KR20030034762A - Method of preparing positive active material for rechargeable lithium batteries and preparing the same - Google Patents

Abstract

PURPOSE: A positive electrode active material for a lithium secondary battery and its preparation method are provided, to improve the overcharging property and the stability at a high voltage. CONSTITUTION: The positive electrode active material comprises 100 parts by weight of a lithium cobalt-based oxide; and 10-50 parts by weight of a lithium-manganese-based oxide. Preferably the lithium cobalt-based oxide is represented by LixCo(1-y)MyA2, wherein 1.0<=x<=1.1, 0.01<=y0.1, 0.01<=z<=0.5; M is at least one transition metal or lanthanide metal selected from the group consisting of Ni, Al, Cr, Co, Mg, La, Ce, Sr and V; and A is O, F, S or P. Preferably the lithium-manganese-based oxide is represented by LixMn(1-y)MyO(2-z)Az or LixMn(2-y)MyO(4-z)Az, wherein 1.0<=x<=1.1, 0.01<=y0.1, 0.01<=z<=0.5; M is at least one transition metal or lanthanide metal selected from the group consisting of Ni, Al, Cr, Co, Mg, La, Ce, Sr and V; and A is O, F, S or P.

Description

A cathode active material for a lithium secondary battery and a method of manufacturing the same {METHOD OF PREPARING POSITIVE ACTIVE MATERIAL FOR RECHARGEABLE LITHIUM BATTERIES AND PREPARING THE SAME}

The present invention relates to a positive electrode active material for a lithium secondary battery and a method for manufacturing the same, and more particularly, to a positive electrode active material for a lithium secondary battery with improved overcharge characteristics and high voltage safety and a method for manufacturing the same.

Lithium secondary batteries are manufactured by reversibly inserting and detaching lithium ions as a positive electrode and a negative electrode, and filling an organic or polymer electrolyte between the positive electrode and the negative electrode, and lithium ions are inserted / Electrical energy is generated by oxidation and reduction reactions when desorption.

Lithium metal was used as a negative electrode active material of a lithium secondary battery. However, when lithium metal is used, a carbon-based material such as amorphous carbon or crystalline carbon may be used instead of lithium metal due to a risk of explosion due to a short circuit of the battery due to the formation of dendrite. Is being replaced. In particular, in recent years, boron-coated graphite (BOC) is manufactured by adding boron to a carbon-based material to increase the capacity of the carbon-based material.

A chalcogenide compound is used as the positive electrode active material, and examples thereof include a composite metal such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1), LiMnO _2, and the like. Oxides are being studied. Among the positive electrode active materials, LiCoO ₂ shows good electrical conductivity, high battery voltage, and excellent electrode characteristics, and is a representative positive electrode active material currently commercialized and sold by Sony, etc., but has a disadvantage of high price. Manganese-based positive electrode active materials such as LiMnO ₂ and LiMn ₂ O ₄ have been known as attractive materials because they are easy to synthesize, relatively inexpensive, and have little pollution to the environment. However, the manganese-based positive electrode active material has a disadvantage that the capacity is small and deteriorated at high temperature, which may cause an explosion.

Accordingly, in order to synthesize a manganese-based cathode active material having thermal properties comparable to that of the cobalt-based cathode active material while improving the thermal stability of the manganese-based cathode active material, a portion of the complex oxide in which manganese is replaced with another nickel, cobalt, or the like is used. Research is ongoing.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a positive electrode active material for a lithium secondary battery with improved overcharge characteristics and high voltage stability and a method of manufacturing the same.

In order to achieve the above object, the present invention provides a cathode active material for a lithium secondary battery comprising a lithium cobalt oxide and a lithium manganese oxide.

In another aspect, the present invention provides a method for producing a positive electrode active material for a lithium secondary battery comprising a step of mixing a lithium cobalt oxide and a lithium manganese oxide.

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

Lithium cobalt oxide is widely used as a cathode active material for lithium secondary batteries because of its excellent capacity characteristics and charge / discharge characteristics, but has a problem in that its lifetime characteristics are lowered during overcharging. In addition, lithium manganese oxide, which is used as a cathode active material for lithium secondary batteries, has a problem in that its charge and discharge characteristics are excellent, but its capacity is small and may be degraded at high temperature. The present invention provides the positive electrode active material for a lithium secondary battery with excellent charging and discharging characteristics, high voltage stability, and improved overcharge characteristics by utilizing the advantages of cobalt oxide and manganese oxide to the maximum, and a method of manufacturing the same.

The positive electrode active material for a lithium secondary battery of the present invention contains a mixture of a lithium cobalt oxide and a lithium manganese oxide. As the lithium cobalt oxide, an oxide of Formula 1 may be used, and as the lithium manganese oxide, a compound of Formula 2 or 3 may be used.

[Formula 1]

Li _x Co _1-y M _y A ₂

[Formula 2]

Li _x Mn _1-y M _y O _2-z A _z

[Formula 3]

Li _x Mn _2-y M _y O _4-z A _z

(Wherein, 1.0 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, and M is a transition metal selected from the group consisting of Ni, Al, Cr, Co, Mg, La, Ce, Sr and V) Or at least one metal of the lanthanide metal, and A is selected from the group consisting of O, F, S and P.)

The positive electrode active material preferably contains lithium manganese oxide in an amount of 10 to 50 parts by weight based on 100 parts by weight of lithium cobalt oxide. When the lithium manganese oxide is less than 10 parts by weight relative to 100 parts by weight of the lithium cobalt oxide, the amount of the lithium manganese oxide is insignificant, and thus there is a problem that the overcharge characteristic of the positive electrode active material is not improved.

The positive electrode active material for a lithium secondary battery of the present invention is prepared by mixing a lithium cobalt oxide and a lithium manganese oxide. The amount of the lithium manganese oxide used is 10 to 50 parts by weight, preferably 20 to 30 parts by weight based on 100 parts by weight of the lithium cobalt oxide. When the lithium manganese oxide is less than 10 parts by weight relative to 100 parts by weight of the lithium cobalt oxide, the amount of the lithium manganese oxide is insignificant, and thus there is a problem that the overcharge characteristic of the positive electrode active material is not improved.

In order to manufacture the lithium cobalt oxide and lithium manganese oxide used in the present invention, first, a lithium salt and a metal salt are mixed in a desired equivalent ratio. Lithium nitrate, lithium acetate or lithium hydroxide may be used as the lithium salt, and the metal salt may include manganese salt, cobalt salt, and Ni, Al, Cr, Co, Mg, La, Ce, Sr, and V. Metal salts comprising a transition metal or lanthanide metal selected from the group can be used.

Cobalt oxide, cobalt nitrate, or cobalt carbonate may be used as the cobalt salt, and manganese acetate or manganese dioxide may be used as the manganese salt. In addition, as the metal salt, fluorine salt, sulfur salt or phosphorus salt may be precipitated together with manganese salt and cobalt salt. Manganese fluoride or lithium fluoride may be used as the fluorine salt, manganese sulfide or lithium sulfide may be used as the sulfur salt, and H ₃ PO ₄ may be used as the phosphate salt. The manganese salt, cobalt salt and fluorine salt, sulfur salt and phosphorus salt are not limited to the compound.

The mixing method may use, for example, mortar grinder mixing, in which an appropriate solvent such as ethanol, methanol, water, acetone is added and there is little solvent in order to promote the reaction of lithium salt and metal salt. It is desirable to perform a mortar grinder mixture until solvent-free.

The obtained mixture is heat-treated at a temperature of about 400 to 600 ° C. to prepare compound precursor powders of formulas 1 to 3 in a semi-crystalline state. If the heat treatment temperature is lower than 400 ℃ there is a problem that the reaction between the lithium salt and the metal salt is not sufficient. In addition, after drying the precursor powder prepared by the heat treatment, or after the heat treatment process (blowing) dry air may be uniformly distributed by remixing the precursor powder at room temperature (remixing).

The semi-crystalline precursor powder obtained is subjected to secondary heat treatment at a temperature of 700 to 900 ° C. for about 10 to 15 hours. If the secondary heat treatment temperature is lower than 700 ° C, there is a problem that the crystalline material is difficult to form. The heat treatment step is carried out by heating at a rate of 1 to 5 ℃ / min under the conditions of blowing dry air or oxygen, it is maintained by a certain time at each heat treatment temperature and then naturally cooled.

A lithium secondary battery is manufactured according to a conventional method using the cathode active material for a lithium secondary battery manufactured as described above. The prepared positive electrode active material is added to an organic solvent such as N-methyl-2-pyrrolidone together with a binder such as polyvinylidone and conductive materials such as acetylene black and carbon black to prepare a positive electrode active material slurry composition. The slurry composition is applied to a current collector such as aluminum foil so as to have a thickness of 60 to 70 μm, including the current collector thickness, and then dried to prepare a positive electrode.

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

(Example 1)

Lithium salt and cobalt salt were mixed to prepare a lithium cobalt oxide LiCoO ₂ powder, and then lithium salt and manganese salt was mixed to prepare a lithium manganese oxide LiMn ₂ O ₄ powder. 30 parts by weight of the lithium manganese oxide powder was mixed with respect to 100 parts by weight of the prepared lithium cobalt oxide powder to prepare a cathode active material for a lithium secondary battery.

The prepared positive electrode active material, carbon conductive material, and polyvinylidene fluoride were weighed in a weight ratio of 94: 3: 3, and dissolved in N-methyl-2-pyrrolidone organic solvent to prepare a slurry for the positive electrode. Was prepared. The slurry was coated on aluminum foil to form a thin electrode plate, and then dried in an oven at 135 ° C. for at least 3 hours, and then pressed to prepare a cathode. Subsequently, a coin type half cell was produced using a lithium metal as a counter electrode using lithium metal as a counter electrode in a glove box.

(Example 2)

LiMn ₂ O ₄ powder was carried out in the same manner as in Example 1 except for mixing 50 parts by weight with respect to 100 parts by weight of LiCoO ₂ powder.

(Example 3)

LiMn ₂ O ₄ powder was carried out in the same manner as in Example 1, except that 30 parts by weight to 100 parts by weight of LiCoO ₂ powder was mixed.

(Example 4)

LiMn ₂ O ₄ powder was carried out in the same manner as in Example 1 except for mixing 20 parts by weight with respect to 100 parts by weight of LiCoO ₂ powder.

(Example 5)

Except for mixing the LiMn ₂ O ₄ powder 10 parts by weight with respect to 100 parts by weight of LiCoO ₂ powder was carried out in the same manner as in Example 1.

(Comparative Example 1)

The same procedure as in Example 1 was carried out except that only LiMn ₂ O ₄ powder was used.

(Comparative Example 2)

The same procedure as in Example 1 was carried out except that only LiCoO ₂ powder was used.

An overcharge life test was performed using the lithium secondary batteries prepared in Examples 2 to 5 and Comparative Examples 1 to 2. After charging and discharging in the range of 4.5-2.75 V, charging / discharging evaluation of the battery was performed to evaluate the life characteristics of the battery. Table 1 shows discharge capacities and discharge voltages of the positive electrode active materials prepared by the methods of Examples 2 to 5 and Comparative Examples 1 to 2 of the battery.

division Overcharge Life Test Discharge Capacity (mAh / g) Safety test result Example 2 Bad 126 Not burst Example 3 Great 132 Not burst Example 4 Great 136 Not burst Example 5 Bad 139 Not burst Comparative Example 1 Bad 110 Not burst Comparative Example 2 Bad 142 rupture

As shown in Table 1, the mixed positive electrode active material of Examples 2 to 5 showed a discharge capacity similar to those of the positive electrode active materials of Comparative Examples 1 to 2, 20 to 30 parts by weight of lithium manganese based on 100 parts by weight of lithium cobalt-based oxide The discharge capacity of Example 3 and Example 4 using an oxide was particularly excellent.

In addition, as a result of testing the safety of the battery at 2C, it was confirmed that the lithium secondary battery using the mixed positive electrode active material of Examples 2 to 5 is safe without being ruptured by overcurrent. On the other hand, the battery using the positive electrode active material of Comparative Example 2, despite the excellent discharge capacity, burst (L5) occurred when an overcurrent was applied to the battery.

This is a stable life characteristics because it can prevent the rapid deterioration even when overcurrent is applied in the battery using a lithium manganese oxide.

As shown in Table 1, it can be seen that the battery using the cathode active materials of Examples 3 to 4 has excellent performance even during the progress of high voltage life.

Through the manufacturing method of the present invention, it is possible to manufacture a cathode active material for lithium secondary battery with improved overcharge characteristics and high voltage stability.

Claims (8)

A cathode active material for a lithium secondary battery containing lithium cobalt oxide and lithium manganese oxide. The cathode active material of claim 1, wherein the lithium cobalt oxide is a compound represented by Formula 1 below. [Formula 1] Li _x Co _1-y M _y A ₂ (Wherein, 1.0 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, and M is a transition metal selected from the group consisting of Ni, Al, Cr, Co, Mg, La, Ce, Sr and V) Or at least one metal of the lanthanide metal, and A is selected from the group consisting of O, F, S and P.) The cathode active material of claim 1, wherein the lithium manganese oxide is a compound represented by the following Chemical Formula 2 or 3. [Formula 2] Li _x Mn _1-y M _y O _2-z A _z [Formula 3] Li _x Mn _2-y M _y O _4-z A _z (Wherein, 1.0 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, and M is a transition metal selected from the group consisting of Ni, Al, Cr, Co, Mg, La, Ce, Sr and V) Or at least one metal of the lanthanide metal, and A is selected from the group consisting of O, F, S and P.) The cathode active material of claim 1, wherein the cathode active material comprises lithium manganese oxide in an amount of 10 to 50 parts by weight based on 100 parts by weight of the lithium cobalt oxide. A method for producing a cathode active material for a lithium secondary battery, comprising the step of mixing a lithium cobalt oxide and a lithium manganese oxide. The method of claim 5, wherein the lithium cobalt oxide is a compound represented by Chemical Formula 1 below. [Formula 1] Li _x Co _1-y M _y A ₂ (Wherein, 1.0 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, and M is a transition metal selected from the group consisting of Ni, Al, Cr, Co, Mg, La, Ce, Sr and V) Or at least one metal of the lanthanide metal, and A is selected from the group consisting of O, F, S and P.) The method of claim 5, wherein the lithium manganese oxide is a compound represented by Formula 2 or 3 below. [Formula 2] Li _x Mn _1-y M _y O _2-z A _z [Formula 3] Li _x Mn _2-y M _y O _4-z A _z (Wherein, 1.0 ≦ x ≦ 1.1, 0.01 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.5, and M is a transition metal selected from the group consisting of Ni, Al, Cr, Co, Mg, La, Ce, Sr and V) Or at least one metal of the lanthanide metal, and A is selected from the group consisting of O, F, S and P.) The method of claim 5, wherein the lithium manganese oxide is used in an amount of 10 to 50 parts by weight based on 100 parts by weight of the lithium cobalt oxide.