Patent Publication Number: US-2023143528-A1

Title: Electrode Assembly and Method for Manufacturing Same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of the priority of Korean Patent Application No. 10-2019-0153475, filed on Nov. 26, 2019, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to an electrode assembly and a method for manufacturing same, and more particularly, to: a method for manufacturing an electrode assembly, wherein, during the method, a fixing tape according to the related art is not used, and thus problems occurring upon attachment of the fixing tape may be resolved; and an electrode assembly which may be manufactured through the manufacturing method above. 
     BACKGROUND ART 
     Batteries for storing electric energy are generally classified into a primary battery and a secondary battery. The primary battery is a disposable consumable battery, but on the other hand, the secondary battery is a rechargeable battery which is manufactured by using a material in which oxidation and reduction processes between electric current and substances are repeatable. That is, when the reduction reaction to the material is performed by the current, power is recharged. Also, when the oxidation reaction to the material is performed, the power is discharged. Such recharging and discharging may be performed repeatedly. 
     Among various types of secondary batteries, a lithium secondary battery is generally manufactured by mounting, to a case, an electrode assembly in which a positive electrode (cathode), a separator, and a negative electrode (an anode) are stacked. The recharging and discharging of the lithium secondary battery are performed while lithium ions are intercalated into the negative electrode from lithium metal oxide of the positive electrode and deintercalated therefrom repeatedly. 
     The electrode assembly is provided as one electrode assembly obtained by: stacking a fixed number of unit cells, each of which comprises a negative electrode, a separator, and a positive electrode stacked in a predetermined order; or stacking a positive electrode, a separator, and a negative electrode one by one repeatedly. Also, the electrode assembly is accommodated in a case such as a cylindrical can, a prismatic pouch, or the like, and finally, a secondary battery is manufactured. 
     Also, a winding method, a stacking method, a stacking and folding method, and the like are well-known as a method for manufacturing the electrode assembly. In the winding method, a separator is stacked between the negative electrode and the positive electrode and then rolled. In the stacking method, a negative electrode and a positive electrode are cut into desired width and length and then the negative electrode, a separator, and the negative electrode are repeatedly stacked. In the stack and folding method, unit cells are placed side by side on a folding separator and then folded from one side. 
     An electrode assembly through the stacking method of the above-described methods is manufactured in a manner as shown in  FIG.  1 A  schematically illustrating a manufacturing process of the related art in which a predetermined number of positive electrodes  2 , separators  1 , and negative electrodes  3  are stacked on each other to manufacture a unit cell  10 , and then, a predetermined number of unit cells  10  are stacked on each other to manufacture an electrode assembly  100 . For reference, in the electrode assembly illustrated in  FIG.  1 A , a mono cell, in which a separator/a positive electrode/a separator/a negative electrode are stacked from the bottom, is manufactured as a unit cell  10 , and a plurality of unit cells  10  are stacked on each other. Here, a half cell  20 , in which a separator/an electrode (a negative electrode or a positive electrode)/a separator are stacked in the order, is placed on the uppermost layer so that the separator  1  is positioned on the uppermost layer. 
     Also, when a predetermined number of unit cells  10  are stacked, fixing tapes  200  for fixing the electrode assembly  100  are attached to wrap the circumference of the electrode assembly  100  (or to bind a side surface to a top surface and a bottom surface), thereby binding the unit cells  10 . 
     However, as shown in  FIG.  1 B  illustrating a state in which folding and wrinkling of a separator occur in a structure of an electrode assembly according to the related art, a structure of making the binding through the fixing tape  200  described above may have a problem in which an end of the separator  1  is folded and wrinkled due to pressure applied when the fixing tape  200  is attached. 
     The folding and wrinkling of the separator  1  may cause the negative electrode  3  and the positive electrode  2  to come into contact with each other, which is likely to cause short circuit. 
     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     Thus, to solve the problems described above, a main object of the present invention is to provide an electrode assembly and a method for manufacturing same, wherein, a process of additionally attaching a fixing tape after stacking of electrode assemblies is completed may be removed. 
     Technical Solution 
     An electrode assembly according to the present invention in order to achieve the object described above is an electrode assembly in which a negative electrode, a separator, and a positive electrode are repeatedly stacked, the electrode assembly comprising a film disposed to cover one of side surfaces defined by stacking the negative electrode, the separator, and the positive electrode, wherein the film is thermally fused to the side surface defined by stacking the negative electrode, the separator, and the positive electrode. Here, two or more sheets of the separators are merged at an end and bonded to each other to form a bonding portion, and the film is thermally fused to the bonding portion. 
     The film is disposed on each of two facing side surfaces of the side surfaces defined by stacking the negative electrode, the separator, and the positive electrode. 
     The film is made of a thermoplastic material which is plastically deformed when subjected to heat and a pressure. More particularly, the film is made of a polyethylene terephthalate (PET) material. 
     In addition, the present invention further provides a manufacturing method by which the electrode assembly having the configuration described above may be manufactured. A manufacturing method according to the present invention is a method for manufacturing an electrode assembly in which a negative electrode, a separator, and a positive electrode are repeatedly stacked, the method comprising: a unit cell manufacturing step (S 10 ) of manufacturing a unit cell having a predetermined stack structure of the negative electrode, the separator, and the positive electrode, wherein ends of the separators are bonded to each other to form a bonding portion; a film inserting step (S 20 ) of inserting a film into a die; a unit cell stacking step (S 30 ) of stacking the unit cell into the die; and a thermal fusing step (S 40 ) of applying heat and a pressure to thermally fuse the film to the bonding portion of the stacked unit cell within the die. 
     In the film inserting step (S 20 ), two films are inserted to come into contact with both side wall surfaces, respectively, which face each other within the die. 
     The unit cell stacking step (S 30 ) and the thermal fusing step (S 40 ) are repeatedly performed until stacking of predetermined unit cells is completed after the film inserting step (S 20 ). 
     Alternatively, the unit cell stacking step (S 30 ) may be repeated until stacking of predetermined unit cells is completed after the film inserting step (S 20 ), and when the unit cell stacking step (S 30 ) is complete, the thermal fusing step (S 40 ) may be repeated to thermally fuse the film to each of the stacked unit cells. 
     In the unit cell manufacturing step (S 10 ), a mono cell in which the separator/the negative electrode/the separator/the positive electrode are stacked sequentially from the bottom or a mono cell in which the separator/the positive electrode/the separator/the negative electrode are stacked sequentially from the bottom is manufactured as the unit cell. In addition, in the unit cell manufacturing step (S 10 ), a half cell in which the separator/the negative electrode/the separator are stacked sequentially from the bottom or a half cell in which the separator/the positive electrode/the separator are stacked sequentially from the bottom is separately manufactured as the unit cell in addition to the mono cell. 
     Also, while the unit cell stacking step (S 30 ) is repeatedly performed, the mono cells are stacked, wherein, when the unit cell stacking step (S 30 ) is finally performed, the half cell is stacked. 
     The film is made of a thermoplastic material which is plastically deformed when subjected to heat and a pressure, and in the thermal fusing step (S 40 ), the film is pressed and simultaneously heated by a tip of a soldering tool and thermally fused to the unit cell. 
     The die is configured to allow the tip of the soldering tool to enter the die or allow the soldering tool to be embedded in the die, and the thermal fusion of the film is performed within the die. 
     Advantageous Effects 
     In the present invention having the configuration described above, the film is thermally fused and fixed to the side surface of the electrode assembly instead of using the fixing tape (that is, subjected to lower pressure than pressure generated when the fixing tape is attached). Thus, the folding or wrinkling of the separator occurring in the structure of the related art may be prevent. 
     Particularly, in the present invention, two or more sheets of the separators are merged at the end to form the bonding portion, and the film is thermally fused to the bonding portion. Thus, the separator may be prevented from being folded or deformed during the thermal fusion. That is, when the thermal fusion is made, the ends of the separators are bonded to each other to restrict movements thereof, and in a region in which the bonding portion is formed, the thickness is increased. Thus, the area of thermal fusion to the film is enlarged, and fixing force may increase. 
     Also, in the present invention, the thermal fusion is performed right after the unit cell is stacked, and then, the next unit cell is stacked. Alternatively, in the present invention, the stacking of all the unit cells is complete, and then, the thermal fusion is performed. Thus, the manufacturing process may be flexible according to conditions of the electrode assembly. 
     Also, the thermal fusion is performed within the die by the soldering tool that enters the die in which the unit cell is stacked or the soldering tool that is embedded in the die. Thus, the unit cell is prevented from shaking during the thermal fusing process, and more stable thermal fusion may be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a view schematically illustrating a manufacturing process of an electrode assembly of the related art. 
         FIG.  1 B  is a view schematically illustrating a state in which a separator is folded and wrinkled in a structure of an electrode assembly of the related art. 
         FIG.  2    is a flow chart of a method for manufacturing an electrode assembly of the present invention. 
         FIG.  3    is a view illustrating a state in which, during a unit cell manufacturing step, a negative electrode, a separator, and a positive electrode are stacked on each other and manufactured as a unit cell. 
         FIG.  4 A  is a view showing: a cross-section (a) of a die in a method for manufacturing an electrode assembly of the present invention; and a state (b) in which a film is attached to the inside of the die. 
         FIG.  4 B  is a view additionally illustrating a state (c) in which a unit cell is placed between the films inside the die illustrated in  FIG.  4 A . 
         FIG.  4 C  is a view additionally illustrating states (c, d, and e) in which a film and a bonding portion of a unit cell are bonded to each other by a soldering tool within the die illustrated in  FIG.  4 B . 
         FIG.  5    is a view illustrating a plan view, a front view, and a left side view of an electrode assembly which is manufactured by a method for manufacturing an electrode assembly of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that the present invention can be easily carried out by a person skill in the art to which the present invention pertains. However, the present invention may be embodied in several different forms, and not be limited to the embodiments set forth herein. 
     A part unrelated to the description will be omitted so as to clearly describe the present invention, and the same reference symbols are affixed to identical or similar elements throughout the specification. 
     Also, terms or words used in this specification and claims should not be restrictively interpreted as ordinary meanings or dictionary-based meanings, but should be interpreted as meanings and concepts conforming to the scope of the present invention on the basis of the principle that an inventor can properly define the concept of a term to describe and explain his or her invention in the best ways. 
     The present invention relates to an electrode assembly in which a negative electrode  3 , a separator  1 , and a positive electrode  2  are repeatedly stacked on each other, and a method for manufacturing the electrode assembly. Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. 
     First Embodiment 
     The present invention provides, as a first embodiment, a method for manufacturing an electrode assembly. As illustrated in  FIG.  2    showing a sequence of a method for manufacturing an electrode assembly according to the present invention, a manufacturing method according to the embodiment comprises a unit cell manufacturing step (S 10 ), a film inserting step (S 20 ), a unit cell stacking step (S 30 ), and a thermal fusing step (S 40 ). 
     During the unit cell manufacturing step (S 10 ), a unit cell  10  having a predetermined stack structure of a negative electrode  3 , a separator  1 , and a positive electrode  2  is manufactured, and ends of separators  1  are bonded to each other to form a bonding portion  1   a.    
     That is, as illustrated in  FIG.  3    showing a state in which a negative electrode  3 , a separator  1 , a positive electrode  2  are stacked on each other and manufactured into a unit cell  10 , a mono cell and a half cell, each of which has a predetermined stack structure, are manufactured as a unit cell. As illustrated in the drawing, the mono cell may have a structure in which the separator  1 /the positive electrode  2 /the separator  1 /the negative electrode  3  are stacked sequentially from the bottom or a structure in which the separator  1 /the negative electrode  3 /the separator  1 /the positive electrode  2  are stacked sequentially from the bottom. Also, a half cell is additionally provided, in which the uppermost electrode (a positive electrode or a negative electrode) is removed from the mono cell. In order for the separator  1  to be placed on the uppermost layer after the stacking of mono cells is complete, the half cell has a structure in which the separator  1 /the negative electrode  3 /the separator  1  are stacked sequentially from the bottom or a structure in which the separator  1 /the positive electrode  2 /the separator  1  are stacked sequentially from the bottom. Thus, the half cell is stacked after stacking of mono cells is complete, and thus, an electrode assembly stacked according to the present invention has a structure in which the separator is placed in each of the lowermost layer and the uppermost layer. 
     Here, in the unit cell  10  manufactured with the mono cell and the half cell, the separator  1  has an area larger than each of areas of the positive electrode  2  and the negative electrode  3 , and has ends protruding to both sides, respectively, as illustrated in the drawing. During the unit cell manufacturing step (S 10 ), upper and lower surfaces of the ends of the separators  1  are bonded to each other to form the bonding portion  1   a . The bonding portion  1   a  is not necessarily formed at all of the protruding ends of the separators  1 , but it is desirable to be formed at the ends that face the film  30  when the unit cells  10  are stacked. 
       FIGS.  4 A to  4 C  illustrate, in a method for manufacturing an electrode assembly of the invention: a cross-section (a) of a die M; a state (b) in which films  3  are attached inside the die M; a state (c) in which a unit cell  10  is placed between the films  30  inside the die M; and states (d and e) in which the films  30  and bonding portions  1   a  of unit cells  10  are bonded to each other by the soldering tool G within the die M. 
     Referring to  FIGS.  4 A to  4 C , during the film inserting step (S 20 ), the films  30  are disposed on the both inner circumferential surfaces facing each other inside the die M. The die M is manufactured to have a size enough to stack the unit cells  10  between the films  30  disposed therein and also manufactured to have sufficient strength. The die M may be configured such that the inner space thereof for stacking the unit cells  10  has a hexahedral shape, and one side surface or both side surfaces thereof on which the film  30  is not disposed may be provided in an open state so that an operation of an gripper (not shown) or the like for conveying and stacking the unit cell  10  when the unit cells  10  are stacked is not interfered. 
     Also, the film  30  inside the die M may be disposed in a temporarily fixed state on the inner circumferential surface of the die M so that vertically standing state thereof is maintained before thermal fusion is performed. That is, a clip, a holder, or the like for temporarily fixing the film may be installed in the die M. Alternatively, the film  30 , having an adhesive with relatively weak adhesion applied on the surface thereof before disposed, may be disposed inside the die M. Such a means for temporarily fixing the film  30  may be embodied using other well-known methods as long as the film  30  may be easily separated from the inner circumferential surface of the die M after the manufacturing of the electrode assembly is completed. 
     Also, in order for the soldering tool G to enter when thermally fusing the film  30  and the unit cell  10 , the die M may have a slit (not shown) or the like through which the soldering tool G may enter vertically or a structure in which the soldering tool G is mounted inside the die M in a slidable manner. 
     Next, the unit cell stacking step (S 30 ) is performed, in a state in which the film  30  is disposed inside the die M, and the soldering tool G is ready to operate. During the unit cell stacking step (S 30 ), the unit cells  10  are stacked at the right position between the two films  30  inside the die M. Here, each of the unit cells  10  is the mono cell as described above, and the stacking is performed such that the separator  1  is placed on a lower side. 
     Also, the thermal fusing step (S 40 ) is performed, in which heat and a pressure are applied inside the die M to thermally fuse the film  30  to the bonding portion  1   a  of the stacked unit cell  10 . 
     In the embodiment, the two films  30  are inserted to come into contact with both side wall surfaces, respectively, which face each other within the die M. Thus, the thermal fusion is simultaneously performed on the both side wall surfaces of the die M. 
     Also,  FIG.  4 C  illustrates that the unit cell stacking step (S 30 ) and the thermal fusing step (S 40 ) are repeatedly performed until the stacking of predetermined unit cells  10  is completed after the film inserting step (S 20 ). So, when one unit cell  10  is stacked, the unit cell  10  is thermally fused, and then, a next unit cell  10  is stacked and thermally fused. 
     However, there is no change in position of the unit cell  10  between the films  30  within the die M. Thus, the manufacturing process may be made in a manner in which, after all of the unit cells  10  are stacked without thermal fusion and in a state in which the stacking is complete, the thermal fusion of the unit cells  10  is performed sequentially from a unit cell  10  on the bottom layer (or from a unit cell from the top layer). That is, in the present invention, the order of the unit cell stacking step (S 30 ) and the thermal fusing step (S 40 ) may be changed flexibly. 
     Also, as described above, the mono cells are stacked while the unit cell stacking step (S 30 ) is performed repeatedly, and when the unit cell stacking step (S 30 ) is performed finally, the half cell is stacked. Thus, the electrode assembly manufactured by the above manner has a structure in which the separator  1  is disposed on each of the uppermost layer and the lowermost layer. 
     Here, the film  30  of the present invention is made of a thermoplastic material which is plastically deformed when subjected to heat and a pressure. For example, the film may be made of a polyethylene terephthalate (PET) material. 
     During the thermal fusing step (S 40 ), the film  30  is pressed and simultaneously heated by a tip of the soldering tool G and thermally fused to the bonding portion  1   a  of the unit cell  10 . Also, the temperature and pressure to be applied may be changed according to the thickness and material properties of the film  30  or the relative position and size of the bonding portion. Here, as described above, the die M is configured to allow the tip of the soldering tool G to enter the die or the soldering tool G to be embedded in the die, and the thermal fusion of the film  30  is performed within the die M. 
     Second Embodiment 
     The present invention provides, as a second embodiment, an electrode assembly which may be manufactured through the manufacturing method according to the first embodiment. 
     The electrode assembly provided in the embodiment is an electrode assembly in which a negative electrode  3 , a separator  1 , and a positive electrode  2  are repeatedly stacked, and the electrode assembly comprises a film  30  disposed to cover one of the side surfaces defined by stacking the negative electrode  3 , the separator  1 , and the positive electrode  2 . The film  30  is thermally fused to the side surface defined by stacking the negative electrode  3 , the separator  1 , and the positive electrode  2 . 
     That is, referring to  FIG.  5    illustrating a plan view, a front view, and a left side view of the electrode assembly which is manufactured by the method for manufacturing an electrode assembly of the present invention, the negative electrode  3  and the positive electrode  2  according to the present invention have a negative electrode tab  3   a  and a positive electrode tab  2   a  protruding to the sides, respectively. The positive electrode tab  2   a  and the negative electrode tab  3   a  are configured to protrude in directions opposite to each other, and the film  30  is attached to each of the side surfaces of the electrode assembly having two sides perpendicular to the sides from which the positive electrode tab  2   a  and the negative electrode tab  3   a  protrude. 
     In the present invention having the configuration described above, the film  30  is thermally fused and fixed to the side surface of the electrode assembly instead of using the fixing tape and is subjected to lower pressure than pressure generated when the fixing tape of the related art is attached. Thus, the folding or wrinkling of the separator  1  occurring in the structure of the related art may be prevent. 
     Particularly, in the present invention, two or more sheets of the separators  1  are merged at the end to form the bonding portion  1   a , and the film  30  is thermally fused to the bonding portion  1   a . Thus, the separator  1  may be prevented from being folded or deformed during the thermal fusion. That is, when the thermal fusion is made, ends of the separators  1  are bonded to each other to restrict movements thereof, and in a region in which the bonding portion  1   a  is formed, the thickness is increased. Thus, the area of thermal fusion to the film  30  is enlarged, and fixing force may increase. 
     Also, in the present invention, the thermal fusion is performed right after the unit cell  10  is stacked, and then, the next unit cell  10  is stacked. Alternatively, in the present invention, the stacking of all the unit cells  10  is complete, and then, the thermal fusion is performed. Thus, the manufacturing process may be flexible according to conditions of the electrode assembly. 
     Also, the thermal fusion is performed within the die M by the soldering tool G that enters the die M in which the unit  10  cell is stacked or the soldering tool G that is embedded in the die. Thus, the unit cell  10  is prevented from shaking during the thermal fusing process, and more stable thermal fusion may be achieved. 
     Although the present invention is described by specific embodiments and drawings, the present invention is not limited thereto, and various changes and modifications may be made by a person skilled in the art to which the present invention pertains within the technical idea of the present invention and equivalent scope of the appended claims.