Positive electrode active material for lithium secondary battery, positive electrode including the same, and lithium secondary battery including the same

Abstract

To provide a positive electrode active material with high energy density, high average voltage, and an excellent lifetime characteristic despite its economical property.SOLUTION: The present invention relates to a positive electrode for a lithium secondary battery, and a lithium secondary battery including the same. More specifically, the positive electrode for a secondary battery includes a current collector, a first positive electrode active material layer on the current collector, and a second positive electrode active material layer on the first positive electrode active material layer. The first positive electrode active material layer includes first particles containing a compound of Chemical Formula 1 and having an olivine structure, and second particles containing a compound of Chemical Formula 2 and having a layered structure. The second active material layer includes third particles containing a compound of Chemical Formula 3 and having an olivine structure. Each of the first to third particles is in a single particle form. The average particle diameter of the second particles is larger than those of the first particles and the third particles.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery including the same, and more particularly to a positive electrode active material including an olivine-based lithium compound, a positive electrode active material including a layered lithium compound, a positive electrode including the same, and a lithium secondary battery including the same. [Background technology]

[0002] Recently, the demand for high-energy-density, high-capacity secondary batteries has been increasing rapidly due to the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles. Therefore, research and development efforts to improve the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, which contain active materials that allow the intercalation and deintercalation of lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted / deintercalated at the cathode and anode. [Prior art documents] [Patent documents]

[0004] Korean Patent Registration No. 10-1718054 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a positive electrode active material that is economical and has high energy density, high average voltage, and excellent life characteristics.

[0006] Another problem to be solved by the present invention is to provide a positive electrode that is economical and has a high energy density, a high average voltage, and excellent life characteristics. [Means for solving the problem]

[0007] The positive electrode of the lithium secondary battery according to the concept of the present invention can include a current collector, a first positive electrode active material layer on the current collector, and a second positive electrode active material layer on the first positive electrode active material layer.

[0008] The first positive electrode active material layer can include first particles represented by the following Chemical Formula 1 and having an olivine structure, and second particles represented by the following Chemical Formula 2 and having a layered structure. The second positive electrode active material layer is represented by the following Chemical Formula 3 and can include third particles having an olivine structure. Each of the first particles and the third particles can have a single-particle shape.

[0009] The average particle diameter of the second particles can be larger than the average particle diameter of each of the first particles and the third particles.

[0010] [Chemical Formula 1] Li b2 , z2 , , 2-c2 Mn z1 Fe x1 B1 y1 PO 4-c1 In Chemical Formula 1, B1 is one or more elements selected from the group consisting of Al, Ti, V, and Mg, and 0.8 < a1 ≦ 1.2, 0.4 ≦ z1 ≦ 0.8, 0.2 ≦ x1 ≦ 0.6, 0 ≦ y1 ≦ 0.05, 0 < c1 ≦ 0.05, and x1 + y1 + z1 = 1 can hold.

[0011] [Chemical Formula 2] Li a2 Ni x2 Co y2 Mn z2 B2 b2 O 2-c2 In Chemical Formula 2, B2 is at least one element selected from the group consisting of Al, Ti, Mg, Zr, Mo, and Nb, and 0.8 ≦ a2 ≦ 1.2, 0.5 ≦ x2 ≦ 0.8, 0.0 ≦ y2 ≦ 0.10, 0.1 ≦ z2 ≦ 0.35, 0 ≦ b2 ≦ 0.10 < c2 ≦ 0.05, and x2 + y2 + z2 + b2 = 1 can hold.

[0012] [Chemical Formula 3] Li a3 Mn z3 Fe x3 B3 y3 PO 4-c3 In the above Chemical Formula 3, B3 is one or more elements selected from the group consisting of Al, Ti, V, and Mg, and 0.8 < a3 ≤ 1.2, 0.4 ≤ z3 ≤ 0.8, 0 ≤ x3 ≤ 0.6, 0 ≤ y3 ≤ 0.05, 0 < c3 ≤ 0.05, and x3 + y3 + z3 = 1 may hold.

Advantages of the Invention

[0013] The positive electrode according to the present invention includes a first positive electrode active material layer containing olivine-based first particles with a size of several hundred nm to several μm and layered second particles with a size of several μm, and a second positive electrode active material layer containing olivine-based third particles with a size of several hundred nm to several μm laminated on the first positive electrode active material layer. By doing so, the pellet density, capacity, and energy density can be improved. The positive electrode according to the present invention is easy to manufacture an electrode plate and can improve the resistance of the electrode plate. The lithium secondary battery according to the present invention can relatively improve the life characteristics.

Brief Description of the Drawings

[0014] [Figure 1] It is a conceptual diagram schematically showing a lithium secondary battery according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 3] It is a schematic view showing a lithium secondary battery according to an embodiment, which is a cylindrical battery form. [Figure 4] It is a schematic view showing a lithium secondary battery according to an embodiment, which is a rectangular battery form. [Figure 5] It is a schematic view showing a lithium secondary battery according to an embodiment, which is a pouch-type battery form. [Figure 6] It is a cross-sectional view of a positive electrode for a lithium secondary battery according to an embodiment of the present invention. [Figure 7] 2 is an enlarged view of a first positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 8] 3 is an enlarged view of a second positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 9] 1 is a SEM photograph of a first particle according to an embodiment of the present invention. [Figure 10] 1 is an SEM photograph of a second particle according to an embodiment of the present invention. [Figure 11] 10 is an SEM photograph of a third particle according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] In this specification, when a component is referred to as being on another component, it means that the component may be directly formed on the other component, or that a third component may be interposed between them. However, the present invention is not limited to the embodiments disclosed below, and may be realized in various forms and may undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0016] In this specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component, or a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0017] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, elements referred to as "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements.

[0018] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0019] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that utilizes dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0020] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte solution ELL.

[0021] The positive electrode 10 and the negative electrode 20 can be separated from each other by a separator 30. The separator 30 can be disposed 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 solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 can be immersed in the electrolyte solution ELL.

[0022] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0023] 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. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIGS. 6A and 6B. The current collector COL1 may be made of, but is not limited to, aluminum.

[0024] negative electrode 20 The negative electrode 20 for a lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located 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.

[0025] For example, the negative electrode active material layer AML2 may contain 90 to 99 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % of the conductive material.

[0026] The binder serves to firmly adhere the negative active material particles to each other and to firmly adhere the negative active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0027] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0028] The water-based binder may be selected from styrene-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0029] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0030] The dry binder may be a polymeric material that can be fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0031] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery may be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0032] The current collector COL2 may be made of a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0033] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0034] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0035] 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.

[0036] As the substance capable of doping and undoping the 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 an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof), or a combination of these. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0037] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, it can include secondary particles (cores) assembled from primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, for example, coating the primary silicon particles with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0038] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and a first coating layer of amorphous carbon located on the surface of the core.

[0039] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by being mixed with a carbon-based negative electrode active material.

[0040] 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. As such a separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that 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.

[0041] Separator 30 can include a porous substrate and a first coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0042] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0043] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0044] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0045] The organic material and the inorganic material may be mixed in one first coating layer, or may be stacked in a form in which a first coating layer containing an organic material and a first coating layer containing an inorganic material are stacked.

[0046] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0047] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0048] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0049] Examples of the carbonate solvent that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0050] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0051] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0052] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0053] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0054] The lithium salt dissolves in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. 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, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethersulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0055] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to embodiments, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a prismatic type, and FIGS. 4 and 5 illustrating pouch types. Referring to FIGS. 2 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 2. Also, as shown in FIG. 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 FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0056] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0057] 6 is a cross-sectional view of a positive electrode for a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 6, the positive electrode 10 for a lithium secondary battery may include a current collector COL1 (see FIG. 1) and a positive electrode active material layer AML1 (see FIG. 1), as described above. The positive electrode active material layer AML1 may include a first positive electrode active material layer ATL1 and a second positive electrode active material layer ATL2 stacked on the first positive electrode active material layer ATL1.

[0058] Hereinafter, the first positive electrode active material layer ATL1 and the second positive electrode active material layer ATL2 will be described in more detail.

[0059] First positive electrode active material layer ATL1 FIG. 7 is an enlarged view of the first positive electrode active material layer ATL1 of the positive electrode for a lithium secondary battery according to an embodiment of the present invention.

[0060] The first positive electrode active material layer ATL1 may include first particles PTC1, second particles PTC2, and a first functional additive ADD1. The first functional additive ADD1 may include a first binder BND1 and a first conductive material CDM1.

[0061] The first binder BND1 can bind the first particles PTC1 and the first conductive material CDM1 to each other. The first binder BND1 can also stably fix the first positive electrode active material layer ATL1 to the current collector COL1. For example, the first binder BND1 can include, but is not limited to, at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl fluoride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, an epoxy resin, a (meth)acrylic resin, a polyester resin, and nylon.

[0062] The first conductive material CDM1 can be used to improve the conductivity of the first positive electrode active material layer ATL1. Any conductive material that does not cause a chemical change in the first positive electrode active material layer ATL1 can be used as the first conductive material CDM1 without limitation. For example, the first conductive material CDM1 can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0063] Hereinafter, each of the first particles PTC1 and the second particles PTC2 in the first positive electrode active material layer ATL1 will be described in more detail.

[0064] 1st particle PTC1 The first particles PTC1 can include an olivine-based lithium compound represented by Chemical Formula 1 below.

[0065] [Chemical Formula 1] Li a1 Mn z1 Fe x1 B1 y1 PO 4-c1 In the above Chemical Formula 1, 0.8 < a1 ≤ 1.2, 0.4 ≤ z1 ≤ 0.8, 0.2 ≤ x1 ≤ 0.6, 0 ≤ y1 ≤ 0.05, 0 < c1 ≤ 0.05 can be satisfied. B1 can be one or more elements selected from the group consisting of Al, Ti, V, and Mg. B1 can be a dopant doped into the first particles PTC1. For example, B1 can include Ti.

[0066] The first particles PTC1 can further include carbon derived from the above-described positive electrode active material layer AML1. The carbon element content in the first particles PTC1 can be 0.5 wt% to 5 wt%, 0.5 wt% to 3 wt%, or 0.5 wt% to 2 wt%.

[0067] The first particles PTC1 may have a single particle shape. In this specification, a single particle may refer to a single particle without an internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are morphologically present in an independent phase without aggregation with each other. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a separately separated form. Alternatively, a single particle may be in a form in which two to 100 first primary particles NNP_1 are attached to each other.

[0068] The first particles PTC1 may be a nano-shaped cathode active material. The first particles PTC1 may include at least one first primary particle NNP_1. In one embodiment, the first particles PTC1 may have a spherical or elliptical shape formed by aggregation of the first primary particles. In another embodiment, the first particles PTC1 may have a random shape, not a spherical shape, even if the first primary particles NNP_1 are aggregated.

[0069] In one embodiment, the average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution. In one embodiment, the average particle size (D50) of the first particles PTC1 may be a value measured using a particle size analyzer.

[0070] In one embodiment, the average particle size of the first particles PTC1 may be 500 nm to 5 μm, 100 nm to 3 μm, 500 nm to 2.5 μm, or about 1 μm. The average particle size (D50) of the first particles PTC1 may be smaller than the average particle size (D50) of the second particles PTC2 described below.

[0071] The size of at least one first primary particle NNP_1 constituting the first particle PTC1 can be measured using a scanning electron microscope (SEM). In one embodiment, the size of the first primary particle NNP_1 may refer to the diameter measured by randomly selecting approximately 30 first primary particles NNP_1 from an electron microscope photograph of the positive electrode active material. The size of the first primary particles NNP_1 may be uniform. The size of the at least one first primary particle NNP_1 constituting the first particle PTC1 may be 100 nm to 200 nm, 50 nm to 150 nm, 50 nm to 100 nm, 100 nm to 150 nm, or 200 nm to 300 nm. The average size of the first primary particles NNP_2 may be smaller than the size of the second primary particles NNP_2 described below.

[0072] The first particle PTC1 may include at least one primary particle (or single particle). The size of the at least one first primary particle NNP_1 constituting the first particle PTC1 may be measured using a scanning electron microscope (SEM). In one embodiment, the size of the first primary particle NNP_1 may refer to the diameter measured by randomly selecting approximately 30 first primary particles NNP_1 from an electron microscope photograph of the positive electrode active material. The size of the first primary particles NNP_1 may be uniform.

[0073] In one embodiment, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or a portion of the surface of the first particles PTC1. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the metal-containing compound may further include lithium. The coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[0074] In one embodiment, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the first primary particles NNP_1. The grain boundary coating layer may be present inside the first particle PTC1. The grain boundary coating layer may be formed by coating along the interface between the first primary particles NNP_1 inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1.

[0075] The grain boundary coating layer may contain carbon and / or a carbon-containing compound, and may further contain at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0076] The interior of the first particle PTC1 described above may refer to the entire interior of the first particle PTC1 excluding the surface of the first particle PTC1. For example, the interior of the first particle PTC1 may refer to a region from a depth of about 10 nm to the entire interior of the surface of the first particle PTC1, or from a depth of 10 nm to a depth of about 2 μm.

[0077] The first particles PTC1 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which further improves the electrical conductivity of the first particles PTC1.

[0078] The first particles PTC1 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt% to 10 wt%, 1 wt% to 3 wt%, or 1.5 wt% to 2.5 wt%. For example, the carbon content in the first particles PTC1 in the form of secondary particles may be higher than the content in the form of single particles.

[0079] The first particles PTC1 may have a spherical shape formed by agglomeration of a plurality of first primary particles NNP_1. The first particles PTC1 may exhibit the following properties due to the first primary particles NNP_1 closely agglomerating to one another: The above-described coating layer and / or grain boundary coating layer of the first particles are well maintained, thereby increasing electrical conductivity and improving low-temperature characteristics. The increased electrode plate binding strength reduces the binder capacity. The first particles PTC1 may have a spherical or elliptical shape.

[0080] 2nd particle PTC2 The second particles PTC2 may include a lithium compound having a layered structure represented by the following Chemical Formula 2.

[0081] [Chemical formula 2] Li a2 Ni x2 Coy2 Mn z2 B2 b2 O 2-c2 In Chemical Formula 2 above, 0.8 ≦ a2 ≦ 1.2, 0.5 ≦ x2 ≦ 0.8, 0.0 ≦ y2 ≦ 0.10, 0.1 ≦ z2 ≦ 0.35, 0 ≦ b2 ≦ 0.10 < c2 ≦ 0.05, and x2 + y2 + z2 + b2 = 1 may hold. B2 may be at least one element selected from the group consisting of Al, Ti, Mg, Zr, Mo, and Nb. B2 may be a dopant doped into the second particle PTC2. The dopant can enhance the surface stability and structural stability of the second particle PTC2.

[0082] The second particle PTC2 can include a layered compound having excellent electrochemical properties by combining the high capacity of nickel, the thermal stability and low price of manganese, and the stable electrochemical properties of cobalt.

[0083] The second particle PTC2 can include a lithium nickel-based composite oxide as a nickel-based active material. As one embodiment, the second particle PTC2 can include a high-nickel-based cathode active material containing a high content of nickel. The high-nickel-based cathode active material can achieve high capacity and high performance. As another embodiment, the second particle PTC2 can include a mid-nickel-based cathode active material containing a medium content of nickel. The mid-nickel-based cathode active material can achieve high capacity and high performance. By including the second particle PTC2 according to the present invention, high capacity and high energy density of the secondary battery can be realized.

[0084] Referring to FIG. 7, the second particles PTC2 may have a single particle shape. Herein, a single particle may refer to a single particle without an internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are morphologically present in an independent phase without cohesion. For example, a single particle may be a single crystal. Alternatively, a single particle may contain several crystals. A single particle may be in a separately separated form. Alternatively, a single particle may be in a form in which two to 100 second primary particles NNP_2 are attached to each other. Herein, a single particle of the second particles PTC2 may be defined as a small particle SP2 or small grain SP2.

[0085] When the second particles PTC2 are single particles, the second particles PTC2 may include at least one second primary particle. In one embodiment, the second particles PTC2 may have a spherical or elliptical shape formed by the aggregation of the second primary particles NNP_2. In another embodiment, the second particles PTC2 may have a random shape rather than a spherical shape even when the second primary particles NNP_2 are aggregated. When the second particles PTC2 are in the form of aggregation of the second primary particles NNP_2, the second particles PTC2 may have a less structured form than the polycrystalline second particles PTC2 described below. In other words, the form may be more random.

[0086] In one embodiment, the average particle size may refer to the diameter (D50) of particles at 50% by volume of cumulative volume in the particle size distribution. In one embodiment, the average particle size (D50) of the second particles PTC2 may be a value measured using a particle size analyzer. The average particle size (D50) of the small particles SP2 may be 2 μm to 5 μm, 1 μm to 4 μm, 2 μm to 3 μm, 3 μm to 7 μm, 4 μm to 6 μm, or about 5 μm.

[0087] 7, the second particles PTC2 may have a polycrystalline form and may include secondary particles formed by agglomeration of at least two or more second primary particles NNP_2. In other words, one second particle PTC2 may include a plurality of second primary particles NNP_2 agglomerated together. The second particles PTC2 formed by a plurality of second primary particles NNP_2 may have an agglomerated spherical shape, or may have a random shape even when the second primary particles NNP_2 are gathered. In this specification, the second particles PTC2, which are single particles, may be defined as large particles PC2.

[0088] In one embodiment, the average particle size may refer to the diameter (D50) of particles at 50% cumulative volume in the particle size distribution. In one embodiment, the average particle size (D50) of the large particles PC2 may be 10 μm to 20 μm, 12 μm to 15 μm, 12 μm to 18 μm, 14 μm to 18 μm, 15 μm to 20 μm, or approximately 16 μm. The average particle size (D50) of the large particles PC2 may be larger than the average particle size (D50) of the small particles SP2. The number of second primary particles NNP_2 constituting the large particles PC2 may be greater than the number of second primary particles NNP_2 constituting the small particles SP2. That is, the large particles PC2 may have a higher density and a more structured morphology than the small particles SP2.

[0089] The second particles PTC2 may refer to both the large particles PC2 and the small particles SP2. The average particle size (D50) of the second particles PTC2 may be 3 μm to 20 μm, 4 μm to 15 μm, 4 μm to 10 μm, 10 μm to 20 μm, 12 μm to 15 μm, or 5 μm to 12 μm. For example, the average particle size (D50) of the second particles PTC2 may be approximately 11 μm. The average particle size (D50) of the second particles PTC2 may be larger than those of the first particles PTC1 and the third particles PTC3.

[0090] The average size of the second primary particles NNP_2 constituting the second particles PTC2 may be 0.5 μm to 5 μm, 1 μm to 3 μm, 2 μm to 3 μm, or about 2 μm. In one embodiment, the average size of the second primary particles NNP_2 may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the positive electrode active material. The size of the second primary particles NNP_2 may be uniform. The average size of the second primary particles NNP_2 may be larger than the average size of the first primary particles NNP_1.

[0091] In one embodiment, the second particles PTC2 may include a coating layer on their surfaces. By including the coating layer, the second particles can effectively prevent structural collapse due to repeated charge and discharge, thereby improving the lifespan of the secondary battery.

[0092] The coating layer may include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the coating layer may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the coating layer may further include lithium, manganese, and / or nickel.

[0093] A method for measuring the metal content in the coating layer of the second particles PTC2 may include performing scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) on the second particles PTC2. The aluminum and / or magnesium content in the coating layer may be determined through this analysis. In addition to SEM-EDS, other methods for measuring the metal content in the coating layer include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0094] In one embodiment, the second particles PTC2 may be in a form in which the large particles PC2 and the small particles SP2 coexist. When the second particles PTC2 coexist in the form of the large particles PC2 and the small particles SP2 in the positive electrode active material, the positive electrode active material may be considered to be bimodal.

[0095] In one embodiment, the content of small particles SP2 may be less than the content of large particles PC2 relative to the total content of bimodal second particles PTC2. In one embodiment, the content of small particles SP2 may be 20 wt % to 40 wt % relative to the total content of the second particles PTC2.

[0096] The BET specific surface area of ​​the second particles PTC2 may be smaller than that of the first particles PTC2, for example, the BET specific surface area of ​​the second particles may be 0.3 to 1.2.

[0097] The first positive electrode active material layer ATL1 will be described in more detail below. The first positive electrode active material layer ATL1 may include first particles PTC1 and second particles PTC2. In the first positive electrode active material layer ATL1, the weight of the second particles PTC2 may be smaller than that of the first particles PTC1.

[0098] Since both the first particle PTC1 and the second particle PTC2 contain manganese (Mn), the operating voltage of the secondary battery can be improved. Since the second particle PTC2 contains nickel, the energy density of the secondary battery can be improved compared to the first particle PTC1, and a higher capacity can be achieved.

[0099] The first particles PTC1 have the advantages of high stability and long lifespan. By using the structurally stable first particles PTC1 as the main material of the positive electrode active material, the relatively low stability and lifespan of the second particles PTC2 can be compensated for.

[0100] The positive electrode active material according to the present invention can improve the energy density, capacity, and operating voltage compared to batteries containing general lithium iron phosphate compounds or lithium manganese iron phosphate compounds by mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio.

[0101] Since the first particles PTC1 have a very small particle size, a large amount of binder BND may be required to attach the first particles PTC1 to the current collector COL1 (see FIG. 1).

[0102] The average particle size (D50) of the second particles PTC2 may be several μm. In the present invention, by providing the first positive electrode active material layer ATL1 additionally including the second particles PTC2 with a large average particle size (D50), it is possible to improve the binding strength with the current collector COL1 while containing a large amount of nano-sized olivine-based compound. In other words, the first positive electrode active material layer ATL1, in which the first particles PTC1 and the second particles PTC2 are mixed, may make it easier to manufacture an electrode plate.

[0103] As a result, by first attaching the first positive electrode active material layer ATL1 to the current collector, the electrode plate can be manufactured more easily. By first forming the first positive electrode active material layer ATL1, which has a strong binding strength with the current collector COL1, the electrode plate resistance can be improved. Furthermore, a lithium secondary battery with excellent performance can be provided.

[0104] Second positive electrode active material layer ATL2 FIG. 8 is an enlarged view of a second positive electrode active material layer of a positive electrode for a lithium secondary battery according to an embodiment of the present invention.

[0105] 8, the second positive electrode active material layer ATL2 may include third particles PTC3 and a second functional additive ADD2. The second functional additive ADD2 may include a second binder BND2 and a second conductive material CDM2.

[0106] The second binder BND2 can bind the third particles PTC3 and the second conductive material CDM2 to each other. The second binder BND1 can also stably fix the second positive electrode active material layer ATL2 on the first positive electrode active material layer ATL1. In one embodiment, the second binder BND2 can include, but is not limited to, at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl fluoride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, an epoxy resin, a (meth)acrylic resin, a polyester resin, and nylon.

[0107] The second conductive material CDM2 can be used to improve the conductivity of the second positive electrode active material layer ATL2. Any conductive material that does not cause a chemical change in the second positive electrode active material layer ATL2 can be used as the second conductive material CDM2 without limitation. In one embodiment, the second conductive material CDM1 can include a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, or carbon nanotube; a metal-based material in the form of a metal powder or metal fiber containing copper, nickel, aluminum, silver, or the like; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

[0108] Third particle PTC3 The third particle PTC3 can contain an olivine-based lithium compound represented by the following Chemical Formula 3.

[0109] [Chemical Formula 3] Li a3 Mn z3 Fe x3 B3 y3 PO 4-c3 In Chemical Formula 3, 0.8 < a3 ≤ 1.2, 0.4 ≤ z3 ≤ 0.8, 0 ≤ x3 ≤ 0.6, 0 ≤ y3 ≤ 0.05, and 0 < c3 ≤ 0.05 may hold. B3 can be one or more elements selected from the group consisting of Al, Ti, V, and Mg. B3 can be a dopant doped into the third particle PTC3. For example, B3 can contain Ti.

[0110] The third particle PTC3 can further contain carbon derived from the above-described positive electrode active material layer AML1. The carbon element content in the third particle PTC3 can be 0.5 wt% to 5 wt%, 0.5 wt% to 3 wt%, or 0.5 wt% to 2 wt%.

[0111] The third particle PTC3 can have a single particle shape. In this specification, a single particle can mean an independent particle having no grain boundary inside. A single particle can mean a single particle, a monolith structure, a single body structure, or a non-aggregated particle that exists as an independent phase where particles do not aggregate morphologically. As an example, a single particle can be a single crystal. Or, a single particle can be a particle containing several crystals. A single particle can be in a form separated alone. Or, a single particle can be in a form where 2 to 100 third primary particles NNP_3 are attached to each other.

[0112] The third particles PTC3 may be a nano-shaped positive electrode active material. The third particles PTC3 may include at least one third primary particle NNP_3. In one embodiment, the third particles PTC3 may have a spherical or elliptical shape formed by aggregation of the third primary particles. In another embodiment, the third particles PTC3 may have a random shape, not a spherical shape, even if the third primary particles NNP_3 are aggregated.

[0113] In one embodiment, the average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution. In one embodiment, the average particle size (D50) of the third particles PTC3 may be a value measured using a particle size analyzer.

[0114] In one embodiment, the average particle size of the third particles PTC3 may be 500 nm to 2.5 μm, or about 1 μm. The size of at least one third primary particle NNP_3 constituting the third particles PTC3 may be measured using a scanning electron microscope (SEM). In one embodiment, the size of the third primary particles NNP_3 may refer to the diameter measured by randomly selecting about 30 third primary particles NNP_3 from an electron microscope photograph of the positive electrode active material. The size of the third primary particles NNP_3 may be uniform. The size of the third primary particles NNP_3 may be 100 nm to 500 nm, or 100 nm to 200 μm.

[0115] The third particles PTC3 may include at least one primary particle (or single particle). The size of the at least one third primary particle NNP_3 constituting the third particles PTC3 may be measured using a scanning electron microscope (SEM). In one embodiment, the size of the third primary particles NNP_3 may refer to the diameter measured by randomly selecting approximately 30 third primary particles NNP_3 from an electron microscope photograph of the positive electrode active material. The size of the third primary particles NNP_3 may be uniform.

[0116] The size of at least one third primary particle NNP_3 constituting the third particles PTC3 may be 100 nm to 200 nm, 50 nm to 150 nm, 50 nm to 100 nm, 100 nm to 150 nm, or 200 nm to 300 nm.

[0117] In one embodiment, the third PTC3 particles may include a coating layer on their surfaces. The coating layer may cover the entire surface of the third PTC3 particles or a portion of the surface of the third PTC3 particles. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the metal-containing compound may further include lithium. The coating layer may improve the structural stability and electrical conductivity of the third PTC3 particles.

[0118] In one embodiment, the third particle PTC3 may further include a grain boundary coating layer on the surface of each of the third primary particles NNP_3. The grain boundary coating layer may be present inside the third particle PTC3. The grain boundary coating layer may be formed by coating along the interface between the third primary particles NNP_3 inside the third particle PTC3. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the third particle PTC3.

[0119] The grain boundary coating layer may contain carbon and / or a carbon-containing compound, and may further contain at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0120] The interior of the third particle PTC3 described above may refer to the entire interior of the third particle PTC3 excluding the surface of the third particle PTC3. For example, the interior of the third particle PTC3 may refer to a region from a depth of about 10 nm to the entire inside of the surface of the third particle PTC3, or from a depth of 10 nm to a depth of about 2 μm.

[0121] The third particles PTC3 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the third particles PTC3. In addition, the third particles PTC3 further include a grain boundary coating portion, which further improves the electrical conductivity of the third particles PTC3.

[0122] The third particles PTC3 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the third particles PTC3 may be 0.5 wt% to 10 wt%, 1 wt% to 3 wt%, or 1.5 wt% to 2.5 wt%. For example, the carbon content in the third particles PTC3 in the form of secondary particles may be higher than that in the form of single particles.

[0123] The weight of the second particles PTC2 relative to the total weight of the first particles PTC1, the second particles PTC2, and the third particles PTC3 in the positive electrode active material layer AML1 may be 5 wt % to 20 wt %, 10 wt % to 20 wt %, 15 wt % to 30 wt %, 20 wt % to 30 wt %, or 25 wt % to 40 wt %.

[0124] The positive electrode or positive electrode active material layer AML1 may contain manganese (Mn). The total doping amount of manganese (Mn) may be defined as the sum of the doping amount (M1) of manganese (Mn) contained in the first positive electrode active material layer ATL1 and the doping amount (M2) of manganese (Mn) contained in the second positive electrode active material layer ATL2. The doping amount (M1) of manganese (Mn) contained in the first positive electrode active material layer ATL1 may be defined as the sum of the product of the doping amount of manganese (Mn) in the first particles PTC1 (z1 in Formula 1 above) and the weight ratio of the first particles PTC1, and the doping amount of manganese (Mn) in the second particles PTC2 (z2 in Formula 2 above) and the weight ratio of the second particles PTC2. The manganese (Mn) doping amount (M2) contained in the second positive electrode active material layer ATL2 can be defined as the product of the manganese (Mn) doping amount (z3 in the above-mentioned Formula 3) in the third particles PTC3 and the weight ratio of the third particles PTC3.

[0125] The total doping amount of manganese (Mn) in the positive electrode active material layer AML1 may be 0.40 to 0.90, 0.40 to 0.60, 0.50 to 0.90, 0.50 to 0.70, 0.60 to 0.80, 0.60 to 0.70, 0.50 to 0.60, or about 0.50.

[0126] According to an embodiment of the present invention, the positive electrode active material layer AML1 may have a double layer structure in which a second positive electrode active material layer ATL2 is stacked on a first positive electrode active material layer ATL1. The positive electrode active material layer AML1 may include a functional additive ADD. The first positive electrode active material layer ATL1 may include a first functional additive ADD1, and the second positive electrode active material layer ATL2 may include a second functional additive ADD2. The functional additive ADD may refer to at least one of the first functional additive ADD1 and the second functional additive ADD2.

[0127] The functional additives can include a conductive material CDM and a binder BND. The inclusion of the functional additives can improve the performance of the positive electrode active material layer. For example, the functional additives can better bind materials in the positive electrode active material layer to each other, improving the electrode plate adhesion and the conductivity of the positive electrode active material layer.

[0128] Because the first particles PTC1 have a very small particle size, they have low adhesion to the current collector COL1, making the electrode plate less manufacturable. In one embodiment, when an active material layer is fabricated using only the first particles PTC1, a large amount of functional additives may be required. For example, a relatively large amount of binder BND may be required to adhere the first particles PTC1, which have a small average particle size, to the current collector, whereas a relatively small amount of binder BND may be required to adhere the second particles PTC2, which have a large average particle size, to the current collector. The amount of binder BND required can be reduced by using a first positive electrode active material layer ATL1 including the first particles PTC1 and the second particles PTC2.

[0129] The cathode active material layer AML1 of the present invention may have a double layer structure in which a first cathode active material layer ATL1, which requires a relatively small amount of functional additive for adhesion to a current collector, is first bonded, and a second cathode active material layer ATL2 is then bonded on the first cathode active material layer ATL1.

[0130] The positive electrode active material layer AML1 of the present invention may have a double layer structure including a first positive electrode active material layer ATL1 that requires a relatively small amount of functional additives and a second positive electrode active material layer ATL2 disposed on the first positive electrode active material layer ATL1.

[0131] The dual-layer structure facilitates the fabrication of electrode plates. More specifically, a first cathode active material layer ATL1, which includes a mixture of first particles PTC1 and second particles PTC2, can be first stacked on a current collector, and then a second cathode active material layer ATL2 can be stacked on the first cathode active material layer ATL1. Fewer functional additives are required than when the first cathode active material layer ATL1, which has excellent electrode plate adhesion, is first stacked on the current collector, resulting in improved energy density. Furthermore, by first stacking the first cathode active material layer ATL1, which has stronger adhesion to the current collector, the resistance of the electrode plate can be improved.

[0132] The weight ratio of the first binder BND1 in the first positive electrode active material layer ATL1 may be 1 wt % to 3 wt %, or 1.5 wt % to 3 wt %.

[0133] The weight ratio of the second binder BND2 in the second positive electrode active material layer ATL2 may be 1 wt % to 4 wt %, or 2.0 wt % to 4.0 wt %.

[0134] The weight ratio of the first binder BND1 in the first positive electrode active material layer ATL1 may be smaller than the weight ratio of the second binder BND2 in the second positive electrode active material layer ATL2. In one embodiment, the ratio of the weight ratio of the second binder BND2 to the weight ratio of the first binder BND1 may be 1 to 4.

[0135] The weight ratio of the first conductive material CDM1 in the first positive electrode active material layer ATL1 may be 1 wt % to 3 wt %, or 1.5 wt % to 3 wt %.

[0136] The weight ratio of the second conductive material CDM2 in the second positive electrode active material layer ATL2 may be 1 wt % to 4 wt %, or 2.0 wt % to 4.0 wt %.

[0137] The weight ratio of the first conductive material CDM1 in the first positive electrode active material layer ATL1 may be smaller than the weight ratio of the second conductive material CDM2 in the second positive electrode active material layer ATL2. In one embodiment, the ratio of the weight ratio of the second conductive material CDM2 to the weight ratio of the first conductive material CDM1 may be 1 to 4, or 0.65 to 2.81.

[0138] The weight ratio of the first functional additive ADD1 in the first positive electrode active material layer ATL1 may be 2 wt % to 6 wt %, or 3.0 wt % to 6.0 wt %.

[0139] The weight ratio of the second functional additive ADD2 in the second positive electrode active material layer ATL2 may be 2 wt % to 8 wt %, or 4.0 wt % to 8.0 wt %.

[0140] The weight ratio of the first functional additive ADD1 in the first positive electrode active material layer ATL1 may be smaller than the weight ratio of the second functional additive ADD2 in the second positive electrode active material layer ATL2.

[0141] In one embodiment, the weight ratio of the second functional additive to the weight ratio of the first functional additive may be 1 to 4, or 0.65 to 2.81.

[0142] The first positive electrode active material layer ATL1 may have a thickness T1. In one embodiment, T1 may increase as the weight of the first particles PTC1 and the second particles PTC2 included in the first positive electrode active material layer ATL1 increases. The second positive electrode active material layer ATL2 may have a thickness T2. In one embodiment, T2 may increase as the weight of the third particles PTC3 included in the second active material layer ATL2 increases. In one embodiment, the ratio of T2 to T1 (T2 / T1) may be 0.4 to 2.0, 0.9 to 1.5, 0.8 to 1.2, or about 1. Within these ranges, excellent high voltage performance and energy density may be maintained while improving stability and life characteristics.

[0143] In one embodiment, the compressed density of the positive electrode active material layer AML1 of the present invention may be 2.3 g / cc to 2.8 g / cc.

[0144] In one embodiment, the loading level of the first positive electrode active material layer ATL1 is 5 mg / cm 2 ~10mg / cm 2 The loading level of the second positive electrode active material layer ATL2 may be 5 mg / cm. 2 ~25mg / cm 2 It could be.

[0145] A lithium secondary battery including the positive electrode active material of the present invention can have improved low-temperature characteristics. In one embodiment, the capacity at −20° C. relative to the initial capacity of the lithium secondary battery (capacity at −20° C. / initial capacity) may be 40% or more. For example, the capacity at −20° C. relative to the initial capacity of the lithium secondary battery of the present invention (capacity at −20° C. / initial capacity) may be 40% to 100%, 50% to 100%, or 96% to 99%.

[0146] A lithium secondary battery including the positive electrode active material of the present invention can have an improved operating voltage. In one embodiment, the operating voltage range of the lithium secondary battery of the present invention may be 3 V to 5 V. For example, the operating voltage range may be 3 V to 4.5 V, or 3.5 V to 4 V.

[0147] A lithium secondary battery including the positive electrode active material of the present invention can have improved life characteristics. In one embodiment, the lithium secondary battery of the present invention can have a capacity retention rate of 98% or more after 50 charge / discharge cycles at a constant current of 0.1 C at the above-mentioned voltage. For example, the capacity retention rate can be 98% to 100%, or 99.8% to 100%.

[0148] Method for producing positive electrode active material Hereinafter, production examples, examples, and comparative examples of the present invention will be described. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0149] Production example 1: Production of first particle PTC1 Mn 0.6 Fe 0.4Manganese iron phosphate precursor (PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004. 10 wt% glucose was added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 120°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain primary particles in the form of single particles. The average size of the primary particles was approximately 100 nm to approximately 200 nm.

[0150] Preparation Example 2-1: Preparation of small second particles PTC2 The small particle precursor was manufactured using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 60:10:30 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, and sodium hydroxide were added to a reactor and reacted. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 210°C for 24 hours to obtain a small particle precursor (NiSO4·6H2O) with an average particle size of approximately 4 μm. 0.6 Co 0.1 Mn 0.3 (OH)2) powder was obtained.

[0151] The small-particle precursor and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. The lithium and transition metals were mixed in a molar ratio of approximately 1:1. The transition metals were the sum of the transition metals (Ni + Co + Mn) contained in the mid-nickel precursor. A melting agent was added to the mixture, and the mixture was heat-treated (i.e., calcined) at approximately 910°C in an oxygen atmosphere for 8 hours to synthesize small-particle lithium composite oxide particles. The particles were pulverized in a jet mill at a pressure of 3 bar. The chemical formula of the particles was LiNi 0.6 Co 0.1 Mn 0.3 O2. After adding aluminum oxide to the oxide, a second heat treatment was performed at 800°C for 8 hours in an oxygen atmosphere to prepare a positive electrode active material. The chemical formula of the second particles was LiNi0.6 Co 0.1 Mn 0.3 It was O2.

[0152] Production Example 2-2: Production of large second particles PTC2 The large-particle precursor was manufactured using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 60:10:30 to prepare a metal source mixture. To form a complex compound, a dilute solution of ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant. The metal source mixture, ammonia water, and sodium hydroxide were then added to a reactor. The sodium hydroxide was added to maintain the pH of the mixture in the reactor. The reaction was carried out for approximately 20 hours while stirring the mixture in the reactor. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 750°C for 24 hours to obtain a large-particle precursor (NiSO4·6H2O) with a particle size of approximately 18 μm. 0.6 Co 0.1 Mn 0.3 (OH)2) powder was obtained.

[0153] The large-particle precursor and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. The lithium and transition metals were mixed in a molar ratio of approximately 1:1. The transition metals were the sum of the transition metals (Ni + Co + Mn) contained in the large-particle precursor. The mixture was heat-treated (i.e., calcined) at approximately 800°C for 15 hours in an oxygen atmosphere to synthesize large-particle lithium composite oxide particles. The particles were pulverized in a jet mill at a pressure of 3 bar. The chemical formula of the particles was LiNi 0.6 Co 0.1 Mn 0.3 O2. After adding aluminum oxide to the oxide, a second heat treatment was performed at 800°C for 8 hours in an oxygen atmosphere to prepare a positive electrode active material. The chemical formula of the second particles was LiNi 0.6 Co 0.1 Mn 0.3 It was O2.

[0154] Preparation Example 2-3: Preparation of bimodal second particles PTC2 The small particles of Preparation Example 2-1 and the large particles of Preparation Example 2-2 were mixed in a weight ratio of 30:70 to prepare second particles having a bimodal structure.

[0155] Production example 3: Third particle PTC3 production Mn 0.6 Fe 0.4 Manganese iron phosphate precursor (PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004. 10 wt% glucose was added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 120°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain third particles in the form of single particles. The average size of the third particles was approximately 100 nm to approximately 200 nm.

[0156] Single-layer electrode plate manufacturing Comparative Example 1-1 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were mixed in a weight ratio of 30:70 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0157] Comparative Example 1-2 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were mixed in a weight ratio of 40:60 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0158] Comparative Examples 1-3 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were mixed in a weight ratio of 50:50 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0159] Comparative Examples 1-4 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were mixed in a weight ratio of 60:40 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0160] Comparative Examples 1-5 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were mixed in a weight ratio of 70:30 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0161] Comparative Examples 1-6 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were mixed in a weight ratio of 80:20 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0162] Comparative Examples 1-7 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were mixed in a weight ratio of 90:10 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0163] Comparative Example 2-1 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-2 were mixed in a weight ratio of 70:30 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0164] Comparative Example 2-2 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-3 were mixed in a weight ratio of 70:30 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer electrode plate.

[0165] Double-layered electrode plate manufacturing Example 1-1 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a first positive electrode active material slurry. The third particles of Preparation Example 3 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a second positive electrode active material slurry.

[0166] The first positive electrode active material slurry was coated on a positive electrode current collector and dried to form a first positive electrode active material layer, and the second positive electrode active material slurry was coated on the first positive electrode active material layer and dried to form a second positive electrode active material layer.

[0167] At this time, the active material layer was formed so that the weight ratio of the first particles, second particles, and third particles in the double-layered positive electrode was 30:40:30. A roll press was performed to manufacture a positive electrode in which a current collector, a first positive electrode active material layer, and a second positive electrode active material layer were sequentially stacked.

[0168] Example 1-2 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-2 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a first positive electrode active material slurry. The third particles of Preparation Example 3 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a second positive electrode active material slurry.

[0169] The first positive electrode active material slurry was coated on a positive electrode current collector and dried to form a first positive electrode active material layer, and the second positive electrode active material slurry was coated on the first positive electrode active material layer and dried to form a second positive electrode active material layer.

[0170] At this time, the active material layer was formed so that the weight ratio of the first particles, second particles, and third particles in the double-layered positive electrode was 30:40:30. A roll press was performed to manufacture a positive electrode in which a current collector, a first positive electrode active material layer, and a second positive electrode active material layer were sequentially stacked.

[0171] Examples 1-3 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-3 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a first positive electrode active material slurry. The third particles of Preparation Example 3 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a second positive electrode active material slurry.

[0172] The first positive electrode active material slurry was coated on a positive electrode current collector and dried to form a first positive electrode active material layer, and the second positive electrode active material slurry was coated on the first positive electrode active material layer and dried to form a second positive electrode active material layer.

[0173] At this time, the active material layer was formed so that the weight ratio of the first particles, second particles, and third particles in the double-layered positive electrode was 30:40:30. A roll press was performed to manufacture a positive electrode in which a current collector, a first positive electrode active material layer, and a second positive electrode active material layer were sequentially stacked.

[0174] Example 2-1 A positive electrode was manufactured in the same manner as in Example 1-1, but the active material layer was formed so that the weight ratio of the first particles, second particles, and third particles in the double-layer positive electrode was 35:30:35.

[0175] Example 2-2 A positive electrode was fabricated in the same manner as in Example 1-2, but the active material layer was formed so that the weight ratio of the first particles, second particles, and third particles in the double-layer positive electrode was 35:30:35.

[0176] Example 2-3 The positive electrode was manufactured in the same manner as in Examples 1-3, but the material layers were formed so that the weight ratio of the first particles, the second particles, and the third particles in the double-layer positive electrode was 35:30:35.

[0177] Example 3-1 A positive electrode was manufactured in the same manner as in Example 1-1, but an active material layer was formed such that the weight ratio of the first particles, second particles, and third particles in the double-layer positive electrode was 40:20:40.

[0178] Example 3-2 A positive electrode was manufactured in the same manner as in Example 1-2, but the active material layer was formed so that the weight ratio of the first particles, second particles, and third particles in the double-layer positive electrode was 40:20:40.

[0179] Example 3-3 A positive electrode was manufactured in the same manner as in Examples 1-3, but the active material layer was formed so that the weight ratio of the first particles, second particles, and third particles in the double-layer positive electrode was 40:20:40.

[0180] Comparative Example 3-1 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a first positive electrode active material slurry. The third particles of Preparation Example 3 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a second positive electrode active material slurry.

[0181] Unlike Example 1-1, the second positive electrode active material slurry was first coated on a positive electrode current collector and dried to form a first positive electrode active material layer, and then the first positive electrode active material slurry was coated on the first positive electrode active material layer and dried to form a second positive electrode active material layer.

[0182] Comparative Example 3-2 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a first positive electrode active material slurry. The third particles of Preparation Example 3 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a second positive electrode active material slurry.

[0183] Unlike Example 2-1, the second positive electrode active material slurry was first coated on a positive electrode current collector and dried to form a first positive electrode active material layer, and then the first positive electrode active material slurry was coated on the first positive electrode active material layer and dried to form a second positive electrode active material layer.

[0184] Comparative Example 3-3 The first particles of Preparation Example 1 and the second particles of Preparation Example 2-1 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a first positive electrode active material slurry. The third particles of Preparation Example 3 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a second positive electrode active material slurry.

[0185] Unlike Example 3-1, the second positive electrode active material slurry was first coated on a positive electrode current collector and dried to form a first positive electrode active material layer, and then the first positive electrode active material slurry was coated on the first positive electrode active material layer and dried to form a second positive electrode active material layer.

[0186] Anode manufacturing Graphite, a binder, and a conductive material were mixed in N-methylpyrrolidone solvent to prepare a negative electrode active material slurry, which was then coated on a copper current collector, dried, and rolled to prepare a negative electrode.

[0187] Lithium secondary battery manufacturing A coin half cell was fabricated using the prepared positive and negative electrodes. A polypropylene membrane (Celgard 3510) was used as the separator. The electrolyte was a solution prepared by mixing 1.3M LiPF6 with a mixed solvent of EC (ethylene carbonate): DEC (diethyl carbonate): FEC (fluoroethylene carbonate) (2:6:2 volume ratio).

[0188] [Table 1]

[0189] Evaluation example 1: Analysis of the surface of the positive electrode active material FIG. 9 shows an SEM image of the first particles prepared in Preparation Example 1. FIG. 10 shows an SEM image of the second particles prepared in Preparation Examples 2-3. Referring to FIG. 9, it can be seen that the first particles according to an embodiment of the present invention are in the form of nano-sized fine single particles. Referring to FIG. 10, it can be seen that the second particles according to an embodiment of the present invention are in the form of single particles or aggregates of multiple single particles. Compared to the first particles, it can be seen that the second particles have various shapes and are larger in size.

[0190] Evaluation example 2: Active material evaluation The pellet densities (PD) of the positive electrode active material layers prepared in Examples 1-1 to 3-3 and Comparative Examples 1-1 to 3-3 were measured, and the results are shown in Table 2.

[0191] [Table 2]

[0192] Referring to Table 2, the positive electrode active material layers according to Examples 1-1 to 1-3 can maintain pellet density and energy density at similar levels compared to the positive electrode active material layers according to Comparative Examples 1-4 to 1-6, which have a single layer structure.

[0193] Evaluation example 3: Battery characteristic evaluation The characteristics of the lithium secondary batteries fabricated using the positive electrodes of Examples 1-1 to 3-3 and Comparative Examples 1-1 to 3-3 were evaluated.

[0194] The lithium secondary battery was initially charged at a constant current (0.2C) and constant voltage (4.25V), rested for 10 minutes, and then discharged at a constant current (0.2C) until the voltage reached 2.5V. It was then charged and discharged 50 times at 1.0C / 1.0C at 45°C. An additional coin cell was also fabricated and the 0.2C capacity was measured at -20°C. The battery characteristics were evaluated and are shown in Table 3 below.

[0195] [Table 3]

[0196] Referring to Table 3, it can be seen that the lithium secondary batteries according to Examples 1-1 to 3-3 have improved 1C lifespans compared to the lithium secondary batteries according to Comparative Examples 1-1 to 1-7. Considering the charge / discharge efficiency and average voltage of the lithium secondary batteries according to Examples 1-1 to 3-3, they can be used as batteries with excellent overall characteristics.

[0197] Evaluation Example 4: Content of functional additives in active material layer The weight ratio of functional additives required for manufacturing the positive electrodes of the single-layer structures of Comparative Examples 1-1 to 2-2 was measured.

[0198] The weight ratio of the functional additive in the first positive electrode active material layer and the weight ratio of the functional additive in the second positive electrode active material layer required for manufacturing the positive electrodes in the double layer structures of Comparative Examples 3-1 to 3-3 were measured.

[0199] The weight ratio of the functional additive in the first positive electrode active material layer and the weight ratio of the functional additive in the second positive electrode active material layer were measured for the positive electrodes of Examples 1-1 to 3-3. The weight ratios of the functional additive in the active material layers are shown in Table 4.

[0200] [Table 4]

[0201] Referring to Examples 1-1 to 3-3, it can be seen that the weight ratio of the first functional additive in the first positive electrode active material layer is smaller than the weight ratio of the second functional additive in the second positive electrode active material layer. A smaller amount of functional additive is required to laminate the first positive electrode active material layer on the current collector, and as a result, the first positive electrode active material layer is first formed through the combination of the first positive electrode active material slurry, which facilitates the fabrication of the positive electrode, thereby facilitating the fabrication of the electrode plate.

[0202] Unlike the embodiments of the present invention, Comparative Examples 3-1 to 3-3 have the first and second positive electrode active material layers reversed in construction, which indicates that a large amount of functional additive is required to form the first positive electrode active material layer on the current collector.

[0203] More specifically, when compared to the single-layer structures of Comparative Examples 1-4, 1-5, and 1-6, it can be seen that the total amount of functional additives is even less. Compared to single-layer structures having the same amount of active material, the reduced content of functional additives can improve the energy density of the active material layer.

[0204] Unlike the present invention, Comparative Examples 3-1 and 3-3 reverse the active materials constituting the first and second positive electrode active material layers. In this case, a larger amount of functional additive is required to form the first positive electrode active material layer on the current collector. That is, rather than directly bonding the first particles, which have weak adhesion to the electrode plate, to the electrode plate, first forming the first positive electrode active material layer, which has strong adhesion, can improve the packing density or energy density compared to a positive electrode containing the same amount of active material.

[0205] Evaluation example 5: Resistance and energy density evaluation The characteristics of the lithium secondary batteries fabricated using the positive electrodes of the Examples and Comparative Examples were evaluated.

[0206] The lithium secondary battery was initially charged at a constant current (0.2 C), rested for 10 minutes, and then discharged at a constant current (0.2 C) until the battery reached 3.0 V. The average voltage was evaluated after initial charging and discharging. The battery was then rested for 1 hour at a State of Charge (SOC) of 50, discharged at 1.0 C for 10 seconds, and then rested for another 10 seconds. The cell resistance (DC-IR) was calculated by dividing the difference between the voltage after the discharge and the voltage after the 10-second rest by the current. The results are shown in Table 5 below.

[0207] [Table 5]

[0208] Table 5 shows that the resistance of the positive electrodes according to Examples 1-1, 2-1, and 3-1 of the present invention is lower than that of the positive electrodes according to Comparative Examples 3-1 to 3-3. The positive electrodes according to Examples 1-1, 2-1, and 3-1 of the present invention have opposite structures of the first and second positive electrode active material layers. However, by using the first positive electrode active material layer, which has high adhesive strength, in the portion in contact with the current collector, as in the present invention, the resistance of the entire positive electrode can be reduced.

[0209] As a result, by having a double layer structure as in this embodiment, the resistance of the electrode plate can be reduced and the energy density can be improved.

[0210] The above-described content is a specific example for carrying out the present invention. The present invention may include not only the above-described embodiments, but also embodiments that can be simply modified or easily changed. The present invention may also include techniques that can be easily implemented by modifying the embodiments. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be defined by not only the claims but also equivalents to the claims of the present invention. [Explanation of symbols]

[0211] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. A current collector; a first positive electrode active material layer on the current collector; a second positive electrode active material layer on the first positive electrode active material layer, The first positive electrode active material layer includes first particles having an olivine structure represented by Chemical Formula 1 below, and second particles having a layered structure represented by Chemical Formula 2 below: The second positive electrode active material layer includes third particles having an olivine structure and represented by the following Chemical Formula 3: each of the first particle and the third particle has a single particle shape; The second particles have an average particle size larger than the average particle size of each of the first particles and the third particles. [Chemical formula 1] Li a1 Mn z1 Fe x1 B1 y1 PO 4-c1 (In the above Chemical Formula 1, B1 is one or more elements selected from the group consisting of Al, Ti, V, and Mg, and 0.8<a1≦1.2, 0.4≦z1≦0.8, 0.2≦x1≦0.6, 0≦y1≦0.05, 0<c1≦0.05, and x1+y1+z1=1.) [Chemical formula 2] Li a2 Ni x2 Co y2 Mn z2 B2 b2 O 2-c2 (In Chemical Formula 2, B2 is at least one element selected from the group consisting of Al, Ti, Mg, Zr, Mo, and Nb, and 0.8≦a2≦1.2, 0.5≦x2≦0.8, 0.0≦y2≦0.10, 0.1≦z2≦0.35, 0≦b2≦0.10<c2≦0.05, and x2+y2+z2+b2=1.) [Chemical formula 3] Li a3 Mn z3 Fe x3 B3 y3 PO 4-c3 (In Chemical Formula 3, B3 is one or more elements selected from the group consisting of Al, Ti, V, and Mg, and 0.8<a3≦1.2, 0.4≦z3≦0.8, 0≦x3≦0.6, 0≦y3≦0.05, 0<c3≦0.05, and x3+y3+z3=1.)

2. the first particles include at least one first primary particle; the third particles include at least one third primary particle; The average size of the first primary particles is 100 nm to 200 nm; The first particles have an average particle size (D50) of 0.5 μm to 2.5 μm; The average size of the third primary particles is 100 nm to 200 nm; 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the third particles have an average particle size (D50) of 0.5 μm to 2.5 μm.

3. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein a weight ratio of the second particles to a total weight of the first particles, the second particles, and the third particles in the positive electrode is 20 wt % to 30 wt %.

4. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the total doping amount of manganese (Mn) in the positive electrode is 0.50 to 0.

60.

5. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein a ratio of the thickness of the second positive electrode active material layer to the thickness of the first positive electrode active material layer is 0.8 to 1.

2.

6. The positive electrode for a lithium secondary battery according to claim 1 , wherein the second particles have a bimodal shape including large particles and small particles.

7. 7. The positive electrode for a lithium secondary battery according to claim 6, wherein the small particles have an average particle size (D50) of 2 μm to 5 μm.

8. 7. The positive electrode for a lithium secondary battery according to claim 6, wherein the large particles have an average particle size (D50) of 10 μm to 20 μm.

9. The positive electrode for a lithium secondary battery according to claim 6 , wherein the content of the small particles is less than the content of the large particles relative to the total content of the second particles.

10. 7. The positive electrode for a lithium secondary battery according to claim 6, wherein the content of the small second particles with respect to the total content of the second particles is 20 to 40 wt%.

11. A current collector; a first positive electrode active material layer on the current collector; a second positive electrode active material layer on the first positive electrode active material layer, The first positive electrode active material layer includes first particles having an olivine structure represented by the following Chemical Formula 1, second particles having a layered structure represented by the following Chemical Formula 2, and a first functional additive: The second positive electrode active material layer includes third particles having an olivine structure represented by the following Chemical Formula 3, and a second functional additive: each of the first functional additive and the second functional additive includes a conductive material and a binder; A positive electrode for a lithium secondary battery, wherein a weight ratio of the first functional additive in the first positive electrode active material layer is smaller than a weight ratio of the second functional additive in the second positive electrode active material layer. [Chemical formula 1] Li a1 Mn z1 Fe x1 B1 y1 PO 4-c1 (In the above Chemical Formula 1, B1 is one or more elements selected from the group consisting of Al, Ti, V, and Mg, and 0.8<a1≦1.2, 0.4≦z1≦0.8, 0.2≦x1≦0.6, 0≦y1≦0.05, 0<c1≦0.05, and x1+y1+z1=1.) [Chemical formula 2] Li a2 Ni x2 Co y2 Mn z2 B2 b2 O 2-c2 In Chemical Formula 2, B2 is at least one element selected from the group consisting of Al, Ti, Mg, Zr, Mo, and Nb, and 0.8≦a2≦1.2, 0.5≦x2≦0.8, 0.0≦y2≦0.10, 0.1≦z2≦0.35, 0≦b2≦0.10<c2≦0.05, and x2+y2+z2+b2=1. [Chemical formula 3] Li a3 Mn z3 Fe x3 B3 y3 PO 4-c3 (In Chemical Formula 3, B3 is one or more elements selected from the group consisting of Al, Ti, V, and Mg, and 0.8<a3≦1.2, 0.4≦z3≦0.8, 0≦x3≦0.6, 0≦y3≦0.05, 0<c3≦0.05, and x3+y3+z3=1.)

12. The positive electrode for a lithium secondary battery according to claim 11, wherein the weight ratio of the second functional additive to the first functional additive is 0.65 to 2.

81.

13. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein the weight ratio of the first functional additive is 3.0 wt% to 6.0 wt%.

14. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein the weight ratio of the second functional additive is 4.0 wt% to 8.0 wt%.

15. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein the binder comprises at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, an epoxy resin, a (meth)acrylic resin, a polyester resin, and nylon.

16. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein a weight ratio of the second particles to a total weight of the first particles, the second particles, and the third particles in the positive electrode is 20 wt % to 30 wt %.

17. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein a total doping amount of manganese (Mn) in the positive electrode is 0.50 to 0.

60.

18. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein a thickness ratio of the second positive electrode active material layer to the first positive electrode active material layer is 0.8 to 1.

2.

19. The positive electrode for a lithium secondary battery according to claim 11, wherein the second particles have a BET specific surface area of ​​0.3 to 1.

2.

20. A lithium secondary battery comprising the positive electrode according to claim 1.

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