JPS6122423B2 - - 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. The purpose is to prevent deterioration of battery performance.

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, the organic solvent of the electrolyte decomposes during battery storage and generates gas, and the decomposition products increase the internal resistance of the battery, which deteriorates storage performance. This is the biggest cause of this.

Propylene carbonate and γ-butyrolactone, which are electrochemically stable, are often used as organic solvents, but since these 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, the battery will expand.
Not only are there inconveniences caused, but the decomposition products degrade battery performance.

The above phenomenon is remarkable 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. That is, there are a considerable amount of hydroxyl groups on the surface of the metal oxide, and the proportion varies depending on the type of metal oxide, but there are 1 to 9 hydroxyl groups in an area of 10 Å x 10 Å. For example, if we take electrolytic manganese dioxide with a specific surface area of 50 m ² /g, 1 g has (1 to 9) x
There are 50×10 ¹⁸ hydroxyl groups. and,
These hydroxyl groups can become acids or bases depending on how they are bonded to metal atoms, thereby decomposing organic solvents such as propylene carbonate and γ-butyrolactone.

In view of the above, the present inventors have conducted various studies to eliminate the above-mentioned disadvantages of batteries using metal oxides as positive electrode active materials. It has been found that forming a chelate bond with a cation is effective. This chelate bond deactivates the hydroxyl groups on the surface of the metal oxide and suppresses the decomposition of the organic solvent. Therefore, the present invention involves adding a salt containing these ions to the electrolyte.

First, we will explain how to deactivate hydroxyl groups with anions. Lithium borofluoride LiBF ₄ , lithium borofluoride
A small amount of LiAsF ₆ , lithium aluminum chloride, LiAlCl ₄ , etc. is added to the electrolyte to selectively react with surface hydroxyl groups.

The optimum concentration of solute salts in organic electrolytes is
It is around 1 mol/mole/mole/mole/mole based on conductivity, and this concentration is used in actual batteries as well.
However, if the above-mentioned salts are used at a high concentration of 1 mol/mol, problems such as dissolution of the metal oxide positive electrode and the resulting reduction in storage performance, adhesion of the separator to the negative electrode surface, and corrosion of the battery case will occur. actual,
In batteries that use metal oxides as active materials, it is common to use LiClO ₄ as the solute. this
In LiClO ₄ and other solutes, such as LiPF ₆ , Cl and P in their anions cannot form chelate bonds with hydroxyl groups, so the hydroxyl groups cannot be deactivated.

On the other hand, in LiBF ₄ , LiAsF ₆ , and LiAlCl ₄ , the B, As, and Al atoms in their anions easily and stably form chelate bonds with hydroxyl groups, so they can be used in trace amounts that do not cause the above-mentioned disadvantages. The hydroxyl group can be deactivated by adding it to the electrolyte.

The hydroxyl groups can then be deactivated with the cations in the added salt. In this case, the cation is
Copper, nickel, lead, cobalt, zinc, iron, palladium, cadmium, manganese, magnesium, aluminum, etc. are used.

The present invention will be explained below by taking as an example manganese dioxide, which is common among metal oxides and has high voltage and low cost.

Generally, manganese dioxide is heat-treated in air. When heat treated, the surface area decreases considerably, but the hydroxyl groups, which are surface active species, remain almost unchanged.

First, add (1 to 9) x 50 to electrolytic manganese dioxide.
As mentioned above, there are 18 x ¹⁰ hydroxyl groups/g, but when this is deactivated with LiBF ₄ , as shown in Figure 1,
One BF ^- ₄ ion deactivates 2 to 3 hydroxyl groups. The same applies when LiAsF ₆ and LiAlCl ₄ are used. Therefore, to deactivate the hydroxyl group on 1 g of electrolytic manganese dioxide, (1 to 9) x 50 x 10 ¹⁸ / (2 to 3) x 6 x 10 ²³ = 2.8
×10 ^-5 to 3.8 × 10 ^-4 moles (gram molecule) of _LiBF4 ,
LiAsF ₆ and LiAlCl ₄ are sufficient.

On the other hand, in the case of cations, for example, copper ions, it is thought that chelates are formed by the mechanism shown in Figure 2, and similarly calculated.
It is sufficient to add 4.2×10 ⁻⁵ to 3.8×10 ⁻⁴ mol per g. In this case, the anion that should serve as a counter ion to the cation is preferably the aforementioned ClO ^- ₄ , AsF ^- ₆ , or AlCl ^- ₄ , but in the case of electrolytic manganese dioxide,
When using a material electrodeposited _from a manganese sulfate bath or a manganese chloride bath, it contains about 10 ^-5 moles of Cl ^- and SO ^2-4 , so ions of the same type as these may be used.

Next, an example will be described in which manganese dioxide electrodeposited from a manganese sulfate bath was heat-treated at 400° C. for 4 hours in air and applied to a lithium battery using the positive electrode active material.

In Fig. 3, 1 is a case made of stainless steel, 2 is a sealing plate made of the same material, and 3 is a case made of stainless steel.
A lithium sheet 4 as a negative electrode 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 (including 0.70 g of MnO ₂ ) into a disk shape. 6 is a titanium current collector welded to the inner surface of case 1, 7 is a polypropylene separator, 8 is a polypropylene liquid retaining material, 9
is a polypropylene gasket. The electrolyte used was LiClO ₄ dissolved in a mixed solvent of equal volumes of propylene carbonate and 1,2-dimethoxyethane at a ratio of 1.0 mole/mole, and 200 μ of the solution was injected and the container was sealed.

In the above configuration, LiBF ₄ , LiAsF ₆ ,
Figure 4 shows the internal resistance of batteries made by adding LiAlCl ₄ to the electrolyte in various proportions and stored at 60°C for 30 days. Note that the internal resistance is a value measured at 1KHz AC. In addition, the amount of the above salt added in this case is 2.8×10 ^-5 and 6× per 1 g of manganese dioxide.
10 ^-5 , 15 x 10 ^-5 , equivalent to 40 x 10 ^-5 moles, i.e. 2.0 in 200 μ of electrolyte for 0.70 g of manganese dioxide.
×10 ⁻⁵ , 4.2×10 ⁻⁵ , 10.5×10 ⁻⁵ , and 28×10 ⁻⁵ moles.

Furthermore, FIG. 5 shows the change in internal resistance over time when a battery containing the above-mentioned salt added in an amount of 4.2×10 ⁻⁵ mol was stored at 60° C. As shown in Figure 5, the internal resistance of batteries with the above salt added increases slightly during storage, but
The rate is significantly lower than that without additives.

Figure 6 shows Cu(ClO ₄ ) ₂ , Ni(ClO ₄ ) ₂ , Pb
(ClO ₄ ) ₂ , Co(ClO ₄ ) ₂ , Zn(ClO ₄ ) ₂ per gram of manganese dioxide at 4.0×10 ^-5 , 8.0×10 ^-5 , 20×
The internal resistance after storage at 60°C for 30 days is shown for a battery in which 10 ^-5 , equivalent to 40 x 10 ^-5 moles, is added to the electrolyte.

It can be seen from FIGS. 4 and 6 that the storage stability of the battery according to the present invention is superior to that of conventional batteries. When forming a chelate bond with anion, the amount of salt added is 1×10 ^-5 to 35× from Figure 4.
It seems that the effect is recognized in the range of 10 ^-5 mol, so 1.3 x 10 ^-5 per 1 g of manganese dioxide.
When the addition amount of ~5 x 10 ^- ₄ moles forms a chelate bond with a cation, similarly from Figure 6,
1×10 ^-5 to 8× for 1g of manganese dioxide
The amount added is preferably 10 ⁻⁴ mol.

In the examples, lithium was used as the negative electrode, but
Light metals 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, etc. Since all oxides have hydroxyl groups on their surfaces, and the specific surface areas of these oxides are approximately in the same range, the above-mentioned amount ratio is sufficient. It is also similarly effective when using ethylene carbonate or γ-butyrolactone as the organic solvent constituting the electrolyte.

When forming a chelate bond with an anion, the most preferable metal ion is lithium, which is the cation of the added salt. However, since the amount added is very small and its influence is considered to be small, alkali metals and alkaline earth metals are preferred. It may also be made of other metals.

In addition, when forming a chelate bond with a cation, the most preferable ion in the added salt is ClO ^- ₄ ion, which is said to have the least effect on oxides.
Since the amount added is very small, other anions such as SO ^2-4 and Cl ^- ions contained in _electrolytic manganese dioxide may also be used. In addition, since this method relies on the coordination of metal cations,
A similar effect can be expected when iron, palladium, cadmium, manganese, or aluminum ions are used.

As described above, according to the present invention, an organic electrolyte battery with excellent storage performance can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the mechanism by which the surface hydroxyl groups of manganese dioxide form a chelate bond with BF ^- ₄ .
The figure is also a schematic diagram showing the mechanism of forming a chelate bond with copper ions, Figure 3 is a longitudinal cross-sectional view of a manganese dioxide-lithium battery according to an embodiment of the present invention, and Figures 4 and 6 are various additions in the electrolyte. FIG. 5 is a diagram showing the relationship between the amount of salt and the internal resistance after storage of the battery, and FIG. 5 is a diagram showing the change over time in the internal resistance during storage of the battery. 4... Negative electrode, 5... Positive electrode, 7... Separator. 〓〓〓〓

Claims (1)

[Claims] 1. A negative electrode containing a light metal as an active material, an organic electrolyte containing at least one of propylene carbonate, ethylene carbonate, γ-butyrolactone, and 1,2-dimexyethane as a solvent, and a metal oxide as an active material. 1. A battery comprising a positive electrode, wherein the electrolyte contains a salt containing an ion that forms a chelate bond with a hydroxyl group on the surface of the metal oxide. 2. The battery according to claim 1, wherein the salt is a salt containing one selected from the group consisting of BF ^- ₄ , AsF ^- ₆ , and AlCl ^- ₄ . 3. The battery according to claim 1, wherein the salt is a salt containing ions of a metal selected from the group consisting of copper, nickel, lead, cobalt, zinc, iron, palladium, cadmium, manganese, magnesium, and aluminum. . 4. The battery according to any one of claims 1 to 3, wherein the content of the salt is 10 ^-5 to ^{10 -3} gram molecules per gram of the metal oxide. 5. A patent in which the metal oxide is selected from the group consisting of manganese dioxide, molybdenum trioxide, vanadium pentoxide, trilead tetroxide, bismuth sesmuth oxide, cupric oxide, tricobalt tetroxide, and cobalt sesquioxide. A battery according to claim 1.