Lanthanum nickel hydride LaNi

Figure 5.28 Van t Hoff plots for some selected hydrides. The stabilization of the hydride of LaNis by the partial substitution of nickel with aluminum in LaNis is shown, and also the substitution of lanthanum with mischmetal (e.g. 51% La, 33% Ce, 12% Nd,4% Pr).

The positive electrode, the cathode, is similar to that in nicad cells and consists of a mixture of NiO(OH)/Ni(OH)3 and Ni(OH)2. An alloy that supports hydride formation replaces the cadmium as the negative anode. The alloy most commonly used is derived from LaNis, in which a mixture of other lanthanides replaces the lanthanum, and a nickel-rich alloy replaces the nickel, to give a general formula LnA/5. The anode is composed of an agglomeration of alloy powder. A small amount of potassium hydroxide is added as an electrolyte. The cell voltage is 1.3 V, making these cells suitable for the direct replacement of nicad batteries. The cell construction is identical to that of the nicad cell (Figure 9.10), with the cadmium replaced by metal hydride. The approximate cell reactions are as follows. 

Lanthanum is a metal, soft enough to be exit with a knife, and one of the most reactive of the rare earth metals. It oxidizes rapidly when exposed to air and is attacked by hot water. It is a component of mischmetaU, used for cigarette-lighter flints. The in-termetalhc compound LaNiS is the negative electrode, MH (metal hydride), in the modern Ni-MH alkaline battery. It is an ecofriendly alternative to the nickel-cadmium battery. 

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