Negative electrode active material, negative electrode containing the same, secondary battery containing the same, and method for producing negative electrode active material

Abstract

The present invention relates to a negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for manufacturing the negative electrode active material.

Description

Technical Field

[0001] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2022-0150562, filed with the Korean Intellectual Property Office on November 11, 2022, and Korean Patent Application No. 10-2023-0154765, filed with the Korean Intellectual Property Office on November 9, 2023, and all of its contents are incorporated herein by reference.

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

Background Art

[0003] In recent years, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries that are small, lightweight, and relatively high in capacity has been rapidly increasing. In particular, lithium secondary batteries are lightweight and have a high energy density, and have been in the spotlight as a driving power source for portable devices. Accordingly, research and development efforts to improve the performance of lithium secondary batteries have been actively carried out.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. Further, an active material layer including a positive electrode active material and a negative electrode active material can be formed on a current collector for the positive electrode and the negative electrode. Generally, lithium-containing metal oxides such as LiCoO 2 , LiMn 2 O 4 are used as the positive electrode active material, and a carbon-based active material or a silicon-based active material that does not contain lithium is used as the negative electrode active material.

[0005] In the case of a silicon-based active material among negative electrode active materials, it is noted for having a higher capacity and excellent fast charging characteristics compared to carbon-based active materials. However, silicon-based active materials have a disadvantage in that the degree of volume expansion / contraction due to charge and discharge is large and the irreversible capacity is large, resulting in low initial efficiency.

[0006] On the one hand, among silicon-based active materials, silicon-based oxides, specifically SiO x In the case of silicon-based oxides represented by (0 < x < 2), there is an advantage in that the degree of volume expansion / contraction due to charge and discharge is lower than that of other silicon-based active materials such as silicon (Si). However, there is still a drawback that the initial efficiency decreases due to the presence of irreversible capacity in silicon-based oxides as well.

[0007] In connection with this, research has been continuously conducted to reduce the irreversible capacity and improve the initial efficiency by doping or inserting metals such as Li, Al, and Mg into silicon-based oxides. However, in the case of a negative electrode slurry containing a metal-doped silicon-based oxide as a negative electrode active material, there is a problem that the metal oxide formed by doping reacts with moisture to increase the pH of the negative electrode slurry and change the viscosity. For this reason, the state of the manufactured negative electrode becomes poor, and there is a problem that the charge and discharge efficiency of the negative electrode decreases.

[0008] In addition, as the cycle progresses, there is a problem that swelling of the negative electrode occurs and many side reactions of the electrolytic solution occur.

[0009] Therefore, in a situation where it is necessary to develop a negative electrode active material that can suppress the surface reaction of the negative electrode active material containing silicon-based oxides, improve the phase stability of the slurry, and improve the charge and discharge efficiency of the negative electrode manufactured therefrom.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] The present invention relates to a negative electrode active material, a negative electrode containing the same, a secondary battery containing the same, and a method for producing the negative electrode active material.

Means for Solving the Problems

[0012] One embodiment of the present invention is silicon-based particles containing SiO x (0 < x < 2) and a Mg compound; and a negative electrode active material including a carbon layer provided on at least a part of the silicon-based particles, wherein the negative electrode active material contains N element and H element, and the total content of the N element and the H element is 250 ppm or more and less than 3000 ppm based on 100 parts by weight of the negative electrode active material, and the weight ratio of the H element to the N element is 1 or less.

[0013] One embodiment of the present invention provides a negative electrode.

[0014] One embodiment of the present invention provides a secondary battery including the negative electrode.

[0015] One embodiment of the present invention includes a step of vaporizing Si powder, SiO 2 powder, and Mg respectively and mixing them, and then cooling the mixed gas to form silicon-based particles; and a step of mixing the silicon-based particles and a carbon-based material to provide a carbon layer on at least a part of the surface of the silicon-based particles, and provides a method for producing a negative electrode active material according to the present invention.

Effects of the Invention

[0016] The negative electrode active material according to one embodiment of the present invention contains a Mg compound, and is characterized in that the total of N and H in the negative electrode active material is 250 ppm or more and less than 3000 ppm, and the weight ratio of H to N is 1 or less. A negative electrode active material that satisfies this has high hardness and elasticity, has characteristics advantageous for swelling of the negative electrode, has high conductivity of the carbon layer, and has an effect of improving life characteristics.

[0017] Therefore, the negative electrode containing the negative electrode active material according to one embodiment of the present invention and the secondary battery including the negative electrode have the effect of improving the discharge capacity, initial efficiency, resistance performance, and / or life characteristics of the battery.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the present specification will be described in more detail.

[0019] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0020] In this specification, when a certain member is "on" another member, this includes not only the case where a certain member is in contact with another member, but also the case where there is another member between the two members.

[0021] The terms and words used in this specification should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the principle that they can appropriately define the concepts of the terms in order to explain their invention in the best way, and they should be interpreted in a meaning and concept consistent with the technical idea of the present invention.

[0022] The terms used in this specification are merely used to explain exemplary embodiments and are not intended to limit the present invention. The singular expressions of the terms used in this specification include plural expressions unless the context clearly indicates otherwise.

[0023] In this specification, the crystallinity of the structure contained in the negative electrode active material can be confirmed by X-ray diffraction analysis. The X-ray diffraction analysis can be performed using an XRD (X-ray diffraction) analyzer (product name: D4-endavor, manufacturer: bruker). In addition to this device, devices used in the art can also be appropriately adopted.

[0024] In this specification, the presence or absence of elements and the element content in the negative electrode active material can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0025] In this specification, the average particle diameter (D 50 ) can be defined as the particle diameter corresponding to 50% of the volume accumulation amount in the particle size distribution curve (graph curve of the particle size distribution diagram) of the particles. The average particle diameter (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle diameters in the range from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolvable results.

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

[0027] <Negative electrode active material> One embodiment of the present invention is a negative electrode active material including silicon-based particles containing SiO x (0 < x < 2) and an Mg compound; and a carbon layer provided on at least a part of the silicon-based particles, wherein the negative electrode active material contains N element and H element, and the total content of the N element and H element is 250 ppm or more and less than 3000 ppm based on 100 parts by weight of the negative electrode active material, and the weight ratio of the H element to the N element is 1 or less.

[0028] The negative electrode active material according to one embodiment of the present invention includes silicon-based particles. The silicon-based particles contain SiO x (0 < x < 2) and an Mg compound.

[0029] The SiO x (0 < x < 2) may correspond to a matrix in the silicon-based particles. The SiOx (0 < x < 2) may be in a form containing Si and / or SiO 2 and the Si may form a phase. For example, the SiO x (0 < x < 2) may be a composite containing amorphous SiO 2 and Si crystals. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0030] The Mg compound may correspond to a matrix within the silicon-based particles. The Mg compound may exist in at least one form of magnesium atoms, magnesium silicate, magnesium silicide, and magnesium oxide within the silicon-based particles. When the silicon-based particles contain the Mg compound, there is an effect that the initial efficiency is improved.

[0031] The Mg compound may be in a form doped into the silicon-based particles and distributed on the surface and / or inside of the silicon-based particles. The Mg compound is distributed on the surface and / or inside of the silicon-based particles, can control the expansion / contraction of the volume of the silicon-based particles to an appropriate level, and can play a role in preventing damage to the active material. Also, the Mg compound may be contained in terms of reducing the ratio of the irreversible phase (e.g., SiO 2 ) of the silicon-based oxide particles and increasing the efficiency of the active material.

[0032] The Mg compound may contain at least any one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may contain at least any one of Mg 2 SiO 4 and MgSiO 3 . The Mg silicide may contain Mg 2 Si. The Mg oxide may contain MgO.

[0033] The Mg compound may be present in the form of magnesium silicate. The Mg silicate can be classified into crystalline magnesium silicate and amorphous magnesium silicate.

[0034] The Mg compound is Mg within the silicon-based particles 2 SiO 4 and MgSiO 3 and may be present in the form of at least one kind of magnesium silicate.

[0035] The Mg element may be contained in an amount of 0.1 part by weight to 40 parts by weight based on 100 parts by weight in total of the negative electrode active material, specifically may be contained in an amount of 0.1 part by weight to 20 parts by weight, or may be contained in an amount of 0.1 part by weight to 10 parts by weight, and more specifically may be contained in an amount of 0.5 part by weight to 8 parts by weight. When the content of Mg exceeds the above range, although the initial efficiency increases as the content of Mg increases, there is a problem that the discharge capacity decreases. Therefore, when the above range is satisfied, appropriate discharge capacity and initial efficiency can be realized.

[0036] The content of the Mg element can be confirmed by ICP analysis. Specifically, after collecting a certain amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible, nitric acid, hydrofluoric acid, and sulfuric acid are added, and it is completely decomposed on a hot plate. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), at the wavelength specific to the element to be analyzed, the intensity of the standard solution prepared using a standard solution (5 mg / kg) is measured to create a standard calibration curve. Then, the pretreated sample solution and the blank sample are introduced into the instrument, the intensity of each is measured to calculate the actual intensity, and after calculating the concentration of each component with respect to the created calibration curve, it is converted so that the total of all becomes the theoretical value, and the content of the elements of the manufactured negative electrode active material can be analyzed.

[0037] In one embodiment of the present invention, the silicon-based particles may contain additional metal atoms. The metal atoms may exist in at least one form of metal atoms, metal silicates, metal silicides, and metal oxides within the silicon-based particles. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Thereby, the initial efficiency of the negative electrode active material can be improved.

[0038] In one embodiment of the present invention, a carbon layer is provided on at least a part of the surface of the silicon-based particles. At this time, the carbon layer may be in a form that partially covers at least a part of the surface, that is, the surface of the particles, or covers the entire surface of the particles. The carbon layer imparts conductivity to the negative electrode active material, and can improve the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery.

[0039] In one embodiment of the present invention, the carbon layer contains amorphous carbon. Further, the carbon layer may further contain crystalline carbon.

[0040] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0041] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based particles. The amorphous carbon may be at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a carbon-based substance formed using a carbide or hydrocarbon of other organic substances as a source in chemical vapor deposition.

[0042] The carbide of the other organic substances may be a carbide of an organic substance selected from the group consisting of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose and combinations thereof.

[0043] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. Examples of the aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0044] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

[0045] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight based on 100 parts by weight in total of the negative electrode active material. More specifically, it may be included in an amount of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the above range is satisfied, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0046] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, and specifically may be 5 nm to 300 nm. When the above range is satisfied, there is an effect that the conductivity of the negative electrode active material is improved, the volume change of the negative electrode active material is easily suppressed, the side reaction between the electrolyte and the negative electrode active material is suppressed, and the initial efficiency and / or life of the battery are improved.

[0047] Specifically, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0048] In the present invention, the crystallinity of the carbon layer can be confirmed by calculating the D / G band ratio through Raman spectroscopy. Specifically, it can be measured using a Renishaw 2000 Raman microscope system and a 532 nm laser excitation, with a low laser output density and an exposure time of 30 seconds to avoid the thermal effect of the laser, and using a 100-fold optical lens. To reduce the deviation by position, a total of 25 points are measured for a 5 μm × 5 μm region, and after fitting using a Lorentzian function, the average values of the D band and the G band can be calculated for the calculation.

[0049] In one embodiment of the present invention, the negative electrode active material may contain N element and H element.

[0050] In one embodiment of the present invention, the total content of the N element and the H element may be 250 ppm or more and less than 3000 ppm. Specifically, it may be 280 ppm or more and 2000 ppm or less, 280 ppm or more and 1800 ppm or less, or 300 ppm or more and 1800 ppm or less. The lower limit of the content of the N element and the H element may be 250 ppm, 280 ppm, 290 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 550 ppm, 600 ppm, or 700 ppm, and the upper limit of the content of the N element and the H element may be 2900 ppm, 2500 ppm, 2000 ppm, 1800 ppm, 1600 ppm, 1500 ppm, 1300 ppm, or 1000 ppm.

[0051] When the contents of the N element and the H element satisfy the above range, an Mg—Si—O—N film is effectively formed on the surface of the silicon-based particles, the swelling of the material can be controlled, the conductivity of the carbon layer is increased, and the life characteristics are improved. On the contrary, when the contents of N and H are less than the above range, the Mg—Si—O—N film is not sufficiently formed on the surface of the silicon-based particles, and there is a problem that it is difficult to control swelling. When the contents of N and H exceed the above range, there is a problem that the hardness and elasticity of the Mg—Si—O—N film are lowered and it is difficult to control swelling. Specifically, when present in an Mg—Si—O—N structure rather than a structure such as Si—O—N glass, Mg can form a bond with O and provide a relatively firm structure. The present invention is advantageous for forming an Mg—Si—O—N structure by satisfying the contents and ratios of N and H described above, whereby the hardness and elasticity can be improved, and thereby the swelling can be controlled. When the contents of N and H are excessively large or do not satisfy the above-described ratio, the possibility of forming Si—O—H or other structures is relatively higher than the probability of forming Mg—Si—O—N.

[0052] The contents and ratios of the N element and the H element described above can be determined according to the process conditions or materials used in the process of manufacturing the negative electrode active material. For example, by mixing a material containing an appropriate amount of N and H, for example, an appropriate amount of ammonia, with the material that provides the carbon source during the formation of the carbon layer, the above-described range can be satisfied.

[0053] In one embodiment of the present invention, the negative electrode active material may include an Mg—Si—O—N film provided on the surface of the silicon-based particles. The Mg—Si—O—N film may be in a form including silicon oxynitride having an Si—N bond.

[0054] Said N may exist in the form of silicon oxynitride on the surface of silicon-based particles containing an Mg compound, or may exist in a form contained in the carbon layer. Specifically, N may have an Si-N bond and exist in the form of silicon oxynitride on the surface of the silicon-based particles, or N may be contained in the carbon layer in a form having a C-N bond.

[0055] That is, at least a part of N in the negative electrode active material according to the present invention may exist having an Si-N bond. In another embodiment, at least a part of N in the negative electrode active material according to the present invention may be contained in the carbon layer.

[0056] Said H may exist in a form having an Si-O-H bond on the surface of silicon-based particles containing an Mg compound, or may exist in a form contained in the carbon layer. Specifically, H may be contained in the carbon layer in a form having a C-H bond.

[0057] In one embodiment of the present invention, the content of said N may be 125 ppm or more and less than 3000 ppm. Specifically, it may be 150 ppm or more and 2500 ppm or less, 175 ppm or more and 2000 ppm or less, 200 ppm or more and 1500 ppm or less, or 210 ppm or more and 1200 ppm or less. The lower limit of the content of said N may be 125 ppm, 150 ppm, 175 ppm, 200 ppm, 210 ppm, 220 ppm, 250 ppm, 350 ppm, 400 ppm, or 430 ppm, and the upper limit of the content of N may be 2900 ppm, 2500 ppm, 2000 ppm, 1500 ppm, 1200 ppm, 1000 ppm, 800 ppm, 600 ppm, or 500 ppm.

[0058] When the content of N satisfies the above range, the Mg-Si-O-N film is effectively formed on the surface of the silicon-based particles, controlling the swelling of the material to improve the life characteristics, increasing the conductivity of the carbon layer, and having the effect of improving the life characteristics. On the contrary, when the content of N is less than the above range, the Mg-Si-O-N film is not effectively formed on the surface of the silicon-based particles, and there is a problem that it is difficult to control the swelling. When the content of N exceeds the above range, the hardness and elasticity of the Mg-Si-O-N film decrease, and there is a problem that it is difficult to control the swelling.

[0059] In one embodiment of the present invention, the content of H may be 1 ppm or more and less than 1500 ppm. Specifically, it may be 10 ppm or more and 1200 ppm or less, 50 ppm or more and 1000 ppm or less, 70 ppm or more and 800 ppm or less, 70 ppm or more and 600 ppm or less. The lower limit of the content of H may be 1 ppm, 10 ppm, 50 ppm, 70 ppm, 80 ppm, 100 ppm, 200 ppm, or 300 ppm, and the upper limit of the content of H may be 1400 ppm, 1200 ppm, 1000 ppm, 800 ppm, 600 ppm, 500 ppm, or 400 ppm.

[0060] When the content of H satisfies the above range, the functional groups in the carbon layer are few, the side reactions with the electrolyte are few, and there is an effect of improving the life. On the contrary, when the content of H is less than the above range, the hydrophobicity of the active material becomes excessively large, and there is a problem that the dispersion is not sufficiently performed in the aqueous slurry. When the content of H exceeds the above range, the functional groups in the carbon layer are excessively present, and the side reaction of the electrolyte becomes large, so there is a problem that the performance of the battery deteriorates.

[0061] In one embodiment of the present invention, the weight ratio of H to N may be 1 or less. Specifically, it may be more than 0 and 1 or less, or 0.1 or more and 1 or less.

[0062] The weight ratio of H to N may be 0.95 or less, 0.9 or less, 0.85 or less, or 0.8 or less, and may also be 0 or more, more than 0, 0.01 or more, 0.1 or more, more than 0.1, 0.2 or more, or 0.3 or more. When the weight ratio of H to N satisfies the above range, the negative electrode active material is sufficiently dispersed in the aqueous slurry, and the conductivity of the negative electrode active material and the extraction of Li ions are excellent. On the other hand, when the weight ratio of H to N is less than the above range, many defects occur in the carbon layer, and the side reaction of the electrolytic solution becomes large, so the cycle characteristics are inferior. When it exceeds the above range, there is a problem that the hydrophobicity of the carbon layer increases and the dispersion is not sufficiently performed in the aqueous slurry.

[0063] In this specification, the contents of the N element and the H element can be measured by putting 0.1 g of the negative electrode active material sample to be measured into a crucible and introducing it into an ONH analyzer (Bruker, G8 Galileo) to measure the content (concentration).

[0064] The average particle size (D 50 ) of the negative electrode active material may be 0.1 μm to 30 μm, specifically may be 1 μm to 20 μm, and more specifically may be 1 μm to 10 μm. When the above range is satisfied, the structural stability of the active material during charge and discharge can be achieved, and problems such as an increase in the volume expansion / shrinkage level due to an excessively large particle size can be prevented, and problems such as a decrease in the initial efficiency due to an excessively low particle size can be prevented.

[0065] The BET specific surface area of the negative electrode active material is 1 m 2 / g to 100 m 2 / g, specifically may be 1 m 2 / g to 70 m 2 / g, and more specifically may be 1 m 2 / g to 50 m 2 / g, for example, 2 m 2 / g to 30 m 2 / g. When the above range is satisfied, the side reaction with the electrolytic solution during charging and discharging of the battery can be reduced, so the life characteristics of the battery can be improved.

[0066] <Method for manufacturing negative electrode active material> One embodiment of the present invention vaporizes Si powder, SiO 2 powder, and Mg respectively and mixes them, and then cools the mixed gas to form silicon-based particles; and mixing the silicon-based particles and a carbon-based substance to provide a carbon layer on at least a part of the surface of the silicon-based particles, a method for manufacturing a negative electrode active material is provided.

[0067] The Si powder and SiO 2 powder can be manufactured by heating and vaporizing them in a vacuum and then depositing the vaporized mixed gas. At this time, the Si powder and SiO 2 powder may be heated and vaporized respectively, or heated and vaporized in a mixed state.

[0068] The Si powder and SiO 2 powder may be contained in a weight ratio of 2:8 to 8:2, specifically, may be contained in a weight ratio of 4:6 to 6:4 or 5:5.

[0069] Specifically, the Si powder and SiO 2 powder may be heat-treated at 1300°C to 1800°C, 1400°C to 1800°C, or 1400°C to 1600°C under vacuum.

[0070] The mixed gas vaporized by the heat treatment can be cooled under vacuum and deposited on a solid phase. Further, the deposited solid phase can be heat-treated in an inert atmosphere to produce preliminary silicon-based particles. The heat treatment may be performed at 500°C to 1000°C or 700°C to 900°C.

[0071] A carbon layer can be provided on the surface of the silicon-based particles.

[0072] The carbon layer may be formed by using a chemical vapor deposition method (CVD) using a carbon-based substance, for example, a hydrocarbon gas, or a method of carbonizing a substance serving as a carbon source.

[0073] Specifically, after the formed silicon-based particles are introduced into the reactor, hydrocarbon gas may be formed by chemical vapor deposition (CVD) at 600°C to 1200°C. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 900°C to 1000°C.

[0074] At this time, N and H may be included in the negative electrode active material in the above-described ranges by the following method.

[0075] (1) A method of performing a step of heat-treating the silicon-based particles in a nitrogen atmosphere after the step of forming the silicon-based particles

[0076] In one embodiment of the present invention, after vaporizing and mixing Si powder, SiO 2 powder, and Mg respectively, and then cooling the mixed gas to form silicon-based particles, a step of heat-treating the silicon-based particles in a nitrogen (N2) atmosphere may be performed. Specifically, the silicon-based particles containing an Mg compound may be heat-treated in a nitrogen atmosphere to introduce silicon oxynitride on the surface of the silicon-based particles.

[0077] At this time, the heat treatment temperature may be 850°C to 1200°C, and specifically may be 900°C to 1100°C.

[0078] Thereafter, a carbon layer may be formed on the surface of the silicon-based particles using the above-described chemical vapor deposition method (CVD) under an Ar atmosphere.

[0079] (2) A method of performing a step of mixing the silicon-based particles and a carbon-based substance to provide a carbon layer on at least a part of the surface of the silicon-based particles in an N 2 atmosphere

[0080] In one embodiment of the present invention, the step of mixing the silicon-based particles and the carbon-based material to provide a carbon layer on at least a part of the surface of the silicon-based particles is carried out in an N 2 atmosphere and may be performed.

[0081] At this time, in this step, a carbon layer may be formed on the surface of the silicon-based particles using chemical vapor deposition (CVD). At this time, the carbon-based material may be a hydrocarbon gas.

[0082] In another embodiment, in this step, a carbon layer may be formed by coating a carbon source on the surface of the silicon-based particles. At this time, the carbon-based material may be pitch.

[0083] In one embodiment of the present invention, before the step of mixing the silicon-based particles and the carbon-based material to provide a carbon layer on at least a part of the surface of the silicon-based particles, the silicon-based particles are subjected to N 2 heat treatment in an atmosphere may be further performed.

[0084] At this time, the heat treatment temperature may be 850 °C to 1200 °C, and specifically may be 900 °C to 1100 °C.

[0085] (3) In the step of mixing the silicon-based particles and the carbon-based material to provide a carbon layer on at least a part of the surface of the silicon-based particles, in addition to the carbon-based material, NH 3 gas is further included

[0086] In one embodiment of the present invention, in the step of providing a carbon layer on at least a part of the surface of the silicon-based particles, in addition to the carbon-based material, NH 3 may be further included.

[0087] At this time, the carbon-based material and NH 3The weight ratio may be 0.8:1 to 30:1. Specifically, it may be 0.8:1 to 20:1, 0.8:1 to 10:1, 0.8:1 to 5:1, 0.8:1 to 2:1, 0.8:1 to 1.5:1, or 0.8:1 to 1.2:1. When the above range is satisfied, N and H are introduced into the negative electrode active material within a suitable range, and it is possible to impart suitable hardness and elasticity to the negative electrode active material, and there is an effect of improving the conductivity.

[0088] The above step may be performed using a chemical vapor deposition method (CVD).

[0089] The negative electrode active material according to the present invention can be manufactured by appropriately using the above methods (1) to (3), and is not limited thereto. The negative electrode active material according to the present invention can be manufactured by appropriately adopting a combination of the methods (1) to (3).

[0090] When forming a negative electrode active material by the above method, N and H are introduced into the negative electrode active material within a suitable range, and the performance of a battery using this can be improved.

[0091] <Negative electrode> The negative electrode according to an embodiment of the present invention may contain the above-described negative electrode active material.

[0092] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may contain the negative electrode active material. Further, the negative electrode active material layer may further contain a binder, a thickener, and / or a conductive material.

[0093] The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, a thickener, and / or a conductive material to at least one side of the current collector, followed by drying and rolling.

[0094] The negative electrode slurry may further contain an additional negative electrode active material.

[0095] As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0 < β < 2), SnO 2 , metal oxides capable of doping and undoping lithium such as vanadium oxide, lithium titanate oxide, and lithium vanadate oxide; or composites containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, etc. Any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Further, as the carbon material, either low-crystalline carbon or high-crystalline carbon may be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0096] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0097] In one embodiment of the present invention, the weight ratio of the negative electrode active material contained in the negative electrode slurry to the additional negative electrode active material may be 10:90 to 90:10, specifically, it may also be 10:90 to 50:50.

[0098] The negative electrode slurry may contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry is at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol in terms of facilitating the dispersion of components, and specifically, it may contain distilled water.

[0099] The negative electrode slurry containing the negative electrode active material according to one embodiment of the present invention may have a pH of 7 to 11 at 25°C. When the pH of the negative electrode slurry satisfies the above range, there is an effect that the rheological properties of the slurry are stabilized. On the contrary, when the pH of the negative electrode slurry is less than 7 or the pH of the negative electrode slurry exceeds 11, there is a problem that carboxymethyl cellulose (CMC) used as a thickener decomposes, the viscosity of the slurry decreases, and the degree of dispersion of the active material contained in the slurry decreases.

[0100] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0101] The binder may include at least one selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0102] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbons, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0103] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and thickeners used in the technical field may be appropriately employed.

[0104] In one embodiment of the present invention, the weight ratio of the negative electrode active material contained in the negative electrode slurry to the additional negative electrode active material may be 1:99 to 30:70, specifically 5:95 to 30:70, or 10:90 to 20:80.

[0105] In one embodiment of the present invention, all the negative electrode active materials contained in the negative electrode slurry may be contained in an amount of 60 to 99 parts by weight, specifically 70 to 98 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0106] In one embodiment of the present invention, the binder may be contained in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0107] In one embodiment of the present invention, the conductive material may be contained in an amount of 0.5 to 25 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0108] In one embodiment of the present invention, the thickener may be contained in an amount of 0.5 to 25 parts by weight, specifically 0.5 to 20 parts by weight, more specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0109] The negative electrode slurry according to one embodiment of the present invention may further contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may be at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically, it may contain distilled water, in terms of facilitating the dispersion of components.

[0110] In one embodiment of the present invention, the solid content weight of the negative electrode slurry may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight, based on 100 parts by weight of the total negative electrode slurry.

[0111] <Secondary battery> The secondary battery according to an embodiment of the present invention may include the negative electrode according to the above-described embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution, and the negative electrode is the same as the above-described negative electrode. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0112] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0113] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0114] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ) or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe 3 O 4 ; lithium manganese oxides such as chemical formula Li 1+c1 Mn 2-c1 O 4 (0≦c1≦0.33), LiMnO 3 , LiMn 2 O 3 , LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); LiV 3 O 8 , V 2 O5 , Cu 2 V 2 O 7 and other vanadium oxides; chemical formula LiNi 1-c2 M c2 O 2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.5) nickel site type lithium nickel oxide represented by; chemical formula LiMn 2-c3 M c3 O 2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1), or Li 2 Mn 3 MO 8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn) lithium manganese composite oxide represented by; or a part of Li in the chemical formula is substituted with an alkaline earth metal ion, LiMn 2 O 4 and the like, but not limited thereto. The positive electrode may be Li metal.

[0115] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0116] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0117] In addition, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. Among these, one kind alone or a mixture of two or more kinds may be used.

[0118] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any material that can be used as a separator in a secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to the ion migration of the electrolytic solution and excellent in the ability to hold the electrolytic solution moisture. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single layer or a multilayer structure.

[0119] Examples of the electrolytic solution include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used during the manufacture of lithium secondary batteries.

[0120] Specifically, the electrolytic solution may contain a non-aqueous organic solvent and a metal salt.

[0121] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0122] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents because they have a high dielectric constant and can well dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate at an appropriate ratio and used, an electrolytic solution having high electrical conductivity can be prepared, so they can be more preferably used.

[0123] As the metal salt, a lithium salt may be used. The lithium salt is a substance that is easily soluble in the non-aqueous electrolytic solution. For example, as the anion of the lithium salt, F - , Cl - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH - , (SF 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - , and (CF 3 CF 2 SO 2 ) 2 N -One or more selected from the group consisting of may be used.

[0124] In addition to the constituent components of the electrolytic solution, the electrolytic solution may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery.

[0125] According to another embodiment of the present invention, there are provided a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

Examples

[0126] Hereinafter, preferred examples are presented to assist in the understanding of the present invention. However, the following examples are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the scope of the technical idea, and it is natural that such modifications and variations belong to the appended claims.

[0127] <Examples and Comparative Examples> 〔Example 1〕 Si and SiO 2 92 g of a powder obtained by mixing Si and SiO in a molar ratio of 1:1 and 8 g of Mg were mixed and vacuum-heated in a reactor at a sublimation temperature of 1,400°C. Then, the sublimated Mg, Si, and SiO 2The mixed gas was reacted in a cooling zone under vacuum with a cooling temperature of 800 °C and condensed into a solid phase to form silicon-based particles. Thereafter, heat treatment was performed in an inert atmosphere at a temperature of 800 °C. Thereafter, 15 sus ball media were introduced into the silicon-based particles, and then pulverized using a ball mill for 3 hours to produce particles with a size of 6 μm (D 50 ). Thereafter, while flowing Ar gas to maintain an inert atmosphere, the silicon-based particles were positioned in the hot zone of a CVD apparatus, and using Ar as a carrier gas, methane and ammonia were introduced at a weight ratio of 9:1 and blown into a hot zone at 950 °C and reacted at 10 -1 torr for 20 minutes to form a carbon layer on the surface of the silicon-based particles.

[0128] The substance produced as described above was used as the negative electrode active material of Example 1. The D 50 of the negative electrode active material was 6 μm, and the specific surface area was 6 m 2 / g.

[0129] As a result of measurement using an ONH component analyzer, the nitrogen content contained in the negative electrode active material was 450 ppm, and the hydrogen content was 360 ppm.

[0130] [Example 2] In Example 1, a negative electrode active material was produced in the same manner except that the weight ratio of methane to ammonia was changed to 1:1.

[0131] As a result of measurement using an ONH component analyzer, the nitrogen content contained in the negative electrode active material was 1100 ppm, and the hydrogen content was 500 ppm.

[0132] [Example 3] In Example 1, a negative electrode active material was produced in the same manner except that the weight ratio of methane to ammonia was changed to 95:5.

[0133] As a result of measurement using an ONH component analyzer, the nitrogen content in the negative electrode active material was 220 ppm, and the hydrogen content was 80 ppm.

[0134] [Comparative Example 1] In Example 1, a negative electrode active material was produced in the same manner except that the weight ratio of methane to ammonia was changed to 1:2.

[0135] As a result of measurement using an ONH component analyzer, the nitrogen content in the negative electrode active material was 1600 ppm, and the hydrogen content was 1500 ppm.

[0136] [Comparative Example 2] In Example 1, an active material was produced in the same manner except that the CVD temperature was set to 900°C.

[0137] As a result of measurement using an ONH component analyzer, the nitrogen content in the negative electrode active material was 400 ppm, and the hydrogen content was 430 ppm.

[0138] [Comparative Example 3] In Example 1, an active material was produced in the same manner except that the weight ratio of methane to ammonia was changed to 1:3.

[0139] As a result of measurement using an ONH component analyzer, the nitrogen content in the negative electrode active material was 1500 ppm, and the hydrogen content was 1600 ppm.

[0140] [Comparative Example 4] In Example 1, an active material was produced in the same manner except that ammonia was not introduced.

[0141] As a result of measurement using an ONH component analyzer, the nitrogen content in the negative electrode active material was 10 ppm, and the hydrogen content was 1 ppm.

[0142] The compositions of the negative electrode active materials produced in the above Examples and Comparative Examples are as shown in Table 1 below.

[0143]

Table 1

[0144] In this specification, for the contents of the N element and the H element, 0.1 g of the negative electrode active material sample to be measured was placed in a crucible and introduced into an ONH analyzer (Bruker, G8 Galileo) to measure its content (concentration). The content of the Mg element was confirmed by ICP analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES manufactured by Perkin-Elmer 7300, AVIO 500).

[0145] The content of the carbon layer was confirmed under oxygen conditions by elemental analysis by combustion (G4 ICARUS manufactured by Bruker).

[0146] The D of the negative electrode active material 50 was analyzed by the PSD measurement method using a microtrac device.

[0147] The specific surface area of the negative electrode active material was measured using a BET measurement device (BEL-SORP-MAX, Nippon Bell). The gas was removed (degassed) at 200 °C for 8 hours, and N 2 adsorption / desorption was performed at 77 K for measurement.

[0148] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Life (Capacity Retention Rate) Characteristics> Negative electrodes and batteries were manufactured using the negative electrode active materials of the examples and comparative examples, respectively.

[0149] The negative electrode active material, carbon black as the conductive material, and PAA (poly acrylic acid) as the binder were mixed at a weight ratio of 80:10:10 to produce a mixture. Then, 7.8 g of distilled water was added to 5 g of the mixture, followed by stirring to produce a negative electrode slurry. The negative electrode slurry was applied to and dried on a copper (Cu) metal thin film, which was a negative electrode current collector with a thickness of 20 μm. At this time, the temperature of the circulating air was 60°C. Next, it was roll-pressed and dried in a vacuum oven at 130°C for 12 hours to produce a negative electrode.

[0150] The produced negative electrode was cut into a circle with a diameter of 1.7671 cm 2 and a lithium (Li) metal thin film was used as the positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, and vinylene carbonate dissolved at 0.5 parts by weight was dissolved in a mixed solution with a mixed volume ratio of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) of 7:3. An electrolyte solution in which 1 M concentration of LiPF 6 was dissolved was injected to produce a lithium coin half-cell.

[0151] Charging and discharging were performed on the produced battery to evaluate the discharge capacity, initial efficiency, and capacity retention rate, which are shown in Table 2 below.

[0152] For the first cycle and the second cycle, charging and discharging were performed at 0.1C, and from the third cycle to the 49th cycle, charging and discharging were performed at 0.5C. The 50th cycle ended in a charged state (with lithium in the negative electrode). Charging conditions: CC (constant current) / CV (constant voltage) (5 mV / 0.005C current cut-off) Discharging conditions: CC (constant current) condition 1.5V

[0153] From the results of the first charge-discharge, the discharge capacity (mAh / g) and the initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived by the following calculation. Initial efficiency (%) = (first discharge capacity / first charge capacity) × 100

[0154] The capacity retention rates were respectively derived by the following calculations. Capacity retention rate (%) = (49th discharge capacity / 1st discharge capacity) × 100

[0155]

Table 2

[0156] In Table 2 above, Examples 1 to 3 using the negative electrode active material according to the present invention contain N element and H element in the negative electrode active material, and the total content of the N element and the H element is 250 ppm or more and less than 3000 ppm based on 100 parts by weight of the negative electrode active material, and the weight ratio of the H element to the N element is 1 or less. It was confirmed that the discharge capacity, initial efficiency, and capacity retention rate of the battery were improved. This is presumably because the Mg-Si-O-N film appropriately formed on the surface of the silicon-based particles of the present invention effectively controls the swelling of the material and increases the conductivity of the carbon layer. On the other hand, in Comparative Examples 1 to 4, the total content of the N element and the H element is less than 250 ppm, 3000 ppm or more, or the weight ratio of the H element to the N in the active material exceeds 1. The negative electrode active materials of the comparative examples are such that the Mg-Si-O-N film is not sufficiently formed on the surface of the silicon-based particles, or the hardness and elasticity of the formed Mg-Si-O-N film are reduced, making it difficult to control the swelling. It can be confirmed that they are inferior in the discharge capacity, initial efficiency, and life characteristics of the battery.

Claims

1. SiO ｘ silicon-based particles containing SiO (0 < x < 2) and an Mg compound; and A negative electrode active material containing a carbon layer provided on at least a part of the silicon-based particles, wherein the negative electrode active material contains N element and H element, the total content of the N element and the H element is 250 ppm or more and less than 3000 ppm based on 100 parts by weight of the negative electrode active material, and the weight ratio of the H element to the N element is 1 or less. Negative electrode active material.

2. The negative electrode active material according to claim 1, wherein the N element is contained in an amount of 125 ppm or more and less than 3000 ppm based on 100 parts by weight of the negative electrode active material.

3. The negative electrode active material according to claim 1, wherein the H element is contained in an amount of 1 ppm or more and less than 1500 ppm based on 100 parts by weight of the negative electrode active material.

4. The negative electrode active material according to claim 1, wherein the weight ratio of the H element to the N element is 0.1 or more and 1 or less.

5. The negative electrode active material according to claim 1, wherein at least a part of the N exists with an Si-N bond.

6. The negative electrode active material according to claim 1, wherein at least a part of the N exists in the carbon layer.

7. The negative electrode active material according to claim 1, wherein the Mg compound contains Mg silicate.

8. The negative electrode active material according to claim 1, wherein the Mg element is contained in an amount of 0.1 part by weight or more and 40 parts by weight or less based on 100 parts by weight of the total negative electrode active material.

9. The negative electrode active material according to claim 1, wherein the carbon layer is contained in an amount of 0.1 part by weight or more and 50 parts by weight or less based on 100 parts by weight of the total negative electrode active material.

10. Si powder, SiO ２ powder, and Mg are each vaporized and mixed, and then the mixed gas is cooled to form silicon-based particles; and A step of mixing the silicon-based particles and a carbon-based material to provide a carbon layer on at least a part of the surface of the silicon-based particles The method for producing a negative electrode active material according to any one of claims 1 to 9.

11. The method for producing a negative electrode active material according to claim 10, further comprising a step of heat-treating the silicon-based particles in a nitrogen atmosphere after the step of forming the silicon-based particles.

12. In the step of mixing the silicon-based particles and the carbon-based material to provide a carbon layer on at least a part of the surface of the silicon-based particles, in addition to the carbon-based material, NH ３ gas is further included, The method for producing a negative electrode active material according to claim 10.

13. A negative electrode containing the negative electrode active material according to any one of claims 1 to 9.

14. A secondary battery containing the negative electrode according to claim 13.

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