JPH0638334B2 - Method for manufacturing organic electrolyte battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an improvement in the positive electrode of an organic electrolyte battery using lithium as a negative electrode main active material and bismuth trioxide Bi ₂ O ₃ as a positive electrode main active material. is there.

[Conventional technology]

Conventionally, in this type of battery, for example, when manufacturing a button battery, the positive electrode has been manufactured as follows. That is, bismuth trioxide as an active material, a conductive agent such as carbon powder or metal powder such as graphite or carbon black, and a resin binder such as fluororesin or polystyrene are mixed at a predetermined composition ratio, and then this positive electrode mixture is mixed. A pellet of a positive electrode molded body is obtained by filling a predetermined amount of the agent into a mold of a molding machine and press-molding. The positive electrode pellets thus obtained have a temperature within a range that does not cause thermal decomposition of the resin binder or oxidation of the conductive agent.
After being dried by heating under reduced pressure (up to 300 ° C or less) and sufficiently dehydrated, it is incorporated into a battery. Organic electrolyte batteries using bismuth trioxide as the positive electrode active material are disclosed in, for example, Japanese Patent Laid-Open Nos. 52-12425 and 59-49673.

[Problems to be solved by the invention]

However, as shown in FIG. 2 (c), the discharge characteristics of a battery prepared by the above-mentioned conventional method using bismuth trioxide as the positive electrode active material are as follows. Shows,
The operating voltage is low when the depth of discharge is about 40-60% or more. For this reason, when this battery is used in equipment that requires large-current discharge, the voltage required to operate the equipment normally is maintained even though the battery capacity still remains due to the drop in battery voltage. Since it cannot be obtained, there is a problem that the effective battery capacity (life) is significantly reduced. In particular, in devices such as electronic watches and calculators, the average current consumption is as low as several μA, and the expected service life of batteries is from months to 10 years or longer, and at the same time, lamps, Due to the use of buzzers, step motors, etc., pulsed large current discharge is required, and the batteries used for these are required to have long-term reliability as well as large current discharge performance. The above-mentioned problem was a very important problem.

First, in order to solve the above-mentioned problems, the inventors of the present invention used bismuth trioxide heat-treated at a temperature of 650 ° C. or higher as a positive electrode active material of this type battery to operate this type battery. It has been found that the voltage, particularly the operating voltage at a discharge depth of about 40% or more, is improved, and the effective discharge capacity is significantly improved, and a patent application has already been made (Japanese Patent Application No. 61-27).
0766). That is, when manufacturing a positive electrode, before mixing bismuth trioxide with a conductive agent, a binder, etc., bismuth trioxide is heat-treated in advance at a temperature of 650 ° C. or higher, and if necessary, a conductive agent or a binder is then added. It was mixed with a binder and molded into a predetermined shape.

However, with this method, the discharge characteristics of this type of battery were remarkably improved and almost reached a satisfactory level.
When this type of battery is used for a long time of, for example, 10 years or more, long-term reliability such as self-discharge and deterioration of discharge characteristics over time, that is, storage characteristics, especially storage characteristics at high temperature, is Compared to the case where bismuth oxide was not heat-treated, it was equal or worse in some cases, and the level was still insufficient.

An object of the present invention is to solve such problems, and even in an application involving a large-current pulse discharge and continuously used for a long period, an organic electrolyte battery that can be effectively used up to the end of the capacity of the battery. To provide.

[Means for solving problems]

As a result of various investigations by the present inventors in order to solve the above-mentioned problems, the discharge characteristics of the battery using the heat-treated bismuth trioxide were determined by the heat treatment temperature as described in the above-mentioned prior application. The effect is the greatest, and the discharge performance is almost determined by the heat treatment temperature. However, for long-term deterioration of the battery over time, that is, storage characteristics (especially under high temperature), the cooling path and cooling method after heat treatment of bismuth trioxide It was found that the effect of

That is, as the positive electrode active material, bismuth trioxide has a melting point (about 820
(° C) or higher, heat treated in a molten state, rapidly cooled the molten state, solidified in a short time, in the case of a battery using bismuth trioxide that is not heat treated in the conventional In comparison, not only the discharge characteristics but also the storage characteristics are significantly improved, while bismuth trioxide is melt-heat treated,
In the case of a battery that was slowly cooled by natural cooling of an electric furnace, etc., the discharge characteristics were improved almost as in the case of a battery using rapidly cooled bismuth trioxide. It was found that it was equal to or worse than the conventional battery using bismuth oxide.

That is, the present invention proposes to use, as the positive electrode active material, bismuth trioxide that has been melt-heated at a temperature equal to or higher than its melting point, quenched in a molten state, and solidified in a short time.

The atmosphere in which bismuth trioxide is melted and rapidly cooled may be an atmosphere that does not reduce bismuth trioxide to Bi metal, BiO, or the like, and may be the air, an inert gas, or a vacuum.

The method of melting bismuth trioxide and then quenching it may be such that bismuth trioxide does not undergo alteration such as redox or reaction with other substances and solidifies in a short time, for example, heating in an electric furnace or the like. It can be carried out by pouring the molten bismuth trioxide below the melting point of Bi ₂ O ₃ , preferably below room temperature, onto a corrosion-resistant stainless steel (for example, SUS304) or a metal such as platinum or a ceramics container such as alumina.

Further, when using melted and quenched bismuth trioxide for the positive electrode, in order to uniformly mix it with a carbon conductive agent, a binder, etc., if necessary, the lump of bismuth trioxide solidified after cooling is sufficiently ground. It is preferable that the particles are about 100 μm or less.

[Action]

As described above, in the battery using the bismuth trioxide melt-heated and rapidly cooled as the positive electrode active material, the discharge property and the storage property are remarkably improved as compared with the conventional battery using the non-heat-treated bismuth trioxide.

The reason why the discharge characteristics are improved by the heat treatment of bismuth trioxide, and especially the storage characteristics are remarkably improved when the material is rapidly cooled after melting, is not necessarily clear, but it is presumed as follows. That is, bismuth trioxide has an orthorhombic α-type, 70
There are several crystal modifications such as tetragonal β-type and cubic γ-type which are formed by transformation at 0 to 710 ° C. It is generally said that when bismuth trioxide is melted, slowly cooled and solidified, α-type is easily formed, and when rapidly cooled, γ-type is easily formed. In any case, it is presumed that there is a significant difference in the crystal state of bismuth trioxide after cooling due to the difference in the cooling method, and the surface state of the particles is also significantly different. It is presumed that this difference causes a difference in stability over time of the battery when these are used as the positive electrode active material in the organic electrolyte battery.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 FIG. 1 is a sectional view of a button type battery showing an example of the present invention. In the figure, reference numeral 1 denotes a negative electrode can which also serves as a negative electrode terminal, which is obtained by drawing a three-layered clad plate of Ni-SUS-Ni. The negative electrode 2 is obtained by punching out a lithium sheet having a thickness of 1.4 mm to a diameter of 6.2 mm and press-bonding it to the inner surface of the negative electrode can. Reference numeral 6 denotes a Ni-plated SUS positive electrode can, which also serves as a positive electrode terminal. A positive electrode 5 according to the present invention described below is filled in the positive electrode can, and a separator 4 made of a microporous polypropylene film is placed thereon. An impregnating material 3 holds an electrolytic solution between the positive electrode and the negative electrode, and is made of a nonwoven fabric containing polypropylene as a main element.
Reference numeral 7 denotes a gasket mainly made of polypropylene, which is interposed between the negative electrode can 1 and the positive electrode can 6 to maintain the electrical insulation between the positive electrode and the negative electrode, and at the same time, the opening edge of the positive electrode can is bent and crimped inward. The battery contents are hermetically sealed. The electrolytic solution was butylene carbonate, ethylene carbonate and 1,2-dimethoxyethane 45:
A 5:50 mixed solvent containing 1 mol / mol of lithium perchlorate was used. The size of the battery is 9.5 mm in outer diameter and 3.0 in total thickness.
It was mm.

Three types of positive electrodes were prepared as follows. Commercially available bismuth trioxide powder with a purity of 99.99% was melt-heated in an electric furnace at a temperature of 900 ° C for 5 hours in the air,
The Bi ₂ O ₃ melt was rapidly cooled by pouring it into a stainless (SUS304) container placed on a heat dissipation iron plate at room temperature (about 20 ° C.), and solidified into a flat plate having a thickness of about 1 mm. At this time Bi ₂
The time required for the O ₃ melt to completely solidify was about several seconds at most. Next, after cooling to almost room temperature, it was pulverized and sized to 100 μm or less. In this way, it was melted and then quenched.
A positive electrode active material (a) made of Bi ₂ O ₃ powder was produced. Also,
Similarly, the commercially available bismuth trioxide powder described above was used in an electric furnace.
After the melt heat treatment at 00 ° C. for 5 hours, the electric furnace was switched off and naturally cooled in the electric furnace for about 1 day and then taken out, pulverized and sized to 100 μm or less to prepare a positive electrode active material (b). A positive electrode active material (a) or (b) made of the Bi ₂ O ₃ powder thus produced, or a positive electrode active material using the commercially available Bi ₂ O ₃ powder without heat treatment as a comparative example.
(c) and a carbon conductive agent (graphite, carbon black, etc.) and a binder made of polytetrafluoroethylene are mixed in a weight ratio of 94.5: 5: 0.5 to form an S-shaped L-shaped section.
A positive electrode was obtained by press-molding into a pellet shape together with a US positive electrode retaining ring 8 and then sufficiently drying under reduced pressure at 100 ° C. The diameter of each positive electrode was 9.0 mm, and the weight of the mixture was 0.28 g.

Using the three types of positive electrodes thus produced, three types of batteries were made in the same manner except for the positive electrode.

Fig. 2 shows the 7.5 kΩ constant resistance discharge characteristics of these three types of batteries at 20 ° C. Also, as shown in FIG.
After storing in the same temperature atmosphere for a specified number of days,
The relationship between the discharge capacity and the number of storage days when a constant resistance discharge of 7.5 kΩ is shown. The discharge cutoff voltage was 1.0V. Similar to Fig. 3, Fig. 4 shows that these batteries were stored in an atmosphere at a temperature of 80 ° C for a specified number of days and then stored at 2 ° C at -10 ° C.
The comparison of the minimum voltage when 7.8 mS pulse discharge was performed is shown.

As is clear from FIG. 2, the batteries (a) and (b) using the melt-heat-treated Bi ₂ O ₃ as the positive electrode active material are the same as the conventional batteries (c) using Bi ₂ O ₃ without heat treatment. In comparison, the discharge voltage is higher in the latter half of the voltage plateau where the depth of discharge is about 40% or more, and the discharge time up to the cutoff voltage of 1.2 V is longer, and the discharge characteristics and effective discharge capacity are significantly improved. . or,
It can be seen that there is almost no difference in discharge characteristics between the battery (a) using Bi ₂ O ₃ that has been melt-heat treated and then rapidly cooled and the battery (b) that uses Bi ₂ O ₃ that has been melt-heat treated and then gradually cooled.

On the other hand, from FIG. 3 and FIG. 4, the discharge capacity and pulse discharge voltage after long-term storage at high temperature (80 ° C.) were found to be as follows for the battery (a) using Bi ₂ O ₃ quenched after the melt heat treatment: While it is significantly improved compared to the conventional battery (c) using Bi ₂ O ₃ without heat treatment, the battery (b) using gradually cooled Bi ₂ O ₃ after heat treatment does not improve, Rather, it can be seen that it is getting a little worse. That is, it is understood that the cooling method after the heat treatment of Bi ₂ O ₃ has a great influence on the storage characteristics, and the quenching method is very effective.

Example 2 In this example, bismuth trioxide was added to 1100 in an argon atmosphere.
After melting heat treatment at ℃, quenching in argon atmosphere, 100μ
What was pulverized and sized to m or less was used as a positive electrode active material. In addition, propylene carbonate and 1, as an organic electrolyte
A solution in which 1 mol / mol of lithium perchlorate was dissolved in a 1: 1 mixed solvent of 2-dimethoxyethane was used. Others were the same as in Example 1, and similar batteries were produced. The battery thus prepared was subjected to the same 7.5 kΩ constant resistance discharge and storage test at 80 ° C. as in Example 1, and the result is the battery of Example 1.
It was almost the same level as (a).

Example 3 In this example, a similar battery was manufactured in the same manner as in Example 1 except that bismuth trioxide was subjected to melt heat treatment at 850 ° C. in a reduced pressure of 10 ⁻² to 10 ⁻³ Torr and then quenched. did. The battery thus produced was subjected to the same 7.5 kΩ constant resistance discharge and 80 ° C. storage test as in Example 1, and the result is also the battery of Example 1.
It was almost the same level as (a).

In the examples, the melting heat treatment temperature of Bi ₂ O ₃ is 850
° C., showed only a 900 ° C. and 1100 ° C., the gist of the present invention melts the heat treatment the Bi ₂ O ₃ at a temperature higher than the melting point, and lies in the rapidly cooling solidification from the molten state (solidification), Bi ₂ O ₃
May be in a temperature range (and atmosphere) in which the composition does not change remarkably due to reduction, thermal decomposition or the like. Bi ₂ O ₃ is generally very stable to high temperature heating, and in a non-reducing atmosphere
No substantial composition change is observed up to about 1700 ° C.

However, regarding the improvement of discharge characteristics and storage characteristics, there is no noticeable difference at 1000 ° C or higher compared to the case of 1000 ° C or lower, so in actual industrial production, equipment such as electric furnaces, operating costs, and handling are difficult. considering, as the melt processing temperature of the Bi ₂ O _3, ranging from the melting point (about 820 ° C.) of 1000 ° C. of Bi ₂ O ₃ is preferred.

Also, the organic electrolyte is not limited to the examples, and for example, LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ and the like in a single or mixed solvent of aprotic organic solvents such as γ-butyrolactone, tetrahydrofuran and dioxolane. ⁺ Any ion-dissociable salt may be dissolved.

〔The invention's effect〕

As described above in detail, the present invention uses the bismuth trioxide that has been subjected to the melt heat treatment at a temperature equal to or higher than the melting point and then quenched from the melted state as the positive electrode active material to obtain the operating voltage of the Li / Bi ₂ O ₃ system battery, In particular, it significantly improves the discharge characteristics by increasing the operating voltage at a discharge depth of about 40% or more and significantly improving the effective discharge capacity, and at the same time significantly improves the storage characteristics such as self-discharge and deterioration of panel discharge characteristics over time. And so on, it has an excellent effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a battery implemented in the present invention, FIG. 2 is a comparison diagram of 7.5 kΩ constant resistance discharge characteristics, and FIG. 3 is
Comparison of changes in discharge capacity due to storage at 80 ℃, Fig. 4 shows 80 ℃
It is a comparison figure of the change of the pulse discharge voltage by storage. 1 ... Negative electrode can, 5 ... Positive electrode 2 ... Negative electrode lithium, 6 ... Positive electrode can 3 ... Impregnating material, 7 ... Gasket 4 ... Separator, 8 ... Positive electrode holding ring

Claims (2)

[Claims] 1. A bismuth trioxide Bi ₂ O ₃ which is composed of at least a negative electrode containing lithium as a main active material, an organic electrolyte, and a positive electrode, and which has been melt-heat-treated at a temperature equal to or higher than the melting point and rapidly cooled as a positive electrode main active material. A method for producing an organic electrolyte battery, which is characterized by being used. _2. Bismuth trioxide Bi ₂ O ₃ melt-heat-treated at a temperature not lower than the melting point and not higher than 1000 ° C. in the atmosphere, an inert gas, or a vacuum, and then quenched is used as the positive electrode main active material. The method for producing an organic electrolyte battery according to claim 1, wherein