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

Abstract

To provide an electrode, a secondary battery comprising the same, and an energy storage device.SOLUTION: An electrode comprises: an electrode current collector; and an electrode layer located on the electrode current collector, and comprising an active material, a conductive material, and a fluorine-containing binder. The electrode layer has a quantified binder ratio (QBR) of 1.1 or less, and the QBR is defined by the following equation: QBR=Bs / Bf, where Bs denotes an average fluorine content in an electrode layer surface region within 15% of a total thickness of the electrode layer from an outermost surface of the electrode layer, and Bf denotes an average fluorine content in an electrode layer bottom region within 15% of the total thickness of the electrode layer from an interface of the electrode layer facing the current collector.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode, a secondary battery including the electrode, and a manufacturing method thereof, and more particularly to an electrode having a binder distribution that is uniform in the thickness direction of the electrode layer, a secondary battery including the electrode, and a manufacturing method thereof.

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0131944 filed on October 5, 2021, and Korean Patent Application No. 10-2022-0049210 filed on April 20, 2022, and the contents disclosed in the specifications and drawings of those applications are incorporated herein in their entirety. [Background technology]

[0003] The recent dramatic increase in fossil fuel use has led to a rapid increase in the demand for alternative and clean energy sources. One of the most active research areas is electrochemical power generation and storage. Currently, secondary batteries are a representative example of electrochemical devices that utilize electrochemical energy, and their range of applications is expanding. Lithium secondary batteries, a representative example of such secondary batteries, are not only used as energy sources for mobile devices, but are also now being used practically as power sources for electric and hybrid electric vehicles (EVs) that can replace fossil fuel-powered vehicles, such as gasoline and diesel vehicles, which are major causes of air pollution. Their use is also expanding to include auxiliary power sources for grid-connected systems.

[0004] The manufacturing process of such a lithium secondary battery can be roughly divided into three steps: an electrode manufacturing process, an electrode assembly manufacturing process, and a chemical formation process. The electrode manufacturing process can be further divided into an electrode mixture mixing process, an electrode coating process, a drying process, a rolling process, a slitting (cutting) process, and a winding process.

[0005] Among these, the electrode mixture mixing process is a process of blending components for forming an electrode active layer where an electrochemical reaction actually occurs in the electrode. More specifically, the electrode mixture is produced in the form of a fluid slurry by mixing an electrode active material, which is an essential element of an electrode, other additives such as a conductive material and a filler, a binder for binding the powder particles together and adhering them to the current collector, and a solvent for imparting viscosity and dispersing the powder.

[0006] An electrode coating process is performed in which the slurry is applied onto an electrically conductive current collector, and a drying process is performed to remove the solvent contained in the electrode mixture slurry. The electrode is then rolled to produce an electrode with a predetermined thickness.

[0007] In this electrode manufacturing process, the slurry liquid is coated and then dried in a drying oven within a short time. This causes the binder to migrate to the surface of the electrode, resulting in an uneven distribution of the binder in the thickness direction of the electrode layer. This results in a problem of reduced adhesive strength with the current collector. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide an electrode having a uniform binder distribution in the thickness direction of the electrode layer, a secondary battery including the same, and a method for manufacturing the same. [Means for solving the problem]

[0009] In order to solve the problems of the present invention, according to one aspect of the present invention, there is provided an electrode having the following aspects.

[0010] According to a first aspect, there is provided 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, and a fluorine-containing binder, wherein the electrode layer has a quantified binder ratio (QBR) of 1.1 or less, and the quantified binder ratio (QBR) is defined by the following mathematical formula:

[0011] QBR=Bs / Bf

[0012] In the above formula, Bs represents the average value of the fluorine content in the surface region of the electrode layer extending 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 extending from the interface of the electrode layer facing the current collector to within 15% of the total thickness of the electrode layer.

[0013] According to a second aspect, the electrode may be as described in the first aspect, wherein the conductive material is a carbon-based material, a metal material, a conductive whisker, a conductive metal oxide, a conductive polymer, or two or more of these.

[0014] According to a third aspect, the electrode may be the electrode according to the first or second aspect, in which the fluorine-containing binder contains polytetrafluoroethylene (PTFE).

[0015] According to a fourth aspect, the electrode may be the electrode according to any one of the first to third aspects, in which the active material is a positive electrode active material or a negative electrode active material.

[0016] According to a fifth aspect, the electrode may be the electrode according to any one of the first to fourth aspects, in which the content of the active material is 85 to 98 parts by weight, the content of the conductive material is 0.5 to 5 parts by weight, and the content of the fluorine-containing binder is 0.5 to 10 parts by weight.

[0017] According to a sixth aspect, the electrode may be the electrode according to any one of the first to fifth aspects, wherein the electrode current collector further includes a conductive primer layer on at least one surface thereof.

[0018] According to a seventh aspect, the electrode may be the electrode according to any one of the first to sixth aspects, in which the electrode layer has a quantified binder ratio (QBR) of 0.95 to 1.05.

[0019] According to an eighth aspect, the electrode may be the electrode according to any one of the first to seventh aspects, which has a bending resistance of a diameter (Φ) of 10 mm or less.

[0020] According to a ninth aspect, the electrode may be the electrode according to the eighth aspect, wherein the bending resistance of the electrode is evaluated in accordance with the method of measurement standard JIS K5600-5-1.

[0021] According to a tenth aspect, the electrode may be the electrode according to the eighth or ninth aspect, wherein the bending resistance of the electrode is evaluated through the steps of: manufacturing a rectangular electrode sample of 100 mm × 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, bringing the electrode sample into contact with the measuring rod with the measuring rod having the largest diameter among the measuring rods, and then determining whether cracks occur in the composite film of the electrode sample when both ends of the electrode sample are lifted; and if no cracks occur in the determining step, repeating the step of determining whether cracks occur in the composite film of the electrode sample in the same manner as the previous step using the measuring rod with the next largest diameter, and determining the smallest diameter value of the measuring rod at which cracks do not occur in the composite film of the electrode sample as the bending resistance.

[0022] According to an eleventh aspect, there may be provided an electrode according to any one of the first to tenth aspects, in which the crystallinity of the fluorine-containing binder is 10% or less.

[0023] According to a twelfth aspect, the electrode layer may be the electrode according to any one of the first to eleventh aspects, which is produced by a dry process.

[0024] According to a thirteenth aspect, there is provided a method for manufacturing an electrode according to any one of the first to twelfth aspects, comprising the steps of: producing a mixture containing an active material, a conductive material, and a fluorine-containing binder; kneading the mixture at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mixture mass; pulverizing the mixture mass to obtain a mixed powder for an electrode; feeding the mixed powder for an electrode between a plurality of rolls and calendering it to form a film for an electrode; and laminating the film for an electrode on a metal current collector.

[0025] According to a fourteenth aspect, there may be provided a method for producing an electrode according to the thirteenth aspect, wherein the step of kneading to produce a mass of mixture is carried out in a kneader under a pressure equal to or higher than atmospheric pressure.

[0026] According to a fifteenth aspect, there may be provided a method for producing an electrode according to the thirteenth or fourteenth aspect, wherein in the laminating step, the compression ratio of the film for the electrode is 30 to 50%.

[0027] According to a sixteenth aspect, there may be provided a method for producing an electrode according to any one of the thirteenth to fifteenth aspects, wherein the rolling ratio of the film for the electrode is 20% or less.

[0028] According to a 17th aspect, the method for producing an electrode may be any one of the 13th to 16th aspects, in which the increase rate of apparent density of the electrode film before and after lamination with a current collector is 5 to 30%.

[0029] According to an eighteenth aspect, the method for producing an electrode according to any one of the thirteenth to seventeenth aspects may be performed by using a lamination roll at 25 to 250°C.

[0030] According to a nineteenth aspect, there is provided an electrode produced by the production method of any one of the thirteenth to eighteenth aspects.

[0031] According to a twentieth aspect, there is provided a secondary battery comprising a positive electrode, a negative electrode, and a separator 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 the first to twelfth aspects.

[0032] According to a twenty-first aspect, there is provided an energy storage device including the secondary battery according to the twentieth aspect as a unit cell. [Effects of the Invention]

[0033] According to one aspect of the present invention, an electrode is manufactured by uniformly mixing constituent materials, such as an active material, a conductive material, and a fluorine-containing binder, without a solvent drying process, to produce an electrode film, which is then laminated with a current collector. This makes it possible to uniformly distribute the binder in the thickness direction, thereby effectively improving defects such as reduced adhesive strength due to uneven binder distribution, reduced conductivity on the surface of the electrode layer, and the resulting reduced charge / discharge rate.

[0034] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical concepts of the present invention as well as the content of the invention, and therefore the present invention should not be interpreted as being limited to only the matters described in the drawings. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a schematic diagram of an electrode according to one embodiment of the present invention. [Figure 2]FIG. 1 is a schematic diagram of calculating the QBR value of an electrode layer. [Figure 3] 1 is a schematic diagram of a manufacturing process for a film for an electrode according to one embodiment of the present invention. [Figure 4] 1 is a schematic diagram of an electrode lamination process according to one embodiment of the present invention. [Figure 5] 1 is a graph showing the change in normalized intensity of the fluorine component of the binder of the electrode layer extracted and analyzed from the results of EDS mapping, over the distance from the surface of the electrode layer toward the current collector for the electrode of Example 1. [Figure 6] 1 is a graph showing the change in normalized intensity of the fluorine component of the binder of the electrode layer extracted and analyzed from the results of EDS mapping, over the distance from the surface of the electrode layer toward the current collector for the electrode of Comparative Example 1. [Figure 7] 1 is a graph showing the percentage values ​​of the discharge capacities of secondary batteries including electrodes manufactured in Example 1 and Comparative Example 1 at 0.33C, 0.5C, 1C, 2C, 2.5C, and 3C based on the discharge capacity at 0.1C. DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will now be described in more detail to provide a better understanding of the present invention.

[0037] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that corresponds to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of the terms in order to best explain the invention.

[0038] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.

[0039] Furthermore, throughout this specification, when a part is said to "comprise" a certain component, this does not mean that other components are excluded, but that other components may also be included, unless otherwise specified.

[0040] According to one aspect of the present invention, there is provided 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, and a fluorine-containing binder, wherein the electrode layer has a quantified binder ratio (QBR) of 1.1 or less.

[0041] The QBR is defined by the following formula:

[0042] QBR=Bs / Bf

[0043] In the above formula, Bs represents the average value of the fluorine content in the surface region of the electrode layer extending 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 extending from the interface of the electrode layer facing the current collector to within 15% of the total thickness of the electrode layer.

[0044] 1 is a schematic diagram of an electrode according to one embodiment of the present invention. Referring to FIG. 1, the electrode 10 comprises an electrode current collector 12 and an electrode layer 11 disposed on the electrode current collector 12 and including an active material, a conductive material, and a fluorine-containing binder.

[0045] The electrode layer 11 has a surface region 11s of the electrode layer that extends from the outermost surface of the electrode layer to within 15% of the entire thickness d of the electrode layer, based on the entire thickness d of the electrode layer, and a bottom region 11f of the electrode layer that extends from the interface of the electrode layer that faces the current collector to within 15% of the entire thickness d of the electrode layer.

[0046] In the above formula QBR, Bs means the average value of the fluorine content in the surface region 11s of the electrode layer, and Bf means the average value of the fluorine content in the bottom region 11f of the electrode layer.

[0047] In this case, the QBR can be calculated as follows:

[0048] First, an electrode for which QBR is to be confirmed is selected, and the edge of the selected electrode is prepared using argon ion milling. Then, an energy dispersive X-ray spectroscopy (EDS) detector in a scanning electron microscope (SEM) is used to perform EDS mapping of the components in the electrode layer on the edge of the prepared electrode.

[0049] 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 fluorine content Bs of the fluorine-containing binder in the surface region of the electrode layer and the average fluorine content Bf of the fluorine-containing binder in the bottom region of the electrode layer are extracted, and the QBR value is calculated using the following formula.

[0050] QBR=Bs / Bf

[0051] 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.

[0052] Figure 2 is a schematic diagram for calculating the QBR value of an electrode layer. Referring to Figure 2, the X-axis represents the thickness of the electrode layer, i.e., the distance from the surface toward the current collector, and the Y-axis represents the intensity of the fluorine component. Line A represents the intensity of the fluorine component of the fluorine-containing binder extracted by EDS mapping of the fluorine component in the electrode layer on the edge surface of the electrode. Line B is a trend line showing the tendency of Line A, which is a line smoothed using the LOWESS smoothing method, i.e., a locally weighted scatterplot smoother method.

[0053] The QBR value is a value that indicates the uniformity of the distribution of the fluorine-containing binder in the thickness direction within the electrode layer, calculated by the ratio of the content of the fluorine-containing binder contained in the surface region to the content of the fluorine-containing binder contained in the bottom region of the electrode layer. Here, the content of the fluorine-containing binder can be estimated using the fluorine component contained in the fluorine-containing binder used.

[0054] The QBR value is 1.1 or less, and according to one embodiment of the present invention, the QBR value may be 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, and may be 0.95 to 1.05.

[0055] When the QBR value exceeds 1.1, the fluorine-containing binder migrates to the surface of the electrode, and the content of the fluorine-containing binder contained in the surface region of the electrode layer is higher than the content of the fluorine-containing binder contained in the bottom region thereof. As a result, the binder distribution in the thickness direction of the electrode layer is uneven, and the binder content in the portion close to the current collector is low, which reduces the adhesive strength between the current collector and the electrode layer. This is disadvantageous because it may also reduce the conductivity at the surface of the electrode layer and the charge / discharge rate.

[0056] According to one aspect of the present invention, the electrode may be a positive electrode or a negative electrode, and the active material may be a positive electrode active material or a negative electrode active material.

[0057] As the positive electrode active material, there is no particular limitation as long as it is in the form of a lithium transition metal oxide or a lithium metal iron phosphate or a metal oxide. For example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3), Ni-site type lithium nickel oxides represented by; chemical formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn); LiNi 1-x-y-z Co x M1 y M2 z O2 (M1 and M2 are each independently any one selected from the group consisting of Al, Ni, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z are each independently the atomic fraction of the oxide composition element, 0 < x < 0.5, 0 < y < 0.5, 0 < z < 0.5, 0 < x + y + z ≦ 1), disulfide compounds; Fe2(MoO4)3 and the like can be mentioned, but it is not limited only to these.

[0058] In addition, as the negative electrode active material, carbon such as non-graphitizable carbon and graphite-based carbon; Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Snx Me 1-x Me' y O z Metal composite oxides such as (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si), elements of Groups 1, 2, and 3 of the periodic table, and halogens; 0≦x≦1; 1≦y≦3; 1≦z≦8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; silicon-based oxides such as SiO, SiO / C, and 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.

[0059] According to one embodiment of the present invention, the electrode may be a positive electrode, and therefore the active material may be, in particular, a positive electrode active material, and more particularly, may be a lithium transition metal oxide, a lithium nickel-manganese-cobalt oxide, an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with Al or another transition metal, or a lithium iron phosphate.

[0060] The conductive material is not particularly limited as long as it has conductivity without causing any chemical change in the battery, and for example, carbon-based materials, metal materials (metal powder or metal fiber), conductive whiskers, conductive metal oxides, conductive polymers, etc., or two or more of these can be used. Examples of carbon-based substances 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. Examples of metal substances include copper, nickel, aluminum, and silver. Examples of 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. Examples of conductive metal oxides include titanium oxide. Examples of conductive polymers include polyphenylene derivatives. These can be used alone or as a mixture of two or more of them.

[0061] According to one aspect of the present invention, in order to uniformly mix the conductive material and improve conductivity, the conductive material may contain at least one material selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, may contain carbon black or activated carbon.

[0062] The fluorine-containing binder may be a fluorine-containing polymer, specifically, polytetrafluoroethylene (PTFE). The fluorine-containing binder may include polytetrafluoroethylene alone, or may further include one or more PVdF-based copolymers such as polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0063] In one embodiment of the present invention, the crystallinity of the fluorine-containing binder in the electrode layer may be 10% or less, or the crystallinity of the fluorine-containing binder in the electrode layer may be 0% to 10%, or 0% to 5%, or 0% to 3%, or 0% to 1.2%, or 0% to 0.5%, or 0.5 to 1.2%.

[0064] The crystallinity (Xc) according to one embodiment of the present invention can be measured using a differential scanning calorimetry (DSC) analyzer, and can be based on the temperature (peak temperature) at which the highest enthalpy is observed during crystallization. Specifically, the crystallinity can be calculated based on the melting enthalpy (ΔH m ) value is calculated from the theoretical enthalpy of fusion (ΔH m 0 ) (equilibrium fusion heat) and expressed as a percentage, and can be calculated by the following relational expression 1. Here, the theoretical fusion enthalpy value of a perfect crystal (ΔH m 0For details on the enthalpy of melting, see the Polymer Handbook (J. Brandrup et al., 2003) and academic papers such as Polymer magazine. For example, the theoretical enthalpy of melting for a perfectly crystalline PTFE is 85.4 J / g (8872-8882 in Polymer magazine, Vol. 46 (2005)). Meanwhile, thermal analysis of polymers using DSC and other methods can usually be measured and calculated according to ASTM (American Society for Testing and Materials) D 3418-21.

[0065] [Equation 1] Xc(%)=(ΔH m ÷ΔH m 0 ) x 100

[0066] 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, and the content of the fluorine-containing binder may be 0.5 to 10 parts by weight. Also, 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, and the content of the fluorine-containing binder may be 0.5 to 5 parts by weight.

[0067] When the contents of the active material, conductive material, and fluorine-containing binder satisfy these ranges, the fluorine-containing binder can be sufficiently fiberized in a subsequent kneading process to form a mixture mass, the mixed powder formed using a pulverization process can be easily molded into an electrode film, the physical properties of the electrode film can be ensured, the content of the active material can be ensured to prevent the problem of capacity reduction, and sufficient conductivity can be ensured.

[0068] On the other hand, in some cases, a filler, which is a component that suppresses expansion of the electrode, may 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 to the battery, and for example, olefin polymers such as polyethylene and polypropylene, and fibrous materials such as glass fiber and carbon fiber are used.

[0069] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include stainless steel, aluminum, nickel, titanium, baked carbon, copper, or aluminum or stainless steel whose surface has been surface-treated with carbon, nickel, titanium, silver, etc. The current collector can also be formed with minute irregularities on its surface to increase the adhesive strength of the positive electrode active material, and a wide variety of forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric can be used.

[0070] Furthermore, the current collector may be entirely or partially coated with a conductive primer layer to reduce surface resistance and improve adhesion. Here, the conductive primer layer may include a conductive material and a binder. The conductive material may be any conductive material, including, but not limited to, a carbon-based material, a metal material (metal powder or metal fiber), a conductive whisker, a conductive metal oxide, or a conductive polymer. Examples of carbon-based substances 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. Examples of metal substances include copper, nickel, aluminum, and silver. Examples of 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. Examples of conductive metal oxides include titanium oxide. Examples of conductive polymers include polyphenylene derivatives. These can be used alone or as a mixture of two or more of them.

[0071] The binder for the conductive primer layer may be a solvent-soluble fluorine-based binder (including PVDF and PVDF copolymers) or an acrylic binder, or may include a water-based binder such as styrene butadiene rubber (SBR).

[0072] The flexibility of an electrode can be evaluated by its bending resistance.

[0073] According to one embodiment of the present invention, the bending resistance of the electrode may be a diameter (Φ) of 10 mm or less, or a diameter (Φ) of 8 mm or less, or a diameter (Φ) of 5 mm or less, or a diameter (Φ) of 2 to 8 mm, or a diameter (Φ) of 2 to 5 mm, or a diameter (Φ) of 2 to 4 mm.

[0074] The bending resistance can be evaluated in accordance with the method of measurement standard JIS K5600-5-1. Specifically, the manufactured electrode is 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 cracks do not occur.

[0075] According to one aspect of the present invention, the bending resistance of the electrode can be evaluated through the following steps: manufacturing a rectangular electrode sample of 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, respectively; bringing the electrode sample into contact with the measuring rod with the largest diameter among these measuring rods; and determining whether cracks occur in the composite film of the electrode sample when both ends of the electrode sample are lifted; and if no cracks occur in the determining step, repeating the step of determining whether cracks occur in the composite film of the electrode sample in the same manner as in the previous step using measuring rods with larger diameters, and determining the smallest diameter value of the measuring rod at which cracks do not occur in the composite film of the electrode sample as the bending resistance.

[0076] According to one aspect of the present invention, the binder can be fiberized to bind the active material and conductive material. The electrode can include a fiberized binder as a means for binding the active material and conductive material. Such a fiberized binder exhibits less breakage than conventional non-fiberized binders and has excellent longitudinal extensibility, thereby improving the flexibility of the electrode layer and the electrode itself including the same. The fiberization process of the binder will be specifically described in the section on the electrode manufacturing method described below.

[0077] According to one aspect of the present invention, there is provided a method for manufacturing an electrode, comprising the steps of: preparing a mixture containing an active material, a conductive material, and a fluorine-containing binder; kneading the mixture at a temperature in the range of 70°C to 200°C and at or above atmospheric pressure to prepare a mixture mass; pulverizing the mixture mass to obtain a mixed powder for an electrode; feeding the mixed powder for an electrode between a plurality of rolls and calendering it to form a film for an electrode; and laminating the film for an electrode onto a metal current collector.

[0078] The method for producing an electrode according to the present invention will now be described in more detail.

[0079] First, a mixture containing an active material, a conductive material, and a fluorine-containing binder is prepared.

[0080] The mixing for preparing the mixture is performed so that the active material, conductive material, and fluorine-containing binder resin are uniformly distributed, and since they are mixed in powder form, various methods that allow simple mixing of these materials are not particularly limited. However, since the electrode of the present invention is prepared by dry mixing without using a dispersion medium, the mixing may be performed by dry mixing, and may be performed by putting the materials into a device such as a blender.

[0081] To ensure uniformity, the mixture can be produced by mixing in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, more specifically, at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute.

[0082] The fluorine-containing binder can be microfibrillated during the step of preparing the mixed powder, and as described above, is not limited to a specific one as long as it contains fluorine for calculating the QBR. The microfibrillation refers to a process of finely dividing a polymer, and can be performed, for example, using mechanical shear force. Specific examples of such fluorine-containing binders include, as described above, fluorine-containing polymers. Specifically, PTFE may be used alone, or may further contain one or more PVdF-based copolymers, such as PVdF (polyvinylidene fluoride) and PVdF-HFP (polyvinylidene fluoride-co-hexafluoropropylene) in addition to PTFE.

[0083] Next, the mixture is kneaded at a temperature in the range of 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mass mixture.

[0084] In conventional techniques, high shear mixing, such as that using a jet mill, is performed to fiberize the binder resin. However, this mixing pulverizes the active material, which can cause problems such as cutting the formed fibers. Therefore, in the present invention, the above-mentioned problems are solved by using a low shear kneading method instead of high shear mixing.

[0085] The kneading method is not limited to any particular method, and in a specific embodiment of the present invention, the kneading may be performed using a kneading machine such as a kneader.

[0086] This kneading is a step in which the fluorine-containing binder is fiberized to bond or connect the active material and conductive material powder, thereby forming a mixture mass with a solid content of 100%.

[0087] Specifically, the kneading may be controlled at a speed of 10 rpm to 100 rpm. For example, the kneading may be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. The kneading may be performed for 3 minutes to 30 minutes. For example, the kneading may be performed at a speed of 40 rpm to 70 rpm within the above range for 3 minutes to 20 minutes. Meanwhile, the kneading may be controlled at a shear rate in the range of 10 / s to 500 / s. In one specific embodiment of the present invention, the kneading may be performed for 3 minutes to 20 minutes, and the shear rate may be controlled in the range of 30 / s to 100 / s.

[0088] The kneading step may be carried out at a high temperature and a pressure equal to or higher than atmospheric pressure, more specifically, at a pressure higher than atmospheric pressure. More specifically, the kneading of the mixture may be carried out at a temperature in the range of 70°C to 200°C, more specifically, at a temperature in the range of 90°C to 150°C.

[0089] If the temperature is lower than the above temperature range, the fluorine-containing binder will not be smoothly fibrous during kneading and will not be smoothly agglomerated by kneading, making it difficult to form a film during calendering. If the temperature is too high, the fluorine-containing binder will be rapidly fibrous, and thereafter, there is a risk that the already formed fibers will be cut by excessive shear force, which is undesirable.

[0090] The kneading step may be carried out under a pressure equal to or higher than atmospheric pressure, specifically, a pressure (lid pressure) of 1 to 100 atmospheres, more specifically, a pressure of 2 to 80 atmospheres, or 1 kgf / cm 2 ~100kgf / cm 2 or 2kgf / cm 2 ~80kgf / cm 2When the pressure range is satisfied, problems such as breakage of the formed fibers due to excessive shear force and pressure, or excessively high density of the mixture mass can be prevented. That is, according to the present invention, the intended effect of the present invention can be achieved by performing a low shear mixing process under high temperature and pressure conditions above atmospheric pressure instead of high shear mixing.

[0091] Next, the mixture mass is pulverized to obtain a mixed powder for an electrode.

[0092] Specifically, the mixture mass produced by the kneading may be immediately subjected to a calendering process. However, in this case, the mixture mass must be pressed to produce a thin film, which may result in problems such as the density of the film being too high or the film not being uniform. Therefore, according to the present invention, the produced mixture mass is subjected to the pulverization step.

[0093] In this case, the grinding step may be performed in a device such as a blender or grinder, but is not particularly limited thereto. Specifically, the grinding step may be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, more specifically, at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 2 minutes.

[0094] When the above-mentioned grinding speed and time are satisfied, sufficient grinding can be performed to form powder of a size suitable for film formation, and the problem of a large amount of fine powder being generated in the mixture mass can be prevented. If necessary, a classification process is performed to filter out powder above or below a certain size.

[0095] Next, the mixed powder for the electrode is put between a plurality of rolls and subjected to a calendering process to form a film for the electrode.

[0096] Referring to FIG. 3, in the process 100 for forming an electrode film, a plurality of rolls 110 are arranged at a distance from each other, and the mixed powder 120 for an electrode obtained in the previous step is placed between adjacent rolls 100. The rolls 100 are then rotated in opposite directions, whereby the mixed powder 120 is rolled and formed into a sheet or film 130 through a powder sheeting step, and then a film for an electrode having a final target thickness is obtained by performing multiple calendering processes.

[0097] Specifically, such calendering is a step of processing the mixed powder for an electrode into a film, for example, a step of manufacturing a film having an average thickness of 50 μm to 300 μm.

[0098] At this time, the calendering may be performed, for example, by rolls that are positioned facing each other, and at this time, the temperature of the rolls may be 50°C to 200°C, and the rotation speed ratio of the rolls may be controlled in the range of 1.0 to 5.0.

[0099] By proceeding to this calendering step, a dry electrode film that serves as an electrode mixture can be manufactured. Such a dry electrode film has also been conventionally called a free-standing film.

[0100] The dry electrode film produced in this manner is solvent-free and therefore has almost no fluidity, making it easy to handle and capable of being processed into desired shapes for use in the production of a wide variety of electrodes. Furthermore, when the dry electrode film of the present invention is used in the production of an electrode, the drying step for removing the solvent can be omitted, which not only significantly improves the efficiency of the electrode production process but also solves problems that have been considered problematic in the production of existing dry electrodes, such as cracking of the active material and breakage of the fibrous fluorine-containing binder.

[0101] Meanwhile, in the present invention, the dry electrode film may have a porosity of 20% to 50%, and may be controlled to a value within this range, preferably 40% or less, or 30% or less. When the porosity satisfies this range, impregnation with an electrolyte is facilitated, which can improve life characteristics and output characteristics. Furthermore, since there is no need to increase the volume to achieve the same capacity, the energy density can be improved relative to the volume.

[0102] The porosity according to one embodiment of the present invention can be calculated 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 constituent component according to the following formula 2.

[0103] [Formula 2] Porosity (%) = {1-(apparent density / actual density)} x 100

[0104] Next, the electrode film is laminated onto a metal current collector.

[0105] The lamination step may be a step of rolling and adhering the electrode film obtained in the previous step onto a current collector to a predetermined thickness. The lamination may also be performed using a lamination roll, which may be maintained at a temperature of 25°C to 250°C.

[0106] According to one aspect of the present invention, the compression ratio of the film for the electrode may be 30 to 50%, or 35 to 50%, or 40 to 50%.

[0107] The compression ratio of the electrode film can be defined as the ratio of the thickness to which the electrode film is compressed at the moment of lamination, and is expressed by the following formula 3:

[0108] [Formula 3] Compression ratio (%) = T p / T1×100 In formula 3, T pmeans the pressing thickness of the film for the electrode in the lamination step, T1 denotes the thickness of the film for the electrode before the lamination step.

[0109] In the present invention, by adjusting the compression ratio in the lamination step to satisfy a specific range, it is possible to provide an electrode film with appropriate density and porosity, as well as excellent adhesion between the electrode film and the current collector.

[0110] 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 adhesive strength between the electrode film and the current collector, preventing the electrode film from peeling off from the current collector after the lamination process, and eliminating the problem of the density of the electrode film increasing more than necessary, resulting in a lower porosity than the target porosity or damage to the current collector.

[0111] In one embodiment of the present invention, when a film for an electrode is laminated on both sides of the current collector, the compression ratio (%) in the above formula 3 may be expressed as the following formula 4:

[0112] [Formula 4] 30≦(T1+0.5T c -0.5T gap ) / T1×100≦50 In Equation 4, T1 means the thickness of the film for the electrode before the lamination step, and T c means the thickness of the current collector, and T gap means the distance between the first rolling roll and the second rolling roll.

[0113] Furthermore, the rolling ratio of the film for the electrode after the lamination step may be 20% or less, or 18% or less, or 15% or less, or in the range of 5% to 15%, or 6% to 15%, or 7% to 15%, or 9% to 13%.

[0114] Here, the rolling ratio can be defined as the ratio of the thickness of the film for the electrode after the lamination step to the thickness of the film for the electrode before the lamination step, and is expressed by the following Equation 5.

[0115] [Formula 5] Rolling ratio (%) = (T1-T2) / T1 x 100 In the formula 5, T1 means the thickness of the film for the electrode before the lamination step, T2 denotes the thickness of the film for the electrode after the lamination step.

[0116] When the rolling ratio satisfies the above range, it is possible to achieve an appropriate density and porosity of the electrode film, as well as adhesive strength between the electrode film and the current collector.

[0117] The increase rate of the apparent density of the electrode film before and after lamination with the current collector is expressed by the following formula 6:

[0118] [Formula 6] Apparent density increase rate (%) = (D2 - D1) / D1 x 100 In the formula 6, D1 is the apparent density (g / cm) of the film for the electrode before the lamination step. 3 ) and D2 is the apparent density (g / cm) of the film for the electrode after the lamination step. 3 ) is shown.

[0119] The increase rate of apparent density of the electrode film before and after lamination with the current collector may be 5 to 30%, or 7 to 25%, or 10 to 20%, where D1 and D2 are 2.75 g / cm 3 ~3.5g / cm 3On the other hand, when the increase rate of the apparent density of the electrode film satisfies the above range, the adhesive strength between the electrode film and the current collector can be improved, and problems such as the porosity falling outside the target range or damage to the positive electrode active material or the current collector can be prevented.

[0120] The apparent density of the electrode film before and after lamination 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 determining the weight and thickness of the film excluding the weight and thickness of the current collector.

[0121] The active material loading of the dry electrode film is 3 mAh / cm 2 ~15mAh / cm 2 Specifically, 4 mAh / cm 2 ~10mAh / cm 2 It could be.

[0122] Here, the loading amount of the active material is a value calculated by the following formula 7.

[0123] [Formula 7] Active material loading (mAh / cm 2 ) = Capacity of active material (mAh / g) × Weight content ratio of active material in dry electrode film (wt%) × Weight per unit area of ​​dry electrode film (g / cm 2 )

[0124] The interface resistance between the dry electrode film and the current collector is 5 Ω cm 2 For details, see below. 2Ω·cm 2 Here, the interfacial resistance can be calculated by applying a current of 100 μA to the electrode using a multi-probe (MP) resistance measurement method, measuring the resistance between the dry electrode film and the current collector layer as a potential difference measured between multiple probes. If the interfacial resistance range is satisfied, the battery performance of a subsequently manufactured secondary battery can be improved.

[0125] 4 is a schematic diagram showing a step of laminating an electrode film on both sides of a current collector according to one embodiment of the present invention. That is, in the lamination step 200, the electrode film 230 obtained in the previous step is rolled to a predetermined thickness and attached to the current collector 220 using a pair of lamination rolls 210, thereby finally obtaining an electrode 240.

[0126] According to yet another embodiment of the present invention, there is provided a dry electrode manufactured by the dry electrode manufacturing method, a secondary battery including the dry electrode, wherein the dry electrode is a positive electrode, and an electrode assembly including the positive electrode, a negative electrode, and a separator is housed in a battery case (cylindrical case, prismatic case, pouch, etc.) together with a lithium-containing non-aqueous electrolyte, and an energy storage device including the same as a unit battery is also provided.

[0127] At this time, the specific structures of the secondary battery and the energy storage device are well known and therefore will not be described in this specification.

[0128] Meanwhile, according to one embodiment of the present invention, there is provided an apparatus for manufacturing a dry electrode, the apparatus including: a blender that mixes raw material composites including an active material, a conductive material, and a fluorine-containing binder; a kneader that kneads the mixture to prepare a mass of the mixture; a pulverizer that pulverizes the mass of the mixture to form a mixed powder for an electrode; a calender that forms the mixed powder for an electrode into a dry electrode film; and a lamination roll that positions the dry electrode film on at least one side of a current collector and laminates it.

[0129] The blender is a mixer that mixes raw materials, and as explained above, can mix the raw materials for the combination at a speed of 1000 rpm to 10000 rpm.

[0130] The kneader is a device for fiberizing the fluorine-containing binder and dispersing the raw materials for the composite in the present invention, and the mixture is obtained as a mass mixture by kneading in the kneader. The kneader for obtaining the results of the present invention can be set to a temperature range of 70°C to 200°C and a pressure of at least atmospheric pressure. Specifically, the kneader can be set to a temperature range of 90°C to 180°C and a pressure range of 1 to 100 atmospheres, more specifically, a pressure range of 2 to 80 atmospheres.

[0131] The pulverizer is a device that pulverizes the mixture mass to form a mixed powder for an electrode, and a blender or a grinder can be used as the pulverizer.

[0132] The calender is a device for forming the mixed powder for the electrode into a film, and may be, for example, a pair of rollers facing each other, and the thickness of the film can be adjusted by adjusting the gap between them.

[0133] The lamination roll serves to attach the dry electrode film formed by the calendar to at least one surface of the current collector and roll it.

[0134] The porosity of the dry electrode film according to the present invention can be determined by such a calendar and lamination roll.

[0135] That is, the dry electrode manufacturing apparatus according to the present invention is characterized in that it includes a kneader and a pulverizer.

[0136] The specific structures of the blender, kneader, calendar, and lamination roll are well known and will not be described in detail in this specification.

[0137] The present invention will be described in detail below with reference to examples. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0138] Example 1 Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 96g of O2, 1g of carbon black as a conductive material, and 3g of polytetrafluoroethylene (PTFE) as a fluorine-containing binder were added to a blender and mixed at 10,000 rpm for 1 minute to produce a mixture. The temperature of the kneader was stabilized at 150°C, and the mixture was then added to the kneader and pressurized at 2kgf / cm. 2 The mixture was mixed at 50 rpm for 5 minutes under a lid pressure of 1000 rpm to obtain a mixture mass. The mixture mass was placed in a blender, pulverized at 10,000 rpm for 30 seconds, and sieved using a sieve with 1 mm openings to obtain a mixed powder for an electrode. The mixed powder for an electrode was then placed in a wrap calender (roll diameter: 88 mm, roll temperature: 100°C) to prepare an electrode film. Two sheets of the electrode film were placed on both sides of an aluminum foil (19 μm) coated with a conductive primer layer made of a 5:6 mixture of carbon black and an acrylic binder by weight, and laminated using a lamination roll (compression roll) maintained at 150°C to prepare an electrode (cathode).

[0139] At this time, in the lamination step, the compression ratio of the electrode film was 35.6%, and the rolling ratio of the electrode film was 16.4%.

[0140] Here, the compression ratio of the electrode film is defined as the ratio of the thickness to which the electrode film is compressed at the moment of lamination, and was calculated using the following Equation 3.

[0141] [Formula 3] Compression ratio (%) = T p / T1×100 In formula 3, T p means the pressing thickness of the film for the electrode in the lamination step, T1 denotes the thickness of the film for the electrode before the lamination step.

[0142] In addition, the rolling ratio of the electrode film was 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 was calculated by the following Equation 5.

[0143] [Formula 5] Rolling ratio (%) = {(T1-T2) / T1} x 100 In the formula 5, T1 means the thickness of the film for the electrode before the lamination step, T2 denotes the thickness ratio of the film for the electrode after the lamination step.

[0144] The total thickness of the finally produced electrode was 175 μm, the thickness of the electrode active material layer was 77 μm, and the porosity of the electrode was 25.1%.

[0145] At this time, the porosity of the electrode 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 then calculating the actual density based on the actual density and composition of each constituent component using the following formula 2:

[0146] [Formula 2] Porosity (%) = {1-(apparent density / actual density)} x 100

[0147] The increase in apparent density of the electrode film before and after lamination with the current collector was 19%.

[0148] In this case, the increase rate of apparent density before and after lamination of the electrode film with the current collector was calculated by the following formula 6. The apparent density before and after lamination of the electrode film with the current collector was calculated by measuring the weight and thickness of the electrode film before lamination, measuring the weight and thickness of the electrode after lamination, and then determining the weight and thickness of the film excluding the weight and thickness of the current collector.

[0149] [Formula 6] Apparent density increase rate (%) = {(D2-D1) / D1} x 100 In formula 6, D1 is the apparent density (g / cm) of the film for the electrode before the lamination step. 3 ) and D2 is the apparent density (g / cm) of the film for the electrode after the lamination step. 3 ) is shown.

[0150] Example 2 Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 96g of O2, 1g of carbon black as a conductive material, and 3g of polytetrafluoroethylene (PTFE) as a fluorine-containing binder were added to a blender and mixed at 10,000 rpm for 2 minutes to produce a mixture. The temperature of the kneader was stabilized at 150°C, and the mixture was then added to the kneader and mixed at 2kgf / cm. 2The mixture was mixed at 50 rpm for 5 minutes under a lid pressure of 1000 rpm to obtain a mixture mass. The mixture mass was placed in a blender, pulverized at 10,000 rpm for 30 seconds, and sieved using a sieve with 1 mm openings to obtain a mixed powder for an electrode. The mixed powder for an electrode was then placed in a wrap calender (roll diameter: 88 mm, roll temperature: 100°C) to prepare an electrode film. Two sheets of the electrode film were placed on both sides of an aluminum foil (19 μm) coated with a conductive primer layer made of a 5:6 mixture of carbon black and an acrylic binder by weight, and laminated using a lamination roll (compression roll) maintained at 150°C to prepare an electrode (cathode).

[0151] At this time, in the lamination step, the compression ratio of the electrode film was 35.1%, and the rolling ratio of the electrode film was 16.0%.

[0152] The total thickness of the finally produced electrode was 174 μm, the thickness of the electrode active material layer was 77.5 μm, and the porosity of the electrode was 25.6%.

[0153] The increase in apparent density of the electrode film before and after lamination with the current collector was 18%.

[0154] Example 3 Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 96g of O2, 1g of carbon black as a conductive material, and 3g of polytetrafluoroethylene (PTFE) as a fluorine-containing binder were added to a blender and mixed at 10,000 rpm for 1 minute to produce a mixture. The temperature of the kneader was stabilized at 150°C, and the mixture was then added to the kneader and pressurized at 2kgf / cm. 2The mixture was mixed at 25 rpm for 5 minutes under a lid pressure of 10,000 rpm to obtain a mixture mass. The mixture mass was placed in a blender, pulverized at 10,000 rpm for 30 seconds, and sieved using a sieve with 1 mm openings to obtain a mixed powder for an electrode. The mixed powder for an electrode was then placed in a wrap calender (roll diameter: 88 mm, roll temperature: 100°C) to prepare an electrode film. Two sheets of the electrode film were placed on both sides of an aluminum foil (19 μm) coated with a conductive primer layer composed of a 5:6 mixture of carbon black and an acrylic binder by weight, and laminated using a lamination roll (compression roll) maintained at 150°C to prepare an electrode (cathode).

[0155] At this time, in the lamination step, the compression ratio of the electrode film was 36.0%, and the rolling ratio of the electrode film was 16.8%.

[0156] The total thickness of the finally produced electrode was 176 μm, the thickness of the electrode active material layer was 78.5 μm, and the porosity of the electrode was 24.8%.

[0157] The increase in apparent density of the electrode film before and after lamination with the current collector was 18%.

[0158] Comparative Example 1 Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01300 g of O2, 0.7 g of carbon black as a conductive material, and 1.56 g of polyvinylidene fluoride (PVDF) as a fluorine-containing binder were mixed with N-methylpyrrolidone (NMP) as a dispersion medium in a mixer and mixed at 30,000 rpm for 60 minutes to produce a slurry mixture. (The solids content of the resulting slurry was 70% and the viscosity was approximately 8,000-20,000 cps.) The resulting slurry was dropped onto aluminum foil (19 μm) and uniformly coated using an applicator (50-300 μm). The uniformly coated slurry was placed in a drying chamber at 100°C to evaporate the dispersion medium and confirm whether the target loading was met. The same coating and drying were performed on the back of a current collector. The coated electrode thus produced was then roll-pressed to produce an electrode (cathode) with the target thickness and porosity.

[0159] The total thickness of the finally produced electrode was 174 μm, the thickness of the electrode active material layer was 76 μm, and the porosity of the electrode was 25.2%.

[0160] Comparative Example 2 Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni 0.88 Co 0.07 Mn 0.04 ]Al 0.01 96g of O2, 1g of carbon black as a conductive material, and 3g of polytetrafluoroethylene (PTFE) as a fluorine-containing binder were added to a blender and mixed at 10,000 rpm for 1 minute to produce a mixture. The temperature of the kneader was stabilized at 150°C, and the mixture was then added to the kneader and pressurized at 2kgf / cm. 2The mixture was mixed at 10 rpm for 1 minute under a lid pressure of 1000 rpm to obtain a mixture mass. The mixture mass was placed in a blender, pulverized at 10,000 rpm for 30 seconds, and sieved using a sieve with 1 mm openings to obtain a mixed powder for an electrode. The mixed powder for an electrode was then placed in a wrap calender (roll diameter: 88 mm, roll temperature: 100°C) to prepare an electrode film. Two sheets of the electrode film were placed on both sides of an aluminum foil (19 μm) coated with a conductive primer layer made of a 5:6 mixture of carbon black and an acrylic binder by weight, and laminated using a lamination roll (compression roll) maintained at 150°C to prepare an electrode (cathode).

[0161] At this time, in the lamination step, the compression ratio of the electrode film was 37.5%, and the rolling ratio of the electrode film was 17.7%.

[0162] The total thickness of the finally produced electrode was 178 μm, the thickness of the electrode active material layer was 79.5 μm, and the porosity of the electrode was 26.4%.

[0163] The increase in apparent density of the electrode film before and after lamination with the current collector was 20%.

[0164] Comparative Example 3 96 g of lithium nickel cobalt manganese aluminum oxide as the positive electrode active material, 1 g of carbon black as the conductive material, and 3 g of polytetrafluoroethylene (PTFE) as the fluorine-containing binder were placed in a blender and mixed at 5,000 rpm for 20 minutes to obtain a mixed powder for the electrode. The mixed powder for the electrode was then placed in a wrap calender (roll diameter: 88 mm, roll temperature: 100°C) to attempt to produce a film for the electrode, but feeding into the wrap calender was difficult, and no film formation was possible.

[0165] Performance evaluation The electrodes and secondary batteries provided with the electrodes produced in Examples 1 to 3, Comparative Example 1, and Comparative Example 2 were evaluated as follows. The results are shown in Tables 1 and 2.

[0166] At this time, the secondary batteries provided with the electrodes manufactured in Examples 1 to 3, Comparative Example 1, and Comparative Example 2 were manufactured by the following method.

[0167] A negative electrode was prepared by depositing lithium metal to a thickness of 70 μm on a copper foil.

[0168] An electrode assembly was manufactured using the electrodes manufactured in Examples 1 to 3, Comparative Examples 1, and 2 as the positive electrode and a polyethylene film (thickness: 20 μm) between the positive electrode and the negative electrode. The electrode assembly was placed in a battery case, and then a liquid electrolyte solution in which LiPF6 was dissolved at 1 M in a solvent containing a 1:2:1 (volume ratio) mixture of ethylene carbonate, dimethylene carbonate, and diethyl carbonate was poured into the case and sealed, thereby manufacturing a secondary battery.

[0169] (1) Quantified Binder Ratio (QBR) The end faces of the electrodes of Examples 1 to 3, Comparative Example 1, and Comparative Example 2 were prepared using argon ion milling.

[0170] The components in the electrode layer on the edge of the fabricated electrode were EDS mapped using the EDS detector of the SEM equipment. The measurement area included the entire electrode coating layer and a portion of the current collector area, and was measured with an image pixel size of 1024 and a horizontal / vertical aspect ratio of 4. EDS mapping measurements were performed with an SEM accelerating voltage of 5 kV, with a minimum of 10 frames, and data was collected for the components of the active material, conductive material, binder, and current collector, excluding Li and H.

[0171] Using EDS driver software (Aztec, manufactured by Oxford), deconvoluted line profiles (obtained by unravelling the convolution of EDS peaks) were extracted from the EDS mapping results. From the extracted line profile results, the average fluorine content of the fluorine-containing binder in the surface region of the electrode layer (Bs) and the average fluorine content of the fluorine-containing binder in the bottom region of the electrode layer (Bf) were extracted from a graph showing the change in normalized intensity of the binder component of the electrode layer from the surface of the electrode layer toward the current collector, and the QBR value was calculated using the following equation.

[0172] QBR=Bs / Bf

[0173] 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.

[0174] 5 is a graph showing the change in normalized intensity of the fluorine component of the fluorine-containing binder of the electrode layer extracted and analyzed from the EDS mapping results over the distance from the surface of the electrode layer toward the current collector for the electrode of Example 1. The average value (Bs) of the fluorine content of the fluorine-containing binder in the surface region of the electrode layer of the electrode of Example 1 was calculated as 0.98, the average value (Bf) of the fluorine content of the fluorine-containing binder in the bottom region of the electrode layer was calculated as 0.99, and the QBR value was calculated as 0.99.

[0175] In FIG. 5, line A indicates the intensity in each depth direction when the entire fluorine component of the actually measured fluorine-containing binder is normalized to 1, line B is a trend line showing the tendency of line A, which is a line smoothed by the LOWESS smoothing method, i.e., the locally weighted scatterplot smoother method, and line C is a line that always shows a value of 1.

[0176] 6 is a graph showing the change in normalized intensity of the fluorine component of the fluorine-containing binder of the electrode layer extracted and analyzed from the EDS mapping results over the distance from the surface of the electrode layer toward the current collector for the electrode of Comparative Example 1. The average value (Bs) of the fluorine content of the fluorine-containing binder in the surface region of the electrode layer of the electrode of Comparative Example 1 was calculated to be 1.13, the average value (Bf) of the fluorine content of the fluorine-containing binder in the bottom region of the electrode layer was calculated to be 0.91, and the QBR value was calculated to be 1.24.

[0177] As defined in Figure 5, in Figure 6, line B is a trend line showing the tendency of line A, and is a line shown by smoothing using the LOWESS smoothing method, i.e., the locally weighted scatterplot smoother method, and line C is a line that always shows a value of 1.

[0178] (2) Adhesive strength The electrodes of Examples 1 to 3 and Comparative Examples 1 and 2 were cut into pieces with a width of 20 mm and a length of 100 mm to prepare electrode samples.

[0179] A 55 mm long double-sided adhesive tape was attached to a glass slide, and the electrode samples of Example 1 and Comparative Example 1 prepared above were laminated onto the glass slide using a laminator.

[0180] The adhesive strength between the electrode layer and the current collector of the electrode sample was measured using a universal testing machine (UTM) (90° peeling experiment, load cell: 10 N, speed: 100 mm / min). (3) Cell resistance 1)0.1 seconds As described above, the charge / discharge characteristics of the batteries manufactured in Examples 1 to 3, Comparative Example 1, and Comparative Example 2 were compared using a charge / discharge measuring device (manufactured by PNE Solutions Co., Ltd., Korea). Each battery was charged at 25°C for the first cycle at a constant current (CC) of 0.1 C to 4.2 V, then charged at a constant voltage (CV) until the charging current reached 0.05 C (current limiting value). After this, the battery was left for 30 minutes, then discharged at a constant current (CC) of 0.1 C to 2.5 V, and then left for another 30 minutes. Subsequently, a cycle of charging at a constant current of 0.33 C, discharging at a constant current of 0.33 C, and leaving for 30 minutes was repeated over three cycles, with the final discharge stopped when the battery reached half of the previous discharge capacity. Then, the battery was discharged at a constant current of 2.5 C for 10 seconds, with the voltage change recorded every 0.1 seconds. If the open circuit voltage (OCV) at the end of the 30-minute rest step is V0 and the battery voltage recorded when the battery is discharged for 0.1 seconds at a constant current (I) of 2.5 C is V, the resistance (R) at 0.1 seconds is calculated as follows: R=(V-V0) / I 2) 10 seconds As mentioned above, the same measurement conditions and method were used to calculate the 0.1 second resistance, and the battery voltage recorded after 10 seconds of discharge at a constant current of 2.5C was substituted into the above formula to calculate the 10 second resistance.

[0181] (4)Discharge capacity As described above, secondary batteries equipped with electrodes prepared in Example 1 and Comparative Example 1 were charged at 25°C at a constant current (CC) of 0.33 C to 4.2 V, and then charged at a constant voltage (CV) until the charging current reached 0.05 C (current limit). After 30 minutes of storage, the batteries were discharged at a constant current (CC) of 0.1 C to 2.5 V. After 30 minutes of storage, the batteries were charged, stored, and discharged under the same conditions except that the discharge current was changed to 0.33 C, 0.5 C, 1 C, 2 C, 2.5 C, and 3 C. The percentage values ​​(normalized capacity) of the discharge capacity at 0.33 C, 0.5 C, 1 C, 2 C, 2.5 C, and 3 C relative to the discharge capacity at 0.1 C are shown in FIG. 7 and Table 1.

[0182] (5) Flexibility The flex resistance was evaluated in accordance with the measurement standard JIS K5600-5-1 method.

[0183] Specifically, rectangular electrode samples measuring 100 mm x 50 mm were manufactured using the electrodes manufactured in Examples 1 to 3, Comparative Example 1, and Comparative Example 2, and 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 were prepared. The electrode sample was brought into contact with the measuring rod with the largest diameter among these, and then both ends of the electrode sample were lifted to determine whether cracks occurred in the composite film of the electrode sample.

[0184] If no cracks occurred in the judgment step, the step of judging whether cracks occurred in the composite film of the electrode sample was repeated using a measuring rod with the next larger diameter, as in the previous step, and the smallest diameter value of the measuring rod at which cracks did not occur in the composite film of the electrode sample was determined to be the bending resistance.

[0185] (6) Crystallinity of the fluorine-containing binder in the electrode layer Samples were prepared for measuring the crystallinity of the fluorine-containing binder in the electrode layer of the electrodes produced in Examples 1 to 3, Comparative Example 1, and Comparative Example 2. For each sample, the crystallinity (Xc) was measured by weighing out approximately 5 mg to 12 mg of the sample and placing it in a differential scanning calorimetry (DSC) manufactured by TA Instruments, and measuring the heat of fusion (Δ heat of fusion) according to the temperature while increasing the temperature in a nitrogen atmosphere in the temperature range of 25 to 360°C at a rate of 10°C / min.

[0186] The melting point (Tm) and melting enthalpy (ΔHm) were analyzed using the TROIS program manufactured by TA Instruments, based on the temperature (peak temperature) at which the highest enthalpy was observed during melting. The crystallinity of each sample was determined by the melting enthalpy (ΔH m ) value is calculated from the theoretical enthalpy of fusion (ΔH m 0 ) and expressed as a percentage, and was calculated using the following relational formula 1.

[0187] [Equation 1] Xc(%)=(ΔH m ÷ΔH m 0 ) x 100

[0188] The melting enthalpy value (ΔH) of the perfectly crystalline polytetrafluoroethylene (PTFE) used as a fluorine-containing binder m 0 ) was set to 85.4 J / g, and reference was made to pages 8872-8882 of Polymer, Vol. 46 (2005).

[0189] [Table 1]

[0190] [Table 2]

[0191] Referring to Tables 1 and 2 above, it was confirmed that the positive electrodes of Examples 1 to 3, which have a QBR of 1.1 or less, exhibit improved adhesion compared to the positive electrodes of Comparative Example 1, which have a QBR of 1.24, and Comparative Example 2, which have a QBR of 1.12. The crystallinity of the fluorine-containing binder contained in the electrode layer of the positive electrodes of Examples 1 to 3 was controlled to 10% or less. It was also confirmed that the secondary batteries using the positive electrodes of Examples 1 to 3 had lower cell resistance compared to the secondary batteries using the positive electrodes of Comparative Examples 1 and 2, and the secondary battery using the positive electrode of Example 1 exhibited higher discharge capacity per charge rate compared to the secondary battery using the positive electrode of Comparative Example 1.

Claims

1. an electrode current collector; an electrode layer located on the electrode current collector and including an active material, a conductive material, and a fluorine-containing binder; Equipped with the electrode layer has a quantified binder ratio (QBR) of 1.1 or less; The quantified binder ratio (QBR) is defined by the following formula: QBR = Bs / Bf an electrode, wherein Bs represents an average value of the fluorine content in a surface region of the electrode layer extending from the outermost surface of the electrode layer to within 15% of the entire thickness of the electrode layer, and Bf represents an average value of the fluorine content in a bottom region of the electrode layer extending from the interface of the electrode layer facing the electrode current collector to within 15% of the entire thickness of the electrode layer.

2. The electrode of claim 1 , wherein the conductive material comprises a carbon-based material, a metal material, a conductive whisker, a conductive metal oxide, a conductive polymer, or two or more of these.

3. 10. The electrode of claim 1, wherein the fluorine-containing binder comprises polytetrafluoroethylene (PTFE).

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

5. 2. The electrode of claim 1, wherein the content of the active material is 85 to 98 parts by weight, the content of the conductive material is 0.5 to 5 parts by weight, and the content of the fluorine-containing binder is 0.5 to 10 parts by weight.

6. The electrode of claim 1 , wherein the electrode current collector further comprises a conductive primer layer on at least one surface.

7. 10. The electrode of claim 1, wherein the electrode layer has a quantified binder ratio (QBR) of 0.95 to 1.

05.

8. 10. The electrode of claim 1, wherein the electrode has a bending resistance of 10 mm diameter (Φ) or less.

9. 9. The electrode according to claim 8, wherein the bending resistance of the electrode is evaluated in accordance with the method of measurement standard JIS K5600-5-1.

10. The bending resistance of the electrode is manufacturing a rectangular electrode sample of 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, respectively, and using the measuring rod with the largest diameter among these measuring rods to bring the electrode sample into contact with the measuring rod, and then determining whether or not cracks occur in the composite film of the electrode sample when both ends of the electrode sample are lifted; If no cracks occur in the determining step, repeat 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 a measuring rod with a next larger diameter, and determine the smallest diameter value of the measuring rod that does not cause cracks in the composite film of the electrode sample as the bending resistance; The electrode of claim 8, wherein the electrode is evaluated via

11. 2. The electrode of claim 1, wherein the fluorine-containing binder has a crystallinity of 10% or less.

12. The electrode of claim 1 , wherein the electrode layer is a dry electrode film.

13. A method for manufacturing the electrode according to claim 1, comprising the steps of: preparing a mixture including an active material, a conductive material, and a fluorine-containing binder; kneading the mixture at a temperature in the range of 70°C to 200°C and at a pressure equal to or higher than atmospheric pressure to produce a mixture mass; pulverizing the mixture mass to obtain a mixed powder for an electrode; The electrode powder mixture is placed between a plurality of rolls and subjected to a calendering process to form an electrode film; laminating the electrode film onto a metal current collector; A method for manufacturing an electrode, comprising:

14. The method for producing an electrode according to claim 13 , wherein the step of kneading to produce a mass of the mixture is carried out in a kneader under a pressure equal to or greater than atmospheric pressure.

15. The method for manufacturing an electrode according to claim 13, wherein in the laminating step, the compression ratio of the film for the electrode is 30 to 50%.

16. The method for producing an electrode according to claim 13 , wherein the rolling ratio of the film for the electrode is 20% or less.

17. The method for producing an electrode according to claim 13, wherein the increase in apparent density of the electrode film before and after lamination with the metal current collector is 5 to 30%.

18. The method for manufacturing an electrode according to claim 13, wherein the laminating step is performed by a lamination roll at 25 to 250°C.

19. 19. An electrode produced by the method of any one of claims 13 to 18.

20. A secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode according to any one of claims 1 to 12.

21. An energy storage device comprising the secondary battery according to claim 20 as a unit battery.

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