CalciothermicReductionofSiliconOxideAnodeMaterialsforLithiumIonBatteries

Abstract

Withtheincreaseddemandforhigh-energydensitylithium-ionbatteries(LIBs),Siliconbasedanodematerialsaregainedattentionasnext-generationLIBsanodematerialtoreplacegraphiteduetoitshighgravimetriccapacity,lowworkingpotentialwithlowcost.Siliconmonoxide(SiO)basedanodematerialisoneofthemostpromisinganodematerialsinSi-basedmaterialduetoitsstablecycleperformancethanSiandhighgravimetriccapacitythangraphiteanode.However,SiObasedanodesufferfromlowinitialCoulombicefficiency(ICE),whichhinderthecommercialuseofSiOanodeduetotheirreversiblereactionofa-SiO2inSiOwithLiion.ToimprovetheICEofSiO,variousprelithiationmethodsareproposedsuchaselectrochemicalprelithiationandchemicalprelithiationwhichcausesafetyproblemduetohighreactivityofLimetalandlithiumcontainingreagent.TopracticaluseofSiOanode,safeandreliablemethodofincreasingICEshouldbedeveloped.Here,Si/calciumsilicatecompositeanodematerialsviacalciothermicreductionwerepreparedbyreactionofSiOandCaH2withvariousheattreatmenttemperature.Compositematerialswithc-Siandcalciumsilicateswereobservedabove1000℃heattreatmenttemperaturebyX-raydiffraction,Ramanspectroscopy,transmissionelectronmicroscopyandscanningelectronmicroscopy.CalciothermicreductionofSiOcouldeffectivelyincreasedtheICEofSiOupto87.2%atheattreatmenttemperatureof1000℃.|고에너지밀도리튬이차전지의수요증가추세에의해,실리콘계음극물질은높은중량당용량,낮은작동전압,낮은가격과같은이유로흑연을대체할차세대음극소재로서주목받고있다.일산화규소산화물(SiO)음극소재는실리콘대비안정적인수명특성과흑연대비높은중량당용량을갖는장점으로인해실리콘계음극소재중유망한음극소재로써여겨지고있다.하지만SiO음극재는SiO내부의SiO2와리튬의비가역반응으로인해발생하는낮은초기효율문제로인해SiO음극재의상용화에문제점으로작용한다.SiO음극의초기효율을향상시키기위해electrochemicalprelithiation,chemicalprelithiation같은다양한prelithiation공정들이연구되고있으나해당공정들의경우높은반응성을가진리튬금속이나리튬금속을포함한화합물을사용하여안전성의문제점이존재한다.따라서SiO음극의실용적사용을위해서는SiO음극재의초기효율을향상시킬수있는안전하고신뢰성있는공정의개발이필요하다.이번연구에서는칼슘열환원법을적용하여SiO와CaH2을다양한온도에서열처리를진행하여실리콘-칼슘실리케이트복합체를형성하였다.본연구를통해1000℃이상의열처리온도에서결정질실리콘과칼슘실리케이트로구성된복합체를형성하였으며X선회절분석,Raman분석,투과전자현미경분석을통해확인하였다.SiO소재에칼슘열환원법을적용한결과초기효율을효과적으로상승시킬수있었으며1000℃열처리온도에서최고초기효율인87.2%를확인할수있다.