Positive electrode active material for lithium secondary battery, positive electrode including the same, and lithium secondary battery including the same

Abstract

To provide a positive electrode active material being economical and having high energy density and an excellent lifetime characteristic.SOLUTION: The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method for the same, and a lithium secondary battery including the same. More specifically, the positive electrode active material includes a first particle containing a compound expressed by Chemical Formula 1 and having an olivine structure, a second particle containing a compound expressed by Chemical Formula 2 and having a spinel structure, a third particle containing a compound expressed by Chemical Formula 3 and having a layered structure, and a fourth particle containing a compound expressed by Chemical Formula 4. The first particle and the second particle form a main active material. Based on 100 parts by weight of the positive electrode active material, the content amount of the main active material is 80 parts by weight to 90 parts by weight.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] Recently, with the rapid replenishment of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. Accordingly, research and development to improve the performance of lithium secondary batteries has been actively carried out.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated from the cathode and the anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Publication No. 10-2023-0057858 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a positive electrode active material that is economical and has high energy density and excellent life characteristics.

[0006] Another problem to be solved by the present invention is to provide an economical lithium secondary battery having high energy density and high efficiency. [Means for solving the problem]

[0007] The positive electrode active material according to the present invention may include first particles having an olivine structure including a compound represented by Chemical Formula 1 below, second particles having a spinel structure including a compound represented by Chemical Formula 2 below, third particles having a layered structure including a compound represented by Chemical Formula 3 below, and fourth particles including a compound represented by Chemical Formula 4 below. The content of the third particles may be 10 to 20 parts by weight based on 100 parts by weight of the positive electrode active material. [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In the above Chemical Formula 1, 0.8≦a1≦1.2, 0.1≦x1≦1.0, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1; B is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Mn x2 Mg y2 O 4-b2 In the above Chemical Formula 2, 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05; [Chemical formula 3] Li a3 Ni x3 Co y3 C z3 O 2-b3 In the above Chemical Formula 3, 0.8≦a2≦1.2, 0.9≦x3≦1.0, 0≦y3≦0.1, 0≦z3≦0.1, 0≦b3≦0.05, and x3+y3+z3=1; C is Al, Mn, or a combination thereof; [Chemical formula 4] Li a4 Fe x4 D y4 O 4-b4 In Chemical Formula 4, 4.9≦a4≦5.1, 0.9≦x4≦1.05, 0≦y4≦0.05, 0≦b4≦0.05, and D is Al, Mg, or a combination thereof.

[0008] A positive electrode for a lithium secondary battery according to another aspect of the present invention may include a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material, a conductive material, and a binder.

[0009] A lithium secondary battery according to another aspect of the present invention may include the positive electrode, a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and a separator between the positive electrode and the negative electrode. [Effects of the Invention]

[0010] The cathode active material according to the present invention comprises olivine-based first particles and spinel-based second particles as the main active material, and the addition of layered third particles can improve capacity and energy density. Furthermore, the capacity of the cathode active material can be further improved by including a small amount of fourth particles that function as a sacrificial cathode. The cathode active material according to the present invention can be economical and have high operating voltage and energy density. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 6] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 7] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 8a] 1 is an SEM image of the positive electrode active material of Production Example 1 of the present invention. [Figure 8b] 1 is an SEM image of the positive electrode active material of Production Example 1 of the present invention. [Figure 8c] 1 is an SEM image of the positive electrode active material of Production Example 2 of the present invention. [Figure 8d] 1 is an SEM image of the positive electrode active material of Production Example 2 of the present invention. [Figure 9a] 1 is an SEM image of the positive electrode active material of Production Example 3 of the present invention. [Figure 9b] 1 is an SEM image of the positive electrode active material of Production Example 3 of the present invention. [Figure 10a] 1 is an SEM image of the positive electrode active material of Production Example 4 of the present invention. [Figure 10b] 1 is an SEM image of the positive electrode active material of Production Example 4 of the present invention. [Figure 11] 1 is an SEM image of the positive electrode active material of Production Example 5 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this specification, when a component is referred to as being on another component, it means that the component may be formed directly on the other component, or that a third component may be interposed between them. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may 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.

[0013] In this specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component, or that a third component may be interposed between them. Also, in the drawings, the thickness of the components 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.

[0014] 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, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other elements to the referenced element.

[0015] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0016] 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 using 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 uses 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, when measuring by 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.

[0017] 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.

[0018] 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 an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0019] 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.

[0020] 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 FIGS. 6 and 7. The current collector COL1 may be made of, but is not limited to, aluminum.

[0021] 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.

[0022] 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.

[0023] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly 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.

[0024] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0025] 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.

[0026] 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.

[0027] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0028] 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 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.

[0029] As the current collector COL2, it is possible to use those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof.

[0030] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0031] Examples of materials capable of reversibly inserting / desorbing lithium ions include carbon-based negative electrode active materials, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0032] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0033] As the material capable of doping and undoping 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 (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or combinations thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0034] 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, it may include secondary particles (cores) formed by assembling primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surfaces of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, coating the primary silicon particles with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0035] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and a first coating layer of amorphous carbon disposed on the core.

[0036] A Si-based negative electrode active material or a Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0037] 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 separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may 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 may also be used.

[0038] 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.

[0039] 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.

[0040] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0041] 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.

[0042] 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.

[0043] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0044] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0045] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0046] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0047] 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.

[0048] 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.

[0049] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0050] 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.

[0051] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, 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 tetrafluoroethene sulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0052] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 through 5 are schematic diagrams illustrating 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 through 5, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 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.

[0053] 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.

[0054] 6 and 7 are enlarged views of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. Referring to Figures 6 and 7, as described above, the positive electrode active material layer AML1 (see Figure 1) may include first particles PTC1, second particles PTC2, third particles PTC3, fourth particles PTC4, conductive material CDM, and binder BND. The plurality of first particles PTC1, the plurality of second particles PTC2, the plurality of third particles PTC3, and the plurality of fourth particles PTC4 may constitute a positive electrode active material according to an embodiment of the present invention.

[0055] The positive electrode active material layer AML1 may further include an additive that can act as a sacrificial positive electrode.

[0056] The content of the positive electrode active materials PTC1, PTC2, PTC3, and PTC4 in the positive electrode active material layer AML1 may be 90 wt% to 99.5 wt% relative to 100 wt% of the positive electrode active material layer AML1. The content of the binder BND and the conductive material CDM may be 0.5 wt% to 5 wt% relative to 100 wt% of the positive electrode active material layer AML1.

[0057] The binder BND can bind the first particles PTC1, the second particles PTC2, the third particles PTC3, the fourth particles PTC4, and the conductive material CDM to one another. As an example, the binder BND can include at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer 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, but is not limited thereto.

[0058] A conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM without limitation. For example, the conductive material CDM can 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, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0059] The first to fourth particles (PTC1, PTC2, PTC3, and PTC4) will be described in more detail below.

[0060] 1st particle PTC1 The first particles PTC1 may include a lithium compound having an olivine structure represented by the following Chemical Formula 1.

[0061] [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.1≦x1≦1.0, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1 may be satisfied. B may be at least one element selected from the group consisting of Ti, Mg, V, and Nb, and may be a dopant doped into the first particles PTC1. The dopant B controls the size of the primary particles to be uniform, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery.

[0062] As an example, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or may cover 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 of the first particles PTC1 and thereby improve electrical conductivity.

[0063] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. Metal-containing compounds such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compounds may further include other metals or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0064] The first particles PTC1 may further contain carbon derived from the coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0065] Referring again to FIG. 6, as an example, the first particle PTC1 may have a single particle shape. In this specification, a single particle may refer to a single particle having no internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are morphologically present in an independent phase and are 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.

[0066] The first particles PTC1 may be a nano-shaped cathode active material. 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, not a spherical shape, even if the first primary particles are aggregated.

[0067] The first particles PTC1 may be provided in various sizes. For example, the average particle size of the first particles PTC1 may be 500 nm 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.

[0068] As an example, 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.

[0069] As an example, 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.

[0070] 7, the first particles PTC1 may have a polycrystalline form and include secondary particles formed by agglomeration of at least two or more first primary particles. In other words, one first particle PTC1 may include a plurality of first primary particles agglomerated together. The first particles PTC1 may have a spherical or elliptical shape.

[0071] As an example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the first primary particles. The grain boundary coating layer may be present inside the first particle PTC1. The grain boundary coating layer may be formed by coating along the interface between the first primary particles inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0072] The interior of the first particle PTC1 described above can refer to the entire interior of the first particle PTC1 excluding the surface of the first particle PTC1. For example, the interior of the first particle PTC1 can refer to the region from a depth of about 10 nm from the surface of the first particle PTC1 to the entire inside, or from a depth of 10 nm to a depth of about 2 μm.

[0073] The first particles PTC1 further include a grain boundary coating portion, which strengthens structural stability and allows a uniform coating layer to be formed on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which further improves the electrical conductivity of the first particles PTC1.

[0074] The first particles PTC1 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0075] When the first particles PTC1 are secondary particles, the average particle size of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 10 μm, or 3 μm to 7 μm. For example, the average particle size of the first particles PTC1 may be approximately 5 μm. In one example, the average particle size can be measured using a particle size analyzer. The average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0076] The average size of the first primary particles may be 200 nm or less. For example, the average size of the first primary particles 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 first primary particles may refer to the diameter measured by randomly selecting approximately 30 primary particles from an electron microscope image of the positive electrode active material. The size of the first primary particles may be uniform.

[0077] When the first particles PTC1 are in a polycrystalline form, the size of the first primary particles may be smaller than when the first particles PTC1 are in a monocrystalline form. For example, when the first particles PTC1 are in a polycrystalline form, the size of the first primary particles may be about 100 nm smaller than when the first particles PTC1 are in a monocrystalline form.

[0078] When the average particle size and the average size of the first primary particles PTC1 satisfy the above-described ranges and the size of the first primary particles is uniform, the charge / discharge capacity and low-temperature capacity of a lithium secondary battery containing the same can be improved.

[0079] The first particles PTC1 may have a spherical shape formed by agglomeration of nano-sized first primary particles. The first particles PTC1 may exhibit the following characteristics due to the first primary particles being closely agglomerated to each other: The first particles PTC1 may have a spherical or elliptical shape. The average particle size (D50) of the first particles PTC1 may be 2 μm to 15 μm. The porosity of the first particles PTC1 may be about 20% to about 40%. The Span value of the first particles PTC1 analyzed using a particle size analyzer may be 0.3 to 0.75.

[0080] 2nd particle PTC2 The second particles PTC2 may include a lithium compound having a spinel structure represented by the following Chemical Formula 2.

[0081] [Chemical formula 2] Li a2 Mn x2 Mg y2 O 4-b2 In Chemical Formula 2, a2 ​​may satisfy the following conditions: 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05. Mg may be a dopant doped into the second particles PTC2. Mg controls the size of the primary particles to be uniform and stabilizes the crystalline structure of the positive electrode active material, thereby improving the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery. The second particles PTC2 may further contain Al in addition to Mg as a dopant.

[0082] 6 and 7, the second particles PTC2 may have a polycrystalline form and may include secondary particles formed by agglomeration of at least two or more second primary particles. In other words, one second particle PTC2 may include a plurality of second primary particles agglomerated together. The second particles PTC2 may have a spherical form formed by agglomeration of the second primary particles, or may have a random form even when the second primary particles are agglomerated.

[0083] The average particle size of the second particles PTC2 may be 3 μm to 20 μm, 4 μm to 15 μm, or 5 μm to 10 μm. For example, the average particle size of the first particles PTC1 may be approximately 8 μm. In one example, the average particle size can be measured using a particle size analyzer. The average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution.

[0084] The average size of the second primary particles constituting the second particles PTC2 may be 3 μm or less. For example, the particle size of the first primary particles may be 300 nm to 3 μm, 500 nm to 3 μm, 1 μm to 3 μm, or 2 μm to 3 μm.

[0085] In one embodiment, the average size of the second primary particles may refer to the diameter measured by randomly selecting approximately 30 primary particles from an electron microscope photograph of the positive electrode active material. The size of the second primary particles may be uniform. The second primary particles may have an average size smaller than that of the first primary particles. The difference in average size between the second primary particles and the first primary particles may be 300 nm or more.

[0086] As an example, the second particles PTC2 may include a second coating layer on the surface thereof, which can effectively prevent the second particles PTC2 from collapsing due to repeated charging and discharging.

[0087] The second coating layer may include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the second coating layer may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the second coating layer may further include lithium, manganese, and / or nickel.

[0088] Third particle PTC3 The third particles PTC3 may include a lithium compound having a layered structure represented by the following Chemical Formula 3.

[0089] [Chemical formula 3] Li a3 Ni x3 Co y3 C z3 O 2-b3 In Chemical Formula 3, 0.8≦a2≦1.2, 0.9≦x3≦1.0, 0≦y3≦0.1, 0≦z3≦0.1, 0≦b3≦0.05, and x3+y3+z3=1, and C can be Al, Mn, or a combination thereof.

[0090] The third particles PTC3 may have a single particle shape similar to the first particles PTC1 described above. The description of the single particle may be the same or similar to that described for the first particles PTC1. In one embodiment, the third particles PTC3 may have a shape composed of one single particle. In another embodiment, the third particles PTC3 may have a shape in which a plurality of single particles are attached to each other. The cathode active material according to the present invention includes the third particles PTC3 in a single particle shape, thereby providing a high capacity and high energy density of the secondary battery.

[0091] As an example, the third particles PTC3 may include a third coating layer on their surfaces. By including the third coating layer, the third particles PTC3 can effectively prevent structural collapse due to repeated charge and discharge, thereby improving the life characteristics of the secondary battery.

[0092] The third coating layer may include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the third 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 metals or non-metal elements. For example, the third coating layer may further include lithium, manganese, and / or nickel.

[0093] A method for measuring the metal content in the third coating layer of the third particles PTC3 may include performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the third particles PTC3. The boron and / or aluminum content in the third coating layer can be determined through the analysis. In addition to SEM-EDS, methods for measuring the metal content in the third coating layer include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0094] The average particle size of the third particles PTC3 may be 2 μm to 15 μm, 2 μm to 10 μm, or 2 μm to 5 μm. The average particle size of the third particles PTC3 may be larger than the average particle size of the first particles PTC1.

[0095] In one embodiment, the average particle size of the third particles PTC3 may be determined by measuring the particle sizes of approximately 30 third particles PTC3 randomly selected from an electron microscope photograph of the positive electrode active material, and determining the diameter (D50) of particles whose cumulative volume accounts for 50% by volume in the particle size distribution.

[0096] In another embodiment of the present invention, the third particles PTC3 may have the form of secondary particles formed by aggregation of primary particles. In this case, the third particles PTC3 may have a granular or spherical shape, and the average particle size of the third particles PTC3 may be 10 μm to 30 μm, 10 μm to 20 μm, or 10 μm to 15 μm.

[0097] In yet another embodiment of the present invention, the third particles PTC3 may be present in a mixed form of a compound in the form of a single particle and a compound in the form of a secondary particle.

[0098] 4th particle PTC4 The fourth particles PTC4 may include a lithium compound represented by the following Chemical Formula 4.

[0099] [Chemical formula 4] Li a4 Fe x4 D y4 O 4-b4 In Chemical Formula 4, 4.9≦a4≦5.1, 0.9≦x4≦1.05, 0≦y4≦0.05, 0≦b4≦0.05, and D is Al, Mg, or a combination thereof.

[0100] The fourth particles PTC4 may have a single particle shape similar to the first particles PTC1 described above. The description of the single particle may be the same or similar to that described for the first particles PTC1. In one embodiment, the fourth particles PTC4 may have a shape composed of one single particle. In another embodiment, the fourth particles PTC4 may have a shape in which a plurality of single particles are attached to each other. The cathode active material according to the present invention can provide high energy density by including the fourth particles PTC4 that function as a sacrificial cathode. The role of the fourth particles PTC4 will be described in detail below.

[0101] As an example, the fourth particles PTC4 may include a fourth coating layer on their surfaces. By including the fourth coating layer, the fourth particles PTC4 can effectively suppress structural collapse due to repeated charge and discharge, thereby improving the life characteristics of the secondary battery.

[0102] The fourth coating layer may include a magnesium-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the fourth 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 metals or non-metal elements. For example, the fourth coating layer may further include lithium, manganese, and / or nickel.

[0103] The average particle size of the fourth particles PTC4 may be 2 μm to 15 μm, 2 μm to 10 μm, or 3 μm to 10 μm. The average particle size of the fourth particles PTC4 may be larger than the average particle size of the first particles PTC1. When the fourth particles PTC4 include multiple single particles, the average size of the single particles of the fourth particles PTC4 may be larger than the average particle size of the first particles PTC1.

[0104] As an example, more than 30 second particles PTC2 are randomly selected from an electron microscope photograph of the positive electrode active material, and their particle sizes are measured. The diameter (D50) of the particles whose cumulative volume is 50% by volume in the particle size distribution can be determined as the average particle size.

[0105] The positive electrode active material can participate in the formation of the soil electrolyte interface (SEI) film on the negative electrode surface during charge and discharge. In particular, the Li ions present in the positive electrode during the initial charge reaction can undergo irreversible chemical and physical reactions at the negative electrode, converting into irreversible Li ions that no longer participate in charge and discharge reactions. This can lead to a decrease in the capacity of the positive electrode active material.

[0106] The fourth particles PTC4 according to the embodiment of the present invention are an oxide containing Fe and contain abundant Li, and therefore can serve as a sacrificial positive electrode that can compensate for irreversible Li. The fourth particles PTC4 can be decomposed in the formation process to provide Li, and do not need to participate in the subsequent charge / discharge process.

[0107] For example, when Li5FeO4 is used as a compound constituting the fourth particle PTC4, the fourth particle PTC4 can be decomposed between 3.5 and 3.9 V versus Li to provide four Li ions. When the fourth particle PTC4 is used in the content range described below, it can sufficiently compensate for irreversible Li.

[0108] The second particles PTC2 according to one embodiment of the present invention may include Li5FeO4, LiFeO2, LiFe5O8, or a combination thereof. For example, the second particles PTC2 may include Li5FeO4. Li5FeO4 can provide many Li atoms during the formation process, thereby compensating for the irreversible Li charge more effectively. This can enhance the effect of the sacrificial positive electrode.

[0109] 6 and 7, the cathode active material according to the embodiment of the present invention will be described in more detail. The first particles PTC1 and the second particles PTC2 may constitute a main active material, and the content of the main active material may be 75 to 85 parts by weight based on 100 parts by weight of the cathode active material.

[0110] Lithium iron phosphate-based positive electrode active material (first particle, PTC1) with an olivine crystal structure is cheaper than other positive electrode materials and has excellent stability and lifespan characteristics, but its low energy density makes it difficult to use at high voltages. Lithium manganese oxide-based positive electrode active material (second particle, PTC2) with a spinel structure has high operating voltage, excellent stability, and is cheaper, but like the first particle, PTC1, it has low energy density.

[0111] The cathode active material according to the present invention uses a mixture of first particles PTC1 and second particles PTC2 as the main active material, which is inexpensive and stable, while exhibiting high operating voltage and excellent life characteristics. The relatively low energy density can be improved by adding third particles PTC3, which have excellent capacity and output characteristics. Furthermore, the addition of fourth particles, which function as a sacrificial cathode, can provide even higher capacity and density.

[0112] The mixing ratio of the first particles PTC1 to the second particles PTC2 may be 4:6 to 6:4, or 4.5:5.5 to 5.5:4.5 by weight. The Mn content in the main active material composed of the first particles PTC1 and the second particles PTC2 may be 40 mol% to 70 mol%, 50 mol% to 70 mol%, or 50 mol% to 60 mol%, which is similar to the manganese content in a typical lithium manganese iron phosphate-based positive electrode active material (hereinafter referred to as LMFP).

[0113] By appropriately mixing and using the first particles PTC1 and the second particles PTC2 to have a manganese content, it is possible to obtain a cathode active material that exhibits electrochemical properties similar to those of LMFP but is easier to manufacture and process than LMFP. In this specification, the Mn content in the main active material refers to the number of moles of Mn relative to the total number of moles of all metals in the entire main active material, including the first particles PTC1 and the second particles PTC2, excluding lithium and trace amounts of doping materials (e.g., B in Formula 1 and Mg in Formula 2).

[0114] The content of the third particles PTC3 may be 10 to 20 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the third particles PTC3 satisfies this range, the capacity characteristics can be improved while minimizing the deterioration of the life and stability of the positive electrode active material.

[0115] The positive electrode active material of the present invention may have an improved composite compaction density. In one embodiment, the positive electrode active material of the present invention may have a compaction density of 2 g / cc to 3 g / cc, 2.5 g / cc to 2.8 g / cc, or 2.6 g / cc to 2.7 g / cc.

[0116] A lithium secondary battery including the positive electrode active material of the present invention may have an excellent average voltage. In one embodiment, the average voltage of the lithium secondary battery of the present invention may be 3.2 V to 4.5 V. For example, the operating voltage range may be 3.5 V to 3.7 V, or 3.55 V to 3.65 V. In addition, the energy density of the lithium secondary battery of the present invention may be 450 Wh / kg to 600 Wh / kg, 500 Wh / kg to 600 Wh / kg, or 500 Wh / kg to 550 Wh / kg.

[0117] A lithium secondary battery including the positive electrode active material of the present invention can have improved life characteristics. In one embodiment, the lithium secondary battery of the present invention may have a capacity retention rate of 95% or more after 50 charge / discharge cycles at a constant current of 1.0 C at the above-mentioned voltage. For example, the capacity retention rate may be 98% to 100%, or 99% to 100%.

[0118] Examples of the present invention and comparative examples are described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0119] Preparation Example 1: Preparation of first particles in single particle form Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 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 120°C for 4 hours. The dried mixture was calcined at 750°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized to obtain primary particles in the form of single particles. The average size of the primary particles was approximately 200nm to 300nm.

[0120] Preparation Example 2: Preparation of primary particles in the form of secondary particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.004. 10 wt% glucose was further 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 in a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The average size of the primary particles within the primary particles was approximately 100 nm to approximately 200 nm.

[0121] Preparation Example 3: Preparation of secondary particles 0.170g of MnSO4H2O and 0.228g of (NH4)2S2O8 were dissolved in 100ml of distilled water, and sulfuric acid was added to adjust the pH to 1. The mixture was then reacted at 130°C for 10 hours to obtain a solid precipitate. The resulting precipitate was washed several times with distilled water and dried at 300°C for 3 hours to obtain solid MnO2 with an average particle size of 5μm.

[0122] Li2CO3 and the synthesized MnO2 were mixed so that the molar ratio of Li to Mn was 1:2, and heated at 600°C for 10 hours to synthesize LiMn2O4 particles with an average particle size of 7 μm.

[0123] Preparation Example 4: Preparation of third particles in single particle form A high-nickel precursor was produced using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 93:5:2 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, and sodium hydroxide were added to a reactor and reacted. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 210°C for 24 hours to obtain small-particle precursors (NiSO4·6H2O) with an average particle size of approximately 4 μm. 0.93 0Co 0.05 Mn 0.02 (OH)2) powder was obtained.

[0124] The high-nickel precursor and anhydrous lithium hydroxide (LiOH) were dry mixed using a Henschel mixer. The lithium and transition metals were mixed in a molar ratio of approximately 1:1. The transition metals were the sum of the transition metals contained in the high-nickel precursor (Ni + Co + Mn). A melting agent was further added to the mixture, and the mixture was heat-treated (i.e., calcined) in an oxygen atmosphere at approximately 750°C for 15 hours to synthesize second particles, which are the high-nickel positive electrode active material. The second particles were then pulverized in a jet mill at a pressure of 3 bar.

[0125] The second particles were washed by adding them to distilled water. Boron oxide and aluminum oxide were added in an amount of 3 mol% based on the total transition metal of the second particles to perform boron and aluminum coating. The second particles were dried at 150°C for 12 hours and then heat-treated (i.e., surface-treated) at about 700°C in an oxygen atmosphere for 15 hours.

[0126] Production Example 5: Production of fourth particles in single particle form To prepare Li5FeO4, LiOH·H2O and Fe2O3 were mixed in the ratios of Li:Fe = 5:1 and 6:1, respectively, and the mixed powder was then milled in a Spex mill for 30 minutes, followed by pelletization at a pressure of 6.1 to 6.3 tons. The pellets were then calcined at 850 °C for 20 hours.

[0127] Production Example 6: Production of main active material The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 46:54 to prepare a main active material.

[0128] Manufacturing Example 7 The first particles of Preparation Example 2 and the second particles of Preparation Example 3 were mixed in a weight ratio of 55:45 to prepare a main active material.

[0129] Example 1: Preparation of final positive electrode active material The main active material of Preparation Example 6, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a weight ratio of 79.6:19.9:0.5 to prepare a positive electrode active material.

[0130] Example 2 The main active material of Preparation Example 6, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a weight ratio of 79.2:19.8:1 to prepare a positive electrode active material.

[0131] Example 3 The main active material of Preparation Example 6, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a weight ratio of 78.8:19.7:1.5 to prepare a positive electrode active material.

[0132] Example 4 The main active material of Preparation Example 7, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a weight ratio of 79.6:19.9:0.5 to prepare a positive electrode active material.

[0133] Example 5 The main active material of Preparation Example 7, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a weight ratio of 79.2:19.8:1 to prepare a positive electrode active material.

[0134] Example 6 The main active material of Preparation Example 7, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a weight ratio of 78.8:19.7:1.5 to prepare a positive electrode active material.

[0135] Comparative Example 1 A positive electrode active material was prepared by mixing the main active material of Preparation Example 6 and the third particles of Preparation Example 4 in a weight ratio of 80:20, excluding the fourth particles.

[0136] Comparative Example 2 The main active material of Preparation Example 6, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a weight ratio of 78.4:19.6:2 to prepare a positive electrode active material.

[0137] Comparative Example 3 The main active material of Preparation Example 7 and the third particles of Preparation Example 4 were mixed in a weight ratio of 80:20, excluding the fourth particles, to prepare a positive electrode active material.

[0138] Comparative Example 4 The main active material of Preparation Example 7, the third particles of Preparation Example 4, and the fourth particles of Preparation Example 5 were mixed in a weight ratio of 78.4:19.6:2 to prepare a positive electrode active material.

[0139] Cathode manufacturing A positive electrode active material slurry was prepared by mixing 95 wt% of the final positive electrode active material, 3 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon black conductive material in N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0140] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal 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.

[0141] Evaluation example 1: Analysis of the surface of the positive electrode active material SEM images of the first particles prepared in Preparation Examples 1 and 2 are shown in Figures 8a to 8d. SEM images of the second particles prepared in Preparation Example 3 are shown in Figures 9a and 9b. SEM images of the third particles prepared in Preparation Example 4 are shown in Figures 10a and 10b. SEM images of the fourth particles prepared in Preparation Example 5 are shown in Figure 11.

[0142] 8a and 8b, the primary particles according to Preparation Example 1 of the present invention are in the form of nano-sized fine single particles. 8c and 8d, the primary particles according to Preparation Example 2 of the present invention are in the form of spherical secondary particles formed by aggregation of primary particles. Meanwhile, the primary particles according to Preparation Example 2 are smaller and more uniform in size than the primary particles according to Preparation Example 1.

[0143] 9a and 9b, the second particles have a secondary particle form formed by aggregation of primary particles, and FIG. 10a and 10b, the third particles have a form formed by one single particle or multiple single particles attached to each other. FIG. 11, the fourth particles also have a single particle form.

[0144] Evaluation example 2: Evaluation of active materials The average pellet density (PD) of the positive electrodes of Examples 1 to 6 and Comparative Examples 1 to 4 is shown in Table 1. The average pellet density was measured by placing 3 g of the positive electrode active material in a pellet mold and applying a force of US 4.0 tons for 30 seconds.

[0145] [Table 1]

[0146] Referring to Table 1, it can be seen that the positive electrode active materials according to Examples 1 to 6 have similar average compressed densities when compared with the positive electrode active materials according to Comparative Examples 1 to 4.

[0147] Evaluation example 3: Battery characteristic evaluation The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 6 and Comparative Examples 1 to 4 were evaluated.

[0148] The lithium secondary battery was initially charged under constant current (0.2 C) and constant voltage (4.25 V) conditions, and after a 10-minute rest, discharged to 2.5 V under constant current (0.2 C) conditions to perform the initial charge-discharge. Thereafter, 50 charge-discharge cycles were performed at 0.2 C / 0.2 C. The battery characteristic evaluation results are shown in Table 2 below.

[0149] [Table 2]

[0150] Referring to Table 2, it can be seen that the positive electrode active materials according to Examples 1 to 6 have similar average voltages and efficiencies compared to the positive electrode active materials according to Comparative Examples 1 to 4. It can also be seen that the positive electrode active materials according to Examples 1 to 6 have similar life characteristics compared to the positive electrode active materials according to Comparative Examples 1 to 4, while exhibiting significantly increased energy densities.

[0151] In Examples 3 and 6, where the sacrificial cathode content is 1.5 wt%, the battery efficiency is about 90%, which is lower than the anode efficiency of 91.5%, confirming that there is no capacity improvement effect.

[0152] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention. [Explanation of symbols]

[0153] 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. First particles having an olivine structure and including a compound represented by the following Chemical Formula 1: Second particles having a spinel structure and including a compound represented by the following Chemical Formula 2: a third particle having a layered structure and including a compound represented by the following Chemical Formula 3; and fourth particles including a compound represented by Chemical Formula 4: The content of the third particles is 10 to 20 parts by weight based on 100 parts by weight of the positive electrode active material, [Chemical formula 1] Li a1 Fe x1 B y1 PO 4-b1 In the formula 1, 0.8≦a1≦1.2, 0.1≦x1≦1.0, 0.001≦y1≦0.05, 0≦b1≦0.05, and x1+y1=1; B is at least one element selected from the group consisting of Ti, Mg, V, and Nb; [Chemical formula 2] Li a2 Mn x2 MM y2 O 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 1.9≦x2≦2.05, 0≦y2≦0.05, and 0≦b2≦0.05; [Chemical formula 3] Li a3 Ni x3 Co y3 C z3 O 2-b3 In Chemical Formula 3, 0.8≦a2≦1.2, 0.9≦x3≦1.0, 0≦y3≦0.1, 0≦z3≦0.1, 0≦b3≦0.05, and x3+y3+z3=1; C is Al, Mn, or a combination thereof; [Chemical formula 4] Li a4 Fe x4 D y4 O 4-b4 In Chemical Formula 4, 4.9≦a4≦5.1, 0.9≦x4≦1.05, 0≦y4≦0.05, 0≦b4≦0.05, and D is Al, Mg, or a combination thereof.

2. 10. The cathode active material of claim 1, wherein the fourth particles are configured to be electrochemically inactive after initial cycles.

3. 2. The positive electrode active material of claim 1, wherein the content of the fourth particles is 0.05 to 1.5 parts by weight based on 100 parts by weight of the positive electrode active material.

4. the first particles and the second particles constitute a main active material, 2. The positive electrode active material of claim 1, wherein the content of the main active material is 75 to 85 parts by weight based on 100 parts by weight of the positive electrode active material.

5. The positive electrode active material of claim 4 , wherein the Mn content of the main active material is 40 mol % to 70 mol %.

6. the first particles include at least one first primary particle; The positive electrode active material of claim 1 , wherein the second particles have a secondary particle form in which a plurality of second primary particles are aggregated.

7. The positive electrode active material according to claim 6 , wherein the average size of the first primary particles is smaller than the average size of the second primary particles.

8. the first particles have a single particle form; a first average particle size of the first particles is 0.5 μm to 2.5 μm; The positive electrode active material of claim 6 , wherein the first primary particles have an average size of 200 nm to 300 nm.

9. The first particles include a plurality of primary particles aggregated together, a first average particle size of the first particles is 3 μm to 10 μm; The cathode active material of claim 6 , wherein the first primary particles have an average size of 100 nm to 200 nm.

10. The positive electrode active material of claim 6 , wherein the second primary particles have an average size of 0.5 μm to 3 μm.

11. the first particles include a first coating layer containing carbon; The positive electrode active material of claim 1 , wherein the carbon content in the first particles is 1.5 wt % to 2.5 wt %.

12. the third particles have a single particle morphology; The positive electrode active material of claim 1 , wherein the third particles have a third average particle size of 2 μm to 5 μm.

13. the third particles have a form in which a plurality of single particles are attached to each other, The positive electrode active material according to claim 1 , wherein a first average particle size of the first particles is smaller than an average size of the plurality of single particles.

14. The positive electrode active material according to claim 1 , wherein the fourth particles have a single particle form.

15. The positive electrode active material of claim 1 , wherein the fourth particles have a fourth average particle size of 3 μm to 10 μm.

16. 2. The positive electrode active material of claim 1, wherein the positive electrode active material has a compressed density of 2.6 g / cc to 2.8 g / cc.

17. a positive electrode current collector; a positive electrode active material layer on the positive electrode current collector, The positive electrode for a lithium secondary battery, wherein the positive electrode active material layer comprises the positive electrode active material of claim 1 , a conductive material, and a binder.

18. 18. The positive electrode for a lithium secondary battery of claim 17, wherein the content of the binder is 0.5 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer.

19. 18. The positive electrode for a lithium secondary battery according to claim 17, wherein the conductive material is present in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer.

20. The positive electrode according to claim 17 ; a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector; a separator between the positive electrode and the negative electrode, The negative electrode active material layer of the lithium secondary battery contains a silicon-based active material.

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