System and method for fatigue testing of metal foil

Abstract

The present invention relates to a system and method for fatigue testing of metal foil, wherein charging and discharging of an electrode assembly are simulated by injecting gas into a tube having a roll structure and discharging the gas from the tube, thereby easily predicting fatigue and service life of the metal foil according to the charging and discharging.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0076311, filed on June 23, 2020, and the entire contents of which are incorporated herein by reference.

[0002] The invention relates to a metal foil fatigue testing system and a metal foil fatigue testing method. Background Art

[0003] With the technological development and increase in demand for mobile devices, the demand for batteries as energy sources is rapidly increasing, and among such secondary batteries, much research has been conducted on lithium secondary batteries having high energy density and discharge voltage, and they have been commercialized and widely used.

[0004] According to the shape of a battery case, secondary batteries are classified into cylindrical batteries and prismatic batteries in which an electrode assembly is embedded in a cylindrical or prismatic metal, and pouch batteries in which an electrode assembly is embedded in a pouch-shaped case of an aluminum laminate.

[0005] In addition, the electrode assembly embedded in the battery case is a chargeable / dischargeable power generating element composed of a laminated structure of a positive electrode / separator / negative electrode. Representative examples include: a jelly roll type electrode assembly in which a long sheet of positive and negative electrodes is wound with a separator interposed therebetween; a stacked electrode assembly in which a plurality of positive and negative electrodes cut in units of predetermined sizes are sequentially stacked with a separator interposed therebetween; and a stacked / foldable electrode assembly in which a double cell or a full cell is wound, in which a predetermined unit of positive and negative electrodes is stacked with a separator interposed therebetween.

[0006] Among them, the jelly-roll type electrode assembly (hereinafter also referred to as "jelly-roll") is easy to manufacture and has a high energy density per unit weight.

[0007] In this jelly roll, when preparing a battery, a laminate of positive electrode / separator / negative electrode is wound into a circular shape, the outermost end is fixed with a sealing tape, and then housed in a battery case, i.e., a metal can, after which an electrolyte solution is prepared and a top cap is attached where an electrode terminal (e.g., a positive electrode terminal) has been formed on the open top of the battery case.

[0008] However, in a jelly-roll-type electrode assembly, lithium is repeatedly inserted into and desorbed from the negative electrode as charge and discharge cycles repeat, causing the volume of the electrode active material to expand or contract, and fatigue to accumulate in the current collector supporting the electrode active material. In particular, the outer periphery of the jelly-roll exhibits significant changes due to the increased volume accumulated from the interior of the electrode assembly. This significantly increases the stress applied to the exterior of the metal foil. Furthermore, the accumulation of stress and fatigue can exceed the tensile limit of the metal foil, potentially causing it to break or crack.

[0009] Therefore, a technology is needed to determine the life of a metal foil by simulating repeated charge / discharge of a jelly roll and measuring the stress and fatigue of the metal foil. Summary of the Invention

[0010] Technical issues

[0011] The present invention has been designed to solve the above problems, and an object of the present invention is to provide a metal foil fatigue testing system and a metal foil fatigue testing method for simulating repeated charge / discharge of a jelly roll, measuring the degree of fatigue accumulated in the metal foil as stress according to repeated charge / discharge is applied to the metal foil, and predicting the disconnection time point of the metal foil by the measured fatigue degree.

[0012] Technical Solution

[0013] A metal foil fatigue testing system according to the present invention includes: a flat tube laminated on a metal foil; a charge / discharge simulation unit including a gas injector for injecting gas into the tube and a gas discharger for discharging gas from the tube; and a tensile strength measuring unit configured to measure the tensile strength of the metal foil.

[0014] In one example, the metal foil fatigue testing system further includes a winder configured to wind a laminate produced by laminating the tube onto the metal foil into a roll structure.

[0015] In one example, the system further includes: a controller unit configured to set and change simulation conditions of the charge / discharge simulation unit; and a storage unit configured to store a result of measuring the tensile strength.

[0016] At this time, the tube has a flow path formed inside it along a length direction, gas is allowed to be injected and discharged through the flow path, one end of the flow path is closed, and the other end of the flow path is connected to the charge / discharge simulation unit.

[0017] In one example, the width (W1) of the tube corresponds to or is greater than the width (W2) of the metal foil. In a specific example, the length (L1) of the tube corresponds to or is greater than the length (L2) of the metal foil.

[0018] In addition, a method for testing fatigue of a metal foil according to the present invention includes: a winding step of winding a laminate into a roll structure, the laminate being produced by laminating the tube according to claim 1 on a metal foil; a charge / discharge simulation step of simulating volume expansion and contraction according to charge / discharge of an electrode assembly by repeating a process of injecting gas into the tube and discharging the injected gas one or two times or more; and a measuring step of measuring the tensile strength of the metal foil.

[0019] In one example, the metal foil fatigue testing method according to the present invention includes the step of setting simulation conditions in the charge / discharge simulation step, wherein the injection and discharge of the gas are performed according to the set simulation conditions.

[0020] In a specific example, the simulation conditions include one or more of the total amount of gas injected into the tube, the gas injection amount per hour, the gas discharge amount per hour, the maintenance time from completion of injection to gas discharge, and the number of repetitions of gas injection and discharge.

[0021] Furthermore, the measuring step includes measuring the tensile strength of the metal foil before the winding step and after the charge / discharge simulation step. In a specific example, measuring the tensile strength of the metal foil after the charge / discharge simulation step includes removing the metal foil from the wound roll and measuring the tensile strength of the removed metal foil.

[0022] In another example, the measuring step further includes: comparing the tensile strength (TS1) of the metal foil measured before the winding step with the tensile strength (TS2) of the metal foil measured after the charge / discharge simulation step, calculating the difference (TS1-TS2) thereof, and storing the difference in a storage unit.

[0023] In yet another example, the measuring step further includes preparing each specimen for each of the core region and the outermost region of the metal foil, measuring the tensile strength of each specimen, and comparing the tensile strength of the core region with the tensile strength of the outermost region.

[0024] Furthermore, the winding step winds the metal foil onto an outermost region of the roll structure.

[0025] In yet another example, the metal foil fatigue testing method according to the present invention further includes the step of detecting whether there is a break in the metal foil.

[0026] Beneficial effects

[0027] According to the metal foil fatigue testing system and the metal foil fatigue testing method of the present invention, the fatigue degree and life of the metal foil can be easily predicted by injecting gas into a tube having a roll structure and discharging the gas to simulate the charge / discharge of the electrode assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 FIG. 4 is a block diagram showing each component of the metal foil fatigue testing system according to the present invention.

[0029] Figure 2 FIG. 1 is a flow chart illustrating a metal foil fatigue testing method according to an example of the present invention.

[0030] Figure 3 is a cross-sectional view of a laminate including a metal foil and a tube in one example described herein.

[0031] Figure 4 A cross section of a roll structure when a laminate including a metal foil and a tube is wound in one example described in the present invention is shown.

[0032] Figure 5 A state change of the roll structure when gas is injected into the tube in a state where the laminate including the metal foil and the tube has been wound into the roll structure is shown.

[0033] Figures 6 to 8 1 is a flow chart illustrating the metal foil fatigue testing method according to the present invention. DETAILED DESCRIPTION

[0034] Since the inventive concept allows for various changes and multiple embodiments, specific embodiments will be shown in the drawings and described in detail in the text. However, this is not intended to limit the invention to the specific forms disclosed, and should be understood to include all changes, equivalents, and alternatives included in the spirit and scope of the invention.

[0035] In this application, it should be understood that terms such as "including" or "having" are intended to indicate the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and these terms do not preclude the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts, or combinations thereof. Moreover, 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 further portion is interposed therebetween. On the other hand, 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 further portion is interposed therebetween. In addition, in this application, "placed on..." may include the case where it is placed at the bottom as well as at the top.

[0036] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[0037] The invention relates to a metal foil fatigue testing system and a metal foil fatigue testing method.

[0038] As described above, in a jelly-roll electrode assembly, lithium is repeatedly inserted into and desorbed from the negative electrode during repeated charge / discharge cycles, causing the volume of the electrode active material to expand or contract, and fatigue to accumulate in the current collector supporting the electrode active material. In particular, the outer periphery of the jelly-roll exhibits significant changes due to the increased volume accumulated from the interior of the electrode assembly. This significantly increases the stress applied to the exterior of the metal foil. Furthermore, due to the accumulation of stress and fatigue exceeding the tensile limit of the metal foil, the foil may break or crack.

[0039] Thus, the inventors of the present invention have designed a metal foil fatigue testing system and a metal foil fatigue testing method for simulating repeated charge / discharge of a jelly roll, measuring the degree of fatigue accumulated in the metal foil as stress according to repeated charge / discharge is applied to the metal foil, and predicting the breaking time point of the metal foil by the measured fatigue degree.

[0040] Figure 1 FIG. 4 is a block diagram showing each component of the metal foil fatigue testing system according to the present invention.

[0041] refer to Figure 1The metal foil fatigue testing system 10 includes: a flat tube 120 laminated on a metal foil 110; a charge / discharge simulation unit 200; and a tensile strength measurement unit 300. In a specific example, the metal foil fatigue testing system 10 according to the present invention includes: a flat tube 120 laminated on a metal foil 110; a charge / discharge simulation unit 200 including a gas injector 210 for injecting gas into the tube 120 and a gas discharger 220 for discharging gas from the tube; and a tensile strength measurement unit 300 for measuring the tensile strength of the metal foil.

[0042] The metal foil fatigue testing system 10 according to the present invention may further include a winder (not shown) for winding the laminated product produced by laminating the tube 120 onto the metal foil 110 into a roll structure. Furthermore, when winding the laminated product produced by laminating the tube 120 onto the metal foil 110, the winder preferably winds the metal foil 110 so that it is positioned at the outermost side. The winder may be a winder commonly used in the related art.

[0043] In the present invention, the metal foil 110 is the metal foil that is the subject of fatigue measurement and life prediction, and may specifically comprise at least one of copper, gold, nickel, aluminum, and alloys thereof. Alternatively, the metal foil 110 may be copper foil or aluminum foil, more specifically copper foil. In particular, repeated charge / discharge cycles are highly likely to cause cracks in negative electrode current collectors. Therefore, the system or method of the present invention may be optimally suited for copper foil, which is frequently used as a negative electrode current collector.

[0044] The tube is used to simulate the electrode active material laminated on the metal foil, and injecting gas into the tube and emitting gas is to simulate the expansion and contraction of each electrode active material layer. In the present invention, the tube 120 means a pipe with a flow path formed inside along the length direction. In the present invention, preferably, the metal foil 110 is formed into a flat form or sheet form that can be laminated, and when gas is injected into the tube 120, the tube 120 will expand, so one end of the flow path is preferably formed by a closed structure. In addition, preferably, the tube 120 is made of such a material: when gas is injected into the tube 120, the tube can bulge or expand. For example, the tube 120 can be made of a synthetic resin (such as vinyl resin). Alternatively, the tube 120 can be a variable elastomer and can be made of a material containing an elastic polymer (such as polyurethane or styrene-butadiene-styrene).

[0045] In one example, in the metal foil fatigue testing system according to the present invention, the width (W1) of the tube 120 corresponds to or is greater than the width (W2) of the metal foil 110. This is to uniformly apply stress to the metal foil 110 by allowing the entire area of the tube 120 to swell or expand when gas is injected into the tube 120.

[0046] In another example, when the tube is an elastomer such as polyurethane, the width W1 of the tube is smaller than the width W2 of the metal foil 110. For example, the width W1 of the tube 120 may be within a range of 80 to 90% of the width W2 of the metal foil 110. In a specific example, when gas is injected into the tube 120, if the tube 120 is an elastomer, the metal foil 110 and the tube 120 are successively wound circumferentially. Therefore, the gas injected into the tube 120 can move along the axial direction of the roll structure, allowing the elastomer tube 120 to extend in the axial direction of the roll structure. This also serves to uniformly apply stress to the metal foil 110.

[0047] Furthermore, the length L1 of the tube 120 may correspond to the length L2 of the metal foil 110 or may be greater than the length L2 of the metal foil 110. If the length L1 of the tube 120 is less than the length L2 of the metal foil 110, stress may not be applied to the entire metal foil 110. Therefore, the length L1 of the tube 120 preferably corresponds to or is greater than the length L2 of the metal foil 110.

[0048] In one example, the charge / discharge simulation unit 200 according to the present invention includes a gas injector 210 and a gas exhauster 220 as described above. The charge / discharge simulation unit 200 is connected to the tube 120 in a fluidic manner, and the gas injector 210 and the gas exhauster 220 are preferably connected in a bifurcated manner. In one example, the gas injector 210 can be a gas injection pump, and whether to inject gas can be set by a gas valve or the like. A flow meter or the like for adjusting the injection amount, injection rate, etc. can be connected to the gas injector 210.

[0049] In addition, the gas discharger 220 may generally be a vacuum pump for discharging or injecting gas, and whether to discharge gas or the amount of gas discharged may be set through a gas valve or the like.

[0050] In one example, the tensile strength measurement unit 300 is used to measure the tensile strength of the metal foil 110. In a metal foil fatigue testing method described later, the tensile strength of the metal foil 110 is measured after undergoing a charge / discharge simulation step that simulates the volume expansion and contraction associated with the charge / discharge of the electrode assembly. Simultaneously, charge / discharge simulation conditions are set, and the tensile strength of the metal foil is measured based on the set simulation conditions. A specific method for measuring the tensile strength of the metal foil 110 will be described later.

[0051] To this end, the metal foil fatigue testing system 10 according to the present invention further includes a controller unit 400, which is used to set and change the simulation conditions of the charge / discharge simulation unit 200. The controller unit 400 can input the simulation conditions of the charge / discharge simulation unit 200 and receive input of test results.

[0052] Specifically, the controller unit 400 may include an input tool (not shown) for inputting information about the metal foil 110 to be subjected to the fatigue test, and the controller unit 400 may thereby receive input of the information about the metal foil 110 to be subjected to the fatigue test. For example, the information about the metal foil 110 may include the type, tensile strength, number of windings, and hardness of the metal foil 110. In particular, the tensile strength of the metal foil 110 is the tensile strength of the metal foil 110 before the movement of the metal foil 110, and this tensile strength can be used as a criterion for determining the degree of increase in fatigue of the metal foil 110 after the movement of the metal foil 110, compared with the tensile strength of the metal foil 110 measured after the charge / discharge simulation of the metal foil 110 described later.

[0053] Furthermore, the controller unit 400 may set simulation conditions for the charge / discharge simulation unit 200. In a specific example, the simulation conditions for the charge / discharge simulation unit 200 may include one or more of the total amount of gas injected into the tube, the amount of gas injected per hour, the amount of gas discharged per hour, the duration from completion of injection to gas discharge, and the number of repetitions of gas injection and discharge. The controller unit 400 may control the charge / discharge simulation unit 200 to operate according to the set charge / discharge simulation conditions.

[0054] In addition, the controller unit 400 may include a receiving tool (not shown) configured to receive input of fatigue test results. When the fatigue test is completed, the controller unit 400 may receive input of tensile strength measurement results and transmit the information to the storage unit 500.

[0055] The storage unit 500 receives test results, specifically tensile strength measurement results, from the controller unit 400 and stores the results. The storage unit 500 can store the tensile strength measurement results and use this information to generate a database. Specifically, the types of metal foils can be categorized based on the material, thickness, and hardness of the metal foil 110. The tensile strength measurement results for each simulation condition of the charge / discharge simulation unit 200 can be displayed in a table or line graph. When various simulation conditions are combined, this measurement data can be used as a basis for predicting the fatigue level and lifespan of the metal foil 110.

[0056] Here, the controller unit 400 and storage unit 500 can be operated directly by a user, but they can also be operated by an automated system. For example, when charge / discharge simulation conditions are input to the controller unit 400, the charge / discharge simulation unit 200 operates under predetermined conditions. When the operation of the charge / discharge simulation unit 200 is completed, the metal foil 110 is transferred to the tensile strength measurement unit 300 to thereby measure the tensile strength. The results can be received again by the controller unit 400 and stored in the storage unit 500. When the process is completed, the controller unit 400 can automatically change the movement conditions to repeat the same process.

[0057] Meanwhile, when the injection and discharge of gas are repeatedly performed in the metal foil 110 according to the charge / discharge simulation unit, if stress is applied to the metal foil 110, the metal foil 110 may be disconnected. Such disconnection phenomenon can be detected by cracks or the like generated on the metal foil 110. The present invention can provide a disconnection detection unit 600 for detecting whether the metal foil 110 has been disconnected, thereby identifying under what conditions the disconnection of the metal foil has occurred.

[0058] In the disconnection detection unit, a known method can be used to perform disconnection detection. For example, a camera, ultrasonic wave or eddy current detection scheme can be used to perform disconnection detection.

[0059] An imaging camera can capture cracks generated in the metal foil 110 after passing through the charge / discharge simulation unit 200. In the case of ultrasonic detection methods, ultrasonic waves are oscillated into the metal foil 110, and the waves returned by the echo phenomenon are sensed to thereby detect whether a disconnection has occurred through signal processing. Eddy current detection schemes detect disconnections by generating eddy currents in the metal foil when a coil through which alternating current flows is allowed to approach the foil. This detection method is well known to those skilled in the art, and a detailed description thereof will be omitted here.

[0060] Furthermore, the present invention provides a method for testing fatigue of a metal foil using the above metal foil fatigue testing system.

[0061] Figure 2 FIG. 1 is a flow chart illustrating a metal foil fatigue testing method according to an example of the present invention. Figure 3 is a cross-sectional view of a laminate including a metal foil and a tube in one example according to the present invention. Figure 4 A cross section of a roll structure when a laminate including a metal foil and a tube is wound in one example described in the present invention is shown. Figure 5 A state change of a roll structure when gas is injected into the tube in a state where a laminate including a metal foil and a tube has been wound into the roll structure is shown.

[0062] refer to Figure 2 , a method for testing fatigue of a metal foil according to the present invention includes: a winding step (S10): winding a laminate into a roll structure, the laminate being produced by laminating a tube on a metal foil; a charge / discharge simulation step (S20): simulating volume expansion and contraction according to charge / discharge of the electrode assembly by repeating a process of injecting gas into the tube and discharging the injected gas once or twice or more; and a measuring step (S30): measuring the tensile strength of the metal foil.

[0063] like Figure 3 and Figure 4 As shown in FIG, the step of winding the laminate into a roll (S10) includes the following process: laminating the tube 120 on one surface of the metal foil 110 to form a laminate, and winding the laminate. At this time, the laminate is wound so that the metal foil 110 is located at the outermost portion of the roll structure. The tube 120 simulates an electrode active material layer, specifically a negative electrode active material layer. The thickness of the tube 120 can be greater than that of the metal foil 110.

[0064] As described above, the tube 120 has a structure with a flow path formed inside along its length. Furthermore, the metal foil 110 is formed into a flat or sheet form that can be laminated. Furthermore, when gas is injected into the tube 120, the tube 120 expands, resulting in a closed flow path at one end. Furthermore, the laminate can be wound so that the end of the tube 120 with the closed flow path is located in the core region, while the other end of the tube 120 with the open flow path is located in the outermost winding layer region.

[0065] like Figure 5As shown in , the charge / discharge simulation step (S20) includes the following process: injecting gas into the tube 120 and discharging the gas in the roll structure in which the metal foil 110 and the tube 120 are wound. Specifically, the charge / discharge simulation step (S20) includes simulating the volume expansion and contraction of the tube 120 according to the charge / discharge of the electrode assembly by repeating the process of injecting gas into the tube 120 and discharging the injected gas one or more times. Here, when the gas is injected into the tube 120, the process of expansion of the tube 120 corresponds to the simulation of the expansion process of the negative electrode active material in the jelly-roll type electrode assembly, and the charge / discharge simulation step of the present invention corresponds to the simulation of the charge / discharge process of the jelly-roll type electrode assembly.

[0066] Furthermore, in a roll structure in which metal foil 110 and tube 120 are wound, when gas is injected into tube 120, the volume of tube 120 increases, and the volume of the tube accumulated from the interior of the roll structure increases, causing a change in circumference. Furthermore, due to the increased volume of tube 120, stress is applied to metal foil 110. More specifically, stress is applied in the circumferential direction, and the maximum stress and stretching may occur in metal foil 110 located in the outermost region of the roll structure.

[0067] Figure 6 FIG. 4 is a flow chart illustrating a metal foil fatigue testing method according to another example of the present invention.

[0068] refer to Figure 6 The charge / discharge simulation step (S20) further includes a step of setting charge / discharge simulation conditions (S15), and includes performing a gas injection and discharge process according to predetermined simulation conditions. In a specific example, the simulation conditions may include one or more of the total amount of gas injected into the pipe, the gas injection amount per hour, the gas discharge amount per hour, the duration from completion of injection to gas discharge, and the number of repetitions of gas injection and discharge.

[0069] In one example, in the charge / discharge simulation step ( S20 ), the number of gas injection and discharge simulations can be set. Specifically, as the process of injecting gas into the tube and discharging the injected gas is repeated, the tube also repeatedly expands and contracts. This reduces the elongation of the metal foil. In this case, the condition of the metal foil can be evaluated by accumulating the degree of fatigue of the metal foil in the roll structure. Alternatively, the time point of the metal foil's fracture can be estimated by evaluating the physical properties of the fatigued metal foil.

[0070] That is, in the charge / discharge simulation step (S20), by setting simulation conditions, it is possible to identify under what conditions the fatigue degree of the metal foil is likely to increase or the metal foil is likely to break during the charge / discharge simulation of the metal foil, thereby predicting the fatigue degree and life based on the movement.

[0071] Furthermore, the metal foil fatigue testing method according to the present invention includes a measuring step ( S30 ) of measuring the tensile strength of the metal foil.

[0072] In one example, the measuring step (S30) may include measuring the tensile strength of the metal foil before the winding step and after the charge / discharge simulation step. Here, measuring the tensile strength of the metal foil after the charge / discharge simulation step includes removing the metal foil from the wound roll and measuring the tensile strength of the removed metal foil.

[0073] The tensile strength of the metal foil can be measured using commonly known methods. For example, a tensile force is applied to both sides of the portion of the metal foil to be measured, and the force applied to the metal foil when a fracture occurs can be measured. In this case, the value obtained by dividing the maximum tensile load measured at this time by the cross-sectional area of the metal foil can be defined as the tensile strength. For example, the tensile strength can be measured using a tensile strength measuring device such as a tensile annealing (TA) device or a universal testing machine (UTM). Thus, the method of measuring tensile strength is known to those of ordinary skill in the art, and therefore a detailed description thereof will be omitted here.

[0074] Figure 7 is a flow chart illustrating a metal foil fatigue testing method according to yet another example of the present invention.

[0075] In a specific example, the metal foil fatigue testing method according to the present invention further includes comparing the tensile strength (TS1) of the metal foil measured before the winding step with the tensile strength (TS2) of the metal foil measured after the charge / discharge simulation step, calculating the difference (TS1-TS2), and storing the difference in a storage unit (S40 and S50). More specifically, by comparing the tensile strength (TS1) of the metal foil measured before the winding step with the tensile strength (TS2) of the metal foil measured after the charge / discharge simulation step, a criterion for determining the increase in fatigue level of the metal foil after the charge / discharge simulation of the metal foil can be obtained. That is, by comparing the tensile strength (TS1) of the metal foil measured before the winding step (S10) with the tensile strength (TS2) of the metal foil measured after the charge / discharge simulation step, the lifespan and fatigue level of the metal foil according to the charge / discharge simulation conditions can be easily identified.

[0076] In one example, the measuring step (S30) further includes the following process: preparing each sample for each of the core region and the outermost region of the metal foil, measuring the tensile strength of each sample, and comparing the tensile strength of the core region with the tensile strength of the outermost region. In a specific example, after the charge / discharge simulation step, in the roll structure in which the tube and the metal foil are wound, the core region may be the portion with the smallest change in circumference, and the outermost region may be the portion with the largest change in circumference. That is, by comparing the tensile strengths of the corresponding regions, the life and fatigue degree of the metal foil according to the charge / discharge simulation conditions can be easily identified. In addition, when preparing a jelly roll type electrode assembly, the number of windings of the electrode can be set, or the tensile level of the outermost region compared with the core region can be checked.

[0077] In another example, the measuring step (S30) includes the following process: in a roll structure of a metal foil in which the winding layer is wound n times, preparing the kth layer and the (k+1)th layer of the winding layer as samples, measuring the tensile strength of the metal foil samples, and comparing the tensile strength of each layer. Here, n is an integer of 2 or greater, and k is 1 or greater and n-1 or less. In addition, as described above, by comparing the tensile strength of the corresponding winding layers, the number of windings of the electrode can be set when preparing a jelly roll type electrode assembly, or the tensile level of each winding layer can be checked. That is, the life and fatigue level of the metal foil according to the charge / discharge simulation conditions can be easily identified.

[0078] Figure 8 is a flow chart illustrating a metal foil fatigue testing method according to yet another example of the present invention.

[0079] In addition, the metal foil fatigue testing method may further include a step of detecting whether the metal foil has been broken ( S25 ).

[0080] The metal foil fatigue testing method of the present invention can identify the conditions under which the metal foil breaks, by detecting whether a breakage phenomenon (such as a crack) occurs in the metal foil, separately from measuring the tensile strength. As described above, the breakage detection can be performed using a camera, ultrasonic wave, or eddy current detection scheme.

[0081] The step of detecting whether disconnection has occurred ( S25 ) may be performed during the charge / discharge simulation step. That is, it is possible to identify in real time at which point disconnection has occurred under specific movement conditions during the charge / discharge simulation of the metal foil.

[0082] In addition, the step of detecting whether disconnection has occurred (S25) may be performed after the charge / discharge simulation step. In this case, it is preferably performed before measuring the tensile strength to determine whether disconnection has occurred.

[0083] Hereinafter, various forms of metal foil fatigue testing methods according to the present invention will be described in detail.

[0084] (First embodiment)

[0085] In one example, the method for testing fatigue of a metal foil according to the present invention includes: a winding step (S10) of winding a laminate into a roll structure, the laminate being produced by laminating a tube on a metal foil; a charge / discharge simulation step (S20) of simulating volume expansion and contraction according to charge / discharge of an electrode assembly by repeating a process of injecting gas into the tube and discharging the injected gas one or two or more times; and a measuring step (S30) of measuring the tensile strength of the metal foil.

[0086] At the same time, the measuring step further includes comparing the tensile strength (TS1) of the metal foil measured before the winding step with the tensile strength (TS2) of the metal foil measured after the charge / discharge simulation step, calculating the difference (TS1-TS2), and storing the difference in a memory unit (S40 and S50). More specifically, the tensile strength (TS1) of the metal foil is measured before the winding step, the charge / discharge simulation step is performed, and then the tensile strength (TS2) of the metal foil is measured after the charge / discharge simulation step. Furthermore, the corresponding tensile strength values can be compared and the difference (TS1-TS2) can be calculated, and the result can be stored in the memory unit.

[0087] In one example, the measuring step (S30) includes measuring the tensile strength by preparing corresponding specimens of the outermost region and the core region of the metal foil. In addition, a process of comparing the tensile strength of each region is further included. As described above, after the charge / discharge simulation step, in the roll structure in which the tube and the metal foil are wound, the core region may be the portion with the smallest change in circumference, and the outermost region may be the portion with the largest change in circumference. That is, the life and fatigue degree of the metal foil according to the charge / discharge simulation conditions can be easily identified by comparing the tensile strength of the corresponding regions. In addition, when preparing a jelly roll type electrode assembly, the number of windings of the electrode can be set, or the tensile level of the outermost region compared with the core region can be checked.

[0088] Since each step has been described above, a detailed description of each step will be omitted here.

[0089] (Second embodiment)

[0090] In another example, the measuring step (S30) of the metal foil fatigue testing method according to the present invention includes preparing a test specimen of each of the core region, the middle region, and the outermost region of the metal foil to measure the tensile strength. Furthermore, the process of comparing the tensile strength of each region is included. Here, the middle region refers to the region of the metal foil located between the core region and the outermost region.

[0091] That is, by comparing the tensile strengths of the respective regions, the number of windings of the electrode, etc. can be set when preparing a jelly-roll type electrode assembly, or the tensile level of the outermost region compared with the core region, etc. can be checked.

[0092] Since each step has been described above, a detailed description of each step will be omitted here.

[0093] Although the preferred examples of the present invention have been described with reference to the accompanying drawings, it will be appreciated that those skilled in the art can make various modifications and changes to the present invention without departing from the spirit and scope of the invention as set forth in the appended claims.

[0094] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims

1. A system for testing fatigue of a metal foil, comprising: a flat tube laminated on a metal foil; a charge / discharge simulation unit including a gas injector for injecting gas into the tube and a gas discharger for discharging gas from the tube; and A tensile strength measuring unit is configured to measure the tensile strength of the metal foil. 2 . The system of claim 1 , further comprising a winder configured to wind a laminate produced by laminating the tube onto the metal foil into a roll structure.

3. The system according to claim 1, further comprising: a controller unit configured to set and change simulation conditions of the charge / discharge simulation unit; and A storage unit is configured to store a result of measuring the tensile strength.

4. The system according to claim 1, wherein: The tube has a flow path formed inside it along a length direction, through which gas is allowed to be injected and discharged, and wherein one end of the flow path is closed, and the other end of the flow path is connected to the charge / discharge simulation unit.

5. The system according to claim 1, wherein: The width (W1) of the tube is equal to or greater than the width (W2) of the metal foil.

6. The system according to claim 1, wherein: The length (L1) of the tube is equal to or greater than the length (L2) of the metal foil.

7. A method for testing fatigue of a metal foil, comprising: Winding step: winding a laminate produced by laminating the tube according to claim 1 on a metal foil into a roll structure; a charge / discharge simulation step of simulating volume expansion and contraction according to charge / discharge of the electrode assembly by repeating a process of injecting gas into the tube and discharging the injected gas one or two or more times; and Measuring steps: measuring the tensile strength of the metal foil.

8. The method according to claim 7, further comprising the step of setting simulation conditions in the charge / discharge simulation step, in, The injection and exhaust of the gas are performed according to the set simulation conditions.

9. The method according to claim 8, wherein The simulation conditions include one or more of the total amount of gas injected into the tube, the gas injection amount per hour, the gas discharge amount per hour, the maintenance time from completion of injection to gas discharge, and the number of repetitions of gas injection and discharge.

10. The method according to claim 7, wherein the measuring step comprises measuring the tensile strength of the metal foil before the winding step and after the charge / discharge simulation step.

11. The method according to claim 10, wherein: The process of measuring the tensile strength of the metal foil after the charge / discharge simulation step includes taking out the metal foil from the wound roll and measuring the tensile strength of the taken out metal foil.

12. The method according to claim 10, wherein: The measuring step further includes comparing the tensile strength (TS1) of the metal foil measured before the winding step with the tensile strength (TS2) of the metal foil measured after the charge / discharge simulation step, calculating a difference (TS1-TS2) thereof, and storing the difference in a storage unit.

13. The method according to claim 7, wherein: The measuring step further includes preparing each specimen for each of the core region and the outermost region of the metal foil, measuring the tensile strength of each specimen, and comparing the tensile strength of the core region with the tensile strength of the outermost region.

14. The method according to claim 7, wherein: The winding step winds the metal foil around the outermost area of the roll structure.

15. The method according to claim 7, further comprising the step of detecting whether there is a break in the metal foil before measuring the tensile strength of the metal foil.

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