KR20190091001A - Active material for an anode and a secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode active material for solving the problem. A first aspect of the present invention relates to a negative electrode active material. The negative electrode active material comprises core-shell structured composite particles having a core portion and a shell portion covering at least a part of a surface of the core portion. The core portion comprises: a matrix comprising a metal(M)-silicon composite oxide; and a plurality of crystalline silicon phases dispersed and interspersed in the matrix. The shell portion comprises a carbon material. The composite particle has one or more pores inside and on the surface thereof, and the volume of pores calculated by Barrett-Joyner-Halenda (BJH) according to nitrogen adsorption (N_2 adsorption) is 1.5 X 10^-2 to 10.0 X 10^-2 cm^3/g.

Description

A negative electrode active material for a lithium secondary battery, a negative electrode including the same, and a lithium ion secondary battery including the negative electrode {active material for an anode and a secondary battery comprising the same}

The present invention relates to a negative electrode active material for a lithium secondary battery, a negative electrode including the same, and a lithium ion secondary battery including the negative electrode.

In recent years, with the development and spread of mobile devices, personal computers, electric motors, and temporary power storage devices, high-capacity energy sources are required, and lithium secondary batteries are exemplified as a representative example. As a negative electrode material of the next-generation nonaqueous electrolyte secondary battery, silicon (Si) having a capacity (4200 mAh / g) of 10 times or more that of a conventional graphite-based material (theoretical capacity is 372 mAh / g) has attracted attention. From this, it is proposed to use silicon as a negative electrode active material which alloys with lithium and shows high theoretical capacity as a new material which replaces a carbon-based material. However, silicon causes volume expansion by charging and volume shrinkage upon discharge. For this reason, when the secondary battery repeats charging and discharging, the silicon used as the negative electrode active material is micronized to lose conductive paths in the electrode and to increase the number of isolated particles, resulting in capacity degradation of the secondary battery. As a method for improving the cycle characteristics, 1) the granulation of silicon, 2) the use of silicon oxides (SiO _x ), 3) the use of silicon alloys, and the like have been studied and proposed.

1) In the granulation of silicon, the improvement of cycle characteristics can be expected as the granulation proceeds, but there is a limit in reducing the crystallite size of the crystalline silicon, and the problem that the micronization of silicon proceeds in charge and discharge is sufficient. It was difficult to solve.

2) In the use of silicon oxide (SiO _x ), fine crystals of silicon can be formed in amorphous SiO _y to suppress micronization. However, since the oxide consumes Li, the initial charge and discharge efficiency is low, which is not suitable for high energy of the secondary battery.

3) Silicon alloys can be designed in various materials by the variation of metal elements in combination with silicon. As a result, it is easy to construct a nano structure that improves cycle characteristics, thereby suppressing silicon crystal growth and expecting higher charge and discharge efficiency than using oxides. However, even in the structure as suggested by the prior art, when the crystallites of silicon are large enough to be measured by X-ray diffraction (approximately 5 nm or more), micronization can be suppressed to prevent any decrease in capacity accompanying charge and discharge. The degree of expansion can still be avoided, but the expansion ratio is still large, and when applied to the secondary battery, the factor of the thickness change (particularly increase) of the secondary battery could not be solved. Accordingly, there is a continuous request for research on a new negative electrode active material.

An object of the present invention is to provide a negative electrode active material, a negative electrode and a secondary battery having excellent life and storage performance under high temperature conditions. Other objects and advantages of the present invention will be understood by the following description. On the other hand, it will be readily apparent that the objects and advantages of the present invention may be realized by the means or method described in the claims, and combinations thereof.

The present invention relates to a negative electrode active material for solving the above problems. A first aspect of the invention relates to the negative electrode active material, wherein the negative electrode active material comprises a core-shell structured composite particle (s) having a core portion and a shell portion covering at least a portion of the surface of the core portion, wherein the core portion A matrix comprising a metal (M) -silicon composite oxide; And a plurality of crystalline silicon phases dispersed and interspersed in the matrix, wherein the shell portion comprises a carbon material, wherein the composite particles have one or more pores inside and on the surface thereof, and nitrogen adsorption (N ₂ sorption). is a ² cm ³ / g to about ^{10.0 X 10 -2 cm 3 / g} - a pore volume calculated by the BJH (Barrett-Joyner-Halenda) according to 1.5X10.

According to a second aspect of the present invention, in the first aspect, the anode active material has a diameter of 2 nm to 1 μm based on the longest diameter of the pores.

In a third aspect of the invention, in the first or second aspect, the matrix comprises a metal (M) -silicon composite oxide and SiO _x (0 <x ≦ 2).

According to a fourth aspect of the present invention, in any one of the first to third aspects, the metal (M) is at least one selected from Mg, Li, and Ca.

In a fifth aspect of the present invention, the metal (M) -silicon composite oxide of any one of the first to fourth aspects includes magnesium silicate (Mg-silicate), wherein the Mg-silicate is MgSiO ₃ and Mg ₂ SiO At least one of _four .

The sixth aspect of the present invention is any one of the first to fifth aspects, wherein the metal (M) is contained in a ratio of 4% to 20% by weight relative to 100% by weight of the composite particles.

The seventh aspect of the present invention is any one of the first to sixth aspect, wherein the shell is contained in a ratio of 2% to 7% by weight relative to 100% by weight of the total composite particles.

The negative electrode active material according to the present invention is characterized in that the structure and size of the pores are controlled by the constituent characteristics, and by such a constitutive feature has the effect of improving the life performance and storage performance at high temperature conditions.

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to. On the other hand, the shape, size, scale or ratio of the elements in the drawings included in this specification may be exaggerated to emphasize a more clear description.
1 is a diagram showing the structure of a negative electrode active material according to an embodiment of the present invention.
2 is to compare and confirm the pore distribution in the negative electrode active material according to the Examples and Comparative Examples of the present invention.
3 is an SEM image of the negative electrode active material prepared in Example 1 of the present invention.

The terms used in the present specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to explain their own invention in the best way. Based on the principle, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the configurations shown in the embodiments described herein are only one of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, and various equivalents may be substituted for them at the time of the present application. It should be understood that there may be water and variations.

In the present specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" between other elements in between. .

Throughout this specification, when a part "contains" a certain component, it means that it can further include other components, without excluding the other components unless otherwise stated.

As used throughout this specification, the terms "about", "substantially," and the like are used to refer to, or in close proximity to, the numerical values of the preparations and material tolerances inherent in the meanings indicated, to aid the understanding of the present application. Or absolute figures are used to prevent unfair use of unscrupulous infringers.

Throughout this specification, the term "combination (s) thereof" included on the surface of the mark of the mark is used to mean one or more mixtures or combinations selected from the group consisting of the elements described in the mark of the mark type. It means to include one or more selected from the group consisting of the above components.

Throughout this specification, description of "A and / or B" means "A or B or both."

The present invention relates to a negative electrode active material for an electrochemical device and a negative electrode including the same. In addition, the present invention relates to an electrochemical device including the cathode. In the present invention, the electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples thereof include all kinds of primary, secondary cells, fuel cells, solar cells, or capacitors. In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery among the secondary batteries is preferable.

Hereinafter, the negative electrode active material of this invention is demonstrated in detail.

Anode active material

The negative electrode active material according to the present invention includes a core-shell structured composite particle (s) having a core portion and a shell portion covering at least part of the surface of the core portion.

In the composite particle, the core part includes a plurality of silicon phases made of crystalline silicon, and the silicon phase is evenly distributed and distributed in a matrix including a metal (M) -silicon composite oxide. In the present invention, the silicon phase is present in a form embedded in the matrix. The silicon phase is a group in which one or more silicon crystals are collected, and the group may be present in one, two or more plurality.

In one embodiment of the present invention, the composite particles have a plurality of pores on the inner and outer surfaces of the body. The pores may be open and / or closed, and the open pores may be connected to two or more pores, and components such as ions, gas, and liquid may penetrate the composite particle through the connected pores. In a specific exemplary embodiment of the invention, the composite particles have a nitrogen adsorption _{(N 2 sorption) BJH (Barrett} -Joyner-Halenda) the volume of the pores calculated by the 1.5X10 according to ^{- 2} cm ³ / g to 10.0 X 10 ^-2 cm ³ / g. When the volume of pores in the composite particles falls within the above range, high temperature life characteristics and storage characteristics of a battery using the composite particles may be improved. In the present invention, the pores are pores whose diameter is 2nm to 1㎛ based on the long diameter. The diameter of the pores is preferably 500 nm or less, 200 nm or less, 100 nm or less, or 50 nm or less. If the size of the pores is too large beyond the above range, the consumption of the electrolyte is large and the performance deterioration during high temperature storage is large. The battery performance can be exhibited to some extent at the laboratory scale, such as coin cells, but when applied to commercial full cells, the above-mentioned problems occur and thus do not exhibit the desired effect.

In one specific embodiment of the present invention, the composite particle includes a shell portion covering at least a portion of the core portion, wherein the shell portion includes a carbon material. The carbon material may be bonded, attached or coated to the surface of the core portion. The carbon material may be selected from the group consisting of crystalline carbon, natural graphite, artificial graphite, kish graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, graphene, amorphous carbon, carbon black, acetylene black, and ketjen black. It may include one or more selected. In addition, the graphite is soft carbon, hard carbon, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitch (mesophase pitches), at least one selected from the group consisting of petroleum or coal tar pitch derived cokes and activated carbon may be obtained by heat treatment or calcining (graphitizing) at a high temperature. In addition, according to a specific embodiment of the present invention, the carbon coating layer may be formed using a vapor deposition method such as CVD using a gas containing carbon such as methane gas.

On the other hand, in one embodiment of the present invention, the thickness of the shell portion is 10nm to 150nm, the upper limit of the thickness of the shell portion in the above range can be 100nm, 80nm, 70nm, 50nm, the lower limit is 15nm, 25nm, It can be set as 35 nm or 50 nm.

In the present invention, the matrix is a component that is inactive to Li, so that insertion / desorption of Li does not occur during charging of the battery. Si has a problem that the volume change rate is excessive depending on the component or charge and discharge contribute to the charge and discharge of the battery complexed with Li. To solve this problem, a negative electrode material in which Si is microcrystallized or Si is mixed with SiO ₂ has been developed. However, there is a problem in that irreversible capacity is generated by forming LiO ₂ or forming Li-SO during initial charging of SiO ₂ . Accordingly, the present invention focused on the fact that the generation of the initial irreversible capacity can be reduced by including a metal element in the matrix having a bonding force equal to or higher than Li. In the present invention, the matrix is a metal (M) -silicon composite oxide and silicon oxide (SiO _x (0 <x ≦ 2)), and the metal (M) is at least one selected from Mg, Li, and Ca, and preferably includes Mg. In addition, the metal (M) -silicon composite oxide includes magnesium silicate (Mg-silicate), and the Mg-silicate includes at least one or more of MgSiO ₃ and Mg ₂ SiO ₄ . In the matrix, the metal silicate and the silicon oxide have a small volume change during occlusion and release of lithium ions because the elements of each phase diffuse to each other and the interfaces of the respective phases are bonded to each other. The cracking of the composite particles hardly occurs even by repetition.

In addition, in one specific embodiment of the present invention, the metal (M) relative to 100% by weight of the composite particles comprises 4% to 20% by weight, or 4 to 16% by weight, or 4 to 10% by weight do. When the content of the metal (M) satisfies this range, it may have an efficiency improvement effect while minimizing capacity reduction. In addition, the shell is included in a ratio of 2% to 7% by weight relative to 100% by weight of the total composite particles.

In one specific embodiment of the present invention, the size of the Si grains in the matrix is preferably 1 to 15nm. In the case where the size of the Si crystal, that is, the size of the crystal exceeds the above range, deterioration of the life characteristic can be observed. On the other hand, SiO _x is preferably micronized to the extent that no crystalline is observed with XRD.

According to a preferred embodiment of the present invention, the 50% particle size (D ₅₀ ) of the volume cumulative particle size distribution of the composite particles is 0.1 µm or more and 20 µm or less, or 1 µm or more and 16 µm or less, or 1 µm or more and 10 µm or less. The 90% particle size (D ₉₀ ) of the volume cumulative particle size distribution of the composite particles is 30 µm or less, preferably 15 µm or less, and more preferably 10 µm or less. The maximum particle diameter of the volume cumulative particle size distribution is 35 µm or less, and preferably 25 µm or less. The measurement of 50% particle size, 90% particle size, and maximum particle size of the volume cumulative particle size distribution is performed using, for example, a laser diffraction particle size distribution measuring device (for example, a laser diffraction particle size distribution measuring device manufactured by Nikkiso) which is commonly used. It can be obtained by the cumulative frequency when measured.

Method of producing composite particles

The composite particles are mixed with a gaseous metal (M) and silicon oxide (SiO _x , 0 <x <2) to precipitate on the surface of the substrate, etc. and then pulverize the composite particles to produce a core of the composite particle and to the surface of the core. A composite particle can be manufactured by forming a shell part. This will be described in more detail as follows.

Reacting SiO _x (0 <x <2) gas with a metal (M) gas and cooling to precipitate a silicon oxide composite;

Grinding the precipitated silicon oxide composite to obtain a core; And

And injecting a carbonaceous material raw material gas into the core and performing heat treatment to form a shell portion including a carbonaceous material on a surface of the core.

Herein, the cooling may be performed at 400 ° C to 900 ° C. In addition, the heat treatment step may be performed for 30 minutes to 8 hours at 850 ℃ to 1,150 ℃. According to one embodiment of the present invention, the SiO x (0 <x <2) gas can be prepared by evaporating Si / SiO ₂ in the range of 1,000 ℃ to 1,800 ℃, metal (M) gas is also 800 ℃ to 1,600 It can be prepared by evaporating the metal (M) by evaporating in the range.

The reaction of the SiO _x (0 <x <2) gas and the metal (M) gas may proceed at 800 to 1800 ° C., and within 1 to 6 hours, a target cooling temperature of 400 ° C. to 900 ° C., specifically 500 to It can be quenched at 800 ° C. When the quenching time after the gas phase reaction of the SiO _x (0 <x <2) gas and the metal (M) gas satisfies the above range, the metal (M) in gaseous state is quenched to a low temperature in a short time. The problem of SiO _x not reacting properly to prevent silicate from forming and an unwanted phase such as MgO can be prevented. As a result, the initial efficiency and the swelling prevention effect are greatly improved, resulting in a significant increase in battery life. Can be. After cooling, additional heat treatment may be performed, and the Si grain size and the ratio of Mg silicate may be adjusted according to the heat treatment temperature. For example, when the additional heat treatment temperature is high, the Mg ₂ SiO ₄ phase may increase and Si grain size may increase.

According to one specific embodiment of the present invention, the preparation of the core can be made using, for example, a deposition reactor. For example, such deposition reactors include a bubbler, a fill port, a gas intake port, and an outlet port connected to the deposition chamber. As the carrier gas, hydrogen, helium, nitrogen, argon and mixtures thereof may be used, and a precursor compound that forms a core part with a carrier gas is introduced into the deposition reactor through a gas inlet port, together with the carrier gas. Flows inside. Thereafter, the precursor compound may be chemically adsorbed on the surface of the substrate in the reactor, and the core material may be deposited in a bulk state.

According to one embodiment of the present invention, the precipitated silicon oxide composite may include a crystalline silicon phase and a matrix embedded in a shape interspersed with the silicon phase, and the matrix includes Mg-silicate and silicon-oxide. In addition, the size of the silicon phase and the matrix can be made into fine crystals of 30 nm or less, or 9 nm to 20 nm, or 9 nm to 15 nm, by selecting a composition close to the process point.

Next, the silicon oxide composite may be a silicon oxide composite powder having a core part having a particle diameter (D50) of 0.1 μm to 20 μm through mechanical milling or the like. Next, a carbon-based raw material gas such as methane gas is injected and heat treatment is performed in a rotary tubular furnace to form a carbon coating layer, which is a shell, on the surface of the silicon oxide composite, which is the core. The shell portion includes a carbon material which is a result of heat treatment of a carbonaceous raw material gas such as methane. Formation of the carbon coating layer which is the shell portion is specifically as follows. The core particles are introduced into a rotary tubular furnace, and after argon gas is flowed, the temperature is raised to 850 ° C to 1,150 ° C at a rate of about 5 ° C / min. While rotating the rotary tubular furnace, argon gas and carbonaceous material source gas are flowed and heat treatment is performed for 30 minutes to 8 hours to form a shell portion.

cathode

The negative electrode according to the present invention may be prepared by applying a mixture of a negative electrode active material, a conductive material, and a binder on a negative electrode current collector, followed by drying. If necessary, the negative electrode may further include a filler in the mixture. The negative electrode active material includes composite particles having a core-shell structure having the aforementioned characteristics.

In the present invention, the current collector is generally made to a thickness of 3 to 500 ㎛. Such a current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the current collector may be formed on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like can be used. Among them, it may be appropriately selected according to the polarity of the positive electrode or the negative electrode.

The binder is a component that assists in bonding the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the electrode mixture. The high molecular weight polyacrylonitrile-acrylic acid copolymer may be used as such a binder, but is not limited thereto. Other examples include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like.

The conductive material is a component that does not cause chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, Ketjen black (brand name), carbon nanotube, carbon nanofiber, channel black, furnace black, lamp black, thermal black, conductive fibers such as carbon fiber and metal fiber, fluorocarbon, Metal powders such as aluminum and nickel powders; Conductive metal oxides such as conductive whiskers such as zinc oxide and potassium titanate and titanium oxide; Conductive materials, such as a polyphenylene derivative, can be used.

Lithium secondary battery

The present invention provides a lithium secondary battery including a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode, wherein the negative electrode includes a negative electrode according to the present invention.

The positive electrode may be prepared by applying a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector, followed by drying. If necessary, the positive electrode may further include a filler. The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 - x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _{1 - x} MxO ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _{2 -x} M _x O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

Concerning the positive electrode, the conductive material, the current collector, and the binder may refer to the contents of the negative electrode described above.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 μm to 10 μm, and the thickness is generally 5 μm to 300 μm. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Films, sheets, nonwoven fabrics, etc. made of glass fibers or polyethylene are used. The separator may further include a porous layer including a mixture of inorganic particles and a binder resin on an outermost surface.

In the present invention, the electrolyte solution contains an organic solvent and a predetermined amount of lithium salt, and as the component of the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), Diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propionate (MP), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl 2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), vinylene carbonate (VC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate , Ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, butyl propionate, or mixtures thereof, and halogen derivatives of the organic solvents may also be used. And linear ester materials can also be used. The lithium salt is a good material to be dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

The secondary battery of the present invention can be manufactured by storing and sealing the positive electrode and the negative electrode in an electrode assembly in which a separator and an electrode are laminated together with an electrolyte solution in an exterior material such as a battery case. The manufacturing method of a secondary battery can use a conventional method without limitation.

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 a secondary battery exhibiting excellent fast charging characteristics in high loading, the battery module and the battery pack may be used as a power source for an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

On the other hand, with respect to battery elements, for example, conductive materials, which are not described in detail herein, reference may be made to elements commonly used in the battery field, particularly in the lithium secondary battery field.

Hereinafter, examples will be described in detail to help understand the present invention. However, embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as limited to the following examples. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Example

(1) Preparation of Composite Particles

1) Example 1

Si / SiO ₂ powder was mixed at a ratio of 1: 1 (molar ratio), and then heat-treated in a reduced pressure atmosphere of 1 torr to evaporate to a gaseous state of SiO _x (0 <x <2), and Mg was also evaporated to a gaseous state. . Thereafter, the gaseous Mg was allowed to react with SiO _x (0 <x <2) at 1300 ° C. for 3 hours, and then cooled to 800 ° C. within 4 hours to precipitate it on a substrate. The evaporation temperature was 1400 ° C. for Si / SiO ₂ and 900 ° C. for Mg. The resultant precipitate was silicon oxide containing Mg. The bulk precipitated product was ground to a diameter (D ₅₀ ) of about 5 μm using a jet mill. Subsequently, a shell portion was formed in the powder of the milled product by using the CVD method. The CVD process was performed by injecting methane gas at 950 ° C. under argon (Ar) atmosphere. Process time was 2 hours. As a result of analyzing the obtained composite particle powder, the Mg content was about 6% to 100% by weight, and the carbon content of the shell part was about 5%. The Mg content was according to ICP analysis and the carbon content was according to C / S analysis.

2) Example 2

A precipitated product in bulk was obtained in the same manner as in Example 1, except that the evaporation temperature of Mg was set to 50 ° C higher than that of Example 1. The bulk precipitated product was ground to a diameter (D ₅₀ ) of about 5 μm. Subsequently, a shell portion was formed in the powder of the milled product by using the CVD method. The CVD process was performed by injecting acetylene gas under an argon (Ar) atmosphere at 950 ° C. As a result of analyzing the obtained composite particle powder, the Mg content was about 8% to 100% by weight, and the carbon content of the shell part was about 5%. The Mg content was according to ICP analysis and the carbon content was according to C / S analysis.

3) Comparative Example 1)

In the same manner as in Example 1, a bulk precipitated product was obtained. The bulk precipitated product was ground to a diameter (D ₅₀ ) of about 5 μm. The pulverized product and the pitch were mixed and carbonized under an N ₂ atmosphere at 1,100 ° C. to form a shell portion. As a result of analyzing the obtained composite particle powder, the Mg content was about 6% to 100% by weight, and the carbon content of the shell part was about 6%. The Mg content was according to ICP analysis and the carbon content was according to C / S analysis.

4) Comparative Example 2)

A precipitated product in a bulk state was obtained in the same manner as in Example 1 except that the evaporation temperature of Mg was set to 100 ° C. higher than that of Example 1. The bulk precipitated product was ground to a diameter (D ₅₀ ) of about 5 μm. Subsequently, a shell portion was formed in the powder of the milled product by using the CVD method. The CVD process was performed by injecting methane gas at 950 ° C. under argon (Ar) atmosphere. In the analysis of the composite particle powder obtained in Comparative Example 2, the Mg content was about 10% to 100% by weight, and the carbon content of the shell part was about 2%. The Mg content was according to ICP analysis and the carbon content was according to C / S analysis.

Pore distribution and pore volume confirmed by the BJH method for the composite particles obtained through the above Examples and Comparative Examples are shown in Table 1 and FIG.

Pore volume Example 1 1.61X10 ^-2 cm ³ / g Example 2 2.52X10 ^-2 cm ³ / g Comparative Example 1 1.07X10 ^-2 cm ³ / g Comparative Example 2 11.05X10 ^-2 cm ³ / g

(2) production of batteries

A negative electrode slurry was prepared by mixing the negative electrode active material, the conductive material (Super C) and the binder (Li-PAA) with water in a ratio of 8: 1: 1 by weight. The slurry was uniformly coated on a 20 μm thick copper thin film. Coating was performed at an electrode drying temperature of 80 ° C. and a coating rate of 0.2 m / min. The prepared electrode was rolled to match the porosity of 28% by using a roll press equipment to match the target thickness. Next, it was dried for 8 hours in a 130 ℃ vacuum oven. Lithium metal is used as a cathode and a cathode prepared in the above, and an electrode assembly is prepared by interposing a porous film of polypropylene (30 µm, Celgard) between the cathode and the cathode, followed by pouring the electrolyte and leaving the electrolyte for 30 hours. This electrode was allowed to sufficiently infiltrate inside. The electrolyte is a mixture of ethylene carbonate (Ethylene Carbonate) and ethyl methyl carbonate (Ethyl-methyl Carbonate) in a mass ratio of 3: 7.

(3) cycle characteristics

Cycle characteristics were confirmed for the batteries prepared in each of Examples and Comparative Examples. Charging proceeds in 0.1C, 5mV, and 0.005C cut conditions in CC / CV mode, and discharge proceeds in CC mode up to 1.5V at 0.1C, followed by an additional 0.5C charge / discharge reaction cycle. Cycle proceeded. The charge and discharge test was conducted at 25 ℃ conditions. The capacity retention rate in the experiment was calculated based on Equation 1 below. The results are summarized in Table 2.

<Equation 1>

Capacity retention rate (%) = [50th cycle discharge capacity / 2nd cycle discharge capacity] X 100

(3) storage characteristics

Storage characteristics of the batteries prepared in each of Examples and Comparative Examples were confirmed. Capacity of the two sets of batteries prepared in each of Examples and Comparative Examples was maintained at 25 ° C. and 60 ° C. for 7 days, respectively. The capacity retention rate in the experiment was calculated based on Equation 2 below. The results are summarized in Table 2.

<Equation 2>

Capacity retention rate (%) = [Discharge capacity after 7 days of maintenance / 2nd cycle discharge capacity] X 100

Capacity retention rate (%)
25 ℃, 50 cycles Capacity retention rate (%)
60 ℃, after 7 days storage Example 1 81.2% 82.7% Example 2 80.8% 80.3% Comparative Example 1 70.1% 81.5% Comparative Example 2 78.7% 64.2%

Claims (7)

A core-shell structured composite particle (s) having a core portion and a shell portion covering at least a portion of the surface of the core portion,
The core portion includes a matrix including a metal (M) -silicon composite oxide; And a plurality of crystalline silicon phases dispersed and interspersed in the matrix,
The shell portion comprises a carbon material,
The composite particles, and one or more of the pores present in the inside and surface of the particles, nitrogen adsorption _{(N 2 sorption) BJH (Barrett} -Joyner-Halenda) the volume of the pores calculated by the 1.5X10 according to ^{- 2} cm ³ / g To 10.0 X 10 ⁻² cm ³ / g.
The method of claim 1,
The negative electrode active material has a diameter of 2 nm to 1 μm based on the longest diameter of the pores, negative electrode active material.
The method of claim 1,
Wherein the matrix comprises a metal (M) -silicon composite oxide and SiO _x (0 <x ≦ 2).
The method of claim 1,
The metal (M) is one or more selected from Mg, Li and Ca, the negative electrode active material.
The method of claim 1,
The metal (M) -silicon composite oxide comprises magnesium silicate (Mg-silicate), wherein Mg-silicate includes at least one or more of MgSiO ₃ and Mg ₂ SiO ₄ .
The method of claim 1,
The metal (M) is contained in a ratio of 4% to 20% by weight based on 100% by weight of the composite particles, the negative electrode active material.
The method of claim 1,
Wherein the shell is included in the ratio of 2% to 7% by weight relative to 100% by weight of the total composite particles, the negative electrode active material.

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