Positive electrode and lithium secondary battery including the same

Abstract

To provide a positive electrode in which the binding strength between a positive electrode active material and a current collector is increased to make it easy to manufacture an electrode plate, and the capacitance characteristic and the lifetime characteristic are improved.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 on the current collector, and a second active material layer on the first active material layer. The first active material layer includes first particles containing a compound expressed by Chemical Formula 1 and having an olivine structure, second particles containing a compound expressed by a particular formula and having a layered structure, a first conductive material, and a first binder. The second active material layer includes third particles containing a compound expressed by Chemical Formula 3 and having the olivine structure, a second conductive material, and a second binder. The first particles are in a secondary particle form in which a plurality of first primary particles are aggregated together. The first particles have an average particle diameter D50 of 3 μm to 7 μm. The second particles have an average particle diameter D50 of 3 μm to 14 μm. The details of Chemical Formulae 1, 2, and 3 are as described in the specification.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] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy density, high-capacity secondary batteries has been growing rapidly. Accordingly, research and development efforts to improve the performance of lithium secondary batteries have been actively pursued. For example, a method has been proposed for fabricating a double-coated positive electrode by coating a lithium iron phosphate compound containing a mixture of primary and secondary particles with different particle sizes on a positive electrode current collector and then separating the primary and secondary particles using magnetism (Korean Patent Application Publication No. 10-2015-0024703).

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

[0004] SUMMARY OF THE INVENTION An object of the present invention is to provide a positive electrode that can be easily manufactured by increasing the binding strength between a current collector and a positive electrode active material.

[0005] Another object to be achieved by the present invention is to provide a positive electrode having improved capacity characteristics and life characteristics. [Means for solving the problem]

[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, and a second active material layer on the first active material layer. The first active material layer includes first particles including a compound with an olivine structure represented by Chemical Formula 1 below, second particles including a compound with a layered structure represented by Chemical Formula 2 below, a first conductive material, and a first binder. The second active material layer includes third particles including a compound with an olivine structure represented by Chemical Formula 3 below, a second conductive material, and a second binder. The first particles have a secondary particle form formed by agglomeration of a plurality of first primary particles. The first particles may have an average particle diameter D50 of 3 μm to 7 μm, and the second particles may have an average particle diameter D50 of 3 μm to 14 μm. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, and 0≦c1≦0.05; B1 is at least one element selected from the group consisting of Ti and transition metals having an oxidation state of 4; [Chemical formula 2] Li a2 Ni x2 Co y2 B2 z2 O 2-c2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.9≦x2≦1.05, 0.03≦y2≦0.10, 0≦z2≦0.05, and 0≦c2≦0.05; B2 is at least one element selected from the group consisting of Al and Mn; [Chemical formula 3] Li a3 Fe x3 B3 y3 PO 4-c3 In Chemical Formula 3, 0.8≦a3≦1.2, 0.95≦x3≦0.999, 0.001≦y3≦0.05, and 0≦c3≦0.05, and B3 can be at least one element selected from the group consisting of Ti and transition metals having an oxidation number of 4.

[0007] According to another aspect of the present invention, a positive electrode for a lithium secondary battery includes a current collector, a first active material layer on the current collector, and a second active material layer on the first active material layer. The first active material layer includes first particles including a compound with an olivine structure represented by Chemical Formula 1 below, second particles including a compound with a layered structure represented by Chemical Formula 2 below, a first conductive material, and a first binder. The second active material layer includes third particles including a compound with an olivine structure represented by Chemical Formula 3 below, a second conductive material, and a second binder. The first particles have a secondary particle form formed by agglomeration of a plurality of primary particles. The first binder and the first conductive material constitute a first functional additive, and 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 may be smaller than the weight ratio of the second functional additive in the second active material layer. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, and 0≦c1≦0.05; B1 is at least one element selected from the group consisting of Ti and transition metals having an oxidation state of 4; [Chemical formula 2] Li a2 Ni x2 Co y2 B2 z2 O 2-c2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.9≦x2≦1.05, 0.03≦y2≦0.10, 0≦z2≦0.05, and 0≦c2≦0.05; B2 is at least one element selected from the group consisting of Al and Mn; [Chemical formula 3] Li a3 Fe x3 B3 y3 PO 4-c3 In Chemical Formula 3, 0.8≦a3≦1.2, 0.95≦x3≦0.999, 0.001≦y3≦0.05, and 0≦c3≦0.05, and B3 can be at least one element selected from the group consisting of Ti and transition metals having an oxidation number of 4.

[0008] A lithium secondary battery according to an embodiment of the present invention may include the above-described positive electrode. [Effects of the Invention]

[0009] The positive electrode according to the present invention includes the first particles and the third particles having an olivine structure, thereby making it possible to improve economy and average voltage.

[0010] The positive electrode according to the present invention can improve the capacity and energy density by including the second particles having a layered structure.

[0011] In the positive electrode according to the present invention, the second particles and the first particles in the form of secondary particles are mixed and disposed in the first active material layer, thereby improving ease of manufacturing the electrode plate.

[0012] The positive electrode according to the present invention has an effect of improving battery characteristics by mixing the first particles, the second particles, and the third particles in an optimal ratio and arranging them in a double layer structure, and at the same time, can have an effect of facilitating the manufacture of the electrode plate. [Brief explanation of the drawings]

[0013] [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. 3 is an enlarged view of a second active material layer according to an embodiment of the present invention. [Figure 10] 1 is an SEM image of the first particle of Production Example 1 of the present invention. [Figure 11] 1 is an SEM image of second particles of Production Example 2 of the present invention. [Figure 12] 10 is an SEM image of a second particle according to an embodiment of the present invention. [Figure 13] 1 is an SEM image of the third particle of Production Example 3-1 of the present invention. [Figure 14] 1 is an SEM image of the third particle of Production Example 3-2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] In this specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component, or that a third component may be interposed between them. Also, in the drawings, the thickness of the components may be 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.

[0016] 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.

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

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

[0019] Unless otherwise defined in this specification, the particle size may be the average particle size. Also, the particle size is the average particle size D, which means the diameter of particles with a cumulative volume of 50% by volume in the particle size distribution. 50 Average particle size D 50The measurement of the average particle diameter D may be performed by a method well known to those skilled in the art, for example, by using a particle size analyzer, or by using a transmission electron microscope or a scanning electron microscope. Another method is to use a measuring device that uses dynamic light-scattering, and then perform data analysis to count the number of particles in each particle size range, and then calculate the average particle diameter D. 50 Alternatively, measurements can be made using the laser diffraction method. More specifically, when measuring by the laser diffraction method, particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. Then, the average particle size D at 50% of the particle size distribution measured by the measuring device is measured. 50 can be calculated.

[0020] 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.

[0021] 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.

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

[0023] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material, and may further include a binder and / or a conductive material.

[0024] As an example, the positive electrode 10 may further include an additive that can act as a sacrificial anode.

[0025] The current collector COL1 can be made of Al, but is not limited to this.

[0026] The cathode 10 according to an embodiment of the present invention will be described in detail below with reference to FIG.

[0027] 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.

[0028] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0029] 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.

[0030] 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.

[0031] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butazide 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.

[0032] 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.

[0033] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0034] The conductive material is used to impart conductivity to the electrodes, and any electron-conductive material that does not undergo 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.

[0035] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof can be used.

[0036] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes substances that can reversibly intercalate / deintercalate lithium ions, lithium metal, alloys of lithium metal, substances that can be doped and undoped with lithium, or transition metal oxides.

[0037] Examples of substances that can reversibly intercalate / deintercalate lithium ions include carbon-based negative electrode active materials, which may include, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0038] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0039] As the substance that can be doped and undoped with lithium, an 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), an 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 combinations thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0040] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, the silicon-carbon composite may include secondary particles (cores) formed by the aggregation of primary silicon particles and amorphous carbon coating layers (shells) located on the surfaces of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, e.g., the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0041] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer disposed on the core.

[0042] The Si-based negative electrode active material or the Sn-based negative electrode active material is used in combination with a carbon-based negative electrode active material.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0047] 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.

[0048] 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.

[0049] Electrolyte ELL The electrolyte solution ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0050] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate.

[0051] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0052] 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).

[0053] 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.

[0054] 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.

[0055] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0056] 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.

[0057] 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+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0058] Lithium secondary battery Lithium secondary batteries are classified into cylindrical, prismatic, pouch, and coin shapes depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to an embodiment, with FIG. 2 showing a cylindrical battery, FIG. 3 showing a prismatic battery, and FIGS. 4 and 5 showing pouch-shaped batteries. Referring to FIGS. 2 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 2. Also, in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, and a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0059] 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.

[0060] The first particles PTC1, the second particles PTC2, the third particles PTC3, the first active material layer ATL1, the second active material layer ATL2, and the positive electrode having a double layer structure will be described in more detail below.

[0061] 1st particle PTC1 The first particles PTC1 may include a lithium compound having an olivine structure represented by Chemical Formula 1. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, and 0≦c1≦0.05, and B1 may be at least one element selected from the group consisting of Ti and transition metals having an oxidation number of 4. B1 may be a dopant doped into the first particle PTC1. In one embodiment, in Chemical Formula 1, x1+y1=1. In another embodiment, in Chemical Formula 1, 1≦x1+y1≦1.05.

[0062] The first particle PTC1 has the advantages of being highly economical, structurally stable, and having excellent lifespan characteristics. Because it is mainly composed of Fe, it is relatively inexpensive, and because it is structurally stable, it is likely to undergo relatively little chemical change even after repeated charging and discharging.

[0063] 7 and 10, the first particles PTC1 may be in the form of secondary particles. The secondary particles may be polycrystalline, meaning that at least two or more first primary particles are aggregated. In other words, one first particle PTC1 may include multiple first primary particles NNP1 aggregated together. The first particles PTC1 may have a spherical or elliptical shape.

[0064] The dopant can exert an effect of controlling the uniform growth of the first primary particles NNP1 of the first particles PTC1, thereby improving the charge / discharge efficiency, low temperature characteristics, and life characteristics of the lithium secondary battery.

[0065] 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.

[0066] The coating layer may further include at least one element selected from the group consisting of titanium and a transition metal with an oxidation state of 4. Metal-containing compounds, such as titanium-containing compounds and transition metal-containing compounds with an oxidation state of 4, 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.

[0067] 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. 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 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 and a transition metal-containing compound with an oxidation state of 4.

[0068] The interior of the first particle PTC1 may refer to the entire interior of the first particle PTC1 excluding the surface of the first particle PTC1. For example, the interior of the first particle PTC1 may refer to the region from a depth of about 10 nm to the entire inside, or from a depth of 10 nm to a depth of about 2 μm, at the surface of the first particle PTC1.

[0069] 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.

[0070] 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% by weight to 10% by weight, 1% by weight to 3% by weight, or 1.5% by weight to 2.5% by weight.

[0071] The first particles PTC1 may have a spherical shape formed by agglomeration of nano-sized first primary particles NNP1. The first particles PTC1 may exhibit the following characteristics due to the first primary particles NNP1 being closely agglomerated to each other. The first particles PTC1 may have a spherical or elliptical shape. The average particle size D of the first particles PTC1 50 The diameter of the first particles PTC1 may be 3 μm to 10 μm or 3 μm to 7 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.

[0072] Because the first particles PTC1 have a secondary particle form, electrode plate production may be easier than when they have a single particle form. If the particle size is too small, the binding strength between the current collector and the positive electrode active material may be weak, which may increase resistance, making electrode plate production difficult and requiring a large amount of binder. The first particles PTC1 of the present invention have a secondary particle form rather than a single particle form, which may facilitate electrode plate production.

[0073] 2nd particle PTC2 The second particles PTC2 may include a lithium compound having a layered structure represented by Chemical Formula 2. [Chemical formula 2] Li a2 Ni x2 Co y2 B2 z2 O 2-c2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.9≦x2≦1.05, 0.03≦y2≦0.10, 0≦z2≦0.05, and 0≦c2≦0.05, and B2 can be at least one element selected from the group consisting of Al and Mn. In one embodiment, in Chemical Formula 2, x2+y2+z2=1. In another embodiment, in Chemical Formula 2, 1≦x2+y2+z2≦1.2.

[0074] B2 may be Al.

[0075] The second particles PTC2 have the advantages of high capacity and high energy density.

[0076] The second particles PTC2 may include a lithium-nickel composite oxide as a nickel-based active material. For example, the second particles PTC2 may include a high-nickel-based positive electrode active material having a high nickel content. The high-nickel-based positive electrode active material can achieve high capacity and high performance.

[0077] 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 may effectively suppress structural collapse due to repeated charge and discharge. This may improve the life characteristics of the secondary battery.

[0078] The second coating layer may include an aluminum-containing compound, a titanium-containing compound, a magnesium-containing compound, a zirconium-containing compound, a molybdenum-containing compound, a niobium-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.

[0079] 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 PTC2. The analysis may confirm the content of aluminum, titanium, magnesium, zirconium, molybdenum, and / or niobium in the second coating layer. In addition to SEM-EDS, other methods for measuring the metal content in the second coating layer may include inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0080] The second particles PTC2 may have a smaller BET specific surface area than the first particles PTC1. The BET specific surface area of ​​the second particles PTC2 may be 0.3 to 0.6. The BET specific surface area may refer to the surface area per unit mass. As the BET is smaller, the contact area between the positive electrode active material and the current collector is reduced, which may reduce resistance and increase the binding strength with the electrode plate. In other words, a positive electrode active material including the second particles PTC2 with a small BET specific surface area may facilitate the production of an electrode plate with a small amount of binder.

[0081] The second particles PTC2 may be in the form of single particles and / or secondary particles. For example, the second particles PTC2 may exist only in the form of single particles, only in the form of secondary particles, or in the form of a mixture of single particles and secondary particles. In one embodiment, when the second particles PTC2 are in a bimodal form, in which the second particles PTC2 are in the form of a mixture of single particles and secondary particles, the density may be improved. The second particles PTC2 in the form of single particles and / or secondary particles will be described below with reference to FIGS. 7, 11, and 12.

[0082] In one embodiment, referring to FIG. 11, the second particle PTC2 may have the form of a single particle. 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 that is not aggregated with each other. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly isolated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0083] When the second particles PTC2 are single particles, the second particles PTC2 may include at least one second primary particle. In one embodiment, the second particles PTC2 may have a spherical or elliptical shape formed by agglomeration of the second primary particles. In another embodiment, the second particles PTC2 may have a random shape rather than a spherical shape, even when the second primary particles are agglomerated. When the second particles PTC2 are in the form of agglomeration of the second primary particles, they may be less structured than when they are in the form of secondary particles. In other words, they may be more random.

[0084] When the second particles are single particles, the average particle size of the second particles PTC2 may be 3 μm to 10 μm. The average particle size of the second particles PTC2 may be the same as or larger than the average particle size of the first particles PTC1 described above. In one embodiment, the average particle size can be measured by a particle size analyzer. The average particle size is the diameter D of the particles whose cumulative volume is 50% by volume in the particle size distribution. 50 can mean:

[0085] When the second particles PTC2 are single particles, the average size of the second primary particles of the second particles may be larger than the average size of the first primary particles NNP1 of the first particles PTC1.

[0086] In another example, referring to FIG. 12, the second particles PTC2 may be in the form of secondary particles. The secondary particles may be polycrystalline, meaning that at least two or more second primary particles are aggregated together. In other words, one second particle PTC2 may include multiple second primary particles (FIG. 7, NNP2) aggregated together. The second particles PTC2 may have a spherical or ellipsoidal shape.

[0087] When the second particles are secondary particles, the average particle size of the second particles PTC2 may be 10 μm to 14 μm. The average particle size of the second particles PTC2 may be the same as or larger than the average particle size of the first particles PTC1. In one embodiment, the average particle size may be measured using a particle size analyzer. The average particle size may be determined by randomly selecting about 30 second particles PTC2 from an electron microscope photograph of the positive electrode active material, measuring the particle size, and determining the diameter D of the particles that make up 50% by volume of the cumulative volume in the particle size distribution. 50 can mean:

[0088] In another embodiment, referring to FIG. 7, the second particles may be in a bimodal form, in which single particles PTC2(SP) and secondary particles PTC2(PC) are mixed. When the second particles are in a bimodal form, they may have improved density. Explaining FIG. 7 in more detail, the second particles PTC2(PC), which are secondary particles, refer to a form in which at least two or more second primary particles NNP2 are aggregated. The second particles PTC2(SP), which are single particles, refer to a form containing at least one second primary particle. The second particles PTC2(SP), which are single particles, have a larger second primary particle size than the second particles PTC2(PC), which are secondary particles. Even if the second primary particles are aggregated, the second primary particles may have a random shape, not a spherical shape.

[0089] Third particle PTC3 The third particles PTC3 may include a lithium compound having an olivine structure represented by the following Chemical Formula 3. [Chemical formula 3] Li a3 Fe x3 B3 y3 PO 4-c3 In Chemical Formula 3, 0.8≦a3≦1.2, 0.95≦x3≦0.999, 0.001≦y3≦0.05, and 0≦c3≦0.05, and B3 may be at least one element selected from the group consisting of Ti and transition metals having an oxidation number of 4. B3 may be a dopant doped into the third particle PTC3. In one embodiment, in Chemical Formula 3, x3+y3=1. In another embodiment, in Chemical Formula 3, 1≦x3+y3≦1.05.

[0090] The third particle PTC3 has the advantages of being highly economical, structurally stable, and having excellent lifespan characteristics. Because it is mainly composed of Fe, it is relatively inexpensive, and because it is structurally stable, there is a possibility that it will undergo relatively little chemical change even after repeated charging and discharging.

[0091] The dopant can exert an effect of controlling the uniform growth of the third primary particles of the third particles PTC3, thereby improving the charge / discharge efficiency, low temperature characteristics, and life characteristics of the lithium secondary battery.

[0092] 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.

[0093] The coating layer may further include at least one element selected from the group consisting of titanium and a transition metal with an oxidation state of 4. Metal-containing compounds, such as titanium-containing compounds and transition metal-containing compounds with an oxidation state of 4, 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.

[0094] The third particles PTC3 may be in the form of single particles and / or secondary particles. For example, the third particles PTC3 may exist only in the form of single particles, only in the form of secondary particles, or in the form of a mixture of single particles and secondary particles. In one embodiment, when the third particles PTC3 are in a bimodal form, in which the third particles PTC3 are in the form of a mixture of single particles and secondary particles, the density may be further improved. Below, the third particles PTC3 in the form of single particles will be described with reference to FIG. 13, and the third particles PTC3 in the form of secondary particles will be described with reference to FIG. 14.

[0095] In one example, referring to FIG. 13 , the third particles PTC3 may have a single particle form. In this specification, a single particle may refer to a single particle having no internal particle boundaries. A single particle may refer to a single particle, a monolith structure, a single body structure, or a non-aggregated particle, in which particles are morphologically present as an independent phase that is not aggregated with each other. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly isolated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0096] When the third particles PTC3 are single particles, the third particles PTC3 may include at least one third primary particle. In one embodiment, the third particles PTC3 may have a spherical or elliptical shape formed by agglomeration of the third primary particles. In another embodiment, the third particles PTC3 may have a random shape rather than a spherical shape, even if the third primary particles are agglomerated.

[0097] When the third particles PTC3 are single particles, the third particles PTC3 may be provided in various sizes. For example, the average particle size of the third particles PTC3 may be 0.5 μm to 2.5 μm or approximately 1 μm. The minimum particle size of the third particles PTC3, i.e., the size of the third primary particles NNP3, may be 100 nm to 500 nm or 200 nm to 300 nm. The average size of the third primary particles NNP3 may be larger than the average size of the first primary particles NNP1.

[0098] In one embodiment, the average particle size can be measured by a particle size analyzer. The average particle size is the diameter D of the particles with a cumulative volume of 50% by volume in the particle size distribution. 50 can mean:

[0099] In one embodiment, the minimum particle size, i.e., the size of the third primary particles NNP3, may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the third particles PTC3.

[0100] When the third particles PTC3 are single particles, the porosity of the third particles PTC3 may be less than 30%. The span value of the third particles PTC3 analyzed by a particle size analyzer may be outside the range of 0.3 to 0.75.

[0101] In another embodiment, referring again to FIG. 14, the third particles PTC3 may be in the form of secondary particles. The secondary particles may be in a polycrystalline form, meaning that at least two or more third primary particles NNP3 are aggregated together. In other words, one third particle PTC3 may include multiple third primary particles NNP3 aggregated together. The third particles PTC3 may have a spherical or elliptical shape.

[0102] When the third particles PTC3 are in the form of secondary particles, the third particles PTC3 may further include a grain boundary coating layer on the surface of each of the third primary particles NNP3. The grain boundary coating layer may be present inside the third particles PTC3. The grain boundary coating layer may be formed by coating along the interfaces between the third primary particles NNP3 inside the third particles PTC3. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries within the third particles 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 and a transition metal-containing compound of oxidized water 4.

[0103] When the third particles PTC3 are secondary particles, the interior of the third particles PTC3 may refer to the entire interior of the third particles PTC3 excluding the surface of the third particles PTC3. For example, the interior of the third particles PTC3 may refer to the region from a depth of about 10 nm to the entire inside of the surface of the third particles PTC3, or from a depth of 10 nm to a depth of about 2 μm.

[0104] When the third particles PTC3 are secondary particles, the third particles PTC3 may further include a grain boundary coating, thereby enhancing structural stability and forming a uniform coating layer on the surface of the third particles PTC3. In addition, the third particles PTC3 may further include a grain boundary coating portion, thereby further improving the electrical conductivity of the third particles PTC3.

[0105] When the third particles PTC3 are secondary particles, the third particles PTC3 may further contain carbon derived from the above-mentioned coating layer and / or grain boundary coating layer. The carbon element content in the third particles PTC3 may be 0.5 wt% to 10 wt%, 1 wt% to 3 wt%, or 1.5 wt% to 2.5 wt%. When the third particles PTC3 are secondary particles, the carbon content may be higher than when they are single particles.

[0106] When the third particles PTC3 are secondary particles, the average particle size 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 about 5 μm. In one embodiment, the average particle size can be measured by a particle size analyzer. The average particle size is the diameter D of particles whose cumulative volume is 50% by volume in the particle size distribution. 50 can mean:

[0107] When the third particles PTC3 are secondary particles, the average size of the third primary particles NNP3 may be 200 nm or less. For example, the average size of the third primary particles NNP3 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 average size of the third primary particles NNP3 may refer to the diameter measured by randomly selecting approximately 30 third primary particles NNP3 from an electron microscope photograph of the positive electrode active material. The size of the third primary particles NNP3 may be uniform.

[0108] When the third particles PTC3 are secondary particles, the size of the third primary particles NNP3 may be smaller than when the third particles PTC3 are single particles. For example, when the third particles PTC3 are in the form of secondary particles, the size of the third primary particles NNP3 may be approximately 100 nm smaller than the size of the third primary particles NNP3 when the third particles PTC3 are in the form of single crystals.

[0109] When the third particles PTC3 are secondary particles, if the average particle size of the third particles PTC3 and the average size of the third primary particles NNP3 satisfy the above-mentioned ranges and the size of the third primary particles NNP3 is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery containing them can be improved.

[0110] When the third particles PTC3 are secondary particles, the porosity of the third particles PTC3 may be about 20% to about 40%.The span value of the third particles PTC3 analyzed by a particle size analyzer may be 0.3 to 0.75.

[0111] First active material layer ATL1 FIG. 7 is an enlarged view of the first active material layer ATL1 of the positive electrode for a lithium secondary battery according to an embodiment of the present invention.

[0112] 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. Although not shown in the drawing, the second particles PTC2 may be in the form of secondary particles or may be in a bimodal form that combines the form of single particles and the form of secondary particles.

[0113] The first active material layer ATL1 contains the first particles PTC1 mixed with the second particles PTC2, thereby compensating for the drawbacks of the lithium iron phosphate-based positive electrode active material, such as low capacity and low energy density. That is, it is possible to simultaneously achieve the economical advantage of the first particles PTC1 and the high capacity and high energy density of the second particles PTC2.

[0114] The first active material layer ATL1 can reduce the weight ratio of the first functional additive FAD1 in the first active material layer ATL1 by mixing the first particles PTC1 with the second particles PTC2, which have a lower BET. 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 weight of the first active material layer. If the particle size is too small, the binding strength between the current collector and the positive electrode active material may be weak, which may increase resistance. This may make electrode plate manufacturing difficult and require a large amount of binder. The first active material layer ATL1 of the present invention can facilitate electrode plate manufacturing by including the second particles PTC2, which have a lower BET than the lithium iron phosphate-based positive electrode active material.

[0115] The first active material layer ATL1 contains the first particles PTC1 in the form of secondary particles rather than single particles, thereby further reducing the weight ratio of the first functional additive FAD1 in the first active material layer ATL1.

[0116] The weight ratio of the first functional additive FAD1 in the first active material layer ATL1 may be 2.4 wt % to 4.0 wt %.

[0117] The weight ratio of the first functional additive FAD1 in the first active material layer ATL1 may be smaller than or equal to the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 (described later). The ratio of the weight ratio of the second functional additive FAD2 to the weight ratio of the first functional additive FAD1 may be 1.0 to 2.6. Alternatively, the ratio of the weight ratio of the second functional additive FAD2 to the weight ratio of the first functional additive FAD1 may be 1.1 to 2.6.

[0118] The content of the first binder BND1 may be 1.2 to 2.0 parts by weight per 100 parts by weight of the first active material layer ATL1. The content of the first conductive material CDM1 may be 1.2 to 2.0 parts by weight per 100 parts by weight of the first active material layer ATL1. The content of the first binder BND1 may be less than the content of the second binder BND2 described below. When the first active material layer ATL1 satisfies the first binder content range and first conductive material content range conditions, the capacity and energy density of the battery can be maximized and ease of electrode plate processing can be achieved.

[0119] The first binder BND1 serves to firmly adhere the positive electrode active material particles (PTC1 and PTC2) to each other and to firmly adhere the positive electrode active materials (PTC1, PTC2) to the current collector COL1. Representative examples of the first binder BND1 include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl fluoride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0120] The first conductive material CDM1 is used to impart conductivity to the electrode, and any electrically conductive material that does not undergo chemical changes in the battery that is constructed can be used. Examples of the first conductive material CDM1 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.

[0121] The first active material layer ATL1 can be in contact with one surface of the current collector (COL1 in FIG. 6).

[0122] The first active material layer ATL1 may have a thickness T1. In one example, 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.

[0123] Second active material layer ATL2 8 and 9 are enlarged views of the second active material layer ATL2 of the positive electrode for a lithium secondary battery according to an embodiment of the present invention, in which the third particles PTC3 are in the form of single particles, and in which the third particles PTC3 are in the form of secondary particles.

[0124] 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. Although not shown in the drawings, the third particles PTC3 may have a bimodal form in which a single particle form and a secondary particle form are mixed.

[0125] The second binder BND2 serves to effectively adhere the positive electrode active material particles PTC3 to one another. Representative examples of the second binder BND2 include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl fluoride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon. The second binder BND2 may or may not be the same as the first binder BND1 described above.

[0126] The first conductive material CDM1 is used to impart conductivity to the electrode and can be any material that is electrically conductive without causing a chemical change in the resulting battery. Examples of the first conductive material CDM1 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. The second conductive material CDM2 may or may not be the same as the first conductive material CDM1 described above.

[0127] The content of the second binder BND2 may be 2.0 to 3.0 parts by weight per 100 parts by weight of the second active material layer ATL2. The content of the second conductive material CDM2 may be 2.0 to 3.0 parts by weight per 100 parts by weight of the second active material layer ATL2. The content of the second binder BND2 may be greater than the content of the first binder BND1 described above. If the second active material layer ATL2 satisfies the ranges of the second binder content and the second conductive material content, battery performance can be maximized and electrode plate processing can be facilitated.

[0128] 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. The weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be 4.0 wt % to 6.0 wt %.

[0129] The ratio by weight of the second functional additive FAD2 to the weight of the first functional additive FAD1 (weight ratio of second functional additive / weight ratio of first functional additive) may be 1.0 to 2.6. Alternatively, the ratio by weight of the second functional additive FAD2 to the weight of the first functional additive FAD1 may be 1.1 to 2.6. When the ratio by weight of the second functional additive FAD2 to the weight of the first functional additive FAD1 satisfies the above-mentioned numerical range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 is improved, maximizing the capacity and energy density of the battery while also achieving ease of electrode plate processing.

[0130] The second active material layer ATL2 may be applied to contact one side of the first active material layer ATL1. The one side of the first active material layer ATL1 may be a side of the first active material layer ATL1 that is not in contact with the current collector (COL1 in FIG. 6). For example, the current collector (COL1 in FIG. 6), the first active material layer ATL1, and the second active material layer ATL2 may be disposed in this order.

[0131] The second active material layer ATL2 may have a thickness T2. In one example, T2 may increase as the weight of the third particles PTC3 included in the second active material layer ATL2 increases.

[0132] A positive electrode including first and second active material layers 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.

[0133] The positive electrode active material layer AML1 may contain positive electrode active materials PTC1, PTC2, and PTC3. The content of the positive electrode active materials PTC1, PTC2, and PTC3 in the positive electrode active material layer AML1 may be 90% by weight to 99% by weight relative to 100% by weight of the positive electrode active material layer BML1.

[0134] The positive electrode active material layer AML1 may contain binders BND1 and BND2 and conductive materials CDM1 and CDM2. The contents of the binders BND1 and BND2 and the conductive materials CDM1 and CDM2 may each be 0.5% by weight to 5% by weight relative to 100% by weight of the positive electrode active material layer AML1.

[0135] 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 adhesive strength to the current collector is enhanced, making it possible to easily manufacture an electrode plate and reducing the resistance of the electrode plate. This also makes it possible to provide a lithium secondary battery with excellent performance.

[0136] 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.

[0137] 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-mentioned numerical range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 is improved, maximizing the capacity and energy density of the battery while also achieving ease of electrode plate processing.

[0138] As shown in Figures 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. This also improves capacity, density characteristics, high-temperature stability, and life characteristics. Furthermore, by including the second particles PTC2 in a bimodal form, which is a mixture of single particle and secondary particle forms, further improved density can be achieved.

[0139] 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, ATL2 may be 20% by weight to 40% by weight. For example, 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, ATL2 may be 35% by weight.

[0140] The content of second particles PTC2 relative to the total content of first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1, ATL2 may be 10% by weight to 30% by weight. For example, the content of second particles PTC2 relative to the total content of first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1, ATL2 may be 20% by weight to 30% by weight.

[0141] 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, 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, ATL2 may be 35% by weight.

[0142] The content of the second particles PTC2 relative to the total content of the first particles PTC1 and the second particles PTC2 contained in the first active material layer ATL1 can be 30% by weight to 60% by weight. For example, the content of the second particles PTC2 relative to the total content of the first particles PTC1 and the second particles PTC2 contained in the first active material layer ATL1 can be 45% by weight to 50% by weight.

[0143] When the contents of the first particles PTC1, the second particles PTC2, and the third particles PTC3 satisfy the above-mentioned 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-mentioned ranges, it makes it possible to provide a lithium secondary battery with excellent performance.

[0144] The following describes the preparation examples, examples, and comparative examples of the present invention. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0145] Production Example 1: Production of first particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti = 1:1.03:0.004. 10 wt% glucose was further added to the mixture. The mixture, which was 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 primary particles in the form of secondary particles. The average particle size D of the primary particles was 1000 nm. 50 The size of the first primary particles was 100 nm to 200 nm.

[0146] Production Example 2: Production of second particles (single particle form) Ni 0.92 Co 0.07 Al 0.01 (OH)2 and LiOH were mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 810°C for 8 hours in an oxygen atmosphere to obtain a composition of Li 1.05 Ni 0.92Co 0.07 Al 0.01 O2 and an oxide with an average particle size D50 of approximately 4 μm was prepared. After adding aluminum oxide to the oxide, a second heat treatment was performed in an oxygen atmosphere at 740°C for 8 hours to prepare a cathode active material. The chemical formula of the second particles was LiNi 0.92 Co 0.07 Al 0.01 It was O2.

[0147] Production Example 3-1: Production of third particles (single particle form) Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti = 1:1.03:0.004. 10 wt% glucose was added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized at a rotation speed of 8000 rpm to obtain single-particle tertiary particles. The average particle size of the tertiary particles was 0.5 μm to 2.5 μm. The size of the primary particles of the tertiary particles was 200 nm to 300 nm.

[0148] Production Example 3-2: Production of third particles (secondary particle form) Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti = 1:1.03:0.004. 10 wt% glucose was further added to the mixture. The mixture, which was 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 third particles in the form of secondary particles. The average particle size D of the third particles was 1000 nm. 50 The size of the third primary particles was 100 nm to 200 nm.

[0149] Example 1: Fabrication of a positive electrode including a first active material layer and a second active material layer The first particles of Preparation Example 1 and the second particles of Preparation Example 2 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a first positive electrode active material slurry. The third particles of Preparation Example 3-1 were dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a second positive electrode active material slurry.

[0150] The first positive electrode active material slurry was applied to a positive electrode current collector and dried to form a first active material layer, and the second positive electrode active material slurry was applied to the first active material layer and dried to form a second active material layer.

[0151] The active material layers were formed so that the weight ratio of the first particles, second particles, and third particles in the double-layer positive electrode was 35:30:35. Roll pressing was performed to produce a positive electrode in which the current collector, the first active material layer, and the second active material layer were stacked in this order.

[0152] Example 2 A positive electrode was prepared in the same manner as in Example 1, except that the third particles (secondary particle form) of Preparation Example 3-2 were used instead of the third particles (single particle form) of Preparation Example 3-1.

[0153] Example 3 A positive electrode was prepared in the same manner as in Example 1, except that the second particles (single particle form) of Preparation Example 2 were replaced with second particles of bimodal form. The method for producing the second particles of bimodal morphology is as follows. Ni 0.92 Co 0.07 Al 0.01 (OH)2 and LiOH were mixed in a molar ratio of (Ni + Co + Al):Li = 1:1.05, and flux was added to the mixture. Then, a first heat treatment was performed at 750 °C for 15 hours in an oxygen atmosphere to obtain first heat-treated particles. The first heat-treated particles were pulverized in a jet mill under a pressure of 3 bar and then washed with distilled water. After washing, aluminum oxide was added and the particles were dried at 150°C for 12 hours. After drying, the particles were subjected to a second heat treatment in an oxygen atmosphere at 700°C for 15 hours to produce secondary particles. The second particles in the form of single particles obtained in Preparation Example 2 and the second particles in the form of secondary particles prepared as described above were mixed in a weight ratio of 2:8 to prepare second particles in the form of bimodal particles.

[0154] Comparative Example 1: Preparation of a positive electrode containing one active material layer The first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 30:70 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer positive electrode.

[0155] Comparative Example 2 A positive electrode was manufactured in the same manner as in Comparative Example 1, except that the first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 40:60.

[0156] Comparative Example 3 A positive electrode was manufactured in the same manner as in Comparative Example 1, except that the first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 50:50.

[0157] Comparative Example 4 A positive electrode was manufactured in the same manner as in Comparative Example 1, except that the first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 60:40.

[0158] Comparative Example 5 A positive electrode was manufactured in the same manner as in Comparative Example 1, except that the first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 70:30.

[0159] Comparative Example 6 A positive electrode was manufactured in the same manner as in Comparative Example 1, except that the first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 80:20.

[0160] Comparative Example 7 A positive electrode was manufactured in the same manner as in Comparative Example 1, except that the first particles of Preparation Example 1 and the second particles of Preparation Example 2 were mixed in a weight ratio of 90:10.

[0161] Comparative Example 8 The first particles of Preparation Example 1, the second particles of Preparation Example 2, and the third particles of Preparation Example 3-1 were mixed in a weight ratio of 35:30:35 and dispersed in N-methylpyrrolidone together with a conductive material (carbon black) and a binder (polyvinylidene fluoride) to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer positive electrode.

[0162] Comparative Example 9 A positive electrode was manufactured in the same manner as in Example 1, except that the weights of the first binder, the first conductive material, the second binder, and the second conductive material were changed. The weight changes were adjusted so that the ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive was 0.83.

[0163] Comparative Example 10 A positive electrode was manufactured in the same manner as in Example 1, except that the weights of the first binder, the first conductive material, the second binder, and the second conductive material were changed. The weight changes were adjusted so that the ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive was 3.33.

[0164] Comparative Example 11 The primary particles (Preparation Example 1) in the form of secondary particles, a conductive material (carbon black), and a binder (polyvinylidene fluoride) were dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to a positive electrode current collector and dried to prepare a single-layer positive electrode.

[0165] Comparative Example 12 The single-particle first particles, a conductive material (carbon black), and a binder (polyvinylidene fluoride) were dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry, which was then coated on a positive electrode current collector and dried to prepare a single-layer positive electrode.

[0166] 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 solution obtained by mixing 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0167] Evaluation example 1: Analysis of the surface of the positive electrode active material SEM images of the first particles, second particles, third particles (single particle form), and third particles (secondary particle form) produced in Production Examples 1 to 3-2 are shown in FIGS. 10, 11, 13, and 14, respectively.

[0168] Referring to FIG. 10, it can be seen that the primary particles according to the preparation example of the present invention are spherical secondary particles formed by agglomeration of nano-sized fine primary particles.

[0169] 11, it can be seen that the second particles according to the present invention are in the form of single particles of micro size. Referring to FIGS. 10 and 11, when the second particles are in the form of single particles, the average particle size D 50 is the average particle size of the first particle, D 50 It can be seen that it is equal to or larger than

[0170] Referring to FIG. 12, it can be seen that the secondary particles according to an embodiment of the present invention are in the form of spherical secondary particles formed by agglomeration of nano-sized fine primary particles.

[0171] Referring to FIG. 13, it can be seen that the third particles according to the preparation example of the present invention are in the form of single particles.

[0172] 14, the third particles according to the present invention are spherical secondary particles formed by the aggregation of nano-sized primary particles. Referring to FIGS. 13 and 14, it can be seen that the size of the third primary particles is smaller when the third particles are in the form of secondary particles than when they are in the form of single particles.

[0173] 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 1 below.

[0174] [Table 1]

[0175] *1) Use of second particles in bimodal form

[0176] Evaluation example 3: 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.

[0177] The lithium secondary battery was initially charged at a constant current (0.2C), rested for 10 minutes, and then discharged at a constant current (0.2C) until it reached 3.0V, and the average voltage was measured. It was then charged and discharged 50 times at 1.0C / 1.0C at 45°C. Furthermore, coin cells were fabricated, and the batteries were initially charged at a constant current (0.2C), rested for 10 minutes, and then discharged at a constant current (0.2C) until it reached 3.0V. After further charging, the capacity was measured at -20°C. The results of the battery characteristic evaluation are shown in Tables 2 and 3 below.

[0178] In Table 2, the weight of the second particles means the weight of the second particles relative to the total weight of the first, second and third particles.

[0179] [Table 2]

[0180] *2) Use of second particles in bimodal form

[0181] [Table 3]

[0182] Referring to Table 2, it can be seen that the lithium secondary batteries including the positive electrodes according to Examples 1 and 2 have substantially the same or superior levels of efficiency, capacity, lifespan, resistance, and energy density as the lithium secondary battery including the positive electrode according to Comparative Example 8. That is, even though the mixing ratio of the first, second, and third particles is the same, it can be seen that the arrangement of the positive electrode active material in a double layer results in superior performance compared to a battery including only a single layer of positive electrode active material.

[0183] Referring to Table 3, it can be seen that the lithium secondary battery including the positive electrode of Comparative Example 11 is superior in all of charge / discharge capacity, efficiency, low-temperature capacity, resistance, and energy density compared to the lithium secondary battery including the positive electrode of Comparative Example 12. In particular, it can be seen that the resistance is significantly reduced. That is, it can be seen that the resistance is significantly reduced when the primary particles are included in the form of secondary particles rather than single particles.

[0184] Evaluation example 4: Evaluation of resistance and cohesion The resistance and binding strength characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of the Examples and Comparative Examples were evaluated, and the results are shown in Table 4 below.

[0185] The lithium secondary battery was initially charged at a constant current (0.2C), rested for 10 minutes, and then discharged at a constant current (0.2C) until it reached 3.0V, and the average voltage was evaluated. Under a constant current (0.2C) condition, the battery was discharged at 1.0C for 1 second at SOC50, and then discharged at a constant current (0.2C) to calculate the DCIR.

[0186] The contents of the first functional additive and the second functional additive, and the ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive (weight ratio of FAD2 / FAD1) were calculated.

[0187] [Table 4]

[0188] Referring to Table 4, it can be seen that the lithium secondary batteries including the positive electrodes according to Examples 1 and 2 have lower resistances DCIR than the lithium secondary batteries including the positive electrodes according to Comparative Examples 9 and 10. In other words, it can be seen that if the weight ratio of the second functional additive to the weight ratio of the first functional additive (weight ratio of FAD2 / FAD1) satisfies the range targeted by the present invention, the binding strength with the current collector can be increased. [Explanation of symbols]

[0189] 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 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. A current collector; a first active material layer on the current collector; a second active material layer on the first active material layer, The first active material layer includes first particles including a compound with an olivine structure represented by the following Chemical Formula 1, second particles including a compound with a layered structure represented by the following Chemical Formula 2, a first conductive material, and a first binder: [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1 (In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, and 0≦c1≦0.05, and B1 is at least one element selected from the group consisting of Ti and transition metals having an oxidation number of 4.) [Chemical formula 2] Li a2 Ni x2 Co y2 B2 z2 O 2-c2 (In Chemical Formula 2, 0.8≦a2≦1.2, 0.9≦x2≦1.05, 0.03≦y2≦0.10, 0≦z2≦0.05, and 0≦c2≦0.05, and B2 is at least one element selected from the group consisting of Al and Mn.) The second active material layer includes third particles including a compound having an olivine structure represented by the following Chemical Formula 3, a second conductive material, and a second binder, [Chemical formula 3] Li a3 Fe x3 B3 y3 PO 4-c3 (In Chemical Formula 3, 0.8≦a3≦1.2, 0.95≦x3≦0.999, 0.001≦y3≦0.05, and 0≦c3≦0.05, and B3 is at least one element selected from the group consisting of Ti and transition metals having an oxidation number of 4.) The first particles have a secondary particle form in which a plurality of first primary particles are aggregated, The average particle size D of the first particles 50 is 3 μm to 7 μm, The average particle size D of the second particles 50 is 3 μm to 14 μm, Positive electrode for lithium secondary batteries.

2. In the above Chemical Formula 2, B2 is Al; the second particles have a single particle morphology; The average particle size D of the second particles 50 is 3 μm to 10 μm, The positive electrode for a lithium secondary battery according to claim 1 .

3. B2 in the above Chemical Formula 2 is Al; The second particles have a secondary particle form in which a plurality of second primary particles are aggregated, The average particle size D of the second particles 50 is 10 μm to 14 μm, The positive electrode for a lithium secondary battery according to claim 1 .

4. the third particles have a secondary particle form in which a plurality of third primary particles are aggregated, the average size of the third primary particles is 100 nm to 200 nm; The average particle size D of the third particles 50 is 3 μm to 7 μm, The positive electrode for a lithium secondary battery according to claim 1 .

5. the third particles have a single particle morphology; The third particles have an average particle size D50 of 0.5 μm to 2.5 μm. The positive electrode for a lithium secondary battery according to claim 1 .

6. The average size of the first primary particles is 100 nm to 200 nm; The positive electrode for a lithium secondary battery according to claim 1 .

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

8. The span value of the first particles analyzed by a particle size analyzer is 0.3 to 0.

75. The positive electrode for a lithium secondary battery according to claim 1 .

9. the first particles include a coating layer including 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 .

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

11. the weight of the second particles contained in the first and second active material layers is 10 wt % to 30 wt % with respect to the total weight of the first, second, and third particles; The positive electrode for a lithium secondary battery according to claim 1 .

12. the weight of the second particles contained in the first and second active material layers is 20 wt % to 30 wt % with respect to the total weight of the first, second, and third particles; The positive electrode for a lithium secondary battery according to claim 1 .

13. 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 .

14. The weight ratio of the second functional additive to the weight ratio of the first functional additive is 1.1 to 2.6; The positive electrode for a lithium secondary battery according to claim 13.

15. the content of the first binder is 1.2 parts by weight to 2.0 parts by weight with respect to 100 parts by weight of the first active material layer; the content of the second binder is 2.0 parts by weight to 3.0 parts by weight based on 100 parts by weight of the second active material layer; The positive electrode for a lithium secondary battery according to claim 1 .

16. A current collector; a first active material layer on the current collector; a second active material layer on the first active material layer, The first active material layer includes first particles including a compound with an olivine structure represented by the following Chemical Formula 1, second particles including a compound with a layered structure represented by the following Chemical Formula 2, a first conductive material, and a first binder: [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1 (In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, and 0≦c1≦0.05, and B1 is at least one element selected from the group consisting of Ti and transition metals having an oxidation number of 4.) [Chemical formula 2] Li a2 Ni x2 Co y2 B2 z2 O 2-c2 (In Chemical Formula 2, 0.8≦a2≦1.2, 0.9≦x2≦1.05, 0.03≦y2≦0.10, 0≦z2≦0.05, and 0≦c2≦0.05, and B2 is at least one element selected from the group consisting of Al and Mn.) The second active material layer includes third particles including a compound having an olivine structure represented by the following Chemical Formula 3, a second conductive material, and a second binder, [Chemical formula 3] Li a3 Fe x3 B3 y3 PO 4-c3 (In Chemical Formula 3, 0.8≦a3≦1.2, 0.95≦x3≦0.999, 0.001≦y3≦0.05, and 0≦c3≦0.05, and B3 is at least one element selected from the group consisting of Ti and transition metals having an oxidation number of 4.) The first particles have a secondary particle form in which a plurality of primary particles are aggregated, 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; Positive electrode for lithium secondary batteries.

17. the thickness ratio of the first active material layer to the second active material layer is 3:7 to 7:3; The positive electrode for a lithium secondary battery according to claim 16.

18. the weight of the second particles contained in the first and second active material layers is 10 wt % to 30 wt % with respect to the total weight of the first, second, and third particles; The positive electrode for a lithium secondary battery according to claim 16.

19. the content of the first binder is 1.2 parts by weight to 2.0 parts by weight with respect to 100 parts by weight of the first active material layer; the content of the second binder is 2.0 parts by weight to 3.0 parts by weight based on 100 parts by weight of the second active material layer; The positive electrode for a lithium secondary battery according to claim 16.

20. The positive electrode according to claim 1, Lithium secondary battery.

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