Fatigue testing apparatus for metal foils and method of using the same

Abstract

The present invention relates to a fatigue test apparatus for a metal foil and a fatigue test method for a metal foil using the same, wherein the fatigue test apparatus for a metal foil includes a metal foil driving unit including an unwinding roller from which the metal foil is unwound, a plurality of guide rollers for supporting and transferring the metal foil supplied from the unwinding roller, a rewinding roller on which the metal foil transferred from the guide rollers is wound, and a tensile strength measuring unit for measuring a tensile strength of the metal foil.

Description

TECHNICAL FIELD

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2020-0076337, filed on June 23, 2020, and the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a metal foil fatigue test apparatus and a metal foil fatigue test method using the same. BACKGROUND

[0003] As technology for mobile devices develops and demand for mobile devices increases, demand for secondary batteries as energy sources has rapidly increased. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] In recent years, there has been increasing interest in environmental issues, and as a result, recently, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil fuel vehicles such as gasoline vehicles and diesel vehicles, have been widely researched. Although nickel-metal hydride (Ni-MH) secondary batteries are mainly used as power sources for such electric vehicles (EVs) and hybrid electric vehicles (HEVs), research on the use of lithium secondary batteries having high energy density, high discharge voltage, and output stability has been actively conducted, and some lithium secondary batteries have been commercialized.

[0005] A lithium secondary battery has a structure in which an electrode assembly of a positive electrode / separator / negative electrode is embedded together with an electrolyte in a sealed container. To manufacture a positive electrode or a negative electrode, an electrode mixture including an electrode active material is coated on an electrode current collector made of a long metal foil in one direction.

[0006] At this time, in most processes for manufacturing an electrode such as a roll pressing process, a slitting process, a slotting process, a lamination process, and a folding process, a roll-to-roll process is used. The "roll-to-roll process" means a system in which various processes are sequentially performed as a web made of a material having a width and a transmission length greater than its thickness passes through a plurality of rollers. In the roll-to-roll process, several bendable metal foils or the like can move between a plurality of rollers, during which coating, printing, or the like can be performed. The roll-to-roll process has advantages in terms of efficiency, storage space, and convenience of high-speed operation, etc.

[0007] Figure 1 is a schematic diagram showing a form of a metal foil moving apparatus used in a roll-to-roll process.

[0008] REFERENCE Figure 1, the metal foil moving device includes an unwinding roller, a guide roller, and a winding roller. In a state in which the metal foil has been wound on the unwinding roller, one end of the metal foil is transferred toward the guide roller. The metal foil is transferred by rotation of each roller in a state of being supported by the guide roller, and is wound on the winding roller after being subjected to necessary processes during the transfer process.

[0009] Similarly, when a substrate such as a metal foil is repeatedly transferred on the rollers, the degree of fatigue of the metal foil is increased due to the tension applied between the rollers and the stress applied when the metal foil is wound by the rollers. If this phenomenon occurs, a crack or a breakage phenomenon can occur in the metal foil, which causes a defect in a product.

[0010] Therefore, there is a need to appropriately set the moving conditions of a metal foil during a roll-to-roll process, and there is a need to develop an accurate evaluation method for setting such moving conditions. SUMMARY

[0011] TECHNICAL PROBLEM

[0012] An object of the present application is to provide a metal foil fatigue test apparatus capable of measuring the degree of fatigue of a metal foil according to the movement of the metal foil and predicting the life of the metal foil, and a metal foil fatigue test method using the apparatus, the metal foil being used as a substrate in a roll-to-roll process.

[0013] TECHNICAL SOLUTION

[0014] The apparatus for testing fatigue of a metal foil according to the present application includes a metal foil moving unit including an unwinding roller from which a metal foil is unwound, a plurality of guide rollers configured to support and transfer the metal foil supplied from the unwinding roller, and a rewinding roller on which the metal foil transferred from the guide rollers is wound, and a tensile strength measuring unit configured to measure the tensile strength of the metal foil.

[0015] In an embodiment of the present application, the metal foil fatigue test apparatus further includes a controller unit configured to set and change the moving conditions of the metal foil, and a storage unit configured to store the measurement results of the tensile strength.

[0016] In one embodiment of the present application, the metal foil fatigue test apparatus further includes a breakage detection unit configured to detect whether the metal foil has been broken.

[0017] In one embodiment of the present application, the breakage detection unit can be located on a moving path of the metal foil.

[0018] Further, the present application provides a metal foil fatigue test method using a metal foil fatigue test apparatus. The metal foil fatigue test method includes the steps of mounting a metal foil on a metal foil moving unit of the metal foil fatigue test apparatus, repeatedly moving the metal foil in a forward direction and a reverse direction between an unwinding roller and a rewinding roller, and measuring a tensile strength of the metal foil repeatedly moved.

[0019] In one embodiment of the present application, the metal foil can be made of aluminum or copper.

[0020] In one embodiment of the present application, the metal foil fatigue test method can further include the step of setting a moving condition of the metal foil.

[0021] Here, the moving condition of the metal foil can include one or more of a winding direction of the metal foil, a winding number of the metal foil, a tensile force applied to the metal foil, and a moving speed of the metal foil.

[0022] In one embodiment of the present application, the step of setting the moving condition of the metal foil can be performed before the step of repeatedly moving the metal foil.

[0023] In another embodiment of the present application, the step of setting the moving condition of the metal foil can be performed during the step of repeatedly moving the metal foil.

[0024] In another embodiment of the present application, the metal foil fatigue test method can further include the steps of measuring a tensile strength of the metal foil before moving, and calculating a change in the tensile strength according to the moving condition of the metal foil before and after moving.

[0025] In another embodiment of the present application, the metal foil fatigue test method can further include the step of storing the moving condition of the metal foil and the tensile strength of the metal foil according to the moving condition.

[0026] In another embodiment of the present application, the metal foil fatigue test method can further include the step of detecting whether a break has occurred in the metal foil.

[0027] Here, the step of detecting whether a break has occurred can be performed during or after the moving step.

[0028] Advantageous Effects

[0029] According to the metal foil fatigue test apparatus and the metal foil fatigue test method of the present application, a fatigue degree and a life of a metal can be predicted by appropriately setting a moving condition of the metal foil in a roll-to-roll process and simulating a movement of the metal foil accordingly.

[0030] Further, by storing the degree of fatigue of the metal foil according to the moving conditions of the metal foil in a database, the conditions can be appropriately set in an actual roll-to-roll process, and the defects of the metal foil in the roll-to-roll process can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram showing a form of a metal foil moving apparatus used in a roll-to-roll process.

[0032] Figure 2 is a block diagram showing each component of a metal foil fatigue test apparatus according to the present application.

[0033] Figure 3 is a schematic diagram showing a configuration of a metal foil moving unit in a metal foil fatigue test apparatus according to the present application.

[0034] Figure 4 is a flowchart showing a metal foil fatigue test method according to one embodiment of the present application.

[0035] Figure 5 is a flowchart showing a metal foil fatigue test method according to another embodiment of the present application.

[0036] Figure 6 is a flowchart showing a metal foil fatigue test method according to still another embodiment of the present application. DETAILED DESCRIPTION

[0037] Hereinafter, the present application will be described in detail with reference to the accompanying drawings. The terms and words used in the present specification and claims should not be interpreted as being limited to the commonly- used meanings and meanings in dictionaries, but should be interpreted based on the concept and ideas of the present application from the technical idea of the present application. The terms and words should be interpreted as having meanings and concepts consistent with the technical idea of the present application.

[0038] In this application, it should be understood that terms such as "include" or "has" are intended to indicate that there are the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and these terms do not preclude the possibility that one or more other features, numbers, steps, operations, components, parts, or combinations thereof will be added. Also, when a portion such as a layer, film, region, plate, etc. is referred to as being "on" another portion, this includes not only the case where the portion is "directly" on the other portion, but also the case where another portion is interposed therebetween. In another aspect, when a portion such as a layer, film, region, plate, etc. is referred to as being "under" another portion, this includes not only the case where the portion is "directly" under the other portion, but also the case where another portion is interposed therebetween. In addition, "placed on" in this application can include the case of being placed at the bottom as well as the top.

[0039] Hereinafter, the present application will be described in detail with reference to the accompanying drawings.

[0040] Figure 2 is a block diagram illustrating each component of a metal foil fatigue test apparatus according to the present application.

[0041] Referring to Figure 2 The metal foil fatigue test apparatus 100 according to the present application includes a metal foil moving unit 110 and a tensile strength measuring unit 120.

[0042] As described above, in a roll-to-roll process, when a substrate such as a metal foil is repeatedly transferred on a roller, the fatigue degree of the metal foil is increased due to stress received between the rollers and stress received when the metal foil is wound and unwound. If this phenomenon occurs, a crack or a breakage phenomenon can occur in the metal foil, which causes a product defect.

[0043] Thus, in order to predict the fatigue degree and life of a metal foil, the inventors of the present application have designed a metal foil fatigue test apparatus for easily identifying the fatigue degree and life of a metal foil due to repeated movement of the metal foil by repeatedly moving the metal foil while applying a specific stress on a metal foil moving unit simulating a roll-to-roll device, and then measuring the tensile strength of the metal foil.

[0044] Figure 3 is a schematic view illustrating a configuration of the metal foil moving unit 110 in the metal foil fatigue test apparatus according to the present application.

[0045] Referring to Figure 3In the metal foil fatigue test apparatus, the metal foil moving unit 110 is implemented to accurately simulate the movement of a roller moving in an actual roll-to-roll process. Specifically, the metal foil moving unit 110 includes an unwinding roller 111 on which the metal foil 114 is unwound, a plurality of guide rollers 112 for supporting and transferring the metal foil 114 supplied from the unwinding roller 111, and a rewinding roller 113 on which the metal foil transferred from the guide rollers 112 is wound. This simulates the configuration of the apparatus in the actual roll-to-roll process. The metal foil 114 is repeatedly transferred in a forward direction and a reverse direction, and is repeatedly wound and unwound on the unwinding roller 111 and the rewinding roller 113. The forward direction means a direction (A direction) moving from the unwinding roller 111 to the rewinding roller 113, and the reverse direction means a direction (B direction) moving from the rewinding roller 113 to the unwinding roller 111. At least one guide roller 112 is located between the unwinding roller 111 and the rewinding roller 113, thereby preventing the metal foil from being bent in the direction of gravity and transferring the metal foil.

[0046] According to the metal foil fatigue test apparatus of the present application, by appropriately setting the movement conditions of the metal foil moving on the metal foil moving unit, conditions in which the fatigue degree of the metal foil is likely to increase, or conditions in which the metal foil is broken during the movement of the metal foil, can be identified, thereby enabling the fatigue degree and the life of the metal foil to be predicted according to the movement.

[0047] The tensile strength measuring unit 120 measures the tensile strength of the metal foil repeatedly moved in the metal foil moving unit 110. The tensile strength measuring unit 120 can be provided separately from the metal foil moving unit 110. In this case, the metal foil which has stopped moving in the metal foil moving unit 110 can thereby be taken out and transferred to the tensile strength measuring unit 120, and the tensile strength can be measured.

[0048] To this end, the metal foil fatigue test apparatus 100 can further include a controller unit 130 for setting and changing the movement conditions of the metal foil. The controller unit 130 can input the conditions of the movement fatigue test, and receive the input of the test results.

[0049] Specifically, the controller unit 130 can include an input tool (not shown) for inputting information of the metal foil to be a subject of the fatigue test, and the controller unit can receive input of the information of the metal foil to be a subject of the fatigue test therefrom. For example, the information about the metal foil can include information such as a type of the metal foil, a tensile strength, and a hardness. In particular, the tensile strength of the metal foil is a tensile strength of the metal foil moving device before the metal foil is repeatedly moved. This can be compared with the tensile strength of the metal foil after the metal foil is repeatedly moved, and then this can be used as a criterion for determining an increase in the degree of fatigue of the metal foil after the metal foil is moved.

[0050] Further, the controller unit 130 can set a moving condition of the metal foil, and input the moving condition to the metal foil moving unit. Here, the moving condition of the metal foil can include one or more of a winding direction of the metal foil, a winding number of the metal foil, a tensile force applied to the metal foil, and a moving speed of the metal foil. Further, the controller unit can adjust a direction in which stress is applied to the metal foil by adjusting a position of each roller constituting the metal foil moving unit 110. The controller unit 130 can control the metal foil moving unit 110 to operate according to a preset moving condition.

[0051] Further, the controller unit 130 can include a receiving tool (not shown) configured to receive input of a result of the moving fatigue test. When the fatigue test is completed, the controller unit 130 can receive input of the result of the fatigue test, and transmit information to the storage unit.

[0052] The storage unit 140 receives the test result, specifically, a measurement result of the tensile strength, from the controller unit 130, and stores the result. The storage unit 140 can store the measurement result of the tensile strength, and generate a database using the result information. Specifically, a type of the metal foil can be classified according to a material, a thickness, and a hardness of the metal foil, and a measurement result of the tensile strength for each moving condition can be displayed through a table or a line graph. When various moving conditions are combined, such measurement data can be used as a basis for predicting a degree of fatigue and a lifespan of the metal foil.

[0053] Here, the user can directly operate the controller unit 130 and the storage unit 140, but the controller unit 130 and the storage unit 140 can also be operated by an automated system. For example, when a moving condition is input to the controller unit 130, the metal foil moving unit 110 operates with the predetermined moving condition, when completed, the metal foil is transferred to the tensile strength measuring unit 120 to thereby measure the tensile strength. The result can be received again by the controller unit 130 and stored in the storage unit 140. When this process is completed, the controller unit 130 can automatically change the moving condition to repeat the same process.

[0054] Meanwhile, when the metal foil repeatedly moves on the metal foil moving unit 110, if stress applied to the metal foil is severe, this can cause the metal foil to be broken. Such a breaking phenomenon can be checked by a crack or the like generated on the metal foil. The present invention can provide a breaking detection unit 150 for detecting whether the metal foil has been broken to thereby identify under what condition the metal foil has been broken.

[0055] Referring to Figure 3 , the breaking detection unit 150 can be located on a moving path of the metal foil 114. In other words, the breaking detection unit 150 can be located at an upper portion or a lower portion of the metal foil 114 repeatedly moving on the moving path, and can detect the breaking of the metal foil 114 in real time. Further, at least one breaking detection unit 150 can be located on the moving path of the metal foil. Referring to Figure 3 , the breaking detection unit 150 is located on the moving path between the guide rollers 112, but the breaking detection unit 150 can also be located on the moving path between the unwinding roller 111 and the guide roller 112 or between the guide roller 112 and the rewinding roller 113.

[0056] Meanwhile, in the breaking detection unit 150, breaking detection can be performed using a known method. For example, breaking detection can be performed using a camera, an ultrasonic wave, or an eddy current detection scheme.

[0057] In the case of using an imaging camera, a crack generated in the metal foil moving between the rollers can be directly photographed and detected. In the case of using an ultrasonic wave detection method, an ultrasonic wave is oscillated to the metal foil, and a wave returned through a reflection phenomenon is sensed, thereby detecting whether breaking has occurred through signal processing. The eddy current detection scheme is a scheme of detecting breaking through an eddy current generated in the metal foil when a coil allowing alternating current to flow is allowed to approach the metal foil. Such a detection method is known to those skilled in the art, and thus a detailed description thereof will be omitted here.

[0058] Further, the present application provides a method for testing fatigue of a metal foil using the metal foil fatigue testing apparatus described above.

[0059] Figure 4 is a flowchart illustrating a metal foil fatigue testing method according to an embodiment of the present application.

[0060] Referring to Figure 4 The metal foil fatigue testing method according to the embodiment of the present application includes the steps of installing a metal foil on a metal foil moving unit of the metal foil fatigue testing apparatus (S10), repeatedly moving the metal foil in a forward direction and a reverse direction between an unwinding roller and a rewinding roller (S20), and measuring tensile strength of the metal foil after the repeated movement (S30).

[0061] In the step of installing the metal foil (S10), the metal foil is placed on a moving path, and both sides of the metal foil are wound on the unwinding roller and the rewinding roller, respectively. At this time, the number of winding can be appropriately set according to a moving condition of the metal foil.

[0062] In the step of repeatedly moving the metal foil (S20), the metal foil is repeatedly moved in the forward direction and the reverse direction under a predetermined moving condition. As described above, the forward direction means a direction (A direction) of moving from the unwinding roller to the rewinding roller, and the reverse direction means a direction (B direction) of moving from the rewinding roller to the unwinding roller.

[0063] In the tensile strength measuring step (S30), the tensile strength is measured with respect to a predetermined point of the repeated movement measuring step. The tensile strength of the metal foil can be measured according to a generally known method. For example, a tensile force is applied to both sides of a portion to be measured in the metal foil, and a force applied to the metal foil when a fracture occurs can be measured. At this time, a value obtained by dividing a maximum tensile load measured at this time by a cross-sectional area of the metal foil can be defined as the tensile strength. In this way, the method of measuring the tensile strength is known to those of ordinary skill in the art, and thus a detailed description thereof will be omitted here.

[0064] When the tensile strength measuring step (S30) is completed, by returning to the step of installing the metal foil (S10), a new metal foil can be installed on the metal foil installation portion, thereby performing a test under a new moving condition.

[0065] In an embodiment of the present application, the material of the metal foil is not particularly limited, but aluminum or copper mainly used as an electrode current collector in a lithium secondary battery can be used.

[0066] Further, the metal foil fatigue test method according to the present application includes a step (S15) of setting a moving condition of the metal foil. The metal foil fatigue test method according to the present application can easily identify the degree of fatigue and the life of the metal foil due to repeated movement of the metal foil by simulating movement of the metal foil under various environments and conditions that the metal foil can face in an actual roll-to-roll process.

[0067] For example, the moving condition of the metal foil can include one or more of a winding direction of the metal foil, a winding number of the metal foil, a tension applied to the metal foil, and a moving speed of the metal foil.

[0068] Here, the winding direction of the metal foil means a direction in which the metal foil is moved, and the metal foil can be wound in a forward direction or a reverse direction. The winding number means the number of times the metal foil is moved in the forward direction and the reverse direction. At this time, the metal foil can be set to be completely wound on the unwinding roller or the rewinding roller by one movement. Further, for example, the metal foil can be moved again in the opposite direction in a state in which the metal foil has been partially wound on the unwinding roller or the rewinding roller.

[0069] Next, the tension applied to the metal foil means a tension applied to the metal foil in a portion between the unwinding roller and the guide roller, between the guide rollers, or between the guide roller and the rewinding roller. That is, when the tension applied to the metal foil is large, this means that the metal foil has been pulled tightly. For example, the tension applied to the metal foil can be set by adjusting the torque of the rollers.

[0070] The moving speed of the metal foil is the speed at which the metal foil moves between the rollers. The moving speed of the metal foil can be changed, for example, by adjusting the angular velocity of the rollers.

[0071] In addition, the moving condition of the metal foil can be set while appropriately adjusting the number and positions of the guide rollers or the atmospheric environment that the metal foil faces.

[0072] The step (S15) of setting the moving condition of the metal foil can be performed before the step (S20) of repeatedly moving the metal foil. In this case, one moving condition can be set for each metal foil, and when measurement is completed in one moving condition, a new metal foil is installed, and a different moving condition from before can be set.

[0073] Further, the step of setting the moving condition of the metal foil can be performed during the step of repeatedly moving the metal foil (S20). In this case, the moving condition that has been set is changed during the movement of the metal foil. This allows the influence of a change that can occur during the movement of the metal foil to be predicted.

[0074] In a more specific example, the metal foil fatigue test method can further include a step of measuring the tensile strength of the metal foil before movement, and calculating a change in the tensile strength according to the moving condition of the metal foil before and after movement.

[0075] Further, the metal foil fatigue test method can further include a step of storing the moving condition of the metal foil and the tensile strength of the metal foil according to the moving condition.

[0076] Figure 5 is a flowchart illustrating a metal foil fatigue test method according to another embodiment of the present application.

[0077] Referring to Figure 5 , the metal foil fatigue test method can include a step of mounting a metal foil on a metal foil moving unit of the metal foil fatigue test apparatus (S10), a step of setting a moving condition of the metal foil (S15), a step of repeatedly moving the metal foil in a forward direction and a reverse direction between an unwinding roller and a rewinding roller (S20), a step of measuring the tensile strength of the repeatedly moved metal foil (S30), a step of calculating a change in the tensile strength according to the moving condition of the metal foil before and after movement (S40), and a step of storing the moving condition of the metal foil and the tensile strength of the metal foil according to the moving condition (S50).

[0078] In this case, when the storing step (S50) is terminated, a test can be performed on a new metal foil under a new moving condition by returning to the first step.

[0079] Meanwhile, the step of measuring the tensile strength of the metal foil before movement can be performed before the metal foil is mounted on the moving unit. Here, the measured tensile strength data can be pre-stored in a storage unit.

[0080] According to the metal foil fatigue test method according to the present application, the degree of fatigue of a metal can be measured by measuring a change in the tensile strength of the metal foil before and after movement, and the life of the metal foil can be predicted.

[0081] Further, when a database is formed by using the stored moving condition of the metal foil and the tensile strength according to the moving condition to combine various moving conditions, this can be used as a basis for predicting the degree of fatigue and the life of the metal foil.

[0082] Further, the metal foil fatigue test method can further include a step of detecting whether the metal foil has been disconnected.

[0083] Figure 6 is a flowchart illustrating a metal foil fatigue test method according to still another embodiment of the present application.

[0084] Reference Figure 6 , the metal foil fatigue test method can include the steps of mounting a metal foil on a metal foil moving unit of the metal foil fatigue test apparatus (S10), setting a moving condition of the metal foil (S15), repeatedly moving the metal foil in a forward direction and a reverse direction between an unwinding roller and a rewinding roller (S20), detecting whether a disconnection has occurred in the metal foil (S25), measuring a tensile strength of the repeatedly moved metal foil (S30), calculating a change in the tensile strength according to the moving condition of the metal foil before and after the moving (S40), and storing the moving condition of the metal foil and the tensile strength of the metal foil according to the moving condition (S50).

[0085] According to the metal foil fatigue test method of the present application, it is possible to identify under what condition the metal foil is disconnected by detecting whether a disconnection phenomenon such as a crack occurs in the metal foil separately from the measurement of the tensile strength. As described above, the disconnection detection can be performed using a camera, an ultrasonic wave, or an eddy current detection scheme.

[0086] The step of detecting whether a disconnection has occurred (S25) can be performed during the moving step. That is, it is possible to identify at what time point a disconnection occurs under a specific moving condition in real time during the moving of the metal foil.

[0087] Further, the step of detecting whether a disconnection has occurred (S25) can be performed after the moving step. In this case, it is preferable to check whether a disconnection has occurred before measuring the tensile strength.

[0088] The above description merely illustrates the technical idea of the present application, and those skilled in the art to which the present application pertains can make various modifications and changes without departing from the essential characteristics of the present application. Therefore, the drawings disclosed in the present application are not intended to limit the technical idea of the present application but to describe the present application, and the scope of the technical idea of the present application is not limited by these drawings. The scope of protection of the present application should be interpreted by the appended claims, and all technical ideas within the equivalent scope of this should be understood to be included in the scope of the present application.

[0089] In another aspect, in this specification, terms indicating directions such as up, down, left, right, front and rear are used, but it is obvious that these terms are only for convenience of description and can change depending on the position of the object or the position of the observer.

Claims

1. An apparatus for testing fatigue of a metal foil, comprising: a metal foil moving unit including: an unwinding roller from which a metal foil is unwound; a plurality of guide rollers configured to support and transfer the metal foil supplied from the unwinding roller; and a rewinding roller on which the metal foil transferred from the guide rollers is wound; and a tensile strength measuring unit configured to measure a tensile strength of the metal foil repeatedly moved in the metal foil moving unit in a forward direction and a reverse direction, the forward direction being a direction moved from the unwinding roller to the rewinding roller, the reverse direction being a direction moved from the rewinding roller to the unwinding roller.

2. The apparatus according to claim 1, comprising: a controller unit configured to set and change a moving condition of the metal foil; and a storage unit configured to store a measurement result of the tensile strength.

3. The apparatus according to claim 1, further comprising a break detection unit configured to detect whether the metal foil has been broken. The break detection unit is located on a moving path of the metal foil.

4. The apparatus of claim 3, wherein, 5. A method of testing fatigue of a metal foil, the method comprising the steps of: mounting a metal foil on a metal foil moving unit of an apparatus according to any one of claims 1 to 4; repeatedly moving the metal foil between an unwinding roller and a rewinding roller in a forward direction and a reverse direction, the forward direction being a direction moved from the unwinding roller to the rewinding roller, the reverse direction being a direction moved from the rewinding roller to the unwinding roller; and measuring a tensile strength of the metal foil repeatedly moved. The metal foil is made of aluminum or copper.

6. The method of claim 5, wherein, 7. The method according to claim 5, further comprising the step of setting a moving condition of the metal foil. The moving condition of the metal foil includes one or more of a winding direction of the metal foil, a winding number of the metal foil, a tensile force applied to the metal foil, and a moving speed of the metal foil.

8. The method of claim 7, wherein, The step of setting the moving condition of the metal foil is performed before the step of repeatedly moving the metal foil.

9. The method of claim 7, wherein, The step of setting the moving condition of the metal foil is performed during the step of repeatedly moving the metal foil.

10. The method of claim 7, wherein, 11. The method according to claim 7, further comprising the step of measuring a tensile strength of the metal foil before moving, and calculating a change in tensile strength according to the moving condition of the metal foil before and after moving.

12. The method according to claim 11, further comprising the step of storing the moving condition of the metal foil and the tensile strength of the metal foil according to the moving condition.

13. The method according to claim 5, further comprising the step of detecting whether a break has occurred in the metal foil. The step of detecting whether a break has occurred is performed during or after the moving step.

14. The method of claim 13, wherein, ​

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