Construction of Nickel Iron Cell

Construction of Nickel Iron Cell Points : Construction of Nickel Iron Cell, Positive plate, Negative plate, Electrolyte, Container, Separator The various parts of the alkaline cell are as given below:
(i) Positive plate
(ii) Negative plate
(iii) Electrolyte
(iv) Container
(v) Separator 1. Positive Plate Is constructed from many perforated steel tubes which contain active material of nickel hydroxide (Ni (OH4)] Nickel hydroxide is having poor electrical conductivity. Pure nickel flakes are alternatively added to the active material in the steel tubes to increase electrical conductivity of the cell. Steel tube about 15 mm diameters and 100 mm length contains nearly 300 such layers. These tubes are then clamped in nickel plates steel frame. 2. Negative plate The negative plate is made from perforated nickel steel pockets into which powdered iron oxide is filled. The electrical conductivity of iron oxide is less and hence small quantity of mercury is added in pocket to, improve conductivity. These pockets are clamped in a steel rip which forms negative plate: 3. Electrolyte It is an alkaline solution of 21% potassium hydroxide (KOH) of specific gravity 1.220 which remains constant during discharging and charging. The cell is sealed to avoid atmospheric contact of hydroxide because it combines with carbon dioxide forming potassium carbonate which reduces the capacity of the cell. A small quantity of lithium hydroxide is added to the electrolyte for further increasing the cell capacity. 4. Container The container consists of steel box. Due to steel box at the inside and top of the cell cover is provided with a thick layer of insulating compound to avoid short-circuiting. A small hole is provided in the vent plug to allow the gases to escape out from the cell during discharging and charging. 5. Separators Separators are made up of hard rubber and are placed between plates to avoid short-circuiting of plate. The resistance of separator should be high. Discharging of Battery When the cell is fully charged the positive plate is of nickel hydroxide [(Ni(0H₄)] and the negative plate is of iron (Fe). When load is connected to the terminal of the cell, current flow from positive plate outside the cell and from negative to positive inside cell. The current through the electrodes breaks it into potassium ions (IC) and hydroxide ions (OH⁺). The K⁺ moves toward the anode and OFF towards cathode the chemical reactions is as given below:

At Negative plate:
Fe + 2OH = Fe (OH)₂

At Positive plate:
Ni(OH)₄ + 2K₊ = Ni (OH)₂ + 2KOH

The following changes occur during discharging:
(i) The negative plate turns into ferrous oxide,
(ii) The positive plate turns into the lower hydroxide of nickel,
(iii) The strength of electrolyte remains constant. Charging of Battery In nickel iron battery the current supplied from charging is of direct current of voltage 1.7 volts/cell. During charging battery terminals are connected to D.C. supply. During recharging the reaction are as below;

At Negative Plate:
Fe(OH)₂ + 2K⁺ = Fe⁺⁺+ 2KOH

At Positive Plate:
Ni(OH)2 + 2OH = Ni(OH)₄

The following changers occur during recharging:
(i) Negative plate turns into iron (Fe),
(ii) Positive plate turns into nickel hydroxide,
(iii) Specific gravity of electrolyte remains constant.