KR20020065191A - Positive active material for lithium secondary battery and method for preparing the same - Google Patents

Abstract

PURPOSE: Provided are a cathode active material of a lithium secondary battery, which can improve the capacity and the lifetime property of the lithium secondary battery, and a process for producing the same. CONSTITUTION: The cathode active material of the lithium secondary battery contains a lithium manganese spinel oxide(formula 1: Li(1-x)Mn(2-x-y)MyO(4+d)) and a lithium metal composite oxide(formula 2: Li(1-z)Mn(2-z-w)ZrzMewO4) coated on the lithium manganese spinel oxide(formula 1). And the cathode active material is produced by a process comprising the steps of: preparing the lithium manganese spinel oxide(formula 1) as a central particle; preparing the mixture of the material of the coating layer(formula 2); coating the central particles with the mixture of the material of the coating layer(formula 2); calcining the coated central particles. In the formula, M is at least one selected from the group consisting of Ti, Cr, Co, Zr, V, Ni, Ga, and Gd, x is a real number of 0-0.12, y is a real number of 0-0.5, d is a real number of 0-0.05, Me is at least one selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd, z is a real number of more than 0 and less than 0.1, and w is a real number of 0-0.7.

Description

A positive electrode active material of a lithium secondary battery and a method of manufacturing the same {POSITIVE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND METHOD FOR PREPARING THE SAME}

[Industrial use]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material of a lithium secondary battery and a method of manufacturing the same, and more particularly, to a positive electrode active material capable of improving the capacity and lifespan characteristics of a lithium secondary battery and a method of manufacturing the same.

[Private Technology]

Lithium ion secondary batteries are in the spotlight as one of the three high-tech components along with semiconductors and display devices in the information and electronics industry. Recently, as communication devices such as mobile phones and PDAs (personal digital assistants) become portable, the volume and weight thereof have been reduced in size and weight. In this case, the size and weight of the battery are also essential.

However, as the size of the battery becomes smaller, the capacity for charging and discharging becomes smaller. Therefore, there is a need for the development of a lithium secondary battery with improved capacity, which is portable and small, and does not require external power supply for a long time.

To improve the capacity of the cell, the design of the cell must be optimized. The lithium ion secondary battery uses a material that absorbs and releases lithium as the active material of the positive electrode and the negative electrode, and the lithium ion secondary battery delivers energy by reciprocating the positive electrode and the negative electrode like a rocking chair, so it is a rocking chair battery. In the first charging process, the surface of the carbon particles, the negative electrode active material, and the electrolyte react at the negative electrode of the battery to form a solid electrolyte film (SEI film). The formed solid electrolyte membrane serves to stabilize the battery by inhibiting the decomposition of further electrolyte on the surface of the carbon particles, at which time the amount of reversible lithium is reduced to reduce the capacity of the battery.

Therefore, it is important to increase the capacity per unit weight of the active material of the electrode to increase the capacity of the battery, but it is also important to minimize the amount of lithium consumed to form the solid electrolyte membrane.

On the other hand, the representative positive electrode active material of the lithium ion secondary battery is a lithium metal composite oxide, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and the like, the negative electrode active material is mainly used graphite (graphite). Spinel-structured lithium manganese composite oxide that can be used as a positive electrode active material has been studied in recent years because it has advantages in terms of battery safety and cost compared to other positive electrode active materials of a lithium ion secondary battery having a 4 V potential. Since the capacity per unit weight of lithium manganese spinel oxide is about 120 to 125 mAh / g, which is smaller than other cathode active materials, there is a limitation in application to a small battery requiring a high capacity per unit weight.

SUMMARY OF THE INVENTION In view of the problems of the prior art, an object of the present invention is to provide a cathode active material capable of improving battery capacity by using a cathode active material in which a lithium metal manganese spinel oxide is formed with a coating layer of a lithium metal composite oxide, and a method of manufacturing the same. It is done.

1 is a graph showing a charge and discharge curve of a lithium ion secondary battery using the positive electrode active material prepared in Example 1.

Figure 2 is a graph showing the life characteristics at room temperature (25 ℃) of the lithium ion secondary battery using the positive electrode active material prepared in Examples 1 to 3, and Comparative Examples 1 and 2.

Figure 3 is a graph showing the life characteristics at high temperature (55 ℃) of the lithium ion secondary battery using the positive electrode active material prepared in Examples 1 to 3, and Comparative Examples 1 and 2.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a positive electrode active material of a lithium secondary battery,

a) lithium manganese spinel oxide represented by Chemical Formula 1; And

b) represented by the following formula (2) coated on the lithium manganese spinel oxide of a)

Lithium metal composite oxide

It provides a positive electrode active material comprising:

[Formula 1]

Li _{1 + x} Mn _2-xy M _y O _{4 + d}

In Chemical Formula 1,

M is at least one selected from the group consisting of Ti, Cr, Co, Zr, V, Ni, Ga, and Gd,

x is a real number from 0 to 0.12,

y is a real number from 0 to 0.5,

d is a real number from 0 to 0.05,

[Formula 2]

Li _{1 + z} Mn _2-zw Zr _z Me _w O ₄

In Chemical Formula 2,

Me is at least one selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd,

z is a real number greater than 0 and less than or equal to 0.1,

w is a real number from 0 to 0.7.

In addition, the present invention provides a method for producing a positive electrode active material of a lithium secondary battery,

a) preparing a core particle of lithium manganese spinel oxide represented by Chemical Formula 1

Making;

b) preparing a mixture of the coating layer raw material represented by Formula 2;

c) coating the mixture of the coating layer raw material of step b) to the central particle of step a)

Making; And

d) calcining the coated central particle of step c)

It provides a method comprising a.

In another aspect, the present invention provides a lithium secondary battery comprising the positive electrode active material.

Hereinafter, the present invention will be described in detail.

[Action]

The positive electrode active material of the present invention comprises a) lithium manganese spinel oxide as a core particle and b) a lithium metal composite compound as a coating layer.

The a) lithium manganese spinel oxide is represented by the formula (1), which can occlude and release lithium ions and has a spinel structure has the advantages of excellent safety and low cost compared to other cathode active materials of lithium secondary batteries.

The b) lithium metal composite compound is represented by the formula (2) and a) is coated on the surface of the core particles of lithium manganese spinel oxide to form a coating layer, which is transferred to the cathode during the first charging process of the lithium secondary battery Lithium contributes to the formation of irreversible lithium, which does not return to the positive electrode upon discharge. The irreversible lithium is consumed in the formation of a solid electrolyte film formed on the surface of the negative electrode active material during the first charging process of the lithium secondary battery. By reducing the consumption of the serves to improve the capacity of the battery.

The coating layer is a lithium metal composite oxide, which essentially contains a Zr element, and Zr serves to increase the irreversible capacity. In other words, the increase in irreversible capacity per unit weight of the first cycle of lithium manganese spinel oxide is achieved through the surface treatment of lithium manganese spinel oxide.

In addition, the lithium metal composite oxide of the coating layer is chemically stable to block the reaction between the electrolyte and the lithium manganese spinel oxide, which is the core particle, and to suppress the elution of Mn from the spinel to improve the life characteristics.

The present invention includes a) preparing a core particle, b) preparing a mixture of coating layer raw material, c) coating the mixture of coating layer raw material on the central particle, and d) firing the coated central particle. It provides a method for producing a positive electrode active material of a lithium secondary battery.

The core particles of step a) are iii) a mixture comprising a lithium compound and ii) a manganese compound at a temperature of 300 to 900 ° C. for 1 to 50 hours under air or a mixed gas atmosphere containing at least 2% by weight of oxygen. It is prepared by heat treatment. (Iii) the lithium compound is at least one selected from the group consisting of LiOH, LiOH.H ₂ O, LiCH ₃ COO, LiCHO ₂ , LiCHO ₂ .H ₂ O, and LiNO ₃ , and ii) the manganese compound is manganese carbonate. , At least one selected from the group consisting of nitrates, oxalates, sulfates, acetates, citrates, chlorides, and oxides.

The central particle may optionally include metal M as shown in Formula 1, wherein metal M is provided from a metal compound containing metal M). The metal M is at least one selected from the group consisting of Ti, V, Cr, Co, Ni, Mg, Zr, Fe, Gd and Ga, and the metal compound containing the metal M is carbonate, nitrate, oxalate of the metal M. , At least one selected from the group consisting of sulfates, acetates, citrates, chlorides, and oxides.

The coating material of step b) is prepared by dissolving a mixture containing i) a lithium compound, ii) a manganese compound, and iii) a zirconium compound using water or an organic solvent and stirring. By using an organic solvent such as water or alcohol, a uniform lithium manganese mixture can be easily prepared.

(Iii) the lithium compound is at least one selected from the group consisting of LiOH, LiOH.H ₂ O, LiCH ₃ COO, LiCHO ₂ , LiCHO ₂ .H ₂ O, and LiNO ₃ , and ii) the manganese compound is manganese carbonate. At least one selected from the group consisting of nitrates, oxalates, sulfates, acetates, citrates, chlorides, and oxides. At least one selected from the group consisting of.

The coating layer may optionally include a metal Me, as shown in Formula 2, wherein the metal Me is prepared from a metal compound comprising i) metal Me. The metal Me is at least one selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd, the metal compound containing a metal Me is a carbonate of the metal Me, At least one selected from the group consisting of nitrates, oxalates, sulfates, acetates, citrates, chlorides, and oxides.

The b) lithium metal composite oxide has a composition of 0.1 to 50 mol% based on a) lithium manganese spinel oxide.

Step c) is a step of coating the coating layer material prepared in step b) on the core particles of the lithium manganese spinel composite oxide component of step a), it can be carried out in two ways. One method is to make a slurry by adding a lithium manganese spinel composite oxide powder of step a), which is a core particle, to an aqueous solution of a compound of a coating material of a lithium metal composite oxide component of step b) or a sol of an organic solution. After sufficiently mixing the slurry using the heat is added to evaporate the solvent. As the solvent evaporates, a coating layer is formed on the surface of the central particle.

The other method is a simple coating method, which is performed by fluidizing the core particles of step a) in air and then spraying the raw material of the coating layer of step b) onto the lithium manganese spinel composite oxide, which is the core particle, and drying the solvent. .

In step d), the coated lithium manganese spinel composite oxide powder is heat-treated at a temperature of 300 to 900 ° C. in a mixed gas atmosphere having an air or oxygen content of 10 wt% or more. At this time, the gas flow rate is 0.05 to 3.0 l / gH (volume per hour weight) and the heat treatment time is 1 to 30 hours are suitable.

The heat treatment time and temperature can be adjusted within the above-mentioned range according to the purpose, and part of the coating layer may be doped on the surface of the central particle during the heat treatment process depending on the heat treatment temperature.

And in order to control the irreversible capacity, the above-mentioned positive electrode active material may be mixed with other positive electrode active materials other than the positive electrode active material according to the present invention, and the present invention also provides a lithium secondary battery comprising the positive electrode active material.

The present invention will be described in more detail with reference to the following examples and comparative examples. However, an Example is for illustrating this invention and is not limited only to these.

EXAMPLE

Example 1

(Production of Core Particles)

In order to synthesize a lithium manganese composite oxide powder having a spinel structure, Li ₂ CO ₃ and MnO ₂ were mixed so that the molar ratio [Li] / [Mn] of lithium and manganese was 0.538. After uniformly mixing the raw materials and heat-treated at 480 ℃ for 10 hours in an air atmosphere, and cooled to promote the reaction to sufficiently remix, and then reacted in an air atmosphere at 750 ℃ for 20 hours to spinel powder Synthesized. The flow rate of air was 0.1 L / gH during the heat treatment. The lithium manganese spinel compound obtained through the above process was composed of Li _1.05 Mn _1.94 O ₄ .

(Manufacture of coating layer raw material)

For LiOH · H ₂ O to provide the lithium in the coating material, to provide a manganese Mn (CH ₃ COO) ₂ · use of the _{4H 2 O, ZrOCl 2 · 8H} 2 O to provide a Zr, and these raw materials It was dissolved in anhydrous alcohol and stirred for 30 minutes to prepare a mixed solution of a uniform lithium-metal compound.

The composition of lithium and metal was [Li]: [Mn]: [Zr] in a molar ratio of 1.05: 1.90: 0.05, and the amount of coating layer was 10 mol% based on the core particle, assuming that the amount of oxide became an oxide after heat treatment. .

(covering)

Lithium manganese spinel oxide was added to the mixed solution of the lithium-metal compound prepared in the above step to prepare a mixed solution, and the mixed solution was stirred for 30 minutes and then removed by heating to remove the solvent and coated.

(Firing)

The lithium manganese spinel oxide coated in the above step was heat treated at 700 ° C. for 10 hours using a tube type electric furnace. The heat treatment was carried out in an air atmosphere, and the flow rate of air was 0.1 L / gH.

(Production of test cell)

An electrode was prepared using the coated lithium manganese spinel oxide prepared in the above step as an active material. At this time, the conductor was graphite and the binder was polyvinylidene fluoride (PVdF), and the ratio of the active material: conductor: binder was 85: 10: 5 in weight ratio. First, the binder was dissolved in n-methylpyrrolidinone (n-methyl pyrrolidinone; NMP), and the slurry was prepared by adding the active material and the conductor. The obtained slurry was coated on aluminum foil using a tape casting method, and then dried in a vacuum dryer at 130 ° C. for 2 hours to prepare a positive electrode. Lithium metal was used as the negative electrode. After cutting the positive electrode and the negative electrode to a suitable size to produce a button cell (coin cell).

The electrolyte used was a 1 mole solution of LiPF ₆ , and an electrolyte solution was used in which a ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a molar ratio of 1: 2.

(Property measurement)

The cell obtained in the above step is represented by [Li ₂ MnO ₄ / LiPF ₆ (1 M) in EC + 2 EMC / Li], the charge and discharge characteristics and life characteristics of this cell were evaluated. In this case, the charge and discharge voltage range was set to 3.0 to 4.5 V when the capacity was evaluated. The results are shown in FIG. 1.

The evaluation of the life characteristics was performed in the range of 3.4 to 4.3 V and the change of the irreversible capacity according to the cycle at room temperature is shown in FIG. 2, and the change in the irreversible capacity according to the cycle is shown in FIG. 3. In addition, Table 1 shows the change of irreversible capacity according to the content of Zr and the content of the surface layer.

Example 2

It carried out similarly to Example 1, but the conditions of the said baking step was 450 degreeC and 5 hours.

Example 3

In the same manner as in Example 1, the composition of the coating layer material in the manufacturing step of the coating layer raw material was carried out so that [Li]: [Mn + Zr] is 1: 1 in a molar ratio. At this time, the molar ratio of Zr to Mn was [Mn]: [Zn] = 1.95: 0.05.

Example 4

In the same manner as in Example 1, the amount of the coating layer raw material in the manufacturing step of the coating layer raw material was carried out to 20 mol% with respect to the central particle.

Example 5

It carried out similarly to Example 1, but carried out so that content of Zr in a coating material may be 0.07 mol, and the content of the surface layer with respect to a core particle shall be 5 mol%.

Comparative Example 1

The same process as in Example 1 was carried out, except that the manufacturing step of the coating layer raw material, and the coating step was omitted, using an uncoated lithium manganese spinel oxide.

Comparative Example 2

In order to synthesize a spinel-structure lithium manganese composite oxide powder, LiCH ₃ COO and Mn (CH ₃ COO) ₂ were mixed so that the molar ratio [Li] / [Mn] of lithium and manganese was 0.538, and Zr was 5 mol%. It was. After mixing the raw materials uniformly, heat treatment at 480 ℃ for 10 hours in an air atmosphere and then cooled to promote the reaction to sufficiently remixing, and then reacted in an air atmosphere at 700 ℃ for 20 hours to synthesize a spinel powder It was. The flow rate of air was 0.1 L / gH during the heat treatment. The lithium manganese spinel compound obtained through the above process had a composition of Li _1.05 Mn _1.90 Zr _0.05 0 ₄ .

After the process was carried out in the same manner as in Example 1 to prepare a positive electrode and a cell, and the characteristics were evaluated under the same conditions as in Example 1.

Table 1 below shows the change of irreversible capacity according to the content of the surface layer and the content of Zr present in the surface layer with respect to the central particle obtained in Example 1. This irreversible capacity is consumed to form a solid electrolyte film in an actual battery in which carbon is used as a negative electrode, thereby preventing reversible lithium from being used to form a solid electrolyte film.

TABLE 1

Frequency Zr content in surface layer and surface layer Initial capacity (mAh / g) Irreversible capacity (mAh / g) Surface layer amount (mol%) Zr content (mol%) of the surface layer Charging capacity Discharge capacity One 5 One 130 125 5 2 10 One 132 124 8 3 20 One 134 123 11 4 40 One 134 123 11 5 5 3 136 120 16 6 10 3 139 120 19 7 20 3 140 121 19 8 40 3 141 120 21 9 5 5 146 118 28 10 10 5 148 117 31 11 20 5 148 119 29 12 40 5 148 118 30 13 5 7 150 118 32 14 10 7 152 117 35 15 20 7 154 117 37 16 40 7 155 119 36

1 shows a charge / discharge curve of a test cell prepared using the positive electrode active material prepared in Example 1, indicating that the charge capacity is 150 mAh / g and the discharge capacity is 118 mAh / g, and thus the irreversible capacity is It was found to be about 32 mAh / g.

2 and 3 show the life characteristics at room temperature (25 ° C.) and high temperature (55 ° C.) of Examples 1 to 3 and Comparative Examples 1 and 2, respectively. In Comparative Examples 1 and 2, as the number of cycles increases, Compared with Examples 1 to 3, it was found that the reduction in specific capacity was remarkably large.

The present invention is to provide a positive electrode active material and a method of manufacturing the same by coating a lithium metal complex oxide on the surface of the lithium manganese spinel oxide to form irreversible lithium, reduce the consumption of reversible lithium to improve capacity and life characteristics Has

Claims (21)

In the positive electrode active material of a lithium secondary battery, a) lithium manganese spinel oxide represented by Chemical Formula 1; And b) represented by the following formula (2) coated on the lithium manganese spinel oxide of a) Lithium metal composite oxide A cathode active material comprising: [Formula 1] Li _{1 + x} Mn _2-xy M _y O _{4 + d} In Chemical Formula 1, M is at least one selected from the group consisting of Ti, Cr, Co, Zr, V, Ni, Ga, and Gd, x is a real number from 0 to 0.12, y is a real number from 0 to 0.5, d is a real number from 0 to 0.05, [Formula 2] Li _{1 + z} Mn _2-zw Zr _z Me _w O ₄ In Chemical Formula 2, Me is at least one selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd, z is a real number greater than 0 and less than or equal to 0.1, w is a real number from 0 to 0.7. The method of claim 1, The lithium metal composite oxide of b) is 0.1 to 50 mol% of the lithium manganese spinel oxide of a). In the manufacturing method of the positive electrode active material of a lithium secondary battery, a) preparing a core particle which is a lithium manganese spinel oxide represented by Chemical Formula 1; b) preparing a mixture of the coating layer raw material represented by the following Chemical Formula 2; c) coating the mixture of the coating layer material of step b) to the central particle of step a) Making; And d) calcining the coated central particle of step c) How to include: [Formula 1] Li _{1 + x} Mn _2-xy M _y O _{4 + d} In Chemical Formula 1, M is at least one selected from the group consisting of Ti, Cr, Co, Zr, V, Ni, Ga, and Gd, x is a real number from 0 to 0.12, y is a real number from 0 to 0.5, d is a real number from 0 to 0.05, [Formula 2] Li _{1 + z} Mn _2-zw Zr _z Me _w O ₄ In Chemical Formula 2, Me is at least one selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd, z is a real number greater than 0 and less than or equal to 0.1, w is a real number from 0 to 0.7. The method of claim 3 The central particle of step a) Iii) a lithium compound; And Ii) manganese compounds Method for producing a mixture comprising a heat treatment at a temperature of 300 to 900 ℃ for 1 to 50 hours under air or a mixed gas atmosphere containing at least 2% by weight of oxygen. The method of claim 3, wherein The central particle of step a) To the mixture of claim 4 Iii) a metal compound comprising a metal M selected at least one from the group consisting of Ti, Cr, Co, Zr, V, Ni, Gd, and Ga Method for producing a mixture further comprising a heat treatment at a temperature of 300 to 900 ℃ for 1 to 50 hours under air or a mixed gas atmosphere containing at least 2% by weight of oxygen. The method of claim 4, wherein And iii) at least one lithium compound is selected from the group consisting of LiOH, LiOH.H ₂ O, LiCH ₃ COO, LiCHO ₂ , LiCHO _2. H ₂ O, and LiNO ₃ . The method of claim 4, wherein Said ii) manganese compound is selected from the group consisting of manganese carbonate, nitrate, oxalate, sulfate, acetate, citrate, chloride, and oxide. The method of claim 5, The metal compound comprising metal M selected from the group consisting of Ti, V, Cr, Co, Ni, Mg, Zr, Fe, Gd and Ga is carbonate, nitrate, oxalate and sulfate of the metal M. , At least one selected from the group consisting of acetates, citrates, chlorides, and oxides. The method of claim 3, wherein The raw material of the coating layer of step b) Iii) a lithium compound; Ii) manganese compounds; And Iii) zirconium compounds A method comprising preparing a mixture comprising dissolving in water or an organic solvent and then stirring. The method of claim 3 The raw material of the coating layer of step b) To the mixture of claim 9 Iii) a metal compound comprising at least one metal Me selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd The method is prepared by dissolving the mixture further comprises water or in an organic solvent and stirring. The method of claim 9, And iii) at least one lithium compound is selected from the group consisting of LiOH, LiOH.H ₂ O, LiCH ₃ COO, LiCHO ₂ , LiCHO _2. H ₂ O, and LiNO ₃ . The method of claim 9, Said ii) manganese compound is selected from the group consisting of manganese carbonate, nitrate, oxalate, sulfate, acetate, citrate, chloride, and oxide. The method of claim 9, And (iii) the zirconium compound is selected from the group consisting of carbonates, nitrates, oxalates, sulfates, acetates, citrates, chlorides, and oxides of zirconium. The method of claim 10, Iii) a metal compound comprising at least one metal Me selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd; At least one selected from the group consisting of oxalate, sulfate, acetate, citrate, chloride, and oxide. The method of claim 3, wherein The coating layer of step b) is 0.1 to 50 mol% of the central particles of step a). The method of claim 3, wherein The coating of step c) is carried out by preparing a slurry comprising the core particles of step a) and the raw material of the coating layer of step b), and then heating and drying the slurry of the mixture with stirring. The method of claim 3, wherein Wherein the coating of step c) is made by fluidizing the core particles of step a) in air and then spraying and drying the raw material of the coating layer of step b) onto the core particles. The method of claim 3, wherein The firing of step d) is carried out by heat treatment at a temperature of 300 to 900 ° C. for 1 to 30 hours in an atmosphere of air at a flow rate of 0.05 to 3.0 l / gH or a mixed gas having an oxygen content of 10 wt% or more. A cathode active material mixture for a lithium secondary battery comprising the cathode active material according to claim 1. A lithium secondary battery comprising the cathode active material of claim 1. A lithium secondary battery comprising the positive electrode active material mixture of claim 19.