Cathode active material and preparation method thereof

Abstract

The present invention relates to a positive electrode active material and a positive electrode comprising the same. The positive electrode active material contains a compound represented by chemical formula 1 having an olivine structure in a core, thereby achieving high safety and excellent economical efficiency. Further, the positive electrode active material includes a compound represented by Chemical Formula 1, not only has a large core specific surface area, but also is manufactured by chemical vapor deposition (CVD) using a solid carbon source, which makes the porous carbon layer on the surface of the core more uniform. Therefore, the positive electrode including the same has the advantages of excellent output performance and excellent life characteristics during charging and discharging.

Description

Technical Field

[0001] This invention relates to a positive electrode active material and its manufacturing method.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0003890, filed on January 10, 2024, the entire contents of which are incorporated herein by reference. Background Technology

[0003] In recent years, rechargeable batteries have been widely used not only in small devices such as portable electronic devices, but also in medium and large devices such as battery packs or energy storage devices in hybrid or electric vehicles. In particular, with the recent increase in interest in environmental issues, a great deal of research has been conducted on electric vehicles, hybrid electric vehicles, etc., which can replace vehicles using fossil fuels, such as gasoline and diesel vehicles, which are one of the main causes of air pollution.

[0004] Typically, lithium-ion secondary batteries have the following structure: an electrode assembly comprising a positive electrode, a negative electrode, and a separator is impregnated with a lithium electrolyte. In this case, the individual electrodes are manufactured by coating an electrode slurry onto a current collector. The electrode slurry is prepared by mixing electrode active materials for energy storage, conductive materials for providing conductivity, and an adhesive for adhering them to the current collector and providing bonding between them in a solvent such as NMP (N-methylpyrrolidone).

[0005] The positive electrode includes metal oxides such as LCO (LiCoO2), LMO (LiMn2O4), LFP (LiFePO4), or NCM (LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2) is used as a positive electrode active material that can reversibly insert and deintercalate lithium.

[0006] Compounds with layered crystal structures, such as NCM, LCO, and NCA compounds, are well-suited for lithium-ion storage and exhibit high lithium-ion diffusion rates, making them suitable as positive electrode active materials in high-capacity and high-power secondary batteries. However, compounds with layered crystal structures suffer from low chemical and structural stability, which can easily lead to decomposition under high-temperature conditions. This reduces the safety of secondary batteries.

[0007] On the other hand, LFP compounds with an olivine crystal structure exhibit high structural stability due to their hexagonal crystal system in which phosphorus (P) and oxygen (O) are strongly bonded. Therefore, even if lithium ions are completely intercalated or deintercalated during charging, LFP compounds with an olivine crystal structure can easily maintain their crystal structure, which is also not easily decomposed under high-temperature conditions. However, compounds with an olivine crystal structure have low energy density, which represents the amount of energy that can be stored per unit weight / volume of the battery. Therefore, to achieve high energy density in compounds with an olivine crystal structure, the weight / volume of the positive electrode active material must be increased, leading to excessive increases in the size or weight of the secondary battery. Furthermore, LFP compounds are limited by their low ion diffusivity and conductivity, which significantly restricts their charge-discharge performance.

[0008] To this end, conventional cathode active materials are developed in one of the following ways: by containing a metal such as manganese in an LFP-type compound with an olivine crystal structure, or by coating the particle surface with a conductive material to improve energy density. In the former case, using a structure in which manganese is partially substituted at the positions of iron atoms, an energy density improvement of about 5% or more is achieved in ferrophosphate. Despite this effect, LFP-type compounds used in medium to large-sized secondary batteries require further energy density expression. In the latter case, although the conductivity of the cathode active material may be improved due to the conductive layer on the surface, it is difficult to expect a significant improvement in conductivity not only because a uniform coating is not easily formed on the surface, but also because of the limitation of poor cathode lifetime performance.

[0009] Therefore, it is necessary to develop technologies for the cathode of lithium secondary batteries to achieve high energy density, while incorporating LFP-type compounds with olivine structures as cathode active materials, thereby achieving high safety for lithium secondary batteries.

[0010] [Existing Technical Documents]

[0011] [Patent Literature]

[0012] Korean Patent Application Publication Number: 10-2013-0136796

[0013] Korean Patent Application Publication Number: 10-2016-0111213 Summary of the Invention

[0014] Technical issues

[0015] One object of the present invention is to provide a positive electrode for lithium secondary batteries and a method for manufacturing the same. The positive electrode for lithium secondary batteries can achieve high energy density and contains LFP-type compounds with olivine structures as positive electrode active materials, thereby achieving high safety of lithium secondary batteries.

[0016] Technical solution

[0017] To address the above problems, the present invention provides a positive electrode, the positive electrode comprising: Positive current collector, and A positive electrode active layer is disposed on at least one side of the positive electrode current collector and comprises a compound represented by the following chemical formula 1 as a positive electrode active material: [Chemical Formula 1] Li 1+a Mn 1-b-c Fe b M 1 c PO4 In the above chemical formula 1, M 1 It is one or more of Ti, V, Zr, Sr, Sb, B, and Nb. a, b, and c are -0.5≤a≤0.5, 0.1≤b≤0.8, and 0.001≤c≤0.2.

[0018] In this case, the positive electrode active material may contain one or more compounds represented by the following chemical formulas 2 to 5: [Chemical Formula 2] Li 1+a Mn 1-b-x Fe b Ti x PO4 [Chemical Formula 3] Li 1+a Mn 1-b-x-y Fe b Ti x V y PO4 [Chemical Formula 4] Li 1+a Mn 1-b-x-y-z Fe b Ti x V y Nb z PO4 [Chemical Formula 5] Li 1+a Mn 1-b-x-y-z Fe b Ti x Zr y Nb z PO4 In the above chemical formulas 2 to 5, a, b, x, y, and z are such that -0.5 ≤ a ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0 < x ≤ 0.2, 0 < y ≤ 0.1, 0 < z ≤ 0.1, provided that 0.001 ≤ x + y ≤ 0.2 or 0.001 ≤ x + y + z ≤ 0.2.

[0019] In addition, when analyzed by X-ray diffraction, the lattice constant c of the positive electrode active material can be from 4.69165 Å to 4.80 Å and satisfy the following Mathematical Formula 1: [Mathematical Formula 1] y = -px + q In the above Mathematical Formula 1, y represents the lattice constant c, x represents , where a and b are the lattice constants a and b respectively, p and q are -0.08 ≤ p ≤ -0.07 and 5 ≤ q ≤ 6 respectively.

[0020] The average particle diameter (D 50 ) of the positive electrode active material can be from 0.5 μm to 10 μm, and the average thickness of the carbon layer can be 50 nm or less.

[0021] In addition, in one embodiment, the present invention provides a method for manufacturing a positive electrode active material, the method comprising: forming a carbon layer on the surface of particles of a compound represented by the following Chemical Formula 1, where the carbon layer is formed by chemical vapor deposition (CVD) under an inert gas condition, [Chemical Formula 1] Li 1+a Mn 1-b-c Fe b M 1 c PO4 In Chemical Formula 1, M 1 is one or more selected from Ti, V, Zr, Sr, Sb, B, and Nb, a, b, and c are -0.5 ≤ a ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0.001 ≤ c ≤ 0.2.

[0022] Here, chemical vapor deposition (CVD) can use one or more of the following substances as a carbon source: a carbon structure containing one or more of a dot-like carbon compound and a linear carbon compound; and a polymer compound.

[0023] Dot-like carbon compounds may include one or more selected from acetylene black, channel black, furnace black, lamp black, thermal cracking black, and graphene, and linear carbon compounds may include one or more selected from carbon nanotubes and carbon fibers.

[0024] In addition, the polymer compound may contain one or more selected from polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polypyrrole (PPy), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethyl acrylate (PMA), and poly(methyl methacrylate) (PMMA).

[0025] In addition, chemical vapor deposition (CVD) can be performed at temperatures ranging from 500°C to 1,500°C.

[0026] Furthermore, the present invention provides a positive electrode, the positive electrode comprising: Positive current collector; and A positive electrode active layer is disposed on at least one side of a positive electrode current collector and comprises the positive electrode active material according to the present invention as described above.

[0027] Beneficial effects

[0028] The positive electrode active material according to the present invention contains a compound represented by Chemical Formula 1 with an olivine structure in the core, resulting in high safety and excellent economy. Furthermore, the positive electrode active material contains a compound represented by Chemical Formula 1, which not only has a large core specific surface area but is also manufactured using a solid carbon source via chemical vapor deposition (CVD), resulting in a more uniform porous carbon layer on the surface of the core. Therefore, the positive electrode containing this active material has the advantages of excellent output performance and outstanding lifetime characteristics during charge and discharge. Attached Figure Description

[0029] Figure 1 A graph showing the correlation between the lattice constant c of the positive electrode active material and the lattice constants a and b in X-ray diffraction (XRD) analysis. Detailed Implementation

[0030] This invention can have various modifications and implementations, and specific implementations will be described in detail in the following specific implementations.

[0031] However, it should be understood that the present invention is not limited to the specific embodiments, but includes all modifications, equivalents or substitutions within the spirit and scope of the present invention.

[0032] As used herein, the terms “comprising,” “including,” and “having” mean the presence of the features, figures, steps, actions, constituent elements, or components described in the specification, or combinations thereof, and it should be understood that the possibility of the presence or addition of one or more other features, figures, steps, actions, constituent elements, components, or combinations thereof is not excluded in advance.

[0033] Furthermore, in this specification, "average particle size (D)" 50 The average particle size refers to the particle size at which the cumulative value in the particle size distribution becomes 50%, also known as the median particle size. The average particle size can be measured by methods commonly used in the art. For example, an analyzer can be used to measure the average particle size, such as a particle size analyzer or an analyzer that uses laser diffraction scattering particle size distribution measurement, but is not limited to these.

[0034] The invention will be described in more detail below.

[0035] Positive electrode active material

[0036] This invention provides a positive electrode active material, the positive electrode active material comprising: Contains a core of a compound represented by the following chemical formula 1, and The carbon layer surrounding the nucleus, [Chemical Formula 1] Li 1+a Mn 1-b-c Fe b M 1 c PO4 In chemical formula 1, M 1 It is selected from one or more of Ti, V, Zr, Sr, Sb, B, and Nb. a, b, and c are -0.5≤a≤0.5, 0.1≤b≤0.8, and 0.001≤c≤0.2.

[0037] The positive electrode active material according to the present invention refers to a positive electrode active material used in the positive electrode of a lithium secondary battery. The positive electrode active material has a core-shell structure comprising a core in which an electrochemical reaction occurs during the charging and discharging of the lithium secondary battery, and a shell surrounding the surface of the core. Here, the core comprises a compound represented by Chemical Formula 1. The positive electrode active material according to the present invention comprises a compound represented by Chemical Formula 1 with an olivine structure in the core, resulting in high safety and excellent economy. Furthermore, the positive electrode active material has a high core specific surface area, making the carbon layer on the surface more uniform. Therefore, the positive electrode containing this active material has the advantages of excellent output performance and outstanding lifetime characteristics during charging and discharging.

[0038] Specifically, the core contains a compound represented by Formula 1 with an olivine structure. The olivine structure has a hexagonal crystal system and exhibits strong bonding between phosphorus (P) and oxygen (O), demonstrating high structural stability. Therefore, even when all lithium ions are intercalated or deintercalated during charging, the compound represented by Formula 1 can easily maintain its crystal structure and is not prone to crystal structure decomposition even at high temperatures. As a result, the positive electrode active material containing the compound represented by Formula 1 in the core exhibits excellent lifetime characteristics and outstanding safety features in all aspects, including overcharge and overdischarge. Furthermore, because this compound contains abundant and inexpensive iron, it is superior to, for example, LiNi... 1 / 3 Co 1 / 3 Mn 1 / 3 Lithium composite oxides such as O2, LiCoO2, LiNiO2, or LiMn2O4 are cheaper and less toxic, thus having a smaller environmental impact.

[0039] Furthermore, compared to lithium iron phosphate (LiFePO4), lithium manganese iron phosphate (LiMn) contains only lithium (Li), manganese (Mn), and iron (Fe) as metals. 1-b Fe b The energy density of PO4 is slightly higher, but the difference is not significant. However, the compounds represented by Formula 1 used in this invention can have higher energy densities by doping and / or substituting with more than one metal. Specifically, the compounds represented by Formula 1 may contain compounds in which lithium manganese iron phosphate is doped and / or substituting with more than one of titanium (Ti), vanadium (V), zirconium (Zr), and niobium (Nb). For example, the compounds represented by Formula 1 may include more than one of the compounds represented by Formulas 2 to 5: [Chemical Formula 2] Li 1+a Mn 1-b-x Fe b Ti x PO4 [Chemical Formula 3] Li 1+a Mn 1-b-x-y Fe b Ti x V y PO4 [Chemical Formula 4] Li 1+a Mn 1-b-x-y-z Fe b Ti x V y Nb z PO4 [Chemical Formula 5] Li 1+a Mn1-b-x-y-z Fe b Ti x Zr y Nb z PO4 In Chemical Formulas 2 to 5, a, b, x, y, and z are such that -0.5 ≤ a ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0 < x ≤ 0.2, 0 < y ≤ 0.1, 0 < z ≤ 0.1, provided that 0.001 ≤ x + y ≤ 0.2 or 0.001 ≤ x + y + z ≤ 0.2.

[0040] The compounds represented by Chemical Formulas 2 to 5 are lithium manganese iron phosphate (LiMn 1-b Fe b PO4) doped or substituted with titanium (Ti), vanadium (V), zirconium (Zr), and / or niobium (Nb). Here, the doped or substituted metals can each be doped or substituted at a total mole fraction of 0.1 mole fraction or less based on the metals other than lithium (Li), and the ratio of lithium (Li) to these metals (Li / Me) can be 1.01 to 1.50, specifically 1.01 to 1.30; 1.01 to 1.20; or 1.01 to 1.15. The concentration of lithium (Li) in the positive electrode active material is closely related to the density of the particles. Specifically, the higher the lithium concentration, the higher the density, which is beneficial for removing voids within the particles, thereby achieving a high calendering density. However, an excessively high lithium concentration will reduce the mobility of lithium ions, resulting in a decline in electrical performance. In addition, a significantly low lithium concentration will lead to a low particle density, resulting in a low calendering density and a low energy density per unit volume / mass during the preparation of the positive electrode. The present invention can overcome these problems by adjusting the ratio of lithium (Li) to metal (Me) contained in the positive electrode active material to the above range.

[0041] Such compounds represented by Chemical Formula 1 can include one or more of the following compounds: The compound represented by Chemical Formula 2, such as LiMn 0.8 Fe 0.19 Ti 0.01 PO4, LiMn 0.7 Fe 0.29 Ti 0.01 PO4, LiMn 0.6 Fe 0.39 Ti 0.01 PO4, LiMn 0.8 Fe 0.17 Ti 0.03 PO4, LiMn 0.7 Fe 0.27 Ti 0.03 PO4, LiMn 0.6 Fe0.37 Ti 0.03 PO4, LiMn 0.8 Fe 0.15 Ti 0.05 PO4, LiMn 0.7 Fe 0.25 Ti 0.05 PO4, LiMn 0.6 Fe 0.35 Ti 0.05 PO4; Compounds represented by chemical formula 3, such as LiMn 0.8 Fe 0.18 Ti 0.01 V 0.01 PO4, LiMn 0.7 Fe 0.28 Ti 0.01 V 0.01 PO4, LiMn 0.6 Fe 0.38 Ti 0.01 V 0.01 PO4, LiMn 0.8 Fe 0.15 Ti 0.025 V 0.025 PO4, LiMn 0.7 Fe 0.25 Ti 0.025 V 0.025 PO4, LiMn 0.6 Fe 0.35 Ti 0.025 V 0.025 PO4, LiMn 0.8 Fe 0.1 Ti 0.05 V 0.05 PO4, LiMn 0.7 Fe 0.2 Ti 0.05 V 0.05 PO4, LiMn 0.6 Fe 0.3 Ti 0.05 V 0.05 PO4; Compounds represented by chemical formula 4, such as LiMn 0.8 Fe 0.17 Ti 0.01 V 0.01 Nb 0.01 PO4, LiMn 0.7 Fe 0.27 Ti 0.0 1V 0.01 Nb 0.01 PO4, LiMn 0.6Fe 0.37 Ti 0.01 V 0.01 Nb 0.01 PO4, LiMn 0.8 Fe 0.12 Ti 0.03 V 0.025 Nb 0.025 PO4, LiMn 0.7 Fe 0.22 Ti 0.03 V 0.025 Nb 0.025 PO4, LiMn 0.6 Fe 0.32 Ti 0.03 V 0.025 Nb 0.025 PO4, LiMn 0.8 Fe 0.05 Ti 0.05 V 0.05 Nb 0.05 PO4, LiMn 0.7 Fe 0.15 Ti 0.05 V 0.05 Nb 0.05 PO4, LiMn 0.6 Fe 0.25 Ti 0.05 V 0.05 Nb 0.05 PO4; and a compound represented by Chemical Formula 5, such as LiMn 0.8 Fe 0.17 Ti 0.01 Zr 0.01 Nb 0.01 PO4, LiMn 0.7 Fe 0.27 Ti 0.01 Zr 0.01 Nb 0.01 PO4, LiMn 0.6 Fe 0.37 Ti 0.01 Zr 0.01 Nb 0.01 PO4, LiMn 0.8 Fe 0.12 Ti 0.03 Zr 0.025 Nb 0.025 PO4, LiMn 0.7 Fe 0.22 Ti 0.03 Zr 0.025 Nb 0.025 PO4, LiMn 0.6 Fe0.32 Ti 0.03 Zr 0.025 Nb 0.025 PO4, LiMn 0.8 Fe 0.05 Ti 0.05 Zr 0.05 Nb 0.05 PO4, LiMn 0.7 Fe 0.15 Ti 0.05 Zr 0.05 Nb 0.05 PO4, LiMn 0.6 Fe 0.25 Ti 0.05 Zr 0.05 Nb 0.05 PO4.

[0042] The compound represented by Formula 1 can have a particle size adjusted to a predetermined range according to the amount and / or molar fraction of the metals doped and / or substituted in lithium manganese iron phosphate. This is achieved by using lithium manganese iron phosphate containing one or more metals doped and / or substituted, in conjunction with lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiMn). 1-b Fe b Compared to PO4, the core of the positive electrode active material can have a smaller size. Therefore, the core containing the compound represented by Formula 1 has a larger specific surface area, which makes it possible to form a more uniform carbon layer on the core surface.

[0043] More specifically, as the type or molar fraction of the metal being doped or substituted increases, the lattice constant c of lithium manganese iron phosphate, represented by chemical formula 1, can increase, and the grain size can decrease.

[0044] In other words, the present invention is characterized in that the core contains a compound represented by chemical formula 1, wherein one or more metals are doped or replaced in lithium manganese iron phosphate, thereby making the core size smaller and the specific surface area larger, resulting in a more uniformly coated carbon layer on the core surface.

[0045] Here, the crystallite size of the compound represented by chemical formula 1 can be measured in the form of lattice constants a, b, c, etc., which represent the lengths of the sides of the crystallite during X-ray spectroscopy analysis. Here, "particle" refers to micrometer-sized particles, which, when observed at magnification, can be divided into "grains" with crystals on the order of tens of nanometers. When the grains are further magnified, unit regions (i.e., lattices) where atoms form a lattice structure along specific directions can be identified, and these are called "crystallites".

[0046] As an example, the compound represented by Formula 1 according to the present invention, due to doping or substitution with titanium (Ti), vanadium (V), zirconium (Zr) and / or niobium (Nb) along with manganese (Mn), can therefore have a higher degree of oxidation than lithium manganese iron phosphate (LiMn) without transition metals. 1-b Fe b The lattice constant c of PO4 is approximately 4.6916. A larger lattice constant c. For example, when analyzed by X-ray diffraction, the lattice constant c of the positive electrode active material can be 4.69165. Up to 4.80 Specifically, when analyzed by X-ray diffraction, the lattice constant c of the positive electrode active material can be 4.69165. Up to 4.80 ; 4.69165 Up to 4.75 ; 4.69165 Up to 4.70 ; 4.69165 Up to 4.695 ; 4.69165 Up to 4.694 ; 4.69165 Up to 4.693 ; 4.6917 Up to 4.6925 ; or 4.6918 Up to 4.6925 .

[0047] The "lattice constant" refers to the value representing the edge length of a crystallite. It describes the size and arrangement of a material and can be expressed in various forms depending on the crystal structure. In the case of an olivine structure, which has an orthorhombic crystal structure, it can have lattice constants a, b, and c. The lattice constant c is a factor representing the cell size of the crystal along the c-axis and is closely related to the structure and chemical properties of the crystallite. For example, in lithium manganese iron phosphate (LiMn) with an olivine structure... 1-b Fe b In the case of PO4, the c-axis direction can serve as the primary path for lithium ion movement. The lattice constant c (which represents the dimension along the c-axis) is determined when the radius of the doped ion is greater than that of Fe. 2+ and Mn 2+ Larger Ti 4+ V 5+ 、Nb 5+The lattice constant c can be increased. Increasing the lattice constant c can extend the lithium-ion pathway and increase the lithium-ion diffusion coefficient. Therefore, the cathode active material according to the present invention can have excellent electrical performance within the above-mentioned range of lattice constant c. However, when the upper limit of this range is exceeded, a secondary phase may form inside the olivine structure. When a secondary phase forms inside the olivine structure, the electrochemical activity may actually decrease. Furthermore, when the range is lower than the lower limit, the electrical performance of the cathode active material may decrease significantly.

[0048] Furthermore, compounds represented by Formula 1 exhibit a linear relationship when the lattice constant c is expressed as a function of lattice constants a and b, which conforms to Vegard's law. Specifically, the lattice constant c can have a particular correlation with the square root of the sum of the squares of lattice constants a and b, and this correlation can be represented by the following mathematical formula 1: [Mathematical Expression 1] y = -px + q In the above mathematical formula 1, y represents the lattice constant c. x represents Where a and b are the lattice constants a and b, respectively. p and q are -0.08≤p≤-0.07 and 5≤q≤6, respectively.

[0049] Mathematical Formula 1 shows the correlation between the lattice constants a and b and the lattice constant c of lithium manganese iron phosphate represented by Chemical Formula 1. The lattice constants a, b, and c, and their correlation, vary not only according to the type or mole fraction of the doped and / or substituted metal, but also according to the manufacturing method or process conditions. In the case of this invention, as... Figure 1 As shown, the lattice constant c tends to increase with increasing quantity or molar fraction of doped and / or substituted metals in lithium manganese iron phosphate. In other words, the positive electrode active material of the present invention satisfies the range of the lattice constant c as described above, and because the lattice constant c increases with increasing quantity or molar fraction of doped and / or substituted metals in lithium manganese iron phosphate (LiMn 1-b Fe b Metals (M) doped and / or substituted in PO4 1 The lattice constant c tends to increase with the increase of the quantity or mole fraction of , and therefore it can satisfy mathematical equation 1. The fact that the lattice constant c shows a linear relationship when expressed as a relation to the lattice constants a and b means that even in lithium manganese iron phosphate (LiMn) 1-b Fe b Even when doped or substituted with multiple components (e.g., Ti, V, Zr, Sr, Sb, B, Nb, etc.) in olivine (PO4), the olivine crystal structure can still be maintained. In other words, this indirectly shows that even when doped or substituted with multiple components, the structural safety of the positive electrode active material according to the present invention remains at a high level.

[0050] The size of the grains formed by such lattice units can be identified by the X-axis dimension during X-ray diffraction analysis. The grain size can be greater than about 70 nm and less than 120 nm. More specifically, the grain size can be about 70 nm to 115 nm; about 70 nm to 105 nm; about 70 nm to 99 nm; about 70 nm to 95 nm; or about 80 nm to 99 nm.

[0051] By adjusting the grain size of the compound represented by Chemical Formula 1 contained in the core to the aforementioned range, the cathode active material according to the present invention can increase the specific surface area of ​​the core while minimizing interparticle aggregation. Consequently, the cathode active material can have a more uniform carbon layer on the core surface, thereby further improving the electrical performance of the cathode containing it. Grains are particles formed by the aggregation of microcrystals; generally, as the size of the microcrystals increases, the grain size can also increase. However, in the case of the cathode active material according to the present invention, when multiple components are doped or replaced, lattice interference effects may occur. In this case, structural changes in the microcrystal boundaries or an increase in the number of microcrystal boundaries may occur, thus the tendency for the grain size to increase with the increase in microcrystal size may not be observed.

[0052] On the other hand, the carbon layer of the positive electrode active material has a structure that uniformly surrounds the surface of the core. Here, the carbon layer can have a porous structure with high surface area and a form that uniformly surrounds the core surface with high crystallinity. This structure of the carbon layer can further enhance the electrochemical reactivity and electrical performance of the positive electrode active material, thereby improving the output and lifetime characteristics of the positive electrode active material.

[0053] Here, the thickness of the carbon layer can be adjusted within a range without reducing the energy density of the positive electrode active material. Specifically, the average thickness of the carbon layer can be less than 50 nm. More specifically, the average thickness of the carbon layer can be within the following ranges: less than 40 nm; less than 30 nm; less than 20 nm; less than 10 nm; 5 nm to 40 nm; 5 nm to 20 nm; 10 nm to 30 nm; 20 nm to 45 nm; 10 nm to 20 nm; 5 nm to 10 nm; 1 nm to 10 nm; or 3 nm to 9 nm.

[0054] Furthermore, the positive electrode active material, including the aforementioned core and carbon layer, can have specific dimensions. For example, the average particle size (D) of the positive electrode active material... 50It can be in the range of 0.5 μm to 10 μm, specifically in the following ranges: 0.5 μm to 8 μm; 0.5 μm to 6 μm; 0.5 μm to 4 μm; 0.5 μm to 2 μm; 1 μm to 5 μm; 2 μm to 4 μm; 4 μm to 8 μm; 5 μm to 9 μm; 3 μm to 6 μm; 0.5 μm to 1.5 μm; or 0.7 μm to 1.4 μm.

[0055] This invention utilizes the average particle size (D) of the positive electrode active material 50 Adjusting the particle size to the aforementioned range to prevent the diameter from falling below the lower limit of that range can prevent the agglomeration of the positive electrode active material, which would reduce processability and reliability during positive electrode manufacturing. Furthermore, if the particle size exceeds the upper limit of the aforementioned range, electrical performance deteriorates, and there is a risk of damage to the positive electrode active material during the calendering process, such as breakage.

[0056] The positive electrode active material according to the present invention possesses high structural safety and economy due to the above-described structure. Furthermore, by including a compound represented by Chemical Formula 1 in the core, the positive electrode active material has a high core-to-core surface area, resulting in a more uniform carbon layer on the surface. Therefore, the positive electrode containing this material exhibits excellent output performance and outstanding lifetime characteristics during charge and discharge.

[0057] Methods for manufacturing positive electrode active materials

[0058] Furthermore, the present invention provides a method for manufacturing the above-mentioned positive electrode active material, the method comprising: A carbon layer is formed on the surface of particles of a compound represented by the following chemical formula 1. The carbon layer is formed by chemical vapor deposition (CVD) under inert gas conditions. [Chemical Formula 1] Li 1+a Mn 1-b-c Fe b M 1 c PO4 In chemical formula 1, M 1 It is selected from one or more of Ti, V, Zr, Sr, Sb, B, and Nb. Furthermore, a, b, and c are -0.5≤a≤0.5, 0.1≤b≤0.8, and 0.001≤c≤0.2.

[0059] The method for manufacturing a positive electrode active material according to the present invention refers to the method for manufacturing a positive electrode active material as described above. The method for manufacturing a positive electrode active material according to the present invention includes a process of forming a carbon layer on the surface of a particle of a compound represented by Chemical Formula 1, which serves as the core.

[0060] Here, the core, on which a carbon layer is disposed, can be manufactured through a specific process. The manufacturing process of the core includes the production of a compound represented by chemical formula 1, which can be produced by calcining a mixture of a compound represented by chemical formula 6 and a metal precursor compound at temperatures above 500°C, more specifically at 500°C to 1,000°C; 500°C to 900°C; 500°C to 800°C; or 500°C to 750°C.

[0061] [Chemical Formula 6]

[0062] Li 1+m Mn 1-n Fe n PO4

[0063] In chemical formula 6, m and n are -0.5≤m≤0.5 and 0.1≤n≤0.8.

[0064] Conventional metallic compounds with an olivine structure are typically manufactured by mixing a lithium phosphate compound, which serves as a lithium feedstock, with precursor compounds each containing a transition metal other than lithium, and then calcining the mixture at a high temperature. However, in this invention, the compound represented by Formula 1 can be manufactured by first calcining a mixture of a manganese precursor compound, an iron precursor compound, and a lithium phosphate compound to form lithium manganese iron phosphate represented by Formula 6; subsequently, the precursor compound containing the metal to be doped and / or replaced in the generated lithium manganese iron phosphate is mixed and calcined.

[0065] Here, the compound represented by Formula 6 may be pre-heat-treated at 500°C to 900°C for 0.1 to 20 hours before being mixed with the metal precursor compound. Specifically, the compound represented by Formula 6 may undergo a pre-calcination process for 1 to 6 hours; or 1 to 3 hours; before being mixed with the metal precursor compound. Here, the pre-calcination temperature may be 500°C to 800°C; or 550°C to 750°C.

[0066] This invention can significantly reduce the moisture content of lithium manganese iron phosphate (represented by chemical formula 6) by heat-treating it under the above-described conditions before mixing it with a metal precursor compound. As a result, the metal contained in the metal precursor compound can be readily doped into the lithium manganese iron phosphate or replaced at iron atom positions. However, at temperatures below the above-described temperature range, there is a limitation that the moisture in the lithium manganese iron phosphate cannot be sufficiently removed, and at temperatures above the above-described temperature range, the crystallinity of the lithium manganese iron phosphate may increase, making metal doping and / or substitution more difficult.

[0067] The heat-treated compound of Formula 6 can be mixed with a metal precursor compound and sintered to produce the compound of Formula 1 of the present invention. Here, the metal precursor compound refers to the lithium manganese iron phosphate represented by Formula 6, which supplies titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), etc. The metal precursor compound is not particularly limited, as long as it can supply titanium (Ti), vanadium (V), zirconium (Zr), and / or niobium (Nb).

[0068] Preferably, the titanium (Ti) precursor compound may contain one or more titanium oxides or titanium alkoxides selected from those containing titanium (Ti) as a component. For example, the titanium (Ti) precursor compound may contain titanium oxides (e.g., TiO, TiO2) or titanium alkoxides (e.g., Ti[OCH(CH3)2]4), but is not limited thereto.

[0069] Furthermore, vanadium (V) precursor compounds can be vanadium oxides, vanadium ammonium salts, or combinations thereof. For example, vanadium (V) precursor compounds may include vanadium oxides such as VO2, V2O3, V2O5, or ammonium vanadate (NH4VO3), but are not limited thereto.

[0070] Zirconium (Zr) precursor compounds can be zirconium oxides, zirconium acetates, or combinations thereof. For example, zirconium (Zr) precursor compounds can contain zirconium oxides, such as ZrO2, or zirconium compounds, such as Zr6O4(OH)4(O2CCH3). 12 However, it is not limited to this.

[0071] Furthermore, niobium (Nb) precursor compounds can be niobium-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, hydroxyoxides, or combinations thereof. For example, niobium (Nb) precursor compounds may include niobium oxides, such as NbO, NbO2, Nb2O5; niobium salts, such as NbCO3, Nb(NO3)2, NbSO4, niobium acetate, niobium dicarboxylate, niobium citrate, niobium fatty acid salts; niobium hydroxyoxides; niobium chlorides; or combinations thereof, but are not limited thereto.

[0072] Furthermore, the method for manufacturing positive electrode active materials according to the present invention can perform chemical vapor deposition (CVD) under inactive gas conditions to uniformly coat a carbon layer on a core containing a compound represented by chemical formula 1.

[0073] Chemical vapor deposition (CVD) is a method of depositing evaporated feedstock as a thin film onto a substrate injected into a reactor under vacuum or inert gas conditions. The advantage of this invention is that, by using such chemical vapor deposition (CVD), a thin carbon layer can be formed more uniformly on a core containing a compound represented by chemical formula 1.

[0074] Here, chemical vapor deposition (CVD) can be carried out under conditions where the interior of the reactor is replaced with an inactive gas, such as nitrogen, argon or helium, thereby preventing impurities from flowing into the carbon layer during carbon layer deposition and preventing side reactions from occurring on the carbon layer surface.

[0075] Furthermore, chemical vapor deposition (CVD) can be performed during deposition in a reactor filled with a partially mixed hydrogen gas. For example, CVD can be performed with a primary deposition while argon gas is supplied at a flow rate of 150 sccm to 250 sccm inside a reactor purged with argon, followed by a secondary deposition by continuously supplying hydrogen gas at a flow rate of 10 sccm to 20 sccm and argon gas at a flow rate of 250 sccm to 350 sccm to the reactor. In this case, carbon seeds for carbon layer deposition are generated during the primary deposition, and the growth of the generated carbon seeds can be promoted during the secondary deposition.

[0076] Chemical vapor deposition (CVD) can be performed within 100 minutes, specifically, from 1 minute to 100 minutes; from 1 minute to 75 minutes; from 1 minute to 50 minutes; from 1 minute to 30 minutes; from 1 minute to 20 minutes; from 1 minute to 10 minutes; or from 10 minutes to 70 minutes.

[0077] Furthermore, as mentioned above, when hydrogen is mixed during deposition, a single deposition can be carried out within 30 minutes, followed by a second deposition lasting 30 to 70 minutes.

[0078] As an example, chemical vapor deposition (CVD) can be performed with a first deposition of 10 minutes under inert gas conditions, followed by a second deposition of 30 to 40 minutes under conditions of partial mixing of hydrogen and inert gas.

[0079] The present invention can effectively control the thickness of the carbon layer on the core surface by adjusting the chemical vapor deposition (CVD) process time to the above range.

[0080] Furthermore, chemical vapor deposition (CVD) can be performed at high temperatures to evaporate the carbon source for carbon layer formation. Specifically, the CVD temperature can be from 500°C to 1500°C, more specifically from 500°C to 1300°C; 500°C to 1100°C; 500°C to 1000°C; 500°C to 900°C; 600°C to 1300°C; 800°C to 1100°C; 1000°C to 1500°C; 750°C to 990°C; or 600°C to 900°C.

[0081] This invention not only enables the uniform formation of a carbon layer on the core by controlling the chemical vapor deposition (CVD) temperature within the aforementioned range, but also transforms the carbon deposited on the core surface into a highly crystalline carbon layer. This highly crystalline carbon layer can significantly enhance the electrical properties of the positive electrode active material, such as conductivity, thereby providing the advantage of improved output performance of the positive electrode during the charge and discharge of the secondary battery.

[0082] As an example, the positive electrode active material according to the present invention comprises a carbon layer deposited by chemical vapor deposition (CVD) within the aforementioned temperature range, such that during Raman spectroscopy analysis, at 1580±50 cm⁻¹... -1 The area of ​​the peak appearing at this location can be greater than 1360±50 cm². -1 The area of ​​the peak that appears at that location.

[0083] In Raman spectroscopy analysis, at 1360±50 cm⁻¹... -1 and 1580±50 cm -1 The peak appearing at this point is a peak observed in carbon compounds such as graphite, carbon black, graphene, and carbon nanotubes (CNTs). Specifically, the peak at 1360±50 cm⁻¹ is... -1 The peak appearing at 1580±50 cm⁻¹ is a peak that occurs during Raman spectroscopy analysis when phonons scatter inelasticly and elastically around defect / substitution points in carbon compounds. A higher intensity and / or area ratio of this peak indicates that the compound has more defects or substitutions in its structure and lower crystallinity. Conversely, at 1580±50 cm⁻¹... -1 The peak appearing at a certain point is due to first-order Raman scattering, indicating that the higher the intensity and / or area ratio of the peak, the higher the crystallinity. In other words, according to the present invention, the peak area representing the crystallinity of carbon contained in the carbon layer is larger than the peak area representing the amorphousness of the carbon compound during Raman spectroscopy analysis of the positive electrode active material, indicating that the carbon layer has high crystallinity.

[0084] In this case, the carbon coating is at 1360±50 cm. -1 The peak area at 1580±50 cm⁻¹ is similar to that at 1580±50 cm⁻¹. -1The ratio of peak areas appearing at a given location can be 30% to 90%, and more specifically, it can be 50% to 90%; 60% to 90%; 70% to 90%; 60% to 85%; or 55% to 80%.

[0085] Furthermore, chemical vapor deposition (CVD) can be performed using solid carbon sources. Specifically, CVD can use carbon structures comprising one or more of point-like and linear carbon compounds, as well as polymer compounds, as carbon sources, either alone or in combination.

[0086] More specifically, the dot-like carbon compound may contain one or more selected from acetylene black, channel black, furnace black, lamp black, thermal cracking black, and graphene. Furthermore, the linear carbon compound may contain one or more selected from carbon nanotubes and carbon fibers.

[0087] In addition, the polymer compound may contain one or more selected from polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polypyrrole (PPy), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethyl methacrylate (PMA), and poly(methyl methacrylate) (PMMA).

[0088] As an example, the carbon source can be a dotted carbon compound, and the dotted carbon compound can contain acetylene black.

[0089] As another example, the carbon source can comprise both dot-shaped and linear carbon compounds. Here, the dot-shaped carbon compound can comprise acetylene black, and the linear carbon compound can comprise carbon nanotubes (CNTs). Furthermore, in this case, the dot-shaped and linear carbon compounds can be contained in a weight ratio of 1:10 to 10:1, specifically, in weight ratios of 1:5 to 5:1, 1:3 to 3:1, 1:2 to 2:1, 1:5 to 1:1.5, 1:1.5 to 1.5, or 1:1.5 to 1.5:1.

[0090] As another example, the carbon source can comprise dotted carbon compounds, linear carbon compounds, and polymer compounds. Here, the dotted carbon compound can comprise acetylene black, the linear carbon compound can comprise carbon nanotubes (CNTs), and the polymer compound can comprise polyvinylpyrrolidone (PVP). In this case, based on 100 parts by weight of the dotted carbon compound, the content of the linear carbon compound and the polymer compound can each be 10 to 90 parts by weight, specifically, based on 100 parts by weight of the dotted carbon compound, they can each be 10 to 80 parts by weight; 10 to 70 parts by weight; 10 to 60 parts by weight; 10 to 50 parts by weight; 10 to 40 parts by weight; 30 to 70 parts by weight; 60 to 80 parts by weight; or 20 to 40 parts by weight.

[0091] Conventional chemical vapor deposition (CVD) for forming carbon layers uses hydrocarbon gases such as methane (CH4), ethane (CH3CH3), propane (CH3CH2CH3), ethylene (CH2CH2), and acetylene (CHCH). In this case, since a carbon source vaporization process is not required, the process can be carried out at lower temperatures. However, limitations exist: it is not easy to control the gaseous carbon source during deposition, and the high reactivity of the carbon source can cause side reactions on the core surface, reducing the activity of the positive electrode active layer. Furthermore, the formed carbon layer is an amorphous layer with low crystallinity, and therefore does not have a large specific surface area. However, the present invention not only has high operability during deposition using a solid carbon source, but also exhibits excellent electrical properties such as conductivity due to the high crystallinity of the carbon layer. In particular, when a polymer compound such as polyvinylpyrrolidone (PVP) is used as the carbon source, a carbon layer with a porous structure can be formed, resulting in a carbon layer with a high surface area on the core surface. In this case, the ion transfer capability of the carbon layer increases, improving the lithium diffusion coefficient, and the resulting positive electrode active material exhibits excellent output performance.

[0092] The method for manufacturing positive electrode active materials according to the present invention can produce positive electrode active materials having a uniformly coated carbon layer on a core comprising a compound represented by Chemical Formula 1 by having the above-described structure. Furthermore, the correspondingly manufactured positive electrode active materials not only possess high structural safety but also have the advantages of excellent output performance during charge and discharge and outstanding lifetime characteristics.

[0093] positive electrode

[0094] Furthermore, the present invention provides a positive electrode, the positive electrode comprising: Positive current collector, and A positive electrode active layer is disposed on at least one side of a positive electrode current collector and comprises the positive electrode active material according to the present invention as described above.

[0095] The positive electrode according to the present invention comprises a positive electrode active layer disposed on at least one side of a positive electrode current collector. Here, the positive electrode active layer is a layer that realizes the electroactivity of the positive electrode, mainly comprising positive electrode active material that undergoes electrochemical redox reactions during battery charging and discharging. Specifically, based on the total weight of the positive electrode active layer, the content of the positive electrode active material can be from 80 parts by weight to 99.8 parts by weight, specifically, it can be 95 parts by weight or more, 98 parts by weight or more, 84 parts by weight to 99.8 parts by weight, 90 parts by weight to 99.8 parts by weight, 94 parts by weight to 99.8 parts by weight, 88 parts by weight to 96 parts by weight, or 92 parts by weight to 97.5 parts by weight.

[0096] Furthermore, since the composition of the positive electrode active material is the same as that of the positive electrode active material according to the present invention described above, detailed description is omitted.

[0097] On the other hand, in addition to the main component, the positive electrode active material, the positive electrode active layer can also selectively contain conductive materials, adhesives, and other additives.

[0098] Here, the conductive material may include one or more of acetylene black, channel black, furnace black, lamp black, thermal cracking black, graphene, carbon nanotubes and carbon fibers, but is not limited to these.

[0099] Based on a total of 100 parts by weight of electrode active layer, the content of conductive material can be from 0.1 to 10 parts by weight, specifically from 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight. By controlling the content of conductive material within the above range, this invention can prevent a decrease in charging capacity due to increased electrode resistance caused by a low content of conductive material, and can also prevent a decrease in charging capacity due to an excessive amount of conductive material, such as a decrease in the content of electrode active material, or a decrease in fast charging characteristics due to an increased load on the electrode active layer.

[0100] In addition, the adhesive, as a component that assists in the bonding of the positive electrode active material with conductive materials and the current collector, can be appropriately used within the range of not impairing the positive electrode electrical performance. Specifically, it can include any one or more of the following: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber.

[0101] Based on a total of 100 parts by weight of the positive electrode active layer, the content of the binder can be from 0.1 to 10 parts by weight, specifically from 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight. By controlling the content of the binder in the positive electrode active layer within the above range, this invention can prevent a decrease in the adhesion of the active layer due to a low binder content or a decrease in the electrical performance of the positive electrode due to an excessive binder content.

[0102] Furthermore, the average thickness of the positive electrode active layer can be from 50 μm to 500 μm. Specifically, the average thickness of the positive electrode active layer can be 100 μm to 400 μm; 200 μm to 350 μm; 50 μm to 180 μm; 80 μm to 150 μm; 100 μm to 250 μm; or 130 μm to 190 μm. By adjusting the average thickness of the positive electrode active layer to the above range, this invention not only achieves high adhesion between the positive electrode active layer and the positive electrode current collector, but also achieves high energy density of the positive electrode.

[0103] Furthermore, the positive electrode current collector can be made of materials with high conductivity that will not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, etc., can be used. In the case of aluminum or stainless steel, aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver can also be used. Moreover, considering the conductivity and overall thickness of the manufactured positive electrode, the average thickness of the current collector can be appropriately applied between 3 μm and 500 μm.

[0104] The positive electrode for lithium secondary batteries according to the present invention has the advantages of excellent safety and lifespan characteristics by having the above-described structure.

[0105] The invention will now be described in more detail by way of examples and comparative examples.

[0106] However, the following embodiments and comparative examples are only used to illustrate the present invention, and the content of the present invention is not limited to the following embodiments and comparative examples.

[0107] Preparation Examples 1 to 5: Fabrication of Cores for Positive Electrode Active Materials

[0108] First, a compound represented by chemical formula 1 is manufactured to serve as the core of the positive electrode active material. For this purpose, lithium manganese iron phosphate (LiMn) is commercially purchased. 0.7 Fe 0.3 PO4). The purchased lithium manganese iron phosphate was heat-treated at 700°C for 1 hour, and then mixed with titanium dioxide (TiO2), ammonium vanadate (NH4VO3), and niobium oxide (Nb2O5), and calcined at 700±20°C under a nitrogen atmosphere to produce a compound powder represented by chemical formula 1. Here, the mixing amounts of titanium dioxide (TiO2), ammonium vanadate (NH4VO3), and niobium oxide (Nb2O5) were adjusted to meet the molar fractions of metals contained in the metal precursor compound as shown in Table 1 (based on a molar fraction of 1 for all metals except lithium in the manufactured compound).

[0109] The manufactured compound powder was subjected to X-ray diffraction (XRD) to measure ① the lattice constants a, b, and c, and ② the X-axis dimensions representing the grain size. Specifically, lithium manganese iron phosphate (LiMn) was considered. 0.7 Fe0.3 Metals doped and / or substituted in PO4 were analyzed by X-ray diffraction spectroscopy using the Rietveld refinement method. Here, X-ray diffraction analysis was performed using a Bruker D8 Endeavor (Cu-Kα, λ=1.54) equipped with a LynxEye XE-T position-sensitive detector or a LynxEye position-sensitive detector. The sample was placed in the groove of a general-purpose powder holder. A glass slide was then used to homogenize the sample surface, and the sample height was filled to match the edge of the holder. Measurements were then performed using FDS 0.5°, 2θ = 15°–90° region, step size = 0.02°, for a total scan time of approximately 20 minutes. For crystallite size analysis, the fundamental parameter method (FPA) built into the Bruker TOPAS program was used to account for instrument broadening, and all peaks within the measurement range were used for fitting. Peak shapes were obtained from TOPAS using FP (first principles), and Lorentz contributions were used for fitting. Strain was not considered at this point. The measured lattice constant c and crystallite size (i.e., X-axis dimension) are shown in Table 1, and the correlation between lattice constant c and lattice constants a and b is shown in Table 1. Figure 1 (Chinese) Reference Figure 1 It was confirmed that when the lattice constant c is expressed in relation to the lattice constants a and b, a linear relationship is observed, and this tends to shift towards the lower right as the concentration of lithium (Li) in the structure increases. Furthermore, it was confirmed that a linear relationship, following Vigarde's law, is observed as the variety of doped and / or substituted metals in the positive electrode active material increases.

[0110] In addition, particle size distribution (PSD) analysis was performed on each manufactured nucleus to measure the nucleus's density. 50 Specifically, particle size distribution (PSD) was determined using laser diffraction. The PSD instrument used was a Malvern Mastersizer 3000, with the laser refractive index adjusted to 2.0 to 2.2. Using an internal ultrasonic irradiator, individual nuclei smaller than 1 g were dispersed in deionized water (DI water), and the particle size distribution was calculated by measuring the difference in diffraction pattern with particle size as the dispersed particles passed through the laser beam. Here, D... 50 The particle size was measured by calculating the particle size at a point that represents 50% of the cumulative area distribution based on particle size in the measuring instrument. The measurement results are shown in Table 1 below.

[0111] [Table 1]

[0112] Examples 1 to 10 and Comparative Example 1. Fabrication of positive electrode active material

[0113] In the preparation example, the positive electrode active material was introduced into a chemical vapor deposition reactor using nuclei, and the interior of the reactor was purged with argon gas. Then, the interior of the reactor was heated to 800°C at a heating rate of 50°C / min, and chemical vapor deposition was performed for 15 to 20 minutes while argon gas was supplied at 180 to 220 sccm. Subsequently, chemical vapor deposition was performed for an additional 25 to 35 minutes while hydrogen and argon gas were continuously supplied at 10 to 20 sccm and 280 to 320 sccm, respectively, thereby producing a positive electrode active material for lithium-ion batteries having a carbon layer formed on the nuclei surface.

[0114] Here, ① the type of nucleus used is shown in Table 2 below. Furthermore, the carbon sources used during chemical vapor deposition are acetylene black (AB), carbon nanotubes (CNTs), and polyvinylpyrrolidone (PVP) particles, which are used as dotted carbon compounds, linear carbon compounds, and polymer compounds, respectively. The carbon sources used account for 4 to 6% of the total weight of the positive electrode active material, and ② the weight ratios of the dotted carbon compounds, linear carbon compounds, and polymer compounds included as carbon sources are shown in Table 2 below.

[0115] Particle size distribution (PSD) analysis was performed on each manufactured cathode active material to measure the D of the cathode active material. 50 Here, the D of the positive electrode active material... 50 By comparing with the previously measured kernel D 50 The same method is used for measurement.

[0116] The measurement results are shown in Table 2 below.

[0117] Furthermore, the fabricated positive electrode active material was analyzed by transmission electron microscopy (TEM) to measure the average thickness of the carbon layer deposited on the core surface. The results confirmed that the average thickness of the carbon layer formed on the core surface was approximately 5 nm to 10 nm.

[0118] [Table 2]

[0119] Comparative Example 2. Manufacturing of Positive Electrode Active Materials

[0120] The positive electrode active material was manufactured using the same method as in Example 8, except that a core containing a compound represented by Formula 1, acetylene black, carbon nanotubes, and polyvinylpyrrolidone (PVP) were uniformly mixed and then calcined at 800±50°C for 5 minutes.

[0121] Examples 11 to 20 and Comparative Examples 3 to 4. Manufacturing of lithium secondary batteries

[0122] N-methylpyrrolidone solvent was injected into a homogenizing stirrer, and 90 parts by weight of each of the positive electrode active materials prepared in Examples 1 to 10 and Comparative Examples 1 to 2, 5 parts by weight of carbon black (as a conductive material), and 5 parts by weight of polyvinylidene fluoride (PVdF) (as a binder) were added respectively. The mixture was then mixed at 3,000 rpm for 60 minutes to prepare a positive electrode slurry. An aluminum foil (average thickness: 12 μm) was prepared as the positive electrode current collector, and the pre-prepared positive electrode slurry was cast onto one side of the prepared aluminum foil. The aluminum foil with the cast positive electrode slurry was dried in a vacuum oven at 130°C and then calendered to manufacture the positive electrode. Here, the total thickness of the calendered positive electrode active layer was 150 μm, and the porosity was 25% to 35%.

[0123] Prepare a lithium metal disk as the negative electrode. Place the prepared negative electrode and the positive electrode prepared in Examples 1 to 6 and Comparative Example 1 (as shown in Table 3 below) facing each other, and insert a separator made of 18 μm polypropylene between them to manufacture an electrode assembly. Insert each manufactured electrode assembly into a battery case, inject the electrolyte composition into the battery case, and then seal the case to manufacture a half cell. Here, as the electrolyte composition, a solution prepared by mixing lithium hexafluorophosphate (LiPF6, 1.0 M) in a mixture of ethylene carbonate (EC): methyl ethyl carbonate (EMC) = 1:1 (volume ratio) is used.

[0124] [Table 3]

[0125] Experimental Example

[0126] The following experiments were conducted to evaluate the performance of the positive electrode active material according to the present invention.

[0127] 1) Output characteristics of lithium secondary batteries

[0128] For each half-cell manufactured in Examples 11 to 20 and Comparative Examples 3 to 4, constant current / constant voltage charging (CC / CV charging) was performed at 25°C, followed by constant current discharging (CC discharging) to measure the initial discharge capacity. Here, constant current / constant voltage charging was performed at a constant current rate of 0.1 C until the voltage reached 4.2 V, and then maintained at a constant voltage of 4.2 V until cutoff at a 0.1 C rate. Furthermore, constant current discharging was performed at a 1.0 C rate until 1.5 V was reached.

[0129] Then, each half-cell was fully charged at 25°C with a charging current of 1.0 C until the charging termination voltage reached 4.2 V to 4.25 V. High-rate discharge capacity was measured simultaneously while discharging within a range of 1.0 to 5.0 C. Based on the measured discharge capacity, the high-rate discharge characteristics of each lithium-ion battery were evaluated by calculating the relative discharge capacity ratio based on the initial discharge capacity for each discharge rate. The measurement results are shown in Table 4.

[0130] 2) High temperature life characteristics

[0131] For each half-cell manufactured in Examples 11 to 20 and Comparative Examples 3 to 4, the charge-discharge capacity retention rate under high-temperature conditions was measured. Specifically, each half-cell was subjected to 300 charge-discharge cycles after being charged at 45°C with a constant current of 1 C until the voltage reached 4.25 V and discharged at a constant current of 1 C until the voltage reached 2.5 V as one cycle.

[0132] Here, the charge capacity of each half-cell during the first and 300th cycles was measured. The high-temperature lifetime of each half-cell was evaluated by calculating the retention rate of the charge capacity after the 300th cycle based on the charge capacity after the first cycle. The results are shown in Table 4 below.

[0133] [Table 4]

[0134] As shown in Table 4 above, it can be seen that the positive electrode for lithium secondary batteries according to the present invention has excellent output performance and outstanding high-temperature life characteristics.

[0135] Specifically, the half-cell containing the positive electrode of the embodiment has a carbon layer formed by chemical vapor deposition (CVD) on a core containing a compound represented by chemical formula 1, exhibiting a high discharge capacity ratio of about 73.0% or more even at high rates above 5 C, and confirming that the capacity retention rate is still about 80% or more even after 300 charge-discharge cycles at high temperatures.

[0136] This means that when a carbon layer is formed on the core by chemical vapor deposition (CVD) during the manufacturing of the positive electrode active material, a highly crystalline carbon layer is uniformly formed on the core surface, which has high structural safety and a large specific surface area, thereby improving the electrochemical performance and lifetime characteristics of the positive electrode active material.

[0137] These results demonstrate that the positive electrode active material and the positive electrode containing it according to the present invention have excellent output performance and outstanding lifetime characteristics during charge and discharge.

[0138] Although the present invention has been described with reference to its exemplary embodiments, those skilled in the art will understand that various modifications and variations can be made therein without departing from the scope of the invention as defined by the appended claims.

[0139] Therefore, the scope of the present invention should not be limited by the specific embodiments described in the specification, but should be determined by the appended claims.

Claims

1. A positive electrode active material, the positive electrode active material comprising: a core containing a compound represented by the following Chemical Formula 1, and a carbon layer surrounding the core, [Chemical Formula 1] Li 1+a Mn 1-b-c Fe b M 1 c PO4 In Chemical Formula 1, M 1 It is selected from one or more of Ti, V, Zr, Sr, Sb, B and Nb, and a, b, and c are -0.5 ≤ a ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0.001 ≤ c ≤ 0.

2.

2. The positive electrode active material according to claim 1, wherein the compound represented by Chemical Formula 1 includes one or more of the compounds represented by the following Chemical Formulas 2 to 5: [Chemical Formula 2] Li 1+a Mn 1-b-x Fe b You x PO4 [Chemical Formula 3] Li 1+a Mn 1-b-x-y Fe b You x V y PO4 [Chemical Formula 4] Li 1+a Mn 1-b-x-y-z Fe b You x V y Nb z PO4 [Chemical Formula 5] Li 1+a Mn 1-b-x-y-z Fe b You x Zr y Nb z PO4 In Chemical Formulas 2 to 5, a, b, x, y, and z are -0.5 ≤ a ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0 < x ≤ 0.2, 0 < y ≤ 0.1, 0 < z ≤ 0.1, provided that 0.001 ≤ x + y ≤ 0.2 or 0.001 ≤ x + y + z ≤ 0.

2.

3. The positive electrode according to claim 1, wherein when the core is analyzed by X-ray diffraction, the lattice constant c is 4.69165 Å to 4.80 Å and satisfies the following Mathematical Formula 1: [Mathematical Formula 1] y = -px + q In Mathematical Formula 1, y represents the lattice constant c, x represents Where a and b are the lattice constants a and b, respectively. p and q are -0.08 ≤ p ≤ -0.07 and 5 ≤ q ≤ 6, respectively.

4. The positive electrode active material according to claim 1, wherein the average particle size (D) of the positive electrode active material is... 50 The thickness ranges from 0.5 μm to 10 μm.

5. The positive electrode active material according to claim 1, wherein the average thickness of the carbon layer is 50 nm or less.

6. A method for manufacturing a positive electrode active material, the method comprising the following steps: forming a carbon layer on the surface of particles of a compound represented by the following Chemical Formula 1, wherein the carbon layer is formed by chemical vapor deposition (CVD) under an inert gas condition, [Chemical Formula 1] Li 1+a Mn 1-b-c Fe b M 1 c PO4 In Chemical Formula 1, M 1 It is selected from one or more of Ti, V, Zr, Sr, Sb, B and Nb, and a, b, and c are -0.5 ≤ a ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0.001 ≤ c ≤ 0.

2.

7. The method for manufacturing a positive electrode active material according to claim 6, wherein the chemical vapor deposition (CVD) uses one or more of the following substances as a carbon source: a carbon structure, the carbon structure including one or more of a dot-like carbon compound and a linear carbon compound; and a polymer compound.

8. The method for manufacturing a positive electrode active material according to claim 7, wherein the dot-like carbon compound includes one or more selected from acetylene black, channel black, furnace black, lamp black, thermal black, and graphene, and [[ID=�0]]wherein the linear carbon compound includes one or more selected from carbon nanotubes and carbon fibers.

9. The method for manufacturing a positive electrode active material according to claim 7, wherein the polymer compound includes one or more of polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polypyrrole (PPy), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethyl acrylate (PMA), and poly(methyl methacrylate) (PMMA).

10. The method for manufacturing a positive electrode active material according to claim 7, wherein the chemical vapor deposition (CVD) is carried out at a temperature of 500 °C to 1,500 °C.

11. A positive electrode, the positive electrode comprising: a positive electrode current collector; and A positive electrode active layer is disposed on at least one side of the positive electrode current collector and comprises the positive electrode active material as described in claim 1.

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