KR101216572B1 - Cathode active material and Preparation method, Lithium secondary battery and Preparation method - Google Patents

Abstract

The present invention relates to a positive electrode active material, a lithium secondary battery comprising the same, a method of manufacturing a positive electrode active material, and a method of manufacturing a lithium secondary battery including the same. More specifically, by coating lithium oxide containing nickel and manganese on the surface of LiMn ₂ O ₄ , a cathode active material capable of suppressing the elution of Mn ions and improving the cycle characteristics at room temperature and high temperature without reducing the capacity And it relates to a method of manufacturing a lithium secondary battery, a positive electrode active material comprising the same and a method of manufacturing a lithium secondary battery comprising the same.

To this end, the present invention is capable of occluding and releasing lithium ions, and provides a cathode active material characterized by coating lithium oxide containing nickel and manganese on the surface of LiMn ₂ O ₄ .

Cathode active material, lithium secondary battery, manganese, energy capacity, lifetime characteristics

Description

A cathode active material, a lithium secondary battery comprising the same, a method of manufacturing a cathode active material and a method of manufacturing a lithium secondary battery including the same {Cathode active material and Preparation method, Lithium secondary battery and Preparation method}

The present invention relates to a positive electrode active material, a lithium secondary battery comprising the same, a method of manufacturing a positive electrode active material, and a method of manufacturing a lithium secondary battery including the same. More specifically, by coating lithium oxide containing nickel and manganese on the surface of LiMn ₂ O ₄ , a cathode active material capable of suppressing the elution of Mn ions and improving the cycle characteristics at room temperature and high temperature without reducing the capacity And it relates to a method of manufacturing a lithium secondary battery, a positive electrode active material comprising the same and a method of manufacturing a lithium secondary battery comprising the same.

In recent years, the market of portable electronic devices such as camcorders, cellular phones, notebook PCs, and so-called 3C markets has been rapidly growing, and the lithium secondary battery market, which is its power source, is also rapidly growing. In particular, the use of secondary batteries as a power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs) has been realized. Accordingly, many researches have been conducted on secondary batteries capable of meeting various requirements, and particularly, there is a high demand for lithium secondary batteries having high energy density, high discharge voltage, and long lifespan.

Lithium secondary batteries can be classified into cylindrical and square according to their shape. Cylindrical batteries are used mainly for notebook computers and camcorders, while square batteries are used for mobile phones. Ni-Cd and Ni-MH batteries may exhibit a memory effect that reduces their capacity when fully charged without being fully discharged.However, lithium secondary batteries have a large capacity and no memory effect, so they can be recharged as they remain. It is convenient because it is possible.

A lithium secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, a separator, and the like. LiCoO ₂ is used for the positive electrode, and carbon including graphite is mainly used for the negative electrode. The separator is interposed between the anode and the cathode, and a polyolefin-based porous separator is mainly used. As the electrolyte, a non-aqueous electrolyte having a lithium salt such as LiPF ₆ is used. These electrode materials have a structure that allows lithium (Li ⁺ ) in an ionic state to be reversibly inserted inside and out. That is, in the lithium secondary battery, lithium located in the inside of LiCoO ₂ exits and moves along the electrolyte into the carbon, which corresponds to the charging, and the movement in the opposite direction corresponds to the discharge.

Recently, various attempts have been made to improve the output of lithium secondary batteries. Among them, in particular, LiMn ₂ O ₄ is a material attracting attention as a cathode material for high-output lithium secondary batteries. However, LiMn ₂ O ₄ has a problem that Mn ions are eluted into the electrolyte at a high temperature, thereby deteriorating the life characteristics. In order to solve this problem, doping of dissimilar metals such as Al and Mg, or a surface coating with a material such as Al ₂ O ₃ , ZnO has been made.

When doping different metals, there is a problem that the available capacity is lowered by increasing the oxidation number of the transition metal Mn. In addition, in the case of the surface coating is electrochemically inert, there is a problem that the overall capacity is reduced by coating a material having no capacity. Therefore, there is a need for research on a method of coating an electrochemically active material on the surface of LiMn ₂ O ₄ to improve high temperature cycling characteristics without reducing the capacity.

The present invention has been made to solve the above problems, in particular, a positive electrode active material and a lithium secondary battery comprising the same to suppress the elution of Mn ions to improve the cycle characteristics at room temperature and high temperature while reducing the capacity It is an object of the present invention to provide a method of manufacturing a cathode active material and a method of manufacturing a lithium secondary battery including the same.

In order to achieve the above object, the cathode active material according to the present invention is capable of occluding and releasing lithium ions, and is characterized by coating lithium oxide containing nickel and manganese on the surface of LiMn ₂ O ₄ .

In addition, the lithium oxide may be LiNi _x Mn _1-x O ₂ .

In addition, the lithium oxide may be LiNi _0.5 Mn _0.5 O ₂ .

In addition, the coating amount of the lithium oxide is preferably 0.5 to 20% on a molar ratio basis with respect to the LiMn ₂ O ₄ .

In addition, the coating amount of the lithium oxide is more preferably 1 to 5% on a molar ratio basis with respect to the LiMn ₂ O ₄ .

Lithium secondary battery according to the invention is characterized in that it comprises a positive electrode active material.

Method for producing a positive electrode active material according to the present invention comprises the steps of (a) preparing a sol (sol) of lithium oxide containing nickel and manganese; And (b) coating the sol of the lithium oxide on the surface of LiMn ₂ O ₄ .

In addition, the step (a) comprises the steps of (a1) preparing and mixing each of the aqueous solution of Mn (CH ₃ COO) ₂ and Ni (CH ₃ COO) ₂ ; (a2) adding and dissolving CHCOO ₃ Li and citric acid to the mixed solution of step (a1); And (a3) adding ethylene glycol to the mixed solution of step (a2) to prepare the sol by stirring.

In addition, the lithium oxide may be LiNi _x Mn _1-x O ₂ .

In addition, the lithium oxide may be LiNi _0.5 Mn _0.5 O ₂ .

In addition, the coating amount of the lithium oxide in the step (b) is preferably 1 to 5% on a molar ratio basis with respect to the LiMn ₂ O ₄ .

In addition, the step (b) may be performed by adding LiMn ₂ O ₄ to the sol of the lithium oxide, stirring and gelating, followed by drying.

In addition, the method of manufacturing the cathode active material may further include (c) heat treating the lithium oxide coated LiMn ₂ O ₄ .

In addition, the heat treatment temperature in the step (c) is preferably 600 ~ 900 degrees Celsius.

Method of manufacturing a lithium secondary battery according to the present invention comprises the steps of preparing a positive electrode active material; And preparing a positive electrode plate by applying the positive electrode active material to a positive electrode current collector.

According to the present invention, by coating a lithium oxide containing nickel and manganese on the surface of LiMn ₂ O ₄ , the effect of suppressing the elution of Mn ions to reduce the capacity and improving the cycle characteristics at room temperature and high temperature have.

The positive electrode active material according to the present invention is capable of intercalation and deintercalation of lithium ions, and by coating lithium oxide containing nickel and manganese on the surface of LiMn ₂ O ₄ to suppress the elution of Mn ions It is characterized by improving the cycle characteristics at normal temperature and high temperature, without lowering.

At this time, the lithium oxide contains nickel and manganese, and has a chemical formula of LiNi _x Mn _1-x O ₂ . For example, x = 0.5, in which case the formula is LiNi _0.5 Mn _0.5 O ₂ .

The coating amount of lithium oxide is preferably 0.5 to 20% based on the molar ratio with respect to LiMn ₂ O ₄ . If the molar ratio of the lithium oxide is less than 0.5%, it is difficult to achieve the object of the present invention to prevent the elution of Mn ions at high temperature to improve the life characteristics, to prevent a decrease in capacity, and to improve the cycle characteristics at high temperatures.

On the other hand, when the molar ratio of lithium oxide exceeds 20%, there is a problem that the lithium oxide is not coated on the surface of LiMn ₂ O ₄ and is separated from each other. More preferably, the coating amount of lithium oxide is 1 to 5% on a molar ratio basis with respect to LiMn ₂ O ₄ .

The cathode active material according to the present invention is prepared by coating lithium oxide on the surface of LiMn ₂ O ₄ using the sol-gel method. Manufacturing process comprises the step of heat treatment steps of preparing a sol (sol) of lithium oxide, LiMn ₂ O step of coating a sol of lithium oxide on the surface of the _4, LiMn ₂ O ₄ lithium oxide coating. To prepare a sol of lithium oxide, Mn (CH ₃ COO) ₂ aqueous solution and Ni (CH ₃ COO) ₂ aqueous solution were prepared and mixed, and CH ₃ COOLi and citric acid were dissolved in the mixed solution. Add ethylene glycol and stir for a certain time. To coat a sol of lithium oxide on the surface of LiMn ₂ O ₄ was dried gel (gelation) by stirring the LiMn ₂ O ₄ in the sol of the lithium oxide.

The cathode active material thus prepared is coated on a cathode current collector to prepare a cathode plate. The present invention provides a lithium secondary battery comprising a cathode active material coated with lithium oxide on the surface of LiMn ₂ O ₄ . The lithium secondary battery has a structure in which a non-aqueous electrolyte containing lithium salt is impregnated in an electrode assembly having a separator interposed between a positive electrode plate and a negative electrode plate.

The positive electrode plate is manufactured by, for example, applying and drying a positive electrode active material on a positive electrode current collector, and may optionally further include components such as a conductive material, a binder, and a filler as necessary.

The positive electrode current collector may be manufactured to a thickness of approximately 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver or the like on the surface of aluminum or stainless steel may be used. The positive electrode current collector may increase the adhesion of the positive electrode active material by forming minute unevenness on the surface, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foaming agent, and a nonwoven fabric.

Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose , Polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, high polymer polyvinyl alcohol Etc. can be mentioned.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Specific examples of commercially available conductive materials include Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack, and EC series, which are acetylene black series. Membrane company (Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal).

In some cases, a filler may be optionally added as a component that suppresses the expansion of the positive electrode. Such a filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

In addition, other components, such as viscosity modifiers, adhesion promoters, may optionally be further included, or as a combination of two or more.

The viscosity modifier is a component that adjusts the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the current collector thereof can be easily added, up to 30% by weight based on the total weight of the electrode mixture. Examples of such viscosity modifiers include carboxymethylcellulose, polyvinylidene fluoride and the like, but are not limited thereto. In some cases, the solvent described above can serve as a viscosity modifier.

The adhesion promoter may be added in an amount of 10% by weight or less based on the binder, for example, oxalic acid, adipic acid, Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

The cathode is fabricated by coating, drying, and compressing a cathode material on a current collector, and if necessary, the components described above with respect to the configuration of the anode may be further included.

The negative electrode current collector is generally made of a thickness of 3 to 500 ㎛. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

As said negative electrode material, For example, carbon, such as hardly graphitized carbon and graphite type carbon; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; _{Li 4 Ti 5 O 12, Li} 4/3 Ti 5/3 O 2, Li 3 Ti 3 O 8, LiTi 2 O 4, Li 4/5 Ti 11/5 O 4, Li 2 Ti 3 O 7, Li 7 Li _x Ti _y O _z including Ti ₅ O ₁₂ (0 < _x ≦ 7, ₂ ≦ _y ≦ 11, 4 ≦ _z ≦ 20) and TiO ₂ , Si-based alloys or Sn-based alloys and carbon composites may be used. .

The binder, the conductive material and the filler added as necessary are the same as those described for the positive electrode.

The separator is an insulating thin film interposed between the anode and the cathode and having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. As such a separation membrane, for example, a sheet or a nonwoven fabric made of an olefin-based polymer such as polypropylene which is chemically resistant and hydrophobic, glass fiber, polyethylene or the like is used.

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative of such gel polymers are polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile and the like. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing non-aqueous electrolyte is composed of an organic solvent electrolyte and a lithium salt.

As said electrolyte solution, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, Gamma-butylo lactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolon, 4 -Methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxolon derivatives Aprotic organic solvents such as sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrionate and ethyl propionate can be used. have.

The lithium salt is a good material to dissolve 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, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4 Lithium phenyl borate, imide and the like can be used.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The present invention can also provide a high-output large-capacity battery pack using the lithium secondary battery as a unit cell. The medium-large battery pack is a kind of medium-large battery module configured by combining a plurality of lithium secondary batteries into unit modules in order to provide a desired output and capacity, and may be used as a power source for a vehicle. It can be preferably used as a power source for electric vehicles (EVs), hybrid electric vehicles (HEV), etc. that are proposed as a solution for air pollution of existing gasoline vehicles, diesel vehicles and the like. LiMn ₂ O ₄ is particularly preferable for unit cells of medium and large battery systems such as electric automobiles and hybrid electric vehicles.

The following presents a preferred embodiment to aid the understanding of the present invention. However, the following examples are merely provided to more easily understand the present invention, and the present invention is not limited to the following examples.

Example  One

Mn (CH ₃ COO) ₂ aqueous solution and Ni (CH ₃ COO) ₂ aqueous solution were prepared and mixed, and CH ₃ COOLi and citric acid were dissolved in the mixed solution, followed by dissolution, followed by ethylene glycol. To prepare a sol by stirring for 1 hour. A predetermined amount of LiMn ₂ O ₄ was added to the sol thus prepared, stirred at 140 ° C., gelled, and dried to coat 1 wt% LiNi _0.5 Mn _0.5 O ₂ on the surface.

LiMn ₂ O ₄ coated with LiNi _0.5 Mn _0.5 O ₂ is heat-treated at 600 degrees Celsius.

After the heat treatment is completed, the material properties are evaluated using XRD (X-Ray Diffraction), SEM (Scanning Electron Microscope), and TEM (Transmission Electron Microscope).

In addition, in order to evaluate the performance of the produced positive electrode active material, a lithium half-cell is manufactured. Lithium half-cell is coated using a slurry (anode material: binder: conductive material = 80: 10: 10) containing a cathode material prepared by the above process on an aluminum foil, dried, and then manufactured using a stainless steel two-electrode cell (cell) do. At this time, PVDF was used as the binder and acetylene black was used as the conductive material. In addition, lithium foil was used as a negative electrode and a reference electrode.

Example 2

Example 2 was treated in the same manner as in Example 1 except that 3 wt% LiNi _0.5 Mn _0.5 O ₂ was coated.

Example 3

Example 3 was treated in the same manner as in Example 1 except for coating 5 wt% LiNi _0.5 Mn _0.5 O ₂ .

Comparative example

A positive electrode active material was prepared using only LiMn ₂ O ₄ without coating LiNi _0.5 Mn _0.5 O ₂ , and a lithium _half paper was manufactured using the same.

1 (a) ~ (c) is a SEM photograph coated with 1 wt% LiNi _0.5 Mn _0.5 O ₂ by Example 1, respectively, SEM photograph coated with 3 wt% LiNi _0.5 Mn _0.5 O ₂ by Example 2 , SEM image of 5 wt% LiNi _0.5 Mn _0.5 O ₂ coated by Example 3. FIG. 2 is a TEM photograph coated with 5 wt% LiNi _0.5 Mn _0.5 O ₂ according to Example 3. FIG.

Referring to FIG. 1, it is observed that the coating layer is thickly located on the surface of LiMn ₂ O ₄ as the coating amount increases. The LiNi _0.5 Mn _0.5 O ₂ coating layer is not simply coated independently of the surface of LiMn ₂ O ₄ , but the LiNi _0.5 Mn _0.5 O ₂ coating layer is thermally diffused into the LiMn ₂ O ₄ to form a solid solution. It seems to be. Through this, the coating layer suppresses the phenomenon of Mn ions eluting from the surface of LiMn ₂ O ₄ in a high temperature environment. In the TEM photograph of FIG. 2, it can be seen that a coating layer of about 10 nm level is found.

(A) is a rate characteristic curve of a comparative example, (b)-(d) is a rate characteristic curve of Examples 1-3. In FIG. 3, the horizontal axis represents specific capacity [mAh / g], and the vertical axis represents voltage [Vol] [V].

Referring to Figure 3, it can be seen that the rate characteristic is excellent as the coating amount increases. In addition, it can be seen that even if the coating amount increases, the initial capacity hardly decreases and the initial charge and discharge efficiency is also excellent.

4 is a graph of room temperature life characteristics of Comparative Examples and Examples 1 to 3. FIG. 4 and 5, the horizontal axis represents cycles and the vertical axis represents specific capacity [mAh / g]. 4 and 5 are 50 times the charge and discharge life characteristics of the evaluation at room temperature and 60 ° C in the region of 3 ~ 4.3 V, respectively.

In FIG. 4, blue corresponds to a comparative example, orange corresponds to example 1, red corresponds to example 2, and green corresponds to example 3. Referring to Figure 4, it can be seen that the life characteristics are improved as the coating amount increases. Specifically, in Example 1, 92.48% of the initial capacity for 900 cycles, Example. 97.57% of the initial capacity for 900 cycles, and Example 3, 98.77% of the initial capacity for 900 cycles. Showed the dose. On the other hand, the comparative example shows a capacity of 90.44% of the initial capacity in the repetition of 110 cycles, it can be seen that the room temperature life characteristics easily deteriorate despite a small cycle.

5 is a high temperature lifetime characteristic graph of Comparative Examples and Examples 1 to 3.

The legend is the same as in FIG. 4. Referring to Figure 5, as in the case of Figure 4 it can be seen that the high temperature life characteristics are very excellent as the coating amount increases. Specifically, in the comparative example, as a result of performing 110 cycles, the capacity of 75.96% of the initial capacity was shown, so that the life characteristics were easily deteriorated at a higher temperature than at room temperature. On the other hand, in the case of Examples 1 to 3 it can be seen that even if the cycle increases the life characteristics hardly deteriorated. That is, Examples 1 to 3 show a capacity retention rate of 90% or more relative to the initial capacity even if the number of cycles is increased, but the comparative example shows an abnormal life characteristic by showing a capacity retention rate of about 76% relative to the initial capacity.

As such, the improvement of life characteristics at room temperature and high temperature may be attributed to the fact that the coating layer reduces the contact area between the electrode and the electrolyte to suppress side reactions and to mitigate the change in the crystal structure of LiMn ₂ O ₄ . In addition, the coating layer is thought to block the contact between the positive electrode active material and the electrolyte by forming a solid solution by diffusing into the positive electrode active material.

The heat treatment temperature after the coating of the lithium oxide is preferably about 600 degrees to 900 degrees. If the heat treatment temperature is less than 600 degrees, the formation of lithium oxide is not performed properly, and if it exceeds 900 degrees, there is a problem in that the transition metal contained in the lithium oxide diffuses into LiMn ₂ O ₄ to form a single phase.

It will be apparent to those skilled in the art that various modifications, substitutions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. will be. Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical spirit of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by the embodiments and the accompanying drawings. . The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

The present invention can be applied to various fields including portable electronic devices such as camcorders, cellular phones, notebook PCs, power sources such as electric vehicles (EVs) and hybrid electric vehicles (HEVs).

1 (a) ~ (c) is a SEM photograph coated with 1 wt% LiNi _0.5 Mn _0.5 O ₂ by Example 1, respectively, SEM photograph coated with 3 wt% LiNi _0.5 Mn _0.5 O ₂ by Example 2 , SEM image of 5 wt% LiNi _0.5 Mn _0.5 O ₂ coated by Example 3,

2 is a TEM photograph coated with 5 wt% LiNi _0.5 Mn _0.5 O ₂ by Example 3,

(A) is a rate characteristic curve of a comparative example, (b)-(d) is a rate characteristic curve of Examples 1-3,

4 is a graph of room temperature life characteristics of Comparative Examples and Examples 1 to 3;

5 is a high temperature lifetime characteristic graph of Comparative Examples and Examples 1 to 3.

Claims (15)

It can occlude and release lithium ions, LiMn ₂ O lithium oxide on the surface of LiNi _0.5 Mn _0.5 O ₂ is ₄ LiMn ₂ O ₄ cathode materials ~ 1, characterized in that the coating in an amount of 5 wt% with respect to. delete delete delete delete Lithium secondary battery comprising the positive electrode active material according to claim 1. (a) preparing and mixing an aqueous solution of Mn (CH ₃ COO) _{2 and an} aqueous solution of Ni (CH ₃ COO) ₂ , respectively; (b) adding and dissolving CHCOO ₃ Li and citric acid to the mixed solution of step (a); (c) preparing sol of lithium oxide LiNi _0.5 Mn _0.5 O ₂ by adding ethylene glycol to ethylene glycol in the mixed solution of step (b); And (d) Preparation of a positive electrode active material characterized in that the surface of LiMn ₂ O ₄ comprising the step of coating in an amount of 1 ~ 5 wt% with respect to the lithium oxide LiNi _0.5 sol of Mn _0.5 O ₂ in the LiMn ₂ O ₄ Way. delete delete delete delete The method of claim 7, wherein The step (d) is a method of producing a positive electrode active material, characterized in that the lithium oxide sol LiMn ₂ O _{4 It} is carried out by stirring and gelation (gelation), followed by drying. The method of claim 7, wherein The method further comprises (e) heat treating the lithium oxide coated LiMn ₂ O ₄ . 14. The method of claim 13, The heat treatment temperature in the step (e) is a method of producing a positive electrode active material, characterized in that 600 ~ 900 degrees Celsius. 15. A method for preparing a cathode active material, the method comprising: preparing a cathode active material according to any one of claims 7 and 12 to 14; And Manufacturing a positive electrode plate by applying the positive electrode active material to a positive electrode current collector Method of manufacturing a lithium secondary battery comprising a.

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