JP2698180B2 - Non-aqueous secondary battery - Google Patents

Description

The present invention relates to a non-aqueous secondary battery provided with a negative electrode made of lithium or a lithium alloy, and more particularly to an improvement in a positive electrode.

(B) Conventional technology Manganese dioxide and fluorocarbon are known as typical examples of the positive electrode active material of this type of secondary battery, and these have already been put to practical use.

Here, manganese dioxide in particular has the advantage of being excellent in preservability, abundant in resources, and inexpensive.

In view of the background described above, it is considered to be beneficial to use manganese dioxide as the positive electrode active material of the non-aqueous secondary battery. However, manganese dioxide has difficulty in reversibility and has a problem in charge / discharge cycle characteristics.

(C) Problems to be Solved by the Invention By using a manganese oxide having excellent reversibility as the positive electrode active material, a non-aqueous secondary battery having excellent storage stability, low cost, and excellent charge / discharge cycle characteristics can be obtained. The purpose is to provide.

(D) Means for Solving the Problems According to the present invention, as a positive electrode active material, an X-ray diffraction diagram in a charged state shows a diffraction peak of only Li ₂ MnO ₃ and a Li / Mn ratio of 2
It is characterized in that a smaller lithium-containing manganese oxide is used.

(E) Function As proposed by the present applicant in Japanese Patent Application No. 61-258940,
When manganese dioxide to which Li ₂ MnO ₃ is added is used as the positive electrode active material, the reversibility is improved as compared with the case of using manganese dioxide alone, but there are some drawbacks in the charge / discharge cycle characteristics at a shallow depth.

In view of this, the present applicant has proposed in Japanese Patent Application No. 63-34151 that manganese oxide represented by Li ₂ MnO ₃ is used as a positive electrode active material.

Here, the present inventors have for the Li ₂ MnO _3, further result of pursuing, those dedoped lithium from Li ₂ MnO _3, the increase in discharge capacity was observed while maintaining the structure of Li ₂ MnO ₃ Was. In addition, since the structure of Li ₂ MnO ₃ was maintained, the reversibility to charge and discharge was as excellent as that of Li ₂ MnO ₃ alone.

The following methods are available for undoping lithium while maintaining the structure of Li ₂ MnO ₃ . That is, Li ₂ MnO
_This is a method in which ₃ is immersed in water and then heat-treated. Li ₂ Mn
When O ₃ is immersed in water, lithium ions are replaced by an ion exchange reaction with protons. Here, by performing the heat treatment at a relatively low temperature (200 ° C. or lower), protons can be removed while maintaining the crystal structure.

(F) Examples Examples of the present invention will be described in detail below.

Example 1 After mixing 50 g of chemical manganese dioxide having an average particle diameter of 30 μm or less and 28 g of lithium hydroxide in a mortar, the mixture was mixed in air in a volume of 375 μm.
Heat treat at 20 ° C for 20 hours. By this heat treatment, Li ₂ MnO ₃ is obtained.

After immersing the thus obtained Li ₂ MnO ₃ in water for 24 hours, a heat treatment is performed at 150 ° C. in a vacuum. By this heat treatment, the X-ray diffraction diagram shows a diffraction peak of Li ₂ MnO ₃ only,
A lithium-containing manganese oxide having an i / Mn ratio of 1.5 is obtained.

The lithium-containing manganese oxide as a positive electrode active material,
This active material powder, acetylene black as a conductive agent and a fluororesin powder as a binder were mixed at a weight ratio of 90: 6: 4 to form a positive electrode mixture, and the positive electrode mixture was mixed at 2 ton / c.
After pressure molding to a diameter of 20 mm with m ² , heat treatment is performed at 150 ° C. in vacuum to obtain a positive electrode.

The negative electrode is obtained by punching a lithium plate having a predetermined thickness to a diameter of 20 mm.

FIG. 1 shows a half cross-sectional view of a flat nonaqueous electrolyte secondary battery assembled using the positive and negative electrodes described above. Insulated by insulating packing (3). (4)
Is a positive electrode as the gist of the present invention, and is pressed against a positive electrode current collector (5) fixed to the inner bottom surface of the positive electrode can (1).
Reference numeral (6) denotes a negative electrode, which is crimped to a negative electrode current collector (7) fixed to the inner bottom surface of the negative electrode can (2). (8) is a separator made of a polypropylene microporous thin film, and used as an electrolytic solution was 1 mol / dissolved lithium perchlorate in a mixed solvent of propylene carbonate and dimethoxyethane. The battery dimensions were 24.0 mm in diameter and 3.0 mm in thickness.

 This battery of the present invention is referred to as (A1).

Example 2 After immersing Li ₂ MnO ₃ obtained in Example 1 in water for one week, heat treatment is performed at 150 ° C. in a vacuum. By this heat treatment, an X-ray diffraction diagram shows a diffraction peak of only Li ₂ MnO ₃ and a lithium-containing manganese oxide having a Li / Mn ratio of 1.0 is obtained.

A battery of the present invention (A2) was produced in the same manner as in Example 1 except that this lithium-containing manganese oxide was used as a positive electrode active material.

Comparative Example 1 a positive electrode active material, but using Li ₂ MnO ₃ The resulting Li ₂ MnO _3, i.e. Li / Mn ratio of 2 in Example 1 alone without immersion in water treatment, others A comparative battery (B1) similar to that of Example 1 was produced.

Comparative Example 2 After mixing 50 g of chemical manganese dioxide having an average particle size of 30 μm or less and 6 g of lithium hydroxide in a mortar, the mixture was 375 in air.
Heat treat at 20 ° C for 20 hours.

By this heat treatment, a composite of lithium-containing manganese oxide having a Li / Mn ratio of 3/7 and MnO ₂ (manganese dioxide) is obtained. The X-ray diffraction pattern of this composite shows the diffraction peaks of Li ₂ MnO ₃ and MnO ₂ . Using this composite as a positive electrode active material,
A comparative battery (B2) similar to that of Example 1 was made, except that it was used.

Comparative Example 3 After mixing 50 g of chemical manganese dioxide having an average particle size of 30 μm or less and 25 g of lithium hydroxide in a mortar, the mixture was mixed in the air at 375 g.
Heat treat at 20 ° C for 20 hours. By this heat treatment, the Li / Mn ratio becomes 1.5
And a complex of lithium-containing manganese oxide and MnO ₂ (manganese dioxide). The X-ray diffraction pattern of this composite shows the diffraction peaks of Li ₂ MnO ₃ and MnO ₂ . A comparative battery (B3) similar to that of Example 1 was made except that this composite was used as a positive electrode active material.

2 and 3 show charge / discharge cycle characteristics of these batteries.

The charging / discharging conditions in FIG. 2 are as follows.
The battery was charged with mA to a final charge voltage of 4.0 V. The charge / discharge conditions in FIG. 3 were discharge at a current of 3 mA for 8 hours, charged at a current of 3 mA, and set to a charge termination voltage of 4.0 V.

2 and 3, the batteries (A1) and (A2) of the present invention
It can be seen that excellent charge / discharge cycle characteristics are exhibited under both shallow and deep conditions as compared with the comparative batteries (B1), (B2), and (B3).

(G) Effect of the Invention As described above, in a non-aqueous secondary battery provided with a negative electrode made of lithium or a lithium alloy, the X-ray diffraction diagram in the charged state as a positive electrode active material shows a diffraction peak of only Li ₂ MnO ₃ . By using a lithium-containing manganese oxide having a Li / Mn ratio smaller than 2, the charge / discharge cycle characteristics of this type of battery can be improved, and its industrial value is extremely large.

In the description of the present invention, a non-aqueous electrolyte secondary battery has been described as an example, but the present invention can also be applied to a solid electrolyte secondary battery.

[Brief description of the drawings]

1 is a half sectional view of the battery of the present invention, FIGS. 2 and 3 are charge / discharge cycle characteristics of the battery, FIG. 2 shows the characteristics at a shallow depth, and FIG. 3 shows the characteristics at a deep depth. Shown respectively. (1) Positive electrode can, (2) Negative electrode can, (3) Insulating packing, (4) Positive electrode, (5) Positive electrode current collector,
(6)… negative electrode, (7)… negative electrode current collector, (8)… separator, (A1) (A2)… battery of the present invention, (B1) (B2)
(B3)… Comparative battery.

Claims (1)

(57) [Claims] 1. An active material comprising a negative electrode made of lithium or a lithium alloy and a lithium-containing manganese oxide having a Li / Mn ratio of less than 2 in an X-ray diffraction pattern in a charged state showing a diffraction peak of only Li ₂ MnO ₃ . Non-aqueous secondary battery comprising a positive electrode.