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Battery Technology
MSE 6080 Spring 12
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Where our energy comes from
MRS Bull 33 (2008) 264
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Renewable energy
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Power Generation Devices
Chem Soc Rev38, 226
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Electrochemical Power Sources Chemical energy transformed directly into
electrical currents Portable sources of electrical power (watches,
portable electronics, start-up of cars)
Store electrical energy supplied by an external source
(electric vehicles, supplementary power supply duringpeak requests)
First battery Volta, 1800
Today 8 15 batteries for every human onEarth
World market in excess of $ 200 billion
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Mobile Power Portable electronic
devices
increasing powerrequirements
Microsized,autonomous
systems (MEMS)may requirebatteries withperformancesunavailable today
Electric car:capacity, weight,
cost
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Nomenclature Primary battery life has ended once the
reactants have been consumed
Secondary battery can be recharged
when the reactants have been used up
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Survey Battery energies: 10-6 Wh
to 3 MWh Miniature batteries
watches and otherminiature apps 0.5 2
uA, 15-60 mWh/yr
Dry batteries toysradios 10 mAh 15 Ah
SLI batteries Pb acid 12 V, 40-60 Ah, 45 Wh/kg
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Future/current uses A Pb acid battery capable to
drive a vehicle is 50x heavier,
25x the room of the equivalent ICengine Longer time to recharge
Currently NiMH
Na or Li based batteries up to100 Wh/kg
Stationary batteries standbypower emergency (250 Wh 5MWh)
Load leveling public powersupply. increase base loadcapacity to stockpile energy andmeet peak energy needs
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Theoretical An electrochemical reaction
provides current throughchemical transformations at theelectrodes and in the electrolyte
Max energy obtainable:G = -zFE
Amount of transformation
proportional to the chargepassed through the cell
Cathode: e flow from theexternal circuit (red)
Anode: e flow to the externalcircuit (ox)
Discharge Charge
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Theoretical 2 The EMF of a battery
tends to decrease with
operation
Design to provide for
small changes in OCP Pt/Fe3+,Fe2+Ce4+, Ce3+/PtFe2+ + Ce4+ Fe3+ + Ce3+
Zn/ZnO/KOH/HgO/HgZn + HgO ZnO + Hg
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Losses Due to the passage of current
Ohmic drop in the electrolyte bulk Electrode losses due to CT step
Processes of formation of a solid phase
(crystallization overvoltage) Porous electrodes interface increase,
resistivity decrease
Impregnation to immobilize liquidelectrolyte
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Characteristics Capacity, Energy, Power Polarization curve cell voltage
vs. current Electrode polarization Cell resistance
Diffusion overvoltage (reactantdepletion)
Discharge curve OCP vs. fraction discharge
Cell voltage during deep discharge
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Theoretical Energy p.u. weight
EMF in 30% KOH is 1.29 V
zFE = 2.5105 Ws ~ 6 Wh MNi = 58.7, MCd = 112.4, Mtot = 331.8
Energy density = 208 Wh/kg
Practical values ~ 40 Wh/kg ~ 20%
2NiO(OH) + Cd + 2H2O = 2Ni(OH)2 + Cd(OH)2
Discharge
Charge
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Primary Batteries Leclanch (1866)
Zn chloride Alkaline manganese
oxide
Al- and Mg-basedLeclanch
Schematics of a Leclanche batteryhttp://www.wisedude.com/science_engineering/batteries.htm
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Leclanch Cell Zn anode, MnO2 cathode,electrolyte ZnCl2 + NH4Cl
Cathode: carbon rod in amixture C/MnO2
Anode: Zn rod in satNH4Cl
Electrolyte immobilizedwith a paste
Zn/ZnCl2, NH4Cl/MnO2,C
E ~ 1.5 V
Zn + 2H2O Zn(OH)2 + 2H+ + 2e
2MnO2 + 2H+ + 2e 2MnO(OH)
Zn + 2MnO2 + 2H2O Zn(OH)2 + 2MnO(OH)
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Leclanch Cell, cont
Self-discharge and gas build-up Slow down by amalgamating Zn with Hg
(recently eliminated)
Other drawbacks Short shelf life (needs refrigeration)
Small energy density (75 Wh/kg)
Voltage decreases over time
Alternative: alk battery (KOH)
Zn + 2H2O Zn(OH)2 + H2
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Rechargeable batteries Charge factor: charge used during charge
vs. charge passed during discharge
CF > 1 if side rxns occur during charging
Cycle life: # of charge/discharge cycles
before battery performance degrades ~ 103
Full charging can often be achieved onlyby overcharging. Careful not to evolve
gases! Self-discharge less important
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Pb acid
Why water does not dissociate?
Theor 171 Wh/kg, actual 40
Wh/kg ~ 23% Cyclability depends strongly onmicrostructure
Heavy, low cost
Pb + SO42- PbSO4 + 2e
PbO2 + 2H2SO4 + 2e PbSO4 + SO42- + 2H2O
PbO2 + Pb + 2H2SO4 2PbSO4 + 2H2Odischarge
25% H2SO4
EMF = 2.1 V
Pb
PbSO4
PbO2
PbSO4
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Microstructural evolution of Pb
electrode
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Ni-Cd
EMF 1.29 V
En density 208 Wh/kg
Rate of discharge, T affectcapacity
Longer cycle life than Pb
(up to 3500, 5-10 yrs) High cost, but decreasing
NiO(OH) + H2O + e Ni(OH)2 + OH-
Cd + 2OH- Cd(OH)2 + 2e
2NiO(OH) + Cd + 2H2O = 2Ni(OH)2 + Cd(OH)2
Discharge
Charge
J Power Sources 100, 125
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Ni-Metal hydride Anode LaNi5 based
(high H2 storage) Electrolyte 30%
KOH
En density 40-110Wh/kg
109 sales/yr
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Li-ion battery Li ve
electrode TM oxide +ve
electrode (Liintercalation)
EMF up to 4.5 V
LIanode
Cathode
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Electrodes Anode graphite
Cathode
Technological trends
Better graphite
Enhance +ve electrode
Improve solvent stability
LiC6 Li+ + 6C + e
Li+ + Mn2O4 + e LiMn2O4
Li+ + Mn2IVO4 + e LiMn
IIIMnIVO4
Li+ + FeIIIPO4 + e LiFeIIPO4
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Trends in R&D
100 200 400 800 1,400
Spec. Power Density (W/kg)
Sp
ec.
EnergyDensity(Wh/kg)
50
100
150
200
LeadAcidNi/Cd
Ni/MH
Lithium-Ion Battery
High PowerLIB
High EnergyLIB
MobileIT
HEV
NextGenerationBattery ?
Courtesy Hyun-Soo Kim
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Some designs
Hardpreparation,
Mndissolution
Low electricconductivity
Low electricconductivity
Low tapdensity
Mndissolution
(@E.T.)
Hardpreparation,Low thermal
stability
High cost,toxicity
Demerits
Low cost,
nontoxic
Low cost,
thermal
stability
High
capacity
High
capacity &
thermal
stability, low
cost
Low cost,
nontoxic
High
capacity
High electric
conductivity,
easypreparation
Merits
3.4V3.45V3.6V3.6V3.8V3.5V3.6VOperationVoltage
180mAh/g4.4-3V:90
3-2.0V:90
150mAh/g170mAh/g170mAh/g120mAh/g180mAh/g140mAh/gPracticalCapacity
344mAh/g170mAh/g285mAh/g285mAh/g148mAh/g275mAh/g274mAh/gTheoretical Capacity
LayeredOlivineLayeredLayeredSpinelLayeredLayeredStructure
LiMnO2LiFePO4LiNiMnO2
Li[CoNiMn]O2
LiMn2O4LiNiO2LiCoO2
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Thermal management Above T2, corrosion and degradation
processes become very fast Below T1 the electrolyte has too high a
resistance and charge transfer is too slow
Heat must be dissipated during highcharge/discharge rates
High T batteries: need to heat, avoid heatloss, use a cooling system to avoidoverheating
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Summary Seek high energy density, high power, low
cost EMF is approaching its limits
Room to improve on rates, lifetime 3D geometries for high rates
Low cost
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Energy Density E = 0.5CV2 = 0.5QV
Increase in V advantageous but limited 0.8-1.2 V in aq electrolytes
3-4 V in non aq (lower Cdl)
Increase in spec area energy/weight
7-10% capacity of a battery
Better cycle life
Fast charge/discharge