Patent Publication Number: US-2021167431-A1

Title: System for and method of manufacturing lithium ion secondary battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Korean Patent Application No. 10-2019-0156297, filed Nov. 29, 2019, the entire contents of which is incorporated herein for all purposes by this reference 
     BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to a system for and a method of manufacturing a lithium ion secondary battery. 
     Description of the Related Art 
     In order to cope with air pollution and global warming, a reduction in emission of carbon dioxide is required. For this reason, recently, the automobile industry has made a great effort to commercialize electric vehicles or hybrid vehicles, and development of cost-effective and safe lithium ion secondary batteries for powering motors holds a key to the practical use of electrical vehicles or hybrid vehicles. Therefore, advanced lithium ion secondary batteries are being actively developed. 
     Production of a lithium ion secondary battery consists of three main process steps: electrode manufacturing, cell assembly, and cell formation. The cell formation refers to a process of forming a passivation film to prevent damage to a battery cell and to secure the function of the battery cell. Conventionally, such a formation process requires a long process time, a large space proportional to the process time, and many labor hours, resulting in low production productivity. The formation process also has a problem in that degassed gas  14  flows back into an electrode assembly as illustrated in  FIG. 1 , and thus cell performance is deteriorated due to the gas. In  FIG. 1 , the reference number  11  refers to a cathode, the reference number  12  refers to an anode, and the reference number  13  refers to a separation membrane. 
     The foregoing is intended merely to aid in understanding the background of the present disclosure and therefore should not be interpreted to admit that the present disclosure falls within the purview of the related art that is already known to those skilled in the art. 
     SUMMARY 
     The present disclosure provides a solution to the problems occurring in the related art. That is, an objective of the present disclosure is to provide a method of manufacturing a lithium ion secondary battery, the method being capable of preventing gas occurring during a battery finishing step from flowing back into an electrode assembly by removing the gas in real time. Another objective of the present invention is to provide a lithium ion secondary battery manufactured through the method. 
     In order to accomplish one objective of the present disclosure, according to one aspect of the present disclosure, there is provided a lithium ion secondary battery manufacturing system including: a chamber configured to contain a lithium ion secondary battery; a charging/discharging device configured to charge and discharge the lithium ion secondary battery contained in the chamber; a pressure plate provided in the chamber and configured to press the lithium ion secondary battery when the lithium ion secondary battery is electrically charged; a pointed portion provided in the chamber and configured to bore a hole in a pouch of the lithium ion secondary battery to enable gas generated during the electrical charging to be removed from the pouch when the pressure plate presses the lithium ion secondary battery; and a sealer configured to seal the pouch after the gas is removed. 
     The system may further include at least one of the following: a temperature control device provided in the chamber and configured to adjust an internal temperature of the chamber; multiple drive devices configured to drive the pressure plate, the pointed portion, and the sealer, respectively; a pump configured to create a vacuum pressure in the chamber; and a controller for controlling operation of the drive devices, the temperature control device, and the pump. 
     When the lithium ion secondary battery is electrically charged by the charging/discharging device, the controller may operate the pressure plate to press the lithium ion secondary battery, operate the temperature control device to raise or lower the internal temperature of the chamber, and operate the pointed portion to bore the hole in the pouch of the lithium ion secondary battery to enable the gas to be discharged out of the pouch in real time. 
     When the lithium ion secondary battery is electrically charged, the controller may operate the pressure plate to press the lithium ion secondary battery and operate the temperature control device to adjust the internal temperature of the chamber to be within a range of 0° to 80° C. 
     The controller may operate the pressure plate to apply a pressing force of 0 Kgf/cm 2  to 10 Kgf/cm 2  to the lithium ion secondary battery when the lithium ion secondary battery is electrically charged. 
     The controller may operate the pressure plate during the electrical charging or discharging of the lithium ion secondary battery so that the gas generated during the electrical charge and discharge can be removed. 
     The controller may operate the pressure plate immediately after the lithium ion secondary battery is electrically charged or discharged so that the gas generated during the electrical charging or discharging can be removed. 
     According to another aspect of the present disclosure, there is provided a method of manufacturing a lithium ion secondary battery, the method including: putting a lithium ion secondary battery into a chamber; pressing the lithium ion secondary battery by driving a pressure plate when the lithium ion secondary battery is electrically charged; and removing gas generated during the electrical charging of the lithium ion secondary battery by driving a pointed portion to bore a hole in a pouch of the lithium ion secondary battery. 
     The method may further include: operating a pump to create a vacuum pressure in the chamber before the removing of the gas. 
     During the pressing of the lithium ion secondary battery, a temperature control device may be operated to adjust an internal temperature of the chamber to be within a range of 0° to 80° C. 
     During the pressing of the lithium ion secondary battery, a pressing force of 0 Kgf/cm 2  to 10 Kgf/cm 2  may be applied to the lithium ion secondary battery. 
     With the use of the lithium ion secondary battery manufacturing system according to the present disclosure, when a lithium ion secondary battery is electrically charged, the pressure plate is driven to press the lithium ion secondary battery and the pointed portion is driven to bore a hole in the pouch of the lithium ion secondary battery so that gas generated during the electrical charging of the lithium ion secondary battery can be discharged to the outside of the pouch in real time. Therefore, it is possible to reduce time for initial charging of the lithium ion secondary battery and time for forming the lithium ion secondary battery, resulting improvement in the overall production productivity and efficiency of lithium ion secondary batteries. 
     The charging temperature at which the lithium ion secondary battery is electrically charged can be controlled with the temperature control device provided in the chamber. The resistance of the lithium ion secondary battery decreases as the charging temperature decreases. In the case of designing batteries that are for use in the field where safety is important, high-temperature charging may be selected to increase the battery cell resistance. On the other hand, in the case of designing batteries of which output power is important, low-temperature charging may be selected. That is, the battery cell resistance is adjusted according to the battery specifications required. 
     In addition, when the lithium ion secondary battery is electrically charged, the pressure plate is driven to press the lithium ion secondary battery and the pointed portion is driven to bore a hole in the pouch of the lithium ion secondary battery. In this way, the gas generated during the electrical charging of the lithium ion secondary battery can be removed from the pouch in real time. Therefore, it is possible to prevent the back flow of toxic gas into the electrode assembly in the lithium ion secondary battery, thereby preventing the capacity reduction attributable to side reactions (side effects) during the electrical charging or discharging of the lithium ion secondary battery and improving the practical service life of the lithium ion secondary battery. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a view illustrating a state in which degassed gas flows back into an electrode assembly during a battery formation process according to a conventional art; 
         FIG. 2  is a view illustrating the overall construction of a lithium ion secondary battery manufacturing system according to one embodiment of the present disclosure; 
         FIG. 3  is a cross-sectional view of an electrode assembly of a lithium ion secondary battery that is finished/packaged by using the manufacturing system according to one embodiment of the present disclosure; 
         FIG. 4  is a flowchart illustrating a method of manufacturing a lithium ion secondary battery according to one embodiment of the present disclosure; 
         FIG. 5  is a diagram illustrating efficiencies of a conventional formation process, a conventional pressure formation process, and a formation process according to one embodiment of the present disclosure; and 
         FIG. 6  is a diagram illustrating lifespans of lithium ion secondary batteries manufactured through the conventional formation process and the finishing process according to the present disclosure, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. Prior to giving the following detailed description of the present disclosure, it should be noted that the terms and words used in the specification and the claims should not be construed as being limited to ordinary meanings or dictionary definitions but should be construed in a sense and concept consistent with the technical idea of the present disclosure, on the basis that the inventor can properly define the concept of a term to describe its invention in the best way possible. 
     The exemplary embodiments described herein and the configurations illustrated in the drawings are presented for illustrative purposes and do not exhaustively represent the technical spirit of the present invention. Accordingly, it should be appreciated that there will be various equivalents and modifications that can replace the exemplary embodiments and the configurations at the time at which the present application is filed. 
       FIG. 2  is a view illustrating the overall construction of a lithium ion secondary battery manufacturing system according to one embodiment of the present disclosure. Referring to  FIG. 2 , a lithium ion secondary battery manufacturing system according to an exemplary embodiment of the present disclosure includes a chamber  100 , a charging/discharging device  200 , a pressure plate  300 , a pointed portion  400 , and a sealer  500 . The system may further include at least one device selected from among a temperature control device  600 , multiple driving devices  700 , a pump  800 , and a controller  900 . 
     Specifically, the chamber  100  has an accommodation space in which a lithium ion secondary battery  10  can be accommodated. The chamber  100  can block external air and can degas internal gas during electrical charging or discharging of the lithium ion secondary battery  10  contained in the chamber. 
     Although not illustrated in detail in the drawings, the chamber  100  may be provided with a connector (not illustrated) to be connected with the charging/discharging  200  and the pump  800 . 
     The charging/discharging device  200  serves to electrically charge and discharge the lithium ion secondary battery  10  contained in the chamber  100 . According to an embodiment of the present disclosure, the charging/discharging device  200  is provided in the chamber  100 . According to another embodiment of the present disclosure, the charging/discharging device  200  may be provided outside the chamber  100 . In this case, the charging/discharging device  200  may be connected to an electrode tab of the lithium ion secondary battery  10  via the connector (not illustrated) so that the lithium ion secondary battery  10  can be electrically charged and discharged. 
     The pressure plate  300  provided in the chamber  100  serves to press the lithium ion secondary battery  10  when the lithium ion secondary battery  10  is electrically charged. The area of the pressure plate  300  is preferably larger than the area of the lithium ion secondary battery  10 . The pressure plate  300  needs to be small enough not to interfere with the operations of the pointed portion  400  and the sealer  500 . The configuration in which the area of the pressure plate  300  is larger than the area of the lithium ion secondary battery  10  is required to apply the uniform pressing force to the lithium ion secondary battery  10 . 
     The pointed portion  400  is disposed in the chamber  100  and is driven to bore a hole in the pouch of the lithium ion secondary battery  10  when the lithium ion secondary battery  10  is pressed by the pressure plate  300 , thereby enabling the gas generated during the electrical charging of the lithium ion secondary battery to be discharged to the outside of the pouch. Normally, gas is generated during electrical charging or discharging of lithium ion secondary battery cells. Therefore, a lithium ion secondary battery has a gas room provided in the pouch thereof so that the generated gas can be collected in the gas room. The pointed portion  400  is disposed in the chamber  100  and is specifically disposed at a position corresponding to the gas room. Thus, when the pointed portion  400  is driven, the pouch is bored at the position where the gas room is provided so that the gas generated during the electrical charging can be removed from the electrode assembly through the hole. 
     The shape of the pointed portion  400  is not limited to a specific shape. The pointed portion  400  can have any shape if the pointed portion  400  can bore a hole in the pouch of the lithium ion secondary battery so that the gas during the electrical charging can be discharged to the outside of the pouch. 
     The sealer  500  blocks external air from being introduced into the pouch by sealing the pouch of the lithium ion secondary battery bored by the pointed portion  400  after the gas is discharged from the pouch. 
     The temperature control device  600  is disposed in the chamber  100  and serves to adjust the internal temperature of the chamber  100 . In the lithium ion secondary battery manufacturing system according to the present disclosure, the temperature control device raises the temperature of the lithium ion secondary battery contained in the chamber by using heat radiation or convection. 
     A conventional pressure plate for pressing a lithium ion secondary battery is provided with heating wires buried therein. Thus, the temperature of a lithium ion secondary battery is increased and decreased in a conductive manner using the heating wires. However, in conventional cases, the heat of the heating wires is conducted only in a direction of thickness of a lithium ion secondary battery cell. Therefore, the flank surfaces of the lithium ion secondary battery cell easily experience heat loss, resulting in a temperature imbalance between the center of the cell and the flank surfaces of the cell. This causes a problem that the ionic conductivity is uneven and the adhesion between the separator and the electrode is uneven. 
     To solve this problem, the present disclosure uses the temperature control device  600  to uniformly raise and lower the temperature of the lithium ion secondary battery contained in the chamber through heat radiation or convection, thereby attaining the advantages of uniform ion conductivity across the entire area of the lithium ion secondary battery cell during electrical charging and discharging and of uniform adhesion between the separator and the electrode. 
     On the other hand, according to an exemplary embodiment of the present disclosure, the temperature control device  600  can be installed on or above the chamber  100 . However, such an arrangement is only one example. The installation position of the temperature control device  600  is not particularly limited. The temperature control device  600  can be installed at any place if it can operate to increase or decrease the temperature of the air in the chamber  100  so that the lithium ion secondary battery  10  can be evenly heated when the lithium ion secondary battery is pressed by the pressure plate  300 . 
     The multiple drive devices  700  serve to drive the pressure plate  300 , the pointed portion  400 , and the sealer  500 . In other words, according to an exemplary embodiment of the present disclosure, the lithium ion secondary battery manufacturing system includes multiple drive devices for driving the pressure plate  300 , the pointed portion  400 , and the sealer  500 , respectively. Depending on embodiment, the drive device may be motors. 
     The pump  800  serves to purging the inside of the chamber  100 , thereby creating a vacuum pressure in the chamber  100 . In an exemplary embodiment of the present disclosure, when the pump  800  is driven to create a vacuum pressure in the chamber  100 , the pouch of the lithium ion secondary battery is bored by the pointed portion  400  so that the gas collected in the gas room provided in the pouch can be discharged to the outside of the pouch. 
     The controller  900  controls the operations of the charging/discharging device  200 , the temperature control device  600 , the driver device  700 , and the pump  800 . Specifically, when the lithium ion secondary battery  10  is electrically charged by the charging/discharging device  200 , the controller  900  controls the operation of the pressure plate  300  such that the lithium ion secondary battery is pressed by the pressure plate  300 , controls the operation of the temperature control device  600  such that the internal temperature of the chamber  100  is raised or lowered, and controls the operation of the pointed portion  400  such that a hole is bored in the pouch of the lithium ion secondary battery so that the gas generated during the electrical charging of the lithium ion secondary battery can be removed in real time. 
     In detail, when the lithium ion secondary battery is electrically charged, the controller  900  controls the operation of the pressure plate  300  such that the lithium ion secondary battery is pressed. At this time, the pressure plate  300  presses the lithium ion secondary battery with a pressing force of 0 Kgf/cm 2  to 10 Kgf/cm 2 . 
     In addition, when the lithium ion secondary battery  10  is electrically charged by the charging/discharging device, the controller  900  controls the operation of the pressure plate such that the lithium ion secondary battery is pressed and controls the operation of the temperature control device  600  such that the internal temperature of the chamber is adjusted to be within a range of 0° to 80° C. Depending on embodiment, when the lithium ion secondary battery  10  is electrically charged by the charging/discharging device, the controller  900  controls the operation of the pressure plate such that the lithium ion secondary battery is pressed and controls the operation of the temperature control device  600  such that the internal temperature of the chamber is adjusted to be 60° C. However, 60° is only an exemplary temperature, and the internal temperature which is to be reached may be determined according to the pressing force applied to the lithium ion secondary battery and other conditions including the resistance, output power, capacity, and the like of the lithium ion secondary battery. 
     According to an embodiment of the present disclosure, the controller  900  may drive the pressure plate during electrical charging/discharging of the lithium ion secondary battery so that the gas generated during the electrical charging/discharging can be discharged to the outside of the pouch. According to another embodiment, the controller  900  may drive the pressure plate immediately after the electrical charging/discharging of the lithium ion secondary battery is finished so that the gas generated during the electrical charging/discharging can be discharged to the outside of the pouch. 
       FIG. 3  is a cross-sectional view of an electrode assembly of a lithium ion secondary battery which is finished/packaged by using a lithium ion secondary battery manufacturing system according to one embodiment of the present disclosure.  FIG. 3  shows a cathode  11 , an anode  12 , and a separation membrane  13 . Referring to  FIG. 3 , with the use of the lithium ion secondary battery manufacturing system according to an embodiment of the present disclosure, when the lithium ion secondary battery is electrically charged, the pressure plate is driven to press the lithium ion secondary battery and the pointed portion is driven to bore a hole in the pouch of the lithium ion secondary battery so that gas generated during the electrical charging of the lithium ion secondary battery can be discharged to the outside of the pouch in real time. Therefore, it is possible to reduce the time for the first charging performed for activation of the lithium ion secondary battery and the time for formation the lithium ion secondary battery, resulting improvement in the overall production productivity and efficiency of the lithium ion secondary battery. 
       FIG. 4  is a flowchart illustrating a method of manufacturing a lithium ion secondary battery according to one embodiment of the present disclosure. Referring to  FIG. 4 , the method of manufacturing a lithium ion secondary battery, according to an embodiment of the present disclosure, includes: Step S 100  of putting a lithium ion secondary battery into a chamber; Step S 200  of pressing the lithium ion secondary battery by driving a pressure plate when the lithium ion secondary battery is electrically charged; Step S 300  of discharging gas generated during the electrical charging of the lithium ion secondary battery by boring a hole in a portion of the pouch of the lithium ion secondary battery by driving a pointed portion. 
     Before the boring of the hole in the pouch of the lithium ion secondary battery, a step of creating a vacuum pressure in the chamber may be performed by driving a pump. 
     When the lithium ion secondary battery is electrically charged, at the step of driving the pressure plate to press the lithium ion secondary battery, a temperature control device is operated to adjust an internal temperature of the chamber to be within a range of 0° to 80° C. According to one embodiment, when the lithium ion secondary battery is electrically charged, at the step of driving the pressure plate to press the lithium ion secondary battery, the temperature control device is operated to adjust the internal temperature of the chamber to be 60° C. However, 60° is only an exemplary temperature, and the internal temperature which is to be reached may be determined according to the pressing force applied to the lithium ion secondary battery and other conditions such as the capacity of the lithium ion secondary battery. 
     When the lithium ion secondary battery is electrically charged, at the step of driving the pressure plate to press the lithium ion secondary battery, a pressing force of 0 Kgf/cm 2  to 10 Kgf/cm 2  is applied to the lithium ion secondary battery. 
       FIG. 5  is a diagram illustrating the efficiency of a conventional formation process, the efficiency of a conventional formation process, and the efficiency of a pressure formation process according to one exemplary embodiment of the present disclosure, and  FIG. 6  is a diagram illustrating comparison between the lifespan of a lithium ion secondary battery manufactured through the conventional formation process and the lifespan of a lithium ion secondary battery manufactured through the pressure formation process according to one embodiment of the present disclosure. 
     Referring to  FIG. 5 , with the use of a lithium ion secondary battery manufacturing system according to one embodiment of the present disclosure, when a lithium ion secondary battery is electrically charged, a pressure plate is driven to press the lithium ion secondary battery and a pointed portion is driven to bore a hole in the pouch of the lithium ion secondary battery so that gas generated during the electrical charging of the lithium ion secondary battery is discharged to the outside of the pouch in real time. Therefore, it is possible to reduce the time for the first charging of the lithium ion secondary battery and the time for formation the lithium ion secondary battery, resulting improvement in the overall production productivity and efficiency of lithium ion secondary batteries. 
     In addition, referring to  FIG. 6 , with the use of a lithium ion secondary battery manufacturing system according to an embodiment of the present disclosure, when a lithium ion secondary battery is electrically charged, a pressure plate is driven to press the lithium ion secondary battery and a pointed portion is driven to bore a hole in the pouch of the lithium ion secondary battery. In this way, the gas generated during the electrical charging of the lithium ion secondary battery can be removed from the pouch in real time. Therefore, it is possible to prevent the back flow of toxic gas into an electrode assembly of the lithium ion secondary battery, thereby preventing the capacity reduction attributable to side reactions (i.e., side effects) during the electrical charging and discharging of the lithium ion secondary battery, resulting in improvement in the practical service life of the lithium ion secondary battery. In particular, under the condition in which a pressing force of  0  to 10 Kgf/cm 2  is applied to the lithium ion secondary battery, it is possible to ensure a longer service life than comparative examples. When the pressing force is excessively large, there is a risk that electrolyte held in an electrode or a separator oozes out of the electrode or the separator, thereby shortening the service life of the lithium ion secondary battery. Therefore, the pressing force applied to the lithium ion secondary battery is preferably not stronger than 10 Kgf/cm 2 . 
     Referring to  FIG. 6 , the DC cell resistance decreases with decreasing temperature at which the pressure formation is performed. Conversely, the higher the temperature, the higher the DC cell resistance. This is because the properties of a passivation film change with temperature. Since the DC cell resistance has a negative correlation with the output power, the cell resistance is adjusted by varying the temperature at which the formation process is performed according to the specifications of the battery. However, since the DC-IR rapidly increases and there is concern that side reactions occur at a temperature of 85° C., the temperature is preferably set to be lower than 85°. 
     While the disclosure has been described with reference to the accompanying drawings and the preferred embodiments described above, the disclosure is not limited thereto, but is defined by the claims. Accordingly, those skilled in the art may variously change and modify the present disclosure without departing from the technical spirit of the appended claims.