【Technical Field】 5 This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0142661, filed on October 30, 2020, and the entire contents of the Korean patent application are incorporated herein by reference. The present invention relates to a negative electrode active material for a lithium secondary battery, a negative electrode, and a lithium secondary battery, and more particularly, 10 to a negative electrode active material for a lithium secondary battery, a negative electrode, and a lithium secondary battery, in which adhesive force and rolling rate of the negative electrode can be enhanced by the increase of the tap density of the negative electrode active material. 【Background Art】 15 As the use of fossil fuels rapidly increases, the demand for alternative energy and clean energy is on the increase, and accordingly, fields related to energy generation and storage by using electrochemical reaction are currently mostly actively studied. A representative example of an electrochemical device, which uses such electrochemical energy, is a secondary battery, and the range of use of the secondary battery 20 is on the gradual increase. Recently, as technologies for portable devices such as portable 2 computers, portable phones, and cameras are developed and their demands increase, the demand for secondary batteries as an energy source is also rapidly growing. Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte and a separator. The negative electrode includes a negative electrode active material which intercalates and deintercalates lithium ions from the positive electrode, and graphite-based 5 active material such as natural graphite or artificial graphite may be used as the negative electrode active material. The artificial graphite is mainly used in the form of secondary particles. To this end, generally, cokes, which are materials of initial particles, are granulated as secondary particles, which are graphited through heat treatment, to thereby obtain artificial graphite in the form of 10 secondary particles. Herein, when following the general manufacturing method in which the size of the initial particles is not controlled, artificial graphite in the form of secondary particles has a limit in increasing the tap density due to irregular shapes (less than 1.1 g/cc), and if the tap density is low, the content of the solids of the slurry for formation of a negative electrode 15 becomes low, which causes the drop of the adhesive force and the decrease of the rolling rate during the electrode manufacturing process. As such, in order to increase the tap density of artificial graphite, a method of mixing initial particles and secondary particles has been proposed, but this had a problem that a swelling phenomenon occurs or a rapid charging performance is deteriorated due to the 20 increase of the orientation degree of the negative electrode. Korean Patent Publication No. 2020-0076504 discloses a technology in which a negative electrode active material, which uses particle-size-controlled green cokes, improves 3 the discharge capacity and charge/discharge efficiency of a secondary battery and also improves high speed discharge and charge output characteristics of a secondary battery. However, since the technology uses green coke as the material, an additional process of carbonizing secondary particles is required. Hence, there is a need for a technology for improving the tap density without a 5 separate process while following the conventional artificial graphite manufacturing process. 【Disclosure】 【Technical Problem】 The present invention is believed to solve at least some of the above problems. For example, an aspect of the present invention provides a negative electrode active material for a 10 lithium secondary battery, which improves the tap density without an additional process in a conventional process of manufacturing secondary particle artificial graphite. 【Technical Solution】 A negative electrode active material for a lithium secondary battery according to the 15 present invention is composed of artificial graphite secondary particles obtained by granulating carbon-based initial particles having different average particle diameters (D50), in which the carbon-based initial particles include particle group A where an average particle diameter (D50) is a, and particle group B where an average particle diameter (D50) is b, and b < 0.6a. 20 Herein, a tap density may be equal to or greater than 1.1 g/cc and may preferably be 4 in a range of 1.2 to 1.4 g/cc. In an embodiment of the present invention, the a may be in a range of 11 to 15 ㎛. In an embodiment of the present invention, the carbon-based initial particles may further include particle group C where an average particle diameter is c, and c < b. In an embodiment of the present invention, c < 0.4a. 5 In an embodiment of the present invention, c < 0.6b. An average particle diameter (D50) of the negative electrode active material particles according to an embodiment of the present invention is in a range of 10 to 25 ㎛. In an embodiment of the present invention, the secondary particles include adhesive binders located between the initial particles. 10 In an embodiment of the present invention, the carbon-based initial particles are composed of one or a combination of two or more selected from the group consisting of petroleum coke, pitch coke and needle coke. The present invention provides a negative electrode including the above-mentioned negative electrode active material for a lithium secondary battery. 15 The present invention provides a lithium secondary battery including the above-mentioned negative electrode active material for a lithium secondary battery. A method of manufacturing a negative electrode active material for a lithium secondary battery according to the present invention includes: mixing carbon-based initial particles having different average particle diameters (D50); forming secondary particles by 20 mixing adhesive binders; and graphitizing the secondary particles. In an embodiment of the present invention, the carbon-based initial particles include 5 particle group A where an average particle diameter (D50) is a, and particle group B where an average particle diameter (D50) is b, and a mixing ratio of the particle group A and the particle group B is in a range of 2: 1 to 1: 2 based on a weight. In an embodiment of the present invention, the carbon-based initial particles further include particle group C where an average particle diameter (D50) is c, and a content of the 5 particle group C corresponds to 5 to 25% of a total weight of the particle group A and the particle group B. 【Advantageous Effects】 In the present invention, as secondary particles are granulated from carbon-based initial particles having different average particle diameters, relatively small initial particles are 10 filled in the pores of relatively large initial particles, which significantly increases the tap density, which shows the effect of increasing the adhesive force and high temperature storage performance of the negative electrode. 【Detailed Description of the Preferred Embodiments】 Hereinafter, the present invention will be described in detail with reference to the 15 drawings. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may properly define the concept of the terms in order to best describe its invention. The terms and words should be construed as meaning and concept consistent with the technical idea of the present invention. In this application, it should be understood that terms such as "include" or "have" are 20 intended to indicate that there is a feature, number, step, operation, component, part, or a combination thereof described on the specification, and they do not exclude in advance the 6 possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof. In the present specification, D50 may be defined as a particle size corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve of particles, Dmax may be defined as the largest particle size among particle sizes shown in the particle 5 diameter distribution curve, and Dmin may be defined as the smallest particle size among particle sizes shown in the particle diameter distribution curve. D50, Dmin and Dmax may be measured using the particle size distribution (PSD) which is derived through a laser diffraction method. The laser diffraction method can generally measure a particle diameter of several mm from a submicron region, and can obtain results of high reproducibility and high 10 resolution. In the present specification, the tap density may be a density which is calculated by putting 40g negative electrode active material particles in a container and tapping the container 1000 times. Hereinafter, the present invention will be described in detail. 15 A negative electrode active material for a lithium secondary battery according to the present invention is composed of artificial graphite secondary particles obtained by granulating carbon-based initial particles having different average particle diameters (D50), in which the carbon-based initial particles include particle group A where an average particle 20 diameter (D50) is a, and particle group B where an average particle diameter (D50) is b, and b < 0.6a. In the present specification, the term "initial particle" means an original particle when 7 another kind of particle is formed from a certain particle, and secondary particles may be formed by combination or granulation of a plurality of initial particles. In the present specification, the term "secondary particle" means a large particle which can be physically recognized formed by combination or granulation of initial particles. In the present specification, the "granulation" of initial particles means formation of 5 secondary particles by voluntary or artificial aggregation of a plurality of initial particles. The carbon-based initial particles are composed of one or a combination of two or more selected from the group consisting of petroleum coke, pitch coke and needle coke. In the present invention, the particle size of the carbon-based initial particles was controlled to improve the tap density of the negative electrode active material composed of 10 artificial graphite of secondary particles. In the present invention, the tap density was improved by reducing the inner pore formed between particles by assembling initial particles having different average particle diameters (D50). The inventors of the present invention found that when carbon-based initial particles include particle group A where an average particle diameter (D50) is a, and particle group B where an average particle diameter (D50) is b, and b 15 < 0.6a, the tap density of secondary particles of artificial graphite becomes equal to or greater than 1.1 g/cc. and reached the present invention. According to an embodiment of the present invention, it is possible to provide a negative electrode active material for a lithium secondary battery where the tap density is in the range of 1.2 to 1.4 g/cc by controlling the particle size and the mixing ratio of particle 20 group A where an average particle diameter (D50) is a, and particle group B where an average particle diameter (D50) is b. Further, when manufacturing a slurry for formation of a negative electrode using a negative electrode active material where the tap density is equal to or greater 8 than 1.1 g/cc, the content of solids in the slurry may be made to be equal to or greater than 56 wt%. Accordingly, as the migration of the binder is restricted during the drying process, the adhesive force between the negative electrode and the current collector may be improved, and as the thickness of the electrode decreases, the rolling rate can be improved during the rolling process, and the high temperature storage performance can be improved by the reduction of 5 the damage to the electrode. According to an embodiment of the present invention, the average particle diameter a of the particle group A where an average particle diameter (D50) is a is in the range of 11 to 15 ㎛, and preferably 12 to 13 ㎛. According to an embodiment of the present invention, the carbon-based initial 10 particles may further include particle group C where an average particle diameter is c in addition to particle group A where an average particle diameter (D50) is a, and particle group B where an average particle diameter (D50) is b. At this time, the c is smaller than the b. The tap density can be further improved as the particle group C where an average particle diameter is c is filled in fine pores formed by the particle group A where an average particle diameter 15 (D50) is a and the particle group B where an average particle diameter (D50) is b. At this time, in order to maximize the improvement effects of the tap density, it is preferable that c < 0.4a and c < 0.6b. The secondary particles of the present invention can be formed by granulating carbon-based initial particles. Namely, the secondary particles may be a structure formed by 20 aggregation of the initial particles. The secondary particles may contain adhesive binders which allow aggregation of the initial particles. The adhesive binders are positioned between 9 initial particles to provide adhesive force between the initial particles, to thereby form secondary particles by granulation of the initial particles. Some examples of the adhesive binder include one or a combination of two or more selected from the group consisting of petroleum-based pitch, coal-based pitch and mesophase pitch. Likewise, the average particle diameter (D50) of artificial graphite secondary particles, 5 which are obtained by granulating particle-size-controlled carbon-based initial particles, may be in the range of 10 to 25 ㎛, and preferably 11 to 20 ㎛. When the above range is satisfied, the negative electrode active material particles may be evenly dispersed in the negative electrode slurry, and the charging performance of the battery can also be improved. A method of manufacturing a negative electrode active material for a lithium secondary battery according to the present invention may include: mixing carbon-based initial particles having different average particle diameters (D50); forming secondary particles by mixing adhesive binders; and graphitizing the secondary particles. 15 In a method of manufacturing a negative electrode active material of the present invention, the mixing for manufacturing the negative electrode active material can be performed by a mechanical milling or a simple mixing which uses a scheme known in the related field. For example, the mixing can be performed by simply using mortar or may be performed by mechanically applying compressive stress by performing rotation at 100 to 20 1000 rpm using a blade or a ball mill. The step of mixing carbon-based initial particles having different average particle 10 diameters (D50) is a step of controlling the diameter of initial particles and includes a step of preparing and mixing particle group A where the average particle diameter (D50) is a and particle group B where the average particle diameter (D50) is b. The mixing ratio of the particle group A and the particle group B is preferably in the range of 2: 1 to 1: 2. The tap density enhancement effect can be maximized when the mixing ratio is satisfied. 5 In an embodiment of the present invention, the step of mixing carbon-based initial particles having different average particle diameters (D50) may further include a step of mixing particle group C where the average particle diameter (D50) is c in addition to particle group A where the average particle diameter (D50) is a and particle group B where the average particle diameter (D50) is b. At this time, the content of the particle group C is preferably in 10 the range of 5 to 25 wt% of the total weight of the particle group A and the particle group B because the tap density improvement effects can be maximized in this range. Since the specific numerical ranges and relationships of above a, b and c have been described in detail above, further description will be omitted. The step of forming secondary particles by mixing the adhesive binders may include 15 mixing and stirring adhesive binders with particle-size-controlled carbon-based initial particles. Through this, the carbon-based initial particles can be aggregated to thereby be granulated. The adhesive binder may be a coal-based pitch or a petroleum-based pitch, and the mixing and stirring may be performed at a temperature of 200 to 900°C, and specifically 300 to 500°C. 20 The step of graphitizing the secondary particles may include a process of graphitizing the secondary particles, which are formed by the mixture of the carbon-based initial particles and adhesive binders, through calcination. 11 The calcination may be performed by performing heating at a temperature of 2500 to 3500°C, and specifically a temperature of 2800 to 3200°C. The average particle diameter (D50) of the secondary particles graphitized by the calcination may be in the range of 10 to 25 ㎛. 5 The present invention provides a negative electrode for a secondary battery containing the above-described negative electrode active material. The negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer. Any negative electrode current collector, which is generally used in the related art, 10 may be used as the negative electrode current collector. For example, any negative electrode current collector, which has a high conductivity while not causing chemical changes to a lithium secondary battery, may be used as the negative electrode current collector. For example, a negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, cooper or stainless steel of which the surface 15 has been treated with carbon, nickel, titanium, silver or the like, or an aluminum-cadmium alloy. In addition, in the negative electrode current collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a 20 nonwoven fabric. The negative electrode current collector may generally have a thickness of 3 to 500 12 ㎛. The negative electrode active material layer is formed on the negative electrode current collector. The negative electrode active material layer includes the negative electrode active material for a lithium secondary battery of artificial graphite secondary particles obtained by 5 granulation of carbon-based initial particles having different average particle diameters (D50) of the present invention. The content of the negative electrode active material for the lithium secondary battery may be in the range of 80 to 90 wt% of the total weight of the negative electrode active material layer. The negative electrode active material layer may further include at least one selected 10 from a binder and a conductive material in addition to a negative electrode active material. The binder is a component that assists the bonding between the conductive material, the active material and the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVdF), polyvinyl alcohol, 15 carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, and various combinations thereof. Any thickener, which is conventionally used for a lithium secondary battery, may be 20 used as the thickener. For example, carboxymethylcellulose (CMC) may be used. The conductive material is a component for further improving the conductivity of the 13 negative electrode active material, and may be added in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, 5 Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskey such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives and the like. Specific examples of commercially available conductive materials 10 include products of Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company products, Ketjenblack, EC series (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (Timcal). The negative electrode active material layer may be manufactured by preparing a negative electrode slurry by mixing a negative electrode active material for a lithium 15 secondary battery with at least one additive selected from a binder and a conductive material and a thickener in a solvent, applying the negative electrode slurry on the negative electrode current collector, and rolling and drying the negative electrode current collector. The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that becomes a desirable viscosity when the 20 negative electrode active material and optionally a binder and a conductive material are included. For example, the concentration of solids, which contain a negative electrode active material for a lithium secondary battery, and optionally contain a binder, a thickener and a 14 conductive material, may be in the range of 50 to 95 wt%. In addition, the present invention provides a lithium secondary battery including the negative electrode for the lithium secondary battery described above. The lithium secondary battery may include a negative electrode for a lithium 5 secondary battery, a positive electrode for a lithium secondary battery, and a separator interposed between the negative electrode for the lithium secondary battery and the positive electrode for the lithium secondary battery. Specifically, the lithium secondary battery of the present invention may be manufactured by injecting a non-aqueous electrolyte solution into an electrode structure 10 composed of a negative electrode for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a separator interposed between the negative electrode for the lithium secondary battery and the positive electrode for the lithium secondary battery. At this time, a positive electrode, a negative electrode and a separator, which have been commonly used in manufacturing a lithium secondary battery, may be used as the positive electrode, the 15 negative electrode, and the separator which form an electrode structure. At this time, the positive electrode may be manufactured by coating a positive electrode active material slurry including a positive electrode active material and optionally a binder, a conductive material, and a solvent, etc. on a positive electrode current collector and then performing drying and rolling. 20 The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon 15 or aluminum or stainless steel of which the surface has been treated with carbon, nickel, titanium, silver, or the like. The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may specifically include a lithium composite metal oxide containing lithium and at least one metal such as cobalt, manganese, nickel or 5 aluminum. More specifically, some examples of the lithium composite metal oxide include lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt oxide (e.g., LiCoO2, etc.), lithium-nickel oxide (e.g., LiNiO2, etc.), lithium-nickel-manganese oxide (e.g., LiNi1-YMnYO2 (herein, 0