JPS6378460A - Nickel-zinc storage battery - Google Patents

Abstract

PURPOSE:To obtain a battery with long cycle life by separating a zinc electrode from a nickel electrode by means of a tubular separator and making a structure where caustic potash based electrolyfic solution is used for the zinc electrode and electrolytic solution containing caustic soda for the nickel electrode. CONSTITUTION:Caustic soda with concentration of 0.5-1.0 times of caustic potash concentration is used as electrolytic solution for nickel electrodes 3, and the amount of the electrolytic solution used is set to 0.8-1cc/AH for nickel contents(AH) of the nickel electrodes. Besides, a desirable range of total alkaline concentration for the electrolytic solution used for the nickel electrodes is 25-40 percent by weight. In the meantime, material such as a microporous membrance, a semipermeable membrance or an ion-exchange membrance with low permeability for electrolytic solution or zincic acid is used as at least one sheet of a tubular separator 1. The amount of caustic soda migrating to the zinc pole through the tubular separator is reduced, thus restricting accelerated electrodeposition of to dendritic zinc in the zinc electrode caused by contamination of caustic potash.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a nickel-zinc storage battery constructed using a nickel electrode as an anode and a zinc electrode as a cathode.

<Prior Art> Nickel-zinc storage batteries have features such as higher energy density and lower cost than nickel-cadmium storage batteries.

However, in this nickel-zinc storage battery, like other alkaline zinc storage batteries, zincate ions in the electrolyte that are eluted from the zinc electrode during discharge are deposited in a dendritic form on the surface of the zinc electrode during charging, resulting in repeated charging and discharging. As a result, this electrodeposited zinc penetrates the separator and reaches the opposite electrode, causing internal (D) jam, resulting in a short cycle life. Therefore, in order to improve the cycle life, it is necessary to restrict the electrolyte inlet in the battery to prevent the diffusion of zincate ions, or to prevent the diffusion of zincate ions between nickel and zinc electrodes, as shown in Japanese Patent Application Laid-Open No. 59-63672. Techniques such as improving the separator and suppressing the growth of dendritic zinc onto the nickel electrode by using a stack of multiple separator materials as a separator between the Used together. In addition, in this Japanese Patent Application Laid-Open No. 59-63672, zinc (*) is inserted into a bag-shaped separator, and a nickel electrode is placed outside the separator, and an electrolyte is injected into the zinc electrode side. By using a caustic potassium aqueous solution in which zinc oxide has been dissolved to a saturated state, and by injecting a caustic potassium aqueous solution that does not contain zinc oxide into the nickel electrode side, a nickel electrode with zinc ions released from the zinc electrode by charging and discharging is used. The deterioration of the nickel electrode is prevented by preventing migration to the side, the dissolution of the zinc electrode is suppressed, and further the deterioration of the nickel electrode due to zinc oxide is prevented.

<Problems to be Solved by the Invention> By using these conventional techniques, internal short circuits caused by dendritic zinc can be suppressed, and the one-cycle life can be improved. However, when this type of nickel-zinc storage battery is used in a high-temperature environment, the oxygen overvoltage at the nickel electrode decreases, making it easier to generate oxygen gas during charging, which reduces the charging efficiency of the nickel electrode. This causes problems such as a decrease in battery capacity, and an increase in the absorption and consumption of generated oxygen gas by the zinc electrode, which accelerates the deterioration of the zinc electrode and shortens the cycle life. However, the above-mentioned conventional techniques cannot deal with such problems and cannot contribute to improving the high-temperature characteristics of the battery.

It is also conceivable to use a caustic soda aqueous solution instead of a caustic potassium aqueous solution as the electrolyte, as is employed, for example, in nickel-cadmium storage batteries that similarly use a nickel electrode as an anode. If this caustic soda aqueous solution is used, the oxygen overvoltage of the nickel electrode will increase, the decrease in charging efficiency of the nickel electrode that is opened during high-temperature use will be alleviated, and the cycle characteristics can be improved. However, since the solubility of zinc is higher in a caustic soda aqueous solution than in a caustic potassium aqueous solution, when a caustic soda aqueous solution is used as the electrolyte of a nickel-zinc storage battery, more zincate ions are eluted during discharge, and the dendritic zinc There is a problem in that the cycle life is reduced due to accelerated analysis.

Means for Solving the Problems> The nickel-zinc storage battery of the present invention has an electrode body in which a zinc electrode and a nickel electrode are arranged separately inside and outside a bag-shaped bag to form one groove, and the electrode body is housed in a battery container. For nickel-zinc storage batteries,
The electrolyte used on the zinc electrode side is a caustic potassium aqueous solution in which zinc oxide is dissolved to a saturated state, and the electrolyte used on the nickel electrode side is an alkaline aqueous solution containing caustic potash and caustic soda. The gist is that it does not.

The electrolytic solution used on the nickel electrode side has a caustic soda concentration (gravitational %) of 0.5 of the caustic potash temperature (type can %).
It is sufficient to use one that has been increased to ~1 times. Also, the amount of this electrolyte used is the nickel volume ff1 (AI-
1> may be 0.8 to lcc/Al-1,
Within this range, the electrolytic solution level is regulated to the extent that it impregnates the pores of the nickel electrode, and there is substantially no free electrolytic solution in the nickel electrode, which is preferable. Furthermore, the preferable range of the total alkali 1) concentration (the sum of the caustic potassium concentration and the caustic soda concentration) in this electrolytic solution used for the nickel electrode is 2.
If it is thinner than this range, the ionic conductivity will decrease, and if it is too full, the viscosity of the electrolyte will become too large, and in either case, the battery characteristics will deteriorate.

On the other hand, as a bag-shaped separator, one or more separator materials are used as they are or in a stacked state. For example, when using multiple layers of separator materials, at least one of these separator materials should be made of a microporous film, semipermeable membrane, or ion exchange membrane to absorb the electrolyte and zinc ions as much as possible. It is preferable to use something that does not allow it to pass through.

<Function> As mentioned above, the sub1)) electrode and the nickel electrode are separated by a bag-shaped separator, and the zinc (* side contains an electrolytic solution containing caustic potassium, and the nickel electrode side contains an electrolytic solution containing caustic soda. By using an electrolyte, it is possible to suppress cycle deterioration caused by dendritic snow-dried zinc and improve the high temperature characteristics of the battery.In addition, the electrolyte on the nickel electrode side is a mixed alkali of caustic potash and caustic soda. Since it was made into an aqueous solution,
The amount of caustic soda transferred to the zinc electrode side through the bag-like separator is reduced, and promotion of electrodeposition of dendritic zinc on the zinc electrode due to the mixing of caustic soda is suppressed.

<Example> Example-1 Figure 1 shows a bag-shaped separator 1 used in this example, and in the figure, 1a is a polypropylene microporous film,
1b is a nylon nonwoven fabric, 1C is a polypropylene microporous film, and after these separator cord materials are overlapped, the three surrounding sides are heat-sealed (the shaded area in the figure is the heat-sealed area).
It is processed into a bag shape.

Using the bag-shaped separator 1 described above, insert the zinc electrodes 2 into the bag-shaped separator 1, and arrange the nickel electrodes 3 on the outside of the bag-shaped separator 1 and overlap them alternately. The nickel-zinc storage battery (Battery A of the present invention) shown in FIG.
)made. At this time, a 30% by weight aqueous potassium hydroxide solution saturated with zinc oxide was used as the electrolyte on the zinc electrode side.
An amount of electrolyte solution was injected into the inside of the separator so that the level of the electrolyte was below the opening of the bag-shaped separator 1. In addition, the nickel electrode side contains 18% caustic potash by weight and 12% by weight caustic soda, with a total alkali concentration of 30% by weight? 6 alkaline aqueous solution)
0.9 cc of the solution was injected into the outside of the bag-like separator 1 using one day.

On the other hand, the electrolyte used on the nickel electrode side is 30% by weight.
A comparative nickel-zinc storage battery (comparative battery B) was prepared in the same manner as battery A of the present invention except that a caustic potassium aqueous solution was used, and the electrolyte used on the zinc electrode side was 18% by weight of caustic potassium,
A comparative nickel-zinc storage battery (comparative battery C) had the same configuration as the invention battery A, except that the alkali concentration was 30 mw% with 12 mw% of caustic soda and the zinc oxide was saturated.
) were prepared respectively.

These three batteries were tested for 250m at a temperature of 40'C.
A charge/discharge cycle of charging at a current of A for 5 hours and discharging at a current of 250 mA until the battery voltage reached i, ov was repeated to examine cycle changes in battery capacity (%) for batteries A to C.

The results are shown in Figure 2. If the cycle life is defined as the point in time when the battery capacity drops to about 65% or less of the initial capacity, the cycle life of comparative batteries B and C is about 140 cycles, respectively.
It was about 200 cycles. On the other hand, the present invention battery A
Even after 300 cycles, more than 80% of the batteries remained intact, indicating that the batteries had a long life with little cycle deterioration.

Furthermore, after the above cycle test, the electrolyte on the zinc electrode side of Battery A of the present invention was analyzed for sodium ions contained therein by atomic absorption spectrometry, and it was found that it contained only 1 to 2% by weight of sodium ions. It was demonstrated that the bag-shaped separator used in the battery of the present invention effectively suppresses the migration of caustic soda injected into the nickel electrode side to the zinc electrode side.

Example 2 Same as inventive battery A except that the electrolyte with the composition shown in Table 1 was used as the electrolytic solution used on the nickel electrode side. did.

*1 Same as comparative battery B *2 Same as invention battery A *3 Ratio of caustic soda temperature to caustic potash concentration (N
aOHW degrees/KOHC degrees) These batteries were subjected to the same charging and discharging cycles as in Example 1, and the cycle life of each battery was examined, with the point in time when the battery capacity became approximately 65% or less as the cycle life. The above test results were plotted with the above ratio on the horizontal axis and the cycle life on the vertical axis to obtain the graph shown in FIG. 4.

From this graph, it can be seen that the cycle life is significantly improved when the above ratio is 0.5 to 1. In other words,
If the electrolyte used on the nickel electrode side is an electrolyte whose caustic soda temperature is 0.5 to 1 times the caustic potassium concentration, the cycle life of this type of nickel-zinc storage battery will be greatly improved. . When the concentration of caustic soda exceeds this range, the amount of caustic soda that passes through the bag-like separator and moves to the zinc 4~ side increases.
The cycle life decreases significantly due to the dendritic deposited zinc, and on the other hand, if the caustic soda concentration is lower than this range, the high temperature characteristics cannot be effectively improved by using caustic soda.

<Effects of the Invention> The nickel-zinc storage battery of the present invention as described above has good high-temperature characteristics, effectively suppresses deterioration caused by dendritic zinc deposits, and has a long cycle life. Batteries can be provided.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the bag-shaped separator used in the example, Figure 2
The figure is an explanatory diagram of the battery of Example, FIG. 3 is a graph showing the cycle change of battery bedding of the battery of the present invention and the comparative battery, and FIG. This is a graph showing the change in battery cycle life when the ratio of caustic soda concentration to temperature is changed. 1... Bag-shaped separator, 2... Zinc electrode, 3... Nickel electrode.

Claims (1)

[Scope of Claims] 1. A nickel-zinc storage battery in which an electrode body consisting of a zinc electrode and a nickel electrode arranged separately inside and outside a bag-shaped separator is housed in a battery container, wherein the zinc electrode side The electrolyte used for this is a caustic potassium aqueous solution in which zinc oxide is dissolved to a saturated state, and the electrolyte used for the nickel electrode is an alkaline aqueous solution containing a mixture of caustic potash and caustic soda and does not contain zinc oxide. A nickel-zinc storage battery characterized by: 2. The nickel-zinc storage battery according to claim 1, wherein the concentration of caustic soda in the electrolytic solution used on the nickel electrode side is 0.5 to 1 times the concentration of caustic potassium. 3. A patent characterized in that the bag-shaped separator is made by stacking a plurality of separator materials, and at least one of these separator materials is a microporous film, semipermeable membrane, or ion exchange membrane. A nickel-zinc storage battery according to claim 1 or 2.