JP2002053321A - Lithium manganese multiple oxide, its manufacturing method and use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain lithium manganese multiple oxide having a cluster particle form and a dense and uniform composition excellent in packing property as an electrode active material, to provide a method for manifesturing the oxide at a low cost without processes of pulverization or repeated heat treatment, to obtain a positive electrode material by using the lithium manganese multiple oxide, and to provide a high-performance lithium secondary cell by using the positive electrode active material. SOLUTION: The lithium manganese multiple oxide has a secondary particle form prepared by aggregating almost spheric primary particles essentially comprising LiMn2O4 into clusters. The median diameter of the secondary particle form ranges from 1 to 100 μm and the specific surface area is 0.1 to 10 m2/g. The obtained particles are used as the positive electrode active material to manufacture a lithium secondary cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium manganese composite oxide useful as an active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art Lithium manganate, which is a lithium-manganese composite oxide, is represented by a general formula Li _x Mn _Y O ₄ , and a typical example is LiMn ₂ O ₄ having a spinel structure.
This LiMn ₂ O ₄ has a reserve of C as a resource of the raw material Mn.
Therefore, it is attracting attention as an inexpensive positive electrode material for lithium secondary batteries because it is more than o.

[0003] LiMn ₂ O ₄ having a spinel structure has a lower theoretical density and a lower theoretical electric capacity than lithium cobalt oxide or lithium nickel oxide having a layered structure. In this respect, the active material of the high capacity battery is disadvantageous as compared with lithium cobalt oxide and lithium nickel oxide. Therefore, in order to improve the filling property of LiMn ₂ O ₄ , dense manganese oxide has been used as a synthesis raw material. However,
In general, in synthesis by a solid phase reaction, it is considered advantageous to use a fine raw material that is not dense in order to obtain a synthesized product having a uniform composition.

From such a viewpoint, in the synthesis of LiMn ₂ O ₄ , a dense and large-particle manganese compound is used as a raw material, and heat treatment and mechanical pulverization are repeated to obtain LiMn ₂ having a high filling property and a uniform composition. A method for obtaining O ₄ has been used (for example, Japanese Patent Application Laid-Open No. Hei 8-29221).

[0005] However, lithium manganate obtained by the conventional manufacturing method has a non-uniform shape, and has poor fluidity, making it difficult to obtain a dense LiMn ₂ O ₄ electrode layer.
In addition, handling at the time of mixing with a conductive agent or a binder at the time of manufacturing an electrode is poor, and uniform mixing is difficult.

[0006] On the other hand, LiMn ₂ O ₄ has problems such as poor cycle characteristics considered to be caused by the phase transition due to the Jahn-Teller effect of Mn ³⁺ and elution of Mn into an electrolyte at a high temperature. For the purpose of improvement, substitution of Mn with a different element has been proposed (for example, JP-A-11-71115).

[0007] Dissimilar element-substituted lithium manganate suppresses Jahn-Teller distortion and reduces the amount of Mn eluted to improve cycle characteristics. For this purpose, a more uniform composition is required.

[0008]

DISCLOSURE OF THE INVENTION The present invention relates to a lithium manganese composite oxide having a fine and uniform composition having excellent filling properties and having a grape-like particle shape as an electrode active material. It is an object of the present invention to provide a low-cost production method without a process, a positive electrode active material using the lithium-manganese composite oxide, and a high-performance lithium secondary battery using the positive electrode active material.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and have found that γ-MnO ₂ and manganese dioxide, which are generally used as a raw material for synthesizing LiMn ₂ O ₄ , have been obtained. Instead of Mn ₂ O ₃ obtained by heat treatment, the specific surface area is 100 to 300 m ² / g and the average secondary particle diameter is 5
Ε-MnO ₂ having a grape-like particle shape of 0 μm or less
And, mixed with a water-soluble lithium compound, lithium manganese composite oxide formed by a specific method forms secondary particles having a specific shape and dimensions, such a grape-like lithium having a specific particle size A manganese composite oxide is excellent in operability at the time of electrode preparation, and a non-aqueous solvent-based lithium secondary battery using the lithium manganese composite oxide is excellent in charge and discharge.
The present inventors have found that they exhibit discharge characteristics, and have completed the present invention.

That is, the lithium manganese composite oxide of the present invention has a main component of LiMn ₂ O ₄ and has a secondary particle shape obtained by assembling a substantially spherical primary particle shape into a grape cluster. Particle diameter is 1 to 100 μm, specific surface area is 0.1
-10 m ² / g. In the lithium manganese composite oxide of the present invention, it is preferable that the primary particle diameter is around 0.1 to 0.2 μm.

Further, the production method of the present invention comprises a crystal form ε-MnO ₂ by X-ray diffraction as a main component and a specific surface area of 100%.
~300m ² / g, the molar ratio of the ε- manganese dioxide having the following grape bunch shaped secondary particle shape particle diameter 50 [mu] m, and a water-soluble lithium compound Li / Mn from .50 to .60
And a step of drying the mixed solution so as to maintain the particle shape of the lithium-manganese composite oxide, and then performing a heat treatment at 500 to 900 ° C.

Also, a battery positive electrode having excellent charge / discharge characteristics can be manufactured by using the lithium manganese composite oxide according to the present invention as a positive electrode active material.

Further, a lithium secondary battery can be manufactured using the positive electrode active material. In the case of a coin battery, the initial discharge capacity is at least 120 mAh / g or more.
Alternatively, a non-aqueous solvent-based lithium ion secondary battery having a discharge capacity maintenance ratio at the 20th cycle of 80% or more can be manufactured.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The chemical composition of the lithium manganese composite oxide of the present invention is characterized in that the main component is composed of LiMn ₂ O ₄ . JCPDS (Joint committee on powder diff)
raction standards): No. It suffices if it matches or is equal to LiMn ₂ O ₄ shown in 35-782.

In the lithium manganese composite oxide of the present invention, the main component is the above-mentioned LiMn ₂ O ₄ , and the form is 1 μm.
Fine primary particles less than m form aggregate units having a secondary particle diameter (median diameter) of 1 to 100 μm. By observing this with an electron microscope or the like, it can be seen that each of the primary particles has an appropriate grape cluster-like bonding state in which the particles are uniform even in the secondary particle shape, which is an aggregate, while maintaining a uniform substantially spherical shape. In other words, the primary particles having a uniform particle size are gathered in an appropriate number, so that the secondary particles have a uniform particle size with a good particle size distribution and a uniform and natural tuft shape. The primary particles serving as the basis of this tuft shape have a particle size (median diameter) of 0.1 to
Fine particles having a particle size of about 0.2 μm are preferable. Due to such a bunched form, when used as a positive electrode active material for a battery, the active material has excellent filling properties and is denser than conventional particles having irregular particle shapes and particle diameters (primary particles or secondary particles). Layers can be formed. Also, the handling is good, and the mixing with the conductive agent and the binder becomes uniform. The improvement of the filling property and the handling mainly contributes to having a secondary particle diameter having a good particle size distribution and a grape-like shape.

Furthermore, in order to minimize the elution of Mn in the object and high temperature to form a dense active material layer, and a specific surface area of 0.1 to 10 m ² / g selfishness, 0.1~5.0m ² /
g is more preferred. The lithium manganese composite oxide having a grape-like secondary particle diameter and a small specific surface area according to the present invention has a large charge / discharge capacity when used as a battery active material, and can provide a secondary battery having excellent cycle characteristics. Secondary particle size is 1
１００100 μm, but the distribution range is narrow and 1
More preferably, it is distributed in a range of 70 μm.

In the method for producing a lithium manganese composite oxide according to the present invention, ε-manganese dioxide having a specific particle shape and a water-soluble lithium compound are wet-mixed at a predetermined ratio, and the mixture is mixed with the manganese dioxide as a raw material. After drying while maintaining the grain shape, heat treatment is performed.

The ε-manganese dioxide is obtained by X-ray diffraction.
Is ε-MnO_TwoAnd specifically, X-ray diffraction
The peak in the figure is JCPDS: No. Shown at 30-820
Ε-MnO_TwoShould be equal to or equal to Toes
Thus, the production method of the present invention uses the conventional LiMn_TwoO_FourSynthetic raw materials and
Γ by electrolytic synthesis method and chemical synthesis method used as
-MnO_TwoHeat manganese dioxide at temperatures above 550 ° C
Mn obtained by treatment_TwoO _ThreeIs not a raw material.

The ε-manganese dioxide has a specific surface area of 100 to 300 m ² / g, preferably 150 to 20 m ² / g.
0 m ² / g, and the average secondary particle size is 50 μm or less, preferably 30 μm or less. Specific surface area is 100m ² / g
If it is less than 1, a non-uniform portion may be generated during wet mixing with a water-soluble lithium compound, and the shape of the produced LiMn ₂ O ₄ may not be maintained in a grape-like state, and the lithium-manganese composite oxide having a uniform composition as the object of the present invention may have. I can't get things. On the other hand, if the specific surface area exceeds 300 m ² / g, it becomes difficult to handle due to scattering or the like, which is not preferable in production. In addition, when an average secondary particle size exceeding 50 μm is used, sedimentation and separation of the manganese compound do not occur in the water slurry.
This requires an intense stirring or grinding step, which is not preferable.

The above-mentioned ε-manganese dioxide is typically produced by passing ozone gas containing oxygen through an aqueous manganese sulfate solution.
A precipitate can be produced by oxidizing n ions, and the precipitate is filtered, washed with water, and dried.

Examples of the water-soluble lithium compound used in the present invention include lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate and the like, and lithium hydroxide or lithium hydroxide monohydrate having high solubility in water. Salts are more preferred.

The mixing ratio of the ε-manganese dioxide and the water-soluble lithium compound is 0.50 to 0.5% in molar ratio of Li / Mn.
0.60, preferably 0.51 to 0.55. If it is less than 0.50, the charge / discharge capacity of a lithium secondary battery is greatly deteriorated by cycle, and good battery characteristics are not exhibited. The reason for this is considered to be that Li acts as the third component as reported in the improvement of the cycle characteristics by the addition of the third component. When the molar ratio of Li / Mn is greater than 0.60, products other than LiMn ₂ O ₄ , for example, Li ₂ MnO ₃ are formed, and the pure content of LiMn ₂ O ₄ is reduced, which causes a reduction in battery capacity. Is not preferred.

The slurry concentration of the wet mixture is 0.48 to 4.8 mol / L for the Li raw material and 0.50 to 1 for the Mn raw material.
It may be 0.0 mol / L. If the concentration is higher than the above range, a strong stirring force is required for uniform mixing. Further, it is not preferable because it causes a trouble of a pipe clogging during drying. If the concentration is lower than the above range, the amount of evaporated water increases, and the drying cost undesirably increases.

As the drying method, spray drying, fluidized bed drying, tumbling granulation drying, or freeze drying can be used alone or in combination. The dried product is heat-treated in the atmosphere. Heat treatment is 5
One heat treatment may be performed at a temperature of 00 to 1000 ° C, but more preferably 700 to 850 ° C. If the temperature is lower than 500 ° C., the reaction between the manganese compound and the lithium compound is not sufficient.
If the temperature exceeds 1000 ° C., sintering occurs and the secondary particle shape of the present invention cannot be maintained, resulting in poor battery characteristics.

When the lithium manganese composite oxide synthesized as described above is used as a positive electrode active material to form a positive electrode for a battery, and a lithium battery is manufactured using Li metal as a negative electrode, as described later, charge and discharge are performed as described below. Voltage is 3.9-4.
A lithium secondary battery having 1 V, an initial discharge capacity of 120 mAh / g or more, and a capacity deterioration at the 20th cycle of 20% or less can be obtained.

[0026]

EXAMPLES Examples of the present invention and comparative examples will be described with reference to the drawings, but the present invention is not limited to these examples. The identification and crystal structure of the reaction product were determined by X-ray diffraction (RIGAKU Cu-Kα 50 kV 200 m
A). The shape of the particles was observed with a scanning electron microscope (manufactured by JEOL Ltd.), and the particle size distribution was measured by a laser diffraction / scattering method (Microtrack particle size distribution meter manufactured by HONEYWELL). The specific surface area was measured by the BET one point method.

[0027]

Example 1 0.1 mol / L manganese sulfate and
An aqueous solution containing 0.5 mol / L sulfuric acid was placed in a thermostat at 30 ° C., and an oxygen gas containing ozone having an ozone concentration of 20 g / Nm ³ was passed for 5.5 hours to perform an oxidation reaction. The obtained solid was filtered, washed with water and dried at 110 ° C. FIG. 1 shows X
FIG. The product was JCPDS: No. 30-8
20 showed a diffraction pattern similar to that of ε-MnO ₂ . The specific surface area was 174 m ² / g, and the median diameter determined by particle size distribution measurement was 21 μm. According to the EDTA method, Mn
As a result of analyzing the content, the Mn content was 54.6%.

The ε-MnO ₂ and a 2.86 mol / L aqueous solution of LiOH · H ₂ O were mixed with a Li / Mn molar ratio of 0.515.
And wet mixed. After spray drying the mixture at 110 ° C.,
The dried product was heat-treated at 850 ° C. for 6 hours in the atmosphere to prepare a lithium manganese composite oxide.

The sample was subjected to X-ray diffraction using Cu as a target, measurement of specific surface area, and photography of a scanning electron microscope. FIG. 2 shows an X-ray diffraction diagram. The product is J
CPDS: No. It showed a diffraction pattern similar to that of LiMn ₂ O _{4 of} No. 35-782. The specific surface area was 1.9 m ² / g, and the median diameter was 19 μm. Figure 3 shows the product S
An EM photograph is shown. The SEM photograph shows that the secondary particle shape of the product is grape-like.

Next, a positive electrode mixture was prepared using the dried and calcined unground material as an active material. 82 parts by weight of the lithium manganese composite oxide obtained as an active material, 9 parts by weight of acetylene black as a conductive additive, and 9 parts by weight of a fluororesin as a binder were mixed using n-methyl-2-pyrrolidone as a solvent. did. The electrode mixture was applied to an aluminum foil by a doctor blade method so that the weight after drying was 0.01 g / cm ² . After vacuum drying at 150 ° C., roll pressing was performed to 80% of the thickness of the initial electrode mixture. After punching with an area of 1 cm ² , the positive electrode 4 of the coin battery shown in FIG. 4 was obtained.

In FIG. 4, a negative electrode 5 is a metal Li plate, an electrolytic solution is a mixture of ethylene carbonate and dimethyl carbonate in the same volume of LiPF ₆ dissolved at 1 mol / L, and a separator 6 is a porous polypropylene film. 1. Positive electrode case containing positive electrode and negative electrode respectively The overall size of the battery including the negative electrode case 1 is approximately 20 mm in outer shape,
The height was about 3 mm.

Using the coin battery prepared as described above, the battery was charged at a constant current of 0.2 mA / cm ² to 4.3 V, and further charged at a constant voltage until the current value became 1 μA or less. Discharged to 0V. This cycle is 2
Repeated 0 times. FIG. 5 (solid line) shows a charge / discharge curve of a coin battery in which the lithium-manganese composite oxide of this example was used as a positive electrode active material and Li metal was used as a negative electrode. Thus, the coin battery of the present example has a discharge capacity of 12
7 mAh / g, and the discharge capacity at the 20th cycle was 12
At 0 mAh / g, the discharge capacity retention ratio was 94%.

[0033]

Comparative Example Synthesis was carried out in the same manner as in Example 1, except that manganese dioxide was used as a Mn source. The electrolytic manganese dioxide used was JCPDS: No. 14-644 showed the same diffraction pattern as that of γ-MnO ₂ . The specific surface area was 47 m ² / g, and the median diameter determined by particle size distribution measurement was 3.5 μm. As a result of analyzing the Mn content by the EDTA method, the Mn content was 58.6%.

The γ-MnO ₂ and a 2.86 mol / L aqueous solution of LiOH · H ₂ O were mixed with a Li / Mn molar ratio of 0.515.
And wet mixed. Thereafter, drying and heat treatment were performed in the same manner as in the examples.

The sample was subjected to X-ray diffraction using Cu as a target, measurement of specific surface area, and photography of a scanning electron microscope. The X-ray diffraction pattern of the product is JCPDS: N
o. It showed a diffraction pattern similar to that of LiMn ₂ O _{4 of} No. 35-782. The specific surface area was 2.4 m ² / g, and the median diameter was 22 μm.

A coin battery was manufactured in the same manner as in the example, and a charge / discharge test was performed. FIG. 5 (broken line) shows the lithium manganese composite oxide of this comparative example as a positive electrode active material, and L
4 shows a discharge curve of a coin battery using i-metal as a negative electrode. As a result, in the coin battery of this comparative example, the discharge capacity at the first cycle was 117 mAh / g, the discharge capacity at the 20th cycle was 81 mAh / g, and the discharge capacity maintenance ratio was 69%.

As is clear from the comparison between the examples and comparative examples, it is possible to synthesize a grape-like lithium manganese composite oxide from ε-MnO ₂ having a specific surface area of 100 to 300 m ² / g as a raw material. There is a coin battery using this lithium manganese composite oxide as a positive electrode active material, γ-Mn
Compared with a coin battery using a lithium manganese composite oxide synthesized by a similar method using O ₂ as a raw material, the coin battery has a higher initial discharge capacity and less cycle deterioration.

[0038]

According to the present invention, as a raw material for a lithium manganese composite oxide, a BET having an average secondary particle size of 50 μm or less is used.
Using ε-MnO ₂ having a specific surface area of 100 to 300 m ² / g as a raw material, it is possible to provide a lithium manganese composite oxide having a grape-like shape, and without the steps of pulverization and repeated heat treatment,
Further, a non-aqueous electrolyte secondary battery having a high charge / discharge capacity and excellent cycle characteristics can be supplied without replacing Mn with another different element.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a manganese oxide manufactured in an example.

FIG. 2 is an X-ray diffraction diagram of a lithium manganese composite oxide manufactured in an example.

FIG. 3 is an SEM photograph of a lithium manganese composite oxide produced in an example.

FIG. 4 is a schematic view of a coin battery using the lithium manganese composite oxide prepared in Examples and Comparative Examples as a positive electrode active material.

FIG. 5 is a diagram showing charge / discharge curves of the first cycle and the twentieth cycle of a coin battery using the lithium manganese composite oxide of the example and the comparative example as a positive electrode active material;
The solid curve shows the charge / discharge curve of the example, and the broken curve shows the charge / discharge curve of the comparative example.

[Explanation of symbols]

 1 and 2 Case 3 Gasket 4 Positive electrode 5 Negative electrode 6 Separator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Nakahara Inside 1925 Kogushi, Ogushi, Ube City, Yamaguchi Prefecture Inside (25) Inventor Ryosuke Nakajima 25 Chitan Kogyo, 1978 Kogushi, Ube City, Yamaguchi Prefecture In-house F term (reference) 4G048 AA04 AB01 AB05 AC06 AD04 AD06 AE05 5H029 AJ03 AJ05 AJ14 AK03 AL12 AM03 AM05 AM07 BJ03 DJ16 HJ02 HJ05 HJ07 HJ14 HJ19 5H050 AA07 AA08 BA17 CA09 FA17 GA02 HA02 HA05 HA07 HA14

Claims (6)

[Claims] The main component is LiMn ₂ O ₄ , having a secondary particle shape obtained by assembling a substantially spherical primary particle shape into a grape cluster, having a secondary particle diameter of 1 to 100 μm and a specific surface area of 0.
A lithium manganese composite oxide having a mass of ^{1 to} 10 m ² / g. 2. The lithium manganese composite oxide according to claim 1, wherein the primary particle diameter is 0.1 to 0.2 μm. 3. An ε-manganese dioxide having a crystal form ε-MnO ₂ by X-ray diffraction as a main component, a specific surface area of 100 to 300 m ² / g, and a grape-like secondary particle shape having a particle diameter of 50 μm or less; , A water-soluble lithium compound and Li / Mn
Wet mixing at a molar ratio of 0.50 to 0.60, and drying the mixed solution so that the particle shape of the lithium manganese composite oxide is maintained, and then performing a heat treatment at 500 to 900 ° C. A method for producing a lithium-manganese composite oxide. 4. A positive electrode for a battery using the lithium manganese composite oxide according to claim 1 or 2 or the lithium manganese composite oxide obtained by the production method according to claim 3 as a positive electrode active material. 5. A lithium secondary battery using the lithium manganese composite oxide according to claim 1 or 2, or a lithium manganese composite oxide obtained by the production method according to claim 3, as a positive electrode active material. 6. At least an initial discharge capacity of 120 mAh
/ G or more, or the discharge capacity retention rate at the 20th cycle is 80
% Of the coin battery.
4. The lithium secondary battery according to 1.