JP2639911B2 - Zinc electrode for alkaline storage batteries - Google Patents

Description

The present invention relates to a zinc electrode for an alkaline storage battery containing calcium hydroxide.

(B) Conventional technology An alkaline storage battery using zinc as a negative electrode active material has advantages of high energy density and low cost. However, the zinc electrode is a soluble electrode, and zinc elutes and deposits repeatedly in the charge / discharge reaction.Therefore, the shape of the electrode plate changes with the progress of the charge / discharge cycle. And the dendritic zinc penetrates through the separator and short-circuits with the counter electrode. In order to improve this, for example, as disclosed in Japanese Patent Publication No. 54-9696, the powder of calcium hydroxide is uniformly mixed in the zinc active material of the negative electrode, thereby eluting from the negative electrode with the discharge reaction. Calcium zincate CaZn
It has been proposed to fix in the form (OH) ₄ . However, mixing calcium hydroxide powder in the zinc active material,
When water is added to form a paste, the formation of calcium zincate occurs, causing the paste to harden, resulting in reduced workability in the manufacturing process, reduced adhesion between the aggregate and the active material, and easy peeling. There is.

(C) Problems to be solved by the present invention When a zinc active material and calcium hydroxide are mixed and water is added to form a paste, curing of the zinc active material paste is suppressed, workability is excellent, and the active material falls off. It is intended to obtain a zinc electrode for an alkaline storage battery which is excellent in cycle characteristics with a small amount.

(D) Means for solving the problem An oxycarboxylic acid or a salt thereof is added to a zinc active material containing calcium hydroxide. As the oxycarboxylic acid, citric acid, gluconic acid, lactic acid, malic acid, tartaric acid and the like can be used, and as the salts thereof, lithium oxycarboxylate, sodium oxycarboxylate, potassium oxycarboxylate, calcium oxycarboxylate and the like are used. It is possible.

(E) Action When oxycarboxylic acid or oxycarboxylic acid salt is dissolved in a dispersing medium such as water at the time of kneading the paste, in the case of oxycarboxylic acid, the hydrogen atom of the carboxyl group dissociates to form an anion portion of oxycarboxylic acid. On the other hand, in the case of an oxycarboxylate, a cation constituting the oxycarboxylate is dissociated to generate an anion portion of the oxycarboxylate. The oxycarboxylate anion portion is composed of a hydrophilic portion and a hydrophobic portion, and it is considered that the hydrophobic portion is oriented and adsorbed on the surface of calcium hydroxide. This makes it possible to delay the production of calcium zincate by calcium hydroxide and zinc.

(F) Examples 75% by weight of zinc oxide powder and 10% by weight of zinc powder as active materials, 5% by weight of cadmium oxide powder and 5% by weight of calcium hydroxide as additives, 5% by weight of fluororesin as a binder and 5% by weight of oxy Sodium gluconate as a carboxylate was mixed at 10% by weight with respect to calcium hydroxide, water was added to the mixture, kneaded, rolled by a roller and formed into a sheet, and placed on a punching metal current collector. The pressed product was dried to obtain a zinc electrode, and this zinc electrode was combined with a known sintered nickel positive electrode to obtain a battery A of the present invention having an AA size.

Comparative Example A comparative battery B was obtained in the same manner as the battery A of the present invention except that sodium gluconate was not added.

FIG. 1 shows the dependency of the discharge average voltage when the discharge current is changed using the battery A of the present invention and the comparative battery B. The battery A of the present invention has a higher discharge average voltage than the comparative battery B. Particularly, as the current value increases, the difference in the characteristics is remarkable.

FIG. 2 shows the cycle characteristics using the battery A of the present invention and the comparative battery B. After charging at a current of 1/4 C for 5 hours, discharging at a current of 1/4 C, the battery voltage was reduced. The charge and discharge are performed under the cycle condition that the discharge is stopped when the voltage reaches 1.2 V, and the initial battery capacity is compared with 100%. From FIG. 2, it can be seen that the battery A of the present invention has remarkably improved cycle characteristics as compared with the comparative battery B.

1 and 2, the effect of the addition of the oxycarboxylate on the battery characteristics is clear. Considering these facts, it is presumed that the addition of the oxycarboxylate to the zinc electrode makes it possible to delay or control the curing of the zinc active material and improve the adhesion with the current collector. . This dissociates the cations constituting the oxycarboxylate in the paste to form an anion portion of the oxycarboxylic acid. The hydrophobic part of the anion part is oriented and adsorbed on the surface of the calcium hydroxide, delays the formation of calcium zincate, and makes it possible to delay the curing of the paste. As described above, it is possible to use those which form an anion portion of oxycarboxylic acid when dissolved in the paste, and it is apparent that oxycarboxylic acid can be used without being limited to oxycarboxylic acid salt.

To compare the hardening time of the paste during kneading and rolling of the zinc active material, 75% by weight of zinc oxide powder and zinc powder were used.
10% by weight as an active material, 5% by weight of cadmium oxide powder and 5% by weight of calcium hydroxide as additives, 5% by weight of fluororesin as a binder, and calcium citrate as an oxycarboxylate to calcium hydroxide On the other hand, the cases where 6 wt%, 10 wt%, and 20 wt% were added and the case where no additive was added were mixed well, then water was added, kneaded and rolled by a roller to form a sheet. A comparative study was performed by the penetration resistance method.
FIG. 3 is a graph comparing the amount of calcium citrate added with the elapsed time after water injection on the horizontal axis and the degree of cure of the paste, that is, the resistance to penetration of the proctor, on the vertical axis. (1)
Is without calcium citrate, (2),
In (3) and (4), calcium citrate was added to calcium hydroxide at 6% by weight, 10% by weight and 20% by weight, respectively. Once the hardening of the paste is started once, it progresses at a stretch, but it can be seen from FIG. 3 that the addition of calcium citrate suppresses the start time and the speed of hardening of the paste. The curing time of the paste is different by about 8 hours between the case where calcium citrate is not added and the case where 10% by weight is added to calcium hydroxide. If the curing time of the paste is to be delayed by about 2 to 3 hours, 6% by weight of calcium citrate may be added to calcium hydroxide.
Delaying the curing of this paste is very important in the process. In addition, these calcium citrate various additions, rolls of the paste without addition by a roller, the sheet-shaped thing was placed on a punching metal current collector and pressed and molded, and the one with no water content added was 100%. % Is shown in FIG. As a result, it was found that the water content decreased as the added amount of calcium citrate increased. It is considered that this is because the water content of the paste was reduced because the wetting action of the oxycarboxylic acid, that is, the citric acid, caused water to permeate the surface of the zinc electrode active material particles to easily disperse the water. Since the water content of the active material when attaching the active material can be suppressed, the packing density of the active material can be improved and the capacity of the electrode can be improved, and the residual pores in the zinc electrode decrease, so the smooth surface It is estimated that an electrode was obtained and the generation of dendrite was reduced.

As an additive, an oxycarboxylic acid having little effect on the battery, such as citric acid, gluconic acid, lactic acid, malic acid, or tartaric acid, can be used, or a salt thereof can be used. Lithium oxycarboxylate and potassium oxycarboxylate are preferred as salts.

(G) Effect of the Invention By adding an oxycarboxylic acid or a salt thereof to a zinc active material containing calcium hydroxide, the curing of the paste can be suppressed, and as a result, the workability is good, the active material is less likely to fall off, and It has various effects such as a low water content, a smooth electrode surface, little dendrite generation, and a high packing density per unit volume.
A zinc electrode for an alkaline storage battery having excellent cycle characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the discharge current and the battery voltage, FIG. 2 is a diagram showing the cycle characteristics, and FIG. 3 is a diagram showing the relationship between the elapsed time after water injection and the proctor penetration resistance of the paste for various amounts of calcium citrate added. FIG. 4 is a diagram showing the relationship between the calcium citrate addition amount and the water content ratio. (A) ... battery of the present invention, (B) ... comparative battery

Claims (3)

(57) [Claims] 1. A zinc electrode for an alkaline storage battery, wherein an oxycarboxylic acid or an oxycarboxylate is added to a zinc active material containing calcium hydroxide. 2. The zinc electrode for an alkaline storage battery according to claim 1, wherein said oxycarboxylic acid is selected from citric acid, gluconic acid, lactic acid, malic acid and tartaric acid. 3. The alkaline storage battery according to claim 1, wherein the oxycarboxylate is selected from lithium oxycarboxylate, sodium oxycarboxylate, potassium oxycarboxylate, and calcium oxycarboxylate. Zinc pole.