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.SOLUTION: 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 containing a compound expressed by Chemical Formula 1 and having an olivine structure, second particles containing a compound expressed by Chemical Formula 2 and having a layered structure, a first conductive material, and a first binder. The second active material layer includes third particles expressed by Chemical Formula 3 and having the olivine structure, a second conductive material, and a second binder. The first particles and the third particles are in a single particle form. The first binder and the first conductive material form a first functional additive. The second binder and the second conductive material form a second functional additive. [Chemical Formula 1]Lia1Fex1B1y1 PO4-c1, [Chemical Formula 2]Lia2 Nix2COy2B2z2O2-c2, and [Chemical Formula 3]Lia3Fex3B3y3 PO4-c3.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] In recent years, with the rapid spread of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for high-capacity secondary batteries with high energy density has been rapidly increasing. As a result, research and development to improve the performance of lithium secondary batteries has been actively carried out (Patent Document 1).

[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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent No. 10-2012-0104484 Summary of the Invention [Problem to be solved by the invention]

[0005] 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.

[0006] 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]

[0007] 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 an olivine structure compound represented by Chemical Formula 1 below, second particles including a layered structure compound represented by Chemical Formula 2 below, a first conductive material, and a first binder. The second active material layer includes third particles including an olivine structure compound represented by Chemical Formula 3 below, a second conductive material, and a second binder. The first and third particles have a single particle form, 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 second functional additive in the second active material layer to the weight ratio of the first functional additive in the first active material layer may be 1.0 to 2.6.

[0008] [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≦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;

[0009] [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;

[0010] [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≦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.

[0011] 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 an olivine-structured compound represented by Chemical Formula 1 below, second particles including a layered-structured compound represented by Chemical Formula 2 below, a first conductive material, and a first binder. The second active material layer includes third particles including an olivine-structured compound represented by Chemical Formula 3 below, a second conductive material, and a second binder. The first and third particles have a single-particle morphology, and the content of the first binder in the first active material layer may be smaller than the content of the second binder in the second active material layer.

[0012] [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≦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;

[0013] [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;

[0014] [Chemical formula 3] Li a3 Fe x3B3 y3 PO 4-c3 In Chemical Formula 3, 0.8≦a3≦1.2, 0.95≦x3≦0.999, 0≦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.

[0015] A lithium secondary battery according to an embodiment of the present invention may include the above-described positive electrode. [Effects of the Invention]

[0016] 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.

[0017] The positive electrode according to the present invention can improve the capacity and energy density by including the second particles having a layered structure.

[0018] The positive electrode according to the present invention can be easily manufactured into an electrode plate by mixing the second particles and the first particles and disposing the mixture in the first active material layer.

[0019] 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]

[0020] [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] 1 is an SEM image of the first particle of Preparation Example 1 of the present invention. [Figure 10] 1 is an SEM image of second particles (single particle form) of Preparation Example 2 of the present invention. [Figure 11] 1 is a SEM image of secondary particles (secondary particle form) according to an embodiment of the present invention. [Figure 12] 1 is an SEM image of the third particle of Preparation Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] In order to fully understand the configuration and effects of the present invention, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiment disclosed below, and may be implemented in various forms and may undergo various modifications. The description of the embodiment is merely provided to understand the disclosure of the present invention and to help those skilled in the art to understand the scope of the present invention.

[0022] In this specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component, or a third component may be interposed between them. Also, in the drawings, the thickness of the components 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.

[0023] 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.

[0024] 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.

[0025] As used herein, "combinations thereof" can refer to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0026] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size D50, which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size D50 can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope or scanning electron microscope. Alternatively, the average particle size D50 can be measured using a measuring device that uses dynamic light scattering, and data analysis is performed to count the number of particles in each particle size range, after which the average particle size D50 value can be calculated. Alternatively, the average particle size D50 can be measured using a laser diffraction method. When measuring by the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and the average particle size D50 based on 50% of the particle size distribution in the measuring device can be calculated.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] As an example, the positive electrode 10 may further include an additive that can act as a sacrificial anode.

[0032] The current collector COL1 can be made of Al, but is not limited to this.

[0033] The positive electrode 10 according to the embodiment of the present invention will be described in detail below with reference to FIG.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0038] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0039] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0040] The dry binder-sintered pellets may be a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0041] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive without causing chemical changes in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0042] The current collector COL2 can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0043] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped and dedoped with lithium, or a transition metal oxide.

[0044] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, and examples of the amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0045] The lithium metal alloy may be an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, GeAl, and Sn.

[0046] As the substance capable of being doped and undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination of these. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0047] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it may include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may exist dispersed in an amorphous carbon matrix.

[0048] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0049] The Si-based negative electrode active material or the Sn-based negative electrode active material is used by being mixed with a carbon-based negative electrode active material.

[0050] 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. Naturally, 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.

[0051] 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.

[0052] 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, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0053] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0054] 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.

[0055] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0056] Electrolyte ELL The electrolyte solution ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0057] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0058] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0059] Examples of the carbonate solvent 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.

[0060] 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.

[0061] 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.

[0062] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0063] 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.

[0064] The lithium salt is dissolved in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 1st particle PTC1 The first particles PTC1 may include a lithium compound having an olivine structure represented by formula 1.

[0069] [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1

[0070] In Chemical Formula 1, 0.8≦a1≦1.2, 0.95≦x1≦0.999, 0≦y1≦0.05 (or 0.01≦y1≦0.05), and 0≦c1≦0.05 are satisfied, 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.

[0071] 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.

[0072] 7 and 9, the first particle PTC1 may have a single particle form. 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 exist as an independent phase that is not aggregated with each other in terms of morphology. 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.

[0073] The first particles PTC1 may include at least one first primary particle. In one embodiment, the first particles PTC1 may have a spherical or elliptical shape formed by agglomeration of the first primary particles. In another embodiment, the first particles PTC1 may have a random shape rather than a spherical shape, even when the first primary particles are agglomerated.

[0074] The first particles PTC1 may be provided in various sizes. For example, the average particle size of the first particles PTC1 may be 0.5 μm to 2.5 μm, or about 1 μm. The minimum particle size of the first particles PTC1, i.e., the size of the first primary particles, may be 100 nm to 500 nm, or 200 nm to 300 nm.

[0075] In one embodiment, the average particle size can be measured by a particle size analyzer. The average particle size can refer to the diameter D50 of particles whose cumulative volume is 50% by volume in the particle size distribution.

[0076] In one embodiment, the minimum particle size, i.e., the size of the first primary particles, may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the first particles PTC1.

[0077] The dopant can exert an effect of controlling the uniform growth of the first primary particles of the first particles PTC1, thereby improving the charge / discharge efficiency, low temperature characteristics, and life characteristics of the lithium secondary battery.

[0078] In one embodiment, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or a portion of the surface of the first particles PTC1. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability and electrical conductivity of the first particles PTC1.

[0079] The coating layer may further include at least one element selected from the group consisting of titanium and a transition metal having an oxidation state of 4. Metal-containing compounds, such as titanium-containing compounds and transition metal-containing compounds having 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.

[0080] The first particles PTC1 may further include a coating to enhance structural stability and form a uniform coating layer on the surface of the first particles PTC1. In addition, the first particles PTC1 may further include a coating to further improve the electrical conductivity of the first particles PTC1.

[0081] The first particles PTC1 may further contain carbon derived from the coating layer. The carbon content in the first particles PTC1 may be 0.5 wt % to 5 wt %, 0.5 wt % to 3 wt %, or 1.0 wt % to 2.0 wt %. The carbon content in the first particles PTC1 may be less than the carbon content in the third particles PTC3.

[0082] 2nd particle PTC2 The second particles PTC2 may include a lithium compound having a layered structure represented by the following chemical formula 2.

[0083] [Chemical formula 2] Li a2 Ni x2 CO y2 B2 z2 O 2-c2

[0084] In the chemical formula 2, 0.8≦a2≦1.2, 0.9≦x2≦1.05 (or 0.9≦x2≦0.94), 0.03≦y2≦0.10 (or 0.05≦y2≦0.09), 0≦z2≦0.05 (or 0.01≦z2≦0.05), and 0≦c2≦0.05, and the B2 may 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.

[0085] B2 may be Al.

[0086] The second particles PTC2 have the advantages of high capacity and high energy density.

[0087] 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.

[0088] In one embodiment, the second particles PTC2 may include a second coating layer on their surfaces. By including the second coating layer, the second particles PTC2 can effectively suppress structural collapse caused by repeated charge and discharge. This can improve the life characteristics of the secondary battery.

[0089] 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.

[0090] 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. This 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).

[0091] 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. The smaller the BET, the smaller the contact area between the positive electrode active material and the current collector, 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 can easily produce an electrode plate with a small amount of binder.

[0092] 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, 10, and 11.

[0093] In one embodiment, referring to FIG. 10, 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.

[0094] 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, the second particles PTC2 may have a less structured morphology than when they are in the form of secondary particles, i.e., a more random morphology.

[0095] 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 larger than the average particle size of the first particles PTC1 described above. In one embodiment, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter D50 of particles whose cumulative volume is 50% by volume in the particle size distribution. The average particle size D50 of the second particles may be larger than the average particle size D50 of each of the first particles described above and the third particles described below.

[0096] Referring to FIGS. 9 and 10, 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 of the first particles PTC1.

[0097] In another example, referring to FIG. 11, 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 elliptical shape.

[0098] When the second particles are secondary particles, the average particle size of the second particles PTC2 may be 10 μm to 14 μm. Referring to FIGS. 9 and 11, the average particle size of the second particles PTC2 is the same as or larger than the average particle size of the first particles PTC1. In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter D50 of particles whose cumulative volume is 50% by volume in the particle size distribution.

[0099] 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 size of the second primary particles in the second particles PTC2(SP), which are secondary particles, is larger than that of 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, rather than a spherical shape.

[0100] Third particle PTC3 The third particles PTC3 may include a lithium compound having an olivine structure represented by the following Chemical Formula 3.

[0101] [Chemical formula 3] Li a3 Fe x3 B3y3 PO 4-c3

[0102] In Chemical Formula 3, 0.8≦a3≦1.2, 0.95≦x3≦0.999, 0≦y3≦0.05 (or 0.01≦y3≦0.05), and 0≦c3≦0.05 are satisfied, 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 particles PTC3. In one embodiment, in Formula 3, x3+y3=1. In another embodiment, in Formula 3, 1≦x3+y3≦1.05.

[0103] 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.

[0104] The dopant can exert an effect of controlling the uniform growth of the third primary particles of the third particles (PTC), thereby improving the charge / discharge efficiency, low temperature characteristics, and life characteristics of the lithium secondary battery.

[0105] 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.

[0106] The coating layer may further include at least one element selected from the group consisting of titanium and a transition metal having an oxidation state of 4. Metal-containing compounds, such as titanium-containing compounds and transition metal-containing compounds having 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.

[0107] The third particles PTC3 further include a coating, which can enhance structural stability and form a uniform coating layer on the surface of the third particles PTC3. In addition, the third particles PTC3 further include a coating portion, which can further improve the electrical conductivity of the third particles PTC3.

[0108] The third particles PTC3 may further contain carbon derived from the coating layer described above. The carbon element content in the third particles PTC3 may be 0.5 wt % to 5 wt %, 0.5 wt % to 3 wt %, or 1.0 wt % to 2.0 wt %.

[0109] Referring to FIG. 12, the third particle PTC3 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.

[0110] 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.

[0111] 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 about 1 μm. The minimum particle size of the third particles PTC3, i.e., the size of the third primary particles, may be 100 nm to 500 nm or 200 nm to 300 nm.

[0112] In one embodiment, the average particle size can be measured by a particle size analyzer. The average particle size can refer to the diameter D50 of particles whose cumulative volume is 50% by volume in the particle size distribution.

[0113] In one embodiment, the minimum particle size, i.e., the size of the third primary particles, may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the third particles PTC3.

[0114] 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.

[0115] 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 in a bimodal form that combines the form of single particles and the form of secondary particles.

[0116] The first active material layer ATL1 contains a mixture of the first particles PTC1 and 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.

[0117] 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 is weak, which can increase resistance, making electrode plate manufacturing difficult and requiring a large amount of binder. The first active material layer ATL1 of the present invention includes the second particles PTC2, which have a lower BET than the lithium iron phosphate-based positive electrode active material, making electrode plate manufacturing easier.

[0118] The weight ratio of the first functional additive FAD1 in the first active material layer ATL1 may be 2.4 to 4.0.

[0119] 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 2.44 or 1.0 to 2.6.

[0120] 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 in the first active material layer ATL1 may be smaller than the content of the second binder BND2 in the second active material layer ATL2, which will be described later. When the first active material layer ATL1 satisfies the range conditions for the content of the first binder and the content of the first conductive material, it is possible to maximize the capacity and energy density of the battery and also achieve ease of electrode plate processing.

[0121] 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 material particles (PTC1 and 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.

[0122] The first conductive material CDM1 is used to impart conductivity to the electrode, and any material that is electrically conductive without causing a chemical change in the battery that is being 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.

[0123] The first active material layer ATL1 can be in contact with one surface of the current collector (COL1 in FIG. 6).

[0124] 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.

[0125] The carbon content in the first active material layer may be smaller than the carbon content in the second active material layer. The "carbon content in the first active material layer" can be defined as the "content of elemental carbon in the first active material layer relative to the weight of the first active material layer." In other words, it can be defined as the "content of elemental carbon in the first active material layer / weight of the first active material layer." The carbon content can be measured, for example, by carbon-sulfur analysis. However, the measurement method is not limited thereto.

[0126] Second active material layer ATL2 FIG. 8 is an enlarged view of the second active material layer ATL2 of the positive electrode for a lithium secondary battery according to an embodiment of the present invention.

[0127] 8, 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.

[0128] 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.

[0129] 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.

[0130] 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 in the second active material layer ATL2 may be greater than the content of the first binder BND1 in the first active material layer ATL1. Alternatively, the ratio of the content of the second binder BND2 in the second active material layer ATL2 to the content of the first binder BND1 in the first active material layer ATL1 may be 1.0 to 2.5, 1.0 to 2.44, or 1.3 to 1.8.

[0131] If the second active material layer ATL2 satisfies the range conditions for the second conductive material content and the second binder content, the battery performance can be maximized and the electrode plate can be easily processed.

[0132] 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 to 6.0.

[0133] 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 2.44 or 1.0 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-described 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 and facilitating the processing of the electrode plate.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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 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.

[0139] 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.

[0140] 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.

[0141] The thickness ratio (T1:T2) of the first active material layer ATL1 to the second active material layer ATL2 may be 3:7 to 7:3. For example, the thickness ratio (T1:T2) of the first active material layer ATL1 to the second active material layer ATL2 may be 5:5. When the thickness ratio (T1:T2) of the first active material layer ATL1 to the second active material layer ATL2 satisfies the above-described numerical range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 is improved, maximizing the capacity and energy density of the battery and facilitating the processing of the electrode plate.

[0142] 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 adhesive strength of the electrode plate 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, the density can be further improved.

[0143] 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 30% 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] When the contents of the first particles PTC1, the second particles PTC2, and the third particles PTC3 satisfy the above-described ranges, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 can be improved. This makes it possible to provide a lithium secondary battery with reduced resistance. Furthermore, when the contents of the first particles PTC1, the second particles PTC2, and the third particles PTC3 satisfy the above-described ranges, it makes it possible to provide a lithium secondary battery with excellent performance.

[0148] 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.

[0149] 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 was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized at a rotation speed of 8000 rpm to obtain primary particles in the form of single particles. The average particle size of the primary particles was 0.5 μm to 2.5 μm. The primary particle size of the primary particles was 200 nm to 300 nm.

[0150] 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 (Ni+Co+Al):Li=1:1.05, and the mixture was 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 0.92 Co 0.07 Al 0.01 O2 and an oxide having an average particle size D50 of about 4 μm was prepared. After adding aluminum oxide to the oxide, a second heat treatment was performed at 740°C for 8 hours in an oxygen atmosphere 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

[0151] Production Example 3: Production of third 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 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.

[0152] 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 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.

[0153] The first positive electrode active material slurry was coated on a positive electrode current collector and dried to form a first active material layer, and the second positive electrode active material slurry was coated on the first active material layer and dried to form a second active material layer.

[0154] The active material layers were formed so that the weight ratio of the first particles, second particles, and third particles in the double-layered positive electrode was 35:30:35. Roll pressing was performed to manufacture a positive electrode in which the current collector, the first active material layer, and the second active material layer were sequentially stacked.

[0155] Example 2 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. Ni0.92 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, a second heat treatment was performed in an oxygen atmosphere at 700°C for 15 hours to produce second particles in the form of 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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 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.

[0164] Comparative Example 9 A positive electrode was prepared 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 0.75.

[0165] Comparative Example 10 A positive electrode was prepared 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 3.25.

[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 mixture of 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 particle, the second particle, and the third particle produced in Production Examples 1 to 3 are shown in FIGS. 9, 10, and 12, respectively.

[0168] Referring to FIG. 9, it can be seen that the first particles according to the preparation example of the present invention are in the form of single particles.

[0169] 10, the second particles according to the present invention are in the form of micro-sized single particles. 9 and 10 show that when the second particles are in the form of single particles, the average particle size D50 of the second particles is larger than the average particle size D50 of the first particles.

[0170] Referring to FIG. 11, 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. 12, 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] 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.

[0173] [Table 1]

[0174] *1) Use of bimodal second particles

[0175] 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.

[0176] 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 battery characteristic evaluation results are shown in Table 2 below. Next, the cell was charged and discharged at 25° C. in a voltage range of 3.0 V to 4.45 V at a charge / discharge rate of 0.2 C / 0.2 C, and the energy density was calculated. The energy density was calculated using the formula: [average operating voltage (V) x capacity (Ah) / cell weight (kg)]. Here, the capacity was calculated by multiplying the positive electrode weight (g) by the discharge capacity (mAh / g).

[0177] 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.

[0178] [Table 2]

[0179] *2) Use of bimodal second particles

[0180] 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 better efficiency, capacity, lifespan, resistance, and energy density than 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 performance is improved compared to a battery including only a single layer of positive electrode active material by arranging the positive electrode active material in a double layer.

[0181] 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 3 below.

[0182] 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. After discharging at 1.0C for 1 second at SOC50 under a constant current (0.2C) condition, DCIR was calculated by discharging at a constant current (0.2C).

[0183] 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.

[0184] [Table 3]

[0185] Referring to Table 3, it can be seen that the lithium secondary batteries including the positive electrodes according to Examples 1 and 2 have lower resistance (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 when 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 is increased. [Explanation of symbols]

[0186] 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: 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, the first particles and the third particles have a single particle morphology; 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 second functional additive in the second active material layer to the weight ratio of the first functional additive in the first active material layer is 1.0 to 2.6; Positive electrodes for lithium secondary batteries: [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≦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≦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.

2. B2 in the above Chemical Formula 2 is Al; the second particles have a single particle morphology; The second particles have an average particle size D50 of 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 second particles have an average particle size D50 of 10 μm to 14 μm. The positive electrode for a lithium secondary battery according to claim 1 .

4. the first particles include at least one first primary particle; The average size of the first primary particles is 200 nm to 300 nm; The first 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 .

5. the third particles include at least one third primary particle; the average size of the third primary particles is 200 nm to 300 nm; 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 second particles are in a bimodal form, including a single particle form and a secondary particle form. The positive electrode for a lithium secondary battery according to claim 1 .

7. the BET specific surface area of ​​the second particles is smaller than the BET specific surface area of ​​the first particles; The positive electrode for a lithium secondary battery according to claim 1 .

8. the first particles include a coating layer including carbon; The carbon content in the first particles is 1.0 wt % to 2.0 wt %. The positive electrode for a lithium secondary battery according to claim 1 .

9. 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 .

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

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

12. 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 per 100 parts by weight of the second active material layer; The positive electrode for a lithium secondary battery according to claim 1 .

13. a ratio of the content of the second binder in the second active material layer to the content of the first binder in the first active material layer is 1.0 to 2.44; The positive electrode for a lithium secondary battery according to claim 1 .

14. the first particles and the third particles include a coating layer containing carbon; the carbon content of the first active material layer is smaller than the carbon content of the second active material layer; The positive electrode for a lithium secondary battery according to claim 1 .

15. a current collector; a first active material layer on the current collector; 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: 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, the first particles and the third particles have a single particle morphology; the content of the first binder in the first active material layer is smaller than the content of the second binder in the second active material layer; Positive electrodes for lithium secondary batteries: [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≦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≦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.

16. 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 15.

17. relative to the total weight of the first, second, and third particles contained in the first and second active material layers, The weight of the second particles is 10% by weight to 30% by weight. The positive electrode for a lithium secondary battery according to claim 15.

18. 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 per 100 parts by weight of the second active material layer; The positive electrode for a lithium secondary battery according to claim 15.

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

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