Lithium-ion secondary battery negative electrode active material and lithium-ion secondary battery containing the same.

Abstract

This invention relates to a negative electrode active material for lithium secondary batteries, comprising silicon particles having a single-particle morphology and a polycrystalline structure, an average HS sphericity of 0.875 or higher, and satisfying the following formula 1. [Formula 1] Dv1≥2μm In Formula 1, Dv1 is the particle size corresponding to 1% of the volume accumulation in the particle size distribution curve of the silicon particles.

Description

Technical Field

[0001] This invention relates to a negative electrode active material for lithium secondary batteries and a lithium secondary battery containing the same. Background Technology

[0002] Lithium-ion batteries are currently the most widely used rechargeable battery system in portable electronic communication devices, electric vehicles, and energy storage devices. Compared with commercially available aqueous rechargeable batteries (Ni-Cd, Ni-MH, etc.), lithium-ion batteries have advantages such as higher energy density and operating voltage, as well as relatively lower self-discharge rates, thus becoming a focus of attention. However, considering the needs for more efficient usage time in portable devices and improved energy characteristics in electric vehicles, improving electrochemical properties remains an unsolved technical challenge. Therefore, research and development work on the four major raw materials—cathode, anode, electrolyte, and separator—is ongoing.

[0003] Among these raw materials, graphite-based materials, exhibiting excellent capacity retention and efficiency for the negative electrode, have been commercialized. However, the relatively low theoretical capacity (LiC6: 372 mAh / g) and low discharge capacity ratio of graphite-based materials make it difficult to meet the market's demand for high energy and high output density batteries. Therefore, many researchers have become interested in Group III elements (Si, Ge, Sn), especially silicon (Si) due to its extremely high theoretical capacity (LiC6: 372 mAh / g). 15 Si4: 3600mAh / g) and lower operating voltage (~0.1V vs. Li / Li + It has attracted much attention due to its characteristics.

[0004] However, for ordinary silicon-based anode materials, the cycle process involves volume changes of up to 300%. Due to particle cracks caused by continuous charging and discharging, fine powder is generated and electrical contacts are lost, resulting in a significant deterioration in discharge capacity ratio and lifetime characteristics, making it difficult to apply to actual batteries.

[0005] In particular, silicon-based anode materials are made by pulverizing metallic silicon raw material powder. During this pulverization process, needle-like or flake-like silicon particles may be generated. For needle-like or flake-like silicon particles, the lithium-ion reaction uniformity is poor, which can cause uneven volume expansion during cycling. The further pulverization of silicon particles exacerbates the problem of further deterioration in lifetime characteristics. Summary of the Invention

[0006] Technical problems to be solved Therefore, one technical problem of the present invention is to provide a silicon-based negative electrode active material and a lithium secondary battery containing the same, which improves capacity and lifespan characteristics by finely adjusting the crushing process during the preparation of silicon particles to reduce needle-like or scaly silicon particles.

[0007] Technical solution One embodiment of the present invention provides a lithium secondary battery negative electrode active material comprising silicon particles having a single particle morphology and a polycrystalline structure, having an average HS sphericity of 0.875 or higher, and satisfying the following formula 1.

[0008] [Formula 1] Dv1≥2μm In Equation 1, Dv1 is the particle size corresponding to 1% of the volumetric accumulation in the particle size distribution curve of silicon particles.

[0009] For the silicon particles, the average aspect ratio can be 0.695 or higher.

[0010] The silicon particles can satisfy the following formula 2.

[0011] [Equation 2] 0.70≤[Dv50-Dv10] / [Dv90-Dv50]≤0.80 In Equation 1, Dv50 is the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of silicon particles, Dv10 is the particle size corresponding to 10% of the cumulative volume in the particle size distribution curve of silicon particles, and Dv90 is the particle size corresponding to 90% of the cumulative volume in the particle size distribution curve of silicon particles.

[0012] The silicon particles can satisfy the following formula 3.

[0013] [Formula 3] Dv90≤10μm In Equation 3, Dv90 is the particle size corresponding to 90% of the volumetric accumulation in the particle size distribution curve of silicon particles.

[0014] The silicon particles can satisfy the following equation 4.

[0015] [Formula 4] [Dv90-Dv10] / Dv50≤1.1 In Equation 4, Dv50 is the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of silicon particles, Dv10 is the particle size corresponding to 10% of the cumulative volume in the particle size distribution curve of silicon particles, and Dv90 is the particle size corresponding to 90% of the cumulative volume in the particle size distribution curve of silicon particles.

[0016] The volume average particle size (Dv50) of the silicon particles can be 4 to 6 μm.

[0017] The average grain size of the silicon particles can be below 200 nm.

[0018] The silicon particles can have a Si purity of over 98%.

[0019] Another embodiment of the present invention provides a lithium secondary battery anode comprising the aforementioned anode active material.

[0020] Another embodiment of the present invention provides a lithium secondary battery comprising the negative electrode of the lithium secondary battery.

[0021] Beneficial effects According to one embodiment of the present invention, the negative electrode active material of a lithium secondary battery contains silicon particles, while the number of needle-like or flake-like silicon particles is reduced and the particle size distribution is controlled, thereby achieving excellent capacity and lifespan characteristics. Attached Figure Description

[0022] Figure 1 This is a SEM image of the negative electrode active material prepared according to Example 1. Detailed Implementation

[0023] The terms first, second, and third are used to describe various parts, components, regions, layers, and / or segments, but are not limited thereto. These terms are used only to distinguish a particular part, component, region, layer, or segment from other parts, components, regions, layers, or segments. Therefore, without departing from the scope of this invention, the first part, component, region, layer, or segment described below may be referred to as the second part, component, region, layer, or segment.

[0024] The technical terms used herein are for reference only to specific embodiments and are not intended to limit the invention. The singular forms used herein also include the plural forms unless the opposite is expressly stated herein. The word "comprising" as used in the specification means to embody specific features, regions, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, actions, elements, and / or components.

[0025] When describing one part as "above" or "on top of" another part, it can be directly on top of or on the other part, or there can be other parts in between. Conversely, when describing one part as "directly above" another part, there are no other parts in between.

[0026] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries are further interpreted as having meanings consistent with relevant technical literature and the present disclosure, and are not to be construed as having idealized or highly formal meanings unless otherwise defined.

[0027] In addition, unless otherwise specified, % refers to weight, 1ppm refers to 0.0001 ppm by weight.

[0028] In this specification, "the combination of them" as described in the Markush form means a mixture or combination of one or more of the constituent elements selected from the group of constituent elements described in the Markush form, indicating that it includes any one or more of the constituent elements selected from the group of constituent elements.

[0029] The embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different ways and is not limited to the embodiments described below.

[0030] 1. Negative electrode active materials The lithium-ion battery anode active material according to one embodiment of the present invention comprises silicon particles. Because the lithium-ion battery anode active material according to the present invention comprises silicon particles, it can achieve significantly higher capacity characteristics compared to conventionally used carbon-based anode active materials.

[0031] Specifically, the Si purity of the silicon particles can be above 98%, more specifically above 99% or 99.5%.

[0032] Furthermore, the silicon particles can have a single-particle morphology. That is, the silicon particles can have a single-particle morphology consisting of one primary particle, rather than a secondary particle morphology formed by the aggregation of multiple primary particles. Since the silicon particles are single particles, they have the advantage of uniform particle size distribution. On the other hand, a "primary particle" refers to the smallest particle unit that can be distinguished as a block when the cross-section of the negative electrode active material is observed using a scanning electron microscope (SEM). It can consist of a single grain or multiple grains. In addition, a "grain" refers to the region within a primary particle where atoms form a directional crystal lattice structure, which is used to distinguish the particles.

[0033] Furthermore, the silicon particles can have a polycrystalline structure. Since silicon particles are polycrystalline, they offer the advantage of improved cycle life. On the other hand, the polycrystalline structure of silicon particles can be confirmed by calculating the grain size using X-ray diffraction (XRD) analysis.

[0034] However, for typical silicon anode materials, the cycle process involves volume changes of up to 300%. Due to particle cracks caused by continuous charging and discharging, fine powder is generated and electrical contacts are lost, resulting in a significant deterioration in discharge capacity ratio and lifetime characteristics, making it difficult to apply to actual batteries.

[0035] Furthermore, silicon-based anode materials are made by pulverizing metallic silicon raw material powder. During this pulverization process, needle-like or flake-like silicon particles may be generated. These needle-like or flake-like silicon particles exhibit poor uniformity in lithium-ion reaction, leading to uneven volume expansion during cycling. The further refinement of the silicon particles exacerbates the problem of deteriorating lifetime characteristics.

[0036] Furthermore, if the pulverization process conditions are not precisely adjusted, there will be too much fine silicon powder, which may degrade the lifespan characteristics.

[0037] Therefore, in the lithium secondary battery anode active material according to one embodiment of the present invention, the pulverization process conditions are finely adjusted as described in the preparation method below (specific pulverization process conditions are given below). As a result, needle-like or flake-like silicon particles are reduced, and fine powder particles are also reduced. The reduction of needle-like or flake-like silicon particles and fine powder particles improves the uniformity of lithium-ion reaction and suppresses uneven volume expansion during cycling, thereby minimizing the fine powdering of silicon particles. Furthermore, the reduction of fine powder particles also improves capacity and lifespan characteristics. The results show that the lithium secondary battery anode active material according to the present invention can achieve good battery capacity and lifespan characteristics.

[0038] Specifically, according to one embodiment of the present invention, the average HS sphericity of the lithium secondary battery negative electrode active material can be 0.875 or higher, more specifically 0.89 or 0.9 or higher. An increase in the average HS sphericity of the negative electrode active material indicates a reduction in the number of needle-like or flake-like silicon particles. Therefore, as the average HS sphericity of the negative electrode active material meets the aforementioned range, the battery's capacity and lifespan characteristics can be well achieved.

[0039] On the other hand, in this specification, the average HS (High Sensitivity) roundness of the negative electrode active material can be obtained by deriving the average HS roundness of 10,000 silicon particles with a solidity value exceeding 0.96. Here, "solidity value" refers to the value obtained by dividing the actual area of ​​the particle by the area of ​​the particle's bulge region. By measuring the HS roundness only for silicon particles with solidity values ​​within the aforementioned range, overlapping or non-aggregated particles can be excluded, and only the roundness of single-particle silicon particles can be measured. Therefore, the roundness of the particles can be measured more precisely. Furthermore, the HS roundness of a single silicon particle can be obtained using the following formula: [Relation 1]

[0040] In Equation 1, the area refers to the total area of ​​the particle obtained from the individual 2D image of each particle by the image analysis device, and the perimeter refers to the total perimeter of the particle obtained from the individual 2D image of each particle by the image analysis device.

[0041] This roundness can be measured using an analyzer (Malvern Panalytical, Morphologi 4) used to acquire optical images.

[0042] Furthermore, the lithium secondary battery negative electrode active material according to one embodiment of the present invention satisfies the following formula 1.

[0043] [Formula 1] Dv1≥2 μm In Equation 1, Dv1 is the particle size corresponding to 1% of the volumetric accumulation in the particle size distribution curve of silicon particles.

[0044] As silicon particles satisfy Equation 2, the proportion of fine powder with excessively small particle size is reduced, thereby improving capacity, lifetime characteristics and tap density.

[0045] More specifically, the Dv1 value can be 2.2 or 2.4 μm or higher.

[0046] Furthermore, the average aspect ratio of the silicon particles can be 0.695 or higher, more specifically 0.74 or 0.75 or higher. When the average aspect ratio of the silicon particles meets the above range, the volume expansion is uniform due to the uniform reaction with lithium ions, thereby achieving more ideal capacity and lifetime characteristics.

[0047] On the other hand, in this specification, "aspect ratio" can refer to the ratio of the shortest side to the longest side within a silicon particle. In this case, the "average aspect ratio" can be obtained by calculating the average aspect ratio measured from any 50 silicon particles observed in an SEM (scanning electron microscope) image. This aspect ratio can be measured using an analyzer (Malvern Panalytical, Morphologi 4) used to acquire optical images.

[0048] On the other hand, the silicon particles can satisfy the following formula 2.

[0049] [Equation 2] 0.70≤[Dv50-Dv10] / [Dv90-Dv50]≤0.80 In Equation 1, Dv50 is the particle size corresponding to 50% of the volumetric cumulative amount in the particle size distribution curve of silicon particles, Dv10 is the particle size corresponding to 10% of the volumetric cumulative amount in the particle size distribution curve of silicon particles, and Dv90 is the particle size corresponding to 90% of the volumetric cumulative amount in the particle size distribution curve of silicon particles. Dv50, Dv90, and Dv10 can be measured, for example, using a laser diffraction method. Laser diffraction can typically measure particle sizes from the submicron region to several millimeters, and can obtain highly reproducible and high-resolution results. As a laser diffraction analysis instrument, the Shimadzu SALD-2300 instrument can be used, and ethanol can be used as a solvent for particle size analysis.

[0050] With silicon particles satisfying Equation 2, the capacity, initial efficiency, and lifespan characteristics of the battery can be significantly improved.

[0051] More specifically, the [Dv50-Dv10] / [Dv90-Dv50] value represents the ratio of fine powder to coarse powder in a silicon powder mix. A smaller [Dv50-Dv10] / [Dv90-Dv50] value indicates a lower proportion of fine powder to coarse powder, while a larger value indicates a higher proportion of fine powder to coarse powder. If the [Dv50-Dv10] / [Dv90-Dv50] value is too large, it means an excessive proportion of fine powder, which may lead to side reactions with the electrolyte, resulting in gas generation, loss of electrical contact, and other problems, thus reducing lifetime characteristics. Conversely, if the [Dv50-Dv10] / [Dv90-Dv50] value is too small, it means an excessive proportion of coarse powder, increasing the volume expansion rate and also leading to a decrease in lifetime characteristics.

[0052] Furthermore, the inventors have experimentally demonstrated that as the silicon particles according to the present invention satisfy Equation 2, not only are the lifetime characteristics improved, but also the capacity and initial efficiency are enhanced. This appears to be because the optimal ratio of fine to coarse powder allows the silicon particles to participate uniformly in the electrochemical reaction.

[0053] The silicon particles can satisfy the following formula 3.

[0054] [Formula 3] Dv90≤10μm In Equation 3, Dv90 is the particle size corresponding to 90% of the volumetric accumulation in the particle size distribution curve of silicon particles.

[0055] As silicon particles satisfy Equation 3, the proportion of excessively large coarse particles decreases. With a large number of coarse particles, repeated charging and discharging leading to continuous contraction and expansion can cause cracks and generate a large amount of fine powder. Furthermore, the increased migration distance of lithium ions within the silicon particles can lead to capacity or initial efficiency degradation. Therefore, reducing the proportion of coarse particles decreases the rate of fine powder generation caused by repeated charging and discharging, thereby improving lifetime characteristics. Additionally, shortening the migration distance of lithium ions within the silicon particles can improve both capacity and initial efficiency.

[0056] More specifically, the Dv90 may be 9μm, 8μm, or less than 7.7μm.

[0057] The silicon particles can satisfy the following equation 4.

[0058] [Formula 4] [Dv90-Dv10] / Dv50≤1.1 In Equation 4, Dv50 is the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of silicon particles, Dv10 is the particle size corresponding to 10% of the cumulative volume in the particle size distribution curve of silicon particles, and Dv90 is the particle size corresponding to 90% of the cumulative volume in the particle size distribution curve of silicon particles.

[0059] If the [Dv90-Dv10] / Dv50 value of silicon particles is too large, it means that the particle size distribution is too wide, which may lead to a deterioration of lifespan characteristics due to a large amount of coarse and fine powder.

[0060] The volume average particle size (Dv50) of the silicon particles can be 4 to 6 μm. If the volume average particle size of the silicon particles is too small, the efficiency will decrease due to the increased specific surface area, and there may be a problem with the lifetime characteristics. If the volume average particle size of the silicon particles is too large, the fine powdering will intensify, and there may be a problem with the lifetime characteristics.

[0061] The tap density of the silicon particles can be 0.9 g / cm³. 3 The above, more specifically, is 1.0 g / cm³. 3 Or 1.04 g / cm 3 The above is an explanation of the principle that as the tap density of silicon particles becomes sufficiently high, the electrode energy density can be improved. The tap density of silicon particles represents the degree of filling of a sample per unit volume and can be measured using methods commonly used in the art. For example, it can be calculated as the density (sample weight / volume) by mechanically dropping a measuring container containing the sample from a predetermined height a predetermined number of times, using the measuring instruments and methods specified in ASTM B527.

[0062] The BET specific surface area of the silicon particles may be 1.4 to 2.2 m 2 / g. If the specific surface area of the silicon particles is too small, it means there is too much coarse powder, and the capacity, initial efficiency, and life characteristics may deteriorate. If the specific surface area of the silicon particles is too large, it means there is too much fine powder, and the capacity, initial efficiency, and life characteristics may deteriorate. For the BET specific surface area, it can be measured by the BET method (specific surface area and porosity analyzer) (Micromeritics, ASAP2020).

[0063] The average grain size of the silicon particles may be 200 nm or less, more specifically 180 nm or 160 nm or less, and 140 nm or 145 nm or more. Since the average grain size of the silicon particles is so small enough, the degree of volume expansion and contraction during charge and discharge becomes smaller, and the life characteristics of the battery can be improved. However, if the grain size of the silicon particles is too small, particle breakage may occur due to excessive processing or the charge-discharge volume change pattern may change.

[0064] In this specification, the grain size of the silicon particles can be measured by analyzing the X-ray diffraction data of the active material cross-section by the Rietveld refinement method. For example, the grain size can be obtained by performing X-ray diffraction analysis using a Bruker D8 Discover with GADDS XRD device under the following conditions to obtain XRD data, and then processing the XRD data using the Bruker DIFFRAC.TOPAS program. At this time, the full width at half maximum is set to be measured using the Caglioti equation.

[0065] <X-ray diffraction analysis conditions> Light source: Cu-target, 45 kV, 40 mA output, wavelength = 1.54 Å Detector: GaliPIX3D Sample preparation: Fill about 2 g of the sample into a sample holder with a diameter of 2 cm and load it onto a rotation stage.

[0066] Measurement time: about 20 minutes Measurement area: 2θ = 10° ~ 90° In addition, the strain of the silicon particles may be 10×10 -5 or more, more specifically 10.5×10 -5 or 11.7×10 -5 or more, and 13×10 -5 or less or 12.5×10 -5As mentioned above, sufficiently large strain on silicon particles can improve battery life characteristics. However, if the strain on silicon particles is too large, the internal stress of the particles increases, potentially making them more brittle to impacts. Furthermore, volume expansion during charging leads to rapid pulverization of the particles, which can result in rapid electrode degradation.

[0067] In this specification, strain is a value measured by Rietveld refinement analysis of X-ray diffraction data, representing the average deviation of the lattice spacing d, which is a value representing the degree of lattice distortion and satisfies the following formula.

[0068]

[0069] at this time, This represents the full width at half maximum (FWHM) of the profile component associated with micro-strain widening.

[0070] 2. Preparation method of negative electrode active material For the various physical properties of silicon particles according to the present invention, including the above-mentioned HS roundness, Dv1 value, average aspect ratio, and [Dv50-Dv10] / [Dv90-Dv50] value, various physical properties can be appropriately obtained within the scope of the present invention when prepared according to the following series of preparation methods.

[0071] The following describes a method for preparing a lithium secondary battery negative electrode active material according to another embodiment of the present invention.

[0072] A method for preparing a lithium secondary battery negative electrode active material according to another embodiment of the present invention may include: a step of first pulverizing metallic silicon powder; a step of second pulverizing the first pulverized metallic silicon powder; a step of first classifying the second pulverized metallic silicon powder; a step of third pulverizing the first classified metallic silicon powder; and a step of second classification of the third pulverized metallic silicon powder. These steps will be described in further detail below.

[0073] First, the metallic silicon powder is first pulverized.

[0074] At this point, the metallic silicon powder may contain more than 98% silicon and other unavoidable impurities by total weight.

[0075] The first pulverization can be carried out using equipment commonly used in the art, and there are no particular limitations. For example, the first pulverization can be carried out using a rotary cutter mill, but it is not limited to this.

[0076] At this point, the first pulverization can be carried out until the volumetric particle size (D90) of the silicon metal powder reaches below 4 mm. This improves the pulverization efficiency in the subsequent second pulverization process and allows for the initial removal of excessively large coarse powder.

[0077] Next, the first pulverized silicon metal powder is subjected to a second pulverization.

[0078] The second pulverization can be carried out using equipment commonly used in the art, and there are no particular limitations. For example, the second pulverization can be carried out using one or more selected from jet mills, ball mills, stirred media mills, roll mills, hammer mills, pin mills, disk mills, colloid mills, and atomizer mills, but is not limited thereto.

[0079] At this point, the second pulverization can be carried out until the volumetric reference particle size (Dv30) of the silicon powder reaches 150 μm or more. This prevents the generation of large amounts of fine or ultrafine powder during the subsequent third pulverization process. More specifically, by removing silicon powder with an excessively small volumetric reference particle size (Dv30) during the second pulverization, collisions between particles of appropriate size can be induced during the subsequent third pulverization process, thereby preventing the generation of large amounts of fine or ultrafine powder in the final product. Therefore, within the scope of the present invention, the Dv1 value, average HS roundness, average aspect ratio, and [Dv50-Dv10] / [Dv90-Dv50] value of the silicon particles as the final product can be appropriately obtained.

[0080] Next, the second pulverized silicon metal powder is subjected to a first classification.

[0081] The first grading can be performed, for example, by grading through a mesh screen, but is not necessarily limited to this.

[0082] At this point, the first classification can be carried out to remove metallic silicon powder with a particle size of less than 100 μm. Accordingly, the grinding efficiency in the subsequent third grinding process can be improved, thereby reducing the fine powder generation rate in the final product. The upper limit of the particle size of the removed metallic silicon powder can be controlled, for example, by appropriately adjusting the sieve aperture. Therefore, within the scope of the present invention, the Dv1 value, average HS roundness, average aspect ratio, [Dv50-Dv10] / [Dv90-Dv50] value, etc., of the silicon particles as the final product can be appropriately obtained.

[0083] Next, the first graded silicon metal powder is subjected to a third pulverization.

[0084] The third grinding process can be carried out using grinding equipment commonly used in the art, and there are no particular limitations. For example, the third grinding can be carried out using one or more selected from jet mills, spiral jet mills, ball mills, stirred media mills, roll mills, hammer mills, pin mills, disk mills, colloid mills, and atomizer mills, but is not limited thereto.

[0085] At this point, the third pulverization can be carried out until the average particle size (D50) of the silicon metal powder reaches 4 to 6 μm. Accordingly, the average particle size (D50) of the final product can be appropriately obtained within the scope of this invention.

[0086] Next, the third pulverized silicon metal powder is subjected to a second classification.

[0087] For the second classification, for example, any one of gravity type, inertial type, or centrifugal type can be used, but it is not necessarily limited to this.

[0088] At this point, the second grading can be adjusted so that the yield of silicon powder (as the final product) with a second grading result span (SPAN) ((D90-D10) / D50) value of less than 1 based on the total weight of the starting raw material silicon powder is 30 to 40%, more specifically 32 to 38%. Therefore, within the scope of the present invention, the Dv1 value, average HS roundness, average aspect ratio, [Dv50-Dv10] / [Dv90-Dv50] value, etc., of the silicon particles as the final product can be appropriately obtained.

[0089] In this specification, the span (SPAN) value refers to the value obtained by calculating [particle size (D90) - particle size (D10)] / particle size (D50). In this case, particle size (D90), particle size (D10), and particle size (D50) can be defined as the particle size corresponding to 90%, 10%, and 50% of the cumulative volume in the particle size distribution curve, respectively.

[0090] More specifically, the second classification may include: a step of removing fine powder from the third pulverized silicon metal powder; and a step of removing coarse powder from the third pulverized silicon metal powder. In the step of removing the fine powder, fine powder with a particle size of less than 0.5 μm may be removed, and in the step of removing the coarse powder, coarse powder with a particle size of more than 25 μm may be removed.

[0091] Through the above series of processes, the lithium secondary battery negative electrode active material according to the present invention can be prepared. For the prepared negative electrode active material, various physical properties such as average HS roundness, Dv1 value, average aspect ratio, and [Dv50-Dv10] / [Dv90-Dv50] value can be appropriately obtained within the scope of the present invention. Accordingly, the battery capacity, initial efficiency, and lifespan characteristics can be uniformly improved.

[0092] 3. Negative electrode and lithium secondary battery Another embodiment of the present invention provides a negative electrode comprising the aforementioned negative electrode active material and a lithium secondary battery comprising the negative electrode.

[0093] More specifically, the lithium secondary battery negative electrode according to another embodiment of the present invention may include: a negative electrode current collector; and a negative electrode active material layer located on the negative electrode current collector and comprising the aforementioned lithium secondary battery negative electrode active material.

[0094] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, it can be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or copper or stainless steel and aluminum with surface treatments using carbon, nickel, titanium, silver, etc. Cadmium alloys, etc. Furthermore, the negative electrode current collector typically has a thickness of 3 to 500 μm, similar to the positive electrode current collector. Fine irregularities can also be formed on the surface of the current collector to enhance the adhesion of the negative electrode active material. For example, it can be in various forms such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0095] In addition to the negative electrode active material, the negative electrode active material layer may optionally contain an adhesive and / or a conductive material.

[0096] The adhesive enhances the adhesion between the negative electrode active material particles and the bonding force between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF) and polyvinylidene fluoride... Hexafluoropropylene copolymer (PVDF) co HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene Diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, may be used alone or in mixtures of two or more. The adhesive may comprise 1 to 30% by weight relative to the total weight of the negative electrode active material layer.

[0097] The conductive material is used to impart conductivity to the electrode. The conductive material can be used without restriction, as long as it does not cause chemical changes in the assembled battery and possesses electronic conductivity. Specific examples include graphite such as natural or artificial graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these materials can be used alone or in mixtures of two or more. Typically, the conductive material can comprise 1 to 30% by weight relative to the total weight of the negative electrode active material layer.

[0098] For the lithium secondary battery anode according to one embodiment of the present invention, in addition to using the aforementioned anode active material, it can be prepared according to conventional anode preparation methods.

[0099] Specifically, the negative electrode can be prepared by coating a negative electrode active material layer forming composition comprising the aforementioned negative electrode active material and optionally a binder, a conductive material, and a solvent onto a negative electrode current collector, followed by pressing and drying. In this case, the types and amounts of the negative electrode active material, binder, and conductive material are as described above.

[0100] The solvent can be any solvent commonly used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N2, etc. The solvent can be NMP, acetone, or water, or a mixture of two or more of these solvents. The amount of solvent used should be sufficient to dissolve or disperse the negative electrode active material, conductive material, and binder, taking into account the coating thickness and preparation yield of the slurry, and should exhibit excellent thickness uniformity during the coating preparation of the negative electrode.

[0101] As another method, the negative electrode can also be prepared by casting the negative electrode active material layer forming composition onto a separate support, and then stacking the film layer obtained by peeling it off from the support onto the negative electrode current collector.

[0102] Another embodiment of the present invention provides a lithium secondary battery comprising the aforementioned lithium secondary battery negative electrode.

[0103] More specifically, the lithium secondary battery may include: a positive electrode; a negative electrode located opposite the positive electrode; a separator sandwiched between the positive and negative electrodes; and an electrolyte.

[0104] Apart from the negative electrode, the positive electrode, separator, and electrolyte can be used without restriction as long as they are commonly used in this field.

[0105] The embodiments of the present invention will be further described in detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0106] Example 1 (1) Preparation of negative electrode active materials (First Grinding) The 98% pure metallic silicon powder is first ground using a rotary cutter mill. At this time, the process conditions are adjusted to form metallic silicon powder with a volumetric particle size (Dv90) of less than 4 mm.

[0107] (Second Crush) Subsequently, the silicon metal powder is subjected to a second crushing using a disk mill. At this time, the disk spacing is adjusted to form silicon metal powder with a volumetric particle size (Dv30) of 200 μm or more.

[0108] (First Classification) Subsequently, the silicon metal powder is first classified using a mesh classification method. At this time, a 200-mesh sieve is used to remove silicon metal powder with a particle size of less than 100 μm.

[0109] (Third Grinding) Subsequently, the silicon metal powder is ground a third time using a jet mill. At this stage, the air pressure (above 6 bar) and feed rate are adjusted to achieve a volumetric average particle size (Dv50) of 4 to 6 μm. The optimal conditions for air pressure and feed rate may vary depending on the specifications of the jet mill.

[0110] (Second Classification) Subsequently, the metallic silicon powder is subjected to a second classification using an airflow classification method. At this time, coarse powder with a particle size of 25 μm or larger and fine powder with a particle size of 0.5 μm or smaller are removed by airflow classification. Thus, the yield of silicon particles (final product) with a span (SPAN) ((D90-D10) / D50) value of 1 or less based on the total weight of the starting material metallic silicon powder is controlled at 35%.

[0111] (2) Preparation of negative electrode The prepared negative electrode active material was mixed with a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a mass ratio of 96:1:1.5:1.5, and then dispersed in deionized distilled water to prepare a negative electrode active material layer composition. This composition was coated onto a copper foil current collector, then dried and pressed to prepare an electrode with a density of 1.40 ± 0.05 g / cm³. 3 The negative electrode.

[0112] (3) Preparation of lithium secondary batteries The negative electrode was used as the working electrode, and lithium metal was used as the counter electrode to fabricate a coin-type 2032 half-cell. A membrane made of porous polypropylene film was inserted between the working electrode and the counter electrode as the electrolyte. A 1M LiPF6 electrolyte was dissolved in a mixed solution of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0113] Example 2 In the first classification step, a 270-mesh sieve was used to remove metallic silicon powder with a particle size of less than 70 μm. Otherwise, the implementation method was the same as in Example 1, thereby preparing the negative electrode active material, the negative electrode, and the lithium secondary battery.

[0114] Example 3 In the first classification step, a 325-mesh sieve was used to remove metallic silicon powder with a particle size of less than 50 μm. Otherwise, the implementation method was the same as in Example 1, thereby preparing the negative electrode active material, the negative electrode, and the lithium secondary battery.

[0115] Example 4 In the second pulverization step, the disk spacing is adjusted to form metallic silicon powder with a volume reference particle size (Dv30) of 150 μm or more. Otherwise, the implementation method is the same as in Example 1, thereby preparing a negative electrode active material, a negative electrode and a lithium secondary battery.

[0116] Comparative Example 1 The first grading step was omitted, but the implementation method was the same as in Example 1, thereby preparing the negative electrode active material, the negative electrode, and the lithium secondary battery.

[0117] Comparative Example 2 In the second classification step, the speed of the fine powder adjustment classification wheel is increased to partially increase the fine powder content. The yield of span (SPAN) values ​​below 1 is set at 41%. Otherwise, the implementation method is the same as in Example 1, thereby preparing the negative electrode active material, the negative electrode, and the lithium secondary battery.

[0118] Comparative Example 3 In the second pulverization step, the pulverization intensity is adjusted to be strong to form metallic silicon powder with a volume reference particle size (Dv30) of less than 100 μm, and the first classification step is not performed. Otherwise, the implementation method is the same as in Example 1, thereby preparing the negative electrode active material, the negative electrode and the lithium secondary battery.

[0119] Comparative Example 4 The second grading step was not performed. Otherwise, the implementation method was the same as in Example 1, thereby preparing the negative electrode active material, the negative electrode, and the lithium secondary battery.

[0120] Table 1 below is a table summarizing the process conditions for the examples and comparative examples.

[0121] Table 1

[0122] Experimental Example 1: Evaluation of SEM Images of Negative Electrode Active Materials SEM images of the negative electrode active material prepared according to Example 1 were evaluated and are shown below. Figure 1 middle.

[0123] Reference Figure 1 It can be confirmed that the negative electrode active material of Example 1 has a single-particle morphology. In addition, it can be confirmed that no needle-like or scaly particles were observed.

[0124] Experimental Example 2: Evaluation of the physical properties of negative electrode active materials (1) Evaluation of volume reference particle sizes (Dv1, Dv10, Dv50, Dv90) The volumetric reference particle sizes (Dv1, Dv10, Dv50, Dv90) were evaluated using the laser diffraction method. Dv1, Dv10, Dv50, and Dv90 can be defined as the particle sizes corresponding to 1%, 10%, 50%, and 90% of the cumulative volume fraction in the particle size distribution curve. A Shimadzu SALD-2300 laser diffraction instrument was used for the analysis, and ethanol was used as the solvent.

[0125] (2) Evaluation of average HS roundness The average HS (High Sensitivity) roundness of the negative electrode active material is obtained by deriving the average HS roundness of 10,000 silicon particles with a solidity value exceeding 0.96. Here, the "solidity value" refers to the value obtained by dividing the actual area of ​​the particle by the area of ​​the particle's bulge region.

[0126] On the other hand, the HS roundness of a single silicon particle is obtained through the following relationship 1: [Relation 1]

[0127] In Equation 1, the area refers to the total area of ​​the particle obtained from the individual 2D image of each particle by the image analysis device, and the perimeter refers to the total perimeter of the particle obtained from the individual 2D image of each particle by the image analysis device.

[0128] This roundness was measured using an analyzer (Malvern Panalytical, Morphologi 4) used to acquire optical images.

[0129] (3) Evaluate the average aspect ratio The "average aspect ratio" can be obtained by calculating the average aspect ratio of any 50 silicon particles observed in a SEM (scanning electron microscope) image. This aspect ratio can be measured using an analyzer (Malvern Panalytical, Morphologi 4) used to acquire optical images. In this case, the "aspect ratio" can refer to the ratio of the shortest side to the longest side within the silicon particle.

[0130] (4) Evaluation of tap density According to ASTM-B527, 15g of active material powder was placed in a 25mL graduated cylinder and then tapped 3000 times at 284 times / minute to measure the filling density.

[0131] (5) Evaluation of BET specific surface area The specific surface area was measured using the BET method (Specific Surface Area and Porosity Analyzer) (Micromeritics, ASAP2020).

[0132] (6) Evaluation of average grain size XRD data of the active material were measured using a Bruker D8 Discover with GADDS XRD instrument, and the average crystal size was evaluated using the Rietveld refinement method built into the Bruker DIFFRAC.TOPAS program.

[0133] Table 2

[0134] Table 3

[0135] Referring to Tables 2 and 3, it can be confirmed that for the negative electrode active material of the embodiment according to the present invention, with the process conditions properly controlled, various physical properties, including the average HS roundness and Dv1 value, are appropriately obtained within the scope of the present invention. On the other hand, for Comparative Example 1, since the first classification was not performed, it can be confirmed that the average HS roundness and average aspect ratio are slightly reduced, and the obtained [Dv50-Dv10] / [Dv90-Dv50] value is too large.

[0136] For Comparative Example 2, when the second classification was performed, the speed of the fine powder adjusting classification wheel was too fast, resulting in the yield of the span value below 1 being adjusted too high. As a result, the obtained Dv1 value was small, the average HS roundness and the average length-to-width ratio decreased slightly, and the obtained [Dv50-Dv10] / [Dv90-Dv50] value was too large.

[0137] For Comparative Example 3, when the second crushing was performed, Dv30 was adjusted too small and the first grading was not performed. As a result, the obtained Dv1 value was small. Compared with Comparative Example 1, the average HS roundness and average length and width further decreased, and the obtained [Dv50-Dv10] / [Dv90-Dv50] value was too large.

[0138] For Comparative Example 4, since the second grading was not performed, the resulting Dv1 value was very small, the average HS roundness and average aspect ratio were reduced, and the resulting [Dv50-Dv10] / [Dv90-Dv50] value was too large.

[0139] At this point, the reason for the deterioration of the HS roundness in Comparative Examples 1 to 3 is that the process conditions were not properly controlled during the second crushing, first classification, or second classification, resulting in an increase in the fine powder content in the silicon particles added to the third crushing process, thereby generating a large number of needle-like or scaly particles during the third crushing process.

[0140] Furthermore, the reason for the deterioration of the roundness of HS in Comparative Example 4 is that fine and coarse powders were not properly removed during the second grading process.

[0141] Experiment Example 3: Evaluation of the Electrochemical Characteristics of Lithium Secondary Batteries (1) Evaluate the initial discharge capacity and initial efficiency After fabricating the CR2032 lithium-ion rechargeable battery half-cell, it was aged at 25°C for 30 hours, followed by charge-discharge testing. To evaluate the initial capacity, using 3500 mAh / g as the baseline capacity, it was charged at a constant current of 0.1C to 5mV, and then switched to constant voltage charging until the cutoff current reached 0.005C. After charging, it was allowed to stand for 10 minutes, and then discharged at a constant current of 0.1C to 1.0V, using 3500 mAh / g as the baseline capacity.

[0142] (2) Evaluation of life characteristics For lifetime characteristics, the cells were charged at 25°C with a constant current of 0.5C to 5mV, then switched to a constant voltage and charged until the cutoff current reached 0.005C. After charging, the cells were allowed to rest for 10 minutes, and then discharged with a constant current of 0.5C to 1.0V. This charge-discharge condition was repeated 100 times, and the capacity retention rate relative to the first cycle was calculated for the 100th cycle.

[0143] Table 4

[0144] Referring to Table 4, it can be confirmed that for the embodiments where the average HS roundness and Dv1 value of the negative electrode active material meet the scope of the present invention, the initial capacity, initial efficiency, and lifetime characteristics are all excellent. On the other hand, for the comparative examples, the results, such as the average HS roundness, are outside the scope of the present invention, and the initial capacity, initial efficiency, and lifetime characteristics are deteriorated compared to the embodiments.

[0145] Furthermore, for Comparative Examples 2 to 4, results such as Dv1 value and average HS roundness are outside the scope of the present invention, and the initial capacity, initial efficiency, and lifetime characteristics are degraded compared to the examples.

[0146] On the other hand, comparing Examples 1 to 2 with Examples 3 to 4, it can be confirmed that Examples 1 to 2, which have better control over Dv1 value, average HS roundness, or average aspect ratio, have better capacity, lifespan characteristics, and tap density (see Tables 3 and 4) than Examples 3 to 4.

[0147] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto. Various modifications can be made within the scope of the claims, specification, and drawings, and these modifications also fall within the scope of the present invention.

[0148] Therefore, the substantive scope of the present invention is defined by the claims and their equivalents.

Claims

1. A lithium secondary battery anode active material, wherein, The lithium secondary battery negative electrode active material comprises silicon particles with a single particle morphology and a polycrystalline structure. The average HS roundness is 0.875 or higher, and satisfies the following formula 1. [Formula 1] Dv1≥2μm In Equation 1, Dv1 is the particle size corresponding to 1% of the volumetric accumulation in the particle size distribution curve of silicon particles.

2. The lithium secondary battery negative electrode active material according to claim 1, wherein, For the silicon particles, the average aspect ratio can be 0.695 or higher.

3. The lithium secondary battery negative electrode active material according to claim 1, wherein, The silicon particles satisfy the following formula 2. [Equation 2] 0.70≤[Dv50-Dv10] / [Dv90-Dv50]≤0.80 In Equation 1, Dv50 is the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of silicon particles, Dv10 is the particle size corresponding to 10% of the cumulative volume in the particle size distribution curve of silicon particles, and Dv90 is the particle size corresponding to 90% of the cumulative volume in the particle size distribution curve of silicon particles.

4. The lithium secondary battery negative electrode active material according to claim 1, wherein, The silicon particles satisfy the following formula 3. [Formula 3] Dv90≤10μm In Equation 3, Dv90 is the particle size corresponding to 90% of the volumetric accumulation in the particle size distribution curve of silicon particles.

5. The lithium secondary battery negative electrode active material according to claim 1, wherein, The silicon particles satisfy the following formula 4. [Formula 4] [Dv90-Dv10] / Dv50≤1.1 In Equation 4, Dv50 is the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of silicon particles, Dv10 is the particle size corresponding to 10% of the cumulative volume in the particle size distribution curve of silicon particles, and Dv90 is the particle size corresponding to 90% of the cumulative volume in the particle size distribution curve of silicon particles.

6. The lithium secondary battery negative electrode active material according to claim 1, wherein, The volume average particle size (Dv50) of the silicon particles is 4 to 6 μm.

7. The lithium secondary battery negative electrode active material according to claim 1, wherein, The average grain size of the silicon particles is below 200 nm.

8. The lithium secondary battery negative electrode active material according to claim 1, wherein, The silicon particles have a Si purity of over 98%.

9. A lithium secondary battery negative electrode comprising the negative electrode active material according to any one of claims 1 to 8.

10. A lithium secondary battery comprising the lithium secondary battery negative electrode of claim 9.

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