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 first particles include a plurality of first primary particles that are aggregated together. The first particles have an average particle diameter of 2 μm to 15 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 intercalation / deintercalation (insertion / extraction) of lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted / extracted into / from the positive electrode and 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] 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 particles include a plurality of first primary particles agglomerated with each other, the first particles may have an average particle size of 2 μm to 15 μm, the first primary particles may have a particle size of 200 nm or less, and the third particles may be single particles, and the third particles may have an average particle size of 100 nm to 2 μm. [Chemical formula 1] Li a1 Mn x1 Fe y1 B1 z1 PO 4-b1 In the above 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 CO y2 Mn z2 B2 c2 O 2-b2 In the chemical formula 2, 0.8≦a2≦1.2, 0.5≦x2≦0.8, 0≦y2≦0.3, 0.1≦z2≦0.5, 0≦c2≦0.1, 0≦b2≦0.05, and x2+y2+z2+c2=1; and B2 includes at least one selected from the group consisting of Ti, Mg, V, Nb, and Al; [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 particles include a plurality of first primary particles aggregated together, the first particles having an average particle size of 2 μm to 15 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 2 μm to 15 μm, and each of the fourth particles is 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 the above 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 CO y2 Mn z2 B2 c2 O 2-b2 In the chemical formula 2, 0.8≦a2≦1.2, 0.5≦x2≦0.8, 0≦y2≦0.3, 0.1≦z2≦0.5, 0≦c2≦0.1, 0≦b2≦0.05, and x2+y2+z2+c2=1; and B2 includes at least one selected from the group consisting of Ti, Mg, V, Nb, and Al; [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.

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

[0008] The positive electrode for a lithium secondary battery according to an embodiment of the present invention includes a large amount of nano-sized olivine-based compounds, and has enhanced binding strength to a current collector, thereby facilitating the manufacture of an electrode plate and reducing the resistance of the electrode plate.

[0009] A lithium secondary battery according to an embodiment of the present invention may have excellent capacity and life characteristics, as well as high operating voltage and energy density. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery has a cylindrical shape. [Figure 3] FIG. 3 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery has a prismatic shape. [Figure 4] FIG. 4 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery is in the form of a pouch. [Figure 5] FIG. 5 is a schematic diagram showing a lithium secondary battery according to an embodiment, in which the battery is in the form of a pouch. [Figure 6] 1 is a cross-sectional view of a positive electrode for a 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 a 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 a third particle in the form of a secondary particle 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 wt % to 99.5 wt % of the negative electrode active material, 0.5 wt % to 5 wt % of the binder, and 0 wt % to 5 wt % 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-sintered pellets may 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 inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and de-doped from lithium, or a transition metal oxide.

[0032] The material capable of reversibly inserting / extracting 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 de-doped 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 (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 can also be 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 stacked.

[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 move.

[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 in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, 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 (LiDBOP), 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 5, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 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, 90% by weight to 97.6% by weight, or 92% by weight to 97.6% 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 be 2.4% by weight to 10% by weight or 2.4% by weight to 8% by weight, respectively, relative to 100% by weight 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. Furthermore, 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 parts by weight to 3 parts by weight or 1.2 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 parts by weight to 3 parts by weight or 1.2 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 can be equal to or 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) can 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 can be 1.5 to 4 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 the electrode plate and reducing the electrode plate resistance. 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 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 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 equal to or greater than the content of the first conductive material CDM1. For example, the content of the second conductive material CDM2 may be 1.2 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 materials 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 first particles PTC1, the second particles PTC2, and the third particles PTC3 will be described in more detail below.

[0074] 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.

[0075] 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.

[0076] The maximum particle size Dmax of the first particles PTC1 may be 10 μm or more, or 15 μm or more.

[0077] 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.

[0078] If the particle sizes of the first particles PTC1 and the first primary particles NNP satisfy the ranges described above 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.

[0079] The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1:

[0080] [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 (e.g., 0.2≦y1≦0.6), 0≦z1≦0.05, 0≦b1≦0.05, and x1+y1+z1=1 may be satisfied. 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.

[0081] 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 range, the size of the first particles PTC1 can be controlled to be uniform.

[0082] 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.

[0083] 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.

[0084] 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 material 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.

[0085] 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 of the surface of the first particle PTC1, or from a depth of 10 nm to a depth of about 2 μm.

[0086] The first particles PTC1 further include a grain boundary coating, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which further improves the electrical conductivity of the first particles PTC1.

[0087] 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%.

[0088] The first particles PTC1 may have a spherical shape formed by the aggregation of nano-sized first primary particles NNP. The first particles PTC1 may exhibit the following characteristics due to the first primary particles NNP closely agglomerating 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.

[0089] 2nd particle PTC2 Referring again to FIG. 7, the second particles PTC2 may include a lithium-nickel-based composite oxide as a nickel-based active material. As an example, the second particles PTC2 may include a high-nickel-based positive electrode active material containing a high amount of nickel. The high-nickel-based positive electrode active material can achieve high capacity and high performance. As another example, the second particles PTC2 may include a mid-nickel-based positive electrode active material containing a medium amount of nickel. The mid-nickel-based positive electrode active material can achieve high capacity and high performance.

[0090] The second particles PTC2 may include a lithium nickel composite oxide having a layered structure represented by the following chemical formula 2.

[0091] [Chemical formula 2] Li a2 Ni x2 Co y2 Mn z2 B2 c2 O 2-b2 In Formula 2, 0.8≦a2≦1.2, 0.5≦x2≦0.8, 0≦y2≦0.3, 0.1≦z2≦0.5, 0≦c2≦0.1, 0≦b2≦0.05, and x2+y2+z2+c2=1. For example, c2 can be 0.005.

[0092] B2 may be a dopant doped into the second particle PTC2. B2 may include at least one selected from the group consisting of Ti, Mg, V, Nb, and Al. For example, B2 may be Al.

[0093] In one embodiment, the second particles PTC2 may include a second coating layer on their surfaces. By including the second coating layer, the second particles PTC2 can effectively prevent structural collapse due to repeated charge and discharge. This can improve the life characteristics of the secondary battery.

[0094] The second coating layer may include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the second coating layer may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound may further include other metal or non-metal elements. For example, the second coating layer may further include lithium, manganese, and / or nickel.

[0095] A method for measuring the metal content in the second coating layer of the second particles PTC2 may include performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the second particles. The analysis can confirm the content of boron and / or aluminum in the second coating layer. In addition to SEM-EDS, methods for measuring the metal content in the second coating layer include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0096] The size of the second particles PTC2 can be in the micron range. By incorporating 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 nanosized olivine-based compounds. This allows for easy production of electrode plates and reduces the resistance of the electrode plates. Furthermore, a lithium secondary battery with excellent performance can be provided.

[0097] For example, the second particles PTC2 may have a single particle shape, similar to the first particles PTC1 described above. The description of the single particle may be the same or similar to that of the first particles PTC1 described above. In one embodiment, the second particles PTC2 may have a shape consisting of one single particle. In one embodiment, the second particles PTC2 may have a shape in which a plurality of single particles are attached to each other. The cathode active material according to the present invention includes the second particles PTC2 in a single particle shape, thereby achieving a high capacity and high energy density of the secondary battery. In this specification, the second particles PTC2 that are single particles may be defined as second single particles. In addition, in this specification, the second single particles may be defined as small particles.

[0098] The average particle size D50 of the second particles PTC2, which are single particles, may be 2 μm to 15 μm, 2 μm to 10 μm, 2 μm to 5 μm, or 3 μm to 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.

[0099] In another example, the second particles PTC2 may have a polycrystalline form and include secondary particles formed by agglomeration of at least two second primary particles. In other words, one second particle PTC2 may include a plurality of second primary particles agglomerated together. The second particles PTC2 formed from a plurality of second primary particles 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. In addition, in this specification, the second secondary particles may be defined as large particles.

[0100] 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 may be 10 μm to 25 μm or 12 μm to 18 μm. The average particle size D50 of the second secondary particles may be larger than the average particle size D50 of the first particles PTC1.

[0101] In the present invention, the second particles PTC2 can exist as second single particles or second secondary particles, and the second particles PTC2 may be a positive electrode active material including second single particles and second secondary particles.

[0102] In this specification, the second single particle and the second secondary particle can both be interpreted as meaning the second particle PTC2. Furthermore, the second particle PTC2 can be interpreted as including the second single particle and the second secondary particle.

[0103] In this specification, the positive electrode active material can be defined 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.

[0104] 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. 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 amount of binder to be reduced when mixed with the nano-sized olivine-based compound.

[0105] Third particle PTC3 Referring to FIG. 8, the third particles PTC3 may have a single particle morphology. In this specification, a single particle may refer to a single particle having no internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are morphologically present as an independent phase and not aggregated with each other. For example, a single particle may be a single crystal. Alternatively, a single particle may contain several crystals. A single particle may be in a singly isolated form. Alternatively, a 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 arbitrarily selecting about 30 primary particles (hereinafter referred to as third primary particles) from an electron microscope photograph of the positive electrode active material.

[0106] 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.

[0107] The third particles PTC3 may include an olivine structure compound represented by the following Chemical Formula 3.

[0108] [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 (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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] When the third particle PTC3 is a single particle, 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 of the second functional additive FAD2 to the weight of the first functional additive FAD1 may be 1.5 to 4.

[0114] When the third particles PTC3 are single particles, the content of the second functional additive FAD2 may be 4 to 10 parts by weight, 4 to 8 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, 2 to 4 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, 2 to 4 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] The third particles PTC3 further include a grain boundary coating, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the third particles PTC3. In addition, the third particles PTC3 further include a grain boundary coating portion, which further improves the electrical conductivity of the third particles PTC3.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] If the fourth particles and the average particle size of the fourth particles satisfy the ranges described above and the size of the fourth particles is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery containing the fourth particles can be improved.

[0123] 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.

[0124] When the third particles PTC3 are 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 of the second functional additive FAD2 to the weight of the first functional additive FAD1 may be 1 to 4.

[0125] 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.

[0126] 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.

[0127] According to the comparative example of the present invention shown in FIG. 10, the positive electrode active material layer AML1 may include only 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.

[0128] 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.

[0129] 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.

[0130] 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 may require a large amount of binder.

[0131] 6 and 7, by inserting the first active material layer ATL1 between the current collector COL1 and the second active material layer ATL2 and mixing the first particles PTC1 and the 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 them, the capacity, density characteristics, high-temperature stability, and life characteristics can be improved.

[0132] 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% by weight. 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. 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.

[0133] 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 and 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 and ATL2 may be 20% to 30% by weight or 30% by weight. In other words, the ratio of the weight of second particles PTC2 to the total weight of first particles PTC1, second particles PTC2, and third particles PTC3 (weight ratio of second particles PTC2) may be 0.15 to 0.3.

[0134] 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.

[0135] 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. That is, the ratio of the weight of the third particles PTC3 to the total weight of the first particles PTC1, second particles PTC2, and third particles PTC3 (the weight ratio of the third particles PTC3) may be 0.3 to 0.4.

[0136] 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.

[0137] The total doping amount of Mn may be 0.49 to 0.53. For example, the total doping amount of Mn may be 0.51. 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.

[0138] When the total doping amount of Mn satisfies the above 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.

[0139] The positive electrode for a lithium secondary battery according to the embodiment of the present invention has the following effects.

[0140] 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 high energy density may be provided.

[0141] 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.

[0142] Production Example 1: Production of NCM particles A mid-nickel precursor was produced using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 6:1:3 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, and sodium hydroxide were added to a reactor and reacted. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 210°C for 24 hours to obtain small-particle precursors (NiSO4·6H2O) with an average particle size of approximately 4 μm. 0.6 0Co 0.1 Mn 0. 3(OH)2) powder was obtained.

[0143] A mid-nickel precursor and anhydrous lithium hydroxide (LiOH) were dry mixed using a Henschel mixer. The lithium and transition metals were mixed in a molar ratio of approximately 1.05:1. The transition metals were the sum of the transition metals contained in the mid-nickel precursor (Ni + Co + Mn). A melting agent was further added to the mixture, and the mixture was heat-treated (i.e., calcined) in an oxygen atmosphere at approximately 850°C for 15 hours to synthesize particles of the mid-nickel positive electrode active material. The particles were then pulverized in a jet mill at a pressure of 3 bar.

[0144] The particles were washed by adding distilled water. Aluminum oxide was added in an amount of 0.5 mol% based on the total transition metals of the particles to perform aluminum coating. The second particles were dried at 150°C for 12 hours and then heat-treated (i.e., surface treatment) at about 800°C in an oxygen atmosphere for 15 hours. The chemical formula of the NCM particles is approximately LiNi 0.6 Co 0.1 Mn 0.3 It was O2.

[0145] Production Example 2: Production of LMFP particles in the form of secondary particles 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 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 It was PO4.

[0146] Production Example 3: Production of LMFP particles in single particle form 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 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 is approximately LiMn 0.6 Fe 0.4 It was PO4.

[0147] Example 1: Fabrication of a positive electrode including a first active material layer and a second active material layer NCM 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 0.450:0.526:0.012:0.012 to prepare a first active material slurry.

[0148] 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.

[0149] 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 NCM particles, LMFP particles in the secondary particle form of the first active material layer, and LMFP particles in the single particle form of 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.

[0150] 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.

[0151] Comparative Example 1: Production of a positive electrode including a first active material layer A positive electrode was fabricated that included a first active material layer containing only NCM particles.

[0152] A first active material slurry was prepared by dispersing NCM 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.

[0153] Comparative Example 2: Production of a positive electrode including a first active material layer A positive electrode including a first active material layer containing only LMFP particles in the form of secondary particles was prepared.

[0154] 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.

[0155] Comparative Example 3: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer containing single-particle LMFP particles was prepared.

[0156] 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.

[0157] Comparative Example 4: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer in which the weight ratio of NCM particles and secondary particle-form LMFP particles was 70:30 was prepared.

[0158] The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NCM 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 0.683:0.293:0.012:0.012.

[0159] Comparative Example 5: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer in which the weight ratio of NCM particles and secondary particle-form LMFP particles was 60:40 was prepared.

[0160] The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NCM 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 0.586:0.390:0.012:0.012.

[0161] Comparative Example 6: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer with a weight ratio of NCM particles and secondary particle-form LMFP particles of 50:50 was prepared.

[0162] 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 NCM 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 0.488:0.488:0.012:0.012.

[0163] Comparative Example 7: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer in which the weight ratio of NCM particles and secondary particle-form LMFP particles was 40:60 was prepared.

[0164] The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NCM 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 0.390:0.586:0.012:0.012.

[0165] Comparative Example 8: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer in which the weight ratio of NCM particles and secondary particle-form LMFP particles was 30:70 was prepared.

[0166] The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NCM 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 0.293:0.683:0.012:0.012.

[0167] Comparative Example 9: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer in which the weight ratio of NCM particles and secondary particle-form LMFP particles was 20:80 was prepared.

[0168] The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NCM 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 0.195:0.781:0.012:0.012.

[0169] Comparative Example 10: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer in which the weight ratio of NCM particles and secondary particle-form LMFP particles was 10:90 was prepared.

[0170] The first active material slurry was prepared in the same manner as in Comparative Example 1, except that NCM 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 0.098:0.878:0.012:0.012.

[0171] Comparative Example 11: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer in which the weight ratio of NCM particles, secondary particle-form LMFP particles, and single particle-form LMFP particles was 30:35:35 was prepared.

[0172] NCM particles, secondary particle LMFP particles, single particle LMRP particles, first binder (polyvinylidene fluoride), first conductive material (carbon black) in a ratio of 0.292:0.3 4 2:0.3 4 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 active material in N-methylpyrrolidone at a weight ratio of 2:0.012:0.012.

[0173] Comparative Example 12: Production of a positive electrode including a first active material layer A positive electrode containing only a first active material layer in which the weight ratio of NCM particles and single-particle LMFP particles was 30:70 was prepared.

[0174] 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 NCM particles, single-particle LMFP particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone in a weight ratio of 0.293:0.683:0.012:0.012.

[0175] 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.

[0176] LMX particles, secondary particle form LMFP particles, first binder (polyvinylidene fluoride), first conductive material (carbon black) 0. 4 The same method as in Example 1 was used to prepare the first active material slurry, which was prepared by dispersing the first active material in N-methylpyrrolidone at a weight ratio of 50:0.526:0.012:0.012, and the second active material slurry was prepared by dispersing the single particle LMRP particles, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) in N-methylpyrrolidine at a weight ratio of 0.976:0.012:0.012.

[0177] 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.

[0178] LMX particles, secondary particle form LMFP particles, first binder (polyvinylidene fluoride), first conductive material (carbon black) 0. 4 The same method as in Example 1 was used to prepare the first active material slurry, which was prepared by dispersing the first active material in N-methylpyrrolidone at a weight ratio of 50:0.526:0.012:0.012, and the second active material slurry was prepared by dispersing the single particle LMRP particles, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.9:0.05:0.05.

[0179] 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 mixture of 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3.

[0180] [Table 1]

[0181] [Table 2]

[0182] 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 Figures 111 to 114. Referring to Figure 111, 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 Figure 12, it can be seen that the second particles prepared in Preparation Example 1 are micro-sized single particles. Referring to Figure 13, it can be seen that the third particles prepared in Preparation Example 3 are nano-sized fine single particles. Referring to Figure 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.

[0183] 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.

[0184] [Table 3]

[0185] Evaluation example 3: Evaluation of resistance and cohesion The characteristics of the lithium secondary batteries fabricated using the positive electrode active materials of the Examples and Comparative Examples were evaluated.

[0186] 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) to 3.0V. The average voltage was evaluated after the initial charge and discharge. After discharging at 1.0C for 1 second at SOC50 under a constant current (0.2C) condition, the battery was discharged at a constant current (0.2C) to calculate the DCIR. The results are shown in Table 4 below.

[0187] [Table 4]

[0188] Referring to Table 4, the lithium secondary batteries including the positive electrodes according to Examples 1 and 2 have higher discharge capacities and lower resistances than those according to Comparative Examples 2, 3, and 12. This indicates that the addition of NCM particles can enhance the binding strength of the positive electrode including the olivine-based compound.

[0189] 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 confirmed 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 the desired range.

[0190] Evaluation example 4: Battery characteristic evaluation The characteristics of the lithium secondary batteries fabricated using the positive electrode active materials of the Examples and Comparative Examples were evaluated.

[0191] The lithium secondary battery was initially charged at 25°C under constant current (0.2C) and constant voltage (4.45V) conditions (cutoff 0.05C). After a 10-minute rest, it was discharged to 3.0V under constant current (0.2C) conditions to obtain the initial charge and discharge capacities. The average voltage and energy density were then evaluated. The battery was then charged and discharged 50 times at 1.0C / 1.0C at 45°C. Furthermore, coin cells were fabricated, and the battery was initially charged at constant current (0.2C) conditions. After a 10-minute rest, it was discharged to 3.0V under constant current (0.2C). After further charging, the capacity was measured at -20°C. The battery characteristics evaluation results are shown in Table 5 below.

[0192] [Table 5]

[0193] 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.

[0194] 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. [Explanation of symbols]

[0195] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case

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 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 Co y2 Mn z2 B2 c2 O 2-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.5≦x2≦0.8, 0≦y2≦0.3, 0.1≦z2≦0.5, 0≦c2≦0.1, 0≦b2≦0.05, and x2+y2+z2+c2=1; B2 includes at least one selected from the group consisting of Ti, Mg, V, Nb, and Al, [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 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 .

3. The ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive is 1.5 to 4; The positive electrode for a lithium secondary battery according to claim 2 .

4. the content of the first binder is 1.2 parts by weight to 3 parts by weight with respect to 100 parts by weight of the first active material layer; the content of the second binder is 1.2 parts by weight to 5 parts by weight per 100 parts by weight of the second active material layer; The positive electrode for a lithium secondary battery according to claim 1 .

5. the content of the first conductive material is 1.2 parts by weight to 3 parts by weight per 100 parts by weight of the first active material layer; the content of the second conductive material is 1.2 parts by weight to 5 parts by weight per 100 parts by weight of the second active material layer; The positive electrode for a lithium secondary battery according to claim 1 .

6. 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 .

7. a total doping amount of Mn contained in the first and second active material layers is 0.49 to 0.53; The positive electrode for a lithium secondary battery according to claim 1 .

8. the first particles include a coating layer containing carbon; The carbon content in the first particles is 1.5% by weight to 2.5% by weight. The positive electrode for a lithium secondary battery according to claim 1 .

9. the first particles further include a grain boundary coating layer on the interface between the first primary particles; The grain boundary coating layer contains carbon. The positive electrode for a lithium secondary battery according to claim 1 .

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

11. The first particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer. The positive electrode for a lithium secondary battery according to claim 1 .

12. the second particles are single crystals; The second particles have an average particle size of 2 μm to 5 μm. The positive electrode for a lithium secondary battery according to claim 1 .

13. The second particles include at least one of single particles and secondary particles. The positive electrode for a lithium secondary battery according to claim 1 .

14. 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 .

15. 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 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 Co y2 Mn z2 B2 c2 O 2-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.5≦x2≦0.8, 0≦y2≦0.3, 0.1≦z2≦0.5, 0≦c2≦0.1, 0≦b2≦0.05, and x2+y2+z2+c2=1; B2 includes at least one selected from the group consisting of Ti, Mg, V, Nb, and Al, [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.

16. 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 15.

17. The ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive is 1 to 4; The positive electrode for a lithium secondary battery according to claim 16.

18. the content of the first binder is 1.2 parts by weight to 3 parts by weight with respect to 100 parts by weight of the first active material layer; the content of the second binder is 1.2 parts by weight to 3 parts by weight per 100 parts by weight of the second active material layer; The positive electrode for a lithium secondary battery according to claim 15.

19. the content of the first conductive material is 1.2 parts by weight to 3 parts by weight per 100 parts by weight of the first active material layer; the content of the second conductive material is 1.2 parts by weight to 3 parts by weight per 100 parts by weight of the second active material layer; The positive electrode for a lithium secondary battery according to claim 15.

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

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