Abstract:
Disclosed is a winding type battery comprising a center pin, and a wound power generation element formed by interposing a first separator in one interspace between a positive electrode plate and a negative electrode plate, interposing a second separator in another interspace between the positive electrode plate and the negative electrode plate, fixing the first and second separators to the center pin and then winding in one direction. Also disclosed is a method for manufacturing a winding type battery. A winding type battery belongs to batteries demand of which is increasing recently. A center pin of an inventive winding type battery is provided with an inside clamp portion and an outside clamp portion, portions to be clamped of first and second separators are clamped between the inside and outside clamp portions while being extended in the forward winding direction, and then the first separator is touched along the outside clamp portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a national phase application filed under 35 U.S.C. 371 of PCT/JP2009/056434 filed on Mar. 30, 2009, which claims the benefit of priority from the prior Japanese Patent Application No. 2008-098373 filed on Apr. 4, 2008, the entire contents of all of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a winding type battery having a center pin and a method for manufacturing this winding type battery. 
     BACKGROUND ART 
     With the recent popularization of portable electronic devices such as cellular phones, notebook-size personal computers, and video camcorders and also vehicles such as hybrid electric vehicles, there is an increasing demand for batteries to be used as drive power sources of the above devices and vehicles. 
     Those batteries include a winding type battery produced by winding a positive electrode plate and a negative electrode plate while interposing a separator therebetween. For instance, Patent Literature 1 discloses a battery (a winding type battery) provided with a spiral type electrode body (a winding power generation element) that includes a center pin in which a cotter pin supporting one end of a separator is inserted, the separator being extended from a slit of the center pin, and a strip-shaped positive electrode (a positive electrode plate) and a strip-shaped a negative electrode (a negative electrode plate) being wound around the center pin while interposing the separator therebetween. 
     In this winding type battery disclosed in Patent Literature 1, the separator extending from the slit of the center pin in a radially outward direction is bent at almost right angle to extend along a peripheral surface of the center pin and then wound around the center pin. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP7(1995)-335249A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the battery has a tendency that the position of the separator may slightly vary due to expansion and contraction of the volume of the winding power generation element in association with charge and discharge thereof. In the winding type battery disclosed in Patent Literature 1, repetition of such variation may cause fatigue cracks in a bent portion of the separator, thus resulting in breakage or break-off of the separator. 
     The present invention has been made in view of the circumstances to solve the above problems and has a purpose to provide a winding type battery capable of preventing breakage of a separator due to bending and a method for manufacturing such winding type battery. 
     Solution to Problem 
     One aspect of the invention provides a winding type battery comprising: a center pin having a shape that extends along an axial line; and a wound power generation element in which a strip-shaped positive electrode plate and a strip-shaped negative electrode plate are wound in an overlapping state so that a strip-shaped first separator longer than the positive electrode plate and the negative electrode plate is interposed in one interspace between the positive electrode plate and the negative electrode plate and a strip-shaped second separator longer than the positive electrode plate and the negative electrode plate is interposed in another interspace between the positive electrode plate and the negative electrode plate, at least one of the first separator and the second separator being fixed to the center pin and wound from a start end side around the center pin in one direction, wherein when a circumferential direction around the axial line, in which winding of the wound power generation element advances, is referred to as a forward winding direction, at least one of the first separator and the second separator has a clamped portion clamped by the center pin, the center pin includes; an inside clamp portion; and a plate-like outside clamp portion located radially outside of the inside clamp portion relative to the axial line; the clamped portion is clamped between an outer peripheral surface of the inside clamp portion and an inner peripheral surface of the outside clamp portion while the clamped portion is extended in the forward winding direction along the inner peripheral surface of the outside clamp portion, and one of the first separator and the second separator is extended along in contact with the outer peripheral surface of the outside clamp portion. 
     In this winding type battery, the clamped portion of at least one of the first separator and the second separator is clamped between the outer peripheral surface of the inside clamp portion and the inner peripheral surface of the outside clamp portion of the center pin to extend along the inner peripheral surface of the outside clamp portion. In addition, the clamped portion extends in the forward winding direction in which winding of the winding power generation element advances. Furthermore, the first separator, the second separator, the positive electrode plate, and the negative electrode plate are wound around the center pin in one direction (the forward winding direction). 
     Accordingly, in either one of the first separator and the second separator, which includes the clamped portion, the clamped portion also extends in the forward winding direction, extends from between the inside clamp portion and the outside clamp portion of the center pin and is wound in the forward winding direction. In other words, the separator is wound around the center pin without being bent at or near this clamped portion. Thus, a winding type battery can be provided in which the separator is prevented from breaking by bending at or near the clamped portion. 
     Since the clamped portion is clamped by the center pin, the separator including this clamped portion can be fixed to the center pin without use of for example adhesive agent, adhesive tape, etc. 
     Furthermore, for example, a step by the thickness of the adhesive agent and the adhesive tape does not occur. Thus, wrinkles resulting from such step do not occur in the separator and others. 
     In the aforementioned winding type battery, either one of the first separator and the second separator both being wound in the forward winding direction contacts along the outer peripheral surface of the outside clamp portion of the center pin. 
     Accordingly, the inner peripheral surface and the outer peripheral surface of the outside clamp portion of the center pin are made contact with the separators advancing in the same direction toward the rear ends. At the tail end of this outside clamp portion in the forward winding direction, the separators are overlapped each other at an interval corresponding to the thickness of the tail end of the outside clamp portion in the radial direction of the axial line. Thus, a winding type battery can be configured such that the two separators, the positive electrode plate, and the negative electrode plate are wound around the center pin without forming any large step at the tail end of the outside clamp portion. 
     As above, the separators, the positive electrode plate, and the negative electrode plate can be wound substantially along the outer peripheral shape of the center pin. Even when repetition of charge and discharge of this winding type battery causes repeated variations of the volumes of the positive electrode plate and the negative electrode plate, the separators and others can be prevented from warping due to the step. 
     The outside clamp portion may be configured to have a uniform thickness in the forward winding direction but it is preferably formed in a tapered shape having a gradually thinner thickness forward in the forward winding direction. 
     If only at least one of the first separator and the second separator is clamped, that is, has the clamped portion, the start end of the separator(s) can be fixed to the center pin to start winding. Accordingly, for example, in the case where they are wound with the first separator being placed inside, there are conceivable cases; one is to clamp only the first separator (where only the first separator includes the clamped portion), another is to clamp only the second separator (where only the second separator includes the clamped portion), and further another is to clamp the first and second separators (where the first separator and the second separator include the clamped portions). 
     Of the above cases, the case where both the first separator and the second separator are clamped is more preferable. This is because the clamped portions of two separators are clamped respectively and therefore a winding type battery can be produced by reliably winding those two separators, the positive electrode plate, and the negative electrode plate. 
     As an alternative, the first separator and the second separator may be provided as separate members. Another alternative is to fold a single strip-shaped separator into two so that one side of a fold line is used as the first separator and the other side is used as the second separator. In this case, a fold line side is preferably placed on a start end side. 
     The shape of the outer peripheral surface of the center pin may include for example a circular cylindrical shape and a polygonal tube shape such as a rectangular tube shape and a hexagonal tube shape. At that time, the winding power generation element is accordingly wound into for example a cylindrical shape or a polygonal tube shape such as a rectangular tube shape and a hexagonal tube shape. 
     In the above winding type battery, preferably, the outside clamp portion of the center pin is designed so that at least an end portion located forward in the forward winding direction has a tapered shape that is gradually thinner in thickness forward in the forward winding direction. 
     In the above winding type battery, the outside clamp portion is designed such that at least its end portion in the forward winding direction has a tapered shape. Accordingly, this outside clamp portion has a thin thickness at the tail end in the forward winding direction. As described above, the inner peripheral surface and the outer peripheral surface of this outside clamp portion contact with the separators. At the tail end of this outside clamp portion, the separators are overlapped each other at an interval corresponding to the thickness of the outside clamp portion at the tail end. Consequently, the above configuration can further reduce a step occurring between the separators or substantially eliminate the step in such portion. Thus, a winding type battery can be provided in which the separators and others are prevented from warping by the existence of such a gap. 
     In the above winding type battery, preferably, the center pin is elastically deformable in a direction perpendicular to the axial line. 
     In the above winding type battery, the center pin is elastically deformable in a direction perpendicular to the center pin. Even when the volume of the winding power generation element expands and contracts during charge and discharge, the center pin can be elastically deformed along the separator that contacts with the center pin. To be concrete, when the volume of the winding power generation element expands due to charge, the center pin can be elastically deformed so as to reduce its diameter. To the contrary, when the volume of the winding power generation element contracts, the center pin can be elastically deformed so as to increase its diameter. According to expansion and contraction of the winding power generation element, the diameter of the center pin can also be decreased and increased. This can reduce the stress caused by expansion of the winding power generation element and others to be exerted on the separator, the positive electrode plate, and the negative electrode plate. 
     In the above winding type battery, preferably, the center pin is constituted of a plate material wound in a spiral shape beyond one turn about the axial line. 
     In the above winding battery, the center pin has the aforementioned spiral shape. Thus, the center pin can be elastically deformed along the separator contacting therewith in the direction perpendicular to the axial line. Specifically, according to expansion and contraction of the winding power generation element, the diameter of the center pin can also be decrease and increase. This can reduce the stress caused by expansion of the winding power generation element and others to be exerted on the separator, the positive electrode plate, and the negative electrode plate. 
     Furthermore, another aspect is to provide a method for manufacturing a winding type battery comprising: a center pin having a shape that extends along an axial line; and a wound power generation element in which a strip-shaped positive electrode plate and a strip-shaped negative electrode plate are wound in an overlapping state so that a strip-shaped first separator longer than the positive electrode plate and the negative electrode plate is interposed in one interspace between the positive electrode plate and the negative electrode plate and a strip-shaped second separator longer than the positive electrode plate and the negative electrode plate is interposed in another interspace between the positive electrode plate and the negative electrode plate, at least one of the first separator and the second separator being fixed to the center pin and wound from a start end side around the center pin in one direction, wherein when a circumferential direction around the axial line, in which winding of the wound power generation element advances, is referred to as a forward winding direction, the center pin includes an inside clamp portion; and a plate-like outside clamp portion located radially outward of the axial line than the inside clamp portion; the method comprises: a clamping step of clamping a clamped portion of at least one of the first separator and the second separator between the outer peripheral surface of the inside clamp portion and the inner peripheral surface of the outside clamp portion of the center pin and along the inner peripheral surface of the outside clamp portion while maintaining a shape extending in the forward winding direction; and a winding step of winding the first separator, the second separator, the positive electrode plate, and the negative electrode plate around the center pin so that one of the first separator and the second separator wound in the forward winding direction is in contact with the outer peripheral surface of the outside clamp portion of the center pin. 
     In the above method for manufacturing the winding type battery, in the clamping step, the clamped portion is placed to take such a shape that the clamped portion is extended in the winding forward direction in which winding of the winding power generation element advances, which is one of circumferential directions around the axial line. Simultaneously, the clamped portion of at least one of the first separator and the second separator is clamped between the outer peripheral surface of the inside clamp portion and the inner peripheral surface of the outside clamp portion of the center pin. Then, in the winding step, the two separators, the positive electrode plate, and the negative electrode plate are wound around the center pin so that either one of the first separator and the second separator wound in the forward winding direction extends along in contact with the outer peripheral surface of the outside clamp portion. 
     Consequently, the first separator, the second separator, and others can be wound around the center pin while the separators are fixedly clamped by the center pin without being bent at or near the clamped portion. This method can therefore manufacture the winding type battery in which the separators are prevented from breaking at or near the clamped portion. 
     Furthermore, in the above method for manufacturing the winding type battery, preferably, the outside clamp portion of the center pin is designed so that at least an end portion located forward in the forward winding direction has a tapered shape that is gradually thinner in thickness forward in the forward winding direction. 
     In the above manufacturing method of the winding type battery, the outside clamp portion is formed such that at least the end portion in the forward winding direction has a tapered shape. Thus, the outside clamp portion is thinner in thickness at the terminal end thereof in the forward winding direction. As described above, the separators contact with the inner peripheral surface and the outer peripheral surface of the outside clamp portion. At this tail end of the outside clamp portion, the separators are overlapped each other at an interval corresponding to the plate thickness. With the above configuration, the step that may occur between the separators in that portion can be made smaller or substantially eliminated. This method can therefore manufacture the winding type battery in which the separator and others are prevented from warping by the existence of the gap. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a battery in a first embodiment and a first modified example; 
         FIG. 2  is a sectional view (an axial line AX in  FIG. 1 ) in the first embodiment; 
         FIG. 3  is a sectional view (a section A-A in  FIG. 1 ) in the first embodiment; 
         FIG. 4  is an enlarged sectional view of the battery (a part B in  FIG. 3 ) in the first embodiment; 
         FIG. 5  is an explanatory view of a clamping step in the first embodiment; 
         FIG. 6  is an explanatory view of the clamping step in the first embodiment; 
         FIG. 7  is an explanatory view of a winding step in the first embodiment; 
         FIG. 8  is an explanatory view of the winding step in the first embodiment; 
         FIG. 9  is an enlarged sectional view of the battery (the section A-A in  FIG. 1 ) in the first modified example; 
         FIG. 10  is an explanatory view of a battery in a modified example; 
         FIG. 11  is an explanatory view of a battery in another modified example; and 
         FIG. 12  is an explanatory view of a battery in another modified example. 
     
    
    
     REFERENCE SIGNS LIST 
     
         
           1 ,  101 ,  201 ,  301 ,  401  Battery (Winding type battery) 
           20 ,  420  Center pin 
           21 ,  421  Inside clamp portion 
           121  Body-side clamp portion (Inside clamp portion) 
           23 ,  123 ,  423  Outer peripheral surface (Outer peripheral surface of inside clamp portion) 
           25 ,  425  Outside clamp portion 
           125  Extended portion (Outside clamp portion) 
           25 P,  125 P End portion 
           26 ,  126 ,  426  Inner peripheral surface (Inner peripheral surface of outside clamp portion) 
           27 ,  127 ,  427  Outer peripheral surface (Outer peripheral surface of outside clamp portion) 
           30 ,  430  Power generation element (Winding power generation element) 
           31 ,  231 ,  331  First separator 
           31 E Rear end (of First separator) 
           32 ,  132 ,  232  First clamped portion (Clamped portion) 
           35 ,  235 ,  335  Second separator 
           35 E Rear end (of Second separator) 
           36 ,  136 ,  336  Second clamped portion (Clamped portion) 
           38  Positive electrode plate 
           39  Negative electrode plate 
         AX, BX Axial line 
         FW Forward winding direction 
       
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A detailed description of a first embodiment will now be given referring to the accompanying drawings. 
     A battery  1  in the first embodiment includes a center pin  20 , a power generation element  30 , and a battery case  10  and is a cylindrical lithium ion secondary battery having an axial line (see  FIGS. 1 and 2 ). 
     The battery case  10  has a battery case body  11  made of metal having a bottom-closed cylindrical shape and a closing lid  12  having a circular disk shape as shown in  FIGS. 1 and 2 . The battery case body  11  contains a power generation element  30  produced by winding a strip-shaped positive electrode plate  38  and a strip-shaped negative electrode plate  39  while interposing a first separator  31  and a second separator  35  therebetween (see  FIGS. 2 and 3 ). 
     The closing lid  12  made of metal and a safety valve mechanism  13  placed inside the lid  12  are fixed by caulking in an opening portion  11 H of the battery case body  11  through a gasket  19  made of insulating resin (see  FIG. 2 ). Thus, the battery case body  11  is sealingly closed. The safety valve mechanism  13  is configured to cut off an electrical connection between the closing lid  12  and the power generation element  30  by causing a disk plate  13 D to turn upward when the internal pressure of the battery  1  becomes a predetermined value or higher due to internal short circuit of the battery  1 , exterior heat, or other reasons. 
     The following explanation is given to the power generation element  30 . This power generation element  30  is wound around the center pin  20  extending along the axial line AX (see  FIGS. 2 ,  3 , and  4 ). Specifically, the strip-shaped positive electrode plate  38  and the strip-shaped negative electrode plate  39  are wound in an overlapping manner. In one of interspaces between the positive electrode plate  38  and the negative electrode plate  39 , the first separator  31  having a longer stripe shape than the electrode plates  38  and  39  is interposed. In another interspace, the second separator  35  having a longer stripe shape than the electrode plates  38  and  39  is interposed. That is, the first separator  31 , the positive electrode plate  38 , the second separator  35 , and the negative electrode plate  39  are laminated in this order from a side closer to the center pin  20  and they are wound in layers two or more times. The positive electrode plate  38 , the negative electrode plate  39 , the first separator  31 , and the second separator  35  are wound clockwise in one direction around the center pin  20  in  FIG. 4 . This direction (clockwise) in which winding of the power generation element  30  advances is referred to as a forward winding direction FW. 
     The positive electrode plate  38  of the power generation element  30  is connected to a positive lead member  71  (see  FIG. 2 ). This positive lead member  71  is welded to the safety valve mechanism  13  and hence the positive electrode plate  38  and the closing lid  12  are electrically connected to each other. On the other hand, the negative electrode plate  39  is connected to a negative lead member  72 . This negative lead member  72  is welded to the battery case body  11  and hence the negative electrode plate  39  and the battery case body  11  are electrically connected to each other. 
     The positive electrode plate  38  is constituted of a positive metal foil (not shown) made of a long-strip-shaped metal foil and a positive active material layer (not shown) carried on each surface of this positive metal foil. The positive active material layer includes a positive active material constituted of LiCoO 2 , a binding material, and a conductive material. 
     The negative electrode plate  39  is constituted of a negative metal foil (not shown) made of a long-strip-shaped metal foil and a negative active material layer (not shown) carried on each surface of this negative metal foil. The negative active material layer includes a negative active material constituted of graphite and a binding material. 
     The first separator  31  and the second separator  35  both being made of polyethylene are formed by folding a signal strip-shaped separator longer than the above positive electrode plate  38  and negative electrode plate  39  into two in a longitudinal direction. Specifically, with respect to a fold line BP along which the separator is folded, an inner side closer to the axial line AX is used as the first separator  31  and the other side is used as the second separator  35  (see  FIGS. 3 and 4 ). 
     Next, the center pin  20  clamping the first separator  31  and the second separator  35  is explained. The center pin  20  made of insulating resin has a hollow spirally cylindrical shape that extends in a direction along the axial line AX and is wound so that one portion overlaps another portion, that is, wound beyond one turn about the axial line AX, and hence has a spiral cross section in a direction perpendicular to the axial line AX (see  FIGS. 4 and 5 ). 
     This center pin  20  includes an arc-shaped inside clamp portion  21  located relatively inside and an arc-shaped outside clamp portion  25  located radially outside of the inside clamp portion  21  relative to the axial line AX (see  FIGS. 4 and 5 ). 
     The center pin  20  elastically clamps the first separator  31  and the second separator  35  between the inside clamp portion  21  and the outside clamp portion  25 . To be concrete, between an outer peripheral surface  23  of the inside clamp portion  21  facing radially outward of the axial line AX and an inner peripheral surface  26  of the outside clamp portion  25  facing radially inward of the axial line AX, a first clamped portion  32  located on a start end side of the first separator  31  and a second clamped portion  36  located on a start end side of the second separator  35 , both portions  32  and  35  being near the fold line BP, are clamped. Accordingly, the battery  1  can be provided in which the above first separator  31  and second separator  35  are fixed to and wound around the center pin  20  and besides the positive electrode plate  38  and the negative electrode plate  39  are reliably wound. 
     In the center pin  20 , the fold line BP corresponding to the start ends of the first separator  31  and the second separator  35  is placed (see  FIGS. 3 and 4 ). The first clamped portion  32  of the first separator  31  extends in the forward winding direction FW (see  FIG. 3 ). The second clamped portion  36  of the second separator  35  also extends in the forward winding direction FW. 
     The first clamped portion  32  of the first separator  31  and the second clamped portion  36  of the second separator  35  also extend in the forward winding direction FW and from between the inside clamp portion  21  and the outside clamp portion  25  of the center pin  20 , and are wound in the forward winding direction FW, as keeping its extending direction. In other words, the first separator  31  and the second separator  35  are wound around the center pin  20  without being bent at or near the first clamped portion  32  and the second clamped portion  36  respectively. Accordingly, the battery  1  can include the first separator  31  and the second separator  35  prevented from breaking by bending at and near the clamped portions  32  and  36 . 
     In addition, both the first clamped portion  32  and the second clamped portion  36  are clamped by the center pin  20 . The separator  31  including the first clamped portion  32  and the separator  35  including the second clamped portion  36  can be fixed to the center pin  20  without using for example adhesive agent, adhesive tape, etc. 
     Furthermore, for example, no step is caused due to the thickness of the adhesive agent or the adhesive tape, so that wrinkles resulting from such step do not occur in the separators  31  and  35  and others. 
     In the battery  1  of the first embodiment, the first separator  31  wound in the forward winding direction FW contacts with the outer peripheral surface  27  of the outside clamp portion  25  of the center pin  20  along the outer peripheral surface  27  of the outside clamp portion  25 . 
     In other words, the inner peripheral surface  26  of the outside clamp portion  25  of the center pin  20  contacts with the second separator  35  and the outer peripheral surface  27  of the outside clamp portion  25  of the center pin  20  contacts with the first separator  31 . The first separator  31  and the second separator  35  extend to a first rear end  31 E and a second rear end  35 E respectively in the same direction as shown in  FIG. 3 . Thus, at a terminal or tail end  25 E of the outside clamp portion  25  in the forward winding direction FW, the first separator  31  is overlapped on the second separator  35  at an interval in a radial direction relative to the axial line AX by the thickness of the outside clamp portion  25  at the tail end  25 E. Accordingly, the battery  1  can be provided in which two separators (the first separator  31  and the second separator  35 ), the positive electrode plate  38 , and the negative electrode plate  39  are wound around the center pin  20  without forming a large step in the above area. 
     As above, the separators  31  and  35 , the positive electrode plate  38 , and the negative electrode plate  39  can be wound substantially along the outer periphery of the center pin  20 . Thus, even when repetition of charge and discharge of the battery  1  causes repeated variations in the volumes of the positive electrode plate  38  and the negative electrode plate  39 , the separators  31  and  35  and others can be prevented from warping due to the step. 
     The outside clamp portion  25  has a tapered shape having a gradually thinner thickness forward in the forward winding direction FW. To be concrete, the outside clamp portion  25  is designed so that its entire shape including an end portion  25 P is gradually thinner toward the tail end  25 E in the forward winding direction FW (see  FIG. 4 ). 
     Accordingly, the outside clamp portion  25  has a thin thickness at the tail end  25 E in the forward winding direction FW. As described above, the second separator  35  contacts with the inner peripheral surface  26  of the outside clamp portion  25  and the first separator  31  contacts with the outer peripheral surface  27  respectively. At the tail end  25 E of the outside clamp portion  25 , the separators  31  and  35  are overlapped at the interval corresponding to the thickness of the outside clamp portion  25  at the tail end  25 E. The configuration in the first embodiment can reduce the size of a step that may occur between the separators  31  and  35  or substantially eliminate the step. Consequently, the battery  1  can include the separators  31  and  35  and others prevented from warping by the existence of such a gap. 
     The center pin  20  has the hollow spirally cylindrical shape around the axial line AX as described above (see  FIG. 4 ). Thus, even when the volume of the power generation element  30  expands and contracts, this center pin  20  can be elastically deformed in association therewith. 
     When the volume of the power generation element  30  expands, for example, the center pin  20  accordingly tends to wholly decrease its diameter. To the contrary, when the volume of the power generation element  30  contracts, for example, the center pin  20  accordingly tends to wholly increase its diameter. 
     In the battery  1  in the first embodiment, therefore, the center pin  20  is elastically deformable in the radial direction perpendicular to the axial line AX. Accordingly, even when the volume of the power generation element  30  expands or contracts during charge and discharge, the center pin  20  contacting the first separator  31  can be elastically deformed along the first separator  31  and others. 
     As above, the diameter of the center pin  20  can be decreased or increased according to expansion or contraction of the power generation element  30 . This can reduce the stress to be exerted on the first separator  31 , the second separator  35 , the positive electrode plate  38 , and the negative electrode plate  39  in association with expansion and contraction of the power generation element  30 . 
     A method for manufacturing the battery  1  in the first embodiment will be explained with reference to  FIGS. 5 to 8 . 
       FIG. 5  shows a not-yet-clamping center pin  20 E before clamping the separators  31  and  35 . This center pin  20 E made of insulating resin has a spirally cylindrical shape that extends in a direction along an axial line AX and is wound in the forward winding direction FW beyond one turn about the axial line AX. In this center pin  20 E, the outer peripheral surface  23  of the inside clamp portion  21  and the inner peripheral surface  26  of the outside clamp portion  25  elastically contact under pressure with each other. Accordingly, the center pin  20 E has a configuration capable of elastically clamping the separators  31  and  35  between the inside clamp portion  21  and the outside clamp portion  25 . 
     The outside clamp portion  25  of the not-yet-clamping center pin  20 E has a tapered shape having a gradually thinner thickness forward in the forward winding direction FW. To be concrete, the outside clamp portion  25  is designed so that its entire shape including the tail end  25 E is gradually thinner in the forward winding direction FW. 
     A clamping step is first explained with reference to  FIG. 6 . A long strip-shaped separator SP made of polyethylene is folded into two along a fold line BP extending along the axial line AX, thereby providing the first separator  31  and the second separator  35 . Then, the first clamped portion of the first separator  31  and the second clamped portion  36  of the second separator  35  are inserted between the inside clamp portion  21  and the outside clamp portion  25 , which are kept separated in advance, of the not-yet-clamping center pin  20 E. Between the inside clamp portion  21  and the outside clamp portion  25 , accordingly, the first clamped portion  32  of the first separator  31  and the second clamped portion  36  of the second separator  35  are elastically clamped (see  FIG. 7 ). 
     In the above clamping step, the first clamped portion  32  of the first separator  31  is placed to extend the forward winding direction FW. That is, the first clamped portion  32  is placed to take such a shape that the extending direction of the first clamped portion  32  toward the first rear end  31 E of the first separator  31  in the circumferential direction about the axial line AX is the same as the forward winding direction FW in which winding of the power generation element  30  advances. Simultaneously, the second clamped portion  36  of the second separator  35  is extended in the forward winding direction FW. That is, the second clamped portion  36  is placed to take such a shape that the extending direction of the second clamped portion  36  toward the second rear end  35 E of the second separator  35  is the same as the forward winding direction FW in which winding of the power generation element  30  advances. 
     Furthermore, the first clamped portion  32  of the first separator  31  and the second clamped portion  36  of the second separator  35  are clamped by the center pin  20  between the outer peripheral surface  23  of the inside clamp portion  21  and the inner peripheral surface  26  of the outside clamp portion  25 . 
     The winding step is explained below referring to  FIGS. 7 and 8 . Around the center pin  20  clamping the first separator  31  and the second separator  35 , these first separator  31  and second separator  35 , the positive electrode plate  38 , and the negative electrode plate  39  are wound together in the forward winding direction FW. To be concrete, the positive electrode plate  38  is placed between the first separator  31  and the second separator  35  so as to contact with the radially outer surface of the first separator  31 . The negative electrode plate  39  is also placed between the second separator  35  and the first separator  31  so as to contact with the radially outer surface of the second separator  35  (see  FIG. 8 ). 
     The first separator  31  is first directly wound about one turn from the outer peripheral surface  23  of the inside clamp portion  21  to the outer peripheral surface  27  of the outside clamp portion  25  (see  FIG. 8(   a )). Then, the positive electrode plate  38  placed between the first separator  31  and the second separator  35  is wound about three quarters along the first separator  31 . 
     Then, the second separator  35  is wound along the positive electrode plate  38 . The negative electrode plate  39  is then wound along the second separator  35  so as to hold the second separator  35  against the positive electrode plate  38 . 
     Subsequently, the first separator  31 , the positive electrode plate  38 , the second separator  35 , and the negative electrode plate  39  are further wound (see  FIG. 8(   b )). 
     In this way, the positive electrode plate  38  and the negative electrode plate  39  are overlapped by interposing the first separator  31  in one of the interspaces therebetween and the second separator  35  in the other interspace. Thus, the power generation element  30  wound around the center pin  20  is completed. 
     After the above winding step, the positive lead member  71  is welded to the positive electrode plate  38  of the power generation element  30  and the negative lead member  72  is welded to the negative electrode plate  39  of the power generation element  30 . The positive lead member  71  is also welded to the disk plate  13 D of the safety valve mechanism  13  and the negative lead member  72  is also welded to the bottom of the battery case body  11 . Thereafter, the power generation element  30  is set in the battery case body  11 . An electrolyte not shows is poured and then the closing lid  12  and the safety valve mechanism  13  are placed in the opening portion  11 H of the battery case body  11  by interposing a gasket  19  therebetween. The opening portion  11 H is caulked. 
     As above, the battery  1  is completed (see  FIGS. 1 ,  2 , and  3 ). 
     In the method for manufacturing the battery  1  in the first embodiment, the first separator  31  and the second separator  35  can be clamped and fixed by the center pin  20  without bending the first clamped portion  32  of the first separator  31  and the second clamped portion  36  of the second separator  35  and their vicinities. Furthermore, the first separator  31 , the second separator  35 , and others can be wound around the center pin  20 . Accordingly, this method can manufacture the battery  1  in which the first separator  31  and the second separator  35  are prevented from breaking at or near the first clamped portion  31  and the second clamped portion  36 . 
     In the method for manufacturing the battery  1  in the first embodiment, the outside clamp portion  25  is designed so that at least the tail end  25 E in the forward winding direction FW has the tapered shape. Accordingly, this outside clamp portion  25  is thinner in thickness at the tail end  25 E in the forward winding direction FW. 
     As described above, the inner peripheral surface  26  and the outer peripheral surface  27  of the outside clamp portion  25  contact with the second separator  35  and the first separator  31  respectively. At the tail end  25 E of the outside clamp portion  25 , the first separator  31  and the second separator  35  are overlapped at an interval corresponding to the thickness of the tail end  25 E of the outside clamp portion  25 . The above configuration of the first embodiment can further reduce or substantially eliminate a step that may occur between the first separator  31  and the second separator  35 . Consequently, the battery  1  can be manufactured so that the first separator  31  and others are prevented from warping due to the existence of such a gap. 
     First Modified Example 
     A battery  101  in a first modified example is explained below referring to  FIGS. 1 and 9 . 
     The battery  101  in the first modified example is identical to that in the first embodiment except that an inside clamp portion of a center pin is continuous with an inner portion of the center pin. 
     The following explanation is therefore given with a focus on the differences from the first embodiment and the details of identical parts are not repeated or are simplified. The identical parts can provide the same operations and effects as those in the first embodiment and also are assigned with the same reference signs as those in the first embodiment. 
     In the battery  101  in this first modified example, a center pin  120  made of insulating resin includes a hollow cylindrical body part  128  extending along an axial line AX and a plate-like extended portion  125  radially outwardly branching off from the body part  128  and extending along the body part  128  (see  FIG. 9 ). This center pin  120  includes a body-side clamp portion  121  included in the body part  128 . Between this clamp portion  121  and the extended portion  125 , the first separator  31  and the second separator  35  are elastically clamped and fixed. The extended portion  125  is located radially outward of the axial line AX than the clamp portion  121 . 
     To be concrete, a first clamped portion  132  located on a start end side of the first separator  31  and a second clamped portion  136  located on a start end side of the second separator  35  including a fold line BP are clamped between an outer peripheral surface  123  of the body-side clamp portion  121 , which faces radially outward of the axial line AX, and an inner peripheral surface  126  of the extended portion  125 , which faces radially inward of the axial line AX. Accordingly, those first separator  31  and the second separator  35  can be fixed by and wound around the center pin  120 . The battery  101  can therefore be provided in which the positive electrode plate  38  and the negative electrode plate  39  are wound as well as the above components. 
     The body-side clamp portion  121  is less likely to move radially inwardly as compared with the inside clamp portion  21  in the first embodiment. In other words, the body-side clamp portion  121  is hard to move radially inwardly by the extended portion  125  elastically clamping the first and second separators  31  and  35  in cooperation with the body-side clamp portion  121 . After clamping the separators  31  and  35 , the center pin  120  in the first modified example can maintain the cylindrical shape of the body part  128 . 
     As above, the present invention is explained in the first embodiment and the first modified example but is not limited thereto. The present invention may be embodied in other specific forms without departing from the essential characteristics thereof. 
     For instance, the battery in the first embodiment and the first modified example is a lithium ion battery. As an alternative, the battery may be applied to a secondary battery such as a nickel-metal hydride battery and a primary battery such as an alkaline dry cell and a manganese dry cell. 
     The single strip-shaped separator SP is folded into two and one side of the fold line BP is used as the first separator and the other side is used as the second separator. Alternatively, the first separator and the second separator may be separate members. 
     In the first embodiment and the first modified example, both the first separator and the second separator are clamped by and wound around the center pin. However, it is only necessary to clamp and fix at least one of the first separator and the second separator by the center pin. For example, in the case where a first separator  231  is wound inside (on a close side to the center pin  20 ), only a first clamped portion  232  of the first separator  231  may be clamped by and fixed to the center pin  20  without clamping a second separator  235  (see  FIG. 10 ). Alternatively, only a second clamped portion  336  of a second separator  335  may be clamped and fixed without clamping a first separator  331  (see  FIG. 11 ). 
     Furthermore, the shape of the outer peripheral surface of the center pin is cylindrical. As alternatives, polygonal center pins may be adopted, such as a rectangular tubular center pin  420  having an inside clamp portion  421  and an outside clamp portion  425  (see  FIG. 12 ), a hexagonal center pin, or the like. In such cases, the power generation element is wound along for example the polygonal tubular shape such as a rectangular tubular shape (see  FIG. 12 ), a hexagonal tubular shape, and others.