Method for measuring the degree of dispersion of conductive material in an electrode for an electrochemical element

Abstract

The method for evaluating the dispersion degree of a conductive material according to the present invention can quantitatively evaluate the dispersion degree of the conductive material in an electrode. Specifically, a conductive material region is defined from the result (2D mapping image) obtained by performing two-dimensional scale visual image processing on an arbitrary cross section of an electrode active material layer, and the perimeter and area of ​​the part defined as the conductive material region are calculated, thereby quantitatively expressing the dispersion degree of the conductive material.

Description

[Technical Field]

[0001] This application claims priority to Korean Patent Application No. 10-2022-0049197, filed on April 20, 2022. The present invention relates to a quantified dispersibility index that can quantitatively represent the dispersibility of a conductive material for an electrochemical device. The present invention also relates to a dispersibility measurement method including a method for calculating the dispersibility index. [Background technology]

[0002] As interest in energy storage technology grows, its application fields are expanding to include mobile phones, tablets, laptops, and video cameras, as well as the energy sources of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and research and development on electrochemical devices is gradually increasing. Electrochemical devices are the field that has attracted the most attention in this regard, and the development of rechargeable lithium-ion secondary batteries has been a focus of attention. Recently, in the development of such batteries, research and development has been conducted on new electrode and battery designs to improve capacity density and specific energy.

[0003] When manufacturing electrodes for these secondary batteries, increasing the active material content in the electrode has been considered to improve energy density. However, this results in a relatively low conductive material content, making it important to uniformly distribute the conductive material within the electrode to prevent a decrease in electrical conductivity. Because the distribution of the conductive material in the electrode is closely related to the electrode manufacturing process, research is needed on dry electrode manufacturing methods that can improve the dispersion of the conductive material during electrode manufacturing. Furthermore, to establish a manufacturing process that improves the dispersion of the conductive material, it is necessary to develop an evaluation tool that can accurately confirm the dispersion of the conductive material in the electrode. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a quantified dispersibility index that can quantitatively represent the dispersibility of a conductive material for an electrochemical element. Another object is to provide a dispersibility measurement method that includes a method for calculating the dispersibility index. It will be easily understood that other objects and advantages of the present invention can be achieved by the means or methods recited in the claims, and combinations thereof. [Means for solving the problem]

[0005] A first aspect of the present invention relates to a method for evaluating the dispersion degree of a conductive material, the method comprising: measuring a perimeter (Boundary A) of a portion defined as a conductive material region in one or more arbitrary cross sections inside the electrode active material layer in an electrode for an electrochemical device including an electrode active material and a conductive material; measured ) and area (A) as variables.

[0006] A second aspect of the present invention is the first aspect, wherein the formula is a conductive material dispersion index 1 (Index 1) according to the following [Formula 1], or a conductive material dispersion index 2 (Index 1) according to the following [Formula 2]: [Formula 1] Index 1 (μm -1 )=Boundary measured / A [Formula 2] Index 2=Boundary measured / L circle In the above [Equation 1], Boundary measured means the perimeter of the portion defined as the conductive material region measured at a predetermined cross section of the electrode active material layer, and A means the area of ​​the portion defined as the conductive material region measured at a predetermined cross section of the electrode active material layer. In the above [Equation 2], L circle is the circumference of a circle having the same area as the area of ​​the conductive material region defined above.

[0007] A third aspect of the present invention, in the first or second aspect, includes the steps of: (Step 1) obtaining a cross-sectional sample in which an arbitrary cross section inside the electrode active material layer is exposed; (Step 2) obtaining a 2D scale map of the resistance distribution in the cross section of the sample; (Step 3) masking a conductive material region; and (Step 4) calculating the perimeter and area of ​​the masked region and substituting them into the above-mentioned formula 1 and / or formula 2 to confirm the dispersion degree of the conductive material in the electrode active material layer.

[0008] A fourth aspect of the present invention is any one of the first to third aspects, wherein the electrode active material layer is formed on either side of an electrode current collector, and the cross section (or multiple cross sections) is a plane parallel to or perpendicular to the opposing part of the electrode active material layer to the current collector.

[0009] A fifth aspect of the present invention is the method for evaluating the dispersion degree of a conductive material according to the third aspect, wherein the cross-sectional sample is prepared by etching the electrode surface to a predetermined depth by ion milling.

[0010] A sixth aspect of the present invention is that, in any of the third to fifth aspects, the step of obtaining a 2D scale map of the resistance distribution in the cross section of the sample is performed by scanning spreading resistance microscopy, which scans the surface of the cross section of the sample using an AFM (Atomic force microscopy) device.

[0011] A seventh aspect of the present invention, in any of the third to sixth aspects, includes the step of masking the conductive material region, which includes a first step of processing and converting the resistance value data obtained in (Step 2) into a log scale to obtain a log scale image (log (resistance) image), a second step of extracting a [log resistance distribution histogram] in which materials constituting the electrode cross section sample are displayed in a divided manner from the log scale image, and a third step of setting a log(R / Ω) value corresponding to the minimum value between the conductive material peak and the electrode active material peak in the histogram as a threshold, and masking a region having a value smaller than that value as a conductive material region.

[0012] An eighth aspect of the present invention, in accordance with the seventh aspect, further comprises the step of correcting the threshold by adding a value from 0.1 to 0.5 to the minimum value.

[0013] In a ninth aspect of the present invention, in any one of the first to eighth aspects, the electrode for an electrochemical element includes a current collector and an electrode active material layer formed on at least one surface of the current collector, and the electrode active material layer includes an electrode active material, a conductive material, and a binder.

[0014] A tenth aspect of the present invention is based on any one of the first to ninth aspects, wherein the cross section is in a direction parallel or perpendicular to a portion of the electrode active material layer facing the current collector. [Effects of the Invention]

[0015] The method for evaluating the dispersion degree of a conductive material according to the present invention can quantitatively evaluate the dispersion degree of a conductive material in an electrode. Specifically, a conductive material region is defined from the result (2D mapping image) obtained by performing two-dimensional visual image processing on an arbitrary cross section of an electrode active material layer, and the perimeter and area of ​​the portion defined as the conductive material region are calculated, thereby quantitatively expressing the dispersion degree of the conductive material.

[0016] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concept of the present invention, so the present invention should not be interpreted as being limited to only the matters depicted in the drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings attached to this specification may be exaggerated to emphasize a clearer description. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 1 shows an SSRM image of the electrode of Example 4 obtained by scanning spreading resistance microscopy. [Figure 1B] This is an image confirmed by masking the conductive material area of ​​FIG. 1A. [Figure 2] 10 is a graph of a log(resistance distribution) histogram of Example 4. [Figure 3] 1 shows an SSRM image of Example 1. [Figure 4] This is an image confirmed by masking the conductive material area in Figure 3. [Figure 5] 10 is an SSRM image of Example 2. [Figure 6] This is an image confirmed by masking the conductive material area in Figure 5. [Figure 7] 10 is an SSRM image of Example 3. [Figure 8] This is an image confirmed by masking the conductive material area in Figure 7. [Figure 9A] 1A-1C are schematic diagrams showing a method for preparing a sample of an electrode cross section. [Figure 9B] 1A-1C are schematic diagrams showing a method for preparing a sample of an electrode cross section. [Figure 10] 2 is an image showing the result of masking the conductive material region in FIG. 1 in the electrode of Example 4 without correction using the obtained histogram. [Figure 11] 10 is an image showing the result of masking the conductive material region in FIG. 1 after correction in the electrode of Example 4. [Figure 12]10 is an exemplary graph showing an overlapping portion of the graphs in the conductive material region and the active material region in the histogram. [Figure 13] 10 shows an SSRM image of the electrode of Example 5 and an image showing the result of masking the conductive material region after correction. [Figure 14] 10 shows an SSRM image of the electrode of Example 6 and an image showing the result of masking the conductive material region after correction. [Figure 15] FIG. 10 shows a display screen showing the area and perimeter of a conductive material region calculated using Gwyddion software. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will now be described in more detail for better understanding of the present invention.

[0019] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary and dictionary meanings, but should be interpreted as having meanings and concepts that correspond to the technical ideas of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best explain the invention.

[0020] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. Unless otherwise clearly indicated in the context, singular expressions include plural expressions.

[0021] Also, throughout the specification, when a part is said to "comprise" a certain element, this means that it can further include other elements, rather than excluding other elements, unless specifically stated to the contrary.

[0022] Furthermore, the terms "about," "substantially," and the like used throughout this specification are used to mean a numerical value or a value close to that numerical value when the tolerances of manufacturing and materials inherent in the referred meaning are given, and are used to prevent unscrupulous infringers from unfairly taking advantage of the disclosure in which precise and absolute numerical values ​​are mentioned for the understanding of this application.

[0023] Throughout this specification, the phrase "A and / or B" means "A or B, or both."

[0024] Dispersion of conductive material The present invention proposes a method for defining a conductive material region from the results (2D mapping image) obtained by performing two-dimensional visual image processing on an arbitrary cross section of an electrode active material layer, a method for calculating the perimeter and area of ​​the portion defined as the conductive material region, and a dispersion index that can quantitatively represent the dispersion degree of the conductive material based on the method.

[0025] In the present invention, the dispersibility index can be expressed as a dispersibility index 1 (Index 1) of the conductive material according to the following [Equation 1] for one or more arbitrary cross sections inside the electrode active material layer. Meanwhile, the dispersibility index can be expressed as a dispersibility index 2 (Index 2) of the conductive material according to the following [Equation 2] together with or independently of the index 1. The dispersibility index 1 and the dispersibility index 2 of the conductive material are calculated based on the perimeter (Boundary A) of the part defined as the conductive material region measured in the cross section. measured ) and area (A) as variables.

[0026] [Formula 1] Index 1(a -1 )=Boundary measured / A In the above [Equation 1], Boundary measuredmeans the perimeter of a portion defined as a conductive material region measured at a predetermined cross section of the electrode active material layer, and A means the area of ​​a portion defined as a conductive material region measured at a predetermined cross section of the electrode active material layer. In the above formula 1, a is the unit used. If the unit of perimeter is μm, the unit of the index 1 is μm. -1 It could be.

[0027] [Formula 2] Index 2=Boundary measured / L circle In the above [Equation 2], Boundary measured is defined as in Equation 1, and L circle is the circumference of a circle having the same area as the area of ​​the conductive material region defined above. For any closed curve, the smallest perimeter is when the shape of the closed curve is a circle. Therefore, imagine a virtual circle having the same area as the entire area (A) of the conductive material region, calculate the perimeter of said circle, and divide the perimeter of the actual conductive material region by the perimeter of said virtual circle. The larger the value of Index 2, the higher the degree of dispersion can be interpreted as.

[0028] Said L circle can be calculated using the following formulas 1 and 2.

number

number

[0029] Therefore, the above formula 2 can be expressed as the following formula 2A.

number

[0030] In other words, the area of ​​a circle is {(radius of the circle (r))} 2×π}, which allows the radius (r) of the virtual circle to be found, and once the radius is found, the perimeter (circumference, 2πr) of the virtual circle can be calculated.

[0031] The higher the dispersibility index 1 and dispersibility index 2, the more uniformly the conductive material is dispersed in the electrode active material layer, without being locally unevenly distributed due to aggregation.

[0032] In the present invention, the cross section (or multiple cross sections) can be formed parallel to the facing surface of the current collector of the electrode active material layer. Alternatively, the cross section (or multiple cross sections) can be formed in a direction parallel to the facing surface of the current collector, in a direction perpendicular to the facing surface of the current collector, or at a predetermined angle with the facing surface of the current collector. Since the present invention is intended to confirm the dispersion degree of the conductive material inside the electrode active material layer, the angle between the exposed surface and the facing surface of the current collector is not limited to a specific range as long as the inside is exposed to an extent that allows confirmation of the indexes 1 and 2.

[0033] Index 1 and Index 2 can be determined by visualizing the distribution of the electrode material, particularly the conductive material, for any cross section of the electrode active material layer, calculating the perimeter and area of ​​the portion where the conductive material is distributed (the conductive material region), and substituting the calculated values ​​into the above equation. The distribution of the electrode material contained in the electrode active material layer is determined on a microscopic scale below the microscale. Therefore, the visualization of the conductive material distribution can be confirmed using electronic visualization devices such as atomic force microscopy and scanning diffusion resistance microscopy, as described below.

[0034] Next, the method for calculating Index 1 and Index 2 will be described in detail.

[0035] The method includes a step (Step 1) of exposing an arbitrary cross section inside an electrode for an electrochemical device to obtain a sample of the electrode cross section; Step 2: Obtaining resistance data of the electrode active material and the conductive material of the electrode cross-section sample using a scanning diffusion resistance microscope; Step 3: obtaining a log scale image and a histogram for the resistance data; and a step (Step 4) of calculating the index 1 and / or the index 2. Each step will be explained in more detail below.

[0036] (Step 1) First, an electrode cross-section sample is prepared by exposing a desired cross-section of the interior of an electrode for an electrochemical device. The electrode may include an electrode active material layer formed on at least one surface of a current collector. The electrode active material layer includes an electrode active material, a conductive material, and a binder resin. Next, the surface of the electrode active material layer is removed to a predetermined thickness using an ion beam for ion milling to expose the interior cross-section of the electrode active material layer. Ion milling refers to a method of etching a material by accelerating inert gas ions from a wide beam ion source onto a sample surface in a vacuum. Ion milling is based on the sputtering phenomenon, in which ions or atoms of an inert gas (argon) are accelerated with an appropriate voltage to remove atoms from the sample surface. This allows for the preparation of an electrode cross-section sample with a clean cross-section free of physical damage, and allows for more clearly identified conductive material regions in the electrode.

[0037] According to an embodiment of the present invention, the inert gas may be argon. By irradiating the secondary battery electrode with an argon ion beam in this manner, the cross-sectional sample of the electrode can be more stably produced.

[0038] In one embodiment of the present invention, the ion beam current of the ion milling apparatus may be 100 μA to 250 μA. Specifically, the ion beam current of the ion milling apparatus may be 110 μA to 150 μA, or 200 μA to 230 μA. By adjusting the ion beam current of the ion milling apparatus within the above range, the time required to prepare the electrode cross-section sample can be shortened, and redeposition of electrode material on the cross-section of the sample can be prevented, thereby preparing an electrode cross-section sample with a cleaner cross-section.

[0039] By using such ion milling, it is possible to obtain information on the electrode surface with a very high degree of roughness, and desired information such as observation through an electron microscope or visualization data can be obtained.

[0040] 9A and 9B are diagrams schematically illustrating a method for preparing a cross-sectional sample of an electrode. The cross-sectional sample is prepared by etching and removing a portion 11s from the surface to a predetermined depth in the thickness direction (height) of the electrode active material layer by ion milling, thereby exposing a predetermined plane inside the electrode active material layer (FIG. 9B).

[0041] Meanwhile, in one embodiment of the present invention, the step of preparing the electrode cross-section sample may further include the step of impregnating the electrode with a polymer containing epoxy groups, thereby filling internal pores of the secondary battery electrode with the polymer containing epoxy groups, before performing the ion milling. The method of impregnating the electrode with the polymer containing epoxy groups may be performed using a conventional method in the art. For example, the polymer containing epoxy groups may be applied to the electrode, or the electrode may be immersed in a solution of the polymer containing epoxy groups to impregnate the electrode with the solution.

[0042] According to one embodiment of the present invention, the method for analyzing a battery electrode may further include measuring the resistance of the epoxy-containing polymer filled in the pores of the electrode cross-section sample. By filling the internal pores of the secondary battery electrode with the epoxy-containing polymer, the resistance of the pores in the electrode cross-section sample can be obtained using a scanning diffusion resistance microscope. Specifically, the resistance of the polymer material filling the pores can be measured to obtain resistance data. This allows the regions where the pores are located to be identified, and the electrode active material region, the conductive material region, and the pore region of the electrode cross-section sample to be more accurately distinguished from the merged image (see FIG. 12).

[0043] According to one embodiment of the present invention, the epoxy group-containing polymer may be an epoxy resin polymer containing a cyclic structure within its molecular structure, specifically, an epoxy resin polymer containing an aromatic group (e.g., a phenyl group). Specific examples of the epoxy group-containing polymer containing an aromatic group include, but are not limited to, biphenyl-type epoxy group-containing polymers, dicyclopentadiene-type epoxy group-containing polymers, naphthalene-type epoxy group-containing polymers, dicyclopentadiene-modified phenol-type epoxy group-containing polymers, cresol-type epoxy group-containing polymers, bisphenol-type epoxy group-containing polymers, xylose-type epoxy group-containing polymers, multifunctional epoxy group-containing polymers, phenol novolac epoxy group-containing polymers, triphenolmethane-type epoxy group-containing polymers, and alkyl-modified triphenolmethane epoxy group-containing polymers. Specific examples include, but are not limited to, any one of epoxyethane (ethylene oxide), 1,3-epoxypropane (trimethylene oxide), and bisphenol-A-epichlorohydrin.

[0044] (Step 2) Next, after the electrode cross-section sample is prepared in Step 1, a 2D-scale map of the resistance distribution of the sample cross-section is obtained using a conductive network analysis method (Scanning Spreading Resistance Microscopy). Figure 1A is an exemplary diagram showing a 2D-scale map image of Example 4 obtained by the above method.

[0045] Specifically, an atomic force microscopy (AFM) device can be used to scan the surface of the cross-sectional sample to obtain an image converted to a 2D scale. This measurement produces a map in which the electrical resistance values ​​are indicated by different shades of color, and the distribution of surface resistance can be visually confirmed by the difference in color tone (shade).

[0046] First, a sample is prepared for measurement using an atomic force microscopy (AFM) device. The cross-section sample prepared in the above process is attached to an AFM metal disk with the cross-section facing upward, and a silver paste is applied to the AFM metal disk so that a conductive path can be formed between the area other than the milled cross-section. The prepared AFM sample is loaded into the device and laser aligned. The cross-section is then selected as the measurement area using an optical microscope. An atomic force microscope probe is then contacted with the electrode cross-section, and the current flowing through the sample between the atomic force microscope probe and the contact electrode is measured. The diffusion resistance is obtained from the measured current.

[0047] According to one embodiment of the present invention, the driving conditions of the scanning diffusion resistance microscope for analyzing the electrode cross-section sample are, for example, as follows.

[0048] The AFM device is not particularly limited as long as it can visually image the resistance distribution using the scanning diffused resistance microscope method. For example, a cypher ES (Oxford Instruments) can be used. In a specific example of the present invention, a Dual-gain ORCA can be used as the cantilever holder, and AR (Oxford Instruments) can be used as the driving software.

[0049] Specific operating conditions include contact mode, image pixel size (512 × 512 to 1024 × 1024), scan rate (0.2 Hz or higher, 1.0 Hz or lower), bias (2.0 V or lower), and set point (1.0 V or lower). For example, image pixel size (512 × 512), scan rate (0.5 Hz), bias (2.0 V or lower), and set point (0.2 V) are possible. Solid diamond AFM probes (AD-40-As, Adama) made of boron-doped single crystal diamond can be used as the AFM probe.

[0050] Meanwhile, in one embodiment of the present invention, the obtained cross-sectional sample is preferably subjected to AFM measurement under conditions where it is not exposed to the atmosphere, such as in a glove box, and the cross-sectional sample can be loaded into a sealed cell body to maintain a state where it is not exposed to the atmosphere.

[0051] (Step 3) Once the 2D scale map is obtained in Step 2, the conductive material regions are defined. The term "definition" can also be interpreted as "masking" since a visual display method is applied. For example, FIGS. 10 and 11 show the conductive material regions identified from the histogram for the electrode of Example 4, masked in black. The method for defining the conductive material regions can be described in detail as follows.

[0052] First, the resistance data obtained using a scanning diffusion resistance microscope is processed and converted to a log scale, and a log scale image (log (resistance) image) can be obtained. Once such a log scale image is obtained, a log resistance distribution histogram (log histogram) is extracted from it, which classifies and displays the materials that make up the electrode cross section of the sample.

[0053] It is possible to determine whether the region corresponding to each pixel on the histogram is an electrode active material region, a pore or binder region, or a conductive material region, and the conductive material region distribution in the 2D mapping image can be quantified using information on each pixel whose corresponding region has been determined.

[0054] Specifically, the log(R / Ω) value corresponding to the minimum value between the conductive material peak and the electrode active material peak in the histogram is set as a threshold, and the region having a value smaller than that value is masked as the conductive material region. In this case, to obtain more accurate data for the conductive material region, the minimum value can be corrected by adding or subtracting 0.1 to 0.5.

[0055] In one embodiment, the correction may be performed by adding a value of 0.1 to 0.5 to the log(R / Ω) value corresponding to the minimum value. This is to correct for the portion of the histogram where the active material region and the conductive material region overlap and are not displayed as the conductive material region. For example, the correction value may be determined by dividing the histogram into left and right sides based on the peak of the conductive material region, and correcting the low point of the right region so that it has the same value as the horizontal distance from the peak to the low point on the left side.

[0056] By making the correction as described above, even the portion that overlaps with the electrode active material region and is not displayed as the conductive material region can be displayed as the conductive material region, thereby ensuring more accurate dispersion degree data.

[0057] FIG. 2 shows a log resistance distribution histogram extracted from the log-scale image (log (resistance) image) of the electrode of Example 4. Referring to this, the conductive material peak and the electrode active material peak can be confirmed, and the minimum value between them can be identified. However, as mentioned above, even in the section after the minimum value, there is a conductive material section that overlaps with the active material region and is not displayed, so the numerical values ​​are corrected as described above. FIG. 12 is an example diagram showing the predicted shape of the overlapping active material region and conductive material region.

[0058] On the other hand, FIG. 10 is a diagram showing masked conductive material regions in an SSRM image based on values ​​before correction. The masked conductive material regions are masked in a color not present in the original image, and in the present embodiment, are shown masked in black. When examining the circled area indicated by the dotted line in FIG. 10, it is possible to confirm that the conductive material remains unmasked. When the color of the unmasked portion is confirmed, it is confirmed that the portion maintained in blue. On the other hand, FIG. 11 shows masked conductive material regions based on values ​​after correction, and it can be confirmed that the unmasked portion in FIG. 10 (portion maintained in blue) is masked in black in FIG. 11.

[0059] Meanwhile, the area masked with the conductive material that is located within the active material is removed to eliminate errors. This is due to errors that occur during the sample manufacturing process, such as conductive material adhering to the exposed cross-section of the active material during the cross-section sample preparation process, or errors that occur during image processing. It is therefore desirable to remove this area because it is clear that the conductive material is not actually distributed within the active material in the electrode.

[0060] On the other hand, after the conductive material area is masked, an image showing only the conductive material area is extracted (contrast masked) as shown in Figures 1B, 4, 6, 8, the lower part of Figure 13, and the lower part of Figure 14, and is used for the calculation in Step 4.

[0061] In one embodiment of the present invention, the masking of the conductive material region can be performed using a program that visualizes data obtained by scanning probe microscopy, such as AFM. In one embodiment of the present invention, the masking can be performed using Gwyddion software. However, if many of the images contain pixels with too small a pixel size, it can be difficult to accurately determine the perimeter and area of ​​the conductive material region, which can act as noise and cause errors when calculating the dispersity. Therefore, images with too small pixels can be removed during the masking process. For example, when using the Gwyddion program, grain-filtering can be used to remove fine regions of less than 3 pixels from the conductive material region to prevent them from being masked by the conductive material region. If fine regions of less than 3 pixels are included, they may be calculated as excessively high values ​​for the perimeter of the conductive material region, so they are removed before measurement. Meanwhile, Figure 2 shows a histogram obtained using the above method, confirming that the active material region and the conductive material region can be separated.

[0062] (Step 4) When the masking of the conductive material area is completed in Step 3 (i.e., the conductive material area is determined), the perimeter and area of ​​the masked area are confirmed, and Index 1 can be calculated using Equation 1. In Equation 1, the perimeter value of the masked area is calculated as Boundary measured and the area value of the masking region is applied to A.

[0063] Also, the radius of a circle having the same area as the area of ​​the masking region can be calculated, and the circumference of the circle can be calculated by using the radius of the circle. circle By substituting the above, Index 2 can be calculated using [Equation 2].

[0064] Meanwhile, in the present invention, the area and perimeter of the masked conductive material region can be calculated using an image processing program such as Gwyddion software. Figure 15 shows a display screen showing the area and perimeter calculated by the program.

[0065] Electrodes for electrochemical devices In the present invention, the electrode to be evaluated for the dispersion degree of the conductive material is not particularly limited as long as it is an electrode for an electrochemical device. The electrochemical device may include any device that performs an electrochemical reaction. Specific examples of the electrochemical device include all types of primary batteries, secondary batteries, fuel cells, solar cells, and capacitors such as supercapacitors. The secondary battery may be a lithium ion secondary battery using a lithium salt as an ion-conductive salt. In one embodiment of the present invention, the electrode may include a current collector and an electrode active material layer disposed on at least one surface of the current collector. In addition, the electrode active material layer may include an electrode active material, a conductive material, and a binder material.

[0066] electrode active material The electrode active material layer may include a positive electrode active material or a negative electrode active material depending on the polarity of the battery.

[0067] Non-limiting examples of the positive electrode active material include lithium transition metal oxides or lithium metal iron phosphates, and are not limited to metal oxides, such as layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals, and compounds having the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7, and oxides with the 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), and Ni-site lithium nickel oxide represented by the chemical formula LiMn 2-x M x Lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn), LiMn2O4 in which part of the Li in the chemical formula is replaced with an alkaline earth metal ion, lithium metal phosphate oxide 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 Lithium Nickel-Manganese-Cobalt Oxide, in which a portion of the oxide is replaced by aluminum. 1+x (Ni a Co b Mn c Al d ) 1-xO2 (where x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, and a + b + c + d = 1), and an oxide in which part of the lithium nickel - manganese - cobalt oxide is substituted with another transition metal, Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (where x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, and M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo), a disulfide compound, and Fe2(MoO4)3 and the like, but not limited thereto.

[0068] Non - limiting examples of the negative electrode active material include 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 (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1, 1 ≤ y ≤ 3, 1 ≤ z ≤ 8) and other metal composite oxides, lithium metal, lithium alloy, silicon - based alloy, tin - based alloy, silicon - based 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.

[0069] Binder material In the present invention, the binder material is not particularly limited as long as it can achieve binding of materials contained in the electrode such as the electrode active material and binding between the electrode active material layer and the separator or current collector facing it, and can be used as a binder material for secondary batteries.

[0070] Conductive material The conductive material may be incorporated into the electrode active material layer by being included in the electrode powder mixture. The conductive material may be any material that is conductive without causing chemical changes in the battery, and may include, for example, graphite (e.g., natural graphite or artificial graphite), carbon black (e.g., carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or summer black), conductive fiber (e.g., carbon fiber or metal fiber), metal powder (e.g., carbon fluoride, aluminum, or nickel powder), conductive whisker (e.g., zinc oxide or potassium titanate), conductive metal oxide (e.g., titanium oxide), or conductive material (e.g., polyphenylene derivative). Specifically, the conductive material may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, activated carbon, in order to achieve uniform mixing of the conductive material and improve conductivity.

[0071] current collector Meanwhile, in one embodiment of the present invention, the current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity, and examples thereof include stainless steel, aluminum, nickel, titanium, calcined carbon, copper or aluminum, or stainless steel whose surface has been surface-treated with carbon, nickel, titanium, silver, etc. Furthermore, the current collector can have fine irregularities formed on its surface to improve the adhesive strength of the positive electrode active material, and can be in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0072] Meanwhile, in one embodiment of the present invention, the current collector may be fully or partially coated with a conductive primer to reduce surface resistance and improve adhesion. Here, the conductive primer may include a conductive material and a binder. The conductive material may be any conductive material, for example, a carbon-based material. The binder may include a solvent-soluble fluorine-based binder (including PVDF and PVDF copolymers), an acrylic binder, or a water-based binder.

[0073] Meanwhile, in the present invention, the method for manufacturing the electrode is not particularly limited. For example, the electrode can be manufactured by a wet method in which a slurry for forming an electrode active material layer is applied to a current collector, or a dry method in which electrode mixture particles are compressed to form a layer structure.

[0074] The wet electrode manufacturing method can be described as follows. First, electrode materials, such as an electrode active material, a conductive material, and a binder, are added to a suitable solvent to prepare a slurry for forming an electrode active material layer. In addition to the electrode materials, additives that can improve electrochemical performance or the dispersibility of the slurry can be added to the slurry. The slurry is then coated onto an electrode current collector. The coating method can be any known coating method, such as slot die coating, gravure coating, dip coating, or blade coating, and is not limited to a specific method. The solvent is then removed to obtain an electrode having an electrode active material layer disposed on the current collector surface. The slurry can be dried by natural drying or air drying, and heating can be used to accelerate drying. A pressing process can then be performed to ensure an appropriate thickness and electrode active material loading.

[0075] The dry method may involve preparing a dry mixture containing an electrode material or mixed particles containing an electrode material, and then compressing the powdered material without using a solvent to form a layered structure.

[0076] A dry manufacturing method according to one embodiment of the present invention can be described as follows. First, powdered electrode materials are dry-mixed. Here, the electrode materials may further include an electrode active material, a binder, and a conductive material. Furthermore, the mixed particles may further contain additives that promote electrochemical performance or particle formation in addition to the electrode materials. Then, shear force is applied to the resulting mixture to fiberize the binder. The shear force can be applied by high-speed mixing or kneading the electrode materials. Here, the applied shear force during kneading may be lower than that during mixing. In one embodiment of the present invention, the kneading can be performed at a high temperature, for example, at a temperature of 80°C or higher, such as 100°C or higher. Alternatively, the temperature can be controlled to 200°C or lower, preferably 150°C or lower. Through this process, the binder resin is fiberized and the electrode materials are entangled, resulting in mixed particles of a desired size. Alternatively, a mixed mass can be obtained through the kneading process, and a pulverization process can be further performed to produce mixed particles of a desired size. The mixed particles may contain a binder resin, such as polytetrafluoroethylene (PTFE) or polyolefin, that can be fiberized by shear force. Once the mixed particles are obtained, they can be pressed to form a plate-shaped electrode film, which can then be bonded to a current collector to obtain an electrode. Alternatively, the mixed particles can be directly sprayed onto a current collector and then pressed. In the method for producing the mixed particles, the electrode material can be added to a solvent to form a slurry, which can then be spray-dried to produce the mixed particles. In this case, a binder resin such as SBR can be used. However, in the present invention, the electrode for measuring the dispersion degree of the conductive material is not limited to a specific shape or manufacturing method, and any electrode that can be used with the above-mentioned dispersion degree measurement method can be used.

[0077] Hereinafter, the present invention will be described in detail based on examples, comparative examples, and experimental examples in order to enable those skilled in the art to easily understand the present invention.

[0078] [Example] Electrode manufacturing Example 1 Lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2), carbon black (specific surface area 1400 m 2 1 / g) and polytetrafluoroethylene (PTFE) were added to a blender in a ratio of 96.0:1.5:2.5 and mixed at 10,000 rpm for 1 minute to prepare a mixture. The mixture was then pulverized using a jet mill (feeding pressure: 50 psi, grinding pressure: 45 psi) to obtain a mixed powder for an electrode. The mixed powder for an electrode was then fed into a first lap calender (roll diameter: 88 mm, roll temperature: 100°C, 20 rpm) and pressed to prepare a dry electrode film. The obtained dry electrode film was then placed on both sides of an aluminum thin film (thickness: 19 μm) and bonded by a lamination process maintained at 150°C to obtain an electrode. The thickness of the electrode active material layer on one side of the obtained electrode was approximately 80 μm. The lithium-nickel-cobalt-manganese-aluminum composite oxide had a bimodal distribution and contained large particles (secondary particles) with a diameter of approximately 10 μm and single particles with a diameter of approximately 5 μm. FIG. 3 is an SSRM image of Example 1, and FIG. 4 is a diagram showing an image confirmed by masking the conductive material region.

[0079] Examples 2 to 4 Lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O), carbon black, and polytetrafluoroethylene (PTFE) were added to a blender in a ratio of 96.0:1.5:2.5 and mixed at 10,000 rpm for 1 minute to prepare a mixture. The kneader temperature was then stabilized at 150°C, and the mixture was added to the kneader and kneaded under a pressure of 1.1 atm to obtain a mixture mass. In Examples 2 and 4, the kneading speed was controlled to vary from 40 to 70 rpm, and the kneading time was controlled to vary from 3 to 7 minutes. The mixture mass was then added to the blender, pulverized at 10,000 rpm for 40 seconds, and sieved through a 1 mm sieve to obtain a mixed powder for an electrode. The mixed powder for an electrode was then introduced into a first lap calender (roll diameter: 88 mm, roll temperature: 100°C, 20 rpm) and compressed to prepare a dry electrode film. Next, the obtained dry electrode film was placed on both sides of an aluminum thin film (thickness 19 μm) and bonded by a lamination process maintained at 150°C to obtain an electrode. The thickness of the electrode active material layer on one side of the obtained electrode was approximately 80 μm. Meanwhile, the lithium nickel cobalt manganese aluminum composite oxide had a bimodal distribution, containing large particles (secondary particles) with a diameter of approximately 10 μm and single particles with a diameter of approximately 5 μm. In addition, the conductive materials used in Examples 2 and 4 were different from each other. FIGS. 1A and 1B are SSRM images of the electrode of Example 4 and images observed after masking the conductive material region. FIG. 5 is an SSRM image of the electrode of Example 2, and FIG. 6 is an SSRM image observed after masking the conductive material region. FIG. 7 is an SSRM image of the electrode of Example 3, and FIG. 8 is an SSRM image observed after masking the conductive material region.

[0080] Examples 5 and 6 Lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2), carbon black (specific surface area 1400 m 21 / g) and polytetrafluoroethylene (PTFE) were added to a blender and mixed at 10,000 rpm for 1 minute to prepare a mixture. The kneader temperature was then stabilized at 150°C, and the mixture was added to the kneader and kneaded under a pressure of 1.1 atm to obtain a mixture mass. In Examples 5 and 6, the kneading speed was controlled to be between 40 and 70 rpm, and the kneading time was controlled to be between 3 and 7 minutes. The mixture mass was added to a blender, pulverized at 10,000 rpm for 40 seconds, and sieved through a 1 mm sieve to obtain a mixed powder for an electrode. The mixed powder for an electrode was then placed in a first lap calender (roll diameter: 88 mm, roll temperature: 100°C, 20 rpm) and pressed to prepare a dry electrode film. The obtained dry electrode film was then placed on both sides of an aluminum thin film (thickness: 19 μm) and bonded by a lamination process maintained at 150°C to obtain an electrode. The thickness of the electrode active material layer on one side of the obtained electrode was approximately 80 μm. On the other hand, the lithium nickel cobalt manganese aluminum composite oxide had a monomodal distribution, and single particles with a diameter of approximately 5 μm were used. Example 4 was prepared by using a lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2), carbon black (specific surface area 1400 m), and a 10 ... 2 The ratio of SiO2 (0.15 / g) to polytetrafluoroethylene (PTFE) was 96.0:1.8:2.2 in Example 5, and 96.2:1.6:2.2 in Example 6. Fig. 13 shows an SSRM image of Example 5 and an image confirmed by masking the conductive material area. Fig. 14 shows an SSRM image of Example 6 and an image confirmed by masking the conductive material area.

[0081] Preparation of electrode cross-section samples As a polymer containing an epoxy group, a solution containing an epoxy-based polymer having a weight-average molecular weight of about 700 g / mol or less was prepared.

[0082] The positive electrodes prepared in Examples 1 to 6 were impregnated with the prepared epoxy polymer solution to fill the pores with the polymer. Then, using an ion milling device (IB19520CCP, Jeol Co.), a focused argon (Ar) ion beam was irradiated onto the positive electrodes for secondary batteries to remove the surface, producing cross-sectional samples with a clean cross section. The ion beam current was set to 170 μA, and the gas flow rate was 1.5 cm. 3 / min and irradiation was carried out for 3 hours.

[0083] SSRM analysis conditions Equipment used: cypher ES (Oxford Instrument), Dual-gain ORCA cantilever holder [Parameters] Mode:contact Sample / line: 512×512, Scan rate: 0.5Hz Bias:~2V, Deflection Setpoint Volts:~0.2 Scan Angle: 90° [AFM Mode] Model: AD-40-As (Manufacturer: Adama) Tip: Highly doped (B) single crystal diamond, tip height 300nm Cantilever&bulk tip:diamond coated silicon, Reflexcoating(Au) F=180kHz, k=40N / m Typical contact resistance:~10kΩ

[0084] SSRM analysis method After ion milling, the sample was transferred to a glove box without exposure to the atmosphere and loaded into an AFM puck. Silver (Ag) paste was then applied between the electrode and the AFM puck, forming an additional conductive path. The sample with the additional conductive path was then loaded into a sealed cell body and attached to the AFM instrument without exposure to the atmosphere. After laser alignment, the milled area was selected as the measurement area using an optical microscope and measured under Ar flow. SSRM images were obtained using this method. Figures 3, 5, 7, and 1A are SSRM images of the electrodes of Examples 1, 2, 3, and 4, respectively. The upper figures in Figures 13 and 14 are SSRM images of the electrodes of Examples 5 and 6, respectively. The observed image size was 30 μm × 30 μm.

[0085] Masking conductive material areas The conductive material regions were masked using Gwyddion software on the SSRM images obtained above.

[0086] First, a log(resistance) image was obtained, and a histogram of the log(resistance) distribution within the image was obtained. This was obtained using the Height distribution function in the Calculate 1D Statistical function provided by the software. The threshold was determined by adding 0.2 to the log(R / Ω) value corresponding to the lowest point between the peak corresponding to the conductive material and the peak corresponding to the electrode active material in the histogram. Figure 2 shows the histogram for electrode 3, and the threshold was set to log(R / Ω) = 7.2. Based on this, the conductive material region was masked. Grain filtering was used to remove regions corresponding to pixels smaller than 3 pixels, and regions located within the electrode active material. Figure 2 shows that pixels corresponding to the electrode active material and the conductive material can be distinguished from each other on the histogram obtained from the log-scale image. In other words, it was found that the distribution of the conductive material region could be easily quantified using information on each pixel whose corresponding region was determined.

[0087] In addition, Fig. 1B is a SSRM image of the electrode of Example 4, Fig. 4 is a SSRM image of the electrode of Example 1 (Fig. 3), Fig. 6 is a SSRM image of the electrode of Example 2 (Fig. 5), and Fig. 8 is a SSRM image of the electrode of Example 3 (Fig. 7), in which the conductive material regions are masked and only the masked conductive material regions are displayed in shades of color. In addition, the lower drawings in Fig. 13 and Fig. 14 are figures in which only the masked conductive material regions of the electrodes of Examples 5 and 6, respectively, are displayed in shades of color.

[0088] The perimeter and area of ​​the masked region were then confirmed using the Grain-Summary function.

[0089] Next, the respective values ​​were substituted into the above [Equation 1] and [Equation 2] to calculate index 1 and index 2, and the results are shown in the following [Table 1]. As can be seen from [Table 1], it was confirmed that index 1 and index 2 were calculated differently depending on the type and / or content of the conductive material in the electrode active material layer and the electrode manufacturing process, and the degree of dispersion of the conductive material could be quantitatively confirmed. In this way, the conductive material index of the present invention can be used to quantitatively confirm the degree of dispersion of the conductive material in the electrode. Furthermore, the conductive material dispersion index can be used to select the content and / or type of conductive material during electrode manufacturing, select the electrode manufacturing method, and set the electrode manufacturing process conditions.

[0090] [Table 1] [Explanation of symbols]

[0091] 10 electrodes 11 Electrode active material layer 11s The area from the surface to a specified depth 11f: A portion of the current collector at a specified height from the opposing surface 12 Current collector

Claims

1. In an electrode for an electrochemical element including an electrode active material layer containing an electrode active material and a conductive material, the perimeter (Boundary ｍｅａｓｕｒｅｄ 1. A method for quantifying the dispersion degree of a conductive material based on a mathematical formula defined using the surface area (A) and the surface area (B) as variables, The above formula is a dispersibility index 1 (Index 1) of the conductive material according to the following [Formula 1], or a dispersibility index 2 of the conductive material according to the following [Formula 2], a method for quantifying the dispersibility of the conductive material. [Formula 1] Index 1 (μm −1 )=Boundary measured / A [Formula 2] Index 2=Boundary measured / L circle In the above [Equation 1], Boundary measured is measured at a predetermined cross section of the electrode active material layer and means the perimeter of the portion defined as the conductive material region, A is measured at a predetermined cross section of the electrode active material layer and means the area of ​​the portion defined as the conductive material region, and in the above [Equation 2], Boundary measured is the same as in the above Equation 1, and L circle is the circumference of a circle having the same area as the area of ​​the conductive material region defined above. [Equation 1] is.

2. (Step 1) obtaining a cross-sectional sample in which an arbitrary cross section of the inside of an electrode active material layer is exposed; (Step 2) Obtaining a 2D scale map of the resistance distribution in the cross section of the sample; (Step 3) masking the conductive material area; (Step 4) calculating the perimeter and area of ​​the masked region and substituting the results into the above-mentioned formula 1 and / or formula 2 to confirm the dispersion degree of the conductive material in the electrode active material layer; The method of claim 1 for quantifying the degree of dispersion of a conductive material, comprising:

3. 3. The method for quantifying the degree of dispersion of a conductive material according to claim 1 or 2, wherein the electrode active material layer is formed on either side of an electrode current collector, and the cross section (or a plurality of cross sections) is a plane parallel to or perpendicular to a facing portion of the electrode active material layer with respect to the current collector.

4. 3. The method for quantifying the dispersion degree of a conductive material according to claim 2, wherein the cross-sectional sample is prepared by etching the electrode surface to a predetermined depth by ion milling.

5. 3. The method for quantifying the dispersion degree of a conductive material according to claim 2, wherein the step of obtaining a 2D-scale map of the resistance distribution in the cross section of the sample is performed by scanning spreading resistance microscopy, which scans the surface of the cross-sectional sample using an AFM (Atomic force microscopy) device.

6. The step of masking the conductive material region comprises: A first step of processing and converting the resistance value data obtained in (Step 2) into a log scale (Log Scale) to obtain a log scale image (log (resistance) image); a second step of extracting a log resistance distribution histogram in which materials constituting the electrode cross section of the sample are displayed in a divided manner from the log-scale image; a third step of setting a log(R / Ω) value corresponding to the minimum value between the conductive material peak and the electrode active material peak in the log resistance distribution histogram as a threshold, and masking a region having a value smaller than the threshold as a conductive material region; The method for quantifying the degree of dispersion of a conductive material according to claim 2, comprising:

7. The method for quantifying the degree of dispersion of a conductive material according to claim 6 , further comprising the step of correcting the threshold value by adding a value of 0.1 to 0.5 to the minimum value.

8. 2. The method of claim 1, wherein the electrode for an electrochemical element comprises a current collector and an electrode active material layer formed on at least one surface of the current collector, the electrode active material layer comprising an electrode active material, a conductive material, and a binder.

9. The method for quantifying the dispersion degree of a conductive material according to claim 1 , wherein the cross section is in a direction parallel or perpendicular to a facing portion of the electrode active material layer facing the current collector.

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