Patent Publication Number: US-2022223953-A1

Title: Gasket for Cylindrical Batteries Configured to Prevent Corrosion of Battery Case and Cylindrical Battery Including the Same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2020/004670 filed Apr. 7, 2020, which claims the benefit of priority to Korean Patent Application No. 2019-0053969 filed on May 8, 2019, the disclosure of which is hereby incorporated by reference herein its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a gasket for cylindrical batteries configured to prevent corrosion of a battery case and a cylindrical battery including the same, and more particularly to a gasket for cylindrical batteries having a structure configured to wrap the upper part of a cylindrical battery case, from which an anticorrosive layer is removed, in order to prevent corrosion of the battery case and a cylindrical battery including the same. 
     BACKGROUND ART 
     There is an increasing trend of mobile devices including mobile phones, earphones and cleaners, most of which are wired products, being manufactured as wireless products. A lithium secondary battery having high energy density, high operating voltage, and excellent lifespan characteristics has been widely used as an energy source that is applied to wireless products. 
     Depending on the shape of a battery case, the lithium secondary battery is classified as a cylindrical secondary battery, configured such that an electrode assembly is mounted in a cylindrical metal can, a prismatic secondary battery, configured such that an electrode assembly is mounted in a prismatic metal can, or a pouch-shaped secondary battery, configured such that an electrode assembly is mounted in a pouch case made of an aluminum laminate sheet. Thereamong, the cylindrical secondary battery has advantages in that the cylindrical secondary battery has a relatively large capacity and is structurally stable. 
     In the cylindrical secondary battery, a steel plate made of an iron (Fe) material coated with nickel or the like is used as the battery case in order to prevent corrosion of the battery case, and a process of cutting a cylindrical battery case portion from the steel plate, which is the basic material, is performed after a forming process, such as deep drawing. 
     At this time, the cut surface of the battery case is a portion at which no nickel coating layer is formed, and therefore the section of the iron material is exposed. The cut surface is still exposed even after a crimping process, whereby the cut surface may rust or corrode. 
     Korean Patent Application Publication No. 2012-0047114, published on May 11, 2012 (“Patent Document 1”) relates to a secondary battery including a battery can configured to receive the electrode assembly without provision of a beading portion and a cap assembly coupled to an open end of the battery can. 
     In Patent Document 1, a cap cover having a structure configured to wrap the upper part of the edge of the cap assembly and the upper part of the battery can, wherein it is possible to prevent exposure of the battery case using the cap cover, but a structure in which the upper part of the battery case is deformed is used in order to fix the cap cover. In the case in which the upper part of the battery case is deformed, as described above, an additional process is required, and therefore a battery manufacturing process is complicated. 
     Korean Patent Application Publication No. 2018-0127938, published on Nov. 30, 2018 (“Patent Document 2”) relates to a cylindrical battery to which a vaporizable anticorrosive agent including a polymer resin and a sodium nitrate-based material and an anticorrosive gasket including a base resin are applied. 
     Patent Document 2 discloses a method in which a material in the anticorrosive gasket reacts with moisture to generate a nitrogen oxide, and the nitrogen oxide oxidizes the surface of a cylindrical can, whereby it is possible to prevent corrosion of a crimping portion even under high-temperature, high-humidity conditions. 
     Korean Patent Application Publication No. 1998-0030967, published on Jul. 25, 1998 (“Patent Document 3”) relates to a cylindrical battery including a gasket having a first part including an insertion recess, to which the end of a cylindrical case is fixed by insertion, and a second part extending from the first part to the interior of the case in order to support a cap assembly. 
     In Patent Document 3, the gasket having the insertion recess, into which the end of the battery case is inserted, is used; however, the gasket is applied to a cylindrical battery having no beading portion and no crimping portion formed thereat, and has a structure in which the distal end of the battery case is inserted into the first part before the crimping portion of the battery case is formed. 
     Therefore, there is a high necessity for a gasket for cylindrical secondary batteries having a crimping structure, wherein the gasket is configured to have a structure capable of preventing corrosion of a battery case even in the case in which nickel coating is removed from the distal end of the upper part of the battery case, thus forming an exposed portion. 
     DISCLOSURE 
     Technical Problem 
     The present invention has been made in view of the above problems, and it is an object of the present invention to provide a gasket for cylindrical batteries having a structure configured to wrap the distal end of a battery case, from which an anticorrosive coating is easily removed, in order to prevent corrosion of the battery case and a cylindrical battery including the same. 
     Technical Solution 
     In order to accomplish the above object, the present invention may provide a gasket for cylindrical batteries configured to have a doughnut shape, the gasket for cylindrical batteries including a supporting portion constituting the lower part of the gasket, the supporting portion being configured to support a cap assembly, and a crimping portion constituting the side part of the gasket, the crimping portion extending upwards from the outside of the supporting portion, wherein an extension portion is formed at the outside of the distal end of the crimping portion so as to extend downwards. 
     A protrusion structure may be formed at the upper surface of the supporting portion. 
     The outermost radius of the extension portion may be less than the inner radius of the crimping portion in the state in which the crimping portion is deformed in order to assemble a cylindrical battery. 
     The gasket for cylindrical batteries may further include a lower end portion formed at the inside of the supporting portion so as to extend downwards. 
     In addition, the present invention may provide a cylindrical battery including the gasket for cylindrical batteries, wherein the cylindrical battery includes a cylindrical battery case having an electrode assembly received therein, a cap assembly loaded in an open part of the cylindrical battery case, and the gasket for cylindrical batteries interposed between the cylindrical battery case and the cap assembly, and wherein the upper part of the cylindrical battery case wraps the outer circumference of the cap assembly and is bent toward the central part of the cylindrical battery case, and the distal end of the upper part of the cylindrical battery case is received in a reception portion defined by the extension portion of the gasket for cylindrical batteries. 
     The distance between the crimping portion and the distal end of the extension portion may be equal to or less than the thickness of the upper part of the battery case. 
     The reception portion may have a structure inclined downwards in the direction toward the center of the battery case in the state in which the cylindrical battery is coupled. 
     The extension portion may be formed in a shape in which the thickness of the extension portion gradually decreases from the proximal end of the extension portion to the distal end of the extension portion. 
     A non-coating portion, from which an anticorrosive layer is removed, may be formed on at least a portion of the upper part of the battery case, and the extension portion may have a structure configured to wrap the non-coating portion. 
     The cap assembly may include a top cap and a safety vent, a concave portion may be formed in the lower surface of the safety vent, and the concave portion may be located so as to engage with the protrusion structure formed at the upper surface of the supporting portion of the gasket for cylindrical batteries, whereby the safety vent and the gasket for cylindrical batteries may be coupled to each other. 
     The battery case may include a beading portion configured to support the cap assembly and the gasket for cylindrical batteries, and a lower end portion formed at an inside of the supporting portion of the gasket for cylindrical batteries so as to extend downwards may be located between the beading portion and the cap assembly. 
     The cap assembly may further include a current interrupt device coupled to the lower surface of the safety vent, and the lower end portion of the gasket may include a structure extending in the direction toward the center of the gasket so as to support the current interrupt device. 
     The present invention may provide a battery pack including the cylindrical battery. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is an upper sectional view of a cylindrical secondary battery including a gasket according to the present invention before being assembled. 
         FIG. 2  is a partial cutaway perspective view of the gasket according to the present invention. 
         FIG. 3  is an upper sectional view of the cylindrical secondary battery including the gasket according to the present invention after being assembled. 
         FIG. 4  is an enlarged sectional view of an extension portion of the gasket according to the present invention. 
     
    
    
     BEST MODE 
     Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings such that the present invention can be easily implemented by a person having ordinary skill in the art to which the present invention pertains. In describing the principle of operation of preferred embodiments of the present invention in detail, however, a detailed description of known functions and configurations incorporated herein will be omitted when the same may obscure the subject matter of the present invention. 
     In addition, the same reference numbers will be used throughout the drawings to refer to parts that perform similar functions or operations. In the case in which one part is said to be connected to another part in the specification, not only may the one part be directly connected to the other part, but also, the one part may be indirectly connected to the other part via a further part. In addition, that a certain element is included does not mean that other elements are excluded, but means that such elements may be further included unless mentioned otherwise. 
     In the present invention, the structure of a gasket, which is a sealing member of a cylindrical battery, is deformed in order to prevent corrosion of a battery case of the cylindrical battery. 
     In general, a steel plate having a nickel coating layer formed on the surface thereof is used in order to prevent corrosion of a cylindrical battery. The steel plate is deep drawn so as to be formed into the shape of a battery case, and the formed portion is cut from the steel plate in order to be used as a battery case. 
     At this time, the cut surface of the battery case is a portion at which no nickel coating layer is formed, and the cut surface may rust or corrode when exposed to the air. 
     Therefore, the present invention solves the above problem by applying a new structure to a gasket used as a sealing member of the cylindrical battery. That is, the structure is changed such that the gasket surrounds the distal end of the upper part of the battery case at which no nickel coating layer is formed. 
     In connection therewith,  FIG. 1  is an upper sectional view of a cylindrical secondary battery including a gasket according to the present invention before being assembled, and  FIG. 2  is a partial cutaway perspective view of the gasket according to the present invention. 
     Referring to  FIGS. 1 and 2 , a cap assembly  110  includes a top cap  101  having a protruding structure functioning as a positive electrode terminal, a safety vent  102  located at the lower part of the top cap  101  while wrapping the outer circumference of the top cap  101 , a current interrupt device  104  disposed so as to contact the lower surface of the safety vent  102 , and a CID gasket  103  configured to prevent contact between the current interrupt device  104  and the outer circumference of the safety vent  102 . 
     The gasket, which is used to provide insulation between the cap assembly  110  and a battery case and to seal the battery case, includes a supporting portion  121  configured to support the cap assembly and a crimping portion  122  extending upwards from the outside of the supporting portion  121 , and an extension portion  123  is formed at the outside of the distal end of the crimping portion  122  so as to extend downwards. 
     The gasket further includes a lower end portion  124  formed at the inside of the supporting portion  121  so as to extend downwards, and the lower end portion  124  includes a structure extending more in the direction toward the center thereof so as to support the current interrupt device  104  and the CID gasket  103  configured to provide insulation between the current interrupt device  104  and the safety vent  102 . 
     The safety vent  102  has a concave portion  105  formed in the lower surface thereof, and a protrusion structure  125  is formed at the upper surface of the supporting portion  121 . The protrusion structure  125  may be inserted into the concave portion  105 , whereby the cap assembly, including the safety vent, may be stably coupled to the gasket, and the cap assembly may be fixed in position via such coupling. 
     Although the protrusion structure  125  is shown as being a two-line ring-shaped structure, one or more protrusions spaced apart from each other may be continuously or non-continuously formed. 
     The extension portion  123  defines a reception portion  126  configured to receive the distal end of the battery case, and is formed in a shape in which the thickness of the extension portion  123  gradually decreases from a proximal end  123   a  of the extension portion to a distal end  123   b  of the extension portion, whereby the distal end  123   b  of the extension portion may more tightly contact the battery case in the state in which the battery case is received in the reception portion  126 . 
       FIG. 3  is an upper sectional view of the cylindrical secondary battery including the gasket according to the present invention after being assembled, and  FIG. 4  is an enlarged sectional view of the extension portion of the gasket according to the present invention. Referring to  FIGS. 3 and 4 , the state in which the gasket and the cap assembly  110  of  FIGS. 1 and 2  are received in a battery case  200  of the cylindrical battery of  FIG. 3  so as to be sealed is shown. 
     An upper part  201  of the battery case  200  is bent in the direction toward the central part of the battery case through a crimping process and thus is deformed into a structure configured to wrap the upper part of the gasket and the upper surface of the outer circumference of the cap assembly, and a distal end  202  of the upper part  201  of the deformed battery case  200  is received in the reception portion  126  of the gasket defined by the extension portion  123 . 
     The length of the extension portion  123  is not particularly restricted but is a length sufficient to wrap an uncoated portion  201   a , from which an anticorrosive layer is removed, formed at the upper part of the battery case. The uncoated portion  201   a , from which the anticorrosive layer is removed, is not formed at the distal end but is pushed from the upper part of the battery case toward an outer or inner lower end portion due to deformation of the metal during manufacture of the battery case. Conventionally, design is conducted based on an expectation that corrosion will be prevented due to contact between the distal end portion and the gasket, under the assumption that the uncoated portion is formed at the distal end portion. However, that is without the recognition that it is not possible to prevent continuous corrosion at the uncoated portion that has been pushed from the upper part of the case toward the outer or inner lower end portion. 
     Particularly, in the case in which a battery is exposed to the outside, it is very important to prevent corrosion of the battery caused by condensation of vapor due to a change in atmospheric temperature, contamination due to rain or snow, and the like. However, corrosion continuously occurs as the result of failure to recognize such a minute difference, and such a problem is still not solved. In contrast, the present invention is capable of solving this problem through recognition of the fact that the uncoated portion is displaced. 
     In consideration of the fact that the extension portion  123  is located at the outer surface of the upper part of the battery case, however, the extension portion may be formed so as to have a length that does not extend the full height of the crimping portion of the battery case, in order to prevent an increase in total length of the cylindrical battery. 
     Specifically, referring to  FIG. 4 , the outermost radius a 1  of the extension portion may be formed so as to be less than the inner radius a 2  of the crimping portion. 
     In addition, the thickness of the extension portion decreases in the direction toward the distal end thereof in order to prevent an increase in total length of the cylindrical battery due to addition of the extension portion. 
     When the gasket and the cap assembly  110  come into tight contact with each other in the state in which the crimping portion  122  and a beading portion  203  are formed, after the cap assembly  110  and the gasket are received in the battery case  200 , the protrusion structure  125  of the gasket is inserted into the concave portion  105  of the safety vent, whereby it is possible to provide a structure capable of achieving stable fixing therebetween. 
     The battery case  200  is formed to have the beading portion  203 , wherein the lower end portion  124  of the gasket is located between the beading portion  203  and the cap assembly  110  in order to prevent contact therebetween. 
     Preferably, the extension portion  123  is located at the outer surface of the battery case  200  so as to be in tight contact with the battery case  200 . The distance b 1  between the crimping portion  122  and the distal end of the extension portion  123  of the gasket may be equal to the thickness b 2  of the upper part of the battery case. 
     Alternatively, the gasket may be made of an elastic member, wherein the distance b 1  between the crimping portion  122  and the distal end of the extension portion  123  may be less than the thickness b 2  of the upper part of the battery case. When the upper part of the battery case  200  is inserted into the reception portion  126 , the reception portion  126  may be deformed so as to stretch such that the upper part of the battery case is seated therein. 
     Meanwhile, the reception portion  126  may have a structure inclined downwards in the direction toward the center of the battery case. Even in the case in which force returning the upper part of the battery case to the state before the upper part of the battery case is crimped is applied to the crimped upper part of the battery case due to a rollback phenomenon, therefore, it is possible to minimize exposure of the non-coating portion and, as an additional effect, to stably maintain sealing of the battery case. 
     In addition, the present invention may provide a battery pack configured such that cylindrical batteries, each of which has the above structure, are connected to each other in series and/or in parallel, and may provide a battery pack having high output, high capacity, and improved safety. 
     Those skilled in the art to which the present invention pertains will appreciate that various applications and modifications are possible based on the above description, without departing from the scope of the present invention. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
         
         
           
               101 : Top cap 
               102 : Safety vent 
               103 : CID gasket 
               104 : Current interrupt device 
               105 : Concave portion 
               110 : Cap assembly 
               121 : Supporting portion 
               122 : Crimping portion 
               123 : Extension portion 
               123   a : Proximal end of extension portion 
               123   b : Distal end of extension portion 
               124 : Lower end portion 
               125 : Protrusion structure 
               126 : Reception portion 
               200 : Battery case 
               201 : Upper part of battery case 
               201   a : Uncoated portion 
               202 : Distal end of upper part of battery case 
               203 : Beading portion 
             a 1 : Outermost radius of extension portion 
             a 2 : Inner radius of crimping portion 
             b 1 : Distance between crimping portion and distal end of extension portion 
             b 2 : Thickness of upper part of battery case 
           
         
       
    
     INDUSTRIAL APPLICABILITY 
     As is apparent from the above description, the present invention has a structure in which a reception portion configured to receive the distal end of the upper part of a battery case is formed in a crimping portion of a gasket, whereby it is possible to prevent corrosion of an exposed iron (Fe) portion, where a nickel (Ni) plating is ruptured, which inevitably occurs at the distal end of the upper part of the battery case during a manufacturing process of the battery case. 
     In addition, an extension portion of the gasket is formed so as to have a structure inclined downwards in the direction toward the center of the battery case, whereby it is possible to prevent the distal end of the upper part of the battery case from being separated from the reception portion of the gasket due to rollback of the crimping portion. 
     In addition, the length of the extension portion of the gasket is limited to a predetermined range, whereby it is possible to prevent an increase in total size of a cylindrical secondary battery even in the case in which the extension portion is formed.