TheOriginoftheOxygenRedoxActivityinLayeredandCation-Disordered
Li-ExcessCathodeMaterials
Dong-HwaSeo,1 Jinhyuk Lee,1AlexanderUrban1 andGerbrand Ceder1,2
1UCBerkeley,2LawrenceBerkeleyNationalLaboratory
Dong-HwaSeo- ALSTheory&Experiment(Apr.13,2017)
OxygenredoxenablesveryhighcapacityLi-excesscathodematerials,leadingtounprecedentedenergydensity.
ExtracapacitiesofLiexcessmaterialsthatcannotbeprovidedbythetransitionmetal(TM)redoxactivitiesareexplainedbytheoxygenoxidation.
2
N.Yabuuchi etal.,PNAS112 (2015)7650R.Wangetal.,Electrochem.Commun.60(2015)70
M.Sathiya etal.,Nat.Mater.12 (2013)827
layered Li2Ru0.75Sn0.25O3
Ru4+/Ru5+O2-/O1-
cation-disordered Li1.3Nb0.3Mn0.4O2
O2-/O1-Mn3+/Mn4+
K.Luoetal.,Nat.Chem.8 (2016)684
layered Li1.2Ni0.13Co0.13Mn0.54O2
Ni2+/Ni4+Co3+/Co4+
OxygenholelocalizationinLixNi1-xO
G.A.Sawatzky etal.,Phys.Rev.B45 (1992)1612
Li2O
LiNiO2
NiO
O1sXAS
LixNi1-xO
3
TheOredoxmechanismwashowevercontroversial,preventingrationaldesignofhighcapacitycathodematerialswithoptimumOredoxactivity.
Formationofperoxo-likespecies(O2
2-)inLi2RuxSn1-xO3
OchargetransferbycovalencyinLiCoxAl1-xO2
Cederetal.,Nature392 (1998)694 Tarascon etal.,Nat.Mater.12 (2013)827
covalentCo-Obonding
ItiscommonlybelievedthatTM-ObondcovalencyleadstotheextracapacitybeyondTMredoxcapacityinLi-excessmaterials.
ConventionalviewofM-Obonding
Morbital
Oorbital
bonding“O”state
antibonding“M”stateregularredoxstates
e- Energy
Voltage
OxygenchargetransferfromM-Ocovalency
Cederetal.,Nature392 (1998)694
OxygenelectronsalsoparticipateinaredoxprocessbecausesomeportionofantibondingstateactuallycomesfromoxygenelectronsduetothecovalentnatureofM-Obonding.
Morbital
Oorbital
bonding“O”state
Partialcontributionfromoxygen2p
regularredoxstate
e-
5
M-OcovalencydoesNOTincreasecapacity.TMcontribution
Ocontribution
ThenumberofelectronsstayssameatregularredoxstatesregardlessofOcontribution,whichwerealreadycountedintoTMredoxcapacity.Therefore,oxygencontributiontoantibondingstatebycovalencycannotleadtoextracapacitybeyondsocalledTMredoxcapacity.
vs.
vs.
vs.Morbital
Oorbital
bonding“O”state
regularredoxstate
e-
Togetextracapacityoneneedstoextractthiselectron.
6
Energy
Voltage
Covalencyactuallymakesoxygenredoxmoredifficult.
Energy
Voltage
Morbital
Oorbital
Morbital
Oorbital
morecovalent
Covalencyisnotthesourceofextracapacitythroughoxygenredox!!
7
morestable(hardertobeoxidized)
Instead,lesscovalentmakesoxygenredoxeasier.
Energy
Voltage
Morbital
Oorbital
Morbital
Oorbital
lesscovalent(unhybridized)
8
lessstable(easiertobeoxidized)
WhatmakesOstateslessstable?
9
Toresolvesuchcontroversy,itisimportanttounderstandtheeffectoflocalenvironmentsontheoxygenelectronicstate.
Li
MM M
LiLi
O
StoichiometriclayeredLi-Moxides(LiMO2)
LiLiLi
M MM
O
Li
Li
LiLi
MM
O
Li-excesslayeredLi-Moxides(Li1.2M0.8O2)
Li Li
Li Li
Li
Li
Li LiM
MM
O O
Li
Li
Li Li
MM
O
Li Li
Li
M
MMO
Li LiLi
LiLiM
M M M MM M
O O
Li-excesscation-disorderedLi-Moxides (Li1.2M0.8O2)
Li
• ConventionalDFTsuchasGGAandGGA+Ucannotpredictbothanelectronicstructureandavoltageprofileduetoself-interactionerrorforTMandO.SotheyarenotpropertoinvestigateOoxidation.
PredictionoftheoxygenredoxactivityrequiresnovelcomputationalmethodologybeyondsimpleGGAorGGA+U.
D.-H.Seo,A.Urban,G.Ceder, Phys. Rev. B92 (2015) 11511810
GGApredictswrongelectronicstructureofLiCoO2.
GGAandGGA+UpredictwrongvoltageprofileofLiCoO2.
OuradvancedDFT(optimizedHSEhybridfunctional)methodpredictsaccurateelectronicstructureaswellasvoltageprofileofLiCoO2.
CalculatedvoltageprofileofLiCoO2DensityofState(DOS)ofLiCoO2
Modelsystem- Li/Ni-mixedLiNiO2
LiNiO2:oneofthemoststudiedmaterialsandthebasisformanyimportant
derivedcompositions
Li/Nicationmixing:variouslocalenvironmentsofoxygenions
1pairofLi/NisiteexchangeinLi12Ni12O24
AmodelstudyontheeffectoflocalenvironmentaroundoxygenionontheelectronicstateinlayeredLi-TMoxides
Li Ni O
11
Li
Ni
VariousenvironmentsaroundoxygeninLi/Ni-mixedLiNiO2
1pairofLi/NisiteexchangeinLi12Ni12O24
Li Ni O
4Liand2Ni
3Liand3Ni
2Liand4Ni
In Li/Ni-mixed LiNiO2, there are three major local environments for oxygen : oxygencoordinated with (a) four Li and two Ni, (b) three Li and three Ni, and (c) two Li andfour Ni. 12
Modelsystem- Li/Ni-mixedLiNiO2
The electrons bound to an oxygen ion in the local Li-excess environments areenergetically less stable than electrons bound to the other types of oxygen ions.
pDOS onanoxygenionsclearlyshowsthedifferenceintheoxygenelectronicstatesbythelocalenvironment.
13
4Liand2Ni3Liand3Ni2Liand4Ni
D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692
ElectronlocalizedalongLi-O-Liconfiguration
1 e- perLiNiO2
Yellowiso-surface:electrondensity
à This labile electron along Li-O-Li configuration will be easier to be extractedthan the electron from O bond states.
OoxidationoccursfromtheseO2pelectronsalongtheLi-O-LiconfigurationsinbothLi-excesslayeredandcation-disorderedcathodematerials.
TheoxygenoxidationintheseLi-excessmaterialsaccompaniestheelectronextractionalongtheLi-O-Liconfiguration,leadingtoextracapacitybeyondTMredoxcapacity.
14
isosurface of spin density around oxygen ions
D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692
layeredLi1.17Ni0.25Mn0.58O2
Ni2+
Mn4+Li-O-Li
Li+
cation-disorderedLi1.25Mn0.5Nb0.25O2
Nb5+
Li+
Mn3+
Ni3+
Li0.67Ni0.25Mn0.58O2
Mn4+
-0.5Li+
-0.75Li+
Li0.50Mn0.5Nb0.25O2
Nb5+Mn4+
Ni4+
Li0.33Ni0.25Mn0.58O2
Mn4+
-0.33Li+
-0.25Li+
Li0.25Mn0.5Nb0.25O2
Nb5+Mn4+
Spindensitiesaround(transition)metalarenotshownhere.
OoxidationalongtheLi-O-Liconfigurationisuniversalinallthelithiumexcesslayeredandcationdisorderedmaterials.
D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692
Li0.33Ni0.33Ti0.42Mo0.08O2Li0.67Ni0.33Ti0.42Mo0.08O2
-0.5Li+ -0.33Li+Ti4+
Mo6+
Ti4+
Mo6+
Ti4+
Li+
Mo6+
Ni2+
Ni3+
Ni4+ Ni4+
isosurface of spin density around oxygen ions
layeredLi2Ru0.5Sn0.5O3
Sn4+
Ru4+Li+
-0.5Li+Ru4.x+
Sn4+
-1Li+
Li1.5Ru0.5Sn0.5O3
Ru5.x+
Li0.5Ru0.5Sn0.5O3
Sn4+
cationdisorderedLi1.17Ni0.33Ti0.42Mo0.08O2
TheoxygenoxidationintheseLi-excessmaterialsaccompaniestheelectronextractionalongtheLi-O-Liconfiguration,leadingtoextracapacitybeyondTMredoxcapacity.
15
Spindensitiesaround(transition)metalarenotshownhere.
LackofhybridizationmakesoxygenelectronsintheLi-O-Listateshighinenergy(labile).
Seo†,Lee†,Urban,Malik,Kang,Ceder,NatureChem. (2016)
HybridizationofO2p orbitalswithMd/s/porbitalstabilizedthe(bonding)O2pstates.
threeLi-O-Me.g.,stoichiometriclayeredLi-Moxides
Mbands
Obands
LiMO2
Li-O-M
t1u*
a1g*eg*
t2gt1ub
E
egba1gb
16
LackofhybridizationmakesoxygenelectronsintheLi-O-Listateshighinenergy(labile).
Seo†,Lee†,Urban,Malik,Kang,Ceder,NatureChem. (2016)
HybridizationofO2p orbitalswithMd/s/porbitalstabilizedthe(bonding)O2pstates.
threeLi-O-Me.g.,stoichiometriclayeredLi-Moxides
Mbands
Obands
LiMO2
Li-O-M
t1u*
a1g*eg*
t2gt1ub
E
egba1gb
LackofhybridizationalongtheLi-O-LiconfigurationmakestoO2pelectronsalongthedirectionlabile(unstable).
oneLi-O-Li,twoLi-O-Me.g.,Li-excesslayered/cation-disordered
Li-MoxidesMbands
Obands
e.g.,Li(Li1/3M2/3)O2
Li-O-Li
Li-O-Li
t1u*
a1g*eg*
t2gt1ub
E
egba1gb
17
LackofhybridizationmakesoxygenelectronsintheLi-O-Listateshighinenergy(labile).
Seo†,Lee†,Urban,Malik,Kang,Ceder,NatureChem. (2016)
HybridizationofO2p orbitalswithMd/s/porbitalstabilizedthe(bonding)O2pstates.
threeLi-O-Me.g.,stoichiometriclayeredLi-Moxides
Mbands
Obands
LiMO2
Li-O-M
t1u*
a1g*eg*
t2gt1ub
E
egba1gb
LackofhybridizationalongtheLi-O-LiconfigurationmakestoO2pelectronsalongthedirectionlabile(unstable).
oneLi-O-Li,twoLi-O-Me.g.,Li-excesslayered/cation-disordered
Li-MoxidesMbands
Obands
e.g.,Li(Li1/3M2/3)O2
Li-O-Li
Li-O-Li
t1u*
a1g*eg*
t2gt1ub
E
egba1gb
Morbital
Oorbital
bondingOstate
anti-bondingMstate
unhybridizedstate(Li-O-Li)
18
Li-O-LioxidationleadstoextracapacityinLi-excessmaterials.
Seo†,Lee†,Urban,Malik,Kang,Ceder,NatureChem. (2016)
TwodifferentoxygenchargetransferupondelithiationinLi-excessmaterials
1.fromthehybridizedTM-Ostates(socalledcovalency):cannotaddextracapacitybeyondtheTMredoxcapacity
- eg*,t2g:alreadycountedasTMredoxcapacity- t1ub,a1gb,egb:toostabletobeoxidized
2.fromtheLi-O-Listates (pureoxygenstate):canaddextracapacitybeyondTMredoxcapacitybecausetheyareindependentoxygenstates
TheoxygenoxidationfromunhybridizedO2pstatesalongLi-O-LiconfigurationsistheoriginoftheextracapacityintheLi-excessmaterials.
t1u*
a1g*eg*
t2gt1ub
a1gbegb
E
Li‒O‒Li
19
1. Covalency/HybridizationbetweentheTMandoxygendoesnotcreateextracapacitybeyondTMredoxcapacity.
2. TheO2p orbitalsalongLi-O-LiconfigurationformunhybridizedO2p statesthatarehigherinenergythanbondingOstates,thuseasieroxidized.
3. ThelabileelectronfromunhybridizedO2p statesalongtheLi-O-LiconfigurationsisthesourceoftheextracapacitybeyondTMredoxcapacityinLi-excessmaterials.
4. Webelieveourin-depthunderstandingonoxygenredoxmechanismprovidesclearguidelinesforthedesignofhigh-capacitycathodeswithoptimumOredox.
Summary
20
Thankyouverymuch!!
Acknowledgments • Robert Bosch Corporation and Umicore Specialty Oxides and Chemicals
• XSEDE (ACI-1053575) and NERSC (DE-C02-05CH11231)
This presentation is available at http://ceder.berkeley.edu/ Dong-HwaSeoetal.,NatureChem.,8 (2016)692Dong-HwaSeoetal.,Phys.Rev.B,92 (2015)115118
D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692
TheLi-O-LiconfigurationresultsinunstableOelectronsinLi2MnO3.
The electrons along the Li-O-Li configuration in Li2MnO3 contribute to the large pDOSof the oxygen ion near below the Fermi level.
22
Li2MnO3
EFLi-O-LiinLi2MnO3
Li Mn O Li Mn O
ElectronlocalizedalongLi-O-Liconfiguration
2 e- perLi2MnO3
Yellowiso-surface:electrondensity
Li-O-Li
Oxygenoxidationoccursfrom“unhybridized”O2p statesalongtheLi-O-LiconfigurationsinLi-excessmaterials.
Li-excesscation-disorderedoxide
Li0.25Mn0.5Nb0.25O2
Nb5+
Nb5+
Li0.75Mn0.5Nb0.25O2N.Yabuuchi etal.PNAS112 (2015)7650.
Li1.3Nb0.3Mn0.4O2
O2-/O-Mn3+/Mn4+
D.-H.Seo,† J.Lee,† A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692
Li1.25Mn0.5Nb0.25O2
Nb5+
O-
Mn4+
Mn3+
Mn4+
Mn3+
Mn4+
Mn3+
Mn4+
BenchmarkingHybridfunctionaltoexperimentalbandgap
24
• HSE mixing parameters can be adjusted for oxides to experimental band gaps.[S. Han et al., Curr. Appl. Phys. 11 S337 (2011)]
• Density of State (DOS) of transition monoxides with HSE06 and optimal mixingparameters are in better agreement with experimental results than those withGGA and GGA+U.
• G0W0@GGA+U band gaps agree well with experimental values, suggestingthat it can be used as a reference in cases when no experimental band gap hasbeen reported.
-8 -6 -4 -2 0 2 4 6
GGA GGA+U HSE06 (0.20) G0W0@GGA+U Exp. (PES-BIS)
Den
sity
of S
tate
s (a
.u.)
Energy (eV)-4 -2 0 2 4 6 8
GGA GGA+U HSE06 (0.25) G0W0@GGA+U Exp. (PES-BIS)
Den
sity
of S
tate
(a.u
.)Energy (eV)
-4 -2 0 2 4 6 8
Den
sity
of S
tate
s (a
.u.)
Energy (eV)
GGA GGA+U HSE06 (0.30) G0W0@GGA+U Exp. (PES-BIS)
MnO NiO CoO
D.-H.Seo,A.Urban,G.Ceder, Phys. Rev. B92 (2015) 115118
DensityofState(DOS)ofMO(M=Mn,Ni,Co)
0.0 0.1 0.2 0.3 0.40
1
2
3
4
5
Band
gap
(eV)
HSE06 Mixing Parameter
LiNiO2 NiO2 G0W0@GGA+U
0.0 0.1 0.2 0.3 0.4 0.50
1
2
3
4
5
6
7
8 LiCoO2
CoO2
G0W0@GGA+U
Ban
d ga
p (e
V)
HSE06 Mixing Parameter
Simplewaytoobtainoptimalmixingparameters
25
BandgapsofLiCoO2 andCoO2 BandgapsofLiNiO2 andNiO2
ThebandgapsincreaselinearlywiththeamountofexactHFexchangeenergywithin 0≤α≤0.3.Thus,theoptimalmixingparametercanbeobtainedbycomparingareferencebandgapwiththelinearinterpolatedbandgapbetweenGGA (α=0) andHSE06 (α=0.25).
D.-H.Seo,A.Urban,G.Ceder, Phys. Rev. B92 (2015) 115118
OptimalmixingparametersofvariousLi-excessmaterials
26
Li1.17Ni0.25Mn0.58O2
WeusedoptimalmixingparameterforeachLi-excesscompound.D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692
27
CompetitionbetweenTMredoxandoxygenredox
OxygenionsstarttogetoxidizedbeforefulloxidationofNi2+/Ni4+
OxygenionsstarttogetoxidizedafterfulloxidationofMn3+/Mn4+
NiredoxbasedLi-excessmaterials
MnredoxbasedLi-excessmaterials
