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

Abstract

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

Description

Negative electrode active material, negative electrode, non-aqueous electrolyte secondary battery, and method for producing negative electrode active material Embodiments of the present invention relate to a negative electrode active material, a negative electrode, a non-aqueous electrolyte secondary battery, and a method for producing the negative electrode active material. This application claims priority from Japanese Application No. 2023-221546, filed December 27, 2023, the entire contents of which are incorporated herein by reference. Recently, a technology for adding silicon oxide to the negative electrode active material of a lithium ion secondary battery has been developed. For example, patent document 1 describes a technology for adding silicon oxide pre-doped with lithium to the negative electrode active material. However, in the case of negative electrode materials with added silicon oxide, the initial efficiency is often low due to the lithium silicate phase that is formed during charging. In addition, when lithium is pre-doped into silicon oxide as in Patent Document 1, there is a possibility that the battery capacity will be low due to the formation of the lithium silicate phase. The problem to be solved by the present invention is to provide a negative electrode active material, a negative electrode, a non-aqueous electrolyte secondary battery, and a method for manufacturing the negative electrode active material, which can improve at least one of the initial efficiency, battery capacity, and cycle characteristics of a non-aqueous electrolyte secondary battery. The inventors of the present invention conceived the idea that by reducing silicon oxide with metal magnesium (Mg), Si, which contributes to battery capacity, could be increased while at the same time easily removing the produced magnesium oxide (MgO). As a result of careful examination, the inventors of the present invention found that by performing a predetermined process starting with a reduction treatment with metal magnesium (Mg), the initial efficiency, battery capacity, and / or cycle characteristics of a non-aqueous electrolyte secondary battery could be improved. The present invention may include the following forms. [1] Silicon and silicon oxide (SiO x, comprising porous composite particles containing 0<x≤2), A negative active material for a non-aqueous electrolyte secondary battery, wherein part or all of the pores of the porous composite particles are filled with carbon, and part or all of the surface of the porous composite particles is covered with carbon. [2] The negative active material described in [1], wherein the porous composite particles further contain silicate magnesium oxide. [3] The negative active material described in [2], wherein the silicate magnesium oxide comprises at least one of MgSiO3 and Mg2SiO4. [4] The negative electrode active material described in [2], wherein the material ratio of Si atoms and Mg atoms (Si / Mg) in the negative electrode active material is 10 or more and 50 or less. [5] The porous composite particle is a negative active material according to any one of [1] to [4], which does not contain magnesium oxide (MgO) at least on the surface. [6] The negative electrode active material according to any one of [1] to [5], wherein the total amount of carbon filling the pores of the porous composite particles and carbon covering the surface is 5 mass% or more and 20 mass% or less based on the porous composite particles. [7] The negative active material according to any one of [1] to [6], wherein the average particle size of the porous composite particles is 100 nm or more and 20 μm or less. [8] Negative current collector, and A negative electrode having a negative electrode active material layer formed on the negative electrode current collector and including the negative electrode active material described in any one of [1] to [7]. [9] A non-aqueous electrolyte secondary battery having a negative electrode as described in [8].

[0010] Silicon oxide (SiO a , 0<a≤2) and a reduction step of reacting metal magnesium (Mg), An acid treatment step of treating the material after the above reaction with acid, and A method for producing a negative active material for a non-aqueous electrolyte secondary battery, comprising a carbon deposition step of depositing carbon on a material after the above acid treatment.

[0011] A method as described in

[0010] , wherein in the acid treatment step, porous composite particles having pores on the surface and inside are formed.

[0012] A method as described in

[0011] , wherein in the carbon deposition step, carbon is filled into some or all of the pores.

[0013] A method according to any one of

[0010] to

[0012] , wherein in the reduction step, the material ratio of Si atoms to Mg atoms (Si / Mg) is 0.1 or more and 3 or less.

[0014] A method according to any one of

[0010] to

[0013] , wherein in the acid treatment step, the amount of acid added per 1 g of the material obtained in the reduction step is 1 mmol or more and 100 mmol or less.

[0015] The method according to any one of

[0010] to

[0014] , wherein the carbon deposition step is performed by depositing carbon at a temperature of 500°C or higher and 900°C or lower. According to the present invention, a negative electrode active material, a negative electrode, a non-aqueous electrolyte secondary battery, and a method for producing 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 from a silicon oxide-based negative electrode active material. Figure 1 is a schematic diagram showing a method for manufacturing a negative active material according to an embodiment. Figure 2 is an SEM image of a cross-section of the negative active material particles of Example 5. Figure 3 is a map of Si atoms obtained by EDS analysis of a cross-section of a negative electrode active material particle of Example 5. Figure 4 is a map of C atoms obtained by EDS analysis of a cross-section of a negative electrode active material particle of Example 5. Figure 5 is a map of O atoms obtained by EDS analysis of a cross-section of a negative electrode active material particle of Example 5. Figure 6 is a map of Mg atoms obtained by EDS analysis of a cross-section of a negative electrode active material particle of Example 5. Figure 7 is a diagram showing the cycle characteristics of coin cells of each embodiment and comparative example. Hereinafter, a negative electrode active material, a negative electrode, a non-aqueous electrolyte secondary battery, and a method for manufacturing the negative electrode active material according to an embodiment will be described. In addition, the following embodiments represent one embodiment of the present invention, do not limit the present invention, and may be arbitrarily changed within the scope of the technical idea of ​​the present invention. In addition, each configuration and each feature of the embodiments may be arbitrarily combined. [Non-aqueous electrolyte secondary battery] One embodiment of the present invention relates to a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to the present embodiment includes a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte. A specific example of the secondary battery may be a lithium ion secondary battery having advantages such as high energy density, discharge voltage, and output stability. Hereinafter, the present invention will be described mainly using lithium ion secondary batteries as an example. However, the present invention is not limited to lithium ion secondary batteries and can be applied to various non-aqueous electrolyte secondary batteries. A lithium ion secondary battery according to one embodiment of the present invention includes a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte. In addition, the lithium ion secondary battery may optionally include a battery case accommodating an electrode assembly composed of the negative electrode, the positive electrode, and the separator, and a sealing member sealing the battery case. [cathode] The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector. The negative electrode active material layer may be formed on the entire surface of the negative electrode current collector or only on a portion of the surface. (negative current collector) The negative electrode current collector used in the negative electrode is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, as the negative electrode current collector, copper; stainless steel; aluminum; nickel; titanium; sintered carbon; copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.; aluminum-cadmium alloy, etc. can be used. The negative electrode current collector may have a thickness of 3 ㎛ or more and 500 ㎛ or less. Fine unevenness may be formed on the surface of the negative electrode current collector to increase adhesion to the negative electrode active material. The negative electrode current collector may have various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, or a non-woven fabric. (negative active material layer) The negative active material layer may include a negative active material, a binder, a conductive agent, and optional additives. For example, the negative active material layer may be formed by applying a negative active material slurry, in which a mixture of the negative active material, the binder, and the conductive agent is dissolved or dispersed in a solvent, to a negative current collector, and then drying and rolling, or by casting the negative active material slurry onto another support, and then peeling off the support to obtain a film, and laminating the resulting film onto a negative current collector. The mixture may further include a dispersant, a filler, or optional additives, as needed. (negative active material) In a lithium ion secondary battery according to an embodiment, the negative active material is silicon and silicon oxide (SiO x, 0<x≤2) includes porous composite particles. Part or all of the pores of the porous composite particles are filled with carbon, and part or all of the surface of the porous composite particles is covered with carbon. Meanwhile, the negative electrode active material layer may further include a negative electrode active material different from the porous composite particles. In this specification, all substances contributing to the charge and discharge reaction at the negative electrode are referred to as “negative electrode active materials.” As used herein, “covered with carbon” means that the outer surface of the particle is physically covered at least partially with carbon. Another material (e.g., another covering layer) may be present between the outer surface of the particle and the carbon covering it. As used herein, “filled with carbon” means that carbon is present in the pores inside the particle. The entire interior of the pores does not necessarily have to be densely filled with carbon, and there may be parts where the inner walls of the pores are not in contact with the carbon. In addition, another material (e.g., a layer covering the inner walls of the pores) may be present between the inner walls of the pores and the carbon. The negative electrode active material may be included in an amount of 80 mass% or more and 99 mass% or less based on the total mass of the negative electrode active material layer. (Porous composite particles) The porous composite particle is a particle composed of multiple types of materials and has a plurality of pores inside. However, as described above, some or all of the pores of the porous composite particle are filled with carbon. Therefore, the porous composite particle may not include substantial pores inside (for example, when all of the pores are filled with carbon, the porous composite particle does not include pores inside). The porous composite particles (excluding carbon in the surface and pores) may be included in an amount of, for example, 0.1 mass% or more and 99 mass% or less, 1 mass% or more and 90 mass% or less, 5 mass% or more and 50 mass% or less, or 10 mass% or more and 30 mass% or less, based on the total mass of the negative electrode active material. Silicon (Si) and silicon oxide (SiO) contained in porous composite particles x ) is, for example, amorphous silicon oxide (SiO x ) has a composite structure in which Si particles are dispersed in a microcrystalline or amorphous form in the matrix of silicon oxide (SiO x ) the ratio x of oxygen to silicon is 0<x≤2, preferably 0.5≤x≤1.6, and more preferably 0.8≤x≤1.5. Since silicon (Si) particles have lithium absorption capability, they can be responsible for charge and discharge reactions at the negative electrode. The silicon oxide matrix surrounding the Si particles can alleviate the expansion and contraction of the volume of the silicon particles that accompany lithium absorption and release. The total amount of the silicon phase and the silicon oxide phase contained in the porous composite particles is, for example, 50 mass% or more and 99 mass% or less, 60 mass% or more and 90 mass% or less, or 70 mass% or more and 80 mass% or less, based on the total mass of the porous composite particles. When it is 50 mass% or more, sufficient battery capacity is obtained. The porous composite particles may further contain silicided magnesium oxide. For example, the silicided magnesium oxide includes, but is not limited to, at least one of MgSiO3 and Mg2SiO4. The total amount of silicided magnesium oxide contained in the porous composite particles is, for example, 0.1 mass% or more and 20 mass% or less, 0.5 mass% or more and 10 mass% or less, or 1 mass% or more and 5 mass% or less, based on the total mass of the porous composite particles. When it is 0.1 mass% or more, the silicided magnesium oxide is likely to alleviate volume expansion of the silicon phase. When it is 20 mass% or less, the effect of sufficiently increasing battery capacity due to the silicon phase can be obtained. When the porous composite particles contain silicified magnesium oxide, the material ratio of Si atoms to Mg atoms (Si / Mg) in the negative electrode active material is, for example, 10 or more and 50 or less, preferably 15 or more and 40 or less, and more preferably 20 or more and 30 or less. When it is 10 or more, since the amount of Si is relatively large, a large energy density can be obtained. When it is 50 or less, it is thought that a sufficient reduction reaction occurs. The porous composite particles may further contain magnesium oxide (MgO) and / or metallic magnesium (Mg). These may correspond to components remaining in the reduction treatment or acid treatment described below. However, preferably, the porous composite particles do not contain magnesium oxide (MgO) and / or metallic magnesium (Mg) at least on the surface. Here, the "surface" means the surface of the porous composite particles located under the carbon coating. That is, "does not contain magnesium oxide (MgO) and / or metallic magnesium (Mg) on ​​the surface" means that magnesium oxide (MgO) and / or metallic magnesium (Mg) does not exist directly under the carbon coating of the porous composite particles. Preferably, the porous composite particles do not contain magnesium oxide (MgO) and / or metallic magnesium (Mg) in contact with the carbon coating. More preferably, the porous composite particles do not contain magnesium oxide (MgO) and / or metallic magnesium (Mg). The amount of magnesium oxide (MgO) contained in the porous composite particles is, for example, 5 mass% or less, 1 mass% or less, 0.1 mass% or less, or 0.01 mass% or less, based on the total mass of the porous composite particles. The amount of metal magnesium (Mg) contained in the porous composite particles is, for example, 5 mass% or less, 1 mass% or less, 0.1 mass% or less, or 0.01 mass% or less, based on the total mass of the porous composite particles. The porous composite particles may preferably be composed of Si, O and Mg elements. However, the porous composite particles may further contain materials other than the above (including unavoidable impurities). The amount of silicon atoms contained in the porous composite particles (total amount of Si atoms in all silicon-containing materials, such as silicon phase, silicon oxide phase, and silicide magnesium oxide phase) is, for example, 10 mass% or more and 90 mass% or less, 30 mass% or more and 80 mass% or less, or 50 mass% or more and 70 mass% or less, based on the total mass of the porous composite particles. The amount of magnesium atoms contained in the porous composite particles (total amount of Mg atoms in all magnesium-containing materials, such as silicide magnesium oxide phase, magnesium oxide (MgO) phase, and metallic magnesium (Mg) phase) is, for example, 0.1 mass% or more and 20 mass% or less, 0.5 mass% or more and 10 mass% or less, or 1 mass% or more and 5 mass% or less, based on the total mass of the porous composite particles. 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. In this specification, the "average particle size" means the particle size at 50% of the integrated value in the particle size distribution measured by the laser diffraction scattering method, that is, the median diameter (D50). The shape of the pores is irregular in cross-section, and some are close to spherical, and some are thin and long (high aspect ratio) pores. The size of the pores is not particularly limited, but, for example, in the case of close to spherical, the average diameter is 1 nm to 500 nm, and in the case of pores with a high aspect ratio, the length of the short side is 1 nm to 500 nm. The arrangement of pores in the porous composite particle need not be spatially uniform. For example, pores may be formed by removing a component constituting a part of the composite particle by the acid treatment described below, so that pores inside the particle are connected to the particle surface. As a result, pores inside the particle may be present more near the surface than in the center of the particle. However, since the arrangement or shape of pores may vary depending on the manufacturing conditions of the porous composite particle including the acid treatment, they are not limited to the above examples, and pores may be arranged and shaped arbitrarily. (Carbon deposition as a negative active material) As described above, the surface of the porous composite particles is at least partially covered with carbon, and the pores of the porous composite particles are at least partially filled with carbon. In this specification, such carbon is collectively called 'sedimentary carbon'. The sedimentary carbon can impart electrical conductivity to the porous composite particles. In addition, since the sedimentary carbon covers the surface of the porous composite particles, side reactions between the porous composite particles and other materials (e.g., electrolyte) can be suppressed. In addition, since the pores of the porous composite particles are filled with carbon, the possibility of cracks occurring in the pores due to volume expansion and contraction of silicon accompanying charge and discharge can be reduced. The carbon material constituting the sedimentary carbon may include graphite such as natural graphite or artificial graphite; carbon fibers such as mesocarbon microbeads (MCMB), carbon nanotubes, and carbon nanofibers; carbon black such as Ketjen black, Denka black, and acetylene black; graphene or graphene oxide; or mixtures thereof; but in order to fill the deep pores inside the fine particles with carbon, it is preferable that it be a film or deposit using a chemical vapor deposition (CVD) method using acetylene gas or methane gas as a raw material. The amount of sedimentary carbon formed on the surface of the porous composite particles, that is, the total amount of carbon filling the pores of the porous composite particles and carbon covering the surface, is, for example, 5 mass% or more and 20 mass% or less, preferably 6 mass% or more and 18 mass% or less, and more preferably 8 mass% or more and 15 mass% or less, based on the porous composite particles (excluding the sedimentary carbon content). When it is 5 mass% or more, it is thought that pore filling with carbon will proceed appropriately. When it is 20 mass% or less, not only can a certain level of battery capacity or more be obtained, but also aggregation of the porous composite particles through the sedimentary carbon can be suppressed. However, the amount of carbon is not limited to the above range, and even if it is outside the above range, the secondary battery can function although the battery performance is somewhat reduced. The sedimentary carbon covers, for example, 50% to 100%, 60% to 99%, or 70% to 95% of the surface area of ​​the porous composite particle (excluding pores inside the particle). The sedimentary carbon fills, for example, 50% to 100%, 60% to 99%, or 70% to 95% of the total volume of the internal pores of the porous composite particle. The average thickness of the sedimentary carbon formed on the surface of the porous composite particles may be, for example, 10 nm or more and 10 μm or less, 50 nm or more and 5 μm or less, 100 nm or more and 2 μm or less, or 200 nm or more and 1 μm or less. (carbon material) The negative electrode active material layer may further include a carbon material as a negative electrode active material different from the porous composite material in which the sedimentary carbon is formed. For example, the carbon material may be included in the negative electrode active material layer in the form of a powder. When a carbon material is included in the negative active material, the carbon material may include any carbon material that can generally be used as an negative active material of a non-aqueous electrolyte secondary battery. For example, the carbon material may include, but is not limited to, one or a mixture of two or more of natural graphite, artificial graphite, graphitized carbon fiber, and amorphous carbon. A composite material with an element other than carbon may also be used. Meanwhile, the carbon material may be either low-crystalline carbon or high-crystalline carbon. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitch, and high-temperature calcined carbon such as petroleum / coal-based coke. When the negative electrode active material additionally includes a carbon material in addition to the porous composite particles, the mass ratio of the porous composite particles and the carbon material in the negative electrode active material may be, for example, 1:99 to 50:50, preferably 5:95 to 30:80, and more preferably 8:92 to 20:80. (bookbinder) A binder is added as a component that promotes bonding between the active material and the conductive agent or bonding with the current collector. Examples of the binder include polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), polyacrylic acid, acrylamide, polyimide, fluororubber, various copolymers thereof, and one or a mixture of two or more of these may be used, but the present invention is not limited thereto. The content of the binder may be 0.1 mass% or more and 30 mass% or less based on the total mass of the negative electrode active material layer. The content of the binder may be preferably 0.5 mass% or more and 20 mass% or less, and more preferably 1 mass% or more and 10 mass% or less. When the content of the binder polymer satisfies the above range, sufficient adhesive strength within the electrode can be provided while preventing a decrease in the capacity characteristics of the battery. (Challenge) The conductive material is not particularly limited as long as it is an electrically conductive material that does not cause a chemical change. Examples of the conductive material include carbon-based materials such as artificial graphite, natural graphite, single-layer carbon nanotubes, double-layer carbon nanotubes, graphene, carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and carbon fibers; metal powders or metal fibers such as aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, and iridium; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Examples of the conductive polymer include polyaniline, polythiophene, polyacetylene, polypyrrole, and polyphenylene derivatives, and one or a mixture of two or more of these may be used, but the present invention is not limited thereto. The content of the conductive agent may be 0.1 mass% or more and 30 mass% or less based on the total mass of the negative electrode active material layer. The content of the conductive agent may be preferably 0.5 mass% or more and 15 mass% or less, and more preferably 0.5 mass% or more and 10 mass% or less. When the content of the conductive agent satisfies the above range, sufficient conductivity can be provided, and it is advantageous in that the battery capacity can be secured because the amount of the negative electrode active material is not reduced. (thickener) When applying the negative electrode active material to the negative electrode current collector, the negative electrode active material slurry may contain a thickener. Specifically, the thickener may be a cellulose-based compound such as carboxymethyl cellulose (CMC). The thickener may be contained in an amount of, for example, 0.5 mass% or more and 10 mass% or less based on the total mass of the negative electrode active material layer. (menstruum) The solvent used in the negative electrode active material slurry is not particularly limited as long as it is generally used in the manufacture of the negative electrode. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, acetone, water, etc., and one or a mixture of two or more of these may be used, but the present invention is not limited thereto. [Method for manufacturing cathode] A method for manufacturing a negative electrode for a lithium ion secondary battery according to an embodiment comprises the following steps. (1) Step for manufacturing negative active material (2) Step of preparing a negative electrode active material slurry from a negative electrode active material (3) Step of manufacturing a negative electrode from a negative electrode active material slurry (1) Manufacture a negative active material. When the manufacturing step (1) of the negative electrode active material is subdivided into a ‘method for manufacturing the negative electrode active material’, it includes the following steps. (a) Reduction step: Silicon oxide (SiO a , 0<a≤2) and metallic magnesium (Mg) are reacted. (b) Acid treatment step: The material after the reaction of (1) above is treated with acid. (c) Carbon deposition step: Carbon is deposited on the material after the acid treatment of (b). Fig. 1 is a schematic diagram showing a method for manufacturing a negative electrode active material according to the present embodiment. Hereinafter, the description will be given with reference to Fig. 1, but Fig. 1 is merely a conceptual diagram for easy understanding and does not accurately represent the microscopic state of actual particles. (a) Reduction step In the reduction step, metal magnesium (Mg) acts as a reducing agent. Specifically, silicon oxide (SiO a ) and metallic magnesium (Mg) are thought to undergo the following chemical reaction. SiO a+ aMg → Si + aMgO Silicon oxide used as a raw material is, for example, SiO a (0<a≤2) can be a powder of SiO a For example, as in (a) of Fig. 1, the Si particles may have a structure in which Si particles are dispersed in a microcrystalline or amorphous form in a matrix of amorphous silicon oxide. Meanwhile, in the description of the porous composite particles described above, for convenience, Si particles and silicon oxide (SiO x ) matrix is ​​expressed separately, but here, the Si particles and silicon oxide matrix are expressed together as silicon oxide (SiO a ) is collectively called. That is, a is an average value of the entire Si fine particles and silicon oxide matrix. 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 raw material is silicon monoxide (SiO) (a=1) or silicon dioxide (SiO2). In addition, the silicon oxide powder of the raw material is SiO having a specific value of a. a It may include only two or more types of SiO with different values ​​of a. a Any mixture of powders will do. The average particle size of the silicon oxide particles of the raw material is, for example, 100 nm to 20 μm, preferably 200 nm to 10 μm, more preferably 500 nm to 5 μm or less or 500 nm to 1 μm. When the average particle size is small, the reaction point of the charge / discharge reaction is advantageously relatively increased, so that the battery capacity may increase, and the insertion and deintercalation of lithium ions within the particles may be facilitated, so that the life characteristics of the battery may be improved. When the average particle size is 100 nm or more, a sufficient specific surface area of ​​the porous composite particles can be secured, appropriate reactivity with the electrolyte can be achieved, and the energy density of the battery can be increased to a certain extent. When the average particle size is 20 μm or less, the life characteristics due to volume expansion can be suppressed. In the reduction step, the material ratio of Si atoms to Mg atoms (Si / Mg) is 0.1 or more and 3 or less, preferably 0.3 or more and 2.5 or less, more preferably 0.5 or more and 2 or less, even more preferably 0.6 or more and 1.8 or less, and still more preferably 0.8 or more and 1.5 or less. When it is 0.1 or more, a certain amount of Si, which becomes a charge / discharge reaction site, is included, so that a certain level of energy density can be obtained. When it is 3 or less, a sufficient reduction reaction occurs, and the battery capacity is sufficiently improved. In addition to the above, when silicon oxide and metallic magnesium (Mg) or generated magnesium oxide (MgO) react, silicided magnesium oxide can be generated as a by-product. Examples of silicided magnesium oxide include MgSiO3 and Mg2SiO4. The reaction conditions are arbitrary as long as the above reaction proceeds. In terms of ease of processing, a method of mixing and heating silicon oxide powder and metal magnesium (Mg) powder is preferable, but the present invention is not limited thereto, and for example, these materials may be reacted in a solution. Since a reduction reaction is performed, it is preferable to perform the reaction under an inert gas (nitrogen, argon, etc.) atmosphere or a reducing atmosphere. The reaction temperature is, for example, 500°C or more and 1000°C or less, preferably 600°C or more and 900°C or less, more preferably 650°C or more and 850°C or less, and even more preferably 700°C or more and 800°C or less. The reaction pressure is not particularly limited. The reaction time is, for example, 10 minutes or more and 3 hours or less, and preferably 30 minutes or more and 2 hours or less. The above reduction reaction is assumed to proceed, for example, by the following mechanism. However, the following is merely a guess and does not bind the present invention by theory. The silicon oxide particles of the raw material react with metal magnesium (Mg), and the Si fine particles in the silicon oxide matrix increase. At the same time, magnesium oxide (MgO) or magnesium silicide oxide is generated. As a result, as shown in Fig. 1 (b), the silicon fine particles are dispersed in the silicon oxide matrix, forming silicon oxide (SiO). x ), magnesium oxide (MgO), silicided magnesium oxide, and unreacted metallic magnesium (Mg) can be obtained as integrated and / or aggregated composite particles. (b) Acid treatment step In the acid treatment step, magnesium oxide (MgO) and unreacted metallic magnesium (Mg) produced in the reduction step react with protons to form magnesium ions (Mg 2+ ) becomes magnesium ion (Mg 2+ ) can be removed by washing, and as a result, magnesium oxide (MgO) and unreacted metallic magnesium (Mg) can be removed. MgO + 2H + → Mg 2+ + H2O Mg 2+ + 2H + → Mg 2+ + H2 The acid treatment step includes adding an acid to the product of the reduction step. The acid is, for example, an aqueous acid solution. The aqueous acid solution is, for example, an aqueous solution of a strong acid. The strong acid may be an inorganic acid or an organic acid, and examples thereof include hydrochloric acid, nitric acid, sulfuric acid, hydrogen bromide, hydrogen iodide, and sulfonic acid. These may be arbitrarily combined. That is, the acid treatment step may include a step of reacting the material after the reduction step with at least one acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrogen bromide, hydrogen iodide, and sulfonic acid. For example, when hydrochloric acid is used, the following chemical reaction occurs between magnesium oxide (MgO) and metallic magnesium (Mg) and hydrochloric acid. MgO + 2HCl → MgCl2+ H2O Mg + 2HCl → MgCl2+ H2 The above acid may not contain anything that can strongly dissolve silicon oxide (SiOx), such as hydrogen fluoride (HF). The concentration of the acid solution is, for example, 0.1 M or more and 10 M or less, and preferably 0.5 M or more and 5 M or less. When the concentration is 0.1 M or more, impurities can be sufficiently removed. When the concentration is 10 M or less, sufficient manufacturing efficiency can be maintained. The amount of the acid solution added per 1 g of the composite particles obtained in the reduction step is, for example, 1 mL or more and 100 mL or less, preferably 5 mL or more and 80 mL or less, and more preferably 10 mL or more and 50 mL or less. When the concentration of the acid solution is 1 M, the amount of acid substance added per 1 g of the composite particles is, for example, 1 mmol or more and 100 mmol or less, preferably 5 mmol or more and 80 mmol or less, and more preferably 10 mmol or more and 50 mmol or less. The reaction conditions are arbitrary as long as the above reaction proceeds. The reaction temperature is, for example, 10°C or more and 90°C or less, preferably room temperature or more and 50°C or less. The reaction pressure is not particularly limited. The reaction time is, for example, 1 hour or more and 48 hours or less, preferably 6 hours or more and 36 hours or less, and more preferably 12 hours or more and 30 hours or less. It is assumed that the acid treatment of composite particles proceeds, for example, by the following mechanism. However, the following is merely a guess and does not bind the present invention by theory. The acid that comes into contact with the composite particles after the reduction step first reacts with the magnesium oxide (MgO) or metallic magnesium (Mg) on ​​the surface or near the surface of the composite particles. As a result of the magnesium oxide (MgO) or metallic magnesium (Mg) reacting with the acid being eluted from the composite particles, pores are formed in the portion where the magnesium oxide (MgO) or metallic magnesium (Mg) has been removed from the composite particles. The acid enters these pores and further reacts with the magnesium oxide (MgO) or metallic magnesium (Mg) inside the particles. In this way, the magnesium oxide (MgO) or metallic magnesium (Mg) in the composite particles is decomposed and removed. As a result of the acid treatment, pores are formed inside the composite particles, so that porous composite particles having pores on the surface and inside are obtained, as shown in Fig. 1 (c). Since silicified magnesium oxide has low reactivity with acids, at least some of it may remain after acid treatment; however, depending on the raw materials, acid, and reaction conditions used, some or all of the silicified magnesium oxide may be decomposed. After adding an acid and causing a reaction, the substance dissolved in the acid can be removed by general washing. After the washing and drying process, a porous composite material can be obtained. (c) Carbon deposition stage In the carbon deposition step, carbon is deposited on the obtained porous composite particles, thereby covering the surface of the porous composite particles with carbon, and filling the inside of the pores of the porous composite particles with carbon. The carbon deposition treatment can be performed by any generally used carbon deposition method, and the carbon deposition method is not particularly limited. The carbon deposition method may be either a dry method or a wet method. An example of the former may include a method of depositing carbon on a porous composite material by a chemical vapor deposition (CVD) method. An example of the latter may include a method of mixing a carbon source and a porous composite material in a solution and heating and drying them. For example, when performing carbon deposition such as CVD, it is preferable to perform it at a relatively low temperature for a long time in order to sufficiently fill the inside of the pores with carbon. For example, the temperature for performing carbon deposition is 500℃ or more and 900℃ or less, preferably 600℃ or more and 800℃ or less. For example, the time for performing carbon deposition is 10 minutes or more and 24 hours or less, preferably 30 minutes or more and 10 hours or less, and more preferably 30 minutes or more and 2 hours or less. By forming a sedimentary carbon layer on the surface and internal pores of the porous composite particles, electrical conductivity is imparted to the porous composite particles and the surface of the porous composite particles is protected, so that at least one of battery capacity, initial efficiency, and cycle characteristics can be improved. By carbon deposition, as shown in (d) of Fig. 1, part or all of the surface of the porous composite particle is covered with carbon, and part or all of the pores inside the particle are filled with carbon. The porous composite particle in which the deposition carbon is formed in this way is used as a negative electrode active material. Meanwhile, the method for manufacturing a negative active material according to the present embodiment does not require a process for actively forming pores in the composite material, and pores are formed by themselves by removing magnesium oxide (MgO) and metallic magnesium (Mg) through an acid treatment step. For example, the method for manufacturing a negative active material according to the present embodiment does not include a conventional pore forming process (e.g., a process for depositing a target material in a vapor state onto a metal plate). (2) A negative electrode active material slurry is prepared from a negative electrode active material. A solvent is added to the negative electrode active material obtained in the above (1). At this time, a conductive agent, a binder, a thickener, etc. may be added as needed. A negative electrode active material slurry is obtained by dissolving or dispersing the negative electrode active material, the conductive agent, the binder, the thickener, etc. in the solvent. (3) A negative electrode is manufactured from a negative electrode active material slurry. By applying a slurry of a negative active material to a negative electrode collector, followed by drying and rolling, an anode can be manufactured in which a layer of a negative active material is formed on the negative electrode collector. Alternatively, the negative electrode may be manufactured by casting the negative active material slurry onto another support, peeling the film from the support, and laminating the resulting film onto a negative current collector. In addition, the negative active material layer may be formed on the negative current collector using any other method. [anode] In a lithium ion secondary battery according to an embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on one side or both sides of the positive electrode current collector. The positive electrode active material layer may be formed on the entire surface of the positive electrode current collector or may be formed on only a portion of the surface. (positive current collector) The positive electrode current collector used in the positive electrode is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, as the positive electrode current collector, stainless steel; aluminum; nickel; titanium; sintered carbon; aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector may have a thickness of 3 ㎛ or more and 500 ㎛ or less. Fine unevenness may be formed on the surface of the positive electrode current collector to increase adhesion to the positive electrode active material. The positive electrode current collector may have various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, or a non-woven fabric. (positive active material layer) The positive electrode active material layer can be formed, for example, by applying a positive electrode active material slurry, in which a mixture of a positive electrode active material, a conductive agent, and a binder is dissolved and dispersed in a solvent, to a positive electrode current collector, and then drying and rolling. The mixture may further include a dispersant, a filler, or other optional additives, as necessary. The cathode active material may be included in an amount of 80 mass% or more and 99 mass% or less based on the total mass of the cathode active material layer. (positive active material) As a cathode active material, a compound capable of reversible insertion (intercalation) and deintercalation (deintercalation) of lithium can be used. A specific example thereof may include a lithium metal composite oxide containing lithium and one or more metals such as cobalt, manganese, nickel, copper, vanadium, and aluminum. More specifically, examples of such lithium metal composite oxides 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(0<z<1), LiMn 2-z Ni z O4(0<z<2) etc.); lithium-nickel-cobalt oxides (e.g., LiNi 1-y Co y O2(0<y<1) etc.); lithium-manganese-cobalt oxides (e.g., LiCo 1-z Mn z O2(0<z<1), LiMn 2-y Co y O4(0<y<2) etc.); 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), Li(Ni x Co y Mn z )O4(0<x<2, 0<y<2, 0<z<2, x+y+z=2) etc.); lithium-nickel-cobalt-metal(M) oxide (e.g., Li(Ni x Co y Mn z M w )O2(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) etc.); compounds in which a transition metal element in these compounds is partially substituted with one or more other metal elements, etc. The positive electrode active material layer may contain any one or two or more compounds among these. However, the present invention is not limited to these. In particular, in terms of improving the capacity characteristics and stability of the battery, LiCoO2, LiMnO2, LiMn2O4, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni) 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 oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.) are preferable. (Binders and Challenges) The type and content of the binder and conductive agent used in the positive electrode active material slurry may be the same as those described for the negative electrode. (menstruum) The solvent used in the positive electrode active material slurry is not particularly limited as long as it is generally used in the manufacture of the positive electrode. Examples of the solvent include amine solvents such as N,N-dimethylaminopropylamine, diethylenetriamine, and N,N-dimethylformamide (DMF); ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; ester solvents such as methyl acetate; amide solvents such as dimethylacetamide and 1-methyl-2-pyrrolidone (NMP); dimethylsulfoxide (DMSO), and the like. One type or a mixture of two or more types thereof may be used, but the present invention is not limited thereto. The amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied to the positive electrode current collector. [Method of manufacturing positive electrode] A method for manufacturing a positive electrode for a lithium ion secondary battery according to an embodiment may include a step of obtaining a positive electrode active material slurry by dissolving or dispersing a positive electrode active material in a solvent together with a binder, a conductive agent, a thickener, etc., as necessary, and a step of forming a positive electrode active material layer on a positive electrode current collector, such as by applying the positive electrode active material slurry onto a positive electrode current collector, similar to a method for manufacturing an anode, thereby obtaining a positive electrode. [Separator] In the lithium ion secondary battery according to the embodiment, the separator separates the negative electrode and the positive electrode to provide a passage for lithium ions to move. If it is a separator that is usually used as a separator in a lithium ion secondary battery, it can be used without any particular limitation. In particular, it is preferable that the separator have low resistance to ion movement of the electrolyte and excellent moisture retention capacity of the electrolyte. For example, a porous polymer film manufactured from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof can be used as the separator. In addition, a general porous nonwoven fabric, for example, a nonwoven fabric manufactured from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. In addition, a separator coated with a ceramic component or a polymer material may be used in order to secure heat resistance or mechanical strength. [Electrolyte] In the non-aqueous electrolyte secondary battery according to the embodiment, the non-aqueous electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid electrolyte, etc. that can be used in the manufacture of a secondary battery. The non-aqueous electrolyte may contain an organic solvent and a lithium salt, and may further contain additives as needed. Hereinafter, the liquid electrolyte is also referred to as an 'electrolyte'. Any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Examples of the organic solvent include 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), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; Examples thereof include nitrile solvents such as R-CN (wherein R is a C2∼C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or ether bond); amide solvents such as dimethyl formamide; dioxolane solvents such as 1,3-dioxolane; sulfolane solvents, and the like, and one or a mixture of two or more of these may be used, but the present invention is not limited thereto. The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium ion secondary battery. Examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2, and one or a mixture of two or more of these may be used, but the present invention is not limited thereto. The lithium salt may be contained in the electrolyte at a concentration of, for example, 0.1 mol / L or more and 2 mol / L or less. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited, allowing lithium ions to move effectively. Additives can be used as needed for the purposes of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Examples of additives include haloalkylene carbonate compounds such as fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC), pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, aluminum trichloride, and the like, and one kind or a mixture of two or more kinds of these can be used, but the present invention is not limited thereto. The additive may be contained, for example, in an amount of 0.1 mass% or more and 15 mass% or less with respect to the total mass of the electrolyte. [Method for manufacturing non-aqueous electrolyte secondary battery] The non-aqueous electrolyte secondary battery according to the embodiment can be manufactured by interposing a separator (e.g., a separator) and an electrolyte between the negative electrode manufactured as described above and the positive electrode manufactured as described above. More specifically, the electrode assembly can be formed by arranging a separator between the negative electrode and the positive electrode, placing the electrode assembly in a battery case such as a cylindrical battery case or a square battery case, and then injecting an electrolyte to manufacture the battery. Alternatively, the electrode assembly can be laminated, and then the resultant resultant can be impregnated with an electrolyte and then placed in a battery case and sealed to manufacture the battery. The above battery case may be one commonly used in the field. The shape of the battery case may be, for example, a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape. The lithium ion secondary battery according to the embodiment can be used not only as a power source for small devices, but also as a unit battery of a medium- to large-sized battery module including a plurality of battery cells, etc. Preferable examples of such medium- to large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [effect] Recently, the use of silicon-based materials as negative electrodes has been frequently studied to increase the capacity of lithium-ion secondary batteries. However, pure silicon (Si) has significantly reduced life characteristics due to cracks that occur due to expansion during charging, which breaks the electron conduction path. Therefore, a negative electrode active material mixed with a small amount of silicon monoxide and graphite has been put to practical use. Silicon monoxide is SiO, which functions to alleviate the expansion of Si. x It has a composite structure in which a Si phase is dispersed within the matrix of the electrode. However, when silicon monoxide (SiO) is used, the lithium silicate phase formed during the first charge of the battery is irreversibly generated, so that the discharge capacity is significantly reduced with respect to the charge capacity, and the initial efficiency is very low at 65-70%. Therefore, when the amount of silicon monoxide (SiO) in the negative electrode material is increased, it is difficult to achieve a balance with the initial efficiency of the positive electrode material. To solve this problem, SiO pre-doped with Li x Materials have been proposed. However, depending on the amount of doping, lithium silicate phases of various compositions are formed, resulting in reduced capacity, gas generation due to the elution of Si by basic slurry, or increased viscosity. For this reason, although there is no problem with the process of battery manufacturing at the laboratory level, in mass production, coating becomes impossible, or even if coating is possible, there is a problem of pinholes being formed after drying of the electrode, so practical use is still difficult. According to the negative active material according to the embodiment, by reducing silicon oxide of the raw material, the amount of silicon (Si), which contributes to high capacity, is increased, and by depositing carbon on the surface of the porous composite particle and in the pores remaining after removing the MgO phase or Mg phase, not only electrical conductivity is imparted to the porous composite particle, but also side reactions between the porous composite particle and the electrolyte can be suppressed. Accordingly, the battery capacity, charge / discharge efficiency, and cycle characteristics can be improved. In addition, since all the materials constituting the porous composite particle are stable in water, there is an advantage in that no gas is generated as in the past. When the negative active material contains magnesium oxide, the magnesium oxide is replaced with silicon oxide (SiO x ) functions as a matrix of Si, and can alleviate the volume expansion of Si. Therefore, the cycle characteristics can be further improved. 《Example》 Hereinafter, examples and comparative examples will be described, but the present invention is not limited thereto. In addition, the considerations described below are merely exemplary conjectures to assist understanding of the present invention, and do not limit the present invention at all. [Example 1] (Manufacture of negative active material) Silicon monoxide (SiO) powder with an average particle size of 5 ㎛ and metallic magnesium (Mg) powder with an average particle size of 300 ㎛ were mixed at a mass ratio of 1:1. The mixture was put into a plasma sintering device (Microphase product) and maintained at 800°C for 1 hour under an inert gas atmosphere to cause a reduction reaction of SiO powder by Mg powder. Through X-ray diffraction pattern (XRD) measurement and elemental analysis, the product was found to be silicon (Si), silicon oxide (SiO). x , 0<x≤1), it was confirmed to contain metallic magnesium (Mg), magnesium oxide (MgO), and silicide magnesium oxide (MgSiO3, Mg2SiO4). 10 g of the above product was placed in 200 mL of 2 M hydrochloric acid and stirred for 24 hours to remove the Mg phase and MgO phase. Thereafter, washing and drying were performed. Subsequently, CVD treatment using ethylene gas was performed while rotating the core tube at 800°C. From the mass ratio before and after the CVD treatment, it was confirmed that the product after the treatment contained 7 mass% of carbon. The particles were appropriately pulverized and sieved to adjust the particle size so that the average particle diameter was 8 μm, thereby obtaining a negative electrode active material. (Manufacturing of coin cells) The obtained negative active material, carbon black (CB) as a conductive material and an aqueous dispersion (solid content 0.4%) of single-walled carbon nanotubes (SWCNT), styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were prepared at a mass ratio of 88.8:3.3:0.25:3.65:4.0. First, the negative active material, CB, and CMC were mixed, and then the SWCNT dispersion and water were added and kneaded. Finally, SBR was added and mixed to prepare a negative active material slurry. The obtained slurry was uniformly applied to copper foil, vacuum dried at 110°C for 10 hours, and then cut into circles with a diameter of 13 mm to manufacture a 2016-type coin cell using lithium metal as the counter electrode. [Example 2] A negative active material was manufactured and a coin cell was manufactured in the same manner as in Example 1, except that the concentration of hydrochloric acid for the reduction product was doubled as in Example 1 and washing was performed five times. [Example 3] A negative active material was manufactured in the same manner as in Example 2, except that the mass ratio of silicon monoxide (SiO) powder and magnesium powder (Mg) was set to 2:1, and a coin cell was manufactured in the same manner. [Example 4] A negative active material was manufactured in the same manner as in Example 2, except that the mass ratio of silicon monoxide (SiO) powder and magnesium powder (Mg) was set to 4:1, and a coin cell was manufactured in the same manner. [Example 5] A negative active material was manufactured in the same manner as in Example 3, except that the amount of carbon covered in the CVD treatment was increased to 11 mass%, and a coin cell was manufactured in the same manner. [Example 6] A negative active material was manufactured in the same manner as in Example 3, except that silicon monoxide (SiO) powder having an average particle size of 1 ㎛ was used as a raw material, and a coin cell was manufactured in the same manner. [Example 7] A negative active material was manufactured and a coin cell was manufactured in the same manner as in Example 6, except that the temperature for reduction using metal magnesium (Mg) was changed from 800°C to 680°C. [Comparative Example 1] A negative electrode active material was manufactured in the same manner as in Example 1, except that 5 mass% of carbon was deposited on the silicon monoxide (SiO) powder used in Example 1 and used as a negative electrode active material, and a coin cell was manufactured in the same manner. [Evaluation Example 1: SEM observation and EDS analysis] The negative active material particles obtained in Example 5 were observed using a scanning electron microscope (SEM) capable of energy dispersive X-ray analysis (EDS). Fig. 2 is an SEM image of a cross-section of the negative active material particles of Example 5. Figs. 3 to 6 are maps of Si atoms, C atoms, O atoms, and Mg atoms obtained by EDS analysis of the cross-section of the negative active material particles of Example 5, respectively. In Figs. 3 to 6, target atoms exist in the white portions. The light-colored portions in Fig. 2 mainly contain silicon (Si) or silicon oxide (SiO). x) are located, while the dark-colored part corresponds to the pores generated by the acid treatment, and it is thought that mainly carbon (C) or silicified magnesium oxide are located. From the comparison of Fig. 3 (Si map) and Fig. 4 (C map), it is thought that a lot of C exists in the part where Si does not exist. From the comparison of Fig. 3 (Si map) and Fig. 6 (Mg map), Mg is dotted throughout the particle. Considering that MgO and Mg are removed by the acid treatment, it is thought that silicified magnesium oxide is dotted throughout the particle. Meanwhile, the upper left area and the lower right area of ​​the image are the resin of the substrate. The following facts were confirmed from this SEM image and EDS analysis results. (1) A composite particle formed by integrating silicon-based material and magnesium-based material through a reduction reaction. (2) Pores are formed inside the composite particles by removing Mg or MgO from the composite particles through acid treatment. (3) By CVD treatment, not only is the surface of the composite particle covered with carbon, but carbon also penetrates into the pores of the composite particle and fills the pores. [Evaluation Example 2: XRD Measurement and Elemental Analysis] By elemental analysis by XRD measurement and X-ray fluorescence analysis (XRF), the negative active material obtained in each example was found to contain silicon (Si), silicon oxide (SiO x , 0<x≤1), and silicided magnesium oxide (MgSiO3, Mg2SiO4). According to XRF, the material ratio of Si atoms and Mg atoms (Si / Mg) in Example 1 was 29.5. [Evaluation Example 3: Initial characteristics of the battery] For each coin cell of the examples and comparative examples, charge and discharge were performed at a constant current of 0.2 C and a cutoff voltage of 1.5 V. The 'initial capacity' is defined as the value obtained by dividing the discharge capacity in this first charge and discharge process by the mass (g) of the negative active material powder used in each example and comparative example as follows. In addition, the charge / discharge efficiency in this initial charge / discharge process (hereinafter referred to as “initial efficiency”) is defined as follows. The results of Evaluation Example 3 are summarized in the table below along with the manufacturing conditions mentioned above. [Evaluation Example 4: Battery Life Characteristics] For the coin cells manufactured by each example and comparative example, following the first charge / discharge process performed in Evaluation Example 1, charge / discharge was performed once more under the same conditions, and then the same charge / discharge was repeated 48 times at a constant current of 0.5 C. That is, a total of 50 charge / discharge processes were repeated, including the first and second charge / discharge processes. Fig. 7 is a diagram showing the cycle characteristics of the coin cells of each example and comparative example. Specifically, Fig. 7 is a graph plotting the number of cycles of the charge / discharge process on the vertical axis and the discharge capacity of the coin cells of each example and comparative example on the horizontal axis. [Consideration of evaluation results of practical and comparative examples] Below, the above evaluation results are discussed. However, the following discussion is only a hypothesis at this point in time and does not bind the present invention by theory. Examples 1 to 6 in which Mg was introduced to reduce SiO were superior to Comparative Example 1 in which no reduction treatment was performed in terms of initial capacity, initial efficiency, and cycle characteristics for at least the first 20 cycles. It is thought that the battery capacity of the coin cell was improved as a result of the increase in the Si portion having lithium absorption characteristics by the reduction treatment. In addition, the reduction treatment produced silicon oxide (SiO) which generates a lithium silicate phase, which is an irreversible component, in the first charge / discharge. x ) is reduced, so it is thought that the initial efficiency of the coin cell is improved. In particular, in Example 6, since the particle size of the raw material SiO was made small, the reduction and acid treatment proceeded more quickly, so it is thought that the initial capacity and initial efficiency were increased. In addition, since the particle size of the SiO is small, the insertion and extraction of lithium ions proceed smoothly, so it is thought that the life characteristics of the battery were also improved. Example 7 also uses the same 1 μm SiO as Example 6 as a raw material, but since the reduction temperature is low, the degree of reduction of the SiO is lower than in Example 6, and as a result, it is thought that the initial capacity and initial efficiency are lower than in Example 6. The reason why the cycle characteristics were relatively stable in Examples 1 to 7 can be considered as follows. (1) The generated silicate magnesium oxide phase and the remaining silicon oxide phase act as a silicon (Si) matrix, alleviating expansion and contraction during charge and discharge. (2) As carbon is filled in the pores formed in the acid treatment, side reactions with the electrolyte are suppressed and conductivity is imparted, thereby suppressing deterioration of the negative electrode active material.

Claims

1. Silicon and silicon oxide (SiO x , comprising porous composite particles containing 0<x≤2), A negative active material for a non-aqueous electrolyte secondary battery, wherein part or all of the pores of the porous composite particles are filled with carbon, and part or all of the surface of the porous composite particles is covered with carbon.

2. In paragraph 1, A negative active material, wherein the porous composite particles further contain silicate magnesium oxide.

3. In paragraph 2, A negative active material, wherein the above-mentioned silicate magnesium oxide comprises at least one of MgSiO3 and Mg2SiO4.

4. In paragraph 2, A negative electrode active material, wherein the material ratio of Si atoms to Mg atoms (Si / Mg) among the above negative electrode active materials is 10 or more and 50 or less.

5. In any one of paragraphs 1 to 4, A negative active material, wherein the porous composite particles do not contain magnesium oxide (MgO) at least on the surface.

6. In any one of paragraphs 1 to 4, A negative electrode active material, wherein the total amount of carbon filling the pores of the porous composite particles and carbon covering the surface is 5 mass% or more and 20 mass% or less based on the porous composite particles.

7. In any one of paragraphs 1 to 4, A negative electrode active material, wherein the average particle size of the porous composite particles is 100 nm or more and 20 μm or less.

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

9. Negative current collector, and A negative electrode having a negative electrode active material layer formed on the negative electrode current collector and including the negative electrode active material according to any one of claims 1 to 4.

10. A non-aqueous electrolyte secondary battery having the negative electrode described in Article 9.

11. Silicon oxide (SiO a , 0<a≤2) and a reduction step of reacting metal magnesium (Mg), An acid treatment step of treating the material after the above reaction with acid, and A method for producing a negative active material for a non-aqueous electrolyte secondary battery, comprising a carbon deposition step of depositing carbon on a material after the above acid treatment.

12. In paragraph 11, A method in which porous composite particles having pores on the surface and inside are formed in the above acid treatment step.

13. In paragraph 12, A method wherein carbon is filled into some or all of the pores in the carbon deposition step.

14. In any one of paragraphs 11 to 13, A method wherein, in the above reduction step, the material ratio of Si atoms and Mg atoms (Si / Mg) is 0.1 or more and 3 or less.

15. In any one of paragraphs 11 to 13, A method wherein, in the acid treatment step, the amount of acid substance added per 1 g of the material obtained in the reduction step is 1 mmol or more and 100 mmol or less.

16. In any one of paragraphs 11 to 13, A method wherein the above carbon deposition step is performed by depositing carbon at a temperature of 500°C or higher and 900°C or lower.

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