Negative electrode and electrochemical device comprising the same

Abstract

A negative electrode for an electrochemical device and an electrochemical device including the same are provided. The negative electrode for the electrochemical device comprises: a current collector; and a negative electrode active material layer present on the current collector, wherein the negative electrode active material layer comprises particles containing a silicon-based active material, a linearly conductive material, and a binder for the particles, wherein the dispersion of the particles within the negative electrode active material layer is 1 × 10⁻⁶. ‑2 Up to 10×10 ‑2 The standard deviation of particle dispersion is 1×10⁻⁶. ‑3 Up to 4×10 ‑3 The volume expansion rate of the negative electrode active material layer is 3% to 30%.

Description

Technical Field

[0001] This disclosure relates to a negative electrode and an electrochemical device including the negative electrode.

[0002] This application is based on and claims priority to Korean Patent Application Nos. 10-2024-0088547 and 10-2024-0088548, both filed with the Korean Intellectual Property Office on July 4, 2024, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] Due to the increasing use of fossil fuels, the demand for alternative and clean energy sources is growing, leading to extensive research in the field of electrochemical power generation and storage. Currently, a typical example of an electrochemical device utilizing both electrical and chemical energy is the secondary battery, and its applications are gradually expanding. One typical secondary battery, the lithium-ion battery, is not only used as an energy source for mobile devices but also as a power source for electric vehicles and hybrid electric vehicles, serving as alternatives to fossil fuel-powered vehicles such as gasoline and diesel vehicles (considered a major cause of air pollution). Furthermore, the application of lithium-ion batteries is extending to auxiliary power supplies connected to the power grid.

[0004] A lithium secondary battery has the following structure: an electrode assembly is filled with an electrolyte containing lithium salt, the electrode assembly includes a positive electrode and a negative electrode and a porous separator between the positive electrode and the negative electrode, each electrode contains an active material coated on an electrode current collector, and the electrodes are manufactured by applying a slurry to the current collector, followed by drying and pressing / rolling, the slurry containing active material dispersed in a solvent, a binder for the granules and a conductive material.

[0005] Furthermore, the fundamental performance characteristics of lithium-ion batteries, such as capacity, output, and lifespan, are significantly affected by the anode material. To maximize battery performance, the anode active material needs to meet the following requirements: an electrochemical reaction potential close to that of lithium metal, high reversibility of the reaction with lithium ions, and rapid diffusion of lithium ions within the active material.

[0006] Carbon-based materials are primarily used as anode materials in lithium-ion batteries, but their theoretical capacity limit of 372 mAh / g is a barrier to increasing energy density. To address this issue, silicon-based materials are considered promising alternatives. Silicon has a theoretical capacity of 4010 mAh / g, at least 10 times that of carbon-based materials. However, carbon-based materials have a charge / discharge efficiency of 92%, while silicon-based materials have an efficiency as low as 80%. Furthermore, the volume change during charging and discharging is as high as 300%, causing the conductive path to break during continuous charging and discharging, thus rendering it unsuitable as an active material.

[0007] When the negative electrode contains a mixture of silicon-based and carbon-based materials (e.g., graphite-based materials), attempts have been made to use high-modulus granular binders or to increase the amount of granular binder to prevent swelling caused by the expansion of the silicon-based material during charging. Furthermore, since silicon-based materials have lower conductivity than graphite-based materials, conductive materials such as carbon nanotubes (CNTs) are added to increase conductivity. However, in practical situations where the amount of granular binder and conductive material is limited by capacity and material cost considerations, high-modulus granular binders and conductive materials such as CNTs uniformly distributed throughout the silicon-based and graphite-based materials within the electrode do not adequately suppress the expansion of the silicon-based material and improve conductivity. Summary of the Invention

[0008] Technical issues

[0009] This disclosure aims to provide a negative electrode with minimized volume expansion characteristics and improved particle dispersion, as well as an electrochemical device including the negative electrode.

[0010] Technical solution

[0011] To address the aforementioned problems, according to one aspect of this disclosure, a negative electrode for an electrochemical device is provided according to the following embodiments.

[0012] According to a first embodiment of this disclosure, a negative electrode for an electrochemical device is provided, comprising:

[0013] Current collector; and

[0014] The negative electrode active material layer existing on the current collector.

[0015] The negative electrode active material layer comprises granules, which contain silicon-based active materials, linear conductive materials, and a binder for the granules.

[0016] The dispersion degree of the granules in the negative electrode active material layer is 1×10⁻⁶. -2 Up to 10×10 -2 And the standard deviation of particle dispersion is 1×10 -3 Up to 4×10 -3 ,as well as

[0017] The volume expansion rate of the negative electrode active material layer is 3% to 35%.

[0018] According to the second embodiment of this disclosure, in the first embodiment...

[0019] The dispersion of the granules within the negative electrode active material layer can be 1×10⁻⁶. -2 Up to 5×10 -2 The standard deviation of particle dispersion can be 1×10⁻⁶. -3to 3.5×10 -3 。

[0020] According to the third embodiment of the present disclosure, in the first embodiment or the second embodiment,

[0021] The volume expansion rate of the negative electrode active material layer can be 3% to 33%.

[0022] According to the fourth embodiment of the present disclosure, in any one of the first embodiment to the third embodiment,

[0023] The negative electrode active material layer may include pellets, carbon-based active material, and a binder for the negative electrode layer.

[0024] According to the fifth embodiment of the present disclosure, in the fourth embodiment,

[0025] Based on 100 parts by weight of the negative electrode active material layer, the negative electrode active material layer may include 1 to 10 parts by weight of pellets, 70 to 99 parts by weight of carbon-based active material, and 0.1 to 10 parts by weight of a binder for the negative electrode layer.

[0026] According to the sixth embodiment of the present disclosure, in any one of the first embodiment to the fifth embodiment,

[0027] The negative electrode active material layer may include pellets, carbon-based active material, a binder for the negative electrode layer, and a conductive material for the negative electrode layer.

[0028] According to the seventh embodiment of the present disclosure, in the sixth embodiment,

[0029] Based on 100 parts by weight of the negative electrode active material layer, the negative electrode active material layer may include 1 to 10 parts by weight of pellets, 70 to 99 parts by weight of carbon-based active material, 0.01 to 5 parts by weight of a conductive material for the negative electrode layer, and 0.1 to 10 parts by weight of a binder for the negative electrode layer.

[0030] According to the eighth embodiment of the present disclosure, in any one of the first embodiment to the seventh embodiment,

[0031] The silicon-based active material may include silicon (Si), silicon oxide (SiOx (0 < x ≤ 2)), Si / C composite, or two or more of them.

[0032] According to the ninth embodiment of the present disclosure, in any one of the first embodiment to the eighth embodiment,

[0033] The linear conductive material may include single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanofibers, or two or more of them.

[0034] According to the tenth embodiment of this disclosure, in any one of the first to ninth embodiments,

[0035] The adhesive may include at least one of linear adhesives and dot adhesives.

[0036] According to the eleventh embodiment of this disclosure, in the tenth embodiment,

[0037] Adhesives can include linear adhesives and dot adhesives.

[0038] According to the twelfth embodiment of this disclosure, in the tenth or eleventh embodiment,

[0039] Linear adhesives may include acrylate-based polymers, and dot-type adhesives may include diene-based polymers, styrene-based polymers, or both or more thereof.

[0040] According to the thirteenth embodiment of this disclosure, in any of the first to twelfth embodiments,

[0041] The pellets may include a central portion comprising a silicon-based active material and a linearly conductive material; and a surface portion present on all or part of the outer side of the central portion, the surface portion comprising a pellet binder that holds the silicon-based active material and the linearly conductive material together.

[0042] According to the fourteenth embodiment of this disclosure, in the thirteenth embodiment,

[0043] Relative to the total weight of 100% by weight of silicon-based active materials, linearly conductive materials, and granule binder, the amount (by weight) of granule binder can be greater on the surface portion of the granule than in the central portion.

[0044] The surface portion can be the area close to the surface of the pellet to a predetermined depth in the direction from the surface of the pellet to the center of the pellet, and the center portion can be the area other than the surface portion.

[0045] According to the fifteenth embodiment of this disclosure, in any of the first to fourteenth embodiments,

[0046] Based on 100 parts by weight of granules, the granules may contain 80 to 98 parts by weight of silicon-based active material, 0.2 to 10 parts by weight of linear conductive material, and 0.5 to 10 parts by weight of granule binder.

[0047] According to the sixteenth embodiment of this disclosure, in any one of the first to fifteenth embodiments,

[0048] The pellets may also contain carbon-based active materials.

[0049] According to the seventeenth embodiment of this disclosure, in any one of the first to sixteenth embodiments,

[0050] Granules may also contain dispersants.

[0051] According to the eighteenth embodiment of this disclosure, in the seventeenth embodiment...

[0052] Dispersants may include carboxymethyl cellulose (CMC).

[0053] According to the nineteenth implementation scheme of this disclosure

[0054] A method is provided for manufacturing a negative electrode for an electrochemical device as defined in any of the first to eighteenth embodiments, the method comprising forming a layer of negative electrode active material using granules, said granules comprising a silicon-based active material, a linearly conductive material, and a binder for the granules.

[0055] According to the twentieth embodiment of this disclosure, in the nineteenth embodiment...

[0056] Methods for manufacturing negative electrodes may include wet processes, dry processes, or both.

[0057] According to the twenty-first embodiment of this disclosure, in the twenty-ninth embodiment...

[0058] The wet process may include mixing granules and a negative electrode layer together in a dispersion medium with a binder, or mixing granules, a negative electrode layer with a binder and a negative electrode layer with a conductive material in a dispersion medium to prepare a negative electrode slurry; and applying the negative electrode slurry to at least one surface of a current collector and drying it to form a negative electrode active material layer.

[0059] According to the twenty-second embodiment of this disclosure, in the twenty-tenth or twenty-first embodiment...

[0060] Dry processes may include dry mixing of granules and a fiberizable binder, or dry mixing of granules, a fiberizable binder, and a negative electrode layer with a conductive material to prepare a mixture;

[0061] The prepared mixture is kneaded to produce a mixture block, and the mixture block is ground to obtain electrode mixture granules;

[0062] Electrode mixture granules are fed between multiple rollers for calendering to form an electrode film; and

[0063] The electrode film is laminated onto the metal current collector.

[0064] According to the twenty-third embodiment of this disclosure, in any one of the twenty-second to twenty-second embodiments,

[0065] Dry processes may include applying the granules directly to the current collector alone, applying the granules and the negative electrode layer together to the current collector with a binder, or applying the granules, the negative electrode layer with a binder and the negative electrode layer with a conductive material together to the current collector and then pressing / rolling them.

[0066] According to the twenty-fourth embodiment of this disclosure, in any one of the nineteenth to twenty-third embodiments,

[0067] The negative electrode active material layer may also contain carbon-based active materials.

[0068] According to the twenty-fifth implementation scheme of this disclosure

[0069] An electrochemical device is provided, which includes a negative electrode for an electrochemical device as defined in any one of the first to eighteenth embodiments.

[0070] According to the twenty-sixth embodiment of this disclosure, in the twenty-fifth embodiment...

[0071] Electrochemical devices can be secondary batteries.

[0072] Beneficial effects

[0073] According to one embodiment of the present disclosure, the negative electrode has a uniform distribution of particles comprising a silicon-based active material, a linear conductive material, and a particle binder within the negative electrode active material layer, without particle agglomeration in some areas. This results in the particle dispersion falling within a predetermined range and having a low standard deviation. Consequently, compared to conventional negative electrodes using silicon-based active materials, it prevents degradation caused by the shrinkage and expansion of silicon-based active materials, resulting in a very low volume expansion rate. It also significantly improves the conductivity in the negative electrode active material layer and significantly enhances the electrochemical performance of the secondary battery, such as its lifetime characteristics.

[0074] According to one embodiment of this disclosure, the negative electrode can be applied to both wet and dry electrodes, thereby significantly improving the performance of secondary batteries including these electrodes. Attached Figure Description

[0075] The accompanying drawings illustrate exemplary embodiments of the present disclosure and, together with the above description, are used to provide a better understanding of the technical aspects of the present disclosure, and therefore the present disclosure should not be construed as limited to the drawings.

[0076] Figures 1 to 3 The image shows a scanning electron microscope (SEM) image of the granules contained in the negative electrode according to Example 1.

[0077] Figure 4 This is an SEM image of the granules contained in the negative electrode according to Example 2.

[0078] Figures 5a to 5c SEM images of the granules contained in the negative electrodes of Comparative Examples 1-1, 2-1, and 3-1, respectively.

[0079] Figure 6 An image of an apparatus for manufacturing pellets according to one embodiment of this disclosure.

[0080] Figure 7 This is a schematic diagram of granules (C), spherical granules (A), and crushed granules (B) obtained by high shear force when manufacturing an electrode using spherical granules, according to one embodiment of the present disclosure.

[0081] Figure 8 Images are shown to illustrate the dispersion evaluation of particles within the negative electrode active material layer of the electrodes of Examples 2 (T2-3), Comparative Examples 1-1 (T1-1), Comparative Examples 2-2 (T2-2), and Comparative Example 4 (Reference). Detailed Implementation

[0082] This disclosure will be described in further detail below to aid in understanding it.

[0083] It should be understood that the terms or words used in the specification and appended claims should not be construed as limited to their general or dictionary meanings, but should be interpreted based on their meanings and concepts corresponding to the technical aspects of this disclosure, on the basis of the principle that the inventors are allowed to define terms appropriately for the purpose of best description.

[0084] The terminology used herein is for describing exemplary embodiments of this disclosure and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular form includes the plural form.

[0085] It should be further understood that, unless otherwise expressly stated, "comprising," "including," or "having," when used in the specification, specifies the presence of the stated element and does not exclude the presence or addition of one or more other elements.

[0086] The terms “about” and “substantially” are used herein in the sense of being equal to or nearly equal to, taking into account the manufacturing and material tolerances inherent in the stated circumstances, and are intended to prevent unethical infringers from unfairly exploiting the precise or absolute values ​​stated herein for the purpose of understanding this disclosure.

[0087] In this specification, 'A and / or B' means A or B or both.

[0088] In this specification, the "glass transition temperature (Tg)" can be measured by commonly known methods in the art, and can be measured, for example, by differential scanning calorimetry (DSC).

[0089] As used herein, the term "porosity" refers to the ratio of pore volume to total volume in a structure and is expressed as a percentage of volume (%), and can be used interchangeably with void fraction, porosity, etc. In this disclosure, the measurement of porosity is not limited to a particular method, and according to one embodiment of this disclosure, porosity can be measured, for example, by the Brunauer-Emmett-Teller (BET) method using nitrogen, an Hg porosimeter, or ASTM D-2873. Alternatively, the porosity of a separator can be calculated from the difference between apparent density and net density, wherein the net density of the separator is calculated from the density of the separator (apparent density), the compositional ratio of the materials contained in the separator, and the density of each component.

[0090] The “thickness” of the layers included in the electrodes used herein can be a value measured by methods commonly used to measure thickness. Thickness can be a value measured, for example, using a thickness measuring device (Mitutoyo, VL-50S-B) or on an image obtained by observing a horizontal cross-section using an X-ray microscope (XRM) (e.g., ZEISS Xradia Versa 620), but the methods used to measure thickness are not limited to these.

[0091] As used herein, "specific surface area" can refer to a value measured by methods commonly used to measure specific surface area. Specific surface area can be a value measured, for example, by a flow method or a stationary method, but the methods used to measure specific surface area are not limited to these.

[0092] According to one aspect of this disclosure, a negative electrode for an electrochemical device is provided, comprising: a current collector; and a negative electrode active material layer present on the current collector, wherein the negative electrode active material layer comprises particles containing a silicon-based active material, a linearly conductive material, and a binder for the particles.

[0093] The dispersion degree of the granules in the negative electrode active material layer is 1×10⁻⁶. -2 Up to 10×10 -2 And the standard deviation of particle dispersion is 1×10 -3 Up to 4×10 -3 ,as well as

[0094] The volume expansion rate of the negative electrode active material layer is 3% to 35%.

[0095] The dispersion of the granules within the negative electrode active material layer is 1×10⁻⁶. -2 Up to 10×10 -2According to one embodiment of this disclosure, the dispersion of the granules within the negative electrode active material layer can be 1×10⁻⁶. -2 Up to 5×10 -2 or 1×10 -2 Up to 4.4×10 -2 or 4.4×10 -2 Up to 10×10 -2 or 2×10 -2 Up to 5×10 -2 or 2×10 -2 Up to 4.4×10 -2 or 4.4×10 -2 Up to 5×10 -2 .

[0096] Dispersion is a numerical value representing the uniformity of the distribution of silicon-based active material particles within the negative electrode active material layer. When the dispersion is zero (0) or close to 0, it means that the silicon-based active material particles are uniformly distributed within the negative electrode active material layer. When the dispersion is closer to 1, it means that the silicon-based active material particles are bonded together in some regions of the negative electrode active material layer.

[0097] When the dispersion of the granules in the negative electrode active material layer falls below 1×10 -2 Up to 10×10 -2 Within a certain range, the uniform distribution of granules throughout the entire negative electrode active material layer can prevent degradation caused by the shrinkage and expansion of silicon-based active materials, improve the conductivity in the negative electrode active material layer, and significantly improve the electrochemical performance of secondary batteries, such as lifetime characteristics.

[0098] The standard deviation of particle dispersion within the negative electrode active material layer is 1×10⁻⁶. -3 Up to 4×10 -3 According to one embodiment of this disclosure, the standard deviation of particle dispersion within the negative electrode active material layer can be 1 × 10⁻⁶. -3 Up to 3.5×10 -3 or 1.5×10 -3 Up to 3.5×10 -3 or 1×10 -3 Up to 2.85×10 -3 or 2.85×10 -3 Up to 4×10 -3 or 1.5×10 -3 Up to 2.85×10 -3 or 2.85×10 -3 Up to 3.5×10 -3 .

[0099] When the standard deviation of the particle dispersion within the negative electrode active material layer falls within the aforementioned range, the negative electrode can be reproduced and its high-quality uniformity can be ensured due to the small deviation between the particle dispersions.

[0100] In this case, the dispersion of the granules in the negative electrode active material layer and its standard deviation can be determined by the following method.

[0101] First, a target negative electrode can be selected to evaluate the dispersion of granules within the negative electrode active material layer. A cross-section of the negative electrode active material layer can be measured using a scanning electron microscope (SEM) (e.g., manufacturer: JEOL, model name: JSM-7200) to obtain an image, and the image obtained by SEM measurement can be analyzed pixel by pixel using an image analysis program.

[0102] The contrast between the silicon-based active material (Si) and the carbon-based active material (e.g., graphite) in the negative electrode active material layer can be used to identify whether an image pixel represents a carbon-based active material or a silicon-based active material.

[0103] For example, the image pixels of the analysis area in the negative electrode active material layer can be divided into 20×20 (width×height) segments. The area ratio of the region of interest (containing particles of silicon-based active material) in each segment can be calculated, and the sample variance of 400 area ratios can be defined as the dispersion.

[0104] In this case, the sample variance can be calculated from the individual values ​​of the 400 area ratios using the following Equation 1 and provided as the dispersion.

[0105] Equation 1

[0106] s 2 =Σ(y-y') 2 / (n-1)

[0107] In the above equation, s 2 This represents the sample variance (i.e., dispersion), and this represents the variance calculated from the sample. To compare this with the population variance σ... 2 Distinguish them, and represent them as s 2 .

[0108] Σ(y-y') 2 It is the sum of squared deviations.

[0109] Where y represents each observation value.

[0110] y': Sample mean (y-bar)

[0111] (y-y'): The difference (deviation) between each observation and the sample mean.

[0112] (y-y') 2 : square deviation

[0113] Σ: Sum of the squared deviations of all observations

[0114] n-1 represents the degrees of freedom.

[0115] Where n: sample size (number of observations)

[0116] Due to Bessel correction, n-1 is used instead of n.

[0117] In Equation 1 above, the reason for dividing the sum of squared deviations by 'n-1' is that when using the sample mean to calculate the variance, since the sample mean is a value calculated from the sample data, a constraint is created. That is, when n-1 deviations are determined, since the sum of the n deviations is always 0, the last one is automatically determined, and therefore the actual degrees of freedom are n-1, from which an unbiased estimator of the population variance can be obtained. The above equation allows for an accurate measurement of the dispersion of the sample data.

[0118] Although the above example of calculating dispersion shows that the image pixels of the analysis area in the negative electrode active material layer can be divided into 20×20 (width×height) segments, various segments can be set when calculating dispersion for more accurate analysis, such as larger segments, such as 900 30×30 segments or 2500 50×50 segments.

[0119] In one embodiment of this disclosure, the cross section of the negative electrode active material layer used to evaluate the dispersion of particles within the negative electrode active material layer can be measured using SEM to obtain four SEM images of different regions. The dispersion can be calculated from each image based on the area of ​​particles containing silicon-based active material that are not present in a total of 400 20×20 segments. The standard deviation of the calculated dispersion from the four images can also be calculated.

[0120] According to one embodiment of this disclosure, the SEM image may have a magnification of 100x to 500x or 200x to 400x, and a length and width of 500 mm to 2000 mm and 700 mm to 1500 mm, or 900 mm to 1300 mm and 1000 mm to 1200 mm, respectively.

[0121] The volume expansion rate of the negative electrode active material layer is 3% to 35%. According to one embodiment of this disclosure, the volume expansion rate of the negative electrode active material layer can be 3% to 33%, or 5% to 31%, or 14.1% to 30.6%, or 3% to 14.1%, or 14.1% to 35%, 3% to 16.6%, or 16.6% to 35%, or 3% to 30.6%.

[0122] When the volume expansion rate of the negative electrode active material layer falls within the aforementioned range, the linear conductive material included together with the silicon-based active material in the granules and the granule binder can be connected and maintained, and the volume expansion rate can be controlled below the inherent expansion rate of the silicon-based active material, thereby stably maintaining the conductive network formed by the linear conductive material in the negative electrode active material layer, and achieving improved resistance characteristics and enhanced lifetime stability of the electrochemical device including it.

[0123] The volume expansion rate of the negative electrode active material layer can be calculated using the thickness of the negative electrode active material layer measured with an X-ray microscope by the following equation.

[0124] The volume expansion rate of the negative electrode active material layer can be defined by the following Equation 2.

[0125] Equation 2

[0126] Volume expansion rate (%) = (Electrode thickness at 100 charge cycles - Initial electrode thickness) / Initial electrode thickness × 100

[0127] The negative electrode active material layer may include granules, carbon-based active materials, and a binder for the negative electrode layer.

[0128] Based on 100 parts by weight of a negative electrode active material layer, the negative electrode active material layer may include 1 to 10 parts by weight, or 2 to 8 parts by weight, or 1 to 5 parts by weight, or 5 to 10 parts by weight of granules, 70 to 99 parts by weight, or 80 to 98 parts by weight, or 70 to 92 parts by weight, or 92 to 99 parts by weight of carbon-based active material, and 0.1 to 10 parts by weight, or 0.8 to 5 parts by weight, or 0.1 to 2 parts by weight, or 2 to 10 parts by weight, or 2 to 5 parts by weight of a binder for the negative electrode layer.

[0129] The negative electrode active material layer may include granules, carbon-based active materials, binders for the negative electrode layer, and conductive materials for the negative electrode layer.

[0130] Based on 100 parts by weight of a negative electrode active material layer, the negative electrode active material layer may include 1 to 10 parts by weight, or 2 to 8 parts by weight, or 1 to 5 parts by weight, or 5 to 10 parts by weight of granules, 70 to 99 parts by weight, or 80 to 98 parts by weight, or 70 to 92 parts by weight, or 92 to 99 parts by weight of carbon-based active material, 0.01 to 5 parts by weight, or 0.1 to 2 parts by weight, or 0.01 to 1 part by weight, or 1 to 5 parts by weight, or 1 to 2 parts by weight of conductive material for the negative electrode layer, and 0.1 to 10 parts by weight, or 0.8 to 5 parts by weight, or 0.1 to 2 parts by weight, or 2 to 10 parts by weight, or 2 to 5 parts by weight of binder for the negative electrode layer.

[0131] The pellets comprise silicon-based active materials, linearly conductive materials, and a pellet binder. The pellet binder is used to connect and hold the silicon-based active materials and the linearly conductive materials together.

[0132] In this disclosure, granules may be referred to as powder, particles, or coarse particles.

[0133] In this disclosure, the granules may have the shape of composite granules comprising a silicon-based active material, a linearly conductive material, and a binder for the granules, and optionally, if necessary, additional conductive material.

[0134] In one embodiment of this disclosure, the silicon-based active material may comprise one or more silicon-based active material particles.

[0135] The granules can be secondary particles in which one or more silicon-based active material particles are joined and held together by a granule binder.

[0136] According to one embodiment of this disclosure, a negative electrode active material comprising a silicon-based active material having high capacity but large volume variation (which limits the scope of applications) is prepared into granules of a predetermined shape, and the silicon-based active material is connected and held together by a linear conductive material uniformly distributed within the granules and a binder for the granules. Even if there is subsequent volume variation of the silicon-based active material within the negative electrode active material layer, the conductive network within the negative electrode active material layer can be stably formed by the linear conductive material connected by line contacts through the uniform distribution of the silicon-based active material, and thus, the electrical characteristics, such as lifetime characteristics, in electrochemical devices or secondary batteries including a negative electrode can be significantly improved.

[0137] According to one embodiment of this disclosure, the product of the roundness and density of the aggregate can be 0.7 to 0.9, or 0.7 to 0.88, or 0.7 to 0.87, or 0.7 to 0.86. In this case, the roundness and density can be defined by Equations 3 and 4 below, respectively.

[0138] Equation 3

[0139] Roundness = 4π * (actual area of ​​the aggregate) / (circumference of the aggregate) 2

[0140] Equation 4

[0141] Density = (Actual area of ​​aggregate) / Convex hull area of ​​aggregate

[0142] Here, the convex hull area of ​​the granules is the total area enclosed by the convex hull of the granules, and refers to the area of ​​the simplest convex polygon formed by connecting the outermost points of the granules.

[0143] The roundness of the granules can be 0.96 or less, or 0.60 to 0.96, or 0.70 to 0.90.

[0144] The roundness of the granules can be defined by the following equation.

[0145] The roundness of the aggregate = 4π × (measured area of ​​the aggregate) / (measured perimeter of the aggregate) 2

[0146] The roundness value of the pellets ranges from 0 to 1, meaning that when the roundness is closer to 1, the pellets have a perfect spherical shape.

[0147] The roundness of the granules can be measured using standard testing methods.

[0148] For example, a particle size analyzer (e.g., Malvern Morphology 4) can be used to optically image 10,000 particles, and the roundness of the particles can be calculated by numerical averaging.

[0149] Density is a measure of the degree of irregularity in the shape of aggregates or the degree of compaction of aggregates. Since density is calculated by Equation 2 above, namely "Density = (Actual area of ​​aggregate) / Area of ​​convex hull of aggregate", it means that when density is 1, the aggregate has a perfectly convex shape and no grooves or defects on the surface, and when density is less than 1, the aggregate has an irregular surface or a structure with a hollow center.

[0150] The solidity can be determined as follows: optically image 10,000 pellets using a particle size analyzer (e.g., Malvern Morphology 4), obtain the actual area (a) of each pellet and the convex outer area (b) of the pellet in the obtained image, and calculate their ratio (a / b).

[0151] When the product of the roundness and solidity of the pellets according to an embodiment of the present disclosure falls within the aforementioned range, the shape of the pellets is not a perfect sphere, but has some irregular parts on the outer surface, so that the specific surface area is larger, resulting in favorable results in terms of electrochemical performance.

[0152] In an embodiment of the present disclosure, the average particle size D50 of the pellets can be 10 μm to 25 μm, or 14 μm to 20 μm.

[0153] In addition, the particle size D10 of the pellets can be 5 μm to 10 μm, and the particle size D90 of the pellets can be 25 μm to 35 μm.

[0154] As used herein, "average particle size D50" refers to the particle size at 50% of the cumulative particle size distribution, and the particle size can be measured using laser diffraction. Specifically, after dispersing the powder to be measured in a dispersion medium, a commercially available particle size analyzer (e.g., Malvern Morphology 4) can be used to calculate the particle size distribution. The particle size D50 can be measured by calculating the particle diameter at 50% of the cumulative particle size distribution in the measuring instrument. Similarly, the particle size D10 and the particle size D90 can be measured by calculating the particle diameters at 10% and 90% of the cumulative particle size distribution in the measuring instrument, respectively.

[0155] According to an embodiment of the present invention, the angle of repose of the pellets can be 35° to 80°, or 40° to 70°. When the angle of repose of the pellets falls within the aforementioned range, the pellets can have good fluidity, so the process of transporting the pellets or mixing and supplying the slurry can continue stably, achieving high productivity, and the miscibility in the slurry can be improved, thereby preventing agglomeration and sedimentation of the pellets in the slurry, and obtaining an electrode with a uniform thickness and improved surface quality.

[0156] The angle of repose of the pellets can be measured by the USP 1274 or ASTM D 6393-99 method.

[0157] The silicon-based active material can include silicon (Si), silicon oxide (SiOx (0 < x ≤ 2)), Si / C composite, or two or more of them. Specific examples of the silicon-based active material can include, but are not limited to, Si, SiO, SiO / C, or SiO2.

[0158] The Si / C composite (silicon-carbon composite) can include a structure in which silicon-based particles (e.g., silicon (Si), silicon oxide (SiOx (0 < x ≤ 2))) are physically dispersed or chemically bonded within a carbon-based carrier (carbon matrix). The carbon carrier can include amorphous carbon (carbon black, activated carbon, hard carbon), graphite, carbon nanotubes, carbon nanofibers, graphene, or two or more of them. In addition, the carbon carrier can be composed of amorphous carbon, graphite, carbon nanotubes, carbon nanofibers, graphene, or two or more of them.

[0159] According to one embodiment of the present disclosure, based on 100 parts by weight of the carbon carrier, the amount of the silicon-based particles can be 5 to 45 parts by weight, or 10 to 40 parts by weight, or 15 to 35 parts by weight, or 20 to 30 parts by weight, or 5 to 20 parts by weight, or 20 to 45 parts by weight. According to one embodiment of the present disclosure, the carbon carrier can include activated carbon, and the silicon-based particles can include pure Si particles. The pellet can also contain other types of negative electrode active materials in addition to the silicon-based active material.

[0160] When the amount of the silicon-based particles relative to the carbon carrier falls within the foregoing range, the lithium storage capacity can be increased while maintaining sufficient conductivity, and the carbon carrier can effectively mitigate the volume expansion of silicon, thereby suppressing cracking and peeling of the electrode structure, improving the mechanical stability of the electrode and the charge / discharge characteristics (life characteristics) of the secondary battery.

[0161] Other types of negative electrode active materials can include, for example, carbon-based active materials, such as non-graphitized carbon or graphite-based carbon (natural graphite, artificial graphite); metal composite oxides, such as 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 and Group 3 elements in the periodic table, halogens; 0≤x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; 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. According to one embodiment of this disclosure, the pellets may also contain at least one type of carbon-based active material, such as natural graphite or artificial graphite.

[0162] Linear conductive materials may include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon nanofibers, or both or more thereof.

[0163] Carbon nanotubes are allotropes of carbon, including graphite sheets and arrays thereof with cylindrical shapes having nanometer-sized diameters and characterized by sp2 bonding structures. A carbon nanotube array refers to a secondary structure formed by the arrangement or aggregation of carbon nanotubes. For example, a carbon nanotube array can include: bundle-type carbon nanotubes in the shape of bundles or ropes, wherein a plurality of carbon nanotubes are arranged side-by-side or aligned in a specific direction; or entangled carbon nanotubes in the shape of spheres or potatoes, wherein a plurality of carbon nanotubes are entangled in a non-specific direction.

[0164] In this context, multi-walled carbon nanotubes are hollow tubes composed of coaxial cylindrical surfaces formed by multiple hexagonal lattices of carbon atoms, while single-walled carbon nanotubes consist of only a single carbon cylindrical surface. The walls of these tubular structures are composed of hexagonal lattices similar to graphite sheets, with the intersections of the hexagonal lattices representing the locations of carbon atoms. Each carbon atom is adjacent to its neighboring carbon atom, and simultaneously, the two ends (end caps) of the tube are closed by polygonal structures composed of pentagonal carbon rings.

[0165] Linearly conductive materials, especially single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs), can have a BET specific surface area of ​​500 m². 2 / g or greater, or 500 m 2 / g to 5,000 m 2 / g, or 800 m 2 / g or greater, or 800 m 2 / g to 5,000 m 2 / g, or 900 m 2 / g to 2,000 m 2 / g. When using linear conductive materials with the aforementioned BET specific surface area, this can have a beneficial effect on forming a conductive network between silicon-based negative electrode active materials, thereby further improving the cycle characteristics of the secondary battery.

[0166] The length of linearly conductive materials can range from 0.5 μm to 100 μm. For example, the average length of single-walled carbon nanotubes can range from 2 μm to 100 μm, and the average length of multi-walled carbon nanotubes can range from 0.3 μm to 30 μm. The cross-sectional diameter of linearly conductive materials can range from 1 nm to 100 nm.

[0167] According to one embodiment of this disclosure, based on 100 parts by weight of granules, the linear conductive material may be included in amounts ranging from 0.2 parts by weight to 10 parts by weight, or 0.2 parts by weight to 5 parts by weight, or 0.3 parts by weight to 5 parts by weight, or 0.2 parts by weight to 3 parts by weight, or 0.2 parts by weight to 2 parts by weight, or 0.2 parts by weight to 1.6 parts by weight, or 0.3 parts by weight to 1.6 parts by weight. When the amount of linear conductive material falls within the aforementioned range, the linear conductive material can effectively form a conductive network between the silicon-based negative electrode active material in the granules, and further improve the cycle characteristics of the secondary battery containing the granules.

[0168] When linear conductive materials in solid form are directly added to produce granules, the linear conductive materials may form agglomerates and may not mix uniformly with silicon-based active materials and binders, thus failing to achieve the desired effect of adding the linear conductive materials. Therefore, granules can be produced by adding linear conductive materials in the form of a dispersion containing dispersants and dispersion media.

[0169] According to one embodiment of this disclosure, the linear conductive material dispersion may comprise a linear conductive material, an amine-containing polymer dispersant, and a dispersion medium.

[0170] Alternatively, according to one embodiment of this disclosure, the linear conductive material dispersion may comprise a linear conductive material, an amine-containing polymeric dispersant, a phenol-based compound containing two or more aromatic rings, and a dispersion medium.

[0171] When linear conductive materials are added in dispersion form as described above, despite the large specific surface area, the initial viscosity of the dispersion is low and viscosity changes over time are suppressed due to the good dispersion of linear conductive materials such as carbon nanotubes. Furthermore, when used to prepare slurries for granule production, the linear conductive materials can be uniformly distributed among the active materials, and the small spaces between the electrode active materials can be maintained constant during the drying of the slurry in granule production. Moreover, since the linear conductive materials can be uniformly distributed without forming agglomerates, sufficient conductive paths can be formed even in small quantities. The average diameter of the linear conductive materials can be measured by scanning electron microscopy (SEM) imaging of the linear conductive material powder, and the average length of the linear conductive materials can be measured by SEM of the linear conductive material dispersion. Furthermore, the linear conductive materials contained in the negative electrode active material layer can be measured using SEM. That is, when an electrode active material layer containing linear conductive material is dissolved and dispersed in a solvent such as a dispersion medium (e.g., water) and separated into a top layer and a bottom layer by centrifugation, the active material mainly settles in the bottom layer, while the linear conductive material exists in the top layer, and the average diameter and average length of the linear conductive material in the negative electrode active material layer can be measured by SEM observation using the supernatant.

[0172] Based on the total weight of the linear conductive material dispersion, the linear conductive material may be included in an amount of 0.01 wt% to 5 wt%, preferably 0.01 wt% to 3 wt%, more preferably 0.1 wt% to 2 wt%, and even more preferably 0.1 wt% to 1 wt%. When the amount of linear conductive material falls within the aforementioned range, this can have a beneficial effect on improving the viscosity of the dispersion and enhancing the cycle characteristics of the secondary battery.

[0173] Dispersants are used to prevent the agglomeration of linearly conductive materials and to achieve uniform distribution within the linearly conductive material dispersion. The linearly conductive material dispersion may contain both an amine-containing polymeric dispersant and a phenol-based compound containing two or more aromatic rings as dispersants. When two specific types of dispersants are used together, the viscosity of the linearly conductive material dispersion over time can be significantly reduced.

[0174] In one embodiment of this disclosure, based on 100 parts by weight of the linear conductive material, the dispersant may be included in an amount of 10 to 2000 parts by weight, preferably 50 to 1000 parts by weight, and more preferably 70 to 500 parts by weight. When the amount of dispersant falls within the aforementioned range, the viscosity of the linear conductive material dispersion can be appropriately maintained, and the deterioration of the secondary battery characteristics caused by the dispersant acting as an impurity can be prevented.

[0175] Amine-containing polymer dispersants may include, for example, at least one selected from: polyvinylpyrrolidone, polyacrylhydrazide, poly-N-vinyl-5-methyl Zolpidemone, N-alkyl polyimide, N-acetyl polyimide, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethyleneimine.

[0176] When using specific polymer dispersants containing amines in the polymer structure, this can have a more beneficial effect on improving viscosity and suppressing viscosity changes over time.

[0177] Phenolic compounds containing two or more aromatic rings can reduce the viscosity of linear conductive material dispersions, especially aqueous linear conductive material dispersions, and significantly suppress the increase in viscosity over time due to the bulk structure generated by the two or more aromatic rings and the influence of the hydroxyl groups contained in the phenolic group.

[0178] The phenol-based compound may contain at least one structure selected from phenol, catechol, gallol, and naphthol in at least one of its aromatic rings, and specifically, may contain at least one structure selected from catechol and gallol in at least one of its aromatic rings. The phenol structure has one hydroxyl group bonded to the benzene ring, the catechol structure has two hydroxyl groups bonded to the benzene ring, the gallol structure has three hydroxyl groups bonded to the benzene ring, and the naphthol structure has one hydroxyl group bonded to naphthalene.

[0179] When a phenol-based compound containing two or more aromatic rings includes the above-described structure, it may be possible to achieve a proper balance between the interaction between the aromatic rings and the linearly conductive material in the linearly conductive material dispersion and the interaction between the -OH group of the phenol-based compound and the polymer dispersant via hydrogen bonding, thereby reducing the viscosity of the linearly conductive material dispersion and suppressing the increase in viscosity over time.

[0180] Specific examples of phenol-based compounds containing two or more aromatic rings may include at least one selected from baicalin, luteolin, taxol, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, zeaxanthin, leucine, and tannic acid, and preferably tannic acid, quercetin, epigallocatechin gallate, or combinations thereof.

[0181] In one embodiment of this disclosure, the aromatic rings contained in a phenol-based compound containing two or more aromatic rings may be a single unfused aromatic ring or a structure in which two aromatic rings are fused together, and may not include a structure in which three or more aromatic rings are fused together.

[0182] That is, the range of phenol-based compounds containing two or more aromatic rings can be excluded from structures in which three or more aromatic rings are fused together within the molecular structure.

[0183] When phenol-based compounds containing two or more aromatic rings include a structure in which three or more aromatic rings are fused together within their molecular structure, in a linear conductive material dispersion, this fused structure may form a strong binding strength with the linear conductive material at or above the optimal level, causing aggregation between the linear conductive materials. Therefore, this may not be suitable for improving the dispersion of the linear conductive material. Furthermore, it may lead to an imbalance between the interaction between the aromatic rings and the linear conductive material in the dispersion and the interaction through hydrogen bonds between the -OH group of the phenol-based compound and the polymer dispersant, thus failing to adequately reduce the viscosity of the linear conductive material dispersion and suppress the increase in viscosity over time.

[0184] Furthermore, based on 100 parts by weight of the amine-containing polymer dispersant, the phenol-based compound may be included in an amount of 1 to 100 parts by weight, or 5 to 100 parts by weight, or 10 to 100 parts by weight. When the amount of the amine-containing polymer dispersant and the amount of the phenol-based compound fall within the aforementioned ranges, this can have a more beneficial effect on reducing the viscosity of the dispersion and enhancing storage stability.

[0185] The dispersion medium (solvent) is a liquid medium used to disperse linear conductive materials, polymer dispersants, and phenol-based compounds containing two or more aromatic rings, and is used to provide a dispersion of linear conductive materials by pre-dispersion to prevent agglomeration that may occur when the linear conductive materials are directly mixed with negative electrode active materials to prepare slurries for granules.

[0186] The dispersion medium can include any liquid medium within the technical field of this disclosure for dissolving or dispersing linearly conductive materials, polymeric dispersants, and phenol-based compounds containing two or more aromatic rings at predetermined levels or above. The dispersion medium can include a water-based solvent, such as water.

[0187] The linear conductive material dispersion of the present disclosure as described above can be prepared by a preparation method comprising the following steps: (1) mixing a linear conductive material (e.g., carbon nanotubes), a polymer dispersant, a phenol-based compound containing two or more aromatic rings and a dispersion medium to prepare a mixture; and (2) grinding the mixture.

[0188] In step (1), a linear conductive material, a polymer dispersant, a phenol-based compound containing two or more aromatic rings, and a dispersion medium are mixed to prepare a mixture.

[0189] The steps for preparing the mixture can be carried out at temperatures in which the properties of the mixture (including its viscosity) will not change due to the evaporation of the dispersion medium. For example, the steps for preparing the mixture can be carried out at 50°C or lower, and more specifically at temperatures between 5°C and 50°C.

[0190] In step (2), the mixture is subjected to dispersion treatment to prepare a linear conductive material dispersion.

[0191] Grinding can be carried out, for example, by using a ball mill, bead mill, disc mill, basket mill or high-pressure homogenizer, and more specifically, by using a grinding method using a disc mill or high-pressure homogenizer.

[0192] When grinding with a disc mill, the bead size can be appropriately determined according to the type and amount of linear conductive material and the type of dispersant. Specifically, the bead diameter can be from 0.1 mm to 5 mm, and more specifically from 0.5 mm to 4 mm. Furthermore, the bead milling process can be carried out at speeds from 2,000 rpm to 10,000 rpm, and more specifically from 5,000 rpm to 9,000 rpm.

[0193] Grinding via a high-pressure homogenizer is performed, for example, by applying pressure to the mixture using a plunger pump of the high-pressure homogenizer and forcing it through a narrow opening in a homogenizing valve to generate cavitation, shearing, impact, and bursting forces.

[0194] The grinding process can be carried out according to the dispersion of the linear conductive material dispersion, and specifically, it can be carried out for 30 minutes to 120 minutes, and more specifically, for 60 minutes to 90 minutes.

[0195] In one embodiment of this disclosure, based on 100 parts by weight of granules, the amount of binder for the granules can be 0.5 to 10 parts by weight, or 0.5 to 8 parts by weight, or 0.5 to 7 parts by weight, or 0.5 to 6 parts by weight, or 0.5 to 5 parts by weight, or 0.5 to 4 parts by weight, or 0.5 to 2 parts by weight, or 1 to 8 parts by weight, or 1 to 7 parts by weight, or 1 to 6 parts by weight, or 1 to 5 parts by weight, or 1 to 4 parts by weight, or 1 to 2 parts by weight. When the amount of binder for the granules falls within the aforementioned range, the binder for the granules functions to connect and hold the silicon-based active material and the linear conductive material together within the granules, thereby minimizing the effect of volume expansion of the silicon-based active material and preventing the increase in resistance caused by the blockage of lithium-ion movement when the granules are used in the negative electrode of a secondary battery, thus achieving improved cycle characteristics of the secondary battery.

[0196] In one embodiment of this disclosure, the binder for granules may comprise at least one of a linear binder and a dot-type binder.

[0197] Linear binders act as binders in compositions containing active materials and can refer to polymer compounds having a structure in which the polymer chains are predominantly linearly arranged without branches, or having a limited branching or network structure by containing crosslinkable monomers or free radical polymerizable monomers. Linear binders are typically dissolved in a solvent, and the polymer exists in a homogeneous solution state without particulate form. Linear binders can be uniformly mixed with the active and conductive materials in the slurry upon dissolution, and after electrode fabrication, they can stably bond the active and conductive materials to the current collector by forming a film or adhesive layer through interactions between the polymer chains during drying and heat treatment.

[0198] Dot-type binders refer to binders that, when dispersed in a solvent, do not completely dissolve within it but instead maintain a dot-like morphology with a size of approximately several hundred nanometers. Due to this morphology, such binders exhibit excellent dispersibility, effectively coating or surrounding the surface of active material particles, and possess relatively low viscosity relative to solids content, making it easy to control the binder content relative to the active material. When dot-type binders are used in granules together with silicon-based active materials and linearly conductive materials, they can adequately cover the surface of the active material while maintaining the dispersion of the linearly conductive material.

[0199] Dot-type binders are not limited to a specific shape, but particulate phases are preferred because they have good binding ability and can suppress the decrease or degradation of electrode capacitance due to repeated charging / discharging. Examples of particulate phase dot-type binders can include dispersions of dispersible binder particles in a solvent such as water, like latex, and powder phases obtained by drying the dispersion.

[0200] Meanwhile, binders such as polytetrafluoroethylene (PTFE) have a linear polymer chain structure but do not dissolve in solvents and remain in a solid powder state. Such binders are typically used in dry processes and cannot be processed into slurries using solvents or dispersion media. PTFE binders can exist in electrode compositions as a fibrous phase or a combination of particulate and fibrous phases, and function to bond active and conductive materials to the current collector through hot pressing or physical entanglement. Therefore, in contrast to typical slurry-based linear binders or dot-type binders, PTFE binders can have a bonding mechanism based on structural entanglement and compressive forces rather than solubility or dispersibility.

[0201] Linear adhesives may include acrylate-based polymers.

[0202] Examples of acrylate-based polymers may include polymers containing monomer units derived from acrylates and / or methacrylates. The ratio of monomer units derived from acrylates and / or methacrylates in acrylate-based polymers is typically 40% by weight or more, preferably 50% by weight or more, and more preferably 60% by weight or more. Specific examples of acrylate-based polymers may include polymers based on crosslinked acrylates, such as acrylamide-acrylate copolymers, 2-ethylhexyl acrylate-methacrylic acid-acrylonitrile-ethylene glycol dimethacrylate copolymers, 2-ethylhexyl acrylate-methacrylic acid-methacrylonitrile-diethylene glycol dimethacrylate copolymers, 2-ethylhexyl acrylate-styrene-methacrylic acid-ethylene glycol dimethacrylate copolymers, butyl acrylate-acrylonitrile-diethylene glycol dimethacrylate copolymers, or butyl acrylate-acrylic acid-trimethylolpropane trimethacrylate copolymers; copolymers of ethylene and (meth)acrylates, such as ethylene-methyl acrylate copolymers, ethylene-methyl methacrylate copolymers, ethylene-ethyl acrylate copolymers, or ethylene-ethyl methacrylate copolymers; or graft polymers having radically polymerizable monomers grafted onto copolymers of ethylene and (meth)acrylates. The radically polymerizable monomers used in the graft polymers may include, for example, methyl methacrylate, acrylonitrile, or methacrylic acid.

[0203] According to one embodiment of this disclosure, the acrylate-based polymer may include an acrylamide-acrylate copolymer.

[0204] Dot-type adhesives may include diene-based polymers, styrene-based polymers, or both or more thereof.

[0205] Examples of diene-based polymers may include polymers containing monomer units derived from conjugated dienes such as butadiene or isoprene, and their hydrogenated products. The ratio of conjugated diene-derived monomer units in diene-based polymers is typically 40% by weight or more, preferably 50% by weight or more, and more preferably 60% by weight or more. Specifically, diene-based polymers may include conjugated diene homopolymers, such as polybutadiene or polyisoprene; aromatic vinyl-conjugated diene copolymers, such as carboxyl-modified styrene-butadiene copolymers (SBR); cyanided vinyl-conjugated diene copolymers, such as acrylonitrile-butadiene copolymers (NBR); hydrogenated SBRs or hydrogenated NBRs.

[0206] Styrene-based polymers may include polymers having repeating units derived from styrene monomers, such as styrene homopolymers (polystyrene) or styrene copolymers. Examples of styrene copolymers may include block copolymers, such as styrene-ethylene-butadiene copolymers, styrene-butadiene-propylene copolymers, styrene-isoprene copolymers, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymers, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymers, styrene-butadiene block copolymers, styrene-butadiene-styrene block copolymers, styrene-ethylene-butene-styrene block copolymers, styrene-isoprene block copolymers, or styrene-ethylene-propylene-styrene block copolymers.

[0207] Furthermore, in one embodiment of this disclosure, the binder for granules may comprise a linear binder and a dot-type binder. In one embodiment of this disclosure, the binder may comprise an acrylate-based polymer (e.g., acrylamide-acrylate copolymer or acrylamide-acrylic acid-acrylonitrile copolymer) as a linear binder and a diene-based polymer or a styrene-based polymer (e.g., styrene-butadiene copolymer (SBR)) as a dot-type binder.

[0208] When the binder for granules contains both linear and dot-type binders, it can provide a synergistic effect in improving the mechanical, electrical, and chemical stability of the electrodes and secondary batteries, which can be advantageous in secondary battery designs that require high energy density, long life, and high reliability.

[0209] Because linear binders have long and continuous molecular structures, they can increase the bonding strength between the active material and the current collector in the electrode and be effectively distributed during electrode manufacturing and mechanical stress that may occur during the operation of the secondary battery, thereby preventing delamination or cracking in the electrode. Because point binders have three-dimensional bonding structures, they can locally improve the bonding strength and absorb the stress caused by volume expansion during charging / discharging, thereby preventing physical damage to the electrode caused by repeated charging / discharging. Therefore, the combined use of linear binders and point binders can improve the mechanical stability of the electrode and maintain stability after repeated charge and discharge cycles, thereby extending battery life.

[0210] Furthermore, linear binders can help achieve uniform distribution of active materials within the electrode, thereby improving the electrode's conductivity and electrical contact. Dot binders can form strong bonds at small contact points, thus optimizing the contact between the active material and the electrolyte, which helps reduce ion movement resistance. Therefore, the combination of linear and dot binders can more effectively form ion and electron movement paths within the electrode, thereby improving energy density and output characteristics.

[0211] According to one embodiment of this disclosure, when the binder for the granules comprises a linear binder and a dot-type binder, the weight ratio of the linear binder to the dot-type binder can be 70:30 to 30:70, or 60:40 to 40:60, or 70:50 to 50:70. When the weight ratio of the linear binder to the dot-type binder falls within the aforementioned ranges, it may be possible to maximize the synergistic effect of using the combined linear binder and the dot-type binder, thereby improving the mechanical stability of the electrode and increasing the battery life after repeated charge and discharge cycles.

[0212] According to one embodiment of this disclosure, the granules may comprise 80 to 98 parts by weight of a silicon-based active material, 0.5 to 10 parts by weight of a linear conductive material, and 0.5 to 10 parts by weight of a granule binder. Alternatively, the granules may comprise 85 to 95 parts by weight of a silicon-based active material, 0.5 to 5 parts by weight of a linear conductive material, and 0.5 to 8 parts by weight, or 0.5 to 7 parts by weight, or 0.5 to 6 parts by weight, or 0.5 to 5 parts by weight, or 0.5 to 4 parts by weight, or 1 to 8 parts by weight, or 1 to 7 parts by weight, or 1 to 6 parts by weight, or 1 to 5 parts by weight, or 1 to 4 parts by weight of a granule binder.

[0213] When the amounts of silicon-based active material, linear conductive material, and granular binder fall within the aforementioned range, the cohesive strength between the active materials in the negative electrode can be increased, and the dispersion of the linear conductive material and the granular binder can be significantly improved. Therefore, the battery performance, such as lifespan characteristics, of the electrochemical device including the negative electrode can be significantly improved.

[0214] In addition to silicon-based active materials, the granules can also contain other types of negative electrode active materials.

[0215] Examples of other types of anode active materials can include carbon-based active materials, such as non-graphitized carbon, graphite-based carbon (natural graphite, artificial graphite); and metal composite oxides, such as Li. x Fe2O3 (0≤x≤1), Li x WO2 (0≤x≤1), Sn x Me1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2 and Group 3 elements in the periodic table, halogens; 0≤x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; 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. According to one embodiment of this disclosure, the pellets may also contain at least one type of carbon-based active material selected from natural graphite or artificial graphite.

[0216] According to one embodiment of this disclosure, the granules may comprise 30 to 70 parts by weight of a silicon-based active material, 30 to 70 parts by weight of other types of negative electrode active material, 0.5 to 10 parts by weight of a linear conductive material, and 0.5 to 10 parts by weight of a binder.

[0217] Alternatively, the granules may contain 35 to 70 parts by weight of silicon-based active material, 35 to 70 parts by weight of other types of negative electrode active material, 0.5 to 5 parts by weight of linear conductive material, and 0.5 to 5 parts by weight of binder.

[0218] In one embodiment of this disclosure, based on the total weight of the granules, the silicon-based active material may be included in an amount of 75% by weight or more, or 90% by weight or more, and the binder for the granules may be included in an amount of 20% by weight or less, or 10% by weight or less.

[0219] Based on 100% by weight of granules, the conductive material for the granules may be included in an amount of 0.1% to 20% by weight, and preferably 0.1% to 10% by weight. For example, the conductive material may be included in the granules in an amount of about 0.1% to 5% by weight.

[0220] According to one embodiment of this disclosure, the amount of silicon-based active material in the granules can be from 75% to 98% by weight. Within the aforementioned range, the amount of binder for the granules can be from 0.5% to 10% by weight, and the amount of conductive material for the granules can be from 0.5% to 5% by weight. According to another embodiment, the amount of silicon-based active material can be from 90% to 98% by weight, the amount of binder for the granules can be from 0.5% to 5% by weight, and the amount of electrode conductive material can be from 0.5% to 5% by weight.

[0221] In one embodiment of this disclosure, the pellets may include a surface portion and a central portion which is the remaining area excluding the surface portion. Specifically, the pellet center may be defined as the intersection of the long axis (the longest part of the pellet) and the short axis (the shortest part of the pellet), the surface portion may be defined as the area obtained by connecting positions downward toward the pellet center and away from the various positions on the pellet surface at a predetermined distance, and the central portion may be defined as the remaining area excluding the surface portion.

[0222] At the same time or independently of this, based on the total weight of the granules 100% by weight, the amount of granule binder contained in the surface portion of the granules (by weight %) (B s / G t (B) greater than the amount of binder (by weight) of the granules contained in the central portion (B) c / G t Here, B c B represents the weight of the binder used to bind the granules contained in the central portion. s This indicates the weight of the granular binder contained in the surface portion, and G. t This indicates the total weight of the granular material.

[0223] At the same time or independently of this, based on the total volume of the granules 100% by volume, the amount of granules containing binder in the surface portion of the granules (by volume) (B) s / G t (B) is greater than the amount (by volume) of binder used for the granules contained in the central portion. c / G t Here, B c B represents the volume of the granular binder contained in the central portion. s This indicates the volume of the granular binder contained in the surface portion, and G. t This indicates the total volume of the granular material.

[0224] In one embodiment of this disclosure, the surface portion may refer to a surface area extending inward from the particle surface to a maximum of 30% of the distance (center distance) from various locations on the surface portion to the particle center. In another embodiment of this disclosure, the surface portion may refer to a surface area extending from the particle surface to a maximum of 30%, 20%, 15%, 10%, or 5% of the center distance. Preferably, the surface portion may refer to a surface area extending from the particle surface to a maximum of 20% of the center distance.

[0225] As described above, in this disclosure, the center of the pellet can be defined as the intersection of the major axis (the longest part of the pellet) and the minor axis (the shortest part of the pellet).

[0226] Furthermore, in one embodiment of this disclosure, the surface portion may refer to the area extending 70% or more of the center-to-center distance from the center of the pellet to the pellet surface. In another embodiment of this disclosure, the surface portion may, for example, refer to the area extending 80% or more, 85% or more, 90% or more, or 95% or more of the center-to-center distance to the pellet surface.

[0227] In one embodiment of this disclosure, the center of the pellet may refer to the location at half the longest diameter of the pellet. In this disclosure, the center distance may refer to the distance from the center of the pellet to various locations on the surface of the pellet. In one embodiment of this disclosure, the surface portion and the center portion may be distinguished based on points equidistant from each pellet surface along each center distance, and specifically, may be distinguished based on points at most 30%, 20%, 10%, 5%, or 1% of the corresponding center distance from the surface.

[0228] In one embodiment of this disclosure, the amount of binder for the pellets in the region from 90% or more of the distance from the pellet center to the pellet surface can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% of the total weight of the pellets in that respective region.

[0229] In another embodiment of this disclosure, the amount of binder for the pellets in the region from 95% or more of the distance from the pellet center to the pellet surface can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% of the total weight of the pellets in that respective region.

[0230] In another embodiment of this disclosure, the amount of binder for the pellets in the region from 99% or more of the distance from the pellet center to the pellet surface can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% of the total weight of the pellets in that respective region.

[0231] In one embodiment of this disclosure, the amount of binder for the pellets in the region from 90% or more of the distance from the pellet center to the pellet surface can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% or more of the total volume of the pellets in that respective region.

[0232] In another embodiment of this disclosure, the amount of binder for the pellets in the region from 95% or more of the distance from the pellet center to the pellet surface can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% or more of the total volume of the pellets in that respective region.

[0233] In another embodiment of this disclosure, the amount of binder for the pellets in the region from 99% or more of the distance from the pellet center to the pellet surface can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% or more of the total volume of the pellets in that respective region.

[0234] In one embodiment of this disclosure, the amount of binder for the pellets in a pellet surface region of up to 10% of the distance from the pellet surface to the center can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% of the total weight of the pellets in that corresponding region.

[0235] In another embodiment of this disclosure, the amount of binder for the pellets in a pellet surface region of up to 5% of the distance from the pellet surface to the center can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% of the total weight of the pellets in that corresponding region.

[0236] In another embodiment of this disclosure, the amount of binder for the granules in the region from 1% or more of the center distance from the surface of the granules to the surface of the granules can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% of the total weight of the granules in that respective region.

[0237] In one embodiment of this disclosure, the amount of binder for the pellets in a pellet surface region of up to 10% of the distance from the pellet surface to the center can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% of the total weight of the pellets in that corresponding region.

[0238] In another embodiment of this disclosure, the amount of binder for the pellets in a pellet surface region of up to 5% of the distance from the pellet surface to the center can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% of the total weight of the pellets in that corresponding region.

[0239] In another embodiment of this disclosure, the amount of binder for the granules in the region from 1% or more of the center distance from the surface of the granules to the surface of the granules can be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, based on 100% by weight of the total granules in that respective region.

[0240] According to one embodiment of this disclosure, as determined, the surface portion region may have a larger amount of granular binder up to a predetermined depth in the direction from the surface to the particle center, and the central portion (core) surrounded by the surface portion, excluding the surface portion, may have a lower granular binder distribution than the surface portion.

[0241] The pellets can be described in more detail as follows: a central portion comprising a plurality of silicon-based active materials; and a surface portion located entirely or partially outside the central portion and comprising a pellet binder for bonding the silicon-based active materials. Specifically, in the central portion of the pellet, the plurality of silicon-based active materials can be in surface contact, line contact, point contact, or two or more of these contact methods to form an agglomerate, and in the surface portion of the pellet, the pellet binder can be located entirely or partially outside the agglomerate to bond and hold the plurality of silicon-based active materials in the central portion of the pellet together.

[0242] According to one embodiment of this disclosure, a small amount of granular binder may also be included in the central portion to connect and hold together the plurality of silicon-based active materials in the central portion. However, as mentioned above, the amount of granular binder in the surface portion is preferably present in a larger ratio than the amount of granular binder in the central portion.

[0243] In one embodiment of this disclosure, the aspect ratio of the pellets can be 0.5 to 0.94, or 0.7 to 0.93, or 0.75 to 0.91. The aspect ratio can refer to the ratio of the major axis length to the minor axis length of the pellets. In another embodiment of this disclosure, the average aspect ratio of the pellets can be 0.5 to 0.94, or 0.7 to 0.93, or 0.75 to 0.91, and in this case, the average aspect ratio can refer to the ratio of the average major axis length to the average minor axis length of the pellets. In this case, the average minor axis length can refer to the average length of the pellets in the axial direction with the shortest length, and the average major axis length can refer to the average length of the pellets in the axial direction with the longest length. When the aspect ratio or average aspect ratio of the pellets falls within the aforementioned ranges, it is advantageous in terms of sufficient flowability suitable for the process.

[0244] According to one embodiment of this disclosure, the granules may further comprise a dispersant. The dispersant may include carboxymethyl cellulose (CMC). When a dispersant is also included in the composition comprising a silicon-based active material, a linearly conductive material, a granule binder, and an aqueous dispersion medium during the granule production steps described below, the dispersant helps to uniformly distribute the solid components, such as the silicon-based active material, the linearly conductive material, and the granule binder, within the composition, thereby improving the stability of the composition and controlling its viscosity and flowability. The quality and performance of the granules produced by this composition can be improved.

[0245] In one embodiment of this disclosure, the porosity of the negative electrode active material layer can be from 20% to 40% by volume, and when the porosity falls within the aforementioned range, the wettability, shape stability and ion conductivity of the electrolyte can be further improved.

[0246] Meanwhile, according to one embodiment of this disclosure, the thickness of the negative electrode active material layer can be, for example, from 30 μm to 300 μm, but is not limited thereto.

[0247] According to another embodiment of this disclosure, the negative electrode active material layer can be a single layer comprising a unit active material layer.

[0248] According to one embodiment of this disclosure, the negative electrode active material layer may have a multilayer structure comprising two or more unit active material layers stacked together. In this case, the electrode materials, such as electrode active materials and granular binders contained in each unit active material layer may be the same or different in each layer, but are not limited thereto.

[0249] Carbon-based active materials can include carbon, such as non-graphitized carbon, graphite-based carbon, such as natural graphite or artificial graphite.

[0250] In one embodiment of this disclosure, the binder for the negative electrode layer may include at least one of the above-mentioned binders for granules. Specifically, the binder for the negative electrode layer may include styrene-butadiene copolymer (SBR).

[0251] In addition, the conductive material for the negative electrode layer may include any conductive material commonly used in electrodes, namely plate-shaped conductive material, dot-shaped conductive material, linear conductive material or fiber conductive material, and may include, for example, carbon black, denca black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, or two or more thereof, but is not limited thereto.

[0252] When the amounts of granules, carbon-based active materials, conductive materials for the negative electrode layer, and binders for the negative electrode layer fall within the aforementioned ranges, it can be more advantageous to simultaneously provide optimal energy density and sufficient lifetime characteristics.

[0253] According to one embodiment of this disclosure, the total weight parts of the linear conductive material and the binder for the granules can be greater than the total weight parts of the conductive material and the binder for the negative electrode layer. Specifically, the total weight parts of the linear conductive material and the binder for the granules can be 1.1 to 10 times, or 1.5 to 5 times, the total weight parts of the conductive material and the binder for the negative electrode layer. In this case, it may be more advantageous when the total weight parts of the linear conductive material and the binder for the granules are greater than the total weight parts of the conductive material and the binder for the negative electrode layer, because a sufficient amount of high-modulus binder for the granules can be located on the surface of the silicon-based active material.

[0254] In some cases, the negative electrode active material layer may also contain fillers to suppress its expansion. The fillers are not limited to a specific type and may include any fibrous material that will not cause any chemical changes in the corresponding battery, such as olefin-based polymers like polyethylene or polypropylene; or fibrous materials like glass fiber or carbon fiber.

[0255] The current collector is not limited to a specific type and can include any material with high conductivity that will not cause any chemical changes in the battery, such as stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, or silver. Furthermore, the current collector can have a microtextured surface to improve adhesion strength to the electrode active material and can be presented in various types such as films, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0256] In one embodiment of this disclosure, the current collector may have a base layer, either wholly or partially.

[0257] The underlayment may include an underlayment adhesive and an underlayment conductive material, and the total amount of the granular adhesive and conductive material in the underlayment may be 90% by weight or more.

[0258] An electrode according to one embodiment of the present disclosure includes a negative electrode active material layer comprising granules, and in this case, when the underlayer comprises granules, a binder, and a conductive material such that the sum of their amounts is 90% by weight or more, it may be possible to ensure the stability of the underlayer over time, thereby achieving good properties such as adhesive strength and lifespan characteristics, but the present disclosure is not limited thereto.

[0259] According to one embodiment of this disclosure, the underlayment includes an underlayment adhesive and an underlayment conductive material, and may also include a dispersant.

[0260] According to one embodiment of this disclosure, the underlay may include an underlay adhesive and an underlay conductive material, but may substantially not include a dispersant.

[0261] According to one embodiment of this disclosure, the binder for the underlayment can include any known granular binder for the underlayment, without limitation.

[0262] According to another embodiment of this disclosure, the adhesive for the underlayment may preferably comprise any type of polymer that ensures the stability of the underlayment over time. Specifically, the glass transition temperature (Tg) of the adhesive for the underlayment may be 45°C or lower.

[0263] According to another embodiment of this disclosure, the adhesive for the underlayment may include, for example, styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile rubber (NBR), styrene-butadiene-styrene block polymer (SBS), styrene-vinyl butadiene block polymer (SEB), styrene-(styrene-butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), ethylene-propylene-diene terpolymer (EPDM), poly(ethylene-copoly-propylene-copoly-5-methylene-2-norbornene), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-copoly-hexafluoropropylene, polyvinylidene fluoride-copoly-trichloroethylene, polymethyl methacrylate, ethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene, polypropylene, polyethylene-copolyvinyl acetate, polyethylene oxide, polypropylene oxide, polyarylate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, or both or more thereof. Specifically, the binder for the granules may include styrene-butadiene rubber (SBR), nitrile rubber (NBR), polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, or both or more thereof.

[0264] According to another embodiment of this disclosure, the adhesive for the underlayment may include any one or a mixture thereof selected from the above-described types of adhesives having the above-described glass transition temperature values.

[0265] According to another embodiment of this disclosure, the adhesive for the underlayment may include styrene-butadiene rubber (SBR) with a glass transition temperature (Tg) of -40°C to 45°C, nitrile-butadiene rubber (NBR) with a glass transition temperature (Tg) of -40°C to 45°C, or a mixture thereof.

[0266] According to one embodiment of this disclosure, the conductive material used for the underlayer can have a 30 μm... 2 / g to 1,400 m 2 The specific surface area per g and the spherical shape. In this case, the primary particle size of the conductive material with a spherical shape can be, for example, 10 nm to 100 nm, and specifically 15 nm to 70 nm, but is not limited thereto.

[0267] According to another embodiment of this disclosure, the conductive material used for the underlayment can have a specific surface area of ​​10 μm². 2 / g to 400 m 2 / g tubular (tube-shaped) shape. In this case, in a conductive material having a tubular shape, the diameter of the cross section in the direction perpendicular to the length direction can be from 0.1 nm to 3 nm, and specifically from 0.3 nm to 1.5 nm, but is not limited thereto.

[0268] The conductive material used for the underlayer is not limited to a specific type and can include any material that is conductive without causing any chemical change in the corresponding battery, and may include, for example, graphite, such as natural or artificial graphite; carbon black-based carbon compounds, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, or thermal cracking black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbon compounds; metal powders, such as aluminum or nickel powder; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive materials, such as polyphenylene derivatives. Specifically, in order to uniformly mix the conductive material and improve conductivity, the conductive material may include activated carbon, graphite, carbon black, carbon nanotubes, or mixtures thereof, and more specifically activated carbon.

[0269] According to one embodiment of this disclosure, the underlayer may include the above-described components and have a thickness of 300 nm to 1.5 μm, and specifically 700 nm to 1.3 μm, but is not limited thereto.

[0270] According to one aspect of this disclosure, a method for manufacturing a negative electrode for an electrochemical device according to one embodiment of this disclosure is provided, the method comprising the step of forming a negative electrode active material layer using granules comprising a silicon-based active material, a linearly conductive material, and a granule binder.

[0271] According to one embodiment of this disclosure, the negative electrode comprising granules can be an electrode obtained by various manufacturing methods such as wet or dry processes.

[0272] The wet process may include the following steps: mixing the granules with a binder for the negative electrode layer and optionally a conductive material for the negative electrode layer in a dispersion medium, applying the mixture to a current collector, and drying.

[0273] The dry process may include the following steps: dry mixing granules with a fiberizable binder, or dry mixing granules with a fiberizable binder and a negative electrode layer using a conductive material to prepare a mixture; kneading the prepared mixture to produce a mixture block, and grinding the mixture block to obtain electrode mixture granules; feeding the electrode mixture granules between a plurality of rollers for calendering to form an electrode film; and laminating the electrode film onto a metal current collector.

[0274] In the step of preparing the mixture, in addition to the granules and the fiberizable binder, a conductive material for the negative electrode layer may also be included. In this case, the step of preparing the mixture can be carried out without a dispersion medium, or it can be carried out with the addition of at least one additive from the following: a very small amount of dispersion medium, lubricant, or processing aid. Here, the additive may include any substance commonly used in electrode processing. Here, "very small amount" means an amount that, when used in the step of preparing the mixture, is too little to significantly affect the appearance, flowability, or viscosity of the mixture, and may be, for example, less than 0.1 wt% based on 100% of the total weight of the mixture.

[0275] In this case, kneading conditions may include a range of 70°C to 200°C and pressures equal to or higher than atmospheric pressure.

[0276] Mixing can be performed in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, and specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute to ensure uniformity.

[0277] Fiberizable binders are not limited to a specific type and can include any type of binder that can be microfibriled through the step of producing the mixture pellets. Fluorinated binders may be preferred. Microfibrilation refers to a process that breaks the polymer into smaller fragments and can be performed, for example, using mechanical shear forces. Specific examples of fiberizable binders may include fluoropolymers, and specifically, may include polytetrafluoroethylene (PTFE) alone, or, in addition to PTFE, at least one of a copolymer based on polyvinylidene fluoride (PVdF) (e.g., PVdF or polyvinylidene fluoride-copolymer-hexafluoropropylene (PVdF-HFP)).

[0278] Kneading is not limited to a specific method. In one specific embodiment of this disclosure, kneading can be performed, for example, by a kneading machine.

[0279] Specifically, the kneading can be controlled at a speed of 10 rpm to 100 rpm. For example, the kneading can be controlled at a speed of 20 rpm or greater or 70 rpm or less within the aforementioned range. The kneading can be performed for 1 minute to 30 minutes. For example, the kneading can be performed for 3 minutes to 10 minutes at a speed of 40 rpm to 70 rpm within the aforementioned range. Simultaneously, the kneading can be controlled at a shear rate in the range of 10 / sec to 500 / sec. In one specific embodiment of this disclosure, the kneading can be performed for 1 minute to 30 minutes, and the shear rate can be controlled in the range of 30 / sec to 100 / sec.

[0280] Furthermore, the kneading step can be carried out at high temperatures and pressures equal to or higher than atmospheric pressure, and more specifically, pressures higher than atmospheric pressure.

[0281] More specifically, kneading can be performed on the mixture in the range of 70°C to 200°C, and more specifically, 90°C to 150°C.

[0282] Furthermore, kneading can be performed at pressures equal to or higher than atmospheric pressure, specifically 1 to 100 atmospheres, and more specifically 10 to 80 atmospheres. When the pressure falls within the aforementioned range, it may be possible to prevent fiber breakage or excessively high mixture density due to the application of excessively high shear forces and pressures. That is, according to this disclosure, the desired effects of this disclosure can be achieved by replacing high-shear mixing with low-shear mixing under conditions of high temperature and pressure equal to or higher than atmospheric pressure.

[0283] The grinding step can be performed using a mixer or a grinder, but is not limited to this, and specifically, the grinding step can be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, and specifically at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 2 minutes.

[0284] When the grinding speed and time fall within the aforementioned range, sufficient grinding can be performed to form granules of the appropriate size for film formation, and to prevent the mixture from being ground into a large number of fine particles. If necessary, a sieving process can be performed to filter out particles smaller or larger than a predetermined size.

[0285] Calendering can be carried out, for example, by rollers facing each other, and in this case, the roller temperature can be from 50°C to 200°C, and the roller speed ratio can be controlled in the range of 1.0 to 2.0.

[0286] In addition, dry electrodes using granules can include dry electrodes manufactured by applying the granules alone directly to the current collector or by applying the granules in combination with the negative electrode layer using a binder and / or the negative electrode layer using a conductive material to the current collector, followed by pressing / rolling.

[0287] According to one embodiment of the present disclosure, a method for manufacturing an electrode according to one embodiment of the present disclosure can be provided, the method comprising the steps of: drying a composition comprising a silicon-based active material, a linear conductive material, a granule binder and an aqueous dispersion medium by spray drying to produce granules;

[0288] Electrode slurry is prepared by mixing granules with carbon-based active materials, conductive materials for the negative electrode layer, binders for the negative electrode layer, and an aqueous dispersion medium (water); and

[0289] The electrode slurry is applied to at least one surface of the current collector and then dried and pressed / rolled.

[0290] First, a composition comprising a silicon-based active material, a linear conductive material, a granule binder, and an aqueous dispersion medium is dried by spray drying to produce granules.

[0291] A composition is obtained by dispersing or dissolving a silicon-based active material, a linear conductive material, a granular binder, and optional additives in a dispersion medium (a solvent for the granular binder).

[0292] The dispersion medium most suitable for obtaining the slurry is water, but may include organic solvents. Organic solvents may include, for example, alkyl alcohols, such as methanol, ethanol, or propanol; alkyl ketones, such as acetone or methyl ethyl ketone; ethers, such as tetrahydrofuran, dimethyl ethyl ketone, etc. Alkane or diethylene glycol dimethyl ether; amides, such as diethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter referred to as NMP), or dimethylimidazolinone; or sulfur-based solvents, such as dimethyl sulfoxide or sulfolane, but alcohols are preferred. The drying rate in fluidized bed granulation can be increased when using organic solvents with boiling points below water. Furthermore, since the dispersion or dissolution of the electrode granules with the binder can be varied, the viscosity or flowability of the slurry can be adjusted according to the amount or type of dispersion medium to improve production efficiency.

[0293] The dispersion medium used to prepare the slurry may be included in an amount such that the solid concentration of the composition is typically in the range of 1% to 50% by weight, or 5% to 50% by weight, or 10% to 30% by weight.

[0294] The method or sequence of dispersing or dissolving silicon-based active materials, linearly conductive materials, and granules in a dispersion medium using a binder is not limited to a specific method or sequence, and may include, for example, adding silicon-based active materials, linearly conductive materials, and granules to the dispersion medium using a binder and mixing them; or dissolving or dispersing granules in the dispersion medium using a binder, and finally adding silicon-based active materials and linearly conductive materials and mixing them. The mixing apparatus may include, for example, a ball mill, sand mill, bead mill, pigment disperser, stone mill, ultrasonic disperser, homogenizer, or planetary mixer. Mixing is typically carried out from 10 minutes to several hours in the range of room temperature to 80°C.

[0295] Subsequently, the composition is spray-dried. Spray drying is a method of drying a slurry while it is sprayed into hot air. The spraying methods used in spray drying include rotary disc drying and nozzle spraying. Rotary disc drying involves feeding the composition to approximately the center of a high-speed rotating disc, where the centrifugal force of the disc pushes the composition towards the periphery, creating a mist and drying it. The rotational speed of the disc depends on its size, but is typically between 5,000 rpm and 35,000 rpm, and preferably between 15,000 rpm and 30,000 rpm. Meanwhile, nozzle spraying involves spraying the composition along with air or a liquid, such as a high-pressure fluid, through a fine nozzle to convert it into a mist and dry it.

[0296] In one embodiment of this disclosure, the temperature of the hot air can be controlled from 80°C to 250°C based on the reactor inlet temperature (input) to form a granular structure with a large amount of granular binder on the surface. In this disclosure, taking into account the gradient of the amount of granular binder and the aspect ratio, the temperature of the hot air can be controlled from 170°C to 250°C, and more preferably from 180°C to 200°C. In the spray drying method, the hot air suction method is not limited to a specific method and may include, for example, a method of co-flowing the hot air and the spray direction in the horizontal direction; a method of spraying from the top of the drying tower so that it falls together with the hot air; a method of countercurrent contact between the spray droplets and the hot air; or a method of co-flowing the spray droplets and the hot air, falling by gravity and contacting each other countercurrently. Meanwhile, in one embodiment of this disclosure, in spray drying, the reactor outlet temperature (the temperature of the hot air released from the reactor) can be controlled from 90°C to 130°C.

[0297] When the outlet temperature and / or the temperature difference ΔT between the inlet and outlet is low, proper drying cannot be achieved, potentially resulting in particles containing a large amount of residual solvent. This prevents the formation of uniformly shaped spherical particles, leading to particle agglomeration or amorphous particles. Conversely, when the inlet temperature is too high and ΔT is large, granulation fails due to over-drying, potentially producing particles with very small particle size D50 and low aspect ratio. Therefore, to control particle size at appropriate levels and to achieve high aspect ratios and minimal particle agglomeration with binder, the inlet and outlet temperatures must be controlled within their optimal ranges.

[0298] In addition, heating can be optionally performed to cure the surface of the product obtained by spray drying (i.e., granules), and in this case, the heat treatment temperature can typically be from 80°C to 300°C.

[0299] Subsequently, the granules are mixed with carbon-based active materials, conductive materials for the negative electrode layer, binders for the negative electrode layer, and slurry with an aqueous dispersion medium to prepare an electrode slurry.

[0300] In this case, for the aqueous dispersion medium of the slurry, reference can be made to the above-mentioned aqueous dispersion medium, and for the method of preparing the slurry, reference can be made to the method of preparing the composition for producing granules.

[0301] The viscosity of the electrode paste can be from 1,000 cPs to 10,000 cPs, or from 1,000 cPs to 9,000 cPs.

[0302] Subsequently, the electrode slurry is applied to at least one surface of the current collector, dried, and pressed / rolled to form a negative electrode active material layer.

[0303] The slurry prepared by the above method is applied to the current collector. In this case, the current collector may have an underlayer on all or part of at least one surface, the underlayer comprising the conductive material for the negative electrode layer and the binder for the negative electrode layer as described above.

[0304] In one embodiment of this disclosure, the method of coating the slurry onto at least one surface of the current collector may include any method commonly used in the art, such as spraying, dip coating, gravure coating, slot die coating, or comma coating.

[0305] In one embodiment of this disclosure, drying can be performed using drying methods commonly used in the manufacture of electrodes. For example, drying can be performed at 30°C to 100°C, or 40°C to 80°C. Alternatively, drying can be performed in air for 2 to 20 minutes, or 2 to 10 minutes.

[0306] The pressing / rolling step is typically performed using a pressing process with rollers. During rolling, two cylindrical rollers are arranged vertically in parallel with a narrow gap and rotate in opposite directions to apply pressure to an electrode located between them. The temperature of the rollers can be controlled by heating or cooling.

[0307] Furthermore, according to one aspect of this disclosure, an electrochemical device including an electrode according to one embodiment of this disclosure is provided.

[0308] Electrochemical devices may include any apparatus in which an electrochemical reaction occurs, and specifically, electrochemical devices may include, for example, any type of primary battery, secondary battery, fuel cell, solar cell, or capacitor, such as a supercapacitor. In this disclosure, electrochemical devices may preferably include secondary batteries, and more preferably lithium-ion secondary batteries.

[0309] Furthermore, according to one embodiment of this disclosure, an energy storage device comprising a secondary battery as a unit battery can be provided.

[0310] The secondary battery may include: an electrode assembly comprising a negative electrode, a positive electrode, and a separator according to one embodiment of the present disclosure; and a battery case (cylindrical case, prismatic case, or bag) for housing the electrode assembly and a lithium-containing non-aqueous electrolyte.

[0311] The positive electrode may have a positive electrode active material layer on at least one surface of the current collector, the positive electrode active material layer comprising a positive electrode active material, a granular binder, and optionally a conductive material.

[0312] The positive electrode active material can include any type of lithium transition metal oxide, lithium iron phosphate, or metal oxide, such as layered compounds, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; lithium manganese oxide, such as Li... 1+x Mn 2-x O4 (x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; and LiNi 1- x M x Ni-site type lithium nickel oxides represented by O2 (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); LiMn 2-x M xLithium-manganese composite oxides represented by O2 (M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (M = Fe, Co, Ni, Cu or Zn); Li 1+x (Ni a Co b Mn c Al d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a+b+c+d = 1), wherein some of the Li in the chemical formula is replaced by aluminum ions; lithium metal phosphate LiMPO4 (M = Fe, Co, Ni or Mn); disulfide compounds; or Fe2(MoO4)3, but not limited thereto.

[0313] In one embodiment of this disclosure, the binder contained in the positive electrode is not limited to a particular type and may include any binder material for granules used in electrochemical devices, and may include, for example, diene-based polymers, acrylate-based polymers, fluorine-based polymers, styrene-based polymers, or both or more thereof.

[0314] Examples of diene-based polymers may include polymers containing monomer units derived from conjugated dienes such as butadiene or isoprene, and their hydrogenated products. The proportion of conjugated diene-derived monomer units in diene-based polymers is typically 40% by weight or more, preferably 50% by weight or more, and more preferably 60% by weight or more.

[0315] Specifically, diene-based polymers may include conjugated diene homopolymers, such as polybutadiene or polyisoprene; aromatic vinyl-conjugated diene copolymers, such as styrene-butadiene copolymers (SBR) with carboxyl modification; cyanided vinyl-conjugated diene copolymers, such as acrylonitrile-butadiene copolymers (NBR); hydrogenated SBR or hydrogenated NBR.

[0316] Styrene-based polymers may include polymers having repeating units derived from styrene monomers, such as styrene homopolymers (polystyrene) or styrene copolymers. Examples of styrene copolymers may include block copolymers, such as styrene-ethylene-butadiene copolymers, styrene-butadiene-propylene copolymers, styrene-isoprene copolymers, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymers, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymers, styrene-butadiene block copolymers, styrene-butadiene-styrene block copolymers, styrene-ethylene-butene-styrene block copolymers, styrene-isoprene block copolymers, or styrene-ethylene-propylene-styrene block copolymers.

[0317] Examples of acrylate-based polymers may include polymers containing monomer units derived from acrylates and / or methacrylates. The ratio of monomer units derived from acrylates and / or methacrylates in acrylate-based polymers is typically 40% by weight or more, preferably 50% by weight or more, and more preferably 60% by weight or more. Specific examples of acrylate-based polymers may include polymers based on crosslinked acrylates, such as 2-ethylhexyl acrylate-methacrylic acid-acrylonitrile-ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-methacrylic acid-methacrylonitrile-diethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-styrene-methacrylic acid-ethylene glycol dimethacrylate copolymer, butyl acrylate-acrylonitrile-diethylene glycol dimethacrylate copolymer, or butyl acrylate-acrylic acid-trimethylolpropane trimethacrylate copolymer; copolymers of ethylene and (meth)acrylates, such as ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer, or ethylene-ethyl methacrylate copolymer; or graft polymers having radically polymerizable monomers grafted onto copolymers of ethylene and (meth)acrylates. The radically polymerizable monomers used in the graft polymers may include, for example, methyl methacrylate, acrylonitrile, or methacrylic acid. Furthermore, copolymers of ethylene and (meth)acrylates, such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, may be used as dispersible binders.

[0318] Fluorine-based polymers may include copolymers based on polyvinylidene fluoride, such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), or PVdF-HFP. Specifically, they may include polytetrafluoroethylene (PTFE), and more specifically, they may be polytetrafluoroethylene (PTFE).

[0319] The separator may include a porous polymer membrane commonly used as a separator, such as a porous polymer membrane made of a polyolefin-based polymer (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer), which may be used alone or in a stack. Additionally, an insulating film with high ion permeability and mechanical strength may be used. The separator may include a safety-reinforced separator (SRS) with a thin ceramic coating on its surface. Furthermore, the separator may include, but is not limited to, a porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber.

[0320] The electrolyte contains a lithium salt as the electrolyte and an organic solvent for dissolving the lithium salt.

[0321] Lithium salts are not limited to a specific type and may include any lithium salt commonly used in electrolytes for secondary batteries, and, for example, the anion of the lithium salt may include any of the following: F - Cl - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - .

[0322] The organic solvent contained in the electrolyte is not limited to a specific type and may include any organic solvent commonly used in the art. Typically, the organic solvent may include at least one of the following: propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran.

[0323] In particular, among these carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferably high-viscosity organic solvents with high dielectric constants that readily dissociate lithium salts in the electrolyte. More preferably, when cyclic carbonates are used in combination with low-viscosity, low-dielectric-constant linear carbonates (e.g., dimethyl carbonate and diethyl carbonate) in an optimal ratio, electrolytes with high conductivity can be prepared.

[0324] Optionally, the electrolyte contained according to this disclosure may also contain additives commonly used in electrolytes, such as overcharge protection agents.

[0325] A lithium secondary battery according to one embodiment of this disclosure can be manufactured by: providing a positive electrode and a negative electrode and a separator between them to form an electrode assembly, placing the electrode assembly in, for example, a bag, a cylindrical battery case, or a prismatic battery case, and injecting an electrolyte. Alternatively, a lithium secondary battery can be manufactured by: stacking the electrode assembly, filling it with an electrolyte, placing the result in a battery case, and sealing it.

[0326] In this case, the detailed structure of the secondary battery and energy storage device is well known in the art, and its description is omitted.

[0327] In the following detailed description of embodiments, this disclosure will be further described. However, embodiments according to this disclosure may be modified in many other forms, and the scope of this disclosure should not be construed as limited to the following embodiments. Embodiments of this disclosure are provided to illustrate this disclosure thoroughly and fully to those skilled in the art.

[0328] Example

[0329] Example 1

[0330] (1) Manufacturing of the negative electrode

[0331] A composition with a viscosity of approximately 9000 cPs was prepared by mixing Si (pure Si, FH6, average particle size D50: 10 μm) as the silicon-based active material, single-walled carbon nanotubes (SWCNTs) as the linear conductive material, graphite-based plate-like conductive material (SFG-6L), styrene-butadiene rubber (SBR A, styrene:butadiene molar ratio = 64:36) as the granule binder, and carboxymethyl cellulose (CMC, Daicell 2200) as the dispersant with water as the dispersion medium in a weight ratio of 75:2:8:8:7 through a homogenizer. In this case, the solids content in the composition was 15% by weight.

[0332] The prepared composition was fed into a spray dryer along with hot air under a pressure range of -40 mm H2O to dry it. In this case, the conditions of the spray dryer were controlled as follows: inlet temperature of 250°C, outlet temperature of 105°C, pressure of the two-fluid nozzle of the spray dryer of 2.5 bar, and feed rate of the spray dryer of 10 cc / min. Figure 6 Image of the spray dryer used.

[0333] Industrial sieves are used to remove large particles of 150 μm or larger from half of the dried product.

[0334] The granules have: a central portion comprising a plurality of silicon-based active materials and linearly conductive materials; and a surface portion located outside the central portion and comprising a granule binder for bonding the plurality of silicon-based active materials and linearly conductive materials.

[0335] The obtained granules, a graphite-based active material (a mixture of artificial graphite and / or natural graphite in a 1:1 weight ratio), carbon black (C65) as a conductive material for the negative electrode layer, and styrene-butadiene rubber (SBR, styrene:butadiene molar ratio = 64:36) as a binder for the negative electrode layer were mixed with water as a dispersion medium in a weight ratio of 5:92:1:2 using a homogenizer at 3000 rpm to prepare a slurry with a viscosity of approximately 9000 cPs. In this case, the solids content in the slurry was 40% by weight.

[0336] The prepared slurry was applied to both surfaces of a copper current collector (thickness: 10 μm) using a slit-die method, dried in a convection oven at 80°C for 0.5 hours, and then pressed / rolled to produce a loading of 300 mg / 25 cm² per unit area on both surfaces of the current collector. 2 The negative electrode is the negative electrode active material layer.

[0337] (2) Manufacturing of the positive electrode

[0338] Li[Ni] will be used as the positive electrode active material 0.88 Co 0.07 Mn 0.04 Al 0.01 O2, a carbon black pre-dispersion used as the positive electrode conductive material, and polyvinylidene fluoride (PVdF) used as a binder for the positive electrode granules were added to NMP as the dispersion medium at a weight ratio of 96.5:1.5:2. The mixture was stirred at 3500 rpm for 1 hour using a homogenizer to prepare a positive electrode active material slurry. The solid content in the carbon black pre-dispersion was 16%, and the final solid content in the slurry was 68%. The slurry was coated on both surfaces of a 12 μm thick aluminum current collector, and the coated slurry was dried using a dryer equipped with a hot air blower and an IR heater to form a positive electrode active material layer.

[0339] Subsequently, the positive electrode active material layer is pressed / rolled using a rolling process to produce a dried material with a loading of 590 mg / 25 cm² per unit area. 2 The positive electrode is the positive electrode active material layer.

[0340] (3) Manufacturing of secondary batteries

[0341] 1) Single-cell secondary battery

[0342] The prepared positive and negative electrodes, along with a porous polyethylene membrane (thickness: 10 μm) serving as a separator between them, are used to fabricate an electrode assembly. The electrode assembly is placed in a battery case, and then an electrolyte containing 1 M LiPF6 dissolved in a solvent comprising a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a 1:2:1 (volume ratio) is injected. The case is then sealed and formed / activated to fabricate a single-cell secondary battery unit.

[0343] 2) Semi-coin battery secondary battery

[0344] Lithium metal and the prepared negative electrode are placed in a coin-shaped battery box, and then an electrolyte containing 1 M LiPF6 dissolved in a solvent comprising a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a 1:2:1 (volume ratio) is injected. The box is then sealed and formed / activated to manufacture a semi-coin battery secondary battery.

[0345] Example 2

[0346] Granules were prepared using the same method as in Example 1, except that Si (pure Si, FH6, average particle size D50: 10 μm) as the silicon-based active material, single-walled carbon nanotubes (SWCNT, SFG-6L) as the linear conductive material, graphite-based plate-like conductive material (SFG-6L), styrene-butadiene rubber (SBR A, styrene:butadiene molar ratio = 64:36) as the granule binder, acrylate polymers (e.g., polyacrylic acid copolymer (acrylamide / acrylonitrile / acrylic acid copolymer)), and carboxymethyl cellulose (CMC, Daicell 2200) as the dispersant were mixed with water as the dispersion medium in a weight ratio of 75:2:4:4:8:7 through a homogenizer to prepare a composition with a viscosity of approximately 9000 cPs.

[0347] The obtained pellets were used to manufacture the negative electrode and the secondary battery using the same method as in Example 1.

[0348] Example 3

[0349] Granules were prepared using the same method as in Example 1, except that Si (pure Si, FH6, average particle size D50: 10 μm) as a silicon-based active material, single-walled carbon nanotubes (SWCNT, SFG-6L) as a linear conductive material, graphite-based plate-like conductive material (SFG-6L), styrene-butadiene rubber (SBR B, styrene:butadiene molar ratio = 42:58) as a binder for the granules, and carboxymethyl cellulose (CMC, Daicell 2200) as a dispersant were mixed with water as a dispersion medium in a weight ratio of 75:2:8:8:7 through a homogenizer to prepare a composition with a viscosity of approximately 9000 cPs.

[0350] The obtained pellets were used to manufacture the negative electrode and the secondary battery using the same method as in Example 1.

[0351] Comparative Example 1-1

[0352] The granules were prepared using the same method as in Example 1, except that the prepared composition was fed into a spray dryer along with hot air under a pressure range of -40 mmH2O to dry it. In this case, the conditions of the spray dryer were controlled as follows: inlet temperature of 250°C, outlet temperature of 105°C, pressure of the two-fluid nozzle of the spray dryer of 0.2 bar, and feed rate of the spray dryer of 50 cc / min.

[0353] The negative electrode and secondary battery were manufactured using the same method as in Example 1, except that the obtained granules were mixed in a homogenizer at 1000 rpm to prepare a slurry.

[0354] Comparative Examples 1-2

[0355] The granules were prepared using the same method as in Example 1, except that the prepared composition was fed into a spray dryer along with hot air under a pressure range of -40 mmH2O to dry it. In this case, the conditions of the spray dryer were controlled as follows: inlet temperature of 250°C, outlet temperature of 105°C, pressure of the two-fluid nozzle of the spray dryer of 0.2 bar, and feed rate of the spray dryer of 50 cc / min.

[0356] The obtained pellets were used to manufacture the negative electrode and the secondary battery using the same method as in Example 1.

[0357] Comparative Example 2-1

[0358] Granules were prepared using the same method as in Comparative Example 1-1, except that SBR A and a polyacrylic acid copolymer (acrylamide / acrylonitrile / acrylic acid copolymer) were used as binders for the granules.

[0359] The negative electrode and secondary battery were manufactured using the same method as in Example 1, except that the obtained granules were mixed in a homogenizer at 1000 rpm to prepare a slurry.

[0360] Comparative Example 2-2

[0361] The granules were prepared by the same method as in Comparative Example 2-1, except that the prepared composition was fed into a spray dryer along with hot air under a pressure range of -40 mm H2O to dry it, and in this case, the conditions of the spray dryer were controlled as follows: inlet temperature of 250°C, outlet temperature of 105°C, pressure of the two-fluid nozzle of the spray dryer of 0.2 bar, and feed rate of the spray dryer of 50 cc / min.

[0362] The obtained pellets were used to manufacture the negative electrode and the secondary battery using the same method as in Example 1.

[0363] Comparative Example 3-1

[0364] The granules were prepared using the same method as in Example 3, except that the prepared composition was fed into a spray dryer along with hot air under a pressure range of -40 mmH2O to dry it. In this case, the conditions of the spray dryer were controlled as follows: inlet temperature of 250°C, outlet temperature of 105°C, pressure of the two-fluid nozzle of the spray dryer of 0.2 bar, and feed rate of the spray dryer of 50 cc / min.

[0365] The negative electrode and secondary battery were manufactured using the same method as in Example 1, except that the obtained granules were mixed in a homogenizer at 1000 rpm to prepare a slurry.

[0366] Comparative Example 3-2

[0367] The granules were prepared by the same method as in Comparative Example 3-1, except that the prepared composition was fed into a spray dryer along with hot air under a pressure range of -40 mm H2O to dry it, and in this case, the conditions of the spray dryer were controlled as follows: inlet temperature of 250°C, outlet temperature of 105°C, pressure of the two-fluid nozzle of the spray dryer of 0.2 bar, and feed rate of the spray dryer of 50 cc / min.

[0368] The obtained pellets were used to manufacture the negative electrode and the secondary battery using the same method as in Example 1.

[0369] Comparative Example 4

[0370] (1) Manufacturing of the negative electrode

[0371] A slurry with a viscosity of approximately 9000 cPs was prepared by mixing Si (pure Si, FH6, average particle size D50: 10 μm) as the silicon-based active material, single-walled carbon nanotubes (SWCNT, SFG-6L) as the linear conductive material, carbon black (SuperC65) as the conductive material for the negative electrode layer, styrene-butadiene rubber (SBR A, styrene:butadiene molar ratio = 64:36) as the granule binder, and carboxymethyl cellulose (CMC, Daicell 2200) as the dispersant with water as the dispersion medium in a weight ratio of 76.1:1.6:8.1:8.1:6.1 through a homogenizer at 3000 rpm. In this case, the solids content in the composition was 40% by weight.

[0372] The prepared slurry was applied to both surfaces of a copper current collector (thickness: 10 μm) using a slit-die method, dried in a convection oven at 80°C for 0.5 hours, and then pressed / rolled to produce a loading of 300 mg / 25 cm² per unit area on both surfaces of the current collector. 2 The negative electrode is the negative electrode active material layer.

[0373] Figure 7 A diagram illustrating pellet C (corresponding to the pellets of Examples 1 to 3), spherical pellet A (corresponding to the pellets of Comparative Examples 1-1, 2-1, and 3-1), and crushed pellet B (corresponding to Comparative Examples 1-2, 2-2, and 3-2) according to one embodiment of the present disclosure is provided. (Refer to...) Figure 7Spherical pellet A has a large particle size, approaching a spherical shape with high roundness, and has high density due to its non-concave surface. Crushed pellet B, as a result of physical impact crushing by collision under high shear force when manufacturing electrodes using spherical pellets, has a smaller particle size than spherical pellets and low roundness due to the exposure of sharp crushed surfaces. In contrast, pellet C, determined according to one embodiment of this disclosure, has a smaller particle size than spherical pellet A and low roundness, and exhibits an uneven binder distribution due to the exposure of the crushed surfaces (the binder distribution is determined by…). Figure 7 Compared to crushed granules (as indicated by the line in the text), granule C has a uniform binder distribution across the entire granule surface because no crushing occurred during the manufacturing process.

[0374] Evaluation methods

[0375] Dispersion and standard deviation of granules in the negative electrode active material layer

[0376] The following method is used to measure the dispersion and standard deviation of the granules in the negative electrode active material layer of Example 2 and Comparative Examples 1-1, 2-2 and 4.

[0377] A cross-section of the negative electrode active material layer of the negative electrode to be measured was obtained using a scanning electron microscope (SEM) (manufacturer: JEOL, name: JSM-7200). The images measured by the SEM were analyzed pixel-by-pixel using the ImageJ program (SEM images) to measure the dispersion of particles containing silicon-based active material within the negative electrode active material. In this case, the dispersion was calculated for each of the four SEM images, and its standard deviation was calculated from the dispersion of each image. A smaller dispersion was assessed as a more uniform distribution of particles within the negative electrode active material layer without agglomeration in some areas, and a lower standard deviation of dispersion was assessed as a more uniform dispersion with lower deviation within the same negative electrode active material layer.

[0378] Specifically, when measuring dispersion, the SEM image pixels of the analysis area in the negative electrode active material layer are divided into 20×20 (width×height) segments, and the area ratio of the region of interest (containing particles of silicon-based active material) in each segment is calculated. The sample distribution of 400 area ratios is defined as dispersion.

[0379] In this case, the sample variance is calculated from the individual values ​​of the 400 area ratios using the following Equation 1 and provided as the dispersion.

[0380] Equation 1

[0381] s 2 =Σ(y-y') 2 / (n-1)

[0382] In the above equation, s 2 Let represent the sample variance (i.e., dispersion), and let represent the variance calculated from the sample, and in order to compare it with the population variance σ 2 Distinguish them, and represent them as s 2 .

[0383] Σ(y-y') 2 It is the sum of squared deviations.

[0384] Where y represents each observation value.

[0385] y': Sample mean (y-bar)

[0386] (y-y'): The difference (deviation) between each observation and the sample mean.

[0387] (y-y') 2 : square deviation

[0388] Σ: Sum of the squared deviations of all observations

[0389] n-1 represents the degrees of freedom.

[0390] Where n: sample size (number of observations)

[0391] The dispersion standard deviation is calculated from the dispersion of four SEM images using a common method. Specifically, the arithmetic mean of the dispersion of the four SEM images is calculated, the average of the squares of the results obtained by subtracting the mean from each dispersion is calculated, and the square root of this average is taken as the dispersion standard deviation.

[0392] The results are shown in Table 1 and Figure 8 In the middle. For reference, in Figure 8 In Comparative Example 1-1, the circles indicate some of the locations where granular material is present, and in Comparative Example 4, the numbers 1 to 4 indicate four analysis areas in the SEM image.

[0393] Table 1

[0394]

[0395] Volume expansion rate of the negative electrode active material layer

[0396] The volume expansion rate of the negative electrode active material layer of each of Examples 1 to 3 and Comparative Example 4 was calculated using the following Equation 2, based on the measured thickness of the negative electrode active material layer, using an X-ray microscope (XRM) (ZEISS Xradia Versa 620). The results are summarized in Table 2 below.

[0397] Equation 2

[0398] Volume expansion rate (%) = (Electrode thickness at 100 charge cycles - Initial electrode thickness) / Initial electrode thickness × 100

[0399] Table 2

[0400]

[0401] Evaluation of the adhesive strength of the negative electrode

[0402] Double-sided adhesive tape was attached to a glass slide, and negative electrodes cut to 20 mm × 100 mm size, representing Examples 2 to 3 and Comparative Examples 1-1 and 2-2, were placed on top and adhered by moving a 2 kg roller back and forth 10 times. The force required to peel off the slide (adhesive strength) was measured using a UTM (TA) machine at 10 mm / min. In this case, the measurement angle between the slide and the electrode was 90°. Table 3 below summarizes the measured adhesive strengths.

[0403] Table 3

[0404]

[0405] Battery performance evaluation

[0406] The semi-coin battery secondary cells and single-cell secondary cells manufactured in Examples 2 to 3 and Comparative Examples 1-1, 1-2, 2-2, and 3-2 were evaluated. After full formation, the discharge capacity and capacity retention of the secondary cells were evaluated using a battery charge / discharge tester (battery cycler). In this case, the measurements were performed in a constant temperature chamber at 25°C to minimize the influence of temperature.

[0407] The semi-coin cell rechargeable battery was discharged at 0.1 C in constant current (CC) discharge mode. When the lower voltage limit (0.05 V) was reached, the CC mode was switched to constant voltage (CV) mode and the discharge was continued until the current dropped below 0.05 C. Subsequently, the battery was charged at 0.1 C in CC mode to the upper voltage limit (1.5 V), and the measurement was repeated until the third cycle.

[0408] The battery's first discharge efficiency was calculated as the ratio of the discharge capacity to the charge capacity during the first cycle, and the battery's discharge efficiency during the third cycle was calculated as the ratio of the discharge capacity to the charge capacity during the third cycle. Table 4 below summarizes the results.

[0409] Referring to Table 4 below, the semi-coin battery rechargeable cells of Examples 2 and 3 were found to have significantly higher charge and discharge capacities than Comparative Examples 1-1, 1-2, 2-2, and 3-2 in the first and third cycles, and exhibited high discharge efficiency in each cycle. It can be considered that the granules used in the semi-coin battery rechargeable cells of Examples 2 and 3 have lower sphericity and density than the granules used in the comparative examples, resulting in a larger granular specific surface area and a greater number of reaction sites, leading to a more uniform distribution within the electrodes and thus improved performance characteristics.

[0410] Table 4

[0411]

[0412] The single-cell rechargeable batteries were evaluated to determine the average capacity, standard deviation, actual capacity relative to the design capacity, and standard deviation of the single-cell rechargeable batteries manufactured in Examples 1 to 3. The batteries were charged at 0.33 C in CC mode, and when the upper voltage limit (4.2 V) was reached, the CC mode was changed to CV mode, and charging was continued until the current dropped below 0.05 C. Subsequently, measurements were taken under the condition that the batteries were discharged at 0.33 C in CC mode until the minimum voltage (2.5 V), and the results are summarized in Table 5 below. In this case, the measured capacity was determined for three batteries, and their average value and standard deviation were calculated. The actual capacity (%) relative to the design capacity refers to the percentage of the measured capacity at 1 C relative to the design capacity.

[0413] The discharge resistances (SOC50 (30 seconds) (Ω) and SOC50 (0.1 seconds) (Ω)) are indicators calculated based on the voltage drop over specific times using the single-cell secondary batteries manufactured in Examples 1 to 3, and are based on the voltage drops measured by discharging at a constant current for 30 seconds and 0.1 seconds respectively at 50% state of charge (SOC). Specifically, after charging the single cell to 50% SOC, a set discharge current of 2.5 C-rate is applied, and the terminal voltages are measured at 0.1 seconds and 30 seconds after the start of discharge. In this case, the difference between the open-circuit voltage before the start and the voltage at each time point is divided by the current, and each discharge resistance is calculated according to the following equation:

[0414] SOC50 (0.1 seconds) (Ω) = (V0 - V 0.1秒 ) / I

[0415] SOC50 (30 seconds) (Ω) = (V0 - V 30秒 ) / I

[0416] Here, V0 represents the open-circuit voltage (V) immediately preceding the start of discharge. 0.1秒This represents the voltage (V) 0.1 seconds after the start of discharge. 30秒 The voltage (V) represents the voltage 30 seconds after the start of discharge, and I represents the discharge current (A).

[0417] Table 5

[0418]

[0419] Observation of granules

[0420] The granules prepared in Examples 1 and 2, as well as Comparative Examples 1-1, 2-1, and 3-1, were imaged using a FE-SEM (Hitachi S-4800 scanning electron microscope) at magnifications from 300x to 8,000x, and in this case, imaging was performed at an accelerating voltage of 5 kV to observe the detailed surface structure. Figure 1 Figure 5 shows the results. Specifically, Figures 1 to 3 To observe the SEM images of the granules prepared in Example 1 at different magnifications, Figure 4 SEM images of the granules prepared in Example 2, and Figure 5a , Figure 5b and Figure 5c The images are SEM images of the granules prepared in Comparative Examples 1-1, 2-1, and 3-1, respectively.

[0421] sphericity of granules

[0422] To determine the roundness of the granules prepared in Example 2 and Comparative Examples 1-1, optical images of 10,000 particles for each granule were obtained using a particle size analyzer (Malvern Morphology 4), and the roundness of the granule images was calculated by numerical averaging using the following Equation 3. The results are summarized in Table 6 below.

[0423] Equation 3

[0424] The roundness of the aggregate = 4π * (measured area of ​​the aggregate) / (measured perimeter of the aggregate) 2

[0425] Particle density

[0426] To determine the density of the granules prepared in Example 2 and Comparative Examples 1-1, optical images of 10,000 granules were obtained using a particle size analyzer (Malvern Morphology 4). The actual area (a) and convex hull area (b) of each granule in the obtained images were calculated, and their ratio (a / b) was calculated using the following Equation 4. Table 6 summarizes the results.

[0427] Equation 4

[0428] Density = (Actual area of ​​the aggregate) / Area of ​​the convex bulge of the aggregate

[0429] Here, the convex hull area of ​​the granules is the total area enclosed by the convex hull of the granules, and refers to the area of ​​the simplest convex polygon formed by connecting the outermost points of the granules.

[0430] Average particle size of granules

[0431] The particle size distribution of the granules prepared in Example 2 and Comparative Examples 1-1 was calculated using a particle size analyzer (Malvern Morphology 4). The D50 particle size was measured by calculating the particle size at 50% of the cumulative particle size distribution in the measuring instrument. Similarly, the D10 and D90 particle sizes were calculated as the particle sizes at 10% and 90% of the cumulative particle size distribution, respectively. Table 6 below summarizes the measurement results of the D50, D10, and D90 particle sizes.

[0432] Angle of repose of granules

[0433] The angle of repose of the particles contained in the negative electrodes of Example 2 and Comparative Example 1-1 was measured using ASTM D 6393-99. The results are summarized in Table 5 below.

[0434] Table 6

[0435]

Claims

1. A negative electrode for an electrochemical device, comprising: a current collector; and a negative electrode active material layer present on the current collector, wherein the negative electrode active material layer contains pellets, and the pellets contain a silicon-based active material, a linear conductive material, and a binder for the pellets, The dispersion of the granules within the negative electrode active material layer is 1×10⁻⁶. -2 Up to 10×10 -2 The standard deviation of the dispersion of the granules is 1×10⁻⁶. -3 Up to 4×10 -3 ,as well as wherein the volume expansion rate of the negative electrode active material layer is 3% to 35%.

2. The negative electrode for an electrochemical device according to claim 1, The dispersion of the granules within the negative electrode active material layer is 1×10⁻⁶. -2 Up to 5×10 -2 The standard deviation of the dispersion of the granules is 1×10⁻⁶. -3 Up to 3.5×10 -3 .

3. The negative electrode for an electrochemical device according to claim 1, wherein the volume expansion rate of the negative electrode active material layer is 3% to 33%.

4. The negative electrode for an electrochemical device according to claim 1, wherein the negative electrode active material layer contains the pellets, a carbon-based active material, and a binder for the negative electrode layer.

5. The negative electrode for an electrochemical device according to claim 4, wherein, based on 100 parts by weight of the negative electrode active material layer, the negative electrode active material layer contains 1 to 10 parts by weight of the pellets, 70 to 99 parts by weight of the carbon-based active material, and 0.1 to 10 parts by weight of the binder for the negative electrode layer.

6. The negative electrode for an electrochemical device according to claim 1, wherein the negative electrode active material layer contains the pellets, a carbon-based active material, a binder for the negative electrode layer, and a conductive material for the negative electrode layer.

7. The negative electrode for an electrochemical device according to claim 6, wherein, based on 100 parts by weight of the negative electrode active material layer, the negative electrode active material layer contains 1 to 10 parts by weight of the pellets, 70 to 99 parts by weight of the carbon-based active material, 0.01 to 5 parts by weight of the conductive material for the negative electrode layer, and 0.1 to 10 parts by weight of the binder for the negative electrode layer.

8. The negative electrode for an electrochemical device according to claim 1, wherein the silicon-based active material includes silicon (Si); silicon oxide (SiOx (0 < x ≤ 2)); Si / C composite; or two or more of them.

9. The negative electrode for an electrochemical device according to claim 1, wherein the linear conductive material includes single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanofibers, or two or more of them.

10. The negative electrode for an electrochemical device according to claim 1, wherein the binder contains at least one of a linear binder and a dot-shaped binder.

11. The negative electrode for an electrochemical device according to claim 10, wherein the binder contains the linear binder and the dot-shaped binder.

12. The negative electrode for an electrochemical device according to claim 10, wherein the linear binder includes an acrylate-based polymer, and the dot-shaped binder includes a diene-based polymer, a styrene-based polymer, or two or more of them.

13. The negative electrode for an electrochemical device according to claim 1, The granules include a central portion comprising the silicon-based active material and the linearly conductive material; and a surface portion present on all or part of the outer side of the central portion, the surface portion comprising a binder for holding the silicon-based active material and the linearly conductive material together.

14. The negative electrode for the electrochemical device according to claim 13, Of which, relative to the total weight of 100% by weight of the silicon-based active material, the linear conductive material, and the granule binder, the amount (by weight) of the granule binder is greater in the surface portion of the granule than in the central portion, and The surface portion is the region extending from the surface of the granule to a predetermined depth in the direction from the surface of the granule to the center of the granule, and the center portion is the region other than the surface portion.

15. The negative electrode for the electrochemical device according to claim 1, The granules, based on 100 parts by weight, comprise 80 to 98 parts by weight of the silicon-based active material, 0.2 to 10 parts by weight of the linear conductive material, and 0.5 to 10 parts by weight of the binder for the granules.

16. The negative electrode for the electrochemical device according to claim 1, The granules also contain carbon-based active materials.

17. The negative electrode for the electrochemical device according to claim 1, The granules also contain a dispersant.

18. The negative electrode for the electrochemical device according to claim 17, The dispersant mentioned above includes carboxymethyl cellulose (CMC).

19. A method for manufacturing a negative electrode for an electrochemical device according to claim 1, the method comprising: The negative electrode active material layer is formed using granules comprising the silicon-based active material, the linear conductive material, and the granule binder.

20. The method for manufacturing a negative electrode for an electrochemical device according to claim 19, The method for manufacturing the negative electrode includes a wet process, a dry process, or both.

21. The method for manufacturing a negative electrode for an electrochemical device according to claim 20, The wet process includes mixing the granules and the negative electrode layer with a binder in a dispersion medium, or mixing the granules, the negative electrode layer with a binder, and the negative electrode layer with a conductive material in a dispersion medium to prepare a negative electrode slurry; and applying the negative electrode slurry to at least one surface of the current collector and drying it to form the negative electrode active material layer.

22. The method for manufacturing a negative electrode for an electrochemical device according to claim 20, The dry process includes dry mixing the granules and the fiberizable binder, or dry mixing the granules, the fiberizable binder, and the negative electrode layer with a conductive material to prepare a mixture; The prepared mixture is kneaded to produce a mixture block, and the mixture block is ground to obtain electrode mixture granules; The electrode mixture granules are fed between a plurality of rollers for calendering, thereby forming an electrode film; as well as The electrode film is laminated onto the metal current collector.

23. The method for manufacturing a negative electrode for an electrochemical device according to claim 20, The dry process includes applying the granules directly to the current collector alone, applying the granules and the negative electrode layer together with a binder to the current collector, or applying the granules, the negative electrode layer with a binder and the negative electrode layer with a conductive material together to the current collector and then pressing / rolling them.

24. The method for manufacturing a negative electrode for an electrochemical device according to claim 19, The negative electrode active material layer further comprises a carbon-based active material.

25. An electrochemical device comprising a negative electrode according to any one of claims 1 to 18.

26. The electrochemical device according to claim 25, The electrochemical device is a secondary battery.

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