TheOriginoftheOxygenRedoxActivityinLayeredandCation-Disordered

Li-ExcessCathodeMaterials

Dong-HwaSeo,1 Jinhyuk Lee,1AlexanderUrban1 andGerbrand Ceder1,2

1UCBerkeley,2LawrenceBerkeleyNationalLaboratory

Thispresentationisavailableathttp://ceder.berkeley.edu/

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+

3

TheOredoxmechanismwashowevercontroversial,preventingrationaldesignofhighcapacitycathodematerialswithoptimumOredoxactivity.

Formationofperoxo-likespecies(O2

2-)inLi2RuxSn1-xO3

OchargetransferbycovalencyinLiCoxAl1-xO2

LocalizedOholeatLaAlO3/SrTiO3 interfaces

Cederetal.,Nature392 (1998)694 R.Pentcheva etal.,Phys.Rev.B74 (2006)035112 Tarascon etal.,Nat.Mater.12 (2013)827

localizedOhole

Al

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-interactionerrorforoxygen.

PredictionoftheoxygenredoxactivityrequiresnovelcomputationalmethodologybeyondsimpleGGAorGGA+U.

D.-H.Seo,A.Urban,G.Ceder, Phys. Rev. B92 (2015) 11511810

GGApredictswrongelectronicstructureofLiCoO2.

GGAandGGA+UpredictwrongvoltageprofileofLiCoO2.

CalculatedvoltageprofileofLiCoO2DensityofState(DOS)ofLiCoO2

• ConventionalDFTsuchasGGAandGGA+Ucannotpredictbothanelectronicstructureandavoltageprofileduetoself-interactionerrorforoxygen.

PredictionoftheoxygenredoxactivityrequiresnovelcomputationalmethodologybeyondsimpleGGAorGGA+U.

D.-H.Seo,A.Urban,G.Ceder, Phys. Rev. B92 (2015) 11511811

GGApredictswrongelectronicstructureofLiCoO2.

GGAandGGA+UpredictwrongvoltageprofileofLiCoO2.

OuroptimizedHSEhybridfunctionalpredictsaccurateelectronicstructureaswellasvoltageprofileofLiCoO2.

CalculatedvoltageprofileofLiCoO2DensityofState(DOS)ofLiCoO2

Modelsystem- Li/Ni-mixedLiNiO2

LiNiO2:oneofthemoststudiedmaterialsandthebasisformanyimportant

derivedcompositions

Li/Nicationmixing:variouslocalenvironmentsofoxygenions

1pairofLi/NisiteexchangeinLi12Ni12O24

AmodelstudyontheeffectoflocalenvironmentaroundoxygenionontheelectronicstateinlayeredLi-TMoxides

Li Ni O

12

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. 13

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.

14

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

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.

15

Li2MnO3

EFLi-O-LiinLi2MnO3

Li Mn O Li Mn O

ElectronlocalizedalongLi-O-Liconfiguration

2 e- perLi2MnO3

Yellowiso-surface:electrondensity

Li-O-Li

WefindthatoxygenoxidationoccursfromtheseO2pelectronsalongtheLi-O-LiconfigurationsinbothLi-excesslayeredandcation-disorderedcathodematerials.

TheoxygenoxidationintheseLi-excessmaterialsaccompaniestheelectronextractionalongtheLi-O-Liconfiguration,leadingtoextracapacitybeyondTMredoxcapacity.

16

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-LiLi+

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.

Li-O-Li

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.

17

Spindensitiesaround(transition)metalarenotshownhere.

LigandfieldtheoryexplainsourobservationonpreferredoxygenoxidationalongLi-O-Liconfiguration.

D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692

HybridizationofO2p orbitalswithMd/s/porbitalstabilizedthe(bonding)O2pstates.

threeLi-O-Me.g.,stoichiometriclayeredLi-Moxides

Mbands

Obands

LiMO2

Li-O-M

t1u*

a1g*eg*

t2gt1ub

E

egba1gb

18

LigandfieldtheoryexplainsourobservationonpreferredoxygenoxidationalongLi-O-Liconfiguration.

D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692

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

19

LigandfieldtheoryexplainsourobservationonpreferredoxygenoxidationalongLi-O-Liconfiguration.

D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692

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

20

Morbital

Oorbital

bondingOstate

anti-bondingMstate

unhybridizedstate(Li-O-Li)

Extracapacityfromwhichoxygenoxidation?

TwodifferentoxygenchargetransferupondelithiationinLi-excessmaterials

1.fromthehybridizedTM-Ostates(socalledcovalency):cannotaddextracapacitybeyondtheTMredoxcapacity

- eg*,t2g:alreadycountedasTMredoxcapacity- t1ub,a1gb,egb:toostabletobeoxidized

2.fromtheLi-O-Listates (pureoxygenstate):canaddextracapacitybeyondTMredoxcapacitybecausetheyareindependentoxygenstates

TheoxygenoxidationfromunhybridizedO2pstatesalongLi-O-LiconfigurationsistheoriginoftheextracapacityintheLi-excessmaterials.

21

t1u*

a1g*eg*

t2gt1ub

a1gbegb

E

Li‒O‒Li

D.-H.Seo,J.Lee,A.Urban,R.Malik,S.Y.Kang,G.Ceder,NatureChem.8 (2016) 692

1. Covalency/HybridizationbetweentheTMandoxygendoesnotcreateextracapacitybeyondTMredoxcapacity.

2. TheO2p orbitalsalongLi-O-LiconfigurationformunhybridizedO2p statesthatarehigherinenergythanbondingOstates,thuseasieroxidized.

3. ThelabileelectronfromunhybridizedO2p statesalongtheLi-O-LiconfigurationsisthesourceoftheextracapacitybeyondTMredoxcapacityinLi-excessmaterials.

4. Webelieveourin-depthunderstandingonoxygenredoxmechanismprovidesclearguidelinesforthedesignofhigh-capacitycathodeswithoptimumOredox.

Summary

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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