KR20150107656A - Negative electrode active material for lithium ion secondary battery, negative electrode for lithium ion secondary battery using the same, and lithium ion secondary battery - Google Patents

Abstract

The present invention provides a negative electrode active material for a lithium ion secondary battery which has a high capacity per unit volume (weight) and possesses practical characteristics related to the discharge capacity, initial efficiency, input characteristics, capacity retention rate, etc. of a lithium ion secondary battery that make it possible for the active substance to be used in vehicles such as HEVs, PHEVs, etc.; and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same. The present invention provides the negative electrode active material for the lithium ion secondary battery, formed from a carbon material having a true specific gravity of 2.00-2.6 g/cm^3, having a particle size distribution based on volume that is within a range in which D10 is 2-5 μm, D50 is 8-12 μm, D90 is 16-26 μm and D50-D10 is 5-10 μm, having a tap density of 0.4 g/cc or higher, and having a BET specific surface area of 5.1-9.0 m^2/g by a nitrogen gas adsorption-flow method; and the negative electrode for the lithium ion secondary battery and the lithium ion secondary battery using the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode active material for a lithium ion secondary battery and a lithium ion secondary battery negative electrode and a lithium ion secondary battery using the negative electrode active material and a lithium ion secondary battery using the negative electrode active material and a lithium ion secondary battery using the same.

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

The lithium-ion secondary battery has excellent performance characteristics such as a high operating potential, a large battery capacity, and a long cycle life. Therefore, since environmental pollution is small, a nickel-cadmium battery or a nickel metal hydride battery .

In addition, in order to cope with energy problems and environmental problems, a hybrid electric vehicle (HEV: Hybrid Electric Assistant) which combines a motor driven by an electric vehicle or a nickel metal hydride battery and a gasoline engine, and a mobile electronic device such as a handy video camera And it is expected that the demand will gradually increase in the future.

As a negative electrode active material constituting the negative electrode of a lithium ion secondary battery, a carbon material is generally used in terms of safety and life span. Among the carbon materials, the graphite material is an excellent material having a high energy density obtained at a high temperature of about 2000 ° C or higher, usually about 2600 to 3000 ° C, and has problems in high input / output characteristics and cycle characteristics. For this reason, for example, graphite materials are not suitable for high input / output applications such as power storage and electric vehicles, and input / output characteristics at low temperatures, and utilization of carbon materials having other structures has been studied.

In recent years, from the viewpoint of further enhancing the performance of the HEV, a further increase in the performance of the lithium ion secondary battery is required, and the improvement of the performance is urgently required. Concretely, the discharge capacity of the lithium ion secondary battery is an important characteristic in order to sufficiently supply the current source of the HEV. In addition, it is required that the ratio of the charging capacity to the discharge capacity, that is, the initial efficiency is high, so that the discharge current amount is sufficiently higher than the charging current amount. In order to enable charging in a short time, the lithium ion secondary battery preferably maintains a high charging capacity up to a high current density, and a high capacity retention ratio is also required. That is, it is required to balance the characteristics of the output characteristics, the discharge capacity, the initial efficiency, and the capacity retention rate.

In order to provide such a lithium ion secondary battery, many carbon materials such as coke and graphite have been studied as the negative electrode active material. Although the above-mentioned discharge capacity can be increased, initial efficiency is not sufficient. In addition, since the actual battery voltage is insufficient, the recent high output characteristics can not be satisfied and the requirements of the capacity retention rate can not be satisfied.

Thus, it is possible to use calcined cokes such as coal-based and / or petroleum-based coal (hereinafter referred to as "coal-based coal"), coal-based coal, etc., A negative electrode active material for a lithium ion secondary battery.

For example, Patent Document 1 shows that high-input-output characteristics are exhibited by an active material having a large crystal-layer interlayer and a fine pore volume compared to graphite by firing at a temperature of 2000 ° C or less to modify the active material surface. In Patent Document 2, it has been proposed to use a catalyst at the time of firing to widen the interstices between crystals, and an active material having a wider crystal layer gap than that of graphite can be produced by processing at a lower firing temperature than in graphite production have.

The calcined cokes such as coal-based raw coke and coal-based coke are advantageous in that the calcination temperature is lower than that of the graphite material, so that the crystallinity of carbon is low and the capacity per unit volume (weight) of the electrode is lowered there is a problem. That is, the electrode using a general graphite material has a capacity of 360 mAh / g and the volume density of 1.4 to 1.8 g / cm ³ , whereas the electrode using the above material has a capacity of 240 to 340 mAh / g and a volume density of 1.0 to 1.2 g / cm < ^{3 &} gt ;, the capacity as an electrode is lowered. For this reason, in calcined cokes such as coal-based raw coke and coal-based coke, there is a problem that the capacity of the active material is increased and the volume density at the time of the electrode is increased.

For example, Patent Document 3 discloses that two types of graphite materials having different fracture strengths and specific surface areas, that is, a medium-diameter (D ₅₀ ) diameter of 13 μm or more Like spherical graphite particles having a spheroidized shape similar to scaly artificial graphite having a mean particle diameter of 15 μm or less and mesophase particles having a median diameter (D ₅₀ ) of 12 μm or more and 19 μm or less ) Spherical Crystals of Small Spheres It is shown that a negative electrode active material layer having a suitable gap is obtained while being filled with high density even after a small press pressure after mixing graphite.

Patent Document 4 discloses a negative electrode active material for a lithium ion secondary battery having a high electrode density and excellent electrolyte permeability, a small capacity loss due to charge and discharge, and excellent cycle performance, and has an average particle diameter (D ₅₀ ) and a D ₉₀ / D ₁₀ in the graphite powder.

Japanese Patent Application Laid-Open No. 2009-224322 Japanese Patent Laid-Open Publication No. 2011-9185 Japanese Patent Application Laid-Open No. 2009-164013 Japanese Patent Application Laid-Open No. 2007-324067

The present invention relates to a lithium ion secondary battery having a capacity per unit volume (weight), which has practical characteristics capable of coping with the in-vehicle use of HEV, PHEV and the like such as discharge capacity, initial efficiency, input characteristics, It is an object of the present invention to provide a negative electrode active material which can obtain such a high lithium ion secondary battery. Another object of the present invention is to provide a lithium ion secondary battery negative electrode and a lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery.

As a result of intensive studies to achieve the above object, the present inventors have found that the above problems can be solved by controlling the particle size distribution of the active material based on a specific raw material to a predetermined value while setting the surface area of the active material to a predetermined value, And has reached the completion of the invention.

That is, the present invention is characterized in that the carbon material has a true specific gravity of 2.00 to 2.16 g / cm ³ , D ₁₀ in the particle size distribution on the volume basis is 2 to 5 탆, D ₅₀ is 8 to 12 ㎛, D ₉₀ in the range of 16 ~ 26㎛, and D ₅₀ -D ₁₀ is 5 ~ 10㎛, the tap density and 0.4g / cc or higher, BET specific surface area by nitrogen gas adsorption flow process (hereinafter, BET (Hereinafter referred to as " specific surface area ") of 5.1 to 9.0 m 2 / g is a negative electrode active material for a lithium ion secondary battery.

As such an active material, it is preferable to use calcined coke such as coal-based and / or petroleum-based (coal-based or the like) raw coke or coal-based coke,

Further, the present invention is a negative electrode having a current collector on a current collector formed by mixing a negative electrode active material for a lithium ion secondary battery and a binder, wherein in the shape of the active material when the cross section of the negative electrode is observed, More than 80% of the active material particles can have, corresponding oval section while Danielle (ellipses corresponding shortened length / long-axis length of the ellipse corresponds to) 0.05 to 0.70, a bulk density of the laminated material layers, characterized in that 1.10 ~ 1.25g / cm ³ It is a negative electrode of a lithium ion secondary battery.

The lithium ion secondary battery of the present invention is characterized in that the lithium ion secondary battery negative electrode and the positive electrode are opposed to each other with a separator interposed therebetween.

According to the present invention, it is possible to increase the volume density at the electrode (negative electrode) while satisfying the discharge capacity, initial efficiency, input characteristics, and capacity retention rate required for in-vehicle applications such as HEV and PHEV, Can provide a negative electrode active material capable of obtaining a lithium ion secondary battery having excellent lithium ion secondary battery.

Hereinafter, embodiments of the present invention will be described in detail.

The negative electrode active material for a lithium ion secondary battery of the present invention has a true specific gravity in the range of 2.00 to 2.16 g / cm < ^{3 &} gt ;. The negative electrode active material for a lithium ion secondary battery giving such true specific gravity can be obtained by calcining a raw coke of a coal type and / or a petroleum type (such as coal type), a calcined coke of a coal type or the like alone or in a mixture thereof , "Coal-based and / or petroleum-based", that is, either coal-based or petroleum-based, or a mixed system of both). If the true specific gravity does not reach 2.00 g / cm < ³ >, when applied to a lithium ion secondary battery, side reactions occur during charging and discharging, leading to deterioration in capacity and efficiency. When the true specific gravity exceeds 2.16 g / cm ³ , the characteristics of the input / output characteristics and the capacity retention rate are lowered when applied to a battery. The coal-derived raw coke can be obtained by using a petroleum-based and / or coal-based heavy oil, for example, a coking plant such as a delayed coker, at a maximum temperature of about 400 ° C. to 700 ° C. for about 24 hours, And calcined coke of coal or the like means calcined coke of coal or the like, and means a product obtained by calcining a petroleum-based and / or coal-based coal which is calcined at a maximum reaching temperature of about 800 ° C to 1500 ° C It means coke.

A method for obtaining a negative electrode active material for a lithium ion secondary battery in which the true specific gravity has the above range is described in detail. First, a coking facility such as a coal-based heavy oil is used, for example, And a pyrolysis / polycondensation reaction is carried out at a temperature of about 700 ° C to 24 hours to obtain a coal-based raw coke. Thereafter, the obtained coal-derived green coke is pulverized to a predetermined size as required. A grinder used industrially can be used for grinding. Specific examples include an atomizer, a Raymond mill, an impeller mill, a ball mill, a cutter mill, a jet mill, a hybridizer, and an orient mill. However, the present invention is not limited thereto. In the pulverizing step, one or two or more of these apparatuses may be used, or may be pulverized a plurality of times by a single apparatus.

Coal-based heavy oil may be either a petroleum heavy oil or a coal-based heavy oil because coal-based heavy oil is rich in aromatics and contains less impurities such as S, V, Fe and less volatile components. It is preferable to use a heavy oil.

Further, in order to produce a coal-based calcined coke, the coal-derived raw coke obtained as described above is calcined at a maximum attainable temperature of 800 ° C to 1500 ° C under a low-oxygen atmosphere. The treatment temperature at calcination is preferably in the range of 1000 ° C to 1500 ° C, more preferably 1200 ° C to 1500 ° C. As a lead hammer capable of mass processing, a facility such as a shuttle, a tunnel, a rotary kiln, a roller hearth kiln, or a microwave can be used for calcination of coal-based raw coke when producing calcined coke. It is not. These calcining facilities may be either continuous or batch type. Subsequently, as in the case of raw coke, the obtained coal-based calcined coke is pulverized to a predetermined size by using a pulverizer such as an industrially used pulverizer. The pulverized coke powder can be finely divided by classifying or can be sized to a predetermined particle size by removing coarse powder with a sieve or the like.

The raw coke and the calcined coke obtained as described above are preferably subjected to a further calcination treatment. The firing temperature is preferably 800 占 폚 to 1500 占 폚 at the maximum attained temperature. When the firing temperature exceeds the upper limit, the crystal growth of the coke material is excessively promoted, making it difficult to set the true specific gravity to 2.16 g / cm ³ or less. When the true specific gravity exceeds 2.16 g / cm ³ , the crystal structure of the coke is oriented like graphite at the time of firing, and the distance between crystal layers becomes narrow. As described above, the structure of the coke The characteristics are degraded. When the firing temperature is lower than the lower limit, the crystal structure becomes undeveloped and the true specific gravity becomes not more than 2.00 g / cm ³ , and the functional groups (such as OH group and COOH group) derived from the raw material remain on the surface of the coke, Side reaction occurs when the battery is charged and discharged as a battery, leading to a decrease in capacity and efficiency. The holding time at the maximum reached temperature of the firing treatment is not particularly limited, but is preferably 30 minutes or more. The firing atmosphere is preferably an inert gas atmosphere such as argon or nitrogen.

The firing treatment may be performed by firing raw cokes such as coal-based cokes or calcined cokes, alone or in combination, and firing may be carried out a plurality of times in the course of firing. In addition, if necessary, it may include a shape control process such as granulation or the like, or may include a step of modifying or coating the surface of the active material with an organic or inorganic component as long as it satisfies the conditions of the active material of the present invention Or the metal component may be uniformly or dispersed on the surface.

Further, the true specific gravity of the negative electrode active material is measured by a liquid phase substitution method (alias a pycnometer method). Specifically, a powder (active material) is placed in a pycnometer, a solvent such as distilled water is added, and the air and the solvent liquid on the sample surface are replaced by vacuum degassing or the like to obtain an accurate sample weight and volume, The specific gravity value is calculated.

Lithium-ion secondary battery negative electrode active material of the present invention, while that the D ₁₀ of the particle size distribution of the negative electrode active material is 2 ~ 5㎛, D ₅₀ is 8 ~ 12㎛, D ₉₀ is 16 ~ 26㎛, D ₅₀ -D ₁₀ Should be in the range of 5 to 10 mu m. Preferably, D ₁₀ is 2 to 4 탆, D ₅₀ is 8 to 12 탆, D ₉₀ is 18 to 24 탆, and D ₅₀ -D ₁₀ is 6 to 10 탆. This means that the raw material is obtained by calcining either one of calcined cokes such as coal-based raw coke and coal-based coal either singly or in combination, but the particles after crushing have the above-mentioned particle size distribution. In this case, the BET specific surface area of the negative electrode active material is set to 5.1 to 9.0 m ² / g. The negative electrode active material having the above-described particle size distribution may be obtained by subjecting the calcined cokes such as coal-based raw coke or coal-based calcined coke to a coarse crushing process by using an orienting mill or the like and then by a hammer mill or a jet mill Finely pulverized, and, if necessary, fine powders are removed by wind power classification or the like. These pulverization methods and classification methods are not particularly limited, and general methods can be used.

With respect to the particle size distribution of the above-mentioned negative electrode active material, if D ₁₀ does not reach 2 탆, the specific surface area excessively increases, and the initial efficiency of the obtained secondary battery decreases. When D ₉₀ exceeds 26 탆, it is difficult to obtain an electrode having a smooth surface property uniformly at the time of electrode production due to the presence of coarse powder. If D ₅₀ -D ₁₀ is less than 5 탆, the particle size distribution of the particles becomes sharp, and the ratio of the fine particles having a small particle diameter becomes large, making it difficult for the particles to form a finely packed structure at the time of electrode production. As a result, do. When D ₅₀ -D ₁₀ exceeds ₁₀ 탆, there is a high possibility that coarse particles having a D ₉₀ of more than 26 탆 are present. Coarse particles having a size of more than 26 mu m will lower the smoothness of the surface of the electrode, which may adversely affect adhesion to the current collector, damage to the separator, and drop of coarse particles. In addition, D ₁₀ is greater than 5㎛ becomes D ₁₀ is smaller than the proportion of fine powder of 2㎛ particles becomes difficult to form a close packed structure. For this reason, the above-described particle size distribution is required in the present invention. D ₅₀ -D ₁₀ represents diffusion of the distribution shape in the particle size distribution of the active material particles. It has been found that the diffusion of the particle size distribution is not defined in the conventional central value D ₅₀ and that the electrode having excellent filling ability can be manufactured by having the diffusion of the distribution shown in the present invention. The coke powder as the raw material of the negative electrode active material having the above-described particle size distribution can be obtained either by using either one of the aforementioned coal-based raw coke powder or coal-based calcined coke powder singly or by using both of them It is acceptable.

Here, for the measurement of the particle size distribution of the negative electrode active material (carbon material), the apparatus of LMS-30 (manufactured by Seishin Kiki) was used in the present invention and the dispersion medium was measured by using water + activator. The volume distribution was measured using a laser diffraction / scattering method as a criterion of the presence ratio of the particles, and the particle size distribution was evaluated using the cumulative distribution based on the volume standard. That is, the particle size distribution of the negative electrode active material was measured by a laser diffraction / scattering method, and a cumulative 10 volume% particle diameter in the particle size distribution was defined as D ₁₀ . Similarly, a cumulative 50% volume particle diameter as D _50, and, and the cumulative 90% volume particle diameter as D _90, was also a difference between the D ₅₀ and D ₁₀ to D ₅₀ -D _10.

The negative electrode active material according to the present invention has a shape of flake and scaly in the process of pulverizing and controlling the particle size distribution. As for the shape of the negative electrode active material, when the cross-section of the prepared electrode is observed, 80% or more of the observed active material particles have an elliptical equivalent ratio (short axis equivalent to ellipse / major axis length corresponding to ellipse) of 0.05 to 0.70. When the elliptic equivalent long-end ratio is more than 0.70, the negative electrode active material becomes spherical in shape, and the method of fine filling and the tap density change in the same particle size distribution, and electrode density and cell performance change. In addition, when the elliptic equivalent long-end ratio is less than 0.05, the negative electrode active material has a more acicular shape and likewise changes the charging method and tap density, and the surface area of the negative electrode active material becomes excessively large. Therefore, in the present invention, it is preferable that 80% or more of the number of observed anode active materials in the shape of the negative electrode active material when observed from the end face of the electrode (negative electrode) having the composite layer formed by mixing with the binder on the current collector, Negative electrode active material having an elliptical equivalent length ratio (ellipse equivalent short axis length / elliptically equivalent major axis length) of 0.05 to 0.70 is used.

As an observation method of the electrode cross section, an electrode having a thickness of 50 탆 or more can be manufactured by a method such as a mechanical polishing, a microtome method, a cross-section polisher (CP) method or a focused ion beam (FIB) To measure the particle size of the minimum particle size of 1 mu m or more by a method such as SEM. For the observed particles, the elliptical equivalent ratio (elliptically equivalent short axis length / elliptically equivalent major axis length) is measured. Observation at 20 or more fields is preferable because there are variations in the distribution of the particles in the observation section. The particle size may be measured by using an image analysis software (WinRooF: manufactured by Mitani Shoji Co., Ltd.) or the like.

The tap density of the negative electrode active material for a lithium ion secondary battery of the present invention is preferably 0.4 g / cc or more, more preferably 0.4 to 0.8 g / cc, in order to increase the initial density at the time of manufacturing the electrode. If the tap density does not reach 0.4 g / cc, the contact between the negative electrode active materials at the time of manufacturing the electrode becomes insufficient, the conduction pass decreases, and battery performance deteriorates. If the press pressure is increased to increase the density, The active material is broken, leading to an increase in the surface area and a further reduction in the conduction path due to the deterioration of the adhesion of the electrode, leading to a deterioration in the battery performance. Therefore, in order to increase the filling density before pressing, it is necessary to set the tap density to at least 0.4 g / cc as an index. Further, in order to exceed 0.8 g / cc, for example, it is necessary to increase the ratio of the fine particles having a D ₁₀ of less than 1 탆 or to increase the ratio of the coarse particles around the D _90. As a result, The uniformity and performance of the electrode are disturbed due to the influence of the coarse particles, which leads to deterioration of the battery performance, so that the tap density need not exceed 0.8 g / cc.

With respect to the tap density of the negative electrode active material in the present invention, a tap capacitor KYT-400 (product of Seishin Kiki) was used, and the measured value at a cylinder volume of 100 cc, a tapping distance of 38 mm, Were used.

The negative electrode active material for a lithium ion secondary battery of the present invention has a BET specific surface area of 5.1 to 9.0 m ² / g. This BET specific surface area is determined by the shape at the time of milling due to the crystal state of the carbon material (origin) and the particle size distribution after milling. If the BET specific surface area is less than 5.1 m ² / g, the charging / discharging rate of lithium ions is decreased. If the BET specific surface area is more than 9.0 m ² / g, the tap density is not increased and the electrode density is not increased. Since the BET specific surface area affects the rate of the surface reaction when lithium ions enter and exit the carbon structure, it is important to control the BET specific surface area to an appropriate value.

In the present invention, the BET specific surface area was determined by a nitrogen gas adsorption / distribution method, and a device of BELSORP-miniII (manufactured by Nippon Berry Co., Ltd.) was used.

The present invention is also a lithium ion secondary battery negative electrode using the negative electrode active material for a lithium ion secondary battery, wherein the negative electrode is composed of a composite layer formed by mixing a negative electrode active material for a lithium ion secondary battery with a binder in a current collector phase (generally a copper foil) .

In general, a fluorine resin powder such as polyvinylidene fluoride (PVDF) or a water-soluble binder such as polyimide (PI) resin, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) is used as the binder.

The formation of the composite layer on the current collector can be achieved by forming the above-described negative electrode active material and the binder in a slurry by using a solvent, coating the current collector on a current collector (generally a copper foil), drying, . The solvent to be used is not particularly limited, but N-methylpyrrolidone (NMP), dimethylformamide, water, alcohol and the like are used.

More specifically, for example, the negative electrode active material and the binder are mixed and kneaded in a weight ratio of 93 to 97: 7 to 3 (negative electrode active material: binder), the slurry is coated on a copper foil of a predetermined thickness, Cm < 2 > / cm < 3 >, and then pressed at a linear pressure of 100 to 600 kg / cm to form a negative electrode. ³ < / RTI > Here, when the line pressure at the time of pressing is excessively increased, the volume density of the electrode is increased, but the active material is deformed and broken and the contact in the electrode is deteriorated, leading to deterioration of capacity and efficiency. .

The negative electrode thus produced can be used as the lithium ion secondary battery of the present invention. The lithium ion secondary battery of the present invention is arranged such that a separator is present between the negative electrode and the positive electrode. The positive electrode and the positive electrode are opposed to each other through a separator. The positive electrode to be opposed to each other is a lithium-containing transition metal oxide LiM (1) xO ₂ where x is a value in the range of 0? X? (1) yM (2) _2- yO ₄ (wherein the transition metal is at least one of Co, Ni, Mn, Ti, Cr, V, Fe, Zn, Al, Sn and In) Mn, Ti, Cr, V, Fe, Zn, Al, Sn, and the like are represented by M (1) consisting of at least one of in, the transition metal chalcogenide (Ti, S _2, NbSe the like), vanadium oxide (such as _{V 2 O 5, V 6 O} 13, V 2 O 4, V 3 O 6) and a lithium compound , A general formula MxMo ₆ Ch ₆ -y wherein x is 0? X? 4 and y is a number in the range of 0? Y? 1, wherein M represents a metal including a transition metal and Ch represents a chalcogen metal ), Or a positive electrode active material such as activated carbon or activated carbon fiber can be exemplified.

As the electrolyte filling between the positive electrode and the negative electrode, any of conventionally known electrolytes may be used. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiB (C ₆ H ₅ ), LiCl, LiBr, Li ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ ) ₃ SO ₂ ) ₃ C, Li) CF ₃ CH ₂ OSO _{2 2} N, Li (CF ₃ CF ₂ CH ₂ OSO ₂ ) ₂ N, _{Li (HCF 2 CF 2 CH 2} OSO 2) 2 N, Li ((CF 3) 2 CHOSO 2) 2 N, LiB [C 6 H 3 (CF 3) 2] a of one or more mixture of ₄ .

Examples of the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1 , 2-diethoxyethane, -butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, anisole, diethyl ether , Methylsulfuron, acetonitrile, chloronitrile, propionitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethyl formamide, N-methyl pyrrolidone, ethyl acetate, trimethyl orthoformate, It is possible to use a single solvent such as benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, sulfite and dimethyl sulfite, The.

[Example]

Hereinafter, the present invention will be described in detail based on examples. However, the contents of the present invention are not limited by these examples. Further, true specific gravity, particle size distribution, tap density, and BET specific surface area were measured by the above-described method.

(Example 1)

(Raw coke) produced by heat treatment at a temperature of 500 DEG C for 24 hours by a delicated coking method using a purified pitch obtained by removing quinoline insoluble matter from coal-based heavy oil was obtained and finely pulverized by an orienting mill and a jet mill, Raw coke pieces (fine pulverized raw coke) having an average particle diameter (D ₅₀ ) of 10.5 占 퐉 were obtained.

The raw coke pieces thus obtained were calcined in a rotary kiln under a low-oxygen atmosphere at a temperature near the inlet of 700 DEG C and a temperature near the outlet of 1500 DEG C (maximum attained temperature) for 1 hour or more to obtain a calcined coke. This calcined coke is pulverized by appropriately adjusting the throughput per unit time and the gas flow rate at the time of the treatment with the jet mill as described above and then removing most of the fine powder of 3 μm or less by wind power classification, and 2.15g / cm ^3, D ₁₀ is 3.7㎛, D ₅₀ is 10.2㎛, D ₉₀ is 19.7㎛, and D ₅₀ -D ₁₀ is 6.5㎛ obtain a lithium ion secondary battery negative electrode active material. The tap density of the negative electrode active material was 0.52 g / cm ³ , and the BET specific surface area measured by the nitrogen gas adsorption / distribution method was 6.7 m ² / g.

Subsequently, to the negative electrode active material for lithium ion secondary battery, a mixture of styrene-butadiene rubber (SBR, manufactured by JSR Corporation) and carboxymethyl cellulose (CMC, manufactured by Nippon Seishi K.K.) as a binder was added to 5 mass% And the mixture was kneaded to prepare a slurry. The obtained slurry was applied to the surface of the copper foil having a thickness of 15 mu m so as to be uniform, dried at a temperature of 60 to 120 DEG C and then pressed at a linear pressure of 300 kg / cm to obtain a sheet-like negative electrode. The volume density of this electrode was 1.15 g / cm < ^{3 &} gt ;. From this sheet, a circular negative electrode having a diameter of 15 mm was cut out to produce a negative electrode for testing. In order to evaluate the electrode characteristics of the negative electrode single pole for this test, metal lithium cut to about 15.5 mm in diameter was used for the counter electrode. The prepared electrode was cut by the CP method, and its cross-section was observed by FE-SEM (magnification: 1,500 times). The active material particles observed within the range of viewing angle 75 占 30 占 퐉 had? 0.70 was found to be 88%. For the observation field, an average value of 20 fields was used to reduce the deviation.

The electrolyte solution was prepared by dissolving LiPF ₆ in a concentration of 1 mol / l in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio of 1: 1), using a porous film of propylene as a separator and using the above- To prepare a coin cell to produce a lithium ion secondary battery. The capacity of the produced battery was 1 mA / cm ² . Of 25 ℃ the charging voltage of the constant temperature and the lower limit, the terminal voltage in a voltage range of an upper limit voltage of 0V, and discharged at 1.5V from the charging ratio of when subjected to constant current discharge with a constant current discharge of 20mA / cm ² of 1mA / cm ² And the retention ratio was calculated. The results are shown in Table 1.

Using the above-described lithium ion secondary battery, the negative electrode active material was charged at a current density of 30 mA / g at a constant current of 1.5 V to 0 V and charged at a constant voltage for 90 minutes to measure the initial discharge capacity. The battery was discharged at a constant current of 30 mA / g from 0 V to 1.5 V, and the initial charge capacity was measured. The initial efficiency was calculated from the ratio of the initial discharge capacity to the initial charge capacity expressed by the following formula. The results are shown in Table 1.

Initial efficiency (%) = 100 × initial discharging capacity / initial charging capacity

Also, the determination in Table 1 was made by evaluating the capacity, rapid chargeability, and initial efficiency per volume of the negative electrode active material. It was confirmed that the capacity density was 1.10 to 1.25 g / cm ³ , the initial efficiency exceeded 80% %, &Quot;& cir &≤

(Examples 2 to 3 and Comparative Examples 1 to 3)

The same operation as in Example 1 was carried out except that the condition at the time of milling of the jet mill after the calcined coke was changed to obtain the negative electrode active material for a lithium ion secondary battery having different particle size distribution as shown in Table 1. Table 1 shows the characteristics of the obtained negative electrode active material. Further, the cross-section of the electrode produced in the same manner as in Example 1 was observed, and it was confirmed that the active material particles having an ellipticity equivalent ratio of 0.05 to 0.70 were 85 to 89% in either sample. Using them, a negative electrode and a lithium ion secondary battery were obtained in the same manner as in Example 1, and the charge retentivity and the initial efficiency were examined. The results are shown in Table 1.

(Example 4)

The raw coke pieces were subjected to the same operation as in Example 1 except that the calcined coke was obtained by calcining the raw coke oven under a low-oxygen atmosphere at a temperature near the inlet of 700 ° C and a temperature near the outlet of 1000 ° C (maximum attained temperature) for 1 hour or more To obtain a lithium ion secondary battery. Table 1 shows the characteristics of the obtained negative electrode active material. The cross-section of the electrode fabricated in the same manner as in Example 1 was observed, and it was confirmed that the active material particles having an ellipticity equivalent ratio of 0.05 to 0.70 were 90%. Also, the charge retention rate and the initial efficiency were examined in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 4)

The raw coke pieces were subjected to the same operation as in Example 1 except that the calcined coke was heat-treated under a low-oxygen atmosphere by a rotary kiln at a temperature near the inlet of 700 ° C and a temperature of around 1800 ° C (maximum attained temperature) for 1 hour or more To obtain a lithium ion secondary battery. Table 1 shows the characteristics of the obtained negative electrode active material. The cross section of the electrode was observed in the same manner as in Example 1, and it was confirmed that the active material particle having an ellipticity equivalent ratio of 0.05 to 0.70 was 87%. Also, the charge retention rate and the initial efficiency were examined in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)

(Raw coke) produced by heat treatment at a temperature of 500 DEG C for 24 hours using a purified pitch obtained by removing quinoline insoluble matter from coal-based heavy oil by a delayed caulking method to obtain a coal-based massive coke (raw coke) ) Was calcined in a rotary kiln under a low-oxygen atmosphere at a temperature of about 800 ° C at the inlet and a temperature of about 1,500 ° C (maximum attainable temperature) near the outlet for one hour or longer to obtain coal-based lump calcined coke.

The coal-based agglomerated calcined coke obtained as described above is finely pulverized by appropriately adjusting the throughput per unit time and the gas flow rate at the time of jet milling, and then most of the fine powder of 3 탆 or less is removed by wind power classification Coal-based calcined coke was obtained. The coal-based calcined coke obtained by baking for more than one hour at the highest temperature reached 1500 ℃ in a nitrogen gas atmosphere by a roller hearth kiln, true specific gravity and is 2.15g / cm ^3, D ₁₀ is 3.0㎛, D ₅₀ is 10.2㎛, D ₉₀ is 20.0㎛, and D ₅₀ -D ₁₀ is 7.2㎛ obtain a lithium ion secondary battery negative electrode active material. The tap density of the negative electrode active material was 0.55 g / cm ³ , and the BET specific surface area measured by the nitrogen gas adsorption / distribution method was 6.6 m ² / g.

When the cross section of the electrode was observed in the same manner as in Example 1, it was confirmed that the active material particles having an ellipticity equivalent ratio of 0.05 to 0.70 were 89%. Also, the charge retention rate and the initial efficiency were examined in the same manner as in Example 1. The results are shown in Table 1.

(Examples 6 to 7)

The same operation as in Example 5 was carried out except that the conditions at the time of milling the jet mill after obtaining the coal-based mass agglomerated calcined coke were changed to obtain the negative electrode active material for a lithium ion secondary battery having different particle size distribution as shown in Table 1. [ Table 1 shows the characteristics of the obtained negative electrode active material. Further, the cross section of the electrode produced in the same manner as in Example 1 was observed, and it was confirmed that the active material particles having an ellipticity equivalent ratio in the range of 0.05 to 0.70 were 82 to 90% in either sample. Using them, a negative electrode and a lithium ion secondary battery were obtained in the same manner as in Example 1, and the charge retentivity and initial efficiency were examined. The results are shown in Table 1.

(Example 8)

A calcined coal calcined coke was subjected to the same operation as in Example 5 except that the calcined coke was calcined at a maximum attainable temperature of 1000 캜 for 1 hour or more under a nitrogen gas atmosphere by a roller husk kiln to obtain a lithium ion secondary battery. Table 1 shows the characteristics of the obtained negative electrode active material. The cross section of the electrode was observed in the same manner as in Example 1, and it was confirmed that the active material particles having an ellipticity equivalent ratio in the range of 0.05 to 0.70 were 88%. Also, the charge retention rate and the initial efficiency were examined in the same manner as in Example 1. The results are shown in Table 1.

As apparent from Table 1, the lithium ion secondary battery using the negative electrode active material for a lithium ion secondary battery satisfying the requirements of the present invention exhibits a high charge retention ratio and has a volume density exceeding 1.10 g / cm < ³ > , And that the initial efficiency, which is worried by the increase of the surface area, also maintains a high value.

It can also be seen that when the true specific gravity of the negative electrode active material is increased, the rapid charging property is damaged. This is considered to be one of the causes of the crystallization of carbon due to the increase of firing temperature and the like, and the distance between layers is narrowed like graphite.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Various modifications and changes may be made thereto without departing from the scope of the present invention.

Claims (4)

Wherein D ₁₀ is 2 to 5 탆, D ₅₀ is 8 to 12 탆, D ₉₀ is a particle size distribution on a volume basis, and a specific gravity is 2.00 to 2.16 g / cm ³ . to be 16 ~ 26㎛, and D ₅₀ -D ₁₀ is in the range of 5 ~ 10㎛, and a tap density of 0.4g / cc or more and a BET specific surface area by nitrogen gas adsorption flow process 5.1 ~ 9.0㎡ / g Characterized in that the negative active material for a lithium ion secondary battery. The method according to claim 1,
Characterized in that the active material is obtained by firing either a coal-based and / or petroleum-based raw coke, or a coal-based and / or petroleum-based calcined coke either singly or in combination, and then firing the active material for lithium ion secondary battery . A lithium secondary battery comprising: a negative electrode having on a current collector a composite layer (mixture layer) formed by mixing a negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3 with a binder; a shape of an active material , 80% or more of the number of observed active material particles has an elliptic equivalent ratio (elliptically equivalent short axis length / elliptically equivalent major axis length) of 0.05 to 0.70 and a volume density of 1.10 to 1.25 g / cm ³ Wherein the negative electrode is a lithium ion secondary battery negative electrode. The lithium ion secondary battery according to claim 3, wherein the lithium ion secondary battery negative electrode and the positive electrode are opposed to each other with a separator interposed therebetween.