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 operation voltage, and high conductivity.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 includes a current collector, a first active material layer on the current collector, and a second active material layer on the first active material layer. The first active material layer includes first particles that are single particles. The second active material layer includes second particles that are secondary particles. The first particles include a compound of Chemical Formula 1 below, and the second particles include a compound of Chemical Formula 2 below.SELECTED DRAWING: Figure 7

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 including the same, and a lithium secondary battery including the same. [Background technology]

[0002] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density and high-capacity secondary batteries has been increasing rapidly. Accordingly, research and development to improve the performance of lithium secondary batteries has 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] [Patent Document 1] Korean Patent No. 10-1792750 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 having high energy density, high operating voltage, and high conductivity.

[0006] Another object of the present invention is to provide a lithium secondary battery having high energy density, high operating voltage, and excellent low-temperature characteristics. [Means for solving the problem]

[0007] A lithium secondary battery positive electrode according to the present invention may include a current collector, a first active material layer on the current collector, and a second active material layer on the first active material layer. The first active material layer may include first particles that are single particles, and the second active material layer may include second particles that are spherical secondary particles. The first particles may include a compound represented by Formula 1 below, and the second particles may include a compound represented by Formula 2 below. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-b1

[0008] In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1. In Chemical Formula 1, B1 may be at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al. [Chemical formula 2] Li a2 Fe x2 B2 y2 PO 4-b2

[0009] In Chemical Formula 2, 0.8≦a2≦1.2, 0.95≦x2≦0.999, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2=1. In Chemical Formula 2, B2 may be at least one element selected from the group consisting of Ti, Mg, V, and Al.

[0010] A lithium secondary battery positive electrode according to another aspect of the present invention may include a current collector, a first active material layer on the current collector, and a second active material layer on the first active material layer. The first active material layer may include first particles, a first binder, and a first conductive material, and the second active material layer may include second particles, a second binder, and a second conductive material. The content of the first binder in the first active material layer may be greater than the content of the second binder in the second active material layer. The first particles may include a compound represented by Chemical Formula 1 below, and the second particles may include a compound represented by Chemical Formula 2 below. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-b1

[0011] In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1. In Chemical Formula 1, B1 may be at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al. [Chemical formula 2] Li a2 Fe x2 B2 y2 PO 4-b2

[0012] In Chemical Formula 2, 0.8≦a2≦1.2, 0.95≦x2≦0.999, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2=1. In Chemical Formula 2, B2 may be at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al.

[0013] A lithium secondary battery according to another aspect of the present invention may include the positive electrode described above. [Effects of the Invention]

[0014] The positive electrode according to the present invention includes a first active material layer including olivine-based first particles having a size of several hundred nanometers to several micrometers, and a second active material layer including layered-type second particles having a size of several micrometers stacked on the first active material layer, thereby improving pellet density, capacity, and energy density. The second active material layer according to the present invention can be smoothly fixed on the first active material layer even with a relatively small amount of binder. The lithium secondary battery according to the present invention can have a relatively high average voltage. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery has a cylindrical shape. [Figure 3] FIG. 3 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery has a prismatic shape. [Figure 4] FIG. 4 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery is in the form of a pouch. [Figure 5] FIG. 5 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery is in the form of a pouch. [Figure 6] 1 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 active material layer of a positive electrode for a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 8] 2 is an enlarged view of a first active material layer of a positive electrode for a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 9A] 1 is an SEM image of first particles prepared in Preparation Example 1 of the present invention. [Figure 9B] 1 is an SEM image of first particles prepared in Preparation Example 1 of the present invention. [Figure 10] 1 is an SEM image of second particles prepared in Preparation Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] In this specification, when a component is referred to as being on another component, it means that the component may be formed directly 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 embodied 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.

[0017] 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 that 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.

[0018] 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, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other elements to the referenced element.

[0019] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0020] 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 uses 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.

[0021] 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 ELL.

[0022] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0023] 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.

[0024] 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. 6 to 10. The current collector COL1 may be made of aluminum, but is not limited thereto.

[0025] 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.

[0026] 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.

[0027] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode 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.

[0028] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0029] 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.

[0030] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. The cellulose-based compound may be a mixture of 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.

[0031] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0032] 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 that is constructed can 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.

[0033] As the current collector COL2, a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof can be used.

[0034] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping with lithium, or a transition metal oxide.

[0035] Examples of the material capable of reversibly inserting / desorbing lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, etc.

[0036] As the alloy of 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.

[0037] As the material capable of doping and undoping with 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 (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 thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0038] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by assembling primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, coating the primary silicon particles with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0039] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and a first coating layer of amorphous carbon disposed on the core.

[0040] A Si-based negative electrode active material or a Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0041] 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 separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may 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 may also be used.

[0042] 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.

[0043] 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.

[0044] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0045] 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.

[0046] 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.

[0047] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0048] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0049] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0050] Examples of carbonate solvents 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).

[0051] 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.

[0052] 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.

[0053] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0054] 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.

[0055] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0056] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 through 5 are schematic diagrams illustrating 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 through 5, 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 impregnated with 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.

[0057] 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.

[0058] 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 active material layer ATL1 and a second active material layer ATL2 stacked on the first active material layer.

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

[0060] 7, the first active material layer ATL1 may include first particles PTC1, a first binder BND1, and a first conductive material CDM1. The first active material layer ATL1 may further include an additive that can function as a sacrificial positive electrode.

[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 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, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0062] The first conductive material CDM1 can be used to improve the conductivity of the first active material layer ATL1. Any conductive material that does not cause a chemical change in the first 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, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0063] FIG. 8 is an enlarged view of a second active material layer of a positive electrode for a lithium secondary battery according to an embodiment of the present invention.

[0064] 8, the second active material layer ATL2 may include second particles PTC2, a second binder BND2, and a second conductive material CDM2. The second active material layer ATL2 may further include an additive that can function as a sacrificial positive electrode.

[0065] The second binder BND2 can bind the second particles PTC2 and the second conductive material CDM2 to each other. The second binder BND1 can also stably fix the second active material layer ATL2 on the first 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, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0066] The second conductive material CDM2 can be used to improve the conductivity of the second active material layer ATL2. Any conductive material that does not cause a chemical change in the second 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 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.

[0067] Hereinafter, the first particles PTC1 and the second particles PTC2 will be described in more detail.

[0068] 1st particle PTC1 The first particle 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. 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 singly separated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0069] The first particles PTC1, which include at least one first primary particle PTC1_1, may have an average particle size of 50 nm to 5 μm, 100 nm to 3 μm, 500 nm to 2.5 μm, or approximately 1 μm. In one embodiment, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0070] The minimum particle size of the first primary particles PTC1_1, i.e., the particle size of the first primary particles PTC1_1, may be 10 nm to 900 nm, 50 nm to 500 nm, or 200 nm to 300 nm. In one embodiment, the minimum particle size of the first primary particles PTC1_1, i.e., the particle size of the first primary particles PTC1_1, may refer to the diameter measured by randomly selecting about 30 first primary particles PTC1_1 from an electron microscope photograph of the positive electrode active material. The particle size of the first primary particles PTC1_1 may be uniform.

[0071] For example, the minimum particle size of the first primary particles PTC1_1 measured by a scanning electron microscope (SEM) may be 200 nm to 300 μm, and the average particle size (D50) of the first particles PTC1 measured by a scanning electron microscope (SEM) may be 0.5 μm to 2.5 μm.

[0072] 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. The metal-containing compound, such as a titanium-containing compound, a magnesium-containing compound, or a vanadium-containing compound, 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 metal-containing compound may further include lithium. The coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[0073] The first particles PTC1 may include an olivine-based lithium compound represented by Chemical Formula 1 below. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-b1

[0074] In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1 may be satisfied. B1 may be at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al. B1 may be a dopant doped into the first particle PTC1. For example, B1 may include Ti.

[0075] The first particles PTC1 may further include carbon derived from the first active material layer. The carbon element content in the first particles PTC1 may be 0.5 wt % to 5 wt %, 0.5 wt % to 3 wt %, or 0.5 wt % to 2 wt %.

[0076] 2nd particle PTC2 The second particles PTC2 may have a polycrystalline form and may include second secondary particles formed by agglomeration of at least two or more second primary particles PTC2_1. In other words, one second particle PTC2 may include a plurality of second primary particles PTC2_1 agglomerated together. The second particles PTC2 may have a spherical or elliptical shape.

[0077] In one embodiment, the second particles PTC2 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the second particles PTC2 or a portion of the surface of the second particles PTC2. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability of the second particles PTC2 and may improve electrical conductivity.

[0078] 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 compounds may further include other metals or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0079] In one embodiment, the second particle PTC2 may further include a grain boundary coating layer on the surface of each primary particle PTC2_1. The grain boundary coating layer may be present inside the second particle PTC2. The grain boundary coating layer may be formed by coating along the interface between the primary particles PTC2_1 inside the second particle PTC2. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the second particle PTC2. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary 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.

[0080] The interior of the second particle PTC2 described above may refer to the entire interior of the second particle PTC2 excluding the surface of the second particle PTC2. For example, the interior of the second particle PTC2 may refer to the region from a depth of about 10 nm to the entire inside of the surface of the second particle PTC2, or from a depth of 10 nm to a depth of about 2 μm.

[0081] The second particles PTC2 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 second particles PTC2. In addition, the second particles PTC2 further include a grain boundary coating portion, which further improves the electrical conductivity of the second particles PTC2.

[0082] The average particle size of the second particles PTC2 may be 2 μm to 15 μm, 3 μm to 12 μm, or 3 μm to 7 μm. The average particle size of the second particles PTC2 may be larger than the average particle size of the first particles PTC2. In one embodiment, about 30 second particles PTC2 are randomly selected from an electron microscope photograph of the positive electrode active material, and their particle sizes are measured. The diameter (D50) of the particles corresponding to 50% by volume of the cumulative volume in the particle size distribution may be taken as the average particle size.

[0083] The minimum particle size of the second primary particles PTC2_1 included in the second particles PTC2, i.e., the particle size of the second primary particles PTC2_1, may be 10 nm to 400 nm, 20 nm to 300 nm, 50 nm to 200 nm, or 100 nm to 200 nm. In one embodiment, the minimum particle size of the second primary particles PTC2_1, i.e., the particle size of the second primary particles PTC2_1, may refer to the diameter measured by randomly selecting approximately 30 first primary particles from an electron microscope photograph of the positive electrode active material. The particle size of the second primary particles PTC2_1 may be uniform.

[0084] For example, the average particle size of the second particles PTC2 measured by a scanning electron microscope (SEM) may be 3 μm to 7 μm, and the particle size of the second primary particles PTC2_1 included in the second particles PTC2 may be 100 nm to 200 nm.

[0085] The second particles PTC2 may include an olivine-based lithium compound represented by Chemical Formula 2 below. [Chemical formula 2] Li a2 Fe x2 B2 y2 PO 4-b2

[0086] In Chemical Formula 2, 0.8≦a2≦1.2, 0.95≦x2≦0.999, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2=1 may be satisfied. B2 may be at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al. B2 may be a dopant doped into the second particles PTC2. For example, B2 may include Ti.

[0087] The second particles PTC2 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the second particles PTC2 may be 0.5 wt % to 10 wt %, 1 wt % to 4 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0088] The second particles PTC2 may have a spherical shape formed by the aggregation of nano-sized primary particles PTC2_1. The second particles PTC2 may exhibit the following characteristics due to the close aggregation of the primary particles PTC2_1: The second particles PTC2 may have a spherical or elliptical shape; The average particle size (D50) of the second particles PTC2 may be 2 μm to 15 μm; The porosity of the second particles PTC2 may be about 20% to about 40%; The Span value of the second particles PTC2 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0089] Referring again to FIG. 6, the positive electrode active material layer AML1 according to the embodiment of the present invention will be described in more detail.

[0090] The positive electrode active material layer AML1 may include a first active material layer ATL1 and a second active material layer ATL2 stacked on the first active material layer ATL1. The first active material layer ATL1 may include first particles PTC1, a first binder BND1, and a first conductive material CDM1. The second active material layer ATL2 may include second particles PTC2, a second binder BND2, and a second conductive material CDM2.

[0091] The first particles PTC1, which are single particles, can improve energy density, and the second particles PTC2, which are secondary particles, can improve low-temperature characteristics and life characteristics. The positive electrode active material layer AML1 of the present invention has a double-layer structure including a first active material layer ATL1 containing the first particles PTC1 and a second active material layer ATL2 containing the second particles PTC2, thereby improving energy density, low-temperature characteristics, and life characteristics. In particular, the low-temperature characteristics can be significantly improved by positioning the second active material layer containing the second particles PTC2 on the positive electrode surface where the electrochemical reaction is most active.

[0092] The first active material layer ATL1 may contain 3 to 10 parts by weight of the first binder BND1 relative to 100 parts by weight of the first active material layer ATL1.

[0093] The second active material layer ATL2 may contain 2 to 5 parts by weight of the second binder BND2 per 100 parts by weight of the second active material layer ATL2.

[0094] The content of the first binder BND1 included in the first active material layer ATL1 may be greater than the content of the second binder BND2 included in the second active material layer ATL2. In one embodiment, the ratio of the content of the first binder BND1 in the first active material layer ATL1 to the content of the second binder BND2 in the second active material layer ATL2 may be 1.5 to 5.

[0095] A relatively large amount of first binder BND1 is required to adhere first particles PCT1, which have a small average particle size, to current collector COL1 (see FIG. 1 ), but a relatively small amount of second binder BND2 may be required to fix second particles PTC2, which have a large average particle size, on first active material layer ATL1. The positive electrode active material layer AML1 of the present invention includes second active material layer ATL2, which requires a relatively small amount of binder, thereby improving energy density.

[0096] The first active material layer ATL1 may contain 1 to 5 parts by weight of the first conductive material CDM1 relative to 100 parts by weight of the first active material layer ATL1.

[0097] The second active material layer ATL2 may contain 0.5 to 5 parts by weight of the second conductive material CDM2 relative to 100 parts by weight of the second active material layer ATL2.

[0098] The content of the first conductive material CDM1 in the first active material layer ATL1 may be greater than the content of the second conductive material CDM2 in the second active material layer ATL2. In one embodiment, the ratio of the content of the first conductive material CDM1 in the first active material layer ATL1 to the content of the second conductive material CDM2 in the second active material layer ATL2 may be 1 to 4.

[0099] The weight of the second particles PTC2 in the second active material layer ATL2 relative to the total weight of the first particles PTC1 in the first active material layer ATL1 and the second particles PTC2 in the second active material layer ATL2 may be 10% by weight to 50% by weight, 20% by weight to 40% by weight, or 25% by weight to 35% by weight.

[0100] In one embodiment, the loading level of the first active material layer ATL1 is 5 mg / cm 2 ~10mg / cm 2 The loading level of the second active material layer ATL2 may be 5 mg / cm 2 ~25mg / cm 2 It could be.

[0101] The first active material layer ATL1 may have a thickness T1. In one embodiment, T1 may increase as the weight of the first particles PTC1 included in the first active material layer ATL1 increases. The second active material layer ATL2 may have a thickness T2. In one embodiment, T2 may increase as the weight of the second particles PTC2 included in the second active material layer ATL2 increases. In one embodiment, the ratio of T2 to the sum of T1 and T2 (T2 / (T1+T2)) may be 0.1 to 0.5, 0.2 to 0.4, or 0.25 to 0.35. Within this range, low-temperature characteristics may be improved while maintaining excellent energy density.

[0102] In one embodiment, the positive electrode active material layer AML1 of the present invention may have a compressed density of 2.0 g / cc to 2.5 g / cc. A lithium secondary battery including the positive electrode of the present invention may have improved low-temperature characteristics.

[0103] Hereinafter, the present invention will be described with reference to Preparation Examples, Examples, and Comparative Examples. However, the following Examples are merely examples of the present invention, and the present invention is not limited to the following Examples.

[0104] Preparation Example 1: Preparation of first particles in single particle form Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti:1:1.03:0.03. 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 dried 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 single-particle primary particles. Scanning electron microscopy (SEM) confirmed that the particle size of the primary particles was approximately 200 nm to 300 nm, and the D50 of the primary particles was approximately 1 μm. Furthermore, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) confirmed that the carbon content within the primary particles of the primary particles was 1.52 wt%.

[0105] Production Example 2: Production of secondary particles in the form of secondary particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti:1:1.03:0.03. 10 wt% glucose was added to the mixture. The slurry mixture was spray-dried at a pressure of 0.5 MPa and a temperature of 230°C to evaporate it to dryness. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere to obtain secondary particles. Scanning electron microscopy (SEM) confirmed that the particle size of the secondary primary particles was approximately 100 nm to approximately 200 nm, and the D50 of the secondary particles was approximately 5 μm. Additionally, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) confirmed that the carbon content of the primary particles was 1.84 wt%.

[0106] Example 1: Positive electrode including a first active material layer containing first particles and a second active material layer containing second particles (nano-type LFP: assembled LFP = 90:10) The first particles prepared in Preparation Example 1, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 1:0.1:0.03 to prepare a first active material slurry.

[0107] The second particles prepared in Preparation Example 2, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 1:0.05:0.02 to prepare a second active material slurry.

[0108] The first active material slurry was applied to a 15 μm-thick aluminum (Al) thin film, which served as a positive electrode current collector, and dried to form a first active material layer. The second active material slurry was applied to the first active material layer and dried to form a second active material layer. The first and second active material layers were formed so that the weight ratio of the first particles in the first active material slurry to the second particles in the second active material slurry was "first particles:second particles = 9:1." A roll press was performed to fabricate a positive electrode in which the aluminum current collector, first active material layer, and second active material layer were stacked in that order.

[0109] Example 2: Positive electrode including a first active material layer including first particles and a second active material layer including second particles (nano-type LFP: assembled LFP = 80:20) A positive electrode was manufactured in the same manner as in Example 1, except that the weight ratio of the first particles in the first active material slurry to the second particles in the second active material slurry was first particles:second particles=4:1.

[0110] Example 3: Positive electrode including a first active material layer including first particles and a second active material layer including second particles (nano-type LFP: assembled LFP = 70:30) A positive electrode was manufactured in the same manner as in Example 1, except that the weight ratio of the first particles in the first active material slurry to the second particles in the second active material slurry was first particles:second particles=7:3.

[0111] Example 4: Positive electrode including a first active material layer including first particles and a second active material layer including second particles (nano-type LFP: assembled LFP = 60:40) A positive electrode was manufactured in the same manner as in Example 1, except that the weight ratio of the first particles in the first active material slurry to the second particles in the second active material slurry was first particles:second particles=3:2.

[0112] Example 5: Positive electrode including a first active material layer including first particles and a second active material layer including second particles (nano-type LFP: assembled LFP = 50:50) A positive electrode was manufactured in the same manner as in Example 1, except that the weight ratio of the first particles in the first active material slurry to the second particles in the second active material slurry was first particles:second particles=1:1.

[0113] Comparative Example 1: Positive electrode including single-layer active material layer (first particles) The first particles prepared in Preparation Example 1, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 1:0.1:0.03 to prepare a positive electrode active material slurry.

[0114] The positive electrode active material slurry was applied to a 15 μm thick aluminum (Al) thin film, which was a positive electrode current collector, and dried. A roll press was performed to fabricate a positive electrode in which a positive electrode active material layer was laminated on the aluminum current collector.

[0115] Comparative Example 2: Positive electrode including active material layer with single-layer structure (second particles) The second particles prepared in Preparation Example 2, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 1:0.05:0.02 to prepare a positive electrode active material slurry.

[0116] The positive electrode active material slurry was applied to a 15 μm thick aluminum (Al) thin film, which was a positive electrode current collector, and dried. A roll press was performed to fabricate a positive electrode in which a positive electrode active material layer was laminated on the aluminum current collector.

[0117] Comparative Example 3: Positive electrode including a single-layer active material layer (first particles + second particles, nano-type LFP: assembled LFP = 50:50) The first particles and second particles prepared in Preparation Examples 1 and 2 were mixed in a weight ratio of 1:1 to prepare a mixed active material. The mixed active material, binder (polyvinylidene fluoride), and conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 1:0.1:0.03 to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a 15 μm-thick aluminum (Al) thin film, which served as a positive electrode current collector, and dried. A roll press was performed to prepare a positive electrode in which a positive electrode active material layer was laminated on the aluminum current collector.

[0118] Comparative Example 4: Positive electrode including a first active material layer containing second particles and a second active material layer containing first particles (nano-type LFP: assembled LFP = 50:50) A positive electrode was prepared in the same manner as in Example 5, except that the aluminum current collector, the second active material layer, and the first active material layer were stacked in this order.

[0119] The second active material slurry was applied to the aluminum thin film and dried to form a second active material layer, and the first active material slurry was applied to the second active material layer and dried to form a first active material layer.

[0120] Comparative Example 5: Positive electrode including a first active material layer containing second particles and a second active material layer containing first particles (weight ratio of first binder:weight ratio of second binder = 6:1) A positive electrode was manufactured in the same manner as in Example 5, except that the second active material slurry was prepared by dispersing the second particles, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 1:0.017:0.003.

[0121] Comparative Example 6: Positive electrode including a first active material layer containing second particles and a second active material layer containing first particles (weight of first binder:weight of second binder=1:1) A positive electrode was manufactured in the same manner as in Example 5, except that the second active material slurry was prepared by dispersing the second particles, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 1:0.1:0.3.

[0122] Anode manufacturing Graphite, a binder, and a conductive material were mixed in N-methylpyrrolidone solvent to prepare a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper current collector, dried, and then rolled to prepare a negative electrode.

[0123] Lithium secondary battery manufacturing A coin-pull cell was fabricated using the prepared positive and negative electrodes. A polypropylene membrane (Celgard 3510) was used as the separator. The electrolyte used was a 1.3M LiPF6 solution mixed with a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and FEC (fluoroethylene carbonate) (volume ratio: 2:6:2).

[0124] Evaluation example 1: Analysis of the surface of the positive electrode active material SEM images of the first particles prepared in Preparation Example 1 are shown in Figures 9A and 9B. SEM images of the second particles prepared in Preparation Example 2 are shown in Figure 10. Referring to Figures 9A and 9B, it can be seen that the first particles according to an embodiment of the present invention are in the form of fine single particles of nano-size. Referring to Figure 10, it can be seen that the second particles according to an embodiment of the present invention are in the form of secondary particles of μm-size. It can be seen that the second particles are in the form of spherical secondary particles formed by agglomeration of multiple primary particles.

[0125] Evaluation example 2: Positive electrode characteristic analysis Table 1 shows the thickness and pallet density (PD) of each active material layer of the positive electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 6.

[0126] [Table 1]

[0127] Referring to Example 5 and Comparative Example 5, it can be seen that when the weight ratio of the first binder to the second binder is greater than 5, i.e., when the amount of the second binder is too small, the binding strength to the active material decreases, resulting in a decrease in the pellet density.

[0128] Furthermore, referring to Example 5 and Comparative Example 6, when the weight of the first binder relative to the weight of the second binder is the same, it can be seen that the amount of the positive electrode active material is relatively reduced, resulting in a decrease in the pellet density.

[0129] Evaluation example 3: Battery characteristic evaluation The characteristics of the lithium secondary batteries manufactured using the positive electrodes of Examples 1 to 5 and Comparative Examples 1 to 4 were evaluated.

[0130] The lithium secondary battery was initially charged under constant current (0.1 C) and constant voltage (3.8 V) conditions, and after a 10-minute rest, it was discharged under constant current (0.1 C) conditions until the voltage reached 3.0 V. The initial discharge capacity was measured, and the ratio of the discharge capacity to the charge capacity was calculated as the efficiency. The results (charge amount, discharge amount, efficiency) are shown in Table 2 below.

[0131] In addition, the charge / discharge cycle was repeated 50 times at 1.0C / 1.0C at 45°C, and the discharge capacity after 50 cycles was measured. The ratio of the 50th discharge capacity to the initial discharge capacity was evaluated, and the results (3.8V lifespan) are shown in Table 2 below.

[0132] Additionally, a coin cell was fabricated and the 0.2C capacity was measured at -20°C. The battery characteristic evaluation results are shown in Table 2 below.

[0133] [Table 2]

[0134] Referring to Table 2, it can be seen that the secondary batteries according to Examples 1 to 5 of the present invention have superior −20° C. capacity compared to the secondary battery according to Comparative Example 1. It can also be seen that the secondary batteries according to Examples 1 to 5 have superior energy density compared to the secondary battery according to Comparative Example 2.

[0135] In particular, it can be seen that the secondary batteries according to Examples 2 to 4 have a capacity greater than mAh / g at −20° C. and an energy density that is reduced by only about 0.8% compared to the secondary battery according to Comparative Example 1. That is, it can be seen that the secondary batteries according to Examples 2 to 4 have significantly excellent energy density and low-temperature performance.

[0136] In addition, it can be seen that the secondary battery according to Example 5 has improved life characteristics and energy density compared to the secondary battery according to Comparative Example 5, in which the second binder and second conductive material in the second active material layer were contained in too little amount.

[0137] In addition, it can be seen that the secondary battery according to Example 5 has superior energy density compared to the secondary battery according to Comparative Example 6, in which the second binder and the second conductive material are contained in the second active material layer in excessive amounts. This difference in energy density can become even more pronounced when manufacturing large cells.

[0138] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this and can be implemented in various modified forms within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is natural that this also falls within the scope of the present invention. [Explanation of symbols]

[0139] 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 active material layer on the current collector; a second active material layer on the first active material layer, the first active material layer includes first particles having a single particle shape, and the second active material layer includes second particles having a secondary particle shape; The first particles include a compound represented by the following Chemical Formula 1, and the second particles include a compound represented by the following Chemical Formula 2: [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1; In Formula 1, B1 is at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al; [Chemical formula 2] Li a2 Fe x2 B2 y2 PO 4-b2 In the formula 2, 0.8≦a2≦1.2, 0.95≦x2≦0.999, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2=1; In Formula 2, B2 is at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al.

2. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein a weight of the second particles is 10 to 50% by weight based on a total weight of the first particles and the second particles.

3. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the ratio of the thickness of the second active material layer to the sum of the thicknesses of the first active material layer and the second active material layer is 0.1 to 0.

5.

4. the first particles include at least one first primary particle; The particle diameter of the first primary particles is 200 nm to 300 nm, 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the first particles have an average particle size (D50) of 0.5 μm to 2.5 μm.

5. The positive electrode for a lithium secondary battery according to claim 1 , wherein the second particles have an average particle size (D50) of 3 μm to 7 μm.

6. the first particles include a first coating layer containing carbon; 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the carbon content in the first particles is 0.5 to 3.0 wt%.

7. the second particles include a second coating layer containing carbon; the carbon content in the second particles is 1% to 4% by weight; The positive electrode for a lithium secondary battery according to claim 1 , wherein the carbon content in the second particles is greater than the carbon content in the first particles.

8. The positive electrode for a lithium secondary battery according to claim 1 , wherein the porosity of the second particles is 20% to 40%.

9. the second particles include a plurality of second primary particles aggregated together, 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the particle diameter of the second primary particles is 100 nm to 200 nm.

10. the first active material layer further comprises a first binder; the second active material layer further comprises a second binder; 2. The positive electrode for a lithium secondary battery according to claim 1, wherein a ratio of the content of the first binder in the first active material layer to the content of the second binder in the second active material layer is 1.5 or more.

11. A current collector; a first active material layer on the current collector; a second active material layer on the first active material layer, the first active material layer includes first particles, a first binder, and a first conductive material; and the second active material layer includes second particles, a second binder, and a second conductive material. a content of the first binder in the first active material layer is greater than a content of the second binder in the second active material layer; a content of the first conductive material in the first active material layer is greater than a content of the second conductive material in the second active material layer; The first particles include a compound represented by the following Chemical Formula 1, and the second particles include a compound represented by the following Chemical Formula 2: [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1; In Formula 1, B1 is at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al; [Chemical formula 2] Li a2 Fe x2 B2 y2 PO 4-b2 In the formula 2, 0.8≦a2≦1.2, 0.95≦x2≦0.999, 0.001≦y2≦0.05, 0≦b2≦0.05, and x2+y2=1; In Formula 2, B2 is at least one element selected from the group consisting of Ti, Mg, V, Nb, and Al.

12. 12. The positive electrode for a lithium secondary battery of claim 11, wherein the first binder and the second binder each comprise 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.

13. The content of the first binder is 3 to 10 parts by weight based on 100 parts by weight of the first active material layer, 12. The positive electrode for a lithium secondary battery of claim 11, wherein the content of the second binder is 2 to 5 parts by weight based on 100 parts by weight of the second active material layer.

14. the content of the first conductive material is 1 to 5 parts by weight based on 100 parts by weight of the first active material layer; 12. The positive electrode for a lithium secondary battery of claim 11, wherein the content of the second conductive material is 0.5 to 5 parts by weight based on 100 parts by weight of the second active material layer.

15. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein a weight of the second particles relative to a total weight of the first particles and the second particles is 10 wt % to 50 wt %.

16. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein the ratio of the thickness of the second active material layer to the sum of the thicknesses of the first active material layer and the second active material layer is 0.1 to 0.

5.

17. the first particles include at least one or more first primary particles, The particle diameter of the first primary particles is 200 nm to 300 nm, The positive electrode for a lithium secondary battery according to claim 11, wherein the first particles have an average particle size (D50) of 0.5 μm to 2.5 μm.

18. the second particles include a plurality of second primary particles aggregated together, The particle diameter of the second primary particles is 100 nm to 200 nm, The positive electrode for a lithium secondary battery according to claim 11, wherein the second particles have an average particle size of 3 μm to 7 μm.

19. 12. The positive electrode for a lithium secondary battery according to claim 11, wherein the second particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer.

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

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