A battery is a device containing one or more cells that convert chemical energy directly into electrical energy.
Basics of Battery
A battery consists of one or more voltaic cells connected in series. Each cell contains two electrodes, each of which is made of a different material, and a conductive electrolyte.
The positive electrode is referred to as the Anode and the negative electrode is called the Cathode.
Most batteries utilize a single electrolyte, some have different electrolytic requirements for the anode than they do for the cathode. But In these cases, two different electrolytes are used and the cells contain a separator that prevents mixing of the electrolytes but allows electron transfer.
When the electrodes are connected by the electrolyte, a specific chemical reaction Which is known as a Redox (Reduction and Oxidation) reaction takes place. This reaction causes reduction (electron addition) to take place at the cathode and oxidation (electron removal) to take place at the anode.
It is this migration of electrons which produces the electromotive force (EMF) within the cell. The EMF as measured across the two electrodes Whenever the cell is neither charging nor discharging is the open circuit voltage that the cell is capable of producing. The voltage varies depending upon the materials used to make the cell.
- As an example:
1) Nickel-Cadmium cell has an emf of about Approx.1.2 volts,
- Nominal voltage 24 volts
- Nominal capacity 53 Ah at 1 hour rate
- Recommended charging voltage on aircraft 28.5 volts
- Length (max.) 331 mm (13.03 in)
- Width (max.) 280 mm (11.02 in)
- Height (max.) 290 mm (11.41 in)
- Weight (max.) 43.54 kg (95.98 lbs)
2) Zinc-Carbon cell has an emf of approximately Approx.1.5 volts
3) Lithium cell can produce Approx. an emf of between 3 and 4.2 volts.
Cells are connected in series to achieve the desired voltage. 10 nickel-cadmium cells would be required to build a battery that yields 12 volts whereas it could take as few as 3 lithium cells to produce a battery of the same voltage. Within a battery, a number of these cell groups can also be connected in parallel to increase electrical capacity.
- In a primary or non-rechargeable battery, once the redox reaction is complete, all of the available electrons have migrated from the anode to the cathode. The battery will no longer produce any current and must be replaced.
- In a secondary or rechargeable battery, the Redox reaction can be reversed by connecting an external power source to the battery. This process allows the battery to be recharged by driving the electrons back to the anode. This, in turn, allows the Redox reaction to be repeated once the charger has been removed. Note that a secondary battery cannot be recharged indefinitely and therefore the battery must eventually be replaced.