Negative electrode active material, negative electrode, secondary battery, and method for manufacturing negative electrode active material

Abstract

The negative electrode active material of the present invention includes silicon-based particles; and silicon carbide distributed within the silicon-based particles, and the silicon carbide is included in an amount of 0.1 to 1 part by weight based on 100 parts by weight of the total negative electrode active material.

Description

Technical Field

[0001] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2023-0058454 filed with the Korean Intellectual Property Office on May 4, 2023, and Korean Patent Application No. 10-2024-0016464 filed with the Korean Intellectual Property Office on February 2, 2024, the entire contents of which are incorporated herein.

[0002] The present invention relates to a negative electrode active material, a negative electrode, a secondary battery, and a method for producing a negative electrode active material.

Background Art

[0003] With the rapid popularization of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, demand for secondary batteries that are compact and lightweight while having relatively high capacity is rapidly increasing. Lithium secondary batteries are lightweight and have high energy density, so they are attracting attention as driving power sources for portable devices. Accordingly, research and development efforts to improve the performance of lithium secondary batteries are being actively carried out.

[0004] In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, an electrolytic solution, and an organic solvent. Further, on the positive electrode and the negative electrode, active material layers respectively containing a positive electrode active material and a negative electrode active material on a current collector may be formed. A lithium-containing metal oxide such as LiCoO2 or LiMn2O4 is used as the positive electrode active material for the positive electrode, and a lithium-free carbon-based active material and a silicon-based negative electrode active material are used as the negative electrode active material for the negative electrode.

[0005] In general, a carbon material such as graphite is used as an active material for the negative electrode of a lithium secondary battery, but the theoretical capacity density of carbon is 372 mAh / g (833 mAh / cm 3Therefore, in order to improve the energy density of the negative electrode, silicon (Si), tin (Sn), and their oxides and alloys, which can be alloyed with lithium, are being considered as negative electrode active materials. Among these, silicon-based materials are attracting attention because they have lower cost and higher capacity (4200 mAh / g) compared to carbon-based active materials, and they have excellent fast charging characteristics (see Korean Patent Publication No. 10-2020-0065514). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Korean Published Patent No. 10-2020-0065514 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention relates to a negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for producing a negative electrode active material. [Means for solving the problem]

[0008] One embodiment of the present invention provides a negative electrode active material comprising silicon-based particles and silicon carbide distributed within the silicon-based particles, wherein the silicon carbide is present in an amount of about 0.1 parts by weight or more and 1 part by weight or less based on 100 parts by weight of the total negative electrode active material.

[0009] One embodiment of the present invention provides a negative electrode containing the negative electrode active material. One embodiment of the present invention provides a secondary battery including the negative electrode. One embodiment of the present invention provides a method for producing the negative electrode active material. [Effects of the Invention]

[0010] One embodiment of the present invention provides a negative electrode active material containing a small amount of silicon carbide distributed within silicon-based particles. Silicon carbide is a mechanically stable material with very strong bonding properties, and when distributed within Si, it can suppress particle cracking of the active material due to charging and discharging, thereby improving electrode life characteristics. Therefore, for example, when a small amount of silicon carbide is distributed within the silicon-based particles within the range described above, the electrode life characteristics can be effectively improved. Such a negative electrode active material is advantageous in terms of cost and process because, during synthesis, silicon carbide is formed during the reduction process of the raw materials without the addition of any other materials.

[0011] Therefore, a negative electrode containing a negative electrode active material according to one embodiment of the present invention, and a secondary battery containing the negative electrode, have the effect of improving the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery. [Modes for carrying out the invention]

[0012] The following provides a more detailed explanation of this specification. In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0013] In this specification, when one member is described as being "on top of" another member, this includes not only cases where one member is in contact with another member, but also cases where another member exists between the two members.

[0014] The terms and words used herein should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best explain their invention.

[0015] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless the context clearly indicates otherwise, the singular expressions of the terms herein include plural expressions.

[0016] In this specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis. X-ray diffraction analysis may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endeavor, manufacturer: bruker), or other instruments used in this industry may be appropriately employed.

[0017] In this specification, the presence and content of elements in the negative electrode active material can be confirmed by inductively coupled plasma (ICP) analysis, which may be performed using an inductively coupled plasma emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0018] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size at 50% of the cumulative volume in the particle size distribution curve (graph curve of the particle size distribution diagram). 50 This can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can obtain highly reproducible and high-resolution results.

[0019] As used herein, “approximately,” “abstractly,” and “substantially” are used to mean within or near the range of their numerical or degree, taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly exploiting disclosures that refer to precise or absolute numerical values ​​provided to aid in understanding the invention.

[0020] Silicon-based negative electrode active materials, used as negative electrode active materials in lithium secondary batteries, have the disadvantage of low initial efficiency due to their relatively large volume expansion / contraction during charging and discharging, and their relatively large irreversible capacity. In the charge-discharge reaction of lithium secondary batteries, lithium ions released from the positive electrode are inserted into the negative electrode during charging, and lithium ions inserted into the negative electrode are released from the negative electrode and return to the positive electrode during discharging. However, in the case of silicon-based negative electrode active materials, the volume change and surface side reactions are strong, and a large portion of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode, resulting in a problem of large initial irreversible capacity. A large initial irreversible capacity leads to a problem of rapid decrease in battery capacity and cycle life. In addition, as the charge / discharge cycle progresses, silicon-based negative electrode active materials experience cracking, inducing a sustained degradation of lifespan. Conventional silicon-based negative electrode active material materials are composed only of pure silicon, and the mechanical strength of the material itself is low, which is disadvantageous in terms of suppressing electrode volume expansion.

[0021] The present invention provides a silicon-based negative electrode active material in which cracking phenomena are improved, a method for manufacturing the same, and a lithium secondary battery in which discharge capacity, initial efficiency, resistance performance and / or life characteristics are improved by employing such an improved negative electrode active material.

[0022] Embodiments of the present invention will be described in detail below. However, embodiments of the present invention may be modified into various forms, and the scope of the present invention is not limited to the embodiments described below.

[0023] <Negative electrode active material> One embodiment of the present invention provides a negative electrode active material comprising silicon-based particles and silicon carbide distributed within the silicon-based particles, wherein the silicon carbide is present in an amount of about 0.1 parts by weight or more and 1 part by weight or less based on 100 parts by weight of the total negative electrode active material.

[0024] Compared with conventionally used graphite-based active materials, silicon-based particles have a significantly higher capacity. For this reason, there have been many attempts to apply silicon-based particles as negative electrode active materials. However, the volume expansion rate of silicon-based particles becomes large during charge and discharge cycles, and various side effects occur due to this expansion, so silicon-based particles are currently only used in applications such as being mixed in trace amounts with graphite-based active materials.

[0025] A negative electrode active material according to one embodiment of the present invention has silicon carbide distributed in silicon-based particles at a content of about 0.1 parts by weight or more and 1 part by weight or less based on 100 parts by weight of the total negative electrode active material, thereby effectively improving electrode life characteristics, and thus suppressing particle cracking of the negative electrode active material during charge and discharge cycles of a battery. In addition, when the above-described negative electrode active material is synthesized, silicon carbide is formed during the reduction process of the raw material without adding a separate material, which is advantageous in terms of cost and process compared to methods involving adding an additional separate material.

[0026] According to one embodiment, silicon oxide (SiO₂) powder is heated at about 1,800°C in a carbon atmosphere (2C) to be reduced into molten silicon. Thereafter, the molten silicon is cooled at a preset cooling rate, for example, a rate of about 20°C / min to 70°C / min, to additionally form silicon carbide (SiC) particles outside the silicon (Si) particles. Through this cooling step, silicon oxide (SiO₂) remaining unreacted from the preceding reduction step reacts with carbon (C) to additionally form silicon carbide (SiC) particles. Meanwhile, when the cooling step is performed at the preset rate of about 20°C / min to 70°C / min, silicon carbide (SiC) is distributed in the silicon (Si) particles at a content of about 0.1 parts by weight or more and 1 part by weight or less based on 100 parts by weight of the total negative electrode active material.

[0027] A negative electrode active material according to one embodiment of the present invention comprises silicon-based particles. In one embodiment of the present invention, the silicon-based particles may comprise one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and Si alloys.

[0028] The silicon-based particles may include one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2).

[0029] The silicon-based particles may include SiOx (x=0). Based on 100 parts by weight of the negative electrode active material, the silicon-based particles may include about 70 parts by weight or more of SiOx (x=0). For example, based on 100 parts by weight of the negative electrode active material, the silicon-based particles may include 80 parts by weight or more, or 90 parts by weight or more of SiOx (x=0), and may include 100 parts by weight or less, for example, 99.5 parts by weight or less, or 99 parts by weight or less of SiOx (x=0).

[0030] In one embodiment of the present invention, when the silicon-based particles include SiOx (x=0) within the above content range, the present invention has an advantage of exhibiting a higher discharge capacity per weight than a case where the silicon-based particles include SiOx (0<x<2) within the above content range instead of SiOx (x=0).

[0031] For example, when the silicon-based particles include SiOx (x=0) within the above content range, the discharge capacity per weight of a secondary battery including the same is about 3400 mAh / g or more; when the silicon-based particles include SiOx (0<x<2) within the above content range, the discharge capacity per weight of a secondary battery including the same is about 1400 mAh / g. Therefore, in the secondary battery to which the negative electrode active material according to an example of the present invention is applied, since the silicon-based particles include SiOx (x=0) within the above content range, the secondary battery can exhibit a capacity about twice or more higher than that when the silicon-based particles include SiOx (0<x<2) within the above content range.

[0032] However, in the case of a negative electrode active material containing SiOx (x=0) as the silicon-based particles within the above content range, particle cracking occurs due to excessive volume expansion during charge and discharge in a secondary battery using the same, which may impair the capacity retention rate. Therefore, there may be application problems in actual products. Accordingly, the negative electrode active material according to an example of the present invention contains SiOx (x=0) as the silicon-based particles within the above content range, and further contains silicon carbide in the silicon-based particles in an amount of about 0.1 part by weight or more and 1 part by weight or less based on 100 parts by weight of the total negative electrode active material, whereby the above-mentioned problems can be improved.

[0033] When SiOx (x=0) is contained as the silicon-based particles within the above content range and silicon carbide is contained within the above content range in the silicon-based particles, particle cracking caused by volume expansion during charge and discharge that occurs when using silicon-based particles as a negative electrode active material is minimized, the capacity retention rate of the negative electrode active material is improved, application problems are compensated for, and a negative electrode active material, a negative electrode, and / or a secondary battery that exhibits a relatively higher discharge capacity per weight compared to conventional cases can be provided.

[0034] In one embodiment of the present invention, pure silicon (Si) particles may be used as the silicon-based particles. Using pure silicon (Si) particles as the silicon-based particles can mean that, based on 100 parts by weight of the total silicon-based particles, pure Si particles (SiOx (x=0)) not bound to other particles or elements are contained within the above range. That is, in one embodiment of the present invention, the silicon-based particles may consist of silicon-based particles containing 100 parts by weight of SiOx (x=0) based on 100 parts by weight of the total silicon-based particles.

[0035] In one embodiment of the present invention, the silicon-based particles may contain SiOx (0<x<2) in an amount of about 10 parts by weight or less, for example 5 parts by weight or less, or 3 parts by weight to 5 parts by weight, based on 100 parts by weight of the negative electrode active material. That is, the silicon-based particles may further contain other trace amounts of impurities.

[0036] In one embodiment of the present invention, the silicon-based particles may contain metallic impurities, in which case the metallic impurities may be metals that can be commonly found in silicon-based particles, for example, in an amount of about 0.1 parts by weight or less based on 100 parts by weight of silicon-based particles.

[0037] In one embodiment of the present invention, the silicon-based particles may exist, for example, in a crystalline or amorphous form, and may be porous or non-porous. In one example, the silicon-based particles may not be porous. The silicon-based particles may be, for example, spherical or multi-piece particles. Alternatively, the silicon-based particles may have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0038] A negative electrode active material according to one embodiment of the present invention includes silicon carbide distributed in the silicon-based particles.

[0039] In this specification, the silicon carbide has a bond between Si and C. Silicon carbide is a mechanically stable material with very strong bonding forces, and when distributed within Si, it can suppress particle cracking of the active material due to charging and discharging, thereby improving electrode life characteristics. Therefore, as described above, by distributing silicon carbide within the silicon-based particles, particle cracking of the active material can be prevented, and electrode life characteristics can be effectively improved.

[0040] In one embodiment of the present invention, the silicon carbide may be included in an amount of about 0.1 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the total negative electrode active material. For example, the silicon carbide may be included in an amount of more than 0.1 parts by weight and 1 part by weight or less, based on 100 parts by weight of the total negative electrode active material, the silicon carbide may be included in an amount of about 0.2 parts by weight or more and 0.8 parts by weight or less, based on 100 parts by weight of the total negative electrode active material, or the silicon carbide may be included in an amount of about 0.4 parts by weight or more and 0.8 parts by weight or less, based on 100 parts by weight of the total negative electrode active material.

[0041] Therefore, when a small amount of silicon carbide is distributed inside or on the surface of silicon-based particles within the range described above, the decrease in electrode capacity can be minimized, particle cracking of the active material can be effectively prevented, and the life characteristics of the electrode can be effectively improved. Since such a negative electrode active material can be formed during the reduction process of the raw materials without adding any other materials during synthesis, it is advantageous in terms of cost and process compared to the case where other materials are added. In one embodiment of the present invention, carbon may be included in a quantity of about 0.03 parts by weight to 0.3 parts by weight based on a total of 100 parts by weight of the negative electrode active material.

[0042] The silicon carbide content can be analyzed using the Rietveld refinement method of an XRD measuring device.

[0043] One embodiment of the present invention, the average particle size (D) of the negative electrode active material. 50 The particle size may be approximately 0.01 μm to 100 μm, for example, 0.5 μm to 20 μm, or 1 μm to 10 μm. When the average particle size falls within the above range, the specific surface area of ​​the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, since the size of the negative electrode active material is greater than or equal to the lower limit, the contact area between the negative electrode active material particles and the conductive material is excellent due to the composite of the conductive material and binder in the negative electrode slurry, increasing the likelihood of sustained conductive network formation and increasing the capacity retention rate. On the other hand, when the average particle size is less than or equal to the upper limit, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of uneven current density during charging and discharging.

[0044] In one embodiment of the present invention, the negative electrode active material typically has a specific BET specific surface area. The BET specific surface area of ​​the negative electrode active material is, for example, 0.01 m². 2 / g~100.0m 2 / g, or 0.1m 2 / g~50.0m 2 / g, or 0.1m2 / g to 10.0 m 2 / g, or 0.5 m 2 / g to 5 m 2 / g. The BET specific surface area is measured (using nitrogen) in accordance with DIN 66131.

[0045] <Method for Producing Negative Electrode Active Material> One embodiment of the present invention provides the above-mentioned method for producing a negative electrode active material. For example, the production method comprises: a step of reacting silicon dioxide with carbon and reducing the same to obtain silicon; and a step of forming silicon carbide by using residual carbon after the reduction. The present invention provides the method for producing the negative electrode active material, comprising: obtaining silicon by reducing silicon dioxide using carbon; and forming silicon carbide by adjusting cooling conditions after silicon synthesis.

[0046] The method for producing the negative electrode active material as described above is advantageous in terms of cost and process, because silicon carbide is formed in the reduction process of the raw material without adding any additional material during synthesis.

[0047] The step of reacting silicon dioxide with carbon and reducing the same to obtain silicon may be performed at a high temperature of about 1800°C or higher. Further, when the cooling rate is adjusted after the reduction reaction, Si or unreacted silicon dioxide in the reduction reaction reacts with residual carbon to form silicon carbide in Si. In this case, the cooling rate ranges from about 20°C / min to 70°C / min, and the content of silicon carbide in Si can be adjusted by adjusting the cooling rate. According to one embodiment, the cooling rate is, for example, more than about 20°C / min and not more than 55°C / min, for example, not less than about 23°C / min and not more than 50°C / min. After silicon carbide is formed, when XRD measurement is performed on Si particles, a Si-C peak can be confirmed, and the distribution ratio of silicon carbide can be confirmed by using the Rietveld analysis method.

[0048] On the other hand, in this embodiment, the method of producing a negative electrode active material containing silicon carbide was described as silicon reduction and cooling as described above, but it is not limited to this, and a negative electrode active material containing silicon carbide may be produced by other methods. For example, a negative electrode active material containing silicon carbide may be produced by implanting nanocarbon particles into silicon particles, under the conditions described above, for example, with a total of 100 parts by weight of the negative electrode active material, in an amount of approximately 0.1 parts by weight to 1 part by weight.

[0049] <Negative electrode> The negative electrode according to one embodiment of the present invention may include the negative electrode active material described above. For example, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material in which silicon carbide manufactured in the above process is formed within Si. Furthermore, the negative electrode active material layer may further include a binder, a thickener, and / or a conductive material.

[0050] In one embodiment of the present invention, the negative electrode current collector may generally have a thickness of about 1 μm to 100 μm. Such a negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, net, porous body, foam, nonwoven fabric.

[0051] In one embodiment of the present invention, the thickness of the negative electrode current collector may be approximately 1 μm to 100 μm, and the thickness of the negative electrode active material layer may be approximately 20 μm to 500 μm. However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0052] The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, a thickener, and / or a conductive material to at least one surface of a current collector, drying, and rolling.

[0053] In one embodiment of the present invention, the negative electrode slurry may include a negative electrode active material layer composition and a slurry solvent.

[0054] In one embodiment of the present invention, the solid content of the negative electrode slurry can be approximately 5% to 40%.

[0055] In another embodiment, the solid content of the negative electrode slurry can be in the range of approximately 5% to 40%, for example, 7% to 35%, or 10% to 30%.

[0056] The solid content of the negative electrode slurry can refer to the content of the negative electrode active material layer composition contained in the negative electrode slurry, and can also refer to the content of the negative electrode active material composition based on 100 parts by weight of the negative electrode slurry.

[0057] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity is appropriate during the formation of the negative electrode active material layer, minimizing the particle clumping phenomenon of the negative electrode active material layer composition and enabling efficient formation of the negative electrode active material layer.

[0058] In one embodiment of the present invention, the slurry solvent is not limited to any solvent that can dissolve the negative electrode active material layer composition, and for example, distilled water may be used.

[0059] In one embodiment of the present invention, the negative electrode may be formed by coating and drying the negative electrode slurry on a negative electrode current collector layer.

[0060] The slurry solvent in the negative electrode slurry may be dried during the drying step.

[0061] In one embodiment of the present invention, the negative electrode active material layer composition may contain one or more selected from the group consisting of negative electrode active material; negative electrode conductive material; and negative electrode binder.

[0062] In one embodiment of the present invention, the negative electrode active material of the present invention may be used as the negative electrode active material, or the negative electrode active material of the present invention may be used together with an additional negative electrode active material. In this case, a lithium secondary battery with improved performance in various aspects, such as cycle life characteristics, can be manufactured.

[0063] The additional negative electrode active material may be a compound that allows for the reversible insertion and removal of lithium. For example, it may be a carbon-based negative electrode active material. The additional negative electrode active material layer may also be a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; a metallic compound that can alloy with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; or SiO βMetal oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, may be used, and one or more mixtures of these may be used. A metallic lithium thin film may also be used as the negative electrode active material. In addition, either low-crystalline carbon or high-crystalline carbon may be used as the carbon material. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0064] In one embodiment of the present invention, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer comprises the negative electrode active material according to the present invention, and the negative electrode active material may be present in an amount of about 60 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer.

[0065] In another embodiment, the negative electrode active material may be included in an amount of about 60 parts by weight or more, for example, about 65 parts by weight or more, or about 70 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition, or in an amount of about 95 parts by weight or less, or 90 parts by weight or less, or 80 parts by weight or less.

[0066] The negative electrode active material layer composition according to the present invention includes a negative electrode conductive material and a negative electrode binder that together allow the volume expansion rate to be controlled during the charge and discharge process even when the negative electrode active material, which has a remarkably high capacity, is used within the specified range. As a result, the performance of the negative electrode is not reduced, and the composition exhibits excellent output characteristics during charging and discharging.

[0067] In one embodiment of the present invention, the negative electrode active material may have a non-spherical shape, and its degree of circularity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0068] In this application, the sphericity is determined by the following formula A, where A is the area and P is the boundary line. [Formula A] 4πA / P 2

[0069] Traditionally, graphite-based compounds were the only active materials used for the negative electrode. However, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based compounds to increase capacity. However, silicon-based compounds have a limitation: they rapidly expand in volume during the charge / discharge process, disrupting the conductive pathways formed within the negative electrode active material layer and actually degrading battery performance. Therefore, the type of negative electrode conductive material used in conjunction with the negative electrode active material is crucial.

[0070] In one embodiment of the present invention, the negative electrode conductive material may include one or more selected from the group consisting of point conductive material; planar conductive material; and linear conductive material.

[0071] In one embodiment of the present invention, the point-shaped conductive material can be used to improve conductivity in the negative electrode and means a conductive material that has conductivity without inducing chemical changes. For example, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and in one embodiment, carbon black may be included in terms of embodying high conductivity and having excellent dispersibility.

[0072] In one embodiment of the present invention, the point-shaped conductive material has a BET specific surface area of ​​approximately 40 m². 2 / g or more 70m 2 It may be less than / g, for example, 45m 2 / g or more 65m 2 Less than / g, or 50m 2 / g or more 60m 2 It may be less than / g.

[0073] In one embodiment of the present invention, the particle size of the dot-like conductive material may be about 10 nm to 100 nm, for example, about 20 nm to 90 nm, or 40 nm to 60 nm.

[0074] In one embodiment of the present invention, the negative electrode conductive material may include a planar conductive material.

[0075] The aforementioned planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, while simultaneously suppressing the disruption of the conductive path due to volume expansion. It is used in the concept of bulk conductive materials or plate-shaped conductive materials.

[0076] In one embodiment of the present invention, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and in one embodiment it may be plate graphite.

[0077] In one embodiment of the present invention, the average particle size (D) of the planar conductive material 50 The particle size may be 2 μm to 7 μm, for example, about 3 μm to 6 μm, or about 4 μm to 5 μm. When the above range is met, the particle size is sufficient, so dispersion becomes easy without the viscosity of the negative electrode slurry increasing too much. Therefore, the dispersion effect is superior when dispersion is performed using the same equipment and time.

[0078] In one embodiment of the present invention, the planar conductive material is D 10 The size is approximately 0.5 μm to 1.5 μm, D 50 The size is approximately 2.5 μm to 3.5 μm, D 90 The particle size may be approximately 7.0 μm or more and 15.0 μm or less.

[0079] In one embodiment of the present invention, the planar conductive material may be a planar conductive material with a high specific surface area and a high BET specific surface area, or a planar conductive material with a low specific surface area.

[0080] In one embodiment of the present invention, the planar conductive material may be any planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area without limitation. However, in one embodiment, the planar conductive material according to the present invention may be affected to some extent by dispersion in terms of electrode performance, and a planar conductive material with a low specific surface area in which dispersion problems do not occur may be used.

[0081] In one embodiment of the present invention, the planar conductive material has a BET specific surface area of ​​approximately 5 m². 2 It may be more than / g.

[0082] In another embodiment, the planar conductive material has a BET specific surface area of ​​approximately 5 m². 2 / g or more 500m 2 It may be less than / g, for example, 5m 2 / g or more 300m 2 / g or less, or 5m 2 / g or more 250m 2 / g is also acceptable.

[0083] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and its BET specific surface area is approximately 50 m². 2 / g or more 500m 2 Less than / g, for example, about 80m 2 / g or more 300m 2 / g or less, or 100m 2 / g or more 300m 2 It can satisfy the range of / g or less.

[0084] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and its BET specific surface area is approximately 5 m². 2 / g or more 40m 2 Less than / g, for example, 5m 2 / g or more 30m 2 / g or less, or 5m 2 / g or more 25m 2 It can satisfy the range of / g or less.

[0085] In addition, linear conductive materials such as carbon nanotubes may be used as the negative electrode conductive material. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may contain multiple carbon nanotube units. For example, here, "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged in parallel with substantially the same orientation along their longitudinal axes, or are twisted into a bundle or rope. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, depending on the angle and structure in which the graphite sheet is wound, it can exhibit conductive or semiconductor properties. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed during the manufacture of the negative electrode, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0086] In one embodiment of the present invention, the negative electrode conductive material may be included in an amount of about 10 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0087] In another embodiment, the negative electrode conductive material may be included in an amount of about 10 to 40 parts by weight, for example, 10 to 30 parts by weight, or 15 to 25 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0088] The negative electrode conductive material according to the present invention has a substantially different configuration from the conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present invention plays a role in controlling the contact points between the negative electrode active material, which undergoes very large volume expansion due to charging and discharging, while the positive electrode conductive material acts as a buffer during rolling, while also imparting some conductivity, and thus its configuration and role differ from that of the negative electrode conductive material according to the present invention.

[0089] Furthermore, the negative electrode conductive material according to the present invention is applied to silicon-based negative electrode active materials and has a substantially different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes with graphite-based active materials simply have smaller particles compared to the active material, and thus have the properties of improving output characteristics and imparting some conductivity. Therefore, their structure and role differ from negative electrode conductive materials applied together with silicon-based negative electrode active materials, as in the present invention.

[0090] In one embodiment of the present invention, the planar conductive material used as the negative electrode conductive material has a structure and role different from that of carbon-based active materials generally used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form to facilitate the storage and release of lithium ions.

[0091] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be represented as plate-like graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather are substances that secure conductive pathways in a planar form within the negative electrode active material layer.

[0092] In other words, in this invention, the use of plate-shaped graphite as a conductive material means that it was processed into a planar or plate-like form and used as a material to secure a conductive path, rather than to play a role in lithium storage or release. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0093] On the other hand, in the present invention, the use of a carbon-based active material as an active material means that it is processed into a point-like or spherical shape and used as a substance that plays a role in storing or releasing lithium.

[0094] In one embodiment of the present invention, the carbon-based active material, artificial graphite or natural graphite, has a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 It can satisfy the range of less than / g. In addition, plate-shaped graphite, which is a planar conductive material, has a surface form and a BET specific surface area of ​​5m². 2 It may be more than / g.

[0095] In one embodiment of the present invention, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogens of these substances are substituted with Li, Na, or Ca, or may contain a variety of copolymers thereof.

[0096] A binder according to one embodiment of the present invention plays a role in controlling the negative electrode active material and negative electrode conductive material in order to prevent twisting and structural deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based negative electrode active material. Any general binder can be applied as long as it fulfills the above role, and specifically, an aqueous binder or a PAM-based binder may be used.

[0097] In one embodiment of the present invention, the negative electrode binder may be included in a quantity of approximately 30 parts by weight or less, for example, 25 parts by weight or less, or 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition, or it may be included in a quantity of 1 part by weight or more, or 3 parts by weight or more.

[0098] <Secondary battery> A secondary battery according to one embodiment of the present invention may include a negative electrode according to the embodiment described above. For example, the secondary battery may include a negative electrode, a positive electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0099] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, which contains the positive electrode active material.

[0100] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of about 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0101] The positive electrode active material may be a commonly used positive electrode active material. For example, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.5); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples but are not limited thereto. For example, the positive electrode may be metallic lithium (Li-metal).

[0102] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0103] The positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it has conductivity in the battery without causing a chemical change. Examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal 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 alone or a mixture of two or more may be used.

[0104] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0105] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. It can be any membrane commonly used as a separation membrane in secondary batteries, and may have low resistance to ion movement in the electrolyte and excellent electrolyte moisture absorption capacity. In one embodiment, a porous polymer film, such as a porous polymer film made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, a coated separation membrane containing ceramic components or polymeric substances may be used, and may be selectively used as a single-layer or multi-layer structure.

[0106] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0107] For example, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0108] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0109] Among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents, have high dielectric constants, and dissociate lithium salts well, so they may be used as non-aqueous organic solvents. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high conductivity can be prepared.

[0110] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, as the anion of the lithium salt, 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 - You may use one or more selected from the group consisting of the following:

[0111] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0112] Another embodiment of the present invention provides a battery module and a battery pack containing the secondary battery as a unit cell. Since the battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Examples]

[0113] <Examples and Comparative Examples> Example 1 After a reduction reaction using carbon to synthesize silicon at a high temperature of 1800°C or higher, the cooling rate was adjusted as shown in Table 1 below. This allowed Si and / or remaining unreacted silicon dioxide to react with residual carbon, forming silicon carbide within the Si. Based on 100 parts by weight of the negative electrode active material, a negative electrode active material containing 0.6 parts by weight of silicon carbide and the remaining 99.4 parts by weight of Si was obtained.

[0114] Example 2 Except for varying the cooling rates after the reduction reaction as shown in Table 1 below, the experiment was carried out in the same manner as in Example 1 to obtain a negative electrode active material containing 0.1 parts by weight of silicon carbide and the remaining 99.9 parts by weight of Si, based on 100 parts by weight of the negative electrode active material.

[0115] Example 3 Except for varying the cooling rates after the reduction reaction as shown in Table 1 below, the procedure was carried out in the same manner as in Example 1 to obtain a negative electrode active material containing 0.2 parts by weight of silicon carbide and the remaining 99.8 parts by weight of Si, based on 100 parts by weight of the negative electrode active material.

[0116] Example 4 Except for varying the cooling rates after the reduction reaction as shown in Table 1 below, the procedure was carried out in the same manner as in Example 1 to obtain a negative electrode active material containing 0.4 parts by weight of silicon carbide and the remaining 99.6 parts by weight of Si, based on 100 parts by weight of the negative electrode active material.

[0117] Example 5 Except for varying the cooling rates after the reduction reaction as shown in Table 1 below, the experiment was carried out in the same manner as in Example 1 to obtain a negative electrode active material containing 0.8 parts by weight of silicon carbide and the remaining 99.2 parts by weight of Si, based on 100 parts by weight of the negative electrode active material.

[0118] Example 6 Except for varying the cooling rate after the reduction reaction as shown in Table 1 below, the procedure was carried out in the same manner as in Example 1 to obtain a negative electrode active material containing 1.0 part by weight of silicon carbide and the remaining 99.0 parts by weight of Si, based on 100 parts by weight of the negative electrode active material.

[0119] Comparative Example 1 Except for varying the cooling rate after the reduction reaction as shown in Table 1 below, the experiment was carried out in the same manner as in Example 1 to obtain a negative electrode active material consisting only of Si and no silicon carbide, based on 100 parts by weight of the negative electrode active material.

[0120] Comparative Example 2 Except for varying the cooling rates after the reduction reaction as shown in Table 1 below, the experiment was carried out in the same manner as in Example 1 to obtain a negative electrode active material containing 0.05 parts by weight of silicon carbide and the remaining 99.95 parts by weight of Si, based on 100 parts by weight of the negative electrode active material.

[0121] Comparative Example 3 Except for varying the cooling rate after the reduction reaction as shown in Table 1 below, the experiment was carried out in the same manner as in Example 1 to obtain a negative electrode active material containing 1.5 parts by weight of silicon carbide and the remaining approximately 98.5 parts by weight of Si, based on 100 parts by weight of the negative electrode active material.

[0122] Comparative Example 4 Except for varying the cooling rate after the reduction reaction as shown in Table 1 below, the experiment was carried out in the same manner as in Example 1 to obtain a negative electrode active material containing 2.0 parts by weight of silicon carbide and the remaining 98.0 parts by weight of Si, based on 100 parts by weight of the negative electrode active material.

[0123] The composition of the negative electrode active material produced in the above examples and comparative examples is shown in Table 1 below.

[0124] [Table 1]

[0125] The content of silicon carbide and C was measured using the Rietveld analysis method of an XRD analyzer.

[0126] Discharge capacity, initial efficiency, lifespan (capacity retention rate), capacity characteristic evaluation The positive electrode, negative electrode, and battery were manufactured using the positive electrode and negative electrode active materials, respectively, according to the methods described below.

[0127] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by adding the silicon-based active material listed in Table 1, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10 to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 28% by weight).

[0128] For example, the first conductive material is a plate-shaped graphite (specific surface area: 17 m²). 2 / g, average particle size (D 50 The thickness was 3.5 μm, and the second conductive material was SWCNT.

[0129] As a mixing method, the first conductive material, binder, and water were dispersed using a homo mixer at 2500 rpm for 30 minutes. Then, the second conductive material was added and dispersed for 10 minutes. After that, the silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to produce a slurry.

[0130] As the negative electrode current collector, 227 mg / 50 cm of the first negative electrode slurry was applied to one side of a copper current collector (thickness: 15 μm). 2 The material was coated with the specified load and rolled (roll press), then dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 23 μm), which was used as the negative electrode (negative electrode thickness: 38 μm, negative electrode porosity: 40.0%).

[0131] <Manufacturing of positive electrodes> As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2A cathode slurry was prepared by adding O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation (solid content concentration 78% by weight).

[0132] As the positive electrode current collector, an aluminum current collector (thickness: 12 μm) is coated on both sides with the positive electrode slurry at a rate of 537 mg / 25 cm². 2 The positive electrode was manufactured by coating the supported material with a coating and rolling it (roll press), then drying it in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) (positive electrode thickness: 77 μm, porosity: 26%).

[0133] A lithium secondary battery was manufactured by interposing a polyethylene separation membrane between the positive electrode and the negative electrodes of the above examples and comparative examples, and then injecting an electrolyte.

[0134] The electrolyte was prepared by adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte to an organic solvent mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0135] <Example of experiment> Experimental Example 1: Cycle Life and Capacity Data The life retention rate and capacity of the secondary battery containing the negative electrode manufactured as described above were evaluated using an electrochemical charge / discharge device. The secondary battery underwent in-situ cycle testing at 4.2-3.0V and 1C / 0.5C. During the test, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles. Life retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0136] Furthermore, in order to measure capacity data, a Li metal / negative electrode cell was manufactured using the negative electrode produced as described above. Subsequently, the discharge capacity of the Li metal / negative electrode cell in the first cycle performed at 1.5V-0.005V and 0.1C / 0.1C is shown.

[0137] [Table 2]

[0138] As can be seen in Table 2, Examples 1 to 6, in which electrodes were fabricated using silicon-based active materials that meet the silicon carbide content range of the present invention, showed excellent life retention rates and capacity after 200 cycles. For example, since Examples 1 to 6 contain silicon carbide within the scope of the present invention, it is thought that the stress on the silicon-based active material during charging and discharging was reduced while minimizing capacity degradation, thereby suppressing changes in electrode structure and resulting in excellent electrode life retention rates and capacity. On the other hand, Comparative Examples 1 and 2, which were electrodes with a silicon carbide content of less than 0.1 parts by weight based on 100 parts by weight of the total negative electrode active material, showed relatively low life retention rates. This is understood to be a phenomenon in which the particle cracking suppression effect by silicon carbide was reduced.

[0139] In Comparative Examples 3 and 4, electrodes with a silicon carbide content exceeding 1 part by weight (based on 100 parts by weight of the total negative electrode active material) exhibited relatively low lifetime retention and capacity. This is understood to be a phenomenon where the silicon carbide content deviates from the scope of the present invention, resulting in a lower silicon energy density.

[0140] Experimental Example 2: Cycle Resistance Increase Rate In Experimental Example 1, during testing, the battery was charged / discharged at 0.33C / 0.33C (4.2-3.0V) every 50 cycles to measure its lifespan. Then, it was discharged with a 2.5C pulse at SOC50, and the resistance was measured to compare and analyze the resistance increase rate.

[0141] For the measurement and evaluation of the aforementioned resistance increase rate, data was calculated for 200 cycles, and the results are shown in Table 3 below.

[0142] [Table 3]

[0143] As can be seen in Table 3, the resistance increase rate of the comparative example after 200 cycles was higher than that of the example. In other words, it was confirmed that when the proportion of silicon carbide does not meet the scope of the present invention, the silicon electrode structure is unstable and the resistance increases.

[0144] Although the present invention has been described above with reference to embodiments, a person skilled in the art or a person with ordinary knowledge in the art should understand that the present invention can be modified and altered in various ways without departing from the spirit and technical domain of the invention as described in the claims. Therefore, the technical scope of the present invention is not limited to what is described in the detailed description of the specification, but should be determined by the claims.

Claims

1. Silicon-based particles; and Silicon carbide distributed within the aforementioned silicon-based particles; A negative electrode active material containing, The silicon carbide is included in an amount of 0.1 parts by weight or more and 1 part by weight or less, based on a total of 100 parts by weight of the negative electrode active material. The silicon-based particles contain SiOx (x=0) in an amount of 90 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode active material. The silicon-based particles are one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and Si alloys, and are a negative electrode active material.

2. The negative electrode active material according to claim 1, wherein the silicon carbide is contained in an amount of 0.2 parts by weight or more and 0.8 parts by weight or less, based on 100 parts by weight of the total negative electrode active material.

3. The negative electrode active material according to claim 1, wherein the silicon-based particles contain 10 parts by weight or less of SiOx (0 < x < 2) based on 100 parts by weight of the negative electrode active material.

4. The negative electrode active material according to claim 1, wherein the carbon content is 0.03 parts by weight or more and 0.3 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material.

5. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 4.

6. The negative electrode according to claim 5, further comprising a negative electrode conductive material and a negative electrode binder.

7. A secondary battery comprising the negative electrode described in claim 5.

8. Silicon-based particles; and Silicon carbide distributed within the aforementioned silicon-based particles; A method for producing a negative electrode active material containing, The silicon carbide is included in an amount of 0.1 parts by weight or more and 1 part by weight or less, based on a total of 100 parts by weight of the negative electrode active material. The silicon-based particles contain SiOx (x=0) in an amount of 90 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode active material. A method for producing a negative electrode active material, wherein the silicon-based particles are one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and Si alloy.

9. The method for producing a negative electrode active material according to claim 8, wherein the silicon carbide is included in an amount of 0.2 parts by weight or more and 0.8 parts by weight or less, based on 100 parts by weight of the total negative electrode active material.

10. The method for producing a negative electrode active material according to claim 8, wherein the silicon-based particles contain 10 parts by weight or less of SiOx (0 < x < 2) based on 100 parts by weight of the negative electrode active material.

11. A method for producing a negative electrode active material according to claim 8, wherein the carbon content is 0.03 parts by weight or more and 0.3 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material.

12. A method for producing a negative electrode active material according to claim 1, The step of reducing silicon dioxide to silicon by reacting it with carbon; and A step of forming silicon carbide using residual carbon after the reduction step; A method for producing a negative electrode active material, including the material itself.

13. The step of forming the silicon carbide is, A method for producing a negative electrode active material according to claim 12, comprising the step of cooling silicon reduced at a predetermined cooling rate to form silicon carbide.

14. The method for producing a negative electrode active material according to claim 13, wherein the pre-set cooling rate is 20°C / min to 70°C / min.

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