Self-supporting film, electrode for secondary battery, secondary battery including the electrode, and method for manufacturing electrode

Abstract

A self-supporting film according to one embodiment of the present disclosure includes a pattern having directionality on at least one surface.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims the benefits of Korean Patent Application No. 10-2021-0004143, filed with the Korean Intellectual Property Office on January 12, 2021, and Korean Patent Application No. 10-2022-0002294, filed with the Korean Intellectual Property Office on January 6, 2022, the contents of which are incorporated herein by reference in their entirety.

[0003] This disclosure relates to a self-supporting membrane, an electrode for a secondary battery, a secondary battery including the electrode, and a method for manufacturing the electrode, and more specifically, to a self-supporting membrane having improved peel strength and adhesion, an electrode for a secondary battery, a secondary battery including the electrode, and a method for manufacturing the electrode. Background Technology

[0004] With the development of mobile device technology and increasing demand, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and high voltage, long cycle life and low self-discharge rate, are commercially available and widely used.

[0005] In particular, secondary batteries are attracting attention as an energy source for power-driven devices such as electric bicycles, electric cars, and hybrid electric vehicles, as well as for mobile devices such as mobile phones, digital cameras, laptops, and wearable devices.

[0006] Furthermore, with increasing attention to environmental issues, research on electric vehicles and hybrid electric vehicles is becoming more frequent, as they can replace fossil fuel-powered cars such as gasoline and diesel vehicles, which are major contributors to air pollution. While nickel-metal hydride batteries are primarily used as power sources for electric and hybrid electric vehicles, research is actively underway on lithium-ion batteries with high energy density and discharge voltage, some of which are already in the commercialization stage.

[0007] Conventional electrodes for secondary batteries are typically manufactured using wet processes. However, wet manufacturing inherently requires high-temperature heat treatment and carries the risk of damage to metal oxides. Therefore, there is a growing need to develop electrodes manufactured using dry processes. Summary of the Invention

[0008] Technical issues

[0009] The purpose of this disclosure is to provide a self-supporting membrane with improved peel strength and adhesion, an electrode for a secondary battery, a secondary battery including the electrode, and a method for manufacturing the electrode.

[0010] The purpose of this disclosure is not limited to the above-described purposes, and those skilled in the art should clearly understand other purposes not described herein through the following detailed description and accompanying drawings.

[0011] Technical solution

[0012] According to one aspect of this disclosure, a self-supporting membrane is provided, the self-supporting membrane comprising a directional pattern on at least one surface.

[0013] The pattern can be an embossed pattern.

[0014] The pattern can have an interval of 100 μm to 2000 μm.

[0015] The pattern can have a depth of 1.5 μm to 35 μm.

[0016] According to another aspect of this disclosure, an electrode for a secondary battery is provided, comprising: an electrode current collector; and an electrode layer located on the electrode current collector, wherein the electrode layer may comprise an electrode composition thereof, wherein an active material, a conductive material and a binder are dry-mixed, wherein the electrode composition may be prepared as a self-supporting film, and wherein the self-supporting film may comprise a directional pattern on at least one surface.

[0017] The pattern can be an embossed pattern.

[0018] The pattern can have an interval of 100 μm to 2000 μm.

[0019] The pattern can have a depth of 1.5 μm to 35 μm.

[0020] The self-supporting film can be attached to the electrode current collector, such that a patterned surface on it contacts the electrode current collector.

[0021] The active material may include at least one selected from the group consisting of: lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium copper oxide (Li2CuO2), vanadium oxide, Ni-position lithium nickel oxide, lithium manganese composite oxide, lithium manganese composite oxide having a spinel structure, LiMn2O4 wherein the Li in the formula is partially replaced by alkaline earth metal ions, disulfide, Fe2(MoO4)3, and lithium manganese oxide (LMO, Lithium Manganese Oxide).

[0022] The adhesive may include polytetrafluoroethylene (PTFE).

[0023] The self-supporting membrane may have a peel strength of 10 gf / 20 mm or more and 15 gf / 20 mm or less.

[0024] According to another aspect of this disclosure, a method for manufacturing an electrode for a secondary battery is provided, the method comprising the steps of: dry mixing an active material, a conductive material and a binder to prepare a mixture; applying a shear force to the mixture to prepare a self-supporting film; forming a directional pattern at regular intervals on the self-supporting film; and attaching the self-supporting film to an electrode current collector to form an electrode for a secondary battery.

[0025] The pattern can be an embossed pattern.

[0026] The pattern can have an interval of 100 μm to 2000 μm.

[0027] The pattern can have a depth of 1.5 μm to 35 μm.

[0028] The self-supporting film can be attached to the electrode current collector, such that a patterned surface on it contacts the electrode current collector.

[0029] The pattern-forming step may include any of the following steps: forming a pattern on the self-supporting film by forming an embossed pattern on a roll used for winding the self-supporting film, adjusting the speed of the roll, and setting the gear ratio of the two-roll mill to be different.

[0030] Setting different gear ratios in a 2-roll mill may include setting different gear ratios to produce backlash.

[0031] The adhesive may include polytetrafluoroethylene (PTFE).

[0032] According to another aspect of this disclosure, a secondary battery is provided, which includes the aforementioned self-supporting membrane.

[0033] Beneficial effects

[0034] According to embodiments of this disclosure, electrodes for secondary batteries can be manufactured by a dry process including a step of forming patterns on a self-supporting film, thereby improving peel strength and adhesion.

[0035] The effects of this disclosure are not limited to those described above, and those skilled in the art will clearly understand from the description of the appended claims other additional effects not described above. Attached Figure Description

[0036] Figure 1 A pattern of a self-supporting membrane according to an embodiment of the present disclosure is schematically shown;

[0037] Figure 2 This is a cross-sectional view of the pattern of a self-supporting membrane according to an embodiment of the present disclosure;

[0038] Figure 3 This is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present disclosure;

[0039] Figure 4 This is a graph used in the embodiments and comparative examples of this disclosure to compare peel strength based on patterns formed on self-supporting films included in electrodes for secondary batteries.

[0040] Figure 5 This is a graph used in embodiments and comparative examples of this disclosure to compare peel strength based on the spacing of patterns formed on a self-supporting film included in an electrode for a secondary battery; and

[0041] Figure 6 This is a graph used in the embodiments and comparative examples of this disclosure to compare peel strength based on the depth of the pattern formed on the self-supporting film included in the electrode for a secondary battery. Detailed Implementation

[0042] In the following description, various embodiments of this disclosure will be illustrated with reference to the accompanying drawings to enable those skilled in the art to readily implement them. This disclosure can be modified in various ways and is not limited to the embodiments set forth herein.

[0043] Electrodes for secondary batteries according to embodiments of this disclosure will now be described.

[0044] An electrode for a secondary battery according to an embodiment of this disclosure includes: an electrode current collector; and an electrode layer formed of a free-standing film located on the electrode current collector. The electrode layer includes an electrode composition in which an active material, a conductive material, and a binder are dry-mixed.

[0045] An electrode layer can be formed during the fabrication of a self-supporting film, and the electrode layer can be attached to an electrode current collector via a lamination process. Here, the electrode layer may have a pattern, which is directional. The pattern according to this embodiment may have a spacing of approximately 100 μm to 2000 μm. Furthermore, the pattern according to this embodiment may have a depth of approximately 1.5 μm to approximately 35 μm. In this case, the spacing of the pattern can be defined as the distance between adjacent grooves, and the depth of the pattern can be defined as the depth of the groove recess. The pattern can be formed on one surface of the electrode layer attached to the electrode current collector.

[0046] Therefore, when the electrode layer is attached to the electrode current collector, it can exhibit high adhesion, and the electrode layer can have a peel strength of 10 gf / 20 mm or more and 15 gf / 20 mm or less relative to the electrode current collector. Furthermore, by using a pattern to enhance adhesion, the use of existing adhesives can be minimized.

[0047] When the pattern spacing of the electrode layer according to this embodiment is too small, cracks may appear in the electrodes used in the secondary battery, and they may be cut without maintaining a strength higher than the specified level. Furthermore, if the pattern spacing of the electrode layer is too large, it is essentially the same as the case without a pattern, and therefore the effect of improved adhesion due to pattern formation may not be obtained, or the aforementioned effect may be reduced.

[0048] Furthermore, if the pattern depth of the electrode layer is too deep, cracks may form in the electrodes used in the secondary battery, potentially leading to electrode breakage. Conversely, if the pattern depth of the electrode layer is too shallow, it is essentially the same as having no pattern at all, and therefore the improved adhesion due to pattern formation may not be achieved, or the effect may be reduced.

[0049] Next, the components included in the electrode for a secondary battery according to embodiments of the present disclosure will be described in detail.

[0050] Figure 1 A pattern of a self-supporting membrane according to an embodiment of the present disclosure is schematically shown. Figure 2 This is a cross-sectional view of the pattern of a self-supporting membrane according to an embodiment of the present disclosure.

[0051] Reference Figure 1 and Figure 2The electrode layer included in the electrode for a secondary battery according to this embodiment comprises an electrode composition in which an active material, a conductive material, and a binder are dry-mixed, wherein the electrode composition is prepared as a self-supporting film. In this case, the self-supporting film included in the electrode for a secondary battery according to this embodiment comprises a directional pattern on at least one surface. Specifically, the directional pattern may include multiple patterns formed in one direction, such as... Figure 1 As shown, the directional pattern can be a raised or recessed pattern.

[0052] More specifically, in the electrode layer of the electrode for a secondary battery according to this embodiment, the pattern includes a plurality of protrusions 100 and grooves 200 alternately formed and located on a self-supporting film. Here, the plurality of protrusions 100 may be formed such that their heights are constant, and the plurality of grooves 200 may be formed such that their recess depths are constant, but are not limited thereto. In this case, the interval between adjacent grooves 200 can be defined as the pattern interval (d1). When the pattern interval (d1) is outside a certain range, the effects to be achieved by the embodiments of this disclosure may not be realized, or the effects may be reduced.

[0053] At this time, the directional pattern may include the groove portion 200 being formed in an elongated direction ( Figure 1 The horizontal direction in the middle) and the direction of the spacing (d1) forming the pattern ( Figure 1 (Vertical direction in the text). That is, the orientation of the directional pattern can refer to the direction in which the groove portion 200 is formed into an elongated shape. As will be described later, the pattern can be formed when the self-supporting film passes through the roll mill, and the direction of the groove portion 200 forming the pattern can be formed in a direction perpendicular to the direction in which the self-supporting film passes through the roll mill. Thus, the orientation of the directional pattern can be a direction perpendicular to the direction in which the self-supporting film passes through the roll mill. Therefore, the direction of the interval (d1) in forming the pattern can be consistent with the direction in which the self-supporting film passes through the roll mill.

[0054] The pattern is used to improve the adhesion between the self-supporting film and the electrode layer and the electrode current collector.

[0055] The pattern spacing (d1) can be 100 μm or more and 2000 μm or less. More preferably, the pattern spacing (d1) can be 150 μm or more and 1900 μm or less. As an example, the pattern spacing (d1) can be 200 μm or more and 1800 μm or less.

[0056] Therefore, in the electrode for a secondary battery according to this embodiment, the pattern spacing (d1) is within the above-mentioned range, thus the adhesion between the self-supporting film and the electrode current collector can be improved by the pattern, and the peel strength of the self-supporting film can be improved. Furthermore, by forming a pattern on the self-supporting film, the use of adhesives can be minimized.

[0057] On the other hand, when the pattern spacing (d1) is outside the aforementioned range, the effect of the pattern on improving adhesion may be reduced, and the peel strength may also decrease. More specifically, when the pattern spacing (d1) is less than 100 μm, cracks may appear in the electrodes used for secondary batteries due to the excessive patterning on the self-supporting film, and the strength of the electrodes may be weakened. Furthermore, the weakened strength may increase the likelihood of cutting the secondary battery electrodes. On the other hand, when the pattern spacing (d1) exceeds 2000 μm, this may be similar to the case where no pattern is formed, and therefore may not have the effect of improving adhesion, or the effect may be reduced.

[0058] Furthermore, the depth (H) of the pattern can be defined as the depth of the recess 200 from the protrusion 100 or the height of the protrusion 100 from the recess 200.

[0059] In this case, the pattern depth (H) can be 1.5 μm or more and 35 μm or less. More preferably, the pattern depth (H) can be 1.8 μm or more and 32 μm or less. As an example, the pattern depth (H) can be 2 μm or more and 30 μm or less.

[0060] Therefore, in the electrode for a secondary battery according to this embodiment, the depth (H) of the pattern is within the aforementioned range, thus improving the adhesion between the self-supporting film and the electrode current collector, and also improving the peel strength of the self-supporting film. Furthermore, by forming a pattern on the self-supporting film, the use of adhesives can be minimized.

[0061] On the other hand, when the pattern depth (H) is outside the aforementioned range, the effect of the pattern on improving adhesion may be reduced, and the peel strength may also decrease. More specifically, when the pattern depth (H) exceeds 35 μm, cracks may appear in the electrodes used for secondary batteries due to the excessive patterning on the self-supporting film, and the strength of the electrodes may be weakened. Furthermore, the weakened strength increases the likelihood of cutting the secondary battery electrodes. Conversely, when the pattern depth (H) is less than 1.5 μm, the situation may be similar to the case where no pattern is formed, and therefore the effect on improving adhesion may not be observed, or the effect may be reduced.

[0062] To form the pattern according to this embodiment, an embossed pattern is formed on the rollers winding the self-supporting film, thereby transferring the pattern from the rollers to the surface of the self-supporting film. Alternatively, by adjusting the speed of the rollers winding the self-supporting film, a pattern can be formed on the surface of the self-supporting film. Alternatively, a roll mill can pass through the self-supporting film simultaneously with different gear ratios, forming a pattern on the surface of the self-supporting film. When using a roll mill, different gear ratios can result in backlash. Backlash refers to the gap that occurs when the drive roller rotates and the slave roller stops, as the gears are connected to rotate in two directions on one shaft of the roll mill. This generates a shearing force to form a pattern on the self-supporting film. Furthermore, the pattern spacing (d1) and pattern depth (H) can be adjusted according to the size of the backlash.

[0063] The active material can be a positive electrode active material. Examples of active materials may include: lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide, lithium copper oxide (Li2CuO2), vanadium oxide, Ni-position lithium nickel oxide, lithium manganese composite oxide, lithium manganese composite oxide with a spinel structure, LiMn2O4 in which the Li in the formula is partially replaced by alkaline earth metal ions, disulfide compounds, Fe2(MoO4)3, and the like.

[0064] As an example, the active material may include lithium manganese oxide (LMO). Here, the active material may be included in an amount of 85% to 99% by weight based on the total weight of the electrode composition. More preferably, the active material may be included in an amount of 87% to 98% by weight based on the total weight of the electrode composition. As an example, the active material may be included in an amount of 89% to 97% by weight based on the total weight of the electrode composition.

[0065] Adhesives enhance the adhesion between active material particles and between the active material and the current collector. Specific examples of adhesives include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), PVDF-co-HFP, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and these adhesives can be used alone or as a mixture of two or more.

[0066] In one example, the adhesive may include polytetrafluoroethylene (PTFE). Here, the adhesive content may be 1% by weight or more and 5% by weight or less, based on the total weight of the electrode composition. More preferably, the adhesive content may be 1.5% by weight or more and 4.5% by weight or less, based on the total weight of the electrode composition. As an example, the adhesive content may be 2% by weight or more and 4% by weight or less, based on the total weight of the electrode composition.

[0067] Conductive materials are used to impart conductivity to the electrodes, and there are no particular limitations on the types of conductive materials that can be used, as long as they are electronically conductive and do not cause chemical changes in the battery to be constructed. Specific examples of conductive materials include: carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon graphene, and carbon fibers; graphite such as natural graphite and artificial graphite; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. These conductive materials can be used alone or as a mixture of two or more. Here, the conductive material can be included in an amount of 1% to 10% by weight based on the total weight of the electrode composition. More preferably, the content of the conductive material can be 1% by weight or more and 5% by weight or less based on the total weight of the electrode composition. As an example, the content of the conductive material can be 2% by weight or more and 4% by weight or less based on the total weight of the electrode composition.

[0068] The electrodes described above for a secondary battery may be included as the positive electrode in a secondary battery according to another embodiment of the present disclosure. More specifically, a secondary battery according to another embodiment of the present disclosure may include an electrode assembly and an electrolyte, the electrode assembly including a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode.

[0069] Similar to the electrodes for secondary batteries described above, a negative electrode can be manufactured by applying a negative electrode composition, including a negative electrode active material, a polymer material, a conductive material, and the like, to a negative electrode current collector.

[0070] The negative electrode can also be manufactured by attaching or applying a negative electrode composition, including a negative electrode active material, to a negative electrode current collector, and the negative electrode composition may further include, together with the negative electrode active material, the conductive material and polymer material as described above.

[0071] The negative electrode active material can be any material commonly used in the art for lithium secondary batteries. In one example, materials such as lithium metal, lithium alloy, petroleum coke, activated carbon, graphite, silicon, tin, metal oxides, or other carbon materials can be used.

[0072] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes to the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatments of carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, and similar materials can be used.

[0073] The separator separates the negative and positive electrodes and provides a channel for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, a separator with excellent moisture retention of the electrolyte solution and low resistance to the migration of electrolyte ions is preferred.

[0074] In addition, the electrolyte solutions used herein may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, or the like that can be used in the preparation of lithium secondary batteries.

[0075] Specifically, the electrolyte solution may include organic solvents and lithium salts. As an organic solvent, any solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reactions of the battery can migrate. Lithium salts can be used without particular limitation, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries.

[0076] To improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, in addition to the electrolyte components described above, the electrolyte solution may further include, for example, one or more additives, such as haloalkyl carbonate compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, ethylene glycol dimethyl ether (glyme), triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the additives may be included in an amount from 0.1% to 5% by weight, based on the total weight of the electrolyte solution.

[0077] Figure 3 This is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present disclosure.

[0078] Reference Figure 3The method for manufacturing an electrode for a secondary battery according to this embodiment includes: a premixing step (S10) of mixing an active material, a conductive material and a binder; a high-shear mixing step (S20) of applying a high shear force to the mixture mixed in the premixing step; a step of manufacturing a self-supporting film using the high-shear mixed mixture (S30); a step of forming a pattern on the surface of the self-supporting film (S40); and a step of attaching the patterned self-supporting film to an electrode current collector by a lamination process to manufacture an electrode for a secondary battery (S50).

[0079] Here, in the premixing step (S10), the active material, conductive material and adhesive can be dry-mixed.

[0080] The present disclosure will be described below through more specific embodiments. However, the following embodiments are for illustrative purposes only, and the scope of the present disclosure is not limited thereto.

[0081] <Example 1>

[0082] A premixing step for preparing the mixture is performed, wherein the positive electrode active material, conductive material, and binder are dry-mixed using a blender (available from Waring). Here, the positive electrode active material is 94 wt% lithium manganese oxide (LMO), and the conductive material is 3 wt% Super C65. Furthermore, the binder is 3 wt% polytetrafluoroethylene (PTFE). At this point, the premixing step (S10) is performed for 1 minute at 5000 rpm at room temperature, and only the mixing of the active material, conductive material, and binder is induced.

[0083] Then, a high-shear mixing step (S20) was performed using a Bench Kneader PBV-0.1L apparatus (available from Irie Shokai), in which shear force was applied to the mixture prepared in the premixing step (S10) to activate polytetrafluoroethylene (PTFE) and to prepare the electrode composition. At this time, the high-shear mixing step (S20) was performed at 30 rpm for 5 minutes.

[0084] Then, a self-supporting membrane manufacturing step (S30) is performed using a two-roll mill MR-3 apparatus (available from Inoue MFG), in which the electrode composition prepared in the high-shear mixing step (S20) is formed into a membrane with a length of 20 mm and a width of 20 mm to prepare a self-supporting membrane. Furthermore, the self-supporting membrane is manufactured to have a thickness of 200 μm and a porosity of 30%.

[0085] At this point, a pattern is formed on the self-supporting film using the following method. A two-roll mill is used, with each roll having a different gear ratio to create backlash. When the gears are connected and rotate in two directions on one shaft of the two-roll mill, the backlash refers to the gap created when the driving roll rotates and the slave roll stops. Due to the instantaneous shear force generated at this moment, a pattern can be formed on the self-supporting film. The size of the backlash is adjusted using the above method to form a pattern with a spacing of 200 μm and a depth of 10 μm.

[0086] <Example 2>

[0087] The self-supporting membrane was prepared in the same manner as in Example 1, except that in Example 2, the pattern spacing was formed to be 500 μm.

[0088] <Example 3>

[0089] The self-supporting membrane was prepared in the same manner as in Example 1, except that in Example 3, the pattern spacing was formed to be 1700 μm.

[0090] <Example 4>

[0091] The self-supporting membrane was prepared in the same manner as in Example 2, except that in Example 4, the depth of the pattern was formed to be 2 μm.

[0092] <Example 5>

[0093] The self-supporting membrane was prepared in the same manner as in Example 2, except that in Example 5, the pattern depth was formed to be 30 μm.

[0094] <Comparative Example 1>

[0095] The self-supporting membrane was prepared in the same manner as in Example 1, except that no pattern was formed in Comparative Example 1.

[0096] <Comparative Example 2>

[0097] The self-supporting membrane was prepared in the same manner as in Example 1, except that in Comparative Example 2, the pattern spacing was formed to be 70 μm.

[0098] <Comparative Example 3>

[0099] The self-supporting membrane was prepared in the same manner as in Example 1, except that in Comparative Example 3, the pattern spacing was formed to be 2500 μm.

[0100] <Comparative Example 4>

[0101] The self-supporting membrane was prepared in the same manner as in Example 2, except that in Comparative Example 4, the depth of the pattern was formed to be 1 μm.

[0102] <Comparative Example 5>

[0103] The self-supporting membrane was prepared in the same manner as in Example 2, except that in Comparative Example 5, the depth of the pattern was formed to be 40 μm.

[0104] <Experimental Example 1 (Determination of Peel Strength)>

[0105] For each self-supporting membrane prepared in Examples 1 to 5 and Comparative Examples 1 to 5, double-sided adhesive tape was attached to a glass slide, and then the self-supporting membrane side was attached to the surface of the double-sided adhesive tape. The glass slide was then fixed in a flat position, and the end of the electrode current collector was fixed to a clamp. The electrode current collector was then pulled in a direction perpendicular to the ground on which the glass slide was placed (90 degrees) using an Instron UTM device. The peel strength between the electrode current collector and the self-supporting membrane was measured at a speed of 300 mm / min, and the average value was taken. The results are shown in Table 1 below.

[0106] [Table 1]

[0107]

[0108] <Experimental Results Analysis 1 - Pattern Spacing>

[0109] Figure 4 This is a graph used in the embodiments and comparative examples of this disclosure to compare peel strength based on patterns formed on self-supporting films included in electrodes for secondary batteries.

[0110] Figure 5 This is a graph used in the embodiments and comparative examples of this disclosure to compare peel strength based on the spacing of patterns formed on a self-supporting film included in an electrode for a secondary battery.

[0111] At this point, it was confirmed that the peel strength gradually decreased in the order of Example 1, Example 2, Example 3, Comparative Example 3, and Comparative Example 1.

[0112] Reference Figure 4 It was confirmed that in Comparative Example 2, the electrode could not be measured because it was cut by a crack during the measurement process. Therefore, when the gap between the patterns of the self-supporting film was too narrow, the strength of the electrode could not be maintained. Furthermore, it was confirmed that Comparative Example 3 was substantially the same as the self-supporting film without patterns, but because the pattern spacing of the self-supporting film was wider, the peel strength was not excellent. That is, it was confirmed that when the pattern spacing of the self-supporting film is too narrow or too wide compared to the examples, the peel strength is not excellent.

[0113] Therefore, it was confirmed that when the pattern spacing of the self-supporting film has the same spacing as in Examples 1 to 3, the peel strength is excellent.

[0114] <Experimental Results Analysis 2 - Pattern Depth>

[0115] Figure 6 This is a graph used in the embodiments and comparative examples of this disclosure to compare peel strength based on the depth of the pattern formed on the self-supporting film included in the electrode for a secondary battery.

[0116] At this point, it was confirmed that the peel strength gradually decreased in the order of Example 5, Example 2, Example 4, and Comparative Example 4.

[0117] Reference Figure 6 It was confirmed that in Comparative Example 5, the electrode was cut due to a crack during measurement, making measurement impossible. Therefore, when the pattern depth of the self-supporting film was too deep, the electrode strength could not be maintained. Furthermore, it was confirmed that in Comparative Example 4, as the pattern depth of the self-supporting film became shallower, it became substantially the same as a self-supporting film without a pattern, and therefore the peel strength was not excellent. In other words, it was confirmed that when the pattern depth of the self-supporting film was too high or too shallow compared to the examples, the peel strength was not excellent.

[0118] Therefore, it was confirmed that when the pattern depth of the self-supporting film is within the range disclosed in Examples 2, 4 and 5, the peel strength is excellent.

[0119] Furthermore, the peel strength of Example 5 was confirmed to be the best from the examples and comparative examples. Therefore, it was confirmed that a self-supporting film with the best peel strength can be manufactured when the spacing and depth of the pattern are as disclosed in Example 5.

[0120] Although the invention has been shown and described above with reference to preferred embodiments, the scope of this disclosure is not limited thereto, and those skilled in the art can use the basic principles of the invention as defined in the appended claims to design many other modifications and improvements that will also fall within the spirit and scope of this disclosure.

Claims

1. An electrode for a secondary battery, comprising: Electrode current collector; and The electrode layer located on the electrode current collector, The electrode layer comprises an electrode composition in which active materials, conductive materials, and binders are dry-mixed. The electrode composition is prepared as a self-supporting membrane. The self-supporting membrane comprises a directional pattern on at least one surface, and The pattern has a spacing of 100 μm to 2000 μm and a depth of 1.5 μm to 35 μm.

2. The electrode for a secondary battery according to claim 1, wherein: The pattern is a raised or recessed pattern.

3. The electrode for a secondary battery according to claim 2, wherein: The self-supporting film is attached to the electrode current collector such that a surface on which the pattern is formed is in contact with the electrode current collector.

4. The electrode for a secondary battery according to claim 1, wherein: The active material includes at least one selected from the group consisting of: lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium copper oxide (Li2CuO2), vanadium oxide, disulfide compounds, Fe2(MoO4)3, and lithium manganese oxide (LMO).

5. The electrode for a secondary battery according to claim 1, wherein: The adhesive comprises polytetrafluoroethylene (PTFE).

6. The electrode for a secondary battery according to claim 1, wherein: The self-supporting membrane has a peel strength of 10 gf / 20 mm or more and 15 gf / 20 mm or less.

7. A method for manufacturing an electrode for a secondary battery, the method comprising the following steps: The active material, conductive material and adhesive are dry-mixed to prepare a mixture; A shear force is applied to the mixture to prepare a self-supporting membrane; A directional pattern is formed at regular intervals on the self-supporting membrane; and The self-supporting film is attached to the electrode current collector to form an electrode for a secondary battery. The pattern has a spacing of 100 μm to 2000 μm and a depth of 1.5 μm to 35 μm.

8. The method for manufacturing an electrode for a secondary battery according to claim 7, wherein: The pattern is a raised or recessed pattern.

9. The method for manufacturing an electrode for a secondary battery according to claim 7, wherein: The self-supporting film is attached to the electrode current collector such that a surface on which the pattern is formed is in contact with the electrode current collector.

10. The method for manufacturing an electrode for a secondary battery according to claim 7, wherein: The steps of forming the pattern include any of the following steps: forming the pattern on the self-supporting film by forming an embossing pattern on a roller for winding the self-supporting film, adjusting the speed of the roller, and setting the gear ratio of the twin-roll mill to be different.

11. The method for manufacturing an electrode for a secondary battery according to claim 10, wherein: Setting the gear ratio of the twin-roll mill to different values ​​includes setting the gear ratio to different values ​​to produce backlash.

12. The method of manufacturing an electrode for a secondary battery according to claim 7, wherein: the binder includes polytetrafluoroethylene (PTFE).

13. A secondary battery comprising the electrode for a secondary battery according to claim 1.

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