Negative electrode material for secondary batteries

Abstract

The present invention relates to an anode material for secondary batteries, the anode material for secondary batteries comprising a matrix containing a composite oxide of silicon and a doping element selected from at least one of a group consisting of silicon oxide, alkali metals, alkaline earth metals and base metals, or a mixture thereof, and silicon nanoparticles dispersed and contained in the matrix, and by satisfying crystallographic characteristics based on an X-ray diffraction pattern and residual tensile stress characteristics based on Raman spectroscopy, the anode material can improve the initial reversible efficiency of a secondary battery having the silicon-based anode material, and at the same time, can have a capacity retention rate at a level that allows practical commercialization, and can effectively suppress the volume expansion phenomenon of the anode.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode material for secondary batteries, and more particularly to a negative electrode material for secondary batteries having improved initial reversibility efficiency and cycle characteristics. [Background technology]

[0002] In diverse industrial sectors such as electronic products, electric / hybrid vehicles, and aerospace / drones, the demand for rechargeable batteries with not only high energy density and high power density characteristics, but also long lifespan and long usability is continuously increasing.

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

[0004] Therefore, in order to realize high-energy-density secondary batteries, research is continuously being conducted to use chalcogen-based materials such as sulfur (maximum capacity 1,675 mAh / g), silicon-based materials such as silicon (maximum capacity 4,200 mAh / g) and silicon oxide (maximum capacity 1,500 mAh / g), and transition metal oxides as negative electrode materials for secondary batteries, and among various materials, silicon-based negative electrode materials are attracting the most attention.

[0005] However, when particulate silicon is used as the negative electrode material, repeated charge-discharge cycling causes a rapid deterioration of battery characteristics due to large volume changes in silicon, leading to insulation loss, particle desorption, and increased contact resistance, resulting in the battery losing its function in less than 100 cycles. In the case of silicon oxide, lithium is lost due to irreversible products such as lithium silicate and lithium oxide, leading to a rapid decrease in initial charge-discharge efficiency.

[0006] In order to solve the problems of such silicon-based negative electrode materials, technologies such as nanosizing silicon in the form of wires or the like and compositing it with a carbon material, doping a silicon oxide with a different metal to form a composite oxide state, or pre-lithiating a silicon oxide have been proposed. However, there are still problems such as inferior initial charge-discharge efficiency, cycle characteristics, high-speed characteristics, etc., and it is difficult to commercialize.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a negative electrode material for a silicon-based secondary battery having improved initial reversible efficiency and stable cycle characteristics.

Means for Solving the Problems

[0009] In the negative electrode material for a secondary battery according to the present invention, the negative electrode material for a secondary battery includes a matrix containing a composite oxide of a silicon oxide, a doping element selected from one or more of an alkali metal, an alkaline earth metal, and a base metal group, and silicon, or a mixture thereof, and silicon nanoparticles dispersed and incorporated in the matrix. In an X-ray diffraction pattern using CuKα rays, The ratio (A1 / A2) between the area of ​​the first peak (A1) located in the diffraction angle 2θ range of 10° to 27.4° and the area of ​​the second peak (A2) located in the range of 28±0.5° is 0.8 to 6. When the above negative electrode material is subjected to Raman spectroscopy at 20 random positions, the number of tensile stresses is greater than the number of residual compressive stresses defined based on the center wavenumber of the Raman peak of bulk single-crystal silicon. The difference between the maximum and minimum values ​​of the difference obtained by selecting only the case of tensile stress in the deviation defined by Equation 1 below and excluding the maximum and minimum values ​​is 15 cm. -1 The following characteristics apply: [Formula 1] Deviation=WN(Si)-WN(ref) In Equation 1, WN(ref) is the center wave number of the Raman peak of bulk single-crystal silicon, and WN(Si) is the center wave number of the Raman peak of nanoparticle-sized silicon contained in the negative electrode material.

[0010] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the difference between the maximum and minimum values ​​of the difference in the case of tensile stress among the deviation values ​​defined by the above formula 1 is 11 cm. -1 It can be the following:

[0011] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the ratio (C / T) of the number of residual compressive stresses (C) to the number of residual tensile stresses (T) can be 0.5 or less.

[0012] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the ratio (L1 / L2) of the full width at half maximum (FWHM) of the first peak (L1) to the FWHM of the second peak (L2) in the X-ray diffraction pattern can be 6 to 15.

[0013] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the intensity ratio (I1 / I2) between the maximum intensity of the first peak (I1) and the maximum intensity of the second peak (I2) can be 0.05 to 1.25.

[0014] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the first peak may originate from amorphous silicon oxide, and the second peak may originate from crystalline silicon.

[0015] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the FWHM of the nanoparticle-like silicon Raman peak contained in the negative electrode material can be greater than the FWHM of the Raman peak of bulk single-crystal silicon.

[0016] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the FWHM of the nanoparticle-like silicon Raman peak contained in the negative electrode material is 4 to 20 cm². -1 It can be.

[0017] An anode material for a secondary battery according to one embodiment of the present invention contains a plurality of anode material particles and can have inter-particle composition uniformity according to the following formula 2. [Formula 2] 1.3 ≤ UF(D) In Equation 2, UF(D) is the value obtained by dividing the average doping element composition between negative electrode material particles by the standard deviation of the doping element composition, based on the weight % composition.

[0018] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the average diameter of the silicon nanoparticles can be 2 to 30 nm.

[0019] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the doping element is lithium One or more of the following can be selected: (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and bismuth (Bi).

[0020] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the negative electrode material can be in the form of parts with a volume-based average diameter (D50) of 1 to 50 μm.

[0021] In a negative electrode material for a secondary battery according to one embodiment of the present invention, the negative electrode material may further include a coating layer containing carbon.

[0022] The present invention includes a secondary battery comprising the above-described negative electrode material for secondary batteries. [Effects of the Invention]

[0023] The negative electrode material for secondary batteries according to the present invention comprises a matrix containing silicon oxide, a composite oxide of silicon and one or more doping elements selected from alkali metals, alkaline earth metals, and base metals, or a mixture thereof, and silicon nanoparticles dispersed in the matrix. By satisfying crystallographic properties based on X-ray diffraction patterns and residual tensile stress properties based on Raman spectroscopy analysis, the expansion of the aforementioned negative electrode material can be effectively suppressed, and the initial reversible efficiency of secondary batteries equipped with silicon-based negative electrode materials can be improved while simultaneously achieving a capacity retention rate at a level suitable for commercialization. [Brief explanation of the drawing]

[0024] [Figure 1] This is a diagram showing the X-ray diffraction (XRD) pattern of a negative electrode material manufactured by one embodiment of the present invention. [Figure 2] This diagram shows the Raman spectrum of a negative electrode material manufactured by one embodiment of the present invention. [Modes for carrying out the invention]

[0025] The negative electrode material for secondary batteries of the present invention will be described in detail below with reference to the attached drawings. The drawings presented below are provided as examples so that the concept of the present invention may be fully conveyed to those skilled in the art. Therefore, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the concept of the present invention. In this case, unless otherwise defined, the technical and scientific terms used have the meaning that a person skilled in the art to which this invention belongs would normally understand, and descriptions of known functions and configurations that could unnecessarily obscure the gist of the present invention in the following description and attached drawings will be omitted.

[0026] Furthermore, the singular form used in the specification and the attached claims may be intended to include plural forms unless otherwise indicated in the context.

[0027] In this specification and the appended claims, terms such as "first," "second," etc., are used not as limiting terms, but to distinguish one component from another.

[0028] In this specification and the appended claims, terms such as “includes” or “having” mean that the features or components described in the specification exist, and do not preclude the possibility that one or more other features or components may be added unless otherwise specified.

[0029] In this specification and the appended claims, parts such as films (layers), regions, and components are other When we say that a part is "on top of" another part, this includes not only cases where it is directly above or in contact with another part, but also cases where another membrane (layer), another region, or another component is interposed between them.

[0030] The applicant has found that in silicon-based anode materials, which are composites of silicon and silicon-based oxides, the electrochemical properties of the anode material are significantly affected by the residual stress of the silicon contained in the anode material. Based on this discovery, the applicant deepened their research and found that when silicon is dispersed in nanoparticle form in a silicon-based oxide matrix, and the number of residual tensile stresses is greater than the number of residual compressive stresses, while simultaneously exhibiting excellent uniformity of residual stress, the electrochemical properties of the anode material are significantly improved, thus completing the present invention.

[0031] Therefore, based on the above-mentioned discovery, the anode material according to the present invention exhibits electrochemical properties that cannot be obtained with conventional silicon-based anode materials, due to the bonding of silicon and matrix, which is dispersed in nanoparticle form and has a greater amount of uniform residual tensile stress. Thus, the present invention includes a variety of forms based on the properties of the silicon-based anode material according to the present invention.

[0032] In the present invention, the matrix can mean a solid medium in which nanoparticle-sized silicon is dispersed, and can mean a substance that forms a continuum with respect to the dispersed silicon nanoparticles in the negative electrode material. In the present invention, the matrix can mean a substance in the negative electrode material from which metallic silicon (Si) has been removed.

[0033] In this invention, the nanoparticles are 10, which is the size (diameter) that is normally defined for nanoparticles. 0 Nanometer order ~ 10 2 This can mean particles on the nanometer order, essentially particles with a diameter of 500 nm or less, specifically 200 nm or less, more specifically 100 nm or less, and even more specifically 50 nm or less.

[0034] In the present invention, the negative electrode material for secondary batteries includes, but is not necessarily limited to, a negative electrode material for lithium secondary batteries. The negative electrode material of the present invention can be used as an active material for secondary batteries such as sodium batteries, aluminum batteries, magnesium batteries, calcium batteries, and zinc batteries, and can also be used in other energy storage / generation devices that use conventional silicon-based materials, such as supercapacitors, dye-sensitive solar cells, and fuel cells.

[0035] The negative electrode material for secondary batteries according to the present invention comprises a matrix containing silicon oxide, a composite oxide of silicon and one or more doping elements selected from alkali metals, alkaline earth metals, and base metals, or a mixture thereof, and silicon nanoparticles dispersed in the matrix. In the X-ray diffraction pattern using CuKα rays, the ratio (A1 / A2) between the area of ​​the first peak (A1) located in the diffraction angle 2θ range of 10° to 27.4° and the area of ​​the second peak (A2) located in the range of 28±0.5° is 0.8 to 6. When the negative electrode material is subjected to Raman spectroscopy at 20 random positions, the number of tensile stresses is greater than the number of residual compressive stresses defined with respect to the center wavenumber of the Raman peak of bulk single-crystal silicon. In the displacement defined by the following formula 1, the difference between the maximum and minimum values ​​of the difference obtained by selecting only the case of tensile stress and excluding the maximum and minimum values ​​is 15 cm. -1 The following conditions must be met. [Formula 1] Deviation=WN(Si)-WN(ref) In the formula, WN(ref) is the center wavenumber of the Raman peak of bulk single-crystal silicon, and WN(Si) is the center wavenumber of the Raman peak of nanoparticle-sized silicon contained in the negative electrode material.

[0036] In the case of conventional secondary batteries containing silicon-based negative electrode materials, although the theoretical capacity can reach up to 4,200 mAh / g, a volume change of more than 300% occurs during charging, causing the negative electrode material to detach from the current collector, resulting in a significant decrease in cycle characteristics. Therefore, in practical use... Its use is limited.

[0037] On the other hand, the negative electrode material for secondary batteries according to the present invention comprises a matrix containing silicon oxide, a composite oxide of silicon and one or more doping elements selected from alkali metals, alkaline earth metals, and base metals, or a mixture thereof, and silicon nanoparticles dispersed in the matrix. By satisfying crystallographic properties based on X-ray diffraction patterns and residual tensile stress properties based on Raman spectroscopy analysis, it is possible to effectively suppress the volume expansion of the electrode, and it has the advantage of improving the initial reversible efficiency of secondary batteries equipped with silicon-based negative electrode materials while simultaneously having a capacity retention rate at a level that makes it possible to commercialize.

[0038] Specifically, in the Raman spectrum obtained through the Raman spectroscopy analysis of the negative electrode material described above, the ratio WN(ref) / WN(Si) between the central wave number WN(ref) of the Raman peak of bulk single-crystal silicon and the central wave number WN(Si) of the Raman peak of nanoparticle-like silicon contained in the negative electrode material can be used as a parameter to indicate the type and magnitude of residual stress remaining in the silicon nanoparticles dispersed in the matrix.

[0039] More specifically, when WN(ref) / WN(Si) is greater than 1, relative to the central wavenumber of the Raman peak of bulk single-crystal silicon, it means that the nanoparticle-like silicon has residual tensile stress, and when WN(ref) / WN(Si) is less than 1, it means that it has compressive residual stress.

[0040] In this context, the term "bulk single-crystal silicon" should be interpreted as meaning silicon of a size that exhibits the physical properties of bulk single-crystal silicon. To provide a clear comparison standard and ensure easy purchase, bulk single-crystal silicon can refer to single-crystal silicon wafers with a thickness of sub-mm order, specifically, 0.4 to 0.7 mm.

[0041] In addition, the Raman peaks of silicon in bulk single-crystal silicon and nano-particle silicon can refer to the Raman peaks located in the range of 400 to 560 cm -1 in the region, specifically in the range of 450 to 540 cm -1 in the region, more specifically in the range of 490 to 530 cm -1 in the region.

[0042] The center frequency of the peak, that is, the frequency corresponding to the center of the peak, can refer to the frequency with the maximum intensity value at the peak. At this time, when there are two or more Raman peaks in the above-mentioned Raman Shift region, the peak with the maximum intensity can correspond to the Raman peak of silicon. When two or more Raman peaks overlap and represent a bimodal form, the frequency with the maximum intensity value in the peak with the greater intensity among the two peaks can correspond to the center frequency of the peak.

[0043] The full width at half maximum (FWHM) of the Raman peak of the nano-particle silicon contained in the negative electrode material described above can be greater than the FWHM of the Raman peak of bulk single-crystal silicon. The larger FWHM value for bulk single-crystal silicon can be due to the structure in which the silicon contained in the negative electrode material is in the form of extremely fine particles and is dispersed and incorporated into the matrix.

[0044] Specifically, the FWHM of the Raman peak of the nano-particle silicon contained in the negative electrode material can be 4 to 20 cm -1 、6 to 20 cm -1 、6 to 18 cm -1 、6 to 16 cm -1 、8 to 20 cm -1 、8 to 18 cm -1 、8 to 16 cm -1 、10 to 20 cm -1 、10 to 18 cm -1 、or 10 to 16 cm -1 . At this time, the Raman peak of the nano-particle silicon contained in the negative electrode material can refer to a single peak rather than a deconvolved peak.

[0045] In one embodiment, when the anode material is subjected to Raman spectroscopy at 20 random positions, the number of tensile stresses in the nanoparticle silicon is greater than the number of residual compressive stresses defined with respect to the central wavenumber of the Raman peak of bulk single-crystal silicon.

[0046] As a specific example, the ratio (C / T) of the number of residual compressive stresses (C) to the number of residual tensile stresses (T) contained in nanoparticle silicon can be 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, and substantially 0 or greater, or more substantially 0.01 or greater.

[0047] As a specific example, C / T can be 0-0.5, 0-0.4, 0-0.3, 0-0.2, 0-0.1, 0.01-0.5, 0.01-0.4, 0.01-0.3, 0.01-0.2, or 0.01-0.1.

[0048] In addition, in the displacement defined by Equation 1 below, selecting only the case of tensile stress and excluding the maximum and minimum values, the difference between the maximum and minimum values ​​of the difference is 15 cm. -1 The following conditions must be met. [Formula 1] Deviation=WN(Si)-WN(ref) In Equation 1, WN(ref) is the center wave number of the Raman peak of bulk single-crystal silicon, and WN(Si) is the center wave number of the Raman peak of nanoparticle-sized silicon contained in the negative electrode material.

[0049] In the deviation defined by Equation 1, the deviation value can be positive or negative depending on the type of residual stress contained in the nanoparticle silicon. Selecting only the case of tensile stress in the deviation, the difference between the maximum and minimum values ​​of the difference, excluding the maximum and minimum values, can be used as an indicator of the uniformity of the residual tensile stress of the silicon nanoparticles dispersed in the negative electrode material.

[0050] As a specific example, in the displacement defined by Equation 1 above, selecting only the case of tensile stress and excluding the maximum and minimum values, the difference between the maximum and minimum values ​​of the difference is 15 cm. -1 Below, 14cm -1 Below, 13cm -1 Below, 12cm -1 Below, 11cm -1 Below, 10cm -1 Below, 9cm -1 less than or 5cm -1 The following is possible, and not limited to 0cm -1 More than 0.1cm -1 In summary, this is effectively 1 cm -1 The above is possible. More specifically, the difference between the maximum and minimum differences is 0 to 15 cm. -1 , 0-11cm -1 , 0-10cm -1 , 0.1~11cm -1 , 0.1~10cm -1 , 1-11cm -1 , 1-10cm -1 , 0.1~9cm -1 , 1-9cm -1 , 0.1~5cm -1 or 1-5cm -1 It can be.

[0051] In the deviation defined by Equation 1 mentioned above, if we select only the case of tensile stress, the difference between the maximum and minimum values ​​of the difference, excluding the maximum and minimum values, can be said to represent a uniform magnitude of residual stress in the silicon nanoparticles dispersed in the negative electrode material.

[0052] At this time, the difference between the maximum and minimum values ​​of the tensile stress difference that satisfy the aforementioned range is the difference between the maximum and minimum values ​​of the difference obtained by excluding the maximum and minimum values ​​of the residual tensile stress deviation values ​​(excluding residual compressive stress) in the deviation defined by Equation 1 above, which means that the magnitude of the tensile stress remaining in the silicon nanoparticles is substantially almost the same.

[0053] Thus, by satisfying the residual tensile stress characteristics based on the above-described Raman spectroscopy analysis, the negative electrode material for secondary batteries according to one embodiment of the present invention can effectively suppress the volume expansion of the electrode, and significantly improve the capacity retention characteristics of secondary batteries equipped with silicon-based negative electrode materials. It is possible.

[0054] In one example, the expansion rate of the negative electrode containing the aforementioned negative electrode material can be 55% or less, specifically 54% or less, 53% or less, 52% or less, 51% or less, 50% or less, or 45% or less. While there is no lower limit, it can be effectively 10% or more.

[0055] In this case, the expansion rate of the negative electrode can be said to represent the expansion rate of the negative electrode active material layer after 50 charge-discharge cycles in which a half-cell containing the aforementioned negative electrode material and a counter electrode made of metallic lithium is charged (lithiated) to 0.005V with a constant current of 0.5C, charged at a constant voltage of 0.005V until it reaches 0.005C, and then discharged (de-lithiated) to 1.5V with a constant current of 0.5C.

[0056] Specifically, the negative electrode expansion rate can be defined as (thickness of negative electrode active material layer after charging - thickness of negative electrode active material layer before charging) / (thickness of negative electrode active material layer before charging) × 100 for the negative electrode active material layer obtained by disassembling the battery after 50 charge-discharge cycles and when the battery is fully charged to 100% SOC (state of charge), and the thickness of the negative electrode active material layer before charging can be the thickness of the negative electrode active material layer contained in the dried negative electrode before battery assembly.

[0057] The half-cell can be a cell comprising a negative electrode current collector and a negative electrode having a negative electrode active material layer containing a negative electrode material according to one embodiment of the present invention located on at least one surface of the current collector, a counter electrode which is metallic lithium foil, a separation membrane interposed between the negative electrode and the counter electrode, and an electrolyte in which LiPF6 is dissolved at a concentration of 1 M in a mixed solvent which is a mixture of ethylene carbonate and ethyl methyl carbonate in a 1:1 volume ratio.

[0058] As a specific example, the negative electrode active material layer containing the negative electrode material may further contain a carbon-based negative electrode active material.

[0059] The carbon-based anode active material can be one or more selected from artificial graphite, natural graphite, hard carbon, graphene, and carbon nanotubes, but the present invention is not limited thereto.

[0060] As an example, the weight ratio of the negative electrode material to the carbon-based negative electrode active material contained in the negative electrode active material layer can be 1:99 to 99:1, more specifically 5:95 to 95:5, more specifically 5:95 to 50:50, and even more specifically 5:95 to 20:80.

[0061] In one embodiment, the ratio (A1 / A2) between the area of ​​a first peak (A1) located in the diffraction angle 2θ range of 10° to 27.4° and the area of ​​a second peak (A2) located in the range of 28±0.5° in the X-ray diffraction pattern of a negative electrode material using CuKα rays can be 0.8 to 8, more specifically 0.8 to 6, and more specifically 0.8 to 5.5.

[0062] In this case, the area of ​​each peak in the X-ray diffraction pattern represents the integrated area occupied by each peak. Here, the integrated area can be the integrated area after peak fitting using a Gaussian function and / or Lorentz function on the peaks from which the noise level has been removed. However, as long as the areas of the first and second peaks described above are derived in the same way, any XRD peak area derivation method known in the industry can be used without restriction.

[0063] As a specific example, Origin Pro, one of the application software programs... While it is possible to use the tools of Gram's peak analyzer to remove noise levels around the peaks to be separated, apply a Gaussian function to separate the peaks into two, and then calculate the area of ​​the XRD peaks as described above, the present invention is not limited to this.

[0064] In one specific example, the ratio (L1 / L2) of the full width at half maximum (FWHM) of the first peak (L1) to the FWHM of the second peak (L2) in the X-ray diffraction pattern can be 1 to 20, more specifically 3 to 18, more specifically 6 to 15, and even more specifically 6.5 to 13.

[0065] As another specific example, the intensity ratio (I1 / I2) between the maximum intensity of the first peak (I1) and the maximum intensity of the second peak (I2) can be 0.05 to 1.25, more specifically 0.05 to 1.05, and even more specifically 0.08 to 0.75. In this case, the first peak can originate from amorphous silicon oxide, and the second peak can originate from crystalline silicon. Thus, a negative electrode material for secondary batteries containing amorphous silicon oxide can achieve a full charge effect against volume expansion during charging of the secondary battery, and therefore can have an excellent capacity retention rate.

[0066] In one embodiment, the negative electrode material for a secondary battery can have compositional uniformity that satisfies the following formula 3. [Formula 3] B / A ≤ 0.65 In Equation 3, A and B are the mean (A) and standard deviation (B) of the doping element content (wt%) measured at any 100 points, with respect to a cross-section across the center of the negative electrode material.

[0067] Specifically, A and B can be the average content (wt%, A) and standard deviation (B) of the doping element calculated at any 100 points in the linear composition (line profile) of the doping element across the center of the cross-section of the negative electrode material. More specifically, B / A in Equation 3 can satisfy the conditions of 0.65 or less, 0.60 or less, 0.55 or less, 0.50 or less, 0.40 or less, or 0.30 or less, and can be 0.2 or greater.

[0068] In Equation 3, B / A is a parameter representing the compositional uniformity of the anode material based on the doping element (D). Excellent compositional uniformity of B / A that satisfies the above range allows the anode material to exhibit uniform electrochemical properties.

[0069] In a negative electrode material for secondary batteries that satisfies the above-mentioned compositional uniformity, the matrix may contain, based on elemental components, one or more doping elements (D) selected from alkali metals, alkaline earth metals, and base metals, silicon (Si), and oxygen (O). Based on compound components, the matrix may contain silicon oxide and composite oxides of doping elements and silicon. Therefore, the compositional uniformity of the doping elements defined in Equation 3 may correspond to the compositional uniformity of the composite oxide, but is not necessarily limited to this interpretation.

[0070] Here, the content and linear composition analysis of doping elements are experimentally performed using energy-dispersive X-ray spectroscopy (Energy Dispersive X-ray Spectroscopy) equipped in electron probe microanalyzers (EPMA), transmission electron microscopes, or scanning electron microscopes. This can be performed using, but is not limited to, methods such as Dispersive X-ray Spectroscopy (EDS).

[0071] Furthermore, in one embodiment, the negative electrode material containing a plurality of negative electrode material particles is expressed by the following formula 2 between particles It can have a uniform composition. [Formula 2] 1.3 ≤ UF(D) In Equation 2, UF(D) is the value obtained by dividing the average doping element composition between anode material particles by the standard deviation of the doping element composition, based on the weight percent composition. In this case, the number of anode material particles can be 10 to 500, effectively 50 to 300, or more effectively 100 to 200.

[0072] Specifically, UF(D) in Equation 2 can satisfy values ​​of 1.3 or more, 1.5 or more, 2 or more, 2.5 or more, 3 or more, or 5 or more, and can be substantially 8 or less. The aforementioned UF(D) is a parameter that represents the compositional uniformity between negative electrode material particles in a negative electrode material containing multiple negative electrode material particles. When UF(D) in Equation 2 satisfies the above range, the negative electrode material containing multiple negative electrode material particles has excellent compositional uniformity, and even when multiple negative electrode material particles are included, the electrochemical properties of the negative electrode material can be expressed more uniformly.

[0073] In one specific example, the negative electrode material may contain one or more doping elements selected from silicon, oxygen, alkali metals, alkaline earth metals, and base metals based on its elemental composition.

[0074] Silicon can include silicon components in the elemental silicon state and silicon components in the oxide state, and the silicon components in the oxide state can include silicon alone as an oxide state, a composite oxide state of silicon and a doping element, or all of these.

[0075] Doping elements may include doping element components in oxide states, and doping elements in oxide states may include the oxide state of the doping element alone, a composite oxide state of silicon and the doping element, or all of these.

[0076] Based on the compound components, the negative electrode material may contain silicon oxide, a composite oxide of doping elements and silicon, or a mixture thereof, and may also contain elemental silicon (Si).

[0077] Silicon oxide is SiO xx can be a real number between 0.1 and 2, and the composite oxide is D l Si m O n D is a doping element, l is a real number from 1 to 6, m is a real number from 0.5 to 2, and n can be a real number that satisfies charge neutrality depending on the oxidation states of D and Si respectively, l and m, and specifically n can be a real number from 1 to 6.

[0078] For example, if D is Mg, the composite oxide may include one or more oxides selected from MgSiO3 and Mg2SiO4, but in the present invention, D and the composite oxide are not necessarily limited to Mg and Mg-Si oxides.

[0079] Based on the microstructure, the negative electrode material may include a matrix containing silicon oxide and a composite oxide of silicon with one or more doping elements selected from alkali metals and alkaline earth metals, or a mixture thereof, and a dispersed phase containing silicon nanoparticles. The dispersed phase can be uniformly dispersed and embedded within the matrix.

[0080] In one specific example, silicon nanoparticles can be crystalline, amorphous, or a composite phase containing both crystalline and amorphous phases, and can be substantially crystalline.

[0081] In one specific example, the matrix can be crystalline, amorphous, or a composite phase containing both crystalline and amorphous materials. More specifically, the matrix can be crystalline or a composite phase containing both crystalline and amorphous materials. It can be a composite phase. Specifically, the matrix can include amorphous, crystalline, or a mixture of amorphous and crystalline silicon oxides and crystalline composite oxides.

[0082] In one specific example, the average diameter of silicon nanoparticles is 10 0 Nanometer order ~ 10 1The nanometer order can be, but is not limited to, 1-50 nm, 2-40 nm, 2-35 nm, 2-30 nm, 2-20 nm, or 2-15 nm.

[0083] In one specific example, the doping element can be selected from one or more of the following: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and bismuth (Bi). Thus, the composite oxide can 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), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and bismuth (Bi).

[0084] To facilitate the formation of a compatible interface with silicon nanoparticles, the doping element can be one or more elements selected from alkali metals and alkaline earth metals, specifically lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). More preferably, it can be one or more elements selected from alkaline earth metals, specifically magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Even more preferably, it can be magnesium (Mg).

[0085] As described above, doping elements can be incorporated into the anode material in the form of a composite oxide with silicon and / or an oxide form of the doping element, and can be incorporated into the anode material mainly in the form of a composite oxide. Specifically, when the matrix contains doping elements in the form of a composite oxide with silicon, the composite oxide can be crystalline, and more substantially the composite oxide can be crystalline. Therefore, the matrix can contain a crystalline composite oxide.

[0086] In one specific example, the silicon oxide contained in the matrix is ​​SiO x Here, x can be a real number between 0.1 and 2, more specifically between 0.5 and 2, and can include a first silicon oxide and a second silicon oxide having different x values. As a substantial example, the silicon oxide contained in the matrix is ​​SiO x1 (x1 is a real number between 1.8 and 2) First silicon oxide and SiO x2 The matrix may contain a second silicon oxide (where x² is a real number between 0.8 and 1.2). The silicon oxide contained in the matrix can be crystalline, amorphous, or a composite phase of crystalline and amorphous, and can be substantially amorphous.

[0087] In one specific example, the negative electrode material may contain 15 to 50% by weight of nanoparticle-like silicon and the remainder as a matrix.

[0088] In one specific example, the matrix of the negative electrode material can contain both silicon oxide and composite oxide. In the matrix, when the amount of composite oxide by weight is A based on 100 parts by weight of silicon oxide, and the concentration of doping elements in the negative electrode material is B based on weight percent, the ratio A / B can satisfy 2 to 50, 2 to 40, 2 to 30, or 2 to 20.

[0089] In one specific example, the negative electrode material can be particulate. The particulate negative electrode material has a particle size that is typically required for secondary battery applications, for example, 10 0 μm order (order) ~ 10 1The average diameter can be on the order of micrometers, specifically in the range of 1 μm to 50 μm.

[0090] As a specific example, the negative electrode material can be in the form of parts with an average diameter (D50) based on volume of 1 to 50 μm, more specifically 1 to 30 μm, more specifically 1 to 20 μm, and even more specifically 2 to 10 μm.

[0091] In one specific example, the negative electrode material may further include a carbon-containing coating layer, specifically a surface coating layer applied to the surface of the negative electrode material. Such a surface coating layer is advantageous because it can improve the electrical properties of the negative electrode material. The thickness of the coating layer is sufficient if it is at the level of 2 to 30 nm, but is not necessarily limited to this.

[0092] As a specific example, the negative electrode material can have an alloying ratio of 3.5 (or more) to 3.75 moles of lithium per mole of silicon, specifically 3.6 to 3.75 moles, during electrochemical alloying (lithiation) with lithium. Such a high alloying ratio is very advantageous for high capacity. Furthermore, in this specific example, the negative electrode material can have high initial charge-discharge efficiency and capacity retention characteristics.

[0093] The present invention includes a negative electrode containing the negative electrode material described above. The negative electrode may be the negative electrode of a secondary battery, specifically a lithium secondary battery. The negative electrode may include a current collector and a negative electrode active material layer located on at least one surface of the current collector, the negative electrode active material layer containing the negative electrode material described above, and the negative electrode active material layer may further include, if necessary, a binder and conductive material commonly used in secondary battery negative electrodes with the negative electrode material.

[0094] The present invention includes a secondary battery comprising the negative electrode described above. Specifically, the present invention includes a lithium secondary battery comprising the negative electrode described above. The lithium secondary battery may include a positive electrode comprising a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector, the negative electrode described above, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte that conducts lithium ions. The positive electrode current collector, negative electrode current collector, positive electrode active material and composition of the positive electrode active material layer, the solvent and electrolyte salt or concentration of the electrolyte of the separation membrane and electrolyte can be any material and composition that is normally adopted in lithium secondary batteries.

[0095] The following describes in more detail, through examples, a negative electrode material for a secondary battery according to one embodiment of the present invention. However, the following embodiments are merely references to illustrate the present invention in detail, and the present invention is not limited thereto, and can be embodied in various forms.

[0096] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as they are commonly understood in the art to which this invention pertains. The terms used in this application are solely for the purpose of effectively describing specific embodiments and are not intended to limit the invention.

[0097] (Example 1) Si, SiO2, and MgO raw materials were added to a powder mixer in a molar ratio of 6(Si):4.68(SiO2):1.32(MgO), respectively. After homogeneous mixing to produce a mixed raw material, the mixed raw material was pelletized using a mold.

[0098] 26 kg of the pelletized mixed raw materials were placed in a crucible in a vacuum chamber with a pressure of 0.1 torr or less, heated to 1,400°C to vaporize, and then condensed on a collection plate at 400°C to obtain magnesium-doped silicon oxide.

[0099] The resulting magnesium-doped silicon oxide was subjected to a first heat treatment at 650°C for 1 hour, followed by a second heat treatment at 850°C for 24 hours to produce a bulk negative electrode material for secondary batteries.

[0100] During this process, the first and second heat treatments were carried out under an argon (Ar) atmosphere.

[0101] The manufactured bulk negative electrode material for secondary batteries was mechanically crushed to produce particulate negative electrode material, and carbon-coated negative electrode material powder was produced by coating the particulate negative electrode material with 5% by weight of carbon through a CVD process at 850°C using hydrocarbon gas.

[0102] (Example 2) The procedure was carried out in the same manner as in Example 1, except that the respective raw materials were mixed in a molar ratio of 6(Si):4.2(SiO2):1.74(MgO).

[0103] (Example 3) The procedure was carried out in the same manner as in Example 1, except that the respective raw materials were mixed in a molar ratio of 6(Si):3.9(SiO2):2.1(MgO).

[0104] (Example 4) The procedure was carried out in the same manner as in Example 1, except that the respective raw materials were mixed in a molar ratio of 6(Si):3.66(SiO2):2.34(MgO).

[0105] (Example 5) The procedure was carried out in the same manner as in Example 1, except that the raw materials were mixed in a molar ratio of 6(Si):4.5(SiO2):1.5(MgO), and only the second heat treatment was performed, without the first heat treatment.

[0106] (Comparative Example 1) 24 kg of a mixed raw material consisting of Si and SiO2 in a 1:1 molar ratio was placed in crucible A, and 2 kg of a lump of metallic Mg was placed in crucible B. Crucible A was heated to 1,500°C and crucible B to 900°C to vaporize the mixture, and then condensed on a collection plate at 900°C to obtain magnesium-doped silicon oxide.

[0107] The resulting magnesium-doped silicon oxide (anode material for bulk secondary batteries) was mechanically pulverized to produce particulate anode material. Using hydrocarbon gas, the particulate anode material was coated with 5% by weight of carbon through a CVD process at 850°C to produce carbon-coated anode material powder.

[0108] (Comparative Example 2) The procedure was carried out in the same manner as in Comparative Example 1, except that a 5 kg block of metallic Mg was used as the raw material.

[0109] (Experimental Example 1) Deviation of doping element content Using the cross-section crossing the center of the magnesium-doped silicon oxide before pulverization (Comparative Example 1) and the bulk secondary battery anode material obtained by heat treatment (Example 1) as a reference, the cross-section crossing the center of the cross-section was analyzed using EDS (Electron Disperse Spectroscopy). In the linear composition, the average content (wt%) of the doping element, calculated by measuring at 100 arbitrary points, was defined as A, and the standard deviation of the content was defined as B. As a result of the compositional analysis, the B / A ratio for the negative electrode material sample produced in Example 1 was 0.23, while the B / A ratio for Comparative Example 1 was 0.73.

[0110] Furthermore, after crushing the anode material of Example 1, 150 anode material particles were sampled, and the compositional uniformity of the doping elements contained between the anode material particles was analyzed. At this time, the UF(D), which is the value obtained by dividing the average doping element composition (wt%) between the anode material particles by the standard deviation of the doping element composition, was confirmed to be 6.7.

[0111] (Experimental Example 2) X-ray diffraction (XRD) analysis The anode material after pulverization was analyzed by X-ray diffraction (XRD, Rigaku D / MAX-2500 / PC, 40kV, 15mA, 4°min). -1 The structure was confirmed through Cu-Kα radiation (λ=0.15406nm) analysis.

[0112] Figure 1 shows the XRD patterns of Examples 1 to 3. As can be seen from the figure, a peak of crystalline silicon 111 was observed at approximately 28° in all three Examples 1 to 3. The peaks in Examples 1 to 3 with diffraction angles 2θ in the range of 10° to 27.4° were observed to be broad peaks originating from amorphous silicon oxide.

[0113] Examples 1 to 3, which include amorphous silicon oxide, are advantageous in terms of the capacity retention rate of secondary batteries because they can fully charge the secondary battery despite volume expansion during charging.

[0114] Furthermore, when comparing the ratio (A1 / A2) between the area of ​​the first peak (A1) located in the diffraction angle 2θ range of 10° to 27.4° and the area of ​​the second peak (A2) located in the range of 28±0.5° in the X-ray diffraction pattern, it was confirmed that Examples 1 to 3 fell within the range of 0.8 to 6.

[0115] Additionally, when comparing the intensity ratio (I1 / I2) between the maximum intensity of the first peak (I1) located in the diffraction angle 2θ range of 10° to 27.4° and the maximum intensity of the second peak (I2) located in the range of 28±0.5° in the X-ray diffraction pattern, it was confirmed that Examples 1 to 3 were within the range of 0.1 to 1.25. Furthermore, a comparative analysis of the ratio (L1 / L2) of the FWHM (L1) of the first peak to the FWHM (L2) of the second peak revealed that Examples 1 to 3 were within the range of 6 to 12.

[0116] (Experimental Example 3) Raman Analysis After grinding, the negative electrode material was subjected to μ-Raman (equipment name: XperRam C, Nanobase, Korea) analysis. Using the silicon Raman signal as a reference, Raman spectroscopy was performed at 20 random positions under the following analytical conditions, and the results are summarized in Table 1 below. Figure 2 shows the Raman signal corresponding to tensile stress among the Raman signals of the negative electrode material powder from Example 1 measured at 20 random positions.

[0117] Analysis conditions: Excitation laser wavelength 532 nm, laser power 0.5 mW, spectrometer resolution 1 cm -1 1g of powdered negative electrode material, detector exposure time 15s

[0118] At this time, the central wavenumber of the Raman peak of single-crystal silicon is (520.4 cm⁻¹). -1 When comparing WN(ref) / WN(Si), which is the center wavenumber of the Raman peak of silicon contained in the negative electrode material powder, with WN(ref) being the reference value, if WN(ref) / WN(Si) is greater than 1, it means that the silicon contained in the negative electrode material powder has residual tensile stress, and WN(ref) / WN(Si) i) If it is less than 1, it means that compressive residual stress is present.

[0119] The number of residual tensile stresses (T) and the number of residual compressive stresses (C) in the silicon contained in the negative electrode material powder were compared. Only the tensile stress was selected from the total residual stress, and the difference between the maximum and minimum values ​​of the difference in the deviation defined by the formula WN(Si)-WN(ref), excluding the maximum and minimum values ​​(difference in residual tensile stress deviation), was compared and analyzed.

[0120] [Table 1]

[0121] As shown in Table 1, in Examples 1 to 5, while the ratio of the number of residual compressive stresses (C) to the number of residual tensile stresses (T) (C / T) was 0.5 or less, it was confirmed that the number of residual tensile stresses was greater than the number of residual compressive stresses. This resulted in a significant reduction in the difference in residual tensile stress displacement compared to Comparative Examples 1 and 2, demonstrating excellent uniformity of residual tensile stress.

[0122] (Experimental Example 4) Battery Manufacturing and Evaluation of Battery Performance A negative electrode slurry was prepared by adding a mixture of the manufactured negative electrode powders, graphite (D50: 20 μm) and styrene-butadiene rubber (SBR), conductive material (Super C65), and carboxymethylcellulose (CMC) in a weight ratio of 96:1:1:2 to distilled water.

[0123] Next, the manufactured negative electrode slurry is placed on a 10 μm thick copper current collector and tested at 8 mAh / cm². 2 The negative electrode was coated with the specified loading amount, rolled (roll pressed), and then dried in a vacuum oven at 120°C for 10 hours to produce a negative electrode containing a 50 μm thick negative electrode active material layer.

[0124] A CR2032 coin-shaped half-cell was manufactured by using metallic lithium foil (16 mm in diameter, 0.2 mm thick) as the negative electrode and relative electrode, sandwiching a separation membrane between them, and filling them with electrolyte. The electrolyte used was a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 1:1, to which 1 M LiPF6 was dissolved, and 1% by weight of VC (vinylene carbonate) and 10% by weight of FEC (fluoroethylene carbonate) were added as additives.

[0125] Next, the manufactured batteries were charged (lithiated) to 0.005V with a constant current of 0.1C, charged at a constant voltage of 0.005V until it reached 0.005C, and then discharged (delithiated) to 1.5V with a constant current of 0.1C to perform the chemical conversion process.

[0126] After the chemical conversion process, the battery performance was evaluated by performing 50 charge-discharge cycles: charging to 0.005V with a constant current of 0.5C until the voltage reached 0.005C, then discharging to 1.5V with a constant current of 0.5C until the voltage reached 1.5V. The results are summarized in Table 2 below.

[0127] [Table 2]

[0128] In Table 2, the initial reversible efficiency is the initial efficiency based on the charge and discharge cycles in the chemical conversion process, while the capacity retention rate and negative electrode expansion rate represent the cycle characteristics measured after 50 charge and discharge cycles following the chemical conversion process.

[0129] At this time, the negative electrode expansion rate was calculated using the following formula after disassembling the battery to obtain the negative electrode after 50 charge-discharge cycles and when it was fully charged to 100% SOC (state of charge), thoroughly washing it with dimethyl carbonate (DMC), drying it, and then disassembling it.

[0130] Expansion rate = (Thickness of negative electrode active material layer after charging - Thickness of negative electrode active material layer before charging) / (Thickness of negative electrode active material layer before charging) × 100

[0131] Here, the thickness of the negative electrode active material layer before charging was measured by first measuring the thickness of the negative electrode dried before battery assembly, excluding the thickness of the copper current collector. The thickness of the negative electrode active material layer after charging was measured after measuring the thickness of the negative electrode obtained by decomposing it in a state of charge (SOC) of 100% after 50 cycles, excluding the thickness of the copper current collector.

[0132] Furthermore, although not shown in the drawings, in the dQ / dV graph of a half-cell equipped with a negative electrode containing the negative electrode material manufactured by Examples 1 to 4, Li 3.75 The presence of a lithium insertion peak corresponding to the Si reaction was confirmed, and through this, it was found that during the lithiation of the negative electrode materials produced by Examples 1 to 4, lithiation occurred at an alloying rate of 3.75 moles of lithium per mole of silicon.

[0133] Additionally, measurements of the particle size distribution of the crushed and carbon-coated negative electrode material powder confirmed that the negative electrode material powder particles had a volume-based average diameter (D50) of 5.1 μm. Analysis using a high-resolution transmission electron microscope (HR-TEM) confirmed that the average diameter of the crystalline silicon nanoparticles was approximately 7.1 nm. Analysis of the ected area diffusion pattern (ADI) confirmed that the matrix contains crystalline magnesium silicate, and that silicon nanoparticles form a compatible interface with the crystalline magnesium silicate.

[0134] As described above, the present invention has been explained by specified features, limited embodiments, and drawings, but these are provided only to aid in a more general understanding of the invention. The present invention is not limited to the above embodiments, and various modifications and variations can be made from such descriptions by those with ordinary skill in the art to which the invention pertains.

[0135] Therefore, the concept of the present invention should not be limited to the embodiments described, and it can be said that not only the claims described later, but also everything equivalent to or with equivalent variations to these claims, falls within the scope of the concept of the present invention.

Claims

1. In negative electrode materials for secondary batteries, A matrix comprising silicon oxide, a composite oxide of silicon and one or more doping elements selected from alkali metals, alkaline earth metals, and base metals, or a mixture thereof, and silicon nanoparticles dispersed and embedded in the matrix, In an X-ray diffraction pattern using CuKα rays, the area of ​​the first peak located in the diffraction angle 2θ range of 10° to 27.4° (A １ ) and the area of ​​the second peak located in the range of 28 ± 0.5° (A ２ ) ratio (A １ / A ２ ) is between 0.8 and 5.5, The first peak is derived from amorphous silicon oxide. When Raman spectroscopy analysis of the pulverized powdered anode material was performed at 20 random locations, the number of Raman signals corresponding to tensile stress was greater than the number of Raman signals corresponding to residual compressive stress, which is defined based on the central wavenumber of the Raman peak of bulk single-crystal silicon. The ratio (C / T) of the number of Raman signals corresponding to residual compressive stress (C) to the number of Raman signals corresponding to residual tensile stress (T) was between 1 / 19 and 5 / 15. In the displacement defined by Equation 1 below, selecting only the case of tensile stress, the difference between the maximum and minimum values ​​of the difference, excluding the maximum and minimum values, is 15 cm. －１ A negative electrode material for secondary batteries, characterized by the following: [Formula 1] Deviation=WN(Si)-WN(ref) (In Equation 1, WN(ref) is the center wavenumber of the Raman peak of bulk single-crystal silicon, and WN(Si) is the center wavenumber of the Raman peak of nanoparticle-sized silicon contained in the negative electrode material.)

2. The difference between the maximum and minimum values ​​of the difference is 11 cm. －１ The negative electrode material for a secondary battery according to claim 1, which is as follows:

3. In the X-ray diffraction pattern, the ratio of the full width at half maximum FWHM (L １ ), of the first peak, to the FWHM (L ２ ) of the second peak (L １ / L ２ ) is from 6 to 15. The secondary battery according to claim 1 Negative electrode material.

4. The anode material for a secondary battery according to claim 1, wherein the second peak is derived from crystalline silicon.

5. The negative electrode material for a secondary battery according to claim 1, wherein the FWHM of the nanoparticle-like silicon Raman peak contained in the negative electrode material is greater than the FWHM of the Raman peak of bulk single-crystal silicon.

6. The FWHM of the nanoparticle-like silicon Raman peak contained in the negative electrode material is 4 to 20 cm. －１ The negative electrode material for a secondary battery according to claim 5.

7. The negative electrode material for a secondary battery according to claim 1, comprising a plurality of negative electrode material particles and having uniform inter-particle composition according to the following formula 2. [Formula 2] 1.3 ≤ UF(D) (In Equation 2, UF(D) is the value obtained by dividing the average doping element composition between negative electrode material particles by the standard deviation of the doping element composition, based on the weight percent composition.)

8. The negative electrode material for a secondary battery according to claim 1, wherein the average diameter of the silicon nanoparticles is 2 to 30 nm.

9. The negative electrode material for a secondary battery according to claim 1, wherein the doping element is selected from one or more of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and bismuth (Bi).

10. The negative electrode material for a secondary battery according to claim 1, wherein the negative electrode material is particulate with a volume-based average diameter (D50) of 1 to 50 μm.

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

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

Images