KR20230025314A - Silicon-based negative electrode active material, negative electrode comprising same, and secondary battery comprising same - Google Patents

Abstract

The present invention relates to a silicon-based negative electrode active material, a negative electrode including the same, and a secondary battery including the same, wherein the silicon-based negative electrode active material includes a core and a carbon layer disposed on the core, the core includes SiO_x (0 < x < 2) and metal atoms, the metal atoms include at least one selected from a group consisting of Mg, Li, Al and Ca, D_5/D_50 is 0.5 or more, and D_50 is 4 to 11 μm.

Description

Silicon-based negative electrode active material, negative electrode including the same, and secondary battery including the same

This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0107512 filed with the Korean Intellectual Property Office on August 13, 2021, all of which are incorporated herein.

The present invention relates to a silicon-based negative electrode active material having a specific particle size distribution, a negative electrode including the same, and a secondary battery including the same.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing, and as part of this, the most actively researched fields are power generation and storage using electrochemical reactions.

Currently, a secondary battery is a representative example of an electrochemical device using such electrochemical energy, and its use area is gradually expanding. Recently, as technology development and demand for portable devices such as portable computers, mobile phones, and cameras increase, the demand for secondary batteries as an energy source is rapidly increasing. A lot of research has been done on it, and it is also commercialized and widely used.

In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material for intercalating and deintercalating lithium ions from the positive electrode, and a silicon-based active material having a high discharge capacity may be used as the negative electrode active material.

However, in the case of a silicon-based active material, an excessive volume change is accompanied during a battery driving process. Accordingly, a problem in that the life of the battery is reduced occurs. Conventionally, in order to solve this problem, methods of reducing the use ratio of the silicon-based active material or using a binder capable of showing high negative electrode adhesion have been used, but there is a limit to solving the problem because it is not an improvement of the silicon-based active material itself. In addition, a technique of making the silicon-based active material porous to accommodate the volume expansion internally is also used, but this reduces the capacity per weight of the negative electrode and reduces the effect by destroying the particles during rolling after manufacturing the electrode. .

Accordingly, there is an urgent need to develop a silicon-based negative electrode active material capable of effectively improving lifespan characteristics of a battery.

Korean Registered Patent Publication No. 10-1586816

One problem to be solved by the present invention is to provide a silicon-based negative electrode active material capable of improving capacity, efficiency and/or lifespan characteristics of a battery, a negative electrode including the same, and a secondary battery including the same.

An exemplary embodiment of the present invention includes a core and a carbon layer disposed on the core, the core includes SiO _x (0<x<2) and metal atoms, and the metal atoms include Mg, Li, Al and A silicon-based negative active material comprising at least one selected from the group consisting of Ca, D ₅ /D ₅₀ is 0.5 or more, and D ₅₀ is 4 μm to 11 μm.

An exemplary embodiment of the present invention provides an anode including an anode active material, wherein the anode active material includes the silicon-based anode active material.

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

Since the silicon-based negative electrode active material according to an exemplary embodiment of the present invention has a D ₅ /D ₅₀ of 0.5 or more and a D ₅₀ of 4 μm to 11 μm, it is possible to prevent excessive side reactions with the electrolyte and insert/discharge lithium ions during charging and discharging. It is easily desorbed and does not cause excessive swelling, so the lifespan characteristics of the battery can be improved. In addition, the silicon-based negative electrode active material includes metal atoms, and since the metal atoms exist in the form of a metal compound such as metal silicate, initial efficiency of a battery may be improved.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

Terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, number, step, component, or combination thereof, but one or more other features or It should be understood that the presence or addition of numbers, steps, components, or combinations thereof is not precluded.

In the present specification, D ₅ and D ₅₀ may be defined as particle diameters corresponding to 5% and 50% of the cumulative volume in the particle size distribution curve (graph curve of the particle size distribution), respectively. In addition, in the present specification, D _max and D _min may respectively correspond to the largest particle diameter and the smallest particle diameter in the particle size distribution curve of the particles. The D ₅ , D ₅₀ , D _max and D _min may each 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. The measurement of D ₅ and D ₅₀ can be confirmed using a Microtrac device (manufacturer: Microtrac model name: S3500), using water and a triton-X100 dispersant under conditions of a refractive index of 1.97.

In this specification, the BET specific surface area is measured by degassing at 130 ° C. for 2 hours using BET measuring equipment (BEL-SORP-MAX, Nippon Bell), and N ₂ adsorption/desorption at 77K. It can be measured by proceeding with absorption/desorption.

In the present specification, the presence or absence of metal elements and the content of the 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 (ICP-OES, AVIO 500, manufactured by Perkin-Elmer 7300). can

<Silicon-based negative electrode active material>

A silicon-based negative electrode active material according to an exemplary embodiment of the present invention includes a core and a carbon layer disposed on the core, the core includes SiO _x (0<x<2) and a metal atom, and the metal atom is Mg , Li, Al, and includes at least one selected from the group consisting of Ca, D ₅ /D ₅₀ is 0.5 or more, D ₅₀ is characterized in that 4 ㎛ to 11 ㎛.

In one embodiment of the present invention, the silicon-based negative active material includes a core.

In one embodiment of the present invention, the core includes SiO _x (0<x<2).

The SiO _x (0<x<2) corresponds to a matrix in the silicon-based negative active material. 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 negative active material 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 core may include a metal atom. 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 negative electrode active material.

The metal atom may include at least one selected from the group consisting of Mg, Li, Al, and Ca. Accordingly, initial efficiency of the silicon-based negative electrode active material may be improved.

Specifically, the metal atom may include Mg, Li or Al. The silicon-based negative electrode active material of the present invention is characterized in that relatively small-sized particles are removed. When the metal atom is Mg, Li, or Al, it can be uniformly doped to the inside of the core, so the silicon-based negative active material having the above characteristics Manufacturing of the negative electrode active material may be smooth. In addition, in the silicon-based negative electrode active material having a particle size distribution of the present invention, since metal atoms having a low atomic number are small in size and can be more uniformly doped to the inside, the metal atom is most preferably Mg or Li.

The metal atoms (Li, Mg, etc.) may be distributed on the surface and/or inside the silicon-based particle in a doped form. The metal atoms may be distributed on the surface and/or inside of the silicon-based particle to control volume expansion/contraction of the silicon-based particle to an appropriate level and prevent damage to the active material. In addition, the metal atom may be contained in order to increase the efficiency of the active material by lowering the ratio of the irreversible phase (eg, SiO ₂ ) in the SiO _x (0<x<2) particle.

The metal atom may exist in the form of a metal silicate. The metal silicate may be classified into crystalline metal silicate and amorphous metal silicate.

When the metal atom is Li, Li may be present in the core 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 .

When the metal atom is Mg, Mg may exist in the form of at least one magnesium silicate selected from Mg ₂ SiO ₄ and MgSiO ₃ in the core.

In one embodiment of the present invention, the metal atom may be included in an amount of 0.1 part by weight to 40 parts by weight, specifically 1 part by weight to 25 parts by weight, based on a total of 100 parts by weight of the silicon-based negative active material. It may be included in 2 parts by weight to 20 parts by weight or 2 parts by weight to 10 parts by weight. When the content of metal atoms exceeds the above range, the initial efficiency increases as the content of metal atoms 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. there is.

In one embodiment of the present invention, the metal atom may be included in an amount of 1 part by weight to 25 parts by weight based on a total of 100 parts by weight of the core, and more specifically, 2 parts by weight to 20 parts by weight or 2 parts by weight to 10 parts by weight. can be included When the content of metal atoms exceeds the above range, the initial efficiency increases as the content of metal atoms 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. there is.

In one embodiment of the present invention, the silicon-based negative electrode active material may include a carbon layer. The carbon layer may be disposed on the core and cover at least a portion of a surface of the core. That is, the carbon layer may partially cover the surface of the core or cover the entire surface of the core. Conductivity is imparted to the silicon-based negative electrode active material by the carbon layer, and initial efficiency, lifespan characteristics, and battery capacity characteristics of a secondary battery may be improved.

The carbon layer may include at least one of amorphous carbon and crystalline carbon.

The crystalline carbon may further improve conductivity of the silicon-based negative electrode 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 metherine, 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 part by weight to 50 parts by weight, 0.1 part by weight to 30 parts by weight, or 0.1 part by weight to 20 parts by weight based on the total 100 parts by weight of the silicon-based negative electrode active material. More specifically, it may be included in 0.5 parts by weight to 15 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 silicon-based negative active material is improved, and thus the initial efficiency and lifespan of the battery are improved.

In one embodiment of the present invention, D ₅₀ of the silicon-based negative electrode active material may be 4 μm to 11 μm. When the D ₅₀ of the silicon-based negative active material is less than 4 μm, the particle size is too small and the specific surface area of the material increases, so there is a problem in that a lot of side reactions with the electrolyte occur and lifespan is severely deteriorated. When the D ₅₀ of the silicon-based negative active material is greater than 11 μm, since the size of the particles is too large, charging and discharging are not easy, and thus, it is difficult to realize capacity/efficiency during charging and discharging. Therefore, when the D ₅₀ of the silicon-based negative active material is 4 μm to 11 μm, charging and discharging are easy, capacity/efficiency is completely realized, and life characteristics are stable. In particular, D ₅₀ of the silicon-based negative active material may be 4.2 μm to 10 μm, specifically 4.5 μm to 9 μm, and more specifically, 5 μm to 7 μm. In this case, in addition to the above-mentioned effects, there may be an effect of facilitating electrode production.

D ₅ /D ₅₀ of the silicon-based negative active material may be 0.5 or more, specifically 0.6 or more. When the D ₅ /D ₅₀ is less than 0.5, since the volume occupied by the silicon-based negative electrode active material of an excessively small size in the negative electrode increases, the side reaction with the electrolyte increases according to the increase in the specific surface area of the material, so the battery life is reduced. there is Accordingly, the lifespan characteristics of the battery may be improved by satisfying the D ₅ /D ₅₀ of 0.5 or more. An upper limit of D ₅ /D ₅₀ of the silicon-based negative active material may be 1.

At this time, even if D ₅₀ of the silicon-based negative active material satisfies the above range, when D ₅ /D ₅₀ is less than 0.5, the volume occupied by the active material much smaller than D ₅₀ in the negative electrode increases, so that a side reaction with the electrolyte solution occurs. increases and battery life decreases. Conversely, when D ₅ /D ₅₀ satisfies 0.5 or more, but D ₅₀ does not satisfy the above range, the average particle size is too small or large, and life and/or efficiency are difficult to implement. Therefore, as in the present invention, when D ₅₀ and D ₅ /D ₅₀ of the silicon-based negative active material satisfy the above ranges, life and/or efficiency of the battery may be improved.

In one embodiment of the present invention, D ₅ of the silicon-based negative active material may be 2 μm to 11 μm. When the above range is satisfied, since the content of the silicon-based negative electrode active material having an excessively small particle size in the negative electrode is reduced, the lifespan and stability of the battery can be improved by reducing side reactions with the electrolyte.

In particular, D ₅ of the silicon-based negative active material may be 2.1 μm to 9 μm, specifically 2.5 μm to 5 μm, and more specifically, 3 μm to 4.2 μm.

In one embodiment of the present invention, the BET specific surface area of the silicon-based negative active material may be 1 m ² /g or more and 20 m ² /g or less, 1 m ² /g or more and 15 m ² /g or less, and 2 m 2 /g or more. ² /g and less than 10 m ² /g, and may be 2.5 m ² /g or more and 8 m ² /g or less.

The upper limit of the BET specific surface area may be 20 m ² /g, 18 m ² /g, 15 m ² /g, 10 m ² /g, 8 m ² /g, 5 m ² /g or 4m ² /g, and , the lower limit may be 1 m ² /g, 1.5 m ² /g, 2 m ² /g or 2.5 m ² /g.

In one embodiment of the present invention, D _max of the silicon-based negative active material may be 35 μm or less, specifically 30 μm or less, more specifically 25 μm or less or 20 μm or less. If the above range is not satisfied, the particles are too large, so the electrode is not well manufactured and there is a problem that the electrode is non-uniformly manufactured during rolling.

D _min of the silicon-based negative active material may be 1.3 μm or more, specifically 1.5 μm or more, and more specifically 1.7 μm or more. When the above range is satisfied, since the specific surface area of the material is not excessively increased, there is an effect of reducing side reactions with the electrolyte.

In one embodiment of the present invention, the silicon-based negative electrode active material comprising the steps of preparing a preliminary silicon-based negative electrode active material; adjusting the particle size of the preliminary silicon-based negative electrode active material; and forming a carbon layer on the preliminary silicon-based negative electrode active material having a controlled particle size.

Specifically, in the step of preparing the preliminary silicon-based negative electrode active material, the preliminary silicon-based negative electrode active material is vaporized after mixing Si powder, SiO ₂ powder and metal powder; condensing the vaporized mixed gas into a solid phase; And it may be formed through the step of heat treatment in an inert atmosphere.

Alternatively, the preliminary silicon-based negative electrode active material may include vaporizing Si powder and SiO ₂ powder by heating in a vacuum, and then depositing the vaporized mixed gas to form silicon-based particles; And it may be formed through the step of heat-treating after mixing the formed silicon-based particles and metal powder.

The heat treatment may be performed at 700 °C to 900 °C for 4 hours to 6 hours, and specifically, at 800 °C for 5 hours.

The metal powder may be Mg powder or Li powder.

When Mg powder is used as the metal powder, an anode active material may be prepared by vaporizing it.

In the case of using Li powder as the metal powder, the negative electrode active material may be prepared by mixing silicon-based particles and Li powder and then heat-treating.

The silicon-based particle may be SiOx (x = 1).

In the preliminary silicon-based negative active material, the Mg compound phase may include the aforementioned Mg silicate, Mg silicide, Mg oxide, and the like.

In the preliminary silicon-based negative electrode active material, the Li compound phase may include the aforementioned Li silicate, Li silicide, Li oxide, and the like.

In the step of adjusting the particle size of the preliminary silicon-based negative electrode active material, the particle size can be adjusted through a method such as a ball mill, a jet mill, or air flow classification, but is not limited thereto. For example, when the particle size of the preliminary silicon-based negative electrode active material is adjusted using a ball mill, 5 to 20 sus ball media may be added, and specifically 10 to 15 may be added, but is not limited thereto .

In the step of adjusting the particle size, the grinding time of the preliminary silicon-based negative electrode active material may be 2 hours to 5 hours, specifically 2 hours to 4 hours, and more specifically 3 hours, 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 the preliminary silicon-based negative electrode active material is introduced into a reaction furnace, 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.

<cathode>

An anode according to an exemplary embodiment of the present invention may include an anode active material, wherein the anode active material may include the above-described silicon-based anode active material.

In one embodiment of the present invention, the negative active material may further include a carbon-based negative active material. The carbon-based negative electrode active material may be at least one selected from natural graphite and artificial graphite.

In one embodiment of the present invention, the weight ratio of the silicon-based negative active material and the carbon-based negative active material in the negative electrode active material may be 10:90 to 90:10, specifically 10:90 to 50:50.

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 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 anode 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; or LiMn ₂ O ₄ in which Li in the formula is partially substituted with alkaline earth metal ions, 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 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.

<Examples and Comparative Examples>

Example 1

After mixing Si and SiO ₂ in a 1:1 molar ratio of 94 g of powder and 6 g of Mg in a reaction furnace, the mixture was vacuum-heated to a sublimation temperature of 1,400°C. Thereafter, the vaporized Si, SiO ₂ , and Mg mixed gas were 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 in an inert atmosphere at a temperature of 800° C. (additional heat treatment temperature) to prepare a preliminary silicon-based negative electrode active material. Thereafter, 15 sus ball media were added to the preliminary silicon-based negative electrode active material using a ball mill, and then pulverized for 3 hours to prepare a size of D ₅₀ =6 μm. Thereafter, while maintaining an inert atmosphere by flowing Ar gas, the preliminary silicon-based negative electrode active material is 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 to 20 The reaction was performed at 10 ⁻¹ torr per minute to prepare a silicon-based negative electrode active material having a carbon layer formed on the surface.

Example 2

A silicon-based negative electrode active material was prepared in the same manner as in Example 1, except that 10 Sus ball media were added.

Example 3

In the method of Example 1, after synthesizing 94 g of SiO particles without using Mg, 6 g of Li metal powder was added, and heat treatment was performed at a temperature of 800 ° C in an inert atmosphere to obtain a preliminary silicon-based negative electrode active material. manufactured. Thereafter, 15 sus ball media were added to the preliminary silicon-based negative electrode active material using a ball mill, and then pulverized for 3 hours to prepare a size of D ₅₀ =6 μm. Thereafter, while maintaining an inert atmosphere by flowing Ar gas, the preliminary silicon-based negative electrode active material is 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 to 20 The reaction was performed at 10 ⁻¹ torr per minute to prepare a silicon-based negative electrode active material having a carbon layer formed on the surface.

Example 4

A silicon-based negative electrode active material was prepared in the same manner as in Example 3, except that 10 Sus ball media were added.

Comparative Example 1

A silicon-based negative active material was prepared in the same manner as in Example 1, except that the grinding time was modified to 8 hours.

Comparative Example 2

A silicon-based negative active material was prepared in the same manner as in Example 1, except that the grinding time was modified to 1 hour.

Comparative Example 3

A silicon-based negative electrode active material was prepared in the same manner as in Example 1, except that 30 sus ball media were added and the grinding time was modified to 8 hours.

Comparative Example 4

A silicon-based negative electrode active material was prepared in the same manner as in Example 1, except that 30 sus ball media were added and the grinding time was modified to 1 hour.

Comparative Example 5

A silicon-based negative active material was prepared in the same manner as in Example 3, except that the grinding time was changed to 8 hours.

Comparative Example 6

A silicon-based negative active material was prepared in the same manner as in Example 3, except that the grinding time was modified to 1 hour.

Comparative Example 7

A silicon-based negative electrode active material was prepared in the same manner as in Example 3, except that 30 pieces of sus ball media were added and the grinding time was modified to 8 hours.

Comparative Example 8

A silicon-based negative electrode active material was prepared in the same manner as in Example 3, except that 30 sus ball media were added and the grinding time was modified to 1 hour.

Comparative Example 9

A silicon-based negative electrode active material was prepared in the same manner as in Example 1, except that 30 Sus ball media were added.

Comparative Example 10

A silicon-based negative electrode active material was prepared in the same manner as in Example 3, except that 30 Sus ball media were added .

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

Particle size analysis of silicon-based negative electrode active material Specific surface area of silicon-based negative electrode active material (m ² /g) Parts by weight of metal atoms included based on 100 parts by weight in the core of the silicon-based negative electrode active material _D5 / _D50 D ₅₀ (μm) D _max (μm) D _min (μm) Mg content (parts by weight) Li content (parts by weight) Example 1 0.5 6 19 2 3.5 6 - Example 2 0.6 6 17 2.5 2.5 6 - Example 3 0.5 6 19 2 3.5 - 6 Example 4 0.6 6 17 2.5 2.5 - 6 Comparative Example 1 0.5 3 20 One 5.0 6 - Comparative Example 2 0.5 12 40 5 2.0 6 - Comparative Example 3 0.3 3 20 0.5 6.0 6 - Comparative Example 4 0.3 12 40 2.5 2.5 6 - Comparative Example 5 0.5 3 20 One 5.0 - 6 Comparative Example 6 0.5 12 40 5 2.0 - 6 Comparative Example 7 0.3 3 20 0.5 6.0 - 6 Comparative Example 8 0.3 12 40 2.5 2.5 - 6 Comparative Example 9 0.3 6 20 0.5 4.0 6 - Comparative Example 10 0.3 6 20 0.5 4.0 - 6

The particle size analysis of the silicon-based negative electrode active material was analyzed by the PSD measurement method using a microtac device.

The specific surface area was measured by degassing at 130° C. for 2 hours using BET measuring equipment (BEL-SORP-MAX, Nippon Bell), and adsorption/desorption of N ₂ at 77K. was measured.

The metal atom content was confirmed through ICP analysis using an inductively coupled plasma emission spectrometer (ICP-OES, AVIO 500, manufactured by Perkin-Elmer 7300).

<Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, Life (Capacity Retention Rate) Characteristics>

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 cycle was charged and discharged at 0.5C. The 300 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 (%) = (300 discharge capacity / 1 discharge capacity) × 100

battery Discharge capacity (mAh/g) Initial Efficiency (%) Capacity retention rate (%) Example 1 1430 80 50 Example 2 1450 80 52 Example 3 1350 85 50 Example 4 1360 85 52 Comparative Example 1 1420 79 35 Comparative Example 2 1380 78 25 Comparative Example 3 1390 78 25 Comparative Example 4 1370 78 15 Comparative Example 5 1320 84 35 Comparative Example 6 1300 80 25 Comparative Example 7 1320 83 25 Comparative Example 8 1300 80 15 Comparative Example 9 1420 79 45 Comparative Example 10 1330 84 42

The silicon-based negative electrode active material according to the present invention includes metal atoms, D ₅ /D ₅₀ is 0.5 or more, and D ₅₀ is 4 μm to 11 μm, and the particle size distribution of D ₅₀ and D ₅ /D ₅₀ is appropriate By having it, side reactions with the electrolyte are suppressed, charging and discharging are facilitated, capacity/efficiency implementation occurs completely, and life characteristics are stable.

In Table 2, Examples 1 and 2 are negative active materials containing Mg, and have a discharge capacity compared to Comparative Examples 1 to 4 and 9 that do not satisfy the D ₅ /D ₅₀ value or the D ₅₀ value. , it can be confirmed that both the initial efficiency and the capacity retention rate are excellent. In addition, Examples 3 and 4 are negative electrode active materials containing Li, and it can be seen that they are superior in discharge capacity, initial efficiency, and capacity retention rate compared to Comparative Examples 5 to 8 and 10.

On the other hand, Comparative Examples 1 and 5 satisfy the D ₅ /D ₅₀ range of the present invention, but the D ₅₀ is smaller than 4 μm, and the overall particle size is too small to increase the specific surface area of the material and cause a lot of side reactions with the electrolyte. , It was confirmed that the capacity, efficiency and lifespan were lowered than in the Example.

Comparative Examples 2 and 6 satisfy the D ₅ /D ₅₀ range of the present invention, but the D ₅₀ is greater than 11 μm, and the overall particle size is too large to make charging and discharging difficult. This degradation was observed.

Comparative Examples 3, 4, 7, and 8 did not satisfy all of the D ₅ /D ₅₀ and D ₅₀ ranges of the present invention, and it was confirmed that capacity, efficiency, and lifespan were significantly lowered than Examples.

Comparative Examples 9 and 10 satisfy the D ₅₀ range of the present invention, but D ₅ /D ₅₀ is less than 0.5, and the volume occupied by the negative electrode active material much smaller than D ₅₀ in the negative electrode increases, so the side reaction with the electrolyte increases. As a result, it was confirmed that the lifespan of the battery was reduced compared to the example.

Therefore, by adjusting the ranges of D ₅₀ and D ₅ /D ₅₀ of the negative electrode active material, side reactions with the electrolyte were reduced, and life, efficiency, and capacity retention rate of the battery could be easily improved.

Claims (12)

Including a core and a carbon layer disposed on the core,
The core includes SiO _x (0<x<2) and metal atoms,
The metal atom includes at least one selected from the group consisting of Mg, Li, Al and Ca,
A silicon-based negative electrode active material having D ₅ /D ₅₀ of 0.5 or more and D ₅₀ of 4 μm to 11 μm. The method of claim 1,
The D ₅ /D ₅₀ is a silicon-based negative active material that is 0.6 or more. The method of claim 1,
The D ₅₀ is a silicon-based negative electrode active material of 4.2 μm to 10 μm. The method of claim 1,
The D ₅ is a negative electrode active material of 2 μm to 11 μm. The method of claim 1,
D _max of the silicon-based negative electrode active material is 35 ㎛ or less of the silicon-based negative active material. The method of claim 1,
The metal atom is contained in 0.1 part by weight to 40 parts by weight based on a total of 100 parts by weight of the silicon-based negative electrode active material. The method of claim 1,
The metal atom is a silicon-based negative electrode active material containing Mg or Li. The method of claim 1,
The carbon layer is a silicon-based negative electrode active material that is included in 0.1 part by weight to 50 parts by weight based on the total 100 parts by weight of the silicon-based negative electrode active material. The method of claim 1,
A BET specific surface area of more than 2 m ² /g and less than 10 m ² /g, which is a silicon-based negative electrode active material. Contains an anode active material,
The negative electrode active material includes the silicon-based negative electrode active material according to any one of claims 1 to 9. The method of claim 10,
The negative electrode active material further comprises a carbon-based negative electrode active material. A secondary battery comprising the negative electrode according to claim 10 .