Capacity nickel metal hydride batteries

Hydrogen-storage alloys (18,19) are commercially available from several companies in the United States, Japan, and Europe. A commercial use has been developed in rechargeable nickel—metal hydride batteries which are superior to nickel—cadmium batteries by virtue of improved capacity and elimination of the toxic metal cadmium (see BATTERIES, SECONDARYCELLS-ALKALINe). Other uses are expected to develop in nonpolluting internal combustion engines and fuel cells (qv), heat pumps and refrigerators, and electric utility peak-load shaving. 

Figure 20 shows the charge-discharge characteristics of the AA-size nickel-metal hydride battery in comparison with the nickel-cadmium battery produced by Sanyo Electric. Its capacity density is 1.5 to 1.8 higher than that of nickel-cadmium batteries. 

ABS is most common (e.g., nickel-metal hydride batteries with 1-1.25 reversible wt% H2 capacity). 

As a matter of fact, the first hydrides with practical hydrogen storage capacities were realized in rechargeable nickel metal hydride batteries. For more information on electrochemical hydrogen storage in rechargeable batteries a reader can be referred to several recent reviews on this subject [71-73]. 

AB2 hydrides, on the other hand, have higher pressures with sloping isotherms and have been claimed to give higher specific capacities [100]. Almost all of the commercial Ni-MH batteries use AB5 compounds for reasons of durability and cost. Nickel metal hydride batteries had an impressive start [99] during the 1990s when... 

Iwakura C, Ikoma K, Nohara S, Furukawa N, Inoe H (2005) Capacity retention characteristics of nickel/ metal hydride batteries with polymer hydrogel electrolyte. Electrochem Solid-State Lett 8 A45... 

Figure 1.37 Balance of electrode capacities (cell balance) in a nickel/metal hydride battery by means of charge reserve and discharge reserve.

Figure 1.38 Comparison of discharge voltage and capacity between nickel/cadmium and nickel/metal hydride batteries of the same size. Cylindrical cells, AA type, discharging current 0.2CA ( 5 hours) (from Ref. 74).

The lead-acid battery system is by far the least costly of the secondary batteries, particularly the SLI type. The lead-acid traction and stationary batteries, having more expensive constmctional features and not as broad a production base, are several times more costly, but are still less expensive than the other secondary batteries. The nickel-cadmium and the rechargeable zinc/manganese dioxide batteries are next lowest in cost, followed by the nickel/metal hydride battery. The cost is very dependent on the cell size or capacity, the smaller button cells being considerably more expensive than the larger cylindrical and prismatic cells. The nickel-iron battery is more expensive and, for this reason among others, lost out to the less expensive battery system. 

The metal hydride electrode has a higher energy density than the cadmium electrode. Therefore the amount of the negative electrode used in the nickel-metal hydride cell can be less than that used in the nickel-cadmium cell. This allows for a larger volume for the positive electrode, which results in a higher capacity or longer service life for the metal hydride battery. Furthermore, as the nickel-metal hydride battery is free of cadmium, it is considered more environmentally friendly than the nickel-cadmium battery and may reduce the problems associated with the disposal of rechargeable nickel batteries. 

FIGURE 29.7 (a) Discharge capacity vs. ambient temperature for sealed cylindrical nickel-metal hydride batteries at various discharge rates end voltage 1.0 V/cell. (b) Discharge capacity % of 0.2C rate) vs. discharge rate (C-rate) for sealed cylindrical nickel-metal hydride batteries at various temperatures end voltage 1.0 V/cell. 

---