Nickel hydrogen battery

Nickel–hydrogen battery

Schematics of a nickel-hydrogen battery
Specific energy	55-75 W·h/kg
Energy density	~60 W·h/L
Specific power	~220 W/kg
Charge/discharge efficiency	85%
Cycle durability	>20,000 cycles

A nickel–hydrogen battery (NiH₂ or Ni–H₂) is a rechargeable electrochemical power source based on nickel and hydrogen. It differs from a nickel–metal hydride (NIMH) battery by the use of hydrogen in gaseous form, stored in a pressurized cell at up to 1200 psi (82.7 bar) pressure. The Nickel–hydrogen battery was patented on Feb 25, 1971 by Alexandr Ilich Kloss and Boris Ioselevich Tsenter in the United States.

NiH₂ cells using 26% potassium hydroxide (KOH) as an electrolyte have shown a service life of 15 years or more at 80% depth of discharge (DOD) The energy density is 75 Wh/kg, 60 Wh/dm³specific power 220 W/kg. The open-circuit voltage is 1.55 V, the average voltage during discharge is 1.25 V.

While the energy density is only around one third as that of a lithium battery, the distinctive virtue of the nickel–hydrogen battery is its long life: the cells handle more than 20,000 charge cycles with 85% energy efficiency and 100% faradaic efficiency.

NiH₂rechargeable batteries possess properties which make them attractive for the energy storage of electrical energy in satellites and space probes. For example, the ISS,Mercury Messenger,Mars Odyssey and the Mars Global Surveyor are equipped with nickel–hydrogen batteries. The Hubble Space Telescope, when its original batteries were changed in May 2009 more than 19 years after launch, led with the highest number of charge and discharge cycles of any NiH₂ battery in low earth orbit.