KR20230025328A - Negative electrode active material, negative electrode and secondary battery comprising same - Google Patents

Abstract

The present invention relates to a negative electrode active material including: silicon-based composite particles including SiO_x (0 < x < 2) and a Li compound, and having a carbon layer on at least a part of the surface thereof; and a surface layer provided on at least a part of the silicon-based composite particles, wherein the negative electrode active material includes a group 13 element and a group 15 element, and the surface layer includes an amorphous phase.

Description

Negative active material, negative electrode and secondary battery containing the same

This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0107524 filed with the Korean Intellectual Property Office on August 13, 2021, all of which are incorporated herein.

The present invention relates to an anode active material, a cathode and a secondary battery including the same.

Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries is rapidly increasing. In particular, lithium secondary batteries are in the limelight as a driving power source for portable devices because they are lightweight and have high energy density. Accordingly, research and development efforts to improve the performance of lithium secondary batteries are being actively conducted.

In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. In addition, active material layers each including a positive electrode active material and a negative electrode active material may be formed on the current collector on the positive electrode and the negative electrode. In general, a lithium-containing metal oxide such as LiCoO ₂ or LiMn ₂ O ₄ is used as a cathode active material for the cathode, and a carbon-based active material or a silicon-based active material that does not contain lithium is used as an anode active material for the anode.

Among negative active materials, silicon-based active materials have attracted attention in that they have higher capacity than carbon-based active materials and excellent high-speed charging characteristics. However, the silicon-based active material has a high degree of volume expansion/contraction due to charging and discharging, and has a high irreversible capacity, so the initial efficiency is low.

On the other hand, in the case of silicon-based oxide among silicon-based active materials, specifically silicon-based oxide represented by SiO _x (0 < x < 2), the degree of volume expansion / contraction due to charging and discharging is lower than that of other silicon-based active materials such as silicon (Si). There are advantages. However, silicon-based oxide still has a disadvantage in that initial efficiency is lowered depending on the presence of irreversible capacitance.

In this regard, research on reducing irreversible capacity and improving initial efficiency by doping or intercalating metals such as Li, Al, and Mg into silicon-based oxide has been continued. However, in the case of an anode slurry containing a metal-doped silicon-based oxide as an anode active material, there is a problem in that the metal oxide formed by doping the metal reacts with moisture to increase the pH of the anode slurry and change the viscosity. There is a problem that the state is poor and the charging and discharging efficiency of the negative electrode is lowered.

Accordingly, there is a need to develop an anode active material capable of improving the phase stability of an anode slurry containing silicon-based oxide and improving the charge/discharge efficiency of an anode prepared therefrom.

Korean Patent Registration No. 10-0794192 relates to a method for manufacturing a carbon-coated silicon-graphite composite negative electrode material for a lithium secondary battery and a method for manufacturing a secondary battery including the same, but has limitations in solving the above-mentioned problems.

Korean Patent Registration No. 10-0794192

The present invention relates to an anode active material, a cathode and a secondary battery including the same.

An exemplary embodiment of the present invention includes SiO _x (0<x<2) and a Li compound, and a silicon-based composite particle having a carbon layer on at least a portion of the surface; and a surface layer provided on at least a portion of the silicon-based composite particle, wherein the negative active material includes a Group 13 element and a Group 15 element, and the surface layer includes an amorphous phase.

One embodiment of the present invention provides an anode including the anode active material.

One embodiment of the present invention provides a secondary battery including the negative electrode.

An anode active material according to an exemplary embodiment of the present invention includes a surface layer provided on the silicon-based composite particle, and the surface layer includes an amorphous phase. By providing the surface layer as described above on the surface of the silicon-based composite particle, the silicon-based composite particle It is possible to effectively remove the lithium by-product contained in the slurry, and effectively cover the unreacted lithium by-product, thereby preventing a phenomenon in which the lithium by-product or the lithium compound in the silicon-based composite particle reacts with moisture in the slurry to deteriorate the physical properties of the slurry. In addition, since the surface layer is formed in an amorphous phase to facilitate the inflow and outflow of Li ions, side reactions in the slurry phase can be effectively reduced while capacity, efficiency, resistance performance and/or lifespan of the battery can be stably implemented.

In addition, since the surface layer of the negative active material according to an exemplary embodiment of the present invention contains Li, lithium diffusion resistance on the surface of the negative active material is lowered, thereby providing excellent discharge rate capability.

Hereinafter, this specification will be described in more detail.

In the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

In this specification, when a member is said to be located “on” another member, this includes not only the case where a member is in contact with another member, but also the case where another member exists between the two members.

The terms or words used in this specification should not be construed as being limited to their ordinary or dictionary meanings, and the inventors are guided by the principle that the concept of terms can be appropriately defined in order to best explain their invention. Based on this, it should be interpreted as a meaning and concept consistent with the technical spirit of the present invention.

Singular expressions of terms used in this specification include plural expressions unless the context clearly dictates otherwise.

In the present specification, the crystallinity of the structure included in the negative electrode active material can be confirmed through X-ray diffraction analysis, and the X-ray diffraction analysis is performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker). In addition to the above devices, devices used in the art may be appropriately employed.

In the present specification, the presence or absence of elements and the content of elements in the negative electrode active material can be confirmed through ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma emission spectrometer (ICPAES, Perkin-Elmer 7300).

In the present specification, the average particle diameter (D ₅₀ ) may be defined as a particle diameter corresponding to 50% of the cumulative volume in the particle size distribution curve (graph curve of the particle size distribution). The average particle diameter (D ₅₀ ) may be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle diameters of several millimeters in the submicron region, and can obtain results with high reproducibility and high resolution.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

<Negative electrode active material>

An exemplary embodiment of the present invention includes SiO _x (0<x<2) and a Li compound, and a silicon-based composite particle having a carbon layer on at least a portion of the surface; and a surface layer provided on at least a portion of the silicon-based composite particle, wherein the negative active material includes a Group 13 element and a Group 15 element, and the surface layer includes an amorphous phase.

In general, lithium by-products formed due to unreacted lithium in the process of doping silicon-based particles with Li exist on the particles, and thus become basic when forming the slurry. Therefore, there is a problem in that the rheological properties of the slurry are changed and gas is generated by reacting Si of the silicon-based particles with a base.

Therefore, in the present invention, a surface layer is provided on the silicon-based composite particle doped with Li to effectively remove the lithium by-product formed during the Li doping process, and the surface layer formed on the silicon-based composite particle is formed on the silicon-based composite particle to passivate the particle. . At this time, since the formed surface layer includes an amorphous phase and facilitates the inflow and outflow of Li ions, there is an effect of stably implementing the capacity, efficiency, resistance performance and / or lifespan of the battery while effectively reducing side reactions in the slurry phase.

In addition, when the surface layer further includes Li, the lithium diffusion resistance of the surface of the negative electrode active material is lowered, so that the discharge rate capability is excellent.

An anode active material according to an exemplary embodiment of the present invention includes silicon-based composite particles. The silicon-based composite particle includes SiO _x (0<x<2) and a Li compound, and a carbon layer is provided on at least a part of the surface.

The SiO _x (0<x<2) may correspond to a matrix in the silicon-based composite particle. The SiO _x (0<x<2) may include Si and SiO ₂ , and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si included in the SiO _x (0<x<2). When the silicon-based composite particle includes the SiO _x (0<x<2), the discharge capacity of the secondary battery may be improved.

In one embodiment of the present invention, the silicon-based composite particle may include a Li compound.

The Li compound may correspond to a matrix in the silicon-based composite particle. The Li compound may exist in the form of at least one of a lithium atom, lithium silicate, lithium silicide, and lithium oxide in the silicon-based composite particle. When the silicon-based composite particle includes a Li compound, there is an effect of improving initial efficiency.

The Li compound may be distributed on the surface and/or inside of the silicon-based composite particle in a doped form. The Li compound may be distributed on the surface and/or inside of the silicon-based composite particle to control volume expansion/contraction of the silicon-based composite particle to an appropriate level and prevent damage to the active material. In addition, the Li compound may be included in order to increase the efficiency of the active material by lowering the ratio of the non-reversible phase (eg, SiO ₂ ) of the silicon-based oxide particles.

In one embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is represented by Li _a Si _b O _c (2≤a≤4, 0<b≤2, 2≤c≤5), and may be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one type of lithium silicate selected from the group consisting of Li ₂ SiO ₃ , Li ₄ SiO ₄ and Li ₂ Si ₂ O ₅ in the silicon-based particle, and the amorphous lithium silicate may be Li _a It may be made of a complex structure in the form of Si _b O _c (2≤a≤4, 0<b≤2, 2≤c≤5), but is not limited to the above form.

In one embodiment of the present invention, upon X-ray diffraction analysis of the negative electrode active material, a peak derived from Si may appear, and a peak derived from at least one of Li ₂ SiO ₃ and Li ₂ Si ₂ O ₅ may appear.

The peak originating from Si may include a diffraction peak due to Si(111) and/or Si(220), and the diffraction peak due to Si(111) has a diffraction angle (2θ) = 27.5° to 29.5°. It may appear in the range, and the diffraction peak by Si (220) may appear in the range of diffraction angle (2θ) = 45 ° to 50 °.

The peak derived from Li ₂ SiO ₃ may appear in the range of diffraction angle (2θ) = 17.5° to 20.5°, and the peak derived from Li ₂ Si ₂ O ₅ may appear at diffraction angle (2θ) = 23.0° to 25.5 It can appear in a range of degrees. However, peaks derived from the compounds may include peaks appearing in other diffraction angle ranges in addition to the aforementioned diffraction angle range.

X-ray diffraction analysis of the negative active material may be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker). Specifically, an X-ray wavelength generated from Cu Kα can be used, 0.3 g of the negative electrode active material is placed in a cylindrical holder with a diameter of 2.5 cm and a height of 2.5 mm, and a flattening operation is performed with a slide glass so that the height of the sample in the holder is constant, XRD After preparing the sample for analysis, the SCAN TIME of the XRD analysis device is set to 1 hour and 15 minutes, the measurement area is set to an area where 2θ is 10˚ to 90˚, and STEP to scan 2θ at 0.02˚ per second Peak can be measured by setting TIME and STEP SIZE.

In one embodiment of the present invention, 0.1 part by weight to 25 parts by weight of Li may be included based on 100 parts by weight of the total amount of the negative electrode active material. Specifically, it may be included in 1 part by weight to 15 parts by weight, and more specifically, it may be included in 2 parts by weight to 11 parts by weight. In one example, the amount of Li may be 4 parts by weight or more, 6 parts by weight or more, 8 parts by weight or more, or 10 parts by weight or less based on 100 parts by weight of the total amount of the negative electrode active material. As the Li content increases, the initial efficiency increases, but there is a problem in that the discharge capacity decreases. Therefore, when the above range is satisfied, appropriate discharge capacity and initial efficiency can be implemented.

The content of the Li element can be confirmed through ICP analysis. Specifically, after fractionating a certain amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Then, using an induced plasma emission spectrometer (ICPAES, Perkin-Elmer 7300), a standard calibration curve is prepared by measuring the intensity of the standard solution prepared using the standard solution (5 mg/kg) at the intrinsic wavelength of the element to be analyzed. . Thereafter, the pretreated sample solution and the blank sample are introduced into the instrument, each intensity is measured to calculate the actual intensity, and after calculating the concentration of each component against the calibration curve prepared above, the total sum is converted to the theoretical value. It is possible to analyze the element content of the negative electrode active material prepared by the method.

In one embodiment of the present invention, the silicon-based composite particle may include additional metal atoms. The metal atom may exist in the form of at least one of a metal atom, a metal silicate, a metal silicide, and a metal oxide in the silicon-based composite particle. The metal atom may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Accordingly, initial efficiency of the anode active material may be improved.

A carbon layer is provided on at least a part of the surface of the silicon-based composite particle according to an exemplary embodiment of the present invention. In this case, the carbon layer may be coated on at least a part of the particle surface including SiO _x (0<x<2) and a Li compound. That is, the carbon layer may partially cover the surface of the particle or may cover the entire surface of the particle. Conductivity is imparted to the anode active material by the carbon layer, and initial efficiency, lifespan characteristics, and battery capacity characteristics of a secondary battery may be improved.

In one embodiment of the present invention, the carbon layer includes an amorphous phase.

Specifically, the carbon layer may include amorphous carbon. Alternatively, the carbon layer may be an amorphous carbon layer. The amorphous carbon can properly maintain the strength of the carbon layer and suppress expansion of the silicon-based composite particles.

In addition, the carbon layer may or may not additionally include crystalline carbon.

The crystalline carbon may further improve conductivity of the anode active material. The crystalline carbon may include at least one selected from the group consisting of florene, carbon nanotubes, and graphene.

The amorphous carbon can properly maintain the strength of the carbon layer and suppress expansion of the silicon-based composite particles. The amorphous carbon may be a carbon-based material formed by using at least one carbide selected from the group consisting of tar, pitch, and other organic materials, or a hydrocarbon as a source of chemical vapor deposition.

The other organic carbide may be an organic carbide selected from carbides of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose, and combinations thereof.

The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be metherin, etherin, ethylene, acetylene, propane, butane, butene, pentane, isobutane or hexane. Aromatic hydrocarbons of the substituted or unsubstituted aromatic hydrocarbons include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumaron, pyridine, Anthracene, phenanthrene, etc. are mentioned.

In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight based on 100 parts by weight of the negative electrode active material. More specifically, it may be included in 0.5 parts by weight to 15 parts by weight, 1 part by weight to 10 parts by weight, 2 parts by weight to 8 parts by weight, or 3 parts by weight to 5 parts by weight. When the above range is satisfied, reduction in capacity and efficiency of the negative electrode active material may be prevented.

In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm. When the above range is satisfied, the conductivity of the negative active material is improved, the volume change of the negative active material is easily suppressed, and the side reaction between the electrolyte and the negative active material is suppressed, thereby improving the initial efficiency and/or lifespan of the battery.

Specifically, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane and acetylene.

The silicon-based composite particle according to an exemplary embodiment of the present invention includes a surface layer provided on at least a part of the silicon-based composite particle.

The surface layer may be coated on at least a portion of the silicon-based composite particle having a carbon layer on its surface. That is, the surface layer may be partially coated on the particle surface or coated on the entire particle surface. The shape of the surface layer may include an island type or a thin film type, but the shape of the surface layer is not limited thereto.

The surface layer may be provided on at least a portion of the carbon layer. That is, the surface layer may be coated adjacently on the carbon layer and provided in the form of a particle-carbon layer-surface layer containing SiO _x (0<x<2) and a Li compound.

The surface layer may be provided on a region not provided with a carbon layer among the particle surfaces including the SiO _x (0<x<2) and the Li compound. That is, the surface layer is adjacently coated on the particle containing SiO _x (0<x<2) and Li compound, in the form of a particle-surface layer containing SiO _x (0<x<2) and Li compound. may be provided.

In one embodiment of the present invention, the negative electrode active material includes a group 13 element and a group 15 element.

In one embodiment of the present invention, the negative electrode active material includes Al and P.

In one embodiment of the present invention, the negative electrode active material includes Li, a group 13 element, and a group 15 element.

In one embodiment of the present invention, the negative electrode active material includes Li, Al and P.

In one embodiment of the present invention, Li, a group 13 element, and a group 15 element may be detected during ICP analysis of the negative electrode active material. Specifically, the group 13 element may be Al, and the group 15 element may be P.

In one embodiment of the present invention, the surface layer may include Al and P.

In one embodiment of the present invention, the surface layer may include Al, P and O elements.

In one embodiment of the present invention, the surface layer may include Li, Al, P, and O elements.

In one embodiment of the present invention, the Group 13 element may be included in an amount of 0.05 parts by weight to 0.3 parts by weight based on 100 parts by weight of the total amount of the negative electrode active material. Specifically, 0.1 part by weight to 0.4 parts by weight may be included, 0.12 parts by weight to 0.35 parts by weight may be included, or 0.15 parts by weight to 0.3 parts by weight may be included.

In one embodiment of the present invention, the Group 15 element may be included in an amount of 0.05 parts by weight to 2 parts by weight based on 100 parts by weight of the total amount of the negative electrode active material. Specifically, 0.1 part by weight to 1.5 parts by weight may be included, or 0.15 parts by weight to 1 part by weight may be included.

The surface layer may include an Al _z P _w O _v (0<z≤10, 0<w≤10, 0<v≤10) phase. The Al _z P _w O _v phase may include aluminum oxide, phosphorus oxide, aluminum phosphate, and the like, and z, y, and v mean the number ratio of each atom. In one example, the Al _z P _w O _v phase may include a mixture or compound formed from AlPO ₄ or Al(PO ₃ ) ₃ , but is not limited thereto.

The surface layer may include a Li _y Al _z P _w O _v (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10) phase. The Li _y Al _z P _w O _v phase may include aluminum oxide, phosphorus oxide, lithium oxide, aluminum phosphate, lithium salt, lithium phosphate, lithium aluminate, etc., and y, z, w, and v represent the number of atoms means defense. In one example, the Li _y Al _z P _w O _v phase may include a mixture or compound formed from Li ₃ PO ₄ , AlPO ₄ , Al(PO ₃ ) ₃ or LiAlO ₂ , but is not limited thereto.

When the inorganic surface layer including the above phase is provided, it is possible to prevent a phenomenon in which the Li compound included in the silicon-based composite particles reacts with moisture in the slurry to lower the viscosity of the slurry, thereby improving the stability of the electrode state and / or there is an effect of improving the charge / discharge capacity.

In one embodiment of the present invention, the surface layer may include an amorphous phase.

In one embodiment of the present invention, the surface layer may be made of an amorphous phase.

The surface layer may include an Al _z P _w O _v (0<z≤10, 0<w≤10, 0<v≤10) phase, and the Al _z P _w O _v (0<z≤10, 0 <w≤10, 0<v≤10) The phase may be an amorphous phase.

The surface layer may include a Li _y Al _z P _w O _v (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10) phase, and the Li _y Al _z P _w The O _v (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10) phase may be an amorphous phase.

When the surface layer is made of crystal, it is difficult for Li ions to enter and exit, resulting in a decrease in resistance and lifespan characteristics. In the negative electrode active material of the present invention, when the surface layer includes the amorphous phase as described above, Li ions are easier to enter and exit than when the amorphous phase is not included, so that side reactions in the slurry phase can be effectively reduced while capacity and/or efficiency can be stably implemented. There are possible effects.

In one embodiment of the present invention, the surface layer may further include one or more selected from the group consisting of Li ₂ O, LiOH, and Li ₂ CO ₃ . In general, since materials remaining in the process of doping silicon-based particles with lithium may be exposed to moisture or air to form lithium by-products such as Li ₂ O, LiOH, and Li ₂ CO ₃ , the surface layer is Li ₂ O, LiOH And Li ₂ CO ₃ It may be a form containing one or more selected from the group consisting of.

In one embodiment of the present invention, the y may satisfy 0<y≤3.

In one embodiment of the present invention, the z may satisfy 0<z≤1.

In one embodiment of the present invention, the w may satisfy 0.5≤w≤3.

In one embodiment of the present invention, v may satisfy 4<v≤12.

The surface layer is heat-treated by dry mixing i) silicon-based composite particles and aluminum phosphate, ii) silicon-based composite particles, aluminum precursor, and phosphorus precursor, or iii) silicon-based composite particles and Li-Al-P-O-based precursor, or mixed with a solvent and vaporized the solvent. It can be formed by reacting while doing it.

In one embodiment of the present invention, upon X-ray diffraction analysis of the negative electrode active material, no crystalline peak derived from the surface layer appears. Specifically, no crystalline peak derived from the Li _y Al _z P _w O _v (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10) phase included in the surface layer is detected. When a crystalline peak derived from the surface layer appears, the surface layer is made of crystalline or contains an excessive amount of crystalline, resulting in a decrease in capacity and/or efficiency. In one example, in the case of a crystalline peak derived from the surface layer, it can be found through a change according to before/after coating the surface layer. Specifically, in the case of XRD, a crystalline peak is detected, and when there is no difference in the XRD graph of the negative electrode active material before and after coating the surface layer, no crystalline peak derived from the surface layer appears, and the surface layer is formed in an amorphous phase. It can be confirmed.

In one embodiment of the present invention, the amorphous phase included in the surface layer may include more than 50 parts by weight based on 100 parts by weight of the total surface layer. Specifically, the amorphous phase may be included in an amount of 60 parts by weight or more, 70 parts by weight or more, 80 parts by weight or more, 90 parts by weight or more, 95 parts by weight or more, or 99 parts by weight or more based on 100 parts by weight of the total surface layer, and 100 parts by weight or less than 100 parts by weight. By satisfying the above range, side reactions in the slurry phase can be effectively suppressed, and capacity and/or efficiency can be stably implemented.

In one embodiment of the present invention, the surface layer may be included in 10 parts by weight or less based on 100 parts by weight of the total amount of the negative electrode active material. Specifically, it may be included in 8 parts by weight or less, 6 parts by weight or less, or 5 parts by weight or less, and may be included in 0.1 parts by weight or more or 0.5 parts by weight or more. More specifically, it may be included in 1 part by weight or more and 5 parts by weight or less, or 1.5 parts by weight or more and 3 parts by weight or less. When the content of the surface layer is less than the above range, it is difficult to prevent gas generation in the slurry phase, and when it is more than the above range, it is difficult to realize capacity or efficiency.

In one embodiment of the present invention, the weight ratio of the surface layer and the carbon layer may be 1:0.1 to 1:30. Specifically, it may be 1:0.5 to 1:5, or it may be 1:1 to 1:4, or it may be 1:1 to 1:3. By satisfying the above range, the carbon layer and the surface layer effectively cover the silicon-based composite particles to effectively suppress side reactions in the slurry phase, and the capacity and/or efficiency can be stably implemented. On the other hand, when the content of the surface layer is too large compared to the carbon layer, it is difficult to realize capacity or efficiency, and when the content of the carbon layer is too large than that of the surface layer, it is difficult to prevent gas generation in the slurry.

In one embodiment of the present invention, the surface layer may be included in 90 parts by weight or less based on 100 parts by weight of the carbon layer. Specifically, the surface layer may be included in an amount of 80 parts by weight or less, 70 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less based on 100 parts by weight of the carbon layer. In addition, the surface layer may be included in an amount of 0.1 parts by weight or more, 1 part by weight or more, 5 parts by weight or more, or 10 parts by weight or more based on 100 parts by weight of the carbon layer. By satisfying the above range, the carbon layer and the surface layer effectively cover the silicon-based composite particles to effectively suppress side reactions in the slurry phase, and there is an effect of stably implementing capacity and/or efficiency.

The negative active material may have an average particle diameter (D50) of 0.1 μm to 30 μm, specifically 1 μm to 20 μm, and more specifically, 1 μm to 10 μm. When the above range is satisfied, the structural stability of the active material during charging and discharging is ensured, the problem of increasing the level of volume expansion / contraction as the particle size becomes excessively large, and the problem of reducing the initial efficiency due to the excessively low particle size It can be prevented.

<Method of manufacturing negative electrode active material>

In one embodiment of the present invention, the manufacturing method of the negative electrode active material, preparing a silicon-based composite particle; and providing a surface layer on at least a portion of the silicon-based composite particle.

The silicon-based composite particles are vaporized by heating Si powder and SiO ₂ powder in a vacuum, and then depositing the vaporized mixed gas to form preliminary particles; Forming a carbon layer on the preliminary particles; And it may be formed through a step of heat-treating after mixing the preliminary particles on which the carbon layer is formed with Li powder.

Alternatively, the silicon-based composite particles are vaporized by heating Si powder and SiO ₂ powder in a vacuum, and then depositing the vaporized mixed gas to form preliminary particles; And it may be formed through a step of heat-treating after mixing the preliminary particles and Li powder.

Specifically, the mixed powder of the Si powder and SiO ₂ powder may be heat treated at 1400 °C to 1800 °C or 1400 °C to 1600 °C under vacuum.

The preliminary particles formed may exist in the form of SiO _x (x=1).

The silicon-based composite particle may include the aforementioned Li silicate, Li silicide, Li oxide, and the like.

The particle size of the silicon-based composite particles may be adjusted through a method such as a ball mill, a jet mill, or air flow classification, but is not limited thereto.

In the step of forming the carbon layer, the carbon layer may be prepared by using chemical vapor deposition (CVD) using hydrocarbon gas or by carbonizing a material serving as a carbon source.

Specifically, after introducing the formed preliminary particles into a reactor, hydrocarbon gas may be formed by chemical vapor deposition (CVD) at 600 ° C to 1200 ° C. The hydrocarbon gas may be at least one type of hydrocarbon gas selected from the group consisting of methane, ethane, propane and acetylene, and heat treatment may be performed at 900 °C to 1000 °C.

The step of providing a surface layer on at least a portion of the silicon-based composite particles may include performing heat treatment by dry mixing the silicon-based composite particles and aluminum phosphate, or mixing the silicon-based composite particles and aluminum phosphate in a solvent and then heat-treating the silicon-based composite particles while vaporizing the solvent. It may include reacting the composite particles and aluminum phosphate. When the surface layer is formed by the above method, the surface layer can be easily formed by reacting the aluminum phosphate with the Li by-product formed during the manufacturing process of the silicon-based composite particles.

The aluminum phosphate may be in the form of Al _b P _c O _d (0<b≤10, 0<c≤10, 0<d≤10). Specifically, it may be Al(PO ₃ ) ₃ or AlPO ₄ , but is not limited thereto, and salts used in the art may be appropriately employed to form the surface layer.

Alternatively, providing a surface layer on at least a portion of the silicon-based composite particles may include performing heat treatment by dry mixing the silicon-based composite particles, aluminum precursor, and phosphorus precursor, or heat treatment after mixing the silicon-based composite particles, aluminum precursor, and phosphorus precursor in a solvent. and reacting the silicon-based composite particle, the aluminum precursor, and the phosphorus precursor while vaporizing the solvent. When the surface layer is formed by the above method, the surface layer can be easily formed by reacting the Li by-product, the aluminum precursor, and the phosphorus precursor formed during the manufacturing process of the silicon-based composite particle.

The aluminum precursor may be aluminum oxide in the form of Al _a O _b (0<a≤10, 0<b≤10), and may specifically be Al ₂ O ₃ .

Alternatively, the aluminum precursor may be aluminum hydroxide, aluminum nitrate or aluminum sulfate, and specifically, may be Al(OH) ₃ , Al(NO ₃ ) ₃ .9H ₂ 0 or Al ₂ (SO ₄ ) ₃ , and is limited thereto. Instead, an aluminum precursor used in the art may be appropriately employed to form the surface layer.

The phosphorus precursor may be phosphorus oxide in the form of P _c O _d (0<c≤10, 0<d≤10).

Alternatively, the phosphorus precursor may be ammonium phosphate, diammonium phosphate or phosphoric acid, and specifically, (NH ₄ ) ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ , H ₃ PO ₄ or NH ₄ H ₂ PO ₄ , , It is not limited thereto, and a phosphorus precursor used in the art may be appropriately employed to form the surface layer.

Alternatively, the step of providing a surface layer on at least a portion of the silicon-based composite particles may include dry mixing and heat-treating the silicon-based composite particles and the Li-Al-P-O-based precursor or the silicon-based composite particles and the Li-Al-P-O-based precursor in a solvent. It may include a step of reacting the silicon-based composite particle and the Li-Al-P-O-based precursor while vaporizing the solvent by heat treatment after mixing. When the surface layer is formed by the above method, the surface layer may be formed by directly introducing a Li-Al-P-O-based precursor.

The Li-Al-PO-based precursor may be in the form of Li _y Al _z P _w O _v (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10). Specifically, it may be a mixture or compound complexly formed from Li ₃ PO ₄ , AlPO ₄ , Al(PO ₃ ) _{3 ,} or LiAlO ₂ , but is not limited thereto, and a configuration used in the art to form the surface layer is suitably used. can be hired

In the step of providing a surface layer on at least a portion of the silicon-based composite particle, the heat treatment may be performed at 500 °C to 700 °C, specifically at 550 °C to 650 °C. However, it is not limited thereto, and may be different depending on the salt or precursor used. When the heat treatment temperature is higher than the above range, the surface layer is formed in a crystalline form, making it difficult for Li ions to enter and exit through the surface layer, resulting in reduced resistance and lifetime characteristics, and reduced capacity and/or efficiency. When the heat treatment temperature satisfies the above range, the reaction between the salt or precursor and Li by-product occurs easily and the surface layer contains Li, so that the durability of the formed negative active material against moisture increases, and the lithium diffusion on the surface of the negative active material (Li diffusion) ) has the effect of improving the discharge rate capability because the resistance is lowered.

The solvent may be water or ethanol, but is not limited thereto, and solvents used in the art may be appropriately employed.

The surface layer formed on the silicon-based composite particle preferably includes a Li _y Al _z P _w O _v (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10) phase, The Li _y Al _z P _w O _v phase may be an amorphous phase.

Details of the surface layer are as described above.

<cathode>

An anode according to an exemplary embodiment of the present invention may include the anode active material described above.

Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative active material layer may include the negative active material. Furthermore, the negative electrode active material layer may further include a binder and/or a conductive material.

The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, and/or a conductive material to at least one surface of a negative electrode current collector, followed by drying and rolling.

The anode slurry includes the anode active material, a binder, and/or a conductive material.

The anode slurry may further include an additional anode active material.

As the additional anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and undoping lithium, such as SiO _β (0 < β < 2), SnO ₂ , vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or a composite including the metallic compound and the carbonaceous material, such as a Si—C composite or a Sn—C composite, and any one or a mixture of two or more of these may be used. In addition, a metal lithium thin film may be used as the anode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical examples of low crystalline carbon, and high crystalline carbon includes amorphous, platy, scaly, spherical or fibrous natural graphite, artificial graphite, or kish graphite. graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is representative.

The additional anode active material may be a carbon-based anode active material.

In one embodiment of the present invention, the weight ratio of the negative electrode active material and the additional negative electrode active material included in the negative electrode slurry may be 10:90 to 90:10, specifically 10:90 to 50:50.

The anode current collector may be any material having conductivity without causing chemical change in the battery, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver may be used. Specifically, a transition metal that adsorbs carbon well, such as copper and nickel, can be used as the current collector. The current collector may have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

The binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, poly Vinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), alcohol It may include at least one selected from the group consisting of phononized EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen is substituted with Li, Na, or Ca, and Various copolymers thereof may be included.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, farnes black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

<Secondary Battery>

A secondary battery according to an exemplary embodiment of the present invention may include the negative electrode according to the aforementioned exemplary embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the cathode has been described above, a detailed description thereof will be omitted.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , those surface-treated with nickel, titanium, silver, etc. may be used. In addition, the cathode current collector may have a thickness of typically 3 to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The cathode active material may be a commonly used cathode active material. Specifically, the cathode active material may include layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds substituted with one or more transition metals; lithium iron oxides such as LiFe ₃ O ₄ ; lithium manganese oxides such as Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Formula LiNi _1-c2 M _c2 O ₂ (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3) Ni site-type lithium nickel oxide; Formula LiMn _2-c3 M _c3 O ₂ (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO ₈ (Here, M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn.) Lithium manganese composite oxide represented by; Examples include LiMn ₂ O ₄ in which Li in the formula is partially substituted with an alkaline earth metal ion, but is not limited thereto. The anode may be Li-metal.

The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, any material that does not cause chemical change and has electronic conductivity can be used without particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of them alone or a mixture of two or more may be used.

In addition, the positive electrode binder serves to improve adhesion between particles of the positive electrode active material and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC) ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like may be used alone or in a mixture of two or more of them.

The separator separates the negative electrode and the positive electrode and provides a passage for lithium ion movement. If it is normally used as a separator in a secondary battery, it can be used without particular limitation. it is desirable Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.

Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing a lithium secondary battery.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dimethine Toxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxorane, formamide, dimethylformamide, dioxorane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid Triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, propionic acid An aprotic organic solvent such as ethyl may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can be preferably used because they dissociate lithium salts well, and dimethyl carbonate and diethyl carbonate and When the same low-viscosity, low-dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be made and can be used more preferably.

The metal salt may be a lithium salt, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte. For example, the anion of the lithium salt is F ^- , Cl ^- , I ^- , NO ₃ ^- , N (CN ) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- At least one selected from the group consisting of may be used.

In addition to the above electrolyte components, the electrolyte may include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and triglycerides for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included.

According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include the secondary battery having high capacity, high rate and cycle characteristics, a medium or large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system can be used as a power source for

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the above embodiments are merely illustrative of the present description, and various changes and modifications are possible within the scope and spirit of the present description. It is obvious to those skilled in the art, Naturally, such variations and modifications fall within the scope of the appended claims.

Example 1-1

100 g of powder obtained by mixing Si and SiO ₂ in a molar ratio of 1:1 was vacuum-heated to a sublimation temperature of 1,400° C. in a reaction furnace. Thereafter, the vaporized Si and SiO ₂ mixed gas was reacted in a cooling zone in a vacuum state having a cooling temperature of 800° C. and condensed into a solid phase. Thereafter, heat treatment was performed at a temperature of 800° C. in an inert atmosphere to prepare preliminary silicon-based particles. Thereafter, 15 sus ball media were added to the preliminary silicon-based particles using a ball mill, and then pulverized for 3 hours to prepare silicon-based particles having a size of 6 μm (D ₅₀ ). Thereafter, while maintaining an inert atmosphere by flowing Ar gas, the silicon-based particles are placed in a hot zone of a CVD apparatus, and methane is blown into the hot zone at 900 ° C. using Ar as a carrier gas, followed by 10 minutes for 20 minutes. By reacting at ^-1 torr, a carbon layer was formed on the surface of the silicon-based particle.

10 g of Li metal powder was added to 90 g of the silicon-based particles, and heat treatment was performed at a temperature of 800° C. in an inert atmosphere to prepare silicon-based composite particles doped with Li.

After mixing 1.5 g of Al(PO ₃ ) ₃ with 98.5 g of the silicon-based composite particles, heat treatment was performed at 600° C. to prepare a negative electrode active material having a surface layer containing Li, Al, P, and O formed on the surface of the silicon-based composite particles.

Upon ICP analysis of the anode active material, the contents of Li, Al, and P were 9.5 wt%, 0.15 wt%, and 0.5 wt%, respectively, based on 100 wt% of the total amount of the anode active material.

Example 1-2

A negative electrode active material was prepared in the same manner as in Example 1-1, except that AlPO ₄ was used instead of Al(PO ₃ ) ₃ .

Upon ICP analysis of the anode active material, contents of Li, Al, and P were 9.5 wt%, 0.15 wt%, and 0.17 wt%, respectively, based on 100 wt% of the anode active material.

Examples 1-3

An anode active material was prepared in the same manner as in Example 1-1, except that 97 g of the silicon-based composite particles and ₃ g of Al(PO ₃ ) 3 were used.

Upon ICP analysis of the anode active material, the contents of Li, Al, and P were 9.4 wt%, 0.3 wt%, and 0.9 wt%, respectively, based on 100 wt% of the anode active material.

Comparative Example 1-1

An anode active material was prepared in the same manner as in Example 1-1, except that the heat treatment temperature was set at 800° C. when forming the surface layer.

Comparative Example 1-2

An anode active material was prepared in the same manner as in Example 1-1, except that Al(PO ₃ ) ₃ was not mixed with the silicon-based composite particles.

The silicon-based negative electrode active materials prepared in Examples and Comparative Examples are shown in Table 1 below.

Presence or absence of surface layer phase of the surface layer Based on 100 parts by weight of negative electrode active material D ₅₀ (㎛) of negative active material Specific surface area of negative electrode active material (m ² /g) content of the surface layer
(parts by weight) content of carbon layer
(parts by weight) Li content
(parts by weight) Example 1-1 O amorphous 1.5 4.5 9.5 6 2.5 Example 1-2 O amorphous 1.5 4.5 9.5 6 2.5 Example 1-3 O amorphous 3 4.3 9.4 6 2.5 Comparative Example 1-1 O crystalline 1.5 4.5 9.5 6 2.5 Comparative Example 1-2 X - 0 5 9.5 6 2.5

The Li, Al, and P atomic contents were confirmed through ICP analysis using an inductively coupled plasma emission spectrometer (ICP-OES, AVIO 500, manufactured by Perkin-Elmer 7300).

The phase of the surface layer was confirmed through changes in XRD graphs before and after coating the surface layer. When the surface layer was amorphous, there was no difference in XRD patterns before and after coating.

The content of the carbon layer was confirmed under oxygen conditions through elemental analysis through combustion (Bruker's G4 ICARUS).

D50 of the anode active material was analyzed by a PSD measurement method using a microtac device.

The specific surface area was measured by degassing at 200° C. for 8 hours using BET measuring equipment (BEL-SORP-MAX, Nippon Bell), and adsorption/desorption of N ₂ at 77K. was measured.

<Experimental Example 1: Evaluation of discharge capacity, initial efficiency and capacity retention rate>

A negative electrode and a battery were manufactured using the negative electrode active materials of Examples and Comparative Examples, respectively.

A mixture was prepared by mixing the anode active material, carbon black as a conductive material, and polyacrylic acid (PAA) as a binder in a weight ratio of 80:10:10. Thereafter, 7.8 g of distilled water was added to 5 g of the mixture and stirred to prepare an anode slurry. The anode slurry was applied to a copper (Cu) metal thin film as an anode current collector having a thickness of 20 μm and dried. At this time, the temperature of the circulated air was 60°C. Subsequently, a negative electrode was prepared by roll pressing and drying in a vacuum oven at 130° C. for 12 hours.

A lithium (Li) metal thin film obtained by cutting the prepared negative electrode into a circular shape of 1.7671 cm 2 was used as a positive electrode. A separator of porous polyethylene is interposed between the positive electrode and the negative electrode, and vinylene carbonate dissolved in 0.5 parts by weight is dissolved in a mixed solution having a mixed volume ratio of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) of 7: 3, and 1M A lithium coin half-cell was prepared by injecting an electrolyte solution in which a concentration of LiPF ₆ was dissolved.

The prepared battery was charged and discharged to evaluate discharge capacity, initial efficiency, and capacity retention rate, which are shown in Table 2 below.

The first and second cycles were charged and discharged at 0.1C, and the third to 49th cycles were charged and discharged at 0.5C. 50 cycles were terminated in the state of charge (with lithium in the negative electrode).

Charging conditions: CC (constant current)/CV (constant voltage) (5mV/0.005C current cut-off)

Discharge condition: CC (constant current) condition 1.5V

Through the results of one charge and discharge, discharge capacity (mAh / g) and initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived by the following calculation.

Initial efficiency (%) = (discharge capacity after one discharge / one charge capacity) × 100

The capacity retention rates were derived by the following calculations, respectively.

Capacity retention rate (%) = (50 discharge capacity / 1 discharge capacity) × 100

battery Discharge capacity (mAh/g) Initial Efficiency (%) Capacity retention rate (%) Example 1-1 1380 91 40 Example 1-2 1380 91 40 Examples 1-3 1370 90 40 Comparative Example 1-1 1300 89 35 Comparative Example 1-2 1250 86 30

In Table 2, in Examples 1-1 to 1-3, by providing an amorphous surface layer on the silicon-based composite particle, it is possible to effectively remove lithium by-products included in the silicon-based composite particle, and the surface layer forms the silicon-based composite particle. It can be confirmed that the discharge capacity, initial efficiency, and capacity retention rate are all excellent because the effective coating prevents the lithium by-product and the lithium compound of the silicon-based composite particles from reacting with moisture in the slurry to deteriorate the physical properties of the slurry.

On the other hand, in Comparative Example 1-1, the surface layer was formed in a crystalline form due to the high heat treatment temperature, and it was confirmed that Li ion entry and exit became difficult, and discharge capacity, initial efficiency, and lifespan characteristics were deteriorated.

Comparative Example 1-2 does not include a surface layer, so the Li compound contained in the silicon-based composite particles easily reacts with moisture in the slurry to change the viscosity of the slurry, and side reactions of the slurry occur, so that the initial efficiency and life characteristics are lowered. I was able to confirm.

Example 2-1

Al, P, and O were included in the same manner as in Example 1-1, except that the silicon-based composite particles and Al(PO ₃ ) ₃ were dispersed in ethanol and then heated to 90° C. to evaporate the ethanol. An anode active material having a surface layer formed thereon was prepared.

The surface layer of the formed negative active material was amorphous, and the contents of the surface layer were 1.5 parts by weight, 4.5 parts by weight of the carbon layer, and 9.5 parts by weight of Li based on 100 parts by weight of the total negative electrode active material. The negative electrode active material had a D ₅₀ of 6 μm and a specific surface area of 2.5 m ² /g.

<Experimental Example 2: Evaluation of speed characteristics>

An anode and a battery were prepared in the same manner as in Experimental Example 1 using the anode active materials of Examples 1-1 and 2-1.

Charge and discharge were evaluated for the batteries manufactured in Examples 1-1 and 2-1. While fixing the charging rate at 0.2C and changing the discharging rate to 0.2C, 1.0C, 3.0C, and 5.0C, the rate capability was measured to determine how much the discharge capacity was reduced, which is shown in Table 3 below. described. On the other hand, the discharge capacity at the time of discharging at 0.2 C was set to 100%.

Discharge capacity (%) battery 0.2C 1.0C 3.0C 5.0C Example 1-1 100 95 90 80 Example 2-1 100 90 77 65

In Examples 1-1 and 2-1, the surface layer is provided on the surface of the silicon-based composite particle in an amorphous state, so that the surface layer effectively covers the silicon-based composite particle, so that the lithium by-product and the lithium compound of the silicon-based composite particle react with moisture in the slurry. It serves to prevent deterioration of the physical properties of the slurry.

Among them, in Example 2-1, the surface layer does not contain Li, whereas in Example 1-1, since the surface layer contains Li, the lithium diffusion resistance on the surface of the negative electrode active material is lowered, resulting in discharge rate capability ) is excellent, it was confirmed that the discharge capacity according to the discharge rate of Example 1-1 was more excellent than that of Example 2-1.

Claims (15)

A silicon-based composite particle including SiO _x (0<x<2) and a Li compound and having a carbon layer on at least a part of the surface; and
As an anode active material comprising a surface layer provided on at least a part of the silicon-based composite particle,
The negative electrode active material includes a group 13 element and a group 15 element,
The surface layer is a negative electrode active material containing an amorphous phase. The method of claim 1,
The surface layer is a negative electrode active material containing Al, P and O elements. The method of claim 1,
The surface layer is a negative electrode active material containing Li, Al, P and O elements. The method of claim 1,
The surface layer includes a Li _y Al _z P _w O _v (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10) phase,
The Li _y Al _z P _w O _v (0<y≤10, 0<z≤10, 0<w≤10, 0<v≤10) phase is an amorphous negative active material. The method of claim 1,
A negative electrode active material that does not show a crystalline peak derived from the surface layer when X-ray diffraction analysis of the negative electrode active material. The method of claim 1,
A negative electrode active material wherein, upon X-ray diffraction analysis of the negative electrode active material, a peak derived from Si appears and a peak derived from at least one of Li ₂ SiO ₃ and Li ₂ Si ₂ O ₅ appears. The method of claim 1,
The amorphous phase included in the surface layer is a negative electrode active material that is included in more than 50 parts by weight based on 100 parts by weight of the total surface layer. The method of claim 1,
A weight ratio of the surface layer and the carbon layer is 1:0.1 to 1:30 of the negative electrode active material. The method of claim 1,
The surface layer is a negative active material that is included in 90 parts by weight or less based on 100 parts by weight of the carbon layer. The method of claim 1,
The surface layer further comprises at least one member selected from the group consisting of Li ₂ O, LiOH, and Li ₂ CO ₃ . The method of claim 1,
A negative electrode active material comprising 0.1 part by weight to 25 parts by weight of Li based on 100 parts by weight of the total amount of the negative electrode active material. The method of claim 1,
The negative electrode active material comprising the carbon layer is an amorphous phase. The method of claim 1,
The negative electrode active material of which the carbon layer is included in 0.1 part by weight to 50 parts by weight based on 100 parts by weight of the total amount of the negative electrode active material. An anode comprising the anode active material according to any one of claims 1 to 13. A secondary battery comprising the negative electrode according to claim 14.