al (aluminum), Zr (zinc), and Ti (titanium). A metallic element forms a compound, a mixture, or an alloy with another element, and examples thereof include silicon oxide (SiO x  (0&lt;x≤2)), silicon carbide (SiC), an alloy of carbon and silicon, and lithium titanium oxide (LTO). 
     The negative electrode foil  22 A may have a thickness within a range from 5 μm to 20 μm both inclusive. A reason for this is that setting the thickness of the negative electrode foil  22 A to 5 μm or more allows manufacturing without breakage of the negative electrode  22  when the positive electrode  21 , the negative electrode  22 , and the separator  23  are laid over each other and wound. A further reason is that setting the thickness of the negative electrode foil  22 A to 20 μm or less makes it possible to prevent a decrease in energy density of the battery  1  and allows the positive electrode  21  and the negative electrode  22  to be opposed to each other over a large area, thus allowing the battery  1  to have high output power. 
     The separator  23  is a porous film including resin, and may be a layered film including two or more kinds of porous films. Examples of the resin include polypropylene and polyethylene. The separator  23  may include a base layer including the porous film, and a resin layer provided on one side or each of both sides of the base layer. A reason for this is that adherence of the separator  23  to each of the positive electrode  21  and the negative electrode  22  improves to suppress distortion of the electrode wound body  20 . 
     The resin layer includes a resin such as PVdF. In a case of forming the resin layer, a solution including an organic solvent and the resin dissolved therein is applied on the base layer, following which the base layer is dried. Note that the base layer may be immersed in the solution and thereafter the base layer may be dried. From the viewpoint of improving heat resistance and battery safety, the resin layer may include inorganic particles or organic particles. Examples of the kind of the inorganic particles include aluminum oxide, aluminum nitride, aluminum hydroxide, magnesium hydroxide, boehmite, talc, silica, and mica. Alternatively, a surface layer including inorganic particles and formed by a method such as a sputtering method or an atomic layer deposition (ALD) method may be used instead of the resin layer. 
     The separator  23  may have a thickness within a range from 4 μm to 30 μm both inclusive. Setting the thickness of the separator  23  to 4 μm or more makes it possible to prevent an internal short circuit caused by contact between the positive electrode  21  and the negative electrode  22  which are opposed to each other with the separator  23  interposed therebetween. Setting the thickness of the separator  23  to 30 μm or less makes it possible for lithium ions and the electrolytic solution to easily pass through the separator  23 , and makes it possible for the positive electrode  21  and the negative electrode  22  to achieve high electrode density when wound. 
     The electrolytic solution includes a solvent and an electrolyte salt, and may further include other materials such as additives on an as-needed basis. The solvent is a nonaqueous solvent such as an organic solvent, or water. The electrolytic solution including a nonaqueous solvent is called a nonaqueous electrolytic solution. Examples of the nonaqueous solvent include a cyclic carbonic acid ester, a chain carbonic acid ester, a lactone, a chain carboxylic acid ester, and a nitrile (mononitrile). 
     Although a typical example of the electrolyte salt is a lithium salt, the electrolyte salt may include any salt other than the lithium salt. Examples of the lithium salt include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium methanesulfonate (LiCH 3 SO 3 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), and dilithium hexafluorosilicate (Li 2 SF 6 ). These salts may also be used in mixture with each other. From the viewpoint of improving a battery characteristic, a mixture of LiPF 6  and LiBF 4  may be used, in particular. Although not particularly limited, a content of the electrolyte salt is preferably in a range from 0.3 mol/kg to 3 mol/kg both inclusive with respect to the solvent. 
     A description will be given of a method of fabricating the lithium ion battery  1  according to the embodiment with reference to  FIGS.  4 A to  4 F . First, the positive electrode active material was applied on the surface of the positive electrode foil  21 A having a band shape to form the covered part of the positive electrode  21 , and the negative electrode active material was applied on the surface of the negative electrode foil  22 A having a band shape to form the covered part of the negative electrode  22 . At this time, the active material uncovered part  21 C without the positive electrode active material applied thereon and the active material uncovered part  22 C without the negative electrode active material applied thereon were provided at one end in a transverse direction of the positive electrode  21  and one end in the transverse direction of the negative electrode  22 , respectively. The cutouts were formed in the respective portions of the active material uncovered parts  21 C and  22 C that correspond to the ends of winding of the electrodes as wound. The positive electrode  21  and the negative electrode  22  were subjected to processes including a drying process. Thereafter, the positive electrode  21  and the negative electrode  22  were laid over each other with the separator  23  interposed therebetween in such a manner that the active material uncovered part  21 C of the positive electrode and the active material uncovered part  22 C of the negative electrode faced toward opposite directions, and they were wound in a spiral shape to allow the through hole  26  to be present at the center and to allow the formed cutouts to be located on an outer periphery side of the electrode wound body. Thus, the electrode wound body  20  as illustrated in  FIG.  4 A  was fabricated. 
     Next, as illustrated in  FIG.  4 B , the grooves  43  were formed in portions of the end faces  41  and  42  by pressing an end of a material such as a thin flat plate (for example, 0.5 mm in thickness) perpendicularly against the end faces  41  and  42 . In this way, the grooves  43  were formed to extend radially from the through hole  26 . The number and arrangement of the grooves  43  illustrated in  FIG.  4 B  are merely one example. Thereafter, as illustrated in  FIG.  4 C , the end faces  41  and  42  were made into flat surfaces by applying equal pressures to the end faces  41  and  42  simultaneously from both electrode sides in directions generally perpendicular to the end faces  41  and  42  to thereby bend the active material uncovered part  21 C of the positive electrode and the active material uncovered part  22 C of the negative electrode. At this time, a load was applied with, for example, a plate surface of a flat plate to cause the active material uncovered part located at each of the end faces  41  and  42  to be bent toward the central axis and cause portions of the active material uncovered part to overlap each other. Thereafter, the plate-like part  31  of the positive electrode current collector plate  24  was laser-welded to the end face  41 , and the plate-like part  33  of the negative electrode current collector plate  25  was laser-welded to the end face  42 . 
     Thereafter, as illustrated in  FIG.  4 D , the band-like parts  32  and  34  of the current collector plates  24  and  25  were bent and the insulating plates  12  and  13  (or insulating tapes) were respectively attached to the positive electrode current collector plate  24  and the negative electrode current collector plate  25 . The electrode wound body  20  assembled in the above-described manner was placed into the battery can  11  illustrated in  FIG.  4 E , and the bottom of the battery can  11  was welded. The electrolytic solution was injected into the battery can  11 , following which the battery can  11  was sealed with the gasket  15  and the battery cover  14  as illustrated in  FIG.  4 F . 
     EXAMPLES 
     In the following, the present technology will be described with reference, without limitation, to Examples in which the lithium ion batteries  1  fabricated in the above-described manner were used to compare the numbers of open circuit voltage defects, the numbers of welding defects, and impedances. 
     In each of all Examples and Comparative examples described below, the size of the cylindrical battery was set to be 21 mm in diameter and 70 mm in height, the number of the grooves  43  was set to eight, and the grooves  43  were arranged at generally equal angular intervals. Laser welding was performed at positions arranged as illustrated in  FIG.  5    to join the positive electrode current collector plate  24  and the active material uncovered part  21 C of the positive electrode to each other, and to join the negative electrode current collector plate  25  and the active material uncovered part  22 C of the negative electrode to each other.  FIG.  5    is a schematic diagram illustrating the end face of the wound body and the grooves as viewed through the current collector plate in order to describe positions of laser welding marks. Thick solid-line portions in  FIG.  5    represent laser welding marks  51 . The laser welding marks  51  were each provided in a linear shape to extend from a position near the hole  35  or  36  to the outer periphery, and were arranged at generally equal angular intervals, one each between adjacent grooves  43 . As illustrated in  FIG.  5   , six laser welding marks  51  were arranged in a region covered by each of the current collector plate  24  and  25 . Each laser welding mark  51  had a length of 6 mm. 
       FIG.  6    is a diagram that describes a cutout  61  provided in the active material uncovered part  21 C of the positive electrode  21 . The positive electrode  21  is in a state of being spread on a plane, and the illustration of the insulating layer  101  is omitted. As illustrated in  FIG.  6   , the cutout  61  was formed at one end in the transverse direction of the positive electrode  21  on a winding-end side (the right side in  FIG.  6   ) of the electrode wound body  20 . The cutout  61  is intended to prevent generation of a turned-up portion in the positive electrode  21  (a turned-up portion in a winding end part  63 ) in the electrode wound body  20  (see  FIG.  4 A ). If there is a turned-up portion in the positive electrode  21 , as will be described later, the turned-up portion of the positive electrode  21  can break through the separator  23  to come into contact with the negative electrode  22  after bending of the active material uncovered part  21 C of the positive electrode. To avoid a short circuit due to such contact, a length L of the cutout  61  along a longitudinal direction of the positive electrode  21  may fall within a range from 1/16 winds to ¼ winds both inclusive. Note that the length L of the cutout  61  along the longitudinal direction of the positive electrode  21  being 1/16 winds means that a proportion of the length L to a length of one wind on the peripheral surface of the electrode wound body  20  is 1/16. The length of one wind on the peripheral surface of the electrode wound body  20  is calculable by measuring a diameter of the electrode wound body  20 . Any length L described hereinafter has a similar meaning to the above. For example,  FIG.  9 B- 1    is a side view of the electrode wound body with the cutout  61 .  FIG.  9 B- 2    is a plan view of the end face of the same electrode wound body as viewed in a central axis direction. The cutout  61  on the outer periphery of the wound body is indicated in a thick solid line. The proportion of the length L of the cutout  61  to a circumferential length of the wound body is ¼. If the cutout  61  extends to the active material covered part  21 B of the positive electrode, an internal short circuit of the battery easily occurs due to the active material coming off a cut surface of the cutout  61 . It is thus necessary for the cutout  61  to be within the active material uncovered part  21 C of the positive electrode. It is necessary that Hc1≥Hc2 where Hc1 is the width of the active material uncovered part  21 C, and Hc2 is the width of the cutout  61  in the transverse direction. The grooves  43  were so arranged that an end  62  of the cutout  61  on the winding end side is located on an extension of one of the eight grooves  43  on the end face  41  illustrated in each of  FIGS.  9 A -2 to 9D-2. 
     First, comparisons were made between a case with the cutout  61  at one end in the transverse direction of the positive electrode  21  on the winding end side of the electrode wound body  20  and a case without the cutout  61 . After winding, the cutout  61  or the winding end part  63  of the positive electrode is located in an outermost wind of the electrode wound body.  FIGS.  7 A to  7 C  are schematic diagrams for describing Example 1 and Comparative examples 1 and 2. Each of  FIGS.  7 A to  7 C  is a side view of the electrode wound body  20  illustrating the active material uncovered part  21 C of the positive electrode and the vicinity thereof. The electrode wound body  20  in each of  FIGS.  7 A to  7 C  is in a state before the active material uncovered part  21 C of the positive electrode is bent toward the through hole  26  (see  FIG.  4 A ). 
     Example 1 
     As illustrated in  FIGS.  6  and  7 A , the cutout  61  was formed at one end in the transverse direction of the positive electrode  21  on the winding end side of the electrode wound body  20 , and the length L of the cutout  61  along the longitudinal direction of the positive electrode  21  was set to ⅛ winds. The positive electrode  21  was wound together with the negative electrode  22  with the separator  23  interposed therebetween, and the active material uncovered part  21 C of the positive electrode was bent to form the end face  41 . Hc1 was set to 7 mm, and Hc2 was set to 5 mm. 
     Comparative Example 1 
     As illustrated in  FIG.  7 B , no cutout  61  was formed. The positive electrode  21  was wound together with the negative electrode  22  with the separator  23  interposed therebetween, and the active material uncovered part  21 C of the positive electrode was bent to form the end face  41 . 
     Comparative Example 2 
     As illustrated in  FIG.  7 C , no cutout  61  was formed. The positive electrode  21  was wound together with the negative electrode  22  with the separator  23  interposed therebetween, and a tape  64  was attached to the active material uncovered part  21 C of the positive electrode in the winding end part  63  of the positive electrode. A base layer of the tape  64  included polyimide. The tape  64  had a thickness of 18 μm, including an adhesive layer. Dimensions of the tape  64  were 2 mm in an axial direction of the electrode wound body  20 , and 10 mm in a circumferential direction. Thereafter, the active material uncovered part  21 C of the positive electrode was bent to form the end face  41 . At this time, the entire tape  64  was allowed to be located on the end face  41 . 
     Batteries having the characteristics described in Example and Comparative examples above were subjected to an open circuit voltage defect test and a welding defect test. In the open circuit voltage defect test, the batteries  1  were subjected to constant current and constant voltage charging at 500 mA at an ambient temperature of 25° C. Where a voltage of the battery  1  immediately (within 1 hour) after reaching 4.2 V is denoted as V 1  and a voltage of the battery  1  having been left to stand for two weeks from the point in time immediately after the voltage reached 4.2 V is denoted as V 2 , the battery  1  in which V 1 −V 2 ≥50 mV was evaluated as having an open circuit voltage defect, and the number of such batteries  1  was counted. In the welding defect test, the positive electrode current collector plate  24  and the electrode wound body  20  were pulled away from each other with a force of  10 N after laser-welding the positive electrode current collector plate  24  and the active material uncovered part  21 C of the positive electrode to each other. The battery in which separation of the positive electrode current collector plate  24  was observed was evaluated as having a welding defect, and the number of such batteries was counted. The number of batteries subjected to each test was 100 for each example. The results are given in Table 1 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Number of open 
                 Number of welding 
               
               
                   
                 circuit voltage defects 
                 defects 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Example 1 
                 0 
                 0 
               
               
                 Comparative example 1 
                 6 
                 0 
               
               
                 Comparative example 2 
                 0 
                 23 
               
               
                   
               
            
           
         
       
     
     In Example 1, the number of the open circuit voltage defects and the number of the welding defects were both zero, whereas in Comparative example 1, the number of the open circuit voltage defects was six and the number of the welding defects was zero, and in Comparative example 2, the number of the open circuit voltage defects was zero and the number of the welding defects was 23. Regarding Comparative example 1, a reason for the defects is considered to be as follows. In the course of a manufacturing process or conveyance, as illustrated in  FIG.  8 A , an outwardly turned-up portion  65  can sometimes develop in the winding end part  63  on the winding end side of the positive electrode  21 . If the active material uncovered part of the positive electrode is bent in such a state to form the end face  41 , the turned-up portion  65  can sometimes be bent outwardly as illustrated in  FIG.  8 B . At this time, the turned-up portion  65  can break through the separator  23  located in the outermost wind of the electrode wound body  20 , and can thus come into contact with the negative electrode  22  located on an inner side relative to the separator  23  (the broken line in  FIG.  8 B  indicates an upper end of the negative electrode  22 ). It is considered that in Comparative example 1, the occurrence of such contact resulted in a short circuit. Forming the cutout  61  at one end in the transverse direction of the positive electrode  21  on the winding end side of the electrode wound body  20 , as in Example 1, prevents the generation of the outwardly turned-up portion  65  on the winding end side of the positive electrode  21 . This is considered to be a reason why no short circuit occurred in Example 1. In Comparative example 2, the tape  64  was attached to the winding end part  63  of the positive electrode  21 . It is thus considered that the tape  64  prevented a portion of the positive electrode  21  on the winding end side from being turned up outwardly, and thereby prevented the occurrence of a short circuit. However, it is considered that the presence of the tape  64  on the end face  41  as illustrated in  FIG.  8 C  resulted in the welding defect. From the experiment results presented in Table 1, it is determinable that neither an internal short circuit nor a welding defect will occur in a battery provided with the cutout  61  at one end in the transverse direction of the positive electrode  21  on the winding end side of the electrode wound body. 
     Next, comparisons were made between cases with varying lengths L of the cutout  61  along the longitudinal direction of the positive electrode  21 . In Examples 2 to 5, Hc1 was set to 7 mm, and Hc2 was set to 5 mm.  FIGS.  9 A -1 to 9D-1 and  FIGS.  9 A -2 to 9D-2 are diagrams illustrating Examples 2 to 5. Each of  FIGS.  9 A -1 to 9D-1 is a side view of the electrode wound body  20  illustrating the active material uncovered part  21 C of the positive electrode and the vicinity thereof. Each of  FIGS.  9 A -2 to 9D-2 is a plan view of the end face  41  on the positive electrode side after formation of the grooves  43 . A thick solid-line portion in each of the plan views represents the cutout  61 . The electrode wound body  20  in each of  FIGS.  9 A -1 to 9D-1 and  FIGS.  9 A -2 to 9D-2 is in a state before the active material uncovered part  21 C of the positive electrode is bent toward the through hole  26  (see  FIG.  4 A or  4 B ). 
     Example 2 
     As illustrated in  FIGS.  9 A -1 and 9A-2, Example 2 was similar to Example 1 except that L was set to 1/16 winds. 
     Example 3 
     As illustrated in  FIGS.  9 B- 1  and  9 B- 2   , Example 3 was similar to Example 1 except that L was set to ¼ winds. 
     Example 4 
     As illustrated in  FIGS.  9 C- 1  and  9 C- 2   , Example 4 was similar to Example 1 except that L was set to 1/32 winds. 
     Example 5 
     As illustrated in  FIGS.  9 D -1 and 9D-2, Example 5 was similar to Example 1 except that L was set to 5/16 winds. 
     In a manner similar to the foregoing, batteries having the characteristics described in Example above were subjected to the open circuit voltage defect test, the welding defect test, and impedance (direct resistance) measurements. The direct resistance is obtainable by calculating a gradient of voltage when a discharge current is increased from 0 (A) to 100 (A) in five seconds. For the impedance measurements, a value of Example 1 was assumed as 100.00%. The results are given in Table 2 below. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Number of 
                 Number of 
                   
               
               
                   
                   
                 open circuit 
                 welding 
                 Impedance 
               
               
                   
                 L 
                 voltage defects 
                 defects 
                 (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Example 2 
                  1/16 winds 
                 0 
                 0 
                 99.97 
               
               
                 Example 3 
                 ¼ winds 
                 0 
                 0 
                 100.06 
               
               
                 Example 4 
                  1/32 winds 
                 2 
                 0 
                 99.94 
               
               
                 Example 5 
                  5/16 winds 
                 0 
                 0 
                 100.10 
               
               
                   
               
            
           
         
       
     
     In Examples 2 to 5, the number of the batteries with the open circuit voltage defects due to internal short circuits attributable to generation of a turned-up portion in the positive electrode was zero or two. It was thus confirmed that these examples were able to suppress the occurrence of the voltage defect, as compared with Comparative example 1. It was confirmed that the provision of the cutout in the active material uncovered part of the positive electrode at one end on the outer periphery side of the electrode wound body helps to prevent an internal short circuit from occurring due to generation of a turned-up portion in the positive electrode. It was confirmed that Example 5 resulted in an increase in impedance by 0.10%. This is presumably because the increased length L of the cutout  61  resulted in a decrease in area of joining between the positive electrode current collector plate  24  and the active material uncovered part  21 C. These experiment results indicate that in a case where the length L of the cutout  61  falls within a range from 1/16 winds to ¼ winds both inclusive, it is possible to fabricate a battery that suppresses the occurrence of an internal short circuit, that is free from a welding defect, and that is relatively low in impedance. 
     Although one or more embodiments of the present technology have been described above, the contents of the present technology are not limited thereto, and various suitable modifications may be made. 
     The cutout formed at the end in the transverse direction on the winding end side of the positive electrode does not have to be linear in shape such as one illustrated in  FIG.  6   . For example, the cutout may have a curved shape as illustrated in  FIG.  10   , and may have any shape that forms no turned-up portion  65  in the winding end part  63 . 
     In an embodiment, as illustrated in  FIG.  5   , one laser welding mark is provided between two adjacent grooves  43 ; however, multiple laser welding marks may be provided between two adjacent grooves  43 . In such a case, the internal resistance of the battery is further reduced owing to a further increase in area of the laser welding marks. 
     Although the number of the grooves  43  is eight in Examples and Comparative examples, any other number may be employed. Although the battery size employed is 21700 (21 mm in diameter and 70 mm in height), the battery size may be 18650 (18 mm in diameter and 65 mm in height) or any other size. 
     Although the positive electrode current collector plate  24  and the negative electrode current collector plate  25  respectively include the plate-like parts  31  and  33  each shaped like a fan, any other shape may be employed. 
     In an embodiment, the positive electrode  21  and the negative electrode  22  have respective structures in which the active material uncovered parts  21 C and  22 C are bent to be respectively welded to the current collector plates  24  and  25 ; however, the negative electrode  22  may have any other structure. 
     The present technology is applicable to any battery other than the lithium ion battery, and to any battery having a shape other than the cylindrical shape, such as a laminated battery, a prismatic battery, a coin-type battery, or a button-type battery, without departing from the scope of the present technology. In such a case, the shape of the “end face of the electrode wound body” is not limited to the cylindrical shape, and may be an elliptical shape, an elongated shape, or any other shape. 
       FIG.  11    is a block diagram illustrating a circuit configuration example where the battery  1  according to an embodiment including Examples of the present technology is applied to a battery pack  300 . The battery pack  300  includes an assembled battery  301 , a switch unit  304 , a current detection resistor  307 , a temperature detection device  308 , and a controller  310 . The switch unit  304  includes a charge control switch  302   a  and a discharge control switch  303   a . The controller  310  controls each device. Further, the controller  310  is able to perform charge and discharge control upon abnormal heat generation, and to perform calculation and correction of a remaining capacity of the battery pack  300 . The battery pack  300  includes a positive electrode terminal  321  and a negative electrode terminal  322  that are couplable to a charger or electronic equipment for charging and discharging. 
     The assembled battery  301  includes multiple secondary batteries  301   a  coupled in series or in parallel.  FIG.  11    illustrates an example case in which six secondary batteries  301   a  are coupled in a two parallel coupling and three series coupling (2P3S) configuration. 
     A temperature detector  318  is coupled to the temperature detection device  308  (for example, a thermistor). The temperature detector  318  measures the temperature of the assembled battery  301  or the battery pack  300 , and supplies the measured temperature to the controller  310 . A voltage detector  311  measures the voltages of the assembled battery  301  and each of the secondary batteries  301   a  included therein, performs A/D conversion on the measured voltages, and supplies the converted voltages to the controller  310 . A current measurement unit  313  measures currents using the current detection resistor  307  and supplies the measured currents to the controller  310 . 
     A switch controller  314  controls the charge control switch  302   a  and the discharge control switch  303   a  of the switch unit  304  on the basis of the voltage and the currents respectively supplied from the voltage detector  311  and the current measurement unit  313 . When the voltage of any of the secondary batteries  301   a  becomes greater than or equal to an overcharge detection voltage or becomes lower than or equal to an overdischarge detection voltage, the switch controller  314  transmits a turn-off control signal to the switch unit  304  to thereby prevent overcharging or overdischarging. The overcharge detection voltage is, for example, 4.20 V±0.05 V. The overdischarge detection voltage is, for example, 2.4 V±0.1 V. 
     After the charge control switch  302   a  or the discharge control switch  303   a  is turned off, charging or discharging is enabled only through a diode  302   b  or a diode  303   b . Semiconductor switches such as MOSFETs are employable as these charge and discharge control switches. Note that although the switch unit  304  is provided on a positive side in  FIG.  11   , the switch unit  304  may be provided on a negative side. 
     A memory  317  includes a RAM and a ROM. Numerical values including, for example, battery characteristic values, a full charge capacity, and a remaining capacity calculated by the controller  310  are stored and rewritten therein. 
     The battery  1  according to an embodiment including Examples of the present technology described herein is mountable on equipment such as electronic equipment, electric transport equipment, or a power storage apparatus, and is usable to supply electric power. 
     Examples of the electronic equipment include laptop personal computers, smartphones, tablet terminals, personal digital assistants (PDAs) (mobile information terminals), mobile phones, wearable terminals, digital still cameras, electronic books, music players, game machines, hearing aids, electric tools, televisions, lighting equipment, toys, medical equipment, and robots. In addition, electric transport equipment, power storage apparatuses, and electric unmanned aerial vehicles, which will be described later, may also be included in the electronic equipment in a broad sense. 
     Examples of the electric transport equipment include electric automobiles (including hybrid electric automobiles), electric motorcycles, electric-assisted bicycles, electric buses, electric carts, automated guided vehicles (AGVs), and railway vehicles. Examples of the electric transport equipment further include electric passenger aircrafts and electric unmanned aerial vehicles for transportation. The secondary battery according to an embodiment is used not only as a driving power source for the foregoing electric transport equipment but also as, for example, an auxiliary power source or an energy-regenerative power source therefor. 
     Examples of the power storage apparatuses include a power storage module for commercial or household use, and a power source for power storage for architectural structures including residential houses, buildings, and offices, or for power generation facilities. 
     As an example of the electric tools to which the present technology is applicable, an electric screwdriver will be schematically described with reference to  FIG.  12   . An electric screwdriver  431  includes a motor  433  and a trigger switch  432 . The motor  433  transmits rotational power to a shaft  434 . The trigger switch  432  is operated by a user. A battery pack  430  according to the present technology and a motor controller  435  are contained in a lower housing of a handle of the electric screwdriver  431 . The battery pack  430  is built in or detachably attached to the electric screwdriver  431 . The battery  1  is applicable to a battery included in the battery pack  430 . 
     The battery pack  430  and the motor controller  435  may include respective microcomputers (not illustrated) communicable with each other to transmit and receive charge and discharge data on the battery pack  430 . The motor controller  435  controls operation of the motor  433 , and is able to cut off power supply to the motor  433  under abnormal conditions such as overdischarging. 
     As an example of application of the present technology to a power storage system for electric vehicles,  FIG.  13    schematically illustrates a configuration example of a hybrid vehicle (HV) that employs a series hybrid system. The series hybrid system relates to a vehicle that travels with an electric-power-to-driving-force conversion apparatus by using electric power generated by a generator that uses an engine as a power source, or using electric power temporarily stored in a battery. 
     A hybrid vehicle  600  is equipped with an engine  601 , a generator  602 , an electric-power-to-driving-force conversion apparatus  603  (a direct-current motor or an alternating-current motor; hereinafter, simply “motor  603 ”), a driving wheel  604   a , a driving wheel  604   b , a wheel  605   a , a wheel  605   b , a battery  608 , a vehicle control apparatus  609 , various sensors  610 , and a charging port  611 . The battery pack  300 , or a power storage module equipped with a plurality of batteries  1  is applicable to the battery  608 . 
     The motor  603  operates under the electric power of the battery  608 , and a rotational force of the motor  603  is transmitted to the driving wheels  604   a  and  604   b . Electric power generated by the generator  602  using a rotational force generated by the engine  601  is storable in the battery  608 . The various sensors  610  control an engine speed via the vehicle control apparatus  609 , and control an opening angle of an unillustrated throttle valve. 
     When the hybrid vehicle  600  is decelerated by an unillustrated brake mechanism, a resistance force at the time of deceleration is applied to the motor  603  as a rotational force, and regenerative electric power generated from the rotational force is stored in the battery  608 . In addition, the battery  608  is chargeable by being coupled to an external power source via the charging port  611  of the hybrid vehicle  600 . Such an HV vehicle is referred to as a plug-in hybrid vehicle (PHV or PHEV). 
     Note that the secondary battery according to the present technology may be applied to a small-sized primary battery and used as a power source of an air pressure sensor system (a tire pressure monitoring system; TMPS) built in the wheels  604  and  605 . 
     Although the series hybrid vehicle has been described above as an example, the present technology is applicable also to a hybrid vehicle of a parallel system in which an engine and a motor are used in combination, or of a combination of the series system and the parallel system. Furthermore, the present technology is applicable to an electric vehicle (EV or BEV) and a fuel cell vehicle (FCV) that travel by means of only a driving motor without using an engine. 
     REFERENCE SIGNS LIST 
     
         
           1 : lithium ion battery 
           12 : insulating plate 
           21 : positive electrode 
           21 A: positive electrode foil 
           21 B: positive electrode active material covered part 
           21 C: active material uncovered part of a positive electrode 
           22 : negative electrode 
           22 A: negative electrode foil 
           22 B: negative electrode active material covered part 
           22 C: active material uncovered part of a negative electrode 
           23 : separator 
           24 : positive electrode current collector plate 
           25 : negative electrode current collector plate 
           26 : through hole 
           27 ,  28 : outer edge part 
           41 ,  42 : end face 
           43 : groove 
           51 : laser welding mark 
           61 : cutout 
       
    
     According to an embodiment, the cutout is provided on a winding end side of the electrode wound body. This makes it possible to provide a battery that suppresses the occurrence of an internal short circuit due to a turned-up portion generated in the positive electrode. It should be understood that the contents of the present technology are not to be construed as being limited by the effects exemplified herein. 
     It should be appreciated 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.