18 - Lead-acid secondary batteries

Abstract

In lead-acid secondary batteries the negative plates have a spongy lead as their active material, while the positive plates of the lead-acid cell have an active material of brown lead dioxide. The plates are immersed in an electrolyte of dilute sulphuric acid. There are two types of pates available: tubular and flat. The tubular positive consists of rods of antimonial lead, which are surrounded by sleeves of an inert porous material, such as terylene. The annular spaces in the tubes of the sleeves and around the rods are filled with the active material lead dioxide. In the case of the flat plate design, the plate is made from lead alloy grids with lattices containing lead dioxide. The negative plate of the tubular cell, which must match the electrical capacity of the positive plate to enable efficient chemical reaction to take place, is of a similar design to that of the flat plate positive, but the lattices in this case are filled with a sponge of pure lead. The positive and negative plates are placed into a container, each positive being placed next to a negative and so on. Further, charging is done by A passing a direct current through the cell in the opposite direction to that during discharge, liberating the acid from the plates, i.e. the concentration of acid in the electrolyte increases. This reverses the action of the discharge and restores the battery to its original charged condition. The capacity of the battery varies according to the current at which it is discharged. The higher the current being taken out of the battery, the lower the available capacity.