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

Abstract

The present invention relates to a negative electrode material for a secondary battery and a secondary battery including the same. The negative electrode material for a secondary battery according to the present invention comprises a silicon-based core and a carbon coating layer located on the surface of the silicon-based core, and can have high power output, excellent cycle characteristics, and uniform electrochemical characteristics.

Description

Technology Field

[0001] The present invention relates to a negative electrode material for a lithium secondary battery and a secondary battery including the same. Background Technology

[0002] In various industrial sectors such as electronics, electric vehicles (EVs), energy storage systems (ESS), and aerospace / drones, there is a continuing demand for rechargeable batteries that not only feature high energy and power density but also have a long lifespan.

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

[0004] 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 to realize high energy density secondary batteries. Among these materials, silicon-based anode materials are receiving the most attention due to their high theoretical capacity, low reaction potential with lithium, and eco-friendly nature.

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

[0006] To address the problems associated with such silicon-based cathode materials, a cathode material is disclosed in which a carbon coating layer is formed on the surface of a silicon oxide cathode material via Chemical Vapor Deposition (CVD). However, the above cathode material requires the use of expensive hydrocarbon gases and has low economic feasibility due to the low conversion efficiency to carbon at high temperatures. Furthermore, it is difficult to uniformly coat the surface of silicon oxide particles with the above cathode material during mass production.

[0007] Furthermore, since the CVD coating process has a structure in which hydrocarbon gas is continuously supplied from the outside and heat is supplied through the outer wall of the reactor, a temperature gradient inevitably occurs inside the reactor. Moreover, because the hydrocarbon decomposition reaction is an endothermic reaction, the temperature gradient becomes larger as the silicon oxide particles move further away from the heat source, thereby reducing the uniformity of the deposited carbon coating layer.

[0008] The non-uniformity of such carbon coating layers leads to non-uniformity in the electrochemical properties of the anode material, which has an undesirable impact on initial charge / discharge efficiency, cycle characteristics, and lifespan characteristics. Therefore, there is still a need to develop silicon-based secondary battery anode materials that possess excellent initial charge / discharge efficiency, cycle characteristics, and lifespan characteristics, as well as high power characteristics. Prior art literature

[0009] : Korean Registered Patent Publication No. 10-2342309 : Korean Registered Patent Publication No. 10-2236365 The problem to be solved

[0010] According to one embodiment of the present invention, 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 may be provided.

[0011] According to one embodiment of the present invention, a silicon-based secondary battery negative electrode material having not only uniform electrochemical properties between negative electrode particles but also uniform electrochemical properties within the negative electrode particles, and a lithium secondary battery including the same can be provided.

[0012] The problems of the present invention are not limited to those described above. A person skilled in the art to which the present invention pertains will have no difficulty understanding additional problems of the present invention from the overall contents of this specification. means of solving the problem

[0013] A negative electrode material for a secondary battery according to one embodiment of the present invention comprises a matrix comprising silicon oxide, a silicon-based core comprising silicon nanocrystals dispersed and embedded in the matrix, and a carbon coating layer located on the surface of the silicon-based core.

[0014] It satisfies the following Equations 1 and 2.

[0015] (Equation 1)

[0016] WN(Si) MAX - WN(Si) MIN ≤ 7 cm -1

[0017] (In Equation 1, WN(Si) is 460 cm -1 to 560 cm -1 It is the wavenumber corresponding to the maximum scattering intensity in the Raman spectroscopic spectrum of the silicon-based core located in the wavenumber region, and WN(Si) MAX wa WN(Si) MIN ) are the maximum and minimum values ​​of WN(Si) calculated from each of the above Raman spectroscopic spectra measured at 10 different locations.

[0018] (Equation 2)

[0019] W AVE ≤ 17 cm -1

[0020] (In Equation 2, W AVE560 cm⁻¹ in each of the Raman spectroscopic spectra measured at the 10 different locations mentioned above. -1 It is the average value of the width of the Raman spectroscopic spectrum corresponding to 75% of the maximum scattering intensity value based on the Raman scattering intensity of the wavenumber.

[0021] In a negative electrode material for a secondary battery according to one embodiment, the ratio of the intensity of the D band peak and the G band peak (I) in the Raman spectroscopic spectrum of the carbon coating layer D / I G ) is 1.3 or less, and the ratio of the above strength (I D / I G ) is the ratio of the full width at half maximum (FWHM) of the D band peak to the G band peak (F D / F G It can be smaller than ).

[0022] In a negative electrode material for a secondary battery according to one embodiment, the ratio of the full width at half maximum (FWHM) of the D band and G band peaks (F D / F G ) can be 1.4 or higher.

[0023] In a negative electrode material for a secondary battery according to one embodiment, the full width at half maximum (F) of the G band peak G ) is 60 cm -1 It could be more than that.

[0024] In a negative electrode material for a secondary battery according to one embodiment, the W AVE The standard deviation is 5 cm -1 It may be less than.

[0025] In a negative electrode material for a secondary battery according to one embodiment, the negative electrode material for a secondary battery may further satisfy the following Equation 3.

[0026] (Equation 3)

[0027] 1 > WN(Si) AVE / WN(ref)

[0028] (In Equation 3, WN(Si) AVE is the average value of the above WN(Si), and WN(ref) is 460 cm-1 to 560 cm -1 It is the wavenumber corresponding to the maximum scattering intensity in the Raman spectroscopic spectrum of bulk single-crystal silicon located in the wavenumber region.

[0029] In a negative electrode material for a secondary battery according to one embodiment, the specific surface area of ​​the negative electrode material is 10 m² 2 It may be less than / g.

[0030] In a negative electrode material for a secondary battery according to one embodiment, the carbon coating layer may include a plurality of carbon nanoparticles.

[0031] In a negative electrode material for a secondary battery according to one embodiment, the carbon coating layer may comprise a dispersed phase comprising a plurality of carbon nanoparticles and a continuous phase composed of carbon that physically binds the dispersed phase.

[0032] In a negative electrode material for a secondary battery according to one embodiment, the carbon coating layer may be included in an amount of 0.5 to 8 weight percent of the total weight of the negative electrode material.

[0033] In a negative electrode material for a secondary battery according to one embodiment, the carbon coating layer may be derived from coal tar or petroleum residue oil.

[0034] In a negative electrode material for a secondary battery according to one embodiment, the D1 particle size of the negative electrode material is 1.2 to 5 μm, and D 10 / D1 can be 1 to 3.

[0035] In a negative electrode material for a secondary battery according to one embodiment, D of the negative electrode material 90 The particle size is 8.5 to 14 μm, and D 99 / D 90 It can be 1.1 to 2.5.

[0036] A secondary battery according to one embodiment of the present invention may include the negative electrode material for a secondary battery described above. Effects of the invention

[0037] A negative electrode material for a silicon-based secondary battery according to one embodiment of the present invention has a high initial capacity and can have excellent initial charge / discharge efficiency and lifespan characteristics.

[0038] A negative electrode material for a silicon-based secondary battery according to one embodiment of the present invention has uniform electrochemical characteristics at any position within a single negative electrode particle, and furthermore, can have uniform electrochemical characteristics between negative electrode particles. Brief explanation of the drawing

[0039] FIG. 1 is a graph showing the silicon-based core Raman spectroscopic spectrum of a negative electrode material for a secondary battery according to an embodiment of the present invention, FIG. 2 is a graph showing the Raman spectroscopic spectrum of a carbon coating layer of a negative electrode material for a secondary battery according to one embodiment of the present invention, Figure 3 is a graph showing the Raman spectroscopic spectrum of a carbon coating layer of a comparative example of the present invention. Specific details for implementing the invention

[0040] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0041] In addition, embodiments of the present invention are provided to more fully explain the present invention to those with average knowledge in the relevant technical field.

[0042] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0043] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0044] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0045] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0046] In this specification, terms such as 'top', 'upper', 'upper surface', 'lower', 'lower surface', 'lower surface', and 'side surface' are based on the drawings and may actually vary depending on the direction in which the elements or components are arranged.

[0047] Additionally, throughout the specification, when it is said that one part is 'connected' to another part, this includes not only cases where they are 'directly connected,' but also cases where they are 'indirectly connected' with other elements in between.

[0048] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0049] In this specification, the particle size distribution refers to that measured using the laser diffraction method. To analyze the particle size distribution, the powder to be measured is dispersed in a dispersion medium, then introduced into a laser diffraction particle size measuring device, and the particle size distribution is calculated by measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam.

[0050] The applicant discovered that in a silicon-based cathode material in which a carbon coating layer is formed on a silicon-based oxide, the mechanical and electrochemical properties of the cathode material are significantly affected by Raman spectroscopic characteristics. Based on this discovery, further research was conducted, and the present invention was completed by discovering that in a cathode material in which a carbon coating layer is coated on a silicon-based core, the electrochemical properties of the cathode material are significantly improved when a specific aspect is satisfied in the Raman spectroscopic spectrum of the silicon-based core.

[0051] In the present invention, the negative electrode material for a secondary battery includes a negative electrode material for a lithium secondary battery, but is not necessarily limited thereto. The negative electrode material of the present invention may also be used as an active material for secondary batteries such as sodium batteries, aluminum batteries, magnesium batteries, calcium batteries, and zinc batteries.

[0052] The cathode material according to the present invention comprises a silicon-based core comprising a matrix including silicon oxide and silicon nanocrystals dispersed and embedded in the matrix; and a carbon coating layer located on the surface of the silicon-based core, and is characterized by satisfying the following formulas 1 and 2.

[0053] (Equation 1)

[0054] WN(Si) MAX - WN(Si) MIN ≤ 7 cm -1

[0055] In Equation 1, WN(Si) is 460 cm -1 to 560 cm -1 It is the wavenumber corresponding to the maximum scattering intensity in the Raman spectroscopic spectrum of the silicon-based core located in the wavenumber region, and WN(Si) MAX wa WN(Si) MIN These are the maximum and minimum values ​​of WN(Si) calculated from each of the above Raman spectroscopic spectra measured at 10 different locations.

[0056] (Equation 2)

[0057] W AVE ≤ 17 cm -1

[0058] In Equation 2, W AVE 560 cm⁻¹ in each of the Raman spectroscopic spectra measured at the 10 different locations mentioned above. -1 It is the average value of the width of the Raman spectroscopic spectrum corresponding to 75% of the maximum scattering intensity value based on the Raman scattering intensity of the wavenumber.

[0059] Experimentally, the Raman spectroscopic spectrum of the silicon-based core was obtained at room temperature (20 to 25°C) under 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 have been measured under conditions of 1 g of cathode material and a detector exposure time of 15 s.

[0060] Specifically, in the Raman spectroscopic spectrum, the silicon-based core is 460 cm⁻¹ -1 to 560 cm -1 It has a distinct peak due to Raman scattering in the wavenumber region. At this point, 560 cm⁻¹ -1 It can have a minimum Raman scattering intensity (I0) close to the baseline at the wavenumber of , also 560 cm -1 Less than, 490 cm -1 to 550 cm -1 , 490 cm -1 to 530 cm -1 or 500 cm -1 to 525 cm -1 Maximum scattering intensity (I) in the wavenumber region max Having ), at this time, I max The wavenumber representing is WN(Si) of Equation 1 above.

[0061] The Raman spectroscopic spectrum of the above silicon-based core is measured independently at 10 different locations, and the maximum value among the 10 WN(Si) values ​​calculated from each Raman spectroscopic spectrum is WN(Si) of Equation 1 above MAX It means that, among the 10 WN(Si), the minimum value is WN(Si) of Equation 1 above MIN It means.

[0062] In one embodiment, the standard deviation of the average value of WN(Si), excluding the maximum and minimum values ​​among the WN(Si), is 3 cm -1 Less than 2.5 cm -1 Less than 2 cm -1 Less than, or 1.5 cm -1 It may be less than or equal to 0.1 to 3 cm -1 , 0.5 to 2.5 cm -1 , 0.7 to 2 cm -1 or 0.9 to 1.5 cm -1 It could be.

[0063] As described above, the silicon-based core has a peak in the wavenumber region. 560 cm -1Raman scattering intensity at the wavenumber, i.e., maximum scattering intensity (I) based on the minimum scattering intensity (I0). max -I0) may represent the height of the above peak. In this case, the average value of the width at the 75% point of the peak height of each of the 10 peaks is W in Equation 2 above. AVE is. I0 and I max represents the height of the peak calculated from the baseline, and the average value of Equation 2 above may represent the average value excluding the maximum and minimum values ​​from the peak widths measured at 10 different random locations.

[0064] In the above Raman spectroscopic spectrum, a peak may appear as a single peak, but it may also exhibit a convoluted pattern of multiple peaks. When multiple peaks appear convoluted, the peak can be obtained through deconvolution, and the peak width can be calculated from the separated peaks.

[0065] As such, the silicon-based negative electrode material for a secondary battery satisfying Equations 1 and 2 in the Raman spectroscopic spectra measured at 10 different locations of the silicon-based core has a silicon-based core and a carbon coating layer that are very organically bonded compared to conventional silicon-based negative electrode materials known in the art, so that it can effectively disperse stress caused by volume changes of silicon while maintaining excellent ionic conductivity. With such a silicon-based negative electrode material for a secondary battery, capacity, lifespan, and charge / discharge performance can be improved overall.

[0066] In one embodiment, in Formula 1 above, WN(Si) MAX - WN(Si) MIN 6.5 cm -1 Less than 6 cm -1 Below, 5.5 cm -1 Less than 5 cm -1 Below, 4.5 cm -1 Less than or equal to 0.1 cm -1It may be more than 0.1 to 7 cm -1 , 0.5 to 6.5 cm -1 , 1 to 6 cm -1 , 1 to 5 cm -1 or 2 to 4.5 cm -1 It could be.

[0067] At this time, in the above Equation 1, WN(Si) MAX - WN(Si) MIN The standard deviation of is 5 cm -1 Less than 3 cm -1 Less than 2 cm -1 Less than 1.5 cm -1 Less than or equal to 0.1 cm -1 It may be more than 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.

[0068] WN(Si) in Equation 1 above MAX - WN(Si) MIN A small value of may mean that the stress applied to the silicon nanocrystals contained in the cathode material is nearly constant and uniform. Furthermore, it may mean that the magnitude of residual stress in all silicon nanocrystals dispersed in the silicon oxide matrix is ​​substantially nearly the same.

[0069] In one embodiment, W of Formula 2 AVE is 16.5 cm -1 Below, 16 cm -1 Below, 15.5 cm -1 Less than or equal to 1 cm -1 It may be more than 1 to 17 cm -1 , 5 to 16.5 cm -1 , 8 to 16 cm -1 , or 10 to 15.5 cm -1 It could be.

[0070] At this time, in the above Equation 1, W AVEThe standard deviation of is 5 cm -1 Less than 4 cm -1 Less than 3 cm -1 Less than 2 cm -1 Less than or equal to 0.1 cm -1 It may be more than 0.1 to 5 cm -1 , 0.3 to 4 cm -1 , 0.5 to 3 cm -1 , or 0.7 to 2 cm -1 It could be.

[0071] A silicon-based core may include silicon components in the elemental silicon state and silicon components in the oxide state, and the silicon component in the oxide state may refer to an oxide state of silicon alone. Silicon oxide is SiO x (x can satisfy 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.

[0072] In one embodiment, the silicon-based core may comprise a silicon oxide matrix and silicon nanocrystals dispersed and embedded on the silicon oxide matrix. However, the present invention does not exclude an embodiment in which the silicon-based core comprises only a silicon oxide matrix and substantially does not comprise silicon nanocrystals.

[0073] In one embodiment, the silicon-based core may contain silicon nanocrystals in an amount of 1 to 70 weight%, 2 to 60 weight%, 5 to 50 weight%, or 10 to 50 weight% based on the total weight of the silicon-based core, and may contain the remainder being a silicon oxide matrix.

[0074] The above silicon oxide matrix may refer to a solid medium in which silicon nanocrystals are dispersed and embedded, and may refer to a material that forms a continuum relative to the silicon nanocrystals, which are the dispersed phase in the cathode material. In this specification, the matrix may refer to a material excluding silicon (Si) nanocrystals in the cathode material.

[0075] For example, the silicon oxide contained in the silicon oxide matrix is ​​SiO y (y can satisfy a real number less than 2, specifically a real number from 0.1 to 1.8, more specifically a real number from 0.1 to 1.5).

[0076] 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 silicone of a singer corresponding to one or more combinations selected from the group consisting of

[0077] Silicon nanocrystals may have a size (diameter) that is typically defined as nanocrystals. They may substantially have a diameter of 100 nm or less, 50 nm or less, 20 nm or less, or 15 nm or less, and may mean 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 (220) crystal planes measured by X-ray diffraction into the Scherrer equation.

[0078] The above carbon coating layer refers to a carbon film coated on the surface of a silicon-based core, which can protect the silicon-based core and suppress volume changes of the silicon in the silicon-based core, and can impart excellent conductivity and electrochemical properties despite having properties close to amorphous.

[0079] 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 to prevent volume change of silicon.

[0080] In one embodiment, the carbon coating layer may be included in an amount of 0.5 to 8 weight%, specifically 0.5 to 6 weight%, of the total weight of the cathode material.

[0081] 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 determined by measuring the thickness of the carbon coating layer at at least 10 random locations, substantially 10 to 20 locations, using images obtained through a transmission electron microscope (TEM), scanning transmission electron microscope (STEM), etc., and taking the average value. Within the above range, the surface of the core can be stably wrapped while minimizing the electrical resistance component.

[0082] In one embodiment, the carbon coating layer may include a plurality of carbon nanoparticles. At least a portion of the carbon nanoparticles may be located in one or more selected regions among the interior and surface of the carbon coating layer.

[0083] Specifically, the carbon coating layer may consist of a dispersed phase and a continuous phase. Within the carbon coating layer, a plurality of carbon nanoparticles may form a dispersed phase, and a continuous phase composed of carbon may be formed by physically binding the dispersed phase. Although the dispersed phase and the continuous phase are common in that they are composed of carbon, they can be distinguished as different phases within the carbon coating layer. For example, when observed through a scanning electron microscope (SEM), the dispersed phase can be visually identified in an image obtained from the fracture surface analysis of the cathode material.

[0084] Carbon nanoparticles may be primary particles of carbon or secondary particles that are aggregates of primary particles, and the primary particles and secondary particles may exist individually or be provided in a mixture of primary particles and secondary particles in the carbon coating layer.

[0085] Specifically, the carbon nanoparticles may be in a state in which they are embedded within the carbon coating layer while in contact with the core, in a state in which a portion of them protrudes from the surface of the carbon coating layer while in contact with the core, in a state in which a portion is embedded within the carbon coating layer and the remaining portion protrudes from the surface of the carbon coating layer, or in a state in which they are bound to the surface of the carbon coating layer.

[0086] In this way, the carbon coating layer containing carbon nanoparticles can improve the electrical conductivity of the externally exposed surface and suppress adverse reactions with the electrolyte. Additionally, the resistance component (contact resistance) between cathode particles can be lowered, and stable and smooth electrical contact between cathode particles can be maintained.

[0087] The carbon nanoparticles may be spherical or elliptical, but are not limited to a specific shape; specifically, they may be in the shape of spherical beads. The average particle size 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, so they can provide stable contact between the cathode materials even when the volume of the cathode material changes due to silicon. At this time, the ratio of the area occupied by the carbon nanoparticles on the surface of the particulate cathode 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 may be obtained by using images obtained through a transmission electron microscope (TEM) or a scanning electron microscope (SEM), assuming a surface formed in which the core is completely wrapped by a virtual film having the same thickness as the carbon coating layer without carbon nanoparticles, calculating the total surface area, and measuring the area occupied by carbon nanoparticles within the said film (virtual film).

[0088] 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.

[0089] 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 consisting of 3 to 10 aromatic rings, but is not limited thereto.

[0090] As a non-limiting example, the liquid carbon precursor may be coal tar or petroleum residual oil, and more specifically, the liquid carbon precursor may be liquid coal tar.

[0091] The above liquid coal tar may refer to coal tar that is liquid in itself at room temperature (25±5 ℃) and atmospheric pressure (1 atm) without the help of chemicals such as solvents or the application of external energy such as heat.

[0092] Specifically, the liquid coal tar may have a specific gravity of 1.1 to 1.3 g / cc, specifically 1.13 to 1.28 g / cc, more specifically 1.2 to 1.26 g / cc.

[0093] In addition, the liquid coal tar may have an initial boiling point (IBP) of 50 to 70°C, 55 to 70°C, 60 to 70°C, or 65 to 70°C. In this case, the IBP may be measured according to ASTM D86.

[0094] The liquid coal tar described above is advantageous not only because it can be uniformly coated on the surface of the core particles, but also because it can easily penetrate into the internal pores of the core particles.

[0095] In one embodiment, the ratio of the intensity of the D band peak and the G band peak in the Raman spectroscopic spectrum of the carbon coating layer (I D / I G ) is 1.3 or less, and the ratio of the above strength (I D / I G ) is the ratio of the full width at half maximum (FWHM) of the D band and G band peaks (F D / F G It can be smaller than ).

[0096] Specifically, the D band peak intensity (I in the Raman spectroscopic spectrum of the carbon coating layer D ) is 1310 to 1380 cm -1It is the maximum intensity of the peak located in the wavenumber region, and the intensity of the G band peak (I G ) in the same Raman spectroscopic analysis, 1560 to 1630 cm⁻¹ -1 It refers to the maximum intensity of a peak located in the wavenumber region. Although not necessarily limited to this, experimentally, the Raman spectroscopic spectrum may be measured using a Raman spectroscopic analyzer (WITec GmbH) at room temperature and in an atmospheric environment using a laser with a wavelength of 532 nm.

[0097] The above Full Width at Half Maximum (FWHM) is the width of the spectrum measured at half the height of each spectral peak (D band and G band) measured from the baseline, after peak deconvolution of the D band and G band with respect to the baseline of the Raman spectroscopic spectrum.

[0098] In one embodiment, the ratio of the intensity of the D band peak and the G band peak in the Raman spectroscopic spectrum (I D / I G ) is the ratio of the full width at half maximum intensity of the D-band peak to the G-band peak (F D / F G It may be smaller than ). Specifically, the ratio of the above strength (I D / I G ) may be less than 1.3, 1.25 or less, 1.2 or less, 1.15 or less, or 1.13 or less, and may be 0.5 or more without limitation. Specifically, it may be 0.5 or more but less than 1.3, 0.5 to 1.25, 0.6 to 1.2, or 0.7 to 1.15. In addition, the ratio of the full half-width (F) above D / F G ) may be 1.3 or more, 1.4 or more, 1.5 or more, or 1.7 or more, and may be 2.5 or less without limitation. Specifically, it may be 1.3 to 2.5, 1.4 to 2.5, 1.5 to 2.5, 1.6 to 2.3, or 1.7 to 2.1.

[0099] In one embodiment, the ratio of the Raman intensity (I) in the Raman spectroscopic spectrum D / I G ) is 0.5 to 1.25, and the ratio of the above full half-width (F D / F G ) is 1.3 to 2.5, and the ratio of Raman intensity (I D / I G ) is 0.6 to 1.2, and the ratio of the above full half-width (F D / F G ) is 1.5 to 2.1, or the ratio of the Raman intensities (I D / I G ) is 0.7 to 1.15, and the ratio of the above half-width (F D / F G ) may satisfy 1.7 to 2.1 simultaneously.

[0100] In one embodiment, the full width at half maximum (F) of the G band peak is G ) is 60 cm -1 Over 80 cm -1 Over 90 cm -1 Lee Sang, 95 cm -1 Over, 100 cm -1 It may be more than 130 cm, and is not limited to 130 cm -1 It may be less than or equal to 60 to 130 cm. More specifically, 60 to 130 cm -1 , 80 to 120 cm -1 , 95 to 110 cm -1 It could be.

[0101] In one embodiment, the specific surface area of ​​the cathode material according to the present invention is 10 m² 2 / g or less, specifically 5 m 2 / g or less, more specifically 0.5 to 5 m 2 / g. Accordingly, the negative electrode material for a secondary battery according to the present invention can suppress irreversible side reactions and reduce the adsorption of the electrode binder, thereby having improved electrical characteristics.

[0102] In one embodiment, the negative electrode material for a secondary battery according to the present invention can satisfy the following Equation 3.

[0103] (Equation 3)

[0104] 1 > WN(Si) AVE / WN(ref)

[0105] In Equation 3, WN(Si) AVE is the average value of the above WN(Si), and WN(ref) is 460 cm -1 to 560 cm -1 It is the wavenumber corresponding to the maximum scattering intensity in the Raman spectroscopic spectrum of bulk single-crystal silicon located in the wavenumber region.

[0106] WN(Si) in Equation 3 AVE / WN(ref) is a parameter that indicates the type and magnitude of residual stress remaining in silicon nanoparticles dispersed and embedded in a matrix.

[0107] In Equation 3, the term bulk single-crystal silicon should be interpreted to mean silicon of a size in which the physical properties of bulk single-crystal silicon are substantially exhibited. In terms of providing a clear comparison standard and ensuring ease of purchase, bulk single-crystal silicon may refer to a single-crystal silicon wafer having a thickness in the sub-mm order, specifically, as an example, a thickness of 0.4 to 0.7 mm.

[0108] In Equation 3, WN(Si) / WN(ref) being 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 that the silicon nanocrystals have residual tensile stress.

[0109] In Equation 3, the Raman peak of bulk single-crystal silicon is 460 cm⁻¹ in the Raman spectroscopic spectrum of the silicon-based core. -1 to 560 cm -1 Area, 480 to 530 cm -1 , 500 to 525 cm-1 Area, or 510 to 520 cm -1 It may refer to a peak located in the region. The center wavenumber of the peak may refer to the wavenumber corresponding to the maximum scattering intensity. In this case, if there are two or more Raman peaks in the Raman shift region described above, the peak with the greatest intensity may correspond to the peak of Equation 3, and if two or more Raman peaks overlap to form a bipeak shape, the wavenumber having the maximum intensity value in the bipeak with greater intensity may correspond to the center wavenumber of the peak.

[0110] The full width at half maximum (FWHM) of the Raman peak of the silicon nanocrystals contained in the aforementioned cathode material may be greater than the full width at half maximum (FWHM) of the Raman peak of bulk single-crystal silicon. The larger FWHM value compared to bulk single-crystal silicon may be due to the structure in which the silicon contained in the cathode material is dispersed and embedded in the matrix as ultrafine particles.

[0111] Specifically, the full width at half maximum 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 is possible. In this case, the Raman peak of the silicon nanocrystals contained in the cathode material may refer to a single peak rather than a deconvolved peak.

[0112] As described above, the silicon-based core is SiO xIt refers to silicon oxide expressed as (where 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 be undoped with metal. Generally, a technique is known for doping silicon oxide-based anode materials with metals such as lithium or magnesium to suppress the formation of lithium oxide, which causes initial irreversibility during the charging and discharging of secondary batteries. Metal-doped silicon oxide-based anode materials improve initial charge-discharge efficiency by converting lithium oxide, which does not participate in electrochemical reactions, into an irreversible phase. Furthermore, they improve cycle characteristics by reducing the size of silicon nanocrystals and allow silicon nanocrystals to have generally uniform characteristics as the matrix is ​​converted to a metal-silicon oxide. For example, the size, crystal, and stress characteristics of silicon nanocrystals can be more uniform and significantly improved in a metal-doped silicon oxide matrix compared to a silicon oxide matrix.

[0113] 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 despite not being doped with metal, and 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 (FWHM) of the Raman peaks of the silicon nanocrystals contained in the negative electrode material exhibits a low value, thereby not only allowing the size of the silicon nanocrystals to be controlled to be very small, but also allowing the stress applied to the silicon nanocrystals to be controlled uniformly.

[0114] In addition, the cathode material satisfying the above formulas 1 to 3 implies that most of the silicon nanocrystals dispersed in the silicon oxide matrix have residual tensile stress, and furthermore, implies that the magnitude of the residual tensile stress in most of the silicon nanocrystals dispersed in the silicon oxide matrix is ​​substantially nearly the same. As a specific example, the ratio of residual tensile stress measured in silicon nanocrystals 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%.

[0115] Such a negative electrode material for a secondary battery can have excellent rate capability characteristics as it has uniform electrochemical characteristics at any location within a single negative electrode particle and, furthermore, uniform electrochemical characteristics between different negative electrode particles. Specifically, the negative electrode material for a secondary battery according to the present invention may have an average capacity retention rate of 90% or more, 91% or more, 93% or more, specifically 95% or more, and more specifically 98% or more within 3 to 25 charge-discharge cycles.

[0116] In addition, the initial charge / discharge efficiency of the cathode material according to the present invention may be 70% or more, 73% or more, or 74% or more, and the initial discharge capacity may be 1300 mAh / g or more, 1400 mAh / g or more, 1500 mAh / g or more, 1600 mAh / g, or 1700 mAh / g.

[0117] The negative electrode material for a secondary battery according to the present invention is provided in a particulate form. Specifically, the negative electrode material may be a particle selected from one or more primary particles and secondary particles. That is, the negative electrode material may be primary particles, secondary particles, or particles mixed with primary particles and secondary particles. A primary particle may refer to a single particle, and a secondary particle may refer to an aggregate formed by the aggregation of two or more particles.

[0118] Average particle size of the cathode material (D 50 ) is not specifically limited. The average particle size is calculated by laser diffraction. Volume-based median diameter (D 50 It can mean ). Volume reference D 50 represents the particle diameter at the point where the cumulative volume % is 50 volume % in the cumulative distribution curve (cumulative distribution curve) accumulated in order of particle diameter. Experimentally, D 50 A cumulative distribution curve including can be obtained by a conventional particle size analyzer using a laser diffraction method or a dynamic light scattering method.

[0119] D of the cathode material 50 The value may be 1 μm to 20 μm, 2 μm to 18 μm, 3 to 15 μm, or 5 to 15 μm.

[0120] At this time, the D1 particle size of the cathode material is 1.2 to 5 μm, 1.5 to 4.5 μm, or 2 to 4 μm, and D 10 / D1 may be 1 to 3, 1.1 to 2.5, or 1.2 to 2.3.

[0121] The above D1 particle size 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 increasing the composite density of the electrode without causing excessive side reactions with the electrolyte.

[0122] In addition, D of the cathode material 90The particle size is 7 to 15 μm, specifically 8 to 11 μm, and D 99 / D 90 It may be 1 to 2.5, specifically 1.1 to 2.3, and more specifically 1.1 to 1.7.

[0123] The above D 90 Particle size and D 99 / D 90 As the value satisfies the above conditions, an appropriate balance is achieved between the composite density of the electrode and the expansion of the electrode, so that the output characteristics and lifespan characteristics of the battery can be improved.

[0124] Average particle size of the cathode material (D 50 Similar to the definition of ), the above D1, D 10 , D 90 , D 99 represents the particle size at points where the cumulative volume% on the cumulative distribution curve is 1, 10, 90, and 99 volume%, respectively, based on volume.

[0125] The cathode material described above is a particle having a relatively uniform particle size distribution, and while ensuring stable conductivity when forming the cathode composite layer, it can reduce the diffusion time of metal ions involved in charging and discharging, such as lithium ions, thereby exhibiting improved and more stable charge-discharge cycle characteristics.

[0126] The negative electrode material for a secondary battery according to the present invention can be obtained through S1) a step of manufacturing a silicon-based core and S2) a step of forming a carbon coating layer.

[0127] S1) The silicon-based core manufacturing step is not particularly limited as long as it is a conventional method for manufacturing silicon-based particles used as active materials, and SiO₂, which is a commercially produced silicon oxide. x (where 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 may be manufactured by vaporizing Si and SiO2.

[0128] To give a specific example, step S1) is a) a step of obtaining a mixed raw material by mixing metallic silicon powder (Si) and silicon dioxide powder (SiO2); 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 gaseous silicon oxide gas; d) a step of condensing the gaseous silicon oxide gas onto a heated collection plate to obtain silicon oxide (SiO2 x It may include the step of obtaining a silicon-based core.

[0129] In step a) above, the molar ratio of Si to SiO2 to be mixed may be 1:0.1 to 7, 1:0.5 to 5, 1:0.5 to 3, 1:0.7 to 2, or 1:0.9 to 1.5. The mixing may be performed by introducing Si and SiO2 into a powder mixer and then homogeneously mixing them.

[0130] Step b) above is a step of pelletizing the mixed raw materials, which can be performed, for example, by molding the mixed raw materials into a pellet mold. Step c) above is a step of vaporizing the pellets, which can be performed at a temperature of 1,000 to 1,700°C, specifically 1,200 to 1,600°C, more specifically 1,300 to 1,500°C during heating and vaporization, and can be performed under reduced pressure conditions. Step d) above is a step of obtaining particulate silicon oxide by condensing the gaseous silicon oxide gas, which can be performed by maintaining the temperature of the aggregation plate at 300 to 1,200°C, specifically 400 to 1,000°C.

[0131] In one embodiment, step S1) may further include a step of grinding the obtained silicon-based core after step d). The grinding may be performed using a grinding device such as a jet mill, and the ground silicon-based core may be recovered through a cyclone after grinding at a high rotational speed. Through grinding, the central particle size (D) of the silicon-based core 50 By appropriately controlling the ) and distribution, the central particle size (D) of the cathode material 50) and distribution can be easily controlled.

[0132] Step S2) above is a step of forming a carbon coating layer on a silicon-based core, which is a silicon oxide manufactured in Step S1).

[0133] Step S2) comprises f) a step of mixing a liquid carbon precursor with the silicon oxide obtained in Step S1) to obtain a mixture; and g) a step of carbonizing the mixture.

[0134] In step f) above, the mixing ratio of silicon oxide and liquid carbon precursor is not particularly limited. For example, the mixing ratio of silicon oxide to carbon precursor can be mixed in a weight ratio of 20 to 0.5 to 1, specifically 15 to 1 to 1. The liquid carbon precursor to be introduced can advantageously be a sulfur-containing carbon precursor, and as described above, it can be coal tar or petroleum residue oil in a liquid state at room temperature. In step f), the mixing time can be appropriately adjusted in proportion to the amount of mixture to be mixed, and the mixing can be performed at a linear speed of 5 to 40 m / s, specifically 10 to 30 m / s, but is not limited thereto.

[0135] Step g) above is a step of carbonizing the mixture, and is not particularly limited as long as it is a method capable of forming a carbon coating layer on silicon oxide by carbonizing a carbon precursor. Specifically, carbonization can 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.

[0136] The carbonization in step g) above may be performed as a multi-stage carbonization step. Specifically, the carbonization may be performed in n carbonization steps (where n is a natural number greater than 1). As a non-limiting example, when n is 3, the carbonization may be performed by increasing the temperature to reach a first temperature condition, followed by a first carbonization step under the first temperature condition, a second carbonization step under the second temperature condition, followed by a third carbonization step under the third temperature condition, followed by reaching a third temperature condition. The first to third temperatures may all have different values, or two of the temperatures may have the same value, but all three temperatures do not have the same value. The cathode material produced in step g) above may be naturally cooled from room temperature (20±5℃) to room temperature.

[0137] In one embodiment, after step g), a step of disintegrating the obtained cathode material may be further included.

[0138] The above disintegration can be performed through various mechanical means, and mechanical shear force is applied within a device such as a pin mill to uniformly control the thickness and characteristics of the carbon coating layer, and at the same time, the central particle size (D) of the cathode material 50 The distribution and distribution can be easily controlled. The above disintegration step may not need to be performed when the content of the carbon precursor relative to the silicon oxide is low. However, when the content of the carbon precursor relative to the silicon oxide is high, it may be desirable to perform the disintegration step further, as this can improve cycle characteristics and lifespan characteristics.

[0139] The present invention provides a cathode containing the cathode material described above. The cathode may be a cathode for a secondary battery, specifically a cathode for a lithium secondary battery. The cathode may include a current collector and a cathode composite layer containing the cathode material described above, located on at least one surface of the cathode current collector.

[0140] According to one embodiment, the cathode composite layer comprising a cathode material may further include a carbon-based cathode active material. The carbon-based cathode active material may be one or more selected from artificial graphite, natural graphite, and hard carbon, but the present invention is not limited thereto.

[0141] For example, the weight ratio of the cathode material to the carbon-based cathode active material according to one embodiment included in the cathode composite layer 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.

[0142] The negative electrode for the secondary battery described above may be manufactured by coating and drying a slurry comprising a negative electrode material, a binder, a conductive material, and a solvent according to the embodiments described above onto a negative electrode current collector. The method for manufacturing the negative electrode is known in the art, and any known method for manufacturing the negative electrode may be used without limitation.

[0143] The above conductive material is, for example, carbon black, ultrafine graphite particles, acetylene black, graphene, Carbon-based conductive materials such as carbon nanotubes or carbon nanofibers may be exemplified, but are not limited thereto.

[0144] The binder may comprise one or more combinations selected from the group consisting of styrene-butadiene rubber (SBR), fluororubber, ethylene-propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, silane rubber, polyacrylic acid (PAA), copolymers containing acrylic acid structural units, polyvinyl alcohol (PVA), and copolymers containing vinyl alcohol structural units. Specifically, the binder may be a copolymer containing polyacrylic acid (PAA) or acrylic acid structural units.

[0145] The present invention provides a secondary battery comprising the aforementioned negative electrode.

[0146] 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.

[0147] The above anode may include an anode current collector and an anode composite layer located on at least one surface of the current collector.

[0148] The anode composite layer includes an anode material as a major component and may include, for example, a Li compound comprising 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-metal elements selected from the group consisting of O, F, S, and P. The anode composite layer may include anode material particles having a size of 0.01 μm to 200 μm, and may be appropriately selected according to the required characteristics of the battery.

[0149] The above anode may be manufactured by coating and drying a slurry comprising an anode material, a binder, a conductive material, and a solvent as described above in the embodiments onto an anode current collector. The method of manufacturing the electrode is known in the art, and any known method of manufacturing the electrode may be used without limitation.

[0150] The above conductive material is, for example, carbon black, ultrafine graphite particles, acetylene black, graphene, Examples may include carbon-based conductive materials such as carbon nanotubes or carbon nanofibers, or nano metal particle pastes, but are not limited thereto.

[0151] The positive current collector serves to support the above-mentioned positive composite layer. As the positive current collector, for example, an aluminum foil, a nickel foil, or a combination thereof may be used, but is not limited thereto.

[0152] The above-mentioned separator separates the positive and negative electrodes and provides a pathway for the movement of lithium ions; any separator commonly used in lithium secondary batteries can be used. That is, a separator with high lithium mobility for the movement of electrolyte ions and excellent electrolyte wettability may 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 nonwoven fabric or a microporous membrane. Meanwhile, when a solid electrolyte is used as the above-mentioned electrolyte, a conventional separator may not be included, and the solid electrolyte may serve as the substitute for the separator.

[0153] A lithium secondary battery can first be assembled into an electrode assembly comprising a positive electrode, a negative electrode, and a separator located between the negative electrodes. The electrode assembly is wound or folded and accommodated in a battery container. The battery container may have a shape such as cylindrical, prismatic, pouch, or coin. An electrolyte is injected into the battery container and sealed to complete the lithium secondary battery.

[0154] As an electrolyte injected into the above lithium secondary battery, an electrolyte that conducts active ions involved in the charging and discharging of the battery, such as lithium ions, may be selected, such as a non-aqueous electrolyte or a solid electrolyte.

[0155] The above-mentioned non-aqueous electrolyte may include a lithium salt and an organic solvent. As for the lithium salt, for example, the anion is 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.

[0156] Organic solvents commonly used in electrolytes for lithium secondary batteries may be used without limitation, and for example, any one or a combination of two or more 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, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran may be used.

[0157] The above solid electrolyte may be, for example, a gel-type polymer electrolyte in which an electrolyte solution is impregnated into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N.

[0158] Meanwhile, a secondary battery according to one embodiment may be a half battery.

[0159] A half-cell may be a cell comprising: a negative electrode comprising a negative current collector and a negative electrode material according to one embodiment located on at least one surface of the current collector; a counter electrode which is a metal 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 ether methyl carbonate mixed in a volume ratio of 1:1 in which LiPF6 is dissolved at a concentration of 1 M.

[0160] 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 for secondary batteries such as sodium batteries, aluminum batteries, magnesium batteries, calcium batteries, and zinc batteries.

[0161] In addition, the present invention provides a power supply source equipped with a secondary battery comprising a negative electrode material according to one embodiment. Examples of the power supply source include a battery module, a battery pack, an Energy Storage System (ESS), etc., but are not limited thereto.

[0162] The present invention will be described in detail below through examples. However, it should be noted that the examples described below are intended merely to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0164] <Example 1>

[0165] 1) Silicon oxide (SiO x Manufacturing of )

[0166] Powdered Si and SiO2 were fed into a powder mixer in a 1:1 molar ratio and homogeneously mixed to produce a mixed raw material, and then the mixed raw material was molded through a mold to produce pellets.

[0167] 26 kg of pellets are placed in a crucible inside a vacuum chamber of 0.1 torr or less, heated to 1,400°C to vaporize them, and then condensed onto a collection plate maintained at 800°C (± 25°C) to form solid silicon oxide (SiO₂). x ) was obtained. The obtained solid silicon oxide was coarsely ground using a grinder, then finely ground using an air jet mill to obtain a central particle size (D 50 Silicon oxide (SiO₂) in the form of fine powder with a thickness of 5.6 μm x ) obtained.

[0168] 2) Formation of carbon coating layer

[0169] As a liquid carbon precursor, room-temperature liquid coal tar (specific gravity = 1.1-1.3 g / cc, carbonization yield of about 25% at 900℃) produced during the carbonization of raw coal in steel mills was used.

[0170] The finely powdered silicon oxide obtained in 1) and coal tar were introduced into a planetary mixer maintained at 37°C (±3°C) in a weight ratio of 10:1 and mixed at a linear velocity of 0.6 m / s for 1 hour to obtain a mixture. Subsequently, 5 kg of the mixture was loaded into a graphite crucible, and after reaching 900°C under a nitrogen atmosphere, the temperature was maintained at 900°C for 120 minutes. Then, the temperature inside the crucible was raised again to 930°C and maintained at 930°C for 30 minutes. Afterward, the inside of the crucible was naturally cooled to 900°C and maintained at 900°C for 30 minutes. Finally, the particulate cathode material was prepared by natural cooling to room temperature (20±5°C). The specific surface area (SSA, m²) of the cathode material 2 The specific surface area (g) was measured by BET analysis based on the amount of nitrogen gas adsorbed using a specific surface area measuring device (BELSORP-mino II), and the average particle size was measured using a laser diffraction particle size measuring device (Microtrac S3500), and the results are listed in Table 1 below.

[0171] <Example 2>

[0172] In the above Example 1, the cathode material was prepared in the same manner as in Example 1, except that the temperature reached in the graphite crucible was different during the formation of the carbon coating layer in step 2). Specifically, after reaching 950°C in the graphite crucible into which the mixture was introduced, the temperature was maintained at 950°C for 120 minutes, then the temperature inside the crucible was raised again to reach 980°C and maintained at 980°C for 30 minutes, and finally, the temperature inside the crucible was naturally cooled to 950°C and maintained at 950°C for 30 minutes.

[0173] <Example 3>

[0174] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that the temperature reached by the graphite crucible was different during the formation of the carbon coating layer in step 2). Specifically, the graphite crucible into which the mixture was introduced was brought to 1000°C and maintained at 1000°C for 120 minutes, then the inside of the crucible was heated again to 1030°C and maintained at 1030°C for 30 minutes, and finally, the inside of the crucible was naturally cooled to 1000°C and maintained at 1000°C for 30 minutes.

[0175] <Example 4>

[0176] In the above Example 1, a cathode material was prepared by the same method as Example 1, except that when the finely powdered silicon oxide and coal tar obtained in 1) were introduced into a mixer, the weight ratio of the silicon oxide to coal tar introduced was 5:1.

[0177] <Example 5>

[0178] In the above Example 4, the manufactured particulate cathode material is fed into a feed classification grinder (ACM) and the average particle size (D 50 A cathode material was prepared in the same manner as in Example 1, except that the ) was crushed to 5.8 μm.

[0179] <Example 6>

[0180] In the above Example 1, the cathode material was prepared in the same manner as in Example 1, except that when forming the carbon coating layer in step 2), the graphite crucible into which the mixture was introduced was heated to 950°C, maintained at 950°C for 40 minutes, then the inside of the crucible was heated again to 980°C, maintained at 980°C for 10 minutes, and finally the inside of the crucible was naturally cooled to 950°C and maintained at 950°C for 10 minutes.

[0181] <Example 7>

[0182] In Example 1, the cathode material was prepared in the same manner as in Example 1, except that the temperature reached by the graphite crucible was kept constant during the formation of the carbon coating layer in step 2). Specifically, the graphite crucible into which the mixture was introduced was brought to 900°C and maintained for 1 hour.

[0183] <Comparative Example 1>

[0184] In the above Example 1, in step 2), silicon oxide (SiO x A cathode material was prepared in the same manner as in Example 1, except that 50 g of powder was loaded into a thermal CVD apparatus maintained at 900 ℃, and methane and argon were continuously supplied into the apparatus at 1 L / min each to perform carbon deposition for 1 hour.

[0185] <Comparative Example 2>

[0186] In the above Example 1, in step 2), silicon oxide (SiO x A cathode material was prepared in the same manner as in Example 1, except that 50 g of powder was loaded into a thermal CVD apparatus maintained at 950°C, and methane and argon were continuously supplied into the apparatus at 1 L / min each to perform carbon deposition for 1 hour.

[0187] <Comparative Example 2>

[0188] In Comparative Example 1 above, the cathode material was prepared in the same manner as Example 1, except that carbon deposition was performed for 3 hours.

[0190]

[0191] It was confirmed that the cathode material according to the present invention generally has a smaller specific surface area compared to the comparative example, and in particular, the cathode material according to Examples 1 to 4 has a specific surface area of ​​2 m² 2 It was confirmed that it was less than / g.

[0192] [Measurement of Cathode Material Properties]

[0193] 1. Raman Spectroscopic Analysis

[0194] Raman spectroscopic spectra of silicon-based cores at 10 different random locations of cathode materials according to the examples and comparative examples were measured using μ-Raman (instrument name: XperRam C, Nanobase, Korea) under the following analysis conditions and are shown in Fig. 1.

[0195] [WN(Si) according to the following relationship 1 MAX-MIN ], [WN(Si) MAX wa WN(Si) MIN Average of WN(Si) excluding (WN(Si) AVE Standard deviation for )], [W AVE ] and [W AVE The standard deviation of was calculated and shown in Table 2 below.

[0196] (Relationship 1)

[0197] WN(Si) MAX-MIN = WN(Si) MAX - WN(Si) MIN

[0198] In Equation 1, WN(Si) is 460 cm -1 - 560 cm -1 It is the wavenumber corresponding to the maximum scattering intensity in the Raman spectroscopic spectrum of the silicon-based core located in the wavenumber region, and WN(Si) MAX wa WN(Si)MIN These are the maximum and minimum values ​​of WN(Si) calculated from each of the above Raman spectroscopic spectra measured at 10 different locations.

[0199] W AVE 560 cm⁻¹ in each of the Raman spectroscopic spectra measured at the 10 different locations mentioned above. -1 It is the average value of the width of the Raman spectroscopic spectrum corresponding to 75% of the maximum scattering intensity value based on the Raman scattering intensity of the wavenumber. In this case, W AVE The average is the average of the values ​​excluding the maximum and minimum values.

[0200] In addition, the Raman spectroscopic spectra of the carbon coating layer were measured at five different locations of the cathode material according to the examples and comparative examples and are shown in FIGS. 2 and 3. Furthermore, the D band intensity (I) in the Raman spectroscopic spectrum of the carbon coating layer D ) and G band intensity (I G ), the ratio of their intensity (I D / I G The average value of ) and the ratio of the full width at half maximum (FWHM) of the D band and G band peaks (F D / F G The average value of ) was calculated and listed in Table 3 below. In addition, the full width at half maximum (FWHM) of the D band and G band peaks is listed in Table 4 below.

[0201] Analysis conditions: Excitation laser wavelength 532 nm, laser power 0.5 mW, spectrometer resolution 1 cm -1 , powdered cathode material 1 g, detector exposure time 15 sec.

[0202]

[0203]

[0204]

[0205] Referring to FIG. 1 and Table 2 above, the cathode material according to the embodiment is WN(Si) MAX-MIN The value is 6.2 cm -1Below, and WN(Si) MAX wa WN(Si) MIN Average of WN(Si) excluding (WN(Si) AVE The standard deviation for ) is 1.8 cm -1 Below, W AVE This is 17 cm -1 Less than, W AVE The standard deviation of is 3 cm -1 It was possible to confirm that it was less than

[0206] In addition, referring to FIGS. 2 and 3 and Table 3, the cathode material according to the embodiment has, on average, a ratio of the intensity of the D band peak to the G band peak (I D / I G )go Ratio of average full width at half maximum (F D / F G It was confirmed that it is smaller than ) and satisfies an average full width at half maximum (FWHM) of 1.3 or more.

[0207] In addition, referring to Table 4, the average full width at half maximum (FWHM) of the G band is 60 cm -1 It was possible to confirm that it was abnormal.

[0208] Battery Manufacturing

[0209] Using the final cathode powder as the active material, the active material:conductive material (carbon black):CMC (Carboxymethyl cellulose):SBR (Styrene Butadiene Rubber) were mixed in a weight ratio of 8:1:0.5:0.5, coated onto a copper foil 17 μm thick, and dried at 90°C for 40 minutes. After drying, the material was die-cut to a diameter of 14 mm. A CR2032 coin-type half-cell was fabricated by using a metallic lithium 16 mm in diameter as the counter electrode, placing an 18 mm diameter separator between the electrodes, and filling the electrolyte. For the electrolyte, 1 M LiPF6 was dissolved in a solvent mixed with EC (Ethylene carbonate) and DEC (Diethyl carbonate) in a volume ratio of 1:1, and 3 wt% FEC (fluoroethylene carbonate) was used as an additive.

[0210] Battery Performance Evaluation

[0211] The formation process was performed by charging the manufactured battery to 0.005 V with a constant current of 0.1 C (lithiation), charging at a constant voltage of 0.005 V until it reached 0.01 C, and then discharging to 1.5 V with a constant current of 0.1 C (de-lithiation) (first formation step), and then charging 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 then discharging to 1.0 V with a constant current of 0.1 C (second formation step).

[0212] The charge-discharge cycle characteristics of the half-cell subjected to the formation process were evaluated by lithiating it to 0.005 V with a constant current of 0.5 C, charging it at a constant voltage of 0.005 V until it reached 0.05 C, and then delithiating it to 1.0 V with a constant current of 0.5 C. The discharge capacity retention rate according to the charge-discharge cycles (total 30 cycles) was evaluated. The discharge capacity (initial capacity) and initial efficiency of the first charge-discharge cycle were measured and are listed in Table 5 below. Capacity retention rate ((C 25 / C3)×100, C 25 is the 25th charge / discharge cycle, and C3 is the discharge capacity at the 3rd charge / discharge cycle.) This is also listed in Table 5 below.

[0213]

[0214] It was confirmed that the cathode material according to the example has excellent electrochemical characteristics compared to the comparative example, with an initial discharge capacity of 1700 mAh / g or more, an initial efficiency of 74% or more, and a charge / discharge capacity retention rate (rate capability) of 92% or more.

Claims

Claim 1 A negative electrode material for a secondary battery comprising a matrix containing silicon oxide, a silicon-based core containing silicon nanocrystals dispersed and embedded in the matrix, and a carbon coating layer located on the surface of the silicon-based core, satisfying the following Equations 1 and 2. (Equation 1)WN(Si) MAX - WN(Si) MIN ≤ 7 cm -1 (In Equation 1, WN(Si) is 460 cm -1 to 560 cm -1 It is the wavenumber corresponding to the maximum scattering intensity in the Raman spectroscopic spectrum of the silicon-based core located in the wavenumber region, and WN(Si) MAX wa WN(Si) MIN )(Equation 2)W are the maximum and minimum values ​​of WN(Si) calculated from each of the above Raman spectroscopic spectra measured at 10 different locations.) AVE ≤ 17 cm -1 (In Equation 2, W AVE 560 cm⁻¹ in each of the Raman spectroscopic spectra measured at the 10 different locations mentioned above. -1 It is the average value of the width of the Raman spectroscopic spectrum corresponding to 75% of the maximum scattering intensity value based on the Raman scattering intensity of the wavenumber. Claim 2 In claim 1, the ratio of the intensity of the D band peak and the G band peak (I) in the Raman spectroscopic spectrum of the carbon coating layer D / I G ) is 1.3 or less, and the ratio of the above strength (I D / I G ) is the ratio of the full width at half maximum (FWHM) of the D band peak to the G band peak (F D / F G A negative electrode material for a secondary battery that is smaller than ). Claim 3 In paragraph 2, the ratio of the full width at half maximum (FWHM) of the D band and G band peaks (F D / F G A negative electrode material for a secondary battery having a value of 1.4 or higher. Claim 4 In paragraph 2, the full width at half maximum (F) of the G band peak above G ) is 60 cm -1 Lee Sang-in, anode material for secondary batteries. Claim 5 In paragraph 1, the above W AVE The standard deviation is 5 cm -1 Lee Ha-in, negative electrode material for secondary batteries. Claim 6 A negative electrode material for a secondary battery according to claim 1, further satisfying the following Equation 3. (Equation 3)1 > WN(Si) AVE / WN(ref)(in Equation 3, WN(Si) AVE is the average value of the above WN(Si), and WN(ref) is 460 cm -1 to 560 cm -1 It is the wavenumber corresponding to the maximum scattering intensity in the Raman spectroscopic spectrum of bulk single-crystal silicon located in the wavenumber region. Claim 7 In claim 6, the specific surface area of ​​the cathode material is 10 m² 2 A negative electrode material for secondary batteries with a g or less. Claim 8 A negative electrode material for a secondary battery according to claim 1, wherein the carbon coating layer comprises a plurality of carbon nanoparticles. Claim 9 A negative electrode material for a secondary battery according to claim 8, wherein the carbon coating layer comprises a dispersed phase containing a plurality of carbon nanoparticles and a continuous phase made of carbon that physically binds the dispersed phase. Claim 10 A negative electrode material for a secondary battery according to claim 1, wherein the carbon coating layer is included in an amount of 0.5 to 8 weight percent of the total weight of the negative electrode material. Claim 11 A negative electrode material for a secondary battery according to claim 1, wherein the carbon coating layer is derived from coal tar or petroleum residue oil. Claim 12 In claim 1, the D1 particle size of the cathode material is 1.2 to 5 μm, and D 10 / D1 is a negative electrode material for a secondary battery, having 1 to 3. Claim 13 In claim 1, D of the cathode material 90 The particle size is 8.5 to 14 μm, and D 99 / D 90 A negative electrode material for a secondary battery having a content of 1.1 to 2.

5. Claim 14 A secondary battery comprising a negative electrode material for a secondary battery according to any one of claims 1 to 13.

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