Negative electrode material for secondary batteries

Abstract

The present invention relates to an anode material for secondary batteries having excellent initial charge-discharge efficiency. Specifically, the anode material for secondary batteries includes a matrix containing a composite oxide of silicon and a doping element selected from the group consisting of at least one of alkali metals, alkaline earth metals, and post-transition metals, or a mixture thereof; and silicon nanocrystals dispersed and contained in the matrix. In an X-ray diffraction pattern using CuKα radiation, the anode material includes a first peak located at a diffraction angle 2θ in the range of 20.3° to 21.3°, a second peak located at a diffraction angle 2θ in the range of 26° to 27°, a third peak located at a diffraction angle 2θ in the range of 28° to 29°, and a fourth peak located at a diffraction angle 2θ in the range of 30.5° to 31.5°, and the intensity ratio (I2 / I4) between the maximum intensity of the second peak (I2) and the maximum intensity of the fourth peak (I4) satisfies a range of 1 to 20.

Description

[Technical Field]

[0001] The present invention relates to an anode material for a secondary battery, and more particularly to an anode material for a secondary battery having a significantly improved initial coulombic efficiency. [Background technology]

[0002] Demand for secondary batteries with high energy density and high power density as well as long-term usability, i.e., long lifespan, continues to increase in various industrial fields, including electronic products, electric / hybrid vehicles, and aerospace / drones.

[0003] Generally, rechargeable secondary batteries consist of a positive electrode, a negative electrode, an electrolyte, and a separator. Among these, graphite is the most commonly used negative electrode material, but the theoretical maximum capacity of graphite is only 372mAh / g.

[0004] As a result, in order to realize high-energy density secondary batteries, continuous research is being conducted into using chalcogen-based materials such as sulfur (maximum capacity 1,675mAh / g), silicon-based materials such as silicon (maximum capacity 4,200mAh / g) and silicon oxide (maximum capacity 1,500mAh / g), and transition metal oxides as secondary battery anode materials, and among the various materials, silicon-based anode materials are attracting the most attention.

[0005] However, when particulate silicon is used as the anode material, repeated charge-discharge cycling causes the battery characteristics to deteriorate rapidly due to insulation caused by large volume changes in silicon, particle detachment, and increased contact resistance, resulting in the battery losing its function within less than 100 cycles.In the case of silicon oxide, there is also the problem that lithium is lost due to irreversible products such as lithium silicate and lithium oxide, resulting in a rapid decrease in initial charge-discharge efficiency.

[0006] To solve these problems with silicon-based anode materials, various techniques have been proposed, such as nano-silicon in the form of wires and combining them with carbon materials, doping silicon oxide with different metals to form a composite oxide phase, and pre-lithiating silicon oxide. However, these techniques still have problems such as reduced initial charge / discharge efficiency, cycle characteristics, and high-rate characteristics, making commercialization difficult. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a negative electrode material for a silicon-based secondary battery having excellent battery capacity and significantly improved initial charge-discharge efficiency characteristics. [Means for solving the problem]

[0008] According to one embodiment of the present invention, there is provided a negative electrode material for a secondary battery, comprising: a matrix containing a composite oxide of silicon and a doping element selected from the group consisting of alkali metals, alkaline earth metals, and post-transition metals, or a mixture thereof; and silicon nanocrystals dispersed and contained in the matrix; wherein an X-ray diffraction pattern using CuKα radiation includes a first peak located at a diffraction angle 2θ in the range of 20.3° to 21.3°, a second peak located at a diffraction angle 2θ in the range of 26° to 27°, a third peak located at a diffraction angle 2θ in the range of 28° to 29°, and a fourth peak located at a diffraction angle 2θ in the range of 30.5° to 31.5°, and the intensity ratio (I2 / I4) between the maximum intensity (I2) of the second peak and the maximum intensity (I4) of the fourth peak satisfies a range of 1 to 20.

[0009] In the negative electrode material for secondary batteries according to one embodiment of the present invention, the fourth peak may be derived from magnesium silicate.

[0010] In the negative electrode material for secondary batteries according to one embodiment of the present invention, the intensity ratio (I2 / I3) between the maximum intensity of the second peak (I2) and the maximum intensity of the third peak (I3) may be 0.2 to 5.0.

[0011] In the negative electrode material for secondary batteries according to one embodiment of the present invention, the full width at half maximum of the first peak or the second peak in the X-ray diffraction pattern may be narrower than the full width at half maximum of the third peak.

[0012] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the negative electrode material for a secondary battery may include an alkali metal and an alkaline earth metal.

[0013] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the negative electrode material for a secondary battery may contain 3 to 15 mass % of an alkaline earth metal based on the total mass of the negative electrode material.

[0014] In the negative electrode material for secondary batteries according to one embodiment of the present invention, the mass ratio of alkali metal to alkaline earth metal contained in the negative electrode material for secondary batteries may be 1:1-100.

[0015] In the negative electrode material for secondary batteries according to one embodiment of the present invention, the mass ratio of alkali metal to alkaline earth metal contained in the negative electrode material for secondary batteries may be 1:1-15.

[0016] In the negative electrode material for secondary batteries according to one embodiment of the present invention, the alkali metal may be lithium (Li) and the alkaline earth metal may be magnesium (Mg).

[0017] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the silicon nanocrystals may have an average diameter of 2 to 30 nm.

[0018] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the negative electrode material may further include a coating layer containing carbon.

[0019] According to another aspect, the present invention includes a secondary battery including the above-described negative electrode material for a secondary battery. [Effects of the Invention]

[0020] The negative electrode material for secondary batteries according to the present invention comprises a matrix containing silicon oxide, a composite oxide of silicon and a doping element selected from one or more of alkali metals, alkaline earth metals, and post-transition metals, or a mixture thereof; and silicon nanocrystals dispersed and contained in the matrix. The negative electrode material has specific crystallographic characteristics based on an X-ray diffraction pattern using CuKα radiation, thereby providing a secondary battery equipped with a silicon-based negative electrode material that has excellent battery capacity and significantly improved initial charge / discharge efficiency. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram showing X-ray diffraction (XRD) patterns of Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, the negative electrode material for a secondary battery of the present invention will be described in detail with reference to the accompanying drawings. The drawings introduced below are provided as examples to fully convey the concept of the present invention to those skilled in the art. Therefore, the present invention is not limited to the drawings presented below, and may be embodied in other forms. The drawings presented below are exaggerated to clarify the concept of the present invention. In this case, unless otherwise defined, the technical and scientific terms used have the meanings that are commonly understood by a person of ordinary skill in the art to which the present invention belongs, and in the following description and accompanying drawings, descriptions of known functions and configurations that may obscure the gist of the present invention will be omitted.

[0023] Also, as used in the specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0024] In this specification and the appended claims, the terms "first," "second," etc. are not meant to be limiting but are used to distinguish one element from another element.

[0025] In this specification and the appended claims, the terms "comprise" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may also be added, unless specifically limited.

[0026] In this specification and the appended claims, when a part such as a film (layer), region, or component is said to be on top of another part, this includes not only the case where it is directly on top of and in contact with the other part, but also the case where another film (layer), other region, other component, etc. is interposed between them.

[0027] The matrix in the present invention may refer to a solid phase medium in which nanocrystalline silicon is dispersed, or may refer to a material that forms a continuous phase for the silicon nanocrystals that are the dispersed phase in the anode material. The matrix in the present invention may refer to a material excluding metallic silicon (Si) from the anode material.

[0028] The nanocrystals in the present invention have a size (diameter) of 10, which is the size usually defined for nanocrystals. 0 Nanometer order ~ 10 2 Nanometer-order crystals can refer to crystals having a diameter of substantially 500 nm or less, specifically 200 nm or less, more specifically 100 nm or less, and even more specifically 50 nm or less.

[0029] The negative electrode material for secondary batteries of the present invention includes, but is not necessarily limited to, a negative electrode material for lithium secondary batteries. The negative electrode material of the present invention can be used as an active material for secondary batteries such as sodium batteries, aluminum batteries, magnesium batteries, calcium batteries, and zinc batteries, and can also be used in other energy storage / generation devices that use conventional silicon-based materials, such as supercapacitors, dye-sensitized solar cells, and fuel cells.

[0030] According to one embodiment of the present invention, there is provided a negative electrode material for a secondary battery, comprising: a matrix containing a composite oxide of silicon and a doping element selected from the group consisting of alkali metals, alkaline earth metals, and post-transition metals, or a mixture thereof; and silicon nanocrystals dispersed and contained in the matrix; wherein an X-ray diffraction pattern using CuKα radiation includes a first peak located at a diffraction angle 2θ in the range of 20.3° to 21.3°, a second peak located at a diffraction angle 2θ in the range of 26° to 27°, a third peak located at a diffraction angle 2θ in the range of 28° to 29°, and a fourth peak located at a diffraction angle 2θ in the range of 30.5° to 31.5°, and the intensity ratio (I2 / I4) between the maximum intensity (I2) of the second peak and the maximum intensity (I4) of the fourth peak satisfies a range of 1 to 20.

[0031] In secondary batteries that use conventional anode materials containing silicon oxide, lithium reacts with silicon oxide during initial charging to produce lithium silicide and lithium oxide, but since lithium oxide no longer participates in the electrochemical reaction after it is generated, an irreversible reaction occurs in which some of the lithium that moved to the anode during initial charging does not return to the cathode during discharge. In the case of silicon oxide, this irreversible capacity is larger than that of other silicon-based anodes, so the initial charge / discharge time, which is defined as the ratio of the discharge capacity to the initial charge capacity, is The initial charge-discharge efficiency (ICE) is very low at about 70%. Such low initial charge-discharge efficiency poses the problem that when constructing a secondary battery, excessive positive electrode capacity is required, which offsets the negative electrode's capacity per unit mass.

[0032] Meanwhile, an anode material for a secondary battery according to one embodiment of the present invention includes a matrix containing a composite oxide of silicon and a doping element selected from one or more of a group consisting of an alkali metal, an alkaline earth metal, and a post-transition metal, or a mixture thereof; and silicon nanocrystals dispersed and contained in the matrix. The anode material has specific crystallographic characteristics based on an X-ray diffraction pattern using CuKα radiation, thereby effectively removing an inactive phase that induces an irreversible reaction. As a result, a secondary battery including the anode material according to one embodiment of the present invention has an advantage of being able to have significantly improved initial charge / discharge efficiency compared to conventional batteries.

[0033] In one embodiment, in an X-ray diffraction pattern using CuKα radiation, the intensity ratio (I2 / I4) between the maximum intensity (I2) of the second peak located in the diffraction angle 2θ range of 26° to 27° and the maximum intensity (I4) of the fourth peak located in the diffraction angle 2θ range of 30.5° to 31.5° may be 1 to 20, specifically 1.5 to 15, more specifically 1.5 to 13, even more specifically 2 to 12, and particularly specifically 5 to 11.

[0034] In the X-ray diffraction pattern of the negative electrode material for secondary batteries, when the intensity ratio (I2 / I4) between the maximum intensity of the second peak (I2) and the maximum intensity of the fourth peak (I4) satisfies the above-mentioned range, irreversible reactions of lithium can be effectively suppressed, unlike conventional methods, and the initial charge-discharge efficiency of the secondary battery can be significantly improved.

[0035] In one embodiment, in an X-ray diffraction pattern using CuKα radiation, the intensity ratio (I2 / I3) between the maximum intensity (I2) of the second peak located in the diffraction angle 2θ range of 26° to 27° and the maximum intensity (I3) of the third peak located in the diffraction angle 2θ range of 28° to 29° may be 0.2 to 5.0, specifically 0.5 to 5.0, more specifically 0.5 to 4.0, even more specifically 0.5 to 2.5, and particularly specifically 1.9 to 2.3.

[0036] When the intensity ratio (I2 / I4) between the maximum intensity of the second peak (I2) and the maximum intensity of the fourth peak (I4) and the intensity ratio (I2 / I3) between the maximum intensity of the second peak (I2) and the maximum intensity of the third peak (I3) satisfy the above ranges, there is an advantage that the initial charge / discharge efficiency of the secondary battery is improved and at the same time the secondary battery can have excellent capacity retention characteristics.

[0037] For example, the capacity retention rate of the secondary battery may be 80% or more, 85% or more, 90% or more, or 93% or more, and preferably 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more, and although there is no upper limit, it may be 100% or less.

[0038] In this case, the capacity retention rate is calculated by dividing the discharge capacity (C1) in the first charge-discharge cycle after the formation process by the discharge capacity (C) in the 50th charge-discharge cycle. 50 ) may be calculated based on the

[0039] For example, the formation process may include a first process in which charge and discharge are performed under conditions of CC / CV, cut-off voltage 0.005V to 1.5V, and 0.1C-rate, and a second process in which charge and discharge are performed under conditions of CC / CV, cut-off voltage 0.005V to 1.0V, and 0.1C-rate. However, the present invention is not limited by the formation process conditions, and any formation process typically performed in batteries used to test the electrochemical properties of conventional negative electrode materials may be used.

[0040] Furthermore, the full width at half maximum (FWHM) of the first or second peak in the X-ray diffraction pattern using CuKα radiation may be even narrower than the full width at half maximum of the third peak.

[0041] In this case, the first and second peaks may be due to quartz, and the third peak may be due to crystalline silicon.

[0042] In one embodiment, in the X-ray diffraction pattern using CuKα radiation, a fourth peak located in the diffraction angle 2θ range of 30.5° to 31.5° may be derived from magnesium silicate.

[0043] In this case, the magnesium silicate may be one or more selected from MgSiO3 and Mg2SiO4.

[0044] As described above, the anode material according to one embodiment of the present invention includes specific crystallographic characteristics based on an X-ray diffraction pattern using CuKα radiation, thereby effectively removing inactive phases that induce irreversible reactions contained in the anode material, and allowing lithium that migrates to the anode during initial charge to return to the cathode during discharge, thereby significantly improving initial charge / discharge efficiency and providing excellent capacity retention.

[0045] For example, the negative electrode material for a secondary battery of the present invention may contain one or more doping elements selected from the group consisting of alkali metals, alkaline earth metals, and post-transition metals.

[0046] In one embodiment, the doping elements may include one or more alkali metals selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs), and one or more alkaline earth metals selected from beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).

[0047] In order to improve the initial charge / discharge efficiency of secondary batteries, the industry has provided silicon-based or silicon oxide-based anode materials containing alkaline earth metals such as magnesium (Mg) or calcium (Ca) as doping elements, and the content of the doped alkaline earth metal must be increased to improve the initial charge / discharge efficiency. Although secondary batteries using anode materials with an increased alkaline earth metal content can improve the initial charge / discharge efficiency, the increased alkaline earth metal content can cause a rapid decrease in discharge capacity and cycle life characteristics of the secondary battery.

[0048] Meanwhile, the negative electrode material according to one embodiment contains an alkali metal together with an alkaline earth metal, thereby improving the initial charge-discharge efficiency while minimizing the deterioration of the discharge capacity and cycle life characteristics of the secondary battery.

[0049] In one preferred example, the alkali metal may be lithium (Li) and the alkaline earth metal may be magnesium (Mg).

[0050] By simultaneously including lithium (Li) and magnesium (Mg) as doping elements in the anode material, the content of alkaline earth metals included as doping elements has been reduced compared to conventional materials in order to improve the initial charge-discharge efficiency. However, the inactive phases that induce irreversible reactions in the anode material can be effectively removed. This means that the initial charge-discharge efficiency can be improved without reducing the discharge capacity and cycle life characteristics of the secondary battery. It is preferable that the alloy contains lithium (Li) and magnesium (Mg) as the alloying elements.

[0051] In one embodiment, the negative electrode material for a secondary battery can contain 3 to 15 mass %, specifically 3 to 10 mass %, more specifically 3 to 5 mass % of alkaline earth metal based on the total mass of the negative electrode material.

[0052] If the content of alkaline earth metal contained in the negative electrode material for secondary batteries exceeds 15% by mass, the initial charge-discharge efficiency of the secondary battery can be improved, but the discharge capacity and / or cycle life characteristics of the secondary battery may be reduced. If the content of alkaline earth metal contained in the negative electrode material is less than 3% by mass, the improvement in the initial charge-discharge efficiency of the secondary battery may be limited. Therefore, it is preferable that the negative electrode material for secondary batteries contains an alkaline earth metal in the above-mentioned range.

[0053] In one embodiment, the mass ratio of alkali metal to alkaline earth metal contained in the negative electrode material for secondary batteries may be 1:1-100, specifically 1:1-50, and more specifically 1:1-40.

[0054] As an advantageous example, the mass ratio of alkali metal:alkaline earth metal may be 1:1-35, 1:1-30, 1:8-30, 1:1-25, 1:8-25, 1:1-20, 1:8-20, 1:1-15, or 1:8-15.

[0055] If the mass ratio of alkali metal to alkaline earth metal contained in the negative electrode material for secondary batteries is outside the above-mentioned range, i.e., if the amount of alkali metal contained is greater than the amount of alkaline earth metal, an inactive phase that induces an irreversible reaction due to the alkali metal is formed, which may reduce the initial charge / discharge efficiency of the secondary battery. If the amount of alkaline earth metal contained is greater than the amount of alkali metal so as to be outside the above-mentioned range, the discharge capacity and / or cycle life characteristics of the secondary battery may be reduced. Therefore, it is advantageous that the mass ratio of alkali metal to alkaline earth metal contained in the negative electrode material for secondary batteries satisfies the above-mentioned range.

[0056] In one embodiment, the negative electrode material for a secondary battery may contain 0.01 to 10 mass %, specifically 0.1 to 5 mass %, more specifically 0.15 to 1.5 mass %, and even more specifically 0.15 to 0.8 mass % of alkali metal based on the total mass of the negative electrode material.

[0057] In one embodiment, the average diameter of the silicon nanocrystals is 10 0Nanometer order ~ 10 1 It may be on the order of nanometers, specifically 1 to 50 nm, 2 to 40 nm, 2 to 35 nm, 2 nm to 30 nm, 2 nm to 20 nm, or 2 nm to 15 nm, but is not limited to these.

[0058] Experimentally, the average diameter of silicon nanocrystals can be calculated by measuring the size of silicon nanocrystals in the negative electrode material through images observed with a transmission electron microscope and averaging the measured sizes of 10 or more, 20 or more, or 30 or more silicon nanocrystals.

[0059] In one embodiment, the negative electrode material may be in a particulate form. The particulate negative electrode material has a particle size typically required for use in secondary batteries, for example, 10 0 μm order ~ 10 1 The average diameter may be on the order of μm, specifically, an average diameter of 1 μm to 99 μm, 1 μm to 90 μm, 1 μm to 80 μm, 1 μm to 70 μm, 1 μm to 60 μm, 1 μm to 50 μm, 1 μm to 40 μm, 1 μm to 30 μm, or 5 μm to 30 μm, but is not limited thereto.

[0060] In one embodiment, the negative electrode material may further include a coating layer containing carbon, specifically a surface coating layer coated on the surface of the negative electrode material. The surface coating layer is advantageous because it can improve the electrical properties of the negative electrode material. The thickness of the coating layer is sufficient if it is on the order of 2 to 30 nm, but is not necessarily limited to this.

[0061] The present invention includes a negative electrode containing the above-described negative electrode material. The negative electrode may be a negative electrode of a secondary battery, specifically a lithium secondary battery. The negative electrode may include a current collector; and a negative electrode active material layer located on at least one surface of the current collector and containing the above-described negative electrode material. The negative electrode active material layer may further contain the negative electrode material and a binder and a conductive material typically used in negative electrodes of secondary batteries, as needed.

[0062] The present invention includes a secondary battery including the above-described negative electrode. Specifically, the present invention includes a lithium secondary battery including the above-described negative electrode. The lithium secondary battery may include a positive electrode including a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector; the above-described negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte that conducts lithium ions. The positive electrode active material and composition of the positive electrode current collector, negative electrode current collector, and positive electrode active material layer, the separator, and the electrolyte solvent, electrolyte salt, or the concentration of the electrolyte salt, may be materials and compositions typically used in lithium secondary batteries.

[0063] In one embodiment, the initial charge / discharge efficiency of the lithium secondary battery may be 75% or more, 80% or more, 85% or more, 86% or more, 87% or more, or may be substantially 95% or less.

[0064] Hereinafter, the negative electrode material for a secondary battery according to the present invention will be described in more detail with reference to the following examples. However, the following examples are merely a reference for explaining the present invention in detail, and the present invention is not limited thereto and may be realized in various forms.

[0065] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used in the description herein are merely for the purpose of effectively describing particular embodiments and are not intended to limit the present invention.

[0066] Example 1 The mixed raw materials, Si, SiO2, MgO and LiOH, were mixed in 20 L of ethanol at a molar ratio of 40:31:6.7:2.4, and dried at 120°C for 24 hours.

[0067] 26 kg of the mixed raw material was placed in a crucible in a vacuum chamber of 0.1 torr or less, and then heated to 1,400°C to vaporize it. The vapor was then condensed on a collection plate at 400°C to obtain silicon oxide composited with magnesium and lithium.

[0068] The obtained magnesium-lithium-silicon composite oxide was heat-treated in an inert atmosphere at 800° C. or higher for 20 hours or more.

[0069] The heat-treated magnesium-lithium-silicon composite oxide was mechanically crushed, and then the crushed powder was coated with 5% by mass of carbon using a hydrocarbon gas at 950°C in a CVD process to produce the anode material.

[0070] At this time, it was confirmed that the negative electrode material contained 5 mass % of Mg and 0.1 mass % of Li based on the total mass of the negative electrode material.

[0071] Example 2 The same procedure as in Example 1 was carried out, except that LiOH was added so that the negative electrode material contained 0.2 mass % of Li. The same procedure was carried out except that the mixing ratio of

[0072] Example 3 The same procedure as in Example 1 was carried out, except that the mixing ratio of LiOH was changed so that the negative electrode material contained 0.5 mass % Li.

[0073] Example 4 The same procedure as in Example 1 was carried out, except that the mixing ratio of LiOH was changed so that the negative electrode material contained 1 mass % of Li.

[0074] Example 5 The same procedure as in Example 1 was carried out, except that the mixing ratio of MgO was changed so that the negative electrode material contained 7 mass % of Mg.

[0075] Example 6 The same procedure as in Example 2 was carried out, except that the mixing ratio of MgO was changed so that the negative electrode material contained 7 mass % of Mg.

[0076] Example 7 The same procedure as in Example 3 was carried out, except that the mixing ratio of MgO was changed so that the negative electrode material contained 7 mass % of Mg.

[0077] Example 8 The same procedure as in Example 4 was carried out, except that the mixing ratio of MgO was changed so that the negative electrode material contained 7 mass % of Mg.

[0078] (Comparative Example 1) The same procedure as in Example 1 was carried out, except that no LiOH starting material was used.

[0079] (Comparative Example 2) The same procedure as in Example 5 was carried out, except that no LiOH starting material was used.

[0080] (Comparative Example 3) The procedure was the same as in Example 1, except that LiF was used instead of LiOH.

[0081] (Experimental Example 1) X-ray diffraction analysis The structure of the crushed negative electrode material was analyzed by X-ray diffraction (XRD, Rigaku D / MAX-2500 / PC, 40 kV, 15 mA, 4 min -1 , Cu-Kα radiation, λ=0.15406 nm) analysis.

[0082] FIG. 1 is a diagram showing XRD patterns of Examples 1 to 4.

[0083] Referring to FIG. 1, it can be seen that all of Examples 1 to 4 have a first peak in the diffraction angle 2θ range of 20.3° to 21.3°, a second peak in the range of 26° to 27°, a third peak in the range of 28° to 29°, and a fourth peak in the range of 30.5° to 31.5°.

[0084] Furthermore, it was confirmed that all of Examples 1 to 4 contained a fourth peak corresponding to magnesium silicate (MgSiO3), and no peak associated with Li mixed in the raw material was observed.

[0085] Although not shown, all of the first to fourth peaks were observed in Examples 5 to 8. On the other hand, the first peak was not observed in Comparative Examples 1 and 2, and the MgSiO3 peak corresponding to the fourth peak was not observed in Comparative Example 3, but a LiF peak located in the diffraction angle 2θ range of 38° to 41° was observed.

[0086] The intensity ratio (I2 / I4) between the maximum intensity of the second peak (I2) and the maximum intensity of the fourth peak (I4) and the intensity ratio (I2 / I3) between the maximum intensity of the second peak (I2) and the maximum intensity of the third peak (I3), calculated based on the XRD pattern observed for each negative electrode material, are summarized in Table 1 below.

[0087] (Experimental Example 2) Battery production and battery performance evaluation The final negative electrode powder was used as the active material, and the active material was: conductive material (carbon black), CMC (Carboxymethyl cellulose), SBR (Styrene The mixture was coated on a 17-μm-thick copper foil and then dried at 90°C for 40 minutes. After drying, a 14-mm diameter plate was punched out and a 16-mm diameter lithium metal counter electrode was used. An 18-mm diameter separator was sandwiched between the plate and the foil, and the electrolyte was filled to fabricate a CR2032 coin-type half-cell. The electrolyte was prepared by dissolving 1M LiPF6 in a 1:1 volumetric mixture of EC (Ethylene carbonate) and DEC (Diethyl carbonate), with 3 wt% FEC (fluoroethylene carbonate) added.

[0088] The resulting battery was then charged (lithiated) to 0.005 V at a constant current of 0.1 C, charged at a constant voltage of 0.005 V until it reached 0.01 C, and then discharged (de-lithiated) to 1.5 V at a constant current of 0.1 C (first formation step). It was then again charged (lithiated) to 0.005 V at a constant current of 0.1 C, charged at a constant voltage of 0.005 V until it reached 0.01 C, and then discharged (de-lithiated) to 1.0 V at a constant current of 0.1 C (second formation step).

[0089] The initial charge-discharge efficiency based on the charge-discharge in the first chemical formation step was evaluated. After the chemical formation step, 50 charge-discharge cycles were performed according to the following conditions, and the discharge capacity of the first cycle (C1) and the discharge capacity after 50 cycles (C 50 ) based on the formula C 50 The capacity retention rate was calculated using / C1*100, and the results are summarized in Table 1 below. Charge / discharge cycle conditions: Charge to 0.005V at a constant current of 0.5C (lithiation), charge at a constant voltage of 0.005V until it reaches 0.05C, then discharge to 1.0V at a constant current of 0.5C (de-lithiation).

[0090] [Table 1]

[0091] Referring to Table 1, it was confirmed that the secondary batteries containing the negative electrode materials of Examples 1 to 8 exhibited initial charge-discharge efficiencies of 85% or more, and in particular, when the negative electrode materials of Examples 2 and 3 were contained, it was confirmed that the initial charge-discharge efficiencies were significantly improved to 85% or more, along with excellent capacity retention characteristics of 99% or more.

[0092] On the other hand, in the cases of Comparative Examples 1 and 2, the initial charge-discharge efficiency was observed to be at a level of approximately 81%, which was similar to that of the conventional case, and in the case of Comparative Example 3, the initial charge-discharge efficiency was shown to be 91%, but the capacity retention rate was confirmed to be at a level of 32.2%, which was a significantly deteriorated characteristic.

[0093] As described above, the present invention has been described using specific matters and limited examples and drawings, but these are provided to help a more general understanding of the present invention, and the present invention is not limited to the above examples. Those skilled in the art will recognize that various modifications and variations can be made from such descriptions.

[0094] Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the scope of the claims below, but also all equivalent or equivalent modifications to the scope of these claims may fall within the scope of the spirit of the present invention.

Claims

1. The present invention comprises a matrix containing a composite oxide of silicon and one or more doping elements selected from the group consisting of silicon oxide, alkali metals, alkaline earth metals, and post-transition metals, or a mixture thereof; and silicon nanocrystals dispersed and contained in the matrix, In an X-ray diffraction pattern using CuKα radiation, the diffraction angle 2θ includes a first peak located in the range of 20.3° to 21.3°, a second peak located in the range of 26° to 27°, a third peak located in the range of 28° to 29°, and a fourth peak located in the range of 30.5° to 31.5°, The maximum intensity of the second peak (I ２ ) and the maximum intensity of the fourth peak (I ４ ) and the intensity ratio (I ２ / I ４ ) is 1 to 20.

2. 2. The negative electrode material for secondary batteries according to claim 1, wherein the fourth peak is derived from magnesium silicate.

3. The maximum intensity of the second peak (I ２ ) and the maximum intensity of the third peak (I ３ ) and the intensity ratio (I ２ / I ３ 2. The negative electrode material for secondary batteries according to claim 1, wherein the value of (I) is 0.2 to 5.

0.

4. 2 . The negative electrode material for secondary batteries according to claim 1 , wherein a full width at half maximum of the first peak or the second peak in the X-ray diffraction pattern is narrower than a full width at half maximum of the third peak.

5. 2. The negative electrode material for a secondary battery according to claim 1, wherein the negative electrode material for a secondary battery contains an alkali metal and an alkaline earth metal.

6. The negative electrode material for secondary batteries according to claim 5, wherein the negative electrode material for secondary batteries contains 3 to 15 mass% of alkaline earth metal based on the total mass of the negative electrode material.

7. 6. The negative electrode material for secondary batteries according to claim 5, wherein the mass ratio of alkali metal to alkaline earth metal contained in the negative electrode material for secondary batteries is 1:1 to 100.

8. 8. The negative electrode material for secondary batteries according to claim 7, wherein the mass ratio of alkali metal to alkaline earth metal contained in the negative electrode material for secondary batteries is 1:1 to 15.

9. 6. The negative electrode material for a secondary battery according to claim 5, wherein the alkali metal is lithium (Li) and the alkaline earth metal is magnesium (Mg).

10. 2. The negative electrode material for secondary batteries according to claim 1, wherein the silicon nanocrystals have an average diameter of 2 to 30 nm.

11. The negative electrode material for a secondary battery according to claim 1 , further comprising a coating layer containing carbon.

12. A secondary battery comprising the negative electrode material for secondary batteries according to any one of claims 1 to 11.

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