Electric cells or batteries

Electric cells or batteries and their recent breakthrough:

Introduction -

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.

NaS battery consists of sulfur at positive electrode, sodium at negative electrode as active materials, and Beta alumina of sodium ion conductive ceramic which separates both electrodes. This hermetically sealed battery is kept at approx. 300 degree centigrade and is operated under the condition that the active materials at both electrodes are liquid and its electrolyte is solid. At this temperature, since both active materials react smoothly, and internal resistance becomes low enough, NAS battery has an excellent performance. Because of reversible charging and discharging, NAS battery can be continuously used.

A module battery contains many single cells in a thermal enclosure which is equipped with an electric heater to raise or maintain temperature. The single cells are densely arranged and connected with metallic bars inside the enclosure. This module battery is a basic unit to consist a system; however, the module itself can be operated as well. To make an enclosure compact, a module battery employs a heat insulating structure, which makes inside the walls of enclosure vacuum. Several safety measures are adopted inside a module battery; therefore, it can be utilized without care.

Features of the NaS Battery System:

a) Large capacity - By connecting many batteries, several MW systems can be easily designed,

b) Compactness - Required area for installation is approx. one third of that for a lead acid battery,

c) High efficiency - 75% of energy charge/discharge efficiency,

d) Long-term durability - Durability for about 15years,

e) Preservation of the environment - No discharging of any pollution gases, no vibration, low noise.

Development of efficient ‘Energy Storage Technology’ is Need-Of-The-Hour -

* As there is continuous thrust on optimal utilization of the renewable energy sources due to various environmental issues, it has become a challenge to us to deliver proper power quality, keeping reliability of power with stability and efficiency to the industry from these energy sources. The power generation, transmission & distribution system must be able to supply the power reliably while maintaining the power quality through out the year.

* The renewable energy sources like Photo Voltaic Solar Cell, Wind energy system the power production depends upon availability of sunlight & wind respectively so the nature of power available to loads is intermittent, thus making them non-dispatchable sources. With the help of reliable energy storage system the non-dispatchable energy can be made into the dispatchable energy source.

* Therefore, there is urgent need to study different energy storage technology available and to enhance the system performance by properly designing energy storage technology for application in the power system at different stages.