Silicon nitride composite and method for producing same

Abstract

The present invention relates to a method for producing a silicon nitride composite, the method comprising: (S1) a step for mixing an amorphous silicon nitride powder and a reducing agent powder; and (S2) a step for crystallizing at least a portion of the silicon contained in the amorphous silicon nitride by heat-treating the mixed powder. The method can be used to produce the silicon nitride composite at a low cost using a simple process. The silicon nitride composite produced by the method has both a crystalline portion and an amorphous portion, and thus can improve capacity, rate capability, and lifespan characteristics when used as a negative electrode for a lithium secondary battery.

Description

Silicon nitride composite and method for producing the same

[0001] The present invention relates to a silicon nitride composite and a method for producing the same.

[0002] Lithium secondary batteries are widely used as power supplies for portable electronic devices such as laptops, tablet PCs, and smartphones, as well as electric vehicles such as hybrid electric vehicles and plug-in electric vehicles. Recently, demand has been increasing for high-performance lithium secondary batteries with higher energy density and longer lifespan than commercially available lithium secondary batteries. However, graphite, the anode material typically used in lithium secondary batteries, has limited capacity and cannot meet growing energy demands.

[0003] Among various anode materials, silicon (Si) is considered a strong candidate to replace commercialized graphite, boasting approximately 10 times the capacity of graphite. However, silicon suffers from inevitable volume expansion during the calcification process and low electrical conductivity. Excessive volume expansion leads to cracking and breakage of silicon particles, weakening the interfacial contact between the anode active material and the current collector. Furthermore, the formation of byproducts on the silicon anode surface leads to the continuous consumption of electrolyte, accelerating the decline in battery life.

[0004] Accordingly, research has been conducted to combine silicon (Si) with various conductive materials, such as carbon, polymers, and metal particles, to enhance conductivity and mitigate the volume expansion of the silicon anode during battery operation. Among these, silicon nitride, a nitrogen-doped silicon, is being considered as a promising anode material.

[0005] However, when manufacturing silicon nitride using gaseous reactants such as silane (SiH4) and ammonia (NH3), the synthesis conditions are difficult and high temperatures and special control equipment are required, so not only is the process complicated, but the manufacturing cost also increases rapidly.

[0006] The purpose of the present invention is to solve the problems of the above-mentioned prior art, and to provide a method for producing a silicon nitride composite in a cheap and simple manner.

[0007] Another object of the present invention is to provide a silicon nitride composite having improved capacity, rate characteristics and life characteristics and a method for producing the same.

[0008] Another object of the present invention is to provide a silicon nitride composite and a method for producing the same, which can minimize volume expansion due to repeated charging and discharging when used as an anode material for a lithium secondary battery.

[0009] A method for manufacturing a silicon nitride composite according to the present invention comprises the steps of (S1) mixing amorphous silicon nitride powder and reducing agent powder; and (S2) heat-treating the mixed powder to crystallize at least a portion of the silicon contained in the amorphous silicon nitride.

[0010] In one example, the silicon nitride powder and reducing agent powder may be mixed in a weight ratio of 1:0.2 to 2.

[0011] In one example, the reducing agent may include an alkali metal, an alkaline earth metal, a post-transition metal, or a combination thereof.

[0012] In one example, the heat treatment may be performed at a temperature higher than the melting point of the reducing agent.

[0013] In one example, in the step (S2), the reducing agent and nitrogen may react.

[0014] In one example, after the step (S2), a step of removing the reducing agent and nitrogen reaction product may be further included.

[0015] In one example, after the step (S2), a step of mixing the silicon nitride complex and the carbon body may be further included.

[0016] In one example, in the step (S1), a heat dispersant may be further added.

[0017] The present invention includes a silicon nitride composite manufactured by the above-described method.

[0018] The silicon nitride composite according to the present invention comprises amorphous silicon nitride and crystalline silicon represented by the following chemical formula 1, wherein the crystalline silicon is formed by the generation of nitrogen defects in the amorphous silicon nitride.

[0019] [Chemical Formula 1]

[0020] Si3N 4-x

[0021] (The above x is 0 <x<4를 만족하는 실수이다)

[0022] In one example, the silicon particles in the silicon nitride composite may be a mixture of amorphous and crystalline portions.

[0023] In one example, the silicon nitride composite may be porous.

[0024] In one example, the average particle diameter of the pores may be 2 to 20 nm.

[0025] In one example, the silicon nitride composite may be used as a negative electrode active material.

[0026] In one example, in the Si 2p XPS analysis spectrum of the silicon nitride composite, the percentage of the area occupied by the crystalline silicon peak relative to the area of ​​the total peak may be 5 to 90%.

[0027] In one example, the silicon:nitrogen atomic ratio included in the silicon nitride composite may be 1 to 10:1.

[0028] In one example, the silicon nitride composite may further comprise a carbon body.

[0029] The negative electrode for a lithium secondary battery according to the present invention includes a silicon nitride composite manufactured by the above-described method.

[0030] The method for manufacturing a silicon nitride composite of the present invention has a simple process and can manufacture a silicon nitride composite at low cost.

[0031] The silicon nitride composite of the present invention can improve capacity, rate characteristics, and life characteristics when used as an anode for a lithium secondary battery.

[0032] In addition, when the silicon nitride composite of the present invention is used as an anode material for a lithium secondary battery, volume expansion due to repeated charging and discharging can be minimized.

[0033] FIG. 1 is a schematic diagram illustrating a method for manufacturing a silicon nitride composite according to one embodiment of the present invention.

[0034] FIG. 2 is an X-ray photoelectron spectroscopy (XPS) spectrum for N 1s and Si 2p of the silicon nitride composites of Examples 1 to 3 and the silicon nitride according to Comparative Example 1.

[0035] FIG. 3 is a graph showing (a) X-ray diffraction (XRD) analysis spectra, (b) Raman spectra, (c) nitrogen adsorption / desorption isotherms, and (d) pore size distributions of silicon nitride composites of Examples 1 to 3 and silicon nitride according to Comparative Example 1.

[0036] Figure 4 is a transmission electron microscope (TEM) image of silicon nitride composites according to (a) and (e) Comparative Example 1 (Si3N4), (b) and (f) Example 1 (NDSiN-0.8), (c) and (g) Example 2 (NDSiN-1.0), and (d) and (h) Example 3 (NDSiN-1.2).

[0037] FIG. 5 is a graph showing the atomic percentages of nitrogen and silicon included in the silicon nitride composites of Examples 1 to 3 and the silicon nitride composites of Comparative Example 1.

[0038] FIGS. 6 (a) to (c) are graphs showing (a) the initial potential profile, (b) the rate characteristics, and (c) the cycle performance of half-cells including the negative electrodes of Examples 1 to 3 and Comparative Example 2, and FIGS. 6 (d) and (e) are graphs showing (d) the potential profile and (e) the cycle performance of half-cells including the negative electrode of Comparative Example 1.

[0039] Figure 7 is a graph showing (a) the initial potential profile and (b) the cycle performance of half-cells including the negative electrodes of Examples 4 to 6 and Comparative Example 3.

[0040] Figure 8 is a schematic diagram showing the change in volume of the negative electrode during charging and discharging of a battery including the negative electrode according to Comparative Example 2 and Example 1.

[0041] FIG. 9(a) and (b) are scanning electron microscope (SEM) images of the cathode surfaces of Comparative Example 2 (Si) and Example 1 (NDSiN-0.8), respectively, and FIG. 9(c) and (d) are scanning electron microscope (SEM) images of the cathode surfaces of half-cells including the cathodes of Comparative Example 2 (Si) and Example 1 (NDSiN-0.8), respectively, after driving for 50 cycles.

[0042] Figures 10(a) and (b) are N 1s high-resolution X-ray photoelectron spectroscopy (XPS) spectra of Comparative Example 2 (Si) and Example 1 (NDSiN-0.8), respectively.

[0043] FIG. 11(a) is a schematic diagram showing a full battery including a graphite anode, the anodes of Example 4 (Gr-NDSiN-0.8) and Example 1 (NDSiN-0.8), and FIGS. 11(b) to (d) are graphs showing (b) the initial voltage profile, (c) the rate characteristics, and (d) the cycle performance of a full battery including the anodes of Example 4 (Gr-NDSiN-0.8), Example 5 (Gr-NDSiN-1.0), Example 6 (Gr-NDSiN-1.2), and Comparative Example 3 (Gr-Si).

[0044] The silicon nitride composite of the present invention and its manufacturing method are described in detail. The terminology used in this specification has been selected from widely used terms as much as possible, taking into account the functions of the present invention. However, this may vary depending on the intentions of engineers working in the relevant fields, precedents, the emergence of new technologies, etc. Unless otherwise defined, the technical and scientific terms used may have the meaning commonly understood by those of ordinary skill in the technical field to which this invention pertains.

[0045] In this specification and the appended claims, the terms “include” or “have” mean that a feature or component described in the specification is present, and unless specifically limited, does not preclude the possibility that one or more other features or components may be added.

[0046] In this specification and the appended claims, the terms first, second, etc. are not used in a limiting sense but are used for the purpose of distinguishing one component from another.

[0047] As used herein and in the appended claims, the singular expression "singular" includes the plural expression unless the context clearly dictates otherwise. Furthermore, the plural expression "singular" includes the singular expression unless the context clearly dictates otherwise.

[0048] Additionally, the numerical ranges used herein include lower and upper limits and all values ​​within that range, increments logically derived from the shape and width of the defined range, all doubly defined values, and all possible combinations of upper and lower limits of numerical ranges defined in different shapes. Unless otherwise specifically defined in the specification of the present invention, values ​​outside the numerical range that may arise due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0049] The term "about" or the like used in this specification and the appended claims is used to encompass the tolerance when an tolerance exists.

[0050] Lithium secondary batteries are widely used as power supplies for portable electronic devices such as laptops, tablet PCs, and smartphones, as well as electric vehicles such as hybrid electric vehicles and plug-in electric vehicles. Recently, demand has been increasing for high-performance lithium secondary batteries with higher energy density and longer lifespan than commercially available lithium secondary batteries. However, graphite, the anode material typically used in lithium secondary batteries, has limited capacity and cannot meet growing energy demands.

[0051] Accordingly, research has been conducted to develop new anode materials. Among them, silicon is considered a strong candidate to replace commercialized graphite, boasting approximately 10 times the capacity of graphite. However, silicon suffers from inevitable volume expansion during the calcification process and low electrical conductivity. Cracks and breakage of silicon particles due to excessive volume expansion weaken the interfacial contact between the anode active material and the current collector. Furthermore, the formation of byproducts on the silicon anode surface leads to continuous electrolyte consumption, accelerating the deterioration of cell performance.

[0052] Accordingly, research has been conducted to combine silicon (Si) with various conductive materials, such as carbon, polymers, and metal particles, to improve conductivity and mitigate the volume expansion of silicon anodes during battery operation. Among these, nitrogen-doped silicon (Si) is being considered as a promising anode material. However, silicon nitride manufacturing methods using gaseous reactants such as silane (SiH4) and ammonia (NH3) are problematic due to demanding synthesis conditions, high temperatures, and the need for specialized control equipment. This complicates the process and rapidly increases manufacturing costs.

[0053] Accordingly, the applicant of the present invention can simplify the process and reduce the process cost by manufacturing a silicon nitride composite in a simple manner using a solid-state method rather than a vapor-phase process, and, in addition, since crystalline silicon and amorphous silicon nitride coexist in the silicon nitride composite, when it is used as an anode active material, the energy density, capacity characteristics, and long-term stability of the battery can be improved.

[0054] A method for manufacturing a silicon nitride composite according to the present invention comprises the steps of (S1) mixing amorphous silicon nitride powder and reducing agent powder; and (S2) heat-treating the mixed powder to crystallize at least a portion of the silicon contained in the amorphous silicon nitride.

[0055] By mixing amorphous silicon nitride powder and reducing agent powder and then reacting them to crystallize at least a portion of the silicon in the amorphous silicon nitride, a silicon nitride composite in which amorphous silicon nitride and crystalline silicon coexist can be manufactured, thereby improving electrochemical performance and mechanical strength.

[0056] Since the silicon nitride composite is manufactured using solid silicon nitride and a reducing agent, the process is simple. Furthermore, since the weight ratio of the amorphous silicon nitride powder and the reducing agent powder can be easily controlled, the crystal structure of the resulting silicon nitride composite can be easily controlled. Consequently, the ratio of amorphous silicon nitride to crystalline silicon in the silicon nitride composite can also be easily controlled.

[0057] In one example, in the step (S1), the silicon nitride powder: reducing agent powder can be mixed in a weight ratio of 1:0.2 to 2, 1:0.5 to 1.8, 1:0.6 to 1.6, or 1:0.7 to 1.2. When mixed in the above weight ratio, a silicon nitride composite in which amorphous silicon nitride and crystalline silicon coexist can be produced.

[0058] As described below, when the silicon nitride powder and the reducing agent powder are mixed in a weight ratio of 1:1 to 2, the specific surface area and capacity characteristics can be maximized as the proportion of the crystalline phase in the resulting silicon nitride composite increases. When the silicon nitride powder and the reducing agent powder are mixed in a weight ratio of 1:0.5 to 1, the proportion of the amorphous phase in the resulting silicon nitride composite increases, so that when used as a negative electrode of a secondary battery, the long-term stability and life characteristics of the battery can be maximized.

[0059] In one example, the reducing agent may be a metal reducing agent, and specifically, the reducing agent may include an alkali metal, an alkaline earth metal, a post-transition metal, or a combination thereof. More specifically, the reducing agent may include one or more metals selected from the group consisting of lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), zinc (Zn), tin (Sn), indium (In), aluminum (Al), and gallium (Ga), and preferably, highly reducing magnesium (Mg). Specifically, the reducing agent may include magnesium, magnesium hydrate (MgH2), or a combination thereof, but the present invention is not limited by the specific type of the reducing agent.

[0060] In one example, during the mixing step (S1), a heat dispersant may be further added. By adding the heat dispersant powder together with the amorphous silicon nitride powder and the reducing agent powder, the crystallinity of the silicon nitride composite can be more finely controlled, thereby enabling the silicon nitride composite to be manufactured more easily.

[0061] The heat dispersant may include, without limitation, any material that can rapidly disperse heat and enhance the reactivity of the (S2) step described later, and specifically, may include at least one selected from the group consisting of aluminum chloride (AlCl3), sodium chloride (NaCl), and magnesium chloride (MgCl2), and preferably aluminum chloride (AlCl3), but the present disclosure is not limited by the specific type of the heat dispersant.

[0062] In one specific example, when the mixed powder further includes a heat dispersant, the amorphous silicon nitride powder: heat dispersant is added in a weight ratio of 1:0.1 to 20, specifically 1:0.5 to 10, so that the crystal structure can be more precisely controlled.

[0063] The heat treatment in step (S2) above can be performed at a temperature higher than the melting point of the reducing agent. Within the above temperature range, the highly reactive reducing agent melts, creating an environment in which the reducing agent and nitrogen can react.

[0064] In a specific and non-limiting example, the heat treatment temperature may be 50 to 1500°C, 100 to 1000°C or 300 to 800°C, but the present invention is not limited thereto.

[0065] Additionally, the heat treatment in step (S2) may be performed for 30 minutes to 12 hours, but the present invention is not limited to the heat treatment temperature, and the heat treatment time may be adjusted depending on the heat treatment temperature. In one specific example, as the heat treatment temperature increases, the heat treatment time may be adjusted to be shorter, thereby providing optimized reaction efficiency.

[0066] For example, in step (S2), the nitrogen of silicon nitride and a metal reducing agent can react to form a metal nitride. More specifically, when the reducing agent is magnesium, the magnesium and nitrogen can react to form Mg3N2. As the reducing agent and nitrogen react, the remaining silicon can retain crystallinity. Accordingly, a silicon nitride composite having a structure in which crystalline silicon is embedded in amorphous silicon nitride can be manufactured.

[0067] After the above step (S2), a step of removing the reducing agent and the nitrogen reaction product may be further included. By removing the reaction product generated by the reaction of the reducing agent and nitrogen, a plurality of pores may be formed in the silicon nitride composite. The silicon nitride composite having a porous structure including a plurality of pores has an improved specific surface area, and thus, when used as a negative electrode active material, the capacity characteristics may be improved.

[0068] In one example, the silicon nitride composite can be contacted with an etchant to selectively remove the reducing agent and nitrogen reaction products and impurities remaining in the silicon nitride composite.

[0069] Specifically, the etchant may be one or more mixed solutions selected from the group consisting of hydrochloric acid (HCl), hydrofluoric acid (HF), nitric acid (HNO3), acetic acid (CH3COOH), potassium hydroxide (KOH), and phosphoric acid (H3PO4), but the present invention is not limited by the specific type of the etchant.

[0070] In one example, after the step (S2), a step of mixing the silicon nitride composite and a carbon body may be further included. The capacity and long-term stability of the battery can be further improved by the synergistic effect between the carbon body with excellent electrical conductivity and the silicon nitride composite. Specifically, based on 1 part by weight of the silicon nitride composite, the carbon body can be mixed in an amount of 5 to 40 parts by weight, 10 to 30 parts by weight, or 15 to 25 parts by weight.

[0071] The above carbon body can be used without limitation as long as it is a carbon-based material that has conductivity, and may include graphite as an example, but the present invention is not limited by the specific type of the carbon body and the content of the carbon body.

[0072] The present invention includes a silicon nitride composite manufactured by the above-described method.

[0073] The silicon nitride composite according to the present invention comprises amorphous silicon nitride and crystalline silicon represented by the following chemical formula 1, wherein the crystalline silicon is formed by the generation of nitrogen defects in the amorphous silicon nitride.

[0074] [Chemical Formula 1]

[0075] Si3N 4-x

[0076] (The above x is 0 <x<4를 만족하는 실수이다)

[0077] As described above, a portion of the amorphous silicon nitride can be converted to crystalline silicon as nitrogen defects are generated when amorphous silicon nitride reacts with a reducing agent to remove nitrogen. Silicon nitride composites in which amorphous and crystalline phases coexist can exhibit superior electrochemical performance, particularly improved capacity and cycle life characteristics, when used as negative electrode active materials for lithium secondary batteries.

[0078] The silicon particles in the above silicon nitride composite may be a mixture of amorphous and crystalline portions, and specifically, may exist in a form in which crystalline silicon is embedded in amorphous silicon nitride. The silicon nitride composite having such structural features can improve rate characteristics and capacity through the crystalline portion, and can improve cycle characteristics through the amorphous portion. The amorphous silicon nitride has the effect of minimizing volume expansion due to repeated charging and discharging of the battery, thereby suppressing damage and breakage of the silicon nitride composite particles due to volume expansion.

[0079] In one example, the BET surface area of ​​a silicon nitride composite is 60 to 500 m 2 / g, 70 to 450 m 2 / g or 80 to 400 m 2 / g may be. In addition, the average particle diameter of the pores included in the silicon nitride composite may be 2 to 20 nm, 2.5 to 15 nm, or 3 to 10 nm.

[0080] By controlling the pore size to have the above particle size range, the specific surface area of ​​the silicon nitride composite particles can be improved. When applied to a negative electrode active material, a silicon nitride composite with a porous structure having an excellent specific surface area can mitigate the volume expansion of the negative electrode that occurs during the charge and discharge process of a battery, and since the pore structure of the silicon nitride composite facilitates the diffusion of lithium ions, it can maintain a high charge and discharge capacity at high current densities.

[0081] In one example, in the Si 2p XPS analysis spectrum of the silicon nitride composite, the area percentage of the crystalline silicon peak relative to the area of ​​the total peak may be 5 to 90%, 10 to 85%, 20 to 80%, 25 to 75%, or 30 to 70%.

[0082] More specifically, the total peak area refers to the sum of the areas of peaks existing in the binding energy range of 110 to 96 eV in the Si 2p XPS analysis spectrum, and the area of ​​the crystalline silicon peak refers to the area of ​​the peak having a binding energy of the peak center of 100.5 to 98.5 eV in the Si 2p XPS analysis spectrum. Even more specifically, a peak having a central binding energy within the range of 100 to 99 eV, and more specifically, 99.9 to 99.5 eV, may refer to a peak for crystalline silicon.

[0083] That is, among the total silicon contained in the silicon nitride composite, crystalline silicon can be contained in an amount of 5 to 90 atomic%, 10 to 85 atomic%, 20 to 80 atomic%, 25 to 75 atomic%, or 30 to 70 atomic%. By controlling the ratio of crystalline silicon contained in the silicon nitride composite within the above range, a silicon nitride composite having improved rate characteristics and improved life characteristics can be realized.

[0084] In one example, the silicon nitride composite contains more silicon than nitrogen, and specifically, the silicon:nitrogen atomic ratio contained in the silicon nitride composite may be 1 to 10:1, 1.5 to 8, or 2 to 7. By containing silicon and nitrogen in the above range, when the battery is operated, nitrogen and lithium ions can react to produce lithium silicon nitride and / or lithium nitride having excellent ion conductivity on the negative electrode surface. By significantly improving the conductivity of lithium ions on the negative electrode surface through lithium silicon nitride and lithium nitride, the battery performance can also be improved.

[0085] In one example, the silicon nitride composite may further include a carbon body. A silicon nitride composite further including a carbon body not only significantly improves electrical conductivity, but is also effective in improving life characteristics by alleviating volume expansion of the negative electrode during charge and discharge.

[0086] The present invention includes a negative electrode for a lithium secondary battery comprising a silicon nitride composite manufactured by the aforementioned method. Since the silicon nitride composite is identical to that described above, a detailed description thereof will be omitted.

[0087] As described above, the silicon nitride composite of the present invention includes amorphous silicon nitride and crystalline silicon formed by nitrogen defects in the amorphous silicon nitride, and thus, when used as an anode material for a lithium secondary battery, it can improve electrochemical performance, including the capacity and rate characteristics of the battery. In addition, by minimizing volume expansion of the anode during repeated charge and discharge, it can prevent cracks from occurring on the surface of the anode, thereby improving long-term stability and life characteristics. In addition, since the silicon nitride composite is manufactured by a solid-state method, not only can the process be simplified and manufacturing costs reduced, but also the ratio of amorphous silicon nitride and crystalline silicon contained in the silicon nitride composite can be easily controlled, thereby realizing the above-described battery performance improvement effect.

[0088] In one example, the cathode may further include a conductive material and a binder.

[0089] The conductive material may be, but is not limited to, one or a mixture of two or more selected from among graphite-based materials selected from one or more selected from natural graphite and artificial graphite; graphene; carbon-based materials selected from one or more selected from Super-P, Ketjen black, Denka black, acetylene black, and carbon black; and conductive polymers selected from one or more selected from polyaniline-based polymers, polythiophene-based polymers, polyacetylene-based polymers, and polypyrrole-based polymers.

[0090] The binder may include poly(vinylidene fluoride)-co-hexafluoropropylene, poly(vinylidene fluoride) (PVDF), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene-butadiene rubber polymer (SBR), or a mixture thereof, which are commonly used in lithium secondary batteries. However, any binder known in the art may be used without limitation, and the present invention is not limited by the specific type of the binder.

[0091] Hereinafter, the present invention will be described in more detail through examples.

[0092] (Example 1) Manufacturing of NDSiN-0.8

[0093] Manufacturing of silicon nitride composites

[0094] As illustrated in Fig. 1, a silicon nitride composite was prepared. Amorphous Si3N4 (<50 nm, Aldrich) and magnesium (Aldrich) were mixed in a weight ratio of 1:0.8 in a mixer (Lab Ram, Bruker Co.). The uniformly mixed powder was placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min under an inert gas, and then maintained for 5 h. The annealed mixed powder was then naturally cooled, washed with 2.0 M HCl to remove Mg3N2 and other impurities, and filtered and washed with deionized (DI) water. Thereafter, the silicon nitride composite was prepared by drying at 60°C. This was designated NDSiN-0.8 (N-deficient silicon nitride).

[0095] Cathode manufacturing

[0096] A negative electrode slurry was prepared by mixing a negative electrode active material, a conductive agent, and a binder at a weight ratio of 8:1:1. The negative electrode active material used the above silicon nitride composite powder, the conductive agent used Super-P, and the binder was prepared by mixing carboxymethyl cellulose (CMC, Welcos Co.) and styrene-butadiene rubber (SBR, Welcos Co.) with distilled water at a weight ratio of 1:1. The negative electrode active material, conductive agent, and binder were uniformly mixed using a thinky mixer at 2000 rpm. Thereafter, the negative electrode slurry was coated on a Cu foil with a doctor blade and dried at 100°C for 2 hours under vacuum to prepare a negative electrode.

[0097] (Example 2) Manufacturing of NDSiN-1.0

[0098] A silicon nitride composite and a cathode were manufactured in the same manner as in Example 1, except that Si3N4 and magnesium powders were added to the mixer at a weight ratio of 1:1 when manufacturing the silicon nitride composite. This was designated NDSiN-1.0.

[0099] (Example 3) Manufacturing of NDSiN-1.2

[0100] A silicon nitride composite and a cathode were manufactured in the same manner as in Example 1, except that Si3N4 and magnesium powders were added to the mixer at a weight ratio of 1:1.2 when manufacturing the silicon nitride composite. This was designated NDSiN-1.2.

[0101] (Example 4) Preparation of Gr-NDSiN-0.8

[0102] A silicon nitride composite and a negative electrode were manufactured in the same manner as in Example 1, but a mixture of silicon nitride composite: graphite at a weight ratio of 5:95 was used as the negative electrode active material, and a negative electrode slurry was manufactured by mixing the negative electrode active material: conductive material: binder at a weight ratio of 96:2:2 with deionized water. This was designated as Gr-NDSiN-0.8.

[0103] (Example 5) Preparation of Gr-NDSiN-1.0

[0104] A silicon nitride composite and a negative electrode were manufactured in the same manner as in Example 2, except that a mixture of silicon nitride composite and graphite in a weight ratio of 5:95 was used as the negative active material, and a negative electrode slurry was manufactured by mixing the negative active material: conductive material: binder with deionized water in a weight ratio of 96:2:2. This was designated as Gr-NDSiN-1.0.

[0105] (Example 6) Preparation of Gr-NDSiN-1.2

[0106] A silicon nitride composite and a negative electrode were manufactured in the same manner as in Example 3, except that a mixture of silicon nitride composite and graphite in a weight ratio of 5:95 was used as the negative active material, and a negative electrode slurry was manufactured by mixing the negative active material: conductive material: binder with deionized water in a weight ratio of 96:2:2. This was designated Gr-NDSiN-1.2.

[0107] (Comparative Example 1)

[0108] A negative electrode was manufactured in the same manner as in Example 1, except that commercial Si3N4 (<50 nm, Aldrich) was used as the negative electrode active material instead of the silicon nitride composite.

[0109] (Comparative Example 2)

[0110] A negative electrode was manufactured in the same manner as in Example 1, except that commercial Si (<50 nm, Aldrich) was used as the negative electrode active material instead of the silicon nitride composite.

[0111] (Comparative Example 3) Gr-Si manufacturing

[0112] A mixture of commercial Si: graphite at a weight ratio of 5:95 was used as the negative active material, and a negative electrode was manufactured in the same manner as in Comparative Example 2, except that the negative active material: conductive material: binder was mixed in a weight ratio of 96:2:2 in deionized water to manufacture a negative electrode slurry.

[0113] (Experimental Example 1) Characteristics of silicon nitride composites

[0114] High-resolution X-ray photoelectron analysis (HR-XPS, PA326, Thermo Fisher Scientific Co.), X-ray diffraction analysis (XRD, Mini flex 600, Horiba Co.), and Raman spectroscopy (Nicolet Almega XR, Thermo scientific Co.) were performed on the silicon nitride composite. In addition, adsorption-desorption isotherms were measured using the BET method at -196°C to analyze the specific surface area and pore size distribution. In addition, the surface of the silicon nitride composite was observed using a field emission scanning electron microscope (FE-SEM, SU8230, Hitachi Co.) and a transmission electron microscope (TEM, Tecnai G2 F20 TWIN TMP, FEI Co.).

[0115] Fig. 2 is an XPS analysis spectrum for N 1s and Si 2p of the silicon nitride composites of Examples 1 to 3 and the silicon nitride according to Comparative Example 1. As shown in Fig. 2, in N 1s, only the peak corresponding to Si3N4 was observed very strongly at 397.1 eV in the amorphous silicon nitride (Si3N4) of Comparative Example 1, but in the silicon nitride composites of Examples 1 to 3, not only at 397.1 eV but also at 397.8 eV, the peak corresponding to Si3N 4-x (0 <x<4)에 해당하는 피크가 관측되었다. 보다 구체적으로, 실시예 1 대비 실시예 3에서 397.1 eV 및 397.8 eV의 피크 강도가 감소하는 양상을 보여, 질화규소 복합체 제조 시 비정질 질화규소 분말 대비 Mg 분말의 함량이 증가할수록 피크 강도가 감소하는 것을 알 수 있다.

[0116] XPS spectrum for Si 2p Also, in Comparative Example 1 (Si3N4), only a peak corresponding to SiO2 at 103.2 eV and a peak corresponding to Si3N4 at 102.3 eV were observed, but in the case of Examples 1 to 3, the peak intensities at 103.2 eV and 102.3 eV were significantly reduced compared to Comparative Example 1. In addition, the silicon nitride composites of Examples 1 to 3 showed a peak corresponding to zero-valent Si at 99.7 eV and a peak corresponding to Si3N at 101.3 eV. 4-x (0 <x<4)에 해당하는 피크가 관측되어, 실시예 1 내지 3의 질화규소 복합체는 환원제와 질소가 반응하여 결정질의 규소가 형성되었음을 확인하였다.

[0117] FIG. 3 is a graph showing (a) XRD analysis spectra, (b) Raman spectra, (c) nitrogen adsorption / desorption isotherm profiles, and (d) pore size distributions of silicon nitride composites of Examples 1 to 3 and silicon nitride according to Comparative Example 1.

[0118] Referring to Fig. 3(a), the silicon nitride of Comparative Example 1 (Si3N4) exhibits a broad peak around 22.0°, indicating that the silicon has a completely amorphous phase. However, in the silicon nitride composites of Examples 1 to 3, in addition to the peak for amorphous silicon, a peak corresponding to crystalline silicon (JCPDS card No.: 01-077-2109) was observed. In Fig. 3(b), in addition, no Raman signal was observed in the silicon nitride of Comparative Example 1 (Si3N4), but in the silicon nitride composites of Examples 1 to 3, a Raman signal was observed at 510 cm -1 A broad peak was observed nearby. Thus, it was confirmed that the silicon nitride composites manufactured by the methods of Examples 1 to 3 were a mixture of amorphous silicon and crystalline silicon.

[0119] The BET (Brunauer Emmett Teller) analysis results of the silicon nitride composites of Examples 1 to 3 and the silicon nitride according to Comparative Example 1 are shown in Figs. 3(c) and (d) and Table 1 below. Here, as defined by the International Union of Pure and Applied Chemistry (IUPAC), in Table 1 below, micropore means a pore having a diameter of 2 nm or less, mesopore means a pore having a diameter of 2 to 50 nm, and macropore means a pore having a diameter of 50 nm or more.

[0120] BET surface area (m 2 / g) Microscopic volume (cm) 3 / g) Macroscopic pore volume (cm) 3 / g)Total pore volume (cm) 3 / g) Comparative Example 1 (Si3N4) 38.00.000.030.03Example 1 (NDSiN-0.8) 81.70.010.190.20Example 2 (NDSiN-1.0) 156.50.030.340.37Example 3 (NDSiN-1.2) 347.30.050.590.64

[0121] Referring to Table 1 and FIG. 3(c), the silicon nitride composites of Examples 1 to 3 and the silicon nitride of Comparative Example 1 all showed a type IV adsorption / desorption isotherm (IUPAC standard) in which the adsorption amount continuously increased with increasing relative pressure (P / P0) and a hysteresis loop in which the adsorption curve and the desorption curve did not match at a relative pressure (P / P0) of 0.1 to 1.0. Specifically, the silicon nitride composites of Example 1 (NDSiN-0.8), Example 2 (NDSiN-1.0), and Example 3 (NDSiN-1.2) had BET specific surface areas of 81.7, 145.5, and 347.3 m, respectively. 2 / g, but Si3N4 of comparative example 1 has a BET surface area of ​​38.0 m 2 / g was very low.

[0122] In addition, as shown in Table 1 and Fig. 3(d), Comparative Example 1 (Si3N4) not only measured a micropore volume of 0, but also a total pore volume of 0.03 cm 2 / g, very few pores were formed, and the specific surface area was very low. However, the silicon nitride composites of Examples 1 to 3 produced a large number of mesopores with a diameter of 3 to 5 nm, and the total pore volume was also 0.20 cm each. 2 / g, 0.37 cm 2 / g and 0.64 cm 2 / g, indicating that it has excellent porous properties. As nitrogen atoms reacted with the reducing agent (Mg) from the parent amorphous silicon nitride powder were removed, a porous structure was formed, and the specific surface area was significantly improved as the porous structure developed. Accordingly, it can be seen that the pores develop further as the content of reducing agent powder increases compared to the silicon nitride powder.

[0123] Fig. 4 is a transmission electron microscope image according to the magnification of the silicon nitride composite. Specifically, Figs. 4(a) and (e) are TEM images of Comparative Example 1 (Si3N4), (b) and (f) are TEM images of Example 1 (NDSiN-0.8), (c) and (g) are TEM images of Example 2 (NDSiN-1.0), and (d) and (h) are TEM images of Example 3 (NDSiN-1.2). Referring to Figs. 4(a) to (h), it was confirmed that the silicon nitride of Comparative Example 1 (Si3N4) only has an amorphous phase, whereas the silicon nitride composites of Examples 1 to 3 have a coexistence of amorphous and crystalline phases.

[0124] Figure 5 and Table 2 are graphs analyzing the atomic % of nitrogen and silicon contained in the silicon nitride of Example 1 (NDSiN-0.8), Example 2 (NDSiN-1.0), and Example 3 (NDSiN-1.2) and the silicon nitride of Comparative Example 1 (Si3N4). The element distribution was measured through energy dispersive x-ray spectroscopy (EDS) element mapping using a high-angle annular dark-field (HAADF) image. Comparative Example 1 (Si3N4) contained 45.8 at% of Si and 54.2 at% of N, which were close to the theoretical atomic % of Si3N4. On the other hand, Example 1 (NDSiN-0.8) was measured to have a ratio of Si 67.2 at% and N 39.8 at%, Example 2 (NDSiN-1.0) to have a ratio of Si 72.4 at% and N 28.6 at%, and Example 3 (NDSiN-1.2) to have a ratio of Si 88.3 at% and N 14.3 at%. As the content of reducing agent (Mg) powder increased compared to the amorphous silicon nitride powder during the manufacturing process, the amount of nitrogen removed by reacting with the reducing agent increased, so the silicon content increased and the nitrogen content showed a linear decrease pattern.

[0125] (Experimental Example 2) Half-cell performance evaluation

[0126] Half cells were manufactured using the negative electrodes of Examples 1 to 6 and Comparative Examples 1 to 3, and then charge-discharged to evaluate their performance. Specifically, the half cells used a Li foil having a thickness of 100 μm and a diameter of 16 mm as a counter electrode for the negative electrode. The negative electrode was punched into a circle with a diameter of 14 mm and used. The separator used polypropylene (Celgard 2320), and the electrolyte contained 5 wt% of fluoroethylene carbonate and 5 wt% of vinylene carbonate, and was prepared by mixing 1.0 M LiPF6 in a solvent containing ethylene carbonate and diethyl carbonate in a volume ratio of 1:1. The negative electrode, separator, and positive electrode were assembled in an Ar-filled glove box, and the electrolyte was filled to manufacture a 2032-type coin cell. All cells were evaluated for performance under constant current (CC) conditions.

[0127] Figures 6(a) to (d) are graphs showing (a) the initial voltage profile at a current density of 420 mA / g, (b) the rate characteristics, and (c) the cycle performance for 500 cycles at a current density of 2100 mA / g for half cells including the negative electrodes of Example 1 (NDSiN-0.8), Example 2 (NDSiN-1.0), Example 3 (NDSiN-1.2), and Comparative Example 2 (Si).

[0128] Referring to Fig. 6(a), Example 1 (NDSiN-0.8), Example 2 (NDSiN-1.0), and Example 3 (NDSiN-1.2) showed initial Coulombic efficiencies of 85.8, 83.3, and 81.6%, and capacities of 1611.2, 2075.2, and 2297.3 mAh / g, respectively. Example 3, which added the largest amount of reducing agent during the manufacture of the silicon nitride composite, had a high crystalline silicon ratio in the manufactured silicon nitride composite, so the capacity was higher than that of Examples 1 and 2, but the initial Coulombic efficiency was measured to be lower than that of Examples 1 and 2. In the case of Example 1, which had the lowest crystalline silicon ratio, the capacity was lower than that of Examples 2 and 3, but the initial Coulombic efficiency was measured to be the highest at 85.8%. In the case of Comparative Example 2 (Si) using commercial silicon as the negative electrode active material, the capacity was 2467.9 mAh / g, which was higher than that of Examples 1 to 3, but the initial Coulombic efficiency was the lowest at 78.3%.

[0129] As shown in Fig. 6(b), the capacity was measured at various current densities ranging from 420 to 42000 mA / g, and the capacity retention rate of the anode according to Example 3 (NDSiN-1.2) was the highest, indicating that the rate characteristics improved as the ratio of crystalline silicon increased. On the other hand, in the case of Comparative Example 2 (Si) using commercial Si as the anode active material, the rate characteristics deteriorated rapidly after 30 cycles.

[0130] Referring to Fig. 6(c), Comparative Example 2 (Si) showed a rapid capacity decrease along with battery failure after 100 cycles. On the other hand, Examples 1 (NDSiN-0.8), 2 (NDSiN-1.0), and 3 (NDSiN-1.2) showed initial capacities of 1255.7, 1504.9, and 1809.7 mAh / g, respectively, and capacity retention rates of 75.2, 56.6, and 43.9%, respectively, even after 500 cycles. Example 3, which had a high proportion of crystalline silicon, had the highest initial capacity, but Example 1, which had a high proportion of amorphous silicon, showed the best capacity retention rate after 500 cycles. Accordingly, as the content of crystalline silicon in the silicon nitride composite increases, the rate characteristics and capacity are improved, and as the ratio of amorphous silicon to crystalline silicon increases, the long-term stability, i.e., the life characteristics, are improved.

[0131] Figures 6(d) and (e) are graphs showing the voltage profile at (d) 420 mA / g and the cycle performance for 500 cycles at (e) a current density of 2100 mA / g of a half-cell including the cathode of Comparative Example 1 (Si3N4).

[0132] Referring to Fig. 6(d), Comparative Example 1 using commercial Si3N4 as the negative electrode active material exhibited an initial coulombic efficiency of 62.9% and a capacity of 139.1 mAh / g, which were significantly lower than those of Examples 1 to 3. Referring to Fig. 6(e), Comparative Example 1 (Si3N4) not only had a very low initial capacity of 100 mAh / g, but also exhibited a decrease in capacity after 100 cycles, and after 500 cycles, the capacity decreased to 40 mAh / g, showing very inferior life characteristics compared to Examples 1 to 3.

[0133] FIG. 7 is a graph showing (a) the initial voltage profile and (b) the cycle performance for 500 cycles for half-cells including the negative electrodes of Example 4 (Gr-NDSiN-0.8), Example 5 (Gr-NDSiN-1.0), Example 6 (Gr-NDSiN-1.2), and Comparative Example 3 (Gr-Si).

[0134] As shown in Fig. 7(a), for Examples 4 (Gr-NDSiN-0.8), 5 (Gr-NDSiN-1.0), and 6 (Gr-NDSiN-1.2), the initial Coulombic efficiencies were 87.0, 86.6, and 85.2%, and the capacities were 456.2, 473.2, and 497.1 mAh / g, respectively, demonstrating excellent capacities and Coulombic efficiencies. For Comparative Example 3 (Gr-Si), the capacity was 516.4 mAh / g, and the initial Coulombic efficiency was 83.7%, indicating that the initial performance of Comparative Example 3 was superior to that of Examples 4 to 6. However, referring to Fig. 7(b), Examples 4 to 6 showed significantly superior capacity retention compared to Comparative Example 3, indicating improved long-term stability. In detail, Comparative Example 3 (Gr-Si) had a capacity retention rate of only 66.6%, but Example 4 (Gr-NDSiN-0.8), Example 5 (Gr-NDSiN-1.0), and Example 6 (Gr-NDSiN-1.2) showed capacity retention rates of 89.5%, 84.5%, and 81.7%, respectively, for 500 cycles, indicating an effect of improving life characteristics.

[0135] Figure 8 is a schematic diagram showing the volume change of the negative electrode during charge and discharge of a battery including the negative electrode according to Comparative Example 2 (Si) and Example 1 (NDSiN-0.8). When commercial Si is used as the negative electrode active material as in Comparative Example 2 (Si), as extreme volume expansion and contraction are repeated in the Si during charge and discharge, cracks occur in the negative electrode as the charge and discharge cycles are repeated. As a result, peeling occurs between the Cu current collector and the negative electrode, and there is a problem that the lifespan of the battery is rapidly reduced in a short period of time due to the continuous consumption of electrolyte caused by cracks on the surface of the negative electrode. However, when a silicon nitride composite (NDSiN) including crystalline silicon and amorphous silicon nitride as in Example 1 is used as the negative electrode active material, cracks are suppressed by the amorphous phase even during repeated charge and discharge, thereby having the effect of alleviating volume expansion and cracks. As a result, the life characteristics and long-term stability of the battery can be improved.

[0136] FIG. 9(a) and (b) are scanning electron microscope (SEM) images of the cathode surfaces of Comparative Example 2 (Si) and Example 1 (NDSiN-0.8), respectively, and FIG. 9(c) and (d) are scanning electron microscope (SEM) images of the cathode surfaces of half-cells including the cathodes of Comparative Example 2 (Si) and Example 1 (NDSiN-0.8), respectively, after driving at a current density of 2100 mA / g for 50 cycles.

[0137] As shown in Figs. 9(a) and (b), the negative electrodes before battery operation had smooth surfaces in both Comparative Example 2 (Si) and Example 1 (NDSiN-0.8). However, after 50 cycles, referring to Figs. 9(c) and (d), the surface roughness of the negative electrode of Comparative Example 2 (Si) increased and cracks occurred due to repeated volume changes of the negative electrode during battery operation. On the other hand, in the case of Example 1 (NDSiN-0.8), the surface was smooth and cracks hardly occurred even after 50 cycles. Therefore, when the silicon nitride composite of the present invention is used as an negative electrode active material, the occurrence of cracks in the electrode due to volume expansion can be minimized, thereby improving long-term stability.

[0138] Figures 10(a) and (b) are N 1s high-resolution XPS analysis spectra of the negative electrodes according to Comparative Example 2 (Si) and Example 1 (NDSiN-0.8) before and after battery operation, respectively. As shown in Figure 10(a), no peaks were observed for the negative electrode of Comparative Example 2 (Si) before and after 3 cycles of battery operation. On the other hand, as shown in Figure 10(b), the negative electrode of Example 1 (NDSiN-0.8) showed Si3N4 and Si3N at 397.1 eV and 397.8 eV, respectively, before battery operation. 4-x (0 <x<4)에 대한 피크가 관측되었고, 3 사이클 이후에는 LiSi x N y Additional peaks corresponding to (399.0 eV) and Li3N (399.9 eV) were observed. Lithium silicon nitride (LiSi) is known to have excellent lithium ion conductivity during battery charge and discharge. x N y ) and lithium nitride (Li3N) were observed only in the cathode of Example 1, which can further improve the electrochemical performance of the battery.

[0139] (Experimental Example 3) Full cell performance evaluation

[0140] After manufacturing a full battery using the negative electrodes of Examples 1 to 6 and Comparative Examples 2 and 3, the performance was evaluated by performing charge and discharge. Specifically, the positive electrode was LiNi 0.8 Mn 0.1 Co 0.1 O2 (NMC811), super-p, and polyvinylidene fluoride (PVDF) were added to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 90:5:5 and homogeneously mixed at 2000 rpm in a thinky mixer to prepare a cathode slurry. The cathode slurry was coated on an Al foil using a doctor blade and then dried at 100°C for 2 hours under vacuum to prepare the cathode. The cathode and anode were punched into circular shapes with diameters of 13 mm and 14 mm, respectively.

[0141] The separator was made of polypropylene (Celgard 2320), and the electrolyte contained 5 wt% fluoroethylene carbonate and 5 wt% vinylene carbonate. It was prepared by mixing 1.0 M LiPF6 in a solvent containing ethylene carbonate and diethyl carbonate in a volume ratio of 1:1. The negative electrode, separator, and positive electrode were assembled in an Ar-filled glove box, and the electrolyte was filled to manufacture a 2032-type coin cell. All cells had a capacity of 2.5 mAh / cm 2 It was operated under the condition of positive current density and negative and positive capacitance ratio (N / P) of 1.2, and its performance was evaluated in a constant current (CC) state.

[0142] Fig. 11(a) is a schematic diagram illustrating a full battery including a graphite anode, the anodes of Example 4 (Gr-NDSiN-0.8) and Example 1 (NDSiN-0.8). Compared to a conventional anode using graphite as an anode active material, when the silicon nitride composite (NDSiN) of the present invention is included as an anode active material, the thickness and weight of the anode can be reduced while improving the energy density and long-term stability of the cell. Therefore, by using the silicon nitride composite of the present invention, a high-performance and ultra-small battery can be realized.

[0143] Figures 11(b) to (d) show the full batteries including the negative electrodes of Example 4 (Gr-NDSiN-0.8), Example 5 (Gr-NDSiN-1.0), Example 6 (Gr-NDSiN-1.2) and Comparative Example 3 (Gr-Si), (b) 2.5 mAh / cm 2 Initial voltage profiles at current densities of (c) 0.25 to 5 mAh / cm 2 Rate characteristics at a current density of (d) 0.5 mAh / cm 2 This is a graph measuring the current density and cycle performance for 500 cycles.

[0144] Referring to Fig. 11(b), the initial Coulombic efficiency of Comparative Example 3 (Gr-Si) was 80.4%, and the discharge capacity was measured to be 179.1 mAh / g. For Examples 4 (Gr-NDSiN-0.8), 5 (Gr-NDSiN-1.0), and 6 (Gr-NDSiN-1.2), the initial Coulombic efficiencies were 84.3, 83.3, and 83.0%, respectively, and the discharge capacities were 188.6, 187.9, and 185.9 mAh / g, respectively, showing higher initial Coulombic efficiency and capacity characteristics than Comparative Example 3.

[0145] As shown in Fig. 11(c), the capacity characteristics of the full battery were measured at various current densities, and Comparative Example 3 (Gr-Si) showed lower rate characteristics than Examples 4 to 6. In the case of Examples 4 to 6, the capacity characteristics of the full battery at various current densities (1.25 mA / cm) were lower than those of Examples 4 to 6. 2 ) showed similar discharge capacities, but as the current density increased, a difference in discharge capacity occurred. Example 6 (Gr-NDSiN-1.2) showed the best rate characteristics, followed by Example 5 (Gr-NDSiN-1.0) and Example 4 (Gr-NDSiN-0.8).

[0146] 0.5 mAh / cm 2 Referring to Fig. 11(d) where the long-term cycle performance was measured at a current density of , Comparative Example 3 (Gr-Si) had a low capacity retention rate of 60.6% for 500 cycles, whereas Examples 4 to 6 had high capacity retention rates of 81.9, 80.4, and 78.7%, respectively, confirming excellent life characteristics.

[0147] Figure 11(e) is a graph showing the cycle performance measured for 200 cycles for a full battery including the negative electrodes of Example 1 (NDSiN-0.8), Example 2 (NDSiN-1.0), Example 3 (NDSiN-1.2), and Comparative Example 2 (Si).

[0148] As shown in Fig. 11(e), Examples 1 to 3, in which the negative active material does not include graphite, also exhibit excellent cycle stability. On the other hand, Comparative Example 2 (Si), which used commercial silicon as the negative active material, exhibited significantly lower cycle performance than Examples 1 to 3, with battery failure occurring within 20 cycles. On the other hand, Example 1 (NDSiN-0.8) exhibited an excellent capacity retention rate of 75.3% over 200 cycles, confirming excellent life characteristics.

[0149] As described above, the present invention has been described with specific details and limited examples and drawings, but these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those skilled in the art to which the present invention pertains can make various modifications and variations based on this description.

[0150] Therefore, the idea of ​​the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the claims described below as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

Claims

1. (S1) A step of mixing amorphous silicon nitride powder and reducing agent powder; and (S2) A method for producing a silicon nitride composite, comprising the step of heat-treating the above mixed powder to crystallize at least a portion of the silicon contained in the amorphous silicon nitride.

2. In paragraph 1, A method for producing a silicon nitride composite, wherein the silicon nitride powder and reducing agent powder are mixed in a weight ratio of 1:0.2 to 2.

3. In paragraph 1, A method for producing a silicon nitride composite, wherein the reducing agent comprises an alkali metal, an alkaline earth metal, a post-transition metal, or a combination thereof.

4. In paragraph 1, A method for producing a silicon nitride composite, wherein the above heat treatment is performed at a temperature higher than the melting point of the reducing agent.

5. In paragraph 1, A method for producing a silicon nitride composite, wherein, in the step (S2), the reducing agent and nitrogen react.

6. In paragraph 5, A method for producing a silicon nitride composite, further comprising, after the above step (S2), a step of removing the reducing agent and nitrogen reaction product.

7. In paragraph 1, A method for manufacturing a silicon nitride composite, further comprising, after the above step (S2), a step of mixing the silicon nitride composite and a carbon body.

8. In paragraph 1, A method for manufacturing a silicon nitride composite, wherein, in the above step (S1), a heat dispersant is further added.

9. Contains amorphous silicon nitride and crystalline silicon represented by the following chemical formula 1, A silicon nitride composite, wherein the above crystalline silicon is formed by the generation of nitrogen defects in the above amorphous silicon nitride. [Chemical Formula 1] Si3N 4-x (The above x is 0 <x<4를 만족하는 실수이다) 10. In paragraph 9, A silicon nitride composite in which the silicon particles in the above silicon nitride composite are a mixture of amorphous and crystalline portions.

11. In paragraph 9, The above silicon nitride composite is a porous silicon nitride composite.

12. In paragraph 11, A silicon nitride composite having an average particle diameter of the above pores of 2 to 20 nm.

13. In paragraph 9, The above silicon nitride composite is a silicon nitride composite for use as a negative electrode active material.

14. In paragraph 9, A silicon nitride composite, wherein the percentage of the area occupied by the crystalline silicon peak relative to the area of ​​the total peak in the Si 2p XPS analysis spectrum of the above silicon nitride composite is 5 to 90%.

15. In paragraph 9, A silicon nitride complex, wherein the silicon:nitrogen atomic ratio contained in the silicon nitride complex is 1 to 10:

1.

16. In paragraph 9, The above silicon nitride composite further comprises a carbon body.

17. A negative electrode for a lithium secondary battery comprising a silicon nitride composite manufactured by a method according to any one of claims 1 to 8.

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