JP2000285961A - Lithium manganese secondary battery - Google Patents

Abstract

(57) [Problem] To provide a lithium manganese secondary battery excellent in charge / discharge cycle characteristics. SOLUTION: As constituent elements, (1) a positive electrode using a lithium manganese composite oxide as an active material, (2) a negative electrode using metallic lithium or an alloy thereof, or a carbon material into which lithium can be inserted and released, (3) non-aqueous It contains an electrolytic solution and (4) a dehydrating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium manganese secondary battery having excellent charge / discharge cycle characteristics.

[0002]

2. Description of the Related Art In recent years, with the advance of electronic technology, high performance, miniaturization, and portability of electronic devices have been advanced, and secondary batteries with high energy density have been required for these electronic devices. Conventionally, as a secondary battery used for these electronic devices, a nickel-cadmium secondary battery, a lead storage battery, a nickel-metal hydride battery, a lithium ion secondary battery, and the like are exemplified. In particular, lithium ion secondary batteries are the most promising batteries that have high battery voltage, high energy density, low self-discharge, excellent charge / discharge cycle characteristics, and can be adapted to small and light batteries.

As a positive electrode material for such a lithium ion secondary battery, use of lithium manganese oxides such as LiCoO ₂ , LiNiO _2, and lower cost LiMn ₂ O ₄ has been studied, and active development research has been conducted. Have been done. However, batteries using manganese oxide as a cathode material are inexpensive, have high voltage and high energy density, but have the problem of short charge / discharge cycle life, and are widely used as practical batteries. Not yet used.

In a lithium manganese secondary battery, a positive electrode using a lithium manganese composite oxide as an active material, a negative electrode using lithium metal or an alloy thereof, or a lithium compound, and a lithium salt as a non-aqueous electrolyte are used in a polar solvent. A dissolved non-aqueous electrolyte is used. As the polar solvent, alkyl carbonates such as ethylene carbonate and propylene carbonate are preferably used. Since these alkyl carbonates are solid at room temperature or have a high viscosity, they are usually used after being diluted with another organic solvent. As such a diluting solvent, 1,
Low-viscosity solvents such as 2-dimethoxyethane, dimethyl carbonate and diethyl carbonate are used.
As lithium salts, LiPF ₆ , LiBF ₄ , Li
ClO ₄ or the like is used. Among them, LiP
F ₆ has the best performance and is widely used.

[0005]

However, as a lithium manganese secondary battery, as an example of a non-aqueous electrolyte,
When LiPF ₆ is used, it reacts with moisture, elutes Mn, and the cycle characteristics tend to deteriorate.

It is presumed that the elution of Mn occurs in the mode represented by the following chemical formulas (1) to (4).

Formula 1 LiPF ₆ → LiF + PF ₅ Formula 2 PF ₅ + H ₂ O → 2HF + POF ₃ Formula 3 2Li MnO ₄ + 4H ⁺ → 2Li ⁺ + Mn ²⁺
+ 2H ₂ O + 3λ-MnO ₂ Formula 4 Mn ²⁺ + 2e ⁻ → Mn Explaining the above formula: Formula 1 The electrolyte is decomposed to form PF ₅ . And Equation 2 PF ₅ and water reaction, HF will be generated. Formula 2 H ⁺ reacts with LiMn ₂ O ₄ and the dissolution reaction proceeds. Formula 3 The dissolution reaction is irreversible, Mn ²⁺ elutes and Li
It does not return to Mn ₂ O ₄ . Formula 4 The eluted Mn ²⁺ precipitates on the negative electrode and deteriorates the characteristics of the negative electrode. As described above, when LiPF ₆ is used, Mn is eluted from the positive electrode due to the influence of moisture, which also has a negative effect on the negative electrode, and lowers the charge / discharge cycle characteristics of the battery. Conventionally, a desiccant is inserted into the battery in order to avoid such an influence of moisture (Japanese Patent Laid-Open No. 61-39464). However, the solid desiccant is not easy to insert into the battery, and it is necessary to form the solid desiccant in accordance with the shape of the electrode or to secure a storage portion in the battery, which has a problem in battery production. Also, instead of removing water, a solid additive such as alumina is added to the electrolyte to absorb free acid components in the electrolyte such as generated HF (Japanese Unexamined Patent Application Publication No. Hei 5 (1993) -195). -315006). However, such solid powder adhered to the electrode surface and blocked the eyes of the separator, thereby adversely affecting the battery characteristics.

The present invention uses LiPF ₆ as a non-aqueous electrolyte by using a dehydrating agent mixed in the non-aqueous electrolyte.
It is an object of the present invention to provide a lithium manganese secondary battery in which a decrease in charge / discharge cycle characteristics is small even when the battery is used.

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have found that a positive electrode using a lithium manganese composite oxide as an active material, metallic lithium or an alloy thereof, or lithium A negative electrode using the compound,
In a lithium manganese secondary battery comprising a non-aqueous electrolyte, further, by dissolving or mixing a dehydrating agent in the non-aqueous electrolyte, a lithium manganese secondary battery having excellent charge / discharge cycle characteristics can be manufactured. Heading that
The present invention has been reached. By including the dehydrating agent in the electrolytic solution, there is no need to change the design of battery components such as a solid dehydrating agent, and there is no need to worry about adhesion or precipitation to electrodes or separators.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The lithium-manganese composite oxide used in the present invention is obtained, for example, by wet mixing lithium hydroxide and a manganese compound selected from manganese dioxide and manganese carbonate, drying the obtained slurry, and crushing it. , 350
It is obtained by primary baking at ~ 500 ° C, cooling to 45 ° C or less, crushing again, and secondary baking at 600-800 ° C.

As the lithium hydroxide, one commercially available as a monohydrate represented by LiOH.H ₂ O is used.

As the manganese compound, manganese dioxide or manganese carbonate is used.

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.

In the wet mixing of lithium hydroxide and a manganese compound, the lithium hydroxide is in a state of being dissolved in a slurry state, and the dissolved lithium hydroxide is in a state of being highly dispersed in the manganese compound. Therefore, the lithium manganese composite oxide obtained through the steps described below is very uniform in composition, and therefore has a high discharge capacity. On the other hand, when these compounds are dry-mixed, mixing tends to be insufficient, the composition of lithium manganate in the obtained lithium-manganese composite oxide tends to be non-uniform, and a lithium-manganese composite oxide having a high discharge capacity is obtained. Difficult to get.

In the wet mixing, for example, lithium hydroxide (L
iOH.H ₂ O) and a manganese compound, usually Li
And Mn in a molar ratio of 1: 1.8 to 1: 2.2, preferably 1: 1.9 to 1: 2.1, and adding water to form a slurry. By mixing using a pot mill. The amount of water is, for example, 10 to 40 based on the amount of lithium hydroxide and the manganese compound.
%, Preferably 15 to 25% by weight. If it is less than 10% by weight, the amount of lithium hydroxide dissolved is not sufficient, the viscosity is high, and it is difficult to disperse. If it exceeds 40% by weight,
When the drying rate is reduced, solid-liquid separation during drying is increased, and the uniform dispersion of lithium is easily inhibited.

The slurry obtained is then preferably treated with 7
Dry at 0-180 ° C, preferably 130-160 ° C. If the drying temperature is lower than 70 ° C., the drying rate is decreased, and the production efficiency is apt to decrease, which is not preferable. On the other hand, if the temperature exceeds 180 ° C., it is necessary to improve the performance of the dryer itself, and the equipment equipment cost, and eventually the operation cost, are high, which is economically undesirable. In addition, the contact time between Li and Mn becomes relatively short, and the reaction time for infiltration of Li into Mn becomes short, which is not preferable.

The resulting dried product is then crushed. The average particle size of the dried and crushed product is usually 1 to 100 μm, preferably 5 to 40 μm. 100 μm
With the above, crushing and uniform mixing are not sufficient. If it is 1 μm or less, there is a concern that the compound is excessively disintegrated and destroys the structure of the compound. In addition, it increases inhalation of dust to workers.

The granules thus obtained are then heated at 350-500 ° C., preferably at 400-500 ° C.
C., more preferably at a temperature of 450 to 500C. Since the melting point of lithium hydroxide is 445 ° C., by firing at a temperature of 500 ° C. or less, 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 45 ° C. or lower, preferably 25 ° C. or lower, more preferably 20 ° C. or lower, secondary pulverization is performed again. As a lower limit, 0 ° C. or more is appropriate for practical operation. By this cooling operation, a more uniform lithium manganese composite oxide can be obtained. Secondary crushing is the same as in the case of crushing before primary firing.

The second crushed material is then subjected to a second firing (second firing). This secondary firing is performed at 600 to 800 ° C.
Preferably 650-750 ° C, particularly preferably 68
Perform at 0-720 ° C. By this secondary firing, the composition can be made uniform and the reaction of unreacted substances can be efficiently promoted, so that a high capacity lithium manganese composite oxide can be obtained. By firing at 600 to 800 ° C., the reaction is completed. If the secondary firing temperature is lower than 600 ° C., the reaction is insufficient, so that not only the crystallinity of the lithium manganese composite oxide becomes insufficient, but also unreacted substances remain and by-products are generated, and the positive electrode active material is produced. As a result, sufficient characteristics cannot be obtained. On the other hand, when the temperature exceeds 800 ° C., the crystallinity of the lithium manganese composite oxide becomes too high, so that the crystal collapse due to insertion and desorption of lithium ions easily occurs, and the cycle characteristics of the lithium manganese composite oxide tend to deteriorate. .

The lithium manganese composite oxide is used as a positive electrode material of the lithium manganese secondary battery of the present invention.
The method of use as a positive electrode material is the same as in the case of the conventional method of using a positive electrode material, in which acetylene black as a conductive additive and polyvinylidene fluoride as a binder are blended and mixed to form a uniform composition. And then press molding,
It is applied on a current collector to form a positive electrode.

As the negative electrode in the lithium manganese secondary battery, conventionally used metallic lithium, a lithium alloy and a carbon material into which lithium can be inserted and released can be used. Examples of the carbon material include, but are not particularly limited to, graphite and coal-based coke, petroleum-based coke,
Carbide of coal-based pitch, carbide of petroleum-based pitch, needle coke, pitch coke, phenolic resin, carbide such as crystalline cellulose and carbon materials partially graphitized thereof, furnace black, acetylene black, pitch-based carbon fiber, etc. Can be

As the non-electrolytic solution used in the present invention, for example, a non-aqueous electrolytic solution obtained by dissolving a lithium salt as an electrolyte in an organic solvent at a concentration of 0.5 to 1.5 mol / l is used. . Here, the organic solvent is not particularly limited, for example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone,
Dimethyl carbonate, ethyl methyl carbonate, acetate compound, propionate compound, diacetate compound, dimethoxyethane, diethoxyethane, dimethoxypropane, diethoxypropane, tetrahydrofuran, dioxolane or a mixture of two or more mixed solvents No.

Examples of the electrolyte include lithium perchlorate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate and the like.

The dehydrating agent used in the present invention includes a dehydrating agent.
It is not particularly limited as long as it has an action,
Various dehydrating agents can be used. Such dehydration
Examples of the agent include orthoformic acid methyl ester and o-formic acid.
Ethyl formate, methyl orthoacetate,
Orthoacetic acid ethyl ester, orthobenzoic acid ethyl ester
Ter, ethyl orthopropionate, diphenyl
Methane diisocyanate, p-toluenesulfonic acid iso
Cyanate, aluminum alcoholate [Al (O-te
rt-C_Three H₇ )_Three , Al (OC_Two H_Five )_Three , Al (O
-Tert-C_Three H ₇ )_Two (O-sec-C_Four H₉ ), Al (O
-Sec-C_Four H₉ O)_Three Etc.], aluminum chelate [A
Luminium tris (acetylacetonate)], 3-E
Tyl-2-methyl-2- (3-methylbutyl) -1,3
-Oxazolidine, molecular sieves and the like
You.

[0027]

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: 2, and 20% by weight of the total amount of the blend was removed. Ionic water was added to form a slurry. The slurry was mixed in a pot mill, dried at 150 ° C., and then crushed. The average particle size of the crushed product was 20 μm. This crushed material was primarily fired at 470 ° 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 10 μm, and subjected to secondary firing at 700 ° C. for 12 hours in an air atmosphere.

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 that the material was lithium manganate which was Mn ₂ O ₄ .

The fired product was used as a positive electrode active material in an amount of 82 parts by weight, and acetylene black 1 was used as a conductive agent.
0 parts by weight, 7 parts by weight of polyvinylidene fluoride as a binder, and 1 part by weight of paratoluenesulfonic acid isocyanate as a dehydrating agent previously dissolved in 58 parts by weight of N-methyl-2-pyrrolidone are added and mixed well. I got

This paste is applied to an aluminum rope,
A positive electrode plate was prepared by pressing and drying. A metal lithium plate having the same size as the positive electrode was used for the negative electrode, and a metal lithium reference electrode was used for positive electrode potential measurement.

1 mol / dm ³ of LiPF _{6 as an} electrolytic solution
A test battery was prepared by using a mixed solvent of ethylene carbonate and diethyl carbonate in which 1 was dissolved. Examples 2 to 8 Test batteries were prepared in the same manner as in Example 1 except that the dehydrating agents shown in Table 1 were used. Example 9 The amount of the binder was changed to 7.9 parts by weight, and the amount of the dehydrating agent was set to 0.
A test battery was prepared in the same manner as in Example 1 except that the amount was changed to 1 part by weight. Example 10 A test battery was prepared in the same manner as in Example 1 except that the amount of the binder was changed to 6 parts by weight and the amount of the dehydrating agent was changed to 2 parts by weight. Comparative Example 1 A test battery was prepared in the same manner as in Example 1 except that the amount of the binder was changed to 8 parts by weight and no dehydrating agent was used. Comparative Example 2 A test battery was prepared in the same manner as in Example 1 except that 1 part by weight of distilled water was added without using a dehydrating agent. Characteristic test The test battery prepared as described above was subjected to a current density of 0.5 m.
After charging to 4.3 V with a constant current of A / cm ² , 3.0
Discharge characteristics were evaluated by repeating a charge / discharge cycle of discharging to V. At this time, the discharge capacity in the first cycle was defined as the initial capacity (mAh / g),
The discharge capacity at the cycle was defined as a capacity retention rate (%). Table 1 shows the results.

[0032]

[Table 1] Table 1

[0033]

[Table 2] Table 1 (continued)

As shown in Table 1, Examples 1 to 9 of the present invention
In the battery of No. 5, a high initial capacity and a high capacity retention were obtained under the predetermined charge and discharge conditions. On the other hand, in Comparative Example 1 in which no dehydrating agent was used, 100 ppm of Mn was eluted. In Comparative Example 2 in which distilled water was added without using a dehydrating agent, the initial capacity and capacity retention were low, Mn was eluted at 15,000 ppm, and the cycle characteristics were poor.

[0035]

According to the present invention, a lithium manganese secondary battery having excellent charge / discharge cycle characteristics can be obtained.

 ──────────────────────────────────────────────────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 Inomaba-cho, Minami-ku, Kyoto-shi, Kyoto Prefecture Nippon Battery Co., Ltd. (72) Inventor Hiroshi Mukai Kyoto, Kyoto 1F, Nippon Battery Co., Ltd. F term (reference) 5H029 AJ05 AK03 AL12 AM03 AM04 AM05 AM07

Claims (1)

[Claims] (1) a positive electrode using a lithium-manganese composite oxide as an active material; (2) a negative electrode using lithium metal or an alloy thereof, or a carbon material capable of inserting and releasing lithium; (3) a non-aqueous electrolyte; And (4) a dehydrating agent, comprising: a lithium manganese secondary battery.