Negative electrode material for lithium secondary battery, and secondary battery comprising same

Abstract

The present invention relates to a negative electrode material for a secondary battery having high output, excellent cycle characteristics, and uniform electrochemical characteristics. The negative electrode material for a secondary battery, according to the present invention, comprises: a silicon-based core; and a carbon coating layer positioned on the surface of the silicon-based core, wherein the intensity ratio (ID / IG) of a D band peak and a G band peak in a Raman spectrum of the carbon coating layer is 1.3 or less, the ratio (FD / FG) of the full width at half maximum (FWHM) of the D band and G band peaks is 1.3 or more, and, in an infrared spectrum, the area (A1) of a peak of a first wavenumber (n1) in the range of 1400 to 1625±5 ㎝-1 is smaller than the area (A2) of a peak of a second wavenumber (n2) in the range of 1625±5 to 2100 ㎝-1 .

Description

Anode material for lithium secondary batteries and secondary batteries containing the same

[0001] The present invention relates to a negative electrode material for a secondary battery and a secondary battery including the same, and more particularly, to a negative electrode material for a secondary battery having high output, excellent cycle characteristics, and uniform electrochemical characteristics.

[0002] Demand for secondary batteries with high energy density, high power density, and long lifespan continues to grow across a wide range of industries, including electronics, electric vehicles (EVs), energy storage systems (ESS), and aerospace / drones.

[0003] Typically, a rechargeable lithium secondary battery is composed of a cathode, an anode, an electrolyte, and a separator. Among these, the representative cathode material used commercially as an anode is graphite, but the theoretical maximum capacity of graphite is only 372 mAh / g.

[0004] In order to realize high-energy-density secondary batteries, research is continuously being conducted to use chalcogen-based materials such as sulfur (maximum capacity 1,675 mAh / g), silicon-based materials such as silicon (maximum capacity 4,200 mAh / g) or silicon oxide (maximum capacity 1,500 mAh / g), and transition metal oxides as secondary battery anode materials. Among various materials, silicon-based anode materials are receiving the most attention because they have a high theoretical capacity, low reaction potential with lithium, and are environmentally friendly.

[0005] However, when using particulate silicon as an anode material, there is a problem that the battery characteristics rapidly deteriorate due to insulation, particle detachment, and increased contact resistance caused by large volume changes in the silicon as charge and discharge cycling are repeated, thereby losing its function as a battery. On the other hand, in the case of silicon oxide, there is a problem that lithium is lost due to irreversible products such as lithium silicate or lithium oxide, and the initial charge and discharge efficiency rapidly decreases.

[0006] To address these issues with silicon-based anode materials, a carbon coating layer has been formed on the surface of a metal-doped silicon oxide anode through chemical vapor deposition (CVD). However, this anode material is not economical due to the need for expensive hydrocarbon gas or low conversion efficiency to carbon at high temperatures, and it is difficult to uniformly coat the surface of silicon oxide particles during mass production. Furthermore, the CVD coating process inevitably generates a temperature gradient within the reactor because hydrocarbon gas is continuously supplied from the outside and heat is supplied through the outer wall of the reactor.

[0007] Furthermore, since the hydrocarbon decomposition reaction is an endothermic reaction, the temperature gradient becomes larger as the silicon oxide particles move away from the heat source, which reduces the uniformity of the deposited carbon coating layer.

[0008] This non-uniformity of the carbon coating layer leads to non-uniformity in the electrochemical properties of the anode material, which negatively impacts initial charge / discharge efficiency, cycle characteristics, and cycle life. Therefore, there is a continuing need for the development of anode materials for silicon-based secondary batteries that exhibit superior initial charge / discharge efficiency, cycle characteristics, and cycle life, as well as high-power characteristics.

[0009] The problem solved by the present invention is to provide a negative electrode material for a silicon-based secondary battery with improved initial charge / discharge efficiency, cycle characteristics, and life characteristics, and a lithium secondary battery including the same.

[0010] Another object of the present invention is to provide a silicon-based secondary battery negative electrode material having uniform electrochemical properties not only among different negative electrode particles but also within the negative electrode particles, and a lithium secondary battery including the same.

[0011] Another problem of the present invention is to provide a silicon-based secondary battery negative electrode material having high output characteristics and a lithium secondary battery including the same.

[0012] The negative electrode material for a secondary battery according to the present invention includes a silicon-based core and a carbon coating layer positioned on the surface of the silicon-based core, and the ratio of intensities of the D band peak and the G band peak in the Raman spectroscopy spectrum of the carbon coating layer (I D / I G ) is 1.3 or less, and the ratio of the full width at half maximum (FWHM) of the D band and G band peaks (F D / F G ) is 1.3 or more, and the infrared spectrum is 1400 to 1625±5 cm -1 The area (A1) of the peak of the first wave number (n1) of the range is 1625±5 to 2100 cm -1 It is characterized by being smaller than the area (A2) of the peak of the second wave number (n2) of the range.

[0013] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the ratio (A2 / A1) of the area (A1) of the peak of the first wave number (n1) and the area (A2) of the peak of the second wave number (n2) may be 2 or more.

[0014] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the silicon-based core may include a silicon oxide matrix and silicon nanocrystals dispersed and embedded in the silicon oxide matrix.

[0015] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the ratio of the strength (I D / I G ) is the ratio of the full width at half maximum (F D / F G ) may be less than.

[0016] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the full width at half maximum (F) of the G band peak G ) is 60 cm -1 It could be strange.

[0017] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the following equation 1 can be satisfied based on a silicon Raman signal.

[0018] (Formula 1)

[0019] 1 > WN(Si) / WN(ref)

[0020] In the above equation 1, WN(ref) is the center wavenumber of the Raman peak of bulk single crystal silicon, and WN(Si) is the center wavenumber of the Raman peak of silicon nanocrystals contained in the cathode material.

[0021] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the silicon-based core is formed such that the difference between the maximum and minimum values ​​of the central wavenumber WN(Si) of the Raman peak of the silicon nanocrystal at 10 different random locations is 5 cm. -1 It could be as follows:

[0022] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the specific surface area of ​​the negative electrode material is 10 m 2 / g can be less.

[0023] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the ratio of the full width at half maximum (F D / F G ) can be 1.7 or higher.

[0024] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the carbon coating layer may include a plurality of carbon nanoparticles.

[0025] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the carbon coating layer may include a dispersed phase including a plurality of carbon nanoparticles and a continuous phase physically bonding the dispersed phase and made of carbon.

[0026] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the carbon coating layer may be included in an amount of 0.5 to 8 wt% of the total weight of the negative electrode material.

[0027] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the carbon coating layer may be derived from coal tar or petroleum residue.

[0028] In the negative electrode material for a secondary battery according to one embodiment of the present invention, the D1 particle size of the negative electrode material is 1.2 to 3.5 ㎛, and D 10 / D1 can be 1.3 to 3.

[0029] In a negative electrode material for a secondary battery according to one embodiment of the present invention, D of the negative electrode material 90 The particle size is 8.5 to 14 ㎛, D 99 / D 90 can be between 1.1 and 2.5.

[0030] The secondary battery according to the present invention may include any one of the negative electrode materials for secondary batteries.

[0031] The negative electrode material for a silicon-based secondary battery according to the present invention has excellent initial charge / discharge efficiency, cycle characteristics, and life characteristics, and can have excellent high-output characteristics.

[0032] In addition, the negative electrode material for a silicon-based secondary battery according to the present invention has uniform electrochemical properties at any location within a single negative electrode material particle, and further, can have uniform electrochemical properties between different negative electrode material particles.

[0033] Figure 1 is a Raman spectroscopy analysis graph of a negative electrode material for a secondary battery according to one embodiment of the present invention.

[0034] Figure 2 is a graph showing the silicon Raman signal of a negative electrode material for a secondary battery according to one embodiment of the present invention.

[0035] Figure 3 is an FTIR analysis graph of a negative electrode material for a secondary battery according to one embodiment of the present invention.

[0036] Figure 4 is a graph showing the rate efficiency of a battery including a negative electrode material for a secondary battery according to one embodiment of the present invention.

[0037] Hereinafter, the present invention will be described in detail with reference to the attached drawings. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed 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, and the drawings presented below may be shown exaggeratedly to clarify the spirit of the present invention. In this case, unless otherwise defined, the technical and scientific terms used have the meaning commonly understood by those of ordinary skill in the art to which this invention pertains, and the description of well-known functions and structures that may unnecessarily obscure the gist of the present invention in the following description and the attached drawings are omitted.

[0038] Additionally, the singular forms used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly dictates otherwise.

[0039] 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.

[0040] In this specification and the appended claims, terms such as “include” or “have” mean that a feature or component described in the specification is present, and unless specifically limited, do not preclude the possibility that one or more other features or components may be added.

[0041] In this specification and the appended claims, when a part such as a film (layer), region, component, etc. is said to be on or above another part, it includes not only the case where it is directly above and in contact with another part, but also the case where another film (layer), another region, another component, etc. is interposed therebetween.

[0042] In this specification, particle size distribution refers to a measurement using the laser diffraction method. To analyze the particle size distribution, the target powder is dispersed in a dispersion medium, then introduced into a laser diffraction particle size measuring device. When the particles pass through the laser beam, the difference in diffraction pattern according to particle size is measured to calculate the particle size distribution.

[0043] The present applicant discovered that in a silicon-based anode material having a carbon coating layer formed on a silicon-based oxide, the mechanical and electrochemical properties of the anode material are significantly affected by Raman and infrared spectral characteristics. Based on this discovery, the applicant further researched and found that in an anode material having a carbon coating layer coated on a silicon-based core, when the Raman and infrared spectral spectra of the carbon coating layer satisfy specific aspects, the electrochemical properties of the anode material are significantly improved, thereby completing the present invention.

[0044] The negative electrode material according to the present invention based on the above-described discovery has a silicon-based core and a carbon coating layer that satisfy special aspects in Raman spectroscopy and infrared spectroscopy, and can exhibit electrochemical properties that cannot be obtained from conventional silicon-based negative electrode materials.

[0045] In the present invention, the negative electrode material for a secondary battery includes, but is not necessarily limited to, a negative electrode material for a lithium secondary battery. The negative electrode material of the present invention may also be utilized as an active material in secondary batteries such as sodium batteries, aluminum batteries, magnesium batteries, calcium batteries, and zinc batteries.

[0046] The negative electrode material according to the present invention includes a silicon-based core and a carbon coating layer positioned on the surface of the silicon-based core, and the ratio of intensities of the D band peak and the G band peak in the Raman spectroscopy spectrum of the carbon coating layer (I D / I G ) is 1.3 or less, and the ratio of the full width half maximum (FWHM) of the D band and G band peaks (F D / F G ) is 1.3 or more, and the infrared spectrum is 1400 to 1625±5 cm -1 The area (A1) of the peak of the first wave number (n1) of the range is 1625±5 to 2100 cm -1 It is characterized by being smaller than the area (A2) of the peak of the second wave number (n2) of the range.

[0047] Specifically, the D band peak intensity (I) in the Raman spectroscopy spectrum of the carbon coating layer D ) is 1320 to 1380 cm -1 The maximum intensity of the peak located in the waveband region, and the ratio of the intensity of the G band peak (I G ) in the same Raman spectroscopy analysis, 1560 to 1630 cm -1 It refers to the maximum intensity of a peak located in the wavenumber region. Although not necessarily limited to this, experimentally, the Raman spectroscopy spectrum may be measured using a Raman spectroscopy analyzer (WITec GmbH) at room temperature and in an air atmosphere using a laser with a wavelength of 532 nm.

[0048] Infrared spectroscopy can be obtained by Fourier transform infrared spectroscopy (FTIR). In the infrared spectroscopy, the first and second wave numbers each represent the range of wave numbers, and the point where the first and second wave numbers are separated is 1625±5 cm. -1 can be defined as the position where peaks are separated from each other in the vicinity of . For example, 1625 cm -1 1625 cm with one or more peaks in a smaller wavenumber range. -1 The peak converges at 1625 cm -1 1625 cm, with one or more peaks in a larger wavenumber range. -1 When the peak converges at 1625 cm -1 can be defined as the position that separates the peak of the first wave and the peak of the second wave.

[0049] Peak areas can be derived by direct integration, for example, 1400 to 1625 cm -1 The area (A1) of the peak of the first wave number (n1) of the range is 1400 cm -1 Spectral position at 1625 cm -1 The spectral position in the range of 1625 to 2100 cm can be defined as the area of ​​the region enclosed by the curve of the infrared spectral spectrum and the straight line. Similarly, -1 The area (A2) of the peak of the second wave number (n2) of the range is 1625 cm -1 Location in and 2100 cm -1 The position in can be defined as a straight line drawn through the infrared spectral curve and the area of ​​the region closed by the straight line.

[0050] There is no particular limitation as long as the area (A1) of the peak of the first wave number (n1) in the infrared spectroscopy spectrum is smaller than the area (A2) of the peak of the second wave number (n2). In non-limiting terms, the ratio (A2 / A1) of the area (A1) of the peak of the first wave number (n1) to the area (A2) of the peak of the second wave number (n2) may be 2 or more or 3 or more, and specifically may be 2.5 to 10, and more specifically may be 3 to 7.

[0051] In one embodiment, the ratio of the intensities of the D band peak and the G band peak in the Raman spectroscopy spectrum (I D / I G ) is the ratio of the full width at half maximum of the intensity of the D band peak and the G band peak (F D / F G ) may be smaller than that. Specifically, the ratio of the above intensities (I D / I G ) may be 1.2 or less, 1.1 or less, or 1.0 or less, and may be, but is not limited to, 0.5 or more. Specifically, it may be 0.5 to 1.2, 0.6 to 1.2, or 0.7 to 1.1. In addition, the ratio of the full width at half maximum (F D / F G) may be 1.4 or greater, 1.5 or greater, or 1.7 or greater, and may be, but is not limited to, 2.5 or less. Specifically, it may be 1.3 to 2.5, 1.4 to 2.5, 1.5 to 2.5, 1.7 to 2.5, or 1.9 to 2.5.

[0052] In one embodiment, the ratio of the Raman intensities in the Raman spectral spectrum (I D / I G ) is 0.5 to 1.2 and the ratio of the full width at half maximum (F D / F G ) is 1.3 to 2.5, the ratio of Raman intensities (I D / I G ) is 0.6 to 1.1 and the ratio of the full width at half maximum (F D / F G ) is 1.7 to 2.5, or the ratio of the Raman intensities (I D / I G ) is 0.7 to 1.1 and the ratio of the full width at half maximum (F D / F G ) may satisfy 1.9 to 2.5 simultaneously.

[0053] In this way, the silicon-based secondary battery anode material satisfying the above-described aspects in the Raman spectroscopy spectrum and the infrared spectroscopy spectrum can have a silicon-based core and a carbon coating layer that are more organically bonded than silicon-based secondary battery materials known in the art, and can also have superior carbon film quality. Accordingly, the silicon-based secondary battery anode material according to the present invention can have significantly improved electrochemical characteristics, and thus can exhibit excellent initial charge / discharge efficiency, cycle characteristics, and lifespan characteristics.

[0054] In one embodiment, the full width at half maximum (F) of the G band peak G ) is 60 cm -1 Ideal, 80 cm -1 Ideal, 90 cm -1 Ideal, 95 cm -1 Ideal, 100 cm -1 It can be any height, but is not limited to 130 cm -1It may be less than 60 to 130 cm. More specifically, it may be less than 60 to 130 cm. -1 , 80 to 120 cm -1 , 95 to 110 cm -1 It could be.

[0055] In one embodiment, the specific surface area of ​​the negative electrode material according to the present invention is 10 m 2 / g or less, specifically 5 m 2 / g or less, more specifically 0.5 to 5 m 2 / g may be. Accordingly, the negative electrode material for a secondary battery according to the present invention can suppress irreversible side reactions and reduce the adsorption of electrode binder, thereby having improved electrical characteristics.

[0056] The silicon-based core may contain silicon components in an elemental silicon state and silicon components in an oxide state, and the silicon component in an oxide state may mean the oxide state of silicon alone. Silicon oxide is SiO x (x is a real number greater than 0.1 and less than 2, specifically a real number greater than 0.3 and less than 1.8), and may include a first silicon oxide and a second silicon oxide having different x.

[0057] In one embodiment, the silicon-based core may include a silicon oxide matrix and silicon nanocrystals dispersed and embedded in the silicon oxide matrix. However, the present invention does not exclude an embodiment in which the silicon-based core includes only a silicon oxide matrix without substantially including silicon nanocrystals.

[0058] In one embodiment, the silicon-based core may comprise 1 to 70 wt %, 2 to 60 wt %, 5 to 50 wt %, or 10 to 50 wt % of silicon nanocrystals relative to the total weight of the silicon-based core, with the remainder comprising a silicon oxide matrix.

[0059] The above silicon oxide matrix may refer to a solid medium in which silicon nanocrystals are dispersed and incorporated, and may refer to a material that forms a continuum compared to the silicon nanocrystals that are dispersed in the negative electrode material. In the present specification, the matrix may refer to a material excluding silicon (Si) nanocrystals in the negative electrode material.

[0060] For example, silicon oxide contained in a silicon oxide matrix is ​​SiO y (y is a real number from 0.5 to 2, specifically a real number from 1.2 to 2) can be satisfied, and the SiO x SiO than x defined by y y defined as can have a larger value.

[0061] The silicon oxide matrix may be crystalline, amorphous, or a composite phase in which crystalline and amorphous phases are mixed. Specifically, the matrix may be crystalline or a composite phase in which crystalline and amorphous phases are mixed. In addition, the silicon included in the silicon oxide matrix is ​​Si 1+ , Si 2+ , Si 3+ and Si 4+ It may include a silicon of a singer corresponding to one or more combinations selected from the group consisting of .

[0062] The silicon nanocrystals may have a size (diameter) that is typically defined as a nanocrystal. In practice, they may have a diameter of less than or equal to 100 nm, a diameter of less than or equal to 50 nm, a diameter of less than or equal to 20 nm, a diameter of less than or equal to 15 nm, and may refer to crystals having a diameter of, for example, 1 to 20 nm, 1 to 15 nm, or 1 to 10 nm. The size of the silicon nanocrystals can be calculated by substituting the full width at half maximum of the Si (111) crystal plane measured by X-ray diffraction into the Scherrer equation.

[0063] The above carbon coating layer refers to a carbon film coated on the surface of a silicon core, which can protect the silicon core and suppress volume change of silicon of the silicon core, and can impart excellent conductivity and electrochemical properties despite having properties close to amorphous.

[0064] In one embodiment, the carbon coating layer may be an amorphous carbon layer. The amorphous carbon layer can stably wrap the surface of the core and prevent volume changes in the silicon.

[0065] In one embodiment, the carbon coating layer may be included in an amount of 0.5 to 8 wt%, specifically 0.5 to 6 wt%, of the total weight of the negative electrode material.

[0066] The thickness of the carbon coating layer is not particularly limited, but the average thickness of the carbon coating layer may be 1 to 200 nm, 1 to 150 nm, 1 to 100 nm, 2 to 50 nm, 3 to 30 nm, or 5 to 15 nm. Experimentally, the thickness of the carbon coating layer may be obtained by randomly measuring the thickness of the carbon coating layer at 10 or more locations, or practically 10 to 20 locations, using images obtained through a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), etc., and taking the average value. In the above range, the surface of the core can be stably wrapped while minimizing the electrical resistance component.

[0067] In one embodiment, the carbon coating layer may include a plurality of carbon nanoparticles. The carbon nanoparticles may be positioned at least partially in one or more regions selected from the interior and surface of the carbon coating layer.

[0068] Specifically, the carbon coating layer may be composed of a dispersed phase and a continuous phase. Within the carbon coating layer, a plurality of carbon nanoparticles may form a dispersed phase, and the dispersed phase may be physically bonded to form a continuous phase composed of carbon. Although the dispersed phase and the continuous phase are both composed of carbon, they may be distinguished as different phases within the carbon coating layer. For example, when observed through a scanning electron microscope (SEM), the dispersed phase may be visually identified in an image obtained from a fracture surface analysis of the negative electrode material.

[0069] Carbon nanoparticles may be primary particles of carbon, or secondary particles that are aggregates of primary particles, and the carbon coating layer may be provided with primary particles and secondary particles alone or in a mixture of primary particles and secondary particles.

[0070] Specifically, the carbon nanoparticles may be in a state where they are embedded in the carbon coating layer and in contact with the core, in a state where some of them are protruding from the surface of the carbon coating layer and in a state where some of them are embedded in the carbon coating layer and the remaining part is protruding from the surface of the carbon coating layer, or in a state where they are bound to the surface of the carbon coating layer.

[0071] In this way, a carbon coating layer containing carbon nanoparticles can improve the electrical conductivity of the externally exposed surface and suppress side reactions with the electrolyte. Furthermore, the inter-particle resistance (contact resistance) of the negative electrode material can be reduced, and stable and smooth electrical contact between the negative electrode material particles can be maintained.

[0072] The above carbon nanoparticles may be spherical or elliptical, but are not limited to a specific shape, and specifically may be spherical bead-shaped. The average particle diameter of the carbon nanoparticles is not particularly limited, but may be 2 nm to 1 μm, specifically 5 to 0.5 μm, and more specifically 5 to 200 nm. Such carbon nanoparticles are relatively coarse compared to the thickness of the carbon coating layer, and thus can provide stable contact between the negative electrode materials even when the volume of the negative electrode material changes due to silicon. At this time, the ratio of the area occupied by the carbon nanoparticles among the surface of the particle-shaped negative electrode material may be 30% or more, specifically 50% or more, and more specifically 70% or more and less than 100%. Experimentally, the ratio of the area occupied by carbon nanoparticles can be obtained by calculating the total surface area by using an image obtained through a transmission electron microscope (TEM) or a scanning electron microscope (SEM), assuming that the surface is formed by completely covering the core with a virtual film having the same thickness as the carbon coating layer without carbon nanoparticles, and then measuring the area occupied by carbon nanoparticles in the film (virtual film).

[0073] Preferably, the carbon coating layer may be derived from a liquid carbon precursor. The liquid carbon precursor may refer to a carbon precursor that is liquid at room temperature, for example, 25° C., and may be a polycyclic aromatic compound having an average molecular weight of 100 to 2,000 Da, specifically 100 to 1,000 Da, as measured by MALDI-TOF.

[0074] The above carbon precursor may be a compound having a polycyclic aromatic structure with three or more aromatic rings. Specifically, it may be a polycyclic aromatic structure composed of three to ten aromatic rings, but is not limited thereto.

[0075] As a non-limiting example, the liquid carbon precursor may contain sulfur. The sulfur-containing liquid carbon precursor can induce sulfur doping into the carbon coating layer during the carbonization process, thereby enabling the formation of a carbon coating layer with enhanced conductivity due to sulfur. Examples of the sulfur-containing liquid carbon precursor include coal tar or petroleum residues, and more specifically, coal tar.

[0076] In one embodiment, the negative electrode material for a secondary battery according to the present invention can satisfy the following equation 1 based on a silicon Raman signal.

[0077] (Formula 1)

[0078] 1 > WN(Si) / WN(ref)

[0079] In Equation 1, WN(ref) is the center wavenumber of the Raman peak of bulk single crystal silicon, and WN(Si) is the center wavenumber of the Raman peak of silicon nanocrystals contained in the cathode material.

[0080] Experimentally, the Raman spectrum of silicon contained in the cathode material was obtained at room temperature (20 to 25°C), atmospheric pressure, with an excitation laser wavelength of 532 nm, a laser power of 0.5 mW, and a spectrometer resolution of 1 cm. -1 , it may be measured under the conditions of 1 g of cathode material and 15 s of detector exposure time.

[0081] In Equation 1, the ratio of the Raman peak center wavenumber of the silicon nanocrystals contained in the cathode material to the Raman peak center wavenumber of the bulk single crystal silicon is a parameter indicating the type and magnitude of the stress (residual stress) remaining in the silicon nanoparticles dispersed and embedded in the matrix.

[0082] In Equation 1, the term "bulk single-crystal silicon" should be interpreted to mean silicon having a size that substantially exhibits the properties of bulk single-crystal silicon. To provide a clear comparison standard and ensure ease of purchase, bulk single-crystal silicon may refer to a single-crystal silicon wafer having a thickness on the sub-mm order, specifically, a thickness of 0.4 to 0.7 mm.

[0083] In Equation 1, the fact that WN(Si) / WN(ref) is less than 1 means that the center wavenumber of the Raman peak of the silicon nanocrystals contained in the cathode material is shifted to a shorter wavenumber compared to bulk single crystal silicon, and means that the silicon nanocrystals have residual tensile stress.

[0084] In Equation 1, the Raman peak of silicon in bulk single crystal silicon and silicon nanocrystals, respectively, is 450 to 540 cm in the Raman spectrum of silicon. -1 Area, 480 to 530 cm -1 , 500 to 525 cm -1 Area, or 510 to 520 cm -1 It can mean a Raman peak located in the region. The central wavenumber of the peak, that is, the wavenumber corresponding to the center of the peak, can mean the wavenumber having the maximum intensity value at the peak. At this time, if two or more Raman peaks exist in the Raman Shift region described above, the peak with the highest intensity can correspond to the Raman peak of silicon in Equation 1, and if two or more Raman peaks overlap each other to form a twin peak shape, the wavenumber having the maximum intensity value in the twin peak with the higher intensity can correspond to the central wavenumber of the peak.

[0085] The full width at half maximum of the Raman peak of the silicon nanocrystals contained in the above-described negative electrode material may be larger than the full width at half maximum of the Raman peak of bulk single crystal silicon. The larger full width at half maximum value compared to bulk single crystal silicon may be due to the structure in which the silicon contained in the negative electrode material is dispersed and incorporated into the matrix in the form of ultrafine particles.

[0086] Specifically, the half-maximum width of the Raman peak of the silicon nanocrystals contained in the cathode material is 4 to 25 cm. -1 , 5 to 22 cm -1 , 6 to 20 cm -1 , 6 to 18 cm -1 or 8 to 15 cm -1 It may be. At this time, the Raman peak of the silicon nanocrystals contained in the cathode material may mean a single peak rather than a deconvoluted peak.

[0087] As described above, the silicon core is SiO x (x is a real number greater than 0.1 and less than 2, specifically greater than 0.3 and less than 1.8) refers to silicon oxide, which may be undoped with metal. In general, a technology for doping a silicon oxide-based negative electrode material with a metal such as lithium or magnesium is known to suppress the generation of lithium oxide, which causes initial irreversibility during charge and discharge of a secondary battery. Metal-doped silicon oxide-based negative electrode materials can improve the initial charge and discharge efficiency by converting lithium oxide, which does not participate in the electrochemical reaction, into an irreversible phase, and can improve the cycle characteristics by reducing the size of silicon nanocrystals, and can make the silicon nanocrystals have generally uniform characteristics as the matrix is ​​converted to metal-silicon oxide. For example, the size, crystallinity, and stress characteristics of silicon nanocrystals can be more uniform and significantly improved in a metal-doped silicon oxide matrix than in a silicon oxide matrix.

[0088] In contrast, the negative electrode material for a secondary battery according to the present invention has a technical advantage in that the size of silicon nanocrystals can be controlled to be very small even though the material is not doped with metal, and the crystal and stress characteristics can be maintained at a level equivalent to that of a metal-doped silicon oxide matrix. As described above, the full width at half maximum of the Raman peak of the silicon nanocrystals contained in the negative electrode material exhibits a low value, so not only can the size of the silicon nanocrystals be controlled to be very small, but the stress applied to the silicon nanocrystals can also be uniformly controlled.

[0089] In one embodiment, the silicon-based core is randomly arranged at 10 different locations such that the difference between the maximum and minimum values ​​of the central wavenumber WN(Si) of the Raman peak of the silicon nanocrystal is 10 cm. -1 Below, 8 cm -1 Below, 6 cm -1 Below and 1 cm -1 It can be 1 to 10 cm in diameter. -1 , 2 to 8 cm -1 , or 2 to 6 cm -1 It could be.

[0090] At this time, the standard deviation of the maximum and minimum values ​​of the central wave number WN(Si) of the Raman peak of the silicon nanocrystal is 5 cm. -1 Below, 3 cm -1 Below, 2 cm -1 Below, 1.5 cm -1 Below and 0.1 cm -1 It can be abnormal, 0.1 to 5 cm -1 , 0.1 to 3 cm -1 , 0.1 to 2 cm -1 , or 0.1 to 1.5 cm -1 It could be.

[0091] The small difference between the maximum and minimum values ​​indicates that the stress applied to the silicon nanocrystals contained in the cathode material is nearly constant and uniform. Furthermore, it implies that the magnitude of the residual tensile stress in all silicon nanocrystals dispersed in the silicon oxide matrix is ​​virtually identical.

[0092] In addition, as defined in the above equation 1, it means that most of the silicon nanocrystals dispersed in the silicon oxide matrix have residual tensile stress, and further, it means that the magnitude of the residual tensile stress in most of the silicon nanocrystals dispersed in the silicon oxide matrix is ​​substantially almost the same. As a specific example, the ratio of the residual tensile stress measured in the silicon nanocrystals present at different locations may be 80% or more, 90% or more, or 95% or more, and may be 90% to 100%, 95% to 100%, or 98% to 100%.

[0093] The negative electrode material for a secondary battery according to the present invention has uniform electrochemical characteristics at any location within a single negative electrode particle, and further, has uniform electrochemical characteristics between different negative electrode particles, thereby enabling very excellent rate characteristics. Specifically, the negative electrode material for a secondary battery according to the present invention may have an average capacity retention rate of 88% or more, 90% or more, specifically 93% or more, and more specifically 97% or more within 3 to 30 charge and discharge cycles.

[0094] In addition, the initial charge / discharge efficiency of the negative electrode material according to the present invention may be 75% or more, and the initial discharge capacity may be 1700 mAh / g or more.

[0095] The negative electrode material for a secondary battery according to the present invention is provided in the form of particles. Specifically, the negative electrode material may be one or more particles selected from primary particles and secondary particles. That is, the negative electrode material may be primary particles, secondary particles, or particles in which primary particles and secondary particles are mixed. A primary particle may refer to a single particle, and a secondary particle may refer to an aggregate formed by coagulating two or more particles.

[0096] Average particle diameter of cathode material (D 50 ) is not particularly limited. The average particle diameter is the volume-based median diameter (D) calculated by laser diffraction method. 50 ) can mean volume criterion D 50 It means the particle diameter at the point where the cumulative volume % is 50% in the cumulative distribution curve (cumulative distribution curve) accumulated in order of particle diameter. Experimentally, D 50 The cumulative distribution curve including can be obtained by a conventional particle size analyzer using a laser diffraction method or a dynamic light scattering method.

[0097] D of cathode material 50 The value may be from 1 μm to 20 μm, specifically from 1 μm to 10 μm, more specifically from 2 to 10 μm, and even more specifically from 3 to 8 μm.

[0098] At this time, the D1 particle size of the negative electrode material is 1.2 to 3.5 ㎛, specifically 1.5 to 3 ㎛, and more specifically, 1.7 to 2.8 ㎛, and D 10 / D1 can be 1.3 to 3, 1.3 to 2, 1.3 to 1.7, specifically 1.35 to 1.6.

[0099] The above D1 diameter and D 10 As the value of / D1 satisfies the above conditions, the initial efficiency and output characteristics of the battery can be improved by improving the composite density of the electrode without causing excessive side reactions with the electrolyte.

[0100] Also, D of the negative electrode material 90 The particle size is 8.5 to 14 ㎛, specifically 9 to 13 ㎛, and D 99 / D 90 may be 1 to 2.5, specifically 1.1 to 2.3, and more specifically 1.1 to 2.1.

[0101] Above D 90 Entry and D 99 / D 90 As the value satisfies the above conditions, an appropriate balance can be achieved between the composite density of the electrode and the expansion of the electrode, thereby improving the output characteristics and life characteristics of the battery.

[0102] Average particle diameter of cathode material (D 50 ) as defined above, D1, D 10 , D 90 , D 99 refers to the particle size at points where the cumulative volume % is 1, 10, 90 and 99 volume %, respectively, on the cumulative distribution curve based on volume.

[0103] The negative electrode material as described above is a particle having a relatively uniform particle size distribution, and when forming a negative electrode composite layer, stable conductivity is secured while reducing the diffusion time of metal ions involved in charge and discharge, for example, lithium ions, thereby exhibiting improved and more stable charge and discharge cycle characteristics.

[0104] The negative electrode material for a secondary battery according to the present invention can be obtained through the steps of S1) manufacturing a silicon-based core and S2) forming a carbon coating layer.

[0105] S1) The silicon core manufacturing step is not particularly limited as long as it is a method for manufacturing silicon particles conventionally used as an active material, and is a commercialized silicon oxide, SiO. x(x is a real number greater than 0.1 and less than 2, specifically a real number greater than 0.3 and less than 1.8) can be obtained and used, or it can be manufactured by vaporizing Si and SiO2.

[0106] For a specific example, step S1) comprises: a) a step of mixing metal silicon powder (Si) and silicon dioxide powder (SiO2) to obtain a mixed raw material; b) a step of molding the mixed raw material into pellets; c) a step of heating and vaporizing the pellets under vacuum conditions to obtain a gaseous silicon oxide gas; d) a step of condensing the gaseous silicon oxide gas on a heated collecting plate to obtain silicon oxide (SiO x ) may include a step of obtaining a silicon-based core.

[0107] The above step a) may be performed at a molar ratio of Si:SiO2 of 6:1 to 7, specifically 6:2 to 6, and more specifically 6:3 to 5. The mixing may be performed by homogeneously mixing Si and SiO2 after they are introduced into a powder mixer.

[0108] The above step b) is a step of pelletizing the mixed raw material, and can be performed, for example, by molding the mixed raw material in a pellet mold. The above step c) is a step of vaporizing the pellet, and the temperature during heating and vaporization can be performed at 1,000 to 1,700°C, specifically 1,200 to 1,600°C, and more specifically 1,300 to 1,500°C, and can be performed under reduced pressure conditions. The above step d) is a step of condensing the gaseous silicon oxide gas to obtain particulate silicon oxide, and can be performed by maintaining the temperature of the condensing plate at 300 to 1,200°C, specifically 400 to 1,000°C.

[0109] In one embodiment, step S1) may further include a step of crushing the obtained silicon core after step d). The crushing may be performed using a crushing device such as a jet mill, and after crushing at a high rotational speed, the crushed silicon core may be recovered through a cyclone. Through crushing, the center particle diameter (D) of the silicon core may be reduced. 50 ) and distribution by appropriately controlling the center particle diameter (D) of the cathode material. 50 ) and distribution can be easily controlled.

[0110] The above step S2) is a step of forming a carbon coating layer on the silicon-based core, which is a silicon oxide manufactured in step S1).

[0111] Step S2) comprises the steps of: f) mixing a liquid carbon precursor into the silicon oxide obtained in step S1) to obtain a mixture; and g) carbonizing the mixture.

[0112] In the above step f), the mixing ratio of the silicon oxide and the liquid carbon precursor is not particularly limited. For example, the mixing ratio of silicon oxide:carbon precursor may be mixed at a weight ratio of 20 to 0.5:1, specifically 15 to 1:1. The liquid carbon precursor to be introduced may advantageously be a sulfur-containing carbon precursor, and may be coal tar or petroleum residue in a liquid state at room temperature as described above. In the above step f), the mixing time may be appropriately adjusted in proportion to the amount of the mixture to be mixed, and may be mixed at a linear speed of 5 to 40 m / s, specifically 10 to 30 m / s, but is not limited thereto.

[0113] The above step g) is a step of carbonizing the mixture, and is not particularly limited as long as it is a method capable of carbonizing a carbon precursor to form a carbon coating layer on silicon oxide. Specifically, the carbonization may be performed at a temperature of 700 to 1,500°C, specifically 800 to 1,200°C, for 0.5 to 3 hours, specifically 0.6 to 2 hours.

[0114] The carbonization in the above step g) may be performed as a multi-stage carbonization step. Specifically, the carbonization may be performed in n carbonization steps (n is a natural number greater than 1). As a non-limiting example, when n is 3, the carbonization may include a step of first carbonization under the first temperature condition after the temperature is raised to reach a first temperature condition, a step of second carbonization under the second temperature condition after reaching a second temperature condition, and a step of third carbonization under the third temperature condition after reaching a third temperature condition. The first to third temperatures may all have different values, or the two temperatures may have the same value, but the three temperatures do not all have the same value. The negative electrode material manufactured in the above step g) may be naturally cooled from room temperature (20±5°C) to room temperature.

[0115] In one embodiment, after step g), a step of crushing the obtained negative electrode material may be further included.

[0116] The above-mentioned disintegration can be performed through various mechanical means, and the thickness and properties of the carbon coating layer can be uniformly controlled by applying a mechanical shear force in a device such as a pin mill crusher, and at the same time the center particle diameter (D) of the negative electrode material 50 ) and distribution can be easily controlled. The above disintegration step may not be performed when the content of carbon precursor is low compared to silicon oxide. However, when the content of carbon precursor is high compared to silicon oxide, performing the disintegration step further may be preferable because the cycle characteristics and life characteristics can be improved.

[0117] The present invention provides a negative electrode containing the above-described negative electrode material. The negative electrode may be an negative electrode for a secondary battery, specifically, an negative electrode for a lithium secondary battery. The negative electrode may include a current collector and a negative electrode composite layer positioned on at least one surface of the negative electrode current collector and containing the above-described negative electrode material.

[0118] According to one embodiment, the negative electrode composite layer including the negative electrode material may further include a carbon-based negative electrode active material. The carbon-based negative electrode active material may be at least one selected from artificial graphite, natural graphite, and hard carbon, but the present invention is not limited thereto.

[0119] For example, the weight ratio of the negative electrode material: carbon-based negative electrode active material included in the negative electrode composite layer according to one embodiment may be 1:99 to 99:1, specifically 5:95 to 95:5, more specifically 5:95 to 50:50, and even more specifically 5:95 to 20:80.

[0120] The above-described negative electrode for a secondary battery can be manufactured by coating and drying a slurry containing the negative electrode material, binder, conductive material, and solvent according to the above-described embodiments on a negative electrode current collector. Methods for manufacturing negative electrodes are known in the art, and known methods for manufacturing negative electrodes can be used without limitation.

[0121] The above conductive material may be, for example, a carbon-based conductive material such as carbon black, ultrafine graphite particles, acetylene black, graphene, carbon nanotubes, or carbon nanofibers, but is not limited thereto.

[0122] The above binder may include one or a combination of two or more selected from the group consisting of styrene-butadiene rubber (SBR), fluorine rubber, ethylene-propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, silane rubber, polyacrylic acid (PAA), a copolymer including an acrylic acid structural unit, polyvinyl alcohol (PVA), and a copolymer including a vinyl alcohol structural unit. Specifically, the binder may be a copolymer including polyacrylic acid (PAA) or an acrylic acid structural unit.

[0123] The present invention provides a secondary battery including the above-described negative electrode.

[0124] A secondary battery according to one embodiment may be a lithium secondary battery, and the lithium secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0125] The above positive electrode may include a positive electrode current collector and a positive electrode composite layer positioned on at least one surface of the positive electrode current collector.

[0126] The cathode composite layer includes a cathode material as a main component and may include, for example, a Li compound including one or more metals selected from the group consisting of Ni, Co, Mn, Al, Cr, Fe, Mg, Sr, V, La, and Ce and one or more non-metallic elements selected from the group consisting of O, F, S, and P. The cathode composite layer may include cathode material particles having a size of 0.01 μm to 200 μm and may be appropriately selected depending on the required characteristics of the battery.

[0127] The above-described positive electrode can be manufactured by coating and drying a slurry containing the positive electrode material, binder, conductive material, and solvent as described above on a positive electrode current collector. Methods for manufacturing electrodes are known in the art, and known methods for manufacturing electrodes can be used without limitation.

[0128] The above conductive material may include, but is not limited to, carbon-based conductive materials such as carbon black, ultrafine graphite particles, acetylene black, graphene, carbon nanotubes, or carbon nanofibers, or nano-metal particle paste.

[0129] The positive electrode current collector serves to support the positive electrode composite layer. Examples of positive electrode current collectors that can be used include, but are not limited to, aluminum foil, nickel foil, or a combination thereof.

[0130] The separator above separates the positive and negative electrodes and provides a passage for lithium ions, and any separator commonly used in lithium secondary batteries can be used. That is, a separator having high lithium mobility for ion movement of the electrolyte and excellent electrolyte moisture retention capacity can be used. The separator may be selected from, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a non-woven fabric or a microporous membrane. Meanwhile, when a solid electrolyte is used as the electrolyte, a conventional separator may not be included, and the solid electrolyte may be replaced with the separator and serve as both.

[0131] A lithium secondary battery may be first assembled into an electrode assembly comprising a positive electrode, a negative electrode, and a separator positioned between the positive electrode. The electrode assembly is wound or folded and housed in a battery case. The battery case may have a cylindrical, square, pouch-shaped, coin-shaped, or other shape. An electrolyte may be injected into the battery case and sealed to complete the lithium secondary battery.

[0132] As the electrolyte injected into the lithium secondary battery, an electrolyte that conducts active ions involved in charging and discharging of the battery, for example, lithium ions, may be selected, such as a non-aqueous electrolyte or a solid electrolyte.

[0133] The above non-aqueous electrolyte may include a lithium salt and an organic solvent. The lithium salt may include, for example, anions F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It can be any one selected from the group consisting of .

[0134] As the organic solvent, any one or a combination of two or more solvents commonly used in electrolytes for lithium secondary batteries can be used without limitation, and for example, any one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran can be used.

[0135] The above solid electrolyte may be, for example, a gel polymer electrolyte in which an electrolyte is impregnated into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N.

[0136] Meanwhile, the secondary battery according to one embodiment may be a half battery.

[0137] A half-cell may be a cell comprising: a negative electrode including a negative electrode current collector and a negative electrode material positioned on at least one surface of the current collector according to one embodiment; a counter electrode being a metallic lithium foil; a separator interposed between the negative electrode and the counter electrode; and an electrolyte. For example, the electrolyte may be a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1 in which LiPF6 is dissolved at a concentration of 1 M.

[0138] The negative electrode material according to the present invention is not limited to lithium secondary batteries, and can also be used as an active material in secondary batteries such as sodium batteries, aluminum batteries, magnesium batteries, calcium batteries, and zinc batteries.

[0139] The present invention also provides a power supply comprising a secondary battery including a cathode material according to one specific embodiment. Examples of the power supply include, but are not limited to, a battery module, a battery pack, or an ESS (Energy Storage System).

[0140] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and the present invention is not limited thereto, and the present invention is defined solely by the scope of the claims set forth below.

[0141] <Example 1>

[0142] 1) Silicon oxide (SiO x ) manufacturing

[0143] Powdered Si and SiO2 were added to a powder mixer at a molar ratio of 6.5:3.5, mixed homogeneously to produce a mixed raw material, and then the mixed raw material was molded through a mold to produce pellets.

[0144] 26 kg of pellets were placed in a crucible in a vacuum chamber of 0.1 torr or less, heated to 1,400°C to vaporize, and then condensed onto a collecting plate maintained at 900°C (±25°C) to form solid silicon oxide (SiO x ) was obtained. The obtained solid silicon oxide was coarsely pulverized through a pulverizer and then finely pulverized through an air jet mill to obtain a center particle size (D 50 ) Silicon oxide (SiO) in fine powder form with a diameter of 5.6 ㎛ x ) was obtained.

[0145] 2) Formation of carbon coating layer

[0146] Coal tar (specific gravity = 1.1-1.3 g / cc, carbonization yield of approximately 25% when carbonized at 900℃) was used as a liquid carbon precursor containing sulfur, which is a liquid at room temperature and is produced during the dry distillation of raw coal in a steel mill.

[0147] The fine powder silicon oxide obtained in 1) and coal tar were added to a planetary mixer maintained at 37℃ (±3℃) in a weight ratio of 10:1 and mixed at a linear speed of 0.6 m / s for 1 hour to obtain a mixture. After that, 5 kg of the mixture was placed in a graphite crucible, and after reaching 900℃ in a nitrogen atmosphere, 900℃ was maintained for 40 minutes. Then, the inside of the crucible was heated again to 930℃ and maintained at 930℃ for 10 minutes. After naturally cooling the inside of the crucible to 900℃, 900℃ was maintained for 10 minutes. After that, the inside of the crucible was naturally cooled to room temperature (20±5℃) to manufacture a particle-shaped negative electrode material. The specific surface area (SSA, m) of the negative electrode material 2 / g) was measured through BET analysis by nitrogen gas adsorption using a surface area measuring device (BELSORP-mino II), and the average particle diameter was measured using a laser diffraction particle diameter measuring device (Microtrac S3500), and the results are shown in Table 1 below.

[0148] <Example 2>

[0149] In the above Example 1, a negative electrode material was manufactured in the same manner as in Example 1 except that the temperature reached in the graphite crucible was changed. Specifically, after the mixture was introduced into the graphite crucible and reached 950°C, it was maintained at 950°C for 40 minutes, then the inside of the crucible was heated again to reach 980°C, and then 980°C was maintained for 10 minutes, and finally, the inside of the crucible was naturally cooled to 950°C and then 950°C was maintained for 10 minutes.

[0150] <Example 3>

[0151] In the above Example 1, a negative electrode material was manufactured in the same manner as in Example 1 except that the temperature reached by the graphite crucible was changed. Specifically, the graphite crucible containing the mixture was heated to 1000°C, maintained at 1000°C for 40 minutes, then the inside of the crucible was heated again to 1030°C, maintained at 1030°C for 10 minutes, and finally, the inside of the crucible was naturally cooled to 1000°C, and then maintained at 1000°C for 10 minutes.

[0152] <Example 4>

[0153] In the above Example 1, the silicon oxide in the form of fine powder obtained in 1) : coal tar was added at a weight ratio of 5:1, and the manufactured particle-shaped negative electrode material was added to an ACM (Automatic Classification Mill) to obtain an average particle diameter (D 50 ) was crushed to 5.8 μm, and the negative electrode material was manufactured in the same manner as in Example 1.

[0154] <Example 5>

[0155] In the above Example 1, the negative electrode material was manufactured in the same manner as in Example 1, except that the temperature reached by the graphite crucible was kept constant. Specifically, the graphite crucible containing the mixture was allowed to reach 900°C and then maintained for 1 hour.

[0156] <Comparative Example 1>

[0157] In the above Example 1, in step 2), silicon oxide (SiO x ) A cathode material was manufactured in the same manner as in Example 1, except that 50 g of powder was charged into a thermal CVD device maintained at 900°C, and methane and argon were continuously supplied into the device at 1 L / min each to perform carbon deposition for 2 hours.

[0158] Comparative Example 2

[0159] In the above Example 1, in step 2), silicon oxide (SiO x) A cathode material was manufactured in the same manner as in Example 1, except that 50 g of powder was charged into a thermal CVD device maintained at 950°C, methane and argon were continuously supplied into the device at 1 L / min each, and carbon deposition was performed for 2 hours.

[0160] <Comparative Example 3>

[0161] In the above Example 4, a negative electrode material was manufactured in the same manner as in Example 4, except that pulverization was not performed.

[0162]

[0163] Referring to Table 1 above, the negative electrode material according to the present invention has a relatively specific surface area of ​​2 m 2 It was confirmed that the value was very small compared to Comparative Examples 1 and 2, less than / g, and in particular, it was confirmed that the values ​​of Examples 1 to 3 were less than 1.5, which is smaller than the minimum value of Comparative Examples, 1.7.

[0164] [Measurement of cathode material properties]

[0165] 1. Raman spectroscopy

[0166] Using μ-Raman (equipment name: XperRam C, Nanobase, Korea) under the following analysis conditions, Raman spectra of carbon coating layers were measured at 10 different random locations of the negative electrode materials according to Example 4 and Comparative Examples 1 and 2, and silicon Raman signals of the negative electrode materials according to Example 1, Example 4, and Comparative Example 1 were also measured at 10 different random locations of the negative electrode materials.

[0167] Analysis conditions: Laser wavelength 532 nm, laser power 0.5 mW, spectrometer resolution 1 cm -1 , 1 g of powdered cathode material, detector exposure time 15 sec.

[0168] In Fig. 1, the ratio of the intensities of the D band peak and the G band peak of the carbon coating layer is shown. D / I G, and Table 2 below shows comparative examples 1 to 2 and example 1 I D / I G The maximum, minimum, average and deviation values ​​of the full width at half maximum (FWHM) of the D-band peak and the G-band peak are recorded, and the average value of the full width at half maximum of the G-band excluding the maximum and minimum values ​​(F G ) was described.

[0169] In addition, the silicon Raman signals of the negative electrode materials of Example 1, Example 4 and Comparative Example 1 are shown in FIG. 2, and the maximum, minimum, average and standard deviation of the center wavenumber of the Raman peak of the silicon nanocrystals in the Raman signals according to Example 1, Example 4 and Comparative Example 1 are described in Table 3 below.

[0170]

[0171] Center wavenumber of Raman peak of silicon nanocrystals (cm) -1 )Maximum Minimum Mean DeviationExample 1514.0510.8512.61.1Example 2513.8509.9511.51.1Example 3514.5510.3512.91.2Example 4515.5511.8513.81.3Example 5514.1508.5511.81.5Comparative Example 1515.7505.4510.53.5Comparative Example 2514.4505.3509.73.3Comparative Example 3514.2510.6512.41.1

[0172] Referring to Figure 1 and Table 2, the cathode material according to one embodiment has an average of I D / I G It was confirmed that the value was around 1 and that the average full width at half maximum (FWHM) was 1.3 or higher. Referring to Fig. 2 and Table 3, it was confirmed that the negative electrode material according to one embodiment satisfied that the difference between the maximum and minimum values ​​of the central wavenumber of the Raman peak of the silicon nanocrystal was less than 3. On the other hand, it was confirmed that the negative electrode material according to the comparative example was generally heterogeneous with the difference between the maximum and minimum values ​​of the central wavenumber of the Raman peak of the silicon nanocrystal being 3 or higher.

[0173] 2. Infrared spectroscopy

[0174] The results of FTIR measurements according to Example 4 and Comparative Examples 1 to 3 are shown in FIG. 3 using Fourier transform infrared spectroscopy (FTIR). The area of ​​the peak of the first wave number (A1) and the area of ​​the peak of the second wave number (A2) were measured, and their ratio (A2 / A1) is shown in Table 4 below.

[0175] Classification FTIR 1st wavenumber area (A1), 2nd wavenumber (A2) area and A2 / A1A1A2A2 / A1Example 12.2569.9534.412Example 21.8419.4175.115Example 30.8715.7256.573Example 41.5796.6314.199Example 51.3389.2746.931Comparative Example 10.7320.1950.266Comparative Example 20.4203.0137.174Comparative Example 32.6018.0033.077- 1st wavenumber: 1400 to 1625 cm -1 - Second wave: 1625 to 2100 cm -1

[0176] Referring to FIG. 3 and Table 4, the examples confirmed that the area of ​​A2 is larger than the area of ​​A1, and the ratio of the area of ​​the peak of the first wave number (A1) to the area of ​​the peak of the second wave number (A2) is 2 or more when (A2 / A1). <Battery manufacturing>

[0177] The final anode powder was used as an active material, and the active material:conductive material (carbon black):CMC (Carboxymethyl cellulose):SBR (Styrene Butadiene Rubber) was mixed in a weight ratio of 8:1:0.5:0.5, applied to a 17 ㎛ thick copper foil, and dried at 90℃ for 40 minutes. After drying, it was stamped into a diameter of 14 mm, and a 16 mm diameter metallic lithium was used as a counter electrode, and an 18 mm diameter separator was sandwiched between them to fill the electrolyte to manufacture a CR2032 coin-type half-cell. The electrolyte was prepared by dissolving 1 M LiPF6 in a solvent containing 1:1 volume ratio of EC (Ethylene carbonate) / DEC (Diethyl carbonate), and 3 wt% FEC (fluoroethylene carbonate) was used as an additive.

[0178] Battery Performance Evaluation

[0179] The Martian process was performed by charging (lithiating) the manufactured battery to 0.005 V with a constant current of 0.1 C, charging at a constant voltage of 0.005 V until it reached 0.01 C, discharging (delithiating) to 1.5 V with a constant current of 0.1 C (first martian step), charging (lithiating) again to 0.005 V with a constant current of 0.1 C, charging at a constant voltage of 0.005 V until it reached 0.01 C, and discharging (delithiating) to 1.0 V with a constant current of 0.1 C (second martian step).

[0180] The half-cells on which the formation process was performed were charged (lithiated) to 0.005 V with a constant current of 0.5 C, charged at a constant voltage of 0.005 V until 0.05 C was reached, and then discharged (de-lithiated) to 1.0 V with a constant current of 0.5 C to evaluate the charge-discharge cycle characteristics, and the discharge capacity retention rate according to the charge-discharge cycle (a total of 30 times) is shown in Fig. 4. In addition, the discharge capacity of the first charge-discharge cycle is listed as the initial discharge capacity in Table 1, and the initial efficiency based on the charge-discharge in the first formation step and the capacity retention rate of (C25 / C3)*100 (C25 is the discharge capacity in the 25th charge-discharge cycle, and C3 is the discharge capacity in the 3rd charge-discharge cycle) are also listed in Table 5.

[0181] Electrochemical characteristics of the battery Initial capacity (mAh / g) Initial efficiency (ICE, %) Capacity retention rate (%) Example 1 170 275.9 97.3 Example 2 173 076.199.6 Example 3 170 676.394.5 Example 4 173 076.799.9 Example 5 171 075.191.9 Comparative example 1 164 374.789.3 Comparative example 2 165 174.284.9 Comparative example 3 167 874.188.2

[0182] Referring to Table 5 and Fig. 4, it was confirmed that the negative electrode material according to the example had very excellent electrochemical properties compared to the comparative example, such as an initial discharge capacity of 1700 mAh / g or more, an initial efficiency of 75% or more, and a charge / discharge capacity retention rate (rate characteristic) of 91% or more.

[0183] 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.

Claims

1. Comprising a silicon core and a carbon coating layer positioned on the surface of the silicon core, The ratio of the intensities of the D band peak and the G band peak in the Raman spectrum of the carbon coating layer (I D / I G ) is 1.3 or less, and the ratio of the full width at half maximum (FWHM) of the D band and G band peaks (F D / F G ) is 1.3 or higher, Infrared spectrum from 1400 to 1625±5 cm -1 The peak area (A1) of the first wave number (n1) of the range is 1625±5 to 2100 cm -1 A negative electrode material for a secondary battery, the area (A2) of the peak of the second wave number (n2) of the range being smaller.

2. In paragraph 1, A negative electrode material for a secondary battery, wherein the ratio (A2 / A1) of the area (A1) of the peak of the first wave number (n1) and the area (A2) of the peak of the second wave number (n2) is 2 or more.

3. In paragraph 1, A negative electrode material for a secondary battery, wherein the silicon-based core comprises a silicon oxide matrix and silicon nanocrystals dispersed and embedded in the silicon oxide matrix.

4. In paragraph 1, The ratio of the above intensities (I D / I G ) is the ratio of the full width at half maximum (F D / F G ) A negative electrode material for secondary batteries.

5. In paragraph 1, The full width at half maximum (F) of the above G band peak G ) is 60 cm -1 Ideal, negative electrode material for secondary batteries.

6. In paragraph 3, A negative electrode material for a secondary battery satisfying Equation 1 based on a silicon Raman signal. (Formula 1) 1 > WN(Si) / WN(ref) (In Equation 1, WN(ref) is the central wavenumber of the Raman peak of bulk single crystal silicon, and WN(Si) is the central wavenumber of the Raman peak of the silicon nanocrystals contained in the cathode material.) 7. In paragraph 6, The above silicon core has a difference between the maximum and minimum values ​​of the central wavenumber WN(Si) of the Raman peak of the silicon nanocrystal at 10 different random locations of 5 cm. -1 Below, negative electrode material for secondary batteries.

8. In paragraph 1, The specific surface area of ​​the above cathode material is 10 m 2 / g or less, negative electrode material for secondary batteries.

9. In paragraph 1, The ratio of the above half-width (F D / F G ) is a negative electrode material for secondary batteries with a value of 1.7 or higher.

10. In paragraph 1, A negative electrode material for a secondary battery, wherein the carbon coating layer comprises a plurality of carbon nanoparticles.

11. In paragraph 10, A negative electrode material for a secondary battery, wherein the carbon coating layer comprises a dispersed phase including a plurality of carbon nanoparticles and a continuous phase physically bonding the dispersed phase and made of carbon.

12. In paragraph 1, A negative electrode material for a secondary battery, wherein the carbon coating layer is included in an amount of 0.5 to 8 wt% of the total weight of the negative electrode material.

13. In paragraph 1, A negative electrode material for a secondary battery, wherein the carbon coating layer is derived from coal tar or petroleum residue.

14. In paragraph 1, The D1 particle size of the above cathode material is 1.2 to 3.5 ㎛, and D 10 / D1 is 1.3 to 3, negative electrode material for secondary batteries.

15. In paragraph 1, D of the above cathode material 90 The particle size is 8.5 to 14 ㎛, D 99 / D 90 A negative electrode material for secondary batteries, having a value of 1.1 to 2.

5.

16. A secondary battery comprising a negative electrode material for a secondary battery according to any one of claims 1 to 15.

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