|
Anode:Hydrogen Gas
Cathode: Nickel oxyhydroxide
Electrolyte: Potassium hydroxide
Applications:Space satellites that require long
cycle life, over 40,000 cycles. Nickel/Hydrogen batteries have a high
self-discharge rate, something like 80% a month, which isn't a problem for
satellite applications.
The NiH2 cell is a welded pressure vessel. It
has a high specific energy, 60WH/kg, long life, can tolerate overcharge and
cell reversal, but has a low volumetric energy density, 50 WH/liter.
Here are the cell reactions:
| Location |
Reactions |
Voltage |
| Anode |
½H2 + OH- —>
H2O + e- |
0.83 |
| Cathode |
NiOOH + H2O + e- —>
Ni(OH)2 + OH- |
0.52 |
| Overall |
NiOOH + ½H2 —>
Ni(OH)2 |
1.35 |
In order to get the hydrogen gas into solution a
Teflon-bonded platinum black catalyst is used, similar to that used in fuel
cells. This platinum electrode has the added advantage that it can recombine
oxygen with hydrogen extremely fast. Since the only bad chemical reaction
during over charge is the creation of oxygen at the positive electrode this
means that the Nickel/Hydrogen battery is impossible to overcharge (though
there may be a thermal runaway problem if the excess heat isn't dissipated.) A
similar reaction keeps any damage from being done if the cell is
reverse-charged.
The battery weight for a 10kW satellite is about 350 kg,
or 770 lbs. |
