JPH0520861B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in an organic electrolyte battery that uses lithium as a negative electrode main active material and bismuth trioxide Bi ₂ O ₃ as a positive electrode main active material.

In organic electrolyte batteries that use lithium as the negative electrode active material, depending on the type of active material used in the positive electrode,
Batteries with various operating voltages are possible, but in practice, the 3V type, which has an operating voltage of about 3V, and the 3V type, which has an operating voltage of about 1.5V
It is roughly divided into 1.5V type with an operating voltage of 1.5V.
Known positive electrode active materials belonging to the 1.5V type include cupric oxide, iron oxide, iron disulfide, lead oxide, bismuth trioxide, and the like. Among these, batteries using bismuth trioxide have a high operating voltage of 1.5V to 1.8V, so they are a particularly advantageous battery system for applications requiring large current discharge. The present invention relates to an improvement in the positive electrode of a lithium-organic electrolyte battery using such bismuth trioxide as the positive electrode.

[Conventional technology]

Conventionally, in this type of battery, for example, when manufacturing a button-type battery, a positive electrode has been made as follows. That is, the active material bismuth trioxide, a conductive agent such as carbon powder or metal powder such as graphite or carbon black, and a resin binder such as fluorine resin or polystyrene are mixed in a predetermined composition ratio, and then this mixture is mixed in a predetermined composition ratio. A predetermined amount of the positive electrode mixture is filled into a mold of a molding machine and press-molded to form a pellet-like positive electrode molded body. The thus obtained positive electrode pellets are thoroughly dehydrated by heating and drying under reduced pressure at a temperature within a range where thermal decomposition of the resin binder and oxidation of the conductive agent do not occur (at most 300°C or less), and then incorporated into a battery.
Organic electrolyte batteries using bismuth trioxide as a positive electrode active material are disclosed in, for example, Japanese Patent Application Laid-Open No. 12425/1982 and Japanese Patent Publication No. 49673/1989.

[Problem that the invention seeks to solve]

However, when a battery made using bismuth trioxide as the positive electrode active material is discharged using the conventional method described above, the discharge characteristics show two stages of discharge voltage, as shown in a in Figure 2. , the operating voltage becomes low when the depth of discharge is approximately 40% or more. Therefore, when this battery is used in equipment that requires large current discharge, the battery voltage will drop and the voltage required to operate the equipment normally will not be available even though there is still sufficient battery capacity remaining. Therefore, there was a problem in that the effective battery capacity (life) was significantly reduced.

The object of the present invention is to increase the operating voltage of this type of battery, particularly at a depth of discharge of about 40% or more, and to improve the effective discharge capacity by improving such a bismuth trioxide positive electrode.

[Means for solving problems]

As a result of various studies to solve the above-mentioned problems, the present inventors found that 650
It has been found that by using bismuth trioxide heat-treated at a temperature of 0.degree. C. or higher, the operating voltage of this type of battery, especially at a depth of discharge of about 40% or more, is improved and the effective discharge capacity is significantly improved.
That is, when manufacturing a positive electrode, before mixing bismuth trioxide with a conductive agent, a binder, etc., bismuth trioxide is heat-treated at a temperature of 650°C or higher, and then,
It was mixed with a conductive agent and a binder as necessary and molded into a predetermined shape. The atmosphere for the heat treatment may be any atmosphere that does not reduce bismuth trioxide, such as air, inert gas, or vacuum.

In addition, when powdered bismuth trioxide is heat-treated at a temperature of 650°C or higher, it hardens into a bond when cooled due to sintering, melting, etc. It is preferable to thoroughly grind the materials into fine particles of 100 μm or less before mixing.

In particular, when heat-treated at a temperature near or above the melting point of bismuth trioxide, 820°C, it melts and becomes a strong bond after cooling, so it is important to thoroughly grind it into fine particles.

[Effect]

As mentioned above, when a battery made using bismuth trioxide heat-treated at a temperature of 650°C is discharged, the operating voltage, especially at a depth of discharge of about 40% or more, increases and improves, so it remains constant. The effective discharge capacity up to the cut-off voltage of is significantly improved.

The reason why the working voltage is improved is not necessarily clear, but it is estimated as follows. In other words, when bismuth trioxide is heat-treated at 650℃ or higher, the atoms that make up each particle of bismuth trioxide move significantly, causing subtle changes in the crystal surface and internal structure of each particle, increasing the electrochemical activity. . Conversely, at temperatures below 650°C, such atomic movement is small, so the operating voltage is not improved.

〔Example〕

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

Example 1 The positive electrode active material was prepared by heating 99.99% pure bismuth trioxide powder in the air at a temperature of 300 to 1000°C.
After heat treatment for a period of time and cooling, the powder was pulverized to a particle size of 100 μm or less, and as a comparative example, the powder as it was without heat treatment was used. This heat-treated or untreated bismuth trioxide, a carbon conductive agent (graphite or carbon black, etc.), and a binder made of fluororesin are mixed in a weight ratio of 94.5:5:0.5, and the cross-section is L-shaped. The positive electrode was formed into a pellet together with a positive electrode holding ring made of SUS, and then dried under reduced pressure at 100° C. for 10 hours. The positive electrode thus produced had a diameter of 9.0 mm, a thickness of 1.1 mm, and a theoretical capacity of 90 mAH.

FIG. 3 is a sectional view of a battery showing an example of the present invention. In the figure, numeral 1 is a negative electrode can that also serves as a negative electrode terminal, and is made by drawing a Ni/SUS clad plate with a thickness of 0.22 mm. The negative electrode 2 was a 1.3 mm thick lithium sheet punched out to a diameter of 6.4 mm and pressed onto the inner surface of the negative electrode can. 6 is 0.22mm thick
A positive electrode can made of Ni/SUS clad plate, which also serves as a positive terminal. This positive electrode can is filled with the positive electrode 5 described above, and a separator 4 made of a microporous polypropylene sheet is placed thereon. 3 is an impregnating material that holds the electrolyte between the positive electrode and the negative electrode, and is made of a nonwoven fabric whose main element is polypropylene. 7 is a gasket mainly made of polypropylene, which is interposed between the negative electrode can 1 and the positive electrode can 6 to maintain electrical insulation between the positive electrode and the negative electrode, and at the same time, the opening edge of the positive electrode can can be bent inward and caulked. The battery contents are sealed and sealed. The electrolytic solution used was one in which 1 mol/mol of lithium perchlorate was dissolved in a 1:1 mixed solvent of propylene carbonate and 1,2-dimethoxyethane. The size of the battery is 9.5mm in outer diameter and 3.0mm in total thickness.
mm.

Figure 2 shows the heat treatment temperatures of bismuth trioxide mentioned above: (a) no heat treatment, (b) 500℃, (c) 650℃, (d)
800℃ (e) For the above battery at 1000℃,
Shows 3KΩ constant resistance discharge characteristics at 24℃. From this result, when the heat treatment temperature of bismuth trioxide is 650°C or higher, the discharge voltage becomes higher than when it is lower than that, and the discharge voltage is especially high in the second half of the voltage plateau when the depth of discharge is about 40% or more. It can be seen that the discharge time up to the cut-off voltage of 1.2V is also longer, and the discharge characteristics and effective discharge capacity are significantly improved.

FIG. 1 shows the relationship between heat treatment temperature and discharge capacity of bismuth trioxide. As is clear from the figure, when the heat treatment temperature of bismuth trioxide is 650°C or higher, the discharge capacity increases rapidly until it reaches approximately 800°C.
At this point, the increase in capacity is saturated, and even if the heat treatment temperature is further increased, the capacity hardly increases and becomes almost constant. The reason for this is that the melting point of bismuth trioxide is 820℃, and bismuth trioxide remains in a stable molten state at temperatures higher than this, so even if it is heat-treated at a temperature higher than this, the state after cooling will remain almost the same. It is presumed that this is because In any case, it is clear from the figure that when bismuth trioxide is heat-treated at a temperature of 650°C or higher, the discharge capacity is improved compared to when it is heat-treated at a temperature lower than that or when it is not heat-treated. In addition, the effect of heat treatment becomes particularly large at temperatures above 700℃, but at temperatures above 850℃, there is little further increase in capacity, and equipment such as electric furnaces for heat-treating bismuth trioxide, operating costs, and handling are required. In consideration of shading, etc., the heat treatment temperature is preferably 700 to 1000°C.

Example 2 In this example, a similar battery was made in the same manner as in Example 1, except that bismuth trioxide was heat-treated in nitrogen gas. The results of discharging such a battery at a constant resistance of 3KΩ at 24° C. in the same manner as in Example 1 were almost the same as in Example 1.

Example 3 In this example, the heat treatment of bismuth trioxide was performed at 10 ^-2 ~
Everything was carried out in Example 1, except that it was carried out under reduced pressure of 10 ^-3 Torr.
A similar battery was fabricated using the same method.

Such a battery was heated at 24°C in the same manner as in Example 1.
When the battery was discharged at a constant resistance of 3KΩ, almost the same results as in Example 1 were obtained.

In addition, the organic electrolytes include γ-butyrolactone, propylene carbonate, butylene carbonate,
LiCl ₄ , LiBF ₄ , LiPF ₆ , as a supporting salt in a single or mixed aprotic organic solvent such as 1,2-dimethoxyethane, tetrahydrofuran, dioxolane, dimethylformamide, etc.
An organic electrolyte in which an ionically dissociable salt such as LiCF ₃ SO ₃ is dissolved may be selected.

〔Effect of the invention〕

As described in detail above, the present invention uses bismuth trioxide heat-treated at a temperature of 650°C or higher as a positive electrode active material, thereby increasing the operating voltage of Li/Bi ₂ O ₃ batteries, especially the depth of discharge of approximately 40°C. It has excellent effects, such as increasing the operating voltage by more than %, significantly increasing the effective discharge capacity, and significantly improving the discharge characteristics.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between heat treatment temperature and discharge capacity of bismuth trioxide, Figure 2 is a comparison diagram of discharge characteristics of batteries using bismuth trioxide heat treated at various temperatures, and Figure 3 is a diagram showing the relationship between heat treatment temperature and discharge capacity of bismuth trioxide. FIG. 2 is a cross-sectional view showing an example of a battery that was used. DESCRIPTION OF SYMBOLS 1... Negative electrode can, 2... Negative electrode lithium, 3... Impregnating material, 4... Separator, 5... Positive electrode, 6... Positive electrode can, 7... Gasket, 8... Positive electrode holding ring.

Claims (1)

[Claims] 1. Consisting of at least a negative electrode containing lithium as the main active material, an organic electrolyte, and a positive electrode, using bismuth trioxide Bi ₂ O ₃ heat-treated at a temperature of 650°C or higher as the positive electrode active material. A method for manufacturing an organic electrolyte battery characterized by: 2. The method according to claim 1, characterized in that bismuth trioxide Bi ₂ O ₃ heat-treated at a temperature of 700 to 1000°C in air, inert gas, or vacuum is used as the positive electrode active material. A method for manufacturing an organic electrolyte battery.