WO2015093894A1 - Anode active material, and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to an anode active material characterized by comprising a natural graphite and a mosaic cokes-based artificial graphite, and a lithium secondary battery comprising the anode active material. According to one embodiment of the present invention, the use of an anode active material comprising a natural graphite and a mosaic cokes-based artificial graphite further facilitates intercalation and deintercalation of a lithium ion if applied to a lithium secondary battery, and can increase conductivity of an electrode even when using no conductive material or using a small amount of conductive material. Also, due to the increase in conductivity, the rate limiting characteristics of the lithium secondary battery can be increased and interfacial resistance can be reduced.

Description

Anode active material and lithium secondary battery comprising same

The present invention relates to a negative electrode active material and a lithium secondary battery, and more particularly, to a negative electrode active material including natural graphite and mosaic cokes artificial graphite and a lithium secondary battery including the same.

In recent years, as the electronic devices become smaller, lighter, thinner, and portable with the development of the information and communication industry, the demand for high energy density of batteries used as power sources for such electronic devices is increasing. Lithium secondary batteries are the batteries that can best meet these demands, and research on these is being actively conducted.

As the negative electrode material of the lithium secondary battery, a carbon-based material is mainly used, and the carbon-based material includes crystalline carbon and amorphous carbon. Crystalline carbon is typical of graphite carbon such as natural graphite and artificial graphite, and amorphous carbon is heat treated to non-graphitizable carbons (hard carbons) and pitch obtained by carbonizing a polymer resin. Graphitizable carbons (soft carbons).

Generally, soft carbons are made by applying 1000 levels of heat to coke, a by-product generated from crude oil refining process. Unlike conventional graphite anode active materials or hardened carbon-based anode active materials, soft carbons have high output and require time for charging. short.

Hard carbons may be prepared by carbonizing materials such as resin, thermosetting polymer, wood, and the like. When the cured carbon is used as a lithium secondary battery negative electrode material, the reversible capacity is superior to 400 mAh / g due to micropores, but the initial efficiency is about 70% or less, so it is irreversibly consumed when used as an electrode of a lithium secondary battery. The disadvantage is that the amount of lithium is large.

This irreversible occurrence is due to the decomposition reaction of the electrolyte at the surface of the electrode during charging and the formation of a solid electrolyte interphase (SEI), which is a surface coating, and the discharge of lithium stored in the carbon particles during charging. Sometimes it is due to not being able to. More problematic than this is the former case, and the formation of the surface coating is known as a major irreversible cause.

It is also known that most of the high capacity graphite materials have a highly developed layered structure, which has a high degree of graphitization and takes a flake shape. And since such flake graphite has few sites where Li ions invade between the layers, that is, the edge surface, when the flake graphite is used for a negative electrode active material of a lithium secondary battery, the characteristics when discharged at a large current, namely There is a problem in that the high rate discharge characteristics deteriorate.

In addition, spherical natural graphite has a limited ion conductivity, and when only the spherical natural graphite is used as a negative electrode active material, a void space is formed between the active material and the active material to increase the resistance of the electrode, thereby reducing the rate characteristic There is a problem.

Accordingly, there is a demand for development of a negative electrode active material that can replace a conventional negative electrode active material and can reduce interfacial resistance and improve rate rate characteristics when applied to a lithium secondary battery.

The problem to be solved of the present invention is to provide a negative electrode active material that not only improves conductivity, but also reduces interfacial resistance and has excellent rate characteristics.

In addition, another problem to be solved by the present invention is to provide a negative electrode having a specific orientation index and electrode density, and thereby a lithium secondary battery with improved performance by including the negative electrode active material.

The problem to be solved by the present invention is not limited to the above-mentioned problem, another task that is not mentioned will be clearly understood by those skilled in the art from the following description.

In order to solve the above problems, according to an embodiment of the present invention, there is provided a negative electrode active material comprising natural graphite and mosaic cokes-based artificial graphite.

In addition, according to an embodiment of the present invention, a negative electrode including the negative electrode active material is provided.

Furthermore, the present invention provides a lithium secondary battery including a cathode, a cathode, and a separator interposed between the cathode and the anode using the anode.

According to an embodiment of the present invention, by using a negative electrode active material containing natural graphite and mosaic coke-based artificial graphite, when applied to a lithium secondary battery, the insertion / desorption of lithium ions more easily, and a conductive material is not used. Otherwise, even small amounts can increase the conductivity of the electrode. In addition, by increasing the conductivity, not only the rate characteristic of the lithium secondary battery may be further improved, but also the interface resistance may be reduced.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 shows a schematic diagram of a negative electrode active material according to an embodiment of the present invention.

2 is a diagram illustrating a structure of graphite particles.

Figure 3 is a graph of the XRD measurement results of the mosaic coke-based artificial graphite used according to an embodiment of the present invention.

FIG. 4 is a graph illustrating measurement results of rate rate characteristics of lithium secondary batteries prepared in Example 3 and Comparative Example 4 according to an embodiment of the present disclosure.

5 is a graph illustrating a result of measuring resistance of an electrode with respect to a negative electrode in a lithium secondary battery prepared in Example 3 and Comparative Example 4 according to an embodiment of the present invention.

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

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The negative electrode active material according to the embodiment of the present invention may include natural graphite and mosaic cokes-based artificial graphite.

More specifically, the negative electrode active material according to an embodiment of the present invention, as shown in the schematic diagram shown in Figure 1, by containing natural graphite and mosaic coke-based artificial graphite is mixed together, compared to when using the natural graphite alone active material and active material By filling the empty space between the mosaic coke-based artificial graphite, the conductivity can be increased, thereby improving the rate characteristic of the secondary battery, the interface resistance can be reduced.

In addition, the mosaic coke-based artificial graphite is due to the random crystal structure of only the mosaic coke-based artificial graphite, it is easier to insert and detach the lithium ions can further improve the performance of the secondary battery. In addition, since the mosaic coke-based artificial graphite may serve as a conductive material by being included in the negative electrode active material together with the natural graphite, even if the conductive material is not used or the amount thereof is reduced, the mosaic coke-based artificial graphite is equivalent to or higher than the conventional negative electrode active material using the conductive material Can be represented.

Furthermore, since the mosaic coke artificial graphite may be expressed due to the random crystal structure of the mosaic phase, lithium ion may be used as the needle coke artificial graphite having a plate or needle shape that can be generally used. It may be difficult to facilitate the insertion and desorption of, and thus it may be difficult to obtain the advantages of improving the rate characteristic or decreasing the interface resistance.

Specifically, the mosaic coke-based artificial graphite included in the negative electrode active material according to an embodiment of the present invention is based on coal coke, for example, and when the polishing surface of the carbonized sample is observed with a polarization microscope, It may have an anisotropic texture shown as a mosaic texture. In addition, since the crystal structure of the anisotropic mosaic is random (random), when applied to a lithium secondary battery, insertion and desorption of lithium ions may be easier.

The average major axis length of the mosaic coke-based artificial graphite usable in accordance with an embodiment of the present invention may be, for example, 5 μm to 30 μm, preferably 10 μm to 25 μm.

When the long axis length of the mosaic coke artificial graphite is less than 5 μm, the initial efficiency of the battery may decrease due to an increase in specific surface area, thereby degrading battery performance, and when exceeding 30 μm, they may penetrate through the separator. In addition, since the filling density is low, the capacity retention rate may be low.

In addition, the mosaic coke artificial graphite according to an embodiment of the present invention has a specific surface area of 3.0 / g to 4.0 / g, the compression density of 1.5 g / cc to 2.1 g / cc under a pressure of 8 mPa to 25 mPa It is preferable to have.

When the compression density is less than 1.5 g / cc, the energy density per unit volume may decrease, and when the compression density exceeds 2.1 g / cc, it may cause a decrease in initial efficiency and deterioration of high temperature characteristics, and may also decrease the adhesion of the electrode. have.

In addition, the mosaic coke artificial graphite has a Lc (002) of 21.6 nm to 21.9 nm, which is the size of the crystallite in the C-axis direction, and the surface spacing d ₀₀₂ of the (002) plane is 0.3377 nm or less, preferably 0.3357. It is preferred that it is a crystalline phase of nm to 0.3377 nm, most preferably 0.3376 nm.

D ₀₀₂ of the mosaic coke-based artificial graphite is obtained by obtaining a graph of two values measured using XRD, and the peak position of the graph can be obtained by the integration method, and it can be calculated by the following equation (1) by the Bragg formula.

<Equation 1>

d ₀₀₂ = λ / 2sinθ

In addition, the crystallite size Lc of the mosaic coke-based artificial graphite can calculate the crystallite size Lc (002) in the C-axis direction of the particle by the equation of Scherrer of Equation 2 below.

<Equation 2>

K = Scherrer constant (K = 0.9)

β = half width

λ = wavelength (0.154056 nm)

θ = angle at maximum peak

According to an embodiment of the present invention, the mosaic coke-based artificial graphite may have a crystallite size Lc (002) of 21.6 nm to 21.9 nm in the C-axis direction when measured by XRD using CuK. When the Lc of the mosaic coke artificial graphite is within the above range, the electrical conductivity is excellent and the diffusion rate of lithium ions is faster, so that insertion and desorption of lithium ions may occur more easily. If Lc is greater than 21.9 nm, the movement distance of lithium ions may be increased to act as a resistance, thereby lowering output characteristics, and when less than 21.6 nm, it may be difficult to express a capacity inherent in graphite.

On the other hand, the negative electrode active material according to an embodiment of the present invention preferably comprises natural graphite together with the mosaic coke-based artificial graphite.

In the case of artificial graphite, the charging and discharging efficiency is high, but the cost is not only high, dispersibility in the aqueous slurry is very low, there is difficulty in terms of processability, and the capacity is low, it is difficult to obtain the properties of the battery of the desired level.

On the other hand, natural graphite exhibits high voltage flatness and high capacity close to the theoretical capacity at low cost, and thus has high utility as an active material.

According to one embodiment of the present invention, the natural graphite may be used in the form of a plate or a sphere, spherical natural graphite may be preferred.

In the negative electrode active material according to an embodiment of the present invention, the content ratio of the natural graphite and mosaic coke artificial graphite is preferably 1: 0.1 to 1: 1 weight ratio, preferably 1: 0.3 to 1: 1 weight ratio. .

In this case, when the weight of the mosaic coke artificial graphite exceeds the above range, the mosaic coke-based artificial graphite is covered with an excessive amount of natural graphite, there is a problem that the specific surface area is increased to increase the decomposition reaction of the electrolyte, If it is less than the range, the conductivity may be degraded because the void space between the natural graphite cannot be filled as a whole.

According to one embodiment of the present invention, the natural graphite may use an average particle diameter (D ₅₀ ) of 5 to 30, preferably 20 to 25. When the average particle diameter (D ₅₀ ) of the spherical natural graphite is less than 5, the initial efficiency of the secondary battery may decrease due to an increase in specific surface area, thereby degrading battery performance, and when the average particle diameter (D ₅₀ ) exceeds 30 They may penetrate the separator and cause a short circuit. Since the filling density is low, the capacity retention rate may be low.

The average particle diameter of natural graphite according to an embodiment of the present invention may be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure the particle diameter of several mm from the submicron region, and high reproducibility and high resolution can be obtained. The average particle diameter (D ₅₀ ) of the natural graphite may be defined as the particle size based on 50% of the particle size distribution.

According to an embodiment of the present invention, a method for measuring the average particle diameter (D ₅₀ ) of natural graphite is, for example, after dispersing natural graphite in a solution of ethanol / water, a commercially available laser diffraction particle size measuring apparatus (eg Microtrac MT 3000), and irradiated with an ultrasonic wave of about 28 kHz at an output of 60 W, the average particle diameter D ₅₀ at the 50% reference of the particle size distribution in the measuring device can be calculated.

According to one embodiment of the present invention, the spherical natural graphite satisfying the average particle size range of the natural graphite is introduced into the spheronization apparatus (Nara Hybridization System, NHS-2), for example, the rotor speed ( rotor speed) can be obtained by spheroidizing for about 30 m / s to 100 m / s, 10 minutes to 30 minutes, but is not limited thereto.

In addition, according to an embodiment of the present invention, it is preferable that the natural graphite has a specific surface area (BET-SSA) of 2 m ² / g to 8 m ² / g. If the specific surface area of the natural graphite is less than 2 m ² / g, the adhesion between the electrodes may be lowered, and if it exceeds 8 m ² / g is preferable because it leads to an increase of the initial irreversible capacity during charging and discharging not.

According to an embodiment of the present invention, the specific surface area may be measured by Brunauer-Emmett-Teller (BET) method. For example, it can be measured by BET 6-point method by nitrogen gas adsorption distribution method using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

On the other hand, the manufacturing method of the negative electrode active material according to an embodiment of the present invention may include mixing natural graphite and mosaic coke-based artificial graphite.

In the manufacturing method of the negative electrode active material of the present invention, the mixing method for producing the negative electrode active material may be mixed by simple mixing or mechanical milling using conventional methods known in the art. For example, it is possible to simply mix by using a mortar, or to rotate at a rotational speed of 100 to 1000rpm using a blade or ball mill to mechanically apply compressive stress to form a carbon composite.

According to an embodiment of the present invention, a negative electrode including a current collector and the negative electrode active material formed on at least one surface of the current collector may be provided using the negative electrode active material.

The negative electrode according to an embodiment of the present invention includes a natural graphite and mosaic coke artificial graphite in the negative electrode active material, so that the orientation index (I110 / I004) at a compression density of 1.40 g / cc to 1.85 g / cc is 0.08 to 0.086 , Preferably 0.0819 to 0.0836.

According to one embodiment of the present invention, by adjusting the orientation index of the negative electrode due to the use of the mosaic coke-based artificial graphite, it is possible to further improve the performance of the lithium secondary battery.

According to one embodiment of the present invention, by adjusting the orientation index of the negative electrode due to the use of the mosaic coke-based artificial graphite, it is possible to further improve the performance of the lithium secondary battery.

According to one embodiment of the present invention, the index of orientation of the negative electrode may depend on the compressive force applied when the negative electrode active material is coated and rolled on the negative electrode current collector.

In the cathode according to an embodiment of the present invention, the orientation index may be measured by, for example, X-ray diffraction (XRD).

Orientation index of the negative electrode according to an embodiment of the present invention is the negative electrode, more specifically, the (110) and (004) plane of the negative electrode active material included in the negative electrode after the XRD of the (110) and (004) plane It is the area ratio (110) / (004) obtained by integrating peak intensity. More specifically, XRD measurement conditions are as follows.

Target: Cu (Kα-ray) graphite monochromator

Slit: diverging slit = 1 degree, receiving slit = 0.1, scattering slit = 1 degree

Measuring zone and step angle / measuring time:

(110) plane: 76.5 degrees <2θ <78.5 degrees, 0.01 degrees / 3 seconds

(004) plane: 53.5 degrees <2θ <56.0 degrees, 0.01 degrees / 3 seconds, where 2θ represents the diffraction angle. The XRD measurement is one example, other measurement methods may also be used, and the orientation index of the negative electrode may be measured by the above method.

The negative electrode according to an embodiment of the present invention can be prepared by conventional methods known in the art. For example, a negative electrode may be manufactured by mixing and stirring a solvent in a negative electrode active material and, if necessary, a binder to prepare a slurry, and then applying the coating (coating) to a current collector of a metal material, compressing the same, and drying the same.

According to an embodiment of the present invention, the negative electrode active material slurry may further include a conductive material. Available conductive materials include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, carbon nanotube, fullerene, carbon fiber, metal fiber, carbon fluoride, aluminum, nickel It may be any one selected from the group consisting of powder, zinc oxide, potassium titanate, titanium oxide and polyphenylene derivatives, or a mixture of two or more thereof, and preferably carbon black.

In addition, the positive electrode according to the present invention may be manufactured by a conventional method in the art similar to the negative electrode.

For example, a binder and a solvent, and a conductive material and a dispersant may be mixed and stirred in the positive electrode active material of the present invention to prepare a slurry, and then coated on a current collector and compressed to prepare an electrode.

The binder used in the present invention is used to bind the positive electrode active material and the negative electrode active material particles to maintain the molded body, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), styrene-butadiene rubber (styrene binders such as butadiene rubber (SBR). The binder is any one selected from the group consisting of a solvent-based binder represented by polyvinylidene (PVdF) (that is, a binder having an organic solvent as a solvent), acrylonitrile-butadiene rubber, styrene-butadiene rubber, and acrylic rubber Or an aqueous binder (that is, a binder having water as a solvent) which is a mixture of two or more of them. Aqueous binders, unlike solvent binders, are economical, environmentally friendly, harmless to the health of workers, and have a greater binding effect than solvent-based binders. The aqueous binder is preferably styrene-butadiene rubber.

As the cathode active material, a lithium-containing transition metal oxide commonly used in the art may be preferably used. In addition, the lithium-containing transition metal oxide may be coated with a metal or metal oxide such as aluminum (Al). In addition, sulfides, selenides, and halides may be used in addition to the lithium-containing transition metal oxides.

When the electrode is manufactured, a lithium secondary battery having a separator and an electrolyte interposed between the positive electrode and the negative electrode, which is commonly used in the art, may be manufactured using the electrode.

In the electrolytic solution used in the present invention, the lithium salt that may be included as an electrolyte may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, such as the lithium salt, the anion is F ^-, Cl ^-, Br ^{- _{, I -, NO 3 -,}} N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 _{^{PF 2 -, (CF 3)}} 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N _{^{-, CF 3 CF 2 (CF}} 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO ₃ ^-, CF ₃ CO ₂ ^- may be any one selected from the group consisting of _{^{-, CH 3 CO 2 -,}} SCN - , and _{(CF 3 CF 2 SO 2)} 2 N.

In the electrolyte solution used in the present invention, as the organic solvent included in the electrolyte solution, those conventionally used in the electrolyte solution for lithium secondary batteries may be used without limitation.

In addition, as the separator, conventional porous polymer films conventionally used as separators, for example, polyolefins such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, etc. The porous polymer film made of the polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. It is not.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, square, pouch type, or coin type using a can.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Although the following Examples and Experimental Examples will be further described, the present invention is not limited to these Examples and Experimental Examples.

<Production of Anode Active Material>

Example 1

Natural graphite particles having an average particle diameter of 100 µm were introduced into a spherical hybridization apparatus (Nara Hybridization System, NHS-2), spheroidized at a rotor speed of 65 m / sec for 10 minutes, and an average particle diameter (D ₅₀ ) of 20 µm. Spherical natural graphite particles having a FWHM of 7.0 µm and a BET specific surface area of 2.60 m ² / g.

Mosaic coke artificial graphite having a long axis length of about 20 μm and a specific density of 1.7 g / cc to 1.8 g / cc under a pressure of 3 m ² / g to 4 m ² / g and 12 mPa to 16 mPa ( Hitachi Chemical, MAGE3) was used.

The spherical natural graphite and mosaic coke-based artificial graphite were mixed at a weight ratio of 1: 0.3, and uniformly stirred using mortar to prepare a negative electrode active material.

Example 2

A negative electrode active material was manufactured in the same manner as in Example 1, except that the spherical natural graphite and mosaic coke-based artificial graphite were mixed in a weight ratio of 1: 1.

Comparative Example 1

A negative electrode active material was manufactured in the same manner as in Example 1, except that 100% of spherical natural graphite was used without using a mosaic coke-based artificial graphite.

Comparative Example 2

A negative electrode active material was manufactured in the same manner as in Example 1, except that the spherical natural graphite and mosaic coke-based artificial graphite were mixed at a weight ratio of 1: 0.05.

Comparative Example 3

A negative electrode active material was manufactured in the same manner as in Example 1, except that the spherical natural graphite and mosaic coke artificial graphite were mixed in a weight ratio of 1.2.

<Production of Lithium Secondary Battery>

Example 3

Preparation of Cathode

The negative electrode active material obtained in Example 1, SBR (styrene-butadiene rubber) as a binder, CMC (carboxy methyl cellulose) as a thickener and acetylene black as a conductive material in a weight ratio of 95: 2: 2: 1, and these are solvent Mixing with water (H ₂ O) produced a uniform negative electrode slurry. The prepared negative electrode slurry was coated on one surface of a copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a required size to prepare a negative electrode.

Fabrication of Lithium Secondary Battery

Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:70, and LiPF ₆ was added to the nonaqueous electrolyte solvent to prepare a 1M LiPF ₆ nonaqueous electrolyte.

In addition, a lithium metal foil was used as a counter electrode, that is, a positive electrode, a polyolefin separator was interposed between both electrodes, and the electrolyte was injected to prepare a coin-type half cell.

Example 4

A negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 3, except that the negative electrode active material prepared in Example 2 was used.

Comparative Examples 4 to 6

A negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 3, except that the negative electrode active materials prepared in Comparative Examples 1 to 3 were used.

Example 5

A negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 3, except that the negative electrode active material prepared in Example 2 was used and no conductive material was added during the preparation of the negative electrode.

Comparative Example 7

In the same manner as in Example 5, except that needle coke artificial graphite was mixed with natural graphite in a weight ratio of 1: 1, instead of mosaic coke artificial graphite, and a conductive material was not added in the preparation of the negative electrode. A negative electrode and a lithium secondary battery were prepared.

Experimental Example 1 Orientation Index Measurement

XRD diffraction measurements using Cu (K-rays) were performed on the cathodes prepared in Example 3 and Comparative Example 4. The orientation index is obtained by measuring the (110) and (004) planes of the negative electrode active material included in the negative electrode by XRD and then integrating the peak intensities of the (110) plane and (004) plane ((110) / (004) ) More specifically, XRD measurement conditions are as follows.

Target: Cu (Kα-ray) graphite monochromator

Slit: diverging slit = 1 degree, receiving slit = 0.1, scattering slit = 1 degree

Measuring zone and step angle / measuring time:

(110) plane: 76.5 degrees <2θ <78.5 degrees, 0.01 degrees / 3 seconds

(004) plane: 53.5 degrees <2θ <56.0 degrees, 0.01 degrees / 3 seconds, where 2θ represents the diffraction angle.

In addition, the mosaic coke-based artificial graphite used in Examples 1 and 2 was measured by XRD, the results are shown in FIG. Lc (002) and d ₀₀₂ of mosaic coke artificial graphite were calculated using the following equations (1) and (2):

<Equation 1>

d ₀₀₂ = λ / 2sinθ

In addition, the crystallite size Lc of the mosaic coke-based artificial graphite can calculate the crystallite size Lc (002) in the C-axis direction of the particle by the equation of Scherrer of Equation 2 below.

<Equation 2>

K = Scherrer constant (K = 0.9)

β = half width

λ = wavelength (0.154056 nm)

θ = angle at maximum peak

As shown in FIG. 3, the mosaic coke artificial graphite has Lc (002) of 21.6 nm to 21.9 nm, which is the size of crystallites in the C-axis direction at the time of XRD measurement, and the plane spacing d ₀₀₂ of the (002) plane is 0.3376 nm. The crystalline phase is shown.

Experimental Example 2: Rate property evaluation A

Rate characteristics of the lithium secondary batteries obtained in Examples 3 and 4 and Comparative Examples 4 to 6 in a voltage range of 0 V to 1.5 V at room temperature were measured. The battery was charged under 0.1 C constant current / constant voltage (CC / CV) conditions up to 1.5 V, then discharged in constant current mode until the current reached 0.1 C at 5 mV, and then finished.

As shown in FIG. 4, the comparative analysis of the rate characteristics of 0.2C, 0.5C, and 1C in the voltage range of 0 V to 1.5 V at room temperature was performed. As a result, Example 1 was mixed with natural graphite and mosaic coke-based artificial graphite. It can be seen that the lithium secondary battery of Example 3 using the negative electrode active material has improved rate characteristics about 5 to 10% compared to the lithium secondary battery of Comparative Example 4 using the negative electrode active material of Comparative Example 1, which does not use the mosaic coke system. have.

In addition, in order to determine the rate-rate characteristic according to the mixing weight ratio of natural graphite and mosaic coke artificial artificial graphite, the lithium secondary batteries of Examples 3 and 4 and Comparative Examples 5 and 6 were used in a voltage range of 0 V to 1.5 V at room temperature. The rate-rate characteristics of 0.2C, 0.5C, and 1C were compared, respectively, and the results are shown in Table 1 below.

Table 1

	Negative electrode active material (weight ratio of natural graphite: mosaic coke-based artificial graphite)	Rate characteristics
		0.2C	0.5C	1C
Example 3	1: 0.3	100%	97.5%	81.2%
Example 4	1: 1	100%	98.6%	89.7%
Comparative Example 6	1: 0.05	100%	95.9%	76.7%
Comparative Example 7	1: 1.2	100%	94.8%	75.8%

As can be seen in Table 1, Examples 3 and 4 using the negative active material mixed with spherical natural graphite and mosaic coke artificial graphite in the range of 1: 0.3 to 1 by weight, natural graphite: mosaic coke-based artificial Compared to Comparative Examples 5 and 1 in which a graphite coke artificial graphite was added in a 1: 0.05 weight ratio and comparative example 6 in which an excessive amount of mosaic coke artificial graphite was mixed in a weight ratio, the rate characteristic, in particular, 0.5C and 1C It can be seen that it is remarkably excellent.

Experimental Example 3: Rate property evaluation B

In order to determine the rate characteristic according to the form of artificial graphite mixed with natural graphite, the rate characteristic during charging and discharging of the lithium secondary batteries of Example 5 and Comparative Example 8 was evaluated. Charging measures the rate of charging to 0.005 V at 0.2C constant current / constant voltage (CC / CV), 0.2C constant current, 0.5C constant current and 1.0C constant current, respectively, and discharge ranges from 0.005 V to 1.5 V at room temperature. At 0.2C, 0.5C, 1C and 2C at the rate of discharge was measured, respectively, the results are shown in Table 2 below.

TABLE 2

	Charging rate				Discharge rate
	0.2C	0.2C	0.5C	1.0C	0.2C	0.5C	1C	2C
Example 5	100	76.0	39.3	15.1	100	99.6	94.6	70.8
Comparative Example 8	100	70.0	33.6	10.0	100.0	86.5	86.5	56.8

As can be seen in Table 2, Example 5 using a negative electrode active material in which spherical natural graphite and mosaic coke artificial graphite were mixed in a range of 1: 1 by weight, the natural graphite: needle coke artificial graphite 1: It can be seen that the rate characteristic at the time of charging is about 5 to 10% superior to the comparative example 8 mixed in 1 weight ratio, and the rate characteristic at the time of discharge is about 10 to 15% excellent.

Experimental Example 4: Evaluation of Electrode Resistance

The electrode resistance after long-term charge and discharge of the lithium secondary battery of Example 3 using the negative electrode containing spherical natural graphite and mosaic coke artificial graphite and the lithium secondary battery of Comparative Example 4 using the negative electrode containing only spherical natural graphite for a long time Was measured. The results are shown in FIG. Measurement conditions are as follows.

Sample preparation: After charging and discharging the lithium secondary batteries of Example 3 and Comparative Example 200 for 200 cycles, the battery was disassembled to obtain only the negative electrode, which was then formed into a symmetric cell with the negative electrode, and then the impedance was measured.

Impedance frequency range: 100,000 to 0.005 Hz

As shown in FIG. 5, when the lithium secondary battery of Example 3 is subjected to a long-term charge / discharge process, when the negative electrode including spherical natural graphite and mosaic coke artificial graphite is used as in Example 3, spherical natural Since the semicircle of the graph is smaller than that of Comparative Example 4 using the negative electrode containing only graphite, it can be seen that the interface resistance decreased.

Claims (12)

1. An anode active material comprising natural graphite and mosaic cokes artificial graphite.
2. The method of claim 1,

   The content ratio of the natural graphite and mosaic coke-based artificial graphite is 1: 0.1 to 1: 1 weight ratio of the negative electrode active material, characterized in that.
3. The method of claim 1,

   An average active material length of the mosaic coke-based artificial graphite is 5 to 30, characterized in that the negative electrode active material.
4. The method of claim 1,

   The mosaic coke artificial graphite is an anode active material, characterized in that Lc (002), the size of the crystallite in the C-axis direction when measured XRD is 21.6 nm to 21.9 nm.
5. The method of claim 4, wherein

   The mosaic coke-based artificial graphite has a surface spacing d ₀₀₂ of (002) plane when measured XRD is 0.3377 nm or less.
6. The method of claim 1,

   The mosaic coke-based artificial graphite has a specific surface area of 3.0 m ² / g to 4.0 m ² / g, and has a compressive density of 1.5 g / cc to 2.1 g / cc under a pressure of 8 mPa to 25 mPa. Negative electrode active material.
7. The method of claim 1,

   The negative active material, characterized in that the natural graphite is spherical.
8. The method of claim 7, wherein

   The average particle diameter (D ₅₀ ) of the natural graphite is a negative electrode active material, characterized in that 5 to 30 ㎛.
9. The method of claim 1,

   A specific surface area (BET) of the natural graphite is characterized in that 2 m ² / g to 8 m ² / g.
10. A negative electrode comprising a current collector and the negative electrode active material of claim 1 formed on at least one surface of the current collector.
11. The method of claim 10,

    An anode characterized by an orientation index (I110 / I004) of 0.08 to 0.086 at a compression density of 1.40 g / cc to 1.85 g / cc.
12. A lithium secondary battery comprising the negative electrode of claim 10.

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