Table Of ContentEnergy Storage Devices for Electronic Systems
Energy Storage Devices
for Electronic Systems
Rechargeable Batteries
and Supercapacitors
Nihal Kularatna
School ofEngineering, The University of Waikato
Hamilton, New Zealand
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ISBN:978-0-12-407947-2
Dedication
This book is dedicated to Professor W. P Jayasekara,
who honourably dedicated his long academic career in Sri Lanka
to teach fundamentals of electrical
engineering to many engineering students,
supported by his capable team of academic staff at the Faculty of
Engineering,
and giving me,
the wisdom of applying simple fundamentals to practical circuits.
Preface
Electronic engineering advancesat a rapid rate where designers and researchers are
expectedtomaintaintheirknowledgehalf-lifeat3-5yearlevels.Newsubjectsenter
thefieldofelectronics,andwehavetokeepup-to-datebylearningthesenewsubjects
andstillmaintainourhistoricandpracticalexperience-basedknow-howintheback-
groundtomixwiththenewsubjectareas.Inthisprocessonesimplethinghasnever
changed—that isthe simple fundamentals we apply incircuitson adaily basis.
Duringmylast13yearsofthefull-timeacademiccareer,Ihavelearnedsomething
important. If the simple fundamentals can be practically and effectively applied to
newcircuittopologiesandstate-of-the-artdevices,wecancomeupwithnoveltech-
niques, and develop them into very useful industrial applications, provided we also
learnfromourgloballydistributedsubjectexpertsandmixthoseknowledgeelements
with our own work. In this exercise, attributes such as perseverance, creativity, and
life-long learning help us immensely.
Thisbookismyeighthmajorwork,andthisismostlybasedonmylast10yearsof
the academic and industrial experience in working with energy storage devices
(ESDs), particularly in the subject of nontraditional supercapacitor applications. In
this subject area, I was once again convincing myself of the most important aspect
of learning—how to apply simple circuit fundamentals with new (energy storage
or other) devices, with persevering efforts to understand the underlying physics
andelectrochemistry.ParticularlyindevelopingtheChapters2,3,and5ofthework,
Ipracticallylearntthatthereisamassiveongoingconcertedeffortbytheelectroche-
mists, physicists, and technologists to enhance the performance specifications of
ESDs. I sincerely thank all of them for their concerted efforts to give the electronic
circuitandsystemdesignersnewpackageddeviceswherewecouldstartwithsimpli-
fiedequivalentcircuits,andindustrialdevicedatasheetstodevelopnewapplications.
Thisworkreflectsasummaryoftheapplicationsknowledgegainedbyateamof
researchersleadbymeinNewZealand,directlyandindirectlysupportedbythecon-
certedeffortsoftheglobalteam.Inthiswork,mostofresearchprojectsweworkon
couldhelp the natureandthe environment too,with aneffort tounderstand thatthe
energyresourcesarelimitedandrenewableenergyareashouldbewellsupportedby
new research efforts on ESDs and applications.
Thank you,
Nihal Kularatna
School of Engineering
TheUniversityof Waikato
Hamilton
New Zealand
8thSeptember2014
Acknowledgments
From myuniversitygraduationwith adegreeinelectricalengineering, Ihave spent
over38yearsintheindustryandacademia,andcompletingalmost13yearsinafull-
timeacademiccareerinNewZealand.Allmysubjectlearningmixedwithlifeexpe-
riencetellsmeonething...learningasubjectisalife-longexercise,anditisamoving
target. In this journey, all my school teachers, university teachers, senior industry
engineers,andthementors/advisorshave helpedmeimmensely.Ithankallofthem
who helped me come along-way inan electronic-engineeringcareer.
FormyengineeringexpertiseIthankProfessorW.P.JaysekaraandhisteamatUni-
versity of Peradeniya, Sri Lanka who gave me the courage and the perseverance to
think of fundamentals first in any EE project. My previous work places such as the
Area Control Centre of Department of Civil Aviation, Sri Lanka; Saudi Telephone;
Arthur CClarkeInstituteforModernTechnologies(ACCIMT),SriLankaprovided
me all the opportunities to gain real-world on-the-job engineering experience, for
whichIamverygrateful.AtACCIMTIwasinspiredbySirArthurCClarke,andalso
heintroducedmetopUSengineerssuchasJohnRobinsonPiercewhonamedthetran-
sistor.Istronglybelievethatmymid-careerwaswellsupportedbytheopportunities,
facilities,andtheteamattheACCIMTandIamverythankfultoSirArthurandthe
ACCIMTteamwithwhomIworkedfor16years.Iamverygratefultoamentorsuch
as Prof Pierce, who guided me in 1992 on how to complete a book project
successfully.
IamverythankfultoProf.JohnT.BoysofUniversityofAuckland,whoinvitedme
tocomeintotheacademiain2002.After25yearsintheindustry,thismovemademe
developanewresearchareawithanacademicinclinationintothedepthofaselected
subject utilizing mybreadthofthe subject area and astrong team work.
IthankallmycolleaguesandtheseniormanagementattheUniversityofWaikato
whocontinuallyencouragemetocontribute.Duringthelast7yearswithvariouscom-
mercial type grants from the university’s commercial arm, WaikatoLink Limited
(WLL), we were very much encouraged to develop new commercially useful
supercapacitor-based techniques, and I am very thankful to the whole team at
WLL. I am very thankful to Professors Janis Swan, Ilanko Sinniah, Brian Gabbitas
who were my line managers who encouraged me to develop my academic research
programswithastrongindustrialflavor.Inmypostgraduateresearchwork,forcosu-
pervision, I am very grateful to my colleagues such as Alistair Steyn-Ross, Rainer
Kunnemeyer, Howell Round, and Sadhana Talele. I am also very thankful to my
schooladministratorsJanineWilliamsandMaryDalbethforassistingmeonadaily
basistoperform myteachingand researchtaskseffectively.
xiv Acknowledgments
My former PhD student Kosala Gunawardane and the current student Jayathu
Fernando are gratefully acknowledged for coauthoring three chapters of the work.
Many other postgraduate students helped me developed lot of details in various
researchprojectsandIamthankfultoallofthemfortheirefforts,whicharedirectly
or indirectly used in chapter contents. Jayathu Fernando, Tanya Jayasuriya, and
Dhanya Herath were helping me immensely to generate a significant number of
figures requiredfor the bookand Iam very thankful to himfor thatwork.
FromestablishingtheinitialcontractintothefinalproductionoftheprintedworkI
gratefully acknowledge the editorial and the production team of Elsevier with
special thank you notes to Joe Hayton, Tiffany Gasbarriny, Kattie Washington,
Preethy Mampally, and Chelsea Johnston. I also thank IEEE, PET Magazine,
EDN,CRCPress,andElsevierPublicationsformetoreusevariousfiguresrequired
in developing the manuscript. Natalie Guest, Nicoloy Gurusinghe, and Jayathu
Fernando are gratefullyacknowledged for the cover page image ofthe book.
Inmyhomeenvironment,Iamfullysupportedandalwaysencouragedbymylov-
ingwife Priyani, daughtersDulshaandMalsha,son-in-lawsRajith andKasuntodo
mytechnicalwriting.Iammostgratefultothemforthiscontinuousencouragement.
Twolittlegrand-daughtersNethuliandMineliarekeepingmeandPriyanientertained
and it provides me areasonto thinkoffuture and the environment.
Ithankallmyfriendsandextendedfamilieswhohavealwaysappreciatedmytech-
nicalwork and the authorshipof technical books.
ItrustthatmycurrentworkonESDapplicationswillhelptheenvironmentinthe
longerrun, andprovidesus creative means apply these devices in unique ways.
Last,Ithankallmypastandfuturestudentswhowillusethisnewbookandencour-
age them topoint anyerrors, and suggestive improvements.
Nihal Kularatna
29, LangdaleCourt
Huntington
Hamilton 3210
New Zealand
9thSeptember 2014
1
Energy storage devices—
a general overview
1.1 Introduction
From the invention of the transistor in late 1940s, electronic products and systems
havebecomeanessentialpartofthemodernworldwithinterconnectedglobalcom-
munication systems, intelligent white goods, electronic subsystem dominated auto-
motive and a plethora of portable devices. With the world population growing
beyond7billionin2012,andwiththeportableelectronicdevicesgettingpopulareven
inthepoorestpartsoftheworld,worldwideenergyconsumptionkeepsgrowingata
steady rate. In 2008, world’s energy consumption was estimated to be around
144,000TWh.Energysupplyusuallycomesfromseveraldominantsources,namely,
fossil fuel and nuclear (as nondominant major sources), and from many renewable
sourcessuch ashydroelectric,solar,wind, geothermal, biomass,and biofuels.
Intheworldofenergyusage,energystoragerequirementcomesindifferentforms.
Inourhomeandworkenvironments,sometimesweneedtostoreenergyinsystems
suchastheuninterruptiblepowersupplies(UPSs)usedforinformationsystemsand
othercriticalfacilitiessuchashospitals,airports,andfactoriesinordertosafeguard
againstpoweroutages.Inthesesituations,differenttypesofenergystoragesystems
(ESS)suchasbatteries,supercapacitor(SC)banks,flywheels,andcompressedairare
used together with suitable electromechanical energy conversion systems. In these
systems,weusuallydealwithfew100Wtofewmegawattsorderrequirementswith
the outagesexpected inthe range offractionalseconds tofew hours.
Inourmodernhybridelectricvehicles(HEV) andelectricvehicles(EV),battery
banksandfuelcellsareusedtodealwithkilowattorderrequirementslastingforfew
minutestofewhoursofdriving,wheretheESScomesintoplay.Withtheinefficien-
ciesofinternalcombustionenginetogetherwithmechanicaldrivesystemsinthecars,
overallenergyefficiencyisintherangeof15%toover20%,encouragingthedevel-
opmentofmoreenergyefficientHEVsandEVs.Intheseapplications,wheretensof
kilowatts of power is required, the capacity of the battery banks in terms of energy
storage should be inthe range of kilowatt-hours.
Compared to the above scenario, if we consider our portable electronic devices
suchascellphones,PDAs,andlaptopswherebatterypacksareused,wecommonly
comeacrossthecapacityintermsofmilliampere-hours(mAh)orampere-hours(Ah),
withbatterypackswithnominalvoltagevaluesvaryingfromabout2.5toabout16V.
Given these nominal voltage values, assumed to be constant over the operational
range, will give us the energy storage capacity in mWh to Wh. Compared to the
twoaboveapplicationareas,ifwetakemuchsmallerpowerandenergyrequirements
such as wrist watches, hearing aids and implants, the battery pack capacity may be
specifiedinmicrowatt-hourstofewmilliwatt-hoursonly.Terminalvoltagesofthese
EnergyStorageDevicesforElectronicSystems.http://dx.doi.org/10.1016/B978-0-12-407947-2.00001-8
Copyright©2015ElsevierInc.Allrightsreserved.
2 EnergyStorageDevicesforElectronicSystems
battery packs, mostly coming in the form of one or few single cells, may be in the
range of0.5Vto fewVoltsper cell.
Given a few common day-to-day examples of battery-based systems, we could
practically appreciate that a few commonly identified electrical parameters such as
terminal voltage, and the energy storage capacity in terms of Watt-hours or
milliwatt-hoursallowustocomparethecapabilitiesofthebatterypacks.Ifaloadcon-
sumespoweratasteadyrateof1Wfor1h,thedevicehasconsumedatotalenergyof
1Whduringthatperiod.InstandardSIunits,thistranslatestoavalueof3600J,since
1W dissipated during 1sis equal to1J.
Sofarwehaveconsideredonlybatteriesasanenergystoragedevice(ESD)family,
butingeneralmanydifferentmethodsanddevicescanbeusedforenergystoragesuit-
ableforelectricalandelectronicsystems.Thischapterprovidesanoverviewofenergy
storage and delivery devices, methods, and the essential fundamentals applicable to
energy transfer into electronic systems and devices. With some quantification
approach,thecontentswillassistcomparingthedetailsofenergystoragecapabilities,
andenergydeliverycapabilitiesandlimitationsofESDsinelectronicenvironmentsin
apracticallyusefulway.Thecontentsofthisandtheoverallworkareaimedasaprac-
ticalguidelinetoengineers,designers,andresearchersworkingintheseareas.Reader
isexpectedtohavesomeessentialpriorknowledgeoncircuittheoryapplicabletosim-
ple circuits.
1.2 Simple fundamentals
Letusstartwiththesimpleanalogyofawatertankatacertainheightabovetheground
level.Ifwehaveahoseconnectedfromthebottomofthetank,withatapconnectedat
theendofthehose,waterflowstartswhenthetapisopened.Wecanmeasuretherate
ofwaterflowintermsofliters/second.Ifyouconsiderthetankasthestoragedevice,at
thisratewecanestimatethetimetoreleasethetotalquantityofwater.Ifwemakethe
tankbigger,wegetmorequantityofwaterstoredinthetank.Ifthebottomofthetank
isatthesamelevelasbefore,wewillhavethesamerateofflowattheendofthepipe.
Wewilltakealongertimetoreleasethatwateratthatsamerate.Nowwecanraisethe
bottomlevelofthetankwhichwillincreasetherateofflow.Thismeansthetankwill
emptyfaster.Wecanalsoincreasethediameterofthewaterhoseconnectedtoachieve
ahigherflowrateofwater.Thishappenssincetheresistancetowaterflowwillreduce
duetohigherdiameterofthehose.Ifyouincreasethelengthofthehose,theflowrate
will be slower.
TheabovesimpleanalogyhelpsusunderstandESDs.Thelevelofthewatertank
(abovethereferencelevelofground)isanalogoustothe(positive)terminalvoltageof
thedeviceofthewithrespecttothenegativeterminal(whichisthereferencevoltage
level).Volumeofthetankisanalogoustotheamountoftotalcharge(orenergy)avail-
able for release into the external circuit. Water flow in the hose is analogous to the
current(inAmperesorcoulombs/second)intheexternalcircuit.Bychanginglength
ordiameterofthehose,wecreatetheanalogyofaresistanceofaconductor(which
Energystoragedevices—ageneraloverview 3
decreaseswiththediameterandincreaseswiththelength).Sometimeschangingthe
materialofthehose, we can noticethe differentrate offlow forthe same diameter/
length,whichindicatesustheanalogyoftheresistivityofanelectricalmaterial.Ifwe
extendthistothebehaviorofthetap,openingandclosingisanalogoustoashortcir-
cuit(withideallyzeroresistance)andanopencircuit(ofinfiniteresistance)condition,
respectively.
1.2.1 Work, power, and energy
Weallhaveanintuitivesenseofthetermwork.Precisedefinitionofworkreflectsthis
!
intuitionandwecandefineworkdone,W,byanappliedforce F (avectorquantity,
which hasan amplitude anda direction)movingan object bya distanceDx,
!
W¼FDx (1.1)
InSIunits,forceismeasuredinNewtonsanddistancemovedisinmeters,givingunits
ofNewton-meter.Newton-meterisgiventhenameJoule.Itisimportanttonotethatto
have distance moved and force applied should be in the same direction. Otherwise,
respective directional components need to be used. Work is a scalar quantity and
has nodirection, but the force anddistance both are vector quantities.
Closelyrelatedtowork,energyistheabilitytodowork.Workandenergyhavethe
sameunit,Joule.Energy,whichisoneofthemostimportantconceptsinallofphysics,
comesindifferentforms.Forexample,amovingobjectofmassmmovingatvelocity
ofvm/scarriesakineticenergy,K,givenby(1/2)mv2.Work-energytheoremindicates
usthatthechangeinanobject’skineticenergyisequaltothenetworkdoneonthe
object:
Dk¼W (1.2)
net
Inpractice,wecomeacrossmanydifferentunitsthatareusedforenergy,particularly
applicable to different subject areas. Examples are electron-volt used in nuclear,
atomic,andmolecularphysics;andthecalorieusedinthermodynamicsandchemis-
try.OlderEnglishunitsincludefoot-poundandtheBritishthermalunit(BTU)andthe
latterisusedinheatingandcoolingsystems.Electricitycompaniesusekilowatt-hours
(kWh).Forallthesecommonlyusedpracticalunits,onecanuseconversionfactorsas
inTable 1.1 toconvert toJoules.
NextimportantiteminenergyconversionandESDsisthepower,whichistherate
of doing work or rate of change of energy, which is measured in watts. Power is
defined asthe rate of doing work. Average power,P,can beexpressed as
DW
P¼ (1.3)
Dt
Inpractice,astherateofdoingworkvarieswithtimeitisusefultodefinetheinstan-
taneouspower, P, as
