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ClassificationCharacteristicsAg2O-Zn, Ni-Cd, Zn-Air, Ni-MHLithium Batteries: Li-MnO2 and Li-ion cells BATTERY TECHNOLOGYMODULE 1Dr. Siju N. AntonyAssociate ProfessorDepartment of ChemistryNHCE, Bangalore

1Dr. Siju N. AntonyBattery is a device consisting of two or more galvanic cells connected in series, parallel or both.Battery can store chemical energy in the form of active materials and on demand converts in to electrical energy through electrochemical redox reaction.Battery acts as a portable source of electrical energy. Batteries are used in calculators, digital watches, hearing aids, laptops, car engines, space applications etc.BATTERY

Baghdad Battery

The jars are believed to be about 2,000 years old and consist of an earthenware shell, with a stopper composed of asphalt. Sticking through the top of the stopper is an iron rod. Inside the jar the rod is surrounded by a cylinder of copper. Konig thought these things looked like electric batteries and published a paper on the subject in 1940. Parthians may have used these batteries for electroplating.The little jar in Baghdad suggests that Volta didn't invent the battery, but reinvented it.Classification of batteriesPrimary batteries (irreversible): A primary battery is one in which electrical energy can be obtained at the expense of chemical energy only as long as the active materials are still present. Once these have been consumed, the cell can not be profitably or readily rejuvenated and must be discarded. Ex: Dry cell, alkaline-MnO2 battery, lithium battery, Silver oxide zinc battery2.Secondary batteries: (rechargeable battery): In secondary batteries the cell reactions are reversible. They are also called storage batteries. The discharged battery can be recharged by passing current through it in the direction opposite to that of discharge current. Ex: Ni-Cd battery, Li ion battery, Lead-acid battery etc

3. Reserve batteriesOne of the components is stored separately and is incorporated into the battery when required. Usually, the electrolyte is stored separately. They have long shelf life and high performance reliability.Activated by a) Using water b) Using electrolyteEx: Mg CuCl, Zn-silver oxide batteries etc.Uses: Mines, artillery, pilot balloons, radars and submarines.

DifferencesPrimary BatteriesCell reaction is irreversible. Must be discarded after use. Have relatively short shelf lifeFunction only as galvanic cellsCannot be used as storage devicesThey cannot be recharged. Ex: Dry cell, Li-MnO2 battery. Secondary BatteriesCell reaction is reversibleMay be recharged Have long shelf life.

Functions as both galvanic & electrolytic cell.Can be used as energy storage devicesThey can be rechargedLead acid, Ni-Cd battery

7Dr. Siju N. AntonyBattery Characteristics Cell Potential: Depends on the free energy change in the overall cell reaction Ecell = Ecell 2.303 RT log Q nF

Current: Current is the rate at which discharge reaction occurs Capacity: Capacity is the charge in ampere hours (A h) that could be obtained from the battery. C = WnF M Electricity storage density: Amount of electricity per unit weight which the accumulator can hold Energy efficiency:

% of Energy efficiency = Energy released on discharge X 100 Energy required for charging Cycle Life: The number of charge/discharge cycles that are possible before failure occurs.Ag2O-Zn battery Construction

Anode : Zn Cathode : Ag2O Electrolyte: KOH solution Separator: Cellophane/nylon fibre mats/polypropylene

Working Applications Satellites, military aircraft and submarines

Ni-Cd BatteryConstruction Anode : spongy Cd with 78% Cd(OH)2 , 18% Fe, 1% Ni and 1% graphite Cathode : 80% Ni(OH)2 and Ni(OH)3 , 2% Co(OH)2, 18% graphite and traces of barium Electrolyte: KOH solution Separator: felted nylon

Working

Anode: Cd(s)+2OH-(aq)Cd(OH)2(s)+ 2e- Cathode: 2Ni(OH)3(s)+2e- 2Ni(OH)2(s)+2OH-(aq)

Net Reaction: Cd(s)+2Ni(OH)3(s) 2Ni(OH)2(s)+ Cd(OH)2(s) Applications

Phones, alarms systems, transmitters, receivers, computers, emergency lighting, hearing aids, telemeter and calculators

Zn-Air battery Construction

Anode : granulated ZnCathode : O2 with carbon + oxides of Mn Electrolyte: KOH solutionSeparator : Asbestos/polypropylene WorkingAt anode : Zn + 2OH- Zn O +H2O + 2e-At cathode : O2 + 2e- + H2O 2OH-Net Cell Reaction: Zn + 1/2O2 ZnO Applications Hearing aids, electronic pagers, telemetry, portable battery chargers and medical devices

Ni-MH battery Construction

Anode: Hydrogen adsorbed in a metal alloyCathode: NiOOH on porous Ni foil Electrolyte: 5.35 M KOHSeparator : Polypropylene WorkingAt anode : MH + OH-- M + H2O + e-At cathode : NiOOH + e- + H2O Ni (OH)2 + OH-Net Cell Reaction: MH + NiOOH M + Ni (OH)2 Applications cell phones, laptops, emergency backup lighting, electric vehicles, medical instruments, cameras, electric razors etc.

Lithium batteries Advantages

Li-MnO2 batteries Construction

Anode : Li Cathode : MnO2 Electrolyte: Li salts + propylene carbonate + 1,2-dimethoxyethane Separator : Non-woven Polypropylene

High voltage High energy density Wide operational temperature range Good power density Flat discharge characteristics Superior shelf life

WorkingAt anode : Li Li+ + e-At cathode : MnO2 + e- + Li+ LiMnO2Net Cell Reaction: Li + MnO2 LiMnO2 ApplicationsCalculators, watches, memory back up, sensors, bar code readers, transmitters, security and electronic equipments.Li-Ion cells Construction

Anode : Carbon Cathode : LiCoO2 Electrolyte: Ether Separator : Microperforated plastic

Working

At anode : 6C + Li+ + e- LiC6 At cathode : LiCoO2 Li+ e- Li0.5CoO2 Net Cell Reaction: C + LiCoO2 LiC6 + Li0.5CoO2Advantages

High energy density, Does not need prolonged priming when new. One regular charge is all that's needed. Low self-discharge. Low Maintenance Specialty cells can provide very high current to applications such as power tools.

Limitations

Requires protection circuit to maintain voltage and current within safe limits.Subject to aging. Transportation restrictions. Expensive to manufacture. Not fully mature.

Applications Consumer electronic devices (laptopes, cell phones and iPods)

Fuel Cells Generally Contain

Anode Anode Catalyst Cathode Cathode Catalyst Gas Diffusion Layer Electrolyte A load to complete the circuit Continuous feed of fuel Continuous feed of air or oxygen

A fuel cell is a galvanic cell in which chemical energy of a fuel oxidant system is converted directly into electrical energy in a continuous electrochemical process.

Cell Schematic Representation:

Fuel/electrode/electrolyte/electrode/oxidant

e.g. H2 / Pt / KOH / Pt /O2

18Dr. Siju N. AntonyThe reactants (i.e. fuel + oxidant) are constantly supplied from outside and the products are removed at the same rate as they are formed.Anode: Fuel+ oxygen Oxidation products+ ne-Cathode: Oxidant + ne- Reduction products.19Dr. Siju N. AntonyClassification of Fuel CellsBased on

Temperature

Fuel

Electrolyte

Low temp. (25 C-100 C)Intermediate temp. (100 C-500 C)High temp. (500 C-1000 C)Very high temp. (>1000 C)

Gaseous (H2, NH3)Liquid (Alcohols, hydrocarbons)Solid (Coal, hydrides)

PEMFC, AFC,DMFC, PAFC, MCFC,SOFC

CH3OH-O2 Fuel CellBoth electrodes: Made of porous nickel plates impregnated with finely divided Platinum.

Fuel : Methyl alcohol.

Oxidant : Pure oxygen / air.

Electrolyte : 3.7M H2SO421Dr. Siju N. AntonyCH3OH-O2 Fuel Cell

Working

CO2, a product of the reaction can be easily removed.

The cell potential is 1.21V at 25C.

Used in military applications

In large scale power production

Marine applications such as in boats and ships

In automobilesMeOH is one of the most electro active organic fuels in the low temperature range as*It has low carbon content *It posseses a readily oxidizable OH group *It is miscible in all proportions in aqueous electrolytes.24Dr. Siju N. AntonyAdvantages of Fuel CellsHigh efficiency of the energy conversion process.Silent operation.No moving parts and so elimination of wear and tear.Absence of harmful waste products.No need of charging. 25Dr. Siju N. AntonyLimitations of Fuel CellsCost of power is high as a result of the cost of electrodes.Fuels in the form of gases and O2 need to be stored in tanks under high pressure.Power output is moderate.They are sensitive to fuel contaminants such as CO,H2S, NH3 & halides, depending on the type of fuel cell. 26Dr. Siju N. AntonyDifferences Fuel Cell Galvanic Cell*Do not store chemical Stores chemical energy energy *Reactants are fed from The reactants form an outside continuously. integral part of it. *Need expensive noble These conditions are metal catalysts. not required*No need of charging Get-discharged when stored up energy is exhausted. *Never become dead Limited life span in use *Useful for long-term Useful as portable power services electricity generation.27Dr. Siju N. AntonyFuel cell applicationsCell phones that dont quit in mid conversation because the batteries have died

Laptop computers that run all day without power cords

Efficient automobiles that emit virtually no nitrogen oxide or hydrocarbon pollutants

Fuel cell applicationsTiny self-powered gas sensors built on integrated circuits

Home electrical systems that keep working even if the power grid fails

Sensors, electronic weapons, and communication gear for soldiers in the field

Replacement for Li ion batteries in portable electronic devices

What are the types of fuel cell applications?

ProblemsCalculate the potential of a Daniel cell at 298 K if the free energy change of the cell reaction is -212.3kJ mol-1. F=96.5kJV-1mol-1A zinc rod is placed in 0.1M solution of ZnSO4 at 25 C. Assuming that the salt is 95% dissociated, calculate EZn2+/Zn at this temperature. Given E Zn2+/Zn = -0.76VCalculate the potential of the cell formed from silver and copper electrodes if the concentration of Ag+ and Cu2+ are 4.2 x 10-6 M and 1.3 x 10-3 M respectively. E cell = 0.46V. Calculate G for the reduction of one mol of Ag+ by Cu. F=96.5kJV-1mol-1The spontaneous galvanic cell tin/tin ion (0.024M)// tin ion (0.064 M)/tin develops a potential of 0.0126V at 298 K. Calculate the valency of tin.