Patent Publication Number: US-11024927-B2

Title: Electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

Description:
TECHNICAL FIELD 
     The present disclosure relates to an electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery. 
     BACKGROUND ART 
     Non-aqueous electrolyte secondary batteries include a wound electrode assembly manufactured by winding a positive electrode and a negative electrode with a separator interposed therebetween, for example. In the positive electrode and the negative electrode constituting the wound electrode assembly, typically, a mixture layer is formed on each surface of a belt-like current collector, and a lead is bonded to an exposed portion where the surfaces of the current collector are exposed. In recent years, electrodes with various structures have been proposed to improve the battery performance, such as battery capacity or output. For example, Patent Literature 1 discloses an electrode in which an exposed portion to which a lead is to be bonded is formed on only one end side of a current collector in the width direction to increase the area of a mixture layer and thereby increase battery capacity. Patent Literature 2 discloses an electrode in which an exposed portion is formed over the full width of a current collector. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Published Unexamined Patent Application No. 2003-68271 
     PTL 2: Japanese Published Unexamined Patent Application No. 2008-234855 
     SUMMARY OF INVENTION 
     Technical Problem 
     When an exposed portion is formed on only one end side of a current collector in the width direction, a lead is typically unevenly bonded to one end side of the current collector in the width direction. Because the lead has a larger thickness than a mixture layer, in a wound electrode assembly including the electrode disclosed in Patent Literature 1, the electrode assembly bulges locally on one end side in the axial direction due to the large thickness of the lead. Thus, when such an electrode is used, it is difficult to form a stable winding structure outside the lead bonded portion, and winding misalignment of an electrode assembly is likely to occur. 
     Winding misalignment is reduced when an exposed portion is formed over the full width of a current collector, as in the electrode disclosed in Patent Literature 2, and when a lead is bonded to a current collector so as not to be unevenly bonded to one end side of the current collector in the width direction. In this case, however, an electrically conductive foreign material may easily enter an electrode assembly through a front edge of a lead disposed on a current collector, for example, in a battery manufacturing process, and the foreign material may cause a decrease in open-circuit voltage (OCV) or cause internal short-circuit. 
     Solution to Problem 
     An electrode for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a belt-like current collector, a mixture layer formed on each surface of the current collector, and a lead bonded to an exposed portion of the current collector where the surfaces of the current collector are exposed, the lead extending from one end of the current collector, the one end and another end constituting both ends of the current collector in a width direction, wherein the mixture layer on at least one surface of the current collector is formed in the width direction and adjacent to the exposed portion on the other end side, and the length in the width direction of a portion of the lead disposed on the current collector ranges from 60% to 98% of the width of the current collector. 
     A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a wound electrode assembly manufactured by winding a positive electrode and a negative electrode with a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode is constituted by the electrode for a non-aqueous electrolyte secondary battery described above. 
     Advantageous Effects of Invention 
     An electrode for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure can be used to provide a wound electrode assembly in which winding misalignment is sufficiently reduced and with which the decrease in open-circuit voltage (OCV) of the battery is reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a non-aqueous electrolyte secondary battery according to one embodiment. 
         FIG. 2  is a perspective view of a wound electrode assembly according to one embodiment. 
         FIG. 3  includes a front view and a rear view of a positive electrode according to one embodiment. 
         FIG. 4  is an explanatory view of a method for manufacturing a positive electrode according to one embodiment. 
         FIG. 5  is an explanatory view of a method for manufacturing a positive electrode according to one embodiment. 
         FIG. 6  includes a front view and a rear view of a positive electrode according to another embodiment. 
         FIG. 7  includes a front view and a rear view of a positive electrode according to another embodiment. 
         FIG. 8  is a schematic view of a known electrode for a non-aqueous electrolyte secondary battery. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In an electrode for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, winding misalignment of a wound electrode assembly constituted by the electrode is reduced by extending an exposed portion where a surface of a current collector is exposed in the width direction and by adjusting the length of a portion of a lead on the current collector to be 60% or more of the width of the current collector. The lead extends from one end side of the current collector in the width direction. In a known electrode  100  illustrated in  FIG. 8 , exposed portions  102 A and  102 B where the surfaces of a current collector are exposed without being covered with mixture layers  103 A and  103 B are formed on only one end side of a current collector  101  in the width direction, and a lead  104  is unevenly bonded to the current collector  101  on one end side in the width direction. Because a portion to which the lead  104  is bonded has a larger thickness than the other portion in the width direction of the current collector  101 , in a wound electrode assembly constituted by the electrode  100 , the electrode assembly bulges locally on one end side in the axial direction, which is likely to cause winding misalignment of the electrode assembly. In an electrode for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, a lead is disposed on the current collector so as not to be unevenly disposed on one end side of the current collector in the width direction. This reduces winding misalignment of an electrode assembly, which can be problematic when the electrode  100  is used. 
     In an electrode for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, an exposed portion is not formed over the full width of the electrode, but a mixture layer is formed in the width direction and adjacent to the exposed portion on the other end side. The other end is one of both ends of the current collector in the width direction from which a lead is not extended. This can potentially prevent electrically conductive foreign materials from entering the electrode assembly. 
     Electrically conductive foreign materials that possibly cause the decrease in the OCV of a battery are spatters, for example. Spatters may occur when a lead extending from a wound electrode assembly is welded to a battery case. In a typical wound electrode assembly constituting a cylindrical battery, a positive-electrode lead extends from one side of the electrode assembly in the axial direction, and a negative-electrode lead extends from the other side of the electrode assembly in the axial direction. In this case, although spatters may enter the electrode assembly through a front edge of a lead disposed on a current collector, a mixture layer formed on a portion of an exposed portion adjacent to the other end can potentially prevent the spatters from entering the electrode assembly. In a non-aqueous electrolyte secondary battery including an electrode according to one aspect of the present disclosure, therefore, this can reduce the decrease in open-circuit voltage (OCV) and reduce the occurrence of internal short-circuit caused by electrically conductive foreign materials, such as spatters. 
     Embodiments of the present disclosure will be described in detail below. 
     Figures referred in the embodiments are schematically illustrated, and the specific dimensions of each component should be determined in consideration of the following description. The term “almost”, as used herein, means to include, for example, in the context of almost the same, substantially the same as well as completely the same. The term “end portion” refers to an end of an object and the vicinity thereof. The term “central portion” refers to the center of an object and the vicinity thereof. 
     One embodiment is a non-aqueous electrolyte secondary battery  10 , which is a cylindrical battery including a cylindrical metallic case. However, a non-aqueous electrolyte secondary battery according to the present disclosure is not limited to this. A non-aqueous electrolyte secondary battery according to the present disclosure may be a prismatic battery including a prismatic metallic case or a laminated battery including a resin sheet exterior, for example. 
       FIG. 1  is a cross-sectional view of the non-aqueous electrolyte secondary battery  10 .  FIG. 2  is a perspective view of an electrode assembly  14  constituting the non-aqueous electrolyte secondary battery  10 . As illustrated in  FIGS. 1 and 2 , the non-aqueous electrolyte secondary battery  10  includes a wound electrode assembly  14  and a non-aqueous electrolyte (not shown). The electrode assembly  14  includes a positive electrode  11 , a negative electrode  12 , and a separator  13 . The positive electrode  11  and the negative electrode  12  are wound with the separator  13  interposed therebetween. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte and may be a solid electrolyte containing a gel polymer. One side of the electrode assembly  14  in the axial direction is hereinafter sometimes referred to as “upper”, and the other side in the axial direction is sometimes referred to as “lower”. 
     The positive electrode  11  includes a belt-like positive-electrode current collector  30 , a positive-electrode mixture layer  35  formed on the positive-electrode current collector  30 , and a positive-electrode lead  19 . The positive-electrode lead  19  is an electrically conductive member for electrically connecting the positive-electrode current collector  30  to a positive-electrode terminal and extends from an upper end of an electrode group. The electrode group refers to the electrode assembly  14  except leads. In the present embodiment, the positive-electrode lead  19  is disposed almost midway between the winding start portion and the winding end portion of the electrode assembly  14 . 
     The negative electrode  12  includes a belt-like negative-electrode current collector  50 , a negative-electrode mixture layer  55  formed on the negative-electrode current collector  50 , and a negative-electrode lead  20 . The negative-electrode lead  20  is an electrically conductive member for electrically connecting the negative-electrode current collector  50  to a negative-electrode terminal and extends from a lower end of the electrode group. In the present embodiment, the negative-electrode lead  20  is disposed on the winding start portion of the electrode assembly  14  and on winding end portion of the electrode assembly  14 . 
     The positive-electrode lead  19  and the negative-electrode lead  20  are belt-like electrically conductive members with a larger thickness than the current collector and the mixture layer. The thickness of each lead is 3 to 30 times the thickness of the current collector, for example, and typically ranges from 50 to 300 μm. Although the constituent material of each lead is not particularly limited, the positive-electrode lead  19  is preferably composed of an aluminum-based metal, and the negative-electrode lead  20  is preferably composed of a nickel- or copper-based metal. The number and position of leads are not particularly limited. For example, the negative-electrode lead  20  may be disposed on only the winding start portion or the winding end portion of the electrode assembly  14 . 
     In the embodiment illustrated in  FIG. 1 , a case main body  15  and a seal  16  constitute a metallic battery case that contains the electrode assembly  14  and the non-aqueous electrolyte. Insulating plates  17  and  18  are disposed on the top and bottom of the electrode assembly  14 . The positive-electrode lead  19  extends to the seal  16  through a through-hole of the insulating plate  17  and is welded to the bottom of a filter  22 , which is a bottom plate of the seal  16 . In the non-aqueous electrolyte secondary battery  10 , a cap  26 , which is a top plate of the seal  16  electrically connected to the filter  22 , serves as a positive-electrode terminal. The negative-electrode leads  20  extend to the bottom of the case main body  15  and are welded to the bottom inner surface of the case main body  15 . In the non-aqueous electrolyte secondary battery  10 , the case main body  15  serves as a negative-electrode terminal. 
     As described above, the electrode assembly  14  has a winding structure in which the positive electrode  11  and the negative electrode  12  are wound with the separator  13  interposed therebetween. The positive electrode  11 , the negative electrode  12 , and the separator  13  are belt-like and are wound to be stacked in the radial direction of the electrode assembly  14 . In the electrode assembly  14 , the longitudinal direction of each electrode is the winding direction (the circumferential direction), and the width direction of each electrode is the axial direction. 
     The case main body  15  is a closed-end cylindrical metallic container. A gasket  27  is disposed between the case main body  15  and the seal  16  and ensures the sealing performance of the battery case. The case main body  15  has a protrusion  21  for supporting the seal  16 . The protrusion  21  is formed by pressing the side surface of the case main body  15  from the outside, for example. The protrusion  21  is preferably formed circularly along the circumferential direction of the case main body  15  and supports the seal  16  on the top surface thereof. 
     The seal  16  has a layered structure of the filter  22 , a lower valve body  23 , an insulating member  24 , an upper valve body  25 , and the cap  26  stacked over the electrode assembly  14  in this order. Each member of the seal  16  is discoidal or ring-shaped, for example, and each member except the insulating member  24  is electrically connected to each other. The lower valve body  23  and the upper valve body  25  are connected to each other at their central portions. The insulating member  24  is disposed between the peripheries of the lower valve body  23  and the upper valve body  25 . If abnormal heat generation increases the internal pressure of the battery, the upper valve body  25  expands toward the cap  26  and separates from the lower valve body  23 , thereby breaking the electrical connection between the upper valve body  25  and the lower valve body  23 . A further increase in internal pressure results in the rupture of the upper valve body  25  and causes a gas to be discharged from an opening in the cap  26 . 
     The structure of the positive electrode  11  will be described in detail below with reference to  FIG. 3 .  FIG. 3  includes a front view and a rear view of the positive electrode  11 . 
     As illustrated in  FIG. 3 , the positive electrode  11  includes the belt-like positive-electrode current collector  30  and the positive-electrode mixture layer  35  formed on each surface of the positive-electrode current collector  30  (see  FIG. 2 ). The positive-electrode mixture layers  35  include a positive-electrode mixture layer  35 A formed on a first surface of the positive-electrode current collector  30  and a positive-electrode mixture layer  35 B formed on a second surface of the positive-electrode current collector  30 . The positive-electrode mixture layers  35 A and  35 B have almost the same pattern. In the present specification, the first surface of the current collector refers to a surface to which a lead is bonded, and the second surface refers to a surface to which no lead is bonded. 
     The positive electrode  11  has an exposed portion where both surfaces of the positive-electrode current collector  30  are exposed. The exposed portion includes an exposed portion  33 A disposed on the first surface of the positive-electrode current collector  30  and an exposed portion  33 B disposed on the second surface of the positive-electrode current collector  30 . The positive electrode  11  further includes the positive-electrode lead  19 , which is bonded to one of the exposed portions  33 A and  33 B and extends from one end  31  of the positive-electrode current collector  30  in the width direction. In the embodiment illustrated in  FIG. 3 , the positive-electrode lead  19  is bonded to the exposed portion  33 A on the first surface of the positive-electrode current collector  30 . The exposed portion  33 A enables the positive-electrode lead  19  to be directly connected to the positive-electrode current collector  30 . Although the details are described later, the length of a portion of the positive-electrode lead  19  disposed on the positive-electrode current collector  30  in the width direction of the current collector ranges from 60% to 98% of the width of the positive-electrode current collector  30 . 
     The positive-electrode current collector  30  is a long electrically conductive member with an almost constant width. The positive-electrode current collector  30  may be made of a sheet of a metal, such as aluminum, or a film including the metal as a surface layer. A suitable example of the positive-electrode current collector  30  is made of a metal sheet composed mainly of aluminum or an aluminum alloy. The positive-electrode current collector  30  has a thickness in the range of 5 to 30 μm, for example. The exposed portions  33 A and  33 B where the surfaces of the positive-electrode current collector  30  are exposed extend from one end  31  of the positive-electrode current collector  30  in the width direction and are rectangular in the front and rear views. The positive-electrode mixture layers  35 A and  35 B are preferably almost entirely formed on each surface of the positive-electrode current collector  30  except the exposed portions  33 A and  33 B. The positive-electrode mixture layers  35 A and  35 B contain a positive-electrode active material, an electrically conductive agent, and a binder, for example. The positive electrode  11  can be manufactured by applying a positive-electrode mixture slurry, which contains a positive-electrode active material, an electrically conductive agent, such as a carbon powder, a binder, such as a fluoropolymer powder, and a solvent, such as N-methyl-2-pyrrolidone (NMP), to the surfaces of the positive-electrode current collector  30  and by pressing the film. The positive-electrode mixture layers  35 A and  35 B have a thickness in the range of 50 to 100 μm, for example. 
     The positive-electrode active material may be a lithium-containing transition metal oxide containing at least one transition metal element, such as Co, Mn, and/or Ni. The lithium-containing transition metal oxide is preferably, but not limited to, a composite oxide represented by the general formula Li 1+x MO 2  (wherein −0.2&lt;x≤0.2, and M contains at least one of Ni, Co, Mn, and Al). The constituents of a first region and a second region of the positive-electrode mixture layers  35 A and  35 B described later may be almost the same or different from each other. For example, the constituent ratio may be different between the first region and the second region. 
     The exposed portion  33 A is a portion to which the positive-electrode lead  19  is to be bonded and is a portion of the first surface of the positive-electrode current collector  30  where the first surface is exposed without being covered with the positive-electrode mixture layer  35 A. The exposed portion  33 B is a portion of the second surface of the positive-electrode current collector  30  where the second surface is exposed without being covered with the positive-electrode mixture layer  35 B. The exposed portion  33 B overlaps the exposed portion  33 A in the thickness direction of the positive electrode  11  (the positive-electrode current collector  30 ). If the exposed portion  33 A overlaps the positive-electrode mixture layer  35 B, for example, welding of the positive-electrode lead  19  to the exposed portion  33 A may be inhibited. Thus, the exposed portion  33 B is disposed opposite the exposed portion  33 A. The overlap between the exposed portions  33 A and  33 B preferably includes at least the region of the positive-electrode lead  19  on the positive-electrode current collector  30 . 
     Although the exposed portions  33 A and  33 B may be formed by forming the positive-electrode mixture layers  35 A and  35 B on the entire surfaces of the positive-electrode current collector  30  and subsequently removing part of the mixture layers, the exposed portions  33 A and  33 B are preferably formed by intermittent application of the positive-electrode mixture slurry, as described in detail later. This can eliminate the mixture layer removal process and reduce the material cost. 
     Although the exposed portions  33 A and  33 B may be formed in an end portion of the positive electrode  11  in the longitudinal direction, the exposed portions  33 A and  33 B are preferably formed in the central portion of the positive electrode  11  in the longitudinal direction. For example, the exposed portions  33 A and  33 B are disposed at almost equal distances from each end of the positive electrode  11  in the longitudinal direction. In this case, because the positive-electrode lead  19  is bonded in the central portion of the positive-electrode current collector  30  in the longitudinal direction, the positive electrode  11  has improved current collecting performance compared with the case where the positive-electrode lead  19  is bonded in an end portion in the longitudinal direction, thus contributing to increasing the power of the battery. The first surface of the positive-electrode current collector  30  may have a plurality of exposed portions, and a plurality of leads may be welded on the first surface. 
     In the positive electrode  11 , the positive-electrode mixture layer is formed on at least one surface of the positive-electrode current collector  30  in the width direction of the positive-electrode current collector  30  and adjacent to the exposed portion on the other end  32  side. The mixture layer formed adjacent to the exposed portion on the other end  32  side can decrease the lower end space of the electrode assembly  14  made by welding of the positive-electrode lead  19 , for example, and can potentially prevent electrically conductive foreign materials from entering the electrode assembly  14 . 
     In the present embodiment, the positive-electrode mixture layer  35 A is formed on the first surface of the positive-electrode current collector  30  between the other end  32  of the positive-electrode current collector  30  and an end  19   t  of the positive-electrode lead  19 . The positive-electrode mixture layer  35 B is also formed on the second surface of the positive-electrode current collector  30  between the other end  32  of the positive-electrode current collector  30  and the position corresponding to the end  19   t  of the positive-electrode lead  19 . Thus, the positive-electrode mixture layers  35 A and  35 B are formed along the exposed portions  33 A and  33 B, respectively, on the surfaces of the positive-electrode current collector  30  in the width direction of the current collector. The position corresponding to the end  19   t  of the positive-electrode lead  19  refers to the position overlapping the end  19   t  on the second surface of the positive-electrode current collector  30  in the thickness direction of the positive electrode  11 . 
     In the present specification, the portions of the positive-electrode mixture layers  35 A and  35 B adjacent to the exposed portions  33 A and  33 B, respectively, in the width direction of the positive-electrode current collector  30  are referred to as second regions  37 A and  37 B. The portion adjacent to the exposed portion  33 A and the second region  37 A is referred to as a first region  36 A of the positive-electrode mixture layer  35 A, and the portion adjacent to the exposed portion  33 B and the second region  37 B is referred to as a first region  36 B of the positive-electrode mixture layer  35 B. 
     The exposed portion  33 A to which the positive-electrode lead  19  is to be welded is adjacent to the first region  36 A in the longitudinal direction of the positive-electrode current collector  30 , and three sides of the exposed portion  33 A except one end  31  are surrounded by the first region  36 A and the second region  37 A. The second region  37 A may be separated from the first region  36 A formed on both sides of the exposed portion  33 A in the width direction but is preferably in contact with the first region  36 A. The exposed portion  33 B and the second region  37 B have basically the same pattern as the exposed portion  33 A and the second region  37 A, respectively. In the present embodiment, the positive-electrode mixture layers  35 A and  35 B are continuously formed on the end portions on the other end  32  side on both surfaces of the positive-electrode current collector  30  over the entire length of the positive-electrode current collector  30 . 
     As described above, the length L 19  of the portion of the positive-electrode lead  19  disposed on the positive-electrode current collector  30  in the width direction of the current collector ranges from 60% to 98%, preferably 80% to 98%, particularly preferably 80% to 95%, of the width W 30  of the positive-electrode current collector  30 . The length L 19  in this range results in suppression of winding misalignment of the electrode assembly  14  resulting from the large thickness of the positive-electrode lead  19 . 
     In the second regions  37 A and  37 B, the lengths L 37A  and L 37B  in the width direction of the positive-electrode current collector  30  preferably range from 0.1% to 40% of the width W 30  of the current collector. The second regions  37 A and  37 B preferably do not overlap the positive-electrode lead  19  in the thickness direction of the positive-electrode current collector  30 . In other words, the second regions  37 A and  37 B are preferably formed only between the end  19   t  of the positive-electrode lead  19  or the position corresponding to the end  19   t  and the other end  32  of the positive-electrode current collector  30 . For example, when the length L 19  of the positive-electrode lead  19  ranges from 80% to 98% of the width W 30 , the lengths L 37A  and L 37B  range from 0.1% to 20% of the width W 30 , that is, approximately 0.5 to 5 mm. 
     In the present embodiment, there is a space between the second region  37 A and the end  19   t  of the positive-electrode lead  19 . The positive-electrode lead  19  is not disposed over the entire length of the exposed portion  33 A, and the length L 19  of the positive-electrode lead  19  is 60% or more of the width W 30  of the positive-electrode current collector  30  and is the length at which the positive-electrode lead  19  is not in contact with the second region  37 A. Thus, the lengths L 33A  and L 33B  of the exposed portions  33 A and  33 B in the width direction of the positive-electrode current collector  30  are longer than the length L 19 . The lengths L 33A  and L 33B  may range from 1.05 to 1.5 times the length L 19 , for example. The lengths L 33B  and L 37B  are almost the same as the lengths L 33A  and L 37A . The widths of the exposed portions  33 A and  33 B (the lengths in the longitudinal direction of the positive-electrode current collector  30 ) are preferably close to the width of the positive-electrode lead  19 , for example, slightly longer than the width of the positive-electrode lead  19 , provided that the positive-electrode lead  19  can be bonded to the exposed portion  33 A without any trouble. 
     Although the second regions  37 A and  37 B are formed to cover the other end  32  of the positive-electrode current collector  30 , there may be an exposed portion where the surfaces of the current collector are exposed between the second regions  37 A and  37 B and the other end  32 . The second regions  37 A and  37 B have a thickness in the range of 50 to 100 μm, for example, which is almost the same as the thickness of the first regions  36 A and  36 B. Alternatively, the second regions  37 A and  37 B may have a smaller thickness than the first regions  36 A and  36 B. 
     In the positive electrode  11 , the exposed portions  33 A and  33 B are covered with insulating tapes  38 A and  38 B. The insulating tape  38 A covers not only the positive-electrode lead  19  but also the first region  36 A and the second region  37 A. In the embodiment illustrated in  FIG. 3 , the exposed portion  33 A and the second region  37 A are entirely covered with the insulating tape  38 A. The insulating tape  38 B has almost the same size as the insulating tape  38 A and entirely covers the exposed portion  33 B and the second region  37 B. The insulating tapes  38 A and  38 B have a thickness in the range of 20 to 70 μm, for example. 
     A method for manufacturing the positive electrode  11  with the above structure will be described below with reference to  FIGS. 4 and 5 . In  FIG. 5 , for convenience of explanation, positive-electrode mixture layers  45  and  46  are illustrated in different dot densities. As illustrated in  FIGS. 4 and 5 , the positive electrode  11  is manufactured by sequentially forming the positive-electrode mixture layers  45  and  46  on a long current collector  40  and cutting the long current collector  40  at cutting positions X and Y. The positive-electrode mixture layers  45  and  46  formed on both surfaces of the long current collector  40  serve as the positive-electrode mixture layers  35 A and  35 B, and the long current collector  40  is cut at the cutting positions X and Y and serves as the positive-electrode current collector  30 . 
     In the embodiment illustrated in  FIGS. 4 and 5 , the positive-electrode mixture slurry is intermittently applied to both surfaces of the long current collector  40  except exposed portions  43  and  44  where the current collector surfaces are exposed, thereby forming the positive-electrode mixture layer  45 . The positive-electrode mixture slurry is then applied to the exposed portion  44  to form the positive-electrode mixture layer  46 . The exposed portions  43  extend in the width direction of the long current collector  40  and are disposed at almost regular intervals in the longitudinal direction of the current collector. The exposed portions  44  are formed almost perpendicular to the exposed portions  43  in the longitudinal direction of the long current collector  40 . The positive-electrode mixture slurry is applied to the exposed portions  44  to form the positive-electrode mixture layer  46 , thereby forming the positive-electrode mixture layer serving as the first regions  36 A and  36 B and the second regions  37 A and  37 B while leaving exposed portions serving as the exposed portions  33 A and  33 B. 
     The positive electrode  11  is manufactured, for example, by pressing the films of the positive-electrode mixture layers  45  and  46  and cutting the long current collector  40 , on which the mixture layers are formed, at the cutting positions X and Y. In the formation of the positive-electrode mixture layers  45  and  46 , the constituents and thicknesses of the first regions  36 A and  36 B and the second regions  37 A and  37 B are almost equalized by applying the same positive-electrode mixture slurry at the same thickness. The exposed portion  43  has a width in the range of approximately 5 to 10 mm, for example, which is wider than the width of the positive-electrode lead  19 . The exposed portion  44  has a width in the range of approximately 0.5 to 5 mm, for example, depending on the length of the second regions  37 A and  37 B (the exposed portions  33 A and  33 B) in the width direction of the current collector. 
       FIGS. 6 and 7  illustrate positive electrodes  11 X and  11 Y according to another embodiment (insulating tapes are not shown). The positive electrode  11 X illustrated in  FIG. 6  is different from the positive electrode  11  in that the second region  37 B is not formed on the second surface of the positive-electrode current collector  30 . Thus, in the positive electrode  11 X, the second region  37 A of the positive-electrode mixture layer  35 A adjacent to the exposed portion  33 A in the width direction of the current collector is formed only in an end portion on the other end  32  side of the first surface of the positive-electrode current collector  30  to which the positive-electrode lead  19  is bonded. The positive-electrode mixture layer  35 BX does not have the second region  37 B, and the exposed portion  33 BX is formed over the full width of the positive-electrode current collector  30 . 
     The positive electrode  11 Y illustrated in  FIG. 7  is different from the positive electrode  11  in that the second region  37 A is not formed on the first surface of the positive-electrode current collector  30 . Thus, in the positive electrode  11 Y, the second region  37 B of the positive-electrode mixture layer  35 B adjacent to the exposed portion  33 B in the width direction of the current collector is formed only in an end portion on the other end  32  side of the second surface of the positive-electrode current collector  30  to which the positive-electrode lead  19  is not bonded. The positive-electrode mixture layer  35 AY does not have the second region  37 A, and the exposed portion  33 AY is formed over the full width of the positive-electrode current collector  30 . 
     Like the positive electrode  11 , the negative electrode  12  includes the belt-like negative-electrode current collector  50  and the negative-electrode mixture layer  55  formed on both surfaces of the negative-electrode current collector  50  (see  FIG. 2 ). The negative-electrode current collector  50  may be made of a sheet of a metal, such as copper, or a film including the metal as a surface layer. A negative-electrode active material in the negative-electrode mixture layer  55  may be any material that can reversibly adsorb and desorb lithium ions and is preferably a carbon material, such as graphite, a metal that can be alloyed with lithium, such as Si or Sn, or an alloy thereof, an oxide, or the like. The negative-electrode mixture layer  55  may contain carboxymethylcellulose (CMC) or styrene-butadiene rubber (SBR) as a binder, for example. 
     The negative electrode  12  includes the negative-electrode lead  20  that is bonded to one of exposed portions (not shown) where part of each surface of the negative-electrode current collector  50  is exposed and that extends from one end of the negative-electrode current collector  50  in the width direction (in the present embodiment, the lower side of the electrode assembly  14 ). The negative electrode  12  is larger than the positive electrode  11  and has an exposed portion at both ends in the longitudinal direction. The negative-electrode lead  20  is welded to each exposed portion, for example. 
     The negative electrode  12  can also have basically the same structure as the positive electrode  11 . The length of a portion of the negative-electrode lead  20  on the negative-electrode current collector  50  in the width direction of the negative-electrode current collector  50  ranges from 60% to 98% of the width of the negative-electrode current collector  50 , for example. In at least one surface of the negative-electrode current collector  50 , the negative-electrode mixture layer  55  may be formed in the width direction of the current collector and adjacent to the other end side of the exposed portion (in the present embodiment, the upper side of the electrode assembly  14 ). 
     EXAMPLES 
     Although the present disclosure will be further described in the following examples, the present disclosure is not limited to these examples. 
     Example 1 
     [Preparation of Positive Electrode] 
     Lithium cobalt oxide, a carbon powder, and a fluoropolymer powder were mixed at a weight ratio of 100:1:1. A proper amount of N-methyl-2-pyrrolidone was added to the mixture to prepare a positive-electrode mixture slurry. The positive-electrode mixture slurry was then intermittently applied to both surfaces of a long current collector made of aluminum foil 15 μm in thickness, and the film was pressed with a rolling mill to an electrode plate thickness of 140 μm to form a positive-electrode mixture layer. The long current collector that had the positive-electrode mixture layer on each surface was cut in a predetermined electrode size, and a positive-electrode lead was welded to an exposed portion on one surface (first surface) of the current collector to prepare a positive electrode. 
     The positive-electrode lead was an aluminum lead 4 mm in width, 67 mm in length, and 150 μm in thickness. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 53.1 mm, which corresponds to 90% of the width of the current collector (59 mm). 
     The slurry was applied twice to each surface of the long current collector, four times in total, to form the positive-electrode mixture layer, as illustrated in  FIGS. 4 and 5 . In the first application step, the positive-electrode mixture slurry was intermittently applied to one surface (first surface) of the long current collector except the exposed portion  43  with a width of 7 mm extending in the width direction of the current collector and except the exposed portion  44  with a width of 1 mm extending in the longitudinal direction of the current collector, thereby forming the positive-electrode mixture layer  45  with a width of 58 mm. In the second application step, the positive-electrode mixture slurry was continuously applied to the exposed portion  44  extending in the longitudinal direction of the current collector to form the positive-electrode mixture layer  46  with a width of 1 mm. The slurry was applied to the other surface (second surface) of the long current collector in the same manner as in the first surface to form the positive-electrode mixture layers  45  and  46 , which overlapped the mixture layer on the first surface in the thickness direction of the electrode plate. 
     The exposed portion in the resulting positive electrode had a length of 58 mm in the width direction of the current collector, and the second region of the positive-electrode mixture layer formed adjacent to the exposed portion in the width direction of the current collector had a length of 1 mm (approximately 1.7% of the width of the current collector) in the width direction. In the positive electrode, the exposed portions and the second regions were entirely covered with a polyimide insulating tape 12 mm in width, 63 mm in length, and 50 μm in thickness. 
     [Preparation of Negative Electrode] 
     A natural graphite powder, carboxymethylcellulose (CMC), and styrene-butadiene rubber (SBR) were mixed at a weight ratio of 100:1:1. A proper amount of water was added to the mixture to prepare a negative-electrode mixture slurry. The negative-electrode mixture slurry was then intermittently applied to both surfaces of a long current collector made of copper foil, and the film was pressed with a rolling mill to an electrode plate thickness of 160 μm to form a negative-electrode mixture layer. The long current collector that had the negative-electrode mixture layer on each surface was cut in a predetermined electrode size, and a negative-electrode lead was welded to an exposed portion to prepare a negative electrode. The exposed portion was formed at both ends of the negative electrode in the longitudinal direction, and the negative-electrode lead was welded to each exposed portion. The exposed portion was covered with the polyimide insulating tape. 
     [Preparation of Non-Aqueous Electrolyte] 
     Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:70. Lithium hexafluorophosphate (LiPF 6 ) was dissolved in the mixed solvent at a concentration of 1 mol/L to prepare a non-aqueous electrolyte. 
     [Manufacture of Battery] 
     The positive electrode and the negative electrode were wound with a polyethylene separator interposed therebetween to prepare a wound electrode assembly. The electrode assembly was placed in a closed-end cylindrical metallic case main body. An upper end of the positive-electrode lead was welded to a bottom plate of a seal, and a lower end of the negative-electrode lead was welded to a bottom inner surface of the case main body. The non-aqueous electrolyte was poured into the case main body, and the opening of the case main body was hermetically sealed with a seal with a polypropylene gasket interposed therebetween, thus manufacturing a cylindrical battery. An insulating plate was disposed on the top and bottom of the electrode group. 
     Example 2 
     The positive-electrode lead was an aluminum lead 4 mm in width, 71.7 mm in length, and 150 μm in thickness. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 57.8 mm, which corresponds to 98% of the width of the current collector (59 mm). Except for these, a cylindrical battery was manufactured in the same manner as in Example 1. 
     Example 3 
     The positive-electrode lead was an aluminum lead 4 mm in width, 49.3 mm in length, and 150 μm in thickness. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 35.4 mm, which corresponds to 60% of the width of the current collector (59 mm). Except for these, a cylindrical battery was manufactured in the same manner as in Example 1. 
     Example 4 
     The positive-electrode mixture slurry was intermittently applied to the second surface of the long current collector except the exposed portion  43  with a width of 7 mm extending in the width direction of the current collector, thereby forming a positive-electrode mixture layer 59 mm in width. Except for this, a cylindrical battery was manufactured in the same manner as in Example 1. The positive electrode in Example 4 is different from the positive electrode in Example 1 in that the second region of the positive-electrode mixture layer is not formed on the second surface of the positive-electrode current collector (see  FIG. 6 ). 
     Example 5 
     The positive-electrode lead was an aluminum lead 4 mm in width, 71.7 mm in length, and 150 μm in thickness. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 57.8 mm, which corresponds to 98% of the width of the current collector (59 mm). Except for these, a cylindrical battery was manufactured in the same manner as in Example 4. 
     Example 6 
     The positive-electrode lead was an aluminum lead 4 mm in width, 49.3 mm in length, and 150 μm in thickness. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 35.4 mm, which corresponds to 60% of the width of the current collector (59 mm). Except for these, a cylindrical battery was manufactured in the same manner as in Example 4. 
     Example 7 
     The positive-electrode mixture slurry was intermittently applied to the first surface of the long current collector except the exposed portion  43  with a width of 7 mm extending in the width direction of the current collector, thereby forming a positive-electrode mixture layer 59 mm in width. Except for this, a cylindrical battery was manufactured in the same manner as in Example 1. The positive electrode in Example 7 is different from the positive electrode in Example 1 in that the second region of the positive-electrode mixture layer is not formed on the first surface of the positive-electrode current collector (see  FIG. 7 ). 
     Example 8 
     The positive-electrode lead was an aluminum lead 4 mm in width, 71.7 mm in length, and 150 μm in thickness. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 57.8 mm, which corresponds to 98% of the width of the current collector (59 mm). Except for these, a cylindrical battery was manufactured in the same manner as in Example 7. 
     Example 9 
     The positive-electrode lead was an aluminum lead 4 mm in width, 49.3 mm in length, and 150 μm in thickness. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 35.4 mm, which corresponds to 60% of the width of the current collector (59 mm). Except for these, a cylindrical battery was manufactured in the same manner as in Example 7. 
     Comparative Example 1 
     In the same manner as in Example 1, the slurry was applied twice to each surface of the long current collector, four times in total, to form the positive-electrode mixture layer. In the first application step, the positive-electrode mixture slurry was intermittently applied to the first surface of the long current collector except the exposed portion 7 mm in width extending in the width direction of the current collector and except the exposed portion 45 mm in width extending in the longitudinal direction of the current collector, thereby forming the positive-electrode mixture layer 14 mm in width. In the second application step, the positive-electrode mixture slurry was continuously applied to the exposed portion extending in the longitudinal direction of the current collector to form the positive-electrode mixture layer 45 mm in width. The slurry was applied to the second surface of the long current collector in the same manner as in the first surface to form the positive-electrode mixture layers, which overlapped the mixture layer on the first surface in the thickness direction of the electrode plate. 
     The positive-electrode lead was an aluminum lead 4 mm in width, 25.7 mm in length, and 150 μm in thickness. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 11.8 mm, which corresponds to 20% of the width of the current collector (59 mm) (see  FIG. 8 ). The length of the exposed portion in the width direction of the current collector was 14 mm. In the positive electrode, the exposed portions were entirely covered with a polyimide insulating tape 12 mm in width, 18 mm in length, and 50 μm in thickness. Except for these, a cylindrical battery was manufactured in the same manner as in Example 1. 
     Comparative Example 2 
     A positive-electrode mixture layer was formed such that the length of the exposed portion in the width direction of the current collector was 31 mm. The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 29.5 mm, which corresponds to 50% of the width of the current collector (59 mm). Except for these, a cylindrical battery was manufactured in the same manner as in Comparative Example 1. The positive-electrode lead was an aluminum lead 4 mm in width, 43.4 mm in length, and 150 μm in thickness. 
     Comparative Example 3 
     The length of a portion of the positive-electrode lead disposed on the positive-electrode current collector was 29.5 mm, which corresponds to 50% of the width of the current collector (59 mm). Except for this, a cylindrical battery was manufactured in the same manner as in Example 1. The positive-electrode lead was an aluminum lead 4 mm in width, 49.3 mm in length, and 150 μm in thickness. 
     Comparative Example 4 
     The second region of the positive-electrode mixture layer was not formed on each surface of the positive-electrode current collector. An exposed portion extending in the width direction of the current collector was formed over the full width of the electrode plate. Except for these, a cylindrical battery was manufactured in the same manner as in Example 1. 
     The cylindrical batteries according to the examples and comparative examples were evaluated for positive-electrode winding misalignment and OCV by the following methods. 
     [Evaluation of Positive-Electrode Winding Misalignment] 
     An electrode assembly in a battery case was examined using X-rays. A misalignment exceeding a predetermined threshold between positive and negative electrodes was considered to be winding misalignment. The test was performed on 10,000 batteries. The winding misalignment percentage was calculated using the following formula.
 
Winding misalignment percentage (%)=(Number of batteries with winding misalignment/10,000)×100
 
[Evaluation of OCV]
 
     A charge-discharge cycle including constant-current charging at 0.3C to a battery voltage of 4.1 V and constant-current discharging at 0.3C to 2.5 V was performed three times at 25° C. The battery charged to 4.1 V was then left standing at 45° C. for 1 week. The OCV difference (ΔOCV) was calculated from the OCVs of the battery measured before and after standing. A battery with ΔOCV beyond 3σ from the average value was considered to have poor OCV. The test was performed on 10,000 batteries. The poor OCV percentage was calculated using the following formula.
 
Poor OCV percentage (%)=(Number of batteries with poor OCV/10,000)×100
 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                   
                 Length of second 
                   
                   
               
               
                   
                   
                 region in width 
               
               
                   
                   
                 direction of current 
                 Winding 
               
               
                   
                 Lead 
                 collector (mm) 
                 misalignment 
                 Poor OCV 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 length* 
                 First 
                 Second 
                 percentage 
                 percentage 
               
               
                   
                 (%) 
                 surface 
                 surface 
                 (%) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 1 
                 90 
                 1 
                 1 
                 0.12 
                 0.02 
               
               
                 Example 2 
                 98 
                 1 
                 1 
                 0.13 
                 0.01 
               
               
                 Example 3 
                 60 
                 1 
                 1 
                 0.20 
                 0.02 
               
               
                 Example 4 
                 90 
                 1 
                 — 
                 0.12 
                 0.01 
               
               
                 Example 5 
                 98 
                 1 
                 — 
                 0.11 
                 0.02 
               
               
                 Example 6 
                 60 
                 1 
                 — 
                 0.19 
                 0.02 
               
               
                 Example 7 
                 90 
                 — 
                 1 
                 0.14 
                 0.02 
               
               
                 Example 8 
                 98 
                 — 
                 1 
                 0.11 
                 0.02 
               
               
                 Example 9 
                 60 
                 — 
                 1 
                 0.23 
                 0.03 
               
               
                 Comparative 
                 20 
                 45  
                 45  
                 0.72 
                 0.02 
               
               
                 example 1 
               
               
                 Comparative 
                 50 
                 28  
                 28  
                 0.54 
                 0.03 
               
               
                 example 2 
               
               
                 Comparative 
                 50 
                 1 
                 1 
                 0.48 
                 0.03 
               
               
                 example 3 
               
               
                 Comparative 
                 90 
                 — 
                 — 
                 0.15 
                 0.34 
               
               
                 example 4 
               
               
                   
               
               
                 *The percentage of the length of a portion of a positive-electrode lead disposed on a positive-electrode current collector relative to the width of the positive-electrode current collector. 
               
            
           
         
       
     
     Table 1 shows that the winding misalignment percentage of an electrode assembly was lower in the batteries according to Examples 1 to 9 than in the batteries according to Comparative Examples 1 to 3. Thus, winding misalignment of an electrode assembly can be reduced when the length of a portion of a positive-electrode lead disposed on a current collector is 60% or more of the width of the current collector and when the lead is disposed so as not to be unevenly disposed on one end side of the current collector in the width direction. 
     The poor OCV percentage was lower in the batteries according to Examples 1 to 9 than in the battery according to Comparative Example 4. Thus, a high OCV can be achieved when a mixture layer (a second region) along an exposed portion in the width direction of a current collector is formed in an end portion on the other end side on at least one surface of the current collector in the width direction. The second region can potentially prevent spatters from entering an electrode assembly when a negative-electrode lead is welded to a case main body and thereby achieve high OCV. 
     REFERENCE SIGNS LIST 
       10  non-aqueous electrolyte secondary battery,  11  positive electrode,  12  negative electrode,  13  separator,  14  electrode assembly,  15  case main body,  16  seal,  17 ,  18  insulating plate,  19  positive-electrode lead,  20  negative-electrode lead,  21  protrusion,  22  filter,  23  lower valve body,  24  insulating member,  25  upper valve body,  26  cap, gasket,  30  positive-electrode current collector,  31  one end,  32  the other end,  33 A,  33 B exposed portion,  35 ,  35 A,  35 B positive-electrode mixture layer,  36 A,  36 B first region,  37 A,  37 B second region,  38 A,  38 B insulating tape,  40  long current collector,  43 ,  44  exposed portion,  45 ,  46  positive-electrode mixture layer,  50  negative-electrode current collector,  55  negative-electrode mixture layer