KR101561274B1 - Negative active material for rechargeable lithium battery, method of preparing the same, and negative electrode and rechargeable lithium battery including the same - Google Patents

Abstract

Core particles comprising active particles, ground graphite, first amorphous carbon and voids; And a shell layer coated on the surface of the core particle and comprising scaly graphite and a second amorphous carbon, wherein the active particles comprise metal particles, metal-containing compound particles, or combinations thereof, and the first amorphous carbon And the second amorphous carbon are the same or different from each other and include soft carbon, hard carbon or a combination thereof, a method for producing the negative active material, and a negative electrode and a lithium secondary battery comprising the same.

Description

TECHNICAL FIELD The present invention relates to a negative electrode active material for a lithium secondary battery, a method for producing the same, a negative electrode and a lithium secondary battery including the negative electrode active material, a method for producing the same,

A negative electrode active material for a lithium secondary battery, a production method thereof, and a negative electrode and a lithium secondary battery comprising the same.

2. Description of the Related Art Recently, with the progress of miniaturization or high performance of electronic devices, there is an increasing need to improve the energy density of lithium secondary batteries used as power sources for these devices.

Currently, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of inserting and separating lithium are being applied to the anode active material of a lithium secondary battery. Among carbon-based materials, graphite has a low discharge voltage as compared to lithium, and a battery using graphite as an anode active material exhibits a high discharge voltage, thereby providing an advantage in terms of energy density of a lithium secondary battery and also exhibiting excellent reversibility, And is most widely used. However, it is necessary to develop a new high capacity anode active material having a larger lithium storage capacity than graphite in order to increase the energy density of the battery because the storage capacity of lithium is limited to the theoretical capacity (372 mAh / g) as the anode active material currently commercialized.

Silicon (Si) and its compounds have been conventionally studied as a novel material that can replace graphite. Silicon reversibly intercalates and deintercalates lithium through compound formation reaction with lithium, and its theoretical maximum capacity is 4020 mAh / g (9800 mAh / cm ³ , specific gravity: 2.23), which is very large compared to graphite and is therefore promising as a high capacity cathode material. However, a large volume change occurs due to the reaction with lithium during charging and discharging (300% volume expansion when Li _{4 .4} Si phase is formed), resulting in undifferentiation of the silicon active material powder and poor electrical contact between the silicon active material powder and the current collector Occurs. As a result, as the charge / discharge cycle of the battery progresses, the battery capacity sharply decreases, shortening the cycle life.

One embodiment of the present invention is to provide a negative electrode active material for a lithium secondary battery having improved conductivity, suppressed volume expansion, and having a large charge / discharge capacity and excellent cycle life characteristics.

Another embodiment is to provide a method for producing the negative electrode active material.

Another embodiment is to provide a negative electrode for a lithium secondary battery comprising the negative electrode active material.

Another embodiment is to provide a lithium secondary battery including the negative electrode.

One embodiment includes a core particle comprising an active particle, a ground graphite, a first amorphous carbon and a pore; And a shell layer coated on the surface of the core particle and comprising scaly graphite and a second amorphous carbon, wherein the active particles comprise metal particles, metal-containing compound particles, or combinations thereof, and the first amorphous carbon And the second amorphous carbon are the same as or different from each other, and include soft carbon, hard carbon, or a combination thereof, for a negative electrode active material for a lithium secondary battery.

The metal-containing compound particles may include Si, Sn, Sb, Al, Ge, Zn, Pb, or combinations thereof. , A complex of the metal and carbon, or a combination thereof. The oxide of the metal may include a compound represented by the following formula (1), a compound represented by the following formula (2), or a combination thereof.

[Chemical Formula 1]

SiO _x

(In the formula 1, 0 < x < 1.5.)

(2)

Si _{1 - x} M _x O _y

(M is at least one element selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Hf, Re, Os, Mg, Ca, B, P, Al, Ge, Sn, Sb, Bi, Li or combinations thereof; 0 <x <1 and 0.1? Y?

The average particle size (D50) of the active particles may be 1 nm to 5 탆, and may be included in an amount of 3 to 70% by weight based on the total amount of the core particles.

The active particles may be physically or chemically bonded to the surface of the earth graphite.

The average particle size (D50) of the ground graphite may be 0.1 to 3 占 퐉 and may be included in an amount of 5 to 90% by weight based on the total amount of the core particles.

The first amorphous carbon may be included in an amount of 5 to 80% by weight based on the total amount of the core particles.

The voids may be contained in an amount of 2 to 60% by volume based on the total volume of the core particles.

The average particle diameter (D50) of the core particles may be 2 to 30 mu m.

The thickness of the scratched graphite may be 0.01 to 5 탆, and the average particle size (D50) may be 1 to 50 탆.

The second amorphous carbon may be included in an amount of 10 to 90% by weight based on the total amount of the shell layer.

The thickness of the shell layer may be 0.1 to 10 mu m.

A third amorphous carbon may be impregnated on or in the surface of the void, wherein the third amorphous carbon may comprise soft carbon, hard carbon, or a combination thereof.

And a carbon layer coated on the surface of the core particle between the core particle and the shell layer and containing a third amorphous carbon.

Another embodiment provides a method for preparing a core particle mixture, the method comprising: mixing a core particle mixture by mixing active particles, ground graphite, a first amorphous carbon precursor, and a solvent; Spray drying the core particle mixture to obtain granulated core particles; Mixing the core particles, scaly graphite and a second amorphous carbon precursor to obtain a composite particle having a shell layer containing scaly graphite and a second amorphous carbon formed on a surface of the core particle; And heat treating the composite particles, wherein the active particles comprise metal particles, metal-containing compound particles, or combinations thereof, wherein the first amorphous carbon precursor and the second amorphous carbon precursor are the same or different from each other , A soft carbon raw material, a hard carbon raw material, or a combination thereof.

The active particles and the ground graphite may be mixed with the active particles attached to the surface of the ground graphite.

And mixing and drying the solution in which the core particles and the third amorphous carbon precursor are dissolved before the step of obtaining the composite particles after the step of obtaining the core particles, and the third amorphous carbon precursor may be soft carbon A raw material, a hard carbon raw material, or a combination thereof.

The soft carbon material may include a coal pitch, a petroleum pitch, a mesophase pitch, a tar, a low molecular weight heavy oil, glucose, a gelatin, a saccharide, or a combination thereof. The hard carbon raw material may be a phenol resin, a naphthalene resin, Polyvinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (CMC), hydroxypropylmethylcellulose (CMC), polyvinylpyrrolidone resin, Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, polyacrylic acid, polyacrylic sodium, polyacrylonitrile, polyacrylonitrile, polyvinylpyrrolidone, Cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, or combinations thereof.

The first amorphous carbon precursor may be mixed in an amount of 1 to 100 parts by weight based on 100 parts by weight of the total amount of the active particles and the ground graphite.

The solvent may be selected from the group consisting of N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, water, . &Lt; / RTI &gt;

The spray drying may be carried out at a temperature of 50 to 300 캜 and may be carried out by a drying method including rotary spraying, nozzle spraying, ultrasonic spraying or a combination thereof.

The heat treatment may be performed at a temperature of 600 to 2000 ° C.

Another embodiment provides a negative electrode for a lithium secondary battery comprising the negative electrode active material.

Another embodiment further comprises: the cathode; anode; And a lithium secondary battery comprising the electrolyte.

The details of other embodiments are included in the detailed description below.

A lithium secondary battery having a large charge / discharge capacity and excellent cycle life characteristics can be realized.

FIG. 1 is a schematic view showing a structure of a negative electrode active material according to one embodiment.
2A is a scanning electron microscope (SEM) photograph of mixed particles of ground graphite and silicon used in Example 4, and FIG. 2B is a component analysis (EDX) photograph of mixed particles of ground graphite and silicon used in Example 4 .
3A to 3K are scanning electron microscope (SEM) photographs of the negative electrode active material according to Examples 1 to 4 and Comparative Examples 1 to 7, respectively.
4A and 4B are graphs of particle size distribution analysis of the to-be-used graphite used in Example 1 and the negative active material prepared in Example 1, respectively.
FIG. 5A is an X-ray diffraction (XRD) pattern of graphite, and FIG. 5B is an X-ray diffraction (XRD) pattern of the negative electrode active material prepared in Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

The anode active material for a lithium secondary battery according to an embodiment may have a structure of core particles and a shell layer coated on the surface of the core particles. The core particles may comprise active particles, ground graphite, first amorphous carbon and voids, and the shell layer may comprise graphite graphite and a second amorphous carbon.

The graphite constituting the core particles and the graphite constituting the shell layer all belong to natural graphite as the crystalline graphite. However, the soil graphite and the scaly graphite are different materials.

The ground graphite is a state in which fine particles are agglomerated, and the agglomerated graphite agglomerate has an average particle diameter of 0.1 to 50 탆, which can be easily pulverized. Such earthy graphite is sometimes referred to as microcrystalline graphite or amorphous graphite. On the other hand, the flake graphite has an average particle size of 2 to 200 탆 in the form of multiple layers of flaky tabular grains. In addition, when the ground graphite and the scaly graphite are pulverized by an air jet milling process, the above-mentioned toe graphite uses the term "pulverization" but its structure is similar to the concept of "separating & Although graphite crystallinity is maintained even after crushing and crushing, scratched graphite crushes broad plate-shaped particles, which is different in that crushing is relatively difficult and crystallinity in the crushing process can be lowered.

Since the graphite has a structure similar to that of clay by aggregation of fine graphite, it is preferable that the graphite is separated or crushed into fine particles. Specifically, the earth graphite may be fine particles having an average particle diameter (D50) of 3 mu m or less, specifically 0.1 to 3 mu m, and more specifically 0.1 to 2 mu m. When the toothed graphite of the above-mentioned size is used, the active particles can be uniformly dispersed by the ground graphite in the core particles, and the voids formed inside the core particles can buffer the volume expansion of the active particles have.

When the shell layer is formed using the flaky graphite, the volume expansion of the core particles can be suppressed during charging / discharging due to the multiple layered structure of flaky flake-like particles, and side reactions with the electrolyte can be suppressed.

The structure of the negative electrode active material will be described with reference to FIG. 1, but FIG. 1 corresponds to an example, and the negative electrode active material according to one embodiment is not limited to this structure.

FIG. 1 is a schematic view showing a structure of a negative electrode active material according to one embodiment.

1, the negative electrode active material 10 according to one embodiment includes core particles including active particles 11, ground graphite 12, first amorphous carbon 13, and void 14, A graphite 15 and a second amorphous carbon 16, as shown in FIG. The active particles 11 can be uniformly dispersed by the earth graphite 12 within the core particles and the volume expansion of the active particles 11 due to the voids 14 formed inside the core particles can be suppressed Can be buffered. Also, due to the structure in which the shell layer coatings the core particles, the core particles are prevented from expanding in volume during charging and discharging to serve as a protective layer and a buffer layer, thereby achieving high charge-discharge capacity and excellent cycle life characteristics .

The active particles include a metal element capable of alloying with lithium, and metal particles, metal-containing compound particles, or a combination thereof can be used.

The metal particles may be Si, Sn, Sb, Al, Ge, Zn, Pb or a combination thereof. Among them, Si may be preferably used.

The metal-containing compound particle may be an oxide of a metal containing Si, Sn, Sb, Al, Ge, Zn, Pb or a combination thereof, or may be a composite of the metal and carbon, And a composite of the metal and carbon may be mixed and used.

Examples of the metal oxide include compounds represented by the following general formula (1), compounds represented by the following general formula (2), and combinations thereof.

[Chemical Formula 1]

SiO _x

In the formula 1, 0 < x < 1.5, specifically 0.001 x 1. When x is within the above range, the reversible capacity per unit weight increases.

(2)

Si _{1 - x} M _x O _y

In the above formula (2), 0 < x < 1, specifically 0.001 x 0.4. When x is within the above range, the reversible capacity per unit weight increases.

Wherein M is at least one element selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Hf, Ta, Os, Mg, Ca, B, P, Al, Ge, Sn, Sb, Bi, Li or combinations thereof.

In Formula 2, 0.1? Y? 1.7, specifically 0.3? Y? 1.5. When y is within the above range, the cycle life characteristics are excellent and the lithium storage capacity is increased.

In the compound represented by Formula 2, M may be doped in SiO _x to form an amorphous matrix of Si-OM or a crystalline compound, which is structurally stable and can improve conductivity.

The average particle size (D50) of the active particles may be from 1 nm to 5 占 퐉, and more specifically from 10 nm to 3 占 퐉. When the average particle size of the active particles is within the above range, the volume expansion of the active particles during reaction with lithium is suppressed, thereby improving cycle life characteristics.

The active particles may be physically or chemically bonded to the surface of the ground graphite. When the active particles are positioned as described above, the distribution of the active particles in the core particles becomes more uniform during the production of the core particles by the spray drying process, and the electrical conductivity of the active particles is further improved during the charge- Life characteristics are improved.

The active particles may be contained in an amount of 3 to 70% by weight, and particularly 5 to 40% by weight based on the total amount of the core particles. When the active particles are contained within the above range, the reversible capacity increases, the volume expansion is buffered easily, and the cycle life characteristics are improved.

The soil graphite can improve the conductivity of the negative electrode active material and assist in the uniform dispersion of the active particles.

The average particle size (D50) of the ground graphite may be 0.1 to 3 mu m, and specifically 0.5 to 2 mu m. When the average particle size of the earth graphite is within the above range, a void having a proper porosity is formed in the core particle, thereby improving the buffering property against the volume expansion of the active particles during charging and discharging, As a result, cycle life characteristics can be improved.

The ground graphite may be included in an amount of 5 to 90% by weight, specifically 10 to 80% by weight, based on the total weight of the core particles. When the earth graphite is used within the above range, voids having a proper porosity are formed in the core particles, thereby improving the buffering property against the volume expansion of the active particles during charging and discharging, resulting in excellent cycle life characteristics have.

The first amorphous carbon enhances the bonding between the active particles and the ground graphite and increases the packing density inside the core particles.

The first amorphous carbon may be soft carbon, hard carbon, or a combination thereof.

The first amorphous carbon may be included in an amount of 5 to 80% by weight, and more preferably 5 to 50% by weight based on the total amount of the core particles. When the first amorphous carbon is used within the above range, the binding force between the active particles and the ground graphite is strong, so that the structure of the core particles becomes stable. In addition, voids having an appropriate porosity are formed in the core particles, and the active particles and the ground graphite are easily dispersed, so that the buffering property against the volume expansion of the active particles during charging and discharging can be improved.

The voids are formed in the core particles. The pores provide a buffer space in which the active particles efficiently absorb volume expansion upon reaction with lithium ions.

The voids exist as voids formed inside the core particles, may have an amorphous shape, and may form a mesh network within the core particles.

The voids may be contained in an amount of 2 to 60% by volume based on the total volume of the core particles, specifically, 10 to 50% by volume. When the voids are formed within the above volume range, a buffer space due to the reaction between the active particles and the lithium ions is provided at the time of charging and discharging. The lithium ion conductivity is excellent and the packing density is high, Cycle life characteristics can be improved.

The average particle diameter (D50) of the core particles may be 2 to 30 mu m, and may be 5 to 20 mu m. When the average particle diameter of the core particles is within the above range, the core particles are easily formed and the charge / discharge output is improved.

The shell layer is formed by laminating the scratched graphite in a concentric direction on the surface of the core particle, and the shell layer protects the core particle from the electrolyte during charging and discharging and suppresses the volume expansion of the core particle And the movement and electrical conductivity of lithium ions can be improved due to the shell layer.

The thickness of the scratched graphite may be 0.01 to 5 탆, specifically 0.01 to 3 탆. When the thickness of the scratched graphite is within the above range, the surface of the core particles can be easily stacked in the concentric direction, and the core particles can be protected from the electrolyte solution during charging and discharging, and volume expansion of the core particles can be suppressed.

The average particle size (D50) of the scratched graphite may be 1 to 50 m, and may be 2 to 30 m. When the average particle size of the graphite graphite is within the above range, the effect of suppressing the volume expansion of the core particles during charging and discharging is excellent, the specific surface area of the graphite graphite is reduced, and the initial charging / discharging efficiency is excellent. The movement is improved and the charging / discharging output characteristic is improved.

The second amorphous carbon is the same as the description of the first amorphous carbon in the core particle.

The flaky graphite may be included in an amount of 10 to 90% by weight, specifically 20 to 80% by weight, based on the total amount of the shell layer. The second amorphous carbon may be contained in an amount of 10 to 90% by weight, specifically 20 to 80% by weight based on the total amount of the shell layer. When the scratched graphite and the second amorphous carbon are used within the above ranges, sufficient binding between the scratched graphite in the shell layer can be obtained, volume expansion of the core particles can be suppressed, and electrical conductivity can be improved .

The thickness of the shell layer may be from 0.1 to 10 탆, and specifically from 1 to 5 탆. When the thickness of the shell layer is within the above range, the volume expansion of the core particles can be suppressed, the movement of the lithium ions can be smoothly performed, and the reaction between the core particles and lithium can sufficiently occur and the reversible capacity can be increased.

The third amorphous carbon may be impregnated on the surface or inside of the void existing in the core particle or the negative electrode active material may further include a carbon layer coated on the surface of the core particle between the core particle and the shell layer . &Lt; / RTI &gt; The carbon layer may include a third amorphous carbon. The third amorphous carbon may include soft carbon, hard carbon, or a combination thereof, such as the first amorphous carbon and the second amorphous carbon described above. When having the above structure, the adhesion between the core particle and the shell layer is improved, and the active particles can be prevented from flowing into the shell layer during formation of the shell layer.

The negative electrode active material may be prepared by the following method.

First, the core particle mixture is obtained by mixing the active particles, the ground graphite, the first amorphous carbon precursor, and the solvent, and spraying the core particle mixture to obtain assembled core particles.

Specifically, when the tolactic graphite, the active particles, the first amorphous carbon precursor, and the solvent are mixed, the first amorphous carbon precursor may be a precursor dissolved in the solvent and a non-dissolved precursor. Also, the ground graphite and the active particles can be uniformly dispersed in a solution in which the first amorphous carbon precursor is dissolved.

The core particles thus obtained are subjected to a subsequent heat treatment to carbonize the first amorphous carbon precursor so that the active particles including the metal element capable of alloying with lithium are bonded to each other by the tolaid graphite and the first amorphous carbon, And may have a complex porous structure in which pores are distributed.

The active particles and the ground graphite may be mixed with the active particles physically or chemically bonded to the surface of the earth graphite. Specifically, the ground particles of fine particles having a size of 1 탆 or less can be attached to the surface of the ground graphite.

The first amorphous carbon precursor may be a hard carbon source, a soft carbon source, or a combination thereof. Specifically, when the solvent is used as an aqueous solvent, a first amorphous carbon precursor dissolved in an aqueous solvent and a first amorphous carbon precursor not soluble in an aqueous solvent may be mixed together.

The first amorphous carbon precursor may be mixed in an amount of 1 to 100 parts by weight, specifically 10 to 80 parts by weight, based on 100 parts by weight of the total amount of the active particles and the ground graphite. When the first amorphous carbon precursor is used within the above-mentioned content range, it is possible to manufacture core particles having a spherical shape of the particles and having a composite porosity structure having an appropriate range of internal voids.

The solvent may be selected from the group consisting of N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, water, Can be used.

The solvent may be mixed in an amount of 500 to 30,000 parts by weight, specifically 2,000 to 10,000 parts by weight, based on 100 parts by weight of the total amount of the active particles and the graphite. When the solvent is used within the above-mentioned content range, it is possible to prepare core particles of a composite porous structure having a proper range of suitable internal voids, which are easy to assemble the particles.

The spray drying may be carried out at a temperature of 50 to 300 캜, specifically at a temperature of 80 to 200 캜. When spray dried in the above temperature range, drying of the solvent is stably performed, so that it is easy to control the complex porous structure and shape of the core particles.

The spray drying may be performed by a drying method including rotary spraying, nozzle spraying, ultrasonic spraying, or a combination thereof, but is not limited thereto.

Next, by mixing the prepared core particles with scaly graphite and a second amorphous carbon precursor to obtain a composite particle mixture, a shell layer containing the scaly graphite and the second amorphous carbon is formed on the surface of the core particle, Whereby the formed composite particles can be obtained. At this time, the composite particles having the shell layer formed on the core particles can be assembled and spheronized by a milling method in which the composite particle mixture is subjected to a shear force.

The method may further include mixing and drying a solution in which the core particles and the third amorphous carbon precursor are dissolved before the composite particle mixture is obtained. In this case, a carbon layer containing a third amorphous carbon coated on the surface of the core particle may be further coated between the core particle and the shell layer, or the third amorphous carbon may be coated inside the void formed inside the core particle It may be impregnated.

The first amorphous carbon, the second amorphous carbon and the third amorphous carbon may be the same or different from each other and each may comprise a soft carbon raw material, a hard carbon raw material, or a combination thereof.

The soft carbon feedstock may include coal pitch, petroleum pitch, mesophase pitch, tar, low molecular weight heavy oil, glucose, gelatin, sugars or combinations thereof.

The hard carbon material may be selected from the group consisting of phenol resin, naphthalene resin, furfuryl alcohol resin, polyamide resin, furan resin, polyimide resin, epoxy resin, vinyl chloride resin, gum arabic, citric acid, Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, polyvinylpyrrolidone, polyethylene, polypropylene, polyvinylidene fluoride, vinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose , Polyacrylic acid, polyacrylic sodium, polyacrylonitrile, cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, or combinations thereof.

Next, the above-described negative electrode active material can be produced by heat-treating the composite particles.

The heat treatment may be performed at a temperature of 600 to 2000 ° C, and more specifically, at a temperature of 800 to 1500 ° C. When the heat treatment is performed within the temperature range, the reactivity of the active particles with lithium is excellent, and the carbonization processes of the first amorphous carbon precursor and the second amorphous carbon precursor are sufficiently performed, and the cycle life characteristics can be improved.

The heat treatment may be performed in an atmosphere containing nitrogen, argon, hydrogen or a mixed gas thereof, or under a vacuum.

Another embodiment provides a negative electrode for a lithium secondary battery including the negative active material, and another embodiment provides a lithium secondary battery including the negative electrode.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of the separator and electrolyte used. The lithium secondary battery may be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

A lithium secondary battery according to an embodiment includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode assembly includes a sealing member that is housed in a battery container, impregnates the electrolyte, and seals the battery container.

The negative electrode may be prepared by mixing the above-described negative electrode active material, a binder and optionally a conductive material to prepare a composition for forming the negative electrode active material layer, and then applying the composition to an anode current collector such as copper.

Examples of the binder include polyvinyl alcohol, carboxymethylcellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene Polypropylene and the like can be used, but the present invention is not limited thereto.

The binder may be mixed in an amount of 1 to 30% by weight based on the total amount of the composition for forming the negative electrode active material layer.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and specifically includes graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The conductive material may be mixed in an amount of 0.1 to 30% by weight based on the total amount of the composition for forming the anode active material layer.

The anode current collector may have a thickness of 3 to 500 mu m. Examples of the negative electrode current collector may include stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface treated with carbon, nickel, titanium, silver or the like on the surface of aluminum or stainless steel. The negative electrode current collector may have fine irregularities on its surface to increase the adhesive force of the negative electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The positive electrode may be prepared by mixing the positive electrode active material, the binder and optionally a conductive material to prepare a composition for forming a positive electrode active material layer, and then applying the composition to a positive electrode current collector such as aluminum.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, at least one of complex oxides of lithium and at least one kind selected from cobalt, manganese and nickel can be used.

The electrolyte solution may be a lithium salt, a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte.

The lithium salt is _{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 ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium 4-phenylborate, and imide.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, But are not limited to, ricifrcr, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, An ether, a methyl ethyl pyrophonate, an ethyl propionate, a methyl ethyl ketone derivative, a methyl ethyl ketone derivative, a methyl ethyl ketone derivative, Etc. may be used.

Examples of the organic solid electrolytic solution include a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene and an ionic dissociation group And the like can be used.

As the inorganic solid electrolytic solution, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ - Nitrides, halides and sulfates of Li such as LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the electrolyte solution is preferably used in the form of a solution containing at least one member selected from the group consisting of pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like can be added. Further, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride or the like may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

Depending on the type of the lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. As such a separator, an insulating thin film having high ion permeability and mechanical strength can be used. The pore diameter of the separator may be 0.01 to 10 mu m and the thickness may be 5 to 300 mu m.

The separator specifically includes an olefin-based polymer such as polypropylene having chemical resistance and hydrophobicity; A sheet or a nonwoven fabric made of glass fiber, polyethylene or the like can be used. When a solid electrolyte such as a polymer is used as the electrolytic solution, the solid electrolytic solution may also serve as a separation membrane.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

(Preparation of negative electrode active material)

Example  One

The toe graphite having an average particle diameter (D50) of 1.7 占 퐉 and the average particle diameter (D50) 34 parts by weight of gum arabic and 1000 parts by weight of water were added to 100 parts by weight of a mixture obtained by mixing 30 nm of silicon at a weight ratio of 30:70 and stirred to prepare a suspension and spray dried at 160 DEG C to obtain core particles.

A tetrahydrofuran solution in which 100 parts by weight of the core particles and 7 parts by weight of petroleum pitch (carbon yield: 27% by weight) were dissolved was mixed and stirred, followed by vacuum drying at 80 캜 to obtain composite particles.

The composite particles, the graphite graphite having a particle size of 5 탆 And petroleum pitch (carbon yield: 54 mass%) were mixed at a weight ratio of 80:10:10 to prepare a composite particle mixture.

The composite particle mixture was poured into a rotor blade mill to obtain sphericalized core-shell composite particles by blade rotation force and frictional force.

The spheroidized core-shell composite particles were heat-treated at a temperature of 1,000 ° C under an argon atmosphere to prepare an anode active material.

Example  2

The toothed graphite having an average particle diameter (D50) of 1.7 mu m and the average particle size (D50) A negative electrode active material was prepared in the same manner as in Example 1, except that silicon of 30 nm was mixed at a weight ratio of 25:85.

Example  3

The toothed graphite having an average particle diameter (D50) of 1.7 mu m and the average particle size (D50) 34 parts by weight of gum arabic, 13 parts by weight of petroleum pitch (carbon yield: 76% by mass) and 1000 parts by weight of water were added to 100 parts by weight of a mixture of 30 nm and 30 nm of silicon at a weight ratio of 30:70, And spray-dried at a hot air temperature of 160 DEG C to obtain core particles.

A tetrahydrofuran solution in which 100 parts by weight of the core particles and 7 parts by weight of petroleum pitch (carbon yield: 27% by weight) were dissolved was mixed and stirred, followed by vacuum drying at 80 캜 to obtain composite particles.

The composite particles, the flaky graphite having a particle size of about 10 μm or less and the petroleum pitch (carbon yield: 54 mass%) were mixed at a weight ratio of 80:10:10 to prepare a composite particle mixture. To prepare an anode active material.

Example  4

The toothed graphite having an average particle diameter (D50) of 1.7 mu m and the average particle size (D50) 34 parts by weight of gum arabic, a petroleum pitch (carbon yield: 76% by mass) 13 (weight percentage of carbon) was added to 100 parts by weight of mixed particles obtained by ball milling 30 nm of silicon at a weight ratio of 30: And 1000 parts by weight of water were added and stirred to prepare a suspension, followed by spray drying at a hot air temperature of 160 캜 to obtain core particles.

A tetrahydrofuran solution in which 100 parts by weight of the core particles and 7 parts by weight of petroleum pitch (carbon yield: 27% by weight) were dissolved was mixed and stirred, followed by vacuum drying at 80 캜 to obtain composite particles.

The composite particles, the flaky graphite having a particle size of about 20 占 퐉 and the petroleum pitch (carbon yield: 54 mass%) were mixed at an 80:10:10 weight ratio to prepare a composite particle mixture. To prepare an anode active material.

Comparative Example  One

The toothed graphite having an average particle diameter (D50) of 1.7 mu m and the average particle size (D50) 34 parts by weight of gum arabic and 1000 parts by weight of water were added to 100 parts by weight of a mixture obtained by mixing 30 nm of silicon at a weight ratio of 30:70 and stirred to prepare a suspension and spray dried at 160 DEG C to obtain particles. The particles were heat-treated at a temperature of 1,000 DEG C under an argon atmosphere to prepare an anode active material.

Comparative Example  2

The toothed graphite having an average particle diameter (D50) of 1.7 mu m and the average particle size (D50) 34 parts by weight of gum arabic and 1000 parts by weight of water were added to 100 parts by weight of a mixture obtained by mixing 30 nm of silicon at a weight ratio of 30:70 and stirred to prepare a suspension and spray dried at 160 DEG C to obtain particles. 100 parts by weight of the particles thus prepared and a tetrahydrofuran solution in which 7 parts by weight of petroleum pitch (carbon yield: 27% by weight) were dissolved were mixed and stirred, followed by vacuum drying at 80 DEG C to obtain composite particles. The composite particles were heat-treated at a temperature of 1,000 ° C under an argon atmosphere to prepare an anode active material.

Comparative Example  3

A negative electrode active material was prepared in the same manner as in Example 1, except that scaly graphite having a mean particle size (D50) of 3.2 占 퐉 was used instead of earth graphite having an average particle size (D50) of 1.7 占 퐉 in Example 1.

Comparative Example  4

The toothed graphite having an average particle diameter (D50) of 1.7 mu m and the average particle size (D50) 34 parts by weight of gum arabic, 13 parts by weight of petroleum pitch (carbon yield: 76% by mass) and 1000 parts by weight of water were added to 100 parts by weight of a mixture of 30 nm and 30 nm of silicon at a weight ratio of 30:70, And spray-dried at a hot air temperature of 160 DEG C to obtain particles. The particles were heat-treated at a temperature of 1,000 DEG C under an argon atmosphere to prepare an anode active material.

Comparative Example  5

100 parts by weight of the particles prepared in Comparative Example 4 and a tetrahydrofuran solution containing 7 parts by weight of petroleum pitch (27% by mass of carbon) were mixed and stirred, followed by vacuum drying at 80 占 폚 to obtain composite particles. The composite particles were heat-treated at a temperature of 1,000 ° C under an argon atmosphere to prepare an anode active material.

Comparative Example  6

The toothed graphite having an average particle diameter (D50) of 1.7 mu m and the average particle size (D50) 34 parts by weight of gum arabic, a petroleum pitch (carbon yield: 76% by mass) 13 (weight percentage of carbon) was added to 100 parts by weight of mixed particles obtained by ball milling 30 nm of silicon at a weight ratio of 30: And 1000 parts by weight of water were added and stirred to prepare a suspension and spray dried at a hot air temperature of 160 캜 to obtain particles. The particles were heat-treated at a temperature of 1,000 DEG C under an argon atmosphere to prepare an anode active material.

Comparative Example  7

100 parts by weight of the particles prepared in Comparative Example 6 and a tetrahydrofuran solution containing 7 parts by weight of petroleum pitch (27% by mass of carbon) were mixed and stirred, followed by vacuum drying at 80 캜 to obtain composite particles. The composite particles were heat-treated at a temperature of 1,000 ° C under an argon atmosphere to prepare an anode active material.

Evaluation 1: Scanning electron microscope of negative electrode active material SEM ) analysis

2A is a scanning electron microscope (SEM) photograph of mixed particles of ground graphite and silicon used in Example 4, and FIG. 2B is a component analysis (EDX) photograph of mixed particles of ground graphite and silicon used in Example 4 .

Referring to FIGS. 2A and 2B, it can be seen that silicon is uniformly adhered to the surface of the graphite.

3A to 3K are scanning electron microscope (SEM) photographs of the negative electrode active material according to Examples 1 to 4 and Comparative Examples 1 to 7, respectively.

3A, 3B, 3C, 3D and 3G, amorphous carbon and flaky graphite were coated on the core particles in Examples 1 to 4 and Comparative Example 3, so that the anode active material particles had a spherical shape You can see that it has a smooth surface.

Referring to FIGS. 3E, 3H and 3J, it can be seen that only the core particles are present in Comparative Example 1, Comparative Example 4 and Comparative Example 6, so that the surface is uneven.

Referring to FIGS. 3F, 3I and 3K, since the core particles were coated with amorphous carbon in Comparative Example 2, Comparative Example 5, and Comparative Example 7, a smoother surface was confirmed than in FIGS. 3E, 3H and 3J .

Evaluation 2: Analysis of particle size distribution of anode active material

4A and 4B are graphs of particle size distribution analysis of the to-be-used graphite used in Example 1 and the negative active material prepared in Example 1, respectively.

The particle size distribution analysis was performed by particle size distribution laser diffraction scattering particle size distribution measurement method.

4A and 4B, it can be seen that the ground graphite has an average particle diameter (D50) of 1.7 mu m, and the negative electrode active material of Example 1 has an average particle diameter (D50) of 18.5 mu m.

Evaluation 3: X-ray of anode active material diffraction ( XRD ) Pattern analysis

5A is an X-ray diffraction (XRD) pattern of graphite, showing the crystallinity of graphite. 5B is an X-ray diffraction (XRD) pattern of the negative electrode active material prepared in Example 1. Fig.

Referring to FIG. 5B, it can be seen that the crystalline graphite and silicon of the ground graphite and the silicon particles of the prepared negative electrode active material are maintained and there is no additional new phase.

(Production of lithium secondary battery)

Each of the negative electrode active materials, carbon black, and polyacrylic acid (PAA) prepared in Examples 1 to 4 and Comparative Examples 1 to 7 was mixed in distilled water at a weight ratio of 85: 5: 10 to prepare an anode slurry. The negative electrode slurry was coated on a copper foil, followed by drying and rolling to prepare respective negative electrodes.

A separator made of a polypropylene film was inserted between the negative electrode and the positive electrode using the negative electrode and lithium metal as positive electrodes and a mixed solvent of DEC and EC (DEC: EC = 1: 1) dissolved in 1 M of LiPF ₆ was added to prepare a test cell.

Evaluation 4: Cycle life characteristics of lithium secondary battery

The life characteristics of the lithium secondary batteries fabricated in Examples 1 to 4 and Comparative Examples 1 to 7 were evaluated in the following manner.

Charging was performed in a CC / CV mode with a current density of 0.2 mA / cm ^2, the end voltage was maintained at 0.02 V, and charging was terminated when the current was 0.02 mA. The discharge was performed in CC mode with a current density of 0.2 mA / cm ² and the end voltage was maintained at 1.5V.

The discharge capacity at the initial cycle and the capacity retention at the 40th cycle were measured, and the results are shown in Table 1 below.

In the following Table 1, the capacity retention rate (%) is a percentage value of the discharge capacity at 40 cycles to the discharge capacity at the initial cycle.

Discharge capacity (mAh / g) Capacity retention rate (%) Example 1 739 90.1 Example 2 635 92.2 Example 3 742 93.4 Example 4 733 95.1 Comparative Example 1 765 52.8 Comparative Example 2 758 58.1 Comparative Example 3 765 78 Comparative Example 4 751 55.4 Comparative Example 5 747 59.3 Comparative Example 6 753 55.8 Comparative Example 7 746 59.9

It can be seen from Table 1 that the cycle life characteristics are superior to those of Examples 1 to 4 and Comparative Examples 1 to 7 using the negative electrode active material according to one embodiment. From this, it can be seen that excellent cycle life characteristics can be obtained in the case of an anode active material having a spherical core-shell structure according to an embodiment.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

10: anode active material
11: active particles
12: Ground graphite
13: First amorphous carbon
14: Pore
15: Scaly graphite
16: Second amorphous carbon

Claims (31)

Porous core particles comprising an active particle, a ground graphite having an average particle diameter (D50) of 0.1 to 3 占 퐉, a first amorphous carbon and a void; And
A shell layer coated on the surface of the core particle and comprising scaly graphite and a second amorphous carbon,
Wherein the active particles comprise metal particles, metal-containing compound particles, or combinations thereof,
The first amorphous carbon and the second amorphous carbon may be the same or different from each other and include soft carbon, hard carbon or a combination thereof
Negative electrode active material for lithium secondary battery.
The method according to claim 1,
Wherein the metal particles include Si, Sn, Sb, Al, Ge, Zn, Pb or combinations thereof.
The method according to claim 1,
Wherein the metal-containing compound particle comprises an oxide of a metal including Si, Sn, Sb, Al, Ge, Zn, Pb or a combination thereof, a complex of the metal and carbon, or a combination thereof.
The method of claim 3,
The oxide of the metal includes a compound represented by the following formula (1), a compound represented by the following formula (2), or a combination thereof.
[Chemical Formula 1]
SiO _x
(In the formula 1, 0 < x < 1.5.)
(2)
Si _{1 - x} M _x O _y
(M is at least one element selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Hf, Re, Os, Mg, Ca, B, P, Al, Ge, Sn, Sb, Bi, Li or combinations thereof; 0 <x <1 and 0.1? Y?
The method according to claim 1,
Wherein the average particle size (D50) of the active particles is 1 nm to 5 占 퐉.
The method according to claim 1,
Wherein the active particles are contained in an amount of 3 to 70% by weight based on the total amount of the core particles.
The method according to claim 1,
Wherein the active particles are physically or chemically bonded to the surface of the ground graphite and are attached to the negative active material for a lithium secondary battery.
delete The method according to claim 1,
Wherein the ground graphite is contained in an amount of 5 to 90% by weight based on the total amount of the core particles.
The method according to claim 1,
Wherein the first amorphous carbon is contained in an amount of 5 to 80% by weight based on the total amount of the core particles.
The method according to claim 1,
Wherein the voids are contained in an amount of 2 to 60% by volume based on the total volume of the core particles.
The method according to claim 1,
Wherein the average particle diameter (D50) of the core particles is 2 to 30 占 퐉.
The method according to claim 1,
And the thickness of the graphite graphite is 0.01 to 5 탆.
The method according to claim 1,
The average particle size (D50) of the graphite graphite is 1 to 50 占 퐉.
The method according to claim 1,
And the second amorphous carbon is contained in an amount of 10 to 90% by weight based on the total amount of the shell layer.
The method according to claim 1,
And the thickness of the shell layer is 0.1 to 10 [micro] m.
The method according to claim 1,
A third amorphous carbon impregnated on the surface or inside of the void,
And the third amorphous carbon includes soft carbon, hard carbon, or a combination thereof.
The method according to claim 1,
A carbon layer coated on the surface of the core particle between the core particle and the shell layer and containing a third amorphous carbon
And a negative electrode active material for a lithium secondary battery.
Obtaining a core particle mixture by mixing the active particles, the ground graphite having an average particle diameter (D50) of 0.1 to 3 占 퐉, the first amorphous carbon precursor and a solvent;
Spray drying the core particle mixture to obtain granulated porous core particles;
Mixing the core particles, scaly graphite and a second amorphous carbon precursor to obtain composite particles having a shell layer comprising the scaly graphite and the second amorphous carbon formed on a surface of the core particle; And
And heat treating the composite particles,
Wherein the active particles comprise metal particles, metal-containing compound particles, or combinations thereof,
Wherein the first amorphous carbon precursor and the second amorphous carbon precursor are the same or different and comprise a soft carbon raw material, a hard carbon raw material, or a combination thereof.
20. The method of claim 19,
Wherein the active particles and the earth graphite are mixed in a form in which the active particles are adhered to the surface of the earth graphite.
20. The method of claim 19,
Before the step of obtaining the composite particles after the step of obtaining the core particles,
Mixing and drying the solution in which the core particles and the third amorphous carbon precursor are dissolved
Further comprising:
Wherein the third amorphous carbon precursor comprises a soft carbon source, a hard carbon source, or a combination thereof.
The method according to claim 19 or 21,
Wherein the soft carbon material comprises a coal pitch, a petroleum pitch, a mesophase pitch, tar, a low molecular weight heavy oil, glucose, gelatin, a saccharide or a combination thereof,
The hard carbon material may be selected from the group consisting of phenol resin, naphthalene resin, furfuryl alcohol resin, polyamide resin, furan resin, polyimide resin, epoxy resin, vinyl chloride resin, gum arabic, citric acid, Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, polyvinylpyrrolidone, polyethylene, polypropylene, polyvinylidene fluoride, vinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose , Polyacrylic acid, polyacrylic sodium, polyacrylonitrile, cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, or a combination thereof.
20. The method of claim 19,
Wherein the first amorphous carbon precursor is mixed in an amount of 1 to 100 parts by weight based on 100 parts by weight of the total amount of the active particles and the ground graphite.
20. The method of claim 19,
The solvent may be selected from the group consisting of N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, water, And a negative electrode active material for lithium secondary batteries.
20. The method of claim 19,
Wherein the spray drying is performed at a temperature of 50 to 300 캜.
20. The method of claim 19,
Wherein the spray drying is performed by a drying method including rotary spraying, nozzle spraying, ultrasonic spraying, or a combination thereof.
20. The method of claim 19,
Wherein the metal particles include Si, Sn, Sb, Al, Ge, Zn, Pb, or combinations thereof.
20. The method of claim 19,
The metal-containing compound particle may be an oxide of a metal containing Si, Sn, Sb, Al, Ge, Zn, Pb or a combination thereof, a composite of the metal and carbon, Gt;
20. The method of claim 19,
Wherein the heat treatment is performed at a temperature of 600 to 2000 占 폚.
The negative electrode active material according to any one of claims 1 to 7 and 9 to 18
And a negative electrode for a lithium secondary battery.
A negative electrode of claim 30;
anode; And
Electrolyte
&Lt; / RTI &gt;

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