JPH11302019A - Production of lithium manganese spinel oxide particulate powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce lithium manganese spinel oxide capable of being fired in a short time, having a narrow particle size distribution, uniform in particle size and useful as a material for a positive electrode active material. SOLUTION: Dimanganese trioxide particulate powder having >=50 m<2> /g BET specific surface area is mixed with a lithium compd. in an Li to Mn molar ratio of 0.50-0.60, 1-30 wt.% water is added to the powdery mixture and the water-contg. powdery mixture is compression-molded to obtain a molding having >=1.5 g/cc molding density. This molding is fired in an oxygen-contg. gas and comminuted.

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 lithium manganese spinel oxide particles, and more particularly, to lithium manganese which can be fired in a short time and has a uniform particle size, and is particularly useful as a positive electrode active material for lithium batteries. The present invention relates to a method for producing spinel oxide particles.

[0002]

2. Description of the Related Art In recent years, with the development of portable devices such as personal computers and mobile phones, demand for batteries as power sources has been increasing. In particular, lithium batteries have been actively studied in various fields because lithium is a substance with a small atomic weight and a large ionization energy, and a battery with high electromotive force and high energy density can be expected. Has been done. As a positive electrode active material used for a lithium battery, lithium cobalt oxide (Li) capable of generating a high voltage of about 4 V is used.
CoO ₂ ), lithium nickel oxide (LiNi
O ₂ ), lithium manganese spinel oxide (Li _{1 + X} M
Study of n _2-X O ₄₎ or the like composite oxide has been actively conducted. These compounds are obtained by mixing an oxide raw material powder containing cobalt, nickel, and manganese with a lithium compound powder and firing at a high temperature of 500 ° C. or higher.

However, in this high-temperature sintering method, since the reactivity of the cobalt oxide, nickel oxide, and manganese oxide particles during the solid phase reaction is low, it is necessary to perform calcination for a long time. Lithium evaporates by baking. For this reason, there is a problem that Li is deficient, the composition is easily changed, and it is difficult to obtain stable quality lithium cobalt oxide, lithium nickel oxide, and lithium manganese spinel oxide.

In addition, these composite oxides are used as a positive electrode of a battery by dispersing the powder in a binder, applying the powder to a metal plate such as copper, and drying it. Since the resulting composite oxide has powder particles fused together strongly, it is necessary to perform strong pulverization in order to obtain a powder sufficient for use as a positive electrode active material, which only increases the energy cost. However, problems have been pointed out, such as the grinding media being worn and being mixed into the composite oxide powder.

Further, these positive electrode active material powders are dispersed in a binder as described above, applied to a metal plate such as copper, dried and used as a positive electrode of a battery.
The higher the filling degree of the particle powder in the coating film, the higher the capacity of the battery. Therefore, it is important that the composite oxides have uniform particle shapes and particle sizes.

In view of the above background, there is a need for a method for producing a lithium manganese spinel oxide which can be fired in a short time, has a narrow particle size distribution, and has a uniform particle size, and is useful as a material powder for a positive electrode active material.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a lithium manganese spinel oxide having a narrow particle size distribution and uniform particle size, which is useful as a positive electrode active material for a lithium battery, by a firing reaction at a relatively low temperature and for a short time. It aims to provide a manufacturing method.

[0008]

That is, the present invention provides a BET
Limanganese trioxide particles having a specific surface area of at least 50 m ² / g and a lithium compound having a Li / Mn (molar ratio) of 0.
The mixture is mixed within a range of 50 to 0.60, 1 to 30% by weight of water is added to the mixed powder, and the water-containing mixed powder is compression-molded to obtain a molded article having a molding density of 1.5 g / cc or more. Get
A method for producing lithium manganese spinel oxide particles is characterized in that the molded body is fired in an oxygen-containing gas and then pulverized. In the present invention, the BET specific surface area is a value measured by a nitrogen adsorption method.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The dimanganese trioxide (Mn ₂ O ₃ ) particles used in the present invention have a BET specific surface area of 50.
It is necessary to be at least m ² / g. When the BET specific surface area is less than 50 m ² / g, dimanganese trioxide, a raw material that is not a positive electrode active material, remains in addition to the target lithium manganese spinel oxide. Although the upper limit of the BET specific surface area is not particularly limited, it is preferably about 100 m ² / g from the viewpoint of handling. The dimanganese trioxide particles preferably have a uniform particle size.

In the present invention, the BET specific surface area is 50 m ² / g.
As described above, the dimanganese trioxide particles having a uniform particle size distribution are obtained by heating a manganese (II) hydroxide suspension obtained by mixing an aqueous manganese salt solution and an excess aqueous alkali solution that is neutralized or more. Oxygen-containing gas, such as air, is passed through to oxidize manganese ions to form a precipitate, which is filtered, washed and dried, and manganese carbonate is heated in an oxygen-containing gas, such as air, at about 400 to 850 ° C. It can be obtained by a method such as thermal decomposition, but the one obtained by the former method is advantageous in that the particle size is fine and the reactivity is high.

The lithium compound used in the present invention includes lithium carbonate, lithium oxide, lithium hydroxide, lithium hydroxide monohydrate and the like, and these can be used alone or in combination of two or more.

The mixing ratio of the lithium compound to dimanganese trioxide in the present invention is in the range of 0.50 to 0.60 in terms of the molar ratio of lithium to manganese (Li / Mn). If lithium is less than the above range, dimanganese trioxide, a raw material that is not a positive electrode active material, remains in addition to the lithium manganese spinel oxide, and it is extremely difficult to remove the dimanganese trioxide. When the positive electrode is formed using a powder containing dimanganese trioxide, it is difficult to obtain good battery characteristics, that is, electrochemical activity in an electrolyte having lithium ion conductivity. On the other hand, when lithium is in excess of the above range, there are substances other than the lithium manganese spinel oxide that are not the positive electrode active material, for example, lithium carbonate or Li ₂ MnO ₃ , and these lithium carbonates and Li ₂ MnO ₃ are also present. Since it is extremely difficult to remove, when a positive electrode is formed using a powder containing these, similarly, it is difficult to obtain good battery characteristics and electrochemical activity.

Next, 1 to 30% by weight, preferably 10 to 25% by weight of water is added to the mixed powder of the dimanganese trioxide particles and the lithium compound, and the mixed powder containing the water is added. Is subjected to compression molding using an extruder, a roller compactor, a disk pelleter or the like to form a molded body having a molding density of 1.5 g / cc or more, preferably 2 to 5 g / cc. Bake.

If the amount of water is less than 1% by weight with respect to the mixed powder, it is difficult to handle the molded body because the strength is not sufficiently obtained, and the compressed density in the molded body varies. As a result, the particle size distribution of the lithium manganese spinel oxide particles obtained by pulverizing after firing becomes wide. On the other hand, if the water content exceeds 30% by weight, the water-soluble lithium compound tends to flow out, resulting in a change in the composition and a lack of stability of the quality of the lithium manganese spinel oxide particles.

Further, when a molded body having a molding density of less than 1.5 g / cc is fired, the degree of filling of the coating film is not sufficient because the lithium manganese spinel oxide has insufficient grain growth. Cannot be obtained. The upper limit of the molding density is not particularly limited. However, if it is too large, the production becomes difficult. Therefore, it is usually 5 g / cc, preferably about 3 g / cc.

The firing temperature of the mixed powder in the present invention is usually in the range of 500 to 800 ° C., preferably 600 to 750 ° C., and the firing time is usually 2 to 20 hours, preferably 5 to 10 hours. The fired molded body is pulverized into particle powder. The grinding method is not particularly limited, and a usual grinding method is used. Lithium manganese spinel oxide obtained in the above manner is represented by _{Li 1 + x Mn 2-x} O 4, x is preferably in the range of 0 to 0.1 in terms of battery characteristics.

[0017]

The most important point in the present invention is that dimanganese trioxide particles having a BET specific surface area of 50 m ² / g or more are used as a manganese raw material, and then mixed with a lithium compound. Then, the mixed powder is compression-molded by an extruder, a roller compactor, a disk pelleter or the like to prepare a molded body having a molding density of 1.5 g / cc or more. The fact is that the firing is completed in an oxygen-containing gas, the reaction is completed in a short time, and the lithium manganese spinel oxide having a uniform particle size distribution can be produced by crushing.

It is generally considered that the solid phase reaction during firing proceeds by mutual diffusion at the contact point between the raw material powder particles. The present inventors have found that, in the case of a lithium compound and dimanganese trioxide, the melting point of lithium is significantly lower than the melting point of dimanganese trioxide, and diffusion of lithium is easier than diffusion of manganese. It is thought that the reaction proceeds by diffusing into dimanganese trioxide particles. Based on this idea, making the dimanganese trioxide particles finer requires a shorter diffusion distance of lithium to complete the reaction than making the lithium compound particles smaller. The reaction seems to be complete. Therefore, when dimanganese trioxide particles having a BET specific surface area of 50 m ² / g or more are used as a manganese raw material, the reaction with lithium proceeds rapidly during firing (ie,
It is considered that the reactivity of the manganese raw material is improved) and the reaction is completed in a short time.

Further, the raw material powder has a fine particle size and is highly reactive, and 1 to 30% by weight based on the mixed powder.
By compressing and molding this mixed powder to produce a molded body having a molding density of 1.5 g / cc or more.
It is considered that lithium manganese spinel oxide particles having a uniform particle size distribution are formed. At the time of compression molding, dry powder containing no water causes the particle powder to be less slippery, and thus it is difficult to uniformly transmit the compression pressure to the entire system, and therefore, the compression density varies. On the other hand, by containing a specific amount of water in the system, the particle powder becomes slippery, and the compression pressure is uniformly transmitted to the entire system to form a uniform molded body. It is considered that the obtained lithium manganese spinel oxide particles have a uniform particle size distribution.

[0020]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. The identification of the reaction product particle powder and the analysis of its crystal structure were performed by X-ray diffraction (RIGAKU, Mn-filte
red Fe-Kα, 40 kV and 20 mA). The morphology of the particles was observed with a scanning electron microscope.

Example 1 Dimanganese trioxide particle powder (γ-Mn ₂ O ₃ ) 3 having a BET specific surface area of 50 m ² / g or more was used as a manganese raw material powder.
0.95 g and lithium hydroxide monohydrate (LiOH.H ₂
O) 9.05 g (Li / Mn molar ratio = 0.55) was mechanically mixed, and 5% by weight of water was sprayed on the obtained mixed powder. This powder was compression-molded with a roller compactor to prepare a molded body having a molding density of 2.2 g / cc. The molded body was placed in an electric furnace, heated to 650 ° C., and fired in air for 10 hours. The obtained powder was ground in a mortar to obtain a black powder. As shown in the X-ray diffraction diagram of FIG. 1, the obtained black powder was made of lithium manganese spinel oxide (Li
_{1 + X} Mn _2-X O ₄ ) powder, and the particles were uniform in particle size as shown in the scanning electron micrograph of FIG.

Next, the electrochemical properties of the lithium manganese spinel oxide obtained as described above as an electrode active material were evaluated by a potential sweep method. Lithium manganese spinel oxide as a positive electrode for measurement, polytetrafluoroethylene as a binder, and ketjen black as a conductive material were mixed at 10% by weight with respect to the lithium manganese spinel oxide, and 0.1 g of this mixture was weighed. Then, the titanium mesh was charged as a current collector to form a working electrode. As a negative electrode, a metal lithium foil was filled in a stainless steel mesh. Further, lithium metal was used as a reference electrode. Lithium perchlorate (Li
A solution obtained by dissolving ClO ₄ ) at a concentration of 1 M in a solvent in which propylene carbonate and dimethoxyethane were mixed at a volume ratio of 1: 1 was used as an electrolyte.

An electrochemical measurement cell was constructed using the above-mentioned positive electrode working electrode for measurement, negative electrode, reference electrode and electrolyte. Using this electrochemical cell, 2.5 to 2.5
The charge / discharge curve was examined in a potential range of 4.2 V and a current of 0.5 mA / cm ² . When the electric capacity of this charge / discharge was determined as an index of the electrochemical activity of this lithium manganese spinel oxide, it was 122 mA / g.

Examples 2 to 5 and Comparative Examples 1 to 4 The same procedures as described above were carried out except that the particle size, water content, molding density, firing temperature and firing time of the dimanganese trioxide raw material powder were changed as shown in Table 1. A reaction product powder was obtained in the same manner as in Example 1. Table 1 shows the reaction production conditions and the characteristics of the obtained reaction products. The particle powders obtained in Examples 2 to 5 were all lithium manganese spinel oxides (Li
_{1 + X} Mn _2-X O ₄ ), and was confirmed to be composed of particles having a uniform particle size distribution. on the other hand,
The particle powders obtained in Comparative Examples 1 and 2 were a mixture of lithium manganese spinel oxide and dimanganese trioxide. The powder obtained in Comparative Example 3 had the same structure as that of the lithium manganese spinel oxide, but was composed of particles having an uneven particle size distribution. Further, the powder obtained in Comparative Example 4 was composed of lithium manganese spinel oxide and L
It was a mixture with i ₂ MnO ₃ . Table 1 also shows the charge / discharge capacity examined in the same manner as in Example 1. From these results, the charge / discharge capacity when the lithium manganese spinel oxide obtained in Examples 1 to 5 was used was as follows:
The value is larger than that of the sample No. 4, which indicates that the present invention can provide a lithium manganese spinel oxide having high electrochemical activity.

[0025]

[Table 1]

[0026]

According to the present invention, it is possible to provide lithium manganese spinel oxide particles having a uniform particle size by firing for a short time. In addition, the lithium manganese spinel oxide particles obtained by the present invention act as a positive electrode active material of a lithium battery, have a high electromotive force, and are useful as a material for a positive electrode active material of a lithium battery capable of increasing energy density. .

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a lithium manganese spinel oxide particle powder obtained in Example 1.

FIG. 2 is a scanning electron micrograph (× 10000) of the lithium manganese spinel oxide obtained in Example 1.

Continuation of the front page (72) Inventor Mitsuaki Hataya 1-1-1 Shinoki, Onoda-shi, Yamaguchi Prefecture Toda Kogyo Co., Ltd. Onoda Development Center

Claims (1)

[Claims] 1. A method according to claim 1, wherein dimanganese trioxide particles having a BET specific surface area of 50 m ² / g or more and a lithium compound are mixed with Li /
Mn (molar ratio) is mixed within the range of 0.50 to 0.60, 1 to 30% by weight of water is added to the mixed powder, and the water-containing mixed powder is compression-molded to a molding density of 1 .5
A method for producing lithium manganese spinel oxide particles, characterized in that a molded body having a g / cc or more is obtained, and the molded body is baked in an oxygen-containing gas and then pulverized.