JP2002234796A - Method for synthesizing lithium cobaltate and method for growing its single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To synthesize lithium cobaltate (LiCoO2) from a molten state and to produce its single crystal. SOLUTION: Lithium cobaltate (LiCoO2) is synthesized from a melt obtained by meting a mixture containing lithium carbonate (LiCO3), cobalt oxide (Co2O3) and boron oxide (B2O3) in a molar ratio of LiCO3:Co2O3:B2O3 of (1+x):1:x, at a high temperature, and then LiCoO2 is crystallized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lithium cobalt oxide (LiCo
The present invention relates to a method for synthesizing O2) and a method for growing a lithium cobaltate (LiCoO2) single crystal that can be used also as a single crystal growth substrate.

[0002]

2. Description of the Related Art Lithium cobaltate (LiCoO2)
At present, is mainly used as a positive electrode active material of a lithium ion battery. In this case, as the lithium cobalt oxide (LiCoO2), it is general to use a ceramic powder, that is, a polycrystal obtained by a solid phase reaction such as baking a mixture of lithium carbonate and cobalt oxide at a high temperature.

[0003]

However, in the case of the solid-phase reaction, when the raw material powders are mixed unevenly, there is a possibility that Li and Co become uneven. Further, it is difficult to adjust the size of the granular system by the solid-phase reaction. Therefore, a method of synthesizing lithium cobalt oxide (LiCoO2) from a high-temperature molten state in which the raw materials are uniformly mixed can be considered, but there is no report on a specific method.

[0004] Further, a method for growing high-quality crystals has not been known. In general, large crystals of matter have a variety of uses. For example, a large single crystal of a substance can be used as a crystal growth substrate of a substance having a close lattice constant. Therefore, it is very useful to establish a single crystal growing method in consideration of a case where new industrially usable properties of lithium cobalt oxide are found in the future.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for producing lithium cobalt oxide from a melt in which a mixture of lithium carbonate Li2CO3, cobalt oxide Co2O3, and boron oxide B2O3 is melted at a high temperature. LiCo
O2) is crystallized to synthesize lithium cobalt oxide (LiCoO2). This is a crystallization from a melt in which the raw materials are mixed uniformly, and the uniformity of the constituent elements of lithium cobalt oxide is essentially higher than that obtained by synthesis by a solid-phase reaction. Further, according to the present invention, a lithium carbonate L
i2CO3, oxidation edge A single crystal of lithium cobaltate (LiCoO2) is grown by crystallizing lithium cobaltate (LiCoO2) from a melt in which the mixture is melted at a high temperature.

[0006]

According to the first aspect of the present invention, lithium cobalt oxide (LiCoO2) can be crystallized from the melt, and lithium cobalt oxide (LiCoO2) having high uniformity can be synthesized. According to the invention of claim 2, lithium cobalt oxide (LiCoO 2) is crystallized from the melt to grow a single crystal of lithium cobalt oxide (LiCoO 2), whereby a high quality lithium cobalt oxide (LiCoO 2) single crystal is obtained. Can be. Further, the flux and the single crystal can be easily separated.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

EXAMPLE Li melted at a high temperature and then cooled to room temperature
When the CoO 2 powder was analyzed by powder X-ray diffraction,
And Li2O2. That is,
It was confirmed that LiCoO2 was decomposed and melted. LiC
The so-called flux method is optimal as a method for synthesizing and further crystallizing oO2.

Hereinafter, a specific example of a method of melting a raw material powder at a high temperature using a solvent (flux), synthesizing and crystallizing LiCoO 2, and growing it as a single crystal will be described.

[0009] Weigh to 100 g and then mix until the whole is uniform. Solvent 25 g of the mixture resulting from the above mixing
Is placed in a platinum crucible (30 mmφ × 40 mm), and heated to 1070 ° C. in an electric furnace to be melted. At such a high temperature, the lithium carbonate Li2CO3 is decomposed like Li2CO3 → Li2O + CO2 (gas), and it is presumed that the melting is a mixture of Li2O, Co2O3, and B2O3.

After maintaining the molten state for 2 to 3 hours, it is gradually cooled at a cooling rate of 3 ° C./hr. After the temperature is lowered to 920 ° C., it is rapidly cooled to room temperature (25 ° C.) at a cooling rate of 190 ° C./hr. After reaching room temperature, it can be confirmed that the surface of the solidified mixture is uniformly covered with black plate-like crystals. The portion other than the crystals on the surface is a white solid, which corresponds to the solidified solvent (flux).
Since the specific gravity of the single crystal crystallized from the melt is smaller than the specific gravity of the melt, the crystal is crystallized and grown on the surface. Water (H20) is put into a crucible and boiled, whereby a white solid (flux) is half-dissolved in water, and the crystal and the white solid can be easily separated. The white solid is not very soluble in water and does not completely dissolve.
The crystal taken out of the crucible with tweezers slightly adheres to the white solid, but can be completely removed from the crystal by ultrasonic cleaning.

The size of the crystal on the flat plate thus obtained is 7 mm × 7 mm × 0.02 mm at maximum.
Typically, it is 3 mm × 3 mm × 0.02 mm. FIG. 1 shows a photograph of the single crystal. When several crystals were crushed and subjected to powder X-ray analysis, the diffraction pattern showed that the crystals were single-phase lithium cobalt oxide (LiCoO2), and the molar ratio of lithium carbonate Li2CO3, cobalt oxide Co2O3, and boron oxide B2O3 was It can be seen that lithium cobalt oxide (LiCoO 2) was synthesized from the melt obtained by melting the mixture mixed at (1 + x): 1: x at a high temperature, and further crystallized.

X in a plane perpendicular to the surface of the crystal on the plate
FIG. 2 shows an X-ray diffraction pattern by the 2Θ-Θ method obtained by injecting a line. Referring to FIG. 2, a peak corresponding to diffraction from the (003), (006), and (009) planes when a hexagonal unit cell is applied appears in the X-ray diffraction pattern. This result suggests that this single crystal is a very good single crystal in which the c-axes of the crystal axes are aligned. The fact that the single crystal is flat is a result of reflecting the layered hexagonal structure of lithium cobaltate. Since the layered material is difficult to grow in a direction perpendicular to the layer, a crystal on a flat plate is obtained. The ICP composition analysis shows that the ratio of lithium to cobalt is almost 1 to 1, further indicating that the single crystal is lithium cobalt oxide.

The crystal size can be easily controlled by increasing the cooling rate, the concentration of the solvent with respect to the solute, and the like. It is also possible to use LiCoO2 as a solvent (flux) and to make the molar ratio between LiCoO2 and LiBO2 1: x for the synthesis and crystal growth of LiCoO2. The present invention is not limited to the scope of the above-described embodiments, and various modifications can be made within the scope of the technical idea. For example, Li2O can be used instead of Li2CO3, and Co3O4 can be used instead of Co2O3. The present invention relates to LiNiO2, LiMn2
It can be easily conceived that the present invention can be applied to a positive electrode material of Li ion battery such as O4 or a crystal of a lithium transition metal oxide.

[Brief description of the drawings]

FIG. 1 is a photograph of a LiCoO2 single crystal obtained from a melt of Li2CO3, Co2O3, and B2O3.

FIG. 2 is an X-ray diffraction pattern of a LiCoO2 single crystal obtained from a melt of Li2CO3, Co2O3, and B2O3.

Claims (2)

[Claims] (1) The molar ratio of lithium carbonate Li2CO3, cobalt oxide Co2O3, and boron oxide B2O3 is (1+
x): Lithium cobaltate (LiCoO2) is crystallized from a melt obtained by dissolving a mixture mixed at 1: x at a high temperature, characterized in that lithium cobaltate (LiCoO2) is crystallized.
O2) Synthesis method. 2. The lithium carbonate Li2CO3, cobalt oxide Co2O3, and boron oxide B2O3 having a molar ratio of (1+
x): Lithium cobaltate (LiCoO2) is crystallized from a melt obtained by melting a mixture mixed at 1: x at a high temperature, characterized in that lithium cobaltate (LiCoO2) is crystallized.
O2) Single crystal growing method.