THEORYThe main method of generating electricity through chemical action isthrough the use of cells or batteries. When two dissimilar substances, usually metals or metallic materials,are immersed into a solution that produces a greater chemical action on one thanthe other, an electrical potential difference is created. If a conductor isconnected between them, electrons will flow to equalize the charges. Thearrangement is a simple voltaic cell, where the two metallic substances areelectrodes and the solution is the electrolyte.
Electrochemistry is the branch ofphysical chemistry that reviews the connection between electricity, as aquantifiable and quantitative phenomenon, and identifiable chemical change,with either electricity considered a result of a specific substance change orthe other way around. Electriccharges moving between electrodes and an electrolyte or ionic species in asolution are part of these reactions. Therefore, the communication betweenelectrical energy and chemical change is shown in electrochemistry.At the point when electrolysis, a chemical reaction caused by remotelyprovided current, or if a battery, which is an electric current created byimpulsive chemical reaction response, it is called an electrochemical response.As a rule, electrochemistryportrays the overall reactions when singular redox responses are isolated yetassociated by an external electric circuit and an interceding electrolyte.One of the common ways ofelectricity generation via chemical means of generating electricity throughchemical action is using cells or batteries.
At the point when two differentsubstances, normally metals or metallic materials, are drenched into a solutionthat delivers a more prominent chemical action on one than the other, anelectrical potential difference is made. In the event that a conductor isconnected between them, electrons will stream to equalise the charges. Thecourse of action is a basic voltaic cell, where the two metallic substances areelectrodes and the solution is the electrolyte.Next, we are going to explore thecomponents of cells, of which there are two main types: primary and secondarycells. COMPONENTS OF A BATTERYIn a battery, the anode is the negative electrode from which electronsflow out towards the external part of the circuit. Internally the positivelycharged cations are flowing away from the anode (even though it is negative andtherefore would be expected to attract them, this is due to electrode potentialrelative to the electrolyte solution being different for the anode and cathodemetal/electrolyte systems); but, external to the cell in the circuit, electronsare being pushed out through the negative contact and thus through the circuitby the voltage potential as would be expected.A cathode is the electrode from which a conventional current exits apolarized electrical device.
A conventional current shows the direction inwhich positive electric charges move. Electrons have a negative electricalcharge, so the movement of electrons is opposite to that of the conventionalcurrent flow. In a battery or galvanic cell, the cathode is the positiveterminal since that is where the current flows out of the device. This outwardcurrent is carried internally by positive ions moving from the electrolyte tothe positive cathode (chemical energy is responsible for this”uphill” motion). It is continued externally by electrons moving intothe battery which comprises of positive current flowing outwards.When electrodes are placed in an electrolyte and a voltage is supplied,the electrolyte will conduct electricity.
Lone electrons normally cannot passthrough the electrolyte; instead, a chemical reaction occurs at the cathode,providing electrons to the electrolyte. Another reaction occurs at the anode,consuming electrons from the electrolyte. As a result, a negative charge clouddevelops in the electrolyte around the cathode, and a positive charge developsaround the anode. The ions in the electrolyte neutralize these charges,enabling the electrons to keep flowing and the reactions to continue.PRIMARY CELLA primary cell is a cell which the chemical action erodes one of theelectrodes, usually anode.
When it happens, either the electrode, or sometimeselectrolyte, has to be substituted. Examples of primary cells include Leclanchecell and alkaline cell.SECONDARY CELLA secondary cell is a cell which the chemical action switches theelectrodes and the electrolyte as the cell sends current. They can be restoredthrough discharging, where electric current is forced through the cell in thealternate direction.
Batteries of vehicles, such as cars and aircraft, arecommonly known to be of the secondary cell variation. Examples of secondarycells include lead-acid cell, nickel-cadmium cell, nickel metal hydride celland lithium ion cell. TYPES OF CELLS & ITSMECHANISMSPRIMARY CELLSLECLANCHE CELLElectricity is produced in a Leclanché cell when zinc atoms on thesurface of the anode oxidizes.
They lose valence electrons to become positivelycharged ions. As the zinc ions move away from the anode, their electrons stayon its surface. The anode now becomes more negatively charged than the cathode.When the cells connected in an external electrical circuit, the excesselectrons on the zinc anode will flow through the circuit to the carbon rod,forming an electric current.When the electrons enter the cathode (Carbon rod), they react withmanganese dioxide (MnO2) and water (H2O) to produce manganese oxide (Mn2O3) andnegatively charged hydroxide ions. A secondary reaction is produced in whichthe negative hydroxide ions react with positive ammonium ions in the ammoniumchloride electrolyte to produce molecules of ammonia and water.
ALKALINE CELLA cylindrical cell is contained in a drawn stainless steel can, which isthe cathode connection. The positive electrode mixture is a compressed paste ofmanganese dioxide with carbon powder added for increased conductivity. Thepaste may be pressed into the can or deposited as pre-molded rings. The hollowcentre of the cathode is lined with a separator, which prevents contact of theelectrode materials and short-circuiting of the cell.
The separator is made ofa non-woven layer of cellulose or a synthetic polymer. The separator mustconduct ions and remain stable in the highly alkaline electrolyte solution.The negative electrode is composed of a dispersion of zinc powder in agel containing the potassium hydroxide electrolyte. The zinc powder providesmore surface area for chemical reactions to take place, compared to a metalcan.
This lowers the internal resistance of the cell. To prevent gassing of thecell at the end of its life, more manganese dioxide is used than required toreact with all the zinc. Also, plastic-made gasket is usually added to increaseleakage resistance.Aluminium foil is wrapped as the final process of battery manufacturing,as a decoration as well as providing superior protection for the batterycompared to a cardboard wrapper. In an alkalinebattery, the negative electrode is zinc, the positive electrode is manganesedioxide and the electrolyte are potassium hydroxide. Only the zinc andmanganese dioxide are used up during discharging process. The alkalineelectrolyte of potassium hydroxide remains, as there are equal amounts of OH?consumed and produced.
SECONDARY CELLSLEAD-ACID CELLRechargeable Small Sealed Lead Acid (SSLA) batteries are valve-regulatedlead acid batteries (VRLA batteries). They do not require regular addition ofwater as compared to primary cells, and they vent less gas than flooded (wet)lead-acid batteries. Hence, they are often referred to as “maintenance free”batteries, as it does not require much maintenanceto maintain it. The reduced venting is an advantage as they can be usedin confined or poorly ventilated spaces.There are two types of VRLA batteries:1. Absorbedglass mat (AGM) battery2.
Gelbattery (“Gel Cell”)An absorbed glass mat battery has the electrolyte absorbed in afibre-glass mat separator while a gel cell has the electrolyte mixed withsilica dust to form an stablised gel.NICKEL CADMIUM BATTERIESA rechargeable Nickel Cadmium battery in the charged state consist ofnickel hydroxide (NiOOH) in the anode and cadmium (Cd) in the cathode. Potassium hydroxide (KOH) is normally usedfor the electrolyte. Due to their low internal resistance and the very goodcurrent conducting properties, NiCad batteries can supply extremely highcurrents and they have the ability to recharge rapidly. In addition, thesecells are capable of sustaining extremely low temperatures (-20°C). Theselection of the separator (nylon or polypropylene) and the electrolyte (KOH,LiOH, NaOH) affect the voltage conditions in the case of a high currentdischarge, the service life and the overcharging capability.
Nickel Cadmiumcells generally offer a long service life thereby ensuring a high degree ofeconomy. For this reason, cells require a safety valve. In the case of misuse,a very high-pressure may arise quickly.NICKEL METAL HYDRIDE BATTERIESA Nickel Metal Hydride Battery is a rechargeable NiMH battery whichconsist of nickel hydroxide (NiOOH) in the cathode and a hydrogen storing metalalloy (MH) in the anode. Potassium hydroxide (KOH) acts as the electrolyte inthis battery setup. Compared to NiCadbatteries, Nickel Metal Hydride batteries tend to have a much higher energydensity per volume and weight.LITHIUM ION BATTERIESLithium ion battery is a rechargeable battery where the negativeelectrode (anode) and positive electrode (cathode) materials where reaction forthe lithium ion (Li+) takes place.
Lithium ions move from the anode and isattracted to cathode during discharge and are form into the cathode. The ionsreverse direction during charging. Sincelithium ions are form into the cathode materials during charge or discharge,there is no free lithium metal within a lithium-ion cell.
Commercially, lithium ion cells have a voltage range of approximately3.0V to 4.2V. The electrolyte used is composed of an organic solvent anddissolved lithium salt. This provides a medium for the lithium ion to move. Ina lithium ion cell, alternating layers of anode and cathode are separated by aseparator which is a porous film. APPLICATIONSPRIMARY CELLSLECLANCHE CELLThe electromotive force (EMF) produced by a Leclanche cell is around 1.
4volts, with a resistance of several ohms where a porous pot is used. It isoften used in telegraphy and signalling, where infrequent current is needed andit is advisable that a battery should require maintenance.The Leclanché battery wet cell was the forerunner of the modernzinc-carbon battery (a dry cell). The addition of zinc chloride to theelectrolyte paste actually increased the EMF to 1.5 volts. Later developmentsprovided ammonium chloride completely, giving the cell to endure more sustaineddischarge without its internal resistance rising as quickly (the zinc chloridecell).
SECONDARY CELLSLEAD-ACID CELLThe lead-acid batteries are primarily used in the automobile industry.It used to as starters, for lighting and ignition of the car. The wet cell standby batteries are designed for deep discharge and aremainly used as a backup power supply. Lead-acid batteries are used in poweringthe emergency lighting and to power sump pumps in case of a power failure. Traction (propulsion) batteries are used in golf carts and otherelectric vehicles are powered by batteries. Large lead-acid batteries are usedto power the electric motors in conventional submarines when they areunderwater and also as a back-up power on nuclear submarines. Moreover,electrolyte spillage does not occur in valve-regulated lead acid batteries.
This makes them practical in applications where spillage is not favoured suchas alarms and smaller computer systems, (particularly in uninterruptible powersupplies; UPS), powering electric scooters, electric wheelchairs, electrifiedbicycles, micro hybrid vehicles, and motorcycles. Lead-acid batteries were used to supply the filament (heater) voltage,with 2 V common in early vacuum tube (valve) radio receivers.Headlamps found in a miner’s headgear are usually powered by two orthree cells.NICKEL CADMIUM BATTERIESClosed Ni-Cad cells may be assembled into battery packs which has two ormore cells, or it may just be used individually. Smaller cells are normallyused in kid’s toys or other portable electrical devices, which often using thecells that are like the sizing of primary cells.
Performance will be reducedwhen primary cells are substituted by Ni-Cad batteries because Ni-Cad batterieshave lower terminal voltage and smaller ampere-hour capacity. Photographic equipment, flashlights, watchesand toys sometimes use miniature button cells.Specialty Ni-Cad batteries is a favourable choice for camera flashunits, boats, cars and cordless power tools as they have low internalresistance and can supply high surge currents.
They are also used in emergencylighting and cordless home telephones etc.Larger flooded cells are used for standby power and also aircraftstarting batteries.NICKEL METAL HYDRIDE BATTERIESThe primary use of the NiMH batteries is in electric plug-in vehicles(i.
e. General Motors EV1, First-generation Toyota RAV4 EV, Honda EV Plus, FordRanger EV and Vectrix scooter) and hybrid vehicles (i.e. the Toyota Prius,Honda Insight, Ford Escape Hybrid, Chevrolet Malibu Hybrid and Honda CivicHybrid). However, this is slowly being taken over by lithium ion batteries. LITHIUM ION BATTERIESLithium-Ion batteries are lightweight and have a high energy density.Due to this, it is used as the power source for a variety of devices.
Suchdevices include many of the latest mobile devices (i.e. smartphones,tablets,laptops), power tools (i.e. cordless drills, saws and sanders) andelectric vehicles (i.e. electric cars, hybrid vehicles, electric bicycles,personal transporters and advanced electric wheelchairs).
In order to powerlarger devices such as the electric vehicles multiple batteries in parallelrather than a single unit as it is much more effective.LIthium-Ion batteries are also used in telecommunication applications.Secondary non-aqueous lithium batteries provide reliable backup power to loadequipment located in a network environment of a typical telecommunicationsservice provider 4. Advantages andDisadvantages of Batteries There are several advantages of using batteries over other methods ofgenerating EMF. Firstly, batteries are able to be used in applicationsrequiring high current.
They have high energy density and are able to becharged and discharged easily. Moreover, they are more eco-friendly compared tocombustion of fossil fuel as the exhaust gas from the electrolysis is onlywater vapour. Next, they are able to produce stable voltage, unlike frictionmethod which makes it good for practical applications.
Lastly, they are moreportable and can store energy. However, using chemical means for powergeneration also has its disadvantages. This method is resistant to high temperatures and can vary the output ofthe voltage produced and can also restrict applications in certain situations.
Using batteries needs regular maintenance. This makes it troublesome andinjuries can occur during maintenance check. An example could be acid runninginto the eyes and eventually blinding the person. Moreover batteries suffer from thermal runaway (especially so in NiCadbattery), a condition where they are not properly charged despite long hours ofcharging. Possible explosions due to chemical reaction happening when gases arereleased at electrodes. This is known as Polarization. Polarization inbatteries requires it to be regularly filled with electrolyte.
Batteries haveinternal resistance and are unable to produce large industrial amounts ofelectricity unlike light, combustion methods.