JPH05343096A - Nickel-zinc battery - Google Patents

Abstract

PURPOSE:To restrain a dendrite phenomenon, and lengthen the service life by using a microporous film separator on whose surface a nickel layer having a specific thickness is formed. CONSTITUTION:A nickel layer of 20-180 angstrom is formed on the surface of a microporous film separator. Thereby, an electrolyte preservable ability can be improved without increasing electric resistance, and a zincic dendrite crystal is decomposed efficiently, so that service life performance of a battery can be improved. When this microporous film separator and a cellulose separator are provided, an effect becomes particularly large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microporous film separator having a nickel layer of 20 to 180 angstrom formed on the surface, or a nickel-zinc battery provided with the microporous film separator and a cellulose separator. .

[0002]

2. Description of the Related Art In recent years, electric vehicles have been attracting attention due to environmental problems, and new high-performance batteries are expected to emerge as a power source for them. Among them, nickel / zinc batteries have higher energy densities than conventional lead batteries, and thus the demand for their practical use is increasing. Nickel-zinc batteries have the potential as secondary batteries, but their practical use was difficult due to their short cycle life. The major technical issues are the dendrite phenomenon and the shape change phenomenon of zinc. In order to overcome these problems, improvement of zinc itself, for example, by adding copper powder or cadmium powder as a conductive material to make the current distribution uniform, in addition to attempts to reduce these problems, nickel on the separator Attempts have been made to coat.

[0003]

At present, nickel-zinc batteries are expected as high energy density batteries, but at present they have not reached the level of practical use because of insufficient life performance. One of the reasons is that a highly reliable microporous film separator has not been obtained. The required function of this separator is to effectively suppress the dendrite phenomenon of the zinc negative electrode, which causes the deterioration of life performance. In order to enhance this function, attempts have been made to coat the separator with nickel to decompose the dendrite crystals of zinc. This method includes a vacuum vapor deposition method, a sputtering method and a coating method. Since the vacuum deposition method is expensive, it is difficult to put it to practical use.
Although the sputtering method and the coating method are being studied (for example, NSWC / TR-82-128, Feb.82), the sputtering method has the advantage that the nickel thickness is uniform, but the separator is particularly fine. If the surface of the porous film is evenly coated, there is a drawback that the electric resistance remarkably increases. Further, the adhesion to the substrate is weak, and there is a problem of peeling due to charge and discharge. The coating method, after coating a mixture of nickel powder with a suitable binder and solvent on the surface of the separator,
Although this is a method of drying and evaporating the solvent, there are drawbacks that the thickness becomes non-uniform and the coating amount increases.

In no case has a detailed study of the optimum amount been carried out.

[0005]

According to the present invention, when a microporous film separator is provided with a nickel layer having a thickness of 20 to 180 angstroms on the surface thereof, the electrolyte holding capacity is significantly improved without increasing the electric resistance. . When this separator is applied to a nickel-zinc battery, the dendrite crystal of zinc is efficiently decomposed, so that the life performance of the battery is improved. In particular, the effect is great when the microporous film separator and the cellulose separator are provided.

[0006]

[Function] First, in order to investigate how the nickel coating thickness affects the basic characteristics of the separator,
An aqueous solution containing 0.1% nonionic surfactant was dipped in a microporous film separator with a thickness of 25 μm and porosity of 38%, and dried, and then the coating thickness of nickel was measured by sputtering and vacuum deposition. I made something that changed.

The electrical resistance of this separator in a potassium hydroxide aqueous solution and the liquid retention rate of the electrolytic solution were measured. The measurement results of the electric resistance are divided into the sputtering method (A) and the vacuum vapor deposition method (B) and are shown in FIG. These measurements used an electrolytic solution of 7MKOH, and the liquid retention rate of the electrolytic solution was calculated from the following equation.

Electrolytic solution retention rate = (weight after dipping separator in electrolytic solution / separator weight) × 100

[0009]

[Table 1] The electric resistance value increases rapidly when the nickel film thickness exceeds 150 Å, and the rate of increase is larger in the case of the vacuum deposition method (B). As a result of investigating the surface of the separator using an electron micrograph, it was found that the holes formed in the separator became covered with nickel when the nickel film thickness became 150 Å or more. In addition, in the case of using the vapor deposition method, nickel deposition is more likely to be formed on the side surface of the hole than in the case of the sputtering method, and there is a tendency to close the hole. It is presumed that the value of the electric resistance becomes higher when

On the other hand, as can be seen from the values shown in Table 1, the electrolyte retention rate is higher than that of the standard nickel-free one when the nickel thickness is 20 angstroms or more. The value is more than doubled. Further, there is almost no difference between the vapor deposition method and the sputtering method. As described above, it was found that the nickel-coated separator has an effect of remarkably improving the liquid retention rate of the electrolytic solution. This is because the conventional microporous film separator is hydrophobic polyethylene or polypropylene, so it was necessary to treat the surface with a surfactant to impart hydrophilicity, whereas the nickel-coated separator was Since the coated nickel itself has hydrophilicity, it is considered that the liquid retention rate was significantly improved. From the above, it can be said that the thickness of the nickel coating is preferably 20 to 150 angstroms from the viewpoint of the basic characteristics of the separator, that is, the electrical resistance and the electrolyte retention rate. Further, it can be said that the sputtering method is preferable as the means for applying the nickel coat.

[0011]

EXAMPLES The present invention will be described below with reference to preferred examples. 2m cobalt nitrate on sintered nickel substrate with 80% porosity
It is impregnated with a 5M nickel nitrate aqueous solution containing ol% at 80 ° C, and then immersed in a 5M aqueous sodium hydroxide solution at 80 ° C. After that, it is washed with hot water and dried, and the positive electrode plate (size is 160 × 145 × 1 m
m) was produced. Next, 80 parts of zinc oxide powder, 10 parts of zinc metal powder and 0.2 part of 1 mm long nylon short fibers are mixed, and then 30 parts of propylene glycol are added and mixed to form a paste. Further, 3 parts of a 60% aqueous dispersion solution of polytetrafluoroethylene powder is added and kneaded. Then, it was pressure-bonded to a copper punching metal having a thickness of 0.1 mm with a pressure roller, dried at 150 ° C. and pressed again to manufacture a negative electrode plate (size: 160 × 145 × 0.8 mm).
This positive electrode plate was nickel-coated with a 0.12 mm polyamide nonwoven fabric by a sputtering method to a thickness of 25 μm and a pore diameter of 0.02 ×
Microporous membrane made of polypropylene with 0.2 μm and porosity of 38% 1
After wrapping with a separator composed of one sheet, it was heat-sealed. Subsequently, the negative electrode plate was wrapped with one piece of 0.12 mm polyamide nonwoven fabric, and then the positive electrode plate and the negative electrode plate were alternately stacked to form an electrode plate group. Nickel-zinc battery using this electrode group and 550 ml of 8.5M potassium hydroxide aqueous solution saturated with zinc oxide as electrolyte, and a synthetic resin battery case with a nominal capacity of 200 Ah.
I made (C). The external dimensions are 170 × 227 × 65 mm,
The battery is equipped with a safety valve that operates at 0.5 kg / cm ² .
For comparison, a battery was also manufactured using a non-nickel-coated polypropylene microporous membrane having a thickness of 25 μm and a pore size of 0.02 × 0.2 μm.

In the above embodiment, a nickel-zinc battery having a nominal capacity of 200 Ah (similar structure) is used except that cellophane is double wound as a cellulosic separator from one polypropylene microporous membrane. D) was produced.

A life cycle test was carried out in which these batteries were charged to 2.0 V at 25 ° C. and 0.5 C, further charged to 0.05 C for 3 hours, and then discharged to 1.40 V at the same temperature and the same current.

FIG. 2 shows the relationship between the number of cycles and the nickel film thickness when the discharge capacity reaches 60% of the nominal capacity.
From the figure, it can be seen that the cycle life improves when the nickel coating thickness exceeds 20 angstroms, and conversely decreases when it exceeds 180 angstroms. When the batteries were disassembled and examined after the end of the life cycle test, in all the batteries, zinc dendrites penetrated the microporous membrane made of polypropylene and a micro short circuit occurred. This means that when the nickel coating thickness is 20 angstroms or more, it becomes difficult for zinc dendrites to penetrate, and when the nickel coating thickness exceeds 180 angstroms, zinc dendrites increase in reverse. . Probably
It is considered that the zinc dendrites grown on the nickel surface disappear in the range of 20 to 180 by the following equation.

Zn + 2 H ₂ O + 2 OH ⁻ → H ₂ + Zn (OH) ₄ ² On the other hand, when the coating thickness of nickel exceeds 180 Å, nickel deposition is likely to be formed on the side surface of the hole and the charging is performed because the hole is blocked. Also, it is considered that the current density during discharge was concentrated and the growth of zinc dendrite was large, and the growth rate thereof was higher than the disappearance rate, resulting in a short life.

Next, a battery (D) with cellophane added
Shows that the battery has a longer life performance than the cell (C) that does not use cellophane, and its effect is remarkable especially when the nickel film thickness is in the range of 20 to 180 angstroms.
This means that the combination of the nickel-coated separator and cellophane produces a synergistic effect. Probably, the dendrite growth rate of zinc penetrates the cellophane, and it is considered that the zinc is sufficiently decomposed on the nickel film. A similar charge / discharge cycle test was also conducted on a battery using a nickel-coated polypropylene microporous film by the coating method, and a two-stage plateau appeared in the discharge characteristics from the beginning of the cycle test. Fell sharply and was not practical.

[0017]

As described above, the battery of the present invention uses a microporous film separator having a nickel layer having a thickness of 20 to 180 angstroms formed on the surface thereof.
The life can be extended. In particular, the effect can be further enhanced by providing the microporous film separator having the nickel layer formed on the surface thereof and the cellulose separator.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a value of electric resistance of a separator and a film thickness of nickel.

FIG. 2 is a diagram showing the relationship between the number of charge / discharge life cycles of a nickel-zinc battery and the film thickness of nickel.

Claims (2)

[Claims] 1. A nickel-zinc battery comprising a microporous film separator having a nickel layer having a thickness of 20 to 180 angstrom formed on the surface thereof. 2. A nickel-zinc battery comprising a microporous film separator having a nickel layer having a thickness of 20 to 180 angstrom formed on the surface thereof and a cellulose separator.