JPH04328255A - Paste type nickel electrode - Google Patents

Abstract

PURPOSE:To improve the cyclic characteristics, and obtain a long-life paste type nickel electrode by regulating a dehydration temperature by heating nickel hydroxide so as to increase a ratio of beta-NiOOH crystals and increase an active material utilization factor. CONSTITUTION:A paste type nickel electrode is composed of a porous metal body for a base plate, and active material mainly comprising nickel hydroxide filled in it. For the nickel hydroxide, one with which dehydration reaction by heating occurs at a temperature of 270 deg.C or less is used, and the paste type nickel electrode includes metal cobalt or cobalt oxide without becoming eutectic crystals with the nickel hydroxide.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste-type nickel electrode which is a positive electrode for an alkaline storage battery and uses cadmium, zinc, hydrogen storage alloy, etc. as a negative electrode.

0002

[Prior Art] Conventionally, nickel electrodes for alkaline storage batteries are made by filling a substrate made of carbonyl nickel sintered on a punched metal with a nickel salt such as nickel nitrate in the form of an aqueous solution, and then nickel hydroxide in an alkaline solution. The so-called sintering method was the mainstream. The advantage of the sintering method is that the carbonyl nickel sintered body that is the substrate has a pore diameter of
Because it has a very fine pore structure of 10 μm, it has excellent current collecting ability from nickel hydroxide, which is originally a nonconductor. On the other hand, the ratio of the substrate volume to the entire nickel electrode is required to be about 20%, which limits the amount of active material filled, and the capacity density of the nickel electrode is 450%.
There was a drawback that only about mAh/cc could be obtained.

Paste type nickel electrodes have been proposed as an attempt to improve these drawbacks. Paste-type nickel electrodes use a sponge-like or felt-like porous metal material with a pore diameter of 100 to 500 μm as a substrate, and the pores of this substrate are filled with a paste of powdered nickel hydroxide prepared with an appropriate solvent or binder, and then dried. , obtained by applying pressure. In addition, since the volume ratio of the substrate to the entire nickel electrode can be reduced to less than 10%, it is possible to increase the amount of active material filled, and when converted to the same capacity density, it can be increased to about 600 mAh/cc. Can be done. In principle, the powdered nickel hydroxide used in this paste type nickel electrode is made by mixing an aqueous solution of a nickel salt such as nickel nitrate or nickel sulfate with an excess alkaline aqueous solution such as caustic soda or caustic potash, as in the sintering type. 1 to number 1
It is generally obtained by reacting to produce 0 micron particles, washing the precipitate with water, and drying it.

0004

However, the paste-type nickel electrode produced by the above method has a number of problems. Particularly, the problem is that the utilization rate of nickel hydroxide is low during charging and discharging, and the problem that swelling of the active material due to charging and discharging cycles is extremely noticeable. One of the causes of such problems is the difference in current collection performance of the substrates. As mentioned above, the pore diameter of the sintered substrate is several to 10 μm, whereas the pore diameter of the sponge-like and felt-like metal porous materials, which are paste-type substrates, is 100 to 500 μm.
It is several tens of times larger than m. That is, the distance of charge transfer in the active material during reaction becomes longer, and polarization due to resistance tends to increase. Disadvantages of highly polarized electrodes include a reduction in discharge voltage and the formation of irreversible charging products during charging. This irreversible charging product is generally known as γ-NiOOH, and it is less likely to be discharged compared to β-NiOOH, which is a charging product of a normal nickel electrode, and because the crystals are elongated in the C-axis direction. It is known that active materials tend to swell. In other words, when comparing the sintering method and the paste method, when the same nickel hydroxide is used, the paste method has the drawback that the utilization rate decreases and the active material is more likely to swell due to the difference in the current collecting ability of the substrate. It can be said that the cause of this is largely related to the generation of γ-NiOOH, which is an irreversible charging product.

As a countermeasure to this problem, the addition of a cobalt compound, which was widely known in the sintering method, was added to the paste method.
60449, metallic cobalt, JP-A-61-
As shown in No. 138458, attempts have been made widely to suppress polarization by incorporating a form of cobalt with excellent conductivity such as cobalt monoxide. Also, JP-A-1-26
0762 and JP-A-2-30061, attempts have also been made to add cadmium, zinc, etc. in a eutectic state to nickel hydroxide crystals. However, neither method can be said to be a sufficient countermeasure against the above problems; for example, in terms of utilization rate, the sintering method is over 95%, while the paste method has a limit of around 90%, and the cycle life is also limited. Currently, the sinter type has a cycle life of over 500 cycles, while the paste type has an inferior cycle life of around 300 cycles, and these problems have been a major obstacle to the spread of paste type nickel electrodes.

The present invention has been made to solve the above-mentioned conventional problems, and aims to provide a paste-type nickel electrode that has a high utilization rate and a long life.

[0007]

[Means for Solving the Problems] The present invention provides a paste formed by using a metal porous body having a three-dimensional structure as a substrate and filling it with an active material mainly consisting of nickel hydroxide, which can be expressed by the chemical formula Ni(OH)2. In the type nickel electrode, the nickel hydroxide is converted into Ni(OH) by successive heating.
The active material is characterized in that the reaction temperature at which the dehydration reaction to 2→NiO occurs is 270°C or lower, and the active material contains metallic cobalt or cobalt oxide that does not form a eutectic state with the nickel hydroxide. This is a paste-type nickel electrode.

Examples of the metal porous body having the three-dimensional structure include sponge-like nickel and felt-like nickel. The method for producing nickel hydroxide is a neutralization reaction between an aqueous solution of a nickel salt such as nickel nitrate or nickel sulfate and an alkaline aqueous solution such as caustic soda or caustic potash, but by adjusting the pH of the reaction atmosphere,
Even with the same nickel hydroxide, it is possible to obtain crystals with different temperatures at which the dehydration reaction from Ni(OH)2 to NiO takes place.

Furthermore, the performance is improved by adding a metal element selected from cadmium and zinc in a eutectic state to nickel hydroxide, and adding metal cobalt, cobalt hydroxide, and generalized cobalt.

0010

[Operation] Even with the same nickel hydroxide, Ni(OH)2, the degree of production of γ-NiOOH tends to vary depending on the degree of crystallinity. It is a reaction during charging and Ni(OH)2
The degree of freedom of proton movement at the interface of the electrolyte differs depending on the degree of crystallization, and the less crystallinity tends to have a higher degree of freedom of proton movement, whereas the less free the movement of protons, the less γ-NiOOH Since Ni(OH)2 has a tendency to easily generate γ-NiOOH, it can be said that Ni(OH)2 having high crystallinity as a whole tends to easily generate γ-NiOOH.

[0011] There are many methods for indicating the crystallinity of Ni(OH)2, but the inventor specifically found that the Ni(OH)2→
The present invention was created by finding a high correlation between the dehydration reaction temperature to NiO and the production ratio of γ-NiOOH. γ- for β-NiOOH+γ-NiOOH amount during charging
The smaller the ratio of NiOOH, the higher the utilization rate of the nickel electrode, and the smaller the degree of swelling of the active material, so the cycle life tends to be longer.

0012

EXAMPLES The effects of the present invention will be explained in detail with reference to examples. First, nickel hydroxide, which is the main active material, was prepared by the following method. In an environment where the pH of the reaction atmosphere was controlled to be constant, a nickel sulfate aqueous solution and a caustic soda aqueous solution were sequentially added, and nickel hydroxide with a particle size of 1 to 30 μm was produced through crystal growth, water washing, and drying. By changing the pH value of the reaction atmosphere to four types, it was possible to obtain four types of Ni(OH)2 with different crystallinity.

This nickel hydroxide was subjected to thermogravimetric analysis (TGA).
) and measured the dehydration temperature from Ni(OH)2 to NiO, which was 260, 270, 280, 290 in descending order
It was ℃. An example of the chart is shown in FIG. To 100 parts by weight of this nickel hydroxide, 10 parts by weight of cobalt monoxide and 0.3 parts by weight of carboxymethyl cellulose were added to 30 parts by weight of water.
After kneading with parts by weight to form a paste, this paste was filled into a sponge-like porous nickel body with a pore diameter of 300 μm, and was dried, pressurized, and lead welded to produce a paste-type nickel electrode of the present invention.

This paste-type nickel electrode was wound together with a paste-type cadmium electrode and a nylon separator and inserted into a battery can to produce an AA size nickel-cadmium storage battery, and the charge-discharge cycle of 0.3C charging/1C charging was performed for 5 times.
00 cycles were performed. Figure 2 shows the estimated utilization rate for the theoretical capacity of the nickel electrode with respect to the number of cycles at that time.

Next, the battery after 500 cycles was disassembled using a rechargeable bearer, the nickel electrode was taken out and crushed, and X-ray diffraction (XRD-Cu Kα) was measured. The peak height of NiOOH (P-γ) and the peak of β-NiOOH (P-γ) observed around 19°
β) and (P-γ)/(P-γ)+(P-β))
The ratio of γ-NiOOH in the whole was calculated from the value. The ratio of γ-NiOOH to the above dehydration reaction temperature is shown in FIG.

According to FIG. 2, the dehydration reaction temperature is 260°C;
In the case of a nickel electrode using nickel hydroxide at 270°C, the utilization rate is as high as 95%, and there is almost no change in the utilization rate even after 500 cycles. γ-NiO in Figure 3
The OH ratio also tends to be small, less than 20%. On the other hand, at 280 and 290° C., the utilization rate is 90% at the maximum, and the decrease during the cycle is remarkable, dropping to less than 50% of the initial value around 300 cycles. Correspondingly, the γ-NiOOH ratio tended to be extremely high at 40% to 80%, causing uneven distribution of the electrolyte due to swelling of the active material.

Although cobalt monoxide was used as the cobalt-based additive in this embodiment, the same effect can be obtained by using a cobalt oxide such as metallic cobalt or cobalt hydroxide as a substitute. Although detailed results are not shown here,
3-7% by weight of cadmium or zinc in nickel hydroxide
In the paste-type nickel electrode with eutectic addition, no change in utilization rate was observed even after 700 cycles, showing good characteristics.

[0018]

As is clear from the above explanation, according to the present invention, it is possible to obtain a paste-type nickel electrode with a high utilization rate of nickel hydroxide and a long life, and its industrial value is great.

[Brief explanation of drawings]

FIG. 1 is a chart of X-ray diffraction analysis of nickel hydroxide.

FIG. 2 is a diagram showing the relationship between the charge/discharge cycle of a battery using the nickel electrode of the present invention and the utilization rate of the active material of the nickel electrode.

FIG. 3 is a diagram showing the dehydration reaction temperature of nickel hydroxide and the production ratio of γ-NiOOH after 500 cycles.

Claims (2)

[Claims] [Claim 1] In a paste-type nickel electrode in which a metal porous body having a three-dimensional structure is used as a substrate and an active material mainly composed of nickel hydroxide (Ni(OH)2) is filled, the nickel hydroxide is heated. Dehydration reaction (Ni(
A paste-type nickel electrode characterized in that OH)2→NiO+H2O) occurs at a temperature of 270° C. or lower, and contains metallic cobalt or cobalt oxide that does not eutectic with nickel hydroxide. [Claim 2] Claim 1, wherein the nickel hydroxide is eutectic with cadmium or zinc metal.
Paste type nickel electrode as described.