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 comprising a core comprising silicon nanoparticles and graphite particles in a dispersed phase and a carbon body in a continuous phase, and a carbon coating layer located on the surface of the core, and a secondary battery comprising the same. The negative electrode material for a secondary battery according to the present invention can suppress the expansion of silicon nanoparticles during charging and discharging, and can exhibit high capacity and excellent cycle characteristics.

Description

Technology Field

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

[0002] As the electrification of transportation accelerates and the demand for high-capacity energy storage systems (ESS) increases, the demand for high-energy density secondary batteries continues to rise.

[0003] Lithium secondary batteries generally consist of a positive electrode, a negative electrode, an electrolyte, and a separator, and graphite is widely used as the active material for the negative electrode. Since high-energy-density lithium secondary batteries must store a large amount of energy per unit volume, they must satisfy both the requirements for rapid charging and high capacity. However, graphite used as a negative electrode active material has a theoretical maximum capacity of only 372 mAh / g, making it unsuitable for high capacity requirements. Furthermore, rapid charging may also have limitations, as structural changes in graphite can stress the internal structure of the battery and lead to a shortened battery life.

[0004] For the development of high-capacity lithium secondary batteries, silicon, with a theoretical maximum capacity of 4,200 mAh / g, is emerging as a negative electrode active material. However, when silicon is used as a negative electrode material, the cycle characteristics deteriorate significantly due to particle detachment caused by large volume changes in silicon and an increase in contact resistance as charge-discharge cycling is repeated.

[0005] Accordingly, there is still a need to develop silicon-based anode materials for secondary batteries that stably maintain the particle structure even with large volume changes of silicon during the charging and discharging process, and possess excellent cycle characteristics and high power characteristics. Prior art literature

[0006] : CN 109103438 B The problem to be solved

[0007] The problem solved by the present invention is to provide a silicon-based negative electrode material for a secondary battery that stably maintains the particle structure even with large volume changes of silicon during the charging and discharging process, and has excellent cycle characteristics and high power characteristics, and a lithium secondary battery including the same. means of solving the problem

[0008] A negative electrode material for a secondary battery according to one embodiment of the present invention comprises: a core comprising silicon nanoparticles and graphite particles in a dispersed phase and a carbon body in a continuous phase; and a carbon coating layer located on the surface of the core, wherein in the Raman spectroscopy of the carbon coating layer, the ratio of the maximum intensity of the D band peak and the G band peak (I D / I G ) is less than 1, and the full width at half maximum (F) of the G band peak G ) is 90 cm -1 It is as follows.

[0009] In a negative electrode material for a secondary battery according to one embodiment, in the Raman spectroscopic spectrum, the difference (D) between the lowest wavenumber of the two intersection points of the G band curve forming the full width at half maximum and the maximum wavenumber of the G band curve peak. A ) and the difference between the highest wavenumber among the two intersection points and the maximum wavenumber (D B The ratio of ) (D A : D B ) can be 1 : 1.1 to 1.5.

[0010] In a negative electrode material for a secondary battery according to one embodiment, the wavenumber of the Raman spectroscopic spectrum is 1581.5 to 1586.0 cm -1 In the above G band maximum peak intensity (I G Can have ).

[0011] In a negative electrode material for a secondary battery according to one embodiment, the silicon crystallite size calculated from the (111) plane of the X-ray diffraction (XRD) pattern of the negative electrode material for the secondary battery may be 10 nm or more.

[0012] In a negative electrode material for a secondary battery according to one embodiment, in an X-ray diffraction (XRD) pattern, 2θ has diffraction peaks at 26.5±0.5° and 28±0.5°, and the peak at 26±0.5° may have a greater intensity than the peak at 28±0.5°.

[0013] In a negative electrode material for a secondary battery according to one embodiment, the negative electrode material for a secondary battery may have a peak intensity at 100±1 eV greater than the peak intensity at 104±1 eV in a Si2p analysis pattern through X-ray photoelectron spectroscopy (XPS).

[0014] In a negative electrode material for a secondary battery according to one embodiment, the negative electrode material for a secondary battery has a difference in adsorption amount (HI) at a relative pressure of 0.8 (P / P0) of a nitrogen adsorption-desorption isotherm graph. 0.8 ) and the difference in adsorption amount at a relative pressure of 0.6 (P / P0) (HI 0.6 The ratio of ) (HI 0.8 / HI 0.6 ) can be 1.5 or higher.

[0015] In a negative electrode material for a secondary battery according to one embodiment, the carbon body may be soft carbon.

[0016] In a negative electrode material for a secondary battery according to one embodiment, the carbon body may be derived from coal-based or petroleum-based pitch.

[0017] In a negative electrode material for a secondary battery according to one embodiment, the silicon nanoparticles have a volume integral D 50 The average diameter corresponding to may be 20 to 70 nm.

[0018] In a negative electrode material for a secondary battery according to one embodiment, silicon nanoparticles may be included in a larger amount than graphite particles in the total weight of the core.

[0019] In a negative electrode material for a secondary battery according to one embodiment, the core may further include an ion-conducting material.

[0020] In a negative electrode material for a secondary battery according to one embodiment, the graphite particles may be natural graphite particles.

[0021] In a negative electrode material for a secondary battery according to one embodiment, the negative electrode material has a volume integral D 50 The average diameter corresponding to may be 8 to 20 μm.

[0022] In a negative electrode material for a secondary battery according to one embodiment, the thickness of the carbon coating layer may be 5 to 200 nm.

[0023] A secondary battery according to one embodiment of the present invention includes the negative electrode material for a secondary battery described above. Brief explanation of the drawing

[0024] FIG. 1 is a scanning electron microscope image of a negative electrode material for a secondary battery according to one embodiment of the present invention, FIGS. 2 and FIGS. 3 are Raman spectroscopic spectra of a negative electrode material for a secondary battery according to an embodiment of the present invention, FIG. 4 is an XPS (X-ray Photoelectron Spectroscopy) result of a negative electrode material for a secondary battery according to one embodiment of the present invention, FIG. 5 is an XRD (X-ray Diffraction) result of a negative electrode material for a secondary battery according to one embodiment of the present invention, FIG. 6 is a nitrogen adsorption / desorption isotherm of a negative electrode material for a secondary battery according to one embodiment of the present invention, Figure 7 is a graph showing the nitrogen adsorption-desorption isotherm shown in Figure 6 converted into a pore volume distribution according to pore size using the BJH (Barrett Jouner Halenda) method. Specific details for implementing the invention

[0025] 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.

[0026] 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.

[0027] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0028] 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.

[0029] 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.

[0030] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] In this specification and the appended claims, terms such as "first," "second," etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another.

[0035] In this specification, the diameter (particle size) distribution refers to that measured using the laser diffraction method unless otherwise specifically defined. For the analysis of the diameter 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.

[0036] In this specification, the classification of pore sizes follows the definitions of the International Union of Pure and Applied Chemistry (IUPAC). Specifically, according to the IUPAC definitions, micropores refer to pores with a diameter of 2 nm or less, mesopores refer to pores with a diameter of 2 nm to 50 nm, and macropores refer to pores with a diameter of 50 nm or more.

[0037] The applicant has discovered that in silicon-carbon composite cathode materials, the electrochemical properties of the cathode material are significantly influenced by Raman spectroscopic characteristics. In particular, the applicant has completed the present invention by discovering that in a cathode material having a core-shell structure, comprising dispersed silicon nanoparticles and graphite particles and a continuous carbon body in the core, and a carbon coating layer in the shell, the electrochemical properties of the cathode material are significantly improved when the Raman spectroscopic spectrum of the carbon coating layer satisfies a specific pattern.

[0038] In the present invention, the negative electrode material for a secondary battery may refer to a negative electrode material for a lithium secondary battery, but is not necessarily limited thereto and may also be utilized as a negative electrode material for various secondary batteries.

[0039] The negative electrode material for a secondary battery according to the present invention comprises: a core comprising a carbon body in a continuous phase containing silicon nanoparticles and graphite particles in a dispersed phase; and a carbon coating layer located on the surface of the core; wherein, in the Raman spectroscopy of the carbon coating layer, the ratio of the maximum intensity of the D band peak to the G band peak (I D / I G ) is less than 1, and the full width at half maximum (F) of the G band peak G ) is 90 cm -1 It is characterized by the following.

[0040] D band peak intensity (I) in the Raman spectroscopic spectrum of the carbon coating layer D ) is 1310 to 1380 cm -1 It is the maximum intensity of the peak located in the wavenumber region, and the ratio of 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.

[0041] Specifically, the ratio of the maximum intensities of the D band peak and the G band peak (I D / I G ) may be less than 1, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or 0.5 or less, and may be 0.05 or more without limitation. More specifically, the ratio of the maximum intensities of the D band peak and the G band peak (I D / I G ) may be 0.05 or more to less than 1, 0.1 to 0.9, 0.1 to 0.8, 0.2 to 0.7, or 0.3 to 0.6.

[0042] 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.

[0043] Specifically, the full width at half maximum (F) of the above G band peak G ) is 90 cm -1 Below, 80 cm -1 Below, 70 cm -1 Less than 60 cm -1 Less than or equal to 50 cm -1 It may be less than or equal to 10 cm, and is not limited to that. -1 It may be more than that. More specifically, the above half-width is 10 to 90 cm -1 , 10 to 80 cm -1, 20 to 70 cm -1 , 30 to 60 cm -1 It could be.

[0044] In one embodiment, the ratio of the maximum intensities of the D band peak and the G band peak in the Raman spectroscopic spectrum (I D / I G ) is 0.1 to 0.9 and the above half-width is 10 to 90 cm -1 It may be. Or the ratio of the maximum intensities of the D-band peak and the G-band peak (I D / I G ) is 0.2 to 0.7, and the above half-width is 20 to 70 cm -1 It can be. As another example, the ratio of the maximum intensities of the D-band peak and the G-band peak (I D / I G ) is 0.3 to 0.6, and the above half-width is 30 to 60 cm -1 It could be.

[0045] As such, a negative electrode material for a secondary battery satisfying the aforementioned characteristics in a Raman spectroscopic spectrum has a core and a carbon coating layer that are much more organically bonded than silicon-carbon composite negative electrode materials known in the art, and can have a very homogeneous carbon film with almost no defects. Accordingly, the electrochemical characteristics of the negative electrode material for a secondary battery can be significantly improved compared to existing silicon-carbon composite negative electrode materials. Specifically, the negative electrode material for a secondary battery forming a homogeneous carbon film has uniform and high electrical conductivity, which can greatly improve the initial charge-discharge efficiency of the secondary battery. In addition, the homogeneous carbon film promotes the formation of a stable and thin SEI (Solid Electrolyte Interphase) layer, which can improve initial charge efficiency. Furthermore, structural stability is improved, and side reactions caused by defects are reduced, thereby improving lifespan characteristics.

[0046] In one embodiment, in the Raman spectroscopic spectrum, the difference (D) between the lowest wavenumber of the two intersection points of the G-band curve forming the full width at half maximum and the maximum wavenumber of the G-band curve peak. A ) and the difference between the highest wavenumber among the two intersection points and the maximum wavenumber (D B The ratio of ) (D A : D B ) may be 1 : 1.1 to 1.5, 1 : 1.15 to 1.4, or 1 : 1.2 to 1.35.

[0047] In one embodiment, the wavenumber of the Raman spectroscopic spectrum is 1581.5 to 1586.0 cm -1 , specifically 1582.5 to 1856.0 cm -1 , more specifically 1582.5 to 1585.5 cm -1 In the above G band maximum peak intensity (I G Can have ).

[0048] In one embodiment, the negative electrode material for the secondary battery may satisfy a specific aspect in an X-ray diffraction (XRD) pattern. Specifically, the negative electrode material for the secondary battery may have diffraction peaks at 2θ of 26.5±0.5° and 28±0.5° in an X-ray diffraction pattern using CuKα rays. In this case, the negative electrode material for the secondary battery may have a peak at 2θ of 26±0.5° with greater intensity than the peak at 28±0.5°.

[0049] In addition, in one embodiment, the silicon crystallite size calculated from the (111) plane in the range of 2θ = 28°±2° of the X-ray diffraction (XRD) pattern of the secondary battery may be 10 nm or more, 11 nm or more, 12 nm or more, or 13 nm or more, and may be, without limitation, 20 nm or less. Specifically, the silicon crystallite size may be 10 to 20 nm, 10 to 18 nm, 10 to 15 nm, or 11 to 15 nm.

[0050] The above silicon crystallite size can be calculated from the following Scherrer equation.

[0051] [Equation 1]

[0052] L = (0.9×λ) / (FWHM×cosθ)

[0053] In Equation 1, L = crystal size, λ = Cu Ka wavelength, FWHM = Full Width at Half Maximum, and θ = center diffraction angle of the full width at half maximum.

[0054] The full width at half maximum of the (111) plane peak in the range 2θ = 28°±2° of the above X-ray diffraction (XRD) pattern may be 0.6° or more, 0.7° or more, 0.8° or more, 0.9° or more, or 1° or more, and may be, without limitation, 1.2° or less. Specifically, the full width at half maximum may be 0.6 to 1.2°, 0.8 to 1.2°, or 0.9 to 1.1°.

[0055] In one embodiment, the negative electrode material for a secondary battery according to the present invention exhibits a full width at half maximum of 0.9° to 1.1° of the (111) plane peak in the range of 2θ = 28°±2° on the X-ray diffraction (XRD) spectrum, and the size of the silicon crystallites calculated therefrom may be 10 nm to 15 nm.

[0056] In a Si2p analysis pattern using X-ray photoelectron spectroscopy (XPS) of a negative electrode material for a secondary battery according to one embodiment, the intensity of the peak at 100±1 eV may be greater than the intensity of the peak at 104±1 eV.

[0057] In addition, in the Si2p analysis pattern via XPS of the above-mentioned negative electrode material for a secondary battery, the area of ​​the peak at 100±1 eV may be larger than the area of ​​the peak at 104±1 eV. Specifically, the area of ​​the peak at 100±1 eV (A 100 ) and the area of ​​the 104±1 eV peak (A 104 Area ratio of ) (A 100 / A 104 ) may be greater than 1, 1.3 or more, 1.5 or more, 1.7 or more, or 1.9 or more, and may be 3 or less without limitation. Specifically, the above area ratio (A 100 / A 104 ) can be 1.1 to 3, 1.3 to 2.5, 1.5 to 2.5, 1.7 to 2.3, or 1.9 to 2.1. The peak at 100±1 eV represents the Si-Si bond peak, and the peak at 100±4 eV represents the Si-O bond peak. As the negative electrode material for a secondary battery satisfies this, the negative electrode material for a secondary battery maintains a high electrode capacity and facilitates the insertion / extraction of lithium ions, thereby further improving charge / discharge performance.

[0058] A negative electrode material for a secondary battery according to one embodiment has a difference in adsorption amount (HI) at a relative pressure of 0.8 (P / P0) on a nitrogen adsorption-desorption isotherm graph. 0.8 ) and the difference in adsorption amount at a relative pressure of 0.6 (P / P0) (HI 0.6 The ratio of ) (HI 0.8 / HI 0.6 ) may be 1.5 or more, 1.7 or more, 1.9 or more, 2.0 or more, 2.1 or more, 2.3 or more, or 2.5 or more, and, without limitation, may be 3.0 or less. Specifically, the ratio of the adsorption amount (HI 0.8 / HI 0.6 ) may be 1.5 to 3.0, 1.7 to 2.9, 1.9 to 2.8, 2.0 to 2.7, or 2.3 to 2.7.

[0059] As a non-limiting example, the difference in adsorption amount (HI) at the relative pressure 0.8 (P / P0) mentioned above. 0.8 ) is 0.5 to 1.5 cm 3 / g, 0.6 to 1.4 cm 3 / g, or 0.7 to 1.3 cm 3 It may be / g. Also, as a non-limiting example, the difference in adsorption amount (HI) at the relative pressure 0.6 (P / P0) mentioned above. 0.6 ) is 0.1 to 1 cm 3 / g, 0.2 to 0.9 cm 3 / g or 0.3 to 0.7 cm 3 It can be / g.

[0060] The above nitrogen adsorption-desorption isotherm graph refers to an isotherm graph formed by combining the isotherm of the nitrogen adsorption process (adsorption isotherm) and the isotherm of the nitrogen desorption process (desorption isotherm), obtained by measuring nitrogen adsorption of the negative electrode material for a secondary battery. The x-axis represents the relative nitrogen pressure (P / P0) and the nitrogen adsorption amount (cm²). 3 To describe the graph of the y-axis of / g STP), the nitrogen adsorption-desorption isotherm has the same x-axis and y-axis, and means a graph in which the nitrogen adsorption isotherm and the nitrogen desorption isotherm are plotted together.

[0061] The difference in adsorption amount at the above relative pressure of 0.8 (P / P0) and the difference in adsorption amount at the relative pressure of 0.6 (HI) 0.6) may refer to the difference between the amount of nitrogen adsorbed at the nitrogen desorption isotherm and the amount of nitrogen adsorbed at the nitrogen adsorption isotherm at each relative pressure in the nitrogen adsorption isotherm, that is, the magnitude of the separation between the nitrogen desorption isotherm and the nitrogen adsorption isotherm. Specifically, a negative electrode material for a secondary battery according to one embodiment may have a shape separated from each other, i.e., hysteresis, in the nitrogen adsorption isotherm at least in the nitrogen relative pressure (P / P0) range of 0.10 to 0.98.

[0062] Such a negative electrode material for a secondary battery may imply that mesopores of various sizes are highly developed and that pores of different sizes are interconnected to form a pore network. Specifically, in one embodiment, the BET specific surface area of ​​the negative electrode material for a secondary battery based on the nitrogen adsorption isotherm is 3.5 to 6 m² 2 / g, 3.7 to 6 m 2 / g, or 4 to 6 m 2 It can have a low specific surface area despite containing a large amount of nano-sized silicon at 1 / g.

[0063] In addition, the negative electrode material for a secondary battery according to one embodiment has a core and a shell, that is, a core and a carbon coating layer, organically bonded as described above, and the carbon coating layer is homogeneously formed and satisfies the pore characteristics described above. As a result, even though it contains a large amount of silicon elements compared to silicon oxide as described above, it can easily accommodate volume changes of silicon that occur during the charging and discharging process, thereby increasing structural stability and improving lifespan characteristics.

[0064] As described above, a negative electrode material for a secondary battery according to one embodiment of the present invention comprises a core; and a carbon coating layer located on the surface of the core. Such a negative electrode material for a secondary battery is not particularly limited as long as it is of a size usable as a negative electrode material. Specifically, the negative electrode material for a secondary battery has an average diameter (D 50 ) may be 8 to 20 μm, 10 to 20 μm, or 10 to 15 μm, but is not limited thereto.

[0065] Specifically, the core comprises silicon nanoparticles and graphite particles in a dispersed phase and a carbon body in a continuous phase.

[0066] Specifically, the silicon nanoparticles may be crystalline, amorphous, or a composite phase in which crystalline and amorphous phases are mixed, and may be substantially crystalline.

[0067] Average diameter (D of the above silicon nanoparticles) 50 ) may be 1 nm to 100 nm, specifically 1 to 90 nm, 10 to 80 nm, 20 to 70 nm, 30 to 60 nm, or 40 to 60 nm, but is not limited thereto.

[0068] The oxygen content present on the surface of the above silicon nanoparticles can be very low compared to the total amount of silicon. That is, the atomic ratio of oxygen to silicon (O / Si) can have a very low value, and accordingly, most of the silicon contained in the cathode material can contribute to charging and discharging.

[0069] The graphite particles may include natural graphite particles or artificial graphite particles, specifically natural graphite particles. Specifically, the graphite particles may be natural graphite particles or a mixture of natural graphite particles and artificial graphite particles.

[0070] Average diameter (D) of the graphite particles above 50) may be 0.01 to 50 μm, 0.01 to 30 μm, 0.01 to 20 μm, or 0.01 to 10 μm, but is not limited thereto.

[0071] In one embodiment, silicon nanoparticles may be included in a greater amount than graphite nanoparticles in the total weight of the core. Specifically, graphite particles may be included in an amount of 1 to 100 parts by weight, 20 to 90 parts by weight, or 40 to 80 parts by weight per 100 parts by weight of silicon nanoparticles.

[0072] The carbon body may be soft carbon. Specifically, the carbon body may be derived from coal-based residual oil, petroleum-based residual oil, coal-based pitch, or petroleum-based pitch. In one embodiment, the average molecular weight of the coal-based or petroleum-based pitch may be 1,000 to 10,000 Da, but is not limited thereto.

[0073] As described above, the core comprises silicon nanoparticles and graphite particles as dispersible components and a carbon body as a continuous phase component. With respect to the total weight of the core, the weight ratio of the dispersible phase component to the continuous phase component may be 1:0.1 to 10, 1:0.5 to 9, 1:1 to 7, or 1:1 to 5.

[0074] In one embodiment, in one embodiment, the core may further include an ion-conducting material. The ion-conducting material may be a Nasicon-based ion conductor, specifically SiC x P y O z It may be an ionic conductor of the (x = a real number from 0.5 to 3, y = a real number from 1 to 5, z = a real number from 2 to 15) system. Specific examples include SiCP2O7 or Si2C3P4O 16Examples may be provided, but are not limited thereto. The ion conductor has excellent thermal stability in which no chemical alteration occurs under high-temperature carbonization conditions after being mixed with a precursor forming a carbon body contained within the core, namely, coal residue oil, petroleum residue oil, coal pitch, or petroleum pitch. The ion conductive material is desirable in that it exhibits excellent conductivity, particularly for lithium ions, within the core.

[0075] The ion-conducting material may be included in an amount of 10 to 80 parts by weight or 30 to 70 parts by weight per 100 parts by weight of the silicon nanoparticles.

[0076] The above carbon coating layer refers to a carbon film coated on the surface of the core, which can protect the core and suppress volume changes of the silicon in the core, and can impart excellent conductivity and electrochemical properties despite having properties close to amorphous.

[0077] 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.

[0078] In one embodiment, the carbon coating layer may be included in an amount of 0.1 to 20 weight%, specifically 0.5 to 15 weight%, of the total weight of the cathode material.

[0079] 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, 5 to 200 nm, 5 to 150 nm, or 10 to 100 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.

[0080] In one embodiment, the carbon coating layer may be soft carbon, hard carbon, or a combination thereof, and may be derived from a carbon precursor. The carbon precursor may be a polycyclic aromatic compound having an average molecular weight of 100 to 10,000 Da as measured by MALDI-TOF.

[0081] As a non-limiting example, the carbon coating layer may be hard carbon derived from a carbon precursor including, but is not limited to, condensed polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, anthracene, and pyrene and their derivatives, thermosetting resins having an aromatic structure such as phenol-formaldehyde resin or furfuryl alcohol resin, thermoplastic resins such as polyacrylonitrile (PAN) and its derivatives, or polysaccharides.

[0082] In contrast, the carbon coating layer may be soft carbon derived from a carbon precursor including, but is not limited to, graphitizing pitches such as petroleum-based pitch, coal tar pitch, and mesophase pitch.

[0083] The present invention provides a secondary battery comprising a negative electrode material for a secondary battery as described above.

[0084] 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.

[0085] The above anode may include an anode current collector and an anode composite layer located on at least one surface of the current collector.

[0086] The above anode may be manufactured by coating and drying a slurry comprising an anode material, a binder, a conductive material, and a solvent 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.

[0087] The above conductive material may be exemplified as carbon-based conductive materials such as carbon black, ultrafine graphite particles, acetylene black, carbon nanotubes, or carbon nanofibers, but is not limited thereto.

[0088] 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.

[0089] 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.

[0090] In addition, the initial charge / discharge efficiency of the cathode material according to the present invention may be 85% or more, and the initial discharge capacity may be 1500 mAh / g or more.

[0091] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0092] (Example 1)

[0093] (1) Preparation of silicon nanoparticles

[0094] Volume integration D 50100 g of silicon powder (99.9% purity) with an average diameter of 50 nm and 1.5 g of polyvinylpyrrolidone (Sigma-Aldrich) with a weight-average molecular weight of 40,000 were mixed in 500 ml of isopropyl alcohol and stirred to prepare a first dispersion.

[0095] Volume integration D 50 70 g of natural graphite powder with an average diameter of 8 μm, 750 g of SiCP2O as an ionic conductive material, and 1.5 g of polyethylene glycol were mixed in 500 ml of isopropyl alcohol and stirred to prepare a second dispersion.

[0096] The first dispersion was introduced into a sand mill equipped with zirconia balls (diameter 0.5 mm) as grinding beads, and primary grinding was performed for 12 hours. The dispersion was introduced into the sand mill such that the weight ratio of zirconia balls to silicon powder was 20:1. Subsequently, the second dispersion was additionally introduced into the sand mill, and secondary grinding was performed for 36 hours.

[0097] The silicon nanoparticle slurry, after grinding, had a weight ratio of silicon nanoparticles:graphite particles:ionic conductive material of 50:35:25, and after measuring the diameter of a total of 100 particles using a scanning electron microscope, the average diameter was calculated and found to be 50 nm.

[0098] (2) Spray drying and classification

[0099] The slurry prepared from (1) above was mixed, and the mixed slurry was dried in a continuous furnace at a temperature of 120°C for 5 hours to produce coarse particles.

[0100] (3) Grinding of coarse particles

[0101] The coarse particles prepared from (2) above were ground in a sand mill to have a sphericity of 0.7 or higher and a diameter distribution of monomodal peaks, and then sieved through a 400 mesh sieve to produce powder.

[0102] (4) Manufacturing of the core

[0103] A dry powder mixed with graphite nanoparticles, silicon nanoparticles, and an ionic conductive material and coal tar pitch were introduced into a planetary mixer and mixed at a linear velocity of 10 m / s for 2 hours to obtain a mixture. At this time, the weight ratio of the dry powder to the coal tar pitch was set to 1:5. Subsequently, 300 g of the mixture was loaded into a crucible, and air was removed in a nitrogen atmosphere until the oxygen content was 50 ppm or less. Then, the mixture was heated to 850 ℃ at a heating rate of 4.1 ℃ / min and a carbonization process was performed for 2 hours to produce composite particles. The prepared composite particles were crushed to an average diameter of 12 μm to produce coarse core particles.

[0104] (5) Grinding of coarse core particles

[0105] The coarse core particles produced from the above (4) were ground in a sand mill to produce core particles with a sphericity of 0.7 or higher and a diameter distribution of monomodal peaks.

[0106] (5) Formation of a carbon coating layer

[0107] The above core was placed in a crucible, and the pitch obtained by pyrolysis was fed into a planetary mixer and mixed at a linear velocity of 10 m / s for 2 hours to obtain a mixture. At this time, composite particles were prepared by performing a carbonization process for 2 hours after reaching 900 ℃ at a heating rate of 3.5 ℃ / min in a nitrogen atmosphere. The amount of pitch used for the coating layer was controlled to be sufficient to coat the surface of the core particles to a thickness of 55 nm and to facilitate classification. The prepared cathode composite particles volume integration D 50 The average diameter was found to be 12.5 μm.

[0108] (Example 2)

[0109] In the above Example 1, a cathode composite particle was prepared in the same manner as in Example 1, except that the weight ratio of silicon nanoparticles:graphite particles:ionic conductive material was 55:35:20, respectively.

[0110] (Example 3)

[0111] In the above Example 1, cathode material composite particles were prepared in the same manner as in Example 1, except that the weight ratio of dry powder to coal tar pitch was set to 1:4 when manufacturing the core.

[0112] [Comparative Example 1]

[0113] In the above Example 1, a cathode composite particle was prepared in the same manner as in Example 1, except that silicon powder with an average diameter of 75 nm was used when preparing silicon nanoparticles, and when preparing the core, a carbonization process was performed for 2 hours after reaching 800 ℃ at a heating rate of 6 ℃ / min.

[0114] The physical properties and electrochemical characteristics described in the detailed description and claims were analyzed and measured according to the analysis and measurement methods presented below.

[0115] [Analysis and Measurement of Cathode Material Properties]

[0116] (1) Surface observation

[0117] The surface of the cathode material according to Example 1 and Comparative Example 1 was observed using a scanning electron microscope (SEM), and the SEM image is shown in Fig. 1.

[0118] (2) Raman spectroscopy

[0119] The Raman spectroscopic spectrum of the carbon coating layer of the cathode material according to Example 1 and Comparative Example 1 was measured at room temperature and in an atmospheric environment using a laser with a wavelength of 532 nm.

[0120] The measured Raman spectroscopic spectrum is plotted in Fig. 2, and the ratio of the intensities of the D-band peak and the G-band peak of the Raman spectroscopic spectrum I is shown in Table 1 below.D / I G , full width at half maximum of the G band (F G ), G band maximum peak intensity (I G The wavenumber in which ) appears, the ratio of the difference between the highest wavenumber and the maximum wavenumber (D A : D B ) was written.

[0121] At this time, the ratio of the difference between the highest wavenumber and the maximum wavenumber (D A : D B ) is the difference (D) between the lowest wavenumber of the two intersection points of the G-band curve forming the full width at half maximum of the G-band and the maximum wavenumber of the peak of the G-band curve, as shown in FIG. 3. A ) and the difference between the highest wavenumber among the two intersection points and the maximum wavenumber (D B The ratio of ) (D A : D B It represents ).

[0122] division Raman spectrospective I D / I G F G I G wave number D A : D B Example 1 0.47 46.7 1584.84 1:1.29 Comparative Example 1 1.02 101 1588.87 1:0.95

[0123] (3) XPS measurement

[0124] XPS was measured for the cathode materials prepared according to Example 1 and Comparative Example 1. XPS analysis was performed using a K-ALPHA (Thermo Fisher Scientific (UK)), X-ray: 12000 V, 6 mA, 72 W, Analyzer Spatial Resolution: < 30 μm (by knife edge method), Analyzer Energy Resolution: < 0.5 eV FWHM (Ag 3d5 / 2 peak), and the results are shown in Figure 4 below. The measured XPS data was processed with Thermo Avantage software, and background signals were removed using the Shirly method. For the Si2p spectrum, assuming there were a total of two peaks—a Si-Si bond peak (100±1 eV) and a Si-O bond peak (104±1 eV)—waveforms were deconvolved by fitting with a Gaussian function, and the area of ​​the separated waveforms was calculated.

[0125] As shown in Fig. 4, unlike Comparative Example 1, it was confirmed that the peak intensity at 100±1 eV in Example 1 was greater than the peak intensity at 104±1 eV, and the area of ​​the Si-Si bonding peak of Example 1 (A 100 ) and the area of ​​the Si-O bonding peak (A 104 Area ratio of ) (A 100 / A 104 It was confirmed that ) is 1.91.

[0126] (4) X-ray diffraction analysis

[0127] XRD was measured for the cathode materials prepared according to Example 1 and Comparative Example 1. XRD was analyzed under analysis conditions of 40 kV, 15 mA, 4° / min, Cu-Kα radiation, λ = 0.15406 nm (Bruker D8 Discover), and the results are shown in Figure 5.

[0128] Referring to Fig. 5, 2θ showed peaks at 26±0.5° and 28±0.5°, respectively, and the peak at 26±0.5° was found to have a greater intensity than the peak at 28±0.5°, and the full width at half maximum of the (111) plane peak in the range of 2θ = 28°±0.5° was 1.0041° for the example and 0.5274° for the comparative example.

[0129] In addition, the silicon crystallite size was calculated using the XRD results and the Scherrer equation of Equation 2 below, and the example was 13.814 nm and the comparative example was 8.159 nm, confirming that the crystallite size of the example was 10 nm or larger.

[0130] [Equation 2]

[0131] L = (0.9×λ) / (FWHM×cosθ)

[0132] In Equation 1, L = crystal size, λ = Cu Ka wavelength, FWHM = Full Width at Half Maximum, and θ = center diffraction angle of the full width at half maximum.

[0133] (5) Nitrogen adsorption / desorption isotherm

[0134] The cathode materials prepared according to Example 1 and Comparative Example 1 were pretreated by drying them at a vacuum of 0.1 Torr or less and a temperature of 150 °C for 12 hours, after which nitrogen adsorption-desorption isotherms were measured. The nitrogen adsorption-desorption isotherms were measured using a specific surface area measuring device (Tristar II 3020, Micromeritics, USA) with a specific surface area measurement precision of 0.05 relative pressure (P / P0) and liquid nitrogen as the adsorbed nitrogen gas, and the nitrogen adsorption-desorption isotherms are plotted in Fig. 6. The nitrogen adsorption curve of the cathode material according to Example 1 was denoted as NH15 ads, and the desorption curve as NH15 des; the nitrogen adsorption curve of the cathode material according to Comparative Example 1 was denoted as NH12 ads, and the desorption curve as NH12 des.

[0135] Referring to FIG. 6, the cathode materials according to Example 1 and Comparative Example 1 have a spaced-apart form, i.e., hysteresis, in the nitrogen relative pressure (P / P0) range of 0.10 to 0.98, whereas the cathode material according to Example 1 has a difference in adsorption amount (HI) at a relative pressure of 0.8 (P / P0). 0.8 ) and the difference in adsorption amount at a relative pressure of 0.6 (P / P0) (HI 0.6 The ratio of ) (HI 0.8 / HI 0.6 While ) was 2.56, Comparative Example 1 was 1.29.

[0136] Subsequently, using the BJH method, the nitrogen relative pressure (P / P0) in the nitrogen adsorption or desorption isotherm is converted to the pore size (Pore Diameter), and the nitrogen adsorption amount (cm²) 3 / g STP) was converted into a distribution of pore volume according to pore size, and the results are shown in Fig. 7 below. Referring to Fig. 7, unlike Comparative Example 1, it was confirmed that mesopores of 10 nm or less were distributed by various sizes and were present in large quantities.

[0137] In addition, the specific surface area measured by the BET method was 3.2973 m² / g for Comparative Example 1, whereas for the Example it was 5.4985 m² 2 It was confirmed that the comparative area of ​​the example increased by about 1.67 times compared to the comparative example in / g.

[0138] [Battery Performance Evaluation]

[0139] 1. Half-cell manufacturing

[0140] A slurry was prepared by mixing the respective cathode composite particles, conductive material, and binder prepared in Examples 1 to 3 and Comparative Example 1 in distilled water at a ratio of 91:3:6. At this time, carbon black (super-P) was used as the conductive material, and polyacrylic acid was used as the binder.

[0141] The above slurry was uniformly coated onto a copper foil, dried in a 100°C oven for 2 hours, then roll-pressed to 40 μm and further dried in a 90°C vacuum oven for about 12 hours to produce a cathode plate. A CR2032 coin-type half-cell was manufactured according to a commonly known manufacturing process using the above-prepared cathode plate, a lithium foil as the counter electrode, a porous polyethylene membrane as the separator, and a liquid electrolyte containing 10 wt% of fluoro-ethylene carbonate (FEC) and LiPF6 dissolved at a concentration of 1.0 M in a solvent mixed with ethylene carbonate and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0142] 2. Measurement of Initial Discharge Capacity and Initial Efficiency

[0143] The manufactured half-cell was charged by applying a constant current at a rate of 0.1 C at 25 ℃ until the cell voltage reached 0.005 V (vs. Li), and then applying a constant voltage until the current reached a rate of 0.002 C when the cell voltage reached 0.005 V. During discharge, the cell was discharged at a constant current of 0.1 C until the voltage reached 1.5 V (vs. Li). The initial discharge capacity and initial efficiency measured from the formation process according to the examples and comparative examples are listed in Table 2 below.

[0144] division Initial discharge capacity (mAh / g) Initial efficiency (%) Example 1 1500 90 Example 2 1670 89 Example 3 1520 91 Comparative Example 1 1180 83

[0145] As a result of the battery performance evaluation, the initial discharge capacity of Example 1 was found to be 1500 mAh / g at 0.1 C, and the initial efficiency was found to be 90%. On the other hand, the initial discharge capacity of Comparative Example 1 was found to be 1180 mAh / g, and the initial efficiency was found to be 83%.

[0146] As described above, the present invention has been explained by specific details, limited embodiments, and drawings; however, this is provided merely to aid in a more comprehensive understanding of the invention, and the invention is not limited to the above embodiments. Those skilled in the art can make various modifications and variations from this description.

Claims

Claim 1 A core comprising silicon nanoparticles and graphite particles in a dispersed phase and a carbon body in a continuous phase; and a carbon coating layer located on the surface of the core; wherein, in the Raman spectroscopic spectrum of the carbon coating layer, the ratio of the maximum intensities of the D band peak and the G band peak (I D / I G ) is less than 1, and the full width at half maximum (F) of the G band peak G ) is 90 cm -1 A negative electrode material for a secondary battery, wherein the difference between the lowest wavenumber of the two intersection points of the G band curve forming the full width at half maximum (DA) and the difference between the highest wavenumber of the two intersection points and the maximum wavenumber (DB) (DA : DB) is 1 : 1.1 to 1.5, and the G band maximum peak intensity (IG) is at a wavenumber of 1581.5 to 1586.0 cm-1 of the Raman spectroscopic spectrum. Claim 2 delete Claim 3 delete Claim 4 In claim 1, the negative electrode material for a secondary battery is a negative electrode material for a secondary battery having a silicon crystallite size of 10 nm or more calculated from the (111) plane of an X-ray diffraction (XRD) pattern. Claim 5 A negative electrode material for a secondary battery according to claim 1, wherein in the X-ray diffraction (XRD) pattern, 2θ has diffraction peaks at 26.5±0.5° and 28±0.5°, and the peak at 26±0.5° has a greater intensity than the peak at 28±0.5°. Claim 6 In claim 1, the negative electrode material for a secondary battery is a negative electrode material for a secondary battery in which, in a Si2p analysis pattern through X-ray photoelectron spectroscopy (XPS), the peak intensity at 100±1 eV is greater than the peak intensity at 104±1 eV. Claim 7 In claim 1, the negative electrode material for the secondary battery is the difference in adsorption amount (HI) at a relative pressure of 0.8 (P / P0) of the nitrogen adsorption-desorption isotherm graph. 0.8 ) and the difference in adsorption amount at a relative pressure of 0.6 (P / P0) (HI 0.6 The ratio of ) (HI 0.8 / HI 0.6 A negative electrode material for a secondary battery having a value of 1.5 or higher. Claim 8 A negative electrode material for a secondary battery, wherein the carbon body is soft carbon, in claim 1. Claim 9 A negative electrode material for a secondary battery according to claim 1, wherein the carbon body is derived from coal-based or petroleum-based pitch. Claim 10 In claim 1, the silicon nanoparticles are volume integrated D 50 A negative electrode material for a secondary battery having an average diameter of 20 to 70 nm. Claim 11 A negative electrode material for a secondary battery according to claim 1, wherein silicon nanoparticles are included in a larger amount than graphite particles in the total weight of the core. Claim 12 A negative electrode material for a secondary battery according to claim 1, wherein the core further comprises an ion-conducting material. Claim 13 A negative electrode material for a secondary battery, wherein the graphite particles in claim 1 are natural graphite particles. Claim 14 In claim 1, the cathode material is volume integrated D 50 A negative electrode material for a secondary battery having an average diameter of 8 to 20 μm. Claim 15 A negative electrode material for a secondary battery according to claim 1, wherein the thickness of the carbon coating layer is 5 to 200 nm. Claim 16 A secondary battery comprising a negative electrode material for a secondary battery according to any one of paragraphs 1 and 4 through 15.

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