TECHNICAL FIELD Cross-reference to Related Applications [0001] This application claims the benefit of the priority of 10 Korean Patent Application No. 10-2020-0117153, filed on September 11, 2020, the disclosure of which is incorporated herein in its entirety by reference. Technical Field [0002] The present invention relates to a negative electrode 15 active material, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode, and specifically, the negative electrode active material is characterized by including silicon-based composite particles containing SiOx (0 [0020] A negative electrode active material according to an 20 embodiment of the present invention includes silicon-based composite particles containing SiOx (0 [0052] A negative electrode according to another embodiment of the present invention may include a negative electrode active 10 material, wherein the negative electrode active material is the same as the negative electrode active material of the abovedescribed embodiments. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode 15 current collector. The negative electrode active material layer may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a binder and/or a conductive agent. [0053] The negative electrode current collector is not 20 particularly limited so long as it has conductivity without causing adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel that is surface-treated with one of carbon, nickel, titanium, silver, or the like may be 25 used. Specifically, a transition metal that adsorbs carbon well, 16 such as copper and nickel, may be used as the current collector. The current collector may have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto. [0054] The binder may include at least one selected from the 5 group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, 10 polytetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene monomer (EPDM), a sulfonated EPDM, a styrene-butadiene rubber (SBR), a fluorine rubber, poly acrylic acid, and a material having hydrogen thereof substituted with lithium (Li), sodium (Na), or calcium (Ca), or may include various 15 copolymers thereof. [0055] The conductive agent is not particularly limited as long as it has conductivity without causing adverse chemical changes in the battery, and, conductive materials, for example, graphite such as natural graphite and artificial graphite; carbon black 20 such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon powder; metal powder such as aluminum powder, and nickel powder; conductive whiskers such as zinc oxide 17 whiskers and potassium titanate whiskers; conductive metal oxide such as titanium oxide; or polyphenylene derivatives, may be used. [0056] 5 [0057] The secondary battery according to another embodiment of the present invention may include the negative electrode of the above-described embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a 10 separator disposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode is the same as the above-described negative electrode. Since the negative electrode has been described above, detailed descriptions thereof will be omitted. 15 [0058] The positive electrode may include a positive electrode current collector and a positive electrode active material layer which is formed on the positive electrode current collector and includes a positive electrode active material. [0059] In the positive electrode, the positive electrode current 20 collector is not particularly limited as long as it has conductivity without causing adverse chemical changes in the battery, and, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel that is surface-treated with one of carbon, nickel, titanium, silver, or 25 the like may be used. Also, the positive electrode current 18 collector may typically have a thickness of 3 μm to 500 μm and may have a surface with fine roughness to improve adhesion to the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as 5 a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric body. [0060] The positive electrode active material may be a typically used positive electrode active material. Specifically, the positive electrode active material may include a layered compound, 10 such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxides such as LiFe3O4; lithium manganese oxides such as Li1+c1Mn2-c1O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, 15 and Cu2V2O7; nickel (Ni)-site type lithium nickel oxide expressed by a chemical formula of LiNi1-c2Mc2O2 (where M is at least one selected from the group consisting of cobalt (Co), manganese (Mn), aluminum (Al), copper (Cu), iron (Fe), magnesium (Mg), boron (B), and gallium (Ga), and c2 satisfies 0.01≤c2≤0.3); lithium manganese 20 composite oxide expressed by a chemical formula of LiMn2-c3Mc3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, chromium (Cr), zinc (Zn), and tantalum (Ta), and c3 satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and 25 LiMn2O4 having a part of Li being substituted with alkaline earth 19 metal ions, but the positive electrode active material is not limited thereto. The positive electrode may be Li-metal. [0061] The positive electrode active material layer may include a positive electrode conductive agent and a positive electrode 5 binder as well as the above-described positive electrode active material. [0062] In this case, the positive electrode conductive agent is used for providing conductivity to the electrode, wherein any conductive agent may be used without particular limitation as long 10 as it has electronic conductivity without causing adverse chemical changes in the battery. Specific examples of the conductive agent may be graphite such as natural graphite or artificial graphite; carbon based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal 15 black, and carbon fibers; powder or fibers of metal such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one thereof or a mixture of two 20 or more thereof may be used. [0063] Also, the positive electrode binder functions to improve binding between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the 25 binder may be polyvinylidene fluoride (PVDF), polyvinylidene 20 fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, 5 polypropylene, an ethylene-propylene-diene monomer (EPDM), a sulfonated EPDM, a styrene-butadiene rubber (SBR), a fluorine rubber, or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used. [0064] The separator separates the negative electrode and the 10 positive electrode and provides a movement path of lithium ions, wherein any separator may be used as the separator without particular limitation as long as it is typically used in a secondary battery, and particularly, a separator having high moisture-retention ability for an electrolyte as well as low 15 resistance to the transfer of electrolyte ions may be used. Specifically, a porous polymer film, for example, a porous polymer film prepared from a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate 20 copolymer, or a laminated structure having two or more layers thereof may be used. In addition, a typical porous non-woven fabric, for example, a non-woven fabric formed of high melting point glass fibers, polyethylene terephthalate fibers, or the like may be used. Furthermore, a coated separator including a ceramic 25 component or a polymer material may be used in order to secure 21 heat resistance or mechanical strength, and may be optionally used in a single-layered or a multi-layered structure. [0065] The electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a 5 gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte which may be used in the preparation of the lithium secondary battery, but is not limited thereto. [0066] Specifically, the electrolyte may include a non-aqueous 10 organic solvent and a metal salt. [0067] For example, aprotic organic solvents, such as N-methyl- 2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxy ethane, tetrahydrofuran, 2-methyl tetrahydrofuran, 15 dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, a dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2- imidazolidinone, a propylene carbonate derivative, a 20 tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate, may be used as the non-aqueous organic solvent. [0068] Particularly, among the carbonate-based organic solvents, since ethylene carbonate and propylene carbonate, as cyclic carbonate, are highly viscous organic solvents and well dissociate 25 a lithium salt due to high permittivity, the cyclic carbonate may 22 be preferably used. Since an electrolyte having high electrical conductivity may be prepared when the above cyclic carbonate is mixed with low viscosity, low permittivity linear carbonate, such as dimethyl carbonate and diethyl carbonate, in an appropriate 5 ratio and used, the cyclic carbonate may be more preferably used. [0069] A lithium salt may be used as the metal salt, and the lithium salt is a material that is readily soluble in the nonaqueous electrolyte solution, wherein, for example, at least one selected from the group consisting of F-, Cl-, I-, NO3 -, N(CN)2 -, BF4 -, ClO4 -, PF6 -, (CF3)2PF4 -, (CF3)3PF3 -, (CF3)4PF2 10 -, (CF3)5PF-, (CF3)6P-, CF3SO3 -, CF3CF2SO3 -, (CF3SO2)2N-, (FSO2)2N-, CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3 -, CF3CO2 -, CH3CO2 -, SCN-, and (CF3CF2SO2)2N- may be used as an anion of the lithium salt. [0070] At least one additive, for example, a haloalkylene 15 carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol 20 dialkyl ether, an ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride, may be further included in the electrolyte in addition to the above-described electrolyte components for the purpose of improving life characteristics of the battery, preventing a decrease in battery capacity, and improving discharge 25 capacity of the battery. 23 [0071] According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the battery module are provided. 5 Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability, and high cycle characteristics, the battery module and the battery pack may be used as a power source of a medium and large sized device selected from the group consisting of an electric vehicle, a hybrid electric 10 vehicle, a plug-in hybrid electric vehicle, and a power storage system. [0072] Hereinafter, preferred examples will be provided for better understanding of the present invention. It will be apparent 15 to those skilled in the art that these examples are only provided to illustrate the present invention and various modifications and alterations are possible within the scope and technical spirit of the present invention, and such modifications and alterations are definitely included in the attached claims. 20 [0073] Examples and Comparative Examples [0074] Example 1: Preparation of Negative Electrode Active Material 24 [0075] Powder (94 g) in which Si and SiO2 was mixed in a mole ratio of 1:1 and Mg (6 g) were mixed in a reaction furnace, and then the resulting mixture was heated under vacuum at a sublimation temperature of 1,400 °C. Then, the mixed gas of Si, SiO2, and Mg 5 gasified was reacted in a cooling zone in a vacuum state having a cooling temperature of 800 °C to cooled to be a solid phase. Then, a heat-treatment was performed in an inert atmosphere at a temperature (further heat-treatment temperature) of 800 °C to prepare Mg-SiO-based particles. Then, the Mg-SiO-based particles 10 were pulverized by using a ball mill to prepare silicon-based composite particles having a size of 6 μm. Then, while an Ar gas was flowed in, thus maintaining the inert atmosphere, the siliconbased composite particles were located in a hot zone of CVD equipment, Ar was used as a carrier gas, and the methane was blown 15 in the hot zone at 900 °C, reacting in 10-1 torr for 20 minutes to prepare a negative electrode active material in which carbon coating layer was formed on a surface of the silicon-based composite particles. 20 [0076] Example 2: Preparation of Negative Electrode Active Material [0077] A negative electrode active material was prepared in the same manner as in Example 1 except that the sublimation temperature was 1,450 °C. 25 25 [0078] Example 3: Preparation of Negative Electrode Active Material [0079] A negative electrode active material was prepared in the same manner as in Example 1 except that the sublimation temperature 5 was 1,350 °C. [0080] Example 4: Preparation of Negative Electrode Active Material [0081] A negative electrode active material was prepared in the 10 same manner as in Example 1 except that the sublimation temperature was 1,000 °C. [0082] Comparative Example 1: Preparation of Negative Electrode Active Material 15 [0083] A negative electrode active material was prepared in the same manner as in Example 1 except that the sublimation temperature was 1,480 °C. [0084] Comparative Example 2: Preparation of Negative Electrode 20 Active Material [0085] A negative electrode active material was prepared in the same manner as in Example 1 except that the sublimation temperature was 1,320 °C. 26 [0086] Comparative Example 3: Preparation of Negative Electrode Active Material [0087] A negative electrode active material was prepared in the same manner as in Example 1 except that the sublimation temperature 5 was 1,500 °C. [0088] Comparative Example 4: Preparation of Negative Electrode Active Material [0089] A negative electrode active material was prepared in the 10 same manner as in Example 1 except that the sublimation temperature was 1,280 °C. [0090] Comparative Example 5: Preparation of Negative Electrode Active Material 15 [0091] A negative electrode active material was prepared in the same manner as in Example 1 except that the further heat-treatment was not performed. [0092] Comparative Example 6: Preparation of Negative Electrode 20 Active Material [0093] A negative electrode active material was prepared in the same manner as in Example 1 except that the further heat-treatment temperature was 600 °C. 27 [0094] Comparative Example 7: Preparation of Negative Electrode Active Material [0095] A negative electrode active material was prepared in the same manner as in Example 1 except that the further heat-treatment 5 temperature was 1,100 °C. [0096] [Table 1] MgSiO3 Content (wt%) of Mg2SiO4 Content (wt%) of MgO Average particle diameter (D50) of siliconbased composite particles Specific surface area (m2/g) of silicon-based composite particles Content (wt%) of MgSiO3 Content (wt%) of first MgSiO3 phase having enstatite structure Content (wt%) of second MgSiO3 phase having clinoenst atite structure Weight ratio of first MgSiO3 phase having enstatite structure and second MgSiO3 phase having clinoenst atite structure . Example 1 20 6 14 1:2.33 3.2 0 6.2 6.6 Example 2 22.5 5 17.5 1:3.50 1.5 0 6.1 6.4 Example 3 19 7.5 11.5 1:1.53 4 0 6.2 6.8 Example 4 20.4 6.2 14.2 1:2.29 3 0 6.5 6.2 Comparative Example 1 23 3 20 1:6.67 1.2 0 6.1 6.8 Comparative Example 2 18.7 9.9 8.8 1:0.89 4.2 0 6.2 6.3 Comparative Example 3 23.5 1 22.5 1:22.50 0.8 0 6.3 6.4 Comparative Example 4 16 15.5 0.5 1:0.03 6 0 6.1 6.5 Comparative Example 5 14.7 8.5 6.2 1:0.73 3.8 1.2 6.3 6.2 Comparative Example 6 14.8 8 6.8 1:0.85 3.8 1.8 6.1 6.6 Comparative Example 7 19.2 3 16.2 1:5.4 3.8 0 6.2 6.4 [0097] The content of MgSiO3, the content of Mg2SiO4, and the content of MgO mean the contents (wt%) of MgSiO3, Mg2SiO4, and MgO 28 in the silicon-based composite particles, respectively, and it was possible to confirm each of the contents through the XRD Rietveld refinement method by using the D4 ENDEAVOR/X-ray diffraction equipment manufactured by Bruker Co. 5 [0098] It was possible to confirm the content of the first MgSiO3 phase having the enstatite structure, the content of the second MgSiO3 phase having the clinoenstatite structure, and the weight ratio of the first MgSiO3 phase having the enstatite structure and the second MgSiO3 phase having the clinoenstatite structure through 10 the XRD Rietveld refinement method by using the D4 ENDEAVOR/X-ray diffraction equipment manufactured by Bruker Co. [0099] The average particle diameter (D50) of the silicon-based composite particles was confirmed through PSD instrument. [00100] The specific surface area of the silicon-based composite 15 particles was confirmed by a BET analyzer. [00101] Experimental Example 1: Evaluation of Discharge Capacity, Initial Efficiency, Life (Capacity Retention) Characteristics 20 [00102] Each negative electrode active material of Examples and Comparative Examples was used to prepare a negative electrode and a battery. [00103] The negative electrode active material, carbon black as a conductive agent, and carboxymethyl cellulose (CMC) and a styrene25 butadiene rubber (SBR) as a binder were mixed at a weight ratio 29 of 95.8:1:1.7:1.5 to prepare a mixture. Then, distilled water (7.8 g) was added to the mixture (5 g) and stirred to prepare a negative electrode slurry. The negative electrode slurry was coated on a 20 μm thick copper (Cu) metal thin film, as a negative 5 electrode current collector, and then dried. In this case, a temperature of circulating air was 60 °C. Subsequently, the negative electrode current collector was roll-pressed and dried in a vacuum oven at 130 °C for 12 hours to prepare a negative electrode. 10 [00104] The prepared negative electrode was cut in a circle having an area of 1.7671 cm2, and a lithium (Li) metal thin film was prepared as a positive electrode. A separator formed of porous polyethylene was interposed between the positive electrode and the negative electrode, then an electrolyte, in which vinylene 15 carbonate was dissolved in an amount of 0.5 wt% in a mixed solution of methylethyl carbonate (EMC) and ethylene carbonate (EC) in a mixed volume ratio of 7:3, and in which LiPF6 having a concentration of 1 M was dissolved, was injected thereto to prepare a lithium coin half-cell. 20 [00105] The prepared battery was charged and discharged, the discharge capacity, initial efficiency, and capacity retention were evaluated, and the results are shown in Table 2 below. [00106] A first cycle and a second cycle were charged and 25 discharged at 0.1 C, and a third cycle to a 49th cycle were charged 30 and discharged at 0.5 C. A 300th cycle was terminated in a charged state (a state in which lithium is in the negative electrode), and the battery was disassembled to measure the thickness, and then the electrode thickness change rate was calculated. 5 [00107] Charging condition: CC (Constant Current) / CV (Constant Voltage) (5 mV / 0.005 C current cut-off) [00108] Discharging condition: CC (Constant Current) condition 1.5 V [00109] The discharge capacity (mAh/g) and initial efficiency (%) 10 were derived from the results during the first charge and discharge. Specifically, the initial efficiency (%) was derived from the following calculation. [00110] Initial efficiency (%) = (discharge capacity after first discharge/first charge capacity) × 100 15 [00111] The capacity retention and the electrode thickness change rate were derived from the following calculations, respectively. [00112] Capacity retention (%) = (300th discharge capacity/first discharge capacity) × 100 [00113] Electrode thickness change rate (%) = (change amount of 20 final negative electrode thickness / initial negative electrode thickness) × 100 31 [00114] [Table 2] Battery Discharge capacity (mAh/g) Initial efficiency (%) Capacity retention (%) Example 1 1460 82.6 92 Example 2 1450 82.4 91 Example 3 1430 82.4 91 Example 4 1455 82.5 88 Comparative Example 1 1400 81.9 85 Comparative Example 2 1380 81.7 86 Comparative Example 3 1360 81.2 84 Comparative Example 4 1350 81.3 83 Comparative Example 5 1280 78.2 80 Comparative Example 6 1300 78.6 81 Comparative Example 7 1456 82.1 70. CLAIMS 1. A negative electrode active material comprising siliconbased composite particles containing SiOx (0