Patent Publication Number: US-2023140192-A1

Title: Welding Apparatus Including Electrode Tab Fixing Portion and Electrode Tab Welding Method Using the Same

Description:
TECHNICAL FIELD 
     This application claims the benefit of priority to Korean Patent Application No. 2020-0136428 filed on Oct. 21, 2020, the disclosure of which is incorporated herein by reference in its entirety. 
     The present invention relates to a welding apparatus including an electrode tab fixing portion and an electrode tab welding method using the same, and more particularly to a welding apparatus including a tab guide configured to gather electrode tabs and an electrode tab fixing portion configured to prevent damage to the electrode tabs when the electrode tabs are gathered by the tab guide and an electrode tab welding method using the same. 
     BACKGROUND ART 
     With recent diversification of devices that use batteries, demand for high-capacity and high-density batteries has increased. Thereamong, a lithium secondary battery, which has high energy density and discharge voltage, has been commercialized and used in various forms. 
     As an example, secondary batteries are classified into a cylindrical secondary battery, a prismatic secondary battery, and a pouch-shaped secondary battery depending on the shape thereof. In addition, a secondary battery may have a structure in which an electrode assembly is received in any one of various cases. 
     The electrode assembly may be a jelly-roll type assembly, which is configured to have a structure in which a long sheet type positive electrode and a long sheet type negative electrode are wound in the state in which a separator is interposed therebetween, a stacked type assembly which is configured to have a structure in which a rectangular positive electrode and a rectangular negative electrode are stacked in the state in which a separator is interposed therebetween, a stacked and folded type assembly, which is configured to have a structure in which unit cells are wound using a long separation film, or a laminated and stacked type assembly, which is configured to have a structure in which unit cells are stacked and attached to each other in the state in which a separator is interposed therebetween. 
     Thereamong, an electrode assembly configured to have a structure in which one or more positive electrodes and one or more negative electrodes are stacked, such as a stacked type assembly, a stacked and folded type assembly, or a laminated and stacked type assembly, is preferred for reasons that the capacity of the electrode assembly compared to the density thereof is increased, the electrode assembly is easily manufactured, and the shape of the electrode assembly is easily changed. 
     In the stacked type electrode assembly, electrode tabs protruding from the electrode assembly are gathered and welded to an electrode lead, which is electrically connected to the outside. 
       FIG.  1    is a schematic view of a stacked type electrode assembly before being pressed by a conventional welding apparatus, and  FIG.  2    is a schematic view of the stacked type electrode assembly after being pressed by the conventional welding apparatus. 
     As can be seen from  FIGS.  1  and  2   , the conventional welding apparatus welds an electrode assembly  10  and a plurality of electrode tabs  11  protruding from the electrode assembly  10 . The electrode assembly  10  may be any one of a stacked type assembly, a stacked and folded type assembly, and a laminated and stacked type assembly. The electrode tabs  11  are gathered by a tab guide  20  to form a tab bundle  12 , and the tab bundle is pressed and welded through a welding jig  30  constituted by a horn  31  and an anvil  32 . 
     The horn  31  and the anvil  32  apply high-frequency vibration generated by an ultrasonic wave having a high frequency of about 20 kHz, and vibration energy is converted into thermal energy between the electrode tabs  11  and an electrode lead, whereby rapid welding is performed therebetween. 
     However, ultrasonic welding using vibration energy may shock the electrode assembly  10 , the electrode tabs  11 , and the electrode lead, and cutting of the electrode tabs  11  or between the electrode tabs  11  and the electrode lead may be caused. In order to prevent this, the conventional welding apparatus secures a relatively long length of the electrode tabs  11  through the tab guide  20 . 
     The tab guide  20  may be constituted by at least two tab guides, such as an upper tab guide  21  and a lower tab guide  22 , and the length of the electrode tabs  11  may be secured using one tab guide  20 . 
     When the electrode tabs  11  are gathered while being pressed by the tab guide  20 , however, the electrode tabs  11  may be damaged, or the electrode tabs  11  may be cut at the portion of the electrode tabs at which the electrode tabs are gathered by the tab guide  20 . In particular, when the electrode tabs  11  are pressed at a steep angle, a danger of the electrode tabs  11  being cut is further increased. 
     In Patent Document 1, an electrode tab is pressed such that the shape of the electrode tab is changed, as mentioned above; however, this document does not recognize problems of damage to or cutting of the electrode tab. 
     In Patent Document 2, a connection portion between an electrode tab and an electrode lead is formed, and the position of a jig is adjusted when the connection portion is formed so as to have a V shape; however, it is not possible to prevent the electrode tab from being cut. 
     Therefore, a construction for preventing an electrode tab from being cut when the electrode tab is welded is needed. 
     PRIOR ART DOCUMENTS 
     (Patent Document 1) Korean Patent Application Publication No. 2003-0066172 (Aug. 9, 2003) 
     (Patent Document 2) Korean Patent Application Publication No. 2016-0007109 (Jan. 20, 2016) 
     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 welding apparatus configured to prevent electrode tabs from being cut when the electrode tab is welded and an electrode tab welding method using the same. 
     It is another object of the present invention to maintain uniform distance between the welded electrode tabs in order to prevent damage to the electrode tabs. 
     It is a further object of the present invention to secure an additional length for outer electrode tabs in order to prevent damage to the electrode tabs due to internal force and external force. 
     Technical Solution 
     In order to accomplish the above objects, a welding apparatus according to the present invention includes a tab guide configured to gather a plurality of electrode tabs protruding from an electrode assembly in order to form a tab bundle, a welding jig configured to weld the tab bundle, and an electrode tab fixing portion disposed between the electrode assembly and the tab guide, the electrode tab fixing portion being configured to maintain a space between the electrode tabs. 
     The electrode tab fixing portion may include a left fixing portion disposed between the electrode tabs at a left side of the electrode tabs and a right fixing portion disposed between the electrode tabs at a right side of the electrode tabs. 
     The left fixing portion and the right fixing portion may be inserted between the electrode tabs so as to be opposite each other at opposite sides thereof. 
     The electrode tab fixing portion may include insertion portions configured to be inserted between the electrode tabs and a body portion configured to allow the insertion portions to be disposed spaced apart from each other therein. 
     The insertion portions may be inserted between the electrode tabs in parallel to the electrode tabs. 
     The insertion portions may be inserted between the electrode tabs in a fitting manner. 
     The electrode tab fixing portion may be disposed closer to the tab guide than the electrode assembly. 
     The tab guide may include an upper tab guide configured to gather the electrode tabs above the electrode tabs and a lower tab guide configured to gather the electrode tabs under the electrode tabs. 
     The upper tab guide and the lower tab guide may press the electrode tabs in a state of partially facing each other in parallel to form the tab bundle. 
     The portion of the tab guide that faces the electrode tabs may be curved. 
     The electrode tab facing portion of the tab guide may have an inclined curve structure configured such that the portion of the tab guide farthest from the electrode assembly further protrudes to bend the electrode tabs. 
     The welding jig may perform welding using ultrasonic waves. 
     The welding jig may be constituted by a horn and an anvil. 
     The welding jig may weld the portion of the tab bundle farthest from the electrode assembly. 
     In addition, the present invention provides an electrode tab welding method including (a) disposing an electrode tab fixing portion between electrode tabs of an electrode assembly configured to have a structure in which pluralities of positive electrodes, separators, and negative electrodes are stacked, (b) gathering the electrode tabs fixed by the electrode tab fixing portion through a tab guide to form a tab bundle, and (c) welding the tab bundle. 
     The electrode tab welding method may further include fixing the electrode assembly before step (a). 
     In step (b), the tab guide may be disposed farther away from the electrode assembly than the electrode tab fixing portion. 
     In the present invention, one or more constructions that do not conflict with each other may be selected and combined from among the above constructions. 
     Advantageous Effects 
     In the present invention, the length of electrode tabs is maximally set through a tab guide between the electrode tabs when the electrode tabs are welded, whereby force applied to the electrode tabs when the electrode tabs are bent is minimized, and therefore damage to the electrode tabs and an electrode assembly is prevented when the electrode tabs are pressed. 
     In addition, a process of forming a tab bundle when the electrode tabs are welded is easily performed. 
     Furthermore, the electrode tabs are gently pressed through the tab guide, whereby electrode tabs having a desired shape are obtained. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic view of a stacked type electrode assembly before being pressed by a conventional welding apparatus. 
         FIG.  2    is a schematic view of the stacked type electrode assembly after being pressed by the conventional welding apparatus. 
         FIG.  3    is a schematic view of a stacked type electrode assembly before being pressed by a welding apparatus according to the present invention. 
         FIG.  4    is a schematic view of the stacked type electrode assembly after being pressed by the welding apparatus according to the present invention. 
         FIG.  5    is a perspective view of an electrode tab fixing portion according to the present invention. 
     
    
    
     BEST MODE 
     In the present application, it should be understood that the terms “comprises,” “has,” “includes,” etc. specify the presence of stated features, numbers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof. 
     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. 
     Hereinafter, a welding apparatus according to the present invention and an electrode tab welding method using the same will be described in detail with reference to the accompanying drawings. 
       FIG.  3    is a schematic view of a stacked type electrode assembly before being pressed by a welding apparatus according to the present invention, and  FIG.  4    is a schematic view of the stacked type electrode assembly after being pressed by the welding apparatus according to the present invention. 
     As can be seen from  FIGS.  3  and  4   , the welding apparatus according to the present invention includes a tab guide  200  configured to gather a plurality of electrode tabs  110  protruding from an electrode assembly  100  in order to form a tab bundle  120 , a welding jig  300  configured to weld the tab bundle  120 , and an electrode tab fixing portion  400  disposed between the electrode assembly  100  and the tab guide  200 , the electrode tab fixing portion being configured to maintain the distance between the electrode tabs  110 . 
     The electrode assembly  100  may have a structure in which a positive electrode, a separator, and a negative electrode are stacked. The separator is located between the positive electrode and the negative electrode to electrically isolate the positive electrode and the negative electrode from each other. 
     The electrode assembly  100  may be a stacked type assembly including unit cells, each of which is configured to have a structure in which a rectangular positive electrode and a rectangular negative electrode are stacked in the state in which a separator is interposed therebetween, a stacked and folded type assembly, which is configured to have a structure in which unit cells are wound using a long separation film, or a laminated and stacked type assembly, which is configured to have a structure in which unit cells are stacked in the state in which a separator is interposed therebetween and are then attached to each other. 
     The electrode tab  110  may extend in a direction parallel to electrode plates of the electrode assembly  100 . Electrode tabs  110  having the same polarity extend in the same direction as the electrode assembly  100 . At this time, a positive electrode tab and a negative electrode tab may extend in the same direction as the electrode assembly  100 , or may extend in different directions. 
     The electrode tab  110  may be made of a material that has high conductivity, such as aluminum, copper, or carbon nanotubes. In addition, all materials suitable for the electrode tab  110  may be generally used. 
     The electrode tab  110  is pressed in a predetermined direction by the tab guide  200 . As an example, the tab guide  200  may bend one or more electrode tabs  110  at an inclination of 5 to 40 degrees to form the tab bundle  120 . If the inclination of the electrode tab  110  is too small, a sufficient length may not be secured in order to bend the electrode tab  110  and to prevent breakage of the electrode tab  110 . If the inclination of the electrode tab  110  is too large, the space occupied by the electrode tab  110  may be large, whereby the shape and capacity of a battery may be adversely affected, and some of the electrode tabs  110  may overlap each other and thus may be cut due to movement of the battery. 
     The thickness w of the tab bundle  120  may be generally 0.1 mm to 1.5 mm, although the thickness of the tab bundle may be changed depending on the electrode assembly  100 . 
     The tab bundle  120  may be connected to an electrode lead by welding, or may be directly connected to an external device. The tab bundle  120  may be connected to one side of the electrode lead or opposite sides of the electrode lead by joining. A welding tape may be adhered to one surface of the electrode tab  110 , whereby joining with the electrode lead or the external device may be easily performed. 
     The welding tape is a double-sided tape having an adhesive material applied to opposite surfaces thereof. As an example, the welding tape may have a structure in which an adhesive is applied to opposite surfaces of a cast polypropylene (CPP) film. An acrylic-based adhesive, a silicone-based adhesive, or hot melt may be used as the adhesive. 
     In order to easily connect the tab bundle  120  to the electrode lead or the external device, the tab bundle  120  may be joined by a welding jig  300  after the tab bundle  120  is formed by the tab guide  200 . Joining may be performed by welding or using ultrasonic waves. 
     As an example, when joining is performed using ultrasonic waves, high-frequency vibration generated by ultrasonic waves having a high frequency of about 20 kHz may be applied, and a horn  310  and an anvil  320  may be operated above and under the tab bundle  120 , whereby vibration energy may be converted into thermal energy through friction, and therefore rapid welding may be performed. 
     In the state in which the electrode assembly  100 , the tab guide  200 , and the welding jig  300  are disposed in that order, the welding jig  300  may weld a joint d farthest from the electrode assembly  100 , which is a portion of the total length c+d of the tab bundle  120 , in which the electrode tabs  110  are gathered, from which a non-joint c is excluded. That is, the portion excluding the non-joint c, which is a small thickness portion of the tab bundle  120 , in which the electrode tabs  110  are gathered, i.e. the portion of the tab bundle in which the electrode tabs  110  are not cut even when the electrode tabs are gathered and pressed. It is preferable for the minimum welding length of the tab bundle  120  that is connected to the electrode lead or the external device to be 2 mm or more. 
     This may be a point corresponding to ⅕ to ⅓ of the total length of the tab bundle  120  based on the portion close to the electrode assembly, which, however, may be changed depending on the thickness of the electrode assembly and the length of the tab bundle  120 . 
     The corner of the tab guide  200  that faces the electrode tab  110  may be curved in order to prevent damage to the electrode tab  110 . The radius of curvature r of the tab guide  200  may be 0.5 mm to 2 mm in order to accurately change the position of the electrode tab  110  at a desired portion while preventing damage to the electrode tab  110 . If the radius of curvature r is less than the above range, the electrode tab  110  may be damaged due to the tab guide  200 . If the radius of curvature r is greater than the above range, the tab guide  200  may not bend the electrode tab  110  at a desired portion into a desired shape. 
     The portion of the tab guide  200  that faces the electrode tab  110  may be configured such that the part thereof farthest from the electrode assembly  100  further protrudes to bend the electrode tab  110 . The part of the tab guide  200  farthest from the electrode assembly  100  is formed so as to further protrude, whereby the electrode tabs  110  may be naturally bent into a single tab bundle  120 . In order to naturally form the tab bundle  120 , it is preferable for the electrode tab facing portion of the tab guide  200  to have an inclined curve structure configured such that the portion of the tab guide farthest from the electrode assembly further protrudes to bend the electrode tab, as shown in  FIGS.  3  and  4   . 
     In addition, although the electrode tab  110  may be bent using only one tab guide  200 , a pair of an upper tab guide  210  and a lower tab guide  220  or a plurality of tab guides  200  may be provided in order to bend the electrode tab  110  at a desired position to a desired extent. 
     In the case in which the pair of the upper tab guide  210  and the lower tab guide  220  or the plurality of tab guides  200  is provided, the upper tab guide  210  may bend the electrode tab  110  further downwards while the lower tab guide  220  may bend the electrode tab  110  further upwards based on a middle portion of the electrode tab  110 , i.e. a position at which the tab bundle  120  is formed. That is, in the figure, the upper tab guide  210  and the lower tab guide  220  may press the electrode tab  110  in a state of partially facing each other in parallel. 
     As a result, a free space is formed between the electrode tabs  110 , whereby it is possible to prevent the electrode tabs  110  from being cut by external impact or movement of the electrode assembly  110 . 
     The thickness of the tab guide  210  may be 1 mm to 2 mm in consideration of the length of the electrode tab  110 . However, the thickness of the tab guide  210  may be changed depending on the thickness of the electrode tab  110  and the size of the electrode assembly  100 . 
     The electrode tab fixing portion  400  may be disposed between the electrode assembly  100  and the tab guide  210  in order to maintain a separation space between one electrode tab  110  and another electrode tab  110 . When only the tab guide  200  is simply provided, the distance between the welding jig  300  and the electrode assembly  100  must be increased, and the distance between the electrode assembly and the tab guide  200  must also be maintained uniform, in order to gently form a bending angle. In the case in which the electrode tab fixing portion  400  is provided, however, it is possible to reduce the distance between the electrode assembly  100  and the tab guide  200 . 
       FIG.  5    is a perspective view of an electrode tab fixing portion according to the present invention. 
     As shown in  FIG.  5   , the electrode tab fixing portion  400  may include a left fixing portion disposed between the electrode tabs  110  at the left side of the electrode tabs  110  and a right fixing portion disposed between the electrode tabs  110  at the right side of the electrode tabs  110 . In the case in which a pair of electrode tab fixing portions  400  is provided, as described above, it is possible to easily insert the electrode tab fixing portions  400  between the electrode tabs  110 . That is, the pair of electrode tab fixing portions  400  may be inserted between the electrode tabs  110  so as to be opposite each other at opposite sides thereof, whereby the separation space may be formed between the electrode tabs  110 . 
     The electrode tab fixing portion  400  may include insertion portions  410  configured to be inserted between the electrode tabs  110  and a body portion  420  in which the insertion portions  410  are disposed spaced apart from each other. 
     The insertion portions  410  may be inserted between the electrode tabs  110  in parallel to the electrode tabs  110 . At this time, the insertion portions  410  may be inserted between the electrode tabs  110  in a fitting manner. The insertion portion  410  may be configured to have a structure in which the thickness of a region  400 ( a ) close to the electrode assembly  100  is greater than the thickness of a region  400 ( b ) close to the tab guide  200  in order to guide the electrode tabs  110  in a predetermined direction. 
     The insertion portion  410  may be made of an electrically insulative material in order to prevent deterioration in performance of the electrode assembly  100 . The electrically insulative material is not limited as long as the electrically insulative material is not curved or deformed when the electrode tab  110  is bent by the tab guide  200 . As an example, the insertion portion  410  may be made of plastic or a polymer composite resin having insulation properties, such as rubber having predetermined rigidity, polyimide (PI), polysulfone (PSF), poly phenylene sulfide (PPS), polyamide imide (PAI), polyacrylate (PAR), polyether sulfone (PES), polyether ether ketone (PEEK), polyether imide (PEI), liquid crystal polyester (LCP), or polyether ketone (PEK), plastic or a polymer composite resin having insulation properties, such as polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), or polyvinyl chloride (PVC), or a fiber-reinforced polymer composite resin having glass or aramid fiber inserted thereinto in order to improve elasticity. 
     In addition, a portion of the electrode tab fixing portion  400  may be made of an elastic material. When the electrode tab fixing portion  400  is made of an elastic material, it is possible to prevent damage to the electrode tab  110 . The elastic material may be disposed at only the portion that faces the electrode tab  110  or the portion at which the electrode tab  110  is bent. 
     The electrode tab fixing portion  400  may be disposed in the order of electrode assembly  100 , the electrode tab fixing portion  400 , and the tab guide  200 . The electrode tab fixing portion  400  may be disposed at a distance of 0 mm to 2.0 mm from the end of the separator of the electrode assembly  100 , and the tab guide  200  may be disposed at a distance of 0 mm to 2.0 mm from the electrode tab fixing portion  400 . At this time, the electrode tab fixing portion  400  may be disposed such that the distance b from the tab guide  200  is less than the distance a from the electrode assembly  100 , whereby the electrode tab  110  may be easily bent by the tab guide  200 . 
     In addition, the electrode tab fixing portion  400  may be disposed between the tab guides  200  such that the electrode tab  110  is naturally shaped by the tab guide  200 . As an example, in the case in which the upper tab guide  210  and the lower tab guide  220  do not bend the electrode tab at the position at which the upper tab guide and the lower tab guide are opposite each other, the tab guide  200  may be disposed such that the electrode tabs  110  are naturally shaped between the tab guides  200 . 
     In addition, when the distance a+b+c from the electrode assembly to the joint is limited, the electrode tab  110  may be configured such that the outer tab length of the electrode tab is increased, whereby it is possible to reduce damage to the electrode tab  110  due to deformation of the tab bundle  120  in a horizontal direction and deformation of the electrode assembly  100  in a thickness direction. 
     In order to fix the electrode assembly  100  when the electrode tab  110  is bent by the tab guide  200 , a plate configured to fix the lower part of the electrode assembly and a pusher configured to hold the electrode assembly at the upper part of the electrode assembly may be provided. At this time, both the plate and the pusher may push the electrode assembly, or only one of the plate and the pusher may push the electrode assembly. In addition, the plate and/or the pusher may have fixing portions in X-axis and Y-axis directions in order to prevent movement of the electrode assembly. 
     An electrode tab welding method according to the present invention may include (a) a step of disposing an electrode tab fixing portion between electrode tabs of an electrode assembly configured to have a structure in which pluralities of positive electrodes, separators, and negative electrodes are stacked, (b) a step of gathering the electrode tabs fixed by the electrode tab fixing portion through a tab guide to form a tab bundle, and (c) a step of welding the tab bundle. 
     In the case in which the electrode tab fixing portion is disposed between the electrode tabs, as described above, the distance between the tab guide and the electrode assembly may be further reduced, and when the electrode tab is bent by the tab guide, the electrode tab may be more naturally shaped. 
     In addition, the tab bundle is welded after the electrode tabs are fixed by the tab guide, whereby a possibility of the electrode tab being cut or deformed is reduced, and therefore it is possible to prevent damage to the electrode tab. 
     The electrode tab welding method according to the present invention may further include a step of fixing the electrode assembly before step (a). This step is performed in order to prevent the electrode tab from not being formed into a desired shape or being cut due to movement of the electrode assembly. Additionally, when the electrode tab of the electrode assembly is bent by the tab guide, it is possible to prevent force necessary to bend the electrode tab from being reduced due to movement of the electrode assembly. 
     In step (b), the tab guide may be disposed farther away from the electrode assembly than the electrode tab fixing portion. As the result of this disposition, it is possible to prevent damage to the electrode tab due to abrupt force while pressing the electrode tab so as to have a desired shape. 
     Although the specific details of the present invention have been described in detail, those skilled in the art will appreciate that the detailed description thereof discloses only preferred embodiments of the present invention and thus does not limit the scope of the present invention. Accordingly, those skilled in the art will appreciate that various changes and modifications are possible, without departing from the category and technical idea of the present invention, and it will be obvious that such changes and modifications fall within the scope of the appended claims. 
     DESCRIPTION OF REFERENCE SYMBOLS 
       10 ,  100 : Electrode assemblies 
       11 ,  110 : Electrode tabs 
       12 ,  120 : Tab bundles 
       20 ,  200 : Tab guides 
       21 ,  210 : Upper tab guides 
       22 ,  220 : Lower tab guides 
       30 ,  300 : Welding jigs 
       31 ,  310 : Horns 
       32 ,  320 : Anvils 
       400 : Electrode tab fixing portion 
       400 ( a ): Region close to electrode assembly 
       400 ( b ): Region close to tab guide 
       410 : Insertion portion 
       420 : Body portion 
     a: Distance from electrode assembly 
     b: Distance from tab guide 
     c: Non-joint 
     d: Joint 
     r: Radius of curvature 
     w: Thickness of tab bundle