A number of secondary, i.e. rechargeable, alkaline batteries or cells incorporate cadmium as an active electrode material. The most important and best known of these is the nickel-cadmium cell which is based on the reversible electrochemical reactions of cadmium and nickel in a potassium hydroxide (alkaline) electrolyte. At the negative electrode (cathode) the cadmium oxidises to cadmium hydroxide on discharge whilst the hydrated nickel compounds at the positive electrode (anode) are reduced to nickel hydroxide, thus:

2Ni(OH)2+Cd(OH)2 <-- charge/discharge --> 2NiO OH + Cd + 2H20