Negative electrode for lithium secondary battery and lithium secondary battery containing the same

Abstract

To provide a negative electrode for lithium secondary batteries that has high capacity and excellent charging characteristics. [Solution] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same, and more particularly to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same, comprising a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, wherein the negative electrode active material layer comprises a first negative electrode active material layer and a second negative electrode active material layer sequentially stacked on the negative electrode current collector, each of the first and second negative electrode active material layers comprising natural graphite and artificial graphite, the average particle size D50 of the natural graphite being smaller than the average particle size of the artificial graphite, and the ratio of the weight of the natural graphite to the weight of the artificial graphite in the second negative electrode active material layer being 1 to 5.

Description

[Technical Field]

[0001] This invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery containing the same. [Background technology]

[0002] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries is rapidly increasing. As a result, research and development to improve the performance of lithium-ion rechargeable batteries is being actively pursued.

[0003] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of intercalation and deintercalation of lithium ions, and an electrolyte, which produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated / deintercalated at the positive and negative electrodes. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The problem that this invention aims to solve is to provide a negative electrode for a lithium secondary battery that has high capacity and excellent charging characteristics.

[0005] Another problem that this invention aims to solve is to provide a lithium secondary battery with excellent rapid charging performance. [Means for solving the problem]

[0006] The negative electrode for a lithium secondary battery according to an embodiment of the present invention includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer may include a first negative electrode active material layer and a second negative electrode active material layer that are sequentially laminated on the negative electrode current collector. Each of the first and second negative electrode active material layers includes natural graphite and artificial graphite, the average particle size D50 of the natural graphite is smaller than the average particle size of the artificial graphite, and the ratio of the weight of the natural graphite to the weight of the artificial graphite in the second negative electrode active material layer may be 1 to 5.

[0007] The negative electrode for a lithium secondary battery according to an embodiment of the present invention includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer may include natural graphite and artificial graphite. The negative electrode active material layer includes a first region adjacent to the negative electrode current collector and a second region adjacent to the upper surface of the negative electrode active material layer, and the content of the natural graphite contained in each of the first and second regions is 45 wt% to 80 wt%, and the average particle size of the natural graphite may be smaller than the average particle size of the artificial graphite.

[0008] The negative electrode for a lithium secondary battery according to an embodiment of the present invention includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer may include a first negative electrode active material layer and a second negative electrode active material layer that are sequentially stacked on the negative electrode current collector. The first negative electrode active material layer includes first natural graphite and first artificial graphite, the second negative electrode active material layer includes second natural graphite and second artificial graphite, the average particle size of the second natural graphite is smaller than the average particle size of the first natural graphite, and the ratio of the weight of the second natural graphite to the weight of the second artificial graphite in the second negative electrode active material layer may be 1 to 3.

Advantages of the Invention

[0009] The negative electrode for a lithium secondary battery according to the present invention includes natural graphite with controlled size, orientation, etc., and the charging characteristics can be improved. The lithium secondary battery according to the present invention has excellent capacity, and the rapid charging performance can be improved.

Brief Description of the Drawings

[0010] [Figure 1]This is a simplified conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention. [Figure 2] This is a schematic diagram showing a lithium secondary battery according to one embodiment, which can be described as having a cylindrical battery form. [Figure 3] This is a schematic diagram showing a lithium secondary battery according to one embodiment, which can be described as having a rectangular battery shape. [Figure 4] This is a schematic diagram showing a lithium secondary battery according to one embodiment, which can be described as a pouch-type battery. [Figure 5] This is a schematic diagram showing a lithium secondary battery according to one embodiment, which can be described as a pouch-type battery. [Figure 6] This is a cross-sectional view of a negative electrode for a lithium secondary battery according to one embodiment. [Figure 7] This is a cross-sectional view of a negative electrode for a lithium secondary battery according to one embodiment. [Figure 8] This is a cross-sectional view of a negative electrode for a lithium secondary battery according to one embodiment. [Modes for carrying out the invention]

[0011] To fully understand the structure and effects of the present invention, preferred embodiments will be described with reference to the accompanying drawings. However, the present invention may be realized in various forms and modified in various ways, not limited to the embodiments disclosed below. These embodiments are provided solely to complete the disclosure of the present invention and to fully inform those who are ordinary skill in the art of the present invention of the scope of the invention.

[0012] In this specification, where one component is referred to as being on top of another, it means that it can be formed directly on top of the other component, or that a third component may be interposed between them. Furthermore, in the drawings, the thickness of components is exaggerated for the sake of effective illustration of the technical content. Throughout the specification, parts indicated by the same reference numeral indicate the same component.

[0013] Unless otherwise specified herein, singular nouns may include plural nouns. Furthermore, unless otherwise specified herein, "A" or "B" may mean "including A, including B, or including A and B." The terms "comprises" and / or "comprising" used herein do not preclude the presence or addition of one or more other components.

[0014] In this specification, each phrase such as “A or B,” “at least one of A and B,” “at least one of A or B,” “A, B, or C,” “at least one of A, B, and C,” and “at least one of A, B, or C” may include any one of the items listed with the corresponding phrase, or any possible combination thereof.

[0015] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0016] In this specification, unless otherwise defined, particle size may refer to average particle size. Furthermore, particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) can be measured by methods widely known to those skilled in the art, such as by a particle size analyzer, or by photographs taken with a transmission electron microscope or scanning electron microscope. Alternatively, it may be measured using a dynamic light-scattering device, followed by data analysis to count the number of particles within each particle size range, and then calculating the average particle size D50 value. Alternatively, it may be measured using the laser diffraction method. When measuring using the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (for example, the MT 3000 from Microtrac), and after irradiating with ultrasound at approximately 28 kHz at an output of 60 W, the average particle size D50 based on the 50% particle size distribution in the analyzer can be calculated.

[0017] Figure 1 is a simplified conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention. Referring to Figure 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0018] The positive electrode 10 and the negative electrode 20 can be separated from each other with a separator 30 in between. The separator 30 can be placed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 can be in contact with the electrolyte ELL. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated in the electrolyte ELL.

[0019] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. Within the electrolyte ELL, the lithium ions can move towards the positive electrode 10 or the negative electrode 20 by passing through the separator 30.

[0020] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material.

[0021] For example, the positive electrode 10 may further include an additive that can act as a sacrificial positive electrode.

[0022] The content of the positive electrode active material in the positive electrode active material layer AML1 may be 90% to 99.5% by weight relative to 100% by weight of the positive electrode active material layer AML1. The content of the binder and conductive material may be 0.5% to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer AML1.

[0023] The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector COL1. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, styrene-butadiene rubber (meth)acrylate, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0024] The conductive material is used to impart conductivity to the electrode, and in the battery being configured, any material can be used as long as it is an electron conductive material and does not cause a chemical change. Examples of the conductive material include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc., conductive polymers such as polyphenylene derivatives, or mixtures thereof.

[0025] Although Al can be used as the current collector COL1, it is not limited thereto.

[0026] positive electrode active material As the positive electrode active material in the positive electrode active material layer AML1, a compound (lithiated intercalation compound) capable of reversible insertion and desorption of lithium can be used. Specifically, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof with lithium can be used.

[0027] The composite oxide can be a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based oxides, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0028] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Mn 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co bX c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni b Co c L 1 d G e O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4 (0.90 ≤ a ≤ 1.8).

[0029] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 It is Mn, Al, or a combination of these.

[0030] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium from the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more, and 99 mol% or less. Since high-nickel positive electrode active materials can achieve high capacity, they can be applied to high-capacity, high-density lithium secondary batteries.

[0031] negative electrode 20 The positive electrode 20 for the lithium secondary battery may include a current collector COL2 and a negative electrode active material layer AML2 formed on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0032] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0033] The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres well to the current collector COL2. The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0034] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0035] The aqueous binder may be selected from styrene-butadiene rubber, styrene-butadiene (meth)acrylate rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0036] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound that provides viscosity. This cellulosic compound may be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal may be Na, K, or Li.

[0037] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0038] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0039] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof can be used.

[0040] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping or undoping lithium, or a transition metal oxide.

[0041] The material capable of reversibly inserting / desorbing the lithium ions is a carbon-based negative electrode active material, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0042] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0043] As the material capable of doping or undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0044] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (core) which are aggregates of primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0045] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon first coating layer located on the surface of the core.

[0046] The Si-based or Sn-based anode active material may be used in combination with a carbon-based anode active material.

[0047] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. Such a separator 30 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can also be used.

[0048] The separator 30 may include a porous substrate and a first coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0049] The porous substrate may be a polymer film made of any one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (e.g., Teflon®), or a copolymer or mixture of two or more of these polymers.

[0050] The aforementioned organic material may include polyvinylidene fluoride polymer or (meth)acrylic polymer.

[0051] The inorganic substances may include, but are not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and inorganic particles selected from combinations thereof.

[0052] The organic and inorganic materials may exist mixed in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0053] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0054] The aforementioned non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0055] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0056] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0057] Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0058] As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran may be used. As ketone-based solvents, cyclohexanone may be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol may be used. As aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether groups), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes may be used.

[0059] The aforementioned non-aqueous organic solvents may be used alone or in combination of two or more.

[0060] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and the cyclic carbonates and linear cyclic carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0061] The aforementioned lithium salts dissolve in organic solvents and act as a source of lithium ions within the battery, enabling the basic operation of lithium secondary batteries and promoting the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are positive numbers from 1 to 20), may comprise one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0062] Lithium-ion battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 2 to 5 are schematic diagrams showing a lithium secondary battery according to one embodiment, where Figure 2 is cylindrical, Figure 3 is prismatic, and Figures 4 and 5 are pouch-type batteries. Referring to Figures 2 to 4, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a housing 50 in which the electrode assembly 40 is embedded. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the housing 50, as shown in Figure 2. Also, in Figure 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in Figures 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for guiding the current formed in the positive electrode assembly 40 to the outside.

[0063] A lithium secondary battery according to one embodiment of the present invention may be applied to automobiles, mobile phones, and / or various forms of electrical devices, but the present invention is not limited thereto.

[0064] Figures 6 to 8 are cross-sectional views of a negative electrode for a lithium secondary battery according to one embodiment. Hereinafter, the negative electrode for a lithium secondary battery and the lithium secondary battery containing the same according to an embodiment of the present invention will be described in more detail with reference to Figures 6 to 8.

[0065] negative electrode active material Referring to Figures 6 and 7, the negative electrode 20 for a lithium secondary battery according to an embodiment of the present invention may contain natural graphite NG and artificial graphite AG as negative electrode active materials. The natural graphite NG according to the present invention may be an improved natural graphite NG in which the degree of orientation, particle size, etc., are adjusted to be advantageous for rapid charging. The natural graphite NG according to the present invention may have other physical properties compared to general natural graphite, and these physical properties will be described in detail.

[0066] More specifically, in the natural graphite NG according to the embodiment of the present invention, when XRD is measured using CuKα radiation, the ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) may be 40 to 80, 45 to 75, or 50 to 70. For example, the ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) may be 60.

[0067] The ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) is an indicator related to the orientation of natural graphite NG, and a smaller peak intensity ratio (I(002) / I(110)) may mean that the orientation of the crystal grains of natural graphite is random. Conversely, a larger peak intensity ratio may mean that the crystal grains are oriented parallel to the negative electrode active material layer.

[0068] If the orientation of natural graphite (NG) is excessively high, it becomes difficult for lithium ions to be inserted / deinserted between the graphite layers, leading to decreased charge / discharge characteristics and potentially increasing diffusion resistance due to restricted ion diffusion pathways within the electrode. If the orientation of natural graphite (NG) is excessively low, the electrical conductivity of the negative electrode may decrease due to the disordered arrangement of graphite, and inefficiencies may occur in the lithium ion insertion / deinsertion process because lithium ions cannot be uniformly inserted between the graphite layers.

[0069] When measuring XRD using CuKα radiation, if the ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) satisfies the range described above, natural graphite NG may exhibit excellent rapid charging performance and excellent conductivity.

[0070] The natural graphite NG according to embodiments of the present invention may have an average particle size D50 of 3 μm to 15 μm, 4 μm to 12 μm, or 5 μm to 10 μm. For example, the average particle size of natural graphite NG may be 7 μm. In one embodiment, the average particle size can be measured with a particle size analyzer. The average particle size may mean the diameter D50 of particles with a cumulative volume of 50 volume% in the particle size distribution.

[0071] If the average particle size of natural graphite NG is excessively large, the diffusion pathway of lithium ions may become longer, potentially slowing down the charging speed. If the average particle size of natural graphite NG is excessively small, the specific surface area may increase, potentially increasing side reactions with the electrolyte. When the average particle size of natural graphite NG satisfies the range described above, excessive side reactions do not occur, and excellent charging characteristics can be observed.

[0072] The BET specific surface area of ​​natural graphite NG according to the embodiment of the present invention is 1.5 m². 2 / g~3m 2 / g, 1.6m 2 / g~2.4m 2 / g, or 1.8m 2 / g~2.2m 2 It can be / g. For example, the BET specific surface area of ​​natural graphite NG is 2.0 m². 2It may be / g. In one embodiment, the specific surface area can be measured by the BET method. Specifically, the gas can be removed from the object to be measured using BET measuring equipment (BEL-SORP-mini, Nippon Bell) at 300°C for 1 hour, and then N2 adsorption / desorption can be performed at 77K to measure the specific surface area.

[0073] The natural graphite NG according to embodiments of the present invention may have a specific capacity of 350 mAh / g to 380 mAh / g, 355 mAh / g to 370 mAh / g, or 355 mAh / g to 360 mAh / g. For example, the specific capacity of natural graphite NG may be 358 mAh / g. In one embodiment, the specific capacity is obtained by measuring the charge-discharge capacity of a half-cell containing natural graphite NG as the negative electrode active material.

[0074] When natural graphite NG is improved to have the aforementioned degree of orientation, average particle size, specific surface area, specific capacity, etc., it can exhibit excellent rapid charging performance.

[0075] Generally, artificial graphite is known to have higher structural stability than natural graphite, allowing for smoother lithium ion movement and offering advantages for rapid charging. Therefore, to achieve superior rapid charging characteristics, it is common practice to increase the artificial graphite content in the negative electrode active material layer, particularly in the upper negative electrode active material layer where lithium ions are inserted / de-inserted first during the charge / discharge process.

[0076] When using improved natural graphite NG, which has various controlled properties as described above, the rapid charging performance of the battery can be improved without increasing the content of artificial graphite AG in the upper negative electrode active material layer, and rather by increasing the content of natural graphite NG. For example, the negative electrode 20 according to an embodiment of the present invention can exhibit excellent rapid charging performance even though the content of natural graphite NG in the upper negative electrode active material layer AML22 is the same as or greater than the content of artificial graphite AG.

[0077] Natural graphite with controlled orientation, average particle size, etc., as described above, can be produced by the following method.

[0078] First, minerals can be extracted from ores containing natural graphite and impurities can be removed. The graphite from which impurities have been removed can be pulverized to a desired size, and then the graphite particles can be spheroidized. The spheroidized natural graphite can be mixed with pitch to form aggregates. Next, a primary heat treatment step can be performed on the aggregates to coat the surface with pitch. By subjecting the natural graphite with pitch coated on its surface to a secondary heat treatment, improved natural graphite can be obtained.

[0079] The artificial graphite AG according to an embodiment of the present invention may have a larger average particle size than the natural graphite NG. For example, the average particle size of the artificial graphite AG may be 10 μm to 20 μm, 12 μm to 18 μm, or 12 μm to 15 μm. By including both the natural graphite NG with a relatively small average particle size and the artificial graphite AG with a relatively large average particle size in the negative electrode active material layer, the electrode density can be improved and the ion and electron transfer paths can be optimized.

[0080] Although not shown, the negative electrode 20 for a lithium secondary battery according to an embodiment of the present invention may further include a silicon-based negative electrode active material as a negative electrode active material. The silicon-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination of these.

[0081] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it may include secondary particles (cores) formed by combining primary silicon particles and a first amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0082] The content of silicon-based anode active material may be 10 wt% or less relative to 100 wt% of the total anode active material, which includes natural graphite (NG), artificial graphite (AG), and silicon-based anode active material. For example, the content of silicon-based anode active material may be 3 wt% to 10 wt%, or 5 wt% to 8 wt%.

[0083] negative electrode Referring to Figure 6, a negative electrode 20 for a lithium secondary battery according to one embodiment may include a negative electrode current collector COL2, a first negative electrode active material layer AML21 on the negative electrode current collector, and a second negative electrode active material layer AML22 on the first negative electrode active material layer AML21. The first and second negative electrode active material layers AML21 and AML22 may each contain the aforementioned natural graphite NG and artificial graphite AG. Although not shown, the first and second negative electrode active material layers AML21 and AML22 may further contain the aforementioned silicon-based negative electrode active material as the negative electrode active material.

[0084] The content of natural graphite NG in the first negative electrode active material layer AML21 may be 45 wt% to 80 wt%, or 50 wt% to 75 wt%, based on 100 wt% of the total first negative electrode active material layer AML21. The content of artificial graphite AG in the first negative electrode active material layer AML21 may be 20 wt% to 50 wt%, or 25 wt% to 45 wt%, based on 100 wt% of the total first negative electrode active material layer AML21. The ratio of the weight of natural graphite NG to the weight of artificial graphite AG in the first negative electrode active material layer AML21 may be 1 to 10, 1 to 5, or 1 to 3.

[0085] The content of natural graphite NG in the second negative electrode active material layer AML22 may be 45 wt% to 80 wt%, or 50 wt% to 75 wt%, based on 100 wt% of the total weight of the second negative electrode active material layer AML22. The content of artificial graphite AG in the second negative electrode active material layer AML22 may be 20 wt% to 50 wt%, or 25 wt% to 45 wt%, based on 100 wt% of the total weight of the second negative electrode active material layer AML22. The ratio of the weight of natural graphite NG to the weight of artificial graphite AG in the second negative electrode active material layer AML22 may be 1 to 10, 1 to 5, or 1 to 3.

[0086] The ratio of the weight of natural graphite NG to the weight of artificial graphite AG in the second negative electrode active material layer AML22 may be the same as, or different from, the ratio of the weight of natural graphite NG to the weight of artificial graphite AG in the first negative electrode active material layer AML21.

[0087] The negative electrode 20 for lithium secondary batteries according to the embodiment of the present invention contains improved natural graphite NG with controlled orientation, particle size, etc., as the negative electrode active material. Therefore, the upper negative electrode active material layer AML22 can have excellent rapid charging characteristics while containing an amount of natural graphite NG equivalent to or greater than that of artificial graphite AG.

[0088] The ratio of the thickness of the first negative electrode active material layer AML21 to the thickness of the second negative electrode active material layer AML22 can be 3:1 to 1:3, or 2:1 to 1:2, and for example, it can be 1:1. When the content of natural graphite NG contained in each layer and the ratio of the thickness of each layer satisfy the range described above, the negative electrode 20 for lithium secondary batteries can have excellent capacity and excellent rapid charging performance.

[0089] The first and second negative electrode active material layers AML21 and AML22 may further contain a binder. The binder content in the first negative electrode active material layer AML21 may be greater than the binder content in the second negative electrode active material layer AML22. The first negative electrode active material layer AML21, which is in direct contact with the negative electrode current collector, should ensure not only the adhesive force between the negative electrode active material particles but also the adhesive force between the negative electrode active material and the negative electrode current collector COL2, so the binder content may be greater than that of the second negative electrode active material layer AML22. For example, the binder content in the first negative electrode active material layer AML21 may be 1.5 to 5 times, or 2 to 4 times, the binder content in the second negative electrode active material layer AML22.

[0090] According to one embodiment, the first negative electrode active material layer AML21 and the second negative electrode active material layer AML22 can be distinguished by a change in binder content. As described above, since the binder content of the first negative electrode active material layer AML21 is 1.5 times higher than that of the second negative electrode active material layer AML22, the layers can be distinguished by identifying the portion where the binder content changes abruptly, as shown in Figure 6.

[0091] Referring to Figure 7, the negative electrode 20 for a lithium secondary battery according to an embodiment of the present invention may include a negative electrode current collector COL2 and a negative electrode active material layer AML2 on the negative electrode current collector COL2. The negative electrode active material layer AML21 may include the above-mentioned natural graphite NG and artificial graphite AG. The negative electrode active material layer AML2 may further include the above-mentioned silicon-based negative electrode active material. The negative electrode active material layer AML2 may include a first region DM1 adjacent to the negative electrode current collector COL2 and a second region DM2 adjacent to the upper surface of the negative electrode active material layer AML2.

[0092] The first region DM1 can be defined as a hexahedron space (for example, 10 μm × 10 μm × 10 μm) centered at a point at a predetermined distance from the negative electrode active material layer COL2 in the third direction D3. The predetermined distance may be 5 μm to 50 μm. Alternatively, the predetermined distance may be a length equivalent to 0.1 to 0.5 times the total thickness of the negative electrode active material layer AML2.

[0093] The second region D2 can be defined as a hexahedron space (for example, 10 μm × 10 μm × 10 μm) centered at a point at a predetermined distance in the third direction D3 from the interface between the separator 30 and the negative electrode 20. The predetermined distance may be 5 μm to 50 μm. Alternatively, the predetermined distance may be a length equivalent to 0.1 to 0.5 times the total thickness of the negative electrode active material layer AML2.

[0094] The content of natural graphite NG in the first region DM1 may be 45 wt% to 80 wt%, or 50 wt% to 75 wt%. The content of artificial graphite AG in the first region DM1 may be 20 wt% to 50 wt%, or 25 wt% to 45 wt%. The ratio of the weight of natural graphite NG to the weight of artificial graphite AG in the first region DM1 may be 1 to 10, 1 to 5, or 1 to 3.

[0095] The content of natural graphite (NG) in the second region DM2 may be 45 wt% to 80 wt%, or 50 wt% to 75 wt%. The content of artificial graphite (AG) in the second region DM2 may be 20 wt% to 50 wt%, or 25 wt% to 45 wt%. The ratio of the weight of natural graphite (NG) to the weight of artificial graphite (AG) in the second region DM2 may be 1 to 10, 1 to 5, or 1 to 3.

[0096] The ratio of the weight of natural graphite NG in the second region DM2 to the weight of natural graphite NG in the first region DM1 may be 0.6 to 1.2, or 0.9 to 1.0. In other words, the content of natural graphite NG contained in the first region DM1 and the second region DM2 may be similar. Because the negative electrode 20 for lithium secondary batteries according to the present invention contains improved natural graphite NG with controlled orientation and particle size as the negative electrode active material, the second region DM2 adjacent to the separator can have excellent rapid charging performance while containing a similar level of natural graphite NG as the first region DM1.

[0097] The first and second regions DM1 and DM2 may each further contain a binder. The binder content in the first region DM1 may be greater than the binder content in the second region DM2. The first region DM1 adjacent to the negative electrode current collector COL2 should ensure not only the adhesive force between the negative electrode active material particles but also the adhesive force between the negative electrode active material and the negative electrode current collector COL2, so the binder content in the first region DM1 may be greater than that in the second region DM2. For example, the binder content in the first region DM1 may be 1.5 to 10 times, 2 to 8 times, or 2 to 4 times the binder content in the second region DM2.

[0098] Referring to Figure 8, a negative electrode 20 for a lithium secondary battery according to another embodiment of the present invention may include a negative electrode current collector COL2, a first negative electrode active material layer AML21 on the negative electrode current collector, and a second negative electrode active material layer AML22 on the first negative electrode active material layer AML21. The first negative electrode active material layer AML21 may include first natural graphite NNG and first artificial graphite NAG, and the second negative electrode active material layer AML22 may include second natural graphite NG and second artificial graphite AG.

[0099] The second natural graphite AG may be an improved natural graphite NG in which the degree of orientation, particle size, etc., are adjusted as described above, as shown in Figures 6 and 7. For example, when measuring XRD using CuKα radiation, the ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) of the second natural graphite NG may be 50 to 70, and the average particle size D50 may be 3 μm to 15 μm, 4 μm to 12 μm, or 5 μm to 10 μm.

[0100] Unlike the second natural graphite (NG), the first natural graphite (NNG) may be natural graphite in which the degree of orientation, particle size, etc., are not precisely controlled. For example, when measuring XRD using CuKα radiation, the ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) of the first natural graphite (NNG) may be between 60 and 120. For example, the average particle size of the first natural graphite (NNG) may be between 12 μm and 20 μm.

[0101] The first and second artificial graphites NAG and AG may be the same as or similar to the artificial graphites described above, with reference to Figures 6 and 7. For example, the average particle size of the first and second artificial graphites NAG and AG may be 12 μm to 15 μm, respectively.

[0102] The content of first natural graphite NNG in the first anode active material layer AML21 may be 45 wt% to 80 wt%, or 50 wt% to 75 wt%, based on 100 wt% of the total first anode active material layer AML21. The content of first artificial graphite NAG in the first anode active material layer AML21 may be 20 wt% to 50 wt%, or 25 wt% to 45 wt%, based on 100 wt% of the total first anode active material layer AML21. The ratio of the weight of natural graphite NNG to the weight of artificial graphite NAG in the first anode active material layer AML21 may be 1 to 10, 1 to 5, or 1 to 3.

[0103] The content of the second natural graphite NG in the second anode active material layer AML22 may be 45 wt% to 80 wt%, or 50 wt% to 75 wt%, based on 100 wt% of the total second anode active material layer AML22. The content of the second artificial graphite AG in the second anode active material layer AML22 may be 20 wt% to 50 wt%, or 25 wt% to 45 wt%, based on 100 wt% of the total second anode active material layer AML22. The ratio of the weight of the second natural graphite NG to the weight of the second artificial graphite AG in the second anode active material layer AML22 may be 1 to 10, 1 to 5, or 1 to 3.

[0104] The upper negative electrode active material layer, where lithium ions are inserted / deinserted first during the charge / discharge process, is a crucial component influencing the rapid charging characteristics. Therefore, if the second negative electrode active material layer AML22 contains improved natural graphite NG, the first negative electrode active material layer can still exhibit excellent rapid charging performance even if it contains first natural graphite NNG whose characteristics are not precisely controlled.

[0105] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

[0106] Example 1 (Preparation of natural graphite with improved physical properties) Spherical natural graphite was mixed with pitch to form aggregates. The aggregates were subjected to a first heat treatment, and the surface was coated with pitch. Next, a second heat treatment process was performed to prepare natural graphite with an average particle size of approximately 7 μm.

[0107] (Manufacturing of negative electrodes) The naturally produced graphite and artificial graphite with an average particle size of approximately 14 μm were mixed in a weight ratio of 75:25. The graphite and silicon were mixed in a weight ratio of 98:2 to produce the first negative electrode active material. A mixture of the first negative electrode active material, SBR (styrene-butadiene rubber), and CMC (carboxymethylcellulose) in a weight ratio of 1:1 was mixed in a weight ratio of 96:4 to prepare the first negative electrode active material slurry.

[0108] The naturally produced graphite and artificial graphite with an average particle size of approximately 14 μm were mixed in a 50:50 weight ratio. The graphite and silicon were mixed in a 94:6 weight ratio to produce a second negative electrode active material. A mixture of the second negative electrode active material, SBR (styrene-butadiene rubber), and CMC (carboxymethylcellulose) in a 1:1 weight ratio was mixed in a 99:1 weight ratio to prepare a second negative electrode active material slurry.

[0109] A first negative electrode active material slurry was coated to a thickness of 40 μm onto an 8 μm thick copper foil, dried at 100°C for more than one hour, and then rolled to produce a primary negative electrode. A second negative electrode active material layer slurry was coated to a thickness of 40 μm onto the primary negative electrode, dried at 100°C for more than one hour, and then rolled to produce a negative electrode.

[0110] (Manufacturing of positive electrodes) Cathode active material (LiNi 0.6 Co 0.2 Mn 0.2 A solution of O2, carbon conductive material (Super P), and PVDF (polyvinylidene fluoride) binder was added and mixed to produce an active material slurry. In the active material slurry, the weight ratio of active material:conductive material:binder was 98:1:1. The active material slurry was coated onto an aluminum current collector with a thickness of 12 μm using a thick-film coating machine, dried at 120°C for more than 1 hour, and then rolled (pressed) to produce a positive electrode.

[0111] (Manufacturing of lithium-ion batteries) (1) Manufacturing of full cells A lithium secondary battery was manufactured by stacking the fabricated negative electrode, PTFE separator, and positive electrode. As the electrolyte, a coin full cell was manufactured using a mixed solvent of EC (ethylene carbonate):EMC (ethylmethyl carbonate):DEC (diethyl carbonate) (3:5:2 volume ratio) in which 1.3M LiPF6 was dissolved.

[0112] (2) Manufacturing of half cells A lithium secondary battery was manufactured by stacking the fabricated negative electrode, PE separator, and lithium counter electrode. As the electrolyte, a 1.3M LiPF6 solution was used to manufacture coin half-cells.

[0113] Example 2 The negative electrode, positive electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that natural graphite and artificial graphite were mixed in a weight ratio of 75:25 when manufacturing the second negative electrode active material slurry.

[0114] Comparative Example 1 (Preparation of natural graphite) Spherical natural graphite was mixed with pitch to form aggregates. The aggregates were then subjected to a heat treatment process to prepare natural graphite with an average particle size of approximately 16 μm.

[0115] (Manufacturing of negative electrodes) The first negative electrode active material was prepared by mixing the aforementioned manufactured natural graphite with artificial graphite having an average particle size of approximately 14 μm in a weight ratio of 75:25. The first negative electrode active material was mixed with a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethylcellulose) in a 1:1 weight ratio, and then mixed in a weight ratio of 96:4 to prepare the first negative electrode active material slurry.

[0116] The naturally produced graphite and artificial graphite with an average particle size of approximately 14 μm were mixed in a weight ratio of 25:75 to produce the second negative electrode active material. The second negative electrode active material was mixed with SBR (styrene-butadiene rubber) and CMC (carboxymethylcellulose) in a weight ratio of 1:1 to prepare a slurry of the second negative electrode active material in a weight ratio of 99:1.

[0117] A first negative electrode active material slurry was coated onto an 8 μm thick copper foil to a thickness of 40 μm, dried at 100°C for more than one hour, and then rolled to produce a primary negative electrode. A second negative electrode active material slurry was coated onto the primary negative electrode to a thickness of 40 μm, dried at 100°C for more than one hour, and then rolled to produce a negative electrode.

[0118] (Manufacturing of lithium-ion batteries) Otherwise, the positive electrode and lithium secondary battery were manufactured using the same method as in Example 1.

[0119] Comparative Example 2 The negative electrode, positive electrode, and lithium secondary battery were manufactured in the same manner as in Comparative Example 1, except that natural graphite and artificial graphite were mixed in a 50:50 weight ratio when manufacturing the second negative electrode active material slurry.

[0120] Comparative Example 3 The negative electrode, positive electrode, and lithium secondary battery were manufactured in the same manner as in Comparative Example 1, except that natural graphite and artificial graphite were mixed in a weight ratio of 75:25 when manufacturing the second negative electrode active material slurry.

[0121] Evaluation Example 1 The ion transfer resistance was measured for the half-cells produced according to the examples and comparative examples, and the results are shown in Table 1 below.

[0122] Ion transfer resistance was measured using the EIS measurement equipment of BIO-LOGIC VMP3, employing a method that measures AC resistance in the frequency range of 30 mHz to 10 kHz.

[0123] Evaluation Example 2 The internal resistance of the full cells produced according to the examples and comparative examples was measured using the method described below and is shown in Table 1.

[0124] A full cell was charged at 25°C with a 0.2C rate current until the voltage reached 4.25V (vs.Li), and then cut off with a 0.05C rate current while maintaining 4.25V in constant voltage mode. Next, the cell was discharged with a constant current at a 0.2C rate until the voltage reached 2.8V (vs.Li) (formation cycle). After the formation cycle, the battery was charged to a state of charge (SOC50) (where the battery is charged to 50% of its total charge capacity when the total charge capacity is to be increased to 100%, which means that the discharge state is 50%) while a current of 1C was applied for 10 seconds, and the voltage drop (V) was measured. The resistance value was calculated from the measured voltage and applied current (1C), and the result is shown as the DC-IR (Direct Current Inertia).

[0125] [Table 1]

[0126] Referring to Table 1, it can be confirmed that the half-cells of the examples have lower movement resistance and superior ion conductivity compared to the half-cells of the comparative examples. Furthermore, it can be confirmed that the full-cells of the examples have lower internal resistance than the full-cells of the comparative examples, making them advantageous for rapid charging.

[0127] Evaluation Example 3 The rapid charging characteristics of the full cells produced according to the examples and comparative examples were evaluated using the following method.

[0128] A fully charged cell that had completed the chemical conversion cycle was charged to SOC20, and the SOC20 battery was then charged with a constant current at 3.6C rate at 30°C to reach SOC80 (4.25V cut-off condition). The time taken to reach SOC80 and the maximum voltage are shown in Table 2 below.

[0129] A fully charged cell that had completed the chemical conversion cycle was charged to SOC8, and the SOC8 battery was then charged with a constant current at a rate of 4.8C at 25°C to reach SOC80 (4.25V cut-off condition). The time taken to reach SOC80 and the maximum voltage are shown in Table 2 below.

[0130] [Table 2]

[0131] Referring to Table 2, it can be confirmed that the lithium secondary battery according to the example has a lower maximum voltage than the lithium secondary battery according to the comparative example, and that overvoltage is effectively prevented. [Explanation of Symbols]

[0132] 100: Lithium-ion secondary battery 10: Positive electrode 11: Positive lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Housing 60: Sealing material 70: Electrode tab 71: Positive tab 72: Negative tab

Claims

1. Negative electrode current collector and The negative electrode active material layer on the negative electrode current collector, Includes, The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer that are sequentially stacked on the negative electrode current collector. Each of the first and second negative electrode active material layers contains natural graphite and artificial graphite. The average particle size D50 of the natural graphite is smaller than the average particle size of the artificial graphite. The ratio of the weight of natural graphite to the weight of artificial graphite in the second negative electrode active material layer is 1 to 5. Negative electrode for lithium secondary batteries.

2. The ratio of the weight of natural graphite to the weight of artificial graphite in the second negative electrode active material layer is 1 to 3. The negative electrode for a lithium secondary battery according to claim 1.

3. The average particle size of the aforementioned natural graphite is 5 μm to 10 μm. The negative electrode for a lithium secondary battery according to claim 1.

4. When measuring XRD using CuKα radiation, the ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) of the aforementioned natural graphite is between 45 and 75. The negative electrode for a lithium secondary battery according to claim 1.

5. The specific surface area of ​​the aforementioned natural graphite is 1.8 m². 2 / g to 2.2m 2 / g is The negative electrode for a lithium secondary battery according to claim 1.

6. The specific capacity of the aforementioned natural graphite is 355 mAh / g to 360 mAh / g. The negative electrode for a lithium secondary battery according to claim 1.

7. The content of the natural graphite contained in the first and second negative electrode active material layers is 45 wt% to 80 wt%. The negative electrode for a lithium secondary battery according to claim 1.

8. Each of the first and second negative electrode active material layers includes a binder. The content of the binder in the second negative electrode active material layer is less than the content of the binder in the first negative electrode active material layer. The negative electrode for a lithium secondary battery according to claim 1.

9. Each of the first and second negative electrode active material layers further contains silicon. The negative electrode for a lithium secondary battery according to claim 1.

10. The ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer is 2:1 to 1:

2. The negative electrode for a lithium secondary battery according to claim 1.

11. Negative electrode current collector and The negative electrode active material layer on the negative electrode current collector, Includes, The negative electrode active material layer contains natural graphite and artificial graphite. The negative electrode active material layer includes a first region adjacent to the negative electrode current collector and a second region adjacent to the upper surface of the negative electrode active material layer. The content of the natural graphite contained in the first and second regions respectively is 45 wt% to 80 wt%, The average particle size of the natural graphite is smaller than the average particle size of the artificial graphite. Negative electrode for lithium secondary batteries.

12. The ratio of the content of natural graphite in the second region to the content of natural graphite in the first region is 0.8 to 1.

4. The negative electrode for a lithium secondary battery according to claim 11.

13. The ratio of the weight of natural graphite to the weight of artificial graphite in the second region is 1 to 3. The negative electrode for a lithium secondary battery according to claim 11.

14. The negative electrode active material layer further comprises a binder, The content of the binder in the second region is less than the content of the binder in the first region. The negative electrode for a lithium secondary battery according to claim 11.

15. The average particle size D50 of the aforementioned natural graphite is 5 μm to 10 μm. The negative electrode for a lithium secondary battery according to claim 11.

16. When measuring XRD using CuKα radiation, the ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) of the aforementioned natural graphite is between 45 and 75. The negative electrode for a lithium secondary battery according to claim 11.

17. Negative electrode current collector and The negative electrode active material layer on the negative electrode current collector, Includes, The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer that are sequentially stacked on the negative electrode current collector. The first negative electrode active material layer comprises first natural graphite and first artificial graphite. The aforementioned second negative electrode active material layer contains a second natural graphite and a second artificial graphite. The average particle size of the second natural graphite is smaller than the average particle size of the first natural graphite. The ratio of the weight of the second natural graphite to the weight of the second artificial graphite in the second negative electrode active material layer is 1 to 3. Negative electrode for lithium secondary batteries.

18. The average particle size of the second natural graphite is 5 μm to 10 μm. The average particle size of the first natural graphite is 12 μm to 20 μm. The negative electrode for a lithium secondary battery according to claim 17.

19. When XRD is measured using CuKα radiation, the ratio of the peak intensity of the (002) plane to the peak intensity of the (110) plane (I(002) / I(110)) of the second natural graphite is between 45 and 75. When measuring XRD using CuKα radiation, the first natural graphite has a ratio (I(002) / I(110)) of 60 to 120 for the peak intensity of the (002) plane to the peak intensity of the (110) plane. The negative electrode for a lithium secondary battery according to claim 18.

20. Each of the first and second negative electrode active material layers further contains silicon. The negative electrode for a lithium secondary battery according to claim 17.

Images