Title of Invention: Anode and lithium secondary battery with improved fast charging performance technical field [One] This application was filed on 2020.07.10. Claims the benefit of priority based on Korean Patent Application No. 10-2020-0085254, and all contents disclosed in the document of the Korean patent application are incorporated as a part of this specification. [2] The present invention relates to a negative electrode having a two-layer structure including coated artificial graphite and uncoated artificial graphite as an anode active material, wherein uncoated artificial graphite is applied to a lower layer and coated artificial graphite is applied to an upper layer, and a lithium secondary battery including the same. background [3] As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and widely used. [4] In the secondary battery, lithium metal was conventionally used as the negative electrode, but as the battery short circuit due to the formation of dendrites and the risk of explosion due to this become a problem, reversible intercalation and desorption of lithium ions are possible, The use of carbon-based active materials that maintain structural and electrical properties is emerging. [5] As the carbon-based active material, various types of carbon-based materials such as artificial graphite, natural graphite, and hard carbon have been applied. have. Since the graphite-based active material has a low cost, structural stability, and a discharge voltage as low as -0.2V compared to lithium, a battery using the graphite-based active material can exhibit a high discharge voltage of 3.6V, so it is a lot in terms of energy density of a lithium battery. provides advantages. [6] However, graphite has problems due to the formation of complex solid electrolyte interphase (SEI) and volume expansion. The SEI layer, which represents a physical barrier between the lithium ionized carbon electrode, the electrolyte, and the binder, may not only cause irreversible charge loss, but also affect the long-term cycle stability of the lithium secondary battery. In addition, graphite has a layered structure, so it expands in volume during the electrochemical reaction. This volume expansion causes capacity loss of the graphite negative electrode material due to long-time charging and discharging. [7] Graphite includes natural graphite that is generated and mined in nature, and artificial graphite manufactured by heat-treating coal-based and petroleum-based pitch at 2,500 °C or higher. Compared to artificial graphite, natural graphite has a high graphitization degree and is inexpensive, and exhibits high lithium ion storage capacity. However, since the particle shape shows a needle-like or flaky structure and the surface area is large due to the irregular structure and the edge surface is exposed as it is, when applied to a battery, the edge surface is peeled off or destroyed by electrolyte penetration or decomposition reaction This leads to a large irreversible reaction. In addition, since the plate-shaped particles are easily oriented in a plane on the current collector, wettability with the electrolyte is not good and the electrode density is low. Therefore, artificial graphite was mostly used as an anode active material for a lithium secondary battery. In particular, artificial graphite is still used for products requiring long life and high output characteristics. [8] On the other hand, although interest in rapid charging technology for anode electrodes to which artificial graphite is applied has been continuously increasing in recent years, commercialization is not easy due to volume expansion of the anode during charging and discharging, deterioration of stability of the anode, etc. Accordingly, there is a need to develop a technology for an anode with improved fast charging performance. DETAILED DESCRIPTION OF THE INVENTION technical challenge [9] An object of the present invention is to improve fast charging performance, capacity, and energy density in an anode for a lithium secondary battery using artificial graphite as an anode active material. means of solving the problem [10] A negative electrode for a lithium secondary battery according to the present invention includes: a first negative electrode active material layer disposed on a current collector; and a second anode active material layer disposed on the first anode active material layer, wherein the first anode active material layer contains uncoated artificial graphite, and the second anode active material layer contains coated artificial graphite . [11] In one embodiment of the present invention, the weight ratio of the uncoated artificial graphite to the coated artificial graphite is 4:6 to 6:4 based on the total weight of the negative electrode active material. [12] In one embodiment of the present invention, the weight ratio of the uncoated artificial graphite to the coated artificial graphite is 45:55 to 55:45 based on the total weight of the negative electrode active material. [13] In an embodiment of the present invention, the negative active material of the first negative active material layer is uncoated artificial graphite, and the negative active material of the second negative active material layer is coated artificial graphite. [14] In one embodiment of the present invention, the coated artificial graphite is composed of an artificial graphite core and a carbon coating layer covering the artificial graphite core. [15] In one embodiment of the present invention, the average particle diameter (D 50 ) of the uncoated artificial graphite is 15㎛ to 22㎛. [16] In one embodiment of the present invention, the average particle diameter (D 50 ) of the coated artificial graphite is 13㎛ to 20㎛. [17] In one embodiment of the present invention, the content of the binder included in the first anode active material layer is 0.5 to 5% by weight in a range greater than the content of the binder included in the second anode active material layer. [18] In one embodiment of the present invention, the uncoated artificial graphite particles are secondary artificial graphite particles formed by agglomeration of one or more primary artificial graphite particles. [19] In one embodiment of the present invention, the coated artificial graphite particles are secondary artificial graphite particles formed by agglomeration of one or more primary artificial graphite particles. [20] In an embodiment of the present invention, the first anode active material layer and the second anode active material layer further include a conductive material, and the amount of the conductive material is 0.1 to 5 wt% based on the anode active material layer. [21] The lithium secondary battery of the present invention includes the negative electrode. Effects of the Invention [22] The negative electrode for a lithium secondary battery according to the present invention and a lithium secondary battery including the same, effectively prevent lithium plating during rapid charging, and have excellent performance. Best mode for carrying out the invention [23] Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention based on the principle that it can be defined as [24] [25] In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It is to be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof. Also, when a part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where it is "on" another part, but also the case where there is another part in between. Conversely, when a part of a layer, film, region, plate, etc. is said to be “under” another part, it includes not only cases where it is “directly under” another part, but also cases where another part is in between. In addition, in the present application, “on” may include the case of being disposed not only on the upper part but also on the lower part. [26] [27] Hereinafter, the present invention will be described in detail. [28] The negative electrode of the present invention, the first negative active material layer disposed on the current collector; and a second anode active material layer disposed on the first anode active material layer, wherein the first anode active material layer contains uncoated artificial graphite, and the second anode active material layer contains coated artificial graphite . [29] In one specific example, the negative active material of the first negative active material layer is uncoated artificial graphite, and the negative active material of the second negative active material layer is coated artificial graphite. That is, 100% of the anode active material contained in the first anode active material layer of the lower layer is uncoated artificial graphite, and 100% of the anode active material contained in the second anode active material layer of the upper layer is coated artificial graphite, and lithium having such a structure The negative electrode for a secondary battery has improved fast charging performance. [30] Artificial graphite has excellent charging and discharging characteristics compared to natural graphite and has an excellent charging rate. The inventors of the present invention, in the negative electrode to which artificial graphite is applied, uncoated artificial graphite as the negative electrode active material of the lower layer, and the negative electrode of the upper layer The anode with a two-layer structure in which coated artificial graphite is selected as the active material, surprisingly, has significantly improved rapid charging performance compared to a negative electrode to which 100% of coated artificial graphite is applied or an anode to which 100% of uncoated artificial graphite is applied, leading to the present invention became [31] In a preferred embodiment of the present invention, the weight ratio of the uncoated artificial graphite to the coated artificial graphite may be 4:6 to 6:4 based on the total weight of the negative electrode active material, more preferably 45:55 to 55:45 can be As the content of the coated artificial graphite in the upper layer increases, it may be preferable in terms of rapid charging performance, but the coated artificial graphite has a higher hardness than the uncoated artificial graphite, so crack issues may occur during rolling, so uncoated artificial graphite and coated artificial graphite The weight ratio of is preferably within the above numerical range. In addition, when the weight ratio of the uncoated artificial graphite and the coated artificial graphite is within the above range, the coating process by the dual slot die coater is easy, especially in the case of a large-capacity battery, when the weight ratio is out of the above weight ratio, the electrical characteristics of the battery are negatively affected can affect And the weight ratio of the uncoated artificial graphite of the lower layer and the coated artificial graphite of the upper layer can be controlled by appropriately adjusting the loading amount of the electrode slurry discharged from the coater. [32] The current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a surface of aluminum or stainless steel treated with carbon, nickel, titanium, silver, or the like may be used. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto. [33] The anode active material layer of the present invention may be disposed on the current collector. Specifically, the anode active material layer may be disposed on one side of the current collector or disposed on both sides of the current collector. The anode active material layer includes a first anode active material layer and a second anode active material layer. [34] The first anode active material layer may be disposed between the current collector and the second anode active material layer. The first anode active material layer may be in contact with the current collector. [35] The uncoated artificial graphite is included in the first anode active material layer. The uncoated artificial graphite particles are preferably secondary artificial graphite particles formed by agglomeration of one or more primary artificial graphite particles. The average particle diameter (D 50 ) of the uncoated artificial graphite is 15 μm to 22 μm, more preferably 16 μm to 21 μm, and most preferably 17 μm to 20 μm. When the average particle diameter (D 50 ) of the uncoated artificial graphite particles is less than the lower limit, the specific surface area increases, making it difficult to uniformly mix when preparing the slurry for secondary battery electrodes, which is undesirable, and the average particle diameter of the uncoated artificial graphite particles ( If D 50 ) is greater than the upper limit, it may be difficult to manufacture the electrode film. [36] In the present specification, the average particle diameter (particle diameter) is a value measured by the weight average value D 50 (particle diameter or median diameter when the cumulative weight is 50% of the total weight ) in particle size distribution measurement by laser light diffraction method. can [37] The uncoated artificial graphite may be included in an amount of 90 wt% to 99 wt%, specifically 93 wt% to 97 wt%, based on the total weight of the first anode active material layer. [38] The uncoated artificial graphite particles may be secondary artificial graphite particles formed by agglomeration of one or more primary artificial graphite particles. When the artificial graphite particles are secondary artificial graphite particles composed of an aggregate of primary artificial graphite particles, there may be first voids inside the secondary artificial graphite particles, and the first voids are between the primary artificial graphite particles. It may be an empty space of , may be amorphous, and there may be two or more. The first pores may have various shapes, such as extending to the surface of the secondary artificial graphite particles and exposed to the outside, or may exist only inside the secondary artificial graphite particles. [39] The primary artificial graphite particles may be formed after pulverizing a carbon precursor. Specifically, the primary artificial graphite particles may be formed by pulverizing the carbon precursor and then heating the powder to 500°C to 3,000°C, preferably 700°C to 2,700°C, by filling the powder in the device. The carbon precursor may be at least one selected from the group consisting of coal-based heavy oil, fiber-based heavy oil, tars, pitches, and cokes. The primary artificial graphite particles formed of the powdered carbon precursor can be more easily aggregated to form primary artificial graphite particles having high hardness. [40] When the artificial graphite particles are secondary artificial graphite particles formed by aggregating one or more primary artificial graphite particles, the secondary artificial graphite particles are operated after inputting the primary artificial graphite particles into the reactor, that is, 1 When the primary artificial graphite particles are rotated (spinning), the primary artificial graphite particles are aggregated with each other by centrifugal force to form secondary artificial graphite particles. In the process of aggregating the primary artificial graphite particles, the primary artificial graphite particles, pitch, etc., together with a resin binder may be put into the reactor, and heat treatment at a temperature of about 1200° C. to 1800° C. may be performed. After obtaining the secondary artificial graphite particles in which the primary artificial graphite particles are aggregated, a heat treatment process may be additionally performed on the secondary graphite particles. Since bonding or rearrangement between the primary artificial graphite particles is possible by the heat treatment process, it is possible to obtain the advantage of improving the microstructure of the secondary artificial graphite particles. [41] The uncoated artificial graphite preferably has a high theoretical capacity in addition to the above advantages, for example, the uncoated artificial graphite has a theoretical capacity of 350 mAh/g or more, preferably 355 to 365 mAh/g, more preferably For example, it may be 358 to 364 mAh/g. [42] [43] The second anode active material layer may be disposed on the first anode active material layer. Specifically, the second anode active material layer may be disposed to be spaced apart from the current collector with the first anode active material layer interposed therebetween. [44] The coated artificial graphite as an active material included in the second anode active material layer is preferably composed of an artificial graphite core and a carbon coating layer covering the artificial graphite core. The artificial graphite core may be the above-described uncoated artificial graphite. [45] Carbon coating on graphite serves to prevent uniform SEI layer formation and volume expansion, and is known to be effective in improving charge/discharge performance in lithium secondary batteries, but the carbon coating layer of the coated artificial graphite of the present invention is, In artificial graphite particles, lithium ions can easily enter and exit, have the effect of lowering the charge transfer resistance of lithium ions, and can improve structural stability compared to other carbon-based particles such as natural graphite, and fast charging performance of batteries can be further improved. [46] The carbon coating layer may include amorphous carbon, specifically, at least one selected from the group consisting of soft carbon and hard carbon, and preferably includes soft carbon. [47] The carbon coating layer may be formed by providing one or more materials selected from the group consisting of coal tar pitch, rayon, and polyacrylonitrile-based resins or a precursor of the materials to the surface of the artificial graphite particles, and then pyrolyzing them. The heat treatment process for forming the carbon coating layer may be performed in a temperature range of 1000°C to 4000°C. At this time, when the heat treatment process is carried out at less than 1000° C., it may be difficult to form a uniform carbon coating layer, and when it is carried out at a temperature exceeding 4000° C., there is a problem in that the carbon coating layer is excessively formed during the process. [48] The average particle diameter (D 50 ) of the coated artificial graphite of the present invention is 13 μm to 20 μm, more preferably 14 μm to 19 μm, and most preferably 15 μm to 19 μm. When the average particle diameter (D 50 ) of the coated artificial graphite particles is less than the lower limit, the specific surface area increases, making it difficult to uniformly mix when preparing a slurry for a secondary battery electrode, which is not preferable, and the average particle diameter (D 50 ) of the coated artificial graphite particles ) is greater than the upper limit, it may be difficult to manufacture the electrode film, it is not preferable. [49] The theoretical capacity of the coated artificial graphite may be 340 mAh/g or more, preferably 345 to 360 mAh/g, and more preferably 348 to 355 mAh/g. [50] The coated artificial graphite may be included in an amount of 90 wt% to 99 wt%, specifically 93 wt% to 97 wt%, based on the total weight of the second anode active material layer. [51] Each of the first anode active material layer and the second anode active material layer may further include a conductive material. In this case, the content of the conductive material included in the first anode active material layer and the second anode active material layer may be 0.1 to 5 wt%, respectively. [52] The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, farness black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. [53] [54] Each of the first anode active material layer and the second anode active material layer may further include a binder. In this case, the content of the binder included in the first anode active material layer may be 0.5 to 5 wt% in a range greater than the content of the binder included in the second anode active material layer. By making the content of the binder contained in the first negative active material layer in contact with the current collector relatively larger than the content of the binder contained in the second active material layer, the adhesive force between the current collector and the active material layer may be improved. [55] The binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride), polyacrylonitrile (polyacrylonitrile), polymethylmethacrylate (polymethylmethacrylate), poly Vinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), alcohol It may include at least one selected from the group consisting of ponified EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and a material in which hydrogen is substituted with Li, Na or Ca, etc., It may also include various copolymers thereof. [56] [57] A lithium secondary battery according to an embodiment of the present invention may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the cathode has been described above, a detailed description thereof will be omitted. [58] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material. [59] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body. [60] The positive active material may include a layered compound such as lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), or a compound substituted with one or more transition metals; lithium manganese oxides such as Formula Li 1+y Mn 2-y O 4 (where y is 0 - 0.33), LiMnO 3 , LiMn 2 O 3 , and LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); LiV 3 O 8 , LiFe 3 O 4 , V 2 O 5 , Cu 2 V 2 O 7vanadium oxide, such as; Ni site-type lithium nickel oxide represented by the formula LiNi 1-y M y O 2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and y = 0.01 - 0.3); Formula LiMn 2-y M y O 2 (wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 - 0.1) or Li 2 Mn 3 MO 8 (where M = Fe, Co, ternary lithium-manganese composite oxide represented by Ni, Cu, or Zn; LiMn 2 O 4 in which a part of Li in the formula is substituted with an alkaline earth metal ion ; disulfide compounds; Fe 2 (MoO 4 ) 3 , Li(Ni a Co band a ternary lithium transition metal composite oxide having Mn c )O 2 (0