Patent Publication Number: US-7588606-B2

Title: Coin type battery and manufacturing method thereof

Description:
REFERENCE TO RELATED APPLICATION 
   This is a divisional of application Ser. No. 10/381,503, filed Apr. 10, 2003 now U.S. Pat. No. 7,070,880. 

   TECHNICAL FIELD 
   The present invention relates to a coin type battery and a manufacturing method thereof. The invention relates particularly to a coin type battery having an electrode plate group of a coiled structure constructed with a positive electrode plate, a negative electrode plate, and a separator interposed therebetween. 
   BACKGROUND ART 
     FIG. 9  illustrates the most commonly adopted electrode plate structure for coin type batteries, in which a disk-shaped positive electrode pellet  32  and a negative electrode pellet  33  are arranged face-to-face with a separator  34  interposed in between them. This coin type battery is manufactured through the following process steps to have the coin-like appearance: The positive electrode pellet  32 , separator  34 , and negative electrode pellet  33  are placed in the face-to-face arrangement inside a sealing case  35  of circular half shell form, liquid electrolyte is injected, a gasket  36  is fitted to a lateral periphery of the sealing case  35 , a cap case  31  is coupled onto the sealing case, and the open end edge of the cap case  31  is crimped or bent inwards so as to tightly seal the battery inner space. 
   Batteries having such electrode plate structure as described above wherein one positive electrode pellet  32  and one negative electrode pellet  33  are arranged face-to-face with each other cannot have a large discharge capacity because of the small reaction area where the positive and negative electrode plates face each other. To achieve a larger discharge capacity, positive and negative electrode plates must face each other in a larger area, and accordingly, for relatively larger batteries other than coin type batteries, various structures that enlarge the reaction area have widely been adopted in an attempt to increase the battery energy density in high rate discharge performance. There is, for example, a layered structure in which a plurality of positive and negative electrode plates are layered upon one another with separators interposed therebetween. Another example is a coiled structure in which strips of positive and negative electrode plates are coiled together with a separator interposed therebetween. The discharge capacity of coin type battery could be increased if electrode plates of such a layered or coiled structure were accommodated in a coin-shaped, flat case. In fact, the applicants of the present invention have proposed a battery containing an electrode plate group of a coiled structure in a coin-shaped, flat case in Japanese Patent Laid-Open Applications Nos. 2000-241678 and 2000-241679. 
   This electrode plate group of the coiled structure is constructed as shown in  FIG. 10A  and  FIG. 10B : A positive electrode plate  7  consists of a plurality of positive electrode layer faces  17   a - 17   e  coupled together by connecting pieces  19   a - 19   d , and a negative electrode plate  8  consists of a plurality of negative electrode layer faces  18   a - 18   e  that are larger than the positive electrode layer faces  17   a - 17   e  and coupled together by connecting pieces  20   a - 20   d . They are coiled around with a separator interposed between them into a flat shape so as to be accommodated in a circular case. The resultant flat shape electrode plate group  1  appears as shown in  FIG. 11 . As shown in  FIG. 12 , this electrode plate group  1  is encased in a sealing case  5 , a negative electrode lead  16  is welded to an inner face of the sealing case  5 , and a positive electrode lead  15  is welded to a cap case  4 . The sealing case  5  is then filled with liquid electrolyte. A gasket  6  is fitted to a lateral periphery of the sealing case  5 , the cap case  4  is coupled thereon, and the open end edge of the cap case  4  is crimped so as to tightly seal the battery inner space. Such coin type battery can be constructed both as a lithium primary battery and rechargeable battery. Such a small and flat shape battery capable of outputting a large discharge current can contribute to realization of even smaller portable electronic devices and the like with higher functionalities. 
   One problem is that, in the manufacture of the electrode plate group  1 , the positive and negative electrode plates  7 ,  8  are not fixed in position relative to each other, and they can easily be displaced in the process step of coiling them into a flat shape. If the positive electrode layer faces  17   a - 17   e  upon the negative electrode layer faces  18   a - 18   e  are largely offset because of the displacement during the coiling process, there is a risk of internal short-circuiting caused by dendritic growth of lithium. Since the coin type battery contains a coiled electrode plate group  1  in a small, flat case, internal short-circuiting may also be caused if the electrode plates are not in register, as they may contact the sealing case  5  upon an impact of a falling accident or the like. 
   Accordingly, it is necessary to detect the presence of discrepancy in position between the positive electrode layer faces  17   a - 17   e  and negative electrode layer faces  18   a - 18   e , which is, however, not possible after the positive and negative electrode plates  7 ,  8  have been coiled around with the separator therebetween, because the finished electrode plate group  1  is covered by the separator that is unified with the electrode plates. Thus there is a need to inspect, by some means, whether there is a discrepancy in position between the positive electrode layer faces  17   a - 17   e  and negative electrode layer faces  18   a - 18   e , so that only the electrode plate groups  1  that are within a permissible range of positional displacement are used for assembling the batteries. 
   An object of the present invention is to provide a coin type battery having a feature that enables detection of positional displacement between positive and negative electrode plates of an assembled electrode plate group, and a manufacturing method of this coin type battery. 
   DISCLOSURE OF THE INVENTION 
   To achieve the above object, according to a first aspect of the present invention, there is provided a coin type battery comprising: 
   a strip of positive electrode plate formed of a plurality of positive electrode layer faces coupled together by a plurality of connecting pieces; 
   a strip of negative electrode plate formed of a plurality of negative electrode layer faces coupled together by a plurality of connecting pieces; 
   a separator interposed between the positive electrode plate and the negative electrode plate, the positive electrode plate and negative electrode plate being folded at the respective connecting pieces and coiled around into an electrode plate group of flat form such that the positive electrode layer faces and the negative electrode layer faces are alternately layered upon one another with the separator interposed therebetween; 
   a sealing case forming an inner space together with a gasket and a cap case for accommodating the electrode plate group, characterized in that 
   the positive electrode plate and the negative electrode plate are respectively formed with positional discrepancy detecting cut-outs for detecting positional displacement between the positive electrode layer faces and the negative electrode layer faces when both electrode plates are coiled around. Preferably, the positional discrepancy detecting cut-outs are holes, centers of which conform to each other when the positive electrode plate and negative electrode plate are coiled around in exact register. Alternatively, the positional discrepancy detecting cut-outs can be notches of same or similar form, peripheral edges of which conform to each other when the positive electrode plate and negative electrode plate are coiled around in exact register. 
   According to the above structure, after coiling around the positive and negative electrode plates formed with positional discrepancy detecting cut-outs into the electrode plate group of flat form, X-ray inspection is carried out to detect positional displacement in the positive and negative electrode plates based on the positional relationship between the positional discrepancy detecting cut-outs in the electrode plates. Non-conforming electrode plate groups in which positional displacement has occurred may cause short circuits if encased and assembled into coin type batteries. The inspection enables only the electrode plate groups that fall in a permissible range of positional displacement to be assembled into coin type batteries. Thus, coin type batteries constructed with coiled electrode plates are manufactured with a good yield. 
   According to a second aspect of the invention, there is also provided a coin type battery comprising: 
   a strip of positive electrode plate formed of a plurality of positive electrode layer faces coupled together by a plurality of connecting pieces; 
   a strip of negative electrode plate formed of a plurality of negative electrode layer faces coupled together by a plurality of connecting pieces; 
   a separator interposed between the positive electrode plate and the negative electrode plate, the positive electrode plate and negative electrode plate being folded at the respective connecting pieces and coiled around into an electrode plate group of flat form such that the positive electrode layer faces and the negative electrode layer faces are alternately layered upon one another with the separator interposed therebetween; 
   a sealing case forming an inner space together with a gasket and a cap case for accommodating the electrode plate group, characterized in that 
   the electrode plate group is provided, at least in one positive electrode layer face and one negative electrode layer face that face each other at a coiling finish end, or at least in the positive electrode layer faces and the negative electrode layer faces that face each other at a coiling start end and at a coiling finish end, with positional discrepancy detecting cut-outs for detecting positional displacement between the positive electrode layer face and the negative electrode layer face when both electrode plates are coiled around. The positional discrepancy detecting cut-outs can be either holes or notches as mentioned above. 
   According to the above structure, after coiling around the positive and negative electrode plates formed with positional discrepancy detecting cut-outs in their respective layer faces into the electrode plate group, X-ray inspection is carried out to detect positional displacement in the positive and negative electrode plates based on the positional relationship between the positional discrepancy detecting cut-outs in the opposing positive and negative electrode layer faces. Thus, short circuits that may occur after encasing and assembling the electrode plate group into the coin type battery is prevented, and coin type batteries constructed with coiled electrode plates are manufactured with a good yield. 
   In the battery above, the positive electrode plate and the negative electrode plate are coiled around such that a first positive electrode layer face is placed upon a negative electrode layer face that is second from the coiling start end; a first negative electrode layer face is folded back at a first connecting piece upon the first positive electrode layer face; the first negative electrode layer face is further folded back at a second connecting piece upon a second positive electrode layer face. The positional discrepancy detecting cut-outs are formed in the first negative electrode layer face and the first and second positive electrode layer faces that face the first negative electrode layer face. The layer faces of positive and negative electrode plates are thus layered alternately, and a positional discrepancy at the coiling start end is reliably detected. 
   The negative electrode layer faces are formed larger than the positive electrode layer faces, and the positional discrepancy detecting cut-outs are formed as holes or notches. The holes or notches formed in either one of the positive electrode layer faces and the negative electrode layer faces are larger than the holes or notches formed in the other, and their positional relationship is determined based on a permissible range of positional displacement between the positive electrode plate and the negative electrode plate. The positional relationship, i.e., whether the smaller detecting hole is located inside the larger detecting hole, can be detected from transmitted X-ray images obtained by irradiating X-rays to the electrode plate group in the layering direction. X-ray inspection thus enables determination of whether the positional displacement is within the permissible range or not. 
   The positional discrepancy detecting cut-outs respectively formed in the first and the second positive electrode layer faces are formed in different sizes. Thereby, a positional discrepancy between the first and second layer faces of the positive electrode at its coiling start end is detected. 
   The detecting holes formed in the positive electrode layer faces are larger than the holes in the negative electrode layer faces. That way, it is prevented that the negative electrode layer face is offset from the positive electrode layer face. When constructing the battery as a lithium rechargeable battery, this will prevent dendritic growth of lithium. 
   The positional discrepancy detecting cut-outs formed in the positive electrode layer face and the negative electrode layer face that face each other at the coiling start end and the positional discrepancy detecting cut-outs formed in the positive electrode layer face and the negative electrode layer face that face each other at the coiling finish end are located at different positions on the positive electrode layer faces and the negative electrode layer faces. Thereby, positional displacement at the coiling start end and the coiling finish end is detected at the same time in the X-ray inspection. 
   According to a third aspect of the invention, there is further provided a method of manufacturing a coin type battery, comprising: 
   folding a strip of positive electrode plate formed of a plurality of positive electrode layer faces coupled together by a plurality of connecting pieces, and a strip of negative electrode plate formed of a plurality of negative electrode layer faces coupled together by a plurality of connecting pieces at the respective connecting pieces and coiling it around into an electrode plate group of flat form such that the positive electrode layer faces and the negative electrode layer faces are alternately layered upon one another with a separator interposed therebetween; 
   accommodating the electrode plate group into a sealing case; 
   injecting liquid electrolyte thereinto; 
   placing a cap case onto the sealing case via a gasket; and 
   crimping the cap case to seal the inside of the sealing case, characterized in that 
   the positive electrode plate and the negative electrode plate are respectively formed with positional discrepancy detecting cut-outs for detecting positional displacement between the positive electrode layer faces and the negative electrode layer faces when both electrode plates are coiled around; 
   after coiling around the positive electrode plate and the negative electrode plate into the electrode plate group, X-rays are irradiated thereto in a direction in which the electrode plates are layered so as to obtain transmitted X-ray images of the electrode plate group; 
   a positional discrepancy is detected, by processing the images, between the positional discrepancy detecting cut-outs in the positive electrode layer faces and the positional discrepancy detecting cut-outs in the negative electrode layer faces; and 
   when the detected positional discrepancy is within a predetermined permissible range, the electrode plate group is accommodated in the sealing case. 
   According to the above method of manufacturing coin type batteries, electrode plate groups formed with positional discrepancy detecting cut-outs are subjected to X-ray inspection for selecting the groups in which no positional displacement has occurred between the positive and negative electrode plates, and these groups are encased and assembled into coin type batteries. Short circuits that may be caused by positional displacement after completing the batteries is thus prevented, and coin type batteries constructed with electrode plates of a coiled structure are manufactured with a good yield. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross section illustrating the structure of a coin type battery according to one embodiment of the present invention; 
       FIG. 2A  is a top plan view of a negative electrode plate, and  FIG. 2B  is a top plan view of a positive electrode plate; 
       FIG. 3A  to  FIG. 3C  are model views illustrating a coiling process step in order; 
       FIG. 4  is a model view of an electrode plate group in the coiled state; 
       FIG. 5  is a model view illustrating the face-to-face arrangement of positional discrepancy detecting holes; 
       FIG. 6  is an image view of an electrode plate group subjected to X-ray inspection; 
       FIG. 7A  is a top plan view of a negative electrode plate according to another embodiment of the invention, and  FIG. 7B  is a top plan view of a positive electrode plate of the same; 
       FIG. 8  is an image view of the electrode plate group of the same embodiment subjected to X-ray inspection; 
       FIG. 9  is a cross section illustrating the structure of a conventional coin type battery; 
       FIG. 10A  is a top plan view of a conventional negative electrode plate, and  FIG. 10B  is a top plan view of a conventional positive electrode plate; 
       FIG. 11  is a top plan view of a conventional electrode plate group of a coiled structure; and 
       FIG. 12  is a cross section of a conventional coin type battery that uses the electrode plate group of the coiled structure. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   Preferred embodiments of the present invention will be described below with reference to the accompanying drawings for a better understanding of the present invention. It should be noted that the embodiments described below are merely examples of carrying out the invention and should not pose any limitation on the technical scope of the invention. 
   The coin type battery according to this embodiment is manufactured through the following process steps: An electrode plate group  10  is encased in a sealing case  5  of circular half shell form as shown in  FIG. 1 , a positive electrode lead  26  and a negative electrode lead  27  drawn out from the electrode plate group  10  are welded to a cap case  4  and the sealing case  5 , respectively, liquid electrolyte is injected, a gasket  6  is fitted to a lateral periphery of the sealing case  5 , the cap case  4  is coupled upon the gasket  6 , and the open end edge of the cap case  4  is crimped or bent inwards so as to tightly seal the battery inner space. 
   The electrode plate group  10  is constructed in a flat coiled shape with wound positive and negative electrode plates  11 ,  12  and a separator interposed therebetween: The negative electrode plate  12  consists of six negative electrode layer faces  23   a - 23   f  coupled together by connecting pieces  25   a - 25   e  and the negative electrode lead  27  formed at the coiling finish end, as shown in  FIG. 2A . The positive electrode plate  11  consists of five positive electrode layer faces  22   a - 22   e  that are smaller than the negative electrode layer faces  23   a - 23   f  and coupled together by connecting pieces  24   a - 24   d  and the positive electrode lead  26  formed at the coiling finish end, as shown in  FIG. 2B . Coiling is achieved by folding the electrode plates at their connecting pieces  24   a - 24   d  and  25   a - 25   e  such that the positive electrode layer faces  22   a - 22   e  and negative electrode layer faces  23   a - 23   f  are alternately layered upon one another with the separator in between them. The following is a description of how the positive electrode layer faces  22   a - 22   e  and negative electrode layer faces  23   a - 23   f  are alternately layered upon one another with the separator in between them in the coiling process steps: 
   As shown in  FIG. 3A , the separator  13  illustrated by broken lines is provided to cover both faces of the positive electrode plate  11 , which is placed upon the negative electrode plate  12 , such that the first positive electrode layer face  22   a  is located upon a negative electrode layer face  23   b  that is second from the coiling start end. The negative electrode layer face  23   a  is then folded back at the connecting piece  25   a  on the positive electrode layer face  22   a  as shown in  FIG. 3B . This portion where the positive electrode layer face  22   a  is sandwiched between the negative electrode layer faces  23   a ,  23   b  via the separator  13  on both sides is folded back at the connecting pieces  24   a  and  25   b  on the next positive electrode layer face  22   b  that is superposed on the negative electrode layer face  23   c  as shown in  FIG. 3C . This folding process is repeated towards the coiling finish end, until the positive and negative electrode plates  11 ,  12  are coiled around in a flat shape into an electrode plate group  10  shown in  FIG. 4 , with the separator  13  therebetween. 
   When coiling around the positive and negative electrodes  11 ,  12  into a flat electrode plate group  10  as described above, if the electrode plates  11 ,  12  are not in register, there may be a discrepancy in face-to-face positions of the positive electrode layer faces  22   a - 22   e  and negative electrode layer faces  23   a - 23   f . If part of the positive electrode layer faces  22   a - 22   e  upon the negative electrode layer faces  23   a - 23   f  is offset because of the positional discrepancy, there are risks of internal short-circuiting caused by dendritic growth of lithium, or of internal short-circuiting across the electrode plates and sealing case  5  upon an impact of a falling accident or the like. Consequently, it is necessary to detect whether there is a positional discrepancy in the finished electrode plate group  10 . For this purpose, the positive and negative electrode plates  11 ,  12  are respectively provided with positional discrepancy detecting holes or cut-outs  41   a ,  41   b ,  42  and  43 ,  44  in the positive electrode layer faces  22   a ,  22   b  and negative electrode layer face  23   a  that face each other at the coiling start end, and in the positive electrode layer face  22   e  and negative electrode layer face  23   f  that face each other at the coiling finish end. 
   Since the negative electrode layer face  23   a  faces the positive electrode layer faces  22   a ,  22   b  at the coiling start end as described above, when the electrode plates are coiled together in exact register, the positional discrepancy detecting hole  43  in the negative electrode layer face  23   a  is concentric with the holes  41   a ,  41   b  respectively formed in the positive electrode layer faces  22   a ,  22   b  as shown in  FIG. 4  and  FIG. 5 . At the coiling finish end where the positive electrode layer face  22   e  faces the negative electrode layer face  23   f , the positional discrepancy detecting hole  44  in the negative electrode layer face  23   f  is concentric with the hole  42  formed in the positive electrode layer face  22   e  as shown in  FIG. 5 , when the electrode plates are coiled together in exact register.  FIG. 5  is a model view illustrating a cross section that is orthogonal to the cross section of  FIG. 4 . The purpose of presenting a cross section in this direction is to illustrate the positions of the detecting holes at the coiling start end and coiling finish end that are offset in a direction orthogonal to the coiling direction. 
   Since the diameter of the layer faces  23   a - 23   f  of the negative electrode plate  12  in the direction of its width is larger than that of the layer faces  22   a - 22   e  of the positive electrode plate  11 , a positional discrepancy of the positive electrode plate  11  in the width direction of the negative electrode plate  12  should be allowable in physical terms by the difference in the widthwise diameter. The widthwise diameter of the negative electrode layer faces  23   a - 23   f  in this embodiment is 24.0 mm, while that of the positive electrode layer faces  22   a - 22   e  is 22.0 mm, and therefore a positional discrepancy of positive electrode layer faces  22   a - 22   e  on the negative electrode layer faces  23   a - 23   f  should be allowable by 1.0 mm on both sides in the widthwise direction. However, it is preferable to ensure that positive electrode layer faces  22   a - 22   e  are placed exactly upon the negative electrode layer faces  23   a - 23   f  in order to suppress the dendritic growth of lithium. If the edges of the positive electrode layer faces  22   a - 22   e  conform to the edges of the negative electrode layer faces  23   a - 23   f , it is likely that a short circuit is formed upon an impact of a falling accident or the like. For this reason, in this embodiment, the permissible range of positional discrepancy is determined by the diameters of the detecting holes  41   a ,  41   b ,  42  in the positive electrode and those  43 ,  44  in the negative electrode. 
   The diameter of the detecting holes  41   a ,  41   b ,  42  in the positive electrode is set larger than the detecting holes  43 ,  44  in the negative electrode, and if the detecting holes  43 ,  44  are located inside the detecting holes  41   a ,  41   b ,  42  with a certain clearance, it is judged that the positional discrepancy is within the permissible range. In this embodiment, the diameter of the detecting holes  41   a ,  42  in the positive electrode is 3.2 mm, and that of the hole  41   b  is 4.2 mm. The diameter of the detecting hole  43  in the negative electrode is 1.5 mm. When the detecting hole  41   a  in the positive electrode is not inside its detecting hole  41   b , it is assumed that there has been a positional discrepancy when folding the positive electrode plate  11  at its connecting piece  24   a  shown in  FIG. 3C . If the positional discrepancy between the centers of the detecting hole  41   a  in the positive electrode and the hole  43  in the negative electrode at the coiling start end is within 0.65 mm and if the discrepancy between the centers of the hole  42  in the positive electrode and the hole  44  in the negative electrode is within 0.65 mm, they are within the permissible range. 
   Detection of positional discrepancy using these detecting holes  41   a ,  41   b ,  42  and  43 ,  44  in the positive and negative electrodes is achieved by irradiating X-rays to the complete electrode plate group  10  and by processing the transmitted X-ray images of the electrode plate group  10 .  FIG. 6  is an example of an image obtained by X-ray transmission; it shows a state in which both electrode plates are in exact register where the centers of the detecting holes  41   a ,  41   b ,  42  in the positive electrode and those of the detecting holes  43 ,  44  in the negative electrode coincide with each other. Since the detecting holes  41   a ,  41   b  in the positive electrode and the hole  43  in the negative electrode at the coiling start end and the detecting holes  42 ,  44  at the coiling finish end are formed at different positions, it is possible to separately detect a positional discrepancy at the coiling start/finish ends. 
   Determination of non-conforming electrode plate groups  10  using the transmitted X-ray images can be made based on whether a positional discrepancy is detected between the centers of the detecting hole  41   a  in the positive electrode and of the hole  43  in the negative electrode, and between the centers of the detecting hole  42  in the positive electrode and of the hole  44  in the negative electrode. Alternatively, it can be made based on whether the detecting hole  41   a  in the positive electrode is located inside its detecting hole  41   b  and by detecting the minimum distance between the peripheral edges of the detecting hole  41   a  in the positive electrode and the hole  43  in the negative electrode, and between the peripheral edges of the detecting hole  42  in the positive electrode and the hole  44  in the negative electrode. 
   The diameter of the detecting holes  41   a ,  42  in the positive electrode is 3.2 mm in this embodiment as mentioned above, while the diameter of the detecting holes  43 ,  44  in the negative electrode is 1.5 mm. In the case where the inspection is based on detected minimum distances between the peripheral edges of the detecting hole  41   a  in the positive electrode and the hole  43  in the negative electrode, and between the peripheral edges of the detecting hole  42  in the positive electrode and the hole  44  in the negative electrode, if it is detected from a processed image of transmitted X-rays that these minimum distances are 0.2 mm or more, it is determined that the positional discrepancy is within the permissible range, and the electrode plate group  10  is identified as a conforming product that can be assembled into a coin type battery. If the detected minimum distances are 0.2 mm or less, then the electrode plate group  10  is disposed as a non-conforming product in which large positional displacement has occurred. 
   In the embodiment described above, the holes for detecting positional displacement formed at the coiling start/finish ends are offset from each other in a direction orthogonal to the coiling direction, but they may be offset from each other along the coiling direction. 
   In the embodiment described above, the holes  41   a ,  41   b ,  42 ,  43 ,  44  or cut-outs for detecting positional displacement are of circular form, but they can be in other forms such as squares. Alternatively, they can be formed as notches  71   a ,  71   b ,  72 ,  73 ,  74  as shown in  FIG. 7A  and  FIG. 7B . The positional discrepancy detecting cut-outs may be formed only in the positive and negative electrode layer faces that face each other at the coiling finish end of the electrode plate group. In the case where the positional discrepancy detecting cut-outs are formed both at the coiling start/finish ends of the electrode plate group, they may be provided only to the first positive electrode layer face  22   a , unlike the case shown in  FIG. 2A  and  FIG. 2B  in which the first layer face  22   a  and the second layer face  22   b  of the positive electrode are both formed with the cut-outs. Forming notches has an advantage over the forming of holes in that electrode plate punching die set can be simplified. 
   The positive and negative electrode plates  11 ,  12  shown in  FIG. 7A  and  FIG. 7B  have basically the same configuration as those illustrated in  FIG. 2A  and  FIG. 2B ; the negative electrode layer faces are larger than the positive electrode layer faces. At the coiling start end, positional discrepancy detecting cut-outs or notches  71   a ,  71   b  and  73  are formed in a right-angled triangular shape in the layer faces  22   a ,  22   b  of the positive electrode plate  11  and in the layer face  23   a  of the negative electrode plate  12 , respectively, at matching positions. In the positive electrode layer face  22   e  and negative electrode layer face  23   f  that face each other at the coiling finish end, positional discrepancy detecting cut-outs or notches  72 ,  74  are formed in a right-angled triangular shape. The notches  71   a ,  71   b ,  73  and  72 ,  74  shown in  FIG. 7A  and  FIG. 7B  are all of the same shape, so that, when the positive and negative electrode plates  11 ,  12  are coiled around in exact register, the straight portions of matching notches are substantially in parallel to each other. Alternatively, matching notches can be formed in shapes analogous to each other. 
     FIG. 8  illustrates an image obtained by transmitted X-rays of an electrode plate group having these positive and negative electrode plates  11 ,  12 . It can be seen from the drawing that a positional discrepancy in the electrode plate group at its coiling start/finish ends are detected based on the relative positional relationships between the corresponding detecting notches  71   a ,  71   b ,  73  and  72 ,  74 . The notches can be in some other forms such as arcs or the like other than right-angled triangles. 
   INDUSTRIAL APPLICABILITY 
   As described above, according to the present invention, it is possible to detect positional displacement in a coiled electrode plate group that is applied to flat shaped batteries such as coin type batteries. It prevents short circuits caused by positional displacement of electrode plates, and is advantageously adopted for the manufacture of coin type batteries with a good yield.