The preparation and structure of electrodeposited sponge cadmium electrodes

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Abstract
A method is described for preparing coherent sponge cadmium electrodes on cadmium‐plated substrates by electrodeposition from cadmium chloride solutions in the absence and presence of potassium chloride. The deposit morphology was shown to be a function of current density, pH, plating bath composition and temperature. Of the five main deposit types observed, only one, a sponge with very small crystallites, displayed high electrochemical activity when cycled in KOH solution and had sufficient coherence and adherence to its substrate to be considered suitable as a battery electrode. This material had a useful capacity approximately twice that of conventional electrodes, implying a net increase in battery capacity of at least 30% if conventional sintered plate positives were used. In addition, the elimination of the sintered nickel substrate and the possibility of continuous production methods promised a lower cost.In a separate series of experiments, ultramicrotome sections of the sponge deposits were examined by transmission electron microscopy. For specimens having a high electrochemical activity (more than 70% of the deposit being capable of reversible cycling in KOH solution) crystallite dimensions up to several microns in length and 0.5 to 1 micron in diameter appeared to predominate. This was consistent with measurements of the depth of oxidation observed on block cadmium electrodes and with the structure inferred from powder X‐ray diffraction examination.

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