JPH11111288A - Method for producing lithium manganese composite oxide for non-aqueous lithium secondary battery and use thereof - Google Patents

Abstract

(57) [Problem] To provide a lithium manganese composite oxide which can be used for a non-aqueous lithium secondary battery having excellent cycle characteristics. SOLUTION: A mixture of lithium hydroxide and a manganese compound selected from manganese dioxide and manganese carbonate,
After first firing at 350 to 500 ° C., cooling to 100 ° C. or less, and crushing, after second firing at 600 to 800 ° C.,
Further, lithium hydroxide is added and uniformly mixed, and 600 to 8
Bake at 00 ° C.

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 a lithium manganese composite oxide for a non-aqueous lithium secondary battery having excellent charge / discharge cycle characteristics and its use.

[0002]

2. Description of the Related Art As a positive electrode material of a nonaqueous lithium secondary battery, sulfides and oxides of titanium and molybdenum,
In addition, oxides of vanadium and phosphorus have been proposed, but these have not been put to practical use yet because of their poor preservability and high cost. On the other hand, manganese dioxide is typically used as a positive electrode active material of a non-aqueous primary battery and has already been put to practical use. Manganese dioxide is abundant and inexpensive in terms of resources, and is chemically stable, and thus has excellent storage stability as a battery. However, since manganese dioxide has difficulty in reversibility, it is not suitable as a positive electrode active material of a non-aqueous secondary battery, and various modified manganese oxides have been proposed.

For example, JP-A-63-114064 and
JP-A-63-187569, JP-A-1-235158
As disclosed in each of the above publications, there has been proposed a manganese oxide containing lithium in its crystal structure by heat-treating a mixture of manganese dioxide and a lithium salt. These manganese oxides, depending on the heat treatment temperature,
The structure of the generated lithium-containing manganese oxide fluctuates,
For example, when the heat treatment temperature is 250 to 300 ° C., in the X-ray diffraction diagram, 2θ = 22 °, 31.7 °, 37 °, 42 °,
It becomes a manganese oxide having a crystal structure having a peak at around 55 °, becomes a manganese oxide containing Li ₂ MnO ₃ at 300 to 430 ° C., and becomes a manganese oxide having a spinel structure at 800 to 900 ° C. .

In these improved methods, manganese dioxide and a lithium salt are reacted with each other in a solid phase, so that the modification does not reach the inside of the manganese dioxide particles, and the deterioration is rapid in a charge / discharge cycle at a high current density. There were drawbacks. Therefore, for example, as disclosed in JP-A-2-183963, manganese dioxide is immersed in an aqueous solution in which a lithium salt is dissolved, moisture is evaporated to dryness, and then heat treatment is performed.
A method has been proposed in which the reforming reaction is advanced to the inside of the pores of the manganese dioxide particles. However, the lithium-containing manganese dioxide proposed so far has insufficient electrochemical activity, and when used for a positive electrode, has a good initial capacity and capacity retention, and has excellent cycle characteristics. It has been difficult to manufacture a lithium secondary battery.

It is to be noted that JP-A-6-203834, JP-A-7-245106 and JP-A-7-307155 disclose that a manganese dioxide or a mixture of a manganese salt and a lithium salt is heat-treated to form lithium. Composite oxides of lithium and manganese for ion batteries have been proposed. However, none of the techniques has provided a lithium manganese composite oxide that provides high initial capacity and high capacity retention.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a non-aqueous lithium secondary battery having excellent initial capacity and capacity retention and excellent cycle characteristics.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, mixed lithium hydroxide with a manganese compound selected from manganese dioxide and manganese carbonate to obtain a mixture of 350 ml Primary firing at ~ 500 ° C, cooling to 100 ° C or less, crushing, 600-80
Lithium manganese composite capable of producing a non-aqueous lithium secondary battery having excellent cycle characteristics by secondary firing at 0 ° C., further adding lithium hydroxide, mixing uniformly, and firing at 600 to 800 ° C. The inventors have found that an oxide can be obtained, and have reached the present invention.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. As the lithium hydroxide used in the present invention,
For example, a commercially available monohydrate represented by LiOH.H ₂ O is preferably used. It is appropriate to use granular lithium hydroxide. The average particle size of the granules is usually 20 to 100 μm, preferably 40 to 80 μm.
Suitably, it is μm. Manganese dioxide or manganese carbonate is used as the manganese compound used in the present invention. It is appropriate to use granular manganese compounds. The average particle size of the granules is usually
Suitably, it is 20 to 100 μm, preferably 40 to 80 μm.

Various materials can be used as manganese dioxide or manganese carbonate. For example, as manganese dioxide, a lower manganese oxide such as Mn ₂ O ₃ or Mn ₃ O ₄ obtained by calcining a manganese ore at a temperature of 400 ° C. or more cannot be treated with a mineral acid such as sulfuric acid, nitric acid, or a mixture thereof. A chemically synthesized manganese dioxide obtained by a leveling reaction can be used. Further, electrolytic manganese dioxide obtained by electrolysis can be used. Lithium hydroxide and a manganese compound can be mixed by wet mixing or dry mixing. In wet mixing, lithium hydroxide is in a state of being dissolved in water in a slurry state, and lithium hydroxide in this dissolved state is
Because it becomes a state highly dispersed in the manganese compound,
The obtained lithium manganese composite oxide is very uniform in composition and is preferable.

The mixing of lithium hydroxide and a manganese compound can be performed, for example, by mixing lithium hydroxide (LiOH.H ₂ O)
And a manganese compound, usually in a molar ratio of Li to Mn of 0.80: 2 to 1.10: 2, preferably 1.90: 2 to 1.00:
The mixture can be prepared by adding water using a pot mill and mixing the mixture in a wet system or in a dry system without adding water. The mixture obtained in this way, after adding water, after evaporating the water,
0 ° C, preferably 400-500 ° C, more preferably 4 ° C
Firing (primary firing) at a temperature of 50 to 500 ° C.
Since the melting point of lithium hydroxide is 445 ° C., preferably, by baking at a temperature of 500 ° C. or less, lithium ions penetrate into the pores of the manganese compound to obtain uniform lithium manganate.

The primary fired product thus obtained is once cooled to 100 ° C. or lower, preferably 45 ° C. or lower, more preferably 20 ° C. or lower, and then crushed. As a lower limit of the cooling temperature, 0 ° C. or more is appropriate for practical operation. By this cooling operation, a more uniform lithium manganese composite oxide can be obtained. The average particle size of the crushed product is usually 20 to 100 μm, preferably 40 to 80 μm. If it is 100 μm or more, crushing and uniform mixing tend to be insufficient. If it is less than 20 μm, there is a concern that the compound may be excessively disintegrated and destroy the structure of the compound.
Further, it is easy to increase the fine powder suction to the operator. The crushed material thus obtained is fired again (secondary firing).
The secondary firing is performed at 600 to 800 ° C., preferably 650 to 7
Suitably, it is carried out at 50 ° C.

[0012] The secondary fired product thus obtained includes:
Again, lithium hydroxide is blended and uniformly mixed. The amount of lithium hydroxide to be added is 0.01 to 0.30: 2 mol, preferably 0.02 to 0.3 mol, as a reforming component, relative to manganese.
It is appropriate that the amount is 0.20: 2 mol. Uniform mixing can be achieved, for example, by dry mixing using a pot mill. The mixture thus obtained is then fired (tertiary firing) at 600 to 800 ° C., preferably 650 to 750 ° C., so that the core having a uniform structure and the surface which has undergone Li modification are advanced. A lithium manganese composite oxide having a two-layer structure is obtained.
The tertiary firing may be performed twice or more with a crushing process interposed therebetween. It is considered that the thus obtained lithium manganese composite oxide has a high initial capacity and a high capacity retention by having a two-layer structure. In particular, it is considered that the surface layer portion that has undergone lithium reforming has reduced the breakage of the internal crystal structure accompanying the inflow and outflow of Li during charging and discharging. On the other hand, when these compounds are dry-mixed only in the process up to the secondary firing, the mixing becomes insufficient, so that the composition of lithium manganate in the obtained lithium-manganese composite oxide becomes entirely uneven. In addition, a lithium manganese composite oxide having a high discharge capacity and a high capacity retention cannot be obtained.

The obtained lithium manganese composite oxide is
Used as a positive electrode material for non-aqueous lithium secondary batteries. The method of using the positive electrode material is the same as the method of using the conventional positive electrode material. In this case, as the negative electrode in the non-aqueous lithium secondary battery, conventionally used metal lithium, a lithium alloy or a carbonaceous material which can be doped or dedoped with lithium, an oxide, or the like can be used.

[0014]

The present invention will be described in more detail with reference to the following examples. Example 1 Lithium hydroxide (LiOH.H ₂ O) and electrolytic manganese dioxide were blended so that the molar ratio of Li to Mn was 1.00: 2, and deionized to 20% by weight of the total blend. Water was added to form a slurry. This slurry was mixed in a pot mill, dried at 150 ° C., and fired at 470 ° C. for 12 hours in an air atmosphere. Next, after lowering the calcined product to room temperature (20 ° C.), the calcined product was crushed so that the average particle size became 55 μm, and secondary calcining was performed at 700 ° C. for 12 hours in an air atmosphere. Lithium hydroxide (LiOH.H ₂ O) was further added to the obtained secondary fired product by a molar ratio of Li to manganese,
After mixing in a pot mill at 0.05: 2 mol, the mixture was baked at 700 ° C. for 12 hours in an air atmosphere. Using 82 parts by weight of the fired product as a positive electrode active material, 10 parts by weight of acetylene black, and 8 parts by weight of polyvinylidene fluoride as a binder previously dissolved in 58 parts by weight of N-methyl-2-pyrrolidone In addition, the mixture was sufficiently mixed to obtain a paste. This paste was applied to an aluminum net, pressed and dried to prepare a positive electrode plate. As a counter electrode, a metal lithium plate having the same size as the positive electrode was used, and a metal lithium reference electrode was used for positive electrode potential measurement. A test battery was prepared by using a mixed solvent of ethylene carbonate and diethyl carbonate 1: 1 in which 1 mol / dm ³ of LiPF ₆ was dissolved as an electrolyte. Example 2 A test battery was prepared in the same manner as in Example 1 except that electrolytic manganese dioxide was replaced with chemically synthesized manganese dioxide when producing a positive electrode active material. Example 3 A test battery was prepared in the same manner as in Example 1 except that manganese carbonate (MnCO ₃ ) was used as a manganese compound.

Comparative Example 1 Lithium hydroxide (LiOH.H ₂ O) and electrolytic manganese dioxide were blended so that the molar ratio of Li to Mn was 1: 2, and 20% by weight of the total blend was blended. A slurry was prepared by adding deionized water. This slurry was wet-mixed in a pot mill, dried at 150 ° C., and then primary fired at 700 ° C. for 12 hours in an air atmosphere. A test battery was prepared in the same manner as in Example 1, except that this fired product was used as a positive electrode active material. Comparative Example 2 Lithium hydroxide (LiOH.H ₂ O) and electrolytic manganese dioxide were blended so that the molar ratio between Li and Mn was 1: 2, and 20% by weight of the total amount of deionized water was calculated. Was added to prepare a slurry, which was wet-mixed in a pot mill. After drying this slurry at 150 ° C., it was first fired at 470 ° C. for 12 hours in the air atmosphere, and then further fired at 700 ° C. for 12 hours. A test battery was prepared in the same manner as in Example 1, except that this fired product was used as a positive electrode active material. Comparative Example 3 (Technique described in JP-A-6-203834) Lithium acetate and manganese acetate tetrahydrate were blended in a molar ratio of 1: 2, and 220% by weight of the total blend was mixed.
Heating and dissolving in ethylene glycol, acetic acid smell disappeared, heating continued until ethylene glycol was removed,
Allowed to solidify. Next, the obtained mixture was heat-treated at 400 ° C. for 3 hours and fired in air at 700 ° C., and the obtained fired product was made into a paste in the same manner as in Example 1 to produce a test battery. Physical properties test The test battery prepared as above was subjected to a current density of 0.5 mA / c.
Discharge characteristics were evaluated by repeating a charge / discharge cycle in which the battery was charged to 4.3 V with a constant current of m ² and then discharged to 3.0 V. At that time, the discharge capacity at the first cycle was defined as the initial capacity (mAh / g), and the discharge capacity at the tenth cycle relative to the initial capacity was defined as the capacity retention (%). Table 1 shows the results.

[0016]

[Table 1] As shown in Table 1, in the batteries of Examples 1 to 3 of the present invention, a high initial capacity and a high capacity retention were obtained under predetermined charge and discharge conditions.

On the other hand, when producing the positive electrode active material, 70%
Comparative Example 1, only primary firing at 0 ° C., Comparative Example 2, after primary firing, secondary firing without cooling to room temperature,
In Comparative Example 3 manufactured according to the known example, the initial capacity and the capacity retention were low, and the cycle characteristics were poor.

[0018]

The lithium manganese composite oxide produced by the method of the present invention provides a non-aqueous lithium secondary battery having excellent cycle characteristics when used as a positive electrode of a non-aqueous lithium secondary battery.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeo Fukuyasu 5-18-6 Sangenya Higashi, Taisho-ku, Osaka-shi, Osaka (72) Inventor Masumi Terauchi 230-4 Minami-Nagai-cho, Nara-shi, Nara (72) Inventor Toshihiko Shioya Parkside Residence 103, 2-4-18 Shiroyama, Otawara-shi, Tochigi Inventor Masanao Terasaki 1st Nippon Shono Inobaba-cho, Kichijo-in, Minami-ku, Kyoto, Kyoto (72) Inside Nihon Battery Co., Ltd. Person Hiroshi Mukai 1st Nishinosho Inonobaba-cho, Minami-ku, Kyoto, Kyoto

Claims (2)

[Claims] 1. A method of mixing lithium hydroxide with a manganese compound selected from manganese dioxide and manganese carbonate,
After first firing at 350 to 500 ° C., cooling to 100 ° C. or less, and crushing, after second firing at 600 to 800 ° C.,
Further, lithium hydroxide is added and uniformly mixed, and 600 to 8
A method for producing a lithium manganese composite oxide for a nonaqueous lithium secondary battery, characterized by firing at 00 ° C. 2. A negative electrode comprising metallic lithium or an alloy thereof,
A non-aqueous lithium secondary battery comprising a lithium manganese composite oxide according to claim 1 or a lithium secondary battery using a substance capable of inserting and extracting lithium and / or lithium ions.