JPS6319767A - Manufacture of zinc electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To retard shape change of zinc electrode or dendritic growth of zinc, and also to retard hardening of zinc active material paste during manufacture by coating an electrode core with zinc active material paste added with calcium gluconate. CONSTITUTION:Zinc active material paste to which calcium gluconate is added is applied to an electrode core, and dried. The adding amount of calcium gluconate is 10-20 wt% based on the zinc active material. Since calcium hydroxide produced by reaction with alkaline electrolyte fixes zincate ion as calcium zincate, the shape change of a zinc electrode 2 or the dendritic growth of zinc attendant upon the progress of charge-discharge cycles is retarded. Since formation of calcium zincate is prevented during manufacture of zinc electrode, hardening of zinc active material paste can be retarded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for manufacturing zinc electrodes used in alkaline storage batteries such as nickel-zinc storage batteries and silver-zinc storage batteries.

(b) Conventional technology Sub-alkaline storage a using zinc as the negative electrode active material has the advantage of high energy density and low cost.

However, zinc electrodes are soluble electrodes, and zinc elutes and precipitates repeatedly during charge/discharge reactions.The shape of the electrode plate changes as the charge/discharge cycle progresses, and the zinc does not deposit uniformly during charging, causing the zinc to elute and precipitate repeatedly. There was a drawback that the dendritic zinc, which grew in the form of a dendritic structure, penetrated the separator and short-circuited with the counter electrode. In order to completely improve this, for example, the Special Publication Publication No. 54-9696
As disclosed in the publication, by uniformly mixing calcium hydroxide powder into the zinc active material of the negative electrode,
It has been proposed to fix zincate ions eluted from the negative electrode during a discharge reaction in the form of calcium zincate Cajn(OH)4. However, when mixing the hydroxide power in the zinc active material and sium powder and adding water to form a single stroke, calcium zincate is formed and the paste hardens, reducing workability in the manufacturing process. There is a problem that the adhesion of the active material on the current collector decreases and it is easy to peel off.

(c) The problem that the invention attempts to solve is complete! The purpose of A is to suppress the change in the shape of the zinc electrode and the growth of dendritic zinc, as well as to suppress the hardening of the zinc active material paste during the construction of the zinc casing.

ni)) The means to resolve the issue has failed! Method A is characterized in that a zinc active material paste to which μsium gluconic acid is fully added is applied to the electrode plate core and dried. The amount of calcium gluconate to be added is preferably 10 to 20% based on the zinc active material.

←) EffectAccording to the method for manufacturing zinc electrodes for alkaline storage batteries according to the present invention, in which a zinc active material paste containing calcium gluconate tC is applied to the electrode plate core and dried, the hydration power A is reduced at the cracking stage of the zinc electrode. The absence of /S/um suppresses the hardening of the paste, eliminating problems such as reduced workability and poor adhesion between the current collector and the active material. When incorporated into a battery, the calcium gluconate in the zinc electrode reacts with the alkaline electrolyte to produce calcium hydroxide, and the presence of calcium hydroxide causes discharge, similar to the conventional case where calcium hydroxide is added from the beginning. Zinc acid ions sometimes eluted from the zinc electrode can be fixed as zinc acid ions, thereby completely preventing capacity reduction due to changes in the shape of the zinc electrode and internal short circuits due to growth of dendritic zinc.

Furthermore, the wetting effect of calcium gluconate can improve the packing density when filling the zinc active material paste.

(f) Example Zinc oxide powder 45% weight mozinc powder 45% as zinc active material
Gravimetric form, 5% by weight of mercury oxide powder as additives, and 15% by weight of gluconic acid for all zinc substances.
Add q6 (hydroxidation power ~ 2.5 weight in terms of sium), mix thoroughly, and add polytetra, F7A/oloethylene (P
TFE) 5 weight 96 of Dinuhershon was added, and water was further added and kneaded. This active material paste is rolled into a sheet using a chiller roller, placed on both sides of a punched metal current collector, pressure-molded, and then dried to form a zinc electrode.

By combining the nine zinc # thus obtained and seven known sintered nickel electrodes, a AA size nickel-zinc storage battery (Battery A of the present invention) was created. FIG. 1 is a longitudinal cross-sectional view of this battery, in which (1) is a nickel electrode, (2) is a zinc electrode, and these electrodes #1. is spirally wound through a multilayer separator +31 to form the entire spiral electrode body, and these positive and negative electrodes and the separator hold electrolyte (KOH), and most of the free electrolyte is (4) is a battery can that also serves as a negative electrode terminal, and (5) is a sealed body that is fully equipped with a gas venting mechanism (not shown) and also serves as a positive electrode terminal. Kiwami, Nikkei/L/Kiwa t/c
They are electrically connected and sealed via an insulating backing (6).

Comparative Example 1 Comparative Denya B was prepared using zinc powder in the same manner as in the example except that 1 ki of calcium gluconate was not added.

As Comparative Example 2, Comparative Battery C was prepared using a zinc electrode obtained in the same manner as in Example except that 2.5% by weight of calcium hydroxide was used instead of calcium gluconate.

FIG. 2 is a comparison diagram of the cycle characteristics of the battery A of the present invention and comparative batteries B and C. The cycle/L/condition is to charge at 360 mA for 5 hours and discharge at 360 mA until the battery voltage reaches 1.0 VK. As is clear from Figure 2,
The cycle characteristics of the battery A of the present invention are excellent. This is because zinc is dissolved as zincate ions during discharge in Pond B2 and is not deposited in the initial form during charging, but instead zinc is deposited in a dendritic or spongy form on the surface of the zinc electrode, and this occurs during charging and discharging. It is thought that the zinc active material paste grows toward the positive electrode as the cycle progresses, causing an internal short circuit.On the other hand, in Comparative Battery C, the zinc active material paste hardens before being pressure-molded into the current collector. This is considered to be the reason why the adhesion between the active material paste and the current collector was poor, and the active material paste peeled off, causing the cycle characteristics to deteriorate without exerting the effects of calcium hydroxide.

In contrast, in battery A of the present invention, since calcium gluconate is added during the manufacture of the zinc electrode, calcium zincate is not produced, and the hardening of the zinc active material paste is suppressed, thereby improving the adhesion between the core and the active material. In addition, due to the wetting action of calcium gluconate, the unit water content in the zinc active material paste was able to be reduced by about 10% compared to the one without additives, so the packing density of the zinc electrode was improved. Furthermore, in the zinc electrode of the battery A of the present invention, when an alkaline electrolyte is injected, calcium gluconate reacts with the alkaline electrolyte to produce calcium hydroxide, and this calcium hydroxide dissolves the zinc acid dissolved during discharge. It is believed that by fixing ions in the form of calcium zincate and suppressing deformation of the zinc electrode and internal short circuit due to dendritic zinc, it is possible to enable long-term charge/discharge cycles. Comparison diagram of cycle characteristics when varying the amount of calcium gluconate added to the substance? It is shown in Figure 3.

The measurement was performed by charging at 360 mA for 5 hours, and at 360 mA, the discharge end voltage 't1. Perform all comparative studies under the cycle conditions set to OV. As is clear from FIG. 3, it can be seen that sagging occurs when the amount of calcium gluconate added is 10 to 20% by weight. If the amount of calcium gluconate added is less than 5% by weight, the amount of calcium hydroxide dissociated from calcium gluconate and generated will not be sufficient to fix the zincate ions eluted during discharge as calcium zincate. it is conceivable that. Furthermore, when the amount of calcium gluconate added exceeds 25% by weight, the proportion of calcium gluconate in the zinc electrode increases, resulting in a decrease in the capacity of the zinc electrode, and at the same time, the amount of calcium gluconate formed from potassium gluconate increases. It is thought that the hydroxide power of sium wraps the entire zinc active material, reducing the reactivity of the active material and causing early deterioration.

(g) Effect of the invention g! By using the zinc electrode obtained by the charging method, the calcium hydroxide produced by the reaction with the alkaline electrolyte fixes zincate ions in the form of calcium zincate, so that the zinc electrode is deformation and growth of dendritic zinc. In addition, during subpolar fissure formation, calcium zincate is not produced, so the hardening of the zinc active material paste is suppressed, the adhesion between the core and the active material is improved, and the ff11M effect of calcium gluconate makes it more active. It has various effects such as lowering the unit water content in the material paste and increasing the packing density of the zinc electrode, and enables long-term cycles, so its industrial value is extremely large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of the battery of the present invention, and FIGS. 2 and 3 are comparison diagrams of cycle characteristics. A...Battery of the present invention, B%C...Comparison battery, 1.
... Nick/I/pole, 2... Zinc electrode, 3... Multilayer separator, 4... Battery can, 5... Sealing body, 6...
Insulated backing.

Claims (2)

[Claims] (1) A method for producing a zinc electrode for an alkaline storage battery, in which a zinc active material paste containing calcium gluconate is applied to an electrode plate core and dried. (2) The method for manufacturing a zinc electrode for an alkaline storage battery according to claim (1), wherein the amount of calcium gluconate added is 10 to 20% by weight based on the zinc active material.