Patent Publication Number: US-2022223872-A1

Title: Secondary battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of PCT patent application no. PCT/JP2020/036875 filed on Sep. 29, 2020, which claims priority to Japanese patent application no. JP2019-180789 filed on Sep. 30, 2019, the entire contents of which are being incorporated herein by reference. 
    
    
     BACKGROUND 
     The present technology relates to a secondary battery. 
     Various kinds of electronic equipment such as mobile phones have been widely used. Such widespread use has promoted development of a secondary battery as a power source that is smaller in size and lighter in weight and allows for a higher energy density. A configuration of the secondary battery influences a battery characteristic. Accordingly, the configuration of the secondary battery has been considered in various ways. 
     Specifically, in order to achieve, for example, a favorable battery characteristic, a positive electrode and a negative electrode are alternately stacked with a polymer electrolyte layer or a separator interposed therebetween, and the positive electrode and the negative electrode have lengths equal to each other. Further, in order to achieve, for example, stable manufacturability, a positive electrode is cut by means of a laser (so-called laser cutting). 
     SUMMARY 
     The present disclosure relates to a secondary battery. 
     Consideration has been given in various ways to solve problems of a secondary battery; however, sufficient measures have not yet been taken to achieve both suppression of a short circuit and an increase in battery capacity, and there is still room for improvement in terms thereof. 
     The technology of the present disclosure has been made in view of such an issue, and thus, to provide a secondary battery that makes it possible to achieve both suppression of a short circuit and an increase in battery capacity according to an embodiment. 
     A secondary battery according to an embodiment of the technology includes a negative electrode, a positive electrode, and an electrolytic solution. The negative electrode includes a negative electrode active material layer. The positive electrode includes a positive electrode active material layer. The positive electrode active material layer has a same dimension as a dimension of the negative electrode active material layer in a width direction. The positive electrode active material layer includes a reaction active part in which charging and discharging reactions proceed, and a reaction less-active part in which the charging and discharging reactions proceed less easily than in the reaction active part. The reaction less-active part includes one end part, another end part, or both of the positive electrode active material layer in the width direction. 
     According to the secondary battery of the embodiment of the technology, the positive electrode active material layer has the same dimension as the dimension of the negative electrode active material layer in the width direction. The positive electrode active material layer includes the reaction active part and the reaction less-active part. The reaction less-active part is the one end part, the other end part, or both of the positive electrode active material layer in the width direction. This makes it possible to achieve both suppression of a short circuit and an increase in battery capacity. 
     Note that effects of the technology are not necessarily limited to those described above and may include any of a series of suitable effects including described below in relation to the technology. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a sectional view of a configuration of a secondary battery according to a first embodiment of the technology. 
         FIG. 2  is an enlarged sectional view of a configuration of a battery device illustrated in  FIG. 1 . 
         FIG. 3  is a sectional view of a configuration of a secondary battery of a first comparative example. 
         FIG. 4  is a sectional view of a configuration of a secondary battery of a second comparative example. 
         FIG. 5  is a sectional view of a configuration of a secondary battery according to a second embodiment of the technology. 
         FIG. 6  is a sectional view of a configuration of a secondary battery according to a third embodiment of the technology. 
         FIG. 7  is a sectional view of a configuration of a secondary battery of Modification 1 according to an embodiment. 
         FIG. 8  is a sectional view of another configuration of the secondary battery of Modification 1 according to an embodiment. 
         FIG. 9  is a sectional view of a configuration of a secondary battery of Modification 2 according to an embodiment. 
         FIG. 10  is a sectional view of another configuration of the secondary battery of Modification 2 according to an embodiment. 
         FIG. 11  is a sectional view of a configuration of a secondary battery of Modification 3 according to an embodiment. 
         FIG. 12  is a sectional view of another configuration of the secondary battery of Modification 3 according to an embodiment. 
         FIG. 13  is a sectional view of a configuration of a secondary battery of Modification 4 according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the technology of the present disclosure are described below in detail with reference to the drawings. 
     A description is given first of a secondary battery according to a first embodiment of the technology. 
     Described here is a secondary battery having a flat and columnar shape. Examples of the secondary battery include a so-called coin-type secondary battery and a so-called button-type secondary battery. As will be described later, the flat and columnar secondary battery includes a pair of bottom parts and a sidewall part. The bottom parts are opposed to each other. The sidewall part lies between the bottom parts. This secondary battery has a height that is small relative to an outer diameter. Note that a description will be given later of specific dimensions (the outer diameter and the height) of the flat and columnar secondary battery. 
     A charge and discharge principle of the secondary battery is not particularly limited. The secondary battery described below obtains a battery capacity by utilizing insertion and extraction of an electrode reactant. The secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. In the secondary battery, in order to prevent precipitation of the electrode reactant on a surface of the negative electrode in the middle of charging, a charge capacity of the negative electrode is greater than a discharge capacity of the positive electrode. In other words, an electrochemical capacity per unit area of the negative electrode is set to be greater than an electrochemical capacity per unit area of the positive electrode. 
     Although not limited to a particular kind, the electrode reactant is a light metal, such as an alkali metal or an alkaline earth metal. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the alkaline earth metal include beryllium, magnesium, and calcium. 
     In the following, a description is given of an example case where the electrode reactant is lithium. A secondary battery that obtains a battery capacity by utilizing insertion and extraction of lithium is a so-called lithium-ion secondary battery. In the lithium-ion secondary battery, lithium is inserted and extracted in an ionic state. 
       FIG. 1  is a sectional view of a configuration of the secondary battery according to the first embodiment. For simplifying the illustration, a positive electrode  21 , a negative electrode  22 , a separator  23 , a positive electrode lead  50 , and a negative electrode lead  60 , which will be described later, are each illustrated in a linear shape in  FIG. 1 . 
     For convenience, the following description is given with an up direction in  FIG. 1  as an upper side of the secondary battery, and a down direction in  FIG. 1  as a lower side of the secondary battery. 
     The secondary battery is a button-type secondary battery, and therefore, as illustrated in  FIG. 1 , has a flat and columnar three-dimensional shape with a height H thereof small relative to an outer diameter D thereof. Here, the secondary battery has a flat and cylindrical (circular columnar) three-dimensional shape. Dimensions of the secondary battery are not particularly limited; however, the outer diameter (here, the diameter of the circular shape) D is from 3 mm to 30 mm both inclusive, and the height H is from 0.5 mm to 70 mm both inclusive. Note that a ratio of the outer diameter D to the height H, i.e., D/H, is greater than 1 and smaller than or equal to 25. 
     Specifically, as illustrated in  FIG. 1 , the secondary battery includes a battery can  10 , a battery device  20 , an electrode terminal  30 , a gasket  40 , the positive electrode lead  50 , and the negative electrode lead  60 . 
     The battery can  10  contains the battery device  20 . The battery can  10  has a three-dimensional shape corresponding to the three-dimensional shape of the secondary battery described above. 
     Here, the battery can  10  has a hollow, flat and cylindrical three-dimensional shape extending in a height direction (a direction corresponding to the height H) in accordance with the three-dimensional shape of the secondary battery described above. The battery can  10  thus includes a pair of bottom parts M 1  and M 2 , and a sidewall part M 3 . The sidewall part M 3  is coupled to the bottom part M 1  at one end, and is coupled to the bottom part M 2  at another end. Because the battery can  10  is flat and cylindrical as described above, the bottom parts M 1  and M 2  are each circular in plan shape, and a surface of the sidewall part M 3  is a convex curved surface. 
     The battery can  10  includes a containing part  11  and a cover part  12 . The containing part  11  is a flat and cylindrical (handleless mug-shaped) member with one end open and another end closed. The containing part  11  contains the battery device  20 . More specifically, the containing part  11  has an opening  11 K at one end to allow the battery device  20  to be contained in the containing part  11 . The cover part  12  is a generally plate-shaped member, and is joined to the containing part  11  to cover the opening  11 K. 
     Here, as will be described later, the cover part  12  is joined to the containing part  11  by a method such as a welding method. The battery can  10  after the cover part  12  has been joined to the containing part  11  is a single member as a whole, that is, not separable into two or more members. 
     As a result, the battery can  10  is a single member including no folded-over portion in the middle or no portion in which two or more members are placed over each other. What is meant by “including no folded-over portion in the middle” is that the battery can  10  is not so processed as to include a portion folded over another portion in the middle. What is meant by “including no portion in which two or more members are placed over each other” is that the battery can  10  is physically a single member and is therefore not a composite body in which two or more members including a container and a cover are so fitted to each other as to be separable later. 
     Thus, the battery can  10  described here is a so-called crimpless can. A reason for employing the crimpless can is that this increases a device space volume inside the battery can  10 , and accordingly, increases also an energy density per unit volume of the secondary battery. The “device space volume” refers to a volume of an internal space of the battery can  10  available for containing the battery device  20  therein. 
     Further, the battery can  10  is electrically conductive. The battery can  10  thus serves as a negative electrode terminal because the battery can  10  is coupled to the negative electrode  22 , which will be described later, of the battery device  20 . A reason for employing such a configuration is that allowing the battery can  10  to serve as the negative electrode terminal makes it unnecessary to provide a negative electrode terminal separate from the battery can  10  in the secondary battery. A decrease in device space volume resulting from the presence of a negative electrode terminal is thereby avoided. This results in an increase in device space volume, and accordingly an increase in energy density per unit volume of the secondary battery. 
     Further, the battery can  10  has a through hole  10 K. The through hole  10 K is used to attach the electrode terminal  30  to the battery can  10 . Here, the through hole  10 K is provided at the bottom part M 1 . 
     The battery can  10  includes one or more of electrically conductive materials including, without limitation, metals (including stainless steel) and alloys. Here, in order to serve as the negative electrode terminal, the battery can  10  includes one or more of materials including, without limitation, iron, copper, nickel, stainless steel, an iron alloy, a copper alloy, and a nickel alloy. The kinds of the stainless steel employable include SUS304 and SUS316, but are not particularly limited thereto. 
     Note that, as will be described later, the battery can  10  is insulated via the gasket  40  from the electrode terminal  30  serving as a positive electrode terminal. This is for the purpose of preventing the occurrence of a contact (a short circuit) between the battery can  10  and the electrode terminal  30 . 
     The battery device  20  is a device causing charging and discharging reactions to proceed, and includes, the positive electrode  21 , the negative electrode  22 , the separator  23 , and an electrolytic solution which is a liquid electrolyte. Note that  FIG. 1  omits the illustration of the electrolytic solution. 
     The battery device  20  has a three-dimensional shape corresponding to the three-dimensional shape of the battery can  10 . The “three-dimensional shape corresponding to the three-dimensional shape of the battery can  10 ” refers to a three-dimensional shape similar to that of the battery can  10 . A reason for allowing the battery device  20  to have such a three-dimensional shape is that this makes it more difficult for a dead space (a gap between the battery can  10  and the battery device  20 ) to result excessively upon placing the battery device  20  in the battery can  10  than in a case where the battery device  20  has a three-dimensional shape different from that of the battery can  10 . This allows for efficient use of the internal space of the battery can  10 , resulting in an increase in device space volume, and accordingly an increase in energy density per unit volume of the secondary battery. Here, the battery can  10  has a flat and cylindrical three-dimensional shape as described above, and therefore the battery device  20  also has a flat and cylindrical three-dimensional shape. 
     Here, the positive electrode  21  and the negative electrode  22  are stacked with the separator  23  interposed therebetween. More specifically, the positive electrode  21  and the negative electrode  22  are alternately stacked in the height direction with the separator  23  interposed therebetween. Thus, the battery device  20  is a stacked electrode body including the positive electrode  21  and the negative electrode  22  that are stacked with the separator  23  interposed therebetween. The number of each of the positive electrodes  21  and the negative electrodes  22  to be stacked is not particularly limited, and may be freely chosen. 
       FIG. 1  also illustrates a stacked body  120  to be used to fabricate the battery device  20  in a process of manufacturing the secondary battery to be described later. The stacked body  120  has a configuration similar to that of the battery device  20  which is a stacked electrode body, except that the positive electrode  21 , the negative electrode  22 , and the separator  23  are each yet to be impregnated with the electrolytic solution. 
     Note that a detailed configuration of the battery device  20  (the positive electrode  21 , the negative electrode  22 , the separator  23 , and the electrolytic solution) will be described later (see  FIG. 2 ). 
     The electrode terminal  30  is an external coupling terminal to be coupled to electronic equipment on which the secondary battery is mountable. The electrode terminal  30  is provided at the bottom part M 1  (the cover part  12 ) of the battery can  10 . 
     The electrode terminal  30  is placed through the through hole  10 K provided in the battery can  10 . The electrode terminal  30  is thus attached to the battery can  10  by means of the through hole  10 K. One end of the electrode terminal  30  is exposed outside the battery can  10 , and another end of the electrode terminal  30  is exposed inside the battery can  10 . 
     Further, the electrode terminal  30  is coupled to the positive electrode  21  (a positive electrode current collector) of the battery device  20 . The electrode terminal  30  thus serves as the positive electrode terminal. The electrode terminal  30  includes a material similar to a material included in the positive electrode current collector to be described later. 
     Note that the three-dimensional shape of the electrode terminal  30  is not particularly limited. Here, the electrode terminal  30  extends in the height direction and has a generally cylindrical three-dimensional shape with an outer diameter reduced partly in the middle. More specifically, the electrode terminal  30  has a three-dimensional shape including a large-outer-diameter cylindrical part, a small-outer-diameter cylindrical part, and a large-outer-diameter cylindrical part coupled in this order in the height direction. The outer diameter of each of the two large-outer-diameter cylindrical parts is larger than an inner diameter of the through hole  10 K, and the outer diameter of the small-outer-diameter cylindrical part is smaller than the inner diameter of the through hole  10 K. A reason for this is that this helps to prevent the large-outer-diameter cylindrical part from passing through the through hole  10 K. A further reason is that the electrode terminal  30  is fixed to the battery can  10  by utilizing a pressing force of the large-outer-diameter cylindrical part on the battery can  10 . This helps to prevent the electrode terminal  30  from falling out of the battery can  10 . 
     The gasket  40  is disposed between the battery can  10  and the electrode terminal  30 . The gasket  40  insulates the electrode terminal  30  from the battery can  10 . The electrode terminal  30  is thus fixed to the battery can  10  with the gasket  40  interposed therebetween. 
     The gasket  40  includes one or more of insulating materials including, without limitation, polypropylene and polyethylene. A mounting range of the gasket  40  is not particularly limited. Here, the gasket  40  is disposed in a gap between the battery can  10  and the electrode terminal  30 . 
     The positive electrode lead  50  couples the electrode terminal  30  and the positive electrode  21  (coupled to a positive electrode current collector  21 A) to be described later to each other. The positive electrode lead  50  includes a material similar to the material included in the positive electrode current collector  21 A. The number of the positive electrode leads  50  is not particularly limited, and may be freely chosen. 
     The negative electrode lead  60  couples the battery can  10  and the negative electrode  22  (a negative electrode current collector  22 A to be described later) to each other. The negative electrode lead  60  includes a material similar to the material included in the battery can  10 . The number of the negative electrode leads  60  is not particularly limited, and may be freely chosen. 
     Note that the secondary battery may further include one or more of other unillustrated components. 
     Specifically, the secondary battery includes a safety valve mechanism. The safety valve mechanism cuts off the electrical coupling between the battery can  10  and the battery device  20  if an internal pressure of the battery can  10  reaches a certain level or higher due to, e.g., an internal short circuit or heating from outside. Although a mounting position of the safety valve mechanism is not particularly limited, the safety valve mechanism is provided at one of the bottom parts M 1  and M 2 , preferably the bottom part M 2  at which the electrode terminal  30  is not provided. 
     Further, the secondary battery includes an insulator between the battery can  10  and the battery device  20 . The insulator includes one or more of materials including, without limitation, an insulating film and an insulating sheet, and prevents a short circuit between the battery can  10  and the battery device  20  (the positive electrode  21 ). A mounting range of the insulator is not particularly limited, and may be freely chosen. 
     Note that the battery can  10  is provided with, for example, a liquid injection hole and a cleavage valve. The liquid injection hole is used for injecting the electrolytic solution into the battery can  10 , and is sealed after use. In a case where the internal pressure of the battery can  10  reaches a certain level or higher due to, e.g., an internal short circuit or heating from outside as described above, the cleavage valve cleaves to release the internal pressure. Although there is no limitation on the respective positions at which the liquid injection hole and the cleavage valve are to be provided, the liquid injection hole and the cleavage valve are each provided at one of the bottom parts M 1  and M 2 , preferably the bottom part M 2  at which the electrode terminal  30  is not provided, as with the mounting position of the safety valve mechanism described above. 
       FIG. 2  illustrates an enlarged sectional configuration of the battery device  20  illustrated in  FIG. 1 . Note that  FIG. 2  illustrates only one set of the positive electrode  21  and the negative electrode  22  opposed to each other with the separator  23  interposed therebetween, and illustrates a state where the positive electrode  21 , the negative electrode  22 , and the separator  23  are separated from each other. 
     The positive electrode  21  and the negative electrode  22  are stacked on each other with the separator  23  interposed therebetween, thus being opposed to each other with the separator  23  interposed therebetween, as illustrated in  FIG. 2 . 
     The positive electrode  21  allows lithium to be easily inserted into and extracted from only a portion of the whole thereof, which enables the charging and discharging reactions to proceed easily only in the portion. The positive electrode  21  extends in a width direction R, and has a dimension (a width L 1 ) in the width direction R. The width L 1  is a distance from one end to another end of the positive electrode  21  in the width direction R. As illustrated in  FIG. 2 , the width direction R described above is a direction along the sheet of  FIG. 2 , more specifically, a horizontal direction in  FIG. 2 . 
     Specifically, the positive electrode  21  includes the positive electrode current collector  21 A, and a positive electrode active material layer  21 B provided on each of both sides of the positive electrode current collector  21 A. Note that the positive electrode active material layer  21 B may be provided only on one side of the positive electrode current collector  21 A. 
     The positive electrode current collector  21 A includes one or more of electrically conductive materials including, without limitation, aluminum, an aluminum alloy, and stainless steel. 
     The positive electrode active material layer  21 B includes a positive electrode active material into which lithium is insertable and from which lithium is extractable. The positive electrode active material includes one or more of lithium-containing compounds including, without limitation, a lithium-containing transition metal compound. Examples of the lithium-containing transition metal compound include an oxide, a phosphoric acid compound, a silicic acid compound, a boric acid compound, etc. each including lithium and one or more transition metal elements as constituent elements. Specific examples of the oxide include LiNiO 2 , LiCoO 2 , and LiMn 2 O 4 . Specific examples of the phosphoric acid compound include LiFePO 4  and LiMnPO 4 . Note that the positive electrode active material layer may further include, without limitation, a positive electrode binder and a positive electrode conductor. The positive electrode binder includes a polymer compound, and the positive electrode conductor includes an electrically conductive material, such as a carbon material, a metal material, or a polymer compound. 
     The negative electrode  22  allows lithium to be easily inserted into and extracted from the whole thereof, which enables the charging and discharging reactions to proceed easily in the whole. The negative electrode  22  extends in the width direction R, and has a dimension (a width L 2 ) in the width direction R. The width L 2  is a distance from one end to another end of the negative electrode  22  in the width direction R. 
     Specifically, the negative electrode  22  includes the negative electrode current collector  22 A, and a negative electrode active material layer  22 B provided on each of both sides of the negative electrode current collector  22 A. Note that the negative electrode active material layer  22 B may be provided only on one side of the negative electrode current collector  22 A. 
     The negative electrode current collector  22 A includes one or more of electrically conductive materials including, without limitation, iron, copper, nickel, stainless steel, an iron alloy, a copper alloy, and a nickel alloy. 
     The negative electrode active material layer  22 B includes a negative electrode active material into which lithium is insertable and from which lithium is extractable. The negative electrode active material includes one or more of materials including, without limitation, a carbon material and a metal-based material. Examples of the carbon material include graphite. The metal-based material is a material that includes, as a constituent element or constituent elements, one or more elements among metal elements and metalloid elements that are each able to form an alloy with lithium. Specifically, the metal-based material includes one or more of elements including, without limitation, silicon and tin, as a constituent element or constituent elements. The metal-based material may be a simple substance, an alloy, a compound, or a mixture of two or more thereof. Note that the negative electrode active material layer may further include, without limitation, a negative electrode binder and a negative electrode conductor. Details of the negative electrode binder are similar to those of the positive electrode binder. Details of the negative electrode conductor are similar to those of the positive electrode conductor. 
     The separator  23  is an insulating porous film interposed between the positive electrode  21  and the negative electrode  22 . The separator  23  allows lithium to pass therethrough while preventing a short circuit between the positive electrode  21  and the negative electrode  22 . The separator  23  extends in the width direction R, and has a dimension (a width L 3 ) in the width direction R. The width L 3  is a distance from one end to another end of the separator  23  in the width direction R. Further, the separator  23  includes one or more of polymer compounds, including polyethylene. 
     The positive electrode  21 , the negative electrode  22 , and the separator  23  are each impregnated with the electrolytic solution. The electrolytic solution includes a solvent and an electrolyte salt. The solvent includes one or more of nonaqueous solvents (organic solvents) including, without limitation, a carbonic-acid-ester-based compound, a carboxylic-acid-ester-based compound, and a lactone-based compound. The electrolyte salt includes one or more of light metal salts, including a lithium salt. 
     The positive electrode  21  has the same dimension as the dimension of the negative electrode  22  in the width direction R. More specifically, the width L 1  of the positive electrode  21  is the same as the width L 2  of the negative electrode  22 . Note that the wording “the width L 1  is the same as the width L 2 ” refers to not only a case where the width L 1  is completely the same as the width L 2 , but also a case where the width L 1  is substantially the same as the width L 2 , taking dimensional deviation caused by a manufacturing error into account. 
     In the negative electrode  22 , the negative electrode active material is present throughout the width direction R. Thus, the negative electrode active material layer  22 B allows lithium to be easily inserted into and extracted from the whole thereof, which enables the charging and discharging reactions to proceed easily in the whole. 
     Specifically, in the negative electrode  22 , the charging and discharging reactions proceed easily in each of one end part and another end part in the width direction R, and the charging and discharging reactions proceed easily also in a middle part between the one end part and the other end part. The “one end part” described here is a left end part in  FIG. 2 , and the “other end part” described here is a right end part in  FIG. 2 . The same applies to the following. 
     In contrast, in the positive electrode  21 , the positive electrode active material is present throughout the width direction R. Lithium is easily inserted into and extracted from a portion of the positive electrode active material layer  21 B, which enables the charging and discharging reactions to proceed easily therein, whereas it is difficult for lithium to be inserted into and extracted from the rest of the positive electrode active material layer  21 B, which makes it difficult for the charging and discharging reactions to proceed therein. In the positive electrode  21 , the charging and discharging reactions thus proceed easily only in a portion of the whole, as described above. 
     Specifically, in the positive electrode active material layer  21 B of the positive electrode  21 , it is difficult for the charging and discharging reactions to proceed in each of one end part (a reaction less-active part  21 X 1 ) and another end part (a reaction less-active part  21 X 2 ) in the width direction R, and the charging and discharging reactions proceed easily in a middle part (a reaction active part  21 Y) between the one end part and the other end part. In other words, in the positive electrode active material layer  21 B, the one end part and the other end part are the reaction less-active parts  21 X 1  and  21 X 2  respectively, and the middle part is the reaction active part  21 Y. 
     The positive electrode  21  thus includes the reaction less-active part  21 X 1 , the reaction active part  21 Y, and the reaction less-active part  21 X 2  in this order in the width direction R. In other words, the positive electrode  21  includes the two reaction less-active parts  21 X 1  and  21 X 2  and the one reaction active part  21 Y. In  FIG. 2 , each of the reaction less-active parts  21 X 1  and  21 X 2  is hatched, and the border between each of the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y is denoted by a dashed line. 
     The reaction active part  21 Y includes the positive electrode current collector  21 A and the positive electrode active material layer  21 B, and the positive electrode active material layer  21 B includes the positive electrode active material. In the reaction active part  21 Y, lithium is easily inserted into and extracted from the positive electrode active material included in the positive electrode active material layer  21 B also after completion of the secondary battery, because the reaction active part  21 Y has not been subjected to a cutting process in the process of manufacturing the secondary battery (a process of fabricating the positive electrode  21 ) to be described later. In the reaction active part  21 Y, the charging and discharging reactions thus proceed easily also after the completion of the secondary battery. 
     In contrast, the reaction less-active part  21 X 1  includes the positive electrode current collector  21 A and the positive electrode active material layer  21 B, and the positive electrode active material layer  21 B includes the positive electrode active material. In the reaction less-active part  21 X 1 , an ultra-thin high-resistance layer is provided on a surface of the positive electrode active material layer  21 B on a side opposed to the negative electrode  22 , because the reaction less-active part  21 X 1  has been subjected to the cutting process in the process of manufacturing the secondary battery (the process of fabricating the positive electrode  21 ). Although not particularly limited, the high-resistance layer has a thickness of about several tens of nanometers to several hundreds of nanometers.  FIG. 2  omits the illustration of the high-resistance layer. The high-resistance layer substantially serves as an insulating layer with low ionic conductivity (low permeability to ions). Accordingly, the presence of the high-resistance layer makes it difficult for lithium to be inserted into and extracted from the positive electrode active material included in the reaction less-active part  21 X 1  after the completion of the secondary battery. In the reaction less-active part  21 X 1 , it is thus difficult for the charging and discharging reactions to proceed after the completion of the secondary battery. More specifically, the charging and discharging reactions proceed less easily in the reaction less-active part  21 X 1  than in the reaction active part  21 Y. 
     In particular, the high-resistance layer is preferably provided to extend onto a side surface of the reaction less-active part  21 X 1  (the positive electrode active material layer  21 B). A reason for this is that this makes it more difficult for the charging and discharging reactions to proceed. 
     Here, the reaction less-active part  21 X 1  does not include a coating layer intended to reduce electrical conductivity. Specifically, a porous coating layer or a gel coating layer having ionic conductivity is not included in the reaction less-active part  21 X 1 , even if the coating layer includes a material, such as aluminum oxide (alumina), having no electrically conductive property. 
     Note that the reaction less-active part  21 X 2  has a configuration similar to that of the reaction less-active part  21 X 2  described above. The reaction less-active part  21 X 2  also does not include the coating layer intended to reduce electrical conductivity, as with the case described in relation to the reaction less-active part  21 X 1  described above. 
     The width L 1  of the positive electrode  21  is the same as the width L 2  of the negative electrode  22  and the positive electrode  21  includes the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y for the following reasons. This helps to prevent occurrence of stacking deviation (positional deviation) between the positive electrode  21  and the negative electrode  22  in the course of manufacture and after manufacture (after completion) of the secondary battery, and also helps to prevent occurrence of a short circuit between the positive electrode  21  and the negative electrode  22 . The reasons described here will be described in detail later. 
     Although not particularly limited, each of the reaction less-active parts  21 X 1  and  21 X 2  preferably has a dimension (a width L 4 ) in the width direction R of from 50 μm to 150 μm both inclusive in particular. A reason for this is that this helps to sufficiently prevent occurrence of positional deviation, and to sufficiently prevent occurrence of a short circuit. In this case, it is difficult for even a minor short circuit to occur, while a battery capacity is secured. 
     In order to determine the width L 4  by determining the border between each of the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y, the positive electrode  21  may be analyzed by an analysis method such as microscopic Raman spectroscopy. 
     A method of determining the width L 4  by the microscopic Raman spectroscopy is as described below. Here, a description is given of a case where the positive electrode active material includes a lithium-containing transition metal compound (lithium cobalt oxide (LiCoO 2 )) which is an oxide, and the width L 4  of the reaction less-active part  21 X 1  is determined. 
     First, the positive electrode active material layer  21 B (the reaction less-active part  21 X 1  and the reaction active part  21 Y) is analyzed by means of a microscopic Raman spectrometer to thereby obtain a Raman spectrum. Examples of the microscopic Raman spectrometer employable include a laser Raman microscope RAMAN-11 manufactured by Nanophoton Corporation. 
     In the Raman spectrum, a peak derived from the A1g mode of the positive electrode active material (LiCoO 2 ) is detected in a Raman shift range of 590 cm −1  to 600 cm −1  or the vicinity thereof. This peak is an analysis parameter related to stretching vibration (stretching) of a Co—O bond, and has an A1g half-width indicating a degree of crystallinity of the positive electrode active material. Specifically, the A1g half-width being small indicates that the positive electrode active material has high crystallinity, and the use of the positive electrode active material thus enables the charging and discharging reactions to proceed easily. The A1g half-width being large indicates that the positive electrode active material has low crystallinity, and the use of the positive electrode active material thus makes it difficult for the charging and discharging reactions to proceed. 
     An analysis result to be used to determine the width L 4  is obtained on the basis of the Raman spectrum described above. In the analysis result, a vertical axis represents an average value of the A1g half-width (cm −1 ) and a horizontal axis represents a distance (μm). In this case, the distance represented by the horizontal axis is a distance from one end of the reaction less-active part  21 X 1  (one end of the reaction less-active part  21 X 1  on a side far from the reaction active part  21 Y) in a direction from the reaction less-active part  21 X 1  toward the reaction active part  21 Y. The average value of the A1g half-width represented by the vertical axis is the average value of five A1g half-widths obtained on the basis of five Raman spectra. The five Raman spectra are detected for each distance. 
     The positive electrode  21  is, as will be described later, formed by cutting (laser cutting) the positive electrode current collector  21 A with the positive electrode active material layer  21 B provided thereon by means of a laser apparatus. In this case, the vicinity (the one end part) of a cut portion of the positive electrode active material layer  21 B is heated at high temperature. This causes the positive electrode active material to be modified (the crystallinity of the positive electrode active material to change) in the one end part. As a result, the reaction less-active part  21 X 1  is formed. 
     Thus, in the analysis result of the positive electrode  21  (the reaction less-active part  21 X 1  and the reaction active part  21 Y) obtained by the microscopic Raman spectroscopy, the average value of the A1g half-width increases and then decreases as represented by an upward convex peak as the distance increases, and thereafter becomes substantially constant. In other words, in the positive electrode  21  (the positive electrode active material layer  21 B) subjected to the laser cutting, in a short distance range (the reaction less-active part  21 X 1 ), the positive electrode active material has low crystallinity, which makes it difficult for the charging and discharging reactions to proceed. In a long distance range (the reaction active part  21 Y), the positive electrode active material has high crystallinity, which enables the charging and discharging reactions to proceed easily. 
     Thereafter, a differential operation is performed on the average value of the A1g half-width with respect to the distance, on the basis of the analysis result described above, to thereby obtain a differential curve in which a vertical axis represents a derivative value and a horizontal axis represents the distance (μm). As described above, the average value of the A1g half-width increases and decreases as the distance increases, and thereafter becomes substantially constant. The derivative value thus increases and decreases and thereafter becomes substantially zero. The derivative value indicates a slope corresponding to a change in the average value of the A1g half-width. 
     Lastly, the position (distance) where the derivative value becomes substantially zero is determined to thereby determine the width L 4 . The position where the derivative value becomes substantially zero is the border position between the reaction less-active part  21 X 1  and the reaction active part  21 Y. Accordingly, the distance corresponding to the border position is the width L 4 . 
     A procedure of determining the width L 4  of the reaction less-active part  21 X 2  is similar to the procedure of determining the width L 4  of the reaction less-active part  21 X 1 , except that an analysis result whose horizontal axis represents a distance in a direction from the reaction less-active part  21 X 2  toward the reaction active part  21 Y is obtained by analyzing the reaction less-active part  21 X 2  and the reaction active part  21 Y in place of the reaction less-active part  21 X 1  and the reaction active part  21 Y. 
     Note that, in a case of determining the width L 4  on the basis of the analysis result of the positive electrode active material layer  21 B obtained by the microscopic Raman spectroscopy described above, the width L 4  may be determined on the basis of another analysis parameter, instead of determining the width L 4  on the basis of the average value of the A1g half-width which is the analysis parameter related to the crystallinity of the positive electrode active material. 
     Specifically, in a case where the positive electrode active material includes LiCoO 2  which is an oxide, the width L 4  may be determined by a similar procedure, except that an analysis result related to the intensity of a peak derived from CoO x  is used in place of the A1g half-width. Further, in a case where the positive electrode active material layer  21 B includes a carbon material as the positive electrode conductor, the width L 4  may be determined by a similar procedure, except that an analysis result related to the intensity of a G band peak derived from the physical property of the carbon material is used in place of the A1g half-width. 
     Here, the width L 3  of the separator  23  is the same as the width L 2  of the negative electrode  22 . Note that the wording “the width L 3  is the width L 1 ” refers to not only a case where the width L 3  is completely the same as the width L 2 , but also a case where the width L 3  is substantially the same as the width L 2 , as with the wording “the width L 1  is the same as the width L 2 ”. A difference between the width L 3  and the width L 2  in the case where the width L 3  is substantially the same as the width L 2  is 0.01 mm or less. 
     The secondary battery operates in a manner described below. Upon charging, in the battery device  20 , lithium is extracted from the positive electrode  21 , and the extracted lithium is inserted into the negative electrode  22  via the electrolytic solution. Upon discharging, in the battery device  20 , lithium is extracted from the negative electrode  22 , and the extracted lithium is inserted into the positive electrode  21  via the electrolytic solution. In these cases, the lithium is inserted and extracted in an ionic state. 
     In a case of manufacturing the secondary battery, the secondary battery is assembled by a procedure described below according to an embodiment. 
     First, the positive electrode active material is mixed with materials including, without limitation, the positive electrode binder and the positive electrode conductor on an as-needed basis to thereby obtain a positive electrode mixture. Thereafter, the positive electrode mixture is put into a solvent such as an organic solvent to thereby prepare a paste positive electrode mixture slurry. Lastly, the positive electrode mixture slurry is applied on each of both sides of the positive electrode current collector  21 A to thereby form the positive electrode active material layer  21 B. Thereafter, the positive electrode active material layer  21 B is compression-molded by means of a machine such as a roll pressing machine on an as-needed basis. In this case, the positive electrode active material layer  21 B may be heated. The positive electrode active material layer  21 B may be compression-molded a plurality of times. 
     Lastly, the cutting process is performed on the positive electrode active material layer  21 B. Specifically, the positive electrode current collector  21 A with the positive electrode active material layer  21 B formed thereon is cut (laser cutting) by means of a laser apparatus. Although not limited to a particular kind, examples of the laser include a YAG laser (having a wavelength of 1064 nm). The use of laser cutting as a cutting method enables the positive electrode current collector  21 A with the positive electrode active material layer  21 B formed thereon to be cut easily with high accuracy. 
     In this case, the vicinity (the one end part and the other end part) of the cut portion of the positive electrode active material layer  21 B is heated at high temperature. This causes a component of a material such as the positive electrode active material included in the positive electrode active material layer  21 B to be vaporized and oxidized, for example, in each of the one end part and the other end part. As a result, the high-resistance layer is formed on the surface of the positive electrode active material layer  21 B. For example, in a case where the positive electrode active material includes LiCoO 2  which is an oxide, the high-resistance layer is considered to include one or more of cobalt compounds including, without limitation, cobalt oxide and cobalt hydroxide. Thus, the reaction less-active part  21 X 1  is formed as the one end part with the high-resistance layer formed thereon, and the reaction less-active part  21 X 2  is similarly formed as the other end part with the high-resistance layer formed thereon. In other words, utilizing a high-temperature heating phenomenon involved in laser cutting makes it possible to intentionally reduce lithium insertability and extractability in a portion (the one end part and the other end part) of the positive electrode active material layer  21 B. This enables each of the reaction less-active parts  21 X 1  and  21 X 2  to be formed. 
     Conditions including a heating temperature and a heating time in the cutting process are not particularly limited, as long as the temperature allows for formation of the high-resistance layer. The heating temperature is adjustable depending on a condition such as an output of the laser. 
     In a case of forming each of the reaction less-active parts  21 X 1  and  21 X 2 , it is possible to adjust the width L 4  by changing the conditions including the heating temperature and the heating time described above. 
     Note that, in the middle part between the one end part and the other end part of the positive electrode active material layer  21 B, the high-resistance layer is not formed because the middle part is not heated at high temperature. The reaction active part  21 Y is thus formed as the middle part. 
     The positive electrode active material layer  21 B including the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y is formed on each of both sides of the positive electrode current collector  21 A in this manner. As a result, the positive electrode  21  is fabricated. 
     The negative electrode  22  is fabricated by a procedure similar to the fabrication procedure of the positive electrode  21  described above, except that the cutting process is not performed. Specifically, the negative electrode active material is mixed with materials including, without limitation, the negative electrode binder and the negative electrode conductor on an as-needed basis to thereby obtain a negative electrode mixture. Thereafter, the negative electrode mixture is put into a solvent such as an organic solvent to thereby prepare a paste negative electrode mixture slurry. Thereafter, the negative electrode mixture slurry is applied on each of both sides of the negative electrode current collector  22 A to thereby form the negative electrode active material layer  22 B. Thereafter, the negative electrode active material layer  22 B is compression-molded on an as-needed basis. Lastly, the negative electrode current collector  22 A with the negative electrode active material layer  22 B formed thereon is punched by means of a punching apparatus. The negative electrode active material layer  22 B is thus formed on each of both sides of the negative electrode current collector  22 A. As a result, the negative electrode  22  is fabricated. 
     The electrolyte salt is added to the solvent. Thus, the electrolyte salt is dissolved or dispersed in the solvent. The electrolytic solution including the solvent and the electrolyte salt is thereby prepared. 
     First, the positive electrode  21  and the negative electrode  22  are alternately stacked with the separator  23  interposed therebetween to thereby fabricate the stacked body  120 . 
     Thereafter, the stacked body  120  is placed into the containing part  11  through the opening  11 K. In this case, one end of the negative electrode lead  60  is coupled to the stacked body  120  (the negative electrode current collector  22 A of the negative electrode  22 ) and another end of the negative electrode lead  60  is coupled to the containing part  11  by a method such as a welding method. Although not limited to a particular kind, the welding method is one or more of welding methods including, without limitation, a laser welding method and a resistance welding method. Details of the kind of the welding method described here apply also to the following. 
     Thereafter, the cover part  12  with the electrode terminal  30  attached to the through hole  10 K with the gasket  40  interposed therebetween is used. The cover part  12  is placed on the containing part  11  to cover the opening  11 K, following which the cover part  12  is joined to the containing part  11  by a method such as a welding method. In this case, one end of the positive electrode lead  50  is coupled to the stacked body  120  (the positive electrode current collector  21 A of the positive electrode  21 ) and another end of the positive electrode lead  50  is coupled to the electrode terminal  30  by a method such as a welding method. The opening  11 K is thereby sealed by the cover part  12 . Thus, the stacked body  120  is enclosed inside the battery can  10 . 
     Lastly, the electrolytic solution is injected into the battery can  10  through the unillustrated liquid injection hole, following which the liquid injection hole is sealed. This causes the stacked body  120  (the positive electrode  21 , the negative electrode  22 , and the separator  23 ) to be impregnated with the electrolytic solution, thereby fabricating the battery device  20 . The battery device  20  is thus sealed into the battery can  10 . As a result, the secondary battery is completed. 
     According to this secondary battery, the positive electrode  21  has the width L 1  that is the same as the width L 2  of the negative electrode  22 , and the positive electrode  21  includes the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y. As a result, for a reason described below, it is possible to obtain a superior battery characteristic. 
       FIG. 3  illustrates a sectional configuration of a secondary battery (the battery device  20 ) of a first comparative example, and corresponds to  FIG. 2 .  FIG. 4  illustrates a sectional configuration of a secondary battery (the battery device  20 ) of a second comparative example, and corresponds to  FIG. 2 . 
     The secondary battery of the first comparative example has a configuration similar to that of the secondary battery according to the present embodiment, except that the positive electrode  21  does not include the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y, that the width L 1  of the positive electrode  21  is smaller than the width L 2  of the negative electrode  22 , and that the width L 3  of the separator  23  is larger than the width L 2  of the negative electrode  22 , as illustrated in  FIG. 3 . In this case, one end part of the positive electrode  21  is recessed back by a width L 5  from one end part of the negative electrode  22  toward an inner side, and another end part of the positive electrode  21  is recessed back by the width L 5  from another end part of the negative electrode  22  toward the inner side. A reason for making the width L 3  of the separator  23  larger than the width L 2  of the negative electrode  22  is that this prevents a short circuit between the positive electrode  21  and the negative electrode  22  caused by precipitation of lithium upon charging and discharging. 
     The secondary battery of the second comparative example has a configuration similar to that of the secondary battery according to the present embodiment, except that the positive electrode  21  does not include the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y, and that the width L 3  of the separator  23  is larger than the width L 2  of the negative electrode  22 , as illustrated in  FIG. 4 . 
     In the secondary battery of the first comparative example, as illustrated in  FIG. 3 , each of the one end part and the other end part of the negative electrode  22  is not opposed to the positive electrode  21 , because the width L 1  of the positive electrode  21  is smaller than the width L 2  of the negative electrode  22 . Note that the separator  23  is interposed between the positive electrode  21  and the negative electrode  22 . 
     However, if positional deviation of each of the positive electrode  21 , the negative electrode  22 , and the separator  23  occurs in the course of manufacture and after manufacture (after completion) of the secondary battery, it becomes easier for lithium to be extracted from each of the one end part and the other end part of the negative electrode  22  toward the positive electrode  21  upon charging and discharging. Lithium is thus precipitated in each of the one end part and the other end part of the negative electrode  22 , which makes it easier for a short circuit between the positive electrode  21  and the negative electrode  22  due to precipitation of lithium to occur. 
     This tendency to make it easier for a short circuit to occur becomes significant, in particular, in a case where the separator  23  interposed between the positive electrode  21  and the negative electrode  22  undergoes great positional deviation. A reason for this is that if the positional deviation results in absence of the separator  23  between the positive electrode  21  and the negative electrode  22 , it becomes easier for lithium to be precipitated in each of the one end part and the other end part of the negative electrode  22 . 
     Moreover, in the secondary battery of the first comparative example, the width L 5  results in a decrease in an area over which the positive electrode  21  and the negative electrode  22  are opposed to each other, which tends to cause a battery capacity to decrease. In this case, making the width L 5  smaller results in an increase in the area over which the positive electrode  21  and the negative electrode  22  correspond to each other, which causes the battery capacity to increase. However, if the width L 5  becomes smaller, the one end part of the positive electrode  21  and the one end part of the negative electrode  22  become closer to each other, and the other end part of the positive electrode  21  and the other end part of the negative electrode  22  become closer to each other. This makes it easier for a short circuit caused by the positional deviation described above to occur. 
     In view of these, in the secondary battery of the first comparative example, suppression of a short circuit and an increase in battery capacity have a trade-off relationship with each other. The trade-off relationship is a relationship in which improvement of one characteristic out of two characteristics causes degradation of the other characteristic. It is thus difficult to achieve both suppression of a short circuit and an increase in battery capacity. 
     In the secondary battery of the second comparative example, the width L 1  of the positive electrode  21  is equal to the width L 2  of the negative electrode  22 , as illustrated in  FIG. 4 . The whole of the negative electrode  22  is therefore opposed to the positive electrode  21 . In this case, the area over which the positive electrode  21  and the negative electrode  22  are opposed to each other increases, which causes the battery capacity to increase. 
     However, if positional deviation occurs to result in no interposition of the separator  23  between the positive electrode  21  and the negative electrode  22 , it becomes easier for a short circuit between the positive electrode  21  and the negative electrode  22  to occur, as described above. In this case, in particular, the one end part of the positive electrode  21  and the one end part of the negative electrode  22  are opposed to each other and the other end part of the positive electrode  21  and the other end part of the negative electrode  22  are opposed to each other even before occurrence of the positional deviation, because the width L 1  is the same as the width L 2 . Thus, if the positional deviation results in no interposition of the separator  23  between the positive electrode  21  and the negative electrode  22 , it becomes significantly easier for a short circuit between the positive electrode  21  and the negative electrode  22  to occur. 
     In view of these, the secondary battery of the second comparative example makes it possible to increase the battery capacity, but it is more difficult to suppress occurrence of a short circuit caused by positional deviation. 
     In contrast, in the secondary battery according to the present embodiment, although the width L 1  of the positive electrode  21  is the same as the width L 2  of the negative electrode  22 , the positive electrode  21  includes the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y, as illustrated in  FIG. 2 . 
     In this case, in the positive electrode active material layer  21 B, the charging and discharging reactions proceed easily in the middle part (the reaction active part  21 Y), whereas it is difficult for the charging and discharging reactions to proceed in each of the one end part (the reaction less-active part  21 X 1 ) and the other end part (the reaction less-active part  21 X 2 ). Thus, even if each of the one end part and the other end part of the positive electrode  21  is opposed to the negative electrode  22 , it is difficult for lithium to be extracted from the negative electrode  22  toward the positive electrode  21  (the reaction less-active parts  21 X 1  and  21 X 2 ). This helps to prevent occurrence of a short circuit between the positive electrode  21  and the negative electrode  22  due to precipitation of lithium, although the width L 1  is the same as the width L 2 . 
     Further, even if positional deviation occurs to result in no interposition of the separator  23  between the positive electrode  21  and the negative electrode  22 , it is difficult for lithium to be inserted into and extracted from each of the one end part (the reaction less-active part  21 X 1 ) and the other end part (the reaction less-active part  21 X 2 ) of the positive electrode  21 , which makes it difficult for lithium to be extracted from the negative electrode  22  toward the positive electrode  21  (the reaction less-active parts  21 X 1  and  21 X 2 ). This helps to prevent occurrence of a short circuit between the positive electrode  21  and the negative electrode  22  due to precipitation of lithium, although the width L 1  is the same as the width L 2 . 
     Moreover, as described above, even slight presence of each of the reaction less-active parts  21 X 1  and  21 X 2  makes it difficult for lithium to be extracted from the negative electrode  22  toward each of the one end part (the reaction less-active part  21 X 1 ) and the other end part (the reaction less-active part  21 X 2 ) of the positive electrode  21 . Accordingly, the width L 4  may be small. Thus, the area over which the positive electrode  21  and the negative electrode  22  are opposed to each other is almost maximum within a range in which a short circuit between the positive electrode  21  and the negative electrode  22  due to precipitation of lithium is preventable. This results in a great increase in battery capacity. 
     In view of these, the secondary battery according to the present embodiment breaks through the trade-off relationship described in relation to the secondary battery of the first comparative example, which makes it possible to achieve both suppression of a short circuit and an increase in battery capacity. 
     In this case, in particular, each of the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y is formed easily and stably by only performing the simple cutting process utilizing a high-temperature heating phenomenon involved in laser cutting on the positive electrode active material layer  21 B, after forming the positive electrode active material layer  21 B including the positive electrode active material. It is thus possible to easily and stably achieve both suppression of a short circuit and an increase in battery capacity. 
     In addition, in the secondary battery according to the present embodiment, the width L 4  may be from 50 μm to 150 μm both inclusive. This not only helps to sufficiently prevent occurrence of positional deviation and to sufficiently prevent occurrence of a short circuit, but also helps to prevent occurrence of even a minor short circuit while securing a battery capacity. Accordingly, it is possible to achieve higher effects. 
     Further, as described above, utilizing the reaction less-active parts  21 X 1  and  21 X 2  makes it difficult for a short circuit between the positive electrode  21  and the negative electrode  22  to occur in the first place. The width L 3  of the separator  23  thus does not have to be larger than the width L 2  of the negative electrode  22 , and the width L 3  of the separator  23  may be the same as the width L 2  of the negative electrode  22 . In this case, the width of the whole battery device  20  is determined on the basis of the width L 2  of the negative electrode  22 , unlike in a case where the width of the whole battery device  20  is determined on the basis of the width L 3  of the separator  23  because the width L 3  of the separator  23  is larger than the width L 2  of the negative electrode  22 . Thus, the separator  23  may have the width L 3  that is the same as the width L 2  of the negative electrode  22 . This results in a further increase in the area over which the positive electrode  21  and the negative electrode  22  are opposed to each other. Accordingly, it is possible to achieve higher effects. 
     Further, in the battery device  20 , the positive electrode  21  and the negative electrode  22  may be stacked with the separator  23  interposed therebetween (the stacked electrode body). This makes it more difficult for a dead space to occur in the battery device  20  than in a case where the positive electrode  21  and the negative electrode  22  are wound with the separator  23  interposed therebetween (a wound electrode body). The dead space that occurs in the wound electrode body is a space such as one formed at a winding core part. Thus, the energy density per unit volume further increases to make it possible to achieve higher effects. 
     Further, the secondary battery may be a button-type secondary battery having a flat and columnar shape. This makes it possible to achieve higher effects because the energy density per unit volume effectively increases in the small-sized secondary battery which is highly constrained in terms of size. 
     Next, a description will be given of a secondary battery according to a second embodiment of the technology. 
       FIG. 5  illustrates a sectional configuration of the secondary battery according to the second embodiment, and corresponds to  FIG. 2 . The secondary battery according to the second embodiment has a configuration similar to that of the secondary battery according to the first embodiment, except for the following configuration. In  FIG. 5 , the same components as the components illustrated in  FIG. 2  are denoted with the same reference signs. In the following description, where appropriate, reference will be made to the components of the secondary battery according to the first embodiment described already. 
     Here, an ultra-thin high-resistance layer is not provided on each of the one end part and the other end part of the positive electrode active material layer  21 B. Instead, the positive electrode  21  includes insulating layers  24  and  25 . In the positive electrode  21 , the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y are thus provided by utilizing presence or absence of the insulating layers  24  and  25 . 
     Specifically, the positive electrode active material layer  21 B has, as a whole, a configuration similar to that of the reaction active part  21 Y described in the first embodiment. More specifically, the middle part of the positive electrode active material layer  21 B includes the positive electrode active material, which enables the charging and discharging reactions to proceed easily in the middle part. Further, each of the one end part and the other end part of the positive electrode active material layer  21 B includes the positive electrode active material, which enables the charging and discharging reactions to proceed easily also in each of the one end part and the other end part. 
     The insulating layer  24  is disposed on the surface of the one end part of the positive electrode active material layer  21 B on the side opposed to the negative electrode  22 . In a region where the insulating layer  24  is disposed, the insulating layer  24  has a role similar to that of the high-resistance layer, which makes it difficult for the charging and discharging reactions to proceed in the one end part of the positive electrode active material layer  21 B. The reaction less-active part  21 X 1  is thus provided as the one end part of the positive electrode active material layer  21 B, by utilizing the insulating layer  24 . 
     In particular, the insulating layer  24  is preferably disposed to extend onto the side surface of the reaction less-active part  21 X 1  (the one end part of the positive electrode active material layer  21 B). A reason for this is that this makes it more difficult for the charging and discharging reactions to proceed. 
     The insulating layer  25  is disposed on the surface of the other end part of the positive electrode active material layer  21 B on the side opposed to the negative electrode  22 . In a region where the insulating layer  25  is disposed, the insulating layer  25  has a role similar to that of the high-resistance layer, which makes it difficult for the charging and discharging reactions to proceed in the other end part of the positive electrode active material layer  21 B. The reaction less-active part  21 X 2  is thus provided as the other end part of the positive electrode active material layer  21 B, by utilizing the insulating layer  25 . 
     In particular, the insulating layer  25  is preferably disposed to extend onto the side surface of the reaction less-active part  21 X 2  (the other end part of the positive electrode active material layer  21 B). A reason for this is that this makes it more difficult for the charging and discharging reactions to proceed. 
     In contrast, in a region where none of the insulating layers  24  and  25  is disposed, the charging and discharging reactions with the negative electrode  22  proceed easily in the positive electrode active material layer  21 B. The reaction active part  21 Y is thus provided as the middle part of the positive electrode active material layer  21 B. 
     Each of the insulating layers  24  and  25  is an insulating resin tape having no ionic conductivity (permeability to ions). This insulating resin tape includes one or more of polymer materials including, without limitation, polyimide, polyethylene terephthalate (PET), and polyolefin. Note that the material included in the insulating layer  24  may be the same as or different from the material included in the insulating layer  25 . 
     Details of a width L 6  of each of the insulating layers  24  and  25  are similar to those of the width L 4 . 
     A method of manufacturing the secondary battery according to the second embodiment is similar to the method of manufacturing the secondary battery according to the first embodiment, except that each of the insulating layers  24  and  25  is formed instead of performing the cutting process. 
     In a case of forming each of the insulating layers  24  and  25 , the insulating resin tape is sticked to the surface of the positive electrode active material layer  21 B. 
     In the secondary battery according to the second embodiment also, the width L 1  of the positive electrode  21  is the same as the width L 2  of the negative electrode  22 , and the insulating layers  24  and  25  are utilized to make the positive electrode  21  include the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y. Thus, for a reason similar to that for the secondary battery according to the first embodiment, it is possible to achieve both suppression of a short circuit and an increase in battery capacity. 
     In particular, each of the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y may include the positive electrode active material, and the insulating layers  24  and  25  may be disposed on the surface of the positive electrode active material layer  21 B on the side opposed to the negative electrode  22 . Thus, a simple configuration utilizing presence or absence of the insulating layers  24  and  25  allows each of the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y to be provided, even without performing the cutting process. As a result, suppression of a short circuit and an increase in battery capacity are both achieved easily and stably, which makes it possible to achieve higher effects. 
     Note that other action and effects related to the secondary battery according to the second embodiment are similar to those related to the secondary battery according to the first embodiment, except for action and effects related to the cutting process. 
     Next, a description will be given of a secondary battery according to a third embodiment of the technology. 
       FIG. 6  illustrates a sectional configuration of the secondary battery according to the third embodiment, and corresponds to  FIG. 2 . The secondary battery according to the third embodiment has a configuration similar to that of the secondary battery according to the first embodiment, except for the following configuration. In  FIG. 6 , the same components as the components illustrated in  FIG. 2  are denoted with the same reference signs. In the following description, where appropriate, reference will be made to the components of the secondary battery according to the first embodiment described already. 
     Here, the positive electrode active material layer  21 B of the positive electrode  21  includes inactive material parts  21 M 1  and  21 M 2  and an active material part  21 N. In the positive electrode  21 , the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y are thus provided by utilizing the inactive material parts  21 M 1  and  21 M 2  and the active material part  21 N. 
     Specifically, each of the one end part and the other end part of the positive electrode active material layer  21 B has not been subjected to the cutting process. Instead, the positive electrode active material layer  21 B includes the inactive material parts  21 M 1  and  21 M 2  into which lithium is not insertable and from which lithium is not extractable, and the active material part  21 N into which lithium is insertable and from which lithium is extractable. Thus, in the positive electrode  21 , the reaction less-active parts  21 X 1  and  21 X 2  are provided by the inactive material parts  21 M 1  and  21 M 2 , and the reaction active part  21 Y is provided by the active material part  21 N. 
     Each of the inactive material parts  21 M 1  and  21 M 2  includes one or more of insulating materials including, without limitation, aluminum oxide (alumina), and does not include the positive electrode active material. Note that the material included in the inactive material part  21 M 1  may be the same as or different from the material included in the inactive material part  21 M 2 . Note that each of the inactive material parts  21 M 1  and  21 M 2  may further include, without limitation, a binder. 
     Each of the inactive material parts  21 M 1  and  21 M 2  thus does not include the positive electrode active material, which prevents lithium from being inserted therein and extracted therefrom. Accordingly, the reaction less-active part  21 X 1  is provided as the one end part of the positive electrode active material layer  21 B (the inactive material part  21 M 1 ), and the reaction less-active part  21 X 2  is provided as the other end part (the inactive material part  21 M 2 ) of the positive electrode active material layer  21 B. 
     The active material part  21 N includes the positive electrode active material. The active material part  21 N has a configuration similar to that of the positive electrode active material layer  21 B not subjected to the cutting process. 
     The active material part  21 N thus includes the positive electrode active material, which allows lithium to be inserted therein and extracted therefrom. Accordingly, the reaction active part  21 Y is provided as the middle part (the active material part  21 N) of the positive electrode active material layer  21 B. 
     Details of a width L 7  of each of the inactive material parts  21 M 1  and  21 M 2  are similar to those of the width L 4 . 
     A method of manufacturing the secondary battery according to the third embodiment is similar to the method of manufacturing the secondary battery according to the first embodiment, except that, instead of performing the cutting process, the positive electrode active material layer  21 B including the inactive material parts  21 M 1  and  21 M 2  and the active material part  21 N is formed. 
     In a case of forming the positive electrode active material layer  21 B, first, the insulating material is mixed with materials including, without limitation, the binder on an as-needed basis, following which the resulting mixture is put into a solvent such as an organic solvent to thereby prepare a paste insulating slurry. Thereafter, the paste positive electrode mixture slurry is applied on a portion of a surface of the positive electrode current collector  21 A by the procedure described above to thereby form the active material part  21 N. Lastly, the paste insulating slurry is applied on the rest of the surface of the positive electrode current collector  21 A to thereby form each of the inactive material parts  21 M 1  and  21 M 2 . 
     In the secondary battery according to the third embodiment also, the width L 1  of the positive electrode  21  is the same as the width L 2  of the negative electrode  22 , and the inactive material parts  21 M 1  and  21 M 2  and the active material part  21 N are utilized to make the positive electrode  21  include the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y. Thus, for a reason similar to that for the secondary battery according to the first embodiment, it is possible to achieve both suppression of a short circuit and an increase in battery capacity. 
     In particular, the active material part  21 N may include the positive electrode active material, and each of the inactive material parts  21 M 1  and  21 M 2  may include the insulating material without including the positive electrode active material. Thus, a simple configuration utilizing presence or absence of the positive electrode active material allows each of the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y to be provided, even without performing the cutting process. As a result, suppression of a short circuit and an increase in battery capacity are both achieved easily and stably, which makes it possible to achieve higher effects. 
     Note that other action and effects related to the secondary battery according to the third embodiment are similar to those related to the secondary battery according to the first embodiment, except for action and effects related to the cutting process. 
     Next, a description will be given of modifications of the secondary battery described above according to an embodiment. The configuration of the secondary battery is appropriately modifiable as described below. Note that any two or more of the following series of modifications may be combined. 
     In the first embodiment ( FIG. 2 ), the positive electrode  21  includes both of the reaction less-active parts  21 X 1  and  21 X 2  formed by means of the cutting process. 
     However, as illustrated in  FIG. 7  corresponding to  FIG. 2 , the positive electrode  21  may include only the reaction less-active part  21 X 1  without including the reaction less-active part  21 X 2 . Alternatively, as illustrated in  FIG. 8  corresponding to  FIG. 2 , the positive electrode  21  may include the reaction less-active part  21 X 2  without including the reaction less-active part  21 X 1 . 
     A method of manufacturing the secondary battery illustrated in  FIG. 7  is similar to the method of manufacturing the secondary battery illustrated in  FIG. 2 , except that, in the process of fabricating the positive electrode  21 , the cutting process is performed on only the one end part of the positive electrode active material layer  21 B, without performing the cutting process on the other end part of the positive electrode active material layer  21 B. A method of manufacturing the secondary battery illustrated in  FIG. 8  is similar to the method of manufacturing the secondary battery illustrated in  FIG. 2 , except that, in the process of fabricating the positive electrode  21 , the cutting process is performed on only the other end part of the positive electrode active material layer  21 B, without performing the cutting process on the one end part of the positive electrode active material layer  21 B. 
     In these cases also, suppression of a short circuit and an increase in battery capacity are both achieved by utilizing either one of the reaction less-active parts  21 X 1  and  21 X 2 , which makes it possible to achieve similar effects. Note that, in order to sufficiently suppress occurrence of a short circuit and to sufficiently increase a battery capacity, the positive electrode  21  preferably includes both of the reaction less-active parts  21 X 1  and  21 X 2 , as illustrated in  FIG. 2 . 
     In the second embodiment ( FIG. 5 ), the positive electrode  21  includes both of the insulating layers  24  and  25 , and therefore includes both of the reaction less-active parts  21 X 1  and  21 X 2 . 
     However, as illustrated in  FIG. 9  corresponding to  FIG. 5 , the positive electrode  21  may include only the insulating layer  24  without including the insulating layer  25 , and therefore may include only the reaction less-active part  21 X 1  without including the reaction less-active part  21 X 2 . Alternatively, as illustrated in  FIG. 10  corresponding to  FIG. 5 , the positive electrode  21  may include only the insulating layer  25  without including the insulating layer  24 , and therefore may include only the reaction less-active part  21 X 2  without including the reaction less-active part  21 X 1 . 
     A method of manufacturing the secondary battery illustrated in  FIG. 9  is similar to the method of manufacturing the secondary battery illustrated in  FIG. 2 , except that only the insulating layer  24  is formed, without forming the insulating layer  25 , in the process of fabricating the positive electrode  21 . A method of manufacturing the secondary battery illustrated in  FIG. 8  is similar to the method of manufacturing the secondary battery illustrated in  FIG. 2 , except that only the insulating layer  25  is formed, without forming the insulating layer  24 , in the process of fabricating the positive electrode  21 . 
     In these cases also, suppression of a short circuit and an increase in battery capacity are both achieved by utilizing either one of the reaction less-active parts  21 X 1  and  21 X 2 , which makes it possible to achieve similar effects. Note that, in order to sufficiently suppress occurrence of a short circuit and to sufficiently increase a battery capacity, the positive electrode  21  preferably includes both of the insulating layers  24  and  25 , as illustrated in  FIG. 2 . 
     In the third embodiment ( FIG. 6 ), the positive electrode  21  includes both of the inactive material parts  21 M 1  and  21 M 2 , and therefore includes both of the reaction less-active parts  21 X 1  and  21 X 2 . 
     However, as illustrated in  FIG. 11  corresponding to  FIG. 6 , the positive electrode  21  may include only the inactive material part  21 M 1  without including the inactive material part  21 M 2 , and therefore may include only the reaction less-active part  21 X 1  without including the reaction less-active part  21 X 2 . Alternatively, as illustrated in  FIG. 12  corresponding to  FIG. 6 , the positive electrode  21  may include only the inactive material part  21 M 2  without including the inactive material part  21 M 1 , and therefore may include only the reaction less-active part  21 X 2  without including the reaction less-active part  21 X 1 . 
     A method of manufacturing the secondary battery illustrated in  FIG. 11  is similar to the method of manufacturing the secondary battery illustrated in  FIG. 2 , except that only the inactive material part  21 M 1  is formed, without forming the inactive material part  21 M 2 , in the process of fabricating the positive electrode  21 . A method of manufacturing the secondary battery illustrated in  FIG. 12  is similar to the method of manufacturing the secondary battery illustrated in  FIG. 2 , except that only the inactive material part  21 M 2  is formed, without forming the inactive material part  21 M 1 , in the process of fabricating the positive electrode  21 . 
     In these cases also, suppression of a short circuit and an increase in battery capacity are both achieved by utilizing either one of the reaction less-active parts  21 X 1  and  21 X 2 , which makes it possible to achieve similar effects. Note that, in order to sufficiently suppress occurrence of a short circuit and to sufficiently increase a battery capacity, the positive electrode  21  preferably includes both of the inactive material parts  21 M 1  and  21 M 2 , as illustrated in  FIG. 2 . 
     In each of the first embodiment, the second embodiment, and the third embodiment ( FIG. 1 ), the secondary battery includes, inside the battery can  10 , the battery device  20  which is a stacked electrode body including the positive electrode  21  and the negative electrode  22  that are stacked with the separator  23  interposed therebetween. 
     However, as illustrated in  FIG. 13  corresponding to  FIG. 1 , the secondary battery may include, inside the battery can  10 , a battery device  70  (a positive electrode  71 , a negative electrode  72 , and a separator  73 ) which is a wound electrode body, in place of the battery device  20  (the positive electrode  21 , the negative electrode  22 , and the separator  23 ) which is a stacked electrode body. In the battery device  70 , the positive electrode  71  and the negative electrode  72  are wound with the separator  73  interposed therebetween. More specifically, in the battery device  70  which is a wound electrode body, the positive electrode  71  and the negative electrode  72  are stacked with the separator  73  interposed therebetween, and are wound in the state where the positive electrode  71  and the negative electrode  72  are alternately stacked with the separator  73  interposed therebetween. The battery device  70  has, at the winding core, a space (a winding center space  70 S) in which none of the positive electrode  71 , the negative electrode  72 , and the separator  73  is present. The positive electrode  71 , the negative electrode  72 , and the separator  73  have configurations similar to those of the positive electrode  21 , the negative electrode  22 , and the separator  23 , respectively. Note that, as illustrated in  FIG. 13 , the width direction R in a case where the battery device  70  which is a wound electrode body is used is a direction intersecting the sheet of  FIG. 13 . 
     A method of manufacturing the secondary battery illustrated in  FIG. 13  is similar to the method of manufacturing the secondary battery illustrated in  FIG. 1  except that, after the positive electrode  71  and the negative electrode  72  are alternately stacked with the separator  73  interposed therebetween, the stack of the positive electrode  71 , the negative electrode  72 , and the separator  73  is wound to thereby fabricate a wound body  170  to be used to fabricate the battery device  70 . In this case, the wound body  170  is enclosed inside the battery can  10  (the containing part  11  and the cover part  12 ), and thereafter the wound body  170  is impregnated with an electrolytic solution injected into the battery can  10 . The battery device  70  is thereby fabricated. 
     In this case also, suppression of a short circuit and an increase in battery capacity are both achieved by means of the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y, which makes it possible to achieve similar effects. Note that, as described above, in order to avoid a decrease in energy density per unit volume due to the occurrence of a dead space (the winding center space  70 S), the battery device  20  which is a stacked electrode body causing no dead space is preferable to the battery device  70  which is a wound electrode body causing the dead space. 
     In the first embodiment, in order to form the high-resistance layer, the cutting process is performed by utilizing laser cutting which is a process that heats an object at high temperature. However, the method of forming the high-resistance layer may be another method other than laser cutting. Examples of the other method include a method of forming the high-resistance layer by punching the positive electrode current collector  21 A with the positive electrode active material layer  21 B formed thereon by means of a punching process, and thereafter locally heating the positive electrode active material layer  21 B by means of a laser irradiation process (a non-cutting process). 
     In this case also, each of the reaction less-active parts  21 X 1  and  21 X 2  is formed by utilizing the high-resistance layer, which makes it possible to achieve similar effects. 
     EXAMPLES 
     Examples of the technology of the present disclosure are described below according to an embodiment. 
     Examples 1 to 5 and Comparative Example 1 
     Secondary batteries were fabricated, following which performance of the secondary batteries was evaluated. 
     [Fabrication of Secondary Batteries of Examples 1 to 5] 
     The button-type secondary batteries (lithium-ion secondary batteries) illustrated in  FIGS. 1 and 2  were fabricated by a procedure described below. 
     (Fabrication of Positive Electrode) 
     First, 91 parts by mass of the positive electrode active material (LiCoO 2 ), 3 parts by mass of the positive electrode binder (polyvinylidene difluoride), and 6 parts by mass of the positive electrode conductor (graphite) were mixed with each other to thereby obtain a positive electrode mixture. Thereafter, the positive electrode mixture was put into a solvent (N-methyl-2-pyrrolidone which is an organic solvent), following which the organic solvent was stirred to thereby prepare a paste positive electrode mixture slurry. Thereafter, the positive electrode mixture slurry was applied on each of both sides of the positive electrode current collector  21 A (an aluminum foil having a thickness of 12 μm) by means of a coating apparatus, following which the applied positive electrode mixture slurry was dried to thereby form the positive electrode active material layer  21 B. Thereafter, the positive electrode active material layer  21 B was compression-molded by means of a roll pressing machine. 
     Lastly, the positive electrode current collector  21 A with the positive electrode active material layer  21 B formed thereon was cut (laser cutting) by means of a laser apparatus whose light source was a YAG laser (having a wavelength of 1064 nm). By the cutting process, the reaction less-active parts  21 X 1  and  21 X 2  were formed, by utilizing high-temperature heating, in the vicinity (the one end part and the other end part) of the cut portion in the positive electrode active material layer  21 B. In addition, the reaction active part  21 Y was formed in the rest of the positive electrode active material layer  21 B. In this case, the width L 4  (μm) of each of the reaction less-active parts  21 X 1  and  21 X 2  was changed by changing the cutting conditions (the heating temperature and the heating time). The positive electrode  21  (having the width L 1  of 16.5 mm) was thereby fabricated. 
     After the fabrication of the positive electrode  21 , the positive electrode active material layer  21 B (LiCoO 2 ) was analyzed by the microscopic Raman spectroscopy to thereby obtain a Raman spectrum. Thereafter, an analysis result to be used to determine the width L 4  was obtained on the basis of the Raman spectrum. In the analysis result, the vertical axis represents the average value of the A1g half-width (cm −1 ) and the horizontal axis represents the distance (μm). Examination of the width L 4  (μm) based on the analysis result revealed the results described in Table 1. Note that a detailed procedure of determining the width L 4  is as described above. 
     (Fabrication of Negative Electrode) 
     First, 95 parts by mass of the negative electrode active material (graphite) and 5 parts by mass of the negative electrode binder (polyvinylidene difluoride) were mixed with each other to thereby obtain a negative electrode mixture. Thereafter, the negative electrode mixture was put into a solvent (N-methyl-2-pyrrolidone which is an organic solvent), following which the organic solvent was stirred to thereby prepare a paste negative electrode mixture slurry. Thereafter, the negative electrode mixture slurry was applied on each of both sides of the negative electrode current collector  22 A (a copper foil having a thickness of 15 μm) by means of a coating apparatus, following which the applied negative electrode mixture slurry was dried to thereby form the negative electrode active material layer  22 B. Lastly, the negative electrode active material layer  22 B was compression-molded by means of a roll pressing machine. The negative electrode  22  (having the width L 2  of 16.5 mm) was thereby fabricated. 
     (Preparation of Electrolytic Solution) 
     The electrolyte salt (LiPF 6 ) was added to a solvent (ethylene carbonate and diethyl carbonate which are organic solvents), following which the solvent was stirred. In this case, a mixture ratio (a weight ratio) between ethylene carbonate and diethyl carbonate in the solvent was set to 30:70, and the content of the electrolyte salt with respect to the solvent was set to 1 mol/kg. The electrolytic solution was thereby prepared. 
     (Assembly of Secondary Battery) 
     First, the positive electrode lead  50  (an aluminum wire) was welded to the positive electrode  21  (the positive electrode current collector  21 A) and the negative electrode lead  60  (an aluminum wire) was welded to the negative electrode  22  (the negative electrode current collector  22 A) by the resistance welding method. 
     Thereafter, the positive electrode  21  with the positive electrode lead  50  coupled thereto and the negative electrode  22  with the negative electrode lead  60  coupled thereto were alternately stacked with the separator  23  (a polyethylene film having a thickness of 10 μm and the width L 3  of 16.5 mm) interposed therebetween to thereby fabricate the stacked body  120 . 
     Thereafter, the stacked body  120  was placed into the containing part  11  (SUS316) through the opening  11 K. In this case, the negative electrode lead  60  was welded to the containing part  11  (the bottom part M 2 ) by the resistance welding method. 
     Thereafter, the electrolytic solution was injected into the containing part  11  through the opening  11 K, following which the cover part  12  (SUS316) was welded to the containing part  11  by the laser welding method. The cover part  12  has the electrode terminal  30  (an aluminum plate) attached thereto with the gasket  40  (a polypropylene film) interposed therebetween. In this case, the positive electrode lead  50  was welded to the electrode terminal  30  by the resistance welding method. 
     Thus, the stacked body  120  (the positive electrode  21 , the negative electrode  22 , and the separator  23 ) was impregnated with the electrolytic solution to thereby fabricate the battery device  20 . In addition, the cover part  12  was joined to the containing part  11  to thereby form the battery can  10 . The battery device  20 , for example, was thus sealed into the battery can  10 . As a result, the secondary battery was assembled. 
     (Stabilization of Secondary Battery) 
     The secondary battery having been assembled was charged and discharged for one cycle in an ambient temperature environment (at a temperature of 23° C.). Upon the charging, the secondary battery was charged with a constant current of 0.1 C until a voltage reached 4.2 V, and was thereafter charged with a constant voltage of 4.2 V until a current reached 0.05 C. Upon the discharging, the secondary battery was discharged with a constant current of 0.1 C until the voltage reached 3.0 V. 0.1 C is a value of a current that causes a battery capacity (a theoretical capacity) to be completely discharged in 10 hours, and 0.05 C is a value of a current that causes a battery capacity to be completely discharged in 20 hours. 
     Thus, a film was formed on a surface of, for example, the negative electrode  22  to electrochemically stabilize the state of the secondary battery. As a result, the secondary battery was completed. 
     [Fabrication of Secondary Battery of Comparative Example 1] 
     The secondary battery was fabricated by a similar procedure, except that the positive electrode  21  was fabricated by means of a punching process without using laser cutting. In this case, the positive electrode active material layer  21 B did not include the reaction less-active parts  21 X 1  and  21 X 2 . 
     Evaluation of the performance (a battery capacity characteristic and voltage stability) of the secondary batteries revealed the results described in Table 1. 
     (Battery Capacity Characteristic) 
     The secondary battery of each of Comparative Example 1 and Examples 1 to 5 was charged and discharged in an ambient temperature environment (at a temperature of 23° C.) to thereby measure a battery capacity (discharge capacity). In this case, twenty secondary batteries were tested to thereby calculate an average value of the battery capacity related to the twenty secondary batteries. Upon the charging, the secondary battery was charged with a constant current of 0.5 C until a voltage reached 4.2 V, and was thereafter charged with a constant voltage of 4.2 V until a total charging time reached 3.5 hours. Upon the discharging, the secondary battery was discharged with a constant current of 0.2 C until the voltage reached 3.0 V. 0.5 C is a value of a current that causes a battery capacity to be completely discharged in 2 hours, and 0.2 C is a value of a current that causes a battery capacity to be completely discharged in 5 hours. 
     Lastly, a capacity decrease rate which is an index for evaluating the battery capacity characteristic was calculated on the basis of the following calculation formula. 
       Capacity decrease rate (%)=[(battery capacity of secondary battery of Comparative Example 1−battery capacity of secondary battery of each of Examples 1 to 5)/battery capacity of secondary battery of Comparative Example 1]×100.
 
     (Voltage Stability) 
     First, the secondary battery was charged in an ambient temperature environment (at a temperature of 23° C.). A charging condition was similar to a charging condition in the process of stabilizing the secondary battery described above, except that the secondary battery was charged until a state of charge (SOC) reached 25%. Thereafter, while the secondary battery in a charged state was left to stand (for a leaving time of 72 hours) in the same environment, an open-circuit voltage (OCV) of the secondary battery was measured. Lastly, the number of secondary batteries (the number of OCV failures (number)) in which the open-circuit voltage decreased by 0.2 mV/h or greater was examined, on the basis of the measurement result of the open-circuit voltage. In this case, the total number of secondary batteries tested was 20. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Capacity 
                 Number of 
               
               
                   
                 Width L4 
                 decrease rate 
                 OCV failures 
               
               
                   
                 (μm) 
                 (%) 
                 (number) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Comparative 
                 0 
                 0.00 
                 8 
               
               
                   
                 Example 1 
               
               
                   
                 Example 1 
                 50 
                 0.92 
                 2 
               
               
                   
                 Example 2 
                 100 
                 1.84 
                 1 
               
               
                   
                 Example 3 
                 150 
                 2.75 
                 0 
               
               
                   
                 Example 4 
                 200 
                 3.66 
                 0 
               
               
                   
                 Example 5 
                 250 
                 4.00 
                 0 
               
               
                   
                   
               
            
           
         
       
     
     [Discussion] 
     As described in Table 1, the battery capacity characteristic and the voltage stability of the secondary battery varied depending on the configuration of the positive electrode  21 . 
     Specifically, in a case where the positive electrode active material layer  21 B did not include the reaction less-active parts  21 X 1  and  21 X 2  (Comparative Example 1), the capacity decrease rate was zero, which allowed a high battery capacity to be obtained. However, it became easier for a minor short circuit to occur, which caused the number of OCV failures to increase. In this case, the number of OCV failures reached about half of the total number of secondary batteries. 
     In contrast, in a case where the positive electrode active material layer  21 B included the reaction less-active parts  21 X 1  and  21 X 2  (Examples 1 to 5), the capacity decrease rate was suppressed to a low single-digit level, which allowed the battery capacity to be secured. In addition, it became difficult for a minor short circuit to occur, which allowed the number of OCV failures to decrease. In this case, the number of OCV failures was substantially zero. 
     In this case, if the width L 4  was from 50 μm to 150 μm both inclusive in particular, the capacity decrease rate was sufficiently suppressed, which allowed a higher battery capacity to be obtained. 
     The results described in Table 1 indicate that, if the positive electrode  21  had the width L 1  that was the same as the width L 2  of the negative electrode  22 , and the positive electrode  21  included the reaction less-active parts  21 X 1  and  21 X 2  and the reaction active part  21 Y, high voltage stability was obtained while the battery capacity characteristic was secured. Thus, suppression of a short circuit and an increase in battery capacity were both achieved, which allowed a superior battery characteristic to be obtained. 
     Although the technology has been described above with reference to some embodiments and examples, configurations of the technology are not limited to those described with reference to the embodiments and examples above, and are therefore modifiable in a variety of ways. 
     For example, while a description has been given of a case of using a liquid electrolyte (an electrolytic solution), the electrolyte is not limited to a particular kind. Thus, a gel electrolyte (an electrolyte layer) may be used, or an electrolyte in a solid form (a solid electrolyte) may be used. 
     Further, while a description has been given of a case where the battery device has a wound-type device structure (a wound electrode body) and a case where the battery device has a stacked-type device structure (a stacked electrode body), the device structure of the battery device is not particularly limited, and any other device structure, such as a zigzag-folded-type device structure where the electrodes (the positive electrode and the negative electrode) are folded in a zigzag shape, may be chosen. 
     Further, while a description has been given of a case where the electrode reactant is lithium, the electrode reactant is not particularly limited. Specifically, the electrode reactant may be, as described above, another alkali metal, such as sodium or potassium, or may be an alkaline earth metal, such as beryllium, magnesium, or calcium. Other than the above, the electrode reactant may be another light metal, such as aluminum. 
     The effects described herein are mere examples. Therefore, the effects of the technology are not limited to the effects described herein. Accordingly, the technology may achieve any other suitable effect. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.