Negative nickel-cadmium battery

The nickel-cadmium battery was invented by Jungner in 1899. The battery used nickel hydroxide for the positive electrode, cadmium hydroxide for the negative electrode, and an alkaline solution for the electrolyte. Jungner s nickel-cadmium battery has undergone various forms of the development using improved materials and manufacturing processes to achieve a superior level of performance. 

C19-0095. After use, a nickel-cadmium battery has 1.55 g of Cd (OH)2 deposited on its anode. It is inserted in a recharger that supplies 125 inA of current at a voltage of 1.45 V. (a) To which electrode, Ni or Cd, should the negative wire from the charger be connected Write the half-reaction occurring at this electrode during charging, (b) Compute the time in hours needed to convert all 1.55 g of Cd (OH)2 back to Cd metal. 

Nickel-cadmium batteries use a hydrate nickel oxide as positive electrode, a metallic cadmium as negative electrode and an aqueous solution of potassium hydroxide as electrolyte [17]. The production of electrons at the negative plate during discharge occurs via the following semi-reaction ... 

Until the 50 s, companies showed little interest in recovering the cadmium, which was not considered hazardous and the negative electrodes available weighed very little. Moreover, putting complete nickel-cadmium batteries in the furnace to produce nickel-based ferroalloys posed absolutely no problem. The cadmium was vaporised on the surface, where it burned to produce cadmium oxide, which was usually released into the environment. At best, some of the dust was picked up by relatively efficient filters, in the case of zinc, lead and other forms of dust. 

The negative electrodes in nickel-cadmium batteries are made up of finely distributed cadmium. The positive electrodes are composed of Ni(III) oxide hydroxide (with graphite or Ni powder added to enhance the conductivity). The electrolyte is usually a 20 % potassium hydroxide solution. 

Figure 10.14 The construction of a cylindrical nickel/ cadmium battery. Key A, seal By positive terminal C, cell lid D, connection to positive plate E, cell case Fy positive plate G, separator H, sintered metal foil Iy negative paste Jy connection to negative plate. Diagram supplied by Berec Ltd.

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. 

Such an effect is called a shuttle . It can, for example, be caused by iron ions in nickel/cadmium batteries which are reduced at the negative electrode according to... 

Another well-known shuttle is the nitrate shuttle in nickel/cadmium batteries caused by relics of nitrate (NO3) that have been left from the manufacturing process and are reduced to NH4 at the negative electrode and subsequently again oxidized to NO2 at the positive electrode, and so form a shuttle. 

Figure 1.31 Equilibrium potentials of the negative and positive electrodes in a nickel/ cadmium battery, and current/voltage curves for O2 and H2 evolution and O2 reduction.

The situation with respect to secondary reactions is shown in Fig. 1.34. It is similar to that in the nickel/cadmium battery shown in Fig. 1.32 as far as the positive electrode is concerned. Different is the situation at the negative electrode. The electrode potential is nearly the same, since the equilibrium potential of the hydrogen electrode is only about 20 mV below that of the cadmium electrode. But now hydrogen is used as active material instead of cadmium, and hydrogen evolution as well as hydrogen oxidation are fast reactions, since both are catalyzed by the platinum surface of the negative electrode. 

Lead-acid and nickel/cadmium batteries differ in plate design, as shown in Figure 7.4. In lead-acid batteries the type of the positive plate designates the cell type. The negative plate always is a grid plate. In traditional nickel/cadmium cells and batteries the positive and the negative plates are of the same construction. 

This is the discharge process. If this were a primary non-rechargeable cell, at the end of discharge, it would be exhausted and discarded. The nickel-cadmium battery system is, however, a secondary (rechargeable) system, and on recharge the reactions are reversed. At the negative electrode the reaction is ... 

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