JP3235098B2 - Lithium manganese composite oxide, method for producing the same and use thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a novel LiMn ₂ O ₄ , and more specifically, a minor axis diameter of 5 μm or less, a major axis diameter of 10 μm or less, and a height of 5 μm or less. The present invention relates to a LiMn ₂ O _{4 made of} needle-like crystals having an equivalent diameter and containing no β-MnO ₂ and Li ₂ CO ₃ , a method for producing the same, and its use.

In recent years, LiMn ₂ O ₄ has attracted attention as a positive electrode material for a lithium secondary battery.

[Prior art] Manganese dioxide having a spinel skeleton structure allows lithium ions to enter octahedral and tetrahedral positions,
In addition, passages through which lithium ions can move are three-dimensionally connected. Therefore, LiMn ₂ O having a spinel skeleton structure
₄ is capable of doping or undoping lithium ions into the crystal structure.

Due to this characteristic, LiMn ₂ O ₄ has recently attracted attention as a positive electrode material for lithium secondary batteries.

When LiMn ₂ O ₄ is used for the positive electrode of a lithium secondary battery, lithium ions are doped and de-doped in the crystal lattice as charge compensation at the time of performing electrochemical oxidation-reduction. It does not involve structural destruction of the crystal lattice. Therefore, since this reaction can be stably repeated, LiMn ₂ O
_{No. 4} is promising as a positive electrode material for secondary batteries, and its practical application is being studied.

For example, JP-A-63-187569 discloses that Mn ₂ O ₃ and Li ₂ CO ₃
Are mixed at a molar ratio of Li: Mn = 1: 2, and heated at 650 ° C. for 6 hours for 850 hours.
LiMn ₂ O ₄ obtained by calcination in air at 14 ° C. for 14 hours is used for the positive electrode. However, according to the studies by the present inventors, sufficient positive electrode performance has not been obtained. This is because the sintering reaction of the particles proceeds because the firing is performed at a high temperature for a long time, the particle diameter grows, the surface area decreases, and the efficiency of using battery energy decreases.

Several methods have been proposed to solve this problem.

In JP-A-63-218156, the aforementioned JP-A-63-187569 is described.
It is proposed that the LiMn ₂ O ₄ be rapidly cooled in water immediately after the completion of calcination by the method disclosed in Japanese Patent Application Laid-Open Publication No. H11-27139 to increase the surface area by pulverizing the crystal particles, thereby improving the utilization efficiency. However, in this method, the spinel structure in which Li ⁺ ions are easily diffused is distorted, and water is mixed therein, so that there is a problem in performance and storage stability.

On the other hand, Japanese Patent Application Laid-Open No. 2-139860 proposes a method in which manganese dioxide having a γ-type structure in which Li ⁺ ions are easily diffused is used as a starting manganese species and calcined at a low temperature of 430 ° C. to 510 ° C. in a short time. I have. This proposal aims at suppressing particle growth by firing at a low temperature for a short period of time and suppressing a decrease in surface area. However, according to the study of the present inventors, LiMn ₂ O ₄ obtained at this firing temperature, although a decrease in surface area is suppressed, the crystal lattice is reduced, and
The three-dimensional channel in which Li ⁺ ions diffuse is narrowed. Therefore, there is a problem that the overvoltage when used for the battery positive electrode increases and the utilization rate of the battery energy decreases.

[Problem to be Solved by the Invention] LiMn ₂ O ₄ proposed so far has insufficient electrochemical activity, and when this is used for a positive electrode, a non-aqueous lithium secondary battery having excellent cycle characteristics. Constructing
Have difficulty.

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, produced LiMn ₂ O ₄ by firing a mixture of a manganese oxide and a lithium material. In the method, the manganese oxide has a minor axis diameter of 1 μm or less, a major axis diameter of 5 μm or less, and a height of 1 μm or less. By baking, the particle growth is suppressed, consisting of needle-like particles having a minor axis diameter of 5 μm or less, a major axis diameter of 10 μm or less, and an equivalent diameter of 5 μm or less, high surface area, electrochemical It has been found that highly active LiMn ₂ O ₄ (hereinafter abbreviated as needle-like LiMn ₂ O ₄ ) can be synthesized. Further, they have found that a lithium secondary battery having a high cycle discharge capacity can be constructed by using this as a positive electrode of a non-aqueous lithium secondary battery using lithium or a lithium alloy as a negative electrode and a non-aqueous electrolyte as an electrolyte. Was completed.

The equivalent diameter used by the present inventors is the definition of Heywood, in which one particle is stably stood on a horizontal plane, and the shape of the particle is indicated by the lengths of axes in three directions orthogonal to each other. (See Yasuo Arai, Material Chemistry of Powder, Baifukan).

 Hereinafter, the present invention will be described specifically.

[Action] Firing a mixture of manganese oxide and lithium material
In the method for producing LiMn ₂ O _4, the use of acicular hydrated manganese oxide or acicular β-manganese dioxide significantly suppresses particle growth. Although the mechanism is not clear, it is considered as follows.

The needle-shaped hydrated manganese oxide used in the present invention easily transforms to β-type manganese dioxide having a rutile crystal structure at a temperature of 300 ° C. or more in the presence of oxygen. Since this transition occurs easily and quickly, the particle shape keeps acicular particles. Therefore, the obtained manganese dioxide becomes β-type manganese dioxide having a high surface area, and the reactivity when reacting with a lithium compound is increased. Further, manganese dioxide having a β-type crystal structure has a (1 × 1) channel structure and a diffusion path for lithium into the crystal is secured. It proceeds easily, and LiMn ₂ O ₄ having a uniform composition is easily generated. Regarding the thermal phase transition of manganese oxide during firing, MMThackeray et al. Reported that the transition from the rutile structure to the spinel skeleton structure was very rapid (Revue De Chimie Minerale 21 , 55 (1984)). This indicates that the firing reaction proceeds easily. Therefore, from the synergistic effect described above, the reaction proceeds without excess lithium remaining on the surface of the manganese dioxide particles, LiMn ₂ O ₄ having a uniform composition is generated, and the surface of the lithium and manganese dioxide containing excessive lithium is formed on the surface. Composite oxide,
For example, a composite oxide having low battery activity such as Li ₂ MnO ₃ is not generated.

Furthermore, under the condition that the lithium concentration on the surface of manganese dioxide and the inside thereof is uniform as in the present invention, the particle growth due to excessive lithium is suppressed, and the surface area and the electrochemical surface of the starting manganese species are kept high while maintaining the acicular particle shape. Highly active LiMn ₂ O
_It is thought that ₄ is obtained.

Even when the starting manganese species is acicular β-manganese dioxide, the same effect as when the acicular hydrated manganese oxide is used appears.

Acicular hydrated manganese oxide used in the present invention is, for example, Ow
en Bricker reported a method of oxidizing manganese hydroxide (Mn (OH) ₂ ) with hydrogen peroxide (H ₂ O ₂ ) (The American Mineralogist vol. 50, 1296P (196
5)) and the method reported by K. Matsuki et al.
A method of adding ammonia (NH ₄ OH) to a mixed solution of manganese sulfate (MnSO ₄ ) and hydrogen peroxide at a temperature of less than ℃ (Electro
chimica Acta vol. 31, 13P (1986)).

The acicular β-manganese dioxide used in the present invention is disclosed in
It can be produced using the method disclosed in Japanese Patent No. 30323.

The lithium material used in the production of LiMn ₂ O ₄ of the present invention is not particularly limited, and any lithium metal and / or lithium compound may be used. Examples thereof include lithium metal, lithium hydroxide, lithium oxide, lithium carbonate, lithium iodide, lithium nitrate, lithium oxalate, and lithium alkyl.

The method of mixing the lithium material and the manganese oxide is not particularly limited, and the mixing may be performed in a solid phase and / or a liquid phase. For example, a method of mixing a lithium material and a powder of manganese oxide in a dry and / or wet manner, a method of adding a manganese oxide to a solution in which a lithium material is dissolved and / or suspended, and mixing the mixture by stirring. Is exemplified.

In the present invention, the firing needs to be performed at a temperature of 650 ° C. or higher. Below this temperature, the reaction does not proceed sufficiently, and LiMn ₂ O ₄ having a uniform composition cannot be obtained.

Further, when hydrated manganese oxide is used in the firing, the firing needs to be performed in the presence of oxygen. Hydrated manganese oxide is in the presence of oxygen to thermal phase transition to β-type manganese dioxide at 300 ° C. or higher, transition manganese oxide of lower oxidation state of Mn ₅ O ₈ and Mn ₃ O ₄ under an inert gas atmosphere Therefore, it is difficult to obtain desired LiMn ₂ O ₄ .

On the other hand, when β manganese dioxide is used, the firing atmosphere is not particularly limited.

As the negative electrode of the nonaqueous lithium secondary battery of the present invention, lithium metal or lithium alloy can be used. Examples of the lithium alloy include a lithium / tin alloy and a lithium / lead alloy.

Further, the electrolyte of the non-aqueous lithium secondary battery of the present invention is not particularly limited. For example, carbonates, sulfolane, lactones, those obtained by dissolving a lithium salt in an organic solvent such as ethers, and lithium ion conductive Solid electrolyte can be used.

Using the LiMn ₂ O ₄ obtained in the present invention, a battery shown in FIG. 1 was constructed. In the figure, 1: Lead wire for positive electrode, 2: Mesh for positive electrode current collector, 3: Positive electrode 4: Separator, 5: Negative electrode, 6: Mesh for negative electrode current collector, 7: Lead wire for negative electrode, 8: Container Is shown.

[Examples] Examples will be described below, but the present invention is not limited thereto.

Example 1 [Preparation of LiMn ₂ O ₄ ] As Example 1, LiMn ₂ O ₄ was produced as follows.

Commercially available acicular hydrated manganese oxide having an equivalent diameter of 1 μm or less, a major axis diameter of 5 μm or less, and a height of 1 μm or less (manufactured by Tosoh Corporation; After 44 g of lithium oxide and 3.75 g of lithium oxide were mixed in a mortar, the temperature was raised from room temperature to 850 ° C. at a rate of 10 ° C./min in an air atmosphere, followed by firing. From the results of X-ray diffraction and chemical composition analysis of the obtained compound shown in FIG. 2 and Table 1, this compound was identified to be LiMn ₂ O ₄ . Further, as a result of SEM observation shown in FIG. 3 (A), it was found that the particle shape was a needle-like particle having an equivalent diameter of 5 μm or less in major axis, 10 μm or less in major axis, and 5 μm or less in height. .

[Configuration of Battery] The obtained LiMn ₂ O ₄ , carbon powder of a conductive material and polytetrafluoroethylene powder of a binder were mixed at a weight ratio of 88: 9: 3.
At a rate of 75 mg of this mixture at a pressure of 5 ton / cm ²
It was molded into 8 mmφ pellets. This was used as the positive electrode in FIG. 3, and the negative electrode in FIG.
m), lithium electrolyte was mixed with propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 1 by mixing lithium perchlorate with 1 mol
The electrolytic solution dissolved at a l / dm ³ concentration was impregnated into the separator shown in FIG. 4 to use the battery shown in FIG. 1 having a cross-sectional area of 0.5 cm ² .

[Evaluation of Battery Performance] Using the battery prepared by the above method, charging and discharging were repeated at a constant current of 5 mA and a battery voltage in a range of 2 V to 4 V. The results are shown in FIG. The discharge capacity at the 50th cycle is
About 90% of the discharge capacity in the first cycle was maintained.

Example 2 In Example 2, an acicular β-manganese dioxide having a minor axis diameter of 1 μm or less, a major axis diameter of 5 μm or less, and an equivalent diameter of 1 μm or less was used as a starting manganese species. The acicular β-manganese dioxide was prepared by the following method. 100 g of commercially available acicular hydrated manganese oxide (manufactured by Tosoh Corporation, hydrated manganese oxide) and 10 ml of concentrated nitric acid (specific gravity: 1.3) were mixed and heat-treated at a temperature of 200 ° C. for 8 hours. The product was crushed in a mortar and washed with hot water. The product was identified as β-manganese dioxide from the X-ray diffraction shown in FIG. Further, from the result of the SEM observation shown in FIG. 6, the particle shape of the product has a minor axis diameter of 1 μm or less,
Needle-like particles having an equivalent diameter of 5 μm or less in major axis and 1 μm or less in height.

Next, LiMn ₂ O ₄ was prepared in the same manner as in Example 1 except that 43.5 g of the obtained acicular β-manganese dioxide was used. From the results of X-ray diffraction and chemical composition analysis shown in FIG. 2 and Table 1, the obtained compound was identified to be LiMn ₂ O ₄ . Also, from the results of the SEM observation shown in FIG. 3 (B), the obtained LiMn ₂ O ₄ particle shape has a minor axis diameter of 5 μm or less, a major axis diameter of 10 μm or less,
Needle-like particles having an equivalent diameter of 5 μm or less in height.
Example 1 was repeated except that this was used for the positive electrode in FIG.
A battery similar to that shown in FIG. 1 was prepared. As a result of the battery characteristic evaluation shown in FIG. 4, the discharge capacity at the 50th cycle was maintained at about 80% of the discharge capacity at the first cycle.

Comparative Example 1 As Comparative Example 1, manganese dioxide was mixed with 43.5 g of commercially available electrolytic manganese dioxide (spherical particles, γ-type crystal structure) and 3.75 g of lithium oxide in a mortar. This mixture was baked at 850 ° C. for 20 hours in an oxygen atmosphere. The compound was identified to be LiMn ₂ O ₄ from the result of X-ray diffraction. In addition, SEM
Observation revealed that the particle shape was spherical and the particle size was about 50 μm. Further, this was used for the positive electrode of FIG.
1 and the battery characteristics were evaluated. As a result, as shown in FIG. 4, the discharge capacity at the 50th cycle was:
Only about 30% of the discharge capacity of the first cycle was retained.

[Effects of the Invention] As described above, the method of the present invention suppresses particle growth, and acicular particles having a minor axis diameter of 5 µm or less, a major axis diameter of 10 µm or less, and a height of 5 µm or less. And high surface area LiMn free of β-MnO ₂ and Li ₂ CO _3
2 O ₄ can be manufactured, and this is used for the positive electrode of non-aqueous lithium secondary batteries using lithium or lithium alloy for the negative electrode and non-aqueous electrolyte for the electrolyte. Can be configured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the batteries prepared in Example 1, Example 2, and Comparative Example 1. In the figure, 1: positive electrode lead wire, 2: positive electrode current collecting mesh 3: positive electrode, 4: separator 5: negative electrode, 6: negative electrode current collecting mesh 7: negative electrode lead wire, 8: container. FIG. 2 shows LiMn used for the positive electrode in Examples 1 and 2.
₂ shows an X-ray diffraction diagram of ₂ O ₄ . FIG. 3 shows the particle structure of LiMn ₂ O ₄ prepared in Example 1 (A) and Example 2 (B). FIG. 4 shows battery characteristic evaluation results of the batteries prepared in Example 1, Example 2, and Comparative Example 1. FIG. 5 shows an X-ray diffraction diagram of the acicular β-manganese dioxide prepared in Example 2. FIG. 6 shows the particle structure of acicular β-manganese dioxide prepared in Example 2.

(56) References JP-A-63-187569 (JP, A) JP-A-3-245839 (JP, A) JP-A-2-139860 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) C01G 45/00 H01M 4/58 CA (STN)

Claims (4)

(57) [Claims] 1. LiMn ₂ O comprising a needle-like particle having a minor axis diameter of 5 μm or less, a major axis diameter of 10 μm or less and a height of 5 μm or less, and not containing β-MnO ₂ and Li ₂ CO _{3. 4} . 2. A method for producing LiMn ₂ O ₄ by using a mixture of a manganese oxide and a lithium material, wherein the manganese oxide has a minor axis diameter of 1 μm or less, a major axis diameter of 5 μm or less, and a height of 1 μm. _{2. The} method for producing LiMn ₂ O _{4 according to} claim 1, wherein the calcination is performed at 650 ° C. or higher using needle-like hydrated manganese oxide (MnOOH) having the following equivalent diameter. 3. A method for producing LiMn ₂ O ₄ by firing a mixture of a manganese oxide and a lithium material, wherein the manganese oxide has a minor axis diameter of 1 μm or less, a major axis diameter of 5 μm or less, and a height of 1 μm. _{2. The} method for producing LiMn ₂ O _{4 according to} claim 1, wherein firing is performed at 650 ° C. or higher using acicular β-manganese dioxide having the following equivalent diameter. 4. A non-aqueous lithium secondary battery using lithium or a lithium alloy for a negative electrode and a non-aqueous electrolyte for an electrolyte, wherein the LiMn ₂ O _{4 according to} claim 1 is used for a positive electrode.
A non-aqueous lithium secondary battery characterized by using: