PRIMARY AND SECONDARY BATTERIES

An electric battery consists of a number of electrochemical cells, connected either in series or parallel. A cell, which is the basic unit of a battery, may be defined as a power generating device, which is capable of converting stored chemical energy into electrical energy. If the stored energy is inherently present in the chemical substances, it is called a primary cell or a non-rechargeable cell. Accordingly, the battery made of these cells is called primary battery. The examples of primary cells are Leclanche cell, zinc-chlorine cell, alkaline-manganese cell and metal air cells etc.

If, on the other hand, energy is induced in the chemical substances by applying an external source, it is called a secondary cell or rechargeable cell. A battery made out of these cells is called a secondary battery or storage battery or rechargeable battery. Examples of secondary cells are lead-acid cell, nickel-cadmium cell, nickel-iron cell, nickel-zinc cell, nickel-hydrogen cell, silver-zinc cell and high temperature cells like lithium-chlorine cell, lithium-sulphur cell, sodium-sulphur cell etc.

CLASSIFICATION OF SECONDARY BATTERIES

Various types of secondary batteries can be grouped in to the following categories as per their use:

1. AUTOMOTIVE BATTERIES OR SLI BATTERIES OR PORTABLE BATTERIES:

These are used for starting, lighting and ignition (SLI) in internal-combustion-engine vehicles.

Examples are; lead-acid batteries, nickel-cadmium batteries etc.

2. VEHICLE TRACTION BATTERIES OR MOTIVE POWER BATTERIES OR INDUSTRIAL BATTERIES:

These are used as a motive power source for a wide variety of vehicles. Lead-acid batteries, nickel-iron batteries, silver-zinc batteries have been used for this purpose. A number of advance batteries including high-temperature batteries are under development for electric vehicle (EV) use.

These high-temperature batteries like sodium-sulphur and lithium-iron sulphide have energy densities in the range of 100-120 Wh/kg.

3. STATIONARY BATTERIES:

These fall into two groups

(a) Standby power system which is used intermittently and
(b) Load leveling system which stores energy when demand is low and, later on, uses it to meet peak demand.