Patent Publication Number: US-2022223987-A1

Title: Cylindrical Secondary Battery Including Positive Electrode Tab Fixing Member

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry under U.S.C. § 371 of International Application No. PCT/KR2020/008409 filed Jun. 26, 2020, which claims the benefit of priority to Korean Patent Application No. 2019-0077738 filed on Jun. 28, 2019, the disclosures of which are hereby incorporated by reference herein their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a cylindrical secondary battery including a positive electrode tab fixing member, and more particularly to a cylindrical secondary battery configured such that a current interrupt device is omitted from a cap assembly, a positive electrode tab is directly coupled to a venting member, and a fixing member configured to fix the positive electrode tab is included. 
     BACKGROUND ART 
     Based on the shape of a battery case, lithium secondary batteries are classified into a cylindrical secondary battery having an electrode assembly mounted in a cylindrical metal can, a prismatic secondary battery having an electrode assembly mounted in a prismatic metal can, and a pouch-shaped secondary battery having an electrode assembly mounted in a pouch-shaped case made of an aluminum laminate sheet. Among these batteries, the cylindrical secondary battery has advantages in that the capacity of the cylindrical secondary battery is relatively large and in that the cylindrical secondary battery is structurally stable. 
     The cylindrical secondary battery is configured such that a cap assembly is located at the upper end of a cylindrical case, which is open, and the cylindrical secondary battery is hermetically sealed in the state in which a gasket is interposed between the cylindrical case and the cap assembly. The gasket also has a function of securing insulation between the cap assembly, which is connected to a positive electrode tab of the electrode assembly, and the cylindrical case, which is connected to a negative electrode tab of the electrode assembly. 
       FIG. 1  is a vertical sectional view of a general cylindrical secondary battery. Referring to  FIG. 1 , the cylindrical secondary battery  100  is configured such that an electrode assembly  110  is received in a cylindrical can  120 , a cap assembly  130  is located at the upper part of the cylindrical can  120 , and the cylindrical secondary battery  100  is hermetically sealed by a crimping gasket  133 . 
     The cap assembly  130  includes a venting member  132  located at the lower part of a top cap  131  in the state of surrounding the outer circumference of the top cap and a current interrupt device  135  located under the venting member  132  in the state of being in contact with the central part of the venting member  132 . A lower gasket  134 , configured to prevent the venting member  132  and the current interrupt device  135  from contacting each other at parts other than the central part of the venting member, is located at the outer circumferential edge of the current interrupt device  135 . 
     A positive electrode tab  111  of the electrode assembly  110  is attached to the lower surface of the current interrupt device  135  such that the cap assembly  130  functions as a positive electrode terminal. 
     As described above, the cap assembly of the cylindrical secondary battery includes the top cap, the venting member, the crimping gasket, the current interrupt device, and the lower gasket, wherein pressure at which short circuit occurs in the secondary battery due to deformation of the current interrupt device is reduced. 
     Also, in the case in which the overall height of the cap assembly is reduced while the components of the cap assembly remain the same, the space in which the venting member is deformed is insufficient, whereby the venting member is gently deformed. As a result, it is difficult to specify the point in time when a short circuit occurs. Furthermore, a gas discharge path is narrowed, which acts as an obstacle to gas discharge. 
     In connection therewith, Korean Patent Application Publication No. 2018-0005455, published on Jan. 16, 2018 (“Patent Document 1”) relates to a cap assembly configured to have a structure in which a positive electrode tab of an electrode assembly and a safety vent are welded to each other; the welded portion between the safety vent and the positive electrode tab is broken when internal pressure increases due to generation of gas, whereby a short circuit occurs; and the positive electrode tab is fixed by a gasket. 
     In Patent Document 1, the positive electrode tab is fixed to the safety vent, whereby structural simplification is achieved. However, the positive electrode tab must be attached so as to cross the central part of the gasket such that the positive electrode tab is fixed by the gasket, and the gasket is used in a deformed shape. 
     Korean Patent Application Publication No. 2014-0082270, published on Jul. 2, 2014 (“Patent Document 2”) relates to a secondary battery configured such that an electrode tab electrically connects an electrode assembly and a cap assembly to each other, the electrode tab being provided with a notch and being attached to the lower part of a safety vent, wherein the notch is cut when current equal to or higher than a reference current flows. 
     Korean Patent Application Publication No. 2000-0026860, published on May 15, 2000 (“Patent Document 3”) relates to a secondary battery assembly configured such that a mesh-shaped metal grid having high electrical conductivity is located at the upper side of an electrode assembly, wherein the secondary battery assembly includes a positive electrode grid configured to contact a positive electrode and a conductive positive electrode current collection plate configured to support the positive electrode grid. The number of contact points between the electrode and a current collector increases, whereby contact resistance may be reduced. 
     Each of Patent Document 2 and Patent Document 3 is capable of providing a battery cell having improved safety but does not propose a method of increasing the capacity of the battery cell even when the structure of the battery cell is changed. 
     Therefore, there is a high necessity for a cylindrical secondary battery configured to have a structure in which a short circuit stably occurs while the overall height of a cap assembly is reduced, whereby the capacity of the battery is increased. 
     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 cylindrical secondary battery having a stable structure in which construction of a cap assembly is simplified, whereby the capacity of the battery is increased, and a venting member is easily separated from a positive electrode tab when internal pressure of the secondary battery increases due to gas generated in the secondary battery, whereby gas discharge is easily achieved. 
     Technical Solution 
     In order to accomplish the above object, a cylindrical secondary battery according to the present invention includes an electrode assembly, a cylindrical can configured to receive the electrode assembly, and a cap assembly mounted to an open upper end of the cylindrical can. The electrode assembly has a structure in which a positive electrode sheet and a negative electrode sheet are wound in a state in which a separator is interposed therebetween. The cap assembly includes a top cap located at the upper part thereof, the top cap having a protruding structure; a venting member located at the lower part of the top cap while surrounding the outer circumferential edge of the top cap, the venting member being concave downwards; and a gasket configured to hermetically seal the cylindrical can. A positive electrode tab of the electrode assembly is directly coupled to the lower surface of the venting member, and the cylindrical secondary battery further includes an insulative fixing member configured to fix the position of the positive electrode tab. 
     The positive electrode tab may include a positive electrode tab body and a coupling portion bent from one end of the positive electrode tab body, the coupling portion being coupled to the lower surface of the venting member, and the fixing member may be interposed between the positive electrode tab body and the coupling portion. 
     The fixing member may be adhered to the coupling portion at the surface of the fixing member that faces the coupling portion. 
     The force of coupling between the fixing member and the coupling portion may be higher than the force of coupling between the coupling portion and the venting member. 
     The fixing member may be located at the lower part of the gasket. 
     The fixing member may be coupled to the gasket by engagement therewith. 
     The fixing member may be formed in a fan shape or a bar shape when viewed in a plan view. 
     The fixing member may be integrally coupled to an upper insulation plate located between the electrode assembly and the cap assembly. 
     The fixing member may extend upwards from an outer circumferential part of the upper insulation plate, may be bent toward the central part of the upper insulation plate, and may be disposed parallel to the upper insulation plate. 
     The present invention provides a method of manufacturing a cylindrical secondary battery according to an embodiment, the method including receiving an electrode assembly in a cylindrical can, locating an upper insulation plate at the upper part of the electrode assembly, forming a beading portion, coupling a positive electrode tab of the electrode assembly to the lower surface of a venting member constituting a cap assembly, coupling a fixing member to a gasket constituting the cap assembly, and coupling the cap assembly to the cylindrical can and crimping the cylindrical can. The electrode structure has a structure in which a positive electrode sheet and a negative electrode sheet are wound in a state in which a separator is interposed therebetween. 
     The step of coupling the fixing member to the gasket may include coupling a coupling portion of the positive electrode tab and the fixing member to each other. 
     The present invention also provides a method of manufacturing a cylindrical secondary battery according to another embodiment, the method including receiving an electrode assembly in a cylindrical can, locating an upper insulation plate at the upper part of the electrode assembly, forming a beading portion, coupling a positive electrode tab of the electrode assembly to the lower surface of a venting member constituting a cap assembly, fixing the positive electrode tab to a fixing member integrally coupled to the upper insulation plate, and coupling the cap assembly to the cylindrical can and crimping the cylindrical can. The electrode structure has a structure in which a positive electrode sheet and a negative electrode sheet are wound in the state in which a separator is interposed therebetween. 
     The step of fixing the positive electrode tab may include extending the positive electrode tab over the lower surface of the fixing member, bending the positive electrode tab, and attaching the positive electrode tab to the upper surface of the fixing member. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a vertical sectional view of a conventional general cylindrical secondary battery. 
         FIG. 2  is a vertical sectional view of a cylindrical secondary battery according to an embodiment. 
         FIG. 3  is enlarged views of the upper parts of  FIGS. 1 and 2 . 
         FIG. 4  is a view showing a portion of a process of manufacturing the cylindrical secondary battery. 
         FIG. 5  is a view showing the state in which a fixing member is coupled to the cylindrical secondary battery of  FIG. 4 . 
         FIG. 6  is a perspective view of a fixing member according to an embodiment. 
         FIG. 7  is a perspective view of an upper insulation plate to which a fixing member according to an embodiment is coupled. 
     
    
    
     BEST MODE 
     Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings such that the preferred embodiments of 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 the 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. 
     Embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 2  is a vertical sectional view of a cylindrical secondary battery according to an embodiment. 
     Referring to  FIG. 2 , the cylindrical secondary battery  200  is configured such that an electrode assembly  210  is received in a cylindrical can  220 , a cap assembly  230  is located at the upper part of the cylindrical can  220 , and the cylindrical secondary battery  200  is hermetically sealed by a gasket  233 . 
     The cap assembly  230  includes a top cap  231  having an upwardly protruding central part, a venting member  232  located at the lower part of the top cap  231  in the state of wrapping the outer circumferential edge of the top cap  231 , the venting member  232  being concave downwards, and a gasket  233  configured to hermetically seal the secondary battery in the state of being in contact with the cylindrical can  220 . 
     That is, the cap assembly  230  according to the present invention does not include a current interrupt device and a gasket added to the outer circumferential edge of the current interrupt device, which are included in a cap assembly applied to a conventional cylindrical secondary battery. 
     In the cylindrical secondary battery  200  according to the present invention, therefore, a positive electrode tab  211  is directly coupled to the lower surface of the venting member  232 . 
     However, in the case in which the venting member is deformed in an inverted shape due to an increase in internal pressure of the cylindrical secondary battery, the venting member must be separated from the positive electrode tab such that a short circuit occurs. To this end, a fixing member  240  configured to fix the position of the positive electrode tab  211  is added. 
     Specifically, the lower end of the positive electrode tab is attached to the electrode assembly, and the upper end of the positive electrode tab is coupled to the lower surface of the venting member. The positive electrode tab may include a positive electrode tab body  211   a  and a coupling portion  211   b  coupled to the lower surface of the venting member. 
     The coupling portion  211   b  is a portion that is bent from the upper end of the positive electrode tab body  211   a  and then extends. The coupling portion  211   b  and the positive electrode tab body  211   a  are located so as to face each other, and the fixing member  240  is located between the coupling portion  211   b  and the positive electrode tab body  211   a . When the venting member  232  is separated from the positive electrode tab, therefore, the positive electrode tab is fixed in position such that the positive electrode tab does not move. 
     Separation of the positive electrode tab body  211   a  may be prevented by the fixing member  240 . In order to prevent the coupling portion  211   b , which is coupled to the venting member  232 , from moving upwards together with the venting member  232 , however, the fixing member  240  and the coupling portion  211   b  may be adhered to each other at the surfaces thereof that face each other. 
     That is, the upper surface of the coupling portion  211   b  is coupled to the venting member  232 , and the lower surface of the coupling portion  211   b  is coupled to the fixing member  240 . When the venting member  232  is deformed and separated from the coupling portion  211   b , however, coupling between the coupling portion  211   b  and the fixing member  240  must be maintained. Therefore, it is preferable that the force of coupling between the coupling portion  211   b  and the fixing member  240  be higher than the force of coupling between the coupling portion  211   b  and the venting member  232 . 
     Since some of the members constituting the conventional cap assembly are omitted, as described above, the overall height of the cap assembly is reduced. When comparing the capacities of battery cells in cylindrical secondary batteries having the same length, therefore, the cylindrical secondary battery according to the present invention is capable of achieving a large electrode assembly reception space, whereby it is possible to provide a high-capacity secondary battery. 
     In connection therewith,  FIG. 3  is enlarged views of the upper parts of  FIGS. 1 and 2 . 
     Referring to  FIG. 3 , the upper part of the cylindrical secondary battery  100  of  FIG. 1  and the upper part of the cylindrical secondary battery  200  of  FIG. 2  are shown side by side, from which it is possible to compare the components of the cap assemblies and the overall heights of the cap assemblies and to confirm a change in size of a space in which the venting member is deformed. 
     Specifically, the cylindrical secondary battery  200  according to the present invention has a structure in which the lower gasket  134  and the current interrupt device  135  are omitted from the conventional cylindrical secondary battery  100 . 
     In addition, the distance between the top cap  231  and the venting member  232  of the cylindrical secondary battery  200  according to the present invention is greater than the distance between the top cap  131  and the venting member  132  of the conventional cylindrical secondary battery  100 . 
     Conventionally, the overall height of the cap assembly is reduced in order to increase the capacity of the battery cell, whereby the distance between the top cap and the venting member is designed to be short. As a result, the venting member is gently deformed, even though a short circuit due to abrupt deformation of the venting member is needed when the internal pressure of the battery cell increases, whereby it is difficult to specify the point in time when short circuit occurs. 
     In the present invention, the distance between the top cap and the venting member is designed to increase, as shown in  FIG. 3 , whereby it is possible to solve the above problem. 
     Also, in the cylindrical secondary battery  200  according to the present invention, the overall height of the cap assembly is reduced compared to the conventional cylindrical secondary battery  100 , whereby it is possible to achieve the object of the present invention for manufacturing a high-capacity secondary battery. 
     A method of manufacturing the cylindrical secondary battery  200  according to the present invention may include a step of receiving an electrode assembly in a cylindrical can, the electrode assembly having a structure in which a positive electrode sheet and a negative electrode sheet are wound in the state in which a separator is interposed therebetween; a step of locating an upper insulation plate at the upper part of the electrode assembly; a step of forming a beading portion; a step of coupling a positive electrode tab of the electrode assembly to the lower surface of a venting member constituting a cap assembly; a step of coupling a fixing member to a gasket constituting the cap assembly; and a step of coupling the cap assembly to the cylindrical can and crimping the cylindrical can. 
     In addition, the step of coupling the fixing member to the gasket may include a step of coupling a coupling portion of the positive electrode tab and the fixing member to each other. 
     In connection therewith,  FIG. 4  is a view showing a portion of a process of manufacturing the cylindrical secondary battery, and  FIG. 5  is a view showing the state in which the fixing member is coupled to the cylindrical secondary battery of  FIG. 4 . 
     Referring to  FIGS. 4 and 5 , the electrode assembly  210  is received in the cylindrical can  220 , an upper insulation plate  250  is located at the upper part of the electrode assembly, and a beading portion  260  is formed at the upper part of the upper insulation plate  250 . 
     The positive electrode tab  211  attached to the electrode assembly  210  is attached to the lower surface of the venting member  232  in the state in which the cap assembly  230  is assembled. One surface of the positive electrode tab  211  is coupled to the venting member  232 , and the other surface of the positive electrode tab  211  is coupled to the fixing member  240 . The cap assembly  230  is coupled to the upper part of the cylindrical can  220  in the state of being coupled with the positive electrode tab  211  and the fixing member  240 , and the cylindrical can  220  is crimped. 
     The fixing member  240  may be located at the lower part of the gasket  233 , and one end of the fixing member  240  overlapping the gasket  233  may be coupled to the gasket  233  by engagement therewith. 
     In a concrete example, the fixing member  240  may be formed in a fan shape or a bar shape when viewed in a plan view. 
     In connection therewith,  FIG. 6  is a perspective view of a fixing member according to an embodiment. 
     Referring to  FIG. 6 , a fixing member  241  is formed in a bar shape when viewed in a plan view, and includes a rectangular base portion  241   a  configured to fix the positive electrode tab and an engagement portion  241   b  configured to be coupled to the gasket by engagement therewith. In the case in which such a small fixing member  241  is used, it is possible to minimize an increase in weight of the cylindrical secondary battery due to addition of the fixing member. 
     Meanwhile, a fixing member  242  is formed in a fan shape, such as a semicircular shape, when viewed in a plan view, and includes a semicircular base portion  242   a  configured to fix the positive electrode tab and an engagement portion  242   b  configured to be coupled to the gasket by engagement therewith. In the case in which a fixing member including a large base portion, such as the fixing member  242 , is used, there is little limitation in setting the position of the fixing member based on the extension position of the positive electrode tab, and even in the case in which a plurality of positive electrode tabs is included, it is possible to stably fix the positive electrode tabs. 
     Additionally, a shape in which the fixing member is integrally added to the conventional battery cell components may be further proposed. For example, the fixing member may be integrally coupled to an upper insulation plate located between the electrode assembly and the cap assembly. Specifically, the fixing member may extend upwards from the outer circumferential part of the upper insulation plate, may be bent toward the central part of the upper insulation plate, and may be disposed parallel to the upper insulation plate. 
     In connection therewith,  FIG. 7  is a perspective view of an upper insulation plate to which a fixing member according to an embodiment is coupled. 
     Referring to  FIG. 7 , a fixing member  243  integrally coupled to an upper insulation plate  251  is added to the outer circumferential part of the upper surface of the upper insulation plate  251 . The fixing member  243  extends perpendicularly upwards from the plane of the upper insulation plate  251 , is bent 90 degrees, and is located so as to be parallel to the upper insulation plate. 
     The upper insulation plate  251  is provided with a plurality of through-holes, through one of which the positive electrode tab  211  attached to the electrode assembly extends. After extending through one of the through-holes, the positive electrode tab  211  extends over the overlapping portion between the fixing member  243  and the upper insulation plate  251 , is bent 180 degrees, and is coupled to the upper surface of the fixing member  243 . 
     However, the positive electrode tab  211  may be located between the fixing member and the upper insulation plate in the state of being coupled to the lower surface of the venting member. A method of manufacturing a cylindrical secondary battery in the case in which the fixing member  243  is used may include a step of receiving an electrode assembly in a cylindrical can, the electrode assembly having a structure in which a positive electrode sheet and a negative electrode sheet are wound in the state in which a separator is interposed therebetween; a step of locating an upper insulation plate at the upper part of the electrode assembly; a step of forming a beading portion; a step of coupling a positive electrode tab of the electrode assembly to the lower surface of a venting member constituting a cap assembly; a step of fixing the positive electrode tab to a fixing member integrally coupled to the upper insulation plate; and a step of coupling the cap assembly to the cylindrical can and crimping the cylindrical can. 
     In the present invention, as described above, the fixing member is included such that the positive electrode tab is completely separated from the venting member when the venting member is deformed, whereby a short circuit occurs; a larger space in which the venting member can be deformed is achieved, such that the short circuit can stably occur; and the overall height of the cap assembly is reduced, whereby it is possible to provide a high-capacity secondary battery. 
     A person having ordinary skill 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 
     
         
         
           
               100 ,  200 : Cylindrical secondary batteries 
               110 ,  210 : Electrode assemblies 
               111 ,  211 : Positive electrode tabs 
               120 ,  220 : Cylindrical cans 
               130 ,  230 : Cap assemblies 
               131 ,  231 : Top caps 
               132 ,  232 : Venting members 
               133 : Crimping gasket 
               134 : Lower gasket 
               135 : Current interrupt device 
               211   a : Positive electrode tab body 
               211   b : Coupling portion 
               233 : Gasket 
               240 ,  241 ,  242 ,  243 : Fixing members 
               241   a ,  242   a : Base portions 
               241   b ,  242   b : Engagement portions 
               250 ,  251 : Upper insulation plates 
               260 : Beading portion 
           
         
       
    
     INDUSTRIAL APPLICABILITY 
     As is apparent from the above description, a cylindrical secondary battery according to the present invention includes a cap assembly, from which a current interrupt device and a gasket added to the outer circumferential edge of the current interrupt device are omitted, wherein the overall height of the cap assembly is reduced, whereby a larger space occupied by an electrode assembly is achieved, and therefore it is possible to provide a secondary battery having increased capacity. 
     In addition, it is possible to stably fix a positive electrode tab attached to a venting member using a fixing member, whereby the venting member is separated from the fixed positive electrode tab when the venting member is deformed due to an increase in internal pressure of the secondary battery, and therefore it is possible to interrupt the flow of current.