Negative electrode active material, negative electrode, non-aqueous electrolyte secondary battery, and method for producing negative electrode active material

Abstract

The present invention improves at least one of initial efficiency, battery capacity, and cycle characteristics of a non-aqueous electrolyte secondary battery. A negative electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention contains porous composite particles containing silicon and a silicon oxide (SiOx, 0 < x < = 2), in which some or all of pores of the porous composite particles are filled with carbon, and some or all of surfaces of the porous composite particles are coated with carbon.

Description

Technical Field

[0001] This disclosure relates to a negative electrode active material, a negative electrode, a non-aqueous electrolyte secondary battery, and a method for preparing the negative electrode active material.

[0002] This application is based on and claims priority to Japanese Patent Application No. 2023-221546, filed on December 27, 2023, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] Recently, techniques for adding silicon oxide to the negative electrode active material of lithium-ion secondary batteries have been developed. For example, Patent Document 1 discloses a technique for adding pre-doped lithium silicon oxide to the negative electrode active material. Summary of the Invention

[0004] Technical issues

[0005] However, in anode materials in which silicon oxide is added, the initial efficiency is often reduced due to the formation of a lithium silicate phase during charging. Furthermore, when lithium is pre-doped into silicon oxide as described in Patent Document 1, the battery capacity may be reduced due to the formation of the lithium silicate phase.

[0006] This disclosure aims to address problems in the related technologies. Therefore, this disclosure aims to provide a negative electrode active material, a negative electrode, a non-aqueous electrolyte secondary battery, and a method for preparing the negative electrode active material that can improve at least one of the initial efficiency, battery capacity, and cycle characteristics of a non-aqueous electrolyte secondary battery.

[0007] Technical solution

[0008] The inventors of this disclosure believe that reducing silicon oxide with metallic magnesium (Mg) helps increase the Si content of the battery capacity, while also facilitating the removal of the resulting magnesium oxide. Therefore, the inventors of this disclosure conducted in-depth research and discovered that the initial efficiency, battery capacity, and / or cycle characteristics of non-aqueous electrolyte secondary batteries can be improved by initiating a predetermined process starting with reduction with metallic magnesium (Mg).

[0009] This disclosure may cover the following implementation methods.

[0010] [1] A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising silicon and silicon oxide (SiO2). x Porous composite particles with x ≤ 2 (0 < x ≤ 2) The porous composite particles have some or all of their pores filled with carbon, and some or all of their surface is coated with carbon.

[0011] [2] The negative electrode active material as defined in [1], wherein the porous composite particles further contain magnesium silicon oxide.

[0012] [3] The negative electrode active material as defined in [2], wherein the magnesium silicon oxide comprises at least one of MgSiO3 and Mg2SiO4.

[0013] [4] The negative electrode active material as defined in [2], wherein the molar ratio of Si atoms to Mg atoms (Si / Mg) in the negative electrode active material is 10-50.

[0014] [5] The negative electrode active material as defined in any of [1] to [4], wherein the porous composite particles are free of magnesium oxide (MgO) at least on their surface.

[0015] [6] The negative electrode active material as defined in any one of [1] to [5], wherein the total weight of carbon filling the pores of the porous composite particles and carbon covering its surface is 5-20 by weight based on the porous composite particles.

[0016] [7] The negative electrode active material as defined in any of [1] to [6], wherein the average particle size of the porous composite particles is from 100 nm to 20 μm.

[0017] [8] A negative electrode, comprising: a negative electrode current collector, and

[0018] A negative electrode active material layer, the negative electrode active material layer being formed on the negative electrode current collector and comprising a negative electrode active material as defined in any one of [1] to [7].

[0019] [9] A non-aqueous electrolyte secondary battery comprising a negative electrode as defined in [8].

[0020]

[10] A method for preparing a negative electrode active material for a non-aqueous electrolyte secondary battery, comprising: The reduction step, in which silicon oxide (SiO) is reduced... a (0 < a ≤ 2) reacts with metallic magnesium (Mg). The acid treatment step involves treating the material obtained after the reaction with an acid, and A carbon deposition step, wherein carbon is deposited on the material obtained after the acid treatment.

[0021]

[11] The method as defined in

[10] wherein, in the acid treatment step, porous composite particles having pores on their surface and inside are formed.

[0022]

[12] The method as defined in

[11] , wherein in the carbon deposition step, part or all of the pores are filled with carbon.

[0023]

[13] The method as defined in any of

[10] to

[12] , wherein in the reduction step, the molar ratio of Si atoms to Mg atoms (Si / Mg) is 0.1-3.

[0024]

[14] The method as defined in any of

[10] to

[13] , wherein in the acid treatment step, the amount of acid added is 1-100 millimoles relative to each gram of material obtained from the reduction step.

[0025]

[15] The method as defined in any of

[10] to

[14] , wherein the carbon deposition step is performed by depositing carbon at 500-900°C.

[0026] Beneficial effects

[0027] According to this disclosure, a silicon oxide-based negative electrode active material, a negative electrode, a non-aqueous electrolyte secondary battery, and a method for preparing the negative electrode active material can be provided, which can improve at least one of the initial efficiency, battery capacity, and cycle characteristics of a non-aqueous electrolyte secondary battery. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating a method for preparing a negative electrode active material according to one embodiment of the present disclosure.

[0029] Figure 2 A scanning electron microscope (SEM) image showing a cross-section of the negative electrode active material particles according to Example 5.

[0030] Figure 3 The map of Si atoms is obtained by energy dispersive spectroscopy (EDS) analysis of the cross-section of the negative electrode active material particles according to Example 5.

[0031] Figure 4 The mapping of C atoms is obtained by EDS analysis of the cross-section of the negative electrode active material particles according to Example 5.

[0032] Figure 5 The mapping of O atoms was obtained by EDS analysis of the cross-section of the negative electrode active material particles according to Example 5.

[0033] Figure 6 The mapping of Mg atoms was obtained by EDS analysis of the cross-section of the negative electrode active material particles according to Example 5.

[0034] Figure 7 A graph illustrating the cycle characteristics of the coin battery according to various embodiments and comparative examples. Detailed Implementation

[0035] The following describes a negative electrode active material, a negative electrode, a non-aqueous electrolyte secondary battery, and a method for preparing the negative electrode active material according to one embodiment of the present disclosure. Furthermore, the following embodiments illustrating one embodiment of the present disclosure do not limit the scope of the present disclosure and can be modified without departing from its scope. Moreover, the various configurations and features of the embodiments can be combined arbitrarily.

[0036] [Non-aqueous electrolyte secondary battery]

[0037] In one aspect of this disclosure, a non-aqueous electrolyte secondary battery is provided. According to one embodiment of this disclosure, the non-aqueous electrolyte secondary battery includes a negative electrode, a positive electrode, a separator inserted between the negative and positive electrodes, and a non-aqueous electrolyte. Specific examples of the secondary battery may include lithium-ion secondary batteries, which have advantages such as high energy density, discharge voltage, and output stability.

[0038] The following description, as an example, will primarily focus on lithium-ion secondary batteries. However, this disclosure is not limited to lithium-ion secondary batteries and can be applied to various non-aqueous electrolyte secondary batteries.

[0039] A lithium-ion secondary battery according to one embodiment of this disclosure includes a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte. Furthermore, the lithium-ion secondary battery may optionally include: a battery casing configured to house an electrode assembly including the negative electrode, the positive electrode, and the separator; and a sealing member configured to seal the battery casing.

[0040] [negative electrode]

[0041] The negative electrode includes a negative electrode current collector and a layer of negative electrode active material formed on one or both surfaces of the negative electrode current collector. The negative electrode active material layer may be formed on all or only a portion of the surface of the negative electrode current collector.

[0042] (Negative electrode current collector)

[0043] There are no particular restrictions on the negative electrode current collector used for the negative electrode, as long as it does not cause any chemical change in the battery and is conductive. Specific examples of such negative electrode current collectors may include: copper; stainless steel; aluminum; nickel; titanium; calcined carbon; copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.; aluminum-cadmium alloys; etc.

[0044] The thickness of the negative electrode current collector can be 3-500 μm. The negative electrode current collector can have fine surface irregularities formed on its surface to enhance adhesion to the negative electrode active material. For example, the negative electrode current collector can have various shapes, such as sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0045] (Negative electrode active material layer)

[0046] The negative electrode active material layer may comprise a negative electrode active material, a binder, a conductive material, and optional additives. For example, the negative electrode active material layer may be formed by applying a negative electrode active material slurry, in which a mixture of the negative electrode active material, binder, and conductive material is dissolved or dispersed in a solvent, to a negative electrode current collector, followed by drying and pressing; or by pressing a film layer obtained by casting the negative electrode active material slurry onto another support and peeling the film from the support onto the negative electrode current collector. If necessary, the mixture may also comprise dispersants, fillers, or other optional additives.

[0047] (Negative electrode active material)

[0048] In a lithium-ion secondary battery according to one embodiment of the present disclosure, the negative electrode active material comprises silicon and silicon oxide (SiO2). x The porous composite particles are composed of carbon particles (0 < x ≤ 2). Furthermore, some or all of the pores of the porous composite particles are filled with carbon, and some or all of the surface of the porous composite particles is coated with carbon. Alternatively, the negative electrode active material layer may also contain negative electrode active materials other than the porous composite particles. As used herein, any material that contributes to the charge-discharge reaction at the negative electrode is referred to as a "negative electrode active material".

[0049] As used herein, “carbon-coated” means that the outer surface of a particle is at least partially physically covered by carbon. Additional materials (e.g., additional coatings) may be present between the outer surface of the particle and the carbon covering the surface. As used herein, “carbon-filled” means that carbon is present in pores within the particle. It is not necessary for the particle's interior to be completely densely filled with carbon; there may be portions of the pore walls that are not in contact with carbon. Furthermore, additional materials (e.g., a layer covering the inner walls of the pores) may be present between the inner walls of the pores and the carbon.

[0050] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80-99% by weight.

[0051] (Porous composite particles)

[0052] The porous composite particles are particles comprising multiple types of materials and having multiple pores. However, as mentioned above, some or all of the pores of the porous composite particles are filled with carbon. Therefore, the porous composite particles may not contain substantial pores (e.g., when the pores are entirely filled with carbon, the porous composite particles do not contain pores).

[0053] Based on the total weight of the negative electrode active material, the content of the porous composite particles (excluding carbon present on the surface and in the pores) can be, for example, 0.1-99% by weight, 1-90% by weight, 5-50% by weight, or 10-30% by weight.

[0054] For example, the porous composite particles contain silicon (Si) and silicon oxide (SiO). x It has a composite structure in which Si particles are dispersed in a crystalline or amorphous state in amorphous silicon oxide (SiO2). x In a matrix of silicon oxide (SiO2). x In the above, the oxygen-to-silicon ratio x satisfies 0 < x ≤ 2, preferably 0.5 ≤ x ≤ 1.6, and more preferably 0.8 ≤ x ≤ 1.5.

[0055] Because silicon (Si) microparticles can intercalate lithium, they can participate in the charge-discharge reaction at the negative electrode. The silicon oxide matrix surrounding the Si microparticles can mitigate the volume expansion / contraction of the silicon microparticles accompanying lithium intercalation / deintercalation.

[0056] Based on the total weight of the porous composite particles, the total content of silicon phase and silicon oxide phase contained in the porous composite particles is, for example, 50-99% by weight, 60-90% by weight, or 70-80% by weight. When this content is above 50% by weight, a sufficient level of battery capacity is obtained.

[0057] The porous composite particles may also contain magnesium silicon oxide. For example, the magnesium silicon oxide may contain at least one of MgSiO3 and Mg2SiO4, but is not limited thereto.

[0058] Based on the total weight of the porous composite particles, the total content of magnesium silicon oxide contained in the porous composite particles is, for example, 0.1-20% by weight, 0.5-10% by weight, or 1-5% by weight. When the content is above 0.1% by weight, the magnesium silicon oxide may alleviate the volume expansion of the silicon phase. When the content is below 20% by weight, the effect of sufficiently increasing the battery capacity through the silicon phase can be achieved.

[0059] When the porous composite particles contain magnesium silicon oxide, the molar ratio of Si atoms to Mg atoms (Si / Mg) in the negative electrode active material is, for example, 10-50, preferably 15-40, and more preferably 20-30. When this molar ratio is 10 or higher, the amount of Si increases relatively and a high energy density can be obtained. When this molar ratio is 50 or lower, it is considered that sufficient reduction has occurred.

[0060] The porous composite particles may further contain magnesium oxide (MgO) and / or metallic magnesium (Mg). These may correspond to components remaining after reduction or acid treatment as described below. However, preferably, the porous composite particles are free of magnesium oxide (MgO) and / or metallic magnesium (Mg) at least on their surface. Here, "surface" refers to the surface of the porous composite particles located below the carbon coating. In other words, "free of magnesium oxide (MgO) and / or metallic magnesium (Mg) on ​​the surface" means that there is no magnesium oxide (MgO) and / or metallic magnesium (Mg) directly below the carbon coating of the porous composite particles. Preferably, the porous composite particles are free of magnesium oxide (MgO) and / or metallic magnesium (Mg) in contact with the carbon coating. More preferably, the porous composite particles are free of magnesium oxide (MgO) and / or metallic magnesium (Mg).

[0061] Based on the total weight of the porous composite particles, the content of magnesium oxide (MgO) contained in the porous composite particles is, for example, less than 5% by weight, less than 1% by weight, less than 0.1% by weight, or less than 0.01% by weight. Based on the total weight of the porous composite particles, the content of metallic magnesium (Mg) contained in the porous composite particles is, for example, less than 5% by weight, less than 1% by weight, less than 0.1% by weight, or less than 0.01% by weight.

[0062] The porous composite particles preferably contain Si, O, and Mg elements. However, the porous composite particles may also contain other components (including unavoidable impurities).

[0063] Based on the total weight of the porous composite particles, the content of silicon atoms contained in the porous composite particles (the total content of Si atoms in all silicon-containing materials such as silicon phase, silicon oxide phase, magnesium silicon oxide, etc.) is, for example, 10-90% by weight, 30-80% by weight, or 50-70% by weight.

[0064] Based on the total weight of the porous composite particles, the content of magnesium atoms contained in the porous composite particles (the total content of Mg atoms in all magnesium-containing materials such as magnesium silicon oxide phase, magnesium oxide (MgO) phase, metallic magnesium (Mg) phase, etc.) is, for example, 0.1-20% by weight, 0.5-10% by weight, or 1-5% by weight.

[0065] The average particle size of the porous composite particles is, for example, 100 nm to 20 μm, preferably 200 nm to 15 μm, and more preferably 500 nm to 10 μm. As used herein, "average particle size" refers to the particle size at which the cumulative value in the particle size distribution determined by laser diffraction scattering is 50%, i.e., the median diameter (D). 50The aperture can have an irregular cross-sectional shape and can be quasi-spherical or elongated (high aspect ratio). Although the aperture is not limited to any particular size, for example, the size of a quasi-spherical aperture can be 1-500 nm, and the short side length of a high aspect ratio aperture can be 1-500 nm.

[0066] The arrangement of pores in the porous composite particles can be non-uniform. For example, pores can be generated by removing components that constitute part of the composite particles through acid treatment, as described later, and the pores inside the particles are connected to the particle surface. As a result, the pores inside the particles may be more abundant near the surface than in the central portion of the particles. However, the arrangement or shape of the pores can vary depending on the preparation conditions of the porous composite particles, and is therefore not limited to the embodiments mentioned above, but can be any arrangement or shape.

[0067] (Carbon deposition on negative electrode active materials)

[0068] As described above, at least a portion of the surface of the porous composite particles is coated with carbon, and at least a portion of the pores of the porous composite particles is filled with carbon. Here, this type of carbon is collectively referred to as "deposited carbon".

[0069] The deposited carbon imparts conductivity to the porous composite particles. Furthermore, since the surface of the porous composite particles is coated with deposited carbon, side reactions between the porous composite particles and other materials (e.g., electrolytes) can be suppressed. Additionally, because the pores of the porous composite particles are filled with carbon, the likelihood of cracks originating from the pores due to silicon volume expansion / contraction during charging and discharging can be reduced.

[0070] Carbon materials that form deposited carbon can include: graphite, such as natural graphite, artificial graphite, etc.; carbon fibers, such as mesophase carbon microspheres (MCMB), carbon nanotubes, carbon nanofibers, etc.; carbon black, such as Ketjen black, Danka black, acetylene black, etc.; graphene or graphene oxide; mixtures thereof; etc. However, coatings or deposits obtained using chemical vapor deposition (CVD) with acetylene gas or methane gas as starting materials are preferred, as this allows even the deep pores inside the particles to be filled.

[0071] Based on the porous composite particles (excluding deposited carbon content), the content of deposited carbon formed on the surface of the porous composite particles, i.e., the total content of carbon filling the pores of the porous composite particles and carbon covering its surface, is, for example, 5-20% by weight, preferably 6-18% by weight, more preferably 8-15% by weight. When this content is 5% by weight or more, it is considered that the carbon filling of the pores is appropriate. When this content is 20% by weight or less, a battery capacity above a predetermined level can be obtained, and agglomeration of the porous composite particles themselves through deposited carbon can be suppressed. However, the carbon content is not limited to the above-defined range, and even if the content does not fall within the above-defined range, the battery can still function as a secondary battery, although the battery performance is slightly reduced.

[0072] The deposited carbon covers, for example, 50%-100%, 60%-99%, or 70%-95% of the surface area of ​​the porous composite particles (excluding the pores inside the particles). The deposited carbon fills, for example, 50-100% of the total volume of the pores inside the porous composite particles, 60-99% of the volume, or 70-95% of the volume.

[0073] The average thickness of the deposited carbon formed on the surface of the porous composite particles can be, for example, 10 nm to 10 μm, 50 nm to 5 μm, 100 nm to 2 μm or 200 nm to 1 μm.

[0074] (Carbon-based materials)

[0075] The negative electrode active material layer may also contain carbonaceous materials as a negative electrode active material in addition to porous composite materials with deposited carbon. For example, the carbonaceous materials may be contained in the negative electrode active material layer in powder form.

[0076] When carbonaceous materials are included in the negative electrode active material, they can comprise any carbonaceous material that is typically used as a negative electrode active material in non-aqueous electrolyte secondary batteries. Specific examples of carbonaceous materials may include, but are not limited to, any of the following: natural graphite, artificial graphite, graphitized carbon fibers, and amorphous carbon, or mixtures of two or more of these. Complexes with elements other than carbon may be used. On the other hand, carbonaceous materials can be either low-crystallinity carbon or high-crystallinity carbon. Low-crystallinity carbon typically includes soft carbon and hard carbon, while high-crystallinity carbon typically includes irregular, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, floating graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon such as petroleum / coal-based coke.

[0077] When the negative electrode active material contains carbonaceous material in addition to the porous composite particles, the weight ratio of the porous composite particles to the carbonaceous material in the negative electrode active material can be, for example, 1:99-50:50, preferably 5:95-30:80, and more preferably 8:92-20:80.

[0078] (Adhesive)

[0079] Adhesives are added as components to promote bonding between active materials and conductive materials or with current collectors. Specific examples of adhesives may include, but are not limited to: polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), polyacrylic acid, polyacrylamide, polyimide, fluororubber, and various copolymers thereof. These adhesive materials may be used alone or in combination.

[0080] Based on the total weight of the negative electrode active material layer, the binder content can be, for example, 0.1-30% by weight. The binder content is preferably 0.5-20% by weight, more preferably 1-10% by weight. When the binder content meets the above range, it can prevent a decrease in battery capacity characteristics while providing sufficient adhesion to the electrode.

[0081] (Conductive materials)

[0082] There are no particular limitations on conductive materials, as long as they are conductive materials that do not cause chemical changes. Specific examples of conductive materials may include, but are not limited to: carbonaceous materials, such as artificial graphite, natural graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, carbon black, acetylene black, Ketjen black, Danka black, thermally cracked carbon black, channel black, furnace black, lamp black, or carbon fibers; metal powders or fibers such as aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, or iridium; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; conductive polymers, such as polyaniline, polythiophene, polyacetylene, polypyrrole, polyphenylene derivatives; etc., and such conductive materials may be used alone or in combination.

[0083] Based on the total weight of the negative electrode active material layer, the content of conductive material can be 0.1-30% by weight. Preferably, the content of conductive material is 0.5-15% by weight, more preferably 0.5-10% by weight. When the content of conductive material meets the above range, the advantage is that sufficient conductivity is provided, and because the content of the negative electrode active material is not reduced, battery capacity is ensured.

[0084] (Thickener)

[0085] The negative electrode active material slurry applied to the negative electrode current collector may contain a thickener. Specifically, the thickener may be a cellulose-based compound, such as carboxymethyl cellulose (CMC). Based on the total weight of the negative electrode active material layer, the content of the thickener may, for example, be 0.5-10% by weight.

[0086] (solvent)

[0087] There are no particular limitations on the solvent used in the negative electrode active material slurry, as long as it is a solvent used to manufacture the negative electrode. Specific examples of solvents may include, but are not limited to, N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropanol, acetone, water, etc., and such solvents may be used alone or in combination.

[0088] [Method for manufacturing the negative electrode]

[0089] A method for manufacturing a negative electrode for a lithium-ion secondary battery according to one embodiment of the present disclosure includes the following steps: (1) Preparation of negative electrode active materials (2) Preparation of negative electrode active material slurry from the negative electrode active material (3) The negative electrode is manufactured from the negative electrode active material slurry. (1) Preparation of negative electrode active material.

[0090] When step (1) of preparing the negative electrode active material is further subdivided as "method for preparing negative electrode active material", it includes the following steps: (a) Reduction step: reducing silicon oxide (SiO2) a (0 < a ≤ 2) reacts with metallic magnesium (Mg).

[0091] (b) Acid treatment step: The material obtained after the reaction in (a) is treated with acid.

[0092] (c) Carbon deposition step: Carbon is deposited on the material obtained after acid treatment in (b).

[0093] Figure 1 This is a schematic diagram illustrating a method for preparing a negative electrode active material according to one embodiment of the present disclosure. Hereinafter, reference will be made to... Figure 1 The method will be described, but Figure 1 This is merely a schematic diagram for the purpose of understanding the contents of this disclosure and cannot accurately represent the microscopic state of actual particles.

[0094] (a) Restoration steps

[0095] In the reduction step, metallic magnesium (Mg) is used as a reducing agent. Specifically, it is considered that in silicon oxide (SiO2)... a The following chemical reaction occurs between the metal (Mg) and the metal (Mg).

[0096] SiO a + aMg → Si + aMgO

[0097] The silicon oxide used as the starting material can be SiO a Powders of (0 < a ≤ 2). For example, such as Figure 1 As shown in (a), SiO a It can have a structure in which Si particles are dispersed in a microcrystalline or amorphous state in an amorphous silicon oxide matrix. On the other hand, in the above description of porous composite particles, for convenience, Si particles and silicon oxide (SiO₂) are used... x The matrix is ​​labeled separately, but here, Si particles and silicon oxide matrix are collectively referred to as silicon oxide (SiO2). a In other words, 'a' is the average value of the Si particles and the silicon oxide matrix as a whole. Here, 0 < a ≤ 2, preferably 0.5 ≤ a ≤ 1.6, and more preferably 0.8 ≤ a ≤ 1.5. For example, the silicon oxide of the starting material can be silicon monoxide (SiO) (a = 1) or silicon dioxide (SiO2) (a = 2). Furthermore, the silicon oxide powder of the starting material can contain only SiO with a specific a value. a Alternatively, it can be two or more SiO₂ with different 'a' values. a A mixture of powders.

[0098] The average particle size of the silicon oxide particles in the starting material can be, for example, 100 nm to 20 μm, preferably 200 nm to 10 μm, more preferably 500 nm to 5 μm or 500 nm to 1 μm. When the average particle size is small, the number of reaction sites for the charge-discharge reaction is advantageously increased, thereby providing the possibility of increasing battery capacity and promoting the insertion / extraction of lithium ions in the particles, thus providing improved battery life characteristics. When the average particle size is above 100 nm, sufficient specific surface area of ​​the porous composite particles can be ensured, thereby achieving appropriate reactivity with the electrolyte and increasing the battery energy density to a certain level. When the average particle size is below 20 μm, the reduction in life characteristics caused by volume expansion can be suppressed.

[0099] In the reduction step, the molar ratio of Si atoms to Mg atoms (Si / Mg) is 0.1-3, preferably 0.3-2.5, more preferably 0.5-2, even more preferably 0.6-1.8, and even more preferably 0.8-1.5. When this molar ratio is 0.1 or higher, a predetermined amount of Si is obtained, which becomes charge / discharge reaction sites, thereby achieving a specific level of energy density. When this molar ratio is 3 or lower, reduction occurs sufficiently, thereby significantly improving battery capacity.

[0100] In addition to the above, silicon oxides can also react with metallic magnesium (Mg) or magnesium oxide (MgO) generated as described above to produce magnesium silicon oxides as byproducts. Specific examples of such magnesium silicon oxides may include MgSiO3, Mg2SiO4, etc.

[0101] The reaction conditions are arbitrary, as long as the reaction proceeds. For simplicity, a method of mixing silicon oxide powder and metallic magnesium (Mg) powder and heating is preferred, but the reaction conditions are not limited to this, and the materials can be reacted, for example, in solution. Since reduction occurs, it is preferred to carry out the reaction in an inert gas atmosphere (e.g., nitrogen, argon, etc.) or a reducing atmosphere. The reaction temperature is, for example, 500-1,000°C, preferably 600-900°C, more preferably 650-850°C, and even more preferably 700-800°C. There is no specific limitation on the reaction pressure. The reaction time is, for example, 10 minutes to 3 hours, preferably 30 minutes to 2 hours.

[0102] For example, the reduction is hypothesized to proceed based on the following mechanism. However, the following is merely speculation and is not intended to confine this disclosure to theory.

[0103] The silicon oxide particles in the starting material react with metallic magnesium (Mg), thereby increasing the number of Si particles in the silicon oxide matrix. Simultaneously, magnesium oxide (MgO) or magnesium silicon oxide is formed. As a result, as... Figure 1 As shown in (b), silicon oxide (SiO) can be obtained. x (Contains silicon microparticles dispersed in a silicon oxide matrix), magnesium oxide (MgO), magnesium silicon oxide and unreacted metallic magnesium (Mg) integrated and / or aggregated composite particles.

[0104] (b) Acid treatment steps

[0105] In the acid treatment step, the magnesium oxide and unreacted metallic magnesium (Mg) generated in the reduction step react with protons to generate magnesium ions (Mg). 2+ Magnesium ions (Mg) 2+ It can be removed by washing with water, and as a result, magnesium oxide and unreacted metallic magnesium (Mg) can be removed.

[0106] MgO + 2H + → Mg 2+ + H2O

[0107] Mg 2+ + 2H + → Mg 2+ + H2

[0108] The acid treatment step includes adding an acid to the product of the reduction step. For example, the acid is an aqueous solution of an acid. For example, the aqueous solution of an acid is an aqueous solution of a strong acid. The strong acid can be an inorganic or organic acid, and specific examples include hydrochloric acid, nitric acid, sulfuric acid, hydrobromic acid, hydroiodic acid, sulfonic acid, etc. Such acids can be used in any combination. In other words, the acid treatment step may include reacting the material obtained after the reduction step with at least one acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrobromic acid, hydroiodic acid, and sulfonic acid. For example, when hydrochloric acid is used, the following chemical reaction occurs between magnesium oxide (MgO) / metallic magnesium (Mg) and hydrochloric acid.

[0109] MgO + 2HCl → MgCl2 + H2O

[0110] Mg + 2HCl → MgCl2 + H2

[0111] The acid may not contain any substances that strongly dissolve silicon oxide (SiO₂). x Acids such as hydrofluoric acid (HF).

[0112] The concentration of the acid-water solution is, for example, 0.1-10 M, preferably 0.5-5 M. When the concentration is 0.1 M or higher, impurities can be sufficiently removed. When the concentration is below 10 M, sufficient production efficiency can be maintained. The amount of acid-water solution added relative to each gram of composite particles obtained from the reduction step is, for example, 1-100 mL, preferably 5-80 mL, more preferably 10-50 mL. When the concentration of the acid-water solution is 1 M, the molar amount of acid added relative to each gram of composite particles is, for example, 1-100 mmol, preferably 5-80 mmol, more preferably 10-50 mmol.

[0113] The reaction conditions are arbitrary, as long as the reaction proceeds. The reaction temperature is, for example, 10-90°C, preferably room temperature to 50°C. There is no specific limitation on the reaction pressure. The reaction time is, for example, 1-48 hours, preferably 6-36 hours, more preferably 12-30 hours.

[0114] For example, it is hypothesized that acid treatment of composite particles proceeds according to the following mechanism. However, the following is merely hypothetical and is not intended to limit this disclosure to theory.

[0115] The acid that comes into contact with the composite particles after the reduction step first reacts with magnesium oxide (MgO) or metallic magnesium (Mg) present on or near the surface of the composite particles. After the magnesium oxide (MgO) or metallic magnesium (Mg) that has reacted with the acid dissolves from the composite particles, pores are formed at the locations where the magnesium oxide (MgO) or metallic magnesium (Mg) has detached from the composite particles. The acid enters these pores and reacts with the magnesium oxide (MgO) or metallic magnesium (Mg) present inside the particles. In this way, the magnesium oxide (MgO) or metallic magnesium (Mg) in the composite particles is decomposed and removed. Following acid treatment, pores are formed in the composite particles, thereby... Figure 1 As shown in (c), porous composite particles with pores are obtained.

[0116] Because magnesium silicon oxide has low reactivity with acids, it remains at least partially even after acid treatment. However, depending on the starting materials, acid, and reaction conditions used, magnesium silicon oxide may decompose partially or completely.

[0117] After reacting with acid, the substances dissolved in the acid can be removed by conventional washing. Following washing and drying steps, a porous composite material is obtained.

[0118] (c) Carbon deposition steps

[0119] In the carbon deposition step, carbon is deposited on the resulting porous composite particles, such that the surface of the porous composite particles is coated with carbon and the interior of the pores of the porous composite particles is filled with carbon. The carbon deposition process can be performed by any carbon deposition method commonly used in the art, and there is no specific limitation on the carbon deposition method. The carbon deposition method can be either a dry method or a wet method. Examples of dry methods include methods such as depositing carbon onto porous composite materials by chemical vapor deposition (CVD). Examples of wet methods include methods such as mixing a carbon source with a porous composite material in a solution and heating it.

[0120] For example, when performing carbon deposition, such as CVD, it is preferable to perform the process at a relatively low temperature for a long time so that the interior of the pores can be fully filled with carbon. For example, the carbon deposition temperature is 500-900°C, preferably 600-800°C. For example, the carbon deposition time is 10 minutes to 24 hours, preferably 30 minutes to 10 hours, more preferably 30 minutes to 2 hours.

[0121] Since the deposited carbon layer forms on the surface and in the internal pores of the porous composite particles, the porous composite particles can be made conductive and their surface can be protected, thereby improving at least one of battery capacity, initial efficiency and cycle characteristics.

[0122] Through carbon deposition, such as Figure 1As shown in (d), part or all of the surface of the porous composite particles is coated with carbon and part or all of the pores inside the particles are filled with carbon. In this way, the porous composite particles containing the deposited carbon formed therein are used as a negative electrode active material.

[0123] On the other hand, in the method for preparing the negative electrode active material according to this embodiment, when magnesium oxide (MgO) and metallic magnesium (Mg) are removed by an acid treatment step, pores are formed automatically, eliminating the need for an active pore-forming step in the composite. For example, the method for preparing the negative electrode active material according to this embodiment does not include a conventional pore-forming step (e.g., the step of depositing gaseous target material onto a metal plate).

[0124] (2) Prepare a negative electrode active material slurry from the negative electrode active material.

[0125] A solvent is added to the negative electrode active material obtained from (1). Here, conductive materials, binders, thickeners, etc., may be added as needed. The negative electrode active material, conductive agent, binder, thickener, etc., are dissolved or dispersed in the solvent to obtain a negative electrode active material slurry.

[0126] (3) Obtain a negative electrode from the negative electrode active material slurry.

[0127] The negative electrode active material slurry is applied to the negative electrode current collector, dried, and pressed. In this way, a negative electrode containing a layer of negative electrode active material formed on the negative electrode current collector can be obtained.

[0128] In one variation, for example, the negative electrode active material slurry can be cast onto another support, and then a film layer obtained by peeling from the support can be pressed onto the negative electrode current collector to obtain a negative electrode. Alternatively, other methods can be used to form a negative electrode active material layer on the negative electrode current collector.

[0129] [positive electrode]

[0130] In a lithium-ion secondary battery according to one embodiment of the present disclosure, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer may be formed on all or part of the surface of the positive electrode current collector.

[0131] (Positive current collector)

[0132] There are no particular restrictions on the positive current collector used for the positive electrode, as long as it does not cause any chemical changes in the battery and is conductive. Specific examples of positive current collectors may include: stainless steel; aluminum; nickel; titanium; calcined carbon; aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.; etc.

[0133] The thickness of the positive electrode current collector can be 3 - 500 μm. The positive electrode current collector can form fine surface irregularities on its surface, thereby enhancing the adhesion to the positive electrode active material. For example, the positive electrode current collector can have various shapes, such as sheets, foils, meshes, porous bodies, foams, non-woven fabric bodies, etc.

[0134] (Positive electrode active material layer)

[0135] For example, the positive electrode active material layer can be formed by applying a positive electrode active material slurry (in which a mixture of a positive electrode active material, a conductive material, and a binder is dissolved or dispersed in a solvent) to the positive electrode current collector, followed by drying and pressing. As needed, the mixture can also contain a dispersant or a filler, or other optional additives.

[0136] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80 - 99% by weight.

[0137] (Positive electrode active material)

[0138] As the positive electrode active material, a compound capable of reversibly inserting / extracting lithium can be used. Specific examples of such compounds can include lithium metal composite oxides containing lithium and at least one metal such as cobalt, manganese, copper, vanadium, aluminum, etc. More specifically, such lithium metal composite oxides can include: lithium - manganese oxides (e.g., LiMnO2, LiMnO3, LiMn2O3, LiMn2O4, etc.); lithium - cobalt oxides (e.g., LiCoO2, etc.); lithium - nickel oxides (e.g., LiNiO2, etc.); lithium - copper oxides (e.g., Li2CuO2, etc.); lithium - vanadium oxides (e.g., LiV3O8, etc.); lithium - nickel - manganese oxides (e.g., LiNi 1-z Mn z O2 (where 0 < z < 1), LiMn 2-z Ni z O4 (where 0 < z < 2)); lithium - nickel - cobalt oxides (e.g., LiNi 1-y Co y O2 (where 0 < y < 1)); lithium - manganese - cobalt oxides (e.g., LiCo 1-z Mn z O2 (where 0 < z < 1), LiMn 2-y Co y O4 (where 0 < y < 2)); lithium - nickel - manganese - cobalt oxides (e.g., Li(Ni x Co y Mn z )O2 (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1) or Li(Ni xCo y Mn z )O4(0 < x < 2, 0 < y < 2, 0 < z < 2, x + y + z = 2)); Lithium-nickel-cobalt-metal (M) oxides (e.g., Li(Ni) x Co y Mn z M w O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < w < 1, x + y + z + w = ​​1)); compounds in which the transition metal element is partially replaced by at least one metal element; etc. The positive electrode active material layer may contain any one compound, or two or more of them. However, the scope of this disclosure is not limited thereto.

[0139] In particular, for improving battery capacity characteristics and stability, LiCoO2, LiMnO2, LiMn2O4, LiNiO2, and lithium nickel manganese cobalt oxides (e.g., Li(Ni)) are preferred. 1 / 3 Mn 1 / 3 Co 1 / 3 O2, Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.4 Mn 0.3 Co 0.3 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 O2, Li(Ni) 0.8 Mn 0.1 Co 0.1 O2, etc.), lithium nickel cobalt aluminum oxides (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 O2, etc.

[0140] (Adhesives and conductive materials)

[0141] The types and amounts of binders and conductive materials used in the positive electrode active material slurry can be the same as those described for the negative electrode.

[0142] (solvent)

[0143] There are no particular restrictions on the solvents used in the positive electrode active material slurry, as long as they are commonly used in the preparation of the positive electrode. Specific examples of solvents include, but are not limited to: amine solvents, such as N,N-dimethylaminopropylamine, diethylenetriamine, N,N-dimethylformamide (DMF), etc.; ether solvents, such as tetrahydrofuran; ketone solvents, such as methyl ethyl ketone; ester solvents, such as methyl acetate; amide solvents, such as dimethylacetamide, N-methyl-2-pyrrolidone (NMP), etc.; dimethyl sulfoxide (DMSO); water; etc. Such solvents can be used alone or in combination.

[0144] The amount of solvent used can be taken into account for the slurry coating thickness or manufacturing yield, so that the positive electrode active material, conductive material and binder are dissolved or dispersed therein, and provide a viscosity that enables excellent thickness uniformity when applied to the positive electrode current collector.

[0145] [Manufacturing method of the positive electrode]

[0146] A method for preparing a positive electrode for a lithium-ion secondary battery according to one embodiment of the present disclosure may include the following steps: dissolving or dispersing a positive electrode active material with an optional binder, conductive material, thickener, etc., in a solvent to obtain a positive electrode active material slurry; similar to the method for manufacturing a negative electrode, for example, forming a positive electrode active material layer on a positive electrode current collector by applying the positive electrode active material slurry onto the positive electrode current collector to obtain a positive electrode.

[0147] [Septum]

[0148] In a lithium-ion secondary battery according to one embodiment of this disclosure, a separator serves to separate the negative electrode from the positive electrode and provide a pathway for lithium-ion migration. Any separator can be used without particular limitation, as long as it is generally used as a separator for lithium-ion secondary batteries. In particular, the separator preferably exhibits low resistance to electrolyte ion migration and high wettability with the electrolyte. Specific examples of separators may include porous polymer membranes, such as porous polymer membranes made of polyolefin polymers (including ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, or ethylene / methacrylate copolymers), or laminates of two or more layers of such porous polymer membranes. Furthermore, conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc., can be used. Additionally, to ensure heat resistance or mechanical strength, separators coated with ceramic components or polymer materials can be used.

[0149] [Non-aqueous electrolytes]

[0150] In one embodiment of the non-aqueous electrolyte secondary battery according to the present disclosure, the non-aqueous electrolyte may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid electrolytes, etc., which can be used to manufacture secondary batteries.

[0151] Non-aqueous electrolytes may contain organic solvents and lithium salts, and may also contain additives as needed. In the following text, liquid electrolytes will also be referred to as "electrolytes".

[0152] There are no particular limitations on organic solvents, as long as they can serve as a medium through which ions participating in the electrochemical reactions of the battery can migrate. Specific examples of organic solvents include, but are not limited to: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether and tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitrile solvents, such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, which may optionally contain a double-bonded aromatic ring or ether bond); amide solvents, such as dimethylformamide; dioxolane solvents, such as 1,3-dioxolane; sulfolane solvents, etc. These solvents can be used alone or in combination.

[0153] There are no particular limitations on lithium salts, as long as they are compounds capable of providing lithium ions for use in lithium-ion secondary batteries. Specific examples of lithium salts may include, but are not limited to: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. These lithium salts can be used alone or in combination. For example, lithium salts can be present in the electrolyte at a concentration of 0.1-2 mol / L. When the concentration of the lithium salt falls within the above-defined range, the electrolyte exhibits suitable conductivity and viscosity and demonstrates excellent electrolyte quality, thereby enabling efficient migration of lithium ions.

[0154] Additives may be optionally used to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. Specific examples of additives may include, but are not limited to: alkylene halide carbonate compounds, such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); pyridine; triethyl phosphite; triethanolamine; cyclic ethers; ethylenediamine; n-glycol dimethyl ether; hexamethylphosphoric triamine; nitrobenzene derivatives; sulfur; quinone imine dyes; N-substituted sulfadiazine ketones; N,N-substituted imidazolidines; ethylene glycol diallyl ether; ammonium salts; pyrrole; 2-methoxyethanol; aluminum trichloride, etc. Such additives may be used alone or in combination. The amount of additive used may be 0.1-15% by weight based on the total weight of the electrolyte.

[0155] [Manufacturing method of non-aqueous electrolyte secondary battery]

[0156] A non-aqueous electrolyte secondary battery according to one embodiment of this disclosure can be manufactured by inserting a separator (e.g., a separator membrane) and an electrolyte between a negative electrode obtained as described above and a positive electrode obtained as described above. More specifically, the separator can be disposed between the negative and positive electrodes to form an electrode assembly, which is then introduced into a battery case, such as a cylindrical or square battery case, and an electrolyte is injected therein to obtain a non-aqueous electrolyte secondary battery. In one variation, a product obtained by stacking electrode assemblies and immersing the resulting stack in an electrolyte can be introduced into a battery case and sealed to obtain a non-aqueous electrolyte secondary battery.

[0157] The battery casing can be selected from those commonly used in the art. For example, the battery casing can have a cylindrical, bag-shaped, or coin-shaped shape, such as that used in a can.

[0158] The lithium-ion secondary battery according to one embodiment of this disclosure can be used not only as a power source for small devices, but also as a unit battery in medium to large-sized battery modules comprising multiple individual cells. Preferred examples of such medium to large-sized devices may include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0159] [Effect]

[0160] Recently, the use of silicon-based materials in the anode to provide high-capacity lithium-ion secondary batteries has been frequently investigated. However, pure silicon (Si) cracks due to expansion during charging, causing disruption of electron conduction pathways and resulting in a significant reduction in lifetime characteristics. Therefore, anode active materials containing graphite mixed with a small amount of silicon monoxide have been commercialized. Silica has a composite structure in which the Si phase is dispersed within SiO to mitigate Si expansion. xIn the matrix of the phase. However, when silicon monoxide (SiO) is used, the lithium silicate phase formed during the initial charging of the battery will be irreversibly generated, resulting in a significant decrease in discharge capacity compared to charge capacity, thus causing extremely low initial efficiency of 65%-70%. Therefore, it is difficult to balance the initial efficiency of the cathode material when the amount of silicon monoxide (SiO) increases.

[0161] To address the aforementioned issues, pre-doped Li-based SiO₂ has been proposed. x Materials. However, due to the formation of lithium silicate phases with various compositions depending on the doping amount, issues arise such as reduced capacity, Si dissolution by alkaline slurry to generate gas, or increased viscosity. Therefore, even if the processability of battery manufacturing is not a problem on a laboratory scale, issues exist at mass production scale, such as the inability to coat the material or the formation of pinholes after electrode drying, making the commercialization of this type of material difficult.

[0162] According to one embodiment of the present disclosure, the negative electrode active material can increase the amount of silicon (Si) that contributes to providing high capacity by reducing silicon oxide in the starting material, while simultaneously imparting conductivity to the porous composite particles by depositing carbon on the surface of the porous composite particles and in the pores (residual after removing the MgO or Mg phase), and suppressing side reactions between the porous composite particles and the electrolyte. In this way, battery capacity, charge / discharge efficiency, and cycle characteristics can be improved. Furthermore, since all materials forming the porous composite particles are stable to water, there is an advantage in preventing gas generation as in the prior art.

[0163] When the negative electrode active material contains magnesium silicon oxide, the magnesium silicon oxide and silicon oxide (SiO) x Together with the Si phase, it is used as a matrix to alleviate the volume expansion of Si. Therefore, it can further improve the cycling characteristics.

[0164] Public content model

[0165] Hereinafter, embodiments and comparative examples will be described. However, this disclosure is not limited thereto. Furthermore, the discussion described below is merely exemplary and speculative, intended to aid in understanding this disclosure, and is not intended to limit the scope of this disclosure.

[0166] [Example 1]

[0167] (Preparation of negative electrode active materials)

[0168] Silicon monoxide (SiO) powder with an average particle size of 5 μm and metallic magnesium (Mg) powder with an average particle size of 300 μm were mixed at a weight ratio of 1:1. The resulting mixture was introduced into a plasma sintering system (available from Microphase), and the reduction of SiO powder using Mg powder was carried out by allowing the mixture to stand at 800 °C for 1 hour in an inert gas atmosphere. After performing X-ray diffraction (XRD) measurement and elemental analysis, it was shown that the product contained silicon (Si), silicon oxide (SiO x , 0 <x ≤ 1), metallic magnesium (Mg), magnesium oxide (MgO), and magnesium silicate oxides (MgSiO3, Mg2SiO4).

[0169] Then, 10 g of the product was introduced into 200 mL of 2 M hydrochloric acid and stirred for 24 hours to remove the Mg phase and MgO phase. Thereafter, the resulting product was washed with water and dried. Then, while rotating the furnace core tube at 800 °C, a chemical vapor deposition (CVD) treatment using ethylene gas was carried out. As determined by the weight ratio before and after the CVD treatment, it was shown that the product after the CVD treatment contained 7 wt% carbon. The particles were appropriately pulverized and sieved to an average particle size of 8 μm to control the particle size, thereby obtaining the negative electrode active material.

[0170] (Manufacture of coin cell)

[0171] Aqueous dispersions (solid content 0.4%) of the negative electrode active material obtained as described above, carbon black (CB) and single-walled carbon nanotubes (SWCNT) as conductive materials, styrene-butadiene rubber (SBR) as an adhesive, and carboxymethyl cellulose (CMC) as a thickener were prepared at a weight ratio of 88.8:3.3:0.25:3.65:4.0. First, the negative electrode material, CB, and CMC were mixed, the SWCNT dispersion and water were added thereto, and then kneaded. Finally, SBR was added thereto and then mixed to prepare a negative electrode active material slurry.

[0172] The resulting slurry was uniformly applied to a copper foil, vacuum dried at 110 °C for 10 hours, the resulting product was cut into a circle with a diameter of 13 mm, and a 2016-type coin cell using lithium metal as a counter electrode was manufactured.

[0173] [Example 2]

[0174] The negative electrode active material was prepared and the coin cell was manufactured in the same manner as in Example 1, except that the hydrochloric acid concentration based on the reduction product was twice that of Example 1 and the water washing was carried out five times.

[0175] [Example 3]

[0176] The negative electrode active material was prepared and the coin battery was manufactured in the same manner as in Example 2, except that the weight ratio of silicon monoxide (SiO) powder to magnesium (Mg) powder was 2:1.

[0177] [Example 4]

[0178] The negative electrode active material was prepared and the coin battery was manufactured in the same manner as in Example 2, except that the weight ratio of silicon monoxide (SiO) powder to magnesium (Mg) powder was 4:1.

[0179] [Example 5]

[0180] The negative electrode active material was prepared and the coin battery was manufactured in the same manner as in Example 3, except that the amount of carbon coated in the CVD process was increased to 11 by weight.

[0181] [Example 6]

[0182] The negative electrode active material was prepared and the coin battery was manufactured in the same manner as in Example 3, except that silicon monoxide (SiO) powder with an average particle size of 1 μm was used as the starting material.

[0183] [Example 7]

[0184] The negative electrode active material was prepared and the coin battery was manufactured in the same manner as in Example 6, except that the temperature in the reduction using metallic magnesium (Mg) was changed from 800°C to 680°C.

[0185] [Comparative Example 1]

[0186] The negative electrode active material was prepared and a coin battery was manufactured in the same manner as in Example 1, except that 5% by weight of carbon was deposited on the same silicon oxide (SiO) powder used in Example 1, and the resulting product was used as the negative electrode active material.

[0187] [Experimental Example 1: SEM Observation and EDS Analysis]

[0188] The negative electrode active material particles obtained in Example 5 were observed using a scanning electron microscope (SEM) capable of energy dispersive X-ray spectroscopy (EDS). Figure 2 This is an SEM image showing the cross-section of the negative electrode active material particles according to Example 5. Figures 3 to 6 Mappings of Si, C, O, and Mg atoms obtained by EDS analysis of cross-sections of the negative electrode active material particles according to Example 5 are shown respectively. Figures 3 to 6 In the image, the atoms of the object are present in the white portion. Figure 2 The lighter-colored portion mainly contains silicon (Si) and silicon oxide (SiO2). xOn the other hand, the darker areas correspond to pores created by acid treatment, suggesting that they primarily contain carbon (C) or magnesium silicon oxide. When... Figure 3 (Si mapping) and Figure 4 When comparing (C mappings), it is assumed that a large amount of C exists in the regions where Si is absent. When... Figure 3 (Si mapping) and Figure 6 When comparing (Mg mapping), Mg is dispersed throughout the particle structure. Considering that MgO and Mg are removed through acid treatment, it is assumed that magnesium silicon oxide is dispersed throughout the particle structure. On the other hand, the upper left and lower right regions of each image correspond to the substrate resin. The following was determined from the SEM images and EDS results.

[0189] (1) A composite particle in which silicon-based materials and magnesium-based materials are integrated is formed by reduction.

[0190] (2) Pores are formed inside the composite particles by removing Mg or MgO from the composite particles through acid treatment.

[0191] (3) The surface of the composite particles is coated with carbon by CVD treatment, and the interior of the pores of the composite particles is filled with carbon that has penetrated into the pores.

[0192] [Experimental Example 2: XRD Determination and Elemental Analysis]

[0193] Elemental analysis using X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF) showed that the negative electrode active materials obtained from the various embodiments contain silicon (Si) and silicon oxide (SiO2). x (0 < x ≤ 1), and magnesium silicon oxides (MgSiO3, Mg2SiO4). According to XRF, the molar ratio of Si atoms to Mg atoms (Si / Mg) in Example 1 is 29.5.

[0194] [Experimental Example 3: Initial Characteristics of the Battery]

[0195] The coin cells according to the embodiments and comparative examples were charged and discharged in a constant current mode of 0.2 C and a cutoff voltage of 1.5 V. The value calculated by dividing the discharge capacity at the initial charge-discharge cycle by the weight of the negative electrode active material used in the embodiments and comparative examples is called the "initial capacity", which is defined by the following mathematical formula 1: [Mathematical Expression 1]

[0196] Furthermore, the charge-discharge efficiency during the initial charge-discharge cycle (hereinafter referred to as "initial efficiency") is defined by the following mathematical formula 2: [Mathematical Expression 2]

[0197] The results of Experiment 3, together with the preparation conditions described above, are shown in Table 1 below.

[0198] [Table 1]

[0199] [Experimental Example 4: Battery Life Characteristics]

[0200] After the initial charge-discharge cycle in Test Example 1, the coin batteries obtained from the various embodiments and comparative examples were subjected to another charge-discharge cycle under the same conditions as in Test Example 1, and the same charge-discharge cycles were repeated 48 times in constant current mode at 0.5 C. In other words, including the first and second charge-discharge cycles, a total of 50 charge-discharge cycles were repeated. Figure 7 Graphs illustrating the cycle characteristics of the coin cells according to various embodiments and comparative examples. Specifically, Figure 7 The graph is plotted with the number of charge-discharge cycles as the vertical axis and the discharge capacity of each embodiment and comparative example as the horizontal axis.

[0201] [Discussion of Experimental Results for Examples and Comparative Examples]

[0202] The experimental results described above will be discussed below. However, the following discussion is based on a current assumption, and the contents of this disclosure are not theoretically construed.

[0203] Compared to Comparative Example 1, which did not undergo reduction treatment, Examples 1 to 6, in which SiO was reduced by introducing Mg, showed superior initial capacity, initial efficiency, and cycling characteristics for at least the first 20 cycles. It is believed that the coin cell exhibits improved battery capacity because the reduction treatment increases the Si portion capable of intercalating lithium. Furthermore, it is believed that the reduction treatment reduces the formation of the lithium silicate phase (SiO₂) as an irreversible component during the initial charge-discharge cycles. x Therefore, the coin cell exhibits improved initial efficiency. Specifically, it is believed that because Example 6 used SiO with a smaller particle size as the starting material, the reduction and acid treatments were completed more rapidly, resulting in high initial capacity and initial efficiency. Furthermore, it is believed that the use of small-particle-size SiO facilitated lithium-ion insertion / extraction, leading to improved battery life characteristics. Although Example 7 used SiO with the same particle size (1 μm) as Example 6 as the starting material, the reduction temperature was lower, resulting in a lower degree of SiO reduction compared to Example 6, leading to lower initial capacity and initial efficiency.

[0204] The reasons for the relatively stable cycling characteristics in Examples 1 to 7 are as follows.

[0205] (1) The generated magnesium silicon oxide phase and the residual silicon oxide phase are used as the matrix of Si, thereby mitigating the expansion / contraction during charging and discharging.

[0206] (2) Since the pores formed by acid treatment are filled with carbon, side reactions with the electrolyte are suppressed and conductivity is imparted, thereby suppressing the deterioration of the negative electrode material.

Claims

1. A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising silicon and silicon oxide (SiO2). x Porous composite particles with 0 < x ≤ 2 The pores of the porous composite particles are partially or entirely filled with carbon, and The surface of the porous composite particles is partially or entirely coated with carbon.

2. The negative electrode active material according to claim 1, The porous composite particles also contain magnesium silicon oxide.

3. The negative electrode active material according to claim 2, The magnesium silicon oxide comprises at least one of MgSiO3 and Mg2SiO4.

4. The negative electrode active material according to claim 2, The molar ratio (Si / Mg) of Si atoms to Mg atoms in the negative electrode active material is 10-50.

5. The negative electrode active material according to any one of claims 1 to 4, The porous composite particles described herein contain no magnesium oxide (MgO) on their surface.

6. The negative electrode active material according to any one of claims 1 to 4, The total weight of the carbon filling the pores of the porous composite particles and the carbon covering their surface is 5-20% by weight.

7. The negative electrode active material according to any one of claims 1 to 4, The average particle size of the porous composite particles is 100 nm to 20 μm.

8. The negative electrode active material according to any one of claims 1 to 4, The porous composite particles are composed of Si, O and Mg elements.

9. A negative electrode comprising: Negative current collector, and A negative electrode active material layer, the negative electrode active material layer being formed on the negative electrode current collector and comprising the negative electrode active material as defined in any one of claims 1 to 4.

10. A non-aqueous electrolyte secondary battery comprising the negative electrode as defined in claim 9.

11. A method for preparing a negative electrode active material for a non-aqueous electrolyte secondary battery, comprising: The reduction step, in which silicon oxide (SiO) is reduced... a (0 < a ≤ 2) reacts with metallic magnesium (Mg). The acid treatment step involves treating the material obtained after the reaction with an acid, and A carbon deposition step, wherein carbon is deposited on the material obtained after the acid treatment.

12. The method according to claim 11, During the acid treatment step, porous composite particles with pores on their surface and inside are formed.

13. The method according to claim 12, In the carbon deposition step, some or all of the pores are filled with carbon.

14. The method according to any one of claims 11 to 13, In the reduction step, the molar ratio of Si atoms to Mg atoms (Si / Mg) is 0.1-3.

15. The method according to any one of claims 11 to 13, In the acid treatment step, the amount of acid added is 1-100 millimoles per gram of material obtained from the reduction step.

16. The method according to any one of claims 11 to 13, The carbon deposition step is performed by depositing carbon at 500-900°C.

Images