.AngewandteReviews
L.F.Nazaretal.
DOI:10.1002/anie.201410376
SodiumIonBatteriesSpecialIssue150YearsofBASF
TheEmergingChemistryofSodiumIonBatteriesforElectrochemicalEnergyStorage
DipanKundu,ElaheTalaie,VictorDuffort,andLindaF.Nazar*
Keywords:
anodes·cathodes·energystorage·gridstorage·sodiumionbatteries
AngewandteChemie??2015Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim
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L.F.Nazaretal.
Energystoragetechnologyhasreceivedsignificantattentionfor
FromtheContents
1.Introduction
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portableelectronicdevices,electricvehiclepropulsion,bulkelectricitystorageatpowerstations,andloadlevelingofrenewablesources,suchassolarenergyandwindpower.Lithiumionbatterieshavedominatedmostofthefirsttwoapplications.Forthelasttwocases,however,movingbeyondlithiumbatteriestotheelementthatliesbelow—sodium—isasensiblestepthatofferssustainabilityandcost-effec-tiveness.Thisrequiresanevaluationofthescienceunderpinningthesedevices,includingthediscoveryofnewmaterials,theirelectro-chemistry,andanincreasedunderstandingofionmobilitybasedoncomputationalmethods.TheReviewconsiderssomeofthecurrentscientificissuesunderpinningsodiumionbatteries.
2.OverviewoftheSodiumIonCell34333.CathodeMaterialsforHighPerformanceSodiumionBatteries
4.ComputationalStudiesofNaIonMobility5.AnodeMaterials6.Electrolytes
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1.Introduction
Energystoragehasbecomeagrowingglobalconcernoverthepastdecadeasaresultofincreasedenergydemand,combinedwithincreasesinthepriceofrefinedfossilfuelsandtheenvironmentalconsequencesoftheiruse.Thishasincreasedthecallforenvironmentallyresponsiblealternativesourcesforbothenergygenerationandstorage.Oftheseveraltechnologiesthataresuitableforlarge-scaleenergystorage,pumpedhydroelectricsystemscurrentlydominate,withcom-pressedairbeingthesecondmostutilizedsystem.However,electrochemicalenergystorage(EES)technologiesbasedonbatteriesarebeginningtoshowconsiderablepromiseasaresultofmanybreakthroughsinthelastfewyears.Theirappealingfeaturesincludehighround-tripefficiency,flexiblepower,andenergycharacteristicstomeetdifferentgridfunctions,longcyclelife,andlowmaintenance.Batteries,inparticular,representaviableenergystoragetechnologyfortheintegrationofrenewableresourcesthatprovideinter-mittentenergyintothegrid.Theseincludesolarenergyfromphotovoltaicsandwindenergy(Figure1).Thecompactsizeofbatterysystemsmakesthemwell-suitedforuseatdistributedlocations(off-gridorminigrid),wheretheycanprovideenergystorageforlocalsolaroutputthatcanbeusedtochargeanelectric/hybridelectricvehicle(EV/HEV),supplyenergyforresidentialuse,orenableelectrificationofentireruralcommunities.On-grid,batteriesareutilizedtostoreandmanagepeakloadenergyfromlargephotovoltaicpowerplantsandload-leveloutputfluctuationsatwindfarms.Thestoragecanbeusedtofeedpowertothegridwhenconsumptionexceedsregularproduction,and/orutilizedforoff-peakutilizationsuchasforEVcharging.
Energystoragefortheelectricalgridhasprimarilybeenfocussedonlithiumion(Liion),redox-flow,andhigh-temperaturebatteriesuptonow.Ofthese,LiionEESiscertainlyacontender.Nonetheless,thedemandforLiionbatteriesasamajorpowersourceinportableelectronicdevicesandvehiclesisrapidlyincreasing.Li-ioncellsarenowpoweringhybrid-electricandplug-inelectricvehiclesandareforecasttocontinuetobetheenergystoragesystemforfuturegenerations.[1]Inthefaceofgreatlyincreaseddemandsonavailablegloballithiumresourcesbecauseoftheeventualrise
7.SummaryandOutlook
Figure1.Aunifiedmodelforthegridandmicrogrid,showingtheinterplaybetweenrenewableenergygenerationthatsuppliesthegrid,energystoragesolutionsforthegrid,andenergysupplyforhybrid/electricvehicletransport.
inthesemarkets,concernsoverpotentiallyrisingcostsandavailabilityhavearisen.Mosteasilyaccessiblegloballithiumreservesareinremoteorinpoliticallysensitiveareas.[2–4]Increasingutilizationoflithiuminenergystorageapplicationswithahigher“pricepoint”willultimatelypushupthepriceoflithiumcompoundsevenwithextensivebatteryrecyclingprogramstherebymakinglarge-scalestoragebasedonthiselementlessaffordable.Limitationsintheavailabilityofthetransitionmetalsforcathodematerialsarealsoofconcern,
[*]Dr.D.Kundu,[+]E.Talaie,[+]Dr.V.Duffort,[+]Prof.L.F.Nazar
DepartmentofChemistry&WaterlooInstituteforNanotechnologyUniversityofWaterloo
200UniversityAvenueWest,Waterloo,Ontario,N2L3G1(Canada)E-mail:lfnazar@uwaterloo.ca[+]Theseauthorscontributedequallytothiswork.
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AngewandteChemiedrivingdevelopmenttowardsmoresustainableelementssuchexcitingpossibilityofaroom-temperatureNa/ScellcloserasFeandMn.
toreality,althoughfurtherdevelopmentsarenecessary.
GiventhehighabundanceandlowcostofsodiumaswellOntheotherhand,sodiumionbatteries(NIBs)basedonasitsverysuitableredoxpotential(Eo(Na+/Na)=à2.71Vversusintercalationmaterialsthatemploynon-aqueouselectro-thestandardhydrogenelectrode)whichisonly0.3Vabovelytes—akintolithiumionbatteries—werefirstexploredinthatoflithium,meaningthereisonlyasmallenergypenaltytothemid-1980s.Theyhaveundergonearenaissanceinthelastpay—rechargeableelectrochemicalcellsbasedonsodiumholdfewyears,witharemarkablenumberofnewmaterialsandmuchmorepromiseforEESapplications.Theelectrochem-approacheshavingbeenreported.Theyofferahigherenergyistryofsodiummaterialshasalonghistory.Fiftyyearsago,thedensitythanaqueousbatteriesandlowercostthanLiiondiscoveryofthehigh-temperaturesolid-statesodiumionicbatteries,withsomenowapproachingtheenergydensityofconductorNaAl11O17(b“-alumina)providedaleapforwardinthelatter.Here,wediscussrecentresearchhighlightsofthefieldsofsolid-stateionicsandsodiumelectrochemistry,[5]sodiumionbasedelectrochemistry,withafocusonrecentalongwithNASICON(natriumsuperionconductor:NaxM2-studiesonintercalationcompoundsforpositiveelectrode(XO4)3;X=P5+,Si4+,S6+,Mo6+,As5+)adecadelater.[6]Asmaterials(layeredtransition-metaloxidesandpolyanionicasolid-stateelectrolyte,b”-aluminawascriticaltothecompounds);computationalstudiesthatprobeNa+iondevelopmentoftwosodiumionbatteries:thesodium/sulfurmobilityinsolid-statelattices;developmentsinopen-frame-(Na-S)andZEBRAcells(zero-emissionbatteryresearchworkmaterials;andnegativeelectrodematerials(hardactivities)thatarebasedonNa/NiCl2.Thesecells,particularlycarbons,alloys,andmetaloxides).Abriefoverviewonthetheformer,arenowcommercialtechnologiesusedtodayforresearchofnon-aqueousandionicliquid-basedelectrolytesisgridstorage.Theyoperatenear3008C,wheresodiumandthealsopresented.Wenotethatafewexcellentreviewarticlespositiveelectrodesaremolten,andtheionconductivityofthehaveappearedin2012and2013,[9–12]soouremphasisisonthesodiumb“-aluminamembraneisenhanced.SafetyconcernsmostrecentsignificantissuesandopportunitiesprovidedbywithNa/Stechnology,andcostlyheatingrequirementsandthefield.AlthoughaqueousNaionbatteriesalsohaveseveraltemperaturemanagementdifficultiesinZEBRAcellsareapparentadvantagesforlarge-scalestorage,acomprehensiveinspiringmuchefforttolowertheiroperatingtemperatures.reviewonthistopichasjustbeenpublished,[13]andwereferNASICONhasbeenexploitedasasolid-stateelectrolytethereaderthere.
membraneforNabatteriesthatoperatebetween110and1308Candwhichalsoencompassamoltensodiumelec-trode.[7]Fundamentalresearchinsolid-stateNaionconduc-2.OverviewoftheSodiumIonCell
torshasloweredtheoperatingtemperatureevenfurther.Room-temperatureoperationofanall-solid-staterecharge-ThedevelopmentofsodiumioncellsparalleledthatofLiablesodiumbatterybasedonasulfideglass-ceramicelectro-ionbatteriesthroughthe1980s.[14–21]Thehigherenergylytehasrecentlybeendemonstrated.[8]Thisbringsthe
densityofthelithiumcounterparts—owingtotheirhigher
DipanKundureceivedhisPhDin2012VictorDuffortreceivedhisPhDin2012fromtheETHZürichinthegroupofProf.fromtheUniversit?deCaenBasse-Norman-ReinhardNesper.Currently,heisapostdoc-die,France,ontheoxygenstoichiometryandtoralresearcherinthegroupofProf.structuralcharacterizationofmagneticironLindaF.NazarattheUniversityofWater-oxides.HejoinedthegroupofProf.LindaF.loo.HisresearchinterestsareinfunctionalNazarin2013,andhasbeenfocusingonmaterialdevelopmentforelectrochemicalthedevelopmentofalternativetechnologiesenergystorageapplications,inparticularoftoLiionbatteries.HiscurrentsresearchNaionandLi-O2batteries.interestsresideinthediscoveryofnewcathodematerialsforsodiumandmagne-siumbatteries.ElaheTalaieiscarryingoutPhDresearchLindaNazarwasborninVancouver,(electricalengineering;Nanotechnologypro-Canada,andreceivedherPhDfromthegram)attheUniversityofWaterloounderUniversityofToronto.AfterapostdoctoralthesupervisionofProf.LindaF.Nazar.fellowshipatExxonCorporateResearchinSince2010shehasbeenactivelyinvolvedinAnnandale,NewJersey,shemovedtothethedevelopmentofcathodematerialsforLiUniversityofWaterloo,wheresheisaProfes-ionandNaionbatteries.ShecurrentlysorofChemistryandElectricalEngineering,worksonthesynthesisandcharacterizationandafellowoftheRoyalSocietyofCanada.oflayeredoxidesascathodematerialsforSheholdsaSeniorCanadaResearchChairNaionbatteries.inSolid-StateEnergyMaterials.Herresearchfocusesonnanostructuredintercala-tionelectrodesforsodiumionbatteries,solid-stateelectrolytes/batteries,andLi-SandLi-O2batteries.Angew.Chem.Int.Ed.2015,54,3431–3448??2015Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim
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potentialandlowermass—resultedintheirdominationofbothresearchandcommercialfields,andledtotheexponen-tialgrowthintheportableelectronicsmarketinthe1990s.However,forstationaryapplications,wheregravimetricenergydensityisnotsomuchofaconcern(suchasgridorminigridstorage),Naionbatteriesareanequallyviabletechnology.RecentreportshaveevenshownthatthesecellscancompetewithLiionbatteriesintermsofenergydensity(seeSection3.1).Nonetheless,severalbarriersneedtobeovercomebeforesuchcellscanbecomeapractical,commer-cialreality.Dependingonthecellchemistry,thesebarriersincludeinsufficientcyclelifeandtheneedforthediscoveryofnewmaterialsforboththepositive(andespecially)negativeelectrodestoincreasetheperformance.Researchinsodiumionbatterieshasincreaseddramaticallyinthelastfewyearsandisnowinfull-swingtoaddressthesehurdlesandtherebyenablethisemergingenergystoragetechnologytobecomeavailableinthecomingyears.
TheprincipleofcelloperationisthesameasitsLiioncousin:sodiumionsareshuttledbetweenthepositive(cathode)andnegative(anode)electrodesthroughanon-aqueous(oraqueous)Naionelectrolytethatiscontainedbetweentheelectrodes(Figure2)ondischargeandcharge.[11]
L.F.Nazaretal.
Atypicalworkingsystemisillustrated,wheretheNa+ionelectrolyteisanon-aqueoussystemcomprised,forexample,ofNaClO4inapolarsolventsuchaspropylenecarbonate.Duringcharge,sodiumionsareextractedfromthehighvoltagepositiveelectrode,withaworkingpotentialaroundorabove3.0VversusNa+/Na(seeFigure2b),andareinsertedintothelowvoltagenegativeelectrode,whoseworkingpotentialisideallylowerthan1.0VversusNa+/Na(seeFigure2b).Oncharge,theelectronsarepumped“uphill”,thermodynamicallyspeaking,fromthepositivetotheneg-ativeelectrodethroughtheexternalcircuit.Theconverseoccursondischarge:thefavorablefreeenergyoftheredoxcoupleallowsthereactiontoproceed“downhill”,thusdeliveringenergytothedevicethatisbeingpoweredbythebattery.
FullNaioncellsdonotemployelementalsodiumasthenegativeelectrode:theyarecomprisedofhardcarbonsormetaloxideintercalationcompounds.ThenegativeelectrodeisoneofthemosttroublesomecomponentsbecausetypicalgraphiticcarbonsemployedinLiioncellsdonotintercalateNa+ions(Section5.1).Thediscoveryofsuitableanodematerialsisamajorchallenge.Furthermore,theNa+ionsarenotreversiblyshuttledbetweentheelectrodeswith100%Coulombicefficiencybecauseofsidereactionsbetweentheelectrolyteandelectrodesurface.Thesecanarisebyreactionoftheelectrolytewiththeoxidizingtransition-metaloxideformedatthecathode,and/orwiththehighlyreducingsodiatedhardcarbon(orlow-potentialmetaloxide)gener-atedattheanode.Forpracticalcells,thesehurdlesmustbeovercome.Thenextsectionstartswiththeoutstandingrecentdevelopmentsinpositiveelectrodematerialsbyavarietyofapproaches,andthechallengesthatarestilltobefacedinthis“highpotential”area.
3.CathodeMaterialsforHighPerformanceSodiumionBatteries
3.1.LayeredSodiumTransition-MetalOxides
Majoreffortshavebeendevotedtothesearchforhigh-performancecathodematerialsinlayeredsystemsofthetypeAMO2(solidsolutionsofNaCoO2,NaMnO2,NaFeO2,NaNiO2).[22–25]Thesematerialsaresoughtafterfortheirhighredoxpotentialsandenergydensities.Thedrivingforce,atleastinpart,derivesfromseveraladvantagesassociatedwithlow-cobalt-contentmaterials,especiallythosebasedonenvironmentallyfriendlyironandmanganese.
Sodiummetaloxidesexistasoneofseveralpolytypeswhichdifferinthestackingoftheclose-packedoxygenlayers.FollowingthenotationofDelmas,[26]thesearedesignatedasO3(ABCABCstacking),P2(ABBAstacking),andP3(ABBCCAstacking).TheNa+ionadoptsdifferentcoordi-nationenvironments(P=prismaticandO=octahedral)dependingonthepolytype.NaMO2materials(unliketheirlithiumanalogues)readilyformthe“ideal”orderedO3-typelayeredstructureasaresultofthelargedifferenceintheionicsizesoftheNa+andthetransition-metalcations,whichdrivesthesegregationoftheAandMintoalternatinglayers.The
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Figure2.a)Operatingprincipleofatypicalnon-aqueousoraqueoussodium-ionbattery.Sodiumionsmigratebackandforthintheelectrolytebetweenthenegativeandpositiveelectrodesupondis-chargeorcharge,andelectronflowcounterbalancestheionflowwithintheelectrodematerialsandexternallythroughtheouterelectricalcircuit.Thepotentialdifferencebetweenthepositiveandnegativeelectrodesdefinesthecellvoltage.b)Relativeworkingpoten-tialoftypicalelectrodematerialsfornon-aqueousandaqueoussodium-ionbatteries.
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AngewandteChemievacancy-dominatedP2-typeNa0.67MO2oxidesarealsoofthephasetransitionfromP2toOP4uponcharge.Asconsiderableinterest.EarlyworkdemonstratedthatP2-typeevidencedbyX-rayabsorptionspectroscopyandM?ssbauerNa0.66Co0.66Mn0.33O2displayspredominantlysolid-solutionspectroscopy,theFe3+/Fe4+redoxcoupleisactiveinthebehavioronextractionofthesodium.[27]RecentreportsdesodiationprocessesofP2-Na2/3Mn1/2Fe1/2O2(incontrasttohavehighlightedmanganeseandironoxides,andtheirlithiumironoxideswhereoxygenevolutionseemstobethecombinationswithaternaryelement;thesematerialshavefavorableprocessathighpotentials).[34]Thisauspiciousbeenshowntobeamongstthemostviableforpositivematerialshowsmuchpromiseforfuturedevelopment,butelectrodes,asdiscussedbelow.
theexactchargecompensationmechanismisnotfullyLayeredNaMnO2,oneofthefirstmaterialsinvestigated,resolvedtodate.AssumingaMn4+oxidationstateintheexhibitstwostructures,[28,29]buta-NaMnO2ismorestable.[30]chargedsample(4.2V,x=0.13inNaxMn0.5Fe0.5O2),moreItcrystallizesintheO3structure.Investigationofitselectro-than70%oftheironionsareexpectedtobeoxidizedonthechemicalpropertiesshowedthat0.8Nacanbereversiblyde/basisofchargebalance(Na+4+30.13Mn+40.5Fe0.37Fe0.13O2).How-intercalatedwithgoodcapacityretention,equivalenttoever,muchlessFe4+wasdetectedbyM?ssbauerspectroscopyacapacityof200mAhgà1.[31]Thevoltageprofilesexhibitinthesamplechargedto4.5V.Therefore,theextractionofpronouncedstepwiseprocessesindicativeofstructuraltran-sodiumfromP2-NaxMn0.5Fe0.5O2maybeaccompaniedbyonesitions.ThesearemorecommoninNaionthaninLiionormorecharge-compensationmechanisms;mostpossiblyintercalationoxidesbecauseofNa-vacancyorderinginter-oxygenremovaland/oroxidationofmanganeseionstohigheractionswhicharestrongerduetothelargerradiusofasodiumoxidationstatesthantetravalent.Theseunresolvedquestionscation.Theseinvolvetheglidingofoxygenplanestoinspirefurtherexplorationforin-depthunderstandingofaccommodateNainbothoctahedralandtrigonalprismaticthesesystems.
environments.ThelattercanonlybeachievedinanO3Inthesearchforelectrodematerialswithstabilitiesstackingbyslidingsomeoftheoxygenlayers.GlidingoftheacceptableforpracticalNaionbatteries,Mengandco-oxygenlayeralsoallowsoptimizationofNacoordinationatworkersconductedacomprehensivestudyontheeffectofLieachstoichiometry—whichisastrongerdrivingforcethaninsubstitutiononthestructuralandelectrochemicalpropertiesthelithiatedoxides.
ofaP2structuredbinarysystem,Nax[LiyNizMn1àyàz]O2(0 upto4.4V,althoughthebroadeningofpeaksonchargingimpliesemerginglocalstackingfaultsasaresultofin-planeglide.DelayintheoccurrenceoftheP2-O2phasetransitionisexplainedbythepresenceofmoreNa+ionsinthestructure(includingatthechargedstate)becauseofsubstitutionoflow-valenceLiions(Na0.8LiyMe1àyO2vs.Na0.67MeO2).Exsitusolid-stateNMRspectroscopyshowedthatLiionsaremostlylocatedinthetransition-metallayersassynthesizedbuttendtomigratetoNalayersuponchargetohighervoltagessinceoctahedralandtetrahedralpositionsareavailableasstackingfaultsdevelop.However,theLimigrationprocessisrever-sible. Figure3.Galvanostaticcharge/dischargecurveofP2-Na2/3Mn1/2Fe1/2O2AlsoonthetopicofLi-richlayeredsodiummetaloxides,inaNacellcycledinthevoltagerangeof1.5–4.3Vatarateof 12mAgà1.ReproducedfromRef.[32]withpermission.Copyright2012,Komabaandco-workersrecentlyreportedahighlyreversibleNaturePublishingGroup. capacityof200mAhgà1forP2-Na5/6[Li1/4Mn3/4]O2cycledat1.5–4.4V,whichishigherthanitstheoreticalcapacitybasedonMn3+/Mn4+redox.Alongvoltageplateauat4.1VattheThecellretainsabout70%ofitsreversiblecapacitywhenfirstchargecharacterizesthissystem,[36]similartolayeredthecyclingrateisincreasedfromC/20to1C.Thesuperiorlithium-richoxides.[37,38]NotransitiontoO2orOP4phasesatratecapabilityofP2-Na2/3Mn1/2Fe1/2O2comparedtothatofthefullychargedstateoccurs,similartotheP2-manyotherlayeredtransitionmetaloxidesiscorrelatedtoitsNa0.8[Li0.12Ni0.22Mn0.66]O2phasediscussedabove.Interestingly,smoothcharge/dischargevoltageprofile,whichsuggestssuperlatticepeaksassociatedwithLi/Mnorderingdisappearafacilede/intercalationreactionandthelackofpronouncedwhenthecellischargedto4.4V,whichindicatesanin-planestructuraltransitions.ThesedominateinNaxCoO2,forcationrearrangement.Asaconsequenceofsimilaritieswithexample.[33]P2-Na2/3Mn1/2Fe1/2O2retainsover75%ofitslithium-richLi2MnO3-basedelectrodes,(highcapacitiesasso-initialcapacityafter30cycles.Capacityfadeisattributedto ciatedwithhighvoltageplateausanddisappearingsuper-Angew.Chem.Int.Ed.2015,54,3431–3448 ??2015Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim www.angewandte.org 3435
