Electrode, secondary battery containing the same, and method for manufacturing the same

Abstract

Provided is an electrode comprising an electrode current collector, and an electrode layer located on the electrode current collector and including an active material, a conductive material, a binder, and a fluoroelastomer, the electrode having a bending resistance of Φ (diameter) of 10 mm or less, as well as a secondary battery and an energy storage device including the electrode.

Description

Technical Field

[0001] The present invention relates to an electrode, a secondary battery including the same, and a method for manufacturing the same, and more particularly, to an electrode with improved flexibility, a secondary battery including the same, and a method for manufacturing the same.

[0002] This application claims priority based on Korean Application No. 10-2022-0049213 filed on April 20, 2022, and all the contents disclosed in the specification and drawings of the application are incorporated herein.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, there is an increasing demand for the use of alternative energy and clean energy. As part of this, the field most actively studied is the field of power generation and power storage using electrochemistry. Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage fields are gradually expanding. A lithium secondary battery as a representative example of such a secondary battery can be used not only as an energy source for mobile devices but also recently as a power source for electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. Its usage fields are also expanding for applications such as a power auxiliary source by grid connection.

[0004] The manufacturing process of such a lithium secondary battery is roughly divided into three stages: an electrode manufacturing process, an electrode assembly manufacturing process, and a forming process. The electrode manufacturing process can also be divided into an electrode binder mixing process, an electrode coating process, a drying process, a rolling process, a slitting process, a winding process, and the like.

[0005] Of these, the electrode mixture mixing process is a process of mixing components for forming the electrode active layer, in which the electrochemical reaction actually takes place at the electrode. Specifically, it is a process of mixing the electrode active material, which is an essential element of the electrode, other additives such as conductive materials and fillers, a binder for binding between powders and adhesion to the current collector, and a solvent for providing viscosity and dispersing the powder, to produce a fluid slurry.

[0006] An electrode coating step is performed in which such a slurry is applied onto an electrically conductive current collector, followed by a drying step to remove the solvent contained in the electrode mixture slurry, and then the electrodes are rolled to produce electrodes of a predetermined thickness.

[0007] On the other hand, during the drying process, the solvent contained in the electrode mixture evaporates, which can cause defects such as pinholes and cracks in the already formed electrode active layer. Furthermore, because the inside and outside of the active layer are not dried uniformly, a powder suspension phenomenon may occur due to the difference in solvent evaporation rates. That is, powder from areas that dry earlier floats to the surface, forming gaps with areas that dry later, which can lead to a decrease in electrode quality.

[0008] Therefore, in order to solve the above problems, drying equipment that can uniformly dry the inside and outside of the active layer and control the evaporation rate of the solvent has been considered. However, such drying equipment is very expensive and requires considerable cost and time to operate, making it disadvantageous from the standpoint of manufacturing process efficiency.

[0009] Therefore, in recent years, there has been a great deal of research being conducted on manufacturing dry electrodes that do not use solvents.

[0010] The dry electrode is generally manufactured by laminating a freestanding film, which contains an active material, binder, conductive material, etc., onto a current collector.

[0011] The conventional dry electrode described above includes a process in which an active material, a carbon material as a conductive material, and a fibrous binder are mixed together in a blender or the like, the binder is fibrousized by a high-shear mixing process such as jet milling, and then this mixture is calendered into a film to produce a free-standing film. Subsequently, the free-standing film produced after calendering is laminated onto a current collector to produce the electrode.

[0012] However, when applying the high-shear mixing process described above to fragile active materials, a large amount of fine powder with small particle sizes is generated, which tends to degrade mechanical and electrochemical properties. Furthermore, if high-shear mixing is performed excessively, it can cut the generated binder fibers and reduce the flexibility of the free-standing film. In addition, during the jet milling process, components can adhere to the inside of the equipment, obstructing the flow of high-pressure air and blocking the flow path, making mass production difficult.

[0013] Furthermore, conventional dry electrode manufacturing techniques had the problem of low flexibility, which meant the dry electrodes could easily break.

[0014] Therefore, the development of dry electrode manufacturing technology that can solve these problems is urgently needed. [Overview of the project] [Problems that the invention aims to solve]

[0015] The present invention aims to solve the above problems and to provide an electrode with improved flexibility, a secondary battery containing the same, and a method for manufacturing the same. [Means for solving the problem]

[0016] To solve the problems of the present invention, according to one aspect of the present invention, an electrode of the following embodiment is provided.

[0017] According to the first embodiment, an electrode is provided that comprises an electrode current collector and an electrode layer located on the electrode current collector and containing an active material, a conductive material, a binder, and a fluoride elastomer, and is characterized by having a bending resistance of Φ (diameter) of 10 mm or less.

[0018] According to the second embodiment, in the first embodiment, the binder is fibrous, and the active material, conductive material, and fluoride elastomer can be bound together.

[0019] According to the third embodiment, in the first or second embodiment, the fluoride elastomer may include vinylidene fluoride rubber (FKM), tetrafluoroethylene propylene rubber (FEPM), tetrafluoroethylene-perfluoromethyl vinyl ether rubber (FFKM), tetrafluoroethylene rubber (TFE), or two or more of these.

[0020] According to the fourth embodiment, in any of the first to third embodiments, the weight ratio of the binder and the fluoride elastomer may be 40:60 to 80:20.

[0021] According to the fifth embodiment, in any of the first to fourth embodiments, the electrode can have a bending resistance of Φ (diameter) from 2 mm to 8 mm.

[0022] According to the sixth embodiment, in any of the first to fifth embodiments, the bending resistance of the electrode can be evaluated by the method of the measurement standard JIS K5600-5-1.

[0023] According to the seventh embodiment, in any of the first to sixth embodiments, the bending resistance of the electrode can be evaluated by the following steps: manufacturing a rectangular electrode sample measuring 100 mm x 50 mm; preparing measuring rods having diameters of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, and 32 mm, and using the measuring rod with the largest diameter to bring the electrode sample into contact with the measuring rod, then lifting both ends of the electrode sample to determine whether or not cracks occur in the composite film of the electrode sample; and, if no cracks occur in the previous step, repeating the step of determining whether or not cracks occur in the composite film of the electrode sample in the same manner as the previous step using the measuring rod with the second largest diameter, thereby determining the minimum diameter of the measuring rod that does not cause cracks in the composite film of the electrode sample as the bending resistance.

[0024] According to the eighth embodiment, in any of the first to seventh embodiments, the degree of crystallinity of the binder may be 10% or less.

[0025] According to the ninth embodiment, in any of the first to eighth embodiments, the binder includes a fluorine-containing binder, the electrode layer has a quantified binder ratio (QBR) of 1.1 or less, and the QBR can be defined by the following formula. QBR=Bs / Bf In the above formula, Bs represents the average value of the fluorine content in the surface region of the electrode layer from the outermost surface of the electrode layer to within 15% of the total thickness of the electrode layer, and Bf represents the average value of the fluorine content in the bottom region of the electrode layer from the interface of the electrode layer facing the current collector to within 15% of the total thickness of the electrode layer.

[0026] According to the tenth embodiment, in any of the first to ninth embodiments, the conductive material may include activated carbon, graphite, carbon black, Ketjenblack, carbon nanotubes, or two or more of these.

[0027] According to the 11th embodiment, in any of the first to tenth embodiments, the binder may include polytetrafluoroethylene (PTFE).

[0028] According to the 12th embodiment, in any of the first to 11th embodiments, the active material may be a positive electrode active material or a negative electrode active material.

[0029] According to the 13th embodiment, in any of the first to 12th embodiments, the content of the active material may be 80 to 98 parts by weight, the content of the conductive material may be 0.5 to 10 parts by weight, the content of the binder may be 0.5 to 5 parts by weight, and the content of the fluoride elastomer may be 0.1 to 5 parts by weight.

[0030] According to the 14th embodiment, in any of the first to 13th embodiments, the electrode current collector may further include a conductive primer layer on at least one surface.

[0031] According to the 15th embodiment, in any of the first to 14th embodiments, the electrode layer may be derived from a film for dry electrodes.

[0032] According to the 16th embodiment, a method for manufacturing an electrode according to any of the 1st to 15th embodiments is provided, characterized by comprising the steps of: manufacturing a mixture containing an active material, a conductive material, a binder, and a fluoride elastomer; kneading the mixture at a temperature in the range of 70°C to 200°C and at a pressure of normal pressure or higher to manufacture a mixture mass; crushing the mixture mass to obtain a mixed powder for electrodes; feeding the mixed powder for electrodes between a plurality of rolls and calendering it to form an electrode film; and laminating the electrode film onto a metal current collector.

[0033] According to the 17th embodiment, in the 16th embodiment, the step of kneading to produce a mixture mass can be carried out in a kneader under a pressure of atmospheric pressure or higher.

[0034] According to the 18th embodiment, in the 16th or 17th embodiment, the rolling ratio of the electrode film may be 20% or less.

[0035] According to the 19th embodiment, a secondary battery is provided that includes a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is an electrode according to any of the first to 15th embodiments.

[0036] According to the 20th embodiment, an energy storage device is provided that includes a secondary battery according to the 19th embodiment as a unit battery. [Effects of the Invention]

[0037] Electrodes are inherently brittle and tend to break easily when subjected to impact or deformation. An electrode according to one embodiment of the present invention improves the tendency of the electrode to break when subjected to impact or deformation by adding a fluoride elastomer with high elastic deformation properties to the dry electrode manufacturing particles, thereby providing an electrode with excellent flexibility (bending resistance) and thus good handling properties.

[0038] The following drawings accompanying this specification illustrate preferred embodiments of the invention and, together with the detailed description of the invention, serve to further illustrate the technical idea of ​​the invention; therefore, the invention shall not be construed as being limited solely to what is shown in the drawings. [Brief explanation of the drawing]

[0039] [Figure 1] This is a schematic diagram of an electrode according to one embodiment of the present invention. [Figure 2] This is a schematic diagram for calculating the QBR value of the electrode layer. [Figure 3A] This is a schematic diagram of the manufacturing process for the electrode film used in an electrode assembly according to one embodiment of the present invention. [Figure 3B] This is a schematic diagram of the manufacturing process for the electrode film used in an electrode assembly according to one embodiment of the present invention. [Figure 4] This is a schematic diagram of an electrode lamination process according to one embodiment of the present invention. [Modes for carrying out the invention]

[0040] The present invention will be described in more detail below to facilitate understanding of it.

[0041] Terms and words used in this specification and in the claims are not to be interpreted in their ordinary and dictionary sense, but rather in a sense and concept appropriate to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself may appropriately define the concept of a term in order to best describe the invention.

[0042] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise clearly indicated by the context, singular expressions include plural expressions.

[0043] Furthermore, throughout the specification, when a part of it "includes" a certain component, this means, unless otherwise stated, that it may include other components rather than excluding them.

[0044] According to one aspect of the present invention, an electrode is provided comprising an electrode current collector and an electrode layer located on the electrode current collector and containing an active material, a conductive material, a binder, and a fluoride elastomer, characterized in that it has a bending resistance of Φ (diameter) of 10 mm or less.

[0045] According to one embodiment of the present invention, the electrode is a positive electrode or a negative electrode, and the active material may be a positive electrode active material or a negative electrode active material.

[0046] The positive electrode active material may include, but is not limited to, two or more of the following: lithium transition metal oxide, lithium metallic iron phosphorus oxide, lithium nickel-manganese-cobalt oxide, and an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal. Specifically, the positive electrode active material may include, for example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals, and a compound with the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, and LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3), and the chemical formula LiMn 2-x M xO2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 - 0.1), or lithium manganese composite oxide represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn), lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn), and lithium nickel - manganese - cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x = 0 - 0.03, a = 0.3 - 0.95, b = 0.01 - 0.35, c = 0.01 - 0.5, a + b + c = 1), and an oxide in which part of the lithium nickel - manganese - cobalt oxide is substituted with aluminum (lithium nickel - manganese - cobalt - aluminum oxide) Li a [Ni b Co c Mn d Al e 1-f M 1 f O2 (where the above - mentioned M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≤ e ≤ 0.1, 0 ≤ f ≤ 0.1), disulfide compounds, and Fe2(MoO4)3 etc. are included, but not limited thereto. Specifically, the above - mentioned lithium nickel - manganese - cobalt - aluminum oxide may be Li[Ni 0.73 Co 0.05 Mn 0.15 Al 0.02 O2 etc.

[0047] Also, as the negative electrode active material, carbon such as graphitizable carbon and graphite - based carbon, and Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Sn x Me 1-x Me’ y O z ​Metal composite oxides such as (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogens; 0≦x≦1, 1≦y≦3, 1≦z≦8), lithium metal, lithium alloys, silicon alloys, tin alloys, silicon oxides such as SiO, SiO / C, SiO2, metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, conductive polymers such as polyacetylene, and Li-Co-Ni based materials can be used.

[0048] According to one embodiment of the present invention, the electrode is a positive electrode, and the active material is specifically a positive electrode active material, and more specifically, it may be a lithium transition metal oxide, lithium nickel-manganese-cobalt oxide, an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with Al or other transition metals, lithium iron phosphorus oxide, and the like.

[0049] The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. Examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, and silver, needle-shaped or branched conductive whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers, conductive metal oxides such as titanium oxide, and conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used. Specifically, to ensure uniform mixing of the conductive material and improve conductivity, the material may include one or more materials selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, activated carbon may be included.

[0050] The binder may contain a fluorine-containing binder, a non-fluorine-containing binder, or two or more of these. The fluorine-containing binder may be a fluorine-containing polymer, and may contain polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), or two or more of these. Specifically, the fluorine-containing binder may contain polytetrafluoroethylene (PTFE). Furthermore, the fluorine-containing binder may contain polytetrafluoroethylene alone, or it may further contain polytetrafluoroethylene plus one or more PVdF copolymers such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene). The non-fluorine-containing binder may include polyolefins, polyethylene oxide (PEO), and the like.

[0051] Typically, elastomers are also called rubber and refer to chemically crosslinked polymers. Because the density of the crosslinked structure in elastomers is much lower than that of thermosetting resins, the elastic regions between each crosslinking point are much larger, and these regions impart elasticity to the elastomer. In this context, elasticity refers to the property of stretching when pulled or pressed, and returning to its original state when the force is removed.

[0052] The aforementioned fluoroelastomer (fluorocarbon, fluororubber) is a high-performance rubber with excellent resistance to high temperatures, ozone, weather conditions, oxygen, mineral oil, fuel, hydraulic oil, aromatic compounds, and various organic solvents and chemical substances.

[0053] The fluoride elastomer is not particularly limited, and known fluororubbers used for forming molded articles can be used. Specifically, examples of fluoride elastomers include vinylidene fluoride rubber (FKM), tetrafluoroethylene propylene rubber (FEPM), tetrafluoroethylene-perfluoromethyl vinyl ether rubber (FFKM), and tetrafluoroethylene rubber (TFE). These can be used individually or in combination of two or more.

[0054] Among the aforementioned fluoride elastomers, vinylidene fluoride-based rubber (FKM) and tetrafluoroethylene-propylene-based rubber (FEPM) are even more preferred.

[0055] The aforementioned vinylidene fluoride rubber (FKM) is a fluoride elastomer with vinylidene fluoride as its main component and excellent heat resistance, oil resistance, chemical resistance, solvent resistance, and processability. While FKM is not particularly limited, examples include a binary copolymer of vinylidene fluoride and hexafluoropropylene, a binary copolymer of vinylidene fluoride and tetrafluoroethylene, a terpolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene, and a quaternary copolymer of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, and vulcanization site monomer. Examples of commercially available products include "Viton®" manufactured by DuPont Elastomers Ltd. and "Daikin Industries, Ltd.'s Daikin® G." Among these, a quaternary copolymer of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, and vulcanization site monomer is preferred. The aforementioned quaternary copolymer is available, for example, as a commercially available product called "Viton GBL-200S" (manufactured by DuPont Elastomers Ltd.).

[0056] The aforementioned tetrafluoroethylene-propylene rubber (FEPM) is a fluorinated elastomer based on an alternating copolymer of tetrafluoroethylene (TFE) and propylene (P), exhibiting excellent heat resistance, chemical resistance, polar solvent resistance, and vapor resistance. While FEPM is not particularly limited, examples include a binary copolymer consisting of tetrafluoroethylene (TFE) and propylene (P), a terpolymer consisting of tetrafluoroethylene (TFE), propylene (P), and vinylidene fluoride (VdF), and a terpolymer consisting of tetrafluoroethylene (TFE), propylene (P), and a crosslinking point monomer (CSM). Examples of commercially available binary copolymers consisting of tetrafluoroethylene (TFE) and propylene (P) include "Aplus® 100" and "Aflas 150" manufactured by Asahi Glass Co., Ltd. Examples of commercially available ternary copolymers consisting of tetrafluoroethylene (TFE), propylene (P), and vinylidene fluoride (VdF) include "Aflas 200" manufactured by Asahi Glass Co., Ltd. Examples of commercially available ternary copolymers consisting of tetrafluoroethylene (TFE), propylene (P), and crosslinking point monomer (CSM) include "Aflas 300" manufactured by Asahi Glass Co., Ltd.

[0057] Examples of the tetrafluoroethylene-perfluoromethyl vinyl ether (FFKM) include tetrafluoroethylene (TFE)-perfluoro(alkyl vinyl ether) copolymers and TFE-perfluoro(alkoxyalkyl vinyl ether) copolymers. These copolymers may further contain constituent units derived from other perfluoro monomers. The perfluoro(alkyl vinyl ether) that forms the tetrafluoroethylene (TFE)-perfluoro(alkyl vinyl ether) copolymer has 1 to 10 carbon atoms in the alkyl group, and may be, for example, perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), or perfluoro(propyl vinyl ether). Preferably, it is perfluoro(methyl vinyl ether). The perfluoro(alkoxyalkyl vinyl ether) that forms the TFE-perfluoro(alkoxyalkyl vinyl ether) copolymer has 3 to 15 carbon atoms in the group bonded to the vinyl ether group (CF2=CFO-), for example, CF2=CFOCF2CF(CF3)OC n F 2n+1 CF2 = CFO(CF2)3OC n F 2n+1 CF2 = CFOCF2CF(CF3)O(CF2O) m C n F 2n+1 , or CF2 = CFO(CF2)2OC n F 2n+1 This is possible. In the above formula, n is, for example, 1 to 5, and m is, for example, 1 to 3.

[0058] Crosslinking properties can be imparted to FFKM by copolymerizing the crosslinking site monomers (incorporating structural units derived from the crosslinking site monomers). A crosslinking site refers to a site that can undergo crosslinking reactions. Examples of crosslinking sites include nitrile groups, halogen groups (e.g., I groups, Br groups, etc.), and perfluorophenyl groups.

[0059] An example of a crosslinking monomer having a nitrile group as the crosslinking site is a nitrile group-containing perfluorovinyl ether. For example, CF2=CFO(CF2) n OCF(CF3)CN(n is, for example, 2 to 4), CF2=CFO(CF2) n CN(n is, for example, 2 to 12), CF2 = CFO[CF2CF(CF3)O] m (CF2) n CN(n is, for example, 2, m is, for example, 1 to 5), CF2 = CFO[CF2CF(CF3)O] m (CF2) n CN(n is, for example, 1 to 4, m is, for example, 1 to 2), CF2 = CFO[CF2CF(CF3)O] n Examples include CF2CF(CF3)CN (where n is, for example, 0 to 4).

[0060] An example of a crosslinking monomer having a halogen group as the crosslinking site is a halogen-containing perfluorovinyl ether. Examples of halogen-containing perfluorovinyl ethers include those obtained by substituting halogen groups with nitrile groups in the nitrile-containing perfluorovinyl ether described above. A commercially available example of the FFKM is DuPont's "Kalrez."

[0061] According to one embodiment of the present invention, the fluoride elastomer may not contain a double bond in its main chain. By not containing a double bond in the main chain of the fluoride elastomer, the problem of oxidation at high potential can be prevented.

[0062] The electrode manufactured according to the present invention improves the electrode's flexibility by adding a fluorine elastomer with high elastic deformation properties to the electrode layer, in addition to the active material, conductive material, and binder, thereby improving the electrode's ability to break when impact or deformation occurs.

[0063] When non-fluorinated elelastomers such as styrene-butadiene rubber (SBR), which contain double bonds, are included, oxidation can occur at high potentials, potentially leading to a decrease in battery performance. In the case of acrylonitrile butadiene rubber (NBR), which also contains double bonds, it can be hydrogenated to break the double bonds for use in batteries, but this has the limitation that the flexibility does not improve.

[0064] The electrode of the present invention, by including a fluorinated elastomer instead of a conventional elastomer, i.e., a non-fluorinated elastomer, does not contain double bonds in its elastomer structure, thus achieving excellent chemical resistance, solvent resistance, and excellent flexibility.

[0065] The flexibility of such electrodes can be evaluated as bending resistance.

[0066] The bending resistance of the present invention is Φ (diameter) 10 mm or less. Furthermore, according to one embodiment of the present invention, the bending resistance of the electrode may be Φ (diameter) 8 mm or less, or Φ (diameter) 5 mm or less, or Φ (diameter) 2 mm to 10 mm, or Φ (diameter) 2 mm to 8 mm, or Φ (diameter) 2 mm to 5 mm, or Φ (diameter) 2 mm to 4 mm, or Φ (diameter) 4 mm to 5 mm, or Φ (diameter) 2 mm to 3 mm.

[0067] The aforementioned bending resistance can be evaluated by the method of the measurement standard JIS K5600-5-1. Specifically, the manufactured electrode can be brought into contact with measuring rods of various diameters, and then both ends are lifted to measure whether cracks occur and the minimum diameter at which no cracks occur.

[0068] According to one embodiment of the present invention, the bending resistance of the electrode can be evaluated by the following steps: manufacturing a rectangular electrode sample measuring 100 mm x 50 mm; preparing measuring rods having diameters of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, and 32 mm, and using the measuring rod with the largest diameter to bring the electrode sample into contact with the measuring rod, then lifting both ends of the electrode sample to determine whether or not cracks occur in the composite film of the electrode sample; and, if no cracks occur in the previous step, repeating the step of determining whether or not cracks occur in the composite film of the electrode sample in the same manner as the previous step using the measuring rod with the second largest diameter, thereby determining the minimum diameter of the measuring rod that does not cause cracks in the composite film of the electrode sample as the bending resistance.

[0069] According to one embodiment of the present invention, the binder is fibrous, allowing it to bind the active material, conductive material, and fluorine elastomer. The electrode may include a fibrous binder as a means of binding the active material, conductive material, and fluorine elastomer. Such a fibrous binder exhibits less breakage than conventional non-fibrous binders and has excellent stretchability in the longitudinal direction, thereby improving the flexibility of the electrode layer and the electrode itself. The process of fibrousizing the binder will be specifically discussed in the electrode manufacturing method described later.

[0070] According to one embodiment of the present invention, the content of the active material may be 85 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, the content of the binder may be 0.5 to 10 parts by weight, and the content of the fluoride elastomer may be 0.1 to 5 parts by weight.

[0071] Furthermore, the content of the active material may be 90 to 98 parts by weight, the content of the conductive material may be 0.5 to 5 parts by weight, the content of the binder may be 0.5 to 5 parts by weight, and the content of the fluoride elastomer may be 0.2 to 5 parts by weight.

[0072] When the content of the active material, conductive material, binder, and fluoride elastomer meets these ranges, the binder can be sufficiently fiberized in the subsequent kneading process to form a mixture mass, the electrode film can be easily manufactured by molding the mixed powder formed in the pulverization process, the physical properties of the electrode film can be ensured, the content of the active material is ensured, the problem of volume reduction is prevented, and sufficient conductivity can be ensured.

[0073] On the other hand, in some cases, a filler, which is a component that suppresses the expansion of the electrodes, can be further added to the electrode layer. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. For example, orifine polymers such as polyethylene and polypropylene, and fibrous materials such as glass fibers and carbon fibers can be used.

[0074] According to one embodiment of the present invention, the weight ratio of the binder to the fluoride elastomer may be 40:60 to 80:20, or 50:50 to 75:25, or 50:50 to 65:35. When the weight ratio satisfies such a range, the characteristic of the electrode not to break when impact or deformation occurs is improved, and the electrode has excellent flexibility (bending resistance), thus providing an electrode that is easy to handle.

[0075] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The current collector can also have minute irregularities formed on its surface to improve the adhesion of the positive electrode active material, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0076] Furthermore, the current collector may be coated entirely or partially with a conductive primer layer to reduce surface resistance and improve adhesion. Here, the conductive primer layer may contain a conductive material and a binder. The conductive material is not limited to any conductive material and may be, for example, a carbon-based material, a metallic material (metal powder or metal fiber), a conductive whisker, a conductive metal oxide, or a conductive polymer. Carbon-based materials include natural graphite, artificial graphite, graphene, carbon black, Denka Black, acetylene black, Ketjen Black, Super P, Channel Black, Furnace Black, Lamp Black, Thermal Black, carbon nanotubes, graphite nanofibers, and carbon nanofibers. Metallic materials include copper, nickel, aluminum, and silver. Conductive whiskers include zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers. Conductive metal oxides include titanium oxide, and conductive polymers include polyphenylene derivatives. These can be used individually or as mixtures of two or more.

[0077] The binder is a solvent-soluble fluorine-based binder (including PVdF and PVdF copolymers) or an acrylic-based binder, and may include water-based binders such as styrene-butadiene rubber (SBR).

[0078] The porosity of the electrode layer of the electrode may be 20 to 50%, or 20 to 45%, or 20 to 40%, or 20 to 35%, or 22 to 30%, or 20 to 28%, or 20 to 26%, or 23.1 to 27.4%, or 23.1 to 24.8%, 23 to 26%, or 24.8 to 27.4%. Such porosity may vary slightly depending on which effect is prioritized.

[0079] However, when the porosity of the electrode layer is within this range, electrolyte impregnation is improved, resulting in superior lifespan and output characteristics, and since there is no need to increase the volume to achieve the same capacity, it is advantageous in terms of energy density relative to volume.

[0080] The porosity of the electrode layer can be determined by measuring the apparent density of the composite film alone by subtracting the volume and weight of the current collector from the volume and weight of the electrode, and using the actual density calculated based on the actual density and composition of each component, according to the following relational formula.

[0081] Porosity (%) = {1 - (Apparent density / Actual density)} × 100

[0082] In one embodiment of the present invention, the degree of crystallinity of the binder in the electrode layer may be 10% or less.

[0083] In this invention, the degree of crystallinity (Xc) can be measured by differential scanning calorimetry (DSC), and is based on the temperature (peak temperature) at the point in time when the highest enthalpy is observed during crystallization. Specifically, the degree of crystallinity is expressed as a percentage by dividing the enthalpy of fusion (β value) measured by DSC by the enthalpy of fusion (β equilibrium heat of fusion) of a theoretical perfect crystal (100% crystallinity), and can be calculated by the following relational equation 1. Here, the enthalpy of fusion value of a theoretical perfect crystal can be found and used in a polymer handbook for well-known polymers, and for unknown substances or newly synthesized substances, it can be calculated by extrapolation by extending the degree of crystallinity at two or more points.

[0084] [Relationship 1] Xc(%)=(βmχβm 0 ) × 100

[0085] According to one embodiment of the present invention, the binder includes a fluorine-containing binder, and the electrode layer can have a quantified binder ratio (QBR) of 1.1 or less.

[0086] The aforementioned QBR is defined by the following formula.

[0087] QBR=Bs / Bf

[0088] In the above formula, Bs represents the average value of the fluorine content in the surface region of the electrode layer from the outermost surface of the electrode layer to within 15% of the total thickness of the electrode layer, and Bf represents the average value of the fluorine content in the bottom region of the electrode layer from the interface of the electrode layer facing the current collector to within 15% of the total thickness of the electrode layer.

[0089] Figure 1 is a schematic diagram of an electrode according to one embodiment of the present invention. Referring to Figure 1, the electrode 10 comprises an electrode current collector 12 and an electrode layer 11 located on the electrode current collector 12, which includes an active material, a conductive material, a binder, and a fluoride elastomer.

[0090] The electrode layer 11 has a surface region 11s of the electrode layer from the outermost surface of the electrode layer to within 15% of the total thickness d of the electrode layer, and a bottom region 11f of the electrode layer from the interface of the electrode layer facing the current collector to within 15% of the total thickness d of the electrode layer.

[0091] In the above formula QBR, Bs represents the average value of the fluorine content in the surface region 11s of the electrode layer, and Bf represents the average value of the fluorine content in the bottom region 11f of the electrode layer.

[0092] In this case, QBR can be calculated using the following method.

[0093] First, an electrode to be examined for QBR is selected, and a cross-section of the selected electrode is fabricated using argon ion milling. Then, the constituent components within the electrode layer of the fabricated electrode cross-section are mapped using an energy dispersive X-ray spectroscopy (EDS) detector on a scanning electron microscope (SEM).

[0094] From the EDS mapping results, a line profile is extracted in the thickness direction of the electrode layer. From the extracted line profile results, the average value of fluorine content in the surface region of the electrode layer (Bs) and the average value of fluorine content in the bottom region of the electrode layer (Bf) are extracted, and the QBR value is calculated using the following formula. In this case, the fluorine content can include all the fluorine content contained in the fluorine-containing binder and fluorine-containing elastomer.

[0095] QBR=Bs / Bf

[0096] In this case, the surface region of the electrode layer is the region from the outermost surface in the thickness direction of the electrode layer to within 15% of the total thickness of the electrode layer, and the bottom region of the electrode layer is the region from the interface of the electrode layer facing the current collector to within 15% of the total thickness of the electrode layer.

[0097] Figure 2 is a schematic diagram for calculating the QBR value of the electrode layer. Referring to Figure 2, the X-axis represents the thickness of the electrode layer, i.e., the distance from the surface in the direction of the current collector, and the Y-axis represents the intensity of the fluorine component. Line A shows the intensity of the fluorine component of the fluorine-containing binder extracted by EDS mapping of the fluorine component in the electrode layer at the electrode cross-section, and line B is a trend line showing the trend of line A, and is shown by smoothing using the LOWESS smoothing method, i.e., the Locally-Weighted Scatterplot Smoother method.

[0098] The QBR value is a numerical value that indicates the uniformity of the distribution of fluorine-containing binder in the electrode layer in the thickness direction, based on the ratio of the fluorine-containing binder content in the surface region to the fluorine-containing binder content in the bottom region of the electrode layer. In this case, the fluorine-containing binder content can be estimated based on the fluorine component contained in the fluorine-containing binder used.

[0099] The aforementioned QBR value is 1.1 or less, and according to one embodiment of the present invention, the aforementioned QBR value is 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, and can also be between 0.95 and 1.05.

[0100] When the QBR value is within the range of 1.1 or less, the fluorine-containing binder migrates to the electrode surface, and the problem of the fluorine-containing binder content in the surface region being greater than the content in the bottom region of the electrode layer does not occur. As a result, the distribution of the binder in the thickness direction of the electrode layer becomes uniform, and the binder content in the part close to the current collector does not decrease. Therefore, the adhesion between the current collector and the electrode layer is improved, and the conductivity on the surface of the electrode layer and the charge / discharge speed thereafter can also be improved.

[0101] The fluorine-containing binder may specifically include polytetrafluoroethylene (PTFE) and PVdF-based copolymers such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene), or two or more of these. Furthermore, the fluorine-containing binder may contain polytetrafluoroethylene alone, or in addition to polytetrafluoroethylene, it may further contain one or more PVdF-based copolymers such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene).

[0102] The electrode layer may be derived from a dry electrode film. Unlike conventional wet electrode manufacturing methods, which involve dissolving and / or dispersing an active material, conductive material, and binder in a dispersion medium such as water or an organic solvent, and then applying the resulting slurry onto a current collector and drying it, the dry electrode film is manufactured using a dry manufacturing method that does not use a dispersion medium. The electrode film thus manufactured is then laminated onto a current collector to finally produce an electrode. The specific manufacturing methods for the electrode film and the electrode will be described below.

[0103] According to one aspect of the present invention, A step of producing a mixture comprising an active material, a conductive material, a binder, and a fluoride elastomer, The steps include kneading the aforementioned mixture at a temperature in the range of 70°C to 200°C and under a pressure equal to or greater than atmospheric pressure to produce a mixture mass, The steps include crushing the aforementioned mixture mass to obtain a mixed powder for electrodes, The steps include feeding the electrode mixture powder between multiple rolls and calendering it to form an electrode film, A method for manufacturing an electrode according to claim 1 is provided, characterized by comprising the step of laminating the electrode film onto a metal current collector.

[0104] The method for manufacturing electrodes according to the present invention will be described in more detail below.

[0105] First, a mixture containing an active material, a conductive material, a binder, and a fluoride elastomer is manufactured.

[0106] In this case, the mixing for producing the mixture is carried out so that the active material, conductive material, binder, and fluoride elastomer are uniformly distributed, and since they are mixed in powder form, the method is not limited to any method that enables simple mixing of these materials, and they can be mixed by various methods. However, since the electrodes of the present invention are manufactured by a dry manufacturing method that does not use a dispersion medium, the above mixing can be carried out by dry mixing, and can be done by putting the materials into a device such as a blender.

[0107] Furthermore, the mixing can be carried out in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute, in order to ensure uniformity.

[0108] According to one embodiment of the present invention, a supermixer or the like can be used in the mixing step for producing the mixture, and specifically, a method can be applied in which the mixture is mixed with a supermixer at 1,000 to 2,000 rpm for 2 to 10 minutes.

[0109] The binder can be microfibrillated by the step of manufacturing the mixed powder. This microfibrillation refers to a process of finely dividing a polymer, which can be done, for example, by using mechanical shear force. Specific examples of such binders are as described above.

[0110] Next, the mixture is kneaded at a temperature in the range of 70°C to 200°C and under a pressure of atmospheric pressure or higher to produce a lump of mixture.

[0111] In well-known techniques, high-shear mixing, such as that performed by a jet mill, is used to fibrousize the binder. However, this mixing process can cause problems such as the active material being pulverized and the resulting fibers being cut. Therefore, in the present invention, these problems are solved by using a low-shear compounding method instead of high-shear mixing.

[0112] The above-mentioned kneading is not limited to any particular method. In one specific embodiment of the present invention, the kneading can be carried out, for example, by a kneader or other mixing machine.

[0113] Such kneading is a step in which the binder becomes fibrous and bonds or connects the active material, conductive material, and fluorine elastomer to form a mixture mass with 100% solid content. Furthermore, in such a kneading step, the fluorine elastomer has improved flowability and uniform dispersion at temperatures above 80°C, for example.

[0114] Specifically, the above mixing can be controlled at a speed of 10 rpm to 100 rpm. For example, the mixing can be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. The above mixing can be carried out for 1 to 30 minutes.

[0115] For example, the mixing can be performed at a speed of 20 rpm to 50 rpm within the above range for 3 to 10 minutes. On the other hand, the mixing can be controlled in the range of 10 / s to 500 / s. In a specific embodiment of the present invention, the mixing can be performed for 1 to 30 minutes, and the shear rate can be controlled in the range of 30 / s to 100 / s.

[0116] Furthermore, such mixing steps can be carried out under high temperature and pressure conditions above atmospheric pressure, and more specifically, under pressure conditions higher than atmospheric pressure.

[0117] More specifically, the above mixing can be carried out in the range of 70°C to 200°C, specifically, 90°C to 150°C.

[0118] If the process is carried out at a temperature lower than the above temperature range, the binder will not fiberize and aggregate properly during kneading, and film formation will not occur easily during calendering. If the process is carried out at an excessively high temperature, the binder will fiberize rapidly, and there is a risk that the already formed fibers will be cut by excessive shear force, which is undesirable.

[0119] Furthermore, the process can be carried out at or above atmospheric pressure, or under pressures of 1 atm to 60 atm, or 1 atm to 30 atm, or 1 atm to 10 atm, or 1 atm to 8 atm, or 1.1 atm to 7 atm, or 1.1 atm to 6 atm.

[0120] When the above pressure range is met, it is possible to prevent problems such as excessive shear force and pressure being applied, which could cause the formed fibers to break or the density of the mixture to be too high. In other words, according to the present invention, the intended effects can be achieved when a low-shear mixing process is performed under high temperature and pressure conditions above atmospheric pressure instead of high-shear mixing.

[0121] Furthermore, according to one embodiment of the present invention, in order to improve the dispersibility of the fluorine elastomer, a method can be used in which a portion of the active material or a portion of the conductive material is pre-mixed and kneaded with the fluorine elastomer, and the result of this pre-mixing and kneading is then mixed and kneaded with the remaining electrode material.

[0122] Next, the mixture mass is crushed to obtain a mixed powder for electrodes.

[0123] Specifically, the mixture mass produced by the aforementioned kneading can be immediately calendered. In this case, it is necessary to press the mixture mass to produce a thin film, which may result in the problem of not being able to obtain a uniform film. Therefore, according to the present invention, the prepared mixture mass undergoes the aforementioned grinding step. That is, if the electrode mixture powder obtained by grinding is excessively large or aggregated, bridges may be formed in the calendering process, potentially causing defects in the film's appearance such as pinholes or resulting in a film with non-uniform surface characteristics. Therefore, the electrode mixture powder is ground to obtain a uniform size before performing calendering.

[0124] In this case, the grinding step is not limited, but can be performed using a device such as a blender or grinder. Specifically, the grinding step can be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, or specifically at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 2 minutes.

[0125] When the aforementioned grinding speed and time are met, sufficient grinding is performed, allowing for the formation of powder particles of a suitable size for film formation, thus preventing the problem of a large amount of fine powder being generated in the mixture clumps. If necessary, a classification process can be carried out to filter out powder particles that exceed or fall below a certain size.

[0126] According to one embodiment of the present invention, a cutter mill, a fine mill, etc., can be used in the grinding step. In this case, the cutter mill can be used to coarsely grind the mixed mass produced by kneading to a level of several millimeters by operating at a rate of 400 to 500 rpm for several seconds. The fine mill can be used to uniformly grind the coarsely ground powder to a size below a certain level, and can be used at a rate of 3,000 to 8,000 rpm.

[0127] Next, the electrode mixture powder is fed between multiple rolls and calendered to form an electrode film.

[0128] Referring to Figures 3A and 3B, in the step 100 for forming the electrode film, a plurality of rolls 110 are arranged spaced apart, and the mixed powder 120 for the electrode obtained in the above step is fed between adjacent rolls 110 and rotated in a direction opposite to the rolls 110, thereby rolling the mixed powder 120, forming it into a sheet or film through a powder sheet step, and then calendering it multiple times to finally obtain an electrode film of the target thickness.

[0129] According to one embodiment of the present invention, the spacing between multiple rolls in the process of forming an electrode film can be appropriately controlled considering the specifications and physical properties of the electrode film to be manufactured. For example, in Figure 3B, compared to Figure 3A, the spacing between the second and third rolls and the spacing between the fourth and fifth rolls can be controlled to be even larger.

[0130] Specifically, such calendering may involve processing the electrode mixture powder into a film, for example, to produce a film with an average thickness of 50 μm to 300 μm.

[0131] In this case, the calendering process can be performed, for example, by opposing rolls. According to one embodiment of the present invention, the calendering process can be repeated one or more times, for example, one to five times, three to four times, or four times.

[0132] In this case, the roll temperature can range from 50°C to 200°C.

[0133] The rotation speed ratio of the roll can be appropriately controlled depending on the size of the roll, the number of calendering cycles, and the thickness of the electrode film, and can be controlled in the range of, for example, 1 to 10 times, 1 to 8 times, 1 to 7 times, or 1.2 to 5 times.

[0134] Furthermore, the spacing between opposing rolls can be variably adjusted according to the desired film thickness and density.

[0135] Once the calendering process reaches this stage, a dry electrode film that acts as an electrode mixture can be manufactured. This type of dry electrode film is also conventionally known as a free-standing film.

[0136] The electrode film manufactured in this manner contains no solvent, has almost no fluidity, is easy to handle, and can be processed into desired shapes to manufacture electrodes of various forms. Furthermore, using the electrode film of the present invention in electrode manufacturing eliminates the drying process for solvent removal, significantly improving the efficiency of electrode manufacturing. It also solves problems that plagued conventional dry electrode manufacturing, such as the tearing of the active material and the breakage of the fibrous binder.

[0137] On the other hand, in the present invention, the electrode film has a porosity of 20% to 50%, and preferably can be controlled to a value of 40% or less or 30% or less within the above range. When the porosity satisfies such a range, electrolyte impregnation is easy, life characteristics and output characteristics can be improved, and since it is not necessary to increase the volume to achieve the same capacity, the energy density relative to the volume can be improved. In one embodiment of the present invention, the porosity can be determined by measuring the apparent density of the dry electrode film and using the actual density calculated based on the actual density and composition of each component, using the following formula.

[0138] Porosity (%) = {1 - (Apparent density / Actual density)} × 100

[0139] Next, the electrode film is laminated onto the metal current collector.

[0140] The lamination step may involve rolling and attaching the electrode film obtained in the above step to a predetermined thickness onto the current collector. The lamination can also be performed using a laminating roll, which can be maintained at a temperature of 25°C to 250°C.

[0141] According to one embodiment of the present invention, the compression ratio of the electrode film may be 30% to 50%, or 35% to 50%, or 40% to 50%.

[0142] The compression ratio of the electrode film can be defined as the ratio of the thickness of the electrode film that is compressed during lamination, and can be expressed by the following formula 1.

[0143] [Formula 1] Compression ratio (%) = T p / T1×100

[0144] In Equation 1, T p T1 refers to the thickness of the electrode film under pressure during the lamination step, while T1 refers to the thickness of the electrode film before the lamination step.

[0145] In the present invention, by adjusting the compression ratio in the lamination step to satisfy a specific range, it is possible to provide the electrode film with appropriate density and porosity, as well as excellent adhesion between the electrode film and the current collector.

[0146] When the compression ratio of the electrode film is within the range of 30% to 50%, the pressure applied to the electrode film is sufficient, improving the adhesion between the electrode film and the current collector. This prevents the electrode film from peeling off the current collector after the lamination process, and eliminates the problems of the electrode film's density increasing excessively, resulting in a porosity lower than the target porosity, or damage to the current collector.

[0147] In one embodiment of the present invention, when electrode films are laminated to both sides of the current collector, the compression ratio (%) in formula 1 above may mean the following formula 2.

[0148] [Formula 2] 30 ≤ (T1 + 0.5T) c -0.5T gap ) / T1×100≦50

[0149] In Equation 2, T1 represents the thickness of the electrode film before the lamination step, and T c This refers to the thickness of the current collector, T gap This refers to the distance between the first and second rolling rolls.

[0150] Furthermore, the rolling ratio of the electrode film after the lamination step may be in the range of 20% or less, 18% or less, 15% or less, 5% to 15%, 6% to 15%, 7% to 15%, or 9% to 13%.

[0151] Here, the rolling ratio can be defined as the ratio of the thickness of the electrode film after the lamination step to the thickness of the electrode film before the lamination step, and can be expressed by the following equation 3.

[0152] [Formula 3] Rolling ratio (%) = (T1 - T2) / T1 × 100

[0153] In the above formula 3, T1 represents the thickness of the electrode film before the lamination step, and T2 represents the thickness of the electrode film after the lamination step.

[0154] When the rolling ratio satisfies the above-mentioned range, appropriate density and porosity of the electrode film, as well as adhesive strength between the electrode film and the current collector, can be achieved.

[0155] The rate of increase in apparent density before and after lamination of the electrode film with the current collector can be expressed by the following equation 4.

[0156] [Formula 4] The rate of increase in apparent density (%) = (D2 - D1) / D1 × 100

[0157] D1 is the apparent density (g / cm³) of the electrode film before the lamination step. 3 ) is shown, and D2 is the apparent density (g / cm³) of the electrode film after the lamination step. 3 ) indicates.

[0158] The rate of increase in apparent density before and after lamination of the electrode film with the current collector may be 5% to 30%, 7% to 25%, or 10% to 20%.

[0159] D1 and D2, which indicate the apparent density of the electrode film, vary diversely depending on the type of active material. According to an embodiment of the present invention, when the active material is lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, a + b + c = 1), and an oxide in which a part of the lithium nickel-manganese-cobalt oxide is substituted with aluminum (lithium nickel-manganese-cobalt-aluminum oxide) Li a [Ni b Co c Mn d Al e 1-f M 1 f O2 (where the M 1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1), etc., the D1 and D2 can be in the range of 2.75 g / cm 3 to 3.75 g / cm 3 .

[0160] On the other hand, when the increase rate of the apparent density of the electrode film satisfies the above range, the adhesion between the electrode film and the current collector can be improved, and problems such as the porosity deviating from the target range or damage to the positive electrode active material or the current collector can be prevented.

[0161] The apparent density before and after lamination of the electrode film with the current collector can be calculated by measuring the weight and thickness of the electrode film before lamination, measuring the weight and thickness of the electrode after lamination, and obtaining the weight and thickness of the film after subtracting the weight and thickness of the current collector.

[0162] Also, the loading amount of the active material of the dry electrode film is 3 mAh / cm 2 ​From 15mAh / cm² 2 Specifically, it is 4mAh / cm². 2 From 10mAh / cm² 2 It is possible.

[0163] Here, the load amount of the active material is the value calculated using the following formula 5.

[0164] [Formula 5] Loading capacity of active material (mAh / cm²) 2 ) = Active material capacity (mAh / g) × Weight content ratio of active material in dry electrode film (wt%) × Weight per unit area of ​​dry electrode film (g / cm²) 2 )

[0165] Furthermore, the interfacial resistance between the electrode film and the current collector is 5 Ω·cm. 2 Specifically, the following is 2Ω·cm 2 The following is possible. Here, the interfacial resistance can be calculated by applying a current of 100 μA to the electrode using the MP (Multi Probe) resistance measurement method and measuring the resistance value between the dry electrode film and the current collector layer by measuring the potential difference between multiple probes. If the interfacial resistance range is met, the battery performance of the secondary battery manufactured thereafter can be improved.

[0166] Figure 4 is a schematic diagram of the step of laminating electrode films to both sides of a current collector according to one embodiment of the present invention. Specifically, the lamination step 200 involves rolling and attaching the electrode film 230 obtained in the above step to the current collector 220 to a predetermined thickness using a pair of laminating rolls 210, thereby ultimately obtaining the electrode 240.

[0167] Another embodiment of the present invention provides an electrode manufactured by the electrode manufacturing method described above. Also provided is a secondary battery including the electrode, wherein the electrode is a positive electrode, and the electrode assembly including the positive electrode, a negative electrode, and a separator membrane is incorporated into a battery case (cylindrical case, rectangular case, pouch, etc.) together with a lithium-containing non-aqueous electrolyte, and an energy storage device including the same as a unit battery.

[0168] Since the specific structure of the secondary battery and energy storage device is well known, a detailed explanation is omitted in this specification.

[0169] On the other hand, according to one embodiment of the present invention, a dry electrode manufacturing apparatus is provided, comprising a blender for mixing a mixture raw material containing an active material, a conductive material, a binder, and a fluoride elastomer; a kneader for kneading the mixture to produce a mixture mass; a pulverizer for crushing the mixture mass to form an electrode mixed powder; a calendar for forming the electrode mixed powder into a dry electrode film; and a laminating roll for arranging and laminating the dry electrode film onto at least one surface of a current collector.

[0170] The blender is a mixer for mixing raw materials, and as described above, it can mix the raw materials for the mixture at a speed of 5,000 rpm to 20,000 rpm. A super mixer or the like can be used as the mixer.

[0171] The kneader is a device for fiberizing the binder and dispersing the raw materials for the mixture according to the present invention, and the mixture can be obtained as a mass by kneading with the kneader. In this case, the kneader for obtaining the results according to the present invention can be operated in a temperature range of 70°C to 200°C, or 90°C to 180°C, and under pressure conditions of atmospheric pressure or above, or 1 atm to 60 atm, or 1 atm to 30 atm, or 1 atm to 10 atm, or 1 atm to 8 atm, or 1.1 atm to 7 atm, or 1.1 atm to 6 atm.

[0172] The aforementioned pulverizer is a device that pulverizes such a mixture mass to form a mixed powder for electrodes, and this can also be a blender or grinder, and examples of grinders include cutter mills and fine mills.

[0173] The calendering process described above is an apparatus for forming the electrode mixture powder into a film, and for example, it consists of a pair of opposing rollers, the thickness of which can be adjusted by the distance between them.

[0174] The laminating roll serves to adhere and roll the dry electrode film, formed by the calender, onto at least one surface of the current collector.

[0175] The porosity of the dry electrode film according to the present invention can be determined by such a calender and laminating roll.

[0176] In other words, the dry electrode manufacturing apparatus according to the present invention is characterized by including a kneader and a pulverizer.

[0177] The specific structures of the aforementioned blender, kneader, calender, and laminating roll are conventionally known, and therefore, a detailed explanation is omitted in this specification.

[0178] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the examples described in detail below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0179] Example 1 A mixture was prepared by adding 950g of lithium manganese oxide (Li2MnO2) (POSCO, L25) as the positive electrode active material, 30g of carbon black as the conductive material, and 13g of polytetrafluoroethylene (PTFE) as the binder to a blender and mixing at 10,000 rpm for 1 minute.

[0180] After adding 7g of FKM (Chemours, FKM10980) as a fluoride elastomer to this mixture, the resulting product was put into a kneader.

[0181] The kneader temperature was stabilized at 150°C, and the mixture was placed in a pressurized kneader and operated at a speed of 40 rpm for 5 minutes under approximately 1.1 atmospheres (atm) to obtain a mixture mass. The mixture mass was placed in a blender and crushed at 10,000 rpm for 30 seconds, and then classified using a sieve with a pore size of 1 mm to obtain an electrode mixed powder. Subsequently, the manufactured electrode mixed powder was placed in a wrap calender (roll diameter: 160 mm, roll temperature: 100°C) to produce an electrode film. Two of the electrode films were placed on both sides of a current collector (aluminum foil (19 μm) coated with a conductive primer layer in which carbon black and acrylic binder were mixed in a weight ratio of 5:6), and laminated using a compression roll maintained at 150°C to produce an electrode (positive electrode).

[0182] The final manufactured electrode had a total thickness of 343 μm, and of the active material layers provided on both sides of the current collector, the thickness of the active material layer formed on one side was 162 μm.

[0183] Example 2 The cathode was manufactured in the same manner as in Example 1, except that 10 g of polytetrafluoroethylene (PTFE) was used as a binder and 10 g of FKM was used as a fluoride elastomer.

[0184] The final manufactured electrode had a total thickness of 342 μm, and of the active material layers provided on both sides of the current collector, the thickness of the active material layer formed on one side was 162 μm.

[0185] Comparative Example 1 The cathode was manufactured in the same manner as in Example 1, except that 20 g of polytetrafluoroethylene (PTFE) was used as the binder and 0 g of FKM was used as the fluoride elastomer.

[0186] The final manufactured electrode had a total thickness of 345 μm, and of the active material layers provided on both sides of the current collector, the thickness of the active material layer formed on one side was 163 μm.

[0187] Comparative Example 2 The cathode was manufactured in the same manner as in Example 1, except that 7 g of polytetrafluoroethylene (PTFE) was used as a binder and 13 g of FKM was used as a fluoride elastomer.

[0188] The final manufactured electrode had a total thickness of 346 μm, and of the active material layers provided on both sides of the current collector, the thickness of the active material layer formed on one side was 164 μm.

[0189] Comparative Example 3 A positive electrode was manufactured in the same manner as in Example 1, except that 0 g of polytetrafluoroethylene (PTFE) was used as a binder and 20 g of FKM as a fluoride elastomer. However, the resulting electrode film easily crumbled, making it impossible to produce a positive electrode sample.

[0190] Performance evaluation The positive electrodes manufactured in Example 1 and Comparative Example 1, and the secondary batteries equipped with the positive electrodes, were evaluated as follows, and the results are shown in Table 1.

[0191] In this case, the secondary batteries equipped with the electrodes manufactured in Example 1 and Comparative Example 1 were manufactured by the following method.

[0192] A negative electrode was manufactured by depositing lithium metal to a thickness of 70 μm onto a copper foil.

[0193] The electrodes produced in Example 1 and Comparative Example 1 were used as the positive electrode, and an electrode assembly was fabricated using polyethylene mac (thickness: 20 μm) between the positive electrode and the fabricated negative electrode. After placing the electrode assembly inside a battery case, a secondary battery was manufactured by injecting and sealing it with a liquid electrolyte in which LiPF6 was dissolved at 1 M in a solvent mixed with ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a 1:2:1 (volume ratio).

[0194] (1) Load amount The load amount was calculated using the following relationship.

[0195] Load capacity (mAh / cm²) 2 ) = Active material capacity (mAh / g) × [Weight content ratio of active material in electrode film (wt%)] × [Weight per unit area of ​​electrode film (g / cm²)] 2 )]

[0196] (2) Porosity (%) In this case, the porosity of the electrodes was determined by measuring the apparent density of only the electrode active material layer by subtracting the volume and weight of the current collector from the volume and weight of the electrode, and using the actual density calculated based on the actual density and composition of each component, the actual porosity of each electrode was determined by the following relational equation.

[0197] Porosity (%) = {1 - (Apparent density / Actual density)} × 100

[0198] (3) Flexibility According to the measurement standard JIS K5600-5-1, each electrode was brought into contact with measuring rods of various diameters, and then both ends were lifted to measure the presence or absence of cracks and the minimum diameter at which no cracks occurred.

[0199] Specifically, the evaluation of flexural resistance was carried out by manufacturing a rectangular electrode sample measuring 100 mm x 50 mm, preparing measuring rods with diameters of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, and 32 mm, bringing the electrode sample into contact with the measuring rod with the largest diameter, and then lifting both ends of the electrode sample to determine whether or not cracks occur in the composite film of the electrode sample. If no cracks occur in the previous step, the step of determining whether or not cracks occur in the composite film of the electrode sample in the same manner as the previous step is repeated using the measuring rod with the second largest diameter, thereby determining the minimum diameter of the measuring rod that does not cause cracks in the composite film of the electrode sample as the flexural resistance.

[0200] For example, if, after bringing an electrode sample into contact with a measuring rod with a diameter of 32 mm to 3 mm, and then lifting both ends of the electrode sample, no cracks occur in the composite film of the electrode sample. However, if, after bringing an electrode sample into contact with a measuring rod with a diameter of 2 mm, and then lifting both ends of the electrode sample, cracks occur in the composite film of the electrode sample, then the bending resistance of this dry electrode is determined to be Φ (diameter) 3 mm, which is the minimum diameter of the measuring rod that does not cause cracks in the composite film of the electrode sample.

[0201] [Table 1]

[0202] Table 1 shows that the electrodes manufactured in Example 1 and Example 2 exhibited improved resistance to cracking when subjected to impact or deformation compared to the electrodes of Comparative Examples 1 to 3, demonstrating superior bending resistance.

Claims

1. Electrode current collector and The electrode current collector comprises an electrode layer located on the electrode current collector, which includes an active material, a conductive material, a binder, and a fluoride elastomer. The binder is fibrous, and the active material, conductive material, and fluoride elastomer are bound to it. An electrode with a diameter of 10 mm or less and with flexibility.

2. The electrode according to claim 1, wherein the fluoride elastomer comprises vinylidene fluoride rubber (FKM), tetrafluoroethylene propylene rubber (FEPM), tetrafluoroethylene-perfluoromethyl vinyl ether rubber (FFKM), tetrafluoroethylene rubber (TFE), or two or more of these.

3. The electrode according to claim 1, wherein the weight ratio of the binder to the fluoride elastomer is 40:60 to 80:

20.

4. The electrode according to claim 1, wherein the electrode has a bending resistance of Φ2 mm to 8 mm.

5. The electrode according to claim 1, wherein the flexibility of the electrode is evaluated by the method of the measurement standard JIS K5600-5-1.

6. The bending resistance of the electrode is The steps include manufacturing a rectangular electrode sample measuring 100 mm x 50 mm, The procedure involves preparing measuring rods with diameters of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, and 32 mm, and using the measuring rod with the largest diameter to bring the electrode sample into contact with the measuring rod, and then lifting both ends of the electrode sample to determine whether or not cracks occur in the composite film of the electrode sample. The electrode according to claim 1, which is evaluated by the following steps: if no crack occurs in the above determination step, the step of determining whether or not a crack occurs in the composite film of the electrode sample is repeated using the measuring rod with the second largest diameter, thereby determining the minimum diameter value of the measuring rod that does not cause a crack in the composite film of the electrode sample as the bending resistance.

7. The electrode according to claim 1, wherein the degree of crystallinity of the binder is 10% or less.

8. The binder includes a fluorine-containing binder, The electrode layer has a QBR (quantification binder ratio) of 1.1 or less. The aforementioned QBR is expressed by the following formula: QBR = Bs / Bf In the above formula, Bs represents the average value of the fluorine content in the surface region of the electrode layer from the outermost surface of the electrode layer to within 15% of the total thickness of the electrode layer, and Bf represents the average value of the fluorine content in the bottom region of the electrode layer from the interface of the electrode layer facing the electrode current collector to within 15% of the total thickness of the electrode layer, as described in claim 1.

9. The electrode according to claim 1, wherein the conductive material comprises activated carbon, graphite, carbon black, Ketjenblack, carbon nanotubes, or two or more of these.

10. The electrode according to claim 1, wherein the binder comprises polytetrafluoroethylene (PTFE).

11. The electrode according to claim 1, wherein the active material is a positive electrode active material or a negative electrode active material.

12. The electrode according to claim 1, wherein the content of the active material is 80 to 98 parts by weight, the content of the conductive material is 0.5 to 10 parts by weight, the content of the binder is 0.5 to 5 parts by weight, and the content of the fluoride elastomer is 0.1 to 5 parts by weight.

13. The electrode according to claim 1, wherein the electrode current collector includes a conductive primer layer on at least one surface.

14. The electrode according to claim 1, wherein the electrode layer is a film for dry electrodes.

15. A method for manufacturing an electrode according to any one of claims 1 to 14, A step of producing a mixture comprising an active material, a conductive material, a binder, and a fluoride elastomer, The steps include kneading the mixture at a temperature of 70°C to 200°C under a pressure of atmospheric pressure or higher to produce a mixture mass, The steps include crushing the aforementioned mixture mass to obtain a mixed powder for electrodes, The steps include feeding the electrode mixture powder between multiple rolls and calendering it to form an electrode film, A method for manufacturing an electrode, comprising the step of laminating the electrode film onto a metal current collector.

16. The method for manufacturing an electrode according to claim 15, wherein the step of kneading to produce a mixture mass is performed in a kneader under a pressure of atmospheric pressure or higher.

17. The method for manufacturing an electrode according to claim 15, wherein the rolling ratio of the electrode film is 20% or less.

18. A secondary battery comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is an electrode according to any one of claims 1 to 14.

19. An energy storage device comprising the secondary battery described in claim 18 as a unit battery.

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