What is a battery
A Battery is a device consisting of one or more electrical cells that convert chemical energy into electrical energy. Every battery is basically a galvanic cell where redox reactions take place between two electrodes which act as the source of the chemical energy.
Batteries can be broadly divided into two major types.
- Primary Cell / Primary battery
- Secondary Cell / Secondary battery
Based on the application of the battery, they can be classified again. They are:
These are the types of batteries which are more likely to be known to the common man. They find uses in everything from torches, clocks to cameras. But then again these batteries are subdivided into two, they are:
- Rechargeable batteries Nickel
Examples: Cadmium batteries, Lithium Ion
- Non-rechargeable batteries
Examples: Silver oxide, Alkaline & carbon zinc
- Rechargeable batteries Nickel
These batteries are built to serve certain high need & heavy duty applications. Some of their applications include railroad, backup power and more for big companies. Some examples are:
Wet Nickel Cadmium (NiCd)
These are more user-friendly and a less complicated version of the industrial batteries. They are more user-friendly and used to power cars, motorcycles, boats & other vehicles. Some examples are:
Lead acid batteries
These are batteries where the redox reactions occur only once, thus rendering the battery dead after a certain period of time. One example of such a primary battery is the dry cell batteries we use in our torches, wall clocks or remotes. They cannot be used once the chemicals inside it are exhausted. In such cells, a zinc container acts as an anode and a carbon rod acts as a cathode. A powdered mixture of manganese dioxide and carbon is placed surrounding the cathode. The space left in between the container and the rod is filled with a moist paste of ammonium chloride and zinc chloride. The redox reaction taking place in such a cell is given by,
Zn(s) –> Zn2+ (aq) + 2e–
2e– + 2 NH4+ (aq) –> 2 NH3 (g) + H2 (g)
2 NH3 (g) +Zn2+ (aq) –> [Zn (NH3)2] 2+ (aq)
H2 (g) + 2 MnO2 (S) –> Mn2O3 (S) + H2O (l)
Thus, the total equation will be:
Zn(s) + 2 NH4+ (aq) + 2 MnO2 (S) –> [Zn (NH3)2] 2+ (aq) + Mn2O3 (S) + H2O (l)
Another example of the primary cell is the mercury cell, where a zinc-mercury amalgam is used as an anode and carbon is used as a cathode. A paste of HgO is used as an electrolyte. These cells are used only in low current devices such as hearing aids and watches.
These are batteries that can be recharged after use by passing current through the electrodes in the opposite direction i.e., from the negative terminal to the positive terminal.
For example, a lead storage battery that is used in automobiles and inverters can be recharged a limited number of times. The lead storage battery consists of a lead anode and the cathode is a lead grid packed with lead dioxide. Sulphuric acid with a concentration of 38% is used as an electrolyte. The oxidation and reduction reactions involved in this process is can be given as,
Pb –> Pb2++ 2 e–
Pb+ SO42– –>PbSO4(electrode) + 2 e–
2 e–+ PbO2+ 4 H+ –> Pb2++ 2 H2O
2 e–+ PbO2+ 4 H++ SO42- –> PbSO4(electrode) + 2 H2O
In order to recharge these batteries, the charge is transferred in the opposite direction and the reaction is reversed, thus converting PbSO4 back to Pb and PbO2.
Another example of the secondary cell is the nickel-cadmium cell. These cells are difficult to manufacture and maintain even though they have high storage capacity and longer life.
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