Active electrode materials and methods for preparing these materials.

Abstract

The invention relates to an anode-active material. The anode-active material comprises a compound represented by Chemical Formula 1 with a proposed olivine structure in the core. The anode-active material comprising the compound represented by Chemical Formula 1 can be prepared by chemical vapor deposition (CVD) using a solid-state carbon source, thereby providing a uniform porous carbon layer on the core surface.

Description

Positive electrode active material and method for producing the same

[0001] The present invention relates to a cathode active material and a method for producing the same.

[0002] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0003890, dated January 10, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Lithium secondary batteries are now widely used not only in small devices like portable electronic devices, but also in medium- to large-sized devices like battery packs for hybrid and electric vehicles and power storage systems. In particular, with growing concern over environmental issues, research is being conducted on electric vehicles and hybrid electric vehicles as alternatives to fossil fuel-powered vehicles like gasoline and diesel, which are major contributors to air pollution.

[0005] Typically, lithium secondary batteries have an electrode assembly structure comprising a positive electrode, a negative electrode, and a separator, each of which is impregnated with a lithium electrolyte. Each electrode is manufactured by coating a current collector with an electrode slurry. The electrode slurry is manufactured by mixing an electrode active material for storing energy, a conductive material for imparting electrical conductivity, and a binder for adhering the electrode active material to the current collector and providing bonding strength between the electrode active material and the current collector, in a solvent such as NMP (N-methyl pyrrolidone).

[0006] The cathode can be a lithium-ion battery such as LCO (LiCoO2), LMO (LiMn2O4), LFP (LiFePO4), or NCM (LiNi) that can reversibly insert or de-insert lithium. 1 / 3 Co 1 / 3 Mn 1 / 3 It includes metal oxides such as O2 as positive electrode active materials.

[0007] Among these, NCM, LCO, and NCA compounds with layered crystal structures facilitate lithium ion storage and exhibit high lithium ion diffusion rates, making them suitable as cathode active materials for high-capacity / high-power secondary batteries. However, compounds with layered crystal structures exhibit poor chemical and structural stability, making them prone to decomposition under high-temperature conditions. This reduces the safety of secondary batteries.

[0008] On the other hand, LFP compounds having an olivine crystal structure have a hexahedral crystal form in which phosphorus (P) and oxygen (O) are strongly bonded, and thus exhibit high structural stability. Therefore, compounds having an olivine crystal structure can easily maintain their crystal structure even when all lithium ions are desorbed during charging, and the crystal structure does not easily decompose even under high-temperature conditions. However, compounds having an olivine crystal structure have low energy density, which indicates the amount of energy that a battery can store per unit weight / volume. Therefore, in order for compounds having an olivine crystal structure to realize high energy density, the weight / volume of the cathode active material must be increased, which leads to a problem in that the size and weight of the secondary battery must increase excessively. In addition, the LFP compounds have low ion diffusivity and electrical conductivity, which significantly limits charge / discharge performance.

[0009] Accordingly, in order to increase the energy density of LFP compounds having a conventional olivine crystal structure, cathode active materials containing metals such as manganese or having particle surfaces coated with conductive materials have been developed. In the former case, the structure in which manganese is partially substituted at the iron valence position has the effect of improving the energy density of iron phosphate by about 5% or more. Despite these effects, there is a demand for additional energy density expression of LFP compounds applied to medium and large secondary batteries. In addition, in the latter case, although the electrical conductivity of the cathode active material may be somewhat improved due to the conductive layer on the surface, it is difficult to form a uniform coating layer on the surface, so it is difficult to expect a significantly improved electrical conductivity, and there is also a limitation that the life performance of the cathode is poor.

[0010] Therefore, in order to realize high safety of lithium secondary batteries, there is a need for technology development for a cathode active material for lithium secondary batteries and a cathode including the same that can realize high energy density and charge / discharge performance while including an LFP compound having an olivine structure as a cathode active material.

[0011]

[0012] [Prior Art Literature]

[0013] Republic of Korea Patent Publication No. 10-2013-0136796

[0014] Republic of Korea Patent Publication No. 10-2016-0111213

[0015]

[0016] Accordingly, the purpose of the present invention is to provide a cathode active material for a lithium secondary battery capable of realizing high energy density and charge / discharge performance while including an LFP compound having an olivine structure as a cathode active material to achieve high safety, and a cathode including the same.

[0017]

[0018] To solve the above-mentioned problem,

[0019] The present invention,

[0020] A core comprising a compound represented by the following chemical formula 1, and

[0021] Provided is a cathode active material comprising a carbon layer surrounding the core:

[0022] [Chemical Formula 1]

[0023] Li 1+a Mn 1-b-c Fe b M 1 c PO4

[0024] In the above chemical formula 1,

[0025] M 1 is at least one of Ti, V, Zr, Sr, Sb, B, and Nb,

[0026] a, b, and c are -0.5≤a≤0.5, 0.1≤b≤0.8, 0.001≤c≤0.2.

[0027] At this time, the compound represented by the chemical formula 1 may include at least one of the compounds represented by the following chemical formulas 2 to 5:

[0028] [Chemical Formula 2]

[0029] Li 1+a Mn 1-b-x Fe b Ti x PO4

[0030] [Chemical Formula 3]

[0031] Li 1+a Mn 1-b-x-y Fe b Ti x V y PO4

[0032] [Chemical Formula 4]

[0033] Li 1+a Mn 1-b-x-y-z Fe b Ti x V y Nb z PO4

[0034] [Chemical Formula 5]

[0035] Li 1+a Mn 1-b-x-y-z Fe b Ti x Zr y Nb z PO4

[0036] In the above chemical formulas 2 to 5,

[0037] 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≤0.1이되, 0.001≤x+y≤0.2 또는 0.001≤x+y+z≤0.2이다.

[0038] In addition, the core may have a lattice constant c of 4.69165 Å to 4.80 Å when analyzed by X-ray diffraction and may satisfy the following equation 1:

[0039] [Formula 1]

[0040] y=-px+q

[0041] In the above equation 1,

[0042] y represents the lattice constant c,

[0043] x is , where a and b are lattice constants a and b, respectively.

[0044] p and q are -0.08≤p≤-0.07 and 5≤q≤6, respectively.

[0045] The average particle diameter (D) of the above cathode active material 50 ) may be 0.5 μm to 10 μm, wherein the average thickness of the carbon layer may be 50 nm or less.

[0046]

[0047] In addition, in one embodiment of the present invention,

[0048] Comprising a step of forming a carbon layer on the particle surface of a compound represented by the following chemical formula 1,

[0049] The above-described method for producing a cathode active material is provided, wherein the carbon layer is formed by chemical vapor deposition (CVD) under inert gas conditions:

[0050] [Chemical Formula 1]

[0051] Li 1+a Mn 1-b-c Fe b M 1 c PO4

[0052] In the above chemical formula 1,

[0053] M 1 is at least one of Ti, V, Zr, Sr, Sb, B, and Nb,

[0054] a, b, and c are -0.5≤a≤0.5, 0.1≤b≤0.8, 0.001≤c≤0.2.

[0055] At this time, the chemical vapor deposition (CVD) may use a carbon structure including at least one of a point-like carbon compound and a linear carbon compound as a carbon source; and at least one of a polymer compound.

[0056] The above-mentioned point-shaped carbon compound may include at least one of acetylene black, channel black, furnace black, lamp black, summer black, and graphene, and the above-mentioned linear carbon compound may include at least one of carbon nanotubes and carbon fibers.

[0057] Additionally, the polymer compound may include at least one of polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polypyrrole (PPy), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethylacrylate (PMA), and poly(methyl methacrylate) (PMMA).

[0058] Additionally, the chemical vapor deposition (CVD) can be performed at a temperature of 500°C to 1,500°C.

[0059]

[0060] Furthermore, the present invention,

[0061] anode current collector, and

[0062] A positive electrode is provided, which includes a positive electrode active layer provided on at least one surface of the positive electrode current collector and including the positive electrode active material according to the present invention described above.

[0063]

[0064] The cathode active material according to the present invention comprises a compound represented by Chemical Formula 1 having an olivine structure in its core, thereby exhibiting high safety and excellent economic efficiency. Furthermore, the cathode active material, which comprises the compound represented by Chemical Formula 1, not only has a large specific surface area of ​​the core, but is also manufactured by chemical vapor deposition (CVD) using a solid-state carbon source, thereby enabling a more uniform inclusion of a porous carbon layer on the surface of the core. Accordingly, a cathode comprising the same has the advantages of excellent output performance during charge and discharge and excellent cycle life characteristics.

[0065]

[0066] Figure 1 is a graph showing the correlation between the lattice constant c of a cathode active material and the lattice constants a and b during X-ray diffraction (XRD) analysis.

[0067]

[0068] The present invention can be modified in various ways and has many embodiments, and specific embodiments will be described in detail in the detailed description.

[0069] However, this is not intended to limit the present invention to a specific embodiment, but should be understood to include all modifications, equivalents, or substitutes included in the technical scope of the present invention.

[0070] In the present invention, it should be understood that terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0071] Also, in this specification, "average particle diameter (D 50 )" means the particle diameter at which the integrated value is 50% in the particle diameter distribution of the particles, and is also called the median diameter. The above average particle diameter can be measured by a method commonly applied in the art. For example, the above average particle diameter can be measured using an analysis device that utilizes a laser diffraction scattering particle size distribution measurement method.

[0072]

[0073] Hereinafter, the present invention will be described in more detail.

[0074]

[0075] cathode active material

[0076] The present invention,

[0077] A core comprising a compound represented by the following chemical formula 1, and

[0078] Provided is a cathode active material comprising a carbon layer surrounding the core:

[0079] [Chemical Formula 1]

[0080] Li 1+a Mn 1-b-c Fe b M 1 c PO4

[0081] In the above chemical formula 1,

[0082] M 1 is at least one of Ti, V, Zr, Sr, Sb, B, and Nb,

[0083] a, b, and c are -0.5≤a≤0.5, 0.1≤b≤0.8, 0.001≤c≤0.2.

[0084]

[0085] The cathode active material according to the present invention may refer to a cathode active material applied to a cathode for a lithium secondary battery. The cathode active material has a core-shell structure including a core that performs an electrochemical reaction during charge / discharge of a lithium secondary battery and a shell surrounding the surface of the core. At this time, the core includes a compound represented by the chemical formula 1. The cathode active material according to the present invention includes a compound represented by the chemical formula 1 in an olivine structure in the core, thereby providing high safety and excellent economic efficiency. In addition, the cathode active material has a high specific surface area of ​​the core, and thus can include a more uniform carbon layer on the surface. Accordingly, a cathode including the same has the advantages of excellent output performance during charge / discharge and excellent life characteristics.

[0086] Specifically, the compound represented by the above chemical formula 1 contained in the core has an olivine structure. The olivine structure has a hexahedral crystal form in which phosphorus (P) and oxygen (O) are strongly bonded, and thus exhibits high structural stability. Accordingly, the compound represented by the above chemical formula 1 can easily maintain its crystal structure even when all lithium ions are desorbed during charging, and the crystal structure does not easily decompose even under high-temperature conditions. Therefore, the cathode active material including the compound represented by the above chemical formula 1 in the core has excellent life characteristics and excellent safety characteristics including overcharge and overdischarge. In addition, since the compound contains iron, which is abundant and inexpensive in resources, it is superior to LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 It is cheaper than lithium composite oxides such as O2, LiCoO2, LiNiO2, or LiMn2O4, and has less toxicity, so it has less impact on the environment.

[0087] Also, lithium manganese iron phosphate (LiMn) containing only lithium (Li), manganese (Mn) and iron (Fe) as metals 1-b Fe b PO4) has a slightly higher energy density than lithium iron phosphate (LiFePO4), but not significantly. However, the compound represented by Chemical Formula 1 applied in the present invention may have a higher energy density by doping and / or substituting one or more metals. Specifically, the compound represented by Chemical Formula 1 may include a compound in which lithium manganese iron phosphate is doped and / or substituted with one or more of titanium (Ti), vanadium (V), zirconium (Zr), and niobium (Nb). For example, the compound represented by Chemical Formula 1 may include one or more of the compounds represented by Chemical Formulas 2 to 5 below:

[0088] [Chemical Formula 2]

[0089] Li 1+a Mn 1-b-x Fe b Ti x PO4

[0090] [Chemical Formula 3]

[0091] Li 1+a Mn 1-b-x-y Fe b Ti x V y PO4

[0092] [Chemical Formula 4]

[0093] Li 1+a Mn 1-b-x-y-z Fe b Ti x V y Nb z PO4

[0094] [Chemical Formula 5]

[0095] Li 1+a Mn 1-b-x-y-z Fe b Ti x Zr y Nb z PO4

[0096] In the above chemical formulas 2 to 5,

[0097] 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≤0.1이되, 0.001≤x+y≤0.2 또는 0.001≤x+y+z≤0.2이다.

[0098] The compounds represented by the above chemical formulas 2 to 5 are lithium manganese iron phosphate (LiMn 1-b Fe b PO4) is doped or substituted with titanium (Ti), vanadium (V), zirconium (Zr) and / or niobium (Nb). At this time, the doped or substituted metals may be doped or substituted in an amount of 0.1 molar fraction or less based on the total 1 molar fraction of metals excluding lithium (Li), and the ratio of lithium (Li) to these metals (Me) (Li / Me) may 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 cathode active material is closely related to the density of the particles. Specifically, the higher the concentration of lithium, the higher the density, and in this case, the easier it is to remove pores within the particles, so that a high rolling density can be realized. However, an excessively high lithium concentration may reduce the movement of lithium ions, which may deteriorate the electrical performance. In addition, the significantly low lithium concentration not only results in a low particle density and thus a low rolling density, but also has the problem of low energy density per unit volume / mass during the manufacture of the positive electrode. The present invention can overcome this problem by controlling the ratio of lithium (Li) to metals (Me) contained in the positive electrode active material (Li / Me) within the above-described range.

[0099] The compound represented by this chemical formula 1 is LiMn 0.8 Fe 0.19 Ti 0.01 PO4, LiMn 0.7 Fe 0.29 Ti 0.01 PO4, LiMn 0.6 Fe0.39 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 Fe 0.37 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 Compound represented by chemical formula 2 such as PO4; 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 Compound represented by chemical formula 3 such as PO4; LiMn 0.8 Fe0.17 The 0.01 V 0.01 Nb 0.01 PO4, LiMn 0.7 Fe 0.27 The 0.01 V 0.01 Nb 0.01 PO4, LiMn 0.6 Fe 0.37 The 0.01 V 0.01 Nb 0.01 PO4, LiMn 0.8 Fe 0.12 The 0.03 V 0.025 Nb 0.025 PO4, LiMn 0.7 Fe 0.22 The 0.03 V 0.025 Nb 0.025 PO4, LiMn 0.6 Fe 0.32 The 0.03 V 0.025 Nb 0.025 PO4, LiMn 0.8 Fe 0.05 The 0.05 V 0.05 Nb 0.05 PO4, LiMn 0.7 Fe 0.15 The 0.05 V 0.05 Nb 0.05 PO4, LiMn 0.6 Fe 0.25 The 0.05 V 0.05 Nb 0.05 PO4등의 화학식 4; 및 LiMn 0.8 Fe 0.17 The 0.01 Zr 0.01 Nb 0.01 PO4, LiMn 0.7 Fe 0.27 The 0.01 Zr 0.01 Nb 0.01 PO4, LiMn 0.6 Fe 0.37 The 0.01 Zr 0.01 Nb 0.01 PO4, LiMn 0.8 Fe 0.12 The0.03 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 Fe 0.32 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 It may include at least one compound represented by chemical formula 5, such as PO4.

[0100] The compound represented by the above chemical formula 1 can have a particle size controlled within a predetermined range depending on the number of metals doped and / or substituted in the lithium manganese iron phosphate and / or the molar fraction of the metal. The core of the positive electrode active material includes lithium manganese iron phosphate doped and / or substituted with one or more metals, such as lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiMn). 1-b Fe b It can have a smaller size compared to the core represented by the chemical formula 1. Accordingly, the core including the compound represented by the chemical formula 1 has a larger specific surface area, so that a carbon layer can be more uniformly formed on the surface of the core.

[0101] More specifically, as the type or mole fraction of the doped or substituted metal increases, the lattice constant c of the lithium manganese iron phosphate represented by the chemical formula 1 may increase and the grain may decrease.

[0102] That is, the present invention is characterized in that it includes a compound represented by the chemical formula 1, in which one or more metals are doped or substituted in lithium manganese iron phosphate, in the core, so that the size of the core can be controlled to be finer while the specific surface area can be controlled to be large, and thereby includes a carbon layer more uniformly coated on the surface of the core.

[0103] Here, the crystal grain size of the compound represented by the above chemical formula 1 can be measured in the form of lattice constants a, b, c, etc., which represent the length of each side of the crystal grain during X-ray spectroscopy analysis. Here, "particle" refers to a grain in the unit of micrometers, and when observed under magnification, it can be distinguished into a "grain" having a crystal in the unit of several tens of nanometers. When the above grain is further magnified, a unit area (i.e., a crystal lattice) in which atoms form a lattice structure in a certain direction can be confirmed, which is called a "crystallite."

[0104] As an example, the compound represented by the chemical formula 1 according to the present invention is a lithium manganese iron phosphate (LiMn) that does not contain the transition metal, doped or substituted with titanium (Ti), vanadium (V), zirconium (Zr) and / or niobium (Nb) together with manganese (Mn). 1-b Fe b PO4) may have a lattice constant c greater than the lattice constant c (about 4.6916 Å). For example, the cathode active material may have a lattice constant c of 4.69165 Å to 4.80 Å when analyzed by X-ray diffraction. Specifically, the cathode active material may have a lattice constant C of 4.69165 Å to 4.80 Å when analyzed by X-ray diffraction; 4.69165 Å to 4.75 Å; 4.69165 Å to 4.70 Å; 4.69165 Å to 4.695 Å; 4.69165 Å to 4.694 Å; 4.69165 Å to 4.693 Å; 4.6917 Å to 4.6925 Å; Or it may be 4.6918 Å to 4.6925 Å.

[0105] "Lattice constant" is a value that represents the edge length of a crystal grain, and is used to describe the size and arrangement of a material, and can be expressed in various forms depending on the crystal structure. In the case of the olivine structure, it has an orthorhombic crystal structure, and therefore can have lattice constants of a, b, and c. Among these, the lattice constant c is a factor that represents the unit cell size in the c-axis direction of the crystal, and is closely related to the structural and chemical properties of the crystal grain. For example, lithium manganese iron phosphate (LiMn) with an olivine structure 1-b Fe b In the case of PO4), the c-axis direction can act as the main movement path of lithium ions. The lattice constant c, which indicates the size of the c-axis direction, is Fe 2+ and Mn 2+ Ti has a larger ionic radius 4+ , V 5+ , Nb 5+ The back can be doped and increase. An increase in the lattice constant c can expand the lithium ion path and increase the diffusion coefficient of lithium ions. Therefore, the cathode active material according to the present invention can have excellent electrical performance within the range of the lattice constant c described above. However, if it exceeds the upper limit of the above range, a secondary phase can be formed within the olivine structure. If a secondary phase is formed within the olivine structure, the electrochemical activity can be reduced. In addition, if it is below the lower limit of the above range, the electrical performance of the cathode active material can be significantly reduced.

[0106] In addition, the compound represented by the above chemical formula 1 can exhibit a linear relationship when the lattice constant c is expressed in relation to the lattice constants a and b, which can follow Vegard's law. Specifically, the lattice constant c can have a predetermined correlation with the square root of (the sum of the squares of the lattice constant a and the squares of the lattice constant b), and this correlation can be expressed by the following formula 1:

[0107] [Formula 1]

[0108] y=-px+q

[0109] In the above equation 1,

[0110] y represents the lattice constant c,

[0111] x is , where a and b are lattice constants a and b, respectively.

[0112] p and q are -0.08≤p≤-0.07 and 5≤q≤6, respectively.

[0113]

[0114] The above 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 may vary depending on the type or mole fraction of the doped and / or substituted metal, as well as the manufacturing method or process conditions of lithium manganese iron phosphate. In the case of the present invention, as shown in Fig. 1, the lattice constant a, b and c tends to increase as the number or mole fraction of the metal doped and / or substituted in lithium manganese iron phosphate increases. That is, the first cathode active material of the present invention satisfies the range of the lattice constant c described above, and lithium manganese iron phosphate (LiMn 1-b Fe b Metal (M) doped and / or substituted in PO4 1 ) tends to increase as the number or mole fraction thereof increases, so that the above equation 1 can be satisfied. When the lattice constant c is expressed for the lattice constants a and b, it shows a linear relationship, which means that lithium manganese iron phosphate (LiMn 1-b Fe bThis means that the olivine crystal structure can be maintained even when multiple components (e.g., Ti, V, Zr, Sr, Sb, B, Nb, etc.) are doped or substituted in PO4. That is, this indirectly indicates that the structural stability of the cathode active material according to the present invention is maintained at a high level even when multiple components are doped or substituted.

[0115] The size of the grains formed by these lattice units can be confirmed through the X-axis size during X-ray diffraction analysis. The size of the grains may be about 70 nm or more and less than 120 nm. More specifically, the size of the grains may 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.

[0116] The cathode active material according to the present invention can increase the specific surface area of ​​the core while minimizing agglomeration between particles by controlling the grain size of the compound represented by Chemical Formula 1 contained in the core within the above-described range. Through this, the cathode active material can have a more uniform carbon layer on the surface of the core, thereby further improving the electrical properties of the cathode including the same. The grains are particles formed by gathering crystal grains, and generally, as the size of the crystal grains increases, the size of the grains may increase. However, when multiple components are doped or substituted, as in the cathode active material according to the present invention, interference effects within their lattices may occur. In this case, structural changes in the crystal grain boundaries occur or the crystal grain boundaries increase, so that an increase in the crystal grain size may not tend to increase the grain size.

[0117] Meanwhile, the carbon layer of the cathode active material has a structure that uniformly surrounds the surface of the core. In this case, the carbon layer has a porous structure, not only providing a high surface area but also possessing high crystallinity, allowing it to uniformly surround the core surface. A carbon layer with this structure can further enhance the electrochemical reactivity and electrical properties of the cathode active material, thereby enhancing its output and lifespan characteristics.

[0118] Here, the thickness of the carbon layer can be controlled within a range that does not lower the energy density of the positive electrode active material. Specifically, the carbon layer can have an average thickness of 50 nm or less. More specifically, the carbon layer can have an average thickness in the range of 40 nm or less; 30 nm or less; 20 nm or less; 10 nm or less; 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.

[0119] Furthermore, the cathode active material including the core and carbon layer described above may have a predetermined size. For example, the cathode active material may have an average particle diameter (D 50 ) may be in the range of 0.5 ㎛ to 10 ㎛, and specifically, may be in the range of 0.5 ㎛ to 8 ㎛; 0.5 ㎛ to 6 ㎛; 0.5 ㎛ to 4 ㎛; 0.5 ㎛ to 2 ㎛; 1 ㎛ to 5 ㎛; 2 ㎛ to 4 ㎛; 4 ㎛ to 8 ㎛; 5 ㎛ to 9 ㎛; 3 ㎛ to 6 ㎛; 0.5 ㎛ to 1.5 ㎛; or 0.7 ㎛ to 1.4 ㎛.

[0120] The present invention relates to an average particle diameter (D) of a cathode active material 50) can be controlled to the above-described range, thereby preventing the agglomeration of positive electrode active materials due to particle sizes lower than the lower limit of the above-described range, which reduces the processability and reliability of the positive electrode during positive electrode manufacturing. In addition, there is a problem in that the positive electrode active materials are damaged, such as broken, during the rolling process due to particle sizes higher than the upper limit of the above-described range, which reduces the electrical performance.

[0121]

[0122] The cathode active material according to the present invention, having the above-described composition, exhibits high structural safety and economic efficiency. Furthermore, the cathode active material comprises a compound represented by Chemical Formula 1 in its core, resulting in a high specific surface area of ​​the core, thereby enabling the formation of a more uniform carbon layer on its surface. Therefore, a cathode comprising this compound exhibits superior output performance during charge / discharge cycles and excellent cycle life characteristics.

[0123]

[0124] Method for manufacturing positive electrode active material

[0125] In addition, the present invention,

[0126] Comprising a step of forming a carbon layer on the particle surface of a compound represented by the following chemical formula 1,

[0127] The above-described method for producing a cathode active material is provided, wherein the carbon layer is formed by chemical vapor deposition (CVD) under inert gas conditions:

[0128] [Chemical Formula 1]

[0129] Li 1+a Mn 1-b-c Fe b M 1 c PO4

[0130] In the above chemical formula 1,

[0131] M 1 is at least one of Ti, V, Zr, Sr, Sb, B, and Nb,

[0132] a, b, and c are -0.5≤a≤0.5, 0.1≤b≤0.8, 0.001≤c≤0.2.

[0133]

[0134] The method for manufacturing a cathode active material according to the present invention refers to the method for manufacturing the cathode active material described above. The method for manufacturing a cathode active material according to the present invention includes a process for forming a carbon layer on the surface of a particle of a compound represented by chemical formula 1, which is a core.

[0135] Here, the core on which the carbon layer is provided can be manufactured through a predetermined process. The process for manufacturing the core includes a process for manufacturing a compound represented by Chemical Formula 1, and the compound represented by Chemical Formula 1 can be manufactured by a step of calcining a mixture of a compound represented by Chemical Formula 6 and a metal precursor compound at a temperature of 500°C or higher, more specifically, 500°C to 1,000°C; 500°C to 900°C; 500°C to 800°C; or 500°C to 750°C.

[0136] [Chemical Formula 6]

[0137] Li 1+m Mn 1-n Fe n PO4

[0138] In the above chemical formula 6,

[0139] m and n are -0.5≤m≤0.5, 0.1≤n≤0.8.

[0140]

[0141] In general, conventional metal compounds having an olivine structure are manufactured by mixing lithium phosphate, which is a lithium raw material, and precursor compounds each containing a transition metal other than lithium, and calcining the mixture at high temperatures. However, in the present invention, the compound represented by Chemical Formula 1 can be manufactured by first producing lithium manganese iron phosphate represented by Chemical Formula 6 by calcining a mixture of a manganese precursor compound, an iron precursor compound, and lithium phosphate, and then mixing precursor compounds of metals to be doped and / or substituted into the produced lithium manganese iron phosphate and calcining the mixture.

[0142] At this time, the compound represented by the above chemical formula 6 may be primarily 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 the chemical formula 5 may be subjected to a pre-sintering process for 1 to 6 hours; or 1 to 3 hours; before being mixed with the metal precursor compound. At this time, the temperature at which the pre-sintering process is performed may be 500°C to 800°C; or 550°C to 750°C.

[0143] The present invention can significantly reduce the moisture content present in lithium manganese iron phosphate by performing heat treatment of lithium manganese iron phosphate represented by chemical formula 6 under the conditions described above before mixing with a metal precursor compound. Through this, metals contained in the metal precursor compound can be easily doped in lithium manganese iron phosphate or substituted at iron atom positions. However, there is a limit to sufficient removal of moisture in lithium manganese iron phosphate at temperatures lower than the above-described temperature range, and at temperatures higher than the above-described temperature range, the crystallinity of lithium manganese iron phosphate increases further, which may make doping and / or substitution of metals more difficult.

[0144] The compound of chemical formula 6, which has been heat-treated in this way, can be mixed with metal precursor compounds and calcined, thereby producing the compound represented by chemical formula 1 of the present invention. Here, the metal precursor compound refers to raw materials that supply titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), etc. to the lithium manganese iron phosphate represented by chemical formula 6. The metal precursor compounds are not particularly limited as long as they can provide titanium (Ti), vanadium (V), zirconium (Zr), and / or niobium (Nb).

[0145] Preferably, the titanium (Ti) precursor compound may include at least one of titanium oxide and titanium alkoxide containing titanium (Ti) as a component. For example, the titanium (Ti) precursor compound may include titanium oxide such as TiO, TiO2, or titanium alkoxide such as Ti[OCH(CH3)2]4, but is not limited thereto.

[0146] Additionally, the vanadium (V) precursor compound may be a vanadium-containing oxide, a vanadium-containing ammonium salt, or a combination thereof. For example, the vanadium (V) precursor compound may include, but is not limited to, vanadium oxide such as VO2, V2O3, V2O5, or ammonium vanadate (NH4VO3).

[0147] The zirconium (Zr) precursor compound may be a zirconium-containing oxide, a zirconium-containing acetate, or a combination thereof. For example, the zirconium (Zr) precursor compound may be a zirconium oxide such as ZrO2, or Zr6O4(OH)4(O2CCH3). 12 May include, but is not limited to, the following:

[0148] In addition, the niobium (Nb) precursor compound may be a niobium-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. For example, the niobium (Nb) precursor compound may be, but is not limited to, a niobium oxide such as NbO, NbO2, Nb2O5; a niobium salt such as NbCO3, Nb(NO3)2, NbSO4, niobium acetate, niobium dicarboxylate, niobium citrate, niobium fatty acid salt; a niobium oxyhydroxide; niobium chloride; or a combination thereof.

[0149] In addition, the method for manufacturing a cathode active material according to the present invention can perform chemical vapor deposition (CVD) under inert gas conditions to uniformly coat a carbon layer on a core including a compound represented by chemical formula 1.

[0150] Chemical Vapor Deposition (CVD) refers to a method of depositing a vaporized raw material as a thin film on a substrate injected into a reactor under vacuum or inert gas conditions. The present invention has the advantage of forming a thin carbon layer more uniformly on a core containing a compound represented by Chemical Formula 1 by utilizing this chemical vapor deposition (CVD).

[0151] At this time, the chemical vapor deposition (CVD) can be performed under conditions in which the inside of the reactor is replaced with an inert gas such as nitrogen gas, argon gas, or helium gas to prevent the inflow of impurities into the carbon layer during carbon layer deposition and to prevent side reactions from occurring on the surface of the carbon layer.

[0152] In addition, the chemical vapor deposition (CVD) may be performed by mixing some hydrogen gas into a reactor filled with an inert gas during deposition. For example, the chemical vapor deposition (CVD) may be performed by first depositing while supplying argon gas at a flow rate of 150 to 250 sccm into a reactor replaced with argon gas, and then continuously supplying hydrogen gas at a flow rate of 10 to 20 sccm and argon gas at a flow rate of 250 to 350 sccm into the reactor together to perform second deposition. In this case, carbon seeds for depositing a carbon layer on the core surface may be generated during the first deposition, and the growth of the carbon seeds generated during the second deposition may be promoted.

[0153] The above chemical vapor deposition (CVD) can be performed within 100 minutes, and specifically, can be performed for 1 minute to 100 minutes; 1 minute to 75 minutes; 1 minute to 50 minutes; 1 minute to 30 minutes; 1 minute to 20 minutes; 1 minute to 10 minutes; and 10 minutes to 70 minutes.

[0154] Additionally, when hydrogen gas is mixed during deposition as described above, the first deposition can be performed within 30 minutes, and the second deposition can be performed for 30 to 70 minutes thereafter.

[0155] As an example, the chemical vapor deposition (CVD) may be performed in such a manner that the first deposition is performed under inert gas conditions for 10 minutes, and the second deposition is performed under conditions in which hydrogen gas is partially mixed with the inert gas for 30 to 40 minutes.

[0156] The present invention can effectively control the thickness of a carbon layer on a core surface by controlling the chemical vapor deposition (CVD) performance time within the above-described range.

[0157] In addition, the chemical vapor deposition (CVD) may be performed at a high temperature for vaporizing a carbon source to form a carbon layer. Specifically, the temperature at which the chemical vapor deposition (CVD) is performed may be 500°C to 1,500°C, and more specifically, 500°C to 1,300°C; 500°C to 1,100°C; 500°C to 1,000°C; 500°C to 900°C; 600°C to 1,300°C; 800°C to 1,100°C; 1,000°C to 1,500°C; 750°C to 990°C; or 600°C to 900°C.

[0158] The present invention not only enables the uniform formation of a carbon layer on a core by controlling the chemical vapor deposition (CVD) temperature within the aforementioned range, but also converts the carbon deposited on the core surface into a carbon layer with high crystallinity. The highly crystallinity carbon layer can significantly improve the electrical properties, such as electrical conductivity, of the cathode active material, thereby enhancing the output performance of the cathode during charge / discharge of a secondary battery.

[0159] As an example, the cathode active material according to the present invention includes a carbon layer chemical vapor deposited (CVD) in the temperature range described above, and when analyzed by Raman spectroscopy, the temperature is 1580±50 cm. -1 The area of ​​the peak appearing in is 1360±50 cm -1 may be larger than the area of ​​the peak appearing in .

[0160] 1360±50 cm for Raman spectroscopy -1 and 1580±50 cm -1 The peaks that appear in each are peaks observed in carbon compounds such as graphite, carbon black, graphene, and carbon nanotubes (CNT). Among these, 1360±50 cm -1The peaks appearing at 1580±50 cm are peaks that appear when inelastic scattering by phonons and elastic scattering occur around the defect / substitution point of carbon compounds during Raman spectroscopy. The higher the intensity and / or area ratio of the peak, the more defects or substitutions the compound has, and the lower the crystallinity. In contrast, -1 The peak appearing in is a peak due to the first-order Raman scattering phenomenon, and the higher the intensity and / or area ratio of the peak, the higher the crystallinity. That is, the cathode active material according to the present invention has a high crystallinity of the carbon layer since the area of ​​the peak indicating the crystallinity of the carbon contained in the carbon layer is larger than the area of ​​the peak indicating the amorphousness of the carbon compound when analyzed by Raman spectroscopy.

[0161] In this case, the carbon coating layer is 1360±50 cm -1 The area of ​​the peak appearing in is 1580±50 cm -1 The peak area may have a ratio of 30% to 90%, and more specifically, a ratio of 50% to 90%; 60% to 90%; 70% to 90%; 60% to 85%; or 55% to 80%.

[0162] Furthermore, the chemical vapor deposition (CVD) can be performed using a solid-state carbon source. Specifically, the chemical vapor deposition (CVD) can use a carbon structure and a polymer compound, each including at least one of a point-like carbon compound and a linear carbon compound, as a carbon source, either alone or in combination.

[0163] More specifically, the dot-shaped carbon compound may include one or more of acetylene black, channel black, furnace black, lamp black, summer black, and graphene. In addition, the linear carbon compound may include one or more of carbon nanotubes and carbon fibers.

[0164] In addition, the polymer compound may include at least one of polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polypyrrole (PPy), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethylacrylate (PMA), and polymethylmethacrylate (PMMA).

[0165] As an example, the carbon source may be a point-like carbon compound, and the point-like carbon compound may comprise acetylene black.

[0166] As another example, the carbon source may include a point-like carbon compound and a linear carbon compound. In this case, the point-like carbon compound may include acetylene black, and the linear carbon compound may include carbon nanotubes (CNTs). In addition, in this case, the point-like carbon compound and the linear carbon compound may be included in a weight ratio of 1:10 to 10:1, and specifically, may be included in a weight ratio 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.

[0167] As another example, the carbon source may include a point-like carbon compound, a linear carbon compound, and a polymer compound. In this case, the point-like carbon compound may include acetylene black, the linear carbon compound may include carbon nanotubes (CNTs), and the polymer compound may include polyvinylpyrrolidone (PVP). In this case, the linear carbon compound and the polymer compound may each be included in an amount of 10 to 90 parts by weight per 100 parts by weight of the point-like carbon compound, and specifically, may each be included in an amount of 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 per 100 parts by weight of the point-like carbon compound.

[0168] Conventionally, chemical vapor deposition (CVD) for forming a carbon layer has been performed using hydrocarbon gases such as methane (CH4), ethane (CH3CH3), propane (CH3CH2CH3), ethylene (CH2CH2), and acetylene (CHCH). In this case, since a process for gasifying the carbon source is not required, it can be performed at a low temperature. However, it is not easy to control the gaseous carbon source during deposition, and there is a limitation that the high reactivity of the carbon source induces side reactions on the core surface, which reduces the activity of the anode active layer. In addition, the formed carbon layer is an amorphous layer with low crystallinity, so the specific surface area is not large. However, the present invention not only has high workability during deposition using a solid-state carbon source, but also has excellent electrical properties such as electrical conductivity due to the high crystallinity of the carbon layer. In particular, when using a polymer compound such as polyvinylpyrrolidone (PVP) as a carbon source, a porous carbon layer can be formed, allowing for the formation of a carbon layer with a high surface area on the core surface. In this case, the ion transport capacity of the carbon layer increases, improving the lithium diffusion coefficient, and thus the manufactured cathode active material exhibits excellent output performance.

[0169]

[0170] The method for manufacturing a cathode active material according to the present invention can manufacture a cathode active material having a carbon layer uniformly coated on a core including a compound represented by Chemical Formula 1 by having the above-described composition. In addition, the cathode active material manufactured thus has the advantages of not only high structural stability, but also excellent output performance during charge and discharge and excellent life characteristics.

[0171]

[0172] anode

[0173] Furthermore, the present invention,

[0174] anode current collector, and

[0175] A positive electrode is provided, which includes a positive electrode active layer provided on at least one surface of the positive electrode current collector and including the positive electrode active material according to the present invention described above.

[0176]

[0177] The positive electrode according to the present invention includes a positive electrode active layer provided on at least one surface of a positive electrode current collector. Here, the positive electrode active layer is a layer that implements electrical activity of the positive electrode, and includes as a main component a positive electrode active material that implements an electrochemical redox reaction during charge and discharge of the battery. Specifically, the positive electrode active material may be included in an amount of 80 parts by weight to 99.8 parts by weight based on the total weight of the positive electrode active layer, and specifically, may be included in an amount of 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.

[0178] In addition, since the above-described positive electrode active material has the same composition as the positive electrode active material according to the present invention described above, a detailed description thereof is omitted.

[0179] Meanwhile, the above-mentioned positive electrode active layer may optionally further include a conductive agent, a binder, other additives, etc., along with the positive electrode active material as the main component.

[0180] At this time, the above-mentioned conductive material may include one or more of acetylene black, channel black, furnace black, lamp black, summer black, graphene, carbon nanotubes, and carbon fibers, but is not limited thereto.

[0181] The content of the conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire electrode active layer, and specifically, may be 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 the conductive material within the above range, the present invention can prevent the electrode resistance from increasing due to a low content of the conductive material, thereby reducing the charging capacity, and can prevent the problem of the charging capacity from decreasing due to a decrease in the content of the electrode active material due to an excessive amount of the conductive material, or the rapid charging characteristics from decreasing due to an increase in the loading amount of the electrode active layer.

[0182] In addition, the binder may be appropriately applied as a component that assists in the bonding of the positive electrode active material and the conductive material and the bonding to the current collector, and may be applied within a range that does not deteriorate the electrical properties of the positive electrode, but specifically may include at least one of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber.

[0183] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire positive electrode active layer, and specifically, may be 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 contained in the positive electrode active layer within the above range, the present invention can prevent the adhesive strength of the active layer from being lowered due to a low content of binder or the electrical properties of the positive electrode from being lowered due to an excessive amount of binder.

[0184] In addition, the average thickness of the positive electrode active layer may be 50 ㎛ to 500 ㎛. Specifically, the average thickness of the positive electrode active layer may be 100 ㎛ to 400 ㎛; 200 ㎛ to 350 ㎛; 50 ㎛ to 180 ㎛; 80 ㎛ to 150 ㎛; 100 ㎛ to 250 ㎛; 100 ㎛ to 250 ㎛; or 130 ㎛ to 190 ㎛. The present invention can not only implement high adhesion between the positive electrode active layer and the positive electrode current collector by controlling the average thickness of the positive electrode active layer within the above range, but also implement high energy density of the positive electrode.

[0185] Furthermore, the positive electrode current collector may be one having high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used. In the case of aluminum or stainless steel, a surface-treated material such as carbon, nickel, titanium, or silver may also be used. In addition, the average thickness of the positive electrode current collector may be appropriately applied within the range of 3 to 500 μm, taking into account the conductivity and total thickness of the positive electrode being manufactured.

[0186]

[0187] The positive electrode for a lithium secondary battery according to the present invention has the advantages of excellent safety and life characteristics by having the above-described configuration.

[0188]

[0189] Hereinafter, the present invention will be described in more detail through examples and comparative examples.

[0190] However, the following examples and comparative examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and comparative examples.

[0191]

[0192] Manufacturing Examples 1 to 5. Manufacturing of cores for cathode active materials

[0193] First, a compound represented by chemical formula 1 to be used as a core of the cathode active material was prepared. For this purpose, lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4) was purchased commercially. The purchased lithium manganese iron phosphate was heat-treated at 700°C for 1 hour, and then titanium dioxide (TiO2), ammonium vanadate (NH4VO3), and niobium oxide (Nb2O5) were mixed and calcined at 700±20°C under a nitrogen atmosphere to prepare a compound powder represented by chemical formula 1. At this time, the mixing amounts of titanium dioxide (TiO2), ammonium vanadate (NH4VO3), and niobium oxide (Nb2O5) were adjusted so that the mole fraction of the metal included in the metal precursor compound satisfied Table 1 based on the mole fraction of 1 of the total metal excluding lithium in the prepared compound.

[0194] X-ray diffraction (XRD) was performed on the manufactured compound powder to measure ① lattice constants a, bc and ② X-axis size representing grain size. Specifically, lithium manganese iron phosphate (LiMn 0.7 Fe 0.3Considering the doped and / or substituted metals in PO4), X-ray diffraction spectroscopic analysis was performed using the Rietveld refinement method. At this time, the X-ray diffraction analysis was performed using a Bruker D8 Endeavor (Cu-Kα, λ=1.54Å) equipped with a LynxEye XE-T position sensitive detector or a LynxEye position sensitive detector, and the sample was placed in the groove of a general powder holder. After that, the sample surface was smoothed using a slide glass, and the sample was filled so that the sample height matched the edge of the holder, and then the measurement was performed under the conditions of FDS 0.5°, 2θ=15°~90° range, step size=0.02°, and total scan time=approximately 20 minutes. When analyzing the grain size, instrumental broadening was considered using the Fundamental Parameter Approach (FPA) built into the Bruker TOPAS program, and the entire peaks of the measurement range were used for fitting. The peak shape was fitted using the Lorentzian contribution as the first principle (FP) among the peak shapes available in TOPAS. Strain was not considered at this time. The measured lattice constant c and the grain size (i.e., X-axis size) are shown in Table 1, and the correlation between the lattice constant c and the lattice constants a and b is shown in Fig. 1. Referring to Fig. 1, the lattice constant c shows a linear relationship when plotted against the lattice constants a and b, and it was confirmed that it moves toward the lower right as the concentration of lithium (Li) in the structure increases. In addition, it was confirmed that as the type of metal doped and / or substituted in the positive electrode active material increases, a linear relationship appears, and it follows Vegard's law.

[0195] In addition, particle size distribution analysis (PSD) was performed on each manufactured core to determine the D of the core. 50 was measured. Specifically, particle size distribution analysis (PSD) was performed by laser diffraction method. The particle size distribution analysis (PSD) device used was Malvern's Mastersizer 3000, and the laser refractive index was adjusted to 2.0 to 2.2. Each core weighing less than 1 g was dispersed in deionized (DI) water using an ultrasonic irradiator installed inside the device, and then the particle size distribution was calculated by measuring the difference in diffraction pattern according to particle size when the dispersed particles pass through the laser beam. At this time, by calculating the particle diameter at the point where it is 50% of the area cumulative distribution according to particle size in the measuring device, D 50 was measured. The measured results are shown in Table 1 below.

[0196] Manufacturing Example 1 Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 4 Manufacturing Example 5 Metal precursor compound TiO2-0.060.030.020.02 NH4VO3--0.030.020.02 Nb2O5---0.020.02 Whether or not heat treatment was performed before mixing the metal precursor compound (700℃, 1 hour) XXXXOXRD Lattice constant c4.69162 Å4.69184 Å4.69202 Å4.69209 Å4.69214 Å X-axis size120nm100nm96nm91nm88nmAverage particle diameter (D 50 )1.40㎛1.20㎛1.03㎛0.90㎛0.81㎛

[0197]

[0198]

[0199] Examples 1 to 10 and Comparative Example 1. Preparation of positive electrode active material

[0200] In the manufacturing example above, core particles for cathode active materials were introduced into a chemical vapor deposition reactor, and the interior of the reactor was replaced with argon gas. Thereafter, 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 supplying argon gas at 180 to 220 sccm. Thereafter, hydrogen gas and argon gas were continuously supplied at 10 to 20 sccm and 280 to 320 sccm, respectively, while additionally performing chemical vapor deposition for 25 to 35 minutes, thereby manufacturing a cathode active material for a lithium secondary battery having a carbon layer formed on the core surface.

[0201] At this time, ① the type of core applied is shown in Table 2 below. In addition, the carbon source used in the chemical vapor deposition was acetylene black (AB), carbon nanotube (CNT), and polyvinylpyrrolidone (PVP) particles as point-like carbon compounds, linear carbon compounds, and polymer compounds, respectively. The carbon source was used in an amount of 4 to 6 wt % based on the total weight of the cathode active material, and ② the weight ratios of point-like carbon compounds, linear carbon compounds, and polymer compounds included as carbon sources are as shown in Table 2 below.

[0202] Particle size distribution analysis (PSD) was performed on each manufactured cathode active material to determine the D of the cathode active material. 50 was measured. At this time, D of the positive electrode active material 50 Silver is the core D 50 The measurement was performed in the same manner as the measurement method.

[0203] The measured results are shown in Table 2 below.

[0204] Furthermore, transmission electron microscopy (TEM) analysis was performed on the manufactured cathode active materials to measure the average thickness of the carbon layer formed on the core surface. The results confirmed that the average thickness of the carbon layer formed on the core surface was approximately 5–10 nm.

[0205] Core type Content ratio of each carbon source [weight %] D of positive electrode active material 50 ABCNTPVPComparative Example 1 Core of Manufacturing Example 1 503515 About 1.8 ㎛Example 1 Core of Manufacturing Example 2 503515 About 1.3 ㎛Example 2 Core of Manufacturing Example 3 503515 About 1.1 ㎛Example 3 Core of Manufacturing Example 4 503515 About 1.0 ㎛Example 4 Core of Manufacturing Example 5 10000 About 1.0 ㎛Example 5 Core of Manufacturing Example 5 66.733.30 About 0.9 ㎛Example 6 Core of Manufacturing Example 5 50500 About 0.9 ㎛Example 7 Core of Manufacturing Example 5 33.366.70 About 0.9 ㎛Example 8 Core of Manufacturing Example 5 503515 About 0.9 ㎛Example 9 Manufacturing Example Core of 5 502525 about 0.9 ㎛ Example 10 Manufacturing example 5 Core of 501535 about 0.9 ㎛

[0206]

[0207]

[0208] Comparative Example 2. Preparation of positive electrode active material

[0209] A cathode active material was manufactured by performing the same method as in Example 8, except that a core containing a compound represented by Chemical Formula 1, acetylene black, carbon nanotubes, and polyvinyl pyrrolidone (PVP) were uniformly mixed and then calcined at 800±50°C for 5 minutes.

[0210]

[0211] Examples 11-20 and Comparative Examples 3-4. Manufacturing of lithium secondary batteries

[0212] N-methylpyrrolidone solvent was injected into a homo mixer, and 90 parts by weight of each of the positive electrode active materials manufactured 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. Then, a positive electrode slurry was prepared by mixing at 3,000 rpm for 60 minutes. An aluminum foil (average thickness: 12 μm) was prepared as a positive electrode current collector, and the positive electrode slurry manufactured previously was cast on one side of the prepared aluminum foil. The aluminum foil on which the positive electrode slurry was cast was dried in a vacuum oven at 130°C and then rolled to manufacture a positive electrode. At this time, the total thickness of the rolled positive electrode active layer was 150 μm, and the porosity was 25 to 35%.

[0213] A lithium metal disk was prepared as a negative electrode. The prepared negative electrode was placed opposite the positive electrode prepared in Examples 1 to 6 and Comparative Example 1, as shown in Table 3 below, and an 18 μm polypropylene separator was interposed therebetween to manufacture an electrode assembly. Each manufactured electrode assembly was inserted into a battery case, an electrolyte composition was injected into the battery case, and the case was sealed to manufacture a half cell. At this time, as the electrolyte composition, a solution in which lithium hexafluorophosphate (LiPF6, 1.0 M) was mixed in a mixture of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1:1 (volume ratio) was used.

[0214] Types of applied positive electrode active materials Example 11 Positive electrode active material manufactured in Example 1 Example 12 Positive electrode active material manufactured in Example 2 Example 13 Positive electrode active material manufactured in Example 3 Example 14 Positive electrode active material manufactured in Example 4 Example 15 Positive electrode active material manufactured in Example 5 Example 16 Positive electrode active material manufactured in Example 6 Example 17 Positive electrode active material manufactured in Example 7 Example 18 Positive electrode active material manufactured in Example 8 Example 19 Positive electrode active material manufactured in Example 9 Example 20 Positive electrode active material manufactured in Example 10 Comparative Example 3 Positive electrode active material manufactured in Comparative Example 1 Comparative Example 4 Positive electrode active material manufactured in Comparative Example 5

[0215]

[0216]

[0217] Experimental example.

[0218] In order to evaluate the performance of the cathode active material according to the present invention, the following experiments were conducted.

[0219]

[0220] 1) Output characteristics of lithium secondary batteries

[0221] The half-cells manufactured in Examples 11 to 20 and Comparative Examples 3 to 4 were subjected to constant current / constant voltage charging (CC / CV charge) at a temperature of 25°C, followed by constant current discharge (CC discharge) to measure the initial discharge capacity. At this time, the constant current / constant voltage charging was performed with a constant current of 0.1C rate until the voltage reached 4.2 V, and then cut-off at a current of 0.1C rate in constant voltage mode to maintain 4.2 V. In addition, the constant current discharge was performed with a 1.0C rate until the voltage reached 1.5 V.

[0222] Then, each half-cell was fully charged at 25°C with a charge current of 1.0C rate to a terminal voltage of 4.2–4.25 V, and the high-rate discharge capacity was measured while discharging at a rate ranging from 1.0C to 5.0C. The high-rate discharge characteristics of each lithium secondary battery were evaluated by calculating the relative discharge capacity ratio based on the initial discharge capacity at each discharge rate from the measured discharge capacity. The measured results are shown in Table 4.

[0223]

[0224] 2) High temperature life characteristics

[0225] The charge-discharge capacity retention rate under high-temperature conditions was measured for each half-cell manufactured in Examples 11-20 and Comparative Examples 3-4. Specifically, one cycle was set as charging at a constant current of 1C at 45°C until the voltage reached 4.25 V, and discharging at a constant current of 1C until the voltage reached 2.5 V. Then, 300 cycles of charge-discharge were performed on each half-cell.

[0226] At this time, when charging and discharging each half battery, 1 st Charging capacity of the cycle and 300 th The charging capacity of the cycle was measured. The measured 1 st 300 based on the charging capacity of the cycle th The high-temperature life of each half-cell was evaluated by calculating the charge capacity retention rate over the cycle. The results are shown in Table 4 below.

[0227] Unit: % Initial discharge capacity by discharge rate Relative discharge capacity ratio 300 thCycle Capacity Retention [%] 1C2C3C5C Example 1 193.88 3.87 9.97 3.28 1.1 Example 1294.38 4.28 0.97 4.88 1.6 Example 1394.88 5.08 1.57 5.38 2.1 Example 1494.98 6.28 1.97 6.18 4.2 Example 1595.98 7.68 2.07 6.88 4.8 Example 1695.18 7.38 1.87 6.58 3.7 Example 1795.48 6.78 1.27 6.08 3.0 Example 1896.08 8.68 3.57 8.18 6.9 Example 1995.888.482.977.885.1 Example 2095.887.882.177.286.2 Comparative Example 392.283.177.371.778.4 Comparative Example 490.581.474.368.771.2

[0228]

[0229]

[0230] As shown in Table 4 above, it can be seen that the positive electrode for a lithium secondary battery according to the present invention has excellent output performance and high-temperature life characteristics.

[0231] Specifically, half-cells including the cathode of the embodiment in which a carbon layer is formed through chemical vapor deposition (CVD) on a core including a compound represented by Chemical Formula 1 exhibited a high discharge capacity ratio of about 73.0% or more even under high-rate conditions of 5C or more, and it was confirmed that the capacity retention ratio was about 80% or more even after 300 charge-discharge cycles were performed under high-temperature conditions.

[0232] This means that when a carbon layer is formed on a core by chemical vapor deposition (CVD) of a compound represented by chemical formula 1 during the manufacture of a cathode active material, a carbon layer with high crystallinity is uniformly formed on the surface of the core with high structural stability and a large specific surface area, thereby improving the electrochemical performance and life characteristics of the cathode active material.

[0233] From these results, it can be seen that the cathode active material according to the present invention and the cathode including the same have excellent output performance during charge and discharge and excellent life characteristics.

[0234]

[0235] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that the present invention can be variously modified and changed within a scope that does not depart from the technical scope of the present invention as set forth in the claims to be described below.

[0236] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the patent claims.

Claims

1. A core comprising a compound represented by the following chemical formula 1, and A cathode active material surrounding the core and including a carbon layer: [Chemical Formula 1] Li 1+a Mn 1-b-c Fe b M 1 c PO4 In the above chemical formula 1, M 1 is at least one of 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.

2. In paragraph 1, The compound represented by the chemical formula 1 above is a cathode active material including at least one of the compounds represented by the chemical formulas 2 to 5 below: [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 the chemical formulas 2 to 5 above, 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≤0.1이되, 0.001≤x+y≤0.2 또는 0.001≤x+y+z≤0.2이다.

3. In paragraph 1, The above core is an anode having a lattice constant c of 4.69165 Å to 4.80 Å when analyzed by X-ray diffraction and satisfying the following equation 1: [Formula 1] y=-px+q In the above equation 1, y represents the lattice constant c, x is , where a and b are lattice constants a and b, respectively. p and q are -0.08≤p≤-0.07 and 5≤q≤6, respectively.

4. In paragraph 1, The average particle diameter (D) of the above cathode active material 50 ) is a cathode active material having a size of 0.5㎛ to 10㎛.

5. In paragraph 1, A cathode active material having an average thickness of the carbon layer of 50 nm or less.

6. A step of forming a carbon layer on the particle surface of a compound represented by the following chemical formula 1 is included. The above carbon layer is formed by a method for manufacturing a cathode active material 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 the above chemical formula 1, M 1 is at least one of 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.

7. In paragraph 1, The above chemical vapor deposition (CVD) is a method for producing a cathode active material using a carbon structure including at least one of a point-like carbon compound and a linear carbon compound as a carbon source; and at least one of a polymer compound.

8. In paragraph 7, The above point-shaped carbon compound comprises at least one of acetylene black, channel black, furnace black, lamp black, summer black and graphene, A method for producing a cathode active material, wherein the linear carbon compound comprises at least one of carbon nanotubes and carbon fibers.

9. In paragraph 7, A method for producing a cathode active material, wherein the polymer compound comprises at least one of polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polypyrrole (PPy), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethyl acrylate (PMA), and (poly(methyl methacrylate) (PMMA).

10. In paragraph 7, The above chemical vapor deposition (CVD) is a method for manufacturing a cathode active material, which is performed at a temperature of 500°C to 1,500°C.

11. Anode current collector, and A cathode comprising a cathode active layer provided on at least one surface of the cathode current collector and including a cathode active material according to claim 1.

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