JP2952352B1 - Method for producing lithium cobaltate for secondary battery - Google Patents

Abstract

Kind Code: A1 Abstract: A method for efficiently producing lithium cobalt oxide, which is crystal-grown particularly in a layer direction and has a stable crystallinity and is suitable as a cathode material for a lithium ion secondary battery, is provided. SOLUTION: In the presence of a lithium-based flux, a lithium compound and a cobalt compound are mixed in an oxygen atmosphere at 400 to 80%.
By heating at a temperature of 0 ° C. to cause a reaction, lithium cobaltate is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a stable crystalline lithium cobaltate which is suitable as a positive electrode material for a secondary battery, in particular, a crystal in which a crystal grows well in a layer direction.

[0002]

2. Description of the Related Art In recent years, notebook computers, video cameras,
Portable devices such as mobile phones and PHS (simplified mobile phones) are rapidly growing, and demand for secondary batteries such as nickel cadmium batteries, lithium ion batteries, and nickel metal hydride batteries is growing rapidly. ing. Each of these three types of secondary batteries has advantages and disadvantages. Among them, lithium ion batteries and nickel hydrogen batteries have particularly remarkable growth.

[0003] Lithium-ion batteries generally have a volume energy density and a weight energy density of about 1.5 to 2 times the characteristics of conventionally used nickel cadmium batteries, and have an output corresponding to about 3 times. It has excellent features such as shown.

In this lithium ion battery, lithium cobalt oxide (LiCoO) is generally used as a cathode material.
O ₂ ) uses lithium metal or the like as a negative electrode material, but when lithium cobalt oxide is used as a positive electrode material,
The theoretical capacity is 274 mAh / g, but the practical capacity is usually about 110 to 120 mAh / g because it is used in a range where no phase change occurs during charging and discharging.

In a lithium ion secondary battery, it is known that the specific surface area of the positive electrode material is an important factor for determining the discharge capacity. As the specific surface area of the positive electrode material increases, the reaction area of the battery increases. Since the size is large, the movement of ions is performed smoothly, and a decrease in capacity with respect to heavy load and discharge is reduced.

[0006] Lithium cobalt oxide generally has a layered rock salt structure, and when used as a positive electrode material of a lithium ion secondary battery, a large discharge capacity and stable charge / discharge cycle characteristics are required to obtain good charge / discharge cycle characteristics. It is desirable that the crystal have good crystallinity and that the crystal grows particularly well in the layer direction.

[0007]

SUMMARY OF THE INVENTION Under such circumstances, the present invention provides lithium cobalt oxide which is particularly suitable as a positive electrode material for a lithium ion secondary battery having stable crystallinity grown in the layer direction. The purpose of the present invention is to provide a method for efficiently manufacturing.

[0008]

The present inventors have conducted intensive studies on a method for producing lithium cobalt oxide having excellent crystallinity, and as a result, have found that a cobalt compound can be produced in the presence of a specific lithium-based flux. By heating at a specific temperature in an oxygen atmosphere and performing a melting reaction, it has been found that crystals grow well in the layer direction, and lithium cobalt oxide having stable crystallinity can be obtained. It was completed.

That is, the present invention provides a method for producing a cobalt compound
A method for producing lithium cobalt oxide for a secondary battery, comprising heating in an oxygen atmosphere at a temperature of 400 to 800 ° C. in the presence of a lithium flux having reactivity with the cobalt compound to cause a melting reaction. To provide.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The cobalt compound used in the method of the present invention is appropriately selected from conventionally known compounds such as carbonates, oxyhydroxides, hydroxides, hydrated oxides and sulfates. Can be used without any particular limitation. These cobalt compounds are usually used alone, but may be used in combination of two or more if desired.

The lithium-based flux used in the method of the present invention is not particularly limited as long as it melts at the reaction temperature and simultaneously reacts with the cobalt compound. preferable.

This lithium-based flux is usually used alone, but if desired, two or more kinds may be used in combination. The amount used varies depending on the shape of the reactor used, the heating temperature, etc., but from the viewpoint of melting the flux and accelerating the reaction, with respect to 1 mol of the cobalt compound,
It is usually selected in a range of 10 mol or more, preferably 10 to 30 mol.

Next, a preferred embodiment of the method of the present invention will be described. First, a cobalt compound and a lithium-based flux are mixed at a predetermined ratio so as to be sufficiently homogeneous, and then heated and melted in an oxygen atmosphere. I do. The heating temperature is
The temperature is selected within the range of 400 to 800 ° C., but may be appropriately selected within the above range according to the type of the flux used. When the flux is a chloride of lithium, the range of 600 to 750C is particularly preferable. When the temperature is lower than 400 ° C., the flux does not melt, and the reaction hardly proceeds. If the temperature is higher than 800 ° C., cobalt oxide is formed, which is not preferable. Examples of the oxygen atmosphere include an oxygen gas, a mixture of an oxygen gas and an inert gas such as nitrogen or argon, or an atmosphere composed of air or the like.

After completion of the reaction, water is added to the reaction product to dissolve the lithium-based flux, followed by solid-liquid separation by a known means such as filtration, centrifugation, decantation, and the like. By performing a drying treatment, a desired lithium cobalt oxide can be obtained. The drying process is
It is usually good to carry out at a temperature of 70 ° C. or higher, preferably 100 ° C. or higher.

In this way, a lithium cobalt oxide having stable crystallinity and having a crystal grown particularly in the layer direction can be obtained. This crystal form can be confirmed by X-ray diffraction. Lithium cobaltate obtained by the method of the present invention has the above-mentioned excellent crystal morphology, and thus is suitably used as a positive electrode material for a lithium ion secondary battery.

[0016]

According to the method of the present invention, lithium cobalt oxide, which has stable and good crystallinity and is particularly suitable as a cathode material for a lithium ion secondary battery, in which crystals grow well in the layer direction, It can be manufactured efficiently.

[0017]

Next, the present invention will be described in more detail by way of examples.

EXAMPLE A mixture of 214 mmol of lithium chloride and 11 mmol of cobalt hydroxide was thoroughly mixed, and placed in a crucible having a diameter of about 80 mm.
The mixture was heated at 650 ° C. for 4 days in an electric furnace while introducing air at a rate of 400 ml / min, and reacted in a molten state. After the heating, the reaction product was taken out, washed well with water in a beaker, and then the solid was collected by filtration and further dried at 100 ° C. to obtain a black powder. This powder was subjected to X-ray diffraction. FIG. 1 shows this X-ray diffraction chart. From this chart, it is clear that the (003) plane is developed. The composition determined by the atomic absorption method was Li _0.88 CoO _2.0 .

Next, in a lithium ion secondary battery,
A cell was prepared using the lithium cobaltate obtained above as a positive electrode and lithium metal as a negative electrode, and a constant current of 0.5 mA / c.
A charge / discharge test was performed at m ² , 4.3 to 3.0 V. FIGS. 2 and 3 show the first charge / discharge curve and the cycle characteristics from the first time to the seventh time, respectively. The first discharge capacity is a high value of 156 mAh / g. Also, x = 0.5
In this case, the discharge capacity could be calculated to be 135 mAh / g, which almost coincided with the theoretical value (137 mAh / g). 7
The Coulomb efficiency of charge and discharge up to the second time showed a high value of 98% or more.

Comparative Example 214 mmol of lithium chloride and 11 mmol of cobalt hydroxide were mixed well, placed in a crucible having a diameter of about 80 mm, and introduced at 850 ° C. in an electric furnace while introducing air at a rate of 400 ml / min. Heat treatment was performed for days. After heating, take out the reaction product and wash it well in a beaker.
The solid was collected by filtration and further dried at 100 ° C. FIG. 4 shows an X-ray diffraction chart of the obtained product. It can be seen that lithium cobaltate was not obtained and Co ₂ O ₃ and CoO were generated.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart of one example of lithium cobaltate obtained by the method of the present invention.

FIG. 2 is a graph showing one example of a charge / discharge curve when lithium cobaltate obtained by the method of the present invention is used for a positive electrode of a lithium ion secondary battery.

FIG. 3 is a graph showing an example of cycle characteristics when lithium cobaltate obtained by the method of the present invention is used for a positive electrode of a lithium ion secondary battery.

FIG. 4 is an X-ray diffraction chart of a cobalt oxide obtained in a comparative example.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-64928 (JP, A) JP-A-10-312805 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 51/00 H01M 4/02 H01M 10/40 H01M 4/58

Claims (2)

(57) [Claims] 1. A secondary compound characterized by heating a cobalt compound at a temperature of 400 to 800 ° C. in an oxygen atmosphere in the presence of a lithium-based flux reactive with the cobalt compound to cause a melting reaction. A method for producing lithium cobaltate for a battery. 2. The method according to claim 1, wherein the lithium flux is a chloride or hydroxide of lithium or a mixture thereof.