JP2001048544A - Production of lithium-manganese multiple oxide for non- aqueous lithium secondary battery and use of the multiple oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject multiple oxide excellent in charge/discharge cycle characteristics both at room temperature and higher temperatures by subjecting a mixture of lithium carbonate and a manganese compound to primary burning at a specific temperature followed by cooling and grinding the product and then by subjecting the product to secondary burning followed by addition of lithium carbonate and then further burning the resultant homogeneous mixture at a specified temperature. SOLUTION: This multiple oxide is obtained by the following steps: lithium carbonate is mixed with manganese dioxide or manganese carbonate so as to be about (0.8-1.2):2 in the molar ratio Li/Mn, the mixture is subjected to primary burning at 400-700 deg.C and then cooled to <=100 deg.C to penetrate lithium ions into the pores of the manganese compound, and the product is ground at <=100 deg.C so as to be about 1-100 μm in average particle size; the ground product is then subjected to secondary burning at 700-950 deg.C followed by adding such an amount of lithium carbonate to the ground product thus burned as to be about (0.01-0.30) :2 in the molar ratio Li/Mn followed by homogeneous mixing; subsequently, the resultant mixture is further burned at 500-950 deg.C, thus obtaining the objective lithium-manganese multiple oxide having two-layer structure.

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 at room temperature and high temperature, and a use thereof.

[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 yet been put to practical use because of their poor preservability and high cost. On the other hand, manganese dioxide is typically used as the positive electrode active material of the non-aqueous primary electrode,
It 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.

[0003] However, manganese dioxide is not suitable as a positive electrode active material for non-aqueous secondary batteries because of its poor reversibility, and various modified manganese oxides have been proposed. For example, JP-A-63-114064
JP-A-63-187569, JP-A-1-235
As disclosed in JP-A-158-158, a manganese oxide containing lithium in a crystal structure of a mixture of manganese dioxide and a lithium salt is heat-treated.

In these manganese oxides, the structure of the lithium-containing manganese oxide to be formed differs depending on the heat treatment temperature. For example, when the heat treatment temperature is 250 to 300 ° C.,
In the X-ray diffraction diagram, 2θ = 22 °, 31.7 °, 37
Manganese oxide having a crystal structure having peaks near °, 42 °, and 55 °, and at 300 to 430 ° C, Li ₂ M
It becomes a manganese oxide containing nO ₃ and 800
At ９００900 ° C., a manganese oxide having a spinel structure is obtained. In addition, in these improved methods, since manganese dioxide and lithium salt are reacted in a solid phase, the inside of the manganese dioxide particles is not reformed, and the deterioration is rapid in a charge / discharge cycle at a high current density. there were.

Therefore, as disclosed in, for example, 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 to form fine manganese dioxide particles. A method has been proposed in which the reforming reaction proceeds to the inside of the hole. However,
The lithium-containing manganese dioxides proposed so far have insufficient electrochemical activity, and when used as a positive electrode, have excellent initial capacity and capacity retention, and have excellent cycle characteristics. It was difficult to manufacture secondary batteries.

[0006] 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 subjected to a heat treatment to obtain 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 long-term capacity retention.

[0007]

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.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, mixed lithium carbonate with a manganese compound selected from manganese dioxide and manganese carbonate, Primary firing at 700 ° C, cooling to 100 ° C or lower, crushing, 700-90
After secondary firing at 0 ° C., lithium carbonate is further added, uniformly mixed, and fired at 500 to 900 ° C.,
The inventors have found that a lithium manganese composite oxide capable of producing a nonaqueous lithium secondary battery having excellent cycle characteristics can be obtained, and have reached the present invention.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. Lithium carbonate used in the present invention is Li ₂ C
It is a compound represented by O ₃ and is commercially available. It is appropriate to use granular lithium carbonate. The average particle size of the granular material is usually 0.1 to 5
It is suitably 0 μm, preferably 1 to 5 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. It is appropriate that the average particle size of the granular material is usually 1 to 100 μm, preferably 3 to 20 μm.

As manganese dioxide or manganese carbonate, various materials can be used. 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 carbonate and the manganese compound can be mixed by a wet method or a dry method. In wet mixing, lithium carbonate hardly dissolves in water and is in the form of a slurry. However, since lithium does not precipitate on the surface of manganese during drying, lithium carbonate is preferably mixed uniformly.

The mixing of the lithium carbonate and the manganese compound is performed, for example, by mixing the lithium carbonate and the manganese compound in a molar ratio of Li to Mn of 0.8 to 1.2: 2, preferably 0.1 to 0.2: 2. 9 to 1.1: 2, and this can be performed by adding water using a pot mill and mixing in a wet system or in a dry system without adding water. The mixture thus obtained is obtained by adding water, evaporating the water, and then 400-700 ° C., preferably 450-6
It is fired (temporary firing) at a temperature of 50 ° C. Since the melting point of lithium carbonate is 618 ° C., it is preferably 65 ° C.
By firing at a temperature of 0 ° C. or lower, lithium ions penetrate into the pores of the manganese compound, and uniform lithium manganate can be obtained.

The fired product thus obtained is once
After cooling to 100 ° C. or lower, preferably 45 ° C. or lower, more preferably 20 ° C. or lower, pulverization is performed. 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 1 to 100 μm, preferably 10 to 30 μm. If it exceeds 100 μm, crushing and uniform mixing tend to be insufficient. If it is less than 1 μm, there is a concern that excessive disintegration may destroy the structure of the compound, which is not preferable. Further, it is easy to increase the fine powder suction to the operator. The crushed material thus obtained is fired again (secondary firing).

[0013] The secondary firing is suitably performed at 700 to 950 ° C, preferably 750 to 900 ° C. The secondary fired product thus obtained is mixed with lithium carbonate again and uniformly mixed. The addition amount of lithium carbonate is 0.01 to
0.30: 2 mol, preferably 0.02 to 0.20:
Suitably, the amount is 2 mol. Uniform mixing can be achieved, for example, by dry mixing using a pot mill. The mixture thus obtained is then heated at 500-950 ° C., preferably at 55 ° C.
By firing (tertiary firing) at 0 to 900 ° C., a lithium manganese composite oxide having a two-layer structure of a core portion having a uniform structure and a surface layer portion subjected to Li modification is obtained. The tertiary firing may be performed twice or more with a crushing process interposed therebetween.

The lithium manganese composite oxide thus obtained is considered to have a high initial capacity and a high capacity retention rate 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, if these compounds are dry-mixed only in the process up to the secondary firing, the mixing becomes insufficient,
The composition of lithium manganate in the obtained lithium manganese composite oxide becomes entirely nonuniform, and a lithium manganese composite oxide having high discharge capacity and high capacity retention cannot be obtained.

The obtained lithium manganese composite oxide is
It can be 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 nonaqueous lithium secondary battery, conventionally used metallic lithium, a lithium alloy or a carbonaceous material which can be doped or dedoped with lithium, an oxide, or the like can be used.

[0016]

The present invention will be described in more detail with reference to the following examples. Example 1 Li and M were mixed with lithium carbonate (Li ₂ CO ₃ ) (average particle size 2 μm) and electrolytic manganese dioxide (average particle size 10 μm).
The mixture was blended so that the molar ratio with n was 1: 2, and 20% by weight of the total amount of the blended deionized water was added to form a slurry. After mixing this slurry in a pot mill,
After drying at 50 ° C., primary firing was performed at 650 ° C. for 12 hours in an air atmosphere. Next, the fired product was cooled to room temperature (20 ° C.), crushed so as to have an average particle size of 50 μm, and subjected to secondary firing at 880 ° C. for 12 hours in an air atmosphere. Lithium carbonate (Li ₂ CO ₃ ) was further added to the obtained secondary fired product such that the molar ratio of Li to manganese was 0.05: 2 mol, and the mixture was uniformly mixed in a pot mill. It was baked at 700 ° C. for 12 hours.

From the results of X-ray diffraction and chemical analysis of the obtained fired product, the composition of the lithium manganese composite oxide was Li
It was confirmed Mn ₂ 0 is a lithium manganese acid, which is a _4. 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 rope, 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 1: 1 mixed solvent of ethylene carbonate and diethyl carbonate in which 1 mol / dm ³ of LiPF ₆ was dissolved as an electrolytic solution.

Comparative Example 1 Lithium hydroxide (LiOH.H ₂ O) (average particle size: 15 μm)
m) and electrolytic manganese dioxide (average particle size 50 μm)
A slurry was prepared by blending so that the molar ratio of Li and Mn was 1.05: 2, and adding 20% by weight of deionized water based on the total amount of the blend. This slurry was wet-mixed in a pot mill, dried at 150 ° C., and then dried under air atmosphere.
Primary baking was performed at 00 ° 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 2 Lithium carbonate (Li ₂ CO ₃ ) (average particle size: 10 μm)
Electrolytic manganese dioxide (average particle size: 50 μm) was blended so that the molar ratio of Li to Mn was 1.05: 2, and 20% by weight of the total amount of deionized water was added to prepare a slurry. This 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 750 ° C.
The secondary firing was performed 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 Example 1 except that lithium carbonate was changed to lithium hydroxide.
A test battery was prepared in the same manner as described above. Characteristic Test The test battery prepared as described above was charged to 4.3 V at a constant current of 1 mA / cm ^{2 in} a 60 ° C. atmosphere, and then charged to 3.0 V at a constant current of ² mA / cm ^2.
The discharge characteristics were evaluated by repeating a charge / discharge cycle in which the discharge was performed until the discharge was completed. At that time, the discharge capacity at the tenth cycle relative to the discharge capacity at the first cycle was defined as the capacity retention (%). Table 1 shows the results.

[0021]

Table 1 Table 1 Example Comparative Example 1 1 2 3 Capacity retention (%) 93 73 66 87

As shown in Table 1, in the battery of Example 1 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 a positive electrode active material, Comparative Example 1 in which only primary firing at 700 ° C. was performed,
In Comparative Example 2 in which the secondary firing was performed without cooling to room temperature after the primary firing, and in Comparative Example 3 in which lithium hydroxide was used instead of lithium carbonate, the capacity retention under a 60 ° C. atmosphere was low. , Cycle characteristics were poor.

[0023]

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 Continued on the front page (72) Inventor Teruyuki Takahashi 2-2,1024, Wakaba-cho, Ashiya-shi, Hyogo (72) Inventor Yutaka Umezu 2-18-14 Imazato, Nagaokakyo-shi, Kyoto (72) Inventor Toshihiko Shiotani Tochigi (72) Inventor Masanao Terasaki 1 Kichijoin Nishinosho Inomabacho, Minami-ku, Kyoto-shi, Kyoto, Japan Inside Nippon Battery Co., Ltd. (72) Inventor Atsuro Kondo Kyoto, Kyoto 1F, Nippon Battery Co., Ltd. F term (reference) 4K048 AA04 AB06 AC06 AE05 5H003 AA02 AA03 AA04 BA01 BA03 BB05 BC01 BD01 5H014 AA02 BB01 BB06 EE10 HH08 5H029 AJ03 AJ03 AJ01 AL01 AM03 AM05 AM07 CJ02 CJ08 HJ14

Claims (2)

[Claims] (1) mixing lithium carbonate and a manganese compound selected from manganese dioxide and manganese carbonate,
Primary firing at 0 to 700 ° C, cooling to 100 ° C or less, crushing, secondary firing at 700 to 950 ° C, further adding lithium carbonate, mixing uniformly, and firing at 500 to 950 ° C A method for producing a lithium manganese composite oxide for a non-aqueous lithium secondary battery, comprising: 2. A non-aqueous lithium secondary battery using metal lithium or an alloy thereof or a lithium compound for a negative electrode, wherein the lithium manganese composite oxide according to claim 1 is used as a positive electrode. Lithium secondary battery.