Positive electrode and lithium secondary battery including the same

Abstract

To provide a positive electrode for a lithium secondary battery, by which the binding strength of a positive electrode active material layer for a current collector is increased, the resistance of an electrode plate is reduced, and the electrode plate can be manufactured easily.SOLUTION: The present invention relates to a positive electrode and a lithium secondary battery including the same. More specifically, the positive electrode includes a current collector, a first active material layer including first particles, second particles, a first binder, and a first conductive material and existing on the current collector, and a second active material layer including third particles, a second binder, and a second conductive material and existing on the first active material layer. The first particles include a compound with an olivine structure. The second particles include a compound with a layered structure. The third particles include a compound with the olivine structure. The content of cobalt in the first and second active material layers is less than 100 ppm. The first particles include a plurality of first primary particles that are aggregated together. The first particles have an average particle diameter of 3 μm to 10 μm. The first primary particles have a particle diameter of 200 nm or less. The third particles are single particles. The third particles have an average particle diameter of 100 nm to 2 μm.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] In recent years, the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles has led to a rapid increase in demand for high-capacity secondary batteries with high energy density, which has led to active research and development into improving the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode containing active materials capable of lithium ion intercalation / deintercalation, and an electrolyte, and produces electrical energy through oxidation and reduction reactions that occur when lithium ions are intercalated / deintercalated in the positive electrode and the negative electrode. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention aims to provide a positive electrode for a lithium secondary battery that can easily manufacture the electrode plate by increasing the adhesive strength of the positive electrode active material layer to the current collector and reducing the resistance of the electrode plate, and also to provide a lithium secondary battery that has excellent capacity and life characteristics, as well as high operating voltage and energy density. [Means for solving the problem]

[0005] The positive electrode for a lithium secondary battery according to an embodiment of the present invention includes a current collector, first particles, second particles, a first binder, and a first conductive material, a first active material layer on the current collector, third particles, a second binder, and a second conductive material, and a second active material layer on the first active material layer. The first particles include an olivine structure compound of Chemical Formula 1 below, the second particles include a layered structure compound of Chemical Formula 2 below, the third particles include an olivine structure compound of Chemical Formula 3 below, the cobalt Co content in the first and second active material layers is less than 100 ppm, the first particles include a plurality of first primary particles aggregated with each other, the average particle size of the first particles is 3 μm to 10 μm, the first primary particles have a particle size of 200 nm or less, the third particles are single particles, and the average particle size of the third particles can be 100 nm to 2 μm. [Chemical Formula 1] Li 4-b3 , y3 , , a3 , z3 , x3 , Mn x1 Fe y1 B1 z1 PO 4-b1 In Chemical Formula 1, 0.8 ≤ a1 ≤ 1.2, 0.4 ≤ x1 ≤ 0.8, 0 ≤ y1 ≤ 0.6, 0 ≤ z1 ≤ 0.05, 0 ≤ b1 ≤ 0.05, and x1 + y1 + z1 = 1, and B1 includes at least one selected from the group consisting of Al, Ti, V, and Mg. [Chemical Formula 2] Li a2 Ni x2 Mn z2 Al c2 Y d2 O 2-b2 In Chemical Formula 2, 0.8 < a2 ≤ 1.2, 0.7 ≤ x2 ≤ 0.8, 0.2 ≤ z2 ≤ 0.3, 0 ≤ c2 ≤ 0.02, 0 ≤ d2 ≤ 0.003, 0 ≤ b2 ≤ 0.05, and x2 + z2 + c2 + d2 = 1, and Y includes at least one selected from the group consisting of Ti, Mg, Zr, Mo, and Nb. [Chemical Formula 3] Li a3 Mn x3 Fe y3 B3 z3 PO 4-b3 In Chemical Formula 3, 0.8≦a3≦1.2, 0.4≦x3≦0.8, 0≦y3≦0.6, 0≦z3≦0.05, 0≦b3≦0.05, and x3+y3+z3=1, and B3 may include at least one selected from the group consisting of Al, Ti, V, and Mg.

[0006] A positive electrode for a lithium secondary battery according to an embodiment of the present invention includes a current collector; a first active material layer on the current collector, the first active material layer including first particles, second particles, a first binder, and a first conductive material; and a second active material layer on the first active material layer, the second active material layer including third particles, a second binder, and a second conductive material, wherein the first particles include an olivine structure compound represented by Chemical Formula 1 below, the second particles include a layered structure compound represented by Chemical Formula 2 below, and the third particles include an olivine structure compound represented by Chemical Formula 3 below, the first and second active material layers may have a cobalt (Co) content of less than 100 ppm, the first particles include a plurality of first primary particles aggregated together, the first particles have an average particle size of 3 μm to 10 μm, and the first primary particles have a particle size of 200 nm or less, the third particles include a plurality of fourth particles aggregated together, the third particles have an average particle size of 3 μm to 10 μm, and each of the fourth particles may be a primary particle, and the fourth particles may have a particle size of 200 nm or less. [Chemical formula 1] Li a1 Mn x1 Fe y1 B1 z1 PO 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.4≦x1≦0.8, 0≦y1≦0.6, 0≦z1≦0.05, 0≦b1≦0.05, and x1+y1+z1=1, and B1 includes at least one selected from the group consisting of Al, Ti, V, and Mg. [Chemical formula 2] Li a2 Ni x2 Mn z2 Al c2 Y d2 O 2-b2 In Chemical Formula 2, 0.8 < a2 ≤ 1.2, 0.7 ≤ x2 ≤ 0.8, 0.2 ≤ z2 ≤ 0.3, 0 ≤ c2 ≤ 0.02, 0 ≤ d2 ≤ 0.003, 0 ≤ b2 ≤ 0.05, and x2 + z2 + c2 + d2 = 1, and Y contains at least one selected from the group consisting of Ti, Mg, Zr, Mo, and Nb. [Chemical Formula 3] Li a3 Mn x3 Fe y3 B3 z3 PO 4-b3 In Chemical Formula 3, 0.8 ≤ a3 ≤ 1.2, 0.4 ≤ x3 ≤ 0.8, 0 ≤ y3 ≤ 0.6, 0 ≤ z3 ≤ 0.05, 0 ≤ b3 ≤ 0.05, and x3 + y3 + z3 = 1, and the B3 may contain at least one selected from the group consisting of Al, Ti, V, and Mg.

[0007] The lithium secondary battery according to an embodiment of the present invention may include the above-described positive electrode.

Advantages of the Invention

[0008] The positive electrode for a lithium secondary battery according to an embodiment of the present invention can easily manufacture a pole plate and reduce the resistance of the pole plate by increasing the adhesion to the current collector while containing a large amount of a nano-sized olivine-based compound.

[0009] The lithium secondary battery according to an embodiment of the present invention may have a high operating voltage and energy density while being excellent in capacity and life characteristics.

Brief Description of the Drawings

[0010] [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 schematic diagram showing a lithium secondary battery according to an embodiment, and FIG. 2 is cylindrical. [Figure 3] It is a schematic diagram showing a lithium secondary battery according to an embodiment, and FIG. 3 is rectangular. [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 secondary battery according to an embodiment of the present invention. [Figure 7] FIG. 2 is an enlarged view of a first active material layer according to an embodiment of the present invention. [Figure 8] FIG. 3 is an enlarged view of a second active material layer according to an embodiment of the present invention. [Figure 9] FIG. 4 is an enlarged view of a second active material layer according to another embodiment of the present invention. [Figure 10] FIG. 4 is an enlarged view of a positive electrode active material layer according to another comparative example of the present invention. [Figure 11] 1 is a SEM image of a first particle according to an embodiment of the present invention. [Figure 12] 10 is a SEM image of a second particle according to an embodiment of the present invention. [Figure 13] 10 is a SEM image of a single particle type third particle according to an embodiment of the present invention. [Figure 14] 10 is a SEM image of third particles in the form of secondary particles according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be implemented in various forms and may undergo various modifications. The description of the 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 to which the present invention pertains.

[0012] 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 purpose of effectively explaining the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0013] The embodiments described herein are described with reference to cross-sectional views and / or plan views that are idealized examples of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical content. Therefore, the regions shown in the drawings have schematic attributes, and the shapes of the regions shown in the drawings are intended to illustrate the specific forms of the regions of the device and are not intended to limit the scope of the present invention. In various embodiments of the present specification, terms such as "first," "second," and "third" are used to describe various components, but these components should not be limited by such terms. These terms are used only to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments thereof.

[0014] The terms used herein are for the purpose of describing examples and are not intended to limit the present invention. As used herein, the singular forms include the plural forms unless otherwise specified. As used herein, the terms "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components to the referenced components.

[0015] 1 is a conceptual diagram showing 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.

[0016] 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 the electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0017] 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.

[0018] 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.

[0019] As an example, the positive electrode 10 may further include an additive that can act as a sacrificial anode.

[0020] The current collector COL1 can be made of Al, but is not limited to this.

[0021] The positive electrode 10 will be described in detail below with reference to FIG.

[0022] 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.

[0023] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0024] The binder serves to properly adhere the negative electrode active material particles to each other and to properly 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.

[0025] 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.

[0026] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0027] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. Examples of the cellulose-based compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. Examples of the alkali metal include sodium, potassium, and lithium.

[0028] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0029] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive without causing chemical changes 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.

[0030] The current collector COL2 can be 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.

[0031] 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 and dedoped with lithium, or a transition metal oxide.

[0032] 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 crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0033] 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, GeAl and Sn can be used.

[0034] As a substance that can be doped and undoped 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 may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0035] 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 silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon is also located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles can exist dispersed in an amorphous carbon matrix.

[0036] The silicon-carbon composite can further contain crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0037] The Si-based negative electrode active material or the Sn-based negative electrode active material is used by being mixed with a carbon-based negative electrode active material.

[0038] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. Such separator 30 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0039] Separator 30 may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0040] The porous substrate may be a polymer membrane formed from 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 copolymers, polyphenylene disulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0041] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0042] 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.

[0043] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be laminated.

[0044] Electrolyte ELL The electrolyte solution ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0045] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0046] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0047] 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.

[0048] Examples of the ester solvent that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0049] 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.

[0050] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0051] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0052] Lithium salts are dissolved in organic solvents and act as a source of lithium ions within 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, and LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and Y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0053] Lithium secondary battery Lithium secondary batteries are classified into cylindrical, prismatic, pouch, and coin shapes depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to an embodiment, with FIG. 2 showing a cylindrical battery, FIG. 3 showing a prismatic battery, and FIGS. 4 and 5 showing pouch-shaped batteries. 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 housing the electrode assembly 40. 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, in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, and 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 the current generated in the electrode assembly 40 to the outside.

[0054] 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.

[0055] 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, as described above, the positive electrode 10 may include a current collector COL1 and a positive electrode active material layer AML1. The positive electrode active material layer AML1 may be provided on the current collector COL1.

[0056] The positive electrode active material layer AML1 may contain positive electrode active material particles PTC1, PTC2, and PTC3 as described below. The content of the positive electrode active material particles PTC1, PTC2, and PTC3 in the positive electrode active material layer AML1 may be 90% by weight to 99% by weight relative to 100% by weight of the positive electrode active material layer AML1.

[0057] The positive electrode active material layer AML1 may contain binders BND1 and BND2 and conductive materials CDM1 and CDM2, as described below. The contents of the binders BND1 and BND2 and the conductive materials CDM1 and CDM2 may each be 1.0 wt % to 10 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0058] The positive electrode active material layer AML1 may include a first active material layer ATL1 and a second active material layer ATL2. By providing the second active material layer ATL2 on the first active material layer ATL1, the positive electrode active material layer AML1 contains a large amount of nano-sized olivine-based compounds, but the bonding strength to the current collector is increased, making it easier to manufacture an electrode plate and reducing the electrode plate resistance. This also makes it possible to provide a lithium secondary battery with excellent performance.

[0059] 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 and / or the second particles PTC2 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 third particles PTC3 included in the second active material layer ATL2 increases.

[0060] The thickness ratio T1:T2 of the first active material layer ATL1 to the second active material layer ATL2 may be 3:7 to 7:3. For example, the thickness ratio T1:T2 of the first active material layer ATL1 to the second active material layer ATL2 may be 5:5. When the thickness ratio T1:T2 of the first active material layer ATL1 to the second active material layer ATL2 satisfies the above-described numerical range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 is improved, making it easier to manufacture the electrode plate and reducing the electrode plate resistance. In addition, a lithium secondary battery with excellent performance can be provided.

[0061] Fig. 7 is an enlarged view of a first active material layer ATL1 according to an embodiment of the present invention. Fig. 8 is an enlarged view of a second active material layer ATL2 according to one embodiment of the present invention. Fig. 9 is an enlarged view of a second active material layer ATL2 according to another embodiment of the present invention. Fig. 10 is an enlarged view of a positive electrode active material layer AML1 according to a comparative example of the present invention.

[0062] 7, the first active material layer ATL1 may include first particles PTC1, second particles PTC2, and a first functional additive FAD1. The first functional additive FAD1 may include a first binder BND1 and a first conductive material CDM1.

[0063] By including the second particles PTC2 in the first active material layer ATL1, the content of the first functional additive FAD1 can be reduced. As an example, the weight ratio of the first functional additive FAD1 in the first active material layer ATL1 can be 0.024 to 0.06. The "weight ratio of the first functional additive FAD1 in the first active material layer ATL1" can be defined as the mass of the first functional additive FAD1 relative to the total weight of the first active material layer ATL1.

[0064] For example, the content of the first binder BND1 may be 1.2 to 3 parts by weight per 100 parts by weight of the first active material layer ATL1, and the content of the first conductive material CDM1 may be 1.2 to 3 parts by weight per 100 parts by weight of the first active material layer ATL1.

[0065] 8 and 9, the second active material layer ATL2 may include third particles PTC3 and a second functional additive FAD2. The second functional additive FAD2 may include a second binder BND2 and a second conductive material CDM2.

[0066] In the present invention, the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be equal to or greater than the weight ratio of the first functional additive FAD1 in the first active material layer ATL1. For example, the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be greater than the weight ratio of the first functional additive FAD1 in the first active material layer ATL1.

[0067] The weight ratio of the second functional additive FAD2 to the weight of the first functional additive FAD1 (weight ratio of second functional additive / weight ratio of first functional additive) may be 1 to 4.5. For example, the weight ratio of the second functional additive FAD2 to the weight of the first functional additive FAD1 may be 1.6 to 4.5 or 1.6 to 4. When the weight ratio of the second functional additive FAD2 to the weight of the first functional additive FAD1 satisfies the above-described numerical range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 is improved, making it easier to manufacture an electrode plate and reducing the resistance of the electrode plate. In addition, a lithium secondary battery with excellent performance can be provided.

[0068] For example, the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be 0.024 to 0.1. For example, the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be 0.04 to 0.1. The "weight ratio of the second functional additive FAD2 in the second active material layer ATL2" may be defined as the weight of the second functional additive FAD2 relative to the weight of the second active material layer.

[0069] The content of the second binder BND2 may be equal to or greater than the content of the first binder BND1. For example, the content of the second binder BND2 may be 1.2 parts by weight to 5 parts by weight per 100 parts by weight of the second active material layer ATL2. For example, the content of the second binder BND2 may be 2 parts by weight to 5 parts by weight per 100 parts by weight of the second active material layer ATL2.

[0070] The content of the second conductive material CDM2 may be greater than the content of the first conductive material CDM1. For example, the content of the second conductive material CDM2 may be 1.2 parts by weight to 5 parts by weight per 100 parts by weight of the second active material layer ATL2. For example, the content of the second conductive material CDM2 may be 2 parts by weight to 5 parts by weight per 100 parts by weight of the second active material layer ATL2.

[0071] The binders BND1 and BND2 serve to favorably adhere the positive electrode active material particles PTC1, PTC2, and PTC3 to one another and to favorably adhere the positive electrode active material particles PTC1 and PTC2 to the current collector COL1. Representative examples of binders BND1 and BND2 include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0072] The conductive materials CDM1 and CDM2 are used to impart conductivity to the electrodes, and any material that is electron-conductive without causing chemical changes in the battery that is constructed can be used. Examples of conductive materials CDM1 and CDM2 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, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0073] The interface between the first active material layer ATL1 and the second active material layer ATL2 may not be clearly distinguishable in an SEM image, etc. However, the interface between the first active material layer ATL1 and the second active material layer ATL2 can be inferred from the differences in the constituent materials, composition, etc. between the layers.

[0074] The first particles PTC1, the second particles PTC2, and the third particles PTC3 will be described in more detail below.

[0075] 1st particle PTC1 7, the first particles PTC1 may have a polycrystalline form and include secondary particles (first secondary particles) formed by agglomeration of at least two or more primary particles. In other words, one first particle PTC1 may include a plurality of first primary particles NNP agglomerated together. Each of the first primary particles NNP may be a primary particle.

[0076] The average particle size D50 of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. For example, the average particle size of the first particles PTC1 may be approximately 5 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 in the particle size distribution.

[0077] The maximum particle size Dmax of the first particles PTC1 may be 10 μm or more, or 15 μm or more.

[0078] The particle size of the first primary particles NNP may be smaller than the average particle size of the first particles PTC1. The particle size of the first primary particles NNP may be 200 nm or less. For example, the particle size of the first primary particles NNP may be 10 nm to 200 nm, 20 nm to 200 nm, 50 nm to 200 nm, or 100 nm to 200 nm. In one embodiment, the particle size of the first primary particles NNP may refer to the diameter measured by randomly selecting more than 30 first primary particles NNP from an electron microscope photograph of the positive electrode active material. The particle size of the first primary particles NNP may be uniform.

[0079] If the particle sizes of the first particles PTC1 and the first primary particles NNP satisfy the above-described ranges and the size of the first primary particles NNP is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery containing them can be improved.

[0080] The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1:

[0081] [Chemical formula 1] Li a1 Mn x1 Fe y1 B1 z1 PO 4-b1

[0082] In Chemical Formula 1, 0.8≦a1≦1.2, 0.4≦x1≦0.8, 0≦y1≦0.6 (e.g., 0.2≦y1≦0.6), 0≦z1≦0.05, 0≦b1≦0.05, and x1+y1+z1=1. For example, z1 may be 0.002.

[0083] B1 may include at least one selected from the group consisting of Al, Ti, V, and Mg. For example, B1 may include Ti. B1 may be a dopant doped into the first particles PTC1. B1 can be controlled so that the size of the first primary particles NNP is uniform.

[0084] The doping amount of B1 may be 500 ppm to 3000 ppm. The doping amount of B1 may be defined as the weight of the doping element B1 relative to the total weight of metals excluding lithium (i.e., Mn, Fe, and B1) in the olivine-based lithium compound represented by Chemical Formula 1. When the doping amount of B1 satisfies the above range, the size of the first particles PTC1 can be controlled to be uniform.

[0085] 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 may cover only 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 improve the structural stability and electrical conductivity of the first particles PTC1.

[0086] 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 metal or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0087] 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. 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 inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a substance coated on the grain boundaries inside the first particle PTC1. 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.

[0088] 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 the region from a depth of about 10 nm to the entire inside or from a depth of 10 nm to a depth of about 2 μm at the surface of the first particle PTC1.

[0089] The first particles PTC1 further include a grain boundary coating, which can enhance structural stability and form a uniform coating layer on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which can further improve the electrical conductivity of the first particles PTC1.

[0090] The first particles PTC1 may further contain carbon derived from the coating layer and / or the grain boundary coating layer described above. The carbon 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%.

[0091] The first particles PTC1 may have a spherical shape formed by agglomeration of nano-sized first primary particles NNP. The first particles PTC1 may exhibit the following characteristics due to the first primary particles NNP being closely agglomerated to each other: The first particles PTC1 may have a spherical or elliptical shape. The average particle size D50 of the first particles PTC1 may be 2 μm to 15 μm. The porosity of the first particles PTC1 may be about 20% to about 40%. The span value of the first particles PTC1 analyzed with a particle size analyzer may be 0.3 to 0.75.

[0092] The BET specific surface area of ​​the first particles PTC1 may be large. For example, the BET specific surface area of ​​the first particles PTC1 may be 10 m 2 / g~30m 2 For example, the BET specific surface area of ​​the first particles PTC1 can be 20 m 2 / g.

[0093] 2nd particle PTC2 Referring again to FIG. 7, the second particles PTC2 may include a layered lithium compound represented by the following Chemical Formula 2:

[0094] [Chemical formula 2] Li a2 Ni x2 Mn z2 Al c2 Y d2 O2-b2

[0095] In the chemical formula 2, 0.8 < a2 ≤ 1.2, 0.7 ≤ x2 ≤ 0.8, 0.2 ≤ z2 ≤ 0.3, 0 ≤ c2 ≤ 0.02, 0 ≤ d2 ≤ 0.003, 0 ≤ b2 ≤ 0.05, and x2 + z2 + c2 + d2 = 1 may hold. For example, c2 may be 0.004. For example, d2 may be 0.001.

[0096] Y may be a dopant doped into the second particle PTC2. Y may contain at least one selected from the group consisting of Ti, Mg, Zr, Mo, and Nb.

[0097] The cobalt Co content of the second particle PTC2 may be less than 100 ppm. In other words, the second particle PTC2 according to the present invention may not substantially contain cobalt Co. The second particle PTC2 according to the present invention may be a cobalt-free cathode active material. The Co content in the second particle PTC2 may be smaller than the Al content in the second particle PTC2.

[0098] The second particle PTC2 can be represented as a layered cobalt-free cathode active material, a cobalt-free nickel-based cathode active material, or a cobalt-free nickel manganese-based cathode active material. Cobalt-free may mean that it does not contain cobalt, cobalt is not used, or only a very small amount of cobalt is contained.

[0099] In one embodiment, the second particle PTC2 may include a coating layer on its surface. The coating layer may cover the entire surface of the second particle PTC2 or a portion of the surface of the second particle PTC2. The coating layer may include a boron-containing compound, a titanium-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 compounds forming these coating layers may be crystalline or amorphous. The metal-containing compound may further include other metal or non-metal elements. For example, the coating layer may further include lithium, manganese, and / or nickel. Surface modification using a coating layer can stabilize the structure and improve thermal stability.

[0100] The size of the second particles PTC2 may be larger than the size of the first particles PTC1. By introducing the first active material layer ATL1 containing the first particles PTC1 and the second particles PTC2, the positive electrode active material layer AML1 can have a high binding strength to the current collector while containing a large amount of nano-sized olivine-based compounds. This makes it possible to easily manufacture the electrode plate and reduce the resistance of the electrode plate. Furthermore, it is possible to provide a lithium secondary battery with excellent performance.

[0101] For example, the second particle PTC2 may have a single particle shape. In this specification, a single particle may refer to a single particle having no internal grain boundary. A single particle may refer to a morphological phase, a single particle in which particles exist as an independent phase that is not aggregated with each other, a monolith structure, a single structure, or a non-aggregated particle. For example, the single particle may be a single crystal. In one embodiment, the single particle may have a shape in which a plurality of second primary particles MMP are attached to each other. Alternatively, the single particle may have a shape in which 2 to 100 second primary particles MMP are attached to each other. In this specification, the second particle PTC2 that is a single particle may be defined as a second single particle SP2. In addition, in this specification, the second single particle SP2 may be defined as a small particle.

[0102] In one embodiment, the average particle size D50 may refer to the diameter of particles whose cumulative volume in the particle size distribution is 50% by volume. The average particle size D50 of the second particles PTC2 may be a value measured using a particle size analyzer. Accordingly, the average particle size D50 of the second single particles SP2 may be 3 μm to 7 μm or 3 μm to 4 μm. The average particle size D50 of the second single particles SP2 may be larger than the average particle size D50 of the first primary particles NNP.

[0103] As another example, the second particles PTC2 may have a polycrystalline form and include secondary particles formed by agglomeration of at least two or more second primary particles MMP. In other words, one second particle PTC2 may include a plurality of second primary particles MMP agglomerated together. The second particles PTC2 formed by a plurality of second primary particles MMP may have a spherical or elliptical shape. In this specification, the second particles PTC2, which are secondary particles, may be defined as second secondary particles PC2. In addition, in this specification, the second secondary particles PC2 may be defined as large particles.

[0104] In one embodiment, the average particle size D50 may refer to the diameter of particles whose cumulative volume in the particle size distribution is 50% by volume. The average particle size D50 of the second particles PTC2 may be a value measured using a particle size analyzer. Accordingly, the average particle size D50 of the second secondary particles PC2 may be 12 μm to 18 μm. The average particle size D50 of the second secondary particles PC2 may be larger than the average particle size D50 of the first particles PTC1.

[0105] In the present invention, the second particles PTC2 can exist as second single particles SP2 or second secondary particles PC2. The second particles PTC2 may also be a positive electrode active material including second single particles SP2 and second secondary particles PC2.

[0106] In this specification, the second single particle SP2 and the second secondary particle PC2 can both be interpreted as meaning the second particle PTC2, and the second particle PTC2 can be interpreted as including the second single particle SP2 and the second secondary particle PC2.

[0107] In this specification, the positive electrode active material may be referred to as being bimodal when the second particles PTC2 coexist in the form of single particles and secondary particles, or when the second particles PTC2 coexist in the form of large particles and small particles.

[0108] The BET specific surface area of ​​the second particles PTC2 may be small. The BET specific surface area of ​​the second particles PTC2 may be smaller than the BET specific surface area of ​​the first particles PTC1 and / or the third particles PTC3. For example, the BET specific surface area of ​​the second particles PTC2 may be 0.8 m 2 / g~1.2m 2 For example, the BET specific surface area of ​​the second particles PTC2 can be 1 m 2 This allows the use of a smaller amount of binder by mixing with a nano-sized olivine compound.

[0109] Third particle PTC3 Referring to FIG. 8, the third particles PTC3 may have a single particle morphology. In this specification, the term "single particle" refers to a single particle having no internal grain boundary. The term "single particle" refers to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are morphologically present as an independent phase without aggregation. For example, the single particle may be a single crystal. Alternatively, the single particle may contain several crystals. The single particle may be in a singly isolated form. Alternatively, the single particle may be in a form in which 2 to 100 single particles are attached to each other. That is, the third particles PTC3 may be provided in various sizes. For example, the average particle size of the third particles PTC3 may be approximately 1 μm. The minimum particle size of the third particles PTC3 may be 20 nm to 500 nm or 200 nm to 300 nm. For example, the minimum particle size may refer to the diameter measured by randomly selecting about 30 primary particles (hereinafter, referred to as third primary particles) from an electron microscope photograph of the positive electrode active material.

[0110] The average particle size D50 of the third particles PTC3 may be 100 nm to 2 μm or 500 nm to 2 μm. For example, the average particle size of the third particles PTC3 may be approximately 1 μm. As an example, 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 in the particle size distribution.

[0111] The third particles PTC3 may include an olivine structure compound represented by the following Chemical Formula 3.

[0112] [Chemical formula 3] Li a3 Mn x3 Fe y3 B3 z3 PO 4-b3

[0113] In Chemical Formula 3, 0.8≦a3≦1.2, 0.4≦x3≦0.8, 0≦y3≦0.6 (e.g., 0.2≦y3≦0.6), 0≦z3≦0.05, 0≦b3≦0.05, and x3+y3+z3=1. For example, z3 can be 0.002.

[0114] B3 may be a dopant doped into the third particles PTC3. B3 may include at least one selected from the group consisting of Al, Ti, V, and Mg. B3 controls the size of the third primary particles to be uniform, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery.

[0115] In one embodiment, the third particles PTC3 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the third particles PTC3 or a portion of the surface of the third particles PTC3. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability and electrical conductivity of the third particles PTC3.

[0116] 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 metal or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0117] The third particles PTC3 may further contain carbon derived from the coating layer described above. The carbon content in the third particles PTC3 may be 0.5% to 10% by weight, 1% to 3% by weight, or 1.5% to 2.5% by weight.

[0118] The BET specific surface area of ​​the third particles PTC3 may be large. For example, the BET specific surface area of ​​the third particles PTC3 may be 10 m2 / g~30m 2 For example, the BET specific surface area of ​​the third particles PTC3 can be 20 m 2 / g.

[0119] When the third particles PTC3 are single particles, the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be the same as or greater than the weight ratio of the first functional additive FAD1 in the first active material layer ATL1. Alternatively, the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be greater than the weight ratio of the first functional additive FAD1 in the first active material layer ATL1. For example, the ratio of the weight ratio of the second functional additive FAD2 to the weight ratio of the first functional additive FAD1 may be 1.6 to 4.0.

[0120] When the third particles PTC3 are single particles, the content of the second functional additive FAD2 may be 4 to 10 parts by weight or 6 parts by weight per 100 parts by weight of the second active material layer ATL2. For example, the content of the second binder BND2 may be 2 to 5 parts by weight or 3 parts by weight per 100 parts by weight of the second active material layer. For example, the content of the second conductive material CDM2 may be 2 to 5 parts by weight or 3 parts by weight per 100 parts by weight of the second active material layer. When the content of the second functional additive FAD2 satisfies the above-described range, the second active material layer ATL2 can have the desired binding strength.

[0121] 9, the third particles PTC3 may have a polycrystalline form and include secondary particles (hereinafter referred to as third secondary particles) formed by agglomeration of at least two or more primary particles. In other words, one third particle PTC3 may include a plurality of fourth particles PTC4 agglomerated together. Each of the fourth particles PTC4 may be a primary particle. The third particles PTC3 may have a spherical or elliptical shape.

[0122] In one embodiment, the third particle PTC3 may further include a grain boundary coating layer on the surface of each of the fourth particles PTC4. 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 fourth particles PTC4 inside the third particle PTC3. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries in the third particle PTC3. 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.

[0123] 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 the 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.

[0124] The third particles PTC3 further include a grain boundary coating, which may enhance structural stability and form a uniform coating layer on the surface of the third particles PTC3. In addition, the third particles PTC3 further include a grain boundary coating portion, which may further improve the electrical conductivity of the third particles PTC3.

[0125] 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% to 10% by weight, 1% to 3% by weight, or 1.5% to 2.5% by weight.

[0126] When the third particles PTC3 are secondary particles (third secondary particles), the average particle size D50 of the third particles PTC3 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. For example, the average particle size of the third particles PTC3 may be approximately 5 μm. The average particle size of the third particles PTC3 may be larger than the average particle size of the fourth particles PTC4 described below. In one embodiment, the average particle size can 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 in the particle size distribution.

[0127] The particle size of the fourth particles PTC4 may be 200 nm or less. For example, the particle size of the fourth particles PTC4 may be 10 nm to 200 nm, 20 nm to 200 nm, 50 nm to 200 nm, or 100 nm to 200 nm. In one embodiment, the particle size may refer to the diameter measured by randomly selecting approximately 30 fourth particles PTC4 in an electron microscope photograph of the positive electrode active material. The particle size of the fourth particles PTC4 may be uniform. The particle size of the fourth particles PTC4 may be smaller than the particle size of the third primary particles. For example, the particle size of the fourth particles PTC4 may be approximately 100 nm smaller than the particle size of the third primary particles.

[0128] If the fourth particles and the average particle size of the fourth particles satisfy the above-described ranges and the size of the fourth particles is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery including the fourth particles can be improved.

[0129] The third particles PTC3 may have a spherical shape formed by agglomeration of nano-sized fourth particles PTC4. The third particles PTC3 may exhibit the following properties due to the fourth particles PTC4 being closely agglomerated to one another: The third particles PTC3 may have a spherical or elliptical shape. The third particles PTC3 may have an average particle size D50 of 2 μm to 15 μm. The third particles PTC3 may have a porosity of about 20% to about 40%. The third particles PTC3 may have a span value of 0.3 to 0.75 when analyzed using a particle size analyzer.

[0130] When the third particles PTC3 are secondary particles (third secondary particles), the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be equal to or greater than the weight ratio of the first functional additive FAD1 in the first active material layer ATL1. For example, the ratio of the weight ratio of the second functional additive FAD2 to the weight ratio of the first functional additive FAD1 may be 1 to 4.5. For example, the ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive may be 1 to 4, 1.6 to 4, or 2.5 parts by weight.

[0131] When the third particles PTC3 are secondary particles, the content of the second functional additive FAD2 may be 2.4 parts by weight to 6.0 parts by weight or 2.4 parts by weight per 100 parts by weight of the second active material layer ATL2. For example, the content of the second binder may be 1.2 parts by weight to 3 parts by weight or 1.2 parts by weight per 100 parts by weight of the second active material layer. For example, the content of the second conductive material may be 1.2 parts by weight to 3 parts by weight or 1.2 parts by weight per 100 parts by weight of the second active material layer. When the content of the second functional additive FAD2 satisfies the above-described range, the second active material layer ATL2 can have the desired binding strength. When the third particles PTC3 are secondary particles (third secondary particles), the particle shape is different from that of single particles, so the amount of binder physically required on the surface may be smaller.

[0132] When the third particles PTC3 are secondary particles, they have a larger average particle size than when the third particles PTC3 are single particles, and therefore the second active material layer ATL2 can have the desired binding strength even if it contains a smaller amount of the second binder BND2 than when the third particles PTC3 are single particles.

[0133] According to the comparative example of the present invention shown in FIG. 10, the positive electrode active material layer AML1 may only include a nano-shaped positive electrode active material. The nano-shaped positive electrode active material may include an olivine-based compound and nano-sized particles NP. For example, the chemical formula of the olivine-based compound may be represented by Chemical Formula 1 and / or Chemical Formula 3. For example, the nano-shaped positive electrode active material may be formed by agglomerating the nano-sized particles NP to have a particle morphology similar to the first particles PTC1 shown in FIG. 7 or the third particles PTC3 shown in FIG. 9. Even if the nano-shaped positive electrode active material is formed by agglomerating the nano-sized particles NP, it does not have to be spherical like the first particles PTC1 shown in FIG. 7 or the third particles PTC3 shown in FIG. 9. That is, the nano-shaped positive electrode active material may have a random morphology. The nano-shaped positive electrode active material may be provided in various sizes. For example, the average particle size of the nano-shaped positive electrode active material may be 500 nm to 2.5 μm, or approximately 1 μm. The minimum particle size of the nano-shaped positive electrode active material may be 100 nm to 500 nm, or 200 nm to 300 nm. In one embodiment, the average particle size D50 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 in the particle size distribution. For example, the minimum particle size may refer to the diameter measured by randomly selecting approximately 30 primary particles from an electron microscope image of the nano-shaped positive electrode active material. The minimum particle size may be approximately 100 nm larger than the particle size of the primary particles (NNP). The nano-shaped positive electrode active material may have a porosity of more than 40%. The nano-shaped positive electrode active material may have a span value outside the range of 0.3 to 0.75 when analyzed using a particle size analyzer.

[0134] Referring again to FIG. 7, the first active material layer ATL1 of the present invention may include both first particles PTC1 and second particles PTC2.

[0135] PTC1 Particle 1 is a lithium iron phosphate compound with an olivine structure, which is extremely stable and chemically stable. Its stable structure generally provides superior lifespan characteristics compared to other cathode materials, but the voltage it can use is limited due to the degradation of lifespan characteristics when used at high voltages. PTC1 Particle 1 contains manganese (Mn), which improves high-voltage characteristics and energy density compared to typical lithium iron phosphate compounds.

[0136] As shown in Figure 10, if the particle size is too small, the binding strength between the current collector and the positive electrode active material is weak, which may make it difficult to process the electrode plate, and a large amount of binder may be required.

[0137] The second particles PTC2 may include a Co-free lithium nickel manganese oxide. The second particles PTC2 may be substantially free of cobalt Co and may include nickel, manganese, and the like as main components. A positive electrode active material including the second particles PTC2 is economical and can achieve high energy density.

[0138] Lithium nickel manganese oxides have a higher pellet density when pressed than compounds with an olivine structure, and can therefore alleviate the problem of low electrode density that phosphate compounds with an olivine structure have.

[0139] As shown in Figures 6 and 7, by inserting a first active material layer ATL1 between a current collector COL1 and a second active material layer ATL2 and mixing first particles PTC1 and second particles PTC2 in an appropriate ratio, the electrode plate binding strength can be improved and the binder BND content can be reduced. Furthermore, by mixing, the capacity, density characteristics, high-temperature stability, and life characteristics can be improved. Furthermore, by mixing the second particles in a bimodal form of large and small particles, even greater density can be achieved.

[0140] The content of the first particles PTC1 relative to the total content of the first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1 and ATL2 may be 35 wt %. That is, the weight ratio of the first particles PTC1 to the total weight of the first particles PTC1, second particles PTC2, and third particles PTC3 (weight ratio of the first particles PTC1) may be 0.3 to 0.4.

[0141] The content of second particles PTC2 relative to the total content of first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1, ATL2 may be 15% to 30% by weight. For example, the content of second particles PTC2 relative to the total content of first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1, ATL2 may be 20% to 30% by weight, or 30% by weight.

[0142] The content of the second particles PTC2 relative to the total content of the first particles PTC1 and the second particles PTC2 contained in the first active material layer ATL1 can be 40% by weight to 60% by weight. For example, the content of the second particles PTC2 relative to the total content of the first particles PTC1 and the second particles PTC2 contained in the first active material layer ATL1 can be 45% by weight to 50% by weight.

[0143] 8 and 9, the second active material layer ATL2 of the present invention may contain third particles PTC3. The content of the third particles PTC3 relative to the total content of the first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1 and ATL2 may be 30% to 40% by weight. For example, the content of the third particles PTC3 relative to the total content of the first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1 and ATL2 may be 35% by weight.

[0144] When the contents of the first particles PTC1, the second particles PTC2, and the third particles satisfy the above-described ranges, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 can be improved. This makes it possible to provide a lithium secondary battery with reduced resistance. Furthermore, when the contents of the first particles PTC1, the second particles PTC2, and the third particles PTC3 satisfy the above-described ranges, it makes it possible to provide a lithium secondary battery with excellent performance.

[0145] The total doping amount of Mn may be 0.46 to 0.52. For example, the total doping amount of Mn may be 0.49 to 0.50. The "total doping amount of Mn A+B" may be defined as the sum of the doping amount A of Mn contained in the first active material layer ATL1 and the doping amount B of Mn contained in the second active material layer ATL2. The doping amount A of Mn contained in the first active material layer ATL1 may be defined as the sum of the product of the doping amount of Mn in the first particles PTC1 (x1 in Chemical Formula 1) and the weight ratio of the first particles PTC1 described above, and the product of the doping amount of Mn in the second particles PTC2 (z2 in Chemical Formula 2) and the weight ratio of the second particles PTC2 described above. The doping amount B of Mn contained in the second active material layer ATL2 may be defined as the product of the doping amount of Mn in the third particles PTC3 (x3 in Chemical Formula 3) and the weight ratio of the third particles PTC3 described above.

[0146] When the total doping amount of Mn satisfies the above-described range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 can be improved, thereby providing a lithium secondary battery with reduced resistance and excellent performance.

[0147] The positive electrode for a lithium secondary battery according to the embodiment of the present invention has the following effects.

[0148] While a relatively large amount of first binder BND1 may be required to adhere nano-sized particles NP (see FIG. 10) with a small average particle size to current collector COL1 (see FIG. 1), a relatively small amount of first binder BND1 may be required to fix first particles PTC1 with a large average particle size and / or second particles PTC2 with a small BET specific surface area and a large average particle size to first active material layer ATL1. The positive electrode active material layer AML1 of the present invention includes first particles PTC1, second particles PTC2, and third particles PTC3. The introduction of the first active material layer ATL1 and the second active material layer ATL2 enhances the binding strength to the current collector despite the inclusion of a large amount of nano-sized olivine-based compound, thereby facilitating the manufacture of an electrode plate and reducing the electrode plate resistance. Furthermore, a lithium secondary battery with excellent capacity and life characteristics, high operating voltage, and energy density may be provided.

[0149] The present invention will be described in more detail with reference to the following examples. However, these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0150] Production Example 1: Production of NMX particles Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH were mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 900°C for 8 hours in an oxygen atmosphere to obtain a composition of Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 O2 and an oxide with an average particle size D50 of about 4 μm was prepared. After adding aluminum oxide to the oxide, a second heat treatment was performed at 825°C for 8 hours in an oxygen atmosphere to prepare NMX particles. The chemical formula of the NMX particles is LiNi 0.75 Mn 0.23 Al 0.02 It was O2.

[0151] Production Example 2: Production of LMFP particles in the form of secondary particles Mn 0.6 Fe 0.4Manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added to water in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.01:0.004. 10% by weight of glucose was further added to the mixture. The mixture in the form of a slurry was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain LMFP particles in the form of secondary particles. The chemical formula of the LMFP particles in the form of secondary particles is approximately LiMn 0.6 Fe 0.4 PO4 and the Ti doping amount was 2000 ppm.

[0152] Production Example 3: Production of LMFP particles in single particle form Mn 0.6 Fe 0.4 Manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added to water in a molar ratio of (Mn+Fe):Li:Mg:Ti=1:1.03:0.01:0.004. 10% by weight of glucose was further added to the mixture. The mixture was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours under a nitrogen atmosphere. The calcined product was ground at a rotation speed of 8000 rpm to obtain single-particle LMFP particles. The chemical formula of the single-particle LMFP particles was approximately LiMn 0.6 Fe 0.4 It was PO4.

[0153] Example 1: Fabrication of a positive electrode including a first active material layer and a second active material layer NMX particles, secondary particle-type LMFP particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 0.460:0.516:0.012:0.012 to prepare a first active material slurry.

[0154] A second active material slurry was prepared by dispersing single particle LMFP particles, a second binder (polyvinylidene fluoride), and a second conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.94:0.03:0.03.

[0155] The first active material slurry was applied to a 15 μm-thick aluminum Al thin film 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 NMX particles, secondary particle-form LMFP particles for the first active material layer, and single particle-form LMFP particles for the second active material layer was 30:35:35. A roll press was performed to produce a positive electrode in which the aluminum current collector, first active material layer, and second active material layer were stacked in order. The thickness ratio of the first active material layer to the second active material layer was 5:5.

[0156] Example 2: Fabrication of a positive electrode including a first active material layer and a second active material layer The second active material slurry was prepared in the same manner as in Example 1, except that the second active material slurry was prepared by dispersing the LMFP particles in the form of secondary particles, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) in N-methylpyrrolidone in a weight ratio of 0.976:0.012:0.012. The thickness ratio of the first active material layer to the second active material layer was 5:5.

[0157] Comparative Example 1: Preparation of a positive electrode containing one active material layer A first active material slurry was prepared by dispersing NMX particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.976:0.012:0.012. The first active material slurry was applied to a 15 μm-thick aluminum Al thin film current collector and dried to form a first active material layer. A roll press was performed to prepare a positive electrode in which the aluminum current collector and the first active material layer were stacked in order.

[0158] Comparative Example 2: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that the first active material slurry was prepared by dispersing the LMFP particles in the form of secondary particles, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.976:0.012:0.012.

[0159] Comparative Example 3: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that the first active material slurry was prepared by dispersing single-particle LMFP particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.94:0.03:0.03.

[0160] Comparative Example 4: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles and secondary particle-type LMFP particles were mixed in a weight ratio of 70:30 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0161] Comparative Example 5: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles and secondary particle-type LMFP particles were mixed in a weight ratio of 60:40 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0162] Comparative Example 6: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles and secondary particle-type LMFP particles were mixed in a weight ratio of 50:50 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0163] Comparative Example 7: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles and secondary particle-type LMFP particles were mixed in a weight ratio of 40:60 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0164] Comparative Example 8: Production of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles and secondary particle-type LMFP particles were mixed in a weight ratio of 30:70 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0165] Comparative Example 9: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles and secondary particle-type LMFP particles were mixed in a weight ratio of 20:80 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0166] Comparative Example 10: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles and secondary particle-type LMFP particles were mixed in a weight ratio of 10:90 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0167] Comparative Example 11: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles, secondary LMFP particles, and single LMFP particles were mixed in a weight ratio of 30:35:35 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black). The amounts of the first binder and first conductive material are as shown in Table 2.

[0168] Comparative Example 12: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NMX particles and single-particle LMFP particles were mixed at a weight ratio of 30:70 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black). The amounts of the first binder and the first conductive material were as shown in Table 2.

[0169] Comparative Example 13: Production of a positive electrode including a first active material layer and a second active material layer A positive electrode with FAD2 / FAD1=1 was produced.

[0170] The same method as in Example 1 was used to prepare a first active material slurry, which was prepared by dispersing NMX particles, secondary particle-type LMFP particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.460:0.516:0.012:0.012, and a second active material slurry, which was prepared by dispersing single particle-type LMFP particles, a second binder (polyvinylidene fluoride), and a second conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.976:0.012:0.012.

[0171] Comparative Example 14: Production of a positive electrode including a first active material layer and a second active material layer A positive electrode with FAD2 / FAD1=4.2 was produced.

[0172] The same method as in Example 1 was used to prepare a first active material slurry by dispersing NMX particles, secondary particle-type LMFP particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.460:0.516:0.012:0.012, and a second active material slurry by dispersing single particle-type LMFP particles, a second binder (polyvinylidene fluoride), and a second conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.90:0.05:0.05.

[0173] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal counter electrode as the counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene PE film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte solution was injected to fabricate a lithium secondary battery. The electrolyte used was a 1.3 M LiPF6 solution mixed with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3.

[0174] [Table 1]

[0175] [Table 2]

[0176] Evaluation example 1: Analysis of the surface of the positive electrode active material SEM images of the first, second, and third particles prepared in Preparation Examples 1 to 3 are shown in FIGS. 11 to 14. Referring to FIG. 11, it can be seen that the first particles prepared in Preparation Example 2 of the present invention are spherical secondary particles formed by agglomeration of a plurality of primary particles. Referring to FIG. 12, it can be seen that the second particles prepared in Preparation Example 1 are micro-sized single particles. Referring to FIG. 13, it can be seen that the third particles prepared in Preparation Example 3 are nano-sized fine single particles. Referring to FIG. 14, it can be seen that the third particles prepared in Preparation Example 2 are spherical secondary particles formed by agglomeration of a plurality of primary particles.

[0177] Evaluation example 2: Active material evaluation The pellet density (PD) of the positive electrode active materials of the examples and comparative examples was measured, and the results are shown in Table 3.

[0178] [Table 3]

[0179] Evaluation example 3: Evaluation of resistance and cohesion The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of the Examples and Comparative Examples were evaluated.

[0180] The lithium secondary battery was initially charged at 25°C under conditions of a constant current (0.2C) and a constant voltage (4.45V) (cutoff 0.05C). After resting for 10 minutes, it was discharged at a constant current (0.2C) to 3.0V to obtain the initial charge capacity at 0.2C and the initial discharge capacity at 0.2C. The efficiency (%) at 0.2C was calculated as the initial discharge capacity at 0.2C / initial charge capacity at 0.2C. The lithium secondary battery was charged to SOC50 at a constant current of 0.2C and then rested for 1 hour at SOC50. It was then discharged for 10 seconds at 1.0°C and rested for another 10 seconds. The cell resistance (DC-IR) was calculated by dividing the voltage after discharge and the voltage after the 10-second rest by the current. The results are shown in Table 4 below.

[0181] [Table 4]

[0182] Referring to Table 4, the lithium secondary batteries including the positive electrodes according to Examples 1 and 2 had higher discharge capacities and lower resistances compared to Comparative Examples 2, 3, and 12. This confirms that the addition of NMX particles can enhance the binding strength of the positive electrode including the olivine-based compound.

[0183] It was also confirmed that the lithium secondary batteries including the positive electrodes according to Examples 1 and 2 had lower resistance than those according to Comparative Examples 13 and 14. This indicates that the binding strength of the positive electrode can be increased when the weight ratio of the second functional additive to the weight ratio of the first functional additive satisfies a desired range.

[0184] Evaluation example 4: Battery characteristics evaluation The characteristics of the lithium secondary batteries fabricated using the positive electrode active materials of the Examples and Comparative Examples were evaluated.

[0185] The lithium secondary battery was initially charged at a constant current (0.2C), rested for 10 minutes, and then discharged at a constant current (0.2C) until it reached 3.0V, and the average voltage was measured. It was then charged and discharged 50 times at 1.0C / 1.0C at 45°C. Furthermore, a coin cell was fabricated, and the battery was initially charged at a constant current (0.2C), rested for 10 minutes, and then discharged at a constant current (0.2C) until it reached 3.0V. After further charging, the capacity was measured at -20°C. The battery characteristic evaluation results are shown in Table 5 below.

[0186] [Table 5]

[0187] Referring to Tables 4 and 5, it was confirmed that the lithium secondary batteries including the positive electrodes according to Examples 1 and 2 had excellent capacity and life characteristics, as well as high operating voltage and energy density.

[0188] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention may be embodied in other specific forms without changing the technical spirit or essential characteristics thereof. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not limiting.

Claims

1. A current collector; a first active material layer on the current collector, the first active material layer including first particles, second particles, a first binder, and a first conductive material; a second active material layer on the first active material layer, the second active material layer including third particles, a second binder, and a second conductive material; The first particles include an olivine structure compound represented by the following Chemical Formula 1: The second particles include a layered structure compound represented by the following Chemical Formula 2: The third particles include an olivine structure compound represented by the following Chemical Formula 3: the content of cobalt (Co) in the first and second active material layers is less than 100 ppm; the first particles include a plurality of first primary particles aggregated together, the first particles have an average particle size of 2 μm to 15 μm; the first primary particles have a particle size of 200 nm or less, the third particle is a single particle, The third particles have an average particle size of 100 nm to 2 μm. Positive electrode for lithium secondary batteries. [Chemical formula 1] Li a1 Mn x1 Fe y1 B1 z1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.4≦x1≦0.8, 0≦y1≦0.6, 0≦z1≦0.05, 0≦b1≦0.05, and x1+y1+z1=1; B1 includes at least one selected from the group consisting of Al, Ti, V, and Mg, [Chemical formula 2] Li a2 Ni x2 Mn z2 Al c2 Y d2 O 2-b2 In Chemical Formula 2, 0.8<a2≦1.2, 0.7≦x2≦0.8, 0.2≦z2≦0.3, 0≦c2≦0.02, 0≦d2≦0.003, 0≦b2≦0.05, and x2+z2+c2+d2=1; The Y includes at least one selected from the group consisting of Ti, Mg, Zr, Mo, and Nb, [Chemical formula 3] Li a3 Mn x3 Fe y3 B3 z3 PO 4-b3 In Chemical Formula 3, 0.8≦a3≦1.2, 0.4≦x3≦0.8, 0≦y3≦0.6, 0≦z3≦0.05, 0≦b3≦0.05, and x3+y3+z3=1; The B3 includes at least one selected from the group consisting of Al, Ti, V, and Mg.

2. the content of the second particles relative to the total content of the first particles, the second particles, and the third particles contained in the first and second active material layers is 15% by weight to 30% by weight; The positive electrode for a lithium secondary battery according to claim 1 .

3. The total doping amount of Mn is 0.46 to 0.52; The positive electrode for a lithium secondary battery according to claim 1 .

4. the thickness ratio of the first active material layer to the second active material layer is 3:7 to 7:3; The positive electrode for a lithium secondary battery according to claim 1 .

5. The porosity of the first particles is 20% to 40%. The positive electrode for a lithium secondary battery according to claim 1 .

6. the second particles are single crystals; The positive electrode for a lithium secondary battery according to claim 1 .

7. The second particles have an average particle size of 3 μm to 7 μm. The positive electrode for a lithium secondary battery according to claim 1 .

8. The BET specific surface area of ​​the second particles is 0.8 m 2 / g~1.2m 2 / g, The positive electrode for a lithium secondary battery according to claim 1 .

9. the first binder and the first conductive material constitute a first functional additive; the second binder and the second conductive material constitute a second functional additive; a weight ratio of the first functional additive in the first active material layer being smaller than a weight ratio of the second functional additive in the second active material layer; The positive electrode for a lithium secondary battery according to claim 1 .

10. the ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive is 1.6 to 4.5; The positive electrode for a lithium secondary battery according to claim 9 .

11. A current collector; a first active material layer on the current collector, the first active material layer including first particles, second particles, a first binder, and a first conductive material; a second active material layer on the first active material layer, the second active material layer including third particles, a second binder, and a second conductive material; The first particles include an olivine structure compound represented by the following Chemical Formula 1: The second particles include a layered structure compound represented by the following Chemical Formula 2: The third particles include an olivine structure compound represented by the following Chemical Formula 3: the content of cobalt (Co) in the first and second active material layers is less than 100 ppm; the first particles include a plurality of first primary particles aggregated together, the first particles have an average particle size of 2 μm to 15 μm; the first primary particles have a particle size of 200 nm or less, the third particles include a plurality of fourth particles aggregated together; the third particles have an average particle size of 2 μm to 15 μm; each of the plurality of fourth particles is a primary particle, and the plurality of fourth particles has a particle size of 200 nm or less; Positive electrode for lithium secondary batteries. [Chemical formula 1] Li a1 Mn x1 Fe y1 B1 z1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.4≦x1≦0.8, 0≦y1≦0.6, 0≦z1≦0.05, 0≦b1≦0.05, and x1+y1+z1=1; B1 includes at least one selected from the group consisting of Al, Ti, V, and Mg, [Chemical formula 2] Li a2 Ni x2 Mn z2 Al c2 Y d2 O 2-b2 In Chemical Formula 2, 0.8<a2≦1.2, 0.7≦x2≦0.8, 0.2≦z2≦0.3, 0≦c2≦0.02, 0≦d2≦0.003, 0≦b2≦0.05, and x2+z2+c2+d2=1; The Y includes at least one selected from the group consisting of Ti, Mg, Zr, Mo, and Nb, [Chemical formula 3] Li a3 Mn x3 Fe y3 B3 z3 PO 4-b3 In Chemical Formula 3, 0.8≦a3≦1.2, 0.4≦x3≦0.8, 0≦y3≦0.6, 0≦z3≦0.05, 0≦b3≦0.05, and x3+y3+z3=1; The B3 includes at least one selected from the group consisting of Al, Ti, V, and Mg.

12. the content of the second particles relative to the total content of the first particles, the second particles, and the third particles contained in the first and second active material layers is 15% by weight to 30% by weight; The positive electrode for a lithium secondary battery according to claim 11.

13. The total doping amount of Mn is 0.46 to 0.52; The positive electrode for a lithium secondary battery according to claim 11.

14. the thickness ratio of the first active material layer to the second active material layer is 3:7 to 7:3; The positive electrode for a lithium secondary battery according to claim 11.

15. the second particles are single crystals; The positive electrode for a lithium secondary battery according to claim 11.

16. The second particles have an average particle size of 3 μm to 7 μm. The positive electrode for a lithium secondary battery according to claim 1 .

17. The BET specific surface area of ​​the second particles is 0.8 m 2 / g~1.2m 2 / g, The positive electrode for a lithium secondary battery according to claim 11.

18. the first binder and the first conductive material constitute a first functional additive; the second binder and the second conductive material constitute a second functional additive; the weight ratio of the first functional additive in the first active material layer is equal to or smaller than the weight ratio of the second functional additive in the second active material layer; The positive electrode for a lithium secondary battery according to claim 1 .

19. The ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive is 1 to 4.5; The positive electrode for a lithium secondary battery according to claim 18.

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

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