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Electric cell or battery and their recent breakthrough:

Electric cell is a device that stores electric energy in the form of chemical energy and delivers electric energy when needed. The electric energy is released when a conductor is connected between the terminals of the cell. All cells consist of an electrolyte, i.e., solution containing ions, a positive electrode and a negative electrode. During energy release stage the negative electrode (cathode) reacts with the electrolyte to release electrons and positive electrode (anode) acquiring these electrons; thereby electricity is generated. When the cell has no power to release electricity, or in other words, electrolyte has reacted fully, the cell is said to be dead or discharged.

On the other hand, some types of cell can be recharged, i.e., the condition of electrolyte can be returned to the original state by passing a current in reverse direction. This type of rechargeable cell is also called storage cell or secondary cell. Primary cell can not be recharged. Following are the list of common type of cells used and also new developments made in storage of electricity:

(i) Alkaline dry cells - One of the commonest and quite old types of primary cell used today is alkaline dry cell. This type of cell consists of a positive electrode made from manganese oxide and a negative electrode made of zinc. Potassium hydroxide as the electrolyte is used. Alkaline cells are used widely in radios, personal stereos, and torches as they can supply quite large currents for long periods.

(ii) Mercury cells - Another major primary cell used is the mercury cell. It can be made in the shape of a small disc to use in small, portable electronic devices. These are so small these can be used very comfortably in hearing aids, wristwatches, calculators etc. In these cells the negative electrode consists of zinc, while the positive electrode is made of mercuric oxide. The electrolyte is a solution of potassium hydroxide.

(iii) Silver oxide primary cells – Silver oxide cells are also primary cell similar to the mercury cell. In silver oxide primary cell negative electrode is made of zinc with potassium hydroxide as the electrolyte. Silver oxide positive electrode in the cell delivers better voltage than mercury cells. These are also often made in the shape of a small disc.

(iv) Lead-acid battery – This is a secondary cell, i.e., it can be recharged when it is discharged fully. It generally consists of three or six cells connected in series. The electrolyte used is a dilute solution of sulfuric acid (H2SO4), the negative electrode consists of lead (Pb) and the positive electrode is made of lead dioxide (PbO2). This type of battery is used mostly in cars, trucks, aircraft, and other vehicles. Its major advantage is that it can deliver a strong current of electricity for starting an engine; however, it runs down very quickly.

A lead-acid storage cell runs down when sulfuric acid is gradually converted into water and the electrodes are converted into lead sulfate. When the lead-acid battery is recharged, these chemical reactions are reversed until the chemicals have been restored to their original condition. A lead-acid battery has a useful life of about two to three years and they produce about 2 V per cell.

(v) Nickel-iron battery (Alkaline cell) - Another widely used secondary cell in heavy industry is the alkaline cell, or nickel-iron battery. The principle of operation is the same as in the lead-acid cell. The only exception is that the negative electrode consists of iron and the positive electrode is made of nickel oxide. The electrolyte used is a solution of potassium hydroxide. The nickel-iron cell has the disadvantage of giving off hydrogen gas during charging.

(vi) Cadmium battery (Nickel-cadmium cell) – This is also very similar to Nickel-iron battery. Here negative iron electrode is replaced by one consisting of cadmium. The positive electrode remains same of nickel oxide. Certain Nickel-cadmium batteries gradually lose their maximum energy capacity if they are repeatedly recharged after being only partially discharged – this phenomenon of losing energy capacity exists in some battery, is called ‘Memory effect’ or ‘Lazy memory effect’.

(vii) Lithium-ion batteries (sometimes abbreviated Li-ion batteries) – This is a rechargeable type battery in which a lithium ion moves between the anode and the cathode. This type of battery is very commonly used in consumer electronics, laptop computers, cell phones, video games etc. Because of the benefits like, one of the best energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use, they are currently one of the most popular types of battery found for portable electronics.

(viii) Nanowire lithium-ion battery – Recently, researchers have found a way to use silicon nanowires to reinvent the rechargeable lithium-ion batteries that power laptops, iPods, video cameras, cell phones, and countless other devices. The new technology produces 10 times the amount of electricity of existing lithium-ion, known as Li-ion, batteries. A laptop that now runs on battery for two hours could operate for 20 hours, a boon to ocean-hopping business travelers.

(ix) Ultra capacitor - A Texas company says recently that, it can make a new ultra-capacitor power system to replace the electrochemical batteries in everything from cars to laptops. Company’s claim that, it is a kind of battery-ultra-capacitor hybrid based on barium-titanate powders, will dramatically outperform the best lithium-ion batteries on the market in terms of energy density, price, charge time, and safety. Much like capacitors, ultra-capacitors store energy in an electrical field between two closely spaced conductors, or plates. When voltage is applied, an electric charge builds up on each plate. Ultra-capacitors have many advantages over traditional electrochemical batteries. Unlike batteries, "ultracaps" can completely absorb and release a charge at high rates and in a virtually endless cycle with little degradation.

(x) Sodium-sulfur (NaS) battery - Until recently, large amounts of electricity could not be efficiently stored. Thus, when you turn on the living-room light, power is instantly drawn from a generator. A new type of a room-size battery, however, may be poised to store energy for the nation's vast electric grid almost as easily as reservoir stockpiles water, transforming the way power is delivered to homes and businesses. Compared with other utility-scale batteries plagued by limited life spans or unwieldy bulk, the sodium-sulfur battery is compact, long-lasting and efficient.