FORM 2 THE PATENTS ACT, 1970 (39 of 1970) 5 & THE PATENT RULES, 2003 COMPLETE SPECIFICATION 10 (See Section 10 and Rule 13) 15 Title of invention: HIGH-CAPACITY ANODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY, MANUFACTURING METHOD THEREFOR, AND LITHIUM SECONDARY BATTERY COMPRISING SAME 20 APPLICANT: LG CHEM, LTD. 25 A Company incorporated in South Korea Having Address: 128, Yeoui-daero, Yeongdeungpo-gu, Seoul 150-721, Republic of Korea 30 The following specification particularly describes the invention and the manner in which it is to be performed. 2 TECHNICAL FIELD The present invention relates to an anode active material for a lithium secondary battery and a lithium secondary battery using the same. More specifically, the present invention relates to an anode active material having high capacity, which can be controlled in volume expansion. 5 This application claims priority to Korean Patent Application No. 10-2012-0141076 filed in the Republic of Korea on December 6, 2012, the entire contents of which are incorporated herein by reference. 10 Also, this application claims priority to Korean Patent Application No. 10-2013- 0147718 filed in the Republic of Korea on November 29, 2013, the entire contents of which are incorporated herein by reference. BACKGROUND ART 15 Recently, there has been an increasing interest in energy storage technology. Electrochemical devices have been widely used as energy sources in the fields of cellular phones, camcorders, notebook computers, PCs and electric cars, resulting in intensive research and development into them. In this regard, electrochemical devices are one of the subjects of great interest. Particularly, development of rechargeable secondary batteries has 20 been the focus of attention. Recently, research and development of such batteries are focused on the designs of new electrodes and batteries to improve capacity density and specific energy. Many secondary batteries are currently available. Among these, lithium secondary 25 batteries developed in the early 1990’s have drawn particular attention due to their advantages of higher operating voltages and much higher energy densities than conventional aqueous electrolyte-based batteries, for example, Ni-MH, Ni-Cd, and H2SO4-Pb batteries. Generally, a lithium secondary battery is prepared by using a cathode and an anode which are each made of a material capable of intercalating and disintercalating lithium ions, and filling 30 an organic or polymer electrolyte solution between the cathode and the anode, and the battery produces electrical energy by oxidation and reduction when the lithium ions are intercalated and disintercalated in the cathode and the anode. 3 In lithium secondary batteries which are currently available, an anode is mostly made of carbon-based materials as an electrode active material. Particularly, graphite which has been commercially available has a real capacity of about 350 to 360 mAh/g which approaches its theoretical capacity of about 372 mAh/g. However, a carbon-based material such as graphite having such a capacity does not meet the demand for high-capacity lithium 5 secondary batteries as an anode active material. In order to meet such a demand, attempts have been made to use metals as an anode active material, for example, Si and Sn that have a higher charge/discharge capacity than the carbon materials and that allow electrochemical alloying with lithium. 10 However, this metal-based electrode active material has a great change in volume during charging/discharging, which may cause cracks and micronization to the active material. Secondary batteries using this metal-based anode active material may suddenly be deteriorated in capacity and have reduced cycle life during repeated charging/discharging 15 cycles. In order to reduce cracks and micronization generated from the use of the metal-based anode active material, an oxide of a metal such as Si and Sn has been used as an anode active material. However, the oxide of a metal such as Si and Sn has low electrical conductivity and 20 requires a conductive coating on the surface thereof. Such a conductive coating may be carried out by a carbon-coating method which specifically comprises pyrolyzing a carbon precursor of a solid, liquid or gas state. In this method, Si crystals present in the Si oxide grow due to heat applied during coating, from which the thickness of the anode active material increases and the life characteristic of secondary batteries deteriorates during lithium 25 intercalation/disintercalation. DISCLOSURE Technical Problem 30 Therefore, it is an object of the present invention to provide an anode active material which can provide high capacity, can be controlled in its thickness increase and volume expansion and can prevent the deterioration of life characteristics, a method of preparing the 4 anode active material, and an anode and a secondary battery comprising the anode active material. Technical Solution In order to achieve the object, in accordance with one aspect of the present invention, 5 there is provided an anode active material, comprising an amorphous SiOx-C composite with a core-shell structure consisting of a core comprising particles of a silicon oxide (SiOx) free of Si crystals and a shell which is a coating layer formed on at least a part of the surface of the core and comprising a carbon material. 10 In the anode active material according to one embodiment of the present invention, the silicon oxide (SiOx) may satisfy that x is 1 or less (x  1), preferably x is 1 (x = 1). That is, the preferred silicon oxide is SiO. Also, in the anode active material according to one embodiment of the present 15 invention, the silicon oxide (SiOx) particles free of Si crystals may have an average diameter of 0.1 to 30 m, and a specific surface area of 0.5 to 100 m2/g, the specific surface area being measured by the BET method. Preferably, the shell may be present in an amount of 1 to 30 parts by weight based on 20 100 parts by weight of the core, and may have a thickness of 0.01 to 5 m. Also, the present invention provides an anode for a lithium secondary battery, comprising a current collector and an anode active material layer formed on at least one surface of the current collector and comprising an anode active material, wherein the anode 25 active material comprises the anode active material defined in the present invention. Further, the present invention provides a lithium secondary battery, comprising a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the anode is the anode defined in the present invention. 30 Furthermore, the present invention provides a method of preparing an anode active material comprising an amorphous SiOx-C composite with a core-shell structure, comprising: 5 providing particles of a silicon oxide (SiOx) as a core, and coating a carbon precursor containing carbon on at least a part of the surface of the core, followed by heat treatment to form a shell as a coating layer, wherein the heat treatment is carried out at a temperature less than 1000 C, preferably a temperature of 900 C or less. Also, the present invention provides an anode active material prepared by the above method. 5 Advantageous Effects The anode active material of the present invention comprises an amorphous SiOx-C composite with a core-shell structure consisting of a core comprising particles of a silicon oxide (SiOx) free of Si crystals and a shell which is a coating layer formed on at least a part 10 of the surface of the core and comprising a carbon material, thereby providing high capacity and effectively inhibiting volume expansion which has been caused in the use of Si, to improve life characteristics, and eventually providing a lithium secondary battery having such characteristics. 15 DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate preferred embodiments of the present invention and, together with the foregoing disclosure, serve to provide further understanding of the technical spirit of the present invention. However, the present invention is not to be construed as being limited to the drawings. 20 FIG. 1 shows X-ray diffraction curves for anode active materials prepared in Example 1 and Comparative Example 1. BEST MODE Hereinafter, the present invention will be described in detail. Prior to the description, 25 it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the embodiments and the drawings proposed herein is just a 30 preferable example for the purpose of illustrations only, not intended to limit the scope of the disclosure, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the disclosure. 6 The anode active material of the present invention is an amorphous SiOx-C composite with a core-shell structure consisting of a core comprising particles of a silicon oxide (SiOx) free of Si crystals and a shell which is a coating layer formed on at least a part of the surface of the core and comprising a carbon material. 5 Anode active material using a silicon oxide have high capacity but may not satisfy a proper degree of electrical conductivity which is an important property capable of facilitating the transfer of electrons in electrochemical reactions. In order to solve this problem, the present inventors have endeavored to develop an anode active material having both high capacity and good electrical conductivity and found that an amorphous SiOx-C composite 10 with a core-shell structure, which consists of a core comprising particles of a silicon oxide (SiOx) free of Si crystals and a shell which is a coating layer formed on at least a part of the surface of the core and comprising a carbon material, can have a proper degree of electrical conductivity by carbon coating and can be controlled in thickness expansion by the silicon oxide (SiOx) free of Si crystals to prevent the deterioration of life characteristics and have 15 high capacity. As used herein, the term “silicon oxide (SiOx) free of Si crystals” refers to a silicon oxide (SiOx) in which Si crystals are not present. Specifically, the Si crystals mean to include microcrystals having a particle diameter of 5 to 50 nm and crystals having a particle 20 diameter greater than such range. According to one aspect of the present invention, in the silicon oxide (SiOx), x is 1 or less (x  1), preferably x is 1 (x = 1). That is, the preferred silicon oxide is SiO. 25 According to one aspect of the present invention, the silicon oxide (SiOx) particles free of Si crystals may have an average diameter of 0.1 to 30 m, and a specific surface area of 0.5 to 100 m2/g, the specific surface area being measured by the BET method. Preferably, the silicon oxide (SiOx) particles free of Si crystals have an average diameter of 0.1 to 10 m and a BET specific surface area of 1.5 to 50 m2/g. 30 7 In the present invention, the shell, i.e., the coating layer comprising a carbon material, is formed on at least a part of the surface of the core which comprises particles of the silicon oxide (SiOx) free of Si crystals. According to one aspect of the present invention, the shell may be present in an 5 amount of 1 to 30 parts by weight, preferably 2 to 10 parts by weight, based on 100 parts by weight of the core. When the amount of the shell satisfies such a range, uniform electrical conductivity can be obtained and the volume expansion of the anode active material can be minimized. 10 Also, according to one aspect of the present invention, the shell may have a thickness of 0.01 to 5 m, preferably 0.02 to 1 m. When the thickness of the shell satisfies such a range, uniform electrical conductivity can be obtained and the volume expansion of the anode active material can be minimized. 15 The present invention also provides a method of preparing an anode active material comprising an amorphous SiOx-C composite with a core-shell structure, comprising: providing particles of a silicon oxide (SiOx) as a core, and coating a carbon precursor containing carbon on at least a part of the surface of the core, followed by heat treatment to form a shell as a coating layer, wherein the heat treatment is carried out at a temperature less 20 than 1000 C. More preferably, the heat treatment is carried out at a temperature of 900 C or less. Under the condition of such heat treatment temperature, the growth of Si crystals can be effectively controlled. 25 Specifically, a core comprising silicon oxide particles is provided, and the core is coated with a carbon material on at least a part of the surface thereof, thereby preparing an amorphous SiOx-C composite according to the present invention. 30 The resulting coating layer as a shell is formed in an amount of 1 to 30 parts by weight, preferably 2 to 10 parts by weight, based on 100 parts by weight of the core, and the shell has a thickness of 0.01 to 5 m, preferably 0.02 to 1 m. 8 The coating of a carbon material on the core may be carried out by coating a carbon precursor, followed by heat treatment, to carbonize the carbon precursor. Such a coating may be made by a wetting method, a drying method, or both. For example, as the carbon precursor, a carbon-containing gas such as methane, ethane, propane, acetylene and ethylene may be used, or a liquid carbon precursor such as toluene which is a liquid phase at room 5 temperature may be used by vaporizing by way of chemical vapor deposition (CVD). Also, as the precursor of amorphous carbon, resins such as phenol resins, naphthalene resins, polyvinyl alcohol resins, urethane resins, polyimide resins, furan resins, cellulose resins, epoxy resins and polystyrene resins; and petroleum-based pitches, tar or low molecular weight heavy oils may be used. Further, sucrose may be used for carbon coating. 10 In the method of the present invention, the heat treatment is carried out at a temperature less than 1000 C, preferably a temperature of 900 C or less, for example, 500 to 1000 C, preferably 600 to 1000 C, or 500 to 900 C, preferably 600 to 900 C. If the temperature of heat treatment exceeds 1000 C, Si crystals increase in the core comprising 15 silicon oxide particles, which may not be effective in controlling volume expansion during the intercalation and disintercalation of lithium ions. The anode active material of the present invention thus prepared can be used in the preparation of an anode according to a conventional method known in the art. Also, in the 20 present invention, a cathode may be prepared by a conventional method known in the art, similar to the preparation of an anode. For example, the anode active material of the present invention is mixed with a binder, a solvent, and optionally a conducting material and a dispersing agent, followed by stirring, to produce a slurry and applying the slurry on a current collector, followed by compression, to prepare an electrode. 25 The binder which may be used in the present invention includes various kinds of binder polymers, for example, polyvinylidene fluoride-co-hexafluoro propylene (PVDF-co-HFP), polyvinylidenefluoride, polyvinylidene fluoride-co-trichloro ethylene, polyvinylidene fluororide-co-chlorotrifluoro ethylene, polymethyl methacrylate, polyacrylonitrile, 30 polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalchol, cyanoethyl cellulose, cyanoethyl sucrose, pulluan, carboxyl 9 methyl cellulose (CMC), acrylonitrile-styrene-butadiene copolymer, polyimide, polyvinylidenefluoride, polyacrylonitrile, stryrene butadiene rubber (SBR) and a mixture thereof, but the present invention is not limited thereto. A cathode active material which may be used in the present invention preferably 5 includes a lithium-containing transition metal oxide, for example, any one selected from the group consisting of LixCoO2 (0.5 20 - Charge condition: Charging of the batteries was conducted up to 5 mV at constant current, and completed when a current density reached 0.005C. - Discharge condition: Discharging of the batteries was conducted up to 1.0 V at constant current (In the first cycle of charging and discharging, discharging was conducted up to 1.5V). 25 - In first cycle of charging and discharging, 0.1C/0.1C of charging/discharging and then 0.1C/0.1C of charging/discharging were conducted. After 50 cycles, batteries were disintegrated at their lithiated state, and salt and remaining electrolyte solution in the anode were removed, followed by measuring the thickness of the anode. 30 15 Table 1 Discharge Capacity (mAh/g) Capacity before charging (mAh/g) Normalized Capacity(%) @ 50th cycle Expansion (1.6 g/cc) Ex. 1 535 636 86 45% Com. Ex. 1 534 634 64 80% As can be seen from Table 1 showing the results of charging/discharging test, the anode active material of Example 1 was effectively controlled in volume expansion to 5 provide good life characteristics, as compared with that of Comparative Example 1. WE CLAIM: 1. An anode active material, comprising an amorphous SiOx-C composite with a core-shell structure consisting of a core comprising particles of a silicon oxide (SiOx) free of Si crystals 5 and a shell which is a coating layer formed on at least a part of the surface of the core and comprising a carbon material. 2. The anode active material of claim 1, wherein the silicon oxide (SiOx) satisfies that x is 1 or less (x  1). 10 3. The anode active material of claim 1, wherein the silicon oxide (SiOx) is SiO satisfying that x is 1 (x = 1). 4. The anode active material of claim 1, wherein the silicon oxide (SiOx) particles free of Si 15 crystals have an average diameter of 0.1 to 30 m. 5. The anode active material of claim 1, wherein the silicon oxide (SiOx) particles free of Si crystals have a specific surface area of 0.5 to 100 m2/g, the specific surface area being measured by the BET method. 20 6. The anode active material of claim 1, wherein the shell is present in an amount of 1 to 30 parts by weight based on 100 parts by weight of the core. 7. The anode active material of claim 1, wherein the shell has a thickness of 0.01 to 5 m. 25 8. An anode for a lithium secondary battery, comprising a current collector and an anode active material layer formed on at least one surface of the current collector and comprising an anode active material, wherein the anode active material comprises the anode active material defined in any 30 one of claims 1 to 7. 9. A lithium secondary battery, comprising a cathode, an anode, and a separator interposed 17 between the cathode and the anode, wherein the anode is defined in claim 8. 10. A method of preparing an anode active material comprising an amorphous SiOx-C composite with a core-shell structure, comprising: 5 providing particles of a silicon oxide (SiOx) as a core; and coating a carbon precursor containing carbon on at least a part of the surface of the core, followed by heat treatment to form a shell as a coating layer, wherein the heat treatment is carried out at a temperature less than 1000 C. 10 11. The method of claim 1, wherein the heat treatment is carried out at a temperature of 900 C or less. 12. An anode active material prepared by the method according to claim 10.