11678 Chemistry Batteries-fuel Cells

7/30/2019 11678 Chemistry Batteries-fuel Cells

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Chapter 18: Electrochemistry

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BatteriesBatteries BatteriesBatteries

Batteries are the most important practical

application of galvanic cells.

Single cell batteries consist of one galvanic cell.

Multicell batteries consist of several galvanic cells

linked in series to obtain the desired voltage

History of Battery DevelopmentHistory of Battery Development

1800 Voltaic pile: silver zinc

1836 Daniell cell: copper zinc

1859 Plant: rechargeable lead-acid cell

1868 Leclanch: carbon zinc wet cell

1888 Gassner: carbon zinc dry cell

1898 Commercial flashlight, D cell

1899 Junger: nickel cadmium cell

Continued History of Battery DevelopmentContinued History of Battery Development

1946 Neumann: sealed NiCd

1960s Alkaline, rechargeable NiCd

1970s Lithium, sealed lead acid

1990 Nickel metal hydride (NiMH)

1991 Lithium ion

1992 Rechargeable alkaline

1999 Lithium ion polymer

Electrochemical PotentialElectrochemical Potential

Want to reduce

(gain electrons)

Gold

Mercury

Silver

Copper

Lead

Nickel

Cadmium

Want to oxidize(lose electrons)

Iron

Zinc

Aluminum

Magnesium

Sodium

Potassium

Lithium

Comparison of Different BatteriesComparison of Different Batteries


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Main Uses for BatteriesMain Uses for Batteries

Lead Acid Storage: Car Battery

Ni/Cd: Calculators, digital cameras,flashlights, electric vehicles

Ni/MH: Cell phones, camcorders, powertools, laptops, electric vehicles

Lithium Ion: pacemakers, watches, cameras,calculators, laptops

Lead Storage Battery

A typical 12 volt lead storage battery consists of sixindividual cells connected in series.

Anode/Oxidation: Lead grid packed with spongy lead.Pb(s) + HSO4

(aq) PbSO4(s) + H+(aq) + 2e

Cathode/Reduction: Lead grid packed with lead oxide.

PbO2(s) + 3H+(aq) + HSO4

(aq) + 2e PbSO4(s) + 2H2O(l)

Electrolyte: 38% by mass Sulfuric Acid.

Cell Potential: 1.924V

Lead Storage Battery

Pb is oxidized to PbSO4 at

the anode, and PbO2 is

reduced to PbSO4 at the

cathode during use.

PbSO4 adheres to the

electrodes causing the

battery to rundown.

Recharging the battery

reverses this reaction toreform Pb and PbO2.

Zinc Dry-CellZinc Dry-Cell

Zinc DryCell is "dry" because uses a viscous paste

rather than a liquid solution.

Anode/Oxidation: Zinc metal can on outside of cell.

Zn(s) Zn2+(aq) + 2e

Cathode/Reduction: MnO2 and carbon black paste on

graphite.

2MnO2(s) + 2NH4+(aq) + 2eMn2O3(s) + 2NH3(aq) +2H2O(l)

Electrolyte: NH4Cl and ZnCl2 paste.

Cell Potential: 1.5V - but deteriorates to 0.8V with use.

Zinc Dry-Cell

Electrode reactions in a

zinc drycell are complex.

Simplified, the Zn is

oxidized to Zn2+, forming 2

electrons.

The two electrons initiate

the reduction of MnO2 and

NH4+ to Mn2O3, NH3, and

H2O.

Alkaline Dry-CellAlkaline Dry-Cell

Dry Cell where the acidic NH4Cl electrolyte isreplaced by a basic electrolyte - either NaOH or KOH.

Anode/Oxidation: Zinc metal can on outside of cell.

Zn(s) + 2OH(aq) ZnO(s) + H2O(l) + 2e

Cathode/Reduction: MnO2 and carbon black paste on

graphite.

2MnO2(s) + H2O(l) + 2eMn2O3(s) + 2OH

(aq)

Electrolyte: NaOH or KOH, and Zn(OH)2 paste.

Cell Potential: 1.5V but longer lasting, higher power, and

more stable current and voltage.


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Discharge of Alkaline BatteryDischarge of Alkaline Battery Nickel-Cadmium BatteryNickel-Cadmium Battery

NickelCadmium Battery is Dry-Cell that isrechargeable.

Anode/Oxidation: Cadmium metal.Cd(s) + 2OH(aq) Cd(OH)2(s) + 2e

Cathode/Reduction: Nickel (III) compound on nickelmetal.

NiO(OH)(s) + H2O(l) + e Ni(OH)2(s) + OH

(aq)

Nickel oxyhydroxide, NiO(OH)

Cell Potential: 1.30V

Nickel-Cadmium BatteryNickel-Cadmium Battery

During discharge, Cd metal is oxidized at theanode and nickel oxyhydroxide is reduced at the

cathode.

During discharge, the solid reaction products(cadmium and nickel hydroxides) adhere to the

electrodes.

Recharging reverses this reaction. Typical Nicad battery packs contain 3 or more cells

in series to produce the higher required emf.

Nickel Metal Hydride BatteryNickel Metal Hydride Battery

Nickel Metal Hydride battery is similar to NiCdbattery. Dry-Cell that is rechargeable.

Anode/Oxidation: Metal Hydride.MH + OH(aq) M + H2O + e

-

Cathode/Reduction: Nickel (III) compound on nickelmetal.

NiO(OH) (s) + H2O(l) + e

Ni(OH)2(s) + OH(aq)

Nickel oxyhydroxide, NiO(OH)Cell Potential: 1.35V

Nickel Metal Hydride BatteriesNickel Metal Hydride Batteries

Hydrogen Stored at Anode as Hydride in MetalAlloy

Hydrogen Storage Metals: LaNi5, FeTi

H2 Storage Capacity: LaNi5 0.11 g/cc (Higher thandensity of liquid hydrogen. Liquid H2 is 0.07 g/cc)

Higher energy density than NiCd by ~40%

More expensive than NiCd by ~20%

NiMH Battery DischargeNiMH Battery Discharge


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Lithium BatteriesLithium Batteries

Lithium growing in popularity for batteries. Lithium islightest of metals. Highest standard potential of over 3 V.

0.2632711.30.13207Pb

0.483218.650.40112Cd

0.824197.10.7665.4Zn

0.9615287.850.4455.8Fe

1.348511.542.8740.1Ca

2.986592.71.726.9Al

2.206501.742.424.3Mg

1.1697.80.972.723.0Na

3.861800.543.056.94Li

Electrochemical

Equivalence (Ah/g)

Melting

point C

Density

g/cm3

Standard

potential (V)

Atomic

mass (g)Anode

0.2632711.30.13207Pb

0.483218.650.40112Cd

0.824197.10.7665.4Zn

0.9615287.850.4455.8Fe

1.348511.542.8740.1Ca

2.986592.71.726.9Al

2.206501.742.424.3Mg

1.1697.80.972.723.0Na

3.861800.543.056.94Li

Electrochemical

Equivalence (Ah/g)

Melting

point C

Density

g/cm3

Standard

potential (V)

Atomic

mass (g)Anode

Lithium Ion BatteriesLithium Ion Batteries

Lithium Ion Batteries based on lithium insertion into differentsolids

Process of lithium insertion is known as intercalation

Lithium has different electrochemical potentials in differentsolids

Anode: Typically graphite; Li+ has lower potential

Cathode: Typically LiCoO2 or LiMnO2; Li+ has larger

potential

Electrochemical Potential Energies forLithium Insertion into Different

Compounds

Electrochemical Potential Energies forLithium Insertion into Different

Compounds

Charge/Discharge Process inLi-Ion Batteries

Charge/Discharge Process inLi-Ion Batteries

Design of Li-Ion Cylindrical BatteriesDesign of Li-Ion Cylindrical Batteries Battery CapacityBattery Capacity

302000Lead acid

801600Rechargeable

1001200Lithium ion

511100NiMH AA

41750NiCd AA

1242850Alkaline AA

Density(Wh/kg)

Capacity(mAh)

Type


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Discharge RatesDischarge Rates

< 1C

0.2C

< 0.5C

1C

< 0.2C

OptimalDrain

2C

5C

5C

20C

0.5C

PeakDrain

2Lead acid

3.6Lithium ion

1.25Nickel metal

1.25NiCd

1.5Alkaline

VoltageType

RechargingRecharging

$8.50

$24.00

$18.50

$7.50

$95.00

Cost perkWh

5%

10%

10%

30%

20%

0.3%

Dischargeper month

2-4h300-500Polymer

8-16h200-2000Lead acid

2-4h500-1000Li-ion

2-4h300-500NiMH

1h1500NiCd

3-10h50 (50%)Alkaline

Chargetime

Cycles (to80%)

Type

Fuel CellsFuel Cells

Fuel Cells use externally fed CH4 or H2 as fuel.These fuels react with O2 to form water.

Anode/Oxidation: Porous carbon containingmetallic catalysts.

2H2(s) + 4OH(aq) 4H2O(l) + 4e

Cathode/Reduction: Porous carbon containing

metallic catalysts.O2(s) + 2H2O(l) + 4e

4OH(aq)

Overall Reaction: 2H2(g) + O2(g) 2H2O(l)

Fuel CellsFuel Cells

Fuel cells are not batteries

because they are not self-

contained.

Fuel cells typically have

about 40% conversion to

electricity, the remainder is

lost as heat.

Excess heat can be used to

drive turbine generators.

Proton Exchange Membrane (PEM) Fuel CellProton Exchange Membrane (PEM) Fuel Cell

PEM is promising fuel cell technology. PEM is the electrolyte.Conducts positively charged ions. PEM blocks electrons.

Fuel Cell Stack for Powering VehicleFuel Cell Stack for Powering Vehicle

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11678 Chemistry Batteries-fuel Cells