Positive electrode active material for rechargeable lithium battery and positive electrode comprising same

Abstract

Examples include a positive electrode active material for a rechargeable lithium battery and a positive electrode including the positive electrode active material. The positive electrode active material includes first particles having an olivine crystal structure and having a first average particle diameter, second particles having an olivine crystal structure and having a second average particle diameter smaller than the first average particle diameter, and third particles having an olivine crystal structure and having a third average particle diameter larger than the first average particle diameter.

Description

[0001] This patent application claims priority to Korean Patent Application No. 10-2024-0075485, filed on June 11, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates herein to a positive electrode active material for a rechargeable lithium battery, a positive electrode including the same, and a rechargeable lithium 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 rechargeable lithium battery including the same. BACKGROUND

[0003] As the use of electronic devices using batteries, such as mobile phones, laptop computers, electric vehicles, and the like, has increased, the demand for rechargeable batteries having high energy density and high capacity has increased.

[0004] A rechargeable lithium battery generally includes a positive electrode and a negative electrode including an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electric energy is generated by oxidation and reduction reactions upon intercalation and deintercalation of lithium ions into and from the positive electrode and the negative electrode. SUMMARY

[0005] The present disclosure relates to a positive electrode active material having high energy density and high conductivity.

[0006] The present disclosure also relates to a rechargeable lithium battery having high energy density and long life.

[0007] Example embodiments of the present disclosure include a positive electrode active material including first particles having an olivine crystal structure and having a first average particle diameter, second particles having an olivine crystal structure and having a second average particle diameter smaller than the first average particle diameter, and third particles having an olivine crystal structure and having a third average particle diameter greater than the first average particle diameter. Each or at least one of the first particles to the third particles can include a compound represented by Formula 1 below.

[0008] Formula 1: Li a1 Fe x1 B1 y1 PO 4-b1 In Formula 1 above, 0.8 ≤ a1 ≤ 1.2, 0.950 ≤ x1 ≤ 0.999, 0.001 ≤ y1 ≤ 0.05, 0 ≤ b1 ≤ 0.05, and 0.99 ≤ x1 + y1 ≤ 1.01 can be satisfied, and B1 can be or include at least one element including at least one of Ti and Mg.

[0009] In example embodiments of the disclosure, a positive electrode for a rechargeable lithium battery can include 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 described above, a conductive material, and a binder. BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate example embodiments of the disclosure and, together with the description, serve to explain principles of the disclosure. In the drawings: Figure 1 is a simplified conceptual diagram illustrating a rechargeable lithium battery according to example embodiments of the disclosure; Figures 2 to 5 is a schematic diagram schematically illustrating a rechargeable lithium battery according to example embodiments; Figure 6 is a magnified view of a positive electrode active material layer of a rechargeable lithium battery according to example embodiments of the disclosure; Figure 7 and Figure 8 are each a flowchart illustrating a method of preparing a positive electrode active material according to example embodiments of the disclosure; and Figures 9A to 9C is a scanning electron microscope (SEM) image of a positive electrode active material according to example embodiments of the disclosure. DETAILED DESCRIPTION

[0011] In order to fully understand the configuration and effects of the disclosure, example embodiments of the disclosure will be described in greater detail below with reference to the accompanying drawings. However, the disclosure can be implemented in various forms, and should not be construed as being limited to the example embodiments set forth herein, and various changes and modifications can be made. Rather, these example embodiments are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art to which the disclosure pertains.

[0012] In this specification, it will be understood that when an element is referred to as being "on" another element, it can be directly on the other element or an intervening element can be present therebetween. In the drawings, the thickness of components can be exaggerated for more effective explanation of the technical content. Throughout the specification, like reference numerals or symbols refer to like elements.

[0013] The singular form "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, the phrase "and / or" can refer to and encompass any possible combinations of one or more of the associated listed items, including one alone. The terms "comprises," "comprising," "includes," "including," and the like can be used herein and are intended to permit a statement that something comprises, includes, and / or contains an element or a plurality of elements without precluding the presence or addition of one or more other components.

[0014] In the present specification, "a combination thereof" can refer to a mixture, a stack, a composite, a copolymer, an alloy, a blend, and a reaction product of components.

[0015] Unless defined otherwise in the present specification, the particle diameter can be an average particle diameter. Further, the particle diameter means an average particle diameter (D50) referring to a particle diameter at which the cumulative volume is about 50% by volume in a particle size distribution. The average particle diameter (D50) can be measured by a method widely known to those skilled in the art, for example, can be measured by a particle size analyzer, or can also be measured using a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle diameter is measured by using a measuring device using dynamic light scattering, in which the number of particles in each particle size range is counted by performing data analysis, and then the average particle diameter (D50) value can be obtained by calculation. Further, the average particle diameter can be measured using a laser diffraction method. When measured by the laser diffraction method, specifically, after dispersing the particles to be measured in a dispersion medium, the dispersion medium is introduced into a commercial laser diffraction particle size measuring instrument (for example, Microtrac MT 3000) and irradiated with ultrasonic waves at about 28 kHz at an output power of about 60 W, and then the average particle diameter (D50) can be calculated based on about 50% of the particle size distribution in the measuring instrument.

[0016] When the term "about" or "substantially" is used in the present specification in connection with a numerical value, it means that the relevant numerical value includes a tolerance of ±10% around the stated numerical value. When a range is specified, the range includes all values therebetween, such as in increments of 0.1%.

[0017] Figure 1 is a simplified conceptual diagram illustrating a rechargeable lithium battery according to an example embodiment of the present disclosure. Referring to Figure 1 The rechargeable lithium battery can 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 spaced apart from each other, and the separator 30 is between the positive electrode 10 and the negative electrode 20. The separator 30 can be disposed 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 immersed in the electrolyte ELL.

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

[0020] Positive electrode 10 The positive electrode 10 for the rechargeable lithium battery can 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 can include a positive electrode active material, and can further include a binder and / or a conductive material. For example, the positive electrode 10 can further include an additive that can constitute a sacrificial positive electrode. The positive electrode active material layer AML1 according to example embodiments of the disclosure will be described later with reference to FIG. 1. Figure 6 The positive electrode active material layer AML1 according to example embodiments of the disclosure will be described later with reference to FIG. 1.

[0021] Negative electrode 20 The negative electrode 20 for the rechargeable lithium battery can include a current collector COL2 and a negative electrode active material layer AML2 on the current collector COL2. The negative electrode active material layer AML2 can include a negative electrode active material, and can further include a binder and / or a conductive material (e.g., an electrically conductive material).

[0022] For example, the negative electrode active material layer AML2 can include a negative electrode active material in a range of about 90 wt% to about 99 wt%, a binder in a range of about 0.5 wt% to about 5 wt%, and a conductive material in a range of about 0 wt% to about 5 wt%.

[0023] The binder can be configured to attach the negative electrode active material particles to each other and also to attach the negative electrode active material to the current collector COL2. The binder can include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0024] The non-aqueous binder can include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or a combination thereof.

[0025] The aqueous binder can be or include at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoro rubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0026] When the aqueous binder is a negative electrode binder, it can further include a cellulose-based compound capable of imparting adhesiveness. The cellulose-based compound can include at least one of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal can include at least one of Na, K, or Li.

[0027] The dry binder can be or include a polymer material capable of being fibrous. For example, the dry binder can be or include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0028] The conductive material can be configured to impart electrical conductivity (e.g., electronic conduction) to the electrode. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery) and conducts electrons can be used in the battery. Non-limiting examples thereof can include: carbon-based materials such as at least one of 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 at least one of copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0029] The current collector COL2 of the negative electrode can include at least one of 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 combinations thereof.

[0030] Negative electrode active material The negative electrode active material can include at least one of a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / de-doping lithium, or a transition metal oxide.

[0031] The material that reversibly intercalates / deintercalates lithium ions can include a carbon-based negative electrode active material, such as exemplified by crystalline carbon, amorphous carbon, or combinations thereof. The crystalline carbon can be or include graphite, such as non-shaped, flaky, flake-like, spherical, or fibrous natural graphite or artificial graphite. The amorphous carbon can be or include at least one of soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, and the like.

[0032] Lithium metal alloys include alloys of lithium with a metal including at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0033] The material capable of doping / dedoping lithium can be or include a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material can include silicon, a silicon-carbon composite, SiO x (0 < x < 2), a Si-Q alloy (where Q is or includes at least one of 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 combinations thereof), or a combination thereof. The Sn-based negative electrode active material can include at least one of Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0034] The silicon-carbon composite can be or include a composite of silicon and amorphous carbon. According to an example embodiment, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated onto the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) assembled with primary silicon particles and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon can also be located between the primary silicon particles, for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0035] The silicon-carbon composite can also include crystalline carbon. For example, the silicon-carbon composite can include a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core.

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

[0037] Separator 30 A separator 30 can be present between the positive electrode 10 and the negative electrode 20 depending on the type of the rechargeable lithium battery. The separator 30 can include at least one of polyethylene, polypropylene, polyvinylidene fluoride, or can include a multi-layer film and a mixed multi-layer film of two or more layers thereof, such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.

[0038] The separator 30 can include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof on one or both surfaces of the porous substrate.

[0039] The porous substrate can be or include a polymer film formed of or including any one of polymers including at least one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyether ketones, polyether imides, polyamide-imides, polybenzimidazoles, polyether sulfones, polyphenylene ethers, cyclic olefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof.

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

[0041] The inorganic material can include inorganic particles including at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but is not limited thereto.

[0042] The organic material and the inorganic material can be mixed in one coating layer, or a coating layer including the organic material and a coating layer including the inorganic material can be stacked.

[0043] Electrolyte ELL The electrolyte ELL for the rechargeable lithium battery can include a non-aqueous organic solvent and a lithium salt.

[0044] The non-aqueous organic solvent can be or include a medium for transporting ions participating in an electrochemical reaction of the battery.

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

[0046] The carbonate-based solvent can include at least one of 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), butylene carbonate (BC), or the like.

[0047] The ester-based solvent can include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, methyl hydroxypivalate, valerolactone, caprolactone, or the like.

[0048] The ether-based solvent can include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, or the like. In addition, the ketone-based solvent can include cyclohexanone or the like. The alcohol-based solvent can include ethanol, isopropyl alcohol, or the like, and the aprotic solvent can include at least one of a nitrile such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and can include a double bond, an aromatic ring, or an ether bond, or the like), an amide such as dimethylformamide, a dioxolane such as 1,3-dioxolane, 1,4-dioxolane, or the like, a sulfolane, or the like.

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

[0050] In addition, when the carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be used in combination, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0051] The lithium salt dissolved in the organic solvent supplies lithium ions in the battery, enabling the rechargeable lithium battery to be substantially operated, and improving the transport of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt include at least one of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiN(C F 2x+1 SO2)(C y F 2y+2 SO2) (wherein x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0052] Rechargeable lithium battery The rechargeable lithium battery can be classified into a cylindrical battery, a prismatic battery, a pouch-type battery, a coin-type battery, or the like, according to its shape. Figures 2 to 5 is a schematic diagram illustrating a rechargeable lithium battery according to an example embodiment. Figure 2 is illustrated a cylindrical battery, Figure 3 is illustrated a prismatic battery, and Figure 4 and Figure 5 is illustrated a pouch-type battery. Referring to Figures 2 to 5The rechargeable lithium battery 100 can include an electrode assembly 40 including a separator 30 positioned between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is accommodated. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated with an electrolyte (not shown). As shown in Figure 2 The rechargeable lithium battery 100 can include a sealing member 60 that seals the case 50. In Figure 3 The rechargeable lithium battery 100 can 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 Figure 4 and Figure 5 The rechargeable lithium battery 100 can include an electrode tab 70 shown in Figure 5 or a positive electrode tab 71 and a negative electrode tab 72 shown in Figure 4 The tab 70 / 71 / 72 forms an electrical path for inducing a current formed in the electrode assembly 40 to the outside of the rechargeable lithium battery 100.

[0053] As non-limiting examples, the rechargeable lithium battery according to example embodiments can be suitable for use in automobiles, mobile phones, and / or various types of electrical devices.

[0054] Figure 6 is a magnified view of a positive electrode active material layer of a rechargeable lithium battery according to example embodiments of the disclosure. Referring to Figure 6 As previously described, the positive electrode active material layer AML1 (see Figure 1 ) can include first particles PTC1, second particles PTC2, third particles PTC3, a conductive material CDM, and a binder BND. The plurality of first particles PTC1, the plurality of second particles PTC2, and the plurality of third particles PTC3 can constitute a positive electrode active material according to example embodiments of the disclosure.

[0055] The amount of the positive electrode active material PTC1, PTC2, PTC3 in the positive electrode active material layer AML1 can be in a range of about 90 wt% to about 99.5 wt% relative to 100 wt% of the positive electrode active material layer AML1. The amount of each of the binder BND and the conductive material CDM can be in a range of about 0.5 wt% to about 5 wt% relative to 100 wt% of the positive electrode active material layer AML1.

[0056] The binder BND can adhere the first particles PTC1, the second particles PTC2, the third particles PTC3, and the conductive material CDM to each other. For example, the binder BND can include at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer including an oxirane, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but example embodiments of the present disclosure are not limited thereto.

[0057] The conductive material CDM can be configured to improve the electrical conductivity of the positive electrode active material layer AML1. As the conductive material CDM, any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used without limitation. Examples of the conductive material CDM can include at least one of 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 at least one of copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or a mixture thereof.

[0058] Hereinafter, each of the first particles PTC1, the second particles PTC2, and the third particles PTC3 will be described in more detail.

[0059] First particles PTC1 The first particles PTC1 can have a polycrystalline form, and can include secondary particles in which at least two first primary particles NNP1 are aggregated. In other words, one first particle PTC1 can include a plurality of first primary particles NNP1 aggregated with each other. The first particles PTC1 can have a spherical shape, and can also have a non-spherical shape. That is, the first particles PTC1 can have an arbitrary shape.

[0060] In example embodiments, the first particles PTC1 can include a coating layer on a surface thereof. The coating layer can cover the entire surface of the first particles PTC1, or can cover a portion of the surface of the first particles PTC1. For example, the coating layer can include carbon and / or a carbon-containing compound. Due to the coating layer, the first particles PTC1 can exhibit improved structural stability and electrical conductivity.

[0061] The coating can further include at least one of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. The metal-containing compound such as the titanium-containing compound, the magnesium-containing compound, and the vanadium-containing compound can be or include, for example, at least one of a metal oxide, a metal hydroxide, a metal carbonate, or a complex or mixture thereof. The metal-containing compound can further include other metal or non-metal elements. For example, the metal-containing compound can further include lithium.

[0062] In an example embodiment, the first particle PTC1 can further include a grain boundary coating on a surface of the first primary particle NNP1. The grain boundary coating can exist inside the first particle PTC1. The grain boundary coating can be formed along interfaces between the first primary particles NNP1 inside the first particle PTC1. In other words, the grain boundary coating can refer to a material applied to grain boundaries inside the first particle PTC1. The grain boundary coating can include carbon and / or a carbon-containing compound. The grain boundary coating can further include at least one of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0063] The inside of the first particle PTC1 can refer to the entire internal region of the first particle PTC1 other than the surface of the first particle PTC1. For example, the inside of the first particle PTC1 can refer to the entire internal region from about 10 nm deep from the outer surface of the first particle PTC1, or a region in the range of about 10 nm deep to about 2 µm deep.

[0064] Since the first particle PTC1 further includes the grain boundary coating, and the coating can be uniformly formed on the surface of the first particle PTC1, the structural stability can be strengthened. Also, since the first particle PTC1 further includes the grain boundary coating, the electrical conductivity of the first particle PTC1 can be further improved.

[0065] The first particle PTC1 can include carbon derived from the above-described coating and / or the grain boundary coating. The amount of carbon element in the first particle PTC1 can be in the range of about 1.1 wt% to about 2.0 wt%, about 1.4 wt% to about 2.0 wt%, or about 1.4 wt% to about 1.7 wt%. The amount of carbon element in the first particle PTC1 can be greater than the amount of carbon element in the second particle PTC2, which will be described later, and less than the amount of carbon element in the third particle PTC3, which will be described later.

[0066] The carbon element according to example embodiments of the present disclosure can be analyzed using an Elementar Micro Cube elemental analyzer. The specific method of operation and conditions are as follows. About 1 mg to 2 mg of a sample is weighed in a tin cup, placed in an automatic sampling tray and introduced into a combustion tube through a ball valve, and combustion is performed at a combustion temperature of about 1000°C. Subsequently, reduction of the combustion gas is performed using reduced copper to form carbon dioxide. The carbon dioxide is detected using a thermal conductivity detector (TCD).

[0067] According to example embodiments of the present disclosure, scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) and quantitative analysis are performed on the surface of the particles to measure the carbon content. In addition to SEM-EDS, inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-OES), etc. can be used to measure the carbon content.

[0068] The first particles PTC1 can have an average particle diameter in the range of about 1 µm to about 7 µm, about 1 µm to about 5 µm, or about 2 µm to about 4 µm. For example, the first average particle diameter of the first particles PTC1 can be about 3 µm. In example embodiments, the average particle diameter can be measured with a particle size analyzer. The average particle diameter can refer to the diameter (D50) of the particles at which the cumulative volume is about 50% by volume in the particle size distribution. The first average particle diameter of the first particles PTC1 can be greater than the second average particle diameter of the second particles PTC2, which will be described later, and less than the third average particle diameter of the third particles PTC3.

[0069] The first primary particles NNP1 of the first particles PTC1 can have an average size (or average particle diameter) in the range of about 100 nm to about 500 nm, about 200 nm to about 400 nm, or about 200 nm to about 350 nm. In example embodiments, the average size of the first primary particles NNP1 can refer to the average of the diameters obtained by measuring the diameters of a plurality of first primary particles NNP1 randomly selected from an electron micrograph of the positive electrode active material, such as, for example, about 30 first primary particles NNP1. The average size of the first primary particles NNP1 can be greater than or equal to the average size of the second primary particles, which will be described later, and can be greater than the average size of the third primary particles NNP3.

[0070] The first particles PTC1 can have a form in which the nanosized first primary particles NNP1 are aggregated. The first particles can have a substantially spherical shape, or can have a non-spherical shape.

[0071] In the case where the first primary particles NNP1 are aggregated with each other as previously described, the first particles PTC1 can have the following properties. The average particle diameter of the first particles PTC1 can be in the range of about 1 μm to about 5 μm. The porosity of the first particles PTC1 can be in the range of about 15% to about 20%, and can be less than the porosity of each or at least one of the second particles PTC2 and the third particles PTC3, which will be described later. The specific surface area of the first particles PTC1 can be in the range of about 8 m 2 / g to about 12 m 2 / g, and a span value thereof obtained by analyzing the first particles PTC1 using a particle size analyzer can be in the range of about 1.33 to about 1.5.

[0072] Second particles PTC2 The second particles PTC2 can have a single particle form. In the present disclosure, a "single" particle can refer to one particle or a separate particle that exists alone without a grain boundary therein. In terms of morphology, a single particle can refer to one particle, a monolithic structure, a single monolithic structure, or a non-aggregated particle that exists in an independent phase where the particles do not aggregate with each other. For example, a single particle can be a single crystal. Alternatively, a single particle can be or include a particle including a small amount of crystals. A single particle can be independently separated. Alternatively, a single particle can be in the form of about 2 to about 100 single particles joined to each other.

[0073] The second particles PTC2 can be or include a nano-shaped positive electrode active material. The second particles PTC2 can include at least one second primary particle. In an example embodiment, the second primary particles can also be aggregated with each other to have a particle shape similar to the particle shape of the first particles PTC1 described previously.

[0074] The second particles PTC2 can be provided in various sizes. For example, the second particles PTC2 can have an average particle diameter in the range of about 500 nm to about 2.5 μm, or about 1 μm. The minimum particle diameter of the second particles PTC2 as the particle diameter of the second primary particles can be in the range of about 100 nm to about 500 nm, or about 100 nm to about 200 nm. In an example embodiment, the average particle diameter can be measured with a particle size analyzer. The average particle diameter can refer to the diameter (D50) of the particles of which the cumulative volume is about 50% by volume in a particle size distribution.

[0075] The porosity of the second particles PTC2 can be greater than about 40%, and can be greater than the porosity of the first particles PTC1. The span value obtained by analyzing the second particles PTC2 using a particle size analyzer can be outside the range of about 3.0 to about 3.95, for example, the span value is less than 3.0 or greater than 3.95.

[0076] In example embodiments, the second particles PTC2 can include a coating layer on a surface thereof. The coating layer can cover an entire surface of the second particles PTC2, or can cover a portion of the surface of the second particles PTC2. For example, the coating layer can include carbon and / or a carbon-containing compound. The coating layer can further include at least one of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. The metal-containing compound such as the titanium-containing compound, the magnesium-containing compound, and the vanadium-containing compound can be or include, for example, at least one of a metal oxide, a metal hydroxide, a metal carbonate, or a complex or mixture thereof. The metal-containing compound can further include other metal or non-metal elements. For example, the metal-containing compound can further include lithium. The second particles PTC2 can have improved structural stability and electrical conductivity due to the coating layer.

[0077] The second particles PTC2 can include carbon derived from the coating layer described previously. The amount of carbon element in the second particles PTC2 can be in a range of about 0.5 wt% to about 5 wt%, about 0.5 wt% to about 3 wt%, or about 0.5 wt% to about 2 wt%. The amount of carbon in the second particles PTC2 can be less than the amount of carbon in the first particles PTC1. This is because it is challenging to form a coating layer smoothly on the second particles PTC2 which are single particles, compared to the first particles PTC1 which are or include secondary particles.

[0078] Third particles PTC3 The third particles PTC3 can have a polycrystalline form, and can include secondary particles in which a plurality of third primary particles NNP3 are aggregated. In other words, one third particle PTC3 can include a plurality of third primary particles NNP3 aggregated with each other. The average number of the third primary particles NNP3 included in the third particles PTC3 can be greater than the average number of the first primary particles NNP1 included in the first particles PTC1. The third particles PTC3 can have a substantially spherical or elliptical shape.

[0079] In example embodiments, the third particles PTC3 can include a coating layer on a surface thereof. The coating layer can cover substantially an entire surface of the third particles PTC3, or can cover a portion of the surface of the third particles PTC3. For example, the coating layer can include carbon and / or a carbon-containing compound. The third particles PTC3 can have improved structural stability and electrical conductivity due to the coating layer.

[0080] The coating layer can further include at least one of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. The metal-containing compound such as the titanium-containing compound, the magnesium-containing compound, and the vanadium-containing compound can be or include, for example, at least one of a metal oxide, a metal hydroxide, a metal carbonate, or a complex or mixture thereof. The metal-containing compound can further include other metal or non-metal elements. For example, the metal-containing compound can further include lithium.

[0081] In example embodiments, the third particulate PTC3 can further include a grain boundary coating on the surface of the third primary particles NNP3. The grain boundary coating can exist inside the third particulate PTC3. The grain boundary coating can be formed along the interface between the third primary particles NNP3 inside the third particulate PTC3. In other words, the grain boundary coating can refer to a material applied to the grain boundaries inside the third particulate PTC3. The grain boundary coating can include carbon and / or a carbon-containing compound. The grain boundary coating can further include at least one of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound.

[0082] The inside of the previously described third particulate PTC3 can refer to the entire internal region of the third particulate PTC3 other than the surface of the third particulate PTC3. For example, the inside of the third particulate PTC3 can refer to the entire internal region from about 10 nm deep from the outer surface of the third particulate PTC3, or a region in the range of about 10 nm deep to about 2 µm deep.

[0083] Since the third particulate PTC3 further includes the grain boundary coating, and the coating can be formed substantially uniformly on the surface of the third particulate PTC3, the structural stability can be strengthened. In addition, since the third particulate PTC3 further includes the grain boundary coating, the electrical conductivity of the third particulate PTC3 can be further improved.

[0084] The third particulate PTC3 can include carbon derived from the above-described coating and / or the grain boundary coating. The amount of carbon elements in the third particulate PTC3 can be in the range of about 0.5 wt% to about 10 wt%, about 1 wt% to about 3 wt%, or about 1.5 wt% to about 2.5 wt%. The amount of carbon elements in the third particulate PTC3 can be greater than the amount of carbon elements in the first particulate PTC1. This can be because the third particulate PTC3 includes a greater number of primary particles and accordingly the amount of carbon derived from the grain boundary coating is greater.

[0085] The third particulate PTC3 can have an average particle diameter in the range of about 2 µm to about 15 µm, about 3 µm to about 10 µm, about 5 µm to about 10 µm, or about 3 µm to about 7 µm. For example, the third average particle diameter of the third particulate PTC3 can be about 5 µm. The average particle diameter of the third particulate PTC3 can be greater than the first average particle diameter of the previously described first particulate PTC1. In example embodiments, the average particle diameter can be measured with a particle size analyzer. The average particle diameter can refer to the diameter (D50) of the particles for which the cumulative volume is about 50% by volume in the particle size distribution.

[0086] The third primary particles NNP3 of the third particles PTC3 can have an average particle diameter in a range of about 10 nm to about 400 nm, about 20 nm to about 300 nm, about 50 nm to about 200 nm, or about 100 nm to about 200 nm. In an example embodiment, the average particle diameter of the third primary particles NNP3 can refer to an average of diameters obtained by measuring diameters of a plurality of third primary particles NNP3, such as about 30 third primary particles NNP3, randomly selected from electron micrographs of the positive electrode active material. The particle diameter of the third primary particles NNP3 can be uniform.

[0087] The third particles PTC3 can have a substantially spherical shape in which the nanosized third primary particles NNP3 are aggregated. In a case in which the third primary particles NNP3 are closely aggregated with each other, the third particles PTC3 can have the following characteristics. The third particles PTC3 can have a substantially spherical or substantially elliptical shape. The average particle diameter (D50) of the third particles PTC3 can be in a range of about 2 µm to about 15 µm. The third particles PTC3 can have a porosity in a range of about 20% to about 40%. The porosity of the third particles PTC3 can be greater than the porosity of the first particles PTC1. A span value obtained by analyzing the third particles PTC3 using a particle size analyzer can be in a range of about 0.44 to about 0.79.

[0088] Referring back to Figure 6 A positive electrode active material according to an example embodiment of the disclosure will be described in more detail. The positive electrode active material according to an example embodiment of the disclosure can include the first particles PTC1, the second particles PTC2, and the third particles PTC3. Each of the first particles PTC1, the second particles PTC2, and the third particles PTC3 can have an olivine crystal structure and include a compound represented by the following Formula 1.

[0089] [Formula 1] Li a1 Fe x1 B1 y1 PO 4-b1 In the above Formula 1, 0.8 ≤ a1 ≤ 1.2, 0.950 ≤ x1 ≤ 0.999, 0.001 ≤ y1 ≤ 0.05, 0 ≤ b1 ≤ 0.05, and 0.99 ≤ x1 + y1 ≤ 1.01 can be satisfied. B1 can be or include at least one element including at least one of Ti and Mg. B1 can be or include a dopant doped into the positive electrode active material, and can control the size of the primary particles to be uniform.

[0090] The positive electrode active material according to example embodiments of the present disclosure can have desired or improved economic feasibility and stability due to including olivine-type positive electrode active materials. In addition, the positive electrode according to example embodiments of the present disclosure can have improved mixture density and current density as compared to a case where only one type of active material is included or a case where only two types of active material are included, since the positive electrode includes the first particles PTC1, the second particles PTC2, and the third particles PTC3 having different average particle diameters.

[0091] According to example embodiments of the present disclosure, the amount of the first particles PTC1 can be in the range of about 50 wt% to about 85 wt% with respect to the total amount of the first particles PTC1, the second particles PTC2, and the third particles PTC3. For example, the amount of the first particles PTC1 can be in the range of about 60 wt% to about 85 wt%, about 50 wt% to about 75 wt%, or about 50 wt% to about 65 wt%.

[0092] For example, the mixing ratio of the second particles PTC2 and the third particles PTC3 can be in the range of about 75:25 to about 25:75, or about 50:50 to about 25:75, based on weight.

[0093] When the first particles PTC1, the second particles PTC2, and the third particles PTC3 have the above-described mixing ratio, the positive electrode including the positive electrode active material according to example embodiments of the present disclosure can have desired or improved mixture density and current density, and the rechargeable lithium battery including the positive electrode active material according to example embodiments of the present disclosure can have desired or improved lifespan characteristics.

[0094] The positive electrode including the positive electrode active material according to example embodiments of the present disclosure can have an electrode plate mixture density equal to or greater than about 2.5 g / cc. In example embodiments, the mixture density of the positive electrode according to example embodiments of the present disclosure can be in the range of about 2.5 g / cc to about 4.0 g / cc, or about 2.5 g / cc to about 3.5 g / cc.

[0095] The positive electrode including the positive electrode active material according to example embodiments of the present disclosure can have a current density equal to or greater than about 4.0 mA / cm 2 . In example embodiments, the current density of the positive electrode according to example embodiments of the present disclosure can be in the range of about 4.0 mA / cm 2 to about 6.0 mA / cm 2 , or about 4.5 mA / cm 2 to about 5.5 mA / cm 2 .

[0096] The rechargeable lithium battery including the positive electrode active material according to the example embodiment of the disclosure can have a capacity retention rate of at least about 80% after at least about 10,000 charge and discharge cycles at about 0.2C / 0.5C at a voltage of about 2.5V to about 3.65V. For example, the capacity retention rate can be in a range of about 80% to about 95%, or about 80% to about 90%.

[0097] Method for producing positive electrode active material Figure 7 and Figure 8 are each a flowchart showing a method of preparing a positive electrode active material according to an example embodiment of the disclosure. Referring to Figure 7 The preparation of the first granule PTC1 according to the example embodiment of the disclosure will be described in more detail.

[0098] The iron phosphate precursor, the lithium source, the carbon source, and the dopant source can be added to a solvent and mixed (S110). For example, the solvent can be or include water, ethanol, or the like. The iron phosphate precursor can be or include a compound including 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 can be or include a mixture of FePO4·H2O, FeSO4, and H3PO4, or a mixture of (NH4)2Fe(SO4)·6H2O and H3PO4.

[0099] The lithium source can include at least one of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, di-lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0100] The carbon source can include at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0101] The dopant source can include an oxide containing a dopant metal and / or a chloride containing a dopant metal. For example, the dopant source can include at least one of titanium oxide, magnesium oxide, vanadium oxide, and niobium oxide.

[0102] The mixture can be wet-milled (S120). For the wet-milling, a general wet-milling machine capable of temperature control can be used. Specifically, at least one of a beads mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill can be used for the wet-milling. Through the wet-milling process, the particles in the mixture can be ground to a fine size. According to the example embodiment of the disclosure, the wet-milling can also be omitted.

[0103] The ground mixture can be subjected to a first calcination (S130). The first calcination can include heat-treating the mixture under a high-temperature and high-voltage solvent. In an example embodiment, the first calcination process can be performed in an autoclave reactor. The temperature at which the first calcination process is performed can be in the range of about 100℃ to about 500℃, or about 150℃ to about 300℃. The execution time of the first calcination process can be in the range of about 4 hours to about 20 hours, or about 6 hours to about 12 hours. When the ground mixture is subjected to calcination, the first particles PTC1 including the compound represented by Formula 1 described above can be formed.

[0104] The first particles PTC1 after calcination can be ground (S140). Accordingly, the first particles PTC1 can have a fine primary particle size.

[0105] The ground first particles PTC1 can be dried (S150). According to an example embodiment of the disclosure, the drying can include spray-drying the mixture. A general spray-drying apparatus can be used for spray-drying. For example, the spray-drying can be performed by using at least one of an ultrasonic spray-drying apparatus, an air nozzle spray-drying apparatus, an ultrasonic nozzle spray-drying apparatus, a filter-expanded droplet generation apparatus, and an electrostatic spray-drying apparatus.

[0106] Particles finely reduced in size to primary particles after the wet-milling process can be aggregated with each other by a spray-drying process to form secondary particles. Accordingly, by adjusting the flow rate and flow velocity of a carrier gas, the temperature, the residence time in the reactor, the internal pressure, etc. during the spray-drying process, the first particles PTC1 can be formed into secondary particles of a desired size.

[0107] In an example embodiment, the mixture to be spray-dried can have a total solid content (TSC) in the range of about 20wt% to about 30wt%. The total solid content can refer to a converted value of the percentage of the weight of a solid substance remaining after solvent evaporation (i.e., the dried mixture) with respect to the total weight of the mixture (i.e., the spray liquid). For example, the spray liquid can have a total solid content of about 25wt%.

[0108] In an example embodiment, the spray-drying can be performed at a temperature in the range of about 200℃ to about 400℃. A spray gas (e.g., air) for spray-drying can be injected at a first temperature and discharged at a second temperature. For example, the first temperature can be in the range of about 200℃ to about 250℃. The second temperature can be in the range of about 300℃ to about 400℃.

[0109] The spray liquid for spray drying can have a flow rate in a range of about 10 mL / min to about 30 mL / min. The spray liquid can have an input pressure in a range of about 0.3 MPa to about 0.7 MPa. For example, the input pressure of the spray liquid can be about 0.5 MPa.

[0110] A second calcination can be performed after the spray drying (S160). The second calcination can be performed in an inert atmosphere. The inert atmosphere can be or include a nitrogen atmosphere and / or an argon atmosphere. The temperature at which the second calcination process is performed can be in a range of about 500°C to about 1000°C, or about 600°C to about 800°C. The execution time of the second calcination process can be in a range of about 4 hours to about 20 hours, or about 6 hours to about 12 hours. As a result of the second calcination on the dried mixture, the first particles PTC1 in the form of secondary particles can be formed.

[0111] A dry milling can be performed on the calcined first particles PTC1. Through this milling process, the size of the first particles as secondary particles can be adjusted. At the same time, the milling process can be omitted.

[0112] Referring to Figure 8 The preparation of the second particles PTC2 according to the example embodiments of the present disclosure will be described in more detail.

[0113] First, an iron phosphate precursor, a lithium source, a carbon source, and a dopant source can be added to a solvent and mixed (S210). For example, the solvent can be or include water, ethanol, etc. The iron phosphate precursor, the lithium source, the carbon source, and the dopant source can be the same as or similar to the iron phosphate precursor, the lithium source, the carbon source, and the dopant source used for the preparation of the first particles PTC1 discussed above.

[0114] A wet milling can be performed on the mixture (S220). The wet milling process can be the same as or similar to the wet milling in the preparation of the first particles PTC1 described previously.

[0115] The solvent can be removed from the mixture to form a dried mixture (S230). The formation of the dried mixture can include performing a direct evaporation on the mixture. For example, the direct evaporation can include a static drying or a spray drying. In order to form the second particles PTC2 as single particles, it can be advantageous to use the static drying.

[0116] The dried mixture can be calcined in an inert atmosphere (S240). The conditions of the calcination process can be the same as or similar to the conditions of the second calcination process of the first particles PTC1 described above. When the dried mixture is calcined, the second particles PTC2 containing the compound represented by Formula 1 described above can be formed.

[0117] The second particles PTC2 after calcination can be dry-milled (S250). Accordingly, the second particles PTC2 can have a single particle form.

[0118] Referring back Figure 8 The preparation of the third particles PTC3 according to example embodiments of the present disclosure will be described in more detail. An iron phosphate precursor, a lithium source, a carbon source, and a dopant source can be added to a solvent and mixed (S210). For example, the solvent can be or include water, ethanol, etc. The iron phosphate precursor, the lithium source, the carbon source, and the dopant source can be the same as or similar to the iron phosphate precursor, the lithium source, the carbon source, and the dopant source included in the preparation of the first particles PTC1 described previously.

[0119] The mixture can be wet-milled (S220). The wet-milling process can be the same as or similar to the wet-milling process in the preparation of the first particles PTC1 described previously.

[0120] The solvent can be removed from the mixture to form a dry mixture (S230). According to example embodiments of the present disclosure, the formation of the dry mixture can include spray-drying the mixture. The spray-drying apparatus can be the same as the apparatus used in the preparation of the first particles PTC1.

[0121] Particles finely reduced in size to primary particles after the wet-milling process can be aggregated with each other by a spray-drying process, thereby forming secondary particles. By changing spray-drying conditions, the third particles of different shapes from the first particles can be formed. That is, by adjusting the flow rate and flow velocity of a carrier gas, temperature, residence time in a reactor, internal pressure, etc. during the spray-drying process, the third particles PTC3 can be formed as secondary particles of a desired shape and size.

[0122] In example embodiments, the mixture to be spray-dried can have a total solid content (TSC) in a range of about 20 wt% to about 40 wt%. The total solid content can refer to a converted value of a percentage of a weight of a solid substance remaining after evaporation of a solvent (i.e., a dry mixture) with respect to a total weight of a mixture (i.e., a spray liquid). For example, the spray liquid can have a total solid content of about 30 wt%.

[0123] When the total solid content is less than about 20 wt%, a disadvantage that the average particle diameter of the third particles PTC3 is reduced and the yield is decreased can occur. When the total solid content is greater than about 40 wt%, it can become challenging to adjust the average particle diameter of the third particles PTC3, and the size difference between the third particles PTC3 can increase.

[0124] The spray liquid according to the example embodiment can have a viscosity in a range of about 1500 mPa·s to about 2500 mPa·s with the above-described total solid content. For example, the spray liquid can have a viscosity of about 2000 mPa·s.

[0125] In an example embodiment, the spray drying can be performed at a temperature of about 100℃ to about 300℃. A spray gas (e.g., air) for the spray drying can be injected at a first temperature and discharged at a second temperature. For example, the first temperature can be in a range of about 200℃ to about 250℃. The second temperature can be in a range of about 80℃ to about 150℃.

[0126] The spray liquid for the spray drying can have a flow rate in a range of about 30 mL / min to about 80 mL / min. When the flow rate is less than about 30 mL / min, disadvantages such as nozzle clogging, reduced yield, etc. can be caused. When the flow rate is greater than about 80 mL / min, the mixture can not be completely dried due to moisture condensation in the spray drying apparatus. The spray liquid can have an input pressure in a range of about 0.3 MPa to about 0.7 MPa. For example, the input pressure of the spray liquid can be about 0.5 MPa.

[0127] The dried mixture can be calcined in an inert atmosphere (S240). The inert atmosphere can be or include a nitrogen atmosphere and / or an argon atmosphere. The temperature at which the calcination process is performed can be in a range of about 500℃ to about 1000℃, or about 600℃ to about 800℃. The execution time of the calcination process can be in a range of about 4 hours to about 20 hours, or about 6 hours to about 12 hours. When the dried mixture is calcined, the third particles PTC3 including the compound represented by Formula 1 described above can be formed.

[0128] In the preparation of the third particles PTC3, according to example embodiments of the present disclosure, a carbon source can be introduced into the iron phosphate precursor to uniformly form a carbon coating layer on the surface of the primary particles. Thereafter, the primary particles can be aggregated by spray drying to form secondary particles. As a result, the third particles PTC3 can include a stable carbon coating layer on the outside and inside of the third particles PTC3, and thus can have a relatively high carbon content. Due to the high carbon content of the third particles PTC3, the positive electrode active material layer AML1 can have improved conductivity.

[0129] By mixing the prepared first particles PTC1, second particles PTC2, and third particles PTC3 in appropriate or desired ratios, a positive electrode active material according to example embodiments of the present disclosure can be formed.

[0130] Hereinafter, examples and comparative examples of the present disclosure are described. However, the following examples are provided for illustrative purposes only and should not be construed as limiting the scope of the present disclosure.

[0131] Preparation Example 1: Preparation of first particles in secondary particle form Iron phosphate precursor (Fe1PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of about 1 : 1.03:0.03. 10 wt% of glucose was further added to the mixture. The mixture was wet-milled by ball milling. The mixture was heated and hydrothermally treated in an oven tray at about 200°C. The mixture was wet-milled again, and the slurry mixture was dried by spray drying, evaporated, at a spray pressure of about 20 MPa and a temperature of about 400°C. The dried mixture was calcined in a nitrogen atmosphere at about 750°C for about 10 hours to obtain first particles in secondary particle form. The average size of the first particles was about 2.5 pm, and the average size of the primary particles in the first particles was about 200 nm to about 300 nm.

[0132] Preparation Example 2: Preparation of second particles in single particle form Iron phosphate precursor (Fe1PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of about 1 : 1.03:0.03. 10 wt% of glucose was added to the mixture. The mixture was wet-milled by ball milling. The mixture was dried by heating on a tray, evaporated, and then dried in a vacuum oven at about 120°C for about 4 hours. The dried mixture was calcined in a nitrogen atmosphere at about 750°C for about 10 hours. The calcined product was ground to obtain second particles in single particle form. The average size of the second particles was about 700 nm.

[0133] Preparation Example 3: Preparation of third particles in secondary particle form Iron phosphate precursor (Fe1PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of about 1 : 1.03:0.03. 10 wt% of glucose was further added to the mixture. The mixture was wet-milled by ball milling. The slurry mixture was dried by spray drying, evaporated, at a spray pressure of about 0.5 MPa and a temperature of about 230°C. The dried mixture was calcined in a nitrogen atmosphere at about 750°C for about 10 hours to obtain third particles in secondary particle form. The average size of the third particles was about 5 pm, and the average size of the primary particles in the third particles was about 100 nm to about 200 nm.

[0134] Example 1: Preparation of a mixed positive electrode active material The first particles according to Preparation Example 1, the second particles according to Preparation Example 2, and the third particles according to Preparation Example 3 were mixed in a mass ratio of about 85:7.5:7.5 to prepare a positive electrode active material.

[0135] Example 2 The first particles according to Preparation Example 1, the second particles according to Preparation Example 2, and the third particles according to Preparation Example 3 were mixed in a mass ratio of about 75:12.5:12.5 to prepare a positive electrode active material.

[0136] Example 3 The first particles according to Preparation Example 1, the second particles according to Preparation Example 2, and the third particles according to Preparation Example 3 were mixed in a mass ratio of about 65:17.5:17.5 to prepare a positive electrode active material.

[0137] Example 4 The first particles according to Preparation Example 1, the second particles according to Preparation Example 2, and the third particles according to Preparation Example 3 were mixed in a mass ratio of about 50:25:25 to prepare a positive electrode active material.

[0138] Comparative Example 1 A positive electrode active material was prepared using only the first particles according to Preparation Example 1.

[0139] Comparative Example 2 A positive electrode active material was prepared using only the second particles according to Preparation Example 2.

[0140] Comparative Example 3 A positive electrode active material was prepared using only the third particles according to Preparation Example 3.

[0141] Comparative Example 4 The first particles according to Preparation Example 1 and the second particles according to Preparation Example 2 were mixed in a mass ratio of about 70:30 to prepare a positive electrode active material.

[0142] Comparative Example 5 The first particles according to Preparation Example 1 and the third particles according to Preparation Example 3 were mixed in a mass ratio of about 70:30 to prepare a positive electrode active material.

[0143] Comparative Example 6 The second particles according to Preparation Example 2 and the third particles according to Preparation Example 3 were mixed in a mass ratio of about 70:30 to prepare a positive electrode active material.

[0144] Producing positive electrode A positive electrode active material slurry was prepared by mixing 95 wt% of the final positive electrode active material, 3 wt% of a polyvinylidene fluoride binder, and 2 wt% of a carbon black conductive material in an N-methylpyrrolidone solvent. The positive electrode active material slurry was coated onto an aluminum current collector and dried, and then roll-pressed to prepare a positive electrode.

[0145] Manufacturing rechargeable lithium battery A 2032-type coin half-battery was prepared using the prepared positive electrode and lithium metal as a counter electrode. A separator (thickness: about 16 μm) formed of a porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte was introduced to manufacture a rechargeable lithium battery. An electrolyte obtained by mixing 1.3 M of LiPF6in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (volume ratio of about 3:4:3) was used as the electrolyte.

[0146] Evaluation Example 1: Surface analysis of positive electrode active material Figure 9A A scanning electron microscope (SEM) image of the positive electrode active material prepared according to Preparation Example 1 is shown. Figure 9B A SEM image of the positive electrode active material prepared according to Preparation Example 2 is shown. Figure 9C A SEM image of the positive electrode active material prepared according to Preparation Example 3 is shown. Referring to Figure 9A As can be seen, the first particles according to the preparation examples of the present disclosure have the form of secondary particles in which a plurality of primary particles are aggregated, and exist in various shapes. Referring to Figure 9B As can be seen, the second particles according to the preparation examples of the present disclosure are in the form of fine single particles of nanometer size. Figure 9C As can be seen, the third particles according to the preparation examples of the present disclosure are in the form of spherical secondary particles in which a plurality of primary particles are aggregated.

[0147] Evaluation Example 2: Evaluation of positive electrode characteristics The current density and mixture density of the positive electrode plates according to Examples 1 to 4 and Comparative Examples 1 to 6 were measured, and the results are listed in Table 1.

[0148] Table 1

[0149] Referring to Table 1, the positive electrode plates according to Examples 1 to 4 have a higher current density than the positive electrode plates according to Comparative Examples 1 to 6. In addition, the positive electrode plates according to Examples 1 to 4 have a similar or higher mixture density than the positive electrode plates according to Comparative Examples 1 to 6.

[0150] Evaluation Example 3: Evaluation of battery characteristics The life characteristics of rechargeable lithium batteries prepared using the positive electrode active materials according to Examples 1 to 4 and Comparative Examples 1 to 6 were evaluated.

[0151] For initial charging and discharging, the rechargeable lithium battery was initially charged at room temperature under the condition of constant current (0.2C) and constant voltage (3.65V), rested for about 10 minutes, and then discharged with constant current (0.2C) until the voltage reached 2.5V. Thereafter, under the condition of 0.2C / 0.2C and at room temperature, charging and discharging were performed by checking which cycle capacity retention rate from the second cycle became about 80%. The capacity retention rate of the Nth cycle was calculated by Equation 1 below.

[0152] Equation 1: Capacity retention rate [%] = [discharge capacity of the Nth cycle / discharge capacity of the first cycle] x 100.

[0153] Table 2

[0154] Referring to Table 2, the rechargeable batteries according to Examples 1 to 4 have more desirable or improved capacity retention rates compared to the capacity retention rates of the rechargeable batteries according to Comparative Examples 1 to 6. In addition, the rechargeable batteries according to the Examples have desirable or improved life characteristics with a capacity retention rate of at least about 80% after 10,000 cycles.

[0155] The positive electrode active material according to the example embodiments of the present disclosure can have improved electrical conductivity, mixture density (compression density, pellet density), and energy density. The rechargeable lithium battery according to the example embodiments of the present disclosure can have desirable or improved life characteristics.

[0156] Although example embodiments of the present disclosure have been described with reference to the accompanying drawings, it is understood that the present disclosure should not be limited to these example embodiments, but can be variously changed and modified within the scope of the claims, the detailed description of the present disclosure, and the drawings, falling within the scope of the present disclosure.

Claims

1. A positive electrode active material, the positive electrode active material comprising: first particles having an olivine crystal structure and having a first average particle diameter; second particles having an olivine crystal structure and having a second average particle diameter smaller than the first average particle diameter; and third particles having an olivine crystal structure and having a third average particle diameter greater than the first average particle diameter, wherein at least one of the first particles to the third particles comprises a compound represented by the following Formula 1: Formula 1: wherein, in the above Formula 1, 0.8 ≤ a1 ≤ 1.2, 0.950 ≤ x1 ≤ 0.999, 0.001 ≤ y1 ≤ 0.05, 0 ≤ b1 ≤ 0.05, and 0.99 ≤ x1 + y1 ≤ 1.01, and B1 comprises at least one of Ti and Mg. Li a1 Fe x1 B1 y1 PO 4-b1 The first particles are secondary particles comprising a plurality of first primary particles.

2. The positive electrode active material according to claim 1, wherein, 3.The positive electrode active material according to claim 2, an average size of the first primary particles is in a range of 100 nm to 500 nm, and wherein the first average particle diameter is in a range of 1 μm to 7 μm. 4.The positive electrode active material according to claim 1, the first particles comprise a first coating layer comprising carbon, and wherein an amount of carbon in the first particles is in a range of 1.1 wt% to 2.0 wt%. a span value obtained by analyzing the first particles using a particle size analyzer is in a range of 1.33 to 1.

5.

5. The positive electrode active material according to claim 1, wherein, The specific surface area of the first particles is in the range of 8 m 2 / g to 12 m 2 / g.

6. The positive electrode active material according to claim 1, wherein, a porosity of the first particles is in a range of 15% to 20%.

7. The positive electrode active material according to claim 1, wherein, an amount of the first particles is in a range of 50 wt% to 85 wt% with respect to a total weight of the first particles to the third particles.

8. The positive electrode active material according to claim 1, wherein, 9.The positive electrode active material according to claim 1, the second average particle diameter is in a range of 0.5 μm to 2.5 μm, and wherein the third average particle diameter is in a range of 2 μm to 15 μm. 10.The positive electrode active material according to claim 1, the second particles comprise at least one second primary particle, and wherein the third particles comprise approximately spherical or approximately ellipsoidal secondary particles comprising a plurality of third primary particles. a mixing ratio of the second particles to the third particles is in a range of 3:1 to 1:3 based on weight.

11. The positive electrode active material according to claim 1, wherein, 12.The positive electrode active material according to claim 1, at least one of the first particles to the third particles comprises a coating layer comprising carbon, wherein, an amount of carbon on a surface of the first particles is greater than an amount of carbon on a surface of the second particles, and the amount of carbon on the surface of the first particles is less than an amount of carbon on a surface of the third particles. 13.The positive electrode active material according to claim 1, a porosity of the first particles is less than a porosity of the second particles, and wherein a porosity of the first particles is less than a porosity of the third particles. 14.A positive electrode for a rechargeable lithium battery, the positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to claim 1, an electrically conductive material, and a binder. ​ 15. The positive electrode of claim 14, wherein, The current density of the positive electrode is equal to or greater than 4.0 mA / cm 2 .

16. The positive electrode of claim 14, wherein, The mixture density of the positive electrode is equal to or greater than 2.5 g / cc.

17. The positive electrode of claim 14, wherein, The amount of the binder is in the range of 0.5 parts by weight to 5 parts by weight with respect to 100 parts by weight of the positive electrode active material layer.

18. The positive electrode of claim 14, wherein, The binder includes at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer including an oxirane, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, an epoxy resin, a (meth)acrylic resin, a polyester resin, and nylon.

19. The positive electrode of claim 14, wherein, The amount of the conductive material is in the range of 0.5 parts by weight to 5 parts by weight with respect to 100 parts by weight of the positive electrode active material layer.

20. The positive electrode of claim 14, wherein, The conductive material includes at least one of a carbon-based material, a metal-based material in the form of a metal powder or a metal fiber, and a conductive polymer.

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