Silicon-based anode active material for secondary battery, and lithium secondary battery comprising same

Abstract

The present invention relates to a silicon-based anode active material for a secondary battery, comprising: a silicon-based core; and a carbon coating layer positioned on the surface of the silicon-based core, wherein the silicon-based core includes: a matrix containing silicon oxide, a composite oxide of silicon and at least one doping element selected from the group consisting of an alkali metal, an alkaline earth metal and a post-transition metal, or a mixture thereof; and silicon nanocrystals dispersed and embedded in the matrix, and includes macropores formed in the depth direction, the carbon coating layer is filled in at least some of the macropores of the silicon-based core, and the value of formula 1 satisfies 0.9 to 1.1. [Formula I] H50 / H10 (In the formula I, H50 denotes the hardness (MPa) obtained from [EQUATION] of 10 silicon-based anode active material particles having diameters of D50±20%, H10 denotes the hardness (MPa) obtained from [EQUATION] of 10 silicon-based anode active material particles having diameters of D10±20%, and a denotes the average aspect ratio of the silicon-based anode active material.)

Description

Silicon-based negative electrode active material for secondary batteries and lithium secondary battery including the same

[0001] The present invention relates to a silicon-based negative electrode active material for a secondary battery and a lithium secondary battery containing the same.

[0002] In various technological fields ranging from small electronic devices such as mobile devices to medium-to-large devices such as electric vehicles and energy storage systems, there is a demand for the development of secondary batteries with excellent electrochemical characteristics, such as high energy density, charge / discharge efficiency, long lifespan, and high stability.

[0003] In particular, among the cathode materials that determine the capacity of secondary batteries, the development of silicon-based cathode materials is actively underway, as they possess high theoretical capacity and are eco-friendly.

[0004] However, as lithium ions are inserted into silicon-based anode materials during charging, the crystal structure changes and undergoes a volume expansion of approximately four times compared to before the insertion of lithium. Consequently, as silicon-based anode materials undergo repeated charging and discharging, they cannot withstand the volume changes, leading to cracks within the crystals and particle destruction, as well as a decrease in electrical connectivity between adjacent particles, resulting in a deterioration of lifespan characteristics.

[0005] To address this, silicon-carbon anode materials were developed by forming a carbon layer on silicon-based particles to buffer the volume change of silicon; however, they failed to sufficiently secure the electrochemical properties—such as high energy density, charge / discharge efficiency, and long-term stability—required for application as power sources in various power devices. As an alternative, porous silicon anode material technology has been developed that induces the formation of nanopores within silicon particles to absorb the volume change occurring during lithium ion insertion. However, an excessive increase in the specific surface area of ​​porous silicon leads to problems such as accelerated adverse reactions with the electrolyte and the excessive formation of the solid electrolyte interface (SEI), resulting in reduced initial charge / discharge efficiency.

[0006] Therefore, structural and process improvements are required to suppress excessive increase in specific surface area and interfacial side reactions while maintaining the advantages of a porous structure that can effectively mitigate the volume expansion of silicon.

[0007] The objective of the present invention is to provide a silicon-based negative electrode active material for a secondary battery capable of securing high energy density, excellent charge / discharge efficiency, excellent lifespan characteristics, and long-term stability.

[0008] 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.

[0009] A silicon-based negative electrode active material according to one aspect of the present invention comprises: a silicon-based core; and a carbon coating layer located on the surface of the silicon-based core; wherein the silicon-based core comprises a matrix containing a complex oxide of silicon and one or more doping elements selected from the group consisting of silicon oxide, alkali metals, alkaline earth metals, and post-transition metals, or a mixture thereof; and silicon nanocrystals dispersed and embedded in the matrix; wherein the silicon-based core comprises macropores formed in the depth direction, and the carbon coating layer fills at least a portion of the silicon-based core macropores, and satisfies Formula 1 below 0.9 to 1.1.

[0010] [Equation 1]

[0011] H50 / H10

[0012] (In the above Equation 1, H50 is of 10 silicon-based negative electrode active material particles with a diameter range of D50±20% It is the hardness (MPa) obtained from, and H10 is of 10 silicon-based negative electrode active material particles with a diameter range of D10±20%. It refers to the hardness (MPa) obtained from, where a represents the average aspect ratio of the silicon-based negative electrode active material.

[0013] According to one embodiment, the silicon-based negative electrode active material may further satisfy 0.9 to 1.1 of the following Formula 2.

[0014] [Equation 2]

[0015] H50 / H90

[0016] (In the above Equation 2, H50 is of 10 silicon-based negative electrode active material particles with a diameter range of D50±20% It is the hardness (MPa) obtained from, and H90 is of 10 silicon-based negative electrode active material particles with a diameter range of D90±20%. It refers to the hardness (MPa) obtained from, where a represents the average aspect ratio of the silicon-based negative electrode active material.

[0017] According to one embodiment, 15 to 90% of the total pore area inside the silicon-based core may be filled with a carbon inner layer.

[0018] According to one embodiment, the matrix of the silicon-based core may be silicon oxide.

[0019] According to one embodiment, the matrix of the silicon-based core may include a complex oxide of silicon and one or more doping elements selected from the group consisting of alkali metals, alkaline earth metals, and post-transition metals.

[0020] According to one embodiment, the carbon inner layer filled in at least a portion of the silicon-based core pores may be electrically connected to the carbon outer layer located on the outer surface of the silicon-based core.

[0021] According to one embodiment, the silicon-based negative electrode active material is in the form of particles, and based on the longest diameter (D) of the silicon-based negative electrode active material particles, the pore depth (P) formed from the outer surface of the silicon-based core toward the center is D ) may include pores satisfying the following Equation 3.

[0022] (Equation 3)

[0023] 0.1 ≤ (PD / D)

[0024] According to one embodiment, the BET specific surface area of ​​the silicon-based core is 20 to 80 m² 2 It can be / g.

[0025] According to one embodiment, the elemental ratio (O / C) of oxygen (O) and carbon (C) of the silicon-based negative electrode active material can satisfy 1 to 8.

[0026] According to one embodiment, the average diameter (D50) of the silicon-based negative electrode active material may be 1 μm to 20 μm.

[0027] According to one embodiment, the carbon coating layer may be manufactured by carbonizing coal tar.

[0028] According to one embodiment, the pores formed in the depth direction of the silicon-based core may be produced by the step of forming pores by treating the matrix with an etching solution having solubility for the matrix; or the step of forming pores by treating the matrix, in which a first phase insoluble for the etching solution and a second phase soluble for the etching solution are mixed together, with the etching solution.

[0029] A lithium secondary battery according to another aspect of the present invention comprises a negative electrode comprising a silicon-based negative electrode active material according to any one of the aforementioned embodiments; a positive electrode; a separator; and an electrolyte.

[0030] The silicon-based negative electrode active material for secondary batteries according to the present invention has excellent electrical conductivity and increased structural stability, so that electrochemical properties such as high energy density, excellent cycle life characteristics, excellent charge / discharge efficiency, and rate capability can be significantly improved.

[0031] Figure 1 is a scanning electron microscope image of a porous silicon-based core according to one embodiment.

[0032] FIG. 2 is a scanning electron microscope image of a silicon-based negative electrode active material having a carbon coating layer formed thereon according to one embodiment.

[0033] Figure 3 is a scanning electron microscope image of a cross-section of a silicon-based negative electrode active material according to one embodiment.

[0034] Unless otherwise defined, technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art to which this invention pertains, and descriptions of known functions and configurations that could unnecessarily obscure the essence of the invention are omitted in the following description and accompanying drawings.

[0035] Additionally, the singular form used in this specification may be intended to include the plural form unless specifically indicated otherwise in the context.

[0036] Additionally, units used herein without special notation are based on weight, and, for example, units of % or ratio mean mass % or mass ratio, and mass % means the mass % of any one component of the total composition within the composition unless otherwise defined.

[0037] Additionally, the numerical ranges used in this specification include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all of which are limited values, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. Unless otherwise specifically defined in this specification, values ​​outside the numerical range that may occur due to experimental error or rounding are also included in the defined numerical range.

[0038] The term "comprising" in this specification is an open description having an equivalent meaning to expressions such as "comprising," "containing," "having," or "characterizing," and does not exclude elements, materials, or processes not additionally listed.

[0039] In this specification, the cumulative volume diameter distribution refers to that measured using the laser diffraction method. To analyze the cumulative volume 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 cumulative volume diameter distribution is calculated by measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam.

[0040] In this specification, the negative electrode active material for a secondary battery specifically includes a negative electrode active material (negative electrode material) for a lithium secondary battery, but is not necessarily limited thereto. The negative electrode active 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.

[0041] Conventional silicon-based negative electrode active materials for secondary batteries include silicon-carbon composites in which a carbon layer is formed on a silicon-based core to prevent volume expansion (change) of silicon due to charging and discharging of the battery. However, there is a trade-off relationship in which cycle life decreases sharply as the proportion of silicon components increases to achieve high capacity, and energy density becomes limited as the proportion of the carbon layer increases to extend cycle life. Furthermore, silicon-based cores have low ion / electron conductivity, and since ion / electron conductivity is improved only by the carbon layer on the surface of the core, issues such as rate capability and SEI formation stabilization are not sufficiently resolved, resulting in limited electrochemical characteristics.

[0042] The silicon-based negative electrode active material according to the present invention comprises: a silicon-based core; and a carbon coating layer located on the surface of the silicon-based core; wherein the silicon-based core comprises a matrix containing a complex oxide of silicon or a mixture thereof with one or more doping elements selected from the group consisting of silicon oxide, alkali metals, alkaline earth metals, and post-transition metals; and silicon nanocrystals dispersed and embedded in the matrix; wherein the silicon-based core comprises macropores formed in the depth direction, and the carbon coating layer fills at least a portion of the silicon-based core macropores, and is characterized in that Formula 1 satisfies 0.9 to 1.1.

[0043] [Equation 1]

[0044] H50 / H10

[0045] In the above Equation 1, H50 is 10 silicon-based negative electrode active material particles with a diameter range of D50±20%. It is the hardness (MPa) obtained from, and H10 is of 10 silicon-based negative electrode active material particles with a diameter range of D10±20%. It means the hardness (MPa) obtained from, and a means the average aspect ratio of the silicon-based negative electrode active material.

[0046] Typically, silicon-based anode active materials have been manufactured by introducing raw materials containing silicon and silicon dioxide into a molten metal, recovering coarse particles through vaporization and condensation, and mechanically grinding the coarse particles. The ground silicon-based particles are difficult to obtain as spherical particles, and anisotropic particles with an aspect ratio exceeding 1 are produced in a high fraction. Anode active materials with a high aspect ratio are prone to a decrease in electrode density during charging and discharging. If electrode density is increased through a rolling process, physical deformation or collapse of the active material particles may occur. Furthermore, active material particles that have undergone physical deformation may experience a decrease in capacity due to the additional formation of an SEI layer resulting from adverse reactions with the electrolyte. In particular, silicon-based anode active materials expand significantly in volume during charging; however, spherical particles undergo isotropic expansion, allowing them to possess a certain degree of resistance to physical deformation caused by volume expansion. However, silicon-based cathode active materials with a large aspect ratio tend to expand intensively along a specific axis in the thickness direction, which can easily lead to physical deformation or collapse of the particles, resulting in loss of the conductive network and reduction in capacity.

[0047] Conventionally, to suppress the expansion of silicon-based anode active materials without considering the particle aspect ratio, micropores, mesopores, or macropores were introduced within the particles to enhance capacity per unit mass and improve cycle characteristics. However, when macropores defined by IUPAC are introduced into high aspect ratio silicon-based anode active materials through an etching process, non-uniformity in etching occurs due to factors such as diffusion resistance for the etchant to diffuse into the particles, various particle diameter distributions, and various aspect ratios. Consequently, this can lead to problems regarding non-uniformity in pores and the electrochemical properties of the anode active material particles.

[0048] In particular, the polydispersity of particle sizes and high expansion during charging characteristics of silicon-based cathode active materials can lead to more pronounced issues of physical deformation or collapse in particles with relatively large particle sizes and high aspect ratios. These problems can inevitably lead to significant variations in the mechanical properties of the particles, degradation of electrochemical characteristics due to insufficient conductive networks within the particles, and reduced cycle performance.

[0049] It was found that the physical properties of polydisperse porous silicon-based cathode active material particles with a high aspect ratio and the characteristics of electrochemical devices have a strong interrelationship in specific variables considering particle hardness and aspect ratio.

[0050] Specifically, the silicon-based negative electrode active material according to the present invention can have a strong correlation between the physical properties of the polydisperse silicon-based negative electrode active material having a high aspect ratio and the characteristics of the electrochemical device.

[0051] In Equation 1 above, 'a' represents the particle aspect ratio. By introducing the particle aspect ratio variable into Equation 1, a higher weight is assigned to inferior properties that may easily occur in particles with a high aspect ratio, thereby serving as an indicator of the uniformity of electrochemical properties between particles. In Equation 1 above, Ni represents the number of particles possessing the i-th property (specifically, particle diameter), and Si represents the hardness of the particles possessing the i-th property. The hardness may refer to the hardness measured through a nano-indentation test. To elaborate, Equation 1 above It does not refer to the average physical properties of the cathode material particles, but may refer to the physical properties at the corresponding particle size calculated by giving higher weight to cathode material particles with high aspect ratios and large particle sizes.

[0052] More specifically, as the above formula 1 satisfies 0.9 to 1.1, 0.92 to 1.08, 0.93 to 1.07, or 0.95 to 1.05, or 0.9 to 1.0, 0.92 to 1.0, 0.93 to 1.0, or 0.95 to 1.0, the electrochemical device comprising the silicon-based negative electrode active material can have high capacity and excellent cycle characteristics despite being a polydisperse particle system with a high aspect ratio.

[0053] Furthermore, the silicon-based negative electrode active material has a carbon coating layer located in the depth direction of the silicon-based core, so the specific surface area of ​​the silicon-carbon interface is very large, and the silicon-carbon interface is formed not only on the particle surface of the silicon-based core but also inside. Accordingly, the silicon-based negative electrode active material exhibits excellent ion / electron conductivity to satisfy high capacity, and can provide an electrochemical device with significantly improved electrochemical characteristics, such as excellent rate capability and high charge / discharge efficiency. In addition, as stress generated during volume change of silicon is dispersed through the pores formed in the silicon-based core, volume expansion of silicon can be effectively mitigated, thereby enhancing structural stability and improving the long-term cycle stability of the battery.

[0054] According to some embodiments, the aspect ratio of the silicon-based negative electrode active material may be greater than 1 and less than or equal to 10, specifically 1.1 or more and less than or equal to 8, or 1.2 or more and less than or equal to 5. The average aspect ratio of the silicon-based negative electrode active material particles may be determined using a particle shape analyzer. For example, it may be an average value obtained by ultrasonically dispersing particles in a solvent medium and then performing image analysis through the analyzer. The average aspect ratio may be a value calculated by analyzing 500 or more, 1000 or more, or 2000 or more particles, for example, a value obtained by image analyzing 500 to 5000 particles.

[0055] According to some embodiments, the parameter represented by the following Formula 2 of the silicon-based negative electrode active material may satisfy 0.9 to 1.1.

[0056] [Equation 2]

[0057] H50 / H90

[0058] In Equation 2 above, H50 is 10 silicon-based negative electrode active material particles with a diameter range of D50±20%. It is the hardness (MPa) obtained from, and H90 is of 10 silicon-based negative electrode active material particles with a diameter range of D90±20%. It means the hardness (MPa) obtained from, and a means the average aspect ratio of the silicon-based negative electrode active material.

[0059] As the parameter represented by Equation 2 of the silicon-based negative electrode active material further satisfies 0.9 to 1.1, 0.92 to 1.08, 0.93 to 1.07, or 0.95 to 1.05, or further satisfies 1.0 to 1.1, 1.0 to 1.08, 1.0 to 1.07, or 1.0 to 1.05, the negative electrode active material of a polydisperse particle system with a high aspect ratio can have an overall homogeneous pore structure and electrochemical properties, and thus can have superior cycle characteristics.

[0060] The above silicon-based negative electrode active material may have an elasticity of 110 to 150 GPa, specifically an elasticity of 120 to 140 GPa. The elasticity may be measured through a nano-indentation test and may refer to the average value of 10 randomly selected particles. As the silicon-based negative electrode active material has the aforementioned elasticity, it may have superior resistance to the volume expansion of silicon.

[0061] The silicon-based core described above has a porous structure containing a plurality of pores internally, through which stress resulting from volume changes occurring during the charging and discharging process of silicon can be effectively dispersed. Accordingly, structural collapse caused by the rapid volume expansion of silicon can be suppressed, and the structural stability of the anode material can be improved, while the long-term cycle stability of the battery can be enhanced.

[0062] The macropores formed in the silicon-based core may have a structure that is continuously connected from the surface to the interior of the silicon-based core. Additionally, the pores formed in the silicon-based core may further include mesopores according to the IUPAC definition, and these pores may be distributed discontinuously or continuously within the silicon-based core. The pore structure contributes to alleviating mechanical stress occurring within the silicon particles and at the interfaces, and preventing a degradation of electrical and mechanical contact within the electrode, by providing a buffer space capable of accommodating the volume expansion of silicon during charging and discharging.

[0063] The porous structure of the silicon-based core may increase the specific surface area due to the formation of pores, thereby expanding the reaction area between the electrode and the electrolyte and allowing a solid electrolyte interface layer to be formed during the charge-discharge process. However, in the negative electrode material according to the present invention, a carbon layer is formed on the surface of the silicon-based core and on a portion of the internal pores, and the carbon layer continuously penetrates into the pores to surround the silicon-based core, so that the actual exposed surface area of ​​silicon in direct contact with the electrolyte may be similar to that of a general silicon-based core that does not contain pores. Accordingly, even though the silicon-based core has an increased specific surface area due to pore formation, the direct interfacial reaction between the electrode and the electrolyte in the silicon-based negative electrode active material can be mitigated, and the electrochemical stability of the electrode can be maintained even during repeated charge-discharge processes.

[0064] The carbon coating layer may include a carbon outer layer located on the outer surface of the silicon-based core and a carbon inner layer filled in at least a portion of the pores located inside the silicon-based core. Specifically, 10 to 100 area%, 15 to 90 area%, and specifically 20 to 70 area% of the total pores inside the silicon-based core may be filled with the carbon inner layer. The area fraction occupied by the carbon inner layer can be defined as the ratio (Ac / Ap) of the total area of ​​the pores (Ap) on the particle cross-section and the total area of ​​the carbon inner layer (Ac), by measuring the cross-section of the silicon-based negative electrode active material with an electron microscope.

[0065] According to some embodiments, a carbon inner layer filled in at least a portion of the silicon-based core pores may be electrically connected to a carbon outer layer located on the outer surface of the silicon-based core. As the carbon outer layer and the carbon inner layer are electrically connected to each other, a pathway for electron movement is secured, which can dramatically improve the conductivity of the silicon-based core having insulating properties. In addition, the resistance inside the electrochemical device is reduced, which not only improves high-rate charge / discharge characteristics but also alleviates the inherent volume change stress of silicon and maintains stable charge transfer, thereby significantly improving cycle life.

[0066] According to some embodiments, the matrix of the silicon-based core may be a silicon oxide matrix.

[0067] 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 in the dispersed phase of the cathode material. In this specification, the matrix refers to a material in the cathode material excluding silicon (Si) nanocrystals.

[0068] 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

[0069] The above silicon-based core may be silicon oxide as a matrix, that is, silicon oxide represented by the chemical formula SiOx, and the oxidation number x may satisfy a real number from 1.5 to 2, but is not limited thereto.

[0070] According to some other embodiments, the matrix of the silicon-based core may comprise a complex oxide of silicon and one or more doping elements selected from the group consisting of alkali metals, alkaline earth metals, and post-transition metals.

[0071] The silicon-based core may be a silicon composite oxide doped with one or more metal elements selected from the group consisting of alkali metals, alkaline earth metals, and post-transition metals as a matrix. The composite oxide may refer to a crystalline composite oxide having a crystal structure different from that of silicon oxide due to the doping of metal elements. The composite oxide may refer to a metal silicate and may be represented by the chemical formula MaSiOb, where a satisfies a real number from 0.5 to 5 and b satisfies a real number from 1 to 8, but is not limited thereto. Specifically, a and b may be real numbers combined such that MaSiOb satisfies charge neutrality. For example, when M is Mg, the composite oxide may include one or more oxides selected from MgSiO3 and Mg2SiO4, but is not limited to the chemical formula of a specific oxide in the present invention.

[0072] The doping element may be selected from one or more of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), manganese (Mn), nickel (Ni), zinc (Zn), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and bismuth (Bi). Accordingly, the composite oxide may be an oxide between silicon and one or more elements selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), manganese (Mn), nickel (Ni), zinc (Zn), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and bismuth (Bi).

[0073] Silicon nanocrystals may have a size (diameter) that is typically defined as a nanocrystal. Non-limitingly, it may refer to crystals having a diameter of 100 nm or less. 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. Specifically, the silicon nanocrystals may be 5 to 80 nm or 7 to 50 nm.

[0074] According to some embodiments, the silicon-based negative electrode active material is in the form of particles, and based on the longest diameter (D) of the silicon-based negative electrode active material particles, the pore depth (P) formed from the outer surface of the silicon-based core toward the center is D ) may include pores satisfying the following Equation 3.

[0075] (Equation 3)

[0076] 0.1 ≤ (P D / D)

[0077] Specifically, the above Equation 3 may be 0.15 or greater or 0.2 or greater, and may be 0.9 or less or 0.8 or less, but is not limited thereto.

[0078] According to some embodiments, the BET specific surface area of ​​the silicon-based core is 10 to 200 m² 2 It may be / g. Specifically, the BET specific surface area is based on the BET (Brunauer-Emmett-Teller) method at the nitrogen adsorption-desorption isotherm of the silicon-based core. Specifically, the BET specific surface area of ​​the core is 15 to 150 m² 2 / g, 20 to 100 m 2 / g, 20 to 80 m 2 / g Specifically 30 to 60 m 2 It may be / g. The BET specific surface area of ​​the silicon-based core may be measured after removing the carbon layer (carbon film) of the silicon-based negative electrode active material by oxidizing it (> 600°C, > 2h) under an oxygen or air atmosphere.

[0079] According to some embodiments, the BET specific surface area of ​​the silicon-based negative electrode active material is 1 to 20 m² 2 / g, 1 to 15 m 2 / g, specifically 1 to 10 m 2 / g or 1 to 8 m 2 It can be / g.

[0080] According to some embodiments, the average particle size (D50) of the silicon-based negative electrode active material is not particularly limited. The average particle size may refer to the volume-based median diameter (D50) calculated by laser diffraction. The volume-based D50 refers to the particle size at the point where the cumulative volume% is 50 volume% in a cumulative distribution curve (cumulative distribution curve) accumulated in order of particle diameter. Experimentally, a cumulative distribution curve including D50 can be obtained by a conventional particle size analyzer using a laser diffraction method or a dynamic light scattering method.

[0081] According to some embodiments, the average diameter (D50) of the silicon-based negative electrode active material may be 1 μm to 20 μm. Specifically, the average diameter (D50) of the silicon-based negative electrode active material may be 2 μm to 18 μm, 4 μm to 15 μm, or 6 μm to 10 μm. Meanwhile, D10 may be 0.1 μm to 10 μm, 1 μm to 10 μm, or 2 μm to 8 μm, and D90 may be 1 μm to 30 μm, 5 μm to 20 μm, or 8 μm to 18 μm. The (D90-D10) / D50 corresponding to the Span may be 2 or less, 1.5 or less, 1.3 or less, or 1 or less, and may be 0.1 or more, 0.2 or more, or 0.3 or more.

[0082] According to some embodiments, the elemental ratio (O / C) of oxygen (O) and carbon (C) of the silicon-based negative electrode active material may be 1 to 12, 1 to 10, or 1.2 to 8, and specifically may satisfy 1.2 to 6 or 1.5 to 4. The elemental ratio (O / C) of the silicon-based negative electrode active material may be calculated through inductively coupled plasma spectroscopy (ICP-OES), and as the elemental ratio (O / C) satisfies the above numerical range, the consumption of lithium ions can be prevented through the reduction of the inactive phase, thereby improving the initial reversible efficiency and improving the energy density, which may be desirable.

[0083] 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 with an average molecular weight of 100 to 2,000 Da, specifically 100 to 1,000 Da, as measured by MALDI-TOF. As a non-limiting example, the liquid carbon precursor may be coal tar or petroleum residual oil.

[0084] 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.

[0085] According to some embodiments, the carbon coating layer may be prepared by carbonizing coal tar. The liquid coal tar may refer to coal tar that is liquid in itself at room temperature (25 °C) and atmospheric pressure (1 atm) without the aid of chemicals such as solvents or the application of external energy such as heat. Specifically, the liquid coal tar may have a specific gravity of 1.1 to 1.5 g / cc, specifically 1.1 to 1.3 g / cc at room temperature. Such liquid coal tar is advantageous because it can easily penetrate into the macropores formed in the silicon-based core particles and form a carbon inner layer after carbonization.

[0086] The content of the carbon coating layer may be 1 to 15 weight%, specifically 2 to 10 weight% or 3 to 8 weight% of the total weight of the silicon-based negative electrode active material.

[0087] The pores formed in the depth direction of the silicon-based core of the silicon-based negative electrode active material may be produced by the step of forming pores by treating with an etching solution having solubility for the matrix; or the step of forming pores by treating with the etching solution a matrix in which a first phase insoluble for the etching solution and a second phase soluble for the etching solution are mixed together.

[0088] Specifically, the first phase, which is insoluble in the etching solution, remains in the silicon-based core even after the etching process, and the second phase, which is soluble in the etching solution, is removed during the etching process to form pores within the silicon-based core. It may be preferable for the second phase to form clusters or domains of a certain size or larger. More specifically, the second phase, which is soluble in the etching solution, may be a silicon oxide phase including silicon oxide, for example, SiO2.

[0089] The etching solution may include a surface protective agent, an organic acid, an inorganic acid, and the remainder being water. Specifically, the etching solution may include 1 to 10 weight percent of a surface protective agent, 2 to 20 weight percent of an organic acid, 0.1 to 5 weight percent of an inorganic acid, and the remainder being water, based on the total weight of the composition. As the etching solution contains the above components and content, it can induce more uniform etching of the second phase.

[0090] The above inorganic acid may be one or more selected from hydrochloric acid, sulfuric acid, and nitric acid, and specifically may be hydrochloric acid.

[0091] The above organic acid may be one or more selected from the group consisting of acetic acid, citric acid, glutaric acid, glycolic acid, formic acid, lactic acid, malic acid, maleic acid, oxalic acid, phthalic acid, succinic acid, tartaric acid, iminodiacetic acid, and propionic acid, and specifically may be acetic acid, formic acid, or iminodiacetic acid.

[0092] To suppress oxidation of Si and protect the surface during the etching process, the above surface protective agent may be selected from methyl lactate, ethyl lactate, or methyl-2-hydroxyisobutyrate.

[0093] The above etching solution may further include one or more additives selected from the group consisting of organic solvents, surfactants, heteroaromatic compounds, and salts to improve the etching selectivity. The organic solvent may be a solvent that is miscible with water.

[0094] The above etching process can be performed at room temperature, and a silicon-based core can be manufactured by etching a second phase that is soluble in the etching solution and then repeatedly washing with an acidic aqueous solution containing an organic acid to remove residual impurities. The silicon-based core can then be used to form a carbon coating layer by carbonizing a liquid carbon precursor as described above, thereby finally manufacturing a silicon-based negative electrode active material.

[0095] The silicon-based negative electrode active material described above may be included as an active material for a negative electrode of a lithium secondary battery, and a negative electrode and a lithium secondary battery including the same will be described below.

[0096] According to another embodiment of the present invention, a negative electrode for a lithium secondary battery is provided, said negative electrode comprises a negative electrode current collector and a negative electrode active material layer comprising a silicon-based negative electrode active material according to any one of the embodiments described above on the negative electrode current collector.

[0097] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the lithium secondary battery, and for example, copper (Cu), stainless steel, aluminum, nickel, titanium, or surfaces treated with carbon, nickel, titanium, silver, etc. may be selected. Specifically, the above negative electrode current collector may be selected as a copper foil that is electrochemically stable and has excellent ductility within the negative potential range of the lithium secondary battery, and may have a thickness of 3㎛ to 100㎛.

[0098] The above-described negative electrode active material layer may further include a graphite-based active material capable of reversibly absorbing and releasing lithium ions, in addition to the silicon-based negative electrode active material described above. Natural graphite and artificial graphite may be used as the graphite-based active material, either alone or in combination. The graphite-based active material has a low lithium absorption and release potential similar to that of lithium metal, which is advantageous for increasing the operating voltage of the battery, and can also provide excellent reversibility and structural stability.

[0099] The above-described negative electrode active material layer may further include a binder and a conductive material together with the above-described negative electrode active material. To suppress volume expansion during charging and discharging and to maintain the structural integrity of the electrode, the binder may include one or more selected from the group consisting of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyimide (PI). Specifically, the polyacrylic acid (PAA)-based binder can effectively prevent the detachment of the active material even during repeated cycling processes by forming strong hydrogen bonds or covalent bonds with the surface of silicon particles.

[0100] The above conductive material serves to lower the resistance of the electrode by securing an electron transport path between the negative electrode active material and the current collector, and a carbon-based material having excellent conductivity without causing chemical side reactions may be used. Specifically, a linear or plate-shaped conductive material selected from the group consisting of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube (CNT), and graphene may be included alone or in combination.

[0101] The above-mentioned cathode can be manufactured according to a conventional cathode manufacturing method and may consist of slurry preparation, coating, drying, and rolling processes. In the slurry preparation step, a cathode active material, a conductive material, a binder, and a solvent can be mixed in a predetermined mixing ratio to form a slurry in a uniformly dispersed state. At this time, water or NMP (N-methyl-2-pyrrolidone) may be used as the solvent depending on the type of binder. When a silicon-based cathode active material is included as the cathode active material, mechanical energy may be applied using a high-shear mixer or a planetary mixer to ensure uniform dispersion of a functional binder such as polyacrylic acid.

[0102] In the coating and drying step, the prepared cathode slurry can be applied to at least one surface of the cathode current collector to a uniform thickness using a doctor blade, slot die, or comma coater. The applied slurry can be passed through a drying oven set to a certain temperature range to remove the solvent. In the rolling step, the dried cathode composite layer is passed through a roll press at high temperature or room temperature to compress it to reach a desired composite density, the rolled electrode sheet is slit to a certain width according to the battery design specifications, and the final cathode can be manufactured by completely removing the residual solvent through vacuum drying.

[0103] <Polar>

[0104] The anode comprises an anode current collector and an anode active material layer formed on the anode current collector. The anode current collector may be made of a material that provides electrical conductivity but does not substantially participate in electrochemical reactions during the charging and discharging process of the battery, and, for example, aluminum, nickel, titanium, stainless steel, or alloys thereof may be used. The anode current collector may be provided in the form of a film, sheet, or foil and may include a fine uneven structure on its surface.

[0105] The above-mentioned positive active material layer may use a positive active material capable of reversible intercalation and deintercalation of lithium ions. The positive active material may include one or more selected from the group consisting of layered structure compounds, spinel structure compounds, and olivine structure compounds. Specifically, NCM-based compounds and NCA-based compounds may be exemplified as layered structure compounds, LMO-based compounds may be exemplified as spinel structure compounds, and LFP-based compounds may be exemplified as olivine structure compounds.

[0106] In addition, the positive active material layer may include a binder to improve the bonding force between the positive active material particles and the adhesion force with the positive current collector. The binder can provide viscosity control and coating stability of the slurry during the electrode manufacturing process, while simultaneously playing a role in stably maintaining the electrode structure against volume changes occurring during the charging and discharging process; for example, a fluorine-based binder such as polyvinylidene fluoride (PVdF) may be exemplified. The positive active material layer may further include a conductive material to reduce the electrical resistance of the electrode and form an electron transfer path. The conductive material may include a linear or plate-shaped conductive material selected from the group consisting of carbon black, acetylene black, Ketjen black, carbon fiber, and carbon nanotubes (CNT), either alone or in combination.

[0107] The above anode can be manufactured according to a conventional cathode manufacturing method and may consist of slurry preparation, coating, drying, and rolling processes.

[0108] In the anode slurry manufacturing step, an anode active material, a conductive material, and a binder are introduced into an organic solvent such as NMP to form a slurry with uniform viscosity. A dispersion process applying strong shear force using a high-speed mixer may be performed on the slurry to ensure that the anode active material and the conductive material are uniformly dispersed. In the coating and drying step, the manufactured anode slurry is applied to a specific thickness onto an anode current collector, such as aluminum foil. Immediately after application, the electrode sheet passes through a drying oven controlled by multi-stage temperature to evaporate the organic solvent. In the rolling step, the dried anode sheet is passed between a pair of rotating roll presses to compress it until it reaches a set composite density. The rolled electrode sheet is then slit to a specific width according to the battery design specifications, and the residual solvent is completely removed through vacuum drying to manufacture the final anode.

[0109] Separator

[0110] The above separator can be interposed between the positive and negative electrodes to prevent electrical short circuits between the electrodes while allowing the movement of lithium ions. The separator may be formed as a polymer film having a porous structure and may include a polyolefin-based polymer such as polyethylene, polypropylene, or a copolymer thereof.

[0111] The above separation membrane may be formed in a single-layer or multi-layer structure, and may further include a coating layer containing inorganic particles on at least one surface of the separation membrane as needed, and the inorganic particles may be alumina, silica, zirconia, or titania.

[0112] Electrolytes

[0113] The above lithium secondary battery may further include an electrolyte within the electrode assembly. The electrolyte performs the role of mediating the movement of lithium ions and may be a non-aqueous electrolyte comprising a lithium salt and an organic solvent capable of dissolving it.

[0114] The above organic solvent may be a solvent having high dielectric constant and low viscosity characteristics, and carbonate-based solvents such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylmethyl carbonate (EMC) may be used, and one of these may be used alone or two or more may be mixed. In the case of a mixed solvent, electrochemical stability is maintained within the operating voltage range of the battery, and low-temperature characteristics can be improved by lowering the freezing point of the electrolyte.

[0115] Lithium salts dissociate in a solvent to serve as a source of lithium ions and can directly affect the output and lifespan characteristics of the battery. For example, LiPF6, LiBF4, LiClO4, LiAsF6, LiTFSI, LiFSI, or mixtures thereof may be used, and the concentration of the lithium salt in the electrolyte may be in the range of 0.5M to 2.0M. In addition, the electrolyte may contain functional additives, which can form a stable SEI layer (Solid Electrolyte Interphase) on the electrode surface to suppress further decomposition of the electrolyte. In particular, by introducing an additive such as vinylene carbonate (VC) to form a robust SEI layer on the negative electrode surface, electrolyte depletion due to volume expansion of the silicon-based active material is prevented, and on the positive electrode side, an explosion-proof function can be performed to suppress heat generation during overcharging.

[0116] Lithium secondary battery

[0117] A lithium secondary battery is provided according to another embodiment of the present invention. The lithium secondary battery may include a positive electrode and a negative electrode disposed opposite to the positive electrode, and the negative electrode may include a porous silicon-based negative electrode active material as described above.

[0118] The above lithium secondary battery may include an electrode assembly and a case housing the electrode assembly, and the electrode assembly may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte impregnated in the electrode assembly.

[0119] The electrode assembly may be formed in a wound, laminated, or mixed laminated / wound structure, and an appropriate shape may be selected according to the application and required characteristics of the battery. Additionally, the electrode assembly may be housed and sealed within a battery case. The battery case may be pouch-type, cylindrical, or prismatic, and various shapes may be applied depending on the intended use of the battery. The electrode assembly and electrolyte are housed inside the battery case, and the case may be configured to protect the battery from the external environment.

[0120] Lithium-ion batteries can be applied in various fields such as portable electronic devices, energy storage systems (ESS), electric vehicles, and hybrid vehicles, and can be designed to meet the electrical characteristics, capacity, output, and durability characteristics required depending on the application field.

[0121] Hereinafter, embodiments and comparative examples according to the present invention are described. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0122] (Analysis and Measurement Methods)

[0123] 1. Average particle size (D 50 )

[0124] 0.01 g of particles were suspended in ethanol, and the prepared suspension was sonicated for 1 minute. Subsequently, the cumulative volumetric diameter distribution was measured using a laser diffraction particle size distribution analyzer (Microtrac S3500). The median diameter D of the analyte 50 represents the diameter at the position where the cumulative volume is 50% in the cumulative volume diameter distribution.

[0125] 2. Aspect ratio of particles

[0126] The aspect ratio of the particles was measured using an analyzer (Flowcam 8100, Fluid Imaging Technologies) commonly used for particle morphology analysis after ultrasonically dispersing 0.01 g of the analyte in 5 mL of ethanol. The calculated aspect ratio of the particles represents the average value, and the average aspect ratio is a statistical average value obtained by securing the aspect ratios of at least 500, and generally 1000, individual particles and averaging the secured aspect ratio values.

[0127] 3. Analysis of Nano-indentation Properties of Particles

[0128] To evaluate the mechanical properties of the particles, hardness and elastic modulus were measured using a nano-indentation test. An ultra-precision nano-indentation tester (Ultra Nanoindentation Tester, UNHT, Anton Paar) was used for the measurements. Specifically, the measurement conditions were set as follows: a Berkovich diamond tip was used as the indenter, Sinus mode was selected as the measurement mode, the maximum load was 50,000 N, the sinus amplitude was 5,000 N, the sinus frequency was 10 Hz, and the loading rate was 0.05 1 / s. For each particle sample, the change in stiffness according to the penetration depth (Pd) was recorded in real time by applying the sinus mode; based on this, hardness, which represents the material's resistance to plastic deformation, and elastic modulus, which represents its deformation recovery characteristics, were calculated, respectively.

[0129] 4. Area fraction (%) of the carbon inner layer

[0130] The cross-section of a silicon-based cathode active material immobilized with resin was measured by magnifying it 2,500 times using a scanning electron microscope, and the total area of ​​the pores (Ap) on the particle cross-section and the total area of ​​the carbon inner layer filled within the pores (Ac) were calculated through image analysis. The area fraction (%) of the carbon inner layer was calculated by calculating (Ac / Ap) from the area calculated through image analysis. The area fraction (%) of each sample was determined as the average value of a total of 10 particles.

[0131]

[0132] (Example 1)

[0133] Silicon oxide (SiO) powder ground to a D50 of 6 μm and Mg metal powder raw materials were each introduced into a powder mixer and homogeneously mixed in a molar ratio of SiO:Mg = 11.5:1. The mixture was heat-treated at 850°C for 12 hours in an inert atmosphere to produce a composite oxide. At this time, it was confirmed that 4.577 wt% of Mg was contained based on the total weight of the composite oxide.

[0134] After obtaining a powder by mechanically grinding a heat-treated composite oxide, the powder was introduced into an aqueous etching solution containing 5 wt% methyl-2-hydroxyisobutyrate, 10 wt% acetic acid, 3 wt% hydrochloric acid, and the remainder being distilled water, and etching was performed in multiple stages until the residual magnesium content was 200 ppm or less to produce a porous cathode substrate (silicon-based core).

[0135] To remove residual etching solution and impurities remaining in the etched porous cathode substrate, repeated washing was performed using an aqueous solution containing 1 wt% hydrochloric acid, followed by repeated washing with distilled water until the pH reached 6 or higher. The cleaned porous cathode substrate was dried at 120°C for 24 hours. The BET specific surface area of ​​the substrate was 45 m² 2 / g, according to Equation 3 (P D / D) was found to be 0.57. Referring to Figure 1, it can be seen that a number of macropores are formed on the surface of the porous cathode substrate.

[0136] Coal tar was introduced into a planetary mixer at a weight ratio of 10:1 to the porous cathode substrate and mixed at 37°C for 1 hour at a linear velocity of 0.6 m / s to obtain a mixture. Subsequently, the mixture was placed in a graphite crucible, heated to 900°C under a nitrogen atmosphere, and maintained at 900°C for 90 minutes. Afterward, the mixture was naturally cooled to room temperature to produce a cathode material with a carbon film formed thereon. As a result of ICP-OES analysis of the cathode material, the elemental ratio of oxygen (O) to carbon (C) (O / C) was found to be 7.7, and the average aspect ratio was found to be 1.7. The average hardness value measured through a nano-indentation test was found to be 10.5 GPa. Referring to Fig. 2, as a carbon coating layer is formed, all macropores present on the surface of the porous cathode substrate are coated with carbon, and no macropores are observed. Referring to Fig. 3, it can be confirmed that a significant portion of the macropores on the cross-section of the silicon-based cathode active material immobilized with resin have been removed and filled with carbon.

[0137] (Example 2)

[0138] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that Ca metal powder raw material was used instead of Mg metal powder raw material, and etching was performed until the residual Ca content, rather than the residual magnesium content, became 200 ppm or less.

[0139] (Example 3)

[0140] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that Mn metal powder raw material was used instead of Mg metal powder raw material, and etching was performed until the residual Mn content, rather than the residual magnesium content, became 200 ppm or less.

[0141] (Example 4)

[0142] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that silicon oxide (SiO) powder and Mg metal powder raw materials were used in a molar ratio of SiO:Mg = 10:1.

[0143] (Example 5)

[0144] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that silicon oxide (SiO) powder and Mg metal powder raw materials were used in a molar ratio of SiO:Mg = 8:1.

[0145] (Example 6)

[0146] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that Ni metal powder raw material was used instead of Mg metal powder raw material, and etching was performed until the residual Ni content, rather than the residual magnesium content, became 200 ppm or less.

[0147] (Example 7)

[0148] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that Zn metal powder raw material was used instead of Mg metal powder raw material, and etching was performed until the residual Zn content, rather than the residual magnesium content, was 200 ppm or less.

[0149] (Example 8)

[0150] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that to form a carbon coating layer on a porous cathode material substrate, methane gas was supplied as a carbon precursor and coated through a CVD process at 900°C for 1 hour.

[0151] (Comparative Example 1)

[0152] Si and SiO2 were homogeneously mixed in a molar ratio of 1:1 and then pelletized using a mold. The pelletized mixed raw material was placed in a crucible inside a vacuum chamber of 0.1 torr or less, heated to 1,400°C to vaporize it, and then condensed on a collection plate at 400°C to obtain silicon oxide.

[0153] The silicon oxide cathode material obtained above was ground to a D50 of 6 μm to produce a particulate cathode material, and a cathode material was produced by supplying methane gas to a carbon precursor and coating it through a CVD process at 900°C for 1 hour.

[0154] (Comparative Example 2)

[0155] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that the heat-treated composite oxide was mechanically ground to obtain a ground powder, and then etched by introducing it into a 1 M aqueous hydrochloric acid (HCl) solution until the residual magnesium content was 200 ppm or less.

[0156] (Comparative Example 3)

[0157] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that the heat-treated composite oxide was mechanically ground to obtain a ground powder, and then etched in multiple stages by adding it to a 2 M aqueous hydrochloric acid (HCl) solution until the residual magnesium content was 200 ppm or less.

[0158] (Comparative Example 4)

[0159] In the above Example 1, a cathode material was prepared in the same manner as in Example 1, except that the heat-treated composite oxide was mechanically ground to obtain a ground powder, and then etched by adding it to a mixed aqueous solution of 10% by weight of 1 M hydrochloric acid (HCl) and 0.5 M acetic acid until the residual magnesium content was 200 ppm or less.

[0160]

[0161] (Battery manufacturing)

[0162] 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 and coated onto a copper foil 17 μm thick. The mixture was then dried at 90°C for 40 minutes, followed by compression using a roll press and vacuum drying at 120°C for 12 hours. After drying, the material was stamped to a diameter of 14 mm. A CR2032 coin-type half-cell was fabricated by using a metallic lithium electrode with a diameter of 16 mm as the counter electrode, placing an electrolyte between the electrodes with a separator with a diameter of 18 mm, 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.

[0163]

[0164] (Battery Performance Evaluation)

[0165] Subsequently, the manufactured battery was charged (lithiated) to 0.005V with a constant current of 0.1C, charged at a constant voltage of 0.005V until it reached 0.01C, and then discharged (de-lithiated) to 1.5V with a constant current of 0.1C (first formation step). Then, the formation process was performed by charging (lithiating) again to 0.005V with a constant current of 0.1C, charging at a constant voltage of 0.005V until it reached 0.01C, and then discharging (de-lithiated) to 1.0V with a constant current of 0.1C (second formation step).

[0166] The initial charge-discharge efficiency was evaluated based on the charge-discharge in the first formation step, and after the formation process, 50 charge-discharge cycles were performed under the condition of charging to 0.005V (Cut-off 0.01C) with a constant current of 0.5C and discharging to 1.0V with a constant current of 0.5C in a room temperature (25℃) environment. The capacity retention rate (%) was calculated using the equation (C50 / C1X100) based on the discharge capacity of the first cycle (C1) and the discharge capacity after 50 cycles (C50). At this time, a rest period of 10 minutes was given between each charge and discharge step.

[0167] Metal Carbon Inner Layer (Area %) (O / C) Atomic Ratio Average Aspect Ratio H50 / H10 H50 / H90 Capacity (mAh / g) Efficiency (%) Lifetime (%) Example 1 Mg 347.7 1.70 0.95 1.05 1.60 786.19 1.3 Example 2 Ca 297.8 1.68 0.93 1.06 1.55 486.59 0.4 Example 3 Mn 338.0 1.77 0.94 1.04 1.52 086.98 9.3 Example 4 Mg 457.2 1.72 0.94 1.07 1.69 288.29 1.0 Example 5 Mg 476.5 1.79 0.92 1.09 1.75 886.79 0.2 Example 6 Ni 257.9 1.63 0. 921.041,47486.490.2 Example 7 Zn238.01.880.941.081,45685.389.1 Example 8 Mg188.51.830.951.071,59185.985.8 Comparative Example 1--12.81.660.981.031,67874.387.8 Comparative Example 2 Mg288.21.720.791.191,58086.782.5 Comparative Example 3 Mg318.01.750.851.151,61085.283.2 Comparative Example 4 Mg327.91.640.881.121,58783.184.7

[0168] Referring to Table 1 above, the battery containing the silicon-based negative electrode active material according to the example showed an increase in capacity and an improvement in lifespan characteristics, whereas the battery containing the silicon-based negative electrode active material without macropores according to Comparative Example 1 showed a low capacity. In the case of Comparative Examples 2 to 4, the efficiency and lifespan characteristics were found to be poor due to the introduction of non-uniform pores.

[0169] 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.

[0170] Accordingly, the scope of the present invention is not limited to the described embodiments, and all things equivalent to or having equivalent variations to the claims set forth below, as well as the claims set forth below, shall be considered to fall within the scope of the concept of the present invention.

Claims

1. A silicon-based core; and a carbon coating layer located on the surface of the silicon-based core; comprising, The silicon-based core comprises: a matrix containing a silicon complex oxide or a mixture thereof, comprising silicon oxide, one or more doping elements selected from the group consisting of silicon oxide, alkali metals, alkaline earth metals, and post-transition metals; and silicon nanocrystals dispersed and embedded in the matrix. The above silicon-based core includes macropores formed in the depth direction, and The carbon coating layer is filled into at least a portion of the silicon-based core macropores, and A silicon-based negative electrode active material satisfying the following formula 1 of 0.9 to 1.

1. [Equation 1] H50 / H10 (In the above Equation 1, H50 is of 10 silicon-based negative electrode active material particles with a diameter range of D50±20% It is the hardness (MPa) obtained from, and H10 is of 10 silicon-based negative electrode active material particles with a diameter range of D10±20%. It refers to the hardness (MPa) obtained from, where a represents the average aspect ratio of the silicon-based negative electrode active material.

2. In Paragraph 1, A silicon-based negative electrode active material that further satisfies Formula 2 below of the above silicon-based negative electrode active material with a value of 0.9 to 1.

1. [Equation 2] H50 / H90 (In the above Equation 2, H50 is of 10 silicon-based negative electrode active material particles with a diameter range of D50±20% It is the hardness (MPa) obtained from, and H90 is of 10 silicon-based negative electrode active material particles with a diameter range of D90±20%. It refers to the hardness (MPa) obtained from, where a represents the average aspect ratio of the silicon-based negative electrode active material.

3. In Paragraph 1, A silicon-based negative electrode active material in which 15 to 90% of the total pore area inside the silicon-based core is filled with a carbon inner layer.

4. In Paragraph 1, The matrix of the above silicon-based core is silicon oxide, a silicon-based negative electrode active material.

5. In Paragraph 1, A silicon-based negative electrode active material, wherein the matrix of the silicon-based core comprises a complex oxide of silicon and one or more doping elements selected from the group consisting of alkali metals, alkaline earth metals, and post-transition metals.

6. In Paragraph 1, A silicon-based negative electrode active material in which a carbon inner layer filled in at least a portion of the silicon-based core pores is electrically connected to a carbon outer layer located on the outer surface of the silicon-based core.

7. In Paragraph 1, The above silicon-based negative electrode active material is in particulate form, and Based on the longest particle diameter (D) of the silicon-based negative electrode active material, the pore depth (P) formed from the outer surface of the silicon-based core toward the center is D A silicon-based negative electrode active material comprising pores satisfying Formula 3 below. (Equation 3) 0.1 ≤ (P D / D) 8. In Paragraph 1, The BET specific surface area of ​​the above silicon-based core is 20 to 80 m² 2 silicon-based negative electrode active material, / g.

9. In Paragraph 1, A silicon-based negative electrode active material having an elemental ratio (O / C) of oxygen (O) and carbon (C) of the silicon-based negative electrode active material satisfying 1 to 8.

10. In Paragraph 1, A silicon-based negative electrode active material having an average diameter (D50) of 4 μm to 15 μm.

11. In Paragraph 1, The above carbon coating layer is a silicon-based negative electrode active material manufactured by carbonizing coal tar.

12. In Paragraph 1, The pores formed in the depth direction of the above silicon-based core are, A step of forming pores by treating with an etching solution having solubility for the above matrix; or A silicon-based negative electrode active material manufactured from the step of forming pores by treating a matrix, wherein a first phase insoluble to an etching solution and a second phase soluble to an etching solution are mixed together, with the etching solution.

13. A lithium secondary battery comprising a negative electrode comprising a silicon-based negative electrode active material according to any one of claims 1 to 12; a positive electrode; a separator; and an electrolyte.

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