Primary Cell

4.2 Primary Cell

It is not rechargeable.  After it is exhausted or depleted, it is discarded. The reason is that the chemical action that takes place in it is not reversible.

The most common primary cell types are the zinc acid cell, Leclanché cell, Manganese-alkaline cell, mercury cell, silver oxide and lithium-air cell.

4.2.1 The Zinc-acid Cell

The diagram below illustrates a zinc-acid cell also referred to as the simple cell. It consists of:

(a)        zinc as the negative electrode,

(b)        copper as the positive electrode, and

(c)        dilute sulphuric acid as the electrolyte.

Simple cell

The chemical reaction that takes place between zinc and sulphuric acid is:

Zinc + Sulphuric acid  à Zinc sulphate + Hydrogen + Electric energy.

The hydrogen gas collects in bubbles around the copper elec­trode. The e.m.f. of this cell is 1.5V. This cell has many defects and for these, it not viably produced commercially.