KR101576274B1 - Positive active material for rechargeable lithium battery, method for manufacturing the same, and rechargeable lithium battery including the same - Google Patents

Abstract

A first lithium-transition metal composite oxide, a second lithium-transition metal composite oxide positioned on the surface of the first lithium-transition metal composite oxide, a first coating layer positioned on a surface of the second lithium-transition metal composite oxide, And a second coating layer disposed on the surface of the coating layer, wherein the first coating layer is represented by the following Formula 1 and the second coating layer is represented by the following Formula 2, a method for producing the same, A lithium secondary battery is provided.
[Chemical Formula 1]
Li _a V _b O _c
(2)
V _d O _e
In the above formulas (1) and (2)
6, 1? B? 6, 2? C? 13, 1? D? 6 and 2? E? 13.

Description

TECHNICAL FIELD The present invention relates to a cathode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same. Technical Field [0001] The present invention relates to a positive active material for a lithium secondary battery,

A cathode active material for a lithium secondary battery, a process for producing the same, and a lithium secondary battery comprising the same.

Recently, with regard to the tendency to miniaturize and lighten portable electronic devices, there is an increasing need for high performance and large capacity of batteries used as power sources for these devices.

Cells generate electricity by using materials that can electrochemically react to the positive and negative electrodes. A representative example of such a battery is a lithium secondary battery that generates electrical energy by a change in chemical potential when the lithium ions are intercalated / deintercalated in the positive electrode and the negative electrode.

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

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

For example, the lithium nickel oxide shows a higher discharge capacity when it is charged at 4.3 V, although the cost is lower than that of the cobalt oxide. The reversible capacity of the doped lithium nickel oxide indicates the capacity of LiCoO ₂ (about 165 mAh / g) To about 200 mAh / g. Therefore, the lithium nickel based cathode active material has been commercialized in a high capacity battery by having an improved energy density despite a slightly low discharge voltage and a volumetric density.

Recently, studies on nickel-rich cathode active materials have been actively conducted to develop high capacity batteries.

However, the biggest problem of the nickel-rich cathode active materials is the high-temperature structural stability and the presence of lithium impurities such as Li ₂ CO ₃ and LiOH which remain on the surface during synthesis. The lithium impurities remaining on the surface react with CO ₂ or H ₂ O in the air to form Li ₂ CO ₃ . In addition, Ni ^{3 +} ions are higher the partial pressure of CO _2, or reduced to Ni ^{2 +} ions during the exposure, or an electrochemical reaction in the long term air but it also leads to reduced capacity.

In addition, lithium impurities determine the pH of the active material, and active materials with high pH cause gelation in the preparation of the electrode slurry, which reduces the uniformity of the electrode plate and is therefore not suitable for commercialization. In addition, Li ₂ CO _{3 not only} causes initial irreversible capacity and interferes with lithium ion movement on the surface, but also causes gas generation by decomposition reaction during electrochemical reaction.

Therefore, many surface treatment studies have been carried out in order to secure the structural stability of the cathode active material and to suppress the side reaction of the surface. Surface treatment materials for ensuring surface stability typically include various metals such as Ag, metal oxides such as Al ₂ O ₃ , ZrO ₂ and CeO ₂ , metal phosphates, metal fluorides such as ZrF ₂ , AlF ₃ and SrF ₂ , Carbon compounds and the like. However, existing surface treatment materials act as insulators, which are disadvantageous in terms of battery conductivity and lithium ion conductivity, resulting in initial capacity decrease and initial resistance increase. In order to remove lithium impurities remaining on the surface which can not be solved by coating, reheat treatment or washing was carried out. In the reheating treatment, lithium impurities are re-crystallized on the surface during cooling, .

By performing surface treatment using a compound capable of reacting with the lithium compound remaining on the surface of the cathode active material, it is possible to prevent gelation of the electrode slurry by removing the lithium compound, suppress gas generation during driving of the battery, Which is capable of suppressing a side reaction between an electrode and an electrolyte, to provide a lithium secondary battery having improved safety, high rate characteristics, and long life characteristics.

One embodiment of the present invention is a lithium secondary battery comprising a first lithium-transition metal composite oxide, a second lithium-transition metal composite oxide positioned on the surface of the first lithium-transition metal composite oxide, 1 coating layer and a second coating layer disposed on a surface of the first coating layer, wherein the first coating layer is represented by the following Formula 1 and the second coating layer is represented by the following Formula 2: do.

[Chemical Formula 1]

Li _a V _b O _c

(2)

V _d O _e

In the above formulas (1) and (2)

6, 1? B? 6, 2? C? 13, 1? D? 6 and 2? E? 13.

The second lithium transition metal complex oxide may be doped with vanadium.

The first coating layer and the second coating layer may be contained in an amount of 0.1 to 5 moles relative to 100 moles of the transition metal of the first lithium-transition metal composite oxide and the second lithium-transition metal composite oxide.

The first lithium-transition metal composite oxide may be represented by the following formula (3), and the second lithium-transition metal composite oxide may be represented by the following formula (4).

(3)

LiM ^O _x M ¹ _y M ² _z O ₂

[Chemical Formula 4]

LiM ^O _x M ¹ _y M ² _z V _i O ₂

In the above formulas (3) and (4)

M ⁰ , M ¹ and M ² are each independently Ni, Co, Mn, Al, Ti, Mg or Zr; 0? X? 1, 0? Y? 1, 0? Z? 1, to be.

The M ⁰ may be Ni.

In Formula 1, 0.05? A? 6, b = 2, and c = 5.

In Formula 2, d = 2 and e = 5.

According to another embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: preparing a lithium-transition metal composite oxide; Mixing the lithium transition metal complex oxide and the vanadium raw material; Coating a vanadium raw material on the surface of the lithium-transition metal composite oxide by spray-drying or using a sol-gel method; Heat treating a material coated with a vanadium raw material on the surface of the lithium-transition metal composite oxide; And obtaining a cathode active material having a first coating layer represented by Formula 1 formed on the surface of the lithium-transition metal composite oxide and a second coating layer represented by Formula 2 formed on the surface of the first coating layer, A method for producing a positive electrode active material for a lithium secondary battery is provided.

In the obtained cathode active material, the lithium-transition metal composite oxide includes a first lithium-transition metal oxide and a second lithium-transition metal oxide, and the second lithium-transition metal oxide is formed on the surface of the first lithium- have.

In the step of mixing the lithium-transition metal composite oxide and the vanadium source material, the vanadium source material may be added in an amount of 0.1 to 5 moles per 100 moles of the transition metal of the lithium-transition metal composite oxide.

The preparation of the lithium-transition metal composite oxide may include preparing a transition metal hydroxide by coprecipitation; Mixing the transition metal hydroxide and a lithium source; And heat treating the mixture of steps.

In the step of heat-treating the material coated with the vanadium raw material on the surface of the lithium-transition metal composite oxide, the heat treatment may be performed at 300 ° C to 500 ° C.

In the step of heat-treating the material coated with the vanadium raw material on the surface of the lithium-transition metal composite oxide, the heat treatment may be performed for 1 hour to 10 hours.

Another embodiment of the present invention is a positive electrode comprising a positive electrode active material for a lithium secondary battery; cathode; And a lithium secondary battery comprising the electrolyte.

The positive electrode active material for a lithium secondary battery according to an embodiment has little side reaction with an electrolyte and almost no lithium compound remains on the surface, so that gelation of the electrode slurry is prevented and there is no risk of gas generation when the battery is driven. Accordingly, the lithium secondary battery according to one embodiment is excellent in stability, high rate characteristics, and life characteristics.

1 is a schematic view of a cathode active material section for explaining a structure of a cathode active material according to one embodiment.
2 is a scanning electron microscope (SEM) photograph of the cathode active material of Example 1 and Comparative Example 1. Fig. (a) and (c) are scanning electron micrographs of the cathode active material of Comparative Example 1, and (b) and (d) are scanning electron micrographs of the cathode active material of Example 1.
3A and 3B are transmission electron microscope (TEM) photographs of the surface of the positive electrode active material of Example 1, FIGS. 3B and 3C are photographs of EDS mapping showing the Ni and V distribution of the surface of the positive electrode active material of Example 1 and line scattering (line scattering) graph.
FIGS. 4A, 4C, and 4E are graphs showing the presence or absence of specific elements and the change in the oxidation number of the positive electrode active material of Comparative Example 1 measured from the surface toward the inside.
4B, 4D and 4F are graphs showing the presence or absence of specific elements and the graph of the change in oxidation number (XPS) measured from the surface to the inside of the cathode active material of Example 1. FIG.
FIGS. 5A and 5B are graphs showing the presence or absence of specific elements and the graph of the change in oxidation number (EELS) measured from the surface to the inside of the cathode active material of Embodiment 1. FIG.
6 is a transmission electron microscope (TEM) photograph of the cathode active material of Example 1 and Comparative Example 1. Fig. (a) and (c) are transmission electron micrographs of the cathode active material of Comparative Example 1, and (b) and (d) are SEM micrographs of the cathode active material of Example 1. Also, (1) and (2) are transformed images to confirm the structural crystallinity of the cathode active material of Comparative Example 1, and (3) and (4) are transformed images in which the structural crystallinity of the cathode active material of Example 1 can be confirmed.
FIG. 7A is a graph showing lifetime characteristics at room temperature for the cells prepared in Example 1 and Comparative Example 1, FIG. 7B is a graph showing rate characteristics at room temperature for the cells prepared in Example 1 and Comparative Example 1, And Fig. 7C is a graph showing lifetime characteristics at a high temperature.
8 is a scanning electron microscope (SEM) photograph of the cathode active material of Example 2 and Comparative Example 2. Fig.
9A and 9B are graphs showing the presence or absence of specific elements measured from the surface to the inside of the cathode active material of Comparative Example 2 and Example 2, respectively.
10 is a graph showing the characteristics of the cells prepared in Example 2 and Comparative Example 2 by rate.
11 is a graph showing lifetime characteristics of the batteries manufactured in Example 2 and Comparative Example 2. FIG.
12 is a scanning electron microscope (SEM) photograph of the cathode active material of Example 3 and Comparative Example 3. Fig.
FIGS. 13A and 13B are graphs showing the presence or absence of specific elements measured from the surface to the inside of the cathode active materials of Comparative Examples 3 and 3, respectively.
FIG. 14 is a graph showing the characteristics of the batteries manufactured in Example 3 and Comparative Example 3 by rate. FIG.
15 is a graph showing lifetime characteristics of the batteries manufactured in Example 3 and Comparative Example 3. Fig.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

In the present specification, as shown in Fig. 1, the first lithium-transition metal composite oxide and the second lithium-transition metal composite oxide are the first lithium-transition metal composite oxide in the lithium transition metal complex oxide, And the portion near the surface is the second lithium transition metal complex oxide.

Further, in this specification, the first coating layer and the second coating layer are the first coating layer inside the coating layer and the second coating layer as the coating layer returning, as shown in Fig.

An embodiment of the present invention is a lithium secondary battery comprising a first lithium-transition metal composite oxide, a second lithium-transition metal composite oxide positioned on the surface of the first lithium-transition metal composite oxide, a coating layer positioned on the surface of the second lithium- And a cathode active material for a lithium secondary battery.

For example, the cathode active material may include a first lithium-transition metal composite oxide, a second lithium-transition metal composite oxide positioned on the surface of the first lithium-transition metal composite oxide, a first lithium- And a second coating layer disposed on a surface of the first coating layer, wherein the first coating layer is represented by the following Formula 1, and the second coating layer is represented by the following Formula 2.

[Chemical Formula 1]

Li _a V _b O _c

(2)

V _d O _e

In the above formulas (1) and (2)

6, 1? B? 6, 2? C? 13, 1? D? 6 and 2? E? 13.

Generally, in the case of the cathode active material, lithium impurities such as Li ₂ CO ₃ and LiOH are present on the surface. Such lithium impurities cause gelation in the production of the electrode slurry, thereby lowering the uniformity of the electrode plate. In addition, lithium impurities form an initial irreversible capacity and interfere with lithium ion movement, and also generate gas during battery operation.

However, the positive electrode active material according to an embodiment of the present invention has a function of removing lithium impurities remaining on the surface of the positive electrode active material, the first coating layer being lithium vanadium oxide represented by Formula 1 and the second coating layer being vanadium oxide represented by Formula 2, Gelation and gas generation and the like are suppressed, and cell characteristics such as high-rate characteristics and life characteristics are improved. The first coating layer and the second coating layer also function to suppress side reactions between the cathode active material and the electrolyte.

For example, in the above formula (1), a may be 0.05 to 6, b may be 2, and c may be 5.

For example, in Formula 2, d may be 2, and e may be 5.

The 'first coating layer and the second coating layer' may be used in an amount of 0.1 to 5 molar parts, for example, 0.1 to 4 molar parts, and 0.1 to 3 molar parts, based on 100 molar parts of the transition metal of the first lithium transition metal complex oxide and the second lithium transition metal complex oxide, Molar fraction, 0.1 to 2 molar fraction, and 0.1 to 1 molar fraction. In this case, the first coating layer and the second coating layer effectively remove lithium impurities remaining on the surface of the second lithium-transition metal composite oxide, thereby exhibiting excellent battery performance.

The first lithium-transition metal composite oxide may be represented by the following formula (3), and the second lithium-transition metal composite oxide may be represented by the following formula (4).

(3)

LiM ^O _x M ¹ _y M ² _z O ₂

[Chemical Formula 4]

LiM ^O _x M ¹ _y M ² _z V _i O ₂

In the above formulas (3) and (4)

M ⁰ , M ¹ and M ² are each independently Ni, Co, Mn, Al, Ti, Mg or Zr; 0? X? 1, 0? Y? 1, 0? Z? 1, to be.

The second lithium-transition metal composite oxide may be doped with vanadium while the coating layer containing vanadium oxide is formed on the surface of the second lithium-transition metal composite oxide. That is, the second lithium-transition metal composite oxide may be doped with vanadium. In this case, the cathode active material containing the cathode active material can improve the lifetime characteristics of the battery while realizing a high capacity.

In Formula 4, i means the doping amount of vanadium, and may be, for example, 0.01 to 0.5 and 0.01 to 0.02.

For example, M ⁰ may be Ni.

For example, the cathode active material according to one embodiment may be a layered cathode active material including nickel.

For example, the first lithium-transition metal composite oxide and the second lithium-transition metal composite oxide may contain at least 60 mol% of nickel, for example, at least 65 mol%, at least 70 mol%, and more preferably at least 70 mol%, based on the total amount of transition metals in the cathode active material, 75 mol% or more, 80 mol% or more, and 90 mol% or less. That is, the first lithium-transition metal composite oxide and the second lithium-transition metal composite oxide may be nickel-based oxide. In this case, the positive electrode active material can realize a high capacity at low cost. As the content of nickel is increased, the problem of residual lithium becomes more serious. In the cathode active material according to one embodiment, residual lithium can be removed even if nickel content is high, and thus, problems due to residual lithium can be overcome.

The particle size of the cathode active material may be from 1 탆 to 20 탆, and the range of particle diameters may vary depending on the types of the first lithium-transition metal composite oxide and the second lithium-transition metal composite oxide. The first coating layer and the second coating layer may have various thicknesses depending on the concentration of the coating.

According to another embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: preparing a lithium-transition metal composite oxide; Mixing the lithium transition metal complex oxide and the vanadium raw material; Coating a vanadium raw material on the surface of the lithium-transition metal composite oxide by spray-drying or using a sol-gel method; Heat treating a material coated with a vanadium raw material on the surface of the lithium-transition metal composite oxide; And a step of obtaining a cathode active material in which a first coating layer represented by the following Chemical Formula 1 is formed on the surface of the lithium-transition metal composite oxide and a second coating layer represented by Chemical Formula 2 is formed on the surface of the first coating layer, A method for producing a positive electrode active material for a lithium secondary battery is provided.

[Chemical Formula 1]

Li _a V _b O _c

(2)

V _d O _e

In the above formulas (1) and (2)

6, 1? B? 6, 2? C? 13, 1? D? 6 and 2? E? 13.

The above-described cathode active material for a lithium secondary battery can be produced through the above-described production method.

In general, lithium impurities are present on the surface of the lithium-transition metal composite oxide, and the cathode active material from which the lithium impurity is removed can be obtained according to the production method of this embodiment.

Specifically, the lithium impurity remaining on the surface of the lithium-transition metal composite oxide reacts with the vanadium raw material or the like to be converted into lithium vanadium oxide or the like, and the lithium vanadium oxide and the like, together with the vanadium oxide and the like, May be a constituent. As a result, a cathode active material from which lithium impurities have been removed can be obtained.

When the cathode active material prepared according to one embodiment is applied to a battery, gelation of the electrode slurry and generation of gas can be suppressed, and high-rate characteristics and life characteristics can be improved.

The preparation of the lithium-transition metal composite oxide may be performed by, for example, preparing a transition metal hydroxide by coprecipitation; Mixing the transition metal hydroxide and a lithium source; And heat treating the mixture of steps.

The heat treatment may be performed at 600 to 900 占 폚 and may be performed for 12 to 24 hours.

The lithium-transition metal composite oxide includes a first lithium-transition metal oxide and a second lithium-transition metal oxide, and the second lithium-transition metal oxide may be formed on the surface of the first lithium-transition metal oxide.

The first lithium-transition metal composite oxide and the second lithium-transition metal composite oxide may be a nickel-rich oxide containing at least 60 mol% of nickel based on the total amount of transition metals in the cathode active material according to an exemplary embodiment.

Specifically, the first lithium-transition metal composite oxide may be represented by the following Chemical Formula 3, and the second lithium-transition metal composite oxide may include a compound represented by Chemical Formula 4 below.

(3)

LiM ^O _x M ¹ _y M ² _z O ₂

[Chemical Formula 4]

LiM ^O _x M ¹ _y M ² _z V _i O ₂

In the above formulas (3) and (4)

M ⁰ , M ¹ and M ² are each independently Ni, Co, Mn, Al, Ti, Mg or Zr; 0? X? 1, 0? Y? 1, 0? Z? 1, to be. For example, M ⁰ may be Ni.

In the step of mixing the lithium-transition metal composite oxide and the vanadium raw material, the vanadium raw material is added in an amount of 0.1 to 5 moles, specifically 0.1 to 4 moles, and 0.1 to 3 moles, , 0.1 to 2 moles, and 0.1 to 1 mole, respectively. In this case, the lithium impurity remaining on the surface of the lithium-transition metal composite oxide is effectively removed while the coating layer is formed, and battery performance can be improved.

In the step of heat-treating the material coated with the vanadium raw material on the surface of the lithium-transition metal composite oxide, the heat treatment may be performed at 300 to 500 ° C, and may be performed for 1 to 10 hours. In this case, a stable coating layer can be formed, and lithium impurities remaining on the surface of the lithium-transition metal composite oxide can be effectively removed.

In another embodiment of the present invention, there is provided a positive electrode comprising the positive electrode active material for the lithium secondary battery; cathode; And a lithium secondary battery comprising the electrolyte.

The positive electrode is prepared by mixing a positive electrode active material according to one embodiment, a conductive material, a binder and a solvent to prepare a positive electrode active material composition, and then directly coating and drying on the aluminum current collector. Or by casting the positive electrode active material composition on a separate support, then peeling the support from the support, and laminating the resulting film on an aluminum current collector.

The conductive material may specifically be carbon black, graphite, metal powder, or the like. The binder may be a vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, and mixtures thereof. Further, N-methylpyrrolidone, acetone, tetrahydrofuran, decane and the like are used as the solvent. At this time, the content of the cathode active material, the conductive material, the binder and the solvent is used at a level normally used in a lithium secondary battery.

The negative electrode is prepared by mixing an anode active material, a binder and a solvent in the same manner as in the case of the anode. The anode active material composition is directly coated on the copper current collector or cast on a separate support, and the anode active material film, Laminated. At this time, the negative electrode active material composition may further contain a conductive material if necessary.

As the negative electrode active material, a material capable of intercalating / deintercalating lithium is used. For example, lithium metal, lithium alloy, coke, artificial graphite, natural graphite, organic polymeric compound combustion material, . The conductive material, the binder and the solvent are used in the same manner as in the case of the above-mentioned anode.

The separator may be polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more thereof. The separator may be a polyethylene / polypropylene double-layer separator, It is needless to say that a mixed multilayer film such as a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator and the like can be used.

As the electrolyte to be charged into the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt dissolved therein may be used.

The solvent of the non-aqueous electrolyte is not particularly limited, but 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? -Butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; Amides such as dimethylformamide and the like can be used. These may be used singly or in combination. Particularly, a mixed solvent of cyclic carbonate and chain carbonate can be preferably used.

As the electrolyte, a gelated polymer electrolyte in which an electrolyte solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCl, and LiI.

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

Example  One

Ni _{0 .75} Co _{0 .11} using a coprecipitation Mn _{0 .14} (OH) _2: The mixture was uniformly mixed it with LiOH to prepare a (average particle size of about 11㎛) under an air atmosphere for 18 hours, 750 calcined at ℃ was prepared _{LiNi 0 .75 Co 0 .11 Mn 0} .14 O 2.

A vanadium starting material such as vanadium oxytripropoxide, vanadyl acetylacetonate, and ammonium vanadate was weighed to 0.4 mol% of the transition metal of the active material in 100 ml of an ethanol solvent And then dispersed uniformly at 65 ° C for 1 hour to prepare a coating solution. It was added to a _{LiNi 0 .75 Co 0 .11 Mn 0} .14 O 2 was prepared in the coating solution to the solution to and uniformly distributed to make a mixed solution. The mixed solution is heated at 110 DEG C for 1 hour, and ethanol is evaporated. When using the spray drying method, the mixed solution is stirred at a constant speed into a spray dryer heated to 200 ° C, dried, and then taken at the bottom of the spray dryer.

This mixed solution was treated by a spray drying method or a sol-gel method to coat the surface of the active material. The dried powder was then fired at 400 ° C for 3 hours to prepare a surface-treated cathode active material having various layers on the surface.

After the polyvinylidene fluoride binder was dissolved in a solvent of N-methyl-2-pyrrolidone, the cathode active material and the carbon black conductive material were added to this solution to prepare a cathode active material slurry. The mixing ratio of the cathode active material, the conductive material and the binder was 92: 4: 4 by weight. The slurry was coated on an Al foil and dried at 110 DEG C for 600 minutes to prepare a positive electrode. A coin battery of size CR2016, which is a half cell, was manufactured using a lithium metal as the anode and cathode, and a mixed solution of 1.15M LiPF ₆ and EC / DMC / DEC = 3/4/3 (v / v) Respectively.

Example  2

Instead of _{LiNi 0 .75 Co 0 .11 Mn 0} .14 O 2 was prepared in the _{LiNi 0 .8 Co 0 .1 Mn 0} .1 O and the positive electrode active material and battery in the same manner as in Example 1 except for using ₂ .

Example  3

Instead of _{LiNi 0 .75 Co 0 .11 Mn 0} .14 O 2 , except that the _{LiNi 0 .8 Co 0 .15 Al 0} .05 O 2 was prepared the positive electrode active material and battery in the same manner as in Example 1 .

Comparative Example  One

Embodiment, except that the _{LiNi 0 .75 Co 0 .11 Mn 0} .14 O 2 produced in Example 1 as a cathode active material without a coating process to prepare a cell in the same manner as in Example 1.

Comparative Example  2

And it was prepared in a cell in the same manner as in Comparative Example 1 except for using a positive electrode active material _{LiNi 0 .8 Co 0 .1 Mn 0} .1 O 2 instead of _{LiNi 0 .75 Co 0 .11 Mn 0} .14 O 2 .

Comparative Example  3

And it was prepared in a cell in the same manner as in Comparative Example 1 except for using a positive electrode active material _{LiNi 0 .8 Co 0 .15 Al 0} .05 O 2 instead of _{LiNi 0 .75 Co 0 .11 Mn 0} .14 O 2 .

Example  1 and Comparative Example  Rating for 1

(1) Appearance evaluation

2 is a scanning electron microscope (SEM) photograph of the cathode active material of Example 1 and Comparative Example 1. Fig. 2 (a) and 2 (c) show the cathode active material of Comparative Example 1, and FIGS. 2 (b) and 2 (d) show the cathode active material of Example 1.

(2) Ni  And V distribution analysis

FIG. 3A is a transmission electron microscope (TEM) photograph of the surface of the positive electrode active material of Example 1, and FIGS. 3B and 3C are EDS photographs and line scattering graphs showing Ni and V distributions of the surface of the positive electrode active material of Example 1. In particular, in FIG. 3C, a region (8 nm) coated with vanadium and a region (8 nm to 25 nm) doped with vanadium in the second lithium-transition metal composite oxide can be identified, from which a vanadium- Metal complex oxides and vanadium in the coating layer.

(3) elemental analysis and Oxidation number  Change analysis

FIG. 4 is a graph showing the presence or absence of specific elements and the graph of the change in oxidation number (XPS) measured from the surface to the inside of the cathode active material of Example 1 and Comparative Example 1. FIG. Figs. 3A, 3C, and 3E are graphs for Comparative Example 1, and Figs. 3B, 3D, and 3F are graphs for Example 1. Fig.

Comparing FIGS. 3A and 3B, it can be seen that the content of Li ₂ CO ₃ is detected in the vicinity of the surface in FIG. 3 A, but is almost not detected in FIG. 3B. Comparing FIG. 3C with FIG. 3D, it can be seen that the vanadium cation is detected by the coating layer only in FIG. 3D. Comparing FIGS. 3E and 3F, in comparison with the comparative example in which the oxidation number of Ni was 3+ due to the fact that some vanadium was doped on the surface, the oxidation number changed to Ni ^{2 +} in the examples.

5 is a graph showing the presence or absence of specific elements and the change in oxidation number (EELS) measured from the surface toward the inside of the positive electrode active material of Example 1. Fig.

5A and 5B, it can be seen that the vanadium oxidation number on the surface of the positive electrode active material is 5+. Vanadium having an oxidation number of 5+ is the most thermodynamically stable vanadium. On the other hand, it can be seen that the vanadium oxidation number at 8 nm slightly shifted from 5+ to 4+. This is because the residual lithium remaining on the surface reacts with the vanadium oxide to form Li _c V ₂ O ₅ (0.01? _C ? 6) and the oxidation number of vanadium changes. In addition, nickel and vanadium coexist at 15 nm, and it was confirmed that the main oxidation number of nickel was 3+ before surface treatment with vanadium, but changed to 2+ after surface treatment. This is due to the fact that oxidation of vanadium is carried out in order to adjust the balance of oxidation as vanadium is doped into the transition metal sites.

(4) Coating layer shape

6 is a transmission electron microscope (TEM) photograph of the cathode active material of Example 1 and Comparative Example 1. Fig. 6 (a) and 6 (c) show the cathode active material of Comparative Example 1, and FIGS. 2 (b) and 2 (d) show the cathode active material of Example 1. Also, (1) and (2) are transformed images to confirm the structural crystallinity of the cathode active material of Comparative Example 1, and (3) and (4) are transformed images in which the structural crystallinity of the cathode active material of Example 1 can be confirmed. It can be seen that the Ni ^{2 +} ion increased due to the doping of vanadium occupies the Li ⁺ ion site on the surface, which may degrade the electrochemical characteristics, and that the vanadium-doped surface structure is more stable than that of Comparative Example 1 .

(5) Electrochemical evaluation

The life characteristics of the cells prepared in Example 1 and Comparative Example 1 were evaluated at a room temperature and a 1 C-rate. The results are shown in FIG. 7a. Referring to FIG. 7A, it can be seen that the life characteristics of Example 1 are superior to those of Comparative Example 1.

The characteristics of the batteries prepared in Example 1 and Comparative Example 1 were evaluated at various rates from 0.1 C-rate to 7 C-rate at room temperature. The results are shown in FIG. 7B. It can be seen from FIG. 7B that the output characteristic at the high rate is better in the case of the first embodiment than the first comparative example.

The life characteristics of the cells prepared in Example 1 and Comparative Example 1 were evaluated at a high temperature of 1 C-rate and the results are shown in FIG. 7c. Referring to FIG. 7C, it can be seen that the life characteristics of Example 1 are superior to those of Comparative Example 1.

Example  2 and Comparative Example  Rating for 2

(1) Appearance evaluation

8 is a scanning electron microscope (SEM) photograph of the cathode active material of Example 2 and Comparative Example 2. Fig. 8 (a) and 8 (c) show the cathode active material of Comparative Example 2, and FIGS. 6 (b) and 6 (d) show the cathode active material of Example 2.

(2) elemental analysis and Oxidation number  Change analysis

FIGS. 9A and 9B are graphs showing the presence or absence of specific elements and the change in oxidation number, respectively, of the cathode active materials of Comparative Example 2 and Example 2 measured from the surface to the inside. 9A and 9B, the left peak is a peak indicating the content of Li ₂ CO ₃ , and the right peak is a peak indicating hydrocarbon.

In FIG. 9A, the content of Li ₂ CO ₃ is detected in the vicinity of the surface, whereas in FIG. 9B, almost no detection is made.

(3) Electrochemical evaluation

The characteristics of the cells prepared in Example 2 and Comparative Example 2 were evaluated at various rates from 0.1 C-rate to 10 C-rate at room temperature. The results are shown in FIG. 10, it can be seen that the output characteristic at the high rate in the case of the second embodiment is better than that of the second comparative example.

The life characteristics of the batteries prepared in Example 2 and Comparative Example 2 were evaluated at a high temperature of 1 C-rate and the results are shown in FIG. Referring to FIG. 11, it can be seen that the life characteristics of Example 2 are better than those of Comparative Example 2.

Example  3 and Comparative Example  Rating for 3

(1) Appearance evaluation

12 is a scanning electron microscope (SEM) photograph of the cathode active material of Example 3 and Comparative Example 3. Fig. 12 (a) and 12 (c) show the cathode active material of Comparative Example 3, and FIGS. 12 (b) and 12 (d) show the cathode active material of Example 3.

(2) elemental analysis and Oxidation number  Change analysis

FIGS. 13A and 13B are graphs showing the presence or absence of specific elements measured from the surface to the inside of the cathode active materials of Comparative Examples 3 and 3, respectively. 13A and 13B, the left peak is a peak indicating the content of Li ₂ CO ₃ , and the right peak is a peak indicating hydrocarbon.

In FIG. 13A, the content of Li ₂ CO ₃ is detected in the vicinity of the surface, whereas in FIG. 13B, it is almost not detected.

(3) Electrochemical evaluation

The characteristics of the batteries prepared in Example 3 and Comparative Example 3 were evaluated at various rates from 0.1 C-rate to 10 C-rate at room temperature. The results are shown in FIG. It can be seen from FIG. 14 that the output characteristic at the high rate is better in the case of the third embodiment than the third embodiment.

The life characteristics of the batteries prepared in Example 3 and Comparative Example 3 were evaluated at a high temperature of 1 C-rate and the results are shown in FIG. Referring to FIG. 15, it can be seen that the life characteristics of Example 3 are better than those of Comparative Example 3.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (19)

A first lithium transition metal complex oxide,
A second lithium-transition metal composite oxide positioned on the surface of the first lithium-transition metal composite oxide,
A first coating layer positioned on the surface of the second lithium-transition metal composite oxide, and
And a second coating layer positioned on a surface of the first coating layer,
Wherein the first coating layer is represented by the following Formula 1,
Wherein the second coating layer is represented by the following formula (2)
Wherein the first lithium-transition metal composite oxide is represented by the following general formula (3)
Wherein the second lithium-transition metal composite oxide is represented by the following Formula 4:
[Chemical Formula 1]
Li _a V _b O _c
(2)
V _d O _e
(3)
LiM ^O _x M ¹ _y M ² _z O ₂
[Chemical Formula 4]
LiM ^O _x M ¹ _y M ² _z V _i O ₂
In the above formulas (1) and (2)
6, 1? B? 6, 2? C? 13, 1? D? 6 and 2? E? 13,
In the above formulas (3) and (4)
M ⁰ , M ¹ and M ² are each independently Ni, Co, Mn, Al, Ti, Mg or Zr; 0? X? 1, 0? Y? 1, 0? Z? 1, to be. The method of claim 1,
Wherein the second lithium-transition metal composite oxide is doped with vanadium. The method of claim 1,
Wherein the first coating layer and the second coating layer are contained in an amount of 0.1 to 5 moles relative to 100 moles of the transition metal of the first lithium-transition metal composite oxide and the second lithium-transition metal composite oxide. delete The method of claim 1,
Wherein M ⁰ is Ni. The method of claim 1,
In Formula 1,
0.05? A? 6, b = 2, and c = 5. The method of claim 1,
In Formula 2,
d = 2 and e = 5. Preparing a lithium-transition metal composite oxide;
Mixing the lithium transition metal complex oxide and the vanadium raw material;
Coating a vanadium raw material on the surface of the lithium-transition metal composite oxide by spray-drying or using a sol-gel method;
Heat treating a material coated with a vanadium raw material on the surface of the lithium-transition metal composite oxide; And
(1) on the surface of the lithium-transition metal composite oxide, and a second coating layer represented by the following formula (2) is formed on the surface of the first coating layer,
In the obtained cathode active material, the lithium-transition metal composite oxide includes a first lithium transition metal oxide and a second lithium transition metal oxide, and the second lithium transition metal oxide is formed on the surface of the first lithium transition metal oxide,
Wherein the first lithium-transition metal composite oxide is represented by the following Chemical Formula 3 and the second lithium-transition metal composite oxide is represented by Chemical Formula 4:
[Chemical Formula 1]
Li _a V _b O _c
(2)
V _d O _e
(3)
LiM ^O _x M ¹ _y M ² _z O ₂
[Chemical Formula 4]
LiM ^O _x M ¹ _y M ² _z V _i O ₂
In the above formulas (1) and (2)
6, 1? B? 6, 2? C? 13, 1? D? 6 and 2? E? 13,
In the above formulas (3) and (4)
M ⁰ , M ¹ and M ² are each independently Ni, Co, Mn, Al, Ti, Mg or Zr; 0? X? 1, 0? Y? 1, 0? Z? 1, to be. delete 9. The method of claim 8,
Wherein the second lithium-transition metal composite oxide is doped with vanadium. 9. The method of claim 8,
In the step of mixing the lithium-transition metal composite oxide and the vanadium raw material,
Wherein the vanadium source material is added in an amount of 0.1 to 5 moles per 100 moles of the transition metal of the lithium-transition metal composite oxide. delete 9. The method of claim 8,
Wherein M ⁰ is Ni. 9. The method of claim 8,
The step of preparing the lithium-transition metal composite oxide
Preparing a transition metal hydroxide by coprecipitation;
Mixing the transition metal hydroxide and a lithium source; And
And heat-treating the mixture of the above-mentioned steps. 9. The method of claim 8,
Wherein the heat treatment is performed at 300 ° C to 500 ° C in the step of heat treating the material coated with the vanadium raw material on the surface of the lithium-transition metal composite oxide. 9. The method of claim 8,
Wherein the heat treatment is performed for 1 hour to 10 hours in the step of heat treating the material coated with the vanadium raw material on the surface of the lithium-transition metal composite oxide. 9. The method of claim 8,
In Formula 1,
0.05? A? 6, b = 2, and c = 5. 9. The method of claim 8,
In Formula 2,
d = 2 and e = 5. A positive electrode comprising a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3 and 5 to 7; cathode; And an electrolyte.

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