Patent Publication Number: US-2022231357-A1

Title: Cylindrical battery

Description:
TECHNICAL FIELD 
     The present disclosure relates to a cylindrical battery. 
     BACKGROUND ART 
     There are conventionally widely known cylindrical batteries which comprise a bottomed cylindrical exterior can, a sealing assembly closing an opening of the exterior can, and a gasket arranged between the exterior can and the sealing assembly (for example, refer to PATENT LITERATURES 1 and 2). In general, in the exterior can, there are formed a grooved part which has a lateral surface part caused to project to the inside from the outside and supports the sealing assembly via the gasket, and a shoulder part which is formed so as to face the grooved part and pinches and holds the sealing assembly via the gasket together with the grooved part. In order to secure a sealing property inside the battery, the shoulder part is crimped onto the peripheral edge of the sealing assembly. 
     In the cylindrical battery, a positive electrode lead is connected to an inner surface of the sealing assembly and the sealing assembly becomes a positive electrode external terminal, and a negative electrode lead is connected to an inner surface of the exterior can and the exterior can becomes a negative electrode external terminal, for example. 
     CITATION LIST 
     Patent Literature 
     
         
         PATENT LITERATURE 1: Japanese Unexamined Patent Application Publication No. 2009-152031 
         PATENT LITERATURE 2: Japanese Translation of PCT International Application Publication No. 2010-512638 
       
    
     SUMMARY 
     Technical Problem 
     There can be a case where a plurality of cylindrical batteries are connected in series via external leads to form a module. In this case, the external leads are connected to positive electrode external terminals and negative electrode external terminals. There can be a case where, in order to make a battery module small in size, external leads are connected to the shoulder parts of the exterior cans as the negative electrode external terminals, the shoulder parts being close to the sealing assemblies. In this case, although it can be considered that the shoulder part is elongated in order to make the area of connection of the external lead on the shoulder part large to improve workability of connection of leads, simply elongating the shoulder part causes the grooved part to readily deform to the electrode assembly side (lower side of the exterior can) in crimping the shoulder part. Such deformation of the grooved part can result in problems such as narrowing a space for housing the electrode assembly, and causing the grooved part to come into contact with the electrode assembly, which results in short circuit between those. 
     Solution to Problem 
     A cylindrical battery which is an aspect of the present disclosure comprises: a bottomed cylindrical exterior can including a bottom surface part and a lateral surface part; a sealing assembly closing an opening of the exterior can; and a gasket arranged between the exterior can and the sealing assembly, wherein the exterior can has a grooved part that is formed such that the lateral surface part is caused to project to an inside from an outside and that supports the sealing assembly via the gasket, and a shoulder part that is formed so as to face the grooved part via the sealing assembly and the gasket and that pinches and holds the sealing assembly together with the grooved part, and at least part of the shoulder part extends more to an inner side of the sealing assembly in a radial direction than an inner end of the grooved part, and a readily deforming part is formed in the shoulder part along a circumferential direction of the exterior can. 
     Advantageous Effects of Invention 
     According to the cylindrical battery which is an aspect of the present disclosure, the shoulder part may be caused to extend more to the inner side of the sealing assembly in the radial direction than the inner end of the grooved part while the grooved part is restrained from deforming. Thereby, the area of connection of the external lead on the shoulder part may be sufficiently secured, and workability of connection of leads may be improved when cylindrical batteries are made into a module. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view of a cylindrical battery which is an example of embodiments. 
         FIG. 2  is an expanded view of a shoulder part of an exterior can and its vicinity in  FIG. 1 . 
         FIG. 3  is a sectional view of a cylindrical battery which is another example of embodiments. 
         FIG. 4A  is a plan view of a cylindrical battery which is another example of embodiments. 
         FIG. 4B  is a view partially showing a cross section taken along the AA line in  FIG. 4A . 
         FIG. 5  is a view of deformation of a grooved part occurring in a cylindrical battery. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereafter, an example of embodiments of a cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. In the present specification, as to the wording “substantially . . . ”, “substantially parallel”, for its exemplary explanation, means any of the state of being completely parallel and the state considered as being substantially parallel. 
       FIG. 1  is a sectional view of a cylindrical battery  10  which is an example of embodiments. As exemplarily shown in  FIG. 1 , the cylindrical battery  10  comprises an electrode assembly  14 , an electrolyte, and an exterior can  16  housing the electrode assembly  14  and the electrolyte. The electrode assembly  14  includes a positive electrode  11 , a negative electrode  12 , and a separator  13 , and has a structure in which the positive electrode  11  and the negative electrode  12  are wound into a spiral shape via the separator  13 . The exterior can  16  has a bottomed cylindrical shape one end of which in the axial direction is opened, and the opening of the exterior can  16  is closed by a sealing assembly  17 . Moreover, a gasket  18  is interposed between the exterior can  16  and the sealing assembly  17 . Hereafter, the sealing assembly  17  side (opening side of the exterior can  16 ) of the cylindrical battery  10  is described as being on the upside, and a bottom surface part  16   a  side of the exterior can  16  is described as being on the downside, for convenience of description. 
     The positive electrode  11  has a positive electrode current collector and a positive electrode mixture layer formed on at least one of surfaces of the electrode current collector. For the positive electrode current collector, there can be used metallic foil, of aluminum, aluminum alloy, or the like, stable in the potential range of the positive electrode  11 , a film having the metal disposed in the surface layer, and the like. The positive electrode mixture layer includes a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride, and is preferably formed on both surfaces of the positive electrode current collector. For the positive electrode active material, there is used lithium-transition metal composite oxide, for example. The positive electrode  11  can be produced by applying positive electrode mixture slurry including the positive electrode active material, the conductive agent, the binder, and the like on the positive electrode current collector, drying the coating film, and after that, compressing the coating film to form the positive electrode mixture layer on both surfaces of the electrode current collector. 
     The negative electrode  12  has a negative electrode current collector and a negative electrode mixture layer formed on at least one of surfaces of the electrode current collector. For the negative electrode current collector, there can be used metallic foil, of copper, copper alloy, or the like, stable in the potential range of the negative electrode  12 , a film having the metal disposed in the surface layer, and the like. The negative electrode mixture layer includes a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably formed on both surfaces of the negative electrode current collector. For the negative electrode active material, there can be used graphite, silicon-containing compounds, and the like, for example. The negative electrode  12  can be produced by applying negative electrode mixture slurry including the negative electrode active material, the binder, and the like on the negative electrode current collector, drying the coating film, and after that, rolling the coating film to form the negative electrode mixture layer on both surfaces of the electrode current collector. 
     For the electrolyte, a non-aqueous electrolyte is used, for example. The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. For the non-aqueous solvent, there can be used esters, ethers, nitriles, amides, mixed solvents of two kinds or more of these, and the like. The non-aqueous solvent may contain a halogen-substituted substance having halogen atom(s) such as fluorine substituted for at least part of hydrogens of these solvents. Note that the non-aqueous electrolyte is not limited to a liquid electrolyte but may be a solid electrolyte. For the electrolyte salt, there can be used lithium salts such as LiPF 6 , for example. The kind of the electrolyte is not specially limited but may be an aqueous electrolyte. 
     The cylindrical battery  10  comprises insulating plates  19  and  20  arranged on the upside and the downside of the electrode assembly  14 , respectively. In the example shown in  FIG. 1 , a positive electrode lead  21  connected to the positive electrode  11  extends to the sealing assembly  17  side through a through hole of the insulating plate  19 , and a negative electrode lead  22  connected to the negative electrode  12  extends to the bottom surface part  16   a  side of the exterior can  16  through the outside of the insulating plate  20 . The positive electrode lead  21  is connected onto a lower surface of an internal terminal plate  25  which is a bottom plate of the sealing assembly  17  by welding or the like, and an external terminal plate  26  of the sealing assembly  17  electrically connected to the internal terminal plate  25  is a positive electrode external terminal. The negative electrode lead  22  is connected onto an inner surface of the bottom surface part  16   a  of the exterior can  16  by welding or the like, and the exterior can  16  is a negative electrode external terminal. 
     As mentioned above, the cylindrical battery  10  comprises the exterior can  16 , the sealing assembly  17  closing the opening of the exterior can  16 , and the gasket  18  arranged between the exterior can  16  and the sealing assembly  17 . The exterior can  16  is a bottomed cylindrical metal-made container including a bottom surface part  16   a  and a lateral surface part  16   b . The bottom surface part  16   a  exhibits a disc shape, and the lateral surface part  16   b  is formed into a cylinder shape along the outer peripheral edge of the bottom surface part  16   a . Moreover, the exterior can  16  has a circular opening, and the sealing assembly  17  is formed into a disc shape corresponding to the opening. The gasket  18  secures a sealing property inside the battery and secures electric insulation between the exterior can  16  and the sealing assembly  17 . 
     The exterior can  16  has a grooved part  30  which is formed such that the lateral surface part  16   b  is caused to project to the inside from the outside and which supports the sealing assembly  17  via the gasket  18 , and a shoulder part  31  which is formed so as to face the grooved part  30  via the sealing assembly  17  and the gasket  18  and which pinches and holds the sealing assembly  17  together with the grooved part  30 . The grooved part  30  is formed into an annular shape along the circumferential direction of the exterior can  16  (lateral surface part  16   b ) by spinning processing from the outside of the lateral surface part  16   b.    
     Similarly to the grooved part  30 , the shoulder part  31  is formed into an annular shape along the circumferential direction of the exterior can  16 . The shoulder part  31  is formed by folding the opening edge part of the exterior can  16  inward, and is crimped onto the peripheral edge of the sealing assembly  17  via the gasket  18 . Its details mentioned later, at least part of the shoulder part  31  extends more to the inner side of the sealing assembly  17  in the radial direction than an inner end  30   a  of the grooved part  30 , and a readily deforming part  34  (refer to  FIG. 2 ) is formed in the shoulder part  31  along the circumferential direction of the exterior can  16 . 
     The sealing assembly  17  is a disc-shaped member comprising a current interruption mechanism. The sealing assembly  17  has a structure in which the internal terminal plate  25 , the insulating plate  27 , and the external terminal plate  26  are stacked sequentially from the electrode assembly  14  side. The internal terminal plate  25  is a metal plate including an annular part  25   a  to which the positive electrode lead  21  is connected, and a thin center part  25   b  which is separated from the annular part  25   a  when an internal pressure of the battery exceeds a predetermined threshold. Vent holes  25   c  are formed in the annular part  25   a.    
     The external terminal plate  26  is arranged to face the internal terminal plate  25 , these interposing the insulating plate  27 . In the insulating plate  27 , an opening  27   a  is formed at the center part in the radial direction, and vent holes  27   b  are formed at respective portions overlapping with the vent holes  25   c  of the internal terminal plate  25 . The external terminal plate  26  has a vent part  26   a  which fractures when the internal pressure of the battery exceeds a predetermined threshold, and the vent part  26   a  is connected to the annular part  25   a  of the internal terminal plate  25  via the opening  27   a  of the insulating plate  27  by welding or the like. The insulating plate  27  insulates the annular part  25   a  of the internal terminal plate  25  and the vent part  26   a  of the external terminal plate  26  from each other at the portion except the connection portion of those. 
     The vent part  26   a  includes a downward projection protruding toward the inner side of the battery, and a thin part formed around the downward projection, and is formed at the center pat of the external terminal plate  26  in the radial direction. In the cylindrical battery  10 , by electrically connecting the internal terminal plate  25  to which the positive electrode lead  21  is connected and the external terminal plate  26  together, there is formed a current path connecting from the electrode assembly  14  to the external terminal plate  26 . When the internal pressure rises upon occurrence of abnormality in the battery, the internal terminal plate  25  fractures, the center part  25   b  is separated from the annular part  25   a , and the vent part  26   a  deforms so as to be convex toward the outside of the battery. Thereby, the current path is interrupted. When the internal pressure of the battery further rises, the vent part  26   a  fractures to form a discharge port for gas. 
     Note that the structure of the sealing assembly is not limited to the structure exemplarily shown in  FIG. 1 . The sealing assembly may have a stack structure including two vent members or may have a convex sealing assembly cap covering the vent members. Moreover, the negative electrode lead may be connected to the inner surface of the sealing assembly and the positive electrode lead may be connected to the inner surface of the exterior can. In this case, the sealing assembly is the negative electrode external terminal and the exterior can is the positive electrode external terminal. 
     For example, a plurality of cylindrical batteries  10  are connected in series to be made into a module. In a battery module including the plurality of cylindrical batteries  10 , external leads are connected to the sealing assembly  17  and the shoulder part  31  of the exterior can  16  by welding or the like. When an external lead is connected to the shoulder part  31  of the exterior can  16 , the module can be made smaller in size as compared with the case where an external lead is connected to the bottom surface part  16   a  of the exterior can  16 . Since in the cylindrical battery  10 , at least part of the shoulder part  31  extends to be elongated more to the inner side of the sealing assembly  17  in the radial direction than the inner end  30   a  of the grooved part  30 , the area of connection of the external lead on the shoulder part  31  can be sufficiently secured, and workability of connection of leads is improved to improve the yield. 
     Hereafter, referring to  FIG. 2 , there are described in detail the shoulder part  31  of the exterior can  16  and the structure around it.  FIG. 2  is an expanded view of the shoulder part  31  and its vicinity in  FIG. 1 . 
     As exemplarily shown in  FIG. 2 , the sealing assembly  17  is pinched and held by the grooved part  30  and the shoulder part  31  which are formed in the lateral surface part  16   b  of the exterior can  16 . The grooved part  30  has, at an upper part of the exterior can  16 , a part of the lateral surface part  16   b  caused to project to the inside from the outside, and is formed into an annular shape along the circumferential direction of the lateral surface part  16   b . Moreover, the grooved part  30  has a substantially U-shaped cross section. The sealing assembly  17  is arranged on the upper surface of the grooved part  30  via the gasket  18 . 
     A length L of the grooved part  30  is 1 mm to 3 mm, for example. Here, the length L of the grooved part  30  means a length along the radial direction β of the exterior can  16  from the inner surface of the exterior can  16  along the axial direction α to the inner end  30   a  of the grooved part  30 . When the length L of the grooved part  30  is in the aforementioned range, the sealing assembly  17  can be stably supported while mechanical strength of the exterior can  16  is being secured. 
     The shoulder part  31  is formed into an annular shape along the opening edge part (upper end part) of the exterior can  16 . The shoulder part  31  is formed by folding the lateral surface part  16   b  in the direction toward the sealing assembly  17  arranged on the upper surface of the grooved part  30  such that the opening edge part of the exterior can  16  faces the grooved part  30  via the sealing assembly  17  and the gasket  18 . The shoulder part  31  presses the sealing assembly  17  via the gasket  18  by being crimped onto the peripheral edge of the sealing assembly  17 . In the present embodiment, in plan view of the cylindrical battery  10 , the shoulder part  31  in the annular shape having a fixed width is formed on the peripheral edge of the sealing assembly  17 . Note that the end part, of the shoulder part  31 , on the outer periphery side is curved toward the outside of the battery. 
     As mentioned above, at least part of the shoulder part  31  extends more to the inner side of the sealing assembly  17  in the radial direction than the inner end  30   a  of the grooved part  30 . That is, in the shoulder part  31 , there are a facing part  32  which faces the grooved part  30  via the sealing assembly  17  and the gasket  18 , and an extending part  33  that does not face the grooved part  30 , and extends more to the inner side of the sealing assembly  17  in the radial direction than the inner end  30   a  of the grooved part  30 . The length of the extending part  33  along the radial direction β of the exterior can  16  may be not less than the length L of the grooved part  30  but is preferably shorter than the length L. The length of the extending part  33  is 10% to 60% of the length L of the grooved part  30 , for example, and is 0.2 mm to 2 mm by way of example. 
     In the present embodiment, the shoulder part  31  formed into an annular shape extends, across its total length in the circumferential direction, more to the inner side of the sealing assembly  17  in the radial direction than the inner end  30   a  of the grooved part  30 . In other words, the extending part  33  of the shoulder part  31  is formed into an annular shape. 
     In the shoulder part  31 , there is formed the readily deforming part  34  along the circumferential direction of the exterior can  16 . The readily deforming part  34  is a portion which deforms more readily than another portion of the shoulder part  31  when the shoulder part  31  is crimped onto the sealing assembly  17 , and stress of the crimping tends to concentrate thereat and is to be folded more readily than the other potions. In other words, the readily deforming part  34  is a portion that has the smallest yield stress and is to deform most readily on a cross section of the shoulder part  31  along the radial direction β of the exterior can  16 . 
     As shown with a comparative example mentioned later, when a shoulder part is formed to have a length exceeding the inner end of a grooved part, reaction force from the grooved part falls below the stress in crimping, and there can arise problems such as downward warping of the grooved part to the electrode assembly side, which causes a housing space for the electrode assembly to be small, and contact of the grooved part with the electrode assembly, which results in short circuit. In this case, there is spoiled the balance between the stress in crimping and the reaction force from the grooved part. With the cylindrical battery  10 , by forming the readily deforming part  34  in the shoulder part  31  to allow the shoulder part  31  to deform in crimping, stress acting on the grooved part  30  can be reduced. Therefore, even when the extending part  33  is formed in the shoulder part  31 , the grooved part  30  can be restrained from deforming. 
     The shoulder part  31  is preferably inclined such that its distance from the grooved part  30  becomes smaller as coming closer to the readily deforming part  34  from the end part on the outer periphery side. In the present embodiment, the facing part  32  of the shoulder part  31  is inclined toward the downside such that its distance from the grooved part  30  becomes smaller, in other words, its distance from the upper surface of the sealing assembly  17  becomes smaller as coming from the inner end of the curved part formed at the end part, of the shoulder part  31 , on the outer periphery side to the readily deforming part  34 . In this case, the gasket  18  is strongly pressed by the shoulder part  31 , which can secure an excellent sealing property inside the battery. 
     On the other hand, the portion of the shoulder part  31  positioned more on the tip side than the readily deforming part  34  is preferably formed to be substantially parallel to the radial direction β of the exterior can  16 . When the shoulder part  31  is crimped, the shoulder part  31  bends at the readily deforming part  34  and is put into the state where the portion of the shoulder part  31  positioned more on the tip side than the readily deforming part  34  is along the radial direction β. That is, there exists a bent part in the shoulder part  31 , and the portion positioned more to the tip side than the bent part, such, for example, as a part of or the entirety of the extending part  33 , is formed to be substantially parallel to the radial direction β. By forming at least part of the extending part  33  to be substantially parallel to the radial direction β, the stress acting on the grooved part  30  can be reduced, and moreover, an external lead can be readily connected to the shoulder part  31 . Furthermore, by making the inclination angle of the facing part  32  small, the external lead can be readily connected to the shoulder part  31 . For example, the inclination angle of the facing part  32  may be set to be substantially parallel to the radial direction β of the exterior can  16 . 
     In the mode exemplarily shown in  FIG. 2 , there is formed, in the shoulder part  31 , an annular groove  35  along the circumferential direction of the exterior can  16 . Although the groove  35  may be formed on the outer surface of the shoulder part  31 , it is preferably formed on the inner surface, of the shoulder part  31 , in contact with the gasket  18 . The groove  35  is formed to have a V-shaped cross section with a depth of 10% to 90% of the thickness of the shoulder part  31 , for example. A portion of the shoulder part  31  where the groove  35  is formed is thinner than the other portions, and is to deform more readily than the other portions due to concentration of the stress when the shoulder part  31  is crimped onto the sealing assembly  17 . That is, the portion where the groove  35  is formed is the readily deforming part  34 , and the readily deforming part  34  in an annular shape is formed across the total length of the shoulder part  31  (exterior can  16 ) in the circumferential direction. 
     The readily deforming part  34  (groove  35 ) is preferably formed in a range of a length corresponding to 50% of the length L of the grooved part  30  in the radial direction β of the exterior can  16  from a position on the shoulder part  31  overlapping with the inner end  30   a  of the grooved part  30  in the axial direction α of the exterior can  16  as a center X. For example, when the length L of the grooved part  30  is 2 mm, the readily deforming part  34  is formed in a range of ±1 mm from the center X in the radial direction β. By forming the readily deforming part  34  in the relevant range, the stress acting on the grooved part  30  in crimping can be sufficiently reduced, and the grooved part  30  can be highly restrained from deforming. 
     The readily deforming part  34  is still preferably formed in a range of a length corresponding to 30% of the length L of the grooved part  30  from the aforementioned center X of the shoulder part  31  in the radial direction β, specially preferably formed in a range of a length corresponding to 15% of the length L. In the present embodiment, the inner end  30   a  of the grooved part  30  and the readily deforming part  34  substantially line up in the axial direction α. That is, the readily deforming part  34  is formed, in the shoulder part  31 , in a portion substantially overlapping with the inner end  30   a  of the grooved part  30  in the axial direction α. The readily deforming part  34  is formed at a boundary position between the facing part  32  and the extending part  33 , and the whole extending part  33  is formed to be substantially parallel to the radial direction β of the exterior can  16 . 
     As exemplarily shown in  FIG. 3 , a step  36  may be formed, in the shoulder part  31 , into an annular shape along the circumferential direction of the exterior can  16 . The step  36  is preferably formed in a range of a length corresponding to 50% of the length L of the grooved part  30  in the radial direction β of the exterior can  16  from the position on the shoulder part  31  overlapping with the inner end  30   a  of the grooved part  30  in the axial direction α of the exterior can  16  as the center X, similarly to the groove  35 . In the example shown in  FIG. 3 , the step  36  is formed, in the shoulder part  31 , in a portion substantially overlapping with the inner end  30   a  of the grooved part  30  in the axial direction α. In this case, the portion of the shoulder part  31  where the step  36  is formed is the readily deforming part  34 . 
     In the mode exemplarily shown in  FIG. 3 , the step  36  (readily deforming part  34 ) is formed at the boundary position between the facing part  32  and the extending part  33 , the shoulder part  31  bends at the relevant boundary position, and the whole extending part  33  is formed to be substantially parallel to the radial direction pi of the exterior can  16 . Moreover, the thickness of the extending part  33  is smaller than the thickness of the facing part  32 , and is not more than 70% of the thickness of the facing part  32 , for example. Note that the groove  35  may also be formed at the position overlapping with the step  36  while the step  36  is formed in the shoulder part  31  to make at least part of the extending part  33  thin. 
       FIG. 4A  is a plan view showing another example of embodiments (the gasket  18  is omitted from the illustration), and  FIG. 4B  is a view partially showing a cross section taken along the AA line in  FIG. 4A . As exemplarily shown in  FIG. 4A  and  FIG. 4B , the shoulder part  31  may have at least one projection  37  which protrudes more to the inner side of the sealing assembly  17  in the radial direction than the inner end  30   a  of the grooved part  30 . In the example shown in  FIG. 4A  and  FIG. 4B , a plurality of (four) projections  37  are formed at the same intervals in the circumferential direction of the shoulder part  31  formed into an annular shape. In this case, the base portions of the projections  37  are the readily deforming parts  34 . 
     The readily deforming parts  34  formed at the base portions of the projections  37  are preferably formed at the similar positions to that of the readily deforming part  34  shown in  FIG. 2  and  FIG. 3 . In the example shown in  FIG. 4A  and  FIG. 4B , the projections  37  protrude from portions substantially overlapping with the inner end  30   a  of the grooved part  30  in the axial direction α to the inner side of the sealing assembly  17  in the radial direction, and the entirety of each of the projections  37  is the extending part  33 . Moreover, the base portions of the projections  37  bend, and the entirety of each of the projections  37  is formed to be substantially parallel to the radial direction β of the exterior can  16 . The length (width) of each of the projections  37  along the circumferential direction of the shoulder part  31  is preferably short in such a range that it does not affect the connection to the external lead, and is twice or less the length L of the grooved part  30 , for example. 
     EXAMPLES 
     While the disclosure will be hereafter further described with examples, the present disclosure is not limited to these examples. 
     Example 1 
     [Production of Positive Electrode] 
     As the positive electrode active material, a lithium-transition metal composite oxide expressed by the general formula, LiNi 0.8 Co 0.15 Al 0.05 O 2 , was used. The positive electrode active material, polyvinylidene fluoride, and acetylene black were mixed in a solid component mass ratio of 100:1.7:2.5, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare the positive electrode mixture slurry. Next, this positive electrode mixture slurry was applied onto both surfaces of a positive electrode current collector composed of aluminum foil except for the connection portion to a positive electrode lead, the coating film was dried and compressed, and after that, was cut to have a predetermined electrode size to produce a positive electrode. Here, the positive electrode lead made of aluminum underwent ultrasonic welding to the exposed part of the positive electrode current collector. 
     [Production of Negative Electrode] 
     As the negative electrode active material, readily graphitizable carbon was used. The negative electrode active material, polyvinylidene fluoride, and carboxymethylcellulose were mixed in a solid component mass ratio of 100:0.6:1, and water was used as a dispersion medium to prepare the negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied onto both surfaces of a negative electrode current collector composed of copper foil except for the connection portion to a negative electrode lead, the coating film was dried and compressed, and after that, was cut to have a predetermined electrode size to produce a negative electrode. Here, the negative electrode lead composed of a Ni—Cu—Ni cladding material underwent ultrasonic welding to the exposed part of the negative electrode current collector. 
     [Preparation of Non-Aqueous Electrolytic Solution] 
     LiPF 6  was dissolved in a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) to have 1.0 mol/L of concentration to prepare a non-aqueous electrolytic solution. 
     [Production of Cylindrical Battery] 
     The aforementioned positive electrode and the aforementioned negative electrode were wound into a spiral shape via a polyolefin-made separator to produce a winding-type electrode assembly. This electrode assembly was inserted into a bottomed tubular exterior can produced by drawing processing of a steel plate via a disc-shaped insulating plate for the bottom of the can, and was welded onto the inner surface of the bottom surface part. Next, an insulating plate was inserted above on the electrode assembly, and a grooved part having a substantially U-shaped cross section was formed more on the upper end side of the exterior can than the insulating plate. The grooved part had a lateral surface part of the exterior can caused to project to the inside from the outside, and was formed into an annular shape along the circumferential direction of the exterior can. Next, the aforementioned non-aqueous electrolytic solution was injected into the exterior can, and the positive electrode lead was welded onto the internal terminal plate of the sealing assembly. After that, the sealing assembly was arranged on the grooved part via the gasket with the positive electrode lead being folded. The opening edge part of the exterior can was crimped onto the peripheral edge of the sealing assembly via the gasket thereby to form the shoulder part and to form a cylindrical battery in which the shoulder part extended more to the inner side of the sealing assembly in the radial direction than the inner end of the grooved part. 
     In the shoulder part (0.25 mm of thickness), there was formed an annular groove (0.1 mm of depth) along the circumferential direction of the exterior can in a portion overlapping with the inner end of the grooved part in the axial direction of the exterior can. Moreover, an extending part which was positioned more on the tip side of the shoulder part than the groove was formed into an annular shape to be substantially parallel to the radial direction of the exterior can, and its length was 0.5 mm. Here, a portion (facing part) which faces the grooved part via the sealing assembly and the gasket was inclined such that its distance from the grooved part became smaller as coming closer to the groove, from the inner end of the curved part formed at the end part on the outer periphery side to the groove. 
     Example 2 
     A cylindrical battery was produced similarly to Example 1 except that an annular step was formed in place of the annular groove in the shoulder part. The thickness of the facing part was set to 0.25 mm and the thickness of the extending part was set to 0.15 mm. 
     Example 3 
     A cylindrical battery was produced similarly to Example 1 except that projections (0.5 mm of length: 2 mm of width) protruding more to the inner side of the sealing assembly in the radial direction than the inner end of the grooved part were formed in place of the annular extending part in the shoulder part. Four projections were formed at the same intervals in the circumferential direction of the shoulder part. 
     Comparative Example 1 
     A cylindrical battery was produced similarly to Example 1 except that the annular groove as the readily deforming part was not formed in the shoulder part. 
     [Observation of Cross Section of Grooved Part] 
     For each of the batteries of the examples and the comparative example, after an epoxy resin was injected into an upper part of the battery and solidified, the upper part of the battery was cut along the axial direction of the exterior can. For each battery, a sectional shape of the grooved part was observed, and as shown in  FIG. 5 , a downward warping angle θ of the upper surface of the grooved part was measured. The angle θ is an inclination angle relative to the direction perpendicular to the inner surface of the lateral surface part along the axial direction of the exterior can, and it is meant that the extent of deformation of the grooved part is larger as the angle θ is larger. 
     The measurement results for the angle θ are as follows. 
     Example 1: 0° to 0.5° 
     Example 2: 0° to 1° 
     Example 3: 1° to 2° 
     Comparative Example 1: 4° to 6° 
     It is clear from the aforementioned evaluation results that any of the batteries of the examples shows a smaller downward warping angle θ of the grooved part and a smaller extent of deformation of the grooved part as compared with the battery of the comparative example. According to the batteries of the examples, the shoulder part can be caused to extend more to the inner side of the sealing assembly in the radial direction than the inner end of the grooved part while restraining the grooved part from deforming. Therefore, the area of connection of the external lead on the shoulder part can be sufficiently secured while the grooved part not causing a problem such as its contact with the electrode assembly, which results in short circuit. On the other hand, as in the comparative example, simply elongating the shoulder part largely causes deformation of the grooved part, which raises the risk of the short circuit. 
     REFERENCE SIGNS LIST 
       10  cylindrical battery,  11  positive electrode,  12  negative electrode.  13  separator,  14  electrode assembly,  16  exterior can,  16   a  bottom surface part.  16   b  lateral surface part.  17  sealing assembly,  18  gasket,  19 ,  20  insulating plate,  21  positive electrode lead,  22  negative electrode lead,  25  internal terminal plate.  25   a  annular part.  25   b  center part,  25   c  vent hole,  26  external terminal plate,  26   a  vent part,  27  insulating plate,  27   a  opening,  27   b  vent hole,  30  grooved part,  30   a  inner end,  31  shoulder part,  32  facing part,  33  extending part,  34  readily deforming part,  35  groove,  36  step,  37  projection