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

Abstract

To provide a positive electrode active material with excellent capacity, high energy density, and excellent lifespan characteristics. [Solution] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode containing the same, and a lithium secondary battery containing the same, and more particularly to a positive electrode active material comprising a first particle having an olivine crystal structure and a first average particle size, a second particle having an olivine crystal structure and a second average particle size smaller than the first average particle size, and a third particle having a layered crystal structure, a positive electrode containing the same, and a lithium secondary battery containing the same. Each of the first and second particles contains a compound represented by chemical formula (1), the third particle contains a compound represented by chemical formula (2), the first particle is a spherical secondary particle containing a plurality of primary particles aggregated with each other, and the second particle is a single particle.

Description

[Technical Field]

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

[0002] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for rechargeable batteries with high energy density and high capacity has been rapidly increasing. Therefore, research and development to improve the performance of lithium-ion rechargeable batteries is actively underway.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode containing an active material capable of inserting and deintercalating lithium ions, and an electrolyte. It produces electrical energy through oxidation and reduction reactions that occur when lithium ions are inserted / deintercalated at the positive and negative electrodes. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] One problem that the present invention aims to solve is to provide a positive electrode active material having excellent capacity, high energy density, and excellent lifetime characteristics.

[0005] Another problem that the present invention aims to solve is to provide a lithium secondary battery having high energy density, high operating voltage, and excellent life characteristics. [Means for solving the problem]

[0006] The positive electrode active material according to an embodiment of the present invention can include first particles having an olivine crystal structure and a first average particle size, second particles having an olivine crystal structure and a second average particle size smaller than the first average particle size, and third particles having a layered crystal structure. Each of the first particles and the second particles contains a compound represented by the following chemical formula (1), the third particle contains a compound represented by the following chemical formula (2), the first particles are spherical secondary particles containing a plurality of primary particles aggregated with each other, and the second particles can be single particles. [Chemical formula 1] Li a1 Fe x1 B1 y1 PO 4-b1 ···(1) (In the chemical formula (1), 0.8 ≤ a1 ≤ 1.2, 0.90 ≤ x1 ≤ 0.999, 0.001 ≤ y1 ≤ 0.1, 0 ≤ b1 ≤ 0.05, and 0.99 ≤ x1 + y1 ≤ 1.01, and B1 can be at least one of Ti, Mg, V, Al, Mn, or a combination thereof.) [Chemical formula 2] Li a2 Ni x2 Co y2 Ma z2 X c2 O 2-b2 ···(2) (In the chemical formula (2), 0.8 ≤ a2 ≤ 1.2, 0.8 ≤ x2 < 1.0, 0 < y2 ≤ 0.1, 0 ≤ z2 ≤ 0.1, 0 ≤ c2 ≤ 0.05, 0 < b2 ≤ 0.05, and 0.9 ≤ x2 + y2 + z2 + c2 ≤ 1.1, and Ma is at least one of Al, Mn, or a combination thereof, and X can be at least one of Ti, Mg, Zr, Al, or a combination thereof.)

[0007] The positive electrode for a lithium secondary battery according to an embodiment of the present invention includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, and the positive electrode active material layer can include the positive electrode active material, a conductive material, and a binder.

[0008] The lithium secondary battery according to an embodiment of the present invention may further include the positive electrode, a negative electrode current collector, a negative electrode including a negative electrode active material layer on the negative electrode current collector, and a separator between the positive electrode and the negative electrode.

Advantages of the Invention

[0009] The positive electrode active material according to an embodiment of the present invention can improve the blending density, capacity, and energy density by blending an olivine-based lithium compound having different sizes and a layered lithium compound. The lithium secondary battery according to an embodiment of the present invention can have a relatively high average voltage and excellent lifespan.

Brief Description of the Drawings

[0010] [Figure 1] It is a conceptual diagram briefly showing a lithium secondary battery according to an embodiment of the present invention. [Figure 2] It is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention, which has a cylindrical battery form. [Figure 3] It is a cross-sectional view showing a lithium secondary battery according to an embodiment of the present invention. [Figure 4] It is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention, which has a rectangular battery form. [Figure 5] It is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention, which has a pouch-type battery form. [Figure 6] It is an enlarged view of the positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. [Figure 7A] It is a SEM image of the positive electrode active material of Production Example 1 of the present invention. [Figure 7B] It is a SEM image of the positive electrode active material of Production Example 2 of the present invention. [Figure 7C] It is a SEM image of the positive electrode active material of Production Example 3 of the present invention.

Modes for Carrying Out the Invention

[0011] To fully understand the structure and effects of the present invention, preferred embodiments will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be embodied in various forms and modified in many ways. This description of the embodiments is merely provided to ensure that the disclosure of the present invention is complete and to fully inform those who are ordinary skill in the art to which the invention pertains.

[0012] In this specification, when a given component is referred to as being on another component, it means either that it is formed directly on the other component or that a third component is interposed between them. Furthermore, in the drawings, the thickness of components is exaggerated for the sake of efficient illustration of the technical content. Parts indicated by the same reference number throughout the specification refer to the same component.

[0013] Unless otherwise specified herein, a singular noun may also include a plural noun. Furthermore, unless otherwise specified, “A or B” may mean “including A, including B, or including A and B.” As used herein, “comprises” and / or “comprising” does not preclude the presence or addition of one or more other components of the component mentioned.

[0014] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0015] In this specification, each of the following phrases may include any one of the items listed together with the phrase in question, or any possible combination thereof.

[0016] Unless otherwise defined herein, particle size may refer to average particle size. Furthermore, particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. Average particle size (D50) can be measured by methods widely known to those skilled in the art, such as using a particle size analyzer, or by using a transmission electron microscope or scanning electron microscope. Alternatively, it can be measured using a dynamic light-scattering device, and after data analysis to count the number of particles for each particle size range, the average particle size (D50) can be calculated. Alternatively, it can be measured using the laser diffraction method. When measuring using the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac MT 3000), and after irradiating with ultrasound at approximately 28 kHz at an output of 60 W, the average particle size (D50) based on the 50% standard of the particle size distribution in the analyzer can be calculated.

[0017] Figure 1 is a simplified conceptual diagram showing a lithium secondary battery according to one embodiment of the present invention. Referring to Figure 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 can be separated from each other via a separator 30. The separator 30 can be placed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 can be in contact with the electrolyte ELL. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated in the electrolyte ELL.

[0019] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. Within the electrolyte ELL, the lithium ions can move towards the positive electrode 10 or the negative electrode 20 by passing through the separator 30.

[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 one embodiment of the present invention will be given below with reference to Figure 6. Al can be used as the current collector COL1, but is not limited to it.

[0021] negative electrode 20 The negative electrode 20 for the lithium secondary battery may include 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% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0023] The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres well to the current collector COL2. The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

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

[0025] The aqueous 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 cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0027] The dry binder may be a polymeric substance that can be formed into fibers, 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 electrodes, and any electronically conductive material that does not cause chemical changes in the battery can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0029] As the current collector COL2, a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof can be selected and used.

[0030] 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 capable of doping and undoping lithium, or a transition metal oxide.

[0031] Examples of the material capable of reversibly intercalating / deintercalating lithium ions can include, as a carbon-based negative electrode active material, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon can include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon can include soft carbon or hard carbon, mesophase pitch carbide, fired 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, SiO x (0 < x < 2), a Si-Q alloy (where Q is selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination 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 amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (core) assembled from primary silicon particles and a first amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0035] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon first coating layer located on the surface of this core.

[0036] The Si-based or Sn-based anode active material can be used in combination with a carbon-based anode 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. Such a separator 30 can be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can also be used.

[0038] The separator 30 may include a porous substrate and a first coating layer containing organic matter, inorganic matter, or a combination thereof located on one or both sides of the porous substrate.

[0039] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon®, and polytetrafluoroethylene, or from copolymers or mixtures of two or more of these polymers.

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

[0041] The inorganic material may include, but is not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and inorganic particles selected from combinations thereof.

[0042] The organic and inorganic materials may exist mixed in a single first coating layer, or they may exist in a form in which a first coating layer containing organic material and a first coating layer containing inorganic material are laminated together.

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

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

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

[0046] Examples of carbonate-based 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] Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0048] As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. As ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes may be used.

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

[0050] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and the cyclic carbonates and linear carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0051] The aforementioned lithium salts dissolve in organic solvents and act as a source of lithium ions within the battery, enabling the basic operation of lithium secondary batteries and promoting the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 It may contain one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluorobis(oxalate) phosphate (LiDFOB), and lithium bis(oxalate) borate (LiBOB).

[0052] Lithium-ion battery Lithium secondary batteries can be classified into cylindrical, rectangular, pouch-shaped, coin-shaped, etc., depending on their form. Figures 2 to 5 are schematic diagrams showing a lithium secondary battery according to one embodiment, where Figure 2 is a cylindrical type, Figure 3 is a cross-sectional view, Figure 4 is a rectangular type, and Figure 5 is a pouch-shaped battery. Referring to Figures 2 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with 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, negative electrode 20, and separator 30 can be impregnated with an electrolyte (not shown). The lithium secondary battery 100 can include a sealing member 60 that seals the case 50, as shown in Figure 2. Also, in Figure 3, the lithium secondary battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in Figures 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0053] A lithium secondary battery according to one embodiment of the present invention can be applied to automobiles, mobile phones, and / or various forms of electrical devices, and the present invention is not limited thereto.

[0054] Figure 6 is an enlarged view of the positive electrode active material layer of a lithium secondary battery according to one embodiment of the present invention. Referring to Figure 6, as described above, the positive electrode active material layer AML1 (see Figure 1) can include first particles PTC1, second particles PTC2, third particles PTC3, conductive material CDM, and binder BND. Multiple first particles PTC1, multiple second particles PTC2, and multiple third particles PTC2 can constitute the positive electrode active material according to one embodiment of the present invention.

[0055] The positive electrode active material layer AML1 may further contain additives that can act as a sacrificial cathode.

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

[0057] The binder BND can bond the first to third particles PTC1, PTC2, PTC3 and the conductive material CDM to each other. As an example, the binder (BND) may include, but is not limited to, at least one of the following: polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, 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, nylon, or a combination thereof.

[0058] The 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) may contain at least one of the following: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, or carbon nanotubes; metallic materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or combinations thereof.

[0059] The following provides a more detailed explanation of each of the three particles: the first particle PTC1, the second particle PTC2, and the third particle PTC3.

[0060] 1st particle PTC1 The first particle PTC1 may exist in a polycrystalline form as a secondary particle formed by the aggregation of multiple primary particles. In other words, a single first particle PTC1 can contain multiple primary particles aggregated together. The first particle PTC1 may have a spherical or elliptical shape.

[0061] In one embodiment, the first particle PTC1 may include a coating layer on its surface. The coating layer may cover the entire surface of the first particle PTC1 or a portion of its surface. For example, the coating layer may contain carbon and / or a carbon-containing compound. The first particle PTC1 may have improved structural stability and improved electrical conductivity due to the coating layer.

[0062] The coating layer may further contain at least one selected from the group consisting of titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds. 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, compounds thereof, or mixtures thereof. The metal-containing compound may further contain other metals or nonmetallic elements. For example, the metal-containing compound may further contain lithium.

[0063] In one embodiment, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the first primary particles. The grain boundary coating layer may be located inside the first particle PTC1. The grain boundary coating layer may be formed by coating along the interfaces between the first primary particles inside the first particle PTC1. Again, the grain boundary coating layer can mean a material coated on the grain boundaries inside the first particle PTC1. The grain boundary coating layer may include carbon and / or carbon-containing compounds. The grain boundary coating layer may further include at least one selected from the group consisting of titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds.

[0064] The interior of the first particle PTC1 described above can mean the entire interior of the first particle PTC1 excluding its surface. For example, the interior of the first particle PTC1 can mean the entire interior from a depth of approximately 10 nm on the surface of the first particle PTC1, or the region from a depth of 10 nm to a depth of approximately 2 μm.

[0065] The structural stability of the first particle PTC1 is enhanced by further inclusion of grain boundary coatings, and a uniform coating layer can be formed on the surface of the first particle PTC1. Therefore, the lifetime characteristics of the positive electrode active material can be improved. Furthermore, the electrical conductivity of the first particle PTC1 can be further improved by further inclusion of grain boundary coatings.

[0066] The first particle PTC1 may contain carbon derived from the coating layer and / or grain boundary coating layer described above. The carbon content in the first particle PTC1 may be 0.5 wt% to 10 wt%, 1 wt% to 3 wt%, or 1.5 wt% to 2.5 wt%.

[0067] The average particle size of the first particle PTC1 may be between 2 μm and 15 μm, between 3 μm and 10 μm, or between 3 μm and 7 μm. For example, the first average particle size of the first particle PTC1 may be approximately 5 μm. In one embodiment, the average particle size can be measured with a particle size analyzer. The average particle size can mean the diameter (D50) of the particle whose cumulative volume in the particle size distribution is 50 volume%.

[0068] The average size of the first primary particles of the first particle PTC1 may be between 10 nm and 400 nm, between 20 nm and 300 nm, between 50 nm and 200 nm, or between 100 nm and 200 nm. In one embodiment, the average size of the first primary particles may mean the average diameter measured by arbitrarily selecting about 30 first primary particles from electron microscope images of the positive electrode active material. The size of the first primary particles may be uniform.

[0069] As described above, the first particle PTC1 can have a secondary particle shape in which nano-sized primary particles are densely aggregated. Due to the close aggregation of the primary particles, the first particle PTC1 can exhibit the following characteristics: The first particle PTC1 can have a spherical or elliptical shape. The average particle size (D50) of the first particle PTC1 may be between 2 μm and 15 μm. The porosity of the first particle PTC1 may be between approximately 20% and approximately 40%. The span value of the first particle PTC1 analyzed by a particle size analyzer may be between 0.3 and 0.75.

[0070] In this specification, porosity refers to the ratio of the volume occupied by pores to the total volume in any structure, and its unit is %. It can be used interchangeably with terms such as porosity, degree of porosity, and density. Porosity is measured by methods such as the Brunauer-Emmett-Teller (BET) method using nitrogen gas or the mercury osmosis method (Hg porosimeter), but the method of measuring porosity is not limited to these.

[0071] The first particle PTC1 may contain an olivine-based lithium compound represented by the following chemical formula (1).

[0072] [C1] Li a1 Fe x1 B1 y1 PO 4-b1 ...(1)

[0073] In the above chemical formula (1), 0.8 ≤ a1 ≤ 1.2, 0.90 ≤ x1 ≤ 0.999, 0.001 ≤ y1 ≤ 0.1, 0 ≤ b1 ≤ 0.05, and 0.99 ≤ x1 + y1 ≤ 1.01, where B1 can be at least one of Ti, Mg, V, Al, Mn, or a combination thereof. B1 can be a dopant doped with the first particle PTC1. For example, B1 can contain Ti. The dopant can control the size of the first primary particles of the first particle PTC1 to be uniform, thereby improving the charge-discharge efficiency and lifetime characteristics of the positive electrode active material.

[0074] The first particle PTC1 contains an olivine-based lithium compound with a stable crystalline structure, enabling it to have excellent lifetime characteristics and superior stability. Furthermore, by having a secondary particle shape formed by the aggregation of the first primary particles, it can exhibit improved capacity and lifetime characteristics. The first particle PTC1 can exhibit excellent electrical conductivity and superior low-temperature characteristics by further including not only a coating layer on the secondary particle surface but also a grain boundary coating layer on the surface of the first primary particle.

[0075] 2nd particle PTC2 The second particle PTC2 may have a single particle shape. In this specification, a single particle can mean a single particle that does not have an internal grain boundary. A single particle can mean a single particle, monolithic structure, single-body structure, or non-aggregated particle that exists on a morpholoegy in an independent phase where particles do not aggregate with each other. For example, a single particle may be a single crystal. Or, a single particle may be a particle containing several crystals. A single particle may be in a form that is separated by itself. Or, a single particle may be in a form in which two to 100 single particles are attached to each other.

[0076] The second particle PTC2 can be a nano-sized positive electrode active material. The second particle PTC2 may contain at least one second primary particle. The second particle PTC2 can be provided in various sizes. For example, the average particle size of the second particle PTC2 may be between 500 nm and 2.5 μm, or about 1 μm. The minimum particle size of the second particle PTC2, i.e., the size of the second primary particle, may be between 100 nm and 500 nm, or between 100 nm and 200 nm. In one embodiment, the average particle size can be measured with a particle size analyzer. The average particle size may mean the diameter (D50) of the particle whose cumulative volume in the particle size distribution is 50 volume%.

[0077] In one embodiment, the second particle PTC2 may include a first coating layer on its surface. The coating layer may cover the entire surface of the second particle PTC2 or a portion of its surface. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may further include at least one selected from the group consisting of titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds. 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, compounds thereof, or mixtures thereof. The metal-containing compound may further include other metals or nonmetallic elements. For example, the metal-containing compound may further include lithium. The second particle PTC2 may have improved structural stability and improved electrical conductivity due to the coating layer.

[0078] The second particle PTC2 may contain carbon derived from the coating layer described above. The carbon content in the second particle PTC2 may be 0.5 wt% to 5 wt%, 0.5 wt% to 3 wt%, or 0.5 wt% to 2 wt%. The carbon content of the second particle PTC2 may be lower than that of the first particle PTC1. This is because, as a single particle, the coating layer is less likely to form smoothly on the second particle PTC2 compared to the first particle PTC1, which is a secondary particle.

[0079] The second particle PTC2, like the first particle PTC1, may contain an olivine-based lithium compound represented by the chemical formula (1). The second particle PTC2 may contain a lithium compound with the same composition as the first particle PTC1, or it may contain a lithium compound with a different composition than the first particle PTC1.

[0080] In one embodiment, the second particle PTC2 may contain a lithium compound having the same composition as the first particle PTC1, but may have a different morphology from the first particle PTC1.

[0081] Third particle PTC3 The third particle PTC3 may be a secondary particle formed by the aggregation of multiple third primary particles, in a polycrystalline form similar to the first particle PTC1. In one embodiment, the third particle PTC3 may have a spherical or elliptical shape formed by the aggregation of third primary particles. Alternatively, the third particle PTC3 may have a random shape even if the third particles are aggregated. By including the third particle PTC3, which is a nickel-based cathode active material, the positive electrode active material according to one embodiment of the present invention can realize high capacity and high energy density in a secondary battery.

[0082] In one embodiment, the third particle PTC3 may include a third coating layer on its surface. By including the third coating layer, the structural breakdown due to repeated charging and discharging can be effectively suppressed. Therefore, the lifespan characteristics of the secondary battery can be improved.

[0083] The third coating layer may contain 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 compound thereof, or a mixture thereof. The metal-containing compound may further contain other metals or nonmetallic elements. For example, the third coating layer may further contain lithium, manganese, and / or nickel, etc.

[0084] A method for measuring the metal content in the third coating layer of the third particle PTC3 may include performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the third particle PTC3. Through this analysis, the content of boron and / or aluminum in the third coating layer can be confirmed. In addition to SEM-EDS, other methods such as inductively coupled plasma-mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES) may be used to measure the metal content in the third coating layer.

[0085] The average particle size of the third particle PTC3 may be 8 μm to 20 μm, 10 μm to 20 μm, or 12 μm to 18 μm. The average particle size of the third particle PTC3 may be larger than the average particle sizes of the first particle PTC1 and the second particle PTC2 described above. The size of the third primary particle of the third particle PTC3 may be larger than the size of the first primary particle of the first particle PTC1 and the second primary particle of the second particle PTC2.

[0086] In one embodiment, the average particle size can be determined by arbitrarily selecting approximately 30 third particles PTC3 from electron microscope images of the positive electrode active material, measuring their particle sizes, and then defining the diameter (D50) of the particle whose cumulative volume in the particle size distribution is 50% by volume as the average particle size.

[0087] The third particle PTC3 can contain a lithium nickel-based composite oxide as a nickel-based active material. For example, the third particle PTC3 can contain a high-nickel cathode active material containing a high amount of nickel. High-nickel cathode active materials can achieve high capacity and high performance.

[0088] Specifically, the third particle PTC3 may contain a lithium nickel-based composite oxide with a layered structure represented by the following chemical formula (2).

[0089] [Chemical formula 2] Li a2 Ni x2 Co y2 Ma z2 X c2 O 2-b2 ···(2)

[0090] In the chemical formula (2), 0.8 ≦ a2 ≦ 1.2, 0.8 ≦ x2 < 1.0, 0 < y2 ≦ 0.1, 0 ≦ z2 ≦ 0.1, 0 ≦ c2 ≦ 0.05, 0 < b2 ≦ 0.05, and 0.9 ≦ x2 + y2 + z2 + c2 ≦ 1.1, Ma is at least one of Al, Mn, or a combination thereof, and X can be at least one of Ti, Mg, Zr, Al, or a combination thereof. X can be a dopant doped with the third particle PTC3.

[0091] As another embodiment of the present invention, the third particle PTC3 can have a single particle shape. The description of the single particle can be the same as or similar to that described for the second particle PTC2 above. As one embodiment, the third particle PTC3 can have a shape composed of one single particle. As one embodiment, the third particle PTC3 can have a shape in which a plurality of single particles are attached to each other.

[0092] As another embodiment of the present invention, the second particle PTC2 can exist in a form in which a compound in the form of secondary particles and a compound in the form of single particles are mixed.

[0093] Referring to FIG. 6 again, the positive electrode active material according to the embodiment of the present invention will be described in more detail. The positive electrode active material of the present invention can include the first particle PTC1, the second particle PTC2, and the third particle PTC3.

[0094] According to embodiments of the present invention, the content of the first and second particles PTC1 and PTC2 may be 70% by weight or more relative to the total weight of the positive electrode active material, and the content of the third particle PTC3 may be 30% by weight or less relative to the total weight of the positive electrode active material. For example, the content of the first and second particles PTC1 and PTC2 may be 85% by weight relative to the total weight of the positive electrode active material, and the content of the third particle PTC3 may be 15% by weight.

[0095] As described above, the first particle PTC1 and the second particle PTC2 can be used as the main material, accounting for 70% or more of the total weight of the positive electrode active material. The first particle PTC1 and the second particle PTC2 are olivine-based active materials and are structurally stable. When the structurally stable first particle PTC1 and the second particle PTC2 are used as the main material of the positive electrode active material, a positive electrode with excellent lifetime characteristics and stability can be obtained.

[0096] The first particle PTC1 and the second particle PTC2, which constitute the main components of the positive electrode active material, can have a certain mixing ratio. For example, the mixing ratio of the first particle PTC1 and the second particle PTC2 may be 3:1 to 1:3, 2:1 to 1:2, or 1.5:1 to 1:1.5 based on weight.

[0097] While the first particle PTC1, which is a spherical secondary particle, has superior capacity and lifetime compared to the second particle PTC2, which is a single particle, there is a problem with the low pellet density and energy density of the cathode when the cathode is manufactured using only the first particle PTC1. When the first particle PTC1 and the second particle PTC2 are mixed in the weight ratio described above, an olivine-based cathode active material with superior lifetime and capacity and improved density can be obtained.

[0098] The content of the third particle PTC3 may be 30% by weight or less relative to the total weight of the positive electrode active material. For example, the content of the third particle PTC3 may be 5% to 30% by weight, 10% to 20% by weight, or 10% to 15% by weight relative to the total weight of the positive electrode active material.

[0099] If the content of the third particle PTC3, a high-nickel active material, is too low, the effect of improving the capacity and density of the lithium secondary battery may be minimal. If the content of the third particle PTC3 in the positive electrode active material is too high, the high-temperature stability and life characteristics of the positive electrode may decrease. When the content of the third particle PTC3 satisfies the range described above, a positive electrode active material can be obtained that exhibits high capacity and high energy density while also having excellent life and high-temperature stability.

[0100] Method for manufacturing positive electrode active material A method for manufacturing the first particle PTC1 according to one embodiment of the present invention will be described in detail.

[0101] First, the iron phosphate precursor, lithium source, carbon source, and dopant source can be added to a solvent and mixed. For example, the solvent may be water, ethanol, etc. The iron phosphate precursor may be a compound containing both iron (Fe) and phosphorus (P), or a mixture of an iron (Fe)-containing compound and a phosphorus (P)-containing compound. For example, the iron phosphate precursor may include FePO4·H2O, or a mixture of FeSO4 and H3PO4.

[0102] The lithium source may include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0103] The carbon source may include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0104] The dopant source may include oxides containing a dopant metal and / or chlorides containing a dopant metal. For example, the dopant source may include at least one selected from the group consisting of titanium oxide, magnesium oxide, vanadium oxide, and niobium oxide.

[0105] The mixture can be subjected to wet grinding. This wet grinding can be carried out using a conventional wet mill with temperature control. Specifically, the wet grinding can utilize at least one selected from a beads mill, ball mill, attrition mill, apex mill, super mill, and basket mill. Through the wet grinding process, the particles in the mixture can be ground to a fine size.

[0106] In one embodiment of the present invention, the wet grinding may be omitted. Specifically, in order to maximize the average particle size of the first particle PTC1 finally produced, wet grinding of the precursor particles may be omitted.

[0107] A mixture can be dried by removing the solvent from the mixture. In one embodiment of the present invention, forming a dried mixture may involve performing spray drying on the mixture. Spray drying can be performed using commonly used spray drying equipment. For example, spray drying can be performed using at least one selected from ultrasonic spray dryers, air nozzle spray dryers, ultrasonic nozzle spray dryers, filter expansion droplet generators, and electrostatic spray dryers.

[0108] In the wet grinding process, the particles, which have been finely ground to the primary particle size, can aggregate with each other through the spray drying process to form secondary particles. Therefore, by adjusting the flow rate and velocity of the transport gas in the spray drying process, the temperature, the residence time in the reactor, and the internal pressure, the first particle PCT1 can be formed into secondary particles of the desired size.

[0109] In one embodiment, the mixture to be spray-dried may have a total solid content of 20 wt% to 40 wt%. The total solid content can be expressed as a percentage of the weight of the solid material remaining after the solvent evaporates (i.e., the dried mixture) relative to the total weight of the mixture (i.e., the spray liquid). For example, the spray liquid may have a total solid content of approximately 30 wt%.

[0110] If the solid content is less than 20%, the average particle size of the first particle PTC1 will be small, which can lead to problems with low productivity. If the solid content is greater than 40%, it becomes difficult to control the average particle size of the first particle PTC1, and the size deviation of the first particle PTC1 may become large.

[0111] The spray liquid according to this embodiment can have a viscosity of 1500 mPa·s or more and 2500 mPa·s or less based on the solid content. For example, the spray liquid can have a viscosity of approximately 2000 mPa·s.

[0112] In one embodiment, the input rate for spray drying may be 0.1 kg / min or more and 0.9 kg / min or less. The input rate for spray drying can be defined as the weight of the solvent and raw material mixture added per hour. In one embodiment, the input rate for spray drying according to the present invention may be approximately 0.5 kg / min.

[0113] In one embodiment, spray drying can be carried out at a temperature of 100°C to 300°C. For example, spray drying can be carried out at a temperature of 200°C to 300°C, above 200°C and below 300°C, or above 230°C and below 270°C. The spray gas (e.g., air) used for spray drying can be introduced at a first temperature and discharged at a second temperature. For example, the first temperature may be 200°C to 250°C. The second temperature may be 80°C to 150°C.

[0114] The injection pressure of the spray liquid may be between 0.3 MPa and 0.7 MPa. For example, the injection pressure of the spray liquid may be approximately 0.5 MPa.

[0115] If the amount of spray drying, the pressure of spray drying, and the temperature satisfy the ranges described above, the first particle PTC1 can have a spherical shape and the desired porosity.

[0116] The flow rate of the spray liquid in spray drying may be between 30 ml / min and 80 ml / min. If the flow rate is less than 30 ml / min, problems such as nozzle clogging and reduced productivity may occur. If the flow rate is greater than 80 ml / min, problems such as incomplete drying of the mixture due to moisture condensation inside the spray dryer may occur. The inlet pressure of the spray liquid may be between 0.3 MPa and 0.7 MPa. For example, the inlet pressure of the spray liquid may be approximately 0.5 MPa.

[0117] The dried mixture can be calcined under an inert atmosphere. The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The calcination temperature may be 500°C to 1000°C or 600°C to 800°C. The calcination time may be 4 hours to 20 hours or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 containing the compound of chemical formula (1) described above may be formed.

[0118] A dry grinding process can be performed on the calcined first particle PTC1. The calcined mixture can be ground using an air jet mill or the like. The calcined mixture can be ground at a rotational speed of 0 rpm to 7000 rpm. For example, the calcined mixture can be ground at a rotational speed of 4000 rpm to 7000 rpm, 4000 rpm to 6000 rpm, or 4500 rpm to 5000 rpm. In one embodiment, dry grinding may be omitted.

[0119] If the rotational speed during the grinding stage satisfies the range described above, the first particle PTC1 can be maintained to have the shape of a secondary particle. Therefore, the first particle PTC1 can have the shape of a secondary particle as shown in Figure 6.

[0120] A method for producing the first particle PTC1 according to one embodiment of the present invention will be described in detail. First, an iron phosphate precursor, a lithium source, a carbon source, and a dopant source can be added to a solvent and mixed. For example, the solvent may be water, ethanol, or the like.

[0121] The iron phosphate precursor, lithium source, carbon source, and dopant source may be the same as, or similar to, those used in the method for producing the first particle PTC1 as described above.

[0122] The mixture can be subjected to wet grinding. The wet grinding process may be the same as, or similar to, the method for producing the first particle PTC1 described above.

[0123] The solvent can be removed from the mixture to form a dried mixture. Forming a dried mixture can include performing a direct evaporation method on the mixture. For example, the direct evaporation method can include static drying or spray drying. Static drying is preferable to form the second particle PTC2 as a single particle.

[0124] The dried mixture can be calcined under an inert atmosphere. The conditions for the calcination step may be the same as, or similar to, those for, the method for producing the first particle PTC1 described above. Through the calcination step, a second particle PTC2 having the composition of chemical formula (1) can be formed.

[0125] A dry grinding process can be performed on the calcined second particle PTC2. Therefore, the second particle PTC2 can have the shape of secondary particles as shown in Figure 6.

[0126] A method for producing the third particle PTC3 according to embodiments of the present invention will be described in detail. First, a high-nickel precursor can be prepared. The high-nickel precursor may contain Ni of chemical formula (2) described above. The content of Ni relative to the total metal content in the high-nickel precursor may be greater than 80 at%. In one embodiment, the high-nickel precursor may further contain at least one of Co, Al, Mn, or a combination thereof.

[0127] In one embodiment, a high-nickel precursor can be obtained by coprecipitation. For example, the coprecipitation method may include dissolving a transition metal raw material in a solvent such as distilled water, and continuously introducing the transition metal salt solution into a reactor together with a chelating agent and a basic aqueous solution to induce precipitation. After collecting the precipitate in slurry form, the slurry solution is filtered and dried to obtain a high-nickel precursor, which is a metal composite oxide.

[0128] In one embodiment of the present invention, the transition metal raw material may include a metal salt of Ni. The transition metal raw material may further include at least one metal salt from Co, Al, and Mn. The metal salt is not particularly limited, as sulfates, nitrates, acetates, halides, hydroxides, etc., can be used and are soluble in a solvent. The transition metal raw material according to this embodiment includes a nickel salt and a cobalt salt, and may further include an aluminum salt and / or a manganese salt. The transition metal raw materials can be mixed by adjusting the molar ratio so that the high-nickel precursor has a Ni content of 80 at% or more.

[0129] A mixture can be formed by mixing a high-nickel precursor and a lithium source in a fixed ratio. For example, the high-nickel precursor and lithium source can be mixed in a molar ratio of about 1:1. The lithium source may include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0130] The mixture can be dried by removing the solvent. The dried mixture can be calcined. The calcination temperature may be 700°C to 1,000°C or 900°C to 1,000°C. The calcination can be carried out in an oxidizing atmosphere such as air or oxygen. The heat treatment time for the calcination may be 10 hours to 30 hours. In another embodiment of the present invention, pre-calcination may be additionally performed at 150°C to 800°C before the calcination process.

[0131] Through the aforementioned calcination process, a third particle PTC3 can be formed from a mixture containing a high-nickel precursor and a lithium source. The synthesized third particle PTC3 can then be subjected to a grinding process.

[0132] A coating process can be performed on the pulverized third particle PTC3. Specifically, the third particle PTC3 and the coating raw material can be placed in a solvent and mixed. For example, the coating raw material may include boron and / or aluminum. After filtering and drying the third particle PTC3, a surface treatment can be performed on the third particle PTC3. The surface treatment may include a heat treatment process performed in an oxidizing atmosphere such as air or oxygen. The surface treatment can be performed at a temperature of 500°C to 800°C.

[0133] In another embodiment of the present invention, the coating step may include a dry coating step. For example, the third particle PTC3 and the coating raw material can be placed in a dry coating machine without a solvent and stirred to mix them. The surface treatment can then be performed on the resulting dry mixture.

[0134] In embodiments of the present invention, the coating step can be omitted.

[0135] The first to third particles PTC1, PTC2, and PTC3, each manufactured by the method described above, can be mixed together to produce a positive electrode active material according to one embodiment of the present invention. The content of the third particle PTC3 in the positive electrode active material may be 10% to 20% by weight, or 10% to 15% by weight, relative to the total weight of the positive electrode active material.

[0136] The content of the first and second particles PTC1 and PTC2 may be 80% to 90% by weight, or 85% to 90% by weight, relative to the total weight of the positive electrode active material. The mixing ratio of the first particle PTC1 to the second particle PTC2 may be 3:1 to 1:3, or 2:1 to 1:2, based on weight.

[0137] Carbon elemental analysis according to embodiments of the present invention can be performed using an Elementar Micro Cube elemental analyzer. The specific operating procedure and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed in an automatic sampling tray, and introduced into the combustion tube through a ball valve, where it is burned at a combustion temperature of 1000°C. Next, the burned gas is reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0138] A method for measuring carbon content according to one embodiment of the present invention can be obtained by performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the surface of particles and conducting quantitative analysis. In addition to SEM-EDS, other methods such as inductively coupled plasma-mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES) can be used to measure carbon content.

[0139] The following describes examples and comparative examples relating to one embodiment of the present invention. However, the following examples are merely one embodiment of the present invention, and the present invention is not limited to the following examples.

[0140] Manufacturing Example 1: Manufacturing of first particles in secondary particle form Iron phosphate precursor (Fe1PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.03. 10 wt% glucose was added to the mixture. The slurry mixture was spray-dried and evaporated under conditions of a spray pressure of 0.5 MPa and a temperature of 230°C. The dried mixture was calcined under a nitrogen atmosphere at 750°C for 10 hours to obtain primary particles in secondary particle form. The average size of the primary particles within the primary particles was approximately 100 nm to 200 nm.

[0141] Manufacturing Example 2: Manufacturing of a second particle in single-particle form Iron phosphate precursor (Fe1PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of 1:1.03:0.03. 10 wt% glucose was added to the mixture. The mixture was subjected to a wet grinding process using ball milling. After evaporating the mixture in a heated oven tray, it was dried in a vacuum oven at 120°C for 4 hours. The dried mixture was calcined under a nitrogen atmosphere at 750°C for 10 hours. The calcined material was ground to obtain the first single-particle form. The average size of the first particles was approximately 200 nm to 300 nm.

[0142] Manufacturing Example 3: Manufacturing of a third particle in single-particle form High-nickel precursors were produced using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·H2O) were dissolved in distilled water as the solvent in a molar ratio of 90:7:3 to prepare a mixture of metal raw materials. A diluted solution of aqueous ammonia (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitating agent for complex compound formation. Subsequently, the mixture of metal raw materials, aqueous ammonia, and sodium hydroxide were added to the reactor and the reaction was initiated. Sodium hydroxide was added to maintain the pH of the mixture in the reactor. The reaction was carried out for approximately 20 hours while stirring the mixture in the reactor. 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 190°C for 24 hours to obtain a large-grain precursor (Ni) with a particle size of approximately 18 μm. 0.90 Co 0.07 Al 0.03 (OH)2) powder was obtained.

[0143] A high-nickel precursor and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. Lithium and a transition metal were mixed in a molar ratio of approximately 1:1. The transition metal was the composite (Ni+Co+Al) of the transition metals contained in the coarse-grain precursor. The mixture was heat-treated in an oxygen atmosphere at approximately 900°C for 10 hours to synthesize a third particle, which was a first lithium composite oxide. The third particle was pulverized in a jet mill at a pressure of 3 bar.

[0144] Example 1 (Cathode active material production) The positive electrode active material was produced by mixing the first particle from Production Example 1, the second particle from Production Example 2, and the third particle from Production Example 3 in a weight ratio of 40:45:15.

[0145] (Lithium-ion battery manufacturing) A cathode active material slurry was prepared by mixing 95% by weight of the manufactured cathode active material, 3% by weight of polyvinylidene fluoride binder, and 2% by weight of carbon black conductive material in an N-methylpyrrolidone solvent. The cathode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare the cathode.

[0146] A negative electrode active material slurry was prepared by mixing graphite, a binder, and a conductive material in an N-methylpyrrolidone solvent. The negative electrode active material slurry was applied to a copper current collector, dried, and then rolled to prepare the negative electrode.

[0147] A 2032 type coin half-cell was fabricated using a prepared positive electrode and a lithium metal counter electrode as the relative electrode. A separator (thickness: approximately 16 μm) made of porous polyethylene (PE) film was interposed between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected to fabricate a lithium secondary battery. As the electrolyte, an electrolyte solution obtained by mixing 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3 was used.

[0148] Example 2 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the first, second, and third particles were mixed in a weight ratio of 42.5:42.5:15 during the production of the positive electrode active material.

[0149] Example 3 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the first, second, and third particles were mixed in a weight ratio of 45:40:15 during the production of the positive electrode active material.

[0150] Example 4 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the first, second, and third particles were mixed in a weight ratio of 60:25:15 during the production of the positive electrode active material.

[0151] Example 5 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the first, second, and third particles were mixed in a weight ratio of 70:15:15 during the production of the positive electrode active material.

[0152] Example 6 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the first, second, and third particles were mixed in a weight ratio of 37.5:37.5:25 during the production of the positive electrode active material.

[0153] Example 7 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the first, second, and third particles were mixed in a weight ratio of 35:35:30 during the production of the positive electrode active material.

[0154] Comparative Example 1 The positive electrode active material and lithium secondary battery were manufactured using the same method as in Example 1, except that only the first particles manufactured in Manufacturing Example 1 were used as the positive electrode active material.

[0155] Comparative Example 2 The positive electrode active material and lithium secondary battery were manufactured using the same method as in Example 1, except that only the second particle manufactured in Manufacturing Example 2 was used as the positive electrode active material.

[0156] Comparative Example 3 During the production of the positive electrode active material, the second particle was omitted. The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the first and third particles were mixed in a weight ratio of 85:15.

[0157] Comparative Example 4 During the production of the positive electrode active material, the second particle was omitted. The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the second and third particles were mixed in a weight ratio of 85:15.

[0158] Evaluation Example 1: Analysis of the surface of the positive electrode active material Figure 7A shows the SEM image of the first particle produced in Production Example 1. Figure 7B shows the SEM image of the second particle produced in Production Example 2. Figure 7C shows the SEM image of the third particle produced in Production Example 3.

[0159] Referring to Figure 7A, it can be confirmed that the first particle according to one embodiment of the present invention is a spherical secondary particle morphology formed by the aggregation of multiple primary particles. Referring to Figure 7B, it can be confirmed that the second particle according to the embodiment of the present invention is a nano-sized fine single particle morphology. Referring to Figure 7C, it can be confirmed that the third particle according to the embodiment of the present invention is a spherical secondary particle morphology formed by the aggregation of multiple primary particles.

[0160] Evaluation Example 2: Active Material Evaluation The average compressive density (Pellet Density, PD) of the positive electrode active materials produced by the examples and comparative examples was measured, and the results are shown in Table 1. The average compressive density was obtained by placing 1 g of positive electrode active material into a pellet manufacturing mold, maintaining a force of 4 tons for 30 seconds, and then calculating the density from the pellet thickness and mold diameter.

[0161] [Table 1]

[0162] Referring to Table 1, it can be confirmed that the positive electrode active material according to one embodiment of the present invention has a superior compressibility compared to the positive electrode active materials of Comparative Examples 1 to 3.

[0163] Evaluation Example 3: Battery Characteristics Evaluation The properties of lithium secondary batteries manufactured according to the examples and comparative examples were evaluated.

[0164] (Initial charge / discharge capacity evaluation) A lithium secondary battery was charged at 25°C with a current of 0.2C rate until the voltage reached 3.8V (vs.Li), and then cut off with a current of 0.05C rate while maintaining 3.8V in constant voltage mode. Subsequently, it was discharged with a constant current of 0.2C rate until the voltage reached 2.5V (vs.Li) (formation cycle). The charge capacity, discharge capacity, and average voltage during the formation cycle were measured and are shown in Table 2 below.

[0165] (Energy density evaluation) The energy density of the cells was evaluated using the following calculations and is shown in Table 2 below. Cell volume measurement (unit, L): width (mm) × length (mm) × thickness (mm) Cell energy measurement (unit, Wh): Cell capacity (Ah) × Average voltage (V) Energy density measurement (unit: Wh / L): Cell energy (Wh) / Cell volume (L)

[0166] [Table 2]

[0167] Referring to Table 2, it can be confirmed that the lithium secondary battery according to the embodiment of the present invention has even better capacity than the lithium secondary batteries of Comparative Examples 1 to 4, and is at an equivalent level or has an even higher average voltage and energy density. On the other hand, in the case of Comparative Example 4, although the energy density is similar to that of Examples 4 and 5, it can be confirmed that the high-temperature capacity recovery rate (ratio of discharge capacity after storage at 60°C for 30 days to the discharge capacity before storage) is superior in Examples 4 and 5.

[0168] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, which naturally also fall within the scope of the present invention. [Explanation of Symbols]

[0169] 100 Lithium-ion rechargeable batteries 10 positive electrode 11 Positive lead tab 12 Positive terminal 20 negative electrode 21 Negative lead tab 22 Negative terminal 30 Separators 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode Tabs 71 Positive Tab 72 Negative Electrode Tabs

Claims

1. A first particle having an olivine crystal structure and a first average particle size, A second particle having an olivine crystal structure and a second average particle size smaller than the first average particle size, A third particle having a layered crystalline structure, Each of the first and second particles contains a compound represented by the following chemical formula (1): The third particle contains a compound represented by the following chemical formula (2): The first particle is a spherical secondary particle containing a plurality of primary particles aggregated with each other, The second particle is a single particle. Cathode active material. [Chemical formula 1] Li ａ１ Fe ｘ１ B1 ｙ１ PO ４－ｂ１ ・・・(1) (In the above chemical formula (1), 0.8 ≤ a1 ≤ 1.2, 0.90 ≤ x1 ≤ 0.999, 0.001 ≤ y1 ≤ 0.1, 0 ≤ b1 ≤ 0.05, and 0.99 ≤ x1 + y1 ≤ 1.01, where B1 is at least one of Ti, Mg, V, Al, Mn, or a combination thereof.) [Case 2] Li ２ Ni ｘ２ Co ｙ２ Ma ｚ２ X ｃ２ O ２－ｂ２ ・・・(2) (In the above chemical formula (2), 0.8 ≤ a² ≤ 1.2, 0.8 ≤ x² < 1.0, 0 < y² ≤ 0.1, 0 ≤ z² ≤ 0.10 ≤ c² ≤ 0.05, 0 < b² ≤ 0.05, and 0.9 ≤ x² + y² + z² + c² ≤ 1.1, where Ma is at least one of Al, Mn, or a combination thereof, and X is at least one of Ti, Mg, Zr, Al, or a combination thereof.)

2. The content of the first and second particles is 70% by weight or more and 95% by weight or less relative to the total weight of the positive electrode active material. The content of the third particle is 5% by weight or more and 30% by weight or less relative to the total weight of the positive electrode active material. The positive electrode active material according to claim 1.

3. The mixing ratio of the first and second particles is 3:1 to 1:3 based on weight. The positive electrode active material according to claim 1.

4. The mixing ratio of the first particle and the second particle is 2:1 to 1:2 based on weight. The positive electrode active material according to claim 1.

5. The first particle comprises a first coating layer containing carbon, The carbon content in the first particle is 1.5 wt% or more and 2.5 wt% or less. The positive electrode active material according to claim 1.

6. The first particle further comprises a grain boundary coating layer on the interface between primary particles, The aforementioned grain boundary coating layer contains carbon, The positive electrode active material according to claim 5.

7. The porosity of the first particle is 20% or more and 40% or less. The positive electrode active material according to claim 1.

8. The first average particle size is 3 μm or more and 7 μm or less. The positive electrode active material according to claim 1.

9. The second particle comprises a second coating layer containing carbon, The carbon content in the second particle is 0.5 wt% or more and 2 wt% or less. The positive electrode active material according to claim 1.

10. The second average particle size is 0.5 μm or more and 2.5 μm or less. The positive electrode active material according to claim 1.

11. The aforementioned third particle includes a third coating layer, The third coating layer comprises at least one of a boron-containing compound, an aluminum-containing compound, or a combination thereof. The positive electrode active material according to claim 1.

12. The third particle is a secondary particle containing multiple primary particles, The third average particle size of the third particle is 8 μm or more and 20 μm or less. The positive electrode active material according to claim 1.

13. The third particle is a single particle, The third average particle size of the third particle is 2 μm or more and 5 μm or less. The positive electrode active material according to claim 1.

14. The third particle includes a secondary particle comprising a plurality of primary particles, and a single particle comprising, The positive electrode active material according to claim 1.

15. Positive electrode current collector and The positive electrode current collector includes a positive electrode active material layer, The positive electrode active material layer comprises the positive electrode active material, conductive material, and binder described in claim 1. Positive electrode for lithium secondary batteries.

16. The content of the binder is 0.5 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the positive electrode active material layer. The positive electrode for a lithium secondary battery according to claim 15.

17. The binder comprises at least one of the following: polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, 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, nylon, or a combination thereof. The positive electrode for a lithium secondary battery according to claim 15.

18. The content of the conductive material is 0.5 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the positive electrode active material layer. The positive electrode for a lithium secondary battery according to claim 15.

19. The conductive material contains carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes, as well as copper, nickel, aluminum, and silver, and includes at least one of the following: a metallic material in the form of metal powder or metal fibers, a conductive polymer of a polyphenylene derivative, or a combination thereof. The positive electrode for a lithium secondary battery according to claim 15.

20. The positive electrode described in claim 15, A negative electrode comprising 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, Lithium-ion rechargeable battery.

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