JPS5821779B2 - silver oxide battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to improve the performance of a silver oxide battery by selecting the composition of an alkaline electrolyte.

Conventionally, in silver oxide batteries, an aqueous solution of potassium hydroxide or sodium hydroxide saturated with zinc oxide has been used as an electrolyte.

When potassium hydroxide was used, the internal resistance of the battery was low and the discharge characteristics were excellent in birate discharge and low temperature characteristics, but the leakage resistance was poor.

When sodium hydroxide is used, the leakage resistance is somewhat improved, but especially for small-sized batteries that operate for a long period of 5 to 10 years while being floatingly charged by solar cells, which have been in the spotlight in recent years. Silver oxide batteries used as power sources in electronic devices are required to have significantly greater leakage resistance than conventional silver oxide batteries, and even this has not been sufficient.

Therefore, compared to potassium hydroxide and sodium hydroxide,
Several proposals have been made to use lithium hydroxide, which is said to have good leakage resistance, to prevent creep, but each of them had the following drawbacks.

The first one is shown in Japanese Patent Application Laid-Open No. 50-96835, and to summarize the gist, in a zinc-alkaline battery, lithium ions are added to an aqueous solution of potassium hydroxide in which zincate ions are dissolved as an electrolyte. By adding , the leakage resistance is improved, and the storage characteristics are improved by preventing the generation of hydrogen gas due to dissolution of zinc without using mercury in the zinc cathode.

However, for example, if we consider the case where lithium hydroxide is mixed to a saturated state, the solubility at 25°C is 12
．． 4 g/100 ccH20, which is about i compared to the activity coefficient of potassium hydroxide at the same concentration, and the OH ions in the electrolyte decrease by the proportion of lithium hydroxide added.

Therefore, it is thought that 0) the so-called dissolution of zinc, in which T ions and zinc react to form zincate ions, can be prevented to some extent.

However, in order to improve leakage resistance, according to our test results, no effect can be expected unless the blending ratio of potassium hydroxide in the electrolyte is 30% or less by weight of the electrolyte.

In the above embodiment of the invention, lithium hydroxide is saturated with potassium hydroxide weighing 35% by weight. % of potassium hydroxide, it seems that even if lithium hydroxide, which causes less creep, is added, a sufficient effect cannot be expected.

The second method is disclosed in Japanese Patent Application Laid-Open No. 110031/1982. To summarize, the leakage resistance of zinc-alkaline batteries is improved by using an aqueous solution containing lithium hydroxide as the electrolyte. The purpose of this invention is to improve the storage characteristics of batteries by increasing the corrosion resistance and reducing the corrosive effect on zinc.

However, the solution of lithium hydroxide. The solubility is 12.4 g/100CC-H2O at 25°C, and the solubility of potassium hydroxide at 20°C is 11 L4g7100cc
-Solubility of H2O and sodium hydroxide 107g/100
It is extremely small compared to CC-H20, and if it is made mainly of lithium hydroxide, it will be in a saturated state.

Even if it becomes, it will not reach the 30 to 40 weight factor of potassium hydroxide or sodium hydroxide used in normal alkaline electrolytes, and will remain at around 11 weight factor.
This is far less than the amount of O ions required for normal battery reactions.

Moreover, when comparing the conductivity of aqueous solutions, lithium hydroxide is only slightly lower than sodium hydroxide at the same concentration, but as mentioned above, even if lithium hydroxide is saturated, it is still lower than that of ordinary water. Compared to the range in which sodium oxide is used, it is only 100% or less, which results in an increase in the internal resistance of the battery, which is not desirable as a battery system.

The third method is disclosed in Japanese Patent Application Laid-open No. 51-81941, and its gist can be summarized as follows: In a silver peroxide battery, sodium hydroxide or potassium hydroxide and lithium hydroxide are used as the electrolyte. By using a mixed aqueous solution saturated with zinc oxide, the decomposition of silver peroxide, which is the main active material of the anode, is also prevented, thereby providing a silver oxide battery with excellent long-term storage stability.

Indeed, this method decomposes the anode. Although the dissolution of the cathode zinc into the alkaline electrolyte can be prevented by the presence of saturated zinc oxide, the following problems occur due to the saturated zinc oxide.

In other words, as the battery reaction progresses, the surface of the negative electrode zinc is covered with zinc oxide, and as the zinc oxide dissolves into the electrolyte, fresh zinc is always in contact with the electrolyte, making the reaction smooth. Proceed to.

However, when the electrolyte is saturated with zinc oxide, the reaction in which the zinc oxide generated on the surface of the cathode dissolves into the electrolyte is also suppressed, especially in the case of birate discharge, for the reasons mentioned above. Dissolution of zinc oxide formed on the surface of the negative electrode zinc into the electrolytic solution becomes the rate-determining step, and the battery reaction may not proceed smoothly, resulting in the inconvenience of shortening the discharge duration.

In addition, as seen in Japanese Patent Publications No. 43-8513 and No. 45-16666, in sealed nickel-cadmium storage batteries, by mixing potassium hydroxide and lithium hydroxide as the electrolyte, potassium hydroxide The purpose is to maintain the conductivity of the electrolytic solution and improve the charging rate of anodized nickel due to the action of lithium hydroxide, but even though the present invention and the present invention are similar in form, I believe that they should be completely differentiated.

The present invention solves the above-mentioned problems by selecting the composition of the electrolyte in silver oxide batteries, and is particularly suitable for charging silver oxide batteries of the type that are used while repeatedly charging and discharging over a long period of time. The object of the present invention is to provide a battery that does not cause any problems in its characteristics during long-term use.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a silver oxide battery constructed according to the present invention.

An anode 1 mainly made of a mixture of monovalent silver oxide and a powder having edible conductivity such as graphite is crimped and fixed in an outer case 2, and a separator 3 made of a processed polyolefin resin and cellophane are sequentially placed on top of the anode 1. A sealing plate 8 sandwiched between a cellulose-based separator 4 such as 4, a liquid-impregnated felt 5, a cathode 6 mainly made of a mixture of zinc hydride and a powder such as carboxymethyl cellulose that gels in an alkaline electrolyte, and an insulating backing 7. The outer case 2 is placed thereon and sealed by bending the end of the outer case 2 inward.

Among its components, an electrolytic solution (not shown) is mainly injected into the anode 1 and cathode 6 before sealing, and is uniformly distributed inside the cell during aging.

This electrolyte was improved as follows.

That is, the electrolyte consists of a mixed aqueous solution of sodium hydroxide, lithium hydroxide, and unsaturated zinc oxide,
The concentration of lithium hydroxide in the electrolyte is between 5 and 12 parts by weight.

By doing this, throughout long-term use,
It is an object of the present invention to improve the reactivity of the negative electrode zinc during discharge without causing any problems such as affecting the characteristics of the battery.

The method of the present invention has the following effects.

First, the electrolytic solution used in the present invention has low corrosivity to the separator, so it is possible to use and store the battery for a long period of time.

In other words, when a separator is exposed to an alkaline electrolyte, the material of the separator undergoes hydrolysis, making the separator brittle and allowing ions and molecules to permeate between the positive and negative electrodes. This causes deterioration of battery characteristics during long-term use.

This hydrolysis reaction is accelerated as the concentration of OH ions in the alkaline electrolyte increases, but as shown in Table 1 below, even at the same concentration of 1°, lithium hydroxide has the highest activity. The coefficient is small, especially for potassium hydroxide.

Therefore, when the alkaline electrolyte does not contain potassium hydroxide and mixes sulfur hydroxide and lithium hydroxide as in the present invention, the separate lake undergoes hydrolysis 2 and becomes brittle. There is no negative effect on the deterioration of battery characteristics due to deterioration of the separator.

In particular, in silver oxide batteries for charging, in order to maintain the so-called gas absorption effect, in which the oxygen gas generated from the anode during overcharging is absorbed by the zinc cathode, oxygen gas is The separator is shaped to have a high gas permeability so that gas can easily pass through the separator.

Normally, separators with high gas permeability are porous, and during storage of the battery, silver oxide from the anode is eluted in the alkaline electrolyte in the form of helotrioidal silver, passing through the fine pores of the separator to the cathode. This causes depletion of the active material and deteriorates the characteristics of the battery during storage.

However, as mentioned above, the electrolytic solution of the present invention has a lower activity coefficient and lower reactivity than conventional electrolytic solutions containing potassium hydroxide or sodium hydroxide, so it is difficult to elute silver oxide. The amount is small, and there is no problem even if you use it for a long time while charging and discharging.

Second, because the alkaline components of the electrolytic solution used in the present invention consist of sodium hydroxide and lithium hydroxide, the electrolytic solution is contaminated by carbon dioxide gas in the air and carbonates are produced. However, it does not adversely affect the battery characteristics.

That is, the solubility of carbonate at 20°C is
2CO3 is 1.328 g7100cc-H2O, Na
2CO3 is 21.58g/100CC-H2O, 2C
O3 is 111.5g/100cc-H2O.

In this way, the amount of carbonate obtained when dissolved in the electrolyte is small, so in the case of lithium hydroxide and thorium hydroxide, even if carbonate is generated in the electrolyte, the conductive dust is reduced and the inside of the battery is The amount of carbonate may increase to the extent that it increases the resistance or reduces the activity of the negative electrode zinc, but even if it is produced in a large amount, it will precipitate, so it will not cause much of a problem.

However, at this time, care must be taken because if the lithium hydroxide concentration exceeds 12% by weight, it may cause an increase in the internal resistance of the battery depending on the manufacturing conditions.

That is, if the electrolyte is left in an injected state during assembly, carbon dioxide gas in the air reacts with lithium hydroxide in the electrolyte to generate lithium carbonate.

As mentioned above, this lithium carbonate has low solubility in the electrolyte, and in particular, if lithium carbonate is formed after being injected into the anode and left to stand, the electrolyte in the anode will penetrate into the inside of the anode. Combined with the decrease in the amount of liquid remaining on the surface,
A layer of solid lithium carbonate is formed on the surface of the anode.

This lithium carbonate is an insulator, and if a certain amount or more of lithium carbonate is interposed between the anode part and the separator, the second
As seen in the table, the internal resistance of the battery shows a large value.

However, if the lithium hydroxide in the electrolyte is less than 12% by weight, if left unattended during assembly, carbon dioxide gas in the air will react with the lithium hydroxide and sodium hydroxide in the electrolyte, causing the respective Even if lithium carbonate and sodium carbonate are produced, the above-mentioned problems do not occur.

This is because lithium carbonate and sodium carbonate are generated simultaneously, and the amount of lithium carbonate is smaller than when lithium hydroxide is used alone. Even if solid lithium carbonate is formed, the amount will be very small.

In addition, as mentioned above, the solubility of sodium carbonate is much higher than that of lithium carbonate, so even if carbonate is produced from a mixed solution of lithium hydroxide and sulfur hydroxide, lithium carbonate is difficult to dissolve. The amount is small and solids are rarely formed.

Therefore, as mentioned above, even if the electrolyte is injected onto the anode surface and left in the air for a long time, it is possible to avoid the problem of increased internal resistance of the battery due to the formation of solid lithium carbonate on the anode surface. It's just a name.

Table 2 shows the characteristics when the electrolyte composition was varied.

The battery used has a diameter of 11.6ii and a height of 4.2m.
m, and uses a separator made by laminating a polyethylene microporous thin film and cellophane.

Third, the electrolytic solution used in the present invention has very little creep phenomenon, so even if the battery is used for a long period of time, no leakage phenomenon occurs.

In other words, since alkaline electrolytes have a creep phenomenon,
This is always a problem when used as a battery electrolyte, but
In the present invention, lithium hydroxide, which has an extremely low creep phenomenon, is used in combination with sodium hydroxide, which has a relatively low creep phenomenon.

However, as shown in Table 2, compared to the electrolyte solution containing only sodium hydroxide, by adding lithium hydroxide,
In order to improve the leakage resistance even a little, it is necessary to replace at least 5 or more parts with lithium hydroxide.

Therefore, compared to conventional batteries that use an electrolyte consisting of at least one of potassium hydroxide and sodium hydroxide, the possibility of leakage is extremely low.
In particular, there is no fear of leakage even when used for long periods of time while charging and discharging, such as with rechargeable silver oxide batteries.

Fourthly, by not saturating the zinc oxide in the electrolytic solution, the discharge reaction of the battery, especially discharge at high current density, can be carried out smoothly as shown in FIGS. 2 and 3.

Figure 2 shows the electrolyte composition as follows: LiOH: NaOH: Z n
O:H2O is 10:30:X:100, and Zn of X
A load of 60 Ω was connected at 20°C to each of the samples A with saturated O, 80% of saturation, C with 50% of saturation, and B with ZnO (no additive). Figure 3 shows the discharge characteristics during continuous discharge, using the electrolytic solution shown in Figure 2 and reducing the resistance to 6.5 Ω at 20°C.
This shows the discharge characteristics when a load is connected and discharge is performed at a low current density.

In the absence of zinc oxide (ZnO), at low current densities, the cathode zinc is eluted into the electrolyte and the capacitance of the cathode is reduced, resulting in a slightly shorter duration as shown in FIG.

That is, zinc oxide is generated on the surface of the negative electrode zinc due to the discharge reaction of the battery.

Normally, in a discharge state, zinc oxide generated electrically tends to dissolve, so even if the zinc oxide in the electrolyte is saturated in advance, the zinc oxide on the surface of the zinc cathode will gradually dissolve. Release the solution into the liquid.

However, by keeping the zinc oxide in the electrolyte in an unsaturated state in advance, the zinc oxide generated on the cathode zinc surface during discharge will be eluted into the electrolyte faster, especially in high current density discharges. In this case, the elution of zinc oxide generated on the surface of the zinc cathode is the rate-determining step.

The effect of keeping the zinc oxide in the solution unsaturated is significant.

Note that if zinc oxide is not mixed in the electrolyte, the aforementioned effects will be greatly apparent, but in the absence of zinc oxide,
During storage of the battery, the negative electrode zinc dissolves into the electrolyte and generates hydrogen gas, resulting in leakage and increased expansion during storage of the battery, as shown in (2) in Table 2.

Therefore, in order to reduce cathodic zinc elution to a negligible level, it is necessary to use zinc oxide in an amount of at least 80 times the saturation amount at that alkaline concentration.

Furthermore, since the zinc oxide in the electrolyte is not saturated, the following effects can be achieved when charging the battery.

That is, when charging a silver oxide battery, cathode zinc dendrites may be generated at a certain current density.

As these dendrites are repeatedly charged and discharged,
It may break through the separator layer from the zinc surface and reach the anode, and as a result of this internal short circuit, the battery will be depleted.
In some cases, this may lead to an accident such as expansion or rupture.

However, at this time, if the zinc oxide in the electrolyte is unsaturated, even if dendritic zinc is generated during charging, it will immediately dissolve into the electrolyte, making it impossible for dendritic zinc to grow. , accidents like the one mentioned above will not occur.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a silver oxide battery using an electrolytic solution in an example of the present invention, FIG. 2 is a diagram showing high rate discharge characteristics, and FIG. 3 is a diagram showing low rate discharge characteristics. 1... Anode, 3, 4... Separator,
6...Cathode.

Claims (1)

[Scope of Claims] 1. An anode mainly made of monovalent silver oxide, a cathode mainly made of zinc, and an alkaline electrolyte, the alkaline electrolyte containing t-IJium hydroxide, lithium hydroxide,
A silver oxide battery comprising an aqueous solution in which unsaturated zinc oxide is mixed and dissolved, and characterized in that the concentration of lithium hydroxide is 5 to 12% by weight. 2. The silver oxide battery according to claim 1, wherein the amount of zinc oxide in the electrolytic solution is 80 to 99 times the amount of saturated zinc oxide at the alkaline concentration.