JPH0787098B2 - Non-aqueous secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-aqueous secondary battery using lithium as a negative electrode active material, and particularly to improvement of a positive electrode.

(B) Conventional Technology Molybdenum trioxide, vanadium pentoxide, titanium or niobium sulfides have been proposed as positive electrode active materials for secondary batteries of this type, but they have not yet been put to practical use.

On the other hand, manganese dioxide and fluorocarbon are known as typical examples of the positive electrode active material of the non-aqueous primary battery.
Moreover, these have already been put to practical use.

Here, manganese dioxide is particularly advantageous in that it has excellent storability, is abundant in resources, and is inexpensive. When using manganese dioxide having such an advantage as a positive electrode active material of a non-aqueous battery, it is necessary to perform a water removal treatment because lithium, which is a negative electrode active material, is highly reactive with water. For example, Japanese Patent Publication Sho-57-
As disclosed in 4064 gazette, exceeding 350 ° C to 430 ° C
It is heat-treated at temperatures up to. This heat treatment changes the crystal structure of electrolytic manganese dioxide from γ type to γ-β or β type. Thus, electrolytic manganese dioxide has the property that the crystal structure changes with the heat treatment temperature.

By the way, it is considered useful to use manganese dioxide, which has various advantages as described above, as a positive electrode active material of a non-aqueous secondary battery, but it has become clear that there is a new problem here. That is, γ-β or β-type manganese dioxide has a large collapse of the crystal structure after discharge and is difficult to be reversible. On the other hand, γ-type manganese dioxide has a small crystal structure collapse after discharge.

(C) Problems to be Solved by the Invention An object of the present invention is to improve the cycle characteristics of a non-aqueous secondary battery by using improved manganese dioxide as a positive electrode active material.

(D) Means for Solving the Problems In the present invention, anhydrous or nearly anhydrous γ-type manganese dioxide obtained by preliminarily doping lithium in the crystal lattice of electrolytic manganese dioxide and then heat-treating it is used as the positive electrode active material. In a non-aqueous secondary battery.

(E) Action According to the present invention, although the reason is not clear, the presence of lithium to be doped in the crystal lattice suppresses the change of the crystal structure even by the heat treatment, so that γ-type manganese dioxide which is anhydrous or nearly anhydrous is obtained. A non-aqueous secondary battery having excellent cycle characteristics can be obtained by using such γ-type manganese dioxide as a positive electrode active material.

(F) Example Hereinafter, an example of the present invention will be described in detail.

Example 1 40 g of electrolytic manganese dioxide having an average particle size of about 100 μ was added at 1 mol / mol.
Immerse in a container put in 30 cc of lithium hydroxide solution of
Then, the microwave of a frequency of about 2.45 GHz is irradiated. When the solution evaporates, the microwave irradiation is stopped, and 30 cc of 1 mol / liter lithium hydroxide solution is put in the container again, and microwave irradiation is performed as in the previous case. After repeating this operation 7 times, it is washed with water 1 to obtain lithium-doped manganese dioxide, and then heat-treated at a temperature of more than 350 ° C. to about 430 ° C. The heat treatment atmosphere may be vacuum, inert, reducing or oxidizing as long as it is an anhydrous atmosphere. The processing time may be 2 hours or more. The manganese dioxide obtained by the above treatment had almost all water removed, and the crystal structure maintained the γ type.

Next, 90% by weight of this treated manganese dioxide, 6% by weight of acetylene black as a conductive agent, and 4% by weight of fluororesin powder as a binder were mixed to form a positive electrode mixture, and this mixture was formed at a molding pressure of 5%. It is pressure-molded at a diameter of 20.0 mmφ at ton / cm ² and then heat-treated at a temperature of 200 to 350 ° C. to obtain a positive electrode. The atmosphere for the heat treatment at this time is not particularly limited as long as it is an atmosphere with a low water content.

FIG. 1 shows a half cross-sectional view of a flat type non-aqueous electrolyte secondary battery assembled by using the above positive electrode. (1) and (2) are positive and negative electrode cans made of stainless steel, which are polypropylene. It is separated by an insulating packing (3) made of.
Reference numeral (4) is a positive electrode, which is pressed against a positive electrode current collector (5) fixed to the inner bottom surface of the positive electrode can (1). (6) is a negative electrode obtained by punching out a rolled lithium plate to a predetermined size, and is pressed onto a negative electrode current collector (7) fixed to the inner bottom surface of the negative electrode can (2). (8) is a separator made of polypropylene nonwoven fabric, which is impregnated with an electrolytic solution. The electrolytic solution used was one in which 1 mol / mol of lithium perchlorate was dissolved in a mixed solvent of equal volume of propylene carbonate and 1,2 dimethoxyethane. The battery dimensions were 24.0 mm in diameter and 3.0 mm in thickness. Let this battery be (A ₁ ).

Comparative Example 1 A first comparative battery (B ₁ ) was prepared in the same manner as in Example 1 except that the positive electrode active material was prepared by subjecting electrolytic manganese dioxide to a heat treatment at a temperature of 150 ° C. without lithium doping. did.

Comparative Example 2 A second comparative battery similar to Example 1 except that lithium manganese dioxide was not doped and electrolytic manganese dioxide was heat-treated at a temperature of higher than 350 ° C. to 430 ° C. as a positive electrode active material. (B ₂ ) was created.

Comparative Example B About 24% of electrolytic manganese dioxide was added to a saturated solution of lithium hydroxide.
After soaking for a time, it was filtered. Then, a comparative battery (C ₁ ) was prepared in the same manner as in Example 1 except that the positive electrode active material was heat-treated at 350 ° C to 430 ° C.

Comparative Example B About 72% of electrolytic manganese dioxide was added to a saturated solution of lithium hydroxide.
After soaking for a time, it was filtered. Then, a comparative battery (C ₂ ) was prepared in the same manner as in Example 1 except that the positive electrode active material was heat treated at 350 ° C to 430 ° C.

Figure 2 shows the cycle characteristics comparison diagram of these batteries (A ₁ ) (B ₁ ) (B ₂ ) (C ₁ ) (C ₂ ). The cycle condition is charging current 2.
The charge end voltage was 4.0 V at 0 mA, and the discharge end voltage was 1.5 V at a discharge current of 2.0 mA.

As is apparent from FIG. 2, the battery (A ₁ ) of the present invention has improved cycle characteristics as compared with the comparative batteries (B ₁ ) (B ₂ ) (C ₁ ) (C ₂ ).

Next, an example using a solid electrolyte will be described in detail.

Example 2 The positive and negative electrodes were the same as in Example 1, and the electrolyte (Li ₄ S
A battery (A ₂ ) of the present invention was prepared in the same manner as in Example 1 except that the lithium ion conductive solid electrolyte represented by iO ₄ ) 0.5 (Li ₃ AsO ₄ ) 0.5 was used.

Comparative Example 3 A third comparative battery (B ₃ ) was prepared in the same manner as in Example 2 except that lithium manganese dioxide was not doped and electrolytic manganese dioxide was heat-treated at a temperature of 150 ° C. to obtain a positive electrode active material. did.

Comparative Example 4 A fourth comparative battery similar to Example 2 except that lithium manganese dioxide was not doped and electrolytic manganese dioxide was heat-treated at a temperature of higher than 350 ° C. to 430 ° C. as a positive electrode active material. (B ₄ ) was created.

Figure 3 these cell _{(A 2) (B 3)} (B 4) shows the cycle characteristics comparison diagram, charge end voltage 4.0V in Cycling conditions charge current 150 mu _A, whereas the discharge current 150 mu _A in discharge end voltage 1.5
V.

As is apparent from FIG. 3, the battery (A ₂ ) of the present invention has improved cycle characteristics as compared with the comparative batteries (B ₃ ) and (B ₄ ).

To consider the reason for this, in the case of the comparative batteries (B ₁ ) (B ₃ ),
Manganese dioxide, which is the positive electrode active material, exhibits a γ-type crystal structure, but the heat treatment temperature is low at 150 ° C, so bound water remains in manganese dioxide, and this bound water reacts with lithium, which is the negative electrode active material. Characteristics deteriorate. or,
In the case of the comparative batteries (B ₂ ) and (B ₄ ), the heat treatment temperature of manganese dioxide is high, so that most of the water content is removed, but it exhibits a γ-β or β-type crystal structure and has difficulty in reversibility. It is considered that the characteristics deteriorate due to the factors.

Furthermore, in the case of the comparative batteries (C ₁ ) and (C ₂ ), only the surface portion was modified after the heat treatment because the lithium was not pre-doped in the crystal lattice of electrolytic manganese dioxide before the heat treatment. Therefore, although the storage characteristics related to the reaction that occurs on the surface of manganese dioxide can be improved, the crystal structure collapses significantly after discharge during charge and discharge, so that lithium is inserted into the crystal lattice. It is considered that the charge / discharge cycle characteristics in which the detachment is repeated are hardly improved.

On the other hand, in the case of the batteries (A ₁ ) and (A ₂ ) of the present invention, the characteristics are considered to be improved because anhydrous or nearly anhydrous γ-type manganese dioxide is used as the positive electrode active material.

(G) Effect of the invention As described above, the use of anhydrous or near anhydrous γ-type manganese dioxide obtained by pre-doping lithium in the crystal lattice of electrolytic manganese dioxide as a positive electrode active material improves cycle characteristics. An excellent non-aqueous secondary battery can be obtained, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a half sectional view of a non-aqueous secondary battery according to an embodiment of the present invention, and FIGS. 2 and 3 are charge / discharge cycle characteristic comparison diagrams, respectively. (1) …… positive electrode can, (2) …… negative electrode can, (3) …… insulating packing, (4) …… positive electrode, (6) …… negative electrode, (8)
...... Separator, (A ₁ ) (A ₂ ) …… Battery of the present invention, (B ₁ )
(B ₂ ) (C ₁ ) (C ₂ ) (B ₃ ) (B ₄ ) …… Comparison battery.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshihiko Saito 2-18, Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-52-73328 (JP, A)

Claims (1)

[Claims] 1. A negative electrode using lithium or a lithium alloy as an active material, and anhydrous or nearly anhydrous γ-type manganese dioxide obtained by pre-doping lithium in a crystal lattice of electrolytic manganese dioxide as an active material. Non-aqueous secondary battery having a positive electrode that