Adhesion strength measuring device for measuring interfacial adhesion between an electrode and a separation membrane, and method for measuring adhesion strength using the same.

Abstract

The present invention relates to an adhesion measuring device for measuring the interfacial adhesion between an electrode and a separator, and an adhesion measuring method using the same. The present invention has the advantage that the interfacial adhesion between an electrode and a separator immersed in an electrolyte solution that replicates conditions equivalent to those in an actual secondary battery can be measured, and the adhesion between the electrode and the separator in an actual secondary battery can be predicted to prevent folding of the separator.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0144739 filed on November 2, 2022, and all the contents disclosed in the document of the Korean Patent Application are included as part of this specification.

[0002] The present invention relates to an adhesion measuring device for measuring an interfacial adhesion force between an electrode and a separator, and an adhesion measuring method using the same.

Background Art

[0003] In recent years, due to the depletion of fossil fuels, the price of energy sources has increased, and concerns about environmental pollution have amplified. The demand for environmentally friendly alternative energy sources has become an essential and indispensable factor for future life. Along with this, research on various power generation technologies such as nuclear power, solar power, wind power, and tidal power has continued, and great attention has also been paid to power storage devices for more efficiently using the energy produced in this way.

[0004] In particular, as the technology development and demand for mobile devices increase, the demand for batteries as an energy source has increased rapidly, and research on batteries that can meet various requirements has been conducted accordingly.

[0005] Typically, in terms of the shape of the battery, there is a high demand for rectangular secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with a thin thickness. In terms of materials, there is a high demand for lithium secondary batteries such as lithium-ion batteries and lithium-ion polymer batteries, which have advantages such as high energy density, discharge voltage, and output stability.

[0006] Generally, such rechargeable batteries have an electrode assembly inside the battery case, consisting of a positive electrode, a negative electrode, and a separator membrane placed between them. The positive and negative electrode tabs are welded to the two electrode tabs and sealed so that they are exposed to the outside of the battery case. These electrode tabs are electrically connected to an external device, and the rechargeable battery either supplies power to the external device or receives power from the external device via the electrode tabs.

[0007] Ensuring the safety of secondary batteries in their manufacture and use is a critical issue. In particular, the separator membranes commonly used in secondary batteries are susceptible to problems such as internal short circuits in the folded portions of the membrane, due to various reasons related to their material properties and manufacturing processes, which can hinder interfacial adhesion between the membranes.

[0008] Figure 1 is a photograph showing an electrode assembly where folding has occurred on the surface of the separation membrane.

[0009] Referring to Figure 1, it can be seen that during the manufacturing process of secondary batteries, the electrode assemblies stacked inside the battery case fold up due to the flow of the electrolyte after the process. This causes the separation membrane from the electrode interface to peel off. In this way, the folded portion of the separation membrane can cause an internal short circuit, inducing low voltage and reducing voltage efficiency, as well as directly leading to stability problems such as degradation. On the other hand, processes such as lamination or heat pressing can be performed to increase the adhesion between the electrode and the separation membrane, but in this case, excessive drying can cause lithium plating on the negative electrode, which degrades battery performance. Therefore, evaluation of the interfacial adhesion between the electrode and the separation membrane is required in the physical property evaluation process performed during the manufacturing process of secondary batteries.

[0010] Conventionally, to evaluate the interfacial adhesion between an electrode and a separation membrane, the electrode with the electrode composite layer formed on it and the separation membrane were cut to a certain size, the electrode and separation membrane were stacked, a PET film was sandwiched between them, and then the test specimens were manufactured by heating and pressurizing them with a flat plate press. After that, the electrode and separation membrane were separated using equipment such as a UTM (Universal Testing Machine) and the adhesion strength was evaluated. However, in this case, the measurement was taken in a dry state, making it difficult to determine the level of adhesion between the electrode and separation membrane when they are actually moistened with electrolyte inside a secondary battery. The measurement results showed a higher adhesion strength than those obtained when measured in a wet state with actual electrolyte, making it difficult to utilize the measured values.

[0011] Furthermore, when measuring the adhesive strength between a wet electrode and a separation membrane using electrodes and separation membranes obtained by disassembling an actual secondary battery, there was a problem in that the electrolyte impregnated in the electrodes and separation membranes evaporated during the time between disassembly and measurement, leading to results that differed from the actual level.

[0012] Therefore, in order to more accurately evaluate the interfacial adhesion force between electrodes and the separation film during the secondary battery manufacturing process, it is necessary to develop technology that can measure the adhesion force of electrodes by replicating the actual electrode state inside a secondary battery. [Overview of the project] [Problems that the invention aims to solve]

[0013] The present invention aims to solve the above-mentioned problems and to provide an apparatus for evaluating the adhesive strength between an electrode and a separation membrane in an environment equivalent to that inside an actual secondary battery, where the electrode and separation membrane are impregnated in an electrolyte, and a method for measuring adhesive strength using the same. [Means for solving the problem]

[0014] The present invention provides an adhesion strength measuring device for measuring the interfacial adhesion force between an electrode and a separation membrane. In one example, the adhesion strength measuring device according to the present invention includes a fixing jig that has a space for placing a test specimen including an electrode and a separation membrane, and contains an electrolyte in the space to fix the test specimen supported in the electrolyte, and an adhesion strength measuring device that has a grip for gripping the end region of the separation membrane of the test specimen, and measures the force that separates the separation membrane from the electrode by pulling the gripped separation membrane in a direction perpendicular to the electrode surface, and a part of the upper surface of the fixing jig curves downward to form a housing portion for containing the electrolyte, and the test specimen is supported in the electrolyte contained in the housing portion, and the interfacial adhesion force between the wet electrode and the separation membrane is measured.

[0015] In a specific example of the present invention, the fixing jig has a structure that includes a lid that seals the open portion of the housing so as to prevent the electrolyte contained in the housing from volatilizing.

[0016] Furthermore, the fixing jig includes a first fixing projection that protrudes upward from the upper surface and is bent inward, and a first guide groove formed between the bottom surface of the first fixing projection and the upper surface of the fixing jig. The cover is inserted into the open end of the first guide groove in a sliding manner, and the open space of the housing is sealed or opened and closed.

[0017] In another specific example of the present invention, the housing includes a second fixing projection formed on the side surface projecting inward, and a second guide groove formed between the bottom surface of the second fixing projection and the bottom surface of the housing, wherein the second fixing projection and the second guide groove each include a pair of second fixing projections and a pair of second guide grooves arranged facing each other in the width direction of the housing, and a measuring specimen is inserted into the open ends of the pair of second guide grooves in a sliding manner.

[0018] Furthermore, the housing section has a structure in which the ratio of the length between a pair of second fixing protrusions to the widthwise length of the area where the second fixing protrusions are not formed is in the range of 0.7 to 0.85.

[0019] Furthermore, the above-mentioned housing section has a structure in which the widthwise length of the area where the second guide groove is not formed is greater than the length between the pair of second guide grooves.

[0020] In another specific example of the present invention, the fixing jig is connected to a cover by a hinge, and the open space of the housing is sealed or opened and closed in such a manner that the cover rotates.

[0021] In another example of the present invention, the adhesion force measuring device further includes a detection unit that detects and displays the force at which the electrode and separation film of the test specimen are separated.

[0022] Furthermore, the present invention provides an adhesion strength measurement method for measuring the interfacial adhesion strength between a wet electrode and a separation film using the adhesion strength measuring device described above.

[0023] In one example of the present invention, the steps include: placing a test specimen in a fixed jig containing an electrolyte solution and supporting the test specimen in the electrolyte solution; fixing the end portion of the separation membrane of the test specimen supported in the electrolyte solution to the grip of an adhesive strength tester; and operating the adhesive strength tester to separate the electrode and separation membrane of the test specimen supported in the electrolyte solution and measuring the interfacial adhesion force between the wet electrode and the separation membrane.

[0024] In a specific example according to the present invention, the test specimen includes a positive or negative electrode obtained by disassembling a secondary battery and a separator membrane.

[0025] In another specific example of the present invention, the electrolyte is an electrolyte having the same components as the electrolyte stored inside the disassembled secondary battery.

[0026] In another specific example of the present invention, the secondary battery is a secondary battery that has undergone an activation process.

[0027] In another example of the present invention, the step of placing the measurement specimen in a fixed jig containing an electrolyte and supporting the measurement specimen in the electrolyte is as follows: double-sided adhesive tape is attached to the electrode surface of the measurement specimen, and the measurement specimen with the double-sided adhesive tape attached to the surface of the glass substrate is supported in the electrolyte with the glass substrate.

[0028] In another example of the present invention, the step of placing the test specimen in a fixed fixture containing an electrolyte and supporting the test specimen in the electrolyte includes the step of covering the fixed fixture with a lid to prevent the electrolyte contained in it from evaporating during a waiting period to allow a sufficient amount of electrolyte to be impregnated into the test specimen supported in the electrolyte. [Effects of the Invention]

[0029] The adhesive strength measuring device and adhesive strength measuring method using the present invention have the advantage of being able to simulate the internal state of a secondary battery containing an actual electrolyte, easily measure the interfacial adhesive strength between the electrode and the separation membrane in an environment equivalent to that inside an actual secondary battery, and predict the interfacial adhesive strength between the electrode and the separation membrane inside an actual secondary battery. [Brief explanation of the drawing]

[0030] [Figure 1] This is a photograph showing the folding of a separation membrane obtained by disassembling a conventional secondary battery. [Figure 2] This is a perspective view showing an adhesive strength measuring device according to one embodiment of the present invention. [Figure 3] This is a plan view showing a fixing jig related to one embodiment of the present invention. [Figure 4] This is a cross-sectional view of the fixing jig shown in Figure 3, obtained by cutting the fixing jig in the direction A-A'. [Figure 5] This is a perspective view showing the connection between a fixing jig and a lid according to one embodiment of the present invention. [Figure 6] This is a perspective view showing the connection between a fixing jig and a lid according to another embodiment of the present invention. [Figure 7]This graph shows the results of measuring the adhesive strength between the negative or positive electrode and the separation membrane, depending on whether or not the electrolyte solution was impregnated. [Figure 8] This graph shows the results of measuring the adhesion strength between the negative electrode and the separation membrane at each stage of the process. [Figure 9] This flowchart shows the procedure for measuring the interfacial adhesion between a wet electrode and a separation membrane. [Modes for carrying out the invention]

[0031] The present invention is subject to various modifications and may take many forms; therefore, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to any particular disclosure, but rather should be understood to include all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0032] In this application, terms such as “includes” and “have” are intended to specify the presence of features, numbers, stages, operations, components, parts, or combinations thereof described in the specification, without prejudice to the existence or possibility of adding one or more other features, numbers, stages, operations, components, parts, or combinations thereof. Furthermore, when a part such as a layer, film, region, or plate is said to be “on top” of another part, this includes not only when it is “directly on top” of the other part, but also when there is another part in between. Conversely, when a part such as a layer, film, region, or plate is said to be “below” another part, this includes not only when it is “directly below” the other part, but also when there is another part in between. Also, in this application, being “placed on top” may include being placed not only at the top but also at the bottom.

[0033] This invention provides an adhesion strength measuring device for measuring the interfacial adhesion force between an electrode and a separation membrane, and an adhesion strength measuring method using the same.

[0034] Typically, the measurement method for the bond between the electrode and the separation membrane involves cutting the electrode and separation membrane, which have an electrode composite layer formed on them, to a certain size, then stacking the electrode and separation membrane, sandwiching a PET film between them, and then heating and pressurizing them with a flat plate press to produce a test specimen. Finally, the electrode and separation membrane are separated using equipment such as a UTM (Universal Testing Machine) and the adhesive strength is measured.

[0035] However, in this case, the measurement was taken in a dry state, making it difficult to determine the level of adhesion between the electrode and the separation membrane, which are actually moistened with electrolyte inside the secondary battery. The measurement results showed a higher adhesion strength than those obtained when measured in an actual electrolyte-moistened state, making it difficult to utilize the measured values.

[0036] Furthermore, when measuring the adhesive strength between a wet electrode and a separation membrane using electrodes and separation membranes obtained by disassembling an actual secondary battery, there was a problem in that the electrolyte impregnated in the electrodes and separation membranes evaporated during the time between disassembly and measurement, leading to results that differed from the actual level.

[0037] Therefore, in order to more accurately evaluate the interfacial adhesion force between electrodes and the separation film during the secondary battery manufacturing process, it is necessary to develop technology that can measure the adhesion force of electrodes by replicating the actual electrode state inside a secondary battery.

[0038] Therefore, in order to solve the above-mentioned problems, the present invention provides an apparatus for evaluating the adhesive strength between an electrode and a separation membrane in an environment equivalent to the conditions inside an actual secondary battery in which the electrode and separation membrane are impregnated in an electrolyte, and a method for measuring adhesive strength using the same.

[0039] The following provides an adhesive strength measuring device for measuring the interfacial adhesive strength between an electrode and a separation membrane, and an adhesive strength measuring method using the same, according to the present invention.

[0040] Figure 2 is a perspective view showing an adhesive strength measuring device according to one embodiment of the present invention. Referring to Figure 2, the adhesive strength measuring device 1 according to the present invention includes a fixing jig 10 that has a space for placing a measuring specimen 30 including an electrode 31 and a separation membrane 32, and contains an electrolyte in the space to fix the measuring specimen 30 supported in the electrolyte, and an adhesive strength measuring device 20 that has a grip 21 for gripping the end region of the separation membrane 32 of the measuring specimen 30, and measures the force that separates the separation membrane 32 from the electrode 31 by pulling the gripped separation membrane 32 in a direction perpendicular to the surface of the electrode 31, and a structure in which a part of the upper surface of the fixing jig 10 curves downward to form a storage section 11 for containing the electrolyte, and the measuring specimen 30 is supported in the electrolyte contained in the storage section 11, and the interfacial adhesive strength between the wet electrode 31 and the separation membrane 32 is measured.

[0041] In the present invention, "measurement specimen 30" means an object to be measured using the adhesive strength measuring device 1 according to the present invention, and specifically may be an electrode 31 assembly. The electrode 31 assembly may include an electrode 31 on which an electrode 31 mixture layer is formed and a separation membrane 32, and the electrode 31 may be a positive electrode or a negative electrode on which an electrode 31 mixture layer is formed on one or both sides of the electrode 31 current collector.

[0042] The fixing jig 10 may have a housing portion 11 formed therein, which has a space provided for placing the test specimen 30 to be measured. The housing portion 11 may be a space formed by a part of the upper surface of the fixing jig 10 curving downwards. This curving space is a space in which the test specimen 30 can be placed and at the same time a space in which an electrolyte can be contained. The housing portion 11 may be formed to a predetermined depth so that an electrolyte can be contained inside and the test specimen 30 can be sufficiently impregnated with the electrolyte. The fixing jig 10 can be formed from various forms of metal, for example, carbon steel, stainless steel, aluminum or its alloys, and is not particularly limited to metal.

[0043] On the other hand, the adhesive strength measuring instrument 20 includes a grip 21 that can grasp the end portion of the separation membrane 32 of the test specimen 30, and can measure the force required to separate the separation membrane 32 from the electrode 31 by pulling the grasped separation membrane 32 in one direction. The adhesive strength measuring instrument 20 is a general universal testing machine (UTM), and one example of this may be a peel-off testing machine. In a specific example, in order to measure the interfacial adhesive strength between the electrode 31 and the separation membrane 32 of the test specimen 30, the electrode 31 and the separation membrane 32 in a part of the test specimen 30 are artificially separated, and then the end portion of the separation membrane 32 separated from the electrode 31 is fixed with the grip 21 of the adhesive strength measuring instrument 20, and the force required to peel the separation membrane 32 from the electrode 31 by pulling at a 90° angle to the surface of the electrode 31 (90° Peel-off test) can be measured.

[0044] Furthermore, the grip 21 of the adhesive strength measuring instrument 20 may include a metal jaw face with a grid formed on its surface. During the operation of the adhesive strength measuring instrument 20, a phenomenon may occur in which the separation membrane 32 slips while being pressurized by the grip 21. Therefore, by forming a grid on the jaw face of the grip 21, the fixing force of the grip 21 to the separation membrane 32 can be increased. The metal jaw face can be formed from various forms of metal, for example, carbon steel, stainless steel, aluminum or its alloys. Also, the metal jaw face may have a grid-like pattern with incisions or reliefs on its surface, and the width and length of the grid-like pattern, the indentation depth of the incisions, or the projection height of the reliefs are not particularly limited and can have various lengths.

[0045] Figure 3 is a plan view showing a fixing jig according to one embodiment of the present invention, and Figure 4 is a cross-sectional view showing a section of the fixing jig obtained by cutting the fixing jig of Figure 3 in the direction A-A'. Referring to Figures 3 and 4, the fixing jig 10 may have a structure that includes a lid 40 that seals the open portion of the housing 11 so as to prevent the evaporation of the electrolyte contained in the housing 11. In a specific example, the measurement specimen 30 obtained by disassembling a secondary battery may have a time interval formed between when the specimen is obtained by disassembling the secondary battery and when it is placed in the housing 11 of the fixing jig 10 containing the electrolyte, and the electrolyte may evaporate into the air during this time interval, so the conditions may differ from those inside the secondary battery. In this case, in order to realize conditions equivalent to those inside the secondary battery, the electrode specimen 31 may be supported in the electrolyte for a certain period of time, and a sufficient waiting time may be required so that the electrolyte can be sufficiently impregnated into the electrode specimen 31. However, during the waiting period, the electrolyte contained in the housing 11 of the fixing jig 10 may evaporate into the air, which can lead to the problem that the electrode 31 specimen may not be sufficiently moistened. This can be prevented by sealing the open portion of the housing 11 of the fixing jig 10 with the lid 40 to prevent the electrolyte from evaporating.

[0046] Figure 5 is a perspective view showing the connection between a fixing jig and a lid according to one embodiment of the present invention. Referring to Figure 5, the fixing jig 10 includes a first fixing projection 12 formed on the upper surface by projecting upward and bending inward, and a first guide groove 13 formed between the bottom surface of the first fixing projection 12 and the upper surface of the fixing jig 10. The cover may be inserted into the open end of the first guide groove 13 in a sliding manner, thereby sealing or opening and closing the open space of the housing 11.

[0047] For example, the first fixing projection 12 may have a ``'' shape, projecting upward from the upper surface of the fixing jig 10 and bending inward on an area of ​​the upper surface of the fixing jig 10 where the housing portion 11 is not formed. The bottom surface of the first fixing projection 12 has a certain step difference with the upper surface of the fixing jig 10, and a first guide groove 13 may be formed between the bottom surface of the first fixing projection 12 and the upper surface of the fixing jig 10. The depth of the first guide groove 13 corresponds to the length of the bent end portion of the first fixing projection 12 and is not limited to a certain depth.

[0048] On the other hand, the first fixing projection 12 and the first guide groove 13 have a structure in which a pair are arranged parallel to each other and facing each other in the width direction of the fixing jig 10, and a cover is attached to the open end of the first guide groove 13 in a sliding manner, so that the open space of the housing 11 can be sealed or opened and closed.

[0049] Figure 6 is a perspective view showing the connection between a fixing jig and a lid according to another embodiment of the present invention. Referring to Figure 6, the fixing jig 10 may be connected to the cover by a hinge 41, and the open space of the housing 11 may be sealed or opened / closed by the rotation of the cover. The hinge 41 is not limited to a hinge 41 having a specific structure, and may include a first cast slab and a second cast slab that are rotatable relative to a virtual pivot axis. For example, the first cast slab may be connected to the side of the fixing jig 10, and the second cast slab may be connected to the cover, so that the first and second cast slabs rotate relative to each other, and the open space of the housing 11 of the fixing jig 10 may be sealed or opened / closed. Also, the number of hinges 41 connecting the fixing jig 10 and the cover is not limited to a specific number, but considering the coupling force between the fixing jig 10 and the cover, it is preferable that they be connected by two or more hinges 41.

[0050] In another example of the present invention, the housing portion 11 comprises a second fixing projection 14 formed on its side surface projecting inward, and a second guide groove 15 formed between the bottom surface of the second fixing projection 14 and the bottom surface of the housing portion 11, wherein the second fixing projection 14 and the second guide groove 15 each include a pair of second fixing projections 14 and a pair of second guide grooves 15 arranged facing each other in the width direction of the housing portion 11, and the measuring specimen 30 may be inserted in a sliding manner into the open ends of the pair of second guide grooves 15. The process of measuring the interfacial adhesion force between the electrode 31 and the separation membrane 32 of the electrode 31 specimen is as follows: With the end portion of the separation membrane 32 grasped by the grip 21 of the adhesion strength measuring instrument 20, the separation membrane 32 is peeled off from the electrode 31 by pulling the separation membrane 32 at a 90° angle to the surface of the electrode 31. In this case, if the electrode 31 specimen is not fixed, when separating the separation membrane 32 from the electrode 31, the electrode 31 will move along with the separation membrane 32, making accurate measurement difficult. Therefore, the housing section 11 is provided with a separate second fixing projection 14 and a second guide groove 15, and the measurement specimen 30 is inserted into the second guide groove 15 and bound together, so that the electrode 31 is fixed so that it does not move along with the separation membrane 32 during the process of separating the separation membrane 32 from the electrode 31 by the adhesive strength measuring instrument 20. In this case, it is necessary to manufacture a measurement specimen 30 in which the width and length of the electrode 31 and the separation membrane 32 are different so that only the electrode 31 of the measurement specimen 30 straddles the second fixing projection 14, and the separation membrane 32 of the measurement specimen 30 does not straddle the second fixing projection 14.

[0051] Referring to Figures 3 and 4, the housing portion 11 may have a structure in which the ratio w' of the length between a pair of second fixing protrusions to the widthwise length w of the region where the second fixing protrusion 14 is not formed is in the range of 0.7 to 0.85.

[0052] If the ratio of the width length w' of the housing portion 11 where the second fixing protrusion 14 is formed to the width length w of the area where the second fixing protrusion 14 is not formed is greater than 0.85, the electrode 31 of the measuring specimen 30 will not sufficiently straddle the second fixing protrusion 14. If the ratio is less than 0.7, it will be smaller than the width length of the separation membrane 32 of the measuring specimen 30, and an additional process of cutting the separation membrane 32 may be required.

[0053] On the other hand, in another specific example of the present invention, the housing portion 11 may have a structure in which the widthwise length w of the region where the second guide groove 15 is not formed is greater than the length w'' between the pair of second guide grooves 15. After the measuring specimen 30 is placed in the space of the housing portion 11 where the second guide groove 15 is not formed, the measuring specimen 30 is pushed into the space where the pair of second guide grooves 15 are formed, causing the measuring specimen 30 to slide and be inserted into the second guide groove 15. In order to fix the measuring specimen 30 inserted into the second guide groove 15 so that it does not swing from side to side, the length w'' between the pair of second guide grooves 15 may be formed to be the same as the width of the measuring specimen 30. In contrast, the space in the housing section 11 where the second guide groove 15 is not formed is a space for placing the measuring specimen 30 before it is inserted between the pair of second guide grooves 15. This space allows the operator to easily place the measuring specimen 30 in the space where the second guide groove 15 is not formed while holding the measuring specimen 30. The widthwise length w of the area where the second guide groove 15 is not formed can be made larger than the widthwise length of the measuring specimen 30. Therefore, the length w'' between the pair of second guide grooves 15 is set to be the same length as the widthwise length of the measuring specimen 30 so that the measuring specimen 30 inserted between the pair of second guide grooves 15 is fixed, while the widthwise length w of the housing section 11 where the second guide groove 15 is not formed is made longer than the length between the pair of second guide grooves 15, allowing the operator to easily place the measuring specimen 30 in the housing section 11 while holding it.

[0054] The adhesion strength measuring device 1 may further include a detection unit (not shown) that detects and displays the force that separates the electrode 31 and the separation film 32 of the test specimen 30. The detection unit can numerically represent the interfacial adhesion force between the electrode 31 and the separation film 32 of the test specimen 30. This may be a structure provided in the adhesion strength measuring instrument 20.

[0055] Furthermore, the adhesion strength measuring device 1 may further include a storage unit (not shown). The storage unit can receive and store interfacial adhesion strength measurement data between the electrode 31 and the separation film 32 of the measurement specimen 30. If necessary, it may further include a function to database the measurement results categorized into various types, such as the type, thickness, and proportion of the metal current collector, electrode 31 composite layer, and separation film 32. This makes it possible to predict, based on the databased data, the possibility of folding of the separation film 32 and the resulting internal short circuit occurring due to a decrease in adhesion strength between the electrode 31 and the separation film 32 inside the actual secondary battery.

[0056] Furthermore, the present invention provides a method for measuring the interfacial adhesion between a wet electrode and a separation film using the adhesion strength measuring device described above.

[0057] Figure 9 is a flowchart showing the flow of a method for measuring the interfacial adhesion between a wet electrode and a separation membrane in one example of the present invention. Referring to Figure 9, the adhesion strength measurement method for measuring the interfacial adhesion between a wet electrode and a separation membrane according to the present invention includes the steps of: placing a test specimen in a fixing jig containing an electrolyte and supporting the test specimen in the electrolyte (S10); fixing the end portion of the separation membrane of the test specimen supported in the electrolyte to the grip of an adhesion strength tester (S20); and operating the adhesion strength tester to separate the electrode and separation membrane of the test specimen supported in the electrolyte and measuring the interfacial adhesion between the wet electrode and the separation membrane (S30).

[0058] First, the step of supporting the test specimen in the electrolyte (S10) means placing the test specimen, which includes the electrode and the separation membrane, into a containment section containing the electrolyte, so that the electrolyte can impregnate the test specimen. This includes cases where the test specimen is placed in the containment section with the electrolyte already present, as well as cases where the test specimen is placed in the containment section and then placed in the electrolyte. In other words, it means that the electrolyte can be contained in the containment section both before and after the test specimen is placed in it. On the other hand, it is preferable to add a sufficient amount of electrolyte so that the test specimen placed in the containment section can be impregnated with the electrolyte.

[0059] Furthermore, the test specimen to be placed in the above-mentioned housing can, of course, be placed on its own, but if necessary, double-sided adhesive tape can be attached to the electrode surface of the test specimen, and the test specimen with the double-sided adhesive tape attached to the glass substrate can be supported in the electrolyte with the test specimen attached to the glass substrate. The process of adhering the electrode specimen to the glass substrate can be carried out by applying pressure with a roller about 5 to 10 times after the test specimen has been attached to the glass substrate.

[0060] On the other hand, during the subsequent process of measuring the adhesive strength using an adhesive strength tester, it is necessary to fix the test specimen so that it does not move in the left-right or up-down direction. As mentioned above, this can be done by inserting and fixing the test specimen into a pair of second guide grooves located inside the housing. Specifically, when the housing is divided into a region where a pair of second guide grooves are formed in the longitudinal direction and a region where they are not, the operator can position the test specimen in the region where the pair of second guide grooves are not formed, and then push it between the pair of second guide grooves to fix it in place so that it is inserted into the pair of second guide grooves.

[0061] Furthermore, the step of placing the test specimen in the electrolyte (S10) may include a process of waiting for a certain period of time so that a sufficient amount of electrolyte can be impregnated into the test specimen placed in the electrolyte. At this time, the process of covering the fixing jig with a lid to prevent the electrolyte contained in the fixing jig from evaporating may be included during the waiting period. After the test specimen is obtained by disassembling the secondary battery, while it is being transferred to the container containing the electrolyte, the electrolyte impregnated in the test specimen may be exposed to the air and evaporate, and a waiting period may be required to place the test specimen in the electrolyte for a sufficient amount of time to replenish the evaporated electrolyte. At this time, the process may further include a process of covering the open part of the container with a lid to prevent the electrolyte contained in the container from evaporating into the air during the waiting period and to prevent the supply of additional electrolyte. Furthermore, when the open part of the container is covered with a lid, the fixing jig can prevent the electrolyte contained in the container from overflowing due to being blocked by the lid, even if the container is subjected to external impact.

[0062] On the other hand, in the step of supporting the test specimen in the electrolyte (S10), the test specimen may include a positive or negative electrode and a separation membrane obtained by disassembling a secondary battery. The present invention aims to measure the interfacial adhesion between an electrode and a separation membrane that has been wetted with electrolyte in order to solve the problem of the separation membrane folding due to a decrease in the adhesive force between the electrode and the separation membrane inside the actual secondary battery after the injection of electrolyte in the electrode assembly built into the battery case. Therefore, the test specimen is characterized by being obtained by disassembling the electrode assembly built into the battery case.

[0063] On the other hand, the electrolyte contained in the storage container can be an electrolyte with the same components as the electrolyte stored inside the disassembled secondary battery. By setting the components of the electrolyte contained in the storage container and the electrolyte composed inside the secondary battery to be the same, the reliability of the measurement results can be improved by simulating the same conditions as the actual inside of the secondary battery.

[0064] Furthermore, the secondary battery is composed of a secondary battery that has undergone an activation process, and a test specimen can be obtained by disassembling the secondary battery that has undergone the above activation process. In the manufacturing process of secondary batteries, when an activation process is performed, volumetric fluidity occurs in the secondary battery due to charging and discharging, which causes a change in the interfacial adhesion force between the electrode and the separator membrane, and the folding of the separator membrane may occur. Therefore, by measuring the adhesion force between the electrode and the separator membrane of a test specimen obtained by disassembling secondary batteries that have been divided into various categories according to the presence and degree of the activation process, it is possible to predict the interfacial adhesion state between the electrode and the separator membrane inside the secondary battery before and after the activation step, or according to the degree of the activation, based on the results.

[0065] On the other hand, "activation" in this specification refers to the process of supplying a certain amount of electricity to a secondary battery cell that does not possess electrical properties so that the positive and negative electrodes acquire electrical properties, and can be understood to include all reactions associated with the initial charging of the secondary battery cell. Non-limiting examples of the reactions associated with the initial charging include the formation of an SEI film, partial charging of the battery capacity, and activation of the negative electrode such as lithiumization of the carbon-based negative electrode active material.

[0066] Next, the present invention includes the step (S20) of fixing the end portion of the separation membrane of the test specimen supported in the electrolyte to the grip of the adhesive strength tester. In order to fix the end portion of the separation membrane of the test specimen supported in the electrolyte to the grip of the adhesive strength tester, a process of separating the electrode and separation membrane at one end of the test specimen may be performed in advance. The adhesive strength tester is a general universal testing machine (UTM), and one example is a peel-off testing machine, and the grip of the adhesive strength tester includes a metal jaw face with a grid formed on its surface, which can prevent the separation membrane fixed by the grip from slipping.

[0067] Next, the present invention may include the step (S30) of operating an adhesive strength tester to separate the electrode and separation membrane of the test specimen supported in the electrolyte, and measuring the interfacial adhesion between the wet electrode and the separation membrane.

[0068] As a specific example, to measure the interfacial adhesion force between the electrode and the separation membrane of a test specimen, the load of the adhesive strength measuring instrument is set to a zero base, the load speed is set to a range of 5 to 200 mm / min, the electrode and separation membrane are artificially separated in a portion of the test specimen, the end of the separation membrane separated from the electrode is fixed with the grip of the adhesive strength measuring instrument, and the adhesive strength measuring instrument is operated. The force at which the separation membrane peels off the electrode by pulling at a 90° angle to the electrode surface (90° Peel-off test) can be measured.

[0069] Furthermore, the process may include classifying the metal current collector, electrode mixture layer, and separation membrane into various types, thicknesses, and proportions, and creating a database of the results of measuring the interfacial adhesion between the electrode and the separation membrane. Based on the data recorded in the above database, it may be possible to predict the possibility of the separation membrane folding and resulting internal short circuits occurring due to a decrease in the adhesion between the electrode and the separation membrane inside the actual secondary battery.

[0070] On the other hand, the electrode of the present invention means either a positive electrode or a negative electrode, and the positive electrode has a structure in which a positive electrode active material layer is laminated on one or both sides of a positive electrode current collector. In one example, the positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder polymer, and may further include positive electrode additives commonly used in the industry as needed.

[0071] The positive electrode active material may be a lithium-containing oxide, and may be the same or different. A lithium-containing transition metal oxide may be used as the lithium-containing oxide.

[0072] For example, lithium-containing transition metal oxides are, x CoO2(0.5 <x<1.3)、Li x NiO2(0.5 <x<1.3)、Li xMnO2(0.5 < x < 1.3), Li x Mn2O4(0.5 < x < 1.3), Li x (Ni a Co b Mn c )O2(0.5 < x < 1.3, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), Li x Ni 1-y Co y O2(0.5 < x < 1.3, 0 < y < 1), Li x Co 1-y Mn y O2(0.5 < x < 1.3,​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ The current collector used for the positive electrode is a highly conductive metal to which the positive electrode active material slurry can easily adhere, and any metal that is non-reactive within the voltage range of the electrochemical element can be used. Specifically, non-restrictive examples of positive electrode current collectors include foils made from aluminum, nickel, or combinations thereof. The positive electrode active material layer further contains a conductive material.

[0075] The binder polymer can be any binder commonly used in the industry without limitation. For example, the binder may be a water-insoluble polymer that is soluble in organic solvents and insoluble in water, or a water-soluble polymer that is insoluble in organic solvents and soluble in water. The water-insoluble polymer may be one or more selected from the group including polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO), polytetrafluoroethylene (PTFE), polyimide (PI), polyetherimide (PEI), styrene-butadiene rubber (SBR), polyacrylate and its derivatives.

[0076] The water-soluble polymer may be one or more selected from the group including various cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropyl methylcellulose (HPMC), and hydroxypropyl methylcellulose phthalate (HPMCP).

[0077] The binder polymer content mentioned above is proportional to the conductive material content in the upper and lower positive electrode active material layers. This is to provide adhesion to the conductive material, which has a relatively small particle size compared to the active material. As the conductive material content increases, more binder polymer is required, and as the conductive material content decreases, less binder polymer can be used.

[0078] The negative electrode has a structure in which a negative electrode active material layer is laminated on one or both sides of a negative electrode current collector. In one example, the negative electrode active material layer includes a negative electrode active material, a conductive material, and a binder polymer, and may further include negative electrode additives commonly used in the industry, as may be specified.

[0079] The negative electrode active material may include carbon materials, lithium metal, silicon, or tin. When carbon materials are used as the negative electrode active material, both low-crystalline carbon and high-crystalline carbon can be used. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0080] Non-limiting examples of current collectors used in the negative electrode include foils made from copper, gold, nickel, or copper alloys, or combinations thereof. Alternatively, the current collector can be constructed by laminating substrates made of the above materials.

[0081] Furthermore, the negative electrode may include conductive materials and binders commonly used in the field.

[0082] Any porous substrate used in lithium secondary batteries can be used as the separation membrane; for example, a polyolefin-based porous membrane or nonwoven fabric can be used, but is not particularly limited to these.

[0083] Examples of polyolefin-based porous membranes include membranes formed from polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, as well as polyolefin polymers such as polypropylene, polybutylene, and polypentene, either individually or as mixtures thereof.

[0084] Examples of nonwoven fabrics include polyolefin-based nonwoven fabrics, as well as nonwoven fabrics formed from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylenenaphthalene, either individually or as mixtures thereof.

[0085] The above polymer is a porous polymer and may be a polyvinylidene fluoride polymer. The above polyvinylidene fluoride polymer is polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate. Acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, or carboxyl methyl cellulose may be used.

[0086] Furthermore, an adhesive layer containing electrically emitted polymer fibers may be formed on one or both sides of the separation membrane. The electrically emitted polymer fibers mentioned above include polyvinylidene fluoride (PVDF) polymers, styrene-butadienerubber (SBR), polytetrafluoroethylene (PTFE), polyethylene glycol (PEG), polypropylene glycol (PPG), toluene diisocyanate (TDI), polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl pullulan. It may be one or more substances selected from the group consisting of pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide.

[0087] The structure of the nonwoven fabric may be a spunbond nonwoven or a meltblown nonwoven, both composed of long fibers.

[0088] The thickness of the porous substrate described above is not particularly limited, but may be 5 to 50 μm. The pore size and pore density of the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

[0089] To improve the mechanical strength of the separation membrane composed of a porous substrate and to suppress short circuits between the positive and negative electrodes, the porous substrate may further include a porous coating layer containing inorganic particles and a binder polymer on at least one surface.

[0090] The electrolyte may contain an organic solvent and an electrolyte salt, the electrolyte salt being a lithium salt. The lithium salt can be any lithium salt commonly used in non-aqueous electrolytes for lithium secondary batteries, without limitation. For example, Li as a cation. + It includes, and as an anion, F - Cl - , Br - , I - NO 3- , N(CN) 2- BF 4- , 4- AlO 4- AlCl 4- , PF 6- SbF 6- AsF 6- BF2C2O 4- BC4O 8- (CF3)2PF 4- (CF3)3PF 3- (CF3)4PF 2- (CF3)5PF - (CF3)6P - CF3SO 3- , C4F9SO 3- , CF3CF2SO 3- , (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH -(SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO 3- CF3CO 2- CH3CO 2- SCN - and (CF3CF2SO2)2N - It may include at least one selected from the group consisting of the following.

[0091] The organic solvents included in the electrolyte described above may be any solvents commonly used in electrolytes for secondary batteries, without limitation. For example, ethers, esters, amides, linear carbonates, and cyclic carbonates may be used individually or in mixtures of two or more. Among these, cyclic carbonates, linear carbonates, or carbonate compounds which are mixtures thereof may be included.

[0092] Specific examples of cyclic carbonate compounds include any one or more compounds selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and their halides. Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).

[0093] Specific examples of linear carbonate compounds include, but are not limited to, any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, or mixtures of two or more of these.

[0094] Among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants, which allows for better dissociation of lithium salts in the electrolyte. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in suitable proportions, an electrolyte with higher electrical conductivity can be produced.

[0095] As the organic solvent, the ether may be one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more of these, but is not limited to this.

[0096] As the ester among the organic solvents, one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone, and β-caprolactone, or a mixture of two or more of these, may be used, but is not limited thereto.

[0097] The present invention will be described in more detail below with reference to examples. However, the configurations described in the examples described herein are merely one embodiment of the present invention and do not represent the entire technical concept of the present invention. Therefore, at the time of filing, there may be various equivalents and modifications that can substitute for them.

[0098] <Examples>

[0099] <Example 1> Cathode active material (LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811), conductive material (carbon black), and binder (Polyvinylidene fluoride, PVDF) were added to N-methyl-2-pyrrolidinone (NMP) in a weight ratio of 96:2:2, and then mixed to produce a positive electrode slurry. The produced positive electrode slurry was then used as a positive electrode current collector on 12 μm thick aluminum foil and tested for a current flow rate of 3.1 mAh / cm². 2 The positive electrode was manufactured by coating it with the specified capacity.

[0100] Artificial graphite, conductive material (carbon black), and binder (polyvinylidene fluoride, PVDF) were added to N-methyl-2-pyrrolidinone (NMP) in a weight ratio of 96:2:2, and then mixed to produce a negative electrode slurry. This prepared negative electrode slurry was then used as a negative electrode current collector on a 10 μm thick copper foil to measure a current flow rate of 3.1 mAh / cm². 2 The negative electrode was manufactured by coating it with this capacity.

[0101] Then, a radioactive solution containing PVDF-HFP (Arkema's LBG, HFP content 5%) is administered at a rate of 0.7 g / m². 2 A porous web made of ultrafine fibers was formed by electrospinning with a loading amount. The above porous web was heated at 190°C and a pressure of 20 kgf / cm². 2 A separation membrane with a thickness of 14 μm was fabricated by heating and pressurizing under specific conditions.

[0102] Subsequently, a jelly roll type electrode assembly was manufactured by interposing a separation membrane between the positive and negative electrodes. After the electrode assembly was placed in a battery case, an electrolyte solution was injected, and the battery case was sealed to manufacture a cylindrical secondary battery with a diameter of 21 mm. The electrolyte solution was prepared by adding LiPF6 at a concentration of 1.4 M to an organic solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:20:60. In addition, vinylene carbonate (3 vol%) and succinonitrile (1 vol%) were mixed into the electrolyte solution.

[0103] The lithium secondary battery manufactured as described above was disassembled, and the negative electrode was punched out to a size of 23 mm x 120 mm, and the separator membrane in contact with the negative electrode was punched out to a size of 20 mm x 120 mm to produce test specimens for measurement.

[0104] <Example 2> The test specimens were manufactured in the same manner as in Example 1, except that the electrode of the test specimen was changed from a positive electrode to a negative electrode.

[0105] <Examples 3-4> Except for changing the thickness of the separation membrane to 13 μm in Examples 1 and 2, the test specimens for Example 3 and 4 were prepared using the same method as in Examples 1 and 2.

[0106] <Example 5> The test specimens were prepared in the same manner as in Example 2, except that the separation membrane for the lithium secondary battery was changed to a polyethylene separation membrane containing an acrylate-based binder mixture with a thickness of 14 μm.

[0107] Specifically, the above acrylate binder mixture was prepared by adding an inorganic substance (Al2O3, 97% by weight), an acrylate binder (GL Chem's SG-L02, 3% by weight), and a fluorine-based nonionic surfactant (3M's FC4430, 0.001% by weight) to water as a solvent, with the total amount of the inorganic substance and acrylate binder being 100% by weight, and stirring the mixture.

[0108] <Example 6> Test specimens were prepared in the same manner as in Example 5, except that the lithium secondary battery produced in Example 5 underwent an activation process. Specifically, the activation process included an initial charging stage (SOC, 3%), a degassing stage including high-temperature aging (60°C, 4 hours), and room-temperature aging (12 hours). After additional charging to SOC 65% during the room-temperature aging stage, stages were performed to fully charge to SOC 100% (4.2V) and discharge to SOC 0% (2.5V).

[0109] <Examples 7-8> Except for changing the thickness of the separation membrane to 13 μm in Examples 5 and 6, the test specimens for Examples 7 and 8 were prepared using the same method as in Examples 5 and 6.

[0110] <Comparative Example>

[0111] <Comparative Example 1> Artificial graphite, conductive material (carbon black), and binder (polyvinylidene fluoride, PVDF) were added to N-methyl-2-pyrrolidinone (NMP) in a weight ratio of 96:2:2, and then mixed to produce a negative electrode slurry. This prepared negative electrode slurry was then used as a negative electrode current collector on a 10 μm thick copper foil to measure a current flow rate of 3.1 mAh / cm². 2 The negative electrode was manufactured by coating it with this capacity.

[0112] Then, a radioactive solution containing PVDF-HFP (Arkema's LBG, HFP content 5%) is administered at a rate of 0.7 g / m². 2A porous web made of ultrafine fibers was formed by electrospinning with a loading amount. The above porous web was heated at 190°C and a pressure of 20 kgf / cm². 2 A separation membrane with a thickness of 14 μm was fabricated by heating and pressurizing under specific conditions.

[0113] Subsequently, the separation membrane was laminated onto the negative electrode surface, and a heat press was used to bond the negative electrode and the separation membrane at 90°C and a pressure of 200 kgf for 40 seconds. After that, the negative electrode was punched out to a size of 23 mm x 120 mm, and the separation membrane in contact with the negative electrode was punched out to a size of 20 mm x 120 mm to produce test specimens for measurement.

[0114] <Comparative Example 2> LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive material (carbon black), and binder (Polyvinylidene fluoride, PVDF) were added to N-methyl-2-pyrrolidinone (NMP) in a weight ratio of 96:2:2, and mixed to produce a positive electrode slurry. The produced positive electrode slurry was then used as a positive electrode current collector on 12 μm thick aluminum foil and tested for a current flow rate of 3.1 mAh / cm². 2 The positive electrode was manufactured by coating it with the specified capacity.

[0115] Then, a radioactive solution containing PVDF-HFP (Arkema's LBG, HFP content 5%) is administered at a rate of 0.7 g / m². 2 A porous web made of ultrafine fibers was formed by electrospinning with a loading amount. The above porous web was heated at 190°C and a pressure of 20 kgf / cm². 2 A separation membrane with a thickness of 14 μm was fabricated by heating and pressurizing under specific conditions.

[0116] Subsequently, the separation membrane was laminated onto the negative electrode surface, and a heat press was used to bond the negative electrode and the separation membrane at 90°C and a pressure of 200 kgf for 40 seconds. After that, the negative electrode was punched out to a size of 23 mm x 120 mm, and the separation membrane in contact with the negative electrode was punched out to a size of 20 mm x 120 mm to produce test specimens for measurement.

[0117] <Comparative Examples 3-4> Except for the change in the thickness of the separation membrane to 13 μm in Comparative Examples 1 and 2, the test specimens for Comparative Examples 3 and 4 were prepared using the same method as in Comparative Examples 1 and 2.

[0118] <Comparative Example 5> The test specimens were prepared in the same manner as in Comparative Example 1, except that the separation membrane was changed to a polyethylene separation membrane containing an acrylate-based binder mixture with a thickness of 14 μm.

[0119] Specifically, the above acrylate binder mixture was prepared by adding an inorganic substance (Al2O3, 97% by weight), an acrylate binder (GL Chem's SG-L02, 3% by weight), and a fluorine-based nonionic surfactant (3M's FC4430, 0.001% by weight) to water as a solvent, with the total amount of the inorganic substance and acrylate binder being 100% by weight, and stirring the mixture.

[0120] <Comparative Example 6> The test specimens were prepared using the same method as in Comparative Example 5, except that the thickness of the separation membrane was changed to 13 μm.

[0121] <Example of experiment>

[0122] 1) Measurement of the adhesion strength between the electrode and the separation membrane according to the dry or wet state. The interfacial adhesion between the electrode and the separation membrane of the test specimens used in Examples 1-4 and Comparative Examples 1-4 was measured using a UTM (LLOYD Instrument LF Plus) system.

[0123] Specifically, in Examples 1 to 4, the test specimens were fixed to a fixed jig containing the electrolyte, and after the test specimens were immersed in the electrolyte for about one hour, the interfacial adhesion between the electrode and the separation membrane was measured. On the other hand, in Comparative Examples 1 to 4, the test specimens were fixed to a fixed jig that did not contain the electrolyte, and the interfacial adhesion between the electrode and the separation membrane was measured immediately afterward.

[0124] Then, the separation membranes of the measurement specimens for Examples 1-4 and Comparative Examples 1-4, which were fixed to the fixing jig, were secured to the grip of the UTM-equipped device. The UTM device was then operated to pull one side of the separation membrane at 100 mm / min, and the force required to detach the separation membrane from the electrode was measured. At this time, the measurement angle between the electrode and the separation membrane was 90°.

[0125] At this time, three test specimens were prepared for each of Examples 1-4 and Comparative Examples 1-4. The adhesive strength of each test specimen was measured using the 90° peel-off test described above, and the average value was calculated. The results are shown in Figure 7.

[0126] As shown in Figure 7, the average adhesive strength between the negative electrode and the separation membrane of Comparative Example 1, which was manufactured via a dry bonding process, was approximately 63 gf / 20 mm, while the average adhesive strength between the negative electrode and the separation membrane of Example 1, which was manufactured via a wet bonding process, was approximately 0.5 gf / 20 mm.

[0127] Furthermore, the average adhesive strength between the positive electrode and the separation membrane of Comparative Example 2, which was manufactured through a dry bonding process, was approximately 141 gf / 20 mm, while the average adhesive strength between the positive electrode and the separation membrane of Example 2, which was manufactured through a wet bonding process, was approximately 5 gf / 20 mm.

[0128] This confirms that a dry bonding process in which the electrolyte is not wetted improves the adhesion between the negative electrode and the separator membrane, while a wet bonding process in which the electrolyte is wetted decreases the adhesion between the negative electrode and the separator membrane. The interfacial adhesion between the positive or negative electrode supported in the electrolyte and the separator membrane, as in the interior of an actual secondary battery, has a considerable difference compared to the interfacial adhesion between the positive or negative electrode and the separator membrane manufactured in a state where the electrolyte is not wetted.

[0129] This necessitates evaluating the interfacial adhesion between the electrode and the separator membrane in an electrolyte-moistened environment under conditions identical to those inside an actual secondary battery. By measuring the interfacial adhesion between the electrode and the separator membrane in an electrolyte-moistened state, mimicking the conditions inside an actual secondary battery, it becomes possible to improve the reliability of predicting changes in the adhesion between the electrode and the separator membrane that occur inside an actual secondary battery.

[0130] On the other hand, as shown in Figure 7, the average adhesive strength between the negative electrode and the separation membrane of Comparative Example 3, which was manufactured through a dry bonding process, was approximately 40 gf / 20 mm, while the average adhesive strength between the negative electrode and the separation membrane of Example 3, which was manufactured through a wet bonding process, was approximately 3 gf / 20 mm.

[0131] Furthermore, the average adhesive strength between the positive electrode and the separation membrane of Comparative Example 4, which was manufactured through a dry bonding process, was approximately 71 gf / 20 mm, while the average adhesive strength between the positive electrode and the separation membrane of Example 4, which was manufactured through a wet bonding process, was approximately 4 gf / 20 mm.

[0132] Examples 3-4 and Comparative Examples 3-4 were conducted under the same conditions as Examples 1-2 and Comparative Examples 1-2, with only the thickness of the separation membrane being changed, and the adhesive strength between the negative or positive electrode and the separation membrane was measured. Examples 3-4 and Comparative Examples 3-4, with their relatively thinner separation membranes, experienced less gravitational force than Examples 1-2 and Comparative Examples 1-2, which had relatively thicker separation membranes, resulting in relatively smaller adhesive strength values ​​between the electrode and the separation membrane. Except for this, Examples 3-4 and Comparative Examples 3-4 exhibited similar adhesive strength behavior to Examples 1-2 and Comparative Examples 1-2. In other words, Comparative Examples 3-4, which underwent a dry bonding process, showed a significant difference in adhesive strength when compared to Examples 3-4, which underwent a wet bonding process.

[0133] As a result, even when the thickness of the separation membrane is changed, there is a large discrepancy in the adhesion strength measurement results between the electrode and the separation membrane under conditions where the electrolyte is not wetted and under conditions where the electrolyte is wetted. Therefore, it is necessary to measure the adhesion strength between the electrode and the separation membrane under conditions where the electrolyte is wetted, just like inside an actual secondary battery. This can improve the reliability of predicting whether or not folding of the separation membrane occurs inside an actual secondary battery.

[0134] 2) Measurement of the adhesion strength between the electrode and the separation membrane at each process stage. The interfacial adhesion between the electrode and the separation film of the test specimens used in Examples 5-8 and Comparative Examples 5-6 was measured using a UTM (LLOYD Instrument LF Plus) system.

[0135] Specifically, in Examples 5 and 7, a test specimen obtained by disassembling a lithium secondary battery that had not undergone the activation process was fixed to a housing in a fixed jig containing electrolyte, and the test specimen was supported in the electrolyte for about 1 hour so that it could be impregnated with the electrolyte, after which the interfacial adhesion force between the negative electrode and the separation membrane was measured. On the other hand, in Examples 6 and 8, a test specimen obtained by disassembling a lithium secondary battery that had undergone the activation process was housed in a fixed jig containing electrolyte, as in Examples 5 and 7, and supported in the electrolyte, after which the interfacial adhesion force between the negative electrode and the separation membrane was measured. On the other hand, in Comparative Examples 5 and 6, the test specimen was fixed to a housing in a fixed jig that did not contain electrolyte, and the interfacial adhesion force between the negative electrode and the separation membrane was measured immediately afterward.

[0136] Then, the separation membranes of the measurement specimens for Examples 5-8 and Comparative Examples 5-6, which were fixed to the fixing jig, were secured to the grip of the UTM-equipped device. The UTM device was then operated to pull one side of the separation membrane at 100 mm / min, and the force required to peel the separation membrane from the negative electrode was measured. At this time, the measurement angle between the electrode and the separation membrane was 90°.

[0137] At this time, three test specimens were prepared for each of Examples 5-8 and Comparative Examples 5-6. The adhesive strength of each test specimen was measured using the 90° peel-off test described above, and the average value was calculated. The results are shown in Figure 8.

[0138] As shown in Figure 8, the average adhesive strength between the negative electrode and the separation membrane of Comparative Example 5, which was manufactured via a dry bonding process, was approximately 14.5 gf / 20 mm, while the average adhesive strength between the negative electrode and the separation membrane of Example 6, which was manufactured via a wet bonding process and produced by disassembling a lithium secondary battery that had not undergone an activation process, was approximately 1.5 gf / 20 mm. On the other hand, the average adhesive strength between the negative electrode and the separation membrane of Example 6, which was manufactured via a wet bonding process and produced by disassembling a lithium secondary battery that had undergone an activation process, was approximately 4.5 gf / 20 mm.

[0139] As confirmed in Experimental Example 1 described above, the dry bonding process improves the adhesion between the negative electrode and the separator membrane, while the wet bonding process, in which the electrolyte is moistened, decreases the adhesion between the negative electrode and the separator membrane. This confirms that the interfacial adhesion between the negative electrode and the separator membrane, supported in the electrolyte as in the interior of an actual secondary battery, has a considerable difference compared to the interfacial adhesion between a positive or negative electrode and the separator membrane manufactured without moistening the electrolyte.

[0140] This necessitates evaluating the interfacial adhesion between the negative electrode and the separator membrane under humid conditions that mimic the conditions inside an actual secondary battery. This improves the reliability of predicting the adhesion strength between the electrode and the separator membrane as it occurs inside an actual secondary battery.

[0141] On the other hand, when comparing the adhesive strength behavior of Example 5, which was manufactured by disassembling a lithium secondary battery that did not undergo the activation process, with that of Example 6, which was manufactured by disassembling a lithium secondary battery that did undergo the activation process, it can be confirmed that Example 6 exhibits a higher adhesive strength than Example 5. This is thought to be because the interfacial adhesive strength between the negative electrode and the separation film improved due to various factors through the stepwise charge-discharge process, aging process, and degassing process.

[0142] Furthermore, by measuring the adhesive strength between the electrode and the separation membrane under wet conditions on test specimens produced from lithium secondary batteries manufactured under varying conditions for each stage of the secondary battery activation process, it becomes possible to predict in advance the behavior of the adhesive strength between the electrode and the separation membrane inside the secondary battery according to the diverse conditions for each stage of the activation process, thereby preventing the folding phenomenon of the separation membrane in advance at each stage of the activation process.

[0143] On the other hand, as shown in Figure 8, the average adhesive strength between the negative electrode and the separation membrane of Comparative Example 6, which was manufactured through a dry bonding process, was approximately 3.5 gf / 20 mm, while the average adhesive strength between the negative electrode and the separation membrane of Example 7, which was manufactured through a wet bonding process and produced by disassembling a lithium secondary battery that had not undergone an activation process, was approximately 0.9 gf / 20 mm. On the other hand, the average adhesive strength between the negative electrode and the separation membrane of Example 8, which was manufactured through a wet bonding process and produced by disassembling a lithium secondary battery that had undergone an activation process, was approximately 1.3 gf / 20 mm.

[0144] Examples 7-8 and Comparative Example 6 measured the adhesive strength between the negative electrode and the separation membrane, with only the thickness of the separation membrane being different from Examples 5-6 and Comparative Example 5. Examples 7-8 and Comparative Example 6, which have relatively thicker membranes, exhibit similar behavior to the adhesive strength results in Examples 5-6 and Comparative Example 5, except that they have relatively higher adhesive strengths than Examples 5-6 and Comparative Example 5, respectively. In other words, Comparative Example 6, which underwent a dry bonding process, differs considerably in the magnitude of the adhesive strength from Examples 7-8, which underwent a wet bonding process. This is because, as explained earlier in Examples 5-6 and Comparative Example 5, there is a large deviation in the adhesive strength measurement results between the electrode and the separation membrane under conditions where the electrolyte is not wetted and under conditions where the electrolyte is wetted. Therefore, it is necessary to measure the adhesive strength between the electrode and the separation membrane under conditions where the electrolyte is wetted, just as in the actual inside of a secondary battery. This can improve the reliability of predicting whether or not folding of the separation membrane occurs inside an actual secondary battery.

[0145] Furthermore, Example 8, manufactured by disassembling a secondary battery that had undergone the activation process, exhibited higher adhesive strength than Example 7, manufactured by disassembling a secondary battery that had not undergone the activation process. This, too, is presumed to be due to improved adhesive strength between the negative electrode and the separation membrane caused by various factors in the activation process. On the other hand, comparing the adhesive strength behavior with Examples 5-6, in which the thickness of the separation membrane was varied, it can be confirmed that the thicker the separation membrane, the greater the difference in adhesive strength due to the presence or absence of the activation process.

[0146] This confirms that differences in adhesion between the negative electrode and the separation membrane occur depending on whether or not the electrolyte is wetted, whether or not the secondary battery has been decomposed after the activation process, and of course, whether or not the thickness of the separation membrane also makes a difference. Therefore, by setting not only the electrolyte wetting conditions but also the activation process conditions and the thickness of the separation membrane to be the same as inside an actual secondary battery and measuring the adhesion between the negative electrode and the separation membrane, the reliability of predicting the adhesion between the negative electrode and the separation membrane inside a secondary battery actually manufactured under various conditions can be improved based on the results. [Explanation of symbols]

[0147] 1: Adhesive force measuring device 10: Fixing fixture 11: Detention Unit 12: 1st fixing protrusion 13: First guide groove 14:Second fixing protrusion 15: Second guide groove 20: Adhesive strength measuring device 21: Grip 30: Measurement specimen 31: Electrode 32: Separation membrane 40: Lid 41: Hinge

Claims

1. A fixing jig comprising a space for placing a measuring specimen including an electrode and a separation membrane, and containing an electrolyte in the space to fix the measuring specimen supported in the electrolyte, The device includes an adhesive strength measuring instrument which has a grip for gripping the end region of the separation membrane of the measuring specimen, and measures the force required to separate the separation membrane from the electrode by pulling the gripped separation membrane in a direction perpendicular to the surface of the electrode, The structure is such that a portion of the upper surface of the fixing jig curves downward to form a storage portion for containing the electrolyte, The measuring specimen is supported in the electrolyte contained in the housing, and the interfacial adhesion between the wet electrode and the separation membrane is measured. The housing portion includes a second fixing projection formed on the side surface projecting inward, and a second guide groove formed between the bottom surface of the second fixing projection and the bottom surface of the housing portion. The second fixing projection and the second guide groove each include a pair of second fixing projections and a pair of second guide grooves, which are arranged facing each other in the width direction of the housing portion. An adhesive strength measuring device having a structure in which the measuring specimen is inserted in a sliding manner into the open ends of the pair of second guide grooves.

2. The adhesive strength measuring device according to claim 1, wherein the fixing jig has a structure that includes a lid that seals the open portion of the housing so as to prevent the evaporation of the electrolyte contained in the housing.

3. The fixing jig includes a first fixing projection formed on the upper surface by projecting upward and bending inward, and a first guide groove formed between the bottom surface of the first fixing projection and the upper surface of the fixing jig. The adhesive force measuring device according to claim 2, wherein a cover is inserted in a sliding manner into the open end of the first guide groove, and the open space of the housing is sealed or opened and closed.

4. The adhesive strength measuring device according to any one of claims 1 to 3, wherein the housing portion has a structure in which the ratio of the length between the pair of second fixing protrusions to the widthwise length of the region in which the second fixing protrusions are not formed is in the range of 0.7 to 0.

85.

5. The adhesive force measuring device according to any one of claims 1 to 3, wherein the housing portion has a structure in which the length in the width direction of the region in which the second guide groove is not formed is greater than the length between the pair of second guide grooves.

6. The adhesive force measuring device according to claim 2, wherein the fixing jig is connected to a cover by a hinge, and the cover rotates in such a manner that the open space of the housing is sealed or opened and closed.

7. The adhesive force measuring device according to any one of claims 1 to 3, further comprising a detection unit that detects and displays the force that separates the electrode and the separation membrane of the measuring specimen.

8. A method for measuring adhesive strength, comprising measuring the interfacial adhesive strength between the electrode and the separation membrane in a wet state using the adhesive strength measuring device according to any one of claims 1 to 3.

9. The steps include: placing the measurement specimen in the fixing jig containing the electrolyte, and supporting the measurement specimen in the electrolyte; The steps include fixing the end portion of the separation membrane of the measuring specimen supported in the electrolyte to the grip of the adhesive strength tester, The adhesive strength measurement method according to claim 8, comprising the steps of operating the adhesive strength tester to separate the electrode and the separation membrane of the measuring specimen supported in the electrolyte, and measuring the interfacial adhesive strength between the wet electrode and the separation membrane.

10. The adhesive strength measurement method according to claim 9, wherein the test specimen for measurement includes a positive or negative electrode and a separation membrane obtained by disassembling a secondary battery.

11. The adhesive strength measurement method according to claim 10, wherein the electrolyte is an electrolyte having the same components as the electrolyte stored inside the disassembled secondary battery.

12. The adhesive strength measurement method according to claim 10, wherein the secondary battery is a secondary battery that has undergone an activation process.

13. The step of placing the measurement specimen on the fixing jig containing the electrolyte and supporting the measurement specimen in the electrolyte is as follows: The adhesive strength measurement method according to claim 9, wherein a double-sided adhesive tape is attached to the surface of the electrode of the measuring specimen, and the measuring specimen with the double-sided adhesive tape attached is attached to the surface of a glass substrate, and the measuring specimen attached to the glass substrate is then supported in the electrolyte.

14. The step of placing the measurement specimen on the fixing jig containing the electrolyte and supporting the measurement specimen in the electrolyte is as follows: The adhesive strength measurement method according to claim 9, further comprising the step of covering the fixing jig with a lid to prevent the electrolyte contained therein from evaporating during a waiting period for a sufficient amount of the electrolyte to be impregnated into the measuring specimen supported in the electrolyte.

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