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

Abstract

The method for evaluating the dispersion of a conductive material according to the present invention can confirm the dispersion of a conductive material within an electrode as a quantitative numerical value. Specifically, the degree of dispersion of the conductive material can be quantitatively represented by defining a conductive material region from a result (2D mapping image) obtained by visualizing a predetermined cross-section of an electrode active material layer on a two-dimensional scale, and calculating the perimeter and area of ​​the part defined as the conductive material region.

Description

Technology Field

[0001] The present invention relates to a quantified dispersion index capable of quantitatively representing the dispersion of a conductive material within an electrode for an electrochemical device. Furthermore, the present invention relates to a dispersion measurement method comprising a method for calculating the dispersion index. Background Technology

[0003] As interest in energy storage technology continues to grow, research and development in electrochemical devices are steadily increasing as application fields expand to include mobile phones, tablets, laptops, camcorders, and even electric vehicles (EVs) and hybrid electric vehicles (HEVs). Electrochemical devices are receiving the most attention in this regard, and among them, the development of rechargeable lithium-ion batteries is a focal point of interest. Recently, research and development in this area has led to the design of new electrodes and batteries to improve capacity density and specific energy.

[0004] When manufacturing electrodes for such secondary batteries, increasing the content of active material within the electrode is being considered to improve energy density. However, since this results in a relative decrease in the content of conductive material, it is important that the conductive material is evenly distributed within the electrode to prevent a decline in electrical conductivity. As the distribution of the conductive material within the electrode is closely related to the electrode manufacturing process, research on dry electrode manufacturing methods capable of enhancing the dispersibility of the conductive material during production is required. Furthermore, in establishing a manufacturing process that improves the dispersibility of the conductive material, it is necessary to develop an evaluation tool capable of accurately verifying the dispersibility of the conductive material within the electrode. The problem to be solved

[0006] The present invention aims to provide a quantified dispersion index capable of quantitatively representing the dispersion of a conductive material within an electrode for an electrochemical device. Another objective is to provide a dispersion measurement method comprising a method for calculating the dispersion index. It will be readily apparent that other objectives and advantages of the present invention can be realized by means or methods described in the claims and combinations thereof. means of solving the problem

[0008] The first aspect of the present invention relates to a method for evaluating the dispersion of a conductive material, wherein the method is based on a formula defined with the perimeter (boundary measured) and area (A) of a portion defined as a conductive material region in one or more arbitrary cross-sections within an electrode for an electrochemical device comprising an electrode active material layer comprising an electrode active material and a conductive material, wherein the method is based on a formula defined with variables.

[0009] A second aspect of the present invention is that, in the first aspect, the formula is a conductive material dispersion index 1 (Index 1) according to [Equation 1] below or a conductive material dispersion index 2 (Index 1) according to [Equation 2] below.

[0011] [Equation 1]

[0012] Index 1(㎛ -1 ) = Boundary measured / A

[0014] [Equation 2]

[0015] Index 2 = Boundary measured / L circle

[0016] In the above [Equation 1], Boundary measuredrepresents the circumference of the portion defined as the conductive material region measured at a predetermined cross-section of the electrode active material layer, and A represents the area of ​​the portion defined as the conductive material region measured at a predetermined cross-section of the electrode active material layer, and in [Equation 2] above, Lcircle is the circumference of a circle having the same area as the area of ​​the defined conductive material region.

[0017] A third aspect of the present invention is, in the first or second aspect,

[0018] (Step 1) A step of obtaining a cross-sectional sample in which an arbitrary cross-section inside the electrode active material layer is exposed;

[0019] (Step 2) A step to obtain a 2D scale map of the resistance distribution of the sample cross-section;

[0020] (Step 3) A step of masking the conductive material region; and

[0021] (Step 4) A step of calculating the perimeter and area of ​​the masked region, substituting them into Equation 1 and / or Equation 2, and verifying the dispersion degree of the conductive material in the electrode active material layer;

[0022] It includes.

[0023] A fourth aspect of the present invention is that, in any one of the first to third aspects, the electrode active material layer is formed on one side of the electrode current collector, and the cross-section(s) are a plane parallel or perpendicular to the surface of the electrode active material layer facing the current collector.

[0024] A fifth aspect of the present invention is a method for evaluating the dispersion of a conductive material in an electrode, wherein, in the third aspect, the cross-sectional sample is prepared by etching the electrode surface to a predetermined depth by ion milling.

[0025] The sixth aspect of the present invention is, in any one of the third to fifth aspects,

[0026] The step of obtaining a 2D scale map of the resistance distribution of the cross-sectional sample is performed by Scanning Spreading Resistance Microscopy, which scans the surface of the cross-sectional sample using an Atomic Force Microscopy (AFM) device.

[0027] A seventh aspect of the present invention is that, in any one of the third to sixth aspects, the step of masking the conductive material region

[0028] A first step of processing and changing the resistance value data obtained in the above (Step 2) into a log scale to obtain a log scale image (log(resistance) image);

[0029] A second step of extracting a [log resistance distribution histogram] in which the materials constituting the electrode cross-section sample are distinguished and displayed in the above log scale image; and

[0030] A third step of setting the log(R / Ω) value corresponding to the minimum value between the conductive material peak and the electrode active material peak in the above histogram as a threshold value and masking the region having a value smaller than that value as a conductive material region; is included.

[0031] The eighth aspect of the present invention further includes the step of correcting the limit value by adding a value of 0.1 to 0.5 to the minimum value in the seventh aspect.

[0032] A ninth aspect of the present invention is that, in any one of the first to eighth aspects, the electrode comprises 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 comprises an electrode active material, a conductive material, and a binder.

[0033] The tenth aspect of the present invention is that, in any one of the first to ninth aspects, the cross-section is in a direction parallel or perpendicular to the surface facing the current collector of the electrode active material layer. Effects of the invention

[0035] The evaluation tool according to the present invention can verify the dispersibility of the conductive material within the electrode as a quantitative value. Brief explanation of the drawing

[0037] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to help to better understand the technical concept of the present invention together with the description of the invention above; therefore, the present invention is not to be interpreted as being limited only to the matters described in such drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation. Figure 1a shows an SSRM image of the electrode of Example 4 obtained through scanning diffusion resistance microscopy, and Figure 1b is an image confirmed by masking the conductive material region thereof. Figure 2 is a graph of the log(resistance distribution) histogram of Example 4. FIG. 3 is an image of the SSRM of Example 1, and FIG. 4 is an image confirmed by masking the conductive material region thereof. Figure 5 is an SSRM image of Example 2, and Figure 6 is an image confirmed by masking the conductive material area. Figure 7 is an SSRM image of Example 3, and Figure 8 is an image confirmed by masking the conductive material area. Figures 9a and 9b schematically illustrate the method of preparing an electrode cross-section sample. FIG. 10 is a result image of the electrode of Example 4 in which the conductive material region of FIG. 1 is masked without correction in the obtained histogram, and FIG. 11 is a result image of the electrode of Example 4 in which the conductive material region of FIG. 1 is masked after correction. Figure 12 is an example graph showing the overlapping portion of the graph in the conductive material region and the active material region in the histogram. Figures 13 and 14 respectively show the SSRM images of the electrodes of Example 5 and Example 6 and the result images of the conductive material area of ​​each example after correction and masking. Figure 15 shows a display screen showing the area and perimeter of the conductive material region calculated using Gwyddion software. Specific details for implementing the invention

[0038] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0039] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0041] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0043] Furthermore, throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0045] Additionally, terms such as “about,” “substantially,” as used throughout this specification, are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the stated meaning, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values ​​are mentioned to aid in understanding this invention.

[0047] Throughout this specification, the description “A and / or B” means “A or B or both.”

[0049] Dispersion of challenge material

[0050] The present invention proposes a method for defining a conductive material region from a result (2D mapping image) obtained by visualizing a predetermined cross-section of an electrode active material layer on a two-dimensional scale, 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 degree of dispersion of the conductive material based thereon.

[0051] In the present invention, the dispersion index can be represented as a conductive material dispersion index 1 (Index 1) according to [Equation 1] below for one or more arbitrary cross-sections within the electrode active material layer. Meanwhile, the dispersion index can be represented as a conductive material dispersion index 2 (Index 2) according to [Equation 2] below, either together with or independently of Index 1. The conductive material dispersion index 1 and dispersion index 2 are measured at the cross-section and are the boundary of the portion defined as the conductive material region. measured It is a value calculated using ) and area (A) as variables.

[0053] [Equation 1]

[0054] Index 1(a -1 ) = Boundary measured / A

[0056] In the above [Equation 1], Boundary measuredrepresents 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 represents the area of ​​the portion defined as the conductive material region, measured at a predetermined cross-section of the electrode active material layer. In Equation 1 above, a is the unit used. If the unit of perimeter were μm, the unit of exponent 1 would be μm. -1 This can be.

[0058] [Equation 2]

[0059] Index 2 = Boundary measured / L circle

[0061] In the above [Equation 2], Boundary measured is equal to the definition 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 case where the circumference is smallest is when the shape of the closed curve is a circle. Accordingly, a virtual circle having the same area as the total area (A) of the conductive material region is assumed, and the length of the circumference of the circle is calculated. The larger the value of Index 2, which is calculated by dividing the actual circumference of the conductive material region by the circumference of the virtual circle, the higher the dispersion can be interpreted.

[0063] The above L circle It can be calculated based on the following formulas 1 and 2.

[0065] [Formula 1]

[0066] r(radius of the circle) =

[0068] [Equation 2]

[0069] L circle = (2× )

[0071] Therefore, the above Equation 2 can be expressed as Equation 2A below.

[0073] [Equation 2A]

[0074] Index 2 = Boundary measured / (2× )

[0076] That is, since the area of ​​the circle is calculated as {(radius of the circle (r)) 2 X π}, the radius (r) of the virtual circle can be determined from this, and once the radius is determined, the circumference (circumference, 2πr) of the virtual circle can be calculated.

[0077] The above dispersion indices 1 and 2 indicate that the higher the value, the more the conductive material is not aggregated or locally distributed, but is uniformly dispersed within the electrode active material layer.

[0079] In the present invention, the cross-section(s) may be formed parallel to the current collector face of the electrode active material layer. Alternatively, the cross-section(s) may be formed in a direction parallel to the current collector face, in a direction perpendicular to the current collector face, or formed at a predetermined angle to the current collector face. Since the present invention is intended to verify the degree of dispersion of the conductive material within the electrode active material layer, the angle between the exposed surface and the current collector face is not limited to a specific range as long as the interior is exposed to the extent that the indices 1 and 2 can be verified.

[0081] The above Index 1 and Index 2 can be verified by visualizing the distribution of electrode materials, particularly conductive materials, over an arbitrary cross-section of the electrode active material layer, and by calculating the perimeter and area of ​​the portion where the conductive material is distributed (conductive material region) and substituting them into the above values. The verification of the distribution of electrode materials included in the electrode active material layer is for microscopic dimensions below the micro scale. Accordingly, the visualization of the distribution of conductive materials can be verified through electronic visualization devices such as atomic force microscopy and scanning diffusion resistivity microscopy, as described below.

[0083] Next, the method for calculating the above Index 1 and Index 2 will be explained in detail.

[0085] The above method comprises the step (step 1) of obtaining an electrode cross-section sample by exposing an arbitrary cross-section inside an electrode for an electrochemical device;

[0086] Step 2: Acquiring resistance value data of the electrode active material and conductive material of the electrode cross-section sample using a scanning diffusion resistance microscope;

[0087] The method includes the step of obtaining a log-scale image and histogram of the resistance value data (step 3); and the step of calculating exponent 1 and / or exponent 2 (step 4). Each step is described in more detail as follows.

[0089] (Step 1)

[0090] First, an electrode cross-section sample is prepared by exposing an arbitrary cross-section inside the electrode for electrochemical investigation. The electrode may include an electrode active material layer formed on at least one surface of a current collector, and the electrode active material layer comprises 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 from an ion mill to expose the cross-section inside the electrode active material layer. Ion milling refers to a method of etching a material by accelerating ions of an inert gas from a broad beam ion source to a sample surface in a vacuum state. Ion milling is based on the sputtering phenomenon, in which ions or atoms of an inert gas (Argon) are accelerated to an appropriate voltage to cause atoms on the sample surface to detach. Through this, an electrode cross-section sample having a clean cross-section without physical damage can be manufactured, and the conductive material region in the electrode can be identified more clearly.

[0091] According to one embodiment of the present invention, the inert gas may be argon. By irradiating the electrode for the secondary battery with an argon ion beam in this way, the electrode cross-sectional sample can be manufactured more stably.

[0092] In one embodiment of the present invention, the ion beam current of the ion milling device may be 100 μA or more and 250 μA or less. Specifically, the ion beam current of the ion milling device may be 110 μA or more and 150 μA or less, or 200 μA or more and 230 μA or less. By adjusting the ion beam current of the ion milling device to the aforementioned range, the manufacturing time of the electrode cross-section sample can be shortened, and the phenomenon of electrode materials being redeposited on the cross-section of the sample can be prevented, thereby enabling the production of an electrode cross-section sample having a cleaner cross-section.

[0093] By utilizing this ion milling, electrode surface information with very good roughness can be obtained, and desired information, such as observation through an electron microscope or visualization data, can be acquired.

[0094] FIGS. 9a and 9b schematically illustrate a method for preparing an electrode cross-section sample. Referring to the above, the cross-section sample is prepared by etching and removing a portion (11s) from the surface to a predetermined depth with respect to the thickness direction (height) of the electrode active material layer using ion milling to expose a predetermined plane inside the electrode active material layer (Fig. 9b).

[0096] Meanwhile, in one embodiment of the present invention, the step of preparing the electrode cross-sectional sample may further include the step of impregnating the electrode with a polymer containing epoxy groups before applying the ion milling, thereby filling the internal pores of the electrode for a secondary battery with the polymer containing epoxy groups. The method of impregnating the electrode with a polymer containing epoxy groups may be carried out by a method conventional in the art. For example, methods such as applying the polymer containing epoxy groups onto the electrode or immersing the electrode in a polymer solution containing epoxy groups so that the electrode is impregnated with the solution may be applied.

[0098] According to one embodiment of the present invention, the method for analyzing the electrode for a battery may further include the step of measuring the resistance value of the polymer containing epoxy groups filled in the pores of the electrode cross-section sample. By filling the internal pores of the electrode for a secondary battery with a polymer containing epoxy groups, the resistance value of the pores within the electrode cross-section sample can be obtained using a scanning diffusion resistance microscope. Specifically, resistance value data can be obtained by measuring the resistance value of the polymer material filling the pores. Through this, the region where the pores are located can be identified, and the electrode active material region, the conductive material region, and the pore region of the electrode cross-section sample can be distinguished more accurately from the composite image. (See FIG. 12)

[0100] According to one embodiment of the present invention, the polymer containing the epoxy group may be an epoxy resin polymer containing a cyclic structure within its molecular structure, and specifically, an epoxy resin polymer containing an aromatic group (e.g., a phenyl group) may be used. Specific examples of the epoxy group-containing polymer containing the aromatic group may be one or more of the following: a biphenyl-type epoxy group-containing polymer, a dicyclopentadiene-type epoxy group-containing polymer, a naphthalene-type epoxy group-containing polymer, a dicyclopentadiene-modified phenol-type epoxy group-containing polymer, a cresol-based epoxy group-containing polymer, a bisphenol-based epoxy group-containing polymer, a xylock-based epoxy group-containing polymer, a polyfunctional epoxy group-containing polymer, a phenol novolak epoxy group-containing polymer, a triphenolmethane-type epoxy group-containing polymer, and an alkyl-modified triphenolmethane epoxy group-containing polymer, but are not limited thereto. Specific examples may include, but are not limited to, any one of epoxyethane (ethylene oxide), 1,3-epoxypropane (trimethylene oxide), and bisphenol-A-epichlorohydrin.

[0101]

[0102] (Step 2)

[0103] Next, when the electrode cross-section sample is prepared in step 1 above, a 2D scale map of the resistance distribution of the sample cross-section is obtained using a conductivity network analysis method (Scanning Spreading Resistance Microscopy). FIG. 1a exemplarily shows a 2D scale map image of Example 4 obtained by the above method.

[0105] ​Specifically, an image converted to a 2D scale can be obtained by scanning the cross-sectional sample surface using an AFM (Atomic force microscopy) device. Through the above measurement, a map is obtained in which the height of the electrical resistance value appears as shades of color, and the distribution of surface resistance can be visually confirmed based on the difference in hue (shade).

[0107] First, a sample is prepared for measurement using an AFM (Atomic Force Microscopy) device. The cross-sectional sample prepared by the above process is attached to a metal disc for the AFM with the cross-section facing upward, and silver paste or the like is applied to the metal disc for the AFM so that a conductive path can be formed between the parts other than the milled cross-section and the portion other than the milled cross-section. The AFM measurement sample prepared in this way is loaded into the device, and after laser alignment, the cross-section is selected as the measurement area using an optical microscope. Subsequently, an atomic force microscope probe is brought into contact with the electrode cross-section, and the current flowing through the sample between the atomic force microscope probe and the contact electrode is measured to obtain the diffusion resistance from the measured current.

[0109] According to one embodiment of the present invention, the operating conditions of a scanning diffusion resistance microscope for analyzing the electrode cross-section sample are, for example, as follows.

[0111] The above AFM equipment is not limited to any specific type as long as it is capable of visualizing the resistance distribution according to the scanning diffusion resistivity microscopy method. For example, one from cypher ES (Oxford Instruments) can be used. According to a specific example of the present invention, Dual-gain ORCA can be used as the cantilever holder, and AR (Oxford Instruments) can be used as the driving software.

[0113] As specific operating conditions, a contact mode can be set, and the acquired image pixels can be set from 512 x 512 to 1024 x 1024, the scan rate can be set from 0.2 Hz to 1.0 Hz, the bias can be set to 2.0 V or less, and the set point can be set to 1.0 V or less. For example, the image pixels can be set to 512x512, the scan rate to 0.5 Hz, the bias to 2.0 V or less, and the set point to 0.2 V. As an AFM probe, a solid diamond AFM probe made of boron-doped single crystal diamond (AD-40-As, Adama) can be used.

[0115] Meanwhile, in one embodiment of the present invention, it is preferable to measure the obtained cross-sectional sample using AFM under conditions of non-exposure to the atmosphere, such as in a glove box. At this time, the cross-sectional sample can be loaded into a sealed cell body to maintain a non-exposure to the atmosphere.

[0117] (Step 3)

[0118] Once a 2D scale map is obtained through Step 2 above, a conductive material region is defined. Since the term 'definition' involves a method of visual representation, it may also be described as 'masking.' For example, FIGS. 10 and 11 show the conductive material region identified from the histogram for the electrode of Example 4 masked in black. The method for defining the conductive material region can be specifically described as follows.

[0120] First, resistance data acquired using a scanning diffusion resistance microscope can be processed and converted to a log scale to obtain a log scale image (log(resistance) image). Once such a log scale image is obtained, a [log resistance distribution histogram] is extracted from it, in which the materials constituting the electrode cross-section sample are distinguished and displayed.

[0122] In the above histogram, it is possible to determine whether the area corresponding to each pixel is an electrode active material area, a pore or binder area, or a conductive material area, and using the information of each pixel for which the area is determined, the distribution of the conductive material area in the above 2D mapping image can be quantified.

[0124] Specifically, the log(R / Ω) value corresponding to the minimum value between the conductive material peak and the electrode active material peak in the above histogram is set as a threshold, and the region having a value smaller than that value is masked as the conductive material region. At this time, in order to obtain more accurate data for the conductive material region, the value can be corrected by adding or subtracting 0.1 to 0.5 from the above minimum value.

[0125] In one embodiment, the correction may be to add a value of 0.1 to 0.5 to the log(R / Ω) value corresponding to the minimum value. This is intended to correct the portion that is not indicated as a conductive material region because the active material region and the conductive material region overlap in the histogram. For example, the correction value may distinguish the left and right sides centered on the conductive material region peak of the histogram, and correct the low point of the right side to have a value equal to the horizontal distance from the peak to the low point on the left.

[0127] By making corrections as described above, even the parts that overlap with the electrode active material region and are not marked as the conductive material region can be marked as the conductive material region, thereby enabling the acquisition of more accurate dispersion data.

[0129] FIG. 2 shows a [log resistance distribution histogram] extracted based on the log scale image (log(resistance) image) for the electrode of Example 4. By referring to this, the conductive material peak and the electrode active material peak can be identified, and the minimum value between them can be determined. However, as previously explained, since there is a conductive material region that is not displayed because it overlaps with the active material region even in the section after the minimum value, the values ​​are corrected as described above. FIG. 12 is an example diagram predicting the shape of the overlap between the active material region and the conductive material region.

[0131] Meanwhile, FIG. 10 shows the conductive material region masked in the SSRM image based on the values ​​before correction. The conductive material region is masked using a color that is not present in the original image, and in the present embodiment, it is masked in black. If you examine the circled area indicated by the dotted line in FIG. 10, you can see that there is a conductive material that remains unmasked. In the unmasked area, if the color is checked, it is confirmed that the area remains blue. Meanwhile, FIG. 11 shows the conductive material region masked based on the values ​​after correction, and it can be seen that the unmasked area in FIG. 10 (the area that remained blue) is masked in black in FIG. 11.

[0133] Meanwhile, among the areas masked by the conductive material, the areas located within the active material are deleted to eliminate errors. This is because the errors are errors that occurred during the sample manufacturing process, such as when the conductive material adheres to the exposed cross-section of the active material during the cross-sectional sample preparation process, or errors that occurred during imaging processing, and it is evident that the conductive material is not distributed within the active material of the actual electrode, so it is desirable to remove them.

[0135] Meanwhile, after the conductive material region is masked, an image showing only the conductive material region is extracted (contrast masking) as illustrated in FIG. 1b, FIG. 4, FIG. 6, FIG. 8, the bottom of FIG. 13, and the bottom of FIG. 14, and is provided for the calculation in Step 4.

[0137] In one embodiment of the present invention, the masking of the conductive material region can be performed using a program that visualizes and processes data obtained through scanning probe microscopy, such as AFM. In one embodiment of the present invention, Gwyddion software can be used for the masking. Meanwhile, if there are many images with excessively small pixel sizes among the images, it is difficult to accurately determine the perimeter or area of ​​the conductive material region, and errors may occur as they act as noise when calculating the dispersion. Accordingly, images with excessively small pixels can be removed during the masking process. For example, when using the Gwyddion program, small areas of less than 3 pixels can be deleted using a grain-filtering function so that they are not masked as the conductive material region. If fine areas of less than 3 pixels are included, the perimeter of the conductive material region may be calculated as an excessively high value, so they are removed for measurement. Meanwhile, FIG. 2 shows a histogram obtained by the above method, which confirms that the active material region and the conductive material region are distinguished.

[0139] (Step 4)

[0140] Once the masking of the conductive material region is completed through the above (step 3) (i.e., the conductive material region is determined), the perimeter and area of ​​the masked region are checked, and through this, Index 1 according to [Equation 1] can be calculated. In [Equation 1], Boundary measured applies the perimeter value of the masking area, and A applies the area value of the masking area.

[0142] In addition, the radius of a circle having an area equal to the area of ​​the masking region can be calculated, and the circumference of the circle can be calculated from this. The circumference of the circle is Boundary measured Index 2 according to [Equation 2] can be calculated by substituting into it.

[0143] 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. FIG. 15 shows a display screen showing the area and perimeter calculated through the program.

[0145] Electrode for electrochemical investigation

[0146] In the present invention, the electrode subject to evaluation of the dispersion of the conductive material is not particularly limited to 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, or capacitors such as supercapacitor devices. The secondary battery may be a lithium-ion secondary battery in which a lithium salt is used as the ion-conducting 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. Additionally, the electrode active material layer may include an electrode active material, a conductive material, and a binder material.

[0148] Electrode active material

[0149] The above electrode active material layer may include a positive electrode active material or a negative electrode active material depending on the polarity of the battery.

[0150] Non-limiting examples of the above-mentioned positive electrode active material include lithium transition metal oxides or lithium metal iron phosphate, provided they are in the form of metal oxides, not limited to, for example, layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxides represented by O2 (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 substituted with alkaline earth metal ions; lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn), and lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, a+b+c=1); Lithium nickel-manganese-cobalt oxide, a lithium oxide in which a portion is substituted with aluminum Li 1+x (Ni a Co b Mn c Al d ) 1-xO2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1); Lithium nickel-manganese-cobalt oxide, a lithium oxide in which a portion is substituted with another transition metal. 1+x (Ni a Co b Mn c M d ) 1-x Examples include O2 (x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg and Mo), disulfide compounds; Fe2(MoO4)3, etc., but are not limited to these.

[0151] Non-limiting examples of the above-mentioned cathode active material include carbon such as non-graphitizable carbon, graphite-based carbon, etc.; Li x Fe2O3(0≤x ≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z Metal composite oxides such as (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, and Group 3 elements of the periodic table, halogens; 0x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithium alloy; silicon alloy; tin alloy; silicon oxides such as SiO, SiO / C, SiO2; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni based materials, etc. may be used.

[0153] Binder material

[0154] In the present invention, the binder material is not limited to a specific type as long as it can achieve binding of materials included in the electrode, such as an electrode active material, and binding with a separator or current collector facing the electrode active material layer, and can be used as a binder material for a secondary battery.

[0156] Challenge

[0157] The conductive material may be included in the electrode mixture powder and introduced into the electrode active material layer. The conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives may be used. However, in detail, to ensure uniform mixing of the conductive material and to improve conductivity, it may include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, it may include activated carbon.

[0159] The whole house

[0160] Meanwhile, in one embodiment of the present invention, the current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may also form fine irregularities on its surface to increase the adhesion of the positive active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

[0162] Meanwhile, in one embodiment of the present invention, the current collector may be used having a conductive primer coated wholly or partially on its surface to lower resistance and improve adhesion. Here, the conductive primer may comprise a conductive material and a binder, and the conductive material is not limited to any material that exhibits conductivity, but may be, for example, a carbon-based material. The binder may include fluorine-based (including PVDF and PVDF copolymers), acrylic binders, and water-based binders that are soluble in solvents.

[0164] Meanwhile, in the present invention, the method of manufacturing the electrode is not particularly limited. For example, the electrode may be manufactured by applying a wet method of applying a slurry for forming an electrode active material layer to a current collector, or a dry method of forming a layered structure by compressing electrode mixed particles.

[0165] The electrode manufacturing method using the above wet method can be described as follows, for example. First, electrode materials such as an electrode active material, a conductive material, and a binder are introduced into a suitable solvent to prepare a slurry for forming an electrode active material layer. In addition to the aforementioned electrode materials, additives capable of improving electrochemical performance or the dispersibility of the slurry may be further added to the slurry. Subsequently, the slurry is applied to an electrode current collector. Known application methods such as slot die, gravure coating, dip coating, and blade coating may be applied, and the method is not limited to a specific method. Afterward, the solvent is removed to obtain an electrode having an electrode active material layer disposed on the surface of the current collector. The drying of the slurry may be performed using methods such as natural drying or air drying, and heating may be applied to accelerate drying. Subsequently, a pressurization process may be further performed to secure an appropriate thickness or electrode active material loading amount.

[0166] The above dry method may involve preparing a dry mixture containing electrode materials or mixed particles containing electrode materials, and then compressing the powdered material without the intervention of a solvent to form a layered structure.

[0167] A dry manufacturing method according to one embodiment of the present invention can be described as follows. First, electrode materials in a powder state are mixed dry. Here, the electrode materials may further include an electrode active material, a binder, and a conductive material. In addition, in addition to the aforementioned electrode materials, additives capable of promoting and improving electrochemical performance or particle formation may be further added to the mixed particles. Subsequently, a shear force is applied to the mixture obtained above to fiberize the binder. The application of the shear force may be performed by mixing the electrode materials at high speed or by kneading. Here, the applied shear force may be lower in kneading compared to mixing. In one embodiment of the present invention, the kneading may be performed at a high temperature, for example, at a temperature of 80°C or higher or 100°C or higher. Meanwhile, the temperature may 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 intertwined to obtain mixed particles of a predetermined size. Meanwhile, a blend lump may be obtained by the above kneading process, and a grinding process may be further performed to produce mixed particles of a predetermined size. The mixed particles may include a binder resin capable of fiberization by shear force, such as polytetrafluoroethylene (PTFE) or polyolefin. Once the mixed particles are obtained in this way, a plate-shaped electrode film may be manufactured by applying pressure, and then an electrode may be obtained by combining the electrode film with a current collector. Alternatively, a method of directly scattering the mixed particles onto a current collector and applying pressure may be applied. Meanwhile, in the above method for manufacturing mixed particles, the electrode materials may be introduced into a solvent to prepare a slurry, and then spray-dried to produce the mixed particles. In this case, a binder resin such as SBR may be used.However, in the present invention, the electrode for measuring the dispersion of a conductive material is not limited to a special shape or manufacturing method, and it goes without saying that any electrode to which the dispersion measurement method described above can be applied may be used.

[0168] Hereinafter, the present invention will be described in detail based on embodiments, comparative examples, and experimental examples according to the present invention so that those skilled in the art can easily understand it.

[0170] [Example]

[0171] Manufacturing of electrodes

[0172] Example 1

[0173] Lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2), carbon black (specific surface area 1400 m² 2 A mixture was prepared by feeding polytetrafluoroethylene (PTFE) and (g) into a blender in a ratio of 96.0:1.5:2.5 and mixing at 10,000 rpm for 1 minute. Next, the mixture was ground through a jet-milling process (feeding pressure 50 psi, grinding pressure 45 psi) to obtain a mixed powder for electrodes. The mixed powder for electrodes was fed into a first lap calender (roll diameter: 88 mm, roll temperature: 100°C, 20 rpm) and compressed to produce 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 a dry electrode. In the obtained electrode, the thickness of the electrode active material layer on one side was approximately 80 µm. Meanwhile, the lithium nickel cobalt manganese aluminum composite oxide has a bimodal distribution and includes large particles (secondary particles) with a diameter of about 10 μm and single particles with a diameter of about 5 μm. FIG. 3 is an SSRM image of Example 1, and FIG. 4 shows an image confirmed by masking the conductive material region thereof.

[0175] Examples 2 to 4

[0176] Lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2), carbon black, and polytetrafluoroethylene (PTFE) were introduced into 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. Next, the temperature of the kneader was stabilized at 150°C, and the mixture was placed into 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 differently between 40 rpm and 70 rpm, and the kneading time was controlled differently between 3 minutes and 7 minutes, respectively. The mixture mass was introduced into a blender, ground for 40 seconds under conditions of 10,000 rpm, and classified through a sieve having 1 mm pores to obtain a mixed powder for electrodes. Next, the above electrode mixture powder was fed into a first lap calender (roll diameter: 88 mm, roll temperature: 100°C, 20 rpm) and compressed to produce 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. In the obtained electrode, the thickness of the electrode active material layer on one side was approximately 80 μm. Meanwhile, the lithium nickel cobalt manganese aluminum composite oxide has a bimodal distribution and includes large particles (secondary particles) with a diameter of approximately 10 μm and single particles with a diameter of approximately 5 μm. In addition, different types of conductive materials were used in Example 2 and Example 4. Figures 1a and 1b show the SSRM image of the electrode of Example 4 and an image confirmed by masking the conductive material region. Figure 5 is an SSRM image of the electrode of Example 2, and Figure 6 shows an image confirmed by masking the conductive material region thereof. Figure 7 is an SSRM image of the electrode of Example 3, and Figure 8 shows an image confirmed by masking the conductive material region thereof.

[0178] Examples 5 and 6

[0179] Lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2), carbon black (specific surface area 1400 m² 2 A mixture was prepared by adding (g) and polytetrafluoroethylene (PTFE) to a blender and mixing at 10,000 rpm for 1 minute. Next, the temperature of the kneader was stabilized to 150°C, 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 differently between 40 rpm and 70 rpm, and the kneading time between 3 minutes and 7 minutes, respectively. The mixture mass was added to a blender, ground for 40 seconds under conditions of 10,000 rpm, and classified through a sieve with 1 mm pores to obtain a mixed powder for electrodes. Next, the mixed powder for electrodes was introduced into a first lap calender (roll diameter: 88 mm, roll temperature: 100°C, 20 rpm) and compressed to produce 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. In the obtained electrode, the thickness of the active material layer on one side was approximately 80 μm. Meanwhile, 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 used lithium nickel cobalt manganese aluminum composite oxide (Li(Ni, Co, Mn, Al)O2), carbon black (specific surface area 1400 m² 2 The ratio of ( / g) and polytetrafluoroethylene (PTFE) was set to 96.0:1.8:22, and for Example 5, it was set to 96.2:1.6:2.2. FIG. 13 shows the SSRM image of Example 5 and the image confirmed by masking the conductive material area. FIG. 14 shows the SSRM image of Example 6 and the image confirmed by masking the conductive material area.

[0182] Preparation of electrode cross-sectional samples

[0183] A solution containing an epoxy polymer having a weight-average molecular weight of about 700 g / mol or less was prepared as a polymer containing epoxy groups.

[0184] The anodes prepared in Examples 1 to 6 above were impregnated with a prepared epoxy-based polymer solution to fill the pores with the polymer. Subsequently, a focused argon (Ar) ion beam was irradiated onto the anodes for the secondary battery using an ion milling device (IB19520CCP, Jeol) to mill the surface, thereby producing a cross-sectional sample having a clean cross-section. During the argon ion beam irradiation, the ion beam current was set to 170 μA, and the gas flow was 1.5 cm⁻¹. 3 It was / minutes, and performed for 3 hours.

[0186] SSRM analysis conditions

[0187] Equipment used: cypher ES (Oxford Instrument), Dual-gain ORCA cantilever holder

[0189] [Parameters]

[0190] Mode: contact

[0191] Sample / line: 512x512, Scan rate: 0.5Hz

[0192] Bias: ~2V, Deflection Setpoint Volts: ~0.2

[0193] Scan Angle: 90°

[0195] [AFM Mode]

[0196] Model: AD-40-As (Manufacturer: Adama)

[0197] Tip: Highly doped (B) single crystal diamond, tip height 300nm

[0198] Cantilever & bulk tip: diamond coated silicon, Reflex coating(Au)

[0199] F=180kHz, k=40N / m

[0200] Typical contact resistance: ~10kΩ

[0202] SSRM analysis method

[0203] After ion milling, the sample was transferred to a glove box under atmospheric non-exposure conditions and loaded onto an AFM puck. Subsequently, silver (Ag) paste was applied between the electrode portion excluding the fabricated cross-section and the AFM puck to form an additional conductive path. Next, the sample with the additional conductive path formed was loaded into a sealed cell body and mounted on an AFM instrument while maintaining an atmospheric non-exposure state. After laser alignment, the milled portion was selected as the measurement area using an optical microscope and measured under Ar flow. In this manner, SSRM images were obtained. Figures 3, 5, 7, and 1a are SSRM images of the electrodes of Examples 1, 2, 3, and 4, respectively. Additionally, the top diagrams of Figures 13 and 14 are SSRM images of the electrodes of Examples 5 and 6, respectively. The size of the observed images was set to 30 µm x 30 µm.

[0205] Masking of the challenge material area

[0206] The conductive material region was masked using Gwyddion software on the SSRM image obtained above.

[0207] First, a log(resistance) image was obtained, and a histogram of the log(resistance) distribution within the image was obtained. This was achieved using the Height distribution function in the Calculate 1D Statistical function provided by the software. A threshold was determined by applying a correction of 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 according to this, log(R / Ω) = 7.2 was set as the threshold. Based on this, the conductive material region was masked. At this time, the Grain filtering function was used to delete regions corresponding to pixels smaller than 3 pixels, and regions located within the electrode active material were also deleted. From Figure 2, it was confirmed that pixels corresponding to the electrode active material and the conductive material were distinguished 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 the information of each pixel whose corresponding region was determined.

[0209] In addition, FIG. 1b shows the SSRM image of the electrode of Example 4, FIG. 4 shows the SSRM image of the electrode of Example 1 (Fig. 3), FIG. 6 shows the SSRM image of the electrode of Example 2 (Fig. 5), and FIG. 8 shows the SSRM image of the electrode of Example 3 (Fig. 7), with the conductive material region masked and only the masked conductive material region indicated by shades. Also, the bottom drawings of FIG. 13 and FIG. 14 show only the masked conductive material region in the electrodes of Example 5 and Example 6, respectively, with shades.

[0210] Afterwards, the perimeter and area of ​​the masked region were checked using the Grain-Summary function.

[0212] Next, indices 1 and 2 were calculated by substituting the respective values ​​into [Equation 1] and [Equation 2] above, and the results are shown in [Table 1] below. As confirmed in [Table 1], it was confirmed that indices 1 and 2 are 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 dispersion of the conductive material in the electrode could be quantitatively verified. In this way, the dispersion of the conductive material in the electrode can be quantitatively verified by utilizing the conductive material index of the present invention. Furthermore, the above conductive material dispersion index can be utilized in selecting the content and / or type of the conductive material, selecting the electrode manufacturing method, and setting the electrode manufacturing process conditions during electrode manufacturing.

[0214] Types of conductive materials Area of ​​the conductive material region (㎛) 2 ) Ratio of conductive material area to total area (%) Perimeter of the conductive material area (㎛) Index 1 (㎛ -1 ) Index 2 Example 1 Carbon Black (A) 125.6 14.0 342.6 2.7 8.6 Example 2 Carbon Black (A) 111.4 12.3 526.0 4.7 14.1 Example 3 Carbon Black (B) 47.0 5.2 380.9 8.1 15.7 Example 4 Carbon Black (B) 50.9 5.6 482.7 9.5 19.1 Example 5 Carbon Black (A) 48.0 5.3 312 6.5 12.7 Example 6 Carbon Black (A) 34.2 3.8 346.8 10.1 16.7

[0216] [Explanation of the symbol]

[0217] 10 Electrode, 11 Electrode active material layer, 11s Part from the surface to a predetermined depth, 11f Part at a predetermined height from the current collector facing portion, 12 Current collector

Claims

Claim 1 An electrode for an electrochemical device comprising an electrode active material layer including an electrode active material and a conductive material, wherein the boundary of a portion defined as a conductive material region in one or more arbitrary cross-sections within the electrode active material layer measured A method for quantifying the dispersion of a conductive material based on a formula defined with ) and area (A) as variables, wherein the above formula is the conductive material dispersion index 1 (Index 1) according to [Equation 1] below or the conductive material dispersion index 2 (Index 2) according to [Equation 2] below: [Equation 1] Index 1 (㎛ -1 ) = Boundary measured / A[Equation 2]Index 2 = Boundary measured / L circle In the above [Equation 1], Boundary measured represents 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 represents the area of ​​the portion defined as the conductive material region measured at a predetermined cross-section of the electrode active material layer, and in the above [Equation 2], Boundary measured is equal to Equation 1 above, and L circle is the circumference of a circle having an area equal to the area of ​​the conductive material region defined above (2× )am. Claim 2 delete Claim 3 A method for quantifying the dispersion of a conductive material according to claim 1, comprising: (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 of the cross-sectional sample; (Step 3) masking a conductive material region; and (Step 4) calculating the perimeter and area of ​​the masked region, substituting them into Equation 1 or Equation 2, or both, and confirming the dispersion of the conductive material in the electrode active material layer. Claim 4 A method for quantifying the dispersion of a conductive material according to claim 1, wherein the electrode active material layer is formed on one side of the electrode current collector, and one or more arbitrary cross-sections are planes parallel or perpendicular to the surface of the electrode active material layer facing the current collector. Claim 5 A method for quantifying the dispersion of a conductive material in paragraph 3, wherein the cross-sectional sample is prepared by etching the electrode surface to a predetermined depth by ion milling. Claim 6 A method for quantifying the dispersion of a conductive material, wherein the step of obtaining a 2D scale map of the resistance distribution of the cross-sectional sample is performed by Scanning Spreading Resistance Microscopy, which scans the surface of the cross-sectional sample using an Atomic Force Microscopy (AFM) device. Claim 7 A method for quantifying the dispersion of a conductive material according to claim 3, wherein the step of masking the conductive material region comprises: a first step of processing and changing the resistance value data obtained in (Step 2) into a log scale to obtain a log scale image; a second step of extracting a [log resistance distribution histogram] in which the material constituting the electrode cross-section sample is distinguished and displayed in the log scale image; and a third step of setting the 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 value and masking the region having a value smaller than that value as the conductive material region. Claim 8 A method for quantifying the dispersion of a conductive material according to claim 7, further comprising the step of correcting a limit value by adding a value of 0.1 to 0.5 to the minimum value. Claim 9 A method for quantifying the dispersion of a conductive material according to claim 1, wherein the electrode comprises 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 comprises an electrode active material, a conductive material, and a binder. Claim 10 A method for quantifying the dispersion of a conductive material according to claim 1, wherein the cross-section is in a direction parallel or perpendicular to the surface of the current collector facing the electrode active material layer.

Images