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Alkaline Batteries

The other types of storage batteries are manufactured besides the ordinary lead acid battery. These are Edison nickel iron batteries and the nickel-cadmium batteries.

1.    Edison Nickel-iron Alkaline Accumulators:  The positive plates of nickel-iron alkaline accumulators are nickel plated tubes containing a mixture of nickel oxides and hydroxides with flakes of metallic nickel for increased conductivity. The negative plates consist of a nickered-steel grid containing powdered iron, with some FeO and Fe(OH)2. The electrolyte is a 20% water solution of potassium hydroxide (KOH) with a small addition f lithium monohydrate containing not less than 50% lithium hydroxide (LiOH). The vessel containing the electrodes and electrolyte is also made of nickel-plated iron with a welded lid provided with holes for ht terminals and for pouring in electrolyte. Ebonite sticks are placed between the positive, and negative plates to prevent them form contacting. The number of negative plates is one more than the number of positive plates. The extreme negative plates are electrically connected to the container.

Operation: In a fully charged condition, the active material in the tubes of the positive plates is nickel hydroxide Ni(OH)3 while that in the pockets of the negative plate is iron Fe. As the cell delivers current to the load, the active material of the positive plate charges form Ni(OH)2. Charging reverses this process, namely the active material in the tubes of plates becomes Ni(OH)3 and that in the tubes of negative plates Fe. The electro-chemical process in the nickel iron accumulators can be expressed by the equation.
+ VE PLATE      - VE PLATE     DISCHARGE    + VE PLATE                  - VE PLATE
2Ni (OH)3 + 2KOH +Fe                 - →              2Ni (OH)2+2KOH + Fe(OH)2 + electrical
                                                   ← -

The equation should be read from left to right for discharge and from right to left for charge.

In the nickel iron accumulators the electrolyte, potassium hydroxide in water does not take part in chemical reactions, but does in fact, maintain its original concentrations both on discharge and charge. This allows a comparatively small equinity of electrolyte to be used and the accumulators to be made more compact.

Electrical Characteristics: The e.m.f. of nickel-iron cell, when fully charged is approximately 1.4 volts, which decreases to 1.3 volts rapidly and then very slowly to 1.1 or 1.0 volt on discharge. Average discharge voltage is 1.2 volts.

The internal resistance of the nickel-iron cell is nearly five times of lead acid cell and for this reason is able to deliver much less current at short circuit or to low resistance load.

The quantity and energy efficiencies of these cells are about 80% and 60% respectively.

Advantages, Disadvantages and Applications: It possess several important advantages over lead acid type such as (i) lighter in weight (ii) rugged contraction (iii) longer life (iv) lower running cost and (v) simple maintenance. The care of nickel-iron accumulators mainly amounts to keep them clean and add water when necessary to maintain a normal electrolyte level.

It main disadvantages  are (i) initial cost (ii) high internal resistance (iii) lower e.m.f. and (iv) lower operating efficiency.

Such accumulators are particularly suitable for severe service. These cells are used for the population of industrial trucks and mine locomotives and for railway car lighting and air-conditioning because of its rugged constriction.

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