Patent Publication Number: US-2021175568-A1

Title: Battery

Description:
TECHNICAL FIELD 
     The present invention relates to a battery including an electrode body and a battery can housing the electrode body. 
     BACKGROUND ART 
     For sealing the opening of a battery can after housing an electrode body in the battery can, typically, a groove is formed first in a battery case (battery can), as disclosed in Patent Literature 1. Then, a gasket and a sealing plate are inserted into the opening of the battery case, and with the outer periphery of the sealing plate covered with gasket, the rim above the groove of the battery can is crimped inward. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Laid-Open Patent Publication No. H7-105933 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, according to the sealing method as disclosed in Patent Document 1, since the gasket and the sealing plate are used in combination as a sealing body, there is a necessity of taking into account an assembling tolerance that occurs during the sealing process. For example, when covering the periphery of the sealing plate with the gasket, and when pressing the periphery and the gasket to bring them into close contact with each other after covering the periphery of the sealing plate with the gasket, the position of the gasket contacting the periphery tends to be varied. Therefore, with such variation taken into account, the shape, size, and the like of the sealing plate and the gasket needs to be designed. 
     Solution to Problem 
     One aspect of the present invention relates to a battery including: a battery can including a cylindrical portion, a bottom wall closing one end of the cylindrical portion, and an open rim continuing to the other end of the cylindrical portion; an electrode body housed in the cylindrical portion, and a sealing body fixed to the open rim so as to seal an opening defined by the open rim, the sealing body including a sealing plate, and a gasket disposed at a peripheral portion of the sealing plate, the gasket having an inner ring portion disposed on the peripheral portion on a side facing the electrode body, an outer ring portion disposed on the peripheral portion on a side opposite to the side facing the electrode body, and a side wall portion covering an end surface of the peripheral portion, the sealing plate and the gasket being integrally molded to be in close contact with each other. 
     Advantageous Effects of Invention 
     According to the present invention, the assembling tolerance that occurs during the battery sealing process can be reduced, which can increase the flexibility in battery design. 
     While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A schematic vertical cross-sectional view of an essential part of a battery according to an embodiment of the present invention. 
         FIG. 2  An oblique view showing an appearance of a battery can in the battery. 
         FIG. 3  A cross-sectional view showing a cross-sectional shape of a sealing body used in the battery. 
         FIG. 4  A schematic vertical cross-sectional view of a battery according to another embodiment of the present invention. 
         FIG. 5A  A schematic oblique view of a cap according to another embodiment of the present invention. 
         FIG. 5B  An oblique view of the cap of  FIG. 5A  as viewed from the side opposite to  FIG. 5A . 
         FIG. 6A  A schematic vertical cross-sectional view of a battery according to yet another embodiment of the present invention. 
         FIG. 6B  A schematic vertical cross-sectional view of an essential part of the battery of  FIG. 6A . 
         FIG. 6C  An oblique view of the battery of  FIG. 6A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A battery according to the present embodiment includes: a battery can including a cylindrical portion, a bottom wall closing one end of the cylindrical portion, and an open rim continuing to the other end of the cylindrical portion; an electrode body housed in the cylindncal portion, and a sealing body fixed to the open rim so as to seal an opening defined by the open rim. The sealing body includes a sealing plate, and a gasket disposed at a peripheral portion of the sealing plate. The sealing plate and the gasket are integrally molded to be in close contact with each other. 
     In the following, a direction from the sealing body toward the electrode body is referred to as a downward direction, and a direction from the electrode body toward the sealing body is referred to as an upward direction. In general, when the battery can is placed upright with the bottom side down, a direction parallel to the axis of the cylindncal portion and toward the open rim is the upward direction. 
     Conventionally, for sealing the open rim of the battery can, a constricted portion has been formed between the open rim and the cylindrical portion, such that the constricted portion becomes smaller in inner diameter than the open rim and the cylindrical portion. On the constricted portion, a sealing plate is placed with a gasket interposed therebetween. Subsequently, the open rim of the metal can is pressed in the upward and downward directions and crimped so as to curl over the gasket and the sealing plate. In this method, however, the contact position within the gasket where it contacts with the peripheral portion of the sealing plate is difficult to make constant, and the contact position tend to be displaced in the upward and downward directions. Therefore, the contact position within the gasket where it contacts with the peripheral portion of the sealing plate tends to vary from place to place on the open rim in its circumferential direction. As a result of the variation, when the battery after sealing is viewed from above, the shape of the gasket (outer ring portion) in contact with the sealing plate on the upper side of the peripheral portion tends to have a distorted ring shape in which the contour of the inner circumference is not circular in shape, and the width differs from place to place in the circumferential direction of the outer ring portion. 
     Especially in the case where a wider outer ring portion is desired in order to provide reliable electrical insulation, if clamping is applied, with the gasket adjusted to be wider on the portion extending above the contact position with the peripheral portion of the sealing plate, the shape of the outer ring portion tends to be distorted like waving, spoiling the aesthetic appearance. Moreover, wrinkles tend to occur in the outer ring portion. 
     The gasket serves to electrically insulate the open rim of the battery can from the sealing plate. However, when the width of the outer ring portion is small, the insulation between the open rim of the battery can and the sealing plate is difficult to be secured. When the shape of the outer ring portion is distorted, the width of the outer ring portion is different from place to place in the circumferential direction. It may occur therefore that although the insulation between the open rim and the sealing plate can be secured at a place where the outer ring portion is wide, the insulation cannot be secured at a place where the outer ring portion is narrow. 
     In contrast, the present embodiment uses a sealing body comprising a sealing plate and a gasket integrally molded together. The integral molding may be done by insert molding. By using such a sealing body, the variation in width of the outer ring portion can be reduced, and the open rim of the battery and the sealing plate can be reliably insulated from each other throughout the entire circumference of the open rim. Furthermore, the outer ring portion can be adjusted wider, thereby to lengthen the insulation distance between the open rim and the sealing plate. 
     In the sealing body comprising a sealing plate and a gasket integrally molded together, the sealing plate and the gasket each may have any shape, and can be designed in a desired shape. The gasket has an inner ring portion disposed on the side facing the electrode body (the inner side) of the peripheral portion of the sealing plate; an outer ring portion disposed on the side opposite to the electrode body (the outer side) of the peripheral portion of the sealing plate; and a side wall portion covering the end surface of the peripheral portion of the sealing plate. In the conventional sealing method, the inner ring portion is compressed in the upward direction, and the outer ring portion is compressed in the downward direction, achieving a close contact between the gasket and the sealing plate. The inner ring portion, the outer ring portion, and the side wall portion each may have any shape, and can be designed in a desired shape. 
     For example, the outer ring portion may be designed to have an inner circumference whose contour shape is rotationally symmetric and/or plane symmetric in any way, such as circular, regular polygonal, or wavy curved. The outer ring portion may be designed in a shape having a function that allows fitting with other components, such as a current collector lead. Moreover, the outer ring portion or the inner ring portion may be provided at a specific position with a hole exposing the sealing plate therefrom or with a bumpy surface. The outer ring portion may be made thick at a predetermined position. 
     In one configuration of the sealing plate, in order to equip an explosion-proof function, a thin-walled portion having a thin thickness is provided in an annular region between the peripheral portion and the center portion. In this case, when the internal pressure of the battery increases and exceeds a threshold value, the thin-walled portion, where the strength is structurally weak, is selectively ruptured. The thin-walled portion thus acts as an explosion-proof valve. On the other hand, due to its low structural strength, the thin-walled portion is prone to break when subjected to an external impact and is susceptible to corrosion from the outside. However, by designing the shape of the outer ring portion so as to cover at least part of the thin-walled portion, the thin-walled portion can be protected against external impact and corrosion by the outer ring portion. The outer ring portion may cover 20% or more of the area of the thin-walled portion, and may cover 100% thereof. 
     In the conventional sealing method, as described above, there occurs a variation in the contact position within the gasket where it contacts with the peripheral portion of the sealing plate, which ma cause the thin-walled portion to be left uncovered at places in the circumferential direction. On the other hand, when the outer ring portion is adjusted wider, with the variation of the contact position taken into account, so that the thin-walled portion can be covered throughout the entire circumference of the open rim with the outer ring portion over a certain area or more, it may happen that the outer ring portion extends over the center portion of the sealing plate at places in the circumferential direction. Therefore, in the conventional sealing method using the sealing plate and the gasket as separate members, it has been difficult to adjust the outer ring portion wider toward inward of the cylinder such that the thin-walled portion is covered with the outer ring portion. However, by using a sealing body comprising a sealing plate and a gasket integrally molded together, the occurrence of the above inconvenience can be reduced. 
     On the other hand, when the integrally-molded sealing body is pressed and crimped via the open rim of the metal can, the gasket undergoes a tensile stress in the radial direction (direction toward the axis of the cylindrical portion) at the time of pressing. As a result cracks may occur in the outer ring portion or the inner ring portion of the gasket, and adhesion may be lost by peeling at the boundary between the outer ring portion or the inner ring portion and the sealing plate. Especially when cracks or peeling occurs in the outer ring portion, the insulation between the open rim and the sealing plate may become insufficient, or the protection against the external impact or corrosion may become insufficient. 
     To prevent cracks and peeling of the outer ring portion in the crimping process, the outer ring portion may have a projecting portion protruding in a direction opposite to the electrode body (in the upward direction). The protruding portion is compressed in the downward direction in the crimping process. Since the projecting portion is compressed, the tensile stress is less transmitted toward the more inner circumference side than the projecting portion, resulting in less cracks and peeling in the outer ring portion on the more inner circumference side than the projecting portion. 
     To enhance the adhesion between the gasket and the sealing plate, the peripheral portion may have a recessed portion on at least one of a surface facing the outer ring portion and a surface facing the inner ring portion, the recessed portion recessed in the thickness direction of the sealing plate. This can increase the surface area where the gasket is in contact with the sealing plate, and enhance the adhesion therebetween. Furthermore, this can suppress the peeling of the outer ring portion or the inner ring portion against the tensile stress applied during the crimping process. 
     The sealing body of the present embodiment can be preferably applicable not only to a battery with the constricted portion provided according to the conventional sealing method, but also to a battery to be sealed by a method without providing the constricted portion. Formed by integrally molding the sealing plate and the gasket together, the sealing body can be handled as one component member, which can simplify the production of a battery. 
     Without providing the constricted portion, the sealing can be accomplished by, for example, pressing the side wall portion of the gasket laterally via the open rim of the battery can in the radial direction of the opening (the direction toward the axis of the cylindrical portion). Specifically, a pressing portion that presses the gasket against the end surface of the peripheral portion of the sealing plate is formed in the open rim, so that the gasket is compressed, by pressing, in the radial direction of the opening between the end surface of the peripheral portion of the sealing plate and the open rim, and the repulsive force of the gasket acts to ensure the airtightness between the sealing body and the open rim. 
     A description will be given below of a battery according to an embodiment of the present invention with reference to the drawings. It is to be noted, however, the present invention is not limited thereto. 
     First Embodiment 
       FIG. 1  is a schematic vertical cross-sectional view of an essential part of a battery OA according to the present embodiment.  FIG. 2  is an oblique view of the battery. The battery  10 A is circular cylindrical in shape, and includes a circular cylindncal bottomed battery can  100 A, a circular cylindrical electrode body  200  housed in the can, and a sealing body  300 A sealing the opening of the battery can  100 A. 
     The battery can  100 A has: a cylindrical portion  120 A housing the electrode body  200 ; a bottom wall  130 A closing one end of the cylindrical portion  120 A; and an open rim  110 A continuing to the other end of the cylindrical portion  120 A. The opening defined by the open rim  110 A is closed by the sealing body  300 A. 
     The sealing body  300 A includes a sealing plate  310 A and a gasket  320 A disposed at a peripheral portion  311 A of the sealing plate  310 A. The sealing plate  310 A is circular-shaped or disk-shaped and has an explosion-proof function. Specifically, the sealing plate  310 A has the peripheral portion  311 A and a center region  312 A, both having a thick wall thickness and serving to provide structural strength, and a thin-walled portion  313 A configured to exhibit an explosion-proof function. The thin-walled portion  313 A is provided in a region between the peripheral portion  311 A and the center region  312 A. To the inner surface of the center region  312 A, one end of a lead wire  210  extended from a positive electrode or a negative electrode constituting the electrode body  200  is connected. Thus, the sealing plate  310 A functions as a terminal of one electrode. 
     When the internal pressure of the battery can  100 A increases, the sealing plate  310 A bulges outward, and the stress due to tension is concentrated, for example, on the boundary between the peripheral portion  311 A and the thin-walled portion  313 A, causing a break to occur from the boundary. As a result, the internal pressure of the battery can  100 A is released, and the safety of the battery  10 A can be ensured. 
     The gasket  320 A has an outer ring portion  321 A and an inner ring portion  322 A, and a side wall portion  323 A connecting the outer ring portion  321 A with the inner ring portion  322 A. The end surface  311 T of the peripheral portion  311 A of the sealing plate  310 A is covered with the side wall portion  323 A. 
     The outer ring portion  321 A, the inner ring portion  322 A, and the side wall portion  323 A are formed as an integrally molded product. The gasket  320 A can be integrally molded with the sealing plate  310 A, for example, by insert molding. 
     The outer ring portion  321 A extends inward in the radial direction beyond the inner ring portion  322 A. The outer ring portion  321 A covers at least part of the thin-walled portion  313  of the sealing plate  310 A. The outer ring portion  321 A thus serves to protect the thin-walled portion  313 A against external impact and corrosion, and can increase the insulating distance between the open rim  110 A and the sealing plate  310 A. 
     A constricted portion  140  having an inner diameter smaller than that of the cylindrical portion of an open rim  110 A and that of the cylindrical portion  120 A is provided between the cylindrical portion  120 A of the battery can  100 A and the open rim  110 A. In short, the open rim  110 A is continuous with the cylindncal portion  120  through the constricted portion  140 . The constricted portion  140  comprises a first constricted portion  141   a  whose inner diameter continuously decreases from the cylindrical portion  120 A, and a second constricted portion  141   b  whose inner diameter continuously decreases from the open rim  110 A and is continuous with the first constricted portion  141   a  at a place where the inner diameter becomes the smallest. The inner ring portion  322 A of the gasket is in contact with the second constricted portion  141   b.    
     One end of the open rim  110 A is continuous with the second constricted portion  141   b . The other end  110 E of the open rim  110 A constitutes an open end, and is bent inward and in contact with the outer ring portion  321 A. 
     The inner ring portion  322 A is compressed in the upward direction via the second constricted portion  141   b , and the outer ring portion  321 A is compressed in the downward direction via the other end  110 E of the open rim  110 A, and thereby, the repulsive force of the gasket acts to bring the sealing body and the open rim into hermetic contact with each other. 
       FIG. 3  is a schematic cross-sectional view of an exemplary configuration of the sealing body  300 A as one component member, before sealing the battery can  100 A with the sealing body  300 A to form the battery  10 A. The sealing body  300 A has, as described above, the sealing plate  310 A and the gasket  320 A. The gasket  320 A has a projecting portion  324  provided in the outer ring portion  321 A, the projecting portion protruding in the upward direction. 
     The projecting portion  324  is not shown in  FIG. 1  because it is compressed in the downward direction in a crimping processing when sealing the battery can. However, since the projecting portion  324  is compressed in the crimping processing, the tensile stress is less transmitted toward the outer ring portion  321  on the more inner circumference side than the projecting portion  324 , resulting in less cracks and peeling in the outer ring portion. 
     The sealing plate  310 A has recessed portions  314  in the peripheral portion  311 A provided on a surface facing the outer ring portion  321 A and on a surface facing the inner ring portion  322 A. 
     The recessed portions  314  serve, when, for example, integrally molding the sealing plate  310 A and the gasket  320 A into a sealing body, to increase the surface area where the gasket  320 A is in contact with the sealing plate  310 A and thereby to enhance the adhesion between the gasket  320 A and the sealing plate  310 A. Moreover, against the tensile stress applied during the crimping processing, the peeling of the outer ring portion or the inner ring portion can be suppressed. 
     The recess of each recessed portion  314  may be inclined with respect to the thickness direction of the sealing plate (see  FIG. 3 ). In this case, the recessed portion  314  acts like a hook. This can enhance the adhesion between the gasket  320 A and the sealing plate  310 A, and prevent the gasket  320 A from being peeled off from the sealing plate  310 A by the impact or the like during transport or assembly. 
     The inner ring portion has a width W 1  and the outer ring portion has a width W 2 , both of which can be constant over the entire circumference of the sealing body, and can be W 2 &gt;W 1 . 
     Second Embodiment 
     The battery may further include an electrically conductive cap covering at least part of the open rim and electrically connected to the open rim, the cap being electrically insulated from the sealing plate. This can reduce the space necessary for wiring in the battery. 
     In the conventionally-configured battery, usually, the battery can functions as an external terminal of one electrode, and the sealing body functions as an external terminal of the other electrode. Electric current from the electrode with the same potential as the battery can is collected from the bottom of the battery can. On the other hand, electric current from the electrode with the same potential as the sealing plate is collected from the sealing plate placed opposite to the bottom of the battery can. In other words, when connecting external lead wires respectively to the electrodes, one external lead wire is extended from the undersurface of the battery, and the other external lead wire is extended from the top surface of the battery. Therefore, a space for wiring is necessary in the upward and downward directions. 
     In the battery of the present embodiment, the sealing body functions as an external terminal of one electrode (e.g. positive electrode) of the battery. The sealing body has a first principal surface facing the interior of the battery can, a second principal surface opposite to the first principal surface, and a side surface connecting the first principal surface with the second principal surface. On the other hand, the cap connected to the battery can is on the open rim side, and functions as an external terminal of the other electrode (e.g., negative electrode) of the battery. Therefore, electric current from the electrodes can be both collected in the vicinity of the sealing body (e.g., on the second principal surface side). Accordingly, a space (wiring space) for arranging a lead wire connected to each external terminal is only necessary to be present on the sealing body side, which can save the wiring space. Moreover, the cap is an accessary part of the battery, which is a separate member from the battery can. The cap can be therefore formed in any shape that suits the use and shape of the battery. Therefore, the present embodiment is applicable regardless of the shape of the battery (battery can). 
     The cap may have a first portion covering at least part of the side surface of the sealing body, with the open rim of the battery can therebetween. This increases the contact area with the battery can and improves the current-collecting ability. The cap may have a second portion covering at least part of an outer periphery of the second principal surface of the sealing body. This makes it easy to collect current from both electrodes on the second principal surface side of the sealing plate. The open rim of the battery can may be present between the second portion and the second principal surface of the sealing body. 
     The cap may have both the first portion and the second portion. In other words, the cap may have an approximately L-shaped cross-section in the axial direction (hereinafter, sometimes referred to as Z direction) of the battery can. By shaping like this, the cap is fixedly secured to the battery can, and moreover, the contact area with the battery is increased and a current-collecting ability can be increased. Furthermore, the edge of the battery on the second principal surface side can be protected with the cap. 
     When the cap includes the first portion having an annular shape, in a no-load state, the first portion may have a minimum inner diameter smaller than the maximum outer diameter of a portion of the open rim, the portion to be covered with the cap. By press-fitting such a cap onto the battery, the cap is more fixedly secured to the battery. 
     The cap may be welded to the open rim of the battery can. In this case, the cap is more fixedly secured to the battery, and, moreover, the resistance is lowered, and the current-collecting ability can be improved. Welding may be performed by any method, which can be selected as appropriate according to the material of the cap and the open rim. Examples of the welding method include laser welding and resistance welding. As a method other than welding, for example, a thread machining may be applied to the inside of the cap, and another thread machining may be applied to the battery at the connecting portion with the cap, so as to correspond to the thread on the cap. By mating the threads, the cap can be fastened to the battery can. A thread machining ma be applied only on either the cap or the battery can. In this case also, the cap can be secured to the battery can. 
     The cap is useful especially when the end surface of the open rim is on the side surface of the sealing body, that is, when the open rim of the battery can does not cover the second principal surface of the sealing body. Usually, in this case, current from both electrodes cannot be collected on the second principal surface side of the sealing body. However, by using the cap electrically connected to the battery can, current from both electrodes can be collected on the second principal surface side of the sealing plate. 
     When the end surface of the open rim is on the side surface of the sealing body, the open rim is preferably smaller in outer diameter at the lowest position in contact with the sealing body, than the cylindrical portion, in the height direction of the battery can. In this case, the cap can be designed in such a thickness that the outer diameter of the cap becomes almost equal to the outer diameter of the cylindrical portion. In other words, even in a state where the cap is fitted onto the battery can, the changes in the diameter of the battery in the axial direction can be reduced. 
     A detailed description will be given below of a battery according to an embodiment of the present invention, the battery including the cap, with reference to the drawings. It is to be noted, however, that the present invention is not limited thereto. 
       FIG. 4  is a schematic vertical cross-sectional view of a battery  10 B according to the present embodiment.  FIG. 5A  is a schematic oblique view of a cap according to the present embodiment.  FIG. 5B  is an oblique view of the cap as viewed from the side opposite to  FIG. 5A . 
     The battery  10 B is circular cylindncal in shape, and includes a circular cylindrical bottomed battery can  100 B, the circular cylindrical electrode body  200  housed in the battery can  100 B, a sealing body  300 B sealing an opening of the battery can  100 B, and an electrically conductive and annular cap  400  electrically connected to the battery can  100 B and electrically insulated from the sealing body  300 B. 
     The battery can  100 B has: a cylindrical portion  120 B housing the electrode body  200 ; a bottom wall  130 B closing one end of the cylindrical portion  120 B; and an open rim  110 B continuing to the other end of the cylindncal portion  120 B. The opening defined by the open rim  110 B is closed by a sealing body  300 B. 
     The sealing body  300 B has a first principal surface  300 X facing the interior of the battery can  100 B, a second principal surface  300 Y opposite to the first principal surface  300 X, and a side surface  300 Z connecting the first principal surface  300 X with the second principal surface  300 Y. An end surface  110 T of the open rim  110 B is on the second principal surface  300 Y of the sealing body  300 , and part of the open nm  110 B covers the outer periphery of the second principal surface  300 Y. 
     The sealing body  300 B includes a sealing plate  310 B and a gasket  320 B disposed at a peripheral portion  311 B of the sealing plate  310 B. The sealing plate  310 B is circular-shaped or disk-shaped, and has an explosion-proof function. Specifically, the sealing plate  310 B has the peripheral portion  311 B and a center region  312 B, both having a thick wall thickness and serving to provide structural strength, and a thin-walled portion  313 B configured to exhibit an explosion-proof function. The thin-walled portion  313 B is provided in an annular region between the peripheral portion  311 B and the center region  312 B. To the inner surface of the center region  312 B, one end of the lead wire  210  extended from a positive electrode or a negative electrode constituting the electrode body  200  is connected. Thus, the sealing plate  310  functions as a terminal of one of the electrodes. Note that the shape of the sealing body  300  is not limited thereto. 
     When the internal pressure of the battery can  100 B increases, the sealing plate  310 B bulges outward, and the stress due to tension is concentrated, for example, on the boundary between the peripheral portion  311 B and the thin-walled portion  313 B, causing a break to occur from the boundary. As a result, the internal pressure of the battery can  100 B is released, and the safety of the battery  10 B can be ensured. 
     The cap  400  has a first portion  401  covering a side surface  300 Z of the sealing body  300 B, with the open rim  110 B of the battery can  100 B therebetween, and a second portion  402  covering an outer periphery of the second principal surface  300 Y of the sealing body  300 B. 
     In view of not disturbing the explosion-proof function, the second portion  402  of the cap  400  preferably does not cover the thin-walled portion  313 B, and more preferably does not cover the boundary between the peripheral portion  311 B and the thin-walled part  313 B. The second portion  402  covers, for example, only part of the peripheral portion  311 B. 
     The cap  400  is electrically conductive, and has the same polarity as that of the battery can  100 B. So, the cap  400  can be configured to function as a terminal having a polarity different from that of the sealing body  300 B (sealing plate  310 B). Thus, current from the electrodes of the battery  10 B can be both collected on the second principal surface  300 Y side of the sealing body  300 B. In other words, regardless of the form of the open rim  110 B of the battery can  100 B, each external lead wire can be extended from the second principal surface  300 Y side. The cap  400  is electrically insulated from the sealing plate  310 B b, for example, the gasket  320 B.  FIG. 5  illustrates an example in which a first external lead wire  501  is connected to the second portion  402  of the cap  400 , and a second external lead wire  502  is connected to an outer surface of the center region  312 B of the sealing plate  310 B. 
     In a no-load state, the first portion  401  of the cap  400  has a minimum inner diameter D 401  (see  FIG. 2B ) smaller than a maximum outer diameter D 110  of a portion of the open rim  110 B to be covered with the first portion  401 . The battery  10 B is press-fitted into the cap  400 , and the cap  400  is fixedly secured to the battery  10 B. In view of the securing fixedness, D 401 /D 110  may be 0.99 or less, and may be less than 0.98 or less. On the other hand, in view of the ease of press-fitting, D 401 /D 110  is preferably 0.9 or more. 
     The first portion  401  of the cap  400  may be provided with one or more notches  403 . 
     The cap  400  is welded to the open rim  110 B. Preferably, the first portion  401  is welded to the open rim  110 B. 
     Third Embodiment 
       FIG. 6A  is a schematic vertical cross-sectional view of a battery  10 C including the cap  400  according to the present embodiment.  FIG. 6B  is a schematic vertical cross-sectional view of an essential part of the battery of  FIG. 6A .  FIG. 6C  is an oblique view of the battery of  FIG. 6A . 
     The end surface  110 T of an open rim  110 C of a battery can  100 C is on the side surface  300 Z of a sealing body  300 C, and the open rim  110 C does not cover the outer periphery of the second principal surface  300 Y of the sealing body  300 C. 
     By using the cap  400 , even when the open nm  110 C does not cover the second principal surface  300 Y, current can be collected from both electrodes in the vicinity of the sealing body  300 C, further, on the second principal surface  300 Y side. A joining material  410  having electrical conductivity may be interposed between the first portion  401  of the cap  400  and the outer surface of the open rim  110 C. 
     The open rim  110 C of the battery can  100 C may be smaller in outer diameter at the lowest position in contact with the sealing body  300 C, than the cylindrical portion  120 C, in the height direction of the battery can  100 C. For example, the open rim  110 C may has a tapered region  110 S where the outer diameter of the cylindrical portion  120 C is gradually reduced (see  FIG. 6B ), at the boundary with the cylindrical portion  120 C. The tapered region  110 S forms an angle of, for example, less than 45° with respect to the Z direction. 
     In this case, the cap  400  can be designed in such a thickness that the outer diameter of the cap  400  becomes almost equal to the outer diameter of the cylindrical portion  120 C. This can reduce the changes in the diameter of the battery  10 C in the Z direction. The difference between the outer diameter or the maximum outer diameter of the cap  400  and the outer diameter or the maximum outer diameter of the cylindrical portion  120 C is, for example, 20% or less of the outer diameter of the cylindrical portion  120 C. The difference may be 10% or less, and may be 5% or less or 2% or less or 1% or less. 
     When the first portion  401  of the cap  400  covers at least part of the tapered region  110 S, the cap  400  and the open rim  110 C may be welded within the tapered region IOS. This can make the positioning easy and suppress a heat-caused deterioration of the gasket  320 . 
     In the present embodiment, at least part of the open rim  110 C preferably presses a side wall portion  323 C of a gasket  320 C against the end surface  311 T of a peripheral portion  311 C of a sealing plate  310 C, so that the side wall portion  323 C is compressed in the radial direction of the opening. In this way, the airtightness between the open rim  110 C of the battery can  100 C and the sealing body  300 C can be easily ensured. For example, the open rim  110 C presses the gasket  320 C not in the Z direction but in the direction perpendicular to the Z direction (hereinafter, sometimes referred to as XY direction). In this case, given that the pressing force of the open rim  110 C exerted on the gasket  320 C is decomposed in two directions: Z and XY, the scalar quantity of the vector in the XY direction is larger than that in the Z direction. 
     A description will be given below of the sealing plate  310 C, the gasket  320 C, and the open rim  11 C that are suitably applicable to the case where the open rim  110 C presses the gasket  320 C in the XY direction. The configuration other than these may be the same as in the second embodiment. 
     The gasket  320 C has an outer ring portion  321 C and an inner ring portion  322 C, and a side wall portion  323 C connecting the outer ring portion  321 C with the inner ring portion  322 C. The end surface  311 T of the peripheral portion  311 C of the sealing plate  310 C is covered with the side wall portion  323 C. The outer ring portion  321 C and the inner ring portion  322 C sandwich the peripheral portion  311 C of the sealing plate  310 C therebetween, and thereby the gasket  320 C is secured to the sealing plate  310 C. 
     The open rim  110 C of the battery can  100 C is smaller in outer diameter at the lowest position in contact with the inner ring portion  322 C of the gasket  320 C, than the cylindrical portion  120 C, in the height direction of the battery can  100 C of the battery  10 C. The outer ring portion  321 C protrudes in the axial direction (Z direction) of the battery can  100 C beyond the end surface  110 T of the open rim  110 C. In this case also, the cap  400  is useful. Usually, in this case, the gasket  320 C becomes an obstacle, making it difficult to collect current from both electrodes on the second principal surface  300 Y side of the sealing body  300 C. However, by using the cap  400 , current can be easily collected from both electrodes on the second principal surface  300 Y side. 
     The outer ring portion  321 C, the inner ring portion  322 C, and the side wall portion  323 C are formed as an integrally molded product. The gasket  320 C can be integrally molded with the sealing plate  310 C, for example, by an insert molding technique. According to the integral molding, the sealing plate  310 C and the gasket  320 C are easily brought into close contact with each other. Formed by integrally molding the sealing plate  310 C and the gasket  320 C together, the sealing body  300 C can be handled as one component member, which can simplify the production of the battery  10 C. 
     In  FIG. 6A , a projection  111  constricted inward is formed on the inner side of the open rim  110 C, along the circumferential direction of the opening. This projection  111  presses the side all portion  323 C against the end surface  311 T. The side wall portion  323 C of the gasket  320 C may be provided with a recessed portion  3231  in advance at a position corresponding to the projection  111 . Providing the recessed portion  3231  on the gasket  320 C can prevent the gasket  320 C from being excessively deformed when the side wall  323 C is compressed. 
     The projection  111  may be formed intermittently in a plurality of numbers along the circumferential direction of the opening, or may be formed continuously along the circumferential direction of the opening. The continuously formed projection  111  can form an annular groove along the circumferential direction of the opening. The projection(s)  111  can press the gasket  320 C or its side wall portion  323 C more strongly toward the end surface  311 T of the peripheral portion  311 C of the sealing plate  310 C. In this way, the airtightness between the sealing body  300 C and the open rim  110 C can be more reliably ensured. When the projection  111  is formed intermittently in a plurality of numbers, the projections  111  (at least two, preferably four or more projections) are provided preferably at equi-angular intervals with respect to the center of the opening. 
     In the height direction of the battery can  100 C, the projection  111  is preferably substantially equal in position to the center of the end surface  311 T. By aligning like this, the deformation of the sealing plate  310 C and the gasket  320 C can be suppressed. Moreover, the pressure applied to the gasket  320 C or its side wall portion is unlikely to be non-uniform. Accordingly, the deformation of the gasket  320 C tends to be suppressed, and the gasket  320 C can be compressed to a higher degree. This can more reliably ensure the airtightness between the sealing body  300 C and the open rim  110 C. 
     Here, that the projection  111  is substantially equal in position to the center of the end surface  311 T of the sealing plate  310 C means that, in the height direction of the battery can  100 C, the difference between the position of the projection  111  and the center position of the end surface  311 T of the sealing plate  310 C is 4% or less of a height H of the battery can  100 C. 
     A recessed groove  3111  is formed at the center position of the end surface  311 T of the peripheral portion  311 C so as to correspond to the projection  111  of the open rim  110 . In the height direction of the battery can  100 C, the difference between the center position of the recessed groove  3111  and the position of the projection  111  is 4% or less of the height H of the battery can  100 C. 
     According to the above configuration, it is not necessary to press the gasket in the Z direction for hermetically sealing the battery can. This eliminates the necessity of providing the battery can  100 C with a constricted portion interposed between the gasket and the electrode body as shown in  FIGS. 1 and 4 . In this case, the shortest distance between the sealing body  300 C and the electrode body  200  can be set to, for example, 2 mm or less, and preferably 1.5 mm or less, more preferably 1 mm or less. 
     The battery cans  100 A,  100 B and  100 C may be made of any material. Examples of the material include iron and/or an iron alloy (including stainless steel), copper, aluminum, and an aluminum alloy (including an alloy containing a trace amount of other metals, such as manganese and copper). The cap  400  also may be made of any material, examples of which include those of the battery cans  100 A and  100 B. 
     The gaskets  320 A,  320 B, and  320 C may be made of any material, but in view of ease of integral molding, examples of the material that can be preferably used include polypropylene (PP), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), and polyamide (PA). 
     Next, an illustrative description will be given of a configuration of the electrode body  200 , with a lithium ion secondary battery taken as an example. 
     The cylindrical electrode body  200  is of a wound type, and is formed by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween. To one of the positive and negative electrodes, a lead wire  210  is connected. The lead wire  210  is connected to the inner surface of the center region of the sealing plate by welding or the like. To the other one of the positive and negative electrodes, another lead wire is connected. The another lead wire is connected to the inner surface of the battery can by welding or the like. 
     (Negative Electrode) 
     The negative electrode has a belt-like negative electrode current collector and a negative electrode active material layer formed on both sides of the negative electrode current collector. The negative electrode current collector is, for example, a metal film, a metal foil, or the like. The material of the negative electrode current collector is preferably at least one selected from the group consisting of copper, nickel, titanium, alloys thereof and stainless steel. The negative electrode current collector preferably has a thickness of for example, 5 to 30 μm. 
     The negative electrode active material layer contains a negative electrode active material, and optionally contains a binder and an electrically conductive material. The negative electrode active material layer may be a deposition film formed by a gas phase method (e.g., vapor deposition). Examples of the negative electrode active material include Li metal, a metal or an alloy that electrochemically reacts with Li, a carbon material (e.g graphite), a silicon alloy, a silicon oxide, and a metal oxide (e.g., lithium titanate). The negative electrode active material layer preferably has a thickness of, for example, 1 to 300 μm. 
     (Positive Electrode) 
     The positive electrode has a belt-like positive electrode current collector and a positive electrode active material layer formed on both sides of the positive electrode current collector. The positive electrode current collector is, for example, a metal film, a metal foil (stainless steel foil, aluminum foil, or aluminum alloy foil), or the like. 
     The positive electrode active material layer contains a positive electrode active material and a binder, and optionally contains an electrically conductive material. The positive electrode active material is not limited, but may be a lithium-containing composite oxide, such as LiCoO 2  or LiNiO 2 . The positive electrode active material layer preferably has a thickness of, for example, 1 to 300 μm. 
     Examples of the conductive material contained in each active material layer include graphite and carbon black. The conductive material is contained in an amount of, for example, 0 to 20 parts by mass per 100 parts by mass of the active material. Examples of the binder contained in the active material layer include fluorocarbon resin, acrylic resin, and rubber particles. The binder is contained in an amount of, for example, 0.5 to 15 parts by mass per 100 parts by mass of the active material. 
     (Separator) 
     The separator is preferably a microporous resin film or a nonwoven resin fabric. Examples of the material (resin) of the separator include polyolefin, polyamide, and polyamide imide. The separator has a thickness of, for example, 8 to 30 μm. 
     (Electrolyte) 
     The electrolyte may be a non-aqueous solvent in which a lithium salt is dissolved. Examples of the lithium salt include LiCO 4 , LiBF 4 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , and imide salts. Examples of the non-aqueous solvent include: cyclic carbonic esters, such as propylene carbonate, ethylene carbonate, and butylene carbonate; chain carbonic esters, such as diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; and cyclic carboxylic acid esters, such as γ-butyrolactone and γ-valerolactone. 
     Although a description is given above with a lithium ion secondary battery taken as an example, the present invention is applicable to a battery including a battery can which is sealed with a sealing body, regardless of whether the battery is a primary or secondary battery. 
     INDUSTRIAL APPLICABILITY 
     The battery according to the present invention is applicable to batteries of various shapes of cans, and is suitably applicable as a power source for, for example, portable devices, hybrid vehicles, electric vehicles, and the like. 
     Although the present invention has been described in term of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains, after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention. 
     REFERENCE SIGNS LIST 
     
         
           10 A,  10 B,  10 C: battery
         100 A,  10 B,  10 C: battery can
             110 A,  110 B,  110 C: open rim
                 110 E: end     110 S: tapered region     110 T: end surface     111 : projection         120 A,  120 B,  120 C: cylindrical portion     130 A,  130 B,  130 C: bottom wall     140 : constricted portion
                 141   a : first constricted portion     141   b : second constricted portion             200 : electrode bod     210 : lead wire     300 A,  300 B,  300 C: sealing body
             300 X: first principal surface     300 Y second principal surface     300 Z: side surface     310 A,  310 B,  310 C: sealing plate
                 311 T: end surface     3111 : recessed groove     311 A,  311 B,  311 C: peripheral portion     312 A,  312 B,  312 C: center region     313 A,  313 B,  313 C: thin-walled portion     314 : recessed portion         320 A,  320 B,  320 C: gasket
                 321 A,  321 B,  321 C: outer ring portion     322 A,  322 B,  322 C: inner ring portion     323 A,  323 B,  323 C: side wall portion
                     3231 : recessed portion         324 : projecting portion         400 : cap
                 401 : first portion     402 : second portion     403 : notch
                     410 : joining material             501 : first external lead wire     502 : second external lead wire