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A battery is device consisting of one or more cells that can produce a direct current by converting chemical energy to electrical energy. Batteries are all over the space - in our cars, our PCs, laptops, portable MP3 players and cell phones.
In a battery, there are two terminals. One is marked positive while other is negative.
In a large car battery, there are two heavy lead posts that act as the terminals. Electrons collect on the negative terminal of the battery. If we connect a wire between the negative and positive terminals, the electrons will flow from the negative to the positive terminal as fast as possible.
ÂIn a battery, chemical reactions produce the electrons. Electrons flow from the battery into a wire, and goes from the negative to the positive terminal for the chemical reaction to take place. So that battery can sit on a shelf for a year and still have plenty of power. Once we connect a wire, the reaction starts.
TYPES OF BATTERIES: -Batteries are mainly two types: single-use and rechargeable.
SINGLE USE BATTERIES, also known as primary batteries, have one life cycle and must be replaced when drained. Example: - alkaline, carbon-zinc, lithium, silver-zinc and zinc air batteries.
RECHARGEABLE BATTERIES, also known as secondary batteries, can be recharged and used repeatedly. Examples of rechargeable batteries include Nickel Metal Hydride (NiMH), Nickel Cadmium (NiCd), and Lithium Ion (Li Ion).
The concept of the rechargeable battery has been came into account in 1859's, when French physicist Gaston Plante invented the lead acid cell, which would later become the world's first rechargeable battery.
The basic idea behind the rechargeable battery is simple: when electrical energy is applied to the battery, the electron flow from negative to positive that occurs during discharge is reversed and power is restored. This requires an adapter in case of devices with built-in batteries or for standard nickel-cadmium or nickel-metal hydride batteries. The most common rechargeable batteries we use today are in remote control, flashlight or digital camera.
Car batteries are one of the oldest kinds of rechargeable batteries. In a standard car, there is a single lead-acid battery that supplies power to the starter, lights and ignition system. The battery charger in this case is the alternator, a device that converts gasoline power to electrical energy and distributes it where needed.
In electric and hybrid cars, traction batteries are used to power the vehicle. Traction batteries come in many varieties, from lead acid, to nickel-cadmium, nickel metal hydride and lithium ion.
The rate of charge is determined by how much electrical current is allowed into the battery by the charger. Some batteries can handle higher voltage in a shorter amount of time without overheating, while others need a lesser voltage applied over a longer period of time. If the rate of charge is fast, then there is more chance of over charging which can ruin a battery's lifetime. To reduce this problem, we should cut off the power supply once maximum power has been reached.
There is a drawback of nickel-cadmium rechargeable batteries that is the memory effect. The term 'Memory effect' refers to the batteries becoming weaker with continuous use, particularly when the batteries have seen light use and do not respond well to further charging.
Memory effect is caused by the formation of cadmium crystals deep within the battery. Cadmium crystals are an unavoidable by-product of discharge; the trick is to keep them small enough to be reformed as cadmium during the charging process. When a battery is not fully discharged, the crystals deep within the battery are not affected by electrical current, so they are not reformed as cadmium and can grow into larger cadmium crystals. The battery will still function normally.
The memory effect can be avoided by fully cycling the battery once every two to three weeks by allowing it to discharge completely, and then fully recharge.
All batteries suffer from aging cells. The longer they are used, the less capacity they ultimately will have. Rechargeable batteries are still a great way to save money and reduce waste. 
1. Nickel Cadmium Batteries:
Nickle Cadmium Batteries were invented in 1899. In these type of batteries, the cathode is nickel hydroxide Ni(OH)2 , anode is cadmium Cd and electrolyte is an alkaline potassium hydroxide KOH solution.
ANODE: -2NiOOH + 2H2O + 2e- <--ïƒ 2Ni (OH)2 + 2OH- E0=0.490V
CATHODE: -Cd + 2OH- <--ïƒ Cd (OH)2 + 2e- E0=0.809V
OVERALL: -Cd + 2H2O + NiOOH <--ïƒ 2Ni (OH)2 + Cd (OH)2 E0=1.299V
where "ïƒ " is for discharging reaction and "<--" is for charging reaction.
Typical cycle life is over 500 cycles.
Low internal resistance.
High charge and discharge rates possible.
The sealed nickel-cadmium cell can be stored in the charged or discharged state without damage.
Tolerates deep discharges - can be recycled.
Available in a large variety of sizes and capacities
Wide temperature range (Up to 70Â°C)
Charging process is strongly endothermic-the battery cools during charging. This makes it possible to charge very quickly, as the I2R heating and endothermic chemical reactions counteract each other.
Rapid charge typically 2 hours, but can be as low as 10 to 15 minutes.
A big disadvantage of this battery is its greater extent to memory effect. Memory effect is caused by the formation of cadmium crystals within the battery. Cadmium crystals are an unavoidable by-product of discharge. When a battery is not fully discharged, the crystals within the battery are not affected by the electric current, so they are not reformed as cadmium and can grow into larger cadmium crystals. The battery will still function normally. The growth of large crystals increases the cell impedance and can eventually prevent the battery from discharging beyond that point and cause rapid self-discharge of the battery, they should be kept small enough to be reformed as cadmium during the charging process.
To avoid the growth of large crystals, we should either completely discharge or use a NiCd battery charger having built-in discharge circuit. NiCad batteries also get damaged by overcharging.
Low cell voltage of 1.2 Volts compared with primary alkaline cells 1.5 Volts
The use of Cadmium in consumer products is now deprecated .
Two way radios
Commercial and industrial portable products
2. Nickel Metal Hydride Batteries: -
In these type of batteries, anode is hydrogen-absorbing alloy with many metals and the cathode is nickel oxyhydroxide.The electrolyte is alkaline potassium hydroxide (KOH). Cell voltage is 1.2 Volts. 
The NiMH battery was invented in 1986 by Stanford Ovshinsky, founder of Ovonics.
The basic concept of the nickel-metal hydride cell negative electrode generated from the research on the storage of hydrogen for use as an alternative energy source in the 1970s. Certain metallic alloys were observed to form hydrides that could capture and release Hydrogen in volumes up to nearly a thousand times of their own volume.
The energy density of NiMH battery is more than double that of Lead acid and 40% higher than that of NiCads batteries.
Nickel-metal Hydride batteries also have a "memory effect" but much lesser. They are more expensive than Lead acid and NiCd batteries, but they are considered to be environmental friendly.
REACTIONS:- In modern NiMH batteries, the anode consists of many metals alloys, including V, Ti, Zr, Ni, Cr, Co, and Fe.
ANODE: MH + OH- -> M + H2O + e- E0 =0.83V
CATHODE: NiOOH + H2O + e- -> Ni(OH)2 + OH- E0 =0.52V
OVERALL REACTION: NiOOH + MH -> Ni(OH)2 + M E0 =1.35V
High energy density
Low internal impedance
Typical cycle life is 500 cycles
Can be recycled.
Robust - NiMH batteries also tolerate over charge and over discharge conditions.
Wide operating temperature range
Rapid charge possible in 1 hour
Trickle charging can not normally be used with NiMH batteries since overcharging can cause deterioration of the battery.
Reconditioning is possible.
Very high self discharge rate.
Can be stored indefinitely either fully charged or fully discharged.
Suffers from memory effect though not as much as with NiCad batteries
Battery deteriorates during long time storage. This problem can be solved by charging and discharging the battery several times before reuse. This reconditioning also serves to overcome the problems of the "memory" effect.
High rate discharge.
Less tolerant of overcharging..
Cell voltage is only 1.2 Volts which means that many cells are required to make up high voltage batteries.
Lower capacity and cell voltage than alkaline primary cells.
Medical instruments and equipment
3. Lithium ion batteries: -
Lithium-ion batteries are popular because of their following advantages:
They are generally much lighter than other types of rechargeable batteries of the same size. The electrodes of a lithium-ion battery are made of lightweight lithium and carbon. Lithium is also a highly reactive element, meaning that a lot of energy can be stored in its atomic bonds. This translates into a very high energy density for lithium-ion batteries.
They hold their charge. A lithium-ion battery pack loses only about 5 percent of its charge per month, compared to a 20 percent loss per month for NiMH batteries.
They have no memory effect, which means that we need not have to completely discharge them before recharging.
Lithium-ion batteries can handle hundreds of charge/discharge cycles.
They start degrading as soon as they leave the factory. They will only last two or three years from the date of manufacture whether we use them or not.
They are extremely sensitive to high temperatures. Heat causes lithium-ion battery packs to degrade much faster.
If we completely discharge a lithium-ion battery, it is ruined.
There is a small chance that, if a lithium-ion battery pack fails, it will burst into flame.
In 2007, over 2.5 billion lithium-ion battery cells for electric devices have ban produced, 66% of total rechargeable battery market. 
Other types of rechargeable batteries includes Lithum sulphur batteries, thin film batteries, Smart batteries, Carbon foam based lead acid batteries
4. Lithium sulphur batteries: -
Lithium-sulphur batteries are new and differ in many ways from lithium ion batteries. Because they use no heavy metals in their construction, lithium-sulfur batteries are environmental friendly than other batteries. They are easily disposable without any danger to people, plants, or wildlife.
Sulphur is a relatively cheap material, so lithium-sulfur batteries have are less expensive than other batteries. There is also a possible cost savings because lithium-sulphur batteries tend to provide much longer charges than lithium ion batteries. They also have a long life
Another advantage of lithium-sulphur batteries is their ability to work well in very cold weather. Extreme cold slows down the chemical reaction in batteries. With thin construction and light materials, lithium-sulfur batteries tend to weigh less than other similar batteries.
Lithium-sulfur batteries provide more power per weight. In devices like cell phones, the use of lithium-sulfur batteries could be a big improvement. Although lithium-sulfur batteries are new, they have a lot of advantages over other types of rechargeable batteries. 
5. Thin film batteries: -
Thin film batteries are the newest in the battery world. It could operate indefinitely without the need for new battery.
Construction of thin film batteries consists of a solid substrate containing electrolyte cathode and anode. Due to this type of construction, these batteries are able to bear a temperature range of -200c to 1400c. Evaporation methods are used to deposit layers of cathode and anode which are generally used in the process of manufacturing of semiconductors. The thickness of a thin-film battery, based on the substrate and type of packaging, ranges from 0.35 to 0.62mm.
Size - they can be very small and very thin, helping us to reduce an application's physical size.
Temperature - bear a temperature range of -200c to 1400c.
Eco-friendly - less toxic to the environment.
6. Carbon foam based lead acid batteries: -
It is believed that these batteries can deliver lead-acid battery performance but at a much lower cost and weight as compared to NiMH or lead-acid batteries. Hence it can play a vital role to adopt hybrid and plug-in hybrid vehicles with reduced cost. These are similar to lead-cid batteries in which lead plates are replaced by light weight carbon or graphite foams to which the chemically active material in the form of paste is applied. The use of foam increases the interface between the electrodes and the active chemistry. The carbon material resists corrosion and sulfating build up, which reduces the weight. 
FUTURE PROSPECTIVES OF RECHARGEABLE BATTERIES: -
The major developments are that, as expected, lithium cobalt oxide cathode material is being replaced by lithium cobalt/nickel oxide and polymer electrolyte batteries are now coming into production. Future developments may include new cathode and electrolyte materials to reduce cost and to improve safety. Some research has been reported on sodium-ion batteries.
Massachusetts Institute of Technology (MIT) is working on lithium-air batteries that will help in generating more powerful and lightweight batteries than available currently.
According to the current technology, energy storage is limited by the lithium cobalt oxide electrode. But The University of St. Andrews proposed a design in which they replaces the lithium cobalt oxide electrode with a porous carbon electrode which allows Li+ and e- in the cell to react with oxygen in the air." This increases the storage capacity up to 10% and is cheaper also.