JPS6155741B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the improvement of a battery consisting of a negative electrode made of a light metal such as lithium as an active material, an organic electrolyte, and a positive electrode made of a metal oxide as an active material, and particularly to prevent deterioration of battery performance due to storage. The purpose is to Carbon fluoride, manganese dioxide, etc. have been put into practical use as positive electrode active materials for this type of battery, and metal oxides such as cupric oxide, bismuth oxide, vanadium pentoxide, trilead tetroxide, copper sulfide, iron sulfide, etc. Metal sulfides such as these are being extensively studied. On the other hand, the electrolyte used includes a supporting salt dissolved in an electrochemically stable aprotic organic solvent such as propylene carbonate or γ-butyrolactone. Such organic electrolyte batteries have high energy density and are suitable as power sources for small electronic devices such as electronic desktop calculators and wristwatches, but they still have unsatisfactory points in terms of storage performance. According to the study results of the present inventors, storage performance is deteriorated because the organic solvent of the electrolyte decomposes during battery storage and generates gas, and the decomposition products have an adverse effect on battery performance. This is the biggest cause. Propylene carbonate and γ-butyrolactone, which are electrochemically stable, are often used as organic solvents, but because they are esters or lactones, they still have some activity. For this reason, it undergoes hydrolysis using acids or alkalis as catalysts, or decomposes in the presence of certain solutes to generate gas. If the generation of such gas becomes significant, it not only causes the inconvenience of expansion of the battery, but also the decomposition products deteriorate the battery performance, and furthermore, the utilization rate of the active material decreases due to a decrease in the amount of liquid. . The above phenomenon is remarkable even when a metal oxide such as manganese dioxide is used as the positive electrode active material. As a result of examining the cause of this, the following was found. In other words, there are trace amounts of hydroxyl groups on the surface of metal oxides, and the proportions vary depending on the type of metal oxide, but under certain conditions, these hydroxyl groups on the surface become active protons, play the role of Brønstedt's acid, and produce carbonic acid. It decomposes organic solvents such as propylene and γ-butyrolactone. In view of the above, the present inventors conducted various studies to eliminate the above-mentioned disadvantages of batteries that use metal oxides as positive electrode active materials, and found that chelation between hydroxyl groups on the surface of metal oxides and metal ions such as zinc ions. It has been found that forming bonds is effective. This chelate bond deactivates the hydroxyl groups on the surface of the metal oxide and suppresses the decomposition of the organic solvent. In addition to zinc ions, metal ions that form stable chelate bonds sufficient to deactivate hydroxyl groups on the surface of metal oxides include copper, nickel, lead, cobalt, iron, palladium, manganese, magnesium,
There are aluminum ions. To form a chelate bond between the hydroxyl group on the surface of a metal oxide and a metal ion, the metal oxide can be immersed in a solution containing metal ions, or a salt containing metal ions can be added to an electrolyte to remove metal ions. Selectively forms a chelate with the surface hydroxyl group of the positive electrode. In any case, the surface hydroxyl groups are neutralized and deactivated. Therefore, the disadvantages of gas generation and internal resistance increase in the battery during storage can be eliminated, and the battery performance can be maintained at a good level. On the metal oxide surface, there is 1 in an area of 10 Å x 10 Å.
It is said that there are ~3 hydroxyl groups. If,
Taking electrolytic manganese dioxide with a specific surface area of 50 m ² /g as an example, there are (1 to 3)×50×10 ¹⁸ hydroxyl groups in 1 g. Generally, manganese dioxide is heat-treated in air at, for example, 400°C. Heat treatment reduces the surface area considerably.
When electrolytic manganese dioxide is heat-treated at 320°C and 450°C, the surface area decreases to about 89% and 69% of its original value, respectively, but the absolute amount of hydroxyl groups, which are active species on the surface, remains almost the same as before. Taking copper ions as an example, the chelate bond is schematically shown in FIG. 1, and it is thought that copper ions form square planar (dsp ² ) bonds. One copper ion can deactivate two surface hydroxyl groups. This deactivation efficiency depends on the coordination structure of metal ions and the spacing between hydroxyl groups, so it is not always limited to two, but only one.
It will be between ~3. In this case, there are (1 to 3) x 50 x 10 ¹⁸ hydroxyl groups on 1 g of electrolytic manganese dioxide, so the amount of copper ions is (4
〜6) ×10 ^-5 mole is sufficient. The order is almost the same for other ions. Even if this amount were added to the electrolyte, it would be so small that it would not affect the battery.When adding this ion as a salt, the counter ion is electrolytic manganese dioxide deposited from a manganese sulfate bath. SO ₄ ^2- ions are more preferred when the ion is from a manganese chloride bath, and Cl ^- ions are more preferred when the ion is from a manganese chloride bath. Also, electrolytic manganese dioxide contains SO ₄ ^2- ions or
Approximately 10 ^-5 moles of Cl ^- ions remain, so there will be no problem as a battery. Also, the anti-anion is
ClO ₄ ^- , BF ₄ ^- , AsF ₆ ^- , AlCl ₄ ^- are more preferred, and ClO ₄ ^- or BF ₄ ^- is even more preferred. The present invention will be explained below using an example in which the present invention is applied to manganese dioxide, which is common among metal oxides and has high voltage and low cost. As manganese dioxide, manganese dioxide obtained by electrolyzing a manganese sulfate bath is heated to 400℃ in the air.
The sample was heat-treated for 4 hours. 50 g of this manganese dioxide was mixed with 200 ml of a propylene carbonate solution containing 6 x 10 ^-13 moles (1.3 g) of copper perchlorate, Cu(ClO ₄ ) ₂ .
After stirring at 45°C for 10 hours, the mixture was filtered, thoroughly washed with purified 1,2-dimethoxyethane, and dried. Similarly, nickel perchlorate, lead perchlorate, cobalt perchlorate, and zinc perchlorate were also treated. The weight ratio of these manganese dioxide and propylene hexafluoride-ethylene tetrafluoride copolymer resin powder is
The mixture was mixed at a ratio of 10:3, 1 g of the mixture was molded into a disk shape, and the mixture was dried at 200° C. for 5 hours under a reduced pressure of 1 mmHg. Five of these manganese dioxide samples each had a moisture content of 27
Soaked in 16 c.c. of μg/cc purified propylene carbonate, 60
A comparison of the amount of gas collected by the gas collection device when it was left at ℃ for 80 hours was as shown in the following table.

[Table] Note that the gas generated is carbon dioxide gas, which dissolves in propylene carbonate in a considerable proportion, but no gas generation was observed in Samples A to E. As is clear from this result, treatment with metal ions that form chelate bonds with hydroxyl groups
It has the effect of suppressing the ability of manganese dioxide to decompose propylene carbonate. Next, an example will be described in which the above-treated manganese dioxide is applied to a battery. In FIG. 2, 1 is a case made of stainless steel, 2 is a sealing plate made of the same material, and 3 is a grid welded to the inner surface of the sealing plate, and a negative electrode lithium sheet 4 is pressure-bonded to the surface of this grid. 5 is a positive electrode, which is made by molding 0.75 g of a mixture of 100 parts by weight of manganese dioxide, 3 parts by weight of acetylene black, and 5 parts by weight of a fluororesin binder into a disk shape. 6 is a titanium current collector welded to the inner surface of the case 1, 7 is a polypropylene separator, and 8 is a polypropylene liquid retaining material. The electrolyte used was LiClO ₄ dissolved at a ratio of 1.0 mol/mole in a mixed solvent of equal volume of propylene carbonate and 1,2-dimethoxyethane, and 200μ of the solution was injected and the container was sealed. 9 is a polypropylene gasket. The size of this battery is 23mm in diameter and 2.45mm in total height. With the above configuration, batteries A to F were constructed using the various manganese dioxides shown in the table above. Figure 3 shows the change in internal resistance of the battery over time, which best indicates the stability of the battery, and the storage temperature is 60°C. Note that the internal resistance is a value measured at 1KHz AC. In addition, Figure 4 shows the 20
℃, 1KΩ discharge characteristics. Note that F' in the figure is the discharge characteristic of battery F immediately after manufacture. It can be seen from FIG. 3 that the storage stability of the battery according to the present invention is superior to that of conventional batteries. Figure 4 shows the degree of deterioration in the falling voltage, discharge voltage, and discharge capacity of the conventional battery when stored at 60°C for 30 days. It was found that both discharge voltage and discharge capacity are excellent, and the discharge characteristics are a single thick line, but in terms of discharge voltage and capacity, it is A ~
E There is almost no difference, only the falling voltage
It can be seen that the larger the internal resistance shown in the figure, the lower the falling voltage (up to about 2.5 hours at the beginning of discharge). In the above examples, lithium was used for the negative electrode, but a light metal such as sodium may also be used. Although manganese dioxide was used as the metal oxide, other oxides such as molybdenum trioxide, cobalt sesquioxide, tricobalt tetroxide, cupric oxide, bismuth sesmuth oxide, vanadium pentoxide, and trilead tetroxide It can be applied to all things. Moreover, the organic solvent of the electrolyte is also effective against aprotic organic solvents such as γ-butyrolactone and ethylene carbonate in addition to propylene carbonate. The gist of the present invention is to form a chelate compound between a hydroxyl group on the surface of an oxide and a metal ion, and thereby the hydroxyl group is just neutralized and deactivated. Metal ions that stably form bonds include those shown in the examples,
Metal ions such as iron, palladium, cadmium, manganese, magnesium, and aluminum may also be used. As described above, according to the present invention, deterioration in storage performance due to decomposition of organic electrolytes can be prevented.

[Brief explanation of the drawing]

Figure 1 is a diagram schematically showing an example in which surface hydroxyl groups of manganese dioxide form chelate bonds with copper ions, Figure 2 is a longitudinal cross-sectional view of the battery used in the example, and Figure 3 is the preservation of battery internal resistance. Figure 4 shows the discharge characteristics of the battery. 4... Negative electrode, 5... Positive electrode, 7... Separator.

Claims (1)

[Claims] 1. A negative electrode using a light metal as an active material, an organic electrolyte,
and a positive electrode using a metal oxide as an active material,
A battery characterized in that the hydroxyl group on the surface of the metal oxide forms a chelate bond with a metal ion. 2. The metal ion forming the chelate bond is an ion of a metal selected from the group consisting of copper, nickel, lead, cobalt, zinc, iron, palladium, cadmium, manganese, magnesium, and aluminum. The battery according to item 1. 3. A patent claim in which the metal oxide is selected from the group consisting of manganese dioxide, molybdenum trioxide, vanadium pentoxide, tricobalt tetroxide, cobalt sesquioxide, cupric oxide, trilead tetroxide, and bismuth sesmuth oxide. The battery according to the range 1 or 2.