Patent Publication Number: US-2021184321-A1

Title: Cylindrical lithium ion secondary battery

Description:
TECHNICAL FIELD 
     The present invention relates to a cylindrical lithium ion secondary battery. 
     BACKGROUND ART 
     Lithium ion secondary batteries are being widely used in portable electronic devices and power sources of hybrid automobiles or electric vehicles because of various advantages, including a high operation voltage, a high energy density per unit weight, and so forth. 
     The lithium ion secondary battery can be largely classified as a cylinder type secondary battery, a prismatic type secondary battery, a pouch type secondary battery. Specifically, the cylindrical lithium ion secondary battery generally includes a cylindrical electrode assembly, a cylindrical can coupled to the electrode assembly, an electrolyte injected into the can to allow movement of lithium ions, and a cap assembly coupled to one side of the can to prevent leakage of the electrolyte and separation of the electrode assembly. 
     DESCRIPTION OF EMBODIMENTS 
     Technical Problem 
     Various embodiments of the present invention provide a cylindrical lithium ion secondary battery which, when an upper end of a cylindrical can is clamped, can prevent deformation of a cap assembly so as to improve safety. 
     Solution to Problem 
     According to various embodiments of the present invention, provided is a cylindrical lithium ion secondary battery comprising: a cylindrical can; an electrode assembly received in the cylindrical can; and a cap assembly for sealing the cylindrical can, wherein the cap assembly comprises a top plate having a notch formed thereon, a support plate disposed in close contact with a lower surface of the top plate and including a first through-hole formed through the center thereof, and a bottom plate electrically connected with the electrode assembly and connected to the lower surface of the top plate through the first through-hole; and wherein the support plate has a strength greater than a strength of the top plate. 
     The support plate may include a first region having the first through-hole formed thereon, a second region positioned at an exterior side of the first region and positioned lower than the first region, and a third region connecting the first region and the second region to each other and including a plurality of second through-holes formed thereon. 
     The third region may be formed to be tilted to disperse the stress generated when an upper end of the cylindrical can is clamped to fix the cap assembly to the cylindrical can. 
     A ring-shaped groove may be formed on the second region to disperse the stress generated when an upper end of the cylindrical can is clamped to fix the cap assembly to the cylindrical can. 
     The groove may be formed to have a depth of 5% to 20% of a thickness of the support plate. 
     The cylindrical lithium ion secondary battery may further include an insulation plate positioned between the support plate and the bottom plate and having a through-hole centrally located to correspond to the first through-hole of the support plate. 
     If the internal gas pressure of the cylindrical can is greater than a predetermined operating pressure and smaller than a predetermined breaking pressure, the top plate may be upwardly convexly deformed, and the top plate may then be electrically disconnected from the bottom plate. 
     If the internal gas pressure of the cylindrical can is greater than a predetermined breaking pressure, the notch of the top plate may be broken. 
     The cylindrical lithium ion secondary battery may further include an insulation gasket positioned between the cap assembly and the cylindrical can and insulating the cap assembly and the cylindrical can from each other. 
     Advantageous Effects of Invention 
     As described above, the cylindrical lithium ion secondary battery according to various embodiments of the present invention includes a support plate having a strength greater than that of a top plate to alleviate the stress generated toward the center of a cap assembly when an upper end of a cylindrical can is clamped, thereby preventing deformation of the top plate and improving safety. 
     The cylindrical lithium ion secondary battery according to various embodiments of the present invention includes a support plate having a stepped portion to decentralize the stress generated toward the center of a cap assembly when an upper end of a cylindrical can is clamped, thereby preventing deformation of the top plate and improving safety. 
     The cylindrical lithium ion secondary battery according to various embodiments of the present invention includes a support plate having a groove to decentralize the stress generated toward the center of a cap assembly when an upper end of a cylindrical can is clamped, thereby preventing deformation of the top plate and improving safety. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a cylindrical lithium ion secondary battery according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the cylindrical lithium ion secondary battery according to an embodiment of the present invention. 
         FIG. 3  is an enlarged cross-sectional view illustrating only a cap assembly of the cylindrical lithium ion secondary battery according to an embodiment of the present invention. 
         FIG. 4  is a plan view illustrating a support plate of the cylindrical lithium ion secondary battery according to an embodiment of the present invention. 
         FIG. 5  is a cross-sectional view illustrating stress generated when a crimping part is formed in the cylindrical lithium ion secondary battery according to an embodiment of the present invention. 
         FIG. 6  is a cross-sectional view of a cylindrical lithium ion secondary battery according to another embodiment of the present invention. 
         FIG. 7  is a plan view illustrating a support plate of the cylindrical lithium ion secondary battery according to another embodiment of the present invention. 
     
    
    
     MODE OF INVENTION 
     Hereinafter, embodiments of the present invention will be described in detail. 
     The embodiments of the present invention, however, may be modified in many different forms and should not be construed as being limited to the example (or exemplary) embodiments set forth herein. Rather, these example embodiments are provided so that this invention will be thorough and complete and will convey the aspects and features of the present invention to those skilled in the art. 
     In addition, in the accompanying drawings, sizes or thicknesses of various components are exaggerated for brevity and clarity. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. In addition, it will be understood that when an element A is referred to as being “connected to” an element B, the element A can be directly connected to the element B or an intervening element C may be present therebetween such that the element A and the element B are indirectly connected to each other. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms that the terms “comprise or include” and/or “comprising or including,” when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various members, elements, regions, layers and/or sections, these members, elements, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one member, element, region, layer and/or section from another. Thus, for example, a first member, a first element, a first region, a first layer and/or a first section discussed below could be termed a second member, a second element, a second region, a second layer and/or a second section without departing from the teachings of the present invention. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the element or feature in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “on” or “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. 
       FIG. 1  is a perspective view of a cylindrical lithium ion secondary battery according to an embodiment of the present invention.  FIG. 2  is a cross-sectional view of the cylindrical lithium ion secondary battery according to an embodiment of the present invention.  FIG. 3  is an enlarged cross-sectional view illustrating only a cap assembly of the cylindrical lithium ion secondary battery according to an embodiment of the present invention.  FIG. 4  is a plan view illustrating a support plate of the cylindrical lithium ion secondary battery according to an embodiment of the present invention. 
     Referring to  FIGS. 1 to 4 , the cylindrical lithium ion secondary battery  100  according to an embodiment includes a cylindrical can  110 , an electrode assembly  120 , and a cap assembly  140 . In some instances, the cylindrical lithium ion secondary battery  100  may further include a center pin  130 . 
     The cylindrical can  110  includes a circular bottom portion  111  and a side wall  112  upwardly extending a predetermined length from the bottom portion  111 . In the process of manufacturing the secondary battery, a top portion or top end of the cylindrical can  110  is left open. Therefore, in the process of assembling the secondary battery  100 , the electrode assembly  120  and the center pin  130  may be inserted into the cylindrical can  110  together with an electrolyte. The cylindrical can  110  may be made of steel, a steel alloy, aluminum, an aluminum alloy, or an equivalent thereof, but embodiments of the present invention are not limited thereto. In addition, an inwardly recessed beading part  113  may be formed below the cap assembly  140  to prevent the cap assembly  140  from being deviated to the outside and an inwardly bent crimping part  114  may be formed on or above the beading part  113 . 
     The electrode assembly  120  is accommodated within the cylindrical can  110 . The electrode assembly  120  includes a negative electrode plate  121  coated with a negative electrode active material (e.g., graphite or carbon), a positive electrode plate  122  coated with a positive electrode active material (e.g., a transition metal oxide, such as LiCoO 2 , LiNiO 2 , or LiMn 2 O 4 ), and a separator  123  interposed between the negative electrode plate  121  and the positive electrode plate  122  to prevent a short circuit between the negative electrode plate  121  and the positive electrode plate  122  while allowing only movement of lithium ions. The negative electrode plate  121 , the positive electrode plate  122 , and the separator  123  are wound in a substantially cylindrical shape or configuration. Here, the negative electrode plate  121  may be formed of a copper (Cu) foil, the positive electrode plate  122  may be formed of an aluminum (Al) foil, and the separator  123  may be made of polyethylene (PE) or polypropylene (PP), but embodiments of the present invention are not limited thereto. In addition, a negative electrode tab  124  may be welded to the negative electrode plate  121  to downwardly protrude and extend a predetermined length therefrom, and a positive electrode tab  125  may be welded to the positive electrode plate  122  to upwardly protrude and extend a predetermined length therefrom, or vice versa. In addition, the negative electrode tab  124  may be made of nickel (Ni), and the positive electrode tab  125  may be made of aluminum, but embodiments of the present invention are not limited thereto. 
     In addition, the negative electrode tab  124  of the electrode assembly  120  may be welded to the bottom portion  111  of the cylindrical can  110 . Therefore, the cylindrical can  110  may function as a negative electrode. In other embodiments, the positive electrode tab  125  may be welded to the bottom portion  111  of the cylindrical can  110 . In these embodiments, the cylindrical can  110  may function as a positive electrode. 
     Additionally, a first insulation plate  126 , which is coupled to the cylindrical can  110  and has a first hole  126   a  formed at its center and a second hole  126   b  formed around the first hole  126   a , may be interposed between the electrode assembly  120  and the bottom portion  111  of the cylindrical can  110 . The first insulation plate  126  may prevent the electrode assembly  120  from electrically contacting the bottom portion  111  of the cylindrical can  110 . Specifically, the first insulation plate  126  prevents the positive electrode plate  122  of the electrode assembly  120  from electrically contacting the bottom portion  111 . Here, when a relatively large amount of gas is generated due to an abnormality in the secondary battery, the first hole  126   a  allows the gas to rapidly move upwardly through the center pin  130 , and the second hole  126   b  allows the negative electrode tab  124  to pass therethrough to be welded to the bottom portion  111 . 
     In addition, a second insulation plate  127 , which is coupled to the cylindrical can  110  and has a first hole  127   a  formed at its center and a plurality of second holes  127   b  formed around the first hole  127   a , may be interposed between the electrode assembly  120  and the cap assembly  140 . The second insulation plate  127  may prevent the electrode assembly  120  from electrically contacting the cap assembly  140 . Specifically, the second insulation plate  127  prevents the negative electrode plate  121  of the electrode assembly  120  from electrically contacting the cap assembly  140 . Here, when a relatively large amount of gas is generated due to an abnormality in the secondary battery, the first hole  127   a  allows the gas to rapidly move to the cap assembly  140 , and the second holes  127   b  allow the positive electrode tab  125  to pass therethrough to be welded to the cap assembly  140 . In addition, during injection of an electrolyte, the other second hole  127   b  allows the electrolyte to rapidly flow into the electrode assembly  120 . 
     Additionally, since diameters of the first holes  126   a  and  127   a  of the first and second insulation plates  126  and  127  are smaller than a diameter of the center pin  130 , the center pin  130  may be prevented from electrically contacting the bottom portion  111  of the cylindrical can  110  or the cap assembly  140  due to external impacts. 
     The center pin  130  is a hollow cylinder pipe and may be coupled to an approximately central area of the electrode assembly  120 . The center pin  130  may be made of steel, a steel alloy, aluminum, an aluminum alloy, or polybutylene terephthalate, but embodiments of the present invention are not limited thereto. The center pin  130  may suppress deformation of the electrode assembly  120  during charging and discharging of the secondary battery and may function as a movement passage for gas generated in the secondary battery. 
     The cap assembly  140  may include a top plate  141 , a support plate  142 , an insulation plate  143 , and a bottom plate  144 . 
     The top plate  141  may include a substantially planar first surface  141   a  and a substantially planar second surface  141   b  opposite to the first surface, and specifically may further include at least one notch  141   c  formed on a lower surface  141   b . The notch  141   c  may be ruptured when the internal gas pressure of the secondary battery is greater than a predetermined breaking pressure, thereby rapidly releasing the internal gas of the secondary battery to the outside. 
     In addition, the top plate  141  may include an upper region  141   d , a side region  141   e  and a lower region  141   f . The upper region  141   d  may positioned on a support plate  142  and may be substantially planar. The upper region  141   d  may serve as a terminal of the secondary battery, and thus may be electrically connected to an external device (e.g., a load or a charger). The side region  141   e  may be downwardly bent from the upper region  141   d  to substantially encompass a side portion of the support plate  142 . The lower region  141   f  is horizontally inwardly bent from the side region  141   e  to then be positioned at a bottom portion of the support plate  142 . In such a manner, the top plate  141  may be integrally formed with the support plate  142  by the upper region  141   d , the side region  141   e , and the lower region  141   f.    
     The top plate  141  may be made of, for example, aluminum, aluminum, an aluminum alloy or equivalents thereof, but embodiments of the present invention are not limited to the above materials. Accordingly, a bus bar or an external lead, made of aluminum, may be easily welded to the top plate  141 . Specifically, the top plate  141  may be made of soft aluminum having a first strength, and thus may be ruptured when the internal pressure of the secondary battery is greater than or equal to a predetermined reference pressure. 
     In some cases, the top plate  141  may further include a bent region  141   g  formed at the upper region  141   d . When viewed from below, the bent region  141   g  may be shaped of a substantially circular ring. As an example, the upper region  141   d  located inside the bent region  141   g  may be positioned higher than the upper region  141   d  located outside the bent region  141   g . In addition, the notch  141   c  may be formed on the upper region  141   d  located inside the bent region  141   g.    
     The support plate  142  may be positioned under the top plate  141  and may include a first region  142   a , a second region  142   b  and a third region  142   c . The first region  142   a  may be formed at a region corresponding to the upper region of the top plate  141 . Specifically, the first region  142   a  is formed in close contact with the upper region  141   d  of the top plate  141  located inside the bent region  141   g . In addition, a first through-hole  142   d  is formed substantially at the center of the first region  142   a . Here, a bottom plate  144 , which will later be described, may pass through the first through-hole  142   d  to then be electrically connected to the top plate  141 , and the first through-hole  142   d  may allow the internal gas pressure to be directly applied to the top plate  141 . The second region  142   b  is positioned at an exterior side of the first region  142   a  and is positioned lower than the first region  142   a . That is to say, a step difference is generated between the first region  142   a  and the second region  142   b . Particularly, the second region  142   b  is disposed in close contact with the upper region  141   d  located outside the bent region  141   g  of the top plate  141 . Therefore, the second region  142   b  is surrounded by the upper region  141   d , the side region  141   e  and the lower region  141   f , which are located outside the bent region  141   g . The third region  142   c  is positioned between the first region  142   a  and the second region  142   b  and connects the first region  142   a  and the second region  142   b  to each other. In addition, the third region  142   c  may be tilted (bent) to connect the first region  142   a  and the second region  142   b  having different heights to each other. That is to say, the third region  142   c  is shaped to correspond to the bent region  141   g  of the top plate  141 . As such, the support plate  142  is generally configured to make contact with the lower surface  141   b  of the top plate  141 . 
     Additionally, the third region  142   c  may prevent deformation of the cap assembly  140  by dispersing the force applied to the cap assembly  140 , specifically the stress generated toward the center of the cap assembly  140  when an upper end of the cylindrical can  110  is clamped. In addition, a plurality of second through-holes  142   e  are formed in the third region  142   c . Here, the second through-holes  142   e  may allow the internal gas pressure to be directly applied to the top plate  141 . For example, the notch  141   c  formed on the lower surface  141   b  of the top plate  141  may be positioned at a region corresponding to the first region  142   a  positioned between the first through-hole  142   d  and each of the second through-holes  142   e  of the support plate  142 , but embodiments of the present invention are not limited thereto. 
     The support plate  142  may be made of aluminum, an aluminum alloy or equivalents thereof. Specifically, the support plate  142  may be made of rigid aluminum having a second strength higher than the first strength of the top plate  141 . Therefore, when an external force is applied to the cap assembly  140 , specifically when the upper end of the cylindrical can  110  is clamped, the support plate  142  may prevent deformation of the top plate  141  by supporting the top plate  141 . 
     The insulation plate  143  may be positioned under (attached to a bottom portion of) the support plate  142  and may include a through-hole  143   a  located to correspond to the first through-hole  142   a . When viewed from below, the insulation plate  143  may be shaped of a substantially circular ring having a predetermined width. In addition, the insulation plate  143  serves to insulate the support plate  142  and the bottom plate  144  from each other. For example, the insulation plate  143  may be positioned between the support plate  142  and the bottom plate  144  and may be subjected to ultrasonic welding, but embodiments of the present invention are not limited thereto. 
     The insulation plate  143  may be made of, for example, polyethylene (PE), polypropylene (PP), ethylene propylene diene monomer (M-class) rubber (EPDM rubber), or equivalents thereof, but embodiments of the present invention are not limited to the above materials. 
     The bottom plate  144  is electrically connected to the top plate  141  through the through-hole  143   a  of the insulation plate  143  and the first through-hole  142   a  of the support plate  142  to then be attached to the insulation plate  143 . That is to say, the bottom plate  144  may include a first area  144   a  connected (welded) to the upper region  141   d  of the top plate  141 , a second area  144   b  bent from the first area  144   a  and passing through the first through-hole  142   a  of the support plate  142  and the through-hole  143   a  of the insulation plate  143 , and a third area  144   c  bent from the second area  144   b  and attached to the insulation plate  143 . In  FIG. 3 , undefined reference numeral  144   e  refers to a welding region in which the first area  144   a  of the bottom plate  144  is welded to the lower surface  141   b  of the upper region  141   d  of the top plate  141 . 
     Here, the positive electrode tab  125  may be electrically connected to the third area  144   c  of the bottom plate  144 . In addition, one or more notches  144   d  may further be formed on the first area  144   a  of the bottom plate  144 . When the internal gas pressure of the battery is greater than a predetermined pressure, the top plate  141  may be upwardly convexly deformed, and the notches  144   d  may serve to electrically separate the first area  144   a  of the bottom plate  144  from the second area  144   b . Accordingly, a current path between the top plate  141  and the bottom plate  144  may be blocked. 
     The bottom plate  144  may be made of, for example, aluminum, aluminum, an aluminum alloy or equivalents thereof, and thus the positive electrode tab  125  made of aluminum may be easily welded thereto. 
     For example, in the cylindrical lithium ion secondary battery  100  according to an embodiment, when the internal gas pressure of the cylindrical can  110  is greater than a predetermined first pressure (operating pressure) and smaller than a predetermined second pressure (breaking pressure), the top plate  141  may be upwardly convexly deformed by the internal gas pressure, so that the top plate  141  is electrically disconnected from the bottom plate  144 . In addition, in the cylindrical lithium ion secondary battery  100  according to an embodiment, when the internal gas pressure of the cylindrical can  110  is greater than the predetermined second pressure (breaking pressure), the notch  141   c  formed on the top plate  141  is ruptured, the internal gas existing inside the secondary battery may be rapidly released to the outside, thereby preventing explosion of the secondary battery and ultimately improving safety. 
     The cap assembly  140  may further include an insulation gasket  145  insulating the top plate  141  and the sidewall  112  of the cylindrical can  110  from each other. Here, the insulation gasket  145  is configured to be substantially compressed between the beading part  113  and the crimping part  114 , each of which are formed at the side wall  112  of the cylindrical can  110 . In addition, the insulation gasket  145  may substantially encompass the side region  141   e  of the top plate  141 , and the upper region  141   d  and the lower region  141   f , which are located around side region  141   e.    
     Additionally, an electrolyte (not shown) is injected into the cylindrical can  110 , and lithium ions generated by an electrochemical reaction in the negative electrode plate  121  and the positive electrode plate  122  in the secondary battery during charging and discharging are allowed to move. The electrolyte may be a non-aqueous, organic electrolyte including a mixture of a lithium salt and a high-purity organic solvent. In addition, the electrolyte may be a polymer using a polymer electrolyte or a solid electrolyte, but embodiments of the present invention are not limited to the above electrolytes. 
       FIG. 5  is a cross-sectional view illustrating stress generated when a crimping part is formed in the cylindrical lithium ion secondary battery according to an embodiment of the present invention. 
     As illustrated in  FIG. 5 , when the upper end of the cylindrical can  110  is clamped to fix the cap assembly  140  to the cylindrical can  110 , a force F 1  is applied in a downward direction with respect to the cap assembly  140  and in an inward direction with respect to the cap assembly  140 . With the force F 1  applied, stress F 2  is generated toward the center of the cap assembly  140 , resulting in deformation of the cap assembly  140 , so that the cap assembly  140  is centrally depressed. Accordingly, the cylindrical lithium ion secondary battery  100  may undergo changes in the component characteristics. Particularly, the first pressure (operating pressure) and the second pressure (breaking pressure) of the top plate  141  may change, and the top plate  141  may not properly operate under a given pressure. 
     In the present invention, however, the support plate  142  having a higher strength than the top plate  141  (that is, having the second strength higher than the first strength of the top plate  141 ) is provided, thereby alleviating the stress generated toward the center of the cap assembly  140  when the upper end of the cylindrical can  110  is clamped. Accordingly, the support plate  142  may improve the safety of the cylindrical lithium ion secondary battery  100  by preventing deformation of the top plate  141 . 
     In addition, since the third region  142   c , in which a step difference is generated due to a height difference between the first region  142   a  and the second region  142   b , is formed in the support plate  142 , the stress generated toward the center of the cap assembly  140  when the upper end of the cylindrical can  110  is clamped, may be decentralized. Accordingly, the support plate  142  may improve the safety of the cylindrical lithium ion secondary battery  100  by preventing deformation of the top plate  141 . 
       FIG. 6  is a cross-sectional view of a cylindrical lithium ion secondary battery according to another embodiment of the present invention, and  FIG. 7  is a plan view illustrating a support plate of the cylindrical lithium ion secondary battery according to another embodiment of the present invention. 
     Referring to  FIGS. 6 and 7 , the cylindrical lithium ion secondary battery  200  according to another embodiment includes a cylindrical can  110 , an electrode assembly  120 , and a cap assembly  240 . Compared with the cap assembly  140  shown in  FIG. 5 , the cap assembly  240  is substantially the same as the cap assembly  140 , except for a configuration of a support plate  242 . Thus, the following description will focus on only the support plate  242 . 
     The support plate  242  may be positioned under the top plate  141  and may include a first region  242   a , a second region  242   b  and a third region  242   c . The first region  242   a  is formed in close contact with an upper region  141   d  located inside a bent region  141   g  of the top plate top plate  141 . In addition, a first through-hole  242   d  is formed roughly at the center of the first region  242   a . The second region  242   b  is positioned at an exterior side of the first region  242   a  and is positioned lower than the first region  242   a . Particularly, the second region  242   b  is disposed in close contact with the upper region  141   d  located outside the bent region  141   g  of the top plate  141 . Therefore, the second region  242   b  is surrounded by the upper region  141   d , a side region  141   e  and a lower region  141   f , which are located outside the bent region  141   g . Additionally, a groove  242   f  is formed on a top surface of the second region  242   b . As illustrated in  FIG. 7 , the groove  242   f  is formed on the top surface of the second region  242   b  in a ring shape and contacts the upper region  141   d  formed at an exterior side of the bent region  141   g  of the top plate  141 . The groove  242   f  may serve to decentralize the stress generated toward the center of the cap assembly  240  when an upper end of the cylindrical can  110  is clamped. 
     The groove  242   f  may be formed to have a depth of approximately 5% to approximately 20% of the thickness of the support plate  242 . If the depth of the groove  242   f  is smaller than 5% of the thickness of the support plate  242 , the stress generated toward the center of the cap assembly  240  when an upper end of the cylindrical can  110  is clamped, may not be sufficiently dispersed. In addition, if the depth of the groove  242   f  is greater than 20% of the thickness of the support plate  242 , the support plate  242  may be easily deformed by the stress generated toward the center of the cap assembly  240  when an upper end of the cylindrical can  110  is clamped. 
     Although the foregoing embodiments have been described to practice the cylindrical lithium ion secondary battery of the present invention, these embodiments are set forth for illustrative purposes and do not serve to limit the invention. Those skilled in the art will readily appreciate that many modifications and variations can be made, without departing from the spirit and scope of the invention as defined in the appended claims, and such modifications and variations are encompassed within the scope and spirit of the present invention.