Patent Publication Number: US-2023163363-A1

Title: Secondary Battery and Manufacturing Method of the Same

Description:
TECHNICAL FIELD 
     Cross Citation with Related Application(s) 
     This application claims the benefit of Korean Patent Application No. 10-2020-0064986 filed on May 29, 2020 with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     The present disclosure relates to a secondary battery and a method for manufacturing the same, and more particularly, to a secondary battery that can discharge gas generated during the activation step, and a method for manufacturing the same. 
     BACKGROUND 
     As the demands for portable electronic products such as notebooks, video cameras and cellular phones are rapidly increased in these days, and development of electric vehicles, energy storage batteries, robots, satellites, etc. is under active progress, numerous studies are being made on secondary batteries being used as the driving power source. 
     The electrode assembly mounted in the battery case is a power generating element, having a cathode/separator/anode stack structure, which can be charged and discharged, and the electrode assembly is classified into a jelly-roll type, a stacked type and a stacked/folded type. The jelly-roll type electrode assembly is configured to have a structure in which a long sheet type cathode and a long sheet type anode, to which active materials are applied, are wound in a state where a separator is interposed between the cathode and the anode, the stacked type electrode assembly is configured to have a structure in which a large number of cathodes having a predetermined size and a large number of anodes having a predetermined size are sequentially stacked in a state in which separators are interposed between the cathodes and the anodes, and the stacked/folded type electrode assembly is a combination of the jelly-roll type electrode assembly and the stacked type electrode assembly. Among them, the jelly-roll type electrode assembly has advantages in that manufacturing is easy and an energy density per unit weight is high. 
     Based on the shape of a battery case, a secondary battery is classified into a cylindrical battery where an electrode assembly is built into a cylindrical metal can, a prismatic battery where an electrode assembly is built into a prismatic metal can, and a pouch-type battery where an electrode assembly is built into a pouch type case formed of an aluminum laminate sheet. Among them, the cylindrical battery has an advantage in that it has a relatively large capacity and is structurally stable. 
     Such a secondary battery includes, for example, nickel-cadmium battery, nickel hydrogen battery, nickel zinc battery, lithium secondary battery, and the like. Among these, since the lithium secondary battery has the advantages in that it has almost no memory effect compared to nickel-based secondary battery and thus, can be charged and discharged freely, and have very low self-discharge rate, high operating voltage, and high energy density per unit weight, it is widely used in the field of advanced electronic devices. 
       FIG.  1    is a partial cross-sectional view of an upper part of a conventional cylindrical secondary battery. 
     Referring to  FIG.  1   , a jelly roll-type electrode assembly  50  is housed in a cylindrical case  20 , and a cap assembly  30  can be mounted onto an open upper part of the cylindrical case  20  to manufacture a cylindrical secondary battery  10 . Specifically, a gasket  40  is positioned between the cap assembly  30  and the cylindrical case  20 , and then the cap assembly  30  and the cylindrical case  20  are crimpled and coupled to manufacture a cylindrical secondary battery  10 . 
     The cap assembly  30  includes an upper end cap  31  and a safety vent  32  for internal pressure drop, and the upper end cap  31  and the safety vent  32  for internal pressure drop may form a structure in close contact with each other. 
     The safety vent  32  may be electrically connected to the electrode assembly  50  via a current interrupt device (CID). A CID gasket  70  can wrap the edge of the current interrupt device  60 . 
     Generally, a lithium secondary battery performs a formation step, that is, an activation step, during the manufacturing process. The activation step is a process of assembling the battery and then performing charging and discharging to activate the battery, wherein lithium ions emitted from the cathode during charging are intercalated while moving to the anode, and at this time, a solid electrolyte interface (SEI) film is formed on the surface of the anode. This activation step is generally performed by repeating charge/discharge with a constant current or constant voltage in a certain range. 
     In this activation step, a large amount of gas is generated due to the formation of the electrode film or the decomposition of moisture inside the cell. Since the amount of gas generated in the activation step is large and it continuously reacts with the electrode film, a step of discharging the same is necessary, which is called a degas process. 
     However, referring to  FIG.  1    again, the conventional cylindrical secondary battery  10  must maintain airtightness after injection of the electrolyte solution and thus, it is not easy to discharge gas generated in the activation step. Consequently, the internal pressure is easily increased and the battery performance is deteriorated. 
     Therefore, there is a need to develop a cylindrical secondary battery capable of discharging gas generated in the activation step. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
     It is an object of the present disclosure to provide a secondary battery that can discharge gas generated during the activation step, and a method for manufacturing the same. 
     However, the technical problem to be solved by embodiments of the present disclosure is not limited to the above-described problems, and can be variously expanded within the scope of the technical idea included in the present disclosure. 
     Technical Solution 
     According to one embodiment of the present disclosure, there is provided a secondary battery comprising: an electrode assembly impregnated with an electrolyte solution; a battery case that houses the electrode assembly and the electrolyte solution; a cap assembly coupled to the battery case; and a gasket positioned between the battery case and the cap assembly, wherein the gasket includes an indented part formed on the inside, and wherein the indented part is spaced apart from the cap assembly while facing the cap assembly. 
     The gasket may include a sealing part that seals between the battery case and the cap assembly while being positioned at one end of the indented part. 
     The sealing part may make contact with the cap assembly. 
     A concave-convex part may be formed on a surface where the sealing part makes contact with the cap assembly. 
     The indented part may be configured to connect in a straight, oblique or zigzag shape along the height direction. 
     The indented part may increase in width as it goes from one end to the other end. The battery case and the cap assembly are crimped and coupled with the gasket interposed therebetween, so that a crimping part may be formed in the battery case. 
     According to another embodiment of the present disclosure, there is provided a method for manufacturing a secondary battery, comprising the steps of: housing an electrode assembly inside a battery case; injecting an electrolyte solution into the electrode assembly; positioning a cap assembly and a gasket on the electrode assembly; and charging and discharging the electrode assembly to activate the electrode assembly, wherein the gasket comprises an indented part formed inside, wherein the indented part is spaced apart from the cap assembly while facing the cap assembly, and wherein in the step of activating the electrode assembly, the generated gas is discharged to the outside along the indented part. 
     The gasket may include a sealing part that seals between the battery case and the cap assembly while being positioned at one end of the indented part. 
     The method for manufacturing a secondary battery may further include crimping and coupling the battery case and the cap assembly with the gasket interposed therebetween, wherein in the crimping and coupling step, the sealing part may make contact with the cap assembly. 
     A concave-convex part may be formed on a surface where the sealing part makes contact with the cap assembly. 
     The method for manufacturing a secondary battery may further include disposing an auxiliary ring on the cap assembly, wherein the auxiliary ring makes contact with the sealing part and interrupts a path formed by the indented part. 
     The step of disposing an auxiliary ring may be performed before the step of activating the electrode assembly. 
     Advantageous Effects 
     According to embodiments of the present disclosure, gas generated in the activation step can be easily discharged by using a gasket in which an indented part is formed, thereby preventing an increase in the internal pressure and a decrease in performance of the secondary battery. In addition, the problems of expansion and deformation of the electrode assembly due to gas, or the problem of inducing lithium precipitation due to residual gas bubbles can be solved. 
     The effects of the present disclosure are not limited to the effects mentioned above and additional other effects not described above will be clearly understood from the description of the appended claims by those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a partial cross-sectional view of an upper part of a conventional cylindrical secondary battery; 
         FIG.  2    is a perspective view of a secondary battery according to an embodiment of the present disclosure; 
         FIG.  3    is a partial cross-sectional view showing a part of the cross-section taken along the cutting line A-A′ of  FIG.  2   ; 
         FIG.  4    is a partial cross-sectional view enlarging and showing a section “B” of  FIG.  3   ; 
         FIG.  5    is a perspective view showing a gasket included in the secondary battery of  FIG.  3   ; 
         FIG.  6    is a partial cross-sectional view explaining a gasket in which a concavo-convex structure is formed according to a modified embodiment of the present disclosure; 
         FIGS.  7   a  to  7   c    are perspective views showing gaskets according to modified embodiments of the present disclosure; 
         FIGS.  8  and  9    are partial cross-sectional views explaining a method for manufacturing a secondary battery according to an embodiment of the present disclosure; and 
         FIG.  10   a    is a partial cross-sectional view explaining the step of disposing the auxiliary ring according to an embodiment of the present disclosure, and  FIG.  10   b    is a perspective view of an auxiliary ring according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement them. The present disclosure can be modified in various different ways, and is not limited to the embodiments set forth herein. 
     Portions that are irrelevant to the description will be omitted to clearly describe the present disclosure, and like reference numerals designate like elements throughout the specification. 
     Further, in the figures, the size and thickness of each element are arbitrarily illustrated for convenience of description, and the present disclosure is not necessarily limited to those illustrated in the figures. In the figures, the thickness of layers, regions, etc. are exaggerated for clarity. In the figures, for convenience of description, the thicknesses of some layers and regions are shown to be exaggerated. 
     In addition, it will be understood that when an element such as a layer, film, region, or plate is referred to as being “on” or “above” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, it means that other intervening elements are not present. Further, the word “on” or “above” means disposed on or below a reference portion, and does not necessarily mean being disposed “on” or “above” the reference portion toward the opposite direction of gravity. 
     Further, throughout the specification, when a portion is referred to as “including” a certain component, it means that the portion can further include other components, without excluding the other components, unless otherwise stated. 
     Further, throughout the specification, when referred to as “planar”, it means when a target portion is viewed from the upper side, and when referred to as “cross-sectional”, it means when a target portion is viewed from the side of a cross section cut vertically.  FIG.  2    is a perspective view of a secondary battery according to an embodiment of the present disclosure.  FIG.  3    is a partial cross-sectional view showing a part of the cross-section taken along the cutting line A-A′ of  FIG.  2   . 
     Referring to  FIGS.  2  and  3   , a secondary battery  100  according to an embodiment of the present disclosure includes an electrode assembly  500  impregnated with an electrolyte solution, a battery case  200  that houses the electrode assembly  500  and the electrolyte solution, a cap assembly  300  coupled to the battery case  200 ; and a gasket  400  positioned between the battery case  200  and the cap assembly  300 . 
     First, the electrode assembly  500  has a jelly-roll type structure in which a cathode  510  and an anode  520  are wound with a separator  530  interposed therebetween, and a center pin (not shown) may be inserted in the central part thereof. The center pin is generally made of a metal material in order to impart a predetermined strength, and has a hollow cylindrical structure obtained by bending a plate material in a round shape. The center pin can serve to fix and support the electrode assembly  500  and can serve as a passage for discharging gas generated by an internal reaction during charge/discharge and operation. In particular, the gas generated in the activation step, which will be described later, may move. 
     The cap assembly  300  includes an upper end cap  310  and a safety vent  320 , the upper end cap  310  is positioned on the safety vent  320 , and can be electrically connected to the safety vent  320  by forming a structure in close contact with each other. The upper end cap  310  protrudes upward at the center, and is indirectly connected to the cathode  510  of the electrode assembly  500  via a cathode tab  511  and the like, and can perform a function as a cathode terminal by connecting with an external circuit. 
     The battery case  200  may have a cylindrical shape and may include a beading part  210  and a crimping part  220  . 
     The beading part  210  refers to a portion where a part of the battery case  200  is indented in the center direction of the electrode assembly  500 , and is for stably coupling the cap assembly  300  and preventing the electrode assembly  500  from flowing. Here, the central direction of the electrode assembly  500  may mean a radial direction from the outer peripheral surface of the jelly-roll type electrode assembly  500  to the center thereof. 
     The crimping part  220  is positioned above the beading part  210  and refers to a portion that wraps the cap assembly  300 , and is for stable coupling the cap assembly  300 . Specifically, the gasket  400  is mounted on the inner surfaces of the crimping part  220  and the beading part  210  to increase the sealing force between the cap assembly  300  and the battery case  200 . That is, the gasket  400  is positioned between the battery case  200  and the cap assembly  300 , and the end part of the battery case  200  is bent to form the crimping part  220 . Thereby, mounting of the cap assembly  300  and sealing of the secondary battery  100  can be performed. 
     On the other hand, a current interrupt device  600  (CID) and the CID gasket  700  may be positioned under the safety vent  320 . The safety vent  320  is a thin film structure through which current flows, and two grooves  321  and  322  having different depths may be formed therein. 
     The current interrupt device  600  is a member of a conductive plate material, and may include an outer peripheral part  610  and an interrupting part  620  surrounded by the outer peripheral part  610 . 
     Also, although not specifically illustrated, a plurality of through holes for discharging gas may be formed. In an abnormal operating situation, when the pressure inside the secondary battery  100  rises, the interrupting part  620  is separated from the outer peripheral part  610 , so that an electrical connection between the external circuit and the electrode assembly  500  may be interrupted. 
     The CID gasket  700  is a member surrounding the edge of the current interrupt device  600 , and may prevent the safety vent  320  from contacting the outer peripheral part  610 . 
     Hereinafter, a gasket in which an indented part is formed according to the present embodiment will be described in detail with reference to  FIGS.  4  and  5   . 
       FIG.  4    is a partial cross-sectional view enlarging and showing a section “B” of  FIG.  3   .  FIG.  5    is a perspective view showing a gasket included in the secondary battery of  FIG.  3   . Referring to  FIGS.  4  and  5   , the secondary battery according to the present embodiment includes a gasket  400  positioned between the battery case  200  and the cap assembly  300 , wherein the gasket  400  includes an indented part  410  formed inside, and the indented part  410  is spaced apart from the cap assembly  300  while facing the cap assembly  300 . 
     The indented part  410  is formed inside the gasket  400 , thereby capable of providing a passage through which gas generated in the activation step can move. Thereby, it is possible to prevent an increase in the internal pressure of the secondary battery  100  and a decrease in performance due to gas. Specifically, it is possible to prevent the problems such as expansion and deformation of the electrode assembly, or induction of lithium precipitation due to residual gas bubbles. The details will be described again with reference to  FIGS.  8  and  9    below. The gasket  400  may have a circular ring shape in order to surround the cap assembly  300 , and the indented part  410  is formed inside the gasket  400  having a circular ring shape, and may be connected in a straight line along the height direction. The number of the indented parts  410  formed in the gasket  400  is not particularly limited and may be configured by a plurality of numbers. However, it is preferable to discharge only the gas generated in the activation step, and in other steps, it is preferable to suppress the inflow to the atmosphere as much as possible, so it is preferable to form by two to four. 
     Meanwhile, the gasket  400  according to the present embodiment may include a sealing part  420  that seals between the battery case  200  and the cap assembly  300  while being positioned at one end of the indented part  410 . This sealing part  420  may make contact with the cap assembly  300 , and for this purpose, the sealing part  420  may form a structure protruding inward than the indented part  410 . The battery case  200  and the cap assembly  300  are crimped and coupled with the gasket  400  interposed therebetween, whereby a crimping part  220  is formed in the battery case  200 , the sealing part  420  of the gasket  400  can seal between the cap assembly  300  and the battery case  200 . After gas is discharged via the indented part, the sealing part  420  can interrupt the discharge path via the indented part  410 . 
       FIG.  6    is a partial cross-sectional view explaining a gasket in which a concavo-convex structure is formed according to a modified embodiment of the present disclosure. 
     Referring to  FIG.  6   , a concavo-convex part  421  may be formed on a surface where the sealing part  420  of the gasket  400  according to the present embodiment makes contact with the cap assembly  300 . The concave-convex part  421  refers to a region in which a concave part and a convex part are repeatedly formed, and when the concave-convex part  421  is provided on the surface in contact with the cap assembly  300 , and the battery case  200  and the cap assembly  300  are crimped and coupled, the degree of sealing between the sealing part  420  and the cap assembly  300  can be increased. 
       FIGS.  7   a  to  7   c    are perspective views showing gaskets according to modified embodiments of the present disclosure. First, referring to  FIG.  7   a   , the indented part  410   a  formed in the gasket  400   a  according to the present embodiment may be connected obliquely along the height direction, unlike the indented part  410  that connects in a straight line shown in  FIG.  5   . 
     Next, referring to  FIG.  7   b   , the indented part  410   b  formed in the gasket  400   b  according to the present embodiment may be connected in a zigzag pattern along the height direction. 
     Gas generated in the activation step is discharged through the indented parts  410   a  and  410 b that are connected in an oblique or zigzag shape, and at the same time, the leakage of the electrolyte or the generation of bubbles can be minimized. 
     Next, referring to  FIG.  7   c   , the indented part  410   c  formed in the gasket  400   c  according to the present embodiment may increase in width as it goes from one end to the other end. More specifically, as the indented part  410   c  moves along the height direction, a trapezoidal shape may be formed in which the width increases as it goes from one end at which the sealing part  420  is positioned, to the other end part facing the one end part. 
     Gas generated in the activation step is discharged through the indented part  410   c  which increases in width as it goes from one end to the other end, and at the same time, the contact of the electrode assembly or electrolyte housed inside the battery case with the atmosphere can be minimized. 
     Hereinafter, a method of manufacturing a secondary battery according to an embodiment of the present disclosure will be described in detail with reference to  FIGS.  8  and  9   .  FIGS.  8  and  9    are partial cross-sectional views explaining a method for manufacturing a secondary battery according to an embodiment of the present disclosure. Specifically,  FIG.  8    is a partial cross-sectional view of the upper part of the secondary battery  100  before crimping and coupling between the battery case  200  and the cap assembly  300 , and  FIG.  9    is a partial cross-sectional view of the upper part of the secondary battery  100  after crimping and coupling between the battery case  200  and the cap assembly  300 . 
     First, referring to  FIG.  8   , a method for manufacturing a secondary battery  100  according to an embodiment of the present disclosure includes the steps of: housing an electrode assembly  500  inside a battery case  200 , injecting an electrolyte solution into the electrode assembly  500 ; positioning a cap assembly  300  and a gasket  400  on the electrode assembly  500 , and charging and discharging the electrode assembly  500  to activate the electrode assembly  500 . 
     After the electrode assembly  500  is housed inside the battery case  200 , a step of indenting the battery case  200  in the center direction of the electrode assembly  500  from the upper part of the electrode assembly  500  to form the beading part  210  may be continued. 
     After that, a step of charging and discharging the electrode assembly  500  to activate the electrode assembly  500  may be continued, wherein the step of activating the electrode assembly  500  corresponds to a formation step, that is, an activation step. The activation step is a step of charging and discharging the secondary battery to activate the secondary battery. Lithium ions emitted from the cathode  510  during charging move to the anode  520  and are intercalated. At this time, a solid electrolyte interface (SEI) film is formed on the surface of the anode  520 . Such activation step is generally performed by repeating charge/discharge with a constant current or constant voltage in a certain range. 
     In this activation step, a large amount of gas is generated due to the formation of the electrode film or the decomposition of moisture inside the cell. Since the amount of gas generated in the activation step is large and it continuously reacts with the electrode film, it is necessary to discharge it. 
     At this time, the gasket  400  according to the present embodiment includes an indented part  410  formed inside, and the indented part  410  is spaced apart from the cap assembly  300  while facing the cap assembly  300 . In the step of activating the electrode assembly  500 , the generated gas is discharged to the outside along the indented part  410 . More specifically, it may be discharged to the outside along a moving passage formed between the indented part  410  and the cap assembly  300 . 
     Since the gas generated in the activation step can be discharged in this way, it is possible to prevent an increase in the internal pressure and a decrease in performance of the secondary battery  100 . More specifically, it is possible to prevent expansion and deformation of the electrode assembly  500  and also to prevent the problem of inducing lithium precipitation due to residual gas bubbles. Next, referring to  FIG.  9   , the gasket  400  according to the present embodiment includes a sealing part  420  that seals between the battery case  200  and the cap assembly  300  while being positioned at one end of the indented part  410 . Further, the method for manufacturing the secondary battery  100  according to the present embodiment may further include a step of crimping and coupling the battery case  200  and the cap assembly  300  with the gasket  400  interposed therebetween, and in the crimping and coupling step, the sealing part  420  may make contact with the upper cap assembly  300  to seal between the battery case  200  and the cap assembly  300 . After the gas is discharged to the outside through the indented part  410  in the activation step, the sealing part  420  passes through the crimping and coupling step and can interrupt a discharge path via the indented part  410 . In other words, in the present embodiment, the indented part  410  is formed in the gasket  400  to secure a path for gas discharge during the activation step, and at the same time, a sealing part  420  protruding from one end of the indented part  410  can be formed to secure the sealing function of the gasket  400 . 
     Meanwhile, as shown in  FIG.  6   , the concave-convex part  421  is formed on the surface of the sealing part  420  in contact with the cap assembly  300 , so that the degree of sealing can be increased. The details overlap with the contents described above, and therefore, is omitted herein. 
       FIG.  10   a    is a partial cross-sectional view explaining the step of disposing the auxiliary ring according to an embodiment of the present disclosure, and  FIG.  10   b    is a perspective view of an auxiliary ring according to an embodiment of the present disclosure. 
     Referring to  FIGS.  10   a  and  10   b   , the method for manufacturing the secondary battery  100  according to the present embodiment may further include a step of disposing the auxiliary ring  800  on the cap assembly  300 . The auxiliary ring  800  is a ring-shaped member, and may make contact with the sealing part  420  to interrupt the path formed by the indented part  410 . 
     The step of disposing the auxiliary ring  800  is preferably performed before the step of activating the electrode assembly  500 . Specifically, it may be performed between the step of injecting the electrolyte and the step of activating the electrode assembly  500 . More specifically, after injecting an electrolyte solution into the electrode assembly  500  and positioning the cap assembly  300  and the gasket  400  on the electrode assembly  500 , the auxiliary ring  800  may be disposed on the cap assembly  300 . By disposing the auxiliary ring  800 , the contact of the electrolyte solution with the external atmosphere can be minimized through the path formed by the indented part  410  until the electrode assembly  500  is activated after injecting the electrolyte solution into the electrode assembly  500 . If the electrolyte solution is exposed to moisture in the outside atmosphere for a certain period of time before the activation step is performed, the performance of the secondary battery may be deteriorated. However, by interrupting the contact path between the electrolyte solution and the external atmosphere during the waiting time until the auxiliary ring  800  according to the present embodiment proceeds with the activation step, these problems can be solved. Subsequently, after removing the auxiliary ring  800 , the activation step may be performed. 
     The material of the auxiliary ring  800  is not particularly limited, and a material having elasticity may be included. 
     Although the terms representing directions such as front, rear, left, right, upper and lower directions are used herein, it is obvious to those skilled in the art that these merely represent for convenience in explanation, and may differ depending on a position of an observer, a position of an object, or the like. 
     One or more secondary batteries according to the present embodiment described above can be applied to various devices. Such a device can be applied to a vehicle means such as an electric bicycle, an electric vehicle, or a hybrid vehicle, but the present disclosure is not limited thereto, and is applicable to various devices that can use a secondary battery. 
     Although preferred embodiments of the present disclosure have been described in detail above, the scope of the present disclosure is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts of the present disclosure, which are defined in the appended claims, also belong to the scope of the present disclosure. 
     DESCRIPTION OF REFERENCE NUMERALS 
       100 : secondary battery 
       200 : battery case 
       300 : cap assembly 
       400 : gasket 
       410 : indented part 
       420 : sealing part 
       421 : concavo-convex part 
       800 : auxiliary ring