Electrode for secondary battery, secondary battery comprising the same, and method of manufacturing electrode

Abstract

An electrode for a secondary battery according to an embodiment of the present disclosure includes: an electrode current collector; and an electrode layer on the electrode current collector, wherein the electrode layer includes an electrode composition having a dry mixture of an active material, a conductive material, and a binder, wherein the binder includes a first fiber and a second fiber that is fibrillated from the first fiber, and wherein a diameter of the first fiber is greater than a diameter of the second fiber.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0137053, filed with the Korean Intellectual Property Office on October 21, 2020, and Korean Patent Application No. 10-2021-0137264, filed with the Korean Intellectual Property Office on October 15, 2021, the disclosures of which are incorporated herein by reference in their entirety.

[0003] This disclosure relates to an electrode for a secondary battery, a secondary battery including the same, and a method of manufacturing the electrode, and more specifically, to an electrode for a secondary battery having improved tensile strength and flexibility, a secondary battery including the same, and a method of manufacturing the electrode. Background Technology

[0004] With technological advancements and increasing demand for mobile devices, the need for secondary batteries as an energy source has grown rapidly. Among these secondary batteries, lithium-ion batteries, characterized by high energy density, high voltage, long cycle life, and low self-discharge rate, are commercially available and widely used.

[0005] In particular, secondary batteries have attracted much attention as a power source for electric drive 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] In addition, with increasing attention to environmental issues, research is frequently conducted on electric vehicles and hybrid electric vehicles, which can replace fossil fuel-powered cars such as gasoline and diesel vehicles, which are major contributors to air pollution. Although nickel-metal hydride batteries are primarily used as power sources for electric and hybrid electric vehicles, research on the use of high-energy-density lithium-ion batteries is actively underway, with some already in the commercialization stage.

[0007] Electrodes for conventional secondary batteries are typically manufactured using a wet process. However, wet manufacturing of electrodes generally requires high-temperature heat treatment, which carries the risk of damage to metal oxides. Therefore, there is an increasing need to develop electrodes manufactured using a dry process. Summary of the Invention

[0008] Technical issues

[0009] The present invention aims to provide an electrode for a secondary battery with improved tensile strength and flexibility, a secondary battery including the electrode, and a method for manufacturing the electrode.

[0010] The inventive objectives of this disclosure are not limited to those described herein, and other inventive objectives not described herein should be clearly understood by those skilled in the art from the following detailed description and accompanying drawings.

[0011] Technical solution

[0012] According to embodiments 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 comprises an electrode composition in which an active material, a conductive material, and an adhesive are dry-mixed, wherein the adhesive comprises a first fiber and a second fiber fiberized from the first fiber, and wherein the diameter of the first fiber is larger than the diameter of the second fiber.

[0013] The diameter of the first fiber may be 6.1 μm or larger and 64.9 μm or smaller.

[0014] The diameter of the second fiber can be 0.01 μm or larger and 2.0 μm or smaller.

[0015] The content of the adhesive can be from 1% to 5% by weight based on the total weight of the electrode composition.

[0016] The electrodes used for the secondary battery may have a contact angle deviation of 0.01 degrees or greater and 5.0 degrees or less.

[0017] The adhesive may include polytetrafluoroethylene (PTFE).

[0018] The active material may include at least one selected from the group consisting of lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide, lithium copper oxide (Li2CuO2), vanadium oxide, Ni-type lithium nickel oxide, lithium manganese composite oxide, lithium manganese composite oxide having a spinel structure, LiMn2O4 in which part of the Li is replaced by an alkaline earth metal ion, disulfide compounds, Fe2(MoO4)3, and lithium manganese oxide (LMO).

[0019] The electrode composition is manufactured as a self-standing membrane, and the self-standing membrane can be attached to the electrode current collector.

[0020] The self-supporting membrane can have a strength of 13 kgf / cm². 2 Or larger and 30 kgf / cm 2 Or even lower tensile strength.

[0021] According to another embodiment 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 at a first speed to prepare a first electrode composition; applying a shear force to the first electrode composition at a second speed to prepare a second electrode composition; and manufacturing an electrode for the secondary battery on an electrode current collector comprising an electrode layer including the second electrode composition, wherein the first speed is faster than the second speed.

[0022] The first electrode composition includes a binder comprising a first fiber, and the second electrode composition includes a binder comprising the first fiber and a second fiber fibrillated from the first fiber, wherein the diameter of the first fiber may be larger than the diameter of the second fiber.

[0023] The diameter of the first fiber may be 6.1 μm or larger and 64.9 μm or smaller.

[0024] The diameter of the second fiber can be 0.01 μm or larger and 2.0 μm or smaller.

[0025] The first speed can be from 2000 rpm to 6000 rpm, and the second speed can be from 1 rpm to 50 rpm.

[0026] The content of the adhesive can be from 1% to 5% by weight based on the total weight of the electrode composition.

[0027] The adhesive may include polytetrafluoroethylene (PTFE).

[0028] The active material may include at least one selected from the group consisting of lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide, lithium copper oxide (Li2CuO2), vanadium oxide, Ni-type lithium nickel oxide, lithium manganese composite oxide, lithium manganese composite oxide having a spinel structure, LiMn2O4 in which part of the Li is replaced by an alkaline earth metal ion, disulfide compounds, Fe2(MoO4)3, and lithium manganese oxide (LMO).

[0029] In the step of manufacturing an electrode for a secondary battery, wherein the electrode layer comprising the second electrode composition is located on an electrode current collector, the second electrode composition may be manufactured as a self-standing membrane and attached to the electrode current collector.

[0030] The self-supporting membrane can have a strength of 13 kgf / cm². 2Or larger and 30 kgf / cm 2 Or even lower tensile strength.

[0031] According to yet another embodiment of this disclosure, a secondary battery including the electrodes for a secondary battery mentioned above is provided.

[0032] Beneficial effects

[0033] According to embodiments of this disclosure, electrodes for secondary batteries and secondary batteries including the electrodes can be manufactured in a dry manner, including a high-speed high-shear mixing step and a low-speed high-shear mixing step, thereby improving the tensile strength and flexibility of the electrodes.

[0034] The effects of this disclosure are not limited to those mentioned above, and any additional effects not described above will be clearly understood by those skilled in the art from the description of the appended claims. Attached Figure Description

[0035] Figure 1 This is a diagram schematically illustrating an electrode composition for a secondary battery according to an embodiment of the present disclosure;

[0036] Figure 2 This is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention;

[0037] Figure 3 This is a graph comparing the tensile strength, elongation, and contact angle deviation of the first fiber diameter of the adhesive included in the electrode of a secondary battery according to embodiments and comparative examples of this disclosure; and

[0038] Figure 4 This is a graph comparing the tensile strength, elongation, and contact angle deviation of the second fiber diameter of the adhesive included in the electrode of a secondary battery according to the embodiments and comparative examples of this disclosure. Detailed Implementation

[0039] In the following description, various embodiments of this disclosure will be described in detail with reference to the accompanying drawings, so that those skilled in the art can readily implement them. This disclosure can be modified in various different ways and is not limited to the embodiments set forth herein.

[0040] An electrode for a secondary battery according to an embodiment of this disclosure will now be described.

[0041] An electrode for a secondary battery according to an embodiment of this disclosure includes an electrode current collector and an electrode layer formed by a free-standing film 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.

[0042] The electrode layer can be formed by lamination after the self-standing membrane is first produced, and the self-standing membrane is attached to the electrode current collector. Here, the self-standing membrane may have a strength of 13 kgf / cm². 2 Or larger and 30 kgf / cm 2 Or even lower tensile strength.

[0043] Therefore, the self-supporting membrane can be in a state where the active material, conductive material, and binder included in the electrode composition are mixed together with high bonding strength, and the self-supporting membrane can be easily stored in roll form. Furthermore, productivity is improved, and the flexibility of the electrode can be effectively improved. However, when the tensile strength of the self-supporting membrane is less than 13 kgf / cm²... 2 During charging and discharging, cracks form between the electrode active materials in the electrode, and the electrode flexibility decreases, making it potentially difficult to store during manufacturing.

[0044] Furthermore, the electrodes for the secondary battery may have a contact angle deviation of 0.01 degrees or greater and 5.0 degrees or less. More preferably, the electrodes for the secondary battery may have a contact angle deviation of 0.05 degrees or greater and 4.0 degrees or less. As an example, the electrodes for the secondary battery may have a contact angle deviation of 0.1 degrees or greater and 3.0 degrees or less. Here, contact angle may refer to the average and standard deviation of the contact angle at each corner and center portion of the electrode surface.

[0045] Therefore, the electrodes used in secondary batteries have a small deviation in contact angle, which improves the dispersibility of the binder included in the electrode composition. Furthermore, the binder has excellent bridging effect, and therefore the electrode comprising this electrode composition can have excellent resistance reduction effect.

[0046] However, when the contact angle of the electrode used in a secondary battery is greater than 5.0 degrees, the deviation of the contact angle may increase, and therefore the dispersibility of the binder included in the electrode composition may decrease. Furthermore, this results in a reduced bridging effect of the binder, high resistance of the electrode comprising the electrode composition, and may also reduce the discharge capacity of the battery cell.

[0047] Next, each component included in the electrode for a secondary battery according to embodiments of this disclosure will be described in detail.

[0048] Figure 1 This is a diagram schematically illustrating an electrode composition for a secondary battery according to an embodiment of the present disclosure.

[0049] Reference Figure 1 In the electrode composition constituting the electrode layer in the electrode for a secondary battery according to an embodiment of the present disclosure, the binder includes a first fiber 200 and a second fiber 300 located between a plurality of active material particles 100. Here, the second fiber 300 may be fibrous from the first fiber 200. That is, the second fiber 300 may be formed to extend from the first fiber 200. More specifically, "the second fiber 300 is fibrous from the first fiber 200" herein means that the second fiber 300 is pulled out from or extends from the first fiber 200 as a predetermined pressure and / or frictional force is applied to the first fiber 200.

[0050] However, in addition to the fact that the second fiber 300 is fiberized from the first fiber 200, the second fiber 300 may also include, but is not limited to, fibers that are separate from the first fiber 200 or formed by separately aggregating adhesive particles.

[0051] Adhesives perform the function of improving the adhesion between active material particles and the adhesion between the active material and the current collector. Specific examples include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and these can be used alone or as a mixture of two or more.

[0052] In one example, the adhesive may include polytetrafluoroethylene (PTFE). Here, PTFE is characterized in that fibers are pulled out of the particles upon application of shear force. That is, in the electrode for a secondary battery according to an embodiment of this disclosure, a strong shear force is applied to an electrode composition comprising PTFE as an adhesive, and the electrode composition may be mixed by a physical mixing method according to the fiberization of the PTFE.

[0053] Therefore, in the electrode for a secondary battery according to the embodiments of the present disclosure, the electrode composition can be dry-mixed without separate solvents or additives, which is very effective for bridging between active material particles or between active material particles and current collectors, and can also prevent damage to the active material during the heat treatment process at high temperatures according to the existing mixing method.

[0054] Because shear forces of different speeds are applied by the method of manufacturing electrodes according to embodiments of this disclosure, the adhesive comprising polytetrafluoroethylene (PTFE) can produce fibers of different diameters drawn from the PTFE particles. In one example, the adhesive comprises a first fiber 200 and a second fiber 300. The diameter of the first fiber 200 is larger than the diameter of the second fiber 300.

[0055] The diameter of the first fiber 200 may be 6.1 μm or larger and 64.9 μm or smaller. More preferably, the diameter of the first fiber 200 may be 8 μm or larger and 60 μm or smaller. In one example, the diameter of the first fiber 200 may be 10 μm or larger and 55 μm or smaller.

[0056] The diameter of the second fiber 300 may be 0.01 μm or larger and 2.0 μm or smaller. More preferably, the diameter of the second fiber 300 may be 0.05 μm or larger and 1.5 μm or smaller. In one example, the diameter of the second fiber 300 may be 0.1 μm or larger and 1.0 μm or smaller.

[0057] Therefore, the electrode for a secondary battery according to embodiments of this disclosure has the diameters of the first fiber 200 and the second fiber 300 of the adhesive within the range mentioned above, such that the tensile strength is improved by the first fiber 200, and the bridging effect between particles within the electrode composition is improved by the second fiber 300. Furthermore, the first fiber 200 prevents adhesive aggregation and improves dispersibility, thus resulting in superior resistance reduction in the electrode comprising the above-described electrode composition.

[0058] In contrast, when the diameter of the first fiber 200 is outside the range mentioned above, aggregation may be reduced by the prevention of aggregation by the first fiber 200, resulting in a decrease in both tensile strength and elongation, and also a decrease in the dispersibility of the electrode composition. Furthermore, when the diameter of the second fiber 300 is too large, the bridging effect between particles within the electrode composition may be reduced.

[0059] Further, the binder content can be from 1% to 5% by weight based on the total weight of the electrode composition. More preferably, the binder content can be from 1.5% to 4.5% by weight based on the total weight of the electrode composition. In one example, the binder content can be from 2% to 4% by weight based on the total weight of the electrode composition.

[0060] Therefore, the electrode for a secondary battery according to embodiments of this disclosure includes an adhesive within the aforementioned scope, thereby maximizing the fiberization of the adhesive and achieving excellent bridging between particles within the electrode composition, resulting in excellent tensile strength. Furthermore, adhesive aggregation is prevented and dispersibility is improved, thus resulting in excellent resistance reduction in the electrode comprising the above-described electrode composition.

[0061] In contrast, when the total binder content is less than 1% by weight, the bridging effect between particles within the electrode composition is insufficient, and therefore the tensile strength can also be greatly reduced. Furthermore, when the total binder content is greater than 5% by weight, the binder acts as a resistor in the electrode comprising this electrode composition, leading to problems where high output is difficult to expect.

[0062] The active material can be a positive electrode active material. Positive electrode active materials may include, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide, lithium copper oxide (Li2CuO2), vanadium oxide, Ni-site lithium nickel oxide, lithium manganese composite oxide, lithium manganese composite oxide with spinel structure, LiMn2O4 in which part of the Li is replaced by alkaline earth metal ions, disulfide compounds, Fe2(MoO4)3, and the like.

[0063] In one 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. In one 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.

[0064] Conductive materials are used to impart conductivity to the electrodes, and there are no particular limitations on the use of conductive materials, provided that they are conductive and do not cause chemical changes in the battery to be configured. Specific examples 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 metal 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, and these can be used alone or as a mixture of two or more. Here, conductive materials can be included in an amount of 1% to 10% by weight based on the total weight of the electrodes.

[0065] The electrodes mentioned above for secondary batteries can be included as positive electrodes in a secondary battery according to another embodiment of this disclosure. More specifically, a secondary battery according to another embodiment of this disclosure may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator inserted between the positive and negative electrodes, and an electrolyte.

[0066] Similar to electrodes used in secondary batteries, a negative electrode can be manufactured by applying a negative electrode slurry, including a negative electrode active material, a polymer material, a conductive material, and the like, to a negative electrode current collector.

[0067] The negative electrode can also be manufactured in the form of a negative electrode slurry, which includes a negative electrode active material, attached to or applied to a negative electrode current collector, and the negative electrode slurry may further include conductive materials and polymer materials together with the negative electrode active material as described above.

[0068] Commonly used negative electrode active materials for lithium secondary batteries can be used as negative electrode active materials. In one example, materials such as lithium metal, lithium alloys, petroleum coke, activated carbon, graphite, silicon, tin, metal oxides, or other carbon materials can be used.

[0069] 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, aluminum-cadmium alloys with surface treatments of carbon, nickel, titanium, silver, etc., and similar materials can be used.

[0070] Separators are used to separate the negative and positive electrodes and provide channels for lithium-ion migration. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium-ion secondary batteries. In particular, separators with excellent moisture retention capabilities for the electrolyte and low resistance to electrolyte ion migration are preferred.

[0071] In addition, the electrolytes used in this article may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, or similar electrolytes, which can be used in the production of lithium secondary batteries, but are not limited thereto.

[0072] Specifically, the electrolyte may include organic solvents and lithium salts. As an organic solvent, any solvent may be used without particular restriction, as long as it can act as a medium for the migration of ions involved in the electrochemical reactions of the battery. Lithium salts may be used without particular restriction, as long as they are compounds used in lithium-ion secondary batteries that can provide lithium ions.

[0073] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may further include one or more additives, such as alkyl halogenated compounds, such as ethylene difluorocarbonate; pyridine; triethyl phosphite; triethanolamine; cyclic ethers; ethylenediamine; ethylene glycol dimethyl ether; triammonium hexaphosphate; nitrobenzene derivatives; sulfur; quinone imine dyes; N-substituted α-azolidinones; N,N-substituted imidazolidinyl ethers; ethylene glycol dialkyl ethers; ammonium salts; pyrrole; 2-methoxyethanol; or aluminum trichloride. In this case, the additives may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

[0074] Figure 2 This is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to another embodiment of the present invention.

[0075] Reference Figure 2 The 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-speed mixing step (S20) of applying shear force at a first speed to prepare a first electrode composition; a low-speed mixing step (S30) of applying shear force to the first electrode composition at a second speed to prepare a second electrode composition; a step of manufacturing a self-standing membrane using the second electrode composition (S40); and a step of manufacturing an electrode by a lamination process after attaching the self-standing membrane to an electrode current collector (S50).

[0076] Here, in the premixing step (S10), the active material, conductive material, and binder can be dry-mixed. The first speed is faster than the second speed.

[0077] More specifically, the first speed can be from 2000 rpm to 6000 rpm, and the second speed can be from 1 rpm to 50 rpm. In one example, the first speed can be from 2500 rpm to 5500 rpm, and the second speed can be from 5 rpm to 40 rpm.

[0078] Therefore, performing the high-speed mixing step (S20) at a speed within the aforementioned range allows sufficient internal pressure and friction to be applied to permit the fiberization of polytetrafluoroethylene (PTFE). However, in the case of the high-speed mixing step (S20), the mixing speed is relatively fast and the aggregation of PTFE can occur more quickly, allowing the formation of first fibers 200 with a relatively large diameter, and thus further improving the tensile strength of the electrode.

[0079] On the other hand, if the high-speed mixing step (S20) is carried out at an excessively high speed outside the range mentioned above, a first fiber 200 with an excessively large diameter is formed, which makes it difficult to fiberize the second fiber 300 from the first fiber 200. In contrast, if the process is carried out at an excessively low speed, a first fiber 200 with an excessively small diameter is formed, thereby reducing the tensile strength of the electrode.

[0080] Furthermore, the low-speed mixing step (S30) is performed at a speed within the range mentioned above, and therefore the mixing speed is relatively very low, and strong internal pressure is applied to the polytetrafluoroethylene (PTFE), while the speed at which frictional force is applied may be very slow. That is, in the low-speed mixing step (S30), a second fiber 300 with a relatively small diameter can be formed at a rate within the range mentioned above through contact between polytetrafluoroethylene (PTFE) particles or contact between polytetrafluoroethylene (PTFE) and the active material, thereby improving the bridging effect between particles within the electrode composition.

[0081] On the other hand, if the low-speed mixing step (S30) is carried out at an excessively high speed outside the range mentioned above, second fibers 300 with excessively large diameters are formed, which can reduce the bridging degree between particles in the electrode composition. Furthermore, in contrast, if the mixing step is carried out at an excessively low speed, there is a problem of aggregation between the second fibers 300.

[0082] The contents of this disclosure will be described below by way of more specific embodiments. However, the following embodiments are for illustrative purposes only, and the scope of this disclosure is not limited thereto.

[0083] <Example 1>

[0084] A premixing step is performed to prepare a mixture in which the active material, conductive material, and binder are dry-mixed using a Waring blender. Here, the active material is 95% by weight lithium manganese oxide (LMO), and the conductive material is 2% by weight Super C65. Further, the binder is 3% by weight polytetrafluoroethylene (PTFE). At this point, the premixing step (S10) is performed at 5000 rpm for 1 minute, thereby inducing mixing only of the active material, conductive material, and binder.

[0085] Then, a high-speed mixing step (S20) is performed using a Nobilta NOB-130 device (available from Hosokawa Micron), in which shear force is applied at a first speed to the mixture prepared in the premixing step (S10) to prepare the first electrode composition. At this time, the high-speed mixing step (S20) is performed at 3000 rpm for 10 minutes, so that the first fiber 200 is formed in the first electrode composition.

[0086] Then, a low-speed mixing step (S30) is performed using a Bench Kneader PBV-0.1L apparatus (available from Irie Shokai), in which shear force is applied at a second speed to the first electrode composition prepared in the high-speed mixing step (S20) to prepare the second electrode composition. At this time, the low-speed mixing step (S30) is performed at 10 rpm for 5 minutes, so that the second fiber 300 is formed together with the first fiber 200 in the second electrode composition.

[0087] <Example 2>

[0088] The electrode composition was prepared in the same manner as in Example 1, except that in Example 1, a high-speed mixing step (S20) was performed at 5000 rpm.

[0089] <Example 3>

[0090] The electrode composition was prepared in the same manner as in Example 1, except that in Example 1, a high-speed mixing step (S20) was performed at 5000 rpm and a low-speed mixing step (S20) was performed at 30 rpm.

[0091] <Comparative Example 1>

[0092] The electrode composition was prepared in the same manner as in Example 1, except that in Example 1, a high-speed mixing step (S20) was performed at 500 rpm.

[0093] <Comparative Example 2>

[0094] The electrode composition was prepared in the same manner as in Example 1, except that in Example 1, a high-speed mixing step (S20) was performed at 5000 rpm for 2 minutes.

[0095] <Comparative Example 3>

[0096] The electrode composition was prepared in the same manner as in Example 1, except that in Example 1, a low-speed mixing step (S30) was performed at 60 rpm.

[0097] <Comparative Example 4>

[0098] The electrode composition was prepared in the same manner as in Example 1, except that in Example 1, a low-speed mixing step (S30) was performed at 100 rpm.

[0099] <Experimental Example 1 (Measurement of Fiber Diameter)>

[0100] About 30 or more SEM images were analyzed for each electrode composition prepared in Examples 1 to 3 and Comparative Examples 1 to 4, and the average value of the measured fiber diameter was calculated. The results are shown in Table 1 below.

[0101] [Table 1]

[0102]

[0103] <Experimental Example 2 (Measurement of Tensile Strength and Elongation)>

[0104] For the electrode compositions prepared in Examples 1 to 3 and Comparative Examples 1 to 4, a self-standing membrane manufacturing step (S30) was performed using a Roll Mill apparatus (available from Inoue MFG) to manufacture self-standing membranes with a length of 20 mm and a width of 20 mm. For each manufactured self-standing membrane, both ends were fixed with clamps, and the tensile strength of the self-standing membrane was measured using an Instron UTM apparatus at a speed of 50 mm / min. The results are shown in Table 2 below.

[0105] Furthermore, the elongation was calculated by multiplying the length at break by the length of the initial sample of each manufactured self-supporting membrane by 100, and the results are shown in Table 2 below.

[0106] [Table 2]

[0107]

[0108]

[0109] <Experiment Example 3 (Measurement of Contact Angle)>

[0110] Reference Figure 2 For Examples 1 to 3 and Comparative Examples 1 to 4, the self-standing film roller manufactured in Experimental Example 2 was pressed onto a current collector serving as aluminum foil, and the load value was then set to 5 mAh / cm². 2 The porosity was set to 30%. Under these conditions, the electrode fabrication step (S40) for manufacturing the positive electrode was performed. Then, each fabricated electrode was randomly sampled into 5cm × 5cm portions, and 200μl of distilled water was dropped onto a total of 5 locations corresponding to each corner and the center portion to measure the contact angle, and the mean and standard deviation were calculated. The results are shown in Table 3 below.

[0111] [Table 3]

[0112]

[0113] <Experimental Results Analysis>

[0114] Figure 3 This is a graph comparing the diameter, tensile strength, elongation, and contact angle deviation of the first fiber 200 used as an adhesive in the electrode of a secondary battery according to embodiments and comparative examples of this disclosure. Specifically, Figure 3 The results shown in Tables 1 to 3 are graphs used to compare the tensile strength, elongation, and contact angle deviation of Examples 1 to 3, and Comparative Examples 1 and 2, respectively. In this case, the diameter of the first fiber 200 gradually decreases in the order of Comparative Example 2, Example 1, Example 2, Example 3, and Comparative Example 1.

[0115] In Comparative Example 2, the diameter of the first fiber 200 is 65 μm, which is larger than that of the Example, while in Comparative Example 1, the diameter of the first fiber 200 is 6 μm, which is smaller than that of the Example.

[0116] Reference Figure 3 It can be confirmed that Comparative Example 2 is not superior in terms of tensile strength, elongation, and contact angle deviation. Furthermore, it can be confirmed that Comparative Example 1 is superior in terms of contact angle deviation, but not superior in terms of tensile strength and elongation. That is, when the diameter of the first fiber 200 is too large compared to the example, it can be confirmed that tensile strength, elongation, and contact angle deviation are not all superior. In addition, when the diameter of the first fiber 200 is too small compared to the example, it can be confirmed that the contact angle deviation is excellent, but the tensile strength and elongation are reduced.

[0117] Therefore, when the first fiber 200 included in the adhesive has the same diameter as in Examples 1 to 3, it can be confirmed that the tensile strength, elongation, and contact angle deviation are excellent as a whole.

[0118] Figure 4 This is a graph comparing the tensile strength, elongation, and contact angle deviation of the second fiber diameter of the adhesive included in the electrode of a secondary battery according to embodiments and comparative examples of this disclosure. Specifically, Figure 4 The results shown in Tables 1 to 3 are graphs used to compare the tensile strength, elongation, and contact angle deviation of Examples 1 to 3, Comparative Example 3, and Comparative Example 4, respectively. In this case, the diameter of the second fiber 300 gradually increases in the order of Examples 1 to 3, Comparative Example 3, and Comparative Example 4.

[0119] Reference Figure 4It can be confirmed that the elongation gradually improves, but as the diameter of the second fiber 300 gradually increases, the tensile strength and contact angle deviation gradually decrease. That is, when the diameter of the second fiber 300 is too large compared to the example, it can be confirmed that the tensile strength and contact angle deviation are not excellent.

[0120] Therefore, when the second fiber included in the adhesive has the same diameter as in Examples 1 to 3, it can be confirmed that the tensile strength, elongation, and contact angle deviation are excellent as a whole.

[0121] Although the invention has been shown and described above with reference to preferred embodiments, the scope of this disclosure is not limited thereto, and various other modifications and improvements can be designed by those skilled in the art using the principles of the invention as defined in the appended claims, which 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 an active material, a conductive material, and a binder are dry-mixed. The adhesive comprises a first fiber and a second fiber fibrillated from the first fiber. The diameter of the first fiber is larger than the diameter of the second fiber. The diameter of the first fiber is 6.1 μm or greater and 64.9 μm or less, and The diameter of the second fiber is 0.01 μm or larger and 2.0 μm or smaller.

2. The electrode for a secondary battery according to claim 1, wherein: The content of the adhesive is from 1% to 5% by weight based on the total weight of the electrode composition.

3. The electrode for a secondary battery according to claim 1, wherein: The electrodes used in the secondary battery have a contact angle deviation of 0.01 degrees or greater and 5.0 degrees or less.

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

5. 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).

6. The electrode for a secondary battery according to claim 1, wherein: The active material includes Ni-type lithium nickel oxide or LiMn2O4 in which part of the Li is replaced by alkaline earth metal ions.

7. The electrode for a secondary battery according to claim 1, wherein: The electrode composition is fabricated into a self-supporting membrane, and The self-supporting membrane is attached to the electrode current collector.

8. The electrode for a secondary battery according to claim 7, wherein: The self-supporting membrane has a strength of 13 kgf / cm². 2 Or larger and 30 kgf / cm 2 Or even lower tensile strength.

9. A method for manufacturing an electrode for a secondary battery, the method comprising the following steps: Dry-mixing active materials, conductive materials, and binders to prepare a mixture; A shear force is applied to the mixture at a first velocity to prepare a first electrode composition; A second electrode composition is prepared by applying a shear force to the first electrode composition at a second velocity; and An electrode for a secondary battery is manufactured with an electrode layer comprising the second electrode composition located on an electrode current collector. The first speed is faster than the second speed. The adhesive included in the first electrode composition includes a first fiber. The binder included in the second electrode composition comprises the first fiber and a second fiber fibrillated from the first fiber. The diameter of the first fiber is larger than the diameter of the second fiber. The diameter of the first fiber is 6.1 μm or greater and 64.9 μm or less, and The diameter of the second fiber is 0.01 μm or larger and 2.0 μm or smaller.

10. The method for manufacturing an electrode for a secondary battery according to claim 9, wherein: The first speed is 2000 rpm to 6000 rpm, and The second speed is from 1 rpm to 50 rpm.

11. The method for manufacturing an electrode for a secondary battery according to claim 9, wherein: The content of the adhesive is from 1% to 5% by weight based on the total weight of the electrode composition.

12. The method for manufacturing an electrode for a secondary battery according to claim 9, wherein: The adhesive comprises polytetrafluoroethylene (PTFE).

13. The method for manufacturing an electrode for a secondary battery according to claim 9, 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).

14. The method for manufacturing an electrode for a secondary battery according to claim 9, wherein: The active material includes Ni-type lithium nickel oxide or LiMn2O4 in which part of the Li is replaced by alkaline earth metal ions.

15. The method for manufacturing an electrode for a secondary battery according to claim 9, wherein: In the step of manufacturing an electrode for a secondary battery, wherein the electrode layer, including the second electrode composition, is located on an electrode current collector, The second electrode composition is manufactured as a self-standing membrane and attached to the electrode current collector.

16. The method of manufacturing an electrode for a secondary battery according to claim 15, wherein: The self-supporting membrane has a strength of 13 kgf / cm². 2 Or larger and 30 kgf / cm 2 Or even lower tensile strength.

17. A secondary battery comprising the electrodes for a secondary battery as described in claim 1.

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