JPH1021903A - Nickel electrode for alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the acceptability of charging at high temperature by depositing an active material mix which contains a specified compound as an indispensable component on an electric collector. SOLUTION: In this Ni electrode, an active material mix deposited on a collector contains Ni(OH)2 powder and a Zr compound powder as indispensable components. As the collector, a non-sintered type Ni electrode may be usable. The Ni(OH)2 works as a positive electrode active material and the Zr compound heightens the oxygen overvoltage on the surface of the manufactured Ni electrode and improves the acceptability of charging. The mixing ratio of the Zr compound powder is preferably set to be 0.02-2.2 pts.wt. (based on ZrO2 ) to 100 pts.wt. of the Ni(OH)2 powder. At this ratio, these two kinds of indispensable components are mixed and an viscous solution contains coaboxymethyl cellulose is added to the resultant mixture to produce a mix paste. The voids of the electric collector are filled with the paste to obtain this Ni electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nickel electrode incorporated as a positive electrode of an alkaline secondary battery, and more particularly, to a nickel electrode for an alkaline secondary battery capable of improving the charge acceptability of a battery at a high temperature.

[0002]

2. Description of the Related Art Nickel electrodes incorporated as positive electrodes in alkaline secondary batteries such as nickel-cadmium secondary batteries, nickel-hydrogen secondary batteries, nickel-zinc secondary batteries are roughly classified into sintered nickel electrodes. And non-sintered nickel electrodes. The sintered nickel electrode is prepared by applying nickel powder to a punching metal sheet together with a thickener and then firing in a reducing atmosphere to form a sintered substrate. By repeating the immersion operation, a predetermined amount of the positive electrode active material Ni (OH) ₂ is produced in the fine pores of the sintered substrate.

On the other hand, non-sintered nickel electrodes are manufactured as follows. First, if necessary, a powder of a Co compound such as cobalt oxide is mixed with Ni (OH) ₂ powder, a predetermined amount of a thickener aqueous solution is added to the obtained mixed powder, and the whole is stirred. A viscous active material mixture paste is prepared. Then, after filling this paste into the fine communication holes of a porous body having a three-dimensional network structure, such as foamed nickel or nickel felt, which is both a current collector and a support, drying and rolling are sequentially performed. A predetermined amount of the active material mixture is carried on the porous body.

[0004] Comparing these sintered nickel electrodes and non-sintered nickel electrodes, the latter allows high-density filling of the active material mixture, is easy to manufacture, and is suitable for increasing the capacity of batteries. Therefore, recently, batteries incorporating the non-sintered nickel electrode as a positive electrode have begun to be widely used.

[0005]

A battery incorporating the above-mentioned non-sintered nickel electrode, particularly a nickel-hydrogen secondary battery, is useful as a high-capacity battery. There is a problem that the charging efficiency is low, the battery capacity corresponding to the calculated charge amount cannot be obtained at high temperatures, and it is difficult to obtain a specified discharge capacity even after charging.

This is a phenomenon based on the fact that the above-mentioned non-sintered nickel electrode is inferior in charge acceptability at high temperatures, and causes a large temperature rise especially at the end of charging. Such a problem is a phenomenon that occurs because the oxygen overvoltage of the built-in nickel electrode is low. That is, at the time of charging, protons (H ⁺ ) are extracted from the nickel electrode, and the extracted H ⁺ becomes water and is integrated with the alkaline electrolyte. Further, H ⁺ is extracted from the alkaline electrolyte, and the hydrogen is absorbed by the negative electrode. Occluded in the alloy. At this time, O ²⁻ generated by the dissociation of the water of the alkaline electrolyte is adsorbed on the surface of the nickel electrode, and the equilibrium state is maintained.

When the oxygen overvoltage of the nickel electrode is low, the adsorbed O ²⁻ is converted into oxygen gas and easily detached from the surface of the nickel electrode. This does not mean that all of the supplied charging current is consumed in the original charging reaction for extracting H ⁺ from Ni (OH) ₂ , but some reactions are useless for the charging reaction, that is, alkaline electrolysis. It is wasted due to water splitting of the liquid, which means that the charging efficiency is reduced.

To solve such a problem, Ni (OH) ₂
It has been attempted to improve the charge acceptability at high temperatures by forming a solid solution of Co or Zn and increasing the amount of the solid solution. However, increasing the amount of solid solution of Co and Zn means that Ni in the active material mixture is correspondingly increased.
Will decrease the relative amount of (OH) ₂ ,
This leads to a reduction in the capacity of the nickel electrode, which causes a reduction in the battery capacity. In addition, even with a hydrogen storage alloy electrode which is a counter electrode of a nickel electrode, the capacity for absorbing oxygen gas generated at the time of charging must be increased more than necessary, which eventually causes a reduction in the capacity of the negative electrode. .

The present invention is a non-sintered nickel electrode which solves the above-mentioned problems in the conventional nickel electrode and improves the charge acceptability at high temperatures by increasing the oxygen overvoltage on the surface thereof. A battery incorporating the same as a positive electrode aims to provide a nickel electrode for an alkaline secondary battery which exhibits high charging efficiency even at high temperatures.

[0010]

In order to achieve the above object, according to the present invention, an active material mixture essentially containing Ni (OH) ₂ powder and Zr compound powder is supported on a current collector. A nickel electrode for an alkaline secondary battery is provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the nickel electrode of the present invention, the active material mixture carried on the current collector contains Ni (OH) ₂ powder and a Zr compound powder described later as essential components. Any current collector may be used as long as it is used in a conventional non-sintered nickel electrode, and examples thereof include a nickel foam having a three-dimensional network structure and nickel felt.

The above-mentioned active material mixture is carried on the current collector. In this active material mixture, the Ni (OH) ₂ powder functions as a positive electrode active material, and the Zr compound powder functions to increase the oxygen overvoltage on the surface of the manufactured nickel electrode. The Ni (OH) ₂ powder is not particularly limited as long as it is conventionally used for a nickel electrode. For example, Ni (OH) ₂ in which a predetermined amount of Co or Zn is dissolved as a solid solution can be given as a preferable example. In addition, it is preferable that the Ni (OH) ₂ powder has a spherical shape because the current collector can be easily filled.

The Zr compound for increasing the oxygen overvoltage of Ni (OH) ₂ includes, for example, ZrO ₂ , Zr
rO ₂ .nH ₂ O (n = 1, 2), Zr (OH) _{4 and the} like. These may be used alone or in combination of two or more. In producing the nickel electrode of the present invention, first, the Ni electrode
(OH) ₂ powder and Zr compound powder are mixed at a predetermined ratio, and a predetermined amount of a thickener aqueous solution obtained by dissolving carboxymethyl cellulose in water is added to the obtained mixed powder, and the whole is stirred. To prepare a mixture paste.

[0014] The proportion of the powder of Zr compound in the mixed powder described above may, Zn to Ni (OH) ₂ powder 100 parts by weight
It is preferred that the O ₂ equivalent amount set within a range of 0.2-2.2 parts by weight. If less than 0.2 parts by weight, Ni
Since the effect of increasing the oxygen overpotential of (OH) ₂ decreases, the effect of improving the charge acceptability under high pressure in the manufactured nickel electrode cannot be obtained. Conversely, if the amount exceeds 2.2 parts by weight, the active material mixture This is because the relative amount of Ni (OH) ₂ therein decreases and it becomes difficult to secure a sufficient battery capacity.

When considering the mixing state of the Ni (OH) ₂ powder and the Zr compound powder, it is preferable that both are uniformly mixed. That is, on the entire surface of the manufactured nickel electrode, in order to increase the oxygen overvoltage at the time of the charging reaction, a Zr compound powder that increases the oxygen overvoltage is adjacent to each of the Ni (OH) ₂ powders that directly contribute to the charging reaction. This is because it is preferably present.

In order to uniformly mix the two and to increase the oxygen overvoltage over the entire surface of the nickel electrode, it is inconvenient that the respective powders have too large or small particle sizes. Therefore, in the present invention, it is preferable to use Ni (OH) ₂ powder of 5 to 20 μm and Zr compound powder of 0.1 to 10 μm. When preparing the mixture paste, an appropriate amount of Co compound powder, Ni powder, C powder, or the like may be further added as in the case of the conventional nickel electrode.

A predetermined amount of the mixture paste thus prepared is filled in a void portion of a current collector such as a nickel foam by a method such as vacuum impregnation, shower impregnation, brush coating, or dipping. , Drying and rolling to produce the desired nickel electrode.

[0018]

【Example】

Examples 1 to 4, Comparative Example 1 1) Production of Nickel Electrode Spherical Ni (OH) ₂ powder having an average particle diameter of 10 μm in which 3% by weight of Zn and 1.5% by weight of Co are dissolved, and the average particle diameter Diameter 5μ
m of CoO powder and ZrO ₂ .H ₂ O having an average particle size of 1 μm
(Amount as ZrO ₂ : 87% by weight) and powder were mixed at the ratio (parts by weight) shown in Table 1.

[0019]

[Table 1]

To these mixed powders, 37.5 parts by weight of a 1.2% carboxymethylcellulose aqueous solution was added, and the whole was stirred to prepare an active material mixture paste. The mixture paste was filled into a nickel foam plate having a basis weight of 550 g / m ² (average pore diameter: 0.3 mm), dried at a temperature of 80 ° C. for 1 hour, and further rolled under a pressure of ² ton / cm ² to form a nickel electrode. did.

These nickel electrodes are 72 mm long and 4 mm wide.
It has a dimension of 1 mm and a thickness of 0.55 mm, and the packing density of Ni (OH) ₂ is within the range of 2.60 to 2.65 g / cm ³ . 2) Battery assembly Composition: 100 parts by weight of hydrogen absorbing alloy powder of MmNi _3.3 Co _1.0 Mn _0.4 Al _0.3 (average particle diameter 60 μm), 10 parts by weight of nickel powder (average particle diameter 0.5 μm) and polyvinylidene fluoride powder (Average particle size: 3 μm) and 2 parts by weight, and 1% carboxymethylcellulose aqueous solution 2
After adding 5 parts by weight, the mixture was stirred to prepare a slurry.
Then, a punched nickel sheet (0.07 mm in thickness, 1.5 mm in opening diameter) having an opening ratio of 38% was dipped in the slurry, pulled up, dried in the air, and rolled at a pressure of 8 ton / cm ² to a thickness of 0 ton. A .37 mm hydrogen storage alloy electrode sheet was formed.

The above-mentioned nickel electrode sheet and hydrogen-absorbing alloy electrode sheet are superposed and wound through a polypropylene separator having a thickness of 0.18 mm and a porosity of 60% to form a power generating element. In a steel cylindrical container, and further, KOH: 23% by weight, Na
OH: 7% by weight, LiOH: 1% by weight, specific gravity 1.
After injecting 2 ml of the 33 alkaline electrolyte, the whole was sealed to assemble a nickel-metal hydride secondary battery having an AA size and a rated capacity of 1100 mAh.

3) Battery characteristics At 20 ° C. for these batteries, 0.2
After activating the battery by performing 2 cycles of 50% charge and discharge until the final voltage reaches 1.0 V at 0.2C, then perform 0.2C, 150% overcharge at a temperature of 40 ° C or 50 ° C. After that, the temperature is lowered to 20 ° C, and then discharge is performed at that temperature until the voltage reaches 1.0 V at 0.2 C. By confirming the discharge capacity at that time, the charge acceptability at high temperature is determined. The test was performed.

Finally, at a temperature of 20 ° C., 0.2 C
And the discharge capacity at that time was confirmed. The discharge capacity at the time of the high-temperature charge was divided by the discharge capacity confirmed at a temperature of 20 ° C. to obtain a capacity retention ratio (%). The result is shown in FIG. In the figure, the symbol ○ indicates a battery incorporating the nickel electrode of Sample 1, the symbol Δ indicates a battery incorporating the nickel electrode of Sample 2, the symbol □ indicates a battery incorporating the nickel electrode of Sample 3, and the symbol △ Indicates the results of the battery in which the nickel electrode of Sample 4 is incorporated, and the crosses indicate the results of the battery in which the nickel electrode of Sample 5 is incorporated.

As is apparent from FIG. 1, ZrO ₂ .H ₂ O
The nickel electrode blended with has improved charge acceptability at high temperatures as compared with the non-blended nickel electrode (Sample 1). In this case, the effect of blending ZrO ₂ · H ₂ O is manifested from 0.22 parts by weight (in the case of sample 2) or more per 100 parts by weight of Ni (OH) ₂ powder. However, even if it is mixed in too much,
As can be seen in Sample 5, the amount of Ni (OH) ₂ powder was relatively small, and the capacity peaked.
Therefore, the amount of ZrO ₂ · H ₂ O is set to Ni
It is preferable that the amount is about 0.2 to 2.2 parts by weight based on 100 parts by weight of the (OH) ₂ powder.

[Brief description of the drawings]

FIG. 1 is a graph showing an influence of a temperature at the time of charging of a nickel-hydrogen secondary battery on a battery capacity.

Claims (3)

[Claims] 1. A nickel electrode for an alkaline secondary battery, wherein an active material mixture essentially containing Ni (OH) ₂ powder and Zr compound powder is supported on a current collector. 2. The method according to claim 1, wherein the Zr compound is ZrO ₂ , ZrO _2.
nH ₂ O (where n represents the number of 1 and 2), Zr (OH) ₄
The nickel electrode for an alkaline secondary battery according to claim 1, which is at least one member selected from the group consisting of: 3. The active material mixture, wherein the ratio of the powder of the Zr compound is 0.2 to 2.2 parts by weight in terms of ZnO _{2 with} respect to 100 parts by weight of the Ni (OH) ₂ powder. The nickel electrode for an alkaline secondary battery according to claim 1.