The nickel–cadmium battery (Ni–Cd battery or NiCad battery) is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes.
The positive electrode in the discharged state is composed of nickel hydroxide, which has been doped and modified to meet the battery requirements, and graphite as the conductive medium. The nickel cycles between two oxidation states during charge and discharge; upon the charge, the nickel hydroxide is converted into nickel oxyhydroxide (NiOOH):
The specific gravity of the electrolyte is 1.2. Since the voltage produced by a single cell is very low, many cells are connected in series to get the desired voltage output and then this arrangement is known as the nickel cadmium battery. In these batteries, the number of positive plates is one more than that of negative plates.
The theoretical capacity of cadmium metal is 480 mAh g −1. However, cadmium is not usually applied as a metal to form a battery anode. The cadmium electrode may be formed starting with a mixed cadmium hydroxide, and/or cadmium oxide and a certain amount of cadmium powder. Two types of cadmium electrode are also widely used.
In 1899, Waldemar Junger invented nickel cadmium battery (Ni–Cd). Ni–Cd which belongs to the family of rechargeable batteries has an effectively high energy density, good life cycle, sustainable efficiency, good system performance at low temperature, with characteristic wide range of sizes and ratings.
A nickel-cadmium cell has two plates. The active material of the positive plate (anode) is Ni (OH) 4 and the negative plate (cathode) is of cadmium (Cd) when fully charged. The electrolyte is a solution of potassium hydroxide (KOH) with a small addition of lithium hydrate which increases the capacity and life of the battery.