KR20200104647A - A preparing method of a cathode active material for a lithium secondary battery - Google Patents

Abstract

The present invention relates to a novel method for manufacturing a positive electrode active material for a lithium secondary battery. The positive electrode active material manufactured by the novel manufacturing method of the present invention can impart sufficiently high conductivity to a positive electrode even without being used in combination with a conductive material. The present invention comprises the following steps: a) heat-treating the positive electrode active material under a gas atmosphere containing nitrogen, thereby doping nitrogen on the surface of the positive electrode active material to generate a nitrogen-doped positive electrode active material; b) generating the nitrogen-doped positive electrode active material coated with graphene oxide on a surface by conducting a reaction of the nitrogen-doped positive electrode active material with a mixed solution including graphene oxide (GO); and c) reducing the GO to reduced graphene oxide (rGO) by heat-treating the nitrogen-doped positive electrode active material coated with GO on the surface under a reducing gas atmosphere.

Description

Manufacturing method of a cathode active material for a lithium secondary battery {A preparing method of a cathode active material for a lithium secondary battery}

The present invention relates to a method for manufacturing a positive electrode active material for a lithium secondary battery, a positive electrode including the positive electrode active material manufactured by the above manufacturing method, and a lithium secondary battery including the positive electrode.

In general, a 　 lithium secondary battery includes a 　 including a positive electrode active material and a negative electrode including a negative active material. Since the positive electrode has low conductivity of the positive electrode active material itself, a conductive material such as carbon nanotubes, graphene, or carbon black may be used as a positive electrode material to compensate.

However, since the conductive material has a high specific surface area and a strong tendency to agglomerate particles due to Van der Waals force, it is difficult to effectively disperse in the positive electrode slurry. In addition, when the positive electrode is manufactured from the positive electrode slurry in which the conductive material is not effectively dispersed, the volume resistance of the positive electrode increases, so that sufficiently high conductivity may not be exhibited. For example, Patent Document 1 uses a positive electrode active material and a conductive material in combination as a positive electrode material of a lithium secondary battery, but there is a problem that the volume resistance value of the positive electrode obtained is not sufficiently satisfactory.

Korean Patent Registration KR 10-1267351 B1

The present invention is to provide a method for producing a positive electrode active material capable of imparting sufficiently high conductivity to a positive electrode without being used in combination with a conductive material.

The present invention,

a) heat-treating the positive electrode active material in a gas atmosphere containing nitrogen, thereby doping nitrogen on the surface of the positive electrode active material to generate a nitrogen-doped positive electrode active material;

b) reacting the nitrogen-doped positive electrode active material with a mixed solution containing graphene oxide (GO) to generate a nitrogen-doped positive electrode active material coated with graphene oxide on the surface; And

c) reducing the graphene oxide to reduced graphene oxide (rGO) by heat-treating the nitrogen-doped positive electrode active material coated with graphene oxide on the surface under a reducing gas atmosphere. ,

It provides a method of preparing a positive electrode active material coated with reduced graphene oxide on the surface.

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the gas atmosphere including nitrogen in step a) may be a nitrogen atmosphere or an ammonia atmosphere.

In the method for producing a positive electrode active material according to an embodiment of the present invention, in the mixed solution of step b), the mixing ratio of the nitrogen-doped positive electrode active material and the graphene oxide is 80:20 to 99:1 by weight. I can.

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the reducing gas atmosphere in step c) may be a hydrogen atmosphere.

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the heat treatment temperature in step c) may be higher than the heat treatment temperature in step a).

The present invention provides a positive electrode including the positive electrode active material manufactured by the manufacturing method of the present invention.

The present invention provides a lithium secondary battery including the positive electrode.

The manufacturing method of the present invention can effectively coat the reduced graphene oxide on the surface of the positive electrode active material by applying graphene oxide on the surface of the positive electrode active material doped with nitrogen and then heat treatment under a reducing gas atmosphere. The active material can be more effectively modified with reduced graphene oxide having excellent conductivity.

In addition, since the manufacturing method of the present invention can prepare a cathode active material coated with reduced graphene oxide on the surface without going through a process of adding a separate additive, a large amount of the cathode active material surface-modified by a more economical process Production can also be made possible.

In addition, the positive electrode active material manufactured by the manufacturing method of the present invention can provide remarkably high conductivity by greatly reducing the volume resistance of the positive electrode, even without being used in combination with a conductive material.

1 is a schematic diagram of a method according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail. If there are no other definitions in the technical and scientific terms used at this time, they have the meanings commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the following description will unnecessarily obscure the subject matter of the present invention. Description of possible known functions and configurations will be omitted.

The present invention,

a) heat-treating the positive electrode active material in a gas atmosphere containing nitrogen, thereby doping nitrogen on the surface of the positive electrode active material to generate a nitrogen-doped positive electrode active material;

b) reacting the nitrogen-doped positive electrode active material with a mixed solution containing graphene oxide (GO) to generate a nitrogen-doped positive electrode active material coated with graphene oxide on the surface; And

c) reducing the graphene oxide to reduced graphene oxide (rGO) by heat-treating the nitrogen-doped positive electrode active material coated with graphene oxide on the surface under a reducing gas atmosphere. ,

It provides a method of preparing a positive electrode active material coated with reduced graphene oxide on the surface.

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the positive electrode active material as a starting material of step a) is preferably at least one selected from cobalt, manganese, nickel, and a composite metal oxide of lithium. The solid solubility between metals can be made variously. In addition to these metals, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, An element selected from the group consisting of Sr, V, and rare earth elements may be further included. Examples of the positive electrode active material is Li _{a A 1 -} (in the above formula, 0.90 ≤ a ≤ 1.8, and _{0 ≤ b ≤ 0.5) b B} b D 2; _{Li a E 1 - b B b} O 2 - ( in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) c D c; _{LiE 2 - b B b O 4} - ( in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) c D c; Li _a Ni _{1 -b- c} Co _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); _{Li a Ni 1 -b- c Co b} B c O 2 - α F α ( wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2 a); Li _a Ni _{1 -bc} Co _b B _c O _2-α F ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Mn _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); _{Li a Ni 1 -b- c Mn b} B c O 2 - α F α ( wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2 a); _{Li a Ni 1 -b- c Mn b} B c O 2 - α F 2 ( wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2 a); Li _a Ni _b E _c G _d O ₂ (in the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li _a NiG _b O ₂ (in the above formula, 0.90≦a≦1.8, 0.001≦b≦0.1); Li _a CoG _b O ₂ (in the above formula, 0.90≦a≦1.8, 0.001≦b≦0.1); Li _a MnG _b O ₂ (in the above formula, 0.90≦a≦1.8, 0.001≦b≦0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90≦a≦1.8 and 0.001≦b≦0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≦f≦2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≦f≦2); And LiFePO _{4 It} is possible to use a compound represented by any one of the formula.

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or combinations thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu, or a combination thereof. For example, LiCoO ₂ , LiMn _x O _2X (x=1, 2), LiNi _{1 - x} Mn _x O _2X (0<x<1), LiNi _{1 -x- y} Co _x Mn _y O ₂ (0≤ x≤0.5, 0≤y≤0.5), may be FePO ₄ or the like.

In the method for manufacturing a positive electrode active material according to an embodiment of the present invention, the gas atmosphere including nitrogen in step a) is not particularly limited, but preferably may be a nitrogen atmosphere or an ammonia atmosphere, and more preferably an ammonia atmosphere. have.

In the method for manufacturing a positive electrode active material according to an embodiment of the present invention, the heat treatment temperature in step a) may be preferably 400 to 650°C, and more preferably 500 to 650°C. By adopting 400 to 650 ℃ as the heat treatment temperature in step a), it is possible to achieve a sufficiently economical nitrogen doping level.

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, in the nitrogen-doped positive electrode active material of step a), nitrogen doped on the surface of the positive electrode active material may be preferably charged with a positive charge. (Fig. 1).

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the reaction of step b) may be mixing and reacting the nitrogen-doped positive electrode active material and the graphene oxide (GO) in a solvent. The solvent is preferably at least selected from the group consisting of dimethylformamide (DMF), dimethylsulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP). It may be one or more, but is not limited thereto.

In the method for producing a positive electrode active material according to an embodiment of the present invention, the reaction temperature in step b) may be preferably 15 to 30°C. The reaction temperature in step b) may be more preferably room temperature.

In the method for producing a positive electrode active material according to an embodiment of the present invention, in the mixed solution of step b), the mixing ratio of the nitrogen-doped positive electrode active material and the graphene oxide is preferably 80:20 to 99 by weight: May be 1. The mixing ratio may be more preferably 90:10 to 99:1 by weight.

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, in the nitrogen-doped positive electrode active material of step b), nitrogen doped on the surface of the positive electrode active material may be preferably positively charged. The graphene oxide of step b) may preferably have a negative charge. Therefore, preferably, an electrostatic attraction acts between the positive charge of nitrogen doped on the surface of the positive electrode active material and the negative charge of graphene oxide, so that graphene oxide can be evenly applied on the surface of the nitrogen-doped positive electrode active material (Fig. One).

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the reducing gas atmosphere in step c) is not particularly limited, but may preferably be a hydrogen atmosphere.

In the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the heat treatment temperature in step c) is preferably higher than the heat treatment temperature in step a). Accordingly, the heat treatment temperature in step c) may be preferably 700 to 1000 °C, more preferably 700 to 900 °C.

In the method for manufacturing a positive electrode active material according to an embodiment of the present invention, graphene oxide coated on the surface of the nitrogen-doped positive electrode active material by the high-temperature heat treatment in step c) is reduced graphene oxide (rGO: reduced graphene). oxide), and finally, the reduced graphene oxide may be coated on the surface of the positive electrode active material (FIG. 1). Preferably, an electrostatic attraction acts between the positive charge of nitrogen doped on the surface of the positive electrode active material and the negative charge of graphene oxide, so that when graphene oxide is evenly applied on the surface of the nitrogen-doped positive electrode active material, the step c) By the heat treatment of the reduced graphene oxide on the surface of the positive electrode active material can be coated more effectively.

The present invention provides a positive electrode including the positive electrode active material manufactured by the manufacturing method of the present invention.

The positive electrode according to an exemplary embodiment of the present invention may selectively include a conductive material in addition to the positive electrode active material, but the volume resistance of the positive electrode may be greatly reduced even if the conductive material is not included.

The present invention provides a lithium secondary battery including the positive electrode.

In addition to the positive electrode, a lithium secondary battery according to an embodiment of the present invention includes a non-aqueous electrolyte; A negative electrode including a negative electrode active material; And a separator; may include.

The non-aqueous electrolyte may be made of an electrolyte and a lithium salt, and a non-aqueous organic solvent or the like may be used as the electrolyte.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dime Oxyethane, tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid tryester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate , Or an aprotic organic solvent such as ethyl propionate may be used.

The lithium salt is a material soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4 phenyl borate, imide, etc. may be used .

The negative active material may be at least one selected from the group consisting of crystalline carbon, amorphous carbon, carbon composites, carbon fibers, and combinations thereof. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbeads (MCMB) or mesophase pitch-based carbon fibers (MPCF) fired at 1500° C. or lower. As the crystalline carbon, graphite-based materials may be exemplified, and specifically, natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like.

The positive or negative electrode may be prepared by dispersing an electrode active material and a binder, if necessary, a conductive material and/or a thickener in a solvent to prepare an electrode slurry composition, and then applying the slurry composition to an electrode current collector. Aluminum or aluminum alloy may be used as the positive electrode current collector, and copper or copper alloy may be commonly used as the negative electrode current collector. The positive electrode current collector and the negative electrode current collector may be in the form of foil or mesh.

The binder is a material that plays a role of a buffering effect on the expansion and contraction of the active material, such as forming a paste of the active material, mutual adhesion of the active material, adhesion to the current collector, and, for example, polyvinylidene fluoride (PVdF), polyhexafluoropropylene. -Copolymer of polyvinylidene fluoride (PVdF/HFP)), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate) ), poly(ethylacrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), acrylonitrile-butadiene Rubber, etc. The content of the binder may be 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the electrode active material. If the content of the binder is too small, the adhesion between the electrode active material and the current collector may be insufficient, and if the content of the binder is too high, the adhesion is improved, but the content of the electrode active material decreases that much, which may be disadvantageous in increasing the battery capacity.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any material can be used as long as it does not cause chemical changes and is an electronic conductive material. At least one selected from the group consisting of conductive materials may be used. Examples of the graphite-based conductive material include artificial graphite and natural graphite, and examples of the carbon black-based conductive material include acetylene black, ketjen black, denkablack, thermal black, and channel black. black), and examples of metal-based or metallic compound-based conductive materials include perovskite materials such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ and LaSrMnO ₃ . However, it is not limited to the conductive materials listed above.

When using a conductive material, the content of the conductive material is preferably 0.1 to 10% by weight based on the electrode active material.

The thickener is not particularly limited as long as it can control the viscosity of the active material slurry, but for example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like may be used.

As a solvent in which an electrode active material, a binder, a conductive material, and the like are dispersed, a non-aqueous organic solvent or an aqueous solvent is used. Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolididone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

A lithium secondary battery according to an embodiment of the present invention may include a separator that prevents a short circuit between a positive electrode and a negative electrode and provides a passage for lithium ions. Such separators include polypropylene, polyethylene, polyethylene/polypropylene, Polyolefin-based polymer films such as polyethylene/polypropylene/polyethylene, polypropylene/polyethylene/polypropylene, or a multilayer thereof, microporous films, woven fabrics, and nonwoven fabrics may be used. In addition, a film coated with a resin having excellent stability on a porous polyolefin film may be used.

The lithium secondary battery according to an embodiment of the present invention may be formed in other shapes such as a cylindrical shape or a pouch type in addition to a square shape. The secondary battery is suitable for applications requiring high voltage, high output, and high temperature driving, such as an electric vehicle, in addition to applications such as conventional mobile phones and portable computers. In addition, the secondary battery can be used in hybrid vehicles, etc. in combination with existing internal combustion engines, fuel cells, supercapacitors, etc., and can be used for electric bicycles, power tools, and all other uses requiring high output, high voltage and high temperature driving. Can be used.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples.

[Example 1]

Positive electrode active material LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ was put in a crucible and heat-treated by flowing ammonia gas at 600° C. for 5 hours at 400 ppm in an electric furnace. Accordingly, positively charged nitrogen was doped on the surface of the heat-treated positive electrode active material.

The nitrogen-doped positive electrode active material and graphene oxide having a negative charge were dissolved in N-methyl-2-pyrrolidone at a weight ratio of 99:1 to form a mixed solution, and the mixed solution was stirred at 400 rpm for 2 hours at room temperature. Reacted. After stirring and reaction, the mixed solution was filtered to extract N-methyl-2-pyrrolidone, to obtain a nitrogen-doped positive electrode active material coated with graphene oxide on the surface. In the positive electrode active material thus obtained, an electrostatic attraction acts between the positive charge of nitrogen doped on the surface of the positive electrode active material and the negative charge of graphene oxide, so that graphene oxide was evenly coated on the surface of the nitrogen-doped positive electrode active material. .

A nitrogen-doped positive electrode active material coated with graphene oxide on the surface was put in a crucible, and heat-treated by flowing hydrogen gas at 800° C. for 8 hours at 800° C. for 8 hours. Accordingly, through a process of reducing the graphene oxide applied on the surface of the nitrogen-doped positive electrode active material to the reduced graphene oxide, the positive electrode active material LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . The} reduced graphene oxide was coated on the surface of ₁ O ₂ .

[Example 2]

The final surface-modified positive electrode active material and binder (polyvinylidene fluoride) prepared in Example 1 were mixed with a solvent (N-methyl-2-pyrrolidone) in a weight ratio of 98:2 to prepare a paste for forming a positive electrode material. I did. Thereafter, after processing the protrusions having openings on both sides of the aluminum foil having a thickness of 20 μm, the positive electrode material forming paste was applied to both sides of the aluminum foil so as to have a coating amount of 20 mg/cm ² on one side. Subsequently, by drying the solvent, grooves were formed in the anode material layer around the protrusions formed in the aluminum foil. Then, the coating, drying, and groove formation were completed by pressing, to increase the density of the positive electrode material layer, and then cut into a 50 mm X 50 mm square shape to prepare a positive electrode for a lithium secondary battery.

For the prepared positive electrode for a lithium secondary battery, a low resistivity meter (manufactured by Mitsubishi Chemical Corporation, product name: Loresta GP, model number: MCP-T610) was used, and a load of 9.8 in an atmosphere of 23° C. and a relative humidity of 15% or less. Volume resistance (bulk resistance) was measured by the four probe method under the condition of Mpa. The results are shown in the following [Table 1].

[Comparative Example 1]

Positive electrode active material LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . A} positive electrode for a lithium secondary battery was prepared in the same manner as in Example 2, except that ₁ O ₂ , a conductive material (carbon black) and a binder were mixed with a solvent in a weight ratio of 97:1:2 to prepare a paste for forming a positive electrode material. And the volume resistance was measured.

[Comparative Example 2]

Positive electrode active material LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . A} positive electrode for a lithium secondary battery was prepared and volume resistance was measured in the same manner as in Example 2, except that ₁ O ₂ and a binder were mixed with a solvent in a weight ratio of 98:2 to prepare a paste for forming a positive electrode material.

Volume resistance (ohm) Example 2 0.9 Comparative Example 1 1.4 Comparative Example 2 12000

As shown in the results of [Table 1], the final surface-modified positive electrode active material prepared in Example 1 is not used in combination with a conductive material, and significantly reduces the volume resistance of the positive electrode, thereby providing remarkably high conductivity ( Example 2).

Claims (7)

a) heat-treating the positive electrode active material in a gas atmosphere containing nitrogen, thereby doping nitrogen on the surface of the positive electrode active material to generate a nitrogen-doped positive electrode active material;
b) reacting the nitrogen-doped positive electrode active material with a mixed solution including graphene oxide (GO) to generate a nitrogen-doped positive electrode active material coated with graphene oxide on the surface; And
c) reducing the graphene oxide to reduced graphene oxide (rGO) by heat-treating the nitrogen-doped positive electrode active material coated with graphene oxide on the surface under a reducing gas atmosphere; ,
Method for producing a positive electrode active material coated with reduced graphene oxide on the surface. The method of claim 1,
The gas atmosphere including nitrogen in step a) is a nitrogen atmosphere or an ammonia atmosphere. The method of claim 1,
In the mixed solution of step b), the mixing ratio of the nitrogen-doped positive electrode active material and the graphene oxide is 80:20 to 99:1 by weight. The method of claim 1,
The reducing gas atmosphere in step c) is a method of manufacturing a positive electrode active material in a hydrogen atmosphere. The method of claim 1,
The heat treatment temperature in step c) is higher than the heat treatment temperature in step a). A positive electrode comprising a positive active material manufactured by the method of any one of claims 1 to 5. A lithium secondary battery comprising the positive electrode of claim 6.

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