Lithium-TitaniumDual-DopedSiliconOxideasAnodeforLithiumStorageMaterial

Abstract

Theever-increasingdemandforhighenergydensity,longcyclelife,safeandenvironmentallyfriendlylithium-ionbattery(LIB)anodematerialsforelectricvehicles(EVs),andsilicon(Si)hasgainedmuchattentionduetoitshighcapacity,moderateworkingpotential,naturalabundance,andlowcost.Siliconmonoxide(SiO)basedanodematerialsareconsideredapromisingcandidatetoreplacethemostwidelyusedgraphiteforLIBsduetotheirsuperiorcyclelifethanpureSianodematerialsresultingfromtheiruniquemicrostructure.However,practicaluseoftheseSiO-basedanodematerialsisbeinghinderedduetoitslowinitialCoulombicefficiency(ICE)duetotheformationofirreversiblephaseduringthefirstlithiationprocess.Therefore,variousprelithiationmethodsofSiO-basedanodematerialsandelectrodeshavebeenconducted,andrecentlyreportedprelithiationmethodofSiOthroughdehydrogenationofLiHhavedemonstratedaLi-metalfreesafeandscalableprocessachievingICEupto90.5%.AmongtheprelithiatedSiOmaterialsusingLiHwithvariousLiandSiatomiccompositions,prelithiatedSiOhavingthehighestICEshowedapoorcycleperformancecomparedtootherprelithiatedSiOmaterialsaddressingtheneedforimprovingthecyclelifeofprelithiatedSiOwithoutsacrificingtheICE.Here,theSi/titaniumsilicide/lithiumsilicatenanocomposites(Li-Tidual-dopedSiO)withvarioustitaniumsilicidecontentwerepreparedbyballmillingofSiOandTiH2followedbyheattreatmentandprelithiationusingLiH.TheuniformlydistributednanosizedinactivetitaniumsilicidecrystallinephaseswithinSiandlithiumsilicatenanocrystalswerevisualizedbyhighresolutiontransmissionelectronmicroscopy(HR-TEM)andscanningtransmissionelectronmicroscopy(STEM).TheLi-Tidual-dopedSiOshowedimprovedcycleperformance,ratecapability,andthermalstabilitycomparedtopristineSiOandSi/lithiumsilicatenanocompositesynthesizedwiththesamepreparationconditions(Lisingle-dopedSiO)withoutsacrificingtheICE.|전기자동차(EVs)시장의가파른성장으로인하여고용량,장수명등우수한전가화학적특성을갖춘리튬이온전지음극소재에대한수요가증가하고있는가운데,고용량,낮은작동전압그리고풍부한매장량을자랑하는실리콘음극소재가주목을받고있다.그러나,실리콘은리튬삽입/탈리과정에서극심한부피변화로인하여낮은용량유지율을보유하고있는상황이다.실리콘산화물계음극소재는이러한실리콘의부피변화를제어할수있는SiOx매트릭스의존재로인하여비교적수명특성이우수하여실리콘계음극소재중가장먼저상용화된음극소재이다.하지만,실리콘산화물계음극소재의초기충전(리튬삽입)시,비가역적LixSiOy상형성으로인하여낮은초기효율을보여리튬이온전지의에너지밀도고도화에대한한계가존재한다.이러한실리콘산화물계소재의낮은초기효율을향상시키기위하여prelithiation기술이주목받고있으며많은연구가진행되고있다.하지만,prelithiation전구체로사용되는리튬금속혹은리튬금속기반화합물을사용한prelithiation은화재및폭발위험성등공정의안전성에문제가있다.최근,수소화리튬을prelithiation전구체로사용하여공정의안전성확보와더불어90%이상의초기효율을갖춘소재합성을구현한바있다.하지만,초기효율과더불어실리콘산화물계소재의수명특성,열안정성을향상시키기위해선추가적인연구가필요한상황이다.본연구에서는실리콘산화물소재의초기효율과더불어수명특성의향상을위해리튬-티타늄이중도핑된복합체를실리콘산화물과수소화티타늄과의고에너지볼밀링과열처리후수소화리튬을사용한prelithiation을통해합성하였다.리튬-티타늄이중도핑된실리콘산화물의나노사이즈실리콘,비가역적LixSiOy상과Ti-Si합금으로이루어진미세구조를고도분석을통해시각화하였다.리튬-티타늄이중도핑된실리콘산화물의미세구조로인하여동일조건으로합성된리튬단일도핑된실리콘산화물대비높은초기효율을유지한상태에서우수한수명특성을발현하였다.본연구에서이루어진구조적특성과전기화학특성을분석한자세한내용은본문에서다루고자한다.