Energy nickel-hydrogen cell

The sealed nickel-metal hydride cell (more consistently metal hydride-nickel oxide cell) has a similar chemistry to the longer-established hydro-gen-nickel oxide cell considered in Chapter 9. In most respects (including OCV and performance characteristics), it is very similar to the sealed nickel-cadmium cell, but with hydrogen absorbed in a metal alloy as the active negative material in place of cadmium. The replacement of cadmium not only increases the energy density, but also produces a more environmentally friendly power source with less severe disposal problems. The nickel-metal hydride cell, however, has lower rate capability, poorer charge retention and is less tolerant of overcharge than the nickel-cadmium cell. 

Because of its high energy density (Table 7.5), the NaS battery has also been proposed for outer-space applicahons, as these cells can be made space-hardened. In fact, in November 1997 a test sodium sulfur cell was flown on the STS-87 Space Shuttle mission to demonstrate its operation in space. The experimental battery had a mass energy density of 150 W hkg (threefold the energy density of a nickel hydrogen battery and about eightfold that of a conventional lead-acid battery) and, when operated at 350 °C, performed sahsfactorily over a 10-day period whilst in orbit... 

Figure 1.35 A module of 38 cells of a nickel/hydrogen battery that forms one half of a 76 cell battery (s lOOV). 24 of such batteries will power the International Space Station (ISS). Cell capacity 85 Ah stored energy 8kWh per battery (from Ref. 61). 

Hydrogen-silver cells are attractive (apart from cost) since the energy density is higher than the hydrogen-nickel analogue. The cell is... 

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