Anode active material for a lithium secondary battery and lithium secondary battery containing this

Abstract

Anode active material for a lithium secondary battery, comprising a secondary particle formed from primary particles, wherein a mean diameter of the primary particles is in a range of 5 µm to 15 µm and a mean diameter of the secondary particle is in a range of 10 µm to 25 µm, wherein the primary particles and the secondary particle are made of an artificial graphite and an I(110) / I(002) of the secondary particle is in a range of 0.0075 to 0.012.

Description

CROSS REFERENCE TO RELATED APPLICATIONSThis application claims priority to Korean Patent Application No. 10-2016-0068987 filed with the Korean Intelligence Property Office (KIPO) on Jun. 2, 2016.BACKGROUND1. Field of InterestExemplary embodiments relate to anode active materials for a lithium secondary battery and anode and lithium secondary batteries including the same.2. Description of the Prior ArtRecently, mobile electronic devices and telecommunication devices such as mobile phones, camcorders, laptop computers, etc. have been widely used because the electronics industry and information technology industry have rapidly developed. Accordingly, lithium secondary batteries have also been actively developed as a power source for such devices. For example, a lithium secondary battery can be used as an environmental friendly power source in an electric vehicle, a non-interrupted power source, an electrically powered tool, an artificial satellite, etc.Lithium secondary batteries developed since the early 1990s may include an anode containing a carbon-based material capable of adsorbing and discharging lithium ions, a cathode containing a lithium-based oxide, and a nonaqueous electrolyte containing a mixed organic solvent and an appropriate amount of a lithium salt dissolved therein.Amorphous or crystalline carbon may be used as an active material of the anode (e.g., a negative electrode). Preferably, crystalline carbon is used due to its high capacity. Crystalline carbon may include a natural graphite, an artificial graphite, etc.The artificial graphite may have improved charging and discharging efficiency, but the capacity may be small.For example, KR 10 2005 004 930 A discloses an anode active material containing an artificial graphite having a limited capacity and performance. In addition, JP H11-354 122 A discloses an anode active material containing amorphous carbon, and U.S. Pat. No. 6,027,833 A discloses a secondary cell having an electrode made of a carbon material as an active substance.SUMMARYAccordingly, it is an aspect of the present invention to provide an anode active material for a lithium secondary battery with improved performance, durability, and thermal stability.Further, it is an aspect of the present invention to provide an anode and a lithium secondary battery containing the anode active material.According to the present invention, there is provided an anode active material for a lithium secondary battery, comprising a secondary particle formed of primary particles. An average diameter of the primary particle is in a range of 5 μm to 15 μm, and an average diameter of the secondary particle is in a range of 10 μm to 25 μm. The primary particles and the secondary particles are made of an artificial graphite, and an I(110) / I(002) of the secondary particle is in a range of 0.0075 to 0.012.In example embodiments, the I(110) / I(002) of the secondary particle may be in a range of about 0.0075 to 0.01.In exemplary embodiments, the average diameter of the primary particle may be in a range of 7 μm to 10 μm.In exemplary embodiments, the average diameter of the secondary particle may be in a range of 13 μm to 20 μm.According to the present invention, there is provided a lithium secondary battery including an anode containing the above anode active material, a cathode, and a separation layer disposed between the anode and the cathode.In embodiments, a density of the anode may be at least 1.6 g / cm 3.In exemplary embodiments, the anode may further include a binder, and the amount of the binder may be equal to or less than 3 weight percent (wt %) based on the total amount of the anode active material and the binder.The anode active material for the lithium secondary battery according to exemplary embodiments described above may improve a performance-related property of a battery such as charge and discharge performance.The anode active material may also improve a life and thermal stability of the battery.BRIEF DESCRIPTION OF THE DRAWINGSExemplary embodiments will become more fully understood from the following detailed description taken in conjunction with the accompanying drawings. FIG. 1 is a diagram showing capacity recovery (%) with respect to weeks of lithium secondary batteries; and FIG. 2 is a diagram showing capacity retention with respect to cycles of the lithium secondary batteries.DETAILED DESCRIPTION OF THE EMBODIMENTSAccording to the present inventive concept, an anode active material for a lithium secondary battery includes a secondary particle having an average diameter of about 10 μm to about 25 μm formed by including primary particles having an average diameter of about 5 μm to about 15 μm. The primary particle is an artificial graphite and the secondary particle has an I(110) / I(002) in a range from about 0.075 to about 0.012. Accordingly, the anode active material for the lithium secondary battery can improve a performance-related property of a battery such as a charge and discharge performance, and can also improve a life, a low temperature property, and a high temperature storage property of the battery.Hereinafter, some example embodiments of the present inventive concept are provided. However, these embodiments are given only for illustrating the present inventive concept and should not be construed as limiting the scope of the present invention.Anode Active Material for Lithium Secondary BatteryThe anode active material (e.g., a negative electrode) for the lithium secondary battery may be used for absorbing or occluding lithium ions, and may include an amorphous graphite or a crystalline graphite. The crystalline graphite may include a natural graphite, an artificial graphite, etc. When the natural graphite is used as an anode active material, filter blocking may be caused during mixing, and a dispersion property of a slurry may be lowered, resulting in defective electrode production. The artificial graphite can be relatively free from the above problems and can have improved durability and high temperature storage property. However, the artificial graphite may be disadvantageous in terms of battery output or battery performance. Thus, the artificial graphite cannot be easily used in a high-performance device (e.g., a vehicle battery).According to the present inventive concept, an artificial graphite in which primary particles having an average diameter in a specific range are joined to a secondary particle having an average diameter in a specific range and an I(110) / I(002) in a specific range is used. Accordingly, when the artificial graphite is used in a battery, a battery output or a battery performance can be increased while maintaining an improved durability and high temperature storage properties. Further, an energy density of the battery can be improved by using the artificial graphite having an improved rolling property.According to the present invention, the secondary particle has an average diameter (D 50) in a range of about 10 μm to about 25 μm, and the secondary particle is formed including the primary particle having an average diameter in a range of about 5 μm to about 15 μm. The I(110) / I(002) of the secondary particle is in a range from about 0.0075 to about 0.012. Accordingly, the battery output or performance during charging and discharging of the battery may be increased while maintaining improved durability and high temperature storage properties as described above.When the average diameter of the primary particle is less than about 5 μm, a production yield in material production may be decreased, and a life of the battery may be deteriorated. When the average diameter of the primary particle exceeds about 15 μm, a size or a dimension of the secondary particle may be too large to be applied to the battery.The primary particles may be agglomerated to form the secondary particle. The number of primary particles for forming the secondary particle is not specifically limited. For example, 3 to 9 primary particles may be joined to form the secondary particle.When the average diameter of the secondary particle is less than about 10 μm, a pore size generated during the production of an electrode may be too small to cause poor impregnation in the battery. When the average diameter of the secondary particle exceeds about 25 μm, a thickness of the electrode may be excessively increased.In some embodiments, the average diameter of the primary particle may be in a range of about 7 μm to about 10 μm, so that the battery performance or the battery output can be further improved while suppressing a decrease in the life and the high-temperature storage properties.In some embodiments, the average diameter of the secondary particle may be in a range from about 13 μm to about 20 μm, so that application to the electrode may be facilitated.When an orientation of each primary particle in the artificial graphite is randomly dispersed, lithium ion transfer by the artificial graphite may be facilitated. According to exemplary embodiments of the present inventive concept, a particle orientation may be controlled to further improve battery output or battery performance.The particle orientation can be determined by X-ray diffraction (XRD) analysis. Specifically, an incident X-ray of a specific wavelength (λ) can produce diffraction reflections of different intensity at a specific incident angle (θ) or a diffraction angle (2θ). A ratio of specific reflexes may be calculated to determine the particle orientation.An I(002) mentioned in the present application indicates an intensity (height) of a reflection near a position 2θ=26.5 in X-ray diffraction analysis. An I(110) mentioned in the present application indicates an intensity (height) of a reflection near a position 2θ=77.5 in X-ray diffraction analysis. A ratio of I(110) relative to I(002) is represented by I(110) / I(002).Conditions well known in the art for X-ray diffraction analysis may be used. For example, the conditions shown below may be employed.X-ray: Cu-Kα, Kα1 wavelength: 1.540598 ÅGenerator voltage: 40 kV, tube current: 30 mAScan Area: 10-80 scans, Step Size: 0,026Ni filter, Soller gap (0.04 rad, 2 ea), diffracted anti-scattering gap 7.5 mmDivergence Slit: 1 / 4°, Anti-scattering slit: 1 / 2°Time per step: 100 sAccording to the present invention, the I(110) / I(002) of the secondary particle is in a range of about 0.0075 to about 0.012 from an aspect of improving the battery output or the battery performance. For example, the battery output or the battery performance during the charging and discharging of the battery can be improved within the above range. In some embodiments, the I(110) / I(002) of the secondary particle may preferably be in a range from about 0.0075 to about 0.01.When the I(110) / I(002) of the secondary particle is less than about 0.0075, the anode active material cannot be easily formed, and a basic electrochemical property (e.g., a capacity) of the artificial graphite may be deteriorated by an excessive control of the particle shape and size.The shape of the primary particle may be selected in consideration of adsorption and desorption of lithium ions, and is not specifically limited thereby. For example, a spherical shape or a plate shape may be used to improve the functional property of the anode active material in the lithium secondary battery.In some embodiments, the anode active material may additionally include a commonly used material without departing from the present inventive concept. For example, a silicon-based active material; a carbon-based active material such as crystalline carbon, amorphous carbon, a carbon composite material, a carbon fiber, etc.; lithium; an alloy of lithium and another element; a transition metal oxide; a material capable of doping and dedoping lithium; and / or a material capable of reversibly reacting with lithium and forming a compound may be used. These may be used alone or in combination thereof.The amorphous carbon may include, for example, hard carbon, coke, mesocarbon microbeads (MCMB)) calcined at a temperature of 1500° C. or less, mesophase pitch-based carbon fiber (MPCF), or the like. The crystalline carbon may include a natural graphite.The other element constituting the lithium alloy may include, for example, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.The silicon-based active material may include any material commonly used as the anode active material in the related art. For example, the silicon-based active material may include silicon, silicon oxide, a silicon alloy, a silicon-carbon composite, etc. These may be used alone or in combination thereof.The transition metal oxide, the material capable of doping and dedoping lithium, and the material capable of reversibly reacting with lithium to form the compound may include vanadium oxide, lithium vanadium oxide, Sn, SnO 2, a tin alloy composite, etc.AnodeThe anode active material according to the above-described embodiments may be mixed and stirred with, for example, a solvent, a binder, a conductive agent, a dispersant to prepare a mixture. The mixture may be coated on a metal-based collector and pressed and dried to form an anode in the lithium secondary battery.The solvent may include a non-aqueous solvent, e.g., N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.Non-limiting examples of the binder may include an organic-based binder such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or an aqueous binder such as styrene-butadiene rubber (SBR) combined with a thickener such as carboxymethyl cellulose (CMC).An amount of the binder may be adjusted appropriately to form an electrode. For example, the amount of the binder may be not greater than about 3 weight percent (wt %) based on the total amount of the anode active material and the binder, so that a resistance property of the electrode can be improved. A lower limit of the amount of the binder may be adjusted appropriately to maintain electrode operation. For example, the lower limit of the amount of the binder may be about 0.5 wt % or about 1 wt % based on the total amount of the anode active material and the binder.The conductive agent may include, for example, a conductive carbon-based material commonly used in the art.The metal-based collector may include a metal having high conductivity and may be capable of being easily coated with a mixture of the cathode or anode active material without reactivity in a voltage range of the battery. An anode collector may include, but is not limited to, copper or an alloy of copper. In some embodiments, the anode collector may include stainless steel, nickel, copper, titanium, or an alloy thereof, or the like, wherein copper or stainless steel is subjected to a surface treatment with carbon, nickel, titanium, or silver.According to exemplary embodiments, the anode active material may be applied to the anode collector by a method commonly used in the art. For example, the anode active material may be mixed and stirred with the solvent and optionally the binder, the conductive agent, the dispersant, etc. to form a mixture. The mixture may be applied to the anode collector by a spray coating method, an immersion method, etc., and dried and pressed to form the anode.An electrode density of the anode is not particularly limited. In some embodiments, the electrode density may be equal to or greater than about 1.5 g / cm 3. Non-limiting examples of an upper limit of the electrode density may be about 1.65 g / cm 3, 1,7 g / cm 3 or the like. Within the above range, performance, durability, and high-temperature storage properties of the battery can be improved.Lithium secondary batteryAccording to the present invention, a lithium secondary battery includes the anode including the aforementioned anode active material, a cathode, and an intermediate separation layer.The separation layer is disposed between the cathode and the anode to form an electrode structure. The electrode structure may be accommodated in a battery case, and then an electrolyte may be injected into the battery case to form the lithium secondary battery.Cathode CathodeThe cathode may include a widely used cathode active material in the art.The cathode active material may be applied to a cathode collector to form the cathode.The cathode collector may include, but is not limited to, aluminum or an alloy of aluminum. In some embodiments, the cathode collector may include stainless steel, nickel, aluminum, titanium, or an alloy thereof, or the like, wherein aluminum or stainless steel is subjected to a surface treatment with carbon, nickel, titanium, or silver.The cathode active material may include any material commonly used in the art, without particular limitation. For example, a composite oxide containing lithium and at least one of cobalt, manganese, or nickel may preferably be used. In some embodiments, lithium-containing compounds represented by the following formulas may be used.Li x Mn 1-y M y A 2Li x Mn 1-y M y O 2-z X zLi x Mn 2 O 4-z X zLi x Mn 2-y M y M' z A 4Li x Co 1-y M y A 2Li x Co 1-y M y O 2-z X zLi x Ni 1-y M y A 2Li x Ni 1-y M y O 2-z X zLi x Ni 1-y Co y O 2-z X zLi x Ni 1-y-z Co y M z AαLi x Ni 1-y-z Co y M z O2-αXαLi x Ni 1-y-z Mn y M z AαLi x Ni 1-y-z Mn y M z O2-αXαIn the above formulas, 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, and M and M' may be the same as or different from each other. M and M' may be selected from Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V or rare earth elements. A may be selected from O, F, S or P and X may be selected from F, S or P.The cathode active material may be applied to the cathode collector by a method commonly used in the art. For example, the cathode active material may be mixed and stirred with a solvent and optionally a binder, a conductive agent, a dispersant, or the like to obtain a mixture. The mixture may be applied to the cathode collector and pressed, and may be dried to form the cathode.The solvent may include a non-aqueous solvent, e.g., N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.Non-limiting examples of the binder may include an organic-based binder such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or an aqueous binder such as styrene-butadiene rubber (SBR) combined with a thickener such as carboxymethyl cellulose (CMC).The conductive agent may include, for example, a conductive carbon-based material commonly used in the art.Release LayerThe release layer may include a conventional porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butane copolymer, ethylene / hexene copolymer or ethylene / methacrylate copolymer, or the like. These may be used alone or in combination thereof. The release layer may include a non-woven fabric formed of a conventional porous non-woven fabric, a high melting temperature glass fiber, a polyethylene terephthalate fiber, etc. The separation layer may be supplied to the battery by winding, lamination with the electrode, or folding.Nonaqueous ElectrolyteA non-aqueous electrolyte may include a lithium salt and an organic solvent.The lithium salt commonly used in a lithium secondary battery may be used without particular limitation, and may be represented by Li + X -.Non-limiting examples of anions of the lithium salt may include F -, Cl -, Br -, I -, NO3 -, N(CN) 2-, BF 4-, ClO 4-, PF 6-, ( CF 3)2 PF4NER82_, (CF3)3PF3NER86_, (CF3)4PF2NER90_, (CF3)5PF-, (cf_ner94_)_ner95_P -, CF 3 SO 3-, CF 3 CF 2 SO 3-, ( CF 3 SO 2)2 N -, ( FSO 2)2 N-, CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (cf_ner123_so_ner124_)_ner125_C -, CF 3( CF 2)7 SO 3-, CF 3 CO 2-, CH 3 CO 2-, SCN -, ( CF 3 CF2SO2)2N-, or the like.The organic solvent usually used in an electrolyte for a lithium secondary battery can be used without particular limitation. For example, the organic solvent may include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, fluoroethylene carbonate (FEC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These may be used alone or in combination thereof.The nonaqueous electrolyte may be supplied between the electrode structure including the cathode, the anode, and the separation layer, so that the lithium secondary battery is obtained.The shape of the lithium secondary battery is not particularly limited. For example, the lithium secondary battery may be made of a cylindrical type using a can, a polygonal type, a pouch type or a button type.Hereinafter, preferred embodiments are proposed to describe the present invention more concretely. However, the following examples are given only for illustrating the present invention, and those skilled in the art will understand that various changes and modifications are possible within the scope and spirit of the present invention. Such changes and modifications are to be properly included in the appended claims.Examples and Comparative ExamplesExample 1An artificial graphite was milled using coke and a impact type mill to form a primary particle whose average diameter (D was 50) 7,5 μm.The primary particles were agglomerated using pitch to form a secondary particle, and then a thermal treatment was performed at 3000° C. to form an anode active material for a lithium secondary battery (D 50= 17,3 μm, La( 100)=31, Lc( 002)=22, I( 110) / I( 002)=0.0108).Example 2An anode active material for the lithium secondary battery was formed by a method similar to that of Example 1, except that the average diameter of the primary particle was 7.2 μm and that in the secondary particle, D was 50= 15,3 μm, La(100)=23, Lc(002)=21, I(110) / I(002)=0.0084.Comparative Example 1An anode active material for the lithium secondary battery was formed by a method similar to that of Example 1, except that D was 50= 19,0 μm, La(100)=27, Lc(002)=20, and I(110) / I(002)=0.0126, and that an artificial graphite which was not an array of a plurality of particles was used.Comparative Example 2An anode active material for the lithium secondary battery was formed by a method similar to that of Example 1, except that D was 50= 11,9 μm, La(100)=79, Lc(002)=19, and I(110) / I(002)=0.0100, and that a natural graphite which was not an array of a plurality of particles was used.Comparative Example 3An anode active material for the lithium secondary battery was formed by a method similar to that of Example 1, except that the average diameter (D 50) of the primary particle was 9.4 μm, and that in the secondary particle, D was 50= 13,8 μm, La(100)= 60, Lc(002)= 25, I(110) / I(002)=0.0169.Comparative Example 4An anode active material for the lithium secondary battery was formed by a method similar to that of Example 1, except that the average diameter (D 50) of the primary particle was 16 μm, and that in the secondary particle, D was 50= 20 μm, La(100)= 70, Lc(002)=20, I(110) / I(002)=0.0110.Comparative Example 5An anode active material for the lithium secondary battery was formed by a method similar to that of Example 1, except that the average diameter (D 50) of the primary particle was 3 μm and that in the secondary particle, D was 50= 12 μm, La(100)= 45, Lc(002)= 27, I(110) / I(002)=0.0900.Comparative Example 6: The average diameter of the secondary particle was outside the range according to the present inventive conceptAn anode active material for the lithium secondary battery was formed by a method similar to that of Example 1, except that the average diameter (D 50) of the primary particle was 12 μm, and that in the secondary particle, D was 50= 26 μm, La(100)= 80, Lc(002)= 40, I(110) / I(002)=0.097.The properties of the anode active materials are listed in Table 1 below. Table 1 Table 1Example 1Particle Arrangement7,517,30,0108Example 2Particle Arrangement7,215,30,0084Comparative Example 1Conventional artificial graphite19,0-0,0126Comparative Example 2Natural graphite11,9-0,0100Comparative Example 3Particle Arrangement9,413,80,0169Comparative Example 4Particle Arrangement16200,0110Comparative Example 5Particle Arrangement3120,0900Comparative Example 6Particle Arrangement12260,097Production ExampleAnode92,2 By weight of the anode active materials described in the Examples and Comparative Examples, 2.8 wt % of a PVDF-based binder, and 5 wt % of dimethyl sulfoxide (DMSO) were mixed to form an anode slurry. The anode slurry was coated on a copper substrate, dried and pressed to form an anode. The density of the anode was 1.6 g / cm 3.Cathode CathodeLi 1.0 Ni 0.6 Co 0.2 Mn 0.2 O 2 as a cathode active material, Denka black as a conductive agent, PVDF as a binder, and N-methylpyrrolidone as a solvent were used in a weight ratio of 46:2.5:1.5:50 to prepare a cathode mixture. The cathode mixture was coated on an aluminum substrate, followed by drying and pressing to produce a cathode.A battery batteryThe cathode and anode prepared above were scored and stacked. A separator layer (polyethylene, 25 μm) was interposed between the cathode and the anode to form a battery structure. Tab portions of the cathode and anode were welded.The electrode structure was placed in a pouch and the tab portions were placed on a sealing portion. Three sides of the pouch except for an injection area for an electrolyte were sealed. The electrolyte was supplied through the injection area and the remaining side of the bag was sealed. The electrode structure was impregnated for more than 12 hours. The electrolyte used herein was formed by preparing a 1M LiPF 6- solution with a mixed solvent of ethylene carbonate (EC) / ethylmethyl carbonate (EMC) / diethyl carbonate (DEC) (25 / 45 / 30; volume ratio) and adding 1 wt % vinylene carbonate (VC), 0.5 wt % 1,3-propene sultone (PRS), and 0.5 wt % lithium bis(oxalato)borate (LiBO).Then, precharge was performed by applying a current corresponding to 0.25 C (2.5 A) for 36 minutes. After 1 hour, degassing, aging for more than 24 hours, and formation charge / discharge were performed (charge conditions: CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharge conditions: CC 0.2C 2.5V CUT-OFF).Next, a standard charge / discharge operation was performed (charge condition: CC-CV 0.5C 4.2V 0.05C CUT-OFF, discharge condition: CC 0.5C 2.5V CUT-OFF).Experimental Example 1A discharge power (10 seconds), a charge power (10 seconds), a discharge HPPC (Hybrid Pulse Power Characterization), a charge HPPC, a discharge DC-IR, and a charge DC-IR of the lithium secondary battery manufactured as above were measured. The results are listed in Table 2 below.<Messung of 10-Second Discharge Power>Under control of a discharge current in a state of 50% SOC, a current when a battery voltage was lowered to 2.5 V in 10 seconds was measured, and an average voltage was measured. The discharge power was determined as multiplication of the current and the average voltage.<Messung of 10-Second Charge Performance>Under control of a charge current in a state of 50% SOC, a current when a battery voltage was increased to 4.3 V in 10 seconds was measured, and an average voltage was measured. The charge power was determined as multiplication of the current and the average voltage.<Messung of Discharge / Charge DC-IR>Discharge / charge currents corresponding to 0.2 C / 0.5 C / 1 C / 2 C / 3 C were flowed to cells, and each voltage drop was measured. The measured values were plotted linearly on a V-I graph, and a peak of the graph was determined as resistance. [Table 2] [Table 2]Example 1565,3661,1265023124,064,17Example 2585,7658,1274624133,944,00Comparative Example 1547,9657,7249822244,314,33Comparative Example 2592,7657,7284025043,783,83Comparative Example 3550,3644,0256322524,224,29Comparative Example 4530629256022304,434,7Comparative Example 5539633197020004,44,7Comparative Example 6522622239021004,564,9Referring to Table 2, the lithium secondary batteries of the examples exhibited improved results relative to the lithium secondary batteries of Comparative Example 1 formed of the conventional artificial graphite.The lithium secondary battery of Comparative Example 2 formed of the natural graphite exhibited improved results in terms of performance, but exhibited inferior results in terms of high-temperature storage and durability as described in Experimental Examples 2 and 3 below.Experimental Example 2The high temperature storage properties at 50° C. were evaluated as described below using the lithium secondary batteries according to Example 1, Example 2, Comparative Example 1, Comparative Example 2 and Comparative Example 3.< Storage Property>Cells having a high capacity of at least 10 Ah were prepared using the same cathode. The cells were fully charged by charging them to 4.2 V at a rate of 1 C in a constant current (CC), and then applying a constant voltage (CV) to 0.1 C. The fully charged cells were left in a chamber at a constant temperature (60°C) for a predetermined time. Subsequently, the cells were taken out of the chamber and cooled, and the capacities of the cells were measured.FIG. 1 is a diagram showing capacity recovery (%) with respect to weeks of lithium secondary batteries.Referring to FIG. 1, the reductions in capacity recovery (%) in the lithium secondary batteries of the examples over a predetermined period of time were smaller than those in the lithium secondary batteries of Comparative Examples 2 or 3.Experimental Example 3The durability characteristics were evaluated as described below using the lithium secondary batteries according to Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3.<Lebensdauer Property>Cells having a high capacity of at least 10 Ah were prepared using the same cathode. The cell life evaluation was performed in a chamber at a constant temperature (25° C.) using conditions of the DOD90 region and a 1 C charge / 1 C discharge rate.FIG. 2 is a diagram showing capacity retention with respect to cycles of the lithium secondary batteries.Referring to FIG. 2, the reductions in retention (%) in the lithium secondary batteries of the examples over a predetermined period of time were smaller than those in the lithium secondary batteries of Comparative Examples 2 or 3.Therefore, the lithium secondary batteries of the examples exhibited improved performance, high-temperature storage, and durability properties relative to those of the lithium secondary batteries of the comparative examples.

Claims

An anode active material for a lithium secondary battery, comprising a secondary particle formed of primary particles, wherein an average diameter of the primary particles is in a range of 5 μm to 15 μm, and an average diameter of the secondary particle is in a range of 10 μm to 25 μm, wherein the primary particles and the secondary particle are made of an artificial graphite, and an I(110) / I(002) of the secondary particle is in a range of 0.0075 to 0.012.The anode active material for a lithium secondary battery according to claim 1, wherein the I(110) / I(002) of the secondary particle is in a range of 0.0075 to 0.01.The anode active material for a lithium secondary battery according to claim 1, wherein the average diameter of the primary particles is in a range of 7 μm to 10 μm.The anode active material for a lithium secondary battery according to claim 1, wherein the average diameter of the secondary particle is in a range of 13 μm to 20 μm.A lithium secondary battery comprising: an anode containing the anode active material according to claim 1; a cathode; and a separation layer disposed between the anode and the cathode.The lithium secondary battery according to claim 5, wherein the density of the anode is at least 1.6 g / cm 3.The lithium secondary battery according to claim 5, wherein the anode further contains a binder, and an amount of the binder is equal to or less than 3 weight percent (wt%), based on a total amount of the anode active material and the binder.

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