KR100812547B1 - Positive active material for lithium secondary battery, method for preparing same, and lithium secondary battery including same - Google Patents

Abstract

A positive electrode active material for a lithium secondary battery, a method for preparing the positive electrode active material, and a lithium secondary battery containing the positive electrode active material are provided to improve lifetime characteristics and discharge capacity. A positive electrode active material comprises a compound represented by Li_(1-x) A_y Co_(1-y) X_z O_(2-z), wherein A is selected from the group consisting of Al, Ti, Mg, Zr and their combination; X is selected from the group consisting of P, W and their combination; 0<x<y; 0<=y<=1; 0<=z<2; and lithium, a metal A and an element X have a concentration gradient that the concentration decreases from the surface of an active material toward the center part.

Description

A positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

The present invention relates to a positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same, and more particularly, a cathode active material for a lithium secondary battery that can improve the life characteristics and discharge capacity of a lithium secondary battery, and a method of manufacturing the same. And it relates to a lithium secondary battery comprising the same.

Recently, with the trend toward miniaturization and light weight of portable electronic devices, the need for high performance and high capacity of batteries used as power sources for these devices is increasing.

A battery generates power by using a material capable of electrochemical reactions between a positive electrode and a negative electrode. A typical example of such a battery is a lithium secondary battery that generates electrical energy by a change in chemical potential when lithium ions are intercalated / deintercalated at a positive electrode and a negative electrode.

The lithium secondary battery is prepared by using a material capable of reversible intercalation / deintercalation of lithium ions as an active material of a positive electrode and a negative electrode, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

As a cathode active material of a lithium secondary battery, a lithium composite metal compound is used. Examples thereof include a composite such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1- x} Co _x O ₂ (0 <x <1), and LiMnO ₂ . Metal oxides are being studied.

In addition, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of inserting and detaching lithium have been used as the cathode active material. However, when the electrode plate is manufactured from graphite, such as artificial graphite or natural graphite, among the carbonaceous materials as an active material, the electrode plate has a low density, which leads to a low capacity in terms of energy density per unit volume of the electrode plate.

Accordingly, a positive electrode active material based on metal or intermetallic compounds has been actively studied as a positive electrode active material.

Japanese Patent Laid-Open No. 10-223221 discloses a lithium secondary battery using a lower crystal or amorphous intermetallic compound of an element selected from Al, Ge, Pb, Si, Sn, and Zn as a negative electrode. Is described as high capacity and excellent in cycle characteristics. In practice, however, lower crystallization or amorphousization of such intermetallic compounds is very difficult. For this reason, from the technical contents described in the above publication, it is difficult to realize a lithium secondary battery having a long cycle life with a high capacity.

In particular, Sn, Si, SnO ₂ system has the advantage that the capacity is more than two times higher than the conventional anode, whereas the conventional SnO or SnO ₂ based cathode active material not only accounts for more than 65% of the total capacity, the lifetime The disadvantage is that the characteristics are also very bad.

The present invention is to provide a positive electrode active material for a lithium secondary battery, and a method for manufacturing the same, which can improve battery life characteristics and discharge capacity.

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

In order to achieve the above object, according to an embodiment of the present invention includes a compound having a structure of formula (1), lithium (Li), metal (A) and element (X) concentration from the surface of the active material particles toward the center It provides a positive electrode active material having a concentration gradient that decreases.

[Formula 1]

_{Li 1 + x A y Co (} 1-y) X z O 2-z

(In Formula 1, A is selected from the group consisting of Al, Ti, Mg, Zr, and combinations thereof, X is selected from the group consisting of P, W, and combinations thereof, and 0 <x <y, 0 ≦ y ≦ 1, and 0 ≦ z <2)

The present invention also comprises the steps of preparing a dispersion comprising the compound particles of formula (2); And adding a core material including a cobalt-containing compound capable of intercalation and deintercalation of lithium ions to the dispersion, followed by drying and heat treatment to prepare a cathode active material comprising the compound of Chemical Formula 1 It provides a method for producing a cathode active material for a lithium secondary battery.

[Formula 2]

Li _{1 + p} A _q X _r O _{2 -r}

(In Formula 2, A is selected from the group consisting of Al, Ti, Mg, Zr, and combinations thereof, X is selected from the group consisting of P, W, and combinations thereof, 0 <p <0.06, 0 <q <0.2 and 0 <r <2)

The present invention also provides a lithium secondary battery comprising the positive electrode active material.

The positive electrode active material of the present invention has excellent lithium ion conductivity and can significantly improve capacity characteristics and life characteristics of a battery.

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

Recently, in order to improve the electrochemical properties of the positive electrode active material for lithium secondary batteries, various researches on composition change, particle size control, or surface treatment have been conducted. For example, Japanese Patent Application Laid-Open No. H9-55210 discloses a method of preparing a cathode active material by coating Mn, Al, or Co with an alkoxide on a LiNi-based oxide, and then performing heat treatment at 300 to 800 ° C. In addition, US Patent Publication No. 5705291 discloses a method of minimizing the dissolution of metal ions at high temperature by coating an oxide such as Al, B, or Si on a lithium intercalation material. However, the biggest problem of these studies is that the uniform coating is difficult for the powder of less than 10㎛, there is a problem that the internal resistance of the initial cell is increased by forming an insulator layer on the surface layer even during coating.

On the other hand, in the present invention, by surface treatment of the active material surface with a surface treatment material having excellent lithium ion conductivity and heat treatment to smooth the mobility of lithium to reduce the initial battery internal resistance of the lithium secondary battery to improve the discharge capacity and life characteristics of the battery Can be improved.

That is, the cathode active material according to one embodiment of the present invention includes a compound having a structure of Formula 1 below, and lithium (Li), metal (A), and element (X) decrease in concentration from the surface of the active material particles toward the center portion. Have a concentration gradient.

[Formula 1]

_{Li 1 + x A y Co (} 1-y) X z O 2-z

In Formula 1, A is selected from the group consisting of Al, Ti, Mg, Zr, and combinations thereof, X is selected from the group consisting of P, W, and combinations thereof, 0 <x <y, 0 ≦ y ≦ 1 and 0 ≦ z <2.

Moreover, it is more preferable that said x is 0 <x <0.06.

The metal (A) is included by substituting a part of cobalt (Co) in a metal component of the core material, for example, lithium cobalt oxide (LiCoO ₂ ), and as a result, y is 0 ≦ y ≦ 1. It is preferable that 0 ≦ y ≦ 0.2 is more preferable, and even more preferably 0.05 <y <0.13.

The element (X) is included in the metal component of the core material, for example, lithium cobalt oxide (LiCoO ₂ ) by substituting a part of oxygen. As a result, z is preferably 0 ≦ z <2. 0≤z≤0.2 is more preferable, and it is still more preferable that 0.015 <z <0.06.

In the compound of Formula 1, Li, A and X may be doped into the active material having a concentration gradient by high temperature heat treatment of 900 ° C. or higher during the active material manufacturing process. In this case, Li, A, and X have a concentration gradient in which the doping concentration decreases from the surface of the active material particles toward the center of the active material.

Unlike the active material in which the surface treatment layer is formed in the form of a metal oxide with respect to the conventional core material, the present invention has a surface because Li, A and X in the surface treatment layer forming compound are doped into the core material by high temperature heat treatment as described above. Li, A and X, which have high concentrations at, minimize the dissolution of cobalt (Co) contained in the core material at high voltage, and also reduce the surface reaction with the electrolyte solution, thereby preventing the formation of insulators formed on the electrolyte and the anode surface. .

The present invention also provides a method for producing a cathode active material as described above.

Accordingly, the method of manufacturing a cathode active material according to another embodiment of the present invention includes the steps of preparing a dispersion including the compound particles of Formula 2 (S11); And adding a core material including a cobalt-containing compound capable of intercalation and deintercalation of lithium ions to the dispersion, followed by drying and heat treatment to prepare a cathode active material including the compound of Formula 1 (S12). It includes.

[Formula 2]

Li _{1 + p} A _q X _r O _{2 -r}

In Formula 2, A is selected from the group consisting of Al, Ti, Mg, Zr, and combinations thereof, X is selected from the group consisting of P, W, and combinations thereof, 0 <p <0.06, 0 <q <0.2 and 0 <r <2.

Hereinafter, a method of manufacturing the cathode active material will be described in more detail. First, a dispersion including the compound particles of Chemical Formula 2 is prepared (S1).

The dispersion including the compound particles of Formula 2 includes the compound particles of Formula 2 by reacting a lithium (Li) -containing raw material, a raw material of metal (A) and a raw material of element (X) by mixing in a solvent. Dispersions can be prepared.

The lithium (Li) -containing raw material may be selected from the group consisting of lithium-containing hydroxide, oxyhydroxide, nitrate, halide, carbonate, acetate, oxalate, citrate, and mixtures thereof, and specifically Lithium nitrate, lithium acetate, etc. can be used as this.

Examples of the metal (A) -containing raw material include hydroxides, oxyhydroxides, nitrates, halides, carbonates, acetates, oxalates and citrates, including elements selected from the group consisting of Al, Ti, Mg, Zr, and combinations thereof. And, and those selected from the group consisting of these may be used, specifically, those selected from the group consisting of aluminum nitrate, aluminum isopropoxide, and mixtures thereof may be used.

In addition, the raw material of the element (X) may be an acid or chloride containing an element selected from the group consisting of P, W, and combinations thereof, and specifically, H ₃ PO ₄ , WCl ₄ , And mixtures thereof.

As the solvent, water, a lower alcohol having 1 to 4 carbon atoms, and a mixed solution thereof may be used. Preferably, ethanol or water may be used.

In the solvent, a lithium (Li) -containing raw material, a metal (A) -containing raw material, and an element (X) raw material are mixed, and the mixing ratio of the raw materials is Li, A, and X in the compound of Formula 2 to be prepared. It can be appropriately adjusted according to the content of.

In addition, the heating process may be optionally further performed when mixing the raw materials in the solvent to facilitate dissolution of the raw materials of each element in the solvent and to increase the reaction efficiency between the raw materials.

It is preferable that the said heating process is performed at 50-70 degreeC, and it is more preferable to carry out at 60-70 degreeC. It is also preferably carried out for 30 minutes to 10 hours, preferably for 5 to 12 hours. The reaction efficiency between the raw materials is high within the temperature and time range.

In addition, after dissolving the raw material of each element in a solvent, it is also possible to selectively adjust the pH of the mixed solution in which the raw material of each element is dissolved using a base.

The base may be selected from the group consisting of ammonia, sodium hydroxide, potassium hydroxide, calcium hydroxide and mixtures thereof, and may be used in an amount such that the pH of the mixed solution is 5 to 7, preferably pH 7. .

When the raw material of each element is dissolved in a solvent, the compound of Formula 2 is precipitated in the form of nano-sized particles in a mixed solution and dispersed in a solvent to form a dispersion.

In this case, in order to increase the precipitation efficiency, a cooling step for the mixed solution may be selectively performed.

The cooling process may be carried out by a conventional method, it is preferable to lower the temperature until the particles of the compound of formula (2) precipitates. It is more preferable to cool to room temperature specifically ,.

After the core material is added to the dispersion prepared by the above method, the cathode active material may be manufactured by drying and heat treating (S12).

The core material includes a cobalt-containing compound capable of intercalation and deintercalation of lithium ions, and may be used without particular limitation as long as it is used as a cathode active material for a conventional lithium secondary battery. Specifically, lithium cobalt oxide, lithium cobalt composite metal oxide, lithium cobalt composite metal sulfide and lithium cobalt composite metal nitride may be used. The core material may be prepared and used directly or may be commercially available. The manufacturing method at the time of manufacture is also not specifically limited, It can manufacture by a conventional method.

When the core material is added to the dispersion, the compound of Formula 2 is surface treated on the surface of the core material.

At this time, the compound of Formula 2 is preferably loaded in an amount of 0.3 to 2 parts by weight, and more preferably in an amount of 0.3 to 1 parts by weight with respect to 100 parts by weight of the core material. If the loading amount of the compound to the core material is less than 0.3 parts by weight, it is not preferable that a uniform surface treatment layer is not formed. If it exceeds 2 parts by weight, the surface treatment layer is thickened, so that A and X are excessively dissolved in the surface during heat treatment. Li _{1 + p} A _q X _r O _{2 -r} is formed, and as a result, a capacity decrease may occur, which is not preferable.

The drying step is for evaporating the dispersion medium, but is not particularly limited, but is preferably performed under oxygen, air, and a mixed atmosphere thereof. Furthermore, it is preferable to carry out at 50-90 degreeC. By being carried out in the above temperature range, the residual of the dispersion medium or impurities can be suppressed.

After the heat treatment step is not particularly limited, but is preferably carried out under oxygen, air and a mixed atmosphere thereof. It is also preferred to be carried out at 900 to 1000 ° C. If the temperature during the heat treatment is less than 900 ℃ do not doping of Li, Al and X into the core material is not preferable because there is a fear that a concentration gradient may not be formed.

The positive electrode active material prepared by the manufacturing method as described above may include a lithium composite metal oxide having a predetermined level of lithium ion conductivity, and thus may exhibit excellent high rate characteristics and lifetime characteristics when applied to a lithium secondary battery. Furthermore, lithium (Li), metal (A), and element (X) may be doped in a concentration that decreases from the surface of the active material particles toward the center portion, thereby stabilizing the active material structure, thereby exhibiting an excellent effect.

Among the A and X, when the average particle radius of the particles of the active material is d, doped from the surface of the active material particles to 0.1 kd, preferably 0.05 kd may be included. When the doping depths of A and X are doped into the negative electrode active material to a depth deeper than the above range, the capacity may decrease, which is not preferable. For example, when the particle diameter of the active material is 20 μm, the active material particles may be doped up to about 1 μm, more preferably, up to 500 nm.

In addition, the metal A has a concentration gradient that decreases from 1 to 10 atomic% per 20 nm from the surface of the active material particles toward the center portion. In addition, the element X preferably has a concentration gradient that decreases from 1 to 10 atomic% per 20 nm from the surface of the active material particles toward the center portion. In addition, the Li has a concentration gradient that decreases from 1 to 50 atomic% per 20 nm from the surface of the active material particles toward the center, and more preferably has a concentration gradient that decreases to 1 to 20 atomic%.

The present invention also provides a lithium secondary battery comprising the positive electrode active material.

Accordingly, the lithium secondary battery according to another embodiment of the present invention includes a positive electrode including a positive electrode active material, a positive electrode including a negative electrode active material, and an electrolytic material present therebetween. In this case, the cathode active material is the same as described above.

1 is an exploded perspective view of a rechargeable lithium battery according to one embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery 1 includes a negative electrode 2 and a positive electrode 3, a separator 4 disposed between the negative electrode 2 and the positive electrode 3, and the negative electrode ( 2), the electrolyte (not shown) impregnated in the positive electrode 3 and the separator 4, the battery container 5, and the sealing member 6 which encloses the said battery container 5 are comprised as a main part. .

The negative electrode 2 and the positive electrode 3 may be prepared by forming a mixture in the form of a film on a current collector for a negative electrode or a positive electrode active material forming composition including respective negative electrode active materials or positive electrode active materials.

In this case, the mixture is prepared by directly coating the positive electrode or positive electrode active material composition on a current collector and then drying or casting the active material composition on a separate support, and then laminating the film obtained by peeling from the support onto the current collector. It can be prepared by.

In addition, the composition for forming the negative electrode or the positive electrode active material may be prepared by dissolving or dispersing the negative electrode or the positive electrode active material, a binder, and optionally a conductive agent in a solvent.

In this case, the cathode active material is the same as described above.

The negative electrode active material may be a lithium metal, a metal material alloyable with lithium, a transition metal oxide, a material capable of doping and undoping lithium, a material capable of reversibly reacting with lithium to form a compound, or a lithium ion reversibly Substances that can be calibrated / deintercalated can be used. Specifically, one selected from the group consisting of vanadium oxide, lithium vanadium oxide, SiO _x (0 <x <2), TiO ₂ , SnO ₂ , and mixtures thereof can be used.

The binder is a chemical substance that is stable in an electrochemical reaction, and functions as a paste for the active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, and a buffering effect on the expansion and contraction of the active material. The binder may be one selected from the group consisting of water-soluble organic polymers, water-insoluble organic polymers, and combinations thereof. As the water-soluble organic polymer, polyvinyl alcohol, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, isopropyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, cyanoethyl cellulose, ethyl-hydroxyethyl One kind selected from the group consisting of cellulose, polyoxyethylene, poly N-vinylpyrrolidone, polyvinylacetate, and combinations thereof is possible. In addition, the water-insoluble organic polymer may be polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene polymer, trifluoroethylene polymer, difluoroethylene polymer, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene Hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinylether copolymer, trifluoroethylene chloride polymer, polyethylene, polypropylene, and one selected from the group consisting of a combination thereof are possible.

The conductive agent is used to impart conductivity to the electrode, and any battery can be used as long as it is an electron conductive material without causing chemical change in the battery. Carbon materials, such as amorphous carbon, such as acetylene black and Ketjen black, and graphite structure carbon, or metal materials, such as nickel, copper, silver, titanium, platinum, aluminum, cobalt, iron, chromium, can be used. Such conductive agents may be spherical, flake, filamentary, fibrous, spiked, or needle-like, and it is preferable to use a mixture of the two shapes in order to increase the tap density.

In addition, as the solvent, organic solvents such as N-methylpyrrolidone (NMP), acetone, tetrahydrofuran, and decane may be used, and preferably N-methylpyrrolidone may be used.

At this time, the composition of the positive electrode active material, the negative electrode active material, the conductive agent, the binder, the solvent for producing the electrode is appropriately selected within a known range, the production method is preferably selected by those skilled in the art.

The current collector collects electrons generated by the electrochemical reaction of the active material or serves to supply electrons required for the electrochemical reaction. The material of the current collector may be stainless steel, aluminum, nickel, copper, titanium, carbon, conductive resin, or the like in which carbon, nickel, or titanium is treated on the surface of copper or stainless steel. A current collector made of material and a current collector made of copper can be used as the negative electrode.

The electrolyte serves as a medium for transporting lithium ions in the positive electrode and the negative electrode, and a non-aqueous electrolyte or a known solid electrolyte may be used. For example, as the non-aqueous electrolyte, a lithium salt dissolved in a non-aqueous organic solvent may be used.

The lithium salt is LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carbonate, LiCl, LiBr, LiI, chloroborane lithium and one selected from the group consisting of a combination thereof are possible.

The non-aqueous organic solvent is not particularly limited to serve as a medium through which ions involved in the electrochemical reaction of the battery may move, but may include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; Chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and γ-butyrolactone 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane Nitriles such as ethers acetonitrile such as 2-methyltetrahydrofuran and the like; Amides, such as dimethylformamide, etc. can be used. These can be used individually or in combination of two or more. In particular, a mixed solvent of a cyclic carbonate and a linear carbonate can be preferably used.

The solid electrolyte is Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₃ PO ₄ -Li ₂ S-SiS ₂ , phosphorus sulfide compound, polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), and a combination thereof are possible.

The lithium secondary battery 1 including these includes a separator 4 capable of blocking electron conduction between the cathode 2 and the anode 3 and conducting lithium ions. The separator 4 plays an important role in improving stability as well as separating the positive electrode and the negative electrode. As the separator, any one conventionally used in a lithium secondary battery may be used. For example, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more thereof may be used.

The shape of the lithium secondary battery according to the present invention having such a component may be any shape such as coin type, button type, sheet type, stacked type, cylindrical type, flat type, rectangular type, and those skilled in the art by those skilled in the art. Design and apply accordingly.

The lithium secondary battery of the present invention can be widely used in portable information terminals, portable electronic devices, small household power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, and the like.

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

Example  One

1 g of Al nitrate, 0.7 g of Li nitrate, and 0.2 g of H ₃ PO ₄ were dissolved in 50 ml of ethanol, and then mixed at 70 ° C. for 30 minutes to prepare a mixed solution, and sodium hydroxide was added to the mixed solution. Add until 7. After cooling to room temperature after adjusting the pH as described above, the nanoparticles have a pale milk color and are precipitated and dispersed in a solvent. After adding 100 g of LiCoO ₂ to the dispersion, the mixture was stirred at 50 ° C. for 20 hours, dried at 100 ° C. in an air atmosphere, and heat-treated again at 950 ° C. for 5 hours in an air atmosphere to prepare a cathode active material having an average particle diameter of 20 μm.

Example  2

2 g of Al nitrate, 0.9 g of Li nitrate, and 0.4 g of H ₃ PO ₄ were dissolved in 50 ml of ethanol, and then mixed at 70 ° C. for 30 minutes to prepare a mixed solution, and sodium hydroxide was added to the mixed solution. Add until 7. After cooling to room temperature after adjusting the pH as described above, the nanoparticles have a pale milk color and are precipitated and dispersed in a solvent. After adding 100 g of LiCoO ₂ to the dispersion, the mixture was stirred at 50 ° C. for 20 hours, dried at 100 ° C. in an air atmosphere, and heat-treated again at 950 ° C. for 5 hours in an air atmosphere to prepare a cathode active material having an average particle diameter of 20 μm.

Example  3

A ㅣ nitrate 2.5g, Li nitrate 3g and H ₃ PO ₄ 0.5g was dissolved in 50ml of ethanol and mixed for 30 minutes at 70 ℃ to prepare a mixed solution, the sodium hydroxide to the mixed solution pH of the mixed solution Was added until 5. After cooling to room temperature after adjusting the pH as described above, the nanoparticles have a pale milk color and are precipitated and dispersed in a solvent. After adding 100 g of LiCoO ₂ to the dispersion, the mixture was stirred at 50 ° C. for 20 hours, dried at 100 ° C. in an air atmosphere, and heat-treated again at 950 ° C. for 5 hours in an air atmosphere to prepare a cathode active material having an average particle diameter of 20 μm.

Example  4

2 g of Al-isopropoxide, 0.5 g of Li acetate, and 0.3 g of H ₃ PO ₄ were dissolved in 50 ml of ethanol, and then mixed at 60 ° C. for 10 hours to prepare a mixed solution. The mixed solution was cooled to room temperature and then stirred after adding 100 g of LiCoO ₂ . Thereafter, the solution was dried at 100 ° C. under air, and then heat-treated at 950 ° C. for 5 hours in an air atmosphere to prepare a cathode active material having an average particle diameter of 20 μm.

Example  5

2 g of Al-isopropoxide, 0.8 g of Li acetate and 0.2 g of H ₃ PO ₄ were dissolved in 50 ml of ethanol and mixed at 60 ° C. for 10 hours to prepare a mixed solution. The mixed solution was cooled to room temperature and then stirred after adding 100 g of LiCoO ₂ . Thereafter, the solution was dried at 100 ° C. in an air atmosphere, and heat-treated again at 950 ° C. in an air atmosphere to prepare a cathode active material having an average particle diameter of 20 μm.

Example  6

2 g of Al-isopropoxide, 0.5 g of Li acetate, and 0.2 g of H ₃ PO ₄ were dissolved in 50 ml of ethanol, and then mixed at 60 ° C. for 10 hours to prepare a mixed solution. The mixed solution was cooled to room temperature and then stirred after adding 100 g of LiCoO ₂ . Thereafter, the solution was dried at 100 ° C. in an air atmosphere, and heat-treated again at 950 ° C. in an air atmosphere to prepare a cathode active material having an average particle diameter of 20 μm.

Comparative example  One

2 g of Al-isopropoxide was dissolved in 50 ml of ethanol, 100 g of LiCoO ₂ powder was added, mixed, dried at 100 ° C., and then heat treated at 700 ° C. to give Al ₂ O ₃ coated on LiCoO ₂ . An average particle diameter of 20 µm of the active material was prepared.

Comparative example  2

2 g of Al-nitrate was dissolved in 40 ml of water, mixed with 100 g of LiCoO ₂ powder, dried at 100 ° C., and then heat treated at 700 ° C. to give Al ₂ O ₃ coated on LiCoO ₂ . Average particle diameter 20 mu m) was prepared.

Comparative example  3

1 g of Al nitrate and 0.5 g of Li nitrate were dissolved in 50 ml of ethanol and mixed at 70 ° C. for 30 minutes to prepare a mixed solution. Sodium hydroxide was added to the mixed solution until the pH of the mixed solution became 7. By adjusting the pH as described above, the nanoparticles are pale milky color precipitated and dispersed in the solvent. After the LiCoO ₂ 100g to the dispersion was added and stirred at 50 ℃ 20 hours, and dried in a 100 ℃, atmospheric air, and again 700 ℃, 5 sigan heat treatment to Li _{0 .03} AlO ₂ oxide is coated on LiCoO ₂ while under a normal atmosphere A positive electrode active material (average particle diameter of the positive electrode active material 20 µm) was prepared.

Comparative example  4

1 g of (NH ₄ ) ₂ HPO ₄ and 1.5 g of Al nitrate (Al (NO ₃ ) ₃ .9H ₂ O) were added to 100 ml of water to prepare a coating solution. At this time, the amorphous AlPO _k phase was precipitated in the colloidal form. 20 g of LiCoO ₂ was added to 10 ml of the coating solution, mixed, and dried at 130 ° C. for 30 minutes. The dried powder was heat-treated at 400 ° C. for 5 hours to prepare a cathode active material (an average particle diameter of the cathode active material of 20 μm) in which a solid solution compound including Al and P and a surface treatment layer including an AlPO _k compound were formed on a surface thereof.

Reference Example  One

1 g of aluminum nitrate and 0.5 g of lithium nitrate were added to a reactor in which 50 ml of water was injected, followed by mixing at 70 ° C. for 30 minutes. 0.4 g of ammonia was slowly added to the reactor to adjust the pH to 5. At this time, aluminum lithium hydrate was precipitated at the bottom of the reactor. The precipitated aluminum lithium hydroxide was recovered and dried under reduced pressure at 50 ° C. for 3 hours to obtain a white nano-sized powder (0.5 g, 10-200 nm).

The aluminum lithium hydrate was dispersed in 100 ml of ethanol, and then 100 g of LiCoO ₂ was added and stirred at 50 ° C. for 20 hours. Then dried to obtain a precursor at 100 ℃ for 3 hours, the heat treatment carried out for 5 hours at 700 ℃ to the positive electrode active material formed on the surface treatment layer, including a compound of Li _{0 .97} AlO ₂ (average particle diameter of the positive electrode active material 20㎛ ) Was prepared.

Experimental Example  One

P, q and Li in the Li _{1 + p} Al _q P _r O _{2 -r} nanoparticles obtained through Inductively Coupled Plasma (ICP) analysis after drying the dispersion prepared in Examples 1 to 6 r was measured. The results are shown in Table 1 below.

Nanoparticles p q r Example 1 _{Li 1 .03 Al 0 .06 P 0} .02 O 1 .98 0.03 0.06 0.02 Example 2 _{Li 1 .04 Al 0 .08 P 0} .04 O 1 .96 0.04 0.08 0.04 Example 3 _{Li 1 .03 Al 0 .13 P 0} .06 O 1 .94 0.03 0.13 0.06 Example 4 _{Li 1 .03 Al 0 .09 P 0} .015 O 1 .985 0.03 0.09 0.015 Example 5 _{Li 1 .01 Al 0 .12 P 0} .02 O 1 .98 0.01 0.12 0.02 Example 6 _{Li 1 .01 Al 0 .05 P 0} .02 O 1 .98 0.01 0.05 0.02

Experimental Example  2

For the positive electrode active materials prepared in Examples 1 and 4 and Comparative Examples 1 and 3, the distribution of Al and P from the surface to the inside of the particles was analyzed by Auger electron spectroscopy. The results are shown in Table 2 below.

Example 1 Example 4 Comparative Example 1 Comparative Example 3 Comparative Example 4 Depth from surface (nm) Al P Al P Al P Al P Al P 0 40 30 40 43 35 - 31 - 40 35 20 38 28 38 40 10 - 13 - 10 10 40 32 26 36 38 0 - 0 - - - 60 30 24 34 36 - - - - - - 80 28 22 33 34 - - - - - - 100 26 20 30 32 - - - - - - 120 24 18 28 30 - - - - - - 140 22 17 26 29 - - - - - - 160 20 15 24 27 - - - - - - 200 18 14 22 25 - - - - - - 220 16 12 21 23 - - - - - - 240 13 10 19 21 - - - - - - 260 10 9 19 19 - - - - - - 280 8 7 17 17 - - - - - - 300 6 4 15 15 - - - - - - 320 6 0 13 13 - - - - - - 340 4 - 12 11 - - - - - - 360 2 - 11 10 - - - - - - 400 0 - 9 8 - - - - - - 420 - - 7 7 - - - - - - 440 - - 5 5 - - - - - - 480 - - 5 4 - - - - - - 500 - - 4 3 - - - - - - 520 - - 2 2 - - - - - - 540 - - 0 0 - - - - - -

In Table 2, the content of each element is atomic%.

As shown in Table 2, it can be seen that the positive electrode active material of Example 4 having a large content of P in the starting material was doped into Al and P more into the core material than the positive electrode active material according to Example 1. This is because P melted at 700 ° C. and promoted diffusion of LiCoO ₂ into particles or through grain boundaries. However, when Al is used alone as in Comparative Examples 1 and 3, it can be seen that Al remains only near the surface. In the case of Comparative Example 4 using Al and P together, it can be seen that Al and P remain only on the surface of the active material to the extent that they can be distinguished by separate surface coating layers.

Experimental Example  3

After the coin cell was prepared using the cathode active materials prepared in Examples 1 to 6 and Comparative Examples 1 to 4, the initial discharge capacity was measured. The results are shown in Table 3 below.

The positive electrode active material, super P (conductor), and polyvinylidene fluoride (binder) prepared in Examples 1 to 6 and Comparative Examples 1 to 4 were mixed at a weight ratio of 96/2/2 to include a positive electrode active material. Slurry was prepared. The slurry including the prepared positive electrode active material was coated on Al-foil to a thickness of about 300 μm, dried at 130 ° C. for 20 minutes, and rolled at a pressure of 1 ton to prepare a positive electrode plate for a coin battery. Using this electrode plate and lithium metal as a counter electrode, a coin-type half cell was produced. In this case, as the electrolyte, 1M LiPF ₆ dissolved in a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a 1: 1 volume ratio was used.

After charging and discharging at 0.1C, 1C, and 2C at room temperature and a voltage range of 4.5V to 3V for the coin-type half cells of Examples 1 to 6 and Comparative Examples 1 to 4, the discharge capacity according to C-rate was measured. It was. In addition, after performing 40 charge / discharge cycles at 1 C in the voltage range, the capacity retention rate was evaluated. The results are shown in Table 3 below.

0.1C discharge capacity (mAh / g) 1C discharge capacity (mAh / g) 2C discharge capacity (mAh / g) Life retention after 40 cycles (1C) (%) Example 1 184 160 143 80 Example 2 184 162 145 85 Example 3 184 170 163 87 Example 4 184 163 155 94 Example 5 175 155 130 82 Example 6 183 160 132 80 Comparative Example 1 180 153 115 50 Comparative Example 2 180 150 114 55 Comparative Example 3 184 160 140 60 Comparative Example 4 180 157 140 50 Reference Example 1 183 160 150 70

As shown in Table 3, in the case of the battery prepared by the positive electrode active material according to Examples 1 to 6 it can be seen that the discharge capacity after 40 times 1C compared with the battery prepared by the positive electrode active material of Comparative Examples 1 to 4. .

In addition, in the case of the battery including the positive electrode active materials of Comparative Examples 1 and 2, the initial discharge capacity is sharply lowered at a high rate (2C) compared to the low rate (0.1C). There was no sudden drop in discharge capacity.

In addition, in the case of using the positive electrode active material of Examples 2 to 4 it can be seen that the discharge capacity is high, the battery life characteristics are excellent. Compared to the active materials of Comparative Examples 1 to 4 having the surface treatment layer of the metal oxide on the surface of the core material, the Al and P phases were more doped to the optimum depth in the core material when the active materials of the above examples were used. This is because the stability of the structure at the time of insertion is improved.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

1 is a schematic view showing a structure of a lithium secondary battery according to an embodiment of the present invention.

Claims (13)

Comprising a compound having a structure of formula (1), lithium (Li), metal (A) and element (X) is a positive electrode active material for a lithium secondary battery having a concentration gradient decreases from the surface of the active material particles toward the center. [Formula 1] _{Li 1 + x A y Co (} 1-y) X z O 2-z (In Formula 1, A is selected from the group consisting of Al, Ti, Mg, Zr, and combinations thereof, X is selected from the group consisting of P, W, and combinations thereof, and 0 <x <y, 0 ≦ y ≦ 1, and 0 ≦ z <2) The method of claim 1, Wherein A and X, when the average particle radius of the particles of the active material is d, the positive electrode active material for a lithium secondary battery that is doped up to 0.1 kd from the surface of the active material particles. The method of claim 1, The lithium is a positive electrode active material for a lithium secondary battery having a concentration gradient of 1 to 50 atomic% per 20nm toward the center from the surface of the active material particles. The method of claim 1, The A is a positive electrode active material for a lithium secondary battery having a concentration gradient decreasing from 1 to 10 atomic% per 20nm toward the center from the surface of the active material particles. The method of claim 1, Wherein X is a positive electrode active material for a lithium secondary battery having a concentration gradient decreasing from 1 to 10 atomic% per 20nm from the surface of the active material particles to the center. Preparing a dispersion comprising the compound particles of Formula 2; And Lithium comprising the step of adding a core material containing a cobalt-containing compound capable of intercalation and deintercalation of lithium ions to the dispersion, followed by drying and heat treatment to prepare a positive electrode active material comprising the compound of Formula 1 Method of manufacturing a positive electrode active material for a secondary battery. [Formula 2] Li _{1 + p} A _q X _r O _{2 -r} (In Formula 2, A is selected from the group consisting of Al, Ti, Mg, Zr, and combinations thereof, X is selected from the group consisting of P, W, and combinations thereof, 0 <p <0.06, 0 <q <0.2 and 0 <r <2) The method of claim 6, A dispersion liquid containing the compound of Formula 2 is prepared by reacting a lithium-containing raw material, a metal A raw material, and a raw material of X in a solvent. The method of claim 7, wherein The lithium-containing raw material is selected from the group consisting of lithium hydroxide, oxy hydroxide, nitrate, halide, carbonate, acetate, oxalate, citrate, and mixtures thereof. . The method of claim 7, wherein The metal A-containing raw material may include hydroxides, oxyhydroxides, nitrates, halides, carbonates, acetates, oxalates, citrates, and the like, including element A selected from the group consisting of Al, Ti, Mg, Zr and combinations thereof. Method for producing a positive electrode active material for a lithium secondary battery that is selected from the group consisting of a mixture thereof. The method of claim 7, wherein The raw material of X is P, W, and a method for producing a positive electrode active material for a lithium secondary battery which is an acid or chloride containing an element selected from the group consisting of a combination thereof. The method of claim 6, Wherein the core material is selected from the group consisting of lithium cobalt composite metal oxide, lithium cobalt composite metal sulfide, lithium cobalt composite metal nitride, and mixtures thereof. The method of claim 6, The heat treatment step is a method of manufacturing a positive electrode active material for a lithium secondary battery that is carried out at 900 to 1000 ° C. A positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; And An electrolyte present between the positive electrode and the negative electrode, A lithium secondary battery, wherein the cathode active material is the cathode active material according to any one of claims 1 to 5.

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