Nickel-Hydrogen (Ni-H2)
Nickel-Hydrogen cells are based on hydrogen gas acting on a carbon electrode (using a design derived from fuel cell technology) plus a nickel hydroxide cathode (positive). The electrolyte uses potassium hydroxide, and the separator is in a zirconium ceramic material. Nickel-Hydrogen cells are rechargeable and deliver a voltage of 1.2 V. The cells are ovoid-shaped with an inconel casing, and the internal pressure inside them can reach 70 bars after charging.
From 1970 to 2003, when Saft completed development work on Li-ion technology for this application, most of the 400 geostationary satellites in orbit (mainly telecommunications satellites) carried nickel-hydrogen batteries.
Nickel-Hydrogen cells benefit from the light weight of hydrogen, and give 50% more energy per unit mass than a Ni-Cd equivalent. And they have an excellent cycling capability.