RU1695788C - Method of manufacture of nickel-oxide electrode for alkaline cell - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: ceramic base is exposed to thermal treatment at temperature of 250-350 C during 1-30 min and then active paste is applied using cathodic polarization method. Thermal treatment provides 3-4-fold increase in wettability of base which makes it possible to pack it with active paste at one impregnation cycle. EFFECT: cut down time of manufacture. 2 tbl

Description

 The invention relates to electrical engineering and can be used in the production of alkaline batteries.

 A known method of manufacturing electrode plates for alkaline batteries, including electrolysis of the base in an alkaline solution, washing, drying, introducing the active material by cathodic polarization, moreover, the nickel porous bases are subjected to electrolysis in an alkaline solution containing lithium hydroxide, which significantly improves the wettability of the bases.

 The disadvantage of this method is the introduction of additional technological operations, such as electrolysis in alkali, washing and drying, which significantly lengthens and complicates the manufacturing process of the oxide-nickel electrode.

 The closest technical solution to the proposed combination of essential features and the achieved effect is a method of filling ceramic-porous substrates with the aim of manufacturing a nickel oxide electrode. The essence of this solution is to fill porous cermet substrates with active material by cathodic polarization in a combination of polarization and leaching in a hot aqueous solution of potassium hydroxide.

Salient features of the prototype are the following operations and modes of filling the base with active material:
The cathodic polarization is carried out in an aqueous solution of nickel nitrate salt with a density of 1.5-1.78 g / cm ³ , preferably 1.6 g / cm ³ .

 the pH of the impregnating solution is 0.5-4, mainly 3.5.

The current density of 30-150 mA / cm ² , mainly 60 mA / cm ² .

Impregnation temperature of 40-100 ^{° C,} preferably 60 ° ^C.

 The duration of the impregnation is 5-60 minutes, mainly 20 minutes, i.e. before the evolution of hydrogen at the cathode (base).

Saturated porous nickel hydroxide bases are placed in an aqueous potassium hydroxide solution of a concentration of 20-30% at a temperature of 85 ^{° C} for 10 min.

 Potassium hydroxide washing and drying.

 The process of filling with active material is repeated 3-4 times.

 The disadvantage of the prototype are multiple impregnations due to insufficient wettability of the bases.

 The purpose of the invention is to reduce the duration of the process by increasing the wettability of the base.

This object is achieved in that in the manufacture of nickel-oxide electrode by a process comprising cathodic polarization, leaching, washing and drying, cermet substrate prior to the cathodic polarization is heat treated at a temperature of 250-350 ^C for 1-30 min.

Thus, the essential features of the proposed method are the following operations and modes:
1. Heat treatment of the sintered bases at a temperature of 250-350 ^C for 1-30 min.

2. The cathodic polarization carried out in an aqueous solution of Nickel nitrate salt with a density of 1.45-1.50 g / cm ³ .

 3. The pH of the impregnation solution is 2-4.

4. The density of the impregnation current is 30-70 mA / cm ² .

5. The temperature of the impregnating solution 70-80 ^about C.

 6. The duration of the impregnation of 5-75 minutes

7. Saturated porous nickel hydroxide bases are placed in an aqueous potassium hydroxide solution at 75-85 ^{° C} for 10-60 min.

 8. Washing from potassium hydroxide and drying.

 The process of filling with active material is repeated 1-2 times.

 Signs 2-8 are common with the signs of the prototype.

 Sign 1 is distinctive, previously not used in the electrochemical method of manufacturing a nickel oxide electrode, improves the wettability of the substrate by 3-4 times (see Table 1). As a result, the filling process with active material is reduced to one impregnation.

Sign 2 is also distinctive. The authors found that with a small dilution of the impregnating solution to a density of 1.45 g / cm ³ there is no so-called “sticking” of the active mass on the electrode surface.

A known method of reducing the corrosion rate of the Nickel base during anodic polarization in an alkali solution. Its essence is the creation on the surface of the base of the protective layer that prevents the oxidation (destruction) of the base. In the work of A.V. Golets, A.A. Volynsky, Yu.M. Pozin Investigation of the conditions of formation and protective properties of the passive oxide layer on nickel, ZhPKh, vol. LVII, N 7, 1984, pp. 1614-1616, a method of formation thick epitaxial layer of nickel oxide in the heat treatment bases in air for 1-30 minutes at a temperature of 250-350 ^C. The resulting protective layer under these conditions is characterized by a good chemical resistance and protects the metal from chemical and electrochemical corrosion.

 In the inventive method, the use of the described heat treatment mode gives a qualitatively new result, namely, it improves the wettability of the base, as a result of which the technological process for the manufacture of ONE is reduced to one impregnation.

, где Δm - привес активного материала, г;
V

- объем пор основы по воде, равный

m

-m

, где m

- масса образца с водой, г; m

- начальная масса образца, г.In table 1, the following notation:
d is the thickness of the base, mm
K _g1 - fill factor of the base with active material at the first impregnation, determined by the formula
K _d =

where Δm is the weight gain of the active material, g;
V

- water base pore volume equal to

m

-m

where m

- mass of sample with water, g; m

- the initial mass of the sample, g

 In the prototype, the total time required to fill the base is 60-80 minutes, while in the present method it takes 50-75 minutes, depending on the thickness of the base (table 1).

 Thus, according to the authors, these data are evidence of a positive effect.

 The data in the same table indicate that the heat-treated base reaches the required fill factor per impregnation, in contrast to non-heat-treated, for which at least three impregnations are required.

PRI me R. Heat treatment of ceramic-metal substrates is carried out in an electric furnace of the СНО-7.6.3-10 / 6-I1 type in the mode of 250-350 ^о С for 1-30 minutes. At temperatures below 250 ^{° C} a nickel oxide layer formed structurally has not yet formed and does not form a continuous oxide film, resulting in inhomogeneous wetting of the substrate. Nickel oxidation at a temperature above 350 ^{° C} and crack the oxide layer recrystallizes, which is also a cause of nonuniform wettability of the substrate. Thus, the optimum temperature oxidation of nickel to increase the wettability of the bases of ≈ 300 ° ^C. When the heat treatment is less than 1 min bases oxide film layer is not formed, and increase the time over 30 minutes is impractical because of the elongation process.

 Table 2 shows the experimental data of the proposed processing method.

After heat treatment, the bases are placed on the cassette and technological plates are welded to the cassette by contact welding. The aqueous solution of nitrates of nickel and cobalt (in a ratio of 9: 1) density of 1,45-1,50 g / cm ³ and at pH 3 + 0.5, heated to 70-80 ^{° C,} the anode was placed in the cassette as cast nickel plates (positive pole of a direct current) and the cartridge with the bases (negative pole of a direct current).

The process of filling porous substrates is carried out using a direct current source such as VAKG-18 / 9-320U4. The density of the impregnating current is 50 ± 5 mA / cm ² . After 5-75 minutes, the current is interrupted and saturated nickel hydroxide bases are placed in an aqueous potassium hydroxide solution density of 1,19-1,21 g / cm ^3, heated to 80 ± 5 ^{° C} and there are 10-60 minutes.

It was experimentally established that the minimum time for the complete conversion of the basic salts of nickel in the pores of the ONE into nickel (II) Ni (OH) ₂ hydroxide is 10 minutes.

After the operation "leaching" electrodes are washed with deionized water until neutral to phenolphthalein (about 120 m) and dried at a temperature of 90-100 ^o C to constant weight (about 180 minutes).

 According to the proposed method, it takes 7 hours 5 minutes to fill the base with active material (30 minutes - heat treatment, 10 minutes - welding to the cartridge and installing the cartridge in the bath, 75 minutes - electrochemical treatment, 10 minutes - leaching, 120 minutes - washing, 180 minutes - drying )

 In the prototype, the technological cycle of filling the base with active material takes 22 hours (20 minutes — electrochemical impregnation, 10 minutes — leaching, 120 minutes — washing, 180 minutes — drying, washing and drying are repeated 4 times).

Thus, the use of the proposed method of manufacturing a nickel oxide electrode provides the following advantages in comparison with the prototype:
1. Preliminary heat treatment of the base allows you to reduce the duration of the technological process of filling with active material by 3 times due to improved wettability of the base.

 2. In addition, the same heat treatment protects the oxide-nickel electrode from corrosion during repeated electrochemical impregnations, as well as during its operation (the resource of such ONE increases by 2 times).

Claims (1)

METHOD FOR MANUFACTURING AN ALKALINE BATTERY OXIDE-NICKEL ELECTRODE BY CATHODIC POLARIZATION OF A CERAMIC BASIS IN AN ANNEAL SOLID OF NITROGEN NICKEL WITH A DENSITY OF 1.45 - 1.50 g / cm ³ AT pH 2 - 4, CURRENT DENSITY 30 - 70 mA / cm ² , TEMPERATURE 70 - 80 ^o C for 5 - 75 minutes, followed by treatment in an aqueous solution of potassium hydroxide for 10 - 60 minutes at 75 - 85 ^o C, washing and drying, characterized in that, in order to reduce the duration, the ceramic-metal base is subjected to heat treatment to cathodic polarization at 250 - 350 ^o C for 1 - 30 in.

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