JP3101709B2 - Method for producing lithium manganese oxide thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a thin film mainly composed of LiMn ₂ O ₄ containing lithium and manganese as cations, which is useful as a secondary battery material, a separating agent and a catalyst.

[0002]

2. Description of the Related Art In recent years, manganese oxides have been applied in various fields and have become increasingly important as materials.
Research and development of manganese oxide as a functional material, such as a cathode material for a lithium-ion secondary battery as a small cordless power supply and a lithium-ion separator, is being conducted on a worldwide scale.

[0003] Among them, lithium manganate is particularly promising as a positive electrode active material for a secondary battery, and much research and development has been carried out. LiMnO ₂ , Li ₂ MnO ₃ , Li
Numerous production methods for producing Mn ₂ O ₄ powder by a heating method or a molten salt method have been proposed (for example, Strobel,
P. Levy, J .; P. Jobert, J .; C.
J. Crystal Growth 1984, 66, 2
57-261. ). Lithium manganate obtained by these methods is a single-crystal solid, and when used as a positive electrode material of a lithium secondary battery, these are formed into a pellet to form a positive electrode. However, when the positive electrode manufactured in this manner is used, a high-voltage power supply can be used, self-discharge is small, and storage stability is excellent, but there are problems in practical use such as a large current cannot be taken out. There is a point.

[0004]

In general, in order to obtain a large current as a secondary battery material, a thin film-shaped material is preferable as an electrode because of its large surface area. Less discharge, excellent storage,
It seems that a secondary battery capable of taking out a large current can be manufactured. Therefore, an object of the present invention is to provide an industrially advantageous production method that can easily produce a thin film containing LiMn ₂ O ₄ as a main component at a high yield, and does not require large-scale equipment and facilities. .

[0005]

Means for Solving the Problems The present inventors have proposed LiMn.
As a result of intensive studies to obtain a thin film lithium manganese oxide containing ₂ O ₄ as a main component, if a lithium compound and a magnesium compound are reacted at the gas-solid interface in the molten salt, lithium manganate in the molten salt In the process of the formation reaction of lithium, the lithium flux present at the interface gradually evaporates and is lost, resulting in manganese supersaturation, making it easy to form a lithium manganate thin film, and expanding two-dimensionally along the interface. That a thin film is obtained.
It has been found that a pure lithium manganate thin film can be separated by washing with water after the reaction to dissolve and remove the remaining lithium flux.

[0006] Since LiMn ₂ O ₄ crystal is a metastable phase, if heating is continued until a thin film is obtained, there is a problem that the composition changes. However, the present inventors have further studied. As a result, they have found that this problem can be solved by switching from an oxidizing atmosphere to a non-oxidizing atmosphere at the stage of growing LiMn ₂ O ₄ crystal particles into a thin film. The present invention has been made based on these findings.

That is, according to the present invention, a lithium compound and a manganese compound are heated and reacted in an oxidizing atmosphere in the presence of an evaporating lithium salt flux, so that LiM
After generating n ₂ O ₄ crystal particles, the crystal particles are grown in a thin film in a non-oxidizing atmosphere.
An object of the present invention is to provide a method for producing a lithium manganese oxide thin film containing iMn ₂ O ₄ as a main component.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of the present invention, as the lithium compound and the manganese compound used as raw material compounds, any of the known compounds used in the production of lithium manganate can be used. As such a lithium compound, lithium chloride, carbonate, bicarbonate, hydroxide and the like are preferable. As the manganese compound, manganese carbonate, oxyhydroxide, hydroxide, hydrated oxide, sulfate and the like are preferable. Are preferred. The mixing ratio of the lithium compound and the manganese compound is such that the molar ratio of lithium to manganese is usually 1: 0.2 to 1: 5, preferably 1: 0.
5 to 1: 2. These may be used alone or in combination of two or more.

In the method of the present invention, it is extremely important to use an evaporating flux to obtain a thin film of lithium manganese oxide. As such a flux, a flux containing lithium chloride or fluoride is preferable. They can also be used simultaneously as lithium compounds that react with manganese compounds. The amount of the flux to be added is usually 5 moles or more, preferably 5 to 20 moles, more preferably 10 to 10 moles per mole of the raw material manganese compound, for the purpose of dissolving the flux and accelerating the reaction. It may be added in an amount of 15 mol, but it depends on the shape of the reactor used and the heating temperature.

In order to produce a lithium manganese oxide thin film, a lithium compound, a manganese compound, and a flux are sufficiently mixed, and the mixture is heated while controlling a gas atmosphere. The heating temperature depends on the flux used, 400 ° C for chloride
As mentioned above, it is preferably 650 to 800 ° C. When a thin film is formed by heating, the product is washed with water, the flux is dissolved, and separated from the lithium manganese compound. By drying the separated thin film, a thin film lithium manganese compound containing LiMn ₂ O ₄ as a main component is obtained. This drying is
Usually, it is carried out at 70 ° C. or higher, preferably at 300 ° C. or higher.

In the method of the present invention, in order to obtain a thin film containing LiMn ₂ O ₄ as a main component, it is very important to control the atmosphere of the electric furnace during the heating process. LiMn ₂ O ₄
The process of forming a crystalline thin film can be divided into a step of first forming LiMn ₂ O ₄ crystal particles and a step of growing a film.
Since the reaction for producing LiMn ₂ O ₄ generally requires oxygen, it is necessary to set the electric furnace in an oxygen atmosphere at this stage. However, at the stage where the LiMn ₂ O ₄ crystal film grows, Li is used.
An oxygen atmosphere must be avoided to avoid the oxidation reaction of Mn ₂ O ₄ . The amount of air introduced at the stage of producing LiMn ₂ O ₄ crystal particles varies depending on the type and amount of reactants, but a stoichiometric value according to a chemical reaction formula is required at a minimum. Generally, the atmosphere is controlled by continuously flowing oxygen.
In this case, the amount of oxygen introduced depends on the flow rate and the size of the furnace, and generally 10 to 40 times the stoichiometric value is appropriate. For example, when MnOOH is used as a starting material, the amount of introduced air is 4000 to 5000 ml / g of starting material,
The rate of introduction ranges from 10 to 11 ml / min.
At the stage of growing the crystal film, the atmosphere needs to be non-oxidizing to avoid oxidation. However, when a non-oxidizing flux such as LiCl is used, no special protective atmosphere is required. This is because the vaporization of the flux causes the inside of the electric furnace to be filled with the flux of the flux, the partial pressure of oxygen decreases, and an oxygen atmosphere can be avoided. Further, the two stages of particle generation and film growth can also be advanced separately. That is, first, LiMn ₂ O ₄ crystal particles are prepared, and the LiMn ₂ O ₄ crystal particles can be used as a starting material for film growth in the second stage.

[0012]

According to the present invention, a thin film containing LiMn ₂ O ₄ as a main component can be produced at a high yield. According to the present invention, a high performance lithium secondary battery and an ion selective adsorbent can be manufactured.

[0013]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples.

Example 1 85 mmol of lithium chloride, manganese oxyhydroxide 11
The mixture was placed in a crucible having a diameter of about 80 mm, air was introduced at 10 ml / min in an electric furnace capable of adjusting the gas atmosphere, and heated at 700 ° C. for 8 hours. Thereafter, the introduction of air was stopped, the temperature was maintained at 700 ° C. for 4 days, and then the product was naturally cooled. After the heating is completed, the product is taken out and washed in a beaker, and further 10 times.
Dried at 0 ° C. The resulting product was a glossy black film having a thickness of 20 to 30 microns.
FIG. 1 shows an X-ray diffraction chart of the thin film. From this figure, (1)
11) It can be seen that the surface is a highly oriented LiMn ₂ O ₄ film. The molar ratio of Li / Mn determined by the atomic absorption method was 0.56, which almost coincided with the theoretical value.

Example 2 83 mmol of lithium chloride, 2 mmol of lithium hydroxide and 11 mmol of manganese oxyhydroxide were mixed well, and air was introduced at 10 ml / min and heated at 650 ° C. for 8 hours. Thereafter, the introduction of air was stopped and the temperature was maintained at 650 ° C. for 4 days. After the heating, the product was taken out, washed with water in a beaker, and further dried at 100 ° C. The resulting product was a glossy black film having a thickness of 20 to 30 microns. The X-ray diffraction chart of the thin film was similar to FIG. As a result, highly oriented Li is formed on the (111) plane.
It turns out that it is a Mn ₂ O ₄ film. Li determined by atomic absorption method
The / Mn molar ratio was 0.52, which almost coincided with the theoretical value.

Comparative Example 1 A reaction was carried out under the same conditions as in Example 1 except that lithium hydroxide having no volatility was used as a flux. No thin film was formed, and a mixture of powdered spinel type LiMn ₂ O ₄ and orthorhombic LiMnO ₂ was formed. From this result, it is understood that an evaporative flux is required for forming a thin film.

Comparative Example 2 The reaction was carried out under the same conditions as in Example 1 while continuously flowing air. The obtained film-like product showed a monoclinic Li ₂ MnO ₃ structure, and no spinel type LiMn ₂ O ₄ thin film was formed. From this result, it is understood that the atmosphere control of the electric furnace is necessary to produce the spinel type LiMn ₂ O ₄ thin film.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart of a lithium manganate crystal film.

Continuation of the front page (56) References JP-A-8-241707 (JP, A) JP-A-10-55797 (JP, A) JP-A-10-324521 (JP, A) JP-A-8-321325 (JP) , A) JP-A-2-183396 (JP, A) JP-A-8-507407 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 45/00 C30B 29/22 CA (STN)

Claims (1)

(57) [Claims] A lithium compound and a manganese compound are heated and reacted in an oxidizing atmosphere in the presence of an evaporating lithium salt flux to generate LiMn ₂ O ₄ crystal particles at an interface of the flux, and A method for producing a lithium manganese oxide thin film containing LiMn ₂ O ₄ as a main component, wherein the crystal particles are grown into a thin film in a non-oxidizing atmosphere.