KR101919470B1 - Negative active material for lithium secondary battery, method for preparing the same and lithium secondary battery comprising thereof - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the negative active material for the lithium secondary battery. More particularly, the present invention relates to a lithium secondary battery, Natural graphite particles having a structure having a gap formed between the surface and the inside of the scaly graphite particles; And a coating layer formed on the surface of the natural graphite particle to produce the gap and the coating layer comprising (i) a silicon or silicon compound particle and (ii) an amorphous or semi-crystalline carbon, Or amorphous or semi-crystalline carbon is distributed between the graphite particles of the graphite particles on the surface of the particles for the negative electrode active material, and the graphite particles of the graphite particles are laminated in a concentric direction And a shell layer, and a lithium secondary battery including the negative active material. The present invention also relates to a lithium secondary battery including the negative active material.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a negative electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including a negative electrode active material for a lithium secondary battery. BACKGROUND OF THE INVENTION [0002]

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

A lithium secondary battery refers to a secondary battery having lithium ion (Li ⁺ ) as a medium of charge transfer. It is manufactured in various forms according to the types of a cathode, a cathode and an electrolyte, and is used as a portable device, an electric bicycle, And is powered by a power source for supplying power to tools and the like.

2. Description of the Related Art In recent years, as lithium secondary battery applications have become diverse, batteries having a high energy density have been required. Accordingly, research and development for increasing the capacity of the positive electrode active material and the negative electrode active material have been carried out in parallel.

At present, a crystalline graphite material is used as an anode active material of a lithium secondary battery. However, the graphite as the anode active material which is currently commercialized is limited to a theoretical capacity of 372 mAh / g, and thus a new high capacity anode active material is required to be developed.

As a new material that can replace graphite, silicon (Si) absorbs lithium reversibly through a compound formation reaction with lithium. And the theoretical maximum capacity is 4020 mAh / g (9800 mAh / g, specific gravity: 2.23), which is very large compared to graphite and is therefore promising as a high capacity cathode material. However, charging. A large volume change of about 300% occurs due to the reaction with lithium at the time of discharging, resulting in mechanical breakdown of the silicon active material particles and electrical contact failure between the silicon active material and the current collector. This causes the battery to charge. As the discharge cycle progresses, there arises a problem that the battery capacity sharply decreases and the cycle life is shortened.

Therefore, most conventional research and development has been focused on improving the charge-discharge cycle characteristics. To overcome such problems, many methods such as forming silicon (Si) or compound particles thereof, or using composite active materials of these compound particles and carbon Have been reviewed. As a result, improved cycle characteristics are being reported.

However, the above-mentioned conventional methods fail to provide sufficient and excellent cycle life characteristics, and they are difficult to be used as a practical anode active material for a lithium secondary battery due to a high manufacturing process and cost. To solve these problems, It is still necessary to develop a low-cost high-capacity anode active material exhibiting characteristics.

Korean Patent No. 10-1126937 (Published on May 19, 2011) Korean Patent Publication No. 10-2013-0071070 (Publication date: 2013.06.28) Korean Patent No. 10-1002539 (published on November 3, 2009) Korean Patent No. 10-0570617 (Publication Date: Aug. 31, 2005)

Disclosure of Invention Technical Problem [8] The present invention provides a negative active material for a lithium secondary battery having excellent high rate charge / discharge characteristics and cycle life characteristics, a method for producing the negative active material, and a lithium secondary battery comprising the negative active material.

In order to accomplish the above object, the present invention provides a method for producing graphite particles, comprising the steps of: forming natural graphite flake particles into a cabbage or random phase, Natural graphite particles; And a coating layer formed on the surface of the natural graphite particle to produce the gap and the coating layer comprising (i) a silicon or silicon compound particle and (ii) an amorphous or semi-crystalline carbon, A negative electrode active material for a lithium secondary battery.

Also, the amorphous or semi-crystalline carbon includes 1 to 40 parts by weight based on 100 parts by weight of the natural graphite particles.

The present invention also provides a negative electrode active material for a lithium secondary battery, wherein the silicon or silicon compound particle is contained in an amount of 1 to 50 parts by weight based on 100 parts by weight of the negative active material.

Also, the average particle diameter (D50) of the silicon or silicon compound particles is 5 nm to 3 탆, and the negative active material for a lithium secondary battery is proposed.

Also, the above-mentioned natural graphite particles have an average particle diameter (D50) of 5 to 40 탆, which suggests an anode active material for a lithium secondary battery.

In another aspect of the present invention, the present invention provides a method for producing a graphite particle, comprising the steps of: Silicon or silicon compound particles; Amorphous or quasi-crystalline carbon precursors; And a solvent; The solution is subjected to ultrasonic treatment to enlarge the gap between the flaky natural graphite flakes particles existing on the surface and inside of the spherical natural graphite particles and to form the flakes on the surface of the flake natural graphite flakes particles And impregnating and coating an amorphous or semi-crystalline carbon precursor with the silicon or silicon compound particles on the surface of the spheroidized natural graphite particle; Drying the ultrasonic treated solution to prepare spherical natural graphite modified particles; And heat-treating the spheroidized natural graphite-modified particles. The present invention also provides a method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1.

According to another aspect of the present invention, there is provided a method for producing graphite particles, comprising the steps of: (1) forming natural graphite slice particles into a cabbage or a random phase and assembling the natural graphite slice particles, Natural graphite particles included on the surface and inside; And a coating layer formed on the surface of the natural graphite particle to produce the gap and the coating layer comprising (i) a silicon or silicon compound particle and (ii) an amorphous or semi-crystalline carbon, Core particles; And (2) a shell layer having a structure in which amorphous or quasi-crystalline carbon is distributed between the flaky graphite flake particles and flake graphite flake particles are stacked in a concentric direction and the flake is formed, and a shell layer formed on the surface of the core particles A negative electrode active material for a secondary battery is proposed.

In addition, the amorphous or semi-crystalline carbon in the core particles includes 1 to 40 parts by weight of the negative electrode active material for a lithium secondary battery.

In addition, the silicon or silicon compound particles in the core particles include 1 to 50 parts by weight based on 100 parts by weight of the core particles.

Also, the average particle size (D50) of the silicon or silicon compound particles in the core particles is 5 nm to 3 탆, and the negative active material for a lithium secondary battery is proposed.

Also, the natural graphite particles have an average particle diameter (D50) of 5 to 40 占 퐉. The negative active material for a lithium secondary battery is proposed.

Also, the thickness of the shell layer is 0.02 to 5 탆, and the negative electrode active material for a lithium secondary battery is proposed.

Also, the average thickness of the flaky graphite flakes particles contained in the shell layer is 0.005 to 1 占 퐉, and proposes a negative active material for a lithium secondary battery.

Also, the scaly graphite contained in the shell layer and the amorphous or semicrystalline carbon are in a weight ratio of 1: 99: 99 to 1. The present invention further provides a negative electrode active material for a lithium secondary battery.

Further, in another aspect of the present invention, the present invention relates to spheroidized natural graphite particles in which scaly natural graphite particle grains are aggregated and assembled; Silicon or silicon compound particles; Amorphous or quasi-crystalline carbon precursors; And a solvent; The solution is subjected to ultrasonic treatment to enlarge the gap between the flaky natural graphite flakes particles existing on the surface and inside of the spherical natural graphite particles and to form the flakes on the surface of the flake natural graphite flakes particles And impregnating and coating an amorphous or semi-crystalline carbon precursor with the silicon or silicon compound particles on the surface of the spheroidized natural graphite particle; Drying the ultrasonic treated solution to prepare spherical natural graphite modified particles; Forming a shell layer having a structure in which amorphous or quasi-crystalline carbon is distributed between the flaky graphite flake particles and flake graphite flake particles are laminated in a concentric direction to form a shell layer on the surface of the first particles, ; And heat-treating the second particles. The method of manufacturing a negative active material for a lithium secondary battery according to claim 7,

The carbon precursor may be selected from the group consisting of citric acid, stearic acid, sucrose, polyvinylidene fluoride, Pluronic F127, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, furfuryl alcohol, polyacrylic acid, polyacrylic sodium, polyacrylonitrile, polyacrylonitrile, Wherein the adhesive layer is made of polyimide, epoxy resin, cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, polyvinyl bellolidone, glycerol, polyol, coal pitch, petroleum pitch, mesophase pitch, low molecular weight heavy oil, glucose, And a negative electrode active material for a lithium secondary battery, Propose ways.

The solvent may be selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, Wherein the negative active material is at least one selected from the group consisting of lithium and lithium.

Also, the ultrasonic treatment is performed for 1 minute to 24 hours under the condition of an oscillation frequency of 10 to 35 kHz and an ultrasonic amplitude of 10 to 150 탆, and proposes a method of manufacturing the anode active material for a lithium secondary battery.

Also, the drying may be carried out by at least one spray drying method selected from rotary spraying, nozzle spraying and ultrasonic spraying; A drying method using a rotary evaporator; Vacuum drying method; Or a natural drying method. The present invention also provides a method for preparing a negative electrode active material for a lithium secondary battery.

Also, the heat treatment is performed at a temperature of 500 to 1500 캜. The present invention also provides a method for preparing a negative active material for a lithium secondary battery.

Also, the heat treatment is performed in an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under a vacuum, and a method for producing the negative electrode active material for a lithium secondary battery.

Also, the carbon precursor is included in an amount of 2 to 80 parts by weight based on 100 parts by weight of the spherical natural graphite particles. The present invention also provides a method for preparing the anode active material for a lithium secondary battery.

According to another aspect of the present invention, there is provided a lithium secondary battery including the negative electrode active material.

The negative electrode active material for a lithium secondary battery according to the present invention can be effectively used for realizing a lithium secondary battery having excellent capacity, high rate charge / discharge characteristics and cycle life characteristics.

1 is a schematic cross-sectional view of a negative active material according to a first embodiment.
2 is a schematic cross-sectional view of a negative electrode active material according to a second embodiment.
3 to 5 are scanning electron microscope (SEM) photographs of the negative electrode active materials according to Examples 1 to 3, respectively.
6 is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Comparative Example 1, respectively.
7 is a scanning electron microscope (SEM) photograph of a cross section of a negative electrode active material according to Example 1. Fig.
8 and 9 are energy dispersive X-ray spectroscopy (EDS) mapping images of a cross section of a negative electrode active material according to Example 1
10 to 12 show X-ray diffraction patterns (XRD) of the negative electrode active material according to Examples 1 to 3, respectively.
13 shows an X-ray diffraction pattern (XRD) of the negative electrode active material according to Comparative Example 1. Fig.
Fig. 14 shows results of evaluating the life characteristics of the negative electrode active material according to Examples 1 to 3 and Comparative Example 1. Fig.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments in accordance with the concepts of the present invention can make various changes and have various forms, so that specific embodiments are illustrated in the drawings and described in detail in this specification or application. It should be understood, however, that the embodiments according to the concepts of the present invention are not intended to be limited to any particular mode of disclosure, but rather all variations, equivalents, and alternatives falling within the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises ", or" having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Hereinafter, the present invention will be described in detail.

1 is a schematic cross-sectional view of a first embodiment of a negative electrode active material for a lithium secondary battery according to the present invention.

Referring to FIG. 1, the negative electrode active material 1 according to the first embodiment has a structure in which scaly graphite particles 10 are assembled and assembled into a cabbage or a random phase, and the scintillation- A natural graphite particle containing a gap (20) formed between the surface and inside thereof; (I) a silicon or silicon compound particle (40) and (ii) an amorphous or semicrystalline carbon (30), and a coating layer formed on the surface of the natural graphite particle, And a coating layer formed on the substrate.

The anode active material according to the first embodiment of the present invention may be prepared as follows.

That is, spherical natural graphite particles assembled by assembly of scaly natural graphite flakes particles; Silicon or silicon compound particles; Amorphous or quasi-crystalline carbon precursors; And a solvent; The solution is subjected to ultrasonic treatment to enlarge the gap between the flaky natural graphite flakes particles existing on the surface and inside of the spherical natural graphite particles and to form the flakes on the surface of the flake natural graphite flakes particles And impregnating and coating an amorphous or semi-crystalline carbon precursor with the silicon or silicon compound particles on the surface of the spheroidized natural graphite particle; Drying the ultrasonic treated solution to prepare spherical natural graphite modified particles; And heat treating the spheroidized natural graphite modified particles.

When the solution containing the spherical natural graphite particles, the silicon and the silicon compound particles and the amorphous or quasi-crystalline carbon precursor is subjected to ultrasonic treatment, the spherical natural graphite surface and the graphite particles existing on the inside of the graphite particles And the amorphous or quasi-crystalline carbon precursor is impregnated with the silicon and silicon compound particles as a gap between the scaly natural graphite particles, and the silicon and silicon compound particles and the silicon compound particles are impregnated on the surface of the spherical natural graphite particles. Together with an amorphous or quasi-crystalline carbon precursor. The ultrasonic treated solution is dried to prepare spherical natural graphite modified particles and then heat treated to form gaps between the scintillated natural graphite particles and the amorphous or quasi-crystalline carbon precursor existing on the spherical natural graphite surface The negative electrode active material for a lithium secondary battery according to the first embodiment is obtained.

Accordingly, the negative active material is present in the gaps between the graphite slices on the surface and the surface of the negative electrode active material particles, so that the lithium and the silicon compounds during the charging and discharging during charging and discharging, The buffering effect on the volume expansion of the particles and the reactivity with the electrolyte are improved, thereby realizing a lithium secondary battery having a high capacity and excellent charge / discharge characteristics and cycle life characteristics.

The spherical natural graphite particles can be formed by the methods disclosed in Korean Patent Publication Nos. 2003-0087986 and 2005-0009245, but are not limited thereto. For example, a step of repeatedly processing the scaly natural graphite having an average particle diameter of 30 탆 or more by using a rotary machine is performed, whereby the friction between the powder and the crushing due to the collision between the inner side of the rotary machine and the scaly natural graphite powder Processing and shearing of the powder by shearing stress, and the like, the scratched natural graphite is assembled and finally spherical natural graphite particles can be manufactured.

The spherical natural graphite particles may be formed into a cabbage or a random phase. In addition, the spheroidized natural graphite particles may be spherical as well as circular, or may be spherical having an index of about 0.8 or more, which is calculated by projecting three-dimensional natural graphite particles on a two-dimensional plane.

The spherical natural graphite particles may have an average particle diameter (D50) of 5 to 40 mu m, more preferably 5 to 30 mu m.

The spheroidized natural graphite particles may be formed by forming truncated natural graphite particles into a cabbage or a random phase. In addition, the spheroidized natural graphite particles may be spherical as well as circular, or may be spherical having an index of about 0.8 or more, which is calculated by projecting three-dimensional natural graphite particles on a two-dimensional plane. The spherical natural graphite particles may have an average particle diameter (D50) of 5 to 40 mu m.

The sizes of the silicon and silicon compound particles preferably have an average particle size of 5 nm to 3 탆, and more preferably 10 nm to 1 탆.

The silicon and silicon compound particles may be included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material particles according to the first embodiment.

On the other hand, the silicon compound may be at least one selected from the group consisting of SiO _x (0 <x <2), Si-C composite, Si-M alloy (M is an alkali metal, an alkaline earth metal, a Group 13 to Group 16 element, And at least one of them may be mixed with SiO ₂ . As the specific element contained in M, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Sb, Bi, S, Se, Te, Po, or a combination thereof.

The solvent is at least one selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, One can be included.

The carbon precursor may be selected from the group consisting of citric acid, stearic acid, sucrose, polyvinylidene fluoride, Pluronic F127, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, per furyl alcohol, polyacrylic acid, polyacrylic sodium, polyacrylonitrile, polyimide At least one member selected from the group consisting of epoxy resin, cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, polyvinyl bellolidone, glycerol, polyol, coal pitch, petroleum pitch, mesophase pitch, low molecular weight heavy oil, glucose, One can be included.

The ultrasonic waves can be irradiated for 1 minute to 24 hours under an operating condition of ultrasonic amplitude of 10 mu m to 150 mu m and can have an oscillation frequency of 10 to 35 kHz.

The drying may be carried out by at least one spray drying method selected from rotary spraying, nozzle spraying and ultrasonic spraying; A drying method using a rotary evaporator; Vacuum drying method; Or by natural drying methods.

The heat treatment may be performed at a temperature of 500 to 1500 DEG C and may be performed in an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under a vacuum.

The carbon precursor may be included in an amount of 2 to 80 parts by weight based on 100 parts by weight of the spherical natural graphite particles. The negative electrode active material according to the first embodiment may include 1 to 40 parts by weight of the amorphous or semi-crystalline carbon based on 100 parts by weight of the negative electrode active material particles.

2 is a schematic cross-sectional view of a second embodiment of a negative electrode active material for a lithium secondary battery according to the present invention.

2, the anode active material 2 according to the second embodiment has (1) a structure in which scaly natural graphite particles 10 are assembled and assembled into a cabbage or a random phase, Natural graphite particles containing on the surface and inside a gap (20) formed between the graphite piece particles; (I) a silicon or silicon compound particle (40) and (ii) an amorphous or semicrystalline carbon (30), and a coating layer formed on the surface of the natural graphite particle, A core particle comprising a coating layer comprising: And (2) amorphous or semicrystalline carbon is distributed between the flaky graphite flake particles, and flake graphite flake particles 50 are stacked in a concentric direction to form a shell layer 60 ). &Lt; / RTI &gt;

The anode active material according to the second embodiment of the present invention can be manufactured as follows.

That is, spherical natural graphite particles assembled by assembly of scaly natural graphite flakes particles; Silicon or silicon compound particles; Amorphous or quasi-crystalline carbon precursors; And a solvent; The solution is subjected to ultrasonic treatment to enlarge the gap between the flaky natural graphite flakes particles existing on the surface and inside of the spherical natural graphite particles and to form the flakes on the surface of the flake natural graphite flakes particles And impregnating and coating an amorphous or semi-crystalline carbon precursor with the silicon or silicon compound particles on the surface of the spheroidized natural graphite particle; Drying the ultrasonic treated solution to prepare spherical natural graphite modified particles; Forming a shell layer having a structure in which amorphous or quasi-crystalline carbon is distributed between the flaky graphite flake particles and flake graphite flake particles are laminated in a concentric direction to form a shell layer on the surface of the first particles, ; And heat-treating the second particles.

When the solution containing spherical natural graphite particles, silicon and silicon compound particles and the amorphous or quasi-crystalline carbon precursor is subjected to ultrasonic treatment, the spherical natural graphite surface and the graphite particles existing inside the graphite particles And at the same time an amorphous or quasi-crystalline carbon precursor is impregnated with the silicon and silicon compound particles as a gap between the scaly natural graphite particles, and the spherical natural graphite surface is impregnated with silicon and silicon compound particles An amorphous or quasi-crystalline carbon precursor is coated. Drying the ultrasonic treated solution to prepare a first particle which is a spherical natural graphite modified particle and forming a shell layer composed of the peeled scaly graphite piece and an amorphous or quasi-crystalline carbon precursor located on the surface of the first particle, And a heat treatment is performed to form a gap between the scaly natural graphite particle particles of the first particle and an amorphous or quasi-crystalline carbon precursor existing in the shell layer of the spherical natural graphite surface and the second particle, A gap opened between the scratched graphite slices existing on the surface and inside of the spheroidized natural graphite particle and a surface of the spheroidized natural graphite particle together with the silicon and silicon compound particles are carbonized to form the amorphous or quasicrystalline carbon Core particle which is a spherical natural graphite-modified composite particle coated on the surface of the core particle PL is provides a process for the preparation of exfoliated flake-like graphite and an amorphous or semi-intercept negative active material of the active material comprising the shell layer to the crystalline carbon composite layer. The shell layer positioned on the surface of the core particles further improves the buffering effect on the volume expansion of the core particles during lithium insertion and desorption during charging and discharging and further enhances the effect of buffering action of the silicon and silicon compound particles and electrolyte And the cycle stability is improved.

 When the negative electrode active material of the spherical natural graphite particles is used to produce electrodes, compression of the spherical natural graphite particles may occur due to the pressing process. In particular, when the gap between the scaly natural graphite slices of the spheroidized graphite is formed by the ultrasonic treatment, the pressing phenomenon due to the pressing process during the production of the electrode may occur more seriously. However, during the ultrasonic treatment, An amorphous or quasi-crystalline carbon precursor is impregnated with silicon and silicon compound particles as a gap between the particles, and an amorphous or a quasi-crystalline carbon precursor is coated on the surface of the spheroidized natural graphite to form the first particles, 1 particles on the surface of the particles and a shell layer composed of a flaky graphite flake and an amorphous or quasi-crystalline carbon precursor, and then, through the heat treatment step, the amorphous or quasi-crystalline carbon Of said spherical natural graphite particles and said spheroidized natural graphite particles The core particles present in the gap between the natural graphite flakes in the graphite particles and the shell layer being the amorphous or semicrystalline carbon composite layer separated from the flake graphite flakes located on the surface of the core particles, The squeezing phenomenon of the spherical natural graphite particles constituting the particles is suppressed and the electrode prepared using the negative electrode active material according to the above embodiment is excellent in reactivity with the electrolytic solution. Accordingly, the cycle stability and the high rate charge / discharge characteristics of the lithium secondary battery can be improved.

The spherical natural graphite particles can be formed by the methods disclosed in Korean Patent Publication Nos. 2003-0087986 and 2005-0009245, but are not limited thereto. For example, a step of repeatedly processing the scaly natural graphite having an average particle diameter of 30 탆 or more by using a rotary machine is performed, whereby the friction between the powder and the crushing due to the collision between the inner side of the rotary machine and the scaly natural graphite powder Processing and shearing of the powder by shearing stress, and the like, the scratched natural graphite is assembled and finally spherical natural graphite particles can be manufactured.

The spherical natural graphite particles may be formed into a cabbage or a random phase. In addition, the spheroidized natural graphite particles may be spherical as well as circular, or may be spherical having an index of about 0.8 or more, which is calculated by projecting three-dimensional natural graphite particles on a two-dimensional plane.

The spherical natural graphite particles may have an average particle diameter (D50) of 5 to 40 mu m, more preferably 5 to 30 mu m.

The solvent is at least one selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, One can be included.

The carbon precursor may be selected from the group consisting of citric acid, stearic acid, sucrose, polyvinylidene fluoride, Pluronic F127, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, per furyl alcohol, polyacrylic acid, polyacrylic sodium, polyacrylonitrile, polyimide At least one member selected from the group consisting of epoxy resin, cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, polyvinyl bellolidone, glycerol, polyol, coal pitch, petroleum pitch, mesophase pitch, low molecular weight heavy oil, glucose, One can be included.

The ultrasonic waves can be irradiated for 1 minute to 24 hours under an operating condition of ultrasonic amplitude of 10 mu m to 150 mu m and can have an oscillation frequency of 10 to 35 kHz.

The drying may be carried out by at least one spray drying method selected from rotary spraying, nozzle spraying and ultrasonic spraying; A drying method using a rotary evaporator; Vacuum drying method; Or by natural drying methods.

The heat treatment may be performed at a temperature of 500 to 1500 ° C, specifically, at a temperature of 500 to 1300 ° C, more specifically, at a temperature of 900 to 1100 ° C. When the heat treatment is performed within the temperature range, it is possible to sufficiently remove the heteroelement corresponding to the impurity in the carbonization process of the carbon precursor, and to suppress the formation of silicon carbide due to the reaction between the silicon and the silicon compound particles and the carbon precursor do. Accordingly, the irreversible capacity can be reduced and the charge / discharge 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.

The carbon precursor of the first primary particles may be included in an amount of 2 to 80 parts by weight, and more preferably 5 to 50 parts by weight based on 100 parts by weight of the spherical natural graphite particles. When the carbon precursor is contained within the above range, the gap between the natural graphite slices formed on the surface and inside of the spherical natural graphite particles can be suitably maintained.

In the negative electrode active material according to the second embodiment, the amorphous or semi-crystalline carbon may be included in the core particles formed from the primary particles in an amount of 1 to 40 parts by weight based on 100 parts by weight of the core particles.

In the core particles formed from the primary particles with respect to the negative electrode active material according to the second embodiment, the silicon and silicon compound particles are preferably contained in an amount of 1 to 50 parts by weight, more preferably 5 to 40 parts by weight, By weight. If the silicon and silicon compound particles are less than 1% by weight, the effect of increasing the capacity is insignificant. If the amount is more than 50% by weight, it is difficult to expect a buffering effect due to excessive volume expansion during lithium occlusion.

The sizes of the silicon and silicon compound particles preferably have an average particle size of 5 nm to 3 탆, and more preferably 10 nm to 1 탆. When the average particle diameter of the silicon and silicon compound particles exceeds 3 mu m, the silicon and the silicon compound particles are hardly impregnated with the silicon and the silicon compound particles into the gaps between the scintillator-like natural graphite particle particles during the ultrasonic treatment. When the sizes of the silicon and silicon compound particles are less than 5 nm, it is difficult to uniformly disperse the silicon and silicon compound particles in the production of the silicon and silicon compound particles and in the production of the core particles.

On the other hand, the silicon compound may be at least one selected from the group consisting of SiO _x (0 <x <2), Si-C composite, Si-M alloy (M is an alkali metal, an alkaline earth metal, a Group 13 to Group 16 element, And at least one of them may be mixed with SiO ₂ . As the specific element contained in M, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Sb, Bi, S, Se, Te, Po, or a combination thereof.

The thickness of the shell layer with respect to the negative electrode active material according to the second embodiment is preferably 0.02 to 5 mu m, more preferably 0.1 to 3 mu m. When the thickness of the shell layer is 0.02 탆 or less, the buffering effect against the volume expansion of the core particles is insufficient and the lifetime characteristics of the battery are degraded. When the thickness of the shell layer is 5 탆 or more, The reaction between lithium and the core particles can not be sufficiently performed, resulting in a decrease in the high rate charge / discharge characteristics.

The average thickness of the peeled scaly graphite constituting the shell layer is preferably 0.005 to 1 mu m, more preferably 0.01 to 0.1 mu m. When the thickness of the flake graphite exceeds 1 탆, it is difficult to laminate the core layer on the surface of the core in the concentric direction of the shell layer. On the other hand, when the average thickness is 0.005 탆 or less, It is not uniformly dispersed when the shell layer is formed due to the agglomeration phenomenon. As a result, the buffering effect of the volume expansion can not be sufficiently performed and the lifetime characteristics may be deteriorated.

The peeled flaky graphite constituting the shell layer and the amorphous or semicrystalline carbon may be contained in a weight ratio of 1 to 99: 99-1. If the content of flaky graphite constituting the shell layer is 1 wt% or less, the effect of the shell layer capable of suppressing the volume expansion of the core particles is deteriorated. If the content is more than 99 wt%, the amorphous and semi- Since the content of crystalline carbon is relatively insufficient, binding between scaly graphite particles is insufficient, so that it is insufficient to suppress the volume expansion of the core particles during charging and discharging, and electrical conductivity in the shell layer is lowered.

According to another embodiment of the present invention, there is provided a lithium secondary battery including the negative electrode, the positive electrode and the electrolyte solution including the negative electrode active material.

The lithium secondary battery can 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 can 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.

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 a negative electrode active material layer, and then applying the negative electrode active material composition to a negative electrode collector. These negative electrode compositions are well known in the art A detailed description thereof will be omitted.

Hereinafter, the present invention will be described in detail by way of examples with reference to the drawings. However, the embodiments according to the present disclosure can be modified in various other forms, and the scope of the present specification is not construed as being limited to the embodiments described below. Embodiments of the present disclosure are provided to more fully describe the present disclosure to those of ordinary skill in the art.

Example 1

5 parts by weight of polyvinyl chloride (PVC), 1 part by weight of F127 (F127, Sigma Aldrich) and 0.4 part by weight of silicon fine particles were put into 200 parts by weight of tetrahydrofuran, mixed using a magnetic stirrer, Ultrasonic waves were irradiated for 30 minutes under an output of 50 W to obtain a solution containing silicon microparticles and polyvinylchloride in which F127 was dispersed.

10 parts by weight of spherical natural graphite particles (POSCO Chemtech, SNG16) having an average particle diameter (D50) of 16 占 퐉 was added to the obtained solution and stirred for 60 minutes using a magnetic stirrer, followed by stirring at a frequency of 20 kHz and a frequency of 55 W And ultrasonic waves were irradiated for 60 minutes under the output to obtain a solution containing silicon fine particles and ultrasonic treated spherical natural graphite modified particles containing F127 and polyvinylchloride. Tetrahydrofuran was evaporated using a rotary evaporator to obtain spherical natural graphite modified particles ultrasonically treated with nanosilicon particles, F127 and polyvinylchloride. The graphite-modified particles were heat-treated at 1,000 ° C for 1 hour in an argon atmosphere, and then subjected to furnace cooling to prepare an anode active material having an average particle size (D50) of 19.5 μm.

Example 2

5 parts by weight of petroleum pitch and 0.4 part by weight of silicon fine particles were put into 200 parts by weight of tetrahydrofuran and then mixed using a magnetic stirrer and ultrasonic waves were irradiated for 30 minutes at a frequency of 20 kHz and an output of 50 W to disperse the silicon fine particles A solution containing the petroleum pitch was obtained.

10 parts by weight of spherical natural graphite particles (POSCO Chemtech, SNG16) having an average particle diameter (D50) of 16 占 퐉 was added to the obtained solution and stirred for 60 minutes using a magnetic stirrer, followed by stirring at a frequency of 20 kHz and a frequency of 55 W Ultrasonic wave was irradiated for 60 minutes under the output to obtain a solution containing ultrasonic treated spherical natural graphite modified particles including silicon fine particles and petroleum pitch. Tetrahydrofuran was evaporated using a rotary evaporator to obtain spherical natural graphite modified particles ultrasonically treated with nanosilicon particles and petroleum pitch. The graphite-modified particles were heat-treated at 1,000 ° C for 1 hour in an argon atmosphere, and then subjected to furnace cooling to prepare an anode active material having an average particle size (D50) of 19.5 μm.

Example 3

(Shell layer component: scaly graphite slab)

The graphite slices having an average particle diameter (D50) of 200 탆 were added to an ethyl alcohol solution and mixed using a magnetic stirrer. The mixture was then mixed with a high shear mixer and ultrasonic waves for 40 minutes at a frequency of 20 KHz and 55 W output To prepare a flaky graphite flake particle having an average thickness of 30 nm.

(Preparation of negative electrode active material having core-shell structure)

3 parts by weight of the negative electrode active material prepared in Example 2, 0.7 parts by weight of petroleum pitch (0.42 part by weight after carbonization) and 0.2 part by weight of flaky graphite flakes were put into 100 parts by weight of tetrahydrofuran, The mixture was stirred for 30 minutes and then tetrahydrofuran was evaporated using a rotary evaporator. The mixture was heat-treated at 1,000 ° C for 1 hour in an argon atmosphere and then cooled to produce an anode active material having an average particle diameter (D50) of 21 μm.

Comparative Example 1

An anode active material having an average particle diameter (D50) of 17.2 占 퐉 was prepared in the same manner as in Example 2 except that spherical natural graphite was added and then ultrasonic waves were not applied.

Evaluation 1: Scanning electron microscope (SEM) photograph of the anode active material

FIGS. 3 to 5 are SEM photographs of the negative electrode active materials according to Examples 1 to 3, respectively. FIG. 6 is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Comparative Example 1,

Referring to FIGS. 3 to 5, it can be seen that the negative electrode active material prepared in Examples 1 to 3 has a gap formed between the natural graphite slices on the surface of the spherical natural graphite particles, It can be confirmed that it exists around the gap.

Referring to FIG. 6, it can be seen that the negative electrode active material prepared in Comparative Examples 1 and 2 does not have a clearance gap on the surface portion and that the nanosilicon fine particles are coated on the surface portion.

Referring to FIG. 7 showing a cross section of the negative active material prepared in Example 1, it can be seen that the negative active material prepared in Example 1 has a gap formed from the surface portion.

Evaluation 2: Energy dispersive X-ray spectroscopy (EDS) mapping analysis of an anode active material

8 and 9 are energy dispersive X-ray spectroscopy (EDS) mapping photographs of a cross section of a negative electrode active material according to Example 1. FIG. Referring to FIGS. 8 and 9, it can be seen that silicon exists in the gap formed by the ultrasonic treatment.

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

FIGS. 10 to 12 are X-ray diffraction patterns (XRD) graphs of the negative electrode active material according to Examples 1 to 3 and FIG. 13 is an XRD graph of a negative electrode active material according to Comparative Example 1. FIG.

Referring to FIGS. 10 to 12, it can be seen that the (002) peak as the main peak of graphite and the (111) peak as the main peak of silicon exist in all of the negative electrode active materials prepared in Examples 1 to 3. Silicon carbide ) Are not observed, which shows that the crystal phase is not greatly influenced by the ultrasonic treatment and the heat treatment.

Referring to FIG. 13, in the case of the negative electrode active material prepared in Comparative Example 1, there is a (002) peak as a main peak of graphite and a (111) peak as a main peak of silicon, but the ratio of peaks is different.

 (Preparation of Test Cell)

The negative electrode active materials, carbon black, and CMC / SBR (carboxymethylcellulose / styrene-butadiene rubber) prepared in Examples 1 to 3 and Comparative Example 1 were mixed in distilled water at a weight ratio of 95: 1: 4, . The negative electrode slurry was coated on a copper foil, followed by drying and pressing to prepare respective negative electrodes.

Using the respective cathodes and lithium metal as positive electrodes, a separator made of a porous polypropylene film was laminated between the negative electrode and the positive electrode to produce an electrode assembly. Thereafter, using an electrolytic solution obtained by dissolving 1 M of LiPF ₆ in a solvent mixed with 10% fluoroethylene carbonate (FEC) in a mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC) (DEC: EC = 1: 1) A test cell was produced.

Evaluation 4: Analysis of initial charge / discharge characteristics of lithium secondary battery

The initial charge-discharge characteristics of Examples 1 to 3 and Comparative Example 1 were evaluated by the following method using the prepared test cell, and the results are shown in Table 1 below.

For the cells prepared according to Examples 1 to 3 and Comparative Example 1, the charging was performed in CC / CV mode with a current density of 100 mA / g, the end voltage was maintained at 0.01 V, the current was 10 mA / % Current density). The discharge was performed in CC mode with a current density of 100 mA / g and the termination voltage was maintained at 1.5V.

In Table 1, the initial efficiency (%) is obtained as a percentage of the initial discharge capacity to the initial charge capacity.

It can be seen from the following Table 1 that the capacity and the initial efficiency are similar to those of Comparative Example 1 which was manufactured without using ultrasonic treatment in Examples 1 to 3 using the negative electrode active material prepared by ultrasonic treatment, It can be seen that there is no significant difference in charge / discharge efficiency or capacity.

Initial reversible capacity (mAh / g) Initial efficiency (%) Example 1 487 88.5 Example 2 491 89.8 Example 3 463 91 Comparative Example 1 470 89

Evaluation 5: Analysis of cycle life characteristics of lithium secondary battery

The results of the cycle life evaluation of the negative electrode active material according to Examples 1 to 3 and Comparative Example 1 using the test cell prepared above are shown in Table 2 below and the cycle life of the negative electrode active material according to Examples 1 to 3 and Comparative Example 1 The evaluation results are shown in Fig.

Charging was performed in a CC / CV mode with a current density of 0.5 C-rate, the end voltage was maintained at 0.01 V, and charging was terminated when the current was 0.05 C-rate (10% current density). The discharge was performed in CC mode at a current density of 0.5 C-rate, and the end voltage was maintained at 1.5 V, and a total of 50 cycles were performed.

It can be seen from the following Table 2 that the life characteristics of Examples 1 to 3 using the negative electrode active material prepared by ultrasonic treatment are superior to those of Comparative Example 1 using the negative active material prepared without the ultrasonic treatment.

3 ^rd cycle discharge capacity (mAh / g) 50 ^th cycle discharge capacity
(mAh / g) 50 ^th Discharge capacity /
3 ^rd Discharge capacity (%) Example 1 477 429.3 90 Example 2 480.3 442 92 Example 3 450.4 428 95 Comparative Example 1 458 371 81

1, 2: anode active material
10: Scaly graphite flake particle
20: Clearance
30: amorphous or quasi-crystalline carbon
40: Silicon or silicon compound particles
50: Peeled flaky graphite flake particle
60: shell layer

Claims (23)

Natural graphite particles having a structure in which flaky natural graphite flakes particles are assembled and assembled into a cabbage or a random phase and having a gap formed between the flake natural graphite flakes particles on the surface and inside thereof; And
And a coating layer formed on the surface of the natural graphite particle to form the gap, the coating layer comprising: (i) a silicon or silicone compound particle; and (ii) a coating layer comprising amorphous or semicrystalline carbon Negative electrode active material for lithium secondary battery. The method according to claim 1,
Wherein the amorphous or semi-crystalline carbon comprises 1 to 40 parts by weight based on 100 parts by weight of the natural graphite particles. The method according to claim 1,
Wherein the silicon or silicon compound particles are contained in an amount of 1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material. The method according to claim 1,
Wherein the silicon or silicon compound particles have an average particle diameter (D50) of 5 nm to 3 占 퐉. The method according to claim 1,
Wherein the natural graphite particles have an average particle diameter (D50) of 5 to 40 占 퐉. Spherical natural graphite particles assembled by assembly of scaly graphite particles; Silicon or silicon compound particles; Amorphous or quasi-crystalline carbon precursors; And a solvent;
The solution is subjected to ultrasonic treatment to enlarge the gap between the flaky natural graphite flakes particles existing on the surface and inside of the spherical natural graphite particles and to form the flakes on the surface of the flake natural graphite flakes particles And impregnating and coating an amorphous or semi-crystalline carbon precursor with the silicon or silicon compound particles on the surface of the spheroidized natural graphite particle;
Drying the ultrasonic treated solution to prepare spherical natural graphite modified particles; And
The method of manufacturing a negative active material for a lithium secondary battery according to claim 1, comprising the step of heat-treating the spheroidized natural graphite modified particles. (1) Natural graphite particles having a structure in which scaly graphite particles are assembled and assembled into a cabbage or a random phase, and having a gap formed between the scaly natural graphite particles; And
And a coating layer formed on the surface of the natural graphite particle to form the gap, the coating layer comprising: (i) a silicon or silicone compound particle; and (ii) a coating layer comprising amorphous or semicrystalline carbon Core particles; And
(2) a shell layer formed on the surface of the core particle, wherein the shell layer has a structure in which amorphous or quasi-crystalline carbon is distributed between the flaky graphite flake particles and flake graphite flake particles are stacked in a concentric direction Negative electrode active material for lithium secondary battery. 8. The method of claim 7,
Wherein the amorphous or semi-crystalline carbon in the core particles comprises 1 to 40 parts by weight based on 100 parts by weight of the natural graphite particles. 8. The method of claim 7,
Wherein the silicon or silicon compound particles in the core particles comprise 1 to 50 parts by weight based on 100 parts by weight of the core particles. 8. The method of claim 7,
Wherein the average particle diameter (D50) of the silicon or silicon compound particles in the core particles is 5 nm to 3 占 퐉. 8. The method of claim 7,
Wherein the natural graphite particles have an average particle diameter (D50) of 5 to 40 占 퐉. 8. The method of claim 7,
And the thickness of the shell layer is 0.02 to 5 占 퐉. 8. The method of claim 7,
Wherein the average thickness of the scaly graphite particle particles contained in the shell layer is 0.005 to 1 占 퐉. 8. The method of claim 7,
Wherein the scaly graphite contained in the shell layer and the amorphous or quasi-crystalline carbon are in a weight ratio of 1 to 99: 99 to 1. A negative active material for a lithium secondary battery, Spherical natural graphite particles assembled by assembly of scaly graphite particles; Silicon or silicon compound particles; Amorphous or quasi-crystalline carbon precursors; And a solvent;
The solution is subjected to ultrasonic treatment to enlarge the gap between the flaky natural graphite flakes particles existing on the surface and inside of the spherical natural graphite particles and to form the flakes on the surface of the flake natural graphite flakes particles And impregnating and coating an amorphous or semi-crystalline carbon precursor with the silicon or silicon compound particles on the surface of the spheroidized natural graphite particle;
Drying the ultrasonic treated solution to prepare spherical natural graphite modified particles;
Forming a shell layer having a structure in which amorphous or quasi-crystalline carbon is distributed between the flaky graphite flake particles and flake graphite flake particles are stacked in a concentric direction on the surface of the first particles to form a shell layer, ; And
The method of manufacturing a negative electrode active material for a lithium secondary battery according to claim 7, comprising a step of heat-treating the second particles. 16. The method according to claim 6 or 15,
The carbon precursor may be selected from the group consisting of citric acid, stearic acid, sucrose, polyvinylidene fluoride, Pluronic F127, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, (EPDM), sulfonated EPDM, starch, phenolic resin, furan resin, per furyl alcohol, polyacrylic acid, polyacrylic sodium, polyacrylonitrile, polyimide From the group consisting of epoxy resin, cellulose, styrene, polyvinyl alcohol, polyvinyl chloride, polyvinyl bellolidone, glycerol, polyol, coal pitch, petroleum pitch, mesophase pitch, low molecular weight heavy oil, glucose, And a negative electrode active material manufacturing chamber for a lithium secondary battery, . 16. The method according to claim 6 or 15,
The solvent may be selected from the group consisting of water, N-methylpyrrolidone, dimethylformamide, toluene, ethylene, dimethylacetamide, acetone, methyl ethyl ketone, hexane, tetrahydrofuran, decane, ethanol, methanol, isopropanol, Wherein the negative electrode active material is at least one selected from the group consisting of lithium, lithium, and lithium. 16. The method according to claim 6 or 15,
Wherein the ultrasonic treatment is performed for 1 minute to 24 hours under the condition of an oscillation frequency of 10 to 35 kHz and an ultrasonic amplitude of 10 to 150 占 퐉. 16. The method according to claim 6 or 15,
The drying may be carried out by at least one spray drying method selected from rotary spraying, nozzle spraying and ultrasonic spraying; A drying method using a rotary evaporator; Vacuum drying method; Or a natural drying method. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, 16. The method according to claim 6 or 15,
Wherein the heat treatment is performed at a temperature of 500 to 1500 ° C. 16. The method according to claim 6 or 15,
Wherein the heat treatment is performed in an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under vacuum. 16. The method according to claim 6 or 15,
Wherein the carbon precursor is included in an amount of 2 to 80 parts by weight based on 100 parts by weight of the spherical natural graphite particles. A lithium secondary battery comprising the negative electrode active material of any one of claims 1 to 7

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