US3449167A - Method of making cadmium plates for alkaline batteries and product thereof - Google Patents

Description

United States Patent US. Cl. 136-76 14 Claims ABSTRACT OF THE DISCLOSURE When forming a cadmium plate for an alkaline battery by depositing cadmium onto a grid electrolytically from a plating solution containing a soluble cadmium salt and then pressing the plate to the desired thickness, it is important that the deposit cadmium should be granular. To maintain the cadmium deposit granular, an amount of arsenic in solution is added to the electrolyte. Preferably, 0.5 gram per liter of arsenious oxide is added.

It has been proposed to form a cadmium plate for an alkaline battery by depositing cadmium onto a grid electrolytically from a plating solution containing cadmium sulphate or some other suitable soluble cadmium salt, and then pressing the plate to the desired thickness. In order that the plate should have maximum porosity, it is important that the structure of the deposited cadmium should be granular, and we have found that the deposited cadmium tends to become crystalline (i) if the current densities used in the process exceed 35 milliamps per sq. cm. and (ii) if the temperature of the solution exceeds 30 C. We have further found that higher current densities and a higher temperature can be used, Without the deposited cadmium becoming crystalline, if arsensic is added to the plating solution, and accordingly the invention resides in a method of forming a cadmium plate, characterized by the addition of arsenic. The arsenic is preferably added in the form of arsenous oxide, which preferably is present in proportions of at least 0.5 gram per litre.

The invention further resides in a cadmium plate whenever formed by a method according to the invention, and in a plating solution for use in performing the method.

In one example, a plating solution was made by dissolving 0.5 gram of arsenious oxide in boiling water, cooling the solution to room temperature, adding 50 grams of cadmium sulphate and then making up the solution to 1 litre with water. The solution was placed in a plating bath including an expanded silver mesh as the cathode and a sheet of cadmium as the anode. Cadmium was then deposited from the solution onto the cathode electrolytically. The process was carried out over a range of current densities from 15 to 150 m.a. per sq. cm., and in each case .a porous granular deposit was obtained. A satisfactory deposit was also obtained at current densities up to 300 milliamps per sq. cm., and the process was found to work satisfactorily with the temperature of the plating solution up to C. and its pH value between 3 and 5.

When sufficient cadmium has been deposited on the grid, the grid is removed from the plating solution, washed in water, pressed to the desired thickness and then dried in a vacuum oven to form the finished plate.

The adhesion of the cadmium to.-the grid can be improved by depositing the cadmium from a solution of cadmium sulphate, arsenious oxide and either sodium sulphate or ammonium sulphate. In thecase of the solution containing sodium sulphate, the pH of the solution is preferably maintained in the range 3' to 6, but using the solution containing ammonium sulphate the upper limit can be raised to 7.5.

Typical plating solutions for this purpose include in addition to water the following constituents in grams per litre:

I II

Cadmium sulphate 50 25 Arsenlous oxide 0. 5 0. 5 Sodium sulphate 50 N11 Ammonium sulphate Nil 75 the .pH of the solution must be maintained in the range After electrodeposition, the grids are treated to form the plates as in the first example, except that where the solution contains ammonium sulphate, the plate is preferably immersed in 2% sulphuric acid before washing.

Having thus described our invention what we claim is new and desire to secure by Letters Patent is:

1. In the method of making a cadmium electrode for an alkaline battery by electrodepositing cadmium onto a grid from an aqueous plating electrolyte containing a soluble cadmium salt, and then pressing the plate to a desired thickness, the improvement in said method consisting in that said electrolyte has present therein an amount of arsenic in solution suflicient to provide a granular cadrnium deposit.

2. A method as claimed in claim 1 in which the arsenic is added in the form of arsenious oxide.

3. A method as claimed in claim 2 in which the solution also contains ammonium sulphate.

4. A method as claimed in claim 3 in which the pH value of the solution lies between 3 and 7.5.

5. A method as claimed in claim 4 in which the plating is carried out at temperatures up to 102 C. at current densities between and 450 milliamps per square centimetre at the cathode.

6. A method as claimed in claim 2 in which the solution also contains sodium sulphate.

7. A method as claimed in claim 6 in which the pH value of the solution lies between 3 and 6.

8. A method as claimed in claim 2 in which the pH value of the solution lies between 3 and 5.

9. A method as claimed in claim 2 in which arsenious oxide is present in proportions of at least 0.5 gram per liter.

10. A method as claimed in claim 1 wherein said soluble salt is cadmium sulphate.

11. An electrode formed by the process as claimed in claim 1.

12. In an aqueous electrolyte for the electrodeposition of cadmium upon a grid to form an electrode for use in an alkaline battery and wherein said electrolyte comprises a soluble cadmium salt, the improvement consisting in said electrolyte having an amount of arsenic in solution sufiicient to provide a granular cadmium electrodeposit, and the pH of said electrolyte being between 3 and,7.5.

13. An aqueous electrolyte as claimed in claim 12, further comprising sodium sulphate.

14. An aqueous electrolyte as claimed in claim 12, further comprising ammonium sulphate.

References Cited UNITED STATES PATENTS 1,194,438 8/1916 Stevens 20450 XR 3,326,721 6/1967 Henderson et a1 136-24 HOWARD S. WILLIAMS, Primary Examiner.

10 G. L. KAPLAN, Assistant Examiner.

US. Cl. X.R. 136-24; 204-43