Positive electrode and lithium secondary battery

Abstract

To provide a positive electrode in which the binding strength between a current collector and a positive electrode active material is improved and an electrode plate can be manufactured easily.SOLUTION: A 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 below 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 expressed by a particular formula and having the olivine structure, a second conductive material, and a second binder. The first particles are in a single particle form. The third particles are in a secondary 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. The ratio of 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 is 1.0 to 2.03. [Chemical Formula 1]Lia1Fex1B1y1 PO4-c1.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, the demand for high-energy-density, high-capacity secondary batteries has been increasing rapidly due to the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles. Therefore, research and development to improve the performance of lithium secondary batteries has been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, which contain active materials that allow the intercalation and deintercalation of lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted / deintercalated at the cathode and anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Publication No. 10-2015-0024703 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a positive electrode that can easily be manufactured by improving the binding strength between a current collector and a positive electrode active material.

[0006] Another problem to be solved by the present invention is to provide a positive electrode having improved capacity and life characteristics. [Means for solving the problem]

[0007] The 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 containing a compound having an olivine structure represented by the following Chemical Formula 1, second particles containing a compound having 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 containing a compound having an olivine structure represented by the following Chemical Formula 3, a second conductive material, and a second binder. The first particles have a single-particle shape, the third particles have a secondary-particle shape, 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, and the ratio of 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 can be 1.0 to 2.03.

[0008] [Chemical Formula 1] Li 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, x1 + y1 = 1, 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.

[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, 0.01 ≤ z2 ≤ 0.05, 0 ≤ c2 ≤ 0.05, and 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[[ID= In Chemical Formula 3, 0.8 < a3 ≤ 1.2, 0.95 ≤ x3 ≤ 0.999, 0.001 ≤ y3 ≤ 0.05, x3 + y3 = 1, 0 ≤ c3 ≤ 0.05, and B3 can be at least one element selected from the group consisting of Ti and transition metals with an oxidation number of 4.

[0011] The positive electrode for a lithium secondary battery according to another concept 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 containing a compound having an olivine structure represented by the following Chemical Formula 1, second particles containing a compound having 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 containing a compound having an olivine structure represented by the following Chemical Formula 3, a second conductive material, and a second binder. The first particles have a single-particle shape, the third particles have a secondary-particle shape, 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, 0.001 ≤ y1 ≤ 0.05, x1 + y1 = 1, 0 ≤ c1 ≤ 0.05, and B1 is at least one element selected from the group consisting of Ti and transition metals with an oxidation number 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, 0.01 ≤ z2 ≤ 0.05, 0 ≤ c2 ≤ 0.05, and B2 is at least one element selected from the group consisting of Al and Mn.

[0014] [Chemical Formula 3] Li a3 Fe x3 B3 y3 PO 4-c3 In the above Chemical Formula 3, 0.8 < a3 ≤ 1.2, 0.95 ≤ x3 ≤ 0.999, 0.001 ≤ y3 ≤ 0.05, x3 + y3 = 1, 0 ≤ c3 ≤ 0.05, and the B3 can be at least one element selected from the group consisting of Ti and transition metals with an oxidation number of 4.

[0015] The lithium secondary battery according to an embodiment of the present invention can include the above-described positive electrode.

Advantages of the Invention

[0016] The positive electrode according to the present invention can improve the economy and average voltage by including the first particles and the third particles having an olivine structure.

[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 improve the ease of manufacturing the electrode plate by mixing the second particles and the first particles and disposing them in the first active material layer.

[0019] The positive electrode according to the present invention can have the effect of improving battery characteristics while at the same time having the effect of facilitating the manufacture of the electrode plate by mixing the first particles, the second particles, and the third particles in an optimal ratio and disposing them in a double-layer structure.

Brief Description of the Drawings

[0020] [Figure 1] It is a conceptual diagram briefly showing the lithium secondary battery according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view showing the lithium secondary battery according to an embodiment. [Figure 3]1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the lithium secondary battery having a cylindrical battery shape. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the battery having a prismatic shape. [Figure 5] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, in the form of a pouch-shaped battery. [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 this specification, when a component is referred to as being on another component, it means that the component can be formed directly on the other component, or that a third component can be interposed between them. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various forms and can undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0022] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component can be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0023] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, elements referred to as "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements.

[0024] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0025] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that utilizes dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, in measurements using the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0026] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0027] 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 immersed in the electrolyte solution ELL.

[0028] 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.

[0029] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIG. 6. The current collector COL1 may be made of, but is not limited to, aluminum.

[0030] 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.

[0031] For example, the negative electrode active material layer AML2 may contain 90 to 99 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % of the conductive material.

[0032] The binder serves to firmly adhere the negative active material particles to each other and to firmly adhere the negative 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.

[0033] 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.

[0034] The water-based binder may be selected from styrene-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0035] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be 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.

[0036] The dry binder may be a polymeric material that can be fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0037] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery may 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.

[0038] As the current collector COL2, those 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 can be used.

[0039] 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, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0040] The material capable of reversibly intercalating / deintercalating the lithium ions can be a carbon-based negative electrode active material, for example, including crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0041] As the alloy of the 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.

[0042] As the material dopable and dedopable with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0043] 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 accumulation of primary silicon particles and a first amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The 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.

[0044] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles and a first coating layer of amorphous carbon located on the core surface.

[0045] The Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0046] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such a separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can also be used.

[0047] Separator 30 can include a porous substrate and a first coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0048] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0049] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0050] 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.

[0051] The organic material and the inorganic material may be mixed in one first coating layer, or may be stacked in a form in which a first coating layer containing an organic material and a first coating layer containing an inorganic material are stacked.

[0052] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0053] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0054] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0055] Examples of the carbonate solvent 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).

[0056] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0057] 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.

[0058] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0059] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0060] The lithium salt dissolves 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+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0061] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to embodiments, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a prismatic type, and FIGS. 4 and 5 illustrating pouch types. Referring to FIGS. 2 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 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 2. Also, as shown in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0062] 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.

[0063] Hereinafter, 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.

[0064] 1st particle PTC1 The first particles PTC1 may include a lithium compound having an olivine structure represented by the following Chemical Formula 1. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1

[0065] In the chemical formula 1, 0.8 < a1 ≤ 1.2, 0.95 ≤ x1 ≤ 0.999, 0.001 ≤ y1 ≤ 0.05, x1 + y1 = 1, and 0 ≤ c1 ≤ 0.05, and the B1 can be at least one element selected from the group consisting of Ti and transition metals with an oxidation number of 4. The B1 can be a dopant doped into the first particle PTC1.

[0066] The first particle PTC1 has the advantages of high economy, high structural stability, and excellent life characteristics. Since it is mainly composed of Fe, it is relatively inexpensive, and because it is structurally stable, the chemical changes can be relatively reduced even when repeatedly charged and discharged.

[0067] <p Referring to FIGS. 7 and 9, the first particle PTC1 can have a single particle shape. In this specification, a single particle can mean a single independent particle without a grain boundary inside. A single particle can mean a single particle, a monolith structure, a single body structure, or a non-aggregated particle that exists as an independent phase where the particles are not mutually aggregated morphologically. As an example, a single particle can be a single crystal. Or, a single particle can be a particle containing several crystals. A single particle can be in a form separated alone. Or, a single particle can be in a form where 2 to 100 single particles are attached to each other.

[0068] The first particle PTC1 can include at least one first primary particle. As one embodiment, the first particle PTC1 can have a spherical or elliptical shape in which the first primary particles are aggregated. As another embodiment, the first particle PTC1 can have a random shape without having a spherical shape even when the first primary particles gather.

[0069] The first particle PTC1 can be provided in various sizes. For example, the average particle size of the first particle PTC1 can be 0.5 μm to 2.5 μm, or about 1 μm. The minimum particle size of the first particle PTC1, that is, the size of the first primary particle, can be 100 nm to 500 nm, or 200 nm to 300 nm.

[0070] In one embodiment, the average particle size can be measured using a particle size analyzer. The average particle size can refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The coating layer may further include at least one element selected from the group consisting of titanium and transition metals 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 metals or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0075] By further including a coating portion in the first particle PTC1, the structural stability is enhanced, and a uniform coating layer can be formed on the surface of the first particle PTC1. Further, by further including a coating portion in the first particle PTC1, the electrical conductivity of the first particle PTC1 can be further improved.

[0076] The first particle PTC1 can further include carbon derived from the coating layer described above. The carbon element content in the first particle PTC1 can be 0.5 wt% to 5 wt%, 0.5 wt% to 3 wt%, or 1.0 wt% to 2 wt%. The carbon element content in the first particle PTC1 may be smaller than the carbon element content in the third particle PTC3.

[0077] 2nd particle PTC2 The second particle PTC2 can include a layered lithium compound represented by the following Chemical Formula 2. [Chemical Formula 2] Li a2 Ni x2 Co y2 B2 z2 O 2-c2

[0078] In Chemical Formula 2, 0.8 < a2 ≤ 1.2, 0.9 ≤ x2 ≤ 1.05, 0.03 ≤ y2 ≤ 0.10, 0.01 ≤ z2 ≤ 0.05, 0 ≤ c2 ≤ 0.05, and the B2 can be at least one element selected from the group consisting of Al and Mn. In one embodiment or a plurality of embodiments, in Chemical Formula 2, 0.8 < a2 ≤ 1.2, 0.9 ≤ x2 ≤ 0.94, 0.05 ≤ y2 ≤ 0.09, 0.01 ≤ z2 ≤ 0.05, 0 ≤ c2 ≤ 0.05, and x2 + y2 + z2 = 1 may be satisfied.

[0079] The B2 can be Al.

[0080] The second particle PTC2 has the advantages of high capacity and high energy density.

[0081] 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 containing a high content of nickel. The high-nickel-based positive electrode active material may achieve high capacity and high performance.

[0082] In one embodiment, the second particles PTC2 may include a second coating layer on their surfaces. By including the second coating layer, the second particles PTC2 can effectively prevent structural collapse due to repeated charge and discharge, thereby improving the lifespan of the secondary battery.

[0083] The second coating layer can 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 can be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound can further include other metals or non-metal elements. For example, the second coating layer can further include lithium, manganese, and / or nickel, etc.

[0084] A method for measuring the metal content in the second coating layer of the second particles PTC2 can include performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the second particles PTC2. Through this analysis, the content of aluminum, titanium, magnesium, zirconium, molybdenum, and / or niobium in the second coating layer can be determined. In addition to SEM-EDS, methods for measuring the metal content in the second coating layer can also include inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0085] 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 decreases, thereby reducing resistance and increasing 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 manufacture of an electrode plate with a small amount of binder.

[0086] 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 forms of single particles and secondary particles are mixed, the density may be further improved. Hereinafter, the second particles PTC2 in the form of single particles and / or secondary particles will be described with reference to FIGS. 7, 10, and 11.

[0087] In one embodiment, referring to FIG. 10, the second particle PTC2 may have a single particle shape. In this specification, a single particle may refer to a single particle without an internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are morphologically present in an independent phase without cohesion 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 separately separated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0088] 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 the aggregation of the second primary particles. In another embodiment, the second particles PTC2 may not have a spherical shape but may have a random shape even when the second primary particles are aggregated. When the second particles PTC2 are in the form of an aggregation of the second primary particles, they may be less structured than when they are in the form of secondary particles. That is, they may have a more random shape.

[0089] 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 of particles at 50% by volume of the cumulative volume in the particle size distribution (D50). 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.

[0090] 9 and 10, when the second particles PTC2 are single particles, the average size of the second primary particles of the second particles PTC2 may be larger than the average size of the first primary particles of the first particles PTC1.

[0091] In another embodiment, referring to FIG. 11, the second particles PTC2 may be in the form of secondary particles. The secondary particles are polycrystalline, meaning that at least two or more second primary particles are aggregated together. In other words, one second particle PTC2 may include a plurality of second primary particles NNP2 (FIG. 7) aggregated together. The second particles PTC2 may have a spherical or elliptical shape.

[0092] When the second particle is a secondary particle, the average particle size of the second particle PTC2 can be 10 μm to 14 μm. Referring to FIGS. 9 and 11, the average particle size of the second particle PTC2 may be the same as or larger than the average particle size of the first particle PTC1 described above. As one embodiment, the average particle size can be measured by a particle size analyzer. The average particle size can mean the diameter (D50) of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0093] As other embodiments, referring to FIG. 7, the second particle can exist in a bimodal form in which single particles PTC2 (SP) and secondary particles PTC2 (PC) are mixed. When the second particle is in a bimodal form, it can have a further improved density. Referring to FIG. 7 in more detail, the second particle PTC2 (PC) as a secondary particle means a shape in which at least two or more second primary particles NNP2 are aggregated. The second particle PTC2 (SP) as a single particle means a shape including at least one second primary particle. The second particle PTC2 (SP) as a single particle has a larger size of the second primary particle than the second particle PTC2 (PC) as a secondary particle, and even if the second primary particles are aggregated, they do not have a spherical shape and can have a random shape.

[0094] Third particle PTC3 The third particle PTC3 can contain 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

[0095] In Chemical Formula 3, 0.8 < a3 ≤ 1.2, 0.95 ≤ x3 ≤ 0.999, 0.001 ≤ y3 ≤ 0.05, x3 + y3 = 1, 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. B3 can be a dopant doped into the third particle PTC3.

[0096] The third particle PTC3 has the advantages of being highly economical, structurally stable, and having excellent lifespan. As it is mainly composed of Fe, it is relatively inexpensive and structurally stable, so chemical changes can be relatively small even after repeated charging and discharging.

[0097] The third particles PTC3 may be in the form of secondary particles. Referring to Figures 8 and 14, the secondary particles are in the form of polycrystals, which means that at least two or more third primary particles NNP3 are aggregated together. In other words, one third particle PTC3 may include a plurality of third primary particles NNP3 aggregated together. The third particles PTC3 may have a spherical or elliptical shape.

[0098] The lithium compound having an olivine structure in the form of secondary particles may be more effective in reducing the resistance of a battery than the lithium compound having an olivine structure in the form of single particles.

[0099] The dopant can exert an effect of controlling the uniform growth of the third primary particles NNP3 of the third particles PTC3, thereby improving the charge / discharge efficiency, low temperature characteristics, and life characteristics of the lithium secondary battery.

[0100] 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.

[0101] The coating layer may further include at least one element selected from the group consisting of titanium and transition metals 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 metals or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0102] The third particle 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 particle PTC3. The grain boundary coating layer may be formed by coating along the interface between the third primary particles NNP3 inside the third particle PTC3. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the third particle PTC3. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound and a transition metal-containing compound having an oxidation number of 4.

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

[0104] The third particles PTC3 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the third particles PTC3. In addition, the third particles PTC3 further include a grain boundary coating portion, which further improves the electrical conductivity of the third particles PTC3.

[0105] The third particles PTC3 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the third particles PTC3 may be 0.5 wt% to 10 wt%, 1 wt% to 3 wt%, or 1.0 wt% to 2.0 wt%. The carbon element content in the third particles PTC3 may be greater than the carbon element content in the first particles PTC1.

[0106] 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 approximately 5 μm. In one embodiment, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0107] 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 about 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] The size of the third primary particles NNP3 of the third particles PTC3 may be smaller than the size of the first primary particles of the first particles PTC1. For example, the size of the third primary particles NNP3 of the third particles PTC3 may be approximately 100 nm smaller than the size of the first primary particles of the first particles PTC1.

[0109] If the average particle size of the third particles PTC3 and the average size of the third primary particles NNP3 satisfy the above-described 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 including the same can be improved.

[0110] 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 a secondary particle form or a bimodal form that is a mixture of a single particle form and a secondary particle form.

[0113] 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-cobalt-based positive electrode active material, such as low capacity and low energy density, and simultaneously achieving 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 weight 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. This can 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 weight ratio of the first functional additive FAD1 in the first active material layer ATL1 may be 2.4 wt % to 4.0 wt %.

[0116] The weight ratio of the first functional additive FAD1 in the first active material layer ATL1 may be equal to or less than 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 2.03.

[0117] 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 less than the content of the second binder BND2 in the second active material layer ATL2 (described below). When the first active material layer ATL1 satisfies the first binder content range and the first conductive material content range, the capacity and energy density of the battery can be maximized while also facilitating electrode plate processing.

[0118] 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 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 chloride, 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.

[0119] The first conductive material CDM1 is used to impart conductivity to the electrode and can be any material that is electronically conductive and does not cause chemical changes in the 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.

[0120] The first active material layer ATL1 can be in contact with one surface of the current collector COL1 (FIG. 6).

[0121] 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.

[0122] The carbon content of the first active material layer may be less than the carbon content of the second active material layer. The "carbon content of the first active material layer" may be defined as the "content of carbon element contained in the first active material layer relative to the weight of the first active material layer." That is, it may be defined as "the content of carbon element contained in the first active material layer / weight of the first active material layer." The carbon content may be measured, for example, by carbon-sulfur analysis. However, the measurement method is not limited thereto.

[0123] 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.

[0124] 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.

[0125] The second binder BND2 serves to firmly 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 chloride, 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.

[0126] The second conductive material CDM2 is used to impart conductivity to the electrode and can be any material that is electronically conductive and does not cause chemical changes in the resulting battery. Examples of the second conductive material CDM2 include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or 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 to 2.5 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 to 2.5 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 2.03.

[0128] When the second active material layer ATL2 satisfies the second conductive material content range and the second binder content range, the battery performance can be maximized and the electrode plate can be easily processed.

[0129] 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 5.0 wt %.

[0130] The ratio of the weight ratio of the second functional additive FAD2 to the weight ratio of the first functional additive FAD1 (weight ratio of second functional additive / weight ratio of first functional additive) may be 1.0 to 2.03. When the ratio of the weight ratio of the second functional additive FAD2 to the weight ratio 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, thereby maximizing the capacity and energy density of the battery while also achieving ease of electrode plate processing.

[0131] The second active material layer ATL2 may be applied to contact one side of the first active material layer ATL1. This side of the first active material layer ATL1 may be the side of the first active material layer ATL1 that does not contact the current collector COL1 (FIG. 6). For example, the current collector COL1 (FIG. 6), the first active material layer ATL1, and the second active material layer ATL2 may be disposed in this order.

[0132] 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.

[0133] 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.

[0134] The positive electrode active material layer AML1 may include 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 wt % to 99 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0135] The positive electrode active material layer AML1 may include binders BND1 and BND2 and conductive materials CDM1 and CDM2, and the content of the binders BND1 and BND2 and conductive materials CDM1 and CDM2 may be 0.5 wt % to 5 wt % respectively, based on 100 wt % of the positive electrode active material layer AML1.

[0136] 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, and improves the binding strength to the current collector, thereby facilitating the manufacture of an electrode plate and reducing the resistance of the electrode plate. This also allows for the provision of a lithium secondary battery with excellent performance.

[0137] 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 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.

[0138] 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 bonding strength of the positive electrode active material layer AML1 to the current collector COL1 is improved, thereby maximizing the capacity and energy density of the battery while also facilitating electrode plate processing.

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

[0140] The content of the first particles PTC1 relative to the total content of the first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1 and ATL2 may be 30 wt% to 40 wt%. 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 and ATL2 may be 35 wt%.

[0141] The content of the second particles PTC2 relative to the total content of the first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1 and ATL2 may be 10 wt % to 30 wt %. For example, the content of the second particles PTC2 relative to the total content of the first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1 and ATL2 may be 20 wt % to 30 wt %.

[0142] The content of the third particles PTC3 relative to the total content of the first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1 and ATL2 may be 30 wt % to 40 wt %. For example, the content of the third particles PTC3 relative to the total content of the first particles PTC1, second particles PTC2, and third particles PTC3 contained in the first and second active material layers ATL1 and ATL2 may be 35 wt %.

[0143] The content of the second particles PTC2 relative to the total content of the first particles PTC1 and second particles PTC2 included in the first active material layer ATL1 may be 30 wt% to 60 wt%. For example, the content of the second particles PTC2 relative to the total content of the first particles PTC1 and second particles PTC2 included in the first active material layer ATL1 may be 45 wt% to 50 wt%.

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

[0145] Hereinafter, production examples, examples, and comparative examples of the present invention will be described. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0146] 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 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 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.

[0147] 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 average particle size (D50) of about 4 μm were prepared. Aluminum oxide was added to the oxide, and 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.

[0148] 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 slurry mixture 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 under a nitrogen atmosphere to obtain secondary particles. The average particle size (D50) of the secondary particles was 3 μm to 7 μm. The size of the primary particles of the secondary 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 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 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.

[0151] At this time, 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. A roll press 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.

[0152] Example 2 A positive electrode was prepared in the same manner as in Example 1, except that bimodal second particles were used instead of the second particles (single particle type) of Preparation Example 2. 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, 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.

[0153] 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.

[0154] Comparative Example 2 A positive electrode was prepared 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.

[0155] Comparative Example 3 A positive electrode was prepared 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.

[0156] Comparative Example 4 A positive electrode was prepared 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.

[0157] Comparative Example 5 A positive electrode was prepared 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.

[0158] Comparative Example 6 A positive electrode was prepared 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.

[0159] Comparative Example 7 A positive electrode was prepared 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.

[0160] 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.

[0161] 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 so that the ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive was 0.8.

[0162] 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 so that the ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive was 2.44.

[0163] Comparative Example 11 A positive electrode containing a lithium compound having an olivine structure in the form of a single particle was prepared. A positive electrode active material slurry was prepared using the first particles of Preparation Example 1, and the positive electrode active material slurry was then applied to a positive electrode current collector and dried to prepare a single-layer positive electrode.

[0164] Comparative Example 12 A positive electrode containing a lithium compound having an olivine structure in the form of secondary particles was prepared. A positive electrode active material slurry was prepared using the first particles of Preparation Example 3, and the positive electrode active material slurry was then applied to a positive electrode current collector and dried to prepare a single-layer positive electrode.

[0165] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal counter electrode as the counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene PE film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte solution was injected to fabricate a lithium secondary battery. The electrolyte used was a 1.3 M LiPF6 solution mixed with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0166] Evaluation example 1: Analysis of the surface of the positive electrode active material SEM images of the first, second, and third particles prepared in Preparation Examples 1 to 3 are shown in FIGS. 9, 10, and 12, respectively.

[0167] 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.

[0168] 10, it can be seen that the second particles according to the present invention are in the form of micro-sized single particles. 9 and 10, it can be seen 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.

[0169] Referring to FIG. 11, 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.

[0170] 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 spherical secondary particles formed by agglomeration of nano-sized fine primary particles.

[0171] 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.

[0172] [Table 1]

[0173] *1) Uses bimodal second particles

[0174] Evaluation example 3: Battery characteristic evaluation The characteristics of the lithium secondary batteries prepared using the positive electrode active materials of the Examples and Comparative Examples were evaluated.

[0175] 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. The average voltage was measured after initial charge-discharge. It was then charged and discharged 50 times at 1.0C / 1.0C at 45°C. An additional coin cell was fabricated and 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 additional charging, the capacity was measured at -20°C. The battery characteristics were evaluated and are shown in Tables 2 and 3 below.

[0176] 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.

[0177] [Table 2]

[0178] *2) Use of bimodal second particles

[0179] [Table 3]

[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 superior levels of efficiency, capacity, lifespan, voltage, 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 performance is superior to that of a battery including only a single layer of positive electrode active material due to the arrangement of the positive electrode active material in a double layer.

[0181] Referring to Table 3, it can be seen that the lithium secondary battery including the positive electrode of Comparative Example 12 is superior in efficiency, low-temperature capacity, lifespan, and resistance to the lithium secondary battery including the positive electrode of Comparative Example 10. 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 olivine-structured lithium compound is contained in the form of secondary particles rather than in the form of single particles. Since the present invention contains the third particles, which are the olivine-based positive electrode active material, in the form of secondary particles, the resistance reduction effect can be further enhanced.

[0182] Evaluation example 4: Resistance and adhesion evaluation 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.

[0183] The lithium secondary battery was initially charged under constant current (0.2C) conditions, rested for 10 minutes, and then discharged under constant current (0.2C) conditions until the battery reached 3.0V, and the average voltage was evaluated. Under constant current (0.2C) conditions, the battery was discharged at 1.0C for 1 second at SOC50, followed by discharging at constant current (0.2C) to calculate the DCIR.

[0184] The contents of the first and second functional additives 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.

[0185] [Table 4]

[0186] 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 resistance (DCIR) than the lithium secondary batteries including the positive electrodes according to Comparative Examples 9 and 10. That is, 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 improved. [Explanation of symbols]

[0187] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. A current collector; a first active material layer on the current collector; a second active material layer on the first active material layer; Including, The first active material layer includes first particles including a compound having an olivine structure represented by Chemical Formula 1 below, second particles including a compound having 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 having an olivine structure represented by the following Chemical Formula 3, a second conductive material, and a second binder: the first particles have a single particle shape, the third particles have a secondary particle shape, 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 ratio of 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 is 1.0 to 2.03; Positive electrode for lithium secondary batteries. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1 (In the above Chemical Formula 1, 0.8<a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, x1+y1=1, 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 the chemical formula 2, 0.8<a2≦1.2, 0.9≦x2≦1.05, 0.03≦y2≦0.10, 0.01≦z2≦0.05, and 0≦c2≦0.05, and 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 the formula 3, 0.8<a3≦1.2, 0.95≦x3≦0.999, 0.001≦y3≦0.05, x3+y3=1, 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 shape, The average particle size (D50) of the second particles 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 shape formed by agglomeration of a plurality of second primary particles, The average particle size (D50) of the second particles is 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 average particle size (D50) of the first particles is 0.5 μm to 2.5 μm. The positive electrode for a lithium secondary battery according to claim 1 .

5. the third particles have a secondary particle shape formed by agglomeration of a plurality of third primary particles, The average size of the third primary particles is 100 nm to 200 nm; The average particle size (D50) of the third particles is 3 μm to 7 μm. The positive electrode for a lithium secondary battery according to claim 1 .

6. The second particles have 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 porosity of the third particles is 20% to 40%. The positive electrode for a lithium secondary battery according to claim 1 .

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

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. 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 .

12. 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 .

13. The content of the first binder is 1.2 to 2.0 parts by weight based on 100 parts by weight of the first active material layer, The content of the second binder is 2.0 to 2.5 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 .

14. 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 2.03; The positive electrode for a lithium secondary battery according to claim 1 .

15. the first particles and the third particles include a coating layer containing carbon; The carbon content of the first particles is lower than the carbon content of the third particles. 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 having an olivine structure represented by Chemical Formula 1 below, second particles including a compound having 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 having an olivine structure represented by the following Chemical Formula 3, a second conductive material, and a second binder: the first particles have a single particle shape, the third particles have a secondary particle shape, the content of the first binder in the first active material layer is less than the content of the second binder in the second active material layer; Positive electrode for lithium secondary batteries. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-c1 (In the above Chemical Formula 1, 0.8<a1≦1.2, 0.95≦x1≦0.999, 0.001≦y1≦0.05, x1+y1=1, 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 the chemical formula 2, 0.8<a2≦1.2, 0.9≦x2≦1.05, 0.03≦y2≦0.10, 0.01≦z2≦0.05, and 0≦c2≦0.05, and 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 the above Chemical Formula 3, 0.8<a3≦1.2, 0.95≦x3≦0.999, 0.001≦y3≦0.05, x3+y3=1, 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.)

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. 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 16.

19. The content of the first binder is 1.2 to 2.0 parts by weight based on 100 parts by weight of the first active material layer, The content of the second binder is 2.0 to 2.5 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. A lithium secondary battery comprising the positive electrode according to claim 1.

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