In this topic, you study the construction and working of Alkaline Cell or Battery.
It is a secondary cell. The active material in case of charged and discharged conditions is Ni02 for positive plate and Fe for negative plates. The electrolyte is a mixture of (KOH + 79%).
Construction. It has the following parts.
(a) Container. It is made of nickel plated steel box. The joints are welded, so that electrolyte may not come out. This box is coated with a thick layer of varnish to avoid short circuit in side the cell.
(b) The positive and negative plates are used in the cell. The active material is filled in perforated tubes and flats pockets of nickel plated steel.
(i) Positive plate. The active material of the positive plates is Ni02 or its hydrates Ni(OH)2. The mixture is filled in the perforated nickel plated steel tubes, having a length of 11.5 cm and dia 6 mm number of these tubes (15, 30 or 45) are assembled in a frame Of nickel plated steel.
(ii) Negative plates. The active material of the negative plate is iron oxide. It is filled in perforated pockets of nickel plated steel. These pockets are assembled in a frame of nickel plated steel. A little amount of mercury is added to improve its conductivity.
All the positive plates are welded together with one terminal and negative plates with other terminal known as negative terminal or negative pole. The number of negative plate are one more than the positive plates. A cell has 9, 13 or 15 plates. The type of the cell is determined by the size of the tubes and number of tubes for positive plate.
1 Positive terminal 2. Vent 3. Negative terminal 4. Frame and plate separators (polystyrene) S. Steel negative plate containing cadmium oxide 6. Hard rubber and steel Suspension less 8. Steel Tank top and bottom welded to sides 9. Plate bus bar (steel) 10. Sided sheet (hard rubber) 11. Positive plate nickel-plated steel containing nickel hydroxide 12. Plate bus bar (steel).
Fig. 9.10. Alkaline battery.
A – type contains two rows of 15 tubes each.
B – type contains one row Of 15 tubes each.
C – type contains three rows of 15 tubes each.
D – type contains two rows of 20 tubes each.
The diameter and length Of tubes in A B C tubes is 0.25″ and 4.5″ respectively and discharging rate is, 0.25 A per tube for five hours, similarly for D-types plates the diameter O. 1875″ and length 4.5″, the discharging rate is 0.1875 amp for five hours.
(c) Separators. To avoid the short circuit between the positive and negative plates, the ebonite separators are used.
(d) Electrolyte. The electrolyte is a mixture Of KOH and 79% water.
(i) Specific gravity. The specific gravity of the electrolyte is 1230 which remains constant in charged and discharged conditions of the cell.
(ii) Level of Electrolyte. It should be 15 mm to 75 mm above the surface Of the plates Or as per makers instructions.
The NiFe battery is of one cell but in some cases if more than one cell are required then these should be joined by means of heavy conductors and proper insulations.
Chemical changes inside the cell. In charged condition, the active material of the positive plate is Ni02 and negative plate Fe. The electrolyte is a solution of KOH and water. While the cell is discharged the hydrogen ions travels towards the positive plate and forms water molecules. The OH ions travels towards the negative plate and forms Fe304.
The complete reversible reaction is shown as under
Note. If Ni(OH)4 is the active material of the positive plate then the reaction is
E.M.F. The e.m.f. of the cell in charged condition is 1.4 volt/cell which drops to 1.2 or 1.3 volt/cell. The discharged voltage is I V/cell. The charging voltage is 1.7 volt/cell.