JPH11157841A - Lithium-manganese multiple oxide, its production and non-aqueous electrolyte accumulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce Li-Mn multiple oxide as a positive electrode material used in a non-aq. electrolyte accumulator typified by a lithium accumulator and to obtain a non-aq. electrolyte accumulator using the Li-Mn multiple oxide. SOLUTION: Manganese dioxide as Mn stock is fired at 800-900 deg.C, mixed with an Li salt and fired at 650-850 deg.C in an atmosphere of oxygen to obtain the objective Li-Mn multiple oxide represented by the formula, Li1+x Mn2-x Oy (where 0.04<=x<=0.08) and having 0.3-0.7 m<3> /g specific surface area and <=4 wt.% SO4 content. The multiple oxide is used as a positive electrode active material for a non-aq. electrolyte accumulator to obtain the objective non-aq. electrolyte accumulator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Li-Mn composite oxide as a cathode material used in a non-aqueous electrolyte secondary battery represented by a lithium secondary battery, a method for producing the same, and a Li-Mn composite oxide. And a non-aqueous electrolyte secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices such as AV devices and personal computers have been rapidly advanced, and there has been a demand for small, lightweight, high energy density secondary batteries as power sources for driving these devices. high. In response to such demands, non-aqueous secondary batteries, particularly lithium secondary batteries, are highly expected as batteries having high voltage and high energy density. Li capable of intercalating and deintercalating lithium as a cathode material for a lithium secondary battery satisfying these requirements.
Studies on layered compounds such as CoO ₂ , LiNiO _2, or composite oxides in which a transition metal element is partially substituted for these oxides have been actively conducted.

[0003] Further, although having no layered structure, LiCoO
_As an inexpensive material having a high voltage of 4V class similar to ₂ or the like, development of LiMn ₂ O ₄ which is a Li—Mn composite oxide and LiMnO ₂ having a slightly lower voltage of about 3 V are also in progress.

[0004]

However, when these Li—Mn composite oxides are used as a cathode material for a lithium secondary battery, conventional LiCoO ₂ and LiNiO ₂
There was a problem that the high-temperature battery characteristics were inferior to the case of using as a positive electrode material. As a countermeasure for this, a method of substituting a part of Mn with Li or substituting with a transition element has been attempted, but some improvement is obtained, but it is not enough. There is also a problem that the battery capacity is small.

For example, a high capacity type LiMn ₂ O
₄ (> 120 mAh / g, using MnO ₂ material, firing 650 ° C. to 800 ° C., a high specific surface area (in the case of 1 m ² / g or higher)), the
There is a problem that the high-temperature battery characteristics are poor (Japanese Patent Laid-Open No. 7-97)
216, JP-A-7-245103).
In addition, a type of Li ₂ MnO ₄ (Mn
The use of O ₂ raw materials, two-stage firing from 900 ° C. to 600 ° C., and a low specific surface area (0.5 m ² / g or less) has the problem of low discharge capacity (<110 mAh / g). (Yuan Gao and
JRDahn; J.Electrochem.Soc.Vol.143, No.6, June 1996
See). Therefore, the appearance of a battery material having good characteristics is desired.

[0006]

Means for Solving the Problems The Li-Mn composite oxide according to claim 1 for solving the above-mentioned problems is Li _{1 + x} Mn _{2- x}
In O _y, it is 0.04 ≦ x ≦ 0.08, a specific surface area
0.3 to 0.7 m ² / g, and the SO ₄ content is 0.4% by weight.
It is characterized by the following.

According to a second aspect of the present invention, there is provided a method for producing a Li—Mn composite oxide, wherein MnO ₂ as a Mn raw material is calcined at 800 ° C. to 900 ° C., mixed with a Li salt, and then mixed with an Li salt at 650 ° C.
It is characterized in that it is fired at from 950C to 950C.

[0008] A third aspect of the invention of a non-aqueous electrolyte secondary battery is characterized in that the Li-Mn composite oxide of the first aspect is used as a positive electrode active material for a non-aqueous electrolyte secondary battery. I do.

[0009]

Embodiments of the present invention will be described below.

[0010] A non-aqueous electrolyte solution for solving the above problems of the present invention.
The invention of the positive electrode active material for a secondary battery is based on Li _{1 + x}Mn_2-xO_yTo
0.04 ≦ x ≦ 0.08, and the specific surface area is 0.3 to
0.7m^Two/ G and SO_FourIf the content is less than 0.4% by weight
There is something.

Here, the amount (x) of Li added excessively is
0.04 ≦ x ≦ 0.08 is satisfied when the added amount (x) of Li is
If it is less than 0.04, lattice defects of lithium manganate are likely to occur, and as shown in Examples described later,
C., the discharge capacity after storage at 85 ° C. is low, while the addition amount (x) is 0.08.
When the temperature exceeds 20 ° C., since the excess lithium is large, the discharge capacity at 20 ° C. is low as shown in the examples described later.
This is because the discharge capacity after storage at 85 ° C. becomes low, which is not preferable. The specific surface area is 0.3 to 0.7 m ² / g.
When the specific surface area is less than 0.3 m ² / g, the discharge capacity at 20 ° C. is low, and the discharge capacity after storage at 85 ° C. is low, as shown in Examples described later. On the other hand, when the specific surface area exceeds 0.7 m ² / g, the hygroscopicity becomes large, and the discharge capacity after storage at 85 ° C. becomes low, as shown in Examples described later, and both are not preferable. It is.
The reason why the SO ₄ content is set to 0.4% by weight or less is that SO 4
_{(4) If the} content exceeds 0.4% by weight, the hygroscopicity becomes large and the discharge capacity after storage at 85 ° C. becomes low, as shown in the examples described later, which is not preferable.

Further, the invention of a method for producing lithium manganate is characterized in that MnO ₂ as a Mn raw material is calcined at 800 ° C. to 900 ° C., then mixed with a Li salt, and heated at 650 ° C. under an oxygen atmosphere.
The Li-Mn composite oxide is fired at 950 ° C.

Here, the sintering of the raw material MnO ₂ is performed at 800 ° C.
The reason why the temperature is set to 900 ° C. is as shown in an example described later.
If the temperature is lower than 800 ° C., the removal of SO ₄ is insufficient, and 2
This is because the capacity retention rate at 0 ° C. is low and the discharge capacity after storage at 85 ° C. is low. On the other hand, when firing is performed at over 900 ° C., decomposition of Mn ₂ O ₃ to Mn ₃ O ₄ occurs, 20
This is because the capacity retention rate at ℃ is low, and the discharge capacity after storage at 85 ° C is low, which is both undesirable.

The firing of the Li—Mn composite oxide must be performed in an oxygen atmosphere in order to sufficiently oxidize Mn, and when the firing is not performed in an oxygen atmosphere. This is because the capacity retention at 20 ° C. is low, and the discharge capacity after storage at 85 ° C. is low, as shown in Examples described below, which is not preferable.

The Li-Mn composite oxide is fired at 65
When the temperature is set to 0 ° C. to 950 ° C., as shown in Examples described below, if the temperature is lower than 650 ° C., the synthesis reaction of lithium manganate is insufficient, and the discharge capacity and the capacity retention at 20 ° C. are low. This is because the discharge capacity after storage at 85 ° C. becomes low. On the other hand, when firing at more than 950 ° C., a decomposition reaction of lithium manganate occurs, resulting in a low discharge capacity at 20 ° C. and a low discharge capacity after storage at 85 ° C.

Further, the invention of a non-aqueous electrolyte secondary battery uses the above-mentioned positive electrode active material for a non-aqueous electrolyte secondary battery. The negative electrode of the non-aqueous electrolyte secondary battery according to the present invention is not particularly limited as long as metallic lithium or a substance capable of inserting and extracting lithium is used. For the electrolyte, for example, carbonates, sulfolane, A solution in which a lithium salt is dissolved in an organic solvent of a lactone or an ether or a solid electrolyte having lithium ion conductivity can be used, and is not limited in the present invention.

[0017]

EXAMPLES Examples showing the effects of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 Manganese dioxide (SO ₄ content: 1.2%) was calcined in an electric furnace at 800 ° C. for 20 hours.
The obtained calcined manganese dioxide and lithium carbonate are
i: Mn was weighed so that Mn = 1.06: 1.94, mixed with a ball mill, and then placed in an electric furnace at 800 ° C. in an oxygen atmosphere at 20 ° C.
It was calcined for a period of time and crushed to produce a Li-Mn composite oxide. A coin battery was manufactured using this Li-Mn composite oxide as a positive electrode active material, and a discharge test was performed. The test contents include the specific surface area of the Li—Mn composite oxide, the SO ₄ content,
The initial discharge capacity (mAh / g) at 20 ° C., the capacity retention rate (%) at 15 cycles, and the discharge capacity (mAh / g) after storage at 85 ° C. for 24 hours after charging were measured.

Example 2 The same operation as in Example 1 was carried out except that manganese dioxide was fired in an electric furnace at 900 ° C.

Example 3 Manganese dioxide was fired in an electric furnace at 900 ° C., and the obtained fired manganese dioxide and lithium carbonate were mixed such that Li: Mn = 1.04: 1.96. The same operation as in Example 1 was performed except for weighing.

Example 4 Manganese dioxide was fired in an electric furnace at 900 ° C., and the obtained fired manganese dioxide and lithium carbonate were mixed such that Li: Mn = 1.08: 1.92. The same operation as in Example 1 was performed except for weighing.

Example 5 The same operation as in Example 1 was carried out except that the calcination of manganese dioxide in an electric furnace was 900 ° C., and the calcination in an electric furnace after mixing with a ball mill was 650 ° C.

Example 6 The same operation as in Example 1 was performed except that calcination of manganese dioxide in an electric furnace was 900 ° C., and calcination in an electric furnace after mixing with a ball mill was 950 ° C.

Example 7 Manganese dioxide was changed from 1.2% SO ₄ content to 0.6% SO ₄ content.
The same operation was performed as in Example 2.

Example 8 The same operation as in Example 2 was carried out, except that the manganese dioxide was changed from the SO ₄ content of 1.2% to 0.01%.

Example 9 The same operation as in Example 1 was performed except that calcination of manganese dioxide in an electric furnace was 900 ° C., and calcination in an electric furnace after mixing with a ball mill was 850 ° C.

Example 10 The same operation as in Example 1 was performed except that calcination of manganese dioxide in an electric furnace was 900 ° C., and calcination in an electric furnace after mixing with a ball mill was 900 ° C.

Comparative Example 1 The same operation as in Example 1 was performed except that manganese dioxide was not calcined.

Comparative Example 2 The procedure of Example 1 was repeated, except that the firing of manganese dioxide in an electric furnace was performed at 700 ° C., and the firing in an electric furnace after mixing with a ball mill was performed at 850 ° C.

(Comparative Example 3) The same operation as in Example 1 was carried out except that manganese dioxide was fired in an electric furnace at 1000 ° C.

COMPARATIVE EXAMPLE 4 Manganese dioxide was fired in an electric furnace at 900 ° C., and the obtained fired manganese dioxide and lithium carbonate were mixed such that Li: Mn = 1.02: 1.98. The same operation as in Example 1 was performed except for weighing.

Comparative Example 5 Manganese dioxide was fired in an electric furnace at 900 ° C., and the obtained fired manganese dioxide and lithium carbonate were mixed such that Li: Mn = 1.10: 1.90. The same operation as in Example 1 was performed except for weighing.

Comparative Example 6 The same operation as in Example 1 was performed except that the manganese dioxide was fired in an electric furnace at 900 ° C., and the calcination in the electric furnace after mixing with the ball mill was performed in an air atmosphere.

Comparative Example 7 The procedure of Example 1 was repeated, except that the firing of manganese dioxide in the electric furnace was 900 ° C. and the firing in the electric furnace after mixing with the ball mill was 600 ° C.

(Comparative Example 8) The same operation as in Example 1 was performed except that calcination of manganese dioxide in an electric furnace was set at 900 ° C, and calcination in an electric furnace after mixing with a ball mill was set at 1000 ° C.

Comparative Example 9 Manganese dioxide was not fired,
The same operation as in Example 1 was carried out except that the firing atmosphere was air and the firing in the electric furnace after mixing the ball mill was 850 ° C.

The results of Examples 1 to 10 are shown in Table 1 below, and the results of Comparative Examples 1 to 9 are shown in Table 2 below.

[0038]

[Table 1]

[0039]

[Table 2]

From the above table, it can be seen that according to the present embodiment
The discharge capacity at 0 ° C. and the capacity retention rate, and the discharge capacity after storage at 85 ° C. were both favorable, and it was confirmed that the battery had favorable secondary battery characteristics as a driving power supply.

[0041]

As described above, according to the present invention, Li
_{1 + x} Mn _2-x O _y (0.04 ≦ x ≦ 0.08), the specific surface area is 0.3 to 0.7 m ² / g, and the SO ₄ content is 0.4.
By using a Li-Mn composite oxide of not more than 10% by weight as a positive electrode active material, a high capacity and good high temperature characteristics are obtained, and a discharge capacity, a capacity retention ratio and a discharge capacity after charge storage are all favorable. Preferred secondary battery characteristics as a power source can be provided.

Claims (3)

[Claims] 1. The method according to claim 1, wherein Li _{1 + x} Mn _2-x O _y has a content of 0.04.
≦ x ≦ 0.08, a specific surface area of 0.3 to 0.7 m ² / g, and a SO ₄ content of 0.4% by weight or less, a Li—Mn composite oxide. 2. An Mn raw material, MnO _2, having a temperature of 800 ° C. to 900 ° C.
C., then mixed with Li salt and dried under oxygen atmosphere for 6 hours.
Li-M characterized by being fired at 50 ° C to 950 ° C
Method for producing n composite oxide. 3. A non-aqueous electrolyte secondary battery comprising the Li-Mn composite oxide according to claim 1 as a positive electrode active material for a non-aqueous electrolyte secondary battery.