INTRODUCTION:- (1)An electrochemical battery - or, more precisely, a "cell" - is a device in which the reaction between two substances can be made to occur in such a way that some of the chemical energy is converted to useful electricity. When the cell can only be used once, it is called a "primary" cell. When the chemical reaction can be reversed repeatedly by applying electrical energy to the cell, it is called a "secondary" cell and can be used in an accumulator or "storage" battery.
Certain cells are capable of only a few charge-discharge cycles and are, therefore, technically "secondary" cells. Such is the case with certain silver oxide-zinc batteries. These batteries are not capable of the repeated cycling required of a satellite battery system, and are, therefore, considered to be "rechargeable primary" rather than storage batteries.(1)
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(3)CHARGING AND DISCHARGING:- All batteries contain one or more cells, but people often use the terms battery and cell interchangeably. A cell is just the working chemical unit inside a battery; one battery can contain any number of cells. A cell has three main parts: a positive electrode (terminal), a negative electrode, and a liquid or solid separating them called the electrolyte.The positive and negative electrodes are separated by the chemical electrolyte. It can be a liquid, but in an ordinary battery it is more likely to be a dry powder.
When you connect the battery to a lamp and switch on, chemical reactions start happening. One of the reactions generates positive ions (shown here as big yellow blobs) and electrons (smaller brown blobs) at the negative electrode. The positive ions flow through the electrolyte to the positive electrode (from the green line to the red one). Meanwhile, the electrons (smaller brown blobs) flow around the outside circuit (blue line) to the positive electrode and make the lamp light up on the way.
The electrons and ions flow because of the chemical reactions happening inside the battery-usually two or three of them going on simultaneously. The exact reactions depend on the materials from which the electrodes and electrolyte are made, and we won't go into them here. (If you want to know what they are, Google the type of the battery you're interested in followed by the words "anode cathode reactions". For example, Google "zinc carbon battery anode cathode reactions") Whatever chemical reactions take place, the general principle of electrons going around the outer circuit and ions flowing in the opposite direction through the electrolyte happens in all batteries. As the battery generates power, the chemicals inside it are gradually converted into different chemicals. Their ability to generate power dwindles, the battery's voltage slowly falls, and the battery eventually runs flat. In other words, if the battery cannot produce positive ions because the chemicals inside it have become depleted, it can't produce electrons for the outer circuit either.(3)
(4) BATTERTIES COMPONENTS:-
The "cathode" or "positive" electrode, which consists of a mass of "electron-receptive" chemical held in intimate contact with a metallic "plate" through which the electrons arrive from the external circuit.
The "anode" or "negative" electrode, which consists of another chemical which readily gives up electrons - an "electron donor" - similarly held in close contact with a metallic member through which electrons can be conducted to the external circuit.
The "electrolyte," usually a liquid solution that permits the transfer of mass necessary to the overall reaction. This movement takes place by "migration" of "ions" - positively or negatively charged molecular fragments - from anode to cathode and from cathode to anode.(4)
TYPES OF BATTERY:- Generally secondary batteries divide in two parts, (1) Common rechargeable battery
(2) Less Common rechargeable battery
Common Rechargeable Battery
1. LEAD ACID BATTERIES
(5)Secondary batteries became practical in 1860 with the invention of the lead acid battery by Raymon Gaston Plante. In 1881, Faure (and others) improved the yield of the lead acid cell by substituting a lead oxide paste for the pure lead of the plante cell.
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The largest problem associated with this battery is the damage caused by leaking acid. German researchers addressed this problem in the early 1960s by developing a gelled electrolyte. Working from another direction, other researchers developed a way to completely sealed the battery, preventing leaks. Either way, the sealed lead acid battery needs a little or no maintenance, which, while costing more, can be an advantage in some situations.(5)
PRINCIPAL:-(6)The most common design has a plate construction.Plate construction are of two type ;grid plate and pasted plate. A grid network contains the active material in pellet form.Lead oxide(PbO) is the starting material for the preparation of the plates.The active material(PbO and PbO2) in the plates are produced electrochemically.The plates are then assembled in the cell.Individual cells are connected in series to attain the desired batteries voltages.Several types of material have been used for the separators between the anode and cathode-e.g.:-cellulose,microglass.Microporous separators are preferred for starter batteries.The basic funtions of the separaters material are to retain the electrolyte in their microporous structure and to prevent electronic contact between the positive and negative electrodes.
The cell reactions are
Positive electrode:-PbO2 + H2SO4 + 2H+ + 2e- = PbSO4 + 2H2O
Negative electrode:-Pb + H2SO4 = PbSO4 + 2H+ + 2e-
From the above equations, it can be seen that during discharge,lead sulfate is the main product for both the cathodic and anodic reactants.sulfuric acid serves as a reactant as well as an electrolyte in this battery.Water is also a product .Thus,during discharge there is a dilutuion of the sulfuric acid electrolyte.The active materials formed during charging are lead ,lead oxide ,and sulfuric acid.During charging,there is an increase in the electrolyte concentration .Hence ,we can use the change in concentration of electrolyte as a measure of the state of charge.Because of the highly positive electrode(v=1.65) and of the high negative reversible electrode potential of the negative electrode (v=-.35v),and those being above and below the reversible potential for oxygen evolution and hydrogen evolution,respectively,these gases are evolved during charging of the lead acid battery .However,these amounts are relatively small because PbO2 and Pb have very low electrocatalytic activities for these electrochemical reactions.The hydrogen evolution reaction is the main contributor to the self-discharge of the lead acid battery.
APPLICATION AND ECONOMICS=The most common application worldwide of lead acid batteries is as a starter battery for transportation vehicles. These are commonly referred to as SLI batteries(starter lighter ignition).There has been great interest in using lead acid batteries for traction.In fact ,the electric automobiles in the beginning of the 20 century used the lead acid batteries as the power source.But due to the rapid progress made in internal combustion engine and diesel powered engine vehicles ,the interest was greatly diminished . There was a revival in the development of the lead acid battery technology for electric vehicles since the late 1980 to the mid 1990 but due to the low range of those vehicles (less than 150 km) and long time (5 to 7h) needed for charging , the interest for developing such vehicles greatly decreased . However, as seen from the ragone plot , even though lead acid batteries have a low energy density , they could attain high power densities. Thus these batteries are still being considered as the second power source with the primary internal combustion engine(ICE) or diesel engine power plants for hybrid electric vehicles.The cost of the battery is variable , depending on its design and capacity. The SLI battery cost about $100kwh ,while batteries with relatively low capacity may have a cost five to ten times higher .One attractive feature of the lead acid battery is the practically 100% of its lead content can be recycled. This is a significant feature, considering the fact that lead toxic element and thus environmental polluted.(6)
(5)A completely sealed battery, whether it is a gel cell or not, also prevents hydrogen gas from escaping when you recharge the battery, which is an improvement in safety when the battery is to be used indoors, such as on a robot or wheelchair. A gelled battery won't leak even if it is punctured, but it can also have a slightly lower energy density than its liquid counterpart, at about 80% or so.
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Deep cycle batteries are a special variety of lead acid battery that can be discharged to low voltage levels without coming on to harm. Deep cycle batteries are typically used in marine or wheelchair applications. Regular car batteries are designed for short bursts of high ampere use to start the vehicle, with no deep discharges allowed. The electrode plates in a deep cycle battery are made thicker and less porous than the car battery, and will last two to four times longer than the car battery in deep cycle applications. Dual marine batteries are a compromise of the two types.(5)
2. NICKEL CADMIUM (NiCd) BATTERIES
(7)The technology behind the nickel cadmium battery was invented in 1899 by Waldmar Jungner, but the battery didn't reach commercial use until the 1930s when new electrodes were developed. The original version of the NiCd battery used a vented, unsealed cell that required regular maintenance. In the 1940s they perfected the sealed NiCd cell, though the cell do retain a need to breathe a bit, which is maintenance free, and the battery came to the fore in the 1950s. In 2000, it accounted for more than 50% of the world's rechargeable batteries for portable applications. Today's NiCd batteries can take a lot of abuse, both mechanical and electrical, and are cheaper than other batteries in cost per hour of use. It was originally proposed that the NiCd battery could be a power source for electric vehicles. This uses a nickel oxide positive electrode, in all other alkaline nickel batteries, and a Cd electrode. The NiCd battery is better than the NiZn or NiFe batteries, which were discovered in the same period. The reason for this is because the Cd/Cd(OH)2 system is quite stable (Cd(OH)2 is formed during discharge), while the products of zinc or iron electrooxidation can dissolve to a significant extent in the potassium hydroxide electrolyte. The latter problem causes morphological changes during charging of the battery. Other advantages of the NiCd battery are its high rate capability, long cycle life, and good low temperature behavior.(7)
PRINCIPAL:- (8)In nickel cadmium cell, nickel oxyhyoxide, NiOOH, is the active material in the positive plate. During discharge it reduces lower valence state, nickel hydoxide Ni(OH)2, by accepting electrons from the external circuit:
2NiOOH + 2H2O +2e- = 2Ni(OH2) + 2OH-
Cadmium metal is the active material in the charged negative plate. During discharge it oxidizes to Cadmium hydoxide ,Cd(OH) , and releases electrons to the external circuit:
Cd + 2OH- = Cd(OH)2 + 2e-
These reactions reverse during charging of the cell.
The net reaction occurring in the potassium hydroxide (KOH) electrolyte is(8)
Cd + 2H2O + 2NiOOH = 2Ni(OH2) + Cd(OH)2
APPLICATION AND ECONOMICS= (6)For a considerable length of time, Ni/Cd batteries have had the second highest share of the secondary battery market . The main applications have been for standby or emergency power, aircraft auxiliary power, power source of portable equipment (calculator, tools, laptop computers, video cameras, toys, etc.). Until recently, it also was used extensively in satellites , but due to the superior behavior of Ni/H2 batteries , Ni/Cd batteries are being gradually displaced. Ni/Cd batteries were also researched on to power electric vehicles, For most of the above mentioned terrestrial applications.
This battery has a surprisingly high capacity for current delivery. The AA battery shown has a recommended maximum continuous current draw of 9 amps, with 18 amp pulses allowed. There are two issues you face when you use a NiCd battery. One is the dreaded memory effect (which doesn't seem to plague other batteries), and the other is cell reversal. Though hotly disputed in hobbyist circles, the memory effect is very real in some, but not all, NiCd batteries. This effect appears because the battery retains the characteristics of previous discharges that is, after repeated shallow discharges, the battery may be unable to discharge beyond the earlier points. It would seem that, under certain conditions, electrodes in the cell can develop a crystalline growth. This growth reduces the area of the electrode exposed to the electrolyte. This leads to a voltage reduction and a loss of performance. Avoiding the memory effect is fairy simple. Fist, quick charge rather than trickle charge your NiCd batteries. Quick charging helps negate the effect of NiCd memory. Second, be sure to fully discharge your batteries to their 1 volt level, under a light load, on a regular basis.
Cell reversal is a condition that can occur with multiple NiCd cells connected in series, such as in a multiple cell battery or a battery pack. Since not all cells are exactly the same, one cell in a chain may use up all of its charge before the others.(6)
3. NICKEL METAL HYDRIDE (NiMH) BATTERIES
(9) The NiMH battery chemistry began its life in the 1970s, but it took more than ten years before its performance was good enough for commercial use. Modern batteries seem to be either incremental improvements on old technologies or inventions of large corporate research departments, so it's harder to name the inventors of this chemistry. Since the 1980s, the performance of the NiMH battery has been improved by many companies, and it is now an excellent battery for portable application.
The NiMH battery comes in the same sizes, with the same nominal voltage and same discharge curves as the NiCd battery. NiMH battery has a higher energy density and a lower internal resistance(9).
4. NICKEL/HYDROGEN CELL:-
(7)The Ni/H2 battery contains the best of both words in respect to the hydrogen oxygen ,i.e. the nickel oxide electrode ,and the idea hydrogen electrode , as in a hydrogen oxygen fuel cell.Both these electrodes have very low activation over potential , in the charging and discharging modes Furthermore , the cycle life of the battery can be as high as tens of thousands of cycle . It is for the reason that it is mainly used in satellites in the low earth (LEO) and geosynchronous earth orbits(GEO)(7).
PRINCIPAL= (8)The cell reactions
Positive electrode:-2NiOOH- +2e- =2NiO + 2 OH-
Negative electrode:-H2 + OH- = 2H2O + 4e-
During overcharge, oxygen is evolved at the Nickel oxide electrode;
4OH- = O2 + 2H2O + 4e-
The Oxygen , however , reduced chemically and electrochemically at the Positive electrode as;
2H2O + O2 +4e- = 4OH-
Even though some of hydrogen evolved during charge has free access to the nickel oxide electrode , it does not cause any problem because of the slow kinetics of electrooxidation of hydrogen on the nickel oxide electrode.For this reaction , it is necessary to have metallic nickel for the initial step of dissociative adorption of hydrogen .The electrolyte in the is KOH.The cells operate in the temperature range of about 10 to 50*. The hydrogen evolved during charge is pressurized (~50atm). The cells operate in pressure range 3 to 50 atm.(8)
APPLICATION AND ECONOMICS=(6)The main application of this satellite power. The capacity of the battery is in the range 90 Ah. The battery voltage is 1.2 to 1.3 v during discharging. For the LEO application, charge/ discharge cycles are of equal duration per day , while for the GEO cycles,the charging time is about 20h and discharge time is about 1-2h. the latter marks the battery cost quite high. If the cost of the battery can be significantly reduced, it can be considered for terrestrial application, e.g., vehicle propulsion, standby/energy power. One drawback of the battery is that the self- discharge rate is about 10%/day at 20*C.(7)
5. LITHIUM ION (Li-ION) BATTERIES
(5)Continuing in the tradition of modern battery chemistries, the lithium ion battery has an increased energy density and can provide a respectable amount of current. High discharge rates don't significantly reduce its capacity, nor does it lose very much capacity after each cycle, still retaining 80% of its energy capacity after 500 recharge
cycles. This is a volatile technology, early versions were prone to exploding in the labs. It is the volatile nature of lithium that gives this battery its punch, though. These benefit come with a price, of course (perhaps to pay for equipment damaged in the research?). As the technology matures, you should expect the price to drop(5).
PRINCIPAL:- (10)The lithium ion battery has a unique characteristics it operates by transport mechanism of a lithium ion, from positive electrode to the negative electrode during charging and during discharging. In this cell anode is made of a conducting carbonaceous material, usually graphite . The cathode is made of a trasition metal oxide such as CoO2, during discharging the cells are;
Positive electrode:- Li = Li+ + e-
Negative electrode:- Li+ + CoO2 + e- = LiCoO2
APPLICATION AND ECONOMICS= The demand of the lithium ion batteries for the portable consumer/military electronic products has been growing exponentially since the 1990s.A lithium ion battery can be recharged literally hundreds time . These desirable characteristics make it suitable for use in cellular phones , digital cameras , laptop computers.(10)
6. FUEL CELLS BATTERIES
(9) Fuel cells aren't available for small, portable applications yet, but they are coming soon. The fuel cell isn't so much a battery as it is a catalytic chemical engine that creates electricity from fuel. The fuel is typically a variation of hydrogen, such as the hydrocarbon fuels methanol, natural gas, or even gasoline. When these reach market you won't be recharging your batteries anymore, you will be refilling them(9).
PRINCIPAL:-(10) A hydrogen oxygen fuel cell consists of an electrolyte solution , such as KOH solution , and two inert electrodes. Hydrogen oxygen gases are bubbled through the anode and cathode . the half cell reactions are
Positive electrode:- 2H2 + 4OH- = 4H2O + 4e-
Negative electrode:- 2H2O + O2 + 4e- = 4OH-
APPLICATION AND ECONOMICS= Properly designed fuel cell have 70% efficient fuel cell are free of the noise, vibrate , heat transfer, thermal pollution. A hydrogen oxygen fuel cell used in the space program. The pure water produces by this cell is consumed by the astronauts.(10)
7. Lithium polymer battery
(5) Lithium polymer batteries can be made in thin, flat or shape fitting forms and their biggest plus is that they won't leak corrosive electrolyte. They provide 500 charge-discharge cycles, but require smart chargers to monitor them closely. Lithium polymer batteries are not suitable for high-power applications, are limited to the operating temperature range 0 - 65Â° and are relatively expends.
(11)Less common types
Lithium sulfur battery
A new battery chemistry developed byÂ Sion PowerÂ since 1994.Â Claims superior energy to weight than current lithium technologies on the market. Also lower material cost may help this product reach the mass market.
Thin film batteryÂ (TFB)
An emerging refinement of the lithium ion technology by Excellatron.Â The developers claim a very large increase in recharge cycles, around 40,000 cycles. Higher charge and discharge rates. At least 5CÂ charge rate. Sustained 60CÂ discharge, and 1000CÂ peak discharge rate. And also a significant increase in specific energy, and energy density.
Also Infinite Power Solutions makes thin film batteries (TFB) for micro-electronic applications, that are flexible, rechargeable, solid-state lithium batteries.
A smart battery has the voltage monitoring circuit built inside. See also:Â Smart Battery System
Carbon foam-based lead acid battery
Firefly Energy has developed a carbon foam-based lead acid battery with a reported energy density of 30-40% more than their original 38 WÂ·h/kg,Â with long life and very high power density.
This type of rechargeable battery can deliver the best known cycleability, in order of a million cycles, due to the extraordinary electrochemical stability of potassium insertion/extraction materials such asÂ Prussian blue.
Developments since 2005
In 2007Â Yi CuiÂ and colleagues atÂ Stanford University's Department of Materials Science and Engineering discovered that usingÂ siliconÂ nanowiresÂ as the anode of a lithium-ion battery increases the volumetric charge density of the anode by up to a factor of 10, theÂ nanowire battery.
Another development is the paper-thin flexible self-rechargeable battery combining aÂ thin-filmÂ organicÂ solar cellÂ with an extremely thin and highly flexible lithium-polymer battery, which recharges itself when exposed to light.
Ceramatec, a research and development subcompany ofÂ CoorsTek, as of 2009Â was testing a battery comprising a chunk of solid sodium metal mated to a sulfur compound by a paper-thin ceramic membrane which conductsÂ ionsÂ back and forth to generate a current. The company claimed that it could fit about 40 kilowatt hours of energy into a package about the size of a refrigerator, and operate below 90Â Â°C; and that their battery would allow about 3,650 discharge/recharge cycles (or roughly 1 per day for one decade.)(11)