Thermodynamic studies of cobalt and cadmium additions to nickel hydroxide as material for positive electrodes

Abstract

Abstract Nickel oxide is used as the positive electrode in nickel–cadmium and nickel–metal-hydride batteries. The physical and the electrochemical effects due to the addition of cobalt and cadmium to nickel hydroxide powders are investigated. X-ray diffraction analysis shows that the d 001 value (interlayer distance in the nickel hydroxide) decreases with increase in cobalt content, while the d 100 value increases with increase in cadmium content. The open-circuit potential in discharge follows an S-shaped curve in 3 M KOH electrolyte. The results are discussed with respect to thermodynamic theory. The experimentally obtained OCP variation is in good agreement with calculated data using thermodynamic theory with one fitting parameter, φ / RT ; φ is an interaction energy parameter (J mol −1 ) and RT is the product of the gas constant and absolute temperature. The φ / RT and E 0 (standard electrode potential) values are found to decrease with increase in cobalt content, while the addition of cadmium has little effect on the φ / RT and E 0 values. A difference between the OCP data and the calculated value occurs at the end of discharge; this difference tends to increase with increase in cobalt content.