Nickel-based rechargeable batteries

Nickel–iron (Ni–Fe), nickel–cadmium (Ni–Cd), nickel–hydrogen $(Ni-H_2)$, nickel–metal hydride (Ni–MH) and nickel–zinc (Ni–Zn) batteries employ nickel oxide electrodes as the positive plates, and are hence, categorised as nickel-based batteries. This article highlights the operating principles and advances made in these battery systems during the recent years. In particular, significant improvements have been made in the Ni–MH batteries which are slowly capturing the market occupied by the ubiquitous Ni–Cd batteries.